Introduction: Usnic acid (UA) is a lichen-derived secondary metabolite with a unique dibenzofuran skeleton and is commonly found in lichenized fungi of the genera Usnea and Cladonia. Usnic acid has been incorporated for years in cosmetics, perfumery, and traditional medicines. It has a wide range of bioactivities, including antimicrobial, antiviral, anticancer, anti-inflammatory properties. Areas covered: This review covers patents on therapeutic activities of UA and its synthetic derivatives published during the period 2000–2017. Expert opinion: UA demonstrates excellent anticancer and antimicrobial properties. However, its application was withdrawn due to acute liver toxicity reported with chronic consumption. The broad spectrum of its biological activity indicates high the variability of UA’s binding preferences. The main idea to be addressed in the future should include the synthesis of UA derivatives because these might possess increased bioactivity, bioavailability and decreased toxicity. It is noteworthy that UA derivatives possessed better antibacterial, antitubercular, and anticancer activity than the parent compound. Most importantly, UA and its analogs (to a greater extent than UA) can be useful in cancer drug treatment. They have the potential for joint application with other anticancer drugs in order to overcome drug resistance.
- Usnic acid