An extensive phytochemical study of a foliose lichen from Indonesia, Parmelia cetrata, resulted in the successful isolation of 13 phenol and depside derivatives (1-13) including the previously unreported depsides 3'-hydroxyl-5'-pentylphenyl 2,4-dihydroxyl-6-methylbenzoate (7), 3'-hydroxyl-5'-propylphenyl 2,4-dihydroxyl-6-methylbenzoate (8) and 3'-hydroxyl-5'-methylphenyl 2-hydroxyl-4-methoxyl-6-propylbenzoate (9). The anti-infective activity of isolated compounds was evaluated against the gram-negative bacterium Aliivibrio fischeri and the nematode Caenorhabditis elegans. 2,4-Dihydroxyl-6-pentylbenzoate (5) and lecanoric acid (6) induced growth inhibition of A. fischeri with inhibition values of 49% and 100% at a concentration of 100 µM, respectively. The antibacterial activity might be due to their free carboxyl group. A phenolic group at C4 also contributed to the antimicrobial activity of the depsides as shown for compounds 7 and 8, which caused 89% and 96% growth inhibition at 100 µM, respectively. Lecanoric acid (6) in addition possesses significant anthelmintic effects causing 80% mortality of C. elegans at 100 µg/mL.
Keywords: Aliivibrio fischeri; Caenorhabditis elegans; Lichen; Parmelia cetrata; anthelmintic; antimicrobial; depsides.