Various 2-N-acyl-5-methylisoxazolone derivatives were prepared, and their antifungal activities were evaluated in vitro with mycelial growth inhibition tests. In contrast with N-alkyl derivatives, the acyl compounds showed significant activity against Pyrenophora graminea, Fusarium graminearum, Alternaria alternata, Cercospora beticola, Rhynchosporium secalis, Septoria tritici, Microdochium nivale, Rhizoctonia solani and Gaeumannomyces graminis. Of note, cinnamoyl, 3-furan-3-ylacryloyland 3-thiophen-3-yl-acryloylamides, and t-butylacetyl and pivaloyl derivatives showed high inhibition rates at 25 mg/L against R. solani and G. graminis, respectively.

The structure of the commercial fungicide hymexazol, 3-hydroxy-5-methylisoxazol, was transformed to acyloxy, 3-alkoxy, alkylcarbamoyloxy and acylamino derivatives, and their antifungal activities or disease control activities were examined. The 3-acyloxy derivatives were much more active than the other derivatives, and some of the 3-acyloxy derivatives exhibited antifungal activities or disease control activities against a wide range of pathogens, such as Pyrenophora graminea, Alternaria alternata, Cercospora beticola, Rhynchosporium secalis, Septoria tritici, Microdochium nivale, Rhizoctonia solani, Puccinia recondita, and Blumeria graminis. Among them, 5-methyl-3-isoxazolyl (α)-naphthoate and (o)-toluate and 2,2-dichloro-1,3,3-trimethylcyclopropanecarboxylate completely inhibited the mycelial growth of Rhizoctonia solani and M. nivale at 25 mg/L, respectively.