Separation methods of quinonoid constituents of plants used in Oriental traditional medicines.

Analysis of molecular constituents of traditional Oriental medicines has acquired a fresh perspective in view of a surge in interest in the consumption of herbal prescriptions all over the world. Several of them contain quinonoid compounds, and the long-standing therapeutic applications of these herbs have been vindicated, to some extent, through recent studies on the significant pharmacological properties of these compounds. In fact, the bioactive quinonoids and their analogues often serve as the 'marker' constituents of the respective plants of major commercial importance. Hence, shikonin, plumbagin, diospyrin, emodin analogues, sennosides, hypericin, tanshinone and related compounds have been discussed in this review which focuses on their extraction, separation and analysis from plant sources, cell cultures and biological fluids. As for the analysis of quinonoids, high-performance liquid chromatography connected with various detectors (ultraviolet, photodiode array, fluorescence, mass, nuclear magnetic resonance) has been the most useful technology succeeding the conventional methods such as thin layer and column chromatography. In some cases, high-performance thin layer chromatography and capillary electrophoresis are also used for this purpose.