Thesis (M.Sc.)--Chulalongkorn University, 2007

In phytochemical investigation for bioactive compounds from Thai medicinal plants in the family Gnetaceae, acetone crude extract from the roots of Gnetum macrostachyum was selected for isolation, purification and structure elucidation. The chromatographic separation of acetone crude extract led to the isolation of five new stilbenoids, macrostachyol A (6), B (7), C (11), D (13), and gnetumacrosin (9) along with eight known stilbenoids, isorhapontigenin (1), trans-resveratrol (2), gnetol (3), gnetin C (4), latifolol (5), parvifolol A (8), bisisorhapontigenin B (10), and oxyresveratrol (12). The structures of all isolated compounds were elucidated by spectroscopic methods as well as comparison with previous literature data. The isolated stilbenoids were tested for inhibitory activity of antioxidant (DPPH radical scavenging and lipidperoxidation inhibition), antiplatelet aggregation, and cytotoxicity on HeLa and KB cell lines. Compounds 1, 3, 4, 5, and 6 showed antioxidant activity on DPPH radical with IC₅₀ value of 0.28, 0.21, 0.24, 0.32, and 0.33 mM respectively. Compound 5 and 6 (IC₅₀ = 0.02 mM) also showed highest activity towards on lipid peroxidation inhibition. For antiplatelet aggregation, compounds 1-8 (IC₅₀ = 0.18-1.26 µM) more potent than ibuprofen (IC₅₀ = 11.2 mM) which was used as a positive control. In addition, compounds 1, 2, 9, and 10 showed mild cytotoxic activity against KB cell line IC₅₀ = 6.90, 8.00, 8.50, and 12.50 and against HeLa cell line with IC₅₀ = 15.00, 15.50, 11.00, and 14.00 µg/mL, respectively.