Cyclized geranyl stilbenes from the rhizomes of Helminthostachys zeylanica.

Three new cyclized geranyl stilbenes, ugonstilbene A ( 1), ugonstilbene B ( 2), and ugonstilbene C ( 3), and one known compound 3-hydroxyacetophenone, were isolated from the dried rhizomes of H. zeylanica. The structures of these three new compounds were elucidated on the basis of spectral analysis. Compounds 1 - 3 exhibited moderate antioxidant activity by the DPPH assay with IC (20) of 11.31 +/- 1.11, 38.72 +/- 0.47, and 30.80 +/- 1.19 microM, respectively, while the IC (20) of Trolox was 8.70 +/- 0.95 microM.