MERCAPTO-SUBSTITUTED PERYLENEQUINONOID PIGMENTS - A NEW-TYPE OF SINGLET OXYGEN SENSITIZER

Mercapto-substituted hypocrellin B derivatives (MHBDs) have recently b een prepared and characterized. Their significantly enhanced red absor ptivities longer than 600nm and singlet oxygen-generating function may qualify them as promising photodynamic therapy (PDT) agents. The gene ration of singlet oxygen during photoirradiation of MHBDs was detected as an oxidation product of a sterically hindered amine (tetramethylpi peridine oxide;TEMPO) by ESR spectroscopic techniques. Sodium azide in hibited the ESR signal intensity in a dose-dependent manner with a que nching rate constant of 2.65x10(8) M(-1)s(-1) and 3.13x10(8) M(-1)s(-1 ) for compound 6 and compound 7 in CHCl3, respectively. Deuterated sol vents, known to increase the lifetime of singlet oxygen, augmented the ESR signal intensity. The rate of production of O-1(2) was dependent not only upon the concentration of MHBDs and the time of irradiation b ut also on the oxygen content of the reaction mixture. The hyperfine s plitting constant and g-value of the photoproduct of TEMP-singlet oxyg en and TEMPO were found to be identical, this indicates that the nitro xide species detected by ESR spectroscopy generated by reacting TEMP w ith photogenerated O-1(2) is TEMPO. (C) 1997 Elsevier Science Ltd.