The novel benzimidazole derivative BRP-7 inhibits ...

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British Journal of Pharmacology

DOI:10.1111/bph.12625 www.brjpharmacol.org

RESEARCH PAPER

Correspondence

The novel benzimidazole derivative BRP-7 inhibits leukotriene biosynthesis in vitro and in vivo by targeting 5-lipoxygenaseactivating protein (FLAP)

Dr Carlo Pergola, Institute of Pharmacy, Friedrich-SchillerUniversity Jena, Philosophenweg 14, D-07743 Jena, Germany. E-mail: [email protected] ----------------------------------------------------------------

Keywords 5-lipoxygenase; 5-lipoxygenase activating protein; leukotriene; benzimidazole; inflammation ----------------------------------------------------------------

Received 4 November 2013

Revised 25 January 2014

Accepted 3 February 2014

C Pergola1, J Gerstmeier1, B Mönch1, B Çalıs¸kan2, S Luderer3, C Weinigel4, D Barz4, J Maczewsky1,5, S Pace1,5, A Rossi5, L Sautebin5, E Banoglu2 and O Werz1 1

Institute of Pharmacy, Friedrich-Schiller-University Jena, Jena, Germany, 2Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Gazi University, Ankara, Turkey, 3Department of Pharmaceutical Analytics, Pharmaceutical Institute, Eberhard-Karls-University Tuebingen, Tuebingen, Germany, 4Institute of Transfusion Medicine, University Hospital Jena, Jena, Germany, and 5Department of Pharmacy, University of Naples Federico II, Naples, Italy

BACKGROUND AND PURPOSE Leukotrienes (LTs) are inflammatory mediators produced via the 5-lipoxygenase (5-LOX) pathway and are linked to diverse disorders, including asthma, allergic rhinitis and cardiovascular diseases. We recently identified the benzimidazole derivative BRP-7 as chemotype for anti-LT agents by virtual screening targeting 5-LOX-activating protein (FLAP). Here, we aimed to reveal the in vitro and in vivo pharmacology of BRP-7 as an inhibitor of LT biosynthesis.

EXPERIMENTAL APPROACH We analysed LT formation and performed mechanistic studies in human neutrophils and monocytes, in human whole blood (HWB) and in cell-free assays. The effectiveness of BRP-7 in vivo was evaluated in rat carrageenan-induced pleurisy and mouse zymosan-induced peritonitis.

KEY RESULTS BRP-7 potently suppressed LT formation in neutrophils and monocytes and this was accompanied by impaired 5-LOX co-localization with FLAP. Neither the cellular viability nor the activity of 5-LOX in cell-free assays was affected by BRP-7, indicating that a functional FLAP is needed for BRP-7 to inhibit LTs, and FLAP bound to BRP-7 linked to a solid matrix. Compared with the FLAP inhibitor MK-886, BRP-7 did not significantly inhibit COX-1 or microsomal prostaglandin E2 synthase-1, implying the selectivity of BRP-7 for FLAP. Finally, BRP-7 was effective in HWB and impaired inflammation in vivo, in rat pleurisy and mouse peritonitis, along with reducing LT levels.

CONCLUSIONS AND IMPLICATIONS BRP-7 potently suppresses LT biosynthesis by interacting with FLAP and exhibits anti-inflammatory effectiveness in vivo, with promising potential for further development.

Abbreviations 12-HHT, 12-hydroxy-5,8,10-heptadecatrienoic acid; 5-HPETE, 5-hydroperoxyeicosatetraenoic acid; 5-LOX, 5-lipoxygenase; AA, arachidonic acid; cPLA2, cytosolic PLA2; cysLTs, cysteinyl LTs; DPPH, 1,1-diphenyl-2-picrylhydrazyl; FLAP, 5-lipoxygenase-activating protein; fMLP, N-formyl-methionyl-leucyl-phenylalanine; hERG, human ether-a-go-go gene; HWB, human whole blood; IFM, immunofluorescence microscopy; mPGES-1, microsomal PGE2 synthase-1; MTT, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide; PGC buffer, PBS pH 7.4 containing 1 mg·mL−1 glucose and 1 mM CaCl2; SDS-b, SDS-PAGE sample loading buffer; STI, soybean trypsin inhibitor © 2014 The British Pharmacological Society

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Introduction The leukotrienes (LTs) comprise two different classes of proinflammatory lipid mediators derived from arachidonic acid (AA) with distinct biological activities. Whereas LTB4 acts as a chemoattractant for leukocytes and promotes immunological responses, the cysteinyl-containing LTS (cysLTs) C4, D4 and E4 induce bronchoconstriction and mucus secretion, cause plasma extravasation and stimulate fibrocyte proliferation (Peters-Golden and Henderson, 2007). Consequently, intervention with LTs represents a pertinent pharmacological approach against inflammatory diseases, and anti-LT therapy has been validated in clinical trials of asthma and allergic rhinitis, with potential in other respiratory and allergic disorders (Peters-Golden and Henderson, 2007), as well as in cardiovascular diseases such as atherosclerosis, myocardial infarction, stroke and abdominal aortic aneurysm (Riccioni and Back, 2012). The biosynthesis of LTs requires first the liberation of AA from membrane phospholipids that is conferred by the cytosolic PLA2 (cPLA2) (Uozumi et al., 1997). Then, 5-lipoxygenase (5-LOX) catalyses the incorporation of molecular oxygen into AA to generate 5-hydroperoxyeicosatetraenoic acid (5-HPETE) that is dehydrated by 5-LOX into LTA4 (for nomenclature see Alexander et al., 2013). This unstable epoxide intermediate is further metabolized to bioactive LTs by LTA4 hydrolase (yielding LTB4) or LTC4 synthase (yielding LTC4) (Radmark et al., 2007). Substantial experimental evidence indicates that the cellular production of LTs from endogenous AA requires the so-called 5-LOX-activating protein (FLAP), which may play an essential role in AA transfer to 5-LOX (Abramovitz et al., 1993; Ferguson et al., 2007). FLAP is a trimeric 18 kD protein localized at the nuclear membrane and belongs to the superfamily of membrane-associated proteins in eicosanoid and glutathione metabolism (MAPEG). However, neither an enzymatic function nor modulation by GSH has been revealed for FLAP thus far (Evans et al., 2008; Ferguson, 2012). Apparently, FLAP acts as a scaffold for 5-LOX at the nuclear envelope (Bair et al., 2012), where it facilitates access of AA to 5-LOX (Ferguson et al., 2007). Importantly, genetic ablation or pharmacological interference of FLAP fully abolishes the generation of 5-LOX-derived products (Byrum et al., 1997; Evans et al., 2008), implying its crucial role in LT biosynthesis. In the past, two chemotypes of FLAP inhibitors, namely the indole series (e.g. MK886) and quinoline-based compounds (e.g. BAY X-1005/DG-031) or hybrids thereof (MK591), have been developed and evaluated in clinical trials, but these compounds were not further explored (Evans et al., 2008; Sampson, 2009; Ferguson, 2012). Recent re-assessment of FLAP inhibitors of the indole series provided GSK2190915 as a promising candidate that is currently undergoing phase II trials in patients with asthma (Stock et al., 2011; Bain et al., 2013; Follows et al., 2013; Kent et al., 2013; Snowise et al., 2013). Also, the anti-inflammatory compound licofelone, which was originally developed as a dual inhibitor of the COX and 5-LOX pathways (Laufer et al., 1994a,b), targets FLAP (Fischer et al., 2007) and has reached clinical phase III for osteoarthritis (Raynauld et al., 2009). Inspired by the therapeutic potential of FLAP inhibitors, we attempted to discover novel chemotypes using a 3052


virtual screening approach targeting FLAP. By means of a combined ligand- and structure-based pharmacophore model, we recently identified BRP-7 [1-(2-chlorobenzyl)-2-(1(4-isobutylphenyl)ethyl)-1H-benzimidazole] (Figure 1A) as a LT synthesis inhibitor in intact neutrophils, without direct effects on 5-LOX (Banoglu et al., 2012). Here, we show that (i) BRP-7 inhibits 5-LOX product synthesis with typical features of well-recognized FLAP inhibitors; (ii) is effective in human whole blood (HWB); and (iii) has anti-inflammatory effects in two LT-related functional in vivo models, suggesting promising potential for further development.

Methods Materials BRP-7 was synthesized and characterized as reported previously (Banoglu et al., 2012). RSC-3388 (N-{(2S,4R)-4(biphenyl-2-ylmethyl-isobutyl-amino)-1-[2-(2,4-difluorobenzoyl)-benzoyl]-pyrrolidin-2-ylmethyl}-3-[4-(2,4-dioxothiazolidin-5-ylidenemethyl)-phenyl]acrylamide) was purchased from Calbiochem (Bad Soden, Germany), zileuton from Sequoia Research Products (Oxford, UK), MK886 from Cayman Chemical (Ann Arbor, MI, USA), and zymosan and λ-carrageenan type IV isolated from Gigartina aciculairis and Gigartina pistillata from Sigma (Milan, Italy). HPLC solvents were from VWR International GmbH (Darmstadt, Germany). AA, Ca2+ ionophore A23187, celecoxib, LPS, N-formylmethionyl-leucyl-phenylalanine (fMLP), indomethacin and all other fine chemicals were from Sigma (Taufkirchen, Germany), unless stated otherwise. BRP-7 probes for fishing approach were synthesized as indicated in the Supporting Information Appendix S1.

Cells Neutrophils and monocytes were isolated from buffy coats from adult healthy volunteers obtained at the Institute of Transfusion Medicine, University Hospital Jena. Neutrophils were immediately isolated by dextran sedimentation and centrifugation on Nycoprep cushions (PAA Laboratories, Linz, Austria) and hypotonic lysis of erythrocytes as described previously (Pergola et al., 2008). Monocytes were separated from peripheral blood mononuclear cells by adherence to culture flasks as described previously (Pergola et al., 2011). To exclude any cytotox effects of the test compounds, cell viability was analysed by the 3-(4,5-dimethyl-2-thiazolyl)-2,5diphenyl-2H-tetrazolium bromide (MTT) assay as described previously (Tretiakova et al., 2008).

Determination of 5-LOX product formation For assays in intact cells, neutrophils or monocytes [5 × 106 and 2 × 106 mL−1, respectively; in PBS (pH 7.4) containing 1 mg·mL−1 glucose and 1 mM CaCl2 (PGC buffer); incubation volume, 1 mL] were pre-incubated with the compounds or vehicle (0.1% DMSO) for 15 min at 37°C. Then, 2.5 μM A23187 plus AA was added. For neutrophils, 40 μM AA was used as a standard concentration, as in previous studies (Werz et al., 2002), whereas 10 μM AA was used for monocytes, because of substrate inhibition at higher AA concentrations. The reaction was stopped after 10 min with 1 mL methanol

BRP-7 suppresses leukotrienes by targeting FLAP

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Figure 1 BRP-7 has features resembling other FLAP inhibitors. (A) BRP-7 structure. (B) 5-LOX product formation in human neutrophils stimulated with A23187 (2.5 μM), without or with AA (40 μM), after pre-incubation with BRP-7 or vehicle (0.1% DMSO). (C) Effects of 10 μM BRP-7, 100 nM MK886 or 10 μM zileuton on 5-LOX product formation in intact neutrophils and in neutrophil homogenates, and on the activity of human recombinant 5-LOX. Intact neutrophils were stimulated with A23187 (2.5 μM). For homogenates and purified 5-LOX, test compounds were added 5 min before the addition of 1 mM Ca2+ plus 40 μM AA. (D) Effects of BRP-7 on the activity of human recombinant 5-LOX at increasing AA substrate concentrations. (E) Reducing conditions do not restore 5-LOX inhibition by BRP-7. GSH (5 mM) or vehicle was added to homogenates of neutrophils, prior to BRP-7 addition. After 10 min on ice, 1 mM CaCl2 and 40 μM AA were added for 10 min at 37°C. The 100% controls correspond to 5-LOX products in (B, C, E) intact cells, 117.5 ± 17.5 and 831.3 ± 50.9 ng·mL−1, for A23187 or A23187 + AA, respectively; purified 5-LOX, 947.8 ± 125.2 ng·mL−1; homogenates, 484.7 ± 72 ng·mL−1 and 429.6 ± 111.8 ng·mL−1, without GSH and after addition of 5 mM GSH, respectively; (D) 37.9 ± 6.1, 153.1 ± 4.6, 610.3 ± 37.8 and 812.3 ± 22.6 ng·mL−1, in the presence of 1, 3, 10 and 20 μM AA respectively. (F) Cell viability of human neutrophils after 30 min of pre-incubation at 37°C with vehicle (0.1% DMSO), 10 μM BRP-7 or 1% Triton X-100. (G) Analysis of radioactivity in supernatants of [3H]-AA-labelled neutrophils after pre-incubation with 10 μM BRP-7, 100 nM MK886, 10 μM zileuton or 1 μM cPLA2 inhibitor (RSC-3388) and stimulation with 2.5 μM A23187 plus 50 μM thiomersal; 100% corresponds to 18 073 ± 1735 cpm. Data are means + SEM; n = 3–9; *P < 0.05; **P < 0.01; ***P < 0.001 (B) versus inhibition by the corresponding BRP-7 concentration without the addition of AA; (C–F) versus 100% control; ANOVA plus Bonferroni. British Journal of Pharmacology (2014) 171 3051–3064

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and 30 μL 1 N HCl, and 200 ng PGB1 and 500 μL of PBS were added. For assays in cell homogenates, 1 mM EDTA was added to cells re-suspended in PBS. Samples were cooled on ice (5 min), sonicated (3 × 10 s) at 4°C, and 1 mM ATP and 1 mM DTT were added, as indicated. For assays with isolated 5-LOX, Escherichia coli BL21 was transformed with pT3-5LO plasmid, human recombinant 5-LOX protein was expressed at 30°C as described previously (Pergola et al., 2012), and partially purified 5-LOX was added to 1 mL of a 5-LOX reaction mix (PBS, pH 7.4, 1 mM EDTA, 1 mM ATP). Samples (0.5–2 μg of partially purified 5-LOX, resulting in about 1000 ng·mL−1 5-LOX products in an activity test performed with 20 μM AA; or cell homogenates, corresponding to 5 × 106 and 2 × 106 cells·mL−1 per sample, for neutrophils and monocytes, respectively) were incubated for 10 min at 4°C with vehicle or test compounds, pre-warmed for 30 s at 37°C, and 2 mM CaCl2 and the indicated concentrations of AA were added. The reaction was stopped as indicated for intact cells. For assays in HWB, freshly withdrawn blood from healthy adult donors was obtained by venipuncture and collected in monovettes containing 16 IE heparin·mL−1. Aliquots of 2 mL were primed with 1 μg·mL−1 LPS for 15 min at 37°C, followed by incubation with vehicle (0.1% DMSO) or test compounds for 15 min at 37°C, and stimulation with 1 μM fMLP for 15 min at 37°C. Samples were prepared for extraction of metabolites and then extracted and analysed by HPLC as described previously (Pergola et al., 2012). 5-LOX products include LTB4, its all-trans isomers and 5-HPETE. The cysteinyl leukotrienes (cysLTs) C4, D4 and E4 were not detected. For the determination of cysLTs in supernatants of monocytes, a cysLT ELISA kit from Enzo Life Sciences International Inc. (Lörrach, Germany) was used.

Determination of 3H-labelled AA release Release of 3H-labelled AA from neutrophils and monocytes was analysed as previously described (Fischer et al., 2005). Briefly, freshly isolated cells were re-suspended at 1 × 107 in 1 mL of RPMI 1640 medium containing 5 nM [3H]-AA (corresponding to 0.5 μCi·mL−1, specific activity 200 Ci·mmol−1) and incubated for 120 min at 37°C in 5% CO2 atmosphere. Cells were then washed twice with PBS containing 1 mg·mL−1 glucose and 2 mg·mL−1 fatty acid-free bovine albumin to remove unincorporated [3H]-AA. Labelled cells (2 × 107 mL−1 PMNL and 5 × 106 mL−1 monocytes) were re-suspended in 1 mL of PGC containing 2 mg·mL−1 fatty acid-free bovine albumin and pre-incubated with 0.1% DMSO or test compounds (15 min, 37°C). Neutrophils were stimulated with 2.5 μM A23187 in the presence of 50 μM thiomersal to block the re-acylation of unconverted AA into membranes (Zarini et al., 2006), and monocytes were stimulated with 2.5 μM A23187. The samples were then placed on ice, centrifuged and aliquots (300 μL) of the supernatants were assayed for radioactivity by scintillation counting (Micro Beta Trilux; PerkinElmer, Waltham, MA, USA).

Analysis of subcellular redistribution of 5-LOX For analysis of 5-LOX subcellular redistribution, neutrophils (3 × 107 mL−1 PGC buffer) were pre-incubated with 0.1% 3054


DMSO or BRP-7 for 15 min at 37°C and stimulated with 2.5 μM A23187. After 5 min, the reaction was stopped on ice and samples were centrifuged (200× g for 5 min at 4°C). Subcellular fractionation was performed by mild detergent (0.1% NP40) lysis, yielding a nuclear and a non-nuclear fraction as described previously (Werz et al., 2001). Aliquots (20 μL) of nuclear and non-nuclear fractions were analysed by SDSPAGE and Western blotting as described previously (Pergola et al., 2012). 5-LOX antiserum (1551, AK7, kindly provided by Dr Olof Rådmark, Karolinska Institutet, Stockholm, Sweden) was used at 1:100 dilution; alkaline phosphatase-conjugated IgGs (Sigma-Aldrich) were used at 1:1000 dilution. Proteins were visualized with nitro blue tetrazolium and 5-bromo-4chloro-3-indolylphosphate in detection buffer [100 mM Tris/ HCl (pH 9.5), 100 mM NaCl, 5 mM MgCl2]. Analysis of 5-LOX subcellular localization by indirect immunofluorescence microscopy (IFM) was performed as described previously (Pergola et al., 2008; 2011). In brief, neutrophils or monocytes were pre-incubated with 0.1% DMSO or test compounds (15 min at 37°C), then placed onto polyL-lysine (MW 150 000–300 000; Sigma-Aldrich)-coated glass coverslips, and activated by the addition of 2.5 μM A23187 for 3 min at 37°C. Cells were fixed in methanol (−20°C, 30 min) and permeabilized with 0.1% Tween 20 in PBS (RT, 10 min), followed by three washing steps with PBS. Samples were blocked with 10% non-immune goat serum (Invitrogen, Darmstadt, Germany) for 10 min at RT, washed with PBS and incubated with mouse anti-5-LOX (kindly provided by Dr Dieter Steinhilber, University of Frankfurt, Germany) and rabbit anti-FLAP (1:200; Abcam, Cambridge, UK) for 1 h at RT. The coverslips were washed 10 times with PBS, incubated for 10 min at RT in the dark with Alexa Fluor 488 goat anti-rabbit (1:1500) and Alexa Fluor 555 anti-mouse IgG (1:1000) (Invitrogen) diluted in PBS, and washed 10 times with PBS. Where indicated, the DNA was stained with 0.1 μg·mL−1 DAPI in PBS for 3 min at RT in the dark. The coverslips were then mounted on glass slides with Mowiol (Calbiochem) containing 2.5% n-propyl gallate (Sigma-Aldrich). The fluorescence was visualized with a Zeiss Axio Observer.Z1 microscope (Carl Zeiss, Jena, Germany) and a Plan-Apochromat 100×/1.40 Oil DIC M27 objective. Images were taken with an AxioCam MR3 camera and were acquired, cut, linearly adjusted in the overall brightness and contrast, and exported to TIF by the AxioVision 4.8 software (Carl Zeiss).

Immobilization of BRP-7 derivatives and pull-down assays Toyopearl AF-Amino-650 M resin (Tosoh Bioscience, Stuttgart, Germany) was washed five times with water and acetate buffer (0.1 M sodium acetate, 0.5 M NaCl; pH 4) and once with 80% MeOH (pH 5). Then, 100 μmol of 1a and 2a carboxylate analogues were solubilized in 10 mL of 80% MeOH by adding 1 M NaOH until the compounds were completely dissolved. Subsequently, pH was adjusted to 5 with 1 M HCl. Toyopearl resin (500 μL) and 40 mg 1-ethyl-3-(3dimethylaminopropyl)carbodiimide were added to form amides 1b and 2b (48 h, pH 5). Probes were washed with acetate buffer and stored in 20% MeOH until use. For preparation of nuclear membranes, 1.5 × 109 neutrophils were lysed by a mild detergent (0.1% NP40) lysis with 1.6 mL of lysis buffer [10 mM Tris–HCl (pH 7.4), 10 mM


NaCl, 3 mM MgCl2, 1 mM EDTA, 0.1% NP-40, 1 mM PMSF, 60 μg·mL−1 soybean trypsin inhibitor (STI) and 10 μg·mL−1 leupeptin], vortexed (3 × 5 s), kept on ice for 10 min and centrifuged (1000× g, 10 min, 4°C) (Werz et al., 2001). The resulting pellets (nuclear fractions) were re-suspended in 500 μL of TKM buffer [50 mM Tris–HCl (pH 7.4), 25 mM KCl, 5 mM MgCl2, 250 mM sucrose, 1 mM EDTA, 1 mM PMSF, 60 μg·mL−1 STI and 10 μg·mL−1 leupeptin]. Nuclei were disrupted by sonication (3 × 5 s), samples were cleared by centrifugation (5 min, 10 000× g, 4°C) and the resulting supernatants were centrifuged for 1 h at 100 000× g, for isolation of membranes. The pellet was then re-suspended in 100 μL of membrane buffer [100 mM Tris–HCl (pH 7.4), 100 mM NaCl, 1 mM EDTA, 0.5 mM DTT, 5% glycerol, 0.05% Tween 20, 1 mM PMSF, 60 μg·mL−1 STI, 10 μg·mL−1 leupeptin], resulting in a protein concentration of about 6.5 mg·mL−1. For pull-down assays, 50 μL of resin was added to 500 μL of binding buffer [50 mM HEPES (pH 7.4), 200 mM NaCl, 1 mM EDTA] and 8 μL of the neutrophil nuclear membranes (corresponding to about 50 μg of protein), incubated (2.5 h, 4°C) and washed three times with 500 μL of binding buffer. Proteins were eluted with 50 μL of 2× SDS-b (SDS-PAGE sample loading buffer) (5 min, 96°C). Equal amounts of protein were loaded onto 16% acrylamide gels and analysed for FLAP by Western blotting using rabbit anti-FLAP (Abcam), anti-rabbit IRDye 800CW (Li-Cor Biosciences, Lincoln, NE, USA), and detection with an Odyssey Infrared Imaging System (Li-Cor Bioscience), and analysis by the Odyssey application software (version 3.0.25).

