A Simple Synthesis of Stable Heterocyclic Phosphorus Ylides Derived from NH-Acids

Crystalline phosphorus ylides are obtained in excellent yields from the addition reaction between triphenylphosphine, dimethyl acetylenedicarboxylate and strong NH-acids, such as 2-acetylpyrrole, indole, ethyl 3-indolylglyoxalate and N -benzyl-2-pyrrolylglyoxamate. Dynamic NMR effects are observed in the 1 H NMR spectra of stabilized ylides obtained from 2-acetylpyrrole and indole ( j G p = 67.1 and 68.8 kJmol m 1 respectively) and are attributed to restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group.     

Identification of Persuasive Antiviral Natural Compounds for COVID-19 by Targeting Endoribonuclease NSP15: A Structural-Bioinformatics Approach

SARS-CoV-2 is a positive-stranded RNA virus that bundles its genomic material as messenger-sense RNA in infectious virions and replicates these genomes through RNA intermediates. Several virus-encoded nonstructural proteins play a key role during the viral life cycle. Endoribonuclease NSP15 is vital for the replication and life cycle of the virus, and is thus considered a compelling druggable target. Here, we performed a combination of multiscoring virtual screening and molecular docking of a library of 1624 natural compounds (Nuclei of Bioassays, Ecophysiology and Biosynthesis of Natural Products (NuBBE) database) on the active sites of NSP15 (PDB:6VWW). After sequential high-throughput screening by LibDock and GOLD, docking optimization by CDOCKER, and final scoring by calculating binding energies, top-ranked compounds NuBBE-1970 and NuBBE-242 were further investigated via an indepth molecular-docking and molecular-dynamics simulation of 60 ns, which revealed that the binding of these two compounds with active site residues of NSP15 was sufficiently strong and stable. The findings strongly suggest that further optimization and clinical investigations of these potent compounds may lead to effective SARS-CoV-2 treatment.     

Electron paramagnetic resonance studies on three copper(II) complexes of 3-amino-5-methylisoxazole

EPR studies have been carried out on three copper(II) complexes of 3-amino-5-methylisoxazole(3-AMI), namely(l)Cu(3-AMI)₄Cl₂,(2)Cu(3-AMI)₂(NO₃)₂and(3)Cu(3-AMI)₂Br₂, in polycrystalline, solution and frozen solution forms in order to elucidate the stereochemistry, metal-ligand bond nature and solute-solvent interactions. The magnitude of the spectral parameters obtained from polycrystalline samples are found to represent the approximate local copper(II) environment with the ground state dominated by the d_x²-_y² orbital. The molecular species obtained in pyridine and N,N '-dimethyl formamide (DMF) solutions of Cu(3-AMI)₂(NO₃), and Cu(3-AMI)₂Br₂ are similar to the corresponding species in complexes of isoxazole and its derivatives studied earlier. But, unlike the above two complexes the spectral parameters obtained in the pyridine and DMF solutions of Cu(3-AMI)₄Cl₂ are characteristic of CuN₄ and CuO₄, chromophores respectively with strong metal-ligand σ-bonding. The 4s-character in the ground state is estimated in all the complexes to indicate the axial field strength.     

Kinetics and mechanism of the aminolysis of aryl phenyl chlorothiophosphates with anilines

Kinetic studies of the reactions of aryl phenyl chlorothiophosphates (1) and aryl 4-chlorophenyl chlorothiophosphates (2) with substituted anilines in acetonitrile at 55.0 degrees C are reported. The negative values of the cross-interaction constant rhoXY (rhoXY = -0.22 and -0.50 for 1 and 2, respectively) between substituents in the nucleophile (X) and substrate (Y) indicate that the reactions proceed by concerted SN2 mechanism. The primary kinetic isotope effects (kH/kD = 1.11-1.13 and 1.10-1.46 for 1 and 2, respectively) involving deuterated aniline nucleophiles are obtained. Front- and back-side nucleophilic attack on the substrates is proposed mainly on the basis of the primary kinetic isotope effects. A hydrogen-bonded, four-center-type transition state is suggested for a front-side attack, while the trigonal bipyramidal pentacoordinate transition state is suggested for a back-side attack. The MO theoretical calculations of the model reactions of dimethyl chlorothiophosphate (1') and dimethyl chlorophosphate (3') with ammonia are carried out. Considering the specific solvation effect, the front-side nucleophilic attack can occur competitively with the back-side attack in the reaction of 1'.     

