N-ALKYL-NOR-TROPINE ESTERS OF 2-PHENYL-CYCLOHEXENIC ACIDS AS NEW BRONCHODILATOR AGENTS - EFFECT OF STRUCTURAL AND CONFORMATIONAL MODIFICATIONS ON AFFINITY FOR MUSCARINIC RECEPTORS

A series of N-alkyl-nor-tropine esters of 2-phenyl-2-cyclohexene-1-carboxylic, 2-phenyl-cyclohexanecarboxylic, and 2-phenyl-1-cyclohexene-1-acetic acids and their quaternary ammonium salts were synthesized and evaluated for bronchodilator activity by binding assays and pharmacological tests. The in vitro and in vivo functional activity results showed that some quaternary derivatives are potent anticholinergic bronchodilator agents, and 4 compounds (14-A, 16-A, 25-A and 28-A) were selected for pharmacotoxicological evaluation. The binding data also indicated that the affinity of these compounds for the tracheal membrane muscarinic receptors is markedly affected by structural modifications of both the cationic head and the acyl moiety of the molecule. In the series of N-alkyl-nor-tropine 2-phenyl-2-cyclohexene-1-carboxylate derivatives, a rather strict limitation of the bulk of the equatorial substituent of tropine nitrogen is required for very high affinity. Conformational analysis and molecular graphics techniques evidenced an influence of the acyl moiety conformation on the affinity of the different tropinic esters, suggesting that the carbonyl oxygen may participate in interaction with the binding site, eliciting a marked increase of potency when it is oriented in a proper conformation with respect to the tropinic nitrogen and the phenyl ring.