Xishacorenes A-C, Diterpenes with Bicyclo[3.3.1]nonane Nucleus from the Xisha Soft Coral Sinularia polydactyla.

Three new diterpenes, xishacorenes A-C, featuring an undescribed bicyclo[3.3.1]nonane nucleus bearing 1-vinyl and 13-[(E)-4-methylpenta-1,3-dien-1-yl] alkyl chains, and a related monocyclic known compound, were isolated from the Xisha soft coral Sinularia polydactyla. The structures of xishacorenes A-C, including their absolute configurations, were elucidated by extensive spectroscopic analysis and TDDFT ECD calculations. The new compounds exhibit an interesting dose-dependent promotion effect on the ConA-induced T lymphocyte proliferation. A plausible biosynthetic pathway of xishacorenes A-C is proposed.