Letters in Drug Design & Discovery, 2009, 6, 531-537
531
On the Synthesis and Anticancer Testing of ,-Unsaturated Ketones as Analogs of Combretastatin-A4 Sameer Chavdaa, Ryan Davisa, Amanda Fergusona, Camille Ridderinga, Kristin Dittenhafera, Hilary Mackaya, Balaji Babua, Moses Lee*,a, Adam Siegfriedb, William Penningtonb, Miriam Shadfanc, Susan L. Mooberryc, Bijay K. Mishrad and Hari N. Patid a
Department of Chemistry and the Division of Natural and Applied Sciences, Hope College 49423, USA
b
Department of Chemistry, Clemson University, SC 29634, USA
c
Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA
d
Department of Chemistry, Sambalpur University, Jyoti Vihar, Orissa-768 019, India Received April 13, 2009: Revised June 24, 2009: Accepted June 26, 2009
Abstract: Twenty-one ,-unsaturated ketone analogs of combretastatin-A4 (CA-4) that were designed for good solubility in aqueous media were synthesized. Compounds defined as Type A were derived from phenylacetone, in which subclass I contained ortho-, meta- or no substituents, sub-class II contained para-substituents, and sub-class III consisted of two substituents. Type B compounds were derived from cyclopropyl 2-fluorobenzyl ketone. The cis-configuration of the target compounds was ascertained through a single crystal X-ray crystallographic analysis of the fluorine-containing compound 8f. Five of the analogs, 8c, 8j and 8l of Type A and 9d and 9i of Type B, were shown to display modest cytotoxic potency (IC50 in the 3.8 – 21 μM range) against the growth of murine melanoma (B16) and leukemia (L1210) cells in culture. Compounds 8j, 8l and 9i were further tested against MDA-MB-435 human melanoma cells. The cyclopropanecontaining compound 9i was the most potent; with an IC50 value of 2.4 μM. Even though no appreciable effects on interphase microtubules were observed when A-10 cells were treated with 30 μM 8j or 8l, compound 9i caused extensive microtubule depolymerization at this concentration. These results suggest that compound 9i of Type B has a similar mechanism of action as CA-4 whilst compounds 8j and 8l of Type B are likely to have a different mechanism of action.
Keywords: Combretastatin, Cytotoxicity, Tubulin, Microtubule, Cancer. INTRODUCTION Vascular disrupting agents (VDAs) act as effective antitumor agents because they initiate rapid shutdown of tumor vasculature, leading to tumor necrosis [1], possibly mediated through the vascular endothelial cadherin signaling pathway [1b] The combretastatins are one class of VDAs that rapidly shutdown tumor vasculature. Combretastatin-A4, (CA-4 or 1 as shown in Fig. (1)) a natural product which consists of a core cis-stilbene moiety, was originally isolated from the African Willow tree, Combretum caffrum, and is known to inhibit tubulin polymerization via interaction with the colchicine binding site of tubulin [2]. CA-4 causes the rapid destruction of aberrant tumor vasculature and these effects are probably mediated through direct effects on tumor endothelial cells. Despite the effectiveness of CA-4 as an antitumor agent, one major drawback leading to the impairment of its antitumor activity is its lack of bioavailability and poor solubility in biological media [3]. As a result there is a significant interest in the design of structural analogs of 1 that exhibit more pharmacologically beneficial properties. Derivatives, such as, compounds 2 (CA-4P) [4], 3 (an amino analog of CA-4) and 4 (an amino acid derivative of CA-4P, AVE*Address correspondence to this author at the Division of Natural and Applied Sciences and Department of Chemistry, Hope College, Holland, MI, 49423, USA; Tel: +1 616 395 7190; Fax: +1 616 395 7923; E-mail:
[email protected] 1570-1808/09 $55.00+.00
H3CO H3CO
R OCH3
OCH3
1, R=OH, cis-CA-4 2, R=OPO32-, water soluble derivative CA-4P 3, R=NH2 4, R=NHCOCH(NH2)CH2OH; AVE-8062
Fig. (1). Structures of combretastatin-A4 (1), CA-4P (2), an amino analog of CA-4 (3) and its derivative AVE-8062 (4).
