This paper concentrates on the enantioseparation of racemic 2-(substituted phenyl)propanoic acids by high-speed countercurrent chromatography with substituted β-cyclodextrin as the chiral selector, and an investigation of the influence of the substituent on the benzene ring in enantiorecognition between the chiral selector and enantiomer of each racemate is presented. This is an extension research of our previous work on the enantioseparation of 2-phenyl propanoic acid derivatives, to investigate the relationship between the value of enantioseparation factor and the different substituent on the benzene ring. In total, ten racemic 2-(substituted phenyl)propanoic acids were investigated, of which four including 2-(4-nitrophenyl)propanoic acid, 2-(4-methylphenyl)propanoic acid, 2-(4-hydroxyphenyl)propanoic acid, and 2-(4-chlorophenyl)propanoic acid, were studied by countercurrent chromatography for the first time, and two racemates were successfully enantioseparated. The distribution ratio and enantioseparation factor for all the ten racemates were determined by enantioselective liquid-liquid extraction. The results showed that an electron-donating group on the benzene ring presents a higher enantiorecognition induced by chiral selector than that of racemates with an electron-withdrawing group on the benzene ring.
In this work, the antitumor constituent β-elemene was selectively separated from the volatile oil of the Curcumae Rhizoma by countercurrent chromatography with silver nitrate as selective reagent based on the formation of coordination complexes. A biphasic solvent system composed of n-hexane/methanol/water (2:1.5:0.5, v/v/v) was selected, in which 0.15 mol/L of silver nitrate was added to the aqueous phase. The aqueous phase was used as the stationary phase for separation of β-elemene by countercurrent chromatography after it was partially purified from the volatile oil by silica gel column chromatography. An enriched β-elemene fraction was obtained by silica gel column chromatography to improve the percentage of β-elemene from 16.5 to 46.1%. Subsequently, β-elemene was further purified from 445 mg of the partially purified sample of volatile oil by countercurrent chromatography with silver nitrate as a selective reagent, yielding 145 mg of β-elemene with greater than 99% purity, as determined by gas chromatography mass spectrometry. The recovery of β-elemene from the crude volatile oil through two steps was around 63.6%.
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