| abstract |
A compound of the formula (I): <CHEM> or a pharmaceutically acceptable salt thereof, wherein: R<1> is a hydrogen atom, a substituted or unsubstituted C1-6 alkyl group, a C2-6 alkenyl group, a C2-6 alkynyl group or a R<7>-CO- group (wherein R<7> is a C1-6 alkyl group, a phenyl group, a C2-6 alkenyl group which may be substituted by a phenyl group, or a C1-6 alkoxy group); R<2> is a hydrogen atom, a substituted or unsubstituted C1-8 alkyl group, or a phenyl group; R<3> is a hydrogen atom, and R<4> is a hydroxyl group, or R<3> and R<4> together form a bond; each of R<5> and R<6> is a C1-4 alkyl group; and Y is a cyano group, a halogen atom, a nitro group, a C1-6 alkyl group, a C2-6 alkynyl group, a C1-6 alkylcarbonyl group, a C1-6 alkoxy group, a di-C1-6 alkylaminocarbonyl group, an aryl group, a C1-6 alkoxycarbonyl group, a carboxyl group or a morpholinocarbonyl group. |