Synthesis of p-trifluoroacetamidophenyl (4,6-dideoxy-4-formamido-3-C-methyl-2-O-methyl-α-l-mannopyranosyl)-(1→3)-(2-O-methyl-α-d-rhamnopyranosyl)-(1→3)-(2-O-methyl-α-l-fucopyranosyl)-(1→3)-(α-l-rhamnopyranosyl)-(1→2)-6-deoxy-α-l-talopyranoside: a spacer-a

Syntheses of p-trifluoroacetamidophenyl glycosides of the haptenic pentasaccharide and the nonreducing disaccharide unit of the title pentasaccharide are reported. The synthesis of the terminal N-formylkansosamine unit started from methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexopyran-4-uloside which, after C-3 methylation, was transformed into a glycosyl donor [3-O-benzyl-4-N-benzylformamido-4,6-dideoxy-3-C-methyl-2-O-methyl-α,β-l-mannopyranosyl trichloroacetimidate (20), and used for the synthesis of p-trifluoroacetamidophenyl (4-formamido-4,6-dideoxy-3-C-methyl-2-O-methyl-α-l-mannopyranosyl)-(1→3)-6-deoxy-2-O-methyl-α-d-mannopyranoside (29). Ethyl (3-O-benzyl-4-N-benzylformamido-4,6-dideoxy-3-C-methyl-2-O-methyl-α-l-mannopyranosyl)-(1→3)-4-O-benzyl-6-deoxy-2-O-methyl-l-thio-α-d-mannopyranoside (31), prepared by glycosylation of ethyl 4-O-benzyl-6-deoxy-2-O-methyl-1-thio-α-d-mannopyranoside with 20, served as glycosyl donor in a 2+3 block synthesis of the title pentasaccharide.