Fungi have evolved many symbioses including different eukaryotes and prokaryotes. Mutualism is one of the symbioses and here both symbionts benefit from the interaction. The most common mutualistic relationships involving fungi are mycorrhiza and lichens. A mycorrhiza is a symbiotic relationship between a roots of a plant and a fungus while lichen associates between a fungus and an algae. Many studies have performed to investigate these symbiotic relationships in depth, however, still have some debates on them, though many taxonomists rely on genetic analyses besides with traditional morphological data. In our study, it highlights the nature, importance, nutritional and pharmaceutical uses, and applications of these mysterious dual between fungi and plant and/or algae.

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The foliose lichen, Parmotrema melanothrix has been chemically screened for the first time and isolated the depside atranorin (1) in significant quantity (2 %) along with methyl 2,4-dihydroxy-3,6-dimethylbenzoate (2) and methyl 3-formyl-2,4-dihydroxy-6methylbenzoate (3). In view of its abundance, interesting structural features and significant biological profile, atranorin was subjected to chemical modification and synthesised five diverse analogues in very good yields (70~93%). The synthesised analogues along with the three isolated compounds were evaluated for their cytotoxic potential against a panel of six human cancer cell lines using MTT assay. Among the tested compounds, 1a showed enhanced activity than the parent compound (1) against almost all the tested cell lines. Significantly, 1a showed highest activity (IC50 = 15.19 μM) against prostate cancer cell line (DU145). The results indicate that complete protection of the phenolic hydroxyls in atranorin as acetates enhances the cytotoxicity, especially against DU 145.

Lichens have attracted considerable interest since ancient time due to their medicinal properties. Lichen produce a variety of orcinol-based compounds such as xanthones, anthraquinones, dibenzofurans, depsides, and depsidones. Several related compounds have shown potent bioactivities as antiviral, antioxidant, anti-herbivore, insecticidal, antifungal, and anticancer. Lichens have been employed as traditional medicines, and these are continuing to be of great interest for their biotechnological potential. The purpose of this review was to systematically evaluate the literature on the orcinol based biologically active secondary metabolites of lichen.