PYRIDAZINONE DERIVATIVE

PURPOSE:To obtain a new derivative effective to prophylaxis or treatment of various thrombotic diseases, having a potent and a wide range spectrum of inhibiting platelet coagulation, and a low incidence of adverse effects with a superior selectivity in its action. CONSTITUTION:This derivative (salt) is expressed by formula I [R is H, a 1-4C alkyl; X is H, Cl or Br; Ar is a pyridyl or a substituted phenyl; Y is a substituted 1-4C alkylene; each one of Z and Z is H, a halogen, a 1-4 alkyl, etc.], e.g. 4-bromo-6-[3-(4chlorophenyl)-3-hydroxypropyloxy]-5-(3- pyridylmethylamino)-3 (2H) pyridazinone. The above mentioned derivative (salt) is obtained by e.g. reacting 5-halo-3 (2H)-pyridazinone compound of formula II (X is Cl or Br) with an arylmethylamine derivative (salt) of formula III in the presence of a hydrogen halogenate eliminating agent if necessary, in an inactive solvent.