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c-h bond activation

Madison Davidson, Meredith McNamee, Ruixi Fan, Yisong Guo, Wei-Chen Chang
Three mononuclear non-heme iron dependent enzymes, L-Ile 4-hydroxylase, L-Leu 5-hydroxylase and polyoxin dihydroxylase, are reported to catalyze the hydroxylation of L-isoleucine, L-leucine and L-α-amino-δ-carbamoylhydroxyvaleric acid (ACV). In this study we showed that these enzymes can accommodate various leucine isomers and catalyze regiospecific hydroxylation. Based on these results, as a proof-of-concept, we demonstrated that the outcome of the reaction can be redirected by installation of an assisting group within the substrate...
February 13, 2019: Journal of the American Chemical Society
Veronique Gouverneur, Robert Szpera, Daniel F J Moseley, Lewis B Smith, Alistair J Sterling
This Review summarizes the advances in fluorination via C(sp2)-H and C(sp3)-H activation. Transition metal catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp2) and C(sp3) sites exploiting the reactivity of high oxidation transition metal fluoride complexes combined with the use of directing group (some transient) to control regio- and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared...
February 13, 2019: Angewandte Chemie
Asfa Rizvi, Bilal Ahmed, Almas Zaidi, Mohd Saghir Khan
Heavy metal pollution destruct soil microbial compositions and functions, plant's performance and subsequently human health. Culturable microbes among many metal abatement strategies are considered inexpensive, viable and environmentally safe. In this study, nitrogen fixing bacterial strain CAZ3 recovered from chilli rhizosphere tolerated 100, 1000 and 1200 µg mL-1 of cadmium, chromium and nickel, respectively and was identified as Azotobacter chroococcum by 16S rDNA sequence analysis. Under metal stress, cellular morphology of A...
February 13, 2019: Ecotoxicology
Yan Xu, Xiaotian Qi, Pengfei Zheng, Carlo C Berti, Peng Liu, Guangbin Dong
Carbon-hydrogen (C-H) and carbon-carbon (C-C) bonds are the main constituents of organic matter. The recent advancement of C-H functionalization technology has vastly expanded our toolbox for organic synthesis1 . In contrast, C-C activation methods that allow editing of the molecular skeleton remain limited2- . So far, a number of methods have appeared for catalytic C-C activation, particularly with ketone substrates, which are typically promoted either by ring-strain release as a thermodynamic driving force4,6 or using directing groups5,7 to control the reaction outcome...
January 30, 2019: Nature
Qiusheng Zhang, Binglian Xu, Jiajia Pan, Danyang Liu, Ruoxian Lv, Dongchun Yan
Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngodon idellus) production and results in high mortality in China. VP7 from GCRV is involved in viral infection and could be suitable for developing vaccines for the control of GCRV infection. To obtain a genetically engineered vaccine and a plant-based oral vaccine and to evaluate their immune efficacy as an oral vaccine against GCRV, cholera toxin B subunit (CTB) of Vibrio cholerae fused to VP7 (CTB-VP7) was transformed into BL21(DE3) for expression...
February 9, 2019: Protein Expression and Purification
Kim N Tu, Scott Kim, Suzanne A Blum
Herein we report an aminoboration reaction that employs inexpensive, Earth-abundant, and commercially available Cu(OTf)2 as an effective catalyst in the direct addition of B-N σ bonds to C-C π bonds, generating borylated pyrazoles, which are useful building blocks for drug discovery. By nature of the mechanism, the reaction produces exclusively one regioisomer and tolerates groups incompatible with alternative lithiation/borylation and iridium-catalyzed C-H activation/borylation methods. The reaction can be scaled up, and the resulting isolable pyrazole pinacol boronates can be further functionalized through palladium-catalyzed Suzuki cross-coupling reactions...
February 12, 2019: Organic Letters
Cai-Hong Guo, Dandan Yang, Xiaoyan Liu, Xiang Zhang, Haijun Jiao
UB3LYP computation including dispersion and toluene solvation has been carried to elucidate the mechanisms of alkene hydrogenation catalyzed by bis(imino)pyridine iron dinitrogen complex (iPr PDI)Fe(N2 )2 , which has low stability towards N2 dissociation. The coordinatively unsaturated complexes, (iPr PDI)Fe(N2 ) and (iPr PDI)Fe(1-C4 H8 ), favor open-shell singlet ground states. On the basis of our computations, we propose a new mechanism of 1-butene coordination and hydrogenation after N2 dissociation. The hydrogenation of 1-butene undergoes a concerted open-shell singlet transition state involving H2 dissociation, C-H bond formation and C=C bond elongation, as well as the subsequent C-H reductive elimination...
