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.