Synthesis and Structure−Activity Relationships of a New Model of Arylpiperazines. 8.1Computational Simulation of Ligand−Receptor Interaction of 5-HT1AR Agonists with Selectivity over α1-Adrenoceptors

Quantitative Monitoring of Cyclic Glycine-Proline in Marine Mangrove-Derived Fungal Metabolites

This study developed and validated a robust UPLC-MS/MS method for quantifying cyclic glycine-proline (cGP) in mangrove-derived Penicillium and Aspergillus strains. The method demonstrated excellent linearity, precision, and recovery, with detection limits as low as 4.8 ng/mL. Penicillium pedernalense extract achieved a cGP content of 67.45 ± 1.11 ng/mL, with a corresponding fermentation yield of 29.31 ± 0.61 mg/L. This surpassed Penicillium steckii, which reached a content of 31.71 ± 0.31 ng/mL, with a yield of 8.51 ± 0.15 mg/L. This quantitative approach for metabolite analysis provides a viable method for screening these fungal strains, highlighting their potential for sustainable production of cyclic glycine-proline (cGP).

Exploring Sources, Biological Functions, and Potential Applications of the Ubiquitous Marine Cyclic Dipeptide: A Concise Review of Cyclic Glycine-Proline

Cyclic glycine-proline (cGP), a prevalent marine cyclic dipeptide, possesses a distinct pyrrolidine-2,5-dione scaffold, which contributes to the chemical diversity and broad bioactivities of cGP. The diverse sources from marine-related, endogenous biological, and synthetic pathways and the in vitro and in vivo activities of cGP are reviewed. The potential applications for cGP are also explored. In particular, the pivotal roles of cGP in regulating insulin-like growth factor-1 homeostasis, enhancing neuroprotective effects, and improving neurotrophic function in central nervous system diseases are described. The potential roles of this endogenous cyclic peptide in drug development and healthcare initiatives are also highlighted. This review underscores the significance of cGP as a fundamental building block in drug discovery with exceptional drug-like properties and safety. By elucidating the considerable value of cGP, this review aims to reignite interest in cGP-related research within marine medicinal chemistry and synthetic biology.

Insights of ligand binding in modeled h5-HT1A receptor: homology modeling, docking, MM-GBSA, screening and molecular dynamics

The pharmacologically characterized receptor subtype of the serotonin family, the 5HT1A receptor is implicated in the pathophysiology and treatment of depression and anxiety-related disorders. Being the most extensively targeted receptor for developing novel antidepressants and anxiolytics, a near-ideal theoretical model can aid in high-throughput screening of promising drug candidates. However, the design of potential drug candidates suffers owing to a lack of complete structural information. In this work, homology models of 5-HT1A receptor are generated using two distinct alignments (CW and PSTA) and model building methods (KB and EB). The developed models are validated for virtual screening using a ligand dataset of agonists and antagonists. The best-suited model was efficient in discriminating agonist/antagonist binding. Correlation plots between pKi and docking (R²_agonist≥ 0.6, R²_antagonist≥ 0.7) and MM-GBSA dG bind values (R²_agonist≥ 0.5, R²_antagonist≥ 0.7) revealed optimum corroboration between in vitro and in silico outcomes, which further suggested the usefulness of the developed model for the design of high-affinity probes for the neurological disorders.Communicated by Ramaswamy H. Sarma.

Lighting Up the Plasma Membrane: Development and Applications of Fluorescent Ligands for Transmembrane Proteins

Despite the fact that transmembrane proteins represent the main therapeutic targets for decades, complete and in-depth knowledge about their biochemical and pharmacological profiling is not fully available. In this regard, target-tailored small-molecule fluorescent ligands are a viable approach to fill in the missing pieces of the puzzle. Such tools, coupled with the ability of high-precision optical techniques to image with an unprecedented resolution at a single-molecule level, helped unraveling many of the conundrums related to plasma proteins' life-cycle and druggability. Herein, we review the recent progress made during the last two decades in fluorescent ligand design and potential applications in fluorescence microscopy of voltage-gated ion channels, ligand-gated ion channels and G-coupled protein receptors.

