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

Patrik C. Eklund*, Otto K. Långvik, Johan P. Wärnå, Tapio O. Salmi, Stefan M. Willför, Rainer E. Sjöholm

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

151 Citations (Scopus)

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 GC-MS, HPLC-MS 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.

Original languageEnglish
Pages (from-to)3336-3347
Number of pages12
JournalOrganic and Biomolecular Chemistry
Volume3
Issue number18
DOIs
Publication statusPublished - 21 Sep 2005
MoE publication typeA1 Journal article-refereed

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