Thesis (Ph.D.)--Chulalongkorn University, 2004

Phytochemical study of the stem bark of Cratoxylum arborescens (Vahl) Blume (Cratoxylaceae) has shown the presence of a new natural xanthone, 1,3-dihydroxy-6,7-dimethoxy-2,8-diprenylxanthone, together with a known xanthone and anthraquinones, fuscaxanthone C, 1,8-dihydroxy-3-geranyloxy-6-methylanthraquinone, and 2-geranyl- emodin. The roots of C. arborescens led to the isolation a known xanthone, 1,7-dihydroxyxanthone, together with the same compounds as from the stem bark. Phytochemical investigation of the stem bark of Millettia decipiens Prain (Fabaceae) led to the isolation of two new compounds, (+)-S-3,4-methylenedioxy-2',4',6',[Beta]-tetramethoxydihydrochalcone and 2,4-dimethoxy-3',4'-methylenedioxydihydrochalcone, along with nine known compounds. The nine known compounds were 3',4'-methylenedioxy-2,4,6,[beta]-tetramethoxychalcone, lanceolatin B, pongaflavone, karanjin, milletenone, desmethoxykanugin, dihydroisomilletenone methyl ether, dihydro-milletenone methyl ether, and pongaglabrone. The roots of M. decipiens led to the isolation of a known [Beta]-methoxydihydrochalcone, ovalitenin B, and the same compounds as from the stem bark. The structure determination of all of the isolates was accomplished by spectroscopic analyses and compared with the literature data of the known compounds. All of the isolates from C. arborescens were subjected for biological activity evaluation, including antimalarial and cytotoxic activity against NCI-H187 cells, KB cells, BC cells, and Vero cells. The new natural xanthone, 1,3-dihydroxy-6,7-dimethoxy-2,8-diprenylxanthone and 2-geranyl- emodin showed moderate activity against NCI-H187. All of the isolates from M. decipiens were subjected for biological activity evaluation, including antimalarial, antimyco- bacterial, and free radical scavenging activity. Most of them showed mild activity and no antimycobacterial activity , except for pongaflavone which showed moderate activity. All of the compounds from M. decipiensexhibited inactive free radical scavenging activity. The isolates from C. arborescens and M. decipiens showed no antimalarial activity.