Probing Fast Enantio-Recognition of Drugs with Multiple Chiral Centers by Electrospray-Tandem Mass Spectrometry and Its Mechanism

Abstract

Chiral drugs are very complex substances since individual enantiomers may differ in pharmacological and toxic effects, making it necessary to analyze enantiomers separately. In this study, we investigated the chiral differentiation of two ezetimibe enantiomers (i.e., SRS-EZM and RSR-EZM) and their mechanisms in complex with β-cyclodextrins (CDs) and metal ions as the auxiliary ligands. For this purpose, two complementary approaches have been employed: electrospray-tandem mass spectrometry (ESI-MS/MS) with collision induced dissociation (CID) and molecular modeling methods, including density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The results showed a good agreement between experimental and theoretical data. It was demonstrated that SRS-EZM can be easily distinguished from RSR-EZM by applying CID in ESI-MS/MS. SRS-EZM is likely to form a more stable complex with β-CD and metal ions, and thus the [SRS-EZM]-Cu-[β-CD] cluster is more energetically difficult to separate from the SRS-EZM molecule compared with RSR-EZM. Such a difference may be attributed to the interactions between the drug molecule and the metal ion, as well as the cavity shape changes of the β-CDs upon complexation with molecular guests. Therefore, enantiomers in chiral drug can be recognized as ternary complexes of metal-analyte-β-CD by ESI-MS/MS with CID.