Studies on the Mechanism of the Oxidation of Tea Leaf Catechins

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  • TAKINO Yoshinori
    Department of Agricultural Chemistry, Faculty of Agriculture, Tokyo University of Education
  • IMAGAWA Hiroshi
    Department of Agricultural Chemistry, Faculty of Agriculture, Tokyo University of Education
  • AOKI Yôko
    Department of Agricultural Chemistry, Faculty of Agriculture, Tokyo University of Education
  • OZAWA Tetsuo
    Department of Agricultural Chemistry, Faculty of Agriculture, Tokyo University of Education

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  • Part II Formation of Diethyl 4, 4', 5, 5', 6, 6'-Hexahydroxydiphenate by the Enzymic Oxidation of Ethyl Gallate

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In order to understand the mechanism of the enzymic oxidation of epigallocatechin, ethyl gallate was taken up as a model substrate on account of its close structural similarity to the vic-trihydroxyphenyl group, which indeed is supposed to be attacked by oxidase, when epigallocatechin is oxidized enzymically. By the action of tea or apple oxidase at pH 5.5, it gave a characteristic polyphenolic substance, which was obtained in prisms, C18H18O10-2H20, and proved to be diethyl 4, 4', 5, 5', 6, 6'-hexahydroxydiphenate, as the product was converted into ellagic acid by hydrolysis of ester linkage and then lactone formation.

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