Design, Synthesis, Crystal Structure, and Fungicidal Activity of L-Carvone Derivatives Containing an Oxime Ester Moiety

L-Carvone is a natural product with fungicidal activity, which can be used as a lead compound for screening new fungicides. A series of L-carvone derivatives containing an oxime ester moiety were synthesized by splicing active substructure strategy with L-carvone as the lead compound. The structures of the L-carvone derivatives were characterized by IR, H-1 NMR, C-13 NMR and HRMS analyses. The antifungal activities of these compounds were evaluated against five plant pathogenic fungi, namely Sclerotinia sclerotiorum, Fusarium graminearum, Pyricularia grisea, Fusariwn oxysporum and Thanatephorus cucumeris. The results indicated that most of the compounds showed good antifungal activities. Among them, (E)-2-methyl-5-(prop-1-en-2-yl)cyclohex-2-en-1-one O-(4-ethylbenzoyl)oxime (4e) had the best fungicidal activity against Fusarium graminearum (EC50=5.07 mg/L), and (S,E)-2-methyl-5-(prop-1-en-2-yl)cyclohex-2-en-1-one O-(3-methylbenzoyl)oxime (4b) had the best fungicidal activity against Sclerotinia sclerotiorum, (EC50=18.84 mg/L), which were better than the commercial fungicide enestroburin. Therefore, L-carvone derivatives have the potential to develop new fungicides.