Eight New Kalihinol Diterpene Derivatives Isolated from the Sponge Acanthella cavernosa Collected in the South China Sea

Eight previously undescribed kalihinol diterpenoids (1–8) were obtained from the South China Sea marine sponge Acanthella cavernosa. Among them, compound 8 represents the first brominated kalihinol diterpene reported to date, while compounds 2 and 3 belong to rare 5-chlorinated kalihinol analogues. Their planar architectures and absolute stereochemistries were unambiguously established through comprehensive spectroscopic characterization including 1D/2D NMR and HRESIMS, combined with single-crystal X-ray diffraction and electronic circular dichroism (CD) analysis. Cytotoxicity assays revealed that compounds 1 and 8 exerted potent inhibitory effects on K562 cells, with IC50 values of 3.0 μM and 1.4 μM, respectively.