the isomerization rate k12 was approximately equal to the apparent degradation rate of the delta 3 ester kdeg, and slower than the hydrolysis rate of the delta 2 ester k24. The isomerization process to the delta 2 ester was found to be the rate-determining step in the degradation of cephalosporin esters. The substituent at the C-3 position of the cephalosporins affected the degradation kinetics. The
研究了
头孢菌素的新戊酰氧基甲基(POM)酯在
磷酸盐缓冲溶液(pH 6-8)中的降解动力学。起始δ3
头孢菌素酯的降解主要通过异构化为δ2酯并随后
水解为δ2酸而进行。
水解为δ3酸(母体酸)非常缓慢。速率常数的分析表明,异构化速率k12大约等于δ3酯kdeg的表观降解速率,并且比δ2酯k24的
水解速率慢。发现到δ2酯的异构化过程是
头孢菌素酯降解的决定速率的步骤。
头孢菌素的C-3位上的取代基影响降解动力学。pH值的升高促进了降解,