Piperidine variations in search for non-imidazole histamine H(3) receptor ligands

Synthesis and biological evaluation of the novel histamine H(3) receptor ligands is described. Two series of ethers (aliphatic and aromatic) have been prepared by four different methods. Compounds were evaluated for their affinities at recombinant human H(3) receptor stably expressed in CHO cells. The ethers show from low to moderate in vitro affinities in nanomolar concentration range. The most potent compound was the 1-[3-(4-tert-butylphenoxy)propyl]-4-piperidino-piperidine 16 (hH(3)R K(i)=100 nM). Several members of the new series investigated under in vivo conditions, proved to be inactive.     

Novel and highly potent histamine H3 receptor ligands. Part 2: exploring the cyclohexylamine-based series

Synthesis and biological evaluation of novel and potent cyclohexylamine-based histamine H3 receptor inverse agonists are described. Compounds in this newly identified series exhibited subnanomolar binding affinities for human receptor and no significant interaction with hERG channel. One derivative (10t) demonstrated enhanced in vivo efficiency and preferential brain distribution, both properties suitable for potential clinical evaluation.     

Tricyclic aminopyrimidine histamine H4 receptor antagonists

This report discloses the development of a series of tricyclic histamine H(4) receptor antagonists. Starting with a low nanomolar benzofuranopyrimidine HTS hit devoid of pharmaceutically acceptable properties, we navigated issues with metabolism and solubility to furnish a potent, stable and water soluble tricyclic histamine H(4) receptor antagonist with desirable physiochemical parameters which demonstrated efficacy a mouse ova model.     

Conformationally-restricted ligands for the histamine H1 receptor

Potent H1-antagonistic activity in a series of novel indeno[2,1-c]pyridines and their 4-arylpiperidinol precursors is reported; one compound shows an in vitro activity four times that of the standard mepyramine that it was screened against. Their failure to translate this protection to in vivo tests is discussed.     

Fluorescent non-imidazole histamine H3 receptor ligands with nanomolar affinities

Omega-piperidinoalkanamine derivatives with fluorescent moieties (2-cyanoisoindol-1-yl, 7-nitrobenzofurazan-4-yl) have been synthesized starting from piperidine in three steps. The compounds display moderate to good histamine hH(3) receptor affinities with K(i) values ranging from 178 to 11nM. The new compounds may act as tools for identification and understanding of the binding site on the histamine H(3) receptor.     

The discovery of the benzazepine class of histamine H3 receptor antagonists

This Letter describes the discovery of a novel series of H₃ receptor antagonists. The initial medicinal chemistry strategy focused on deconstructing and simplifying an early screening hit which rapidly led to the discovery of a novel series of H₃ receptor antagonists based on the benzazepine core. Employing an H₃ driven pharmacodynamic model, the series was then further optimised through to a lead compound that showed robust in vivo functional activity and possessed overall excellent developability properties.     

Benzimidazole-substituted (3-phenoxypropyl)amines as histamine H3 receptor ligands

A series of non-imidazole histamine H(3) receptor antagonists based on the (3-phenoxypropyl)amine motif, which is a common pharmacophore for H(3) antagonists, has been identified. A preliminary SAR study around the amine moiety has identified 8a as a potent H(3) antagonist possessing a good pharmacokinetic profile in the rat.     

Identification of clinical candidates from the benzazepine class of histamine H3 receptor antagonists

This Letter describes the discovery of GSK189254 and GSK239512 that were progressed as clinical candidates to explore the potential of H₃ receptor antagonists as novel therapies for the treatment of Alzheimer’s disease and other dementias. By carefully controlling the physicochemical properties of the benzazepine series and through the implementation of an aggressive and innovative screening strategy that employed high throughput in vivo assays to efficiently triage compounds, the medicinal chemistry effort was able to rapidly progress the benzazepine class of H₃ antagonists through to the identification of clinical candidates with robust in vivo efficacy and excellent developability properties.     

N-Alkenyl and cycloalkyl carbamates as dual acting histamine H3 and H4 receptor ligands

Previous studies have shown that several imidazole derivatives possess affinity to histamine H(3) and H(4) receptors. Continuing our study on structural requirements responsible for affinity and selectivity for H(3)/H(4) receptor subtypes, two series of 3-(1H-imidazol-4-yl)propyl carbamates were prepared: a series of unsaturated alkyl derivatives (1-9) and a series possessing a cycloalkyl group different distances to the carbamate moiety (10-13). The compounds were tested for their affinities at the human histamine H(3) receptor, stably expressed in CHO-K1 cells. Compounds 1, 2, 5-7, 10-13 were investigated for their affinities at the human histamine H(4) receptor co-expressed with Gα(i2) and Gβ(1)γ(2) subunits in Sf9 cells. To expand the pharmacological profile, compounds were further tested for their H(3) receptor antagonist activity on guinea pig ileum and in vivo after oral administration to mice. All tested compounds exhibited good affinity for the human histamine H(3) receptor with K(i) values in the range from 14 to 194nM. All compounds were active in vivo after peroral administration (p.o.) to Swiss mice, thus demonstrating their ability to cross the blood-brain barrier. The most potent H(3) receptor ligand of these series was compound 5, 3-(1H-imidazol-4-yl)propyl pent-4-enylcarbamate with the highest affinity (K(i)=14nM). Additionally, compound 3 showed remarkable central nervous system (CNS) H(3)R activity, increasing the N(τ)-methylhistamine levels in mice with an ED(50) value of 0.55mg/kg, p.o. evidencing therefore, a twofold increase of inverse agonist/antagonist potency compared to the reference inverse agonist/antagonist thioperamide. In this study, the imidazole propyloxy carbamate moiety was kept constant. The different lipophilic moieties connected to the carbamate functionality in the eastern part of the molecule had a range of influences on the human H(4) receptor affinity (154-1326nM).     

