Abstract The compound Ro 19‐6327, N‐(2‐aminoethyl)‐5‐chloropyridine‐2‐carboxamide, is known to inhibit reversibly and site specifically the enzyme monoamine oxidase B (MAO‐B). The 123 I‐labelled iodo‐analogue N‐(2‐aminoethyl)‐5‐iodopyridine‐2‐carboxamide (Ro 43‐0463) was investigated successfully in human volunteers by means of SPET (Single Photon Emission Tomography). We developed therefore the synthesis and radiolabelling of the corresponding fluoro‐analogue N‐(2‐aminoethyl)‐5‐fluoropyridine‐2‐carboxamide with 18 F in order to carry out PET (Positron Emission Tomography) investigations of MAO‐B related neuropsychiatric diseases. For this purpose two synthetic approaches leading to the electrophilic and the nucleophilic methods of 18 F radiolabelling were undertaken. The nucleophilic approach appeared to be superior when factors such as precursor synthesis, beam time, specific activity and radiochemical purity of the product are considered.
The tracer 123I-SCH 23982 was tested with regard to its ability to image dopamine D1 receptor in the human brain in vivo with single photon emission computed tomography (SPECT). The tracer did not reach equilibrium with regard to its binding to dopamine D1 receptors, presumably owing to fast metabolism to hydrophilic products and deiodination. It is concluded that 123I-SCH 23982 is not suitable for dopamine D1 receptor imaging with SPECT in the human brain.
