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 α-l-fucopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-α-d-xylopyranoside and methyl α-l-fucopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-β-d-xylopyranoside, which are related to the side chain of xyloglucan have been synthesised. The β-galactopyranosyl linkage of each was constructed using silver trifluoromethanesulfonate-promoted glycosylations of 2-O-acetyl-3,4,6-tri-O-benzyl-β-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-α-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 α-l-fucopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-α-d-xylopyranoside as the monohydrate was confirmed by an X-ray crystallographic study.