Influence of bulky substituents on histamine h(3) receptor agonist/antagonist properties

Synthesis and antiseizure effect evaluation of nonimidazole histamine H3 receptor antagonists containing the oxazole moiety

The use of histamine H₃ receptor (H₃ R) antagonists is becoming a promising therapeutic approach for epilepsy. In this paper, a series of novel nonimidazole H₃ R antagonists was synthesized and screened as antiepileptic drugs. All of these prepared antagonists displayed micromolar or submicromolar H₃ R antagonistic activities in the cAMP response element luciferase screening assay. Compounds 5a (IC₅₀  = 0.11 μM), 5b (IC₅₀  = 0.56 μM), and 5f (IC₅₀  = 0.78 μM) displayed the most potent H₃ R antagonistic activities, with considerable potency when compared with pitolisant (IC₅₀  = 0.51 μM). In the maximal electroshock (MES)-induced seizure model, compounds 5c, 5e, and 5g showed obvious protection for the electrostimulated mice, and the protection of 5g against the MES-induced seizures was fully abrogated when mice were cotreated with R-(α)-methyl-histamine, a central nervous system-penetrant H₃ R agonist, suggesting that the potential therapeutic effect of 5g was observed to work through H₃ R. These results indicate that the attempt to find a new antiepileptic drug among H₃ R antagonists is practicable, but it is necessary to consider the log P of the molecules to ensure penetration of the blood-brain barrier.

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.

Meta-Substituted Aryl(thio)ethers as Potent Partial Agonists (or Antagonists) for the Histamine H3 Receptor Lacking a Nitrogen Atom in the Side Chain

4-(3-Aryloxypropyl)-1H-imidazoles, which possess a meta-positioned substituent in the aryl ring, have been synthesized and tested for activity at histamine H(3) receptors. The compounds having a CN, Me, or Br substituent were found to be antagonists, whereas CF(3), Et, i-Pr, t-Bu, COCH(3), or NO(2) substituents remarkably afforded partial agonists when tested in vitro on rat cerebral cortex synaptosomes for inhibition of [(3)H]histamine release. The compounds were also active in vivo, and furthermore, the CF(3)-substituted compound trifluproxim (UCL 1470, 7) acted as a potent full agonist in vivo, having ED(50) = 0.6 +/- 0.3 mg/kg per os in mice for inhibition of brain N(tau)-methylhistamine formation. Related structures have also been investigated; homologues 4-[4-(3-(trifluoromethyl)phenoxy)butyl]-1H-imidazole and 4-[2-(3-(trifluoromethyl)phenylthio)ethyl]-1H-imidazole are shown to be partial agonists, whereas the O isostere 4-[2-(3-(trifluoromethyl)phenoxy)ethyl]-1H-imidazole is an antagonist as is the S homologue 4-[3-(3-(trifluoromethyl)phenylthio)propyl]-1H-imidazole and its CH(2) isostere 4-[4-(3-(trifluoromethyl)phenyl)butyl]-1H-imidazole.