February 12, 2019: Journal of Molecular Modeling
Jun Hu, Shenghua Zhang, Rui Xiao, Xiaoxiang Jiang, Yunjun Wang, Yahui Sun, Ping Lu
Using isopropanol as an in situ hydrogen donor, catalytic transfer hydrogenolysis of lignin into monomeric phenols was studied at mild conditions. The performance of catalysts and the effects of H2 , temperature, and time on depolymerization of acid extracted birch lignin (ABL) were extensively examined. Platinum-rhenium supported on titanium dioxide (PtRe/TiO2 ) exhibited much higher activity on disrupting CO bonds than Pd/C, HZSM-5, Pt/TiO2 , and Re/TiO2 . 18.71 wt% monophenols was achieved for depolymerization of ABL over PtRe/TiO2 at 240 °C for 12 h with He...
January 29, 2019: Bioresource Technology
Ronan Rocaboy, Olivier Baudoin
1, n-Metal shift is an elegant alternative approach enabling the functionalization of remote C-H bonds from simple precursors. In this work, we report a novel and simple Pd0 -catalyzed domino reaction involving 1,4-palladium shift and C(sp3 )-H activation and leading to (fused) five-membered rings. This method allowed access to a broad range of valuable arylidene γ-lactams and indanones and was applied to the formal synthesis of (-)-pyrrolam.
February 8, 2019: Organic Letters
Ruixue Tian, Yan Li, Changhai Liang
With the help of DFT calculations, the reaction mechanisms of the rhodium(III)-catalyzed C-H activation/annulation between aromatic amide and α-allenol leading to the formation of isoindolinone have been theoretically investigated. Our calculated results show that the catalytic cycle consists of four stages: N-H deprotonation and C-H activation (Stage I), allene insertion, rearrangement and isomerization (Stage II), β-H elimination and enol-keto tautomerism (Stage III), and catalyst regeneration resulting in the five-membered ring product (Stage IV)...
February 8, 2019: Journal of Organic Chemistry
Alexandria Deliz Liang, Joan Serrano-Plana, Ryan L Peterson, Thomas R Ward
Artificial metalloenzymes (ArMs) result from anchoring a metal-containing moiety within a macromolecular scaffold (protein or oligonucleotide). The resulting hybrid catalyst combines attractive features of both homogeneous catalysts and enzymes. This strategy includes the possibility of optimizing the reaction by both chemical (catalyst design) and genetic means leading to achievement of a novel degree of (enantio)selectivity, broadening of the substrate scope, or increased activity, among others. In the past 20 years, the Ward group has exploited, among others, the biotin-(strept)avidin technology to localize a catalytic moiety within a well-defined protein environment...
February 8, 2019: Accounts of Chemical Research
Neeraj Kumar, Denis Bucher, Pawel M Kozlowski
Vitamin B12-dependent enzymes catalyze several difficult radical reactions. However, there are fundamental open questions that need to be addressed to fully understand the formation of highly reactive radical species, its dynamics, and interaction with substrate and enzyme. In this work, Car-Parrinello molecular dynamics (CPMD) was performed within a QM/MM framework on a reduced AdoCbl cofactor, which was taken as a post-PCET initial step in the activation of the AdoCbl-dependent methylmalonyl CoA mutase (MCM) enzyme...
February 8, 2019: Journal of Physical Chemistry. B
Ángel Manu Martínez, Inés Alonso, Nuria Rodríguez, Ramon Gomez-Arrayas, Juan C Carretero
A new reactivity mode of 1,3-diynes in Rh-catalyzed oxidative annulation enables the rapid assembly of extended π-systems from readily available picolinamide derivatives. The process involves a double C-H bond activation and iterative annulation of two units of 1,3-diyne, each alkyne moiety of which is engaged in an orchestrated insertion sequence with high regiocontrol, leading to the formation of five new C-C bonds and construction of four fused rings in a single operation. Either isoquinoline 1-carboxamides or fused-polycyclic systems can be accessed by a switch in regioselectivity for the second diyne insertion depending on the reaction conditions...
February 8, 2019: Chemistry: a European Journal
Shishir Ghosh, Nathan Hollingsworth, Mark Warren, David A Hrovat, Michael G Richmond, Graeme Hogarth
[FeFe]-hydrogenases contain strongly electronically coupled diiron [2Fe]H and tetrairon [Fe4-S4]H clusters, and thus much recent effort has focused on the chemistry of diiron-dithiolate biomimics with appended redox-active ligands. Here we report on the synthesis and electrocatalytic activity of Fe2(CO)4(μ-edt)(κ2-bpcd) (2) in which the electron-acceptor 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) acts as a surrogate of the [Fe4-S4]H sub-cluster. The complex is prepared in low yield but has been fully characterised, including a crystallographic study which shows that the diphosphine adopts a basal-apical coordination geometry in the solid state...
