Patent ID: 8013018

Claim:
A compound represented by the following formula (Ia) or a pharmaceutically acceptable salt thereof: wherein R 1 is lower alkyl, cycloalkyl, lower alkylene-aryl, aryl which may be substituted, heteroaryl which may be substituted, or lower alkyl substituted with one or more halogens; R 2 and R 3 independently represent lower alkyl, or aryl; R 4 and R 5 independently represent a hydrogen atom, lower alkyl, —O-lower alkyl, —OH, lower alkylene-OH, or lower alkylene-O-lower alkyl; R 6 to R 9 independently represent a hydrogen atom, lower alkyl, —O-lower alkyl, a halogen atom, lower alkyl substituted with one or more halogens, OH, CN, lower alkenyl, or a nitrogen-containing heterocyclic group; and R 10 and R 11 independently represent a hydrogen atom, or lower alkyl, provided that R 2 and R 3 may be taken together with the adjacent carbon atom to form cycloalkyl.