8062) [5] depicted in Fig. (1) are examples of more watersoluble pro-drugs of CA-4. CA-4P is presently undergoing clinical trials [4]. In addition, analogs of combretastatins incorporating a heterocycle capable of mimicking the rigidity of the framework, maintaining the cis-configuration of the aromatic rings (necessary for a good fit into the colchicine binding site in tubulin), as well as increasing the polarity of the molecules so as to improve water solubility have been reported [6]. A class of compounds possessing these criteria reported previously from our laboratory include the 1,2,3triazole derivatives of combretastatin, which were found to possess levels of cytotoxicity in the micro-molar range against the growth of B16 murine melanoma cells [7]. Although the potencies of the representative triazole analogs shown in Fig. (2) range from poor to moderate, we believe © 2009 Bentham Science Publishers Ltd.
532 Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7
Chavda et al.
that compounds bearing the general structure -phenylheterocycle-phenyl- or –phenyl--phenyl- offer favorable solubility in aqueous media and maintain the geometry necessary to fit the colchicine binding site in tubulin, and this model warrants further investigation. With this information in hand, we have synthesized a series of ,-unsaturated ketones 8a-m and 9a-j, which contain the cis-stilbene core present in the combretastatins (Fig. (3)). Even though such enone-containing molecules can potentially undergo Michael reactions with biological nucleophiles such as glutathione [8], they are worthy of further investigation because ,enones, such as chalcones analgues of CA-4, have been found to exhibit potent cytotoxicity against cancer cells in culture [9]. In addition, to the best of our knowledge, these types of combretastatin analogs have not been investigated to date for anticancer activity. N N
NH
R1 R3
R2
R4
5, R1=R3=H, R2=OCH3, R4=CH3, IC50=>100 Molar 6, R1=R3=H, R2=OCH3, R4=NH2, IC50=>100 Molar 7, R1=R2=R3=OCH3, R4=NH2, IC50= 56 Molar
Fig. (2). Structures of triazoles 5, 6 and 7 and their IC50 values against the growth of B16 murine melanoma cells. O
O
CH3
(i) Arylaldehyde
Ph
CH3
(ii) HCl (35%) Ar
Reflux in EtOH, 3 hrs 8e
Ph
8a-d, 8f-m
O
O NaOMe, Arylaldehyde
F
MeOH, reflux 12 hrs F
Ar
9f
9a-9e, 9g-j
Fig. (3). Synthesis of Type A and B compounds.
RESULTS AND DISCUSSION A series of ,-unsaturated ketone analogs of CA-4 which conform to the criteria mentioned above were synthesized: the incorporation of the cis-stilbene core was required to maintain biological activity and the presence of the polar acetyl functionality on the stilbene core to help promote solubility in aqueous media. Twenty-one ,-unsaturated ketones were synthesized and assessed for their ability to inhibit the growth of L1210 and B16 cells (murine leukemia and melanoma cell lines). Three compounds were also selected for testing against the growth of human melanoma
MDA-MB-435 cells and depolymerization of microtubules in rat A-10 aortic cells. Two categories of compounds were synthesized: Type A (derived from phenylacetone [10] 8e) sub-classes I (ortho-, meta- and non substituted 8a-d), II (para-substituted; 8f-8k, Table 1), III (consisting of two disubstituted analogs 8l and 8m, Table 2) and Type B (para-, di- and tri-substituted) derived from cyclopropyl 2-fluorobenzyl ketone [11] (Table 3, 9a-e and 9g-j). The Type A compounds were synthesized using a known literature procedure [10c] by acid catalyzed condensation of the appropriate aldehyde with phenylacetone in good to excellent yield (65-75%, Fig. (3), Tables 1 and 2). Compounds 8a, 8f, 8g, 8h and 8j have been reported previously [12] The Type B compounds were synthesized by refluxing a mixture of cyclopropyl 2-fluorobenzyl ketone, sodium methoxide and the appropriate aryl aldehyde in methanol to give the corresponding ,-unsaturated ketones in good yields (60-75%, Fig. (3), Table 3). Due to commercial availability constraints, we were limited mainly to a series of mono- and disubstituted aldehydes (Tables 1, 2 and 3). The geometry of the aromatic rings about the double bond in these