Synthesis and Chemiluminescence Properties of 6-(4-Methoxyphenyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one and 2-Methyl-6-(2-naphthyl)imidazo[1,2-a]pyrazin-3(7H)-one

New Cypridina luciferin analogues, 6-(4-methoxyphenyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (MCLA) and 2-methyl-6-(2-naphthyl)imidazo[1,2-a]pyrazin-3(7H)-one (NCLA), were prepared together with their oxyluciferin analogues, 2-acetamido-5-(4-methoxyphenyl)pyrazine (MCOLA) and 2-acetamido-5-(2-naphthyl)pyrazine (NCOLA). Various chemiluminescence properties of these compounds were compared with those of known luciferin analogues, 2-methyl-6-phenylimidazo[1,2-a]pyrazin-3(7H)-one (CLA) and 6-(3-indolyl)-2-methylimidazo[1,2-a]pyrazin-3(7H)-one (ICLA). The light yields obtained from ICLA, MCLA, and NCLA were much higher than CLA in diethylene glycol dimethyl ether (diglyme), in which triplet oxygen was the oxidant. In aqueous solution, employing superoxide ion as the oxidant, NCLA emitted light weaker than CLA and MCLA. ICLA gave almost no light on account of no fluorescence intensity of the emitter (oxyluciferin analogue ICOLA) in aqueous solution. For applications to the detection of active oxygen species p...