Ionic Liquid-Based Ultrasonic-Assisted Extraction of Forsythosides from the Leaf ofForsythia suspensa(Thunb.) Vahl and Subsequent Separation and Purification by High-Speed Counter-Current Chromatography

An ionic liquid-based ultrasonic-assisted extraction (ILUAE) method was developed for the extraction of the two forsythosides, namely forsythosides I and A from the leaf of Forsythia suspensa (Thunb.) Vahl. Three kinds of l-alkyl-3-methylimidazolium ionic liquids with different alkyl chain and anion were investigated. The results indicated that ionic liquids showed remarkable effects on the extraction yields of forsythosides. In addition, several ILUAE ultrasonic parameters, such as the solvent concentration, solvent to solid ratio and extraction time have been optimized. Under these optimal conditions (e.g., with 0.6 M [C6MIM]Br, solvent to solid ratio of 15 mL/g and extraction time of 10 min), this approach gained the highest extraction yields of forsythoside I (0.89%) and forsythoside A (10.74%). Meanwhile, forsythosides in the ILUAE extract were separated and purified successfully through the high-speed counter-current chromatography with a two-phase solvent system consisting of ethyl acetate-ethanol-acetic acid-water (4 : 1 : 0.25 : 6, v/v). 5.4 mg of forsythoside I and 59.7 mg of forsythoside A were obtained from 120 mg of the prepurified sample in one-step separation, with the purity of 96.1 and 97.9%, respectively, as determined by high-performance liquid chromatography. Their structures were identified by (1)H nuclear magnetic resonance (NMR) and (13)C NMR.