Design,Synthesis, and In Vivo and In Silico Evaluation of Coumarin Derivatives with Potential Antidepressant Effects

In this study, a series of coumarin derivatives were designed and synthesized, their structures were characterized using nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) testing methods. In the pharmacological experiment, two behavior-monitoring methods, the forced swim test (FST) and the tail suspension test (TST), were used to determine the antidepressant activity of coumarin derivatives. Compounds that showed potential activity were analyzed for their effects on 5-hydroxytryptamine (5-HT) levels in the brains of mice. Molecular docking experiments to simulate the possible interaction of these compounds with the 5-HT_1A receptor was also be predicted. The results of the pharmacological experiments showed that most coumarin derivatives exhibited significant antidepressant activity. Among these compounds, 7-(2-(4-(4-fluorobenzyl)piperazin-1-yl)-2-oxoethoxy)-2H-chromen-2-one (6i) showed the highest antidepressant activity. The results of the measurement of 5-HT levels in the brains of mice indicate that the antidepressant activity of coumarin derivatives may be mediated by elevated 5-HT levels. The results of molecular docking demonstrated that compound 6i had a significant interaction with amino acids around the active site of the 5-HT_1A receptor in the homology model. The physicochemical and pharmacokinetic properties of the target compounds were also predicted using Discovery Studio (DS) 2020 and Chemdraw 14.0.     

Molecular dynamics of 5-HT1A and 5-HT2A serotonin receptors with methylated buspirone analogues

In the present study experimentally determined ligand selectivity of three methylated buspirone analogues (denoted as MM2, MM5 and P55) towards 5-HT_1A and 5-HT_2A serotonin receptors was theoretically investigated on a molecular level. The relationships between the ligand structure and 5-HT_1A and 5-HT_2A receptor affinities were studied and the results were found to be in agreement with the available site-directed mutagenesis and binding affinity data. Molecular dynamics (MD) simulations of ligand-receptor complexes were performed for each investigated analogue, docked twice into the central cavity of 5-HT_1A/5-HT_2A, each time in a different orientation. Present results were compared with our previous theoretical results, obtained for buspirone and its non-methylated analogues. It was found that due to the presence of the methyl group in the piperazine ring the ligand position alters and the structure of the ligand-receptor complex is modified. Further, the positions of derivatives with pyrimidinyl aromatic moiety and quinolinyl moiety are significantly different at the 5-HT_2A receptor. Thus, methylation of such derivatives alters the 3D structures of ligand-receptor complexes in different ways. The ligand-induced changes of the receptor structures were also analysed. The obtained results suggest, that helical domains of both receptors have different dynamical behaviour. Moreover, both location and topography of putative binding sites for buspirone analogues are different at 5-HT_1A and 5-HT_2A receptors.     

Molecular Structure and Affinity to 5-HT1A Receptor of Chlorophenyl(Piperazinylalkyl)Phthalimides

Abstract

X-ray crystallography, quantum-chemical calculations and conformational analysis have been employed to study chlorophenyl(piperazinylalkyl)phthalimides, potential ligands of 5-HT_1A receptor. The molecular recognition of investigated compounds by 5-HT_1Aserotonin receptor has been estimated according to their ability to inhibit the [³H8]-DPAT binding. The model for 5-HT_1A pharmacophore has been proposed based on crystal structures of N-(aryl)piperazinyl — alkylphthalimides.     

3-D QSAR for intrinsic activity of 5-HT1A receptor ligands by the method of comparative molecular field analysis

