Oxidative Cleavage Reaction Research Articles

Uniformly Dispersed Co-Corrin/C Catalysts for the Study of β-O-4 Bonding Activity in Lignin

In this study, Co-Corrin/C catalysts with corrin active skeleton were prepared by pyrolysis under anaerobic conditions using vitamin B12 (VB12) as a precursor and activated carbon with rich mesoporous structure as a carrier. The Co-Corrin/C catalyst was applied to the oxidative cleavage reaction of lignin, showing a 92.74% breakage of β-O-4 bonds. Density functional theory (DFT) calculations indicate that the low energy gap difference of Co-Corrin/C promotes electron transfer between Co and O. Meanwhile, the pyrrole ring in the corrin structure will be adsorbed and bonded to oxygen, which promotes the generation of large amounts of oxygen free radicals. The Cα-OH bond in the lignin aliphatic chain is oxidized to Cα=O bond under the action of oxygen radicals, which reduces the dissociation energy of the β-O-4 bond and significantly improves the oxidation efficiency. Cycling experiments proved that Co-Corrin/C has good stability.

Stereoselective Access to Diverse Alkaloid-Like Scaffolds via an Oxidation/Double-Mannich Reaction Sequence.

Sequential oxidative cleavage and double-Mannich reactions enable the stereoselective conversion of simple norbornenes into complex alkaloid-like structures. The products undergo a wide range of derivatization reactions, including regioselective enol triflate formation/cross-coupling sequences and highly efficient conversion to an unusual tricyclic 8,5,5-fused lactam. Overall, the process represents a formal one-atom aza-ring expansion with concomitant bridging annulation, making it of interest for the broader derivatization of alkene feedstocks.

Cofactor-independent C-C bond cleavage reactions catalyzed by the AlpJ family of oxygenases in atypical angucycline biosynthesis.

Biosynthesis of atypical angucyclines involves unique oxidative B-ring cleavage and rearrangement reactions, which are catalyzed by AlpJ-family oxygenases, including AlpJ, JadG, and GilOII. Prior investigations established the essential requirement for FADH2/FMNH2 as cofactors when utilizing the quinone intermediate dehydrorabelomycin as a substrate. In this study, we unveil a previously unrecognized facet of these enzymes as cofactor-independent oxygenases when employing the hydroquinone intermediate CR1 as a substrate. The enzymes autonomously drive oxidative ring cleavage and rearrangement reactions of CR1, yielding products identical to those observed in cofactor-dependent reactions of AlpJ-family oxygenases. Furthermore, the AlpJ- and JadG-catalyzed reactions of CR1 could be quenched by superoxide dismutase, supporting a catalytic mechanism wherein the substrate CR1 reductively activates molecular oxygen, generating a substrate radical and the superoxide anion O2 •-. Our findings illuminate a substrate-controlled catalytic mechanism of AlpJ-family oxygenases, expanding the realm of cofactor-independent oxygenases. Notably, AlpJ-family oxygenases stand as a pioneering example of enzymes capable of catalyzing oxidative reactions in either an FADH2/FMNH2-dependent or cofactor-independent manner.

Role of galacturonic acid in acrylamide formation: Insights from structural analysis

Acrylamide (AA) is a neoformed compound in heated foods, mainly produced between asparagine (Asn) and glucose (Glc) during the Maillard reaction. Galacturonic acid (GalA), the major component of pectin, exhibits high activity in AA formation. This study investigated the pathway for AA formation between GalA and Asn. Three possible pathways were proposed: 1) The carbonyl group of GalA directly interacts with Asn to produce AA; 2) GalA undergoes an oxidative cleavage reaction to release α-dicarbonyl compounds, which subsequently leads to AA production; 3) 5-formyl-2-furancarboxylic acid, the thermal degradation product of GalA, reacts with Asn to generate AA. Structural analysis revealed that the COOH group in GalA accelerated intramolecular protonation and electron transfer processes, thereby increasing the formation of AA precursors such as decarboxylated Schiff base and α-dicarbonyl compounds, promoting AA formation. This study provides a theoretical basis and new insights into the formation and control of AA.

