Coumarin () or 2H-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by an unsaturated lactone ring , forming a second six-membered heterocycle that shares two carbons with the benzene ring. It belongs to the benzopyrone chemical class and is considered a lactone.
Coumarin is a colorless crystalline solid with a sweet odor resembling the scent of vanilla and a bitter taste. A related compound, the prescription drug anticoagulant warfarin, is used to inhibit formation of blood clots, deep vein thrombosis, and pulmonary embolism.
Etymology
Coumarin is derived from , the French word for the tonka bean, from the Old Tupi word for its tree, .
History
Coumarin was first isolated from tonka beans in 1820 by A. Vogel of Munich, who initially mistook it for benzoic acid.
Synthesis
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 starting from phenol, as does the Kostanecki acylation, which can also be used to produce chromones.
Biosynthesis
From lactonization of ortho-hydroxylated cis-hydroxycinnamic acid.
Natural occurrence
Coumarin is found naturally in many plants. Freshly ground plant parts contain higher amount of desired and undesired phytochemicals than powder. In addition, whole plant parts are harder to counterfeit; for example, one study showed that authentic Ceylon cinnamon bark contained 0.012 to 0.143 mg/g coumarin, but samples purchased at markets contained up to 3.462 mg/g, possibly because those were mixed with other cinnamon varieties.
- Vanilla grass (Anthoxanthum odoratum)
- Sweet woodruff (Galium odoratum)
- Sweet grass (Hierochloe odorata)
- Sweet-clover (genus Melilotus)
- Meranti trees (genus Shorea)
- Tonka bean (Dipteryx odorata)
- Fenugreek (Trigonella foenum-graecum)
- Cinnamon; different varieties containing different levels of coumarin:
- Ceylon cinnamon or true cinnamon (Cinnamomum verum): 0.005 to 0.090 mg/g
- Chinese cinnamon or Chinese cassia (C. cassia): 1.74 to 7.67 mg/g
- Indonesian cinnamon or Padang cassia (C. burmannii): 2.14 to 9.30 mg/g
- Tilo (Justicia pectoralis),
Biological function
Coumarin has appetite-suppressing properties, which may discourage animals from eating plants that contain it. Though the compound has a pleasant sweet odor, it has a bitter taste, and animals tend to avoid it. These chemicals are sometimes also incorrectly referred to as "coumadins" rather than 4-hydroxycoumarins. Some of the 4-hydroxycoumarin anticoagulant class of chemicals are designed to have high potency and long residence times in the body, and these are used specifically as rodenticides ("rat poison"). a low toxicity compared to related compounds. 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. 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.
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