The air-dried leaves of A. scholaris (2.5 kg) were powdered and
extracted with MeOH (6 L × 3, 24 h each) under reflux conditions,
and the solvent was evaporated in vacuum. The residue dissolved in
0.37% HCl, and the solution was subsequently basified using 10% ammonia
to pH 9–10. The basic solution was partitioned with EtOAc, affording
a two-phase mixture including the aqueous phase and the EtOAc/organic
phase. The organic fraction (23 g) was collected and then dissolved in
MeOH, and the resulting solution was subjected to column chromatography
over silica gel eluting with CHCl3/MeOH (from 1:0–0:1) to afford five
fractions (Fr. A–D). Fr. A (7.2 g) was subjected to RP-18 column chromatography
(MeOH/H2O 35:1, 50:1, 70:1, 90:1, 0:1) and silica gel column
chromatography (CHCl3/MeOH 95:5–10:1) to yield compounds 4