Abstract
Magnetic resonance imaging of [1-(13) C]hyperpolarized carboxylates (most notably, [1-(13) C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of (1) H and (13) 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-(13) C-enriched forms with parahydrogen over Rh/TiO(2) catalysts in methanol-d(4) and in D(2) O. The maximum obtained (1) H polarization was 0.6±0.2 % (for propyl acetate in CD(3) OD), while the highest (13) C polarization was 0.10±0.03 % (for ethyl acetate in CD(3) 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 (1) H and (13) 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.