Hippuryl-His-Leu-OH (N-Benzoyl-Gly-His-Leu) hydrate is a specific substrate for angiotensin-converting enzyme ACE I and is a molecular tool used for ACE activity detection in in vitro experiments. Hippuryl-His-Leu-OH hydrate is hydrolyzed by ACE through competitive binding. Under ACE catalysis, Hippuryl-His-Leu-OH hydrate undergoes hydrolysis to produce hippuric acid (HA). The amount of HA produced can be used to quantitatively assess ACE activity or screen for ACE inhibitors. The His-Leu released from Hippuryl-His-Leu-OH hydrate can also react with o-phthalaldehyde or Fluorescamine (HY-D0715) for fluorescence detection. Hippuryl-His-Leu-OH hydrate can be applied to the in vitro screening of ACE inhibitors for hypertension and cardiovascular diseases, and is also used in the study of changes in ACE activity during physiological and pathological processes such as renal compensatory hypertrophy[1][2][3].