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

In order to improve the photo sensitizing activity of HB further, the compl ex of 5,8-di-Br-HB with Al3+ was first designed and synthesized in high yie ld. 5,8-di-Br-HB forms a 2:1 type (metal-ligand ratio) complex with Al3+ me asured by molar ratio and continuous variation methods. The new photosensit izer was characterized by UV-Vis, IR, H-1 NMR and elemental analysis measur ements. Based on the above experimental results, we first proposed a polyme r-like structural model of the complex. The water-solubility and red absorp tion of the [Al-2(5,8-di-Br-HB)Cl-4](n) complex are both enhanced over hypo crellin B. In addition, the EPR and spectrophotometric measurements demonst rate that semiquinone anion radical of [Al-2(5,8-di-Br-HB)Cl-4](n) can be p roduced by [Al,(5,8-di-Br-HB)Cl-4], photosensitization. The generation effi ciency 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 photo therapeutic agent. (C) 2001 Published by Els evier Science B.V.