Kinetics and Mechanism of Decomposition of Cefazolin Ester in Phosphate Buffer Solution.
作者:Yutaka YAMAZAKI、John MCENTAGART、Katsuhiko SHINOZAKI、Hisatoyo YAZAWA
DOI:10.1248/cpb.44.599
日期:——
We evaluated the rate and mechanism of decomposition of cefazolin methyl ester (Δ3 ester) in phosphate buffer (pH 8.4).The decomposition of Δ3 ester proceeded simultaneously via 3 pathways. The first pathway is production of Δ2 ester (rate k12) by isomerization and production of Δ2 acid (k23) by hydrolysis of the Δ2 ester. The second pathway is the cleavage reaction of the β-lactam ring and simultaneous elimination of the substituent at position 3 (k14). The third pathway is production of Δ3 acid (k15) by hydrolysis of the carboxylic ester at position 4.Kinetic analysis of each pathway was performed. The reaction rate constant from Δ2 ester to Δ2 acid (k23) was the highest, and the reaction rate constant for the production of Δ2 ester by isomerization (k12) was similar to that for the elimination of the position 3 substituent by cleavage of the β-lactam ring (k14). The rate of production of Δ3 acid by hydrolysis of the position 4 carboxylic ester was the lowest.These results show that Δ3 ester decomposition under a basic condition predominantly occurs through cleavage reaction of the β-lactam ring and Δ2 ester producion by isomerization.Since the production of Δ2 acid markedly depended on the production of Δ2 ester by isomerization, Δ2 ester production is the rate-limiting step of this pathway.
我们评估了头孢唑啉甲酯(Δ3 酯)在磷酸盐缓冲液(pH 值为 8.4)中的分解速率和机制。第一条途径是通过异构化产生 Δ2 酯(速率 k12),通过水解 Δ2 酯产生 Δ2 酸(速率 k23)。第二个途径是 β-内酰胺环的裂解反应,同时消除第 3 位的取代基(k14)。第三条途径是通过水解第 4 位的羧酸酯产生Δ3 酸(k15)。从Δ2酯到Δ2酸的反应速率常数(k23)最高,而通过异构化生成Δ2酯的反应速率常数(k12)与通过裂解β-内酰胺环消除第3位取代基的反应速率常数(k14)相似。这些结果表明,在碱性条件下,Δ3 酯的分解主要是通过 β-内酰胺环的裂解反应和异构化产生 Δ2 酯。