Semisynthesis and Bioactivities of Lichen Metabolites

Lichens are symbiotic of fungus and algae. Even though secondary metabolites of lichens are unique with respect to higher plants, they have received scarce attention as source of novel chemotypes. 14 compounds from 4 different lichens were isolated. Erythrin was successfully converted into its isomeric diphenyl ether via Smiles rearrangement. Oxidative coupling of diphenyl ether using palladium(II) acetate, lead to an efficient and unambiguous approach to dibenzofurans making it the first report on its semisynthesis via Smiles rearrangement. Isolated & semisynthesized compounds showed a wide range of biological activities includiig Zeorin with highest α-glucosidase inhibitory activity (IC50 = 100.0 ± 0.3 µM), which is 7 times higher than of acarbose, (IC50 = 700.0 ± 10.4 µM) Divericatic, lecanoric, sekikaic, and lobaric acid showed significant antioxidant activity in SOI, with IC50 values being lower than the standard(propyl gallate) Orciniol & orsellenic acid showed 3-4 fold lower IC50 values when compared to standard thiourea in urease inhibitory assay. Compounds were also subjected to antimicrobial and toxicological assays.