Tetradepside

Bryan AJ, Elix JA (1976) 2-0-Acetyltenuiorin, a new tridepside from the lichen Pseudo cyphellaria australiensis. Aust J Chem 29 1147-1151 Bryan AJ, Elix JA, Norfolk S (1976) Synthesis of orcinol tridepsides and aphthosin, an orcinol tetradepside. Aust J Chem 29 1079-1086... 

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). 

No clear mechanisms have been identified that specifically indicate how depsides, tridepsides, tetradepsides, depsidones, anthraquinones, and xanthones target microbial invasion. 

Finally aphthosin (278), an orcinol tetradepside was obtained through condensing evernic acid (279) and methyl lecanorate (280) (Scheme 36) (57). The properties of this synthetic material were identical with those of the natural product isolated by Bachelor and King 10), although a reinvestigation of the constituents of Peltigera aphthosa failed to verify the natural occurrence of this tetradepside 234). 

Of the 43 structurally determined depsides, 37 are didepsides and five are tridepsides only one tetradepside has been discovered. Depsides have typical UV spectra with two bands, such as lecanoric acid with A ax O gio e) at 270 (4.3) and 307 nm (4.2). 

The tridepside gyrophoric acid (60) is the chief component in the Umbili-cariaceae, while a tetradepside, aphthosin (61), has been isolated from Pel-tigera aphthosa (L.) Willd. 

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