N α-Imidazolylalkyl and Pyridylalkyl Derivatives of Histaprodifen:  Synthesis and in Vitro Evaluation of Highly Potent Histamine H1-Receptor Agonists

• Published in: Journal of medicinal chemistry 2003-12, Vol.46 (25), p.5458-5470
• Main Authors: Menghin, Sonja, Pertz, Heinz H, Kramer, Kai, Seifert, Roland, Schunack, Walter, Elz, Sigurd
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Medical sciences; Miscellaneous; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Pharmacology. Drug treatments
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm0309147

A novel series of N α -imidazolylalkyl and pyridylalkyl derivatives of histaprodifen (6, 2-[2-(3,3-diphenylpropyl)imidazol-4-yl]ethanamine) was synthesized and evaluated as histamine H1-receptor agonists. The title compounds displayed partial agonism at contractile H1-receptors of guinea pig ileum and were at least equipotent with histamine. Agonist effects of the new derivatives were susceptible to blockade by the H1-receptor antagonist mepyramine (2−100 nM). In the imidazole series, suprahistaprodifen (51, [2-[2-(3,3-diphenylpropyl)-1H-imidazol-4-yl]ethyl]-[2-(1H-imidazol-4-yl)ethyl]amine, N α-2-[(1H-imidazol-4-yl)ethyl]histaprodifen) showed the highest H1-receptor agonist potency ever reported in the literature (pEC50 8.26, efficacy E max 96%). Elongation of the alkyl spacer from ethyl to butyl decreased activity from 3630% (ethyl, 51) to 163% (butyl, 53) of histamine potency. The exchange of the terminal imidazole nucleus for a pyridine ring resulted in compounds with comparably high potency. A decrease in agonist potency and efficacy was observed when the attachment of the alkyl spacer was consecutively changed from the ortho to the meta and the para position, respectively, of the pyridine ring. The pyridine series that contained a butyl chain possessed the highest potency and affinity. N α-[4-(2-pyridyl)butyl]histaprodifen (56) emerged as a strong partial agonist, being almost equipotent with 51 (pEC50 8.16, E max 89%). Compounds 51 and 56 also showed potent partial agonism at contractile H1 receptors in guinea pig aorta and potently activated H1-receptor-mediated endothelium-dependent relaxation in the rat aorta. Compounds 51 − 65 displayed low to moderate affinity at H2, H3, and M3 receptors in functional models of guinea pig. Collectively, N α-imidazolylalkyl- and N α-pyridylalkyl-substituted histaprodifens represent a novel class of potent H1-receptor agonists. These compounds may be useful to define the (patho)physiological role of the H1-receptor and refine molecular models of H1-receptor activation.