Recent Advances in representative small-molecule DRD2 inhibitors: Synthetic Routes and clinical applications.

The dopamine D2 receptor (DRD2) represents a pivotal target for therapeutic intervention in the treatment of neuropsychiatric disorders, including schizophrenia, bipolar disorder, and Parkinson's disease. The successful discovery of numerous effective DRD2 inhibitors has led to their clinical application and ongoing evaluation in various clinical trials. This review explores the synthetic approaches and clinical applications of prototypical small-molecule DRD2 inhibitors that have received approval or are currently undergoing clinical trials, highlighting their therapeutic potential and challenges. The synthesis of these inhibitors employs various chemical strategies, including modifications of phenothiazine and butyrophenone structures, which have yielded significant antipsychotic agents like chlorpromazine and haloperidol. Additionally, newer classes of inhibitors, such as aripiprazole, exhibit partial agonist activity at DRD2, offering a unique therapeutic profile. Clinically, DRD2 inhibitors demonstrate efficacy in managing positive symptoms of schizophrenia, manic episodes in bipolar disorder, and dopaminergic imbalance in Parkinson's disease. However, the emergence of adverse effects, including tardive dyskinesia, extrapyramidal symptoms and metabolic syndrome, presents substantial challenges. Advances in the development of second-generation antipsychotics aim to balance efficacy with a better side effect profile by targeting additional neurotransmitter receptors. This review aims to deliver an overview of the synthesis and clinical applications of representative small-molecule DRD2 inhibitors across various clinical phases, thereby offering strategic insights for the advancement of DRD2 inhibitor development.

Integrating UPLC-MS/MS with in Silico and in Vitro Screening Accelerates the Discovery of Active Compounds in Stephania epigaea.

Traditional Chinese medicines (TCMs) are popular in clinic because of their safety and efficacy. They contain abundant natural active compounds, which are important sources of new drug discovery. However, how to efficiently identify active compounds from complex ingredients remains a challenge. In this study, a method combining UHPLC-MS/MS characterization and in silico screening was developed to discover compounds with dopamine D2 receptor (D2R) activity in Stephania epigaea (S. epigaea). By combining the compounds identified in S. epigaea by UHPLC-MS/MS with reported compounds, a virtual library of 80 compounds was constructed for in silico screening. Potentially active compounds were chosen based on screening scores and subsequently tested for in vitro activity on a transfected cell line CHO-K1-D2 model using label-free cellular phenotypic assay. Three D2R agonists and five D2R antagonists were identified. (-)-Asimilobine, N-nornuciferine and (-)-roemerine were reported for the first time as D2R agonists, with EC50 values of 0.35 ± 0.04 µM, 1.37 ± 0.10 µM and 0.82 ± 0.22 µM, respectively. Their target specificity was validated by desensitization and antagonism assay. (-)-Isocorypalmine, (-)-tetrahydropalmatine, (-)-discretine, (+)-corydaline and (-)-roemeroline showed strong antagonistic activity on D2R with IC50 values of 92 ± 9.9 nM, 1.73 ± 0.13 µM, 0.34 ± 0.02 µM, 2.09 ± 0.22 µM and 0.85 ± 0.08 µM, respectively. Their kinetic binding profiles were characterized using co-stimulation assay and they were both D2R competitive antagonists. We docked these ligands with human D2R crystal structure and analyzed the structure-activity relationship of aporphine-type D2R agonists and protoberberine-type D2R antagonists. These results would help to elucidate the mechanism of action of S. epigaea for its analgesic and sedative efficacy and benefit for D2R drug design. This study demonstrated the potential of integrating UHPLC-MS/MS with in silico and in vitro screening for accelerating the discovery of active compounds from TCMs.

The dopamine D2 receptors antagonist Veralipride inhibits carbonic anhydrases: solution and crystallographic insights on human isoforms.

