PROBLEM TO BE SOLVED: To provide a compound useful for inhibition of histone deacetylase (HDAC), a pharmaceutically acceptable salt, hydrate and solvate thereof.SOLUTION: There is provided a compound represented by the formula (I). U is a single bond, NR, NR-NRor O, J is NHor SH, V is C or N, when V is N, one of Rto Rdoes not exist, X each independently is H, D, methyl, CFor halogen, two of Rto Rjoint together to be C3 to 8 cycloalkyl, C4 to C8 cycloalkenyl or 3 to 8-membered saturated/partially unsaturated heterocyclic and remaining Rto Rdo not exist or is H, halogen, OH, NHor C1 to 8 alkyl and t is an integer of 0 to 2.SELECTED DRAWING: None【課題】ヒストンデアセチラーゼ(HDAC)の阻害のための有用な化合物、その薬学的に許容される塩、水和物、溶媒和物の提供。【解決手段】式(I)で表される化合物。(Uが一重結合、NR2d、NR2d-NR2d’又はO;JがNH2、又はSH;VがC又N、但しVがNである場合、R2a~R2cのうちの1つは存在しない;Xが各々独立にH、D、メチル、CF3又はハロゲン;R2a~及びR2cのうちの2つが一緒になってC3~8シクロアルキル、C4~C8シクロアルケニル又は3~8員飽和/部分不飽和複素環、かつ残りのR2a~R2cが存在しない又はH、ハロゲン、OH、NH2或いはC1~8アルキル;tが0~2の整数)【選択図】なし