Investigation of various N-heterocyclic substituted piperazine versions of 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol: Effect on affinity and selectivity for dopamine D3 receptor

Here we report on the design and synthesis of several heterocyclic analogues belonging to the 5/7-{[2-(4-aryl-piperazin-1-yl)-ethyl]-propyl-amino}-5,6,7,8-tetrahydro-naphthalen-2-ol series of molecules. Compounds were subjected to [3H]spiperone binding assays, carried out with HEK-293 cells expressing either D2 or D3 dopamine receptors, in order to evaluate their inhibition constant (Ki) at these receptors. Results indicate that N-substitution on the piperazine ring can accommodate various substituted indole rings. The results also show that in order to maintain high affinity and selectivity for the D3 receptor the heterocyclic ring does not need to be connected directly to the piperazine ring as the majority of compounds included here are linked either via an amide or a methylene linker to the heterocyclic moiety. The enantiomers of the most potent racemic compound 10e exhibited differential activity with (−)-10e (Ki; D2 = 47.5 nM, D3 = 0.57 nM) displaying higher affinity at both D2 and D3 receptors compared to its enantiomer (+)-10e (Ki; D2 = 113 nM, D3 = 3.73 nM). Additionally, compound (−)-10e was more potent and selective for the D3 receptor compared to either 7-OH-DPAT or 5-OH-DPAT. Among the bioisosteric derivatives, the indazole derivative 10g and benzo[b]thiophene derivative 10i exhibited the highest affinity for D2 and D3 receptors. In the functional GTPγS binding study, one of the lead molecules, (−)-15, exhibited potent agonist activity at both D2 and D3 receptors with preferential affinity at D3.

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