CONFORMATIONAL-ANALYSIS BY NUCLEAR MAGNETIC-RESONANCE SPECTROSCOPY - N-15 NMR OF A CYCLIC PENTAPEPTIDE

The cyclic pentapeptide cyclo-(Gly(1)-Pro-Gly(2)-D-Ala-Pro), which has been shown by 1H and 13C NMR to incorporate both β and γ turns, has been used as a model system to explore the use of 15N NMR to analyze the conformations of peptides. Assignments of 15N resonances to specific amino acids have been made by analogy with similar peptides and confirmed by 15N labeling. Nitrogen chemical shifts of the peptide, which is soluble in a wide variety of solvents, are sensitive to solvent changes. In water, two conformations corresponding to different cis-trans configurations of the peptide bonds are present. By means of 15N labeling and an analysis of 15N chemical shifts the involvement of Gly(1) in this cis-trans isomerism has been established. These results indicate substantial utility for l5N NMR in the conformational analysis of peptides. © 1979, American Chemical Society. All rights reserved.