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Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...

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Phenolic compounds from Hypericum calycinum and their antioxidant activity.

Hasan Kirmizibekmez1, Carla Bassarello, Sonia Piacente

  • 1Department of Pharmacognosy, Faculty of Pharmacy, Yeditepe University, TR-34755, Kayişdaği, Istanbul, Turkey. hasankbekmez@yahoo.com

Natural Product Communications
|May 30, 2009
PubMed
Summary

Eleven compounds were isolated from Hypericum calycinum, including caffeoylquinic acid derivatives and flavonoids. These compounds demonstrated significant antioxidant properties, particularly (+)-catechin and (-)-epicatechin, in DPPH and nitric oxide scavenging assays.

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Area of Science:

  • Phytochemistry
  • Pharmacology
  • Natural Products Chemistry

Background:

  • Hypericum calycinum is a plant species with potential medicinal properties.
  • Natural products are a rich source of bioactive compounds with therapeutic potential.
  • Antioxidants play a crucial role in combating oxidative stress and related diseases.

Purpose of the Study:

  • To isolate and identify bioactive compounds from the methanol extract of Hypericum calycinum.
  • To evaluate the in-vitro free radical scavenging activities of the isolated compounds.
  • To determine the potential of Hypericum calycinum as a source of natural antioxidants.

Main Methods:

  • Phytochemical analysis involving methanol extraction and isolation techniques.
  • Spectroscopic methods including 1D and 2D NMR and mass spectrometry for compound identification.
  • In-vitro antioxidant assays: 1,1-diphenyl-2-picrylhydrazyl (DPPH) and nitric oxide (NO) radical scavenging models.

Main Results:

  • Eleven compounds were successfully isolated: two caffeoylquinic acid derivatives, seven flavonoids, and two flavanols.
  • All isolated compounds exhibited concentration-dependent free radical scavenging activities.
  • (+)-Catechin and (-)-epicatechin displayed the most potent DPPH radical scavenging activity with IC50 values of 4.16 and 4.67 µM, respectively.
  • (+)-Catechin and (-)-epicatechin also showed moderate nitric oxide scavenging activity with IC50 values of 190 and 170 µM, respectively.

Conclusions:

  • Hypericum calycinum is a valuable source of diverse phytochemicals with significant antioxidant potential.
  • The isolated flavanols, (+)-catechin and (-)-epicatechin, are particularly effective free radical scavengers.
  • These findings support the traditional use of Hypericum calycinum and suggest its utility in developing natural antioxidant agents.