PYRAZINE DERIVATIVES, PROCESS FOR PRODUCING THEM, PHARMACEUTICAL COMPOSITIONS CONTAINING THEM AND THEIR USE

A compound of formula (I) wherein R1 is selected from the group consisting of phenyl substituted by one or more halogen atoms, naphthyl and naphthyl substituted by one or more halogen atoms; R2 is selected from the group consisting of -NH2 and -NHC(=O)Ra; R3 is selected from the group consisting of -NRbRc, -NHC(=O)Ra and hydrogen, R4 is selected from the group consisting of hydrogen, -C1-4 alkyl, -C1-4 alkyl substituted by one or more halogen atoms, -CN, -CH2OH, -CH2ORd and -CH2S(O)xRd; wherein Ra represents C1-4 alkyl or C3-7cycloalkyl, and Rb and Rc, which may be the same or different, are selected from hydrogen and C1-4 alkyl, or together with the nitrogen atom to which they are attached, form a 6-membered nitrogen containing heterocycle, which heterocycle can be further susbtituted with one or more C1-4 alkyl; Rd is selected from C1-4 alkyl or C1-4 alkyl substituted by one or more halogen atoms; x is an integer zero, one or two; and pharmaceutically acceptable derivatives thereof; with the proviso that R1 does not represent (a); when R2 is -NH2, and both R3 and R4 are hydrogen.