Chlorophenoxy aminoalkyl derivatives as histamine H(3)R ligands and antiseizure agents

Terminal Phenoxy Group as a Privileged Moiety of the Drug Scaffold—A Short Review of Most Recent Studies 2013–2022

The terminal phenoxy group is a moiety of many drugs in use today. Numerous literature reports indicated its crucial importance for biological activity; thus, it is a privileged scaffold in medicinal chemistry. This review focuses on the latest achievements in the field of novel potential agents bearing a terminal phenoxy group in 2013–2022. The article provided information on neurological, anticancer, potential lymphoma agent, anti-HIV, antimicrobial, antiparasitic, analgesic, anti-diabetic as well as larvicidal, cholesterol esterase inhibitors, and antithrombotic or agonistic activities towards the adrenergic receptor. Additionally, for selected agents, the Structure–Activity–Relationship (SAR) is also discussed. Thus, this study may help the readers to better understand the nature of the phenoxy group, which will translate into rational drug design and the development of a more efficient drug. To the best of our knowledge, this is the first review devoted to an in-depth analysis of the various activities of compounds bearing terminal phenoxy moiety.

Guided rational design with scaffold hopping leading to novel histamine H3 receptor ligands

During the past decades, histamine H₃ receptors have received widespread attention in pharmaceutical research due to their involvement in pathophysiology of several diseases such as neurodegenerative disorders. In this context, blocking of these receptors is of paramount importance in progression of such diseases. In the current investigation, novel histamine H₃ receptor ligands were designed by exploiting scaffold-hopping drug-design strategy. We inspected the designed molecules in terms of ADME properties, drug-likeness, as well as toxicity profiles. Additionally molecular docking and dynamics simulation studies were performed to predict binding mode and binding free energy calculations, respectively. Among the designed structures, we selected compound d2 and its demethylated derivative as examples for synthesis and affinity measurement. In vitro binding assays of the synthesized molecules demonstrated that d2 has lower binding affinity (K_i = 2.61 μM) in radioligand displacement assay to hH₃R than that of demethylated form (K_i = 12.53 μM). The newly designed compounds avoid of any toxicity predictors resulted from extended in silico and experimental studies, can offer another scaffold for histamine H₃R antagonists for further structure-activity relationship studies.

Discovery of Potential, Dual-Active Histamine H3 Receptor Ligands with Combined Antioxidant Properties

In an attempt to find new dual acting histamine H₃ receptor (H₃R) ligands, we designed a series of compounds, structurally based on previously described in our group, a highly active and selective human histamine H₃ receptor (hH₃R) ligand KSK63. As a result, 15 obtained compounds show moderate hH₃R affinity, the best being the compound 17 (hH₃R K_i = 518 nM). Docking to the histamine H₃R homology model revealed two possible binding modes, with key interactions retained in both cases. In an attempt to find possible dual acting ligands, selected compounds were tested for antioxidant properties. Compound 16 (hH₃R K_i = 592 nM) showed the strongest antioxidant properties at the concentration of 10⁻⁴ mol/L. It significantly reduced the amount of free radicals presenting 50–60% of ascorbic acid activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, as well as showed antioxidative properties in the ferric reducing antioxidant power (FRAP) assay. Despite the yet unknown antioxidation mechanism and moderate hH₃R affinity, 16 (QD13) constitutes a starting point for the search of potential dual acting H₃R ligands-promising tools for the treatment of neurological disorders associated with increased neuronal oxidative stress.

Molecular Modeling of Histamine Receptors-Recent Advances in Drug Discovery

The recent developments of fast reliable docking, virtual screening and other algorithms gave rise to discovery of many novel ligands of histamine receptors that could be used for treatment of allergic inflammatory disorders, central nervous system pathologies, pain, cancer and obesity. Furthermore, the pharmacological profiles of ligands clearly indicate that these receptors may be considered as targets not only for selective but also for multi-target drugs that could be used for treatment of complex disorders such as Alzheimer's disease. Therefore, analysis of protein-ligand recognition in the binding site of histamine receptors and also other molecular targets has become a valuable tool in drug design toolkit. This review covers the period 2014-2020 in the field of theoretical investigations of histamine receptors mostly based on molecular modeling as well as the experimental characterization of novel ligands of these receptors.

Simultaneous Blockade of Histamine H3 Receptors and Inhibition of Acetylcholine Esterase Alleviate Autistic-Like Behaviors in BTBR T+ tf/J Mouse Model of Autism

Autism spectrum disorder (ASD) is a heterogenous neurodevelopmental disorder defined by persistent deficits in social interaction and the presence of patterns of repetitive and restricted behaviors. The central neurotransmitters histamine (HA) and acetylcholine (ACh) play pleiotropic roles in physiological brain functions that include the maintenance of wakefulness, depression, schizophrenia, epilepsy, anxiety and narcolepsy, all of which are found to be comorbid with ASD. Therefore, the palliative effects of subchronic systemic treatment using the multiple-active test compound E100 with high H₃R antagonist affinity and AChE inhibitory effect on ASD-like behaviors in male BTBR T+tf/J (BTBR) mice as an idiopathic ASD model were assessed. E100 (5, 10 and 15 mg/kg, i.p.) dose-dependently palliated social deficits of BTBR mice and significantly alleviated the repetitive/compulsive behaviors of tested animals. Moreover, E100 modulated disturbed anxiety levels, but failed to modulate hyperactivity parameters, whereas the reference AChE inhibitor donepezil (DOZ, one milligram per kilogram) significantly obliterated the increased hyperactivity measures of tested mice. Furthermore, E100 mitigated the increased levels of AChE activity in BTBR mice with observed effects comparable to that of DOZ and significantly reduced the number of activated microglial cells compared to the saline-treated BTBR mice. In addition, the E100-provided effects on ASD-like parameters, AChE activity, and activated microglial cells were entirely reversed by co-administration of the H₃R agonist (R)-α-methylhistamine (RAM). These initial overall results observed in an idiopathic ASD mice model show that E100 (5 mg/kg) alleviated the assessed behavioral deficits and demonstrate that simultaneous targeting of brain histaminergic and cholinergic neurotransmissions is crucial for palliation of ASD-like features, albeit further in vivo assessments on its effects on brain levels of ACh as well as HA are still needed.

Rational design of new multitarget histamine H3 receptor ligands as potential candidates for treatment of Alzheimer's disease

Design and development of multitarget-directed ligands (MTDLs) has become a very important approach in the search of new therapies for Alzheimer's disease (AD). In our present research, a number of xanthone derivatives were first designed using a pharmacophore model for histamine H₃ receptor (H₃R) antagonists/inverse agonists, and virtual docking was then performed for the enzyme acetylcholinesterase. Next, 23 compounds were synthesised and evaluated in vitro for human H₃R (hH₃R) affinity and inhibitory activity on cholinesterases. Most of the target compounds showed hH₃R affinities in nanomolar range and exhibited cholinesterase inhibitory activity with IC₅₀ values in submicromolar range. Furthermore, the inhibitory effects of monoamine oxidases (MAO) A and B were investigated. The results showed low micromolar and selective human MAO B (hMAO B) inhibition. Two azepane derivatives, namely 23 (2-(5-(azepan-1-yl)pentyloxy)-9H-xanthen-9-one) and 25 (2-(5-(azepan-1-yl)pentyloxy)-7-chloro-9H-xanthen-9-one), were especially very promising and showed high affinity for hH₃R (K_i = 170 nM and 100 nM respectively) and high inhibitory activity for acetylcholinesterase (IC₅₀ = 180 nM and 136 nM respectively). Moreover, these compounds showed moderate inhibitory activity for butyrylcholinesterase (IC₅₀ = 880 nM and 394 nM respectively) and hMAO B (IC₅₀ = 775 nM and 897 nM respectively). Furthermore, molecular docking studies were performed for hH₃R, human cholinesterases and hMAO B to describe the mode of interactions with these biological targets. Next, the two most promising compounds 23 and 25 were selected for in vivo studies. The results showed significant memory-enhancing effect of compound 23 in dizocilpine-induced amnesia in rats in two tests: step-through inhibitory avoidance paradigm (SIAP) and transfer latency paradigm time (TLPT). In addition, favourable analgesic effects of compound 23 were observed in neuropathic pain models. Therefore, compound 23 is a particularly promising structure for further design of new MTDLs for AD.

