Epoxide Formation Research Articles

Understanding the Mechanistic Requirements for Efficient and Stereoselective Alkene Epoxidation by a Cytochrome P450 Enzyme

The cytochrome P450 (CYP) family of heme monooxygenase enzymes commonly catalyzes enantioselective hydroxylation and epoxidation reactions. Epoxidation reactions have been hypothesized to proceed via multiple mechanisms involving different reactive intermediates. Here, we use activity, spectroscopic, structural, and molecular dynamics data to investigate the activity and stereoselectivity of 4-vinylbenzoic acid epoxidation by the bacterial enzyme CYP199A4 from Rhodopseudomonas palustris HaA2. The epoxidation of 4-vinylbenzoic acid by CYP199A4 proceeded with high enantioselectivity, giving the (S)-epoxide in 99% ee at an activity of 220 nmol nmol-CYP–1 min–1. Optical and EPR spectroscopy, redox potential measurements, and the crystal structure of 4-vinylbenzoic acid-bound CYP199A4 indicated the partial retention of an aqua ligand at the heme center in the presence of the substrate, providing a justification of the lower activity (∼20%) compared to the oxidative demethylation of 4-methoxybenzoic acid. Mutagenesis at the conserved acid–alcohol pair (D251/T252), which perturbs the generation of the reactive oxygen intermediates, was employed to investigate their role in epoxidation reactions. The T252A mutant increased the rate of turnover of the catalytic cycle, but an elevation in hydrogen peroxide generation via uncoupling resulted in a similar rate of epoxide formation. The activity of epoxidation significantly reduced with the D251N mutant. The chemoselectivity and stereoselectivity of the epoxidation reaction were maintained in the turnovers by these mutants. Overall, there was little evidence that other intermediates, aside from the archetypal reactive ferryl porphyrin cation radical, Compound I, contributed significantly to the epoxidation reaction. The observation of the high selectivity for the (S)-enantiomer was rationalized by molecular dynamics simulations. When the arrangement of the alkene and the active intermediate approached an ideal transition state structure for epoxidation, one face of the alkene was more often exposed to the iron oxo unit.

Investigating reactivity and electronic structure of copper(II)-polypyridyl complexes and hydrogen peroxide

This work presents a detailed study of the reactivity of three mononuclear CuII complexes supported by derivatives of the tetradentate ligand N,N'-bis(2-pyridylmethyl)-1,2-ethylenediamine (bispicen). The CuII complexes are capable of performing CH bond activation in the presence of NEt3 and H2O2 through what has been proposed computationally to be a [CuO]+ intermediate. A wavefunction-based quantum chemical investigation into the electronic structure of the proposed [CuO]+ intermediate reveals a triplet ground state predominantly consistent with an S = ½ CuII center ferromagnetically coupled to an oxyl radical, though contributions from the corresponding biradicaloid CuI-oxene resonance structure may be nontrivial. Furthermore, correlation of the electronic structure of the proposed intermediate with analogous high-valent metal-oxo species capable of olefin epoxidation suggests that the CuII complexes might be also capable of olefin epoxidation in the presence of NEt3 and H2O2. To test this hypothesis experimentally, the CuII complexes are treated with NEt3 and H2O2 in the presence of alkene substrates, resulting in the formation of epoxides.

Influence of hydroperoxide epoxidation reaction conditions of octen-1 on the process of Mo2B activation and on the selectivity of epoxide formation

A study of the process of activation of molybdenumboride catalyst in the reaction of epoxidation of octene-1 with tert-butyl hydroperoxide and the effect on this process of the initial concentration of octene-1, tert-butyl hydroperoxide and the amount of catalyst in the reaction mixture. As well as reaction products (tert-butyl alcohol and epoxy). It is shown that over time a new amorphous phase is formed on the surface of Mo2B, which actually catalyzes the epoxidation reaction of octene-1 with tert-butyl hydroperoxide. The formation of this phase is the reason for the acceleration of the rate of consumption of hydroperoxide and the selectivity of the formation of epoxide over time.