Activity assays of COX-1 and -2, of microsomal PGE2 synthase-1 (mPGES-1) Activities of the purified ovine COX-1 (50 units) or human recombinant COX-2 (20 units) (both from Cayman Chemical) were analysed as described previously (Koeberle et al., 2008). Briefly, the COX enzymes were pre-incubated with the test compound for 5 min at 4°C, samples were pre-warmed for 60 s at 37°C, AA (5 μM for COX-1, 2 μM for COX-2) was added, and after 5 min at 37°C, the COX product 12-hydroxy-5,8,10-heptadecatrienoic acid (12-HHT) was analysed by HPLC. Indomethacin (10 μM) was used as a reference inhibitor. To analyse the effect of BRP-7 on cellular COX-1 activity, freshly isolated human platelets (108 mL−1 PGC buffer) were pre-incubated with test compounds for 15 min at 37°C and stimulated for 10 min at 37°C with 5 μM AA. The COX reaction was stopped and 12-HHT was analysed as for the isolated enzyme. To analyse the effect of BRP-7 on cellular COX-2 activity, A549 cells were stimulated with 2 ng·mL−1 IL-1β for 72 h to induce COX-2 expression, washed twice with PBS, re-suspended in PGC buffer (2 × 106 cells·mL−1) and preincubated with the indicated compounds for 15 min at 37°C. After stimulation for 15 min at 37°C with 3 μM AA, the reaction was stopped on ice, the supernatants were recovered after centrifugation at 60× g for 10 min at 4°C, and 6-keto PGF1α formation was measured by ELISA (6-keto PGF1α from Sapphire Bioscience, Waterloo, Australia). Preparation of A549 cells and determination of mPGES-1 activity was performed as described previously (Koeberle

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et al., 2008). In brief, cells (2 × 106 cells in 20 mL of medium) were plated, incubated for 16 h (37°C, 5% CO2) and then the culture medium was replaced by fresh DMEM/high glucose (4.5 g·L−1) medium containing 2% (v v−1) FCS. mPGES-1 expression was induced by 2 ng·mL−1 IL-1β for 72 h. Cells were sonicated and the microsomal fraction was prepared by differential centrifugation at 10 000× g for 10 min and at 174 000× g for 1 h. The pellet was re-suspended in 1 mL of homogenization buffer [0.1 M potassium phosphate buffer (pH 7.4), 1 mM PMSF, 60 μg·mL−1 STI, 1 μg·mL−1 leupeptin, 2.5 mM glutathione and 250 mM sucrose] and then serially diluted in 0.1 M potassium phosphate buffer (pH 7.4) containing 2.5 mM glutathione for activity test. A dilution leading to about 10 μM PGE2 (using 20 μM PGH2 as substrate; incubation volume, 100 μL) was finally used for the experiments. The microsomal membranes (total volume, 100 μL) were pre-incubated with the test compounds or 0.1% DMSO. After 15 min, PGE2 formation was initiated by the addition of PGH2 (20 μM). After 1 min at 4°C, the reaction was terminated with 100 μL of stop solution (40 mM FeCl2, 80 mM citric acid and 10 μM of 11β-PGE2 as internal standard), and PGE2 was separated by solid-phase extraction (RP-18 material) and analysed by HPLC.

Evaluation of human ether-a-go-go gene (hERG) and CYP3A4 inhibition The experiments for evaluation of hERG and cytochrome P450 (CYP3A4) inhibition were performed by Cyprotex Discovery Ltd (Macclesfield, UK), as indicated in the Supporting Information Appendix S1. Briefly, the hERG assay was performed with CHO cells stably transfected with hERG and electrophysiology measurements by an IonWorksTM HT instrument (Molecular Devices Corporation, Sunnyvale, CA, USA) and specialized multi-well plate (PatchPlateTM). For CYP3A4 assay, the test compound was incubated with human liver microsomes and NADPH in the presence of the specific CYP3A4 substrate, midazolam. 1-Hydroxymidazolam was monitored by LC-MS/MS.

Animal studies The animal studies are reported in accordance with the ARRIVE guidelines for reporting experiments involving animals (Kilkenny et al., 2010; McGrath et al., 2010). Male Wistar Han rats (200–230 g; Harlan, San Pietro al Natisone, Italy, and Charles River, Calco, Italy) and male CD-1 mice (35–40 g; Charles River) (30 rats, 50 mice) were housed at the Department of Pharmacy (Naples, Italy) in a controlled environment (21 ± 2°C) and provided with standard rodent chow and water. Animals were allowed to acclimatize for 4 days before the experiments and were subjected to a 12 h light– 12 h dark schedule. Experiments were conducted during the light phase. Animal care was in compliance with Italian regulations on protection of animals used for experimental and other scientific purpose (Ministerial Decree 116/92) as well as with the European Economic Community regulations (Official Journal of the European Community L 358/1 12/18/ 1986). The animal studies were approved by the local ethical committee of the University of Naples Federico II on 10 February 2011 (approval number 2011/0017635) and on 28 June 2011 (approval number 2011/0075376). British Journal of Pharmacology (2014) 171 3051–3064

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The carrageenan-induced pleurisy in rats was performed as described previously (Pergola et al., 2012). Thus, BRP-7 or MK886 at the indicated dose or vehicle (1.5 mL of 0.9% saline solution containing 4% DMSO) was given i.p. 30 min before λ-carrageenan type IV 1% (w v−1; 0.2 mL), which was injected into the pleural cavity. The animals were killed by inhalation of CO2 at 4 h, the pleural exudates were collected, the cells in the exudates were counted and the amounts of LTB4 were assayed by EIA kit (Cayman Chemical), according to manufacturer’s instructions. For zymosan-induced peritonitis in mice, BRP-7 or MK-886 at the indicated dose or vehicle (0.5 mL of 0.9% saline solution containing 2% DMSO) was given i.p. 30 min before zymosan i.p. injection (0.5 mL of suspension of 2 mg mL−1 in 0.9% w/v saline). Mice were killed by inhalation of CO2 at the indicated time, followed by a peritoneal lavage with 3 mL of cold PBS. Exudates were collected, the cells in the exudates were counted and LTC4 was measured by EIA (Cayman Chemical). Vascular permeability was assessed by the Evans blue method according to Kolaczkowska et al. (2002).

Statistics Results are expressed as mean + SEM of n observations, where n represents the number of experiments performed on different days in duplicates or the number of animals, as indicated. The IC50 values were determined by interpolation on semilogarithmic graphs and validated with GraphPad Prism software (GraphPad, San Diego, CA, ISA). Statistical evaluation of the data was performed by one-way ANOVA) for independent or correlated samples, followed by Tukey’s HSD (honestly significant difference) post hoc tests. Where appropriate, Student’s t-test was applied. A P-value < 0.05 (*) was considered significant.

Results Differential inhibition of 5-LOX product synthesis by BRP-7 in cell-based and cell-free assays Firstly, we studied the ability of BRP-7 to interfere with 5-LOX product synthesis and we addressed whether BRP-7 shares typical mechanistic properties with FLAP inhibitors. As we observed no significant differences in the inhibitory potency between the individual enantiomers (Sardella et al., 2013), racemic BRP-7 was used. In agreement with our previous results (Banoglu et al., 2012), BRP-7 concentrationdependently inhibited the formation of 5-LOX-derived products (i.e. LTB4 and its trans isomers and 5-HPETE) in A23187-stimulated human neutrophils (IC50 = 0.15 ± 0.08 μM; Figure 1B). However, BRP-7 did not inhibit 5-LOX product formation in cell-free assays (i.e. human recombinant 5-LOX or neutrophil homogenates), which was similar to the FLAP inhibitor MK886, whereas the direct 5-LOX inhibitor zileuton was active in this respect (Figure 1C). Failure to inhibit 5-LOX in such cell-free assays was independent of the substrate concentration (Figure 1D), excluding a competitive mode of action, and may indicate the lack of a direct effect on 5-LOX, but it may also be related to a lack 3056


of effect under non-reducing conditions, as reported for nonredox-type 5-LOX inhibitors (Werz et al., 1998). In contrast to this class of compounds, however, inclusion of GSH in homogenates did not restore the inhibitory effect of BRP-7 on 5-LOX (Figure 1E). Also, BRP-7 was ineffective as a radical scavenger in a DPPH (1,1-diphenyl-2-picrylhydrazyl) assay (not shown), excluding interference by redox-related mechanisms. Together, direct interference of BRP-7 with 5-LOX can be excluded. Moreover, non-specific effects of BRP-7 in intact cells due to cell toxicity are unlikely because BRP-7 had no significant effects on cell viability (Figure 1F). Of interest, as described for MK886 (Fischer et al., 2007), the efficiency of BRP-7 in A23187-stimulated neutrophils was significantly reduced when excess (40 μM) exogenous AA was included (Figure 1A), despite it not inducing a significant inhibition of AA release from [3H]-AA-labelled neutrophils (Figure 1G).

BRP-7 blocks 5-LOX co-localization with FLAP at the nuclear envelope in neutrophils FLAP inhibitors were shown to block 5-LOX translocation to the nucleus seemingly by preventing the association between 5-LOX/FLAP (Evans et al., 2008). As shown in Figure 2A, upon stimulation of neutrophils with A23187, cytosolic 5-LOX is translocated to the nucleus, and this was concentrationdependently inhibited by BRP-7, starting at 1 μM, although complete inhibition was not observed even at 10 μM. IFM allowed more detailed analysis of 5-LOX subcellular localization and also of FLAP (Figure 2B). In unstimulated cells, FLAP was localized to the nuclear envelope, whereas 5-LOX was distributed within the cytosol, and co-localization of 5-LOX and FLAP was not evident. Upon A23187 stimulation, 5-LOX clearly co-localized with FLAP at the nuclear envelope. Preincubation of neutrophils with BRP-7 or MK886 (10 μM and 100 nM, concentrations that completely inhibited 5-LOX product formation) prevented the 5-LOX association with FLAP, although only to a partial extent, indicating that inhibition of 5-LOX translocation by FLAP inhibitors is not directly related to LT suppression. To analyse the interaction of BRP-7 with FLAP, we used an affinity chromatography method using an insoluble BRP-7 matrix and solubilized FLAP (from neutrophil membranes) as the protein source. Thus, the 2′-chlorine in BRP-7 was replaced by a methylene ether linked either via an amide function to a sepharose matrix (yielding matrix 1b) or to ethyl carboxylate (yielding 1a) (Figure 3A). Compound 1a inhibited 5-LOX product synthesis, although with a lower potency as compared to BRP-7 (IC50 for 1a = 2.6 ± 1.1 μM). The truncated analogues thereof, that is, matrix 2b and compound 2a, were used as negative, inactive controls (Figure 3A; IC50 for 2a was >10 μM). Interestingly, FLAP was enriched in pull-downs using matrix 1b that carries the bioactive probe, as compared to matrix 2b (Figure 3B). Excess BRP-7 (100 μM) prevented the FLAP enrichment in pull-downs with matrix 1b (Figure 3B), as expected. 5-LOX protein was not detected in the pull-downs (not shown), excluding possible indirect effects on FLAP.

Cellular pharmacology of BRP-7 in monocytes Besides neutrophils, monocytes are a major source of LTs (Surette et al., 1993; Pergola et al., 2011). We thus determined


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Figure 2 BRP-7 reduces the nuclear translocation of 5-LOX in human neutrophils. Analysis of 5-LOX localization by (A) subcellular fractionation and (B) IFM. (A) Neutrophils were pre-incubated for 15 min at 37°C with vehicle (0.1% DMSO) or BRP-7 and then stimulated with 2.5 μM A23187 for 5 min at 37°C and lysed by mild detergent (0.1% NP-40). Non-nuclear (non-nucl) and nuclear (nucl) fractions were analysed by Western blot and densitometric analysis was performed. Data are given as means + SEM; n = 3. (B) Neutrophils were pre-incubated with vehicle (0.1% DMSO), BRP-7 (10 μM), MK-886 (100 nM) and stimulated by A23187 (2.5 μM; 3 min). Cells were fixed, permeabilized and incubated with mouse anti-5-LOX and rabbit anti-FLAP, followed by Alexa Fluor 488 goat anti-rabbit IgG and Alexa Fluor 555 goat anti-mouse IgG. Red: 5-LOX; green: FLAP. Scale bar: 10 μm. The pictures shown are representative of three similar samples.

the effects of BRP-7 on 5-LOX product formation in human monocytes stimulated with A23187 in the presence or absence of exogenous AA (10 μM). BRP-7 potently inhibited the formation of 5-LOX products (LTB4 and its trans isomers and 5-HPETE) in the absence of AA with an IC50 = 0.04 ± 0.01 μM (Figure 4A). In the presence of 10 μM AA, BRP-7 still inhibited 5-LOX activity, but, similar to that observed for neutrophils, with lower potency (IC50 = 0.25 ± 0.1 μM). In

contrast to neutrophils, monocytes may convert LTA4 by LTC4 synthase to LTC4, and BRP-7 efficiently also suppressed the synthesis of cysLTs (IC50 = 0.03 ± 0.01 μM; Figure 4B). In monocyte homogenates, BRP-7 up to 0.3 μM failed to significantly inhibit 5-LOX activity and this was also found for MK886 but not for zileuton, as expected (Figure 4A). Analysis of cell viability revealed no compromising effect of BRP-7 (10 μM) as compared to staurosporine (1 μM), used as control British Journal of Pharmacology (2014) 171 3051–3064

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Figure 3 FLAP binds to an immobilized BRP-7 derivative. (A) Structures of BRP-7 derivatives used for the evaluation of IC50 values for 5-LOX products in A23187-stimulated human neutrophils (compounds 1a and 2a), and for protein fishing experiments after coupling on amino-activated Toyopearl AF-Amino-650 (compounds 1b and 2b). Compounds 2a and 2b were used as inactive controls. In (B), nuclear membrane proteins of human neutrophils were incubated with 1b or 2b functionalized beads. For 1b functionalized beads, competition was performed with 100 μM BRP-7, as indicated. Precipitated proteins were analysed by Western blot for FLAP or by Coomassie staining followed by densitometry. Similar results were obtained in two additional experiments.

(Figure 4C). In addition to 5-LOX products, monocytes also generate other related eicosanoids from AA including 12- and 15-HPETE, as well as the COX product 12-HHT (Pergola et al., 2011). However, neither the formation of 12- and 15-HPETE, nor 12-HHT, nor the amount of radioactivity in the supernatant (from [3H]-AA) after A23187 stimulation was affected by 10 μM BRP-7 (Figure 4D,E), implying it has a selective effect on 5-LOX product synthesis. As observed previously (Pergola et al., 2011), the bulk of the 5-LOX protein in resting monocytes was localized inside the nucleus, whereas FLAP was found at the nuclear membrane (Figure 4F). A23187 stimulation redistributed 5-LOX to the nuclear membrane, where it co-localized with FLAP. BRP-7 and MK886 efficiently prevented the co-localization of 5-LOX and FLAP, even though the compounds failed to restore the pattern to that of resting cells with clear intranuclear 5-LOX. These data indicate that FLAP inhibitors prevent the association of 5-LOX with FLAP in stimulated monocytes but do not generally interfere with the redistribution of 5-LOX in these stimulated cells.

Effects of BRP-7 on COX-1 and -2, mPGES-1, CYP3A4 and hERG FLAP inhibitors such as MK886 tend also to inhibit other enzymes involved in the AA cascade, including COX-1 and mPGES-1 (Claveau et al., 2003; Koeberle et al., 2009), which let us to evaluate their selectivity. BRP-7 (at 10 μM) did not inhibit COX-1 or COX-2 in both cell-free (Figure 5A,B) and cellular (Figure 5C,D) assays, and also failed to significantly block mPGES-1 activity in a cell-free assay (Figure 5E). Reference compounds for COX enzymes (indomethacin) and for mPGES-1 (MK886) confirmed the functionality of the assays respectively. Finally, we tested the ability of BRP-7 to inhibit CYP3A4, the most common CYP-isoforms in drug metabolism for prediction of probable drug interactions. BRP-7 did not significantly inhibit CYP3A4 activity up to 25 μM as compared to the reference drug ketoconazole (which showed an IC50 of 0.04 μM; n = 7). In addition, BRP-7 as a lipophilic benzimidazole derivative could bind to 3058


the human ether-a-go-go gene (hERG) voltage-gated potassium channel thereby prolonging the drug-induced QT interval (Yao et al., 2008). However, there was no appreciable hERG inhibition up to 10 μM (0.97% inhibition; n = 19).

Efficiency of BRP-7 in HWB and efficacy in vivo Given the favourable efficiency and selectivity of BRP-7, we next aimed to estimate its effectiveness and pharmacological relevance under more complex systems and in vivo. Thus, we analysed 5-LOX product synthesis in HWB stimulated with the pathophysiological relevant stimuli LPS and fMLP, which includes important variables such as plasma protein binding, presence of co-factors and cell–cell interactions. BRP-7 significantly inhibited 5-LOX product synthesis in blood with an IC50 of 4.8 ± 1 μM (Figure 6A), which is slightly higher, in the single-digit micromolar range, than that for MK886 (IC50 of 1.1 ± 0.4 μM; not shown). We next studied the effects of BRP-7 in vivo using the carrageenan-induced pleurisy in rats, an animal model of acute inflammation involving 5-LOX. The i.p. pretreatment (30 min before carrageenan administration) of rats with 10, 20 or 30 mg·kg−1 of BRP-7 significantly reduced the inflammatory reaction, measured as exudate volume, inflammatory cell numbers and LTB4 levels in the pleural exudates (Table 1, Figure 6B), with an ID50 value for LTB4 inhibition of about 20 mg·kg−1. For comparison, the reference FLAP inhibitor MK886 (at the maximally effective dose of 1 mg·kg−1, i.p.) also significantly reduced exudate volume, infiltrated cells and LTB4 (Table 1, Figure 6B). In zymosan-induced peritonitis in mice, another well-recognized model of acute inflammation, BRP-7 significantly impaired levels of LTC4 with an ID50 of about 20 mg·kg−1 (Figure 6C). At this dose, BRP-7 reduced vascular permeability by 38% and inhibited neutrophil infiltration by 30% (Table 2), compared to reductions of 76 and 37% by MK886 (1 mg·kg−1), respectively, implying that BRP7-induced inhibition of LT biosynthesis in vivo is associated with its anti-inflammatory efficacy.


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Figure 4 Cellular pharmacology of BRP-7 in human monocytes. (A, B) Effect of BRP-7, 100 nM MK886 or 10 μM zileuton on (A) LTB4 + 5-H(P)ETE and (B) cysLT formation in intact human monocytes stimulated with A23187 (2.5 μM) in the presence or absence of exogenous AA (10 μM) or in monocyte homogenates treated with 1 mM Ca2+ plus 10 μM AA. Pre-incubation with compounds or vehicle (0.1% DMSO) was performed for 15 min at 37°C for intact cells or 5 min at 4°C for homogenates. The 100% controls correspond to (A) A23187, 42.0 ± 4.1 ng·mL−1; A23187 + AA, 29.2 ± 1.3 ng·mL−1; homogenates, 49.7 ± 13.2 ng·mL−1; (B) 583 ± 85 pg·mL−1. (C) Cell viability of human monocytes after a 30 min pre-incubation at 37°C with vehicle (0.1% DMSO), 10 μM BRP-7 or 1 μM staurosporine (stsp). (D) Effect of 10 μM BRP-7 on the formation of 12-HETE, 15-HETE and 12-HHT in monocytes stimulated for 10 min at 37°C with A23187 (2.5 μM). The 100% controls correspond to 12-HETE, 127.5 ± 27.2 ng·mL−1; 15-HETE, 3.9 ± 1.2 ng·mL−1; 12-HHT, 19.4 ± 2.6 ng·mL−1. (E) Analysis of radioactivity in supernatants of [3H]-AA-labelled monocytes after pre-incubation with 10 μM BRP-7 or 1 μM cPLA2 inhibitor (RSC-3388) and stimulation with 2.5 μM A23187;100% corresponds to 25 437 ± 4226 cpm. (F) Analysis of 5-LOX localization by indirect IFM after pre-incubation of adherent monocytes for 15 min at 37°C with vehicle (0.1% DMSO), BRP-7 (10 μM) or MK-886 (100 nM) and stimulation with A23187 (2.5 μM, 3 min). Cells were fixed, permeabilized and incubated with mouse anti-5-LOX and rabbit anti-FLAP, followed by Alexa Fluor 488 goat anti-rabbit IgG, Alexa Fluor 555 goat anti-mouse IgG and DAPI. Red, 5-LOX; green, FLAP; blue, DNA. Scale bar: 10 μm. Sections were generated with the AxioVision 4.8 software from 0.2 μm step Z stacks of adherent monocytes (adhesion substrate on the right side of the view). The cutting plane is indicated in the overlays by white triangles. In (A)–(C), data are expressed as percentage of vehicle control (100%) and are means + SEM; n = 3; *P < 0.05; **P < 0.01; ***P < 0.001 (A) versus 100% control; ANOVA plus Bonferroni. British Journal of Pharmacology (2014) 171 3051–3064

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Figure 5 Effect of BRP-7 on COX-1, COX-2 and mPGES-1 activity. Effect of BRP-7 (10 μM) on the activity of (A) purified ovine COX-1 or (B) human recombinant COX-2 as measured by HPLC analysis of COX-derived 12-HHT after incubation with AA (5 and 2 μM, for COX-1 and COX-2 respectively). Effect of BRP-7 (10 μM) on the activity of (C) COX-1 by HPLC analysis of 12-HHT production in freshly isolated human platelets stimulated with 5 μM AA or of (D) COX-2 by EIA analysis of 6-keto PGF1α in IL-1β-stimulated A549 cells treated with 3 μM AA. (E) Effect of BRP-7 (10 μM) on mPGES-1 activity, measured by HPLC analysis of PGE2 produced in microsomes of IL-1β-stimulated A549 cells treated with 20 μM PGH2. (A–D) 10 μM indomethacin (indo) and (E) 10 μM MK886 were used as positive controls. The 100% controls correspond to (A) 132.0 ± 13.2 ng·mL−1 12-HHT; (B) 103.8 ± 13.4 ng·mL−1 12-HHT; (C) 138.5 ± 24.1 ng·mL−1 12-HHT; (D) 406.8 ± 145.9 pg·mL−1 6-keto PGF1α; (E) 1.1 ± 0.2 nmol PGE2 in 100 μL reaction buffer. Data are expressed as percentage of stimulated vehicle control (100%) and are means + SEM; n = 3–5; *P < 0.05; ***P < 0.001 versus 100% control; ANOVA plus Bonferroni.

