Synthesis of 5-Thio- l -fucose-Containing Disaccharides, as Sequence-Specific Inhibitors, and 2‘-Fucosyllactose, as a Substrate of α- l -Fucosidases

Four 5-thio- l -fucose-containing disaccharides having α(1→6), α(1→3), α(1→4)GlcNAc, and α(1→2)Gal linkages (compounds 1 − 4, respectively) were synthesized as potential α- l -fucosidase inhibitors. The glycosylation reactions using 2,3,4-tri- O -acetyl-5-thio- l -fucopyranosyl trichloroacetimidate as a glycosyl donor and BF 3 ·OEt 2 as a catalyst gave mainly α-linked disaccharides. Only α(1→2)-linked disaccharide 4 showed inhibitory activity ( K i = 0.21 mM) against Bacillus α- l -fucosidase which hydrolyzes the Fucα(1→2) linkage specifically. The results suggested that sequence specificity of an enzyme could be estimated from the inhibitory activities of the compounds 1 − 4 . In contrast, every disaccharide showed inhibitory activity ( K i = 30−91 μM) against bovine epididymis α- l -fucosidase.