- Structural insights into the role of the acid-alcohol pair of residues required for dioxygen activation in cytochrome P450 enzymes
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The cytochrome P450 heme monooxygenases commonly use an acid-alcohol pair of residues, within the I-helix, to activate iron-bound dioxygen. This work aims to clarify conflicting reports on the importance of the alcohol functionality in this process. Mutants of the P450, CYP199A4 (CYP199A4D251N and CYP199A4T252A), were prepared, characterised and their crystal structures were solved. The acid residue of CYP199A4 is not part of a salt bridge network, a key feature of paradigmatic model system P450cam. Instead, there is a direct proton delivery network, via a chain of water molecules, extending to the surface. Nevertheless, CYP199A4D251N dramatically reduced the activity of the enzyme consistent with a role in proton delivery. CYP199A4T252A decreased the coupling efficiency of the enzyme with a concomitant increase in the hydrogen peroxide uncoupling pathway. However, the effect of this mutation was much less pronounced than reported with P450cam. Its crystal structures revealed fewer changes at the I-helix, compared to the P450cam system. The structural changes observed within the I-helix of P450cam during oxygen activation do not seem to be required in this P450. These differences are due to the presence of a second threonine residue at position 253, which is absent in P450cam. This threonine forms part of the hydrogen bonding network, resulting in subtle structural changes and is also present across the majority of the P450 superfamily. Overall, the results suggest that while the acid-alcohol pair is important for dioxygen activation this process and the method of proton delivery can differ across P450s. Graphic abstract[Figure not available: see fulltext.].
- Coleman, Tom,Stok, Jeanette E.,Podgorski, Matthew N.,Bruning, John B.,De Voss, James J.,Bell, Stephen G.
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- High density scaffolding of functional polymer brushes: Surface initiated atom transfer radical polymerization of active esters
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In this Article, we describe a method, for the polymerization of active esters based on N-hydroxysuccinimide 4-vinyl benzoate (NHS4VB) using surface initiated atom, transfer radical polymerization (SI-ATRP). Poly(NHS4VB) brushes have high grafting density and a uniform and smooth morphology, and film thickness increases linearly with reaction time. Block copolymer brushes with 2-hydroxyethyl acrylate, tert-butyl acrylate, and styrene were synthesized, from surface bound poly(NHS4VB) macroinitiators, The active ester brushes show rapid and quantitative conversion under aminolysis conditions with primary amines, which was studied using grazing incidence attenuated total reflection. Fourier transform infrared (GATR-FTIR) and UV-vis spectroscopy. UV-vis was also used to quantify the amount of reactive groups in polymer brush layers of differing thickness. Functionalization of the active ester pendant groups with chromophores containing primary amines showed a linear correlation between the amount of chromophore incorporated, into the brush layer and brush thickness. Grafting densities as high as 25.7 nmol/cm2 were observed for a 50 nm brush. Block copolymer brushes with buried active ester functional moieties also undergo quantitative conversion with primary amines as confirmed by GATR-FTIR, We discuss the potential of activated ester brushes as universal scaffolds for sensor and microarray surfaces, where the twofold, control of functionalizable active ester polymer and block copolymers provides well-ordered, tunable microenvironments.
- Orski, Sara V.,Fries, Kristen H.,Sheppard, Gareth R.,Locklin, Jason
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- Precision polyelectrolytes
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Charged macromolecules with controlled microstructures were prepared. Well-defined non-ionic precursors were first synthesized by sequence-controlled radical polymerization of tert-butyl 4-vinyl benzoate with various N-substituted maleimides. Afterwards, these macromolecules were hydrolyzed into polyanions.
- Srichan, Sansanee,Oswald, Laurence,Zamfir, Mirela,Lutz, Jean-Franois
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- Preparation and Characterization of Some Nickel(II) Tetra-aza Macrocyclic Complexes bearing Pendant Polymerisable Groups as Part of the Ligand Superstructure
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The synthesis and characterisation of some new nickel(II) macrocyclic complexes of the 'lacunar' type have been performed where the ligand has, as part of the ligand superstructure, either 4-vinylphenyl or allyl groups capable of undergoing polymerisation reactions with selected comonomers.The n.m.r. spectra of a number of these new complexes show them to be fluxional on the n.m.r. time-scale and the nature of this fluxional behaviour is discussed.Some copolymerisation reactions of these complexes, with styrene or methyl methacrylate comonomers, have been performed.
