Cytotoxic diterpenoids from the brown alga Dilophus ligulatus

A new xenicane-type diterpene, dilopholide [5], and four known diterpenoids, acetoxycrenulide [1], acetylcoriacenone [2], and its epimer isoacetylcoriacenone [3], and hydroxyacetyldictyolal [4], have been isolated from the brown alga Dilophus ligulatus [syn. spiralis (Montagne) Hamel]. The structure of dilopholide [5] was elucidated by spectroscopic methods, including the concerted application of a number of 2D nmr techniques, including 1H-1H COSY, heteronuclear proton-carbon chemical shift correlation (HETCOSY), and long-range HETCOSY. The cytotoxic activity of compounds 1-5 has been examined against several types of mammalian cells: human nasopharynx carcinoma cells (KB), human lung carcinoma cells (NSCLC-N6), murine leukemia cells (P-388), and murine leukemia cells expressing the multi-drug-resistance gene, mdr (P-388/DOX).