Synthesis and structure-affinity relationships of 1-[omega-(4-aryl-1-piperazinyl)alkyl]-1-aryl ketones as 5-HT(7) receptor ligands

Synthesis of ω-Chloroalkyl Aryl Ketones via C-C Bond Cleavage of tert-Cycloalkanols with Tetramethylammonium Hypochlorite

An oxidative C-C bond cleavage of tert-cycloalkanols with tetramethylammonium hypochlorite (TMAOCl) has been developed. TMAOCl is easy to prepare from tetramethylammonium hydroxide, and the combination of TMAOCl and AcOH effectively promoted the C-C bond cleavage in a two-phase system without additional phase-transfer reagents. Unstrained tert-cycloalkanols were transformed into ω-chloroalkyl aryl ketones in moderate to excellent yields under metal-free and mild reaction conditions.

Photoredox catalysis harvesting multiple photon or electrochemical energies

Photoredox catalysis (PRC) is a cutting-edge frontier for single electron-transfer (SET) reactions, enabling the generation of reactive intermediates for both oxidative and reductive processes via photon activation of a catalyst. Although this represents a significant step towards chemoselective and, more generally, sustainable chemistry, its efficacy is limited by the energy of visible light photons. Nowadays, excellent alternative conditions are available to overcome these limitations, harvesting two different but correlated concepts: the use of multi-photon processes such as consecutive photoinduced electron transfer (conPET) and the combination of photo- and electrochemistry in synthetic photoelectrochemistry (PEC). Herein, we review the most recent contributions to these fields in both oxidative and reductive activations of organic functional groups. New opportunities for organic chemists are captured, such as selective reactions employing super-oxidants and super-reductants to engage unactivated chemical feedstocks, and scalability up to gram scales in continuous flow. This review provides comparisons between the two techniques (multi-photon photoredox catalysis and PEC) to help the reader to fully understand their similarities, differences and potential applications and to therefore choose which method is the most appropriate for a given reaction, scale and purpose of a project.

Electrophotochemical Ring-Opening Bromination of tert-Cycloalkanols

An electrophotochemical ring-opening bromination of unstrained tert-cycloalkanols has been developed. This electrophotochemical method enables the oxidative transformation of cycloalkanols with 5- to 7-membered rings into synthetically useful ω-bromoketones without the use of chemical oxidants or transition-metal catalysts. Alkoxy radical species would be key intermediates in the present transformation, which generate through homolysis of the O-Br bond in hypobromite intermediates under visible light irradiation.

Serotonin Type 6 and 7 Receptors as a Novel Therapeutic Target for the Treatment of Schizophrenia

Schizophrenia is a serious disease of the central nervous system that affects a person's ability to think, feel and behave clearly. Even though the pathophysiological hypothesis of the disease is not clearly understood, dysfunction of dopamine, glutamate, serotonin and other neurotransmitters is widely believed to be involved. Serotonin within the synaptic vesicles functions as neurotransmitter and neurohormone in regulation of emotion, learning, memory, hormone release, cognition and motor function. Dysfunction of normal brain activity of serotonin is associated with schizophrenia. The role of serotonin 6 and 7 receptors in schizophrenia, interaction with neurotransmitters and the effect of drugs on those receptors in schizophrenia are the goal of this review. The aim of this review was to provide information for researchers and other scholars to identify the possible intervention points in the management of schizophrenia. The serotonin 6 and 7 receptors are associated with schizophrenia via modulating cyclic adenosine monophosphate, regulation of Fyn kinase and induction of structural plasticity. The above modulatory effects affect cholinergic, dopaminergic, glutamatergic, adrenergic and GABAergic systems. Recently, diverse numbers of selective agonist and antagonist ligands were developed for both receptors. SGS-518, ABT-354, Lu AE58054, SB-742,457, S-518, AVN-211, AVN-322, SYN-114 and SYN-120 are serotonin 6 receptor antagonists and aripiprazole-controlled release serotonin 7 receptor agonists under clinical trial for schizophrenia. Thus, research on novel drugs that act on serotonin 6 and 7 receptors likely facilitates the intervention into schizophrenia patients seeking better quality of life in the future.

