A compound of formula (I) wherein R is methyl, ethyl, n-propyl, iso-propyl, n-butyl or allyl; R′ is hydrogen, C1-C4 alkyl, C1-C3 alkoxy; halogen, trifluoromethyl or OCHxFy, R″ is hydrogen, fluoro or chloro, that R″ being fluoro or chloro only when R′ is fluoro or chloro; R3 is hydrogen or C1-C5 alkyl R4 is hydrogen, CH2OCOC(CH3)3, pharmaceutically acceptable inorganic or organic cations, or COR4′ wherein R4′ is C1-C5 alkyl, phenyl, benzyl or phenethyl; R7 is methyl or ethyl; one of A and B is sulphur and the other is C-R2; when A is S, R2 is selected from hydrogen and methyl, with the proviso that R2 is methyl only when R3 is not hydrogen; and when B is S, R2 is hydrogen; and any tautomer thereof. A pharmaceutical composition comprising a compound of formula (I), a method of treating malignant tumours or diseases resulting from autoimmunity or pathologic inflammation.