Patent ID: 7563905

Claim:
A compound of formula (I): wherein: R 1 is selected from aryl and heteroaryl, any of which may be optionally substituted with alkoxy, alkyl, trifluoromethyl or halo; R 2 is selected from alkyl, alkenyl, alkynyl, cycloalkyl and C 4 -C 6 heteroaryl, any of which may be optionally substituted with alkoxy, alkyl, trifluoromethyl or halo; R 3 is selected from alkyl, alkenyl, alkynyl, cycloalkyl, aryl and heteroaryl, any of which may be optionally substituted with alkoxy, alkyl, trifluoromethyl or halo; and X 1 and X 2 are independently a bond or a linker group, wherein said linker group consists of 1 to 6 atoms selected from C, N, O, and S and may be optionally substituted or oxidized; or a pharmaceutically acceptable salt thereof; provided that R 3 is not a methyl or ethyl group when X 1 is a bond or a methylene group, R 1 is a methyl or ethyl group and R 2 is a phenyl or naphthyl group.