Comparison of local anesthetic activities between optical isomers of cis-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene.
The optical isomers of cis-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene (YAU-17) were compared for their local anesthetic activity, acute toxicity, spasmolytic activity, and partition coefficient between chloroform and phosphate buffer. 1-YAU-17 was more active than d-YAU-17 in blocking the conduction of action potentials in isolated frog sciatic nerves. The difference in local anesthetic activities between the optical isomers was further substantiated by in vivo tests for corneal anesthesia, intracutaneous anesthesia and sciatic nerve block in quinea-pigs. Similarly, the i.v. injection to mice revealed a higher toxicity for 1-YAU-17 as compared to its d-isomer. In these tests, the potency ratios of the enantiomers ranged from 2 to 4, and the racemate had an intermediate potency. On the contrary, no difference among the compounds was found in their liposolubility, partition coefficient, and spasmolytic activity examined with isolated guinea-pig ileum. These results indicate that the steric factors play an important role in the production of different local anesthetic activities between the optical isomers of YAU-17, and their local anesthetic potency tends to be correlated to their intravenous acute toxicity but not to their spasmolytic activity.