Synthesis of the main metabolite in human blood of the A1 adenosine receptor ligand [18F]CPFPX.

In human blood, the PET radiotracer [18F]CPFPX (1) is metabolized to numerous metabolites, one (M1) being the most prominent in plasma 30 min p.i. Because the mass of injected tracer is ≤5 nmol, concentrations in plasma are too low to analyze. Human liver microsomes generate main metabolites having HPLC retention times identical to those in plasma. HPLC−MS tentatively identified M1 as 2. Synthesis of 2 and identical HPLC−MS spectra of 2 and M1 confirmed that assignment.