Thionated coumarins and quinolones in the light triggered release of a model amino acid: synthesis and photolysis studies

Model amino acid ester conjugates bearing heterocycles with a thiocarbonyl group (thiocoumarins and thioquinolones) were prepared by a thionation reaction of the corresponding carbonyl precursors, with the aim of obtaining conjugates with higher photosensitivity at longer wavelengths. Photolysis studies were carried out under irradiation at different wavelengths in a photochemical reactor (250, 300, 350 and 419 nm), and it was found that the ester bond between the heterocycle and the model amino acid in the thionated analogues cleaved readily with shorter irradiation times than those of the corresponding precursors. Moreover, fast photolysis at 419 nm for thioquinolone ester conjugates (within minutes) was particularly interesting and the fact that some of the reported heterocycles displayed very different irradiation times, may provide the possibility for selective removal of one group in the presence of another photocleavable group. The (quinolin-2-thione-4-yl) methyl group may be considered as a new and very effective addition to the family of photocleavable protecting groups for carboxylic acids.     

Synthesis of [60]fullerene derivatives bearing five-membered heterocyclic wings and an investigation of their photophysical kinetic properties

The preparation, characterization and photophysical properties of six new stable [6,6]-closed fullerene cycloadducts bearing five-membered heterocycles are described. The modified [60]fullerenes are obtained by a simple and rapid synthesis via a Bingel-type reaction with tetrazole and oxadiazole malonate derivatives. The photophysical kinetics of these new fullerene derivatives in toluene solution under ultraviolet illumination (375 nm, UVA) are studied by electron paramagnetic resonance and free-radical spin-trapping using α-phenyl-N-tert-butyl nitrone as a spin-trap. The results are compared with pure [60]fullerene and [6,6]-phenyl C₆₁ butyric acid methyl ester (C₆₀-PCBM). It is concluded that for all six new compounds as well as pure [60]fullerene and PCBM both superoxide and singlet oxygen are produced in the first stages of UVA illumination following the type I and II mechanisms, respectively. In all cases singlet oxygen is produced as the primary dominant species; however, the type I mechanism always occurs in parallel with type II. In the end, the superoxide is self-dismuted into hydroxyl radicals, thus yielding PBN-OH spin adducts (g = 2.007 and a_hf (¹⁴N) = 1.54 mT). The kinetic reaction constants and their efficiencies in the production of reactive oxygen species at 375 nm and per mW of absorbed power are determined. The experimental results are consistent with an autocatalytic reaction model in which the system evolutes under UVA illumination, with superoxide catalyzing the conversion of singlet oxygen into more superoxide.     

An efficient microwave assisted synthesis of N′-aryl/(alkyl)-substituted N-(4-hydroxy-6-phenylpyrimidin-2-yl)guanidines: Scope and limitations

Treatment of N-[(4-hydroxy-6-phenyl)pyrimidin-2-yl]cyanamide with 1° alkyl or arylamines in isopropyl alcohol for only 10 min at 110–120 °C under microwave conditions gave the corresponding N′-alkyl(aryl)guanidine derivatives in excellent yields (65–84%). Isolated yields were greatest when >1.0 equiv. of amines were employed, but excellent results were also obtained when aryl and alkylamines were reacted with a more atom-economical loading (1.0 equiv.; 70% and 72% ave. yields, respectively). Arylamines with either highly electron withdrawing substituents (e.g. CO₂H) or pi-deficient heterocycles (e.g. variously substituted aminopyridines) did not work well under these conditions, and reaction with ureas and/or amino acids did not give detectable products. Work-up was exceedingly simple, and involved simple collection and washing of product on a sintered glass funnel. Products were obtained in analytically pure form and required approximately 1 h to prepare, start to finish.     

Metal or ammonium alginates as Lewis base catalysts for the 1,2-addition of silyl nucleophiles to carbonyl compounds

Several metal (Na⁺, Ca²⁺) or ammonium (n-Bu₄N⁺) derivatives of alginic acid, an abundant bio-polymer obtained from the cell walls of brown algae, were synthesized. Their potential to act as organocatalysts to catalyze the 1,2-addition of various silyl derivatives to carbonyl compounds was evaluated for the first time. Ammonium alginate 1h is able to promote the reaction in modest to good isolated yields (up to 98%) affording access to a large range of substrates (β-cyano alcohols or ester, β-substituted methylacrylate or acrylonitrile, and cyanohydrin) by using only 5 mol % of catalyst.     

