Design, Synthesis, and SAR of Novel 1,3-Disubstituted Imidazolidine or Hexahydropyrimidine Derivatives as Herbicide Safeners

Recent advances in the synthesis of highly substituted imidazolidines

Imidazolidine is a saturated heterocycle with a cyclic aminal core that can be found in natural products and biologically active molecules. Additionally, these heterocyclic compounds have been utilized as chiral ligands, N-heterocyclic carbene precursors, and catalysts in organic synthesis. This review is an attempt to compile the literature of various synthetic procedures of highly substituted imidazolidines, chiral imidazolidines with high diastereoselectivities and enantioselectivities, bis-imidazolidines, and spiro-imidazolidines, as well as their pharmacological properties during the period from 1949 to 2023.

Multiomics Analysis of the Mechanism by Which Gibberellin Alleviates S-Metolachlor Toxicity in Rice Seedlings

S-metolachlor is a selective pre-emergence herbicide used in dryland. However, it is challenging to employ in paddy fields due to its phytotoxic effects on rice. As a common phytohormone, Gibberellin-3 (GA3) is inferred to have the ability to alleviate herbicide phytotoxicity. This study first quantitatively verified the phytotoxicity of s-metolachlor to rice and then demonstrated the mitigative effect of GA3 on these adverse reactions. Furthermore, a transcriptome of rice seedlings subjected to different treatments was constructed to assemble the reference genes, followed by comparative metabolomics and proteomics analyses. Metabolomics revealed an enrichment of flavonoid metabolites in the group of adding GA3, and these flavonoids can eliminate ROS in plants. Proteomics analysis indicated that differential proteins were enriched in the phenylpropanoid biosynthesis pathway responsible for the synthesis of flavonoids and that the functions of most differential proteins are associated with peroxidase. The proteome, combined with the transcriptome, revealed that the expressions of proteins and genes was related to the POD activity in the group of adding GA3. It was speculated that the elimination of ROS is key to alleviating the stress of s-metolachlor on rice growth. It was inferred that the mechanism of GA3 in alleviating the phytotoxicity of the substance s-metolachlor is by increasing the activity of the POD and influencing the growth of rice seedlings through the restoration of flavonoid synthesis. In this study, we screened GA3 as a safener to alleviate the phytotoxicity of s-metolachlor on rice. On this basis, the mechanism of alleviating phytotoxicity was studied. The application range of s-metolachlor might be expanded, providing a new supplementary method for weed control and herbicide resistance management.

Design, Synthesis, and Biological Activity of Novel Triketone-Containing Phenoxy Nicotinyl Inhibitors of HPPD

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a crucial target enzyme in albino herbicides. The inhibition of HPPD activity interferes with the synthesis of carotenoids, blocking photosynthesis and resulting in bleaching and necrosis. To develop herbicides with excellent activity, a series of 3-hydroxy-2-(6-substituted phenoxynicotinoyl)-2-cyclohexen-1-one derivatives were designed via active substructure combination. The title compounds were characterized via infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopies, and high-resolution mass spectrometry. The structure of compound III-17 was confirmed via single-crystal X-ray diffraction. Preliminary tests demonstrated that some compounds had good herbicidal activity. Crop safety tests revealed that compound III-29 was safer than the commercial herbicide mesotrione in wheat and peanuts. Moreover, the compound exhibited the highest inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD), with a half-maximal inhibitory concentration of 0.19 μM, demonstrating superior activity compared with mesotrione (0.28 μM) in vitro. A three-dimensional quantitative structure-activity relationship study revealed that the introduction of smaller groups to the 5-position of cyclohexanedione and negative charges to the 3-position of the benzene ring enhanced the herbicidal activity. A molecular structure comparison demonstrated that compound III-29 was beneficial to plant absorption and conduction. Molecular docking and molecular dynamics simulations further verified the stability of the complex formed by compound III-29 and AtHPPD. Thus, this study may provide insights into the development of green and efficient herbicides.

Design, Synthesis, and Biological Evaluation of Novel Purine Derivatives as Herbicide Safeners

Mesosulfuron-methyl, an inhibitor of acetolactate synthase (ALS), has been extensively used in wheats. However, it can damage wheat (Triticum aestivum) and even lead to crop death. Herbicide safeners selectively shield crops from such damage without compromising weed control. To mitigate the phytotoxicity of mesosulfuron-methyl in crops, several purine derivatives were developed based on active substructure splicing. The synthesized title compounds underwent thorough characterization using infrared spectroscopy, 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry. We evaluated chlorophyll and glutathione contents as well as various enzyme activities to evaluate the safer activity of these compounds. Compounds III-3 and III-7 exhibited superior activity compared with the safener mefenpyr-diethyl. Molecular structure analysis, along with predictions of absorption, distribution, metabolism, excretion, and toxicity, indicated that compound III-7 shared pharmacokinetic traits with the commercial safener mefenpyr-diethyl. Molecular docking simulations revealed that compound III-7 competitively bound to the ALS active site with mesosulfuron-methyl, elucidating the protective mechanism of the safeners. Overall, this study highlights purine derivatives as potential candidates for novel safener development.

