The separation of compounds with similar polarities is challenging. In the present study, five flavone glycosides, including two groups with similar polarities, were obtained from Dracocephalum tanguticum by three high-speed counter-current chromatography modes, including flow rate conversion mode, recycling mode, and heart-cut mode. With flow rate conversion mode, compounds 3 and 4 with similar polarities and compound 5 were separated by highspeed counter-current chromatography with ethyl acetate/methanol/water (5.0% acetic acid) (8:2:10, v/v) system. The flow rate was controlled as: 1.8 mL/min for 0-160 min, 2.2 mL/min for 160-200 min, and 2.5 mL/min for 200-400 min. However, compounds 1 and 2 with similar polarities were not separated due to the similar distributive properties. Then, a recycling and heart-cut mode were introduced to improve the separation efficiency. The heart-cut mode was introduced in the second and third cycles, and compounds 1 and 2 were well separated in the fourth cycle. Consequently, five flavone glycosides, including two groups with similar polarities were obtained and identified as cosmosiin (1), pedaliin (2), quercetin-3-O-rutinoside (3), pedaliin-6''-acetate (4), and sorbifolin-6-O-β-glucopyranoside (5). The current strategy provides a reference for separating compounds with similar polarities from a crude sample.

Five flavonoids with similar polarity were obtained from Caragana korshinskii Kom. by preparative high speed counter-current chromatography. Due to their similar polarity, it is difficult to select a suitable solvent system for one-step separation. Three fractions including one pure compound were only obtained with a relatively suitable solvent system of ethyl acetate: n-butanol:water (0.5% glacial acetic acid) (4:6:10, v:v:v). In order to improve the separation efficiency, recycling and heart cut modes were introduced. As a result, two flavonoids with separation factor value at 1.13 and the other two with separation factor value at 1.20 were successfully separated. Finally, five flavonoids with purity higher than 98% were obtained. Fortunately, a new compound named myricetin 3′-methyl ether 3-Oglucoside-7-O-rhamnoside was obtained. The results indicated that the recycling combined with heart-cut mode could be effective for the preparation of natural compounds with similar polarity.

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