PREPARATION OF SOME (1->6)-LINKED DISACCHARIDES, AND THEIR DERIVATIVES SUITABLE FOR PROTEIN MODIFICATION

Article abstract of DOI:10.1016/S0008-6215(00)80793-4

Synthetic methods for the preparation of per-O-acetylated, (1->6)-linked disaccharides containing either a D-galactose or a D-glucose residue at the reducing end are desribed.In these methods, 1,2,3,4-tetra-O-acetyl-β-trityl-β-D-glucopyranose was first converted into 1,2,3,4-tetra-O-acetyl-β-glucopyranose (1) by rapid treatment with 90percent triflouroacetic acid, followed by rapid isolation designed to minimize O-acyl migration.Disaccharides were formed by glucosylation of 1 or 1,2:3,4-di-O-isopropylidene-D-galactopyranose with per-O-acetylglycosyl halides.Isopropylidene groups in the resulting disaccharide, if present, were removed, and the disaccharide was per-O-acetylated.Per-O-acylated β-Gal-(1->6)-Glc and β-GlcNAc-(1->6)-Gal, and a mixture of per-O-acetylated α-Gal-(1->6)-Gal and β-Gal-(1->6)-Gal (in the ratio 3:7) were thus obtained.The per-O-acetylated Gal-(1->6)-Gal disaccharides were converted, by a reaction sequence previously reported, into (2,2-dimethoxyethyl)aminocarbonylmethyl 1-thio-β-D-glycosides, wich could then be coupled to proteins via reductive alkylation.For the anomeric mixture of per-O-acetylated Gal-(1->6)-Gal, conversion into the corresponding 1-thioglycoside permitted resolution of the isomers by chromatography on silica gel.When disaccharides, as borate complexes, were chromatographed on a column of a strong, anion-exchange resin, all of the (1->6)-linked disaccharides of neutral sugars tested (including melibiose) were eluted later than analogous disaccharides having other linkages, and also later than any neutral monosaccharides.