Asterolaurins A-F, xenicane diterpenoids from the Taiwanese soft coral Asterospicularia laurae

Six new xenicane-type Diterpenoids, designated as asterolaurins A-F (1-6), have been isolated from the organic extract of the soft coral Asterospicularia laurae, collected in southern Taiwan. Compounds 1-4 possess a xenicin skeleton with a 2-oxabicyclo[7.4.0]tridecane ring system, while 5 and 6 are xeniolide A-type compounds. The structures of the new secondary metabolites, including their configurations, were established on the basis of an extensive spectroscopic analysis, including 1D and 2D NMR (1H-1H COSY, HMQC, HMBC, and NOESY), and by comparison of their NMR data with those of the related compounds. The structure of asterolaurin A (1) was confirmed by X-ray diffraction analysis, and its absolute configuration was determined using the modified Mosher's method. Asterolaurin A (1) exhibited moderate cytotoxicity against HepG2 cells with an IC50 of 8.9 microM, while asterolaurin D (4) showed potent inhibition of Elastase release and superoxide anion generation in vitro.