Structure elucidation of a photodegradation product of ciprofloxacin

In the photochemical degradation of ciprofloxacin, 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(piperazinyl)-3-quinolone carboxylic acid, two major decomposition products are formed in acidic solution. The main degradation product, after both artificial and daylight exposure, was 7-amino-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-3-quinolone carboxylic acid. This product was also the dominating compound after more than 5 h irradiation with a high-pressure mercury lamp in aqueous solutions at pH < or = 2 when the solvent additionally contained water-miscible organic solvent. The structure of the isolated compound was elucidated on the basis of the chemical behaviour in thin-layer and high-performance liquid chromatography, and of information from infrared, ultraviolet, mass and nuclear magnetic resonance spectra.