- A re-investigation of the Fries rearrangement of 3-chlorophenyl acetate and synthesis of 2-azido-1-(4-(benzyloxy)-2-chlorophenyl)ethanone from 4-bromo-3-chlorophenol
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The Fries rearrangement of 3-chlorophenyl acetate provided the expected 4-chloro-2-hydroxy-acetophenone as the major product and 2,4-diacetyl resorcinol and 2-chloro-4-hydroxy-acetophenone as minor products. 4-Benzyloxy-2-chloroacetophenone was prepared by a Heck reaction and then elaborated to 4-benzyloxy-2-chlorophenacyl azide.
- Procopiou, Panayiotis A.,Coe, Diane M.,Procopiou, George
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Read Online
- Porous coordination polymers of diverse topologies based on a twisted tetrapyridylbiaryl: Application as nucleophilic catalysts for acetylation of phenols
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Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D2d--symmetric tetradentate organic linker L, that is, 2,2 ',6,6'-tetramethoxy-3,3',5,5'-tetrakis(4-pyridyl)biphenyl, was designed and synthesized for metal-assisted self-assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3- or 4-connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO3)2 and Cd(NO3)2 yields porous 2D CPs of "fes" topology, in which the tetrapyridyl linker L serves as a 3-connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities.
- Seth, Saona,Venugopalan, Paloth,Moorthy, Jarugu Narasimha
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Read Online
- Effect of Solvent on the α-Effect: Nucleophilic Substitution Reactions of p-Nitrophenyl Acetate with m-Chlorophenoxide and Benzohydroxamates in MeCN-H2O Mixtures of Varying Compositions
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Second-order rate constants have been measured spectrophotometrically for the reactions of p-nitrophenyl acetate (PNPA) with three α-effect nucleophiles, benzohydroxamate (BHA-), p- methylbenzohydroxamate (MBHA-), and p-methyl-N-methylbenzohydroxamate (M2BHA-), and a corresponding normal nucleophile, m-chlorophenoxide (ClPhO-), in MeCN-H2O mixtures of varying compositions at 25.0 °C. The reactivity of ClPhO- and M2BHA- toward PNPA decreases upon additions of MeCN into the reaction medium up to near 30-40 mol % MeCN and is followed by a gradual increase upon further additions of MeCN. BHA- and MBHA- also exhibit initial rate decreases upon the addition of MeCN up to near 40 mol % MeCN. However, unlike the ClPhO- and M2BHA- systems, the rate enhancement beyond 40 mol % MeCN is negligible for the BHA- and MBHA- systems. The present benzohydroxamates exert a large α-effect in H2O. Interestingly, BHA- and MBHA- show a decreasing α-effect trend with increasing mol % MeCN, while M2BHA- exhibits an increasing α-effect trend, indicating that the magnitude of the α-effect is significantly solvent dependent. Based on the results of the kinetic study and relative basicity measurements, the decreasing α-effect trend shown by BHA- and MBHA- has been attributed to an equilibrium shift of these hydroxamates (I) toward their isomeric structures (II or III) upon the addition of MeCN. The solvent dependent α-effect has led a conclusion that the solvent effect on the α-effect is significant; however, the ground state contribution is not solely responsible for the α-effect in the present system.
- Um, Ik-Hwan,Yoon, Hye-Won,Lee, Jeoung-Sook,Moon, Hyun-Jeung,Kwon, Dong-Sook
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- Novel p-functionalized chromen-4-on-3-yl chalcones bearing astonishing boronic acid moiety as MDM2 inhibitor: Synthesis, cytotoxic evaluation and simulation studies
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Background: Novel 4-[3-(6/7/8-Substituted 4-Oxo-4H-chromen-3-yl)acryloyl]phenyl-boronic acid derivatives (5a-h) as well as other 6/7/8-substituted-3-(3-oxo-3-(4-substituted-phenyl)prop-1-enyl)-4H-chromen-4-one derivatives (3a-u) have been designed as p53-MDM2 pathway inhibitors and reported to possess significant cytotoxic properties against several cancer cell lines. Objectives: The current project aims to frame the structure-anticancer activity relationship of chromen-4-on-3-yl chalcones (3a-u/5a-h). In addition, docking studies were performed on these chromeno-chalcones in order to have an insight into their interaction possibilities with MDM2 pro-tein. Methods: Twenty-nine chromen-4-on-3-yl chalcone derivatives (3a-u/5a-h) were prepared by utilizing silica supported-HClO4 (green route with magnificent yield) and tested against four cancer cell lines (HCT116, MCF-7, THP-1, NCIH322). Results: Among the series 3a-u, compound 3b exhibited the highest anticancer activity (with IC50 values ranging from 8.6 to 28.4 μM) overall against tested cancer cell lines. Interestingly, para-Boronic acid derivative (5b) showed selective inhibition against colon cancer cell line, HCT-116 with an IC50 value of 2.35 μM. Besides the emblematic hydrophobic interactions of MDM2 inhibi-tors, derivative 5b was found to exhibit extra hydrogen bonding with GLN59 and GLN72 residues of MDM2 in molecular dynamics (MD) simulation. All the compounds were virtually nontoxic against normal fibroblast cells. Conclusion: Novel compounds were obtained with good anticancer activity especially 6-Chlorochromen-4-one substituted boronic acid derivative 5b. The molecular docking study proposed good activity as a MDM-2 inhibitor suggesting hydrophobic as well as hydrogen bonding interactions with MDM2.
