Eco-friendly and facile synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine in aqueous medium by air oxidation

We report a new environmentally-benign, convenient, and facile methodology for the synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine. The reaction of 2,3-diaminopyridine with substituted aryl aldehydes in water under thermal conditions without the use of any oxidative reagent has been studied. The reaction has yielded 1H-imidazo[4,5-b]pyridine derivatives by an air oxidative cyclocondensation reaction in one step in an excellent yield. Furthermore, a series of compounds were synthesized and characterized by melting point, EI-MS, NMR, and IR tools. For comparison, the reference samples were prepared by the reported method. Utilization of aqueous medium, easy reaction conditions, isolation, and purification make this manipulation very interesting from an economic and environmental perspective.     

Ammonium metavanadate： A novel catalyst for synthesis of 2-substituted benzimidazole derivatives

Ammonium metavanadate (10 tool%) was found to be a useful catalyst for the synthesis of various 2-substituted aryl benzimidazoles. It was used as an oxidizing agent for the condensation of o-pbenylenediamine with different substituted aryl aldehydes at room temperature in ethanol. The method was proved to be simple, convenient and the product was isolated with good yields (79-91%).     

1-Heptanesulfonic acid sodium salt： One pot efficient synthesis of 2-aryl- 1-arylmethyl- 1 H- 1,3-benzo[d]imidazoles

Synthesis of 2-aryl-1-arylmethyl-1H-1,3-benzo[d]imidazoles by the reaction of o-phenylenediamine with substituted aromatic aldehydes in the presence of l-heptanesulfonic acid sodium salt (10 mol%) at room temperature.The reactions were performed in acetonitrile:water (8:2).The method was proved to be eco-friendly,convenient and the products were isolated with good yields (82-90%).     

Validated chiral high-performance liquid chromatography method for a novel anti-methicillin-resistant Staphylococcus aureus fluoroquinolone WCK 771

A sensitive, simple, specific, precise, accurate and rugged method for the assay and determination of enantiomeric purity of S-(-)-9-fluoro-6,7-dihydro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-1H,5H-benzo[i,j]quinolizine-2-carboxylic acid L-arginine salt tetrahydrate (WCK 771) in bulk drug has been developed. The method is RP-HPLC using endcapped C-18 stationary phase and chiral mobile phase. Chirality to the mobile phase was imparted with addition of beta-cyclodextrin. The UV-vis detector was operated at 290 nm. The flow rate of mobile phase was 2 ml/min. The method offers excellent separation of two enantiomers with resolution more than 2 and tailing factor less than 1.5. The method was validated for the assay of WCK 771 and quantification of R-(+)-enantiomer impurity in bulk drug. The calibration curves showed excellent linearity over the concentration range of 0.05-0.15 mg/ml for WCK 771 and 0.5-7.5 microg/ml for R-(+)-enantiomer. The precision (RSD) of the assay was 0.23%. The limit of detection and limit of quantitation of the method for WCK 771 were 0.015 and 0.06 microg/ml, respectively. The limit of detection and limit of quantitation for R-(+)-enantiomer were 0.025 and 0.09 microg/ml, respectively. The average recovery of the R-(+)-enantiomer was 100.5%. Same method was applied for the assay and determination of enantiomeric purity of WCK 771 in the intravenous formulation.     

12/10- and 11/13-mixed helices in alpha/gamma- and beta/gamma-hybrid peptides containing C-linked carbo-gamma-amino acids with alternating alpha- and beta-amino acids

New classes of alpha/gamma- and beta/gamma-hybrid peptides have been synthesized with novel 12/10- and 11/13-mixed helical patterns, respectively. The alpha/gamma-peptides were derived from the dipeptide repeats with alternating arrays of l-Ala and gamma-Caa((l)) (C-linked carbo-gamma-amino acid from d-mannose), which generated a new 12/10-mixed helix, for the first time, without a beta-amino acid. The beta/gamma-peptides made from an alternating arrangement of beta-Caa((x)) (C-linked carbo-beta-amino acid) and gamma-Caa((x)) (C-linked carbo-gamma-amino acid from d-xylose), on the other hand, resulted in an unprecedented 11/13-helix. The secondary structures in these peptides have been ascertained from detailed NMR studies, and CD spectroscopy and molecular dynamics investigations provided additional support for the structures derived.     

