Isolation and purification of nootkatone from the essential oil of fruits of Alpinia oxyphylla Miquel by high-speed counter-current chromatography

HSCCC technique in a semi-preparative scale was successfully applied in isolation and purification of nootkatone from the essential oil of fruits of Alpinia oxyphylla Miquel. Twelve kinds of two-phase solvent systems, consisting of seven non-aqueous and five organic-aqueous solvent systems, were selected with not only suitable partition coefficients of nootkatone but also suitable separation factors between nootkatone and valencene, the dominant impurity in the essential oil. Further on HSCCC, n-hexane–chloroform–acetonitrile (10:1:10, v/v) amongst the non-aqueous solvent systems and n-hexane–methanol–water (5:4:1, v/v) amongst the organic-aqueous solvent systems were separately screened out. However, n-hexane–methanol–water (5:4:1, v/v) was thought optimal due to quite shorter elution time and better HSCCC peak form. By eluting the lower phase of this solvent system in head–tail mode, 3.1 mg of nootkatone was obtained at a purity of 92.30% by GC–MS from 80 mg of crude essential oil in one step operation in less than 4 h. The chemical structure of nootkatone fraction was confirmed by EI-MS and 1H NMR.