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In order to discover green herbicides with novel molecular scaffolds, natural tetramic acids were used as lead compounds to design and synthesize four pyrrolidine-2,4-dione derivatives incorporating a chainlike alkoxyalkyl moiety (4a–4d) and nineteen pyrrolidine-2,4-dione derivatives incorporating a substituted phenoxyethyl moiety (10a–10s) via substitution, acylation, cyclization, and acidification reactions. The synthesized target compounds were confirmed by FT-IR, 1H NMR, 13C NMR and HRMS spectral analyses. The single-crystal structure of compound 10a was analyzed by X-ray diffraction, which revealed that the 1-hydroxyethylidene group links the third position of the pyrrolidine heterocycle through a double bond with the Z-configuration. The herbicidal activity was evaluated using barnyard grass (Echinochloa crus-galli) and rape (Brassica campestris) as model plants by a Petri dish culture method. Most target compounds were found to possess moderate to good inhibitory activities against the plant growth at 100 μg mL−1. Among them, the compounds 10q and 10n showed the highest herbicidal activities against the roots of barnyard grass and rape seedlings with the corresponding inhibition rates of 65.6% and 84.0%, respectively. This result indicated that pyrrolidine-2,4-dione derivatives incorporating a substituted phenoxyethyl moiety are worthy of further structural optimization.

In order to screen novel fungicide leads, 19 pyrrolidine-2,4-dione derivatives containing the pharmacophores of both hydrazine and diphenyl ether were designed, synthesized, and characterized by FT-IR, 1H NMR, 13C NMR, and HR-MS. The obtained target compounds were evaluated for their antifungal activity against Rhizoctonia solani (Rs), Botrytis cinerea (Bc), and Fusarium graminearum (Fg). The bioassay results indicated that the majority of the target compounds exhibited striking biological activities against the above-mentioned fungi. Strikingly, target compound 4h obviously inhibited the growth of Rs in vitro with an EC50 value of 0.39 μg mL−1, which was better than the commercialized fungicide boscalid (2.21 μg mL−1). Subsequently, 4h was further evaluated for the in vivo anti-Rs effect on rice leaves, affording a control efficiency of 45.33% at 200 μg mL−1. Scanning electron microscopy (SEM) was used for observing the changes in the mycelium morphology. Numerous abnormal branches and swellings were found on the hyphae that were treated with 4h. Based on the bioassay results against Rs, a comparative molecular similarity index analysis model was formulated to further analyze the quantitative structure–activity relationship (QSAR) of the target compounds. The above 3D-QSAR analyses revealed that introducing hydrophobic 4-FPh, 4-ClPh, or 4-BrPh fragments at the R2 position could considerably increase the antifungal activity against Rs.

A series of quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety were designed, synthesized and evaluated for their biological activities against phytopathogenic microorganisms. Antimicrobial bioassays in vitro indicated that most of the target compounds exhibited more significant antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) than the agricultural bactericide thiadiazole-copper. A comparative molecular similarity index analysis (CoMSIA) model with cross-validated q2 and non-cross-validated r2 values of 0.561 and 0.882 was generated to investigate the structure-activity relationships of title compounds against Xoo. Title compound 6w, which was rationally designed under the guidance of obtained CoMSIA model, exhibited the excellent anti-Xoo effect in vitro with an EC50 value of 29.10 μg/mL, which is approximately 3-folds more effective than thiadiazole-copper (113.93 μg/mL). In addition, compound 6i demonstrated the impressive antifungal effects against Rhizoctonia solani (Rs) and Fusarium graminearum (Fg) in vitro, with the corresponding EC50 values of 11.01 μg/mL and 36.00 μg/mL, which is obviously better than the agricultural fungicide hymexazol (76.74 μg/mL and 56.19 μg/mL, respectively). The above researches indicate that quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety could be further studied as template molecules of novel agricultural microbicides. Keywords: Quinazolin-4(3H)-one, 1,3,4-oxadiazole thioether, Antibacterial activity, Antifungal activity, 3D-QSAR

