2,4‐Disubstituted Pyrrolo[2,3‐ d ]pyrimidine α‐ D ‐ and β‐ D ‐Ribofuranosides Related to 7‐Deazaguanosine

Nucleobase‐anion glycosylation (KOH, tris[2‐(2‐methoxyethoxy)ethyl]amine (TDA‐1), MeCN) of the pyrrolo[2,3‐ d ]pyrimidines 4a – d with 5‐ O ‐[(1,1‐dimethylethyl)dimethylsilyl]‐2,3‐ O ‐(1‐methylethylidene)‐α‐ D ‐ribo‐furanosyl chloride ( 5 ) gave the protected β‐ D ‐nucleosides 6a – d stereoselectively ( Scheme 1 ). Contrary, the β‐ D ‐halogenose 8 yielded the corresponding α‐ D ‐nucleosides ( 9a and 9b ) apart from minor amounts of the β‐ D ‐anomers. The deprotected nucleosides 10a and 11a were converted into 4‐substituted 2‐aminopyrrolo[2,3‐ d ]‐pyrimidine β‐ D ‐ribofuranosides 1 . 10c , 12 , 14 , and 16 and into their α‐ D ‐anomers, respectively ( Scheme 2 ). From the reaction of 4b with 5 , the glycosylation product 7 was isolated, containing two nucleobase moieties.