compounds was exclusively found to be cis as ascertained from the X-ray structure of compound 8f (Fig. (4)). Further evidence for this geometry arises from the NMR chemical shift of the benzylidene proton in these compounds, which appears as a singlet at approximately 7.60. In comparison, for the trans isomer, this particular proton appears to be slightly shifted downfield at approximately 8.00 [13]. With a range of the target molecules in hand, their ability to inhibit the growth of murine B16 (melanoma) and L1210 (leukemia) melanoma cell lines was assessed. These cells were continuously exposed for three days with the growth inhibition properties of Type A and B compounds studied using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide) assay [14]. The concentrations needed to inhibit growth of B16 and L1210 cells for compounds 8a-8m are shown in Tables 1, 2 and 3. The results from these studies display several interesting trends based upon the substitution pattern of the aromatic ring (derived from the benzaldehyde reactant) and the nature of the substituent. As a control, for categories A and B, phenylacetone 8e and cyclopropyl 2-fluorobenzyl ketone 9f were tested for cytotoxicity against both cell lines and, as a result, both gave IC50 values >100 μM suggesting that having two aromatic rings on these molecules is necessary for biological activity. For the Type A compounds, it appears that orthosubstitution of a Cl atom in the Ar ring moderately affects potency (compound 8b) in relation to its non-substituted counterpart 8b. Incorporation of a slightly less polar and larger Br atom in the meta position dramatically results in an increase in cytotoxicity, with IC50 values of around 4 μM, in both B16 and L1210 cell lines, for compound 8c, which is significantly more active than its unsubstituted analog 8a, which gave an IC50 of >100 μM. Meta- substitution of an electron-donating methoxy group moderately diminishes the potency (compound 8d, IC50 values 67 (B16) and 56 (L1210) μM). In comparison to ortho- and meta- substitution, a fluorine or bromine atom in the para- position of the Ar ring (8f and 8g; Table 1; Type A sub-class II) results in very little cytotoxicity. Incorporation of an electron-withdrawing nitro
,-Unsaturated Ketones as Analogs of Combretastatin-A4
Table 1.
Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7
Cytotoxicity Data for Compounds 8a-k (Type A Subclasses I and II) Type A: Sub-class I (o-, m- & no-substitution)
Type A: Sub-class II (para-substitution)
IC50 (μM)
Structure
B16
L1210
Structure
O
IC50 (μM) B16
L1210
>100
>100
70
>100
45.0
46.0
>100
49.7
14.4
21.4
>100
>100
O CH3
CH3
Ar
Ar Ar =
Ar =
>100
>100
F
8a
8f
Cl
45
45
Cl
8g
8b
Br 4.2
3.8
CH3
8c
8h OMe
67
56
OCH3
8d
8i
Phenylacetone >100
8e
>100
NO2 8j
NMe2 8k
Table 2.
Cytotoxicity Data for Compounds 8l and 8m (Type A; Sub-Class III)
Type A: Sub-class III (disubstitution) Structure
IC50 (μM) B16
IC50 (μM) L1210
B16
L1210
>100
80.0
OMe
OPh
F 8l
11.3
11.8
MeO 8m
533
534 Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7
Table 3.
Chavda et al.
Cytotoxicity Data for Compounds 9a-j (Type B) Type B:
IC50 (μ M)
Structure
B16
IC50 (μ M) L1210
B16
L1210
>100
>100
51.7
61.0
54.7
43.0
50.0
6.0
65
41
O F Ar
Ar =
F >100
O
>100
9a 9f
F
60.3
58.0
Cl
9b
9g
Br
37.0
51.0
CH3
9c
9h
OMe
NO2
4.1
4.5
MeO 9d 9i
OMe
OMe
43.0
O
51.0
OMe
O
9e
9j
group into the para-position of the Ar ring (compound 8j) has the most significant positive effect on cytotoxicity (IC50 values 14.4 (B16) and 21.4 (L1210) μM) in comparison to compounds 8h, 8i, 8j and 8k presumably suggesting that the electronic influence (due to inductive and resonance effects) of the para-nitro group enhances the compound’s interactions with its cellular targets. It is interesting to note that 8k, containing a para-substituted dimethylamino moiety capable of exerting an electronic influence through electron donating resonance effects, shows low potency (>100 μM for B16 and L1210 lines). This suggests that substituent size could possibly be a factor contributing to the potency of these compounds as well as substituent polarizability in the paraposition.
