Study on the phenolic constituents of the flowers and leaves of Trifolium repens L.

The flowers and leaves of Trifolium repens L. (Fabaceae) were subjected to phytochemical investigation in order to identify their major chemical constituents and to evaluate in vitro antioxidant activity of the isolated compounds against DPPH. A total of 12 flavonoids, pterocarpan and methyl caffeate were isolated, then characterised by UV, MS, NMR spectroscopy and identified as quercetin and kaempferol 3-O-(6 ''-alpha-rhamnopyranosyl-2 ''-beta-xylopyranosyl)-beta-galactopyranosides (1, 2), kaempferol 3-O-(2 '',6 ''-alpha-dirhamnopyranosyl)-beta-galactopyranoside, mauritianin (3), quercetin and kaempferol 3-O-(2 ''-beta-xylopyranosyl)-beta-galactopyranosides (4, 5), kaempferol and quercetin 3-O-beta-(6 ''-O-acetyl)-galactopyranosides (6, 7), trifolin (8), hyperoside (9), myricetin 3-O-beta-galactopyranoside (10), quercetin (11), ononin (12), medicarpin 3-O-beta-glucopyranoside (13) and methyl caffeate (14). Mauritianin, ononin, pterocarpan and methyl caffeate have been reported in this plant for the first time. The compounds 4, 7, 9, 10, and 11 were tested for their antioxidant effect against DPPH. All studied compounds were found to have potent activity, but the most effective in the test were compounds 9, 10 and 11 (EC50 values in the range 7.51-9.52 mu M).