Synthesis, crystal structure and herbicidal activity of mimics of intermediates of the KARI reaction

Synthesis and Biological Activity Evaluation of Novel Chalcone Analogues Containing a Methylxanthine Moiety and Their N-Acyl Pyrazoline Derivatives

On the basis of the structures of natural methylxanthines and chalcone, a series of novel chalcone analogues containing a methylxanthine moiety, Ia-Ig, and their N-acyl pyrazoline derivatives IIa-IIz and IIaa-IIaf were synthesized and identified through melting points, 1H NMR, 13C NMR, and HRMS. The single crystal of compound IId was obtained, which further illustrated the structural characteristics of the methylxanthine-acylpyrazoline compounds. The biological tests showed that some of them displayed favorable insecticidal activities toward Plutella xylostella L. and were superior to the natural methylxanthine compound caffeine while being comparable with the insecticide triflumuron (e.g., compound Ic: LC50 = 16.8508 mg/L, IIf: LC50 = 1.5721 mg/L, against P. xylostella). Of these compounds, Ic, IIf, and IIu could serve as novel insecticidal leading structures for further study. Some of the compounds showed good fungicidal activities (e.g., compound Ig: EC50 = 14.74 μg/mL, against Rhizoctonia cerealis; IIf: EC50 = 7.06 μg/mL, against Physalospora piricola; IIac: EC50 = 5.37 and 8.19 μg/mL, against Phytophthora capsici and Sclerotinia sclerotiorum, respectively); Ic, Ig, IIa, IIf, IIr, IIs, IIv, IIac, and IIaf could be novel fungicidal leading compounds for further exploration. Furthermore, most of the tested compounds exhibited apparent herbicidal activities against Brassica campestris at a concentration of 100 μg/mL; among others, compound IIa was the best one both toward Brassica campestris and Echinochloa crusgalli and deserves further investigation. The structure-activity relationships of these compounds were also summarized and discussed in detail. The contrast experiment results of compounds C-1 and C-2 showed a positive effect on the biological activity enhancement from the combination of the methylxanthine moiety with the N-dichloroacetyl phenylpyrazoline skeleton. In addition, two 3D-QSAR models with predictive capability were constructed based on the insecticidal and fungicidal activities to afford deep insight into the bioactivity profiles of these compounds. This research provides useful guidance and reference for the discovery and development of novel xanthine natural product-based pesticides.

Discovery of Novel Pyrazole Derivatives with Improved Crop Safety as 4-Hydroxyphenylpyruvate Dioxygenase-Targeted Herbicides

As one of the essential herbicide targets, 4-hydroxyphenylpyruvate dioxygenase (HPPD) has recently been typically used to produce potent new herbicides. In continuation with the previous work, several pyrazole derivatives comprising a benzoyl scaffold were designed and synthesized, and their inhibitory effects on Arabidopsis thaliana hydroxyphenylpyruvate dioxygenase (AtHPPD) and herbicidal activities were comprehensively evaluated in this study. Compound Z9 showed top-rank inhibitory activity to AtHPPD with an half-maximal inhibitory concentration (IC₅₀) value of 0.05 μM, which was superior to topramezone (1.33 μM) and mesotrione (1.76 μM). Compound Z21 exhibited superior preemergence inhibitory activity against Echinochloa crusgalli, with stem and root inhibition rates of 44.3 and 69.6%, respectively, compared to topramezone (16.0 and 53.0%) and mesotrione (12.8 and 41.7%). Compounds Z5, Z15, Z20, and Z21 showed excellent postemergence herbicidal activities at a dosage of 150 g ai/ha, along with distinct bleaching symptoms and higher crop safety than topramezone and mesotrione, and they all were safe for maize, cotton, and wheat with injury rates of 0 or 10%. In addition, the molecular docking analysis also revealed that these compounds formed hydrophobic π-π interactions with Phe360 and Phe403 to AtHPPD. This study suggests that pyrazole derivatives containing a benzoyl scaffold could be used as new HPPD inhibitors to develop pre- and postemergence herbicides and be applied to additional crop fields.

