Synthesis and 15N NMR Signal Amplification by Reversible Exchange of [15N]Dalfampridine at Microtesla Magnetic Fields

Signal Amplification by Reversible Exchange (SABRE) technique enables nuclear spin hyperpolarization of wide range of compounds using parahydrogen. Here we present the synthetic approach to prepare N-15-labeled [N-15]dalfampridine (4-amino[N-15]pyridine) utilized as a drug to reduce the symptoms of multiple sclerosis. The synthesized compound was hyperpolarized using SABRE at microtesla magnetic fields (SABRE-SHEATH technique) with up to 2.0 % N-15 polarization. The 7-hour-long activation of SABRE pre-catalyst [Ir(IMes)(COD)Cl] in the presence of [N-15]dalfampridine can be remedied by the use of pyridine co-ligand for catalyst activation while retaining the N-15 polarization levels of [N-15]dalfampridine. The effects of experimental conditions such as polarization transfer magnetic field, temperature, concentration, parahydrogen flow rate and pressure on N-15 polarization levels of free and equatorial catalyst-bound [N-15]dalfampridine were investigated. Moreover, we studied N-15 polarization build-up and decay at magnetic field of less than 0.04 mu T as well as N-15 polarization decay at the Earth's magnetic field and at 1.4 T.