Crystal structure of HPPD inhibitor sensitive protein from Oryza sativa.

4-hydroxyphenylpyruvate dioxygenase (HPPD) Inhibitor Sensitive 1 (HIS1) is an endogenous gene of rice, conferring broad-spectrum resistance to ß-triketone herbicides. Similar genes, known as HIS1-like genes (HSLs), exhibit analogous functions and can complement the herbicide-resistant characteristics endowed by HIS1. The identification of HIS1 and HSLs represents a valuable asset, as the intentional pairing of herbicides with resistance genes emerges as an effective strategy for crop breeding. Encoded by HIS1 is a Fe(II)/2-oxoglutarate-dependent oxygenase responsible for detoxifying ß-triketone herbicides through hydroxylation. However, the precise structure supporting this function remains unclear. This work, which determined the crystal structure of HIS1, reveals a conserved core motif of Fe(II)/2-oxoglutarate-dependent oxygenase and pinpoints the crucial residue dictating substrate preference between HIS1 and HSL.

A novel Zn2+-coordination fluorescence probe for sensing HPPD inhibitors and its application in environmental media and biological imaging.

Mesotrione, topramezone, tembotrione, and sulcotrione are four types of 4-hydroxyphenylpyruvate dioxidase (HPPD) inhibitor herbicides that are extensively employed in agricultural practices, but their usage also leads to environmental pollution and poses risks to human health. A probe (E)-1-((2-(pyridin-2-yl) hydrazineylidene) methyl) naphthalen-2-ol (CHMN) based on chelation enhancement (CHEF) effect synthesized. CHMN was first chelated with Zn2+ to form a probe system with green, which can be further used to detect mesotrione, topramezone, tembotrione and sulcotrione in complicated environment. CHMN-Zn2+ detection of four pesticides was accurate, with an excellent linear relationship between 0 and 100 µM. The detection limits were LODmesotrione = 7.79 µM, LODtopramezone = 1.91 µM, LODtembotrione = 1.38 µM and LODsulcotrione = 2.43 µM. The detection time is 1 min, and it is successfully applied in real water sample and bioimaging. This work can provide a novel method for studying the migration and behavior of environmental pollutants.

Physiological effects of maize stressed by HPPD inhibitor herbicides via multi-spectral technology and two-dimensional correlation spectrum technology.

Understanding the physiological effects of herbicides on crops is crucial for crop production and environmental management. The effects of 4-hydroxyphenylpyruvate dioxygenase inhibitor (HPPDi) herbicides at different concentrations on chlorophyll content in maize leaves, fresh weight of roots, stems and leaves, and fluorescence substances and functional groups in root exudates (REs) were studied by UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation analysis (2D-COS). The results showed that 5 mg/L and 10 mg/L HPPDi herbicides inhibited the synthesis of chlorophyll in maize leaves. The weight of roots, stems and leaves of maize after application was lighter than that of the control group. HPPDi herbicides affected the early growth of maize seedlings, and the effect was most obvious at high concentration. Synchronous fluorescence spectrum and three-dimensional (3D) fluorescence spectrum revealed that the fluorescence intensity of protein, fulvic acid and humic acid in maize REs changed prominently. With the increase of HPPDi herbicides concentration, the fluorescence intensity decreased gradually. Through FTIR and 2D-COS, functional groups such as C-H, CO, Cl, NO3-, C-O and O-H were found to participate in the interaction between HPPDi herbicides and maize REs as binding sites. C-O, C-Cl and C-C have the strongest binding ability, while CC and CO of aromatic rings, quinones or ketones first take part in the binding between HPPDi herbicides and maize REs. The results can provide a theoretical basis for evaluating the safety of HPPDi herbicides on maize and a method for discovering the effects of pesticides on environmental media and plant physiological effects.

Method validation and dissipation kinetics of the novel HPPD-inhibiting herbicide cypyrafluone in winter wheat using QuEChERS method coupled with UPLC-MS/MS.

