- Enzyme-responsive amphiphilic PEG-dendron hybrids and their assembly into smart micellar nanocarriers
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Enzyme-responsive micelles have great potential as drug delivery platforms due to the high selectivity of the activating enzymes. Here we report a highly modular design for the efficient and simple synthesis of amphiphilic block copolymers based on a line
- Harnoy, Assaf J.,Rosenbaum, Ido,Tirosh, Einat,Ebenstein, Yuval,Shaharabani, Rona,Beck, Roy,Amir, Roey J.
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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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p. 1464 - 1469
(2021/02/01)
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- Base-free Enantioselective C(1)-Ammonium Enolate Catalysis Exploiting Aryloxides: A Synthetic and Mechanistic Study
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An isothiourea-catalyzed enantioselective Michael addition of aryl ester pronucleophiles to vinyl bis-sulfones via C(1)-ammonium enolate intermediates has been developed. This operationally simple method allows the base-free functionalization of aryl esters to form α-functionalized products containing two contiguous tertiary stereogenic centres in excellent yield and stereoselectivity (all ≥99:1 er). Key to the success of this methodology is the multifunctional role of the aryloxide, which operates as a leaving group, Br?nsted base, Br?nsted acid and Lewis base within the catalytic cycle. Comprehensive mechanistic studies, including variable time normalization analysis (VTNA) and isotopologue competition experiments, have been carried out. These studies have identified (i) orders of all reactants; (ii) a turnover-limiting Michael addition step, (iii) product inhibition, (iv) the catalyst resting state and (v) catalyst deactivation through protonation.
- McLaughlin, Calum,Slawin, Alexandra M. Z.,Smith, Andrew D.
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supporting information
p. 15111 - 15119
(2019/11/05)
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- Evaluating aryl esters as bench-stable C(1)-ammonium enolate precursors in catalytic, enantioselective Michael addition-lactonisations
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An evaluation of a range of aryl, alkyl and vinyl esters as prospective C(1)-ammonium enolate precursors in enantioselective Michael addition-lactonisation processes with (E)-trifluoromethylenones using isothiourea catalysis is reported. Electron deficient aryl esters are required for reactivity, with 2,4,6-trichlorophenyl esters providing optimal product yields. Catalyst screening showed that tetramisole was the most effective isothiourea catalyst, giving the desired dihydropyranone product in excellent yield and stereoselectivity (up to 90 : 10 dr and 98 : 2 er). The scope and limitations of this process have been evaluated, with a range of diester products being generated after ring-opening with MeOH to give stereodefined dihydropyranones with excellent stereocontrol (10 examples, typically ~90 : 10 dr and >95 : 5 er).
- Young, Claire M.,Taylor, James E.,Smith, Andrew D.
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supporting information
p. 4747 - 4752
(2019/05/24)
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- Uniting C1-Ammonium Enolates and Transition Metal Electrophiles via Cooperative Catalysis: The Direct Asymmetric α-Allylation of Aryl Acetic Acid Esters
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The direct, catalytic, asymmetric α-functionalization of acyclic esters constitutes a significant challenge in the area of asymmetric catalysis, particularly where the configurational integrity of the products is problematic. Through the unprecedented mer
- Schwarz, Kevin J.,Amos, Jessica L.,Klein, J. Cullen,Do, Dung T.,Snaddon, Thomas N.
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supporting information
p. 5214 - 5217
(2016/05/19)
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- Ethyl 2-cyano-2-(2-nitrobenzenesulfonyloxyimino)acetate (o -NosylOXY): A recyclable coupling reagent for racemization-free synthesis of peptide, amide, hydroxamate, and ester
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Ubiquitousness of amide and ester functionality makes coupling reactions extremely important. Although numerous coupling reagents are available, methods of preparation of the common and efficient reagents are cumbersome. Those reagents generate a substantial amount of chemical waste and lack recyclability. Ethyl 2-cyano-2-(2-nitrobenzenesulfonyloxyimino)acetate (o-NosylOXY), the first member of a new generation of coupling reagents, produces byproducts that can be easily recovered and reused for the synthesis of the same reagent, making the method more environmentally friendly and cost-effective. The synthesis of amides, hydroxamates, peptides, and esters using this reagent is described. The synthesis of the difficult sequences, for example, the islet amyloid polypeptide (22-27) fragment (with a C-terminal Gly, H-Asn-Phe-Gly-Ala-Ile-Leu-Gly-NH 2) and acyl carrier protein (65-74) fragment (H-Val-Gln-Ala-Ala-Ile- Asp-Tyr-Ile-Asn-Gly-OH), following the solid-phase peptide synthesis (SPPS) protocol and Amyloid β (39-42) peptide (Boc-Val-Val-IIe-Ala-OMe), following solution-phase strategy is demonstrated. Remarkable improvement is noticed with respect to reaction time, yield, and retention of stereochemistry. A mechanistic investigation and recyclability are also described.
