Triphenylphosphonium-Driven Targeting of Pyrimorph Fragment Derivatives Greatly Improved Its Action on Phytopathogen Mitochondria

Pyrimorph is a carboxylic acid amide (CAA) fungicide, which shows excellent activity against oomycetes such as pepper phytophthora blight, tomato late blight, and downy mildew of cucumber. It works mainly by inhibiting the biosynthesis of cell wall of oomycetes. However, pyrimorph also shows weak activity of inhibiting mitochondrial complex III, which is the first CAA fungicide found to act on mitochondria. To improve this effect on mitochondria and develop fungicides that may have a novel mechanism of action, in this paper, by disassembling pyrimorph and conjugating the fragments with the mitochondrial-targeted delivery system (triphenylphosphonium), three series of mitochondrial-targeting analogues of pyrimorph were designed and synthesized. The results show that the pyridine-containing 1,1-diaryl is the core module of inhibition mitochondrial function of pyrimorph. Among these conjugates, compound 3b with a short linker showed the highest and broad-spectrum fungicidal activity, strong respiratory inhibition activity, and adenosine 5'-triphosphate synthesis inhibition activity, suggesting its potential as a fungicide candidate. 3b exhibited greatly improved action on mitochondria, such as by destroying the mitochondrial function of pathogens, causing mitochondrial swelling, weakening its influence on cell wall morphology, and so on. More importantly, this study provides a method to strengthen the drugs or pesticides with weak mitochondrial action, which is of special significance for developing mitochondrial bioactive molecules with the novel action mechanism.

Acute toxicity and bioconcentration of pyrimorph in zebrafish, Brachydanio rerio

BACKGROUND

Pyrimorph is a novel fungicide being developed in China that shows high antifungal activity against diseases caused by Phytophthora infestans, Phytophthora capsici, Rhizoctonia solani, Peronophythora litchi and Pseudoperonospora cubensis. Until now, no information on the toxicity of pyrimorph to untargeted organisms has been reported. To assess the potential environmental impacts of pyrimorph in fish, the acute toxicity and bioconcentration of pyrimorph in zebrafish were studied in this paper.

RESULTS

When tested by the semi-static method, the 48, 72 and 96 h median lethal concentration (LC50 ) values of pyrimorph to zebrafish were 24.33, 22.61 and 19.79 mg L(-1) respectively. To study the bioconcentration of pyrimorph in zebrafish, the fish were exposed to sublethal concentrations of pyrimorph (2.00 and 0.25 mg L(-1) ) for 192 h, a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method was applied to extract pyrimorph from samples and the residues of pyrimorph in the water and fish were determined by high-performance liquid chromatography (HPLC). The highest bioconcentration factor (BCF) of pyrimorph in the fish was 1.07 × 10(2) (144 h) and 23.1 (96 h) after exposure to 2.00 and 0.25 mg L(-1) of pyrimorph respectively.

CONCLUSIONS

The novel fungicide pyrimorph has low toxicity to zebrafish; however, it showed medium BCF to zebrafish. Therefore, more attention should be paid to the residue of pyrimorph in fish, as well as to its long-term ecological effects.