Synthesis of N ₄′ -[¹⁸F]fluoroalkylated ciprofloxacin as a potential bacterial infection imaging agent for PET study

Syntheses and evaluation of fluoroalkylated ciprofloxacin analogues are described. Among these analogues, N₄′-3- fluoropropylciprofloxacin (16) showed the most efficient antibacterial activity against E. coli strains (DH5α and TOP10) and a high binding affinity for DNA gyrase of bacteria. To develop bacteria-specific infection imaging agents for positron emission tomography (PET), no-carrier-added N₄α-3- [¹⁸F]fluoropropylciprofloxacin ([¹⁸F]16) was prepared in two steps from N₄α-3-methanesufonyloxypropylciprofloxacin, resulting in a 40% radiochemical yield (decay corrected for 100 min) via the tert-alcohol media radiofluorination protocol with high radiochemical purity (>99%) as well as high specific activity (149 ± 75 GBq/μmol). The agent was stable (>90%), as shown by an in vitro human serum stability assay. A bacterial uptake and blocking study of [¹⁸F]16 using authentic compound 16 in TOP10 cells demonstrated its high specific bacterial uptake. The results suggest that this radiotracer holds promise as a useful bacterial infection radiopharmaceutical for PET imaging.