Table 1 Effect of BRP-7 on carrageenan-induced pleurisy in rats

Treatmenta

LTB4 (ng pro rat)b

Exudate volume (mL)b

Inflammatory cells (× 106)b

Vehicle

0.573 ± 0.130

0.45 ± 0.13

50.0 ± 7.2

0.505 ± 0.092

0.14 ± 0.09*

31.0 ± 1.6**

88.2%

31.1%

62.0%

0. 314 ± 0.078

0.20 ± 0.08*

26.7 ± 3.2***

54.8%

44.4%

53.4%

0.157 ± 0.028

0.03 ± 0.08**

18.6 ± 3.9**

27.4%

6.6%

37.2%

0.113 ± 0.032

0.08 ± 0.08**

36.7 ± 2.7*

19.7%

17.7%

73.4%

−1

10 mg·kg

BRP-7

20 mg·kg−1 BRP-7 −1

30 mg·kg

BRP-7

1 mg·kg−1 MK886

Data are means ± SEM, n = 4–7. Values in italics are percentage of vehicle control. Male rats (n = 5–7) were treated i.p. with 10, 20 or 30 mg·kg−1 BRP-7, vehicle (4% DMSO) or 1 mg·kg−1 MK886, as indicated, 30 min before intrapleural injection of carrageenan. b Analysis was performed 4 h after carrageenan injection. *P < 0.05; **P < 0.01; ***P < 0.001 versus vehicle (ANOVA + Bonferroni). a

Discussion and conclusions There is currently a strong interest in the development of FLAP inhibitors because of their promising potential as therapeutics against inflammatory and allergic disorders as well as against cardiovascular disease (Evans et al., 2008; Back, 2009; Sampson, 2009; Ferguson, 2012; Bain et al., 2013; Kent et al., 2013). However, recent development of drug candidates targeting FLAP (e.g. GSK2190915) concentrates on the classical FLAP inhibitor structure of MK886 and novel chemotypes are rare but urgently in demand. Here, we provide evidence that 3060


BRP-7, a recently identified hit from an in silico FLAP inhibitor discovery approach (Banoglu et al., 2012), acts on FLAP and thereby efficiently suppresses 5-LOX product synthesis in vitro and in vivo with anti-inflammatory effectiveness. Our results demonstrate that BRP-7 (i) efficiently inhibits cellular 5-LOX product synthesis and shares typical features of FLAP inhibitors; (ii) interferes with 5-LOX subcellular localization and co-localization with FLAP; (iii) does not inhibit other related or relevant enzymes involved in AA metabolism; (iv) does not interfere with CYP3A4 or hERG in vitro; and (iv) is effective in HWB and in animal models of acute inflamma-


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Figure 6 BRP-7 suppresses 5-LOX product formation in human whole blood. Effect of BRP-7 on (A) 5-LOX product formation in human whole blood stimulated with LPS (1 μg·mL−1; 30 min, 37°C) and fMLP (1 μM; 15 min, 37°C). BRP-7 or vehicle (0.1% DMSO) were added 10 min before fMLP. 5-LOX products were assessed by HPLC and are means + SEM of percentage of vehicle control (100%, corresponding to 41.3 ± 6.5 ng·mL−1, n = 6); (B) LTB4 levels in carrageenan-induced pleurisy in rats; (C) LTC4 levels in zymosan-induced peritonitis in mice. In (B) and (C), male rats or mice (n = 5–7, each group) were treated i.p. with 10, 20 or 30 mg·kg−1 BRP-7, 1 mg·kg−1 MK886 or vehicle (4 or 2% DMSO, for rat pleurisy and mouse peritonitis, respectively), 30 min before (B) intrapleural injection of carrageenan or (C) i.p. injection of zymosan. Analysis was performed (B) 4 h after carrageenan injection or (C) 30 min after zymosan injection. Data are means + SEM % of vehicle control; 100% corresponds to (B) 0.573 ± 0.130 ng·mL−1 LTB4 or (C) 142.3 ± 17.1 ng·mL−1 LTC4. **P < 0.01; ***P < 0.001 versus vehicle control; ANOVA plus Bonferroni.

Table 2 Effect of BRP-7 on zymosan-induced peritonitis in mice

Treatmenta

LTC4 (ng·mL−1)b

Vehicle

144.1 ± 20.0

BRP-7

70.4 ± 16.0* 48.8%

MK886

7.5 ± 1.6*** 5.2%

Vascular permeability (A650)b

Inflammatory cells (× 106)c

1.35 ± 0.12

24.5 ± 1.9

0.84 ± 0.09*

17.7 ± 1.0**

62.2%

69.7%

0.32 ± 0.05***

16.1 ± 0.5**

23.7%

63.4%

Data are means ± SEM, n = 6. Values in italics are percentage of vehicle control. Male mice (n = 6, each group) were treated i.p. with 20 mg·kg−1 BRP-7, 1 mg·kg−1 MK886 or vehicle (2% DMSO), 30 min before i.p. injection of zymosan. b Analysis was performed 30 min after zymosan injection. c Analysis was performed 4 h after zymosan injection. *P < 0.05; **P < 0.01; ***P < 0.001 versus vehicle (Student’s t-test). a

tion and this is accompanied by reduced LT levels. Therefore, BRP-7 might represent a novel basic structure for the development of alternative FLAP inhibitors suitable for exploitation as tools and/or potential therapeutics.

Pharmacological intervention with the LT pathway encompasses essentially three different strategies, that is, inhibition of enzymes involved in LT biosynthesis (e.g. 5-LOX, LTA4 hydrolase or LTC4 synthase), antagonism of LT British Journal of Pharmacology (2014) 171 3051–3064

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receptors (e.g. the cysLT1 antagonist montelukast) and inhibition of LT formation by interference with FLAP. As compared to LT receptor antagonism and to inhibition of LTA4 hydrolase or LTC4 synthase, targeting 5-LOX or FLAP appears advantageous because it leads to suppression of both classes of LTs (LTB4 and cysLT) and is appealing for its higher efficacy as an anti-inflammatory therapy. Although the possibility of direct inhibition of 5-LOX as a medical intervention has been extensively explored, the successful development of 5-LOX inhibitors has been strongly hampered due to their toxicity or lack of in vivo efficacy (Pergola and Werz, 2010), and until today, only one 5-LOX inhibitor (zileuton) could possibly enter the market. In contrast, targeting FLAP has demonstrated promise in animal studies and in early clinical phases, but no FLAP inhibitor has yet received marketing authorization (Hofmann and Steinhilber, 2013). In fact, the discovery and evaluation of new FLAP-interfering chemotypes has been strongly limited by the fact that FLAP has no specific enzymatic functionality, which might be utilized as a measure for a simple and convenient compound screening approach. For this reason, experimental evidence for direct and functional FLAP targeting is limited and pharmacological evaluation of FLAP inhibitors has to rely on comparative analysis with previously recognized compounds (e.g. in terms of inhibition of 5-LOX product formation in cellular assays without direct 5-LOX inhibition), which has hampered the identification of novel clinically relevant compounds. In fact, research has mainly focused upon the structural optimization of the only two known chemotypes for FLAP inhibition, that is, the indole and quinoline cores (Sampson, 2009). Interestingly, the crystal structure of FLAP bound to two inhibitors has recently been elucidated and these studies have also provided functional insights into the role of FLAP in aiding 5-LOX for LTA4 synthesis, by revealing the location of the inhibitor-binding site (Ferguson et al., 2007; Ferguson, 2012). Although the resolution of the FLAP structure was too low for reliable structure-based design, we made use of the structural knowledge and combined it with ligand-based evidence to implement a rapid virtual screening strategy for the identification of new chemotypes for FLAP inhibitors (Banoglu et al., 2012). Screening of a pre-compiled collection of 2.8 mio vendor compounds (153 mio conformations) using this threedimensional pharmacophore query led to 1792 compounds matching the desired pharmacophoric features, and after filtering according to forcefield refinement and rescoring function, 192 virtual hits remained. Then by use of protein– ligand interaction fingerprint application of MOE, BRP-7 was revealed as the overall hit, but its pharmacological profile remained unexplored. BRP-7, a non-acidic benzimidazole derivative bearing the isobutylphenylethyl fingerprint of ibuprofen, is a novel structure that lacks typical pharmacophoric moieties of FLAP inhibitors, such as indole core, carboxylic acid or a quinoline residue (Evans et al., 2008; Sampson, 2009). Our present data show that BRP-7 displays the typical profile of FLAP inhibitors and exhibits pharmacological properties, which support its further development, that is, in vivo efficacy. Thus, similar to other FLAP inhibitors that typically fail to inhibit soluble 5-LOX in cell-free assays (Miller et al., 1990; Hatzelmann et al., 1993), BRP-7 failed to inhibit the activity of 5-LOX in 3062


cell homogenates (neutrophils and monocytes) or to inhibit isolated human recombinant 5-LOX at concentrations up to 100-fold higher than those needed to block cellular 5-LOX product synthesis by 50%. Similar features were observed for the FLAP inhibitor MK-866, whereas the direct 5-LOX inhibitor zileuton (Carter et al., 1991) blocked 5-LOX activity in the cell-free assay equally well as in intact neutrophils, as expected. A strong loss of potency in cell-free assays also holds true for direct 5-LOX inhibitors of the non-redox type, because of the lack of a reducing environment (Werz et al., 1998; Fischer et al., 2004), and this may also apply to BRP-7. However, unlike the non-redox-type 5-LOX inhibitors (Werz et al., 1998; Fischer et al., 2004), supplementation of neutrophil homogenates with GSH did not confer 5-LOX inhibitory properties to BRP-7, implying that the failure of BRP-7 to inhibit 5-LOX in cell-free assays is not due to a lack of reducing environment, but rather suggesting that BRP-7 acts on FLAP. As FLAP may confer high 5-LOX-mediated product synthesis by increasing the utilization of endogenously released AA by 5-LOX (Abramovitz et al., 1993; Ferguson, 2012), exogenous addition of AA as a substrate to some extent circumvents the requirement of FLAP. Accordingly, the potency of BRP-7 in the presence of exogenously added AA was reduced and no reduction of AA release was observed, again suggesting that BRP-7 interfers with FLAP. Finally, FLAP bound to the BRP-7-affinity matrix 1b more than the control matrix 2b carrying an inactive analogue, and this was reduced after competition with free BRP-7. Note that as compared to other FLAP inhibitors such as MK-866, BRP-7 showed a certain degree of selectivity with respect to other AA metabolizing enzymes (e.g. COX, 12/15-LOX) and MAPEG (e.g. mPGES-1). These data confirm the inhibition of AA transfer to 5-LOX as a primary effect of FLAP-interference, as suggested by previous studies (Ferguson et al., 2007). Interestingly, these effects on 5-LOX translocation and 5-LOX/FLAP localization were only observed at higher concentrations than those required for inhibition of LTs, suggesting that BRP-7’s direct effects on the interaction between 5-LOX and FLAP may be a secondary effect. It is notable that BRP-7 showed a higher potency in monocytes than in neutrophils, which may relate to differences in the role of FLAP or variations in the accessibility of the compound to the nuclear membrane between the different cell types. BRP-7 suppressed 5-LOX product formation in HWB and was effective in vivo in reducing LT levels and the inflammatory reaction, as observed in two well-recognized models of acute inflammation (i.e. carrageenan-induced pleurisy in rats and zymosan-induced peritonitis in mice). This is in contrast to several 5-LOX inhibitors, which are often found to be inactive under these conditions (Pergola and Werz, 2010). Although the actual potency of BRP-7 appears slightly lower as compared to optimized indole- or quinoline-containing derivatives, the chemical nature of BRP-7 and its synthetic accessibility offer several possibilities for lead optimization. Importantly, we did not observe significant inhibition of CYP3A4 by BRP-7, whereas CYP inhibition has been a critical issue for certain FLAP inhibitors (Hutchinson et al., 2009). Indeed, BRP-7 was also inactive on hERG and did not show significant cellular toxicity or obvious toxic effects in mice and rats. Together, we propose BRP-7 as novel chemotype that


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inhibits LT biosynthesis by targeting FLAP, without affecting related enzymes, such as 5-LOX, 12/15-LOX, COX-1, COX-2 and mPGES-1, but with pharmacological relevance in vivo and potential for further development as a lead compound.

Ferguson AD (2012). Structure-based drug design on membrane protein targets: human integral membrane protein 5-lipoxygenase-activating protein. Methods Mol Biol 841: 267–290.

Acknowledgements

Fischer L, Steinhilber D, Werz O (2004). Molecular pharmacological profile of the nonredox-type 5-lipoxygenase inhibitor CJ-13,610. Br J Pharmacol 142: 861–868.

We gratefully acknowledge the financial support by The Scientific and Technological Research Council of Turkey (TÜBI˙TAK Grant No. 112S596). We thank Julia Seegers, Katrin Fischer, Petra Wiecha and Monika Listing for expert technical assistance.

Conflict of interest

Ferguson AD, McKeever BM, Xu S, Wisniewski D, Miller DK, Yamin TT et al. (2007). Crystal structure of inhibitor-bound human 5-lipoxygenase-activating protein. Science 317 (5837): 510–512.

Fischer L, Poeckel D, Buerkert E, Steinhilber D, Werz O (2005). Inhibitors of actin polymerisation stimulate arachidonic acid release and 5-lipoxygenase activation by upregulation of Ca2+ mobilisation in polymorphonuclear leukocytes involving Src family kinases. Biochim Biophys Acta 1736: 109–119. Fischer L, Hornig M, Pergola C, Meindl N, Franke L, Tanrikulu Y et al. (2007). The molecular mechanism of the inhibition by licofelone of the biosynthesis of 5-lipoxygenase products. Br J Pharmacol 152: 471–480.

None.

Follows RM, Snowise NG, Ho SY, Ambery CL, Smart K, McQuade BA (2013). Efficacy, safety and tolerability of GSK2190915, a 5-lipoxygenase activating protein inhibitor, in adults and adolescents with persistent asthma: a randomised dose-ranging study. Respir Res 14: 54.

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Abramovitz M, Wong E, Cox ME, Richardson CD, Li C, Vickers PJ (1993). 5-Lipoxygenase-activating protein stimulates the utilization of arachidonic acid by 5-lipoxygenase. Eur J Biochem 215: 105–111. Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Spedding M, Peters JA, Harmar AJ and CGTP Collaborators (2013). The Concise Guide to PHARMACOLOGY 2013/14: Enzymes. Br J Pharmacol 170: 1797–1867. Back M (2009). Inhibitors of the 5-lipoxygenase pathway in atherosclerosis. Curr Pharm Des 15: 3116–3132. Bain G, King CD, Schaab K, Rewolinski M, Norris V, Ambery C et al. (2013). Pharmacodynamics, pharmacokinetics and safety of GSK2190915, a novel oral anti-inflammatory 5-lipoxygenaseactivating protein inhibitor. Br J Clin Pharmacol 75: 779–790. Bair AM, Turman MV, Vaine CA, Panettieri RA Jr, Soberman RJ (2012). The nuclear membrane leukotriene synthetic complex is a signal integrator and transducer. Mol Biol Cell 23: 4456–4464. Banoglu E, Caliskan B, Luderer S, Eren G, Ozkan Y, Altenhofen W et al. (2012). Identification of novel benzimidazole derivatives as inhibitors of leukotriene biosynthesis by virtual screening targeting 5-lipoxygenase-activating protein (FLAP). Bioorg Med Chem 20: 3728–3741. Byrum RS, Goulet JL, Griffiths RJ, Koller BH (1997). Role of the 5-lipoxygenase-activating protein (FLAP) in murine acute inflammatory responses. J Exp Med 185: 1065–1075. Carter GW, Young PR, Albert DH, Bouska J, Dyer R, Bell RL et al. (1991). 5-Lipoxygenase inhibitory activity of zileuton. J Pharmacol Exp Ther 256: 929–937. Claveau D, Sirinyan M, Guay J, Gordon R, Chan CC, Bureau Y et al. (2003). Microsomal prostaglandin E synthase-1 is a major terminal synthase that is selectively up-regulated during cyclooxygenase-2-dependent prostaglandin E2 production in the rat adjuvant-induced arthritis model. J Immunol 170: 4738–4744. Evans JF, Ferguson AD, Mosley RT, Hutchinson JH (2008). What’s all the FLAP about? 5-Lipoxygenase-activating protein inhibitors for inflammatory diseases. Trends Pharmacol Sci 29: 72–78.

Hofmann B, Steinhilber D (2013). 5-Lipoxygenase inhibitors: a review of recent patents (2010–2012). Expert Opin Ther Pat 23: 895–909. Hutchinson JH, Li Y, Arruda JM, Baccei C, Bain G, Chapman C et al. (2009). 5-Lipoxygenase-activating protein inhibitors: development of 3-[3-tert-butylsulfanyl-1-[4-(6-methoxy-pyridin-3yl)-benzyl]-5-(pyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic acid (AM103). J Med Chem 52: 5803–5815. Kent SE, Boyce M, Diamant Z, Singh D, O’Connor BJ, Saggu PS et al. (2013). The 5-lipoxygenase-activating protein inhibitor, GSK2190915, attenuates the early and late responses to inhaled allergen in mild asthma. Clin Exp Allergy 43: 177–186. Kilkenny C, Browne W, Cuthill IC, Emerson M, Altman DG (2010). Animal research: reporting in vivo experiments: the ARRIVE guidelines. Br J Pharmacol 160: 1577–1579. Koeberle A, Siemoneit U, Buhring U, Northoff H, Laufer S, Albrecht W et al. (2008). Licofelone suppresses prostaglandin E2 formation by interference with the inducible microsomal prostaglandin E2 synthase-1. J Pharmacol Exp Ther 326: 975–982. Koeberle A, Siemoneit U, Northoff H, Hofmann B, Schneider G, Werz O (2009). MK-886, an inhibitor of the 5-lipoxygenaseactivating protein, inhibits cyclooxygenase-1 activity and suppresses platelet aggregation. Eur J Pharmacol 608: 84–90. Kolaczkowska E, Shahzidi S, Seljelid R, van Rooijen N, Plytycz B (2002). Early vascular permeability in murine experimental peritonitis is co-mediated by resident peritoneal macrophages and mast cells: crucial involvement of macrophage-derived cysteinyl-leukotrienes. Inflammation 26: 61–71. Laufer S, Tries S, Augustin J, Dannhardt G (1994a). Pharmacological profile of a new pyrrolizine derivative inhibiting the enzymes cyclo-oxygenase and 5-lipoxygenase. Arzneimittelforschung 44: 629–636.


