Two new biphenanthrenes with cytotoxic activity from Bulbophyllum odoratissimum.

Two new dimeric phenanthrenes, bulbophythrins A (1) and B (2), were isolated from Bulbophyllum odoratissimum. Their structures were elucidated by HR-ESI-MS, 1D and 2DNMR spectroscopy. They were evaluated in vitro for their inhibitory ability against the growth of human leukemia cell lines K562 and HL-60, human lung adenocarcinoma A549, human hepatoma BEL-7402 and human stomach cancer SGC-7901. Both compounds showed significant cytotoxicity against the tested cell lines. Compound 1 exhibited some selectivity against HL-60 and BEL-7402 with IC(50) values of 1.27 x 10(-3) and 1.22 x 10(-3) micromol/ml respectively, whereas 2 was most active against A549 with IC(50) value of 1.18 x 10(-3) micromol/ml.