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Total Synthesis of (6R,10R,13R,14R,16R,17R,19S,20R,21R,24S, 25S,28S,30S,32R,33R,34R,36S,37S,39R)‐Azaspiracid‐3 Reveals Non‐Identity with the Natural Product
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Nathaniel T. Kenton Dr. Daniel Adu‐Ampratwum Dr. Antony A. Okumu Dr. Zhigao Zhang Dr. Yong Chen Dr. Son Nguyen Dr. Jianyan Xu Dr. Yue Ding Dr. Pearse McCarron Dr. Jane Kilcoyne Prof. Dr. Frode Rise Prof. Dr. Alistair L. Wilkins Dr. Christopher O. Miles Prof. Dr. Craig J. Forsyth 《Angewandte Chemie (International ed. in English)》2018,57(3):805-809
A convergent and stereoselective total synthesis of the previously assigned structure of azaspiracid‐3 has been achieved by a late‐stage Nozaki–Hiyama–Kishi coupling to form the C21?C22 bond with the C20 configuration unambiguously established from l ‐(+)‐tartaric acid. Postcoupling steps involved oxidation to an ynone, modified Stryker reduction of the alkyne, global deprotection, and oxidation of the resulting C1 primary alcohol to the carboxylic acid. The synthetic product matched naturally occurring azaspiracid‐3 by mass spectrometry, but differed both chromatographically and spectroscopically. 相似文献
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Krogh-Jespersen K Czerw M Zhu K Singh B Kanzelberger M Darji N Achord PD Renkema KB Goldman AS 《Journal of the American Chemical Society》2002,124(36):10797-10809
The thermodynamics of small-molecule (H(2), arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d(8), four-coordinate d(8), and five-coordinate d(6)) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = eta(3)-1,3,5-C(6)H(2)[CH(2)PR(2)](2)Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H(2), C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)(2). Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)(2), disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H(2), C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences. 相似文献
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Melvyn Rowen Churchill James C. Fettinger Kenton H. Whitmire 《Journal of organometallic chemistry》1985,284(1):13-23
When [HFe(CO)4]? is treated first with NaBiO3 and then dilute H2SO4, a complex mixture of neutral metal carbonyl clusters results, some of which can be extracted into petroleum ether. Upon prolonged standing the extract yields a precipitate which has been characterized by X-ray crystallography as Bi2Fe3(CO)9.The complex Bi2Fe3(CO)9 crystallizes in the centrosymmetric orthorhombic space group Cmcm (D2h17; No. 63) with a 10.616(2) Å, b 13.458(3) Å, c 11.347(3) Å, V 1621.1(7) Å3 and Z = 4. Single-crystal X-ray diffraction data (Mo-Kα, 2θ = 4.5–55.0°) were collected on a Syntex P21 four-circle diffractometer and the structure was refined to RF 5.4% and RWF 4.5% for all 1039 independent data (RF 4.5% and RWF 4.5% for those 851 reflections with |F0| > 3.0σ(|F0|)). The molecule lies on a site of crystallographic C2v symmetry and is disordered. The individual molecules have a trigonal bipyramidal Bi2Fe3 core with the bismuth atoms occupying the apical sites (BiFe 2.617(2)–2.643(2) Å, FeFe 2.735(5)–2.757(5) Å). Each iron atom is linked to three terminal carbonyl ligands and the molecule has approximate C3h symmetry. The nine peripheral oxygen atoms are ordered and define a tricapped trigonal prism. The equatorial iron atoms are disordered with the two Fe3 triangles mutually displaced by approximately 30°; the disordered ensemble has approximate D3h symmetry. 相似文献
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Reactions between triphenyl bismuth, salicylic acid, and niobium or tantalum ethoxide have been explored. Four new coordination complexes incorporating bismuth and the group 5 metals niobium or tantalum have been synthesized and characterized spectroscopically, by elemental analysis, and by single crystal X-ray diffraction. The new complexes are Bi(2)M(2)(mu-O)(sal)(4)(Hsal)(4)(OEt)(2) (1a, M = Nb; 1b, M = Ta) and BiM(4)(mu-O)(4)(sal)(4)(Hsal)(3)(O(i)Pr)(4) (sal = O(2)CC(6)H(4)-2-O, Hsal = O(2)CC(6)H(4)-2-OH) (2a, M = Nb; 2b, M = Ta). Complexes 1a and 1b are isomorphous, as are 2a and 2b. The thermal and hydrolytic decomposition of 1a has been explored by DT/TGA and powder X-ray diffraction, while scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the morphology and composition of the oxides. The heterobimetallic molecules are completely converted to the amorphous bimetallic oxide by heating to 500 degrees C in air. Decomposition of 1a or 1b at 650 degrees C produces the metastable high temperature form of BiNbO(4) as the major crystalline oxide phase. Heating samples of 1a to 850 degrees C favors conversion of the materials to the low temperature phase as well as disproportionation into Bi(5)Nb(3)O(15) and Nb(2)O(5). Thermal decomposition of 1a and 1b produces porous oxides, while hydrolytic decomposition of the complexes has been shown to produce nanometer scale bimetallic oxide particles. The potential of the complexes to act as single-source precursors for ferroelectric materials is considered. 相似文献
