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Stereoisomerism of Cyclic Compounds02:33

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All-cis cyclic peptides.

Romuald Poteau1, Georges Trinquier

  • 1Laboratoire de Physique Quantique (CNRS, UMR5626), IRSAMC, Université Paul-Sabatier, 31062 Toulouse Cedex, France. romuald.poteau@irsamc.ups-tlse.fr

Journal of the American Chemical Society
|October 6, 2005
PubMed
Summary

Researchers explored all-cis cyclic peptides, finding they are stable structures. These cyclic peptides, with cis-amide bonds, show favorable association energies comparable to trans-peptide structures.

Area of Science:

  • Computational Chemistry
  • Peptide Chemistry
  • Structural Biology

Background:

  • Amide bonds (-NH-CO-) typically favor trans conformations due to thermodynamic stability.
  • The cis conformation of amide bonds is energetically unfavorable and presents steric challenges for linear peptide chains.
  • Cyclic peptides offer a unique structural framework where cis-amide bonds can be stabilized.

Purpose of the Study:

  • To investigate the structural and energetic properties of cyclic peptides composed entirely of cis-amide bonds.
  • To determine the feasibility and stability of all-cis cyclic peptide structures using quantum calculations.
  • To compare the energetic favorability of all-cis versus all-trans peptide associations in cyclic systems.

Main Methods:

  • Density Functional Theory (DFT) calculations at the B3LYP level were employed.

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  • Systematic exploration of potential-energy surfaces for all-cis cyclopolyglycines (cG(n)(c)), cyclopolyalanines, and cyclopolyphenylalanines.
  • Analysis of ring strain, conformational flexibility, and plaque-junction energies using isodesmic reactions and Mean Plaque-Junction Energy (MPJE).

    • Main Results:

    • All-cis cyclic peptides (cG(n)(c), n=2-10,15) were confirmed as true minima on the potential-energy surface.
    • Optimal ring sizes around eight peptide units result in planar structures (cG7(c) to cG9(c)).
    • Smaller rings exhibit cup-like distortions, while larger rings adopt saddle-edge conformations.
    • Mean Plaque-Junction Energy (MPJE) indicates that all-cis plaque association is energetically comparable to all-trans association for cyclic peptides with six or more units.

    Conclusions:

    • All-cis cyclic peptides are structurally viable and thermodynamically stable.
    • The energetic favorability of cis-amide bond association in cyclic structures challenges previous assumptions.
    • These all-cis cyclic peptides represent a novel class of peptidic materials with potential self-assembling properties.