- Half-Sandwich (η6-Benzene)Ruthenium(II) Complex of Picolyl Functionalized N-Heterocyclic Carbene as an Efficient Catalyst for Thioether Directed C?H Alkenylation of Arenes
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In this report, a half-sandwich (η6-benzene)Ru(II) complex of picolyl functionalized N-heterocyclic carbene was synthesized and efficiently used for the alkenylation arenes through thioether directed C?H bond activation. The thioether functionality of the substrate directed a selective ortho-vinylation through C?H bond activation. Moreover, reaction significantly works under mild reaction conditions than the previously reported ones which use the precious noble metal catalyst including the Pd(II), Rh(III), and Ir(III). Broad substrate scope using several benzyl thioethers and vinyl were found to be well tolerated for the present catalytic reaction to produces moderate to good yields of the desired products. Moreover, it is the first report where a Ru-based catalyst was used for the alkenylation of thioethers.
- Kumari, Sangeeta,Sharma, Charu,Srivastava, Avinash K.,Satrawala, Naveen,Sharma, Kamal N.,Joshi, Raj K.
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- Novel multi-target compounds in the quest for new chemotherapies against Alzheimer's disease: An experimental and theoretical study
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The lack of any effective therapy along with the aging world population anticipates a growth of the worldwide incidence of Alzheimer's disease (AD) to more than 100 million cases by 2050. Accumulation of extracellular amyloid-β (Aβ) plaques, intracellular tangles in the brain, and formation of reactive oxygen species (ROS) are the major hallmarks of the disease. In the amyloidogenic process, a β-secretase, known as BACE 1, plays a fundamental role in the production of Aβ fragments, and therefore, inhibition of such enzymes represents a major strategy for the rational design of anti-AD drugs. In this work, a series of four multi-target compounds (1–4), inspired by previously described ionophoric polyphenols, have been synthesized and studied. These compounds have been designed to target important aspects of AD, including BACE 1 enzymatic activity, Aβ aggregation, toxic concentrations of Cu2+ metal ions and/or ROS production. Two other compounds (5 and 6), previously reported by some of us as antimalarial agents, have also been studied because of their potential as multi-target species against AD. Interestingly, compounds 3 and 5 showed moderate to good ability to inhibit BACE 1 enzymatic activity in a FRET assay, with IC50′s in the low micromolar range (4.4 ± 0.3 and 1.7 ± 0.3 μM, respectively), comparable to other multi-target species, and showing that the observed activity was in part due to a competitive binding of the compounds at the active site of the enzyme. Theoretical docking calculations overall agreed with FRET assay results, displaying the strongest binding affinities for 3 and 5 at the active site of the enzyme. In addition, all compounds selectively interacted with Cu2+ metal ions forming 2:1 complexes, inhibited the production of Aβ-Cu2+ catalyzed hydroxyl radicals up to a ~100% extent, and scavenged AAPH-induced peroxyl radical species comparably to resveratrol, a compound used as reference in this work. Our results also show good anti-amyloidogenic ability: compounds 1–6 inhibited both the Cu2+-induced and self-induced Aβ(1–40) fibril aggregation to an extent that ranged from 31% to 77%, while they disaggregated pre-formed Aβ(1–40) mature fibrils up to a 37% and a 69% extent in absence and presence of Cu2+, respectively. Cytotoxicity was additionally studied in Tetrahymena thermophila and HEK293 cells, and compared to that of resveratrol, showing that compounds 1–6 display lower toxicity than that of resveratrol, a well-known non-toxic polyphenol.
- Martínez, Alberto,Zahran, Mai,Gomez, Miguel,Cooper, Coreen,Guevara, Johnny,Ekengard, Erik,Nordlander, Ebbe,Alcendor, Ralph,Hambleton, Sarah
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p. 4823 - 4840
(2018/09/11)
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- Thioether–NHC-Ligated PdII Complex for Crafting a Filtration-Free Magnetically Retrievable Catalyst for Suzuki–Miyaura Coupling in Water
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A new benzimidazolium salt, 1-[benzylaminocarbonylmethyl]-3-(2-phenylsulfanylethyl)-1H-benzimidazolium chloride (L), which is a precursor of a novel thioether-functionalized NHC, has been synthesized by subjecting 1H-benzimidazole to a sequence of reactions with 1,2-dichloroethane, sodium thiophenolate, and N-benzyl-2-chloroacetamide, successively. The moisture/air-insensitive complex [Pd(L–HCl)Cl2] (1) was prepared by the reaction of L with PdCl2. The molecular structure of 1, established by X-ray crystallography, revealed a square-planar geometry around Pd. Complex 1 was screened for Suzuki–Miyaura coupling reactions of various aryl/heteroaryl bromides (yields of up to 94 % in 2 h) in water at room temperature. Furthermore, complex 1 was immobilized onto the surface of aminopropyl-functionalized silica-coated magnetite nanoparticles [NPs, Fe3O4@SiO2-(CH2)3-NH2] by a stepwise modification strategy to develop the heterogeneous magnetically retrievable catalyst Fe3O4@SiO2-1′, in which the amide functionality present in the side-arm of the NHC within the NHC–PdII complex serves as linker. This magnetic nanosupport, bearing palladium complexes incorporating a novel thioether-based NHC ligand that functions in aqueous aerobic medium and can be easily separated, renders Fe3O4@SiO2-1′ a most desirable catalyst for the Suzuki–Miyaura coupling reaction. It was also observed that the catalyst was effective for up to seven cycles and was easily separated from the reaction medium by the use of an external magnet, further increasing its appeal.
