Undecanoic acid-d21 (Undecanoate-d21) is the deuterium labeled Undecanoic acid (HY-W004282). Undecanoic acid is a monocarboxylic acid with antifungal property. Undecanoic acid inhibits the production of exocellular keratinase, lipase and the biosynthesis of several phospholipids in T. rubrum[1][2].