Inhibition of melanoma cell proliferation by strobilurins isolated from mushrooms and their synthetic analogues.

Strobilurins A and X, isolated from Mucidula venosolamellata culture extracts, demonstrated potent inhibition of human melanoma G-361 cell proliferation. Strobilurin X exhibited milder inhibitory effects on human fibroblast cells (NB1RGB) compared to strobilurin A. Additional strobilurin-related compounds were isolated from the other mushroom species. Oudemansins A and B displayed weaker activities on G-361 cells than strobilurins A and B, respectively, emphasizing the importance of a conjugated double-bond structure. Among isolated compounds, strobilurin G showed the lowest IC50 value for G-361 cells. Additional strobilurins bearing various substituents on the benzene ring were synthesized. Synthetic intermediates lacking the methyl ß-methoxyacrylate group and a strobilurin analogue bearing modified ß-methoxyacrylate moiety showed almost no inhibitory activity against G-361 cells. The introduction of long or bulky substituents at the 4' position of the benzene ring of strobilurins enhanced the activity and selectivity, suggesting differential recognition of the benzene ring by G-361 and NB1RGB cells.

Efficient synthesis of carbon-14 labeled metabolites of the strobilurin fungicide mandestrobin using biomimetic iron-porphyrin catalyzed oxidation.

Biomimetic oxidation using synthetic iron-porphyrin (F20 TPPFeCl) as a catalyst eliminated a xylene moiety of the fungicide mandestrobin, uniformly labeled with carbon-14 at the benzyl ring, to produce the corresponding radiolabeled metabolite 1. This reaction mechanism was investigated by identifying chemical structures of intermediate 5 and p-xyloquinone derivatives 6 and 7, as by-products. Optimization of reaction factors based on the mechanism improved the yield of 1 from mandestrobin up to 87%. Finally, various carbon-14 labeled metabolites of mandestrobin were prepared from 1.

Bagging and non-bagging treatment on the dissipation and residue of four mixed application pesticides on banana fruit.

BACKGROUND: Bananas are vulnerable to disease and insect pests after producing fruit. In order to increase the yield and produce high-quality fruit, the insecticides and fungicides are mixed and applied 2-3 times on banana, then the fruit is bagged. Buprofezin, imidacloprid, difenoconazole, and pyraclostrobin are widely used on banana. However, there is a lack of research on the effect of fruit bagging on pesticide dissipation and residues on bananas. RESULTS: A versatile liquid chromatography-tandem mass spectrometry method with modified QuEChERS sample preparation has been developed for the determination of buprofezin, imidacloprid, difenoconazole, and pyraclostrobin in bananas. The recovery of four pesticides was satisfactory (74.96-98.63%) with reasonable relative standard deviation (≤ 8.78%). In Hainan and Guangzhou, the half-lives of the four pesticides were 4.68-13.9 and 5.63-20.4 days in non-bagged and bagged bananas, respectively. The significance analysis of the half-lives in the two sites showed that the dissipation rates of the three pesticides (imidacloprid, difenoconazole, pyraclostrobin) on whole bananas were significantly decreased by the effect of bagging (P < 0.05). However, there was no significant difference in the degradation of half-life of buprofezin under bagging and without bagging (P > 0.05). CONCLUSION: The high vapor pressure and the non-systemic property cause buprofezin to evaporate and dissipate the fastest among the four studied pesticides. The ultimate residues of four pesticides in bananas are lower than the maximum residue limits in China after three times of mixed applications under bagging or non-bagging. The results provide scientific data for evaluating the safety of four pesticides in banana bagging. © 2020 Society of Chemical Industry.

Hazard assessment using an in-silico toxicity assessment of the transformation products of boscalid, pyraclostrobin, fenbuconazole and glyphosate generated by exposure to an advanced oxidative process.

Agricultural pesticide use is ongoing and consumer concern regarding the safety of pesticide residues on produce has generated interest in techniques that can safely reduce residues post-harvest. Recently an advanced oxidative process has shown promise in substantial residue reduction on the surface of produce. Given the potential for oxidative transformation of pesticides to generate transformation products with greater toxicity than the parent residue, take for example the oxon products of the organophosphorus insecticides, it is important to consider what transformation products are generated by pesticide exposure to an oxidative process and their potential toxicity. In this study, previously published transformation products of boscalid, pyraclostrobin, fenbuconazole and glyphosate were identified after exposure to 3% hydrogen peroxide, UV-C irradiation or their combination in an advanced oxidative process on glass, their oral toxicity, carcinogenicity and developmental toxicity were identified in-silico and an initial tier hazard assessment was conducted. Of the 87 total structures that were searched for, 53 were detected by UPLC-QTOF-MS and identified by mass spectra: 15, 13, 22 and 3 structures for boscalid, pyraclostrobin, fenbuconazole and glyphosate respectively, including the parent residues. Oral toxicity of the transformation products of pyraclostrobin and glyphosate was similar to or lower than the parent residue. Several transformation products of boscalid and fenbuconazole were estimated to be significantly more orally toxic than their parent residues. While the majority of the transformation products of boscalid, pyraclostrobin and fenbuconazole were predicted to be carcinogenic there were 11 that were consistently identified to have carcinogenic potential by several assessments. 29 of the 53 molecules were predicted to be probable developmental toxicants. An initial tier hazard assessment was conducted for Cramer rules classification and mutagenicity using the threshold of toxicological concern approach and predicted rat oral LD50. Two exposure scenarios were considered, one highly protective considering each transformation product to be at the highest maximum residue limit (MRL) for the pesticide and whole produce consumption at the highest consumption rate from the USEPA Exposures Handbook, the other considering only apple consumption with the relevant MRL. As indicated by the hazard assessment, several transformation products of boscalid, pyraclostrobin and fenbuconazole should be strongly considered for further testing, either by quantifying their production or in-vivo and in-vitro toxicity tests due to their predicted toxicity and associated hazard.

Antimalarial 9-Methoxystrobilurins, Oudemansins, and Related Polyketides from Cultures of Basidiomycete Favolaschia Species.

Fourteen new compounds, oudemansins 1-4, oudemansinols 5-7, favolasins 8-10, favolasinin (12), polyketides 13-15, and (R,E)-2,4-dimethyl-5-phenyl-4-pentene-2,3-diol (16), together with nine known compounds were isolated from the basidiomycete fungus Favolaschia sp. BCC 18686. Two new compounds, favolasin E (11) and 9-oxostrobilurin E (17), were isolated from the closely related organism Favolaschia calocera BCC 36684 along with nine ß-methoxyacrylate-type derivatives. Compounds in the class of oudemansins and strobilurins exhibited moderate to strong antimalarial activity with relatively low cytotoxicity against Vero cells (African green monkey kidney fibroblasts). Potent antimalarial activity was demonstrated for 9-methoxystrobilurins G, K, and E (IC50 values 0.061, 0.089, and 0.14 µM, respectively). The structure-activity relationships (SAR) for antimalarial activity is proposed on the basis of the activity of the new and several known ß-methoxyacrylate derivatives in combination with the data from previously isolated compounds. Furthermore, several compounds showed specific cytotoxicity against NCI-187 cells (human small-cell lung cancer), although the SAR was different from that for antimalarial activity.

Iron-based porous metal-organic frameworks with crop nutritional function as carriers for controlled fungicide release.

Metal-organic frameworks (MOFs) are an emerging class of hybrid inorganic-organic porous materials used in various fields. Considering their excellent performance, MOFs have a considerable application potential in sustainable agriculture. Research projects of MOFs-based platforms for plant protection and nutrition have just started. Environmental stimuli-responsive pesticide release is highly desirable for improved efficacy and decreased side effects. Iron-based MOFs (Fe-MOFs) have a considerable prospect in agriculture as multifunctional materials both for pesticide delivery and plant nutrient replenishment because iron is an essential micronutrient for crop growth. In this work, a simple octahedral Fe-MOFs built from trimers of iron octahedra linked by 1, 3, 5-benzenetricarboxylate (Fe-MIL-100) have been prepared as carriers for fungicide azoxystrobin. Due to the high surface area of 2251 m2/g, the loading content of azoxystrobin into Fe-MIL-100 is satisfactory up to 16.2%. Azoxystrobin-loaded Fe-MOFs (AZOX@Fe-MIL-100) exhibit a pH-responsive initial burst and a subsequent sustained release pattern. Moreover, AZOX@Fe-MIL-100 exhibits good fungicidal activities against two pathogenic fungi-wheat head scab (Fusarium graminearum) and tomato late blight (Phytophthora infestans). The nutritional function of Fe-MIL-100 as iron micronutrient for the enhanced wheat growth was also observed. This research explores the feasibility of MOFs as a platform for potential application in sustainable plant protection.

Identification of Azoxystrobin Glutathione Conjugate Metabolites in Maize Roots by LC-MS.

Xenobiotic detoxification in plant as well as in animals has mostly been studied in relationship to the deactivation of the toxic residues of the compound that, surely for azoxystrobin, is represented by its ß-methoxyacrylate portion. In maize roots treated for 96 h with azoxystrobin, the fungicide accumulated over time and detoxification compounds or conjugates appeared timewise. The main detoxified compound was the methyl ester hydrolysis product (azoxystrobin free acid, 390.14 m/z) thought to be inactive followed by the glutathione conjugated compounds identified as glutathione conjugate (711.21 m/z) and its derivative lacking the glycine residue from the GSH (654.19 m/z). The glycosylated form of azoxystrobin was also found (552.19 m/z) in a minor amount. The identification of these analytes was done by differential untargeted metabolomics analysis using Progenesis QI for label free spectral counting quantification and MS/MS confirmation of the compounds was carried out by either Data Independent Acquisition (DIA) and Data Dependent Acquisition (DDA) using high resolution LC-MS methods. Neutral loss scanning and comparison with MS/MS spectra of azoxystrobin by DDA and MSe confirmed the structures of these new azoxystrobin GSH conjugates.

Crystal structure of bacterial cytochrome bc1 in complex with azoxystrobin reveals a conformational switch of the Rieske iron-sulfur protein subunit.

Cytochrome bc1 complexes (cyt bc1), also known as complex III in mitochondria, are components of the cellular respiratory chain and of the photosynthetic apparatus of non-oxygenic photosynthetic bacteria. They catalyze electron transfer (ET) from ubiquinol to cytochrome c and concomitantly translocate protons across the membrane, contributing to the cross-membrane potential essential for a myriad of cellular activities. This ET-coupled proton translocation reaction requires a gating mechanism that ensures bifurcated electron flow. Here, we report the observation of the Rieske iron-sulfur protein (ISP) in a mobile state, as revealed by the crystal structure of cyt bc1 from the photosynthetic bacterium Rhodobacter sphaeroides in complex with the fungicide azoxystrobin. Unlike cyt bc1 inhibitors stigmatellin and famoxadone that immobilize the ISP, azoxystrobin causes the ISP-ED to separate from the cyt b subunit and to remain in a mobile state. Analysis of anomalous scattering signals from the iron-sulfur cluster of the ISP suggests the existence of a trajectory for electron delivery. This work supports and solidifies the hypothesis that the bimodal conformation switch of the ISP provides a gating mechanism for bifurcated ET, which is essential to the Q-cycle mechanism of cyt bc1 function.

Design, Synthesis, Antiviral Bioactivity, and Defense Mechanisms of Novel Dithioacetal Derivatives Bearing a Strobilurin Moiety.

A series of dithioacetal derivatives bearing a strobilurin moiety were designed and synthesized on the basis of our previous work. The antiviral activities of these compounds against Potato virus Y (PVY), Cucumber mosaic virus (CMV), and Tobacco mosaic virus (TMV) were systematically evaluated. Bioassay results indicated that C14 elicited excellent curative and protective activities against PVY, CMV, and TMV. The former had 50% effective concentrations (EC50) of 125.3, 108.9, and 181.7 µg/mL, respectively, and the latter had 148.4, 113.2, and 214.6 µg/mL, respectively, which were significantly superior to those of lead compound 6f (297.6, 259.6, and 582.4 µg/mL and 281.5, 244.3, and 546.3 µg/mL, respectively), Ningnanmycin (440.5, 549.1, and 373.8 µg/mL and 425.3, 513.3, and 242.7 µg/mL, respectively), Chitosan oligosaccharide (553.4, 582.8, and 513.8 µg/mL and 547.3, 570.6, and 507.9 µg/mL, respectively), and Ribavirin (677.4, 690.3, and 686.5 µg/mL and 652.7, 665.4, and 653.4 µg/mL, respectively). Moreover, defensive enzyme activities and RT-qPCR analysis demonstrated that the antiviral activity was associated with the changes of SOD, CAT, and POD activities in tobacco, which was proved by the related proteins of abscisic acid signaling pathway. This work provided a basis for further design, structural modification, and development of dithioacetal derivatives as new antiviral agents.

Fate Characterization of Benzene Kresoxim-Methyl (a Strobilurin Fungicide) in Different Aerobic Soils.

Benzene kresoxim-methyl (BKM) is a promising broad-spectrum strobilurin fungicide widely used to control fungal pathogens in crops. However, information on its environmental fate is limited. To broaden our understanding of this fungicide's kinetic fate in aerobic soils, we labeled BKM with C on its benzoate ring and used ultralow-level liquid scintillation counting coupled with high-performance liquid chromatography analysis. Results show that degradation, mineralization, and bound residue (BR) formation of BKM was controlled by soil type and microbial community composition. Degradation of BKM followed first-order dynamics, and the half-lives () were 51.7, 30.8, and 26.8 d for clay, loamy, and saline soils, respectively. After 100 d, about 0.13, 4.35, and 5.94% of the initial C-BKM was mineralized, and 14.43, 19.90, and 28.81% was formed as BRs in the clay, loamy, and saline soils, respectively. About 60 to 85% of the C-BKM residue in soil was extractable; of this fraction, 30 to 50% was composed of incomplete degradation intermediates. Up to 40% of extractable C-BKM in soil was readily available. Our results suggest that BKM and its incomplete intermediates had a relatively long persistence in soil, which may lead to exposure for nontarget organisms. Soil microbes may play a dominant role in controlling the fate of BKM in soil as sterilization sharply decreased its mineralization rate from 4.35 to 0.03%, increased from 30.8 to 85.6 d, and decreased the BR fraction from 19.90 to 3.25%.

Influence of commercial formulation on leaching of four pesticides through soil.

Studies with small soil columns (2cm i.d.×5.4cm depth) compared leaching of four pesticides added either as technical material or as commercial formulations. Pesticides were selected to give a gradient of solubility in water between 7 and 93mgL-1, comprising azoxystrobin (emulsifiable concentrate, EC, and suspension concentrate, SC), cyproconazole (SC), propyzamide (SC) and triadimenol (EC). Columns of sandy loam soil were leached with 6 pore volumes of 0.01M CaCl2 either 1 or 7days after treatment. Separate experiments evaluated leaching of triadimenol to full breakthrough following addition of 18 pore volumes of 0.01M CaCl2. The mass of pesticide leached from columns treated with commercial formulation was significantly larger than that from columns treated with technical material for all compounds studied and for both leaching intervals (two-sided t-tests, p<0.001). This difference was conserved when triadimenol was leached to full breakthrough with 79±1.2 and 61±3.1% of applied triadimenol leached from columns treated with formulated and technical material, respectively. There were highly significant effects of formulation for all pesticides (two-way ANOVA, p<0.001), whereas leaching interval was only significant for azoxystrobin EC formulation and cyproconazole (p<0.001 and 0.021, respectively) with greater leaching when irrigation commenced 1day after treatment. Leaching of azoxystrobin increased in the order technical material (6.0% of applied pesticide)