Chiral recognition of amino acid enantiomers using high-definition differential ion mobility mass spectrometry

Abstract

Enantiomeric analysis of small molecules is important in many research fields, including in drug development. Here, chiral recognition of amino acid enantiomers using differential ion mobility spectrometry (DMS) mass spectrometry (MS) is demonstrated. Diastereomeric proton bound complexes were formed between enantiomers of amino acids (tryptophan and phenylalanine) and N-tert-butoxycarbonyl-O-benzyl-l-serine (BBS) by electrospray ionization for analysis by DMS-MS and collision-induced dissociation (CID). If the DMS resolution is sufficiently high, ionic diastereomers (as opposed to enantiomers) can in principle be separated without the use of a chiral gas. Peaks corresponding to the L- and D-enantiomers for both tryptophan and phenylalanine in the DMS-MS spectra were resolved by increasing the ratio of He in the carrier gas from 100% N2 to 50:50 He:N2%. In contrast, CID spectra of the corresponding diastereomeric dimer complex ions were nearly identical, indicating that chiral recognition by CID was not possible under these conditions. For mixtures of L- and D-tryptophan, a linear calibration curve can be obtained by plotting the enantiomeric excess measured by DMS-MS vs. the known values in solution (slope of 1.000, intercept of −0.010 and R2 of 0.997). That is, enantiopurity can be quantified using a separation process that occurs in milliseconds. Thus, DMS-MS analysis of proton bound diastereomeric dimers is a powerful approach for the rapid enantiomeric analysis of relatively small molecules.