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We report synthesis of 15 N-3- 19 F-pyridine via Zincke salt formation with the overall 35% yield and 84% 15 N isotopic purity. Hyperpolarization studies of Signal Amplification by Reversible Exchange (SABRE) and SABRE in SHield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) were performed to investigate the mechanism of polarization transfer from parahydrogen-derived hydride protons to 19 F nucleus in milli-Tesla and micro-Tesla magnetic field regimes in 15 N-3- 19 F-pyridine and 14 N-3- 19 F-pyridine. We found the mismatch between 15 N and 19 F magnetic field hyperpolarization profiles in the micro-Tesla regime indicating that the spontaneous hyperpolarization process likely happens directly from parahydrogen-derived hydride protons to 19 F nucleus without spin-relaying via 15 N site. In case of SABRE magnetic field regime (milli-Tesla magnetic field range), we found that magnetic field profiles for 1 H and 19 F hyperpolarization are very similar, and 19 F polarization levels are significantly lower than 1 H SABRE polarization levels and lower than 19 F SABRE-SHEATH (i.e. obtained at micro-Tesla magnetic field) polarization levels. Our findings support the hypothesis that in milli-Tesla magnetic field regime, the process of 19 F nuclei hyperpolarization is relayed via protons of substrate, and therefore is very inefficient. These findings are important in the context of improvement of the hyperpolarization hardware and rational design of the hyperpolarized molecular probes.

19F Hyperpolarization of 15N-3-19F-Pyridine via Signal Amplification by Reversible Exchange

¹⁹F Hyperpolarization of ¹⁵N-3-¹⁹F-Pyridine via Signal Amplification by Reversible Exchange