Dithranol: further investigations on the structure-activity-relationship. The new series of the...

The in vitro stability of 10-ethyldithranol (1,8-dihydroxy-10-ethyl-9(10H)-anthracenone) and its effects on healthy and psoriatic skin is investigated. 10-Ethyl-dithranol as a representative of the new class of 10-alkyldithranol derivatives neither stains nor irritates and has no antipsoriatic activity at all. This is due to the relatively stable substituent at carbon 10 which enables the fast oxidation processes necessary for the antipsoriatic effect. Therefore, antipsoriatically active dithranol derivatives require a free or easily liberated 10-position and hence the so-called 'minimum structure of antipsoriatic anthrones' keeps its validity.