A number of novel resveratrol (3,5,4'-trihydroxystilbene) oligomers have been recently isolated from the plants belonging to Dipterocarpaceae, Gnetaceae, Vitaceae, Cyperaceae and Leguminosae and the oligomers in this family have a variety of frameworks resulting from different oxidative condensation of nucleus. Their various bioactivities such as chemopreventive and hepatoprotective have been reported. In the preceding study, the structures of new stilbenoid oligomers composed of several resveratrol units in stem bark of Vatica rassak. Shorea hemsleana and Hopea utilis and the distinctive cytotoxicity observed in some stilbenoids were discussed. In the course of our investigation of chemical constituents with biological activity, further phytochemical study on Dipterocarpaceous and Gnetaceaeous plants has been carried out. Examination of chemical constituents in the stem bark of Vatica rassak, Vateria indica and Hopea utilis resulted in isolation of 20 resveratrol derivatives including 7 new compounds. The structural elucidation of the isolates was accomplished by spectroscopic analysis including 2D NMR. Among them, vaticanols H (2), I (3) and J (4) are new types of resveratrol oligomers that are hexamers (2 and 3) and a heptamer (4). Vateriaphenol A (5), isolated from V. indica, was determined to be a novel resveratrol octamer. The molecular formula of 5 was determined by FABMS. The ^1H, ^<13>C NMR, COSY and HMQC spectra of 5 suggested the presence of eight resveratrol units as partial structure (resveratrol A-H) and the HMBC correlations disclosed the connectivity of these partial structures to give the total planar structure which composed of two resveratrol tetramers (tetramers 1 and 2). The ROESY spectra and the coupling constant in the ^1H NMR spectra were useful to determine the relative stereochemistry. In our bioactive screening experiment for above-mentioned compounds including their derivatives, we examined in vitro cytotoxicity on a panel of human tumor cell lines. Among the isolates, vaticanol C (8) displayed significant cytotoxicity on SHSY-5Y, SW480, DLD-1, COLO201, PC3, LNCAP, KOCL44, K562, U937, NB4 and HLE cells.
