Antifungal activity of compounds extracted from Cortex Pseudolaricis against Colletotrichum gloeosporioides

Pseudolaric acid B suppresses NSCLC progression through the ROS/AMPK/mTOR/autophagy signalling pathway

Pseudolaric acid B (PAB), an acid isolated from the roots of Pseudolarix kaempferi gorden, has shown antitumour effects through multiple mechanisms of action. The objective of this study was to investigate the anticancer effect of PAB on non-small cell lung cancer (NSCLC) and its underlying mechanism. In our experiments, we observed that PAB decreased cell viability, inhibited colony formation, induced cell cycle arrest, impeded scratch healing, and increased apoptosis in H1975 and H1650 cells. Additionally, PAB treatment enhanced the fluorescence intensity of MDC staining in NSCLC cells, upregulated the protein expression of microtubule-associated protein light chain 3 II (LC3 II), and downregulated the expression of sequestosome 1 (SQSTM1/P62). Combined treatment with PAB and chloroquine (CQ) increased the protein expression levels of LC3 II and P62 while decreasing the apoptosis of H1975 and H1650 cells. Moreover, treatment with PAB led to significant mTOR inhibition and AMPK activation. PAB combined with compound C (CC) inhibited autophagy and apoptosis. Furthermore, PAB treatment increased intracellular reactive oxygen species (ROS) levels in NSCLC cells, which correlated with the modulation of the AMPK/mTOR signalling pathway and was associated with autophagy and apoptosis. Finally, we validated the antitumour growth activity and mechanism of PAB in vivo using athymic nude mice bearing H1975 tumour cells. In conclusion, our findings suggest that PAB can induce apoptosis and autophagic cell death in NSCLC through the ROS-triggered AMPK/mTOR signalling pathway, making it a promising candidate for future NSCLC treatment.

Novel Flavonol Derivatives Containing 1,3,4-Thiadiazole as Potential Antifungal Agents: Design, Synthesis, and Biological Evaluation

In order to discover novel compounds with excellent agricultural activities, novel flavonol derivatives containing 1,3,4-thiadiazole were synthesized and evaluated for their antifungal activities. The bioassay results showed that some of the target compounds had good antifungal activities against Botrytis cinerea, Phomopsis sp. and Sclerotinia sclerotiorum in vitro. It is worth noting that the half-effective concentration (EC50) value of Y18 against B. cinerea was 2.4 μg/mL, which was obviously superior to that of azoxystrobin (21.7 μg/mL). The curative activity of Y18 at 200 μg/mL (79.9%) was better than that of azoxystrobin (59.1%), and its protective activity (90.9%) was better than that of azoxystrobin (83.9%). Morphological studies by using scanning electron microscopy and fluorescence microscopy revealed that Y18 could affect the normal growth of B. cinerea mycelium. In addition, the mechanism of action studies indicated that Y18 could affect the integrity of cell membranes by inducing the production of endogenous reactive oxygen species and the release of the malondialdehyde content, leading to membrane lipid peroxidation and the release of cell contents. The inhibitory activity of flavonol derivatives containing 1,3,4-thiadiazole on plant fungi is notable, offering significant potential for the development of new antifungal agents.

Discovery of Arylfluorosulfates as Novel Fungicidal Agents against Plant Pathogens

A series of arylfluorosulfates were synthesized as fungicide candidates through a highly efficient sulfur fluoride exchange (SuFEx) reaction. A total of 32 arylfluorosulfate derivatives with simple structures have been synthesized, and most of them exhibited fungal activities in vitro against five agricultural pathogens (Rhizoctonia solani, Botrytis cinerea, Fusarium oxysporum, Pyricularia oryzae, and Phytophthora infestans). Among the target compounds, compound 31 exhibited great antifungal activity against Rhizoctonia solani (EC50 = 1.51 μg/mL), which was comparable to commercial fungicides carbendazim and thiabendazole (EC50 = 0.53 and 0.70 μg/mL, respectively); compounds 17 and 30 exhibited antifungal activities against Pyricularia oryzae (EC50 = 1.64 and 1.73 μg/mL, respectively) comparable to carbendazim (EC50 = 1.02 μg/mL). The in vitro antifungal effect of compound 31 was also evaluated on rice plants against Rhizoctonia solani. Significant preventive and curative efficacies were observed (89.2% and 91.8%, respectively, at 200 μg/mL), exceeding that of thiabendazole. Primary study on the mechanism of action indicated that compound 31 could suppress the sclerotia formation of Rhizoctonia solani even at a very low concentration (1.00 μg/mL), destroy the cell membrane and mitochondria, trigger the release of cellular contents, produce excessive reactive oxygen species (ROS), and suppress the activity of several related enzymes. This work could bring new insights into the development of arylfluorosulfates as novel fungicides.

Pseudoamaolide P, a 1,2:3,4:9,10:9,19-tetraseco-cycloartane triterpene spiroketal lactone from seeds of Pseudolarix amabilis

A 1,2:3,4:9,10:9,19-tetraseco-cycloartane triterpene spiroketal lactone, pseudoamaolide P (1), two new labdane-type diterpenoids, pseudoamains A and B (2-3), and four known cembrane-type diterpenoids (4-7) were isolated from the seeds of Pseudolarix amabilis. The structures of these compounds were elucidated by spectroscopic analyses, including HRESIMS, 1D-, and 2D-NMR. The anti-inflammatory activities of the compounds were evaluated by suppressing the transcription of the NF-κB-dependent reporter gene in LPS-induced 293 T/NF-κB-luc cells. All compounds do not show potent activity.

