[[(Arylpiperazinyl)alkyl]thio]thieno[2,3-d]pyrimidinone derivatives as high-affinity, selective 5-HT1A receptor ligands

Thienopyrimidines. Part III. Synthesis of Novel Substituted Thieno[2,3-d]pyrimidinone Derivatives and their Condensed Products with Molluscicidal and Larvicidal activities

A range of novel substituted thieno[2,3- d]pyrimidinones are synthesized and screened for malluscicidal and larvicidal biological activity.

Synthetic route to 4,5-dihydro-9H-pyrido[1,2-a] thieno[3,2-e]pyrimidine derivatives through 1,3-dipolar cycloaddition

A synthetic route to the title heterocyclic system through 1,3-dipolar cycloaddition of the mesoionic compound 9 with DMAD is described. The structure elucidation of the above system is also reported.

Reactions with Hydrazonoyl Halides 601: Synthesis of Thieno[2′,3′:4,5] Pyrimidino[1,2-b][1,2,4,5]tetrazines, [1]benzothieno[2′,3′:4,5]pyrimidino [1,2-b][1,2,4,5]tetrazines, Pyrazolo[3′,4′:4,5]pyrimidino[1,2-b] [1,2,4,5]tetrazines and Pyrazolo[3,4-d]pyridazines

Thieno[2′,3′:4,5]pyrimidino[1,2- b][1,2,4,5]tetrazine, [1]benzothieno-[2′,3′:4,5]pyrimidino[1,2- b][1,2,4,5]tetrazine, pyrazolo [3′,4′:4,5]pyrimidino[1,2- b][1,2,4,5]tetrazine, triazolo[4,3- a]pyrimidin-5(1 H)-one, 1-{[2-(1-benzofuran-2-yl)-5-phenyl-4,5-dihydro-1 H-pyrazol-1-yl]-4-substituted-1,3-thiazol-5-yl}-2-phenyldiazene, 3-acyl-4-(1-benzofuran-2-ylcarbonyl) pyrazole and pyrazolo[3,4- d]pyridazine derivatives could be obtained via reactions of hydrazonoyl halides with the appropriate pyrimidine-2-thione, 3-amino-5,6-dimethyl-2-sulfanylthieno[2,3- d]pyrimidin-4(3 H)-one, 5-amino-6-mercapto-1-phenyl-1,5-dihydropyrazolo[3,4- d]pyrimidin-4-one and 1-(benzofuran-2-yl)-3-(dimethylamino)prop-2-en-1-one. Structures of the products have been determined by elemental analyses, spectral data studies and alternative synthesis whenever possible.

New N- and O-arylpiperazinylalkyl pyrimidines and 2-methylquinazolines derivatives as 5-HT7 and 5-HT1A receptor ligands: Synthesis, structure-activity relationships, and molecular modeling studies

Based on our earlier studies of structure activity relationships on 4-substituted piperazine derivatives, in this work we synthesized a novel set of long-chain arylpiperazines with the purpose of elucidating if some structural modifications in the terminal fragment could affect the binding affinity for the 5-HT₇ and 5-HT_1A receptors. In this new series, the quinazolinone system of the previous derivatives was replaced by a 6-phenylpyrimidine or a 2-methylquinazoline, which were used as versatile building blocks for the preparation of new compounds. A 4-arylpiperazine moiety through a five methylene chain was anchored at the nitrogen or oxygen atom of the heterocyclic scaffolds. The substituents borne by the piperazine nucleus were phenyl, phenylmethyl, 3- or 4-chlorophenyl, and 2-ethoxyphenyl. Binding tests, performed on human cloned 5-HT₇ and 5-HT_1A receptors, showed that, among the newly synthesized derivatives, 4-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentoxy]-6-phenyl-pyrimidine (13) and 3-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentyl]-2-methyl-4(3H)-quinazolinone (20) displayed the best affinity values, K_i=23.5 and 8.42nM for 5-HT₇ and 6.96 and 2.99nM for 5-HT_1A receptors, respectively. Moreover, the functional properties for both compounds were further evaluated using the cAMP assay. Finally, a molecular modeling study has been performed for 5-HT₇ and 5-HT_1A receptor homology models to investigate the binding mode of N- and O-alkylated pyrimidinones/pyrimidines 4-13, 2-methylquinazolinones/quinazolines 17-22, and previously reported 2- and 3-substituted quinazolinones 23-30.

