Stereoselective protein binding studies of 2-(2-hydroxypropanamido) benzoic acid enantiomers in rat, beagle dog and human plasma

As the stereoselective plasma protein binding is an important factor for the differences in pharmacokinetic or pharmacodynamic properties of chiral drugs, we elucidated the binding of (R)-/(S)-HPABA to plasma protein. A UHPLC–MS/MS method was developed and validated to the quantitation and equilibrium dialysis method was applied to the separation of bound and unbound drugs. Protein binding reached equilibrium within 12 h of incubation at 37 °C. Liquid-liquid extraction with ethyl acetate was used for sample preparation. The separation was achieved through a Thermo Syncronis C18 column (50 mm × 2.1 mm, 1.7 μm; Thermo, USA) using gradient elution at a flow rate of 0.4 ml/min. All of the recovery and matrix effect of the method met the requirements of analytical method validation. The plasma protein binding of (R)-/(S)-HPABA show significant species dependence in enantioselectivity. In addition, the results of molecular docking showed that the combining capacity of (R)-HPABA with HSA was higher than that of (S)-HPABA.