A CONVENIENT SYNTHESIS OF BETA-D-GALACTOSYL DISACCHARIDE DERIVATIVES USING THE BETA-D-GALACTOSIDASE FROM BACILLUS-CIRCULANS

Beta-D-Gal-(1 --> 4)-beta-D-GlcNAc-OC6H4NO2-p (p-nitrophenyl N-acetyl- beta-lactosaminide) and beta-D-Gal-(1 --> 6)-beta-D-GlcNAc-OC6H4NO2-p (p-nitrophenyl N-acetyl-beta-isolactosaminide) were regioselectively s ynthesized from lactose and p-nitrophenyl 2-acetamido-2-deoxy-glucopyr anoside, employing transglycosylation by the beta-D-galactosidase from Bacillus circulans and by controlling the concentration of organic so lvent in the reaction system. The (1 --> 4)-linked disaccharide was fo rmed exclusively when the concentration of organic solvent was high, w hereas the (1 --> 6)-linked isomer was produced with a low concentrati on. Further utilization of the transglycosylation by the enzyme led to the regioselective formation of beta-D-Gal-(1 --> 4)-D-GalNAc and bet a-D-Gal-(1 --> 4)-beta-D-GalNAc-OC6H4NO2-p. With the enzyme, beta-D-ga lactosyl transfer occurred preferentially at the O-4 position of GlcNA c and GalNAc, regardless of the configuration of the hydroxyl group.