A convenient synthesis of 5‐substituted‐7‐β‐D‐arabinofuranosylpyrrolo[2,3‐ d ]pyrimidines structurally related to the antibiotics toyocamycin and sangivamycin

4‐Amino‐7‐(2,3,5‐tri‐ O ‐benzyl‐β‐D‐arabinofuranosyl)pyrrolo[2,3‐ d ]pyrimidine‐5‐carbonitrile ( 6a ), prepared from 2‐ethoxymethyleneamino‐5‐bromopyrrole‐3,4‐dicarbonitrile ( 4 ), was debenzylated with boron trichloride to give ara ‐toyocamycin ( 6b ). Further functional group transformation of 6b provided a route to 4‐amino‐7‐β‐D‐arabinofuranosylpyrrolo[2,3‐ d ]pyrimidine‐5‐thiocarboxamide ( ara ‐thiosangivamycin, 7a ), and the corresponding 5‐carboxamidoxime 8a and 5‐carboxamidine 8b derivatives. Phosphorylation of unprotected 7a with phosphorus oxychloride gave ara ‐thiosangivamycin 5′‐monophosphate ( 7b ). 2′‐ O ‐Acetyl‐ ara ‐thiosangivamycin ( 10b ) was prepared as a prodrug by acetylation of 9a , followed by deprotection of the t ‐butyldimethylsilyl groups under acidic conditions without acyl migration.