The dissociation constants (KB) at the LTD, receptor on guinea pig trachea of a series of monocyclic and bicyclic cyclopentylurethane and cyclopentylacetamide N-arylsulfonyl amides have been measured. The KB was found to be remarkably tolerant of changes in the electronic constitution and lipophilicity of the bicyclic ring system (template).
![methyl 4-[(6-aminobenzimidazol-1-yl)methyl]-3-methoxybenzoate Structure](https://image.chemsrc.com/caspic/410/107754-54-1.png)
![4-[[6-[[(cyclopentyloxy)carbonyl]amino]benzimidazol-1-yl]methyl]-3-methoxybenzoic acid Structure](https://image.chemsrc.com/caspic/334/107754-56-3.png)