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781.
A practical and efficient asymmetric synthesis of the key precursor furanose 3 for the synthesis of K252a and CEP-701 has been achieved in nine steps with an overall yield of 12.8% from (R)-methyl β-hydroxytetradecanoate 5, an industrial intermediate for production of orlistat. 相似文献
782.
A concise asymmetric total synthesis of (12S)-12-hydroxymonocerin (1) and (12R)-12-hydroxymonocerin (2) were efficiently achieved from the known 4-bromo-2,6-dimethoxyphenol. The synthetic approach was inspired by our biomimetic synthesis of (+)-monocerin (3) and 7-O-demethylmonocerin (4). The cis-fused furobenzopyranones of 1 and 2 was efficiently constructed via an intramolecular nucleophilic trapping of a quinonemethide intermediate, which was obtained by benzylic oxidation of compound 10 using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). 相似文献
783.
Chesson LA Valenzuela LO Bowen GJ Cerling TE Ehleringer JR 《Rapid communications in mass spectrometry : RCM》2011,25(24):3713-3722
Published datasets of proteinaceous animal tissues suggest that co-variation between amino acid hydrogen (δ2H) and oxygen (δ1?O) isotope ratios is a common feature in systems where isotopic variation is driven by geographic or temporal variation in the δ2H and δ1?O values of environmental water. This has led to the development of models relating tissue δ2H and δ1?O values to those of water, with potential application in a number of fields. However, the strength and ubiquity of the influence of environmental water on protein isotope ratios across taxonomic groups, and thus the relevance of predictive models, is an open question. Here we report strong co-variation of δ2H and δ1?O values across a suite of terrestrial and aquatic animal meats purchased in American food markets, including beef, poultry (chicken and turkey), chicken eggs, pork, lamb, freshwater fish, and marine fish. Significant isotope co-variation was not found for small collections of marine bivalves and crustaceans. These results imply that isotopic signals from environmental water were propagated similarly through most of the diverse natural and human-managed foodwebs represented by our samples. Freshwater fish had the largest variation in δ2H and δ1?O values, with ranges of 121‰ and 19.2‰, respectively, reflecting the large isotopic variation in environmental freshwaters. In contrast marine animals had the smallest variation for both δ2H (7‰ range, crustaceans) and δ1?O (3.0‰ range, bivalves) values. Known-origin beef samples demonstrated direct relationships between the variance of environmental water isotope ratios and that of collected meats. 相似文献
784.
Richard J. Bowen Manuel A. Fernandes Patricia W. Gitari Marcus Layh 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(2):o113-o114
In the crystal structure of 2,2′‐bipyridinium(1+) bromide monohydrate, C10H9N2+·Br−·H2O, the cation has a cisoid conformation with an intramolecular N—H⋯N hydrogen bond. The cation also forms an N—H⋯O hydrogen bond to an adjacent water molecule, which in turn forms O—H⋯Br− hydrogen bonds to adjacent Br− anions. In this way, a chain is formed extending along the b axis. Additional interactions (C—H⋯Br− and π–π) serve to stabilize the structure further. 相似文献
785.
N. Aoi S. Kanno S. Takeuchi H. Suzuki D. Bazin M.D. Bowen C.M. Campbell J.M. Cook D.-C. Dinca A. Gade T. Glasmacher H. Iwasaki T. Kubo K. Kurita T. Motobayashi W.F. Mueller T. Nakamura H. Sakurai M. Takashina J.R. Terry K. Yoneda H. Zwahlen 《Physics letters. [Part B]》2010
The neutron-rich nucleus 74Ni was studied with inverse-kinematics inelastic proton scattering using a 74Ni radioactive beam incident on a liquid hydrogen target at a center-of-mass energy of 80 MeV. From the measured de-excitation γ rays, the population of the first 2+ state was quantified. The angle-integrated excitation cross section was determined to be 14(4) mb. A deformation length of δ=1.04(16) fm was extracted in comparison with distorted wave theory, which suggests that the enhancement of collectivity established for 70Ni continues up to 74Ni. A comparison with results of shell model and quasi-particle random phase approximation calculations indicates that the magic character of Z=28 or N=50 is weakened in 74Ni. 相似文献
786.