- Cameron, James H.,Graham, Stephen
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- Amphiphilic polymethacrylate- and polystyrene-based chemical delivery systems for damascones
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Amphiphilic polystyrene- and polymethacrylate-based β-acyloxy ketones were investigated as potential delivery systems for the controlled release of damascones by retro-1,4-addition in applications of functional perfumery. A series of random copolymers being composed of the hydrophobic damascone-release unit and a second hydrophilic monomer were obtained by radical polymerization in organic solution by using 2,2-azobis[2-methylpropanenitrile] (AIBN) as the radical source (Schemes 2 and 3). A first evaluation of the polymer conjugates in acidic or alkaline buffered aqueous solution, and in the presence of a surfactant, showed that polymethacrylates and polystyrenes having a carboxylic acid function as hydrophilic group are particularly interesting for the targeted applications (Table 2). The release of δ-damascone (1) from polymers with poly(methacrylic acid) and poly(vinylbenzoic acid) comonomers in different stoichiometric ratios was thus followed over several days at pH 4, 7, and 9 by comparison of fluorescence probing, solvent extraction, and particle-size measurements (Tables 3 and 4). In acidic media, the polymers were found to be stable, and almost no δ-damascone (1) was released. In neutral or alkaline solution, where the carboxylic acid functions are deprotonated, the concentration of 1 increased over time. In the case of the polymethacrylates, the fluorescence probing experiments showed an increasing hydrophilicity of the polymer backbone with increasing fragrance release, whereas in the case of the polystyrene support, the hydrophilicity of the environment remained constant. These results suggest that the nature of the polymer backbone may have a stronger influence on the fragrance release than the ratio of hydrophilic and hydrophobic monomers in the polymer chain.
- Berthier, Damien,Trachsel, Alain,Fehr, Charles,Ouali, Lahoussine,Herrmann, Andreas
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- Selective Transfer Semihydrogenation of Alkynes with H2O (D2O) as the H (D) Source over a Pd-P Cathode
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We reported a selective semihydrogenation (deuteration) of numerous terminal and internal alkynes using H2O (D2O) as the H (D) source over a Pd-P alloy cathode at a lower potential. P-doping caused the enhanced specific adsorption of alkynes and the promoted intrinsic activity for producing adsorbed atomic hydrogen (H*ads) from water electrolysis. The semihydrogenation of alkynes could be accomplished at a lower potential with up to 99 % selectivity and 78 % Faraday efficiency of alkene products, outperforming pure Pd and commercial Pd/C. This electrochemical semihydrogenation of alkynes might proceed via a H*ads addition pathway rather than a proton-coupled electron transfer process. The decreased amount of H*ads at a lower potential and the more preferential adsorption of the Pd-P to C≡C π bond than C=C moiety resulted in the excellent alkene selectivity. This method was capable of producing mono-, di-, and tri-deuterated alkenes with up to 99 % deuterium incorporation.
- Liu, Cuibo,Lu, Siyu,Wang, Changhong,Wu, Yongmeng,Zhang, Bin
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supporting information
p. 21170 - 21175
(2020/09/11)
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- Cobalt-Catalyzed Reductive Carboxylation of Aryl Bromides with Carbon Dioxide
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Cobalt-catalyzed reductive carboxylation of aryl bromides with carbon dioxide has been developed. The reaction proceeded under one atm pressure of CO2 at 40 °C in the presence of cobalt iodide/2,2′-bipyridine catalysts and zinc dust as a reducing reagent. Various aryl bromides could be converted to the corresponding carboxylic acids in good to high yields. Preliminary mechanistic experiments ruled out intervention of intermediate organozinc species for carboxylation with CO2, thus suggesting a direct CO2 insertion into the corresponding ArCoBr species. (Figure presented.).
- Hang, Wei,Yi, Yaping,Xi, Chanjuan
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supporting information
p. 2337 - 2341
(2020/04/30)
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- Pd-Catalyzed Synthesis of Vinyl Arenes from Aryl Halides and Acrylic Acid
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Acrylic acid is presented as an inexpensive, non-volatile vinylating agent in a palladium-catalyzed decarboxylative vinylation of aryl halides. The reaction proceeds through a Heck reaction of acrylic acid, immediately followed by protodecarboxylation of the cinnamic acid intermediate. The use of the carboxylate group as a deciduous directing group ensures high selectivity for monoarylated products. The vinylation process is generally applicable to diversely substituted substrates. Its utility is shown by the synthesis of drug-like molecules and the gram-scale preparation of key intermediates in drug synthesis.
- Gao, Yang,Ou, Yang,Goo?en, Lukas J.
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supporting information
p. 8709 - 8712
(2019/06/17)
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- Manganese-Catalyzed N-Alkylation of Sulfonamides Using Alcohols
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An efficient manganese-catalyzed N-alkylation of sulfonamides has been developed. This borrowing hydrogen approach employs a well-defined and bench-stable Mn(I) PNP pincer precatalyst, allowing benzylic and simple primary aliphatic alcohols to be employed as alkylating agents. A diverse range of aryl and alkyl sulfonamides undergoes mono-N-alkylation in excellent isolated yields (32 examples, 85% average yield).
- Reed-Berendt, Benjamin G.,Morrill, Louis C.
