Cytotoxic Aryltetralin Lignans from Fruits of Cleistanthus indochinensis

Eight new aryltetralin lignans, cleisindosides A-F (1-6), picroburseranin (7), and 7-hydroxypicropolygamain (8), were isolated from the fruits of Cleistanthus indochinensis (Euphorbiaceae). The structures of the isolates were established on the basis of their one- and two-dimensional NMR spectral data, as well as their mass spectrometric data. Compound 7 was found to have potent cytotoxicity against oral epidermoid carcinoma cells with an IC50 value of 0.062 mu M, whereas glycosylation to 3 (IC50 7.5 mu M) and stereochemical changes to 8 (IC50 10.8 mu M) led to marked decreases in biological activity. Thus, it was deter-mined that the C-7 and C-8' positions are critical for the biological activity of the lignans from this plant.