Fig. 1: Synthesis and characterization of [1,5-13C2]Z-OMPD.
a Z-OMPD was synthesized in a two-step approach by using [1-13C]ethyl pyruvate as a precursor. The pH sensitivity of the 13C resonances in the physiological pH range originates from the C5-carboxyl-group with pKa2 = 6.55. b 13C spectra from a titration series of Z-OMPD show strong and weak pH sensitivity for the C5- and C1-resonance, respectively, relative to [13C]urea as a nonshifting reference. c Fitting of chemical shift changes of Z-OMPD as a function of pH relative to [13C]urea with a scaled logistic function yields pH sensor calibration curves. d Comparison of T1 relaxation time curves of 13C-labelled hyperpolarized in vivo pH sensors shows 13C-labels of undeuterated Z-OMPD (OMPD1; OMPD5) to exhibit superior hyperpolarized signal lifetime compared to deuterated zymonic acid (ZAd,1; ZAd,5). Relaxation curves are measured in D2O at 1 T). e T1 relaxation time constant of the 13C-labels of Z-OMPD at different field strengths (1 T and 7 T) and solvents (D2O and blood), as well as measured in vivo at 7 T.
