Utilisation de l'effet overhauser,des mesures de relaxation en RMN 1H et des deplacements chimiques en RMN 13C dans l'etude de la conformation des amides—II: Application a l'etude conformationnelle d'amides alicycliques: acyl-prolines

¹H and ¹³C chemical shifts in the two decoalesced rotamers of the deuteromethyl ester of N-acetyl-l-proline are established by use of NOE and relaxation measurements. This requires the previous determination of the rotational barrier ΔG_c^≠ and the measurement of the relaxation times T₁ of the α-proton in the two conformers. The observed results reinforce the previous structural conclusions inferred from ¹³C studies on several acyl l-prolines and hydroxy l-prolines. The introduction of an acyl group in the prolines does not affect the different carbon atoms of the cycle in the two rotamers in the same way. These results can be interpreted in terms of electric field effects by the examination of X-Pro dipeptides with the N-terminal amino group shifted from α (COCH₂NH₂) to δ position (CO(CH₂)₄NH₂).