Synthesis and enhanced chemiluminescence of new cyclomaltooligosaccharide (cyclodextrin)-bound 6-phenylimidazo[1,2-a]pyrazin-3(7H)-one

In order to provide chemiluminescent substrates that have high light-emitting efficiency in aqueous solution, the structural design on 6-phenylimidazo[1,2-a]pyrazin-3(7H)-one compounds was studied in the covalent attachment of a light-producing chromophore to a cyclomaltooligosaccharide (cyclodextrin). The synthesis of cyclodextrin-bound 6-phenylimidazo[1,2-a]pyrazin-3(7H)-one compounds was achieved by the formation of an amido bond between a 6-phenylimidazo[1,2-a]pyrazin-3(7H)-one and a mono-6-amino-6-deoxycyclodextrin. The properties of oxygen-induced chemiluminescence of the synthesized cyclodextrin-bound light-emitting chromophores were investigated. The light-emitting efficiency in pH 8.3 phosphate buffer was remarkably dependent on the kind of bound cyclodextrin and the binding site between the chromophore and cyclodextrin. The light-emitting efficiency of a cyclodextrin-bound compound in which cyclomaltoheptaose (β-cyclodextrin) had been covalently attached to the 2-position of the imidazo[1,2-a]pyrazin-3(7H)-one ring system showed an up to 11-fold enhancement over that of a non-cyclodextrin chromophore, whereas attachment to cyclomaltohexaose (α-cyclodextrin) resulted in no enhancement. Moreover, this study indicated that the strategy that involves covalently attaching a light-producing chromophore onto a cyclodextrin for the enhancement of chemiluminescence is more efficient than the use of an aqueous solution containing very large amounts of cyclodextrin.