Oligosaccharides related to xyloglucan: synthesis and X-ray crystal structure of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-x ylopyranoside and the synthesis of methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-beta-D-xy lopyranoside

Trisaccharides, methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-alpha-D-xy lopyranoside and methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosyl-(1-->2)-beta-D-xyl opyranoside, which are related to the side chain of xyloglucan have been synthesised. The beta-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-xy lopyranoside as the monohydrate was confirmed by an X-ray crystallographic study.