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Angewandte Chemie

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https://www.readbyqxmd.com/read/28102965/isotope-probing-of-the-udp-apiose-udp-xylose-synthase-reaction-evidence-of-a-mechanism-via-a-coupled-oxidation-and-aldol-cleavage
#1
Thomas Eixelsberger, Doroteja Horvat, Alexander Gutmann, Hansjörg Weber, Bernd Nidetzky
The C-branched sugar d-apiose (Api) is essential for plant cell-wall development. An enzyme-catalyzed decarboxylation/pyranoside ring-contraction reaction leads from UDP-α-d-glucuronic acid (UDP-GlcA) to the Api precursor UDP-α-d-apiose (UDP-Api). We examined the mechanism of UDP-Api/UDP-α-d-xylose synthase (UAXS) with site-selectively (2) H-labeled and deoxygenated substrates. The analogue UDP-2-deoxy-GlcA, which prevents C-2/C-3 aldol cleavage as the plausible initiating step of pyranoside-to-furanoside conversion, did not give the corresponding Api product...
January 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28102964/plasmonic-chirality-imprinting-on-nucleobase-displaying-supramolecular-nanohelices-by-metal-nucleobase-recognition
#2
Yiyang Lin, E Thomas Pashuck, Michael R Thomas, Nadav Amdursky, Shih-Ting Wang, Lesley W Chow, Molly M Stevens
Supramolecular self-assembly is an important process that enables the conception of complex structures mimicking biological motifs. Herein, we constructed helical fibrils through chiral self-assembly of nucleobase-peptide conjugates (NPCs), where achiral nucleobases are helically displayed on the surface of fibrils, comparable to polymerized nucleic acids. Selective binding between DNA and the NPC fibrils was observed with fluorescence polarization. Taking advantage of metal-nucleobase recognition, we highlight the possibility of deposition/assembly of plasmonic nanoparticles onto the fibrillar constructs...
January 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28102962/general-synthesis-of-multishell-mixed-metal-oxyphosphide-particles-with-enhanced-electrocatalytic-activity-in-the-oxygen-evolution-reaction
#3
Bu Yuan Guan, Le Yu, Xiong Wen David Lou
We report a general approach for the synthesis of multishell mixed-metal oxyphosphide particles. Seven-layer Mn-Co oxide particles were first prepared by thermal treatment of Mn-Co coordination polymer precursors. Afterwards, these multishell Mn-Co oxide particles were further transformed into multishell Mn-Co oxyphosphide particles through a phosphidation reaction. This approach is very versatile and can be applied to synthesize other multishell mixed-metal oxyphosphide particles with different compositions...
January 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28102930/modulation-of-the-thermodynamic-signatures-of-an-rna-thermometer-by-osmolytes-and-salts
#4
Mimi Gao, Loana Arns, Roland Winter
Folding of ribonucleic acids (RNAs) is driven by several factors, such as base pairing and stacking, chain entropy, and ion-mediated electrostatics, which have been studied in great detail. However, the power of background molecules in the cellular milieu is often neglected. Herein, we study the effect of common osmolytes on the folding equilibrium of a hairpin-structured RNA and, using pressure perturbation, provide novel thermodynamic and volumetric insights into the modulation mechanism. The presence of TMAO causes an increased thermal stability and a more positive volume change for the helix-to-coil transition, whereas urea destabilizes the hairpin and leads to an increased expansibility of the unfolded state...
January 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28102929/science-award-electrochemistry-for-william%C3%A2-c-chueh
#5
(no author information available yet)
No abstract text is available yet for this article.
