Affinity of 5-thio- -fucose-containing lewis X (LeX) trisaccharide analogs to anti-LeX monoclonal antibody

5-Thiofucose-containing LeX trisaccharide analogs Galβ(1,4){5SFucα(1,3)}GlcNAc-OMe (2) and Galβ(1,4){5SFucβ(1,3)}GlcNAc-OMe (4) were synthesized via 5-thiofucosylation of methyl 2-azidolactoside derivative 6 by the trichloroacetimidate method. Inhibitory activity of these analogs for the binding of LeX to anti-LeX antibody was evaluated by enzyme immunoassay, indicating that anti-LeX strictly recognizes α-configuration of the fucose moiety and its binding pocket includes no advantageous region, such as hydrophobic area, for recognizing the ring sulfur atom of 5-thiofucosyl LeX analog 2.