Synthesis and pharmacological evaluation of carboxamide derivatives as selective serotoninergic 5-HT(4) receptor agonists

A number of new carboxamide derivatives were synthesized. The affinity of these compounds for the serotoninergic 5-HT(4) receptor was evaluated by use of radioligand-binding techniques. The agonistic activity was evaluated as the contractile effect of the ascending colon isolated from guinea-pigs. Among these compounds, 4-amino-5-chloro-2-methoxy-N-[1-[2-[(methylsulfonyl)amino]ethly]-4-piperidinylmethyl]benzamide (24) showed a high affinity for the 5-HT(4) receptor (Ki = 9.6 nM). Compound 24 displayed a higher affinity for 5-HT(4) receptors than the other receptors, including, 5-HT(3) and dopamine D(2) receptors. In addition, compound 24 was confirmed to be a potent 5-HT(4) receptor agonist (ED(50) = 7.0 nM). An interaction model between compound 24 and 5-HT(4) receptor was proposed.     

Synthesis of new hexahydro- and octahydropyrido[1,2-c]pyrimidine derivatives with an arylpiperazine moiety as ligands for 5-HT1A and 5-HT2A receptors. Part 4

New 4-aryl-2H-pyrido[1,2-c]pyrimidine-1,3-dione derivatives of arylpiperazine (6-18) were prepared and evaluated in vitro for their affinity for 5-HT1A, 5-HT2A, and alpha1 receptors. The influence of ortho substitution in the phenyl ring, substitution at position 4 of the pyrido[1,2-c]pyrimidine system, and its unsaturation degree were explored. The tested compounds showed high affinity for the 5-HT1A receptor (Ki = 1.3-79.2 nM) and moderate to low affinity for the 5-HT2A (Ki = 51.7-1405 nM) and alpha1 receptors (Ki = 19.7-382.3 nM). Compounds 8 and 10 showed the highest 5-HT1A receptor affinity (Ki = 1.3 and 2.2 nM, respectively) and were 37- and 35.9-fold, respectively, more selective in relation to alpha1 adrenoreceptors.     

High affinity and selectivity of [[(arylpiperazinyl)alkyl]thio]thieno[2,3-d]pyrimidinone derivatives for the 5-HT(1A) receptor. Synthesis and structure-affinity relationships

In this work we report the affinity of new thienopyrimidinones for 5-HT(1A)Rs and the selectivity versus alpha(1)ARs. The 3-amino-2-[[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]thio]-6-ethyl -thieno[2,3-d]pyrimidin-4(3H)-one 27 is the most potent and selective (Ki 0.19 nM, selectivity 115). Compound 31 with the N4 piperazine orthonitrophenyl nucleus instead of the orthomethoxyphenyl also shows a good affinity and selectivity (Ki 1. 46 nM, selectivity 84). The results of derivatives 28, 29 and 30 (Ki 3.28, 12.59 and 4.38 nM; selectivity 24, 4 and 5, respectively), which have, respectively, an ethyl, an allyl and an acetylamino group instead of an N3 amino group, indicate the importance of this last group for the interaction with 5-HT(1A)R. Comparison of the results for the superior homologue 53 (Ki 3.72 nM, selectivity 51) and the inferior homologue 52 (5-HT(1A) Ki 1499 nM, alpha(1)A Ki NA) of 2-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-6,7-dimethyl-8H-[1, 3,4]thiadiazolo[3,2-a]thieno[2,3-d]pyrimidin-8-one 57 (Ki 23 nM, selectivity 5) shows how important the length of the chain binding the two heterocyclic systems is in the interaction with 5-HT(1A)Rs and alpha(1)ARs.     

