New fluorinated dopamine D2 ligands with benzofuran skeleton. The synthesis and in vitro evaluation

New fluorinated ligands with N-[(1-ethyl-2-pyrrolidinyl)methyl]-2,3-dihydrobenzofuran-7-carboxamide skeleton, which are useful as a prototype to develop 18F labelled in vivo radiotracer for positron emission tomography (PET), were synthesized, and their binding affinities for the dopamine D2 receptors were investigated. Fluorine atom was introduced at C-4 of the pyrrolidine ring (10) or at ethyl substituent at C-5 of the dihydrobenzofuran moiety (20). The in vitro IC50 values of these ligands for the dopamine D2 receptors which were determined by their ability to inhibit the binding of [3H]spiperone binding in rat striatal membrane were 17 and 36 nM, respectively. Thus, the fluorinated compounds 10 and 20 may be possible candidates for further in vivo investigation.