A compound having the following formula (I): wherein R.sup.1 is hydrogen, lower alkyl, lower alkenyl, lower or higher alkynyl, cyclo(lower)alkyl, cyclo(higher)alkyl, cyclo(lower)alkyl(lower)alkyl, cyclo(higher)alkyl(lower)alkyl, cyclo(lower)alkenyl(lower)alkyl, aryl-fused cyclo(lower)alkyl, lower alkoxy, acyl, aryl, ar(lower)alkoxy, ar(lower)alkyl, heteroar(lower) alkyl, amino, heteroaryl, heterocyclyl or heterocyclyl(lower)alkyl, which may be substituted with one or more suitable substituent(s), R.sup.2 is hydrogen or lower alkyl, X is arylene, heteroarylene, cycloalkylene, heterocycloalkylene or aryl-fused cycloalkylene, Y is arylene or heteroarylene, which may be substituted with one or more suitable substituent(s), Z is lower alkenylene, which may be substituted with lower alkyl or halogen, or a salt thereof. The compound is useful as a histone deacetylase inhibitor.