PHOTOREACTION AND ACTIVE OXYGEN GENERATION BY PHOTOSENSITIZATION OF ANEW ANTIBACTERIAL FLUOROQUINOLONE DERIVATIVE, ORBIFLOXACIN, IN THE PRESENCE OF CHLORIDE-ION

The photoreaction of orbifloxacin (ORFX), a fluoroquinolone derivative having a fluorine at the 8 position, was investigated in aqueous solu tion containing chloride ion to determine its photochemical properties , In the presence of chloride ion, ORFX was found to convert into a ph otoproduct substituted by chlorine at the 8 position (8-Cl ORFX) under irradiation by ultraviolet-A (WA) light, Although the formation rate of 8-Cl ORFX increased greatly with increase in chloride ion concentra tion, the apparent photodegradation rate of ORFX in aqueous solution w as not varied by the presence of the ion, This implies that the dissoc iation of the C-F bond at the 8 position is the rate-limiting step in the photodegradation of ORFX. The active oxygen generated by the photo sensitization of ORFX were determined by measuring the bleaching rate of p-nitrosodimethylaniline and the reduction rate of cytochrome c. Th eir generation was inhibited by sodium azide and superoxide dismutase but not by D-mannitol, The photoreaction between ORFX and chloride ion also inhibited their generation, The mechanism is believed to be the photochlorination at the 8 position competing with the reaction betwee n free radical and oxygen.