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.

Synthesis of (E)/(Z)-Verbenone Oxime Ethers and Photoresponsive Behavior to Herbicidal Activity

The accumulation of residual active herbicides in the environment can cause a series of problems. It is thus meaningful to explore a photoresponsive herbicide, whose activity can be weakened under the action of light to reduce the negative effect. To this purpose, a series of (E)/(Z)-verbenone oxime ethers were designed, synthesized, and characterized. Oxime ether groups were adopted as the trigger switches. The preliminary screening for herbicidal activity showed that some of them exhibited better or comparable effects than that of the commercial herbicide flumioxazin against Brassica campestris and Echinochloa crusgalli. Meanwhile, five pairs of the target compounds with significantly different herbicidal effects between E- and Z-forms were further investigated for their reversible isomerization reaction and the accompanying variation of herbicidal activity. As a result, the maximum conversion rates were around 50%, and the herbicidal effect of the resulting mixture of E- and Z-isomers decreased outstandingly. The phototransformation mechanism of a pair of isomers (E)-4a and (Z)-4a was preliminarily explored. Besides, a reasonable and effective 3D-quantitative structure-activity relationship model (r² = 0.984 and q² = 0.571) was established and the binding mode was also investigated by molecular docking.

Efficient Total Synthesis and Herbicidal Activity of 3-Acyltetramic Acids: Endogenous Abscisic Acid Synthesis Regulators

An efficient synthesis method will allow a large number of tetramic acid analogues to be synthesized for property and potency optimization. In this study, a facile and efficient method was described for the synthesis of 3-acyltetramic acids. The synthesis was accomplished mainly via (1) mild intramolecular cyclization and (2) the formation of β-ketoamides between nucleophiles and acyl Meldrum's acids. 3-Acyltetramic acid exhibited phytotoxicity against Echinochloa crusgalli and Portulaca oleracea. At a dosage of 750 g ha^-1, 6k and 6a showed high herbicidal activity against E. crusgalli, Digitaria sanguinalis and P. oleracea, Amaranthus retroflexus, respectively. 6k inhibited the synthesis of endogenous abscisic acid, thus seedling germination and plant growth. The incorporation of various acyl Meldrum's acids and amino acid esters was applicable to the parallel synthesis of 3-acyltetramic acids. The mode of action and herbicidal activity indicate that 3-tetramic acid had good herbicidal performance and was a promising herbicide candidate. This study will provide a reference for novel herbicide development.

Novel Pyrazole Amides as Potential 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an important target for the development of new herbicides. HPPD inhibitors can hinder photosynthesis and induce weed death with bleaching symptoms. To explore the novel skeleton of HPPD inhibitors, a series of novel pyrazole amide derivatives were synthesized and evaluated for their inhibitory effects on Arabidopsis thaliana HPPD (AtHPPD) and herbicidal activities. Some compounds had excellent inhibitory activities against AtHPPD. Among them, compound B5 displayed top-rank inhibitory activity against AtHPPD with an IC₅₀ value of 0.04 μM, which was obviously superior to that of topramezone (IC₅₀ value of 0.11 μM). Furthermore, compounds B2 and B7 had 100% herbicidal activities in Petri dish assays against Portulaca oleracea and Amaranthus tricolor at 100 μg/mL. In particular, compound B7 not only possessed strong AtHPPD inhibitory activity but also exhibited significant preemergence herbicidal activity. However, compound B7 was completely harmless to soybean, cotton, and wheat. In addition, the molecular docking and microscale thermophoresis measurement experiment verified that compounds can bind well with AtHPPD via π-π interactions. The present work provides a new approach for the rational design of more effective HPPD inhibitors, and pyrazole amides could be used as useful substructures for the development of new HPPD inhibitors and preemergence herbicidal agents.

