Mechanism of a Chemical Glycosylation Reaction

摘要

Glycosylation is arguably the most importantnreaction in the field of glycochemistry, yet itninvolves one of the most empirically interpretednmechanisms in the science of organic chemistry.nThe u0001-mannopyranosides, long considered one ofnthe more difficult classes of glycosidic bond to pre-npare, were no exception to this rule. A number ofnlogical but circuitous routes for their preparationnwere described in the literature, but they werenaccompanied by an even greater number of mostly ineffective recipes with which to access them directly.nThis situation changed in 1996 with the discovery of the 4,6-O-benzylidene acetal as a control element permitting directnentry into the u0001-mannopyranosides, typically with high yield and selectivity. The unexpected nature of this phenomenonndemanded study of the mechanism, leading first to the demonstration of the -mannopyranosyl triflates as reaction inter-nmediates and then to the development of -deuterium kinetic isotope effect methods to probe their transformation into thenproduct glycosides. In this Account, we assemble our observations into a comprehensive assessment consistent with a sin-ngle mechanistic scheme.