Collect. Czech. Chem. Commun. 1988, 53, 2810-2824

Salt bridges in model peptides

Ilmars Sekacis, Mark Shenderovich, Gregory Nikiforovich, Edvards Liepinš, Ludmila Polevaya and Gunars Chipens

Institute of Organic Synthesis, Latvian SSR Academy of Sciences, Aizkraukles 21, 226006 Riga, U.S.S.R.


A group of synthetic peptides including Boc-Lys-Phe-X-Y, X = Ala (I, III) or Thr (II), Y = Pro (I, II) or Ala (III) was studied by means of 1H NMR spectroscopy and theoretical conformational analysis. Compound I in DMSO shows two conformers with the trans- and cis-configuration of the peptide bond Ala-Pro. The salt bridge between the Lys ε-amino group and the C-terminal carboxyl is featured by magnetic nonequivalence of the Lys CεH2 protons. The space structure of I and II was found to possess a salt bridge fixed by an unusual turn in the chain formed by the Lys side chain and the C-terminal dipeptide with the trans-peptide bond X-Pro. Since a stable ionic bond in III and in the cis-conformer of I has not been observed, its contribution to stabilization of the space structure of the peptides in DMSO appears rather small.