Abstract
Like chemical drugs, research and development of herbal medicine also have a need to resolve enantiomers. To help illustrating the antiviral bioactivity of Isatidis Radix, a widely used traditional Chinese medicine (TCM), supercritical fluid chromatography (SFC) was used for analytical and preparative separation of (R,S)-goitrin, which was reported as the active ingredient of the herbal. Improved resolution was achieved on Chiralpak IC column, using acetonitrile as the organic modifier, representing a tenfold increase in speed, compared to the previous normal phase HPLC (NPLC) method. The newly developed chromatographic method was validated in terms of linearity, precision, limit of detection (LOD), and limit of quantitation (LOQ). Scale-up purification of (R)-goitrin and (S)-goitrin was performed on a preparative column with >90% total recovery. The absolute stereochemical assignment of the purified isomers was determined through optical rotation study. This attempt explored SFC's application in chiral research of traditional Chinese medicine.
Highlights
As a fundamental characteristic of chemical substances, the phenomenon of chirality exists in natural products
Initial chiral screening was automated on supercritical fluid chromatography (SFC) using 5 different polysaccharide Chiral Stationary Phases (CSPs) (Chiralpak ADH, Chiralpak ASH, Chiralcel ODH, Chiralpak IA, and Chiralpak IC) cross-matched with 5 different organic modifiers (MeOH, EtOH, ACN, IPA, and 50 : 50 MeOH/EtOH solvent)
Though clear separation of R-goitrin and S-goitrin could be observed either on Chiralcel ODH coupled with MeOH or on Chiralpak IC coupled with ACN, the greatest potential for preparative purification was demonstrated on the latter combination
Summary
As a fundamental characteristic of chemical substances, the phenomenon of chirality exists in natural products. While one isomer possesses a therapeutic effect, its enantiomer may be inactive and antagonistic or even has reverse effect With this perspective in mind, it is imperative to investigate pharmacology and toxicology of (R)-goitrin and (S)-goitrin, respectively, which means large amount of resolved enantiomers need to be prepared for tests in vivo and in vitro. Major part of the solvent used in the mobile phase of SFC is supercritical CO2, low viscosity and high diffusivity of which allow higher flow rate than HPLC. This is beneficial when removing solvents after preparative resolution. SFC was adopted to develop a more efficient method for separation of (R,S)-goitrin, broadening its application in chiral investigation of TCM. The preparative method was used in purification of (R)-goitrin and (S)-goitrin
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