A new class of diamine-based human histamine H3 receptor antagonists: 4-(aminoalkoxy)benzylamines

Preliminary studies of 1,5-benzoxazepine derivatives as potential histamine H3 receptor antagonists

Aims: Our research aimed to evaluate how the rigidification of the characteristic 3-aminopropyloxy linker by incorporating it into 1,5-benzoxazepines affects the potency of histamine H3 receptor (H3R) antagonists/inverse agonists. This research constitutes a starting point for the full characterization of the pharmacological properties of this group of compounds. Materials & methods: Several 1,5-benzoxazepine derivatives were synthesized and pharmacologically tested as potential H3R antagonist/inverse agonists. In a addition, the effect of the derivatives on acetylcholinesterase and butyrylcholinesterase inhibition and cytotoxicity were tested. Results: The studies indicated 1,5-benzoxazepine containing three carbon side chains as a compound for further modification. Conclusion: Further optimization of the lead structure is necessary, which will favorably affect biological targets.

Discovery of a Tritiated Radioligand with High Affinity and Selectivity for the Histamine H3 Receptor

Radioligands used previously for histamine H3 receptor (H3R) are accompanied by a number of disadvantages. In this study, we report the synthesis of the new H3R radioligand [3H]UR-MN259 ([3H]11) with high (radio)chemical purity and stability. The radioligand exhibits sub-nanomolar affinity for the target receptor (pKi (H3R) = 9.56) and displays an outstanding selectivity profile within the histamine receptor family (>100,000-fold selective). [3H]UR-MN259 is ideally suitable for the characterization of H3R ligands in competition binding and shows one-site binding to the H3R in saturation binding experiments. The radiotracer shows fast association to the receptor (τassoc = 6.11 min), as well as full dissociation from the receptor (τdissoc = 14.48 min) in kinetic binding studies. The distinguished profile of [3H]UR-MN259 makes it a highly promising pharmacological tool to further investigate the role of the H3R in the CNS.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a...

A Versatile Sub-Nanomolar Fluorescent Ligand Enables NanoBRET Binding Studies and Single-Molecule Microscopy at the Histamine H3 Receptor

The histamine H₃ receptor (H₃R) is considered an attractive drug target for various neurological diseases. We here report the synthesis of UR-NR266, a novel fluorescent H₃R ligand. Broad pharmacological characterization revealed UR-NR266 as a sub-nanomolar compound at the H₃R with an exceptional selectivity profile within the histamine receptor family. The presented neutral antagonist showed fast association to its target and complete dissociation in kinetic binding studies. Detailed characterization of standard H₃R ligands in NanoBRET competition binding using UR-NR266 highlights its value as a versatile pharmacological tool to analyze future H₃R ligands. The low nonspecific binding observed in all experiments could also be verified in TIRF and confocal microscopy. This fluorescent probe allows the highly specific analysis of native H₃R in various assays ranging from optical high throughput technologies to biophysical analyses and single-molecule studies in its natural environment. An off-target screening at 14 receptors revealed UR-NR266 as a selective compound.

4-Hydroxypiperidines and Their Flexible 3-(Amino)propyloxy Analogues as Non-Imidazole Histamine H₃ Receptor Antagonist: Further Structure⁻Activity Relationship Exploration and In Vitro and In Vivo Pharmacological Evaluation

