Gagunins, highly oxygenated diterpenoids from the sponge Phorbas sp.

Gagunins A–G, seven new diterpenoids were isolated from the sponge Phorbas sp. collected from Gagu-Do, Korea. The carbon skeleton of these highly oxygenated metabolites was determined to be an unusual 10,13-bis-epi-homoverrucosane on the basis of combined chemical and spectral methods. Stereochemical assignments of these diterpenoids were accomplished by extensive ROESY and 1D NOESY experiments. The novel compounds exhibited significant cytotoxicity with values ranging from 0.03 to 51 μg/mL, toward a human leukemia cell-line (K-562).