Lanostane Triterpenes from Gloeophyllum odoratum and Their Anti-Influenza Effects

In an in vitro screening for anti-influenza agents from European polypores, the fruit body extract of Gloeophyllum odoratum dose-dependently inhibited the cytopathic effect of the H3N2 influenza virus A/Hong Kong/68 (HK/68) in Madin Darby canine kidney cells with a 50% inhibitory concentration (IC₅₀) of 15 µg/mL, a noncytotoxic concentration. After a chromatographic work-up, eight lanostane triterpenes (1: -8: ) were isolated and their structures were elucidated based on high-resolution electrospray ionization mass spectrometry analyses, and one- and two-dimensional nuclear magnetic resonance experiments. Constituents 1: (gloeophyllin K) and 2: (gloeophyllin L) are reported here for the first time, and compounds 5: , 7: , and 8: have not been described for the investigated fungal material so far. The highest activity was determined for trametenolic acid B (3: ) against HK/68 and the 2009 pandemic H1N1 strain A/Jena/8178/09 with IC₅₀ values of 14 and 11 µM, respectively. In a plaque reduction assay, this compound was able to bind to cell-free viruses and to neutralize their infectivity.