A Novel Glycosyl Donor with a Triisopropylsilyl Nonparticipating Group in Benzyl-Free Stereoselective 1,2- cis -Galactosylation

Abstract

A novel glycosyl donor with a triisopropylsilyl (TIPS) nonparticipating group at O-2 is introduced for use in 1,2- cis -galactosylation. Coupling the 2- O -TIPS-substituted thiogalactoside donor with a series of mono- and disaccharide glycosyl acceptors was found to lead exclusively to α-linked oligosaccharides. The observed exceptionally high α-selectivity was interpreted in terms of conformational changes in the glycosyl cation induced by the bulky 2- O -TIPS group.