Efficient and Environmentally Benign Oxidative Cleavage of Pyrrolidine-2-methanols to γ-Lactams Using 2-Iodobenzamide as a Catalyst and Oxone.

The oxidative cleavage reaction of pyrrolidine-2-methanols to γ-lactams has been described. In this reaction, [4-iodo-3-(isopropylcarbamoyl)phenoxy]acetic acid and powdered Oxone (2KHSO5·KHSO4·K2SO4) were employed as the catalyst and co-oxidant, respectively. The reaction is efficient and environmentally benign because it produces various lactams from readily available substrates in moderate to excellent yields using organocatalyst and inorganic non-toxic co-oxidant.

Integration of rice apocarotenoid profile and expression pattern of Carotenoid Cleavage Dioxygenases reveals a positive effect of β-ionone on mycorrhization

Carotenoids are susceptible to degrading processes initiated by oxidative cleavage reactions mediated by Carotenoid Cleavage Dioxygenases that break their backbone, leading to products called apocarotenoids. These carotenoid-derived metabolites include the phytohormones abscisic acid and strigolactones, and different signaling molecules and growth regulators, which are utilized by plants to coordinate many aspects of their life. Several apocarotenoids have been recruited for the communication between plants and arbuscular mycorrhizal (AM) fungi and as regulators of the establishment of AM symbiosis. However, our knowledge on their biosynthetic pathways and the regulation of their pattern during AM symbiosis is still limited. In this study, we generated a qualitative and quantitative profile of apocarotenoids in roots and shoots of rice plants exposed to high/low phosphate concentrations, and upon AM symbiosis in a time course experiment covering different stages of growth and AM development. To get deeper insights in the biology of apocarotenoids during this plant-fungal symbiosis, we complemented the metabolic profiles by determining the expression pattern of CCD genes, taking advantage of chemometric tools. This analysis revealed the specific profiles of CCD genes and apocarotenoids across different stages of AM symbiosis and phosphate supply conditions, identifying novel reliable markers at both local and systemic levels and indicating a promoting role of β-ionone in AM symbiosis establishment.

Recent Advances in Photoinduced Oxidative Cleavage of Alkenes.

Oxidative cleavage of alkenes leading to valuable carbonyl derivatives is a fundamental transformation in synthetic chemistry. In particular, ozonolysis is the mainstream method for the oxidative cleavage of alkenes that has been widely implemented in the synthesis of natural products and pharmaceutically relevant compounds. However, due to the toxicity and explosive nature of ozone, alternative approaches employing transition metals and enzymes in the presence of oxygen and/or strong oxidants have been developed. These protocols are often conducted under harsh reaction conditions that limit the substrate scope. Photochemical approaches can provide milder and more practical alternatives for this synthetically useful transformation. In this review, we outline recent visible-light-promoted oxidative cleavage reactions that involve photocatalytic activation of oxygen via electron transfer and energy transfer. Also, an emerging field featuring visible-light-promoted oxidative cleavage under anaerobic conditions is discussed. The methods highlighted in this review represent a transformative step toward more sustainable and efficient strategies for the oxidative cleavage of alkenes.

Chemical protein synthesis enabled engineering of saccharide oxidative cleavage activity in artificial metalloenzymes

Chemical protein (semi-)synthesis is a powerful technique allowing the incorporation of unnatural functionalities at any desired protein site. Herein we describe a facile one-pot semi-synthetic strategy for the construction of a type 2 copper center in the active site of azurin, which is achieved by substitution of Met121 with unnatural amino acid residues bearing a strong ligand N,N-bis(pyridylmethyl)amine (DPA) to mimic the function of typical histidine brace-bearing copper monooxygenases, such as lytic polysaccharide monooxygenases (LPMOs) involved in polysaccharide breakdown. The semi-synthetic proteins were routinely obtained in over 10-mg scales to allow for spectroscopic measurements (UV–Vis, CD, and EPR), which provides structural evidences for the CuII–DPA-modified azurins. 4-nitrophenyl-β-D-glucopyranoside (PNPG) was used as a model substrate for the H2O2-driven oxidative cleavage reaction facilitated by semi-synthetic azurins, and the CuII–6 complex showed a highest activity (TTN 253). Interestingly, our semi-synthetic azurins were able to tolerate high H2O2 concentrations (up to 4000-fold of the enzyme), making them promising for practical applications. Collectively, we establish that chemical protein synthesis can be exploited as a reliable technology in affording large quantities of artificial metalloproteins to facilitate the transformation of challenging chemical reactions.

