Chemical models of cytochrome P450 catalyzed insecticide metabolism. Application to the oxidative metabolism of carbamate insecticides

Inoculation with carbofuran-degrading rhizobacteria promotes maize growth through production of IAA and regulation of the release of plant-specialized metabolites

Toxic residues of the insecticide carbofuran in farmland is an urgent problem, and high concentrations of carbofuran have been found in the rhizoshperic soil of maize treated with seed coating agents 120-180 days after planting. Using an enrichment co-culture method, we identify a bacterial strain obtained from these carbofuran-contaminated rhizosphere soils as Leclercia adecarboxylata MCH-1. This strain exhibited a significant ability to degrade both carbofuran and 3-keto carbofuran, with total degradation of 55.6 ± 4.6% and 75.7 ± 3.4%, respectively, 24 h following start of co-culture. Further activity screening revealed that the inoculation of maize roots with L. adecarboxylata MCH-1 promoted maize seedling growth. Quantitative analysis demonstrated that this bacterial strain had the ability to synthesize the phytohormone IAA. Simultaneously, the concentration of IAA in the rhizospheric soil increased following inoculation of maize roots with L. adecarboxylata MCH-1. Moreover, the concentrations of plant specialized metabolites, including phenolics, terpenoids, and alkaloids, decreased in maize seedlings and were elevated in the rhizospheric soil after maize roots had been inoculated with the MCH-1 strain. Interestingly, the growth of the strain MCH-1 was improved by co-culture with root exudates obtained from the rhizospheric soil, specifically 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and zealexin A₁ (ZA₁). Taken together, our results suggest that the carbofuran-degrading rhizobacterium L. adecarboxylata MCH-1 is able to interact with maize plants through the regulation of maize root exudates. Moreover, inoculation with L. adecarboxylata MCH-1 promotes maize growth through the production of IAA and regulation of the release of plant specialized metabolites. Our results provide a new model organism for the remediation of farmland soils from pollution with carbofuran residues.

Degradation features of pesticides: a review on (metallo)porphyrin-mediated catalytic processes

Pesticides have been used to kill pests such as insects, fungi, rodents, and unwanted plants. Since these compounds are potentially toxic to the target organisms, they could also be harmful to human health and the environment. Several chronic adverse effects have been identified even after months or years of exposure. A few pesticide degradation processes have been studied including adsorption, homogeneous and heterogeneous (photo)catalytic oxidation, and biological methods. Although these methods have been playing a significant part in the pesticide's degradation, there are still gaps in many aspects. Here, we review the catalytic degradation of these pollutants by (metallo)porphyrins. To evaluate the P450 cytochrome's biomimetic behavior of these catalysts, various synthesized porphyrins have been used since 1999 and their activities were summarized in this manuscript. The porphyrins appear to act as good catalysts for the degradation of pesticides; in fact, they also have been shown as a useful tool for the elucidation of their degradation products. Achieving pesticide mineralization without intermediate products is still challenging, although the ability of this kind of catalysts to conduct the formation of some lower toxic products comparing their precursors has been verified.

Environmental application of an industrial waste as catalyst for the electro-Fenton-like treatment of organic pollutants

The application of acid mine drainage sludge (AMDS), an industrial waste with high metal content, as catalyst for the electro-Fenton-like technology on the treatment of organic polluted effluents has been investigated.

5,10,15,20-tetrakis(pentafluorophenyl)porphyrin: a versatile platform to novel porphyrinic materials

5,10,15,20-tetrakis(pentafluorophenyl)porphyrin reacts with a range of nucleophiles (amines, alcohols, thiols, nitrogen heterocycles, and others) resulting in the nucleophilic aromatic substitution of the para-F atoms of the pentafluorophenyl groups. This reaction, which was fortuitously discovered by Kadish and collaborators in 1990, is now being extensively used to synthesize porphyrins bearing electron-donating substituents in the para-position of their meso-aryl groups. This mini-review highlights the methods of synthesis of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, the use of its metal complexes in catalysis and its reaction with nucleophiles to yield new monomeric porphyrins, porphyrins supported in polymers or new polymeric porphyrin matrices useful for heterogeneous catalysis.

Biomimetic chemistry as a useful tool for studying reactive metabolites of pesticides

Most organophosphate (OP) pesticides require metabolic activation before attacking the target site, as opposed to chemical nerve agents, such as VX and sarin, which inhibit the enzyme directly. The majority of OP pesticides exhibit weak anticholinesterase activity in vitro compared to their In Vivo activity. Biooxidation is probably the principal route by which these pesticides are activated or detoxified. The oxidized product, usually a short-lived intermediate, may either hit the target directly or hydrolyze rapidly or, following a rearrangement reaction, convert to another species with enhanced reactivity (metaphosphate) or lose its phosphorylation or carbamoylation properties. Biomimetic studies of these processes, using various model systems, have important advantages: in some cases they allow for identifying short-lived intermediates, formed metabolically, and direct monitoring of the systems' properties by NMR. Once identified, they may be synthesized in large amount to investigate their adverse effects, if any. Biomimetic studies allow for monitoring reactions at low temperature seeking transient intermediates and evaluation of activation and detoxification mechanisms as well as mode of action based on chiral isomers. This, in turn, allows for determination of whether certain compounds act directly, on preactivation, or both, and the possible design of safer pesticides. This paper covers over three decades of extensive fundamental and applied research that has been carried out at the Environmental Chemistry and Toxicology Laboratory (ECTL) at the University of California at Berkeley under the supervision of Prof. John E. Casida.

