Chiral liquid chromatography resolution and stereoselective pharmacokinetic study of the enantiomers of a novel anticonvulsant, N-(4-chlorophenyl)-1-(4-pyridyl)ethylamine, in rats

A selective chiral high performance liquid chromatographic (HPLC) method was developed and validated to separate and quantify the enantiomers of a novel anticonvulsant agent, N-(4-chlorophenyl)-1-(4-pyridyl)ethylamine (AAP-Cl), in rat plasma. After extraction of the plasma samples with ethyl acetate, the separation was accomplished by an HPLC system consisting of a Chirex chiral column (250 mm×4.6 mm i.d.) and a mobile phase of hexane:ethanol:tetrahydrofuran (280:20:40 (v/v)) containing trifluroacetic acid (0.3% (v/v)) and triethylamine (0.018% (v/v)) at a flow rate of 0.8 ml/min with UV detection. Male Sprague-Dawley rats were given (+)-AAP-Cl (10 and 20 mg/kg), (−)-AAP-Cl (10 mg/kg) or the racemic mixture (20 mg/kg) by i.v. bolus injection and serial blood samples were collected at different times after drug administration. (+)-AAP-Cl and (−)-AAP-Cl were separated with a resolution factor, Rs, of at least 1.4, and a separation factor, α, greater than 1.09. Linear calibration curves were obtained over the concentration range of 0.5–30 μg/ml in plasma for both (+)-AAP-Cl and (−)-AAP-Cl (R2≥0.996) with a limit of quantitation of 100 ng/ml and the recovery was greater than 80% for both enantiomers. The accuracy and precision for both enantiomers ranged from 96 to 102% (±0.2–7%) at upper and lower concentrations. The plasma concentration–time profiles of the enantiomers of AAP-Cl were best described by a two-compartment open model with a mean terminal half-life of about 5 h, volume of distribution at steady state of 3 l/kg and clearance of about 0.6 l/(h kg) in rats. There was no significant difference between the pharmacokinetic parameters of (+)-AAP-Cl and (−)-AAP-Cl, suggesting that the disposition of AAP-Cl in rats is not enantioselective. In addition, no chiral inversion of (+)-AAP-Cl to (−)-AAP-Cl or vice versa was observed. The results of this investigation have shed some light on the mechanism of action and disposition of AAP-Cl in rats.