Cytotoxic lignans from fruits of Cleistanthus tonkinensis

Seven new lignans, cleistonkinins A-E (1-5), cleistonkisides A and B (6-7) were isolated from the fruits of Cleistanthus tonkinensis (Euphorbiaceae), together with five known aryltetralin lignans, cleisindoside B (8), cleistantoxin (9), cleisindoside D (10), neocleistantoxin (11) and polygamain (12). Their structures were established from spectral analysis, including mass spectrometry and 2D-NMR. The absolute configurations of 4-7 were determined by analysis of their experimental CD spectra and comparison with calculated electronic circular dichroism (ECD) spectra. Compounds 2 and 6 had selective inhibition with moderate cytotoxicity against Pan Cl and A549 cell lines, respectively. Cleistantoxin (9) was significantly active against A549, HeLa, Hep3B, Pan Cl and MCF7 cell lines while it was less cytotoxic against HeLa cells. Neocleistantoxin (11) exhibited remarkable inhibition toward A549, HeLa, MCF7 and Pan Cl. This is the first report for cytotoxicity of 9 and 11 against A549, Hep3B and Pan C1 cell lines.