Design, synthesis and binding properties of novel and selective 5-HT3 and 5-HT4 receptor ligands

This work reports the synthesis and the binding tests on the 5-HT3 and 5-HT4 receptors of new thienopyrimidopiperazine and piperazinylacylaminodimethylthiophene derivatives, in order to identify potent and selective ligands for each receptor. The 3-amino-2-(4-benzyl-1-piperazinyl)-5,6-dimethyl-thieno[2,3-d]pyrimidin-4(3H)-one derivative 28 showed the highest affinity and selectivity for the 5-HT3 over the 5-HT4 receptor (5-HT3 Ki=3.92 nM, 5-HT4 not active), whereas the 2-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butanoylamino]-4,5-dimethyl-3-thiophenecarboxylic acid ethyl ester (41) showed the highest affinity and selectivity for the 5-HT4 over the 5-HT3 receptor (5-HT4 Ki=81.3 nM, 5-HT3 not active). Conformational analyses were carried out on the compounds of the piperazinylacylaminodimethylthiophene series (39-42) taking compound 41 as the template.     

Synthesis and 5-HT(1A), 5-HT(2A) receptor activity of new beta-tetralonohydantoins

A series of new 3-[4-(4-arylpiperazinyl)-butyl]-beta-tetralonohydantoins (8a-13a) were synthesized. The compounds exhibited high affinity for 5-HT(1A) receptors (K(i)=6 to 55 nM) combined with moderate-to-high 5-HT(2A) receptor affinities (K(i)=45 to 213 nM). The results of in vivo studies indicated that of the compounds tested, 3-[4-(4-phenylpiperazinyl)-butyl-beta-tetralonohydantoin (8a) showed features of full (pre- and postsynaptic) 5-HT(1A) receptor agonists, whereas compounds 9a-13a behaved like antagonists of postsynaptic 5-HT(1A) receptors; additionally, compound 13a produced an effect characteristic of presynaptic 5-HT(1A) receptor agonists. Moreover, compounds 8a and 10a-13a exhibited properties of 5-HT(2A) receptor antagonists. Due to the most interesting 5-HT(1A)/5-HT(2A) functional profile compounds 8a and 13a were further tested for their potential psychotropic activity. In fact, compound 8a (but not 13a) showed diazepam-like anxiolytic activity and behaved like a weak antidepressant.     

New 3-[4-(aryl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propane derivatives with dual action at 5-HT1A serotonin receptors and serotonin transporter as a new class of antidepressants

A series of new 3-[4-(aryl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propane derivatives were synthesized in an attempt to find a new class of antidepressant drugs with dual activity at 5-HT1A serotonin receptors and serotonin transporter. Title compounds were evaluated for in vitro activity on 5-HT1A receptor and 5-HT transporter. They show high nanomolar affinity for both activities, and in particular, compounds 1-(5-chlorobenzo[b]thiophen-3-yl)-3-[4-(2-methoxyphenyl)piperazin-1-yl]propan-1-ol (7) and 1-(5-fluorobenzo[b]thiophen-3-yl)-3-[4-(2-methoxyphenyl)piperazin-1-yl]propan-1-ol (8) show values (nM) of K(i)=30 and 2.3 for 5-HT1A receptors and K(i)=30 and 12 for serotonin transporters, respectively. In GTPgammaS binding assays, compound 8 revealed antagonist properties to 5-HT1A receptors. Such a pharmacological profile could lead to potent antidepressant agents with new dual mechanism of action.     

Substituted benzylaminoalkylindoles with preference for the sigma2 binding site

In the attempt to develop new sigma ligands we synthesized a series of N-benzyl-3-[1-(4-fluorophenyl)-1H-indol-3-yl]-N-methylpropan-1-amines and N-benzyl-4-[1-(4-fluorophenyl)-1H-indol-3-yl]-N-methylbutan-1-amines variously substituted on the phenyl ring. The displacement percentages of [3H]-DTG and [3H]-(+)-pentazocine determined in rat liver homogenates by these compounds at the fixed 100 nM concentration have been determined as a preliminary evaluation of their sigma1 and sigma2 affinity, respectively. The results suggested that the phenyl substituents may positively modulate, in comparison with the unsubstituted compound, the ability to displace [3H]-DTG from sigma2 sites, whereas the same phenyl substituents reduced the displacement percentages of [3H]-(+)-pentazocine from sigma1 sites. Some of these compounds were selected for radioligand binding assays. Compounds with a butylene intermediate chain displayed the greatest binding affinity for sigma2 over sigma1 receptors. The butylene derivative with 2,4-dimethyl substitution on the phenyl ring showed the greatest sigma2 affinity (sigma2Ki=5.9 nM) and an appreciable sigma2 over sigma1 selectivity (sigma1Ki/sigma2Ki=22). The obtained results suggest that a butylene chain separating the indole moiety from variously substituted benzylamino groups may be required to their interaction with a hypothetical secondary sigma2 binding site.     

