Kinetics and Mechanism of the Degradation and Epimerization of Sodium Cefsulodin in Aqueous Solution

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The kinetics of the degradation and epimerization of cefsulodin in various buffer solutions were studied at 25℃ and 0.6 ionic strength. The overall degradation was a pseudo-first-order reaction in the pH region studied. The rate law of the degradation could be approximated in terms of specific acid-base and water catalyzed hydrolysis, that is k_1 (total degradation rate constant)=k_<H^+>×α_<H^+>+k_0+k_<OH^->×α_<OH^->. The apparent activation energies of the degradation reaction were 20.7,22.3,23.0 and 27.7 kcal mol^<-1> at pH values of 2,4,6,and 9,respectively. The epimerization of cefsulodin was proved to be catalyzed by hydroxide ion from the epimerization rate constant-pH profile, solvent effects using ethanol, and the apparent activation energies (which were 27.0 and 26.1 kcal mol^<-1> for the apparent forward and reverse epimerization reactions at pH 9.0,respectively). The mechanism of epimerization of cefsulodin is proposed to involve removal of the α-proton of the benzyl side chain by hydroxide ion to form an anioic intermediate. Interactions of cefsulodin with amines and aminoglycosides were also examined. The reaction was pseudo-second-order and the second-order rate constants for various amines and aminoglycosides were compared. It was found that intramolecular catalysis is the predominant factor for amines. An equation is proposed for the second-order rate constants of aminoglycosides. Peaks of unknown products in the alkaline reaction solutions could be separated under the high performance liquid chromatography conditions of the current study.
公益社団法人日本薬学会の論文
1984-09-25

Kinetics and Mechanism of the Degradation and Epimerization of Sodium Cefsulodin in Aqueous Solution

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