Homoprotocatechuate dioxygenase active site: Imitating the secondary sphere base via computational design.

Oxidative ring cleavage reactions have attracted great interest and various studies on the catechol ring-cleaving enzyme homoprotocatechuate dioxygenase (HPCD) have been reported in the literature. The available data on how the proton transfer takes place led us to design a potential HPCD model structure. A secondary sphere effect of utmost importance, the assistance of His200, which is critical for the catechol proton to migrate to dioxygen, was cautiously included on the first coordination shell. This was done mainly by modifying the axial ligands in the first coordination shell of HPCD such that the dual basic/acidic role in the proton transfer pathway of His200 was reproduced. Model systems with mono-, bi-, and tridentate ligands are reported. Energetically feasible reaction channels on synthetically promising ligand structures are identified. Key structural and electronic principles for obtaining viable proton transfer paths are outlined.

Oxidative cleavage of alkene: A new strategy to construct a mitochondria-targeted fluorescent probe for hydrogen peroxide imaging in vitro and in vivo

Hydrogen peroxide (H2O2) is a significant reactive oxygen species (ROS) mainly produced in mitochondria, and it plays crucial roles in many physiological processes. Till now, a plenty of fluorescent probes relying on various organic reactions have been explored for H2O2. However, these probes still suffered from some problems, including the interference from ONOO– and ClO–, unsatisfying limit of detection (LOD > 100 nM), long response time (over 30 min) and lacking mitochondria-targeting ability. Herein, we employ the oxidative cleavage reaction of alkene as a novel sensing strategy, and successfully construct a turn-on fluorescent probe TBBP–Pro for detecting H2O2 in biological system. In this probe, the cyanovinyl-pyridinium moiety not only acts as a specific response site for H2O2, but also targets mitochondria efficiently. Comparing with previous H2O2 probes, TBBP–Pro possesses the advantages of high selectivity, excellent sensitivity (LOD = 47 nM) and fast response (within 5 min) toward H2O2. Additionally, TBBP–Pro successfully visualizes the endogenous H2O2 in mitochondria of HepG2 cells and zebrafish larvae. More importantly, TBBP–Pro is promising to monitor the dynamic change of H2O2 level for the diagnosis and treatment of inflammatory mice.

Oxidative Cleavage and Fluoromethylthiolation of C═C Bonds: A General Route toward Mono-, Di-, and Trifluoromethylthioesters from Alkenes.

A novel oxidative cleavage and fluoromethylthiolation reaction of C═C bonds has been developed that represents the first and general method for the preparation of mono-, di-, and trifluoromethylthioesters from alkenes. The protocol features excellent product selectivity and substrate suitability. Various observations suggested that the protocol proceeded via a two-step radical process and that aldehyde was the key intermediate. What's more meaningful is that this route provides a new direction for converting alkenes into higher-value-added carbonyl-containing chemicals.

Total Synthesis of Illisimonin A and Merrilactone A

AbstractIllicium sesquiterpenes are a large family of biologically active secondary metabolites isolated from Illicium species of plants and are well‐known for their activity of neurite outgrowth in cultured neurons. Herein, we propose a comprehensive biosynthetic pathway for illicium sesquiterpenes and report a synthetic route to illisimonin A and merrilactone A based on it. We think that the carbon scaffolds of most of the illicium sesquiterpenes could be synthesized from a dicarbonyl derivative of allo‐cedrane through retro‐Dieckmann condensation, oxidative cleavage and aldol reaction at suitable oxidation states in Nature. The common intermediate for illisimonin A and merrilactone A similar to the dicarbonyl derivative of allo‐cedrane was assembled with up to 82 % ee by an asymmetric intramolecular desymmetrizing reductive Heck reaction by the use of a new type of chiral phosphine ligand. The syntheses of illisimonin A and merrilactone A supported the key transformations of the proposed biosynthetic pathway.

Total Synthesis of Illisimonin A and Merrilactone A.

