Stereoselective determination of (beta S,gamma R and beta R,gamma S)-4-[3-(4-acetyl-3-hydroxy-2-propylphenoxy) propylthio]-gamma-hydroxy-beta-methylbenzenebutanoic acid in human and rat plasma by normal-phase high-performance liquid chromatography.

A stereoselective high-performance liquid chromatographic method was developed for the determination of the enantiomeric composition comprising (beta S,gamma R and beta R,gamma S)-4-[3-(4-acetyl-3-hydroxy-2-propylphenoxy) propylthio]-gamma-hydroxy-beta-methylbenzenebutanoic acid in human and rat plasma. Both enantiomers, (beta S,gamma R)- and (beta R,gamma S)-1, were isolated from the plasma by liquid-liquid extraction, the organic phase was evaporated to dryness, and the residue was lactonized with p-toluenesulfonic acid followed by derivatization with R(+)-alpha-methylbenzylamine to form diastereomeric Schiff base adducts. Separation was performed on a silica column (Supelcosil) with a mobile phase composed of 97.8% hexane, 2% isopropyl alcohol, and 0.2% triethylamine. The column eluant was monitored with a variable wavelength UV detector set at 280 nm (0.005 AUFS). Based on the peak area ratios, the method shows excellent linear relationships with their corresponding concentrations and satisfactory intraday and interday assay precision and accuracy. The detection limit of this method is 25 ng/mL in plasma for each enantiomer. The method has been applied to the assay of plasma obtained from human subjects administered 1 in safety and tolerability studies and from rats administered 1 intravenously or per os.