Usnic acid

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 biosynthesized via methylphloroacetophenone as an intermediate.

Safety

Usnic acid and its salts are idiosyncratically associated with severe hepatotoxicity and liver failure. | doi-access = free

Sodium usnate 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, yohimbine and 3,5-diiodothyronine.

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 extract using reversed-polarity capillary zone electrophoresis or high performance liquid chromatography analysis. A spot test using anisaldehyde reagent was developed to detect usnic acid in lichens, producing a distinctive magenta color reaction that works reliably in the presence of most other lichen substances and can aid in identification, particularly in species where visual detection of usnic acid's natural pale yellow color is difficult.

References

References

1. (2001). "The Merck index: an encyclopedia of chemicals, drugs, and biologicals". Merck.
2. (1844). "Chemisch-physiologische Untersuchung uber die Flechten". Annalen der Chemie und Pharmacie.
3. (1933). "277. Usnic acid. Part III. Usnetol, usnetic acid, and pyrousnic acid". Journal of the Chemical Society (Resumed).
4. (2002). "A review on usnic acid, an interesting natural compound". Naturwissenschaften.
5. (1996). "Characterization of the tea fungus metabolites". Biotechnology Letters.
6. (Jul 2005). "'Fat burner' herb, usnic acid, induced acute hepatitis in a family". Journal of Gastroenterology and Hepatology.
7. (2006). "Severe Hepatotoxicity Associated with Use of a Dietary Supplement Containing Usnic Acid". Mayo Clinic Proceedings.
8. (November 20, 2001). "Safety Alerts for Human Medical Products > Lipokinetix". U.S. Food and Drug Administration.
9. Harris N. J. (1961), Honors Thesis, Clark University, Worcester, Massachusetts
10. (2024). "Visualizing usnic acid with anisaldehyde reagent". The Lichenologist.