Simultaneous Discrimination and Quantification of Enantiomeric Amino Acids under Physiological Conditions by Chiral ¹⁹F NMR Tag

Abstract

Enantiomeric analysis is of great significance in chemistry, chemical biology and pharmaceutical research. We herein propose a chiral 19F NMR tag containing an amino reactive NHS group to discriminate the enantiomeric amino acids under physiological conditions by NMR spectroscopy. The chiral 19F NMR tag readily forms stable amide products with the amino acids in aqueous solution. The stereospecific chemistry of enantiomeric amino acids is discriminated by a stereogenic carbon bonded with a 19F atom and is therefore decoded by the 19F reporter and manifested in the distinct 19F chemical shift. The chemical shift difference (ΔΔδ) of the chiral 19F NMR tag derived enantiomeric amino acids variants has a broad chemical shift range between −1.13 to 1.68 ppm, indicating the high sensitivity of the chiral 19F NMR tag to the stereospecific environment surrounding the individual amino acids. The distinguishable chemical shift produced by the chiral 19F NMR tag permits simultaneous discrimination and quantification of the enantiomeric amino acids in a mixture. The high fidelity of the chiral 19F NMR tag affords high-accuracy determination of the enantiomeric composition of amino acids by simple 1D NMR under physiological conditions.

Stereospecific recognition of a chiral centre over multiple flexible covalent bonds by19F-NMR

“…5 Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical method that provides a variety of structural and dynamic information of analytes and is able to discriminate between enantiomers by derivatizing analytes or using chiral solvating agents. 6–14 The power of NMR in the stereospecific discrimination of enantiomers has been demonstrated in early seminal reports by using chiral or optically pure solvating agents. 15 In contrast to optical methods, NMR does not require sample separation and allows qualitative and even quantitative analysis of the analyte mixture.…”

“…15 In contrast to optical methods, NMR does not require sample separation and allows qualitative and even quantitative analysis of the analyte mixture. 11–14 The simultaneous discrimination of enantiomers by available methods, especially in biofluids, still remains a challenge. In many cases, the 1 H NMR signals are complex and tend to overlap for a mixture of analytes, whereas 13 C detection has much lower sensitivity for naturally abundant analytes.…”

“…Metal complexes with chiral pincer ligands were used for discriminating among chiral molecules in an association–dissociation manner between the chiral host containing a 19 F-reporter and guest molecules by using 19 F-NMR spectra. 7 a ,9 b ,10,12 a , c The discrimination of chiral molecules via covalent derivatization of analytes has advantages in quantifying analytes in a mixture using 19 F-NMR spectra, 13,14 which contains a chiral probe that is reactive to the analytes. This covalent discrimination strategy allows one to simultaneously quantify biological analytes in biofluids.…”

Small Molecule Probes for 19F Magnetic Resonance Imaging

“…In 2022, Krawczyk and co-workers developed a pair of pH-sensitive chemical shiftchanging 19 F molecular probes. 105 This pair of probes could interconvert under acidic or basic conditions through the switching of hydrazone bond configuration, which led to a significant change in 19 F chemical shift and permitted sensitive detection of environmental pH by 19 F MRI. Recently, Zhou and co-workers constructed another fluorophenol-based chemical shift-changing probe for in vivo imaging of nitroreductase.…”

“…The side chain attached to the hydroxy group on the benzene ring could be selectively cleaved by the enzyme, leading to a substantial change in benzene’s deshielding effect and thus a variation in the chemical shift of the 19 F on the ring. In 2022, Krawczyk and co-workers developed a pair of pH-sensitive chemical shift-changing 19 F molecular probes . This pair of probes could interconvert under acidic or basic conditions through the switching of hydrazone bond configuration, which led to a significant change in 19 F chemical shift and permitted sensitive detection of environmental pH by 19 F MRI.…”