Abstract: A compound represented by formula (III): wherein n is an integer of 2 to 5; and R11 represents a substituent group represented by formula: wherein Ra, Rb and Rc each represents a phenyl, phenylmethyl or naphthyl group (which may be substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, a halogen atom and a nitro group), a hydrogen atom, or an alkyl group having 1 to 4 carbon atoms, with the proviso that Ra, Rb and Rc are different from one another, and a salt thereof.