dical, a (C1-C4)alkoxy(C1-C4)alkyl radical or a C1-C4 alkyl radical substituted with a nitrogen-containing group; R1 and R2 may also form with the nitrogen atom carrying them a 5- or 6-membered nitrogen-containing heterocycle optionally substituted with one or more alkyl, hydroxyl or ureido groups; R3 represents a hydrogen atom, a halogen atom such as a chlorine atom, a C1-C4 alkyl radical, a sulf