RESUMO
The photoisomerization kinetics of aqueous solutions of cefuroxime axetil under irradiation at 254 nm was investigated by HPLC. The overall degradation is the result of a competition between the isomerization of the alkoxyimino group and the photolysis of the beta-lactam ring. Cefuroxime axetil exists as a mixture of two diastereomers which are shown to react at different rates. This is true not only for the photoisomerization step but also for ground-state hydrolysis in alkaline conditions. Photoisomerization of the alkoxyimino group is also observed for the anti isomer of cefuroxime axetil and for some of its degradation products. The quantum yields for all these photoisomerizations are always lower than 1%, which explains the relative importance of the photolysis step. A stationary syn to anti ratio of 1 is measured for cefuroxime axetil and of 2.1 for cefuroxime. From this and previous studies, it appears that cefuroxime axetil is the most sensitive under irradiation at 254 nm when compared to other antibiotics bearing the alkoxyimino group. Azetreonam is the most stable followed by cefotaxime, cefuroxime, and cefuroxime axetil.
Assuntos
Cefuroxima/análogos & derivados , Pró-Fármacos/química , Cefuroxima/química , Cefuroxima/efeitos da radiação , Cromatografia Líquida de Alta Pressão , Hidrólise , Cinética , Fotoquímica , Pró-Fármacos/efeitos da radiação , Estereoisomerismo , Raios UltravioletaRESUMO
Cefuroxime, like all the oximino cephalosporins on the market, has the methoxyimino group in the syn (Z) configuration. By U.V. light irradiation of cefuroxime, a syn/anti isomerization occurs until equilibration of the two isomers is reached. Measurement of the 1H-N.M.R. chemical shift differences of the two isomers allows the assignment of methoxyimine stereochemistry.
