NCO 298, a new selective iodinated salicylamide ligand for the labelling of dopamine D sub(2) receptors

NCQ 298 ((S)-3-iodo-N-((l-ethyl-2-pyrrolidinyl)methyl)-5,6-dimethoxysalicy lamide) has an iodine substituent. We have labelled NCQ 298 with super(123)I and super(125)I, and used the radioligands as tracers in receptor studies in vitro, in vivo in autoradiography and in SPECT studies on Cynomolgus monkeys. NCQ 298 has thus a 10-fold higher affinity for the dopamine D sub(2) receptors than the corresponding des-5-methoxy compound FLA 961 (IBZM), previously used in SPECT studies. Autoradiographical studies in vitro on rat and monkey brain tissue sections showed a distinct binding in caudate-putamen, nucleus accumbens, substantia nigra, and in layer 5 of the cerebral cortex. The specific properties of ( super(123)I)NCQ 298 suggest that this compound is a useful ligand for quantitative SPECT studies of dopamine D sub(2) receptors in man.