Di- and Triterpenoids from the Leaves of Casearia balansae and Neurite Outgrowth Promoting Effects of PC12 Cells

A bioassay-guided phytochemical investigation of the leaves of Casearia balansae led to the isolation of six new cucurbitane-type triterpenoid derivatives (balanterpenes A–F, 1–6) and four new clerdoane-type diterpenoids (balanterpenes G–J, 7–10). The structures of 1–10 were established on the basis of extensive analysis of NMR spectroscopic data, X-ray crystallography, and experimental and calculated electronic circular dichroism spectra. Compound 1 features a ring-expanded triterpenoid skeleton with the C-19 methyl involved in the ring formation, compound 6 possesses a rare hexanortriterpenoid scaffold, and compounds 7–10 may be four new diterpenoid artifacts presumably formed during the extraction and purification processes. Compounds 3 and 7–10 showed promoting effects on neurite outgrowth of PC12 cells with EC50 values in the range 2.9–10.0 μM.