- Bhatia, Richa Kaur,Coutinho, Evans C.,Garg, Ruchika,Kancherla, Satyavathi,Kaur, Maninder,Madan, Jitender,Pissurlenkar, Raghuvir R. S.,Singh, Lakhwinder,Yadav, Manmohan
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p. 212 - 228
(2020/03/10)
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- TRANSCRIPTION FACTOR BRN2 INHIBITORY COMPOUNDS AS THERAPEUTICS AND METHODS FOR THEIR USE
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The invention provides a variety of compounds having the structure of Formula I and uses of such compounds for treatment of various indications, including cancer as well as methods of treatment involving such compounds are also provided. The uses of the compounds may specifically include: bladder cancer, cholangiocarcinoma; colorectal cancer; diffuse large B-cell lymphoma (DLBC); liver cancer; ovarian cancer; thymoma; thyroid cancer; clear cell renal cell carcinoma (CCRCC); chromophobe renal cell carcinoma (ChRCC); prostate cancer; breast cancer; uterine cancer; pancreatic cancer; cervical cancer; uveal melanoma; acute myeloid leukemia (AML); head and neck cancer; small cell lung cancer (SCLC); lung adenocarcinoma sarcoma; mesothelioma; adenoid cystic carcinoma (ACC), sarcoma; testicular germ cell cancer; uterine cancer; pheochromocytoma and paraganglioma (PCPG); melanoma; glioma; glioblastoma multiforme; T-cell Acute Lymphoblastic Leukemia; T-cell Lympohoma, medulloblastoma; and neuroblastoma.
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Page/Page column 111
(2020/05/15)
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- Werner transition-metal complex (WTMC)-mediated mild and efficient chemo-selective acylation of phenols and anilines under solvent-free condition
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Werner-type transition-metal complexes (WTMC) such as [Co(NH3)5Cl]Cl2, Cu[(NH3)4]SO4, Mn(acac)3, Ni[(NH3)6]Cl2, Ni[(en)3]S2O3, and Hg[Co(SCN)4] efficiently promote the chemoselective acetylation of phenols and anilines under solvent-free condition. The results of this study clearly shows that the optimal condition for the acetylation of anilines/phenols (1 mmol) (2a–r) with acetic anhydride (1.2 mmol) in the presence of WTMC (1 mmol) and two drops of H3PO4 on heating for 10 min under solvent-free condition gives the corresponding acetanilides/phenyl acetate (3a–r) in good to excellent yield. Furthermore, the method is simple, efficient, chemoselective, and eco-friendly under solvent-free condition for the acetylation of anilines and phenols promoted by WTMC by using acetic anhydrate as the acetylating agent. The simple preparation of the catalyst, easy procedure of the acetylation reaction, and simple work-up indicate the importance of WTMC for such reactions.
