ROLES OF OXYGEN AND PHOTOINDUCED ACIDIFICATION IN THE LIGHT-DEPENDENTANTIVIRAL ACTIVITY OF HYPOCRELLIN-A

Hypocrellin A displays photoinduced antiviral activity, in particular against the human immunodeficiency virus (HIV), as does its counterpar t, hypericin. Although hypocrellin A, like hypericin, executes an exci ted-state intramolecular proton transfer, it differs from hypericin in two important ways. Unlike hypericin, hypocrellin A absolutely requir es oxygen for its antiviral activity. Also, whereas we have previously demonstrated that hypericin functions as a light-induced proton sourc e, we do not observe that hypocrellin A acidifies its surrounding medi um in the presence of light. These results are discussed in the contex t of the ground- and excited-state photophysics of hypericin and its m echanisms of photoinduced virucidal activity.