Quinic acid is an organic compound with the formula . The compound is classified as a cyclitol, a cyclic polyol, and a cyclohexanecarboxylic acid. It is a colorless solid that can be extracted from plant sources.
Occurrence and preparation Quinic acid is present in many plants as a caffeoylquinic acid, which are esters of quinic acid with caffeic acids. Esterified with one unit of caffeic acid it forms chlorogenic acid. Esterified with two units of caffeic acid, it forms cynarine.
It is found in Cinchona bark at high concentrations. It is also found in coffee beans and the bark of Eucalyptus globulus. It is a constituent of the tara tannins. Kiwifruit also have a high level of quinic acid (1–2% w/w) as a key component of their flavor. It can also be found in high quantities in the fruit of some accessions of Malus coronaria.
It is made synthetically by hydrolysis of chlorogenic acid.
History and biosynthesis This substance was isolated for the first time in 1790 by German pharmacist Friedrich Christian Hofmann in Leer from Cinchona.Hofmann: Crell's chemische Annal. 1790, II, p. 314, cited in S. Baup: Über die Chinasäure und einige ihrer Verbindungen. In: Annalen der Physik und Chemie 1833, p. 64–70 (). Its transformation into hippuric acid by animal metabolism was studied by German chemist Eduard Lautemann in 1863.Lautemann, E. (1863) "Ueber die Reduction der Chinasäure zu Benzoësäure und die Verwandlung derselben in Hippursäure im thierischen Organismus" (On the reduction of quinic acid to benzoic acid and its transformation into hippuric acid in the animal organism), Annalen der Chemie, 125 : 9–13.
Its biosynthesis begins with the transformation of glucose into erythrose 4-phosphate. This four-carbon substrate is condensed with phosphoenol pyruvate to give the seven-carbon 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) by the action of a synthase. Two subsequent steps involving dehydroquinic acid synthase and a dehydrogenase afford the compound.
Derived bicyclic lactones are called quinides. One example is 4-caffeoyl-1,5-quinide.
Dehydrogenation and oxidation of quinic acid affords gallic acid.
Applications and medicinal activity This acid is a versatile chiral starting material for the synthesis of pharmaceuticals. It is a building block in the synthesis of oseltamivir, which is used to treat influenza A and B.
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