Antifungal, phytotoxic, and systemic activity of fenapanil and structural analogs

Abstract

The antifungal activity of the imidazole fenapanil and several closely related analogs was determined, in vitro, for a broad taxonomic range of fungi. Phytotoxicity and systemic translocation were also evaluated for these compounds. Structure-activity relationships demonstrated that chlorine or methyl substitutions to the phenyl ring of fenapanil increased both the antifungal and phytotoxic activity. The presence of a cyano group was also identified as contributing to antifungal activity. Part of the increased antifungal activity was related to the lipophilicity of the various compounds. Increased lipophilicity, via substitutions to the phenyl ring, resulted in increased antifungal activity. There were indications that substitutions to the phenyl ring of fenapanil would increase the stability of the basic molecule to some fungi, based on changes in fungotoxicity with time. All compounds tested demonstrated a broad taxonomic spectrum of activity. The major fungal classes were sensitive to the imidazoles tested, with no complete lack of sensitivity demonstrated by any one group. There was variation among the fungi tested in the various classifications. Phytophthora cactorum and Aspergillus niger were less sensitive to the test compounds than many other fungi. All compounds were, to varying degrees, phytotoxic to barley and soybean. In barley, all compounds tested exhibited systemic translocation, which was limited to apoplastic transport. There was no detectable symplastic translocation with any of the compounds tested.