Stereocontrolled Synthesis of Nucleosides Based on Intramolecular Glycosylation Strategy.

A convenient method for the stereocontrolled synthesis of nucleosides has been developed utilizing intramolecular aglycon delivery system. An important feature is to use 1-thioglycosides as glycosyl donor substrates, which can be counted as stable glycosides during modification steps of the carbohydrate moieties as well as introduction step of the pyrimidine base, but, on the other hand, the 1-thioglycosides can work as powerful glycosyl donors when they are treated with an appropriate thiophilic reagent. The suitable activator was found to be Me2S(SMe)BF4. The synthetic applicability is demonstrated by the syntheses of pharmaceutically important deoxynucleosides exemplified as ddC, AZT, FLT, some base-modified nucleosides, isonucleosides, nucleoside antibiotics, and 4'-thionucleosides.