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 (H-1-H-1 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 mu M, while asterolaurin D (4) showed potent inhibition of elastase release and superoxide anion generation in vitro.