Toward Optimizing and Understanding Reversible Hyperpolarization of Lactate Esters Relayed from para-Hydrogen

The SABRE-Relay hyperpolarization method is used to enhance the H-1 and( 13)C NMR signals of lactate esters, which find use in a wide range of medical, pharmaceutical, and food science applications. This is achieved by the indirect relay of magnetization from para- hydrogen, a spin isomer of dihydrogen, to OH-containing lactate esters via a SABRE-hyperpolarized NH intermediary. This delivers H-1 and C-13 NMR signal enhancements as high as 245-and 985-fold, respectively, which makes the lactate esters far more detectable using NMR. DFT-calculated J-couplings and spin dynamics simulations indicate that, while polarization can be transferred from the lactate OH to other H-1 nuclei via the J-coupling network, incoherent mechanisms are needed to polarize the( 13)C nuclei at the 6.5 mT transfer field used. The resulting sensitivity boost is predicted to be of great benefit for the NMR detection and quantification of low concentrations (< mM) of lactate esters and could provide a useful precursor for the production of hyperpolarized lactate, a key metabolite.