Abstract: The invention provides the compounds of formula (I) and pharmaceutically acceptable salts thereof, in which: R1 and R2 are independently selected from the group consisting of H, C1-6alkyl, C1-2alkyl substituted by one to five fluorine atoms, C3-6alkenyl, C3-6alkynyl, C3-10cycloalkylC0-6alkyl, C4-12bridged cycloalkyl, A(CR7R8)n and B(CR7R8)n; R3 is selected from the group consisting of C1-6alkyl, NH2 and R10CONH; R4 is C1-2alkyl substituted by one to five fluorine atoms; R5 is selected from the group consisting of H, C1-4alkyl, C1-2alkyl substituted with one to five fluorine atoms, halogen and C3-10cycloalkylC0-6alkyl, with the proviso that when R6 is H R5 is not H.