January 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28098952/solving-the-puzzle-of-one-carbon-loss-in-ripostatin-biosynthesis
#6
Chengzhang Fu, David Auerbach, Yanyan Li, Ullrich Scheid, Eva Luxenburger, Ronald Garcia, Herbert Irschik, Rolf Müller
Ripostatin is a promising antibiotic that inhibits RNA polymerase by binding to a novel binding site. In this study, the characterization of the biosynthetic gene cluster of ripostatin, which is a peculiar polyketide synthase (PKS) hybrid cluster encoding cis- and trans-acyltransferase PKS genes, is reported. Moreover, an unprecedented mechanism for phenyl acetic acid formation and loading as a starter unit was discovered. This phenyl-C2 unit is derived from phenylpyruvate (phenyl-C3) and the mechanism described herein explains the mysterious loss of one carbon atom in ripostatin biosynthesis from the phenyl-C3 precursor...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097819/enantiospecific-trifluoromethyl-radical-induced-three-component-coupling-of-boronic-esters-with-furans
#7
Yahui Wang, Adam Noble, Christopher Sandford, Varinder K Aggarwal
In the presence of trifluoromethylsulfonium reagents, boronate complexes derived from 2-lithio furan and non-racemic secondary and tertiary alkyl or aryl boronic esters undergo deborylative three-component coupling to give the corresponding 2,5-disubstituted furans with excellent levels of enantiospecificity. The process proceeds via the reaction of boronate complexes with a trifluoromethyl radical, which triggers 1,2-metallate rearrangement upon single-electron oxidation. Alternative electrophiles can also be used in place of trifluoromethylsulfonium reagents to effect similar three-component coupling reactions...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097801/odd-even-alternation-in-tautomeric-porous-organic-cages-with-exceptional-chemical-stability
#8
Saibal Bera, Arghya Basu, Srinu Tothadi, Bikash Garai, Subhrashis Banerjee, Kumar Vanka, Rahul Banerjee
Amine-linked (C-NH) porous organic cages (POCs) are preferred over the imine-linked (C=N) POCs owing to their enhanced chemical stability. In general, amine-linked cages, obtained by the reduction of corresponding imines, are not shape-persistent in the crystalline form. Moreover, they require multistep synthesis. Herein, a one-pot synthesis of four new amine-linked organic cages by the reaction of 1,3,5-triformylphloroglucinol (Tp) with different analogues of alkanediamine is reported. The POCs resulting from the odd diamine (having an odd number of -CH2 groups) is conformationally eclipsed, while the POCs constructed from even diamines adopt a gauche conformation...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097799/stereocontrolled-total-synthesis-of-stemaphylline
#9
Ana Varela, Lennart K B Garve, Daniele Leonori, Varinder K Aggarwal
Homologation of readily available α-boryl pyrrolidines with metal carbenoids is especially challenging even when good leaving groups (Cl(-) ) are employed. By performing a solvent switch from Et2 O to CHCl3 , efficient 1,2-metalate rearrangement of the intermediate boronate occurs with both halide and ester leaving groups. The methodology was used in the total synthesis of the Stemona alkaloid (-)-stemaphylline in just 11 steps (longest linear sequence), with high stereocontrol (>20:1 d.r.) and 11 % overall yield...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097798/discovery-of-novel-cinchona-alkaloid-inspired-oxazatwistane-autophagy-inhibitors
#10
Luca Laraia, Kosuke Ohsawa, Georgios Konstantinidis, Lucas Robke, Yao-Wen Wu, Kamal Kumar, Herbert Waldmann
The cinchona alkaloids are a privileged class of natural products and are endowed with diverse bioactivities. However, for compounds with the closely-related oxazatricyclo[4.4.0.0]decane ("oxazatwistane") scaffold, which are accessible from cinchonidine and quinidine by means of ring distortion and modification, biological activity has not been identified. We report the synthesis of an oxazatwistane compound collection through employing state-of-the-art C-H functionalization, and metal-catalyzed cross-coupling reactions as key late diversity-generating steps...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097797/an-asymmetric-redox-arylation-chirality-transfer-from-sulfur-to-carbon-through-a-sulfonium-3-3-sigmatropic-rearrangement
#11
Dainis Kaldre, Boris Maryasin, Daniel Kaiser, Oliver Gajsek, Leticia González, Nuno Maulide
A general, asymmetric redox arylation of ynamides and thioalkynes with chiral sulfoxides is reported. This is the first example of a general 1,4-chirality transfer from sulfur to a carbon stereocenter through a sulfonium [3,3]-sigmatropic rearrangement. This reaction delivers α-arylated thioesters and amides under mild conditions in an atom-economical manner. The products are formed in high yields with enantiomeric ratios up to 99.5:0.5. Quantum chemical calculations suggest a mechanism for the chirality transfer from sulfur to carbon and explain the experimentally observed correlation of the enantioselectivity with both the catalyst and the substrate...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097796/reductive-dehydrogenation-of-a-stannane-via-multiple-sn-h-activation-by-frustrated-lewis-pairs
#12
Christian P Sindlinger, Frederik S W Aicher, Hartmut Schubert, Lars Wesemann
A bulky substituted stannane Ar*SnH3 (Ar*=2,6-(2',4',6'-triisopropylphenyl)phenyl) was treated with the well-known frustrated Lewis pair (FLP) PtBu3 /B(C6 F5 )3 in varying stoichiometries. To some degree, hydride abstraction and adduct formation is observed, leading to [Ar*SnH2 (PtBu3 )](+) which is rather unreactive toward further dehydrogenation. In a competing process, the FLP proved to be capable of completely striping-off hydrogen and hydrides to generate the first cationic phosphonio-stannylene [Ar*Sn(PtBu3 )](+) ...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097790/visible-light-mediated-remote-aliphatic-c-h-functionalizations-through-a-1-5-hydrogen-transfer-cascade
