Manaarenolides A-I, diterpenoids from the soft coral Sinularia manaarensis

Nine cembrane-type diterpenoids, manaarenolides A-I(1-9), along with two known cembranolides, 10 and 11, have been isolated from the ethyl acetate extract of the Taiwanese soft coral Sinularia manaarensis. Among these metabolites, diterpenes ( 1, 2, 5, and 6) were discovered for the first time as the hydroperoxycembranolides possessing a delta-lactone ring. The 13-epimeric metabolites 7 and 8 have been shown to exhibit moderate cytotoxic activity against Hepa59T/ VGH, KB, Hela, and Med cancer cell lines. The biosynthetic relationship between these new metabolites and 10 and 11 is also discussed.