Design, synthesis and SAR study of novel sulfonylureas containing an alkenyl moiety

Design, Synthesis, and Fungicidal Activities of Novel N-(Pyrazol-5-yl)benzamide Derivatives Containing a Diphenylamine Moiety

To accelerate the development of novel fungicides, a variety of N-(pyrazol-5-yl)benzamide derivatives with a diphenylamine moiety were designed and synthesized using a pharmacophore recombination strategy based on the structure of pyrazol-5-yl-aminophenyl-benzamides. The bioassay results demonstrated that most of the target compounds had excellent in vitro antifungal activities against Sclerotinia sclerotiorum, Valsa mali, and Botrytis cinerea. In particular, compound 5IIIh exhibited remarkable activity against S. sclerotiorum (EC50 = 0.37 mg/L), which was similar to that of fluxapyroxad (EC50 = 0.27 mg/L). In addition, compound 5IIIc (EC50 = 1.32 mg/L) was observed to be more effective against V. mali than fluxapyroxad (EC50 = 12.8 mg/L) and comparable to trifloxystrobin (EC50 = 1.62 mg/L). Furthermore, compound 5IIIh demonstrated remarkable in vivo protective antifungal properties against S. sclerotiorum, with an inhibition rate of 96.8% at 100 mg/L, which was close to that of fluxapyroxad (99.6%). Compounds 5IIIc (66.7%) and 5IIIh (62.9%) exhibited good in vivo antifungal effects against V. mali at 100 mg/L, which were superior to that of fluxapyroxad (11.1%) but lower than that of trifloxystrobin (88.9%). The succinate dehydrogenase (SDH) enzymatic inhibition assay was conducted to confirm the mechanism of action. Molecular docking analysis further revealed that compound 5IIIh has significant hydrogen-bonding, π-π, and p-π conjugation interactions with ARG 43, SER 39, TRP 173, and TYR 58 in the binding site of SDH, and the binding mode was similar to that of the commercial fungicide fluxapyroxad. All of the results suggest that compound 5IIIh could be a potential SDH inhibitor, offering a valuable reference for future studies.

Molecular Targets of Herbicides and Fungicides─Are There Useful Overlaps for Fungicide Discovery?

New fungicide modes of action are needed for fungicide resistance management strategies. Several commercial herbicide targets found in fungi that are not utilized by commercial fungicides are discussed as possible fungicide molecular targets. These are acetyl CoA carboxylase, acetolactate synthase, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthase, phytoene desaturase, protoporphyrinogen oxidase, long-chain fatty acid synthase, dihydropteroate synthase, hydroxyphenyl pyruvate dioxygenase, and Ser/Thr protein phosphatase. Some of the inhibitors of these herbicide targets appear to be either good fungicides or good leads for new fungicides. For example, some acetolactate synthase and dihydropteroate inhibitors are excellent fungicides. There is evidence that some herbicides have indirect benefits to certain crops due to their effects on fungal crop pathogens. Using a pesticide with both herbicide and fungicide activities based on the same molecular target could reduce the total amount of pesticide used. The limitations of such a product are discussed.

Facile synthesis, crystal structure, quantum calculation, and biological evaluations of novel selenenyl sulfide compounds as potential agrochemicals

BACKGROUND

In order to design compounds with fresh molecular skeleton to break through the limitation of available agrochemicals, a series of 36 novel selenenyl sulfide compounds were chemically synthesized, and their biological activities were fully evaluated against tobacco mosaic virus (TMV), 14 plant pathogenic fungi, three insect species and plant acetohydroxyacid synthase (AHAS).

