A new cytotoxic stilbene from Paphiopedilum hirsutissimum (Lindl. ex Hook.) Stein

A new trans-stilbene, (E)-2,4-bis(4-hydroxybenzyl)-3,5-dihydroxystilbene (1), and ten known compounds including stilbenoids (2, 7, 8, 10), coumaric acid ester (3), flavonoids (4-6), aromatic aldehyde (9) and triterpenoid glycoside (11) were isolated from the leaves and roots of the lady slipper's orchid Paphiopedilum hirsutissimum (Lindl. ex Hook.) Stein. The structures of these chemical constituents were determined based on their spectroscopic data and comparison with literature. In vitro cytotoxicity of all isolated compounds towards human hepatic cancer (HepG2) cell line was examined by MTT assay. Izalpinin (6) was potently cytotoxic to the cancer cells, with an IC₅₀ value of 4.62 ± 1.50 μM. Stilbenoids 2, 7 and 8 also exhibited notable activity in the range of 6.31-6.68 μM. All compounds, except the new stilbene 1, were non-toxic to normal fibroblast (OUMS-36) cell line.