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51.
Edwin B. Villhauer Zhengming Du Kevin Vargas Lech Ciszewski Yansong Lu Michael Girgis Melissa Lin Mahavir Prashad 《Tetrahedron》2009,65(45):9067-1868
A scalable synthetic strategy of a chiral, trisubstituted imidazolidinone (1), a novel cannabinoid-1 antagonist, starting from a commercially available mandelic acid (5) is described. The key step involves a regio- and stereoselective ring-opening of an aziridinium ion by an aniline nucleophile (3). A mechanistic study revealed the insight into rate amplification at a lower temperature for vicinal diamine 12 formation via a aziridinium ion 14. Although most intermediates are not isolable by crystallization due to their intrinsic physical properties (oil or foamy solid), the reported synthesis furnished pure 1 without any chromatography purification throughout the entire synthesis. Employing green chemistry principles, this novel synthesis appears to be highly efficient for the manufacturing of multi-kilogram quantities of an optically-pure active pharmaceutical ingredient. 相似文献
52.
This work presents linear temperature programmed retention indices on the columns with stationary phases of 5% phenylpolydimethyl silicone of 389 organic compounds, including extractive substances of plant tissues and environmentally important compounds. Certain factors which influence the values and reproducibility of retention indices during gas chromatographic analysis of multicomponent mixtures are discussed. 相似文献
53.
Katarzyna Lech Janina Witowska‐Jarosz Maciej Jarosz 《Journal of mass spectrometry : JMS》2009,44(12):1661-1667
Saffron is one of the oldest natural dyestuffs and is obtained from the dried stigmata of Crocus sativus L. Nowadays, saffron is considered as an invaluable spice of golden‐yellow hue, a precious ingredient in the Eastern and Mediterranean cuisines. It is characterized by a bitter taste that is caused by the chemical properties of its constituents. The yellowness of saffron results from the presence of crocins (glycosyl esters of crocetin), its main color compounds, which are examined in the present study in the crude methanol extracts by high performance liquid chromatography (HPLC) coupled with spectrophotometric and electrospray mass spectrometric detection (HPLC–UV‐Vis–ESI MS). This technique allowed the separation and identification of trans‐ and cis‐isomers of crocins. Their mass spectra registered in the negative ion mode comprised the quasi‐molecular and fragment ions, as well as a range of other ions. Doubly charged ions were found for trans‐isomers only, due to the high symmetry of their molecules. Modification of the eluent allowed the identification of several signals corresponding to adduct ions of crocins with the used additives. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
54.
Aleksandra Dubiella-Jackowska Żaneta Polkowska Lech Dariusz Piotr Pasławski Wojciech Staszek Jacek Namieśnik 《Central European Journal of Chemistry》2009,7(1):35-41
A solid phase extraction technique for the determination of platinum(IV) at trace levels by inductively coupled plasma mass
spectromA solid phase extraction technique for the determination of platinum(IV) at trace levels by inductively coupled plasma
mass spectrometry (ICP-MS) was developed. The method was based on retention of platinum in a sample on silica gel modified
with aminepropyl groups. The retention of platinum(IV) from the sample solution and the recovery of platinum with 1.0 mol
L−1 thiourea solution were quantitative. The relative standard deviation (RSD) was calculated as 5% (n = 7) at the 10 ng L−1 level. The enrichment factor was found to be (50-fold) for 250 mL of water sample. Under optimum conditions, the method detection
limit (MDL) was found to be 1 ng L−1 for platinum in water matrices. Recoveries of Pt from spike addition to atmospheric water samples were quantitative (80–95%).
The present method was used for the determination of platinum in precipitation, throughfall and runoff water samples.
相似文献
55.
Lech Drewnowski 《Indagationes Mathematicae》2009,20(1):43-47
A maxitive measure is a nonnegative function η on a σ-algebra Σ and such that η(Uj Aj ) = supj η(Aj) for all countable disjoint families of sets (Aj) in Σ. A representation theorem for such measures is established, and next applied to represent Köthe function M-spaces as L∞-spaces. 相似文献
56.
57.
Lech PapieŻ 《Physics letters. A》1985,107(9):438-442
The evolution of two nuclear spins, interacting between themselves and with an external magnetic field, and situated on molecules of a fluid, is treated, under the assumption of the mixing property of molecular rotations, by the method of limit theorems for random differential equations. The limit diffusion behaviour of the system is derived and the results on relaxation times and (non-thermodynamical) equilibrium are obtained and discussed. 相似文献
58.
59.
The effect of deuterium on the 13C and 15N chemical shifts of enaminones has been investigated. D/H isotope shifts are reported for neutral and protonated species, i.e., when the isotope is exchanged on the C(2)-, N-, or O-atoms. In cases of slow exchange the isotope shifts were obtained from solutions containing both isotopomers, whereas for fast exchange (acidic solutions) either separate NMR. sample tubes (15N-NMR.) or coaxial tubes (13C-NMR.) were used. In neutral molecules the isotope effects δC(D, H) are intrinsic in nature. In acidic solutions, the enaminocarbonyl cations formed exhibit δC(D, H)- and δN(D, H)-values which are discussed in terms of the proton transfer. The mesomeric character of the cations is reflected by characteristic features in the δC(D, H)- and δN(D, H)-values, which can be ascribed to isotopic perturbation of resonance. O-Protonation shifts in the 15N-resonance, observed for the first time, are large and positive (+60 to +76 ppm), in contrast to amides, where the effects are of the same sign but an order of magnitude smaller. Both protonation shifts and solvent-induced isotope effects are discussed in connection with the nucleophilic character of the reactive centers in the enaminone synthon. 相似文献
60.
Lech Ciszewski Daquiang Xu Oljan Repi? Thomas J. Blacklock 《Tetrahedron letters》2004,45(43):8091-8093
A highly practical synthesis of unsymmetrical N,N′-disubstituted thioureas by the reductive alkylation of N-monosubstituted thioureas with aldehydes is described. N-Monosubstituted thioureas can in turn be synthesized by the reductive amination of thiourea with an appropriate aldehyde. This reductive alkylation methodology was also extended to carbamates. 相似文献