The affinity of a ligand for a receptor is usually expressed in terms of the dissociation constant (K_i) of the drug-receptor complex, conveniently measured by the inhibition of radioligand binding. However, a ligand can be an antagonist, a partial agonist, or a full agonist, a property largely independent of its receptor affinity. This property can be quantitated as intrinsic activity (1A), which can range from 0 for a full antagonist to 1 for a full agonist. Although quantitative structure–activity relationship (QSAR) methods have been applied to the prediction of receptor affinity with considerable success, the prediction of IA, even qualitatively, has rarely been attempted. Because most traditional QSAR methods are limited to congeneric series, and there are often major structural differences between agonists and antagonists, this lack of success in predicting IA is understandable. To overcome this limitation, we used the method of comparative molecular field analysis (CoMFA), which, unlike traditional Hansch analysis, permits the inclusion of structurally dissimilar compounds in a single QSAR model. A structurally diverse set of 5-hydroxytryptamine_1A (5-HT_1A) receptor ligands, with literature IA data (determined by the inhibition of 5-HT sensitive forskolin-stimulated adenylate cyclase), was used to develop a 3-D QSAR model correlating intrinsic activity with molecular structure properties of 5HT_1A receptor ligands. This CoMFA model had a crossvalidated r² of 0.481, five components and final conventional r² of 0.943. The receptor model suggests that agonist and antagonist ligands can share parts of a common binding site on the receptor, with a primary agonist binding region that is also occupied by antagonists and a secondary binding site accommodating the excess bulk present in the sidechains of many antagonists and partial agonists. The CoMFA steric field graph clearly shows that agonists tend to be “flatter” (more coplanar) than antagonists, consistent with the difference between the 5-HT_1A agonist and antagonist pharmacophores proposed by Hibert and coworkers. The CoMFA electrostatic field graph suggests that, in the region surrounding the essential protonated aliphatic amino group, the positive molecular electrostatic potential may be weaker in antagonists as compared to agonists. Together, the steric and electrostatic maps suggest that in the secondary binding site region increased hydrophobic binding may enhance antagonist activity. These results demonstrate that CoMFA is capable of generating a statistically crossvalidated 3-D QSAR model that can successfully distinguish between agonist and antagonist 5-HT_1A ligands. To the best of our knowledge, this is the first time this or any other QSAR method has been successfully applied to the correlation of structure with IA rather than potency or affinity. The analysis has suggested various structural features associated with agonist and antagonist behaviors of 5-HT_1A ligands and thus should assist in the future design of drugs that act via 5-HT_1A receptors. © 1993 John Wiley & Sons, Inc.     

A homology-based model of the human 5-HT2A receptor derived from an in silico activated G-protein coupled receptor

A homology-based model of the 5-HT_2A receptor was produced utilizing an activated form of the bovine rhodopsin (Rh) crystal structure [1,2]. In silico activation of the Rh structure was accomplished by isomerization of the 11-cis-retinal (1) chromophore, followed by constrained molecular dynamics to relax the resultant high energy structure. The activated form of Rh was then used as a structural template for development of a human 5-HT_2A receptor model. Both the 5-HT_2A receptor and Rh are members of the G-protein coupled receptor (GPCR) super-family. The resulting homology model of the receptor was then used for docking studies of compounds representing a cross-section of structural classes that activate the 5-HT_2A receptor, including ergolines, tryptamines, and amphetamines. The ligand/receptor complexes that ensued were refined and the final binding orientations were observed to be compatible with much of the data acquired through both diversified ligand design and site directed mutagenesis.     

Design and Synthesis of Arylpiperazine Serotonergic/Dopaminergic Ligands with Neuroprotective Properties

Long-chain arylpiperazine scaffold is a versatile template to design central nervous system (CNS) drugs that target serotonin and dopamine receptors. Here we describe the synthesis and biological evaluation of ten new arylpiperazine derivatives designed to obtain an affinity profile at serotonin 5-HT_1A, 5-HT_2A, 5-HT₇ receptor, and dopamine D₂ receptor of prospective drugs to treat the core symptoms of autism spectrum disorder (ASD) or psychosis. Besides the structural features required for affinity at the target receptors, the new compounds incorporated structural fragments with antioxidant properties to counteract oxidative stress connected with ASD and psychosis. All the new compounds showed CNS MultiParameter Optimization score predictive of desirable ADMET properties and cross the blood–brain barrier. We identified compound 12a that combines an affinity profile compatible with antipsychotic activity (5-HT_1A K_i = 41.5 nM, 5-HT_2A K_i = 315 nM, 5-HT₇ K_i = 42.5 nM, D₂ K_i = 300 nM), and compound 9b that has an affinity profile consistent with studies in the context of ASD (5-HT_1A K_i = 23.9 nM, 5-HT_2A K_i = 39.4 nM, 5-HT₇ K_i = 45.0 nM). Both compounds also had antioxidant properties. All compounds showed low in vitro metabolic stability, the only exception being compound 9b, which might be suitable for studies in vivo.     

