Abstract: The present invention provides a novel compound which is represented by formula (I): ##STR1## wherein preferable examples of R.sup.1 to R.sup.6 are as follows; R.sup.1 and R.sup.2 are each an alkyl group optionally substituted by a halogen atom, an amino group, a hydroxyl group, an alkoxyl group or a thiol group, a hydrogen atom, a halogen atom or an alkoxyl group; R.sup.3 is a hydrogen atom; R.sup.4 is a methyl group; R.sup.5 is a hydrogen atom or an alkyl group; and R.sup.6 is a group of the formula: ##STR2## wherein Z is a phenyl group; and has an antitumor effect.