Minor steroidal alkaloids from the marine sponge Corticium sp

Four new steroidal alkaloids, plakinamine G (1), plakinamine H (2), 4alpha-hydroxydemethylplakinamine B (3), and tetrahydroplakinamine A (4), along with three known compounds, were isolated from the marine sponge Corticium sp. The structures of these metabolites were elucidated largely by 1D and 2D NMR methods and accurate mass measurements (HR-EIMS). Compounds 1, 2, and 4 show significant in vitro cytotoxicity.