Functional group interactions of a 5-HT3R antagonist

Background  

Lerisetron, a competitive serotonin type 3 receptor (5-HT₃R) antagonist, contains five functional groups capable of interacting with amino acids in the 5-HT₃R binding site. Site directed mutagenesis studies of the 5-HT_3AR have revealed several amino acids that are thought to form part of the binding domain of this receptor. The specific functional groups on the ligand that interact with these amino acids are, however, unknown. Using synthetic analogs of lerisetron as molecular probes in combination with site directed mutagenesis, we have identified some of these interactions and have proposed a model of the lerisetron binding site.     

Multiconformational composite molecular potential fields in the analysis of drug action. I. Methodology and first evaluation using 5-HT and histamine action as examples

Summary The quality of molecular electrostatic maps generated by non-quantum mechanical methods has been improved using extended electron distributions. Further simplification has been achieved by distilling these maps down to their energy extrema. A new means of defining surface interaction has been added and the resulting composite map has been plotted for a limited number of low-lying conformers of a series of agonists and antagonists of the H₂ and H₃ receptors and 5-HT_1A and 5-HT_1D receptors. The results from the cross-comparison of these maps indicate their ability to distinguish the specific receptor. Interesting consequences of the method are that structural overlay is irrelevant, that several conformations may contribute to the overall binding pattern and that lesser pharmacological activities may be deduced from the results.     

5-HT1A receptor pharmacophores to screen for off-target activity of α1-adrenoceptor antagonists

The α₁-adrenoceptors (α₁-ARs), in particular the α_1A-AR subtype, are current therapeutic targets of choice for the treatment of urogenital conditions, such as benign prostatic hyperplasia (BPH). Due to the similarity between the transmembrane domains of the α₁-AR subtypes, and the serotonin receptor subtype 1A (5-HT_1A-R), currently used α₁-AR subtype-selective drugs to treat BPH display considerable off-target affinity for the 5-HT_1A-R, leading to side effects. We describe the construction and validation of pharmacophores for 5-HT_1A-R agonists and antagonists. Through the structural diversity of the training sets used in their development, these pharmacophores define the properties of a compound needed to bind to 5-HT_1A receptors. Using these and previously published pharmacophores in virtual screening and profiling, we have identified unique chemical compounds (hits) that fit the requirements to bind to our target, the α_1A-AR, selectively over the off-target, the 5-HT_1A-R. Selected hits have been obtained and their affinities for α_1A-AR, α_1B-AR and 5-HT_1A-R determined in radioligand binding assays, using membrane preparations which contain human receptors expressed individually. Three of the tested hits demonstrate statistically significant selectivity for α_1A-AR over 5-HT_1A-R. All seven tested hits bind to α_1A-AR, with two compounds displaying K _i values below 1 μM, and a further two K _i values of around 10 μM. The insights and knowledge gained through the development of the new 5-HT_1A-R pharmacophores will greatly aid in the design and synthesis of derivatives of our lead compound, and allow the generation of more efficacious and selective ligands.     

Molecular docking,dynamics simulations and 3D-QSAR modeling of arylpiperazine derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine as 5-HT1AR agonists

Serotonin receptor, 5-HT_1AR, agonists and partial agonists have established drug candidates for psychiatric and neurologic disorders. Recently, we reported the synthesis and evaluation of arylpiperazine derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine as 5-HT_1AR ligands. Herein, we generated a homology model of the receptor and docked the ligands against it, predicted the stability of the receptor model and complexes by molecular dynamics and generated a 3D-QSAR model for the arylpiperazine derivatives of 3,5-dioxo-(2H,4H)-1,2,4-triazine. The model suggests the hydrophobic part that arises from the aromatic region and the electron withdrawing parts play a vital role in the agonist activity of the lead molecules.     

