Antioxidant flavonoids from the rhizomes of Helminthostachys zeylanica

Eight flavonoids, ugonins E-L (1-8), were isolated from the rhizomes of Helminthostachys zeylanica, and their structures were established on the basis of spectral evidence. Compounds 3-8 were evaluated for their antioxidative activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Compounds 6, 7 and 8 were more active than Trolox, with IC20 values of 5.29 +/- 10.32, 7.23 +/- 0.22, and 7.93 +/- 0.31, respectively. (C) 2003 Elsevier Ltd. All rights reserved.