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Advanced Synthesis & Catalysis

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https://www.readbyqxmd.com/read/30147639/biocatalytic-parallel-interconnected-dynamic-asymmetric-disproportionation-of-%C3%AE-substituted-aldehydes-atom-efficient-access-to-enantiopure-s-profens-and-profenols
#1
Erika Tassano, Kurt Faber, Mélanie Hall
The biocatalytic asymmetric disproportionation of aldehydes catalyzed by horse liver alcohol dehydrogenase (HLADH) was assessed in detail on a series of racemic 2-arylpropanals. Statistical optimization by means of design of experiments (DoE) allowed the identification of critical interdependencies between several reaction parameters and revealed a specific experimental window for reaching an 'optimal compromise' in the reaction outcome. The biocatalytic system could be applied to a variety of 2-arylpropanals and granted access in a redox-neutral manner to enantioenriched ( S )-profens and profenols following a parallel interconnected dynamic asymmetric transformation (PIDAT)...
July 16, 2018: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29937706/chemoenzymatic-approaches-to-the-synthesis-of-the-calcimimetic-agent-cinacalcet-employing-transaminases-and-ketoreductases
#2
Lisa Marx, Nicolás Ríos-Lombardía, Judith F Farnberger, Wolfgang Kroutil, Ana I Benítez-Mateos, Fernando López-Gallego, Francisco Morís, Javier González-Sabín, Per Berglund
Several chemoenzymatic routes have been explored for the preparation of cinacalcet, a calcimimetic agent. Transaminases (TAs) and ketoreductases (KREDs) turned out to be useful biocatalysts for the preparation of key optically active precursors. Thus, the asymmetric amination of 1-acetonaphthone yielded an enantiopure ( R )-amine, which can be alkylated in one step to yield cinacalcet. Alternatively, the bioreduction of the same ketone resulted in an enantiopure ( S )-alcohol, which was easily converted into the previous ( R )-amine...
June 5, 2018: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/30093851/palladium-catalyzed-triarylation-of-sp-3-c-h-bonds-in-heteroarylmethanes-synthesis-of-triaryl-heteroaryl-methanes
#3
Shuguang Zhang, Bowen Hu, Zhipeng Zheng, Patrick J Walsh
A straightforward method for the palladium-catalyzed triarylation of heteroarylmethanes at the methyl group has been developed. The reaction works with a variety of aryl halides, enabling the rapid synthesis of triaryl(heteroaryl)methanes in moderate to excellent yields.
April 3, 2018: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29861707/a-simple-procedure-for-the-synthesis-of-%C3%AE-hydroxyallenamides-via-homoallenylation-of-aldehydes
#4
Byeong-Seon Kim, Osvaldo Gutierrez, Marisa C Kozlowski, Patrick J Walsh
A simple one-pot synthesis of β-hydroxyallenamides is reported. This procedure entails chemo- and regioselective hydroboration of 3-en-1-ynyl-sulfonylamides with Cy2 BH followed by homoallenylation of aldehydes to yield β-hydroxyallenamides (up to 94% yield and >20:1 dr). Controlled synthesis of up to three continuous stereochemical elements was realized. Density functional theory (DFT) calculations suggest a concerted Zimmerman-Traxler chair-like transition state. Initial results suggest that enantio- and diastereoselective synthesis of β-hydroxyallenamides with optically active hydroboration reagents is viable...
April 3, 2018: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29706853/direct-reductive-amination-of-carbonyl-compounds-catalyzed-by-a-moisture-tolerant-tin-iv-lewis-acid
#5
Joshua S Sapsford, Daniel J Scott, Nathan J Allcock, Matthew J Fuchter, Christopher J Tighe, Andrew E Ashley
Despite the ever-broadening applications of main-group 'frustrated Lewis pair' (FLP) chemistry to both new and established reactions, their typical intolerance of water, especially at elevated temperatures (>100 °C), represents a key barrier to their mainstream adoption. Herein we report that FLPs based on the Lewis acid i Pr3 SnOTf are moisture tolerant in the presence of moderately strong nitrogenous bases, even under high temperature regimes, allowing them to operate as simple and effective catalysts for the reductive amination of organic carbonyls, including for challenging bulky amine and carbonyl substrate partners...