#13
Wei Shu, Cristina Nevado
A redox-neutral, light-mediated functionalization of unactivated C(sp(3) )-H bonds via iminyl radicals is presented here. A 1,5-H transfer followed by the functionalization of a C(sp(2) )-H bond takes place in aqueous media producing a variety of elaborated fused ketones. Mechanistic investigations have revealed 1,5-H transfer as the reversible, rate-determining step in this transformation. Divergent scaffolds are also accessible via C(sp(3) )-N bond formation upon a careful choice of the reaction additives...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097787/a-ternary-solvent-method-for-large-sized-two-dimensional-perovskites
#14
Junnian Chen, Lin Gan, Fuwei Zhuge, Huiqiao Li, Jizhong Song, Haibo Zeng, Tianyou Zhai
Recent reports demonstrate that a two-dimensional (2D) structural characteristic can endow perovskites with both remarkable photoelectric conversion efficiency and high stability, but the synthesis of ultrathin 2D perovskites with large sizes by facile solution methods is still a challenge. Reported herein is the controlled growth of 2D (C4 H9 NH3 )2 PbBr4 perovskites by a chlorobenzene-dimethylformide-acetonitrile ternary solvent method. The critical factors, including solvent volume ratio, crystallization temperature, and solvent polarity on the growth dynamics were systematically studied...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097775/breaking-the-tetra-coordinated-framework-rule-new-clathrate-ba8-m24-p28-%C3%AE-m-cu-zn
#15
Juli-Anna Dolyniuk, Julia V Zaikina, Derrick C Kaseman, Sabyasachi Sen, Kirill Kovnir
A new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba8 M24 P28+δ (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra common to clathrates along with a unique 22-vertex polyhedron with two hexagonal faces capped by additional partially occupied phosphorus sites. This is the first example of a clathrate compound where the framework atoms are not in tetrahedral or trigonal-pyramidal coordination. In Ba8 M24 P28+δ a majority of the framework atoms are five- and six-coordinated, a feature more common to electron-rich intermetallics...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097773/highly-stereoselective-gold-catalyzed-coupling-of-diazo-reagents-and-fluorinated-enol-silyl-ethers-to-tetrasubstituted-alkenes
#16
Fu-Min Liao, Zhong-Yan Cao, Jin-Sheng Yu, Jian Zhou
We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au(I) catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097771/solution-synthesis-structure-and-co2-reduction-reactivity-of-a-scandium-ii-complex-sc-n-sime3-2-3
#17
David H Woen, Guo P Chen, Joseph W Ziller, Timothy J Boyle, Filipp Furche, William J Evans
The first crystallographically characterizable complex of Sc(2+) , [Sc(NR2 )3 ](-) (R=SiMe3 ), has been obtained by LnA3 /M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR2 )3 with K in the presence of 2.2.2-cryptand (crypt) and 18-crown-6 (18-c-6) and with Cs in the presence of crypt. Dark maroon [K(crypt)](+) , [K(18-c-6)](+) , and [Cs(crypt)](+) salts of the [Sc(NR2 )3 ](-) anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight-line EPR spectra arising from the I=7/2 (45) Sc nucleus...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097768/biosynthesis-of-the-carbonylmethylene-structure-found-in-the-ketomemicin-class-of-pseudotripeptides
#18
Junpei Kawata, Taiki Naoe, Yasushi Ogasawara, Tohru Dairi
We recently discovered novel pseudotripeptides, the ketomemicins, which possess a C-terminal pseudodipeptide connected with a carbonylmethylene instead of an amide bond, through heterologous expression of gene clusters identified in actinobacteria. The carbonylmethylene structure is a stable isostere of the amide bond and its biological significance has been shown in several natural and synthetic products. Despite the biological importance of these compounds, little is known about how the carbonylmethylene structure is biosynthesized...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097767/robust-aqua-material-a-pressure-resistant-self-assembled-membrane-for-water-purification
#19
Erez Cohen, Haim Weissman, Eyal Shimoni, Ifat Kaplan-Ashiri, Kai Werle, Wendel Wohlleben, Boris Rybtchinski
"Aqua materials" that contain water as their major component and are as robust as conventional plastics are highly desirable. Yet, the ability of such systems to withstand harsh conditions, for example, high pressures typical of industrial applications has not been demonstrated. We show that a hydrogel-like membrane self-assembled from an aromatic amphiphile and colloidal Nafion is capable of purifying water from organic molecules, including pharmaceuticals, and heavy metals in a very wide range of concentrations...
January 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28097766/water-enabled-catalytic-asymmetric-michael-reactions-of-unreactive-nitroalkenes-one-pot-synthesis-of-chiral-gaba-analogs-with-all-carbon-quaternary-stereogenic-centers
#20
Jae Hun Sim, Choong Eui Song
Water enables new catalytic reactions for otherwise unreactive substrate systems. Under the "on water" reaction conditions, extremely unreactive β,β-disubstituted nitroalkenes smoothly underwent enantioselective Michael addition reactions with dithiomalonates using a chiral squaramide catalyst, affording both enantiomers of highly enantioenriched Michael adducts with all-carbon-substituted quaternary centers. The developed "on water" protocol was successfully applied for the scalable one-pot syntheses of chiral GABA analogs with all-carbon quaternary stereogenic centers at the β-position, which might show highly interesting pharmaceutical properties...
January 18, 2017: Angewandte Chemie
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