Electronic and steric substituent effects on the fluorescence emission of 2-pyrazoline derivatives.

A series of substituted 2-pyrazolines were synthesized, and the steric and electronic effects of substituents on the C - and C -positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro-conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro-conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings.

Photooxidation of 2,3-dihydroquinazolin-4(1H)-ones: retention or elimination of 2-substitution.

A series of mono and disubstituted 2,3-dihydroquinazolin-4(1H)-ones (DHQZs) were synthesized and the electronic and steric effects of the C- and N-substitutions on the retention or elimination of the C-substitution by exposing them to the ultraviolet light were investigated. Electron transfer from photo-excited dihydroquinazolinones to chloroform solvent is proposed, in which both lone pairs on the N- and N-atoms can be involved in this process. The extent of the N- and N-atoms contributions in this electron-transfer process and also the retention or elimination of the C-substitutions are dependent on the nature and steric hindrance of both C- and N-substitutions.

Cyclic Voltammetric Study of 3,5-Diaryl-1-phenyl-2-pyrazolines.

Cyclic voltammetry is used to derive HOMO energies of the 1-phenyl-2-pyrazolines containing electron-donating or electron-withdrawing substituted phenyl rings and or naphthalenyl substitution on the C- or C-positions of the heterocyclic ring to investigate the steric and electronic effects of the aryl substitutions and the type of aryl system on their electrochemical behaviors. The optical HOMO-LUMO gaps needed for the calculation of LUMO (excited state) energies of these compounds are obtained from their UV-vis spectra. Results show that the substitution on the C-aryl ring has significant effect via its π-donor/acceptor ability, compared to the σ-donor/acceptor ability of the C-aryl ring, on the CV oxidation peak and onset potentials.

Thermal electron-transfer-induced oxidation of 2-pyrazolines.

Various 3,5-diaryl-1-phenyl-2-pyrazolines were synthesized, and their thermal oxidation to their corresponding 2-pyrazoles was investigated using tetrabutylammonium peroxydisulfate in acetonitrile solution. Compared to the reported oxidative methods, this oxidizing agent provides a clean and non-expensive oxidative reaction in a short reaction time. Based on the proposed reaction mechanism, the extent of co-planarity of the C-aryl ring toward C=N double bond of the heterocyclic ring affects the electron-donating ability of the heterocyclic ring and decreases the time of oxidative reaction.

Synthesis, Molecular Modelling and Biological Studies of 3-hydroxypyrane- 4-one and 3-hydroxy-pyridine-4-one Derivatives as HIV-1 Integrase Inhibitors.

Background: Despite the progress in the discovery of antiretroviral compounds for treating HIV-1 infection by targeting HIV integrase (IN), a promising and well-known drug target against HIV-1, there is a growing need to increase the armamentarium against HIV, for avoiding the drug resistance issue.

Objective: To develop novel HIV-1 IN inhibitors, a series of 3-hydroxy-pyrane-4-one (HP) and 3- hydroxy-pyridine-4-one (HPO) derivatives have been rationally designed and synthesized.

Methods: To provide a significant characterization of the novel compounds, in-depth computational analysis was performed using a novel HIV-1 IN/DNA binary 3D-model for investigating the binding mode of the newly conceived molecules in complex with IN.

Design, Synthesis, and Anti-HIV-1 Evaluation of a Novel Series of 1,2,3,4-Tetrahydropyrimidine-5-Carboxylic Acid Derivatives.

A series of tetrahydropyrimidine derivatives (2a - 2l) were designed, synthesized, and screened for anti-HIV-1 properties based on the structures of HIV-1 gp41 binding site inhibitors, NB-2 and NB-64. A computational study was performed to predict the pharmacodynamics, pharmacokinetics, and drug-likeness features of the studied molecules. Docking studies revealed that the carboxylic acid group in the molecules forms salt bridges with either Lys574 or Arg579.

Computational and spectroscopic studies of a new Schiff base 3-hydroxy-4-methoxybenzylidene(2-hydroxyphenyl)amine and molecular structure of its corresponding zwitterionic form.

Computational and spectroscopic properties of a novel Schiff base compound, 3-hydroxy-4-methoxybenzylidene(2-hydroxyphenyl)amine were studied. The crystal structures of the title compound and its corresponding zwitterionic form were analyzed by X-ray diffraction. The presence of N-H, C-O and C=N stretching vibrations in IR spectrum strongly suggest that the title compound has zwitterionic form in the solid state.

