Stereospecific Synthesis of A-Anomeric Pyrimidine Nucleoside

Stereospecific synthesis of a-anomeric pyrimidine nucleoside

Kazuo Shinozuka, Noritake Matsumoto, Akiko Nakamura, Hidekazu Hayashi and Hiroaki Sawai Faculty of Engineering, Gunma University, 1-5-1 Tenjincho, Kiryu, Gunma 376-8515, Japan Downloaded from https://academic.oup.com/nass/article/44/1/21/1019127 by guest on 01 October 2021

ABSTRACT INTRODUCTION A facile stereospecific synthetic method Oligodeoxynucleotide consisted of exclusively a- for a-anomeric 2'-deoxypyrimidine anomeric pyrimidine nucleotide units has several nucleoside unit utilizing aminooxazoline interesting features such as parallel annealing with derivative of ribofuranose was its complementary DNA or RNA,1 high nuclease investigated. Thus, easily accessible resistant property,2 and both of paralell and riboaminooxazoline derivative prepared by antiparalell annealing with double stranded DNA to ribose and cyanamid was allowed to react form triple helix.3 The reports of stereospecific with ethyl a-bromoethylacrylate to give preparation of a-anomeric 2'-deoxynucleoside corresponding adduct. The adduct was have been, however, very limited in literature. cyclized by strong base such as potassium Previously we have made a preliminary report *-butokiside. The resulted 2,2'- about facile stereospecific preparation of a- cyclonucleoside was then treated with anomeric thymidine utilizing riboaminooxazoline acetyl bromide followed by n-butyltin derivative.4 Here, we wish to present the results of hydride to give a-anomeric 3',5'-di-0- our farther investigation of the above method to acetylthymidine. 3',5'-Di-0-acety groups prepare a-anomeric 2'-deoxypyrimidine of the nucleoside were easily removed by nucleosides. the action of excess of triethyl amine in methanol. Essentially same procedure afforded corresponding 2'-deoxyuridine, which was further, converted to a- anomeric 2'-deoxycytidine.

COOEt HO. -C 2 CH2Br OH DMAc

NH2

AcO. AcO

AcBr V-^\ Bu3SnH, AIBN OAc CH3CN °y\ Benzene fi Scheme 1 22 Nucleic Acids Symposium Series No. 44

RESULTS AND DISCUSSION REFERENCES The starting material, 2-amino-a-D- 1. Sun, J. S., Asseline, U., Rouzaud, D., ribofurano[r,2':4,5]-2-oxazoline (l),s was Montenay-Garestier, T., Asseline, U., Saison- prepared form unprotected D-ribose and cyanamide Behmoaras, T., Thuong, N. T., and Helene. quantitatively. The oxazoline was then reacted with (1987) Nucleic Acids Res., 15, 6149. ethyl-a-(bromomethyl)acrylate (2) which was 2. Cazenave, C., Chevrier, M., Thuong. N. T., synthesized from ethyl acrylate and formaldehyde and Helene, C. (1987) Nucleic Acids Res., 15, followed by brominarion with hydrogen bromide.6 10507. The reaction afforded the adduct, l-(2- 3. (a) Praseuth, D., Perrouault, L., Le Doan, T., carboethoxyallyl)-a-ribofurano[r ,2':4,5]-2- Chassingnol, M, Thuong, N. T., and Helene, oxazolinium bromide (3), also almost C. (1988) Proc. Nad. Acad. Sci. USA, 85, Downloaded from https://academic.oup.com/nass/article/44/1/21/1019127 by guest on 01 October 2021 quantitatively. We found that the following 1349. (b) Sun, J. S., Giovannangeli, C, cyclization reaction of (3) requires strong alkali Francois, J. C, Kurfurst, R., Montenay- such as potassium f-butoxide. Using sodium Garestier, T., Asseline, U., Saison- methoxide in stead of potassium f-butoxide was not Behmoaras, T., Thuong, N. T., and Helene, effective in this case. Thus, the cyclization of (3) C, (1991) Proc. Nad. Acad. Sci. USA., 88, with 2.2 eq. of potassium f-butoxide followed by 6023. silica gel chromatography gave 34 % of 2,2'- 4. Sawai, H., Nakamura, A., Hayashi, H. and cyclonucleoside (4) along with 20 % of a- Shinozuka, K. (1994) Nucleosides & ribothymidine (5). The later compound may arise Nucleotides, 13, 1647. from the hydrolysis of compound (4) during the 5. Shannahoff, D. H. and Sanchez, R. A. (1973) work up. Reducing the amount of potassium t- J.Org.Chem., 38,593. butoxide was found to be effective to suppress this 6. Williers, J. W. and Rambaud, H. (1987) Org. undesirable side reaction. Thus, the use of 1.1 eq. Syn., 66, 220. of potassium J-butoxide and immediate quenching 7. Ogilivie, K. K., Schifman, A. L., and Penny, of the reaction by the addition of acid such acetic C. L. (1979) Can. J. Chem., 57, 2230. acid (10 eq. to potassium ?-butoxide used) after the completion of the cyclization gave 54.5 % of compound (4) and 3.8 % of (5) after purification. Using stronger acid, however, than acetic acid, such as chloroacetic acid, was also found to promote the hydrolysis even when it was used in relatively small amount (1.5 eq. to the butoxide). The obtained 2,2'-cyclonucleoside was then treated with acetyl bromide followed by rc-tributyltin hydride to give cc-anomeric 3',5'-di-O- acetylthymidine (7). The acetyl protecting groups of (7) were easily removed by the prolonged treatment of the nucleoside with excess of triethyl amine in dry methanol at room temperature. This gives a-anomeric thymidine (8) almost quantitatively. Substitution of the acrylate for methyl propiolate in the above procedure followed by acetylbromide treatment and subsequent reduction by n-tributyltin hydride gave a-anomeric 3',5'-di-C>-acety-2'- deoxyuridine. This nucleoside was converted to the corresponding 4-triazolyl derivative by the action of phosphoryloxychloride and triazole.7 Treatment of the sugar protected a-anomeric 2'-deoxyuridine with ammonium hydroxide in dioxane at room temperature gave a-anomeric 2'-deoxycytidine in good yield.