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Laufer SA, Augustin J, Dannhardt G, Kiefer W (1994b). (6,7-Diaryldihydropyrrolizin-5-yl)acetic acids, a novel class of potent dual inhibitors of both cyclooxygenase and 5-lipoxygenase. J Med Chem 37: 1894–1897. McGrath JC, Drummond GB, McLachlan EM, Kilkenny C, Wainwright CL (2010). Guidelines for reporting experiments involving animals: the ARRIVE guidelines. Br J Pharmacol 160: 1573–1576. Miller DK, Gillard JW, Vickers PJ, Sadowski S, Leveille C, Mancini JA et al. (1990). Identification and isolation of a membrane protein necessary for leukotriene production. Nature 343(6255): 278–281. Pergola C, Werz O (2010). 5-Lipoxygenase inhibitors: a review of recent developments and patents. Expert Opin Ther Pat 20: 355–375. Pergola C, Dodt G, Rossi A, Neunhoeffer E, Lawrenz B, Northoff H et al. (2008). ERK-mediated regulation of leukotriene biosynthesis by androgens: a molecular basis for gender differences in inflammation and asthma. Proc Natl Acad Sci U S A 105: 19881–19886. Pergola C, Rogge A, Dodt G, Northoff H, Weinigel C, Barz D et al. (2011). Testosterone suppresses phospholipase D, causing sex differences in leukotriene biosynthesis in human monocytes. FASEB J 25: 3377–3387. Pergola C, Jazzar B, Rossi A, Northoff H, Hamburger M, Sautebin L et al. (2012). On the inhibition of 5-lipoxygenase product formation by tryptanthrin: mechanistic studies and efficacy in vivo. Br J Pharmacol 165: 765–776. Peters-Golden M, Henderson WR Jr (2007). Leukotrienes. N Engl J Med 357: 1841–1854. Radmark O, Werz O, Steinhilber D, Samuelsson B (2007). 5-Lipoxygenase: regulation of expression and enzyme activity. Trends Biochem Sci 32: 332–341. Raynauld JP, Martel-Pelletier J, Bias P, Laufer S, Haraoui B, Choquette D et al. (2009). Protective effects of licofelone, a 5-lipoxygenase and cyclo-oxygenase inhibitor, versus naproxen on cartilage loss in knee osteoarthritis: a first multicentre clinical trial using quantitative MRI. Ann Rheum Dis 68: 938–947. Riccioni G, Back M (2012). Leukotrienes as modifiers of preclinical atherosclerosis? ScientificWorldJournal 2012: 490968. Sampson AP (2009). FLAP inhibitors for the treatment of inflammatory diseases. Curr Opin Investig Drugs 10: 1163–1172. Sardella R, Levent S, Ianni F, Caliskan B, Gerstmeier J, Pergola C et al. (2013). Chromatographic separation and biological evaluation of benzimidazole derivative enantiomers as inhibitors of leukotriene biosynthesis. J Pharm Biomed Anal 89C: 88–92. Snowise NG, Clements D, Ho SY, Follows RM (2013). Addition of a 5-lipoxygenase-activating protein inhibitor to an inhaled

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corticosteroid (ICS) or an ICS/long-acting beta-2-agonist combination in subjects with asthma. Curr Med Res Opin 29: 1663–1674. Stock NS, Bain G, Zunic J, Li Y, Ziff J, Roppe J et al. (2011). 5-Lipoxygenase-activating protein (FLAP) inhibitors. Part 4: development of 3-[3-tert-butylsulfanyl-1-[4-(6-ethoxypyridin-3-yl) benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2dimethylpropionic acid (AM803), a potent, oral, once daily FLAP inhibitor. J Med Chem 54: 8013–8029. Surette ME, Palmantier R, Gosselin J, Borgeat P (1993). Lipopolysaccharides prime whole human blood and isolated neutrophils for the increased synthesis of 5-lipoxygenase products by enhancing arachidonic acid availability: involvement of the CD14 antigen. J Exp Med 178: 1347–1355. Tretiakova I, Blaesius D, Maxia L, Wesselborg S, Schulze-Osthoff K, Cinatl J Jr et al. (2008). Myrtucommulone from Myrtus communis induces apoptosis in cancer cells via the mitochondrial pathway involving caspase-9. Apoptosis 13: 119–131. Uozumi N, Kume K, Nagase T, Nakatani N, Ishii S, Tashiro F et al. (1997). Role of cytosolic phospholipase A2 in allergic response and parturition. Nature 390 (6660): 618–622. Werz O, Szellas D, Henseler M, Steinhilber D (1998). Nonredox 5-lipoxygenase inhibitors require glutathione peroxidase for efficient inhibition of 5-lipoxygenase activity. Mol Pharmacol 54: 445–451. Werz O, Klemm J, Samuelsson B, Radmark O (2001). Phorbol ester up-regulates capacities for nuclear translocation and phosphorylation of 5-lipoxygenase in Mono Mac 6 cells and human polymorphonuclear leukocytes. Blood 97: 2487–2495. Werz O, Burkert E, Samuelsson B, Radmark O, Steinhilber D (2002). Activation of 5-lipoxygenase by cell stress is calcium independent in human polymorphonuclear leukocytes. Blood 99: 1044–1052. Yao X, Anderson DL, Ross SA, Lang DG, Desai BZ, Cooper DC et al. (2008). Predicting QT prolongation in humans during early drug development using hERG inhibition and an anaesthetized guinea-pig model. Br J Pharmacol 154: 1446–1456. Zarini S, Gijon MA, Folco G, Murphy RC (2006). Effect of arachidonic acid reacylation on leukotriene biosynthesis in human neutrophils stimulated with granulocyte-macrophage colony-stimulating factor and formyl-methionyl-leucylphenylalanine. J Biol Chem 281: 10134–10142.

Supporting information Additional Supporting Information may be found in the online version of this article at the publisher’s web-site: http://dx.doi.org/10.1111/bph.12625 Appendix S1 Supporting methods.

Article pubs.acs.org/jmc

5-Lipoxygenase-Activating Protein (FLAP) Inhibitors. Part 4: Development of 3-[3-tert-Butylsulfanyl-1-[4-(6-ethoxypyridin-3yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2dimethylpropionic Acid (AM803), a Potent, Oral, Once Daily FLAP Inhibitor

Downloaded by UNIV OF ARIZONA on September 3, 2015 | http://pubs.acs.org Publication Date (Web): November 7, 2011 | doi: 10.1021/jm2008369

Nicholas S. Stock,*,† Gretchen Bain,‡ Jasmine Zunic,† Yiwei Li,† Jeannie Ziff,† Jeffrey Roppe,† Angelina Santini,‡ Janice Darlington,‡ Pat Prodanovich,‡ Christopher D. King,§ Christopher Baccei,§ Catherine Lee,§ Haojing Rong,§ Charles Chapman,‡ Alex Broadhead,‡ Dan Lorrain,‡ Lucia Correa,‡ John H. Hutchinson,† Jilly F. Evans,‡ and Peppi Prasit† Departments of †Chemistry, ‡Biology, and §Drug Metabolism, Amira Pharmaceuticals, 9535 Waples Road, Suite 100, San Diego, California 92121, United States S Supporting Information *

ABSTRACT: The potent 5-lipoxygenase-activating protein (FLAP) inhibitor 3-[3-tertbutylsulfanyl-1-[4-(6-ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2yl]-2,2-dimethylpropionic acid 11cc is described (AM803, now GSK2190915). Building upon AM103 (1) (Hutchinson et al. J. Med Chem. 2009, 52, 5803−5815; Stock et al. Bioorg. Med. Chem. Lett. 2010, 20, 213−217; Stock et al. Bioorg. Med. Chem. Lett. 2010, 20, 4598−4601), SAR studies centering around the pyridine moiety led to the discovery of compounds that exhibit significantly increased potency in a human whole blood assay measuring LTB 4 inhibition with longer drug preincubation times (15 min vs 5 h). Further studies identified 11cc with a potency of 2.9 nM in FLAP binding, an IC50 of 76 nM for inhibition of LTB4 in human blood (5 h incubation) and excellent preclinical toxicology and pharmacokinetics in rat and dog. 11cc also demonstrated an extended pharmacodynamic effect in a rodent bronchoalveolar lavage (BAL) model. This compound has successfully completed phase 1 clinical studies in healthy volunteers and is currently undergoing phase 2 trials in asthmatic patients.

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leukotrienes (CysLTs) or historically as the slow-reacting substance of anaphylaxis (SRS-A). The biological effects of the LTs arise through binding to their respective G-protein-coupled receptors (GPCRs).4 LTB4 binds to two distinct GPCRs, namely, BLT1 and BLT2, resulting in neutrophil and eosinophil chemotaxis.5 The CysLTs activate at least two well-defined GPCRs, namely, CysLT16 and CysLT2,7 the activation of the former leading to contraction of smooth muscle (bronchoconstriction), edema, eosinophil migration, and mucus secretion. The precise role of the CysLT2 receptor remains unclear, but mice deficient in this receptor indicate a role for CysLT2 in vascular permeability and inflammation8 and its expression in myocytes, fibroblasts, and vascular smooth muscle cells may point to a function within the cardiovascular system.9 Recent evidence also points to the existence of other receptors that may preferentially bind CysLTs, namely, GPR17,10 P2Y12,11 and a putative CysLTE receptor.12

INTRODUCTION

The leukotrienes (LTs) are a family of eicosanoid bioactive lipids implicated in a variety of pathophysiological states such as asthma, allergic rhinitis, and atherosclerosis. Biosynthesis of leukotrienes is initiated through an immune, allergic, or inflammatory stimulus.2 They are derived from arachidonic acid (AA) through the concerted action of the enzyme 5lipoxygenase (5-LO) with 5-lipoxygenase activating protein (FLAP), initially converting AA to (5S,6E,8Z,11Z,14Z)-5hydroperoxy-6,8,11,14-eicosatetraenoic acid (5-HpETE, Figure 1). Subsequent dehydration of 5-HpETE yields leukotriene A 4 (LTA4), an unstable epoxide that is transformed to either leukotriene B4 (LTB4) by the enzyme LTA4 hydrolase or leukotriene C4 (LTC4) via conjugation of glutathione by LTC4 synthase. 5-HpETE can alternatively be converted to 5-oxoETE, a potent human chemoattractant for eosinophils, immune cells that play important roles in a variety of diseases including asthma and cardiovascular disease (CVD).3 LTC4 is further metabolized to leukotriene D4 (LTD4) and leukotriene E4 (LTE4) through sequential amide bond cleavages, and collectively these three molecules are known as the cysteinyl © 2011 American Chemical Society

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dx.doi.org/10.1021/jm2008369 | J. Med. Chem. 2011, 54, 8013−8029

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(DG-031/BAY X1005 4,14 MK-886 5,15 MK-591 616) in human and shown them to be effective. For various reasons, none of these compounds have reached the market. Development of compounds 4 and 5 was likely halted because of incomplete LT synthesis inhibition at clinically tolerable doses, and compound 6 was halted after phase 2 trials in favor of the LTD4 receptor antagonist 2.17 Significant evidence also points to the potential for LT inhibitors to have a positive impact on CVD. Genetic data implicate polymorphic variants in the ALOX5AP (FLAP) gene that predispose these individuals to an increased risk of myocardial infarction and stroke (deCODE study).18 This genetic correlation has now been confirmed in several other populations19 and more recently associated with an increased risk for coronary arterial disease in a European−American population.20 A murine 5LO-knockout model of CVD also supports the rationale for LT inhibition in this disease setting, as these mice were protected against the development of atherosclerotic lesions when fed a high fat, high cholesterol diet.21 Inhibition of the FLAP protein by 5 has also been shown to reduce atherosclerosis in an apoE/LDLR-double knockout mouse model.22 Of more significance is the observation that in humans, the 5-LO inhibitor 7 (VIA-2291, formerly known as ABT-761) reduces biomarkers of CVD and shows statistically significant reduction in the rate of plaque volume growth in patients with acute coronary syndrome.23 The FLAP inhibitor 4 has also been shown to reduce biomarkers in a CVD setting in a phase 2b study.24 The significant animal and human data implicating leukotrienes in various disease states prompted us to reassess the potential of FLAP inhibitors as an anti-inflammatory treatment paradigm. Safe and potent inhibitors of FLAP would prevent the biosynthesis of all LTs and may provide an improved therapy for respiratory diseases and potentially CVD.


Figure 1. Leukotriene biosynthesis pathway and associated GPCRs (in italics).

Chemical interference in the LT pathway is not a novel concept, as both a 5-LO inhibitor (zileuton, 3) and CysLT1 receptor antagonists (e.g., montelukast, 2) (Figure 2) are currently marketed for the treatment of asthma. Direct 5-LO inhibition has been an active research area for several decades, and only the iron chelator (redox inhibitor) 3 is used clinically, with no nonredox inhibitors currently on the market. However, 3 is not widely prescribed for asthma because of a high dose regimen (600 mg q.i.d. or 1200 mg b.i.d.), low but significant hepatotoxicity, and subsequent need for liver function testing. 13 2, a CysLT1 receptor antagonist, is widely prescribed to asthmatics because of its efficacy, excellent safety profile, and low dosing requirements (10 mg q.d.). CysLT1 antagonism obviously only blocks the action of this receptor and does not perturb the biosynthesis or pathophysiological action of the other LTs. Several clinical trials have evaluated FLAP inhibitors

Figure 2. Structures of leukotriene pathway inhibitors. 8014



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Scheme 1a

(a) R1CH2Br (see Scheme 2), Cs2CO3, MeCN or DMF, room temp to 60 °C; (b) Pd(dppf)Cl2·CH2Cl2 (cat.), bis(pinacolato)diboron, KOAc, pdioxane, 85 °C; (c) heteroaryl-X, Pd(PPh3)4 (cat.), DME/H2O, K2CO3, 80−85 °C; (d) LiOH·H2O, THF, H2O, MeOH, 60 °C.

a

with 2-methylquinoxaline, respectively).25 The symmetrical 2,5dimethylpyrazine gave a mixture of monochlorides and bischlorides that were readily separable by column chromatography. The 2-chloromethyl alkyl substituted pyridines (16a− d,f) and 2-chloromethyl-6-methylquinoline 17 hydrochlorides were prepared through synthesis of the N-oxide (m-CPBA), rearrangement of the N-oxide under refluxing acetic anhydride conditions to furnish the pyridine methylacetate, hydrolysis with concentrated hydrochloric acid, and reaction of the resulting alcohols with thionyl chloride to give the desired chloromethyl pyridines/quinoline as the HCl salt. Pyridine 16d was obtained from reaction of the commercially available 6hydroxymethyl-2-methylpyridine with thionyl chloride. The pyridine N-oxide 16g was synthesized through m-CPBA oxidation of the pyridine 16c. 5-Methoxy-2-methylpyridine, prepared from the corresponding phenol by reaction with TMSN2, was brominated using NBS and benzoyl peroxide in refluxing benzene to afford bromide 18. Similar bromination conditions were used to provide the 5-cyano-2-bromomethylpyridine 19 and the 6- and 7-fluoroquinoline derivatives 20 and 21. Heterocycles 22−25 were prepared from the commercially available alcohols using refluxing thionyl chloride. 5,6Dimethyl-2-chloromethylpyridine hydrochloride 26 was prepared from 2,3-lutidine through conversion to the N-oxide (mCPBA) and then rearrangement to 2-cyano-5,6-dimethylpyridine (TMSCN, diethylcarboamoyl chloride). Acidic methanolysis of the resulting nitrile to the methyl ester, reduction of the ester with DIBAl-H under standard conditions, and treatment of the alcohol with thionyl chloride afforded 26. 5Chloro-2-chloromethylpyridine 27 was derived from borane reduction of 5-chloropyridine-2-carboxylic acid and conversion of the resulting alcohol to the chloride using thionyl chloride. Finally, the Boc-protected indole 28 was synthesized from 1Hindole-2-carboxylic acid ethyl ester via reaction with Boc anhydride under standard conditions (DMAP, MeCN), reduction of the ester with DIBAl-H, and conversion of the resulting alcohol to the corresponding halide using a mixture of LiBr and MsCl in dichloromethane.26 The mixture of products from this halide displacement was used without further

In this paper we detail the design of 3-[3-tert-butylsulfanyl-1-[4(6-ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic acid 11cc (AM803, now GSK2190915), a potent derivative of our recently disclosed FLAP inhibitor AM103 1.1 A key part in the discovery of 11cc was the finding that certain compounds exhibit a heretofore unknown time-dependent increase in potency when assayed for LTB4 inhibition in a human blood assay (hWB). We herein discuss our findings, the SAR around this time-dependent phenomenon, and the ultimate identification of 11cc as a once a day, orally bioavailable FLAP inhibitor that has successfully finished phase 1 clinical trials and is currently in phase 2 trials in asthmatic patients.

CHEMISTRY The compounds prepared in this study were synthesized predominantly through two synthetic routes, A and B, as depicted in Scheme 1, and the resulting product structures are given in Tables 1−4 along with the route employed. Route A involves alkylation of the phenol of the previously reported indole 81 with the appropriate electrophile, using Cs2CO3 as base, yielding the indoles 9. Conversion of these aryl bromides to the pinacol boronate esters 10 was achieved using standard conditions (Pd(dppf)Cl2·CH2Cl2, bis(pinacolato)diboron, pdioxane, heat). This boronate served as a robust handle to cross-couple a variety of heteroaryl halides under Suzuki coupling conditions (Pd(PPh3)4, K2CO3, DME/H2O). Hydrolysis of the hindered geminal dimethyl ester using LiOH in MeOH/THF/H2O yielded the desired carboxylic acids 11. Route B reverses the order of steps by converting the indole 8 to the boronate derivative 12 and cross-coupling with the appropriate heteroaryl halide to generate compounds 13. Alkylation of these phenols using Cs2CO3 as base and the requisite electrophiles and subsequent ester hydrolysis afforded the target compounds 11. The commercially unavailable alkylating reagents were prepared as follows (Scheme 2). The pyrazinyl and quinoxalinyl chlorides 14 and 15 were synthesized using standard radical chlorination conditions (NCS with 2,5-dimethylpyrazine or trichloroisocyanuric acid

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Scheme 2. Preparation of Alkylating Agentsa

a (a) N-Chlorosuccinimide, C6H6, (PhCO)2, reflux; (b) trichloroisocyanuric acid, CHCl3, reflux; (c) m-CPBA, CHCl3; (d) Ac2O, 100 °C to reflux; (e) HCl (conc), reflux; (f) SOCl2, reflux; (g) N-bromosuccinimide, C6H6, (PhCO)2, reflux; (h) TMSCH2N2, toluene, MeOH; (i) TMSCN, Et2NC(O)Cl, CH2Cl2; (j) HCl (g), MeOH; (k) DIBAl-H, THF, −78 °C; (l) BH3·THF, THF, 0 °C; (m) Boc2O, DMAP, MeCN; (n) DIBAl-H, toluene, −40 °C; (o) LiBr, CH3SO2Cl, Et3N, CH2Cl2.

purification in the subsequent alkylation of the indole phenol 8. The Boc-protecting group was also removed during hydrolysis of the ester (route A) to give the indole compound 11g. As shown in Scheme 3, the racemic sulfoxide 29 was prepared via oxidation of 11cc with 1 equiv of m-CPBA. The acyl derivatives 31a,b were prepared through removal of the tert-butylthio group with AlCl3 and water27 to give the 3H indole 30 and subsequent Friedel−Crafts like acylation with AlCl3 and the relevant acid chloride in 1,2-dichloroethane and then ester hydrolysis. The pyridone 11jj was isolated after prolonged reaction of the sodium salt of 11cc in ethylene glycol with excess lithium hydroxide at 165 °C. The amide compound 11q was the result of concomitant hydrolysis of the precursor nitrile (compound 19 used in the alkylation of the phenol 3, Scheme 1) upon synthesis of the final carboxylic acid. Finally, the methoxypyrimidine derivative 11kk was obtained from an SNAr reaction. After cross-coupling of 2-chloro-5-fluoropyrimidine (Scheme 1, route B) and alkylation of the phenol with 2chloromethyl-5-methylpyridine, methanol displaced the aro-

matic fluoride under the hydrolysis reaction conditions to afford the methoxypyrimidine 11kk.

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BIOLOGY

All compounds were assayed in a FLAP binding assay using membranes prepared from human polymorphonuclear cells following a previously described protocol with minor modifications.28 The ligand used was tritiated 3-[5-(pyrid-2ylmethoxy)-3-tert-butylthio-1-benzylindol-2-yl]-2,2-dimethylpropionic acid (American Radiolabeled Chemicals, St. Louis, MO). Compounds were also screened in a cell-based human leukocyte assay (hLA) to measure the inhibition of LTB 4 production following calcium ionophore (A23187) challenge. To investigate the effect of blood protein binding on potency, compounds were tested in a human whole blood (hWB) or rat whole blood (rWB) assay to measure the inhibition of LTB4 production following A23187 challenge (15 min or 5 h of compound preincubation). 17a Selected compounds were 8016



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Scheme 3. SAR at 3-Position of the Indole and Preparation of Pyridinone 11jj a

a

(a) LiOH·H2O, MeOH, THF, H2O, 60 °C; (b) m-CPBA (1 equiv), CH2Cl2, −20 to 0 °C; (c) AlCl3, H2O, CH2Cl2 0 °C to room temp; (d) RC(O)Cl, AlCl3, DCE, 65 °C; (e) 1 N NaOH, EtOH; (f) LiOH·H2O, ethylene glycol, 165 °C.

screened for inhibition of thromboxane B2 synthesis in a human whole blood cyclooxygenase-1 assay (COX-1, 15 min of preincubation; see Experimental Section).

dependent increase in potency represents a previously unrecognized property that has important implications for the design and selection of FLAP inhibitors suitable for clinical development. Furthermore, this phenomenon appears selective for this particular series of FLAP inhibitors, as compound 3 showed no such improvement in LT synthesis inhibition in hWB after prolonged incubation (15 min hWB IC50 = 2.2 ± 1.2 μM (n = 3), 5 h hWB IC50 = 4.2 ± 2.4 μM (n = 3). As discussed in our previous paper,1 both 1 (15 min hWB IC50 = 349 nM) and 6 (15 min hWB IC50 = 536 nM) are potent FLAP inhibitors, the latter of which has demonstrated efficacy in human trials for asthma.16 Replacement of the chlorobenzyl substituent of 6 with a 2-methoxy-5-pyridyl moiety was part of the strategy in the identification of 1 to address some of the perceived liabilities of 6. Keeping the methoxypyridine component constant (R2 = 5-methoxypyridin2-yl, Scheme 1, compound 11), we prepared a small, focused series of compounds, varying R1 with aromatic groups including quinoline or similar aromatic bicycles (Table 1). All compounds were assayed in a human FLAP membrane binding assay to ascertain their intrinsic potency and in a cell-based LTB4 inhibition assay (hLA). Compounds were further profiled in a 15 min LTB4 inhibition assay (hWB) to measure the inhibition of FLAP in the presence of human blood. Inhibitors that showed good activity in the hWB assay (15 min hWB IC 50 < 1 μM) were further profiled using a 5 h compound preincubation period to determine if the blood LT inhibition potency increases over time. As can be seen from Table 1, we identified several quinoline replacement groups that showed good potency in all three assays. Of particular note is the observation that compounds 6, 11a, and 11c show an increase in hWB potency upon extended preincubation in this assay (6, 15 min IC50 = 554 nM, 5 h IC50 = 108 nM; 11a, 15 min IC50 = 502 nM, 5 h IC50 = 194 nM). The quinoxinyl derivative 11b possesses a similar in vitro profile, but the presence of a nitrogen at the 4-position apparently prevents this time

RESULTS AND DISCUSSION During our research to identify a backup compound to the recently disclosed FLAP inhibitor 1, we observed that in a rat bronchoalveolar lavage (BAL) LT inhibition assay compound 6 showed complete inhibition of LTB4 and CysLTs in vivo 16 h after oral dosing. The measured plasma concentration (10 nM) at 16 h was significantly below its rat whole blood assay (rWB) potency against LTB4 inhibition (IC50 = 117 nM, 15 min assay preincubation). The apparent discrepancy between the measured LT inhibition and the in vitro potency of 6 in the rWB assay led us to repeat this assay with an extended compound preincubation time (4 h). Interestingly, when compound 6 was repeated in the rWB assay with this 4 h preincubation, the IC50 had significantly decreased to 10 nM, a value more closely aligned with the in vivo potency observed in the rat BAL model. This indicated that the previous 15 min preincubation protocol did not permit the full potency of this class of FLAP inhibitors to be observed in blood. We had also previously screened and optimized compound selection using the hWB assay at 15 min preincubation times to ascertain their potency in the presence of human blood proteins. Therefore, we reanalyzed compounds in human blood with an extended compound preincubation time and identified certain compounds that gave significantly higher inhibitory potencies after these prolonged assay conditions. A time course analysis of both compounds 5 and 6 (15 min, 5 h, and 11 h) in the hWB assay indicated that near maximal inhibition occurred after 5 h of preincubation in human blood (hWB data for 5, 15 min IC50 = 1.4 μM, 5 h IC50 = 1.1 μM, 11 h IC50 = 1.0 μM; hWB data for 6, 15 min IC50 = 536 nM, 5 h IC50 = 95 nM, 11 h IC50 = 80 nM). For screening purposes the 5 h time point (5 h hWB) was chosen as the routine extended preincubation time. This time-