March 20, 2018: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29399016/the-palladium-acetate-catalyzed-microwave-assisted-hirao-reaction-without-an-added-phosphorus-ligand-as-a-green-protocol-a-quantum-chemical-study-on-the-mechanism
#6
György Keglevich, Réka Henyecz, Zoltán Mucsi, Nóra Zs Kiss
It was proved by our experiments that on microwave irradiation, the mono- or bidentate phosphorus ligands generally applied in the palladium(II)-catalyzed P-C coupling reaction of aryl bromides and dialkyl phosphites or secondary phosphine oxides may be substituted by the excess of the >P(O)H reagent that exists under a tautomeric equilibrium. Taking into account that the reduction of the palladium(II) salt and the ligation of the palladium(0) so formed requires 3 equivalents of the P-species for the catalyst applied in a quantity of 5-10%, all together, 15-30% of the P-reagent is necessary beyond its stoichiometric quantity...
December 19, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29755308/stereoselective-synthesis-of-3-3-bisindolines-by-organocatalytic-michael-additions-of-fluorooxindole-enolates-to-isatylidene-malononitriles-in-aqueous-solution
#7
Kaluvu Balaraman, Ransheng Ding, Christian Wolf
A highly diastereoselective organocatalytic reaction for the synthesis of fluorinated 3,3'-bisindolines exhibiting adjacent tetrasubstituted carbon stereocenters is described. A broad variety of heterochiral bisindolines was prepared in 91-99% yield using 3-fluorooxindoles and isatylidene malononitriles in the presence of catalytic amounts of triethylamine in water or aqueous solution. The reaction can be upscaled without compromising yield and diastereoselectivity and the general usefulness of this method was demonstrated with various Michael acceptors and extended to aldol and Mannich reactions...
December 11, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29483850/gold-catalyzed-fluorination-of-alkynyl-esters-and-ketones-efficient-access-to-fluorinated-1-3-dicarbonyl-compounds
#8
Xiaojun Zeng, Zhichao Lu, Shiwen Liu, Gerald B Hammond, Bo Xu
We developed an efficient synthesis of 2-fluoro-1,3-dicarbonyl compounds using readily available alkynyl ketones or esters as starting material. The key step is the insertion of hydrogen fluoride (HF) to the gold carbene intermediate generated from cationic gold catalyzed addition of N -oxides to alkynyl ketones or esters. This method gives excellent chemical yields and regioselectivity with good functional group tolerance.
November 23, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/30100832/combining-sanford-arylations-on-benzodiazepines-with-the-nuisance-effect
#9
Raysa Khan, Sarote Boonseng, Paul D Kemmitt, Robert Felix, Simon J Coles, Graham J Tizzard, Gareth Williams, Olivia Simmonds, Jessica-Lily Harvey, John Atack, Hazel Cox, John Spencer
5-Phenyl-1,3-dihydro- 2H -1,4-benzodiazepin-2-ones react under palladium- and visible light photoredox catalysis, in refluxing methanol, with aryldiazonium salts to afford the respective 5-(2-arylphenyl) analogues. With 2- or 4-fluorobenzenediazonium derivatives, both fluoroaryl- and methoxyaryl- products were obtained, the latter resulting from a SN Ar on the fluorobenzenediazonium salt ("nuisance effect"). A computational DFT analysis of the palladium-catalysed and the palladium/ruthenium-photocalysed mechanism for the functionalization of benzodiazepines indicated that, in the presence of the photocatalyst, the reaction proceeds via a low-energy SET pathway avoiding the high-energy oxidative addition step in the palladium-only catalysed reaction pathway...
September 18, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29531521/arylation-of-azaarylmethylamines-with-aryl-chlorides-and-a-nibr-2-nixantphos-based-catalyst
#10
Gui Gao, Yue Fu, Minyan Li, Bo Wang, Bing Zheng, Shicong Hou, Patrick J Walsh
A nickel-catalyzed coupling of azaarylmethylamines with aryl chlorides has been achieved. NIXANTPHOS together with low cost NiBr2 was successfully developed and optimized to exhibit high reactivity at 2.5 mol % loading. Under optimized reaction conditions, aryl(azaaryl)methylamine products were afforded in good to excellent yields (22 examples, up to 98% yield).
