Separation of Farrerol Enantiomers and Its Content Determination in Chinese Materia Medica

OBJECTIVE  To establish an HPLC method for the separation of enantiomers of farrerol, and apply it to the determination of the content of enantiomers in Rhododendri Daurici Folium and Rhododendron Micranthum.

METHODS  HPLC was used to separate the farrerol enantiomers, and the chromatographic conditions of chiral column type, mobile phase ratio, flow rate, and column temperature were optimized. The thermodynamic separation of farrerol enantiomers was discussed. Thermodynamic parameters such as enthalpy change, entropy change, enthalpy change and entropy change were calculated. And the contents of two enantiomers in Rhododendri Daurici Folium and Rhododendron Micranthum were determined under the optimum resolution conditions.

RESULTS  The optimum separation conditions for two enantiomers of farrerol were determined as follows: Chiralcel OJ-RH(4.6 mm×150 mm, 5 μm), equilibrium elution of acetonitrile-water(40∶60), the flow rate of 0.5 mL·min^–1, the column temperature of 25 ℃, and the detection wavelength of 295 nm. Under the optimum separation conditions, the resolution of farrerol enantiomers reached 1.5, indicating that the two enantiomers of the farrerol could be completely separated. When the column temperature was between 20 ℃ and 35 ℃, the separation factor decreased with the increase of temperature. The lnα of the two enantiomers of farrerol showed a good linear relationship with 1/T, and the chiral reselution process was controlled by enthalpy. The enantiomer separation method of farrerol was applied to the determination of farrerol enantiomer in Chinese medicinal materials of Rhododendri Daurici Folium and Rhododendron Micranthum. The linear relationship between the two enantiomers of farrerol were good in the range of 0.718–57.44 μg·mL^–1 and 1.28–102.24 μg·mL^–1, respectively. And the contents of the two enantiomers of farrerol in Rhododendri Daurici Folium were 0.228 2 and 0.466 2 mg·g^–1, respectively. And the contents of the two enantiomers of farrerol in Rhododendron Micranthum were 0.416 8 and 0.707 3 mg·g^–1, respectively.

CONCLUSION  This method is simple, efficient and suitable for the determination of farrerol enantiomers in traditional Chinese medicine.