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.     

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).     

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.     

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, binding properties and receptor docking of 4-halo-6-[2-(4-arylpiperazin-1-yl)ethyl]-1H-benzimidazoles, mixed ligands of D2 and 5-HT1A receptors

In this publication we are describing synthesis, binding properties, and receptor docking of 4-halo-6-[2-(4-arylpiperazin-1-yl)ethyl]-1H-benzimidazoles, a new compounds with potential antipsychotics properties. Affinity towards the dopamine D(1)-like and D(2)-like, and serotonin 5-HT(1A) receptors was evaluated using the radioligand binding assays. All compounds tested had affinity for the D(2)-like and 5-HT(1A) receptors, but were inactive towards the D(1)-like receptor. Halogenated 6-[2-(4-arylpiperazin-1-yl)ethyl]-1H-benzimidazoles showed higher affinity compared to their nonhalogenated congeners. In silico docking analysis of selected ligands was performed in order to explain the results of binding assays. Our analysis suggests that stabilizing interactions between the halogen atom at the benzimidazole ring and the Ser-122 of the D(2)-like and Trp-358 of the 5-HT(1A) receptor. Energy contributions for these interactions were calculated using the ab initio method.     

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 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, 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).     

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 serotonergic activity of variously substituted (3-amido)phenylpiperazine derivatives and benzothiophene-4-piperazine derivatives: novel antagonists for the vascular 5-HT1B receptor

The synthesis and vascular 5-HT(1B) receptor activity of a novel series of substituted 3-amido phenylpiperazine and 4-(4-methyl-1-piperazinyl)-1-benzo[b]thiophene derivatives is described. Modifications to the amido linked sidechains of the 3-amidophenyl-piperazine derivatives and to the 2-sidechain of the 1-benzo[b]thiophene derivatives have been explored. Several compounds were identified which exhibited affinity at the vascular 5-HT(1B) receptor of pK(B) > 7.0. From the 3-amidophenyl-piperazine series, N-(4-(4-chlorophenyl)thiazol-2-yl-3-(4-methyl-1-piperazinyl)benzamide (30) and from the benzo[b]thiophene-4-piperazine series N-(2-ethylphenyl)-4-(4-methyl-1- piperazinyl)-1-benzo[b]thiophene-2-carboxamide (38) were identified as a highly potent, silent (as judged by the inability of angiotensin II to unmask 5-HT(1B) receptor mediated agonist activity in the rabbit femoral artery) and competitive vascular 5-HT(1B) receptor antagonist. The affinity of compounds from these two series of compounds for the vascular 5-HT(1B) receptor is discussed as well as a proposed mode of binding to the receptor pharmacophore.     

Synthesis and structure-activity relationships of new arylpiperazines: para substitution with electron-withdrawing groups decrease binding to 5-HT(1A) and D(2A) receptors

Compounds in which N-phenylpiperazines were linked by a propyloxy chain to position 6 or 7 of a coumarin ring were designed and synthesised, and their affinities for 5-HT(1A) and D(2A) receptors were determined by radioligand binding assays. The influence of para substitution in the phenyl ring, substitution at position 4 of the coumarin system, and the coumarin position at which the piperazinylalkyl chain is linked was explored. Electron-withdrawing phenyl ring substituents para to the piperazine strongly reduced activity at both receptors. Binding at 5HT(1A) was influenced by the bulk of substituents at position 4 of the coumarin system, and binding at D(2A) by their electronic properties. Neither binding affinity was significantly affected by whether the piperazinylalkyl chain was inserted at position 6 or 7 of the coumarin system.     

Synthesis of new carbon-11 labeled benzoxazole derivatives for PET imaging of 5-HT(3) receptor

5-HT(3) receptor is an attractive target for the development of therapeutic agents for use in brain, heart and cancer diseases, and imaging agents for use in biomedical imaging technique PET. Benzoxazole derivatives are a novel class of 5-HT(3) receptor partial agonists with high binding affinity. Carbon-11 labeled benzoxazole derivatives have been synthesized as new potential PET radioligands for imaging 5-HT(3) receptor. The target tracers were prepared by N-[(11)C]methylation of their corresponding precursors using [(11)C]CH(3)OTf and isolated by HPLC purification procedure in 40-50% radiochemical yields, which were decay corrected to the end of bombardment (EOB), based on [(11)C]CO(2). The overall synthesis time was 20-25min from EOB. The radiochemical purity was >99%, and specific activity was in a range of 74-111 GBq/micromol at the end of synthesis (EOS).     

