- Development of pH-activatable fluorescent probes for rapid visualization of metastatic tumours and fluorescence-guided surgeryviatopical spraying
-
A series of pH-activatable aza-BODIPY-based fluorescent probes were developed for rapid cancer visualization and real-time fluorescence-guided surgery by harnessing topical spraying. These probes exhibited good water-solubility, a tunable pKafrom 5.0 to 7.9, and stable intense NIR emission at ~725 nm under acidic conditions.AzaB5with a pKavalue of 6.7 was able to rapidly and clearly visualize pulmonary and abdominal metastatic tumours including tiny metastases less than 2 mmviatopical spraying, further improving intraoperative fluorescence-guided resection. We believe thatAzaB5is promising as a powerful tool to rapidly delineate a broad range of malignancies and assist surgical tumour resection.
- Cao, Wenwen,Li, Xiaoxin,Wu, Peng,Xiong, Hu
-
supporting information
p. 10636 - 10639
(2021/10/19)
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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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- Manganese-mediated acetylation of alcohols, phenols, thiols, and amines utilizing acetic anhydride
-
Manganese(II) chloride-catalyzed acetylation of alcohols, phenols thiols and amines with acetic anhydride is reported. This method is environment-friendly and economically viable as it involves inexpensive, relatively benign catalyst, mild reaction condition, and simple workup. Acetylation is performed under the solvent-free condition at ambient temperature and acetylated products obtained in good to excellent yields. Primary, secondary heterocyclic amines, and phenols with various functional groups are smoothly acetylated in good yields. This method exhibits exquisite chemoselectivity, the amino group is preferentially acetylated in the presence of a hydroxyl/thiol group.
- Jain, Isha,Sharma, Ramandeep,Malik, Payal
-
supporting information
p. 2952 - 2960
(2019/09/13)
-
- Total Synthesis and Structure Revision of Palmarumycin B6
-
Palmarumycin B6 and its regioisomer were synthesized via 7- and 13-step routes using 2-chlorophenol and 4-chlorophenyl methyl ether as the starting materials in overall yields of 2.7% and 12%, respectively. Their structures were characterized b
- Liu, Xinlei,Wang, Weiwei,Zhao, Yu,Lai, Daowan,Zhou, Ligang,Liu, Zhilong,Wang, Mingan
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p. 1803 - 1809
(2018/09/10)
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- Electronic and Steric Optimization of Fluorogenic Probes for Biomolecular Imaging
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Fluorogenic probes are invaluable tools for spatiotemporal investigations within live cells. In common fluorogenic probes, the intrinsic fluorescence of a small-molecule fluorophore is masked by esterification until entry into a cell, where endogenous esterases catalyze the hydrolysis of the masking groups, generating fluorescence. The susceptibility of masking groups to spontaneous hydrolysis is a major limitation of these probes. Previous attempts to address this problem have incorporated auto-immolative linkers at the cost of atom economy and synthetic adversity. Here, we report on a linker-free strategy that employs adventitious electronic and steric interactions in easy-to-synthesize probes. We find that X···C = O n→π? interactions and acyl group size are optimized in 2′,7′-dichlorofluorescein diisobutyrate. This probe is relatively stable to spontaneous hydrolysis but is a highly reactive substrate for esterases both in vitro and in cellulo, yielding a bright, photostable fluorophore with utility in biomolecular imaging.
- Chyan, Wen,Kilgore, Henry R.,Gold, Brian,Raines, Ronald T.
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p. 4297 - 4304
(2017/04/28)
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- Diazepinium perchlorate: a neutral catalyst for mild, solvent-free acetylation of carbohydrates and other substances
-
Diazepinium perchlorate, an essentially neutral organic salt possessing excellent stability, has been found to be well suited for the acetylation of free as well as partially protected sugars, phenols, thiophenols, thiols and other alcohols as well as amines. The diazepinium perchlorate-catalyzed acetylation is mild, organic and solvent-free and leaves acid sensitive protecting groups such as TBDMS/TBDPS/Tr ethers and isopropylidene/benzylidene acetals present on a substrate unaffected. Regioselective hydroxyl protection in partially protected carbohydrate derivatives/polyhydroxylic compounds was possible and was proved to be a convenient time-saving alternative to the conventional synthesis of such compounds. Easy preparation of the catalyst, mild reaction conditions and an environmentally benign protocol are some of the notable features of this reaction. The results obtained on the acetylation of phenols and thiophenols could be rationalized through their local nucleophilicity index obtained from DFT calculations.