The inhibitory effects of veralipride, a benzamide-class antipsychotic acting as dopamine D2 receptors antagonist incorporates a primary sulfonamide moiety and was investigated for its interactions with carbonic anhydrase (CA) isoforms. In vitro profiling using the stopped-flow technique revealed that veralipride exhibited potent inhibitory activity across all tested hCA isoforms, with exception of hCA III. Comparative analysis with standard inhibitors, acetazolamide (AAZ), and sulpiride, provided insights for understanding the relative efficacy of veralipride as CA inhibitor. The study reports the X-ray crystal structure analysis of the veralipride adduct with three human (h) isoforms, hCA I, II, and CA XII mimic, allowing the understanding of the molecular interactions rationalizing its inhibitory effects against each isoform. These findings contribute to our understanding of veralipride pharmacological properties and for the design of structural analogs endowed with polypharmacological properties.

Uncariphyllin A-J, indole alkaloids from Uncaria rhynchophylla as antagonists of dopamine D2 and Mu opioid receptors.

Ten new indole alkaloids (1-10) as well as eleven known analogs (11-21) were isolated from the stems and hooks of Uncaria rhynchophylla. Their structure elucidation was based on extensive NMR studies, MS and ECD data, with the essential aid of DFT prediction of ECD spectra. Compound 1 was determined as a 17,19-seco-cadambine-type alkaloid, and compound 3 was confirmed to be a 3,4-seco-tricyclic monoterpene indole alkaloid, which are the first seco-alkaloids possessing such cleavage positions from U. rhynchophylla. All the isolated compounds were evaluated for their bioactivities on dopamine D2 and Mu opioid receptors for discovering natural therapeutic drugs targeting central nervous system (CNS) diseases. Compounds 1, 2, 4, 5, 20 and 21 showed antagonistic bioactivities on the D2 receptor (IC50 0.678-15.200 µM), and compounds 1, 3, 6, 9, 10, 13, 18, 19 and 21 exhibited antagonistic effects on the Mu receptor (IC50 2.243-32.200 µM). Among them, compounds 1 and 21 displayed dual-target activities. Compound 1 showed conspicuous antagonistic activity on D2 and Mu receptors with the IC50 values of 0.678 ± 0.182 µM and 13.520 ± 2.480 µM, respectively. Compound 21 displayed moderate antagonistic activity on the two receptors with the IC50 values at 15.200 ± 1.764 µM and 32.200 ± 5.695 µM, respectively.

Pharmacological Characterization of the Imipridone Anticancer Drug ONC201 Reveals a Negative Allosteric Mechanism of Action at the D2 Dopamine Receptor.

ONC201 is a first-in-class imipridone compound that is in clinical trials for the treatment of high-grade gliomas and other advanced cancers. Recent studies identified that ONC201 antagonizes D2-like dopamine receptors at therapeutically relevant concentrations. In the current study, characterization of ONC201 using radioligand binding and multiple functional assays revealed that it was a full antagonist of the D2 and D3 receptors (D2R and D3R) with low micromolar potencies, similar to its potency for antiproliferative effects. Curve-shift experiments using D2R-mediated ß-arrestin recruitment and cAMP assays revealed that ONC201 exhibited a mixed form of antagonism. An operational model of allostery was used to analyze these data, which suggested that the predominant modulatory effect of ONC201 was on dopamine efficacy with little to no effect on dopamine affinity. To investigate how ONC201 binds to the D2R, we employed scanning mutagenesis coupled with a D2R-mediated calcium efflux assay. Eight residues were identified as being important for ONC201's functional antagonism of the D2R. Mutation of these residues followed by assessing ONC201 antagonism in multiple signaling assays highlighted specific residues involved in ONC201 binding. Together with computational modeling and simulation studies, our results suggest that ONC201 interacts with the D2R in a bitopic manner where the imipridone core of the molecule protrudes into the orthosteric binding site, but does not compete with dopamine, whereas a secondary phenyl ring engages an allosteric binding pocket that may be associated with negative modulation of receptor activity. SIGNIFICANCE STATEMENT: ONC201 is a novel antagonist of the D2 dopamine receptor with demonstrated efficacy in the treatment of various cancers, especially high-grade glioma. This study demonstrates that ONC201 antagonizes the D2 receptor with novel bitopic and negative allosteric mechanisms of action, which may explain its high selectivity and some of its clinical anticancer properties that are distinct from other D2 receptor antagonists widely used for the treatment of schizophrenia and other neuropsychiatric disorders.

