A simple strategy for changing the regioselectivity of glycosidase-catalysed formation of disaccharides.

The regioselectivity of glycosidase-catalysed formation of disaccharides can be changed by using alpha- or beta-glycosyl acceptors with various aglycons. The preponderant formation of other than (1----6) linkages can be effected with glycosidases which normally give (1----6) linkages. Thus, an alpha-D-galactosidase can be induced to catalyse the formation mainly of alpha-(1----2)-, alpha-(1----3), or alpha-(1----6)-linked digalactosides. Both the structure of the aglycon and the configuration of the glycosidic linkage can have a pronounced influence on the regioselectivity of disaccharide formation. Enzymic syntheses, in yields of 20-30%, are described of alpha-D-Galp-(1----3)-alpha-D-Galp-OMe, beta-D-Galp-(1----3)-beta-D-Galp-OMe, beta-D-Galp-(1----6)-alpha-D-Galp-OMe, alpha-D-Manp-(1----2)-alpha-D-Manp-OMe, alpha-D-Manp-(1----6)-alpha-D-Manp-OMe, alpha-D-Galp-(1----2)-alpha-D-Galp-OPhNO2-o, alpha-D-Galp-(1----3)-alpha-D-Galp-OPhNO2-p, alpha-D-Manp-(1----2)-alpha-D-Manp-OPhNO2-p, and alpha-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-OMe. Soluble and immobilised enzymes have been used.