Minor steroidal alkaloids from the marine sponge Corticium sp.

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