Synthesis, Herbicidal Activity, Crop Safety and Soil Degradation of Pyrimidine- and Triazine-Substituted Chlorsulfuron Derivatives

Chlrosulfuron, a classical sulfonylurea herbicide that exhibits good safety for wheat but causes a certain degree of damage to subsequent corn in a wheat-corn rotation mode, has been suspended field application in China since 2014. Our previous study found that diethylamino-substituted chlorsulfuron derivatives accelerated the degradation rate in soil. In order to obtain sulfonylurea herbicides with good crop safety for both wheat and corn, while maintaining high herbicidal activities, a series of pyrimidine- and triazine-based diethylamino-substituted chlorsulfuron derivatives (W102-W111) were systematically evaluated. The structures of the synthesized compounds were confirmed with 1H NMR, 13C NMR, and HRMS. The preliminary biological assay results indicate that the 4,6-disubstituted pyrimidine and triazine derivatives could maintain high herbicidal activity. It was found that the synthesized compounds could accelerate degradation rates, both in acidic and alkaline soil. Especially, in alkaline soil, the degradation rate of the target compounds accelerated more than 22-fold compared to chlorsulfuron. Moreover, most chlorsulfuron analogs exhibited good crop safety for both wheat and corn at high dosages. This study provided a reference for the further design of new sulfonylurea herbicides with high herbicidal activity, fast degradation rates, and high crop safety.

Research on the controllable degradation of N-methylamido and dialkylamino substituted at the 5th position of the benzene ring in chlorsulfuron in acidic soil

Owing to the lengthy residual problems associated with chlorsulfuron, metsulfuron-methyl, and ethametsulfuron, which prevents them from being used in the "annual multi-crop planting system", the application of these sulfonylurea herbicides (SU) has regrettably been terminated in China since 2014. In this field, we were the first to discover that the 5^th position of the benzene ring in chlorsulfuron is a key point for influencing its degradation rate and the amino moiety at this position showed faster degradation rates and maintained their original potent bioactivity. In this study, we further elaborated on N-methylamido and dialkylamino substituents at the same position in chlorsulfuron to obtain 18 novel structures as M and N series. Their half-life degradation (DT₅₀) values were faster, to varying degrees, than chlorsulfuron in acidic soil. It was found that most of the titled structures also retained their potent herbicidal activity and the crop safety of the M series towards corn greatly increased. Based on these data, a comprehensive graph describing the structure/degradation relationship was established first. Relating to the new molecules, their herbicidal activity (A), degradation rates (D), and crop safety (S) relationship were correlated and we used this approach to predict and explore the most preferable molecule, which coincided to the corresponding experimental data. The new concept of controllable degradation will provide us with more insight when searching for new ecological bioactive molecules in the future.

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.

Design and Synthesis of Novel 4-Hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one Derivatives for Use as Herbicides and Evaluation of Their Mode of Action

In order to develop a novel herbicide containing the β-triketone motif, a series of 4-hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one derivatives were designed and synthesized. The bioassay results showed that compound II15 had good pre-emergent herbicidal activity even at a dosage of 187.5 g ha^-1. Moreover, compound II15 showed a broader spectrum of weed control when compared with a commercial herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), and displayed good crop safety to Triticum aestivum L. and Zea mays Linn. when applied at 375 g ha^-1 under pre-emergence conditions, which indicated its great potential as a herbicide. More importantly, studying the molecular mode of action of compound II15 revealed that the novel triketone structure is a proherbicide of its corresponding phenoxyacetic acid auxin herbicide, which has a herbicidal mechanism similar to that of 2,4-D. The present work indicates that the 4-hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one motif may be a potential lead structure for further development of novel auxin-type herbicides.