Synthesis,characterization and solubility studies of four new highly water soluble 1,3,5-triaza-7-phosphaadamantane (PTA) salts and their gold(I) complexes

The synthesis of new water soluble N-alkylated derivatives of 1,3,5-triaza-7-phosphaadamantane is presented. The compounds were characterized by means of NMR and IR spectroscopy, mass spectrometry, high resolution mass spectrometry, elemental analysis and X-ray diffraction analysis. The water solubility of these compounds was found to be up to an astonishing 1450 g/L. Several different reactions were performed utilizing these highly interesting compounds as starting materials. It was shown that the substitution of the counter ion can be performed easily. Also transformations at the PTA framework were possible, as shown by an ester cleavage example. To prove that the resulting PTA derivatives are competent as ligands for transition metals, gold(I) complexes were synthesized, using Au(tht)Cl as the metal source. The resulting gold(I) complexes were characterized by ¹H NMR and IR spectroscopy, mass and high resolution mass spectrometry or elemental analysis.     

Stereo-controlled synthesis of polypropionate ester derivatives using titanium complexes

A method for the stereocontrolled synthesis of polypropionate ester derivatives by means of titanium complexes is described. The general procedure involves an allyltitanium complex which allows the formation of an enolsilane bearing two stereocentres and an alkoxy titanium complex used in a tandem aldol–Tischtschenko reaction. These two steps are very highly diastereoselective. We present here the study of the tandem aldol–Tischtschenko reaction involving enolsilanes possessing different steric hindrance. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAStitanium complexes / aldol reaction / Tischtschenko reaction / asymmetric induction     

Synthesis and anti-neuroinflammatory activity studies of substituted 3,4-dihydroquinoxalin-2-amine derivatives

We demonstrate the synthesis of multifunctional 3,4-dihydroquinoxalin-2-amine derivatives 4 through a three-component condensation reactions of a substituted o-phenylenediamines 1 (OPDA), diverse ketones 2 and various isocyanides 3 in the presence of a catalytic amount of p-toluenesulfonic acid (PTSA) affording excellent yields (82–96%) and 10 mol % of silica gel supported sulfuric acid with good yields (85–98%) in ethanol at room temperature (2–4 h). We also carried out the anti-neuroinflammatory activity of 3,4-dihydroquinoxalin-2-amine derivatives and some of the compounds exhibited good activity.     

An efficient copper mediated synthetic methodology for benzo[d]isothiazol-3(2H)-ones and related sulfur–nitrogen heterocycles

A copper mediated sulfur–nitrogen coupling reaction for the synthesis of benzo[d]isothiazol-3(2H)-ones and related sulfur–nitrogen heterocycles has been presented, which requires 2-halo-arylamides, sulfur powder, 25–50 mol % of copper iodide/1,10-phenanthroline, and potassium carbonate as base.     

High efficient iron-catalyzed transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source under mild conditions

A highly efficient transfer hydrogenation of quinolines with Hantzsch ester as hydrogen source in the presence of 1 mol% Fe(OTf)₂ under mild conditions has been developed. A series of substituted 1,2,3,4-tetrahydroquinoline derivatives were afforded in excellent yields with good functional group tolerance.     

Synthesis of colloidal silver nanoparticles for printed electronics

Colloidal silver particles were successfully prepared by wet chemical synthesis. The pure single phase of silver was confirmed by X-ray diffraction. Transmission electron microscope categorized that the diameters of particles were 100 and 20 nm, depending on the molecular weight of the PVP stabilizer. A schematic drawing model was used to predict the packing efficiency of 1:1 wt% of two mixtures. The mixture of silver solution was deposited as a thin solid film by a desktop inkjet printer. Scanning electron microscope showed that two different sizes of silver particles give higher densely packed structure than the film of single particle size. When a 0–20 V voltage was applied, the current density reached was 0.10 J/cm², suggesting that the silver film has potential to be applied as a cathode layer in organic light emitting diode (OLED) devices.     

Simultaneous determination of diastereoisomeric and enantiomeric impurities in SSS-octahydroindole-2-carboxylic acid by chiral high-performance liquid chromatography with pre-column derivatization

SSS-Octahydroindole-2-carboxylic acid (SSS-Oic) is a key intermediate used in the synthesis of some angiotensin-converting enzyme (ACE) inhibitors. The separation of diastereoisomers and enantiomers of Oic was performed using a pre-column derivatization chiral HPLC method. Phenyl isothiocyanate (PITC) was used as the derivatization reagent. Three PITC derivatives of Oic stereoisomers were separated on an Ultron ES-OVM chiral column (150 mm × 4.6 mm, 5 μm). Derivatization conditions such as reaction temperature, reaction time and derivatization reagent concentration were investigated. The chromatographic conditions for separation of the three PITC-Oic derivatives were optimized. The method was successfully applied in the diastereoisomeric and enantiomeric purity test of SSS-Oic.     

