Patent ID: 8106086

Claim:
A compound represented by the general formula (I-a) or a pharmaceutically acceptable salt thereof: wherein R 1a and R 2a each independently represents a hydrogen atom, a C 1 -C 6 alkyl group, an aryl group, a heteroaryl group or a C 1 -C 6 alkyl group optionally substituted by a substituent selected from the group consisting of a C 3 -C 6 cycloalkyl group, an aryl group and a heteroaryl group; R 4a and R 5a each independently represents a C 1 -C 6 alkyl group, a C 3 -C 6 cycloalkyl group, an aryl group or an aralkyl group, or R 4a and R 5a may form a C 3 -C 6 cycloalkylidene group together with the adjacent carbon atom; R 6a represents a C 1 -C 6 alkyl group, a C 1 -C 6 haloalkyl group, a C 3 -C 6 cycloalkyl group or a C 1 -C 6 alkoxy- C 1 -C 6 alkyl group; wherein the above-described C 3 -C 6 cycloalkyl group, C 3 -C 6 cycloalkylidene group, aryl group, aralkyl group and heteroaryl group may be each independently substituted by a substituent selected from the group consisting of a halogen atom, a C 1 -C 6 alkyl group, a C 1 -C 6 haloalkyl group and a C 1 -C 6 alkoxy group; R 3a represents a hydrogen atom, a C 3 -C 6 cycloalkyl group, an aryl group, a heteroaryl group or a C 1 -C 6 alkyl group optionally substituted by a substituent selected from the group consisting of a C 3 -C 6 cycloalkyl group, an aryl group and a heteroaryl group, wherein the C 3 -C 6 cycloalkyl group, aryl group and heteroaryl group in R 3a each independently represents an unsubstituted group or a C 3 -C 6 cycloalkyl group, an aryl group or a heteroaryl group substituted by one or two substituents selected from the group consisting of a halogen atom, a nitro group, a cyano group, a C 1 -C 6 alkyl group, a C 1 -C 6 haloalkyl group, a C 1 -C 6 alkoxy group, a C 1 -C 6 haloalkoxy group, a carboxyl group, a C 3 -C 6 cycloalkyl group, an aryl group, a heteroaryl group, an aryloxy group, an aralkyl group, —CON(R 7 )R 8 , —N(R 7 )R 8 , —N(R 7 )COR 8 , —N(R 7 )SO 2 R 8 , —OCOR 7 , —OCON(R 7 )R 8 , —SR 7 , —SO 2 N(R 7 )R 8 and R 7 and R 8 each independently represents a hydrogen atom or a C 1 -C 6 alkyl group; and X represents —N(R 7 )— or —O—(provided that in the case where R 2a is a hydrogen atom, R 3a is a phenyl group and R 4a , R 5a and R 6a are methyl groups, then R 1a does not represent an n-butyl group, a phenyl group, a 4-fluorophenyl group, a 3-chlorophenyl group, a 3,4-dichlorophenyl group, a 4-methylphenyl group, a 3,4-dimethylphenyl group, a 3-trifluoromethylphenyl group, a 4-methoxyphenyl group, a furfuryl group, a benzyl group, a phenethyl group, a 4-fluorobenzyl group, a 2-chlorobenzyl group or a 3,4-dimethoxyphenethyl group.