Synthesis of a C-Nucleoside Phosphonate by Base-Promoted Epimerization.

The efficient synthesis of a [2'S] C-nucleoside phosphonate and its corresponding prodrug has been realized. A phosphonomethoxy group was stereoselectively introduced at the anomeric 5'-carbon atom through glycosylation of a benzoyl protected [5'R]-acetoxy-[2'R]-9-deazaadenine. An unexpected epimerization at the 2'-position of the sugar moiety occurred upon removal of the protecting groups, but this was further exploited as a key reaction for improved synthesis of the target compound.