Cytotoxic scalarane sesterterpenoids from the South China Sea sponge Carteriospongia foliascens

Eleven new scalarane sesterterpenoids, including three 20,24-bishomo-25-norscalaranes, carteriofenones A-C (1-3), and eight 20,24-bishomoscalaranes, carteriofenones D-K (4-11), along with two known analogues (12 and 13), were obtained from the marine sponge Carteriospongia foliascens collected from the South China Sea. Their planar structures and relative configurations were elucidated by extensive NMR spectroscopic data. The absolute configuration of 3 was determined using the modified Mosher's method on its hydrolysis product. Scalarane sesterterpenoids with 4-methylpentanate or pentanoate substituents at the 12-position (1-8) were reported for the first time. Carteriofenones E-H (5-8) represented rare naturally occurring scalarane sesterterpenoids with a cyclobutane ring. Compound 4 showed cytotoxicity against the mouse lymphocytic leukemia cell line (P388) with an IC50 value of 0.96 mu M.