Hyperpolarization of 15N-pyridinium and 15N-aniline derivatives by using parahydrogen: new opportunities to store nuclear spin polarization in aqueous media

Hyperpolarization techniques hold the promise to improve the sensitivity of magnetic resonance imaging (MRI) contrast agents by over 10 000-fold. Among these techniques, para-hydrogen induced polarization (PHIP) allows for generating contrast agents within seconds. Typical hyperpolarized contrast agents are traceable for 2-3 minutes only, thus prolonging tracking-times holds great importance for the development of new ways to diagnose and monitor diseases. Here, we report on the design of perdeuterated N-15-containing molecules with longitudinal relaxation times (T-1) of several minutes. T-1 is a measure for how long hyperpolarization can be stored. In particular, we introduce two new hyperpolarizable families of compounds that we signal enhanced with para-hydrogen: tert-amine aniline derivatives and a quaternary pyridinium compound with N-15-T-1 of about 8 minutes. Especially the latter compound has great potential for applicability since we achieved N-15-polarization up to 8% and the pyridinium motif is contained in a variety of drug molecules and is also used in drug delivery systems.