Improving the Hyperpolarization of 31P Nuclei by Synthetic Design

Traditional P-31 NMR or MRI measurements suffer from low sensitivity relative to (1)) detection and consequently require longer scan times. We show here that hyperpolarization of P-31 nuclei through reversible interactions with parahydrogen can deliver substantial signal enhancements in a range of regioisomeric phosphonate esters containing a heteroaromatic motif which were synthesized in order to identify the optimum molecular scaffold for polarization transfer. A 3588-fold P-31 signal enhancement (2.34% polarization) was returned for a partially deuterated pyridyl substituted phosphonate ester. This hyperpolarization level is sufficient to allow single scan P-31 MR images of a phantom to be recorded at a 9.4 T observation field in seconds that have signal-to-noise ratios of up to 94.4 when the analyte concentration is 10 mM. In contrast, a 12 h 2048 scan measurement under standard conditions yields a signal-to-noise ratio of just 11.4. P-31-hyperpolarized images are also reported from a 7 T preclinical scanner.