Knowledge-Based Design of Long-Chain Arylpiperazine Derivatives Targeting Multiple Serotonin Receptors as Potential Candidates for Treatment of Autism Spectrum Disorder

Autism spectrum disorder (ASD) includes a group of neurodevelopmental disorders characterized by core symptoms such as impaired social interaction and communication, repetitive and stereotyped behaviors, and restricted interests. To date, there are no effective treatments for these core symptoms. Several studies have shown that the brain serotonin (5-HT) neurotransmission system is altered in both ASD patients and animal models of the disease. Multiple pieces of evidence suggest that targeting 5-HT receptors may treat the core symptoms of ASD and associated intellectual disabilities. In fact, stimulation of the 5-HT_1A receptor reduces repetitive and restricted behaviors; blockade of the 5-HT_2A receptor reduces both learning deficits and repetitive behavior, and activation of the 5-HT₇ receptor improves cognitive performances and reduces repetitive behavior. On such a basis, we have designed novel arylpiperazine derivatives pursuing unprecedently reported activity profiles: dual 5-HT₇/5-HT_1A receptor agonist properties and mixed 5-HT₇ agonist/5-HT_1A agonist/5-HT_2A antagonist properties. Seventeen new compounds were synthesized and tested in radioligand binding assay at the target receptors. We have identified the dual 5-HT_1AR/5-HT₇R agonists 8c and 29 and the mixed 5-HT_1AR agonist/5-HT₇R agonist/5-HT_2AR antagonist 20b. These compounds are metabolically stable in vitro and have suitable central nervous system druglike properties.

Easy Access to Novel Tetrahydro-1-benzazepine-2-carboxylic Acids and Tetrahydro-1-benzazepines Carrying [a]-Fused Heterocyclic Units from 2-(Allylaryl)glycinates

A concise, efficient, and versatile approach to access novel tetrahydro-1H-benzo[b]azepine-2-carboxylic acids and tricyclic tetra­hydro-1-benzazepines carrying [a]-fused heterocyclic units is reported. The easily accessible 2-(allylaryl)glycinates were used as starting material to synthesize, via the corresponding 1,4-epoxycycloadducts, the required key intermediate benzo[b]azepine-2-carboxylates. Hydrolysis of the latter afforded the targeted benzo[b]azepine-2-carboxylic acids. The key intermediate was also converted into N-2-chloroacetyl derivatives which, in turn, were transformed into the corresponding tricyclic target hexahydrobenzo[f]pyrazino[1,2-a]azepine-1,4-diones by reaction with benzylamine or aminoethanol. The reaction of the common intermediate with hydrazine gave the corresponding intermediate carbohydrazides, which, by reaction with trimethoxymethane, were transformed into another tricyclic target tetrahydrobenzo[f][1,2,4]tri­azino[4,5-a]azepin-4(3H)-ones. Full spectroscopic characterization (IR, HRMS, and 1H and 13C NMR) is also reported for each compound.

Design, synthesis and biological evaluation of novel serotonin and dopamine receptor ligands being 6-bromohexyl saccharine derivatives

Due to numerous side effects of current antidepressants, the search for new, safer bioactive compounds is still a valid research topic in medical chemistry. In our research we decided to synthesize and determine SAR for new hexyl arylpiperazines (LACPs) derivated with saccharin moiety. High biological activity has been explained using molecular modelling methods. The compounds obtained show high affinity for the 5-HT_1A (compound 18, K_i = 4 nM - antagonist mode) and D₂ (compound 15, K_i = 7 nM - antagonist mode) receptor, and in some cases also 5-HT₇ receptor (compound 17, K_i = 20 nM). A preliminary ADME analysis showed that the compounds exhibit CNS drugability properties. We have proved that carbon-chain lengthening may have a beneficial effect on increasing the activity towards serotonin and dopamine receptors.

Synthesis and biological evaluation of N-arylpiperazine derivatives of 4,4-dimethylisoquinoline-1,3(2H,4H)-dione as potential antiplatelet agents

Despite the substantial clinical success of aspirin and clopidogrel in secondary prevention of ischemic stroke, up to 40% of patients remain resistant to the available antiplatelet treatment. Therefore, there is an urgent clinical need to develop novel antiplatelet agents with a novel mechanism of action. Recent studies revealed that potent alpha 2B-adrenergic receptor (alpha 2B-ARs) antagonists could constitute alternative antiplatelet therapy. We have synthesized a series of N-arylpiperazine derivatives of 4,4-dimethylisoquinoline-1,3(2H,4H)-dione as potential alpha 2B receptor antagonists. The most potent compound 3, effectively inhibited the platelet-aggregation induced both by collagen and ADP/adrenaline with IC₅₀ of 26.9 μM and 20.5 μM respectively. Our study confirmed that the alpha 2B-AR antagonists remain an interesting target for the development of novel antiplatelet agents with an alternative mechanism of action.

