Synthesis of 5-thio-L-fucose-containing disaccharides, as sequence-specific inhibitors, and 2'-fucosyllactose, as a substrate of alpha-L-fucosidases

Four 5-thio-L-fucose-containing disaccharides having alpha(1-->6), alpha(1-->3), alpha(1-->4)GlcNAc, and alpha(1-->2-Gal linkages (compounds 1-4, respectively) were synthesized as potential alpha-L-fucosidase inhibitors. The glycosylation reactions using 2,3,4-tri-O-acetyl-5-thio-L-fucopyranosyl trichloroacetimidate as a glycosyl donor and BF3 . OEt(2) as a catalyst gave mainly alpha-linked disaccharides. Only alpha(1-->2)-linked disaccharide 4 showed inhibitory activity (K-i = 0.21 mM) against Bacillus alpha-L-fucosidase which hydrolyzes the Fuc alpha(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 mu M) against bovine epididymis alpha-L-fucosidase.