Cypyrafluone, a novel hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide, can successfully control a wide species of grass and broadleaf weed in wheat fields. However, the dissipation behaviors and terminal residues of cypyrafluone in wheat fields remain unclear. Here, a simple, accurate, and dependable approach for the analysis of cypyrafluone in soil, wheat plant, and grain was constructed utilizing an adapted QuEChERS extraction combined with UPLC-MS/MS. For accurate quantification, matrix-matched calibrations with high linearity (R2 >0.99) were employed to eliminate matrix interference. The method possessed high accuracy with recoveries in the range of 85.5%- 100.6% and precision with relative standard deviations < 14.3%, as well as high sensitivity with limits of quantifications of 0.001 mg kg-1 in the three matrixes. The dissipation kinetics and terminal residues of cypyrafluone were determined at two separate locations with different climates, soil types and cropping systems in 2018. The half-lives of cypyrafluone in soil and wheat plant were 1.47-1.55 d and 1.00-1.03 d, respectively. At harvest, the terminal residue values of cypyrafluone detected in wheat plants were 0-0.0025 mg kg-1 and 0.0044-0.0057 mg kg-1 at the recommended dose and 1.5 times of the recommended dose, respectively, and 0.0049 mg kg-1 of this herbicide was detected in grain at 1.5 times of the recommended dose, which was below the maximum residue limit (MRL). Finally, the risk quotient for cypyrafluone ranged from 0.33% to 0.81% (<1) for different age groups in China, indicating that the impact of residues from the cypyrafluone application on wheat was acceptable. These findings above will offer scientific guidelines for cypyrafluone application in the wheat field ecosystem.

Discovery of novel HPPD inhibitors: Virtual screening, molecular design, structure modification and biological evaluation.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD, a Fe(II)/α-ketoglutarate dependent oxygenases), is a popular herbicide target. In this work, two pharmacophore models based on common molecular characteristics (HipHop) and receptor-ligand complex (CBP) were generated for virtual screening for HPPD inhibitors. About 1,000,000 molecules containing diketone structure from PubChem were filtered by Lipinski's rules to build a 3D database. Then the database was screened through combining HipHop model, CBP model, ADMET (absorption, distribution, metabolism, excretion and toxicity) prediction and molecular docking. Subsequently, based on the specific binding mode and affinity of HPPD inhibitors, 4 molecules with high -CDOCKER energy, good aqueous solubility and human safety predicative properties values were screened. From the screening results and combined with previous work, three novel HPPD inhibitors were designed and synthesized through fragment splicing and bioisosterism strategies. Compound IV-a exhibited similar inhibition of Arabidopsis thaliana HPPD (AtHPPD) and herbicidal activity as mesotrione. Crop selectivity showed that compound IV-a had better crop safety than mesotrione. Comparing the molecular properties, ADMET and molecular docking studies indicated that compounds IV-a exhibited better properties than mesotrione, which could be further modified as novel HPPD inhibitor herbicides.

Identification of 4-hydroxyphenylpyruvate dioxygenase inhibitors by virtual screening, molecular docking, molecular dynamic simulation.

BACKGROUND: 4-Hydroxyphenylpyruvate dioxygenase (HPPD) herbicides control broadleaf and gramineous weeds with better crop safety for corn, sorghum and wheat. Multiple screening models in silico have been established to obtain novel lead compounds as HPPD inhibition herbicides. RESULTS: Topomer comparative molecular field analysis (CoMFA) combined with topomer search technology and Bayesian, genetic approximation functions (GFA) and multiple linear regression (MLR) models generated by calculating different descriptors were constructed for the quinazolindione derivatives of HPPD inhibitors. The coefficient of determination (r2 ) of topomer CoMFA, MLR and GFA were 0.975, 0.970 and 0.968, respectively; all the models established displayed excellent accuracy and high predictive capacity. Five compounds with potential HPPD inhibition were obtained via screening fragment library combined with the validation of the above models and molecular docking studies. After molecular dynamics (MD) validation and absorption, distribution, metabolism, excretion and toxicity (ADMET) prediction, the compound 2-(2-amino-4-(4H-1,2,4-triazol-4-yl) benzoyl)-3-hydroxycyclohex-2-en-1-one not only exhibited stable interactions with the protein but also high solubility and low toxicity, and has potential as a novel HPPD inhibition herbicide. CONCLUSION: In this study, five compounds were obtained through multiple quantitative structure-activity relationship screening. Molecular docking and MD experiments showed that the constructed approach had good screening ability for HPPD inhibitors. This work provided molecular structural information for developing novel, highly efficient and low-toxicity HPPD inhibitors. © 2023 Society of Chemical Industry.

