Synthesis of rotenone-O-monosaccharide derivatives and their phloem mobility

Enhancing Systemic Translocation of Insecticides via Nanoformulations Incorporating β-Cyclodextrin Octadecarboxylate as a Carrier

The conversion of contact-killing pesticides into systemic pesticides can significantly enhance the bioavailability of pesticides, thereby reducing pesticide usage and environmental harm. A series of β-cyclodextrin fatty acid esters with varying branch chains were synthesized and employed as carriers in nanoformulation of insecticide. The investigation revealed that nanoformulations prepared using β-cyclodextrin octadecarboxylate (β-CDs) exhibited superior stability and remarkable systemic translocation within plants. Six contact-killing insecticide nanoformulations were developed utilizing β-CDs as carriers, and tests indicated that β-CDs significantly enhanced the systemic translocation of insecticides in plants compared to carrier-free nanoformulations. It was found that β-CDs increased the level of systemic translocation of insecticides by 5-12 times. Additionally, characterization results from λ-cyhalothrin-β-CDs nanoformulation demonstrated their superior ability to improve photolysis resistance, prolong release time, and extend insecticidal duration. Consequently, β-CDs can be utilized as a green additive in pesticide production to enhance the systemic translocation of pesticides in plants and increase their bioavailability.

An amino acid transporter-like protein (OsATL15) facilitates the systematic distribution of thiamethoxam in rice for controlling the brown planthopper

Characterization and genetic engineering of plant transporters involved in the pesticide uptake and translocation facilitate pesticide relocation to the tissue where the pests feed, thus improving the bioavailability of the agrichemicals. We aimed to identify thiamethoxam (THX) transporters in rice and modify their expression for better brown planthopper (BPH) control with less pesticide application. A yeast library expressing 1385 rice transporters was screened, leading to the identification of an amino acid transporter-like (ATL) gene, namely OsATL15, which facilitates THX uptake in both yeast cells and rice seedlings. In contrast to a decrease in THX content in osatl15 knockout mutants, ectopic expression of OsATL15 under the control of the CaMV 35S promoter or a vascular-bundle-specific promoter gdcsPpro significantly increased THX accumulation in rice plants, thus further enhancing the THX efficacy against BPH. OsATL15 was localized in rice cell membrane and abundant in the root transverse sections, vascular bundles of leaf blade, and stem longitudinal sections, but not in hull and brown rice at filling stages. Our study shows that OsATL15 plays an essential role in THX uptake and its systemic distribution in rice. OsATL15 could be valuable in achieving precise pest control by biotechnology approaches.

High Value-Added Application of Natural Plant Products in Crop Protection: Honokiol Monoester/Diester Derivatives Containing the Novel Core Scaffold of Benzodihydrofuran and Their Agricultural Bioactivities and Control Effects

To discover new potential botanical insecticides from plant secondary metabolites, a series of new honokiol-type monoester/diester derivatives containing the core scaffold of benzodihydrofuran were synthesized by structural modification of honokiol. Against Mythimna separata Walker, 2-hydroxymethy-5-(2'-(para-chlorobenzoyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (5) and 2-(2″-chloropyridin-5″-ylcarbonyloxy)methylene-5-(2'-(2″-chloropyridin-5″-ylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (37) displayed >2.1-fold promising insecticidal activity of the precursor honokiol. Against Aphis citricola Van der Goot, 2-hydroxymethy-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (21) (LD₅₀: 0.049 μg/nymph) and 2-(para-fluorobenzylcarbonyloxy)methylene-5-(2'-(para-fluorobenzylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (31) (LD₅₀: 0.040 μg/nymph) showed 3.5- and 4.3-folds potent aphicidal activity of honokiol (LD₅₀: 0.171 μg/nymph), respectively. Interestingly, 2-(tridecylcarbonyloxy)methylene-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (46) (LC₅₀: 0.186 mg/mL) and 2-(dodecylcarbonyloxy)methylene-5-(2'-(dodecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (53) (LC₅₀: 0.159 mg/mL: >6.4-fold of honokiol (LC₅₀: 1.024 mg/mL)) exhibited promising acaricidal activity and control efficiency against Tetranychus cinnabarinus Boisduval. Structure-activity relationships indicated that a specific length of the aliphatic chain is necessary for the agricultural activities of honokiol monoester/diester derivatives, especially for the acaricidal activity of diester derivatives.

An efficient overexpression method for studying genes in Ricinus that transport vectorized agrochemicals

BACKGROUND

Plant plasma membrane transporters play essential roles during the translocation of vectorized agrochemicals. Therefore, transporters associated with phloem loading of vectorized agrochemicals have drawn increasing attention. As a model system, castor bean (Ricinus communis L.) has been widely used to detect the phloem mobility of agrochemicals. However, there is still a lack of an efficient protocol for the Ricinus seedling model system that can be directly used to investigate the recognition and phloem loading functions of plasmalemma transporters toward vectorized agrochemicals.

RESULTS

Here, using vacuum infiltration strategy, we overexpressed the coding gene for enhanced green fluorescent protein (eGFP) in R. communis seedlings by Agrobacterium tumefaciens-mediated transformation system. Strong fluorescence signals were observed in leaves, demonstrating that exogenous genes can be successfully overexpressed in seedlings. Subsequently, gene expression time and vacuum infiltration parameters were optimized. Observation of fluorescence and qRT-PCR analysis showed that eGFP strength and expression level reached a peak at 72 h after overexpression in seedlings. Parameter optimization showed Agrobacterium concentration at OD₆₀₀ = 1.2, and infiltration for 20 min (0.09 MPa), return to atmospheric pressure, and then infiltration for another 20 min, were the suitable transformation conditions. To test the application of vacuum agroinfiltration in directly examining the loading functions of plasma membrane transporters to vectorized agrochemicals in seedlings, two LHT (lysine/histidine transporter) genes, RcLHT1 and RcLHT7, were overexpressed. Subcellular localization showed the strong fluorescent signals of the fusion proteins RcLHT1-eGFP and RcLHT7-eGFP were observed on the cell membrane of mesophyll cells, and their relative expression levels determined by qRT-PCR were up-regulated 47- and 52-fold, respectively. Furthermore, the concentrations of L-Val-PCA (L-valine-phenazine-1-carboxylic acid conjugate) in phloem sap collected from seedling sieve tubes were significantly increased 1.9- and 2.3-fold after overexpression of RcLHT1 and RcLHT7, respectively, implying their roles in recognition and phloem loading of L-Val-PCA.

CONCLUSIONS

We successfully constructed a transient expression system in Ricinus seedlings and laid the foundation for researchers to directly investigate the loading functions of plasma membrane transporters to vectorized agrochemicals in the Ricinus system.

One pot solvothermal synthesis of novel fluorescent phloem-mobile phenylpyrazole amide pesticides fused olefin moieties to enhance insecticidal bioactivities and photodegradation properties

In order to find a novel type of fluorescent phloem-mobile insecticides, a facile one-pot solvothermal strategy via fipronil addition-elimination substitution reaction with the corresponding acyl chloride derivatives has been employed to construct series of phenylpyrazole amide derivatives (PAs) fused olefin moieties in high yields. The investigation for insecticidal bioactivities of PAs against 3rd instar larvae of Plutella xylostella exhibited better activities than that of fipronil, which can be elucidated by enhanced phloem mobility and calcium ions' coordination with amide N-C=O, CC double bonds and chloride ions, extended conjugate moieties and decreasing steric hindrance of the stereoscopic structure. The introduction of amide units conferred phloem mobility to PAs, which was evaluated by the hydrophobic parameters determined with reversed-phase HPLC through the chromatographic capacity factor. By introducing conjugate moieties and organic chromophore into phenylpyrazole parent structure to increase their conjugation degree and light absorption abilities, PAs exhibited good photodegradation properties. The relationships between extended conjugate moieties of parent structure, electronegativity of substituted groups and photodegradation properties have been discussed. The olefin units connected to PAs caused electronic absorption and fluorescent wavelengths bathochromic shifted. Under simulated solar irradiation, PAs can be reconverted into fipronil parent fragments by photodegradation, thereby enhancing their insecticidal activity. The fluorescent quantum yields of PAs were almost 4 times that of fipronil, which also laid a foundation for the natural degradation and fluorescence detection of insecticide residues.

