[Problem] To provide a novel furanone derivative and a pharmaceutical product composed of the furanone derivative. [Solution] A compound represented by formula (I). (In the formula, A represents -COOR1 or a hydrogen atom； R1 represents a hydrogen atom, an optionally substituted hydrocarbon group or an optionally substituted heterocyclic ring； R2 and R3 may be the same or different and each represents a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted phenyl group, an optionally substituted heterocyclic ring, an optionally substituted heterocyclic fused ring or an optionally substituted amino group, or alternatively, R2 and R3 may form an optionally substituted heterocyclic ring or an optionally substituted heterocyclic fused ring together with a nitrogen atom to which R2 and R3 are bonded； and R4 represents a hydrogen atom or a halogen atom. In this connection, when A represents -COOR1, R2 and R3 are not optionally substituted amino groups at the same time, and when A represents a hydrogen atom, R3 represents a hydrogen atom.)
