5-(2-ethoxy-5-((4-methylpiperazin-1-yl)sulfonyl)phenyl)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one (Sildenafil Impurity）

5-(2-ethoxy-5-((4-methylpiperazin-1-yl)sulfonyl)phenyl)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one (Sildenafil Impurity）