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p. 3715 - 3724
(2019/03/30)
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- Terminal Alkenes from Acrylic Acid Derivatives via Non-Oxidative Enzymatic Decarboxylation by Ferulic Acid Decarboxylases
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Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min?1. Co-solvent compatibility studies revealed FDC's tolerance to some organic solvents up 20 % v/v. Using the in-vitro (de)carboxylase activity of holo-FDC as well as whole-cell biocatalysts, we performed a substrate profiling study of three FDCs, providing insights into structural determinants of activity. FDCs display broad substrate tolerance towards a wide range of acrylic acid derivatives bearing (hetero)cyclic or olefinic substituents at C3 affording conversions of up to >99 %. The synthetic utility of FDCs was demonstrated by a preparative-scale decarboxylation.
- Aleku, Godwin A.,Prause, Christoph,Bradshaw-Allen, Ruth T.,Plasch, Katharina,Glueck, Silvia M.,Bailey, Samuel S.,Payne, Karl A. P.,Parker, David A.,Faber, Kurt,Leys, David
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p. 3736 - 3745
(2018/08/03)
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- Bis(methoxypropyl) ether-promoted oxidation of aromatic alcohols into aromatic carboxylic acids and aromatic ketones with O2 under metal- and base-free conditions
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We describe an eco-friendly, practical and operationally simple procedure for the bis(methoxypropyl) ether-promoted oxidation of aromatic alcohols into aromatic carboxylic acids and aromatic ketones with atmospheric dioxygen as the sole oxidant. This chemical process is clean with high conversion and good selectivity, and an external initiator, catalyst, additive and base are not required. The virtue of this reaction is highlighted by its easily available and economical raw materials and excellent functional group tolerance (acid-, base- and oxidant-labile groups).
- Liu, Kai-Jian,Jiang, Si,Lu, Ling-Hui,Tang, Ling-Li,Tang, Shan-Shan,Tang, Hai-Shan,Tang, Zilong,He, Wei-Min,Xu, Xinhua
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supporting information
p. 3038 - 3043
(2018/07/13)
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- Palladium-catalyzed oxidative coupling of arylboronic acid with isocyanide to form aromatic carboxylic acids
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A valuable palladium-catalyzed oxidative coupling of aryl- and alkenyl borides with isocyanide for the synthesis of corresponding carboxylic acids has been developed. With wide substrate scopes and good functional group tolerance, this reaction offers corresponding carboxylic acids in moderate to excellent yields.
- Chen, Zhen-Bang,Liu, Kui,Zhang, Fang-Ling,Yuan, Qing,Zhu, Yong-Ming
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p. 8078 - 8083
(2017/10/10)
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- Oligo p-Phenylenevinylene Derivatives as Electron Transfer Matrices for UV-MALDI
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Phenylenevinylene oligomers (PVs) have outstanding photophysical characteristics for applications in the growing field of organic electronics. Yet, PVs are also versatile molecules, the optical and physicochemical properties of which can be tuned by manipulation of their structure. We report the synthesis, photophysical, and MS characterization of eight PV derivatives with potential value as electron transfer (ET) matrices for UV-MALDI. UV-vis analysis show the presence of strong characteristic absorption bands in the UV region and molar absorptivities at 355 nm similar or higher than those of traditional proton (CHCA) and ET (DCTB) MALDI matrices. Most of the PVs exhibit non-radiative quantum yields (φ) above 0.5, indicating favorable thermal decay. Ionization potential values (IP) for PVs, calculated by the Electron Propagator Theory (EPT), range from 6.88 to 7.96 eV, making these oligomers good candidates as matrices for ET ionization. LDI analysis of PVs shows only the presence of radical cations (M+.) in positive ion mode and absence of clusters, adducts, or protonated species; in addition, M+. threshold energies for PVs are lower than for DCTB. We also tested the performance of four selected PVs as ET MALDI matrices for analytes ranging from porphyrins and phthalocyanines to polyaromatic compounds. Two of the four PVs show S/N enhancement of 1961% to 304% in comparison to LDI, and laser energy thresholds from 0.17 μJ to 0.47 μJ compared to 0.58 μJ for DCTB. The use of PV matrices also results in lower LODs (low fmol range) whereas LDI LODs range from pmol to nmol. [Figure not available: see fulltext.].
- Castellanos-García, Laura J.,Agudelo, Brian Castro,Rosales, Hernando F.,Cely, Melissa,Ochoa-Puentes, Christian,Blanco-Tirado, Cristian,Sierra, Cesar A.,Combariza, Marianny Y.
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p. 2548 - 2560
(2017/12/12)
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- Photocaging of Single and Dual (Similar or Different) Carboxylic and Amino Acids by Acetyl Carbazole and its Application as Dual Drug Delivery in Cancer Therapy
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A new fluorescent photoremovable protecting group (FPRPG) based on acetylcarbazole framework has been explored for the first time release of single and dual (similar or different) substrates from single chromophore. Mechanistic studies of the photorelease process revealed that photorelease of two (similar or different) substrates from acetyl carbazole proceeds via a stepwise pathway. Further, we constructed photoresponsive dual drug delivery system (DDS) to release two different anticancer drugs (caffeic acid and chlorambucil, 1 equiv each). In vitro study reveals that our DDS exhibit excellent properties like biocompatibility, cellular uptake, and photoregulated dual drug release.
