Bioassay-guided isolation of two antifungal compounds from Magnolia officinalis, and the mechanism of action of honokiol.

Magnolia officinalis, as a well-known herb worldwide, has been widely used to treat multiple diseases for a long time. In this study, the petroleum ether extract from M. officinalis showed effective antifungal activity against seven plant pathogens (particularly against R. solani with an inhibition rate of 100.00% at 250 µg/mL). Honokiol and magnolol, isolated by the bioassay-guided method, exhibited greater antifungal activity than tebuconazole (EC50 = 3.07 µg/mL, p ≤ 0.001) against R. solani, which EC50 values were 2.18 µg/mL and 3.48 µg/mL, respectively. We used transcriptomics to explore the mechanism of action of honokiol against R. solani. Results indicated that honokiol may exert antifungal effects by blocking the oxidative phosphorylation metabolic pathway. Further studies indicated that honokiol induced ROS overproduction, disrupted the mitochondrial function, affected respiration, and blocked the TCA cycle, which eventually inhibited ATP production. Besides, honokiol also damaged cell membranes and caused morphological changes. This study demonstrated that the lignans isolated from M. officinalis possess the potential to be developed as botanical fungicides.

Design, synthesis and antifungal activity evaluation of isocryptolepine derivatives.

In this paper, the nitrogen atom was inserted into the anthracycline system of the isocryptolepine nucleus to obtain the "Aza"-type structure benzo[4,5]imidazo[1,2-c] quinazoline. A series of "Aza"-type derivatives were designed, synthesized and evaluated for their antifungal activity against six plant fungi in vitro. Among all derivatives, compounds A-0, B-1 and B-2 showed significant antifungal activity against B. cinerea with the EC50 values of 2.72 µg/mL, 5.90 µg/mL and 4.00 µg/mL, respectively. Compound A-2 had the highest activity against M. oryzae with the EC50 values of 8.81 µg/mL, and compound A-1 demonstrated the most control efficacy against R. solani (EC50, 6.27 µg/mL). Moreover, compound A-0 was selected to investigate the in vivo tests against B. cinerea and the results indicated that the preventative efficacy of it up to 72.80% at 100 µg/mL. Preliminary mechanism studies revealed that after treatment with A-0 at 5 µg/mL, the B. cinerea mycelia appeared curved, collapsed and the cell membrane integrity may be damaged. The reactive oxygen species production, mitochondrial membrane potential and nuclear morphometry of mycelia have been changed, and the membrane function and cell proliferation of mycelia were destroyed. Compounds A-0, A-1, B-1 and B-2 presented weaker toxicities against two cells lines than isocryptolepine. This study lays the foundation for the future development of isocryptolepine derivatives as environmentally friendly and safe agricultural fungicides.

Design, Synthesis, and Structure-Activity Relationship of Quinazolinone Derivatives as Potential Fungicides.

Plant diseases caused by phytopathogenic fungi reduce the yield and quality of crops. To develop novel antifungal agents, we designed and synthesized eight series of quinazolinone derivatives and evaluated their anti-phytopathogenic fungal activity. The bioassay results revealed that compounds KZL-15, KZL-22, 5b, 6b, 6c, 8e, and 8f exhibited remarkable antifungal activity in vitro. Especially, compound 6c displayed the highest bioactivity against Sclerotinia sclerotiorum, Pellicularia sasakii, Fusarium graminearum, and Fusarium oxysporum, displaying appreciable IC50 values (50% inhibitory concentration) of 2.46, 2.94, 6.03, and 11.9 µg/mL, respectively. A further mechanism interrogation revealed abnormal mycelia, damaged organelles, and changed permeability of cell membranes in S. sclerotiorum treated with compound 6c. In addition, the in vivo bioassay indicated that compound 6c possessed comparable curative and protective effects (87.3 and 90.7%, respectively) to the positive control azoxystrobin (89.5 and 91.2%, respectively) at 100 µg/mL concentration against S. sclerotiorum. This work validated the potential of compound 6c as a new and promising fungicide candidate, contributing to the exploration of potent antifungal agents.

Design and Discovery of Novel Antifungal Quinoline Derivatives with Acylhydrazide as a Promising Pharmacophore.

Inspired by natural 2-quinolinecarboxylic acid derivatives, a series of quinoline compounds containing acylhydrazine, acylhydrazone, sulfonylhydrazine, oxadiazole, thiadiazole, or triazole moieties were synthesized and evaluated for their fungicidal activity. Most of these compounds exhibited excellent fungicidal activity in vitro. Significantly, compound 2e displayed the superior in vitro antifungal activity against Sclerotinia sclerotiorum, Rhizoctonia solani, Botrytis cinerea, and Fusarium graminearum with the EC50 values of 0.39, 0.46, 0.19, and 0.18 µg/mL, respectively, and were more potent than those of carbendazim (EC50, 0.68, 0.14, >100, and 0.65 µg/mL, respectively). Moreover, compound 2e could inhibit spore germination of F. graminearum. Preliminary mechanistic studies showed that compound 2e could cause abnormal morphology of cell walls and vacuoles, loss of mitochondrion, increases in membrane permeability, and release of cellular contents. These results indicate that compound 2e displayed superior fungicidal activities and could be a potential fungicidal candidate against plant fungal diseases.

Synthesis, biological activities and structure-activity relationships for new avermectin analogues.

In an effort to discover new molecules with good insecticidal activities, more than 40 new avermectin derivatives were synthesized and evaluated for their biological activities against three species of arachnids, insects and nematodes, namely, Tetranychus Cinnabarinus, Aphis craccivora and Bursaphelenchus xylophilus. All the tested compounds showed potent inhibitory activities against three insect species. Notably, the majority of compounds exhibited high selectivity against T. cinnabarinus, some of which were much better in comparison with avermectin. Especially compounds 9j (LC50: 0.005 µM) and 16d (LC50: 0.002 µM) were 2.5- and 4.7-fold more active than avermectin (LC50: 0.013 µM), respectively, against T. cinnabarinus. Moreover, compounds 9b, 9d-f, 9h, 9j, 9l, 9n, 9p, 9r, 9v and 17d showed superior activities with LC50 values of 2.959-5.013 µM compared to that of 1 (LC50: 6.746 µM) against B. xylophilus. Meanwhile, the insecticidal activities of compounds 9f, 9g, 9h, and 9m against A. craccivora were 7-8 times better than that of avermectin, with LC50 values of 7.744, 5.634, 6.809, 7.939 and 52.234 µM, respectively. Furthermore, QSAR analysis showed that the molecular shape, size, connectivity degree and electronic distribution of avermectin analogues had substantial effects on insecticidal potency. These preliminary results provided useful insight in guiding further modifications of avermectin in the development of potential new insecticides.

Design, synthesis and bioactivity evaluation of novel benzophenone hydrazone derivatives.

BACKGROUND: Benzophenone hydrazone derivatives are among the most important classes of synthetic insecticides. In an effort to discover new molecules with good insecticidal/acaricidal activities, a series of novel benzophenone hydrazone N-acylated thiourea and urea derivatives was synthesized and bioassayed. RESULTS: All of these compounds exhibited excellent bioactivities against T. cinnabarinus and B. brassicae, especially towards T. cinnabarinus with LC50 values ranging from 0.305 to 2.036 mmol L(-1). Moreover, the acaricidal activities against T. cinnabarinus of compounds 8a-i, 12b-f and 12h were 2.5-5.5-fold that of parent molecule 3 based on the LC50 value. CONCLUSION: Based on the observed bioactivities, the structure-activity relationship of these analogs was also discussed. Structure-activity relationships provided information that could direct further investigation on structure modification. Our studies indicated that benzophenone hydrazone N-acylated thiourea and urea derivatives could be used as potential lead compounds for developing novel acaricides and insecticides.

Design, synthesis, crystal structure, insecticidal activity, molecular docking, and QSAR studies of novel N3-substituted imidacloprid derivatives.

Three novel series of N3-substituted imidacloprid derivatives were designed and synthesized, and their structures were identified on the basis of satisfactory analytical and spectral ((1)H NMR, (13)C NMR, MS, elemental analysis, and X-ray) data. Preliminary bioassays indicated that all of the derivatives exhibited significant insecticidal activities against Aphis craccivora, with LC50 values ranging from 0.00895 to 0.49947 mmol/L, and the insecticidal activities of some of them were comparable to those of the control imidacloprid. Some key structural features related to their insecticidal activities were identified, and the binding modes between target compounds and nAChR model were also further explored by molecular docking. By comparing the interaction features of imidacloprid and compound 26 with highest insecticidal activity, the origin of the high insecticidal activity of compound 26 was identified. On the basis of the conformations generated by molecular docking, a satisfactory 2D-QSAR model with six selected descriptors was built using genetic algorithm-multiple linear regression (GA-MLR) method. The analysis of the built model showed the molecular size, shape, and the ability to form hydrogen bond were important for insecticidal potency. The information obtained in the study will be very helpful for the design of new derivatives with high insecticidal activities.