Fig. (4). X-ray structure of compound 8f.
Based on the cytotoxic behavior of the Type A subclasses I and II compounds, we were curious to probe whether 2,6 and 3,4 disubstitution of the Ar ring could en-
,-Unsaturated Ketones as Analogs of Combretastatin-A4
hance cytotoxicity (8l and 8m, Table 2; Type A sub-class III). Interestingly, the presence of a phenoxy group in the meta-position adjacent to a fluorine atom in the paraposition in 8l resulted in an increase in potency (~11 μM) in comparison to its para-fluorinated counterpart 8f (Table 1), this could be due to potential interaction of the non-polar phenoxy group phenyl ring with its biomolecular target in cells. On the other hand, 2,6-dimethoxy substitution of the Ar ring on 8m furnished poor cytotoxicity in both cell lines.
Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7
535
active portion of the molecule within the binding site for more efficient interaction with its cellular target, presumably the colchicine binding site of tubulin. On the other hand, tubulin may not be the site of action by compounds 8j and 8l, suggesting that small changes in the molecules can have an impact on the mechanism of action. Given their cytotoxicity, compounds 8c, 9d and 9i are worthy of further biological investigations.
Based on the observations (from the Type A sub-classes I and II) that the presence of a fluorine substituent on the aromatic ring(s) does not diminish potential bioactivity, we chose to use cyclopropyl 2-fluorobenzyl ketone as the main framework for the Type B compounds. In this study, we were curious to see whether the cyclopropyl moiety would further enhance the cytotoxicity potency of these analogs. The cytotoxicity results for the Type B compounds, 9a-j, against B16 and L1210 cell lines are given in Table 3. The simple non-substituted compound 9a showed low potency (IC50 >100 μM for both cell lines). For the other compounds, several reoccurring trends were observed in addition to an enhancement of cytotoxicity. The cytotoxicity for both cell lines, 9c > 9g > 9b, suggest that these results are related to the polarity of the halogen atom in the para-position of the Ar ring (Table 3), and it is roughly in line with 8f and 8g (Type A; sub-class II). In addition, the cyclopropyl group seems to moderately enhance the potency of 9b, 9c and 9g in comparison to 8f and 8g (Table 2). This is also true for 9d (Table 3) which contains a para-nitro group on the Ar ring, for which the cytotoxicity is slightly enhanced in comparison to 8j (IC50 for 8j 14.4 (B16) and 21.4 μM verses 4.1 (B16) and 4.5 μM for 9d). A similar scenario exists for 9i which contains a 2,6-dimethoxyphenyl ring (Table 3; IC50 values 50.0 (B16) and 6.0 μM (L1210) when compared to 8m (IC50 values >100 (B16) and 80.0 (L1210) μM). Contrary to these observations, the cyclopropyl group does not seem to enhance the potency of 9h (Table 3; IC50 values 54.7 (B16) and 43.0 (L1210) μM) compared to 8i (Table 1; IC50 values 45.0 (B16) and 46.0 (L1210) μM). Three compounds, 8j and 8l of Type A, and 9i of Type B, were selected for further biological evaluation to provide mechanistic information. These compounds were evaluated for: cytotoxicity in MDA-MB-435, human melanoma cells and microtubule disrupting effects. Compounds 8j, 8l and 9i were effective in MDA-MB-435 cells and gave IC50 values of 9.6, 23.1, and 2.4 μM, respectively. Interestingly, these widely varied structures had relatively minor differences in cytotoxic potency. Furthermore, the results from human cancer cells are within the same range of the results obtained from murine cells. The three compounds were further tested for microtubule disrupting effects in A-10 cells using an immunofluorescence assay [14, 15] The results given in Fig. (5) are striking for Type B compound 9i, which caused 50% microtubule loss at 30 μM. This result is consistent with a classic microtubule depolymerizer [14, 15], including compounds previously studied in our laboratories [14, 15]. Interestingly, the Type A compounds 8j and 8l did not show effects on microtubule structures at 30 μM. Even though the exact mechanism of action by these compounds is unknown, the findings suggest that the strained and rigid nature of the cyclopropane ring in 9i could help orient the biologically
Fig. (5). Effects of 9i on cellular microtubules in A-10 cells. A, vehicle control, and B, 60 μM compound 9i. Cells were treated for 18 h and cellular microtubules visualized by indirect immunofluorescence techniques.
