Isolation, synthesis and structures of cytotoxic ginsenoside derivatives

Four known ginsenosides: ginsenoside-Rb1 (1), Rb3 (2), Rd (3) and Re (4) were isolated from the methanolic extract of the traditional Chinese medicine Panax ginseng C. A. Meyer. Further enzyme reactions and chemical modifications led us to obtain ginsenoside-M1 (5) and synthesize three novel mono-esters of ginsenoside-M1, ginsenoside-DM1 (6), PM1 (7) and SM1 (8) 30 - 50% of yield via a facile and green synthetic strategy. The structures were elucidated on the basis of extensive 1D- and 2DNMR, as well as high resolution ESI-TOF mass spectroscopic analyses. The isolated and synthetic compounds were tested in an anti-tumor bioassay, and compounds 5-8 showed considerable cytotoxicity (SRB) against several human cancer cell lines (breast cancer MCF-7, skin melanoma SK-MEL-2 and human ovarian carcinoma B16), but moderate effects on lung carcinoma COR-L23. The other ginsenosides showed no effects.