The influence of steric configuration of phenazine-1-carboxylic acid-amino acid conjugates on fungicidal activity and systemicity

BACKGROUND

Conjugating an amino acid onto existing fungicidal parent structures has been demonstrated to be an effective way to endow non-phloem mobile fungicides with phloem mobility. To alter the systemicity of the fungicide PCA (phenazine-1-carboxylic acid), 10 amino acids derivatives of this fungicide were designed and synthesized, and their synthesis, characterization, phloem and xylem mobility in Ricinus communis L, and their fungicidal activity in vitro are described.

RESULTS

The systemicity experiments in Ricinus communis system demonstrated that all conjugates exhibited obvious phloem mobility compared with non-phloem-mobile PCA, and the introduction of an L-amino acid to PCA more greatly enhanced the phloem mobility. The five D-amino acid conjugates exhibited higher xylem mobility than that of PCA and of each corresponding L-amino acid conjugate. Most conjugates were found to exhibit moderate in vitro fungicidal activities against six pathogenic fungi, which were lower than that of PCA. The results of the bioassay showed fungicidal activities of PCA-amino acid conjugates associated not only with different amino acids, but also with their conformation. Conjugation with D-amino acid contributed to the in vitro fungicidal activities of PCA-amino acid conjugates.

CONCLUSIONS

The current research offers a new strategy for enhancing the systemicity of non-phloem-mobile fungicides and presents some useful information on the effects of introducing amino acids of different steric configurations on the fungicidal activity, phloem and xylem mobility of the parent fungicide. © 2019 Society of Chemical Industry.

Synthesis and bioactivity of indoleacetic acid-carbendazim and its effects on Cylindrocladium parasiticum

Indoleacetic acid (IAA)-carbendazim was synthesized to assess whether this conjugate could retain the fungicidal activity of carbendazim and gain root-inducing properties upon the addition of an indoleacetic acid group. An indoor virulence test demonstrated that the conjugate retained the fungicidal activity of carbendazim towards Cylindrocladium parasiticum. The conjugate was detected in roots after soaking Ricinus communis L. leaves into a solution of the IAA-carbendazim, which confirmed its phloem mobility. The activities of the cellulase, polygalacturonase and xylanase produced by Cylindrocladium parasiticum treated with different concentrations of the conjugate were determined, and the peak activities appeared at 72 h or 96 h. More importantly, the conjugate showed the ability to promote root growth. These results revealed that indoleacetic acid-carbendazim may be useful in preventing Cylindrocladium parasiticum and other diseases.

Vectorizing agrochemicals: enhancing bioavailability via carrier-mediated transport

Systemicity of agrochemicals is an advantageous property for controlling phloem sucking insects, as well as pathogens and pests not accessible to contact products. After the penetration of the cuticle, the plasma membrane constitutes the main barrier to the entry of an agrochemical into the sap flow. The current strategy for developing systemic agrochemicals is to optimize the physicochemical properties of the molecules so that they can cross the plasma membrane by simple diffusion or ion trapping mechanisms. The main problem with current systemic compounds is that they move everywhere within the plant, and this non-controlled mobility results in the contamination of the plant parts consumed by vertebrates and pollinators. To achieve the site-targeted distribution of agrochemicals, a carrier-mediated propesticide strategy is proposed in this review. After conjugating a non-systemic agrochemical with a nutrient (α-amino acids or sugars), the resulting conjugate may be actively transported across the plasma membrane by nutrient-specific carriers. By applying this strategy, non-systemic active ingredients are expected to be delivered into the target organs of young plants, thus avoiding or minimizing subsequent undesirable redistribution. The development of this innovative strategy presents many challenges, but opens up a wide range of exciting possibilities. © 2018 Society of Chemical Industry.

