MULTIPLE CONFORMATIONAL STATES OF A PRO-PRO PEPTIDE. SOLID-STATE AND SOLUTION CONFORMATIONS OF BOC-AIB-PRO-PRO-NHME.

Article abstract of DOI:10.1021/ja00350a053

The solid-state and solution conformations of the model peptide Boc-Aib-Pro-Pro-NHMe have been studied by X-ray diffraction and NMR. The peptide adopts a poly(proline II) conformation in the solid state. Two molecules are observed in the asymmetric unit differing in the geometry (cis/trans) of the urethane group. The molecules are held together in the crystal by a complex network of hydrogen bonds involving three molecules of water, which cocrystallize. Dissolution of single crystals at low temperature permits NMR observation of the solid-state conformer. In solution, the peptide undergoes a trans-cis isomerization of the Pro-Pro bond. Low-temperature NMR measurements allow the detection of three conformational states of the Pro-Pro segment.