The synthesis of galactopyranosyl derivatives with β-galactosidases of different origins

β-Galactosidases from four different sources were used to catalyze the transfer of β-d-galactopyranosyl from 4-nitrophenyl-β-d-galactopyranoside to a hydroxyl group of 2-acetamido-2-deoxy-galactopyranose in the synthesis of Galβ(1–3)GalNAc (1), Galβ(1–4)GalNAc (2) and Galβ(1–6)GalNAc (3), in triethyl phosphate buffered solutions (20–60%). When β-galactosidases from Penicillium multicolor and Aspergillus oryzae were used as the catalysts, the β(1–6)-linked disaccharide was produced as the major product. However, with β-galactosidase from Bifidobacterium bifidum, the major products were the β(1–4) and β(1–6)-linked disaccharides. On the other hand, with β-galactosidase from Streptococcus 6646K, β(1–3)-linked disaccharide was predominant together with β(1–4)-linked isomer. Galβ(1–3)GlcNAc (4), Galβ(1–4)GlcNAc (5) and Galβ(1–6)GlcNAc (6) were also synthesized with β-galactosidase from S. 6646K and B. bifidum with 2-acetamido-2-deoxy-glucopyranose as the acceptor and PNPGal as the donor. In both cases, the β(1–4)-linked disaccharide was predominantly produced. In addition, a comparative study was carried out to determine the regioselectivity of the transglycosylation reaction as well as the hydrolytic specificity toward the same linked disaccharides.