QSAR and Molecular Docking Studies on Non-Imidazole-Based Histamine H3 Receptor Antagonists

Background: In the recent years, histamine H3 receptor (H3R) has been receiving increasing attention in pharmacotherapy of neurological disorders. The aim of the current study was to investigate structural requirements for the prediction of H3 antagonistic activity using quantitative structure-activity relationship (QSAR) and molecular docking techniques. Methods: To this end, genetic algorithm coupled partial least square and stepwise multiple linear regression methods were employed for developing a QSAR model. The obtained QSAR model was stringently assessed using different validation criteria. Results: The generated model indicated that connectivity information and mean absolute charge are two important descriptors for the prediction of H3 antagonistic activity of the studied compounds. To gain insight into the mechanism of interaction between studied molecules and H3R, molecular docking was performed. The most important residues involved in the ligand-receptor interactions were identified. Conclusion: The result of current study can be used for designing of new H3 antagonist and proposing structural modifications to improve H3 inhibitory potency.

The Dual-Active Histamine H3 Receptor Antagonist and Acetylcholine Esterase Inhibitor E100 Alleviates Autistic-Like Behaviors and Oxidative Stress in Valproic Acid Induced Autism in Mice

The histamine H3 receptor (H3R) functions as auto- and hetero-receptors, regulating the release of brain histamine (HA) and acetylcholine (ACh), respectively. The enzyme acetylcholine esterase (AChE) is involved in the metabolism of brain ACh. Both brain HA and ACh are implicated in several cognitive disorders like Alzheimer’s disease, schizophrenia, anxiety, and narcolepsy, all of which are comorbid with autistic spectrum disorder (ASD). Therefore, the novel dual-active ligand E100 with high H3R antagonist affinity (hH3R: K_i = 203 nM) and balanced AChE inhibitory effect (EeAChE: IC₅₀ = 2 µM and EqBuChE: IC₅₀ = 2 µM) was investigated on autistic-like sociability, repetitive/compulsive behaviour, anxiety, and oxidative stress in male C57BL/6 mice model of ASD induced by prenatal exposure to valproic acid (VPA, 500 mg/kg, intraperitoneal (i.p.)). Subchronic systemic administration with E100 (5, 10, and 15 mg/kg, i.p.) significantly and dose-dependently attenuated sociability deficits of autistic (VPA) mice in three-chamber behaviour (TCB) test (all p < 0.05). Moreover, E100 significantly improved repetitive and compulsive behaviors by reducing the increased percentage of marbles buried in marble-burying behaviour (MBB) (all p < 0.05). Furthermore, pre-treatment with E100 (10 and 15 mg/kg, i.p.) corrected decreased anxiety levels (p < 0.05), however, failed to restore hyperactivity observed in elevated plus maze (EPM) test. In addition, E100 (10 mg/kg, i.p.) mitigated oxidative stress status by increasing the levels of decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT), and decreasing the elevated levels of malondialdehyde (MDA) in the cerebellar tissues (all p < 0.05). Additionally, E100 (10 mg/kg, i.p.) significantly reduced the elevated levels of AChE activity in VPA mice (p < 0.05). These results demonstrate the promising effects of E100 on in-vivo VPA-induced ASD-like features in mice, and provide evidence that a potent dual-active H3R antagonist and AChE inhibitor (AChEI) is a potential drug candidate for future therapeutic management of autistic-like behaviours.

Dual Target Ligands with 4-tert-Butylphenoxy Scaffold as Histamine H3 Receptor Antagonists and Monoamine Oxidase B Inhibitors

Dual target ligands are a promising concept for the treatment of Parkinson's disease (PD). A combination of monoamine oxidase B (MAO B) inhibition with histamine H₃ receptor (H₃R) antagonism could have positive effects on dopamine regulation. Thus, a series of twenty-seven 4-tert-butylphenoxyalkoxyamines were designed as potential dual-target ligands for PD based on the structure of 1-(3-(4-tert-butylphenoxy)propyl)piperidine (DL76). Probed modifications included the introduction of different cyclic amines and elongation of the alkyl chain. Synthesized compounds were investigated for human H₃R (hH₃R) affinity and human MAO B (hMAO B) inhibitory activity. Most compounds showed good hH₃R affinities with K_i values below 400 nM, and some of them showed potent inhibitory activity for hMAO B with IC₅₀ values below 50 nM. However, the most balanced activity against both biological targets showed DL76 (hH₃R: K_i = 38 nM and hMAO B: IC₅₀ = 48 nM). Thus, DL76 was chosen for further studies, revealing the nontoxic nature of DL76 in HEK293 and neuroblastoma SH-SY5Ycells. However, no neuroprotective effect was observed for DL76 in hydrogen peroxide-treated neuroblastoma SH-SY5Y cells. Furthermore, in vivo studies showed antiparkinsonian activity of DL76 in haloperidol-induced catalepsy (Cross Leg Position Test) at a dose of 50 mg/kg body weight.

