Enzymatic synthesis of glycosyl cyclic tetrasaccharide with 6-α-glucosyltransferase and 3-α-isomaltosyltransferase

Transglycosylation reactions to cyclic tetrasaccharide (CTS, cyclo{→6)-α- D-Glc p-(1→3)-α- D-Glc p-(1→6)-α- D-Glc p-(1→3)-α- D-Glc p-(1→}) and its derivatives were investigated. An enzyme, 6-α-glucosyltransferase, which is involved in CTS synthesis from starch, from Bacillus globisporus C11 produced 4- O-α-glucosyl-CTS (4G-CTS) from a mixture containing CTS and maltopentaose. Another enzyme, 3-α-isomaltosyltransferase, synthesized 3- O-α-isomaltosyl-CTS (3IM-CTS) from CTS and panose. Two novel branched CTSs, 3- O-α-isomaltosyl-4- O-α-glucosyl-CTS (3IM-4G-CTS) and 3- O-α-isomaltosyl-(4- O-α-glucosyl)-CTS [3IM-(4G)-CTS], were synthesized by the isomaltosyl transfer of IMT into 4G-CTS. IMT also produced a novel saccharide, 3- O-α-isomaltosyl-3- O-α-isomaltosyl-CTS (3IM-3IM-CTS) from 3IM-CTS. It was confirmed that the oligosaccharides, including 4G-CTS, 3IM-CTS, 3IM-4G-CTS, 3IM-(4G)-CTS and 3IM-3IM-CTS, remaining in the reaction mixture during the production of CTS from starch were the transfer products of 6GT and IMT into CTS.