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Angewandte Chemie

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https://www.readbyqxmd.com/read/28636288/the-first-total-synthesis-of-ovafolinin-a-and-b-unique-polycyclic-benzoxepin-lignans-via-a-cascade-cyclization
#1
Samuel James Davidson, David Barker
Ovafolinins A and B, isolated from Lyonia ovalifolia var. elliptica, are lignans which contain a unique penta- and tetracyclic benzoxepin bridged aryl tetralin structure. We report the first total synthesis of these natural products initially utilizing an acyl-Claisen rearrangement to construct the lignan backbone with correct relative stereochemistry. Judicious use of a bulky protecting group placed reactive moieties in the correct orientation resulting in a cascade reaction forming the benzoxepin bridged aryl tetralin from a linear precursor in a single step...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28636265/switch-of-c-h-activation-mechanism-for-full-selectivity-control-in-cobalt-iii-catalyzed-c-h-alkylations
#2
Daniel Zell, Markus Bursch, Valentin Müller, Stefan Grimme, Lutz Ackermann
Selectivity control in hydroarylation-based C-H alkylation has been dominated by steric interactions. In contrast, we unravel a conceptually distinct strategy that exploits the programmed switch in the C-H activation mechanism by means of cobalt catalysis, setting the stage for expedient C-H alkylations with unactivated alkenes. Detailed mechanistic studies provided compelling evidence for a programmable switch in the C-H activation mechanism from a linear-selective ligand-to-ligand hydrogen transfer (LLHT) to a branched-selective base-assisted internal electrophilic-type substitution (BIES)...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28636246/stretchable-electrochemical-sensor-for-inducing-and-monitoring-cell-mechanotransduction-in-real-time
#3
Yan-Ling Liu, Yu Qin, Zi-He Jin, Xue-Bo Hu, Miao-Miao Chen, Rong Liu, Christian Amatore, Wei-Hua Huang
Existing methods offer little direct and real-time information about stretch-triggered biochemical responses during cell mechanotransduction. Herein, we report a novel stretchable electrochemical sensor that takes advantage of a hierarchical percolation network of carbon nanotubes and gold nanotubes (CNTs- Au NTs). This hybrid nano-structure provides the sensor with excellent time-reproducible mechanical and electrochemical performances while granting very good cellular compatibility, making it perfectly apt to induce and monitor simultaneously transient biochemical signals...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28636238/segmental-domain-selective-perdeuteration-and-small-angle-neutron-scattering-for-structural-analysis-of-multi-domain-proteins
#4
Miriam Sonntag, Pravin Jagtap, Bernd Simon, Marie-Sousai Appavou, Arie Geerlof, Ralf Stehle, Frank Gabel, Janosch Hennig, Michael Sattler
Multi-domain proteins play critical roles in fine-tuning essential processes in cellular signaling and gene regulation. Typically, multiple globular domains that are connected by flexible linkers undergo dynamic re-arrangements upon binding to protein, DNA or RNA ligands. RNA binding proteins (RBPs) represent an important class of multi-domain proteins, which regulate gene expression by recognizing linear or structured RNA sequence motifs. Here, we employ segmental perdeuteration of the three RNA recognition motif (RRM) domains in the RBP TIA-1 using Sortase A-mediated protein ligation...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28636185/decarboxylative-alkynylation
#5
Joel M Smith, Tian Qin, Rohan R Merchant, Jacob T Edwards, Lara R Malins, Zhiqing Liu, Guanda Che, Zichao Shen, Scott A Shaw, Martin D Eastgate, Phil S Baran
The development of a new decarboxylative cross-coupling protocol that affords terminal and substituted alkynes from various carboxylic acids is described using both nickel- and iron-based catalysts. The use of N-hydroxytetrachlorophthalimide (TCNHPI) esters is crucial to the success of the transformation, and the reaction is amenable to in situ carboxylic acid activation. Additionally, an inexpensive, commercially-available alkyne source is employed in this formal homologation process that serves as a surrogate for other well-established alkyne syntheses...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28636128/phosphonium-salts-as-pseudohalides-regioselective-ni-catalyzed-cross-coupling-of-complex-pyridines-and-diazines
#6
Andrew McNally, Xuan Zhang
Heterobiaryls are important pharmacophores that are challenging to prepare by traditional cross-coupling methods. An alternative approach is presented where pyridines and diazines are converted to heteroaryl phosphonium salts and coupled with arylboronic acids. Nickel catalysts are unique for selective heteroaryl transfer, and the reaction has a broad substrate scope that includes complex pharmaceuticals. Phosphonium ions also display orthogonal reactivity in cross-couplings compared to halides enabling chemoselective palladium and nickel-catalyzed coupling sequences...
