Serine/threonine kinase inhibitors

A compound of formula I:

• or a pharmaceutically acceptable salt thereof;
• wherein
• X1 is N or CH;
• X2 is O;
• X3 is C(R4)2;
• X4 is CR2R3;
• R1 is (i) a 4 to 7 membered saturated or partially unsaturated heterocyclyl containing an oxygen atom;
• or, (ii) a heteroaryl selected from the group consisting of 1-methyl-1H-pyrazol-4-yl, 1-methyl-1H-pyrazol-3-yl, 2-ethyl-2H-pyrazol-3-yl, 2-methyl-2H-pyrazol-3-yl, 2-isopropyl-2H-pyrazol-3-yl, 1-methyl-1H-pyrazol-5-yl, 1-ethyl-1H-pyrazol-5-yl, 4-methylthiazol-2-yl, 1-methyl-1H-[1,2,4]triazol-3-yl, 2-methyl-2H-[1,2,3]-triazol-4-yl, 1-methyl-1H-[1,2,4]-triazol-5-yl, 1,3-dimethyl-1H-pyrazol-4-yl, 1,3,5-trimethyl-1H-pyrazol-4-yl, 1-methyl-1H-tetrazol-5-yl, 2-methyl-2H-tetrazol-5-yl, 5-methyl-1,3,4-thiadizol-2-yl, oxetan-3-yl, 3-methyloxetan-3-yl, tetrahydropyran-4-yl, tetrahydro-2H-pyran-4-yl, tetrahydropyran-3-yl, 2-methyl-tetrahydropyran-4-yl, 2,2-dimethyl-tetrahydropyran-4-yl, 2-hydroxymethyltetrahydropyran-4-yl, 3-fluorotetrahydropyran-4-yl and tetrahydrofuran-3-yl;
• R2 is selected from the group consisting of:
• (a) C1-10 alkyl,
• (b) C2-10 alkenyl,
• (c) C1-10 haloalkyl,
• (d) C3-7 cycloalkyl or C3-7 cycloalkyl-C1-6 alkyl,
• (e) C3-7 halocycloalkyl or C3-7 halocycloalkyl-C1-6 alkyl,
• (f) C1-10 hydroxyalkyl or C1-10 dihydroxyalkyl,
• (g) C1-3 alkoxy-C1-6 alkyl,
• (h) C1-3 alkylthio-C1-6 alkyl,
• (i) C1-10 cyanoalkyl,
• (j) phenyl, phenyl-C1-3 alkyl, phenoxy or benzyloxy-C1-3 alkyl,
• (k) heteroaryl, heteroaryl-C1-3 alkyl or heteroaryloxy wherein said heteroaryl moiety is selected from the group consisting of pyrazolyl, imidiazolyl, oxazolyl, isoazolyl, thiazolyl, isothiazolyl, pyridinyl, pyrid-2(1H)-one and 1-alkylpyrid-2(1H)-one and each said heteroaryl is independently optionally substituted with one or more groups selected from the group consisting of halogen, hydroxyl, oxide, C1-6 alkoxy, C1-6 haloalkoxy, cyano, C3-6 cycloalkyl and C1-6 alkyl wherein said C1-6 alkyl is optionally independently substituted with one or more groups independently selected from halogen, oxo, hydroxyl or C1-6 alkoxy;
• and
• (l) phenylthio or phenylthio-C1-6 alkyl;
• and
• R3 and R4 are independently hydrogen or C1-3 alkyl;
• wherein any phenyl moiety is optionally substituted one or more halogen, cyano, hydroxyl, C1-6 alkoxy, C1-6 haloalkoxy or C1-6 alkyl wherein said C1-6 alkyl is optionally independently substituted with one or more groups independently selected from halogen, oxo, hydroxyl or C1-6 alkoxy;
• and,
• wherein each cycloalkyl is independently and optionally substituted with one to three groups selected from halogen, C1-6 haloalkyl, C1-6 alkoxy and C1-6 haloalkoxy.