title: Conformations of proline-containing cyclic peptides. 1H and 13C n.m.r. evidence for a solvent stabilized All-Cis X-Pro conformer of Cyclo-(Pro-Gly-Gly-Pro)2.
abstract: As inferred from 13C, 1H n.m.r. data, CD measurements and ion-binding experiments, the title molecule can assume two major C2 symmetric conformations. One of these has an all-trans X-Pro peptide backbone and two 1 comes from 4 intramolecular H-bonds and represents the predominant (greater than or equal to 95%) form in D2O and nonpolar (CD3CN) solvents. Stabilized by specific solvent-solute interactions, the other conformer becomes competitive (45%) in DMSO solution. It is shown to possess a four-cis X-Pro skeleton and no intramolecular H-bonds. The Mg++ complex of the cyclic peptide in CD3CN is again C2 symmetric and its formation proceeds via a slow trans leads to cis isomerization of two X-Pro peptide bonds.
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D005998:Glycine / Q000032:analysis; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010456:Peptides, Cyclic / Q000032:analysis*; D011392:Proline / Q000032:analysis*; D013696:Temperature
chemical_list: D010456:Peptides, Cyclic; D011392:Proline; D005998:Glycine