- Synthesis, crystal structure of Co(II)(6-methoxybenzothiazole-2-carboxylate)2(DMF)2 and its application to carbonylation of benzyl chloride
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A new complex, Co(MBTC)2(DMF)2 (MBTC(6-methoxybenzothiazole-2-carboxylate, DMF=N,N-dimethylformamide), was synthesized in DMF solution and characterized by single crystal X-ray diffraction analysis. Using the cobalt complex as catalyst, phenylacetic acid was prepared by the carbonylation of benzyl chloride with carbon monoxide (0.1 MPa). The effects of solvents, phase transfer catalysts and temperature on the reactions were investigated. The yield of phenylacetic acid was higher than 90% in optimized condition.
- Zhang, Bin,Li, Jianli,Chen, Wei,Wang, Yunxia,Shi, Zhen
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- Lanthanide-Promoted and Nickel Cyanide Catalyzed Carbonylation Reactions under Phase-Transfer Conditions
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The nickel cyanide and phase transfer catalyzed carbonylation of benzyl chlorides is promoted by lanthanide salts .This simple reaction is sensitive to the concentration of the lanthanide compound, sodium hydroxide, quaternary ammonium salt, and nickel catalyst.The nature of the organic phase and phase transfer agent also influences the reaction rate.The acceleration of the reaction may be a consequence of coordination of a nickel cyanide nitrogen lone pair to the lanthanide salt.
- Amer, Ibrahim,Alper, Howard
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- Photoreactivity of 1-Pyrenylmethyl Esters. Dependence on the Structure of the Carboxylic Acid Moieties and the Nature of the Excited States
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While the photolysis of 1-pyrenylmethyl phenylacetates in methanol gave the original phenylacetic acids, irradation of the 1-naphthoate and 9-anthracenecarboxylate leads to the formation of the intramolecular exciplexes that are inert to the photolysis.The Φf and τf values of these esters have been determined.
- Iwamura, Michiko,Tokuda, Kazuko,Koga, Noboru,Iwamura, Hiizu
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- Penicillin G amidase-catalysed hydrolysis of phenylacetic hydrazides on a solid phase: A new route to enzyme-cleavable linkers
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A novel catalytic property of penicillin G amidase (PGA) is described. Unexpectedly, the enzyme can hydrolyse hydrazide bonds with good efficiency, and in solution the enzyme shows a selectivity that is similar to phenylacetamides. The hydrolysis of phenylacetic hydrazides releases hydrazine, but no inhibition due to the formation of such reactive compounds was observed. This novel catalytic property was assayed also on a solid phase as a pioneering route for the design of enzyme-cleavable linkers and masked scavengers for ketones. On a solid phase a phenylacetic hydrazide compound was chemically synthesised on PEGA1900 and PEGA+ (two co-polymers of acrylamide and ethylene glycol) and the efficiency of PGA in the release of phenylacetic acid depended on the diffusion of the protein inside the polymer. On PEGA+ the enzyme, as previously described, shows a good diffusion due to an improved electrostatic interaction with PGA thus achieving good hydrolytic conversions.
- Basso, Alessandra,Ebert, Cynthia,Gardossi, Lucia,Linda, Paolo,Phuong, Thao Tran,Zhu, Mingzhao,Wessjohann, Ludger
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- Microwave-assisted rapid hydrolysis and preparation of thioamides by Willgerodt-Kindler reaction
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Aldehydes and aryl alkyl ketones were efficiently transformed to thioamides with the same number of carbon atoms via Willgerodt-Kindler reaction under microwave irradiation in solvent-free conditions. The thioamides obtained were hydrolyzed to corresponding carboxylic acids with microwave dielectric heating in one minute. Both reactions are very fast and the yields are excellent.
- Matloubi Moghaddam,Ghaffarzadeh
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- Copper-catalysed Reaction of Arylacetylenes with C,N-Diarylnitrones
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Reaction of arylacetylenes with C,N-diarylnitrones is effectively catalysed by copper(I) iodide-dppe in the presence of potassium carbonate to give the corresponding 1-azabut-1-en-3-yne (iminopropyne) derivatives in good yield.
- Okuro, Kazumi,Enna, Masahiro,Miura, Masahiro,Nomura, Masakatsu
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- Preparation of Protein Conjugates via Homobifunctional Diselenoester Cross-Linker
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Adipic acid diselenoester was developed as an efficient cross-linker for covalent protein conjugation with a variety of small molecular haptens, including mono- and disaccharides, peptide, fluorescence dye, and nicotine. Compared to the counterparts of N-hydroxysuccinimide (NHS) and p-nitrophenyl (PNP) linkers, the diselenoester linker demonstrates improved balance between reactivity and stability and coupling of haptens to proteins under mild conditions with high incorporation efficiency.
- Yin, Xu-Guang,Gao, Xiao-Fei,Du, Jing-Jing,Zhang, Xiao-Kang,Chen, Xiang-Zhao,Wang, Jian,Xin, Ling-Ming,Lei, Ze,Liu, Zheng,Guo, Jun
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- Permanganate Ion Oxidations. 14. Kinetics and Mechanism of the Oxidation of Aliphatic Aldehydes in Acid Media
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The kinetics and mechanism of the permanganate ion oxidation of 2,2-dimethylpropanal (pivalaldehyde, 4) and other aliphatic aldehydes over the pH range 2.80-6.86 have been investigated.The oxidation, which shows general-acid catalysis, is first order in and first order in ->.The mechanism of the Mn(VII) oxidation of aliphatic aldehydes is compared with that proposed for Cr(VI).
- Freeman, Fillmore,Lin, Doris K.,Moore, Gregory R.
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- Towards the rehabilitation of the Mathews' 'dry' hydrolysis reaction using microwave technology
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The Mathews' reaction is a one-pot preparation of carboxylic acids from their corresponding nitriles or amides by a 'dry' hydrolysis with phthalic acid or anhydride in the absence of water and solvent. Excellent isolated yields and selectivity (up to 99%) were attained within short reaction times (typically, 30 minutes) when the reaction was performed under microwave heating.
- Chemat, Farid
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- Relative activity of metal cathodes towards electroorganic coupling of CO2 with benzylic halides
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Electrochemical reduction of benzylic halides represents a convenient route to generating carbanions for their subsequent coupling with CO2 to obtain various carboxylic acids. Despite the industrial prospects of this synthetic process, it still lacks systematic studies of the efficient catalysts and reaction media design. In this work, we performed a detailed analysis of the catalytic activity of a series of different metal electrodes towards electroreduction of benzylic halides to corresponding radicals and carbanions using cyclic voltammetry. Specifically, we screened and summarized the performance of 12 bulk metal cathodes (Ag, Au, Cu, Pd, Pt, Ni, Ti, Zn, Fe, Al, Sn, and Pb) and 3 carbon-based materials (glassy carbon, carbon cloth, and carbon paper) towards electrocarboxylation of eight different benzylic halides and compare it to direct CO2 reduction in acetonitrile. Extensive experimental studies along with a detailed analysis of the results allowed us to map specific electrochemical properties of different metal electrodes, i.e., the potential zones related to the one- and two-electron reduction of organic halides as well as the potential windows where the electrochemical activation of CO2 does not occur. The reported systematic analysis should facilitate the development of nanostructured electrodes based on group 10 and 11 transition metals to further optimize the efficiency of electrocarboxylation of halides bearing specific substituents and make this technology competitive to current synthetic methods for the synthesis of carboxylic acids.
- Engelhardt, Helen,Klinkova, Anna,Medvedev, Jury J.,Medvedeva, Xenia V.
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- Synthesis of Phenylacetic Acid via Carbonylation of Benzyl Chloride in the Presence of a Water-Soluble Complex, 2>, and Surfactants under Two-Phase Conditions
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The addition of surfactants such as n-C7H15SO3Na or n-C7H15COONa is effective in acceleration of the carboxylation of benzyl chloride using a water-soluble catalyst, 2>, in an aqueous NaOH-heptane solution.Phenylacetic acid is easily isolated from the aqueous layer in high yields.However, the addition of n-C7H15SO3Na has no effect on the carboxylation using hydrophobic catalysts, and , under the two phase conditions.
- Okano, Tamon,Hayashi, Tetsuji,Kiji, Jitsuo
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- An 'easy-on, easy-off' protecting group for the enzymatic resolution of (±)-1-phenylethylamine in an aqueous medium
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A new approach has been developed for the biocatalytic resolution of (±)-1-phenylethylamine in 100% aqueous medium based on two integrated enzymatic steps: protection and deprotection of the reactive amine enantiomer catalyzed by the same enzyme-penicillin acylase from Alcaligenes faecalis. An 'easy-on, easy-off' protecting group has been introduced using (R)-phenylglycine amide as the acyl donor. (R)-Phenylglycyl-substituted (R)-1-phenylethylamine was poorly soluble and precipitated at enzymatic acylation in an alkaline medium (pH 10-11), driving the synthesis towards high yields. Conversely at pH 7.5, its solubility was continuously increasing, which rendered the subsequent deacylation by the same enzyme highly efficient. In contrast to the resolutions, which employ one biocatalytic step, the new approach made it possible to exploit two sequential enantioselective enzymatic reactions implementing a double enantioselectivity control. Effective enzymatic resolution of (±)-1-phenylethylamine in an aqueous medium was performed with (R)-phenylglycine amide as an acyl donor using the suggested approach.