Presynaptic histamine H₃ receptors (H₃R) act as auto- or heteroreceptors controlling, respectively, the release of histamine and of other neurotransmitters in the central nervous system (CNS). The extracellular levels of several neurotransmitters are enhanced by H₃R antagonists, and there is a great interest for potent, brain-penetrating H₃ receptor antagonists/inverse agonists to compensate for the neurotransmitter deficits present in various neurological disorders. We have shown that 1-[(benzylfuran-2-yl)methyl]piperidinyl-4-oxyl- and benzyl- derivatives of N-propylpentan-1-amines exhibit high in vitro potencies toward the guinea pig H₃ receptor (jejunum), with pA₂ = 8.47 and 7.79, respectively (the reference compound used was thioperamide with pA₂ = 8.67). Furthermore, following the replacement of 4-hydroxypiperidine with a 3-(methylamino)propyloxy chain, the pA₂ value for the first group decreased, whereas it increased for the second group. Here, we present data on the impact of elongating the aliphatic chain between the nitrogen of 4-hydroxypiperidine or 3-(methylamino)propan-1-ol and the lipophilic residue. Additionally, the most active compound in this series of non-imidazole H₃ receptor antagonists/inverse agonists, i.e., ADS-003, was evaluated for its affinity to the recombinant rat and human histamine H₃ receptors transiently expressed in HEK-293T cells. It was shown that ADS-003, given parenterally for 5 days, reduced the food intake of rats, as well as changed histamine and noradrenaline concentrations in the rats’ brain in a manner and degree similar to the reference H₃ antagonist Ciproxifan.

Studies on the antiplatelet and antithrombotic profile of anti-inflammatory coumarin derivatives

The interest towards coumarin-based structures stems from their polypharmacological profile. Herein, we present a series of Mannich bases and 7-azomethine-linked coumarin derivatives exhibiting antiplatelet and antithrombotic activities, in addition to the already known anti-inflammatory and antioxidant activities. Among others, compounds 15 and 16 were found to be the most potent and selective inhibitors of platelet aggregation whereas compound 3 also proved to be the most potent in the clot retraction assay. Structure-activity relationship studies were conducted to elucidate the molecular determinants responsible for the herein observed activities. The chance of inhibiting cyclooxygenase-1 was also investigated for evaluating the platelet aggregation induced by arachidonic acid. Taken together, these results suggest that the investigation of other targets connected to the antiplatelet activity, such as phosphodiesterase-3 (PDE3), could be a viable strategy to shed light on the polypharmacological profile of coumarin-based compounds. Docking simulations towards PDE3 were also carried out.

Studies on molecular properties prediction and histamine H3 receptor affinities of novel ligands with uracil-based motifs

The histamine H3 receptor (H3R) plays a role in cognitive and memory processes and is involved in different neurological disorders, including Alzheimer's disease, schizophrenia, and narcolepsy. Therefore, several hH3R antagonists/inverse agonists entered clinical phases for a broad spectrum of mainly centrally occurring diseases. However, many other promising candidates failed due to their pharmacokinetic profile, mostly because of their strong lipophilicity accompanied with low solubility. Analysis of previous potential H3R selective antagonists/inverse agonists, e.g. pitolisant, revealed promising results concerning physicochemical properties and drug-likeness. Herein, a series of new hH3R ligands 8-20 consisting of piperidin-1-yl or piperidin-1-yl-propoxyphenyl coupled to different uracil, thymine, and 5,6-dimethyluracil related moieties, were synthesized, evaluated on their binding properties at the hH3R and the estimation of different physicochemical and drug-likeness properties. Due to the coupling to various positions at pyrimidine-2,4-(1H,3H)-dione, affinity at hH3Rs and drug-likeness parameters have been improved. For instance, compound 9 showed in addition to high affinity at the hH3R (pKi (hH3R) = 8.14) clog S, clog P, LE, LipE, and drug-likeness score values of -4.36, 3.47, 0.34, 4.63, and 1.54, respectively. Also, the methyl substituted analog 17 (pKi (hH3R) = 8.15) revealed LE, LipE and drug-likeness score values of -3.29, 2.47, 0.49, 5.52, and 1.76, respectively.

