Urnula craterium, when grown in liquid culture, produces bioactive chemicals that inhibit the growth of other fungi that are pathogenic to aspen; specifically, these chemical are antagonistic to aspen blue-stain fungi Ophiostoma crassivaginatum and O. piliferum, as well as the wood-decay fungus Phellinus tremulae. Chemicals produced by U. craterium include pestalotin, 5,6-dehydropestalotin, 4-methoxy-3,5-dimethyl-pyran-2-one, and (4S)-3,4-dihydro-4,8-dihydroxy-1(2H)-napthalenone. However, none of these isolated compounds inhibits the aspen pathogens in vitro, suggesting the true nature of the antifungal mechanism in the devil’s urn has not yet been resolved.
Urnucratins A–C (1–3), which possess an unusual bisnaphthospiroether skeleton with one oxygen bridge and one C–C bridge and represent a new subclass of bisnaphthalenes, were isolated from the North American cup fungus Urnula craterium. Their structures, including absolute configurations, were determined by means of HRMS, NMR, and quantum chemical CD calculations. Urnucratin A (1) was found to be active against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and Streptococcus pyogenes with MIC values of 2, 1, and 0.5 μg/mL, respectively.