EXPERIMENTAL Proton NMR spectra were recorded using a 400 MHz Varian AVANCE-400 FT NMR using an internal deuterium lock. Chemical shifts are quoted in parts per million downfield from tetramethylsilane. Infrared spectra were recorded on a Perkin Elmer 100 FT-IR spectrophotometer with DRS (Diffuse Reflectance Sampler). Mass spectra were recorded using an API 2000 spectrometer, ion source (ESI /APCI). Characterization data for compounds 8a, 8f, 8g, 8h and 8j was found to be consistent with that of reported previously [12]. General Method of Preparation of Type A Compounds Hydrochloric acid (35%, 0.5 mL) was added drop wise to a solution of Phenylacetone (500 mg, 1 equiv.) and the ap-
536 Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7
propriate aryl aldehyde (2 equiv.) in ethanol (20 mL) at room temperature. The reaction mixture was stirred under reflux for 2-3 hrs. Completion of the reaction was determined by TLC (Hex: EtOAc: 9:1) after which ethanol was removed under vacuum. The resulting crude residue obtained was purified by column chromatography using Hexane- Ethyl acetate (9:1) as eluent.
Chavda et al.
9a: Colorless oil; 1H NMR (400 MHz, CDCl3) 0.87(m, 2H), 1.18(m, 2H), 2.12(m, 1H), 7.12-7.34(m, 8H), 7.40(m, 1H), 7.80(s, 1H); IR (KBr): 3067, 2989, 2951, 2833, 1954, 1698, 1655, 1579, 1501, 1463, 1246,1229,1124, 1001, 933, 831, 765cm-1; ESI (APCI)-MS: m/z 267(M+1).
8a: Colorless oil; 1H NMR (400 MHz, CDCl3) 2.30(s, 3H), 7.01(m, 2H), 7.14-7.33(m, 8H), 7.64(s, 1H); IR (KBr): 3064, 1718, 1600, 1493, 1450, 1317, 1234, 1176, 759, 702cm-1; ESI (APCI)-MS: m/z 223(M+1).
8b: Colorless oil; 1H NMR (400 MHz, CDCl3) 0.87(m, 2H), 1.16(m, 2H), 2.05(m, 1H), 7.05(d, J=8.4Hz, 2H), 7.157.20(m, 5H), 7.38(m, 1H), 7.74(s, 1H); IR (KBr): 3080, 3003, 2950, 2836, 1956, 1699, 1657, 1510, 1461, 1248, 1224,1120, 934, 833, 773cm-1; ESI (APCI)-MS: m/z 285(M+1).
8b: Colorless oil; 1H NMR (400 MHz, CDCl3) 2.39(s, 3H), 6.70(d, J=8.0Hz, 1H), 6.83(m, 1H), 7.08( m, 3H), 7.27(m, 3H), 7.33 (d, J =8.0Hz, 1H), 7.85(s, 1H); IR (KBr): 3054, 2929, 1677, 1593, 1440, 1233, 756, 700cm-1; ESI (APCI)-MS: m/z 257(M+1).