In silico and in vitro studies of two non-imidazole multiple targeting agents at histamine H3 receptors and cholinesterase enzymes

Recently, multi-target directed ligands have been of research interest for multifactorial disorders such as Alzheimer's disease (AD). Since H₃ receptors (H₃ Rs) and cholinesterases are involved in pathophysiology of AD, identification of dual-acting compounds capable of improving cholinergic neurotransmission is of importance in AD pharmacotherapy. In the present study, H₃ R antagonistic activity combined with anticholinesterase properties of two previously computationally identified lead compounds, that is, compound 3 (6-chloro-N-methyl-N-[3-(4-methylpiperazin-1-yl)propyl]-1H-indole-2-carboxamide) and compound 4 (7-chloro-N-[(1-methylpiperidin-3-yl)methyl]-1,2,3,4-tetrahydroisoquinoline-2-carboxamide), was tested. Moreover, molecular docking and binding free energy calculations were conducted for binding mode and affinity prediction of studied ligands toward cholinesterases. Biological evaluations revealed inhibitory activity of ligands in nanomolar (compound 3: H₃ R EC₅₀  = 0.73 nM; compound 4: H₃ R EC₅₀  = 31 nM) and micromolar values (compound 3: AChE IC₅₀  = 9.09 µM, BuChE IC₅₀  = 21.10 µM; compound 4: AChE IC₅₀  = 8.40 µM, BuChE IC₅₀  = 4.93 µM) for H₃ R antagonism and cholinesterase inhibition, respectively. Binding free energies yielded good consistency with cholinesterase inhibitory profiles. The results of this study can be used for lead optimization where dual inhibitory activity on H₃ R and cholinesterases is needed. Such ligands can exert their biological activity in a synergistic manner resulting in higher potency and efficacy.

Search for new multi-target compounds against Alzheimer's disease among histamine H3 receptor ligands

Multi-target-directed ligands seem to be an interesting approach to the treatment of complex disorders such as Alzheimer's disease. The aim of the present study was to find novel multifunctional compounds in a non-imidazole histamine H₃ receptor ligand library. Docking-based virtual screening was applied for selection of twenty-six hits which were subsequently evaluated in Ellman's assay for the inhibitory potency toward acetyl- (AChE) and butyrylcholinesterase (BuChE). The virtual screening with high success ratio enabled to choose multi-target-directed ligands. Based on docking results, all selected ligands were able to bind both catalytic and peripheral sites of AChE and BuChE. The most promising derivatives combined the flavone moiety via a six carbon atom linker with a heterocyclic moiety, such as azepane, piperidine or 3-methylpiperidine. They showed the highest inhibitory activities toward cholinesterases as well as well-balanced potencies against H₃R and both enzymes. Two derivatives were chosen - 5 (IC₅₀ = 0.46 μM (AChE); 0.44 μM (BuChE); K_i = 159.8 nM (H₃R)) and 17 (IC₅₀ = 0.50 μM (AChE); 0.76 μM (BuChE); K_i = 228.2 nM (H₃R)), and their inhibition mechanism was evaluated in kinetic studies. Both compounds displayed non-competitive mode of AChE and BuChE inhibition. Compounds 5 and 17 might serve as good lead structures for further optimization and development of novel multi-target anti-Alzheimer's agents.

Histamine H3 receptor ligands by hybrid virtual screening, docking, molecular dynamics simulations, and investigation of their biological effects

Histamine H₃ receptors (H₃ R), belonging to G-protein coupled receptors (GPCR) class A superfamily, are responsible for modulating the release of histamine as well as of other neurotransmitters by a negative feedback mechanism mainly in the central nervous system (CNS). These receptors have gained increased attention as therapeutic target for several CNS related neurological diseases. In the current study, we aimed to identify novel H₃ R ligands using in silico virtual screening methods. To this end, a combination of ligand- and structure-based approaches was utilized for screening of ZINC database on the homology model of human H₃ R. Structural similarity- and pharmacophore-based approaches were employed to generate compound libraries. Various molecular modeling methodologies such as molecular docking and dynamics simulation along with different drug likeness filtering criteria were applied to select anti-H₃ R ligands as promising candidate molecules based on different known parent lead compounds. In vitro binding assays of the selected molecules demonstrated three of them being active within the micromolar and submicromolar K_i range. The current integrated computational and experimental methods used in this work can provide new general insights for systematic hit identification for novel anti-H₃ R agents from large compound libraries.