RESULTS

All the target compounds were characterized by proton nuclear magnetic resonance (¹ H-NMR), carbon-13 (¹³ C)-NMR, selenium-77 (⁷⁷ Se)-NMR, and high-resolution mass spectrometry (HRMS). The crystal structure of 10j indicated that the Se-S bond was successfully constructed. Compounds 10d, 10h, 10s, 10u, 10aa, 10ac, 10ae, 10ag, and 10ai exhibited 40%, 43%, 39%, 41%, 47%, 46%, 47%, 42%, and 39% anti-TMV activities at 500 mg L^-1 , better than that of ribavirin. The median effective concentration (EC₅₀ ) against Sclerotinia sclerotiorum of 10ac was 6.69 mg L^-1 and EC₅₀ values against Physalospora piricola and Pyricularia grisea of 10z were 12.25 mg L^-1 and 15.27 mg L^-1 , respectively, superior to the corresponding values of chlorothalonil. Compounds 10c and 10v demonstrated 100% larvicidal activity against Culex pipiens pallens at 5 mg L^-1 , while 10a displayed 100% insecticidal activity against Mythimna separata at 200 mg L^-1 . Compounds 10c, 10j, and 10o showed > 60% inhibitions against plant AHAS at 10 μmol L^-1 . From the quantum calculation, highest occupied molecular orbital (HOMO) was considered as a factor that affects the anti-TMV activity.

CONCLUSION

The preliminary results suggested that more efforts should be devoted to exploring the selenenyl sulfides for the discovery of new leads of antiviral agent, fungicide, insecticide or AHAS inhibitors as potential agrochemicals for crop protection. © 2023 Society of Chemical Industry.

Novel Sulfonylurea Derivatives as Potential Antimicrobial Agents: Chemical Synthesis, Biological Evaluation, and Computational Study

Methicillin-resistant Staphylococcus aureus (MRSA) is a worldwide health threat and has already tormented humanity during its long history, creating an urgent need for the development of new classes of antibacterial agents. In this study, twenty-one novel sulfonylurea derivatives containing phenyl-5-vinyl and pyrimidinyl-4-aryl moieties were designed and synthesized, among which, nine compounds exhibited inhibitory potencies against Gram-positive bacterial strains: MRSA (Chaoyang clinical isolates), S. aureus ATCC6538, vancomycin-resistant Enterococci-309 (VRE-309), and Bacillus subtilis ATCC 6633. Especially, 9i and 9q demonstrated inhibitory activities against the four bacterial strains with minimum inhibitory concentrations (MICs) of 0.78-1.56 μg/mL, and quite a few of other MRSA clinical strains with MICs of 0.78 μg/mL, superior to those of the positive controls vancomycin (MIC of 1 μg/mL) and methicillin (MIC of >200 μg/mL). This is the very first time that sulfonylurea derivatives have been identified as promising inhibitors against different MRSA clinical isolates. In addition, all the MIC values of the synthesized compounds against Candida albicans were greater than 100 μg/mL. Since the reported anti-Candida activities of sulfonylureas were due to acetohydroxyacid synthase (AHAS) inhibition, the molecular target against MRSA for the target sulfonylureas was thought to be a different mode of action. Density functional theory (DFT) calculations were finally performed to understand the structure-activity relationships, based on which, significant differences were observed between their HOMO maps for compounds with strong antibacterial activities and weak anti-MRSA effects. The present results hence provide valuable guidance for the discovery of novel agents to treat bacterial infections, especially against MRSA.

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.

Chemical preparation, degradation analysis, computational docking and biological activities of novel sulfonylureas with 2,5-disubstituted groups

Based on the previous finding that a substitution at 5-position of the benzene ring is favorable to enhance the degradation rates of sulfonylurea herbicides, a total of 16 novel 2,5-disubsituted sulfonylurea compounds were chemically synthesized and fully characterized by means of ¹H NMR, ¹³C NMR, HRMS and X-ray diffraction. By using HPLC analysis, the degradation behavior of M03, a compound belonging to this family, was studied and confirmed that chlorsulfuron itself is not a degraded product of the 2,5-disubstituted sulfonylureas. Inhibition constants against plant acetohydroxyacid synthase (AHAS) were determined for selected compounds, among which SU3 showed seven times stronger activity against the mutant W574L enzyme than chlorsulfuron. Molecular docking suggested that the substituted group at 5-position of benzene ring is likely to interact with the surrounding residues Met200 and Asp376 of AtAHAS. From the greenhouse herbicidal assay and crop safety test, SU5 and SU6 are considered as herbicide candidates to control dicotyledon weeds in corn, while SU3 is likely to be a promising candidate to control dicotyledon weed species and barnyard grass in wheat. The present research has therefore provided some new insights to understand the structure-activity relationships of herbicidal sulfonylureas with di-substitutions at benzene ring.