Soybean Oil Epoxidation: Kinetics of the Epoxide Ring Opening Reactions

The epoxide ring opening reaction (ROR) can be considered as the most important side reaction occurring in the epoxidation of soybean oil reaction network. This reaction consistently reduces the selectivity to epoxidized soybean oil (ESBO). The reaction is also important for producing polyols and lubricants. In this work, the reaction was studied in different operative conditions to evaluate the effect on ROR rate respectively: (i) The Bronsted acidity of the mineral acid (H2SO4 or H3PO4), used as catalyst for promoting the oxidation with hydrogen peroxide of formic to performic acid, that is, the reactant in the epoxide formation; (ii) the concentration of the nucleophilic agents, normally present during the ESBO synthesis like HCOOH, HCOOOH, H2O, H2O2; (iii) the stirring rate that changes the oil–water interface area and affects the mass transfer rate; (iv) the adopted temperature. Many different kinetic runs were made in different operative conditions, starting from an already epoxidized soybean oil. On the basis of these runs two different reaction mechanisms were hypothesized, one promoted by the Bronsted acidity mainly occurring at the oil–water interface and one promoted by the nucleophilic agents, in particular by formic acid. As it will be seen, the kinetic laws corresponding to the two mentioned mechanisms are quite different and this explain the divergent data reported in the literature on this subject. All the kinetic runs were correctly interpreted with a new developed biphasic kinetic model.

ONE-POT-TWO-STEP SYNTHESIS OF BIOLUBRICANT BASE STOCK FROM RUBBER SEED OIL

Biolubricant base stock was synthesized in this work from rubber seed oil in a one-pot-two-step process of epoxidation and hydroxylation. Rubber seed oil was extracted using a Soxhlet apparatus. The in situ epoxidation of the rubber seed oil with peracid (hydrogen peroxide and acetic acid) was analysed and optimized considering three process variables with their range of values given as temperature of 35-50 , time of 60-180 mins and mole ratio of hydrogen peroxide to acetic acid of 1:0.25-1:1 by applying the central composite design of response surface methodology. The ring opening reaction (hydroxylation) of the epoxide to polyhydroxylated oil (lubricant basestock) with ethanol was carried out using the optimum conditions obtained from the epoxidation process. The rubber seed oil, epoxide and lubricant basestock were characterized in terms of physico-chemical properties using standard methods and in terms of functional groups using Fourier Transform Infrared (FTIR) spectroscopy. Maximum epoxide content of 4.85% and maximum conversion of 71% of rubber seed oil to epoxide was achieved at a temperature of 50􀀀 , reaction time of 180 mins and 1: 0.39 mol/mol of hydrogen peroxide to acetic acid. The predicted values of the epoxidation process reasonably agreed with the experimental ones and model R-squared value of about 95% showed that response surface method can reasonably predict the epoxidation process using a quadratic polynomial model. There was 75% conversion of the epoxide to polyhydroxylated oil (biolubricant basestock), which represents a very high yield. The formation of epoxides and polyhydroxylated oil lead to modification (improvement) in the properties of rubber seed oil as confirmed by the physico-chemical properties and FTIR spectra analysis of the oil, epoxide and lubricant basestock. The study showed that chemical derivatives of rubber seed oils are an attractive, renewable, and ecofriendly alternative to mineral oils for lubricant formulations.

Optimization On Rubber Seed Oil Epoxidation Process Parameters Using Response Surface Methodology

Pure rubber seed oil was epoxidized via in situ conventional method using hydrogen peroxide and acetic acid in the presence of Sulfuric acid as catalyst. Optimization of the effect of process parameters such as time, temperature, and catalyst concentration was studied using Response Surface Methodology (RSM). The optimal condition for the predicted oxirane value as 1.5333%, was obtained at a reaction time of 6.49 hours, stirring speed of 667.26 and catalyst concentration of 1.82 mol. The resultant epoxide product was confirmed using Fourier transform infrared spectroscopy (FTIR) (at 1636.3 cm-1). These findings demonstrated the effects of process parameters on the rate of epoxide formation and the possibility to synthesize bio-based resin from rubber seed oil.

