Stereochemical studies, oxygen chiral approach

Dinucleoside phosphorothioates are chiral analogues of phosphodiesters in which one of the nonbridging oxygens has been replaced by sulfur. These compounds are important research tools in stereochemical investigations, in mechanistic studies of various enzymatic reactions, and other biochemical stndies [210-212]. There have been only a few methods for the preparation of ribonncleoside phosphorothioates [213-216]. The H-phosphonate approach is the best method for the preparation of phosphorothioate diesters [217-219]. 

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