Suppression of RANKL-Induced Osteoclastogenesis by the Metabolites from the Marine Fungus Aspergillus flocculosus Isolated from a Sponge Stylissa sp.

A new α-pyrone merosesquiterpenoid possessing an angular tetracyclic carbon skeleton, ochraceopone F (), and four known secondary metabolites, aspertetranone D (), cycloechinulin (), wasabidienone E (), and mactanamide (), were isolated from the marine fungus derived from a sponge sp. collected in Vietnam. The structures of Compounds - were elucidated by analysis of 1D and 2D NMR spectra and MS data. All the isolated compounds were evaluated for anti-proliferation activity and their suppression effects on receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation using tartate-resisant acid phosphatase (TRAP). Compounds - had no anti-proliferative effect on human cancer cell lines up to 30 μg/mL. Among these compounds, aspertetranone D () and wasabidienone E () exhibited weak osteoclast differentiation inhibitory activity at 10 μg/mL. However, mactanamide () showed a potent suppression effect of osteoclast differentiation without any evidence of cytotoxicity.