Substituted pyrido[3,4-b]pyrazines as Syk inhibitors

A compound of formula (I):

• and/or a pharmaceutically acceptable salt thereof, wherein
• R1 is independently chosen from hydrogen and C1-C6 alkyl;
• R2 is aryl, or heteroaryl, which is optionally substituted by one or more groups (i) selected from halo, —NR5R6, —OR7, —S(O)nR8, —C(O)R9, —C(O)OR7, —CN, —C(O)NR5R6, —NR5C(O)R9, —NR5S(O)nR8, —NR5S(O)nNR10R11, —NR5C(O)OR7, —NR5C(O)NR10R11, —NO2, or —S(O)nNR5R6, or (ii) selected from C1-6 alkyl, cycloalkyl, heterocycyl, heteroaryl, and aryl, wherein each of (ii) is optionally substituted with one or more groups selected from halo, hydroxy, —C1-C4 alkyl, —C1-C4 haloalkyl, —O—C1-C4 alkyl, —C1-C4 alkyl-OH, —NH2, —N(C1-C4 alkyl)(C1-C4 alkyl), —NH(C1-C4 alkyl), —CON(C1-C4 alkyl)(C1-C4 alkyl), —CONH(C1-C4 alkyl), —CONH2, —N(C1-C4 alkyl)C(O)(C1-C4 alkyl), —C(O) C1-C4 alkyl, —C(O) C1-C4 haloalkyl, —SO2(C1-C4 alkyl), —SO2(C1-C4 haloalkyl), —SO2NH2, —SO2NH(C1-C4 alkyl), —NHSO2(C1-C4 alkyl), and heterocyclyl optionally substituted by —SO2(C1-C4 alkyl),
• R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclyl, each of which, except for hydrogen, is optionally substituted with one or more groups selected from halo, —NR5R6, —OR7, —S(O)nR8, —C(O)R9, —C(O)OR7, —CN, —C(O)NR5R6, —NR5C(O)R9, —NR5S(O)nR8, —NR5S(O)nNR10R11, —NR5C(O)OR7, —NR5C(O)NR10R11, —NO2, —S(O)nNR5R6, C1-6 alkyl, cycloalkyl, heterocyclyl, heteroaryl, aryl, alkenyl, and alkynyl, wherein the heterocyclyl is optionally substituted by one or more groups selected from —C1-C4 alkyl, —C1-C4 haloalkyl, —C1-C4 alkyl-OH, halo, hydroxy, —CON(C1-C4 alkyl)(C1-C4 alkyl), —CONH(C1-C4 alkyl), —CONH2, —C(O)C1-C4 alkyl, —C(O)C1-C4 haloalkyl, —SO2(C1-C4 alkyl), —SO2(C1-C4 haloalkyl), —SO2NH2, and heteroaryl,
• or R3 and R4, together with the N atom to which they are attached, can form a 4-12 membered monocyclic, fused bicyclic or spirocyclic ring optionally containing an additional 1-3 heteroatoms chosen from N and O, which is optionally substituted with one or more groups selected from halo, —NR5R6, —OR7, —S(O)nR8, —C(O)R9, —C(O)OR7, —CN, —C(O)NR5R6, —NR5C(O)R9, —NR5S(O)nR8, —NR5S(O)nNR10R11, —NR5C(O)OR7, —NR5C(O)NR10R11, —NO2, —S(O)nNR5R6, C1-6 alkyl, cycloalkyl, heterocyclyl, heteroaryl, aryl, alkenyl, and alkynyl, wherein the C1-6 alkyl is optionally substituted by one or more groups selected from hydroxy, —NH2, —N(C1-C4 alkyl)(C1-C4 alkyl), —NH(C1-C4 alkyl), and —NHSO2(C1-C4 alkyl),
• m is 0, 1 or 2,
• n is 1 or 2,
• R5, R6, R7, R8, R9, R10, and R11 are independently selected from hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclyl, each of which, except for hydrogen, is optionally substituted with one or more groups selected from halo, hydroxy, C1-6 alkyl, cycloalkyl, heterocyclyl, amino, and amide, wherein the amino is optionally substituted by one or two —C1-C4 alkyl,
• or R5 and R6, R5 and R7, R5 and R8, R5 and R9, and R5 and R10 together with the atom(s) to which they are attached can form a ring, which is optionally substituted with one or more groups selected from halo, hydroxy, C1-6 alkyl, cycloalkyl, heterocycyl, amino, and amide.