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

Quinoline Derivatives in Discovery and Development of Pesticides

Finding highly active molecular scaffold structures is always the key research content of new pesticide discovery. In the research and development of new pesticides, the discovery of new agricultural molecular scaffold structures and new targets still faces great challenges. In recent years, quinoline derivatives have developed rapidly in the discovery of new agriculturally active molecules, especially in the discovery of fungicides. The unique quinoline scaffold has many advantages in the discovery of new pesticides and can provide innovative and feasible solutions for the discovery of new pesticides. Therefore, we reviewed the use of quinoline derivatives and their analogues as molecular scaffolds in the discovery of new pesticides since 2000. We systematically summarized the agricultural biological activity of quinoline compounds and discussed the structure-activity relationship (SAR), physiological and biochemical properties, and mechanism of action of the active compounds, hoping to provide ideas and inspiration for the discovery of new pesticides.

Novel Sulfoximine Derivatives Containing Cyanoguanidine and Nitroguanidine Moieties: Design, Synthesis, and Bioactivities

A total of 32 novel sulfoximines bearing cyanoguanidine and nitroguanidine moieties were designed and synthesized by a rational molecule design strategy. The bioactivities of the title compounds were evaluated and the results revealed that some of the target compounds possessed excellent antifungal activities against six agricultural fungi, including Sclerotinia sclerotiorum, Fusarium graminearum, Phytophthora capsici, Botrytis cinerea, Rhizoctonia solani, and Pyricularia grisea. Among them, compounds 8e1 and 8e4 exhibited significant efficacy against P. grisea with EC50 values of 2.72 and 2.98 μg/mL, respectively, which were much higher than that of commercial fungicides boscalid (47.95 μg/mL). Interestingly, in vivo assays determined compound 8e1 possessed outstanding activity against S. sclerotiorum with protective and curative effectiveness of 98 and 95.6% at 50 μg/mL, which were comparable to those of boscalid (93.2, 91.9%). The further preliminary mechanism investigation disclosed that compound 8e1 could damage the structure of the cell membrane of S. sclerotiorum, increase its permeability, and suppress its growth. Overall, the findings enhanced that these novel sulfoximine derivatives could be potential lead compounds for the development of new fungicides.

Antifungal Activity and Putative Mechanism of HWY-289, a Semisynthetic Protoberberine Derivative, against Botrytis cinerea

The emergence of resistant pathogens has increased the demand for alternative fungicides. The use of natural products as chemical scaffolds is a potential method for developing fungicides. HWY-289, a semisynthetic protoberberine derivative, demonstrated broad-spectrum and potent activities against phytopathogenic fungi, particularly Botrytis cinerea (with EC50 values of 1.34 μg/mL). SEM and TEM imaging indicated that HWY-289 altered the morphology of the mycelium and the internal structure of cells. Transcriptomics revealed that it could break down cellular walls through amino acid sugar and nucleotide sugar metabolism. In addition, it substantially decreased chitinase activity and chitin synthase gene (BcCHSV) expression by 53.03 and 82.18% at 1.5 μg/mL, respectively. Moreover, this impacted the permeability and integrity of cell membranes. Finally, HWY-289 also hindered energy metabolism, resulting in a significant reduction of ATP content, ATPase activities, and key enzyme activities in the TCA cycle. Therefore, HWY-289 may be a potential candidate for the development of plant fungicides.

Application and Mechanism of Cryptolepine and Neocryptolepine Derivatives as T3SS Inhibitors for Control of Bacterial Leaf Blight on Rice

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv oryzae (Xoo) is extremely harmful to rice production. The traditional control approach is to use bactericides that target key bacterial growth factors, but the selection pressure on the pathogen makes resistant strains the dominant bacterial strains, leading to a decline in bactericidal efficacy. Type III secretion system (T3SS) is a conserved and critical virulence factor in most Gram-negative bacteria, and its expression or absence does not affect bacterial growth, rendering it an ideal target for creating drugs against Gram-negative pathogens. In this work, we synthesized a range of derivatives from cryptolepine and neocryptolepine. We found that compound Z-8 could inhibit the expression of Xoo T3SS-related genes without affecting the growth of bacteria. an in vivo bioassay showed that compound Z-8 could effectively reduce the hypersensitive response (HR) induced by Xoo in tobacco and reduce the pathogenicity of Xoo in rice. Furthermore, it exhibited synergy in control of bacterial leaf blight when combined with the quorum quenching bacterial F20.

