Usnic acid is a naturally occurring

dibenzofuran Dibenzofuran is a heterocyclic organic compound with the chemical structure shown at right. It is an aromatic compound that has two benzene rings fused to a central furan ring. All the numbered carbon atoms have a hydrogen atom bonded to each of t ...

derivative found in several

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Usnea ''Usnea'' is a genus of mostly pale grayish-green fruticose lichens that grow like leafless mini-shrubs or tassels anchored on bark or twigs.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the f ...

'', '' Cladonia'', ''

Hypotrachyna ''Hypotrachyna'' is a genus of lichenized fungi within the family Parmeliaceae The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2700 species in 71 genera, it is the largest family of lichen-forming fungi. The most ...

'', ''

Lecanora ''Lecanora'' is a genus of lichen commonly called rim lichens.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, Lichens in the genus '' Squamarina'' are also called rim lichens. Members of the genus have roughly c ...

'', ''

Ramalina ''Ramalina'' is a genus of greenish fruticose lichens that grow in the form of flattened, strap-like branches. Members of the genus are commonly called strap lichensField Guide to California Lichens, Stephen Sharnoff, Yale University Press, 201 ...

'', '' Evernia'', ''

Parmelia Parmelia may refer to: * Parmelia (barque), the vessel that in 1829 transported the first settlers of the British colony of Western Australia * ''Parmelia'' (fungus), a genus of lichens with global distribution * Parmelia, Western Australia Pa ...

'' 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 Kombucha (also tea mushroom, tea fungus, or Manchurian mushroom when referring to the culture; Latin name ''Medusomyces gisevii'') is a fermented, lightly effervescent, sweetened black tea drink commonly consumed for its purported health b ...

tea and non-lichenized

ascomycetes Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...

. 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 In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...

mixture. Salts of usnic acid are called usnates (e.g. copper usnate).

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.

Biosynthesis

Usnic acid is a

polyketide Polyketides are a class of natural products derived from a precursor molecule consisting of a chain of alternating ketone (or reduced forms of a ketone) and methylene groups: (-CO-CH2-). First studied in the early 20th century, discovery, biosynth ...

biosynthesized via methylphloroacetophenone as an intermediate. Proposed biosynthesis for usnic acid

Safety

Usnic acid and its salts are idiosyncratically associated with severe

hepatotoxicity Hepatotoxicity (from ''hepatic toxicity'') implies chemical-driven liver damage. Drug-induced liver injury is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn fr ...

and liver failure. Daily oral intake of 300–1350 mg over a period of weeks has led to severe hepatotoxicity in a number of persons. Sodium usniate was one ingredient in a product called "Lipokinetix" that was claimed to induce weight loss via an 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 aforementioned salt. Lipokinetix also contained norephedrine (PPA),

caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine chemical classification, class. It is mainly recreational drug use, used recreationally as a Nootropic, cognitive enhancer, increasing alertness and attentional perfor ...

yohimbine Yohimbine (), also known as quebrachine, is an indole alkaloid derived from the bark of the African tree '' Pausinystalia johimbe''; also from the bark of the unrelated South American tree ''Aspidosperma quebracho-blanco''. Yohimbine is an α2 ...

and

3,5-diiodothyronine 3,5-Diiodothyronine (3,5-T2) is an active thyroid hormone within the class of iodothyronines. It has two iodine atoms at positions 3 and 5 of its inner ring. Biological effects 3,5-T2 is an active thyroid hormone. It stimulates the TR-beta rece ...

Pharmacology

Usnic acid has been found to have adrenergic activity in both frog and earthworm nerve junction models in preliminary research.

Analytics

It is possible to determine the content of usnic acid in

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.extract An extract is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures, absolutes or in powder form. The aromatic principles of many spices, nuts ...

using reversed-polarity or high performance liquid chromatography. capillary zone electrophoretic analysis.

References

External links

Seeking to Fight Fat, She Lost Her Liver
''New York Times'', March 4, 2003 {{DEFAULTSORT:Usnic Acid Polyphenols Organic acids Dibenzofurans Ketones Polyketides Resorcinols Lichen products