Synthesis and Analysis of [18F]FRPG and [18F]FSPG

[¹⁸F]FRPG and [¹⁸F]FSPG were synthesized from their corresponding naphthalenesulfonyl precursors (Life Molecular Imaging) using a GE FASTlab automated synthesis module using a previously reported method [43 (link)]. The analysis and identification of [¹⁸F]FRPG and [¹⁸F]FSPG was also conducted as reported previously [43 (link)]. For a detailed description of precursor and ¹⁹F reference standard syntheses, along with their corresponding spectra, see Supplementary Information: Synthesis and Spectra. The radiochemical purity and molar activity of [¹⁸F]FRPG and [¹⁸F]FSPG were analysed by pre-column derivatization with ortho-phthalaldehyde reagent (OPA). 20 μL [¹⁸F]FRPG or [¹⁸F]FSPG solution was added to 20 μL OPA reagent followed by addition of 80 μL PBS. The mixture was incubated for 5 min at room temperature and then analysed by HPLC. Next, the appropriate ¹⁹F standard was added to the OPA/tracer reaction mixture and left for 15 min before further analysis by HPLC. Co-elution of the ¹⁹F standard OPA-adduct UV peak with the corresponding ¹⁸F OPA-adduct radioactive peak confirmed the identity of both [¹⁸F]FRPG and [¹⁸F]FSPG (Figure S1). HPLC chromatograms showing the different retention times for the [¹⁸F]FRPG-OPA and [¹⁸F]FSPG-OPA adducts with co-elution of their corresponding ¹⁹F reference compounds can be found in the supplemental information (Figure S2).