Discovery of Novel Compounds for Combating Rising Severity of Plant Diseases Caused by Fungi and Viruses

In recent years, the severity of plant diseases caused by plant pathogenic fungi and viruses has been on the rise. However, there is a limited availability of pesticide chemicals in the market for effectively controlling both fungal and viral infections. To solve this problem, a series of novel pyrimidine derivatives containing a 1,3,4-oxadiazole thioether fragment were synthesized. Among them, compound 6s exhibited remarkable in vivo protection activity against tobacco mosaic virus, demonstrating the superior 50% effective concentration (EC50) value of 0.42 μM, outperforming ningnanmycin (0.60 μM). Meanwhile, compound 6s exhibited remarkable antifungal activity against Botrytis cinerea Pers. in postharvest blueberry in vitro, with an EC50 value of 0.011 μM, surpassing the inhibition rate of Pyrimethanil (0.262 μM). Additionally, compound 6s also demonstrated remarkable curative and protection activities against blueberry fruit gray mold in vivo, with control efficiencies of 54.2 and 60.4% at 200 μg/mL concentration, respectively, which were comparable to those of Pyrimethanil (49.3 and 63.9%, respectively). Scanning electron microscopy showed that the compound 6s-treated hyphae of B. cinerea Pers. in postharvest blueberry became abnormally collapsed and shriveled. Furthermore, the molecular docking simulation demonstrated that compound 6s formed hydrogen bonds with SER-17, ARG-43, and SER-39 of succinate dehydrogenase (SDH), providing a possible explanation for the mechanism of action between the target compounds and SDH. This study represents the first report on the antiviral and antifungal activities of novel pyrimidine derivatives containing a 1,3,4-oxadiazole thioether fragment.

Novel Design of Citral-Thiourea Derivatives for Enhancing Antifungal Potential against Colletotrichum gloeosporioides

Although much progress has been made in developing botanical fungicides to combat fungal diseases in crops, there remains a great need to improve the efficiency and long-term safety of these fungicides. This study proposes a novel strategy for designing citral-thiourea derivatives that feature such desirable properties. The motivation of the work herein was to enhance the antifungal activity of citral against C. gloeosprioides by exploiting the synergistic effect that arises from combining citral and thiourea compounds, thereby producing citral-thiourea derivatives that exhibit good long-term safety. The results revealed that the generated compounds e1, e3, e6, e18, and g showed remarkable antifungal activities against C. gloeosprioides, with corresponding EC50 values reaching 0.16, 1.66, 1.37, 4.76, and 4.60 mg/L, respectively, showing that the compounds significantly outperformed both the positive control kresoxim-methyl and the commercially available fungicide carbendazim. Furthermore, compound g showed stronger protective efficacy against C. gloeosprioides than carbendazim on mango fruit at 25 mg/L. Investigating the preliminary structure-activity relationship (SAR) of the compounds also revealed that the citral-thiourea derivatives exhibited higher antifungal activities against C. gloeosprioides compared to citral and thiourea compounds. This reinforcement of antifungal activity observed in the derivatives was found to be attributable to the two characteristics of low molecular size and the presence of a fluorine atom in the meta-position of the benzene ring. Beyond this, it was determined from QSAR that two molecular descriptors (the Kier-Hall index (order 3) and Tot dipole of the molecules) were negatively related to the antifungal activity of the citral-thiourea derivatives, while one other (the maximum resonance energy of a C-H bond) was positively related to their antifungal activity. More importantly, the citral-thiourea derivatives with high antifungal activities (i.e., compounds e1, e3, e6, e14, e15, e18, and g) exhibited negligible cytotoxicity to LO2 and HEK293T cell lines. The antifungal mechanism of the generated citral-thiourea derivatives was investigated by scanning electron microscopy (SEM) and relative conductivity. The derivatives were found to affect mycelial morphology and increase fungal cell membrane permeability, thereby resulting in the destruction of fungal cell membranes. These promising results provide novel insights into the study and potential application value of citral-thiourea derivatives as high-efficiency antifungal agents against C. gloeosprioides.

Suppressive effect of pseudolaric acid B on Echinococcus multilocularis involving regulation of TGF-β1 signaling in vitro and in vivo

Echinococcus multilocularis, the causative agent of alveolar echinococcosis (AE), severely threats human health and livestock farming. The first line of chemotherapeutic drug for AE is albendazole, which limits rapid extension of E. multilocularis metacestodes, but is rarely curative for AE, with severe side effects in long-term use, thus development of new anti-echinococcal drugs is mandated. Pseudolaric acid B (PAB) has long been used to treat fungal-infected dermatosis, and exerted anti-tumor, -fertility, -angiogenesis, -tubulin and antiparasitic activity. However, the effect of PAB against Echinococcus spp. remains unclear. The present study is to understand the effect of PAB against E. multilocularis in vitro and in vivo, and identify potential anti-echinococcal mechanism, as well as its toxicity. After exposure to PAB at 20 μg/ml, significant reduction of the survival rate and substantial ultrastructural destructions in E. multilocularis protoscoleces were observed in vitro. Furthermore, the wet weight of E. multilocularis cysts in the infected mice was significantly decreased after treatment with PAB (40, 20 or 10 mg/kg) for 12 weeks. Meanwhile, significant increase of both protein and mRNA expression of transforming growth factor beta 1 (TGF-β1) was detected in the serum and liver of the infected mice, whereas PAB administration lowered its expression significantly. The toxicity tests demonstrated that PAB displayed lower cytotoxicity to human liver and kidney cells (HL-7702 and HK-2 cell) with IC₅₀ = 25.29 and 42.94 μg/ml than albendazole with IC₅₀ = 3.71 and 21.22 μg/ml in vitro, and caused lower hepatoxicity and nephrotoxicity in mice than ABZ. Our findings indicated that PAB possesses potent anti-echinococcal effect, with lower toxicity than albendazole, implying a potential chemotherapeutic agent for AE. Additionally, the present study demonstrated that the suppressive effect of PAB on the parasite may involve down-regulation of TGF-β1 signaling.