Illicium sesquiterpenes are a large family of biologically active secondary metabolites isolated from Illicium species of plants and are well-known for their activity of neurite outgrowth in cultured neurons. Herein, we propose a comprehensive biosynthetic pathway for illicium sesquiterpenes and report a synthetic route to illisimonin A and merrilactone A based on it. We think that the carbon scaffolds of most of the illicium sesquiterpenes could be synthesized from a dicarbonyl derivative of allo-cedrane through retro-Dieckmann condensation, oxidative cleavage and aldol reaction at suitable oxidation states in Nature. The common intermediate for illisimonin A and merrilactone A similar to the dicarbonyl derivative of allo-cedrane was assembled with up to 82 % ee by an asymmetric intramolecular desymmetrizing reductive Heck reaction by the use of a new type of chiral phosphine ligand. The syntheses of illisimonin A and merrilactone A supported the key transformations of the proposed biosynthetic pathway.

Functionalization of carbon black for Ru complexation towards the oxidative cleavage of oleic acid

Macroporous oxidized carbon black (CBO) have been functionalized with 4,4′-diamino-2,2′-bipyridine (NH2-bpy) and polydopamine (PDA) allowing the complexation of Ru for the catalytic valorization of oleic acid through its oxidative cleavage. This reaction produces azelaic and pelargonic acids which are highly demanded in pharmacology. Conventional bpy is a well-known chelating agent for Ru and the aim of this work is directed to assess its suitability along with polydopamine in building a stable catalyst in the oxidative cleavage reaction. NH2-bpy was covalently bonded to COOH groups on CBO surface by amidation through an acylation and cross-linking(NHS/EDC). On its side, dopamine was self-polymerized in contact with CBO. The success of the deposition of NH2-bpy and PDA was confirmed by FTIR, TGA, and N2 physisorption, while Ru complexation was determined by ICP and XPS analyses. Among the three catalysts, the catalyst based on PDA was the most promising one, reaching a complete conversion of oleic acid with yields of pelargonic and azelaic acids around 95%. Although hot-filtration tests confirmed the presence of Ru species in the reaction medium, the PDA catalyst remained active even after five runs. Actually, post-catalysis characterization of the solid revealed that catechol groups of PDA re-adsorb Ru species once the reaction ends thereby ensuring the reusability of the heterogeneous catalyst.

Donor-Acceptor Fluorophores and Macrocycles Built Upon Wedge-Shaped π-Extended Phenanthroimidazoles.

A class of wedge-shaped organic π-fluorophores featuring a 6,9-diphenyl-substituted phenanthroimidazole (PI) core was designed, synthesized, and characterized. Among them, a π-extended PI derivative containing two electron-withdrawing aldehyde groups was found to exhibit versatile solid-state packing properties as well as strong solvatofluorochromism in different organic solvents. Another PI derivative that was functionalized with two electron-donating 1,4-dithiafulvenyl (DTF) end groups showed versatile redox reactivities and quenched fluorescence. Treatment of this wedge-shaped bis(DTF)-PI compound with iodine resulted in oxidative coupling reactions, leading to the formation of intriguing macrocyclic products that carry redox-active tetrathiafulvalene vinylogue (TTFV) moieties in their structures. Mixing the bis(DTF)-PI derivative with fullerene (C60 or C70) in an organic solvent resulted in substantial fluorescence enhancement (turn-on). In this process, fullerene acted as a photosensitizer to generate singlet oxygen, which in turn induced oxidative C = C bond cleavages and converted nonfluorescent bis(DTF)-PI into highly fluorescent dialdehyde-substituted PI. Treatment of TTFV-PI macrocycles with a small amount of fullerene also led to a moderate degree of fluorescence enhancement, but this is not because of photosensitized oxidative cleavage reactions. Instead, competitive photoinduced electron transfer from TTFV to fullerene can be attributed to their fluorescence turn-on behavior.