February 8, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Lianshuang Zhang, Qin Chen, Guige Hou, Wei Zhao, Yun Hou
Novel hydroxyl-substituted double Schiff-base 4-piperidone/cyclohexanone derivatives, 3a-e, 4a-e, 5a-d, and 6a-c, were synthesized and fully characterized by 1 H NMR, IR and elemental analysis. The cytotoxicity against human carcinoma cell lines A549, SGC7901, HePG2, HeLa, K562, THP-1 and non-malignant LO2 cell lines were evaluated. The results showed 4-piperidinone derivatives displayed better cytotoxicity than cyclohexanone derivatives, especially for 3,4,5-trihydroxyphenyl-substituted BAP 5c. The western blot and flow cytometry results proved 5c can effectively promote cell apoptosis through up-regulating Bax protein and down-regulating Bcl-2 protein expression...
December 2019: Journal of Enzyme Inhibition and Medicinal Chemistry
Emmanuel O Garuba, Abiodun, A Onilude
In this study, attempts were made to immobilize purified exo-inulinase from mutant thermophic Aspergillus tamarii -U4 onto Kaolinite clay by covalent bonding cross-linked with glutaraldehyde with an immobilization yield of 66% achieved. The free and immobilized inulinases were then characterized and characterization of the enzymes revealed that temperature and pH optima for the activity of the free and immobilized enzymes were both 65 °C and pH 4.5 respectively. The free inulinase completely lost its activity after incubation at 65 °C for 6 h while the immobilized inulinase retained 16...
December 2018: Journal, Genetic Engineering & Biotechnology
Kun Liu, Shan Tang, Ting Wu, Shengchun Wang, Minzhu Zou, Hengjiang Cong, Aiwen Lei
Oxidative C-H/N-H cross-coupling is one of the most atom-economical methods for the construction of C-N bonds. However, traditional oxidative C-H/N-H cross-coupling either required the use of strong oxidants or high reaction temperature, which makes it difficult to tolerate redox active functional groups. Herein we describe an external chemical oxidant-free electrooxidative C-H/N-H cross-coupling between electron-rich arenes and diarylamine derivatives. Under undivided electrolytic conditions, a series of triarylamine derivatives are produced from electron-rich arenes and diarylamine derivatives with high functional group tolerance...
February 7, 2019: Nature Communications
Alicia Vallet, Adrien Favier, Bernhard Brutscher
We propose here SOFAST-HMBC as a new complementary NMR tool for aromatic side chain assignment of protein samples at natural 13 C abundance. The characteristic peak patterns detected in SOFAST-HMBC for each aromatic side chain allow straightforward assignment of all protons and carbons (including quaternary ones) of the aromatic ring, and for tyrosine and phenylalanine, connection to the CB of the aliphatic chain. The performance of SOFAST-HMBC is demonstrated for three small proteins (7-14 kDa) at millimolar sample concentration using modern high-field NMR instruments equipped with cryogenically cooled probes...
January 23, 2019: Journal of Magnetic Resonance
Haixia Li, Jennifer V Obligacion, Paul J Chirik, Michael B Hall
The mechanism for the borylation of an aromatic substrate by a cobalt pincer complex was investigated by density functional theory calculations. Experimental observations identified trans -(iPr PNP)CoH2 (BPin) as the resting state in the borylation of five-membered heteroarenes, and 4-BPin-(iPr PNP)Co(N2 )BPin as the resting state in the catalytic borylation of arene substrates. The active species, 4-R-(iPr PNP)CoBPin (R=H, BPin), were generated by reductive elimination of H2 in the former, through Berry pseudorotation to the cis isomer, and N2 loss in the latter...
November 2, 2018: ACS Catalysis
Andrew S Rosen, Justin M Notestein, Randall Q Snurr
Metal-organic frameworks (MOFs) are a class of nanoporous materials with highly tunable structures in terms of both chemical composition and topology. Due to their tunable nature, high-throughput computational screening is a particularly appealing method to reduce the time-to-discovery of MOFs with desirable physical and chemical properties. In this work, a fully automated, high-throughput periodic density functional theory (DFT) workflow for screening promising MOF candidates was developed and benchmarked, with a specific focus on applications in catalysis...
February 4, 2019: Journal of Computational Chemistry
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