Chlorogenic acid is a phenolic natural product isolated from the leaves and fruits of dicotyledonous plants, including the coffee bean. Structurally, chlorogenic acid is the ester of caffeic acid with the 3-hydroxyl group of quinic acid. Chlorogenic acid is an important factor in plant metabolism. It is also an antioxidant and an inhibitor of the tumor promoting activity of phorbol esters.{1430,1420} Chlorogenic acid, at concentrations as high as 100 μM, does not inhibit the 5-LO activity of ionophore-stimulated human PMNL.{4706}