Dithranol reaction with nitroxide radicals in DMSO, a HPLC study.

Dithranol (1,8-dihydroxy-9-anthrone), an efficient drug for the topical treatment of psoriasis undergoes a complex chemical transformation after topical application. An absorption phase HPLC method has been developed and validated to follow the appearance of its oxidative products in a DMSO solution. In DMSO solution dithranol, chrysazin, and biantrone were monitored simultaneously by HPLC during autooxidation process, as well as in the presence of nitroxide radicals which increase the reaction rate. The kinetics of the very early stage of dithranol transformation is presented for the first time and discussed. Two unknown dithranol-derived intermediates were found and partially characterised.