A Fundamentally New, Simple, Stereospecific Synthesis of Oligosaccharides Containing the β-Mannopyranosyl and β-Rhamnopyranosyl Linkage

Abstract

The important role of oligosaccharides in biological processes1 has been recognized for a long time. Consequently, synthetic oligosaccharides have become indispensable probes for the life sciences.2 Methods for the chemical synthesis of oligosaccharides are based on a two-step process: The first comprises activation of the anomeric center to generate a glycosyl donor, and the second is its transfer to a glycosyl acceptor. The stereochemical outcome of the reaction depends on complex stereoelectronic effects as well as the presence or absence of groups at O-2 in the glycosyl donor capable of neighboring group participation.3 Except for rare cases, when the coupling of a glycosyl donor and a glycosyl acceptor occurs as an almost entirely SN2 process,4 the reaction of the glycosyl donor involves the formation of the oxocarbenium ion (1). Thus, the nonstereospecificity of glycosylation is virtually inherent in the method.