Herbicide Safeners: From Molecular Structure Design to Safener Activity

Herbicide safeners, highly effective antidotes, find widespread application in fields for alleviating the phytotoxicity of herbicides to crops. Designing new herbicide safeners remains a notable issue in pesticide research. This review focuses on discussing and summarizing the structure-activity relationships, molecular structures, physicochemical properties, and molecular docking of herbicide safeners in order to explore how different structures affect the safener activities of target compounds. It also provides insights into the application prospects of computer-aided drug design for designing and synthesizing new safeners in the future.

Design, Synthesis, and Bioactivity of Novel 2-(Arylformyl)cyclohexane-1,3-dione Derivatives as HPPD Inhibitors

4-Hydroxyphenylpyruvate dioxygenase inhibitors (Echinochloa crus-galli 1.13.11.27, HPPD) have gained significant popularity as one of the best-selling herbicides worldwide. To identify highly effective HPPD inhibitors, a rational design approach utilizing bioisosterism was employed to create a series of 2-(arylformyl)cyclohexane-1,3-dione derivatives. A total of 29 novel compounds were synthesized and characterized through various techniques, including IR, 1H NMR, 13C NMR, and HRMS. Evaluation of their inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD) revealed that certain derivatives exhibited superior potency compared to mesotrione (IC50 = 0.204 μM). Initial herbicidal activity tests demonstrated that compounds 27 and 28 were comparable to mesotrione in terms of weed control and crop safety, with compound 28 exhibiting enhanced safety in canola crops. Molecular docking analyses indicated that the quinoline rings of compounds 27 and 28 formed more stable π-π interactions with the amino acid residues Phe-360 and Phe-403 in the active cavity of AtHPPD, surpassing the benzene ring of mesotrione. Molecular dynamics simulations and molecular structure comparisons confirmed the robust binding capabilities of compounds 27 and 28 to AtHPPD. This study provides a valuable reference for the development of novel triketone herbicide structures, serving as a blueprint for future advancements in this field.

Design, Synthesis, and Structure-Activity Relationship of Novel Aryl-Substituted Formyl Oxazolidine Derivatives as Herbicide Safeners

Nicosulfuron is the leading herbicide in the global sulfonylurea (SU) herbicide market; it was jointly developed by DuPont and Ishihara. Recently, the widespread use of nicosulfuron has led to increasingly prominent agricultural production hazards, such as environmental harm and influence on subsequent crops. The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of existing herbicides. A series of novel aryl-substituted formyl oxazolidine derivatives were designed using the active group combination method. Title compounds were synthesized using an efficient one-pot method and characterized by infrared (IR) spectrometry, ¹H and ¹³C nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS). The chemical structure of compound V-25 was further identified by X-ray single crystallography. The bioactivity assay and structure-activity relationship proved that nicosulfuron phytotoxicity to maize could be reduced by most title compounds. The glutathione S-transferase (GST) activity and acetolactate synthase (ALS) in vivo were determined, and compound V-12 showed inspiring activity comparable to that of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound V-12 competed with nicosulfuron for the acetolactate synthase active site and that this is the protective mechanism of safeners. Absorption, distribution, metabolism, excretion, and toxicity (ADMET) predictions demonstrated that compound V-12 exhibited superior pharmacokinetic properties to the commercialized safener isoxadifen-ethyl. The target compound V-12 shows strong herbicide safener activity in maize; thus, it may be a potential candidate compound that can help further protect maize from herbicide damage.

Design, Synthesis, and Bioactivity of Novel Ester-Substituted Cyclohexenone Derivatives as Safeners

Tembotrione, a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, has been widely used in many types of plants. Tembotrione has been reported for its likelihood of causing injury and plant death to certain corn hybrids. Safeners are co-applied with herbicides to protect certain crops without compromising weed control efficacy. Alternatively, herbicide safeners may effectively improve herbicide selectivity. To address tembotrione-induced Zea mays injury, a series of novel ester-substituted cyclohexenone derivatives were designed using the fragment splicing method. In total, 35 title compounds were synthesized via acylation reactions. All the compounds were characterized using infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. The configuration of compound II-15 was confirmed using single-crystal X-ray diffraction. The bioactivity assay proved that tembotrione phytotoxicity to maize could be reduced by most title compounds. In particular, compound II-14 exhibited the highest activity against tembotrione. The molecular structure comparisons as well as absorption, distribution, metabolism, excretion, and toxicity predictions demonstrated that compound II-14 exhibited pharmacokinetic properties similar to those of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound II-14 could prevent tembotrione from reaching or acting with Z. mays HPPD (PDB: 1SP8). Molecular dynamics simulations showed that compound II-14 maintained satisfactory stability with Z. mays HPPD. This research revealed that ester-substituted cyclohexenone derivatives can be developed as potential candidates for discovering novel herbicide safeners in the future.

