Pietrzyński G, Rzeszotarska B, Kubica Z
Department of Organic Chemistry, Pedagogical University of Opole, Poland.
Int J Pept Protein Res. 1992 Dec;40(6):524-31.
Solution conformations of three series of model peptides, homochiral Ac-Pro-L-Xaa-NHCH3 and heterochiral Ac-Pro-D-Xaa-NHCH3 (Xaa = Val, Phe, Leu, Abu, Ala) as well as alpha,beta-unsaturated Ac-Pro-delta Xaa-NHCH3 [delta Xaa = delta Val, (Z)-delta Phe, (Z)-delta Leu, (Z)-delta Abu] were investigated in CDCl3 and CH2Cl2 by 1H-, 13C-NMR, and FTIR spectroscopy. NH stretching absorption spectra, solvent shifts delta delta for NH (Xaa) and NHCH3 on going from CDCl3 to (CD3)2SO, diagnostic interresidue proton NOEs, and trans-cis isomer ratios were examined. These studies performed showed the essential difference in conformational propensities between homochiral peptides (L-Xaa) on the one hand and heterochiral (D-Xaa) and alpha,beta-dehydropeptides (delta Xaa) on the other. Former compounds are conformationally flexible with an inverse gamma-bend, a beta-turn, and open forms in an equilibrium depending on the nature of the Xaa side chain. Conformational preferences of heterochiral and alpha,beta-dehydropeptides are very similar, with the type-II beta-turn as the dominating structure. There is no apparent correlation between conformational properties and the nature of the Xaa side chain within the two groups. The beta-turn formation propensity seems to be somewhat greater in alpha,beta-unsaturated than in heterochiral peptides, but an estimation of beta-folded conformers is risky.
通过1H-、13C-核磁共振和傅里叶变换红外光谱，在CDCl3和CH2Cl2中研究了三个系列模型肽的溶液构象，即同手性的Ac-Pro-L-Xaa-NHCH3和异手性的Ac-Pro-D-Xaa-NHCH3（Xaa = 缬氨酸、苯丙氨酸、亮氨酸、氨基丁酸、丙氨酸）以及α,β-不饱和的Ac-Pro-δXaa-NHCH3 [δXaa = δ缬氨酸、(Z)-δ苯丙氨酸、(Z)-δ亮氨酸、(Z)-δ氨基丁酸]。研究了NH伸缩吸收光谱、从CDCl3到(CD3)2SO时NH（Xaa）和NHCH3的溶剂位移δδ、诊断性的残基间质子核Overhauser效应（NOE）以及反式-顺式异构体比例。所进行的这些研究表明，一方面同手性肽（L-Xaa）与另一方面异手性肽（D-Xaa）和α,β-脱氢肽（δXaa）在构象倾向方面存在本质差异。前一类化合物在构象上具有灵活性，取决于Xaa侧链的性质，以反向γ-转角、β-转角和开放形式处于平衡状态。异手性肽和α,β-脱氢肽的构象偏好非常相似，以II型β-转角为主要结构。在这两组中，构象性质与Xaa侧链的性质之间没有明显的相关性。α,β-不饱和肽中β-转角的形成倾向似乎比异手性肽中的略大，但对β折叠构象的估计存在风险。
