Usnic acid

Usnic acid is a naturally occurring dibenzofuran derivative found in several epiphytic lichen species. It was first isolated by German scientist W. Knop in 1844^[1] and first synthesized between 1933-1937 by Curd and Robertson.^[2] Usnic acid was identified in many genera of lichens including Usnea, Cladonia, Lecanora, Ramalina, Evemia, 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-lichens ascomycetes.

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At normal conditions, usnic acid is a bitter, yellow, solid substance. Occurs 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 deter 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 possess a wide range of interesting biological properties. It is a potent antibiotic effective against gram positive bacteria, including Mycobacterium tuberculosis, Staphylococcus, Streptococcus, and Pneumococcus, as well as 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.

References

1. ^ Knop W. (1844) Chemisch-physiologische Untersuchung uber die Flechten. Justus Lieb. Ann. Chern 49: 103-124.
2. ^ A. Robertson and F. H. Curd. J. Chem. Soc. 1173 (1933)