m alkyl, Ar-alkyl, Ar-O-alkyl and Het1 -alkyl, or that is di-substituted by optionally Ar-containing alkylene, wherein two alkylene carbon atoms may additionally be linked to one another via alkylene and Ar and Het1 are each as defined above, with the proviso that when R2 is --A--R3, A is ethylene and R3 is unsubstituted or C1 -C3 alkyl-substituted amino, R1 is other than hydroxy.