The differential effects of food restriction on 5-HT1A and 5-HT1B receptor mediated control of serotonergic transmission in the hippocampus and hypothalamus of rats

Serotonergic pathways are considered important in the regulation of appetite. We have determined, in female rats, the effects of 4 weeks food restriction (FR) on serotonin function, using in vivo microdialysis. We recorded basal 5-HT release in the hypothalamus and hippocampus, and the sensitivity of the somatodendritic 5-HT1A autoreceptors in the raphe nuclei, and the nerve terminal 5-HT1B autoreceptors which together regulate the synthesis and release of 5-HT in these regions. Sensitivity of the somatodendritic 5-HT1A autoreceptors was assessed by measuring the reduction in extracellular 5-HT induced by systemic administration of the 5-HT1A receptor agonist 8-hydroxy-2-di-n-(propylamino)-tetralin (8-OH-DPAT), while sensitivity of nerve terminal 5-HT1B autoreceptors was measured by observing the increase in 5-HT release after systemic injection of the 5-HT1B receptor antagonist GR 127935. Basal release of 5-HT was not affected by FR. 8-OH-DPAT decreased 5-HT release in the hippocampus and hypothalamus in both groups, while GR 127935 increased 5-HT release in both areas in the control animals but not in the hypothalamus of the FR animals. Since 5-HT1B receptors regulate 5-HT release by a negative feedback mechanism, the decrease in sensitivity of 5-HT1B receptors in the hypothalamus of FR rats indicates increased serotonergic transmission in these rats. The fact that such differential effects on 5-HT release appeared only in the hypothalamus, the center of regulation of energy balance, suggests a compensatory role in FR by increasing 5-HT secretion, thereby reducing feeding behavior.     

Synthesis and biological investigation of potential atypical antipsychotics with a tropane core. Part 1

The synthesis, structure, in vitro and in vivo pharmacological activities of 3β-acylamine derivatives of tropane (4a-n, 5a-g, 6a,b, 8a-c) are described. Among the investigated compounds, several displayed very high (in nM) affinity for the monoamine receptors 5-HT(1A), 5-HT(2A,) and D(2). The most interesting agent 6b revealed very high affinity for the 5-HT(2A) and D(2) receptors and high affinity for the 5-HT(1A) receptor. The in vivo head twitch model was used to demonstrate antagonism of the 5-HT(2A) receptor subtype by this compound. In another test, 6b caused hypothermia in mice, which was not attenuated by WAY 100635. In the climbing test, the compound did not significantly modify climbing behaviour following apomorphine administration. Moreover, 6b significantly reduced locomotor activity in mice. Molecular docking studies using a homology model of the 5-HT(1A) receptor revealed a significant role of the N-8 atom of the tropane core in stabilising the ligand-receptor complex due to strong hydrogen bonding with Asp116 located in the TMH 3 helix. Analogically, in a homology model of the 5-HT(2A) receptor, the N-8 atom formed a hydrogen bond with Gly369. In another homology model of the D(2) receptor, strong hydrogen bonding of the amide moiety in the 3β position of the tropane nucleus with Asp85 was observed. Compound 6b displayed a favourable Meltzer index (1.21) which is a feature of atypical antipsychotic agents.     

Design, synthesis and binding properties of novel and selective 5-HT(3) and 5-HT(4) receptor ligands

This work reports the synthesis and the binding tests on the 5-HT(3) and 5-HT(4) receptors of new thienopyrimidopiperazine and piperazinylacylaminodimethylthiophene derivatives, in order to identify potent and selective ligands for each receptor. The compound with higher affinity and selectivity for the 5-HT(3) over the 5-HT(4) receptor was the 3-amino-2-(4-benzyl-1-piperazinyl)-5,6-dimethyl-thieno[2,3-d]pyrimidin-4(3H)-one 28 (5-HT(3) K(i)=3.92 nM, 5-HT(4) not active), the compound with higher affinity and selectivity for the 5-HT(4) over the 5-HT(3) receptor was the 2-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butanoylamino]-4,5-dimethyl-3-thiophenecarboxylic acid ethyl ester 41 (5-HT(4) K(i)=81.3 nM, 5-HT(3) not active). Conformational analyses were carried out on the compounds of the piperazinylacylaminodimethylthiophene series (39-42) taking compound 41 as the template.     

