Two New α-Glucosidase Inhibitory Depsidones from the Lichen Parmotrema cristiferum (Taylor) Hale.

A bioactivity-guided investigation of the lichen Parmotrema cristiferum (Taylor) Hale (Parmeliaceae) led to the isolation of two new depsidones, cristifones A and B (1 and 2). The structures of the isolated compounds were identified by spectroscopic methods and comparison with the literature data. Compound 1 showed the initial combined structures of depsidone and depside cores. The two isolated compounds were then evaluated for α-glucosidase inhibition. Compounds 1 and 2 were confirmed as potent, with IC50 values of 21.5 and 18.4 µM, respectively. Compound 2 was a non-competitive inhibitor against α-glucosidase, as indicated by the intersect in the second quadrant of each respective plot.