Design and synthesis of histamine H3/H4 receptor ligands with a cyclopropane scaffold

We previously designed and synthesized a series of histamine analogues with an imidazolylcyclopropane scaffold and identified potent non-selective antagonists for histamine H₃ and H₄ receptor subtypes. In this study, to develop H₄ selective ligands, we newly designed and synthesized cyclopropane-based derivatives having an indole, benzimidazole, or piperazine structure, which are components of representative H₄ selective antagonists such as JNJ7777120 and JNJ10191584. Among the synthesized derivatives, imidazolylcyclopropanes 12 and 13 conjugated with a benzimidazole showed binding affinity to the H₃ and H₄ receptors comparable to that of a well-known non-selective H₃/H₄ antagonist, thioperamide. These results suggest that the binding modes of the cyclopropane-based H₃/H₄ ligands in the H₄ receptor can be different from those of the indole/benzimidazole-piperazine derivatives.     

Synthesis and evaluation of pyridone-phenoxypropyl-R-2-methylpyrrolidine analogues as histamine H3 receptor antagonists

6-{4-[3-(R)-2-Methylpyrrolidin-1-yl)propoxy]-phenyl}-2H-pyridazin-3-one 6 (Irdabisant; CEP-26401) was recently reported as a potent H(3)R antagonist with excellent drug-like properties and in vivo activity that advanced into clinical evaluation. A series of pyridone analogs of 6 was synthesized and evaluated as H(3)R antagonists. Structure-activity relationships revealed that the 5-pyridone regiomer was optimal for H(3)R affinity. N-Methyl 9b showed excellent H(3)R affinity, acceptable pharmacokinetics and pharmaceutical properties. In vivo evaluation of 9b showed potent activity in the rat dipsogenia model and robust wake-promoting activity in the rat EEG model.     

Synthesis and histamine H3 receptor activity of 4-(n-alkyl)-1H-imidazoles and 4-(omega-phenylalkyl)-1H-imidazoles

The influence of lipophilic moieties attached to a 4-1H-imidazole ring on the histamine H₃ receptor activity was systematically investigated. Series of 4-(n-alkyl)-1H-imidazoles and 4-(ω-phenylalkyl)-1H-imidazoles were prepared, with an alkyl chain varying from 2–9 methylene groups and from 1–9 methylene groups, respectively. The compounds were tested for their activity on the H₃ receptor under in vitro conditions. For the 4-(n-alkyl)-1H-imidazoles the activity is proportional to chain length, ranging from a pA₂ value of 6.3±0.2 for 4-(n-propyl)-1H-imidazole to a pA₂ value of 7.2±0.1 for 4-(n-decyl)-1H-imidazole. For the series 4-(ω-phenylalkyl)-4H-imidazoles an optimum in H₃ activity was found for the pentylene spacer: 4-(ω-phenylpentyl)-1H-imidazole has a pA₂ value of 7.8±0.1.     

Anticonvulsant properties of histamine H3 receptor ligands belonging to N-substituted carbamates of imidazopropanol

Ligands targeting central histamine H₃ receptors (H₃Rs) for epilepsy might be a promising therapeutic approach. Therefore, the previously described and structurally strongly related imidazole-based derivatives belonging to carbamate class with high H₃R in vitro affinity, in-vivo antagonist potency, and H₃R selectivity profile were investigated on their anticonvulsant activity in maximal electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled seizure models in Wistar rats. The effects of systemic injection of H₃R ligands 1–13 on MES-induced and PTZ-kindled seizures were screened and evaluated against the reference antiepileptic drug (AED) Phenytoin (PHT) and the standard histamine H₃R inverse agonist/antagonist Thioperamide (THP) to determine their potential as new antiepileptic drugs. Following administration of the H₃R ligands 1–13 (5, 10 and 15 mg/kg, ip) there was a significant dose dependent reduction in MES-induced seizure duration. The protective action observed for the pentenyl carbamate derivative 4, the most protective H₃R ligand among 1–13, was significantly higher (P <0.05) than that of standard H₃R antagonist THP, and was reversed when rats were pretreated with the selective H₃R agonist R-(α)-methyl-histamine (RAMH) (10 mg/kg), or with the CNS penetrant H₁R antagonist Pyrilamine (PYR) (10 mg/kg). In addition, subeffective dose of H₃R ligand 4 (5 mg/kg, ip) significantly potentiated the protective action in rats pretreated with PHT (5 mg/kg, ip), a dose without appreciable protective effect when given alone. In contrast, pretreatment with H₃R ligand 4 (10 mg/kg ip) failed to modify PTZ-kindled convulsion, whereas the reference drug PHT was found to fully protect PTZ-induced seizure. These results indicate that some of the investigated imidazole-based H₃R ligands 1–13 may be of future therapeutic value in epilepsy.     

