Low-temperature photooxygenation of coelenterate luciferin analog synthesis and proof of 1,2-dioxetanone as luminescence intermediate

Article abstract of DOI:10.1016/0040-4020(96)00699-0

Coelenterate luciferin analog having bulky tert-butyl group at the 2-position was suitable for studies on chemiluminescence under various conditions. Photooxygenation of the analog(s) at low temperature (-78°C) afforded luminous intermediates which were proved as peroxides by reduction with PPh₃ with resultant loss of luminescence ability. In order to clarify these structures of accumulated luminous intermediates by means of ¹³C NMR, three ¹³C enriched analogs were synthesized at the 2, 3 and 5 positions of 3,7-dihydroimidazo[1,2-a]pyrazin-3-one skeleton in 99% enrichment with site-specificity. These ¹³C-enriched coelenterate luciferin analogs were photooxygenated at -78°C to form two peroxidic products as luminescent intermediates. Structures of these unstable intermediates were deduced by means of ¹³C NMR spectra at low temperature using substrates enriched at three sites by ¹³C. Photooxygenation in a mixture of CF₃CD₂OD and CD₃OD as highly protic solvents afforded the dioxetanone and 2-hydroperoxide. These two peroxides emitted light independently at different temperatures either at 400 nm (neutral species) and/or 475 nm (anionic species) after diluting to 10^-5 M in diglyme (DGM) containing acid or base.