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  • Organic Chemistry  (256)
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  • Wiley-Blackwell  (256)
  • 1995-1999  (85)
  • 1990-1994  (171)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1256-1266 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of an analogue 3a of the acetylcholinesterase inhibitor, huperzine A (1), is described in which the pyridinone moiety of the natural product is replaced with a thiazolone moiety. The synthesis started from cyclohexane-1,4-dione monoethylene ketal (7) by first annulating the thiazole ring using the Gewald protocol (→ 8; Scheme 1) and then constructing the bicyclo[3.3.1]nonane substructure using our previously described Michael addition/aldol condensation methodology (Scheme 3). The central problem was the protection of the thiazolone carbonyl group; only the 2-unsubstituted thiazole survived the reaction conditions of the first half of the synthesis. Refunctionalization was later effected by lithiation and subsequent chlorination with hexachloroethane (30→31). Compound 3a was ineffective in the acetylcholinesterase inhibition assay in concentrations up to 14 μM.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 113-121 
    ISSN: 0899-0042
    Keywords: 1,3,5-triazine ; chiral discrimination ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Hexylamino-4-[(S)-1-(1-naphthyl)ethylamino]-6-L-valyl-L-valyl-L-valine isopropylester-1,3,5-triazine (1), a molecule characterized by two different chiral selectors, and 2-hexylamino-4,6-bis-L-valyl-L-valyl-L-valine isopropylester-1,3,5-triazine (2) and 2-ethoxy-4-hexylamino-6-[(S)-1-(1-naphthyl) ethylamino]-1,3,5-triazine (3), systems in which a single kind of chiral selector is present, have been prepared. The enantiodiscriminating ability in solution of the three compounds toward the N-3,5-dinitrobenzoyl derivatives of 1-phenylethylamine (4) or valine methylester (5) has been investigated by 1H nuclear magnetic resonance (NMR) spectroscopy: 1 shows an improved versatility, relative to 2 and 3, as a chiral solvating agent for NMR spectroscopy. On the basis of the indications obtained, the usefulness of 2-chloro-4-[(S)-1-(1-naphthyl)ethylamino]-6-L-val-L-val-L-valine isopropylester-1,3,5-triazine (1a), a direct precursor of 1, as chiral solvating agent for the determination by NMR of the enantiomeric compositions of derivatives of amines, amino alcohols, amino acids, and carboxyl acids bearing a 3,5-dinitrophenyl moiety, has been demonstrated. Chirality 9:113-121, 1997. © 1997 Wiley-Liss, Inc.
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  • 3
    ISSN: 0899-0042
    Keywords: quartz crystal microbalance ; electronic nose ; fragrance ; odour ; detection ; chemical sensor ; cyclodextrin ; chiral discrimination ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quartz crystal microbalances (QCMB) have been constructed using 10 MHz AT cut quartz crystals coated with heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, heptakis(6-O-methyl-2,3-di-O-pentyl)-β-cyclodextrin, and octakis(6-O-methyl-2,3-di-O-pentyl)-γ-cyclodextrin as 50% and 20% (w/w) solutions in OV1701. The reduction in frequency seen on exposure of each coated QCMB to pure enantiomeric forms of α- and β-pinene and cis- and trans-pinane show that statistically significant (P = 0.05, n = 7) differences are observed between the enantiomeric pairs. The apparent preferential binding shown by the QCMB for enanciomers of α- and β-pinene and cis- and trans-pinane have been compared with the elution order observed on the corresponding gas chromatographic stationary phase. The magnitude of the observed separation factor (calculated as the ratio of the OV1701 normalised frequency shift) is seen to be dependent upon the chiral stationary phase concentration. These results indicate that on-line determination of enantiomeric excess and concentration of certain monoterpenes is possible at room temperature using QCMB in conjunction with chiral gas chromatographic stationary phases. Chirality 9:225-232, 1997. © 1997 Wiley-Liss, Inc.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 335 (1993), S. 699-704 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Mutual Promotion Effect of Molybdates in Multicomponent Molybdate CatalystsMulticomponent molybdate catalysts (e.g. of the composition Bi2Fe1,5Co7Cr10Mo19Oy) are produced by coprecipitation, drying and calcination. These catalysts exhibit high activity and selectivity in the ammoxidation of propene to acrylonitrile. The individual molybdates (Co-, Fe- and Cr-molybdate) exhibit no selectivity in the ammoxidation of propene. Therefore a mutual promotion effect of these molybdates exists. The cause of the promotion effect is the formation of the active and selective phase from the β-phase of Co-molybdate by exchange of protons with ions of Fe3+ and Cr3+ from the molybdates of Fe and Cr. The structure of this catalytic active and selective phase is similar to the structure of the β-phase of Co-molybdate.
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0899-0042
    Keywords: ketoprofen ; stereoisomers ; plasma binding ; binding linearity and competition ; ketoprofen glucuronides ; 2-arylpropanoic acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protein binding of ketoprofen enantiomers was investigated in human plasma at physiological pH and temperature by ultrafiltration. 14C-labelled (RS)-ketoprofen was synthesized and purified by high-performance liquid chromatography and utilized as a means of quantifying the unbound species. In vitro studies were conducted with plasma obtained from six healthy volunteers. The plasma was spiked with (R)-ketoprofen alone, (S)-ketoprofen alone, and (RS)-ketoprofen in the enantiomeric concentration range of 1.0 to 19.0 μg/ml. The plasma protein binding of ketoprofen was nonenantioselective. At a racemic drug concentration of 2.0 μg/ml the mean (± SD) percentage unbound of (R)-ketoprofen was 0.80 (± 0.15)%. The corresponding value for (S)-ketoprofen, 0.78 (± 0.18)%, was not statistically different (P 〉 0.05). At this racemic drug concentration (2.0 μg/ml) the percentage unbound of each enantiomer was unaffected (P 〉 0.05) by the presence of the glucuronoconjugates of ketoprofen (10 μg/ml) in plasma. At clinically relevant concentrations, the plasma binding of ketoprofen did not exhibit enantioselectivity or concentration dependence nor was the binding of either enantiomer influenced by its optical antipode (P 〉 0.05).