Optimization and preclinical evaluation of novel histamine H3receptor ligands: Acetyl and propionyl phenoxyalkyl piperazine derivatives

As a continuation of our search for novel histamine H₃ receptor ligands, a series of new acetyl and propionyl phenoxyalkylamine derivatives (2-25) was synthesized. Compounds with three to four carbon atoms alkyl chain spacer, composed of six various 4N-substituted piperazine moieties were evaluated for their binding properties at human histamine H₃ receptors (hH₃R). In vitro test results proved the 4-pyridylpiperazine moiety as crucial element for high hH₃R affinity (hH₃R K_i = 5.2-115 nM). Moreover introduction of carbonyl group containing residues in the lipophilic part of molecules instead of branched alkyl substituents resulted in increased affinity in correlation to previously described series, whereas propionyl derivatives showed slightly higher affinities than those of acetyl (16 and 22vs.4 and 10; hH₃R K_i = 5.2 and 15.4 nM vs. 10.2 and 115 nM, respectively). These findings were confirmed by molecular modelling studies, demonstrating multiple ligand-receptor interactions. Furthermore, pharmacological in vivo test results of compound 4 clearly indicate that it may affect the amount of calories consumed, thus act as an anorectic compound. Likewise, its protective action against hyperglycemia and the development of overweight has been shown. In order to estimate drug-likeness of compound 4, in silico and experimental evaluation of metabolic stability in human liver microsomes was performed.

4-tert-Pentylphenoxyalkyl derivatives - Histamine H3 receptor ligands and monoamine oxidase B inhibitors

The synthesis and biological activity of 4-tert-pentylphenoxypropyl derivatives are described in this manuscript. All compounds (except one) showed human histamine H₃ receptor affinity with K_i values below 760 nM. The inhibitory activity toward human monoamine oxidase B (hMAO B) was evaluated using a fluorometric Amplex-Red assay, and most of the compounds were effective in the submicromolar range. Among them, 1-(3-(4-tert-pPentylphenoxy)propyl)pyrrolidine (5) exhibited hMAO B inhibitory activity with an IC₅₀ value of 4.5 nM. In addition, hMAO B inhibition by 5 was shown to be non-competitive and reversible. Further, recently described potent histamine H₃ receptor ligands - 4-tert-pentylphenoxyalkyl derivatives (with a 4-8 carbon spacer) - were evaluated for hMAO B inhibitory activity, and some of them displayed activity in the submicromolar range. Selected compounds were also tested for human MAO A (hMAO A) inhibitory potencies and exhibited no activity. Moreover, molecular modeling studies were carried out for tested compounds to explain their molecular mechanism of hMAO B inhibition and the selectivity of compounds for hMAO B over hMAO A.

Studies on Anticonvulsant Effects of Novel Histamine H3R Antagonists in Electrically and Chemically Induced Seizures in Rats

A newly developed series of non-imidazole histamine H3 receptor (H3R) antagonists (1⁻16) was evaluated in vivo for anticonvulsant effects in three different seizure models in Wistar rats. Among the novel H3R antagonists examined, H3R antagonist 4 shortened the duration of tonic hind limb extension (THLE) in a dose-dependent fashion in the maximal electroshock (MES)-induced seizure and offered full protection against pentylenetetrazole (PTZ)-induced generalized tonic-clonic seizure (GTCS), following acute systemic administration (2.5, 5, 10, and 15 mg/kg, i.p.). However, only H3R antagonist 13, without appreciable protective effects in MES- and PTZ-induced seizure, fully protected animals in the strychnine (STR)-induced GTCS following acute systemic pretreatment (10 mg/kg, i.p.). Moreover, the protective effect observed with H3R antagonist 4 in MES-induced seizure was completely abolished when animals were co-administered with the H3R agonist (R)-α-methylhistamine (RAMH, 10 mg/kg, i.p.). However, RAMH failed to abolish the full protection provided by the H3R antagonist 4 in PTZ-induced seizure and H3R antagonist 13 in STR-induced seizure. Furthermore, in vitro antiproliferative effects or possible metabolic interactions could not be observed for compound 4. Additionally, the predictive in silico, as well as in vitro, metabolic stability for the most promising H3R antagonist 4 was assessed. The obtained results show prospective effects of non-imidazole H3R antagonists as innovative antiepileptic drugs (AEDs) for potential single use against epilepsy.

