Three new cytotoxic stilbene dimers from paphiopedilum dianthum

Three new stilbene dimers, paphiodianthins A-C (1-3), and nine known stilbenes, lignan and flavonoids (4-12) were isolated from the roots and leaves of Paphiopedilum dianthum (Orchidaceae). The structures of new compounds were elucidated from their NMR, HRESIMS and IR spectroscopic data. Cytotoxic activity of all isolated compounds was evaluated by in vitro MTT assay against two human cancer cell lines (MCF-7, Caco-2), doxorubicin-resistant and mitoxantrone-resistant MCF-7 sublines, as well as a normal cell line (NIH/3T3). Stilbenes 1, 3, 10 and 11 were strongly cytotoxic to both cancer cell lines with IC₅₀ values ranging from 0.50 to 4.51 µM. Compounds 1, 10 and 11 were also active against chemotherapy-resistant MCF-7 sublines.