Medicinal Plants Classification Biosynthesis and ... - Index of

Biosyntheses and Bioactivities of Flavonoids in the Medicinal...
flavonoids were separated in two runs. In addition, the HPLC method has been used for
quality control of medical products based on S. baicalensis Georgi by the determination of
baicalin content in Pharmacopoeia of the People's Republic of China [Ministry of Health,
1995].
High-speed counter-current chromatography (HSCCC) is a relatively new, all-liquid
separation technique. Because there is no solid support matrix in HSCCC column, it
eliminates irreversible adsorptive loss, denaturation and contamination of samples from the
solid support matrix used in the conventional chromatographic column. The method has been
successfully applied to the analysis and separation of various natural products [Li & Chen,
2008]. Baicalin could be separated and purified from S. baicalensis Georgi by HSCCC [Lu,
Jiang & Chen, 2003]. The separation was performed in two steps with a two-phase solvent
system composed of n-butanol-water (1: 1), in which the lower phase was used as the mobile
phase at a flow-rate of 1.0 ml/min in the head-to-tail elution mode. A total of 37.0 mg of
baicalin at 96.5% purity was yielded from 200 mg of the crude baicalin (containing 21.6%
baicalin) with 86.0% recovery. The HSCCC chromatogram is shown in Figure 2. In order to
isolate baicalein, wogonin and oroxylin A from the same herb, a HSCCC method with a twophase
solvent system composed of n-hexane–ethyl acetate–n-butanol–water (1:1:8:10, v/v)
was developed by increasing the flow-rate of the mobile phase stepwise from 1.0 to
2.0 ml/min after 4 h (Figure 3). The method yielded 144.8 mg of baicalein in 95.7% purity,
50.2 mg of wogonin in 98.5% purity, and 12.4 mg of oroxylin A in 93.2% purity from
500 mg of the crude extract in a one-step separation. The recoveries of baicalein, wogonin
and oroxylin A were 92.7%, 91.6% and 92.5%, respectively [Li & Chen, 2005]. In the future,
bioactive components at highly purity will be used instead of crude extracts in the medicinal
preparations of S. baicalensis. Therefore, separation and purification techniques will play an
important role in these studies, and high-speed counter-current chromatography will be more
widely used for the preparative separation and purification of S. baicalensis active
components on a large scale.
Although gas chromatography was not widely employed for the determination of
flavonoids in S. baicalensis because of their high polarity, low volatility and poor thermal
stability, thin layer chromatography, capillary electrophoresis and micellar electrokinetic
capillary chromatography have been used for the determination of S. baicalensis active
components in various matrices. In the future, high-performance liquid chromatography-mass
spectrometry will play a more important role in the studies of bioactive components of S.
baicalensis. The main advantages of HPLC–MS are its high speed and sensitivity compared
with other hyphenated identification techniques such as HPLC–nuclear magnetic resonance
and HPLC–infrared. In most situations, HPLC–MS/MS or HPLC–(MS) n is preferred over
HPLC–MS for the structure elucidation of unknown mixtures, because multistage MS can
provide additional information on fragmented ions, facilitating structural assignments [Li,
Jiang & Chen, 2004].
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