Boustie & Grube, 2005). Depsides and depsidones are the most common secondary products uniquely produced in lichens by the fungal symbiont, amounting to as large as 5-10% of thallus' dry weight. The core structural motif of this acetyl polymalonylderived family of about 700 depsides and depsidones is uniform across thousands of lichen species and generally consists of two phenolic rings with various substituents, joined by ester and/or ether linkages. Depsides and depsidones have manifold properties, such as antioxidant, antiviral, antibiotic, antitumor, allergenic, plant growth inhibitory, antiherbivore and enzyme inhibitory activities. There are various reports on the antimicrobial activity of crude lichen extracts. However, studies on antimicrobial activity of lichen compounds are scarce and scattered. A correlation between phenolic constituents and antimicrobial activity has been established (Vartia, 1973; Ingolfsdottir et al., 1998; Gulluce et al., 2006; Ranković et al., 2007 a, b). The antimicrobial activity of some common depsides, namely, atranorin (1), lecanoric acid (2), erythrin (3), the meta-depside sekikaic acid (4), the depsidone lobaric acid (5) and mononuclear aromatic compounds methyl orsellinate (6) and methyl-borcinolcarboxylate (7) (Figure 1) were tested against six human and plant pathogenic bacteria and fungi in vitro to evaluate their medical efficacy as pharmacophores. In addition, toxicological studies of lichen metabolites (1)-(7) (Table 1) were carried out using brine shrimp cytotoxicity assay. METHODS AND MATERIALS General experimental: Medium pressure liquid chromatography (MPLC) was employed with accelerating

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