Unique pharmacological properties of serotoninergic G-protein coupled receptors from cestodes

Background

Cestodes are a diverse group of parasites, some of them being agents of neglected diseases. In cestodes, little is known about the functional properties of G protein coupled receptors (GPCRs) which have proved to be highly druggable targets in other organisms. Notably, serotoninergic G-protein coupled receptors (5-HT GPCRs) play major roles in key functions like movement, development and reproduction in parasites.

Methodology/Principal findings

Three 5-HT GPCRs from Echinococcus granulosus and Mesocestoides corti were cloned, sequenced, bioinformatically analyzed and functionally characterized. Multiple sequence alignment with other GPCRs showed the presence of seven transmembrane segments and conserved motifs but interesting differences were also observed. Phylogenetic analysis grouped these new sequences within the 5-HT7 clade of GPCRs. Molecular modeling showed a striking resemblance in the spatial localization of key residues with their mammalian counterparts. Expression analysis using available RNAseq data showed that both E. granulosus sequences are expressed in larval and adult stages. Localization studies performed in E. granulosus larvae with a fluorescent probe produced a punctiform pattern concentrated in suckers. E. granulosus and M. corti larvae showed an increase in motility in response to serotonin. Heterologous expression revealed elevated levels of cAMP production in response to 5-HT and two of the GPCRs showed extremely high sensitivity to 5-HT (picomolar range). While each of these GPCRs was activated by 5-HT, they exhibit distinct pharmacological properties (5-HT sensitivity, differential responsiveness to ligands).

Conclusions/Significance

These data provide the first functional report of GPCRs in parasitic cestodes. The serotoninergic GPCRs characterized here may represent novel druggable targets for antiparasitic intervention.

Cestode parasites are flatworms with the ability to parasitize almost every vertebrate species. Several of these parasites are etiological agents of neglected diseases prioritized by WHO, such as hydatid disease, or hydatidosis, a zoonosis caused by species of the genus Echinococcus that affects millions of people worldwide. Due to the scarcity of anthelmintic drugs available and the emergence of resistant parasites, the discovery of new anthelmintic drugs is mandatory. Neuromuscular function has been the target of commonly used drugs against parasitic diseases to impact movement, parasite development and reproduction. Here we describe three new proteins, some of them highly expressed in cestodes which could be relevant for motility. Using different approaches, the three proteins were identified as G protein coupled receptors for serotonin, an important neurotransmitter and a known modulator of cestode motility. These new receptors exhibit unique characteristics including a particular sensitivity to serotonin as well as a distinctive pharmacology, which will assist their targeting for chemotherapeutic intervention.

New 5-Aryl-Substituted 2-Aminobenzamide-Type HDAC Inhibitors with a Diketopiperazine Group and Their Ameliorating Effects on Ischemia-Induced Neuronal Cell Death

We previously synthesized new 5-thienyl-substituted 2-aminobenzamide-type HDAC1, 2 inhibitors with the (4-ethyl-2,3-dioxopiperazine-1-carboxamido) methyl group. K-560 (1a) protected against neuronal cell death in a Parkinson’s disease model by up-regulating the expression of XIAP. This finding prompted us to design new K-560-related compounds. We examined the structure activity relationship (SAR) for the neuronal protective effects of newly synthesized and known K-560 derivatives after cerebral ischemia. Among them, K-856 (8), containing the (4-methyl-2,5-dioxopiperazin-1-yl) methyl group, exhibited a promising neuronal survival activity. The SAR study strongly suggested that the attachment of a monocyclic 2,3- or 2,5-diketopiperazine group to the 2-amino-5-aryl (but not 2-nitro-5-aryl) scaffold is necessary for K-560-related compounds to exert a potent neuroprotective effect.

