Stereocontrolled synthesis of nucleosides based on intramolecular glycosylation strategy

A convenient method for the stereocontrolled synthesis of nucleosides has b een developed utilizing intramolecular aglycon delivery system. An importan t feature is to use 1-thioglycosides as glycosyl donor substrates, which ca n be counted as stable glycosides during modification steps of the carbohyd rate moieties as well as introduction step of the pyrimidine base, but, on the other hand, the 1-thioglycosides can work as powerful glycosyl donors w hen they are treated with an appropriate thiophilic reagent. The suitable a ctivator was found to be Me2S(SMe)BF4. The synthetic applicability is demon strated by the syntheses of pharmaceutically important deoxynucleosides exe mplified as ddC, AZT, FLT, some base-modified nucleosides, isonucleosides, nucleoside antibiotics, and 4 ' -thionucleosides.