Proton magnetic resonance and model peptides conformations

Derivatives and peptides of β-nitrobenzyl-L-aspartates were studied with high-field nmr. Differences were observed between the chemical shifts of protons located near the extremity of the principal chain as a function of the terminal group. These differences are explained by conformational calculations which exclude the existence of an hydrogen bond and demonstrate the influence of the aromatic ring position on the protons of the main chain. Both nmr experiments and conformational analysis indicate that conformations are nearly the same for ortho, meta, and para nitro substitution. These conclusions are in good agreement with Karplus relationship applied to the α and β protons.