Design, synthesis, radiolabeling, and in vitro and in vivo evaluation of bridgehead iodinated analogues of N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}-N-(pyridin-2-yl)cyclohexanecarboxamide (WAY-100635) as potential SPECT ligands for the 5-HT1A receptor

Here we describe the design, synthesis, and pharmacological profile of 5-HT(1A) receptor ligands related to 1 (WAY-100635). The cyclohexyl moiety in 1 and its O-desmethylated analogue 3 were replaced by the bridgehead iodinated bridge-fused rings: adamantyl, cubyl, bicyclo[2.2.2]octyl, or bicyclo[2.2.1]heptyl. All analogues displayed a (sub)nanomolar affinity for the 5-HT(1A) receptor in vitro. Compounds 6b and 7b appeared to be selective for this receptor over other relevant receptors and could easily be iodinated with radioactive iodine-123. In humane hepatocytes, [(123)I]6b showed a low propensity for amide hydrolysis and a stable carbon-iodine bond. The biodistribution of [(123)I]6b and [(123)I]7b in rats revealed that the carbon-iodine bond was also stable in vivo. Unfortunately, the brain uptake and the specificity for both radioligands were significantly lower than those of the parent molecule 1. In conclusion, the designed tracers are not suitable for SPECT imaging.