A series of novel 1,3,5-thiadiazine-2-thione derivatives bearing a hydrazide moiety were designed, synthesized and evaluated for their antifungal activities against Rhizoctonia solani (Rs), Fusarium graminearum (Fg), Botrytis cinerea (Bc) and Colletotrichum capsici (Cc). The in vitro antifungal bioassays indicated that most of title compounds displayed good selectivity and specificity aganist Rs relative to Fg, Bc and Cc. Strikingly, the title compound N'-(4-chlorophenyl)-2-(5-phenyl-6-thioxo-1,3,5-thiadiazinan-3-yl)acethydrazide (5b) obviously inhibited the Rs growth in vitro with the EC50 value of 0.24 μg/mL, which is approximately 2-folds more effective than the commercialized fungicide carbendazim (0.55 μg/mL). The in vivo anti-Rs effects of title compound 5b were further evaluated on rice leaves with control efficacies of 98.58% at 200 μg/mL and 61.27% at 100 μg/mL. The above researches provide a significant reference for the further structural optimization of 1,3,5-thiadiazine-2-thione derivatives bearing a hydrazide moiety as potential fungicides.

The quantitative structure-activity relationship models of 40 phenylhydrazine-substituted tetronic acid derivatives were established between the 1 H nuclear magnetic resonance (NMR) and 13 C NMR chemical shifts and the antifungal activity against Fusarium graminearum, Botrytis cinerea, Rhizoctonia cerealis, and Colletotrichum capsici. The models were validated by R, R2 , RA2 , variance inflation factor, F, and P values testing and residual analysis. It was concluded from the models that the 13 C NMR chemical shifts of C8, C10, C7, and the 1 H NMR chemical shifts of Ha contributed positively to the activity against Fusarium graminearum, Botrytis cinerea, Colletotrichum capsici, and Rhizoctonia cerealis, respectively. The models indicated that decreasing the election cloud density of specific nucleuses in compounds, for example, by the substituting of electron withdrawing groups, would improve the antifungal activity. These models demonstrated the practical application meaning of chemical shifts in the quantitative structure-activity relationship study. Furthermore, a practical guide was provided for further structural optimization of the antifungal phenylhydrazine-substituted tetronic acid derivatives based on the 1 H NMR and 13 C NMR chemical shifts.

Based on the active substructure combination principle, twenty-four novel 5-chloro-pyrazole derivatives containing a phenylhydrazone moiety were designed, synthesized, and evaluated for their antifungal activity. Their structures were confirmed using 1H NMR, 13C NMR, and HR-MS spectra. The single-crystal structure of compound 8a was analyzed emphatically using X-ray diffraction. The antifungal activities against Fusarium graminearum, Botrytis cinerea, and Rhizoctonia solani were evaluated in vitro. The results of the bioassays revealed that most of the target compounds showed obvious fungicidal activity. Strikingly, the compound 7c exhibited the most potent activity with EC50 values of 0.74, 0.68, and 0.85 μg mL−1 against the above three plant pathogenic fungi, respectively. The compounds 7c, 8d, and 8g showed significant bioactivity against R. solani with EC50 values of 0.85, 0.25, and 0.96 μg mL−1, respectively. In addition, CoMFA and CoMSIA molecular modeling was performed for a 3D-QSAR study, and presented a good predictive ability with q2 values of 0.575 and 0.667, and r2 values of 0.961 and 0.962, respectively. The results provide useful information for guiding the design and synthesis of novel potent pyrazole derivatives with good antifungal activity.

A series of novel pyrazole carboxamide and niacinamide derivatives containing a benzimidazole moiety were designed and synthesized as antifungal candidate agents. All target compounds were characterized by FTIR, 1H NMR, 13C NMR, HRMS and elemental analysis techniques. The structure of compound T1 was further confirmed by single crystal X-ray diffraction analysis. The antifungal activities of the target compounds were evaluated in vitro against four phytopathogenic fungi (namely Botrytis cinerea, Rhizoctonia solani, Fusarium graminearum and Alternaria solani) by the mycelium growth inhibition method. The bioassay results indicated that some of the compounds exhibited good antifungal activity against B. cinerea at 100 μg ML−1 compared to other three fungi. In order to better explore the structure–activity relationship (SAR), the EC50 values of target compounds against B. cinerea were measured and assessed. Subsequently, a 3D quantitative structure–activity relationship (3D-QSAR) study was carried out using the comparative molecular field analysis (CoMFA) technique based on the inhibitory activities of tested compounds against B. cinerea. Molecular modelling results revealed fine predictive ability with cross-validated q2 and non-cross-validated r2 values of 0.578 and 0.850, respectively.

In this paper, we construct a uniform formula for the Riemann solutions of the simplified Chapman-Jouguet model. Firstly, we define a new functional, and then, we obtain that the Riemann solutions can be expressed by the maximum value point of this functional, while Riemann solutions may contain some of strong detonation waves, Chapman-Jouguet detonation waves and contact discontinuities. Finally, Chapman-Jouguet deflagration waves are also discussed.