Butyrophenone analogues in the carbazole series as potential atypical antipsychotics: synthesis and determination of affinities at D(2), 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptors

We describe practical and efficient routes for synthesis of 2-aminomethyl-1,2,3,9-tetrahydro-4H-carbazol-4-ones using the Fischer indole synthesis or palladium-catalysed cyclization methodologies, as well as their affinities for D(2), 5-HT(2A) and 5-HT(2C) receptors, and their activity at the 5-HT(2B) receptor. The most active compounds, 4b (QF 2003B) and 4c (QF 2004B), with a pK(i) (5-HT(2A)/D(2)) ratio of 1.28 show a potential antipsychotic profile according to Meltzer's classification.     

New potent 5-HT(2A) receptor ligands containing an N'-cyanopicolinamidine nucleus: Synthesis and in vitro pharmacological evaluation

N'-cyanopicolinamidine derivatives, linked to an arylpiperazine moiety, were prepared and their affinity to serotonin 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptors were evaluated. The combination of structural elements (heterocyclic nucleus, alkyl chain and 4-substituted piperazine) known to be critical for affinity to 5-HT(1A) receptors and the proper selection of substituents led to compounds with high specificity and affinity towards serotoninergic receptors. In binding studies, several molecules showed affinity in nanomolar and subnanomolar range at 5-HT(2A) and moderate to no affinity for other relevant receptors (5-HT(1A), 5-HT(2C), D(1), D(2), α(1) and α(2)). N'-cyano-N-(3-(4-(3-chlorophenyl)piperazin-1-yl)propyl)-picolinamidine (4l) with K(i)=0.000185nM, was the most active and selective derivative for the 5-HT(2A) receptor compared to other serotoninergic, dopaminergic and adrenergic receptors.     

The Differential Effects of Food Restriction on 5-HT1A and 5-HT1B Receptor Mediated Control of Serotonergic Transmission in the Hippocampus and Hypothalamus of Rats

Abstract

Serotonergic pathways are considered important in the regulation of appetite. We have determined, in female rats, the effects of 4 weeks food restriction (FR) on serotonin function, using in vivo microdialysis. We recorded basal 5-HT release in the hypothalamus and hippocampus, and the sensitivity of the somatodendritic 5-HT<PRE>1A</PRE> autoreceptors in the raphe nuclei, and the nerve terminal 5-HT<PRE>1B</PRE> autoreceptors which together regulate the synthesis and release of 5-HT in these regions. Sensitivity of the somatodendritic 5-HT<PRE>1A</PRE> autoreceptors was assessed by measuring the reduction in extracellular 5-HT induced by systemic administration of the 5-HT<PRE>1A</PRE> receptor agonist 8-hydroxy-2-di-n-(propylamino)-tetralin (8-OH-DPAT), while sensitivity of nerve terminal 5-HT<PRE>1B</PRE> autoreceptors was measured by observing the increase in 5-HT release after systemic injection of the 5-HT<PRE>1B</PRE> receptor antagonist GR 127935. Basal release of 5-HT was not affected by FR. 8-OH-DPAT decreased 5-HT release in the hippocampus and hypothalamus in both groups, while GR 127935 increased 5-HT release in both areas in the control animals but not in the hypothalamus of the FR animals. Since 5-HT<PRE>1B</PRE> receptors regulate 5-HT release by a negative feedback mechanism, the decrease in sensitivity of 5-HT<PRE>1B</PRE> receptors in the hypothalamus of FR rats indicates increased serotonergic transmission in these rats. The fact that such differential effects on 5-HT release appeared only in the hypothalamus, the center of regulation of energy balance, suggests a compensatory role in FR by increasing 5-HT secretion, thereby reducing feeding behavior.     