August 17, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/30008635/nad-p-h-dependent-dehydrogenases-for-the-asymmetric-reductive-amination-of-ketones-structure-mechanism-evolution-and-application
#11
REVIEW
Mahima Sharma, Juan Mangas-Sanchez, Nicholas J Turner, Gideon Grogan
Asymmetric reductive aminations are some of the most important reactions in the preparation of active pharmaceuticals, as chiral amines feature in many of the world's most important drugs. Although many enzymes have been applied to the synthesis of chiral amines, the development of reductive amination reactions that use enzymes is attractive, as it would permit the one-step transformation of readily available prochiral ketones into chiral amines of high optical purity. However, as most natural "reductive aminase" activities operate on keto acids, and many are able to use only ammonia as the amine donor, there is considerable scope for the engineering of natural enzymes for the reductive amination of ketones, and also for the preparation of secondary amines using alkylamines as donors...
June 19, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29606929/metal-substitution-modulates-the-reactivity-and-extends-the-reaction-scope-of-myoglobin-carbene-transfer-catalysts
#12
Gopeekrishnan Sreenilayam, Eric J Moore, Viktoria Steck, Rudi Fasan
Engineered myoglobins have recently emerged as promising scaffolds for catalyzing carbene-mediated transformations. In this work, we investigated the effect of altering the metal center and its first-sphere coordination environment on the carbene transfer reactivity of myoglobin. To this end, we first established an efficient protocol for the recombinant expression of myoglobin variants incorporating metalloporphyrins with non-native metals, including second- and third-row transition metals (ruthenium, rhodium, iridium)...
June 19, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/28919846/a-methylidene-group-in-the-phosphonic-acid-analogue-of-phenylalanine-reverses-the-enantiopreference-of-binding-to-phenylalanine-ammonia-lyases
#13
Zsófia Bata, Renzhe Qian, Alexander Roller, Jeannie Horak, László Csaba Bencze, Csaba Paizs, Friedrich Hammerschmidt, Beáta G Vértessy, László Poppe
Aromatic amino acid ammonia-lyases and aromatic amino acid 2,3-aminomutases contain the post-translationally formed prosthetic 3,5-dihydro-4-methylidene-5H-imidazol-5-one (MIO) group. MIO enzymes catalyze the stereoselective synthesis of α- or β-amino acid enantiomers, making these chemical processes environmentally friendly and affordable. Characterization of novel inhibitors enables structural understanding of enzyme mechanism and recognizes promising herbicide candidates as well. The present study found that both enantiomers of the aminophosphonic acid analogue of the natural substrate phenylalanine and a novel derivative bearing a methylidene at the β-position inhibited phenylalanine ammonia-lyases (PAL), representing MIO enzymes...
June 19, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/28713228/exploring-the-catalytic-promiscuity-of-phenolic-acid-decarboxylases-asymmetric-1-6-conjugate-addition-of-nucleophiles-across-4-hydroxystyrene
#14
Stefan E Payer, Xiang Sheng, Hannah Pollak, Christiane Wuensch, Georg Steinkellner, Fahmi Himo, Silvia M Glueck, Kurt Faber
The catalytic promiscuity of a ferulic acid decarboxylase from Enterobacter sp. (FDC_Es) and phenolic acid decarboxylases (PADs) for the asymmetric conjugate addition of water across the C=C bond of hydroxystyrenes was extended to the N-, C- and S-nucleophiles methoxyamine, cyanide and propanethiol to furnish the corresponding addition products in up to 91% ee. The products obtained from the biotransformation employing the most suitable enzyme/nucleophile pairs were isolated and characterized after optimizing the reaction conditions...
June 19, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29230153/synthesis-of-diarylated-4-pyridylmethyl-ethers-via-palladium-catalyzed-cross-coupling-reactions
#15
Keyume Ablajan, Grace B Panetti, Xiaodong Yang, Byeong-Seon Kim, Patrick J Walsh
The direct arylation of weakly acidic sp3 -hybridized C-H bonds via deprotonated cross-coupling processes (DCCP) is a challenge. Herein, a Pd(NIXANTPHOS)-based catalyst for the mono arylation of 4-pyridylmethyl 2-aryl ethers to generate diarylated 4-pyridyl methyl ethers is introduced. Furthermore, under similar conditions, the diarylation of 4-pyridylmethyl ethers with aryl bromides has been developed. These methods enable the synthesis of new pyridine derivatives, which are common in medicinally active compounds and in application in materials science...
