Coumarin is a colorless crystalline solid with a sweet odor resembling the scent of vanilla and a bitter taste. It is found in many plants, where it may serve as a chemical defense against predators. By inhibiting synthesis of vitamin K, a related compound is used as the prescription drug warfarin – an anticoagulant – to inhibit formation of blood clots, deep vein thrombosis, and pulmonary embolism.
Also in 1820, Nicholas Jean Baptiste Gaston Guibourt (1790–1867) of France independently isolated coumarin, but he realized that it was not benzoic acid. In a subsequent essay he presented to the pharmacy section of the Academie Royale de Medecine, Guibourt named the new substance coumarine.
Coumarin can be prepared by a number of name reactions, with the Perkin reaction between salicylaldehyde and acetic anhydride being a popular example. The Pechmann condensation provides another route to coumarin and its derivatives, as does the Kostanecki acylation, which can also be used to produce chromones.
Other plants with substantial coumarin content are cassia cinnamon (Cinnamomum cassia; not to be confused with true cinnamon, Cinnamomum verum, or Ceylon cinnamon Cinnamomum zeylanicum, which contain little coumarin), deertongue (Dichanthelium clandestinum), mullein (genus Verbascum), and in many cherry blossom tree varieties (of the genus Prunus). Coumarin is also found in extracts of Justicia pectoralis. Related compounds are found in some but not all specimens of genus Glycyrrhiza, from which the root and flavour licorice derives.
Coumarin is transformed into the natural anticoagulant dicoumarol by a number of species of fungi. This occurs as the result of the production of 4-hydroxycoumarin, then further (in the presence of naturally occurring formaldehyde) into the actual anticoagulant dicoumarol, a fermentation product and mycotoxin. Dicoumarol was responsible for the bleeding disease known historically as "sweet clover disease" in cattle eating moldy sweet clover silage. In basic research, preliminary evidence exists for coumarin having various biological activities, including anti-inflammatory, anti-tumor, antibacterial, and antifungal properties, among others.
Warfarin – a coumarin – with brand name, Coumadin, is a prescription drug used as an anticoagulant to inhibit formation of blood clots, and so is a therapy for deep vein thrombosis and pulmonary embolism. It may be used to prevent recurrent blood clot formation from atrial fibrillation, thrombotic stroke, and transient ischemic attacks.
Coumarin is moderately toxic to the liver and kidneys, with a median lethal dose (LD50) of 293 mg/kg, a low toxicity compared to related compounds. Though it is only somewhat dangerous to humans, coumarin is hepatotoxic in rats, but less so in mice. Rodents metabolize it mostly to 3,4-coumarin epoxide, a toxic, unstable compound that on further differential metabolism may cause liver cancer in rats and lung tumors in mice. Humans metabolize it mainly to 7-hydroxycoumarin, a compound of lower toxicity. The German Federal Institute for Risk Assessment has established a tolerable daily intake (TDI) of 0.1 mg coumarin per kg body weight, but also advises that higher intake for a short time is not dangerous. The Occupational Safety and Health Administration (OSHA) of the United States does not classify coumarin as a carcinogen for humans.
The European Regulation (EC) No 1334/2008 describes the following maximum limits for coumarin: 50 mg/kg in traditional and/or seasonal bakery ware containing a reference to cinnamon in the labeling, 20 mg/kg in breakfast cereals including muesli, 15 mg/kg in fine bakery ware, with the exception of traditional and/or seasonal bakery ware containing a reference to cinnamon in the labeling, and 5 mg/kg in desserts.