Stereoselective synthesis of novel 1 '-substituted 2 '-deoxy-4-thionucleosides

Oxidation of 2'-deoxy-5-ethyl-4-thiouridine with sodium metaperiodate affor ded a separable mixture of (R)- and (S)-sulfoxides. These were converted, a fter protection as their tert-butyldimethylsilyl ethers, by reaction with L DA to the 1'-anion which was reacted with a number of electrophiles to furn ish a range of novel nucleoside analogues. Deprotection of the (R)-sulfoxid e of 2'-deoxy-5-ethyl-1'-methyl-4'-thiouridine with triethylamine-trihydrog en fluoride under very mild conditions gave the unprotected sulfoxide.