- Guranda, Dorel T.,Khimiuk, Andrey I.,Van Langen, Luuk M.,Van Rantwijk, Fred,Sheldon, Roger A.,Svedas, Vytas K.
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- The combi-CLEA approach: Enzymatic cascade synthesis of enantiomerically pure (S)-mandelic acid
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Enantiomerically pure (S)-mandelic acid was synthesised from benzaldehyde by sequential hydrocyanation and hydrolysis in a bienzymatic cascade at starting concentrations up to 0.25 M. A cross-linked enzyme aggregate (CLEA) composed of the (S)-selective oxynitrilase from Manihot esculenta and the non-selective nitrilase from Pseudomonas fluorescens EBC 191 was employed as the biocatalyst. The nitrilase produces approx. equal amounts of (S)-mandelic acid and (S)-mandelic amide from (S)-mandelonitrile under standard conditions, but we surprisingly found that high (up to 0.5 M) concentrations of HCN induced a marked drift towards amide production. By including the amidase from Rhodococcus erythopolis in the CLEA we obtained (S)-mandelic acid as the sole product in 90% yield and >99% enantiomeric purity.
- Chmura, Andrzej,Rustler, Sven,Paravidino, Monica,Van Rantwijk, Fred,Stolz, Andreas,Sheldon, Roger A.
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- Cobalt carbonyl catalyzed carbonylation of benzal bromides by phase transfer catalysis
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The reaction of benzal bromides with CO (1 atm) in a binary system (aq.KOH/C6H6) in the presence of a catalytic amount of Co2(CO)8 together with benzyltriethylammonium chloride as a phase transfer catalyst for 8 h at room temperature gives the corresponding carboxylic acids in good to excellent yields.
- Shim, Sang Chul,Doh, Chil Hoon,Park, Woo Hyun,Kwon, Young Gil,Lee, Hyung Soo
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- A recyclable, metal-free mechanochemical approach for the oxidation of alcohols to carboxylic acids
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The oxidation of primary alcohols under mechanochemical conditions in a Spex8000M Mixer/Mill was investigated. To facilitate ease of separation and recyclability, a polystyrene-bound version of a TEMPO catalyst was employed. When paired with Oxone in a stainless-steel vial with a stainless-steel ball, several primary alcohols were successfully oxidized to the corresponding carboxylic acids. The product was isolated using gravity filtration, which also allowed for the polystyrene-bound TEMPO catalyst to be recovered and reused in subsequent oxidation reactions. Furthermore, it was demonstrated that the size and steric hindrance of the primary alcohol does not hinder the rate of the reaction. Finally, the aldehyde was selectively obtained from a primary alcohol under ball milling conditions by using a combination of non-supported TEMPO with a copper vial and copper ball.
- Carr, Preston,Denlinger, Kendra Leahy,Mack, James,Waddell, Daniel C.
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- A versatile procedure for synthesis of organic acids by cobalt carbonyl catalyzed carbonylation of organic halides
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A versatile procedure for synthesis of a broad range of fatty-aromatic and aromatic acids by carbonylation of the corresponding halides under very mild conditions in the presence of cobalt carbonyl as a catalyst was suggested. The main principles of a flexible process for production of practically significant acids and their derivatives were developed.
- Zhesko,Boyarskii,Nikitina
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- Efficient Assay for the Detection of Hydrogen Peroxide by Estimating Enzyme Promiscuous Activity in the Perhydrolysis Reaction
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Hydrogen peroxide is an ideal oxidant in view of its availability, atom economy, or green aspects. Furthermore, it is produced by the cell mitochondria and plays a meaningful role in controlling physiological processes, but its unregulated production leads to the destruction of organs. Due to its diverse roles, a fast and selective method for hydrogen peroxide detection is the major limitation to preventing the negative effects caused by its excess. Therefore, we aimed to develop an efficient assay for the detection of H2O2. For this purpose, we combined the enzymatic method for the detection of hydrogen peroxide with the estimation of the promiscuity of various enzymes. We estimated the activity of an enzyme in the reaction of p-nitrophenyl esters with hydrogen peroxide resulting in the formation of peracid. To our knowledge, there is no example of a simple, multi-sensor demonstrating the promiscuous activity of an enzyme and detecting hydrogen peroxide in aqueous media.
- Wilk, Monika,Ostaszewski, Ryszard
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- Oxidation of aldehydes with Oxone in aqueous acetone
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Several aldehydes have been convened to the corresponding acids in good to excellent yields. The oxidant was Oxone (potassium peroxymonosulfate), the reactions were performed in either 20% aqueous acetone, water, or aqueous acetonitrile, and buffered with sodium bicarbonate.
- Webb, Kevin S.,Ruszkay, Stephen J.
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- Site-selective immobilisation of functional enzymes on to polystyrene nanoparticles
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The immobilisation of proteins on to nanoparticles has a number of applications ranging from biocatalysis through to cellular delivery of biopharmaceuticals. Here we describe a phosphopantetheinyl transferase (Sfp)-catalysed method for immobilising proteins bearing a small 12-mer "ybbR" tag on to nanoparticles functionalised with coenzyme A. The Sfp-catalysed immobilisation of proteins on to nanoparticles is a highly efficient, single step reaction that proceeds under mild conditions and results in a homogeneous population of proteins that are covalently and site-specifically attached to the surface of the nanoparticles. Several enzymes of interest for biocatalysis, including an arylmalonate decarboxylase (AMDase) and a glutamate racemase (GluR), were immobilised on to nanoparticles using this approach. These enzymes retained their activity and showed high operational stability upon immobilisation. The Royal Society of Chemistry 2010.
- Wong, Lu Shin,Okrasa, Krzysztof,MicKlefield, Jason
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- Reductive carboxylation of alkyl halides with CO2by use of photoinduced SmI2/Sm reduction system
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Upon visible-light irradiation, reductive carboxylation of alkyl halides takes place by using a Sml2/Sm mixed system under atmospheric CO 2 to afford the corresponding carboxylic acids in good to excellent yields.
- Nomoto, Akihiro,Kojo, Yusuke,Shiino, Go,Tomisaka, Yuri,Mitani, Ikuko,Tatsumi, Masahiko,Ogawa, Akiya
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- A simple and efficient protocol for the deprenylation of ethers and esters catalysed by zirconium(IV) chloride-sodium iodide
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An efficient protocol for the deprotection of prenyl ethers and esters is developed using 20 mol% ZrCl4-NaI (1:1) in CH3CN as a reagent system. A variety of substrates as well as functional groups well tolerate the present reaction conditions.
- Sharma, Gangavaram V. M.,Reddy, Ch. Govardhan,Krishna, Palakodety Radha
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- SELECTIVE HYDROLYSIS OF NITRILES UNDER MILD CONDITIONS BY AN ENZYME
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A wide range of aromatic/aliphatic nitriles and dinitriles have been selcetively hydrolysed using a commercially available enzyme preparation from a Rhodococcuc sp.
- Cohen, Mark A.,Sawden, Janette,Turner, Nicholas J.
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- Isolation of 2-Alkyl-4-quinolones with Unusual Side Chains from a Chinese Pseudomonas aeruginosa Isolate
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Chemical investigation of a Pseudomonas aeruginosa strain isolated from Hebei, China, led to the isolation of a suite of quinolones, quinolone-N-oxides, and phenazines, the structures of which were elucidated by detailed spectroscopic analysis. Most notable among the secondary metabolites isolated was an unprecedented 4-quinolone containing an S-methyl group in the side chain and a new derivative including a phenyl ring in the side chain, which expand significantly the variety of structural motifs found in the quinolones and raise interesting questions about their biosynthesis.
- Li, Jianye,Sun, Weiwei,Saalim, Muhammad,Wei, Guixiang,Zaleta-Pinet, Diana A.,Clark, Benjamin R.
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- Ultrathin and Vacancy-Rich CoAl-Layered Double Hydroxide/Graphite Oxide Catalysts: Promotional Effect of Cobalt Vacancies and Oxygen Vacancies in Alcohol Oxidation
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Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to afford a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co-O and Co····Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (VO) and cobalt vacancies (VCo), CoAl-ELDH/GO also contains negatively charged VCo-Co-OHδ- sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h-1; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h-1) precursor. O2-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged VCo-Co-OHδ- sites. A kinetic isotope effect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O-H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols.
- Wang, Qian,Chen, Lifang,Guan, Shaoliang,Zhang, Xin,Wang, Bin,Cao, Xingzhong,Yu, Zhi,He, Yufei,Evans, David G.,Feng, Junting,Li, Dianqing
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- Fluorinated analogues of tert-butyl alcohol as novel protecting groups for use in fluorous synthesis
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Figure presented A series of fluorous derivatives of tert-butyl alcohol were prepared and evaluated as reagents for the protection of carboxylic acids for use in fluorous synthesis. Alcohol 3b can be employed efficiently to protect and immobilize medium-size nonpolar carboxylic acids in a fluorous phase.