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  • 6
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For a number of chiral α,β-unsaturated carbonyl compounds, cyclohexanone and cyclohexenone derivatives, existing essentially in the form of single molecular conformation, the correlation dependences were established between the values of the calculated dissymmetry functions (DF) with respect to atomic masses and atom refractions, and the induction effectiveness of helical ordering in the nematic mesophase (twisting power). Such correlative dependencies, as the examples show, allow one to predict safely enough the twisting power of new substances with the ‘fixed’ molecular conformation. Types of dissymmetry functions and kinds of correlative dependences, the most acceptable for these reasons, were revealed. Dissymmetry functions formed on the basis of atom refractions (polarizabilities) describe the influence of the molecular structures of chiral compounds on the twisting power with higher accuracy than those that characterize the dissymmetry of the atomic masses distribution, according to the important role of the dispersion forces in the formation of helical ordering in liquid crystalline systems. The components characterizing the distribution dissymmetry of atomic refractions and masses with respect to the long and two shorter axes as the peculiar characteristics of biaxiality of chiral molecules describe the influence of the molecular structure on the twisting power with the same accuracy as the general DF do. Thus influence of chiral dopant molecules on the interactions between molecules in the uniaxial mesophases is negligible within the limits of the DF method. Based on the calculations for model systems it is established that the presence of the non-linear cinnamoyl fragment has a decisive influence on the molecular dissymmetry of the chiral α,β-unsaturated ketones. The alkyl groups influence the molecular dissymmetry only slightly, but it is important that their presence ensures the stabilization of the chiral conformer with the defined helicity of the cinnamoyl fragment.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 285-292 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Experimental gas-phase acidities of 2-oxopropanaloximes, XCH2COCH=NOH (X = H, CH3S, CH3SO, CH3SO2; compounds 1-4), were determined by Fourier transform ion cyclotron resonance (FT-ICR) spectrometry. The values are δ Gacid° = 1401, 1381, 1360 and 1351 kJ mol-1 for 1, 2, 3, and 4, respectively. Molecular orbital calculations using the semi-empirical AM1 method provided information on the geometry and relative energy of neutrals species 1-4 and their conjugate bases, together with charge distributions and entropies of deprotonation. It is demonstrated that the proton abstraction occurs preferentially at the oxime function; the formation of an enolate as a conjugate base is unfavourable by 70-140 kJ mol-1. The large variation of the gas-phase acidities for 1-4 is explained in terms of the field/inductive empirical substituent constant σF. The variation of solution acidities appears to be comparatively strongly attenuated. This attenuation is attributed mainly to charge delocalization in the anion, which was confirmed by charge density calculations.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 427-432 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The IR spectra of isomeric bicyclobutonium (1), delocalized cyclopropylcarbinyl (2) and 1-methylally (3) cations were recorded at 180 K in SbF5 matrices. Cations 1 and 2 generated from cyclopropylcarbinyl and cyclobutyl chloride, respectively, rearrange to 3 at temperatures above 230 K. The structures 1, 2 and 3 were confirmed by comparison of the recorded frequencies with the MP2/6-31G*-calculated values. These results are in accord with prediction that ions 1 and 2 are rapidly equilibrating non-classical structures.
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  • 9
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Formation constants, K, for hydrogen bonding of weak C—H donors with hexamethylphosphoric triamide were measured in cyclohexane at 35°C by PMR spectroscopy; data were analyzed by the Higuchi method. Donors include terminal alkynes and series of polyfluoro-, polychloro- and polybromobenzenes. The K values for many of these are too small to measure in CCl4. For RC≡CH, K decreases in the order R = BrCH2 〉 C6H5 〉 C2H5O 〉 tert-butyl. For polyhalobenzenes, K is generally larger for F than Cl or Br, and meta halogens facilitate hydrogen bonding most effectively. Among tetrahalobenzenes, 1,2,3,4-isomers show the least evidence of 2:1 complex formation. Pentachlorobenzene has a smaller K than its 1,2,3,4-tetrachlor analog even after statistical correction; for C6HX5, K decreases in the order F 〉 Cl 〉 Br; the K values for 1,3,5-trihalobenzenes are closely similar; and 1,3,5-tribromo-2,4-dimethylbenzene shows no evidence of hydrogen bonding by PMR. The last three observations suggest that buttressing is important in the C6HX5 structure, at least with Cl and Br. A value of K for benzene was measured, suggesting for the first time that the H atoms of benzene engage in hydrogen bonding. The result compares well with values extrapolated from data for polyfluoro- but not polychlorobenzenes, again probably because of buttressing in the latter.
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  • 10
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solid state conformation of the title compound was determined. Conformational analysis based on molecular modelling mechanics allowed the calculation of the energy of the most stable conformers and their comparison with X-ray conformation.
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