A versatile synthesis of cyclic dipeptides using the stepwise construction of the piperazine-2,5-dione ring from simple precursors: synthetic sequence and the structure of a representative product, (3RS)-4-(2-allyl-3,5-dimethylphenyl)-1-benzyl-3-phenylpiperazine-2,5-dione

A versatile synthesis of multiply substituted cyclic dipeptides has been designed, based on the stepwise construction of the piperazine-2,5-dione ring using molecular fragments from four different precursor molecules. Starting from substituted 2-allylanilines, reaction with methyl 2-bromo-2-phenylacetate yields the corresponding methyl 2-(2-allylanilino)-2-phenylacetates, which react with haloacetyl chlorides to give methyl 2-[N-(2-allylphenyl)-2-haloacetamido]-2-phenylacetates, which then undergo ring closure with benzylamine to yield the corresponding cyclic dipeptides of type 4-(2-allylphenyl)-1-benzyl-3-phenylpiperazine-2,5-dione. (3RS)-4-(2-Allyl-3,5-dimethylphenyl)-1-benzyl-3-phenylpiperazine-2,5-dione, C28H28N2O2, (IIId), crystallizes with Z′ = 2 in the space group P21/c; the allyl groups in the two independent molecules adopt different conformations and, in one of them, the allyl group is disordered over two sets of atomic sites having occupancies of 0.534 (4) and 0.466 (4). In both molecules, the piperazine-2,5-dione ring adopts a boat conformation, with the 3-phenyl ring in a quasi-axial site. The molecules of (IIId) are linked into a three-dimensional framework structure by a combination of three C—H...O hydrogen bonds and three C—H...π(arene) hydrogen bonds. Comparisons are made with some related structures.

From Homology Models to a Set of Predictive Binding Pockets-a 5-HT1A Receptor Case Study

Despite its remarkable importance in the arena of drug design, serotonin 1A receptor (5-HT1A) has been elusive to the X-ray crystallography community. This lack of direct structural information not only hampers our knowledge regarding the binding modes of many popular ligands (including the endogenous neurotransmitter-serotonin), but also limits the search for more potent compounds. In this paper we shed new light on the 3D pharmacological properties of the 5-HT1A receptor by using a ligand-guided approach (ALiBERO) grounded in the Internal Coordinate Mechanics (ICM) docking platform. Starting from a homology template and set of known actives, the method introduces receptor flexibility via Normal Mode Analysis and Monte Carlo sampling, to generate a subset of pockets that display enriched discrimination of actives from inactives in retrospective docking. Here, we thoroughly investigated the repercussions of using different protein templates and the effect of compound selection on screening performance. Finally, the best resulting protein models were applied prospectively in a large virtual screening campaign, in which two new active compounds were identified that were chemically distinct from those described in the literature.

Novel 4-aryl-pyrido[1,2-c]pyrimidines with dual SSRI and 5-HT(1A) activity. Part 5

A series of novel 4-aryl-pyrido[1,2-c]pyrimidine derivatives containing a 1-(2-quinoline)piperazine moiety was synthesized. The chemical structure of new compounds was confirmed by FT-IR, (1)H NMR, (13)C NMR and HRMS spectra as well as elemental analysis. Affinity of the novel pyrido[1,2-c]pyrimidine derivatives for 5-HT1A, 5-HT2A receptors and serotonin transporter (SERT) was evaluated in an in vitro radioligand binding assay. Tested compounds showed moderate to high affinity for 5-HT1AR and SERT and low affinity for 5-HT2AR. Selected ligands were subjected to in vivo tests, such as induced hypothermia and the forced swimming test in mice, which determined presynaptic agonistic activity of the ligands 8d, 8e, 9d and 9e and presynaptic antagonistic activity of the ligands 8a, 8b, 9a, 9b. Additionally, metabolic stability evaluation was performed for selected ligands, proving that a para-substitution in the 4-aryl-pyrido[1,2-c]pyrimidine moiety leads to an increase in stability, whereas a substitution in the ortho-position lowers the stability.

Synthesis and evaluation of novel 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives as potential antidepressants

A series of 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives were synthesized and the target compounds were evaluated for their binding affinities at the 5-HT1A receptor and serotonin transporter. Antidepressant-like activities of the compounds were screened using the tail suspension and forced swim tests in mice. Preliminary results indicated that the target compounds exhibited high binding affinities at the 5-HT1A receptor and serotonin transporter, and produced marked antidepressant-like effects. The best example from this study, compound 5, exhibited high binding affinities for the 5-HT1A receptor (Ki  = 96 nM) and serotonin transporter (Ki  = 9.8 nM). The intrinsic activity of compound 5 showed agonistic property to the 5-HT1A receptor and inhibition of the 5-HT transporter. Furthermore, compound 5 exhibited greater antidepressant efficacy than fluoxetine and showed acceptable pharmacokinetic properties.

