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

Trisaccharides, methyl alpha-L-fucopyranosyl-(1-->2)-beta-D-galactopyranosy l-(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-pro moted glycosylations of 2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-galactopyranos yl chloride and the corresponding anomer of methyl 3,4-tri-O-benzyl-D-xylop yranoside. The resulting disaccharides were deacetylated and fucosylated us ing assisted halide reactions with tri-O-benzyl-alpha-L-fucopyranosyl bromi de. 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-galactopyranos yl-(1-->2)-alpha-D-xylopyranoside as the monohydrate was confirmed by an X- ray crystallographic study. (C) 2000 Elsevier Science Ltd. All rights reser ved.