Synthesis of oligosaccharide derivatives related to those from sanqi, a Chinese herbal medicine from Panax notoginseng

Oligosaccharide derivatives from sanqi, a Chinese herbal medicine derived from Panax notoginseng, methyl beta-D-galactopyranosyl-(1-->3)-alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, diosgenyl beta-D-galactopyranosyl-(1-->3)-alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, and methyl beta-D-galactopyranosyl-(1-->3)-alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranosyl-(1-->4)-beta-D-galactopyranosyl-(1-->3)-alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, were synthesized under standard glycosylation conditions. An unexpected alpha-(1-->4) linkage was formed predominantly in the presence of neighboring participation group during regioselective synthesis of hexasaccharide via 3+3 strategy.