- Sarief, Abdulla,Haque, SK Manirul,Feroze, Syed Mudabbir,Arifuddin, Mohammed
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p. 1104 - 1109
(2018/09/27)
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- Size-selective catalysts in five functionalized porous coordination polymers with unsaturated zinc centers
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The five reported structural isomorphic porous coordination polymers (PCPs) 1-5, namely, [Zn(L)(ip) (1), Zn(L)(aip) (2), Zn(L)(hip) (3), Zn(L)(nip) (4), and Zn(L)(HBTC) (5) (L = N4,N4′-di(pyridine-4-yl)biphenyl-4,4′-dicarboxamide, H2ip = isophthalic acid, H2aip = 5-aminoisophthalic acid, H2hip = 5-hydroxyisophthalic acid, H2nip = 5-nitroisophthalic acid, H3BTC = 1,3,5-benzenetricarboxylic acid)] were used to catalyze the acetylation of phenol. All these heterogeneous catalysts exhibit good catalytic efficiency and size-selectivity toward the acetylation of phenols owing to their unsaturated metal centers, non-coordinated amide, and suitable channel size and shape. Among them, 2 displays the highest catalytic activity and excellent cooperative catalysis due to the presence of basic non-coordinated amide groups.
- Deng, Dongsheng,Guo, Hui,Ji, Baoming,Wang, Weizhou,Ma, Lufang,Luo, Feng
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p. 12611 - 12616
(2017/11/06)
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- Inherent vs Apparent Chemoselectivity in the Kumada-Corriu Cross-Coupling Reaction
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The Kumada-Corriu reaction is a powerful tool for C-C bond formation, but is seldom utilized due to perceived chemoselectivity issues. Herein, we demonstrate that high-yielding couplings can occur in the presence of many electrophilic and heterocyclic functional groups. Our strategy is mechanically based, matching oxidative addition rates with the rate of syringe pump addition of the Grignard reagent. The mechanistic reason for the effectiveness of this strategy is uncovered by continuous-infusion ESI-MS studies.
- Hua, Xiye,Masson-Makdissi, Jeanne,Sullivan, Ryan J.,Newman, Stephen G.
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supporting information
p. 5312 - 5315
(2016/11/02)
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- Palladium-Catalyzed Desilylative Acyloxylation of Silicon-Carbon Bonds on (Trimethylsilyl)arenes: Synthesis of Phenol Derivatives from Trimethylsilylarenes
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A strategy for desilylative acetoxylation of (trimethylsilyl)arenes has been developed in which (trimethylsilyl)arenes are converted into acetoxyarenes. The direct acetoxylation is performed in the presence of 5 mol % of Pd(OAc)2 and PhI(OCOCF3)2 (1.5 equiv) in AcOH at 80°C for 17 h. The acetoxyarenes are obtained in good to high yields (67-98%). The synthetic utility is demonstrated with a one-pot transformation of (trimethylsilyl)arenes to phenols by successive acetoxylation and hydrolysis. Furthermore, desilylative acyloxylation of 2-(trimethylsilyl)naphthalene using several carboxylic acids has been conducted.
- Gondo, Keisuke,Oyamada, Juzo,Kitamura, Tsugio
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supporting information
p. 4778 - 4781
(2015/10/12)
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- 3-Formylchromone based topoisomerase IIα inhibitors: Discovery of potent leads
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Substituted 3-formylchromones were synthesized and evaluated as inhibitors of the human DNA topoisomerase IIα (hTopo-IIα) enzyme. The results of the decatenation, relaxation and DNA intercalation assays revealed that the compounds (11b, 12a, 12b, 12d, 12e, 13a and 13b) exhibited potent inhibitory activity against the hTopo-IIα enzyme, and are nonintercalating agents. These compounds also possess significant in vitro cytotoxicity (LC50 ranges from 0.5-8.6 μM) against prostate (PC-3) cancerous cell line as seen in comparison to the standard drug etoposide. To further probe the plausible mode of action of 3-formylchromone derivatives, molecular docking studies have also been carried out, which showed that the compounds under investigation fitted well in the ATP binding pocket of hTopo-IIα enzyme with good docking scores and form nonbonding interactions with the crucial residues of the catalytic site. The Royal Society of Chemistry.
- Singh, Satyajit,Baviskar, Ashish Triambak,Jain, Vaibhav,Mishra, Nidhi,Chand Banerjee, Uttam,Bharatam, Prasad V.,Tikoo, Kulbhushan,Singh Ishar, Mohan Paul
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supporting information
p. 1257 - 1266
(2013/09/12)
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- Steric control of site selectivity in the Pd-catalyzed C-H acetoxylation of simple arenes
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This report describes the use of an oxidant and a ligand to control site selectivity in the Pd(OAc)2-catalyzed C-H acetoxylation of simple arenes. The use of MesI(OAc)2 as the terminal oxidant in combination with acridine as the ligand results in primarily sterically controlled selectivity. In contrast, with Pd(OAc)2 as the catalyst and PhI(OAc)2 as the oxidant, electronic effects dominate the selectivity of arene C-H acetoxylation.