- Pardo, Juan,Cobas, Agustin,Guitian, Enrique,Castedo, Luis
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- SILAFUNCTIONAL COMPOUNDS IN ORGANIC SYMTHESIS. 21. HYDROGEN PEROXIDE OXIDATION OF ALKENYL(ALKOXY)SILANES
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The carbon-silicon bond in alkenyl(alkoxy)silanes is readily cleaved by hydrogen peroxyde to form the corresponding aldehydes, carboxylic acids or ketones, depending upon the nature of the alkenyl group and the reaction conditions.
- Tamao, Kohei,Kumada, Makoto,Maeda, Kimio
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- Design and evolution of an enzyme with a non-canonical organocatalytic mechanism
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The combination of computational design and laboratory evolution is a powerful and potentially versatile strategy for the development of enzymes with new functions1–4. However, the limited functionality presented by the genetic code restricts the range of catalytic mechanisms that are accessible in designed active sites. Inspired by mechanistic strategies from small-molecule organocatalysis5, here we report the generation of a hydrolytic enzyme that uses Nδ-methylhistidine as a non-canonical catalytic nucleophile. Histidine methylation is essential for catalytic function because it prevents the formation of unreactive acyl-enzyme intermediates, which has been a long-standing challenge when using canonical nucleophiles in enzyme design6–10. Enzyme performance was optimized using directed evolution protocols adapted to an expanded genetic code, affording a biocatalyst capable of accelerating ester hydrolysis with greater than 9,000-fold increased efficiency over free Nδ-methylhistidine in solution. Crystallographic snapshots along the evolutionary trajectory highlight the catalytic devices that are responsible for this increase in efficiency. Nδ-methylhistidine can be considered to be a genetically encodable surrogate of the widely employed nucleophilic catalyst dimethylaminopyridine11, and its use will create opportunities to design and engineer enzymes for a wealth of valuable chemical transformations.
- Burke, Ashleigh J.,Lovelock, Sarah L.,Frese, Amina,Crawshaw, Rebecca,Ortmayer, Mary,Dunstan, Mark,Levy, Colin,Green, Anthony P.
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- Cathode made of compacted silver nanoparticles for electrocatalytic carboxylation of 1-phenethyl bromide with CO2
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Silver nanoparticles prepared by the direct reduction of AgNO3 in aqueous solution were compacted into coins and used as the cathode for the electrocatalytic carboxylation of 1-phenethyl bromide with CO2. The influences of the working electrode, charge, current density and temperature were investigated. Under optimized conditions, 98% yield of 2-phenylpropionic acid was obtained. The reaction was performed under very mild conditions and no added catalyst was required in the electrolyte. Yields that varied from moderate to excellent were also achieved with other benzyl bromides. This electrode has good stability and reusability, and the yield and selectivity of 2-phenylpropionic acid could be maintained during reuse for 10 times.
- Yang, Hengpan,Wu, Laxia,Wang, Huan,Lu, Jiaxing
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- Microwave-assisted oxidation of alcohols by hydrogen peroxide catalysed by tetrabutylammonium decatungstate
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This work deals with catalytic activity of tetrabutylammonium decatungstate(VI) in the oxidation of selected alcohols with hydrogen peroxide as an oxidant using 1,2-dichloroethane/water or acetonitrile/water as a solvent system. Different forms of heating were compared. The highest conversions of substrates were achieved in the two phase system acetonitrile/water using microwave irradiation combined with elevated pressure. Finally, optimum parameters for these reactions in a microwave pressurised reactor were established and discussed.
- Galica, Mateusz,Kasprzyk, Wiktor,Bednarz, Szczepan,Bogdal, Dariusz
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- Purification, characterization and in-silico analysis of nitrilase from Gordonia terrae
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An inducible and aromatic nitrilase from Gordonia terrae was purified with a yield of 19%. The enzyme had turnover number of 63 s-1 × 10-3, Km1.4 mM and Vmax95 Umg-1 protein for benzonitrile. The nitrilase of G. terrae was active at basic pH (7-10), moderate temperature (20-45 °C) and has a half-life of 4 h at 35 °C. MALDI analysis and amino acid sequence deduced from cloned nucleotide fragment showed 97% homology with putative amidohydrolase of Gordonia sputi NBRC 100414 and G. namibiensis. The enzyme showed regioselectivity towards hydroxybenzonitriles, as different position of hydroxyl group i.e. meta-, para- and orthosubstitutions on benzonitrile effect enzyme activity. The in-silico interactions of these substrates with the predicted 3D model of this enzyme also showed differential interaction between hydroxyl group of substrates and the polar amino acids surrounding enzyme's active site. This leads to different proximity and orientation of substrates vis-a-vis their interaction with catalytic residues.
- Kumar, Vijay,Seth, Amit,Kumari, Vijaya,Kumar, Virender,Bhalla, Tek C.
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- Resolution of (RS)-phenylglycinonitrile by penicillin acylase-catalyzed acylation in aqueous medium
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A new strategy for the biocatalytic resolution of (R,S)-phenylglycinonitrile, a crucial intermediate in the antibiotic industry, has been developed. While former techniques exploit nitrilases or combinations of nitrile hydratases and amidases, manipulating with nitrile functionality, the current approach is based on a highly efficient and enantioselective acylation of the α-amino group with phenylacetic acid catalyzed by a well known enzyme, penicillin acylase from E. coli, in slightly acidic aqueous medium. It is shown that since the condensation product is poorly soluble, removal of (S)-phenylglycinonitrile from the reaction sphere is almost complete and irreversible, favoring kinetics of the process and making high conversion possible. The proposed approach is characterized by high space-time yield and extends the scope of enzymatic synthesis in aqueous medium.
- Chilov, Ghermes G.,Moody, Harold M.,Boesten, Wilhelmus H. J.,Svedas, Vytas K.
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- Nickel-Catalyzed Carboxylation of Benzylic C-N Bonds with CO2
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A user-friendly Ni-catalyzed reductive carboxylation of benzylic C-N bonds with CO2 is described. This procedure outperforms state-of-the-art techniques for the carboxylation of benzyl electrophiles by avoiding commonly observed parasitic pathways, such as homodimerization or β-hydride elimination, thus leading to new knowledge in cross-electrophile reactions.
- Moragas, Toni,Gaydou, Morgane,Martin, Ruben
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- On the Conformation of the Substrate Binding to the Active Site during the Course of Enzymatic Decarboxylation
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The activation parameters of the enzymatic decarboxylation of malonic acid derivatives catalyzed by arylmalonate decarboxylase (AMDase) were obtained by means of kinetics. In order to understand the conformation of the substrate at the transition state, the activation entropy (ΔS?) for indane-1,1-dicarboxylic acid, a representative molecule that is conformationally restricted, was compared with those of phenylmalonic acid and ortho-chlorophenylmalonic acid, of which the aromatic ring can freely rotate. The obtained value for the former molecule was about 10 cal mol-1 K-1 smaller than those of the latter compounds, clearly indicating that a conformationally restricted substrate, such as the indane derivative, is entropically advantageous for enzymatic decarboxylation. These kinetic studies evidently disclose that the conformation of the substrate at the transition state in the course of AMDase-catalyzed decarboxylation should be synperiplanar with regard to ortho- and α-substituents.
- Kawasaki, Takayasu,Horimai, Emiko,Ohta, Hiromichi
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- A simple and highly practical oxidation of primary alcohols to acids mediated by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)
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Primary alcohols were quantitatively oxidized in one-pot to acids via 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidation. The reported method is simple and suitable for large scale synthesis.
- Zanka, Atsuhiko
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- Ruthenium molecular complexes immobilized on graphene as active catalysts for the synthesis of carboxylic acids from alcohol dehydrogenation
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Ruthenium complexes containing N-heterocyclic carbene ligands functionalized with different polyaromatic groups (pentafluorophenyl, anthracene, and pyrene) are immobilized onto the surface of reduced graphene oxide. The hybrid materials composed of organometallic complexes and graphene are obtained in a single-step process. The hybrid materials are efficient catalysts for the synthesis of carboxylic acids from the dehydrogenation of alcohols in aqueous media. The catalytic materials can be recycled up to ten times without significant loss of activity. The catalytic activity of the pyrene derivative, Pyr-Ru (3) is enhanced when the ruthenium complex is anchored onto the surface of graphene. The carbonaceous material limits the degradation of the ruthenium complex resulting in increased activity and requiring lower catalyst loading. The catalytic process of the pyrene hybrid material is heterogeneous in nature due to the strong interaction between the pyrene and graphene. The catalytic process of the anthracene and pentafluorophenyl hybrid materials is governed by the so-called 'boomerang effect'. The ruthenium molecular complex is released from and returned to the graphene surface during the catalytic reaction. Mechanistic insight has been obtained experimentally and theoretically. The energy profile suggests that the ratedetermining step is the nucleophilic attack of water on a coordinated aldehyde complex to form a gem-diolate complex.
