Natural α‐Methylene‐γ‐Butyrolactone Analogues: Synthesis and Evaluation of Isoaurone Derivatives as Antifungal Agents

In order to develop novel, efficient and green fungicides, a series of novel isoaurone derivatives were designed and synthesized, which were characterized by 1H and 13C NMR, high‐resolution mass spectra and melting points. The target compounds showed different inhibitory activities against seven plant pathogenic fungi. Compounds 1, 12, 17, 20, 22, 24 and intermediate A showed more than 90% inhibition rates against S. s at 50 mg/L. Interestingly, compound 22 and intermediate A showed the great inhibitory effect against S. s with EC50 values of 4.65 and 4.24 mg/L, which were better than the lead compound isoaurone (EC50 = 15.62 mg/L). The EC50 values of compounds 17 and 24 against B. c were 13.94 and 22.13 mg/L. Moreover, compound 19 displayed significant antifungal activity against G. g with the EC50 value of 11.88 mg/L. Theoretical calculations by DFT revealed that the α, β‐unsaturated carbonyl bond and the benzyl ring are very importantly linked to the strength of the fungicidal activity. Therefore, this study identified a valuable antifungal lead compound for further development of green fungicides.