Phenolic Compounds from Lichens

The mononuclear phenol compounds isolated from lichens can be subdivided into three major categories, namely the orsellinic acid, the phloroacetophenone and the phthalide derivatives. These are discussed in turn. 

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Choudhary MI, Azizuddin, Jalil S, Atta-ur-Rahman (2005) Bioactive Phenolic Compounds from a Medicinal Lichen, Usnea longissima. Phytochemistry 66 2346... 

Guo J, Li ZL, Wang AL et al (2011) Three new phenolic compounds from the lichen Thamnolia vermicularis and their antiproliferative effects in prostate cancer cells. Planta Med 77 2042-2046... 

Choudhary MI, Saima Jalil A and Atta-ur-Rahman (2005) Bioactive phenolic compounds from a medicinal lichen, Usnea longissima. Phytochem 66 2346-2350 Cohen PA, Towers GHN (1995) The anthraquinones of Heterodermia obscurata. Phytochemistry... 

Huda-Faujan N, Noriham A, Norrakiah AS et al (2009) Antioxidant activity of plants methanolic extracts containing phenolic compounds. Afr J Biotechnol 8 484-489 Jayaprakasha GK, Rao LJ (2000) Phenolic constituents from the lichen Parmotrema stuppeum (Nyl.) Hale and their antioxidant activity. Z Naturforsch 55 1018-1022 Kekuda PTR, Vinayaka KS, Kumar PSV et al (2009) Antioxidant and antibacterial activity of lichen extracts, honey and their combination. J Pharm Res 2 1875-1878... 

Mastan A, Sreedevi B, Kumari J et al (2014) Evaluation of the in vitro antioxidant and antibacterial activities of secondary metabolites produced from lichens. Asian J Pharm Clin Res 7 193-198 Melo MG, dos Santos JP, Serafini MR et al (2011) Redox properties and cytoprotective actions of atranoiin, a lichen secondary metabolite. Toxicol In Vitro 25 462-468 Michalak A (2006) Phenolic compounds and their antioxidant activity in plants growing under heavy metal. Pol J Environ Stud 15 523-530... 

Lichens had to evolve diverse biosynthetic pathways to produce such complex arrays of secondary metabolites polyketide, shikimic acid, and mevalonic acid pathways. Most of the lichen substances are phenolic compounds. Polyketide-derived aromatic compounds, depsides, depsidones, dibenzofurans, xanthones, and naphthoquinones, are of great interest. Compounds from other pathways are esters, terpenes, steroids, terphenylquinones, and pulvinic acid (Fahselt 1994 Cohen and Towers 1995 Muller 2001 Brunauer et al. 2006, 2007 Stocker-Worgotter and Elix 2002 Johnson et al. 2011 Manojlovic et al. 2012). So, many lichens and lichen products have proved to be a source of important secondary metabolites for food and pharmaceutical industries (Huneck 1999 Oksanen 2006)... 

Lai D, Odimegwu DC, Esimone C el al (2013) Phenolic compounds with in vitro activity against respiratory syncytial virus from the Nigerian lichen Ramalina farinacea. Planta Med 79... 

Odabasoglu F, Aslan A, Cakir A et al (2004) Comparison of antioxidant activity and phenolic content of three lichen species. Phytother Res 18 938-941 Omarsdottir S, Oladottir AK, Amadottir T et al (2006) Antiviral compounds from Icelandic lichens. Planta Med 72 - S 009... 

Impressive antioxidant properties of cmde extracts of lichens have been reported, but ironically the secondary metabolites obtained from lichens have not shown any promising antioxidant property. Due to the presence of large quantities of polyphenolic compounds, lichens are expected to exhibit antioxidant activities [3,102]. CucuUoquinone from Flavocetraria cucullata (Bellardi) Kamefelt A. TheU. exhibited up to 80% inhibition of 2,2-diphenyl-l-picrylhydrazil (DPPH)-free radical where BHT was used as a standard. The activity was found to be twofold higher than that of standard [103]. Bhattarai and coworkers have reported the antioxidant potential of five Uchen species, collected in Antarctica, crmtaining 30-35% phenolic contents. Extracts of aU species were found to be antioxidant in nature. They also evaluated the antioxidant properties of methyl orseUinate (57), atranorine (78),... 

Kinoshita K, Matubara H, Koyama K, Takahashi K, Yoshimura I, Yamamoto Y (1993) A higher alcohol from Solorina crocea. Bibl Lichenol 53 129-135 Kinoshita K, Matsubara H, Koyama K, Takahashi K, Yoshimura I, Yamamoto Y, Higuchi M, Miura Y, Kinoshita Y, Kawai K-I (1994a) New phenolics from Protousnea species. J Hattori Bot Lab 75 359-364 Kinoshita K, Matsubara H, Koyama K, Takahashi K, Yoshimura I, Yamamoto Y, Miura M, Kinoshita Y, Kawai K-I (1994b) Topics in the chemistry of lichen compounds. J Hattori Bot Lab 76 227-234 Kinoshita Y (1993) The production of lichen substances for pharmaceutical use by lichen tissue culture. Dissertation, Kyoto Univ, pp 1-77... 

The most common phenolic acid units derived by the acetate-polymalonate pathway and combined to form the characteristic lichen substances are of two types the orcinol-type units and p-orcinol-type units. While compounds formed from these two types of units are similar in many ways, differences in their structure and especially in their distributimi among the lichens suggest that the usual tendency to consider the orcinol and p-orcinol compounds separately probably has a biosynthetic justification. 

Usnic acid The best known lichen products are the usnic acid, yellow pigments produced in the upper cortex of many species from phylogenetically widely separated families. These pigments are known only in lichens. The usnic acids appear, therefore, to be among the compounds which are most characteristic of lichens, are apparently not synthesised in cultures of the isolated fungal components and are formed by reactions tmiting two or three phenolic units. 

Lichen monoaryl derivates are relatively rare in lichens. All of the lichen monoaryl derivates have lost their free carboxylic acid groups either by esterification or by decarboxylation. These compounds might be synthesised in the lichen from coenzyme A derivates of the initially formed phenolic acid units or by biological decomposition of depsides. 

Several new classes of compounds have been discovered in lichens during this period. For example six diphenyl ethers have been isolated and it would appear that they may arise biogenetically either by catabolism of the more common depsidones or by direct phenolic oxidation resulting in carbon-oxygen coupling of the mononuclear aromatic units [e.g. in leprolomin 118)]. A novel group of nonacyclic diketopiperazines have been isolated 14) and it would appear that these compounds are derived biogenetically from the aromatic amino-acid, tyrosine. 

Evernia prunastri has proved to be a particularly rich source of lichen compounds and extraction and g.c. — m.s. studies have revealed the presence of orcinol (99) 268, 269), 3-methoxy-5-methylphenol (100) 144), 3,5-dimethoxytoluene (101) 144), 2-chloro-3,5-dimethoxytoluene (102) 144), phenol 144), thymol 144), 2-chloro-3-methoxy-5-methylphenol (103) 144), methyl salicylate 144), methyl 4-O-methylorsellinate (90) 268, 269), and methyl (3-orcinolcarboxylate (104) (255). Rhizonic acid (105) has been isolated from Parmelia subnuda 215). 

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