Abstract
Cephalosporins are β-lactam antibiotics, and the important drugs of this group are cephalexin, cefadroxil and cephradine. In the present research, the kinetics and mechanism of oxidation of cephalexin (CEX), cefadroxil (CFL), and cephradine (CPD) with chloramine-T (CAT) in alkaline medium were investigated at 301 K. All the three oxidation reactions follow identical kinetics with a first-order dependence each on [CAT]o and [substrate]o. The reaction is catalyzed by hydroxide ions, and the order is found to be fractional. The dielectric effect is negative. Proton inventory studies in H2O-D2O mixtures with CEX as a probe have been made. Activation parameters and reaction constants have been evaluated. Oxidation products were identified by mass spectral analysis. An isokinetic relation was observed with β = 378 K, indicating that enthalpy factors control the rate. The rate increases in the following order: CPD > CFL > CEX. The proposed mechanism and the derived rate law are consistent with the observed kinetics.
Highlights
Cephalosporins are an important and large class of bactericidal antimicrobial agents [1]
In the light of the above information and in continuation with our ongoing research on the oxidation kinetics and mechanism of important organic substrates [13,14,15], we report here the results obtained on the oxidation kinetics of three cephalosporin drugs, namely, cephalexin (CEX), cefadroxil (CFL), and cephradine (CPD) with CAT in alkaline medium in order to elucidate the mechanism of these redox systems and to assess their relative rates
Our preliminary experimental studies revealed that the oxidation reactions of CEX, CFL, and CPD with CAT were facile in alkaline medium
Summary
Cephalosporins are an important and large class of bactericidal antimicrobial agents [1]. Cephalexin [(2-[[2-amino-2(phenylacetyl)-acetamido]-3-methyl-8-oxo-5-thia-1azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid)], cefadroxil [(2-[2amino-2-(4-hydroxyphenyl)-acetamido]-3-methyl-8-oxo-5thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylicacid), and cephradine [(2-[2-amino-2-(cyclohexa-1,4-dienyl)acetamido]-3-methyl-8-oxo-5-thia-1azabicyclo[4.2.0]oct-2-ene-2carboxylic acid] are important cephalosporins These are widely used antibiotics which differ from each other with diverse group of substituents, namely, phenyl, hydroxyphenyl, and cyclohexadienyl, at the 7th position of the cephem ring. The versatile nature of CAT is due to its ability to act as sources of halonium cations, hypohalite species, and nitrogen anions which act both as bases and nucleophiles [6] It is a potent oxidizing and chlorinating agent in both acidic and alkaline media, with a two electron change per mole, giving p-toluenesulfonamide (PTS) and NaCl. The oxidation potential of PTS/sulfonamide system is pH dependent [7], and it decreases with the increase in pH of the medium (1.139, 0.778, and 0.614 V at pH 0.65, 7.0, and 9.7, resp.). The studies were extended to deduce the appropriate kinetic rate law and to establish the isokinetic relationship through the computed thermodynamic parameters
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