Discrimination of 3-aminopyrrolidine derivatives with chiral and positional isomerism through mobility disparity based on non-covalent interactions

Abstract

The differentiation of 3-AminoPyrrolidine (3AP) and its derivative isomers is significant due to their use as intermediates in drug synthesis. However, the separation of these isomers, which exhibit both chiral and positional isomerism, has consistently posed challenges. In this study, an efficient analytical method was developed to discrimination between the four isomers of R/S-I/N-Boc-3-AminoPyrrolidine (R/S-l/N-Boc-3AP) and four groups of derived chiral isomers, namely R/S-N-Methyl-3-AminoPyrrolidine (R/S-N-Me-3AP), R/S-N-Ethyl-3-AminoPyrrolidine (R/S-N-Et-3AP), R/S-1-Bzl-3-AminoPyrrolidine (R/S-1-Bzl-3AP), and R/S-1-Cbz-3-AminoPyrrolidine (R/S-1-Cbz-3AP). The discrimination was achieved by utilizing natamycin (Nat) as a differentiation agent and 2/3/4-aminobenzenesulphonic acid (2/3/4-ABSA) as ligand. The facile discrimination of the four positional isomers of R/S-1-Boc-3AP and R/S-N-Boc-3AP was achieved using ion mobility spectrometry (IMS) based on their formed diastereomeric complexes [Nat + (Boc-3AP)2 + (2-ABSA)2 + H]+. The isomers were also studied via tandem mass spectrometry (MS/MS) using the formed ternary complexes, different fragment ions were observed for l-Boc-3AP and N-Boc-3AP, but the R/S enantiomers cannot be discriminated either. In addition, the enantiomers R/S-l-Bzl-3AP and R/S-l-Cbz-3AP were differentiated based on mobility using [Nat + (R/S-l-Bzl-3AP) + (3-ABSA)2 + H]+ and [Nat + (R/S-l-Cbz-3AP) + 2-ABSA + H]+; however for the small enantiomeric molecules of R/S-N-Me-3AP and R/S-N-Et-3AP, chiral discrimination was not achieved via the ternary complexes of Nat + R/S-N-Me-3AP-ABSA and Nat + R/S-N-Et-3AP-ABSA. Importantly, the separation was greatly improved by the coordinated alkali metal ions, where the separation resolution (Rp-p) increased with the radius of the metal ions. Finally, quantitative analysis and method validation were carried out for the four Boc-3AP isomers using both MS/MS and IMS-MS. Overall, the proposed method opens possibilities for the rapid discrimination and quantification of isomers exhibiting both chiral and positional isomerism in MS/MS and IMS-MS analyses.