| abstract |
A compound having the formula: ** Formula ** or a pharmaceutically acceptable salt thereof, wherein R1 is C1-3 aliphatic; R2 is hydrogen, fluoro or methyl; R3 is hydrogen, fluoro or methyl; each R4 is independently hydrogen or fluoro; and R5 is hydrogen, chlorine, cyclopropyl or C1-4 aliphatic, optionally substituted with 1 to 3 fluorine atoms. |