Reaction of polarizing agent Ox063 with pyruvic acid under standard sample preparation protocol for dissolution dynamic nuclear polarization.

Dynamic nuclear polarization is a technique that significantly enhances signal intensity in nuclear magnetic resonance spectroscopy and imaging. In a DNP experiment, a sample of interest is doped with a radical, and microwaves are applied in a strong magnetic field, leading to an increase in nuclear spin polarization. Notably, the potential reactions between the sample and the polarization agent are rarely considered. Hyperpolarized C magnetic resonance spectroscopy (MRS) is currently used in clinical trials for various diseases. Herein, we demonstrated that with one of the mostly used DNP systems, pyruvic acid, hyperpolarized with the trityl radical Ox063, the alcohol moieties of the radical undergo esterification during sample preparation, leading to the formation of pyruvate esters on the radical, and that Ox063 has a half-life of ∼30 min in pyruvic acid at room temperature. The biological and physicochemical properties of these derivatives have not yet been studied.