- Venkatesh, Yarra,Rajesh,Karthik,Chetan,Mandal, Mahitosh,Jana, Avijit,Singh, N.D. Pradeep
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supporting information
p. 11168 - 11175
(2016/11/28)
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- Low-Pressure Cobalt-Catalyzed Enantioselective Hydrovinylation of Vinylarenes
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An efficient and practical protocol for the enantioselective cobalt-catalyzed hydrovinylation of vinylarenes with ethylene at low (1.2 bar) pressure has been developed. As precatalysts, stable [L2CoCl2] complexes are employed that are activated in situ with Et2AlCl. A modular chiral TADDOL-derived phosphine-phosphite ligand was identified that allows the conversion of a broad spectrum of substrates, including heterocyclic vinylarenes and vinylferrocene, to smoothly afford the branched products with up to 99 % ee and virtually complete regioselectivity. Even polar functional groups, such as OH, NH2, CN, and CO2R, are tolerated.
- Movahhed, Sohajl,Westphal, Julia,Dindaro?lu, Mehmet,Falk, Anna,Schmalz, Hans-Günther
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supporting information
p. 7381 - 7384
(2016/05/24)
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- A Strained Disilane-Promoted Carboxylation of Organic Halides with CO2 under Transition-Metal-Free Conditions
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By using a strained four-membered ring disilane (3,4-benzo-1,1,2,2-tetraethyldisilacyclobutene) and CsF, a wide range of aryl, alkenyl, alkynyl, benzyl, allyl, and alkyl halides was successfully carboxylated under an ambient CO2 atmosphere (CO2 balloon) at room temperature within 2 h. In this carboxylation, a highly reactive silyl anion, which is generated from the disilane and CsF, is a key to facilitating the formation of a carbanion equivalent. The resulting anionic species can be trapped with CO2 to produce carboxylic acids with high efficiency.
- Mita, Tsuyoshi,Suga, Kenta,Sato, Kaori,Sato, Yoshihiro
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supporting information
p. 5276 - 5279
(2015/11/18)
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- N-heterocyclic carbene catalyzed umpolung of styrenes: Mechanistic elucidation and selective tail-to-tail dimerization
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The reaction between N-heterocyclic carbenes (NHCs) and styrenes yields alkyl-substituted azolium salts, which are able to form nucleophilic deoxy Breslow intermediates by simple deprotonation. This hitherto unknown reaction of NHCs represents a new way to generate deoxy Breslow intermediates and paves the way for the selective NHC-catalyzed tail-to-tail homodimerization of styrenes. This reaction significantly broadens the scope of the Michael umpolung and provides a new method to generate 1,4-diaryl compounds.
- Schedler, Michael,Wurz, Nathalie E.,Daniliuc, Constantin G.,Glorius, Frank
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supporting information
p. 3134 - 3137
(2014/06/23)
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- Heck, Sonogashira, and Hiyama reactions catalyzed by palladium nanoparticles stabilized by tris-imidazolium salt
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Palladium nanoparticles, prepared by the hydrogenation of Pd(dba) 2 in the presence of a tris-imidazolium iodide as stabilizer, act as an efficient catalyst for Heck and copper-free Sonogashira reactions with a range of aryl iodides and bromides at 0.2 mol-% Pd loading. Moreover, we describe a convenient protocol for the fluoride-free Hiyama coupling of vinylsilanes with aryl iodides that involves the use of sodium hydroxide as promoter in a methanol/water mixture. Under the developed conditions, one-pot, double Heck and Hiyama-Heck reactions are successfully achieved.
- Planellas, Marc,Moglie, Yanina,Alonso, Francisco,Yus, Miguel,Pleixats, Roser,Shafir, Alexandr
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supporting information
p. 3001 - 3008
(2014/05/20)
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- Benzo[a]acridinylmethyl esters as pH sensitive fluorescent photoactive precursors: Synthesis, photophysical, photochemical and biological applications
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A newsworthy class of carboxylate esters based on the (benzo[a]acridin-12- yl)methyl (BAM) chromophore has been shown to perform dual functions as a "pH sensitive fluorescent probe" and a "phototrigger" for acids. The photophysical properties of all the BAM ester conjugates were investigated and found to be highly sensitive to solvent polarity, H-bonding capability and pH of the environment. On irradiation using UV light (≥410 nm), BAM ester conjugates underwent heterolytic cleavage of C-O bonds resulting in efficient release of carboxylic and amino acids. Interestingly, the newly synthesized BAM chromophore was also explored for the construction of a drug delivery system (DDS). In the current DDS, the BAM chromophore plays two important roles: (i) a "fluorophore" for cell imaging and (ii) a "phototrigger" for the drug release. In vitro biological studies revealed that the newly developed BAM based DDS has a good biocompatibility, cellular uptake properties and efficient photoregulated anticancer drug release ability. the Partner Organisations 2014.