Dual histamine H3R/serotonin 5-HT4R ligands with antiamnesic properties: pharmacophore-based virtual screening and polypharmacology

In recent years, preclinical and clinical studies have generated considerable interest in the development of histamine H3 receptor (H3R) antagonists as novel treatment for degenerative disorders associated with impaired cholinergic function. To identify novel scaffolds for H3R antagonism, a common feature-based pharmacophore model was developed and used to screen the 17,194 compounds of the CERMN (Centre d'Etudes et de Recherche sur le Médicament de Normandie) chemical library. Out of 268 virtual hits which have been gathered in 34 clusters, we were particularly interested in tricyclic derivatives also exhibiting a potent 5HT4R affinity. Benzo[h][1,6]naphthyridine derivatives showed the highest H3R affinity, and compound 17 (H3R Ki = 41.6 nM; 5-HT4R Ki = 208 nM) completely reversed the amnesiant effect of scopolamine at 3 mg/kg in a spatial working memory experiment. For the first time we demonstrated the feasibility to combine H3R and 5-HT4R activities in a single molecule, raising the exciting possibility that dual H3R antagonist/5HT4R agonist have potential for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Benzylpiperidine variations on histamine H3 receptor ligands for improved drug-likeness

Several hH3R antagonists/inverse agonists entered clinical phases for a broad spectrum of mainly centrally occurring diseases. Nevertheless, many promising candidates failed due to their pharmacokinetic profile, mostly because of their strong lipophilicity and their dibasic character. Analysis of previously, as potential PET ligands synthesized compounds (ST-889, ST-928) revealed promising results concerning physicochemical properties and drug-likeness. Herein, the synthesis, the evaluation of the binding properties at the hH3R and the estimation of different physicochemical and drug-likeness properties of further novel benzylpiperidine variations on H3R antagonists is described. Due to the introduction of various small hydrophilic moieties in the structure, drug-likeness parameters have been improved. For instance, compound 12 (ST-1032) showed in addition to high affinity at the H3R (pKi (hH3R)=9.3) clogS, clogP, LE, LipE, and LELP values of -2.48, 2.18, 0.44, 7.14, and 4.95, respectively. Also, the keto derivative 5 (ST-1703, pKi (hH3R)=8.6) revealed LipE and LELP values of 5.25 and 6.84, respectively.

Structure-activity relationships of new 1-substitutedmethyl-4-[5-(N-methyl-N-propylamino)pentyloxy]piperidines and selected 1-[(N-substituted-N-methyl)-3-propyloxy]-5-(N-methy-l-N-propyl)-pentanediamines as H3 -antagonists

Novel, potent non-imidazole histamine H3 receptor antagonists have been prepared and in vitro tested as H3 -receptor antagonists (the electrically evoked contraction of the guinea-pig jejunum). The present compounds contain a 4-hydroxypiperidine core, which behaves as a conformationally restricted version of the 3-amino-1-propanol moiety common to the many previously described non-imidazole H3 ligands. Detailed structure-activity studies revealed that 1-(2-benzofuranylmethyl)- 5c (pA2 = 8.47 ± 0.05) and 1-(3-benzofuranylmethyl)-4-[5-(N-methyl-N-propyl)pentyloxy]piperidine 5d (pA2 = 8.15 ± 0.07) exhibit high potency for the H3 histamine receptor. In addition, the potency of selected 1-[(N-substituted-N-methyl)-3-propyloxy]-5-(N-methyl-N-propyl)pentanediamines as antagonist of the H3 histamine receptor was also evaluated. Replacement of the 4-hydroxypiperidine of the leads 7 and 5c by a highly flexible 3-(methylamino)propyloxy chain yields compounds 6a (pA2 = 8.02) and 6b (pA2 = 6.23) with higher and lower potency than their piperidine analogues (7, pA2 = 7.79; 5c, pA2 = 8.47), respectively. The histaminergic H1 antagonism of selected compounds 5c, 5d and 6a has been established on the isolated guinea-pig ileum by conventional methods; the pA2 values have compared with the potency of pyrilamine. None of them showed any H1 -antagonistic activity (pA2 < 4; for pyrilamine pA2 = 8.5).

