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

A bioassay-guided phytochemical investigation of the leaves of <i>Casearia balansae</i> led to the isolation of six new cucurbitane-type triterpenoid derivatives (balanterpenes A–F, <b>1</b>–<b>6</b>) and four new clerdoane-type diterpenoids (balanterpenes G–J, <b>7</b>–<b>10</b>). The structures of <b>1</b>–<b>10</b> were established on the basis of extensive analysis of NMR spectroscopic data, X-ray crystallography, and experimental and calculated electronic circular dichroism spectra. Compound <b>1</b> features a ring-expanded triterpenoid skeleton with the C-19 methyl involved in the ring formation, compound <b>6</b> possesses a rare hexanortriterpenoid scaffold, and compounds <b>7</b>–<b>10</b> may be four new diterpenoid artifacts presumably formed during the extraction and purification processes. Compounds <b>3</b> and <b>7</b>–<b>10</b> showed promoting effects on neurite outgrowth of PC12 cells with EC<sub>50</sub> values in the range 2.9–10.0 μM.