Abstract

The antioxidant activity of eight coumarins and two flavonols isolated from Haplopappus multifolius was studied with the DPPH radical method. Results show that a high concentration of phenolic coumarins and the presence of quercetin and rhamnetin in the exudates could account for the protection of the plant against oxidative stress. Structures for the coumarins 6-hydroxy-7-[(E,E)-3′,7′-dimethyl-2′,4′,7′ -octatrienyloxy] coumarin and 7-[(E)-3′-methyl-4′-hydroxy-2′-butenyloxy] coumarin are proposed on the basis of spectroscopic evidence. © 2006 Elsevier Ltd. All rights reserved.