A series of novel myrtenal derivatives bearing 1,2,4-triazole moiety were designed and synthesized by multi-step reactions in an attempt to develop potent antifungal agents. Their structures were confirmed by using UV-vis, FTIR, NMR, and ESI-MS analysis. Antifungal activity of the target compounds was preliminarily evaluated by the in vitro method against Fusarium oxysporum f. sp. cucumerinum, Physalospora piricola, Alternaria solani, Cercospora arachidicola, and Gibberella zeae at 50 µg/mL. Compounds 6c (R = i-Pr), 6l (R = o-NO₂ Bn), and 6a (R = Et) exhibited excellent antifungal activity against P. piricola with inhibition rates of 98.2%, 96.4%, and 90.7%, respectively, showing better or comparable antifungal activity than that of the commercial fungicide azoxystrobin with a 96.0% inhibition rate, which served as a positive control.

A series of novel (Z)- and (E)-3-caren-5-one oxime sulfonates were designed and synthesized in search of potent antifungal agents. The structures of the intermediates and target compounds were confirmed by UV-Vis, FTIR, NMR, and ESI-MS. The in vitro antifungal activity of the target compounds was preliminarily evaluated against Cercospora arachidicola, Physalospora piricola, Alternaria solani, Rhizoeotnia solani, Bipolaris maydis and Colleterichum orbicalare at 50 µg/mL. The bioassay results indicated that the target compounds exhibited the best antifungal activity against P. piricola, in which compounds 4b, 4f, 4m, 4e, 4j, 4l, 4y, 4d, and 4p had excellent inhibition rates of 100%, 100%, 100%, 92.9%, 92.9%, 92.9%, 92.9%, 85.7%, and 85.7%, respectively, showing much better antifungal activity than that of the commercial fungicide chlorothanil. Both the compounds 4y and 4x displayed outstanding antifungal activity of 100% against B. myadis, and the former also displayed outstanding antifungal activity of 100% against R. solani. In order to design more effective antifungal compounds against P. piricola, the analysis of three-dimensional quantitative structure-activity relationship (3D-QSAR) was carried out using the CoMFA method, and a reasonable and effective 3D-QSAR model (r² = 0.990, q² = 0.569) has been established.

Seventeen novel 2-(5-amino-1-(substituted sulfonyl)-1H-1,2,4-triazol-3-ylthio)-6- isopropyl-4,4-dimethyl-3,4-dihydronaphthalen-1(2H)-one compounds were synthesized from the abundant and naturally renewable longifolene and their structures were confirmed by FT-IR, NMR, and ESI-MS. The in vitro cytotoxicity of the synthesized compounds was evaluated by standard MTT assay against five human cancer cell lines, i.e., T-24, MCF-7, HepG2, A549, and HT-29. As a result, compounds 6d, 6g, and 6h exhibited better and more broad-spectrum anticancer activity against almost all the tested cancer cell lines than that of the positive control, 5-FU. Some intriguing structure–activity relationships were found and are discussed herein by theoretical calculation.

Twenty-seven (Z)- and (E)-verbenone derivatives bearing an oxime ester moiety were designed and synthesized in search of novel bioactive molecules. Their structures were confirmed by UV-Vis, FTIR, NMR, ESI-MS, and elemental analysis. The antifungal and herbicidal activities of the target compounds were preliminarily evaluated. As a result, compound (E)-4n (R = β-pyridyl) exhibited excellent antifungal activity with growth inhibition percentages of 92.2%, 80.0% and 76.3% against Alternaria solani, Physalospora piricola, and Cercospora arachidicola at 50 µg/mL, showing comparable or better antifungal activity than the commercial fungicide chlorothalonil with growth inhibition of 96.1%, 75.0% and 73.3%, respectively, and 1.7−5.5-fold more growth inhibition than its stereoisomer (Z)-4n (R = β-pyridyl) with inhibition rates of 22.6%, 28.6% and 43.7%, respectively. In addition, seven compounds displayed significant growth inhibition activity of over 90% against the root of rape (Brassica campestris) at 100 µg/mL, exhibiting much better herbicidal activity than the commercial herbicide flumioxazin with a 63.0% growth inhibition. Among these seven compounds, compound (E)-4n (R = β-pyridyl) inhibited growth by 92.1%, which was 1.7-fold more than its stereoisomer (Z)-4n (R = β-pyridyl) which inhibited growth by 54.0%.

A series of novel 3-caren-5-one oxime esters were designed and synthesized by multi-step reactions in an attempt to develop potent antifungal agents. Two E-Z stereoisomers of the intermediate 3-caren-5-one oxime were separated by column chromatography for the first time. The structures of all the intermediates and target compounds were confirmed by UV-Vis, FTIR, NMR, ESI-MS, and elemental analysis. The antifungal activity of the target compounds was preliminarily evaluated by the in vitro method against Fusarium oxysporum f. sp. cucumerinum, Physalospora piricola, Alternaria solani, Cercospora arachidicola, Gibberella zeae, Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. The target compounds exhibited best antifungal activity against P. piricola, in which compounds (Z)-4r (R = β-pyridyl), (Z)-4q (R = α-thienyl), (E)-4f′ (R = p-F Ph), (Z)-4i (R = m-Me Ph), (Z)-4j (R = p-Me Ph), and (Z)-4p (R = α-furyl) had inhibition rates of 97.1%, 87.4%, 87.4%, 85.0%, 81.9%, and 77.7%, respectively, showing better antifungal activity than that of the commercial fungicide chlorothanil. Also, compound (Z)-4r (R = β-pyridyl) displayed remarkable antifungal activity against all the tested fungi, with inhibition rates of 76.7%, 82.7%, 97.1%, 66.3%, 74.7%, 93.9%, 76.7% and 93.3%, respectively, showing better or comparable antifungal activity than that of the commercial fungicide chlorothanil. Besides, the E-Z isomers of the target oxime esters were found to show obvious differences in antifungal activity. These results provide an encouraging framework that could lead to the development of potent novel antifungal agents.