Nuclear magnetic resonance and conformational energy calculations of repeat peptides of tropoelastin: Correlation of 1J(15N-1H) with nonplanarity of peptide moiety

Abstract

Conformational energy calculations and 'H and I3C nuclear magnetic resonance ( N M R ) studies in CDCI3 of a tripeptide. N-Ac-Glyl-L-Val2-Cly~-OMe. suggested the Occurrence of an I I -membered hydrogen-bonded ring, or y-turn conformation. The theoretical calculations indicated that the Conformation occurs when there is a distortion of the planarity of the peptide moiety. An I5N N M R study of thc tripeptide in CDCI3 was undertaken to see if these spectral parameters might correlate with deviations from planarity. 'H, I3C, and 15N N M R studies were also carried out on the dipcptide N-hc-~.-Vall-Glyz-OMe, which argue for the occurrence of an 8-membered hydrogen-bonded ring. or CX conformation and even greater distortions from peptide planarity. Therefore a theoretical investigation of this problem, using both the empirical and molecular orbital calculations in the C N 1 ) 0 / 2 approximation, was undertaken, the results of which indicate large distortions of the planarity of the peptide moiety. While further work is required before the detailed functional depcndence of N M R parameters to planarity of the peptide moiety can be established, a systematic variation of the 'J(I5N-'H) coupling constant with peptide planarity is observed for the molecules discussed.

Peptide δ‐Turn: Literature Survey and Recent Progress

“…The peptide C 8 turn might exist in linear peptides in solvents of low polarity at very low concentration (to avoid intermolecular amide⋅⋅⋅amide NH⋅⋅⋅OC H bonds). In this connection, in 1977 Urry and co‐workers carried out conformational energy calculations on Ac‐ L ‐Val‐Gly‐OMe (Ac, acetyl; OMe, methoxy) incorporating the effect of solvent and an NMR spectroscopy study on the same terminally blocked dipeptide 41. Their results apparently suggest the co‐existence of the C 8 conformation with other turn structures in equilibrium mixtures in solvents such as CCl 4 and CDCl 3 .…”

Conformational energy calculations on the CNS-active peptide Pro-Leu-Gly-NH2

“…A complete search for different patterns of intramolecularly hydrogen bonded conformations such as Cs and C7 conformations involving the N-H and C=O groups of the same or adjacent peptide unit or units [21], C,O or &turn conformations [22], as well as C11 or y turn conformations [23] was made during the conformational energy calculations. In principle the tripeptide can assume different types of P-turn conformations (see [22]) with a hydrogen bond between the Pro C=O and a carboxamide proton of the glycinamide, or y-turn conformations (see [23]) with a hydrogen bond between the Gly C=O and the proton attached to the Pro nitrogen atom. The results of this study have clearly demonstrated that the tripeptide cannot assume a y-turn conformation without significant deformation of the planarities of the peptide groups and out-of-plane bending of NH protons resulting in a pyramidal configuration at the nitrogen atoms [24].…”