This invention provides a compound represented by formula (1) or a pharmaceutically acceptable salt thereof. Specifically, the present invention provides a compound represented by formula (1) or a pharmaceutically acceptable salt thereof [Therein, A is O, S, or N-R6； ring G is a 5-membered or 6-membered aromatic ring, etc., including 1-3 heteroatoms selected from O, S and N as constituent atoms； R1 and R2 are each independently a hydrogen atom, a halogen atom, or an optionally-substituted C1-6 alkyl carbonyl group, etc.； R3, R4 and R5 are each independently a hydrogen atom, a halogen atom, or an optionally-substituted C1-6 alkyl carbonyl group, etc.； and R6 is a hydrogen atom or an optionally-substituted C1-6 alkyl group, etc.].
