Indole amide derivatives: synthesis, structure–activity relationships and molecular modelling studies of a new series of histamine H 1-receptor antagonists

Abstract

A number of indole amide derivatives bearing a basic side chain, in which the indole ring replaces the isoster benzimidazole nucleus typical of some well-known antihistamines, were prepared and tested for their H 1-antihistaminic activity. The 1-benzyl-3-indolecarboxamides 32– 42 showed antihistaminic (H 1) activity (pA 2 6–8); the 3-indolylglyoxylylamides 7– 16 and the 2-indolecarboxamides 48– 56 showed little or no activity. Insertion of the basic side chain of the active 3-indolecarboxamide derivatives into a piperazine ring (compounds 57– 59) led to a dramatic loss of activity. All the active compounds proved to be competitive antagonists, since the values of the regression slope were not statistically different from 1. The most active compounds, 32, 33, 38– 41, were also tested both in vitro for their anticholinergic activity and in vivo for their ability to antagonize histamine-induced cutaneous vascular permeability in rats. The biological results and the structure–activity relationships of the novel compounds are discussed in the light of molecular modelling studies, taking the molecule of astemizole as a model, and referring to proposed H 1-receptor pharmacophore models.