Synthesis of Myrtenal-Based Nanocellulose/Diacylhydrazine Complexes with Antifungal Activity for Plant Protection

Design, synthesis, antifungal evaluation and mechanism study of novel norbornene derivatives as potential laccase inhibitors

BACKGROUND

To discover novel fungicide candidates, five series of novel norbornene hydrazide, bishydrazide, oxadiazole, carboxamide and acylthiourea derivatives (2a-2t, 3a-3f, 4a-4f, 5a-5f and 7a-7f) were designed, synthesized and assayed for their antifungal activity toward seven representative plant fungal pathogens.

RESULTS

In the in vitro antifungal assay, some title norbornene derivatives presented good antifungal activity against Botryosphaeria dothidea, Sclerotinia sclerotiorum and Fusarium graminearum. Especially, compound 2b exhibited the best inhibitory activity toward B. dothidea with the median effective concentration (EC50) of 0.17 mg L-1, substantially stronger than those of the reference fungicides boscalid and carbendazim. The in vivo antifungal assay on apples revealed that 2b had significant curative and protective effects, both of which were superior to boscalid. In the preliminary antifungal mechanism study, 2b was able to injure the surface morphology of hyphae, destroy the cell membrane integrity and increase the intracellular reactive oxygen species (ROS) level of B. dothidea. In addition, 2b could considerably inhibit the laccase activity with the median inhibitory concentration (IC50) of 1.02 μM, much stronger than that of positive control cysteine (IC50 = 35.50 μM). The binding affinity and interaction mode of 2b with laccase were also confirmed by molecular docking.

CONCLUSION

This study presented a promising lead compound for the study of novel laccase inhibitors as fungicidal agrochemicals, which demonstrate significant anti-B. dothidea activity and laccase inhibitory activity. © 2024 Society of Chemical Industry.

Understanding the Cis-Trans Amide Bond Isomerization of N,N'-Diacylhydrazines to Develop Guidelines for A Priori Prediction of Their Most Stable Solution Conformers

N,N'-diacylhydrazines (R1CO-NR3-NR4-COR2) are a class of small molecules with a wide range of applications in chemistry and biology. They are structurally unique in the sense that their two amide groups are connected via a N-N single bond, and as a result, these molecules can exist in eight different isomeric forms. Four of these are amide isomers [trans-trans (t-t), trans-cis (t-c), cis-trans (c-t), and cis-cis (c-c)] arising from C-N bond restricted rotation. In addition, each of these amide isomers can exist in two different isomeric forms due to N-N bond restricted rotation, especially when R3 and R4 groups are relatively bigger. Herein, we have systematically investigated the conformations of 55 N,N'-diacylhydrazines using a combination of solution NMR spectroscopy, X-ray crystallography, and density functional theory calculations. Our data suggest that when the substituents R3 and R4 on the nitrogen atoms are both hydrogens. These molecules prefer twisted trans-trans (t-t) (>90%) geometries (H-N-C═O ∼ 180°), whereas the N-alkylated and N,N'-dialkylated molecules prefer twisted trans-cis (t-c) geometries. Herein, we have analyzed the stabilization of the various isomers of these molecules in light of steric and stereoelectronic effects. We provide a guideline to a priori predict the most stable conformers of the N,N'-diacylhydrazines just by examining their substituents (R1-R4).

An Effective and Promising Strategy for Plant Protection: Synthesis of L-Carvone-Based Thiazolinone-Hydrazone/Nanochitosan Complexes with Antifungal Activity and Sustained Releasing Performance

The development of novel natural product-derived nano-pesticide systems with loading capacity and sustained releasing performance of bioactive compounds is considered an effective and promising plant protection strategy. In this work, 25 L-carvone-based thiazolinone-hydrazone compounds 4a~4y were synthesized by the multi-step modification of L-carvone and structurally confirmed. Compound 4h was found to show favorable and broad-spectrum antifungal activity through the in vitro antifungal activity evaluation of compounds 4a~4y against eight phytopathogenic fungi. Thus, it could serve as a leading compound for new antifungal agents in agriculture. Moreover, the L-carvone-based nanochitosan carrier 7 bearing the 1,3,4-thiadiazole-amide group was rationally designed for the loading and sustained releasing applications of compound 4h, synthesized, and characterized. It was proven that carrier 7 had good thermal stability below 200 °C, dispersed well in the aqueous phase to form numerous nanoparticles with a size of~20 nm, and exhibited an unconsolidated and multi-aperture micro-structure. Finally, L-carvone-based thiazolinone-hydrazone/nanochitosan complexes were fabricated and investigated for their sustained releasing behaviors. Among them, complex 7/4h-2 with a well-distributed, compact, and columnar micro-structure displayed the highest encapsulation efficiency and desirable sustained releasing property for compound 4h and thus showed great potential as an antifungal nano-pesticide for further studies.

High value-added application of natural forest product α-pinene: design, synthesis and 3D-QSAR study of novel α-campholenic aldehyde-based 4-methyl-1,2,4-triazole-thioether compounds with significant herbicidal activity

For exploring novel natural product-derived herbicides, 16 novel α-campholenic aldehyde-based 4-methyl-1,2,4-triazole-thioether compounds were designed, synthesized, and characterized by FT-IR, 1H NMR, 13C NMR, ESI-MS and elemental analysis. The preliminary bioassay showed that, at 100 µg/mL, most of the target compounds displayed significant inhibition activity against root-growth of rape(Brassica campestris L.), with inhibition rates of 85.0%～98.2%(A-class activity level), much better than that of the positive control flumioxazin. In addition, an effective and reasonable 3D-QSAR model was established by CoMFA method in SYBYL-X 2.1.1 software. It was found that, the steric field was the major factor towards the herbicidal activity of the target compounds against B. campestris L., and the introduction of bulky groups into m- and p-position of the benzene ring was favourable to increase the herbicidal activity. This kind of title compounds deserved further study as potential leading compounds for the discovery and development of novel herbicidal agents.

Discovery of Aryloxy-, Arylthio-, and Arylamino-Containing Acethydrazides as Fungicidal Agents

The development of new green fungicides is an effective way to solve the resistance of agricultural pathogens and plays an important role in promoting high-quality and sustainable development of modern agriculture. In this project, a series of aryloxy-, arylthio-, and arylamino-containing acethydrazide derivatives were designed, synthesized, and characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and high-resolution mass spectrometry (HRMS). The fungicidal bioassays indicated that some compounds showed excellent and broad-spectrum fungicidal activity, and the structure-activity relationship was discussed. The in vivo fungicidal activity demonstrated that compounds C4 and D8 exhibited good preventative effects against Fusarium graminearum infecting wheat leaves, of which the preventative activity of compound D8 was almost equal to that of the positive agents. Transmission electron microscopy (TEM) observation revealed that the plasma membrane in the C4-treated F. graminearum hyphal cells was severely contracted and separated with the cell wall, coupling with the visible lysosomes and the disappeared cytoplasm and organelles, which may be the reasons for the shriveled and even ruptured hyphae observed by scanning electron microscopy (SEM). Subsequently, transcriptomics and metabolomics were performed to further elucidate the fungicidal mechanism. The regulatory networks of differential genes and metabolites in plasma membrane-related sphingolipid metabolism, linoleic acid metabolism, α-linoleic acid metabolism, and arachidonic acid metabolism were constructed and elaborated. Additionally, preliminary investigation of seeding growth suggested that compounds C4 and D8 may have different degrees of influence on the growth indicators of wheat seedlings; however, this effect may be negligible as the plant grows.

Synthesis of (E)/(Z)-Verbenone Oxime Ethers and Photoresponsive Behavior to Herbicidal Activity

The accumulation of residual active herbicides in the environment can cause a series of problems. It is thus meaningful to explore a photoresponsive herbicide, whose activity can be weakened under the action of light to reduce the negative effect. To this purpose, a series of (E)/(Z)-verbenone oxime ethers were designed, synthesized, and characterized. Oxime ether groups were adopted as the trigger switches. The preliminary screening for herbicidal activity showed that some of them exhibited better or comparable effects than that of the commercial herbicide flumioxazin against Brassica campestris and Echinochloa crusgalli. Meanwhile, five pairs of the target compounds with significantly different herbicidal effects between E- and Z-forms were further investigated for their reversible isomerization reaction and the accompanying variation of herbicidal activity. As a result, the maximum conversion rates were around 50%, and the herbicidal effect of the resulting mixture of E- and Z-isomers decreased outstandingly. The phototransformation mechanism of a pair of isomers (E)-4a and (Z)-4a was preliminarily explored. Besides, a reasonable and effective 3D-quantitative structure-activity relationship model (r² = 0.984 and q² = 0.571) was established and the binding mode was also investigated by molecular docking.

Synthesis of 3-carene-derived nanocellulose/1,3,4-thiadiazole-amide complexes with antifungal activity for plant protection

BACKGROUND

Nanopesticides have been proved to be a powerful and promising tool to solve the issues in agriculture. The purpose of the present study was to develop ecofriendly nanopesticide systems by the strategy of comprehensive utilization of two natural biomass resources (bagasse and turpentine oil) because of their incomparable advantages.

RESULTS

In this research, a series of nanocellulose carriers ETOCN-1-ETOCN-4 (ETOCN, esterified TEMPO-oxidized cellulose nanofibers) with different degrees of substitution were prepared and characterized by Fourier-transform infrared (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Then, 21 1,3,4-thiadiazole-amide compounds 8a-8u containing gem-dimethylcyclopropane ring were designed, synthesized and characterized. A preliminary bioassay indicated that compound 8i (R = p-Br Ph) exhibited broad-spectrum antifungal activity against the tested fungi. Furthermore, drug-loading complexes 8i/ETOCN-1-8i/ETOCN-4 were fabricated by integration of nanocellulose-based carriers ETOCN-1-ETOCN-4 with bioactive compound 8i, and the drug-loading capacities, microstructures and sustained-releasing performance of these complexes were also investigated. According to the observation of scanning electron microscopy (SEM) images of complex 8i/ETOCN-2, the small-molecule drug and the carrier formed a well-distributed and compact complex, which led to the excellent drug-loading capacity and sustained-releasing performance in the ethanol/water (1:1, v/v) system.

CONCLUSIONS

Complexes 8i/ETOCN-1-8i/ETOCN-4 deserved further study as the promising candidates for the development of nanopesticides. © 2022 Society of Chemical Industry.

Synthesis, Antifungal Activity and 3D-QSAR Study of Novel Anisaldehyde-Derived Amide-Thiourea Compounds

Succinate dehydrogenase (SDH) is an important target enzyme for designing agricultural chemical fungicides. In order to explore novel natural product-based antifungal agents, twenty-one unreported anisaldehyde-derived amide-thiourea compounds were designed and synthesized using the principle of active splicing, and structurally confirmed by ¹ H-NMR, ¹³ C-NMR, ESI-MS, FT-IR, and element analysis. In vitro antifungal activity of the target compounds was evaluated by the agar dilution method. The results showed that some target compounds exhibited better or comparable antifungal activity than that of the commercial fungicide chlorothalonil, in which compounds 5c, 5o, and 5r displayed excellent antifungal activity of 92.6 %, 92.6 % and 99.1 % against P. piricola, respectively, better than that of the positive control. In addition, 3D-QSAR analysis was carried out by the CoMFA method to reveal the relationship between the structures of the target compounds and their inhibitory activities. The simulative binding mode of the target compounds and SDH was also studied by molecular docking.

Design, Synthesis, and Antimicrobial Activity of Quindoline Derivatives Inspired by the Cryptolepine Alkaloid

Based on the structural characteristics of the cryptolepine alkaloid, a series of new quindoline derivatives bearing various substituents were prepared and evaluated for their fungicidal and antibacterial activities. Bioassay results showed that compound D7 displayed superior in vitro fungicidal activities against Sclerotinia sclerotiorum, Botrytis cinerea, Fusarium graminearum, and Rhizoctonia solani with EC₅₀ values of 0.780, 3.62, 1.59, and 2.85 μg/mL, respectively. Compound A7 showed apparent antibacterial activities toward Xanthomonas oryzae pv. oryzae with a minimum inhibitory concentration (MIC) value of 3.12 μg/mL. Significantly, in vivo antifungal activity suggested that the curative effect (98.3%) of compound D7 was comparable to that of the positive control azoxystrobin (96.7%) at 100 μg/mL. Preliminary mechanistic studies showed that compound D7 might cause mycelial abnormality of S. sclerotiorum, cell membrane breakage, accumulation of reactive oxygen species (ROS), and inhibition of sclerotia formation. Therefore, compound D7 could be a novel broad-spectrum fungicidal candidate against plant fungal diseases.

Recent Advances on Lignocellulosic-Based Nanopesticides for Agricultural Applications

Controlled release systems of agrochemicals have been developed in recent years. However, the design of intelligent nanocarriers that can be manufactured with renewable and low-cost materials is still a challenge for agricultural applications. Lignocellulosic building blocks (cellulose, lignin, and hemicellulose) are ideal candidates to manufacture ecofriendly nanocarriers given their low-cost, abundancy and sustainability. Complexity and heterogeneity of biopolymers have posed challenges in the development of nanocarriers; however, the current engineering toolbox for biopolymer modification has increased remarkably, which enables better control over their properties and tuned interactions with cargoes and plant tissues. In this mini-review, we explore recent advances on lignocellulosic-based nanocarriers for the controlled release of agrochemicals. We also offer a critical discussion regarding the future challenges of potential bio-based nanocarrier for sustainable agricultural development.