New serotonin 5-HT1A receptor agonists endowed with antinociceptive activity in vivo

We report the synthesis of new compounds 4-35 based on two different openings (A and B) of the chromane ring present in the previously identified 5-HT1A receptor (5-HT1AR) ligand 3. The synthesized compounds were assessed for binding affinity, selectivity, and functional activity at the 5-HT1AR. Selected candidates resulting from B opening were also evaluated for their potential antinociceptive effect in vivo and pharmacokinetic properties in vitro. Analogue 19 [2-(4-{[2-(2-ethoxyphenoxy)ethyl]amino}butyl)tetrahydro-1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione] has been characterized as a high-affinity and potent 5-HT1AR agonist (Ki = 2.3 nM; EC50 = 19 nM). Pharmacokinetic studies indicated that compound 19 displays a good metabolic stability in human liver microsomes (t1/2 ∼ 3 h and CLint = 3.5 mL/min/kg, at 5 μM), and a low level of protein binding (25%, at 5 μM). Interestingly, 19 (3 mg/kg, ip, and 30 mg/kg, po) caused significant attenuation of formalin-induced behavior in early and late phases of the mouse intradermal formalin test of pain, and this in vivo effect was reversed by the selective 5-HT1AR antagonist WAY-100635. Thus, the new 5-HT1AR agonist identified in this work, 19, exhibits oral analgesic activity, and the results herein represent a step toward identifying new therapeutics for the control of pain.

Application of chromatographic data in QSAR Studies of 3-[ω-(4-Arylpiperazin-1-yl)alkyl]pyrimido[5,4-c]quinolin-4(3H)-one derivatives as 5-HT1A receptor ligands

The activity of several 3-[ω-(4-arylpiperazin-1-yl)alkyl]pyrimido[5,4-c]quinolin-4(3H)-ones (LCAPs) with well-defined serotonin 1A (5-HT1A) receptor affinity was described by using chromatographic and calculated physicochemical parameters in quantitative structure-activity relationship analysis. Normal-phase thin-layer chromatography plates impregnated with solutions of L-aspartic acid, L-serine, L-phenylalanine, L-tryptophan, L-tyrosine, L-asparagine, L-threonine and their mixtures (denoted as S1-S11 biochromatographic models) were used with two mobile phases as a model of the interaction between LCAP and 5-HT1A receptors. Molecular descriptors for the investigated compounds were calculated by using HyperChem and ACD/Labs programs. The significant relationship explains that 82% of the variance was successfully validated by leave-one-out and leave-many-out tests. The results demonstrated that this model has significant predictive ability and can be used for the preliminary screening of newly synthesized potential 5-HT1A receptor ligands.

New serotonin 5-HT(1A) receptor agonists with neuroprotective effect against ischemic cell damage

We report the synthesis of new compounds 4-35 based on structural modifications of different moieties of previously described lead UCM-2550. The new nonpiperazine derivatives, representing second-generation agonists, were assessed for binding affinity, selectivity, and functional activity at the 5-HT(1A) receptor (5-HT(1A)R). Computational β(2)-based homology models of the ligand-receptor complexes were used to explain the observed structure-affinity relationships. Selected candidates were also evaluated for their potential in vitro and in vivo neuroprotective properties. Interestingly, compound 26 (2-{6-[(3,4-dihydro-2H-chromen-2-ylmethyl)amino]hexyl}tetrahydro-1H-pyrrolo[1,2-c]imidazole-1,3(2H)-dione) has been characterized as a high-affinity and potent 5-HT(1A)R agonist (K(i) = 5.9 nM, EC(50) = 21.8 nM) and exhibits neuroprotective effect in neurotoxicity assays in primary cell cultures from rat hippocampus and in the MCAO model of focal cerebral ischemia in rats.

Development of Fluorescent Ligands for the Human 5-HT1A Receptor

In this work, we report the design and synthesis of a set of fluorescent probes targeting the human 5-HT1A receptor (h5-HT1AR). Among the synthesized compounds, derivative 4 deserves special attention as being a high-affinity ligand (K i = 2 nM) with good fluorescent properties (I em > 1000 au and a fluorescence quantum yield, Φf, of 0.26), which enables direct observation of the h5-HT1AR in cells. Thus, it represents the first efficacious fluorescent probe for the specific labeling of h5-HT1AR in cells. Our results provide the basis for the introduction of a variety of tags in scaffolds of G protein-coupled receptor (GPCR) ligands that enable visualization, covalent binding, or affinity pull-down of receptors. These strategies should contribute to the optimization of the therapeutic exploitation of known or new members of the GPCR superfamily by providing valuable information about their location or level of expression.

