CONFORMATIONS OF PROLINE-CONTAINING CYCLIC PEPTIDES - H-1 AND C-13NMR EVIDENCE FOR A SOLVENT STABILIZED ALL CIS X-PRO CONFORMER OF CYCLO-(PRO-GLY-GLY-PRO)2

  • 1 January 1977
    • journal article
    • research article
    • Vol. 10  (4) , 286-290
Abstract
As inferred from 13C, 1H NMR data, CD [circular dichroism] measurements and ion-binding experiments, the title molecule can assume 2 major C2 symmetric conformations. One of these has an all-trans X-Pro peptide backbone with 2 1 .rarw. 4 intramolecular H-bonds and represents the predominant (.gtoreq. 95%) form in D2O and nonpolar (CD3CN) solvents. Stabilized by specific solvent-solute interactions, the other conformer becomes competitive (45%) in DMSO [dimethyl sulfoxide] solution. It is shown to possess a 4-cis X-Pro skeleton and no intramolecular H-bonds. The Mg2+ complex of the cyclic peptide in CD3CN is again C2 symmetric, and its formation proceeds via a slow trans .fwdarw. cis isomerization of 2 X-Pro peptide bonds.

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