Discovery of a Novel Highly Selective Histamine H4 Receptor Antagonist for the Treatment of Atopic Dermatitis.

The histamine H4 receptor (H4R), a member of the G-protein coupled receptor family, has been considered as a potential therapeutic target for treating atopic dermatitis (AD). A large number of H4R antagonists have been disclosed, but no efficient agents controlling both pruritus and inflammation in AD have been developed yet. Here, we have discovered a novel class of orally available H4R antagonists showing strong anti-itching and anti-inflammation activity as well as excellent selectivity against off-targets. A pharmacophore-based virtual screening system constructed in-house successfully identified initial hit compound 9, and the subsequent homology model-guided optimization efficiently led us to discover pyrido[2,3- e]tetrazolo[1,5- a]pyrazine analogue 48 as a novel chemotype of a potent and highly selective H4R antagonist. Importantly, orally administered compound 48 exhibits remarkable efficacy on antipruritus and anti-inflammation with a favorable pharmacokinetic (PK) profile in several mouse models of AD. Thus, these data strongly suggest that our compound 48 is a promising clinical candidate for treatment of AD.

Synthesis and evaluation of a 2-benzothiazolylphenylmethyl ether class of histamine H4 receptor antagonists.

Synthesis and biological evaluation of a new class of histamine H4 receptor ligands, distinct from the previously reported chemotypes, are described. A virtual screening of our corporate compound collection identified a hit with an undesired dual H3R/H4R activity. Chemical exploration led to the discovery of a more potent and selective 2-benzothiazolylphenylmethyl ether lead compound.

Lead identification and optimization of diaminopyrimidines as histamine H4 receptor ligands.

BACKGROUND: The human histamine H(4) receptor (hH(4)R) is a promising new target in the therapy of inflammatory or immune system diseases. METHODS: For the development of new hH(4)R ligands, a broad virtual screening was performed and two hits were identified. Their annelated heterocyclic core was optimized with regard to affinity and potency. RESULTS: Pharmacological characterization of the resulting diaminopyrimidines revealed different agonist and antagonist properties within the same scaffold.

Novel histamine H3 receptor antagonists based on the 4-[(1H-imidazol-4-yl)methyl]piperidine scaffold.

We report the discovery of novel histamine H(3) receptor antagonists based on 4-[(1H-imidazol-4-yl)methyl]piperidine. The most potent compounds in the series (e.g., 7) result from the attachment of a substituted aniline amide to the main pharmacophore piperidine via a two-methylene linker.

A new class of histamine H(3)-receptor antagonists: synthesis and structure-activity relationships of 7,8,9,10-tetrahydro-6H-cyclohepta[b]quinolines.

The synthesis and biological evaluation of novel cycloheptaquinoline antagonists of the human H(3) receptor are described. Two series of compounds, bearing either an amino substituent or an alkyne linker at the 11-position, were investigated. Modifications of the amino substituents, optimization of chain length and the effect of conformational restraints are described. Several compounds with high affinity and selectivity for the H(3) receptor were discovered.

Synthesis and evaluation of potent pyrrolidine H(3) antagonists.

The synthesis and biological evaluation of novel antagonists of the rat H(3) receptor are described. These compounds differ from prototypical H(3) antagonists in that they do not contain an imidazole moiety, but rather a substituted aminopyrrolidine moiety. A systematic modification of the substituents on the aminopyrrolidine ring was performed using pre-formatted precursor sets, where applicable, to afford several compounds with high affinity and selectivity for the H(3) receptor.

Novel histamine H(3)-receptor antagonists with carbonyl-substituted 4-(3-(phenoxy)propyl)-1H-imidazole structures like ciproxifan and related compounds.

Novel histamine H(3)-receptor antagonists possessing a 4-(3-(phenoxy)propyl)-1H-imidazole structure generally substituted in the para-position of the phenyl ring have been synthesized according to Mitsunobu or S(N)Ar reactions. With in vitro and in vivo screening for H(3)-receptor antagonist potency, the carbonyl-substituted derivatives proved to be highly active compounds. A number of compounds showed in vitro affinities in the subnanomolar concentration range, and the 4-hexanoyl (10) and 4-acetyl-3-methyl (29) substituted derivatives showed in vivo antagonist potencies of about 0.1 mg/kg after po administration. Many proxifans were also tested for their affinities at other histamine receptor subtypes thereby demonstrating their pronounced H(3)-receptor subtype selectivity. Since the cyclopropyl ketone derivative 14 (ciproxifan) had high affinity in vitro as well as high potency in vivo, it was selected for further studies in monkeys. It showed good oral absorption and long-lasting, dose-dependent plasma levels making it a promising compound for drug development.

