Sulfoxide Catalyzed Dehydrative Glycosylation. Reaction Development and Mechanistic Analysis
Boebel, Timothy A.
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https://hdl.handle.net/2142/84181
Description
Title
Sulfoxide Catalyzed Dehydrative Glycosylation. Reaction Development and Mechanistic Analysis
Author(s)
Boebel, Timothy A.
Issue Date
2005
Doctoral Committee Chair(s)
Gin, David Y.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Language
eng
Abstract
A sulfoxide-catalyzed dehydrative glycosylation for the coupling of carbohydrate hemiacetals and nucleophilic alcohols has been developed. In this procedure, a glycosyl hemiacetal is treated with the reagent combination of benzenesulfonic anhydride and a substoichiometric amount of n-butyl sulfoxide, followed by the addition of an appropriate nucleophilic acceptor to provide for the formation of new anomeric linkages. Mechanistic studies focused on the hemiacetal activation process show that this transformation proceeds through the intermediacy of a glycosyl sulfonate species, which serves as resting state prior to the addition of an external nucleophile and glycosidic bond formation. Successful determination of the proportion of 18O-incorporation in the glycosyl sulfonate as a function of its formation, via the technique of dynamic monitoring of 13C-16/18O isotopic chemical shift perturbations, provides strong evidence that hemiacetal activation proceeds through initial nucleophilic addition of the hemiacetal hydroxyl to the S(IV)-center of a putative sulfonium sulfonate intermediate. Further confirmation for this mechanistic pathway was obtained through the independent synthesis, structure verification, and 1H NMR detection of a glycosyl oxosulfonium species during the sulfoxide-catalyzed conversion of a glycosyl hemiacetal to a glycosyl sulfonate.
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