Benzimidazole derivatives as new serotonin 5-HT6 receptor antagonists. Molecular mechanisms of receptor inactivation

On the basis of our previously described pharmacophore model for serotonin 5-HT(6) receptor (5-HT(6)R) antagonists, we have designed, synthesized, and pharmacologically characterized a series of benzimidazole derivatives 1-20 that represent a new family of potent antagonists at the human 5-HT(6)R. Site-directed mutagenesis and a beta(2)-adrenoceptor-based homology model of the 5-HT(6)R were used to predict the mode of binding of antagonist SB-258585 and the new synthesized ligands. Substitution of W6.48, F6.52, or N6.55 by Ala fully impedes compound 4 to block 5-HT-induced activation. Thus, we propose that D3.32 in TM 3 anchors the protonated piperazine ring, the benzimidazole ring expands parallel to EL 2 to hydrogen bond N6.55 in TM 6, and the aromatic ring is placed between TMs 3 and 5 in CH(2)-containing compounds and between TMs 3 and 6 in CO-containing compounds. This combined experimental and computational study has permitted to propose the molecular mechanisms by which the new benzimidazole derivatives act as 5-HT(6)R antagonists.

Pharmacophore-based 3D QSAR studies on a series of high affinity 5-HT1A receptor ligands

5-HT(1A) receptor antagonists have been employed to treat depression, but the lack of structural information on this receptor hampers the design of specific and selective ligands. In this study, we have performed CoMFA studies on a training set of arylpiperazines (high affinity 5-HT(1A) receptor ligands) and to produce an effective alignment of the data set, a pharmacophore model was produced using Galahad. A statistically significant model was obtained, indicating a good internal consistency and predictive ability for untested compounds. The information gathered from our receptor-independent pharmacophore hypothesis is in good agreement with results from independent studies using different approaches. Therefore, this work provides important insights on the chemical and structural basis involved in the molecular recognition of these compounds.

Synthesis of new serotonin 5-HT7 receptor ligands. Determinants of 5-HT7/5-HT1A receptor selectivity

We report the synthesis of a new set of compounds of general structure I (1-20) with structural modifications in the pharmacophoric elements of the previously reported lead UCM-5600. The new derivatives have been evaluated for binding affinity at 5-HT(7) and 5-HT(1A) receptors. The influence of the different structural features in terms of 5-HT(7)/5-HT(1A) receptor affinity and selectivity was analyzed by computational simulations of the complexes between compounds I and beta(2)-based 3-D models of these receptors. Compound 18 (HYD(1) = 1,3-dihydro-2H-indol-2-one; spacer = -(CH(2))(4)-; HYD(2) + HYD(3) = 3,4-dihydroisoquinolin-2(1H)-yl) exhibits high 5-HT(7)R affinity (K(i) = 7 nM) and selectivity over the 5-HT(1A)R (31-fold), and has been characterized as a partial agonist of the human 5-HT(7)R.

Constitutively active mutants of the histamine H1 receptor suggest a conserved hydrophobic asparagine-cage that constrains the activation of class A G protein-coupled receptors

The aim of this study was to create and characterize constitutively active mutant (CAM) histamine H(1) receptors (H(1)R) using random mutagenesis methods to further investigate the activation process of the rhodopsin-like family of G protein-coupled receptors (GPCRs). This approach identified position 6.40 in TM 6 as a "hot spot" because mutation of Ile6.40(420) either to Glu, Gly, Ala, Arg, Lys, or Ser resulted in highly active CAM H(1)Rs, for which almost no histamine-induced receptor activation response could be detected. The highly conserved hydrophobic amino acid at position 6.40 defines, in a computational model of the H(1)R, the asparagine cage motif that restrains the side chain of Asn7.49 of the NPxxY motif toward transmembrane domain (TM 6) in the inactive state of the receptor. Mutation of the asparagine cage into Ala or Gly, removing the interfering bulky constraints, increases the constitutive activity of the receptor. The fact that the Ile6.40(420)Arg/Lys/Glu mutant receptors are highly active CAM H(1)Rs leads us to suggest that a positively charged residue, presumably the highly conserved Arg3.50 from the DRY motif, interacts in a direct or an indirect (through other side chains or/and internal water molecules) manner with the acidic Asp2.50..Asn7.49 pair for receptor activation.