Preclinical Evaluation of the Effects of Trazpiroben (TAK-906), a Novel, Potent Dopamine D2/D3 Receptor Antagonist for the Management of Gastroparesis.

Current therapies for gastroparesis metoclopramide and domperidone carry risks of extrapyramidal symptoms and life-threatening cardiac arrhythmias. Trazpiroben, a novel, potent dopamine D2/D3 receptor antagonist, has low brain permeation and very low affinity for human ether-à-go-go-related gene (hERG) channel inhibition, potentially improving on safety profiles of existing therapies. Trazpiroben demonstrated the following receptor affinities: high for D2 and D3, moderate for D4, and minimal for D1 and D5 It demonstrated moderate affinity for adrenergic α 1B (α 1B) and 5-hydroxytryptamine (5HT) 2A receptors and low potential for off-target adverse events (AEs). Trazpiroben potently inhibited dopamine-activated D2L receptor activation of cognate G-proteins in human embryonic kidney 293 cell membranes and was a neutral D2L receptor antagonist. In vivo, trazpiroben dose-dependently increased prolactin release in orally dosed rat (0.1-1 mg/kg). Additionally, multiple oral doses in the rat (100 mg/kg) and dog (50 mg/kg) for 3 days produced robust plasma exposures and prolactin increases in both species. Trazpiroben inhibited retching/vomiting in the dog with apomorphine-induced emesis with a potency (0.1-1 mg/kg) like that of trazpiroben-mediated prolactin increases in rat. Oral trazpiroben (1, 10, and 30 mg/kg) did not affect rat rotarod performance, suggesting low brain penetration. Trazpiroben concentrations were low in cerebrospinal fluid versus plasma after multiple oral doses for 4 days in rat and dog. Trazpiroben weakly inhibited the hERG channel current (concentration causing half-maximal inhibition of control-specific binding of 15.6 µM), indicating little potential for disrupting cardiac rhythm. Overall, trazpiroben is a potent D2/D3 receptor antagonist designed to avoid the serious potential AEs associated with current gastroparesis therapies. SIGNIFICANCE STATEMENT: Trazpiroben is a novel, potent dopamine D2/D3 selective receptor antagonist designed to avoid adverse effects associated with the current pharmacological therapies metoclopramide and domperidone. Preclinical studies have demonstrated low brain penetration and weak affinity for the hERG channel, indicating that trazpiroben is not expected to be associated with central nervous system or cardiovascular safety issues. With these pharmacological properties, trazpiroben may represent a viable new treatment option for gastroparesis because of a potentially improved safety profile relative to existing therapies.

N-(3-{4-[3-(trifluoromethyl)phenyl]piperazin-1-yl}propyl)-1H-indazole-3-carboxamide (D2AAK3) as a potential antipsychotic: In vitro, in silico and in vivo evaluation of a multi-target ligand.

