Glycoconjugated hypocrellin: photosensitized generation of free radicals (O-2(center dot-), (OH)-O-center dot, and GHB(center dot-)) and singlet oxygen (O-1(2))

To improve water solubility and specific affinity for malignant tumors, gly coconjugated hypocrellin B (GHB) has been synthesized. Illumination of deox ygenated DMSO solution containing GHB generates a strong electron paramagne tic resonance (EPR) signal. The EPR signal is assigned to the semiquinone a nion radical of GHB (GHB(.-)) based on a series of experimental results. Sp ectrophotometric measurements show that the absorption bands at 645 nm and 502 nm (pH 8.0) or 505 nm (pH 11.0) arise from the semiquinone anion radica l (GHB(.-)) and hydroquinone (GHBH(2)) of GHB, respectively. GHBH(2) is rea dily formed via the decay of GHB(.-) in water-contained solution. The incre ase of pH value of the reaction media promotes this process. When oxygen is present, superoxide anion radical (O-2(.-)) is formed, via the electron tr ansfer from GHB(.-), the precursor, to ground state molecular oxygen. Hydro xyl radical can be readily detected by DMPO spin trapping when aerobic aque ous solution containing GHB is irradiated. As compared with the parent comp ound, hypocrellin B (HB), the efficiency of O-2(.-) and (OH)-O-. generation by GHB photosensitization is enhanced significantly. Singlet oxygen (O-1(2 )) can be produced via the energy transfer from triplet GHB to ground state oxygen molecules, with a decreased quantum yield, i.e., 0.19. These findin gs suggest that the new GHB possesses an enhanced type I process and a decr eased type II process as compared with hypocrellin B. (C) 1999 Elsevier Sci ence Inc.