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The separation of minor compounds, especially those with similar polarities from a complex sample, remains challenging. In the proposed study, an effective method based on medium-pressure liquid chromatography and recycling high-speed counter-current chromatography was developed for the enrichment and separation of three minor components from <i>Dracocephalum tanguticum</i>. The crude extract was directly introduced to medium-pressure liquid chromatography for the enrichment of the three minor components. Based on high-performance liquid chromatography analysis, the total content of these three compounds increased from 0.48% in the crude extract to 85.3% in the medium-pressure liquid chromatography fraction. In addition, high-speed counter-current chromatography was employed to separate the enriched compounds using the solvent system hexane/ethyl acetate/methanol/water (1.18:8.82:1.18:8.82, v/v/v/v). As a result, compound <b>3</b> and a mixture of compounds <b>1</b> and <b>2</b> were obtained. In order to improve the resolution of compounds <b>1</b> and <b>2</b> while saving separation time, a recycling and heart-cut mode was used. Finally, compounds <b>1</b> and <b>2</b> were obtained after five cycles. These compounds were identified as 3-phenylethyl β-d-glucopyranoside (<b>1</b>), tazettoside E (<b>2</b>), and cirsiliol-4′-glucoside (<b>3</b>). Compounds <b>1</b> and <b>2</b> were primarily separated from <i>D. tanguticum</i>. Moreover, the developed method provided a reference for the separation of minor components from the complex sample.
Six compounds including two n-butyrophenone isomers and two stibene isomers were obtained from Rheum tanguticum Maxim. Two n-butyrophenone isomers with a separation factor of 1.14 were successfully separated by recycling high-speed counter-current chromatography after ten cycles. Two stibene isomers were successfully separated by preparative high-performance liquid chromatography. High-performance liquid chromatography analysis showed that the purities of the compounds were all over 98%. These compounds were identified as lindleyin, isolindleyin, resveratrol-4'-O-(2″-O-galloyl)-glucopyranoside, resveratrol-4'-O-(6''-O-galloyl)-glucopyranoside, emodin 1-O-β-d-glucoside, and 3,5-dihydroxy-4'-methoxystilbene-3-O-β-d-glucopyranoside. The results indicated that recycling high-speed counter-current chromatography and preparative high-performance liquid chromatography could be effective combination for the preparation of bioactive compounds from Rheum tanguticum Maxim.
This study presents an efficient strategy for separation of three phenolic compounds with high molecular weight from the crude extract of Terminalia chebula Retz. by ultrasound-assisted extraction and high-speed counter-current chromatography. The ultrasound-assisted extraction conditions were optimized by response surface methodology and the results showed the target compounds could be well enriched under the optimized extraction conditions. Then the crude extract was directly separated by high-speed counter-current chromatography without any pretreatment using n-hexane/ethyl acetate/methanol/water (1:7:0.5:3, v/v/v/v) as the solvent system. In 180 min, 13 mg of A, 18 mg of B, and 9 mg of C were obtained from 200 mg of crude sample. Their structures were identified as Chebulagic acid (A, 954 Da), Chebulinic acid (B, 956 Da), and Ellagic acid (C) by (1) H NMR spectroscopy.