Visible Light-Mediated [2 + 2] Cycloaddition Reactions of 1,4-Quinones and Terminal Alkynes

A single-step synthesis of 4-hydroxy-functionalized bi-aryl and aryl/alkyl ketones via oxidative coupling of terminal alkynes with benzoquinones is reported. Furthermore, with naphthoquinones, owing to the cross-resonance of carbonyl with the aromatic ring, alkene-alkyne cycloaddition is more favored to give four-membered carbocyclic adducts, thereby precluding the requirement of preactivated alkynes.

C-C Bond Formation of Benzyl Alcohols and Alkynes Using a Catalytic Amount of KOt Bu: Unusual Regioselectivity through a Radical Mechanism

We report a C-C bond-forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO^t Bu to form α-alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT₇, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT₇ plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT₇ activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT₇ in normal physiology and the therapeutic potential of this interesting drug target.

A Short and Efficient Total Synthesis of Ficuseptamines A and B

A rapid and efficient total synthesis of ficuseptamines A and B by a cross metathesis strategy is described.

3D QSAR based design of novel oxindole derivative as 5HT7 inhibitors

To understand the structural requirements of 5-hydroxytryptamine (5HT7) receptor inhibitors and to design new ligands against 5HT7 receptor with enhanced inhibitory potency, a three-dimensional quantitative structure-activity relationship study with comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) for a data set of 56 molecules consisting of oxindole, tetrahydronaphthalene, aryl ketone substituted arylpiperazinealkylamide derivatives was performed. Derived model showed good statistical reliability in terms of predicting 5HT7 inhibitory activity of the molecules, based on molecular property fields like steric, electrostatic, hydrophobic, hydrogen bond donor and hydrogen bond acceptor fields. This is evident from statistical parameters like conventional r2 and a cross validated (q2) values of 0.985, 0.743 for CoMFA and 0.970, 0.608 for CoMSIA, respectively. Predictive ability of the models to determine 5HT7 antagonistic activity is validated using a test set of 16 molecules that were not included in the training set. Predictive r2 obtained for the test set was 0.560 and 0.619 for CoMFA and CoMSIA, respectively. Steric, electrostatic fields majorly contributed toward activity which forms the basis for design of new molecules. Absorption, distribution, metabolism and elimination (ADME) calculation using QikProp 2.5 (Schrodinger 2010, Portland, OR) reveals that the molecules confer to Lipinski's rule of five in majority of the cases.

The arylpiperazine derivatives N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide and N-benzyl-4-(2-diphenyl)-1-piperazinehexanamide exert a long-lasting inhibition of human serotonin 5-HT7 receptor binding and cAMP signaling

We performed a detailed in vitro pharmacological characterization of two arylpiperazine derivatives, compound N-(4-cyanophenylmethyl)-4-(2-diphenyl)-1-piperazinehexanamide (LP-211) previously identified as a high-affinity brain penetrant ligand for 5-hydroxytryptamine (serotonin) type 7 (5-HT₇) receptors, and its analog N-benzyl-4-(2-diphenyl)-1-piperazinehexanamide (MEL-9). Both ligands exhibited competitive displacement of [³H]-(2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine ([³H]-SB-269970) radioligand binding and insurmountable antagonism of 5-carboxamidotryptamine (5-CT)-stimulated cyclic adenosine monophosphate (cAMP) signaling in human embryonic kidney (HEK293) cells stably expressing human 5-HT₇ receptors. They also inhibited forskolin-stimulated adenylate cyclase activity in 5-HT₇-expressing HEK293 cells but not in the parental cell line. The compounds elicited long-lasting (at least 24 h) concentration-dependent inhibition of radioligand binding at 5-HT₇-binding sites in whole-cell radioligand binding assays, after pretreatment of the cells with the compounds and subsequent compound removal. In cAMP assays, pretreatment of cells with the compounds rendered 5-HT₇ receptors unresponsive to 5-CT and also rendered 5-HT₇-expressing HEK293 cells unresponsive to forskolin. Compound 1-(2-biphenyl)piperazine (RA-7), a known active metabolite of LP-211 present in vivo, was able to partially inhibit 5-HT₇ radioligand binding in a long-lasting irreversible manner. Hence, LP-211 and MEL-9 were identified as high-affinity long-acting inhibitors of human 5-HT₇ receptor binding and function in cell lines. The detailed in vitro characterization of these two pharmacological tools targeting 5-HT₇ receptors may benefit the study of 5-HT₇ receptor function and it may lead to the development of novel selective pharmacological tools with defined functional properties at 5-HT₇ receptors.