Research Progress on the Action Mechanism of Herbicide Safeners: A Review

Herbicide safeners are agricultural chemicals that protect crops from herbicide injury and improve the safety of herbicides and the effectiveness of weed control. Safeners induce and enhance the tolerance of crops to herbicides through the synergism of multiple mechanisms. The principal mechanism is that the metabolic rate of the herbicide in the crop is accelerated by safeners, resulting in the damaging concentration at the site of action being reduced. We focused on discussing and summarizing the multiple mechanisms of safeners to protect crops in this review. It is also emphasized how safeners alleviate herbicide phytotoxicity to crops by regulating the detoxification process and conducting perspectives on future research on the action mechanism of safeners at the molecular level.

Synthesis, herbicidal activity and soil degradation of novel 5-substituted sulfonylureas as AHAS inhibitors

BACKGROUND

Chlorsulfuron, metsulfuron-methyl and ethametsulfuron can damage sensitive crops in rotation pattern as a result of their long persistence in soil. To explore novel sulfonylurea (SU) herbicides with favorable soil degradation rates, four series of SUs were synthesized through a structure-based drug design (SBDD) strategy.

RESULTS

The target compounds, especially Ia, Id and Ie, exhibited prospective herbicidal activity against dicotyledon oil seed rape (Brassica campestris), amaranth (Amaranthus retroflexus), monocotyledon barnyard grass (Echinochloa crusgalli) and crab grass (Digitaria sanguinalis) at a concentration of 15 a.i. g ha^-1 . Additionally, Ia, Id and Ig displayed excellent inhibitory effects against AtAHAS, with Kapp i values of 59.1, 34.5 and 71.8 μm, respectively, which were much lower than that of chlorsulfuron at 149.4 μm. The π-π stack and H-bonds between the Ia conformation and AtAHAS in the molecular docking results confirmed the series of compounds to be conventional AHAS inhibitors. In alkaline soil (pH = 8.46), compounds Ia-Ig revealed various degrees of acceleration in the degradation rate compared with chlorsulfuron. Besides, compound Ia showed considerable wheat and corn safety under postemergence at the concentration of 30, 60 and even 120 a.i. g ha^-1 .

CONCLUSION

Overall, based on the synthetic procedure, herbicidal activity, soil degradation and crop safety, the Ia sulfonylureas series were chosen to be investigated as prospective AHAS inhibitors. The 5-dimethylamino group on SUs accelerated the degradation rate at different levels in alkaline soils which seems to be controllable in conventional cropping systems in their further application. © 2022 Society of Chemical Industry.

The mechanism of exogenous gibberellin A3 protecting sorghum shoots from S-metolachlor Phytotoxicity

BACKGROUND

S-metolachlor (MET) was used to prevent weed infestation in sorghum fields, but inappropriate application could result in phytotoxicity on sorghum. Exogenous gibberellin A₃ (GA₃ ) has been applied for alleviating the phytotoxicity of MET. However, its detoxification mechanism is still not well known.

RESULTS

Leaf deformity of sorghum caused by 200 mg/L MET was alleviated by treating sorghum shoots with 800 mg/L GA₃ , and the injury recovery rate of growth index was over 73%. More importantly, GA₃ could not accelerate the metabolic rate of MET in sorghum. The result of phytohormone metabolomics showed that endogenous GA₃ content in sorghum decreased by 78.10% with MET treatment, while abscisic acid (ABA) content increased by 120.2%, resulting in 10.3-fold increase of ABA/GA₃ ratio. Content of ABA and GA₃ increased by 11.9- and 21.1-fold with MET and GA₃ treatment, respectively, leading to ABA/GA₃ ratio restoration. Moreover, MET inhibited the expression of genes encoding key enzymes related to GA synthesis including CPS1, KO2, KAO, GA20ox1D and ABA8ox gene related to ABA metabolism. The transcription levels of GA metabolism-related genes CYP714D1 and GA2ox were up-regulated by 11.2- and 7.2-fold, while ABA synthesis-related genes NCED and ZEP were up-regulated by 8.0- and 3.0-fold, respectively, with MET and GA₃ treatment.

CONCLUSION

In this study, exogenous GA₃ protecting sorghum shoots from MET phytotoxicity was due to supplement the MET-induced GA₃ deficiency by absorbing exogenous GA₃ , and restore homeostasis of ABA and GA₃ by promoting ABA synthesis, which provides novel insights for mechanism of GA₃ alleviating MET phytotoxicity. © 2022 Society of Chemical Industry.

