A compound of Formula I ** Formula ** or its stereoisomer or mixture of stereoisomers, optionally as its pharmaceutically acceptable salt, wherein: R1 is optionally substituted alkyl, haloalkyl or cycloalkyl； ** Formula ** is a 4, 5 ring , 6 or 7 members, wherein: R2 in each case, is independently halo, hydroxy, alkyl, alkoxy, hydroxyalkyl, haloalkoxy or -C (O) O-alkyl, or two R2 groups may be attached to the carbons to which they are connected to form a bicyclic bridge or condensate ring； n is 0, 1, 2 or 3； X is C or N； where: when X is N: R3 is absent； R3 'is aryl or heteroaryl optionally substituted with one or two groups independently selected from heteroarylalkylloxy； alkyl substituted with arylsulfonylamino； alkyl substituted with cycloalkylcarbonylamino； or R3 'is -SO2-Ra, wherein Ra is optionally substituted alkyl, optionally substituted phenyl, optionally substituted phenyl, optionally substituted phenylalkyl or optionally substituted heteroaryl； when X is C: R3 is cyano, aminoalkyl, alkoxycarbonyl or hydroxy, and R3 'is optionally substituted phenyl； or R3 is hydrogen and R3 'is phenyl, alkyl substituted with 1-phenyl-4,5,6,7-tetrahydro-1H-pyrazolo [3,4-c] pyridinyl, optionally substituted indolyl, 1H-benzo [d] [ 1,2,3] optionally substituted triazolyl, optionally substituted oxoindolinyl, optionally substituted benzoimidazolyl, optionally substituted pyridinyl (furanyl substituted oxadiazolyl), 2-oxo-3,4-dihydroquinazolinyl, -C (O) NRbRc, where Rb is hydrogen or alkyl； and Rc is optionally substituted heteroarylalkyl； or R3 is hydrogen and R3 'is a group of formula (a), (b), (c), (d), (e) or (f): ** Formula ** where: Z1 is O, NH or N optionally substituted with aminoalkyl, alkylaminoalkyl or dialkylaminoalkyl； Z2 is CH or N； A is N, C-H or C-Rd； each Rd, when present, is independently halo, alkyl, optionally substituted alkoxy or optionally substituted heterocycloalkyl, and Re is amino or haloalkyl； or R3 and R3 'are taken together with the carbon to whic