Identification and Structure–Activity Relationship of Recovered Phenolics with Antioxidant and Antihyperglycemic Potential from Sugarcane Molasses Vinasse

Sugarcane molasses vinasse is the residue of the fermentation of molasses and the water and soil environmental pollutants from distilleries. However, its recycling value has been neglected. The chemical analysis of the molasses vinasse led to the isolation of a new benzoyl chloride called 2,3,4-trihydroxy-5-methoxy benzoyl chloride, as well as thirteen known compounds, including six benzoic acids. The structure of the new benzoyl chloride was elucidated on the basis of extensive spectroscopic analysis. The antioxidant activity of all isolated compounds was measured using the ORAC assay. Moreover, we compared the cellular antioxidant activity (CAA) and inhibitory activity against α-amylase and α-glucosidase for structure–activity analysis. The results showed that only vanillic acid had CAA (8.64 μmol QE/100 μmol in the no PBS wash protocol and 6.18 μmol QE/100 μmol in the PBS wash protocol), although other benzoic acid derivatives had high ORAC values ranging between 1879.9 and 32,648.1 μmol TE/g. Additional methoxy groups at the ortho-positions of the p-hydroxy group of benzoic acids enhanced the inhibition of α-glucosidase but reduced the ORAC activity unless at the para-position. This work indicated that phenolics, especially phenolic acids in the sugarcane molasses vinasse, possessed potential antioxidant and antihyperglycemic activity, which improved the utilization rate of resources and reduced the discharge of pollutants.

New 7-Chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-iums as Promising Fungicide Candidates: Design, Synthesis, and Bioactivity

As our further research, a series of new 7-chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-iums were designed and synthesized. Twelve compounds were found with excellent inhibition activity in vitro on three to five out of six phytopathogenic fungi, superior to standard drugs thiabendazole and/or azoxystrobin. Especially, 18 displayed the highest activity against three out of the fungi and the highest comprehensive activity for all of the fungi. The test in vivo revealed that 18 at 50 μg/mL was able to completely control Physalospora piricola infections in apples over 8 days. Scanning/transmission electron microscopic observations found that 18 could damage the hyphal integrity and cell membrane structure of P. piricola. The safety evaluation showed that 18 had no effect on the germination rate of cowpea seed at ≤200 μg/mL. The SAR revealed that the combination of 7-Cl and 2'- or 4'-alkyl is conducive to improvement of the activity. Thus, 7-chloro-9-methyl-2-phenyl-3,4-dihydro-β-carbolin-2-ium is a promising antifungal lead scaffold.

Design, Synthesis, and Antifungal Activity of Novel Chalcone Derivatives Containing a Piperazine Fragment

In an attempt to find the biorational pesticides, 20 novel chalcone derivatives containing a piperazine fragment were designed and synthesized. Their fungicidal activities and preliminarily action mechanism against Rhizoctonia solani were evaluated. Strikingly, the biological activity of compound D2 was obtained by optimizing the structure of the system. Subsequently, the practical value of compound D2 was ascertained by the relative surveys on in vivo anti-R. solani and anti-Colletotrichum gloeosporioides. The results revealed by scanning electron microscopy demonstrated that compound D2 could induce irregular and shrivelled growth of mycelium and rupture of the mycelium surface. This study indicates that chalcone derivatives containing a piperazine skeleton had better inhibitory effect on plant fungi, providing further complementary research on new pesticides.

Metabolite profiles of brown planthopper-susceptible and resistant rice (Oryza sativa) varieties associated with infestation and mechanical stimuli

Understanding brown planthopper (BPH) resistance mechanism will expedite selective breeding of better BPH resistant lines of rice (Oryza sativa). Metabolic responses during BPH infestation derived from wound stress imposed by insect feeding, comparing with mechanical piercing will provide an insight into resistance mechanism in rice. Therefore, this study aimed to compare the metabolic responses of needle piercing treatment and BPH feeding treatment in BPH-susceptible (KD) and BPH-resistant (RH) varieties at four different time points (0, 6, 24 and 96 h) using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Phenotypes of RH were not different among the treatments, whereas KD exhibited hopperburn symptom at 96 h post-BPH infestation. Principal component and cluster analyses revealed that metabolite profiles between KD and RH were different in response to both insect and mechanical stimuli. Metabolite profiles of RH under BPH and mechanical treatments at 24 and 96 h were different from the untreated, whereas metabolite profiles of KD after BPH infestation at 24 and 96 h were distinct from needle piercing and no treatment, suggesting that the resistant variety has an ability to adapt and defend both mechanical and insect stimuli. Metabolomics result showed that BPH infestation perturbed purine salvage biosynthesis (e.g., inosine, hypoxanthine) in both varieties, amino acid biosynthesis (e.g., phenylalanine, tryptophan) in KD, while the infestation perturbed lysine metabolism (pipecolic acid) and phenylpropanoid pathway (2-anisic acid) only in RH. BPH and mechanical stimuli perturbed phenylamide only in RH, but not in KD. These findings revealed that different rice varieties utilize different metabolites in response to insect and mechanical stimuli, resulting in different degrees of resistance.

