Parahydrogen-Induced Polarization of 1-¹³C-Acetates and 1-¹³C-Pyruvates Using Sidearm Hydrogenation of Vinyl, Allyl, and Propargyl Esters

¹³C-hyperpolarized carboxylates, such as pyruvate and acetate, are emerging molecular contrast agents for magnetic resonance imaging (MRI) visualization of various diseases, including cancer. Here, we present a systematic study of ¹H and ¹³C parahydrogen-induced polarization of acetate and pyruvate esters with ethyl, propyl, and allyl alcoholic moieties. It was found that allyl pyruvate is the most efficiently hyperpolarized compound from those under study, yielding 21 and 5.4% polarization of ¹H and ¹³C nuclei, respectively, in CD₃OD solutions. Allyl pyruvate and ethyl acetate were also hyperpolarized in the aqueous phase using homogeneous hydrogenation with parahydrogen over a water-soluble rhodium catalyst. ¹³C polarization values of 0.82 and 2.1% were obtained for allyl pyruvate and ethyl acetate, respectively. ¹³C-hyperpolarized methanolic and aqueous solutions of allyl pyruvate and ethyl acetate were employed for in vitro MRI visualization, demonstrating the prospects for translation of the presented approach to biomedical in vivo studies.