- Ventura-Espinosa, David,Vicent, Cristian,Baya, Miguel,Mata, Jose A.
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- Comparison of Spectroscopic and Electrochemical Studies of Disproportionation Equilibria of 1,3,5-Triphenylverdazyl Radical in DMF Containing Carboxylic Acids
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Stoichiometry and equilibrium constants for the disproportionation of the title radicals in N,N-dimethylformamide containing salicilic, chloroacetic, and phenylacetic acids were determined on the basis of absorption spectra.On the other hand, only apparent equilibrium constants depending on concentrations of an acid and a radical could be obtained from electrochemical measurements at a mercury electrode.Significant differences in reaction stoichiometry and in order of magnitudes of disproportionation constants found under spectroscopic and electrochemical conditionswere discussed in terms of an influence of the electric field in the double layer on the distribution of different associates formed by verdazyl species with acids.Keywords: Disproportionation equilibrium; Effect of the electrode field.
- Jaworski, Jan S.,Krawczyk, Irena
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- Transformation of Thioacids into Carboxylic Acids via a Visible-Light-Promoted Atomic Substitution Process
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A visible-light-promoted atomic substitution reaction for transforming thiocacids into carboxylic acids with dimethyl sulfoxide (DMSO) as the oxygen source has been developed, affording various alkyl and aryl carboxylic acids in over 90% yields. The atomic substitution process proceeds smoothly through the photochemical reactivity of the formed hydrogen-bonding adduct between thioacids and DMSO. A DMSO-involved proton-coupled electron transfer (PCET) and the simultaneous generation of thiyl and hydroxyl radicals are proposed to be key steps for realizing the transformation.
- Fu, Qiang,Liang, Fu-Shun,Lou, Da-Wei,Pan, Gao-Feng,Wang, Rui,Wu, Min,Xie, Kai-Jun
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supporting information
p. 2020 - 2024
(2022/03/31)
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- Direct Aerobic α-Hydroxylation of Arylacetates for the Synthesis of Mandelates
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Aerobic α-hydroxylation of α-methylene esters has proven challenging due to overoxidation and hydrolysis of the materials. In this article, KOtBu-promoted TBAB-catalyzed α-hydroxylation of α-methylene aryl esters using O2as the oxyge
- Xu, Changming,Li, Xiangfan,Bai, Lei
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p. 4298 - 4304
(2022/03/16)
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- Mechanochemical Grignard Reactions with Gaseous CO2 and Sodium Methyl Carbonate**
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A one-pot, three-step protocol for the preparation of Grignard reagents from organobromides in a ball mill and their subsequent reactions with gaseous carbon dioxide (CO2) or sodium methyl carbonate providing aryl and alkyl carboxylic acids in up to 82 % yield is reported. Noteworthy are the short reaction times and the significantly reduced solvent amounts [2.0 equiv. for liquid assisted grinding (LAG) conditions]. Unexpectedly, aryl bromides with methoxy substituents lead to symmetric ketones as major products.
- Pfennig, Victoria S.,Villella, Romina C.,Nikodemus, Julia,Bolm, Carsten
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supporting information
(2022/01/22)
-
- PYRROLIDINE-PYRAZOLES AS PYRUVATE KINASE ACTIVATORS
-
The subject matter described herein is directed to pyruvate kinase activating compounds of Formula I and pharmaceutical salts thereof, methods of preparing the compounds, pharmaceutical compositions comprising the compounds and methods of administering the compounds for the treatment of diseases associated with PKR and/or PKM2, such as pyruvate kinase deficiency, sickle cell disease, and beta-thalassemia.
- -
-
Paragraph 173-175
(2021/10/11)
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- Polyalkynyl-containing alpha, beta-diamino acid ester derivative compound as well as preparation and application of thereof
-
The invention discloses a polyalkynyl-containing alpha, beta-diamino acid ester derivative compound or a pharmaceutically acceptable salt, and an application of the compound or a pharmaceutical composition containing the compound in treating various malignant tumor related diseases such as osteosarcoma, pancreatic cancer, head and neck tumors and the like. The invention further relates to a preparation method of the polyalkynyl-containing alpha, beta-diamino acid ester derivative compound or the pharmaceutically acceptable salt.
- -
-
Paragraph 0057-0058
(2021/04/28)
-
- BiCl3-Facilitated removal of methoxymethyl-ether/ester derivatives and DFT study of -O-C-O- bond cleavage
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A simple method for the cleavage of methoxymethyl (MOM)-ether and ester derivatives using bismuth trichloride (BiCl3) is described. The alkyl, alkenyl, alkynyl, benzyl and anthracene MOM ether derivatives, as well as MOM esters of both aliphatic and aromatic carboxylic acids, were deprotected in good yields. To better understand the molecular roles of BiCl3and water for MOM cleavage, two possible binding pathways were investigated using the density functional theory (DFT) method. The theoretical results indicate the differential initial binding site preferences of phenolic and alcoholic MOM substrates to the Bi atom and suggest that water plays a key role in facilitating the cleavage of the MOM group.
- Pacherille, Angela,Tuga, Beza,Hallooman, Dhanashree,Dos Reis, Isaac,Vermette, Mélodie,Issack, Bilkiss B.,Rhyman, Lydia,Ramasami, Ponnadurai,Sunasee, Rajesh
-
supporting information
p. 7109 - 7116
(2021/05/03)
-
- Iron-catalyzed reductive strecker reaction
-
Strecker reaction is widely applied for the synthesis of amino acids from aldehydes, amines and cyanides. Herein, we report the FeI2-catalyzed reductive Strecker type reaction of formamides instead of aldehydes to produce amino acetonitriles. The challenging capture of carbinolamine intermediates by CN? was achieved via Fe catalysis. This approach afforded better yields than the use of Ir- or Rh-catalysts. The application ability of this methodology is demonstrated by 1) one-pot construction of (13C labeled) complex molecules from CO2 via amino acetonitrile intermediates and 2) convenient production of homologated carboxylic acids from aldehydes.
- Yan, Fachao,Huang, Zijun,Du, Chen-Xia,Bai, Jian-Fei,Li, Yuehui
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p. 188 - 194
(2021/02/03)
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- Hydrolysis of amides to carboxylic acids catalyzed by Nb2O5
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Hydrolysis of amides to carboxylic acids is an industrially important reaction but is challenging due to the difficulty of cleaving the resonance stabilized amidic C-N bond. Twenty-three heterogeneous and homogenous catalysts were examined in the hydrolysis of acetamide. Results showed that Nb2O5was the most effective heterogeneous catalyst with the greatest yield of acetic acid. A series of Nb2O5catalysts calcined at various temperatures were characterized and tested in the hydrolysis of acetamide to determine the effects of crystal phase and surface properties of Nb2O5on catalytic performance. The high catalytic performance observed was attributed mainly to the facile activation of the carbonyl bond by Lewis acid sites that function even in the presence of basic inhibitors (NH3and H2O). The catalytic studies showed the synthetic advantages of the present method, such as simple operation, catalyst recyclability, additive free, solvent free, and wide substrate scope (>40 examples; up to 95% isolated yield).
- Siddiki,Rashed, Md. Nurnobi,Touchy, Abeda Sultana,Jamil, Md. A. R.,Jing, Yuan,Toyao, Takashi,Maeno, Zen,Shimizu, Ken-Ichi
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p. 1949 - 1960
(2021/03/26)
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- An efficient heterogeneous Cu(I) complex for the catalytic oxidation of alcohols and sulfides: synthesis, characterization, and investigation of the catalyst activity
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A heterogeneous Cu(I) complex was synthesized by reaction of C5H4NC(O)NHP(O)[NHC(CH3)3]2 (L) with CuCl and used as a catalyst for green oxidation of aromatic alcohols and sulfides. According to the characterization results obtained from 31P NMR, UV-Vis, FT-IR, mass, XRD, elemental analysis, and molar conductivity techniques, the chemical formula of the complex (1) was suggested as [CuClL2]. Parameters on the catalytic activity (reaction temperature, the substrate to oxidant molar ratio, catalyst amount, and solvent type) were optimized, using H2O2 as a green oxidant, and excellent conversion amounts (100%) were achieved under optimal conditions. Moreover, the generality and recyclability of the catalyst were tested and confirmed. A comparison between the oxidation results of the alcohol and sulfide in the presence of 1 with other catalysts indicated that in most cases 1 showed better efficiency, in a more reasonable reaction time and conditions.
- Oroujzadeh, Nasrin,Baradaran, Zahra,Sedrpoushan, Alireza
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p. 2344 - 2364
(2021/08/06)
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- Alkali-modified heterogeneous Pd-catalyzed synthesis of acids, amides and esters from aryl halides using formic acid as the CO precursor
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To establish an environmentally friendly green chemical process, we minimized and resolved a significant proportion of waste and hazards associated with conventional organic acids and molecular gases, such as carbon monoxide (CO). Herein, we report a facile and milder reaction procedure, using low temperatures/pressures and shorter reaction time for the carboxyl- and carbonylation of diverse arrays of aryl halides over a newly developed cationic Lewis-acid promoted Pd/Co3O4catalyst. Furthermore, the reaction proceeded in the absence of acid co-catalysts, and anhydrides for CO release. Catalyst reusability was achievedviascalable, safer, and practical reactions that provided moderate to high yields, paving the way for developing a novel environmentally benign method for synthesizing carboxylic acids, amides, and esters.
