“…1A), which is more potent than morphine. Substitutions on the nitrogen greatly influence the pharmacology of the compound, with replacement of the N-methyl group of the 4,5a-epoxymorphinans with either an N-allyl or N-methylcyclopropyl group typically converting the compound from an agonist to antagonist, as first demonstrated with N-allylnorcodeine (Von Braun, 1916) and N-allylnormorphine (nalorphine) (McCawley et al, 1941;Weijlard and Erickson, 1942;Unna, 1943) (Fig. 1A).…”