The mechanism of bensulfuron-methyl complexation with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin and effect on soil adsorption and bio-activity

In this work, the inclusion complexes of hydrophobic herbicide bensulfuron-methyl (BSM) with β-cyclodextrin (β-CD) and (2-hydroxypropyl)-β-CD (2-HP-β-CD) were prepared and characterized. Phase solubility study showed that both β-CD and 2-HP-β-CD increased the solubility of BSM. Three-dimensional structures of the inclusion complexes were simulated by the molecular docking method. The docking results indicated that guest BSM could enter into the cavities of host CDs, folded, and centrally aligned inside the inclusion complexes. The benzene ring of the guest molecule was close to the wide rim of the host molecules; the pyrimidine ring and side chains of the guest molecule were oriented toward the narrow rim of the host molecule. The inclusion complexes were successfully prepared by the coprecipitation method. The physiochemical characterization data of 1H NMR, FT-IR, XRD, and DSC showed that the guest and host molecules were well included. BSM had lower soil adsorption and higher herbicidal activity in the complexation form with β-CD or 2-HP-β-CD than in the pure form. The present study provides an approach to develop a novel CDs-based formulation for hydrophobic herbicides.

Deuterated phytantriol - A versatile compound for probing material distribution in liquid crystalline lipid phases using neutron scattering

Phytantriol is an interfacially-active lipid that is chemically robust, non-digestible and forms particles with internal bicontinuous cubic phase structures (cubosomes) when dispersed with non-ionic surfactants at ambient and physiological temperatures. The liquid crystalline internal structure of phytantriol-based cubosomes can be changed to alter the interfacial contact area/topology with the aqueous dispersant to trigger bioactive payload release or to alter the local membrane curvature around bound or embedded proteins. To enable the study of payload distribution, structure and transformation kinetics within phytantriol particles by neutron scattering techniques it is desirable to have access to a deuterated version of this molecule but to date a synthetic route has not been available. The first successful synthesis of phytantriol-d₃₉ is presented here alongside a preliminary physical characterisation of related particle structures when phytantriol-d₃₉ is dispersed using two non-ionic surfactants, Tween® 80 and Pluronic® F127. Synchrotron small angle X-ray scattering (SAXS) was used to confirm that phytantriol-d₃₉-based nanoparticles in D₂O form similar liquid crystalline structures to those of their natural isotopic abundance (phytantriol/H₂O) counterparts as a function of temperature. Finally, small angle neutron scattering (SANS) with solvent contrast to match out the phytantriol-d₃₉ structuring was used to show that the spatial correlations between the Tween® and Pluronic® non-ionic surfactant molecules are different within dispersed phytantriol-d₃₉ particles with different liquid crystalline structures in D₂O. The surfactant molecules in phytantriol-d₃₉/Tween® 80 particles with Im3m cubic structures were found to follow a self-avoiding walk, whereas in phytantriol-d₃₉/Pluronic® F127 particles with Pn3m cubic structures they were found to follow a more rod-like packing arrangement.

Synthesis, biological evaluation and SAR analysis of novel poly-heterocyclic compounds containing pyridylpyrazole group

BACKGROUND

In recent years, pyridylpyrazole derivatives, such as pyridylpyrazole-containing anthranilic diamide have attracted much attention by virtue of their useful insecticidal properties and unique action mode. Moreover, some pyridylpyrazole-containing compounds have also been found to possess significant fungicidal activities. With the aim of discovering new bioactive agrochemicals for crop protection, a series of poly-heterocyclic compounds containing pyridylpyrazole and aziridine, or β-lactam, or thiazolinone moieties were synthesized.

RESULTS

A series of pyridylpyrazole-containing poly-heterocyclic compounds were obtained, and confirmed through IR, ¹ H NMR, ¹³ C NMR, HRMS and elemental analysis. The crystalline structure of 4-(3-bromo-1-(3-chloropyridin-2-yl)-1H-pyrazol-5-yl)-3-chloro-1-mesitylazetidin-2-one (compound 13f) was determined to further illustrate a trans- configuration of the β-lactam motif. In addition, bioassays showed that most of these new compounds exhibited modest insecticidal activity towards Mythimna separate Walker at 200 µg mL^-1 . Some of the compounds displayed excellent fungicidal activity towards some plant fungi, including Cercospora arachidicola (13j: EC₅₀ = 14.5 µg mL^-1 ), Physalospora piricola (12d and 13d: EC₅₀ = 10.5 and 9.70 µg mL^-1 ), Alternaria solani Sorauer (13j: EC₅₀ = 7.29 µg mL^-1 ), Puccinia sorghi Schw. (13d: control efficacy 99.0 ± 2.1% at 200 µg mL^-1 ) and Erysiphe graminis (14d: control efficacy 95.0 ± 1.4% at 200 µg mL^-1 ).

