Synthesis of specifically monofluorinated ligands related to the O-polysaccharide of Shigella dysenteriae type 1.

The synthesis is reported of galactopyranose nucleophiles monofluorinated at positions 3, 4, or 6 and protected by 4,6-O-benzylidene, 3,6-di-O-benzyl, or 3,4-O-isopropylidene groups, respectively. The condensation of these nucleophiles with 2,3,4-tri-O-benzoyl-alpha-L-rhamnosyl bromide gave, after deprotection, the disaccharide analogues of methyl O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-D-galactopyranoside, monofluorinated at position 3, 4, or 6 of the galactoside residue.