9c: Colorless oil; 1H NMR (400 MHz, CDCl3) 0.86(m, 2H), 1.17(m, 2H), 2.07(m, 1H), 6.96(m, 3H), 7.16(m, 4H), 7.34(m, 1H), 7.68(s, 1H); IR (KBr): 3088, 2994, 2960, 2841, 1950, 1693, 1658, 1581, 1510, 1459, 1239, 1218, 1134, 1100, 933, 835, 771cm-1; ESI (APCI)-MS: m/z 347(M+2).
8c: Colorless oil; 1H NMR (400 MHz, CDCl3) 2.31(s, 3H), 6.92(m, 1H), 6.99(m, 1H), 7.14-7.43(m, 7H), 7.54(s, 1H); IR (KBr): 3063, 2997, 1961, 1658, 1428, 1390, 1279, 1234, 1166, 1072, 895, 700 cm-1; ESI (APCI)-MS: m/z 303 (M+2).
9d: Yellow colored semisolid; 1HNMR (400 MHz, CDCl3) 0.89(m, 2H), 1.18(m, 2H), 2.03(m,1H), 7.12(m, 3H), 7.22(d, J= 8.8Hz, 2H), 7.39(m, 1H), 7.76(s, 1H), 8.02(d, J= 9.2Hz, 2H); IR (KBr): 3055, 2997, 2960, 2841, 1918, 1809, 1657, 1600, 1480, 1377, 1250, 1229, 971, 825, 780cm-1; ESI (APCI)-MS: m/z 312(M+1).
8d: Colorless oil; 1H NMR (400 MHz, CDCl3) 2.30(s, 3H), 3.44(s, 3H), 6.46(t, J=2.0Hz, 1H), 6.72(m, 2H), 7.09(m, 1H), 7.16(m, 3H), 7.31(m, 2H), 7.60(s, 1H); IR (KBr): 3061, 2995, 1715, 1657, 1596, 1485, 1433, 1391, 1290, 1159, 948, 794 cm-1; ESI (APCI)-MS: m/z 253(M+1). 8i: Light yellow solid; mp: 47-49 ºC; 1H NMR (400 MHz, CDCl3) 2.28(s, 3H), 3.74(s, 3H), 6.67(d, J= 8.8Hz, 2H), 6.97(d, J= 8.4Hz, 2H), 7.18(m,2H), 7.38(m,3H), 7.62(s, 1H); IR (KBr): 2927, 2835, 1650, 1599, 1509, 1355, 1308, 1255, 1169, 1032, 829, 700cm-1; ESI (APCI)-MS: m/z 253(M+1). 8j: Off white solid; mp: 109-111 ºC; 1H NMR (400 MHz, CDCl3) 2.31(s, 3H), 7.16(m, 4H), 7.41(m, 3H), 7.62(s, 1H), 7.99(d, J=8.8Hz, 2H); IR (KBr): 3112, 3058, 1673, 1661, 1590, 1517, 1350, 1230, 861, 703 cm-1; ESI (APCI)MS: m/z 268(M+1). 8k: Semisolid; 1H NMR (400 MHz, CDCl3) 2.26(s, 3H), 2.93(s, 6H)), 6.44(d, J=8.8Hz, 2H), 6.69(d, J=8.8Hz, 2H), 7.37(m, 3H), 7.62(s, 1H), 7.73(d, J=8.4Hz, 2H); IR (KBr): 2914, 2819, 2740, 1898, 1669, 1597, 1526, 1440, 1370, 1317, 1234, 1165, 1067, 1004, 944, 816, 726, 703 cm1 ; ESI (APCI)-MS: m/z 266(M+1). General Method of Preparation for Type B Compounds A mixture of cyclopropyl 2-fluorobenzyl ketone (500 mg, 1 equiv.), sodium methoxide (2 equiv.), and the appropriate aryl aldehyde (1.2 equiv.) in methanol (10 ml) was stirred at 60 ºC for overnight. Completion of the reaction was monitored by TLC (Hex: EtOAc : 19:1). Methanol was removed under vacuum, residue was dissolved in water and ethyl acetate mixture and neutralized by dilute HCl. Ethyl acetate layer was separated and dried over sodium sulfate. Ethyl acetate was removed under vacuum, and the crude compound obtained was purified by column chromatography using Hexane- Ethyl acetate (9:1) as eluent. In all cases, the RF values were ~ 0.5 in (95:5; hexanes-ethyl acetate).
