Ophiobolin M and analogues, noncompetitive inhibitors of ivermectin binding with nematocidal activity

A series of ophiobolins were isolated from a fungal extract based on their nematocidal activity. These compounds are non-competitive inhibitors of ivermectin binding to membranes prepared from the free-living nematode, Caenorhabditis elegans, with an inhibition constant of 15 microM. The ophiobolins which were most potent in the biological assays, ophiobolin C and ophiobolin M, were also the most potent compounds when evaluated in a C. elegans motility assay. These data suggest that the nematocidal activity of the ophiobolins is mediated via an interaction with the ivermectin binding site. The isolation, structure and biological activity of ophiobolins have been described.