The linker length of glucose-fipronil conjugates has a major effect on the rate of bioactivation by β-glucosidase

BACKGROUND

Endogenous plant β-glucosidases can be utilized to hydrolyze pro-pesticides and release the bioactive pesticide. Two related glucose-fipronil conjugates with different linkers structure, N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazol-5-yl}-1-(2-triazolethyl-β-d-glucopyranoside)-1H-1,2,3-triazole-4-methanamine (GOTF) and N-{3-cyano-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl)-sulfinyl]-1H-pyrazol-5-yl}-2-aminoethyl-β-d-glucopyranoside (GOF), were deglucolysated by β-glucosidase both in vitro and in vivo at different rates. Here, the basis for these differences was investigated by revealing the kinetics of the reaction and by modeling molecular docking between enzyme and substrate.

RESULTS

Results from kinetic study showed that the reaction rate was the main reason for the poorer rate of GOF hydrolysis with respect to GOTF. Modeling of substrate docking indicated that the spacer arm of glucose-fipronil conjugates affects the strength of non-covalent bonds within the active site and the position of fipronil within the pocket. Four glucose-fipronil conjugates and four corresponding aglycones were synthesized, and the hydrolysis data confirmed that the increased tether length between the bulky aglycone and glycone would lead to faster hydrolysis rate. The bioassay results indicated that most glucose-fipronil conjugates displayed moderate to excellent insecticidal activities in vivo against Plutella xylostella larvae.

CONCLUSION

This study provides a potential strategy to optimize the substrate structure to enhance hydrolytic specificity in order to design appropriate phloem mobile pro-pesticides. © 2018 Society of Chemical Industry.

Design, Synthesis, Phloem Mobility, and Bioactivities of a Series of Phenazine-1-Carboxylic Acid-Amino Acid Conjugates

Developing fungicides with phloem mobility that can be applied to leaves to control root or vascular pathogens has long been desirable. To achieve this goal, an efficient and economical strategy involves introducing an amino acid into the existing highly active parent pesticide molecule. Hence, 12 L-phenazine-1-carboxylic acid (PCA)-amino acid conjugates 4a⁻l were designed and synthesized via a simple synthetic route. In vitro bioassays results showed that all synthesized compounds 4a⁻l exhibited certain fungicidal activities against six tested fungi. Compound 4c exhibited relatively good fungicidal activity against Rhizoctonia solani, and the EC₅₀ value was 0.084 ± 0.006 mmol/L. The phloem mobility experiments revealed that introducing an amino acid to PCA could effectively endow PCA with phloem mobility in R. communis L. Among them, nine conjugates were found in phloem sap, and L-PCA-Valine 4d exhibited the highest phloem mobility. Analysis results from the prediction of the Kleier model indicated that an active carrier-mediated mechanism may be involved in L-PCA-amino acid conjugates-a result that needs to be confirmed and complemented with further tests. The current research provides useful data for modifying non-phloem-mobile fungicidal molecules to phloem-mobile types.

Design of a New Glutamine-Fipronil Conjugate with α-Amino Acid Function and Its Uptake by A. thaliana Lysine Histidine Transporter 1 ( AtLHT1)

Creating novel pesticides with phloem mobility is essential for controlling insects in vascular tissue and root, and conjugating existing pesticides with amino acid is an effective approach. In order to obtain a highly phloem-mobile candidate for efficient pesticides, an electro-neutral l-glutamine-fipronil conjugate (l-GlnF) retaining α-amino acid function was designed and synthesized to fit the substrate specificity of an amino acid transporter. Cotyledon uptake and phloem loading tests with Ricinus communis have verified that l-GlnF was phloem mobile, and its phloem mobility was higher than that of its enantiomer d-GlnF and other previously reported amino acid-fipronil conjugates. Inhibition experiments then suggested that the uptake of l-GlnF was, at least partially, mediated by an active transport mechanism. This inference was further strengthened by assimilation experiments with Xenopus oocytes and genetically modified Arabidopsis thaliana, which showed a direct correlation between the uptake of l-GlnF and the expression of amino acid transporter AtLHT1. Thus, conjugation with l-Gln appears to be a potential strategy to ensure the uptake of pesticides via an endogenous amino acid transport system.

