Synthesis of 13C and 2H Labeled Vinyl Pyruvate and Hyperpolarization of Pyruvate

The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, and particularly metabolic imaging. Parahydrogen‐induced polarization (PHIP) offers a fast and cost‐efficient way of hyperpolarization. Nevertheless, PHIP lags behind dynamic nuclear polarization (DNP), which is already being evaluated in clinical studies. This shortcoming is mainly due to problems in the synthesis of the corresponding PHIP precursor molecules. The most widely used DNP tracer in clinical studies, particularly for the detection of prostate cancer, is 1‐13C‐pyruvate. The ideal derivative for PHIP is the deuterated vinyl ester because the spin physics allows for 100 % polarization. Unfortunately, there is no efficient synthesis for vinyl esters of β‐ketocarboxylic acids in general and pyruvate in particular. Here, we present an efficient new method for the preparation of vinyl esters, including 13C labeled, fully deuterated vinyl pyruvate using a palladium‐catalyzed procedure. Using 50 % enriched parahydrogen and mild reaction conditions, a 13C polarization of 12 % was readily achieved; 36 % are expected with 100 % pH2. Higher polarization values can be potentially achieved with optimized reaction conditions. Hyperpolarized pyruvate is a highly promising tracer for in vivo metabolic MRI. A new synthetic approach provides access to the key precursor of 13C labeled vinyl pyruvate with up to 67 % yield (8 times higher than previous methods). After spin order transfer with parahydrogen, 12 % 13C polarization was obtained, which corresponds to a signal gain in NMR and MRI of 16 500 (9.4 T).