(2S,4R)-1-(tert-Butoxycarbonyl)-4-(tosyloxy)pyrrolidine-2-carboxylic Acid is an intermediate in the synthesis of Fosinopril-d5 Sodium Salt (F727803), the labeled analogue of Fosinopril Sodium Salt (F727800), a phosphinic acid containing angiotensin converting enzyme (ACE) inhibitor. Antihypertensive.