A study of the comparative donor properties to CuII of the terminal amino and imidazole nitrogens in peptides

Abstract

The synthesis of the tetrapeptides Ala-Gly-Gly-His, Boc-Ala-Gly-Gly-His (Boc = t-butoxycarbonyl), Ala-Gly-Gly-His(π-bom)(π-bom =N^π-benzoxymethyl), Ala-Gly-Gly-His-OMe, and Ala-Gly-Pro-His is reported, together with the results of a pH-metric and spectroscopic (absorption, c.d., and e.s.r.) study of their complexes with H⁺ and Cu^II. The work was designed to study the initial site of binding to Cu^II in peptides containing both a terminal amino nitrogen and a histidyl residue. Results show that the π-N of the imidazole ring of the histidyl residue is the primary anchoring site for copper(II) co-ordination, and that the next nitrogen to bond can be the terminal amino N, forming a macrocyclic chelate ring.