Non-imidazole histamine H3 ligands: part V. synthesis and preliminary pharmacological investigation of 1-[2-thiazol-4-yl- and 1-[2-thiazol-5-yl-(2-aminoethyl)]-4-n-propylpiperazine derivatives

Series of 1-[2-thiazol-4-yl-(2-aminoethyl)]- and 1-[2-thiazol-5-yl-(2-aminoethyl)]-4-n-propylpiperazine derivatives have been prepared and in vitro tested as H3-receptor antagonists (the electrically evoked contraction of the guinea-pig jejunum). It appeared that by comparison of homologous pairs, the 1-[2-thiazol-5-yl-(2-aminoethyl)]-4-n-propylpiperazines (3a,b and 4a-d) have much higher potency than their analogous 1-[2-thiazol-4-yl-(2-aminoethyl)]-4-n-propylpiperazines (2a-k). Based on the obtained results, we observed the 5-position of 2-methyl-2-R-aminoethyl substituents in the thiazole ring is favourable for histamine H3 receptor antagonist activity, whereas its presence in position 4 leads, almost in each case, to strong decrease of activity.

Improvement of the Prediction Power of the CoMFA and CoMSIA Models on Histamine H3 Antagonists by Different Variable Selection Methods

The aim of this study is to enhance the predictivity power of CoMFA and CoMSIA models by means of different variable selection algorithms. The genetic algorithm (GA), successive projection algorithm (SPA), stepwise multiple linear regression (SW-MLR), and the enhanced replacement method (ERM) were used and tested as variable selection algorithms. Then, the selected variables were used to generate a simple and predictive model by the multilinear regression algorithm. A set of 74 histamine H₃ antagonists were split into 40 compounds as a training set, and 17 compounds as a test set, by the Kennard-Stone algorithm. Before splitting the data, 17 compounds were randomly selected from the pool of the whole data set as an evaluation set without any supervision, pretreatment, or visual inspection. Among applied variable selection algorithms, ERM had noticeable improvement on the statistical parameters. The r² values of training, test, and evaluation sets for the ERM-MLR model using CoMFA fields were 0.9560, 0.8630, and 0.8460 and using the CoMSIA fields were 0.9800, 0.8521, and 0.9080, respectively. In this study, the principles of organization for economic cooperation and development (OECD) for regulatory acceptability of QSARs are considered.

Synthesis and preliminary pharmacological investigation of new N-substituted-N-[ω-(ω-phenoxy-alkylpiperazin-1-yl)alkyl]guanidines as non-imidazole histamine H(3) antagonists

Novel, potent non-imidazole histamine H(3) receptor antagonists were prepared. Detailed structure-activity studies revealed that N-(4-trifluoromethylbenzyl)-N-[4-(7-phenoxyheptylpiperazin-1-yl)butyl]guanidine (pA(2)  = 8.49 ± 0.05), 1h, and N-(4-nitrobenzyl)-N-[4-(7-phenoxyheptylpiperazin-1-yl)butyl]guanidine (pA(2)  = 8.43 ± 0.05), 1l, exhibit high affinity for the H(3) histamine receptor. The most potent antagonists in this series, 1e, 1h, and 1l, were also in vitro tested as H(1) receptor antagonists, showing weak H(1) -antagonistic activity with pA(2)  = 6.70 ± 0.09, pA(2)  = 6.46 ± 0.09, and pA(2)  = 6.65 ± 0.11, respectively.

Novel sulfonylurea derivatives as H3 receptor antagonists. Preliminary SAR studies

The combination of antagonism at histamine H(3) receptor and the stimulation of insulin secretion have been proposed as an approach to new dual therapeutic agents for the treatment of type 2 diabetes mellitus associated with obesity. We have designed and synthesized a new series of non-imidazole derivatives, based on a basic amine ring connected through an alkyl spacer of variable length to a phenoxysulfonylurea moiety. These compounds were initially evaluated for histamine H(3) receptor binding affinities, suggesting that a propoxy chain linker between the amine and the core ring could be essential for optimal binding affinity. Compound 56, 1-(naphthalen-1-yl)-3-[(p-(3-pyrrolidin-1-ylpropoxy)benzene)]sulfonylurea exhibited the best H(3) antagonism affinity. However, since all these derivatives failed to block K(ATP) channels, the link of these two related moieties should not be considered a good pharmacophore for obtaining new dual H(3) antagonists with insulinotropic activity, suggesting the necessity to propose a new chemical hybrid prototype.

