3-(Aminoalkyl)-1,2,3,4-tetrahydro-5H-[1]benzopyrano[3,4-c]pyridin-5-ones as potential anticholinergic bronchodilators

A series of 3-(aminoalkyl)benzopyrano[3,4-c]pyridin-5-ones was prepared and tested as potential orally active anticholinergic bronchodilators. Inhibition of methacholine-induced collapse in guinea pigs and inhibition of pilocarpine-induced bronchoconstriction in dogs served as in vivo models. Simultaneous measurement of salivary inhibition in the dog model allowed determination of a pulmonary selectivity ratio. The benzopyrano[3,4-c]pyridin-5-one parent ring system was prepared by Pechman condensation of phenols with a piperidine beta-keto ester. Alkylation with aminoalkyl halides, or with 1-chloro-2-propanone followed by reductive amination, yielded the 3-substituted target compounds. Bronchodilator potency was related to the extent of steric crowding surrounding the side-chain terminal amine function. Addition of a methyl substituent on the carbon alpha to the terminal amine often increased potency or pulmonary selectivity. After secondary pharmacological evaluation, compound 7a, designated CI-923, was selected for clinical trial as a bronchodilator.