Mushroom chemical defense : Pungent sesquiterpenoid dialdehyde antifeedant to opossum.

A new bioassay employing a natural fungivore, the opossumDidelphis virginiana, is described. Using this bioasssay, eighteen species of fungi were tested for palatability. Five species of mushrooms, all of which taste pungent to humans, were found to be unpalatable to the opossum. From the least palatable of these,Lentinellus ursinus, the pungent principle was isolated and identified as isovelleral, a previously described fungal metabolite. The compound was shown to be a potent antifeedant to opossums. By means of difference NOE and relaxation time NMR studies, the relative configuration and solution conformation of isovelleral were deduced.