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~~ beingfluoro or chloro only when R~ is fluoro or chloro； R3 is hydrogen or C1-C5alkyl, R4 is hydrogen, CH2OCOC(CH3)3, pharmaceutically acceptable inorganic ororganic cations, or COR4~ wherein R4~ is C1-C5 alkyl, phenyl, benzyl orphenethyl； 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 provisothat R2 is methyl only when R3 is not hydrogen； and when B is S, R2 ishydrogen； and any tautomer thereof. A pharmaceutical composition comprising acompound of formula (I), a method of treating malignant tumours or diseasesresulting from autoimmunity or pathologic inflammation.
