DOUBLE STEREODIFFERENTIATION IN CARBOHYDRATE COUPLING REACTIONS - THE MISMATCHED INTERACTION OF DONOR AND ACCEPTOR AS AN UNPRECEDENTED FACTOR GOVERNING THE ALPHA/BETA-RATIO OF GLYCOSIDE FORMATION

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 alpha/beta ratio of 2/1, the second to a ratio of 1/8.4. This and other experiments shown 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.