Mode of Action of Hypericin as an Antiretroviral Agent and Other Relevant Findings

Hypericin (Hy), 4,5,7,4′,5′,7′-hexahydroxy 2,2′dimethyl-meso naphthodian-throne, is a naturally occurring, polycyclic aromatic dianthraquinone (Figure 1). The molecule assumes a planar configuration and exhibits red fluorescence with an excitation peak at 495nm and emission peaks at 595nm and 645nm. It is a lipophilic compound soluble in polar organic solvents such as methanol, ethanol, acetone and DMSO. Hypericin can be extracted from plants of the Hypericum genus, commonly known as Saint Johnswort. Hypericin usually co-purifies with a congener, pseudohypericin, with the two forming up to 0.1% of the total dry weight of the plant. Pseudohypericin differs from hypericin by a single hydroxyl group substitution in one methyl group. Hypericin is also found in the prosthetic group of the photoreceptor of the photophobic ciliated protozoa Stentor ceruleus (1). The compound can also be synthesized from emodin by an alkaline condensation via a method described by Spitzner (2).