Synthesis of β-d-GlcpNAc-(1→3)-α-l-Rhap-(1→2)-[β-l-Xylp-(1→4)]-α-l-Rhap-(1→3)-α-l-Rhap, the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942 Original Research Article

An efficient synthesis of β-d-GlcpNAc-(1→3)-α-l-Rhap-(1→2)-[β-l-Xylp-(1→4)]-α-l-Rhap-(1→3)-α-l-Rhap, the repeating unit of the O-antigen produced by Pseudomonas solanacearum ICMP 7942 and its isomer β-d-GlcpNAc-(1→3)-α-l-Rhap-(1→4)-[β-l-Xylp-(1→2)]-α-l-Rhap-(1→3)-α-l-Rhap was achieved via sequential assembly of the building blocks, allyl 2,3-O-isopropylidene-α-l-rhamnopyranoside (2), allyl 3,4-O-isopropylidene-α-l-rhamnopyranoside (3), allyl 2,4-di-O-benzoyl-α-l-rhamnopyranoside (6), 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl trichloroacetimidate (7), and 2,3,4-tri-O-benzoyl-β-l-xylopyranosyl trichloroacetimidate (12). The process was carried out in a regio- and stereoselective manner using glycosyl trichloroacetimidates as donors and unprotected or partially protected rhamnopyranosides as acceptors in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf).