C2???C4 alkyl) radical, a (C1???C4)alkoxy(C1???C4)alkyl radical or a C1???C4 alkyl radical substituted with a nitrogen-containing group; R3 represents a hydrogen atom, a halogen atom such as a chlorine, bromine, iodine or fluorine atom, a C1???C4 alkyl radical, a monohydroxy(C1???C4 alkyl) radical, a hydroxy(C1???C4 alkoxy) radical, an acetylamino(C1???C4 alkoxy) radical, a mesylamino(C1???C4 alko