Fungicides Acting on Mitosis and Cell Division: Zoxamide, an Antitubulin Fungicide for Control of Oomycete Pathogens

Zoxamide was discovered and commercialized by Rohm and Haas Company in 2001 as a new antitubulin fungicide for control of oomycete pathogens. Zoxamide belongs to a class of benzamides, which show activity toward a broad range of organisms, including both oomycete and nonoomycete fungi, protozoan, plant, and mammalian cells. To date, the only reported example of target-site resistance to zoxamide in an oomycete involves the mutation C239S in lab isolates of Phytophthora sojae generated by selection on zoxamide-amended medium. Key precursors in the preparation of zoxamide are 3,5-dichloro-4-methylbenzoyl chloride and 3-amino-3-methyl-1-pentyne. The lack of field resistance to zoxamide and ethaboxam is in sharp contrast to the serious resistance problems encountered by other antitubulin fungicides, benzimidazoles (BZs), and diethofencarb. Zoxamide is highly active toward a broad range of oomycete fungi and is used commercially on potatoes, vines, and vegetables for control of late blight and downy mildew diseases.