Synthesis and Biodistribution of 2-tert-butyl-4-chloro-5-(2-¹⁸Ffluroethoxy)-2H-pyridazin-3-one

A fluorine-18 labeled pyridazinone derivative: 2-tert-butyl-4-chloro-5-(2-¹⁸Ffluroethoxy)-2H-pyridazin-3-one (¹⁸F-FP2) was designed and prepared as a potential myocardial perfusion imaging agent. The total radiosynthesis time was 70-90 min, typical decay corrected radiochemical yield was 53.0%±5.2%, and the radiochemical purities were >98% after purification. It is a lipophilic compound, and stable in water for 3 h. The results of biodistribution studies in mice showed that ¹⁸F-FP2 had high liver and lung uptake at initial post injection time, the uptake was (14.53±2.36）%ID/g and (33.69±10.79）%ID/g at 2 min post injection, respectively. Radioactivity was washed out very fast from liver and lung, the rate of clearance was 57.7% and 86.2% at 15 min post-injection, respectively. However the heart uptake of ¹⁸F-FP2 was very low, the highest heart uptake was(4.09±0.53)%-ID/g at 2 min post injection. This may due to the removing of phenyl group in the labeling sidechain of pyridazinone, indicating that the aromatic ring has strong influence on the heart uptake and retention.