Synthesis and Structure-Activity Relationships of a New Series of Benzimidazoles as H₁-Antihistaminic Agents

Abstract

New 2-(4-(4-azolybutyl)piperazinyl)-, 2-(4-(4-azolybutyl)piperazinylmethyl)-, 2-(4-(4-azolylbutyl)homopiperazinyl)- and 2-(4-(4-azolylbutyl)homopiperazinyl)methylbenzimidazoles were synthesized, characterized and tested for in vitro and in vivo H₁-antihistaminic activity. Structure-activity relationships impleid that the best antihistaminic activity required the simultaneous presence of a homopiperazinylbenzimidazole system (or a methylene linker between the benzimidazole and the piperazine rings) and an unsubstituted pyrazole ring. 1-(2-Ethoxyethyl)-2-{4-[4-(pyrazol-l-yl)butyl]homopiperazin-l-yl}benzimidazole (17), at its dimaleate salt, has been chosen for further development.