An ethanol extract of "Kijitsu" (Aurantii Fructus Immaturus, Citrus aurantium L.) collected in China was assessed for the antitumor activity using murine leukemia P388 in vivo, and the extract was found to be active by the antitumor bioassay in vivo and in vitro. The extract was separated into a petroleum ether-soluble fraction and an ethyl acetate-soluble fraction. Fractionation was carried out using an index of cell-growth inhibitory activity against mouse leukemia L1210 cells to isolate antitumor active substances or compounds. The active compounds were purified employing silica gel column chromatography and HPLC. The antitumor effect of the isolated active compounds was studied. Five compounds, auraptene, marmin, tangeretin, nobiretin and 5- [ (6', 7'-dihydroxy-3', 7'-dimethyl-2-octenyl) oxy] psoralen were isolated from Citrus aurantium L. Though they are all known compounds, 5 [ (6', 7'-dihydroxy-3', 7'-dimethyl-2-octenyl) oxy] psoralen from this plants was first isolated. These compounds showed a cell-growth inhibitory effect against L1210 and K562 in vitro.
