6-Benzoxazinylpyridazin-3-ones: Potent, Long-Acting Positive Inotrope and Peripheral Vasodilator Agents

J Med Chem. 1990 Jan;33(1):380-6. doi: 10.1021/jm00163a061.


A series of 6-benzoxazinylpyridazin-3-ones was prepared and evaluated for inhibition of cardiac phosphodiesterase (PDE) fraction III in vitro and for positive inotropic activity in vivo. 6-[3,4-Dihydro-3-oxo-1,4(2H)-benzoxazin-7-yl]-2,3,4,5-tetrahydro-5 - methylpyridazin-3-one (bemoradan) was found to be an extremely potent and selective inhibitor of canine PDE fraction III and a long-acting, potent, orally active inotropic vasodilator agent in various canine models. Additional benzoxazin-6-yl and -8-yl compounds were also prepared. Altering the pyridazinone substitution from the 6-position to the 7-position produced a 14-fold increase in the iv cardiotonic potency (ED50) from 77 to 5.4 micrograms/kg while substitution at the 8-position reduced potency. Methyl substitution at various sites in the molecule was also examined. Positive inotropic activity was maintained for between 8 and 24 h after a single oral dose (100 micrograms/kg) of bemoradan in dogs, thus making it one of the most potent and long-acting orally effective inotropes yet described. Bemoradan is currently under development as a cardiotonic agent for use in the management of congestive heart failure.

Publication types

  • Comparative Study

MeSH terms

  • 3',5'-Cyclic-AMP Phosphodiesterases / antagonists & inhibitors
  • Animals
  • Benzoxazines
  • Cardiotonic Agents*
  • Chemical Phenomena
  • Chemistry
  • Dogs
  • Molecular Structure
  • Myocardial Contraction / drug effects*
  • Myocardium / enzymology
  • Oxazines / chemical synthesis
  • Oxazines / pharmacology*
  • Pyridazines / chemical synthesis
  • Pyridazines / pharmacology*
  • Stimulation, Chemical
  • Structure-Activity Relationship
  • Vasodilation / drug effects*


  • Benzoxazines
  • Cardiotonic Agents
  • Oxazines
  • Pyridazines
  • 3',5'-Cyclic-AMP Phosphodiesterases
  • bemoradan