Guanidinium and amidinium fungicides: A new class of carbocation mimetic ergosterol biosynthesis inhibitors

Abstract

AbstractA novel class of chemical has been designed with the aim of inhibiting the Δ14‐reductase and Δ8‐Δ7‐isomerase enzymes in the ergosterol biosynthesis pathway in fungi. Use was made of knowledge about the mechanisms of both enzymes and the mode of action of known, fungicidal inhibitors of these enzymes. Pioneer examples have been synthesised and have been demonstrated to be potent inhibitors of ergosterol biosynthesis in Ustilago maydis (DC) Corda, acting in the same manner as the commercial fungicide fenpropimorph. They also showed excellent fungicidal activity against Erysiphe graminis DC f. sp. hordei Marchal (powdery mildew of barley) and Puccinia recondita Rob. ex Desm. (wheat leaf rust) in in‐vivo glasshouse tests. Using these compounds as a starting point, systematic structural variation has been carried out. Testing of a wide range of analogues at high volume confirms the potential of this class of compound to control mildew and rust pathogens at levels comparable to those of the standards. Correlation of in‐vivo and enzymatic data is good and the structure‐activity relationship developed for this series of compounds closely parallels that found for the morpholine/piperidine class of fungicides, suggesting a common mode of action.