N-Skatyltryptamines—Dual 5-HT6R/D2R Ligands with Antipsychotic and Procognitive Potential

A series of N-skatyltryptamines was synthesized and their affinities for serotonin and dopamine receptors were determined. Compounds exhibited activity toward 5-HT_1A, 5-HT_2A, 5-HT₆, and D₂ receptors. Substitution patterns resulting in affinity/activity switches were identified and studied using homology modeling. Chosen hits were screened to determine their metabolism, permeability, hepatotoxicity, and CYP inhibition. Several D₂ receptor antagonists with additional 5-HT₆R antagonist and agonist properties were identified. The former combination resembled known antipsychotic agents, while the latter was particularly interesting due to the fact that it has not been studied before. Selective 5-HT₆R antagonists have been shown previously to produce procognitive and promnesic effects in several rodent models. Administration of 5-HT₆R agonists was more ambiguous—in naive animals, it did not alter memory or produce slight amnesic effects, while in rodent models of memory impairment, they ameliorated the condition just like antagonists. Using the identified hit compounds 15 and 18, we tried to sort out the difference between ligands exhibiting the D₂R antagonist function combined with 5-HT₆R agonism, and mixed D₂/5-HT₆R antagonists in murine models of psychosis.     

Comparative receptor mapping of serotoninergic 5-HT3 and 5-HT4 binding sites*

The clinical use of currently available drugs acting at the5-HT₄ receptor has been hampered by their lack of selectivityover 5-HT₃ binding sites. For this reason, there is considerableinterest in the medicinal chemistry of these serotonin receptor subtypes, andsignificant effort has been made towards the discovery of potent and selectiveligands. Computer-aided conformational analysis was used to characterizeserotoninergic 5-HT₃ and 5-HT₄ receptorrecognition. On the basis of the generally accepted model of the5-HT₃ antagonist pharmacophore, we have performed a receptormapping of this receptor binding site, following the active analog approach(AAA) defined by Marshall. The receptor excluded volume was calculated as theunion of the van der Waals density maps of nine active ligands(pK_i 8.9), superimposed in pharmacophoric conformations.Six inactive analogs (pK_i < 7.0) were subsequently used todefine the essential volume, which in its turn can be used to define theregions of steric intolerance of the 5-HT₃ receptor. Five activeligands (pK_i 9.3) at 5-HT₄ receptors wereused to construct an antagonist pharmacophore for this receptor, and todetermine its excluded volume by superimposition of pharmacophoricconformations. The volume defined by the superimposition of five inactive5-HT₄ receptor analogs that possess the pharmacophoric elements(pK_i 6.6) did not exceed the excluded volume calculated forthis receptor. In this case, the inactivity may be due to the lack of positiveinteraction of the amino moiety with a hypothetical hydrophobic pocket, whichwould interact with the voluminous substituents of the basic nitrogen ofactive ligands. The difference between the excluded volumes of both receptorshas confirmed that the main difference is indeed in the basic moiety. Thus,the 5-HT₃ receptor can only accommodate small substituents inthe position of the nitrogen atom, whereas the 5-HT₄ receptorrequires more voluminous groups. Also, the basic nitrogen is located at ca.8.0 Å from the aromatic moiety in the 5-HT₄ antagonistpharmacophore, whereas this distance is ca. 7.5 Å in the5-HT₃ antagonist model. The comparative mapping of bothserotoninergic receptors has allowed us to confirm the three-componentpharmacophore accepted for the 5-HT₃ receptor, as well as topropose a steric model for the 5-HT₄ receptor binding site. Thisstudy offers structural insights to aid the design of new selective ligands,and the resulting models have received some support from the synthesis of twonew active and selective ligands: 24 (K_i(5-HT₃)= 3.7 nM; K_i(5-HT₄) > 1000 nM) and 25(K_i(5-HT₄) = 13.7 nM;K_i(5-HT₃) > 10 000 nM).     

