Analgesic and antispasmodic activities of 2-(2-nitro-phenyl)-1H-benzimidazole 5-carboxylic acid: evidence for the importance of the 2-(o-substituted phenyl) group

Abstract

Benzimidazole 5-carboxylic acid derivatives were investigated for analgesic activity in this study. Of the benzimidazole compounds tested, 2-(2-nitro-phenyl)-1 H-benzimidazole 5-carboxylic acid showed remarkable naloxone sensitive analgesic activity in the tail clamp but not in the tail immersion analgesia tests. This centrally active compound showed antispasmodic activity only on KCI induced contractions of isolated rat ileum and not on acetylcholine induced contractions. Acute toxicity of the compounds were > 100 mg/kg i.p mice. It was concluded that substitution of the 2(o-phenyl) by nitro- but not by chloro- or methoxy groups is important for naloxone sensititive analgesic activity of benzimidazole compounds and it was hypothetized that new imidazole compounds having a 2-(o-substituted phenyl) moiety needs to be investigated.