Acceptor hydroxyl group mapping for calf thymus α-(1 → 3)- galactosyltransferase and enzymatic synthesis of α-D-Galp-(1 → 3)-β-D- Galp-(1 → 4)-β D-GlcpNAc analogs

The epitope of the acceptor substrate for α-(1 → 3)- galactosyltransferase from calf thymus has been mapped by using a series of mono-deoxygenated and mono-O-alkylated Type II (β-D-Galp-(1 → 4)-β-D- GlcpNAc) disaccharides. The 4-OH group of the β-D-galactopyranosyl residue is a key polar group essential for glycosyl transfer, tolerating neither deoxygenation nor O-alkylation. Substitution at positions 6 and 6' by a variety of polar alkyl substituents was readily tolerated, allowing the preparative enzymatic synthesis of a series of trisaccharide derivatives carrying polar substituents on each of these hydroxyl groups. These new analogs are potential inhibitors of Clostridium difficile toxin A and of a human anti-α-Gal antibody.