N-Fmoc-D-phenylalanine-d5 is deuterium labelled N-Fmoc-D-phenylalanine (F657575). D-Phenylalanine (P319410) is an essential amino acid that serves as a primary precursor for the biosynthesis of catecholamines in the body. D-Phenylalanine is also known to antagonize stress-induced analgesia in humans, and also acts as an anti-enkephalinase agent.