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.