Show simple item record

dc.contributor.authorPark, Jin
dc.description.abstractA novel strategy for the stereoselective introduction of 1,2-cis-glycosides is described here. The new glycosylation approach is based on neighboring group participation of a (S)-(phenylthiomethyl)benzyl chiral auxiliary at the C-2 of a glycosyl donor which can form a quasi-stable anomeric sulfonium ion. The formation of trans-decalin is expected due to steric and electronic factors. Displacement of the equatorial anomeric sulfonium ion by glycosyl acceptors leads to the stereoselective formation of -glycosides. NMR experiments were employed to show convincingly the presence of the -linked sulfonium ion intermediate. This methodology has been applied to the synthesis of Galili trisaccharide, an epitope that can trigger acute rejections in xeno-transplantations. To explore the possibility of the remote participation of the chiral auxiliary, a series of 2-deoxy glycosyl donors containing a chiral auxiliary at C-6 were synthesized. This methodology proved to be very useful for the synthesis of 2-deoxy glycosides for -selective glycosylations. In situ formation of sulfonium ions by addition of thioethers to the reaction mixture was also investigated. We have observed that glycosylations of 2-azido-2-deoxy-glucosyl donors performed in the presence of a thioether such as PhSEt provide glycosides with excellent -selectivity. Traditional glycosylations with trichloroacetimidates give products within a short period of time. However, the addition of PhSEt led to a different reaction profile. The glycosylation products were formed over a period of several hours. Thus it is reasonable to assume that the intermediate sulfonium-ion had been formed. NMR and computational studies have indicated that steric factors determine the selective formation of the -anomeric sulfonium ion.
dc.subjectChiral auxiliary, Carbohydrate, Glycosylation, Sulfonium ion.
dc.titleChiral auxiliaries for 1,2-cis stereoselective glycosylations
dc.description.advisorGeert Jan Boons
dc.description.committeeGeert Jan Boons
dc.description.committeeRobert Phillips
dc.description.committeeGeorge Majetich

Files in this item


There are no files associated with this item.

This item appears in the following Collection(s)

Show simple item record