Leukotriene A4 is a leukotriene.Leukotriene A4 hydrolase converts it to Leukotriene B4.(2s-(2 alpha,3 beta(1e,3e,5z,8z)))-3-(1,3,5,8-tetradecatetraenyl)oxiranebutanoic acid. An unstable allylic epoxide, formed from the immediate precursor 5-hpete via the stereospecific removal of a proton at c-10 and dehydration. 

 Leukotriene A₄ (LTA₄) is synthesized in mast cells, eosinophils, and neutrophils from arachidonic acid by 5-lipoxygenase (5-LO), which exhibits both lipoxygenase and LTA₄ synthase activities.^1,2 LTA₄ is rapidly metabolized by LTA₄ hydrolase or LTC₄ synthase to LTB₄ or LTC₄, respectively.² LTA₄, from leukocytes, is known to undergo transcellular metabolism in platelets, erythrocytes, and endothelial cells.³ Further metabolism of LTA₄ by 15-LO leads to lipoxin biosynthesis.² LTA₄ as a free acid is highly unstable. The methyl ester is stable and can be readily hydrolyzed to the free acid as needed.