Analogs and derivatives of firefly oxyluciferin, the light emitter in firefly bioluminescence

The 5-methyl analog of firefly oxyluciferin, two isomeric O-methyl ether derivatives of it and an O,O'-dimethyl ether derivative were synthesized and their UV absorption and fluorescence emission spectra were determined. Comparisons of the emission data with the emission wavelength in bioluminescence indicate that the mono-anions of firefly oxyluciferin are candidates for the light-emitters in bioluminescence. Further, we have found that the chemiluminescence of active esters of firefly luciferin produces (from the keto form of oxyluciferin) only red light emission under a variety of conditions; a yellow-green light emission (from the enolic forms of the oxyluciferin product) could not be elicited.