Mechanisms for nucleophilic aliphatic substitution at glycosides

Much of carbohydrate chemistry and biochemistry is centered on bond forming and bond breaking reactions at the anomeric carbon of glycosides. No single mechanism adequately covers the scope of these reactions, because differences in sugar substituents, stereochemistry, leaving groups, nucleophiles, and catalysts can influence the mechanistic pathway taken. The influence of solvent is only now beginning to become apparent in greater detail. Several methods exist to probe the mechanisms of these reactions; they include a variety of kinetic studies, including isotope effects, and computational methods. It has been found that typical reactions will uniquely utilize a mechanism somewhere within a continuum between A(N)D(N) and D(N)+A(N) mechanisms. With knowledge of the factors that determine the mechanism, synthetic method development will be furthered and a deeper understanding of biological catalysis is likely to be gained. (c) 2006 Elsevier Ltd. All rights reserved.