Virtual screening based on pharmacophore model for developing novel HPPD inhibitors.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an important target for herbicide design. A multilayered virtual screening workflow was constructed by combining two pharmacophore models based on ligand and crystal complexes, molecular docking, molecular dynamics (MD), and biological activity determination to identify novel small-molecule inhibitors of HPPD. About 110, 000 compounds of Bailingwei and traditional Chinese medicine databases were screened. Of these, 333 were analyzed through docking experiments. Five compounds were selected by analyzing the binding pattern of inhibitors with amino acid residues in the active pocket. All five compounds could produce stable coordination with cobalt ion, and form favorable π-π interactions. MD simulation demonstrated that Phe381 and Phe424 made large contributions to the strength of binding. The enzyme activity experiment verified that compound-139 displayed excellent potency against AtHPPD (IC50 = 0.742 µM), however, compound-5222 had inhibitory effect on human HPPD (IC50 = 6 nM). Compound-139 exhibited herbicidal activity to some extent on different gramineous weeds. This work provided a strong insight into the design and development of novel HPPD inhibitor using in silico techniques.

Resistance to a nonselective 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide via novel reduction-dehydration-glutathione conjugation in Amaranthus tuberculatus.

Metabolic resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides is a threat in controlling waterhemp (Amaranthus tuberculatus) in the USA. We investigated resistance mechanisms to syncarpic acid-3 (SA3), a nonselective, noncommercial HPPD-inhibiting herbicide metabolically robust to Phase I oxidation, in multiple-herbicide-resistant (MHR) waterhemp populations (SIR and NEB) and HPPD inhibitor-sensitive populations (ACR and SEN). Dose-response experiments with SA3 provided ED50 -based resistant : sensitive ratios of at least 18-fold. Metabolism experiments quantifying parent SA3 remaining in excised leaves during a time course indicated MHR populations displayed faster rates of SA3 metabolism compared to HPPD inhibitor-sensitive populations. SA3 metabolites were identified via LC-MS-based untargeted metabolomics in whole plants. A Phase I metabolite, likely generated by cytochrome P450-mediated alkyl hydroxylation, was detected but was not associated with resistance. A Phase I metabolite consistent with ketone reduction followed by water elimination was detected, creating a putative α,ß-unsaturated carbonyl resembling a Michael acceptor site. A Phase II glutathione-SA3 conjugate was associated with resistance. Our results revealed a novel reduction-dehydration-GSH conjugation detoxification mechanism. SA3 metabolism in MHR waterhemp is thus atypical compared to commercial HPPD-inhibiting herbicides. This previously uncharacterized detoxification mechanism presents a unique opportunity for future biorational design by blocking known sites of herbicide metabolism in weeds.

Design, synthesis, herbicidal activity and CoMFA of aryl-formyl piperidinone HPPD inhibitors.

Isoxazole, nicotinic acid and benzoic acid are important components in many natural products and useful synthons to build macrostructures having valuable biological activities. In continuation of our effort to discover 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) inhibitors and search for active fragments from natural products, a series of substituted aryl-formyl piperidinone derivatives with natural product fragments was rationally designed, synthesized and tested for their herbicidal activity. Compound I-9 was considered the most effective candidate with an IC50 value of 0.260 µM. The molecular docking results showed that the triketone group of compound I-9 forms a bidentate complex with a metal ion, and the benzene ring interacted with Phe424 and Phe381 via π-π stacking, which was similar to the mechanisms of mesotrione. The present work indicates that compound I-9 may serve as a potential lead compound for further development of green HPPD inhibitors.

