Ametoctradin is a Potent <i>Q</i>_o Site Inhibitor of the Mitochondrial Respiration Complex III

Ametoctradin is a new <i>Oomycete</i>-specific fungicide under development by BASF. It is a potent inhibitor of the <i>bc</i>₁ complex in mitochondrial respiration. However, its detailed action mechanism remains unknown. In the present work, the binding mode of ametoctradin was first uncovered by integrating molecular docking, MD simulations, and MM/PBSA calculations, which showed that ametoctradin should be a <i>Q</i>_o site inhibitor of <i>bc</i>₁ complex. Subsequently, a series of new 1,2,4-triazolo­[1,5-<i>a</i>]­pyrimidine derivatives were designed and synthesized to further understand the substituent effects on the 5- and 6-position of 1,2,4-triazolo­[1,5-<i>a</i>]­pyrimidine. The calculated binding free energies (Δ<i>G</i>_cal) of newly synthesized analogues as <i>Q</i>_o site inhibitors correlated very well (<i>R</i>² = 0.96) with their experimental binding free energies (Δ<i>G</i>_exp). Two compounds (<b>4a</b> and <b>4c</b>) with higher inhibitory activity against porcine SQR than ametoctradin were successfully identified. The structural and mechanistic insights obtained from the present study will provide a valuable clue for future designing of a new promising <i>bc</i>₁ inhibitor