A compound represented by the formula wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.6 are the same or different and each is a hydrogen atom or a substituent; one of R.sup.4 and R.sup.5 is a hydrogen atom and the other is a group represented by the formula: --C(.dbd.X)--R.sup.7 wherein X is N--O--R.sup.8 or N--NH--R.sup.9 wherein R.sup.8 and R.sup.9 are the same or different and each is a hydrogen atom or a group bonded via a carbon atom; and R.sup.7 is a hydrogen atom or a substituent, and the like and a salt thereof have a superior I.kappa.B kinase inhibitory activity, and useful as pharmaceutical agents such as agents for preventing or treating diabetes and the like.