Gallic acid enhances reproductive function by modulating oxido-inflammatory and apoptosis mediators in rats exposed to aflatoxin-B1.

Infertility resulting from reproductive deficiency can be stressful. Exposure to aflatoxin B1, a dietary mycotoxin prevalent in improperly stored grains, is reported to elicit reproductive insufficiencies and infertility. We, therefore, examined the likely beneficial effect of gallic acid (GA) a phytochemical, recognized to exhibit in vitro and in vivo pharmacological bioactivities against oxidative stress and related inflammatory damages in rats, since AFB1 toxicities are predicated on oxidative epoxide formation, in a bid to proffer new evidence to advance the field of nutriceutical application from plant-derived chemopreventive agents. Our findings will advance the field of chemoprevention by presenting data absent in the literature on GA. Our results demonstrate further evidence for GA conferred protection against AFB1-mediated histological lesions in testes, epididymis, and hypothalamus of treated rats; suppresses oxidative damages, relieved inflammatory and apoptotic responses, restored sperm functional characteristics, and hormonal levels relevant for reproductive integrity and function.

Vitamin K Tissue Distribution Is Modified by Large-Dose Warfarin and Menaquinone-4 Content of the Diet

Abstract Objectives Investigate the influence of large-dose warfarin (W) on tissue K1 and MK-4 distribution in rats fed a standard K1 diet, or enriched with MK4. Methods Male Wistar rats were fed a regular K1 (750 mcg K1/kg/diet; WK1) or enriched MK-4 (100 mg MK-4/kg/diet; WK1 + MK4) diet for 1 week after which they were administered 14 mg W/kg/day (in drinking water) and subcutaneous K1 (94 mg/kg, 3X/week; to maintain coagulation), for 12 weeks; diets were maintained throughout the experimental period. Respective diet controls (C and C + MK4) received subcutaneous saline and regular water. K1 and M-4 quinone and their epoxide forms (K1O and MK-4O) were assessed in serum, liver, heart, kidney, pancreas, adipose tissue and brain, by HPLC. Group differences were tested by one-way ANOVA, and by t-test for each K vitamer. Results In C group, K1 was the predominant K vitamer in serum, liver and heart, whereas MK-4 was found in relative higher concentrations in kidney, pancreas, brain, and adipose tissue. In MK-4 containing organs, W treatment was associated with significantly lower MK-4 concentration in pancreas, brain, and heart (P < 0.05) despite the local presence of K1, which suggests that W may block the production of MK-4 by UBIAD1. Compared to C group, K1 concentrations were significantly higher in all organs and serum in WK1 and WK1 + MK4 groups as a result of the subcutaneous administration. Interestingly, in WK1 animals who had received a MK-4 enriched diet (WK1 + MK4), K1 concentrations in naturally K1 rich tissues (i.e., liver, heart and serum) were significantly increased when compared to those from the WK1 group (P < 0.05), suggesting that dietary MK-4 may play a role in modulating the uptake of K1 in these tissues. Except in liver, W administration (WK1 and WK1 + MK4) was associated with higher tissue concentrations of K1 and MK-4 epoxide when compared to C group (P < 0.05). Noteworthy, in WK1 animals who had received a MK-4 enriched diet (WK1 + MK4), naturally rich MK-4 containing organs (i.e., kidney, pancreas, adipose tissue and brain) presented significantly higher concentration of MK-4 epoxide (relative to K1 epoxide), suggesting a preferential use of MK4 by these organs when available from the diet. Conclusions In conclusion, results from this study point to modulatory roles of W and dietary MK-4 on tissue distribution of K1 and MK-4 in what appears to be a tissue specific manner. Funding Sources CIHR.

Effect of Oxygen Carrier and Reaction Temperature in Enhancing the Epoxy Ring Stability in the Epoxidation of Palm Kernel Oil

Palm kernel oil (PKO) naturally composed of lauric, myristic and oleic acid. Oleic acid is one of the unsaturated fatty acids that has double bond in its chain. This double bond can be altered into epoxide acid by epoxidation reaction. This study investigated the effect of oxygen carriers and reaction temperature in epoxidation of palm kernel oil. The result showed that formic acid is the best oxygen carrier with the maximum conversion to oxirane (RCO) of 60.59% under optimum temperature of 55°C. The formation of epoxide from palm kernel oil was confirmed by FTIR analysis which shows the functional groups of epoxide ring at 2922.12 cm−1, 1742.74 cm−1 and 650.4 cm−1.

Bioinspired oxidation in cytochrome P450 of isomers orientin and isoorientin using Salen complexes.

Orientin and isoorientin are C-glycosidic flavonoids, considered as markers of some plant species such as Passiflora edulis var. flavicarpa Degener, and reported in the literature to have pharmacological properties. In order to evaluate and characterize the in vitro metabolism of these flavonoids, phase I biotransformation reactions were simulated using Salen complexes. These flavonoids were oxidized separately in biomimetic reactions in different proportions, using one oxidant, m-chloroperbenzoic acid or iodosylbenzene, and one catalyst, the Jacobsen catalyst or [Mn(3-MeOSalen)Cl]. The [Mn(3-MeOSalen)Cl] catalyst was synthesized and characterized using spectrometric techniques. The oxidation potentials of the catalysts were compared. All reactions were monitored and analyzed using ultrahigh-performance liquid chromatography diode-array detection (UHPLC-DAD) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). The analysis by UHPLC-DAD and HPLC/MS/MS showed that isoorientin produces more products than orientin and that [Mn(3-MeOSalen)Cl] produces more products than the Jacobsen catalyst. In addition, [Mn(3-MeOSalen)Cl], which has a higher oxidation potential, formed products with the addition of one or two atoms of oxygen, while the Jacobsen catalyst formed compounds with only one added oxygen atom. The products with the addition of one oxygen atom were mainly epoxides, while those with two added oxygens formed an epoxide in the C-ring and incorporated the other oxygen into the glycosidic moiety. The formation of epoxides is common in biomimetic reactions and they may represent a safety risk in medicinal products due to their high reactivity. This study may serve as a basis for subsequent pharmacological and toxicological studies that investigate the presence of these compounds as phase I metabolites, and ensure the safe use of plant products containing orientin as a chemical marker.

Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization.

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.

Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo‐Ring Formation with 8π‐6π Electrocyclization

AbstractShimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo‐ring formation reactions proceed non‐enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo‐ring formation and 8π‐6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non‐enzymatic conversion to shimalactones in the dark.

Biomimetic Aerobic Epoxidation of Alkenes Catalyzed by Cobalt Porphyrin under Ambient Conditions in the Presence of Sunflower Seeds Oil as a Co-Substrate.

In this work, a mild and sustainable catalytic aerobic epoxidation of alkenes catalyzed by cobalt porphyrin was performed in the presence of sunflower seeds oil. Under ambient conditions, the conversion rate of trans-stilbene reached 99%, and selectivity toward epoxide formation was 88%. The kinetic studies showed that the aerobic epoxidation followed the Michaelis–Menten kinetics. Mass spectroscopy and in situ electron spin resonance indicated that linoleic acid was converted to fatty aldehydes via hydroperoxide intermediates. A plausible mechanism of epoxidation of alkenes was accordingly proposed.

