Indolebutylamines as Selective 5-HT_1A Agonists

Abstract

A series of new 1-[4-(indol-3-yl)butyl]-4-arylpiperazines was prepared to identify highly selective and potent 5-HT(1A) agonists as potential pharmacological tools in studies of mood disorders. The combination of structural elements (indole-alkyl-amine and aryl-piperazine) known to introduce 5-HT(1A) receptor affinity and the proper selection of substituents (R on the indole moiety and R' on the aryl moiety) led to compounds with high receptor specificity and affinity. In particular, the introduction of the methyl ether or the unsubstituted carboxamide as substituents in position 5 of the indole (R) guaranteed serotonergic 5-HT(1A) affinity compared to the unsubstituted analogue. Para-substituted arylpiperazines (R') decreased dopaminergic D(2) binding and increased selectivity for the 5-HT(1A) receptor. Agonistic 5-HT(1A) receptor activity was confirmed in vivo in the ultrasonic vocalization test, and the results suggest that the introduction of the carboxamide residue leads to better bioavailability than the corresponding methyl ether. 3-[4-[4-(4-Carbamoylphenyl)piperazin-1-yl]butyl]-1H-indole-5-carboxamide 54 was identified as a highly selective 5-HT(1A) receptor agonist [GTPgammaS, ED(50) = 4.7 nM] with nanomolar 5-HT(1A) affinity [IC(50) = 0.9 nM] and selectivity [D(2), IC(50) > 850 nM]. 3-[4-[4-(4-Methoxyphenyl)piperazin-1-yl]butyl]-1H-indole-5-carboxamide 45 is one of the most potent and selective 5-HT(1A) agonists known [5-HT(1A), IC(50) = 0.09 nM; D(2), IC(50) = 140 nM].

Synthesis, 5-Hydroxytryptamine_1A Receptor Affinity and Docking Studies of 3-[3-(4-Aryl-1-piperazinyl)-propyl]-1<i>H</i>-Indole Derivatives

“…This observation differs from the results reported by Heinrich et al, 14,19) where the para-methoxylated derivative in their indolebutylphenylpiperazine series are always better ligands than the unsubstituted analogues. On the other hand, our result agrees with those reported by Modica et al,24) where the presence of a para-methoxy group notably reduced the 5-HT 1A affinity in a series of arylpiperazinylthienopyrimidinones.…”

“…The unsubstituted indolepropylphenylpiperazine (12a) showed a marked affinity for 5-HT 1A , which increased after the introduction of a methoxyl group in the ortho position (12b). This result agrees with a number of previous studies 11,14,[24][25][26] in which the 2-methoxyarylpiperazine derivative exhibited one of the highest affinities of the series.…”

“…18) Studies on structural modifications of indolylalkylarylpiperazines carried out by Heinrich et al 14,19) reported a high-affinity pattern for 5-HT 1A agonism and succeeded in optimizing selectivity over dopamine D 2 receptors. This structural pattern considers a C5-substituted indole ring bearing different functional groups and a parasubstituted arylpiperazine.…”

“…15,16) On the other hand, the indole substructure is the basic element in a large number of biologically active natural and synthetic products. In fact, until this day, the indole motif is present in more than 400 drugs and 3000 patents.17) The range of applications for these therapeutically relevant compounds includes anti-inflammatory drugs, protein kinase C inhibitors, 5-HT agonists and antagonists, melatonin agonists and glucocorticoid receptor modulators.18) Studies on structural modifications of indolylalkylarylpiperazines carried out by Heinrich et al 14,19) reported a high-affinity pattern for 5-HT 1A agonism and succeeded in optimizing selectivity over dopamine D 2 receptors. This structural pattern considers a C5-substituted indole ring bearing different functional groups and a parasubstituted arylpiperazine.…”

“…[11][12][13] As a consequence, many compounds containing this scaffold bind with high affinity at 5-HT 1A receptors, but only a few of them also show high selectivity for 5-HT 1A over other receptors. 14) Structure-activity relationship (SAR) studies, performed with numerous generations of arylpiperazine derivatives, showed that CNS activity and both, receptor affinity and selectivity depend basically on the N-1-aryl substituent and a terminal fragment bound to the N-4 atom of the piperazine moiety by an alkyl chain. In these studies, this alkyl spacer is frequently composed of two to four methylene units.…”