Novel pyridyl-fused 3-amino chroman derivatives with dual action at serotonin transporter and 5-HT1A receptor

Structural modifications of the initial lead, 3-aminochroman (4), led to the identification of a novel series of pyridyl-fused amino chroman derivatives (5-8) and the structural isomers (9-12). The compounds described were evaluated for dual 5-HT transporter inhibitory and 5-HT(1A) receptor activities. The design strategy, synthesis, and in vitro biological characterization for these novel compounds are described.

Novel class of arylpiperazines containing N-acylated amino acids: Their synthesis, 5-HT1A, 5-HT2A receptor affinity, and in vivo pharmacological evaluation

Novel arylpiperazines with N-acylated amino acids, selected on the basis of a preliminary screening of two libraries previously synthesized on SynPhase Lanterns, were prepared in solution and their affinity for 5-HT(1A), 5-HT(2A), and D(2) receptors was evaluated. The compounds bearing (3-acylamino)pyrrolidine-2,5-dione (19-26) and N-acylprolinamide (29-34) moieties showed high affinity for 5-HT(1A) (K(i)=3-47 nM), high-to-low for 5-HT(2A) (K(i)=4.2-990 nM), and low for D(2) receptors (K(i)=0.77-21.19 microM). All the new o-methoxy derivatives of (3-acylamino)pyrrolidine-2,5-diones tested in vivo revealed agonistic activity at postsynaptic 5-HT(1A) receptors, while m-chloro derivatives were classified as antagonists of these sites; similar relations were observed for o-methoxy (29) and m-chlorophenylpiperazine derivatives of N-acylprolinamides. The reported results show that the amino acid-derived terminal fragment modified the in vivo functional profile. Finally, the selected compounds 19 and 20, a 5-HT(1A) partial agonist and a full agonist, respectively, and 26, a mixed 5-HT(1A)/5-HT(2A) antagonist, were evaluated in preclinical animal models of depression and anxiety. The project allowed selecting the lead compound 20 which exhibited an anxiolytic-like effect in the four-plate test in mice and revealed distinct antidepressant-like effects in the forced swimming and tail suspension tests in mice.

Pharmacogenomic and Structural Analysis of Constitutive G Protein–Coupled Receptor Activity

G protein-coupled receptors (GPCRs) respond to a chemically diverse plethora of signal transduction molecules. The notion that GPCRs also signal without an external chemical trigger, i.e., in a constitutive or spontaneous manner, resulted in a paradigm shift in the field of GPCR pharmacology. The discovery of constitutive GPCR activity and the fact that GPCR binding and signaling can be strongly affected by a single point mutation drew attention to the evolving area of GPCR pharmacogenomics. For a variety of GPCRs, point mutations have been convincingly linked to human disease. Mutations within conserved motifs, known to be involved in GPCR activation, might explain the properties of some naturally occurring, constitutively active GPCR variants linked to disease. In this review, we provide a brief historical introduction to the concept of constitutive receptor activity and the pharmacogenomic and structural aspects of constitutive receptor activity.

Interaction of arylpiperazine ligands with the hydrophobic part of the 5-HT1A receptor binding site

A flexible docking of a series of arylpiperazine derivatives with structurally different aryl part to the binding site of a model of human 5-HT1A receptor was exercised. The influence of structure and hydrophobic properties of aryl moiety on binding affinities was discussed and a model for ligand binding in the hydrophobic part of the binding site was proposed.

Synthesis of new piperazine–pyridazinone derivatives and their binding affinity toward α1-, α2-adrenergic and 5-HT1A serotoninergic receptors

We report the design and synthesis of a new class of piperazine-pyridazinone analogues. The arylpiperazine moiety, the length of the spacer, and the terminal molecular fragment were varied to evaluate their influence in determining the affinity of the new compounds toward the alpha1-adrenergic receptor (alpha1-AR), alpha2-adrenergic receptor (alpha2-AR), and the 5-HT1A serotoninergic receptor (5-HT1AR). Biological data showed that most of the compounds have an alpha1-AR affinity in the nanomolar or subnanomolar range, while affinity toward the other two receptors was lower in most cases. However, several of the tested compounds also showed very good (in the nanomolar range) or moderate affinity toward the 5-HT1AR subtype.