Ligand recognition by E- and P-selectin: Chemoenzymatic synthesis and inhibitory activity of bivalent sialyl Lewis x derivatives and sialyl Lewis x carboxylic acids

Described is the preparation of five sLe(x) dimers and five sLe(x) carboxylic acids by coupling chemoenzymatically synthesized amino-substituted sialyl Lewis x (sLe(x)) derivative 4 to homobifunctional cross-linkers 20-24 of varying chain length. 20-24 were obtained by alkylating low-molecular-weight oligoethylene glycols with tert-butyl bromoacetate and subsequent transformation of the di-tert-butyl esters into disuccinimide esters. The products were assayed for inhibition against binding of a sLe(a)-polymer to immobilized E- and P-selectin. In the E-selectin assay all dimers had lower IC50 values than the sLex monomer. The results show that comparable binding enhancements can be obtained with linkers of completely different length and rigidity. In the P-selectin assay four of the five sLe(x) carboxylic acids displayed significantly improved inhibitory potency. The lowest IC50 value was observed for the compound with the shortest spacer between the sLex moiety and the additional carboxylate, being ca. 20-40 times more potent than unmodified sLex. These findings should be of importance for the design of new multivalent forms of sLe(x) as well as sLe(x) mimetics as high-affinity selectin ligands.