Interspecific and intraspecific transference of metabolism-based mesotrione resistance in dioecious weedy Amaranthus.

Pollen-mediated gene flow (PMGF) might play an important role in dispersing herbicide resistance alleles in dioecious weedy Amaranthus species. Field experiments in a concentric donor-receptor design were conducted to quantify two sets of PMGF studies, an interspecific (Amaranthus tuberculatus × Amaranthus palmeri) and an intraspecific (A. tuberculatus × A. tuberculatus). In both studies, PMGF was evaluated using a resistant A. tuberculatus phenotype with enhanced mesotrione detoxification via P450 enzymes as a source of resistance alleles. For interspecific hybridization, more than 104 000 putative hybrid seedlings were screened with three markers, one phenotypic and two molecular. The two molecular markers used, including 2-bp polymorphisms in the internal transcribed spacer region, distinguished A. palmeri, A. tuberculatus and their hybrids. Results showed that 0.1% hybridization between A. tuberculatus × A. palmeri occurred under field research conditions. For intraspecific hybridization, 22 582 seedlings were screened to assess the frequency of gene flow. The frequency of gene flow (FGF ) varied with distance, direction and year of the study. The farthest distance for 90% reduction of FGF was at 69 m in 2015 however, after averaging across directions it was 13.1 and 26.1 m in 2014 and 2015, respectively. This study highlights the transfer of metabolism-based mesotrione resistance from A. tuberculatus to A. palmeri under field research conditions. The results presented here might aid in the rapid detection of A. palmeri among other Amaranthus species and show that PMFG could be expediting the increase of herbicide resistance in A. palmeri and A. tuberculatus across US crop production areas.

Integrated Virtual Screening and Validation toward Potential HPPD Inhibition Herbicide.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the most widely studied herbicide targets and has gained significant attention. To identify potential effective HPPD inhibitors, a rational multistep virtual screening workflow was built, which included CBP models (based on the receptor-ligand interactions in the crystal complex), Hypogen models with activity prediction ability (according to the derivation of structure-activity relationships from a set of molecules with reported activity values), and a consensus docking procedure (consisting of LibDock, Glide, and CDOCKER). About 1 million molecules containing diketone or ß-keto-enol substructures were filtered by Lipinski's rules, CBP model, and Hypogen model. A total of 12 compounds with similar docking postures were generated by consensus docking. Eventually, four molecules were screened based on the specific binding pattern and affinity of the HPPD inhibitor. The biological evaluation in vivo displayed that compounds III-1 and III-2 exhibited comparable herbicidal activity to isoxaflutole and possessed superior safety on various crops (wheat, rice, sorghum, and maize). The ADMET prediction (absorption, distribution, metabolism, excretion, and toxicity) showed that compound III possessed relatively good toxicological results. This work provides a theoretical basis and valuable reference for the virtual screening and molecular design of novel HPPD inhibition herbicides.

Discovery of novel benzofuran scaffold as 4-hydroxyphenylpyruvate dioxygenase inhibitors.

BACKGROUND: 4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. This study sheds new light on the differences in molecular scaffold from commercialized HPPD inhibitors. RESULTS: The compounds A1-A18 and B1-B27 were synthesized for in vitro and greenhouse experiments. The greenhouse experiment data indicated that compounds B14 and B18 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. In vitro testing indicated that the compounds were HPPD inhibitors. Moreover, molecular simulation results show that the compounds B14, B18, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on crop selectivity results, compounds B14 and B18 were selected for maize studies (injury≤10%), indicating its potential for weed control in maize fields. CONCLUSION: These results showed that the pyrazole-benzofuran structure could be used as possible lead compounds for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Cobalt (II) complex as a fluorescent sensing platform for the selective and sensitive detection of triketone HPPD inhibitors.

