Thesis (M.Sc.)--Chulalongkorn University, 2004

The preliminary antihistaminic activity screening using RBL-2H3 cells of Mansonia gagei Drumm. revealed that the dichloromethane extracts from the roots and the leaves exhibited high antihistaminic activity. The chemical constituents investigation of the roots disclosed nine pure compounds. By means of physical properties, chemical reactions and spectroscopic evidences, the structures of eight compounds could be elucidated to 2,5-dimethoxy-1,4-benzoquinone, mansonone G, vanillic acid, mansonone H, mansonone C, mansonone E, mansonone T and stigmastane-3beta,6alpha-diol. Mansonone T was disclosed to be a naturally new compound. Other three compounds could be isolated from the leaves of this plant. By means of physical properties, chemical reactions and spectroscopic evidences, the structures of two compounds could be deduced as 3,11-dioxo-beta-amyrin, 11alpha-hydroxy-beta-amyrin together with two mixtures: a mixture of long chain hydrocarbon and a mixture of long chain acid. Among isolated substances, mansonones G and C exhibited the highest antihistaminic activity against RBL-2H3 cells at IC[subscript 50] 212 micrometre and 222 micrometre, respectively