Sucrose ester micellar-mediated synthesis of Ag nanoparticles and the antibacterial properties

Ag nanoparticles with diameter in the range of 10–25 nm had been synthesized using a simple sucrose ester micellar-mediated method. Ag nanoparticles were formed by adding AgNO₃ solution into the sucrose ester micellar solution containing sodium hydroxide at atmospheric condition after 24 h of aging time. Trace amount of dimethyl formamide (DMF) in the sucrose ester solution served as a reducing agent while NaOH acted as a catalyst. The produced Ag nanoparticles were highly stable in the sucrose ester micellar system as there was no precipitation after 6 months of storage. The as-synthesized Ag nanoparticles were characterized using transmission electron microscope (TEM), X-ray diffractometer (XRD), dynamic light scattering (DLS) and UV–vis spectroscopy (UV–vis). Formation mechanism of Ag nanoparticles in the micellar-mediated synthesis is postulated. The antibacterial properties of the Ag nanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (Gram-positive) and Aeromonas hydrophila (Gram-negative) bacteria. This work provides a simple and “green” method for the synthesis of highly stable Ag nanoparticles in aqueous solution with promising antibacterial property.     

A new promising high temperature lithium battery solid electrolyte

Lithium lanthanoid silicates find importance as a solid electrolyte in high temperature lithium batteries in view of its high ionic conductivity at high temperatures. An first ever attempt is made to synthesis a new high temperature solid electrolyte viz., lithium samarium holmium silicate by sol–gel process and it has been characterized by thermal analysis (TGA–DTA), X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Lithium ion conductivity of 0.8087 × 10⁻⁷ Ω⁻¹ cm⁻¹ at 25 °C was obtained and it increases with increasing temperature. For the first time a highest conductivity of 0.1095 × 10⁻² Ω⁻¹ cm⁻¹ was obtained at 850 °C which is high compared to other high temperature lithium battery solid electrolytes.     

Highly efficient thermal cyclization reactions of alkylidene esters in continuous flow to give aromatic/heteroaromatic derivatives

Intramolecular thermal cyclization and benzannulation reactions of the Gould–Jacobs and Conrad–Limpach types were performed in a designed continuous flow reactor system at temperatures in the range of 300–360 °C and under high pressure conditions (100–160 bar) with very short residence times (0.45–4.5 min) in tetrahydrofuran as a low-boiling point solvent. Substituted heteroaromatic compounds including pyridopyrimidinones and hydroxyquinolines were synthesized in moderate to high yields. Application of the reaction conditions also allows the synthesis of naphthol and biphenyl derivatives. The procedure involves an easy work-up and the non-batchwise preparative synthesis method is suitable for automation.     

Antiviral potential of natural compounds against influenza virus hemagglutinin

Influenza virus of different subtypes H1N1, H2N2, H3N2 and H5N1 cause many human pandemic deaths and threatening the people worldwide. The Hemagglutinin (HA) protein mediates viral attachment to host receptors act as an attractive target. The sixteen natural compounds have been chosen to target the HA protein. Molecular docking studies have been performed to find binding affinity of the compounds. Out of the sixteen, three compounds CI, CII and CIII found to posses a higher binding affinity. The molecular dynamics (MD) simulation has been performed to study the structural, dynamical properties for the nine different complexes CI, CII, CIII bound with H1, H2, H3 proteins and the results were compared. The molecular mechanics Poission-Boltzmann surface area (MM-PBSA) method is used to compare the binding free energy, its different energy components and per residue binding contribution. The H1 subtype shows higher binding preference for all the curcumin derivatives than H2 and H3. The binding capability of protein subtypes with curcumin derivatives and the binding affinity of curcumin compounds are in the order H1 > H2 > H3 and CI > CII > CIII respectively. The two -O-CH3- groups present in the CI compound help to have strong binding with HA protein than CII and CIII. The van der Waals interaction energy plays a significant role for binding in all the complexes. The hydrogen bonding interactions were monitored throughout the MD simulation. The conserved region (153–155) and the helix region (193–194) of H1, H2, H3 protein subtypes are found to possess higher binding susceptibility for binding of the curcumin derivatives.     

