Design, Synthesis, and Biological Activity of Silicon-Containing Carboxamide Fungicides.

Bioisosteric silicon replacement has proven to be a valuable strategy in the design of bioactive molecules for crop protection and drug development. Twenty-one novel carboxamides possessing a silicon-containing biphenyl moiety were synthesized and tested for their antifungal activity and succinate dehydrogenase (SDH) enzymatic inhibitory activity. Among these novel succinate dehydrogenase inhibitors (SDHIs), compounds 3a , 3e , 4l, and 4o possessing appropriate c log P and topological polar surface area values showed excellent inhibitory effects against Rhizoctonia solani , Sclerotinia sclerotiorum , Botrytis cinerea , and Fusarium graminearum at 10 mg/L in vitro, and the EC 50 values of 4l and 4o were 0.52 and 0.16 mg/L against R. solani and 0.066 and 0.054 mg/L against S. sclerotiorum , respectively, which were superior to those of Boscalid. Moreover, compound 3a demonstrated superior SDH enzymatic inhibitory activity (IC 50 = 8.70 mg/L), exhibiting 2.54-fold the potency of Boscalid (IC 50 = 22.09 mg/L). Docking results and scanning electron microscope experiments revealed similar mode of action between compound 3a and Boscalid. The new silicon-containing carboxamide 3a is a promising SDHI candidate that deserves further investigation.