Schizophrenia is a mental illness of not adequately understood causes that is not satisfactorily enough treated by current antipsychotics. In search for novel potential antipsychotics we performed structure-based virtual screening aimed to identify new dopamine D2 receptor antagonists. We found compound D2AAK3 with affinity to dopamine D2 receptor of 115 nM. D2AAK3 possesses additional nanomolar or low micromolar affinity to D1, D3, 5-HT1A, 5-HT2A and 5-HT7 receptors, which makes it a good hit for further development as a multifunctional ligand. The compound has also some affinity to M1 and H1 receptors. We used homology modeling, molecular docking and molecular dynamics to study interactions of D2AAK3 with its molecular targets at the molecular level. In behavioral studies D2AAK3 decreases amphetamine-induced hyperactivity (when compared to the amphetamine-treated group) measured as spontaneous locomotor activity in mice. In addition, passive avoidance test demonstrated that D2AAK3 improves memory consolidation after acute treatment in mice. Elevated plus maze tests indicated that D2AAK3 induces anxiogenic activity 30 min after acute treatment, whereas this effect has no longer been observed 60 min after administration of the studied compound in mice.

Formulation of instant disintegrating buccal films without using disintegrant: An in-vitro study.

The current study was conducted to fabricate Metoclopramide HCL (MCH) and Sumatriptan succinate (SS) instant release buccal films (IRBF) without using any super disintegrant. The solvent casting method was used for the preparation of IRBFs and prepared IRBFs were physicochemically evaluated. Spectrophotometric analysis was done to determine the lambda max followed by the linearity determination of both drugs. Different concentrations such as 100, 125, and 150mg of hydrophilic polymer (HPMC E5) were employed but the concentration of glycerol was variable. Comparatively better results were observed for the formulation with 150mg of HPMC E5 and 30% glycerol. Formulated IRBFs showed good tensile strength with a mean disintegration time of 12.4-28.4 seconds and rapid dissolution with more than 50% drug release within 2 minutes. It was concluded that the chosen combination of polymers was appropriate for the fabrication of MCH and SS buccal strips.

A study of the structure-affinity relationship in SYA16263; is a D2 receptor interaction essential for inhibition of apormorphine-induced climbing behavior in mice?

Dopamine (DA) and serotonin (5-HT) receptors are prime targets for the development of antipsychotics. The specific role of each receptor subtype to the pharmacological effects of antipsychotic drugs remains unclear. Understanding the relationship between antipsychotic drugs and their binding affinities at DA and 5-HT receptor subtypes is very important for antipsychotic drug discovery and could lead to new drugs with enhanced efficacies. We have previously disclosed SYA16263 (5) as an interesting compound with moderate radioligand binding affinity at the D2 & D3 receptors (Ki = 124 nM & 86 nM respectively) and high binding affinities towards D4 and 5-HT1A receptors (Ki = 3.5 nM & 1.1 nM respectively). Furthermore, we have demonstrated SYA16263 (5) is functionally selective and produces antipsychotic-like behavior but without inducing catalepsy in rats. Based on its pharmacological profile, we selected SYA16263 (5) to study its structure-affinity relationship with a view to obtaining new analogs that display receptor subtype selectivity. In this study, we present the synthesis of structurally modified SYA16263 (5) analogs and their receptor binding affinities at the DA and 5-HT receptor subtypes associated with antipsychotic action. Furthermore, we have identified compound 21 with no significant binding affinity at the D2 receptor subtype but with moderate binding affinity at the D3 and D4 receptors subtypes. However, because 21 is able to demonstrate antipsychotic-like activity in a preliminary test, using the reversal of apomorphine-induced climbing behavior experiment in mice with SYA16263 and haloperidol as positive controls, we question the essential need of the D2 receptor subtype in reversing apomorphine-induced climbing behavior.

Compound screening in cell-based models of tau inclusion formation: Comparison of primary neuron and HEK293 cell assays.

