Conformational Dynamics and Osteoclastogenesis Inhibition by Cladiellin-Type Diterpenes from the Marine Gastropod Ovula ovum

A cladiellin-type diterpene, 3-O-deacetylcladiellin (1), was isolated from the marine gastropod Ovula ovum, together with a known analogue 2. The NMR spectra of 1 and 2 exhibited unusually broad resonances. The structure and absolute configuration of 1 were unambiguously established by X-ray crystallographic analysis and electronic circular dichroism spectroscopy. DFT-based conformational analysis combined with variable-temperature NMR revealed that the NMR coalescence arises from conformational exchange of the flexible nine-membered ring. Chemical evidence suggests that 1 is likely derived from an unidentified soft coral prey of O. ovum. Compound 1 inhibits RANKL-induced osteoclast differentiation in RAW264 cells.