Diazabicyclo derivatives as safeners protect cotton from injury caused by flumioxazin

Flumioxazin, a protoporphyrinogen oxidase (PPO; EC 1.3.3.4) inhibitor, has been used in soybean, cotton, grapes, and many other crops to control broad leaf weeds. Unfortunately, it can cause damage to cotton. To ameliorate phytotoxicity of flumioxazin to cotton, this work assessed the protective effects of diazabicyclo derivatives as potential safeners in cotton. A bioactivity assay proved that the phytotoxicity of flumioxazin on cotton was alleviated by some of the compounds. In particular, the activity of glutathione S-transferases (GSTs) was significantly enhanced by Compound 32, which showed good safening activity against flumioxazin injury. The physicochemical properties and absorption, distribution, metabolism, excretion and toxicity (ADMET) predictions proved that the pharmacokinetic properties of Compound 32 are similar to those of the commercial safener BAS 145138. The present work demonstrated that diazabicyclo derivatives are potentially efficacious as herbicide safeners, meriting further investigation.

Computer-Aided and AILDE Approaches to Design Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a pivotal enzyme in tocopherol and plastoquinone synthesis and a potential target for novel herbicides. Thirty-five pyridine derivatives were selected to establish a Topomer comparative molecular field analysis (Topomer CoMFA) model to obtain correlation information between HPPD inhibitory activity and the molecular structure. A credible and predictive Topomer CoMFA model was established by "split in two R-groups" cutting methods and fragment combinations (q² = 0.703, r² = 0.957, ONC = 6). The established model was used to screen out more active compounds and was optimized through the auto in silico ligand directing evolution (AILDE) platform to obtain potential HPPD inhibitors. Twenty-two new compounds with theoretically good HPPD inhibition were obtained by combining the high-activity contribution substituents in the existing molecules with the R-group search via Topomer search. Molecular docking results revealed that most of the 22 fresh compounds could form stable π-π interactions. The absorption, distribution, metabolism, excretion and toxicity (ADMET) prediction and drug-like properties made 9 compounds potential HPPD inhibitors. Molecular dynamics simulation indicated that Compounds Y12 and Y14 showed good root mean square deviation (RMSD) and root mean square fluctuation (RMSF) values and stability. According to the AILDE online verification, 5 new compounds with potential HPPD inhibition were discovered as HPPD inhibitor candidates. This study provides beneficial insights for subsequent HPPD inhibitor design.

A Multifunctional and Fast-Response Lysosome-Targetable Fluorescent Probe for Monitoring pH and Isoxaflutole

A new chemosensor, namely N-(2-morpholinoethyl)acetamide-4-morpholine-1,8-naphthimide (MMN), was designed and synthesized through an amidation reaction. MMN was fabricated as a multifunctional fluorescent probe for monitoring pH and isoxaflutole. MMN exhibited excellent stability in MeCN/H₂O (v/v, 9/1), with an obvious "off-on" fluorescence response toward pH changes due to intramolecular charge transfer (ICT), where the linear response ranges of MMN in the weakly acidic system were from 4.2 to 5.0 and from 5.0 to 6.0 with apparent pK_a = 4.62 ± 0.02 and 5.43 ± 0.02. Based on morpholine as the lysosome targetable unit, MMN could selectively locate lysosomes in live cells. MMN also successfully detected the presence of H⁺ in test papers. Finally, MMN could specifically recognize isoxaflutole at a detection limit of 0.88 μM. A possible sensing mechanism was identified based on density function theory calculations. These results indicate that MMN could be a superior potential chemosensor for detecting pH and isoxaflutole selectively and sensitively and could be used in real sample detection.

Discovery of novel phenoxypyridine as promising protoporphyrinogen IX oxidase inhibitors

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is a significant target for the discovery of novel bleaching herbicides. Starting from the active fragments of several known commercial herbicides, a series of PPO inhibitors with diphenyl ether scaffolds were designed and synthesized by substructure splicing and bioisosterism methods. The greenhouse herbicidal activity and the PPO inhibitory activity in vitro were measured. The results showed that the novel synthesized compounds have good PPO inhibitory activity, and the IC₅₀ value against corn PPO ranges from 0.032 ± 0.008 mg/L to 3.245 ± 0.247 mg/L. Among all target compounds, compound P2 showed the best herbicidal activity, with a half inhibitory concentration (IC₅₀) of 0.032 ± 0.008 mg/L. In addition, the molecular docking results showed that the benzene ring part of compound P2 can form a π-π stacking with PHE-392, and the trifluoromethyl group and ARG-98 form two hydrogen bonds. Crop safety experiments and cumulative concentration analysis experiments indicated that compound P2 can be used for weed control in rice, wheat, soybean and corn. Therefore, compound P2 can be selected to develop potential lead compounds for novel PPO inhibitors.

Research Progress in the Design and Synthesis of Herbicide Safeners: A Review

Detoxification plays an important role in herbicide action. Herbicide safeners selectively protect crops from herbicide injury without reducing the herbicidal efficiency against the target weeds. With the large-scale use of herbicides, herbicide safeners have been widely used in sorghum, wheat, rice, corn, and other crops. In recent years, an increasing number of unexpected new herbicide safeners have been designed. The varieties, structural characteristics, uses, and synthetic routes of commercial herbicide safeners are reviewed in this paper. The design ideas and structural characteristics of novel herbicide safeners are summarized, which provide a basis for the design of bioactive molecules as new herbicide safeners in the future.

