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dc.contributor.authorPark, Jin
dc.date.accessioned2014-03-04T18:25:07Z
dc.date.available2014-03-04T18:25:07Z
dc.date.issued2009-12
dc.identifier.otherpark_jin_200912_phd
dc.identifier.urihttp://purl.galileo.usg.edu/uga_etd/park_jin_200912_phd
dc.identifier.urihttp://hdl.handle.net/10724/26117
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.languageeng
dc.publisheruga
dc.rightspublic
dc.subjectChiral auxiliary, Carbohydrate, Glycosylation, Sulfonium ion.
dc.titleChiral auxiliaries for 1,2-cis stereoselective glycosylations
dc.typeDissertation
dc.description.degreePhD
dc.description.departmentChemistry
dc.description.majorChemistry
dc.description.advisorGeert Jan Boons
dc.description.committeeGeert Jan Boons
dc.description.committeeRobert Phillips
dc.description.committeeGeorge Majetich


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