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

Magnetic resonance imaging of [1- C]hyperpolarized carboxylates (most notably, [1- C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of H and C 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-enriched forms with parahydrogen over Rh/TiO catalysts in methanol-d and in D O. The maximum obtained H polarization was 0.6±0.2 % (for propyl acetate in CD OD), while the highest C polarization was 0.10±0.03 % (for ethyl acetate in CD OD). 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 and C 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.