Synthesis and biological activity of novel tert-butyl and tert-pentylphenoxyalkyl piperazine derivatives as histamine H3R ligands

As a continuation of our search for novel histamine H₃ receptor ligands, a series of twenty four new tert-butyl and tert-pentyl phenoxyalkylamine derivatives (2-25) was synthesized. Compounds with three to four carbon atoms alkyl chain spacer were evaluated for their binding properties at human histamine H₃ receptor (hH₃R). The highest affinities were observed for 4-pyridyl derivatives 4, 10, 16 and 22 (K_i = 16.0-120 nM). As it has been shown in docking studies, those specific heteroaromatic 4-N piperazine substituents might interact with one of the key receptor interacting amino acids. Moreover, the most promising compounds exhibited anticonvulsant activity in the maximal electroshock-induced seizure (MES) model in mice. Furthermore, the blood-brain barrier penetration, the functional H₃R antagonist potency as well as the pro-cognitive properties in the passive avoidance test were demonstrated for compound 10. In order to estimate drug-likeness of compound 10,in silico and experimental evaluation of metabolic stability in human liver microsomes was performed. In addition, paying attention to the results obtained within this study, the 4-pyridyl-piperazino moiety has been established as a new bioisosteric piperidine replacement in H₃R ligands.

Hybrid approach to structure modeling of the histamine H3 receptor: Multi-level assessment as a tool for model verification

The crucial role of G-protein coupled receptors and the significant achievements associated with a better understanding of the spatial structure of known receptors in this family encouraged us to undertake a study on the histamine H3 receptor, whose crystal structure is still unresolved. The latest literature data and availability of different software enabled us to build homology models of higher accuracy than previously published ones. The new models are expected to be closer to crystal structures; and therefore, they are much more helpful in the design of potential ligands. In this article, we describe the generation of homology models with the use of diverse tools and a hybrid assessment. Our study incorporates a hybrid assessment connecting knowledge-based scoring algorithms with a two-step ligand-based docking procedure. Knowledge-based scoring employs probability theory for global energy minimum determination based on information about native amino acid conformation from a dataset of experimentally determined protein structures. For a two-step docking procedure two programs were applied: GOLD was used in the first step and Glide in the second. Hybrid approaches offer advantages by combining various theoretical methods in one modeling algorithm. The biggest advantage of hybrid methods is their intrinsic ability to self-update and self-refine when additional structural data are acquired. Moreover, the diversity of computational methods and structural data used in hybrid approaches for structure prediction limit inaccuracies resulting from theoretical approximations or fuzziness of experimental data. The results of docking to the new H3 receptor model allowed us to analyze ligand-receptor interactions for reference compounds.

Biphenyloxy-alkyl-piperidine and azepane derivatives as histamine H3 receptor ligands

Novel biphenyloxy-alkyl derivatives of piperidine and azepane were synthesized and evaluated for their binding properties at the human histamine H₃ receptor. Two series of compounds were obtained with a meta- and a para-biphenyl moiety. The alkyl chain spacer contained five and six carbon atoms. The highest affinity among all compounds was shown by 1-(6-(3-phenylphenoxy)hexyl)azepane (13) with a K_i value of 18nM. Two para-biphenyl derivatives, 1-(5-(4-phenylphenoxy)pentyl)piperidine (14; K_i=25nM) and 1-(5-(4-phenylphenoxy)pentyl)azepane (16; K_i=34nM), classified as antagonists in a cAMP accumulation assay (IC₅₀=4 and 9nM, respectively), were studied in detail. Compounds 14 and 16 blocked RAMH-induced dipsogenia in rats (ED₅₀ of 2.72mg/kg and 1.75mg/kg respectively), and showed high selectivity (hH₄R vs hH₃R>600-fold) and low toxicity (hERG inhibition: IC₅₀>1.70µM; hepatotoxicity IC₅₀>12.5µM; non-mutagenic up to 10µM). Furthermore, the metabolic stability was evaluated in vitro on human liver microsomes (HLMs) and/or rat liver microsomes (RLMs). Metabolites produced were analyzed and tentatively identified by UPLC-MS techniques. The results demonstrated easy hydroxylation of the biphenyl ring.

