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

Stereoselectivity of evodiamine enantiomers in neuroprotective activity, pharmacokinetics and the ability across the blood-brain barrier

Evodiamine, a chiral quinazoline alkaloid in the traditional Chinese medicine Evodiae fructus, exhibited efficacy for CNS diseases. In this study, the pure enantiomers of evodiamine were prepared in large quantities via chemical resolution. Their structures were elucidated by MS, NMR and ECD. The optical purity was determined to be as high as 99.8 %. The differences of the enantiomers in protective effect against neuronal cell injury were evaluated using MTT assay. Notably, R-(-)-evodiamine showed better neuroprotection effects against H2O2-induced damage in PC12 cells. An efficient HPLC-MS/MS method for determination of evodiamine enantiomers in rat plasma and brain was developed and verified. Satisfactory enantioseparation of evodiamine was achieved on a Chiralcel OD-RH column with the mobile phase of acetonitrile-water (70:30, v/v) at a flow rate of 0.6 mL/min. The analytes were measured under multiple reactions monitoring (MRM) mode with m/z 304.3→134.3 for evodiamine and m/z 289.3→97.1 for testosterone (IS) using electrospray ionization source (ESI) in the positive ion mode. The method was validated and fulfilled the requirements of bioanalysis. It was successfully applied to study the stereoselectivity of evodiamine in pharmacokinetics and the ability across the blood-brain barrier in rats. After oral and intravenous administration of racemic evodiamine to rat, the area under the concentration-time curve of R-evodiamine was noticeably 1.70 and 1.33 times higher than those of S-evodiamine, respectively. Furthermore, while there was no significant difference in the B/P values, the concentration of R-(-)-evodiamine in the brain was approximately 1.31 times greater than that of S-(+)-evodiamine. The results indicated that evodiamine enantiomers exhibited significant stereoselectivity in pharmacokinetics after oral administration and intravenous administration. While the two enantiomers showed no significant stereoselectivity in the ability across the blood-brain barrier. These findings provided new insights into the development of a single enantiomer of evodiamine as a potential drug candidate for the treatment of CNS diseases.

Enantioselective analysis of pheniramine in rat using large volume sample stacking or cation-selective exhaustive injection and sweeping coupled with cyclodextrin modified electrokinetic chromatography

For the aim of simultaneously performing the enantioseparation and determination of the trace enantiomers in plasma samples, enantioseparation by HPLC using five kinds of chiral stationary phases were initially investigated. But unfortunately, enantioseparation could not be detected in reversed mobile phase mode with all the five columns. For this reason, two simple, economical and highly efficient online preconcentration methods, large volume sample stacking and sweeping (LVSS-sweeping) and cation-selective exhaustive injection and sweeping (CSEI-sweeping) both followed by the cyclodextrin modified electrokinetic chromatography (CDEKC) were examined in the present work. Parameters affecting the enantioseparation and enhancement efficiency of these two injection modes were monitored in detail, and migration order of the two enantiomers was identified by circular dichroism (CD) and HPLC. Upon optimization, two enantiomers were best separated with the improvement of sensitivity reaching 160-fold and 4000-fold respectively for LVSS-sweeping and CSEI-sweeping comparing with the normal CDEKC separation. Then the optimal condition of CSEI-sweeping-CDEKC was validated and showed high sensitivity (10 ng/mL for lower limit of quantification, LLOQ), satisfactory accuracy (96.8-111.6%) and precision (relative standard deviation, RSD within 9.4%). This demonstrated it to be a suitable strategy for the rapid enantioselective determination and quantitative analysis of pheniramine enantiomers in plasma samples. Therefore, the method was further applied in the enantiomeric analysis of pheniramine in rat pharmacokinetics and plasma protein binding investigations. Stereoselectivity in pharmacokinetics as well as plasma protein binding were observed, suggesting that the stereoselective protein binding might be responsible for the stereoselectivity in pharmacokinetics.