Abstract
AbstractFenpropimorph is an inhibitor of Δ8→Δ7‐isomerase and Δ14‐reductase in fungi and cycloeucalenol‐obtusifoliol‐isomerase and Δ8→Δ7‐isomerase in higher plants. A detailed conformational analysis of the most potent enantiomer (S)‐fenpropimorph is described. The conformational analysis is based on three different methods: molecular mechanics calculations. NMR spectroscopy and X‐ray crystallography.In solution several conformations coexist. The molecular mechanics calculations using MM2(85) show a folded conformation of the unprotonated form of fenpropimorph to be stabilized by at least 3 kcal mol−1 relative to the next lowest energy conformer, suggesting only one conformation of fenpropimorph to be present. A corresponding stabilization of the protonated form (5.4 kcal mol−1) is obtained. However, this stabilization is found partly to be due to attractive steric interactions and may be a phenomenon occurring only in vacuum. In the solid state, fenpropimorph exists in an L‐shaped conformation resembling one of the low‐energy conformers obtained with MM2(85).Based on comparison with the natural substrate, a totally extended conformation of fenpropimorph is suggested to be the biologically active conformation for interaction with the Δ8 → Δ7‐isomerase in fungi.
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