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Issue 18, 2005
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Chemical studies on antioxidant mechanisms and free radical scavenging properties of lignans

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Abstract

The antioxidant activity, in terms of radical scavenging capacity, of altogether 15 different lignans was measured by monitoring the scavenging of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The effect of differences in skeletal arrangement or the degree of oxidation of the lignans was investigated in a structure–activity relationship study. A large variety in the radical scavenging capacities of the different lignans was observed and related to some structural features. Lignans with catechol (3,4-dihydroxyphenyl) moieties exhibited the highest radical scavenging capacity, while the corresponding guaiacyl (3-methoxy-4-hydroxyphenyl) lignans showed a slightly weaker scavenging capacity. In addition, the butanediol structure was found to enhance the activity, whereas a higher degree of oxidation at the benzylic positions decreased the activity. Additionally, the readily available lignans (−)-secoisolariciresinol, a mixture of hydroxymatairesinol epimers and (−)-matairesinol were studied in more detail, including kinetic measurements and identification of oxidation products in the reactions with DPPH and ABAP (2,2-azobis(2-methylpropionamidine) dihydrochloride. The identification of reaction products, by GCMS, HPLCMS and NMR spectroscopy, showed that dimerisation of the two aromatic moieties was the major radical termination reaction. Also, the formation of adducts was a predominant reaction in the experiments with ABAP. The kinetic data obtained from the reactions between the lignans and DPPH indicated a complex reaction mechanism.

Graphical abstract: Chemical studies on antioxidant mechanisms and free radical scavenging properties of lignans

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Article information


Submitted
13 May 2005
Accepted
29 Jun 2005
First published
09 Aug 2005

Org. Biomol. Chem., 2005,3, 3336-3347
Article type
Paper

Chemical studies on antioxidant mechanisms and free radical scavenging properties of lignans

P. C. Eklund, O. K. Långvik, J. P. Wärnå, T. O. Salmi, S. M. Willför and R. E. Sjöholm, Org. Biomol. Chem., 2005, 3, 3336
DOI: 10.1039/B506739A

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