Кумарин

Name and chemistry

Coumarin is derived from coumarou, the French word for the tonka bean, from the Old Tupi word for its tree, kumarú. The lactone is easily hydrolyzed to the corresponding salts of coumarinic acid or o-hydroxy-cis-cinnamic acid. On long exposure to light it is converted to a dimer. Coumarin is bitter to the taste. Its solubility in water is 0.17 g per 100 mL. It is very soluble in ether, chloroform, oil and pyridine, and soluble in ethanol. It is freely soluble in oils and soluble in aqueous alkali and in oxygenated and chlorinated solvents. The taste is bitter, aromatic and burning, with a nut-like flavor on dilution.

Natural occurrence

Coumarin is found in many plants, where it may serve as a chemical defense against predators. The seeds of Dipteryx odorata, a tree native to Northern South America, are known as tonka beans. The seeds are black and wrinkled and have a smooth, brown interior. The seeds normally contain about 1-3% of coumarin, but can rarely reach levels up to 10%. Coumarin is also present in lavender, cinnamon, licorice, strawberries and cherries. Natural complex substances that contain coumarin include hay absolute, osmanthus absolute and tonka bean absolute. The tree is semi-deciduous, belongs to the pea family, and is also called cumaru, kumaru or Brazilian teak. It grows up to 25-30 m tall, with a trunk up to 1 m across, smooth gray bark and red wood. The word tonka comes from the Galibi (Carib) language spoken in French Guiana.

Safety and regulation

Coumarin is moderately toxic to the liver and kidneys of rodents, with a median lethal dose (LD50) of 293 mg/kg in the rat. Coumarin is hepatotoxic in rats, but less so in mice. In large infused doses, it may cause hemorrhages, liver damage, or paralysis of the heart. It is therefore controlled as a food additive by many governments. The German Federal Institute for Risk Assessment has established a tolerable daily intake (TDI) of 0.1 mg coumarin per kg body weight. The European Food Safety Authority derived the same 0.1 mg/kg/day from a no-observed-adverse-effect level of 10 mg/kg/day in a chronic dog study, with an uncertainty factor of 100. In humans, 7-hydroxylation, a detoxification step, is catalyzed only by the enzyme CYP2A6 among the major cytochrome P450 enzymes of the liver. The detoxification rate is rapid in humans and slow in rats. Coumarin is absorbed through the skin as well, at rates of 54.7% to 66.1% in humans. After an oral dose of 200 mg in seven subjects, 63.4% of the dose was recovered in the 24-hour urine as total 7-hydroxycoumarin. Raised liver enzyme levels are the most common adverse finding reported in humans. In one case, a 23-year-old woman was hospitalized with hepatitis after consuming 1-2 g of cinnamon (equivalent to 3.3-6.6 mg of coumarin) daily for two months. In the United States the rules on tonka beans in food are criticized as unreasonable, because it is unlikely that anyone eats enough coumarin to cause ill effects and because coumarin occurs in unregulated foods.

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