4-Hydroxyphenylpyruvatedioxygenase (HPPD) is a Fe(II)/Co(II)-dependent enzyme which has become one of the most effective herbicide targets. HPPD inhibitors have been developed as efficient herbicides for resistant weed control. Developing a method for efficient and rapid HPPD inhibitors detection is still challenging. N-n-butyl-4-methylhydrazinecarbothioamide-1,8-naphthalimide (NMN) was synthesized and used to detect Co2+ efficiently with the limit of detection (LOD) of 7.82 nM with a turn-on fluorescence. Herein a novel fluorescent complex, NMN‒Co2+ was employed to determine HPPD inhibitors which performed a turn-off effect in the sensing process based on the competitive coordination between the probe and HPPD with Co2+. The LODs for three commercial triketone HPPD inhibitors (mesotrione, tembotrione and NTBC) were 6.60 nM, 7.37 nM and 10.22 nM with good sensitivity and selectivity. Furthermore, the present probe has potentials to quantitatively detect mesotrione and tembotrione in real samples.

Genetic architecture underlying HPPD-inhibitor resistance in a Nebraska Amaranthus tuberculatus population.

BACKGROUND: Amaranthus tuberculatus is a problematic weed species in Midwest USA agricultural systems. Inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD) are an important chemistry for weed management in numerous cropping systems. Here, we characterize the genetic architecture underlying the HPPD-inhibitor resistance trait in an A. tuberculatus population (NEB). RESULTS: Dose-response studies of an F1 generation identified HPPD-inhibitor resistance as a dominant trait with a resistance factor of 15.0-21.1 based on dose required for 50% growth reduction. Segregation analysis in a pseudo-F2 generation determined the trait is moderately heritable (H2  = 0.556) and complex. Bulk segregant analysis and validation with molecular markers identified two quantitative trait loci (QTL), one on each of Scaffold 4 and 12. CONCLUSIONS: Resistance to HPPD inhibitors is a complex, largely dominant trait within the NEB population. Two large-effect QTL were identified controlling HPPD-inhibitor resistance in A. tuberculatus. This is the first QTL mapping study to characterize herbicide resistance in a weedy species.

Discovery of novel arylthioacetic acid derivatives as 4-hydroxyphenylpyruvate dioxygenase inhibitors.

BACKGROUND: 4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. In a continuing effort to discover novel HPPD inhibitors, we adopted a bioisosterism strategy to design a series of novel arylthioacetic acid scaffold based on the previously discovered aryloxyacetic acid scaffold. This study sheds new light on the discovery of novel HPPD inhibitors. RESULTS: The compounds A1-A30 and B1-B39 were prepared through an efficient synthetic route for in vitro and glasshouse experiments (herbicidal activities, herbicidal activity spectrum, and crop selectivity). Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD inhibitors, compounds A11 (Ki = 0.021 µmol L-1 ) and B20 (Ki = 0.022 µmol L-1 ), which exhibit similar activities to that of mesotrione (Ki = 0.020 µmol L-1 ). The glasshouse experiments data indicated that compounds B34 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. Moreover, molecular simulation results show that the compounds B20, B34, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on herbicidal results, compound B34 was selected for crop selectivity studies (corn injury ≤ 10%), indicating its potential for weed control in corn fields. CONCLUSION: These bioassay results showed that the compound B34 could be used as a possible lead compound for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Identification of key residues determining the binding specificity of human 4-hydroxyphenylpyruvate dioxygenase.

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is the second enzyme of the tyrosine catabolic pathway. Its physiological function is to catalyze the conversion of 4-hydroxyphenylpyruvic acid to homogentisic acid, which displays different physiological effects in mammals and plants. Insights on the selective inhibition of human HPPD (hHPPD) by triketone inhibitors were furnished by the integrated application of molecular simulation and biological testing. The binding free energy of hHPPD and inhibitors was obtained through molecular dynamics (MD) simulations, and the result was in agreement with the inhibition experiment in vitro. The binding free energy contribution demonstrated that the formation of hHPPD-inhibitor complexes was mainly driven by van der Waals energy. Ser226, Asn241, Gln265, Phe336, Phe359 and Phe364 made great contributions to binding affinities of all the systems. Among the residues involved in the interaction between nitisinone (NTBC) and hHPPD, Tyr221 and Leu224, whose mutation into Ala caused significant decrease of NTBC binding ability, were two key residues in determining the selective binding affinity of inhibitor and hHPPD. This work provides valuable theoretical basis for rational design of highly selective inhibitors targeting hHPPD.

