Chiral bioanalysis of torcetrapib enantiomers in hamster plasma by normal-phase liquid chromatography and detection by atmospheric pressure chemical ionization tandem mass spectrometry

A highly sensitive and enantioselective assay has been developed and validated for the estimation of torcetrapib (TTB) enantiomers [(+)-TTB and (-)-TTB] in hamster plasma with chiral liquid chromatography coupled to tandem mass spectrometry with an atmospheric pressure chemical ionization interface in the negative-ion mode. The assay procedure involves liquid-liquid extraction of TTB enantiomers and IS (DRL-16126) from 100 μL hamster plasma with acetonitrile. TTB enantiomers were separated using n-hexane:propanol (80:20, v/v) at a flow rate of 0.7 mL/min on a Chiralpak AD column. The MS/MS ion transitions monitored were 599.2 → 340.2 for TTB and 623.2 → 298.1 for IS. Absolute recovery was found to be between 64 and 68% for TTB enantiomers and >100% for IS. The standard curves for TTB enantiomers were linear (r² > 0.995) in the concentration range 5-2500 ng/mL for each enantiomer with an LLOQ of 5 ng/mL for each enantiomer. The inter- and intra-day precisions were in the range of 10.5-12.4 and 9.15-11.5% and 3.75-12.9 and 5.16-12.5% for (+)-TTB and (-)-TTB, respectively. Accuracy in the measurement of quality control (QC) samples was in the range 91.3-105 and 88.6-111% for (+)-TTB and (-)-TTB, respectively. This novel method has been applied to the study of stereoselective oral pharmacokinetics of (-)-TTB.