Design, Synthesis and Antifungal/Nematicidal Activity of Novel 1,2,4-Oxadiazole Derivatives Containing Amide Fragments

Plant diseases that are caused by fungi and nematodes have become increasingly serious in recent years. However, there are few pesticide chemicals that can be used for the joint control of fungi and nematodes on the market. To solve this problem, a series of novel 1,2,4-oxadiazole derivatives containing amide fragments were designed and synthesized. Additionally, the bioassays revealed that the compound F15 demonstrated excellent antifungal activity against Sclerotinia sclerotiorum (S. sclerotiorum) in vitro, and the EC₅₀ value of that was 2.9 μg/mL, which is comparable with commonly used fungicides thifluzamide and fluopyram. Meanwhile, F15 demonstrated excellent curative and protective activity against S. sclerotiorum-infected cole in vivo. The scanning electron microscopy results showed that the hyphae of S. sclerotiorum treated with F15 became abnormally collapsed and shriveled, thereby inhibiting the growth of the hyphae. Furthermore, F15 exhibited favorable inhibition against the succinate dehydrogenase (SDH) of the S. sclerotiorum (IC₅₀ = 12.5 μg/mL), and the combination mode and binding ability between compound F15 and SDH were confirmed by molecular docking. In addition, compound F11 showed excellent nematicidal activity against Meloidogyne incognita at 200 μg/mL, the corrected mortality rate was 93.2%, which is higher than that of tioxazafen.

Synthesis of novel antibacterial and antifungal quinoxaline derivatives

A series of quinoxaline derivatives were designed, synthesized and evaluated as antimicrobial agents against plant pathogenic bacteria and fungi. Some of these compounds exhibited significant antibacterial and antifungal activities in vitro. Compound 5k displayed good antibacterial activity against Acidovorax citrulli (Ac). Compounds 5j and 5t exhibited the most potent anti-RS (Rhizoctonia solani) activity, with the corresponding EC₅₀ values of 8.54 and 12.01 μg mL⁻¹, respectively, which are superior to that of the commercial azoxystrobin (26.17 μg mL⁻¹). Further, the scanning electron microscopy results proved that compound 5j had certain effects on the cell morphology of RS. Moreover, an in vivo bioassay also demonstrated that the anti-RS activity of compound 5j could effectively control rice sheath blight. These results indicate that quinoxaline derivatives could be promising agricultural bactericides and fungicides.

Structure of some commercial agents.

Antifungal Exploration of Quinoline Derivatives against Phytopathogenic Fungi Inspired by Quinine Alkaloids

Enlightened from our previous work of structural simplification of quinine and innovative application of natural products against phytopathogenic fungi, lead structure 2,8-bis(trifluoromethyl)-4-quinolinol (3) was selected to be a candidate and its diversified design, synthesis, and antifungal evaluation were carried out. All of the synthesized compounds Aa1-Db1 were evaluated for their antifungal activity against four agriculturally important fungi, Botrytis cinerea, Fusarium graminearum, Rhizoctonia solani, and Sclerotinia sclerotiorum. Results showed that compounds Ac3, Ac4, Ac7, Ac9, Ac12, Bb1, Bb10, Bb11, Bb13, Cb1. and Cb3 exhibited a good antifungal effect, especially Ac12 had the most potent activity with EC₅₀ values of 0.52 and 0.50 μg/mL against S. sclerotiorum and B. cinerea, respectively, which were more potent than those of the lead compound 3 (1.72 and 1.89 μg/mL) and commercial fungicides azoxystrobin (both >30 μg/mL) and 8-hydroxyquinoline (2.12 and 5.28 μg/mL). Moreover, compound Ac12 displayed excellent in vivo antifungal activity, which was comparable in activity to the commercial fungicide boscalid. The preliminary mechanism revealed that compound Ac12 might cause an abnormal morphology of cell membranes, an increase in membrane permeability, and release of cellular contents. These results indicated that compound Ac12 displayed superior in vitro and in vivo fungicidal activities and could be a potential fungicidal candidate against plant fungal diseases.

Design, Synthesis, and Structure-Activity Relationship Studies of Magnolol Derivatives as Antifungal Agents

Plant pathogenic fungi seriously affect agricultural production and are difficult to control. The discovery of new leads based on natural products is an important way to innovate fungicides. In this study, 30 natural-product-based magnolol derivatives were synthesized and characterized on the basis of NMR and mass spectroscopy. Bioactivity tests on phytopathogenic fungi (Rhizoctonia solani, Fusarium graminearum, Botrytis cinerea, and Sclerotinia sclerotiorum) in vitro of these compounds were performed systematically. The results showed that 11 compounds were active against four kinds of phytopathogenic fungi with EC₅₀ values in the range of 1.40-20.00 μg/mL, especially compound L5 that exhibited excellent antifungal properties against B. cinerea with an EC₅₀ value of 2.86 μg/mL, approximately 2.8-fold more potent than magnolol (EC₅₀ = 8.13 μg/mL). Moreover, compound L6 showed the highest antifungal activity against F. graminearum and Rhophitulus solani with EC₅₀ values of 4.39 and 1.40 μg/mL, respectively, and compound L7 showed good antifungal activity against S. sclerotiorum. Then, an in vivo experiment of compound L5 against B. cinerea was further investigated in vivo using infected tomatoes (curative effect, 50/200 and 36%/100 μg/mL). The physiological and biochemical studies illustrated that the primary action mechanism of compound L5 on B. cinerea might change the mycelium morphology, increase cell membrane permeability, and destroy the function of mitochondria. Furthermore, structure-activity relationship (SAR) studies revealed that hydroxyl groups play a key role in antifungal activity. To sum up, this study provides a reference for understanding the application of magnolol-based antifungal agents in crop protection.