The hallmark pathological features of Alzheimer's disease (AD) brains are senile plaques, comprising ß-amyloid (Aß) peptides, and neuronal inclusions formed from tau protein. These plaques form 10-20 years before AD symptom onset, whereas robust tau pathology is more closely associated with symptoms and correlates with cognitive status. This temporal sequence of AD pathology development, coupled with repeated clinical failures of Aß-directed drugs, suggests that molecules that reduce tau inclusions have therapeutic potential. Few tau-directed drugs are presently in clinical testing, in part because of the difficulty in identifying molecules that reduce tau inclusions. We describe here two cell-based assays of tau inclusion formation that we employed to screen for compounds that inhibit tau pathology: a HEK293 cell-based tau overexpression assay, and a primary rat cortical neuron assay with physiological tau expression. Screening a collection of ∼3500 pharmaceutical compounds with the HEK293 cell tau aggregation assay, we obtained only a low number of hit compounds. Moreover, these compounds generally failed to inhibit tau inclusion formation in the cortical neuron assay. We then screened the Prestwick library of mostly approved drugs in the cortical neuron assay, leading to the identification of a greater number of tau inclusion inhibitors. These included four dopamine D2 receptor antagonists, with D2 receptors having previously been suggested to regulate tau inclusions in a Caenorhabditis elegans model. These results suggest that neurons, the cells most affected by tau pathology in AD, are very suitable for screening for tau inclusion inhibitors.

Design of novel dopamine D2 and serotonin 5-HT2A receptors dual antagonists toward schizophrenia: An integrated study with QSAR, molecular docking, virtual screening and molecular dynamics simulations.

The extrapyramidal side effects of schizophrenia treatment can be significantly reduced by simultaneously targeting dopamine D2 and serotonin 5-HT2A receptors. In this study, three-dimensional quantitative structure-activity relationship (3D-QSAR) models of D2 receptor (CoMFA-1, q2 = 0.767, r2 = 0.969; CoMSIA-1, q2 = 0.717, r2 = 0.978) and 5-HT2A receptor antagonists (CoMFA-2, q2 = 0.703, r2 = 0.946; CoMSIA-2, q2 = 0.675, r2 = 0.916) were successfully constructed using 35 tetrahydropyridopyrimidinone derivatives. Topomer CoMFA and HQSAR models were then constructed to further validate and supplement above models. Results showed that all models had good predictive power and stability. Contour map analysis revealed that the electrostatic and hydrophobic fields played vital roles in the bioactivity of dual antagonists. Molecular docking and molecular dynamic studies also suggested that the hydrogen bonding, electrostatic and hydrophobic interactions played key roles in the formation of stable binding sites. Meanwhile, several key residues like ASP114, TRP100, PHE389 of dopamine D2 receptor and ASP134, PHE328, TRP324 of serotonin 5-HT2A receptor were identified. Based on above findings, seven compounds were obtained through bioisostere replacement and ten compounds were designed by contour map analysis, in which the predicted activity of compounds S6 and DS2 were equivalent to that of the template compound 15. 3D-QSAR and ADMET predictions indicated that all newly designed compounds had great biological activity and physicochemical properties. Moreover, based on the best pharmacophore model, four compounds (Z1, Z2, Z3 and Z4) with new backbones were obtained by virtual screening. Overall, this study could provide theoretical guidance for the structural optimization, design and synthesis of novel dopamine D2 and serotonin 5-HT2A receptors dual antagonists. Abbreviations3D-QSARThree-dimensional quantitative structure-activity relationship5-HT2ARSerotonin 5-hydroxytryptamine 5-HT2A receptor5-HT2CRSerotonin 5-hydroxytryptamine 5-HT2C receptor receptorCADDComputer-aided drug designCoMFAComparative molecular field analysisCoMSIAComparative molecular similarity index analysisD2RDopamine D(2) receptorGPCRG-protein coupled receptorPLSPartial least squares regressionHQSARHologram quantitative structure-activity relationship. Communicated by Ramaswamy H. Sarma.

Structure-Kinetic Profiling of Haloperidol Analogues at the Human Dopamine D2 Receptor.

