ZINC-COMPLEXES OF AMINO-ACIDS AND PEPTIDE S .3. ZINC-COMPLEXES OF PEPTIDES WITH N-TERMINAL CYSTEINE

Conventional methods were used to prepare three dipeptides Cys-X-OR (X = Gly, Phe), nine dipeptides Cys-X-NH2 (X = Gly, Ala, Val, Leu, Ile, Pro, Phe, Met, Ser), three tripeptides Cys-X-OR (X = Gly-Gly, Phe-Phe, Met-Phe), and three tripeptides CYS-X-NH2 (X = Gly-Gly, Gly-Ala, Gly- Leu). All these peptides have the unprotected amino acid cysteine at t he N terminus. Their reactions with basic zinc carbonate resulted in t he formation of mononuclear complexes ZnL2, with L being the peptide a nion resulting from SH deprotonation. IR and NMR spectra indicate that in all these complexes the zinc ion is coordinated by the cysteine th iolate and amino functions of two peptide ligands. This tetrahedral Zn N2S2 coordination by two chelating peptides is confirmed by a crystal structure determination of the complex Zn(Cys-Gly-NH2)2.