Synthesis, resolution, and investigation of the rotational interconversion process of atropisomeric 1,n-diaza[n]paracyclophanes using cyclodextrin-mediated capillary zone electrophoresis.
Synthesis, resolution, and investigation of the rotational interconversion process of atropisomeric 1,n-diaza[n]paracyclophanes using cyclodextrin-mediated capillary zone electrophoresis.
复制标题
使用环糊精介导的毛细管区带电泳合成、解析和研究阻转异构体 1,n-二氮杂[n]对环芳烷的旋转互变过程。
作者：
K. Scharwächter;D. H. Hochmuth;H. Dittmann;W. König
通过经典的合成方法，合成了一系列单取代的1，n-二氮杂[n]对环芳（n = 10-12），它们具有平面手性和阻转异构性，并分析了它们的立体动力学性质.在酸性磷酸盐缓冲液（pH 2.5-4.5）中，采用全甲基化β-和γ-环糊精作为手性添加剂，通过毛细管区带电泳（CZE）解析具有10-和11-元桥的外消旋分析物。此外，环糊精介导的CZE用于在不连续驱动模式的构象不稳定的同系物（n = 11）的旋转互变过程的调查。在停流实验中，基线分离后，对映异构体通过加热在毛细管内原位部分对映异构化。速率常数（k（enan）= 1/2 k（rac））和旋转能垒（Delta G（++））由所得对映体比率确定。能垒在113-126 kJ/mol之间，这取决于苯环的取代基和桥头位置氨基的电离度。能垒的增加顺序为NO（2）>> CF（3）> Br > Cl > CH（3），近似为F。此外，在手性选择剂的存在下，转动能垒降低约6-8 kJ/mol。
A number of variously monosubstituted 1,n-diaza[n]paracyclophanes (n = 10-12), which show planar chirality and atropisomerism due to hindered rotation about single bonds, were synthesized via a classical route to analyze their stereodynamic properties. Racemic analytes with 10- and 11-membered bridges were resolved by capillary zone electrophoresis (CZE) in acidic phosphate buffers (pH 2.5-4.5) employing permethylated beta- and gamma-cyclodextrin as chiral additives. Moreover, cyclodextrin mediated CZE was used in a discontinuously driven mode for investigations of the rotational interconversion process of conformationally labile homologues (n = 11). In stopped-flow experiments, after baseline separation enantiomers were partially enantiomerized in situ inside the capillary by heating. The rate constants (k(enan) = 1/2 k(rac)) and rotational energy barriers (Delta G(++)) were determined from the resulting enantiomeric ratios. Energy barriers between 113-126 kJ/mol were found depending on the substituent of the benzene ring and the degree of ionization of the amino groups in bridgehead positions. The energy barriers increased in order of the substituents: NO(2) >> CF(3) > Br > Cl > CH(3) approximately F. In addition, the rotational energy barriers were decreased by approximately 6-8 kJ/mol in the presence of the chiral selector.