Coumarin

[koo-muh-rin]

Coumarin is a chemical compound (benzopyrone); a toxin found in many plants, notably in high concentration in the tonka bean, vanilla grass, woodruff, mullein, and bison grass. It has a sweet scent, readily recognised as the scent of newly-mown hay, and has been used in perfumes since 1882. It has clinical medical value as the precursor for several anticoagulants, notably warfarin, and is used as a gain medium in some dye lasers.

The name comes from a French word, coumarou, for the tonka bean.

Synthesis

The biosynthesis of coumarin in plants is via hydroxylation, glycolysis and cyclization of cinnamic acid. Coumarin can be prepared in a laboratory in a Perkin reaction between salicylaldehyde and acetic anhydride.

The Pechmann condensation provides another synthesis of coumarin and its derivatives.

Biological Function

Coumarin has appetite suppressing properties, suggesting its widespread occurrence in plants, especially grasses, is because of its effect of reducing the impact of grazing animals.

Derivatives

Some naturally occurring coumarin derivatives include umbelliferone (7-hydroxycoumarin), aesculetin (6,7-dihydroxycoumarin), herniarin (7-methoxycoumarin), psoralen and imperatorin. Coumarin and its derivatives are all considered phenylpropanoids.

Medical Use

Coumarin has been used in the treatment of lymphedema.

Toxicity and use in Foods, Beverages, Tobacco, and Cosmetics

Coumarin is moderately toxic to the liver and kidneys, with an LD₅₀ of 275 mg/kg - low compared to related compounds. Although only somewhat dangerous to humans, coumarin is a potent rodenticide: rats and other rodents largely metabolize it to 3,4-coumarin epoxide, a toxic compound that can cause internal hemorrhage and death. Humans largely metabolize it to 7-hydroxycoumarin, a compound of lower toxicity. The German Federal Institute for Risk Assessment has established a tolerable daily intake of 0.1 mg coumarin per kg body weight, but also advises that, [if] this level is exceeded for a short time only, there is no threat to health. For example, a person weighing 135 lbs or about 61 kg would have a TDI of approximately 6.1 mg of coumarin.

European health agencies have warned against consuming high amounts of cassia bark, one of the four species of cinnamon, because of its coumarin content.. According to the German Federal Institute for Risk Assessment, 1 kg of (cassia) cinnamon powder contains approximately 2100 to 4400 mg of coumarin. Powdered Cassia Cinnamon weighs 0.56 g/cc; therefore, 1 kg of Cassia Cinnamon powder is equal to 362.29 teaspoons (1000 g divided by 0.56 g/cc multiplied by 0.20288 tsp/cc). This means 1 teaspoon of cinnamon powder contains 5.8 to 12.1 mg of coumarin, which may be above the Tolerable Daily Intake for smaller individuals. However, it is important to note that the German Federal Institute for Risk Assessment only cautions against high daily intakes of foods containing coumarin.

Coumarin is often found in tobacco products and artificial vanilla substitutes, despite having been banned as a food additive in numerous countries since the mid-20th century. Coumarin was banned as a food additive in the United States in 1978. OSHA considers this compound to be only a lung-specific carcinogen, and "not classifiable as to its carcinogenicity to humans" Coumarin was banned as an adulterant in cigarettes by tobacco companies in 1997, but due to the lack of reporting requirements to the US Department of Health and Human Services it was still being used as a flavoring additive in pipe tobacco. Coumarin is currently listed by the United States Food and Drug Administration (FDA) among "Substances Generally Prohibited From Direct Addition or Use as Human Food", according to 21 CFR 189.130 , but some natural additives containing coumarin (such as sweet woodruff) are allowed "in alcoholic beverages only" (21 CFR 172.510 ). In Europe, such beverages are very popular, for example Maiwein (white wine with woodruff) and Żubrówka (vodka flavored with bison grass).

Coumarin should be avoided by people with perfume allergy. Flexitral (Chantilly, VA) has developed an allergen replacement product called Coumane(TM), GRAS.