stituted by an amino group, a carboxy group or an ester group;an N-dimethylaminoethylamino group;a hydrazino group; ora 6- or 7-membered heterocyclic group having at least one N-atom which may be substituted by a C1-6 -alkyl group, a phenyl group or a 5- to 7-membered heterocyclic group having an N-atom;with the proviso that in formula (I), R1 is not an alkoxy group;R2 and R3 are a halogen atom, a