Synthesis and biological activity of novel hydantoin cyclohexyl sulfonamide derivatives as potential antimicrobial agents in agriculture

BACKGROUND

Plant disease is one of the most serious problems in agriculture that can damage crops. Chemical fungicides are widely used to control plant diseases, but have led to resistance and a series of environmental problems. It is, therefore, necessary to develop highly effective and eco-friendly antimicrobial compounds with novel structures.

RESULTS

A series of novel hydantoin cyclohexyl sulfonamide derivatives were synthesized through an intramolecular condensation reaction. The bioassay results indicated that a majority of the title compounds displayed potent inhibitory activity against Botrytis cinerea, Sclerotinia sclerotiorum and Erwinia carotorora. The in vivo inhibition rate of compound 3h was 91.01% against B. cinerea, which was higher than that of iprodione (84.07%). Compound 3w showed excellent antifungal activity against B. cinerea with a half-maximal effective concentration (EC₅₀ ) of 4.80 μg ml^-1 , which is lower than that of iprodione. Compound 3q had an EC₅₀ value of 1.44 μg ml^-1 against S. sclerotiorum, which was close to that of iprodione (1.39 μg ml^-1 ), and the inhibition rate was also similar to that of iprodione. Compounds 3i and 3w had the best inhibition efficacy against S. sclerotiorum, both on growth of the mycelium and sclerotia and in the greenhouse pot test in vitro. Further study showed that compounds 3h, 3r and 3s have superb antibacterial activity against E. carotorora with EC₅₀ values of 2.65, 4.24 and 4.29 μg ml^-1 respectively, and were superior to streptomycin sulfate (5.96 μg ml^-1 ).

CONCLUSION

Because of their excellent antifungal and antibacterial activity against B. cinerea, S. sclerotiorum and E. carotorora, these hydantoin cyclohexyl sulfonamide derivatives could be considered as suitable candidates for new antimicrobial agents. © 2021 Society of Chemical Industry.

6-Ethoxy-4- N-(2-morpholin-4-ylethyl) -2-N-propan-2-yl-1,3, 5-triazine-2, 4-diamine endows herbicidal activity against Phalaris minor a weed of wheat crop field: An in -silico and experimental approaches of herbicide discovery

Phalaris minor is a major weed of wheat crop which has evolved resistance against herbicides. Isoproturon is the most accepted herbicide developed resistance in 1992. Later, introduced herbicides also developed resistance and cross-resistance to their respective binding sites. Isoproturon binds at the Q_B binding site of the D1 protein of photosystem-II (PS-II), which blocks the electron transfer in photosynthesis. In this work, we have carried out a series of computational studies to prioritize the promising herbicides against D1 protein of P. minor. Through the computational studies, twenty-four lead molecules are prioritized which have shown a higher binding affinity and inhibition constant than the reference ligand molecule. The binding and conformational stability of docked complexes was evaluated by molecular dynamics simulations and binding free energy calculations i.e., MM/PBSA. A list of amino acids such as Ala225, Ser226, Phe227, and Asn229 present in the binding site of protein is obtained to be playing an important role in the stability of the protein-lead complex via hydrogen bond and π-π interactions. Binding free energy calculation revealed that the selected lead molecule binding is energetically favorable and driven by electrostatic interactions. Among 24 leads, computational results have uncovered eight promising compounds as potential herbicides which have shown comparable physiochemical profile, better docking scores, system stability, H-bond occupancy, and binding free energy than terbutryn, a reference molecule. These prioritized molecules were custom synthesized and evaluated for their herbicidal activity and specificity through whole plant assay under laboratory-controlled conditions. The lead molecule ELC5 (6-ethoxy-4-N-(2-morpholin-4-ylethyl)-2-N-propan-2-yl-1,3,5-triazine-2,4-diamine) has shown comparable activity to the reference herbicide(isoproturon) against P. minor.

Design, Synthesis, and Herbicidal Activity of Diphenyl Ether Derivatives Containing a Five-Membered Heterocycle

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is an important target for discovering novel herbicides, and it causes bleaching symptoms by inhibiting the synthesis of chlorophyll and heme. In this study, the active fragments of several commercial herbicides were joined by substructure splicing and bioisosterism, and a series of novel diphenyl ether derivatives containing five-membered heterocycles were synthesized. The greenhouse herbicidal activity and the PPO inhibitory activity in vitro were discussed in detail. The results showed that most compounds had good PPO inhibitory activity, and target compounds containing trifluoromethyl groups tended to have higher activity. Among them, compound G4 showed the best inhibitory activity, with a half-maximal inhibitory concentration (IC₅₀) of 0.0468 μmol/L, which was approximately 3 times better than that of oxyfluorfen (IC₅₀ = 0.150 μmol/L). In addition, molecular docking indicated that compound G4 formed obvious π-π stacking interactions and hydrogen bond interactions with PHE-392 and ARG-98, respectively. Remarkably, compound G4 had good safety for corn, wheat, rice, and soybean, and the cumulative concentration in crops was lower than that of oxyfluorfen. Therefore, compound G4 can be used to develop potential lead compounds for novel PPO inhibitors.

