Patent ID: 7541366

Claim:
A compound of the formula (I) or a pharmaceutically acceptable salt thereof: wherein: R 1 is hydrogen; a straight or branched C 1 -C 6 alkyl group, optionally substituted with one or more substituents selected from the group consisting of C 1 -C 5 alkoxy, C 3 -C 7 cycloalkyl, 1,3-dioxolanyl, cyano, naphthyl, C 2 -C 5 alkenyloxy, and 2,3-dihydrobenzo[1,4]dioxinyl ; a C 2 -C 6 alkenyl group; a C 2 -C 6 alkynyl group; or a benzyl group, optionally substituted with one or more substituents selected from the group consisting of halogen, C 1 -C 3 alkyl, C 1 -C 3 alkoxy, cyano, C 1 -C 3 alkoxycarbonyl, and trifluoro-C 1 -C 3 alkyl, R 2 is a straight or branched C 1 -C 6 alkyl group, R 3 is hydrogen; a straight or branched C 1 -C 6 alkyl group optionally substituted with hydroxyl or cyano, and R 4 is a 1,2,3,4-tetrahydroisoquinolinyl group optionally one or more substituted with halogen or C 1 -C 5 alkyl; a benzyloxy group optionally one or more substituted with halogen or C 1 -C 5 alkyl; or a benzylamino group optionally substituted with halogen.