Synthesis of Novel Amino Acid-Fipronil Conjugates and Study on Their Phloem Loading Mechanism

To develop a new pesticide with phloem mobility, a series of new amino acid–fipronil conjugates were designed and synthesized based on derivatization at the 3-position of the pyrazole ring of fipronil. Experiments using a Ricinus communis seedling system showed that all tested conjugates were phloem mobile except for the isoleucine–fipronil conjugate, and that the serine–fipronil conjugate (4g) exhibited the highest concentration in phloem sap (52.00 ± 5.80 μM). According to prediction with log Cf values and uptake experiments with Xenopus oocytes, the phloem loading process of conjugate 4g involved both passive diffusion and an active carrier system (RcANT15). In particular, compared with for a previously reported glycinergic–fipronil conjugate (GlyF), passive diffusion played a more important role for conjugate 4g in the enhancement of phloem mobility. This study suggests that associating a nutrient at a different position of an existing pesticide structure could still be effective in obtaining phloem-mobile derivatives, but the distinct physicochemical properties of resultant conjugates may lead to different phloem loading mechanisms.

Discovery of Glycosylated Genipin Derivatives as Novel Antiviral, Insecticidal, and Fungicidal Agents

A series of novel genipin glycoside derivatives incorporating 11 glycosidic moieties at either the 1 or 10 position of genipin were designed and synthesized. These compounds exhibited moderate to excellent inhibitory activities against tobacco mosaic virus. Especially, the in vitro and in vivo activities of compounds 6e, 7c, 7d, 7f, 7h, and 7i were comparable to that of ribavirin. In particular, compound 7c, the mannosyl derivative of genipin at the 10 position, showed the best activity. The series of genipin glycosyl derivatives also displayed fungicidal activities against 14 kinds of phytopathogenic fungi, especially for Rhizoctonia cerealis and Sclerotinia sclerotiorum. Moreover, compound 6h exhibited good insecticidal activity against diamondback moth; compounds 7b, 7c, and 7g exhibited moderate insecticidal activity against three kinds of Lepidoptera pests (oriental armyworm, cotton bollworm, and corn borer); and compound 7e showed excellent larvacidal activities against mosquito.

Synthesis, fungicidal activity and phloem mobility of phenazine-1-carboxylic acid-alanine conjugates

Phenazine-1-carboxylic acid (PCA) is a natural product that has been proven effective against a number of soil-borne fungal phytopathogens and registered for biofungicide against rice sheath blight in China. In order to improve the phloem mobility of phenazine-1-carboxylic acid (PCA), four PCA derivatives were designed and synthesized by conjugating PCA with l-alanine methyl ester, d-alanine methyl ester, l-alanine and d-alanine respectively. In vitro and planta bioassays results showed that conjugates L-PAM and D-PAM exhibited higher fungicidal activities against Rhizoctonia solani Kuhn than PCA while L-PA and D-PA were less active than PCA. The concentration of conjugates in Ricinus communis phloem sap was determined by HPLC. The results showed that only L-PA exhibited phloem mobility among these conjugates, and its concentration in Ricinus communis phloem sap increased with the increase of time (the maximum concentration was 12.69μM within 5h). However, the results of pot experiments showed that L-PA and other conjugates didn't exhibited the inhibition for the growth of Rhizoctonia solani Kuhn in the lower leaves after treatment in the upper leaves of rice seedlings. This may be due to the poor plant absorbility for them or their too little amount of accumulation in the lower leaves.