Design, Synthesis and Evaluation of Novel Antimicrobial Polymers Based on the Inclusion of Polyethylene Glycol/TiO2 Nanocomposites in Cyclodextrin as Drug Carriers for Sulfaguanidine

Polymers and their composites have recently attracted attention in both pharmaceutical and biomedical applications. Polyethylene glycol (PEG) is a versatile polymer extensively used in medicine. Herein, three novel PEG-based polymers that are pseudopolyrotaxane (PEG/α-CD) (1), titania–nanocomposite (PEG/TiO₂NPs) (2), and pseudopolyrotaxane–titania–nanocomposite (PEG/α-CD/TiO₂NPs) (3), were synthesized and characterized. The chemical structure, surface morphology, and optical properties of the newly materials were examined by FT-IR, ¹H-NMR, SEM, and UV–Vis., respectively. The prepared polymers were used as drug carriers of sulfaguanidine as PEG/α-CD/Drug (4), PEG/TiO₂NPs/Drug (5), and PEG/α-CD/TiO₂NPs/Drug (6). The influence of these drug-carrying formulations on the physical and chemical characteristics of sulfaguanidine including pharmacokinetic response, solubility, and tissue penetration was explored. Evaluation of the antibacterial and antibiofilm effect of sulfaguanidine was tested before and after loading onto the prepared polymers against some Gram-negative and positive bacteria (E. coli, Pseudomonas aeruginosa, and Staphylococcus aureus (MRSA)), as well. The results of this work turned out to be very promising as they confirmed that loading sulfaguanidine to the newly designed polymers not only showed superior antibacterial and antibiofilm efficacy compared to the pure drug, but also modified the properties of the sulfaguanidine drug itself.

Mechanism of the Fe(iii)-catalyzed synthesis of hexahydropyrimidine with α-phenylstyrene: a DFT study

It is very important to develop multiple C–H substitution reactions of simple alkenes to obtain complex unsaturated components. The present study focuses on a theoretical investigation of the plausible mechanism in the Fe(OTf)₃-catalyzed tandem amidomethylative reactions of α-phenylstyrene. Bis(tosylamido)methane is activated by Fe(OTf)₃ to form tosylformaldimine and its Fe(OTf)₃-adduct. The Fe(OTf)₃-adduct undergoes an intermolecular aza-Prins reaction with α-phenylstyrene to form allylamide. The DFT data support the formation of the hexahydropyrimidine derivative from allylamide, and “condensation/iminium homologation/intramolecular aza-Prins” is the optimal reaction path. At the same time, a possible reaction pathway for the conversion of the hydrolysate 1,3-diamide derivative to the hexahydropyrimidine (HHP) derivative is given. This work is thus instructive for understanding Fe(iii)-based tandem catalysis for the amidomethylative multiple-substitution reactions of alkenes.

It is very important to develop multiple C–H substitution reactions of simple alkenes to obtain complex unsaturated components.

Design, Synthesis, Structure-Activity Relationship, Molecular Docking, and Herbicidal Evaluation of 2-Cinnamoyl-3-Hydroxycyclohex-2-en-1-one Derivatives as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

Cinnamic acid, isolated from cinnamon bark, is a natural product with excellent bioactivity, and it effectively binds with cyclohexanedione to form novel 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. According to the active sub-structure combination principle, a series of novel 3-hydroxy-2-cinnamoyl-2-en-1-one derivatives were designed and synthesized. The title compounds were characterized by infrared, ¹H NMR, ¹³C NMR, and HRMS. The in vitro inhibitory activity of AtHPPD verified that compound II-13 showed the most activity with a half-maximal inhibitory concentration (IC₅₀) value of 0.180 μM, which was superior to that of mesotrione (0.206 μM) in vitro. The preliminary herbicidal activity tests demonstrated that some compounds had good herbicidal activity especially compound II-13 at a concentration of 150 g ai/ha. The binding mode of AtHPPD through molecular docking indicated that two oxygens of compounds II-13 formed bidentate interactions with metal ions, and the benzene ring formed π-π accumulation effects with Phe-381 and Phe-424. The results of molecular dynamics simulations showed that compound II-13 exhibited a more stable binding ability with AtHPPD than mesotrione. This study provided insights into the development of natural and efficient herbicides in the future.

