(R)- and (S)-3-Hydroxy-4,4-dimethyl-1-phenyl-2-pyrrolidinone as chiral auxiliaries in the enantioselective preparation of α-aryloxypropanoic acid herbicides and α-chlorocarboxylic acids

Dynamic changes of fatty acids and (R)-dichlorprop toxicity in Arabidopsis thaliana: correlation, mechanism, and implications

Plant fatty acids (FAs) are critical components of lipids and play an important role in coping with pollution-induced stress. However, the relationship between the fluctuating changes of FAs and the toxic effects of pollutants is not clear. Here, we analyzed and identified 19 FAs, namely 14 medium and long chain fatty acids (MLCFAs) and 5 very long chain fatty acids (VLCFAs). First, a positive correlation between plant biomass and LCFA content was observed. Changes in unsaturation were inversely related to cell membrane permeability, which serves as an indicator of the toxic effects. In particular, the use of herbicides led to a reduction in total FA content, but caused a significant increase in free fatty acids (FFAs), which facilitate oxidative stress. In addition, supplementation with exogenous FAs, particularly linoleic and alpha-linolenic acids, effectively alleviated the toxic inhibition. (R)-dichlorprop causes abnormal FA metabolism that can be reversed by ferrostatin-1, a ferroptosis inhibitor. Under (R)-dichlorprop exposure, the balance of FA unsaturation in plants is disrupted by inhibition of FA desaturase activity, ultimately leading to ferroptosis and disruption of cell membrane integrity. This study aims to enhance the understanding of the ecotoxic effects of herbicides by examining changes in FAs. The findings will provide a scientific basis for controlling environmental risks associated with hazardous substances.

Role of Heme Oxygenase-1 in Dual Stress Response of Herbicide and Micronutrient Fe in Arabidopsis thaliana

Increasingly intensive agricultural practices are leading not only to herbicide contamination but also to nutritional stress on nontarget plants. This study evaluated the role of heme oxygenase-1 (HO-1) in the dual stress response of herbicide dichlorprop and micronutrient Fe in Arabidopsis thaliana. Our results revealed that co-treatment with 20 μM zinc protoporphyrin (a specific inhibitor of HO-1) reduced the activity of HO-1 by 21.6%, Fe²⁺ content by 19.8%, and MDA content by 20.0%, reducing abnormal iron aggregation and oxidative stress in response to the herbicide compared to treatment with (R)-dichloroprop alone, which has herbicidal activity. Thus, free Fe²⁺ released from HO-1 mediated dichlorprop-induced oxidative stress in the Fenton reaction and affected aberrant Fe aggregation, which also had an enantioselective effect. This study contributes to an in-depth understanding of the toxicity mechanism of herbicides under nutrient stresses, thus providing new strategies to control the environmental risks of herbicides.

New Target in an Old Enemy: Herbicide (R)-Dichlorprop Induces Ferroptosis-like Death in Plants

Iron is an essential microelement in plants that is involved in several growth processes. The use of herbicides may cause the abnormal aggregation of iron in leaves, but the regulatory mechanisms underlying this phenomenon remain unclear. Here, we show that chiral herbicide (R)-dichlorprop ((R)-DCPP) triggers ferroptosis-like death in Arabidopsis thaliana. (R)-DCPP led to reactive oxygen species (ROS) accumulation and iron aggregation, and these processes were iron dependent. Under (R)-DCPP treatment, ROS, lipid hydrogen peroxides, and malondialdehyde were significantly accumulated. In addition, (R)-DCPP induced the depletion of glutathione, ascorbic acid, and glutathione peroxidase as well as the accumulation of toxic lipid peroxides. Thus, oxidation imbalance led to cell death, and this mode of action could be inhibited by the ferroptosis inhibitor ferrostatin-1 or ciclopirox olamine. NADPH oxidases were found to be involved in herbicide-induced ROS accumulation, and lipoxygenase and NADPH cytochrome P450 oxidase were shown to positively regulate (R)-DCPP-induced lipid peroxidation. Overall, these results indicate that the iron- and ROS-dependent signaling cascades were involved in the (R)-DCPP-induced phytotoxicity pathway, which disrupted the structure of plant cell membranes and triggered ferroptosis. Generally, this study provides new insight into the mechanisms of pesticide phytotoxicity and suggests new therapeutic directions to protect nontarget plants.

