Synthesis of the α-d-GlcpA-(1→3)-α-l-Rhap-(1→2)-l-Rha trisaccharide isolated from the cell wall hydrolyzate of the green alga, Chlorella vulgaris Original Research Article

The title trisaccharide was synthesized from 6-O-acetyl-2,3,4-tri-O-benzyl-α-d-glucopyranosyl chloride (10), ethyl 2,4-di-O-benzyl-1-thio- (5) and benzyl 3,4-di-O-benzyl-α-l-rhamnopyranoside (9). The disaccharide 11 obtained from compounds 5 and 10 was used as the glycosyl donor to glycosylate the rhamnopyranoside derivative 9 having free OH-2 using the NIS–AgOTf-mediated glycosylation methodology. Zemplén deacetylation of the trisaccharide 12 resulted in the 6′′-OH derivative (13), which was selectively oxidized with CrO3 to the uronic acid derivative 14. The benzyl groups were removed by catalytic hydrogenolysis to furnish the target trisaccharide (1).