| abstract |
The present invention relates to a compound represented by formula (I): (wherein R 1 , R 2 , R 3 and R 4 each independently represent a hydrogen or halogen atom; R 5 and R 6 each independently represent a hydrogen atom or lower alkyl or together represent oxo; X represents C(O) or the like; Y represents an oxygen atom or the like; Z represents a hydrogen atom or the like; R represents 5- or 6-membered heteroaryl having 1-3 hetero atoms selected from the group consisting of nitrogen, sulfur and oxygen atoms, contained within a ring, or the like) or to a pharmaceutically acceptable salt thereof. |