Chiral Recognition by Dissolution DNP NMR Spectroscopy of ¹³C-Labeled dl -Methionine

A method based on d-DNP NMR spectroscopy to study chiral recognition is described for the first time. The enantiodifferentiation of a racemic metabolite in a millimolar aqueous solution using a chiral solvating agent was performed. Hyperpolarized C-13-labeled DL-methionine enantiomers were differently observed with a single-scan C-13 NMR experiment, while the chiral auxiliary at thermal equilibrium remained unobserved. The method developed entails a step forward in the chiral recognition of small molecules by NMR spectroscopy, opening new possibilities in situations where the sensitivity is limited, for example, when a low concentration of analyte is available or when the measurement of an insensitive nucleus, like C-13, is required. The advantages and current limitations of the method, as well as future perspectives, are discussed.