Lichen Metabolites: An Overview of Some Secondary Metabolites and Their Biological Potential

Lichens present a symbiotic association between two or more organisms. These unique organisms produce many chemical compounds, known as secondary metabolites or lichen acids. Most of them are localized in the cortex and form specific crystals on the surface of the fungal hyphae. Approximately 1000 secondary metabolites were discovered so far and most of them are specific for lichens. Lichen secondary metabolites showed many pharmaceutical activities, including antimicrobial, antiproliferative, antioxidant, antiviral, anti-inflammatory, and further allelopathic, antiherbivore, photoprotective activities. Lichens are important source of bioactive compounds, and despite a lot of studies dealing with activity of lichen secondary metabolites, their production in lichens and their role is still very enigmatic. In this chapter, we demonstrated all three main pathways of how secondary compounds originate and chose most characteristic acids with their proposed biological and ecological activities. This chapter gives a basic overview of lichens, secondary metabolites, and their properties.