- Ikbal,Saha, Biswajit,Barman, Shrabani,Atta, Sanghamitra,Banerjee, Deb Ranjan,Ghosh, Sudip Kumar,Singh, N. D. Pradeep
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p. 3459 - 3469
(2014/05/20)
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- PH-Responsive N-heterocyclic carbene copper(i) complexes: Syntheses and recoverable applications in the carboxylation of arylboronic esters and benzoxazole with carbon dioxide
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A pH-controlled monophasic/biphasic switchable system has been developed as a green and novel strategy for homogeneous catalyst recycling, which has been successfully applied to the Cu-NHC-catalyzed carboxylation of organoboronic esters and benzoxazole with carbon dioxide. Additionally, the present strategy could also be extended to the Ag-NHC-catalyzed carboxylation of terminal alkyne. The tertiary amine-functionalized catalysts could be used for at least four times with a slight loss of activity.
- Wang, Wenlong,Zhang, Guodong,Lang, Rui,Xia, Chungu,Li, Fuwei
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p. 635 - 640
(2013/03/29)
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- Synthesis, spectroscopic, and analyte-responsive behavior of a polymerizable naphthalimide-based carboxylate probe and molecularly imprinted polymers prepared thereof
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A naphthalimide-based fluorescent indicator monomer 1 for the integration into chromo- and fluorogenic molecularly imprinted polymers (MIPs) was synthesized and characterized. The monomer was equipped with a urea binding site to respond to carboxylate-containing guests with absorption and fluorescence changes, namely a bathochromic shift in absorption and fluorescence quenching. Detailed spectroscopic analyses of the title compound and various models revealed the signaling mechanism. Titration studies employing benzoate and Z-l-phenylalanine (Z-l-Phe) suggest that indicator monomers such as the title compound undergo a mixture of deprotonation and complex formation in the presence of benzoate but yield hydrogen-bonded complexes, which are desirable for the molecular imprinting process, with weakly basic guests like Z-l-Phe. Compound 1 could be successfully employed in the synthesis of monolithic and thin-film MIPs against Z-l-Phe, Z-l-glutamic acid, and penicillin G. Chromatographic assessment of the selectivity features of the monoliths revealed enantioselective discrimination and clear imprinting effects. Immobilized on glass coverslips, the thin-film MIPs of 1 displayed a clear signaling behavior with a pronounced enantioselective fluorescence quenching dependence and a promising discrimination against cross-analytes.
- Wagner, Ricarda,Wan, Wei,Biyikal, Mustafa,Benito-Pe?a, Elena,Moreno-Bondi, María Cruz,Lazraq, Issam,Rurack, Knut,Sellergren, B?rje
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p. 1377 - 1389
(2013/03/28)
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- Mechanistic studies on the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water: The effect of the solvent and NaOH promoter
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The mechanism of the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water has been studied using different catalytic precursors. The NaOH promoter converts the initial vinylalkoxysilane into a highly reactive water-soluble vinylsilanolate species. Similarly, deuterium-labeling experiments have shown that, irrespective of the catalytic precursor used, vinylation occurs exclusively at the CH vinylic functionality via a Heck reaction and not at the C-Si bond via a Hiyama cross-coupling. The involvement of a Heck mechanism is interpreted in terms of the reduced nucleophilicity of the base in water, which disfavors the transmetalation step. The Heck product (β-silylvinylarene) undergoes partial desilylation, with formation of a vinylarene, by three different routes: (a) hydrolytic desilylation by the aqueous solvent (only at high temperature); (b) transmetalation of the silyl olefin on the PdH Heck intermediate followed by reductive elimination of vinylarene; (c) reinsertion of the silyl olefin into the PdH bond of the Heck intermediate followed by β-Si syn-elimination. Both the Hiyama and Heck catalytic cycles and desilylation mechanisms b and c have been computationally evaluated for the [Pd(en)Cl2] precursor in water as solvent. The calculated Gibbs energy barriers support the reinsertion route proposed on the basis of the experimental results.