Novel [1,2,4]-Triazolo[3,4-b]-[1,3,4]thiadizoles as Potent Pyruvate Kinase Inhibitors for Fungal Control

To discover novel target-based fungicidal candidates, a molecular design model was established with a three-dimensional (3D) structure of Rhizoctonia solani pyruvate kinase (RsPK) simulated with the AlphaFold 2 and YZK-C22 as a fungicidal lead. A series of novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives were rationally designed, synthesized, evaluated for their fungicidal performance, and validated for their mode of action. The in vitro bioassays with R. solani indicated that compounds 5g, 5o, and 5z with an EC₅₀ value ranging from 1.01 to 1.54 μg/mL displayed higher fungicidal activity than the positive control YZK-C22 with its EC₅₀ of 3.14 μg/mL. Especially, 5o exhibited high potency and a broad spectrum against Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Physalospora piricola, R. solani, and Sclerotinia sclerotiorum with its EC₅₀ value falling between 1.54 and 13.10 μg/mL. Like all positive controls, 5g, 5o, and 5z showed excellent in vivo growth inhibition against Pseudoperonospora cubensis at 200 μg/mL. Even though the PK enzymatic inhibition assay showed that 5o was approximately 2.6 times less active than YZK-C22 (IC₅₀: 29.14 vs 11.15 μg/mL, respectively), the similar fluorescence quenching patterns of RsPK by 5o and YZK-C22, and the docking results of interactions between RsPK and 5o or YZK-C22 implied that they might share the similar binding site in the RsPK active pocket. Our studies suggested that 5o could be used as a potent fungicidal lead for further optimization. The results of comparative molecular field analysis (CoMFA) provided a direction for further molecular design.

Computer-Assisted Improvement of Sulfonylureas with Antifungal Properties and Limited Herbicidal Activity: Potential Application in Forage Conservation

This work reports studies at the molecular level of a series of modified sulfonylureas to determine the chemophoric sites responsible for their antifungal and herbicidal activities. For forage conservation, high antifungal potency and low phytotoxicity are required. A molecular modeling study based on multivariate image analysis applied to quantitative structure-activity relationship (MIA-QSAR) was performed to model these properties, as well as to guide the design of new agrochemical candidates. As a result, the MIA-QSAR models were reliable, robust, and predictive; for antifungal activity, the averages of the main validation parameters were r² = 0.936, q² = 0.741, and r²_pred = 0.720, and for herbicidal activity, the model was very predictive (r²_pred = 0.981 and r²_m = 0.944). From the interpretation of the MIA-plots, 46 novel sulfonylureas with likely improved performance were proposed, from which 9 presented promising calculated selectivity indexes. Docking studies were performed to validate the QSAR predictions and to understand the interaction mode of the proposed ligands with the acetohydroxyacid synthase enzyme.

Taking Advantage of the Renewable Forest Bioresource Turpentine to Prepare α,β-Unsaturated Compounds as Highly Efficient Fungicidal Candidates

In a continuous study on the high-value-added exploration of a renewable forest bioresource turpentine in modern organic agriculture, two series of α-pinene derivatives containing amide and α,β-unsaturated ketone pharmacophores were prepared. Through an in-depth fungicidal activity study, the title compounds presented excellent inhibitory activity against common crop fungi, especially Sclerotinia sclerotiorum, and the notable EC₅₀ values of α,β-unsaturated compounds 3u (funan containing) and 3v (thiophene containing) were 1.657 and 1.749 μg/mL, respectively. Further physiological and biochemical studies on S. sclerotiorum revealed that compounds 3u and 3v reduced the ergosterol content in the cell membrane and increased the permeability of the cell membrane. In combination with their effect on mycelial morphology, the title compounds might have inhibitory effects on the biosynthesis of ergosterol, which is a paramount component of the target cell membrane. Moreover, quantitative structure-activity relationship (QSAR) and SAR studies revealed that the charge distribution of α,β-unsaturated carbonyl ketone derivatives played an important role in the observed fungicidal activity. In summary, this study highlights the design and development of novel high-efficacy turpentine-based antifungal agents.

