A kinetic and Mechanistic Study of the Hydrolysis of Camptothecin and Some Analogues
作者:Julianne Fassberg、Valentino J. Stella
DOI:10.1002/jps.2600810718
日期:1992.7
a result suggesting that the mechanism of lactone hydrolysis is independent of a variety of substituents on the A ring. The conversion of the lactone to its carboxylate form occurred under neutral and basic conditions and appeared to be largely dependent on hydroxide ion. The conversion of the carboxylate to the lactone was observed under neutral and acidic conditions and was pH independent at pH values
用高性能液体测定喜树碱(1)和类似物(2-5,全部被1个A环取代)在25°C下水溶液中内酯(E环)水解的定量速率和平衡常数。紫外可见检测和紫外可见分光光度法进行色谱分离。已表明内酯在pH依赖性平衡下转化为羧酸盐。没有观察到1-5的速率和平衡常数的主要差异,结果表明内酯水解的机理独立于A环上的各种取代基。内酯向其羧酸酯形式的转化在中性和碱性条件下发生,并且似乎很大程度上取决于氢氧根离子。在中性和酸性条件下观察到羧酸盐向内酯的转化,并且在pH值大于5时与pH无关,在pH值小于5时取决于水合氢离子。将氧18显着掺入3的内酯环中,在H2(18)O中观察到3的水溶性类似物的开环和随后的闭环。该发现强烈表明内酯环水解的机理涉及酰基裂解而不是烷基裂解。在1的pH值速率曲线上获得的动力学溶剂同位素效应(kH2O / kD2O,其中kH2O和kD2O分别是H2O和D2O中的速率常数)被用于推测开口所涉及的过渡态的性质和内酯环的闭合反应。