Patent ID: 8362052

Claim:
A compound represented by a formula (I): or a pharmaceutically acceptable salt thereof, 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 S(O) 2 ; Y represents an oxygen or sulfur atom, NH or CH 2 ; Z represents a hydrogen or halogen atom; R represents (1) 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, said 5- or 6-membered heteroaryl is optionally substituted with 1 to 3 same or different lower alkyl, lower alkoxy or halogen atoms, said lower alkyl and lower alkoxy is optionally substituted with 1 to 3 same or different halogen atoms, or (2) C 3-7 cycloalkyl substituted with oxo, one of carbon atoms of said C 3-7 cycloalkyl is optionally replaced by nitrogen atom, and said C 3-7 cycloalkyl in which one carbon atom is replaced by nitrogen atom is optionally substituted with 1 to 3, same or different lower alkyl, lower alkoxy or halogen atoms, said lower alkyl and lower alkoxy is optionally substituted with 1 to 3 same or different halogen atoms.