Chemi- and bioluminescence of coelenterazine analogues with a conjugated group at the C-8 position

The chemiliminescent compound coelenterazine is involved in various bioluminescence reactions as the substrates, causing the luminescence with an emission peak in the range of 450–475 nm. Anticipating the introduction of a bathochromicshift of the luminescence, several new coelenterazine analogues that have conjugated olefins or aromatic groups at the 8-position of imidazopyrazinone ring were synthesized. In the chemiluminescence reaction, the emission spectra of a majority of the compounds synthesized showed a bathochromic shift, giving an emission peak in the range of 520–580 nm. In the bioluminescence catalyzed by Oplophorus luciferase, the bisthienyl analogue of coelenterazine emitted a moderate intensity of luminescence (5% of coelenterazine) with an emission maximum at 528 nm, which was the longest wavelength of all the analogues tested.