Synthesis of 2-arylated thiadiazolopyrimidones by Suzuki–Miyaura cross-coupling: a new class of nucleotide pyrophosphatase (NPPs) inhibitors

Over expression of nucleotide pyrophosphatase (NPPs) activity is associated with chondrocalcinosis, osteoarthritis, type 2 diabetes, neurodegenerative diseases, allergies and cancer metastasis.

Discovery of a novel 5-HT(3) antagonist/5-HT(1A) agonist 3-amino-5,6,7,8-tetrahydro-2-{4-[4-(quinolin-2-yl)piperazin-1-yl]butyl}quinazolin-4(3H)-one (TZB-30878) as an orally bioavailable agent for irritable bowel syndrome

We have prepared a series of quinazolinone derivatives linked with piperazinylquinoline for the treatment of irritable bowel syndrome (IBS). Using pharmacophore analysis, we designed and synthesized compounds which bind to both serotonin receptor subtype 1A (5-HT(1A)) and subtype 3 (5-HT(3)). Quinazolinone derivatives with a sulfur atom in the linker showed high affinity in in vitro assays, but low in vivo activity. Focusing on the linker to improve the pharmacokinetic profile, the sulfur atom in the linker was replaced with a methylene group. Further optimization led to the discovery of compound 17m (TZB-30878) ( J. Pharmacol. Exp. Ther. 2007 , 322 , 1315 - 1323 , Patent WO2005082887 (A1), 2005 ), a novel 5-HT(1A) agonist/5-HT(3) antagonist in the 3-aminoquinazolinone series. In in vivo functional assays, 17m dose dependently inhibited the Bezold-Jarisch reflex and induced 5-HT(1A)-mediated behaviors, and in an IBS animal model, 17m significantly inhibited stress-induced defecation. Pretreatment by WAY-100635 (5-HT(1A) antagonist) significantly attenuated but did not abolish the inhibitory effects of 17m. These results suggested that 17m exerted inhibitory effects via both 5-HT(1A) agonistic and 5-HT(3) antagonistic activities and that 17m would be useful as a therapeutic agent for IBS.

Preparation of a 7-arylthieno[3,2-d]pyrimidin-4-amine library

A focused kinase library of 7-arylthieno[3,2-d]pyrimidin-4-amine analogues is readily prepared via solution-phase parallel synthesis. This strategy relies on a key cyclization of a 3-aminothiophene-2-carboxamide with a formamide to construct the thienopyrimidine core. Further elaborations of this core via substitution and Suzuki coupling reactions allow the introduction of other diversity points. This methodology is demonstrated through the preparation of a 72-membered library of 7-arylthieno[3,2-d]pyrimidin-4-amines in good yields and high purities.

Microwave Assisted Synthesis of Some Novel Thiadiazolothienopyrimidines

3-Amino-2-mercapto-3,5,6,7,8,9-hexahydro-4H-cyclohepta[4,5]thieno[2,3-d]pyrimidin-4-one (4) was prepared, and from this a series of 2-(arylaminomethyl)-7,8,9,10-tetrahydro-6H,11H-cyclohepta[4,5]thieno[2,3-d][1,3,4]thiadiazolo [3,2-a]pyrimidin-11-ones (6a–d) were synthesised through the corresponding 2-chloromethyl compound (5) with aromatic amines under microwave irradiation.

Synthesis of some new bioactive 3-amino-2-mercapto-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one derivatives

Nine new 2-(substituted phenyl)/alkyl[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-ones, six new 3-amino-2-[(2-oxo-2-(aryl)ethyl)thio]-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones, one 2-mercapto[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-one and one 2-chloromethyl[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-one were synthesized from 3-amino-2-mercapto-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one. The newly synthesized compounds were characterized by analytical and spectral data. Compounds were screened for anti-inflammatory, CNS depressant and antimicrobial activities. Some of the compounds exhibited promising biological activities.

