Nucleophilic substitutions aglycone carbon

In a different approach to the preparation of glycosides, the nucleophilic substitution takes place at the carbon atom of the aglycone rather than at the anomeric carbon (Scheme 4.53). In contrast to the methods discussed in Section 4.3, there is no scission of the glycosyl-oxygen bond in these reactions. Instead, the R-X bond is cleaved. 

All these instances show the possibility that gly-cosidases can be converted to glycosynthase by single substitution at the active site, which suppresses the hydrolysis activity of glycosidases. At the same time, however, the nucleophilic attack of aglycon at the acceptor site to the anomer carbon should be significantly promoted in these mutants. This molecular mechanism remains to be solved. 

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