Conformational
Analysis and Intramolecular Interactions of l‑Proline Methyl Ester and Its <i>N</i>‑Acetylated Derivative through Spectroscopic and Theoretical Studies
- Publication date
- Publisher
Abstract
This
work reports a detailed study regarding the conformational preferences
of l-proline methyl ester (ProOMe) and its <i>N</i>-acetylated derivative (AcProOMe) to elucidate the effects that rule
their behaviors, through nuclear magnetic resonance (NMR) and infrared
(IR) spectroscopies combined with theoretical calculations. These
compounds do not present a zwitterionic form in solution, simulating
properly amino acid residues in biological media, in a way closer
than amino acids in the gas phase. Experimental <sup>3</sup><i>J</i><sub>HH</sub> coupling constants and infrared data showed
excellent agreement with theoretical calculations, indicating no variations
in conformer populations on changing solvents. Natural bond orbital
(NBO) results showed that hyperconjugative interactions are responsible
for the higher stability of the most populated conformer of ProOMe,
whereas for AcProOMe both hyperconjugative and steric effects rule
its conformational equilibrium