Novel inhibitors of sterol C-14 demethylase and Δ14 Reductase/Δ8 → Δ7 isomerase for cereal disease control

The activity of five experimental fungicides combining structural elements responsible for sterol C‐14 demethylase inhibition and sterol nuclear double‐bond transformations has been investigated by examining sterol accumulation in Ustilago maydis (DC.) Corda, inhibition of sterol‐biosynthesis enzymes in Saccharomyces cerevisiae Meyer using a cell‐free system and protective activity in cereals against Erysiphe graminis DC. and Puccinia coronata Corda. Combining the fenpropidin/fenpropimorph basic structure with a pyridine moiety offered no advantage in fungicidal activity. However, the combination of the pyrifenox structure with a morpholine moiety yielded a compound which was a good inhibitor of C‐14 demethylase and Δ8 → Δ7 isomerase in vitro and gave good cereal protection.