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101.
A synthesis of N-acetylcolchinol, a key intermediate in the synthesis of ZD6126, was developed. The enantiodifferentiating step required the catalytic asymmetric hydrogenation of an enamide. After screening a range of metal and ligand combinations it was found that (S,S)-iPr-FerroTANE Ru(methallyl)2 and [(S,S)-tBuFerroTANE Rh(COD)]BF4 gave both high enantioselectivity (>90% ee) and high catalyst utility (molar S/C = 1000). 相似文献
102.
A network of solar carcinogenic/erythemal ultraviolet radiometers has been established in New Zealand. Daily integrated irradiances of this biologically harmful ultraviolet radiation for 1989, 1990 and 1991 are reported from radiometers located at Wellington (41°S) and Christchurch (43.5°S) and for 1990 and 1991 from the Auckland (37°S) radiometer. Although the monitoring program has not been running sufficiently long to discern any long-term changes in levels of solar ultraviolet radiation, shorter term trends are apparent, which are attributed to a seasonal cycle in levels of ozone at midlatitudes and changes in atmospheric aerosols. 相似文献
103.
Guillard J Meth-Cohn O Rees CW White AJ Williams DJ 《Chemical communications (Cambridge, England)》2002,(3):232-233
The first calixhetarenes with more than one heteroatom in the constituent rings are prepared in one step by treatment of calix[4]furan 1a and calix[6]furan 1b with ethyl carbamate, thionyl chloride and pyridine to give 2, 3, 4 and 5, 6, 7 respectively; these products have been characterised by X-ray crystallography which reveals that in 2 all eight heteroatoms lie on one face of the macrocyle. 相似文献
104.
Wolfgang Dietzsch Norman V. Duffy Aaron M. Lee Brian W. Skelton Allan H. White 《无机化学与普通化学杂志》2006,632(15):2419-2423
The consequences of replacement of the symmetrically chelate ligands in [M(E2CNR2)3] (E = S, Se) complexes of potential 32 symmetry by analogous mixed S,Se unsymmetrical chelates are explored for both small (M = Co) and large (M = In) metal atoms, and R = primary (Et) and secondary (iPr) alkyl substituents by way of low‐temperature single crystal X‐ray studies of [(Co(SSeCNEt2)3] ([Co(Se2CNEt2)3] also determined as datum), and [In(SSeCNR2)3], R = Et, iPr. The structure of [(iPr2N·CS·Se)2] is also recorded. 相似文献
105.
A more general application of the self-consistent field iteration is coupled with a finite-difference Newton–Raphson algorithm to solve the set of coupled second-order integro-differential equations with split boundary conditions which constitutes the Hartree–Fock problem for diatomic molecules. The N orbitals are assumed to be of the form ψα = Lα(λ) Mα (μ)eimα? (2π)?1/2, (α = 1, …?, N), where λ, μ, and ? are the usual confocal elliptical coordinates. Requiring the expectation value of the electronic Hamiltonian to be stationary with respect to independent variations of the functions Lα and Mα, subject to constraints of orthonormality, leads to a set of coupled one-dimensional differential equations for the functions Lα and Mα. In the new method a corresponding set of finite-difference equations including the split boundary conditions for each function, as well as the Lagrange multipliers and associated constraints on normalization and orthogonality, are incorporated into a large system of nonlinear algebraic equations which is solved by means of a coupled self-consistent field-generalized Newton–Raphson iteration. As examples, calculations of the (1)2 1Σ and (1) (2pσu) 3Σ states of H2 are presented. The calculated energy for the 1Σ state of H2 is 99.985% of the three-dimensional Hartree–Fock limit. The discrepancy is due to the assumed factored form of the orbitals ψα, and a generalization of the finite-difference method is suggested to improve the results. 相似文献
106.
A series of commercial monomeric and polymeric C(18), C(27), and C(30) stationary phases were compared with immobilized poly(ethylene-co-acrylic acid) stationary phases synthesized in-house. The columns were characterized on the basis of methylene selectivity, silanol activity, metal activity, pore size, shape selectivity, and the ability to separate tocopherol isomers and carotenoid isomers. Monomeric and polymeric C(30) phases were shown to yield excellent separations of the tocopherol isomers while the polymeric C(30) and polyethylene phases were more appropriate to the separation of carotenoids. 相似文献
107.
Odile Meyer Jean-Franois Hoeffler Catherine Grosdemange-Billiard Michel Rohmer 《Tetrahedron》2004,60(52):12153-12162
An optimised gram scale synthesis allows the production of 1-deoxy-d-xylulose and 1-deoxy-d-xylulose 5-phosphate with possible deuterium labelling at C-5. Such substrates are required for investigations on the mevalonate-independent 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis in bacteria and chloroplasts of phototrophic eukaryotes and for the biosynthesis of vitamins B1 (thiamine diphosphate) and B6 (pyridoxol phosphate) in bacteria. 相似文献
108.
The effect of nine peak measurement/analysis parameters on chiral capillary electrophoresis (CE), followed by UV detection, was studied. The parameters pertained UV-detection (detection wavelength, reference wavelength, and wavelength bandwidths), signal processing (data acquisition rate, type and amount of filtering) and peak detection (detection threshold and peak width). The influence of these factors on the chiral separation of dimethindene enantiomers was studied at two different concentrations (i.e., at high and low signal-to-noise (S/N) ratio) by the means of experimental designs. The electropherogram characteristics considered were the resolution between the two enantiomers, the peak areas, and the S/N ratio. A D-optimal design was first used as screening design to identify the most critical parameters. Afterwards, a modelling of the different responses as a function of these critical parameters was performed based on the results of a face-centered central composite design. The results showed that the signal-processing parameters should be carefully selected when developing a CE separation since very important variations in the separation, the S/N ratio and the peak area of the substances can occur by setting these parameters at different levels. The detection wavelength should also be carefully chosen for optimal peak area measurement. The role of these parameters becomes more important with decreasing concentration of the analytes (i.e., low S/N ratio). This study showed that the peak measurement/analysis parameters should be optimized as the chemical and physical parameters of a method. They also should always be well specified in order to allow a good transfer of a method from one instrument to another. 相似文献
109.
Condensation of allylborane reagents 9 and 12 with aldehydes gave anti-3-[(diphenylmethylene)amino]-1-alken-4-ols 10 and 13 with high relative and absolute stereocontrol. Subsequent deprotection gave the corresponding free anti-3-amino-1-alken-4-ols 11 and 14. Alternatively, reaction of imines 13a, 13f, and 13g with trifluoromethanesulfonic anhydride and acidic methanol gave, via rearrangement, double inversion, and hydrolysis, the isomeric anti-4-amino-1-alken-3-ols 22, 38a, and 38b in good yield. The stereochemistry of the rearrangement products has been established by a single crystal X-ray study of compound 37 and by chemical correlation. 相似文献
110.
Joseph T. Repine Douglas S. Johnson Andrew D. White Michael A. Stier Trent Rankin Samarendra N. Maiti 《Tetrahedron letters》2007,48(31):5539-5541
A series of regioisomerically monofluorinated 1-(naphthalen-1-yl)piperazines is described. 相似文献