Serine/threonine kinase inhibitors

A compound of formula I:

• a pharmaceutically acceptable salt thereof;
• wherein
• X1 is selected from the group consisting of N and CH;
• X2 is selected from the group consisting of NRa, O and S;
• X3 is selected from the group consisting of C(R4)2, (C(R4)2)2, CH2NRb, C(═O), C(═O)NRb and C(═O)O;
• X4 is selected from the group consisting of CR2R3 and NR3;
• except where X2 is O, then X3 is not (C(R4)2)2;
• R1 is (i) a 4 to 7 membered saturated or partially unsaturated heterocyclyl or, (ii) an optionally substituted 5 to 6 membered heteroaryl;
• 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;
• R3 is hydrogen or C1-3 alkyl;
• R4 is hydrogen or C1-3 alkyl;
• Ra and Rb are independently hydrogen or C1-3 alkyl;
• or,
• wherein any phenyl moiety is optionally substituted with one or more groups independently selected from halogen, cyano, hydroxyl, C1-6 alkoxy, C1-6 haloalkoxy and C1-6 alkyl wherein said C1-6 alkyl is optionally and independently substituted with one or more groups independently selected from halogen, oxo, hydroxyl and 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.