Cytotoxic tetraprenylated alkaloids from the South China Sea gorgonian Euplexaura robusta.

Nine achiral tetraprenylated alkaloids, including three new compounds, named malonganenones I-K (1-3, resp.), together with six known analogs, 4-9, were isolated from the gorgonian Euplexaura robusta collected from Weizhou Island of Guangxi Province, China. The structures of compounds 1-3 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 IC(50) values ranging from 0.35 to 10.82 μM. Compound 6 also showed moderate inhibitory activity against c-Met kinase at a concentration of 10 μM.