Serotonin 5-HT7 receptor agents: Structure-activity relationships and potential therapeutic applications in central nervous system disorders

Since its discovery in the 1940s in serum, the mammalian intestinal mucosa, and in the central nervous system, serotonin (5-HT) has been shown to be involved in virtually all cognitive and behavioral human functions, and alterations in its neurochemistry have been implicated in the etiology of a plethora of neuropsychiatric disorders. The cloning of 5-HT receptor subtypes has been of importance in enabling them to be classified as specific protein molecules encoded by specific genes. The 5-HT(7) receptor is the most recently classified member of the serotonin receptor family. Since its identification, it has been the subject of intense research efforts driven by its presence in functionally relevant regions of the brain. The availability of some selective antagonists and agonists, in combination with genetically modified mice lacking the 5-HT(7) receptor, has allowed for a better understanding of the pathophysiological role of this receptor. This paper reviews data on localization and pharmacological properties of the 5-HT(7) receptor, and summarizes the results of structure-activity relationship studies aimed at the discovery of selective 5-HT(7) receptor ligands. Additionally, an overview of the potential therapeutic applications of 5-HT(7) receptor agonists and antagonists in central nervous system disorders is presented.

Studies on 1-arylpiperazine derivatives with affinity for rat 5-HT7 and 5-HT1A receptors

Several 1-aryl-4-(2-arylethyl)piperazine derivatives were synthesized and tested in-vitro for their binding affinity for 5-HT7 and 5-HT1A receptors. These compounds displayed 5-HT7 receptor affinity ranging between Ki = 474 nm and Ki = 8.2 nm, besides high affinity for the 5-HT1A receptor. Intrinsic activity of the most potent compounds was assessed. 4-[2-(3-Methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine (16) and 1-(1,2-benzisoxazol-3-yl)-4-[2-(3-methoxyphenyl)ethyl]piperazine (20) (Ki = 24.5 and 8.2 nm, respectively) behaved as partial agonist and full agonist, respectively, when tested for 5-HT7 receptor-mediated relaxation of substance P-induced guinea-pig ileum contraction.

Sulfonamides with the N-alkyl-N'-dialkylguanidine moiety as 5-HT7 receptor ligands

A series of arylsulfonamides containing guanidine incorporated in the structure of secondary amines (piperidine, piperazine) was synthesized on SynPhase Lanterns and evaluated for 5-HT(1A), 5-HT(2A), and 5-HT(7) receptors. The results demonstrated that N-alkyl-N'-dialkylguanidines displayed good 5-HT(7)/5-HT(1A) selectivity and may be regarded as promising structural core for development of 5-HT(7) ligands.