Aiming to discover novel high-efficient antifungal leads that possess an innovative action mechanism, twenty-three carboxylated pyrroline-2-one derivatives, bearing a phenylhydrazine moiety, were rationally designed and firstly prepared in this letter. The in vitro bioassays showed that most of the compounds possessed excellent antifungal effects with the EC50 values of less than 1 μg/mL against the phytopathogenic fungi Fusarium graminearum (Fg), Botrytis cinerea (Bc), Rhizoctonia solani (Rs) and Colletotrichum capsici (Cc). The further bioassays showed that the compound 6u showed the comparable in vivo control effect with carbendazim against fusarium head blight and rice sheath blight. The 3D-QSAR model revealed the pivotal effects of a bulky electron-donating group at the 1-position of pyrrole ring, a bulky electron-withdrawing group at the 4-position of phenyl ring and a small alkyl at the carbonate group on the anti-Rs activities of target compounds. The abnormal mycelial morphology and delayed spore germination were observed in the treatments of compound 6u. Given the excellent and broad-spectrum antifungal effects the target compounds have, we unfeignedly anticipated that the above finding could motivate the discovery of high-efficient antifungal leads, which might possess an innovative action mechanism against phytopathogenic fungi.

Background Tenuazonic acid (TeA), a putative nonhost-selective mycotoxin isolated from Alternaria alternata, is the main causative agent of brown leaf spot disease of crofton weed (Ageratina adenophora) and some other crops. Previous studies revealed that it is a natural photosystem II inhibitor that binds the D1 protein to block electron transfer. Though the crude metabolite extract of A. alternata containing TeA has been bioassayed, the herbicidal activity of synthesized TeA has not been systematically evaluated yet. Results TeA caused leaves of crofton weed to have brown spots that were more pronounced in older leaves than younger ones. It completely killed 92% of the four-leaf seedlings at 600 g ai/ha but only 81% or less of six-leaf seedlings or bigger. The bioassay of phytotoxicity of TeA to 67 plant species including 54 weeds and 13 crops, showed that TeA had a broad weed spectrum but low toxicity to Solanaceae and Malvaceae species. Further potted- plant experiments demonstrated that TeA had EC90 values that ranged from 119 to 795 μg/mL for 14 important weeds but was 2539 μg/mL for Acalypha australis. Nicotiana tabacum and Gossypium hirsutum had no injury symptoms at 1000 μg/mL. A field trial showed that TeA effectively controlled two important weeds, Digitaria sanguinalis and Amaranthus retroflexus without affecting cotton in the field. Conclusion TeA has potential as a biobased herbicide for controlling important dicotyledon and monocotyledon weeds in cotton and tobacco fields. © 2019 Society of Chemical Industry.

Substituted phenylhydrazone moieties and two carbonate groups were merged in one molecule scaffold to obtain 48 novel compounds. 1H and 13C NMR, MS, elemental analysis, and X-ray single-crystal diffraction were used to confirm their structures. Bioassay results revealed that some of the compounds have strong antifungal activities against Botrytis cinerea, Rhizoctonia solani, and Colletotrichum capsici (especially Rhizoctonia solani). Compound 5H1 is the most promising of the tested compounds against R. solani with an EC50 value of 1.91 mg/L, which is comparable with the positive control fungicide drazoxolon (1.94 mg/L). The structure-activity relationships against R. solani formed three rules: 1) small carbonate groups may improve the antifungal activity of the title compounds; 2) electron-withdrawing groups at the phenyl ring of phenylhydrazone are preferable to their non-substituted counterparts; and 3) halogen at the para position is more beneficial than at the ortho or meta position.

A series of novel 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N′-phenylacethydrazide derivatives were designed, synthesized and evaluated for their antifungal activities against Fusarium graminearum (Fg), Rhizoctonia solani (Rs), Botrytis cinerea (Bc) and Colletotrichum capsici (Cc). The bioassay results in vitro showed that most of the title compounds exhibited impressive antifungal activities against the above plant fungi. Particularly, the compounds 5c, 5f, 5g, 5i, 5m and 5p displayed desirable anti-Rs activities, with the corresponding EC50 values of 0.37, 0.32, 0.49, 0.50, 0.46 and 0.45 µg/mL, respectively, which are superior to the positive control carbendazim (0.55 µg/mL). Further in vivo bioassay results showed that the anti-Rs activity of title compound 5f at 200 µg/mL reached 95.84% on detached rice leaves and 93.96% on rice plants. Featuring convenient synthesis, novel structures and desirable antifungal activity, these 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N′-phenylacethydrazide derivatives could be further studied as the potential candidates of novel agricultural fungicides.

