I. Sulfonium-mediated oxidative glycosylation of glycal donors for the synthesis of C(2)-hydroxy-beta-glycosides. II. Hypervalent iodine (III)-mediated oxidative glycosylation of glycal donors for the synthesis of C(2)-acyloxy-beta-glycosides. III. Effort

Development of two novel glycosylation procedures, and the synthesis of immunologic adjuvant QS-21A_api is reported. In the first glycosylation procedure, glycals were employed as glycosyl donors and activated with a reagent combination of diphenyl sulfoxide and triflic anhydride. This sulfonium-mediated oxidative glycosylation procedure can be used for 1,2-trans-C2-hydroxy-β-glycoside synthesis with the application to assemble C2-branched oligosaccharides. In the second glycosylation procedure, glycals were activated with bisacyliodobenzene and boron trifluoride diethyl etherate for the synthesis of 1,2-trans -C2-acyloxy-β-glycoside with the application to assemble non-C2-branched oligosaccharides. In the third section of this thesis, an acylated triterpene glycoside QS-21A_api was targeted for synthesis using the two oxidative glycosylation procedures as well as a sulfonium-mediated dehydrative glycosylation procedure. Synthesis and extraction of the four components of the saponin, which includes a trisaccharide, a tetrasaccharide, a triterpene and an acyl side chain were accomplished leading to the assembly of these four components to provide the fully protected QS-21A_api.