- Cook, Amanda K.,Emmert, Marion H.,Sanford, Melanie S.
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supporting information
p. 5428 - 5431
(2013/11/19)
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- PtII and PdII complexes with a trans-chelating bis(pyridyl) ligand
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An atropisomeric bis(pyridyl) chelate ligand bis{3,3'-[N-Ph-2-(2'-py) indolyl]} (bpib) has been found to readily form trans-chelating PdII and PtII complexes. Two such complexes, Pt(bpib)Cl2 and Pd(bpib)Cl2 have
- Wang, Nan,McCormick, Theresa M.,Ko, Soo-Byung,Wang, Suning
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p. 4463 - 4469
(2013/01/14)
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- Remarkably high reactivity of Pd(OAc)2/pyridine catalysts: Nondirected C-H oxygenation of arenes
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Less is more: The rational optimization and general applicability of the catalytic system Pd(OAc)2/pyridine is described (see scheme). The catalyst shows excellent reactivity in the C-H oxygenation of simple aromatic substrates. The Pd/pyridine ratio is critical as the use of one equivalent of pyridine per Pd center leads to dramatic enhancements in both reactivity and site selectivity in comparison to Pd(OAc)2 alone.
- Emmert, Marion H.,Cook, Amanda K.,Xie, Yushu J.,Sanford, Melanie S.
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supporting information; experimental part
p. 9409 - 9412
(2011/11/07)
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- Highly efficient dynamic kinetic resolution of secondary aromatic alcohols with low-cost and easily available acid resins as racemization catalysts
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A new and efficient dynamic kinetic resolution (DKR) process of secondary aromatic alcohols was developed with acid resins as racemization catalysts. Acid resin CD8604 was shown to have excellent racemization activity and good biocompatibility. When employing CD8604 and complex acyl donors as racemization catalyst and acyl donor, respectively, enantiomerically pure aromatic acetate was obtained with excellent yield and ee values through the DKR process. It is noteworthy that the system could be reused more than 10 times with little loss of yield and ee value.
- Cheng, Yongmei,Xu, Gang,Wu, Jianping,Zhang, Chensheng,Yang, Lirong
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supporting information; experimental part
p. 2366 - 2369
(2010/06/13)
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- Platinum and palladium complexes containing cationic ligands as catalysts for arene H/D exchange and oxidation
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Cationic catalysts in HD: Palladium(II) and platinum(II) complexes of pyridinium-substituted bipyridine ligands are highly active and stable catalysts for H/D exchange and oxidation of aromatic C-H bonds (TONs up to 3200, TOFs up to 0.1 s-1; se
- Emmert, Marion H.,Gary, J. Brannon,Villalobos, Janette M.,Sanford, Melanie S.
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supporting information; experimental part
p. 5884 - 5886
(2010/11/19)
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- Samarium trifluoromethanesulfonate: An efficient moisture tolerant acylation catalyst under solvent-free condition
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Samarium trifluoromethanesulfonate catalyzed the acylation of phenols, alcohols, thiols, free reducing sugars, and glycosides in excellent yields at ambient temperature under solvent-free condition using stoichiometric amounts of various anhydrides. (Chemical Equation Presented). Copyright Taylor & Francis Group, LLC.
- Roy, Bimalendu,Dasgupta, Somnath,Kumar Rajput, Vishal,Mukhopadhyay, Balaram
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- Synthesis and pharmacological evaluation of chlorinated N-alkyl-3- and -5-(2-hydroxyphenyl)pyrazoles as CB 1 cannabinoid ligands
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The syntheses of several new 3- and 5-(4-chloro-2-hydroxyphenyl)-5- and -3-(2,4-dichlorophenyl)-1-alkylpyrazoles are reported. These syntheses started from simple chlorophenols, 2,4-dichlorobenzaldehyde or ethyl 2,4-dichlorobenzoate in order to prepare py
- Silva, Vera L. M.,Silva, Artur M. S.,Pinto, Diana C. G. A.,Jagerovic, Nadine,Callado, Luis F.,Cavaleiro, Jose A. S.,Elguero, Jose
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p. 797 - 811
(2008/02/10)
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- BENZOPYRAN DERIVATIVES, METHOD OF PRODUCTION AND USE THEREOF
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The invention relates to novel benzopyran derivatives of formula (I), to their method of production, to composition comprising the derivatives and use thereof. Formula (I) wherein: R1, R2, R3 and R4 are independ
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Page/Page column 39-40
(2008/06/13)
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- Substituted 1,3-diphenylprop-2-en-1-one derivatives and preparation and uses thereof
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The invention concerns novel substituted 1,3-diphenylprop-2-en-1-one derivatives, pharmaceutical compositions comprising same, their therapeutic uses, in particular for treating cerebral ischemia. The invention also concerns a method for preparing said derivatives.