Triangular CdS nanostructure: effect of Mn doping on photoluminescence,electron spin resonance,and magneto-optical properties

In this paper, we report synthesis and study of magneto-optic Faraday effect for dilute magnetic semiconductor nanostructure. The colloidal CdS nanocrystals were prepared via hot injection method and successfully doped with Mn²⁺ cations. The synthesized nanoparticles were characterized by using UV–Vis spectroscopy, X-ray diffraction, photoluminescence spectroscopy, transmission electron microscopy, and electron spin resonance spectroscopy. Systematic studies on effect of Mn²⁺ doping on photoluminescence, electron spin resonance, and magneto-optical properties are carried out. UV–Vis spectral analysis confirms blue shift in bandgap of CdS nanoparticles due to quantum confinement effect. The X-ray diffraction study confirms hexagonal wurtzite phase formation of CdS nanoparticles without any impurity phases. TEM analysis confirms uniform particle size, having particle size distribution around 5 nm. As-synthesized undoped CdS shows triangular-shaped nanocrystals with hexagonal structure; however, triangular shape of CdS nanoparticles is not conserved after Mn²⁺ doping. The photoluminescence characteristic spectra of Mn²⁺-doped CdS nanocrystals showed emission band at 660 nm and its intensity was found to increase with increasing Mn²⁺ concentration. Electron spin resonance signal, with six-line hyperfine structure splitting, confirmed doping of Mn²⁺ ions in CdS lattice. Magneto-optic measurements showed linear variation of Faraday rotation with respect to applied magnetic field, indicating paramagnetic behavior of Mn-doped CdS. The highest Verdet constant 24.81 deg/T cm was observed for 2% Mn-doped CdS nanocrystals, which further decreases with increasing Mn²⁺ concentration.

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Graphical abstract Illustration of Magneto-optic Faraday effect using dilute magnetic semiconductors (TEM image of triangular CdS nanoparticles)

     

Copper(II) mediated facile and ultra fast peptide synthesis in methanol

A novel, ultrafast, mild and scalable amide bond formation strategy in methanol using simple thioacids and amines is described. The mechanism suggests that the coupling reactions are initially mediated by CuSO(4)·5H(2)O and subsequently catalyzed by in situ generated copper sulfide. The pure peptides were isolated in satisfactory yields in less than 5 minutes.     

Microwave assisted mild, rapid, solvent-less, and catalyst-free chemoselective N-tert-butyloxycarbonylation of amines

Microwave assisted simple, rapid, solventless, and catalyst-free chemoselective method for the protection of amino group in aromatic, aliphatic, heterocyclic, aralkyl amines, phenyl hydrazine, and amino acid esters in good to excellent isolated yield (83-98%) in short reaction time (2-12 min) has been reported.     

Enantioselective α-benzoyloxylation of ketones promoted by primary amine catalyst

A mixture of 9-amino-(9-deoxy)epi-dihydroquinidine and salicylic acid was able to promote the direct reaction of various cyclohexanones with dibenzoyl peroxide, thus affording the corresponding protected α-hydroxy carbonyl compounds in high yield and enantioselectivity. Interestingly the same catalytic salt was found to be active when 1-indanones derivatives were directly employed in the reaction with dibenzoyl peroxide furnishing chiral 1-oxo-2,3-dihydro-1H-inden-2-yl benzoates in high yields and enantioselectivity. Furthermore their treatment with NaBH(4) gives easy access to the corresponding enantioenriched 1,2-diols in high yields and without any loss of stereoselectivity.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.