Which one is not converted to an active metabolite?
Lisinopril: It is the lysine derivative of enalaprilat; does not require hydrolysis to become active ACE inhibitor. 
 KEY CONCEPT:-
All ACE inhibitors are prodrugs except captopril and lisinopril. Other drugs like enalapril are converted to its active metabolite (enalaprilat) and thus are slow acting.
Reference: Essentials of Medical Pharmacology Eighth Edition KD TRIPATHI page no 532
Quinapril
Fosinopril
Benzopril
Lisinopril