Synthesis of a Gal-β-(1→4)-Gal disaccharide as a ligand for the fimbrial adhesin UcaD

Abstract

The disaccharide Gal-β-(1→4)-Gal was recently identified as a ligand for the adhesin UcaD, a fimbrial protein used by Proteus mirabilis to adhere to exfoliated uroepithelial cells and colonise the urinary tract. To facilitate further studies, Gal-β-(1→4)-Gal was synthesised as the α-methyl glycoside via glycosylation of methyl 2,3,6-tri-O-benzoyl-α-d-galactopyranoside with 2,3,4,6-tetra-O-acetyl-d-galactopyranosyl trichloroacetimidate, followed by deprotection. The disaccharide was fully characterised by NMR spectroscopy. Earlier attempts to use a thiogalactoside as the glycosyl acceptor were hindered by intermolecular aglycone transfer side reactions.