Fungicidal Activity and Mechanism of Action of Glabridin from Glycyrrhiza glabra L

Glycyrrhiza glabra (Licorice) belongs to the Fabaceae family and its extracts have exhibited significant fungicidal activity against phytopathogenic fungi, which has mainly been attributed to the presence of phenolic compounds such as flavonoids, isoflavonoids and chalcones. In this study, a series of licorice flavonoids, isoflavonoids and chalcones were evaluated for their fungicidal activity against phytopathogenic fungi. Among them, glabridin exhibited significant fungicidal activity against ten kinds of phytopathogenic fungi. Notably, glabridin displayed the most active against Sclerotinia sclerotiorum with an EC₅₀ value of 6.78 µg/mL and was 8-fold more potent than azoxystrobin (EC₅₀, 57.39 µg/mL). Moreover, the in vivo bioassay also demonstrated that glabridin could effectively control S. sclerotiorum. The mechanism studies revealed that glabridin could induce reactive oxygen species accumulation, the loss of mitochondrial membrane potential and cell membrane destruction through effecting the expression levels of phosphatidylserine decarboxylase that exerted its fungicidal activity. These findings indicated that glabridin exhibited pronounced fungicidal activities against S. sclerotiorum and could be served as a potential fungicidal candidate.

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 of Novel Pesticidal N,N'-Disubstituted Sulfamide Derivatives Using Sulfur(VI) Fluorine Exchange Click Reaction

Sulfur(VI) fluorine exchange click reaction was applied to the highly efficient synthesis of new N,N'-disubstituted sulfamide (R¹NH-SO₂-NHR²) derivatives as pesticide candidates. Bioassays were conducted to evaluate both insecticidal and fungicidal activities of the target compounds. Preliminary results showed that the target molecules exhibited good bioactivities. In particular, insecticidal activities of compounds D25 and D21 against Plutella xylostella (LC₅₀ = 2.42 and 3.87 μg·mL^-1) were superior or adequate to that of commercial insecticide indoxacarb (LC₅₀ = 3.99 μg·mL^-1). Moreover, some compounds could also exhibit satisfactory fungicidal activity toward plant pathogens Pyricularia grisea, Botrytis cinerea, and Thanatephorus cucumeris. This work could bring new insights into the application of heterocyclic N,N'-disubstituted sulfamides as novel pesticides.

Design, Synthesis, and Antifungal Evaluation of Cryptolepine Derivatives against Phytopathogenic Fungi

Inspired by the widely antiphytopathogenic application of diversified derivatives from natural sources, cryptolepine and its derivatives were subsequently designed, synthesized, and evaluated for their antifungal activities against four agriculturally important fungi Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Sclerotinia sclerotiorum. The results obtained from in vitro assay indicated that compounds a1-a24 showed great fungicidal property against B. cinerea (EC₅₀ < 4 μg/mL); especially, a3 presented significantly prominent inhibitory activity with an EC₅₀ of 0.027 μg/mL. In the pursuit of further expanding the antifungal spectrum of cryptolepine, ring-opened compound f1 produced better activity with an EC₅₀ of 3.632 μg/mL against R. solani and an EC₅₀ of 5.599 μg/mL against F. graminearum. Furthermore, a3 was selected to be a candidate to investigate its preliminary antifungal mechanism to B. cinerea, revealing that not only spore germination was effectively inhibited and the normal physiological structure of mycelium was severely undermined but also detrimental reactive oxygen was obviously accumulated and the normal function of the nucleus was fairly disordered. Besides, in vivo curative experiment against B. cinerea found that the therapeutic action of a3 was comparable to that of the positive control azoxystrobin. These results suggested that compound a3 could be regarded as a novel and promising agent against B. cinerea for its valuable potency.

Improvement of Postharvest Anthracnose Resistance in Mango Fruit by Nitric Oxide and the Possible Mechanisms Involved

The anthracnose rot of postharvest mango fruit is a devastating fungal disease often resulting in tremendous quality deterioration and postharvest losses. Nitric oxide (NO), as an important signaling molecule, is involved in the responses to postharvest fruit diseases. In the present study, the effectiveness of NO donor sodium nitroprusside (SNP) to prevent anthracnose of "Tainong" mango fruit caused by Colletotrichum gloeosporioides was evaluated through in vivo and in vitro tests. Results from in vivo test showed that SNP treatment effectively inhibited the lesion diameter and disease incidence on inoculated mango fruit during storage. SNP treatment could regulate hydrogen peroxide levels by reinforcing the activities of catalase, peroxidase, superoxide dismutase, and ascorbate peroxidase. Furthermore, SNP elevated the accumulation of lignin, total phenolics, anthocyanin, and flavonoids and the activities of chitinase and β-1,3-glucanase. In addition, in vitro tests indicated that SNP markedly suppressed mycelial growth and spore germination of C. gloeosporioides through damaging plasma membrane integrity and increasing the leakage of soluble sugar and protein. Our results suggested that SNP could suppress anthracnose decay in postharvest mango fruit, possibly by directly suppressing pathogen growth and indirectly triggering host defense responses.

Antifungal Activity of Alpha-Mangostin against Colletotrichum gloeosporioides In Vitro and In Vivo

We investigated alpha-mangostin (α-mangostin, α-MG), a xanthone natural product extracted from the pericarp of mangosteen (Garcinia mangostana), for its antifungal activities and possible mechanism against Colletotrichum gloeosporioides, which causes mango anthracnose. The results demonstrated that α-MG had a relatively high in vitro inhibitory activity against C. gloeosporioides among 20 plant pathogenic fungi. The median effective concentration (EC₅₀) values of α-MG against mycelial growth were nearly 10 times higher than those of spore germination inhibition for both strains of C. gloeosporioides, the carbendazim-sensitive (CBD-s) and carbendazim-resistant (CBD-r). The results suggested that α-MG exhibited a better inhibitory effect on spore germination than on the mycelial growth of C. gloeosporioides. Further investigation indicated that the protective effect could be superior to the therapeutic effect for mango leaves for scab development. The morphological observations of mycelium showed that α-MG caused the accumulation of dense bodies. Ultrastructural observation further revealed that α-MG caused a decrease in the quantity and shape of the swelling of mitochondria in the mycelium cells of C. gloeosporioides. In addition, bioassays disclosed that the inhibitory activity of α-MG on spore germination was reduced by adding exogenous adenosine triphosphate (ATP). These results suggested that the mode of action of α-MG could be involved in the destruction of mitochondrial energy metabolism. The current study supports α-MG as a natural antifungal agent in crop protection.

Novel Bithiophene Dimers from Echinops latifolius as Potential Antifungal and Nematicidal Agents

Three novel dimeric bithiophenes, echinbithiophenedimers A-C (1-3), along with two known thiophenes, 4 and 5, were obtained from Echinops latifolius, and their structures were identified through extensive spectroscopic analysis and electronic circular dichroism calculations. Compounds 1-3 possessed new carbon skeletons; they are dimeric bithiophenes with 1 and 2 featuring an unprecedented 1,3-dioxolane ring system and 3 featuring an unusual 1,4-dioxane ring. These compounds are the first examples of bithiophene dimers furnished by different cyclic diethers. Dimeric bithiophenes 1-3 had good antifungal activities against five phytopathogenic fungi, and compound 3 showed excellent activity against Alternaria alternate and Pyricularia oryzae, with a minimal inhibitory concentration value of 8 μg/mL, which was close to or higher than that of carbendazim. Moreover, its effect on the mycelial morphology was observed by scanning electron microscopy. Compounds 1-3, which were demonstrated to be nonphototoxic thiophenes, exhibited better nematicidal activity than the commercial nematicide ethoprophos against Meloidogyne incognita. This study revealed that dimeric bithiophenes containing 1,3-dioxolane or 1,4-dioxane rings could be used as novel antifungal and nematicidal agents for controlling plant fungal and nematode pathogens.

Synergistic Effect of Pseudolaric Acid B with Fluconazole Against Resistant Isolates and Biofilm of Candida tropicalis

Purpose

Candida tropicalis (C. tropicalis) has emerged as an important fungal pathogen due to its increasing resistance to conventional antifungal agents, especially fluconazole (FLC). Pseudolaric acid B (PAB), a herbal-originated diterpene acid from Pseudolarix kaempferi Gordon, has been reported to possess inhibitory activity against fungus. The present study aims to investigate the antifungal effect of PAB alone and in combination with FLC on planktonic and biofilm cells of C. tropicalis.

Methods

The antifungal activity of PAB against planktonic isolates was evaluated alone and in combination with FLC using the chequerboard microdilution method and growth curve assay. The anti-biofilm effects were quantified by tetrazolium (XTT) reduction assay, which were further confirmed by scanning electron microscopy (SEM) and fluorescent microscope to observe morphological changes of biofilm treated with PAB and FLC.

Results

It was revealed that PAB alone exhibited similar inhibitory activity against FLC-resistant and FLC-susceptible strains with median MIC ranging from 8 to 16 µg/mL. When administered in combination, synergism was observed in all (13/13) FLC-resistant and (2/9) FLC-susceptible strains with FICI ranging from 0.070 to 0.375. Moreover, the concomitant use of PAB and FLC exhibited a strong dose-dependent synergistic inhibitory effect on the early and mature biofilm, eliminating more than 80% biofilm formation. SEM found that PAB, different from azoles, could significantly inhibit spore germination and destroy the cell integrity causing cell deformation, swelling, collapse and outer membrane perforation.

Conclusion

PAB was highly active against FLC-resistant isolates and biofilm of C. tropicalis, particularly when combined with FLC. These findings suggest that PAB may have potential as a novel antifungal agent with different targets from azole drugs.

Antifungal activity of water-soluble products obtained following the liquefaction of cornstalk with sub-critical water

Cornstalks are the leftover leaves and stems in a field after corn harvest. They are a potential biomass resource but are underutilized in agricultural production systems. To examine the chemical components in cornstalks and their corresponding functions, blocky cornstalks were treated in water at temperatures of 190, 210, 230, 250, and 270 °C in a high-pressure reactor. Water-soluble products (WSPs) were extracted from these treatments, and their chemical compositions were analyzed using gas chromatography-mass spectrometry (GC-MS), and their antifungal activities were determined using a bioassay. It was found that WSPs contained 28.7-40.1% phenols, 27.9-36.6% ketones, 0-2.6% alcohols, 4.9-10.1% esters, 5.4-7.8% organic acids, 1.3-12% aldehydes, and 5.5-18.4% of other organic compounds such as nitrogen- and sulfur-containing compounds, furan compounds, and benzene compounds. The inhibition the growth of the plant pathogen Fusarium oxysporum by WSPs was affected by temperature. WSP-270 (obtained at 270 °C) exhibited the best growth-inhibition efficacy. Under a biomicroscope, WSP-270-treated F. oxysporum showed a deformed and swollen hypha, and an increased number of bifurcations, as well as an expansion of growing apexes of new bifurcations. Therefore, the antifungal activity of WSPs could be used to manage soilborne plant pathogens.

