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  • 1985-1989  (5)
  • 1905-1909
  • 1870-1879
  • 1989  (5)
  • Organic Chemistry  (5)
  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structures of the Cu2+ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6, respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5, it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu2+ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3-6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3-5 is proportional to the complex concentration and to [OH-] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH-] up to pH 11.5, becoming independent of [OH-] at pH 〉 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH- attack and the results of the X-ray structure analyses.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potentiometric study of the complexation of 1,4,7-triazacyclononane-l-acetic acid (1) with Cu2+ (I = 0.5 (KNO3), T = 25°) indicates the presence of the species [Cu(1)], [Cu(1)OH], [Cu(1)2], and [(Cu(1))2OH], the stability constants of which are determined. The two complexes [Cu(1)]ClO4 and [(Cu(1)2)OH]ClO4 were also characterized by X-ray structure analysis. In both cases, the Cu2+ ion is in a distorted square-pyramidal arrangement, penta-coordinated by the three N-atoms of the macrocycle, an O-atom of the carboxylate, and an additional O-atom either from a second carboxylate or from an OH-, acting as a bridge between two metal centres.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and complexation properties of 1,4-dimethyl-8-[2-(2-pyridyl)ethyl]-1,4,8,11-tetraazacyclotetra-decane (2) are described. This ligand forms with Cu2+ two complexes, one of which has been characterized by X-ray structure analysis. The structural, spectral, and kinetic studies indicate that the two Cu2+ complexes are isomers with the macrocycle in the trans-III and trans-I configuration. The rate of the interconversion of the trans-I isomer to the thermodynamically more stable trans-III species is proportional to [OH-]. A mechanism for this reaction is proposed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By mixing acidic solutions of 1,4,8,11-tetraazacyclotetradecane (Cy) with CuX2 (X = Cl-, Br-), either the hexahalocuprates of the tetraprotonated form of the macrocycle ([CyH4] [CuX6]) or the tetrahalocuprates of its Cu2+ complex ([CuCy] [CuX4]) are obtained. The structures of the chloro derivatives are established by X-ray diffraction analysis. In [CyH4] [CuCl6], the Cu2+ is in a tetragonally distorted octahedral geometry with four short and two long Cu—Cl bonds. The tetraprotonated macrocycle is centrosymmetric, and its conformation is exodentate, so that the four ammonium groups are as far as possible from each other to minimize the electrostatic repulsion. In [CuCy] [CuCl4], the Cu2+ ion complexed by the macrocycle is surrounded by four N-atoms in a square-planar arrangement. In addition, the axial positions are occupied by two Cl- ions of two CuCl42- units, which act as bridges. The macrocycle is in the trans-III-configuration. The other Cu2+ ion is coordinated by four Cl- ions in a distorted tetrahedral geometry. IR and VIS spectra of the chloro and bromo derivatives are used to discuss the structure of the bromo species.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0170-2041
    Keywords: Gloeosporone ; Colletotrichum gloeosporioides ; 4-Pentynoic acid ; Oxidation, alkyne → 1,2-diketone ; 23Na NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Gloeosporon - Ein Pilzkeimungs-Selbsthemmer mit Macrolidstruktur. - Totalsynthese und AktivitätAusgehend von (S)- oder (R)-4-Brom-1,2-epoxybutan [kommerziell erhältlich oder leicht und in hoher Ausbeute aus (S)- bzw. (R)- Apfelsäure zugänglich] wurden die beiden Enantiomeren des Keimungs-Selbstinhibitors Gloeosporon hergestellt. Die absolute Konfiguration des Naturstoffes wurde damit als 4S,7R,13R bewiesen. Mikrobiologische Tests zeigen, daß beide Enantiomere von Gloeosporon die Keimungshemmung der Sporen von Colletotrichum gloeosporioides bewirken, und daß (-)-Gloeosporon gegenüber einer Reihe von anderen Pilzen aktiv ist. Zur Aufklärung des Wirkungsmechanismus wurden 23Na-NMR- sowie Ionenselektivitätsmessungen durchgeführt; es konnten keine Gloeosporon-Metallion-Wechselwirkungen nachgewiesen werden.
    Notes: Starting with (S)- or (R)-4-Bromo-1,2-epoxybutane [commercially available or readily made from (S)- or (R)-malic acid], both enantiomers of the germination self-inhibitor gloeosporone were synthesized. The absolute configuration of the natural product was thus proven to be 4S,7R,13R. Microbiological studies showed that both enantiomers of the compound cause inhibition of germination in spores of Colletotrichum gloeosporioides, and that (-)-gloeosporone is also active against a variety of other fungi. In order to gain some insight into the mode of action, 23Na NMR measurements and ion-selectivity studies were undertaken; none of these experiments provided evidence for a gloeosporone-metal ion interaction.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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