Synthesis of a dimeric Lewis antigen and the evaluation of the epitope specificity of antibodies elicited in mice.

The Lewis(y)-Lewis(x) heptasaccharide, modified by an artificial aminopropyl spacer, was synthesized by an approach that employed two orthogonally protected lactosamine building blocks. A p-(benzoyl)-benzyl glycoside was used as a novel anomeric protecting group, which could be selectively removed at a late stage in the synthesis, thus offering the benefit of enhanced flexibility. The artificial aminopropyl moiety was modified by a thioacetyl group, which allowed an efficient conjugation to keyhole limpet hemocyanin (KLH) that had been activated with electrophilic 3-(bromoacetamido)-propionyl groups. Mice were immunized with the Le(y)Le(x)-BrAc-KLH antigen. Analysis of the sera by ELISA established that a strong helper T-cell immune response was raised against the Le(y)Le(x) saccharide. Further ELISA analysis showed that the titer for monomeric Le(y) tetrasaccharide was tenfold lower whereas recognition of the Le(x) trisaccharide was negligible.