Compounds of formula (I), combinations and uses thereof for disease therapy, or a pharmaceutically acceptable salt or solvate thereof, including all tautomers, stereoisomers and polymorphs thereof wherein: R1 represents C2-8alkyl； C2-8alkenyl； &mdash；(C1-6alkyl)-aryl； &mdash；(C1-6alkyl)-heteroaryl； &mdash；(C1-6alkyl)-carbocyclyl； &mdash；(C1-6alkyl)-heterocyclyl； -aryl； -heteroaryl； -carbocyclyl or -heterocyclyl； wherein said aryl or heteroaryl groups may be optionally substituted by one or more substituents selected from, C1-4alkyl, C1-4-fluoroalkyl, C1-4alkoxy, C1-4-fluoroalkoxy, hydroxy, &mdash；SO2(C1-4alkyl), &mdash；SO2N(C1-4alkyl)(C1-4alkyl), &mdash；SOC1-4alkyl, &mdash；SOC3-6cycloalkyl &mdash；C(O)O(C1-4alkyl), benzyloxy and phenyl； and wherein said carbocyclyl and heterocyclyl groups may be optionally substituted by one or more substituents selected from &mdash；C1-4 alkyl, &mdash；C1-4 alkoxy, hydroxyl, halogen and oxo； R2 represents H； C1-4alkyl or halogen； R3 represents H； C1-4alkyl or halogen； and R4 represents H； C1-4alkyl or halogen.