Diether derivatives of homo- or substituted piperidines as non-imidazole histamine H3 receptor ligands

Synthesis and biological activities of a series of homo- or substituted piperidine unsymmetrical diethers are described. The novel compounds were evaluated for histamine H₃ receptor binding affinities at recombinant human H₃ receptor stably expressed in HEK-293 cells. All diethers showed in vitro affinities in nanomolar concentration range. The most potent compounds are 1-[3-(3-(4-chlorophenoxy)propoxy)propyl]-3-methylpiperidine 11 (K_i = 3.2 nM) and 1-[3-(3-(4-chlorophenoxy)propoxy)propyl]azepane 13 (K_i = 3.5 nM).     

组胺H3受体研究进展

组胺H3受体作为突触前自身受体和异身受体,广泛分布于中枢和外周组织,抑制组胺的释放和合成,调节多种神经递质的释放,组胺H3受体是G蛋白偶联受体家族成员,激活后由G蛋白介导,通过调控N型Ca^2 通道,产生生物学效应,组胺H3受体在中枢和外周器官有着重要的生理功能,对心功能,胃酸分泌,觉醒的睡眠,认知和记忆,惊厥抽搐等都有调节作用。     

Fluorescent ligands for the histamine H2 receptor: synthesis and preliminary characterization

3-[3-(Piperidinomethyl)phenoxy]alkyl, N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidine and 2-(5-methyl-4-imidazolyl)methyl thioethyl derivatives containing fluorescent functionalities were synthesized and the histamine H₂ receptor affinity was evaluated using the H₂ antagonist [¹²⁵I]-aminopotentidine. The compounds exhibited weak to potent H₂ receptor affinity with pK_i values ranging from <4 to 8.85. The highest H₂ receptor affinity was observed for N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidines substituted with methylanthranilate (13), cyanoindolizine (6) and cyanoisoindole (11) moieties via an ethyl or propyl linker.     

Alkyl derivatives of 1,3,5-triazine as histamine H4 receptor ligands

This study focuses on the design, synthesis, molecular modeling and biological evaluation of a novel group of alkyl-1,3,5-triazinyl-methylpiperazines. New compounds were synthesized and their affinities for human histamine H₄ receptor (hH₄R) were evaluated. Among them, 4-(cyclohexylmethyl)-6-(4-methylpiperazin-1-yl)-1,3,5-triazin-2-amine (14) exhibited hH₄R affinity with a K_i of 160?nM and behaved as antagonist in functional assays: the cellular aequorin-based assay (IC₅₀?=?32?nM) and [³⁵S]GTPγS binding assay (pK_b?=?6.67). In addition, antinociceptive activity of 14 in vivo was observed in Formalin test (in mice) and in Carrageenan-induced acute inflammation test (in rats).     

Non-imidazole heterocyclic histamine H3 receptor antagonists

Continued exploration of the SAR around the lead imidazopyridine histamine H(3) antagonist 1 has led to the discovery of several related series of heterocyclic histamine H(3) antagonists. The synthesis and SAR of indolizine, indole and pyrazolopyridine based compounds are now described.     

Fluorinated non-imidazole histamine H3 receptor antagonists

Fluorine substituents have become a widespread and important component in drug design and development. Here, the synthesis of fluorine containing compounds and some corresponding precursor molecules are presented for potential isotope labelling as well as their data obtained with in vitro and in vivo screenings. The compounds vary in the basic centres (piperidine or pyrrolidine) and are fluoro substituted in different positions of the basic alicyclic moiety. Pharmacological evaluation resulted in ligands with high affinities at hH₃ receptor in the nanomolar and subnanomolar concentration range and some with high antagonist in vivo potencies.     

CLIC4 interacts with histamine H3 receptor and enhances the receptor cell surface expression

Histamine H3 receptor (H3R), one of G protein-coupled receptors (GPCRs), has been known to regulate neurotransmitter release negatively in central and peripheral nervous systems. Recently, a variety of intracellular proteins have been identified to interact with carboxy (C)-termini of GPCRs, and control their intracellular trafficking and signal transduction efficiencies. Screening for such proteins that interact with the C-terminus of H3R resulted in identification of one of the chloride intracellular channel (CLIC) proteins, CLIC4. The association of CLIC4 with H3R was confirmed in in vitro pull-down assays, coimmunoprecipitation from rat brain lysate, and immunofluorescence microscopy of rat cerebellar neurons. The data from flowcytometric analysis, radioligand receptor binding assay, and cell-based ELISA indicated that CLIC4 enhanced cell surface expression of wild-type H3R, but not a mutant form of the receptor that failed to interact with CLIC4. These results indicate that, by binding to the C-terminus of H3R, CLIC4 plays a critical role in regulation of the receptor cell surface expression.