Haloperidol is a typical antipsychotic drug (APD) associated with an increased risk of extrapyramidal side effects (EPSs) and hyperprolactinemia relative to atypical APDs such as clozapine. Both drugs are dopamine D2 receptor (D2R) antagonists, with contrasting kinetic profiles. Haloperidol displays fast association/slow dissociation at the D2R, whereas clozapine exhibits relatively slow association/fast dissociation. Recently, we have provided evidence that slow dissociation from the D2R predicts hyperprolactinemia, whereas fast association predicts EPS. Unfortunately, clozapine can cause severe side effects independent of its D2R action. Our results suggest an optimal kinetic profile for D2R antagonist APDs that avoids EPS. To begin exploring this hypothesis, we conducted a structure-kinetic relationship study of haloperidol and revealed that subtle structural modifications dramatically change binding kinetic rate constants, affording compounds with a clozapine-like kinetic profile. Thus, optimization of these kinetic parameters may allow development of novel APDs based on the haloperidol scaffold with improved side-effect profiles.

The Universal 3D QSAR Model for Dopamine D2 Receptor Antagonists.

In order to search for novel antipsychotics acting through the D2 receptor, it is necessary to know the structure-activity relationships for dopamine D2 receptor antagonists. In this context, we constructed the universal three-dimensional quantitative structure-activity relationship (3D- QSAR) model for competitive dopamine D2 receptor antagonists. We took 176 compounds from chemically different groups characterized by the half maximal inhibitory concentration (IC50)from the CHEMBL database and docked them to the X-ray structure of the human D2 receptor in the inactive state. Selected docking poses were applied for Comparative Molecular Field Analysis (CoMFA) alignment. The obtained CoMFA model is characterized by a cross-validated coefficient Q2 of 0.76 with an optimal component of 5, R2 of 0.92, and an F value of 338.9. The steric and electrostatic field contributions are 67.4% and 32.6%, respectively. The statistics obtained prove that the CoMFA model is significant. Next, the IC50 of the 16 compounds from the test set was predicted with R2 of 0.95. Finally, a progressive scrambling test was carried out for additional validation. The CoMFA fields were mapped onto the dopamine D2 receptor binding site, which enabled a discussion of the structure-activity relationship based on ligand-receptor interactions. In particular, it was found that one of the desired steric interactions covers the area of a putative common allosteric pocket suggested for some other G protein-coupled receptors (GPCRs), which would suggest that some of the known dopamine receptor antagonists are bitopic in their essence. The CoMFA model can be applied to predict the potential activity of novel dopamine D2 receptor antagonists.

New dual ligands for the D2 and 5-HT1A receptors from the group of 1,8-naphthyl derivatives of LCAP.

More than 300 million people are suffering from depression, one of the civilization diseases in the 21st century. Serotonin 5-HT1AR and dopamine D2R play an important role in the treatment and pathogenesis of depression. Moreover, in recent years, the efficacy of dual 5-HT1A/D2 receptors ligands has been demonstrated in the fight against depression. In this work the new bulky arylpiperazine derivatives (LCAP) were synthesized in microwave radiation field. The affinities for the selected serotonin (5-HT1A,5-HT2A,5-HT6,5-HT7) and dopamine (D2) receptors have been evaluated in vitro. Compounds 5.3a, 5.4, 5.1c, 5.3d, 5.2a are promising dual 5-HT1AR/D2R ligands. The SAR analysis were additionally supported with molecular docking studies.

Chemical synthesis, microbial transformation and biological evaluation of tetrahydroprotoberberines as dopamine D1/D2 receptor ligands.

Dopamine D1/D2 receptors are important targets for drug discovery in the treatment of central nervous system diseases. To discover new and potential D1/D2 ligands, 17 derivatives of tetrahydroprotoberberine (THPB) with various substituents were prepared by chemical synthesis or microbial transformation using Streptomyces griseus ATCC 13273. Their functional activities on D1 and D2 receptors were determined by cAMP assay and calcium flux assay. Seven compounds showed high activity on D1/D2 receptor with low IC50 values less than 1 µM. Especially, top compound 5 showed strong antagonistic activity on both D1 and D2 receptor with an IC50 of 0.391 and 0.0757 µM, respectively. Five compounds displayed selective antagonistic activity on D1 and D2 receptor. The SAR studies revealed that (1) the hydroxyl group at C-9 position plays an important role in keeping a good activity and small or fewer substituents on ring D of THPBs may also stimulate their effects, (2) the absence of substituents at C-9 position tends to be more selective for D2 receptor, and (3) hydroxyl substitution at C-2 position and the substitution at C-9 position may facilitate the conversion of D1 receptor from antagonist to agonist. Molecular docking simulations found that Asp 103/Asp 114, Ser 107/Cys 118, and Trp 285/ Trp 386 of D1/ D2 receptors are the key residues, which have strong interactions with the active D1/D2 compounds and may influence their functional profiles.