- Fapojuwo, Dele Peter,Maqunga, Nomathamsanqa Prudence,Meijboom, Reinout,Mogudi, Batsile M.,Molokoane, Pule Petrus,Onisuru, Oluwatayo Racheal,Oseghale, Charles O.
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p. 26937 - 26948
(2021/08/17)
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- Suppressing carboxylate nucleophilicity with inorganic salts enables selective electrocarboxylation without sacrificial anodes
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Although electrocarboxylation reactions use CO2as a renewable synthon and can incorporate renewable electricity as a driving force, the overall sustainability and practicality of this process is limited by the use of sacrificial anodes such as magnesium and aluminum. Replacing these anodes for the carboxylation of organic halides is not trivial because the cations produced from their oxidation inhibit a variety of undesired nucleophilic reactions that form esters, carbonates, and alcohols. Herein, a strategy to maintain selectivity without a sacrificial anode is developed by adding a salt with an inorganic cation that blocks nucleophilic reactions. Using anhydrous MgBr2as a low-cost, soluble source of Mg2+cations, carboxylation of a variety of aliphatic, benzylic, and aromatic halides was achieved with moderate to good (34-78%) yields without a sacrificial anode. Moreover, the yields from the sacrificial-anode-free process were often comparable or better than those from a traditional sacrificial-anode process. Examining a wide variety of substrates shows a correlation between known nucleophilic susceptibilities of carbon-halide bonds and selectivity loss in the absence of a Mg2+source. The carboxylate anion product was also discovered to mitigate cathodic passivation by insoluble carbonates produced as byproducts from concomitant CO2reduction to CO, although this protection can eventually become insufficient when sacrificial anodes are used. These results are a key step toward sustainable and practical carboxylation by providing an electrolyte design guideline to obviate the need for sacrificial anodes.
- Corbin, Nathan,Lazouski, Nikifar,Manthiram, Karthish,Steinberg, Katherine,Yang, Deng-Tao
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p. 12365 - 12376
(2021/10/08)
-
- Nonheme manganese(III) complexes for various olefin epoxidation: Synthesis, characterization and catalytic activity
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Three mononuclear imine-based non-heme manganese(III) complexes with tetradentate ligands which have two deprotonated phenolate moieties, ([(X2saloph)Mn(OAc)(H2O)], 1a for X = Cl, 1b for X = H, and 1c for X = CH3, saloph = N,N-o-phenylenebis(salicylidenaminato)), were synthesized and characterized by 1H NMR, 13C NMR, ESI-Mass and elemental analysis. MnIII complexes catalysed efficiently various olefin epoxidation reactions with meta-chloroperbenzoic acid (MCPBA) under the mild condition. MnIII complexes 1a and 1c with the electron-withdrawing group -Cl and electron-donating group –CH3 showed little substituent effect on the epoxidation reactions. Product analysis, Hammett study and competition experiments with cis- and trans-2-octene suggested that MnIV = O, MnV = O, and MnIII-OOC(O)R species might be key oxidants in the epoxidation reaction under this catalytic system. In addition, the use of PPAA as a mechanistic probe demonstrated that Mn-acylperoxo intermediate (MnIII-OOC(O)R) 2 generated from the reaction of peracid with manganese complexes underwent both the heterolysis and the homolysis to produce MnV = O (3) or MnIV = O species (4). Moreover, the MnIII-OOC(O)R 2 species could react directly with the easy-to-oxidize substrate to give epoxide, whereas the species 2 might not be competent to the difficult-to-oxidize substrate for the epoxidation reaction.
- Lee, Sojeong,Park, Soyoung,Lee, Myoung Mi,Lee, Jiyoung,Kim, Cheal
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-
- Visible-Light-Enabled Carboxylation of Benzyl Alcohol Derivatives with CO2 Using a Palladium/Iridium Dual Catalyst
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A highly efficient carboxylation of benzyl alcohol derivatives with CO2 using a palladium/iridium dual catalyst under visible-light irradiation was developed. A wide range of benzyl alcohol derivatives could be employed to provide benzylic carboxylic acids in moderate to high yields. Mechanistic studies indicated that the oxidative addition of benzyl alcohol derivatives was possibly the rate-determining-step. It was also found that a switchable site-selective carboxylation between benzylic C?O and aryl C?Cl moieties could be achieved simply by changing the palladium catalyst.
- Iwasawa, Nobuharu,Jin, Yushu,Toriumi, Naoyuki
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-
- Desulfonylative Electrocarboxylation with Carbon Dioxide
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Electrocarboxylation of organic halides is one of the most investigated electrochemical approaches for converting thermodynamically inert carbon dioxide (CO2) into value-added carboxylic acids. By converting organic halides into their sulfone derivatives, we have developed a highly efficient electrochemical desulfonylative carboxylation protocol. Such a strategy takes advantage of CO2as the abundant C1 building block for the facile preparation of multifunctionalized carboxylic acids, including the nonsteroidal anti-inflammatory drug ibuprofen, under mild reaction conditions.
- Zhong, Jun-Song,Yang, Zi-Xin,Ding, Cheng-Lin,Huang, Ya-Feng,Zhao, Yi,Yan, Hong,Ye, Ke-Yin
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supporting information
p. 16162 - 16170
(2021/09/02)
-
- Preparation method of phenylacetic acid
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The invention discloses a preparation method of phenylacetic acid, and relates to the technical field of organic synthesis. The preparation method of phenylacetic acid specifically comprises the following steps of: carrying out sulfonation reaction on alcohol, namely carrying out sulfonation treatment on 2-butyne-1, 4-diol by using p-toluenesulfonyl chloride to obtain a product A; carrying out Friedel-Crafts alkylation reaction, namely reacting benzene with the product A under the catalytic action of a polymerization ionic liquid catalyst to obtain a product B; and oxidizing alkyne, namely, bytaking tetrabutylammonium bromide as PCT and m-CPBA as an oxidizing agent, treating the product B to obtain phenylacetic acid. According to the preparation method of phenylacetic acid provided by theinvention, the prepared phenylacetic acid is high in yield, the operation is simple, the reaction conditions are easy to operate, and the safety is high.
- -
-
Paragraph 0036-0051
(2021/02/20)
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- Efficient Synthesis of Phenylacetate and 2-Phenylethanol by Modular Cascade Biocatalysis
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The green and sustainable synthesis of chemicals from renewable feedstocks by a biotransformation approach has gained increasing attention in recent years. In this work, we developed enzymatic cascades to efficiently convert l-phenylalanine into 2-phenylethanol (2-PE) and phenylacetic acid (PAA), l-tyrosine into tyrosol (p-hydroxyphenylethanol, p-HPE) and p-hydroxyphenylacetic acid (p-HPAA). The enzymatic cascade was cast into an aromatic aldehyde formation module, followed by an aldehyde reduction module, or aldehyde oxidation module, to achieve one-pot biotransformation by using recombinant Escherichia coli. Biotransformation of 50 mM l-Phe produced 6.76 g/L PAA with more than 99 % conversion and 5.95 g/L of 2-PE with 97 % conversion. The bioconversion efficiencies of p-HPAA and p-HPE from l-Tyr reached to 88 and 94 %, respectively. In addition, m-fluoro-phenylalanine was further employed as an unnatural aromatic amino acid substrate to obtain m-fluoro-phenylacetic acid; '96 % conversion was achieved. Our results thus demonstrated high-yielding and potential industrial synthesis of above aromatic compounds by one-pot cascade biocatalysis.
- Mao, Zuoxi,Liu, Lijun,Zhang, Yang,Yuan, Jifeng
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p. 2676 - 2679
(2020/06/03)
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- Achiral Derivatives of Hydroxamate AR-42 Potently Inhibit Class i HDAC Enzymes and Cancer Cell Proliferation
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AR-42 is an orally active inhibitor of histone deacetylases (HDACs) in clinical trials for multiple myeloma, leukemia, and lymphoma. It has few hydrogen bond donors and acceptors but is a chiral 2-arylbutyrate and potentially prone to racemization. We report achiral AR-42 analogues incorporating a cycloalkyl group linked via a quaternary carbon atom, with up to 40-fold increased potency against human class I HDACs (e.g., JT86, IC50 0.7 nM, HDAC1), 25-fold increased cytotoxicity against five human cancer cell lines, and up to 70-fold less toxicity in normal human cells. JT86 was ninefold more potent than racAR-42 in promoting accumulation of acetylated histone H4 in MM96L melanoma cells. Molecular modeling and structure-activity relationships support binding to HDAC1 with tetrahydropyran acting as a hydrophobic shield from water at the enzyme surface. Such potent inhibitors of class I HDACs may show benefits in diseases (cancers, parasitic infections, inflammatory conditions) where AR-42 is active.
