Glucose positions affect the phloem mobility of glucose-fipronil conjugates

Recent progress in the synthesis of natural product inspired bioactive glycohybrids

Carbohydrates are a basic structural component that are indispensable to all cellular processes. In addition to being employed as chiral starting materials in the synthesis of a variety of natural products, carbohydrates are recognized as naturally occurring molecules having an enormous variety of functional, stereochemical, and structural properties. The understanding and biological roles of carbohydrate derived molecules can be greatly improved by selectively synthesizing functional carbohydrates through incorporating them with privileged scaffolds. For a deeper understanding of their roles and the development of functional materials based on sugar, it is crucial to develop new techniques for efficiently synthesizing, functionalizing, and modifying carbohydrates. Glycohybrids have a wide range of structural and functional characteristics along with protein-carbohydrate interactions that are crucial to mammalian biology and a number of disease states. This review, consisting the literature from January 2017 to July 2023 and provide an overview of recent developments in the chemical synthesis of glycohybrids based on natural product scaffolds of coumarin, quinolone, naphthalene diimide, indole, isatin, naphthoquinone, imidazole and pyrimidine. The biological activity of active glycohybrids are discussed in this review.

Glycoconjugation of Quinoline Derivatives Using the C-6 Position in Sugars as a Strategy for Improving the Selectivity and Cytotoxicity of Functionalized Compounds

Based on the Warburg effect and the increased demand for glucose by tumor cells, a targeted drug delivery strategy was developed. A series of new glycoconjugates with increased ability to interact with GLUT transporters, responsible for the transport of sugars to cancer cells, were synthesized. Glycoconjugation was performed using the C-6 position in the sugar unit, as the least involved in the formation of hydrogen bonds with various aminoacids residues of the transporter. The carbohydrate moiety was connected with the 8-hydroxyquinoline scaffold via a 1,2,3-triazole linker. For the obtained compounds, several in vitro biological tests were performed using HCT-116 and MCF-7 cancer cells as well as NHDF-Neo healthy cells. The highest cytotoxicity of both cancer cell lines in the MTT test was noted for glycoconjugates in which the triazole-quinoline was attached through the triazole nitrogen atom to the d-glucose unit directly to the carbon at the C-6 position. These compounds were more selective than the analogous glycoconjugates formed by the C-1 anomeric position of d-glucose. Experiments with an EDG inhibitor have shown that GLUTs can be involved in the transport of glycoconjugates. The results of apoptosis and cell cycle analyses by flow cytometry confirmed that the new type of glycoconjugates shows pro-apoptotic properties, without significantly affecting changes in the distribution of the cell cycle. Moreover, glycoconjugates were able to decrease the clonogenic potential of cancer cells, inhibit the migration capacity of cells and intercalate with DNA.

Discrimination of isomeric monosaccharide derivatives using collision-induced fingerprinting coupled to ion mobility mass spectrometry

Because of the isomeric heterogeneity that is ubiquitous in analytical science, a formidable analytical challenge is to fully discriminate multiple isomers, especially those candidate isomers with various biological functions. Ion mobility mass spectrometry (IM-MS) has gained impressive advances for gaining molecular conformations, whereas coexisting structurally similar isomers often make unambiguous discrimination impossible due to the limited IM resolution of commercially available instruments. Herein, we demonstrate an energy-resolved collision-induced fingerprint (CIF) method to fully discriminate isomeric monosaccharide derivatives that differ in terms of composition, connectivity and configuration without complex instrument modifications. By simply increasing the collisional energy in the trap cell, the full width at half maximum (FWHM) of IM peaks can be markedly narrowed by at least 2-fold. Given the excellent reproducibility of CIF measurements, the full discrimination of isomers can benefit from their unique feature values and root-mean square deviation (RMSD) in CIF spectra. Moreover, rapid discrimination of each monosaccharide derivate isomer from binary mixtures is demonstrated. This strategy will expand the horizons of IM-MS platform in the rapid differentiation of a wider range of isomers more than monosaccharide derivatives in complex systems, which facilitates the identification and evaluation of innovative isomer candidates with unexplored functions.

First Anti-ToCV Activity Evaluation of Glucopyranoside Derivatives Containing a Dithioacetal Moiety through a Novel ToCVCP-Oriented Screening Method

Tomato chlorosis virus (ToCV) is a newly reported plant virus that has rapidly spread to all parts of the world, resulting in a serious decline in tomato quality and yield due to the lack of effective control agents. In this study, the ToCV coat protein (ToCVCP) was expressed and purified in Escherichia coli, and a series of novel glucopyranoside derivatives containing a dithioacetal moiety was designed and synthesized. The binding affinity of these compounds to ToCVCP was determined using microscale thermophoresis. Results revealed that compounds 6b and 8a interacted with ToCVCP with K_d values of 0.12 and 0.21 μM, respectively. Quantitative reverse transcription polymerase chain reaction was used to evaluate the anti-ToCV activity of 6b and 8a in vivo, and both significantly reduced the expression level of ToCVCP gene in tomato compared with commercial antivirus agents. This study provides an efficient and convenient screening method for anti-ToCV agents and reliable support for the development of novel agrochemicals for ToCV.