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

Synthesis applied to prepare compounds 5-15 and 17-22 discussed in this paper has been presented in Scheme 1. Multi-stage preparation techniques were used to obtain 4-aryl-hexahydro 1-4 and (R,R) and (S,S) 4-aryl-octahydropyrido[1,2-c]pyrimidine-1,3-dione (16) derivatives, being the starting compounds for further modification. N-Alkylation of the imide group in compounds 1-4 and 16 followed, using 1,4-dibromobutane to yield monobromobutyl derivatives 5-8 and 17. Subsequent condensation of those compounds with appropriate 1-aryl or 1-heteroarylpiperazine led to the final hexahydro- 9-15 and octahydro- 18-22 pyrido[1,2-c]pyrimidine-1,3-dione derivatives. The final products were subjected to screening test to elucidate the affinity to 5-HT1A and 5-HT2A receptors.

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.

[1,2,4]Triazole derivatives as 5-HT(1A) serotonin receptor ligands

A series of new 4-amino-3-[3-[4-(2-methoxy or nitro phenyl)-1-piperazinyl] propyl]thio]-5-(substitutedphenyl)[1,2,4]triazoles 11a-t was synthesized in order to obtain compounds with high affinity and selectivity for 5-HT(1A) receptor over the alpha(1)-adrenoceptor. A series of isomeric 4-amino-2-[3-[4-(2-methoxy or nitro phenyl)-1-piperazinyl]propyl]-5-(substitutedphenyl)-2,4-dihydro-3H[1,2,4]triazole-3-thiones 12a-r was also isolated and characterized. New compounds were tested to evaluate their affinity for 5-HT(1A) receptor and alpha(1)-adrenoceptor in radioligand binding experiments. As a general trend, triazoles 11a-t showed a preferential affinity for the 5-HT(1A) receptor whereas isomeric 2,4-dihydro-3H[1,2,4]triazole-3-thiones 12a-r preferentially bind to the alpha(1)-adrenoceptor site. Several molecules showed affinities in the nanomolar range and 4-amino-3-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]thio]-5-(4-propyloxy-phenyl)[1,2,4]triazole (11o) was the most selective derivative for the 5-HT(1A) receptor (K(i) alpha(1)/K(i) 5-HT(1A)=55). The decrease in 5-HT(1A) receptor selectivity in 3-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]thio]-5-(substitutedphenyl)[1,2,4] triazole 14a-b, lacking in the amino group in 4-position of the triazole ring, in comparison with their analogues in the series 11a-t, suggest that the amino function represents a critical structural feature in determining 5-HT(1A) receptor selectivity in this class of compounds.

1,5-Benzodiazepine tricyclic derivatives exerting anti-inflammatory effects in mice by inhibiting interleukin-6 and prostaglandinE(2)production

The 1,4- and the 1,5-benzodiazepines (BDZ) are commonly used as anxiolytic and anticonvulsive drugs. It has been suggested that they influence, particularly through stimulation of peripheral BDZ receptors, some immune cell properties such as pro-inflammatory cytokine production. The availability of a new class of [1,2,4]triazolo[4,3-a][1,5]benzodiazepine derivatives (compounds IV), endowed with anti-inflammatory and/or analgesic properties but no anti-pentylenetetrazole activity, prompted us to investigate in more detail the anti-inflammatory properties of three selected compounds IV (N,N-dimethyl-1-phenyl-4H-[1,2,4]triazolo[4,3-a][1,5]benz- odiazepin-5-amine; N,N-dibutyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine; 1-methyl-N,N-dimethyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine) and one structurally related compound (1-phenyl-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5(6H)-one). These BDZ derivatives have lost their affinity for the central and peripheral BDZ receptors. The in vivo effect on leukocyte migration of these compounds was investigated by using the mouse air-pouch model of local inflammation. Compounds A and B, significantly inhibited the carrageenan-induced leukocyte recruitment in a dose-dependent manner starting from the dose of 50 mgkg(-1), whereas compound C was effective only at the higher dose of 100 mgkg(-1). Compound D did not exert such effects at any of the doses considered. The effect of compounds A, B and C on leukocyte recruitment was paralleled by a significant inhibition of interleukin-6 and prostaglandin E(2)production in the exudate, similarly to indomethacin, and by a partial reduction of vascular permeability. These features may be relevant for the design and development of innovative anti-inflammatory molecules among the 4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepin-5-amine derivatives.