Quinoxaline derivatives as herbicide safeners by improving Zea mays tolerance

Isoxaflutole (IXF), a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, causes injury to crops leading to reductions in grain yield. In order to solve the phytotoxicity caused by IXF, the present work evaluated the protective response of the substituted quinoxaline derivatives as potential safeners on Zea mays. The bioassay results showed that all of the test compounds displayed protection against IXF. In particular, safener I-6 exhibited excellent safener activity against IXF injury via enhancing glutathione (GSH) content, glutathione S transferases (GSTs) and cytochrome P450 monooxygenases (CYP450) activity. The tested compounds induced the activity of CYP450 and GSTs in Z. mays. The physicochemical properties and ADMET properties of safener I-6, benoxacor and diketonitrile (DKN, IXF metabolite) were compared to predict pharmaceutical behavior. The present work demonstrates that the safener I-6 could be considered as a potential candidate for developing novel safeners in the future.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Design, synthesis, and herbicidal activity of novel phenoxypyridine derivatives containing natural product coumarin

BACKGROUND

In recent years, protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors have been widely studied as important agricultural herbicides. Our research focused on the design and synthesis of novel PPO inhibitor herbicides, through linking of a diphenylether pyridine bioisostere structure to substituted coumarins, which aims to enhance environmental and crop safety while retaining high efficacy.

RESULTS

A total of 21 compounds were synthesized via acylation reactions and all compounds were characterized using infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectra. The respective configurations of compounds IV-6 and IV-12 were also confirmed using single crystal X-ray diffraction. The bioassay results showed that the title compounds displayed notable herbicidal activity, particularly compound IV-6 which displayed better herbicidal activity in greenhouse and field experiments, crop selectivity and safety for cotton and soybean compared with the commercial herbicide oxyfluorfen.

CONCLUSION

The work revealed that compound IV-6 deserves further attention as a candidate structure for a novel and safe herbicide. © 2021 Society of Chemical Industry.

Fragmenlt Recombination Design, Synthesis, and Safener Activity of Novel Ester-Substituted Pyrazole Derivatives

Fenoxaprop-p-ethyl (FE), a type of acetyl-CoA carboxylase (ACCase) inhibitor, has been extensively applied to a variety of crop plants. It can cause damage to wheat (Triticum aestivum) even resulting in the death of the crop. On the prerequisite of not reducing herbicidal efficiency on target weed species, herbicide safeners selectively protect crops from herbicide injury. Based on fragment splicing, a series of novel substituted pyrazole derivatives was designed to ultimately address the phytotoxicity to wheat caused by FE. The title compounds were synthesized in a one-pot way and characterized via infrared spectroscopy, ¹H nuclear magnetic resonance, ¹³C nuclear magnetic resonance, and high-resolution mass spectrometry. The bioactivity assay proved that the FE phytotoxicity to wheat could be reduced by most of the title compounds. The molecular docking model indicated that compound IV-21 prevented fenoxaprop acid (FA) from reaching or acting with ACCase. The absorption, distribution, metabolism, excretion, and toxicity predictions demonstrated that compound IV-21 exhibited superior pharmacokinetic properties to the commercialized safener mefenpyr-diethyl. The current work revealed that a series of newly substituted pyrazole derivatives presented strong herbicide safener activity in wheat. This may serve as a potential candidate structure to contribute to the further protection of wheat from herbicide injury.

Phenoxypyridine derivatives containing natural product coumarins with allelopathy as novel and promising proporphyrin IX oxidase-inhibiting herbicides: Design, synthesis and biological activity study

To seek novel and safe protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors with excellent herbicidal activity. A series of novel phenoxypyridine derivatives containing natural product coumarins with allelopathy were designed and synthesized based on bioisosterism and active subunit combination in this research. Compounds W3.1 and W3.4, with the half-maximal inhibitory concentration (IC₅₀) value of 0.02653 mg/L and 0.01937 mg/L, respectively, displayed excellent herbicidal activity in greenhouse. Their herbicidal activity was similar to commercial herbicide oxyfluorfen (IC₅₀ = 0.04943 mg/L). The best field inhibitory effect of compounds W3.1 and W3.4 recorded was at doses of 450 g ai/ha and 300 g ai/ha, respectively. Compound W3.4 had the best herbicidal activity among all the target compounds in this paper. Molecular docking analysis revealed that compounds W3.1 and W3.4 could form a hydrogen bonds with the amino acid AGR-98 and a π-π superposition with the amino acid PHE-398, respectively, which was similar to the oxyfluorfen. The crop selectivity tests results indicated that maize, cotton and soybean showed high tolerance to compound W3.4. Compound W3.4 reduced the C_a and C_b contents of wheat and rice, but had less effect on maize, cotton and soybean. Selectivity of compound W3.4 in maize, cotton and soybean were appeared to be due to reduced absorption of the herbicide compared to wheat and rice. Compound W3.4 deserves further attention as a candidate structure for new herbicides.