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Page/Page column 16
(2008/06/13)
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- Composition based on substituted 1,3-diphenylprop-2-en-1-one derivatives, preparation and uses thereof
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The invention concerns compositions comprising substituted 1,3-diphenylprop-2-en-1-one derivatives designed for therapeutic use. The inventive compositions are useful in particular for preventing or treating cardiovascular diseases, syndrome X, la restenosis, diabetes, obesity, hypertension, inflammatory diseases, cancers or neoplasms (benign or malignant tumors), neurodegenerative, dermatological diseases and disorders related to oxidative stress, for preventing or treating the effects of ageing in general and for example skin ageing, in particular in the field of cosmetics (occurrence of wrinkles and the like).
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Page/Page column 15
(2008/06/13)
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- Highly efficient and enantioselective cyclization of aromatic imines via directed C-H bond activation
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The first highly enantioselective catalytic reaction involving aromatic C-H bond activation is communicated. Enantioselective cyclization of aromatic ketimines containing alkenyl groups tethered at the meta position of an imine directing group has been achieved using 5 mol % [RhCl(coe)2]2 and 15 mol % of an (S)-binol-derived phosphoramidite ligand. Selectivities of up to 96% ee and up to quantitative yields were obtained. Moreover, the identified catalyst system enables the intramolecular alkylation reaction to be performed at temperatures 75 °C lower than our previously reported achiral system. The reaction can even be performed at room temperature for one of the optimal substrates. Copyright
- Thalji, Reema K.,Ellman, Jonathan A.,Bergman, Robert G.
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p. 7192 - 7193
(2007/10/03)
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- Electron-withdrawing substituents decrease the electrophilicity of the carbonyl carbon. An investigation with the aid of 13C NMR chemical shifts, v(C=O) frequency values, charge densities, and isodesmic reactions to interprete substituent effects on reactivity
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13C NMR chemical shifts and v(C=O) frequencies have been measured for several series of phenyl-or acyl-substituted phenyl acetates and for acyl-substituted methyl acetates to investigate the substituent-induced changes in the electrophilic character of the carbonyl carbon. Charge density, bond order, and energy calculations have also been performed. The spectroscopic and charge density results indicate that opposite to the conventional thinking, electron-withdrawing substituents do not increase the electrophilicity of the carbonyl carbon but instead decrease it. On the other hand, reaction energies of the isodesmic reactions designed show that electron-withdrawing substituents destabilize the carbonyl derivatives investigated. So, a significant ground-state destabilization of carboxylic acid esters, and carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents.
- Neuvonen, Helmi,Neuvonen, Kari,Koch, Andreas,Kleinpeter, Erich,Pasanen, Paavo
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p. 6995 - 7003
(2007/10/03)
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- Determination of aromaticity indices of thiophene and furan by nuclear magnetic resonance spectroscopic analysis of their phenyl esters
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A series of m- and p-substituted phenyl benzoates, 2-thienoates, and 2-furoates were prepared and their 1H and 13C nmr spectroscopic characteristics were examined. In general, good correlations were observed between the chemical shift values of protons and carbons of the acyl aromatic rings and the Hammett σ. Plots of the chemical shift values of the carbonyl carbons of the benzoates against those of the 2-thienoates and 2-furoates gave an excellent correlation and the values of the slopes are 0.85 and 0.75, respectively, in dimethyl sulfoxide-d6 and 0.90 and 0.78, respectively, in chloroform-d. The values could be considered as a set of aromaticity indices.
