Synthesis of a non-hydrolyzable dinucleoside analogue

Abstract A non-hydrolyzable dinucleoside analogue 31, which bears an internucleoside thioether linkage, was prepared from the branched-chain nucleoside precursors 26 and 28. Previous attempts to form the sulfide by the displacement of a 5′-mesyl group by thiol gave unsatisfactory results. In the course of preparing 28, it was found that the Vorbruggen coupling of 5-thiosugar 8 and persilylated base results in competing thiopyranone enol acetate formation.