June 21, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28632957/iridium-i-catalyzed-intramolecular-hydrocarbonation-of-alkenes-efficient-access-to-cyclic-systems-bearing-quaternary-stereocenters
#7
Fernando Lopez, David F Fernández, Moises Gulías, Jose L Mascareñas
A catalytic, versatile and atom-economical C-H functionalization process that provides a wide variety of cyclic systems featuring methyl-substituted quaternary stereocenters is described. The method relies on the use of a cationic Ir(I)-bisphosphine catalyst, which promotes a carboxamide-assisted activation of an olefinic C(sp2)-H bond followed by exo-cyclization to a tethered 1,1-disubstituted alkene. The extension of the method to aromatic and heteroaromatic C-H bonds, as well as developments on an enantioselective variant, are also described...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28632913/a-carbene-catalysis-strategy-for-the-synthesis-of-protoilludane-natural-products
#8
Karl Scheidt, Todd Hovey, Daniel Cohen, Daniel Walden, Paul Cheong
The Armillaria and Lactarius genera of fungi produce antimicrobial and cytotoxic mellolide, protoilludane, and marasmane sesquiterpenoids. Herein, we report a unified synthetic strategy to access the protoilludane, mellolide, and marasmane families of natural products. The significance of these syntheses lies in a) the organocatalytic, enantioselective construction of key chiral intermediates from a simple achiral precursor, b) the utility of a key 1,2-butanediol intermediate to serve as a progenitor to each natural product class, and c) a direct chemical conversion of a protoilludane to a marasmane via serendipitous ring contraction, providing experimental support for their proposed biosynthetic relationships...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28632909/catalyst-controlled-enantioselective-and-diastereodivergent-conjugate-addition-of-aldehydes-to-electron-deficient-olefins
#9
Jennifer Kan, Hiroki Maruyama, Matsujiro Akakura, Taichi Kano, Keiji Maruoka
A chiral amine-catalyzed, enantioselective and diastereodivergent method for aldehyde addition to electron deficient olefins is presented. Hydrogen bonding was used as a control element to achieve unusual anti-selectivity, which was further elucidated through mechanistic and computational studies.
