Stereocontrolled synthesis of thiohydantoin spironucleosides from sugar spiroacetals

5-Epithiohydantocidin, N-alkyl and N-glycosylthiohydantoin spironucleosides are prepared from glycosylaminoesters and from furanoid and pyranoid methyl isothiocyanatoulosonates. The aminoesters and the isothiocyanates are obtained, in a stereocontrolled manner, from sugar spiroacetals through a high-yielding sequence involving ring opening with trimethyl azide, formation of an ester group, reduction of the azide, and, in the case of isothiocyanates, reaction with thiophosgene.