Functional characterization and structural basis of a reversible glycosyltransferase involves in plant chemical defence

Plants experience numerous biotic stresses throughout their lifespan, such as pathogens and pests, which can substantially affect crop production. In response, plants have evolved various metabolites that help them withstand these stresses. Here, we show that two specialized metabolites in the herbaceous perennial Belamcanda chinensis, tectorigenin and its glycoside tectoridin, have diverse defensive effects against phytopathogenic microorganisms and antifeeding effects against insect pest. We further functionally characterized a 7-O-uridine diphosphate glycosyltransferase Bc7OUGT, which catalyses a novel reversible glycosylation of tectorigenin and tectoridin. To elucidate the catalytic mechanisms of Bc7OUGT, we solved its crystal structure in complex with UDP and UDP/tectorigenin respectively. Structural analysis revealed the Bc7OUGT possesses a narrow but novel substrate-binding pocket made up by plentiful aromatic residues. Further structure-guided mutagenesis of these residues increased both glycosylation and deglycosylation activities. The catalytic reversibility of Bc7OUGT was also successfully applied in an one-pot aglycon exchange reaction. Our findings demonstrated the promising biopesticide activity of tectorigenin and its glycosides, and the characterization and mechanistic study of Bc7OUGT could facilitate the design of novel reversible UGTs to produce valuable glycosides with health benefits for both plants and humans.

Design, synthesis and antifungal evaluation of phenylthiazole-1,3,4-oxadiazole thione (ketone) derivatives inspired by natural thiasporine A

BACKGROUND

Plant pathogenic fungal infections have become a severe threat to the yield and quality of agricultural products, and new green antifungal agents with high efficiency and low toxicity are needed. In this study, a series of thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione (ketone) structures were designed and synthesized, and their antifungal activities against six invasive and highly destructive phytopathogenic fungi were evaluated.

RESULTS

The results found that all compounds showed moderate to potent antifungal activity against six phytopathogenic fungi, and most of the E series compounds showed remarkable antifungal activity against Sclerotinia sclerotiorum and Colletotrichum camelliaet. In particular, compounds E1-E5, E7, E8, E13, E14, E17, and E22 showed more significant antifungal activity against S. sclerotiorum, with half-maximal effective concentration (EC50 ) values of 0.22, 0.48, 0.56, 0.65, 0.51, 0.39, 0.60, 0.56, 0.60, 0.63, and 0.45 μg mL-1 , respectively, which were superior to that of carbendazim (0.70 μg mL-1 ). Further activity studies showed that compound E1 possessed superior curative activities against S. sclerotiorum in vivo and better inhibitory effects on sclerotia germination and the formation of S. sclerotiorum compared with those of carbendazim.

CONCLUSIONS

This study indicates that these thiasporine A derivatives containing phenylthiazole-1,3,4-oxadiazole thione structures might be used as antifungal agents against S. sclerotiorum. © 2023 Society of Chemical Industry.

Design, synthesis, and antifungal activities of novel sulfoximine derivatives for plant protection

BACKGROUND

Fungicides play a significant role in the integrated management of plant pathogens. However, the irrational application of fungicides with similar structures has led to development of cross-resistance, therefore there is a need to seek novel fungicides with new structures.

RESULTS

Twenty-eight novel sulfoximine derivatives incorporating nitroguanidine moieties were designed, synthesized, and evaluated as antifungal agents. The bioassay results indicated that most of the synthesized compounds displayed excellent fungicidal activities against Sclerotinia sclerotiorum, Rhizoctonia solani, Fusarium graminearum, and Pyricularia grisea. Among these, compounds 6c₄ , 6c₅ , and 6c₆ exhibited remarkable fungicidal activities against P. grisea, with EC₅₀ values of 1.28, 1.17, and 1.68 μg mL^-1 , respectively. In addition, compound 6c₂ displayed the most potent activity against S. sclerotiorum (EC₅₀  = 3.64 μg mL^-1 ). Further in vivo fungicidal activity screening against S. sclerotiorum demonstrated that the protective and curative effects of compound 6c₂ were 98.1% and 91.3% at 25 μg mL^-1 , respectively, comparable to that of boscalid (94.4%, 89.6%). The preliminary mechanism study found that the hyphae of S. sclerotiorum treated with compound 6c₂ was abnormal with mycelial collapse and membrane permeability increase. The present findings can help to develop new fungicides for crop protection.

CONCLUSION

Novel sulfoximine derivatives containing nitroguanidine possess potential antifungal activity, and the unique structure may offer an alternative option for fungicide development in the future. © 2022 Society of Chemical Industry.

Drug repurposing strategy II: from approved drugs to agri-fungicide leads

Epidemic diseases of crops caused by fungi deeply affected the course of human history and processed a major restriction on social and economic development. However, with the enormous misuse of existing antimicrobial drugs, an increasing number of fungi have developed serious resistance to them, making the diseases caused by pathogenic fungi even more challenging to control. Drug repurposing is an attractive alternative, it requires less time and investment in the drug development process than traditional R&D strategies. In this work, we screened 600 existing commercially available drugs, some of which had previously unknown activity against pathogenic fungi. From the primary screen at a fixed concentration of 100 μg/mL, 120, 162, 167, 85, 102, and 82 drugs were found to be effective against Rhizoctonia solani, Sclerotinia sclerotiorum, Botrytis cinerea, Phytophthora capsici, Fusarium graminearum and Fusarium oxysporum, respectively. They were divided into nine groups lead compounds, including quinoline alkaloids, benzimidazoles/carbamate esters, azoles, isothiazoles, pyrimidines, pyridines, piperidines/piperazines, ionic liquids and miscellaneous group, and simple structure-activity relationship analysis was carried out. Comparison with fungicides to identify the most promising drugs or lead structures for the development of new antifungal agents in agriculture.

Expedient Discovery for Novel Antifungal Leads Inhibiting Fusarium graminearum: 3-(Phenylamino)quinazolin-4(3H)-ones Deriving from Systematic Optimizations on a Tryptanthrin Structure

The ever-increasing resistance of Fusarium graminearum has emerged as a pressing agricultural issue that could be settled by developing novel fungicides owning inimitable action mechanisms. With the aim of discovering novel antifungal leads inhibiting F. graminearum, a tryptanthrin structure was dexterously optimized to generate 30 novel quinazolin-4(3H)-one derivatives. The aforementioned optimization generated the molecule C₁₇ that owned exhilarating in vitro anti-F. graminearum effect (EC₅₀ value = 0.76 μg/mL). Whereafter, the in vivo anti-F. graminearum preventative efficacy of the molecule C₁₇ was measured to be 59.5% at 200 μg/mL, which was approximately comparable with that of carbendazim (64.9%). Furthermore, morphological observations indicated that the molecule C₁₇ could cause the hypha to become slender and dense, distort the outline of cell walls, induce an increase in liposome numbers, and cause the reduction of mitochondria numbers. The above results have emerged as an obbligato complement for developing novel antifungal leads that could effectively control Fusarium head blight.

Design, synthesis, and biological evaluation of novel berberine derivatives against phytopathogenic fungi

BACKGROUND

The abuse of chemical fungicides not only leads to toxic residues and resistance in plant pathogenic fungi, but also causes environmental pollution and side effects on in humans and animals. Based on the antifungal activities of berberine, seven different types of berberine derivatives (A1-G1) were synthesized, and their antifungal activities against six plant pathogenic fungi were evaluated (Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, Phytophthora capsici, Sclerotinia sclerotiorum, and Magnaporthe oryzae).

RESULTS

The results for antifungal activities in vitro showed that berberine derivative E1 displayed good antifungal activity against R. solani with a median effective concentration (EC₅₀ ) of 1.77 μg ml^-1 , and berberine derivatives F1 and G1 demonstrated broad-spectrum antifungal activities with EC₅₀ values ranging from 4.43 to 42.23 μg ml^-1 against six plant pathogenic fungi. Berberine derivatives (E2-E29, F2-F18, and G2-G9) were further synthesized to investigate the structure-activity relationship (SAR), and compound E20 displayed significant antifungal activity against R. solani with an EC₅₀ value of 0.065 μg ml^-1 . Preliminary mechanism studies showed that E20 could cause mycelial shrinkage, cell membrane damage, mitochondrial abnormalities and the accumulation of harmful reactive oxygen species, resulting in cell death in R. solani. Moreover, in vivo experimental results showed that the protective effect of E20 was 97.31% at 5 μg ml^-1 , which was better than that of the positive control thifluzamide (50.13% at 5 μg ml^-1 ).

CONCLUSION

Berberine derivative E20 merits further development as a new drug candidate with selective and excellent antifungal activity against R. solani. © 2022 Society of Chemical Industry.