PHOTOREACTIVITY OF BIOLOGICALLY-ACTIVE COMPOUNDS .10. PHOTOREACTIVITYOF CHLOROQUINE IN AQUEOUS-SOLUTION

Photochemical degradation of chloroquine (CQ) as a function of pH was studied in order to obtain information on the photoreactivity of both the dicationic and the monocationic form of CQ. The photodecomposition rate was strongly dependent on the state of ionization of CQ, The mai n degradation product formed from the monocationic form of CQ was iden tified as a dimerization product, confirmed by mass-spectrometry (EI, and high resolution MS). Formation of the secondary amine DesCQ was de tected for both the dicationic and the monocationic form of CQ. Oxygen is probably not directly involved in the main reaction(s) leading to photolysis of CQ. In the monocationic form CQ is a source of superoxid e ions and hydroxyl radicals during irradiation, whereas in the dicati onic form, formation of such radicals could not be detected. Under the experimental conditions used, no photodechlorination of CQ could be d etected. Reactions performed in the darkness showed that monocationic CQ was susceptible to attack by hydroxyl radicals and superoxide ions. Decomposition of the dicationic form of CQ could not be detected unde r the same experimental conditions.