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  • Organic Chemistry  (1)
  • supramolecule  (1)
  • 1990-1994  (2)
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  • 1990-1994  (2)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 14 (1992), S. 205-215 
    ISSN: 1573-1111
    Keywords: Cyclodextrin ; transacylation ; metal ; Cu(II) ; catalysis ; ester ; supramolecule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The paper reports the synthesis of aβ-cyclodextrin (β-CD) derivative (1) functionalized with a ligand subunit at the secondary-hydroxyl rim. The ligand subunit is 2-hydroxymethyl-6-thiomethyl pyridine connected to the macrocycle via a thioether bond. In the presence of Cu(II) ions1 accelerates the cleavage of thep-nitrophenyl esters of picolinic acid (PNPP), quinaldic acid (PNPQ) and its 6-phenyl derivative (PNPQPh) via the nucleophilic attack of the hydroxyl of the pyridine subunit. However, theβ-CD derivative is less effective than the ligand 2-hydroxymethyl-6-methylthiomethyl pyridine (2), indicating no cooperation between the hydrophobic and metal ion recognition sites. However, in the case of PNPQPh, the observed rate constants in the presence of Cu(II) ions are close to that of model2 and this suggests we are approaching a binding mode appropriate for taking advantage of the two binding sites of the metal receptor1 · Cu(II). Interestingly, the most reactive derivative with nativeβ-CD is thep-nitrophenyl quinaldate (PNPQ) in accord with its mode of complexation to the macrocycle and the location of the actual nucleophile (one of the secondary hydroxyls ofβ-CD).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 619-627 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transition metal ions are effective catalysts of the hydrolytic cleavage of amino acid esters and their effects can be enhanced and properly directed when they are chelated to functionalized ligands. The resulting metallocatalysts are attracting increasing attention and the systems so far investigated are briefly reviewed. Particular emphasis is given to supramolecular systems which may add to the metallocatalysts the benefits of the cooperativity, set upon convergent non-covalent interactions of their components, needed for substrate recognition. The results obtained with metallomicellar aggregates and molecular metalloreceptors, with particular reference to those studied in the authors' laboratory, are reported in more detail. In the case of loosely structured metallomicelles, remarkable accelerations and, generally, modest selectivities have been observed; less spectacular kinetic effects, but promising substrate selectivity, have been obtained with structurally well defined metalloreceptors.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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