Antioxidant and cytotoxic activities of quinones from Cetraria laevigata

Chemical investigation of the extracts obtained from the red thallus tips from Cetraria laevigata resulted in the isolation of five known quinoid pigments identified by FT-IR, UV, NMR, MS methods and by comparison with literature data (skyrin (1), 3-ethyl-2,7-dihydroxynaphthazarin (2), graciliformin (3), cuculoquinone (4) and islandoquinone (5)). An antioxidant capacity of compounds 1-5 were evaluated and compared with quercetin using a lipid peroxidation inhibitory assay and superoxide radical (SOR), nitric oxide radical (NOR), 1,1-diphenyl-2-picrylhydrazine (DPPH), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assays. Compounds 2, 4 and 5 were far more active: they demonstrated the antioxidant capacity in various test assays with the IC₅₀ values 5-409 µM comparable to the flavonoid quercetin. While, the isolated quinones (1-5) exhibited weak cytotoxicity in human cancer cell line A549 assessed by MTT assay.