Synthesis, anticonvulsant activity and 5-HT1A, 5-HT2A receptor affinity of new N-[(4-arylpiperazin-1-yl)-alkyl] derivatives of 2-azaspiro[4.4]nonane and [4.5]decane-1,3-dione

The synthesis, physicochemical and pharmacological properties of new N-[(4-arylpiperazin-1-yl)-alkyl]-2-azaspiro[4.4]nonane- (8a-c, 10a-d) and [4.5]decane-1,3-dione (9a-c, 11a-d) derivatives were described. The antiepileptic effects of those compounds were examined by a maximal electroshock (MES) and a pentylenetetrazole (sc. PTZ) tests, and their neurotoxicity was determined using a rota-rod test. Compounds 8c, 9c, 10c, d, 11c, d with a CF(3) group at the 3-position of the 4-arylpiperazine fragment exhibited anti-seizure properties in the MES model; in contrast, their 2-CH(3) and 2-OCH(3) analogues were inactive in both the tests used. Moreover, since the investigated compounds belong to the class of long-chain arylpiperazines, their serotonin 5-HT(1A) and 5-HT(2A) receptor affinity was determined. The relationship between the length of alkylene spacer and 5-HT(1A)/5-HT(2A) receptor activity was observed. Compounds with an ethylene and a propylene bridge (10a-d and 11a-d) were 3-80-fold more potent (K(i) ranged from 3.1 to 94 nM for 5-HT(1A) and 32-465 nM for 5-HT(2A)) than their methylene analogues (8a-c and 9a-c; K(i) ranged from 81 to 370 nM for 5-HT(1A) and 126-1370 nM for 5-HT(2A)). The highest 5-HT(1A) receptor affinity was displayed by 2-OCH(3) and 3-CF(3) phenyl derivatives (10b, 11b: K(i)=6.8 and 5.7 nM, respectively, and 10c, 11c: K(i)=6.0 and 3.1 nM, respectively), while in the case of 5-HT(2A) receptor the highest affinity was observed for the 3-CF(3) phenyl derivatives 10c, d, 11c, d (K(i) ranged from 32 to 86 nM).     

Synthesis by microwave irradiation and binding properties of novel 5-HT(1A) receptor ligands.

This work reports the synthesis by microwave irradiation and the binding tests on the 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptors of new substituted piperazines in order to identify selective ligands for 5-HT(1A) subtype receptor. Conventional heating and microwave irradiation of the reactions was compared. Synthesis by microwave irradiation gave the desired compounds in better yields than those obtained by conventional heating. The overall times for the syntheses were considerably reduced. Some resulting active compounds (29 and 39) were characterised by a good selectivity profile for the 5-HT(1A) subtype receptor. The more active compounds were selected and further evaluated for their binding affinities on D(1), D(2) dopaminergic and alpha(1), alpha(2) adrenergic receptors. The compound with higher affinity and selectivity for the 5-HT(1A) over all the considered receptors was the 3-[4-[4-(1,2,3,4-tetrahydronaphthyl)-1-piperazinyl]butan]-benzotriazinone (-)29 (5-HT(1A) K(i)=36 nM, other receptors not active).     

Synthesis and binding studies of epibatidine analogues as ligands for the nicotinic acetylcholine receptors

Neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane ligand-gated ion channels. Recent research demonstrated that selective nAChR ligands may have therapeutic potential in a number of CNS diseases and disorders. The alkaloid epibatidine is a highly potent non-opioid analgesic and nAChR agonist, but too toxic to be a useful ligand. To develop ligands selective for distinct nAChR subtypes and with reduced toxicity, a series of epibatidine and homoepibatidine analogues were synthesized. (+/-)-8-Methyl-3-(pyridin-3-yl)-8-azabicyclo[3,2,1]oct-2-ene, showed high affinity towards alpha4beta2 (Ki=2 nM), subtype selectivity (alpha4beta2/alpha7 affinity ratio>100) and relatively low toxicity in mice and can be labeled with 11C and 18F as positron emission tomography (PET) tracers for imaging of nAChRs.     

Alterations in serotonin receptor subtypes in ethanol-dependent rats.

