Use of human-milk fucosyltransferase in the chemoenzymic synthesis of analogues of the sialyl Lewis(a) and sialyl Lewis(x) tetrasaccharides modified at the C-2 position of the reducing unit.
Two series of trisaccharides, having the formulas alpha-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-GlcZ-OR and alpha-Neu5Ac-(2-->3)-beta-D-Gal-(1-->3)-beta-D-GlcZ-OR [R = (CH2)8CO2CH3] respectively, in which the 2-deoxy substituent Z is azido, amino, propionamido, or acetamido, were prepared by chemical synthesis. Both types of modified trisaccharides are acceptors for a fucosyltransferase preparation obtained from human milk. Preparative fucosylations using this enzyme provided analogues of the sialyl Lewis(x) and sialyl Lewis(a) tetrasaccharide structures, which have been proposed to be ligands for cell-adhesion molecules. These syntheses further demonstrate the utility of glycosyltransferases in the preparation of oligosaccharide analogues.