N-[4-(arylpiperazin-1-yl)butyl]bicyclo[2.2.1]hept-5-ene-endo-2,endo-3-dicarboximides and Their Epoxy Derivatives. Synthesis and affinity for 5-HT1a receptors

New ligands for 5-HT_1A serotonin receptors, N-[4-(4-arylpiperazin-1-yl)butyl]bicyclo[2.2.1]hept-5-ene-endo-2,endo-3-dicarboximides and their epoxy derivatives, were synthesized, and their affinity for 5-HT_1A receptors was estimated at 16.2 ± 2.0 to 0.60 ± 0.08 nM. Original Russian Text ? S.Yu. Makan, D.I. Tsymbal, S.G. Soboleva, I.N. Tarabara, L.I. Kas’yan, S.A. Andronati, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 2, pp. 303–307.     

Role of 5-HT1A Receptor in Vilazodone-Mediated Suppression of L-DOPA-Induced Dyskinesia and Increased Responsiveness to Cortical Input in Striatal Medium Spiny Neurons in an Animal Model of Parkinson’s Disease

L-DOPA therapy in Parkinson’s disease (PD) is limited due to emerging L-DOPA-induced dyskinesia. Research has identified abnormal dopamine release from serotonergic (5-HT) terminals contributing to this dyskinesia. Selective serotonin reuptake inhibitors (SSRIs) or 5-HT receptor (5-HTr) agonists can regulate 5-HT activity and attenuate dyskinesia, but they often also produce a loss of the antiparkinsonian efficacy of L-DOPA. We investigated vilazodone, a novel multimodal 5-HT agent with SSRI and 5-HTr_1A partial agonist properties, for its potential to reduce dyskinesia without interfering with the prokinetic effects of L-DOPA, and underlying mechanisms. We assessed vilazodone effects on L-DOPA-induced dyskinesia (abnormal involuntary movements, AIMs) and aberrant responsiveness to corticostriatal drive in striatal medium spiny neurons (MSNs) measured with in vivo single-unit extracellular recordings, in the 6-OHDA rat model of PD. Vilazodone (10 mg/kg) suppressed all subtypes (axial, limb, orolingual) of AIMs induced by L-DOPA (5 mg/kg) and the increase in MSN responsiveness to cortical stimulation (shorter spike onset latency). Both the antidyskinetic effects and reversal in MSN excitability by vilazodone were inhibited by the 5-HTr_1A antagonist WAY-100635, demonstrating a critical role for 5-HTr_1A in these vilazodone actions. Our results indicate that vilazodone may serve as an adjunct therapeutic for reducing dyskinesia in patients with PD.     

3D-QSAR using `Multiconformer' alignment: The use of HASL in the analysis of 5-HT1A thienopyrimidinone ligands†

The observed 5-HT_1A and ₁-adrenergic receptor (₁-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-HT_1A receptor binding.     

Synthesis and biological evaluation of <Superscript>99m</Superscript>Tc-HEDTA/HYNIC-MPP4 complex for 5-HT<Subscript>1A</Subscript> receptor imaging

5-HT_1A receptor is associated with a variety of pathophysiology of neuropsychiatric disorders. Accordingly, we have synthesized a new 5-HT_1A receptor ligand (HYNIC-MPP4) and labeled it with ^99mTc using N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) as coligand. ^99mTc-HEDTA/HYNIC-MPP4 was prepared under pH 6 at room temperature. Biodistribution of 99mTc-HEDTA/HYNIC-MPP4 in normal mice showed that this complex had moderate brain uptake (0.60% ID·g⁻¹ at 2 min p.i.) and good retention. The hippocampus had the highest radioactivity uptake at 2 min p.i. (1.84% ID⋆g⁻¹). The ratio of Hipp/CB was 3.1 at 2 min p.i. and increased to 4.4 at 60 min p.i. After blocking with 8-hydroxy-2-(dipropylamino) tetralin, the uptake of hippocampus was decreased significantly from 1.84% ID·g⁻¹ to 0.53% ID·g⁻¹ at 2 min p.i., while the cerebellum had no significant decrease. This ^99mTc complex could be a potent agent for 5-HT_1A receptor imaging. Supported by the National Natural Science Foundation of China (Grant No. 20401004) and the Analysis and Test fund of Beijing Normal University     

