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991.
992.
Toussaint B Streel B Ceccato A Hubert P Crommen J 《Journal of chromatography. A》2000,896(1-2):201-207
The chiral synthesis of beta-blockers such as (S)-timolol requires a sensitive analytical method for the enantioseparation of its intermediate, 3-tert.-butylamino-1,2-propanediol, in the ng/ml range. The method developed is based on on-line normal-phase LC-MS-MS using a chiral stationary phase and an atmospheric pressure chemical ionization (APCI) interface. The MS detection of 3-tert.-butylamino-1,2-propanediol was first optimized with a pneumatically-assisted electrospray interface (ionspray). The APCI interface was then selected for LC-MS-MS because of the incompatibility of electrospray with n-hexane. The method was validated for both enantiomers in the 25-500 ng/ml concentration range. 相似文献
993.
994.
Comins DL Kuethe JT Miller TM Février FC Brooks CA 《The Journal of organic chemistry》2005,70(13):5221-5234
Readily available N-acyl-5-vinyl-2,3-dihydro-4-pyridones undergo Diels-Alder cyclization with various dienophiles to afford novel octahydroquinolines containing synthetically useful functionality. With dihydropyridone 5 and cis-disubstituted dienophiles, the resulting cycloadducts were obtained as single diastereomers in good to excellent yield. The corresponding reaction of 5 with methyl acrylate, acrylonitrile, and phenyl vinyl sulfone showed modest preference for the endo adducts. The effect of the dihydropyridone C-2 and C-4 substituents on the degree of diastereofacial control was examined. By using this methodology, the core decahydroquinoline skeleton of gephyrotoxin was prepared in a stereocontrolled fashion. Interesting reactivity was observed with certain dienophiles leading to ring-opening of the initially formed cycloadducts. This tandem reaction provides a route to uniquely substituted beta-aminoketones, alcohols, and unnatural amino acids. 相似文献
995.
The gas-phase ion—molecule reactions between ionized vinylamine ([CH2 ? CHNH2]+.) as a set of conjugated and unconjugated dienes were studied by Fourier transform is observed. Conjugated dienes lead to the elimination of NH3 or of an hydrocarbon radical from the adduct [M + CH2 ? CHNH2]+.. In the case of unconjugated dienes a regiospecific cyclobutanation-cycloreversion process is observed. Reaction mechanisms are proposed to explain these experimental findings. 相似文献
996.
A number of reducing reagents were assessed in the transformation of chlorophosphine boranes to secondary phosphine boranes. The efficiency of the process requires judicious matching between steric and electronic requirements of reductant and the substrate. The stereochemistry of the reduction was investigated by using a chiral precursor. 相似文献
997.
Sajan D Fischer A Joe IH Jayakumar VS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(3):580-585
The surface geometry of (RS)-phenylsuccinic acid molecule was studied by analysis of the SERS spectra of aromatic dicarboxylic acid adsorbed on silver colloid surfaces. For a reliable analysis of the SERS spectrum, we also performed density functional theoretical calculations. The SERS spectral features indicated that the RSPSA molecules should bound to the silver as dicarboxylate, with a strongly tilted orientation with respect to the normal to the surface. Such a tilted orientation was presumed to occur by the simultaneous sigma and pi-type coordination of carboxylate groups to silver surface caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups, and thereby RSPSA on silver was easily displaced with aromatic carboxylic acids. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for aromatic carboxylic acid derivatives to assemble on a silver surface. The large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'at least vertical' configuration, with the ring perpendicular to the silver surface. 相似文献
998.
The implementation of quality systems in analytical laboratories has now, in general, been achieved. While this requirement significantly modified the way that the laboratories were run, it has also improved the quality of the results. The key idea is to use analytical procedures which produce results that fulfil the users needs and actually help when making decisions. This paper presents the implications of quality systems on the conception and development of an analytical procedure. It introduces the concept of the lifecycle of a method as a model that can be used to organize the selection, development, validation and routine application of a method. It underlines the importance of method validation, and presents a recent approach based on the accuracy profile to illustrate how validation must be fully integrated into the basic design of the method. Thanks to the -expectation tolerance interval introduced by Mee (Technometrics (1984) 26(3):251–253), it is possible to unambiguously demonstrate the fitness for purpose of a new method. Remembering that it is also a requirement for accredited laboratories to express the measurement uncertainty, the authors show that uncertainty can be easily related to the trueness and precision of the data collected when building the method accuracy profile. 相似文献
999.
Nizam M. El-Ashgar Issa M. El-Nahhal Mohamed M. Chehimi Michel Delamar Florence Babonneau Jacques Livage 《Monatshefte für Chemie / Chemical Monthly》2006,41(1):263-275
A new porous solid macrocyclic 1,4,7,11,14-pentaazapentadecane-3,15-dione polysiloxane ligand system of the general formula
P–(CH2)3–C11H22O2N5 (where P represents [Si–O]n siloxane network) has been prepared by the reaction of polysiloxane-immobilized iminobis(N-(2-aminoethyl)acetamide) with 1,3-dibromopropane. The FTIR and XPS results confirm the introduction of the macrocyclic functional
ligand group into the polysiloxane network. The new macrocyclic polysiloxane ligand system exhibits high potential for the
uptake of metal ions (Fe3+, Co2+, Ni2+, Cu2+ and Zn2+). 相似文献
1000.
A chiral five-membered, silyl enol ether containing, steroid ring D precursor has been synthesized from carvone. This silyl enol ether has been applied in the synthesis of a chiral C17 functionalized steroid skeleton using the addition of a carbocation, generated with ZnBr2 from a Torgov reagent, followed by cyclization of the adduct by treatment with acid. 相似文献