LOW-TEMPERATURE PHOTOOXYGENATION OF COELENTERATE LUCIFERIN ANALOG SYNTHESIS AND PROOF OF 1,2-DIOXETANONE AS LUMINESCENCE INTERMEDIATE

Coelenterate luciferin analog having bulky tert-butyl group at the 2-p osition was suitable for studies on chemiluminescence under various co nditions. Photooxygenation of the analog(s) at low temperature (-78 de grees C) afforded luminous intermediates which were proved as peroxide s by reduction with PPh(3) with resultant loss of luminescence ability . In order to clarify these structures of accumulated luminous interme diates by means of C-13 NMR, three C-13 enriched analogs were synthesi zed 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 C-13-enric hed coelenterate luciferin analogs were photooxygenated at -78 degrees C to form two peroxidic products as luminescent intermediates. Struct ures of these unstable intermediates were deducted by means of C-13 NM R spectra at low temperatures using substrates enriched at three sites by C-13. Photooxygenation in a mixture of CF3CD2OD and CD3OD as highl y protic solvents afforded the dioxetanone and 2-hydroperoxide. These two peroxides emitted light independently at different temperatures ei ther at 400 nm (neutral species) and/or 475 nm (anionic species) after diluting to 10(-5) M in diglyme (DGM) containing acid or base. Copyri ght (C) 1996 Elsevier Science Ltd