- Tng, Jiahui,Lim, Junxian,Wu, Kai-Chen,Lucke, Andrew J.,Xu, Weijun,Reid, Robert C.,Fairlie, David P.
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supporting information
p. 5956 - 5971
(2020/06/05)
-
- Oxidation of aromatic and aliphatic aldehydes to carboxylic acids by Geotrichum candidum aldehyde dehydrogenase
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Oxidation reaction is one of the most important and indispensable organic reactions, so that green and sustainable catalysts for oxidation are necessary to be developed. Herein, biocatalytic oxidation of aldehydes was investigated, resulted in the synthesis of both aromatic and aliphatic carboxylic acids using a Geotrichum candidum aldehyde dehydrogenase (GcALDH). Moreover, selective oxidation of dialdehydes to aldehydic acids by GcALDH was also successful.
- Hoshino, Tomoyasu,Yamabe, Emi,Hawari, Muhammad Arisyi,Tamura, Mayumi,Kanamaru, Shuji,Yoshida, Keisuke,Koesoema, Afifa Ayu,Matsuda, Tomoko
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-
- Catalytic Oxidative Deamination by Water with H2Liberation
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Selective oxidative deamination has long been considered to be an important but challenging transformation, although it is a common critical process in the metabolism of bioactive amino compounds. Most of the synthetic methods developed so far rely on the use of stoichiometric amounts of strong and toxic oxidants. Here we present a green and efficient method for oxidative deamination, using water as the oxidant, catalyzed by a ruthenium pincer complex. This unprecedented reaction protocol liberates hydrogen gas and avoids the use of sacrificial oxidants. A wide variety of primary amines are selectively transformed to carboxylates or ketones in good to high yields. It is noteworthy that mechanistic experiments and DFT calculations indicate that in addition to serving as the oxidant, water also plays an important role in assisting the hydrogen liberation steps involved in amine dehydrogenation.
- Tang, Shan,Rauch, Michael,Montag, Michael,Diskin-Posner, Yael,Ben-David, Yehoshoa,Milstein, David
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supporting information
p. 20875 - 20882
(2020/12/23)
-
- Oxidation of Alkynyl Boronates to Carboxylic Acids, Esters, and Amides
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A general efficient protocol was developed for the synthesis of carboxylic acids, esters, and amides through oxidation of alkynyl boronates, generated directly from terminal alkynes. This protocol represents the first example of C(sp)?B bond oxidation. This approach displays a broad substrate scope, including aryl and alkyl alkynes, and exhibits excellent functional group tolerance. Water, primary and secondary alcohols, and amines are suitable nucleophiles for this transformation. Notably, amino acids and peptides can be used as nucleophiles, providing an efficient method for the synthesis and modification of peptides. The practicability of this methodology was further highlighted by the preparation of pharmaceutical molecules.
- Li, Chenchen,Li, Ruoling,Zhang, Bing,Zhao, Pei,Zhao, Wanxiang
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p. 10913 - 10917
(2020/05/25)
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- Palladium supported on a novel ordered mesoporous polypyrrole/carbon nanocomposite as a powerful heterogeneous catalyst for the aerobic oxidation of alcohols to carboxylic acids and ketones on water
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Preparation of an ordered mesoporous polypyrrole/carbon (PPy/OMC) composite has been described through a two-step nanocasting process using KIT-6 as a template. Characterization of the PPy/OMC nanocomposite by various analysis methods such as TEM, XRD, TGA, SEM and N2 sorption confirmed the preparation of a material with ordered mesoporous structure, uniform pore size distribution, high surface area and high stability. This nanocomposite was then used for the immobilization of palladium nanoparticles. The nanoparticles were almost uniformly distributed on the support with a narrow particle size of 20-25 nm, confirmed by various analysis methods. Performance of the Pd?PPy/OMC catalyst was evaluated in the aerobic oxidation of various primary and secondary alcohols on water as a green solvent, giving the corresponding carboxylic acids and ketones in high yields and excellent selectivity. The catalyst could also be reused for at least 10 reaction runs without losing its catalytic activity and selectivity. High catalytic efficiency of the catalyst can be attributed to a strong synergism between the PPy/OMC and that of supported Pd nanoparticles.
- Ganji, Nasim,Karimi, Babak,Najafvand-Derikvandi, Sepideh,Vali, Hojatollah
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p. 13616 - 13631
(2020/04/24)
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- Uncommon overoxidative catalytic activity in a new halo-tolerant alcohol dehydrogenase
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Alcohol dehydrogenases (ADH) are versatile and useful enzymes employed as biocatalysts, especially for the selective oxidation of primary and secondary alcohols, and for the reduction of carbonyl moieties. A new alcohol dehydrogenase (HeADH-II) has been identified from the genome of the halo-adapted bacterium Halomonas elongata, which proved stable in the presence of polar organic solvents and salt exposure. Unusual for this class of enzymes, HeADH-II lacks enantiopreference and is capable of oxidizing both alcohols and aldehydes, enabling a direct overoxidation of primary alcohols to carboxylic acids. HeADH-II was coupled with a NADH-oxidase from Lactobacillus pentosus (LpNOX) to increase the process yields and allowing recycling of the cofactor. The enzymatic oxidation of primary alcohols was also paired with in situ condensation of the intermediate aldehydes with hydroxylamine to prepare the corresponding aldoximes, with particular attention to perillartine (a powerful sweetener), whose enzymatic synthesis starting from natural sources, leads to an equally natural product.
- Contente, Martina L.,Fiore, Noemi,Cannazza, Pietro,Roura Padrosa, David,Molinari, Francesco,Gourlay, Louise,Paradisi, Francesca
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supporting information
p. 5679 - 5685
(2020/09/17)
-
- Cobalt-Catalyzed Acceptorless Dehydrogenation of Alcohols to Carboxylate Salts and Hydrogen
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The facile oxidation of alcohols to carboxylate salts and H2 is achieved using a simple and readily accessible cobalt pincer catalyst (NNNHtBuCoBr2). The reaction follows an acceptorless dehydrogenation pathway and displays good functional group tolerance. The amine-amide metal-ligand cooperation in cobalt catalyst is suggested to facilitate this transformation. The mechanistic studies indicate that in-situ-formed aldehydes react with a base through a Cannizzaro-type pathway, resulting in potassium hemiacetolate, which further undergoes catalytic dehydrogenation to provide the carboxylate salts and H2
- Gunanathan, Chidambaram,Kishore, Jugal,Pattanaik, Sandip,Pradhan, Deepak Ranjan
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supporting information
(2020/03/03)
-
- Carbon dots as photocatalysts for organic synthesis: Metal-free methylene-oxygen-bond photocleavage
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We report for the first time that irradiation of four different citric acid-derived carbon dots (CDs), in the absence of any other redox mediators, promotes an organic reaction. In this proof-of-concept study methylene-oxygen bond reductive photocleavage in N-methyl-4-picolinium esters is demonstrated. Cyclic voltammetry and UV-Vis spectra of the CDs and of the esters indicate that photocleavage reactivity correlates with the redox properties and the relative energies expressed in the Fermi scale. A photo-fragmentation mechanism is proposed. This study offers a new possibility to employ inexpensive and readily available CDs to promote photo-organic reactions.
- Cailotto, Simone,Negrato, Matteo,Daniele, Salvatore,Luque, Rafael,Selva, Maurizio,Amadio, Emanuele,Perosa, Alvise
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p. 1145 - 1149
(2020/03/11)
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- Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions
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A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2-based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.
- Gevorgyan, Ashot,Hopmann, Kathrin H.,Bayer, Annette
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p. 2080 - 2088
(2020/02/20)
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- Method for converting benzyl borate compounds into phenylacetic acid and derivatives thereof by carbon dioxide
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The invention discloses a method for converting benzyl borate compounds into phenylacetic acid and derivatives thereof by carbon dioxide. The method comprises the steps: dissolving the benzyl borate compounds and an alkali in an organic solvent in the absence of a metal catalyst, introducing carbon dioxide into the reaction system, carrying out a reaction at the temperature of 50-150 DEG C for 3-72 hours, and acidifying to obtain phenylacetic acid or the derivatives thereof. The method is a green, simple and efficient method for synthesizing phenylacetic acid and the derivatives thereof, greenhouse gas carbon dioxide is used as a carbon source in the reaction, no transition metal catalyst is used, and the method is environmentally friendly, economical and high in efficiency.
- -
-
Paragraph 0026-0027
(2020/03/06)
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- BF3·OEt2-promoted tandem Meinwald rearrangement and nucleophilic substitution of oxiranecarbonitriles
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Tandem Meinwald rearrangement and nucleophilic substitution of oxiranenitriles was realized. Arylacetic acid derivatives were readily synthesized from 3-aryloxirane-2-carbonitriles with amines, alcohols, or water in the presence of boron trifluoride under microwave irradiation, and the designed synthetic strategy includes introducing a cyano leaving group into arylepoxides and capturing the in situ generated toxic cyanide with boron trifluoride, making the reaction efficient, safe, and environmentally benign. The reaction occurs through an acid-promoted Meinwald rearrangement, producing arylacetyl cyanides, followed by an addition-elimination process with nitrogen or oxygen-containing nucleophilic amines, alcohols or water. The current method provides a new application of the tandem Meinwald rearrangement.