- Lee, Chang Kiu,Yu, Ji Sook,Lee, Hye-Jin
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p. 1207 - 1217
(2007/10/03)
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- Synthesis and in-vitro evaluation of platelet aggregation inhibitory activity of paeonol and its analogues
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Paeonol (1-(2-hydroxy-4-methoxyphenyl)ethanone) and a series of substituted 1-(2-hydroxyphenyl)ethanone derivatives were synthesized and screened as inhibitors of platelet aggregation. The compounds with the greatest anti-platelet potential among the series tested were 1-(2,5-dihydroxyphenyl)ethanone (65.36% inhibition at 300 μM against 5 μM ADP), paeonol(36.31%), 1-(2-hydroxy-5-methoxyphenyl)ethanone (24.47%), 1-(2-hydroxy-5-nitrophenyl) ethanone (30.40%) and 1-(5-chloro-2-hydroxy-4-methylphenyl)ethanone (24.43%).
- Akamanchi,Padmawar,Thatte,Rege,Dahanukar
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p. 323 - 329
(2007/10/03)
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- Therapeutic agents useful for treating inflammatory diseases
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This invention relates to compounds of formula I and pharmaceutically acceptable salts thereof STR1 in which R1, R2 and R3 independently represent hydrogen, halo, alkyl, alkoxy, phenoxy, phenyl, alkoxycarbonyl, --NR13 R14, halogenated alkoxy, halogenated alkyl, benzyloxy, hydroxy, hydroxyalkyl, (C2-6 alkoxycarbonyl)vinyl, --S(O)n R7, carbamoylalkyl, alkoxycarbonylalkyl, --CONR11 R12, or R1 and R2 together with the phenyl ring represent a naphthyl group; R4 and R5 independently represent hydrogen, alkyl, phenyl or together with the carbon atom represent C3-6 cycloalkyl; R6 represents hydrogen, alkyl or ω-hydroxy alkyl; A represents C2-9 alkylene; R8 represents hydrogen, alkyl, halo, alkoxy, hydroxyalkyl, benzyl or phenyl; R9 and R10 independently represent hydrogen, alkyl, halo, alkoxy, phenyl, hydroxyalkyl, alkoxycarbonyl, nitro, --NR30 R31, alkanoyloxyalkyl, or aminomethyl; which are antiinflammatory and antiallergic agents. Compositions containing these compounds and processes to make them are also disclosed.
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- Kinetics and Equilibria of Reactions between Acetic Anhydride and Substituted Phenolate Ions in Aqueous and Chlorobenzene Solutions
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Potassium acetate, solubilised in chlorobenzene by 18-crown-6, displaces the phenolate ion from substituted phenyl acetates by a second-order (kCl-2) process.Potassium phenolate ions, under similar conditions, react with acetic anhydride via a second order (kCl2) to yield the phenyl acetate.The concentration of the crown does not affect the reactivity unless it is not sufficient to solubilise the reactants.The rate constants correlate with the ionisation of the substituted phenols in water: log kCl2=1.60+/-0.23pKArOH(aq)a - 9.06+/-1.4 log kCl-2=-0.97+/-0.12pKArOH(aq)a + 4.78+/-0.78.The equilibrium constant for transfer of the acetyl group between phenolate ions and acetic anhydride in chlorobenzene has a Broensted βCleq of 2.6 measured against pKArOH(aq)a.The second-order rate constants (k2aq) have been measured for the reaction of substituted phenolate ions with acetic anhydride in water and they obey the Broensted equation: log (k2aq) = 0.56 +/- 0.06 pKArOH(aq)a - 2.52 +/- 0.51 Comparison of the value of the Broensted exponent for the equilibrium constant in chlorobenzene (β = 2.6) compared with that for aqueous solution (β = 1.7) indicates a greater development of effective charge consistent with the weaker solvating power of chlorobenzene.The reaction of substituted phenoxide ion with acetic anhydride has a Leffler α value of 0.33 and 0.62 for aqueous and chlorobenzene solutions, respectively, indicating a more advanced bond formation in the transition state of the reaction in the latter solvent even though the reactions in chlorobenzene are faster than in water.
