ZINC-COMPLEXES OF AMINO-ACIDS AND PEPTIDES .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 the N terminus. Their reactions with basic zinc carbonate resulted in the formation of mononuclear complexes ZnL2, with L being the peptide anion resulting from SH deprotonation. IR and NMR spectra indicate that in all these complexes the zinc ion is coordinated by the cysteine thiolate and amino functions of two peptide ligands. This tetrahedral ZnN2S2 coordination by two chelating peptides is confirmed by a crystal structure determination of the complex Zn(Cys-Gly-NH2)2.