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28632333/from-chemical-topology-to-molecular-machines-nobel-lecture
#10
REVIEW
Jean-Pierre Sauvage
To a large extent, the field of "molecular machines" started after several groups were able to prepare, reasonably easily, interlocking ring compounds (named catenanes for compounds consisting of interlocking rings and rotaxanes for rings threaded by molecular filaments or axes). Important families of molecular machines not belonging to the interlocking world were also designed, prepared, and studied but, for most of them, their elaboration was more recent than that of catenanes or rotaxanes. Since the creation of interlocking ring molecules is so important in relation to the molecular machinery area, we will start with this aspect of our work...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28632317/qm-mm-study-on-the-photoreactions-of-dark-and-light-adapted-states-of-a-blue-light-ytva-lov-photoreceptor
#11
Xue-Ping Chang, Yuan-Jun Gao, Wei-Hai Fang, Ganglong Cui, Walter Thiel
The dark- and light-adapted states of YtvA LOV domains exhibit distinct excited-state behavior. We have employed high-level QM(MS-CASPT2)/MM calculations to study the photochemical reactions of the dark- and light-adapted states. The photoreaction from the dark-adapted state starts with an S1→T1 intersystem crossing followed by a triplet-state hydrogen transfer from the thiol to the flavin moiety that produces a diradical intermediate, and a subsequent internal conversion that triggers a barrierless C-S bond formation in the S0 state...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631868/mn-i-catalyzed-regio-and-stereoselective-1-2-diheteroarylation-of-allenes-combination-of-c-h-activation-and-smiles-rearrangement
#12
Shi-Yong Chen, Xiang-Lei Han, Jia-Qiang Wu, Qingjiang Li, Yunyun Chen, Honggen Wang
Heteroarenes are important structural motif in functional molecules. Reported herein is a Mn(I)-catalyzed 1,2-diheteroarylation of allenes via a C-H activation/Smiles rearrangement cascade. The reaction occurred under additive-free or even solvent-free conditions which allowed the creation of two C-C and one C-N bonds in a single operation. A series of structurally diverse bicyclic or tricyclic compounds bearing an exocyclic double bond were constructed in good to excellent efficiency. The decarboxylative ring-opening of the products led to the facile synthesis of vicinal biheteroaryls...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631867/visible-light-irradiated-graphitic-carbon-nitride-g-c3n4-photocatalyzed-cation-radical-diels-alder-reactions-with-dioxygen-as-sustainable-mediator-for-photoinduced-electrons
#13
Yubao Zhao, Markus Antonietti
Photocatalytic Diels-Alder (D-A) reaction with electron rich olefins is realized by graphitic carbon nitride (g-C3N4) under visible light irradiation and aerobic condition. This heterogeneous photo-redox reaction system is highly efficient, and apparent quantum yield reaches a remarkable value of 47 % for the model reaction. Dioxygen plays a critical role as electron mediator, which is distinct from the previous reports in the homogeneous Ru(II) complex photo-redox system. Moreover, the reaction intermediate vinylcyclobutane is captured and monitored during the reaction, serving as a direct evidence for the proposed reaction mechanism...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631866/mg2-dependent-high-mechanical-anisotropy-of-three-way-junction-prna-revealed-by-single-molecule-force-spectroscopy
#14
Yang Sun, Weishuai Di, Yiran Li, Wenmao Huang, Xin Wang, Meng Qin, Wei Wang, Yi Cao
Mechanical anisotropy is ubiquitous in biological tissues but remains hard to be reproduced in synthetic biomaterials. Developing molecular building blocks with anisotropic mechanical response is the key towards engineering anisotropic biomaterials. Here we report that the three-way-junction- (3WJ-) pRNA, derived from φ29 DNA packaging motor, shows strong mechanical anisotropy upon Mg2+ binding. In the absence of Mg2+, 3WJ-pRNA is mechanically weak without noticeable mechanical anisotropy. While in the presence of Mg2+, the unfolding forces can differ by more than 4 folds along different pulling directions, ranging from ~47 pN to ~219 pN...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631861/renewable-molecular-flasks-with-nadh-models-combination-of-light-driven-proton-reduction-and-biomimetic-hydrogenation-of-benzoxazinones
#15
Liang Zhao, Jianwei Wei, Junhua Lu, Cheng He, Chunying Duan