The influence of an ethylene spacer on the 5-HT(1A) and 5-HT(2A) receptor affinity of arylpiperazine derivatives of amides with N-acylated amino acids and 3-differently substituted pyrrolidine-2,5-diones

A library of ethylene analogs of the previously described arylpiperazines with N-acylated amino acids was synthesized on SynPhase Lanterns and the library representatives were evaluated for their 5-HT(1A) and 5-HT(2A) receptor affinities. The obtained results were compared with those reported for compounds containing propylene and a butylene spacer and they revealed that 5-HT(1A) receptor affinity decreased proportionally with the length of the alkyl chain. Furthermore, the synthesized 3-cycloalkyl derivatives containing two methylene group spacers showed that the 3-position of pyrrolidine-2,5-dione preferred substituents of hydrophobic character.     

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.     

Optimization of a pharmacophore model for 5-HT4 agonists using CoMFA and receptor based alignment

Twenty two 5-HT4 agonists obtained from our laboratory and the recent literature were used to develop a CoMFA model to predict 5-HT4 agonist activity. Two models were produced and compared for predictivity, the first by alignments based on atom overlapping (model A) and the second by adding agonist binding site interacting points of the 5-HT4 receptor (model B). Comparison of the two models showed that the q2 value for model A was 0.564 vs. 0.582 for model B. Model B indicated that the predictive power model stems from far lower steric contributions, 0.270 compared to model A's 0.502. The dominant defining features were the electrostatic contributions for model B, 0.664 up from 0.477 in model A. The contributions from the LogP factor were minimal, 0.085 in both models. The synthesized compounds showed agonist activity at mumol level.     

Synthesis and preliminary pharmacological results on new naphthalene derivatives as 5-HT(4) receptor ligands

The indole derivative GR 113808 is currently used as the reference ligand for labelling the 5-HT(4) serotoninergic receptors. Previous works in our laboratories established the bioisosteric equivalency of the indole heterocycle and naphthalene in a series of melatonin receptor ligands. Based on this knowledge we designed new analogues of GR 113808 by introducing two bioisosteric modifications: firstly, the indole ring was replaced by a naphthalene one and secondly, the ester linkage was replaced by an amide group. Compound 8 emerged within this novel series as it displayed high and selective affinity at 5-HT(4) receptors (Ki 5-HT(4) = 6 nM, Ki 5-HT(3) = 100 nM, Ki values at other 5-HT receptors were higher than 1000 nM). Compound 8 is currently undergoing further pharmacological evaluation.     

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.     

Synthesis, dopamine D2 receptor binding studies and docking analysis of 5-[3-(4-arylpiperazin-1-yl)propyl]-1H-benzimidazole, 5-[2-(4-arylpiperazin-1-yl)ethoxy]-1H-benzimidazole and their analogs

5-[3-(4-Arylpiperazin-1-yl)propyl]-1H-benzimidazoles and 5-[2-(4-arylpiperazin-1-yl)ethoxy]-1H-benzimidazoles were synthesized and their affinity for the D1, D2 and 5-HT1A receptors examined. They expressed a rather high affinity for the D2 dopamine receptor. The main features of ligand-D2 receptor interactions revealed by docking analyses were: salt bridge between piperazine ring protonated N1 and Asp 86, hydrogen bonds of ligand bezimidazole part with Ser 141, Ser 122 and His 189, edge-to-face interactions of arylpiperazine aromatic ring with Phe 178, Tyr 216 and Trp 182 and hydrogen bond between ethereal oxygen in ethylenoxy ligands and hydrogen of Phe 185 or Trp 115. The most active 5-[2-[4-(2-methoxyphenyl)-piperazin-1-yl]ethoxy]-1,3-dihydro-2H-benzimidazole-2-thione (27) has a maximal number of attractive interactions. A satisfactory correlation between docking of the compounds into the D2 receptor and competition binding results was observed.     

Inhibition of monoamine oxidase types A and B by 2-aryl-4H-1,3,4-oxadiazin-5(6H)-one derivatives

Monoamine oxidase (MAO) assay specificity based on substrate specificity was investigated by substrate competition experiments. 10 μM serotonin (5-HT) and 5 μM β-phenylethylamine (PEA) were found to ensure total substrate specificity for, respectively, MAO types A and B.Twenty-five 2-aryl-4H-1,3,4-oxadiazin-5(6H)-one derivatives were synthesized and tested in vitro for their inhibitory effects on MAO A and B. Most of them inhibited preferentially MAO B. The 2-(4-biphenylyl)-4-(2-cyanoethyl)-4H-1,3,4-oxadiazin-5(6H)-one 32 was the most efficient MAO B inhibitor and acted as a competitive inhibitor on the two enzymes. Its K_i values for MAO A and B were 11 and 0.15 μM, respectively.Structure-activity relationships suggest that these oxadiazinones should interact with a hydrophobic site and a nucleophilic site on MAO B for binding, while the functional group of the N-4 substituent should compete with the substrate for the active site of the enzyme.