Heterogeneous 1H and 13C Parahydrogen-Induced Polarization of Acetate and Pyruvate Esters

Magnetic resonance imaging of [1-C-13]hyperpolarized carboxylates (most notably, [1-C-13]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of H-1 and C-13 hyperpolarization of acetate and pyruvate esters with ethyl, propyl and allyl alcoholic moieties using heterogeneous hydrogenation of corresponding vinyl, allyl and propargyl precursors in isotopically unlabeled and 1-C-13-enriched forms with parahydrogen over Rh/TiO2 catalysts in methanol-d(4) and in D2O. The maximum obtained H-1 polarization was 0.6 +/- 0.2 % (for propyl acetate in CD3OD), while the highest C-13 polarization was 0.10 +/- 0.03 % (for ethyl acetate in CD3OD). Hyperpolarization of acetate esters surpassed that of pyruvates, while esters with a triple carbon-carbon bond in unsaturated alcoholic moiety were less efficient as parahydrogen-induced polarization precursors than esters with a double bond. Among the compounds studied, the maximum H-1 and C-13 NMR signal intensities were observed for propyl acetate. Ethyl acetate yielded slightly less intense NMR signals which were dramatically greater than those of other esters under study.

Automated summary

The efficiency of H-1 and C-13 hyperpolarization of acetate and pyruvate esters using heterogeneous hydrogenation and parahydrogen over Rh/TiO2 catalysts was investigated. Acetate esters surpassed pyruvates in hyperpolarization, and esters with a double bond in unsaturated alcoholic moieties were more efficient than those with a triple carbon-carbon bond. Among the compounds studied, propyl acetate yielded the maximum H-1 and C-13 NMR signal intensities.