Enantio‐separation of pregabalin by ternary complexation using trapped ion mobility spectrometry

Abstract

Rationale The rapid identification of small‐molecule chiral drugs is challenging due to subtle structural differences. Different enantiomers of chiral drugs may produce inverse biological effects through their different pharmacokinetics. Therefore, it is highly desirable to distinguish the chirality of drug molecules. Methods The chirality of pregabalin was distinguished by studying the ion mobility spectra of the ternary non‐covalent complexes formed with cyclodextrins (CDs), pregabalin, and alkali‐earth cations using trapped ion mobility spectrometry (TIMS). The ternary non‐covalent complex ions were determined by electrospray ionization of mixed solutions. The analyzed sample was simply mixed, without derivatization or sample pretreatment. The relative contents of pregabalin enantiomers were derived using a calibration curve method. Results The ion mobility spectra of several ternary non‐covalent complexes formed with α‐, β‐, and γ‐CD, pregabalin, and alkali‐earth cations were obtained. We compared their ability to distinguish the chirality of pregabalin. The best peak‐to‐peak resolution (Rp‐p) was estimated to be 2.20 for [2β‐CD + pregabalin + Sr]2+, which can be ascribed as baseline separation. The derived relative contents for S‐pregabalin were in agreement with the actual contents. Conclusions A novel and convenient method for discriminating the chirality of the pregabalin molecule by TIMS was developed and optimized. The chirality of pregabalin was recognized by studying the ion mobility spectra of the ternary non‐covalent complexes, such as [2β‐CD + pregabalin + Sr]2+. This TIMS method could also be used to quantify the relative contents of pregabalin enantiomers.

Recent Advances in Separation and Analysis of Chiral Compounds

“…201,202 Chiral reference-metal ion complexes are the most commonly used derivatization reagents. Different chiral reference compounds (e.g., α-, β-, γ-CD, rifamycin and natamycin) 203,204 and metal ions (e.g., Cr 3+ , Ba 2+ , Sr 2+ , Ca 2+ , and Mn 2+ ) 205,206 were reported to achieve satisfactory separation factors. Furthermore, rigid structures in derivatization reagents or analytes are beneficial for high peak-to-peak resolution (R p-p ).…”

“…For example, R/S-1,1,2-triphenyl-1,2-ethanediol (TPED) were separated with high resolution (R p-p = 2.08) after forming [natamycin + TPED + Ba−H] + , 203 while R/S-pregabalin obtained high separation resolution (R p-p = 2.20) after forming [2β-CD + pregabalin + Sr] 2+ . 205 Li et al 89 used estradiol-3-benzoate-17β-chloroformate for the derivati- zation of amino acids (Figure 5) to achieve good enantiomer separation of 19 chiral amino acids in a single analytical run (∼2 s). Cooper-Shepherd et al 207 introduced an interesting method to form diastereomer dimers with aromatic analytes for IM-MS separation.…”

“…Thus, converting enantiomers to diastereomers by derivatization is an alternative method of high-resolution enantiomer separation as diastereomers are highly possible to be baseline-separated by IM-MS with the typical buffer gas. , Chiral reference-metal ion complexes are the most commonly used derivatization reagents. Different chiral reference compounds (e.g., α-, β-, γ-CD, rifamycin and natamycin) , and metal ions (e.g., Cr 3+ , Ba 2+ , Sr 2+ , Ca 2+ , and Mn 2+ ) , were reported to achieve satisfactory separation factors. Furthermore, rigid structures in derivatization reagents or analytes are beneficial for high peak-to-peak resolution ( R p‑p ).…”

Ion Mobility Mass Spectrometry for the Separation and Characterization of Small Molecules

“…Ruskic et al found that the selectivity of DMS for separating isomers depends on the concentration of chiral selectors. Other common chiral selectors are cyclodextrin with metal cations, − methanol, anisole, and so on.…”

Exploiting Self-Association to Evaluate Enantiomeric Composition by Cyclic Ion Mobility–Mass Spectrometry

“…While showing promise, such work has proved difficult to reproduce . More recently, covalent derivatization prior to mobility analysis has been shown to provide an effective means to identify and quantify chiral amino acids in milk and other mixtures. − Particularly interesting is the study of noncovalent chiral modifiers for the formation of diastereomeric complexes prior to or during electrospray ionization, which can subsequently be separated by ion mobility. − A recent study using FAIMS has also characterized protonation-induced chirality through the formation of chiral centers at tertiary amines, leading to diastereomeric ions with distinct mobilities …”