Synthesis of 11C‑Labeled Thiamine and Fursultiamine for in Vivo Molecular Imaging of Vitamin B1 and Its Prodrug Using Positron Emission Tomography

To enable in vivo analysis of the kinetics of vitamin B1 (thiamine) and its derivatives by positron emission tomography (PET), 11C-labeled thiamine ([11C]-1) has been synthesized. This was carried out via a rapid, multistep synthesis consisting of Pd0-mediated C-[11C]­methylation of a thiazole ring for 3 min and benzylation with 5-(bromomethyl)­pyrimidine for 7 min. The [11C]-1 was also converted to 11C-labeled fursultiamine ([11C]-2), a prodrug of vitamin B1, by disulfide formation with S-tetrahydrofurfurylthiosulfuric acid sodium salt. Characterization of [11C]-1 and [11C]-2 showed them to be suitable for use as PET probes for in vivo pharmacokinetic and medical studies. The total durations of the preparations of [11C]-1 and [11C]-2 were shorter than 60 and 70 min, respectively. The [11C]­CH3I-based decay-corrected radiochemical yields of [11C]-1 and [11C]-2 were 9–16% and 4–10%, respectively. The radioactivities of the final injectable solutions of [11C]-1 and [11C]-2 were 400–700 and 100–250 MBq, respectively. The radiochemical purity of both [11C]-1 and [11C]-2 was 99%, and the chemical purities of [11C]-1 and [11C]-2 were 99% and 97–99%, respectively. In vivo PET imaging of normal rats was illustrated by the distribution of [11C]-1 and [11C]-2 following intravenous injection.