Regiospecific synthesis of lactose analog Gal-(β 1,4)-Xyl by transgalactosylation

Abstract

A short enzymatic synthesis of disaccharide 4-O-β-D-galactopyranosyl-D-xylose (1) has been developed, which is of interest as a lactose analog for a non-invasive medicinal determination of lactose intolerance. The starting material, benzyl α-D-xyloside, was obtained by a Fischer-type glycosidation of D-xylose with benzyl alcohol, followed by anomeric differentiation of mixed glycosides using a glycosidase from Aspergillus oryzae. From several commercial β-galactosidases, which were screened for their transgalactosylation capacity, the enzyme from Escherichia coli was found to catalyze a virtually regio- and stereospecific galactosyl transfer from donor compounds o-nitrophenyl β-D-galactoside or lactose to the α-D-xyloside. Subsequent hydrogenolytic deprotection furnished desired disaccharide 1.Key words: oligosaccharide synthesis, β-galactosidase, lactose intolerance.