First synthesis of the 3'-sulfated Lewis(a) pentasaccharide, the most potent human E-selectin ligand so far.

Tri- and pentasaccharides of Lewis(a)-type, sulfated at position 3 of the outer galactose, have been prepared using the new 4-methoxybenzyl glycoside of N-acetylglucosamine 5 as starting material. The synthesis of the pentasaccharide 2 was achieved through a beta-stereoselective coupling of an alpha-trichloroacetimidate activated form of the N-acetamido protected trisaccharide 18 on to a 3',4'-unprotected lactose derivative.