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substituted pyridine derivatives in an attempt to probe the SAR around this group and find compounds that exhibited the same time dependent increase in potency in the hWB assay as demonstrated by 6, 11a, and 11c (Table 2). A scan of methyl

Table 1. IC50 Results of FLAP Inhibitorsa


Table 2. IC 50 Results of FLAP Inhibitors: Pyridine Replacement SARa

a

NA, not applicable. ND, not determined. Values shown are ±standard deviation. bFLAP inhibition of 3H-ligand binding to FLAP membranes. chLA: inhibition of LTB4 synthesis following ionophore (A23187) challenge in human leukocytes. dhWB: inhibition of LTB4 synthesis following ionophore challenge (A23187) in human blood after either 15 min or 5 h of preincubation of target compound.

dependent potency enhancement (15 min IC50 = 542 nM, 5 h IC50 = 486 nM), despite excellent cell-based hLA LTB 4 inhibition and FLAP binding IC50 (0.7 and 11.4 nM, respectively). The 6-fluoro derivative 11c shows good hLA activity, FLAP binding, and 15 min hWB LTB4 inhibition and improves in potency by approximately 2-fold after extended preincubation in hWB. The 7-fluoroquinoline 11d exhibits an unexpected dramatic loss of affinity in FLAP binding, presumably due to an unfavorable electronic effect. The 6methylquinoline derivative 11e also shows marked decrease in binding affinity for the FLAP protein and concomitant reduction in hWB potency. Subsequent to the completion of this work, X-ray crystal data of the FLAP protein were published indicating a restricted binding pocket for the quinoline moiety of 1.29 This correlates well with our findings that the steric nature of the quinoline group alters activity against FLAP (e.g., compounds 11d and 11e). Replacement of the quinoline with the more basic imidazopyridine 11f retained potency in both FLAP binding and leukocyte LTB4 inhibition assays, but the extended preincubation hWB potency proved modest (15 min IC50 = 980 nM, 5 h IC50 = 552 nM). Replacement with an indole, compound 11g, led to a significant decrease in potency in all three assays. With the knowledge that a pyridine replacement for the quinoline maintained high affinity for FLAP (compound 1) we prepared a series of

a

NA, not applicable. ND, not determined. Values shown are ±standard deviation. bFLAP inhibition of 3H-ligand binding to FLAP membranes. chLA: inhibition of LTB4 synthesis following ionophore (A23187) challenge in human leukocytes. dhWB: inhibition of LTB4 synthesis following ionophore challenge (A23187) in human blood after either 15 min or 5 h of preincubation of target compound.

groups around the pyridine moiety (11h, 11i, 11j, and 11k) showed that the 5- and 6-methyl derivatives (11j and 11k) kept intrinsic potency comparable to that of 1, but only the 5-methyl derivative 11j showed a significant increase in potency in the 5 h hWB assay (15 min IC50 = 328 nM, 5 h IC50 = 87 nM for 11j vs 15 min IC50 = 349 nM to 5 h IC50 = 149 nM for 1). 8018




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Surprisingly, the 5-ethyl derivative 11l did not show any increase in potency in blood, presumably because of the steric difference between methyl and ethyl groups, albeit small, highlighting that a subtle difference could have a significant impact on the extended preincubation enhancement in hWB. Combining the 5-methyl group with another methyl substituent as in compounds 11m and 11n showed no advantage, the 3,5dimethyl analogue 11m possessing intrinsically poorer potency in all assays and the 5,6-dimethyl compound 11n exhibiting a weaker 5 h hWB IC50 (225 nm) compared to 11j. On the basis of the 5-methylpyridine imparting a favorable impact on hWB potency, several more 5-substituted analogues were examined. The 5-chloropyridine 11o loses some affinity for FLAP and hence shows less inhibition of LTB4 in the hWB assay, and the carboxamide 11q suffers a dramatic loss in activity. However, the 5-methoxy derivative 11p retained intrinsic hLA and FLAP binding activity but did not demonstrate any time-dependent increase in the 5 h hWB assay, a result similar to that observed with the 5-ethylpyridyl compound 11l. The pyrazinyl derivative 11r, like the quinoxinyl compound 11c, again exemplified that although heterocycles incorporating a nitrogen at the 4-position are well tolerated in hLA and FLAP binding, they also show no significant change in potency with extended preincubation in the hWB assay. Attempts to mimic the 5-methylpyridine with other small heterocycles yielded significantly less potent compounds (11s, 11t, and 11u). After identification of the 5-methylpyridine as a moiety that conferred significant potency in the 5 h hWB assay, continued SAR studies, primarily through modification of the indole Nbenzyl substituent, addressed off-target activities and pharmacokinetic properties (Table 3). Apart from 5-LO and FLAP, several other enzyme systems utilize AA as their substrate, including the cyclooxygenase (COX) enzymes. Therefore, we counterscreened compounds of interest against COX-1 in a human blood thromboxane inhibition assay. We were surprised to discover that heteroaryl rings on the biaryl possessing a meta-substituent (11v, 11x, 11bb, 11dd, 11gg) or pseudo-meta in the case of the ethoxythiazole 11y showed significant affinity for the COX-1 enzyme, with one compound, 11dd, possessing considerable potency (IC50 = 615 nM) in the COX-1 whole blood assay. The unsubstituted pyridines 11hh and 11ii also conferred some affinity for the COX-1 enzyme. Compounds bearing a para-substitutent on the terminal biphenyl ring (11cc, 11ee, 11ff, 11kk) show low affinity for COX-1. The pyridinone derivative 11jj is an example of a very polar biaryl functionality appended to the indole. This proved detrimental to inhibition of LTB4 in the leukocyte assay but retained affinity for FLAP (binding IC50 = 8.3 nM) and also shows the most significant improvement with extended preincubation in the hWB assay (15 min IC50 = 10028 nM to 5 h IC50 = 1279 nM ∼ 8-fold increase). However, this compound was not potent enough to warrant further investigation. To check for a potential timedependent increase in potency against the COX-1 enzyme, we assayed compound 11j, a compound that shows an increase in LT synthesis inhibition over time in hWB, in the COX-1 assay with both a 15 min and 5 h preincubation. Importantly, no increase in potency against COX-1 was measured over time (hWB COX-1, 15 min IC50 = 12.3 μM, 5 h IC50 = 17.3 μM). Manipulation of the 3-position of the indole core via removal of the tert-butylthio group of 11cc significantly attenuates the binding to FLAP and potency in blood (compound 29). Oxidation to the racemic sulfoxides 30 and the pyridine Noxide (11ll) also significantly reduces affinity for the FLAP

Table 3. IC50 Results of FLAP Inhibitors: SAR of Benzylic Biphenyl and COX-1 Counterscreena

a

ND, not determined. Values shown are ±standard deviation. bFLAP inhibition of 3H-ligand binding to FLAP membranes. chLA: inhibition of LTB4 synthesis following ionophore (A23187) challenge in human leukocytes. dhWB: inhibition of LTB4 synthesis following ionophore challenge (A23187) in human blood after either 15 min or 5 h of preincubation of target compound. eInhibition of TXB2 in human whole blood presented as either percent inhibition at 10 μM or IC50.

protein (Table 4). Appreciable activity could be returned to the scaffold through introduction of the tert-butylacetyl group at C3 of the indole, compound 31a, and this was the most potent of these derivatives prepared. However, despite the presence of the 5-methylpyridine, no significant increase in hWB potency was observed in the 5 h preincubation assay for 31a. Investigation of Time Dependent Increase in Potency of FLAP Inhibitors. Having identified the structural motifs responsible for imparting improved 5 h potency in the hWB assay, we attempted to determine the physical basis for this phenomenon. Our initial hypothesis was that compounds exhibiting a potency shift between the 15 min and 5 h hWB time points may reflect an intrinsic difference in the on-rate or off-rate of the compound to the FLAP protein itself. However, 8019



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hLA assay, in the absence of added human serum albumin (hSA) to the assay buffer, no potency increase was apparent between a 5 min and 1 h preincubation time for any of the compounds tested (Table 5). However, addition of 0.5% hSA

Table 4. IC50 Results of FLAP Inhibitors: Modification of 3Indole Positiona

Table 5. Human Leukocyte Assay (hLA) IC50 after Varying Preincubation Time in the Presence or Absence of 0.5% hSAa no hSA (nM)

0.5% hSA (nM)

compd

5 min

1h

10 min

3h

1 5 6 11cc

1.2 2.2 1.0 1.0

1.1 5.7 1.0 1.0

10 19 66 26

14 27 12 4

a


hLA: inhibition of LTB4 synthesis following ionophore (A23187) challenge in human leukocytes resuspended in assay buffer either lacking (no hSA) or containing 0.5% hSA. hSA = human serum albumin.

to the assay buffer resulted in a measurable shift in potency between a 10 min and 3 h preincubation time. These data indicate an equilibrium shift between compounds binding hSA and the target, FLAP. All of the compounds measured in these studies are highly lipophilic carboxylic acids and as such possess a very large degree of protein binding (≥99.5%, individual data not shown). Consequently, the time dependent increase in potency of this class of FLAP inhibitors in hWB might reflect subtle differences in the degree of protein binding that cannot be distinguished using conventional protein binding assays. Additionally, the time-dependent inhibition may also reflect differences in the off-rate from serum albumin. However, this does not fully explain the observed 5 h hWB differences between compounds such as 11z, 11aa, and 11cc, for example. All three possess almost identical in vitro potencies in FLAP binding, hLA, and 15 min hWB, but 11cc is twice as potent after 5 h of incubation in hWB. By analogy to the reported Xray crystal structure for FLAP with compound 6 bound,29 the differences between these three compounds were not anticipated to impart much variation in potency because of the biaryl portion of the molecule being directed away from the target protein and into the membrane space. The fact that 11cc is the significantly more potent of the three compounds in 5 h hWB may be due to other, as yet undetermined factors or that, for certain compounds (e.g., 11z and 11aa), a 5 h preincubation in the hWB assay may still not be a fully equilibrated situation. We recently reported on a similar potency enhancement in our research on prostaglandin D2 receptor (DP2) antagonists using an eosinophil shape change assay in human blood with extended compound preincubation.30 As part of our drug discovery effort, compounds are screened against the common human cytochrome P450 (hCYP) enzymes 3A4, 2C9, and 2D6 to minimize the possibility of drug−drug interactions or drug concentration variations upon long-term dosing. Table 6 shows the hCYP inhibition data for the four most potent compounds in the 5 h hWB assay: 11cc, 11ee, 11ff, 11kk. In general they show modest inhibition toward the hCYP isoforms tested, the fluoropyridine 11ff showing the most activity against 2C9 with an IC50 of 1.5 μM. Of particular note was compound 11cc, which was essentially inactive against all three of the enzymes listed at the highest concentration tested (50 μM).

a

ND, not determined. Values shown are ±standard deviation. Values in parentheses are the results of one experiment with two different donors. bFLAP inhibition of 3H-ligand binding to FLAP membranes. c hLA: inhibition of LTB4 synthesis following ionophore (A23187) challenge in human leukocytes. dhWB: inhibition of LTB4 synthesis following ionophore challenge (A23187) in human blood after either 15 min or 5 h of preincubation of target compound.

after preparing radiolabeled (3H) versions of compounds 1 and 11a, we determined that both compounds display fast on- and off-rates with no significant difference in on- or off-rates between compounds that demonstrate improved potency over time and those that do not (Figure 3). By employment of the

Figure 3. On-rates and off-rates for radiolabeled compounds 1 and 11a. 8020



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preincubation, 239 nM), potentially indicating an extended pharmacodynamic effect. However, the potency of 11cc increased substantially with an extended 4 h preincubation period in rWB, yielding an IC50 of 16 nM. The discrepancy between the measured plasma concentration in this 16 h pretreatment BAL experiment and the 4 h rWB potency (3 nM vs 16 nM) may reflect a concentration difference between lung tissue and plasma in the rat.

Table 6. CYP Inhibition Parameters for Four Most Potent FLAP Inhibitors (5 h hWB)a CYP inhibition IC50 (nM) compd

3A4

2C9

2D6

11cc 11ee 11ff 11kk

>50 8.5 5.5 8.8

>50 12 1.5 4.5

>50 >50 >50 >50

CONCLUSIONS We have discovered that a certain subset of FLAP inhibitors in this indole series require longer incubation times in blood to reach their equilibrium potency for LTB4 inhibition. From the SAR presented, this “time-dependent” effect appears limited to compounds bearing certain functional groups appended to the hydroxymethyl portion of the indole nucleus, the most potent of which are quinolines (for example, compounds 6, 11a, and 11c) or 5-methylpyridines (e.g., 11cc, 11ff, 11kk). Comparing the 5-methylpyridine derivative 11j to 1 clearly shows that addition of the methyl group increases affinity in the FLAP binding assay and potency in the 5 h preincubation hWB LTB4 assay. Utilizing this extended assay paradigm in hWB, we identified compound 11cc (3-[3-tert-butylsulfanyl-1-[4-(6ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)1H-indol-2-yl]-2,2-dimethylpropionic acid), which is a very effective inhibitor of LTB4 production in human blood, does not inhibit any of the major human CYP isoforms or the COX enzymes, and demonstrates excellent pharmacokinetic parameters in rat and dog. Furthermore 11cc demonstrated excellent in vivo inhibition of leukotrienes in a rodent BAL ionophore challenge model. 11cc has subsequently completed phase 1 clinical trials and is currently in phase 2 studies in patients, the results of which will be reported in a separate publication.

■

a


Inhibition assays were performed in a manner similar to those published.32 All positive control inhibitors were within their published IC50 values.

Further Profiling of 11cc (AM803). Compound 11cc, 3[3-tert-butylsulfanyl-1-[4-(6-ethoxypyridin-3-yl)benzyl]-5-(5methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic acid, was selected for further profiling because of its excellent in vitro potency against LTB4 inhibition in the 5 h hWB assay, inactivity against the three major human CYP isoforms, and no COX-1 cross-reactivity. Additionally, it showed no induction or time-dependent inhibition of the CYP3A4 enzyme (measured at 10 μM; 0.01 min−1 vs 0.054 min−1 for troleandomycin control) and no inhibition of the CYP2C19, 2D6, and 1A2 enzymes (IC 50 > 40 μM). Furthermore, 11cc showed very little activity toward other enzymes in the leukotriene pathway (LTA4 hydrolase IC50 > 100 μM, LTC4 synthase IC50 = 36 μM, 5-LO IC50 = 20 μM) and no activity against the COX-2 enzyme (IC50 > 100 μM in a human blood assay measuring PGE2 inhibition). Pharmacokinetic parameters were assessed in Sprague−Dawley rats (Table 7), and upon oral administration (10 mg/kg sodium carboxylate salt), 11cc showed good bioavailability (76%) and a Cmax of 10 μg/mL. Intravenous administration of 11cc (2 mg/ kg) showed a low systemic clearance of 5.2 mL min−1 kg−1 and a low volume of distribution (0.77 L/kg) with a 2−3 h terminal half-life. When dosed in dogs, 11cc demonstrated good bioavailability (51%), very low clearance (0.6 mL min −1 kg−1), low volume of distribution (0.2 L/kg), and a long iv half-life of 13 h. The low volume of distribution observed in dog is primarily attributable to 11cc possessing a very high degree of plasma protein binding (rat, 99.8%; dog, 99.7%; human, 99.5%). To ascertain the ability of 11cc to inhibit leukotriene synthesis in vivo, we employed a rodent BAL model.31 After a 3 mg/kg po dose 4 h prior to A23187 ionophore challenge, LTB4 and CysLT concentrations in the rat BAL fluid were significantly reduced (100% and 80%, respectively, n = 5, average measured plasma concentration of 11cc at 4 h of 1 μM). Of note is the observation that after a 3 mg/kg po dose of 11cc 16 h prior to ionophore challenge in the rat lung, inhibition of LTB4 (86%) and CysLT (41%) was maintained despite the measured plasma concentration (average of 3 nM, n = 5) being below the rWB IC50 (15 min

■

EXPERIMENTAL SECTION

FLAP Binding Assay. Packed human polymorphonuclear cell pellets (1.8 × 109 cells) (Biological Specialty Corporation) were resuspended and lysed, and 75000g pelleted membranes were prepared as described.28 The 75000g pelleted membranes were resuspended in a Tris buffer (50 mM Tris-HCl, pH 7.4, 1 mM EDTA, 1 mM DTT, 30% glycerol) to yield a protein concentration of ∼4 mg/ mL. An amount of 2.5 μg of membrane protein per well was added to 96-well deep well plates containing Tris-Tween buffer (100 mM TrisHCl, pH 7.4, 100 mM NaCl, 1 mM EDTA, 0.5 mM DTT, 5% glycerol, 0.05% Tween-20) and ∼30000 cpm of [3H]-3-[5-(pyrid-2-ylmethoxy)3-tert-butylthio-1-benzylindol-2-yl]-2,2-dimethylpropionic acid and test compound in a total volume of 100 μL and incubated for 60 min at room temperature. The mixtures were then harvested onto GF/ B filter plates using a Brandel 96-tip harvester and washed 3× with 1 mL of ice cold Tris-Tween buffer. The filter plates were dried and the bottoms sealed. An amount of 100 μL of scintillant was added. The plates were incubated for 1 h before reading on a Perkin-Elmer TopCount. Specific binding was defined as total radioactive binding minus nonspecific binding in the presence of 10 μM MK886. IC50

Table 7. Measured Pharmacokinetic Parameters for Four Most Potent FLAP Inhibitors (5 h hWB) a compd

T1/2 iv (h)

Cmax (μM)

F (%)

AUCpo (h·μg/mL)

Cl (mL min−1 kg−1)

Vdss (L/kg)

11cc 11ee 11ff 11kk

2.0 1.0 1.9 1.7

12.2 14.6 23.3 30.6

100 40 100 100

26 26 77 63

8.0 3.0 4.0 3.1

0.70 0.16 0.38 0.18

a

Compounds were dosed as the corresponding sodium carboxylate salt, 10 mg/kg po (0.5% methylcellulose) and 2 mg/kg iv (water) in Sprague− Dawley rats (male). 8021




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injection into the jugular vein (2 mg/mL, 1 mL/kg) and orally (po) (10 mg/kg) to two or three male rats as a suspension in 0.5% methylcellulose via an oral gavage to the stomach (3.33 mg/mL, 3 mL/kg). Blood samples (approximately 300 μL) were taken from each rat via the jugular vein cannula at time intervals up to 24 h postdose (8−9 samples per animal). After each sample, the cannula was flushed with an equivalent volume of heparinized saline (0.1 mL at 40 units/ mL). Plasma samples, prepared by centrifugation of whole blood, were stored frozen (−80 °C) prior to analysis. Sample Preparation and Calibration Curve. Known amounts of compound were added to thawed rat plasma to yield a concentration range from 5 to 5000 ng/mL. Plasma samples were precipitated using MeCN (1:5, v/v) containing the internal standard (IS) buspirone. An amount of 10 μL of the analyte mixture was injected using a Leap PAL autosampler. The calibration curves were constructed by plotting the peak areas of analyzed peaks against known concentrations. The data were subjected to linear regression analysis with 1/x weighting. The lower limits of quantitation (LLOQ) were 1−5 ng/mL. LC/MS Analysis. Analyses were performed using an Agilent Zorbax SB-C8 column (2.1 mm × 50 mm, 5 μm) linked to a Shimadzu LC-10AD VP with SCL-10A VP system controller. Tandem mass spectrometric (MS/MS) detection was carried out on a PE Sciex API3200 in the positive ion mode (ESI) by multiple reaction monitoring (IS 386.2 → 122.2). The mobile phases contained 10 mM ammonium acetate in water with 0.05% formic acid (solvent A) and 10 mM ammonium acetate in 50% MeCN/50% MeOH with 0.05% formic acid (solvent B). The flow rate was maintained at 0.7 mL/min, and the total run time was 3 min. Analytes were separated using a linear gradient as follows: mobile phase was held for 1 min at 5% B; B was increased from 5% to 95% over then next 0.5 min; B was held constant for 1 min at 95%; B was returned to the initial gradient conditions. Pharmacokinetic Calculations. The pharmacokinetic parameters were calculated by a noncompartmental analysis using WinNonlin (Pharsight, Mountain View, CA). Maximum plasma concentrations (Cmax) and their time of occurrence (Tmax) were both obtained directly from the measured data. Half-life values were calculated from 4 to 8 h unless otherwise noted. Dog pharmacokinetic studies were performed at LAB Pre-Clinical Research International, Inc., Laval, Quebec, Canada, using female beagle dogs (n = 3 per group). Compound 11cc was given intravenously at 2 mg/kg (2 mg/mL) in 75% PEG and 25% water and also orally at 5 mg/kg (1.67 mg/mL) dissolved in 0.5% Methocel. Plasma samples were shipped to Amira Pharmaceuticals and analyzed as described for rat. Chemistry. All procedures were carried out under a nitrogen atmosphere using commercially available solvents that were used without further purification. Starting materials were obtained from commercial sources and were used without further purification. Column chromatography was carried out either using glass columns packed with silica gel, eluting with the solvents reported, or using prepacked silica gel cartridges on a CombiFlash Rf separation system by Teledyne ISCO. Yields refer to chromatographically pure compounds as determined by TLC (single spot) and/or HPLC. HPLC analysis was carried out using an Agilent 1100 binary pump system using a diode array detector. The column used was a Waters Symmetry C18 3.5 μm, 4.6 mm × 150 mm. Final products had a purity of ≥95%. LCMS analyses were carried out using a Shimadzu LCMS-2010A system fitted with a SIL-HT autosampler, LC-10AD pumps, and a SPD-10AV UV−visible detector. NMR spectra were recorded using a Bruker Advance 300 MHz NMR spectrometer. Chemical shifts are reported in δ values relative to tetramethylsilane. 2-Chloromethyl-5-methylpyrazine (14). To a solution of 2,5dimethylpyrazine (20.0 mL, 0.187 mol) in benzene (450 mL) were added N-chlorosuccinimide (25.0 g, 0.187 mol) and benzoyl peroxide (400 mg). The mixture was heated under reflux for 18 h. An additional 5.0 g of NCS was added, and heating continued for a further 6 h. TLC analysis indicated almost complete consumption of starting material and the presence of two less polar products. The reaction mixture was evaporated to dryness and purified on silica gel (ISCO, 0−15% EtOAc