9e: Off white solid; mp: 94-96 ºC; 1H NMR (400 MHz, CDCl3) 0.86(m, 2H), 1.16(m, 2H), 2.11( m, 1H), 3.57(s, 6H), 3.81(s, 3H), 6.37(s, 2H), 7.18( m, 3H), 7.35(m, 1H), 7.72(s, 1H); IR (KBr): 3074, 2996, 2941, 2835, 1955, 1698, 1649, 1578, 1507, 1460, 1247, 1225, 1130, 1007, 935, 833, 770cm-1 ; ESI (APCI)-MS: m/z 357(M+1). 9g: Colorless oil; 1H NMR: (400 MHz, CDCl3) 0.87(m, 2H), 1.15(m, 2H), 2.05(m, 1H), 7.00(d, J=8.4Hz, 2H), 7.137.18(m, 5H), 7.38(m, 1H), 7.72(s, 1H); IR (KBr): 3073, 2991, 2953, 2828, 1954, 1701, 1646, 1577, 1501, 1463, 1225, 1127, 1009, 934, 831, 775cm-1; ESI (APCI)-MS: m/z 301(M+1). 9h: Colorless oil; 1H NMR: (400 MHz, CDCl3) 0.85(m, 2H), 1.13(m, 2H), 2.09(m, 1H), 2.28(s, 3H), 6.99(m, 4H), 7.12(m, 3H), 7.36(m, 1H), 7.78(s, 1H); IR (KBr): 3077, 3001, 2943, 2835, 1961, 1692, 1645, 1589, 1506, 1459, 1259, 1230, 1003, 935, 829, 776cm-1; ESI (APCI)-MS: m/z 281( M+1). 9i: Off white solid; mp: 102-103 ºC; 1H NMR (400 MHz, CDCl3): 0.87(m, 2H), 1.17(m, 2H), 2.23(m, 1H), 3.53(s, 6H), 6.38(d, J= 8.4Hz, 2H), 6.88(m, 2H), 7.01(m,1H), 7.14(m, 2H), 7.76(s, 1H); IR (KBr): 3061, 3006, 2952, 2836, 1923, 1810, 1667, 1596, 1472, 1384, 1255, 1225, 1113, 967, 824, 775cm-1; ESI (APCI)-MS: m/z 327(M+1). 9i: Colorless oil; 1H NMR (400 MHz, CDCl3): 0.84(m, 2H), 1.13(m, 2H), 2.05(m, 1H), 5.91(s, 2H), 6.40(s, 1H), 6.67(d, J=8.4Hz, 1H), 6.77(d, J=8.0Hz, 1H), 7.14-7.21(m, 3H), 7.38(m, 1H), 7.71(s, 1H); IR (KBr): 3080, 2999, 2931, 2841, 1953, 1683, 1654, 1577, 1497, 1461, 1253, 1128, 999, 931, 772cm-1; ESI (APCI)-MS: m/z 311(M+1). CONCLUSION This paper reports a systematic study on the synthesis and biological evaluation of a range of , -unsaturated ketones as combretastatin analogs. The results show, first, for
,-Unsaturated Ketones as Analogs of Combretastatin-A4
good levels of cytotoxicity (i) a non-polar substituent in the meta-position of the Ar ring (in particular a non-polar) halogen or (ii) an electron-withdrawing group with some degree of steric bulk in the para-position of Ar ring is required. In addition, incorporation of a strained cyclopropyl moiety adjacent to the carbonyl functionality appeared to enhance these effects, including that of microtubule delpolymerization. We believe that the Type B compounds represent an alternate class of compounds to combretastatins worthy of further investigation. Likewise Type A compounds should also be further investigated since the compounds exert cytotoxicity through a mechanism different from Type B.
Letters in Drug Design & Discovery, 2009, Vol. 6, No. 7 [8]
[9]
ACKNOWLEDGEMENT The authors thank Conjura Pharmaceuticals, LLC for support.
[10]
REFERENCES AND NOTES [1]
[2]
[3]
[4]
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