Depside metabolites

Galloyl esters of D-glucose Depside Metabolites ----------p-Penta-o-galloyl-D-glucose... 

Of the more than 20,000 known species of lichens, only a few have been analyzed and identified as containing biologically active secondary compounds. Most of the unique secondary metabolites that are present in lichens are derived from the polyketide pathway, with a few originating from the shikimic acid and mevalonic acid pathways (Table 1.1). Previous studies have suggested that the para-depsides are precursors to mefa-depsides, depsones, diphenyl ethers, depsidones and dibenzofurans.9,12... 

The potential role of lichen metabolites in allelopathic interactions has recently been reviewed.9,27 The phytotoxic effect of certain lichen metabolites may play a role in the establishment of lichen populations. The depsides, barbatic acid and lecanorin, and the tridepside, gyrophoric acid, have been shown to inhibit... 

The degradation of rutin by Aspergillus flavus proceeds by hydrolysis to the aglycone followed by degradation to a depside with release of the unusual metabolite carbon monoxide (Figure 4.51) and is accomplished by dioxygenation (Krishnamurty and Simpson 1970). 

The secondary metabolites of the lichen are active substances against pathogenic microorganisms. Most known lichen substances with antimicrobial activity are usnic acid, phenolic compounds, triterpenes, steroids, anthraquinones, depsides, depsidones, and dapsones, and most of them are known mechanisms of their antibiotic action. 

Depsides, tridepsides, and tetradepsides consist of two, three, and four hydroxybenzoic acid residues linked by ester groups. These are the most numerous classes of secondary metabolites in lichens. More than one hundred Uchen compounds are depsidones, which have an additional ether bond between aromatic rings. Depsidones in Uchen are believed to arise by oxidative cycUzation of depsides. It has been found that depsidone and depside compounds such as atranorin, divaricatic acid, lecanoric acid, evemic acid, salazinic acid, physodic acid, and stictic acid possess important antimicrobial activity (Manojlovic et al. 2012 Kosanic et al. 2013, 2014a Rankovic et al. 2014). 

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)... 

Bruun and Motzfeld (35) isolated the novel peroxyergosteryl divari-catinate (525) from the lichen Haematomma ventosum. This product is the only known example of a steryl ester of an aromatic polyketide derived acid. The depside divaricatic acid (234) also present in this lichen contains the same A-ring component and it is possible that the ester formation in both of these metabolites is effected by the same enzyme. 

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