Impacts of hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor (mesotrione) on photosynthetic processes in Chlamydomonas reinhardtii.

Mesotrione, an herbicide increasingly found in aquatic systems due to its increased application frequency in corn fields, is an inhibitor of the p-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme for plastoquinone-9, α-tocopherol and indirectly for carotenoid biosynthesis. The direct effect of mesotrione on plastoquinone-9 and α-tocopherol synthesis and their degradation rates are well documented, but few information exists on its action on photosynthetic processes under various light intensities. We therefore investigated the photosynthetic activity, energy dissipation processes, pigment composition and α-tocopherol content when Chlamydomonas reinhardtii were exposed to mesotrione for 24 h under low light condition and then the impacts of HL treatment (75 min) were also investigated. Under low light growth conditions, mesotrione did not induce PSII photoinhihition, while substantially decreased Car:Chl-a ratio, maximal energy-dependant quenching and state 1 to state 2 transition. Under high light conditions (HL), PSII activity was highly decreased in presence of mesotrione, and the non-photochemical energy dissipation processes were drastically affected in these conditions compared to the HL treatment alone. Mesotrinone also prevent the complete recovery of PSII damage caused by HL. Light condition seems therefore to be a non-negligible factor modulating mesotrione toxicity, and this has an obvious importance in agricultural waterbodies where phytoplankton is subjected to fluctuating light intensities.

Metabolic Pathway of Topramezone in Multiple-Resistant Waterhemp (Amaranthus tuberculatus) Differs From Naturally Tolerant Maize.

Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] is a problematic dicot weed in maize, soybean, and cotton production in the United States. Waterhemp has evolved resistance to several commercial herbicides that inhibit the 4-hydroxyphenylpyruvate-dioxygenase (HPPD) enzyme in sensitive dicots, and research to date has shown that HPPD-inhibitor resistance is conferred by rapid oxidative metabolism of the parent compound in resistant populations. Mesotrione and tembotrione (both triketones) have been used exclusively to study HPPD-inhibitor resistance mechanisms in waterhemp and a related species, A. palmeri (S. Wats.), but the commercial HPPD inhibitor topramezone (a pyrazolone) has not been investigated from a mechanistic standpoint despite numerous reports of cross-resistance in the field and greenhouse. The first objective of our research was to determine if two multiple herbicide-resistant (MHR) waterhemp populations (named NEB and SIR) metabolize topramezone more rapidly than two HPPD inhibitor-sensitive waterhemp populations (named SEN and ACR). Our second objective was to determine if initial topramezone metabolite(s) detected in MHR waterhemp are qualitatively different than those formed in maize. An excised leaf assay and whole-plant study investigated initial rates of topramezone metabolism (<24 h) and identified topramezone metabolites at 48 hours after treatment (HAT), respectively, in the four waterhemp populations and maize. Results indicated both MHR waterhemp populations metabolized more topramezone than the sensitive (SEN) population at 6 HAT, while only the SIR population metabolized more topramezone than SEN at 24 HAT. Maize metabolized more topramezone than any waterhemp population at each time point examined. LC-MS analysis of topramezone metabolites at 48 HAT showed maize primarily formed desmethyl and benzoic acid metabolites, as expected based on published reports, whereas SIR formed two putative hydroxylated metabolites. Subsequent LC-MS/MS analyses identified both hydroxytopramezone metabolites in SIR as different hydroxylation products of the isoxazole ring, which were also present in maize 48 HAT but at very low levels. These results indicate that SIR initially metabolizes and detoxifies topramezone in a different manner than tolerant maize.

