Selective defucosylation by mercaptolysis. A potential step in analyzing branched oligosaccharides

Abstract

A method of stepwise chemical degradation was elaborated on a μg quantity of 3- O-α- l-fucosyllactose. The key step, TiCl 4-catalysed dithioacetal formation from the permethylated N-4-nitrophenyl triosylamine (4) was accompanied by quantitative defucosylation. [ 14C]Acetylation of the dried mercaptalation mixture gave radiolabelled 3,5-di- O-[ 14C]acetyl-4- O-(2,3,4,6-tetra- O-methyl-β - d-galactopyranosyl)-2,6-di- O-methyl- d-glucose diethyl dithioacetal (7) and 5- O-[ 14C]acetyl-2,3,4-tri- O-methyl- l-fucose diethyl dithioacetal ( 8). The former was further degraded via the bis(sulfone), and thereby 2,3,4,6-tetra- O-methyl- d-galactose ( 13) was expelled. The monosaccharide branches, fucose and galactose, were identified as derivatives 8 and 13, respectively, by comparison with authentic samples. Isolation of microquantities of products was carried out by preparative TLC.