Synthesis, Crystal Structure, Herbicidal Activity, and SAR Study of Novel N-(Arylmethoxy)-2-chloronicotinamides Derived from Nicotinic Acid

Nicotinic acid, also known as niacin, is a natural product, which is widely found in plants and animals. To discover novel natural-product-based herbicides, a series of N-(arylmethoxy)-2-chloronicotinamides were designed and synthesized. Some of the new N-(arylmethoxy)-2-chloronicotinamides exhibited excellent herbicidal activity against Agrostis stolonifera (bentgrass) at 100 μM. Compound 5f (2-chloro-N-((3,4-dichlorobenzyl)oxy)nicotinamide) possessed excellent herbicidal activity against Lemna paucicostata (duckweed), with an IC₅₀ value of 7.8 μM, whereas the commercial herbicides clomazone and propanil had values of 125 and 2 μM, respectively. The structure-activity relationships reported in this paper could be used for the development of new herbicides against monocotyledonous weeds.

Electrospun Polymer-Free Nanofibers Incorporating Hydroxypropyl-β-cyclodextrin/Difenoconazole via Supramolecular Assembly for Antifungal Activity

In this study, flexible and self-standing hydroxypropyl-β-cyclodextrin/difenoconazole inclusion complex (HPβCD/DZ-IC) nanofibers were prepared by polymer-free electrospinning, which exhibited potential to be a new fast-dissolving pesticide formulation. Scanning electron microscopy and optical microscopy were applied to evaluate the morphology of nanofibers, which showed that the resulting HPβCD/DZ-IC nanofibers were bead-free and uniform. In addition, the proton nuclear magnetic resonance (¹H NMR) spectrum suggested a stoichiometric ratio of 1:0.9 (HPβCD/DZ). Other characterization methods, such as UV-vis absorption, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), were applied in this study. On the one hand, UV-vis absorption, fluorescence spectroscopy, FT-IR, XRD, and TGA provided useful information for the successful formation of an inclusion complex; on the other hand, the results of TGA indicated the thermal stability of DZ was enhanced after the formation of inclusion complexes. Besides, the phase solubility test could explain the increased water solubility of the nanofibers of inclusion complexes formed by DZ and HPβCD. The results of molecular docking studies demonstrated the most favorable binding interactions when HPβCD combined with DZ. The dissolution test and the antifungal performance test exhibited the characteristics of fast dissolution and the excellent antifungal performance of HPβCD/DZ-IC nanofibers, respectively.

Design, synthesis, herbicidal activity and CoMFA of aryl-formyl piperidinone HPPD inhibitors

Isoxazole, nicotinic acid and benzoic acid are important components in many natural products and useful synthons to build macrostructures having valuable biological activities. In continuation of our effort to discover 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) inhibitors and search for active fragments from natural products, a series of substituted aryl-formyl piperidinone derivatives with natural product fragments was rationally designed, synthesized and tested for their herbicidal activity. Compound I-9 was considered the most effective candidate with an IC₅₀ value of 0.260 μM. The molecular docking results showed that the triketone group of compound I-9 forms a bidentate complex with a metal ion, and the benzene ring interacted with Phe424 and Phe381 via π-π stacking, which was similar to the mechanisms of mesotrione. The present work indicates that compound I-9 may serve as a potential lead compound for further development of green HPPD inhibitors.

Thiram/hydroxypropyl-β-cyclodextrin inclusion complex electrospun nanofibers for a fast dissolving water-based drug delivery system

The electrospinning of thiram/hydroxypropyl-β-cyclodextrin inclusion complex nanofiber (thiram/HPβCD-IC-NF) was produced for establishing a quick dissolving water-based drug delivery system. As a dithiocarbamate broad-spectrum fungicide, thiram is insoluble in water. High-concentration HPβCD solutions (180 %, w/v) were applied in thiram/HPβCD systems to implement electrospinning with no extra polymer matrix added. The formation of thiram/HPβCD-IC-NF was identified by Fourier transform infrared spectroscopy, X-ray diffraction as well as nuclear magnetic resonance. Phase solubility study proved HPβCD played a huge role in the improvement in solubility of thiram, and thiram/HPβCD-IC-NF showed an excellent dissolution rate. Scanning electron microscopy was used to examine the configuration of surface of thiram/HPβCD-IC-NF, which exhibited that thiram/HPβCD-IC-NF was uniform and beadless. In addition, thiram/HPβCD-IC-NF exhibited better antifungal activity and thermal stability than pure thiram. In summary, thiram/HPβCD-IC-NF drug delivery system contributed to water solubility, thermal stability and antifungal activity of thiram. It could provide a new idea for the development of new formulations of rapidly dissolving green pesticides, and made efforts to promote the sustainable development of agriculture.

Strain-release enabled [3 + 2] annulation of 3-aminooxetanes with simple CN bonds: facile synthesis of imidazolidines

An unprecedented [3+2] annulation of readily available 1,3,5-triazinanes and 3-aminooxetanes is accomplished for the first time, enabling the convenient synthesis of a range of structurally diverse 4-hydroxymethyl imidazolidines.