Novel 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline (SeQ(1-6)) and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f ]quinoline derivatives (SeQN(1-5)) with R(7), R(8) =H, COOC(2) H(5), COOCH(3), COOH, COCH(3) or CN were synthesized and their spectral characteristics were obtained by UV/Vis spectroscopy. Ultraviolet A photoexcitation of the selenadiazoloquinolones in dimethylsulfoxide or acetonitrile resulted in the formation of paramagnetic species coupled with molecular oxygen activation generating the superoxide radical anion or singlet oxygen, evidenced by electron paramagnetic resonance spectroscopy. The cytotoxic/photocytotoxic impact of selenadiazoloquinolones on murine and human cancer cell lines was demonstrated using the derivative SeQ5 (with R(7)=COCH(3)).

Keywords: Nucleophilic vinylic substitution (S N V) mechanism / Enol ethers / Alkoxymethylene compounds / Quinoxalines / Molecular calculationsTreatment of 6-aminoquinoxaline with β,β-diactivated alkoxymethylene derivatives gave the corresponding N-(quinoxalin-6-yl)enamines. A variant of the S N V reaction mechanism was proposed for substitution of the alkoxymethylene compounds, on the basis of the structures of the precursor

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a 7-R-9-ethyl-6,9-dihydro-6-oxo- [1,2,5]selenadiazolo [3,4-h]quinolines (R = H, COOC 2 H 5 , COOCH 3 , COOH and COCH 3 , E1h-E5h) and 6-ethyl-6,9-dihydro-9-oxo-[1,2,5]selenadiazolo[3,4-f]quinoline (E1f) were characterized by UV/vis, FT-IR and fluorescence spectroscopy. The electronic absorption spectra of the derivatives E1h-E3h and E5h in the aprotic solvents dimethylsulfoxide (DMSO) and acetonitrile (ACN) reveal low-energy absorption maxima with l max > 400 > nm, shifted hypsochromically in water. In DMSO, N-ethyl selenadiazoloquinolones behave as strong fluorescent agents (l em ≥ 550 nm) with the exception of the carboxylic acid derivative E4h which shows only poor emission. Photoinduced reactions of N-ethyl selenadiazoloquinolones were investigated by means of electron paramagnetic resonance (EPR) spectroscopy. Photoexcitation of N-ethyl selenadiazoloquinolones in aerated DMSO with either 385 nm or 400 nm wavelengths, monitored by EPR spin trapping technique, results in the generation of superoxide radical anions; under an inert atmosphere, the generation of methyl radicals originating from the solvent predominates. Upon exposure at either 365 nm, 385 nm or 400 nm, aerated ACN solutions of selenadiazoloquinolones in the presence of sterically hindered amines produce nitroxide radicals via a reaction with photogenerated singlet oxygen. The 7-substituted derivatives of 9-ethyl-6,9-dihydro-6-oxo-[1,2,5]selenadiazolo[3,4-h] quinoline behave as photosensitizers activating molecular oxygen upon photoexcitation and possess the sufficient photochemical stability under the given experimental conditions. The cytotoxic effects of non-photoactivated and UVA photoactivated N-ethyl substituted selenadiazoloquinolones on cancer (human HeLa and murine L1210) and non-cancer (NIH-3T3) cell lines were monitored by the MTT test. The derivative E2h demonstrates the highest cytotoxic/photocytotoxic activity on the neoplastic cell lines.

SummaryActivated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products – pyrazoles 5 – were studied with a focus on tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits.