Triphenylphosphonium (TPP)-Conjugated Quinolone Analogs Displayed Significantly Enhanced Fungicidal Activity Superior to Its Parent Molecule.

Although 1-hydroxy-4-quinolone derivatives, such as 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), aurachin C, and floxacrine, have been reported as effective cytochrome complex inhibitors, the bioactivity of these products is not ideal, presumably due to their low bioavailability in tissues, particularly their poor solubility and low mitochondrial accumulation. In order to overcome the drawbacks of these compounds and develop their use as agricultural fungicides acting by cytochrome inhibition, in this study, three novel mitochondria-targeting quinolone analogs (mitoQNOs) were designed and synthesized by conjugating triphenylphosphonium (TPP) with quinolone. They exhibited greatly enhanced fungicidal activity compared to the parent molecule, especially mitoQNO, which showed high antifungal activity against and with EC values of 7.42 and 4.43 μmol/L, respectively. In addition, mitoQNO could inhibit the activity of the cytochrome complex of in a dose-dependent manner and effectively depress its respiration and ATP production. The greatly decreased mitochondrial membrane potential and massively generated reactive oxygen species (ROS) strongly suggested that the inhibition of complex III led to the leakage of free electrons, which resulted in the damage of the pathogen cell structure. The results of this study indicated that TPP-conjugated QNOs might be used as agricultural fungicides by conjugating them with TPP.