N³-Substituted thymidine analogues III: Radiosynthesis of N ³-[(4-[¹⁸F]fluoromethyl-phenyl)butyl]thymidine ([ ¹⁸F]-FMPBT) and N-[(4-[¹⁸F]fluoromethyl-phenyl)pentyl] thymidine ([¹⁸F]-FMPPT) for PET

Radiosyntheses of two N³-substituted thymidine analogues, N ³-[(4[¹⁸F]fluoromethyl-phenyl)butyl]thymidine ([ ¹⁸F]-FMPBT) and N³-[(4[¹⁸F]fluoromethyl-phenyl) pentyl]thymidine ([¹⁸F]-FMPPT), are reported. The precursor compounds 9 and 10 were synthesized in six steps and the standard compounds 13 and 14 were synthesized from these precursors. For radiosynthesis, compounds 9 and 10 were fluorinated with n-Bu₄N[¹⁸F] to produce [ ¹⁸F]-11 and [¹⁸F]-12, which by acid hydrolysis yielded [¹⁸F]-13 and [¹⁸F]-14, respectively. The crude products were purified by high-performance liquid chromatography to obtain [ ¹⁸F]-FMPBT and [¹⁸F]-FMPPT. The average decay-corrected radiochemical yield for [¹⁸F]-13 was 15% in five runs, and that for [¹⁸F]-14 was 10% in four runs. The radiochemical purity was >99% and the specific activity was >74 GBq/μmol at the end of synthesis. The synthesis time was 80-90 min from the end of bombardment.