Gram scale production of 1-azido-β-d-glucose via enzyme catalysis for the synthesis of 1,2,3-triazole-glucosides

The production of analytical amounts of azido sugars is used as a means of verifying catalytic acid/base mutations of retaining glycosidase, but application of this process to preparative synthesis has not been reported. The catalytic acid/base mutant of Thermoanaerobacterium xylanolyticus GH116 β-glucosidase, TxGH116D593A, catalyzed the gram scale production of 1-azido-β-d-glucose (1) from p-nitropheyl-β-d-glucopyranoside (pNPGlc) and azide via a transglucosylation reaction. Overnight reaction of the enzyme with pNPGlc and NaN₃ in aqueous MES buffer (pH 5.5) at 55 °C produced 1 (3.27 g), which was isolated as a white foamy solid in 96% yield. This 1 was successfully utilized for the synthesis of fifteen 1,2,3-triazole-β-d-glucosyl derivatives (2–16) containing a variety of functional groups, via click chemistry.

The retaining β-glucosidase acid/base mutant TxGH116D593A catalyzed the production of 1-azido-β-d-glucose for synthesis of 15 1,2,3-triazole β-glucosyl derivatives.

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.

Novel amino acid ester-chlorantraniliprole conjugates: design, synthesis, phloem accumulation and bioactivity

BACKGROUND

Conjugating amino acid and glucose fragments with existing pesticide structures has been shown to be an effective way to introduce phloem mobility into non-phloem mobile species. However, the resulting derivatives always suffer from lower bioactivity compared with their parent compound. To solve this problem, we designed and synthesised a series of ester-capped amino-acid-conjugated chlorantraniliproles.

RESULTS

The systemic test showed that all conjugates exhibited excellent phloem mobility and xylem mobility in a Ricinus communis model. In particular, compounds 7b, 8b and 8c were able to accumulate in phloem tissues in the form of their hydrolysis products, and the concentrations in phloem sap can reach 3 times the concentration in the incubation medium. Although their insecticidal activity (LC₅₀ ) against the beet armyworm (Spodoptera exigua) in vitro was weaker than that of chlorantraniliprole, compounds 7b, 8b and 8c showed similar insecticidal activity in vivo against beet armyworm compared with the parent compound.

CONCLUSIONS

This work provides a potential strategy to obtain pesticide derivatives that possess both improved uptake and improved mobility in crops while retaining the in vivo insecticidal effect of the parent compound. © 2017 Society of Chemical Industry.

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.

Glycinergic-Fipronil Uptake Is Mediated by an Amino Acid Carrier System and Induces the Expression of Amino Acid Transporter Genes in Ricinus communis Seedlings

Phloem-mobile insecticides are efficient for piercing and sucking insect control. Introduction of sugar or amino acid groups to the parent compound can improve the phloem mobility of insecticides, so a glycinergic-fipronil conjugate (GlyF), 2-(3-(3-cyano-1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-((trifluoromethyl)sulfinyl)-1H-pyrazole-5-yl)ureido) acetic acid, was designed and synthesized. Although the "Kleier model" predicted that this conjugate is not phloem mobile, GlyF can be continually detected during a 5 h collection of Ricinus communis phloem sap. Furthermore, an R. communis seedling cotyledon disk uptake experiment demonstrates that the uptake of GlyF is sensitive to pH, carbonyl cyanide m-chlorophenylhydrazone (CCCP), temperature, and p-chloromercuribenzenesulfonic acid (pCMBS) and is likely mediated by amino acid carrier system. To explore the roles of amino acid transporters (AATs) in GlyF uptake, a total of 62 AAT genes were identified from the R. communis genome in silico. Phylogenetic analysis revealed that AATs in R. communis were organized into the ATF (amino acid transporter) and APC (amino acid, polyaminem and choline transporter) superfamilies, with five subfamilies in ATF and two in APC. Furthermore, the expression profiles of 20 abundantly expressed AATs (cycle threshold (Ct) values <27) were analyzed at 1, 3, and 6 h after GlyF treatment by RT-qPCR. The results demonstrated that expression levels of four AAT genes, RcLHT6, RcANT15, RcProT2, and RcCAT2, were induced by the GlyF treatment in R. communis seedlings. On the basis of the observation that the expression profile of the four candidate genes is similar to the time course observation for GlyF foliar disk uptake, it is suggested that those four genes are possible candidates involved in the uptake of GlyF. These results contribute to a better understanding of the mechanism of GlyF uptake as well as phloem loading from a molecular biology perspective and facilitate functional characterization of candidate AAT genes in future studies.

Thiourea-based spacers in potent divalent inhibitors of Pseudomonas aeruginosa virulence lectin LecA

A thiourea spacer adopts an extended conformation and forms the basis of a potent bivalent ligand for Pseudomonas aeruginosa lectin LecA.