7H-​Pyrazolo[4,​3-​d]​pyrimidin-​7-​one, 5-​[2-​ethoxy-​5-​[2-​(4-​ethyl-​3-​oxo-​1-​piperazinyl)​-​1-​hydroxyethyl]​phenyl]​-​1,​6-​dihydro-​1-​methyl-​3-​propyl-