Pyridazinone derivatives

PCT No. PCT/JP95/00069 Sec. 371 Date Jul. 23, 1996 Sec. 102(e) Date Jul. 23, 1996 PCT Filed Jan. 24, 1995 PCT Pub. No. WO95/19969 PCT Pub. Date Jul. 27, 1995Pyridazinone derivatives represented by the formula (I) and antiplatelet agents containing them: (I) [wherein R is a hydrogen atom or a C1-C4 alkyl group, X is a hydrogen atom, a chlorine atom or a bromine atom, Ar is a pyridyl group or a phenyl group substituted with OR1 (wherein R1 is a hydrogen atom or a C1-C4 alkyl group) and A {wherein A is a hydrogen atom, a halogen atom, a C1-C4 alkyl group or OR2 (wherein R2 is a hydrogen atom or a C1-C4 alkyl group)}, is C1-C8 alkylene wherein one carbon atom on the straight chain is substituted with one OR1 group (wherein R1 is the same as defined above), and Z1 and Z2 are independently a hydrogen atom, a halogen atom, a C1-C4 alkyl group or a OR1 group (wherein R1 is the same as defined above)]. These compounds have strong antiplatelet effects, are excellently safe, and can be used as active ingredients of prophylactic and therapeutic drugs for various thrombotic diseases.