New Research for Quinazoline-2,4-diones as HPPD Inhibitors Based on 2D-MLR and 3D-QSAR Models.

AIM AND OBJECTIVE: 4-Hydroxyphenylpyruvate dioxygenase (HPPD), converting phydroxyphenylpyruvate (HPPA) to homogentisate (HGA), is an important target for treating type I tyrosinemia and synthesizing novel herbicides due to its significant role in tyrosine catabolism. Hence, it is imperative to design novel HPPD inhibitors that can block HPPA-HGA conversion, which leads to the deficiency in isoprenoid redox cofactors such as plastoquinone and tocopherol, and finally caused growth inhibition. This study was undertaken to investigate structural requirements for their HPPD inhibition with better biological activity. MATERIALS AND METHODS: Based on the structure-activity relationships, a series of quinolinone-2,4- diones derivatives were studied using combined of 2D multiple linear regression (2D-MLR) and 3D quantitative structure-activity relationship (3D-QSAR). Firstly, genetic algorithm (GA) was applied and descriptors generated in DRAGON 5.5 software were used for building 2D-MLR models in the QSARINGS. Then CoMFA and CoMSIA models were performed by using alignment of the common framework and the pharmacophore model. The obtained models were validated through internal and external validation to verify predictive abilities. Especially, the CoMFA and CoMSIA contour maps were used to show vital structural characteristics related to HPPD inhibitors activities. RESULTS: The 2D-MLR liner equation and corresponding parameters were listed as follows: pKi = -38.2034Me+22.4078GATS2m-1.4265EEig15r-2.1849Hy+32.9158 ntr=28, npred=6, R2=0.863, Q2LOO=0.787, Q2LMO=0.607, Q2F1=0.780, Q2F2=0.780, Q2F3=0.860, CCCpred=0.920. RMSEtr=0.253, RMSEpred=0.555, F=36.289 The steric contours graph indicated that small and negative electrostatic substitutions at R1 and R2 regions were favorable for the better activity, and hydrogen-bond donors at this region would also increase the activity. Positive electrostatic and bulky substitutions in the R3 position would enhance the activity. The analysis of these models suggested that the steric factor of R4 position was crucial for activity of quinazoline-2,4-diones HPPD inhibitors, bulky substitutions might improve the bioactivity of these inhibitors greatly, meanwhile, hydrogen-bond acceptor groups in this position were required for higher activity. CONCLUSION: In this study, a combined 2D-MLR, CoMFA and CoMSIA models demonstrated satisfying results through internal and external validation, especially good predictive abilities and the CoMFA and CoMSIA contour maps showed vital structural characteristics related to HPPD inhibitors activities.

Presence of the ß-triketone herbicide tefuryltrione in drinking water sources and its degradation product in drinking waters.

Triketone herbicides are becoming popular because of their herbicidal activity against sulfonylurea-resistant weeds. Among these herbicides, tefuryltrione (TFT) is the first registered herbicide for rice farming, and recently its distribution has grown dramatically. In this study, we developed analytical methods for TFT and its degradation product 2-chloro-4-methylsulfonyl-3-[(tetrahydrofuran-2-yl-methoxy) methyl] benzoic acid (CMTBA). TFT was found frequently in surface waters in rice production areas at concentrations as high as 1.9 µg/L. The maximum observed concentration was lower than but close to 2 µg/L, which is the Japanese reference concentration of ambient water quality for pesticides. However, TFT was not found in any drinking waters even though the source waters were purified by conventional coagulation and filtration processes; this was due to chlorination, which transforms TFT to CMTBA. The conversion rate of TFT to CMBA on chlorination was almost 100%, and CMTBA was stable in the presence of chlorine. Moreover, CMTBA was found in drinking waters sampled from household water taps at a similar concentration to that of TFT in the source water of the water purification plant. Although the acceptable daily intake and the reference concentration of CMTBA are unknown, the highest concentration in drinking water exceeded 0.1 µg/L, which is the maximum allowable concentration for any individual pesticide and its relevant metabolites in the European Union Drinking Directive.