Compounds which can be represented by the general formula (I) indicated below: ##STR00001## and in which: A is selected independently from the carboxamide group, the thiocarboxamide group, and the carbonyl group, R.sub.1 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, R.sub.2 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, R.sub.3 and R.sub.4 are selected independently from hydrogen and an alkyl group having from 1 to 3 carbon atoms, R.sub.5 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 group is in the para or meta position relative to the "-A-NH--" group.