- Gordillo, Alvaro,Ortuno, Manuel A.,Lopez-Mardomingo, Carmen,Lledos, Agusti,Ujaque, Gregori,De Jesus, Ernesto
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supporting information
p. 13749 - 13763
(2013/10/01)
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- Investigation of the substrate range of CYP199A4: Modification of the partition between hydroxylation and desaturation activities by substrate and protein engineering
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The cytochrome P450 enzyme CYP199A4, from Rhodopseudomonas palustris HaA2, can efficiently demethylate 4-methoxybenzoic acid. It is also capable of oxidising a range of other related substrates. By investigating substrates with different substituents and ring systems we have been able to show that the carboxylate group and the nature of the ring system and the substituent are all important for optimal substrate binding and activity. The structures of the veratric acid, 2-naphthoic acid and indole-6-carboxylic acid substrate-bound CYP199A4 complexes reveal the substrate binding modes and the side-chain conformational changes of the active site residues to accommodate these larger substrates. They also provide a rationale for the selectivity of product oxidation. The oxidation of alkyl substituted benzoic acids by CYP199A4 is more complex, with desaturation reactions competing with hydroxylation activity. The structure of 4-ethylbenzoic acid-bound CYP199A4 revealed that the substrate is held in a similar position to 4-methoxybenzoic acid, and that the C β C-H bonds of the ethyl group are closer to the heme iron than those of the Cα (3.5 vs. 4.8 A?). This observation, when coupled to the relative energies of the reaction intermediates, indicates that the positioning of the alkyl group relative to the heme iron may be critical in determining the amount of desaturation that is observed. By mutating a single residue in the active site of CYP199A4 (Phe185) we were able to convert the enzyme into a 4-ethylbenzoic acid desaturase. Engineering a P450 desaturase: The substrate range of CYP199A4 from Rhodopseudomonas palustris was investigated. The partition between the hydroxylation and desaturation activities of 4-ethylbenzoic acid was studied by changing the substrate and by mutation. The activity of CYP199A4 with 4-ethylbenzoic acid was changed to a desaturase by a single mutation at F185. Copyright
- Bell, Stephen G.,Zhou, Ruimin,Yang, Wen,Tan, Adrian B. H.,Gentleman, Alexander S.,Wong, Luet-Lok,Zhou, Weihong
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p. 16677 - 16688
(2013/03/28)
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- Silver(i)-catalyzed carboxylation of arylboronic esters with CO2
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A variety of arylboronic esters were efficiently carboxylated with CO 2 using a simple AgOAc/PPh3 catalyst, affording the corresponding carboxylic acids in good yield. This simple and efficient silver(i) catalytic system showed wide functional group compatibility. The Royal Society of Chemistry 2012.
- Zhang, Xiao,Zhang, Wen-Zhen,Shi, Ling-Long,Guo, Chun-Xiao,Zhang, Ling-Ling,Lu, Xiao-Bing
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supporting information; experimental part
p. 6292 - 6294
(2012/07/16)
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- Process for the carboxylation of aryl halides with palladium catalysts
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A process for the carboxylation of an aryl halide to yield an aryl carboxylic acid, in which the aryl halide and CO2 are contacted in an organic solvent under inert atmosphere and in the presence of a reducing agent and an adequate catalyst system.
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Page/Page column 8
(2011/05/04)
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- Photodeoxygenation of dibenzothiophene S-oxide derivatives in aqueous media
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The use of atomic oxygen (O(3P)) as potent oxidant In water has suffered from the lack of a facile, efficient source. The photodeoxygenatlon of aromatic sulfoxides to the corresponding sulfides in organic solvents has been suggested to produce O(3P) in low quantum yields. The photolysis of 4,6-dihydroxymethyldibenzothiophene S-oxide and 2,8- dihydroxymethyldibenzothiophene S-oxide in water results in deoxygenation at significantly higher quantum yields than In organic solvents. Depending upon conditions, a variable amount of oxidation of the hydroxymethyl substituent into an aldehyde was observed to accompany deoxygenation. Analysis of the photoproducts Indicated the deoxygenation occurred by at least two different pH-sensitive mechanisms. Under basic conditions, photoinduced electron transfer yielding a hydroxysulfuranyl radical that decomposed by heterolytlc S-O cleavage was thermodynamically feasible. The thermodynamics of photoinduced electron transfer were expected to become increasingly unfavorable as the pH of the solution decreased. Thus, at neutral and acidic pH, an S-O bond scission mechanism was suspected. The observed increase In the photodeoxygenation quantum yields was consistent with charge separation accompanying S-O bond scission. Oxidative cleavage of alkenes In aerobic conditions suggested O(3P) was produced during photolysis In these conditions; however, the formation of discrete O-/HO may occur, particularly at low pH.
- Korang, James,Grither, Whitney R.,McCulla, Ryan D.
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scheme or table
p. 4466 - 4476
(2010/06/13)
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- Low pressure vinylation of aryl and vinyl halides via Heck-Mizoroki reactions using ethylene
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Aryl bromides and iodides in the presence of catalytic amounts of a palladacycle derived from acetophenone oxime and 2 equiv of potassium acetate react with ethylene under ambient pressure (15-30 psi) to give the corresponding vinylarenes. The reactions work with both electron-deficient and electron-rich aryl compounds and tolerate wide variety of common functional groups. Vinyl bromides lead to 1,3-dienes in moderate yields.
- Smith, Craig R.,RajanBabu
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supporting information; experimental part
p. 1102 - 1110
(2010/03/25)
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- High density orthogonal surface immobilization via photoactivated copper-free click chemistry
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Surfaces containing reactive ester polymer brushes were functionalized with cyclopropenone-masked dibenzocyclooctynes for the light activated immobilization of azides using catalyst-free click chemistry. The photodecarbonylation reaction in the amorphous brush layer is first order for the first 45 s with a rate constant of 0.022 s-1. The catalyst-free cycloaddition of surface bound dibeznocyclooctynes proceeds rapidly in the presence of azides under ambient conditions. Photolithography using a shadow mask was used to demonstrate patterning with multiple azide containing molecules. This surface immobilization strategy provides a general and facile platform for the generation of multicomponent surfaces with spatially resolved chemical functionality.
