- N-heterocyclic carbene catalyzed enantioselective [3 + 2] dearomatizing annulation of saturated carboxylic esters with n-iminoisoquinolinium ylides
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The dearomatizing annulation reaction is a significant challenge in organic chemistry. The direct activation of α-carbons of simple saturated esters, as nucleophiles, is an important synthesis strategy. In the present study, we disclose [3 + 2] dearomatizing annulation reactions with direct activating α-carbons of saturated carboxylic esters and N-iminoisoquinolinium ylides, which possess highly enantioselective characteristics, catalyzed by N-heterocyclic carbenes (NHCs). The protocol achieves isoquinoline dearomatization and the construction of tricyclic chiral products under mild conditions with good yield, substrate tolerance, and diastereoselectivity as well as excellent enantioselectivity.
- Zhang, Pengfei,Zhou, Yu,Han, Xu,Xu, Jinyi,Liu, Hong
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p. 3879 - 3888
(2018/04/14)
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- Recyclable hypervalent iodine(III) reagent iodosodilactone as an efficient coupling reagent for direct esterification, amidation, and peptide coupling
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A hypervalent iodine(III) reagent plays a novel role as an efficient coupling reagent to promote the direct condensation between carboxylic acids and alcohols or amines to provide esters, macrocyclic lactones, amides, as well as peptides without racemization. The regeneration of iodosodilactone (1) can also be readily achieved. The intermediate acyloxyphosphonium ion C from the activation of a carboxylic acid is thought to be involved in the present esterification reaction.
- Tian, Jun,Gao, Wen-Chao,Zhou, Dong-Mei,Zhang, Chi
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supporting information; experimental part
p. 3020 - 3023
(2012/08/07)
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- Effect of low organic solvents concentration on the stability and catalytic activity of HSL-like carboxylesterases: Analysis from psychrophiles to (hyper)thermophiles
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A comparative study aiming at analysing the catalytic activity and stability of four related enzymes belonging to the HSL family in the presence of several water-miscible organic solvents was performed. The studied enzymes were four carboxylesterases: Psy
- Mandrich, Luigi,De Santi, Concetta,De Pascale, Donatella,Manco, Giuseppe
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experimental part
p. 46 - 52
(2012/10/18)
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- An alternative approach to synthesis of 2-n-butyl-5-nitrobenzofuran derivative: A key starting material for dronedarone hydrochloride
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A practical synthesis of (2-butyl-5-nitrobenzofuran-3-yl)(4-hydroxyphenyl) methanone, a key intermediate in the preparation of anti arrhythmic drug, is described. The commercially available 4-nitrophenol (3) is converted in five steps to 2-butyl-5-nitrobenzofuran (9) which upon Friedel-Crafts acylation with 4-methoxybenzoyl chloride followed by deprotection of methyl group gives (2). Indian Academy of Sciences.
- Gopal, P. Raja,Chandrashekar,Saravanan,Bhaskar, B. Vijaya,Somaiah, P. Veera
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p. 1077 - 1085
(2013/03/13)
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- Fingerprint lipolytic enzymes with chromogenic p-nitrophenyl esters of structurally diverse carboxylic acids
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A series of structurally diverse chromogenic esters, including a new compound (4-nitrophenyl 2-methylpentanoate), has been synthesized, constituting an array of 17 substrates which could be applied to rapidly fingerprint the activity of lipases or esterases to reveal their substrates specificity and functional characteristics. Combined with genetic technology such as "data mining" and directed evolution, such fingerprints might be a promising platform for discovery of potentially useful enzymes in industrial application. The fingerprint of commercially available Lipase-B from Candida antarctica as a model enzyme was first measured to confirm the reliability of this method. Then three new enzymes mined from genomic libraries were successfully fingerprinted, revealing the functional characteristics of those enzymes. Among them, the enzyme SrfAD was founded with specific substrate preference towards cycloalkyl carboxylic esters and aromatic esters, making it more promising in synthetic utilities than other tested enzymes.
- Qian, Le,Liu, Jia-Yan,Liu, Jia-Ying,Yu, Hui-Lei,Li, Chun-Xiu,Xu, Jian-He
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experimental part
p. 22 - 26
(2012/02/06)
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- An invesigation of activities and paraoxon sensitivities of hepatic aliesterases in β-naphthoflavone-treated rats
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Aliesterases (carboxylesterases, EC 3.1.1.1) are serine esterases which may protect acetylcholinesterase during organophosphorus insecticide intoxication by providing alternative phosphorylation sites. Levels of hepatic aliesterase activity were investigated after the intraperitoneal administration of β-naphthoflavone (BNF) to female rats using nine 4-nitrophenyl esters as substrates (including straight and branched chain aliphatic and aromatic esters) and 1-naphthyl acetate. In addition, the in vitro sensitivities of aliesterases to inhibition by paraoxon, the active metabolite of the common insecticide parathion, were studied. Hepatic aliesterases from BNF-treated rats displayed lower activities than those from controls with all substrates except 4-nitrophenyl phenylbutyrate and isovalerate. The aliesterases from BNF-treated rats were more sensitive to paraoxon inhibition with 4-nitrophenyl phenylbutyrate, valerate, and butyrate. Esterases hydrolyzing 4-nitrophenyl butyrate, valerate, and branched chain esters were most sensitive to paraoxon inhibition while those hydrolyzing 4-nitrophenyl hexanoate and aromatic esters were least sensitive. The results suggested that BNF-induced changes in hepatic aliesterases could alter responses to organophosphates. Keywords: Aliesterases; β-Naphthoflavone; Paraoxon; Organophosphate
- Watson, Angela M.,Chambers, Howard,Chambers, Janice E.
