Exploration Of ¹⁹F-Labeled Probes For Highly Sensitive Enantiodifferentiation

When analyzing complex samples using ¹H NMR spectroscopy,issues of signal overlap frequently arise.By contrast,the¹⁹F NMR exhibits high sensitivity,zero background interference,and a simpler spectrum.Due to its broad chemical shift range,it is highly suitable for the analysis of complex mixtures.We developed a strategy,termed Recognition-Enabled Chromatographic（REC）NMR,by combining¹⁹F NMR spectroscopy with supramolecular dynamic recognition.This approach obviates the need for chemical derivatization and directly produces fluorine spectral signals precisely corresponding to each analyte,enabling in situ precise detection of multiple components in complex systems.In this study,we enhanced the detection sensitivity by incorporating a large number of chemically equivalent fluorine atoms into the probe.The chiral fluorine probes we designed contain a chiral recognition cavity.When chiral analytes of different configurations interact with the fluorine probes,differential influences on the chemical shifts of surrounding fluorine atoms are induced,generating NMR detection signals similar to chromatographic peaks corresponding to each enantiomer.Firstly,we used the nonafluoro-tert-butoxy group as building blocks to design and synthesize a series of chiral probes with different structures.We developed asymmetric chiral fluorine probes by introducing a side arm containing 18 fluorine atoms on one side of the probe and a chiral unit with different steric hindrances on the other.Moreover,we synthesized chiral probes with 36 equivalent fluorine atoms and C₂symmetry,achieving high-sensitivity differentiation of chiral analytes such as primary amines,amino alcohols,and amino acid esters.Secondly,based on the REC NMR detection method,we increased the number of fluorine atoms in the probe,significantly enhancing the detection sensitivity and accurately determining the enantiomer composition of different chiral samples at low concentrations.We accurately measured the ee values of samples at 30μM and 10μM concentrations,and the test results showed a good linear relationship with the actual enantiomer composition of the samples.In conclusion,the REC NMR detection strategy we developed not only significantly simplifies the detection signals by incorporating a large number of chemically equivalent fluorine atoms into the probe,but also enhances the detection sensitivity.With the highly sensitive fluorine probes developed in this study,we were able to accurately determine the quantity of chiral analytes at low concentrations,even accurately measuring the enantiomer composition of chiral samples less than 1.0micrograms.This strategy provides a new possibility for the detection and differentiation of trace chiral analytes in complex systems,effectively overcoming the insensitivity of NMR detection.These research results open new horizons for NMR detection and lay a solid foundation for future related research.