Enantioselective biodegradation and enantiomerization of dichlorprop in soils

The dissipation of racemic, R-, and S- dichlorprop (DCPP) in four soils were studied in the laboratory. The half-lives of racemic DCPP were from 10.5 to 19.8 days. Preferential degradation of R- or S-DCPP was detected in all soils, even in one soil that the apparent enantiomeric fraction remained constant during incubation. The enantiomerization of DCPP was found to proceed in both directions, except in forest soil that no enantiomerization of S- to R-DCPP was observed. The isomerization equilibrium constant (K = k_RS/k_SR) in two vegetable soils were 0.54 and 0.53, respectively, favoring herbicidally active R enantiomer, while in paddy soil K was 1.60, favoring an inversion of R into S enantiomer. Real-time PCR showed that the rdpA gene was not detected in all indigenous and DCPP amended microcosms probably because of relative short incubation time and low amendment concentrations. In contrast, the sdpA gene was present in indigenous soils and significantly elevated after DCPP addition with the highest relative abundance around day 10 in all microcosms. Illumina sequencing of the 16S rRNA gene showed that the relative abundance of Proteobacteria significantly increased in all DCPP treated soils. DCPP-degrading related families, Sphingomonadaceae and Comamonadaceae, enhanced in all soils, while Burkholderiaceae elevated only in paddy soil with preferential degradation of S-DCPP and Pseudomonadaceae only in forest soil with R-enantiomer preference. The sdpA gene sequencing revealed that about 92%-99% of bacteria harboring sdpA genes in studied soils belong to Alphaproteobacteria.

Enantioselective Phytotoxic Disturbances of Fatty Acids in Arabidopsis thaliana by Dichlorprop

Plant fatty acids have indispensable physiological functions and nutritional value. However, the overuse of herbicides may cause phytotoxic disturbances of fatty acids in nontarget plants while spraying for weeds. Evidence has shown that the herbicide dichlorprop can inhibit the activity of acetyl-CoA carboxylase (ACCase), a key enzyme involved in fatty acid synthesis. However, the enantioselective phytotoxic effects of dichlorprop enantiomers ((R)-dichlorprop and (S)-dichlorprop) on fatty acids and their related mechanisms remain unclear. To solve this issue, the enantioselective phytotoxicity of dichlorprop in the model plant species Arabidopsis thaliana (A. thaliana) with a focus on fatty acids was evaluated for the first time. The results indicated a significant difference in enantioselectivity and that exposure to (R)-dichlorprop can cause marked fatty acid disturbances in nontarget plant species. Specifically, (R)-dichlorprop decreased the content of three fatty acids by more than 50% by inhibiting the activity of ACCase. In addition, increased malondialdehyde (MDA) and lipid hydroperoxides (LOOHs) contents and membrane permeability reflected herbicide-induced lipid peroxidation, which decreased the unsaturation of fatty acids in membranes and further influenced membrane composition and function. Moreover, an increased level of glutathione peroxidase (GPX) and cytochrome P450 (CYP450) reflected a plant stress-induced response. To summarize, fatty acids represent a new perspective for evaluating the toxicity of chiral pesticides, contributing to a better understanding of the enantioselective phytotoxicity and mechanisms of dichlorprop, and providing evidence for herbicide security and risk assessments.

Applications of chiral naphthyloxycyclohexanols in deracemization of α-substituted carboxylic acids by dynamic thermodynamic resolution

Synthesis of chiral naphthyloxycyclohexanols and their applications in the preparation of optically pure α-substituted carboxylic acids by dynamic thermodynamic resolution.

Dichlorprop induced structural changes of LHCⅡ chiral macroaggregates associated with enantioselective toxicity to Scnedesmus obliquus

The enantioselective toxic mechanisms of chiral herbicides in photosynthetic organisms are closely related to the production of reactive oxygen species (ROS) production, however, there are few reports on how the enantioselective production of ROS can be triggered. In suboptimal conditions, photosynthesis is one of the most important processes in the production of ROS, especially in the process of light utilization and electron transfer. In this study, we investigated the interactions between chiral herbicide dichlorprop (DCPP) enantiomers and the chiral macroaggregates of the photosynthetic light-harvesting chlorophyll a/b pigment-protein complexes (LHCII) in Scenedesmus obliquus, which is of great significance in capturing and utilizing sun light, and also in dissipating the excess excitation energy. The results of the circular dichroism indicated that DCPP induced the structural changes of the LHCII chiral macroaggregates in an enantioselective manner and that the (R)-DCPP treated-group showed a bigger change accompanied by a changed enantioselective dissipation of the excitation energy. The excitation energy was excessed in DCPP treated-groups and the degree of excess was enantioselective and the detrimental non-chemical energy triggered the enantioselective production of ROS, that induced the enantioselective toxicity to green algae S. obliquus. Overall, this study has identified that how the enantioselective production of ROS can be triggered in chloroplasts; this can help to reveal the enantioselective mechanisms of chiral herbicides to photosynthetic organisms.