Rapid synthesis of cross-bridged cyclam chelators for copper(II) complex formation

Copper(II) complexes of 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (cross-bridged cyclam) derived chelators show high kinetic stability relative to less rigid non-bridged azamacrocyclic chelators and have applications as radiopharmaceuticals in PET imaging. Rapid synthesis of two novel bis-benzyl cross-bridged cyclam derivatives was achieved in 24 h compared to the typical synthesis times, between 14 and 30 days. The X-ray crystal structures are reported for the copper(II) complexes with 1,3-dibromobenzyl and tolyl derivatives revealing different ligand coordination environments. Both structures show tetradentate coordination of the tetraazamacrocycle with axial elongation along the N–Cu–N axis for the 1,3-dibromobenzyl derivative (Cu–N distances: axial av. 2.48(8) Å, equatorial av. 2.081(7) Å).     

Thermochemical data for n-alkylmonoamines functionalization into lamellar silicate Al-kanemite

Al-kanemite was synthesized by using inorganic salts as a source for silicon and aluminum in the hydrothermal synthesis of the material. The resulting solid was used as hosts for functionalization of polar n-alkylamine molecules of the general formula H₃C(CH₂)_n?NH₂ (n = 1 to 5) in aqueous solution. The compound was calorimetrically titrated with amine in 1,2-dichloroethane, requiring three independent operations: (i) titration of matrix with amine, (ii) matrix salvation, and (iii) dilution of the amine solution. From those thermal effects the variation in enthalpy was calculated as: (?6.81, ?7.76, ?8.97, ?9.94, and ?11.83) kJ · mol^?1, for n = 1 to 5, respectively. The exothermic enthalpy values reflected a favorable energetic process of amine-host functionalization in 1,2-dichloroethane. The original and modified Al-kanemite samples were characterized by elemental analysis, scanning electron microscopic (SEM), and nuclear magnetic nuclei of silicon-29 and carbon-13. The negative Gibbs free energy results supported the spontaneity of all these functionalization reactions. The positive favorable entropic values, as carbon chain size increased, are in agreement with the free solvent molecules in the solution, as the amines are progressively bonded to the crystalline inorganic matrix at the solid/liquid interface.     

Pyridine-containing chiral macrocycles for the enantioselective recognition of amino acid derivatives and their molecular dynamics simulations

Two novel C₂-symmetric optically active pyridine-15-crown-5 type ligands containing lipophilic chains at the stereogenic centres, macrocycles 5 and 6, were prepared from (S)-1,2-propanediol and (S)-3-aryloxy-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These novel macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K values of up to 1363.5 M^?1, ΔG^o of up to 17.86 kJ mol^?1 and a selectivity ratio of 80:20) by ¹H NMR titration method. These macrocyclic host exhibited enantioselective binding towards the l-enantiomer of phenylalanine methyl ester hydrochloride with K_L/K_D up to 8.57 in CDCl₃ containing 0.25% CD₃OD. Experimental results have been detailed with molecular dynamic calculations at atomic level concerning the molecular recognition and discrimination properties of a chiral pyridino-15-crown-5. The binding free energies were calculated as ～?25 kJ mol^?1. The results indicated that the host binds and discriminates valine salts better than phenylalanine salts. The molecular dynamics, MM/PBSA calculations are consistent with the ¹H NMR results.     

Solid-state synthesis of monazite-type compounds LnPO4 (Ln = La to Gd)

This work is devoted to the synthesis of monazite-type compounds LnPO₄ (with Ln = La, Ce, Pr, Nd, Sm, Eu and Gd) by solid–solid reaction between a lanthanide oxide and a phosphate precursor NH₄H₂PO₄. Starting mixtures and resulting powders were characterized by coupling different techniques, in particular thermal analysis, X-ray diffraction and MAS ³¹P NMR. Results are presented according to the valence state of the lanthanide element in its oxide form. The intermediate chemical reactions occurring during the firing of starting reagents are described for the first time in the case of monazite with one or several cations. It has been highlighted that the solid-state route is an efficient way in order to obtain very pure and very well crystallized monazite powder. Optimum synthesis conditions are 1350 °C–2 h. The synthesis of monazite powders containing several lanthanides appears to be more difficult, because all the lanthanides do not react at the same temperature, leading to the formation of heterogeneous powders.