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.

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.

3D-QSAR using 'multiconformer' alignment: the use of HASL in the analysis of 5-HT1A thienopyrimidinone ligands

The observed 5-HT1A and alpha1-adrenergic receptor (alpha1-AR) receptor binding properties of a series of 23 thienopyrimidinones were used to develop HASL 3D-QSAR models. A single, low energy conformer of the most active analogue in the series, which was consistent with NMR structural studies, was chosen as a template molecule. Alignments of all the molecules to the template were provided by an Amber/MM2 superposition force field. In this manner, each molecule was represented by five separate low energy conformers which were subsequently used in the generation of HASL 3D-QSAR models. Models derived from multiple conformers were found to exhibit enhanced predictivity compared to models based on single, low energy conformers. In addition, the use of contour imaging of HASL multi-conformer model interactions was found to lead to a more consistent interpretation of those molecular features most significant for 5-HT1A receptor binding.

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.

High potent and selective arylpiperazine derivatives as ligands for the 5-HT1A receptor

This paper reports the synthesis and affinities on the 5-HT1A versus the alpha1A receptors of new arylpiperazinylalkylthiothienopyrimidine and thiadiazole derivatives 16-24. Arylpiperazines 16-23 show affinities values in the nanomolar range for the 5-HT1A receptor. The compound 16 is highly potent (Ki 0.26 nM, selectivity 28), the derivatives 20 and 21 are less potent, but highly selective (Ki 9.40 and 5.06 nM, selectivity 207 and 73, respectively).

1-Substituted-4-[3-(1,2,3,4-tetrahydro-5- or 7-methoxynaphthalen-1-yl)propyl]piperazines: influence of the N-1 piperazine substituent on 5-HT1A receptor affinity and selectivity versus D2 and alpha1 receptors. Part 6

In the present paper, we report the synthesis and the binding profiles on 5-HT1A, D2, and alpha1 receptors of 1-substituted-4-[3-(5- or 7-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine derivatives 19-32 and some related heteroalkyl derivatives 33-35. The results obtained are compared to those previously reported for the 1-phenyl, 1-(2-methoxyphenyl), 1-(2-pyridyl) analogues 2-9. The results pointed out the critical role of the group linked in the N-1 position of the piperazine in terms of 5-HT1A binding affinity. In fact, 1-cyclohexyl, 1-(3-benzisoxazolyl), 1-(benzothiazole-2-carbonyl), 1-(2-benzothiazolyl), 1-(2-quinolyl) substituted piperazines 21-30 displayed moderate or low 5-HT1A receptor affinity; on the contrary, 1-(3-benzisothiazolyl) and 1-(1-naphthalenyl) substituted piperazines 19, 20 and 32 displayed high 5-HT1A receptor affinity, the Ki values being in the subnanomolar range. Furthermore, compounds 19, 20 and 32 demonstrated better selectivity over alpha1 receptors than the reference compounds 2-9.

The 5-HT1A receptor and its ligands: structure and function

An overview is presented on progress made in research on 5-HT1A receptors and their ligands since their discovery in 1983. Molecular biology has offered new tools, for example cloned 5-HT1A receptors, their mutants and chimeras to study structure and function. Many compounds, belonging to different chemical classes, display high affinity and selectivity for 5-HT1A receptors. The majority of these compounds are agonists or partial agonists, full antagonists are still scarce. Agonists and partial agonists are active in various animal models of anxiety and depression. Partial receptor agonists have been proven to be effective in general anxiety disorder and depression in man. Potential therapeutic applications for 5-HT1A receptor antagonists are evaluated, for example, in cognition disorders.