Enantioselective Phytotoxicity of Dichlorprop to Arabidopsis thaliana: The Effect of Cytochrome P450 Enzymes and the Role of Fe

The ecotoxicology effects of chiral herbicides have long been recognized and have drawn increasing attention. The toxic mechanisms of herbicides in plants are involved in production of reactive oxygen species (ROS) and cause damage to target enzymes, but the relationship between these two factors in the enantioselectivity of chiral herbicides has rarely been investigated. Furthermore, even though cytochromes P450 enzymes (CYP450s) have been related to the phytotoxicity of herbicides, their roles in the enantioselectivity of chiral herbicides have yet to be explored. To solve this puzzle, the CYP450s suicide inhibitor 1-aminobenzotriazole (ABT) was added to an exposure system made from dichlorprop (DCPP) enantiomers in the model plant Arabidopsis thaliana. The results indicated that different phytotoxicities of DCPP enantiomers by causing oxidative stress and acetyl-CoA carboxylase (ACCase) damage were observed in the presence and the absence of ABT. The addition of ABT decreased the toxicity of (R)-DCPP but was not significantly affected that of (S)-DCPP, resulting in smaller differences between enantiomers. Furthermore, profound differences were also observed in Fe uptake and distribution, exhibiting different distribution patterns in A. thaliana leaves exposed to DCPP and ABT, which helped bridge the relationship between ROS production and target enzyme ACCase damage through the function of CYP450s. These results offer an opportunity for a more-comprehensive understanding of chiral herbicide action mechanism and provide basic evidence for risk assessments of chiral herbicides in the environment.

Stomatal behaviors reflect enantioselective phytotoxicity of chiral herbicide dichlorprop in Arabidopsis thaliana

Stomata in plants play vital roles in water transpiration and gas exchange necessary for photosynthesis, which are critical for the plants growth. Until now, however, the effect of chiral herbicides on the response of stomata was poorly understood. To unveil this puzzle, the enantioselective effect of chiral herbicide dichloroprop (DCPP) on stomata in Arabidopsis thaliana was investigated. It was found that (R)-DCPP preferentially promoted the extent of stomatal opening in Arabidopsis leaves, resulting in 59.84% enhancement at 0.3μmol·L(-1) comparing to the control, where (S)- and (Rac)-DCPP exhibited no significant differences. Enantioselectivity was also observed in the response of stomata to DCPP. To better understand the mechanism involved, the reactive oxygen species (ROS) production and antioxidant system defense were measured. Interestingly, the ROS production in Arabidopsis leaves was also enantioselective. The (R)-DCPP treatments resulted in 6.08-fold enhancement compared with the control, whereas 1.35- and 2.51-fold increases occurred in (S)-DCPP and (Rac)-DCPP treatments, respectively. The promoting of stomatal opening was positively correlated with ROS production. In addition, the antioxidant system response provided evidence of oxidative stress and damage caused by DCPP. This study confirmed that the ROS produced by DCPP promoted stomatal opening and suggested a potential sight to elucidate the phytotoxicity of chiral herbicides.

Total synthesis of trans,trans-Sanguinamide B and conformational isomers

The first total synthesis of Sanguinamide B is reported, prepared via an efficient synthetic strategy. The natural product, trans,trans-Sanguinamide B (1), was generated in a thermodynamic ratio with trans,cis-Sanguinamide B (2) and cis,cis-Sanguinamide B (3). Complete conversion of the cis,cis-Sanguinamide B conformer (3) to the natural product (1) and the trans,cis- conformer (2) was achieved by heating to 170 °C. Biological evaluation indicated that the Sanguinamide B conformers disrupted the activity of a virulence determinant in P. aeruginosa.