Antifungal mechanism of bacillomycin D from Bacillus velezensis HN-2 against Colletotrichum gloeosporioides Penz

Anthracnose is a leaf spot, blossom blight, or fruit rot disease caused by Colletotrichum gloeosporioides (Penz.). It is the most prevalent disease in mango-growing countries worldwide. Lipopeptides, such as those in the iturin family, account for the majority of antifungal secondary metabolites in Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus velezensis, and includes bacillomycin D. Thus far, the mechanism of bacillomycin D's activity has not been clear. In this study, bacillomycin D was isolated from B. velezensis HN-2, which strongly inhibits C. gloeosporioides (Penz.). The median inhibitory concentration of bacillomycin D was 2.162 μg/mL, causing deformation and damage to C. gloeosporioides (Penz.). Bacillomycin D showed more potent activity against C. gloeosporioides (Penz.) than two common fungicides prochloraz and mancozeb. Scanning and transmission electron microscopy revealed that bacillomycin D could injure the cell wall and cell membrane of the hyphae and spores of C. gloeosporioides (Penz.), and the cytoplasm and organelles inside the cell were exuded and formed empty holes. This research clarifies the mechanism underlying bacillomycin D antifungal activity and reveals its high potential as a biopesticide to control phytopathogens.

Anti-phytopathogenic activity and the possible mechanisms of action of isoquinoline alkaloid sanguinarine

Isoquinoline alkaloids possess broad pharmacological activities. In this study, the antifungal activity of twelve isoquinoline alkaloids, including berberine (1), jatrorrhizine (2), coptisine (3), corydaline (4), tetrahydroberberine (5), chelidonine (6), dihydrosanguinarine (7), chelerythrine (8), sanguinarine (9), palmatine (10), tetrahydropalmatine (11) and columbamine (12) were evaluated against eight plant pathogenic fungi in vitro. All the tested compounds showed varying degrees of inhibition against the eight tested plant fungi. Among them, sanguinarine exhibited high antifungal activity (EC₅₀ ranging from 6.96-59.36 μg/mL). It displayed the best inhibitory activity against Magnaporthe oryzae (EC₅₀ = 6.96 μg/mL), compared with azoxystrobin (EC₅₀ = 12.04 μg/mL), and significantly suppressed spore germination of M. oryzae with the inhibition rate reaching 100% (50 μg/mL). The optical microscopy and scanning electron microscopy observations revealed that after treating M. oryzae mycelia with sanguinarine at 10 μg/mL, the mycelia appeared curved, collapsed and the cell membrane integrity was eventually damaged. Furthermore, the reactive oxygen species production, mitochondrial membrane potential and nuclear morphometry of mycelia had been changed, and the membrane function and cell proliferation of mycelia were destroyed. These results will enrich our insights into action mechanisms of antifungal activity of sanguinarine against M. oryzae.

Differences in the Characteristics and Pathogenicity of Colletotrichum camelliae and C. fructicola Isolated From the Tea Plant [Camellia sinensis (L.) O. Kuntze]

Colletotrichum, the causative agent of anthracnose, is an important pathogen that invades the tea plant (Camellia sinensis). In this study, 38 isolates were obtained from the diseased leaves of tea plants collected in different areas of Zhejiang Province, China. A combination of multigene (ITS, ACT, GAPDH, TUB2, CAL, and GS) and morphology analyses showed that the 38 strains belonged to two different species, namely, C. camelliae (CC), and C. fructicola (CF). Pathogenicity tests revealed that CC was more invasive than CF. In vitro inoculation experiments demonstrated that CC formed acervuli at 72 hpi and developed appressoria on wound edges, but CF did not develop these structures. Under treatment with catechins and caffeine, the growth inhibition rates of CF were remarkably higher than those of CC, indicating that the nonpathogenic species CF was more vulnerable to catechins and caffeine. Growth condition testing indicated that CF grew at a wide temperature range of 15-35°C and that the optimum temperature for CC growth was 25°C. Growth of both CC and CF did not differ between acidic and weakly alkaline environments (pH 5-8), but the growth of CC was significantly reduced at pH values of 9 and 10. Furthermore, the PacC/RIM101 gene, which associated with pathogenicity, was identified from CC and CF genomes, and its expression was suppressed in the hyphae of both species under pH value of 5 and 10, and much lower expression level was detected in CC than that in CF at pH 6. These results indicated that temperature has more important effect than pH for the growth of two Colletotrichum species. In conclusion, the inhibition by secondary metabolite is an important reason why the pathogenicity by CC and CF are different to tea plant, although the environmental factors including pH and temperature effect the growth of two Colletotrichum species.

Facile Three-Component Synthesis, Insecticidal and Antifungal Evaluation of Novel Dihydropyridine Derivatives

In an attempt to find the neonicotinoid insecticides, twenty novel dihydropyridine derivatives were designed, "green" synthesized via one pot facile three-component reaction and evaluated for their bioactivities against Tetranychus cinnabarinus, Myzus persicae, Brevicoryne brassicae, Fusarium oxysporum f. sp. vasinfectum, Magnaporthe oryzae, Sclerotinia sclerotiorum and Botrytis cinereal. All of the tested compounds showed potent insecticidal activity, and some were much better in comparison with imidacloprid (IMI). Especially, compounds 3d (LC₅₀: 0.011 mM) and 5c (LC₅₀: 0.025 mM) were 12.2- and 5.4-fold more active than IMI (LC₅₀: 0.135 mM) against T. cinnabarinus, respectively. Moreover, out of all the derivatives, compound 3d (LC₅₀: 0.0015 mM) exhibited the strongest insecticidal activity against B. brassicae and compound 3i (LC₅₀: 0.0007 mM) displayed the strongest insecticidal activity against M. persicae. Surprisingly, when the concentration of compound 4 was 50 mg/L, the inhibition rate against F. oxysporum and S. sclerotiorum reached 45.00% and 65.83%, respectively. The present work indicated that novel dihydropyridine derivatives could be used as potential lead compounds for developing neonicotinoid insecticides and agricultural fungicides.

Effect of pseudolaric acid B on biochemical and physiologic characteristics in Colletotrichum gloeosporioides

In our previous study on natural products with fungicidal activity, pseudolaric acid B (PAB) isolated from Pseudolarix amabilis was examined to inhibit significantly mango anthracnose (Colletotrichum gloeosporioides) in vivo and in vitro. In the current study, sensitivity of 17 plant pathogenic fungi to PAB was determined. Mycelial growth rate results showed that PAB possessed strong antifungal activities to eleven fungi with median effective concentration (EC₅₀) values ranging from 0.087 to 1.927μg/mL. EC₅₀ of PAB against spore germination was greater than that of mycelium growth inhibition, which suggest that PAB could execute antifungal activity through mycelial growth inhibition. Further action mechanism of PAB against C. gloeosporioides was investigated, in which PAB treatment inhibited mycelia dry weight, decreased the mycelia reducing sugar and soluble protein. Furthermore, PAB induced an increase in membrane permeability, inhibited the biosynthesis of ergosterol, caused the extreme alteration in ultrastructure as indicated by the thickened cell wall and increased vesicles. These results will increase our understanding of action mechanism of PAB against plant pathogenic fungi.

Evaluating the Potential Value of Natural Product Cuminic Acid against Plant Pathogenic Fungi in Cucumber

Fusarium wilt and anthracnose are two major diseases which limit the yield and quality of cucumber worldwide. Cuminic acid was extracted from the seed of Cuminum cyminum L. The mean EC50 values of cuminic acid for inhibiting mycelial growth and zoospore germination of five Fusarium oxysporum f. sp. cucumerinum strains were 25.66 ± 3.02 μg/mL and 15.99 ± 2.19 μg/mL, and of four Colletotrichum lagenarium (Pass.) Ellis and Halsted strains were 29.53 ± 3.18 μg/mL and 18.41 ± 2.78 μg/mL, respectively. In greenhouse experiments, cuminic acid at 2000 μg/mL exhibited 70.77% protective and 62.63% curative efficacies against F. oxysporum, and 65.43% protective and 55.46% curative efficacies against C. lagenarium. Moreover, the translocation behavior of cuminic acid, determined by high performance liquid chromatography (HPLC), showed that it could be readily absorbed and transported upward and downward in cucumber. Importantly, superoxide dismutase (SOD) and pyphenol oxidase (PPO) activities of cucumber leaves treated with cuminic acid increased significantly. All results indicated that cuminic acid showed antifungal activity, and could be used as a botanical fungicide in disease management. This study encourages further investigation on the mechanism of action of cuminic acid and the development of alternative antifungal drugs.

Stilbene Derivatives from Photorhabdus temperata SN259 and Their Antifungal Activities against Phytopathogenic Fungi

Chemical investigation of an insect pathogenic enterobacterium, Photorhabdus temperata SN259, led to the isolation and identification of seven metabolites, which include three new compounds, 3-hydroxy-2-isopropyl-5-phenethylphenyl carbamate, 1, 2-(1-hydroxypropan-2-yl)-5-[2-phenylethyl]benzene-1,3-diol, 2, 2-(1-hydroxypropan-2-yl)-5-[(E)-2-phenylethenyl]benzene-1,3-diol, 3, and four known metabolites (4-7). Their structures were elucidated on the basis of MS and NMR data and by comparison with those reported previously. The activities of compounds 1-7 were evaluated against four phytopathogenic fungi (Pythium aphanidermatum, Rhizoctonia solani Kuhn, Exserohilum turcicum, and Fusarium oxysporum). In an agar medium assay, compounds 1 and 7 showed strong inhibition against P.  aphanidermatum with EC₅₀ values of 2.8 and 2.7 μg/mL, respectively. By comparing the structure of compounds 1-7, we deduced that the acylamino group in compound 1 and the isopropyl group in compound 7 contribute to the inhibitory activity.

Metabolic Changes of Caffeine in Tea Plant (Camellia sinensis (L.) O. Kuntze) as Defense Response to Colletotrichum fructicola

Tea plant (Camellia sinensis) is one of the most economically valuable crops in the world. Anthracnose can affect the growth of leaves and cause serious yield losses of tea. Tea plants are rich in secondary metabolites; however, their roles in resistance to anthracnose are unclear. Herein we compared the contents of total phenolics, catechins, and caffeine in two cultivars with different resistances to anthracnose during Colletotrichum fructicola infection. (-)-Epigallocatechin-3-gallate (EGCG), (+)-catechin (C), caffeine, and critical regulatory genes were induced in C. fructicola-resistant tissues. In vitro antifungal tests showed that caffeine more strongly inhibited mycelial growth than tea polyphenols and catechins. Both electron microscopy and bioactivity analysis results showed that caffeine can affect mycelial cell walls and plasma membranes. Through promoter sequences analysis, a number of stress response-related cis-acting elements were identified in S-adenosylmethionine synthetase and tea caffeine synthase. These results demonstrated that (-)-EGCG, (+)-C, and caffeine may be involved in the resistance of tea plants to anthracnose.