Redox and debromination reactions of brominated hypericin

摘要

Phototoxic and radical-generating debromination reactions of monobrominated hypericin with bromine at one of four possible positions were investigated using density functional theory. The study was performed on two closely lying conformational isomers, differing in the relative orientations of the two anthracene units of the hypericin core. Calculated adiabatic electron affinities show that the molecules have the ability to, in aqueous solution, extract an electron from the surrounding. The electron might then be passed on to molecular oxygen, forming reactive superoxide radical anions. If electron extraction from the molecule does not occur in this step, the molecule might dissociate, generating a negatively charged bromine as a leaving group and a hypericin radical capable of forming direct binding to biological molecules. This reaction was found possible for those species substituted by Br at two of the four positions, with barriers of similar to 13 kcal/mol in aqueous solution. Debromination was not found energetically possible for neither the neutral ground state compounds nor the bay-deprotonated species. (c) 2008 Wiley Periodicals, Inc.