Synthesis of the unique trisaccharide repeating unit, isolated from lipopolysaccharides Rhizobium leguminosarum bv. trifolii 24, and its analogue

The synthesis of trisaccharide: 6-d-α-l-Talp(1→2)-α-l-Rhap(1→5)-DHA, and its analogue: 6-d-α-l-Talp(1→2)-β-l-Rhaf(1→5)DHA is described. In the first step a disaccharide, composed of 6-d-l-Talp and l-Rhap was obtained. This, in turn, was converted to the corresponding 1-trichloroacetimidate and coupled with DHA alcohol to afford the required trisaccharide. Its analogue was achieved by the conversion of the above disaccharide to the glycosyl bromide, involving the rhamnopyranose ring scission, followed by condensation with DHA in Koenigs-Knorr procedure.