- Xu, Chuangchuang,Xu, Jiaxi
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p. 127 - 134
(2019/12/26)
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- Oxidations of benzhydrazide and phenylacetic hydrazide by hexachloroiridate(IV): Reaction mechanism and structure–reactivity relationship
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Benz(o)hydrazide (BH) is the basic aryl hydrazide; aryl hydrazides have been pursued in the course of drug discovery. Oxidations of BH and phenylacetic hydrazide (PAH) by hexachloroiridate(IV) ([IrCl6]2?) were investigated by use of stopped-flow spectral, rapid spectral scan, RP-HPLC and NMR spectroscopic techniques. The oxidation reactions followed well-defined second-order kinetics and the observed second-order rate constant k0 versus pH profiles were established over a wide pH range. Product analysis revealed that BH and PAH were cleanly oxidized to benzoic acid and phenylacetic acid, respectively. A reaction mechanism was proposed, resembling those suggested previously for the oxidations of isoniazid (INH) and nicotinic hydrazide (NH) by [IrCl6]2?. Rate constants of the rate-determining steps were evaluated, confirming a huge reactivity span of the protolysis species observed previously. The enolate species of BH is extremely reactive towards reduction of [IrCl6]2?. The determined middle-ranged negative values of activation entropies together with rapid scan spectra manifest that an outer-sphere electron transfer is probably taking place in the rate-determining steps. The reactivity of neutral species of hydrazides is clearly not correlated to the corresponding pKa values of the hydrazides. On the other hand, a linear correlation, logkenolate = (0.16 ± 0.07)pKenol + (6.1 ± 0.8), is found for the aryl hydrazides studied so far. The big intercept and the small slope of this correlation may pave a way for a rational design of new antioxidants based on aryl hydrazides. The present work also provides the pKa values for BH and PAH at 25.0 ?C and 1.0 M ionic strength which were not reported before.
- Zhang, Xiaolai
-
supporting information
(2020/01/31)
-
- Green recyclable synthesis method of phenylacetic acid
-
The invention relates to the field of organic synthesis, and provides a green recyclable synthesis method of phenylacetic acid. The synthesis method comprises the following steps: reacting toluene with carbon monoxide in the presence of a catalyst and a solvent to obtain phenylacetic acid, wherein the catalyst comprises an active component and a carrier, the active component comprises one or moreof Pd, Pt, Au, Ag, Co, Cu, Ni, Fe and Cr, the solvent is an ionic liquid and/or an eutectic solvent, the reaction temperature is 60-90 DEG C, and the reaction pressure is normal pressure. According tothe method, the catalyst can be recycled and regenerated, so that the production cost is effectively reduced, and the resource waste is avoided; moreover, the yield of phenylacetic acid obtained by the method provided by the invention is relatively high and can reach 75% or above, and after the catalyst is recycled for 5 times, the yield of phenylacetic acid can still be kept at 50% or above. Inaddition, the method provided by the invention is mild in condition, and flammable and explosive alkali metal sodium does not need to be used.
- -
-
Paragraph 0040-0050
(2020/12/08)
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- Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the in Situ Methylation of Tertiary Amines
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Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp3-Csp3 bonds. We demonstrate PO(OMe)3 (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: The in situ methylation of tertiary amines by PO(OMe)3, Ni-catalyzed C-N bond cleavage, and concurrent Csp3-Csp3 bond formation.
- Nwachukwu, Chideraa Iheanyi,McFadden, Timothy Patrick,Roberts, Andrew George
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p. 9979 - 9992
(2020/09/03)
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- Hydrodebromination of Aromatic Bromides Catalyzed by Unsupported Nanoporous Gold: Heterolytic Cleavage of Hydrogen Molecule
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Unsupported nanoporous gold (AuNPore) is a highly efficient, practically applicable, and recyclable catalyst for hydrodebromination of aromatic bromides. The AuNPore-catalyzed hydrodebromination of aromatic bromides proceeded smoothly at relatively low hydrogen pressure and temperature to achieve good to excellent yields of the corresponding non-bromine variants. The selective hydrodebromination reaction occurred exclusively in the coexistence of chlorine atom. For the first time, a mechanistic study revealed that the H?H bond splits in a heterolysis manner on the surface of AuNPore to generate Au?H hydride species.
- Bao, Ming,Feng, Xiujuan,Yamamoto, Yoshinori,Zhang, Sheng,Zhao, Yuhui
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p. 4951 - 4957
(2020/09/09)
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- Catalytic C-H aerobic and oxidant-induced oxidation of alkylbenzenes (including toluene derivatives) over VO2+immobilized on core-shell Fe3O4?SiO2at room temperature in water
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Direct C-H bond oxidation of organic materials, and producing the necessary oxygenated compounds under mild conditions, has attracted increasing interest. The selective oxidation of various alkylbenzenes was carried out by means of a new catalyst containing VO2+ species supported on silica-coated Fe3O4 nanoparticles using t-butyl hydroperoxide as an oxidant at room temperature in H2O or solvent-free media. The chemical and structural characterization of the catalyst using several methods such as FTIR spectroscopy, XRD, FETEM, FESEM, SAED, EDX and XPS showed that VO2+ is covalently bonded to the silica surface. High selectivity and excellent conversion of various toluene derivatives, with less reactive aliphatic (sp3) C-H bonds, to related benzoic acids were quite noticeable. The aerobic oxygenation reaction of these alkylbenzenes was studied under the same conditions. All the results accompanied by sustainability of the inexpensive and simple magnetically separable heterogeneous catalyst proved the important criteria for commercial applications. This journal is
- Mohammadpour, Pegah,Safaei, Elham
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p. 23543 - 23553
(2020/07/14)
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- Mechanistic Investigation of the Nickel-Catalyzed Carbonylation of Alcohols
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The carbonylation of alcohols represents a straightforward and atom-efficient methodology for the preparation of carboxylic acids. It is desirable to perform these reactions under precious metal-free and low-pressure conditions, with regioselectivity control. In this work, we present a detailed mechanistic study of a catalytic system based on NiI2, which can carbonylate benzylic alcohols in a highly regioselective manner to the corresponding branched carboxylic acids, core motifs for nonsteroidal drugs. The combination of catalytic amounts of nickel and iodide is crucial for efficient catalytic and regioselective conversion. Quantum-chemical computations were used to evaluate the underlying mechanistic processes. They revealed that a combination of two mechanisms is responsible for the observed reactivity and that the oxidative addition of alkyl halides to the Ni(0) species follows a radical oxidation pathway via two one-electron steps.
- Comba, Peter,Ghosh, Tamal,Hashmi, A. Stephen K.,Krieg, Saskia,Menche, Maximilian,Paciello, Rocco,Rück, Katharina S. L.,Sabater, Sara,Sch?fer, Ansgar,Schaub, Thomas
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supporting information
(2020/03/19)
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- Development of novel support for penicillin acylase and its application in 6-aminopenicillanic acid production
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There is an ever-increasing demand for the β-lactam bulk intermediate 6-aminopenicillanic acid (6-APA) that has wide applications in the synthesis of newer generations of semisynthetic penicillins. It is commercially synthesized by biocatalytic transformation using penicillin acylase. Since the enzyme is soluble, immobilization on a solid porous support is necessary to make the catalyst recycleable and the process profitable. In this study, we developed a novel support of siliceous foam entrapped in a polymer matrix. Penicillin acylase was covalently immobilized on aminopropyl functionalized mesocellular foam silica (MCF) and was further cross-linked using glutaraldehyde without deactivation and upto 95% efficiency. The resulting biocatalyst had an activity of 1185 IU. mg?1 and demonstrated improved resistance to the substrate and product inhibition. These parameters along with improvement in pH and thermal stability enhanced 6-APA yield by 20% in beads. Intrinsic kinetic parameters were calculated from the developed rate equation to deduce enzyme catalytic mechanism.
- Ayakar, Sonal R.,Yadav, Ganapati D.
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- Preparation method of cyclopentolate hydrochloride intermediate
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The invention belongs to the technical field of pharmaceutical chemicals, and relates to a preparation method of a cyclopentolate hydrochloride intermediate. Methyl phenylacetate is used as a raw material, the price is low, the methyl phenylacetate is commercially produced, the goods source is sufficient, and the quality is stable. The commercially available Grignard reagent is adopted, so that the risk that flammable and explosive reagents are used and are not controlled when the Grignard reagent is self-made is avoided. Commercially available Grignard reagents have been industrially produced and are convenient and easy to obtain. And the intermediate is purified by adopting a crystallization solvent, so that the purity of the intermediate is ensured, the preparation yield of the cyclopentolate hydrochloride is increased, and subsequent crystallization and impurity removal processes are reduced. And the production risk and the labor protection requirement of workers are reduced, environmental protection is facilitated, and the economic benefit is improved. The yield of phenylacetic acid can reach 95% or above, the purity of phenylacetic acid can reach 99.9% or above, the production requirements of the cyclopentolate hydrochloride intermediate are completely met, and the yield and purity of the product 2-(1-hydroxycyclopentyl)-phenylacetic acid are much higher than those of 2-(1-hydroxycyclopentyl)-phenylacetic acid produced by a common method.
