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1.
Marianne Gerny Burkhard Alpers 《International Journal of Computers for Mathematical Learning》2004,9(1):25-57
In this article we describe a mathematical microworld for investigating car motion on a racing course and its use with a group of grade 12 students. The microworld is concerned with the mathematical construction of courses and functions which describe car motion. It is implemented in the computer algebra system, Maple®, which provides the means to represent courses and functions symbolically and graphically. We describe the learning opportunities offered by the microworld in relation to the research literature on functions. Various facets and layers of the function concept are addressed in the microworld, and we suggest how work in the microworld might help in overcoming some well-known misconceptions.This revised version was published online in September 2005 with corrections to the Cover Date. 相似文献
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Prostaglandin D2 synthase (PGDS) (beta-trace protein) is a highly abundant cerebrospinal fluid (CSF) glycoprotein. A number of studies have been performed to determine the potential value of this protein for the diagnosis of various neurological disorders. The measurement of total PGDS levels in CSF has proved marginally useful for this purpose, but promising results were obtained while investigating changes in the posttranslational modifications (PTM) pattern. Using 2-DE analysis, we previously showed that PGDS is differentially expressed in ante- and post mortem CSF samples. In the present study, we examined whether the PGDS isoforms may help to distinguish stroke and neurodegenerative disease patients from healthy subjects. The pattern of PGDS PTM was analyzed in CSF from patients with various neurological disorders (n = 44) using IEF/immunoblotting techniques. Strong alterations of this pattern were detected in patients with different forms of degenerative dementia. These findings are consistent with PGDS being altered in some neurological diseases and provide new opportunities for clinical applications. 相似文献
5.
Burkhard Schmidt Ingo Franke Franz-Josef Witteler Michael Binder 《Helvetica chimica acta》1983,66(8):2564-2571
The novel cannabinoids (6aR, 10aR)-N-ethyl-Δ8-tetrahydrocannabinol-18-amide (15) and (6aR, 10aR, 17 RS)-N-ethyl-17-methyl-Δ8- tetrahydrocannabinol-18-amide (16) , designed as cannabinoid affinity ligands, were synthesized from the corresponding acids 11 and 12 via the N-hydroxysuccinimide esters. Amide 16 was tested in the rat and was generalized to Δ9-tetrahydrocannabinol, being 5 times less potent than the training drug. An improved synthesis of (6aR, 10aR)-17,18-didehydro-Δ8-tetrahydrocannabinol (23) is reported. As model reaction for the preparation of a tritiated Δ8-tetrahydrocannabinol, compound 23 was selectively deuterated at C(17) and C(18) in benzene/Et3N using [(C6H5)3P]3RuCl2 as catalyst. 相似文献
6.
The synthesis and structure of an acetal protected 10-membered cyclic enediyne-1,2-diol rac-10 is reported. The conformational constrain of the unsaturated macrocycle by the acetal protection group prevents the thermal cyclization reaction of the endiyne during synthesis and purification. 相似文献
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A practicable and selective liquid chromatography-mass spectrometry assay for the determination of two cyclooxygenase-2 inhibitors, etoricoxib and valdecoxib, in human plasma is presented. The analytical technique is based on reversed-phase high-performance liquid chromatography (HPLC) coupled to atmospheric pressure chemical ionisation (APCI) mass spectrometry (Finnigan Mat LCQ ion trap). Mass analysis was performed in the positive ion mode. The ion trap was operated in the tandem MS mode (MS2) and the transitions of etoricoxib (m/z 359.2 --> 280.3) and valdecoxib (m/z 315.1 --> 235.1) were followed by selected reaction monitoring. Retention times of etoricoxib and valdecoxib were 1.05 and 1.08 min, respectively. The method was validated over a linear range 10-2500 and 5-1000 microg/L using the other substrate as internal standard. After validation, the method was used to study the pharmacokinetic pro fi le of etoricoxib or valdecoxib in a healthy volunteer after administration of a single oral dose (valdecoxib, 20 mg; etoricoxib, 90 mg). The presented method was suf fi cient to cover more than 90% of the area under the plasma concentration time curve. 相似文献
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Alkylation of 1-dimethylamino-1-cyanomethanephosphonic acid diethyl ester (8), easily obtainable from diethyl phosphite and the 0,N-acetal 9, yields 1-alkyl derivatives 14. Elimination of HCN converts 14 into 1-phosphonoenamines 6. Carbonyl compounds react with 8 to give 1-cyanoenamines 15 which may be hydrolyzed to from the homologous carboxylic acid. Alternatively, deprotonation of 15 yields the homoenolate anions 17 which can be alkylated or hydroxyalkylated, permitting chain extension of carbonyl compounds through introduction of an α-carboxyl and a β-alkyl group. Acid catalyzed hydrolysis of 8 results in cleavage of the PC bond, leading to the corresponding α-dimethylamino alkanoic acids. A phosphonic acid 11 can be obtained from 8 by application of the silylester method. An unambigous assignment of E/Z-isomers of the cyanoenamines 15 has been derived from 13C-NMR spectroscopy. 相似文献
9.
Oliver Tietze Birgit Schiefner Burkhard Ziemer A. Zschunke 《Analytical and bioanalytical chemistry》1997,357(5):477-481
The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E,
E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the 1H and 13C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds
N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic
acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding
spectra. To assign the 13C NMR signals we used two-dimensional 13C-1H one-bond (HMQC) and 13C-1H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to
a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition
of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two
CH-O hydrogen bonds.
Received: 31 May 1996 / Revised: 26 June 1996 / Accepted: 1 July 1996 相似文献
10.