Compounds which can be represented by the general formula (I) and in which A is selected independently from the carboxamide group, the thiocarboxamide group, and the carbonyl group, -R1 is selected from an alkyl group having from 1 to 3 carbon atoms and the amino group, unsubstituted or substituted with the nitro group or the methyl group, -R2 is selected independently from hydrogen, an alkyl group having from 1 to 4 carbon atoms, the methoxy, ethoxy, propoxy group, a mono-, bi- or tricyclic cycloalkane residue having from 5 to 12 carbon atoms, the adamantyl group, an aryl, naphthyl or heterocyclic group, unsubstituted or substituted with methyl, methoxy, hydroxy, amino or halogen groups, -R3 and R4 are selected independently from hydrogen and an alkyl group having from 1 to 3 carbon atoms, -R5 represents one or two substituents independently selected from hydrogen and the methyl, methoxyl, and hydroxyl groups, -n is a whole number from 0 to 6, and the amidine groups is in the para or meta position relative to the '-A-NH-' group.