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p. 217 - 226
(2007/10/03)
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- Inhibition of the Hydrolysis of p-Nitrophenyl Esters by Association with an Erythromycin A Derivative
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The alkaline hydrolysis of p-nitrophenyl esters (1) of an homologous series of straight chain acids and derivatives of naphthoic acids was studied in the presence of the antibiotic erythromycin A (E) and its hydrolysis product (Z).While (E) does not affect the hydrolysis of 1, (Z) inhibits this reaction.The observed pseudo-first-order rate constants decrease as the Z concentration increases and they tend to a minimum value.This inhibition is ascribed to the formation of a host-guest complex between Z and 1.It is suggested that the attack of an external HO- at the carbonyl ester group is hindered by steric and electrostatic effects.The association constants and the second-order rate constants for the complexed esters were calculated.The inhibition tends to be complete for esters of alkyl chains with an add number of carbon atoms.Such a trend is probably related to the geometric requirements of inclusion.
- Barra, Monica,Rossi, Rita H. de
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p. 1758 - 1772
(2007/10/02)
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- Metallomicelles as Catalysts of the Hydrolysis of Carboxylic and Phosphoric Acid Esters
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Lipophilic ligands 2-4 have been synthesized.In the presence of Cu(II) ions, they form metallomicelles that are catalytically active in the cleavage of the p-nitrophenyl esters of acetic, hexanoic, and dodecanoic acids.Catalysis was also observed in the cleavage of p-nitrophenyl diphenyl phosphate.The apparent pKa of the Cu(II)-coordinated hydroxyl of ligand 2a, in the micellar aggregate, is 7.7, as estimated from the rate vs pH profiles for both classes of esters: this suggests that the hydroxyl is involved as a nucleophile in the hydrolytic cleavage, which proved to be a really catalytic process.The ligand bearing the free hydroxyl (2a) is more effective in the cleavage of carboxylate esters than ligands with the methylated alcoholic group (2b) or devoid of it (4); the opposite behaviour is observed in the cleavage of the phosphate triester.A rationale is offered that calls for the difference in the coordination ability to the metal center of phosphate and carboxylate esters.
- Scrimin, Paolo,Tecilla, Paolo,Tonellato, Umberto
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p. 161 - 166
(2007/10/02)
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- CATALYSE ET INHIBITION DE DEUX REACTIONS CONCURRENTES EN MILIEU MICELLAIRE CATIONIQUE
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The general acid catalysed hydrolysis and the intramolecular nucleophilic anionic cyclization of acyloximes operate concurrently in water at pH 7-9.Hydrolysis is inhibited by cationic micelles; changing the length of the acyl chain does not affect the micellar effect, possibly because the environment of the reacting species is not influenced by this variation in the structure of the micelle.
- Soto, R.,Meyer, G.,Viout, P.
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p. 2977 - 2982
(2007/10/02)
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- CATALYTIC EFFICIENCY OF SYNTHETIC MICELLAR CATALYSTS BEARING A MERCAPTO GROUP AS THE REACTION CENTER.
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In order to obtain a clue to understanding the micro-environmental effect on the reactivity of a mercapto group placed in a reaction center of enzymes, micellar surfactants bearing a mercapto group were synthesized and their catalytic activity in the degradation of p-nitrophenyl carboxylates was studied. N-Hexadecyl-N** alpha -glutaryl-L-cysteinamide (AM multiplied by (times) Cys-1) has an ability to form anionic micelles in aqueous media. The catalytic activity of AM multiplied by (times) Cys-1 was compared with that of another synthetic surfactant, N-hexadecanoyl-L-cysteine (AM multiplied by (times) Cys-2). These surfactants below their critical micelle concentations markedly accelerated the degradation of several p-nitrophenyl carboxylates. On the contrary, the concentration-rate profiles for the degradation of p-nitrophenyl dodecanoate (PNPL) as catalyzed by the surfactants indicate that the reactivity of the mercapto group is reduced upon formation of the anionic micelles.
- Murakami,Nakano,Matsumoto
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p. 2996 - 3004
(2007/10/05)
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