- Dev, Dharm,Palakurthy, Nani Babu,Thalluri, Kishore,Chandra, Jyoti,Mandal, Bhubaneswar
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p. 5420 - 5431
(2014/07/08)
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- Enantioselective activation of stable carboxylate esters as enolate equivalents via N-heterocyclic carbene catalysts
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The first N-Heterocyclic Carbene (NHC) mediated activation of stable carboxylate esters to generate enolate intermediates is disclosed. The catalytically generated arylacetic ester enolates undergo enantioselective reactions with α,β-unsaturated imines.
- Hao, Lin,Du, Yu,Lv, Hui,Chen, Xingkuan,Jiang, Huishen,Shao, Yaling,Chi, Yonggui Robin
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p. 2154 - 2157
(2012/07/14)
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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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- A New and Effective Synthetic Method for the Preparation of the Esters, Peptides, and Lactones Using 3-(5-Nitro-2-oxo-1,2-dihydro-1-pyridyl)-1,2-benzisothiazole 1,1-Dioxide. Synthesis of (+/-)-E-Dodecen-11-olide, Recifeiolide
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3-(5-nitro-2-oxo-1,2-dihydro-1-pyridyl)-1,2-benzisothiazole 1,1-dioxide (BID-NPy), readily prepared from 3-chloro-1,2-benzisothiazole 1,1-dioxide and 5-nitro-2-pyridone, proved to be a very useful condensing reagent.A variety of esters, dipeptides, and lactones were obtained in excellent yields.Furthemore, BID-NPy was successfully employed for the lactonization step in a new synthesis of a naturally occuring (+/-)-(E)-8-dodecen-11-olide, recifeiolide.
- Ahmed, Alauddin,Taniguchi, Nagahiro,Fukuda, Hirohiko,Kinoshita, Hideki,Inomata, Katsuhiko,Kotake, Hiroshi
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p. 781 - 786
(2007/10/02)
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- Alkaline Hydrolysis of Aryl Phenylacetates and Aryl 4-Nitrophenylacetates. Evidence consistent with an Elimination-Addition Mechanism
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Hydrolysis of the substituted phenyl esters of phenylacetic acid is found to be first order each in the ester and hydroxide ion.Hydrolysis is catalysed by general bases and the catalytic coefficients for the substituted phenoxides obey the Broensted relation with β +0.49.The rate of hydrolysis of the esters of 4-nitrophenylacetic acid is independent of in the range employed.Both series of reactions exhibit low solvent isotope effect and high sensitivity to substituents in the leaving group .These datasuggest an E1cB mechanism for the hydrolysis.The keten intermediate envisaged for such a mechanism has been trapped as the anilide when the reactions are conducted in aniline buffers, without any effect on the rate of hydrolysis for variations in .An increase in the DMSO content in the solvent decreases the rate of hydrolysis of the esters of 4-nitrophenylacetic acid, which is explained by an (E1cB)anion mechanism for the hydrolysis.Transfer to aqueous DMSO results in rate accelerations for the esters of phenylacetic acid which can be accounted for by either an (E1cB)Bion pair or (E1cB)reversible mechanism for the hydrolysis.
- Chandrasekar, Ramamurthy,Venkatasubramanian, Nagaswami
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p. 1625 - 1632
(2007/10/02)
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- 3-(5-NITRO-2-PYRIDON-1-YL)-1,2-BENZOISOTHIAZOLE 1,1-DIOXIDE (BID-NPy) AS A NEW EFFECTIVE CONDENSING REAGENT
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3-(5-Nitro-2-pyridon-1-yl)-1,2-benzoisothiazole 1,1-dioxide (BID-NPy) was found to be a useful condensing reagent.Various dipeptides and esters were prepared in good yields using this reagent.
- Ahmed, Alauddin,Fukuda, Hirohiko,Inomata, Katsuhiko,Kotake, Hiroshi
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p. 1161 - 1164
(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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