DESIGN, SYNTHESIS, AND SUPRAMOLECULAR PROPERTIES OF BIS-CROWN ETHER MODIFIED PEPTIDES

The synthesis of peptides bearing two benzo-18-crown-6 side chains at different positions Is reported, These peptides were designed to under go specific ligand induced conformational changes using the cooperativ e complexation of difunctional guests in between the two crown moietie s. Binding studies show that the peptides indeed complex selectively C s+ and linear alpha,omega-diammonium alkanes using the simultaneous ac tion of the two distant crown ethers. The complexation of Cs+ resulted in a specific conformational change in the backbone of peptide 2, the best Cs+ binder, that switches from a beta-sheet to a beta-turn struc ture, However, peptides 1 and 3 did not change conformation upon compl exing Cs+ since they have their binding side chains already preorganiz ed for complexation.