- Ba-Saif, Salem A.,Maude, Antony B.,Williams, Andrew
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p. 2395 - 2400
(2007/10/02)
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- Structure-reactivity correlations for reactions of substituted phenolate anions with acetate and formate esters
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The reactions of substituted phenolate anions with m-nitrophenyl, p-nitrophenyl, and 3,4-dinitrophenyl formates follow nonlinear Br?nsted-type correlations that might be taken as evidence for a change in the rate-limiting step of a reaction that proceeds through a tetrahedral addition intermediate. However, the correlation actually represents two different Br?nsted lines that are defined by meta- and para-substituted phenolate anions and by meta- and para-substituted o-chlorophenolate anions. A concerted mechanism for both acetyl- and formyl-transfer reactions is supported by the absence of a detectable change in the Br?nsted slope at ΔpK = 0 for the attacking and leaving phenolate anions within each class of Br?nsted correlations. Regular increases in the dependence of log k on the pKa of the nucleophile with increasing pKa of the leaving group correspond to a positive interaction coefficient pxy = ?β1g/?(pKnuc) = ?βnuc/?(pK1g). The observation of two different Br?nsted lines for the reactions of substituted phenolate anions with phenyl acetates is attributed to a steric effect that decreases the rate of reaction of substituted o-chlorophenolate anions by 25-50%. The reactions of meta- and para-substituted phenolate and o-chlorophenolate anions with substituted phenyl acetate esters follow values of βnuc = 0.53-0.66 and -β1g = 0.50-0.63. The reactions of meta- and para-substituted phenolate anions with formate esters are ~ 103 times faster and follow smaller values of βnuc = 0.43-0.64 and -β1g = 0.31-0.48. However, the reactions of meta- and para-substituted o-chlorophenolate anions with the same formate esters follow larger values of βnuc = 0.63-0.90 and -β1g = 0.46-0.90. The large values of βnuc and -β1g for the reactions of substituted o-chlorophenolate anions with formate esters may arise from destabilization by the o-chloro group of a stacking interaction that is present in the transition state for reactions of formate esters, but not acetate esters.
- Stefanidis, Dimitrios,Cho, Sayeon,Dhe-Paganon, Sirano,Jencks, William P.
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p. 1650 - 1656
(2007/10/02)
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- Acetylation of phenols in organic solvent catalyzed by a lipase from chromobacterium viscosum
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Lipase from Chromobacterium viscosum, absorbed on an inert support, was employed as catalyst for the esterification of monohydric phenols in organic solvent, with vinyl acetate as acyl donor. The effect of aromatic ring substitution on the initial rate of transesterification was investigated.
- Nicolosi,Piatelli,Sanfilippo
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p. 2477 - 2482
(2007/10/02)
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- Substituent Effect in o-Nitroperbenzoic Acid Oxidation of m- and p-Substituted Acetophenones
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The Baeyer-Villiger reaction of m- and p-substituted acetophenones (substituents: H, p-MeO, p-t-Bu, p-i-Pr, p-Et, p-Me, p-Cl, p-Br, m-MeO, m-Me, m-Cl) with o-nitroperbenzoic acid was studied in chloroform at 30 deg C.The rate constants for the general acid catalysis were measured at several concentrations of o-nitrobenzoic acid which acted as an acid catalyst.The uncatalyzed and acid-catalyzed rate constants obtained afforded ρ values of -2.16 and -4.11 with ?, respectively.The results indicated that the rate-determining step is the migration of the phenyl group in the peroxy acid-carbonyl adduct for all the substituents studied, whether the reaction is acid-catalyzed or not, and that the acid catalyst intervenes only in the formation of the acid-ketone adduct in the initial state and not in the migration step.The variation of the leaving group abilities required the variation of the substituent constants applied, whereas the acid intervention in the addition step was reflected only in the variation of the ρ value, not in the substituent constants to be applied.The smaller resonance demand for o-nitrobenzoic acid indicated that the structure of the transition state in the migration step was looser and that the position of the transition state was earlier than those for m-chloroperbenzoic acid.
- Token, Katsuo,Hirano, Kenji,Yokoyama, Tai,Goto, Katsumi
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p. 2766 - 2771
(2007/10/02)
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- An Open Transition State in Carbonyl Acyl Group Transfer in Aqueous Solution
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The second-order rate constants have been measured for the reaction of substituted phenolate ions with 2,4-dinitrophenyl acetate, 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate and acetic anhydride in aqueous solution at 25 deg C.The data are over a wide range of phenolate ion basicity and obey good Broensted equations which have βnuc values of, respectively, 0.57 +/- 0.03, 0.15 +/- 0.07 and 0.59 +/- 0.05.The principal conclusion of this work is that the identity reaction of 2,4-dinitrophenolate ion with 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate has anopen transition state, namely one with very weak bonds to entering and departing ligands.The transition state possesses a Kreevoy tightness parameter (τ) of 0.18.The open transition state arises from the stabilising effect of the acyl group substituents on the benzoylium ion and their destabilising effect on the putative tetrahedral intermediate as well as the weak basicities of the nucleophile and nucleofuge.This is the first example of an open transition state in an acyl group transfer which does not require the assistance of a negatively charged internal nucleophile.The data for 2,4-dinitrophenyl acetate may be employed to calculate an identity rate constant (kii) for the reaction of 2,4-dinitrophenolate ion with the ester.This data may be fitted to a theoretical Lewis-Kreevoy plot (log kii vs. pKi) possessing both positive and negative values of βii (slope of the line).Microscopic medium effects place a limit to the accuracy of predictions of rate constants, including kii, from linear free energy relationships.
