oxyalkyl radical, a (C1???C4)alkoxy(C1???C4)alkyl radical or a C1???C4 alkyl radical substituted with one or more nitrogenous groups; R7 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 radica