Development of imidazopyrazinone red-chemiluminescent probes for detecting superoxide anions via a chemiluminescence resonance energy transfer method.

During the development of useful probes for detecting superoxide anions via chemiluminescence with longer wavelengths than that of green, chemiluminescent probes that emit red light (lambda(max) 610 nm) when induced by superoxide anions were synthesized and characterized. These red-chemiluminescent probes consist of a 6-(4-methoxyphenyl)imidazo[1,2-a] pyrazin-3(7H)-one moiety, which reacts with superoxide anions to generate energy, and a sulphorhodamine 101 moiety, which accepts the energy and emits red light. Using a hypoxanthine-xanthine oxidase system for the generation of superoxide anions, it was shown that the superoxide anion-induced chemiluminescences of red-chemiluminescent probes (3 and 4) were more intense than those of the blue- and green-chemiluminescent probes 2-methyl-6-(4-methoxyphenyl)imidazo[1,2-a] pyrazin-3(7H)-one (MCLA) and 6-[4-[2-[N'-(5-fluoresceinyl)thioureido]-ethoxy]phenyl]-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (FCLA), respectively, which are generally considered to be the most sensitive chemiluminescent probes. The ratio between the superoxide-dependent and background chemiluminescence intensities for 3 was comparable to those of MCLA and FCLA, but higher than that of 4. Due to its highly intense superoxide anion-induced chemiluminescence at low probe concentrations, red-chemiluminescent probe 3 is superior to MCLA and FCLA for measurement of superoxide anions.