Moexipril-d5 intended for use as an internal standard for the quantification of moexipril by GC- or LC-MS. Moexipril is a prodrug form of the angiotensin converting enzyme (ACE) inhibitor moexiprilat. It is converted to moexiprilat in vivo by side chain ester hydrolysis. Moexipril inhibits ACE in a cell-free assay (IC50 = 2.7 µM for the rabbit enzyme). It also inhibits phosphodiesterase 4 (IC50s = 38, 160, and 230 µM for PDE4B2, PDE4A5 and PDE4D5, respectively). Moexipril (0.1-30 mg/kg per day) reduces blood pressure in spontaneously hypertensive rats.1 It also reduces infarct volume in a rat model of focal cerebral ischemia when used at a concentration of 0.01 mg/kg.