A compound represented by formula (I):
wherein R is a methyl group or the like, R
1
is a fluorine atom or the like, R
2
is a hydrogen atom or a fluorine atom, R
3
is a hydrogen atom, R
4
is an ethyl group or the like, or a pharmaceutically acceptable salt thereof.
由以下式(I)表示的化合物:其中R是甲基基团或类似物,R1是
氟原子或类似物,R2是氢原子或
氟原子,R3是氢原子,R4是乙基基团或类似物,或其药学上可接受的盐。