Voltammetric oxidation of 2-oxo-1,2,3,4-tetrahydropyrimidin-5-carboxamides: substituent effects.

Electrochemical oxidation of a series of 20 substituted 2-oxo-1,2,3,4-tetrahydropyrimidin-5-carboxamides (THPMs) in acetonitrile has been studied using voltammetric methods at a glassy carbon electrode to investigate the influence of the substituents on the 4- and 5-positions of the heterocyclic ring. Analysis of the results shows that the electronic nature and steric hindrance of the substituents, especially their orientations toward the heterocyclic ring, determine their effects on the oxidation potential. Analysis of the computational results obtained at the DFT-B3LYP/6-31++G** level of theory suggests a mechanism in which the first electron removal occurs from either the N(1) of the heterocyclic ring or N(17) of the amide substitution.

Ultrasound assisted dehydrogenation of 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides.

Dehydrogenation of various 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides (THPMs) to 2-oxo-1,2-dihydropyrimidine-5-carboxamides (DHPMs) using tetrabutylammonium peroxydisulfate (TBAPS) as an efficient oxidizing agent under thermal and sono-thermal conditions has been investigated. In contrast to the thermal reaction, a decrease of the amount of oxidant and an increase of the rate of reaction are observed by simultaneously applying heat and ultrasound. The nature of both C-4 and C-5 substituents on the heterocyclic ring influences the rate of reaction under both conditions.

Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones.

In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogenation of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-thermal conditions were investigated. Whereas the effect of the nature of 4-substituent influences the rate of reaction, the application of sonic waves decreases drastically the time of thermal reaction.

Synthesis and antitubercular activity of novel 4-substituted imidazolyl-2,6-dimethyl-N3,N5-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides.

A series of 4-substituted imidazolyl-2,6-dimethyl-N(3),N(5)-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides were prepared. They were screened as antitubercular agents against Mycobacterium tuberculosis H(37)Rv. Minimum inhibitory concentrations (MICs) were determined using agar proportion method.

Sono-thermal oxidation of dihydropyrimidinones.

Combination of ultrasound and heat has been used for the oxidation of some ethyl 3,4-dihydropyrimidin-2(1H)-one-5-carboxylates to their corresponding ethyl pyrimidin-2(1H)-one-5-carboxylates by using potassium peroxydisulfate in aqueous acetonitrile. An ultrasonic probe of 24 kHz frequency has been used for this study. Whereas the use of ultrasound increases the rate of reactions compared with reactions at reflux conditions, the nature of 4-substituent on the dihydropyrimidinone ring affects also the rate of reaction.

Ultrasound-assisted thiocyanation of aromatic and heteroaromatic compounds using ammonium thiocyanate and DDQ.

Thiocyanation of various aromatic and heteroaromatic compounds has been achieved in the presence of ammonium thiocyanate (NH(4)SCN) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in methanol solution under ultrasound irradiation. An ultrasonic probe of 24 kHz frequency has been used for this study. Whereas the use of ultrasound increases the rate of reactions compared with reactions at reflux conditions, the electron-donor ability of aromatic nucleus enhances also the rate of reaction.

Ultrasound-assisted photochemical oxidation of unsymmetrically substituted 1,4-dihydropyridines.

The combination of ultrasound and photochemistry has been used for the oxidation of unsymmetrical 1,4-dihydropyridines to the pyridine derivatives. An ultrasonic probe of 24 kHz frequency and a Hg-lamp of 100 W have been used for this study. The effect of parameters such as ultrasonic intensity, the presence of oxygen and argon atmospheres and also the separate usage of one of these irradiation sources have been studied.

Photosonochemical catalytic ring opening of alpha-epoxyketones.

The combination of ultrasound and photochemical methods has been used for the catalytic ring opening of alpha-epoxyketones by 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT) as photocatalyst in methanol. Sonication of these compounds in the presence of NBTPT did not result in the opening of epoxide ring, but the use of ultrasound increased the rate of photoreaction.

Solid state photochemistry of 1,4-dihydropyridines.

Photochemical behavior of some 1,4-dihydropyridines has been investigated in the solid state. Whereas upon irradiation of 1,4-dihydropyridines in solution phase, their photo-oxidation and formation of pyridine derivatives have been observed, irradiation of these compounds in the solid state decreases their light sensitivity. In many cases photo-oxidation has been observed only in very low yields.