New histamine H(3)-receptor ligands of the proxifan series: imoproxifan and other selective antagonists with high oral in vivo potency.

Histamine H(3)-receptor antagonists of the proxifan series are described. The novel compounds possess a 4-(3-(phenoxy)propyl)-1H-imidazole structure and various functional groups, e.g., an oxime moiety, on the phenyl ring. Synthesis of the novel compounds and X-ray crystallography of one highly potent oxime derivative, named imoproxifan (4-(3-(1H-imidazol-4-yl)propyloxy)phenylethanone oxime), are described. Most of the title compounds possess high antagonist potency in histamine H(3)-receptor assays in vitro as well as in vivo in mouse CNS following po administration. Structure-activity relationships are discussed. Imoproxifan displays subnanomolar potency on a functional assay on synaptosomes of rat cerebral cortex (K(i) = 0.26 nM). In vivo, imoproxifan increases the central N(tau)-methylhistamine level with an ED(50) of 0.034 mg/kg po. A receptor profile on several functional in vitro assays was determined for imoproxifan, demonstrating high selectivity toward the histamine H(3) receptor for this promising candidate for further development.

[Experimental study on effect of antagonizing platelet-activating factor and histamine of synthetic ginkgolide F in guinea-pigs].

OBJECTIVE: To investigate the antagonizing effect of synthetic Ginkgolide F (SGF) on platelet-activating factor (PAF) and histamine (HA) in guinea-pigs. METHODS: The contraction rate of isolated lung tissue of guinea-pig and the change of pulmonary function of sensitized guinea-pig after SGF treatment were examined. RESULTS: (1) The contraction rate of guinea-pigs' isolated trachea and lung strip induced by HA reduced from (50.97 +/- 16.00)% and (54.24 +/- 12.17)% to (21.69 +/- 3.85)% and (22.97 +/- 17.78)% after SGF treatment (P < 0.05). (2) PAF induced relative contraction of isolated guinea-pig lung strip was reduced from (89.49 +/- 16.00)% to (46.21 +/- 14.23)% in presence of SGF (P < 0.05). (3) The pulmonary function of sensitized animal had a tendency of being improved by SGF. CONCLUSION: SGF can antagonize the contraction of isolated lung tissue induced by HA or PAF in vitro, and has a tendency to improve the pulmonary function of sensitized guinea-pig, therefore, it may be a promising drug in treatment of bronchial asthma.

Development of chiral N-alkylcarbamates as new leads for potent and selective H3-receptor antagonists: synthesis, capillary electrophoresis, and in vitro and oral in vivo activity.

Novel carbamates as derivatives of 3-(1H-imidazol-4-yl)propanol with an N-alkyl chain were prepared as histamine H3-receptor antagonists. Branching of the N-alkyl side chain with methyl groups led to chiral compounds which were synthesized stereospecifically by a Mitsunobu protocol adapted Gabriel synthesis. The optical purity of some of the chiral compounds was determined (ee > 95%) by capillary electrophoresis (CE). The investigated compounds showed pronounced to high antagonist activity (Ki values of 4.1-316 nM) in a functional test for histamine H3 receptors on rat cerebral cortex synaptosomes. Similar H3-receptor antagonist activities were observed in a peripheral model on guinea pig ileum. No stereoselective discrimination for the H3 receptor for the chiral antagonists was found with the in vitro assays. All compounds were also screened for central H3-receptor antagonist activity in vivo in mice after po administration. Most compounds were potent agents of the H3-receptor-mediated enhancement of brain Ntau-methylhistamine levels. The enantiomers of the N-2-heptylcarbamate showed a stereoselective differentiation in their pharmacological effect in vivo (ED50 of 0.39 mg/kg for the (S)-derivative vs 1.5 mg/kg for the (R)-derivative) most probably caused by differences in pharmacokinetic parameters. H1- and H2-receptor activities were determined for some of the novel carbamates, demonstrating that they have a highly selective action at the histamine H3 receptor.