- Giri, Santosh Kumar,Gour, Rajesh,Kartha, K. P. Ravindranathan
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p. 13653 - 13667
(2017/03/11)
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- P4VPy–CuO nanoparticles as a novel and reusable catalyst: application at the protection of alcohols, phenols and amines
-
P4VPy–CuO nanoparticles were synthesized using ultrasound irradiations. Relevant properties of the synthesized nanoparticles were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. After identification, the prepared reagent was used for the promotion of different types of protection reactions of alcohols, phenols and amines. Easy workup, short reaction times, excellent yields, relatively low cost and reusability of the catalyst are the striking features of the reported methods.
- Shirini, Farhad,Fallah-Shojaei, Abdollah,Abedini, Masoumeh,Samavi, Laleh
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p. 1699 - 1712
(2016/07/27)
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- Synthesis and biological evaluation of phenoxyacetic acid derivatives as novel free fatty acid receptor 1 agonists
-
Free fatty acid receptor 1 (FFA1) is a new potential drug target for the treatment of type 2 diabetes because of its role in amplifying glucose-stimulated insulin secretion in pancreatic β-cell. In the present studies, we identified phenoxyacetic acid derivative (18b) as a potent FFA1 agonist (EC50 = 62.3 nM) based on the structure of phenylpropanoic acid derivative 4p. Moreover, compound 18b could significantly improve oral glucose tolerance in ICR mice and dose-dependently reduced glucose levels in type 2 diabetic C57BL/6 mice without observation of hypoglycemic side effect. Additionally, compound 18b exhibited acceptable PK profiles. In summary, compound 18b with ideal PK profiles exhibited good activity in vitro and in vivo, and might be a promising drug candidate for the treatment of diabetes mellitus.
- Wang, Xuekun,Zhao, Tianxiao,Yang, Baowei,Li, Zheng,Cui, Jian,Dai, Yuxuan,Qiu, Qianqian,Qiang, Hao,Huang, Wenlong,Qian, Hai
-
p. 132 - 140
(2015/02/18)
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- Solventless acetylation of alcohols and phenols catalyzed by supported iron oxide nanoparticles
-
Supported iron oxide nanoparticles on silicate catalysts were found to be efficient and easily recoverable materials in the acetylation of alcohols and phenols to their corresponding acetyl compounds using acetic anhydride under mild and solvent-less conditions. The supported iron oxide nanoparticles could be easily recovered from the reaction mixture and reused ten times without any loss in activity.
- Rajabi, Fatemeh,Luque, Rafael
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p. 129 - 132
(2014/01/06)
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- Steric control of site selectivity in the Pd-catalyzed C-H acetoxylation of simple arenes
-
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.
-
supporting information
p. 5428 - 5431
(2013/11/19)
-
- Solvent-free acetylation and tetrahydropyranylation of alcohols catalyzed by recyclable sulfonated ordered nanostructured carbon
-
Rapid and practical green acetylation and tetrahydropyranylation routes of structurally diverse alcohols and phenols were applied under solvent-free reaction conditions providing excellent yields, using catalytic amounts of environmentally friendly sulfonated ordered nanoporous carbon (CMK-5-SO 3H). Non-toxic nature of the catalyst, its easy handling, recovery and reusability, and the absence of any solvent characterize the presented procedures as efficient methods. These procedures provide methods for the separation of the product by simple filtration.
- Zareyee, Daryoush,Alizadeh, Parastoo,Ghandali, Mohammad S.,Khalilzadeh, Mohammad A.
