pyrrolidine-2,5-dicarboxylic acid. The rotations around these residues represent syn/exo – syn/exo and anti/endo – syn/exo hybrid transition states for the meso and racemic diastereomer, respectively. The rotation barriers are lower for the former rotation by about 9 kJ mol−1 (aqueous medium), suggesting a strong preference for the syn/exo (clockwise) rotation over the anti/endo (anticlockwise). The
肽基-脯
氨酰片段的酰胺旋转是蛋白质骨架结构组织的重要因素。计算研究表明,这种旋转优先通过定义的过渡状态结构(syn / exo)进行。在这里,我们通过确定两个对称的脯
氨酸类似物,内消旋和外消旋
吡咯烷-2,5-二
羧酸的酰胺键旋转势垒来补充计算结果。这些残基周围的旋转分别表示内消旋和外消旋非对映异构体的syn / exo – syn / exo和anti / endo – syn / exo杂合过渡态。前者的旋转势垒较低,约为9 kJ mol-1(
水性介质),这表明syn / exo(顺时针)旋转优先于anti / endo(逆时针)旋转。