Oligosaccharides related to xyloglucan:: synthesis and X-ray crystal structure of methyl α-L-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-α-D-xylopyranoside and the synthesis of methyl α-L-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-β-D-xylopyranoside

Trisaccharides, methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-xylopyranoside and methyl alpha-L-fucopyranosyl-(1 -->2)-beta-D-galactopyranosyl-(1-->2)-beta-D-xylopyranoside, which are related to the side chain of xyloglucan have been synthesised. The P-galactopyranosyl linkage of each was constructed using silver trifluoromethanesulfonate-promoted glycosylations of 2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-galactopyranosyl chloride and the corresponding anomer of methyl 3,4-tri-O-benzyl-D-xylopyranoside. The resulting disaccharides were deacetylated and fucosylated using assisted halide reactions with tri-O-benzyl-alpha-L-fucopyranosyl bromide. Hydrogenolytic debenzylation of the resulting protected trisaccharides gave the methyl glycosides of the fucose-containing xyloglucan side chain. The structure of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-xylopyranoside as the monohydrate was confirmed by an X-ray crystallographic study. (C) 2000 Elsevier Science Ltd. All rights reserved.