A New Ir-NHC Catalyst for Signal Amplification by Reversible Exchange in D2O

Abstract

NMR signal amplification by reversible exchange (SABRE) has been observed for pyridine, methyl nicotinate, N-methylnicotinamide, and nicotinamide in D2O with the new catalyst [Ir(Cl)(IDEG)(COD)] (IDEG=1,3-bis(3,4,5-tris(diethyleneglycol)benzyl)imidazole-2-ylidene). During the activation and hyperpolarization steps, exclusively D2O was used, resulting in the first fully biocompatible SABRE system. Hyperpolarized1H substrate signals were observed at 42.5 MHz upon pressurizing the solution with parahydrogen at close to the Earth's magnetic field, at concentrations yielding barely detectable thermal signals. Moreover, 42-, 26-, 22-, and 9-fold enhancements were observed for nicotinamide, pyridine, methyl nicotinate, and N-methylnicotinamide, respectively, in conventional 300 MHz studies. This research opens up new opportunities in a field in which SABRE has hitherto primarily been conducted in CD3OD. This system uses simple hardware, leaves the substrate unaltered, and shows that SABRE is potentially suitable for clinical purposes.