Patent ID: 8822448

Claim:
A compound of formula (I) or a pharmaceutically acceptable salt thereof: wherein one of R 1 and R 2 is hydrogen, halogen, halogeno-lower alkyl, or lower alkyl, —O-lower alkyl or cycloalkyl, each of which may be substituted, and the other is a group of formula (II): R 3 is lower alkyl, cycloalkyl or a saturated hetero ring, each of which may be substituted, R 4 , R 5 and R 6 are the same as or different from each other, and each is hydrogen or lower alkyl, and R a and R b are the same as or different from each other, and each is hydrogen, or lower alkyl, cycloalkyl, aryl or a hetero ring, each of which may be substituted, or R a and R b are combined with the adjacent nitrogen atom to form a monocyclic nitrogen-containing hetero ring or a polycyclic nitrogen-containing hetero ring, each of which may be substituted.