Pannarin

Pannarin is an organic compound of the depsidone class, first isolated in 1941 from Japanese lichens of the genus Pannaria. It has the molecular formula C₁₈H₁₅ClO₆ and forms clear needle-like crystals with a melting point of 216–217 °C (421–423 °F). Its chemical structure was initially proposed on the basis of degradative studies that broke the molecule down into simpler fragments, but this early assignment proved incorrect and was revised in the 1970s using a combination of spectroscopic analysis and chemical synthesis. The revised structure was confirmed by X-ray crystallography in 1991.

Laboratory studies have reported that pannarin inhibits growth and induces cell death in certain human cancer cell lines, and shows synergistic antimicrobial effects with some antibiotics against drug-resistant Staphylococcus aureus. It also displays complex behaviour under ultraviolet light, both promoting and limiting damage to biological molecules depending on conditions, and can reduce symptoms of tobacco mosaic virus infection in experimental treatments of tobacco leaves. In nature, pannarin occurs in various lichen species across several genera, including Pannaria, Psoroma, Megalospora and, more rarely, Buellia and Lepraria. Its presence is used as a taxonomic character in lichen systematics.