New red-shifted coelenterazine analogues with an extended electronic conjugation

A new promising approach to the development of red-shifted coelenterazine analogues was described. In order to alter the photochemical properties of native coelenterazine, we have designed and synthesized analogues bearing a new electron-rich structure. The spectroscopic results obtained, in the presence of the target enzyme (Renilla Luciferase), show a bathochromic emission shift of the entire class of new derivatives. Among them, the 2-benzyl-8-(4-chlorophenylthio)-6-(4-hydroxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one (8) shows an emission at 510 nm and uncommon slow kinetic decay.