A compound represented by the formula ** Formula ** or a pharmaceutically acceptable salt thereof, wherein A is N or CR '； R 'is H, C1-C8 alkyl optionally substituted by one or more halogen atoms； R1 is selected from H； C1-C8 alkyl optionally substituted by one or more halogen atoms, OH, C1-C4 alkoxy, C3-C7 cycloalkyl or C3-C7 cycloalkyloxy； - (C2-C4 alkyl) -NR19R21 and C3-C7 cycloalkyl； or R1 is -X-Y； or R1 is -W-R7-X-Y； or R1 is -S (O) 2-X-Y； or R1 is -S (O) 2-W-R7-X-Y； R2 is selected from H； C1-C8 alkyl optionally substituted by one or more halogen atoms, OH, C1-C4 alkoxy, C3-C7 cycloalkyl or C3-C7 cycloalkyloxy； C1-C4 alkoxy； - (C0-C4 alkyl) -NR19R21 and C3-C7 cycloalkyl； or R2 is -X-Y； or R2 is -W-R7-X-Y； or R2 is -S (O) 2-X-Y； or R2 is -S (O) 2-W-R7-X-Y； R2a is selected from H； C1-C8 alkyl optionally substituted by one or more halogen atoms, OH, C1-C4 alkoxy, C3-C7 cycloalkyl or C3-C7 cycloalkyloxy； and C3-C7 cycloalkyl； or R2 and R2a taken together are oxo； wherein one of R1 and R2 is -X-Y, -W-R7-X-Y, -S (O) 2-X-Y； or -S (O) 2-W-R7-X-Y； R3 is independently selected from H； C1-C8 alkyl optionally substituted by one or more halogen atoms, OH, C1-C4 alkoxy, C3-C7 cycloalkyl or C3-C7 cycloalkyloxy； -OH； OR '； - (C0-C4 alkyl) -NR19R21； CN； halogen； - (C0-C4 alkyl) -C6-C14 aryl； - (C0-C4 alkyl) -heteroaryl of 4 to 14 members； -C (>； = O) H； -C (>； = O) OH； - C (>； = O) NR19R21 and C3-C7 cycloalkyl, wherein the aryl and heteroaryl are optionally substituted by one or more substituents independently selected from OH, C1-C4 alkyl, C1-C4 alkoxy, halogens and C1-C4 haloalkyl； R3a is selected from H； C1-C8 alkyl optionally substituted by one or more halogen atoms, OH, C1-C4 alkoxy, C3-C7 cycloalkyl or C3-C7 cycloalkyloxy； and C3-C7 cycloalkyl； or R3 and R3a taken together are oxo； R5 and R6 are independently selected from - (C0-C4 alkyl) -C6-C14 alkyl and - (C0-C4 alkyl) - 4-14 membered heteroaryl, wherein the aryl and heteroaryl are each optionally substituted by
