New approaches to stereocontrolled glycosylation.

Abstract

The conceptually simple process of linking carbohydrate units by glycosylation has proven to be one of the most difficult synthetic processes to control from a stereochemical perspective. In particular it is the stereocontrolled synthesis of 1,2-cis glycosyl linkages (e.g. α-glucosides, β-mannosides) which poses the most difficult challenge. The research presented in this thesis describes new ways in which stereocontrol in glycosylation reactions can be achieved. New methods of neighbouring group participation have been explored, utilising novel protecting groups at the 2-postion of a series of glycosyl donors.

In particular the use of glucosyl donors bearing a 2-O-(2-(2,4,6- trimethoxyphenyl)thio)ethyl protecting group at the 2-hydroxyl, have shown exceptional α-selectivity especially when a completely armed donor was used. Work within this thesis also describes the use of chiral Brønsted acid catalysts in stereoselective glycosylation reactions. However the yields and stereoselectivity obtained were not very encouraging.