Synthesis and EPR investigations of new aminated hypocrellin derivatives

Hypocrellins are novel photodynamic agents. A recent advance in the synthesis of hypocrellin congeners results in the production of two amino-substituted hypocrellin B derivatives in high yield via photochemical reaction. Both compounds exhibit similar photodynamic activity as hypocrellin B in terms of type I and type II mechanisms. In anaerobic media, semiquinone anion radicals can be detected by electron paramagnetic resonance (EPR) under irradiation; while superoxide anion radical, hydroxyl radical and singlet oxygen are photoproduced when oxygen was present. The quantum yields of singlet oxygen by these two new compounds are determined to be 0.72 and 0.64, respectively, similar to that of hypocrellin B. The comparison of the photosensitization chemistry of compounds 1 and 2 in liposomes with that in homogeneous solution has also been made. In liposomes, the type II photoprocess was favored and predominant over the type I photoprocess due to the decreased interactions between dye molecules. Both compounds exhibit much stronger red light absorption than the parent hypocrellin and therefore, merit investigation as photosensitizers.