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chlorogenic acid[¦klȯr·ə¦jen·ik ′as·əd]
C16H18O9, a complex ester of caffeic acid with one of the stereoisomers of quinic acid. It is obtained in the form of colorless crystals, which have a melting point of 206°–210°C and are readily soluble in water. Alkaline solutions of chlorogenic acid turn green in the air (hence the name). It is very common among the higher plants, frequently occurring together with its isomer isochlorogenic acid. It is contained in large quantities in germinating sunflower seeds and in green coffee beans. Chlorogenic acid probably plays a part in regulating the ripening of fruits by acting on the respiration of the fruits as an inhibitor of oxidative phosphorylation. It is toxic to some pathogenic microorganisms that cause a number of plant diseases, such as potato scab and wilt disease. In a number of plants, for example, rice, the biosynthesis of chlorogenic acid increases in response to a microbial infection.