- Nayan Sharma, Kamal,Satrawala, Naveen,Kumar Joshi, Raj
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p. 1743 - 1751
(2018/05/14)
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- Iron Nanoparticles Embedded in Graphitic Carbon Matrix as Heterogeneous Catalysts for the Oxidative C?N Coupling of Aromatic N?H Compounds and Amides
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Fe or Co nanoparticles (NPs) and two nanoparticulate Fe-Co alloys having different Fe/Co atomic ratio with average particle size ranging from 10.9 to 26.5 nm embedded in turbostratic graphitic carbon matrix have been prepared by pyrolysis at 900 °C under
- He, Jinbao,Dhakshinamoorthy, Amarajothi,Primo, Ana,Garcia, Hermenegildo
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p. 3003 - 3012
(2017/08/15)
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- Trinuclear complexes of palladium(II) with chalcogenated N-heterocyclic carbenes: Catalysis of selective nitrile-primary amide interconversion and Sonogashira coupling
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3-Methyl-1-(2-(phenylthio/seleno)ethyl)-1H-benzo[d]imidazol-3-ium iodide (L1/L2), a precursor of sulfated/selenated N-heterocyclic carbene, was synthesized by the reaction of benzimidazole with 1,2-dichloroethane followed by treatment with PhS/SeNa and MeI. The reaction of L1/L2 with Ag2O followed by treatment with [Pd(CH3CN)2Cl2] (metal to ligand ratio 3:2), i.e. transmetallation, resulted in trinuclear palladium(ii) complexes [Pd3(L1/L2-HI)2(CH3CN)Cl6] (1-2). The complexes were characterized with 1H, 13C{1H} and 77Se{1H} NMR (2 only), elemental analyses, HR-MS and single-crystal X-ray diffraction. The geometry of three Pd atoms in each complex is nearly square planar. The Pd-S/Se, Pd-C, Pd-N and Pd-Cl bond distances (?) in 1/2 are 2.3179(19)/2.4312(10), 1.968(7)/1.952(4), 2.073(8)/2.079(4) and 2.2784(19)-2.298(2)/2.292(2)-2.3003(15), respectively. In both the complexes, all Cl are trans to each other. For the central Pd atom, two benzimidazole rings are also trans to each other. The C-H?Cl non-covalent interactions result in a three-dimensional network. The moisture and air insensitive trinuclear Pd(ii) complexes 1 and 2 are thermally stable and efficient as a catalyst for nitrile-amide interconversion and amine-free Sonogashira C-C coupling (in the presence of CuI). The optimum temperature is 80 °C for the interconversion and 110 °C for the coupling. The catalytic protocols are applicable to both aliphatic and aromatic amides/nitriles. The optimum catalyst loading is 1 mol% for the C-C coupling and 0.5 to 1 mol% for the interconversion. K2CO3 as a base gives the best result for Sonogashira C-C coupling. In the conversion of nitriles to amides, the formation of an acid was not detected. After using once, 1/2 can carry out the conversion of ten fresh lots of nitriles to amides with almost the same efficiency. The real catalytic species for the interconversion and coupling appear to be based on Pd(ii) and Pd(0), respectively.
- Dubey, Pooja,Gupta, Sonu,Singh, Ajai K.
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p. 13065 - 13076
(2017/10/13)
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- H2 Production Mediated by CO2 via Initial Reduction to Formate
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A Ru(NH-NHC) complex with an open coordination site on the metal center adjacent to ligand N-H moieties has been synthesized and characterized. This complex exhibits unique reactivity upon reaction with either CO2 or NaHCO3, yielding a formate-bridged bimetallic complex via a spontaneous deoxygenation reaction and formal reduction at carbon. Dehydrogenation of the formate complex leads to a Ru-carbamate species following carbon-nitrogen bond formation between the CO2 moiety and the NHC ligand. This reactivity opens up new pathways for CO2 reduction and is relevant to H2 storage.
- Norris, Michael R.,Flowers, Sarah E.,Mathews, Ashley M.,Cossairt, Brandi M.
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supporting information
p. 2778 - 2781
(2016/11/02)
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- Synthesis of vinyl monomers with active azaaromatic groups. Phase-transfer catalytic approach
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An efficient method based on the alkylation-elimination reactions under solid-liquid phase transfer-catalysis conditions (S/L PTC) is reported for the preparation of N-vinyl derivatives of azaheterocyclic compounds.
- Bogdal, Dariusz,Jaskot, Krzysztof
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p. 3341 - 3352
(2007/10/03)
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- PHASE TRANSFER CATALYSIS WITHOUT SOLVENT. SYNTHESIS OF BISAZOLYLALKANES
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The reaction of azoles and benzazoles with dihalomethanes and dihaloethanes was performed in the absence of solvent.This method provides a general procedure for the synthesis of bisazolylmethanes and ethanes.No solvent was used during the reaction and, when possible, during the work-up.
- Diez-Barra, Enrique,Hoz, Antonio de la,Sanchez-Migallon, Ana,Tejeda, Juan
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p. 1365 - 1373
(2007/10/02)
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- 6-beta(substituted)-(S)-hydroxymethylpenicillanic acids and derivatives thereof
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Antibacterial penicillins of the formula STR1 or a pharmaceutically acceptable salt thereof wherein R1 is a heterocyclic group and R is hydrogen, the residue of certian carboxy protecting groups or the residue of an ester group readily hydrolyzable in vivo having activity against resistant organisms.
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