Antivertigo Agents. I. Structure-Activity Relationships of 2-(2-Aminoethyl) pyridines

A series of 2-(2-aminoethyl) pyridines derived by the modification of the amine moiety in betahistine, 2-(2-methylaminoethyl) pyridine, was synthesized and evaluated for antivertigo action in terms of inhibitory activity against spontaneous nystagmus in cats. The structure-activity relationships between the amine moieties and antivertigo activities were investigated. The effects of substituents on the phenyl ring of the 4-phenylpiperazine moiety were investigated by means of quantitative regression analysis using various physicochemical parameters. The following equation gave the best correlation. log 1/ID30=-0.417 (±0.322) π+0.166 (±0.048) MR-1.473 (±0.237) (n=15, s=0.239, r=0.910, F212=28.887). In this series of compounds, 1-(2-methoxyphenyl)-4-[2-(2-pyridyl) ethyl] piperazine, 1-(2-methoxyphenyl)-4-[2-[2-(6-methyl) pyridyl] ethyl]-piperazine, and 1-(2-methoxyphenyl)-4-[2-[2-(5-ethyl) pyridyl] ethyl] piperazine were found to show more potent activity than betahistine. Thus, the 4-(2-methoxyphenyl) piperazine group was found to be the most effective amine moiety for activity against spontaneous nystagmus.