Effect of the tetrazole cis-amide bond surrogate on the complexing abilityof some enkephalin analogues toward Cu(II) ions

A study of the effect of the tetrazole moiety, a cis-amide bond surrogate, on the Cu(II) coordinating properties of oligopeptides is reported. The ins ertion of the tetrazole moiety psi (CN4) into the peptide sequence of [Leu( 5)] enkephalin considerably changes the coordination ability of the ligand. Potentiometric and spectroscopic results indicate that if the tetrazole mo iety is in a suitable position in the peptide chain. i.e. if it follows the third residue, an unusual stable CuH-1L species involving 4N coordination is formed in the physiological pH region. The tetrazole psi (CN4) ring prov ides one of these nitrogens. The data indicate that Cu(II) ions are strongl y trapped inside a bent peptide backbone. However, the coordination mode in volving the tetrazole ring nitrogen does not prevent the hydrolysis process under strongly basic conditions. (C) 1999 Elsevier Science Inc. All rights reserved.