Paresordin A, a new diphenyl cyclic peroxide from the lichen Parmotrema praesorediosum

From the lichen Parmotrema praesorediosum, one new diphenyl peroxide, named praesordin A (1), together with four depsidones, including virensic acid (2), protocetraric acid (3), 8'-O-methylprotocetraric acid (4), and furfuric acid (5) were purified. Their structures were chacracterized using extensive HR-ESI-MS and NMR spectroscopic methods. The isolated compounds (2-5) possessed stronger α-glucosidase inhibitory activity (IC₅₀ = 43.7-110.1 μM) than the standard drug acarbose (IC₅₀ = 214.5 μM).