Double Stereodifferentiation in Carbohydrate Coupling Reactions: The Mismatched Interaction of Donor and Acceptor as an Unprecedented Factor Governing the α/β Ratio of Glycoside Formation

Abstract

Two enantiomeric glycosyl donors 1 and 2 were coupled to the glycosyl acceptor 3 under the same conditions. The first case leads to a disaccharide with an α/β ratio of 2/1, the second to a ratio of 1/8.4. This and other experiments show that the stereochemical outcome of glycosylation can be strongly influenced by unfavorable interactions (the formation of matched and mismatched pairs) between glycosyl donor and acceptor.