On the mechanism of selectivity of the corn herbicide BAS 662H: a combination of the novel auxin transport inhibitor diflufenzopyr and the auxin herbicide dicamba

Design, synthesis and biological activity of novel triketone-containing quinoxaline as HPPD inhibitor

BACKGROUND

4-Hydroxyphenyl pyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the important target enzymes used to address the issue of weed control. HPPD-inhibiting herbicides can reduce the carotenoid content in plants and hinder photosynthesis, eventually causing albinism and death. Exploring novel HPPD-inhibiting herbicides is a significant direction in pesticide research. In the process of exploring new high-efficiency HPPD inhibitors, a series of novel quinoxaline derivatives were designed and synthesized using an active fragment splicing strategy.

RESULTS

The title compounds were unambiguously characterized by infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectroscopy. The results of the in vitro tests indicated that the majority of the title compounds showed potent inhibition of Arabidopsis thaliana HPPD (AtHPPD). Preliminary bioevaluation results revealed that a number of novel compounds displayed better or excellent herbicidal activity against broadleaf and monocotyledonous weeds. Compound III-5 showed herbicidal effects comparable to those of mesotrione at a rate of 150 g of active ingredient (ai)/ha for post-emergence application. The results of molecular dynamics verified that compound III-5 had a more stable protein-binding ability. Molecular docking results showed that compound III-5 and mesotrione shared homologous interplay with the surrounding residues. In addition, the enlarged aromatic ring system adds more force, and the hydrogen bond formed can enhance the synergy with π-π stacking.

CONCLUSIONS

The present work indicates that compound III-5 may be a potential lead structure for the development of new HPPD inhibitors.

Damage and recovery from drift of synthetic-auxin herbicide dicamba depends on concentration and varies among floral, vegetative, and lifetime traits in rapid cycling Brassica rapa

Herbicides can drift from intended plants onto non-target species. It remains unclear how drift impacts plant functional traits that are important for fitness. To address this gap, we conducted an experiment where fast cycling Brassica rapa plants were exposed to one of three drift concentrations (0.5%, 1%, 10%) of synthetic-auxin dicamba. We evaluated damage to and capacity of floral and vegetative traits to recover as well as lifetime fitness by comparing treated plants to controls. Response to dicamba exposure was concentration-dependent across all traits but varied with trait type. At 0.5% dicamba, three out of five floral traits were affected, while at 1% dicamba, four floral traits and one out of two vegetative traits were negatively impacted. At 10% dicamba all floral and vegetative traits were stunted. Overall, floral traits were more responsive to all dicamba drift concentrations than vegetative traits and displayed a wide range of variation ranging from no response (e.g., pistil length) to up to 84% reduction (ovule number). However, despite floral traits were more affected across the dicamba drift concentrations they were also more likely to recover than the vegetative traits. There was also variation among lifetime traits; the onset of flowering was delayed, and reproductive fitness was negatively affected in a concentration-dependent manner, but the final biomass and total flower production were not affected. Altogether, we show substantial variation across plant traits in their response to dicamba and conclude that accounting for this variation is essential to understand the full impact of herbicide drift on plants and the ecological interactions these traits mediate.

Evaluation of a pre-formulated post-emergence herbicide mixture of topramezone and dicamba on annual weeds and Bermuda grass in maize in a sub-tropical agro-ecology

