PROBLEM TO BE SOLVED: To provide a free base crystalline form of (6aR,9aS)-5,6a,7,8,9,9a-hexahydro-5-methyl-3-(phenylamino)-2-((4-(6-fluoropyridin-2-yl)phenyl)methyl)-cyclopent[4,5]imidazo[1,2-a]pyrazolo[4,3-e]pyrimidin-4(2H)-one, which is a potent and selective phosphodiesterase 1 (PDE 1) inhibitor.SOLUTION: The invention provides a free base crystalline form of the compound having the formula in the figure.SELECTED DRAWING: NoneCOPYRIGHT: (C)2020,JPO&INPIT【課題】強力かつ選択的なホスホジエステラーゼ1(PDE1)阻害剤である、(6aR,9aS)-5,6a,7,8,9,9a-ヘキサヒドロ-5-メチル-3-(フェニルアミノ)-2-((4-(6-フルオロピリジン-2-イル)フェニル)メチル)-シクロペント[4,5]イミダゾ[1,2-a]ピラゾロ[4,3-e]ピリミジン-4(2H)-オンの遊離塩基の結晶形態の提供。【解決手段】下記式を有する化合物の遊離塩基の結晶形態。【選択図】なし