Family of Ricinus communis Monosaccharide Transporters and RcSTP1 in Promoting the Uptake of a Glucose-Fipronil Conjugate

Enhancing the systemic distribution of a bioactive compound by exploiting the vascular transport system of a plant presents a means of reducing both the volume and frequency of pesticide/fungicide application. The foliar uptake of the glucose-fipronil conjugate N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(β-d-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF) achieved in castor bean (Ricinus communis) and its transport via the phloem are known to be mediated by monosaccharide transporter(s) [MST(s)], although neither the identity of the key MST(s) involved nor the mechanistic basis of its movement have yet to be described. On the basis of homology with Arabidopsis thaliana sugar transporters, the castor bean genome was concluded to harbor 53 genes encoding a sugar transporter, falling into the eight previously defined subfamilies INT, PMT, VGT, STP, ERD6, pGlucT, TMT, and SUT. Transcriptional profiling identified the product of RcSTP1 as a candidate for mediating GTF uptake, because this gene was induced by exposure of the plant to GTF. When RcSTP1 was transiently expressed in onion epidermis cells, the site of RcSTP1 deposition was shown to be the plasma membrane. A functional analysis based on RcSTP1 expression in Xenopus laevis oocytes demonstrated that its product has a high affinity for GTF. The long-distance root-to-shoot transport of GTF was enhanced in a transgenic soybean chimera constitutively expressing RcSTP1.

Influence of Pyranose and Spacer Arm Structures on Phloem Mobility and Insecticidal Activity of New Tralopyril Derivatives

Six new conjugates were designed and synthesized by introducing glucose, methyl glucuronate or glucuronic acid moieties on tralopyril. Phytotoxicity and phloem mobility results demonstrated that the introduction of glucose, methyl glucuronate or glucuronic acid moieties can simultaneously solve the tough phytotoxicity problem and phloem mobility transformation of tralopyril. Conjugates 12 and 18 containing the glucuronic acid moiety exhibited higher phloem mobility than conjugates 9, 11, 15 and 17. Conjugates 15, 17 and 18 with methoxymethyl groups on the tralopyril pyrrole nitrogen atom showed activity against Plutella xylostella, while conjugates 9, 11 and 12 with a methene group on the pyrrole N showed no activity. Cabbage roots were incubated in a buffered solution containing conjugates 15, 17 and 18 at 4 mM for 72 h. Only 18 showed systemic insecticidal activity with 100% mortalityagainst P. xylostella, while 15 and 17 showed lower activity andchlorfenapyr showed no activity. The glucuronic acid promoiety imparted more phloem mobility to tralopyril than glucose and methyl glucuronate. The methoxymethyl group bond on the tralopyril skeleton was the key factor in determining the insecticidal activity of the conjugates. A promising systemic proinsecticide containing glucuronic acid and tralopyril moieties was proposed.

Enhanced intracellular uptake in vitro by glucose-functionalized nanopesticides

Nanopesticides have been increasingly used in agriculture. To improve the uptake of the target organisms for nanopesticides, we designed a dual-ligand nanopesticide based on gold nanoparticles (Au NPs) as a carrier.

A novel fluorescent conjugate applicable to visualize the translocation of glucose-fipronil

The ability to visualize the movement of glycosyl insecticides contributes to learning their translocation and distribution in plants. In our present work, a novel fluorescent glucose-fipronil conjugate N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-β-D-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (2-NBDGTF), was obtained via click chemistry. Disk uptake experiments showed that an active carrier-mediated system was involved in the 2-NBDGTF uptake process. Meanwhile, 2-NBDGTF exhibited comparable phloem mobility with GTF in castor bean seedlings. Visualization of 2-NBDGTF uptake and transport experiment showed that this fluorescent glucose-fipronil conjugate could be loaded into sieve tubes after transiting through epidermal cells and mesophyll cells and then translocate from cotyledon to hypocotyl via phloem in castor bean seedlings. The results above determined that it is a promising fluorescence tagging approach for revealing the activities of glycosyl insecticides and 2-NBDGTF is a reasonable and feasible fluorescent surrogate of GTF for tracing the distribution of glucose-fipronil conjugates.