Concerning the Deprotonation of the Photooxidized 3-Hypericinate Ion

Abstract

By means of AM1 calculations it was established that the radical produced by photooxidation of the 3-hypericinate anion ( (3) 1 . ) possesses strong acidic properties and is at least as acidic as hypericin itself. Dissociation of (3) 1 . yields a proton which stems from the 6-peri-and/or 4-bay-hydroxyl group (which seem to have comparable acidities). The peri-hydroxyl groups of (3) 1 . at positions 1,8, are 13 are signi®cantly less capable of deprotonation. This result sheds new light on the interpretation of a recent experimental ®nding involving intermolecular proton transfer following excitation of hypericinate and several of its alkyl derivatives. On the basis of observing a gradual change of proton transfer from these derivatives one could conclude that the proton might stem from the bay-and/or the peri-region hydroxyl groups.Zusammenfassung. Mit Hilfe von AM1 Rechnungen wurde abgeleitet, daû das Radikal aus der Photooxidation des 3-Hypericinat-Anions ( (3) 1 . ) stark sauer ist ± wenigstens so sauer wie das Hypericin selbst. Die Dissoziation von (3) 1 . ergibt ein Proton, welches von der 6-peri-und/oder 4-bay-Hydroxylgruppe herru Èhrt (diese du Èrften etwa gleiche Acidita Èt aufweisen). Die periHydroxylgruppen von (3) 1 . in den Positionen 1, 8 und 13 unterliegen einer Deprotonierung weniger leicht. Dieses Ergebnis wirft neues Licht auf die Interpretation von ku Èrzlich mitgeteilten experimentellen Ergebnissen u Èber den intermolekularen Protonentransfer, der der Anregung von Hypericinat und einigen seiner Alkylderivate folgt. Auf der Basis des beobachteten graduellen Wechsels des Protonentransfers bei diesen Derivaten kann geschlossen werden, daû der Protonentransfer von den bay-und/oder peri-Hydroxylgruppen stammt.

Toward Hypericin-derived Potential Photodynamic Therapy Agents¶

“…Hypericin (1) the photosensitizing pigment from the ubiquitous proliferating weed, St. John's wort (Hypericum perforatum L.), constitutes a promising agent for the photodynamic therapy of certain viral or tumoral ailments (for reviews see Kraus et al [1] and Falk [2]). Besides its capability to acidify its surroundings following excitation (3)(4)(5)(6) this is thought to be mainly due to its pronounced tendency to sensitize the formation of singlet oxygen and to a smaller extent of superoxide radicals (2). However, the efficiency of 1 for this application might be improved with respect to two issues.…”