Synthesis and substance P antagonist activity of naphthimidazolium derivatives.

The synthesis of unsymmetrical naphth[2,3-d]imidazolium and bridged naphth[2,3-d]imidazolium derivatives and their substance P (SP) antagonist activity are described. All compounds were evaluated for their ability to displace SP from neurokinin-1 (NK-1) receptor sites using standard receptor binding methodology (rat forebrain membrane). 1,3-Diethyl-2-[3-(1,3-dihydro-1,3,3-timethyl-2H-indol-2-ylidene) -1-propenyl]-1H-naphth[2,3-d]imidazolium chloride (7a), a representative compound in this series, was further evaluated for SP antagonist activity in a guinea pig ileum contractility assay. In vivo SP antagonist activity of 7a was demonstrated using SP-induced salivation and paw edema models performed in rats.