- Orski, Sara V.,Poloukhtine, Andrei A.,Arumugam, Selvanathan,Mao, Leidong,Popik, Vladimir V.,Locklin, Jason
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body text
p. 11024 - 11026
(2010/09/17)
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- Palladium-catalyzed direct carboxylation of aryl bromides with carbon dioxide
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(Chemical Equation Presented) A novel protocol for the direct carbon dioxide insertion (CO2) into aryl halides in a catalytic manner is presented herein. Unlike other carboxylation methods using CO2, there is no need for the synthesis of the corresponding organometallic intermediates. Additionally, and in contrast to the well-established carbonylation processes, our protocol does not use highly toxic CO for the preparation of benzoic acids. Furthermore, this method is distinguished by its mild conditions, allowing the tolerance of a wide range of functional groups and substitution patterns. The crucial step of the process involves a challenging catalytic CO2 insertion into Pd-C bonds. Copyright
- Correa, Arkaitz,Martin, Ruben
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supporting information; experimental part
p. 15974 - 15975
(2010/02/15)
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- Carboxylation of organoboronic esters catalyzed by N-heterocyclic carbene copper(I) complexes
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Copper complexes with a CO2 fixation: Copper(I) complexes serve as excellent catalysts for the carboxylation of aryl- and alkenylboronic esters with CO2, affording a variety of functionalized carboxylic acid derivatives (see scheme). Important active intermediates such as the copper(I) aryl and carboxylate complexes, [(IPr)CuR] and [(IPr)CuOCOR] (R = 4-MeOC 6H4, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene), are isolated and structurally characterized. (Chemical Equation Presented).
- Ohishi, Takeshi,Nishiura, Masayoshi,Hou, Zhaomin
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supporting information; experimental part
p. 5792 - 5795
(2009/03/11)
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- Copper(I)-catalyzed carboxylation of aryl- and alkenylboronic esters
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(Chemical Equation Presented) The copper(I)-catalyzed carboxylation reaction of aryl- and alkenylboronic esters proceeded smoothly under CO 2 to give the corresponding carboxylic acid in good yield. This reaction showed wide generality with higher functional group tolerance compared to the corresponding Rh(I)-catalyzed reaction.
- Takaya, Jun,Tadami, Satoshi,Ukai, Kazutoshi,Iwasawa, Nobuharu
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supporting information; experimental part
p. 2697 - 2700
(2009/05/26)
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- Consecutive palladium-catalyzed Hiyama-Heck reactions in aqueous media under ligand-free conditions
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Symmetric and asymmetric (E)-1,2-diarylethenes are synthesized from aryl bromides by consecutive one-pot Hiyama-Heck reactions carried out in water and under air; the only additives required are sodium hydroxide, palladium acetate and poly(ethylene glycol), and the products are isolable in many cases by simple filtration of the water solution. The Royal Society of Chemistry.
- Gordillo, Alvaro,De Jesus, Ernesto,Lopez-Mardomingo, Carmen
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p. 4056 - 4058
(2008/03/14)
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- Cross-linked polystyrene resins containing triorganotin-4-vinylbenzoates: Assessment of their catalytic activity in transesterification reactions
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Three new resins are synthesized by radical co-polymerization of triorganotin-4-vinylbenzoates (substituent at tin = Me, Bu or Ph) with styrene and 1,4-divinylbenzene. The products prepared have been characterized by FT-IR and NMR spectroscopy both in the solid state and as swollen samples, showing a predominantly tetracoordinated tin atom. The catalytic activity of the above resins in a transesterification reaction has been tested using ethyl acetate and primary, secondary or tertiary alcohol, showing good results with the former, but not with the latter ones. Focussing on the different triorganotin substituents, a comparison between the prepared resins and low molecular weight analogues evidences a lower activity of the resins, due to their inhomogeneous operating conditions. However, the triphenyltin functionalized resin shows a transesterification activity comparable to the corresponding model compound. The reaction mechanism and the effects of Lewis acidity of the different groups linked to tin have been investigated by 1H and 119Sn hr-MAS NMR.
- Angiolini, Luigi,Caretti, Daniele,Mazzocchetti, Laura,Salatelli, Elisabetta,Willem, Rudolph,Biesemans, Monique
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p. 3043 - 3052
(2007/10/03)
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- Near-infrared electrochromic and electroluminescent polymers containing pendant ruthenium complex groups
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A series of near-infrared (NIR) electrochromic and electroluminescent polymers containing the pendant dinuclear ruthenium complexes were synthesized and characterized. All the polymers are near-infrared (NIR) electrochromic, displaying an intense absorption centered at 1600 nm upon oxidation to the mixed-valence state. Single-layer diode devices comprising a layer of the complex polymers sandwiched between the ITO and Au electrodes emitted the NIR light centered at 790 nm at ambient temperature.
