在四种季铵表面活性剂的胶束溶液中,已经研究了含组氨酸的三肽对氨基酸苯丙氨酸衍生的手性对硝基苯酯的裂解。酶样对映体选择性高达k I / k D观察到= 131(在0℃下)。通过假设在反应的过渡态下酯的I.对映异构体和三肽之间的疏水性驱动的稳定氢键可以使对映选择性合理化。与酯的D对映体反应中不存在该氢键。过渡态具有两极特性,并被胶束环境稳定。通过改变三肽的组成以及三肽和底物中N-保护基的长度,可以优化影响过渡态的反应物的亲水-疏水平衡。活性和对映选择性取决于季铵表面活性剂头基的结构。该头基的尺寸增加导致L酯的水解速率增加,并因此导致对映选择性增加。该作用归因于肽中存在的具有羧酸根基团的离子对形成程度的变化。与以前的研究相比,结果表明不需要手性表面活性剂即可获得高对映选择性。
Mechanism of enantioselective ester cleavage by histidine containing dipeptides at a micellar interface
作者:Marco C. Cleij、Wiendelt Drenth、Roeland J. M. Nolte
DOI:10.1021/jo00012a019
日期:1991.6
Chiral p-nitrophenyl esters derived from the amino acid phenylalanine are cleaved by histidine-containing dipeptides at a micellar interface. High enantioselectivities (up to k(L)/k(D) = 30.4 at 0-degrees-C) are observed. Both the substrates and the catalysts contain an alternating sequence of hydrophobic and hydrophilic groups. Due to the need for hydration of the hydrophilic groups, the hydrophobic groups cannot dissolve completely into the micellar hydrocarbon phase. The kinetic data suggest that the micellar interface is capable of discriminating between transition states that have different hydrophilic and hydrophobic properties. One of the diastereomeric transition states is characterized by a hydrogen bond between the amide CO group of the ester and an NH group of the histidine-containing dipeptide. Upon formation of this hydrogen bond these polar CO and NH groups lose their hydrophilicity which allows the transfer of the adjacent apolar groups to the micellar hydrocarbon phase. The other diastereomeric transition state cannot form this hydrogen bond and the hydrophobic groups remain hydrated. Consequently, the latter transition state is of higher energy. The kinetic data reveal that it is important to prevent steric hinderance between the reactants in order to allow the unhindered formation of the hydrogen bond.
CLEIJ, MARCO C.;DRENTH, WIENDELT;NOLTE, ROELAND J. M., J. ORG. CHEM., 56,(1991) N2, C. 3883-3891
作者:CLEIJ, MARCO C.、DRENTH, WIENDELT、NOLTE, ROELAND J. M.