Enantioselective determination of pazinaclone, a new isoindoline anxiolytic, and its active metabolite in rat plasma by high-performance liquid chromatography.

A sensitive and specific high-performance liquid chromatographic method has been developed for the simultaneous determination of the enantiomers of pazinaclone (DN-2327), a new anxiolytic agent, and those of its active metabolite, M-II, in rat plasma. Organic solvent extraction of pazinaclone, M-II, and internal standard (I.S.) in plasma was followed by separation of the analytes from other metabolites using an achiral reversed-phase column. Fluorescence detection was employed with excitation and emission wavelengths of 328 and 367 nm, respectively. Separation of all the enantiomers and I.S. was then accomplished with normal- and chiral-phase columns connected in series. For each analyte, the lower quantitation limit was 0.5 ng/ml. The assay has been applied to a chiral inversion study in rats. Chiral conversion from one enantiomer of pazinaclone to the other hardly occurred. This method is suitable for enantioselective pharmacokinetic and toxicokinetic studies in animals.