Fosinopril is a phosphinic acid-containing ester prodrug that belongs to the angiotensin-converting enzyme (ACE) inhibitor class of medications. It is rapidly hydrolyzed to fosinoprilat, its principle active metabolite. Fosinoprilat inhibits ACE, the enzyme responsible for the conversion of angiotensin I (ATI) to angiotensin II (ATII). ATII regulates blood pressure and is a key component of the renin-angiotensin-aldosterone system (RAAS). Fosinopril may be used to treat mild to moderate hypertension, as an adjunct in the treatment of congestive heart failure, and to slow the rate of progression of renal disease in hypertensive individuals with diabetes mellitus and microalbuminuria or overt nephropathy.

Quinapril is the hydrochloride salt of quinapril, the ethyl ester of a non-sulfhydryl, angiotensin-converting enzyme (ACE) inhibitor, quinaprilat. Quinapril hydrochloride is a white to off-white amorphous powder that is freely soluble in aqueous solvents. Quinapril is indicated for the treatment of high blood pressure (hypertension) and as adjunctive therapy in the management of heart failure. It may be used for the treatment of hypertension by itself or in combination with thiazide diuretics, and with diuretics and digoxin for heart failure.

BENAZEPRIL, (±)- is an impurity referred to as Related Compound B, which is a diastereomer of benazepril, an ACE inhibitor, under the brand name Lotensin used primarily in treatment of hypertension, congestive heart failure, and heart attacks, and also in preventing the renal and retinal complications of diabetes. BENAZEPRIL, (±)- is used as USP Reference Standard.