5-HT7 receptor activation inhibits mechanical hypersensitivity secondary to capsaicin sensitization in mice

This work aimed to evaluate the potential role of the 5-HT(7) receptor in nociception secondary to a sensitizing stimulus in mice. For this purpose, the effects of relevant ligands (5-HT(7) receptor agonists: AS-19, MSD-5a, E-55888; 5-HT(7) receptor antagonists: SB-258719, SB-269970; 5-HT(1A) receptor agonist: F-13640; 5-HT(1A) receptor antagonist: WAY-100635) were assessed on capsaicin-induced mechanical hypersensitivity, a pain behavior involving hypersensitivity of dorsal horn neurons (central sensitization). For the 5-HT(7) receptor agonists used, binding profile and intrinsic efficacy to stimulate cAMP formation in HEK-293F cells expressing the human 5-HT(7) receptor were also evaluated. AS-19 and E-55888 were selective for 5-HT(7) receptors. E-55888 was a full agonist whereas AS-19 and MSD-5a behaved as partial agonists, with maximal effects corresponding to 77% and 61%, respectively, of the cAMP response evoked by the full agonist 5-HT. Our in vivo results revealed that systemic administration of 5-HT(7) receptor agonists exerted a clear-cut dose-dependent antinociceptive effect that was prevented by 5-HT(7) receptor antagonists, but not by the 5-HT(1A) receptor antagonist. The order of efficacy (E-55888>AS-19>MSD-5a) matched their in vitro efficacy as 5-HT(7) receptor agonists. Contrary to agonists, a dose-dependent promotion of mechanical hypersensitivity was observed after administration of 5-HT(7) receptor antagonists, substantiating the involvement of the 5-HT(7) receptor in the control of capsaicin-induced mechanical hypersensitivity. These findings suggest that serotonin exerts an inhibitory role in the control of nociception through activation of 5-HT(7) receptors, and point to a new potential therapeutic use of 5-HT(7) receptor agonists in the field of analgesia.

(Phenylpiperazinyl-butyl)oxindoles as selective 5-HT7 receptor antagonists

A series of potent 5-hydroxytryptamine 7 (5-HT 7) ligands has been synthesized that contain a 1,3-dihydro-2 H-indol-2-one (oxindole) skeleton. The binding of these compounds to the 5-HT 7 and 5-HT 1A receptors was measured. Despite the structural similarity of these two serotonin receptor subtypes, several derivatives exhibited a high selectivity to the 5-HT 7 receptor. According to the structure-activity relationship observations, compounds unsubstituted at the oxindole nitrogen atom and containing a tetramethylene spacer between the oxindole skeleton and the basic nitrogen atom are the most potent ligands. Concerning the basic group, besides the moieties of the 4-phenylpiperazine type, halophenyl-1,2,3,6-tetrahydropyridines also proved to be 5-HT 7 receptor-ligands. Because of halogen substitution on the aromatic rings, good metabolic stability could be achieved. A representative of the family, 3-{4-[4-(4-chlorophenyl)-piperazin-1-yl]-butyl}-3-ethyl-6-fluoro-1,3-dihydro-2 H-indol-2-one ( 9e') exhibited selective 5-HT 7 antagonist activity ( K i = 0.79 nM). The in vivo pharmacological potencies of these 5-HT 7 receptor-ligands were estimated by the conflict drinking (Vogel) and the light-dark anxiolytic tests.

Bivalent ligand approach on 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine: Synthesis and binding affinities for 5-HT7 and 5-HT1A receptors

We here report on the synthesis and binding properties at 5-HT(7) and 5-HT(1A) receptors of ligands 3-12, that were designed according to the 'bivalent ligand' approach. Two moieties of the 5-HT(7)/5-HT(1A) ligand 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine (1) were linked through their 3-methoxy substituent by polymethylene chains of variable length, with the aim to increase the affinity for 5-HT(7) receptor and the selectivity over 5-HT(1A) receptors. In the best cases, the dimers showed affinities for 5-HT(7) receptors as high as the monomer with no improvement in selectivity. Some dimers displayed 5-HT(1A) receptor affinities slightly higher than monomer 1.