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p. 713 - 721
(2013/07/26)
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- PtII and PdII complexes with a trans-chelating bis(pyridyl) ligand
-
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)
-
- Affinity and activity profiling of unichiral 8-substituted 1,4-benzodioxane analogues of WB4101 reveals a potent and selective α1B- adrenoceptor antagonist
-
Unichiral 8-substituted analogues of 2-[(2-(2,6-dimethoxyphenoxy)ethyl) aminomethyl]-1,4-benzodioxane (WB4101) were synthesized and tested for binding affinity at cloned human α1a-, α1b-and α1d-adrenoreceptor (α1a/su
- Fumagalli, Laura,Pallavicini, Marco,Budriesi, Roberta,Gobbi, Marco,Straniero, Valentina,Zagami, Michael,Chiodini, Giuseppe,Bolchi, Cristiano,Chiarini, Alberto,Micucci, Matteo,Valoti, Ermanno
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p. 184 - 191
(2013/02/23)
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- Sonochemical synthesis of silica and silica sulfuric acid nanoparticles from rice husk ash: A new and recyclable catalyst for the acetylation of alcohols and phenols under heterogeneous conditions
-
Silica nanoparticles were synthesized from rice husk ash at room temperature by sonochemical method. The feeding rate of percipiteting agent and time of sonication were investigated. The nanostructure of the synthesized powder was realized by the FE-SEM photomicrograph, FT-IR spectroscopy, XRD and XRF analyses. These analytical observations have revealed that the nano-sized amorphous silica particles are formed and they are spheroidal in shape. The average particle size of the silica powders is found to be around 50 nm. The as-synthesized silica nanoparticles were subsequently modified with chlorosulfonic acid and prepared silica sulfuric acid nanoparticles, which were employed as an efficient catalyst for the acylation of alcohols and phenols with acetic anhydride in excellent yields under solvent-free conditions at room temperature. This reported method is simple, mild, and environmentally viable and catalyst can be simply recovered and reused over 9 times without any significant loss of its catalytic activity.
- Salavati-Niasari, Masoud,Javidi, Jaber
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p. 705 - 712
(2013/02/22)
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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.
-
supporting information; experimental part
p. 9409 - 9412
(2011/11/07)
-
- Electron-deficient [TiIV(salophen)(OTf)2]: A new and highly efficient catalyst for the acetylation of alcohols and phenols with acetic anhydride
-
In the present work, a highly efficient method for acetylation of alcohols and phenols with acetic anhydride catalyzed by high-valent [Ti IV(salophen)(OTf)2] is reported. Under these conditions, primary, secondary and tertiary alcohols as well as phenols were acetylated with short reaction times and high yields. The catalyst was reused several times without loss of its catalytic activity.
- Yadegari, Maryam,Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj
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experimental part
p. 2237 - 2243
(2011/10/03)
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- Investigation of catalytic activity of high-valent vanadium(IV) tetraphenylporphyrin: A new, highly efficient and reusable catalyst for acetylation of alcohols and phenols with acetic anhydride
-
In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V IV(TPP)(OTf)2], in the acetylation of alcohols and phenols with Ac2O is reported. This new V(IV) catalyst was used as an efficient catalyst for not only primary alcohols (benzylic and aliphatic) but also sterically-hindered secondary and tertiary alcohols with acetic anhydride and the corresponding acetates were obtained in 85-99% yield and 0.5-15 min. Acetylation of phenols with acetic anhydride was also performed to afford the desired acetates in 88-99% and 1.5-20 min. This catalyst can be reused several times without loss of its catalytic activity.
- Taghavi, S. Abdolmanaf,Moghadam, Majid,Mohammadpoor-Baltork, Iraj,Tangestaninejad, Shahram,Mirkhani, Valiollah,Khosropour, Ahmad Reza
-
experimental part
p. 159 - 164
(2011/12/16)
-
- Platinum and palladium complexes containing cationic ligands as catalysts for arene H/D exchange and oxidation
-
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)
-
- Counterattack mode differential acetylative deprotection of phenylmethyl ethers: Applications to solid phase organic reactions
-
A counterattack protocol for differential acetylative cleavage of phenylmethyl ether has been developed. The phenylmethyl moiety is liberated as benzyl bromide that is isolated and reused providing advantages in terms of waste minimization/utilization and atom economy. The applicability of this methodology has been extended for solid phase organic reactions with the feasibility of reuse of the solid support.
