Five new pregnane-type steroids, sclerosteroids J–N (1–5), and a diterpenoid with a new chemotype 3-methyl-5-(10′-acetoxy-2′,6′,10′-trimethylundecyl)-2-penten-5-olide (6), have been isolated from a soft coral Scleronephthya gracillimum. The structures of the metabolites were determined by extensive spectroscopic analysis. Compound 4 exhibited cytotoxicity against HepG2, A549, and MDA-MB-231 cancer cell lines. Furthermore, steroids 2 and 4 were found to significantly inhibit the accumulation of the pro-inflammatory iNOS protein, and 1, 2, 4 and 5 could effectively reduce the accumulation of COX-2 protein in LPS-stimulated RAW264.7 macrophage cells.

A new chromene derivative, 2-(4',8'-dimethylnona-3'E,7'-dienyl)-8-hydroxy-2,6-dimethyl-2H-chromene (1) together with four known natural products, methylfarnesylquinone (2), isololiolide (3), pheophytin a (4), and β-carotene (5) were isolated from the brown alga Homoeostrichus formosana. The structure of 1 was determined by extensive 1D and 2D spectroscopic analyses. Acetylation of 1 yielded the monoacetylated derivative 2-(4',8'-dimethylnona-3'E,7'-dienyl)-8-acetyl-2,6-dimethyl-2H-chromene (6). Compounds 1–6 exhibited various levels of cytotoxic, antibacterial, and anti-inflammatory activities. Compound 2 was found to display potent in vitro anti-inflammatory activity by inhibiting the generation of superoxide anion (IC₅₀ 0.22 ± 0.03 μg/mL) and elastase release (IC₅₀ 0.48 ± 0.11 μg/mL) in FMLP/CB-induced human neutrophils.