Synthesis of a disaccharide fragment of rhamnogalacturonan II.

A disaccharide portion of the A-side chain of the rhamnogalacturonan II oligosaccharide has been prepared. Glycosylation of methyl (methyl 3,4-O-isopropylidene-alpha-D-galactopyranosid)uronate with p-tolyl 2,3-di-O-acetyl-3-C-(benzyloxymethyl)-1-thio-alpha/beta-D-erythrofuranoside was carried out using N-iodosuccinimide as promoter and silver trifluoromethanesulfonate as catalyst. Removal of the protecting groups gave the beta-d-Apif-(1-->2)-alpha-D-GalpA-OMe disaccharide.