- Wang, Sheng,Li, Xianzhen,Xun, Shidi,Wan, Xinhua,Wang, Zhi Yuan
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p. 7502 - 7507
(2007/10/03)
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- Simple and efficient protocol for the synthesis of functionalized styrenes from 1,2-dibromoethane and arylboronic acids
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(Matrix presented) A simple and efficient protocol for the preparation of functionalized styrenes is disclosed that employs the palladium-catalyzed cross-coupling reaction of arylboronic acids with vinyl bromide, generated in situ from 1,2-dibromoethane. The reaction is carried out under mild reaction conditions. Compared with the cross-coupling reactions usually employed to obtain vinylarenes, this protocol is very simple, overcomes the inconvenience of using of ethylene under pressure, and uses air-stable and widely available arylboronic acids instead of vinyl organometallic reagents.
- Lando, Vanusa R.,Monteiro, Adriano L.
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p. 2891 - 2894
(2007/10/03)
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- Palladium-catalyzed coupling reaction of alkenylgalliums with aryl halides
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Treatment of aryl halides with alkenylgallium dichloride, prepared from GaCl3 and alkenylmagnesium bromide, in the presence of a catalytic amount of palladium provided cross-coupling products in good yields.
- Mikami, Satoshi,Yorimitsu, Hideki,Oshima, Koichiro
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p. 1137 - 1139
(2007/10/03)
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- Process for the preparation of methyl p-vinylbenzoate and p-vinyl benzoic acid, and their use in latex compositions
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The present invention describes a process for the direct preparation of methyl p-vinylbenzoate from methyl p-formylbenzoate using ketene in the presence of potassium acetate. The chief products obtained from the process are about a five to two ratio of methyl p-vinylbenzoate to p-carbomethoxycinnamic acid. The latter may be thermally decarboxylated, especially in the presence of copper powder, to produce additional quantities of methyl p-vinylbenzoate. Methyl p-vinylbenzoate may further undergo hydrolysis to form p-vinyl benzoic acid. Both methyl p-vinyl benzoate and p-vinyl benzoic acid may be polymerized with ethylenically unsaturated monomers to form useful latex compositions of the present invention.
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- Potassium organotrifluoroborates: New partners in palladium-catalysed cross-coupling reactions
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The preparation of various potassium organotrifluoroborates bearing either aryl, alkenyl, or alkynyl substituents is described. These stable salts are shown to be very efficient partners in palladium-catalysed cross- coupling reactions with arenediazonium salts, affording biaryl and styrene derivatives in high yields.
- Darses, Sylvain,Michaud, Guillaume,Genet, Jean-Pierre
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p. 1875 - 1883
(2007/10/03)
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- The stille cross coupling reactions on solid support. Link to solution phase directed ortho metalation. An ester linker approach to styryl, biaryl and heterobiaryl carboxylic acids
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The synthesis of the titled compounds by Stille cross coupling on Merrifield resin - linked halo benzoates with stannanes followed by LiOH hydrolysis is reported.
- Chamoin, Sylvie,Houldsworth, Stephen,Snieckus, Victor
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p. 4175 - 4178
(2007/10/03)
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- Process for the preparation of aromatic vinyl compounds
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A process is described for preparing aromatic vinyl compounds of general formula (I) Ar CH=CH2]nwhich is characterised in that an aromatic acetylene compound of general formula (II) Ar C≡CH]nis selectively hydrogenated at the triple bond on a noble metal catalyst. This process permits ease of access to functional aromatic vinyl compounds. It makes it possible to prepare technically pure products without expensive process measures.
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- Palladium-Catalyzed Stille Couplings of Aryl, Vinyl-, and Alkyltrichlorostannanes in Aqueous Solution
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Stille Coupling of water-soluble aryl and vinyl halides with alkyl, aryl-, and vinyltrichlorostannane derivatives (RSnCl3) are effected in aqueous solution using a catalyst generated in situ from PdCl2 and KOH both with and without added PhP(mC6H4SO3Na)2.The yields are generally good to excellent, although some limitations of the protocol are described.
- Rai, Roopa,Aubrecht, Katherine B.,Collum, David B.
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p. 3111 - 3114
(2007/10/02)
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- Catalyzed process for reacting carboxylic acids with vinyl ethers
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The present invention relates to a process for the reaction of carboxylic acids with vinyl ethers using a non-polymeric pyridine hydrochloride and/or polymeric vinylpyridine hydrochloride as a catalyst.
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- PRODUCTION OF p-FORMYLSTYRENE
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Methods were developed for the synthesis of p-formylstyrene.The first method involves the formylation of β-bromoethylbenzene and the subsequent elimination of hydrogen bromide with the formation of a double bond.The second involves ozonization of p-divinylbenzene with an oxygen-ozone mixture in the presence of pyridine.
- Matveentseva, M.S.,Buloichik, Zh.I.,Lazareva, A.M.,Uvarova, L.R.,Zyat'kov, I.P.
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p. 741 - 744
(2007/10/02)
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