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  • Activation barriers  (1)
  • Conformational analysis  (1)
  • Wiley-Blackwell  (2)
  • 1
    Electronic Resource
    Electronic Resource
    NMR conformational studies of fenamate non-steroidal anti-inflammatory drugs (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 335-342 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 1H NMR ; 13C NMR ; Conformational analysis ; Coupling constants ; NOE ; Non-steroidal anti-inflammatory drugs ; Mefenamic acid ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 13C NMR spectra of the non-steroidal anti-inflammatory drugs mefenamic acid, meclofenamic acid and flufenamic acid were assigned and the solution dynamics and conformations of the compounds were probed by the analysis of NMR chemical shifts, temperature coefficients, 3J(C,H) coupled constants, nuclear Overhauser enhancement (NOE) effects and saturation transfer experiments. At low concentrations the anthranilic acid derivatives (the fenamates) exist as monomer units with intramolecular hydrogen bonding between the amine proton and the carboxylic acid group. At concentrations of 10 mM and above, solution aggregates exist. The intermolecular association does not disrupt the intramolecular N—H…O=C hydrogen bonding, resulting in a similar conformation for mefenamic and flufenamic acids at both low and high concentrations. Meclofenamic acid has an additional intramolecular hydrogen bond, resulting in a slightly different conformation to the other two fenamates. The results from this conformational study are of potential value in molecular and pharmacophore modelling studies on the bioactive conformations of these drugs.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320605
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  • 2
    Electronic Resource
    Electronic Resource
    Variable-temperature NMR studies of thyroid hormone conformations (1988)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 26 (1988), S. 275-280 
    Details
    ISSN: 0749-1581
    Keywords: Thyroxine ; Triiodothyronine ; Variable-temperature ; 1H NMR ; Activation barriers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H NMR spectra at 300 and 400 MHz have been recorded for the thyroid hormones thyroxine (T4) and triiodothyronine (T3) over a range of temperatures from 175 to 298 K in MeOH-d4. Above 200 K the aromatic region of the NMR spectrum of T4 consists of two peaks, one for the H-2′, H-6′ protons and one for H-2,H-6. As the temperature is lowered each of these resonances first broadens and then splits into two peaks of equal intensity at low temperature. This is consistent with slowed exchange between two equally populated conformers. Similar behaviour is noted for T3, although in this case the spectrum is complicated by the presence of spin-spin splitting. Consideration of coalescence temperatures and a line-shape analysis yielded activation barriers in the range 35-38 kJ mol-1. It is concluded that the observed spectral changes are due to dynamic interconversion between proximal and distal forms of the hormones, and that the interconversion takes place by cooperative rotations around the bonds between each phenyl ring and the linking oxygen atom.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260260402
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