Background Tetramic acid, thiophene and hydrazone derivatives were found to exhibit favorable antifungal activity. Aiming to discover novel template molecules with potent antifungal activity, a series of novel 3-(thiophen-2-yl)-1,5-dihydro-2H-pyrrol-2-one derivatives containing a hydrazone group were designed, synthesized, and evaluated for their antifungal activity. Results The structures of 3-(thiophen-2-yl)-1,5-dihydro-2H-pyrrol-2-one derivatives bearing a hydrazone group were confirmed by FT-IR, 1H NMR, 13C NMR, 1H-1H NOESY, EI-MS and elemental analysis. Antifungal assays indicated that some title compounds exhibited antifungal activity against Fusarium graminearum (Fg), Rhizoctorzia solani (Rs), Botrytis cinerea (Bc) and Colletotrichum capsici (Cc) in vitro. Strikingly, the EC50 value of 5e against Rs was 1.26 µg/mL, which is better than that of drazoxolon (1.77 µg/mL). Meanwhile, title compounds 5b, 5d, 5e–5g, 5n–5q and 5t exhibited remarkable anti-Cc activity, with corresponding EC50 values of 7.65, 9.97, 6.04, 6.66, 7.84, 7.59, 9.47, 5.52, 6.41 and 7.53 µg/mL, respectively, which are better than that of drazoxolon (19.46 µg/mL). Conclusions A series of 3-(thiophen-2-yl)-1,5-dihydro-2H-pyrrol-2-one derivatives bearing a hydrazone group were designed, synthesized and evaluated for their antifungal activity against Fg, Rs, Bc and Cc. Bioassays indicated that some target compounds exhibited obvious antifungal activity against the above tested fungi. These results provide a significant basis for the further structural optimization of tetramic acid derivatives as potential fungicides. Electronic supplementary material The online version of this article (10.1186/s13065-018-0452-z) contains supplementary material, which is available to authorized users.

A series of novel fused heterocyclic compounds bearing benzo[4,5]imidazo[1,2-d][1,2,4]triazine 4a–4w were designed and conveniently synthesized via the intermediates 2-(halogenated alkyl)-1H-benzo[d]imidazoles 2a, 2b, and 2-((1-(substituted phenyl)hydrazinyl)alkyl)-1H-benzo[d]imidazoles 3a–3g. The structures of all target compounds were characterized by FT-IR, 1H NMR, 13C NMR, and EI-MS, of which, the structure of compound 4n was further determined by the single crystal X-ray diffraction. The crystal structure of 4n was crystallized in the triclinic crystal system, space group P 1 ¯ with a = 9.033 (6) A, b = 10.136 (7) A, c = 10.396 (7) A, α = 118.323 (7)°, β = 91.750 (8)°, γ = 104.198 (7)°, Z = 2, V = 800.2 (9) A3; total R indices: R1 = 0.0475, wR2 = 0.1284. The antifungal activity of title compounds 4a–4w in vitro against the phytopathogenic fungi Botrytis cinerea (B. cinerea), Rhizoctonia solani (R. solani) and Colletotrichum capsici (C. capsici) were evaluated, the bioassay results demonstrated that most of the title compounds exhibited obvious fungicidal activities at 50 μg/mL. This work indicated that benzo[4,5]imidazo[1,2-d][1,2,4]triazine derivatives could be considered as a new leading structure in searching for novel agricultural fungicides.

For the aim of discovering new fungicide, a series of phenylpyrrole-substituted tetramic acid derivatives bearing carbonates 6a-q were designed and synthesized via 4-(2,4-dioxopyrrolidin-3-ylidene)-4-(phenylamino)butanoic acids 4a-k and the cyclized products 1',3,4,5'-tetrahydro-[2,3'-bipyrrolylidene]-2',4',5(1H)-triones 5a-k. The compounds were characterized using IR, ¹H- and (13)C-NMR spectroscopy, mass spectrometry (EI-MS), and elemental analysis. The structure of 6b was confirmed by X-ray diffraction crystallography. The title compounds 6a-q were bioassayed in vitro against the phytopathogenic fungi Fusarium graminearum, Botrytis cinerea and Rhizoctonia solani at a concentration of 100 μg/mL, respectively. Most compounds displayed good inhibitory activity.