Structure−Activity Relationship Study on N-(1,2,3,4-Tetrahydronaphthalen-1-yl)-4-aryl-1-piperazinehexanamides, a Class of 5-HT7 Receptor Agents. 2

Here we report the synthesis of N-(1,2,3,4-tetrahydronaphthalen-1-yl)-4-aryl-1-piperazinealkylamides 16-29 that were designed to elucidate both structure-affinity and -activity relationships for the 5-HT7 receptor, by targeting the substituent in 2-position of the aryl linked to the piperazine ring. The affinities of 16-29 for 5-HT7, 5-HT1A, 5-HT2A, and D2 receptors were assessed by radioligand binding assays. The intrinsic activities at the 5-HT7 receptor of the most potent compounds were determined. A series of substituents covering a wide range of electronic, steric, and polar properties was evaluated, revealing a key role on 5-HT7 receptor affinity and intrinsic activity. Certain lipophilic substituents (SCH3, CH(CH3)2, N(CH3)2, CH3, Ph) led to high-affinity agonists, whereas OH and NHCH3 substituents switched intrinsic activity toward antagonism. 4-[2-(1-Methylethyl)phenyl]-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (19), 4-(2-diphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (21), and 4-(2-dimethylaminophenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (22) were identified as potent 5-HT7 receptor agonists (Ki = 0.13-1.1 nM, EC50 = 0.90-1.77 microM), showing selectivity over 5-HT1A, 5-HT2A, and D2 receptors.

Novel aminoethylbiphenyls as 5-HT7 receptor ligands

The synthesis of a series of aminoethylbiphenyls as novel 5-HT(7) receptor ligands is described. The novel derivatives exhibit high affinity for the 5-HT(7) receptor with selectivity toward 5-HT(1A) receptor.

Receptor-based pharmacophores for serotonin 5-HT7R antagonists-implications to selectivity

A set of 31 diversified 5-HT7 receptor antagonists was automatically docked to a conformational ensemble of rhodopsin-based 5-HT7R models (flexible docking). It was found that ergolines, aporphines, and tricyclic psychotropic agents were always docked in a pocket formed by TMHs 4-6, and besides the main ionic bond with Asp3.32, they had specific interactions with Phe6.52, Phe6.51, Trp6.48, and Ser5.42. The arylpiperidine, arylpiperazine, or beta-carboline fragment of the complex ligands occupied the same pocket, whereas the terminal amide/imide part of those compounds reached the second cavity formed by TMHs 7-3 and interacted with Phe3.28, Arg7.36, and Tyr7.43. A similar orientation of selective antagonists of the group of arylsulfonamidoalkylamines was observed, that is, the sulfonamide part was located in the second pocket. Coherent docking results allowed the generation of two receptor-based pharmacophores: first containing features necessary for high 5-HT7R affinity and the other defining selectivity for this receptor subtype. The latter model indicated the importance of specific interactions with the residues of the TMHs 7-3 pocket (especially nonconserved Arg7.36) for selectivity over other monoamine GPCRs.

Aminoalkyl phenyl sulfones--a novel series of 5-HT7 receptor ligands

A novel series of 5-HT(7) receptor ligands has been identified and evaluated, providing compounds showing a broad spectrum of functional activities and good selectivity over selected receptors and ion channels.

Phenylpyrroles, a new chemolibrary virtual screening class of 5-HT7 receptor ligands

Virtual screening studies have identified a series of phenylpyrroles as novel 5-HT7 receptor ligands. The synthesis and the affinity for the 5-HT7 receptor of these phenylpyrroles are described. Some of these compounds exhibited high affinity for the 5-HT7 receptors.

Generalization of a targeted library design protocol: application to 5-HT7 receptor ligands

Herein a general concept for the design of targeted libraries for proteins with binding sites that are divided into subsites is laid out, including several practical aspects and their solutions. The design is based on a chemogenomic classification of the subsites followed by collection of bioactive molecular fragments and virtual library generation. The general process is outlined and applied to the assembly of a library of 500 molecules targeting the serotonin type 7 (5-HT7) receptor, a class A G-Protein Coupled Receptor (GPCR). Utilizing commercially available building blocks of similar size and composition, a reference library was created. Control sets of known ligands for the 5-HT7 receptor, other GPCRs, and nuclear receptors were collected from literature sources. Principal component analysis of molecular descriptors for the two libraries and the literature sets, displayed a focusing of the targeted library to the region in the chemical space defined by the literature actives, suggesting a denser coverage of the bioactive region than for the more diverse reference library. Additional computational validations, including PCA class predictions, 3D pharmacophore modeling, and docking calculations all indicated an enrichment factor of 5-HT7 ligand-like molecules in the range of 2-4 for the targeted library compared to the reference library.

