ON THE SYNTHESIS OF HYPERICIN BY OXIDATIVE TRIMETHYL-EMODIN ANTHRONE AND EMODIN ANTHRONE DIMERIZATION - ISOHYPERICIN

The base catalyzed oxidative dimerization of emodin anthrone exclusively yields hypericin. However, on oxidative dimerization of trimethylemodinanthrone a mixture of hexamethylhypericin and hexamethylisohypericin was obtained. Chromatographic separation of the hexabenzoyl derivatives was achieved, and by saponification about equal amounts of hypericin and isohypericrin were produced. Isohypericin could be characterized for the first time by its spectroscopic data and its protonation and deprotonation pK(a) and pK(a)* values.