3beta acetoxyfern 9(11) en 19 one 2 3beta acetoxyfern 9(11) en 19beta ol 2 Argentina 2 Ascomycetes 2 Filicophyta 2 Lichens 2 Molecular Structure 2 Nuclear Magnetic Resonance, Biomolecular 2 Pyxine berteriana 2 Structure-Activity Relationship 2 Triterpenes 2 acetone 2 article 2 chemical structure 2 controlled study 2 fern 9(11) en 3,19 dione 2 fernene triterpenoid derivative 2 infrared radiation 2 isolation procedure 2 lichexanthone 2 nuclear magnetic resonance 2 structure analysis 2 triterpenoid 2 unclassified drug 2