values were determined using Graphpad Prism analysis of drug titration curves. Compounds 1 and 11a were tritiated at American Radiolabeled Chemicals, St. Louis, MO. Analysis of on-rate was performed by incubating membranes with 10 μM cold competitor (for nonspecific binding) or vehicle (DMSO) for 5 min before addition of radioligand and further incubation with the radioligand for 1−60 min before harvesting by filtration. Analysis of the off-rate was performed by incubating membranes with radioligand for 30 min before addition of 10 μM cold competitor and further incubation with the cold competitor for 1−60 min before harvesting and filtration. Human Leukocyte Inhibition Assay (hLA). Blood was drawn from consenting human volunteers into heparinized tubes, and 1/3 volume of 3% dextran was added. After sedimentation of red blood cells a hypotonic lysis of remaining red blood cells was performed and leukocytes were sedimented at 1200 rpm. The pellet was resuspended at 1.25 × 105 cells/mL in assay buffer (Hanks balanced salt solution containing 15 mM Hepes) and 250 μL aliquoted into wells containing 1 μL of DMSO (vehicle) or 1 μL of drug in DMSO. Samples were incubated for 5 min at 37 °C, and 5 μL of calcium ionophore A23817 (freshly diluted from a 50 mM DMSO stock diluted to 0.5 mM in Hanks balanced salt solution) was added, mixed, and the mixture incubated for 5 min at 37 °C. Samples were centrifuged at 1200 rpm (∼300g) for 10 min at 4 °C. The supernatant was removed and a 1:4 dilution assayed for LTB4 concentration using ELISA (Assay Designs). Drug concentrations to achieve 50% inhibition (IC50) of vehicle LTB4 were determined by nonlinear regression analysis (Graphpad Prism) of % inhibition versus logarithmic drug concentration. Modifications to the assay for analysis of time-dependent inhibition included resuspending the leukocytes in assay buffer plus or minus 0.5% human serum albumin and incubating leukocytes with test compound for 5 min to 3 h before stimulation with calcium ionophore. Human Blood LTB4 Inhibition Assay (hWB). Blood was drawn from consenting human volunteers into heparinized tubes, and 150 μL aliquots were added to wells containing 1.5 μL of DMSO (vehicle) or 1.5 μL of test compound in DMSO. Samples were incubated for either 15 min or 5 h at 37 °C. An amount of 2 μL of calcium ionophore A23187 (freshly diluted from a 50 mM DMSO stock to 1.5 mM in Hanks balanced salt solution) was added. The solution was mixed and incubated for 30 min at 37 °C. Samples were centrifuged at 1500 rpm (∼300g) for 10 min at 4 °C. Plasma was removed and a 1:100 dilution assayed for LTB4 concentration using ELISA (Assay Designs). Drug concentrations to achieve 50% inhibition (IC50) of vehicle LTB4 were determined by nonlinear regression analysis (Graphpad Prism) of percent inhibition versus logarithm of drug concentration. Each assay was performed using two different donors; drug concentrations are singletons. COX-1 Human Whole Blood Assay. Human blood was obtained by venipuncture from consenting adult volunteers. Blood was anticoagulated by drawing into heparinized tubes and used within 2 h of draw. Aliquots of fresh blood (150 μL) were incubated for 15 min at 37 °C with 1 μL of test compound diluted in DMSO or with DMSO alone as a vehicle control. A concentration of 10 μM for routine screening was used, or for the generation of IC 50 values the final concentrations of the test compound were 100, 30, 10, 3, 1, 0.3, and 0.1 μM. Calcium ionophore A23187 (25 μM final concentration) was added from a 1.5 mM stock in HBSS (prepared by dilution from a 50 mM stock in DMSO). Incubations were continued for 30 min at 37 °C. Incubation mixtures were centrifuged at 1500 rpm for 10 min at 4 °C, and aliquots of the plasma were diluted 1:100 with assay buffer and analyzed for TXB2 by a competitive enzyme immunoassay according to the manufacturer's instructions (Assay Designs, Ann Harbor, MI, catalog no. 900-002). Pharmacokinetic Studies. Compounds were converted from the acid form to the sodium salt by treatment of the acid in ethanol/water with 1 equiv of 1 N NaOH and then removal of the solvent in vacuo. Male Sprague−Dawley rats surgically cannulated in their jugular vein (approximate weight of 300 g for male) were purchased from Charles River (Wilmington, MA). Compounds were administered intravenously (iv) (2 mg/kg) to two or three male rats (fasted overnight) as a solution in PEG400/ethanol/water (40/10/50, v/v/v) via a bolus 8022




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(trimethylsilyl)diazomethane (2 M in diethyl ether, 9.16 mL, 18.32 mmol). After the mixture was stirred at room temperature for 30 min, another 2 equiv of (trimethylsilyl)diazomethane was added and the solution maintained at ambient temperature for 12 h. Evaporation of the mixture in vacuo afforded 5-methoxy-2-methylpyridine, which was used without further purification. 1H NMR (CDCl3) δ 2.49 (s, 3H), 3.83 (s, 3H), 7.08 (d, 1H), 7.13 (dd, 1H), 8.20 (d, 1H). To a solution of the previously isolated 5-methoxy-2-methylpyridine (400 mg, 3.25 mmol) in benzene (16 mL) was added N-bromosuccinimide (636 mg, 3.57 mmol) and benzoyl peroxide (30 mg). The reaction mixture was refluxed for 16 h, evaporated to dryness and the residue purified using silica gel chromatography (ISCO, 15% EtOAc in hexanes) to afford 320 mg (44%) of the title compound. 2-Bromomethyl-6-fluoroquinoline (20). To a solution of 6fluoro-2-methylquinoline (5.00 g, 31.0 mmol) in benzene (160 mL) was added N-bromosuccinimide (6.07 g, 34.1 mmol) and benzoyl peroxide (370 mg), and the mixture was heated at reflux for 16 h. After the mixture was cooled, the solvent was removed in vacuo and the residue purified by column chromatography on silica gel (ISCO, 0− 20% EtOAc in hexanes) to afford 3.19 g (43%) of the title compound. 1 H NMR (CDCl3) δ 4.70 (s, 2H), 7.50 (m, 2H), 7.58 (d, 1H), 8.06 (dd, 1H), 8.12 (d, 1H). 6-Bromomethylnicotinonitrile (19) and 2-Bromomethyl-7fluoroquinoline (21). 19 and 21 were prepared in a similar manner to that described for 20. 2-Chloromethylimidazo[1,2-a]pyridine Hydrochloride (22). Imidazo[1,2-a]pyridine-2-ylmethanol (500 mg, 3.37 mmol) and SOCl 2 (5 mL) were heated at reflux for 20 min and evaporated to dryness to afford the title compound used without further purification. 3-Chloromethyl-5-methylisoxazole (23), 3-Chloromethyl1,5-dimethyl-1H-pyrazole (24), and 5-Chloromethyl-1,3-dimethyl-1H-pyrazole (25). 23−25 were prepared from their corresponding alcohols in a manner identical to that described for 22. 6-Chloromethyl-2,3-dimethylpyridine Hydrochloride (26). 2,3-Lutidine (30.0 g, 0.28 mol) was dissolved in CHCl3 (500 mL) and cooled to 0 °C, after which m-CPBA (76.0 g, 0.31 mol) was added in small portions over a period of 5 min. The solution was allowed to warm to ambient temperature, and after 12 h solid Ca(OH)2 (52 g) was added with vigorous stirring. A thick precipitate forms, and after a further 4 h of being stirred, the slurry was filtered through Celite, washing with CHCl3. Evaporation of the filtrate afforded a solid which was triturated with Et2O (200 mL) to afford 20 g (58%) of 2,3dimethylpyridine 1-oxide as a colorless solid. 1H NMR (CDCl3) δ 2.35 (s, 3H), 2.51 (s, 3H), 7.04 (m, 2H), 8.16 (m, 1H). To a solution of the previously isolated N-oxide (17.6 g, 0.143 mol) in CH2Cl2 was added trimethylsilyl cyanide (19.8 mL, 0.148 mol). After 30 min, N,N-diethylcarbamoyl chloride (18.6 mL, 0.148 mol) was added slowly and the resulting reaction mixture maintained at ambient temperature for 60 h. A 10% aqueous solution of K 2CO3 was carefully added (100 mL) and the resulting two-phase mixture stirred rapidly for 30 min. The organic phase was separated, the aqueous layer extracted with CH2Cl2, and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo. The residue was purified using silica gel chromatography (ISCO, 0−15% EtOAc in hexanes) to yield 10.1 g (53%) of 5,6-dimethylpyridine-2-carbonitrile as a colorless solid. 1H NMR (CDCl3) δ 2.37 (s, 3H), 2.55 (s, 3H), 7.45 (d, 1H), 7.53 (d, 1H). 5,6-Dimethylpyridine-2-carbonitrile (5.00 g, 37.8 mmol) in MeOH (500 mL) was cooled to −10 °C and dry HCl gas bubbled through the solution for 15 min. The vessel was sealed and allowed to stand at ambient temperature for 72 h. Water (12 mL) was added and the solution evaporated to dryness in vacuo. The residue was diluted with EtOAc, and saturated NaHCO3 solution was added with caution (gas evolution) and vigorously stirred for 30 min. The EtOAc phase was separated, the aqueous layer was extracted (EtOAc), and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo to afford 5.86 g (94%) of 5,6-dimethylpyridine-2-carboxylic acid methyl ester as a light tan solid. To the previously isolated methyl ester (5.86 g, 35.5 mmol) in dry THF (60 mL) cooled to −78 °C was slowly added DIBAl-H (1 M

in hexanes), and the desired fractions repurified (ISCO: 25−100% hexanes in CH2Cl2) to afford the title compound as a colorless oil. 1H NMR (CDCl3) δ 2.60 (s, 3H), 4.67 (s, 2H), 8.44 (s, 1H), 8.61 (s, 1H). Rf = 0.4 (20% EtOAc in hexanes). 2-Chloromethylquinoxaline (15).25 To a refluxing solution of 2-methylquinoxaline (10.0 g, 69.3 mmol) in CHCl3 (100 mL) was added trichloroisocyanuric acid (7.10 g, 30.5 mmol) in ∼100 mg portions over the period of 1 h. The mixture was then heated at reflux for a further 30 min, allowed to cool, and poured into an ice−water mixture. Aliquots of a 50% aqueous NaOH solution were then added to adjust the pH to ∼9. The resulting solution was extracted with CHCl3, dried (MgSO4), filtered, and evaporated to dryness. The residue was purified on silica gel (ISCO, 0−15% EtOAc in hexanes) to afford the title compound as a purple solid. 1H NMR (CDCl3) δ 4.89 (s, 2H), 7.81 (m, 2H), 8.11 (m, 2H), 9.04 (s, 1H). 2-Chloromethyl-5-methylpyridine Hydrochloride (16c). To an ice cooled solution of 2,5-lutidine (46.8 g, 0.436 mol) in CHCl 3 (750 mL) was added m-CPBA (129 g, 0.52 mol) in small portions over a period of 30 min. The reaction mixture was maintained at room temperature for 48 h, and then calcium hydroxide (81 g) was added with vigorous stirring leading to the formation of a thick precipitate. After being stirred for 4 h, the slurry was filtered through Celite, washing the residue with CHCl3. Evaporation of the filtrate afforded 46 g (86%) of 2,5-dimethylpyridine 1-oxide as a colorless oil. 1H NMR (CDCl3) δ 2.28 (s, 3H), 2.49 (s, 3H), 7.00 (d, 1H), 7.14 (d, 1H), 8.13 (s, 1H). To acetic anhydride (150 mL) heated to 100 °C was very carefully added 2,5-dimethylpyridine 1-oxide (46 g, 0.373 mol) over a period of 30 min (caution: significant exotherm can occur after an induction period). After complete addition, an additional 50 mL of Ac2O was added and the reaction mixture heated to reflux for 1 h. Upon completion of heating, the reaction mixture was allowed to cool to ambient temperature and slowly quenched with the addition of EtOH (200 mL) and stirred for 12 h. Evaporation of the reaction mixture afforded a yellow oil which was purified using silica gel chromatography (0−40% EtOAc in hexanes), yielding acetic acid 5methylpyridin-2-ylmethyl ester (52 g, 84%). 1H NMR (CDCl3) δ 2.10 (s, 3H), 2.15 (s, 3H), 2.35 (s, 3H), 7.27 (d, 1H), 7.53 (d, 1H), 8.45 (s, 1H). To acetic acid 5-methyl-pyridin-2-ylmethyl ester (52 g, 0.314 mol) was added concentrated HCl (200 mL), and the mixture was heated to reflux for 1 h. Evaporation of the mixture under vacuum afforded (5methylpyridin-2-yl)methanol hydrochloride as an orange solid which was used without further purification. To (5-methylpyridin-2-yl)methanol hydrochloride (40 g, 0.250 mol) was added SOCl2 (140 mL) slowly with vigorous stirring under a reflux condenser (caution: significant gas evolution). After complete addition the reaction mixture was heated to reflux for 30 min, allowed to cool, and thoroughly evaporated to dryness to afford the title compound as a pale brown solid used without further purification. Compounds 16a, 16b, 16e, 16f were prepared in an identical manner to the procedure given for compound 16b from the commercially available alkylpyridines. Compound 16d was prepared from the commercially available 6-methylpyridine-2-methanol through reaction with thionyl chloride as described for the final step of 16c. Quinoline 17 was also prepared in an identical manner from commercially available 2,6-dimethylquinoline. 2-Chloromethyl-5-methylpyridine 1-Oxide (16g). To a mixture of 2-chloromethyl-5-methylpyridine hydrochloride (16c, 500 mg, 2.81 mmol) and m-CPBA (760 mg, 3.09 mmol) in CH2Cl2 (15 mL) was added NaHCO3 (300 mg, 3.57 mmol). The solution was stirred at ambient temperature for 24 h. The mixture was diluted with CH 2Cl2, washed with water and the organic phase dried (MgSO 4), filtered, and evaporated in vacuo. Purification of the residue on silica gel (ISCO: 0−100% EtOAc in hexanes) afforded 222 mg (50%) of the title compound as a colorless solid. 1H NMR (CDCl3) δ 2.33 (s, 3H), 4.82 (s, 2H), 7.13 (d, 1H), 7.48 (d, 1H), 8.13 (s, 1H). 2-Bromomethyl-5-methoxypyridine (18). To a solution of 5hydroxy-2-methylpyridine (1.0 g, 9.16 mmol) in a mixture of toluene (45 mL) and MeOH (45 mL) was added a solution of 8023




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4.25 mmol), and the suspension was maintained at ambient temperature with vigorous stirring for 16 h. The reaction mixture was partitioned between EtOAc and water. The aqueous phase was extracted with EtOAc, and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo. The product residue was triturated using a mixture of EtOAc and hexanes and the solid collected by filtration to afford 1.43 g of the title compound. The mother liquor was purified by silica gel column chromatography (ISCO, 0−15% EtOAc in hexane gradient) to isolate a further 1.00 g of the title compound. Combined yield obtained was 2.43 g (93%). 1H NMR (CDCl3) δ 1.13 (s, 9H), 1.18 (t, 3H), 1.20 (s, 6H), 3.24 (s, 2H), 4.03 (q, 2H), 5.32 (s, 2H), 5.24 (s, 2H), 6.65 (d, 2H), 6.90 (d, 1H), 7.02 (d, 1H), 7.36 (d, 2H), 7.41 (m, 1H), 7.47 (m, 1H), 7.75 (d, 1H), 8.10 (m, 2H). [M + H]+: m/z calculated 679; observed 679. Step 2: 3-{3-tert-Butylsulfanyl-5-(6-fluoroquinolin-2-ylmethoxy)-1-[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid Ethyl Ester. To a solution of 3-[1-(4-bromobenzyl)-3-tert-butylsulfanyl-5(6-fluoroquinolin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic acid ethyl ester (from step 1, 1.02 g, 1.51 mmol) in p-dioxane (15 mL) were added potassium acetate (443 mg, 4.52 mmol), bis(pinacolato)diboron (1.08 g, 4.25 mmol), and Pd(dppf)Cl2·CH2Cl2 (125 mg, 0.15 mmol) in a sealable vessel. The mixture was sparged with nitrogen gas for 5 min, sealed, and heated to 90 °C for 12 h. After cooling, the reaction mixture was partitioned between EtOAc and water, the aqueous layer was extracted with EtOAc, and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo. The residue was purified on silica gel (ISCO, 0−20% EtOAc in hexanes) to afford the title compound as off-white foam (910 mg, 84%) used without further analysis. Step 3: 3-{3-tert-Butylsulfanyl-5-(6-fluoroquinolin-2-ylmethoxy)-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2dimethylpropionic Acid Ethyl Ester. A solution of the product of step 2 (250 mg, 0.345 mmol), K2CO3 (145 mg, 0.105 mmol), 5bromo-2-methoxypyridine (91 mg, 0.484 mmol), and Pd(PPh3)4 (55 mg, 0.048 mmol) in DME/H2O 2:1 (6 mL) was degassed via sparging with nitrogen and heated at 85 °C for 4 h. After cooling, the mixture was poured into water, extracted with EtOAc (×2) and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo. The residue was purified using silica gel chromatography (ISCO, 0− 15% EtOAc in hexanes) to afford 206 mg (85%) of the title ester. 1H NMR (CDCl3) δ 1.14 (s, 9H), 1.16 (t, 3H), 1.22 (s, 3H), 3.29 (s, 2H), 3.96 (s, 3H), 4.05 (q, 2H), 5.42 (s, 4H), 6.78 (d, 1H), 6.87 (d, 2H), 6.91 (d, 1H), 7.10 (d, 1H), 7.37−7.53 (m, 5H), 7.70 (d, 1H), 7.75 (d, 1H), 8.12 (m, 2H), 8.31 (d, 1H). Step 4: 3-{-3-tert-Butylsulfanyl-5-(6-fluoroquinolin-2-ylmethoxy)-1-[4-(6-methoxypyridine-3-yl)benzyl]-1H-indol-2-yl}2,2-dimethylpropionic Acid (11c). To a solution of the ethyl ester from step 3 (206 mg, 0.304 mmol) in a mixture of THF (3 mL), MeOH (1.5 mL), and H2O (1.5 mL) was added LiOH·H2O (75 mg, 1.79 mmol), and the reaction mixture was heated to 60 °C for 4 h. After cooling, the reaction mixture was diluted with EtOAc and H2O, and solid citric acid was added to achieve an aqueous pH of ∼3. The organic phase was separated and the aqueous layer extracted with EtOAc. The combined organic phases were washed with water, dried (MgSO4), filtered, and evaporated in vacuo to afford the title compound as a colorless solid in quantitative yield. 1H NMR (CDCl3) δ 1.16 (s, 9H), 1.26 (s, 6H), 3.33 (s, 2H), 3.95 (s, 3H), 5.40 (s, 2H), 5.43 (s, 2H), 6.76 (d, 1H), 6.85 (d, 2H), 6.92 (d, 1H), 7.07 (d, 1H), 7.35 (d, 2H), 7.44 (m, 1H), 7.49 (m, 1H), 7.69 (d, 1H), 7.73 (d, 1H), 8.12 (m, 2H), 8.30 (d, 1H). [M + H]+: m/z calculated 678; observed 678. The following compounds were prepared using route A. 3-{-3-tert-Butylsulfanyl-5-(7-fluoroquinolin-2-ylmethoxy)-1[4-(6-methoxypyridine-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11d). For step 1, 21 was used as alkylating agent. 1H NMR (CDCl3) δ 1.16 (s, 9H), 1.26 (s, 3H), 3.34 (s, 2H), 3.95 (s, 3H), 5.41 (s, 2H), 5.54 (s, 2H), 6.76 (d, 1H), 6.85 (d, 2H), 6.91 (d, 1H), 7.07 (d, 1H), 7.36 (m, 4H), 7.67−7.83 (m, 4H), 8.16 (d, 1H), 8.30 (d, 1H). [M + H]+: m/z calculated 678; observed 678.

