Enzymatic synthesis of sulfated disaccharides using beta-D-galactosidase-catalyzed transglycosylation

We have established a unique enzymatic approach for obtaining sulfated disa ccharides using Bacillus circulans beta -D-galactosidase-catalyzed 6-sulfo galactosylation. When 4-methyl umbelliferyl 6-sulfo beta -D-galactopyranosi de (S6Gal beta -4MU) was used as a donor, the enzyme induced transfer of 6- sulfo galactosyl residue to GlcNAc acceptor. As a result, the desired compo und 6'-sulfo N-acetullactosamine (S6Gal beta1-4GlcNAc) and its positional i somer 6'-sulfo N'-acetylisolactosamine (S6Gal beta1-6GlcNAc) were observed by HPAEC-PAD, in 49% total yield based on the donor added, and in a molar r atio of 1:3.5. With a glucose acceptor, the regioselectivity was substantia lly changed and S6Gal beta1-2GIc was mainly produced along with beta-(1-1)a lpha, beta-(1-3), beta-(1-6) isomers in 74% total yield. When methyl alpha -D-glucopyranoside (Glc alpha -OMe) was an acceptor, the enzyme also formed mainly S6Gal beta1-2Glc alpha -OMe with its beta-(1-6)-linked isomer in 41 % total yield based on the donor added. In both cases, it led to the predom inant formation of beta-(1-2)-linked disaccharides. In contrast, with the c orresponding methyl beta -D-glucopyranoside (Glc beta -OMe) acceptor, S6GA beta1-3Glc beta -OMe and S6Gal beta1-6Glc beta -OMe were formed in a low to tal yield of 12%. These results indicate that the regioselectivity and effi ciency on the beta -D-galactosidase-mediated transfer reaction significantl y depend on the anomeric configuration in the glucosyl acceptors.