Enantioselectivity tuning of chiral herbicide dichlorprop by copper: roles of reactive oxygen species

Reactive oxygen species (ROS) are considered to be the key players in cell toxicity. However, cross talk between the enantioselective toxicity of pesticides, heavy metals, and ROS is poorly understood. To decipher the puzzle, the effects of copper (Cu) on the enantioselective ecotoxicity of the chiral pesticide dichlorprop (DCPP) to Scenedesmus obliquus were investigated. The results showed that the presence of DCPP and Cu, both individually and in combination, caused a sudden increase of ROS. This in turn stimulated the response of antioxidant defenses, impaired subcellular structure and physiological function, and finally resulted in cell growth inhibition. In the absence of Cu, ROS production after exposure to the herbicidally active (R)-enantiomer was higher than that of the (S)-enantiomer, suggesting a preference for an (R)-enantiomer-induced production of ROS. When DCPP and Cu were both added to algae simultaneously, (R)-DCPP preferentially induced production of ROS was observed. However, the enantioselective induced production of ROS was reversed when DCPP was mixed with Cu for 24 h prior to addition to the algae solution. It was also found that the generation of ROS, antioxidant response, and growth inhibition rate in Scenedesmus obliquus were all (R)-enantiomer preferentially induced. These findings implied that ROS play a primary role in chemical contaminant toxicity, and interactions between contaminants can tune the enantioselectivity of chiral herbicides, which should be considered in future risk assessment.

Elucidation of the enantioselective enzymatic hydrolysis of chiral herbicide dichlorprop methyl by chemical modification

Up to 25% of the current pesticides are chiral, the molecules have chiral centers, but most of them are used as racemates. In most cases, enantiomers of chiral pesticides have different fates in the environment. Knowledge of the function of amino acids of enzymes involved in enantioselective behaviors contributes to the understanding of the enantioselectivity of chiral pesticides. In this work, Aspergillus niger lipase (ANL, EC3.1.1.3) was chemically modified using bromoacetic acid (BrAc), 2,3-butanedione (BD), N-bromosuccinimide (NBS), and methanal. The enantioselectivity of the enzymatic hydrolysis of 2,4-dichlorprop-methyl (DCPPM) was investigated by chiral GC. The results have suggested that histidine, arginine, and tryptophan are essential for lipase activity and might be involved in the catalytic site of ANL. In addition, histidine and lysine play an important role in determining the observed enantioselective hydrolysis of chiral herbicide dichlorprop methyl. The molecular modeling study revealed that the essential hydrogen bonds formed between DCPPM and catalytic residues of ANL might be responsible for the enantioselectivity of DCPPM. The loss of enantioselectivity can also arise from the fact that the modification of the amino acids may cause changes in both the nature of the ANL enzyme conformation and the binding pattern of DCPPM. Our study provides basic information for the exploration of the enantioselective interaction mechanism of enzymes with chiral pesticides.

Effect of chitosan on the enantioselective bioavailability of the herbicide dichlorprop to Chlorella pyrenoidosa

Chitosan, a natural polysaccharide, is widely regarded as a biocompatible and potential carrier for controlled-release drug formulations. However, the potential effect of chitosan on the environmental behavior of contaminants is poorly understood, especially on chiral chemicals. In this study, the changes in bioavailability of the chiral herbicide dichlorprop to Chlorella pyrenoidosa by chitosan were investigated. The dissipation of (S)-enantiomer in Chlorella pyrenoidosa culture media without chitosan was faster than that of the herbicidally active (R)-enantiomer, whereas it was inversed to (R)-enantiomer being faster than (S)-enantiomer when chitosan was added into the media. In the absence of chitosan, the toxicity of (R)-enantiomer to Chlorella pyrenoidosa was more potent than that of the (S)-enantiomer. On the contrary, in the presence of chitosan, (R)-enantiomer was less toxic than (S)-enantiomer. These observations clearly suggest that chitosan changed the enantioselective bioavailability of dichlorprop. Fluorescence spectroscopic analysis showed that the interaction between chitosan and dichlorprop enantiomers depended greatly on the steric structure of dichlorprop, which offers a possible explanation as to why the addition of chitosan changed the enantioselective dissipation of dichlorprop by Chlorella pyrenoidosa. This work suggests that the enantioselective behaviors of chiral compounds in the environment might be shifted when interactions with other chiral receptors coexist.

Enantioselective Synthesis of Vicinal Halohydrins via Dynamic Kinetic Resolution

[reaction: see text] Expanding the scope of enantioselective catalysis via DKR, transfer hydrogenation of a variety of cyclic alpha-halo ketones was accomplished using the Noyori/Ikariya (R,R)- or (S,S)-I catalysts and either HCO(2)H/Et(3)N or HCO(2)Na/n-Bu(4)NBr in H(2)O/CH(2)Cl(2) as the hydrogen sources. Good yields of vicinal bromo-, chloro-, and fluorohydrins with excellent de and ee levels were achieved in most cases after a simple tuning of reaction conditions.