Regioselectivity of enzymatic glycosylation of 6-O-acyl glycosides in supersaturated solutions

The regioselectivity of enzymatic transglycosylation of 6-O-acetyl glycosid es in supersaturated solutions was investigated using a range of commercial ly available enzymes, Escherichia coli, barley, and Kluyveromyces spp. beta -galactosidase, green coffee bean alpha-galactosidase, jack bean alpha-mann osidase, rice alpha-glucosidase, and almond beta-glucosidase. It has been s hown that 6-O-acetyl glycosides serve as good substrates for these enzymes, which, under the reaction conditions, are "forced" to transfer monosacchar ide units to the secondary hydroxyl groups of the accepters. in a variety o f transglycosylations studied the (1-3)-linked disaccharide products were t he predominant regioisomers isolated. The selectivity of the reaction varie d significantly depending on the acceptor glycosides and the enzyme used. E xquisite specificity was observed in some cases, but in others approximatel y equal quantities of two disaccharides products were isolated. In the best transfers the yield approached 30%. The methodology described offers a qui ck and facile route to disaccharides that may be difficult and/or time cons uming to make by conventional chemical synthesis. (C) 2000 John Wiley & Son s, Inc.