Synthesis and antifungal activity of 5-methylisoxazole-4-carboxylic oxime esters

Isoxazole is a five-membered heterocycle with good activity. Fifteen new 5-methylisoxazole-4-carboxylic oxime esters were designed and synthesized in this paper. Their structures were determined by ¹H NMR, ¹³C NMR and HRMS. The in vitro antifungal activities against Botrytis cinerea, Rhizoctonia solani, Valsa mali and Gaeumannomyces graminis were evaluated. The bioactivity results showed that the target compounds had certain antifungal activities at the concentration of 50 μg/mL. Particularly, compound 5g displayed better activity against B. cinerea than lead compound L1 and trifloxystrobin with an EC₅₀ value of 1.95 μg/mL.