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. Chlorogenic acid, at concentrations as high as 100 µM, does not inhibit the 5-LO activity of ionophore-stimulated human PMNL.