June 6, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/29104524/a-biocatalytic-route-to-highly-enantioenriched-%C3%AE-hydroxydioxinones
#16
Rick C Betori, Eric R Miller, Karl A Scheidt
A novel biocatalytic system to access a wide variety of β-hydroxydioxinones from β-ketodioxinones employing commercial engineered ketoreductases has been developed. This practical system provides a remarkably straightforward solution to limitations in accessing certain chemical scaffolds common in β-hydroxydioxinones that are of great interest due to their diversification capabilities. A few highlights of this system are that it is high yielding, highly enantioselective, and chromatography-free. We have demonstrated both a wide substrate scope and a high degree of scalability...
April 3, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/28450825/regioselective-enzymatic-carboxylation-of-bioactive-poly-phenols
#17
Katharina Plasch, Verena Resch, Julien Hitce, Jarosław Popłoński, Kurt Faber, Silvia M Glueck
In order to extend the applicability of the regioselective enzymatic carboxylation of phenols, the substrate scope of o-benzoic acid (de)carboxylases has been investigated towards complex molecules with an emphasis on flavouring agents and polyphenols possessing antioxidant properties. o-Hydroxycarboxylic acid products were obtained with perfect regioselectivity, in moderate to excellent yields. The applicability of this method was proven by the regioselective bio-carboxylation of resveratrol on a preparative scale with 95% yield...
March 20, 2017: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/28701908/total-synthesis-of-viniferifuran-resveratrol-piceatannol-hybrid-anigopreissin-a-and-analogues-investigation-of-demethylation-strategies
#18
Duc Duy Vo, Mikael Elofsson
Resveratrol-based natural products constitute a valuable source of unique compounds with diverse biological activities. In this report we investigate demethylation strategies to minimize formation of cyclized and dimerized products during the synthesis of viniferifuran and analogues. We found that boron trichloride/tetra-n-butylammonium iodide (BCl3/TBAI) is typically more effective than boron tribromide (BBr3). Based on these findings we carried out the first syntheses of dehydro-δ-viniferin, resveratrol-piceatannol hybrid and anigopreissin A...
December 22, 2016: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/28111537/synthesis-of-functionalized-hydrazines-facile-homogeneous-n-heterocyclic-carbene-palladium-0-catalyzed-diboration-and-silaboration-of-azobenzenes
#19
Melvyn B Ansell, George E Kostakis, Holger Braunschweig, Oscar Navarro, John Spencer
The bis(N-heterocyclic carbene)(diphenylacetylene)palladium complex [Pd(ITMe)2(PhC≡CPh)] (ITMe=1,3,4,5-tetramethylimidazol-2-ylidene) acts as a highly active pre-catalyst in the diboration and silaboration of azobenzenes to synthesize a series of novel functionalized hydrazines. The reactions proceed using commercially available diboranes and silaboranes under mild reaction conditions.
December 7, 2016: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/27917101/selective-enzymatic-transformation-to-aldehydes-in-vivo-by-fungal-carboxylate-reductase-from-neurospora-crassa
#20
Daniel Schwendenwein, Giuseppe Fiume, Hansjörg Weber, Florian Rudroff, Margit Winkler
The enzymatic reduction of carboxylic acids is in its infancy with only a handful of biocatalysts available to this end. We have increased the spectrum of carboxylate-reducing enzymes (CARs) with the sequence of a fungal CAR from Neurospora crassa OR74A (NcCAR). NcCAR was efficiently expressed in E. coli using an autoinduction protocol at low temperature. It was purified and characterized in vitro, revealing a broad substrate acceptance, a pH optimum at pH 5.5-6.0, a Tm of 45 °C and inhibition by the co-product pyrophosphate which can be alleviated by the addition of pyrophosphatase...
November 3, 2016: Advanced Synthesis & Catalysis
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