EFFICIENT COUNTER-CURRENT CHROMATOGRAPHIC ISOLATION AND STRUCTURAL IDENTIFICATION OF PHENOLIC COMPOUNDS FROM SWEET POTATO LEAVES

Abstract

High-speed counter-current chromatography was successfully applied to separate and purify bioactive ingredients from sweet potato leaves. Four caffeoylquinic acid derivatives and a mixture of two flavonoids were successfully obtained in one step. The caffeoylquinic acid derivatives were 3-O-caffeoylquinic acid (1), 4,5-di-O-caffeoylquinic acid (4), 3,5-di-O-caffeoylquinic acid (5), and 3,4-di-O-caffeoylquinic acid (6). The two-phase solvent system was composed of n-hexane\\ethyl acetate\\ethanol\\water\\acetic acid (1:5:2:4:0.1, v/v). The upper layer was used as the stationary phase, and the lower layer was used as the mobile phase. The flow rate was 1.5 mL/min, the revolution speed was 850 rpm, and the injection volume was 280 mg. The mixture of flavonoids was separated by preparative high-performance liquid chromatography into quercetin-3-O-β-D-galactopyranoside (2) and quercetin-3-O-β-D-glucoside (3). The purities of compounds 1–6 were 95.8% (5.4 mg), 99.5% (6.1 mg), 98.7% (15.1 mg), 97.8% (14.5 mg), 96.2% (10.3 mg), and 96.8% (7.8 mg), respectively, as determined by HPLC with a pulsed amperometric detector. The chemical structures were identified by electrospray ionization-tandem mass spectrometry and nuclear magnetic resonance imaging. The results showed the efficiency of the method in purifying bioactive compounds from sweet potato leaves, and compound 2 was separated from sweet potato for the first time.