Physical Organic Chemistry Laboratory, Chemistry Institute, University of Campinas , 13083-970 Campinas, SP, Brazil.
J Phys Chem A. 2014 Mar 6;118(9):1748-58. doi: 10.1021/jp5007632. Epub 2014 Feb 21.
This work reports a detailed study regarding the conformational preferences of L-proline methyl ester (ProOMe) and its N-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 (3)JHH 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.
这项工作详细研究了 L-脯氨酸甲酯（ProOMe）及其 N-乙酰化衍生物（AcProOMe）的构象偏好，通过核磁共振（NMR）和红外（IR）光谱学结合理论计算来阐明影响它们行为的因素。这些化合物在溶液中不呈现两性离子形式，更能模拟生物介质中的氨基酸残基，比气相中的氨基酸更接近。实验（3）JHH 偶合常数和红外数据与理论计算吻合得很好，表明改变溶剂时构象的分布没有变化。自然键轨道（NBO）结果表明，超共轭相互作用是 ProOMe 最稳定构象的主要原因，而对于 AcProOMe，超共轭和空间位阻效应共同决定其构象平衡。