Molecular targets for antifungals in amino acid and protein biosynthetic pathways

Fungi cause death of over 1.5 million people every year, while cutaneous mycoses are among the most common infections in the world. Mycoses vary greatly in severity, there are long-term skin (ringworm), nail or hair infections (tinea capitis), recurrent like vaginal candidiasis or severe, life-threatening systemic, multiorgan infections. In the last few years, increasing importance is attached to the health and economic problems caused by fungal pathogens. There is a growing need for improvement of the availability of antifungal drugs, decreasing their prices and reducing side effects. Searching for novel approaches in this respect, amino acid and protein biosynthesis pathways appear to be competitive. The route that leads from amino acid biosynthesis to protein folding and its activation is rich in enzymes that are descriptive of fungi. Blocking the action of those enzymes often leads to avirulence or growth inhibition. In this review, we want to trace the principal processes of fungi vitality. We present the data of genes encoding enzymes involved in amino acid and protein biosynthesis, potential molecular targets in antifungal chemotherapy, and describe the impact of inhibitors on fungal organisms.

Design, Synthesis and Biological Evaluation of N-((2-phenyloxazol-4-yl)methyl) Pyrimidine Carboxamide Derivatives as Potential Fungicidal Agents

Twelve N-((2-phenyloxazol-4-yl)methyl) pyrimidine carboxamide derivatives were designed, synthesized, and characterized by 1H NMR, 13C NMR, and HRMS. The fungicidal activities of these new compounds against Sclerotinia sclerotiorum, Botrytis cinereal, and Colletotrichum fragariae were evaluated. The results indicated that compounds 5b, 5f, and 5g displayed potential fungicidal activities against tested fungi, especially 5f exhibited IC50 value of 28.9 mg/L against S. sclerotiorum. Moreover, the compounds 5f and 5g showed IC50 values of 54.8 mg/L and 62.2 mg/L against C. fragariae respectively, which shows that they were more active than the commercial fungicide hymexazol. The superficial structure-activity relationships were discussed, which may be of benefit for the development of fungicides and discovery of novel fungicides.

Antifungal Application of Rosin Derivatives from Renewable Pine Resin in Crop Protection

In the current work, we synthesized two series of dehydroabietyl amide derivatives from natural product rosin and evaluated their antifungal effects on Valsa mali, Phytophthora capsici, Botrytis cinerea, Sclerotinia sclerotiorum, and Fusarium oxysporum. In vitro and in vivo antifungal activities results indicated that rosin-based amide compounds containing thiophene heterocycles had better inhibitory effects on B. cinerea. In particular, compound 5b (5-fluoro-2-thiophene dehydroabietyl amide) exhibited the excellent antifungal properties against B. cinerea with an EC₅₀ of 0.490 mg/L, which was lower compared to the positive control penthiopyrad (0.562 mg/L). Physiological and biochemical studies showed that the primary action mechanism of compound 5b on B. cinerea changes mycelial morphology, increases cell membrane permeability, and inhibits the TCA pathway in respiratory metabolism. Furthermore, QSAR and SAR studies revealed that charge distribution of rosin-based amides derivatives have a key role in the antifungal activity through the hydrogen bonding, conjugation, and electrostatic interaction between the compounds and the receptors of the target. To sum up, this study contributes to the development of rosin-based antifungal agents with a novel structure and preferable biological activity.

Controllable Soil Degradation Rate of 5-Substituted Sulfonylurea Herbicides as Novel AHAS Inhibitors

Chlorsulfuron has been applied in wheat fields as a recognized herbicide worldwide, yet it was officially banned in China since 2014 for its soil persistence problem. On the basis of our previous research that 5-dimethylamino distinctively accelerated degradation rate in soils, a modified amino moiety (Ia-c) and monosubstituted amino group (Id-e) were introduced onto the fifth position of the benzene ring in sulfonylurea structures, as well as heterocyclic amino substituents (If-g) to seek a suitable soil degradation rate during such an in situ crop rotation system. Referring to the biological data and ScAHAS inhibition and ScAHAS docking results, they turned out to be AHAS inhibitors with high potent herbicidal activities. The various influence on soil degradation rate along with crop safety indicated that different substituents on the fifth position have exerted an apparent impact. Their united study of structure-activity-safety-degradation relationship has great potential to provide valuable information for further development of eco-friendly agrochemicals.

