Intramolecular General Base Catalysis in the Hydrolysis of a Phosphate Diester. Calculational Guidance to a Choice of Mechanism
作者:Anthony J. Kirby、Michelle Medeiros、José R. Mora、Pedro S. M. Oliveira、Almahdi Amer、Nicholas H. Williams、Faruk Nome
DOI:10.1021/jo302498g
日期:2013.2.15
assisted by intramolecular catalysis by a (weakly basic) pyridine nitrogen acting as a general base. Catalysis is relatively efficient for this mechanism, with an estimated effective molarity (EM) of the general base of >15 M, consistent with the absence of catalysis by typical buffers. Further new results confirm that varying the nonleaving group has minimal effect on the rate of spontaneous diester hydrolysis
尽管它在25°C下的半衰期为70年,但磷酸二-2-吡啶基磷酸酯(DPP)的自发水解速度却快了数千倍(在100°C时约3000倍,在25°C时超过10000倍) C)较预期的二酯键的离去基团p K为9.09。动力学参数不允许在所考虑的五种可能机理之间做出决定性的选择,但是动力学和计算证据的组合支持单步一致的S N图2(P)的机理涉及溶剂水攻击磷,而分子内的催化作用是通过(弱碱性)吡啶氮作为一般碱而辅助的。对于这种机理,催化是相对有效的,一般碱的估计有效摩尔浓度(EM)> 15 M,这与典型缓冲液不存在催化作用相一致。进一步的新结果证实,改变nonleaving组具有自发二酯水解速率的影响最小,在鲜明的对比对三酯的相应反应的主要效果:虽然DPP的一个氮的质子化-通过6个数量增加水解的速率数量级,符合预期。