Lisinopril EP Impurity C

(2S)-2-[(3S,8aS)-3-(4-aminobutyl)-1,4-dioxohexahydropyrrolo[1,2-a]pyrazin-2(1H)-yl]-4-phenylbutanoic acid (as per EP) ; (S)-2-[(3S,8aS)-3-(4-Aminobutyl)-1,4-dioxohexahydropyrrolo[1,2-a]pyrazin-2(1H)-yl]-4-phenylbutanoic acid (as per USP);  S,S,S-Diketopiperazine (EP & USP) ; Lisinopril USP Related Compound A