Glass transition phenomena in two-component plastic crystals: study of hexasubstituted benzenes

We have critically examined the relaxation that is known to occur in the crystalline phase of pentachloronitrobenzene (PCNB) and 2,3,4,5,6-pentabromotoluene using dielectric spectroscopy and differential scanning calorimetry (DSC). Within the resolution of our experimental setup, a relaxation process similar to that of the primary (or alpha-) relaxation is found. A slight deviation from Arrhenius behavior is noticed only in the vicinity of the glass transition temperature (T(g)). This deviation and a small steplike change found in the DSC scans at T(g) indicates that the "fragility" of these plastic crystals is rather low. However, in PCNB, the dielectric strength (Deltaepsilon) of the above said alpha-process did not change appreciably with temperature, and, interestingly, a small addition of an impurity such as pentachlorobenzene (PCB) to the molten state of PCNB drastically lowered the dielectric strength and the calorimetric signature of glass transition phenomena in the DSC data at T(g). The room-temperature powder X-ray diffraction measurements in combination with the DSC data in the melting temperature region did not indicate any observable change in the crystalline structure. A residual alpha-process with no significant change in the shape of the dielectric spectrum indicates that the hindrance to the rotational motion of PCNB molecules is caused by the presence of a small number of PCB molecules in the crystalline lattice of PCNB over a certain region. Outside of this region, the original PCNB disordered phase is preserved, which is the origin of the residual alpha-process. With a further increase in PCB concentration, the alpha-process, characteristic of pure PCNB, vanishes, and instead another relaxation develops. This process is explained with the help of a solid-liquid phase diagram of the alpha-process of the plastic phase of 2:1 and 1:2 compound formations, which are stable below 386 +/- 1 and 366 +/- 1 K, respectively.     

Temperature-dependent Brillouin scattering studies of surface acoustic modes in Nd0.5Sr0.5MnO3

Brillouin scattering experiments are carried out to study the surface acoustic waves in Nd_0.5Sr_0.5MnO₃ as a function of temperature in the range of 40-300 K covering the metal-insulator and charge-ordering phase transitions. The surface modes include surface Rayleigh wave, pseudo-surface acoustic wave (PSAW) and high velocity PSAW. The observed softening of the sound velocities for the surface modes below paramagnetic to ferromagnetic transition, T_c is related to the softening of the C₄₄ elastic constant. The subsequent hardening of the sound velocity below the charge ordering transition temperature T_co is attributed to the coupling of the acoustic phonon to the charge ordered state via long range ordering of the strong Jahn-Teller (JT) distortion.     

Recent advances in the synthesis of 1,1-diarylalkanes by transition-metal catalysis

1,1-Diaryl moieties are core structures in a wide range of bioactive and pharmaceutical compounds.Transition-metal catalysis is a convenient approach to accessing these invaluable compounds affording high yields and enantioselectivities.This review summarizes 1,1-diarylalkanes synthesis through transition metal catalysis.Particular focus is given to recent developments,such as reductive cross-electrophile couplings,benzylic C–H bond arylation,transformations involving metal migration,asymmetric hydrogenation of 1,1-diarylalkenes and three-component coupling reactions.     

Titanium (IV) complexes of some tetra‐dentate symmetrical bis‐Schiff bases of 1,6‐hexanediamine: Synthesis,characterization, and in silico prediction of potential inhibitor against coronavirus (SARS‐CoV‐2)

Symmetrical bis‐Schiff bases (LH ₂) have been synthesized by the condensation of 1,6‐hexanediamine (hn) and carbonyl or dicarbonyl. One of the synthesized Schiff bases has been subjected to the molecular docking for the prediction of their potentiality against coronavirus (SARS‐CoV‐2). Molecular docking revealed that tested Schiff base possessed high binding affinity with the receptor protein of SARS CoV‐2 compared with hydroxychloroquine (HCQ). The ADMET analysis showed that ligand is non‐carcinogenic and less toxic than standard HCQ. Schiff bases acting as dibasic tetra‐dentate ligands formed titanium (IV) complexes of the type [TiL(H₂O)₂Cl₂] or [TiL(H₂O)₂]Cl₂ being coordinated through ONNO donor atoms. Ligands and complexes were characterized by the elemental analysis and physicochemical and spectroscopic data including FTIR, ¹H NMR, mass spectra, UV‐Visible spectra, molar conductance, and magnetic measurement. Optimized structures obtained from quantum chemical calculations supported the formation of complexes. Antibacterial, antifungal, and anti‐oxidant activity assessments have been studied for synthesized ligands and complexes.     

A review on lignocellulose/poly (vinyl alcohol) composites: cleaner approaches for greener materials

Cellulose - Lignocellulose (LC) is an abundant resource in nature often neglected, underutilised, and even disposed of with an extra cost. Though extracting cellulose or starch from LC is very...