Systematic synthesis of sulfated sialyl-alpha-(2 --> 3)-neolactotetraose derivatives and their acceptor specificity for an alpha-(1 --> 3)-fucosyltransferase (Fuc-TVII) involved in the biosynthesis of L-selectin ligand

Sulfated sialyl-alpha-(2 --> 3)-neolactotetraose (IV3NeuAcnLcOse4) derivatives at C-6 of GlcNAc (6-O-sulfo), terminal Gal (6'-O-sulfo), and both GlcNAc and Gal (6,6'-di-O-sulfo) residues have systematically been synthesized. (Methyl 5-acetamido-4,7,8,9- tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosy lonate)-(2 --> 3)-2,4-di-O-benzoyl-6-O-levulinoyl-D-galactopyranosyl trichloroacetimidate was coupled with 2-(trimethylsilyl)ethyl (2-acetamido-2-deoxy- 3-O-benzyl-6-O-p-methoxyphenyl-beta-D-glucopyranosyl)-(1 --> 3)-(2,4,6-tri-O-benzyl-beta-D-galactopyranosyl)-(1 --> 4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside to give the suitably protected pentasaccharide which, upon selective removal of the p-methoxyphenyl and/or levulinoyl groups at C-6 of the GlcNAc and the terminal Gal residues, successive O-sulfation(s) and deprotection, afforded the desired three sulfated IV3NeuAcnLcOse4 derivatives. Acceptor specificity of the synthetic IV3NeuAcnLcOse4 probes for a human alpha-(1 --> 3)-fucosyltransferase (Fuc-TVII) was examined to study the biosynthetic pathway of L-selectin ligand. Only the 6-sulfated derivative at C-6 of GlcNAc was recognized by Fuc-TVII to give 6-O-sulfo sialyl LeX.