SELECTIVE DEFUCOSYLATION BY MERCAPTOLYSIS - A POTENTIAL STEP IN ANALYZING BRANCHED OLIGOSACCHARIDES

A method of stepwise chemical degradation was elaborated on a mu g quantity of 3-O-alpha-L-fucosyllactose. The key step, TiCl4-catalysed dithioacetal formation from the permethylated N-4-nitrophenyl triosylamine (4) was accompanied by quantitative defucosylation. [C-14]Acetylation of the dried mercaptalation mixture gave radiolabelled 3,5-di-O-[C-14]acetyl-4-O-(2,3,4,6-tetra-O-methyl-beta-D-galactopyranosyl)-2,6-diO-methyl-D-glucose diethyl dithioacetal (7) and 5-O-[C-14]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.