CONCLUSION

Compounds 12b-12e, 13a, 13d, 13f, 13j, 13 k and 14d could be considered potential fungicidal lead compounds to do further structural optimization. The structure-activity relationship analysis in this study brings some new understanding to the biological activities of N-pyridylpyrazole-containing compounds, and provides important information for the research and development of novel agricultural fungicides with poly-heterocyclic structures. © 2017 Society of Chemical Industry.

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.

Syntheses, biological activities and SAR studies of novel carboxamide compounds containing piperazine and arylsulfonyl moieties

A series of novel carboxamide compounds 19a-19j, 20a-20j and 22a-22d containing piperazine and arylsulfonyl moieties have been synthesized. The bioassay results showed that some compounds exhibited favorable herbicidal activities against dicotyledonous plants and many of them possessed excellent antifungal activities. Among 24 novel compounds, some showed superiority over the commercial fungicides Chlorothalonil, Dimethomorph, Thiophanate-methyl, Iprodione, and Zhongshengmycin at 500 mg/L concentration. Some compounds also exhibited high KARI inhibitory activity at 100 μg/mL concentration and could be used as new KARI lead inhibitors for further studies. Moreover, SAR of these new compounds were comprehensively investigated using different computational methods in which 3D-QSAR model obtained provided useful information for further structural optimization for the discovery of new fungicides. The results of this research will contribute to explore comprehensive biological activities of piperazine-containing compounds in different areas of chemistry.

Synthesis and herbicidal potential of substituted aurones

BACKGROUND

With the objective of exploring the herbicidal activity of substituted aurones, a series of 4,6-disubstituted and 4,5,6-trisubstituted aurones were synthesised, and their herbicidal activities against Brassica campestris L. and Echinochloa crusgalli (L.) Beauv. were evaluated in laboratory bioassays. Effects of some of the compounds were evaluated on seed germination. The most active compounds in the laboratory were evaluated in the greenhouse.

RESULTS

The compounds were characterised by (1)H NMR, (13)C NMR and HRMS; some of them were further identified by IR. A (Z)-configuration was assigned to the aurones, based on spectroscopic and crystallographic data. Bioassay results of root growth showed that the aurones had a moderate herbicidal activity against the dicotyledonous plant Brassica campestris. (Z)-2-Phenylmethylene-4,6-dimethoxy-3(2H)-benzofuranone(6o) was the most active compound, with 81.3 and 88.5% inhibition at 10 and 100 µg ml(-1) respectively, equal to the activity of mesotrione. Some of the aurones possessed some inhibition of germination on several plant species. For glasshouse tests, the substituted aurones had lower herbicidal activity than metolachlor and mesotrione.

CONCLUSION

It is possible that aurone derivatives, which possess structures different from those of the commercial herbicides, may become novel lead compounds for the development of herbicides against dicotyledonous weeds with further structure modification.

