Synthesis and Enhanced Chemiluminescence of New Mono-Cyclomaltooligosaccharide-Bound 6-Phenylimidazo[1,2-a]Pyrazin-3(7H)-Ones

Abstract

Aequorin is a photoprotein found in the jellyfish, Aequorea victoria, that generates blue light (460 nm) with high light-emitting efficiency (θ = 0.2) upon treating this luminescence system with calcium ions [1–3]. Aequorin is known to consist of apoaequorin, molecular oxygen, and 2-(p-hydroxybenzyl)-6-(p-hydroxyphenyl)-8-benzylimidazo[1,2-a]pyrazin-3(7H)-one (Oplophorus luciferin, coelenterazine) [4,5]. The chemiluminescent reaction of coelenterazine and its analogues such as MCLA without apoaequorin in aqueous buffer solutions in the presence of active oxygen has been being used for analyses, whereas its light-emitting efficiency is extremely low [6– 8]. Many studies on the enhancement of chemiluminescence have dealt with the regulated medium, such as using a micellar surfactant or cyclomaltooligosaccharide (cyclodextrin) [9–13]. It has been shown that cyclodextrin enhances the intensity of chemiluminescence of MCLA in aqueous solvents by Toya [12]. That study showed that very large amounts of cyclodextrin are needed for the enhancement. For analysis by chemiluminescence, the analytical system should not affect the subject except to promote luminescence. It is noteworthy to construct a novel chemiluminescent system which promotes greater chemiluminescent activity. In this communication, we report a first example of the synthesis of light-producing compounds, in which MCLA, a chemiluminescent chromophore, is covalently bound to one cyclodextrin molecule, and show that the chemiluminescence is effectively enhanced in an aqueous solvent.