Pharmacological studies of 3-(3-methyl-3-butenyl)-1,2,3,4,5,6-hexahydro-6,11-dimethyl-8-hydroxy-2,6-methano-3-benzazocine.

3-(3-methyl-3-butenyl)-1,2,3,4,5,6-hexahydro-6, 11-dimethyl-8-hydroxy-2,6-methano-3-benzazocine (KF-1820) is a derivative of benzomorphan and is different from pentazocine only in the site of the double bond. KF-1820 showed potent analgesic activity in all tests performed. KF-1820 was 6 to 12 times and 30 to 40 times more potent than morphine and pentazocine, respectively, when administered subcutaneously. KF-1820 had little or no narcotic antagonist property. Physical dependence liability tests indicated that KF-1820 may be a little less, or as liable as, pentazocine to produce physical dependence. ID50 values of KF-1820, pentazocine and morphine for depression of contractions of isolated guinea pig ileum to coaxial stimulation correlated well with their analgesic activities in the rodent. The dissociation equilibrium constant of KP-1820 confirmed the in vivo finding that KF-1820 had little or no narcotic antagonist property.