Structure-activity relationships in some series of 2-alkyl-1,2,3,-benzotriazinium compounds.

1. The potencies of four series of N-alkyl-1,2,3-benzotriazinium iodides have been estimated on the frog rectus abdominis and chick biventer cervicis preparations.2. The partition coefficients between chloroform and water were measured for all of the compounds, as well as the ionization constants for some members of two of the series.3. The potencies of the compounds increased with the number of carbon atoms in the N-alkyl side chain up to a maximum at the n-butyl homologue while partition coefficients increased up to the n-pentyl homologue, and there may be some association between the lipid solubilities of the compounds and their biological activity.4. The responses of the tissues to the benzotriaziniums were not abolished by tubocurarine, indicating that the site of action was not at acetylcholine receptors.5. The similarity between the actions of the benzotriaziniums and those of quinine and quinidine is discussed.