Synthesis of a novel hypocrellin B derivative and its photogeneration of semiquinone anion radical

In order to improve the photosensitizing activity of HB further, the complex of 5,8-di-Br-HB with Al(3+) was first designed and synthesized in high yield. 5,8-di-Br-HB forms a 2:1 type (metal-ligand ratio) complex with Al(3+) measured by molar ratio and continuous variation methods. The new photosensitizer was characterized by UV-Vis, IR, 1H NMR and elemental analysis measurements. Based on the above experimental results, we first proposed a polymer-like structural model of the complex. The water-solubility and red absorption of the Al(2)(5,8-di-Br-HB)Cl(4)](n) complex are both enhanced over hypocrellin B. In addition, the EPR and spectrophotometric measurements demonstrate that semiquinone anion radical of Al(2)(5,8-di-Br-HB)Cl(4)](n) can be produced by Al(2)(5,8-di-Br-HB)Cl(4)](n) photosensitization. The generation efficiency of (Al(2)(5,8-di-Br-HB)Cl(4)](n))(.-) is almost equal to that of HB(.-). These results obtained indicated that Al(2)(5,8-di-Br-HB)Cl(4)](n)was at least a favorable Type I phototherapeutic agent.