Journal
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
Volume 159, Issue 2, Pages 215-224Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S1381-1169(00)00247-8
Keywords
copper; flavonolate complexes; dioxygenation; quercetinase
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The oxygenation of flavonol (flaH) using Cu-II(fla)(2) and Cu-I(fla)(PPh3)(2) catalysts results in oxidative cleavage of the heterocyclic ring to give O-benzoylsalicylic acid (O-bsH) and CO as primary products. The oxygenolysis of flavonol catalyzed by Cu-II(fla)(2) in DMF was followed by electronic spectroscopy and the rate law was found to be - d[flaH]/dt = k(obs)[flaH][Cu-II(fla)(2)][O-2]. The rate constant, activation energy, activation enthalpy and entropy at 393 K are as follows: k(obs)/s(-1) mol(-2) dm(-6) = (2.02 +/- 0.07) x 10(3), E-a/kJ mol(-1)= 142 +/- 6, Delta H double dagger/kJ mol(-1)= 139 +/- 5, and Delta S double dagger/J mol(-1) K-1 = 168 +/- 13. The results of the kinetic measurements of the Cu-I(fla)(PPh3)(2)-catalyzed oxygenation shows that in the presence of a large excess of the substrate, the Cu-I(fla)(PPh3)(2) reacts with flavonol in an irreversible step to Cu-II(fla)(2), and, then, the mechanism of the oxygenation is the same as that with the Cu-II(fla)(2)-catalyzed reaction. (C) 2000 Elsevier Science B.V. All rights reserved.
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