A practical access to novel 2-amino-5-arylidene-1,3-thiazol-4(5H)-ones via sulfur/nitrogen displacement under solvent-free microwave irradiation

A new effective approach to the synthesis of a small library of 2-amino-5-arylidene-1,3-thiazol-4(5H)-ones was reported using solvent-free reaction conditions under microwave irradiation. In the first step, rhodanines were subjected to Knoevenagel condensation with aryl aldimines according to a facile one-pot protocol. Then the (5Z)-5-arylidene rhodanine derivatives were transformed directly into the corresponding 2-amino-1,3-thiazol-4(5H)-ones by sulfur/nitrogen displacement reaction under microwaves with retention of configuration and good overall yields.     

An expeditious,environment-friendly,and microwave-assisted synthesis of 5-isatinylidenerhodanine derivatives

A series of nine 5-arylidenerhodanine derivatives was prepared in good yields and purity without the use of a solvent or catalyst under microwave-assisted condensation with some substituted isatins. All 5-arylidenerhodanines were evaluated as possible inhibitors of the CK1α/β, CDK5/p25, and GSK-3α/β kinases. None of them showed substantive inhibitory activity against these kinases when evaluated at the concentration of 10 μM.     

A theoretical study of medium effects on the structure of the glycine analogue aminomethylphosphonic acid

alpha-Aminophosphonic acids are analogues of natural alpha-aminoacids and very promising agents for use in various pharmaceutical applications. However, in contrast to the numerous theoretical investigations on the structure of natural alpha-aminoacids, only very few studies on alpha-aminophosphonic acids have been performed. In the present work, we report a detailed investigation of the simplest compound, the glycine analogue aminomethylphosphonic acid (AMPA), by means of quantum mechanical calculations at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) and MP2/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) levels. We focus on the structure of the neutral species looking at the evolution of non-ionized and ionized forms from gas phase to non-polar solvents and aqueous media. Continuum and discrete-continuum solvent models have been employed to account for the effects of the environment. The discussion is centered on: (1) the geometry and relative stability of possible conformers in gas phase and aqueous solution, (2) the free energy of tautomerization in different media, (3) the role of hydrogen bonds in liquid water, and (4) the free energy of transfer from water to a hydrophobic solvent such as cyclohexane. Systematic comparison between AMPA and Gly is performed. Though both systems exhibit many similarities, some important differences have also been found that may be explained, at least in part, by the higher acidity of phosphonic acids compared to carboxylic acids. In particular, in solvents lacking hydrogen-bond formation capability, Gly derivatives should mainly exist as non-ionized molecules while the equivalent AMPA derivatives should adopt a zwitterionic structure in media with dielectric constant above 10. This might have significant environmental or biological consequences that will need to be addressed.     

One‐pot synthesis of new 3‐substituted coumarins by tandem reactions

The synthesis of new 3‐substituted coumarins appended to imidazolium, pyridinium, 3‐dimethylamino pyridinium, 3‐chloro pyridinium and 3‐bromo pyridinium salts is reported. These salts were prepared by tandem reactions, followed by quantitative anionic metathesis. The structure of these new 3‐substituted coumarins was established by NMR (¹H, ¹³C) and high‐resolution mass spectrometry.     

Stereoselective synthesis of (2E) 3‐amino‐2‐(1H‐benzimidazol‐2‐yl)acrylate and symmetric bisacrylates by transamination reactions

A range of various amines 2(a–i) was tested in transamination reactions using ethyl 2‐(1H‐benzimidazol‐2‐yl)‐3‐dimethylamino‐acrylate 1a. The (E)‐s‐cis/trans conformation of some representative products 4 was analyzed by ¹H and ¹³C NMR spectra. The C‐2/C‐3 bond of the compounds 3(a–i) is strongly polarized by a push‐pull effect. In the same manner, reactions of ethyl 2‐(benzoxazol‐2‐yl)‐3‐dimethylamino‐acrylate 1c with 1,4‐diaminobenzene 2i, ethylenediamine 2i, and 1,5‐diaminomaphthalene 2k have been investigated and gave directly the corresponding symmetric bis‐acrylates 4(a–c) in good yields. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 446–454, 1999     

Electrical conductivity and complex impedance analysis of 20% Ti-doped La0.7Sr0.3MnO3 perovskite

The electrical conductance of 20% Ti-doped La_0.7Sr_0.3MnO₃ (LSMO) was measured using admittance spectroscopy over a wide temperature and frequency ranges. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. Activation energy inferred from conductance spectrum matches very well with the value estimated from relaxation time indicating that relaxation process and conductivity have the same origin. The electrical conductance of La_0.7Sr_0.3Mn_0.8Ti_0.2O₃ is found to be dependent on temperature and frequency. Also, the electronic conduction appears to be dominated by thermally activated hopping of small polaron (SPH) at high temperatures and by variable range hopping (VRH) at low temperatures.     

Influence of physical parameters and lubricants on the compaction properties of granulated and non-granulated cross-linked high amylose starch

Cross-linked high amylose starch (CLA) is a pharmaceutical excipient used in direct compression for the preparation of controlled release tablets and implants. In this work the compression properties of CLA in bulk and granulated forms (without binder) were evaluated for the first time. Tablets were prepared on an instrumented single punch machine. The flow properties and the compression characteristics (compressibility, densification behavior, work of compression) of the materials as well as the mechanical strength of the finished compacts (compactibility) were systematically examined. Wet granulation was found to improve the flowability and the compressibility of CLA but concomitantly reduced its compactibility. It was demonstrated that CLA was a plastically deforming material with a plasticity index and a yield pressure value comparable to those of pregelatinized starch. The compactibility of granulated CLA was independent of particle size in the range of 75 to 500 microm, but slightly decreased when the percentage of the fine particles (<75 microm) in the bulk powder was increased. Water and colloidal silicone dioxide facilitated the consolidation of CLA, while magnesium stearate had an opposite effect on the tablet crushing force.     

Effect of synthesis duration on the morphological and structural modification of the sea urchin-nanostructured γ-MnO2 and study of its electrochemical reactivity in alkaline medium

Single-crystalline nanorods and sea urchin-like morphology of the γ-MnO₂ nanostructures were successfully synthesized by hydrothermal method at different synthesis durations. The as-synthesized products were characterized by the techniques X-ray powder diffraction (XRD), field emission gun-scanning electron microscope (FEG-SEM) coupled with energy-dispersive X-ray elemental analysis (EDX), transmission electron microscope (TEM), isotherms of N₂ adsorption/desorption and BET-BJH models. The effect of synthesis duration on the morphology, porous structure, and crystallographic form of MnO₂ powders was studied. The electrochemical reactivity of as-prepared powders was investigated in 1 mol L^?1 KOH by both cyclic voltammetry and impedance spectroscopy by using a micro-cavity electrode. The results show that the best electrochemical reactivity of the MnO₂ powder was obtained with synthesis duration of 24 h.     

Lipschitz behaviour of the Legendre-Fenchel Transform

We give estimates of the modulus of continuity of the Legendre-Fenchel Transform with respect to the Attouch-Wets uniformity. We point out the local Lipschitz behaviour of the conjugacy operation when endowing the set of closed proper convex functions defined on a normed vector space with suitable families of semimetrics.