- Ba-Saif, Salem A.,Colthurst, Matthew,Waring, Mark A.,Williams, Andrew
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p. 1901 - 1908
(2007/10/02)
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- Concerted Acetyl Group Transfer between Substituted Phenolate Ion Nucleophiles: Variation of Transition-State Structure as a Function of Substituent
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Second-order rate constants (kArO) have been measured for the concerted displacement of aryl oxide from aryl acetates in aqueous solution by substituted phenoxide ions.Values of kArO obey linear Bronsted correlations when either the leaving group or the attacking phenolate ion structures are varied.The Bronsted coefficients obey the equations βnuc = 0.20pK1g - 0.68 and β1g = 0.15pKnuc - 1.73 to a good degree of precision, and the variation indicates that the structure of the transition-state changes within the range of phenolate ions studied; this alsoprovides confirmation that a concerted mechanism operates.The equations for βnuc and β1g predict the equation (log kii = 0.17pKa2 - 2.41pKa + C) for kii, the rate constant for the reaction of aryl oxide ion with acetates bearing identical aryl oxide leaving groups.The identity rate constants may be interpolated from the observed rate constants (kArO) and exhibit excellent fit to the above equation with the single disposable parameter, C, set at 6.5.This is the first report of curvature in a Bronsted plot of identity rate constants.Effective charge development and loss on leaving and attacking oxyanions is fully balanced in the transition state when entering and leaving nucleophiles have a pKa of 7.1.Tetrahedral or acylium ion-like transition-state structures are predicted for hypothetical phenols with pKa's of 11.7 and 2.0, respectively.
- Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
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p. 2647 - 2652
(2007/10/02)
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- Concertedness in Acyl Group Transfer in Solution: A Single Transition State in Acetyl Group Transfer between Phenolate Ion Nucleophiles
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Rate constants have been measured for nucleophilic substitution of 4-nitrophenol from 4-nitrophenyl acetate by a series of phenolate anions.The Bronsted type plot is linear for unhindered phenolate ions with pKa values significantly above and below that of the displaced 4-nitrophenol: (log kArO = 0.75pKArOH - 7.28; n = 17, r = 0.984); this is consistent with a mechanism involving a single transition state or a mechanism with an intermediate that has a very low barrier to decomposition.A small change in effective charge on the carbonyl group from reactant to transition state (measured from βnuc and the known βeq for the overall reaction) points to an almost coupled concerted mechanism for the transfer of acetyl function between phenolate ion nucleophiles.The conclusions of this work are consistent with previous results that indicate relatively stable tetrahedral intermedates in reactions at reactive acyl centers; a spectrum of mechanisms exists for substitution reactions of acyl functions in solution that ranges from SN1 (or ElcB for an ester with an α-carbanion) through concerted to BAc2.
- Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
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p. 6362 - 6368
(2007/10/02)
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- Nucleophilicity of Phenolates in the Reaction with p-Nitrophenyl Acetate in Ethanol
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The rate of release of p-nitrophenol in the reaction of nine substituted phenolates with p-nitrophenyl acetate has been determined by spectrophotometric measurements in absolute ethanol at 22 deg C.The phenolate anion is the reactive species and competes with ethoxide anion, arising from solvolysis of the phenolate, for nucleophilic attack on the ester carbonyl carbon atoms.From the observed reaction rates the solvolysis constants and the pKa values of the phenols were obtained.The second-order rate constants for phenoxide anions were correlated with the pKa values of the corresponding phenols giving a Broensted β value of 0.57.A comparison with the nucleophilic reactivity of arenethiolates towards the same substrate in ethanol has been made.The rate-determining step is probably the expulsion of the leaving group in the raection of arenethiolates, whereas it is the nucleophile attack in the reaction of phenoxides.
- Guanti, Giuseppe,Cevasco, Giorgio,Thea, Sergio,Dell'Erba, Carlo,Petrillo, Giovanni
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p. 327 - 330
(2007/10/02)
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