In the investigations of Krebs and Schaltegger between 1964 and 1972 on the structure specificity of the antipsoriatic anthrones it could be shown that at least a 1-hydroxy-9-anthrone is necessary for their efficacy. This structure was then called "minimum structure of the antipsoriatic anthrones'. Since even very minor changes of this structure in most cases lead to inactive compounds, only a few antipsoriatic anthrones have been found so far. Their most important representative chrysarobin, anthralin and I-hydroxy-9-anthrone have been known for more than 60 years. The later discovered antipsoriatic anthralin derivatives, triacetoxy-anthracene and 10-acyl-anthralin, are probably hydrolysed in the skin and thus act as their parent compound anthralin. The strong structure-activity dependence of the antipsoriatic anthrones seems to include a highly specific and complex mechanism of action.
An Uniformly Occurring Aliphatic Benzil-Benzilic-Acid-Type Rearrangement Treatment of 6-bromo-2,2,5,5-tetramethylcyclohex-3-enone (2) with aqueous alkaline and air affords l-hydroxy-2,2,5,5-tetramethylcyclopent-3-enecarboxylic acid (8) as the major product of a benzil-henzilic-acid-type rearrangement. The key compound is 2,2,5,5-tetramethylcyclohex-3-enc-1,2-dione (11). The by-product of the reaction is (E)-2,2,5,5-tetramethylhex-3-enedioic acid (9) as the result of an oxidative cleavage of the 6-membered ring and the isomeriration of the double bond.
Die antipsoriatischen Eigenschaften von Dithranol (1.8-Dihydroxy-9(10H)-anthracenon, 1) scheinen eng an die C-10-Partialstruktur gekoppelt zu sein. Die Frage, ob hierzu eine freie CH,-Gruppe vorliegen rnua'), oder ob auch 10-monosubstituierte Derivate, wie 10-Acyldithranol 22), ihre antipsoriatische Wirkung behalten, sol1 durch Untersuchung der Eigenschaften hydrolysestabiler 10-Alkyldithranolderivate 3 geklart werden3). Diese in der Literatur bisher nicht beschriebenen Derivate lassen sich durch Alkylierung von 1 mit Alkyljodiden in Aceton mit Kaliumcarbonat als Base in iiber 40 % Ausbeute gewinnen.
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-Ethyldithranol 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.
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