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Summary 5,6,pyridin-5-yl)butyl]-2a,3,4,5-tetrahydro-1H-benz[cd ]indole-2-one) is a potent 5-HT 7 receptor antagonist (K i ¼ 9:7 nM) with a high selectivity over other 5-HT family receptors (K i for 5-HT 1A : 770 nM; for other 5-HT receptors: >1000 nM). As a positron emission tomography (PET) tracer for the 5-HT 7 receptor, [ 11 C]DR4446 was synthesized at high radiochemical purity (>98%) with specific activity of 73-120 GBq/mmol at the end of synthesis by the alkylation of the desmethyl precursor (1) with [ 11 C]CH 3 I in the presence of NaH. A PET study in monkey demonstrated that [ 11 C]DR4446 had good permeability into the brain, and had a specific binding component in the brain regions including the thalamus, possibly an area in the 5-HT 7 receptors. Metabolite analysis showed that [ 11 C]DR4446 was relatively stable and low percentages of two radio-labeled metabolites were detected in the plasma of monkey using HPLC.

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