4-Amino-5-vinyl-3(2H)-pyridazinones and analogues as potent antinociceptive agents: Synthesis, SARs, and preliminary studies on the mechanism of action.

A series of 4-amino-5-vinyl-3(2H)-pyridazinones and analogues were synthesized and their antinociceptive effect was evaluated in the mouse abdominal constriction model. Several of the novel compounds showed ED(50) values in the range 6-20mg/kg/sc and demonstrated to be able to completely protect all the treated animals from the effect of the noxious stimulus at 30 mg/kg/sc. SAR studies confirmed the essential role played by an amino or substituted amino function at position 4 and by a vinyl group at position 5 of the diazine system.