- Chakraborti, Asit K.,Chankeshwara, Sunay V.
-
experimental part
p. 1367 - 1370
(2009/07/04)
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- Efficient method for oxidation of ketones to esters with 4-aminoperoxybenzoic acid supported on silica gel
-
4-Aminoperoxybenzoic acid supported on silica gel was found to be a versatile and efficient oxidant for the oxidation of ketones to esters. Copyright Taylor & Francis Group, LLC.
- Ghazanfari, Dadkhoda,Hashemi, Mohammed M.,Shahidi-Zandi, Mehdi
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p. 2037 - 2042
(2008/09/21)
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- TiO2: A simple and an efficient catalyst for esterification of phenols under solvent-free condition
-
In the presence of catalytic amount of titanium oxide (TiO2), without any additional solvent at 25°C, phenols are conveniently acylated by acid chlorides to get phenolic esters in excellent yields. The TiO2 powder can be reused three times after simple washing with CH2Cl 2.
- Pasha, Mohamed Afzal,Manjula, Krishnappa
-
p. 597 - 600
(2008/09/19)
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- Samarium trifluoromethanesulfonate: An efficient moisture tolerant acylation catalyst under solvent-free condition
-
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
-
-
- Al(OTf)3 as a highly efficient catalyst for the rapid acetylation of alcohols, phenols and thiophenols under solvent-free conditions
-
Aluminium triflate (0.01-0.1 mol %) was found to be an efficient catalyst for the acylation of alcohols, phenols, thiols and sugars with acetic anhydride in high yields under solvent-free conditions in a short reaction time at room temperature. Racemization of optically active alcohols and epimerization of sugars were not observed. The acylation efficacy of various acyl donors was also investigated.
- Kamal, Ahmed,Khan, M. Naseer A.,Reddy, K. Srinivasa,Srikanth,Krishnaji
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p. 3813 - 3818
(2008/02/06)
-
- Novel synthesis, reactivity, and stereochemistry of substituted 3-trifluoromethyl- and 3-perfluoroalkyl-3-phenoxyprop-2-enal
-
Substituted 3-phenoxy-3-perfluoroalkylprop-2-enals 3a-s are synthesized in high yields starting from a gem-iodoacetoxy derivative 1 and phenoxides 2. Then efficient syntheses of push-pull derivatives 4, 5, 8a,b, and nonconjugated analogues 6 and 7 illustrate the synthetic potentialities of 3. Stereochemical studies of these perfluoroalkyl-containing trisubstituted olefinic derivatives 3-8b revealed that the 4JCF coupling constant observed in the 13C NMR spectra was crucial in the determination of their configurations and conformations in solution. The solvent polarity effect on the stereochemistry of push-pull compounds 3-5 and 8a,b was studied. Unusual significant medium polarity effect on the stereochemistry of imino enol ether derivative 4 was observed.
- El Kharrat, Salem,Laurent, Philippe,Blancou, Hubert
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p. 6742 - 6752
(2007/10/03)
-
- Synthesis of phenylglycine derivatives as potent and selective antagonists of group III metabotropic glutamate receptors
-
The syntheses of a range of ring and α-substituted 4-phosphonophenylglycines are described. A brief discussion of the antagonist activities of compounds 4-10 on group I, II and III metabotropic glutamate (mGlu) receptors expressed in the neonatal rat spin
- Conway, Stuart J,Miller, Jacqueline C,Howson, Patrick A,Clark, Barry P,Jane, David E
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p. 777 - 780
(2007/10/03)
-
- Lanthanide bis[bis(1,1,1,3,3,3-hexafluoro-2-propoxy)sulfonyl]amide as a novel effective acylation catalyst
-
Lanthanide complexes Ln(BHFPSA)3 {BHFPSA = N[SO2OCH(CF3)2]2} catalyse the acylation of alcohols or phenols under very mild conditions to afford esters in high yields.
