"R20 represents a hydrogen atom, a halogen atom such as fluorine, a C1-C4 alkyl, C1-C4 monohydroxyalkyl, alkoxy(C1-C4)alkyl(C1-C4) or C1-C4 aminoalkyl, or hydroxyalkyl(C1-C4)C1-C4 aminoalkyl radical;" . . . .