Metalloporphyrins as biomimetic models for cytochrome p-450 in the oxidation of atrazine

The aim of this work was to evaluate whether metalloporphyrin models could mimic the action of cytochrome P-450 in the oxidation of atrazine, a herbicide. The commercially available second-generation metalloporphyrins 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin metal(III) chloride [M(TDCPP)Cl] and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin metal(III) chloride [M(TFPP)Cl] (metal = Fe or Mn) and the oxidants iodosylbenzene and metachloroperbenzoic acid were employed in this study. Results showed that the metalloporphyrins used here can oxidize atrazine. Yields as high as 32% were obtained for the Mn(TFPP)Cl/PhIO system, which shows that these catalysts can mimic both the in vivo and the in vitro action of cytochrome P-450, with formation of the metabolites DEA and DIA. The formation of five other unknown products was also detected, but only one of them could be identified, since the other four were present in very low concentrations. The compound COA, identified by mass spectrometry, was the main product in most of the oxidation reactions.

Tomato metabolism and porphyrin-catalyzed oxidation of pyriproxyfen

Investigation of the metabolism of [(14)C]pyriproxyfen [4-phenoxyphenyl (R,S)-2-(2-pyridyloxy)propyl ether] in tomato fruits (Lycopersicon esculentum Mill. cv. Ponterosa) was conducted by topical application of acetonitrile solution or emulsifiable concentration formulation three times at 35, 21, and 7 days before harvest. Most of the radioactivity remained on the fruit surface or in the plant tissues as intact pyriproxyfen with minor metabolites formed via hydroxylation at the 4'-position of the phenoxy ring or cleavage of ether linkages. The biomimic chemical oxidation model using iron porphyrin as a catalyst and hydrogen peroxide was found to well reproduce the primary metabolites detected in the metabolism study. The electrophilic reaction indices obtained by AM1 molecular orbital calculations supposing involvement of cytochrome P-450 were successfully applied to evaluate the potentially higher reactive sites in pyriproxyfen.

A virtual high throughput screen for high affinity cytochrome P450cam substrates. Implications for in silico prediction of drug metabolism

Structure-based virtual screening techniques require reliable scoring functions to discriminate potential substrates effectively. In this study we compared the performance of GOLD, PMF, DOCK and FlexX scoring functions in FlexX flexible docking to cytochrome P450cam binding site. Crystal structures of protein-substrate complexes were most effectively reproduced by the FlexX/PMF method. On the other hand, the FlexX/GOLD approach provided the best correlation between experimental binding constants and predicted scores. Binding modes selected by the FlexX/PMF approach were rescored by GOLD to obtain a reliable measure of binding energetics. The effectiveness of the FlexX/PMF/GOLD method was demonstrated by the correct classification of 32 out of the 33 experimentally studied compounds and also in a virtual HTS test on a library of 10,000 compounds. Although almost all the available functions were developed to be general, our study on cytochrome P450cam substrates suggests that careful selection or even tailoring the scoring function might increase the prediction power of virtual screens significantly. The FlexX/PMF/GOLD methodology was tested on cytochrome P450 3A4 substrates and inhibitors. This preliminary study revealed that the combined function was able to recognise 334 out of the 345 compounds bound to 3A4.

Metalloporphyrin catalyzed oxidation of N-hydroxyguanidines: a biomimetic model for the H2O2-dependent activity of nitric oxide synthase

A chemical model for the H2O2 promoted oxidation by nitric oxide synthase (NOS) has been developed. Biomimetic oxidations were carried out using H2O2 and tetrakis(perfluorophenyl)porphyrinato-iron(III) chloride (FeTPPF20) as a catalyst. Similarly to NOS our model system produces Ndelta-cyanoornithine, citrulline and NO from NOHA and did not oxidize arginine itself. Based on these results we propose a peroxide shunt to be involved in the catalytic cycle of NOS. To the best of our knowledge this is the first chemical system that semiquantitatively mimics NOS activity.

Diversity measures for enhancing ADME admissibility of combinatorial libraries

For general screening libraries, structural diversity descriptors and drug-likeness indicators still do not guarantee the in vivo bioavailability for the candidates, which is considered a major bottleneck in drug development. Early prediction of pharmacokinetics (log P, log D), metabolism, and toxicity makes it possible to deal with ADME (adsorption, distribution, metabolism, excretion) related diversity as an extension to the classical diversity concepts. It opens several new possibilities for optimization of a discovery library before doing any experimental screening. This new diversity concept is demonstrated on a subset of MeDiverse, which is a diverse collection of pharmacologically relevant compounds selected from our in-house library. From consideration of the ADME interface in living systems, virtual secondary libraries of metabolites and retrometabolites (prodrugs) can be generated. These additional libraries readily enhance both the structural and ADME related diversity. This new opportunity in library design can substantially improve the success rate for in vivo lead generation from in vitro hits.