Half‐sandwich Ru (II) complexes containing (N,O) Schiff base ligands: Catalysts for base‐free transfer hydrogenation of ketones

Two new half‐sandwich Ru (II)(p‐cymene) complexes ( 1 and 2 ) containing dopamine‐based (N, O) Schiff base ligands ( L ¹ H and L ² H ) were synthesized and characterized by FT‐IR, UV–Visible and ¹H & ¹³C NMR spectral techniques, and elemental analyses. The spectroscopic and analytical data revealed monobasic bidentate coordination of the ligands with Ru ion. The molecular structures of L ¹ H , L ² H and 2 were further confirmed by single crystal X‐ray diffraction study. Complexes 1 and 2  have been employed as catalysts in the transfer hydrogenation of ketones using 2‐propanol as a hydrogen source at 85 °C under base‐free condition. Good to the excellent yield of secondary alcohols, gram scale synthesis, and high TON and TOF made this catalytic system interesting.     

Synthesis of Peptide Cysteine Dimedone Using Fmoc-Cys(Dmd)-OH: Glutathione Cysteine Dimedone as a Probe in Investigating the Sulfenic Acid Mediated Oxidation of Glutathione

Dimedone is the most widely used chemical probe for detection of cysteine sulfenic acid in peptides and proteins. The reaction of dimedone with cysteine sulfenic acid results in the formation of unique cysteine dimedone motif containing thioether bridge. Based on the structure of cysteine dimedone residue in polypeptide, a new building block of Fmoc-Cys(Dmd)-OH was developed for solid phase synthesis of peptide cysteine dimedone. Mass spectrometric sequencing of synthetic peptides have confirmed successful incorporation of cysteine dimedone in peptide chain using HBTU/HOBt as a coupling agent. The new method permits synthesis of peptides containing both cysteine thiol and cysteine dimedone in the same sequence which was difficult to achieve by conventional methods. The synthetic peptide of glutathione cysteine dimedone was used as a standard in probing the air-mediated oxidation of thiol to disulfide form of glutathione. The co-elution of standard peptide and reaction mixture of oxidation of glutathione in presence of dimedone using RP-HPLC have confirmed the formation of glutathione cysteine sulfenic as an intermediate in the air-mediated oxidation of glutathione. The synthetic peptides of cysteine dimedone may find application in the field of redox proteomics and generation of antibodies against modified cysteine residue.     

A kinetic and mechanistic study on the oxidation of L-cystine by alkaline diperiodatocuprate(III): A free radical intervention

The kinetics of oxidation of L-cystine (L-CYS) by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol/1 was studied spectrophotometrically at 298 K. The reaction between DPC and L-cystine in alkaline medium exhibits 1: 4 stoichiometry (L-cystine: DPC = 1: 4). The reaction is of first order in [DPC] and has less than unit order in [L-CYS] and [alkali], negative fractional order in [periodate] and intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate(III)-L-ystine complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities were also determined.     

Voltammetric oxidation and determination of cinnarizine at glassy carbon electrode modified with multi-walled carbon nanotubes

We discovered a novel method to prepare a protein-based hydrogel, that is, a “Three-Dimensional Nanostructured Protein Hydrogel (3D NPH)”, which is composed of protein–polymer hybrid nanoparticles. In this study, we propose a novel protein microarray whose 3D NPH spots were prepared by dispensing a small volume of the solution of protein–polymer mixture on a substrate. The dispensed solution had a short time for cross-linking before its drying-up and the resulting 3D NPH had loosely cross-linked, thin spongy structure. Therefore, the reaction ratio between ligands and analytes was drastically improved in this system compared with the large volume system for Surface Plasmon Resonance (SPR) protein microarray.     

Mechanistic investigation on the oxidation of ampicillin drug by diperiodatoargentate (III) in aqueous alkaline medium

The kinetics of oxidation of antibiotic drug, ampicillin (AMP) by diperiodatoargentate (III) (DPA) in alkaline medium at a constant ionic strength of 0.25‐mol dm^?3 was studied spectrophotometrically. The reaction between DPA and AMP in alkaline medium exhibits 1:2 stoichiometry (AMP:DPA). The reaction is of first order in [DPA] and has less than unit order in both [AMP] and [alkali]. Added periodate retarded the rate of reaction and intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a DPA–AMP complex, which decomposes slowly in a rate‐determining step followed by other fast steps to give the products. The main products were identified by spot test, IR and NMR studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined. Copyright © 2008 John Wiley & Sons, Ltd.     

Imino Diels-Alder Reactions: Efficient Synthesis of Pyrano- and Furanoquinolines Catalyzed by 4-Nitrophthalic Acid

Summary. 4-Nitrophthalic acid was found to be an effective catalyst for the imino Diels-Alder reaction of N-benzylideneanilines with 3,4-dihydro-2H-pyran and 2,3-dihydrofuran to afford pyrano- and furanoquinolines in good yields. It was also found that aryl amines react smoothly with 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under the same condition to afford the corresponding pyrano- and furanoquinolines in high yields. This catalyst is inexpensive, easily available, water soluble, and stable to aqueous reaction conditions.     

Design and Synthesis of Novel C4‐Linked Substituted 2H‐Chromen‐2‐one‐hypoxanthine Hybrids as Potential Antimicrobial Agents: An Approach to Molecular Docking Studies

We present here design and synthesis of very efficient, high‐yielded and simple approach of a series of C₄‐linked coumarin–hypoxanthine pharmacophores 1 ( a–j ) with moderate to excellent in vitro antimicrobial activity. According to earlier studies, potential modification at C₄‐position of coumarin ring provided excellent bioactive molecules. All the titled compounds were characterized by spectroscopic and elemental analyses. Titled compounds have been developed via systematic tuning of coumarin ring substitutions, which are prepared from the well‐known Pechmann condensation reaction. The addition of a pendent nucleobase in hypoxanthine group improved the in vitro antimicrobial activity. Computational studies were also mimicking the potent biomolecules. A good pharmacokinetic profile is suggested by theoretical calculation of absorption, distribution, metabolism, and excretion properties. Therefore, synthesis of these titled compounds provided an insight towards better antimicrobial agents.     

A facile and expeditious approach for the synthesis of 2-azetidinone derivatives via a multicomponent reaction

Abstract  

New organic reactions allow chemical transformations which were previously unknown. Therefore, new reactions are important contributions to progress in the field of organic synthesis. Herein, we are reporting a simple, one-pot, efficient three-component synthesis of novel 3-chloro-4-[4-(2-oxo-2H-chromen-4-ylmethoxy)phenyl]-1-phenylazetidin-2-one derivatives using 4-(2-oxo-2H-chromen-4-ylmethoxy)benzaldehydes, anilines, and chloroacetyl chloride in the presence of triethyl amine as a catalyst under different conditions. Taking into account environmental and economic considerations, the protocol presented here has the merits of simple operation, convenient work-up, being environmentally benign, and providing good yields. The synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis.     

Dielectric relaxation and related studies of 4-ethylphenol-methanol mixtures using time domain reflectometry

The dielectric relaxation studies of 4-ethylphenol-methanol mixtures have been carried out at various temperatures ranging from 10°C to 40°C using time domain reflectometry in the frequency range 10 MHz to 10 GHz. The relaxation mechanism in these systems is explained by Cole-Davidson model. The excess dielectric parameters, Kirkwood correlation factor and activation energy have been calculated and discussed with respect to molecular arrangements, and microdynamics of the binary mixture composed of both the associative type of liquids.