Biotinylated-spiperone ligands for quantum dot labeling of the dopamine D2 receptor in live cell cultures.

We have synthesized 3 analogs of the dopamine D2 receptor (D2 DR) antagonist spiperone that can be conjugated to streptavidin-coated quantum dots via a pegylated biotin derivative. Using fluorescent imaging we demonstrate that substitution on the spiro position is tolerated, whilst the length and rigidity of a spacer arm attached to spiperone is important in controlling specific labeling as well as minimizing nonspecific labeling to cells and the surface of cell culture dishes. The ligand with the most rigid linker IDT772 (4) had the best binding profile and had high specific binding to D2 DR expressing HEK-293T cells with low nonspecific binding to plates and HEK-293T cells that lacked the D2 DR.

Bioactivity-Guided Separation of Potential D2 Dopamine Receptor Antagonists from Aurantii Fructus based on Molecular Docking Combined with High-Speed Counter-Current Chromatography.

The typical compounds of Aurantii fructus (AF) reported in previous research were screened for their high antagonistic ability on the D2 dopamine receptor (D2R) in silico, and then bioactivity-guided separation was undertaken on the potential D2R antagonists from AF using high-speed counter-current chromatography (HSCCC). Three flavanones, two polymethoxyflavonoids, and three coumarins were effectively isolated from ethanol extracts of Aurantii fructus (AF) by the use of a two-step HSCCC method, and their chemical structures were identified by mass spectrometry, ¹H-NMR, and 13C-NMR and compared with published data. Firstly, crude extract of 70% ethanol eluent (150 mg) was isolated by HSCCC using an n-hexane-ethyl acetate-n-butanol-methanol-0.05% acetic acid (1:3:1.8:1:5, v/v/v/v/v) solvent system, and compounds 1 (naringin, 28 mg), 2 (neohesperidin, 13 mg), 3 (meranzin, 5 mg) and 4 (poncirin, 3 mg) were successfully isolated with 98.5%, 95.1%, 97.7%, and 92.4% purity, respectively. Then, the crude extract of 95% ethanol eluent (120 mg) was isolated by n-hexane-n-butanol-ethanol (methanol)-0.05% acetic acid (2:0.6:1:3, v/v/v/v) solvent system and compounds 3 (meranzin, 3 mg), 5 (meranzin hydrate, 4 mg), 6 (isomeranzin, 6 mg), 7 (nobiletin, 10 mg), and 8 (tangeretin, 7 mg) were successfully isolated with 95.8%, 98.5%, 95.1%, 92.4%, and 97.7% purity, respectively. Naringenin, a parent structure of naringin with the excellent binding score of -9.3 kcal/mol, was completely in conjunction with the active site of D2R, indicating that it is critical for the treatment of gastrointestinal dysfunction. The results indicated that the bioactivity-guided method is practical for the effective separation of active compounds from natural resources.

EXPERIMENTAL STUDY OF PAIN-RELIEVING MECHANISMS OF 4-[4-OXO-(4H)-QUINAZOLIN-3-YL]-BENZOIC ACID (PK-66 COMPOUND).