Parallel solid-phase synthesis and characterization of new sulfonamide and carboxamide proline derivatives as potential CNS agents

A solid-phase synthesis of the 64-member library of novel sulfonamide and carboxamide proline derivatives, focused on the 5-HT7 receptor antagonist SB-258741, was described. The final compounds were obtained in good yields and high purity upon cleavage from SynPhase Lanterns, functionalized by a BAL linker. The library representatives were screened for 5-HT7, 5-HT1A and D2 receptors to explore the impact of a tertiary amine moiety, the length of an alkylene spacer and the aryl fragment on the receptor affinity. The preliminary biological results provided data for further investigation aimed at a search for 5-HT7 receptor agents, and permitted the identification of several compounds with significant 5-HT1A receptor affinity.

Novel 3-aminochromans as potential pharmacological tools for the serotonin 5-HT7 receptor

The synthesis of novel C6-aryl substituted derivatives of 3-(dimethylamino)chroman is described. The novel derivatives display 5-HT(7) receptor affinities that varies from nM to muM, indicating that this small set of derivatives constitute a novel and interesting starting point for further structure-serotonin 5-HT(7) activity relationship (SAR) studies.

Pre- and postsynaptic localization of the 5-HT7 receptor in rat dorsal spinal cord: Immunocytochemical evidence

Several lines of evidence indicate that 5-HT7 receptors are involved in pain control at the level of the spinal cord, although their mechanism of action is poorly understood. To provide a morphological basis for understanding the action of 5-HT on this receptor, we performed an immunocytochemical study of 5-HT7 receptor distribution at the lumbar level. 5-HT7 immunolabelling is localized mainly in the two superficial laminae of the dorsal horn and in small and medium-sized dorsal root ganglion cells, which is consistent with a predominant role in nociception. In addition, moderate labelling is found in the lumbar dorsolateral nucleus (Onuf's nucleus), suggesting involvement in the control of pelvic floor muscles. Electron microscopic examination of the dorsal horn revealed three main localizations: 1) a postsynaptic localization on peptidergic cell bodies in laminae I-III and in numerous dendrites; 2) a presynaptic localization on unmyelinated and thin myelinated peptidergic fibers (two types of axon terminals are observed, large ones, presumably of primary afferent origin, and smaller ones partially from intrinsic cells; this presynaptic labelling represents 60% and 22% of total labelling in laminae I and II, respectively); and 3) 16.9% of labelling in lamina I and 19.8% in lamina II are observed in astrocytes. Labeled astrocytes are either intermingled with neuronal elements or make astrocytic "feet" on blood vessels. In dendrites, the labelling is localized on synaptic differentiations, suggesting that 5-HT may act synaptically on the 5-HT7 receptor. This localization is compared with other 5-HT receptor localizations, and their physiological consequences are discussed.

Novel 5-HT7 receptor inverse agonists. Synthesis and molecular modeling of arylpiperazine- and 1,2,3,4-tetrahydroisoquinoline-based arylsulfonamides

A series of arylpiperazine- and 1,2,3,4-tetrahydroisoquinoline-based arylsulfonamides was synthesized and evaluated for their interactions with the constitutively active 5-HT7 receptor. Effects on basal adenylate cyclase activity were measured using HEK-293 cells expressing the rat 5-HT7. All ligands produced a decrease of adenylate cyclase activity, indicative of their inverse agonism. Additionally, computational studies with a set of 22 inverse agonists, including these novel inverse agonists and inverse agonists known from literature, resulted in a pharmacophore model and a CoMFA model (R2 = 0.97, SE = 0.18). Docking of inverse agonists at the binding site of a model of the helical parts of the 5-HT7 receptor, based on the alpha carbon template for 7-TM GPCRs, revealed interesting molecular interactions and a possible explanation for observed structure-activity relationships.