Serotonin (5-HT) receptor subtypes were investigated during severe ethanol intoxication and withdrawal. Ethanol was administered intragastrically five times a day for 4 days (12 g/kg per day). 5-HT receptor subtypes were studied: (1) in severely intoxicated animals (mean blood ethanol concentration (BEC) = 4.7 g/l); (2) during the withdrawal reaction; and (3) in a control group. The maximal density of [3H] 8-hydroxy-2-(di-n- propylamino)tetralin [( 3H] 8-OH-DPAT) binding (Bmax) to 5-HT1a receptors was decreased by 25 and 17% in the hippocampus during chronic ethanol intoxication and withdrawal, respectively. [3H]Ketanserin binding to 5-HT2 receptors in the cortex, (-)[125I]-iodo-cyanopindolol [( 125I]CYP) binding to 5-HT1b receptors in the striatum and hypothalamus, and [3H] 8-OH-DPAT binding in the cortex were not affected by chronic ethanol administration. Previous in vitro experiments have shown that 5-HT1a receptors in the hippocampus are inhibitory. The down-regulation of these receptors may play a role in physical ethanol dependence, by inducing hyperexcitability of the hippocampus.     

Active conformation of some arylpiperazine postsynaptic 5-HT(1A) receptor antagonists

The synthesis and pharmacological properties of novel conformationally restricted arylpiperazine (2b-4b) or 1,2,3,4-tetrahydroisoquinoline (5b and 6b) derivatives of the known, flexible 5-HT(1A) receptor ligands 2a-6a (K(i)=0.95-7 nM) with different intrinsic activities are reported. Replacement of a tetramethylene chain with a 1e,4e-disubstituted cyclohexane ring in the structure of flexible ligands resulted in insignificant diminution of the 5-HT(1A) receptor affinity in the case of 2b-4b (K(i)=15-52 nM), whereas derivatives 5b and 6b were practically inactive (K(i)>1354 nM). The results of in vivo behavioural tests showed that 2a and 3a acted as postsynaptic 5-HT(1A) receptor partial agonists. Like the flexible 4a, the new rigid compounds 2b-4b showed features of postsynaptic 5-HT(1A) receptor antagonists. Since all possible conformations of the constrained compounds belong to an extended family--as indicated by molecular modelling studies--our hypothesis that such conformations are responsible for the blockade of postsynaptic 5-HT(1A) receptors has been confirmed. Determination of regions explored by terminal amide, or imide and hydrocarbon groups of the restricted compounds as well as the results of in vitro and in vivo studies allowed us to discuss the bioactive conformations of flexible ligands.     

Synthesis of 4-(aminoalkyl) substituted 1,3-dioxanes as potent NMDA and σ receptor antagonists

Elongation of the distance between the oxygen heterocycle and the basic amino moiety or ring expansion of the oxygen heterocycle of the NMDA receptor antagonists dexoxadrol and etoxadrol led to compounds with promising NMDA receptor affinity. Herein the combination of both structural features, i.e. elongation of the O-heterocycle--amine distance with a 1,3-dioxane ring is envisaged. The synthesis of aminoethyl-1,3-dioxanes 13, 22, 23 and 29 was performed by transacetalization of various acetals with pentane-1,3,5-triol, activation of the remaining free OH moiety with tosyl chloride and subsequent nucleophilic substitution. The corresponding 3-aminopropyl derivatives 33-35 were prepared by substitution of the tosylates with KCN and LiAlH4 reduction. The highest NMDA receptor affinity was found for 1,3-dioxanes with a phenyl and an ethyl residue at the acetalic position (23) followed by diphenyl (22) and monophenyl derivatives (13). Generally the NMDA affinity of primary amines is higher than the NMDA affinity of secondary and tertiary amines. Altogether the primary amine 23a (Ki=24 nM) represents the most promising NMDA receptor antagonist of this series exceeding the NMDA affinity of the mono-homologues (2-aminoethyl)-1,3-dioxolanes (3,4) and (aminomethyl)-1,3-dioxanes (5,6). Whereas the primary amine 23a turned out to be selective against σ1 and σ2 receptors the benzylamine 13d was identified as potent (Ki=19 nM) and selective σ1 antagonist, which showed extraordinarily high antiallodynic activity in the capsaicin assay.