Hyperpolarization of ¹⁵N in an amino acid derivative

Hyperpolarization is a nuclear magnetic resonance (NMR) technique which can be used to significantly enhance the signal in NMR experiments. In recent years, the possibility to enhance the NMR signal of heteronuclei by the use of para-hydrogen induced polarization (PHIP) has gained attention, especially in the area of possible applications in magnetic resonance imaging (MRI). Herein we introduce a way to synthesize a fully deuterated, ¹⁵N labelled amino acid derivative and the possibility to polarize the ¹⁵N by means of hydrogenation with para-hydrogen to a polarization level of 0.18%. The longevity of the polarization with a longitudinal relaxation time of more than a minute can allow for the observation of dynamic processes and metabolic imaging in vivo. In addition, we observe the phenomenon of proton-deuterium exchange with a homogeneous catalyst leading to signal enhanced allyl moeities in the precursor.