Application of separation and configuration identification of the four tetrabenazine stereoisomers in determining their pharmacokinetics.

Tetrabenazine (TBZ) is used in the treatment of psychiatric diseases, and it works by inhibiting vesicular monoamine transporter 2 (VMAT2) protein to exert a curative effect. TBZ is administered as the mixture of stereoisomers in clinical treatment. TBZ has two chiral centers, and therefore, it has four stereoisomers, and this greatly makes it difficult to separate the stereoisomers and to identify their configurations because of their high susceptibility to structural transformation. This study aims to develop a method to resolve TBZ into four individual peaks, corresponding to the four stereoisomers (1-4). Based on the different binding affinities between TBZ stereoisomers and VMAT2, the UF-UHPLC-QQQ/MS method is used to determine the absolute configuration of TBZ stereoisomers 1 and 2. Molecular docking simulations are used to verify the accuracy of UF-UHPLC-QQQ/MS. The configurations of stable stereoisomers 3 and 4 were confirmed by electron circular dichroism (ECD). The established analytical method was applied to determine the pharmacokinetics of each TBZ stereoisomer in vivo. It was found that the stereoisomer 1 (3R,11bR-TBZ) showed better bioavailability and more excretion than the other stereoisomers. The results of tissue distribution experiments indicated a much higher content of 3R,11bR-TBZ in the brain, suggesting that it may better penetrate the blood-brain barrier and exert its therapeutic effects there. The paper addresses the complex problem of separating and identifying stereoisomers with multiple chiral centers, which is a significant challenge in pharmaceutical chemistry. And this work could provide a basis for the preparation of TBZ stereoisomers and a reference for the method of separating drugs with multichiral centers and identifying unstable drugs based on their configurations.