Synthesis of an apiose-containing disaccharide fragment of rhamnogalacturonan-II and some analogues

beta-Rhamnosylation of methyl 2-C-hydroxymethyl-2,3-O-isopropylidene-beta-D-erythrofuranoside and methyl 2,3-O-isopropylidene-beta-D-ribofuranoside was achieved using 4-O-acetyl-2,3-O-carbonyl-alpha-L-rhamnopyranosyl bromide and Ag2O as a promoter. Deprotected disaccharides beta-L-Rhap-(l --> 3')-beta-D-Apif-OMe and beta-L-Rhap-(l --> 3')-beta-D-Ribf-OMe were compared to their alpha-rhamnosyl isomers which were prepared using conventional Helferich glycosylation. (C) 2003 Elsevier Ltd. All rights reserved.