--NR1 R2 group (wherein R1 and R2 are the same or different and each is a hydrogen atom or a lower alkyl group optionally substituted by a diloweralkyl-substituted amino group or a nitrogen-containing heterocyclic group), piperazinyl group substituted by lower alkyl group, or --OR3 group (wherein R3 represents a lower alkyl group optionally substituted by di-loweralkyl-substituted amino group).