Dongde Li Di Wu Xiaojiao Zhang Bowen Zeng Mingjun Li Haiming Duan Bingchu Yang Mengqiu Long 《Physics letters. A》2018,382(21):1401-1408
The spin-dependent electronic transport properties of M(dcdmp)2 (M = Cu, Au, Co, Ni; dcdmp = 2,3-dicyano-5,6-dimercaptopyrazyne) molecular devices based on zigzag graphene nanoribbon (ZGNR) electrodes were investigated by density functional theory combined nonequilibrium Green's function method (DFT-NEGF). Our results show that the spin-dependent transport properties of the M(dcdmp)2 molecular devices can be controlled by the spin configurations of the ZGNR electrodes, and the central 3d-transition metal atom can introduce a larger magnetism than that of the nonferrous metal one. Moreover, the perfect spin filtering effect, negative differential resistance, rectifying effect and magnetic resistance phenomena can be observed in our proposed M(dcdmp)2 molecular devices. 相似文献
787.
We use the method of point canonical transformation and the Feynman path integral method to find energy spectra and wavefunction of the effective screcned potential (ESP).We show that ESP has shape invariance.In the some way,we obtain energy levels of ESP. 相似文献
788.
Dr. Bowen Hu Dr. Haoqiang Zhao Yu Wu Prof. Patrick J. Walsh 《Angewandte Chemie (International ed. in English)》2023,62(23):e202300073
A novel, selective and high-yielding palladium-catalyzed carbonylative arylation of a variety of weakly acidic (pKa 25–35 in DMSO) benzylic and heterobenzylic C(sp3)−H bonds with aryl bromides has been achieved. This system is applicable to a range of pro-nucleophiles for access to sterically and electronically diverse α-aryl or α,α-diaryl ketones, which are ubiquitous substructures in biologically active compounds. The Josiphos SL-J001-1-based palladium catalyst was identified as the most efficient and selective, enabling carbonylative arylation with aryl bromides under 1 atm CO to provide the ketone products without the formation of direct coupling byproducts. Additionally, (Josiphos)Pd(CO)2 was identified as the catalyst resting state. A kinetic study suggests that the oxidative addition of aryl bromides is the turnover-limiting step. Key catalytic intermediates were also isolated. 相似文献
789.
The chemistry of alkoxy radicals was extensively explored during the period of 1960s to 1990s, but it has remained dormant for the past few decades. Recently, alkoxy radicals attract the attentions again, because new methods for generating alkoxy radical species have emerged. These newly developed methods are mainly based on the photolysis by visible light under mild conditions, thus allowing for new transformations of the carbon-centered radical species that are generated from the β-scission or hydrogen abstraction of the alkoxy radicals. Herein, we demonstrate that the alkoxy radicals derived from cyclic hemiacetals can be generated through visible-light-induced electron transfer with sodium iodide and triphenylphosphine as the catalyst. The alkoxy radicals subsequently undergo β-scission to generate carbon-centered radicals, which are trapped by cinnamic acids, aryl alkenes, vinylboronic acid and silyl enol ether to deliver the corresponding C—C bond forming products. This catalytic method for ring-opening alkenylation reaction of cyclic hemiacetal derivatives under visible-light irradiation conditions demonstrates the compatibility of the visible light-promoted alkoxy radical generation method with various carbon radical trapping processes. This work opens up new possibilities for the application of alkoxy radicals in organic synthesis. 相似文献
790.
Zhengzheng Liu Dr. Ximeng Lv Dr. Shuyi Kong Mingtai Liu Kunhao Liu Dr. Junbo Zhang Bowen Wu Dr. Quan Zhang Prof. Yi Tang Prof. Linping Qian Prof. Lijuan Zhang Prof. Gengfeng Zheng 《Angewandte Chemie (International ed. in English)》2023,62(43):e202309319
Electroreduction of CO2 to multi-carbon (C2+) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C2+ product selectivity and the stability of Cu-based electrocatalytic sites. Functionalization of long-chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C2+ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO2 supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long-chain alkyl-modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C2+ and a partial current density of 1.81 A cm−2. The toluene-modified Cu catalyst further exhibited highly stable CO2-to-C2H4 conversion of 400 h in a membrane-electrode-assembly electrolyzer, suggesting the attractive feature for both efficient C2+ selectivity and excellent stability. 相似文献