On-line two-dimensional countercurrent chromatography × high performance liquid chromatography system with a novel fragmentary dilution and turbulent mixing interface for preparation of coumarins from Cnidium monnieri

Abstract

This study describes a novel on-line two-dimensional countercurrent chromatography×high performance liquid chromatography (2D CCC×HPLC) system for one-step preparative isolation of coumarins from the fruits of Cnidium monnieri. An optimal biphasic solvent system composed of n-heptane/acetone/water (31:50:19, v/v) with suitable Kd values and a higher retention of the stationary phase was chosen to separate target compounds. In order to address the solvent incompatibility problem between CCC and RP-HPLC, a novel fragmentary dilution and turbulent mixing (FD-TM) interface was successfully developed. In detail, the eluent from the first dimensional CCC column was divided into fractions to form ‘sample-dilution’ stripes in the two switching sample loops, by the dilution water from the makeup pump. Following this, a long, thin tube was applied to mix the CCC eluent with water by in-tube turbulence, to reduce the solvent effect. Each CCC fraction was alternately trapped on the two holding columns for further preparative HPLC separation. This nationally designed FD-TM strategy effectively reduced post-column pressure and allowed a higher water dilution ratio at the post end of CCC, leading to improved sample recovery and a robust 2D CCC×HPLC isolation system. As a result, in a single 2D separation run (6.5h), eight target compounds (1–8) were isolated from 0.5g crude extract of C. monnieri, in overall yields of 1.3, 2.0, 0.5, 0.5, 0.8, 1.5, 8.2, and 15.0%, with HPLC purity of 90.1, 91.1, 94.7, 99.1, 99.2, 98.2, 97.9, and 91.9%, respectively. We anticipate that this improved 2D CCC×HPLC system, based on the novel FD-TM interface, has broad application for simultaneous isolation and purification of multiple components from other complex plant-derived natural products.