Free radical intermediates produced by autoxidation of 1,8-dihydroxy-9-anthrone (dithranol) in pyridine.

The autoxidation of the antipsoriatic agent dithranol, monitored by an ESR-spectrometer, proceeds through several free radical intermediates. The initial radical, attacking a bulky spin trapping agent in a sterically comparatively hindered constellation, may be the active therapeutic form of dithranol.