2-[4-[3-(4-aryl/heteroaryl-1-piperazinyl)propoxy]phenyl]-2H- benzotriazoles and their N-oxides as ligands for serotonin and dopamine receptors

A small set of 2-{4-[3-(4-aryl/heteroaryl-piperazinyl)propoxy]phenyl}-2H-benzo tri azoles and corresponding N-oxides were prepared. The synthesized compounds were able to bind on some serotonin (5-HT1A, 5-HT2A) and dopamine (D2, D3) receptors, while displaying poor or no affinity for 5-HT1B, 5-HT2C, 5-HT3, and 5-HT4 subtypes. The strong contribution of the N-oxide function for the binding on 5-HT1A, D2 and D3 receptors is noteworthy. For 2-{4-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propoxy]phenyl}-2H-benzotr iazole- 1-oxide (4b), the binding constants (Ki) were 11.9 (5-HT1A) and 10.5 nM (D3). In a general pharmacological screening, the 2-{4-[3-(4-phenyl-1-piperazinyl)propoxy]phenyl}-2H-benzotriazole (3a) exhibited only very weak activities, with the exception of protecting mice from cyanide-induced hypoxia.

N-substituted-3-arylpyrrolidines: potent and selective ligands at serotonin 1A receptor

3-Arylpyrrolidines are synthesized through the coupling of N-benzyl-3-(methanesulfonyloxy)pyrrolidine with diarylcuprates. Pharmacological evaluation of a series of N-substituted-3-arylpyrrolidines toward several neurotransmitter receptors indicated that some of them are good ligands for serotonin 1A receptor. Particularly, N-[(N-saccharino)butyl]pyrrolidines were found to be potent and selective ligands. A preliminary biological evaluation for several selected compounds indicated that they are potentially effective antianxiety and antidepressant agents.

New Synthetic Approaches to Fused Heterocyclo-quinazolines

Fused heterocyclo-quinazolines have been prepared from the versatile and easily obtained intermediate 3-amino-2,3-dihydro-2-thioxo-4(1 H)-quinazolinone 2; their structural elucidation is also reported.

Synthesis and structure-activity relationships of a new model of arylpiperazines. 4. 1-[omega-(4-Arylpiperazin-1-yl)alkyl]-3-(diphenylmethylene) - 2, 5-pyrrolidinediones and -3-(9H-fluoren-9-ylidene)-2, 5-pyrrolidinediones: study of the steric requirements of the terminal amide fragment on 5-HT1A affinity/selectivity

In the present paper, we report the synthesis and the binding profile on 5-HT1A, alpha1 and D2 receptors of a new series of 1-[omega-(4-arylpiperazin-1-yl)alkyl]-3-(diphenylmethylene)- 2, 5-pyrrolidinediones (III) (1-4) and -3-(9H-fluoren-9-ylidene)-2, 5-pyrrolidinediones (IV) (1-4), in which the alkyl linker contains 1-4 methylenes and the aryl group is variously substituted. The results obtained are compared to those previously reported for bicyclohydantoin (I) and the related bicyclic amine (II) series. A considerable part of the tested compounds 1-4 demonstrated moderate to high affinity for 5-HT1A and alpha1 receptor binding sites but had no affinity for D2 receptors. The study of the length of the alkyl chain and the imide substructure has allowed us to suggest some differences between the 5-HT1A and the alpha1-adrenergic receptors: (i) for III and IV, affinity for the 5-HT1A receptor as a function of the length of the methylene linker decreases in the order 4 > 1 >> 3 approximately 2, while for the alpha1 receptor affinity decreases in the order 3 approximately 4 > 1 approximately 2; (ii) the no-pharmacophoric steric pocket (receptor zone which does not hold the pharmacophore of the ligand but holds a nonessential fragment of the molecule) in the 5-HT1A receptor has less restriction than the corresponding pocket in the alpha1 receptor. Compounds 3a,e, which are highly selective for alpha1-adrenergic receptors, displayed antagonist activity. On the other hand, the best compromise between affinity and selectivity for 5-HT1A receptors is reached in these new series with n = 1, which is in agreement with our previous results for the bicyclohydantoin derivatives I. Two selected compounds (1d and 4e) retain agonist properties at postsynaptic 5-HT1A receptors. The same 5-HT1A agonist profile found in these compounds suggests the existence of two different no-pharmacophoric steric pockets in this receptor and a different interaction of compounds with n = 1 and n = 4. The information obtained from the interpretation of the energy minimization and 2D-NOESY experiments of compounds 1-4 together with the synthesis and binding data of new conformationally restrained analogues 4k-m is in good agreement with this working hypothesis.