Preparative reversed-phase HPLC was performed at 40 °C on a YMC-Pack ODS-A A-324 column
(10 i.d. × 300 mm) using 0.01 M H3PO4/0.01 M KH2PO4/MeOH [either 43:43:16 (solvent I), 40:40:20 (solvent II), 41:41:18 (solventIII), 41.5:41.5:17 (solvent IV), or 37.5:37.5:25 (solvent V), v/v], at a flow rate of 2 mL/min with detection at 280 nm UV