Galbinic acid is a depsidone lichen metabolite that has been found in U. undulata.1,2 It is active against the Gram-positive bacteria B. cereus, B. subtilis, and S. aureus, but not S. epidermidis (MICs = 62.5, 62.5, 250, and >250 μg/ml, respectively), as well as the Gram-negative bacterium E. coli, but not S. sonnei (MICs = 125 and >250 μg/ml, respectively).3

|1. Salgado, F., Albornoz, L., CortÉz, C., et al. Secondary metabolite profiling of species of the genus Usnea by UHPLC-ESI-OT-MS-MS. Molecules 23(1), E54 (2017).|2. Elix, J.A., and Engkaninan, U. The structure of galbinic acid. A depsidone from the lichen Usnea undulata. Aust. J. Chem. 28(8), 1793-1797 (1975).|3. Sultana, N., and Afolayan, A.J. A new depsidone and antibacterial activities of compounds from Usnea undulata Stirton. J. Asian Nat. Prod. Res. 13(12), 1158-1164 (2011).