R3 represents a hydrogen atom, a halogen atom such as a chlorine, bromine, iodine or fluorine atom, a C1-C4 alkyl radical, a C1-C4 monohydroxyalkyl radical, a C1-C4 hydroxyalkoxy radical, an acetylamino(C1-C4)alkoxy radical, a C1-C4 mesylaminoalkoxy radical or a carbamoylamino(C1-C4)alkoxy radical,