11C-Fallypride: radiosynthesis and preliminary evaluation of a novel dopamine D2/D3 receptor PET radiotracer in non-human primate brain Original Research Article

Fallypride [benzamide, 5-(3-fluoropropyl)-2,3-dimethoxy-N-[(2S)-1-(2-propenyl)-2-pyrrolidinyl]methyl]-, CAS RN 166173-78-0] is a selective dopamine D2/D3 receptor antagonist. Carbon-11 labeled fallypride may serve as a radiotracer for use in biomedical imaging technique positron emission tomography (PET). The precursor, 5-(3-fluoropropyl)-2-hydroxy-3-methoxy-N-[(2S)-1-(2-propenyl)-2-pyrrolidinyl]methyl]benzamide was synthesized from 2-hydroxy-3-methoxy-5-(2-propenyl)benzoic acid, methyl ester in seven steps with approximately 10% overall chemical yield. Using this precursor 11C-fallypride was produced by radiolabeling with 11C-methyl iodide in 25–40% radiochemical yields with specific activities of 200–1000 Ci/mmol. PET imaging studies in nonhuman primates with 11C-fallypride showed radiotracer localization in dopaminergic brain regions such as caudate, putamen, thalamus and cortex. This regional localization of 11C-fallypride is similar to that observed previously for 18F-fallypride. The results suggest 11C-fallypride is a useful PET radiotracer for imaging dopamine D2/D3 receptors.