Synthesis and fluoro-radiolabelling of dopamine D_2 receptor imaging agent ~(18)F-FSABZM

The preparation of a 18F-labeled imaging agent with higher affinity to dopamine D2 receptor is reported. The ligand of (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5- [N-(2-[18F]fluoroethyl)-N-methylsulfonyl]amino-2- methoxybenzamide (18F-FSABZM) was synthesized by nitryl reduction, N-dihydroxyethylation, and methylsulfon- ylation. Finally, 18F-FSABZM was prepared by nucleophilic fluorination of the mesylate with K18F/K222(Kryptofix). The chemical structure of the fluoro-labeling precursor SABZM,the labeling product with non-radioactive fluorine and all other intermediates were validated by 1HNMR and MS. Determined by HPLC, the labeling yield was 12%— 15%. After purifying, the resultant 18F-FSABZM, with a radiochemical purity of over 97%, was stable for more than 4 hours at room temperature. The whole process (including synthesis and analysis) took only 80—90 minutes.