Coumarin, also known as 1,2-benzopyrone and o-oxonaphthone, has a molecular weight of 146.143 and a CAS number of 91-64-5. It can be considered the lactone of cis-o-hydroxycinnamic acid and is the parent nucleus of a large class of coumarin compounds found in plants. Coumarin is an organic compound with the chemical formula C9H6O2. It is an important fragrance, commonly used as a fixative and deodorant, in perfumes and fragrances, and as a flavor enhancer for beverages, foods, cigarettes, plastics, and rubber products. It is also used in the electroplating industry.
Coumarin occurs as colorless or white crystals or crystalline powder with a pleasant vanilla-like aroma. It is insoluble in cold water but soluble in boiling water. It is readily soluble in methanol, ethanol, ether, chloroform, petroleum ether, and oils. It is volatile and can distill with steam and sublime. When coumarin is heated in a hot, dilute alkali solution, its lactone ring slowly hydrolyzes and cleaves, forming cis-o-hydroxycinnamate, which dissolves into a yellow solution. If acidified, the resulting cis-o-hydroxycinnamic acid is extremely unstable and can undergo further cyclization to regenerate coumarin. If left in the alkali solution for a long time, the cis-salt converts to trans-o-hydroxycinnamic acid. Further acidification then yields the stable trans-o-hydroxycinnamic acid, which will not undergo further lactonization.
Coumarins inhibit the synthesis of coagulation factors in the liver. Coumarins have a similar structure to vitamin K. In the liver, coumarins bind to vitamin K epoxide reductase, inhibiting the conversion of vitamin K from the epoxide to the hydroquinone form, thereby inhibiting vitamin K circulation. Coumarins can be considered vitamin K antagonists or competitive inhibitors (see enzymes). They inhibit the carboxylation of coagulation factors II, IX, and X containing glutamic acid residues, as their precursors are inactive, thus inhibiting the coagulation process. However, it has no effect on clotting factors that have already formed.