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Paragraph 0009; 0024; 0026
(2019/12/02)
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- Organocatalyzed Aerobic Oxidation of Aldehydes to Acids
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The first example organocatalyzed aerobic oxidation of aldehydes to carboxylic acids in both organic solvent and water under mild conditions is developed. As low as 5 mol % N-hydroxyphthalimide was used as the organocatalyst, and molecular O2 was used as the sole oxidant. No transition metals or hazardous oxidants or cocatalysts were involved. A wide range of carboxylic acids bearing diverse functional groups were obtained from aldehydes, even from alcohols, in high yields.
- Dai, Peng-Fei,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 1393 - 1396
(2019/02/26)
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- O -Hydroxycinnamate for sequential photouncaging of two different functional groups and its application in releasing cosmeceuticals
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We demonstrated a new approach for the sequential photouncaging of two different functional groups from o-hydroxycinnamate. The second caged molecule initially remains in the locked state and is released only after attaining its unlocked state upon in situ generation of the second phototrigger, i.e., coumarin, thereby leading to the sequential release of alcohol and carboxylic acid. We have utilised the above strategy for the controlled release of cosmeceutical agents.
- Paul, Amrita,Bera, Manoranjan,Gupta, Prakhar,Singh, N. D. Pradeep
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supporting information
p. 7689 - 7693
(2019/08/30)
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- Preparation method of acid with different substituent groups
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The invention discloses a preparation method of an acid with different substituent groups. A terminal alkyne is lithiated with n-butyllithium, and then reacts with isopropoxyboronic acid pinacol ester, hydrogen chloride is added to achieve quenching, then the obtained reaction product is oxidized by an oxidizing agent, and the oxidized reaction product is separated and purified to obtain the acid.The method of the invention has the advantages of simplicity in operation, one-pot process preparation, no metal catalysis, nontoxic reagents, greenness, environmental friendliness and high atomic utilization rate, and provides a novel and quick way for preparing the acid with different substituent groups; and the obtained acid is an important fine chemical product, and can be widely used in fields of medicines, pesticides, spices and other industries.
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Paragraph 0124-0128
(2019/10/23)
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- Synthesis and biological evaluation of 3-arylcoumarin derivatives as potential anti-diabetic agents
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A variety of substituted 3-arylcoumarin derivatives were synthesised through microwave radiation heating. The method has characteristics of environmental friendliness, economy, simple separation, and purification process, less by-products and high reaction yield. Those 3-arylcoumarin derivatives were screened for antioxidant, α-glucosidase inhibitory and advanced glycation end-products (AGEs) formation inhibitory. Most compounds exhibited significant antioxidant and AGEs formation inhibitory activities. Anti-diabetic activity studies showed that compounds 11 and 17 were equipotent to the standard drug glibenclamide in vivo. According to the experimental results, the target compound 35 can be used as a lead compound for the development of new anti-diabetic drugs. The whole experiment showed that anti-diabetic activity is prevalent in 3-arylcoumarins, which added a new natural skeleton to the development of anti-diabetic active drugs.
- Hu, Yuheng,Wang, Bing,Yang, Jie,Liu, Teng,Sun, Jie,Wang, Xiaojing
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- Synthesis and biological evaluation of 3-arylcoumarins as potential anti-Alzheimer's disease agents
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Alzheimer's disease, a neurodegenerative illness, has the extremely complex pathogenesis. Accumulating evidence indicates there is a close relationship between several enzymes and Alzheimer's disease. Various substituted 3-arylcoumarin derivatives were synthesised, and their in vitro activity, including cholinesterase inhibitory activity, monoamine oxidase inhibitory activity, and antioxidant activity were investigated. Most of the compounds exhibited high activity; therefore 3-arylcoumarin compounds have the potential as drug candidates for the treatment of Alzheimer's disease.
- Yang, Jie,Zhang, Pingping,Hu, Yuheng,Liu, Teng,Sun, Jie,Wang, Xiaojing
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p. 651 - 656
(2019/02/19)
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- A Diaminopropane Diolefin Ru(0) Complex Catalyzes Hydrogenation and Dehydrogenation Reactions
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New ruthenium (0) complexes with a cooperative diolefin diaminopropane (DAP) or the dehydrogenated iminopropenamide ligand (IPA) were synthesized for comparison with their diaminoethane (DAE)/ diazadiene (DAD) ruthenium analogues. These DAP/IPA complexes are efficient catalysts in dehydrogenation reactions of alkaline aqueous methanol which proceeds under mild conditions (T=70 °C) and of higher alcohols, forming the corresponding carbonate and carboxylates, respectively. The scope of the reaction includes an example of a 1,2-diol as model for biomass derived alcohols. Their catalytic applications are extended to the atom-efficient dehydrogenative coupling of alcohols and amines to amides. The reaction proceeds without any additives and is applicable to the synthesis of formamides from methanol. Moreover, DAP/IPA complexes catalyze the hydrogenation of a series of esters, lactone, ketone, activated olefin, aldehyde and imine substrates. The diaminopropane Ru catalyst exhibits higher activity compared to the dehydrogenated β-ketiminate (IPA) and previously studied DAD/DAE based catalysts. We present studies on their stoichiometric reactivity with relevance to their possible catalytic mechanisms and the isolation and full characterization of key reaction intermediates.
- Casas, Fernando,Trincado, Monica,Rodriguez-Lugo, Rafael,Baneerje, Dipshikha,Grützmacher, Hansj?rg
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p. 5241 - 5251
(2019/11/16)
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- Ruthenium Catalyzed Dehydrogenation of Alcohols and Mechanistic Study
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We synthesized pyridylamine ligated arene-Ru(II) complexes and employed these complexes for the catalytic acceptorless dehydrogenation of primary alcohols to carboxylic acids. All the synthesized complexes [Ru]-1-[Ru]-10 are characterized using several spectro-analytical techniques, and the structures of complexes [Ru]-1, [Ru]-2, and [Ru]-5 are determined using single crystal X-ray crystallography. Efficient catalytic conversion of primary alcohols to potassium carboxylates or carboxylic acids is achieved in toluene with the quantitative release of hydrogen gas. The studied protocol for carboxylic acid synthesis with hydrogen generation is also employed for a wide range of substrates, including aliphatic alcohols, aromatic alcohols, and heteroaromatic alcohols, to obtain respective carboxylic acids in good yields (up to 86%). The studied arene-Ru catalysts also exhibit superior catalytic activity for the bulk reaction to achieve a turnover number of 1378. Moreover, extensive mass investigations are also performed to elucidate the mechanistic pathway by identifying the crucial catalytic intermediates, including aldehyde and diol coordinated Ru species under the catalytic and controlled reaction conditions.
- Awasthi, Mahendra K.,Singh, Sanjay K.
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supporting information
p. 14912 - 14923
(2019/11/03)
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- Electrogenerated Sm(II)-Catalyzed CO2 Activation for Carboxylation of Benzyl Halides
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Sm(II)-catalyzed carboxylation of benzyl halides is reported through the electrochemical reduction of CO2. The transformation proceeds under mild reaction conditions to afford the corresponding phenylacetic acids in good to excellent yields. This user-friendly and operationally simple protocol represents an alternative to traditional strategies, which usually proceeds through the C(sp3)-halide activation pathway.
- Bazzi, Sakna,Schulz, Emmanuelle,Mellah, Mohamed
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supporting information
p. 10033 - 10037
(2019/12/24)
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- CO2 activation by electrogenerated divalent samarium for aryl halide carboxylation
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The reductive carboxylation of aryl halides has been investigated using a samarium electrode as a sacrificial anode to yield the corresponding benzoic acids, providing a smooth strategy for CO2 activation. Carboxylation occurred after an efficient reduction of carbon dioxide mediated by an electrogenerated Sm(ii)-complex acting as a strong monoelectronic reductive reagent.
- Bazzi, Sakna,Le Duc, Ga?tan,Schulz, Emmanuelle,Gosmini, Corinne,Mellah, Mohamed
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supporting information
p. 8546 - 8550
(2019/10/02)
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- Insertion of CO2 Mediated by a (Xantphos)NiI–Alkyl Species
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The incorporation of CO2 into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of NiII to NiI by either Zn or Mn, followed by CO2 insertion into NiI-alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu-Xantphos)NiIIBr2 by Zn affords NiI species. (tBu-Xantphos)NiI-Me and (tBu-Xantphos)NiI-Et complexes undergo fast insertion of CO2 at 22 °C. The substantially faster rate, relative to that of NiII complexes, serves as the long-sought-after experimental support for the proposed mechanisms of Ni-catalyzed carboxylation reactions.
- Diccianni, Justin B.,Hu, Chunhua T.,Diao, Tianning
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supporting information
p. 13865 - 13868
(2019/08/26)
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