The impact of spacer structure on 5-HT7 and 5-HT1A receptor affinity in the group of long-chain arylpiperazine ligands

New cis-, trans-2-butene and 1,2-bismethylbenzene analogues of MM77 and NAN-190 (1-[4-[4-(2-methoxyphenyl)-piperazin-1-yl]-butyl]-pyrrolidine-2,5-dione and isoindole-1,3-dione, respectively) were synthesized. The differences in their in vitro affinity for serotonin 5-HT(7) and 5-HT(1A) receptors were explained using a conformational analysis. A bioactive conformation of those compounds for the 5-HT(7) receptor, different from that established for 5-HT(1A), was proposed.

Structure−Affinity Relationship Study onN-(1,2,3,4-Tetrahydronaphthalen-1-yl)-4-Aryl-1-Piperazinealkylamides, a New Class of 5-Hydroxytryptamine7Receptor Agents

A series of N-(1,2,3,4-tetrahydronaphthalen-1-yl)-4-aryl-1-piperazinealkylamides was prepared and their affinity for serotonin (5-hydroxytryptamine, 5-HT) 5-HT7, 5-HT(1A), and 5-HT(2A) receptors was measured by in vitro binding assays. In relation to 5-HT7 receptor affinity, receptor binding studies indicated that (i) the optimal alkyl chain length was five methylenes, (ii) an unsubstituted 1,2,3,4-tetrahydronaphthalenyl nucleus was preferred, and (iii) the substitution pattern of the aryl ring linked to the piperazine ring played a crucial role. Several compound with high affinity for 5-HT7 receptors were identified. Among them, 4-(2-methoxyphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (28), 4-(2-acetylphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (34), 4-(2-methylthiophenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (44), 4-(2-hydroxyphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (46), and 4-(2-methylphenyl)-N-(1,2,3,4-tetrahydronaphthalen-1-yl)-1-piperazinehexanamide (49) were assayed for the 5-HT7 receptor-mediated relaxation of substance P-induced guinea pig ileum contraction. Compounds 28, 44, and 49 behaved as full agonists and compound 34 as a partial agonist, whereas derivative 46 acted as an antagonist. Among the compounds presented here, it emerged that 44 was identified as a potent 5-HT7 receptor agonist (Ki = 0.22 nM, EC50 = 2.56 microM), endowed with selectivity over 5-HT(1A) and 5-HT(2A) receptors (200-fold and >1000-fold, respectively).

Novel 2-aminotetralin and 3-aminochroman derivatives as selective serotonin 5-HT7 receptor agonists and antagonists

The understanding of the physiological role of the G-protein coupled serotonin 5-HT(7) receptor is largely rudimentary. Therefore, selective and potent pharmacological tools will add to the understanding of serotonergic effects mediated through this receptor. In this report, we describe two compound classes, chromans and tetralins, encompassing compounds with nanomolar affinity for the 5-HT(7) receptor and with good selectivity. Within theses classes, we have discovered both agonists and antagonists that can be used for further understanding of the pharmacology of the 5-HT(7) receptor.

A new method for evaluating sigma(2) ligand activity in the isolated guinea-pig bladder

We demonstrated the presence of sigma(2) receptors in the guinea-pig ileum by saturation analysis and extended our investigation to guinea-pig bladder and rat bladder. In functional assays of the isolated tissues in organ baths, sigma(2) receptor ligands inhibited electrically evoked contractions in both guinea-pig bladder and ileum and a linear correlation was found between sigma(2) receptor affinity and sigma(2) receptor activity values of selected compounds. The sigma(2) activity of these compounds in the presence of desensitised sigma(1) receptors both in bladder and ileum was also tested. On the basis of our results, we propose the electrically stimulated guinea-pig bladder as a new method for evaluating sigma(2) activity.