A density functional theory study on the Hexa-peri-hexabenzocoronene nanographene oxide

We investigated the structural, energetic, and electronic properties of a Hexa-peri-hexabenzocoronene (HBC) nanographene oxide (NGO), using density functional theory calculations. We found that oxygen atom preferably adds to the rim C–C bonds with Gibbs free energy change (298 K and 1 atm) of about −40.3 kcal/mol, forming epoxide. After the epoxide formation, the gap of HBC is reduced considerably by about 17.2%, which increases the electrical conductivity, and the work function is raised slightly from 3.44 to 3.64 eV. We found that by increasing the number of epoxide rings, the adsorption energy per oxygen atom decreases slightly and the electrical conductivity is increased. The solubility of HBC is increased by oxidation in both the water and benzene solvents. An unusual solubility is reported for the nonpolar HBC molecule in the polar water. The solvation energy of HBC and NGO is about −6.3 and −8.0 kcal/mol in water, and −2.4 and −3.1 kcal/mol in benzene solvent, respectively.

A new approach for characterization of phosphatidylcholines and lysophosphatidylcholine in human plasma.

Aim: Characterization of phosphatidylcholines (PCs) and lysophosphatidylcholine in human plasma using LC-IT-MSn. The characterization approach was based on trapping the eluted positive ions and applying low voltage for fragmentation to MS2 and further fragmentation of the most abundant two peaks to obtain MS3. This approach allowed linking the MS3 data to MS2 and precursor ion. Methodology: The fatty acid part, at sn-1 and sn-2 of the glycerol backbone, could be identified based on the favored cleavage pathway. Conclusion: The dysregulated PCs and lysophosphatidylcholines in human plasma obtained from acute coronary syndrome cases, and Type 2diabetes patients suffering no coronary syndromes were estimated and matched versus healthy volunteers. An epoxide form of 16:0-18:2 PC was confirmed, m/z 774.6.

Demonstrating the Critical Role of Solvation in Supported Ti and Nb Epoxidation Catalysts via Vapor-Phase Kinetics

Catalytic oxidation of hydrocarbons with hydrogen peroxide (H2O2) has been of the utmost importance for several decades. The vast majority of studies have been performed in the condensed phase, even though condensed phases introduce complex solvent effects and can promote the leaching of active sites. In response, we have built a custom reactor system to understand H2O2 activation and selective oxidation in the vapor-phase. In this report, we study the epoxidation of cyclohexene with H2O2 over four Lewis-acidic metal oxide catalysts: Ti and Nb grafted on SiO2 and on the Zr based metal–organic framework, NU-1000. The M–SiO2 materials are highly selective to the formation of epoxides and diols, as they can be in the condensed phase, while the NU-1000 based materials are far more prone to overoxidation to CO2, which appears to be connected to their strong reactant adsorption. Apparent activation energies are calculated for all materials when operating in the same kinetic regime, and the heats of cyclohexene adsorption into their pores are then used to directly compare intrinsic enthalpies of activation in the vapor vs condensed phase for the M–SiO2 catalysts. Nb–SiO2 catalysts exhibit similar intrinsic enthalpies of activation in the vapor and condensed phases, whereas the condensed phase transition state in Ti–SiO2 is 24 kJ/mol lower in energy than that of the same material in the vapor phase. These experiments establish another methodology for understanding the various roles of solvent in selective oxidation reactions and studying these reactions under conditions that differ significantly from the thousands of prior studies in the condensed phase.

Biomimetic Oxidation of Benzofurans with Hydrogen Peroxide Catalyzed by Mn(III) Porphyrins

The modelling of metabolic activation of the benzofuran nucleus is important to obtain eco-sustainable degradation methods and to understand the related mechanisms. The present work reports the catalytic oxidation of benzofuran, 2-methylbenzofuran, and 3-methylbenzofuran by hydrogen peroxide, at room temperature, in the presence of different Mn(III) porphyrins as models of cytochrome P450 enzymes. Conversions above 95% were attained for all the substrates. The key step is the formation of epoxides, which undergo different reaction pathways depending on factors, such as the position of the methyl group and the reaction and work-up conditions used.

