Synthesis of the Rhamnosyl Trisaccharide Repeating Unit To Mimic the Antigen Determinant of Pseudomonas syringae Lipopolysaccharide

Abstract

The trisaccharide 2,3,4-O-tribenzyl-α-l-rhamnosyl-(1→3)-4-O-acetyl-2-O-benzoyl-(1→2)-4-O-acetyl-3-O-benzoyl-α-l-rhamnosyl-1-(4-tolyl)thio-α-l-rhamnopyranoside was prepared from the thio-sugar 1-(4-tolyl)thio-α,β-l-rhamnopyranoside from the nonreducing end to the reducing end. The two acceptors possessing 2- and 3-OH groups for the construction of the trisaccharide were obtained from a 2,3-benzylidine-protected thio-sugar in a one-pot deprotection manner in a respective ratio of 1:2.5. As donors for glycosylation, the thio-sugars of both mono- and disaccharides were converted to trichloroacetimido rhamnosides. Through this chemoselective strategy, a trisaccharide was obtained that retained an anomeric thio group for coupling with ceramide moieties. Bioassays are in progress.