A new benzoquinone and a new stilbenoid from Paphiopedilum exul (Ridl.) Rolfe

One new alkyl benzoquinone, paphionone (1), one new trans-stilbenoid, (E)-6,5 ' -dihydroxy-2,3 ' -dimethoxystilbene (2), and eight known stilbenoids and flavonoids (3-10) were isolated from the leaves and roots of Paphiopedilum exul (Orchidaceae). Their chemical structures were determined based on IR, ECD, MS and NMR analyses. Cytotoxicity of all isolated compounds towards human hepatocellular carcinoma (HepG2) cell line was examined in vitro by MTT assay. The para-hydroxybenzyl substituted stilbene 10 was potently cytotoxic to the cancer cells, with an IC50 value of 4.80 +/- 1.10 mu M (selectivity index = 20.83). All compounds were non-toxic to normal human embryo fibroblast (OUMS-36) cell line.