Using small molecules with defined pockets to catalyze chemical transformations resulted in attractive catalytic syntheses that echo the remarkable properties of enzymes. By modulating the active site of a nicotinamide adenine dinucleotide (NADH) model in a redox-active molecular flask, we combined biomimetic hydrogenation with in situ regeneration of the active site in a one-pot transformation using light as a clean energy source. This molecular flask facilitates the encapsulation of benzoxazinones for biomimetic hydrogenation of the substrates within the inner space of the flask using the active sites of the NADH models...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631860/abi2-io3-2f5-a-k-rb-and-cs-combination-of-halide-and-oxide-anionic-units-to-create-large-shg-response-with-wide-bandgap
#16
Xingguo Chen, Hongming Liu, Qi Wu, Xingxing Jiang, Xianggao Meng, Zheshuai Lin, Jingui Qin
A family of nonlinear optical materials that contain the halide, oxide and oxyhalide polar units simultaneously in a single structure, namely, ABi2(IO3)2F5 (A = K, 1;Rb,2 and Cs,3), have been designed and synthesized. They crystallize in the same polar space group of P21 with a two-dimensional double-layered framework constructed by [BiF5]2- and [BiO2F4]5- units connected to each other by four F atoms, in which two [IO3]- groups are linked to [BiO2F4]5- unit on the same side, and a hanging Bi-F bond of [BiF5]2- unit is located on the other side via ionic interaction with the layer-inserted alkali metal ions to form three-dimensional structure...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631282/biosynthesis-of-complex-indole-alkaloids-elucidation-of-the-concise-pathway-of-okaramines
#17
Chen-Yu Lai, Hsiao-Ching Lin, I-Wen Lo, Ranuka T Hewage, Yi-Chen Chen, Chien-Ting Chen, Chi-Fang Lee, Steven Lin, Man-Cheng Tang
The okaramines are a class of complex indole alkaloids isolated from Penicillium and Aspergillus species. Their potent insecticidal activity arises from selectively activating glutamate-gated chloride channels (GluCls) in invertebrates, not affecting human ligand-gated anion channels. Okaramines B (1) and D (2) contain a polycyclic skeleton, including an azocine ring and an unprecedented 2-dimethyl-3-methyl-azetidine ring. Due to their complex scaffold, okaramines have inspired many total synthesis efforts, but the enzymology of the okaramine biosynthetic pathway remains unexplored...
June 20, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631401/a-polyacrylamide-hydrogel-electrolyte-enabled-intrinsically-1000-stretchable-and-50-compressible-supercapacitor
#18
Yan Huang, Ming Zhong, Fukuan Shi, Xiaoying Liu, Zijie Tang, Yukun Wang, Yang Huang, Haoqing Hou, Xuming Xie, Chunyi Zhi
Stretchability and compressibility of supercapacitors constitute essential elements of modern electronics such as flexible and wearable devices. Widely-used polyvinyl alcohol-based electrolytes are neither very stretchable nor compressible, which fundamentally limit the realization of high stretchability and compressibility of supercapacitors. We present a new electrolyte that is intrinsically super-stretchable and compressible. Vinyl hybrid silica nanoparticle cross-linkers are introduced into polyacrylamide hydrogel backbones to promote dynamic crosslinking of the polymer networks...
June 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28631314/the-covalent-functionalization-of-layered-black-phosphorus
#19
Zdenek Sofer, Jan Luxa, Daniel Bouša, David Sedmidubský, Petr Lazar, Tomas Hartman, Hilde Hardtdegen, Martin Pumera
Layered black phosphorus has been attracting great attention due to its interesting material properties which lead into a plethora of proposed applications. Here we show several approaches for covalent chemical modifications of layered black phosphorus in order to form P-C and P-O-C bonds. We demonstrate that the nucleophilic reagents are highly effective for chemical modification of black phosphorus and that it leads to formation of P-O-C as well as P-C bonds on black phosphorus' surface. Further derivatization approaches investigated were based on the radical reactions...
June 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28628943/molecular-antimony-complexes-for-electrocatalysis-activity-of-a-main-group-element-in-proton-reduction
#20
Jianbing Jiang, Kelly Materna, Svante Hedström, Ke Yang, Robert Crabtree, Victor Batista, Gary Brudvig
Main group complexes are shown to be viable electrocatalysts for the H2-evolution reaction (HER) from acid. A series of antimony porphyrins with varying axial ligands were synthesized for electrocatalysis applications. The proton-reduction catalytic properties of the compound TPSb(OH)2 (TP = 5,10,15,20-tetra(p-tolyl)porphyrin) with two hydroxyl axial ligands was studied in detail, demonstrating catalytic H2 production. Experiments, in conjunction with quantum chemistry calculations, show that the catalytic cycle is driven via the redox activity of both the porphyrin ligand and the Sb center...
June 19, 2017: Angewandte Chemie
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