Enzymic .beta.-Galactosidation of Modified Monosaccharides: Study of the Enzyme Selectivity for the Acceptor and Its Application to the Synthesis of Disaccharides

The selectivity of the E. coli β-galactosidase-catalyzed glycosylation of monosaccharides differently substituted at the anomeric position has been studied. Subtituents bearing a phenyl ring increase the enzyme-acceptor binding; however, partial enzyme inhibition occurs. The regioselectivity of the glycosylation was dependent on small variations in the monosaccharide accceptor, such as the atom linked to the anomeric carbon and the number of methylenes between this atom and aromatic ring. A schematic model is proposed that accounts for the results. The information from this study allows the direct synthesis of disaccharides, with high regioselectivity and yields ranging from 30 to 40%