Relationship between photosensitizing activities and chemical structure of hypocrellin A and B.

Hypocrellins A (HA) and B (HB) are two main pigments isolated from the parasitic fungi Hypocrella bambusae (B. et Br) Sacc. and Shiraia bambusicola P. Heen found in China. These pigments have a long history as traditional medicinal agents. Although HA and HB have the same perylene quinonoid structure, there are different side rings. The different photosensitizing activities of HA and HB due to their different side rings were studied by electron paramagnetic resonance (EPR), spin trapping and spin counteraction techniques. It is demonstrated that the ability to generate active oxygen (1O2, O2.- and .OH) is stronger during HA photosensitization than during HB photosensitization. Under anaerobic conditions, the ability to generate HA.- during HA photosensitization is stronger than the ability to generate HB.- during HB photosensitization. There is a relationship between photosensitizing ability and chemical structure.