“…Though definitely less potent than epibatidine, which is active in the same test at 1 µg/kg, 1a favourably compared with morphine, active at 2 mg/kg. In addition, 1a exhibited the highest ratio (30) between the maximal non-toxic dose and the minimal analgesic dose, when compared to morphine (10) and epibatidine (7). It should be noted that reversion of the chloropyridazine substituent from N 3 to N 8 as in 2a, or the insertion on N 8 of an alkyl (1c) or a propionyl group (1b), markedly reduced or -as for 1b -abolished the activity.…”