An in-depth study of the pharmacological properties of 4-[4-oxo-(4h)-quinazolin-3-yl]-benzoic acid as an analgesic agent established that it had a sufficiently high analgesic effect on models of somatic and neuropathic pain syndromes. Study objective was to study the mechanisms of analgesic action of PK-66 compound in rats using the pharmacological analysis. We evaluated the mechanisms of analgesic effect of PK-66 (1 mg/kg, intraperitoneal) compound on the thermal irritation model on Hours 1, 2, 4 and 6 after administration of study compounds. To evaluate the mechanisms of PK-66 compound pain killing, we determined the changes in its efficacy against the effects of pharmacological analyzers - Naloxon, Tramadolum, Clophelinum (Clonidine), Yohimbine, Noraepinephrine, Reserpinum, Chlorpromazine (Aminazin), Levodopa, Diazepam, and Memantine). The anti-nociceptive effect of PK-66 compound was virtually unchanged during all study terms with underlying administration of Naloxon, an opioid receptor antagonist. The results of administration of Reserpinum in rats and the concomitant administration of Noradrenaline, Clophelinum, Yohimbine and quinazoline derivative demonstrated that the adrenergic system, in particular alpha-2 adrenergic receptors, was involved in the mechanisms of PK-66 activity. Changes in the PK-66 compound effect with underlying previous administration of Levodopa and Chlorpromazine suggested that the dopaminergic system was unquestionably involved in the analgesic activity of the compound. Further study of the involvement of inhibitory and exhilarating amino acids, GABA and glutamate, showed that administration of Diazepam potentiated and extended the PK-66 analgesic effect on the thermal nociception models throughout the experiment. At the same time, increased antinociception with underlying Memantine administration preceding PK-66 was observed only in the first hours of the experiment. Therefore, the studies conducted have shown that the adrenergic system, in particular alpha-2 adrenergic receptors, dopaminergic and GABAergic systems, is involved in the mechanisms of analgesic action of 4-[4-oxo-(4h) -quinazolin-3-yl]-benzoic acid (PK-66) without any effect of PK-66 on opioid receptors.

Synthesis and biological evaluation of a series of novel pyridinecarboxamides as potential multi-receptor antipsychotic drugs.

In previous study, a series of benzamides was identified as potent antipsychotic agents. As a continuation of the program to discover novel antipsychotics, herein we reported the evaluation of a series of pyridinecarboxamide derivatives. The most promising compound 7h not only held good activities on dopamine D2, serotonin 5-HT1A and 5-HT2A receptors, but also exhibited low potency for α1A, H1 and 5-HT2C receptors, indicating a low propensity of side effects like orthostatic hypotension and weight gain. Furthermore, 7h exhibited more potent antipsychotic-like effect than aripiprazole in behavioral studies. The preliminary results were promising enough for further research around this scaffold.

The action of a negative allosteric modulator at the dopamine D2 receptor is dependent upon sodium ions.

Sodium ions (Na+) allosterically modulate the binding of orthosteric agonists and antagonists to many class A G protein-coupled receptors, including the dopamine D2 receptor (D2R). Experimental and computational evidences have revealed that this effect is mediated by the binding of Na+ to a conserved site located beneath the orthosteric binding site (OBS). SB269652 acts as a negative allosteric modulator (NAM) of the D2R that adopts an extended bitopic pose, in which the tetrahydroisoquinoline moiety interacts with the OBS and the indole-2-carboxamide moiety occupies a secondary binding pocket (SBP). In this study, we find that the presence of a Na+ within the conserved Na+-binding pocket is required for the action of SB269652. Using fragments of SB269652 and novel full-length analogues, we show that Na+ is required for the high affinity binding of the tetrahydroisoquinoline moiety within the OBS, and that the interaction of the indole-2-carboxamide moiety with the SBP determines the degree of Na+-sensitivity. Thus, we extend our understanding of the mode of action of this novel class of NAM by showing it acts synergistically with Na+ to modulate the binding of orthosteric ligands at the D2R, providing opportunities for fine-tuning of modulatory effects in future allosteric drug design efforts.