Synthesis and structure-activity relationship of 5-pyridazin-3-one phenoxypiperidines as potent, selective histamine H(3) receptor inverse agonists

Optimization of the R(2) and R(6) positions of (5-{4-[3-(R)-2-methylpyrrolin-1-yl-propoxy]phenyl}-2H-pyridazin-3-one) 2a with constrained phenoxypiperidines led to the identification of 5-[4-(cyclobutyl-piperidin-4-yloxy)-phenyl]-6-methyl-2H-pyridazin-3-one 8b as a potent, selective histamine H(3) receptor antagonist with favorable pharmacokinetic properties. Compound 8b had an excellent safety genotoxocity profile for a CNS-active compound in the Ames and micronucleus tests, also displayed potent H(3)R antagonist activity in the brain in the rat dipsogenia model and robust wake activity in the rat EEG/EMG model.

Modelling of serotonin reuptake inhibitory and histamine H₃antagonistic activity of piperazine and diazepane amides: QSAR rationales for co-optimization of the activity profiles

Selective human serotonin reuptake transporter (hSERT) inhibition is the first line of treatment to deal with the depression. In clinical practice for managing depression, the stimulants are co-prescribed to overcome cognitive impairment and fatigue. Recently, histamine H(3) antagonists with serotonin reuptake inhibition activity have been proposed as alternative approach for the treatment of depression. In this context, a QSAR study of hSERT inhibitory and H(3) antagonistic activity of piperazine and diazepane amide derivatives has been carried out using the combinatorial protocol in multiple linear regression (CP-MLR) with 0D- to 2D-Dragon descriptors. The derived QSAR models have provided a rational approach for the development of new piperazine and diazepane amide derivatives as hSERT inhibitors and H(3) antagonists. In a concomitant partial least-squares (PLS) analysis of the hSERT and histamine H(3) activities, the fraction contributions of identified descriptors revealed their importance in modulating these activities. The PLS analysis of other biological endpoints, namely hNET, hDAT, and histamine H(3) activity in functional assay (H(3)pA(2)) of these analogues with the identified descriptors has further highlighted their scope in modulating these activities.

Triazole ligands reveal distinct molecular features that induce histamine H4 receptor affinity and subtly govern H4/H3 subtype selectivity

The histamine H(3) (H(3)R) and H(4) (H(4)R) receptors attract considerable interest from the medicinal chemistry community. Given their relatively high homology yet widely differing therapeutic promises, ligand selectivity for the two receptors is crucial. We interrogated H(4)R/H(3)R selectivities using ligands with a [1,2,3]triazole core. Cu(I)-assisted "click chemistry" was used to assemble diverse [1,2,3]triazole compounds (6a-w and 7a-f), many containing a peripheral imidazole group. The imidazole ring posed some problems in the click chemistry putatively due to Cu(II) coordination, but Boc protection of the imidazole and removal of oxygen from the reaction mixture provided effective strategies. Pharmacological studies revealed two monosubstituted imidazoles (6h,p) with <10 nM H(4)R affinities and >10-fold H(4)R/H(3)R selectivity. Both compounds possess a cycloalkylmethyl group and appear to target a lipophilic pocket in H(4)R with high steric precision. The use of the [1,2,3]triazole scaffold is further demonstrated by the notion that simple changes in spacer length or peripheral groups can reverse the selectivity toward H(3)R. Computational evidence is provided to account for two key selectivity switches and to pinpoint a lipophilic pocket as an important handle for H(4)R over H(3)R selectivity.

