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|Molar mass||344.315 g/mol|
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Usnic acid is a naturally occurring dibenzofuran derivative found in several lichen species. It was first isolated by German scientist W. Knop in 1844 and first synthesized between 1933-1937 by Curd and Robertson. Usnic acid was identified in many genera of lichens including Usnea, Cladonia, Lecanora, Ramalina, Evernia, Parmelia and Alectoria. Although it is generally believed that usnic acid is exclusively restricted to lichens, in a few unconfirmed isolated cases the compound was found in kombucha tea and non-lichenized ascomycetes.
At normal conditions, usnic acid is a bitter, yellow, solid substance. It is known to occur in nature in both the d- and l-forms as well as a racemic mixture.
Biological role in lichens
Usnic acid is a secondary metabolite in lichens whose role has not been completely elucidated. It is believed that usnic acid protects the lichen from adverse effects of sunlight exposure and deters grazing animals with its bitter taste.
Uses and properties
Lichen extracts containing usnic acid have been utilized in medicine, perfumery, cosmetics, and ecology.
Usnic acid possesses a wide range of interesting biological properties. It is a potent antibiotic effective against Gram-positive bacteria, including Staphylococcus, Streptococcus, and Pneumococcus, other bacteria such as Mycobacterium tuberculosis, and some pathogenic fungi. It also exhibits antiviral, antiprotozoal, antimitotic, anti-inflammatory and analgesic activity. Other characteristics, like ultraviolet absorption, preserving properties, antigrowth, antiherbivore and anti-insect properties, have also been demonstrated.
Usnic acid has been included as an ingredient in creams, powders, toothpastes, mouthwash, deodorants, hair shampoos and sunscreen products. In some of these preparations, usnic acid is employed as an active principle, in others as a preservative.
Usnic acid and its salt form, sodium usniate, have been marketed in the US as an ingredient in food supplements for use in weight reduction, although unsupported by solid scientific proof. These supplements, if taken according to label instructions, can supply daily oral doses of 10–1350 mg for adults. Daily oral intake of 300–1350 mg over a period of weeks has led to severe hepatotoxicity in a number of persons.
Usnea was one ingredient in a product called Lipokinetix, promoted to induce weight loss via increase in metabolic rate. Lipokinetix has been the topic of an FDA warning in the USA, due to potential hepatotoxicity, although it is unclear yet if any toxicity would be attributable to the usnea. Lipokinetix also contained PPA, caffeine, yohimbine and diiodothyronine. There is reason to believe that usnic acid, in high concentrations, could possess some toxicity. The National Toxicology Program is currently evaluating the issue.
Usnic acid has been found to have adrenergic activity in both frog and earthworm nerve junction models in preliminary research.
- Michael Ash; Irene Ash (2004). Handbook of preservatives. Synapse Info Resources. p. 5856. ISBN 978-1-890595-66-1. Retrieved 5 August 2010.
- Knop W. (1844) Chemisch-physiologische Untersuchung uber die Flechten. Justus Lieb. Ann. Chern 49: 103-124.
- A. Robertson and F. H. Curd. J. Chem. Soc. 1173 (1933)
- Hsu LM, Huang YS, Chang FY, Lee SD. 'Fat burner' herb, usnic acid, induced acute hepatitis in a family. J Gastroenterol Hepatol. 2005 Jul;20(7):1138-9.
- Sanchez W, Maple JT, Burgart LJ, Kamath PS. Severe hepatotoxicity associated with use of a dietary supplement containing usnic acid. Mayo Clin Proc. 2006 Apr;81(4):541-4.
- "Safety Alerts for Human Medical Products > Lipokinetix". MedWatch: The FDA Safety Information and Adverse Event Reporting Program. U.S. Food and Drug Administration. November 20, 2001. Retrieved 5 December 2012. "FDA has received multiple reports of persons who developed liver injury or liver failure while using Lipokinetix. The product contains norephedrine (also known as phenylpropanolamine or PPA), caffeine, yohimbine, diiodothyronine, and sodium usniate."
- Harris N. J.(1961), Honors Thesis, Clark University, Worcester, Massachusetts