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Monte Carlo quasiclassical trajectory calculations have been carried out for the reaction Cl + Hl → HCl + I for 300, 1000, and 2000 K. A semi-empirical potential-energy surface (London equation) was obtained by “transfering” parameters from surfaces computed for other reaction systems. The computed results are in general accord with experimental measurements. Thermal rate coefficients, differential scattering cross sections, and product vibrational and rotational distributions were computed for the three temperatures. Angular scattering distributions are in agreement with experiment only at elevated temperatures. 相似文献
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Examination of several accounts regarding the nature of moral responsibility allows the extraction of a conceptual core common
to all of them. Relying on that core conception of moral responsibility, the paper explores what human life without moral
responsibility would be like. That exploration establishes that many robust forms of human relationship and nonmoral normativity
could continue, absent moral responsibility, even if moral responsibility were abandoned on incompatibilist grounds. Much
more importantly, it also establishes, contra Waller and Pereboom, that only some forms of morality—so-called “behavioral”
forms—remain possible without moral responsibility. The paper argues that normative moral approaches that take into account
agent intentions in order to assess the moral status of action cannot be applied without moral responsibility of agents. Thus,
morality without responsibility needs to be behavioral, not consequentialist, as has often been thought. 相似文献
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Aim
The purpose of this study was to evaluate the intra- and interexaminer resegmentation precision of patellar cartilage T2 mapping measurements in healthy subjects.Materials and Methods
T2-weighted images of patellar cartilage for 10 subjects were acquired. Two individuals manually segmented patellar cartilage at each slice location twice, once on each of two separate days. Bulk average and zonal T2 values for the superficial, middle, and deep layers of cartilage were calculated. The root mean square (RMS) and coefficient of variation (COV) were calculated using the repeated measurements of each slice of each subject by each examiner.Results
The intraexaminer bulk T2 differences were 0.2±1.0 ms, with an RMS error of 0.7 ms and a COV of 1.9%. The differences of interexaminer bulk T2 values was 1.0±1.4 ms, with an RMS error of 1.2 ms and a COV of 3.3%. The superficial zone of cartilage had the highest zonal variability of T2 values. The average interexaminer T2 values for the superficial, middle and deep zones were 42.2±5.6, 38.1±5.3 and 31.9±4.6 ms, respectively.Conclusion
The interexaminer variability of calculated T2 values highlights the difficulty of interpreting significant differences of T2 values which are similar in magnitude. The repeatability measurements of patellar cartilage T2 values were less than reported intersession T2 repeatability. 相似文献20.
An alternative strategy for the label‐free electrochemical detection of DNA hypermethylation using a microelectrode array as an oligodinucleotide (ODN) detector is presented. It relies on the oligonucleotide dependent electrostatic affinity interaction firstly with unmethylated ODN and then follow‐up with methylated DNA. The methylated cytosine status is quantified by monitoring the relative change in the exchange current at the ODN‐detector before and after the bisulfite treated DNA samples. This novel aproach displays unique advantages such as small working volumes of the analytes, low damage to DNA samples, easy integration of oligonucleides on the detector and signal evaluation. 相似文献