A compound represented by formula (I) or a pharmaceutically acceptable salt thereof. [In the formula, R1 represents a group represented by formula (II), a group represented by formula (III) or a group represented by formula (IV); and R2 represents a 3-methyltetrahydro-2H-pyran-4-yl group or a 4-methoxycyclohexyl group.]一種由式(I)表示之化合物,或其藥學上可接受的鹽:其中R1係由以下式表示之基團:由以下式表示之基團:或由以下式表示之基團:並且R2係3-甲基四氫-2H-吡喃-4-基基團或4-甲氧基環己基基團。