Terpenoids with neurite outgrowth-promoting activity from the branches and leaves of Illicium merrillianum

Eighteen terpenoids (1–18) were isolated from Illicium merrillianum. Compound 1 was identified as new compound, and its structure was established by comprehensive spectroscopic analysis and single-crystal X-ray diffraction. All compounds were evaluated for nerve growth factor (NGF)-mediated neurite outgrowth activity using rat pheochromocytoma (PC12) cells as a model system of neuronal differentiation. Compounds 1, 3, 18 showed significant neurite outgrowth-promoting activity in the presence of 20 ng/ml NGF in a dose-dependent manner at concentrations of 1–100 μM after 24-h treatment. Subtle difference of functional groups at C-2 position in hopane-type triterpene resulted in enormous bioactivity difference, compound 1 was neurotrophic but 2 was cytotoxic.