Large cyclic peptides as cores of multivalent ligands: application to inhibitors of receptor binding by cholera toxin.

Large cyclic decapeptides (up to 50-atom ring) were synthesized efficiently on the solid phase with allyl-ester protection of the carboxyl terminus during elongation. Pentavalent ligands, in a "core-linker-finger" modular setup, were assembled by using these cyclic peptide cores to demonstrate large affinity gains for inhibition of surface receptor binding by the cholera toxin B pentamer. The results suggest that the peptide cores retain expanded conformation in solution so that shorter flexible linkers are needed for larger peptide cores to achieve the best inhibitory results.