Core-modified coelenterazine luciferin analogues, synthesis and chemiluminescence properties

International audienceIn our work on the design and studies of luciferins related to the blue‐hued coelenterazine, we undertook the synthesis of heterocyclic analogues susceptible to produce a photon, possibly at a different wavelength. We describe here the synthesis of O‐acetylated derivatives of imidazo[1,2‐b]pyridazin‐3(5H)‐one, imidazo[2,1‐f][1,2,4]triazin‐7(1H)‐one, imidazo[1,2‐a]pyridin‐3‐ol, imidazo[1,2‐a]quinoxalin‐1(5H)‐one, benzo[f]imidazo[1,2‐a]quinoxalin‐3(11H)‐one, imidazo[1',2':1,6]pyrazino[2,3‐c]quinolin‐3(11H)‐one and 5,11‐dihydro‐3H‐chromeno[4,3‐e]imidazo[1,2‐a]pyrazin‐3‐one thanks to an extensive use of the Buchwald‐Hartwig N‐arylation. The acidic hydrolysis of these derivatives then gave solutions of the corresponding luciferin analogues which we studied. Not too unexpectedly, even if these were “dressed” with substituents found in actual substrates of the nanoKAZ/NanoLuc luciferase, no bioluminescence was observed with these compounds. However, in a phosphate buffer, all produced a light signal, by chemiluminescence, with extensive variations in their respective intensity and this could be increased by adding a quaternary ammonium salt in the buffer. This aspect was actually instrumental to determine the emission spectra of many of these luciferin analogs