Viktor Milata

Stable radical trianions from reversibly formed sigma-dimers of selenadiazoloquinolones studied by in situ EPR/UV-vis spectroelectrochemistry and quantum chemical calculations.

The redox behavior of the series of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f]quinolines with R(7), R(8) = H, COOC(2)H(5), COOCH(3), COOH, COCH(3), and CN has been studied by in situ EPR and EPR/UV-vis spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigma-dimer (σ-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV-vis cyclovoltammetric experiments. The site of the dimerization in the σ-dimer and the mapping of the unpaired spin density both for radical anions and σ-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.

Fused-ring derivatives of quinoxalines: spectroscopic characterization and photoinduced processes investigated by EPR spin trapping technique.

10-Ethyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline derivatives, synthesized as promising biologically/photobiologically active compounds were characterized by UV/vis, FT-IR and fluorescent spectroscopy. Photoinduced processes of these derivatives were studied by EPR spectroscopy, monitoring in situ the generation of reactive intermediates upon UVA (λmax = 365 nm) irradiation. The formation of reactive oxygen species and further oxygen- and carbon-centered radical intermediates was detected and possible reaction routes were suggested. To quantify the investigated processes, the quantum yields of the superoxide radical anion spin-adduct and 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl generation were determined, reflecting the activation of molecular oxygen by the excited state of the quinoxaline derivative.

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism.

Summary Activated 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.

Conformational, spectroscopic, and molecular dynamics DFT study of precursors for new potential antibacterial fluoroquinolone drugs.

Biological activity, functionality, and synthesis of (fluoro)quinolones is closely related to their precursors (for instance 3-fluoroanilinoethylene derivatives) (i.e., their functional groups, conformational behavior, and/or electronic structure). Herein, the theoretical study of 3-fluoroanilinoethylene derivatives is presented. Impact of substituents (acetyl, methyl ester, and ethyl ester) on the conformational analysis and the spectral behavior is investigated. The B3LYP/6-311++G** computational protocol is utilized. It is found that the intramolecular hydrogen bond N-H···O is responsible for the energetic preference of anti (a) conformer (anti position of 3-fluoroanilino group with respect to the C═C double bond). The Boltzmann ratios of the conformers are related to the differences of the particular dipole moments and/or their dependence on the solvent polarity. The studied acetyl, ethyl ester, and methyl ester substituted fluoroquinolone precursors prefer in the solvent either EZa, ZZa, or both conformers equally, respectively. In order to understand the degree of freedom of rotation of the trans ethyl ester group, B3LYP/6-311G** molecular dynamic simulations were carried out. Vibrational frequencies, electron transitions, as well as NMR spectra are analyzed with respect to conformational analysis, including the effect of the substituent. X-ray structures of the precursors are presented and compared with the results of the conformational analysis.

Theoretical and Experimental NMR Study of a Series of Five Nitrobenzene-1,2-Diamines

ABSTRACT 1H-, 13C-, and 15N-NMR studies of five nitrobenzene-1,2-diamines in solution and solid state have been achieved and the experimental chemical shifts and coupling constants agree with the theoretical values obtained at the B3LYP/6-311 + +G(dp) computational level using the geometries fully optimized with the hybrid HF/DFT B3LYP method and the 6-31G(d) basis set. The GIAO approximation has been used to calculate the absolute shieldings. The contribution of the substituents to the 15N chemical shifts of the amino groups could be quantified using a presence/absence matrix and a multiple regression.

New syntheses of 5,6- and 7,8-diaminoquinolines.

Summary The synthesis of 5,6- and 7,8-diaminoquinoline derivatives starting from angularly annelated selenadiazoloquinolones is presented. Simple chlorination of the pyridone ring followed by reductive deselenation of the 1,2,5-selenadiazole ring afforded novel 4-chloro-o-diaminoquinolines. Dechlorination of 4-chloro-7,8-diaminoquinoline gave 7,8-diaminoquinoline hydrochloride which was successfully employed as starting material in the synthesis of condensed nitrogen heterocycles.

Synthesis and antifungal efficacy of 1,3,5-triazines

Synthesis and antifungal efficacy of 1,3,5-triazines 1,3,5-triazines with tree identical groups: benzotriazol-1/2-yl, imidazol-1-yl, pyrazolyl-1-yl, 3,5-dimethylpyrazolyl-1-yl, 4,5-diphenylimidazol-1-yl, benzimidazolyl-1-yl, 2-methylbenzimidazolyl-1-yl, or 2-phenylbenzimidazolyl-1-yl were synthesised. Their biological activity against wood-destroying fungi Serpula lacrymans, Coniophora puteana and Trametes versicolor was tested by the impregnated filter paper method. S. lacrymans occurred as the most sensitive fungus (from the 3 fungi) in the presence of triazines. Triazines having three imidazol or three 4,5-diphenylimidazol groups were a slightly more effective than others. However, their efficacy in comparison with the commercial fungicides Tebuconazole and IPBC was insufficient.

Radical anions of quinoxalines (an in situ electron paramagnetic resonance spectroelectrochemical and theoretical study)

The cathodic reduction of 10-ethyl-7H,10H-pyrido[2,3-f]quinoxalin-7-one (1a) and ethyl 10-ethyl-7-oxo-7H,10H-pyrido[2,3-f]quinoxaline-8-carboxylate (2a), as well as their 2,3-R,R-substituted derivatives (R = CH3 or C6H5), represents a reversible one-electron process coupled with the generation of corresponding radical monoanions as evidenced by in situ electron paramagnetic resonance (EPR)/UV–vis-near-infrared (NIR) cyclovoltammetric experiments in N,N-dimethylformamide. The detected radical monoanions are characterized by electronic absorption bands in the vis-NIR regions, and their EPR spectra show a dominant interaction of the unpaired electron with the nitrogen and hydrogen nuclei of the pyrazine ring. The reduction behavior of 10-ethyl-7-oxo-7H,10H-pyrido[2,3-f]quinoxaline-8-carboxylic acid (3a) and its 2,3-dimethyl or 2,3-diphenyl derivatives is more complex, revealing an irreversible first reduction peak, followed by a second reversible reduction step. Based on the results of the in situ EPR/UV–vis-NIR spectroelectrochemical measurements for quinoxaline carboxylic acids, the first irreversible reduction peak was assigned to a reduction process on the pyridone ring, followed by a second reversible reduction process on the π-electron deficient pyrazine moiety, generating the radical monoanions detected by EPR spectroscopy.

Preparation and NMR properties of derivatives of arylamino-methylidene malonic acid and pentane-2,4-dione

Abstract A set of 22 anilinomethylidene derivatives (13 new ones) of di(m)ethyl malonate, malononitrile and pentane-2,4-dione with various substituents in position 4- and 3-, respectively were prepared to study the characteristic influence of these substituents and solvents on chemical shifts in 13C NMR spectra and like reference compounds for kinetic measurements.

Preparation and spectral properties of products of the reaction of N,N-dimethylhydrazine with selected enolethers/alkoxymethylene systems

Abstract There were studied series of activated enolethers (alkoxymethylene derivatives of malonic or 3-oxobutanoic acids derivatives of general formula R-O-CH=C(R1, R2) where R1 = R2/ R1 ≠ R2 (R1, R2 = CO2CH3, CO2CH2CH3, COCH3, CN) with N,N-dimethylhydrazine. They smoothly provided products of nucleophilic vinylic substitution reaction - dimethyl hydrazinyl methylene derivatives of malonic or 3-oxobutanoic acids (enhydrazines), respectively from 20 minutes to 2 hours at room temperature.