solution in THF, 100 mL, 100 mmol) over a period of 5 min. The reaction mixture was allowed to warm to 0 °C, after which saturated aqueous sodium potassium tartrate solution was carefully added to quench the reduction. After the mixture was stirred vigorously for 30 min, solid citric acid was added to adjust the pH to ∼8, the aqueous phase was extracted with EtOAc (×3), and the combined organics were dried (MgSO4), filtered, and evaporated. The residue was purified using silica gel chromatography (ISCO, 100% EtOAc) to afford 4.43 g (91%) of (5,6-dimethylpyridin-2-yl)methanol as a colorless solid. 1H NMR (CDCl3) δ 2.27 (s, 3H), 2.49 (s, 3H), 4.21 (br s, 1H), 4.68 (s, 2H), 6.98 (d, 1H), 7.39 (d, 1H). Thionyl chloride (5 mL) and the previously isolated alcohol (1.00 g, 0.73 mmol) were heated to reflux for 15 min, allowed to cool, and thoroughly evaporated to dryness in vacuo to afford the title compound as a pale brown solid used without further purification. 5-Chloro-2-chloromethylpyridine (27). 5-Chloropyridine-2carboxylic acid (0.50 g, 3.17 mmol) in THF (15 mL) was cooled to 0 °C, and BH3·THF (1 M solution in THF, 19 mL, 19 mmol) was added dropwise. The reaction mixture was then heated to 50 °C for 12 h. After the mixture was cooled to ambient temperature, water was slowly added to quench excess reagent, the reaction mixture was partitioned between EtOAc and water, the organic phase was separated, the aqueous layer was extracted (EtOAc), and the combined organic phases were dried (MgSO4), filtered, and evaporated in vacuo. To the isolated alcohol (237 mg, 1.65 mmol) in CH2Cl2 (3 mL) was added SOCl2 (0.6 mL, 8.25 mmol), and the mixture was stirred at ambient temperature for 30 min. Evaporation of the solvent in vacuo afforded the title compound which was used without further purification. 2-Chloromethylindole-1-carboxylic Acid tert-Butyl Ester (28). To a solution of 1H-indole-2-carboxylic acid ethyl ester (5.00 g, 26.0 mmol) in MeCN (85 mL) were added Boc2O (6.92 g, 31.2 mmol) and DMAP (323 mg, 2.60 mmol). After 12 h at ambient temperature, 2-amino-5-diethylaminopentane (0.5 mL) was added and the reaction mixture evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0−10% EtOAc in hexanes) afforded 7.5 g (99%) of indole-1,2-dicarboxylic acid 1-tert -butyl ester 2-ethyl ester. 1H NMR (CDCl3) δ 1.40 (t, 3H), 1.63 (s, 9H), 4.38 (q, 2H), 7.10 (s, 1H), 7.25 (m, 1H), 7.40 (m, 1H), 7.60 (d, 1H), 8.08 (d, 1H). To a solution of the previously isolated tert-butyl ester (7.50 g, 26.0 mmol) in toluene (50 mL) cooled to −40 °C was slowly added DIBAl-H (1 M soln in hexanes, 64.8 mL, 64.8 mmol) over a period of 20 min. After a further 20 min the reaction was carefully quenched upon addition of MeOH (20 mL) and then H2O (20 mL), and the mixture was stirred vigorously at ambient temperature for 10 min. The mixture was filtered and the filtrate washed with water, dried (MgSO4), filtered, and evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0−25% EtOAc in hexanes) afforded 5.3 g (83%) of 2-hydroxymethylindole-1-carboxylic acid tertbutyl ester. 1H NMR (CDCl3) δ 1.71 (s, 9H), 3.77 (t, 1H), 4.80 (d, 2H), 6.57 (s, 1H), 7.16−7.26 (m, 2H), 7.50 (d, 1H), 7.98 (d, 1H). 2-Hydroxymethylindole-1-carboxylic acid tert-butyl ester isolated above (1.60 g, 6.47 mmol) was dissolved in CH2Cl2, and LiBr (5.45 g, 65 mmol) was added. Triethylamine (1.46 mL, 10.4 mmol) was added followed by methanesulfonyl chloride (816 μL, 10.4 mmol) and the solution maintained at ambient temperature for 24 h. The reaction mixture was diluted with CH2Cl2, washed with aqueous saturated NaHCO3 solution, dried (MgSO4), filtered, and evaporated in vacuo to afford the title compound which was used immediately without further purification. Route A. 3-{-3-tert-Butylsulfanyl-5-(6-fluoroquinolin-2-ylmethoxy)-1-[4-(6-methoxypyridine-3-yl)benzyl]-1H-indol-2-yl}2,2-dimethylpropionic Acid (11c). Step 1: 3-[1-(4-Bromobenzyl)-3-tert-butylsulfanyl-5-(6-fluoroquinolin-2-ylmethoxy)-1Hindol-2-yl]-2,2-dimethylpropionic Acid Ethyl Ester. To a solution of 3-[1-(4-bromobenzyl)-3-tert-butylsulfanyl-5-hydroxy-1Hindol-2-yl]-2,2-dimethylpropionic acid ethyl ester 1 (2.00 g, 3.86 mmol) in MeCN (25 mL) was added cesium carbonate (2.50 g, 7.67 mmol) followed by 2-bromomethyl-6-fluoroquinoline 20 (1.02 g, 8024




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3-{-3-tert-Butylsulfanyl-1-[4-(6-methoxypyridine-3-yl)benzyl]-5-(6-methylquinolin-2-ylmethoxy)-1H-indol-2-yl}-2,2dimethylpropionic Acid (11e). For step 1, the alkylation was performed at 45 °C in MeCN using 17 as alkylating agent. 1H NMR (CDCl3) δ 1.17 (s, 9H), 1.26 (s, 6H), 2.54 (s, 3H), 3.33 (s, 2H), 3.95 (s, 3H), 5.40 (s, 2H), 5.43 (s, 2H), 6.76 (d, 1H), 6.87 (d, 2H), 6.91 (d, 1H), 7.04 (d, 1H), 7.37 (m, 3H), 7.55 (m, 2H), 7.68 (m, 2H), 8.03 (d, 1H), 8.08 (d, 1H), 8.30 (d, 1H). [M + H]+: m/z calculated 674; observed 674. 3-{3-tert-Butylsulfanyl-5-(imidazo[1,2-a]pyridine-2-ylmethoxy)-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2dimethylpropionic Acid (11f). For step 1, the alkylation was performed at 55 °C in a 15:1 mixture of MeCN/DMF for 48 h using 22 as alkylating agent. 1H NMR (CDCl3) δ 1.24 (s, 9H), 1.28 (s, 6H), 3.34 (s, 2H), 3.95 (s, 3H), 5.29 (s, 2H), 5.43 (s, 2H), 6.75−6.83 (m, 5H), 6.94 (d, 1H), 7.20 (m, 1H), 7.30 (d, 2H), 7.38 (s, 1H), 7.64− 7.73 (m, 3H), 8.07 (d, 1H), 8.28 (d, 1H). [M + H]+: m/z calculated 649; observed 649. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(3-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11h). For step 1, the alkylation was performed at ambient temperature using DMF as solvent with the addition of catalytic TBAI and 16a as alkylating agent. 1H NMR (CDCl3) δ 1.26 (s, 15H), 2.44 (s, 3H), 3.35 (s, 2H), 3.94 (s, 3H), 5.24 (s, 2H), 5.42 (s, 2H), 6.76 (d, 1H), 6.83 (m, 3H), 6.96 (s, 1H), 7.22 (dd, 1H), 7.32 (d, 2H), 7.40 (d, 1H), 7.55 (d, 1H), 7.68 (dd, 1H), 8.30 (d, 1H), 8.50 (d, 1H). [M + H]+: m/z calculated 624; observed 624. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(4-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11i). For step 1, the alkylation was performed at ambient temperature using DMF as solvent with the addition of catalytic TBAI using 16b as alkylating agent. 1H NMR (CDCl3) δ 1.23 (s, 9H), 1.27 (s, 6H), 2.37 (s, 3H), 3.34 (s, 2H), 3.95 (s, 3H), 5.20 (s, 2H), 5.43 (s, 2H), 6.76 (d, 1H), 6.86 (m, 3H), 7.03 (d, 1H), 7.06 (d, 1H), 7.34 (m, 3H), 7.43 (s, 1H), 7.68 (dd, 1H), 8.29 (d, 1H), 8.48 (d, 1H). [M + H]+: m/z calculated 624; observed 624. 3-[3-tert-Butylsulfanyl-5-(5-ethylpyridin-2ylmethoxy)-1-[4(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11l). For step 1, the alkylation was performed at 45 °C in MeCN with catalytic TBAI for 72 h with 16e as alkylating agent. 1 H NMR (CDCl3) δ 1.23 (s, 9H), 1.26 (m, 9H), 2.65 (q, 2H), 3.34 (s, 2H), 3.95 (s, 3H), 5.20 (s, 2H), 5.43 (s, 2H), 6.76 (d, 1H), 6.83 (m, 3H), 7.01 (d, 1H), 7.33 (m, 3H), 7.54 (m, 2H), 7.68 (dd, 1H), 8.30 (d, 1H), 8.48 (d, 1H). [M + H]+: m/z calculated 638; observed 638. 3-[3-tert-Butylsulfanyl-5-(3,5-dimethylpyridin-2ylmethoxy)1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11m). For step 1, the alkylation reaction was performed at ambient temperature using DMF as solvent with catalytic TBAI and 16f as alkylating agent. 1H NMR (CDCl3) δ 1.20 (s, 6H), 1.25 (s, 9H), 2.31 (s, 3H), 2.40 (s, 3H), 3.35 (s, 2H), 3.95 (s, 3H), 5.20 (s, 2H), 5.41 (s, 2H), 6.74−6.93 (m, 4H), 6.91 (d, 1H), 7.31 (d, 2H), 7.39 (m, 2H), 7.67 (dd, 1H), 8.28 (d, 1H), 8.30 (s, 1H). [M + H]+: m/z calculated 638; observed 638. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(5-methylisoxazol-3-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11s). For step 1, the alkylation reaction was carried out at 45 °C in MeCN for 12 h using 23 as alkylating reagent. 1 H NMR (CDCl3) δ 1.26 (s, 15H), 2.41 (s, 3H), 3.35 (s, 2H), 3.95 (s, 3H), 5.15 (s, 2H), 5.45 (s, 2H), 6.13 (s, 1H), 6.77 (d, 1H), 6.76−6.87 (m, 3H), 7.08 (d, 1H), 7.34 (m, 3H), 7.68 (dd, 1H), 8.31 (d, 1H). [M + H]+: m/z calculated 614; observed 614. 3-[3-tert-Butylsulfanyl-5-(1,5-dimethyl-1H-pyrazol-3-ylmethoxy)-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2dimethylpropionic Acid (11t). For step 1, the alkylation reaction was performed using MeCN as solvent with catalytic TBAI and 24 as alkylating agent. 1H NMR (CDCl3) δ 1.25 (s, 15H), 2.24 (s, 3H), 3.36 (s, 2H), 3.85 (s, 3H), 3.95 (s, 3H), 5.03 (s, 2H), 5.46 (s, 2H), 6.11 (s, 1H), 6.77 (d, 1H), 6.80 (dd, 1H), 6.84 (d, 2H), 7.07 (d, 1H), 7.36 (m, 3H), 7.71 (dd, 1H), 8.32 (d, 1H). [M + H] +: m/z calculated 627; observed 627.

3-[3-tert-Butylsulfanyl-5-(2,5-dimethyl-2H-pyrazol-3-ylmethoxy)-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2dimethylpropionic Acid (11u). For step 1, the alkylation reaction was performed using MeCN as solvent with catalytic TBAI and 25 as alkylating reagent. 1H NMR (CDCl3) δ 1.26 (s, 15H), 2.24 (s, 3H), 3.85 (s, 3H), 3.95 (s, 3H), 5.03 (s, 2H), 5.46 (s, 2H), 6.11 (s, 1H), 6.77 (d, 1H), 6.80 (dd, 1H), 6.84 (d, 2H), 7.07 (d, 1H), 7.36 (m, 3H), 7.71 (dd, 1H), 8.32 (d, 1H). [M + H]+: m/z calculated 627; observed 627. For the following compounds, step 1 was performed using 16c as alkylating agent and the coupling partner in step 3 was chosen accordingly. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11v). For step 3, 6-bromo-2-methoxypyridine was used as the cross-coupling partner. 1H NMR (DMSO-d6) δ 1.11 (s, 15H), 2.28 (s, 3H), 3.91 (s, 3H), 5.15 (s, 2H), 5.53 (s, 2H), 6.74 (d, 1H), 6.83 (dd, 1H), 6.93 (d, 2H), 7.10 (d, 1H), 7.35 (m, 2H), 7.49 (d, 1H), 7.60 (d, 1H), 7.74 (m, 1H), 7.97 (d, 2H), 8.41 (s, 1H). [M + H]+: m/z calculated 624; observed 624. 3-[3-tert-Butylsulfanyl-1-[4-(2-ethoxythiazol-4-yl)benzyl]-5(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11y). For step 3, 4-bromo-2-ethoxythiazole was used as the cross-coupling partner. 1H NMR (CDCl3) δ 1.21 (s, 9H), 1.25 (s, 6H), 1.43 (t, 3H), 2.34 (s, 3H), 3.32 (s, 2H), 4.48 (q, 2H), 5.20 (s, 2H), 5.39 (s, 2H), 6.74 (s, 1H), 6.80 (m, 3H), 7.00 (d, 1H), 7.27 (d, 1H), 7.47 (d, 1H), 7.50 (d, 1H), 7.63 (d, 2H), 8.45 (s, 1H). [M + H]+: m/z calculated 644; observed 644. 3-[3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(6-trifluoromethylpyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11z). For step 3, 5-bromo-2-trifluoromethylpyridine was used as the coupling partner. 1H NMR (CDCl3) δ 1.20 (s, 9H), 1.23 (s, 6H), 2.35 (s, 3H), 3.34 (s, 2H), 5.17 (s, 2H), 5.46 (s, 2H), 6.81 (dd, 1H), 6.90 (d, 2H), 6.95 (d, 1H), 7.32 (d, 1H), 7.41 (d, 2H), 7.47 (d, 1H), 7.54 (dd, 1H), 7.69 (d, 1H), 7.92 (dd, 1H), 8.47 (s, 1H), 8.83 (d, 1H). [M + H]+: m/z calculated 662; observed 662. 3-[3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(5-trifluoromethylpyridin-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11aa). For step 3, 2-chloro-5-trifluoromethylpyridine was used as the coupling partner. 1H NMR (CDCl3) δ 1.20 (s, 9H), 1.23 (s, 6H), 2.34 (s, 3H), 3.34 (s, 2H), 5.20 (s, 2H), 5.46 (s, 2H), 6.81 (dd, 1H), 6.88 (d, 2H), 6.98 (d, 1H), 7.31 (d, 1H), 7.46 (d, 1H), 7.53 (d, 1H), 7.72 (d, 1H), 7.84 (d, 2H), 7.93 (dd. 1H), 8.45 (s, 1H), 8.90 (s, 1H). [M + H]+: m/z calculated 662; observed 662. 3-[3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(5-trifluoromethylpyridin-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11ee). For step 3, 2-chloro-5-methylpyridine was used as the coupling partner. The title compound was purified using preparative HPLC and isolated as the trifluoromethanesulfonic acid salt. 1H NMR (CDCl3) δ 1.20 (s, 6H), 1.23 (s, 9H), 2.52 (s, 3H), 2.55 (s, 3H), 3.35 (s, 2H), 5,46 (s, 2H), 5.52 (s, 2H), 6.84 (d, 1H), 6.99 (m, 3H), 7.29 (m, 1H), 7.67 (d, 2H), 7.85 (d, 1H), 7.92 (d, 1H), 8.13 (m, 2H), 8.70 (s, 1H), 8.76 (s, 1H). [M + H] +: m/z calculated 592; observed 592. Route B. 3-{-3-tert-Butylsulfanyl-1-[4-(6-methoxypyridine-3yl)benzyl]-5-(quinoxalin-2-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11b). Step 1: 3-{3-tert-Butylsulfanyl-5hydroxy-1-[4-(4,4,5,5-tetramethyl-1-[1,3,2]dioxaborolan-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid Ethyl Ester (12). To a solution of 3-[1-(4-bromobenzyl)-3-tert-butylsulfanyl-5hydroxyl-1H-indol-2-yl]-2,2-dimethylpropionic acid ethyl ester1 (35.0 g, 67.5 mmol) in p-dioxane (350 mL) were added potassium acetate (19.9 g, 202.7 mmol), bis(pinacolato)diboron (25.0 g, 98.4 mmol), and [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II) dichloromethane complex (2.50 g, 3.1 mmol), and the solution was sparged with nitrogen for 30 min. The resulting mixture was heated under nitrogen at 85 °C for 12 h, after which the solvent volume was reduced to ∼100 mL in vacuo, the residue taken up in EtOAc (1 L), washed with water, dried (MgSO4), filtered, and evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0− 8025




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15% EtOAc in hexanes) afforded 33.5 g (88%) of the title compound. 1 H NMR (CDCl3) δ 1.16 (t, 3H), 1.21 (s, 6H), 1.25 (s, 9H), 1,31 (s, 12H), 3.25 (s, 2H), 4.04 (q, 2H), 4.69 (s, 1H), 5.37 (s, 2H), 6.65 (dd, 1H), 6.76 (d, 2H), 6.96 (d, 1H), 7.17 (d, 1H), 7.67 (d, 2H). [M + H]+: m/z calculated 566; observed 566. Step 2: 3-{3-tert-Butylsulfanyl-5-hydroxy-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid Ethyl Ester (13, R2 = 6-Methoxypyridin-3-yl). To a solution of 12 (25.3 g, 44.8 mmol) in a mixture of 1,2-dimethoxyethane (300 mL) and water (150 mL) were added potassium carbonate (15.5 g, 112.1 mmol) and 5-bromo-2-methoxypyridine (10.9 g, 58.0 mmol). The mixture was degassed via sparging with nitrogen gas for 30 min and tetrakis(triphenylphosphine)palladium(0) (1.0 g, 0.86 mmol) and heated at 80 °C under nitrogen for 24 h. The reaction mixture was reduced in volume in vacuo and diluted in EtOAc and washed with water. The aqueous phase was extracted with EtOAc, and the combined organic phases were dried (MgSO 4), filtered, and evaporated in vacuo. The residue was purified using silica gel chromatography (0−20% EtOAc in hexanes) to yield 23.7 g (96%) of the title compound as a colorless foam. 1H NMR (CDCl3) δ 1.17 (t, 3H), 1.23 (s, 6H), 1.28 (s, 9H), 3.29 (s, 2H), 3.97 (s, 3H), 4.04 (q, 2H), 5.40 (s, 2H), 6.70 (dd, 1H), 6.79 (d, 1H), 6.85 (d, 2H), 7.20 (d, 1H), 7.37 (d, 2H), 7.72 (dd, 1H), 8.31 (d, 1H). Step 3: 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]-5-(quinoxalin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid Ethyl Ester. To the phenol isolated in step 2 (1.62 g, 2.96 mmol) in MeCN (45 mL) were added cesium carbonate (2.89 g, 8.87 mmol) and 2-chloromethylquinoxaline (15, 0.58 g, 3.25 mmol), and the suspension was stirred at ambient temperature for 12 h. The reaction mixture was partitioned between CH2Cl2 and water, and the organic phase was separated, washed with water, dried (MgSO4), filtered, and evaporated in vacuo. The residue was purified using silica gel chromatography (ISCO, 0−5% EtOAc in CH2Cl2) to afford 1.84 g (90%) of the title ester as a colorless solid. 1H NMR (CDCl3) δ 1.15 (s, 9H), 1.17 (t, 3H), 1.23 (s, 6H), 3.29 (s, 2H), 3.96 (s, 3H), 4.05 (q, 2H), 5.43 (s, 2H), 5.50 (s, 2H), 6.78 (d, 1H), 6.85 (d, 2H), 6.94 (dd, 1H), 7.10 (d, 1H), 7.37 (m, 3H), 7.72 (dd, 1H), 7.78 (m, 2H), 8.11 (m, 2H), 8.31 (d, 1H), 9.14 (s, 1H). Step 4: 3-{-3-tert-Butylsulfanyl-1-[4-(6-methoxypyridine-3yl)benzyl]-5-(quinoxalin-2-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid. To the ester isolated in step 3 (150 mg, 0.22 mmol) in a mixture of THF (4 mL), MeOH (1.3 mL), and water (1.3 mL) was added LiOH·H2O (45 mg, 1.07 mmol), and the solution was heated at 60 °C for 4 h. Upon completion of the reaction the mixture was diluted with EtOAc and water, solid citric acid was added to attain an aqueous pH of ∼3, and the aqueous phase was extracted with EtOAc. The organic phase was washed with water, dried (MgSO 4), filtered, and evaporated in vacuo to yield 140 mg (97%) of the title compound. 1H NMR (CDCl3) δ 1.15 (s, 9H), 1.26 (s, 6H), 3.33 (s, 2H), 3.95 (s, 3H), 5.45 (s, 2H), 5.49 (s, 2H), 6.76 (d, 1H), 6.85 (d, 2H), 6.94 (dd, 1H), 7.10 (d, 1H), 7.38 (m, 3H), 7.70 (dd, 1H), 7.78 (m, 2H), 8.11 (m, 2H), 8.30 (d, 1H), 9.14 (s, 1H). [M + H] +: m/z calculated 661; observed 661. The following compounds were prepared according to route B using the intermediate prepared from step 2 (Scheme 1, R 2 = 6methoxy-pyridin-3-yl). 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(quinolin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11a). For step 3, 2-chloromethylquinoline hydrochloride was used as the alkylating agent with catalytic TBAI and DMF as solvent. 1H NMR (CDCl3) δ 1.16 (s, 15H), 3.32 (s, 2H), 3.95 (s, 3H), 5.43 (s, 4H), 6.77 (d, 1H), 6.84 (d, 2H), 6.90 (dd, 1H), 7.07 (d, 1H), 7.36 (m, 3H), 7.54 (m, 1H), 7.70 (dd, 1H), 7.74 (d, 2H), 7.81 (d, 1H), 8.11 (d, 1H), 8.17 (d, 1H), 8.30 (d, 1H). [M + H] +: m/z calculated 660; observed 660. 3-{3-tert-Butylsulfanyl-5-(1H-indol-2-ylmethoxy)-1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11g). For step 3, 2-chloromethylindole-1-carboxylic acid tert-butyl ester (28) was used as the alkylating agent. 1H NMR (CDCl3) δ 1.23 (s, 9H), 1.26 (s, 6H), 3.34 (s, 2H), 3.95 (s, 3H), 5.27 (s, 2H), 5.44 (s, 2H), 6.53 (s, 1H), 6.76 (d, 1H), 6.85 (m, 3H), 7.07

(d, 1H), 7.08 (m, 1H), 7.13 (m, 1H), 7.32−7.40 (m, 4H), 7.58 (d, 1H), 7.69 (dd, 1H), 8.31 (d, 1H), 8.46 (s, 1H). [M + H] +: m/z calculated 648; observed 648 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11j). For step 3, 2-chloromethyl-5-methylpyridine hydrochloride (16c) was used as the alkylating agent at 55 °C for 24 h. 1 H NMR (CDCl3) δ 1.22 (s, 9H), 1.27 (s, 6H), 2.35 (s, 3H), 3.33 (s, 2H), 3.95 (s, 3H), 5.21 (s, 2H), 5.43 (s, 2H), 6.76 (d, 1H), 6.82 (m, 3H), 6.99 (d, 1H), 7.33 (m, 3H), 7.49 (d, 1H), 7.56 (dd, 1H), 7.68 (dd, 1H), 8.28 (d, 1H), 8.47 (s, 1H). [M + H]+: m/z calculated 624; observed 624. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(6-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11k). For step 3, 16d was used as the alkylating agent using catalytic TBAI in DMF as solvent at 50 °C. 1H NMR (CDCl3) δ 1.24 (s, 15H), 2.81 (s, 3H), 3.34 (s, 2H), 3.95 (s, 3H), 5.45 (s, 2H), 5.54 (s, 2H), 6.78 (d, 1H), 6.88 (m, 3H), 7.07 (d, 1H), 7.35 (m, 4H), 7.71 (m, 2H), 7.95 (m, 1H), 8.32 (s, 1H). [M + H] +: m/z calculated 624; observed 624. 3-{3-tert-Butylsulfanyl-5-(5,6-dimethylpyridin-2ylmethoxy)1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11n). For step 3, compound 26 was used as the alkylating agent at 35 °C for 12 h. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 2.28 (s, 3H), 2.53 (s, 3H), 3.33 (s, 2H), 3.95 (s, 3H), 5.18 (s, 2H), 5.43 (s, 2H), 6.76 (s, 1H), 6.85 (m, 3H), 7.03 (d, 1H), 7.32 (m, 4H), 7.42 (d, 1H), 7.69 (dd, 1H), 8.30 (d, 1H). [M + H] +: m/z calculated 638; observed 638. 3-{3-tert-Butylsulfanyl-5-(5-chloropyridin-2-ylmethoxy)-1[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11o). For step 3, compound 27 was used as the alkylating agent with catalytic TBAI in DMF as solvent for 12 h. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.27 (s, 6H), 3.35 (s, 2H), 3.96 (s, 3H), 5.24 (s, 2H), 5.45 (s, 2H), 6.78 (d, 1H), 6.87 (m, 3H), 7.08 (d, 1H), 7.30 (d, 1H), 7.37 (d, 2H), 7.54 (d, 1H), 7.69 (m, 2H), 8.30 (d, 1H), 8.57 (d, 1H). [M + H]+: m/z calculated 644; observed 644. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(5-methoxypyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11p). For step 3, compound 18 was used as the alkylating agent with catalytic TBAI and DMF as solvent for 12 h. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 3.86 (s, 3H), 3.94 (s, 3H), 5.18 (s, 2H), 5.43 (s, 2H), 6.75 (d, 1H), 6.84 (m, 3H), 7.02 (d, 1H), 7.23 (dd, 1H), 7.32 (m, 3H), 7.49 (d, 1H), 7.68 (dd, 1H), 8.29 (d, 1H), 8.32 (d, 1H).). [M + H]+: m/z calculated 641; observed 641. 3-{3-tert-Butylsulfanyl-5-(5-carbamoylpyridin-2-ylmethoxy)1-[4-(6-methoxypyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11q). For step 3, compound 19 was used as the alkylating agent with catalytic TBAI and DMF as solvent for 12 h. 1H NMR (DMSO-d6) δ 1.14 (s, 15H), 3.26 (s, 2H), 3.89 (s, 3H), 5.24 (s, 2H), 5.56 (s, 2H), 6.92 (m, 4H), 7.11 (d, 1H), 7.38 (d, 1H), 7.58 (d, 2H), 7.66 (d, 1H), 7.99 (dd, 1H), 8.30 (dd, 1H), 8.46 (d, 1H), 9.10 (d, 1H). [M + H]+: m/z calculated 654; observed 654. 3-[3-tert-Butylsulfanyl-1-[4-(6-methoxypyridin-3-yl)benzyl]5-(5-methylpyrazin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11r). For step 3, compound 14 was used as the alkylating agent. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 2.58 (s, 3H), 3.34 (s, 2H), 3.95 (s, 3H), 5.27 (s, 2H), 5.45 (s, 2H), 6.77 (d, 1H), 6.87 (m, 3H), 7.08 (d, 1H), 7.33 (m, 3H), 7.70 (dd, 1H), 8.30 (d, 1H), 8.46 (s, 1H), 8.71 (s, 1H). [M + H] +: m/z calculated 625; observed 625. The following compounds were prepared according to route B but varying the cross-coupling partner in step 2 as described and using compound 16c as the alkylating agent in step 3. 3-[3-tert-Butylsulfanyl-1-[4-(3-methoxypyridin-3-yl)benzyl]5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11w). For step 2, 2-bromo-3-methoxypyridine was used in the cross-coupling reaction. 1H NMR (CDCl3) δ 0.98 (s, 6H), 1.05 (s, 9H), 2.29 (s, 3H), 3.20 (s, 2H), 3.61 (s, 3H), 5.15 (s, 2H), 5.34 (s, 2H), 6.74 (m, 3H), 6.89 (d, 1H), 7.08 (m, 2H), 7.22 (m, 1H), 7.41 (m, 2H), 7.59 (d, 2H), 8.11 (s, 1H), 8.39 (s, 1H). [M + H] +: m/z calculated 624; observed 624. 8026




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complete displacement of the fluoride with methoxide. 1H NMR (CDCl3) δ 1.21 (s, 9H), 1.26 (s, 6H), 2.33 (s, 3H), 3.33 (s, 2H), 3.92 (s, 3H), 5.21 (s, 2H), 5.44 (s, 2H), 6.81 (m, 3H), 6.99 (d, 1H), 7.30 (d, 1H), 7.46 (d, 1H), 7.52 (d, 1H), 8.12 (s, 1H), 8.15 (s, 1H), 8.43 (s, 2H), 8.45 (s, 1H). [M + H]+: m/z calculated 625; observed 625. 3-[3-tert-Butylsulfanyl-1-[4-(6-ethoxypyridin-3-yl)benzyl]-5(5-methyl-1-oxypyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11ll). For step 2, 5-bromo-2-ethoxypyridine was used as the coupling partner, and in step 3 compound 16g was used as the alkylating agent. 1H NMR (CDCl3) δ 1.23 (s, 9H), 1.25 (s, 6H), 1.40 (t, 3H), 2.33 (s, 3H), 3.34 (s, 2H), 4.36 (q, 2H), 5.39 (s, 2H), 5.44 (s, 2H), 6.74 (d, 1H), 6.84 (m, 3H), 7.04 (d, 1H), 7.22 (d, 1H), 7.35 (m, 3H), 7.60 (d, 1H), 7.69 (dd, 1H), 8.29 (s, 2H). [M + H]+: m/z calculated 654; observed 654. 3-{3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(6-oxo-1,6-dihydropyridin-3-yl)benzyl]-1H-indol-2-yl}-2,2dimethylpropionic Acid (11jj). To the sodium salt of 11cc (prepared through reaction of 11cc with 1 equiv of NaOH in EtOH for 1 h and evaporation in vacuo; 700 mg, 1.06 mmol) in ethylene glycol (5 mL) was added LiOH·H2O (400 mg, 10 mmol) in a sealable vessel, and the mixture was heated to 165 °C for 1 week. LCMS analysis indicated incomplete reaction. The reaction mixture was allowed to cool and diluted with EtOAc. Water and solid citric acid were added until aqueous pH was ∼4. The aqueous layer was extracted with EtOAc and the organic phase dried (MgSO4), filtered, and evaporated in vacuo. The residue was purified using silica gel chromatography (0−7% MeOH in CH2Cl2) to afford the title compound as a colorless solid. 1H NMR (CDCl3) δ 1.23 (s, 15H), 2.33 (s, 3H), 3.56 (s, 2H), 5.23 (s, 2H), 5.59 (br s, 2H), 6.54 (d, 1H), 6.66 (d, 1H), 6.75 (dd, 1H), 6.94 (d, 2H), 7.01 (d, 2H), 7.13 (s, 1H), 7.31 (s, 1H), 7.44 (d, 1H), 7.51 (d, 1H), 7.63 (d, 1H), 8.42 (s, 1H). [M + H]+: m/z calculated 610; observed 610. 3-[1-[4-(6-Ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (29). To an ice cooled suspension of anhydrous AlCl3 (1.38 g, 10.34 mmol) in CH2Cl2 (12 mL) was added water (138 μL, 7.66 mmol) dropwise, and the solution was allowed to attain ambient temperature. After 20 min the solution was recooled to 0 °C and a solution of the ethyl ester of 11cc (isolated product from step 3 of route B; 1.70 g, 2.55 mmol) in CH2Cl2 (12 mL) was added over a period of 5 min. After 1 h, TLC analysis indicated a 60:40 product/SM mixture. The mixture was cooled to 0 °C, and anhydrous AlCl3 (1.25 g, 9.37 mmol) and water (125 μL, 6.94 mmol) were added sequentially. The mixture was stirred at ambient temperature for 1 h and the reaction quenched upon addition of 0.5 N aqueous sodium potassium tartrate solution with vigorous stirring for 1 h. The mixture was extracted with CH 2Cl2, and the organic phase was dried (MgSO4), filtered, and evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0−35% EtOAc in hexanes) afforded 1.07 g (73%) of the ethyl ester of 29. To the isolated ester (100 mg, 0.173 mmol) in a mixture of THF (3 mL), MeOH (1 mL) and water (1 mL) were added LiOH·H2O (35 mg, 0.833 mmol). The mixture was heated at 60 °C for 4 h. The mixture was diluted with EtOAc and water, and solid citric acid was added to acidify the aqueous layer to a pH of ∼3, after which the aqueous layer was extracted with EtOAc and the organic phase dried (MgSO4), filtered, and evaporated in vacuo to yield the title compound as a colorless solid in quantitative yield. 1H NMR (CDCl3) δ 1.32 (s, 6H), 1.40 (t, 3H), 2.33 (s, 3H), 3.00 (s, 2H), 4.36 (q, 2H), 5.13 (s, 2H), 5.34 (s, 2H), 6.38 (s, 1H), 6.74 (d, 1H), 6.81 (dd, 1H), 6.90 (d, 2H), 6.99 (d, 1H), 7.03 (d, 1H), 7.33 (d, 2H), 7.46 (d, 1H), 7.53 (dd, 1H), 7.67 (dd, 1H), 8.27 (d, 1H), 8.45 (s, 1H). [M + H] +: m/z calculated 550; observed 550. rac-3-[1-[4-(6-Ethoxypyridin-3-yl)benzyl]-3-(2-methylpropane-2-sulfinyl)-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2yl]-2,2-dimethylpropionic Acid (30). 3-[3-tert-Butylsulfanyl-1-[4(6-ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1Hindol-2-yl]-2,2-dimethylpropionic acid (11cc, 75.0 mg, 0.118 mmol) was dissolved in CH2Cl2 (1 mL) and cooled to −20 °C. m-CPBA (29.0 mg, 0.118 mmol) was added and the solution slowly warmed to 0 °C. Upon completion of the reaction as judged by TLC analysis, the reaction mixture was diluted with CH2Cl2, washed with water and the

3-{3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(4-trifluoromethylpyridin-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11x). For step 2, 2-chloro-4-trifluoromethylpyridine was used in the cross-coupling reaction. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.27 (s, 6H), 2.34 (s, 3H), 3.33 (s, 2H), 5.19 (s, 2H), 5.45 (s, 2H), 6.81 (dd, 1H), 6.84 (d, 2H), 6.96 (d, 1H), 7.31 (d, 1H), 7.41 (d, 1H), 7.47 (d, 1H), 7.52 (d, 1H), 7.82 (m, 3H), 8.46 (s, 1H), 8.32 (d, 1H). [M + H]+: m/z calculated 662; observed 662. 3-{3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1[4-(6-trifluoromethylpyridin-2-yl)benzyl]-1H-indol-2-yl}-2,2-dimethylpropionic Acid (11bb). For step 2, 2-chloro-6-trifluoromethylpyridine was used as the coupling partner. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 2.33 (s, 3H), 3.34 (s, 2H), 5.19 (s, 2H), 5.44 (s, 2H), 6.81 (dd, 1H), 6.89 (d, 2H), 6.96 (d, 1H), 7.30 (d, 1H), 7.45 (d, 1H), 7.51 (dd, 1H), 7.56 (d, 1H), 7.77 (d, 1H), 7.84 (d, 1H), 7.87 (d, 2H), 8.44 (s, 1H). [M + H]+: m/z calculated 662; observed 662. 3-[3-tert-Butylsulfanyl-1-[4-(6-ethoxypyridin-3-yl)benzyl]-5(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (AM803, 11cc). For step 2, 5-bromo-2-ethoxypyridine was used in the cross-coupling reaction. 1H NMR (CDCl3) δ 1.21 (s, 9H), 1.26 (s, 6H), 1.40 (t, 3H), 2.34 (s, 3H), 3.33 (s, 2H), 4.36 (q, 2H), 5.19 (s, 2H), 5.42 (s, 2H), 6.73 (d, 1H), 6.82 (m, 3H), 7.00 (d, 1H), 7.33 (m, 3H), 7.47 (d, 1H), 7.53 (dd, 1H), 7.67 (dd, 1H), 8.27 (d, 1H), 8.46 (s, 1H). [M + H]+: m/z calculated 638; observed 638. 3-[3-tert-Butylsulfanyl-1-[4-(6-ethoxypyridin-2-yl)benzyl]-5(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11dd). For step 2, 2-chloro-6-ethoxypyridine was used in the cross-coupling reaction. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 1.40 (t, 3H), 2.33 (s, 3H), 3.34 (s, 2H), 4.42 (q, 2H), 5.20 (s, 2H), 5.43 (s, 2H), 6.62 (d, 1H), 6.82 (dd, 1H), 6.86 (d, 2H), 7.00 (d, 1H), 7.20 (d, 1H), 7.31 (d, 1H), 7.45−7.58 (m, 3H), 7.85 (d, 2H), 8.45 (s, 1H). [M + H]+: m/z calculated 638; observed 638. 3-[3-tert-Butylsulfanyl-1-[4-(5-fluoropyridine-2-yl)benzyl]-5(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11ff). For step 2, 2-bromo-5-fluoropyridine was used in the cross-coupling reaction. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.26 (s, 6H), 2.34 (s, 3H), 3.33 (s, 2H), 5.20 (s, 2H), 5.43 (s, 2H), 6.83 (m, 3H), 6.99 (d, 1H), 7.31 (d, 1H), 7.38−7.54 (m, 3H), 7.60 (dd, 1H), 7.72 (d, 2H), 8.45 (s, 1H), 8.50 (d, 1H). [M + H] +: m/z calculated 612; observed 612. 3-[3-tert-Butylsulfanyl-1-[4-(5-fluoropyridin-3-yl)benzyl]-5(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11gg). For step 2, 3-bromo-5-fluoropyridine was used as the coupling partner. 1H NMR (CDCl3) δ 1.22 (s, 9H), 1.28 (s, 6H), 2.34 (s, 3H), 5.19 (s, 2H), 5.45 (s, 2H), 6.81 (dd, 1H), 6.88 (d, 2H), 6.96 (d, 1H), 7.32 (d, 1H), 7.36 (d, 2H), 7.49 (m, 3H), 8.40 (d, 1H), 8.47 (s, 1H), 8.53 (s, 1H). [M + H]+: m/z calculated 612; observed 612. 3-[3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1(4-pyridin-3-yl-benzyl)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11hh). For step 2, 3-bromopyridine was used in the crosscoupling reaction. 1H NMR (DMSO-d6) δ 1.11 (s, 6H), 1.14 (s, 9H), 2.28 (s, 3H), 3.23 (s, 2H), 5.15 (s, 2H), 5.54 (s, 2H), 6.83 (dd, 1H), 6.93 (d, 2H), 7.11 (d, 1H), 7.33 (d, 1H), 7.38 (d, 1H), 7.42 (dd, 1H), 7.58 (d, 1H), 7.62 (d, 2H), 8.00 (d, 1H), 8.40 (s, 1H), 8.53 (d, 1H), 8.83 (d, 1H), 12.41 (br s, 1H). [M + H]+: m/z calculated 594; observed 594. 3-[3-tert-Butylsulfanyl-5-(5-methylpyridin-2-ylmethoxy)-1(4-pyridin-2-yl-benzyl)-1H-indol-2-yl]-2,2-dimethylpropionic Acid (11ii). For step 2, 2-chloropyridine was used in the crosscoupling reaction. 1H NMR (DMSO-d6) δ 1.13 (s, 15H), 2.28 (s, 3H), 3.22 (s, 2H), 5.15 (s, 2H), 5.54 (s, 2H), 6.83 (dd, 1H), 6.92 (d, 2H), 7.10 (d, 1H), 7.35 (m, 3H), 7.60 (dd, 1H), 7.80−7.98 (m, 4H), 8.41 (s, 1H), 8.61 (d, 1H), 12.42 (br s, 1H). [M + H] +: m/z calculated 594; observed 594. 3-[3-tert-Butylsulfanyl-1-[4-(5-methoxypyrimidin-2-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2dimethylpropionic Acid (11kk). For step 2, 2-chloro-5-fluoropyrimidine was used in the cross-coupling step. In step 4 (ester hydrolysis), the reaction time was prolonged to 72 h at 65 °C to force 8027




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organic phase separated, dried (MgSO4), filtered, and evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0−5% MeOH in CH2Cl2) afforded 65 mg (85%) of the title compound as a colorless solid. 1H NMR (CDCl3) δ 1.29 (s, 9H), 1.37 (s, 6H), 1.40 (t, 3H), 2.34 (s, 3H), 3.11 (d, 1H), 3.23 (d, 1H), 4.36 (q, 2H), 5.14 (app q, 2H), 5.29 (d, 1H), 5.47 (d, 1H), 6.74 (d, 1H), 6.80 (m, 3H), 7.00 (d, 1H), 7.38 (d, 2H), 7.43 (d, 1H), 7.53 (dd, 1H), 7.67 (dd, 1H), 7.78 (s, 1H), 8.26 (d, 1H), 8.45 (s, 1H). [M + H] +: m/z calculated 654; observed 654. 3-[3-(3,3-Dimethylbutyryl)-1-[4-(6-ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2dimethylpropionic Acid (31a). To a solution of the ethyl ester of 29 (150 mg, 0.26 mmol) in 1,2-dichloroethane were added anhydrous AlCl3 (104 mg, 0.78 mmol) and tert-butylacetyl chloride (72 μL, 0.52 mmol), and the reaction mixture was heated to 65 °C under nitrogen for 1 h. The mixture was diluted with CH2Cl2 (25 mL) and 0.5 N aqueous sodium potassium tartrate solution added (25 mL). The mixture was vigorously stirred for 1 h. The aqueous phase was extracted with CH2Cl2 and the organic phase dried (MgSO4), filtered, and evaporated in vacuo. Purification of the residue using silica gel chromatography (ISCO, 0−40% EtOAc in hexanes) afforded 114 mg (65%) of the ester of the title compound. The isolated ester (114 mg, 0.17 mmol) was dissolved in a mixture of THF (3 mL), MeOH (1 mL), and water (1 mL). LiOH·H2O (40 mg, 0.95 mmol) was added, and the mixture was heated to 60 °C. Upon completion of the hydrolysis (∼2 h) the mixture was allowed to cool and diluted with EtOAc and water. The aqueous pH was adjusted to ∼3 with the addition of solid citric acid, the mixture extracted with EtOAc, and the organic phase dried (MgSO4), filtered, and evaporated in vacuo to yield the title compound as a colorless solid in quantitative yield. 1H NMR (CDCl3) δ 1.09 (s, 9H), 1.32 (s, 6H), 1.40 (t, 3H), 2.36 (s, 3H), 2,90 (s, 2H), 3.64 (s, 2H), 4.36 (q, 2H), 5.17 (s, 2H), 5.40 (s, 2H), 6.74 (d, 1H), 6.81 (dd, 1H), 6.85 (d, 2H), 6.99 (d, 1H), 7.33 (d, 2H), 7.47 (s, 1H), 7.49 (d, 1H), 7.57 (dd, 1H), 7.67 (dd, 1H), 8.26 (d, 1H), 8.48 (s, 1H). [M + H]+: m/z calculated 648; observed 648. 3-[1-[4-(6-Ethoxypyridin-3-yl)benzyl]-5-(5-methylpyridin-2ylmethoxy)-3-phenylacetyl-1H-indol-2-yl]-2,2-dimethylpropionic Acid (31b). 31b was prepared in the same manner as 31a using phenylacetyl chloride as electrophile. 1H NMR (CDCl3) δ 1.29 (s, 6H), 1.40 (t, 3H), 2.35 (s, 3H), 3.66 (s, 2H), 4.33 (s, 2H), 4.36 (q, 2H), 5.08 (s, 2H), 5.36 (s, 2H), 6.74 (d, 1H), 6.79 (dd, 1H), 6.82 (d, 2H), 6.92 (d, 1H), 7.22−7.33 (m, 8H), 7.49 (s, 1H), 7.58 (dd, 1H), 7.65 (dd, 1H), 8.25 (d, 1H), 8.47 (s, 1H). [M + H] +: m/z calculated 668; observed 668.

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blood; BAL, bronchoalveolar lavage; GPCR, G-protein-coupled receptor; IC 50, concentration required to achieve 50% inhibition; hSA, human serum albumin

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Information for the characterization of final compounds 11b, 11d−11z, 11bb−11ll and 29, 30, 31a,b. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Phone: 858 224 7715. Fax: 858 224 7795. E-mail: nstock@ inceptionsci.com.

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ACKNOWLEDGMENTS We thank Dr. Brian Stearns for assistance in preparing the tritiated FLAP ligand used in our binding studies.

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ABBREVIATIONS USED AA, arachidonic acid; LT, leukotriene; 5-LO, 5-lipoxygenase; FLAP, five-lipoxygenase activating protein; 5-HpETE, (5S,6E,8Z,11Z,14Z)-5-hydroperoxy-6,8,11,14-eicosatetraenoic acid; 5-oxo-ETE, 5-oxo-(6E,8Z,11Z,14Z)-6,8,11,14-eicosatetraenoic acid; CysLT, cysteinyl leukotriene; CVD, cardiovascular disease; hLA, human leukocyte assay; hWB, human whole 8028




Article

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