Chemical synthesis, in vitro acetohydroxyacid synthase (AHAS) inhibition, herbicidal activity, and computational studies of isatin derivatives

Acetohydroxyacid synthase (AHAS) catalyzes the first common step in the biosynthesis of the branched-chain amino acids. As a result of its metabolic importance in plants, it is a target for many commercial herbicides. Virtual screening analysis inspired the evaluation of 19 commercially available isatin analogues and 13 newly synthesized isatin derivatives as novel AHAS inhibitors and for their herbicidal activity. The best compound demonstrated 95% inhibition of the activity of Arabidopsis thaliana AHAS at a concentration of 100 mg L(-1), whereas the herbicidal activities of three compounds reached 50% inhibition at a concentration of 10 mg L(-1) using the rape root growth test. CoMFA contour models were established to understand the structure-activity relationships for this class of AHAS inhibitor. The compounds were docked to the active site cavity of A. thaliana AHAS using FlexX, and the dominant binding mode was consistent with frontier molecular orbital from DFT calculations. This is the first comprehensive study of isatin derivatives as AHAS inhibitors and provides a valuable starting point for the design of new herbicides.

Synthesis and biological activity of some novel trifluoromethyl-substituted 1,2,4-triazole and bis(1,2,4-triazole) Mannich bases containing piperazine rings

A series of trifluoromethyl-substituted 1,2,4-triazole Mannich base 6 and bis(1,2,4-triazole) Mannich base 7 containing pyrimidinylpiperazine rings via the Mannich reaction were synthesized and characterized by infrared (IR), (1)H nuclear magnetic resonance (NMR), and elemental analysis. The fungicidal tests indicated that most of compounds 6 and 7 possessed excellent fungicidal activity. Among 19 novel compounds, some showed superiority over commercial fungicides Dimethomorph, Thiophanate-methyl, Iprodione, and Zhongshengmycin. Some compounds also exhibited favorable herbicidal activity in the preliminary studies. On the basis of the comparative molecular field analysis (CoMFA), five novel compounds were subsequently synthesized, their activities were estimated fairly accurately, and compounds 6-A1 and 7-A2 displayed good fungicidal activity against Pseudoperonospora cubensis (96.9 and 84.9%) as 6h and 7c, respectively.

Synthesis and biological activity of 4-(4,6-disubstituted-pyrimidin-2-yloxy)phenoxy acetates

Ten novel 4-(4,6-dimethoxypyrimidin-2-yloxy)phenoxy acetates and 4-(4,6-dimethylpyrimidin-2-yloxy)phenoxy acetates were synthesized with hydroquinone, 2-methylsulfonyl-4,6-disubstituted-pyrimidine and chloroacetic ester as starting materials. The products were characterized by IR, ¹H-NMR, MS spectra and elemental analyses. Preliminary bioassay indicates that the target compounds possess high herbicidal activity against monocotyledonous plants such as Digitaria sanguinalis L. at concentrations of 100 mg/L and 50 mg/L.

Synthesis and herbicidal activities of novel 3-N-substituted amino-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives

4-(3-Trifluoromethylphenyl)pyridazine is a new series of compounds with bleaching and herbicidal activities. Starting from ethyl 2-(3-trifluoromethylphenyl)acetate, an important intermediate 7 was synthesized in five steps with a moderate total yield of 51.5% in a safe and practical way. Twenty-six novel 3-N-substituted amino-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives were synthesized and evaluated through a Spirodela polyrrhiza test and greenhouse test. Some compounds can completely inhibit Chl at 1 microg/mL and exhibit equal or higher herbicidal activities with the commercial bleaching herbicide diflufenican against dicotyledonous plants at a rate of 75 g/ha.

Synthesis and herbicidal activity of novel alpha,alpha,alpha-trifluoro-m-tolyl pyridazinone derivatives

A series of novel alpha,alpha,alpha-trifluoro-m-tolyl pyridazinone derivatives was synthesised. Herbicidal activities of the two intermediate compounds and 15 pyridazinone derivatives were evaluated through barnyardgrass and rape cup tests and Spirodela polyrrhiza (L.) Schleiden tests. Selected compounds were also evaluated under greenhouse conditions. Bleaching activities were observed at 10 microg ml(-1) and some compounds exhibited herbicidal activities at a rate of 300 g ha(-1). The relationship between crystal structures and herbicidal activities is discussed through a comparison of two compounds (5a and 5f).