4-Methylumbelliferone fused oxazole thioether derivatives: synthesis, characterization and antifungal activities

Series of thioether derivatives containing 4-methylumbelliferone fused oxazole moiety were designed and synthesised, their structures were fully characterized by ¹H NMR, ¹³C NMR and HR-ESI-MS as well. Moreover, the in vitro antifungal potency of the title compounds were preliminarily evaluated for their possible use as a fungicide. Meanwhile, ethyl thioethers 3aa and 3ba displayed remarkable inhibitory effect against the mycelium growth of Valsa mali and Botrytis cinerea with EC₅₀ of 12-16 μg/mL. Furthermore, compounds 3aa and 3ba also exhibited > 88% protective and curative effect against B. cinerea on tomato fruits at 90 μg/mL. Additionally, the environmental toxicity of the title compounds against the brine shrimp Artemia salina were evaluated as well. The results indicated that most of the title compounds exhibited weak toxic to aquatic organism A. salina.