Kojic acid derivatives as histamine H(3) receptor ligands

The histamine H(3) receptor (H(3)R) is a promising target in the development of new compounds for the treatment of mainly centrally occurring diseases. However, emerging novel therapeutic concepts have been introduced and some indications in the H(3)R field, e.g. migraine, pain or allergic rhinitis, might take advantage of peripherally acting ligands. In this work, kojic acid-derived structural elements were inserted into a well established H(3)R antagonist/inverse agonist scaffold to investigate the bioisosteric potential of γ-pyranones with respect to the different moieties of the H(3)R pharmacophore. The most affine compounds showed receptor binding in the low nanomolar concentration range. Evaluation and comparison of kojic acid-containing ligands and their corresponding phenyl analogues (3-7) revealed that the newly integrated scaffold greatly influences chemical properties (S Log P, topological polar surface area (tPSA)) and hence, potentially modifies the pharmacokinetic profile of the different derivatives. Benzyl-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)methanamine ligands 3 and 4 belong to the centrally acting diamine-based class of H(3)R antagonist/inverse agonist, whereas kojic acid analogues 6 and 7 might act peripherally. The latter compounds state promising lead structures in the development of H(3)R ligands with a modified profile of action.

Inhibition of gamma-secretase by the CK1 inhibitor IC261 does not depend on CK1delta

CK1 and gamma-secretase are interesting targets for therapeutic intervention in the treatment of cancer and Alzheimer's disease. The CK1 inhibitor IC261 was reported to inhibit gamma-secretase activity. The question is: Does CK1 inhibition directly influence gamma-secretase activity? Therefore we analyzed the SAR of 15 analogues and their impact on gamma-secretase activity. The most active compounds were investigated on CK1delta activity. These findings exclude a direct influence of CK1delta on gamma-secretase, because any change in the substitution pattern of IC261 diminished CK1 inhibition, whereas gamma-secretase inhibition is still exerted by several analogues.

Ocotea quixos Lam. essential oil: in vitro and in vivo investigation on its anti-inflammatory properties

Here we investigated the anti-inflammatory properties of Ocotea quixos essential oil and of its main components, trans-cinnamaldehyde and methyl cinnamate, in in vitro and in vivo models. Ocotea essential oil and trans-cinnamaldehyde but not methyl cinnamate significantly reduced LPS-induced NO release from J774 macrophages at non-toxic concentrations, inhibited LPS-induced COX-2 expression and increased forskolin-induced cAMP production. The essential oil (30-100mg/kg os) and trans-cinnamaldehyde (10mg/kg os) in carrageenan-induced rat paw edema showed anti-inflammatory effect without damaging gastric mucosa. In conclusion we provide the first evidence of a significant anti-inflammatory gastro-sparing activity of O.quixos essential oil.

Synthesis and structure-activity relationships of 2-(1,4'-bipiperidin-1'-yl)thiazolopyridine as H3 receptor antagonists

A series of 2-(1,4'-bipiperidine-1'-yl)thiazolopyridines was synthesized and evaluated as a new lead of non-imidazole histamine H(3) receptor antagonists. Introduction of diversity at the 6-position of the pyridine ring was designed to enhance in vitro potency and decrease hERG activity. The structure-activity relationships for these new thiazolopyridine antagonists are discussed.

New 1-benzyl-4-hydroxypiperidine derivatives as non-imidazole histamine H3 receptor antagonists

A series of 1-benzyl-4-(3-aminopropyloxy)piperidine and 1-benzyl-4-(5-aminopentyloxy)piperidine derivatives has been prepared. The 1-benzyl-4-hydroxypiperidine derivatives obtained were evaluated for their affinities at recombinant human histamine H(3 )receptor, stably expressed in HEK 293T cells. All compounds investigated show moderate to pronounced in-vitro affinities. The most potent antagonists in this series 9b2 (hH(3)R, pK(i) = 7.09), 9b1 (hH(3)R, pK(i) = 6.78), 9b5 (hH(3)R, pK(i) = 6.99), and 9b6 (hH(3)R, pK(i )= 6.97) were also tested in vitro as H(3 )receptor antagonists - the electrically evoked contraction of the guinea-pig jejunum. The histaminergic H(1) antagonism of selected compounds 9b1, 9b2, and 9b4-9b6 was established on the isolated guinea-pig ileum by conventional methods; the pA(2) values were compared with the potency of pyrilamine. The compounds did not show any H(1) antagonistic activity (pA(2) < 4; for pyrilamine pA(2) = 9.53).