PROBLEM TO BE SOLVED: To provide a compound that selectively inhibits phosphodiesterase 1 (PDE1) activity, functioning in brain tissue as a regulator of locomotor activity and learning and memory.SOLUTION: This invention provides a compound represented by the formula: 1- or 2-substituted (6aR,9aS)(phenylamino)-5-6a,7,8,9,9a-hexahydro-5-methyl-cyclopenta[4,5]imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine-4(1H or, 2H)-one.【課題】自発運動活性及び学習並びに記憶の制御因子として脳組織で機能するホスホジエステラーゼ１活性を選択的に阻害する化合物の提供。【解決手段】下式で表わされる化合物１－若しくは２－置換（６ａＲ，９ａＳ）（フェニルアミノ）－５－６ａ，７，８，９，９ａ－ヘキサヒドロ－５－メチル－シクロペンタ［４，５］イミダゾ［１，２－ａ］ピラゾロ［４，３－ｅ］ピリミジン－４（１Ｈ若しくは２Ｈ）－オン。【選択図】なし
