Efficient synthesis of a heptasaccharide, the repeating unit of the O-chain lipopolysaccharide produced by Xanthomonas campestris strain 642 Original Research Article

α-l-Rhap-(1→3)-α-l-Rhap-(1→2)-α-l-Rhap-(1→3)-[β-d-Xylp-(1→2)-][β-d-Xylp-(1→4)-]α-l-Rhap-(1→3)-α-l-Rhap, the repeating unit of the O-chain lipopolysaccharide produced by Xanthomonas campestris strain 642 was synthesized as its methyl glycoside via 3-O-selective glycosylation of methyl α-l-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-l-rhamnopyranoside (9) with 2,3,4-tri-O-benzoyl-α-l-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl-(1→2)-3,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (8), followed by dixylosylation with 2,3,4-tri-O-benzoyl-α,β-d-xylopyranosyl trichloroacetimidate (12) and subsequent deacylation.