P156 - In vitro metabolism of bardoxolone, an activator of NRF2 via reversible covalent modification of KEAP1: Formation of bardoxolone epoxide and novel metabolic pathway for oxidative denitrilation via reductive addition of glutathione

P156 - In vitro metabolism of bardoxolone, an activator of NRF2 via reversible covalent modification of KEAP1: Formation of bardoxolone epoxide and novel metabolic pathway for oxidative denitrilation via reductive addition of glutathione

Castor oil derivatives in the environmentally friendly one-pot synthesis of silver nanoparticles: application in cysteine sensing

Natural products-mediated synthesis has become quite an interesting route for the ecofriendly production of nanomaterials. However, products employed in natura may require long reaction times and high temperatures that lead to non-ideal particle-size distribution. In this work, we developed an optimized one-pot synthesis of silver nanoparticles using isolated ricinoleic acid (extracted from castor bean plant) and its epoxidized form as both reducer and stabilizer agents to convert silver ions into silver nanoparticles at room temperature. Through a design of experiments, we discovered that the epoxidized form of the ricinoleic acid is far more effective than its unmodified counterpart in terms of reaction time and homogeneity of nanoparticles. The silver nanoaparticles were then evaluated as functional chromogenic probes for cysteine sensing, allowing for direct naked-eye detection and a limit of detection of 25.37 μmol L−1. Cysteine sensing mechanisms are also discussed in this work. This approach reinforces the advantages in using purified natural products over their direct natural sources.

The detection of the precursors of the photorearranged products of 3-hydroxyflavones in selected solvents from UV-visible spectra in situ.

Mechanistic studies relating to the photochemistry of 3-hydroxy-2-phenyl-4H-chromen-4-one (3HF) and 6-chloro-3-hydroxy-2-phenyl-4H-chromen-4-one (Cl-3HF) have been reinvestigated in selected solvents. The UV-visible spectra of the photoproduct(s) of 3HF and Cl-3HF have been computed in situ via subtracting the spectra of unreacted substrates, with acetonitrile (ACN) and methanol (MeOH) as solvents. These spectra turn out to be different from the spectra of the corresponding isolated photoproducts: 3-hydroxy-3-phenyl-indan-1,2-dione and 6-chloro-3-hydroxy-3-phenyl-indan-1,2-dione (referred to as dione ). Analyses of the photoproduct(s) via GC-MS show the formation of a single detectable product, i.e., the corresponding dione. On the basis of some experimental observations, it is proposed that the primary photoproduct in situ is 2,3-epoxy-2-hydroxy-1-indanone (referred to as epoxide) instead of dione as reported in previous years. Earlier, epoxide has been proposed to be the intermediate in the mechanism for the formation of dione. This is the first report where the formation of epoxide has been directly detected in the selected solvents. On the other hand, both dione and epoxide (2 : 1) are shown to be formed with MeOH as solvent. The second important finding is that epoxide and dione interconvert in the dark, depending upon the environment. With ACN as solvent, pure dione in the dark is kinetically and partially converted to epoxide. With MeOH as solvent, epoxide is instantly and partially converted to dione until both are in equilibrium. However, a solution of dione in MeOH remains stable in the dark. The photoformation of epoxide is quantitative with ACN as solvent and it is sufficiently stable. It has been further observed that epoxide solutions of 3HF and Cl-3HF in ACN are quantitatively converted into 3-phenylisobenzofuran-1(3H)-one and 6-chloro-3-phenylisobenzofuran-1(3H)-one, i.e., the corresponding phthalides, through the loss of CO when kept in the dark for some days. A mechanism has been proposed where epoxide has been shown to give dione and/or phthalide via selective C-O or C-C bond cleavage in the oxiranyl ring, respectively. The selection of this cleavage depends mainly on the solvent system and the substituents in the parent flavones.