PHIP hyperpolarized [1-(13)C]pyruvate and [1-(13)C]acetate esters via PH-INEPT polarization transfer monitored by (13)C NMR and MRI

Parahydrogen-induced polarization of (13)C nuclei by side-arm hydrogenation (PHIP-SAH) for [1-(13)C]acetate and [1-(13)C]pyruvate esters with application of PH-INEPT-type pulse sequences for (1)H to (13)C polarization transfer is reported, and its efficiency is compared with that of polarization transfer based on magnetic field cycling (MFC). The pulse-sequence transfer approach may have its merits in some applications because the entire hyperpolarization procedure is implemented directly in an NMR or MRI instrument, whereas MFC requires a controlled field variation at low magnetic fields. Optimization of the PH-INEPT-type transfer sequences resulted in (13)C polarization values of 0.66 ± 0.04% and 0.19 ± 0.02% for allyl [1-(13)C]pyruvate and ethyl [1-(13)C]acetate, respectively, which is lower than the corresponding polarization levels obtained with MFC for (1)H to (13)C polarization transfer (3.95 ± 0.05% and 0.65 ± 0.05% for allyl [1-(13)C]pyruvate and ethyl [1-(13)C]acetate, respectively). Nevertheless, a significant (13)C NMR signal enhancement with respect to thermal polarization allowed us to perform (13)C MR imaging of both biologically relevant hyperpolarized molecules which can be used to produce useful contrast agents for the in vivo imaging applications.