Entecavir EP Impurity D,2-Amino-9-((1S,3R,4R)-4-hydroxy-3-(hydroxymethyl)-2-methylenecyclopentyl)-1,9-dihydro-6H-purin-6-one,Impurity in commercial preparation of Entecavir. It is an epimeric impurity of the antiviral drug Entecavir.,Entecavir Therapeutic