Synthesis and biological activity of certain 6-substituted and 2,6-disubstituted 2'-deoxytubercidins prepared via the stereospecific sodium salt glycosylation procedure

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Abstract
A number of 6-substituted and 2,6-disubstituted pyrrolo[2,3-d]pyrimidine 2''-deoxyribonucleosides were prepared by the direct stereospecific sodium salt glycosylation procedure. Reaction of the sodium salt of 4-chloro-6-methyl-2(methylthio)pyrrolo[2,3-d]pyrimidine (6a) or 4,6-dichloro-2-(methylthio)pyrrolo[2,3-d]pyrimidine (6b) with 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-.alpha.-D-erythro-pentofuranose (9) provided the corresponding N7 2''-deoxy-.beta.-D-ribofuranosyl blocked derivatives (8a and 8c) which, on ammonolysis, gave 4-amino-6-methyl-2-(methylthio)-7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrimidine (11a) and 4-amino-6-chloro-2-(methylthio)-7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrimidine (11b), respectively. Dethiation of 11a and 11b afforded 6-methyl-2''-deoxytubercidin (10a) and 6-chloro-2''-deoxytubercidin (10b), respectively. Dehalogenation of 10b provided an alternate route to the reported 2''-deoxytubercidin (3a). Application of this glycosylation procedure to 4,6-dichloro and 4,6-dichloro-2-methyl derivatives of pyrrolo[2,3-d]pyrimidine (15a and 15b) gave the corresponding blocked 2''-deoxyribonucleosides (18a and 18b), which on ammonolysis furnished 10b and 4-amino-6-chloro-2-methyl-7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrimidine (17), respectively. This stereospecific attachment of the 2-deoxy-.beta.-D-ribofuranosyl moiety appears to be due to a Walden inversion at the C1 carbon by the anionic heterocyclic nitrogen. Controlled deacylation of 4-chloro-7-(2-deoxy-3,5-di-O-p-toluoyl-.beta.-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrimidine (20a) gave 4-chloro-7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrimidine (20b). Dehalogenation of 20b gave the 2''-deoxynebularin analogue 7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)-pyrrolo[2,3-d]pyrimidine (19), and reaction of 20b with thiourea gave 7-(2-deoxy-.beta.-D-erythro-pentofuranosyl)-pyrrolo[2,3-D]pyrimidine-4(3H)-thione (21). All of these compounds were tested in vitro against certain viruses and tumor cells. Only compounds 12a, 20b, and 21 showed significant activity against measles in vitro, and the activity is comparable to that of ribavirin. Although compounds 3a and 12b are slightly more active than ribavirin against HSV-2 in vitro, they are relatively more toxic to Vero cells. Compounds 3a and 20b exhibited moderate cytostatic activity against L1210 and P388 leukemia in vitro but are considerably less active than 2-chloro-2''-deoxyadenosine (1).

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