Weed infestation is one of the major causes of low maize grain yield in sub-Saharan Africa (SSA). The perennial grass weed, Cynodon dactylon (L.) Pers., is one of the most problematic weeds in maize in SSA. A pre-formulated post-emergence herbicide mixture (50 g a.i. topramezone litre⁻¹ + 160 g a.i. dicamba litre⁻¹), sold under the trade name Stellar-Star^®, was evaluated for C. dactylon and general weed control in the 2013/14 and 2014/15 season. The experiment was laid out as a randomized complete block design (RCBD) with six treatments replicated thrice, namely; weedy control, hoe weeding at 3 and 6 weeks after crop emergence (WACE), a label recommended dose of Stellar-Star at 3 WACE, a reduced Stellar-Star dose (75% of label dose) at 3 WACE, a double dose of Stellar-Star split applied at 3 and 6 WACE and a tank mix of label doses of Stellar-Star + Atrazine applied at 3 WACE. The Stellar-Star herbicide treatments did not significantly (P > 0.05) affect C. dactylon density at 5 WACE but significantly reduced (P < 0.001) its density at 10 WACE. The Stellar-Star herbicide treatments significantly reduced (P < 0.001) weed biomass compared to the weedy-check at 5 and 10 WACE in both seasons. The Stellar-Star double dose split application and the Stellar-Star Atrazine tank mix were most effective in controlling C.dactylon (90–97% control) followed by the Stellar-Star label dose and Stellar-Star reduced dose (75%–88% control), however, the results of this study suggest that the Stellar-Star Atrazine tank mix provided the most effective early season and overall weed control and resulted in the highest yield, rainfall use efficiency (RUE) and gross margin and is recommended.

Synthesis and fungicidal activity of phenylhydrazone derivatives containing two carbonic acid ester groups

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.

Design, synthesis, antifungal, and antioxidant activities of (E)-6-((2-phenylhydrazono)methyl)quinoxaline derivatives

Different substituted phenylhydrazone groups were linked to the quinoxaline scaffold to provide 26 compounds (6a-6z). Their structures were confirmed by (1)H and (13)C NMR, MS, elemental analysis, and X-ray single-crystal diffraction. The antifungal activities of these compounds against Rhizoctonia solani were evaluated in vitro. Compound 6p is the most promising one among all the tested compounds with an EC50 of 0.16 μg·mL(-1), more potent than the coassayed positive control fungicide carbendazim (EC50: 1.42 μg·mL(-1)). In addition, these compounds were subjected to antioxidant assay by employing diphenylpicrylhydrazyl (DPPH) and mice microsome lipid peroxidation (LPO) methods. Most of these compounds are potent antioxidants. The strongest compounds are 6e (EC50: 7.60 μg·mL(-1), DPPH) and 6a (EC50: 0.96 μg·mL(-1), LPO), comparative to or more potent than the positive control Trolox [EC50: 5.90 μg·mL(-1) (DPPH) and 18.23 μg·mL(-1) (LPO)]. The structure and activity relationships were also discussed.

PCDD/Fs-induced oxidative damage and antioxidant system responses in tobacco cell suspension cultures

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are ubiquitous contaminants and can be considerably accumulated by natural plants. In order to elucidate the biochemical and physiological responses of plant to PCDD/Fs, tobacco Bright Yellow-2 (BY-2) cells were selected as model plant and treated with time- and concentration-dependent PCDD/Fs. The toxic effect and oxidative stress caused by PCDD/Fs were evident, which could be indicted by the reduction in fresh mass, the increase in malondialdehyde (MDA) content, and the damage of tobacco cell ultrastructure. PCDD/Fs tolerance was correlated with changes in antioxidant system and hormones of tobacco cells. Superoxide dismutase (SOD) and peroxidase (POD) exhibited peak enzyme activities at the PCDD/Fs concentration of 1000ng WHO(98)-TEQg(-1)fresh weight. Glutathione reductase (GR) enzyme activity increased monotonically at high level PCDD/Fs, but the activity of catalase (CAT) was only slightly affected at all treatment. Meanwhile, the exposure to PCDD/Fs resulted in the changes of hormones content. With the increase of exposure concentration of PCDD/Fs, the levels of indole-3-acetic acid (IAA) and abscisic acid (ABA) increased, whereas the concentration of jasmonates (JAs) decreased. The above results suggest that tobacco cells had the ability to cope with the oxidative stress induced by low concentration of PCDD/Fs through increasing the activities of antioxidant enzymes and alternating plant hormones levels. However, oxidative stress and toxicity would burst out when plant cells were exposed to the high levels of PCDD/Fs.