Thesis (M.Sc.)--Chulalongkorn University, 2000

The grounded air-dried stem barks of Croton oblongifolius Roxb. was extracted subsequently with organic solvents including hexane, ethyl acetate and methanol. The solvents in each crude extract were evaporated by evaporation under reduce pressure to obtain hexane extract crude, ethyl acetate extract crude and methanol extract crude, respectively. Each extract crude was isolated and purified using the column chromatography technique to result in three compounds. The structure of these compounds were characterized using their physical and chemical properties and spectral data. The structure of compound (1), compound (2), and compound (3) were proved to be kaur-16-en-19-oic acid (1), hardwickiic acid (2) and mixture of beta-sitosterol and stigmasterol, respectively. This research indicated that the kaurane diterpene compound was first observed from the plant of C oblongifolius. The compound (1) derivatives, including methyl kaur-16-en-19-oate (1a), kaur-16-en-19-ol (1b), 16, 17-epoxy-kauran-19-oic acid (1c), and 17-hydroxykaur-15-en-19-oic acid (1d) were synthesized. The cytotoxic activity of isolated natural diterpenoids and their derivatives were assayed against cancer cell lines. The result indicated that most of tested compounds show a weak to moderate activity.