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71.
3-Mercapto-2(1H)-pyridinone (1) can be synthesized in three simple high-yielding steps from readily available 2-tert-butylthiazolo[4,5-b]pyridine (2). Its disodium salt condenses with o-chloronitrobenzene, 2-chloro-3-nitropyridine, and 3-chloro-4-nitropyridine 1-oxide to give respectively 4-azaphenoxathiine (10), 1,6-diazaphenoxathiine (12), and 2,6-diazaphenoxathiine 2-oxide (14) which reduces to 2,6-diazaphenoxathiine (15). The structures of these previously unreported azaphenoxathiine systems were confirmed by assignment of their respective (13)C NMR spectra. 相似文献
72.
Ian Dance Prof. 《化学:亚洲杂志》2007,2(8):936-946
How does the enzyme nitrogenase reduce the inert molecule N2 to NH3 under ambient conditions that are so different from the energy‐expensive conditions of the best industrial practices? This review focuses on recent theoretical investigations of the catalytic site, the iron–molybdenum cofactor FeMo‐co, and the way in which it is hydrogenated by protons and electrons and then binds N2. Density functional calculations provide reaction profiles and activation energies for possible mechanistic steps. This establishes a conceptual framework and the principles for the coordination chemistry of FeMo‐co that are essential to the chemical mechanism of catalysis. The model advanced herein explains relevant experimental data. 相似文献
73.
ZnBr2-catalysed phenylthioalkylation of ketene bis(trimethylsilyl)acetals, obtained from carboxylic acids, with appropriate α-chlorosulphides can be used to prepare γ- and δ- lactones. 相似文献
74.
Paterson I Aceña JL Bach J Chen DY Coster MJ 《Chemical communications (Cambridge, England)》2003,(4):462-463
Simplified analogues of the potent antimitotic marine macrolide spongistatin 1/altohyrtin A were synthesised and evaluated as growth inhibitory agents against a range of human tumour cell lines, including Taxol-resistant strains, revealing that E-ring dehydration leads to enhanced cytotoxicity at the low picomolar level while truncation of the side-chain at C46 results in a drastic decrease in activity. 相似文献
75.
The constrained Hartree-Fock method using experimental X-ray diffraction data is extended and applied to the case of noncentrosymmetric molecular crystals. A new way to estimate the errors in derived properties as a derivative with respect to added Gaussian noise is also described. Three molecular crystals are examined: ammonia [NH(3)], urea [CO(NH(2))(2)], and alloxan [(CO)(4)(NH)(2)]. The energetic and electrical properties of these molecules in the crystalline state are presented. In all cases, an enhancement of the dipole moment is observed upon application of the experimental constraint. It is found that the phases of the structure factors are robustly determined by the constrained Hartree-Fock model, even in the presence of simulated noise. Plots of the electron density, electrostatic potential, and the electron localization function for the molecules in the crystal are displayed. In general, relative to the Hartree-Fock model, there is a depletion of charge around hydrogen atoms and lone pair regions, and a build-up of charge within the molecular framework near nuclei, directed along the bonds. The electron localization function plots reveal an increase in the pair density between vicinal hydrogen atoms. 相似文献
76.
Dimethylphosphoramides react with -chloroperoxybenzoic acid (MCPBA) in anhydrous acetone to yield the previously unknown -dimdethylamino-oxyphosphonous derivatives -oxidation and rearrangement. Further MCPBA oxidation yields formaldehyde and nitrosomethane, isolated as its -dimer. These reactions provide a possible biomimetic model for the metabolic activation of hexamethylphosphoramide as a mutagen and carcinogen. 相似文献
77.
Ian PatersonOscar Delgado 《Tetrahedron letters》2003,44(49):8877-8882
A series of novel structural analogues of the potent microtubule-stabilizing anticancer agent discodermolide were synthesised, with modifications in the C16-C20 region to create new oxygenated H-bonding donor/acceptor sites for tubulin binding. By starting from an advanced C9-C24 intermediate, fully synthetic discodermolide analogues, incorporating either an additional hydroxyl group 3, an oxetane 4 or a cyclic carbonate 5, were obtained in 10 or 11 steps by using a versatile aldol construction of the C6-C7 bond. 相似文献
78.
Interpretation of the chemical and spectral (IR., UV., 1H- and 13C-NMR.) properties of the antitumor antibiotic hedamycin (C41H50N2O11) suggests that the molecule contains a methyl substituted 1-hydroxyanthraquinone nucleus, an α, β-unsaturated ketone, two sugar-like tetrahydropyran rings ( 4 and 8 ) and an aliphatic chain 2 , presumably with an epoxy group (see the Scheme). 相似文献
79.
The ultrafast N-O bond fragmentation in a series of N-methoxypyridyl radicals, formed by one-electron reduction of the corresponding N-methoxypyridiniums, has been investigated as potentially barrierless electron-transfer-initiated chemical reactions. A model for the reaction involving the electronic and geometric factors that control the shape of the potential energy surface for the reaction is described. On the basis of this model, molecular structural features appropriate for ultrafast reactivity are proposed. Femtosecond kinetic measurements on these reactions are consistent with a kinetic definition of an essentially barrierless reaction, i.e., that the lifetime of the radical is a few vibrational periods of the fragmenting bond, for the p-methoxy-N-methoxypyridyl radical. 相似文献
80.
Bernard Gordon Jacqueline S. Butler Ian R. Harrison 《Journal of polymer science. Part A, Polymer chemistry》1987,25(8):2139-2142
Catalysts bound to polymers in the form of crosslinked beads have been demonstrated to have a number of advantages over homogeneous catalysts. However, there are several problems that exist due to the polymer support being in the form of a bead. The rate of reaction depends on the presence of solvents that adequately swell the bead in order to allow access to the catalytic sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed whereby tris(triphenyl phosphine) chlororhodium (I) (Wilkinson's catalyst) is bound to the surface of polyethylene single crystals. Polyethylene single crystals have a very high surface to volume ratio allowing for greater ease of reaction compared to a bead system. In a previous paper we showed that there is a dramatic increase in catalytic activity and that the reaction rate increased as the polarity of solvent was increased, even in ethanol where the homogeneous catalyst is not soluble and the polystyrene bead support would not swell. In this letter we are describing the activity of hydrogenation of olefins contained in both large and/or polar molecules. The results demonstrate the advantages of supported catalysts on polyethylene single crystals rather than on polymer beads. 相似文献