Patent ID: 7521458

Claim:
A compound of formula (1), or a pharmaceutically acceptable salt thereof, wherein: R 1 is a radical selected from hydrogen and (C 1 -C 4 )-alkyl; R 2 is selected from the group consisting of hydroxy-(C 1 -C 4 )-alkyl, phenyl, mono-substituted phenyl and phenyl di-substituted at the positions 3 and 4, the phenyl substituents being selected from the group consisting of halogen, (C 1 -C 4 )-alkyl and (C 1 -C 4 )-alkoxyl; R 3 is selected from the group consisting of phenyl, mono-substituted phenyl and phenyl di-substituted at the positions 3 and 4, the phenyl substitutents being selected from the group consisting of halogen, (C 1 -C 4 )-alkyl and (C 1 -C 4 )-alkoxyl; and R 4 is selected from the group consisting of hydrogen, (C 1 -C 4 )-alkyl; allyl, and homoallyl.