- Nie, Jin,Zhao, Zhongming,Xu, Jun,Liu, Dafan
-
p. 160 - 161
(2007/10/03)
-
- Retention behavior of compounds with active hydrogen atoms and their acetylated derivatives in reversed-phase HPLC
-
In view of poor interlaboratory reproducibility of retention indices I in reversed-phase high-performance liquid chromatography, not the indices themselves but their differences for reactants and products of interaction with various reagents can be used to identify compounds with active hydrogen atoms. For acetylated derivatives of phenols and aromatic amines, the quantity ?I = I(ArXH) -I(ArXCOCH3), where X = O or NH. has statistically significant distinguishable values of 126 ± 15 and 70 ± 20, respectively. The additivity of the parameters ?I is first revealed for the polyfunctional compounds of these classes that are incapable of intramolecular hydrogen bonding. Abnormal ?I values and deviations from the additivity rule are observed only for substances with intramolecular hydrogen bonding. This finding can be used to confirm the presence of relevant structural units in molecules.
- Zenkevich,Kosman
-
p. 1173 - 1176
(2007/10/03)
-
- Kinetics and Equilibria of Reactions between Acetic Anhydride and Substituted Phenolate Ions in Aqueous and Chlorobenzene Solutions
-
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
-
p. 2395 - 2400
(2007/10/02)
-
- Structure-reactivity correlations for reactions of substituted phenolate anions with acetate and formate esters
-
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)
-
- Kinetics of nuclear chlorination of substituted phenyl acetates by trichloroisocyanuric acid
-
Kinetics of nuclear chlorination of phenyl acetate and its substituted derivatives by trichloroisocyanuric acid (TCICA) in aqueous acetic acid-perchloric acid media follows second order kinetics, first order each in and .The second order rate constants marginally increase with increase in +> pointing to a fractional order in +>.The second order rate constants have a diminishing trend with increase in the proportion of acetic acid in the reaction mixture.A mechanism involving electrophilic attack of both HOCl and H2O+Cl produced from hydrolytic equilibria has been suggested.
- Panda, H P,Sahoo, K K
-
p. 978 - 980
(2007/10/02)
-
- Acetylation of phenols in organic solvent catalyzed by a lipase from chromobacterium viscosum
-
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
-
p. 2477 - 2482
(2007/10/02)
-
- An Open Transition State in Carbonyl Acyl Group Transfer in Aqueous Solution
-
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
-
p. 1901 - 1908
(2007/10/02)
-
- Concerted Acetyl Group Transfer between Substituted Phenolate Ion Nucleophiles: Variation of Transition-State Structure as a Function of Substituent
-
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)
-
- Highly Selective Aromatic Chlorinations. Part 2. The Chlorination of Substituted Phenols, Anisoles, Anilines, and Related Compounds with N-Chloroamines in Acidic Solution
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Phenols, anisoles, anilines, and related compounds are chlorinated in trifluoroacetic acid at room temperature by N-chlorodialkylamines and N-chlorotrialkylammonium salts.With monsubstituted compounds and their 2- and 3-substituted derivatives the reaction occurs efficiently and selectively at the 4-position.The reactivity of these substrates and the selectivity of their chlorinations are determined by electronic rather than steric effects of the substituent.Blocking the reaction with a substituent at the 4-position generally leads to only poor or moderate yields of the 2-chlorinated product.Evidence for radical and cation radical intermediates has been obtained in the reactions of some of the 4-substituted reactants and the mechanism of chlorination is discussed in the light of these findings.The reactions of selected substrates have been scaled up to give laboratory syntheses.
- Smith, John R. Lindsay,McKeer, Linda C.,Taylor, Jonathan M.
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p. 385 - 392
(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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