Cytotoxic Tetraprenylated Alkaloids from the South China Sea Gorgonian Euplexaura robusta

Nine achiral tetraprenylated alkaloids, including three new compounds, named malonganenones IK (13, resp.), together with six known analogs, 49, were isolated from the gorgonian Euplexaura robusta collected from Weizhou Island of Guangxi Province, China. The structures of compounds 13 were elucidated by extensive spectral analyses, especially of their 1D- and 2D-NMR data. Compounds 1, 4, 6, and 7 showed moderate cytotoxicities against K562 and HeLa tumor cell lines with IC50 values ranging from 0.35 to 10.82 mu M. Compound 6 also showed moderate inhibitory activity against c-Met kinase at a concentration of 10 mu M.