Synthesis and biological activity of novel tert-amylphenoxyalkyl (homo)piperidine derivatives as histamine H3R ligands

As a continuation of our search for novel histamine H₃ receptor ligands a series of twenty new tert-amyl phenoxyalkylamine derivatives (2-21) was synthesized. Compounds of four to eight carbon atoms spacer alkyl chain were evaluated on their binding properties at human histamine H₃ receptor (hH₃R). The highest affinities were observed for pentyl derivatives 6-8 (K_i=8.8-23.4nM range) and among them piperidine derivative 6 with K_i=8.8nM. Structures 6, 7 were also classified as antagonists in cAMP accumulation assay (with EC₅₀=157 and 164nM, respectively). Moreover, new compounds were also evaluated for anticonvulsant activity in Antiepileptic Screening Program (ASP) at National Institute of Neurological Disorders and Stroke (USA). Seven compounds (2-4, 9, 11, 12 and 20) showed anticonvulsant activity at maximal electroshock (MES) test in the dose of 30mg/kg at 0.5h. In the subcutaneous pentetrazole (scMET) test compound 4 showed protection at 100 and 300mg/kg dose at mice, however compounds showed high neurotoxicity in rotarod test at used doses. Also, molecular modeling studies were undertaken, to explain affinity of compounds at hH₃R (taking into the consideration X-ray analysis of compound 18). In order to estimate "drug-likeness" of selected compounds in silico and experimental evaluation of lipophilicity, metabolic stability and cytotoxicity was performed.

Non-imidazole-based histamine H3 receptor antagonists with anticonvulsant activity in different seizure models in male adult rats

A series of twelve novel non-imidazole-based ligands (3–14) was developed and evaluated for its in vitro binding properties at the human histamine H3 receptor (hH3R). The novel ligands were investigated for their in vivo protective effects in different seizure models in male adult rats. Among the H3R ligands (3–14) tested, ligand 14 showed significant and dose-dependent reduction in the duration of tonic hind limb extension in maximal electroshock (MES)-induced seizure model subsequent to acute systemic administration (5, 10, and 20 mg/kg, intraperitoneally), whereas ligands 4, 6, and 7 without appreciable protection in MES model were most promising in pentylenetetrazole (PTZ) model. Moreover, the protective effect observed for ligand 14 in MES model was lower than that observed for the reference drug phenytoin and was entirely abrogated when rats were co-administered with the brain-penetrant H1R antagonist pyrilamine (PYR) but not the brain-penetrant H2R antagonist zolantidine (ZOL), demonstrating that histaminergic neurotransmission by activation of postsynaptically located H1Rs seems to be involved in the protective action. On the contrary, PYR and ZOL failed to abrogate the full protection provided by 4 in PTZ model and the moderate protective effect by 14 in strychnine (STR) model. Moreover, the experimental and in silico estimation of properties such as metabolism was performed for five selected test compounds. Also, lipophilicity using planar reversed-phase thin-layer chromatography method was included for better understanding of the molecular properties of the tested compounds. Additionally, the absorption, distribution, metabolism, and elimination and toxicity parameters were evaluated for the most promising compounds 2, 4, 6, 7, and 14 utilizing in vitro methods. These interesting results highlight the potential of H3R ligands as new antiepileptic drugs or as adjuvants to available epilepsy medications.

Cholinesterase inhibitory activity of chlorophenoxy derivatives-Histamine H3 receptor ligands

In recent years, multitarget-directed ligands have become an interesting strategy in a search for a new treatment of Alzheimer's disease. Combination of both: a histamine H3 receptor antagonist/inverse agonist and a cholinesterases inhibitor in one molecule could provide a new therapeutic opportunity. Here, we present biological evaluation of histamine H3 receptor ligands-chlorophenoxyalkylamine derivatives against cholinesterases: acetyl- and butyrylcholinesterase. The target compounds showed cholinesterase inhibitory activity in a low micromolar range. The most potent in this group was 1-(7-(4-chlorophenoxy)heptyl)homopiperidine (18) inhibiting the both enzymes (EeAChE IC50=1.93μM and EqBuChE IC50=1.64μM). Molecular modeling studies were performed to explain the binding mode of 18 with histamine H3 receptor as well as with cholinesterases.