Synthesis of 8-dipropylamino-7,8,9,10-tetrahydrophenanthridines as potential serotoninergic agonists

A number of 8-dipropylamino-7,8,9,10-tetrahydrophenanthridines have been prepared as analogs of the known serotoninergic agonist 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) and their affinity for the 5-HT_1A receptor subtype evaluated by radioligand binding assay.     

A New Synthesis of 8-Hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT)

A new synthesis method for 8-OH-DPAT, a specific agonist at the 5-HT_1A serotonin receptor, is described. It employs the Curtius degradation of a tetralin carboxylic acid easily prepared from (2-methoxy benzyl) succinic acid by Friedel-Crafts cyclisation.     

Synthesis and Pharmacological Evaluation of Novel 2,3,4,5-tetrahydro[1,3]diazepino[1,2-a]benzimidazole Derivatives as Promising Anxiolytic and Analgesic Agents

A number of novel 2,3,4,5-tetrahydro[1,3]diazepino[1,2-a]benzimidazole derivatives 2 were obtained by alkylation mainly in the 1H-tautomeric form of 2,3,4,5-tetrahydro[1,3]diazepino[1,2-a]benzimidazole or its 8,9-dimethyl-substituted analog 4-chlorobenzyl bromide, 4-chloroacetic acid fluoroanilide, and 4-tert-butylphenacyl bromide in neutral medium. Compounds 3 were cyclized and synthesized earlier with 11-phenacyl-substituted diazepino[1,2-a]benzimidazoles upon heating in conc. HBr. The chemical structures of the compounds were clarified by using the ¹H Nuclear Magnetic Resonance Spectroscopy (¹H-NMR) technique. Anxiolytic properties were evaluated using the elevated plus maze (EPM) and open field (OF) tests. The analgesic effect of compounds was estimated with the tail flick (TF) and hot plate (HP) methods. Besides, possible the influence of the test compounds on motor activities of the animals was examined by the Grid, Wire, and Rotarod tests. Compounds 2d and 3b were the most active due to their prominent analgesic and anxiolytic potentials, respectively. The results of the performed in silico analysis showed that the high anxiolytic activity of compound 3b is explained by the combination of a pronounced interaction mainly with the benzodiazepine site of the GABA_A receptor with a prominent interaction with both the specific and allosteric sites of the 5-HT_2A receptor.     

Nanosensor for Sensitive Detection of the New Psychedelic Drug 25I-NBOMe

This work reports the synthesis, characterization, and sensing behavior of a hybrid nanodevice for the detection of the potent abuse drug 25I-NBOMe. The system is based on mesoporous silica nanoparticles, loaded with a fluorescent dye, functionalized with a serotonin derivative and capped with the 5-HT_2A receptor antibody. In the presence of 25I-NBOMe the capping antibody is displaced, leading to pore opening and rhodamine B release. This delivery was ascribed to 5-HT_2A receptor antibody detachment from the surface due to its stronger coordination with 25I-NBOMe present in the solution. The prepared nanodevice allowed the sensitive (limit of detection of 0.6 μm ) and selective recognition of the 25I-NBOMe drug (cocaine, heroin, mescaline, lysergic acid diethylamide, MDMA, and morphine were unable to induce pore opening and rhodamine B release). This nanodevice acts as a highly sensitive and selective fluorometric probe for the 25I-NBOMe illicit drug in artificial saliva and in sweets.