Lisinopril EP Impurity D

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