Caffeic Acid-13C3 is an isotopically enriched form of caffeic acid that is intended for use as an internal standard for the quantification of caffeic acid by GC- or LC-MS. Caffeic acid is an inhibitor of 5-LO ,with IC50 values of 3.7-72 μM,and 12-LO,with IC50 values of 5.1-30 μM.