Study on highly diastereoselective synthesis of

© 2000 Oxford University Press

Nucleic Acids Symposium Series No. 44

25-26

Study on2 highly diastereoselective synthesis of (27?)-2'deoxy[2'- H]guanosine Etsuko Kawashima, Yu-suke Terui, Yoshiharu Ishido and Kenzo Yokozeki1 School of Pharmacy, Tokyo University of Pharmacy and Life Science and ^minoScience Laboratories of Ajinomoto Co., Inc.

INTRODUCTION For the NMR spectroscopic conformational analysis of a sugar moiety in DNA,1 and for a solution of a mechanism of a drug,23 (2'R)- and/or (2'S)-2'2

deoxy[2'- HJribonucleosides extremely

important.

with

high

purity

are

(2'fl)-2'-Deoxy[2'- HJadenosine 2

and (2'f?)-2'-deoxy[2'- H]guanosine were very useful for the evidence of intrastrand C2' hydrogen abstraction in photoirradiation of 5-halouracilcontaining oligonucleotides2, and for elucidation of intrastrand 2'-p hydrogen abstraction of 5'-adjacent deoxyguanosine by deoxyuridin-5-yl in Z-form DNA3, respectively. The synthesis of highly diastereoselective (2'R >98% de)-2'-deoxy[2'-2Hjadenosine, -uridine, and -thymidine have already been achieved in our laboratory, however the diastereomer excess (% de) of

(2'fl)-2'-deoxy-/V2-isobutyiyl-3',5'-0-TIPDS-[21-2H]guanosine (3) was lower than that of other nucleosides. Therefore, we searched for a method to improve the stereoselectivity up to - 98 de % of 1. We now report syntheses of 1 by the organic chemical deuteration of 3, and by a biological transdeoxyribofuranosylation of 4. RESULTS AND DISCUSSION To develop an efficient synthesis of highly diastereoselective 1, studies on leaving groups at the 2' position of nucleosides, the effects of protecting groups for the 3' and 5' hydroxyl groups, reaction temperature effects on stereoselectivity, radical generation, and deuteration reagents as organic chemical methods were carried out. We have already reported that the best conditions for synthesis of (2'R >98 % de)-2'-deoxy-3',5'-0-TIPDS-[2'-2H]uridine, adenosine and -thymidine were achieved through the use of Bu3Sn H - Et3B system, of bromo group at the 2' position as the leaving group and of 3',5'-O-TIPDS protection as the deuteration substrate, and of a reaction temperature of -78°C. Even using these conditions for 2, however, a resulting diastereomer excess of 3 was 82 % de. On the other hand, we found that the reductive deuteration reaction of 2'-bromo-2'-deoxy-3',5'-OTIPDS-uridine

with

(Me,Si),Si2H-Et,B 3

3

in

2,2,5,5-

3

tetramethyltetrahydrofuran (TMTHF) gave (2'R 98% de^'-deoxy-S'.S'-O-TIPDS-p'^HJuridine in 89% yield at a diastereoselectivity rate >98% de at 0°C, and 87%

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ABSTRACT To develop an efficient method for the synthesis of a highly diastereoselective (2'fl)-2'-deoxy[2'HJguanosine (1), studies of organic chemical conversion from 21-bromo-2'-deoxy-V2-lsobutyryl3',5'-O-TIPDS-guanosine (2) to 1 and a biological transdeoxyribofuranosylation of {2'R >98 % de )-2'deoxy[2'-2H]uridine (4) were carried out. As the results, a highly diastereoselective synthesis of 1 was achieved by a biological transdeoxyribofuranosylation between 2,6-diaminopurine and 4 by the use of Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. The results will be described in detail.

26

Nucleic Acids Symposium Series No. 44

Bu3Sn2H-EtaB iBu

THF .7

>Si 3 (2'-fl)

91

:

9

biological transdeoxyrlboturanosylatlon

(2'-S)

iBu TMTHF TMTHF =tetramethyl-THF

59% >98% de.

Sheme 1

Scheme 2

point upon donating the deuterium atom from (Me3Si)3Si2H to the 2'-yl radical, resulting from the reaction of the 2'-bromonucIeoside derivative with a tris(trimethylsilyl)silyl radical, in the transition state of the former case is likely to be in somewhat closer proximity to the radical than that of the latter case. Therefore, it might be expected that reductive deuteration reactions, using (Me.Si),Si2H, would reflect 3

3

the steric effect, and yield higher diastereoselectivity in 2

comparison with those using Bu3Sn H. Based on this expectation, reductive deuteration reaction of 2 using the

(Me3Si)3Si2H-Et3B

system

was

performed.

8

Consequently,

2'-deoxy/V -isobutyryl-3',5'-0-TIPDS-

guanosine, which introduced the hydrogen atom at the 2' position of 3, was unexpectedly gave in 59% yield, in addition to 3, even at -78°C. Incidentally, transglycosylation reaction synthesizing 9-/3 -D-arabinofuranosyladenine between adenine and 1 - /? -D-arabinofuranosyluracil was found by Utagawa et al., 6 and 2'-deoxyadenosine and 2'-deoxyguanosine were synthesized by the application of this system by Yokozeki

et al.7 This

successfully

to the

deoxyribofuranosylation

procedure

synthesis between

was

extended

of 1. The trans2,6-diaminopurine

and 4 by Enterobacter aerogenes AJ-11125 (as wet paste)

gave

((2f?)-2-deoxy[2-2Hjribofuranosyl)-2,6-

diaminopurine (5). The resulting 5 is a substrate for deamination by adenosine deaminase, and conversion of 5 to 1 proceeds. After protection of the 3' and 5' OH groups of 1 with acetyl groups, 3',5'-di-O-Ac-2'deoxy[2'-2H]guanosine was purified by silica gel column chromatography in a 43% overall yield from 4 and >98% de., which is the same as that of 4. ACKNOWLEDGMENT This work was supported by the Grant-in-Aid for Scientific Research (C) (No11672117) and Hayashi Memorial Foundation for Female Natural Scientists. REFERENCE 1. Kojima, C; Kyogoku, Y.; Ishido, Y.: Kawashima, E.; Sekine, T.; Kainosho, M.; Nucleic Acids Symp. Series., 1993, No 29 , 185-186. 2 Sugiyama, H.; Fujimoto, K.; Saito, I.; Kawashima, E.; Sekine, T.; Ishido, Y. Tetrahedron Lett., 1996,37. 1805-1808. 3. Kawai, K.; Saito, I.; Kawashima, E.; Ishido, Y.; Sugiyama. H. Tetrahedron Lett. 1999, 40, 2589-2592. 4. Kawashima, E.; Aoyama, Y.; Sekine, T.; Miyahara, M.; Radwan, M. F.; Nakamura, E.; Kainosho, M.; Kyogoku, Y.; Ishido, Y. J. Org. Chem., 1995, 60, 69806986. 5 Kawashima, E.; Uchida, S.; Miyahara, M.; Ishido, Y. Tetrahedron Lett., 1997, 38. 7369-7372. 6. Utagawa. T.; Morisawa. H.; Miyoshi, T.; Yoshinaga, F.; Yamazaki, A.; Mitsugi.K, FEBSLett., 1980,709. 261. 7. Yokozeki. K.; Tsuji, T.; J. Mol. Catalysis B: Enzymatic 2000, in press.

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yield at >98 % de at room temperature. The donating deuterium atom attached to the silicon atom of (MegSi^SpH is rather sterically hindered by the three trimethylsilyl groups, as compared to that attached to the tin atom of Bu3Sn2H. Alternatively, the releasing