Total Syntheses of Allelopathic 4-Oxyprotoilludanes, Melleolides, and Echinocidins

Stereocontrolled total syntheses of allelopathic 4-oxyprotoilludane sesquiterpenes, melleolide, melleolide F, and echinocidins B and D were achieved. The curved 5/6/4 tricyclic system with an angular hydroxy group was built via three key transformations: (1) Me₃Al-catalyzed [2 + 2] cycloaddition of a ketene silyl acetal with a propiolate, (2) reductive ring-opening of a cyclic hemiketal, and (3) the intramolecular Morita-Baylis-Hillman reaction. This synthetic route represents a new and reliable strategy to obtain protoilludanes with several oxy-functional groups.

Chemical synthesis, crystal structure, versatile evaluation of their biological activities and molecular simulations of novel pyrithiobac derivatives

Since pyrithiobac (PTB) is a successful commercial herbicide with very low toxicity against mammals, it is worth exploring its derivatives for an extensive study. Herein, a total of 35 novel compounds were chemically synthesized and single crystal of 6-6 was obtained to confirm the molecular structure of this family of compounds. The novel PTB derivatives were fully evaluated against various biological platforms. From the bioassay results, the best AHAS inhibitor 6-22 displayed weaker herbicidal activity but stronger anti-Candida activity than PTB did. For plant pathogenic fungi, 6-26 showed excellent activity at 50 mg/L dosage. Preliminary insecticidal activity and antiviral activity were also observed for some title compounds. Strikingly, 6-5 exhibited a promising inhibitory activity against SARS-CoV M^pro with IC₅₀ of 4.471 μM and a low cellular cytotoxicity against mammalian 293 T cells. Based on the results of molecular modeling, HOMO-1 was considered to be a factor that affects AHAS inhibition and a possible binding mode of 6-5 with SARS-CoV M^pro was predicted. This is the first time that PTB derivatives have been studied as biological agents other than herbicides. The present research hence has suggested that more attentions should be paid to compounds belonging to this family to develop novel agrochemicals or medicines.

Chemical preparation, biological evaluation and 3D-QSAR of ethoxysulfuron derivatives as novel antifungal agents targeting acetohydroxyacid synthase

Accetohydroxyacid synthase (AHAS) is the first enzyme involved in the biosynthetic pathway of branched-chain amino acids. Earlier gene mutation of Candida albicans in a mouse model suggested that this enzyme is a promising target of antifungals. Recent studies have demonstrated that some commercial AHAS-inhibiting sulfonylurea herbicides exerted desirable antifungal activity. In this study, we have designed and synthesized 68 novel ethoxysulfulron (ES) derivatives and evaluated their inhibition constants (K_i) against C. albicans AHAS and cell based minimum inhibitory concentration (MIC) values. The target compounds 5-1, 5-10, 5-22, 5-31 and 5-37 displayed stronger AHAS inhibitions than ES did. Compound 5-1 had the best K_i of 6.7 nM against fungal AHAS and MIC values of 2.5 mg/L against Candida albicans and Candica parapsilosis after 72 h. A suitable nematode model was established here and the antifungal activity of 5-1 was further evaluated in vivo. A possible binding mode was simulated via molecular docking and a comparative field analysis (CoMFA) model was constructed to understand the structure-activity relationship. The current study has indicated that some ES derivatives should be considered as promising hits to develop antifungal drugs with novel biological target.

Research on Controllable Degradation of Novel Sulfonylurea Herbicides in Acidic and Alkaline Soils

The degradation issue of sulfonylurea (SU) has become one of the biggest challenges that hamper the development and application of this class of herbicides, especially in the alkaline soils of northern China. On the basis of the previous discovery that some substituents on the fifth position of the benzene ring in Chlorsulfuron could hasten its degradation rate, apparently in acidic soil, this work on Metsulfuron-methyl showed more convincing results. Two novel compounds (I-1 and I-2) were designed and synthesized, and they still retained potent herbicidal activity in tests against both dicotyledons and monocotyledons. The half-lives of degradation (DT₅₀) assay revealed that I-1 showed an accelerated degradation rate in acidic soil (pH 5.59). Moreover, we delighted to find that the degradation rate of I-1 was 9-10-fold faster than that of Metsulfuron-methyl and Chlorsulfuron when in alkaline soil (pH 8.46), which has more practical value. This research suggests that a modified structure that has potent herbicidal activity as well as accelerated degradation rate could be realized and this approach may provide a way to improve the residue problem of SUs in farmlands with alkaline soil.