Stereochemical behavior of acyclic peptide‐cation complexes

The role of the β‐turns in the peptide interaction with several cations was investigated. In this work we report the solution studies of four linear peptides: Z‐Aib‐Aib‐Aib‐L‐Val‐OMe, Boc‐D‐alle‐L‐Ile‐D‐alle‐L‐Ile‐OMe, Boc‐L‐Leu‐L‐Leu‐L‐Leu‐L‐Leu‐OMe, and Boc‐L‐Phe‐B‐Phe‐L‐Phe‐D‐Phe‐OMe. CD and 1H‐nmr spectra reveal the presence of multiple ion‐bounding equilibria. The stoichiometry and binding constant of the four peptide in the presence of Ca2+ ions in acetonitrile solution has been determined. Variable‐temperature nmr spectra in the absence and in thepresence of a large excess of cation have shown that the complexation process is not critically dependent on the conformation of the peptide. Copyright © 1990 John Wiley & Sons, Inc.