A compound represented by the general formula (I): wherein R1 is a hydrogen atom, a halogen atom, or the like; R2, R3, and R4 are each independently a hydrogen atom, a halogen atom, C1-C15 alkyl optionally substituted with one or more C1-C12 alkyloxy or the like, or the like; R5 is a hydrogen atom or the like; R6 and R7 are a hydrogen atom or the like; R8 is C1-C3 alkyl or the like; R9 is a hydrogen atom or the like), a prodrug, a pharmaceutically acceptable salt, or solvate thereof.