Electron Paramagnetic Resonance Studies of Radical Species of Proanthocyanidins and Gallate Esters

Electron Paramagnetic Resonance Studies of Radical Species of Proanthocyanidins and Gallate Esters The polyphenols present in green tea or red wine comprise both regular flavon(ol)s and proanthocyanidins, i.e., derivatives of flavan-3-ols, whose distinct antioxidative potential is of great importance for explaining the beneficial effects of these nutrient beverages. Using EPR spectroscopy, we investigated radical structures obtained after oxidation of the parent compounds either by horseradish peroxidase/hydrogen peroxide or after autoxidation in moderately alkaline solutions. Both proanthocyanidins (monomers of condensed tannins, e.g., (+)-catechin, (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, (−)-epigallocatechin gallate, Pycnogenol) and gallate esters (hydrolyzable tannins, e.g., propylgallate, β-glucogallin, pentagalloyl glucose and tannic acid) yielded predominantly semiquinone structures derived from the parent catechol or pyrogallol moieties. Evidence for a time-dependent oligomerization was obtained for (−)-epigallocatechin gallate, supporting our hypothesis that o -quinones formed from the initial semiquinone disproportionation are prone to nucleophilic addition reactions. Such phenolic coupling reactions would retain the numbers of reactive catechol/pyrogallol structures and thus the antioxidative potential. We therefore propose that proanthocyanidins are superior antioxidants as compared to flavon(ol)s proper, whose quinones are more likely to redox-cycle and act as prooxidants. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Biochemistry and Biophysics Elsevier

Electron Paramagnetic Resonance Studies of Radical Species of Proanthocyanidins and Gallate Esters

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Publisher
Elsevier
Copyright
Copyright © 2000 Academic Press
ISSN
0003-9861
eISSN
1096-0384
DOI
10.1006/abbi.1999.1606
Publisher site
See Article on Publisher Site

Abstract

The polyphenols present in green tea or red wine comprise both regular flavon(ol)s and proanthocyanidins, i.e., derivatives of flavan-3-ols, whose distinct antioxidative potential is of great importance for explaining the beneficial effects of these nutrient beverages. Using EPR spectroscopy, we investigated radical structures obtained after oxidation of the parent compounds either by horseradish peroxidase/hydrogen peroxide or after autoxidation in moderately alkaline solutions. Both proanthocyanidins (monomers of condensed tannins, e.g., (+)-catechin, (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, (−)-epigallocatechin gallate, Pycnogenol) and gallate esters (hydrolyzable tannins, e.g., propylgallate, β-glucogallin, pentagalloyl glucose and tannic acid) yielded predominantly semiquinone structures derived from the parent catechol or pyrogallol moieties. Evidence for a time-dependent oligomerization was obtained for (−)-epigallocatechin gallate, supporting our hypothesis that o -quinones formed from the initial semiquinone disproportionation are prone to nucleophilic addition reactions. Such phenolic coupling reactions would retain the numbers of reactive catechol/pyrogallol structures and thus the antioxidative potential. We therefore propose that proanthocyanidins are superior antioxidants as compared to flavon(ol)s proper, whose quinones are more likely to redox-cycle and act as prooxidants.

Journal

Archives of Biochemistry and BiophysicsElsevier

Published: Feb 15, 2000

References

  • Tetrahedron
    Jensen, O.N.; Pedersen, J.A.
  • Biochim. Biophys. Acta
    Ohnishi, T.; Yamazaki, H.; Iyanagi, T.; Nakamura, T.; Yamazaki, I.
  • J. Org. Chem.
    Quideau, S.; Feldman, K.S.; Appel, H.M.
  • J. Chem. Phys.
    Adams, M.; Blois, M.S.; Sands, R.H.

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