[11C]NNC 687 and [11C]NNC 756, dopamine D-1 receptor ligands. Preparation, autoradiography and PET investigation in monkey.

NNC 687 and NNC 756 [(+)-5-(2,3-dihydrobenzofuran-7-yl)-7-hydroxy-3-methyl- 8-nitro-2,3,4,5-tetrahydro-1H-3-benzazepine and (+)-8-chloro-5-(2,3-dihydrobenzofuran-7-yl)-7-hydroxy-3-methyl-2,3,4,5- tetrahydro-1H-3-benzazepine] are two new potent dopamine D-1 receptor antagonists. [11C]NNC 687 and [11C]NNC 756 were both prepared by N-methylation of the corresponding desmethyl compounds with [11C]methyl iodide. The reactions were performed in acetone with subsequent normal-phase semi-preparative HPLC and resulting in 50-60% radiochemical yield (from EOB and decay-corrected) with a total synthesis time of 30-35 min and a radiochemical purity higher than 99%. The specific radioactivity obtained at time of injection was about 1500 Ci/mmol (55 GBq/mumol). Autoradiographic examination of [11C]NNC 687 and [11C]NNC 756 binding in post-mortem human brain sections showed specific binding in the striatum, a region with high density of dopamine D-1 receptors. PET examination of the radioligands in a Cynomolgus monkey demonstrated accumulation of radioactivity predominantly in the striatum. The ratio between radioactivities in the striatum and the cerebellum was about 2 and 8 for [11C]NNC 687 and [11C]NNC 756 after 60 min. [11C]NNC 756 should have potential as PET ligand for examination of central dopamine D-1 receptors in man.