Photoinduced decarboxylation of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid

Abstract

Photoinduced reactions of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid (SeQCA) were investigated in alkaline media (aqueous NaOH solutions) by electron paramagnetic resonance (EPR) spectroscopy, following the in situ formation of paramagnetic species. According to UV–Vis and nuclear magnetic resonance investigations, protonation (pH ≈ 11) and deprotonation (pH ≈ 13) of the imino hydrogen of the 4‐pyridone moiety has to be considered, reflected also in the different EPR spectra observed upon irradiation. Photoinduced generation of radicals was found only for carboxylate substituted SeQCA; other studied selenadiazoloquinolone derivatives, together with those substituted at the C(8) position (R = H, COOCH2CH3, COOCH3, COCH3 or CN), did not generate paramagnetic species during exposure. Consequently, photodecarboxylation was suggested as the decisive step, accompanied by the decomposition of the selenadiazole ring, resulting in the formation of ortho‐hydroxylate anions. EPR parameters elucidated from experimental EPR spectra obtained at pH ≈ 11 and pH ≈ 13 indicate the formation of oxygen‐centered radicals at the decarboxylated 4‐pyridone ring. EPR spin trapping experiments with nitromethane confirmed a very effective photoinduced electron transfer from all the selenadiazoloquinolones investigated. Copyright © 2011 John Wiley & Sons, Ltd.

Spectroscopic characterization, photoinduced processes and cytotoxic properties of substitutedN-ethyl selenadiazoloquinolones

“…Introducing the selenadiazole ring to a 4‐oxoquinoline moiety was expected to enhance the biological activity and to affect the desired photoactivity, via shifting the absorption bands to the visible region. Based on these presumptions, a group of selenadiazoloquinolones were synthesized and studied in our laboratories previously . Detailed investigation of their photoinduced processes confirmed that these compounds can behave as photosensitizers, generating ROS in the presence of molecular oxygen upon UVA irradiation .…”

Synthesis of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones by the application of modified Gould-Jacobs reaction to N-ethyl-2,1,3-benzoselenadiazol-4-amine

“…5,6 In our previous research, 7-substituted selenadiazolo [3,4-h]quinolones and 8-substituted selenadiazolo [3,4-f]quinolones (R 7 , R 8 = H, CN, COCH 3 , COOMe, COOEt, COOH) were successfully synthetized by the GouldJacobs reaction 7,8 and their biological/photobiological activity was investigated together with their EPR spectroscopy. [9][10][11][12] Antimicrobial activity of 7-substituted selenadiazolo [3,4-Analogously, treatment of selenadiazoloquinolone 4 with EtI in the presence of K 2 CO 3 afforded a mixture of N-and O-ethylated products 5 and 6 in almost the same ratio as in the previous case. Despite the fact that formation of selanadiazoloquinoline 6 was not observed when NaH was applied as the base, desired 6-ethylselenadiazoloquinolone 5 was isolated only in 26% yield (Scheme 2).…”

Oxidation of quinolones with peracids (an in situ EPR study)

“…[6][7][8][9][10] Previously, we synthesized a series of novel substituted quinolones and fused selenadiazoloquinolones and investigated the influence of their structure and various substitutions on their chemical, redox, photochemical and biological properties. [11][12][13][14][15] The oxidation of organic nitrogen-containing compounds using oxygen transfer agents like peracids or hydrogen peroxide is intensively applied in synthesis. [16][17][18] The products of the oxidation of amines vary depending on their structure, producing a wide range of organic compounds.…”

“…These have a broad spectrum of activity against Gram‐positive and Gram‐negative bacteria; thus, they have been successfully used to treat various infections, respiratory diseases and tuberculosis . Previously, we synthesized a series of novel substituted quinolones and fused selenadiazoloquinolones and investigated the influence of their structure and various substitutions on their chemical, redox, photochemical and biological properties …”