Theoretical Investigation and Synthesis Strategy of ‘<i>hypervalent’</i> Carbon

<i>Hypervalent</i> compounds using main group elements are often used as reagents in the variety of interesting reactions in chemistry, such as in the total synthesis of some important natural products and/or drugs, as molecular switch, as oxidizing agents, in the synthesis of novel polymers, in rearrangement reactions, in oxidative cleavage reactions, in activation of small molecules (such as H₂, O₂, O₃, P₄…) etc. However, although <i>hypervalent</i> compounds of main group elements are well known, there are a few examples in the literature about DFT-calculation and synthesis strategy of <i>hypervalent</i> carbon compounds. Some scientists are still of the opinion that carbon atom does not have the ability to form hypervalent carbon bonds. Therefore, they argue that <i>multiple</i> bonded (more than 4 bond) carbon atoms should be termed "<i>hypercoordinated</i>". The fact is that both “<i>hypervalent</i>” carbon compounds and “<i>hypercoordinated</i>” carbon compounds existed. However, there are certain requirements for a <i>multiple</i> bonded carbon compound to be called "<i>hypervalent</i>". The most important requirements are the bond length, the existence of 3c–4e bonding mode and the bound ligand to carbon. This review discusses the conditions for the <i>hypevalence</i> and summarizes, analyzes the established synthesis strategy and some important DFT-calculation of <i>hypervalent</i> carbon compounds.

The Malaprade reaction mechanism for ethylene glycol oxidation by periodic acid based on density functional theory (DFT).

A general mechanism of the Malaprade oxidative carbon-carbon bond cleavage reaction of α-glycol in the presence of periodic acid has been proposed on the basis of density functional theory (DFT) computations. Ethylene glycol and periodic acid, both in their neutral forms, have been studied as noble substrate representatives in model reactions. The proposed reaction mechanism has been constructed based on and compared with previously published experimental kinetic, spectroscopic and temperature and pH-dependent studies. In the presented theoretical mechanistic considerations, four alternative molecular transformations have been analyzed from thermodynamic and kinetic points of view. Theoretically, the predicted activation energy barriers have been compared with experimental ones published elsewhere. The presented minimum energy pathway (MEP) unveiled the shape and conformation of the intermediate and transition state structures. The three-step reaction process involves the formation of a seven-membered quasi-ring assisted by an intramolecular hydrogen-bond intermediate structure forming one I-O bond (IC1_B), a cyclic ester intermediate forming two I-O bonds (IC2_C) and the final products formed at the two very last stages (HIO3, water and two formaldehyde molecules). The computed and energetically the most favourable reaction landscape proposed in this work uniforms and refines the mechanistic proposition given by Criegee for Malaprade type of reactions and further gives a detailed molecular understanding of the reaction rate and atomic connections en route the transformation. The molecular geometries of all stationary points (intermediate and transition state structures) lying on the potential energy hypersurface have been optimized at the four alternative DFT levels under the solvation model based on the density approximation: B3PW91, CAM-B3LYP, BMK, ωB97XD. The 6-311+G(2d,p) basis set for C, O, and H atoms and both the full (DGDZVP) and Ahlrichs-Weigend1 (def2-TZVP) basis sets for iodine atoms were used during the computations.

Mechanism and kinetics of 1‐phenyl‐1,2‐ethanediol cleavage catalyzed by Cu/Beta zeolite

AbstractTo explore the feasibility of producing high‐value products from biomass, the copper‐supported off‐Al H‐Beta zeolite was prepared and used as a catalyst. The 1‐phenyl‐1,2‐ethanediol was chosen as a catalyst, a model molecule of biomass, the reaction mechanism and reaction path of the oxidative cleavage were studied. The variation of concentration for different components and products distribution were obtained under different temperatures. Based on these experimental results, a kinetic model of the reaction system was established, and the kinetic parameters were developed through optimization algorithms. Results show that Brønsted acid and Lewis acid have a synergistic role in the oxidative cleavage of 1,2‐diol. The adding of Cu species can regulate the acidity and acid amount of the catalyst and can effectively improve the C─C bond breaking ability of the catalyst. 1‐phenyl‐1,2‐ethanediol firstly underwent oxidative cleavage to produce benzaldehyde, which further underwent parallel tandem reactions to get benzyl alcohol (BP), methyl benzoate (MB), and benzaldehyde dimethyl acetal (BDA), respectively. The highest activation energy is required for the oxidative cleavage reaction in the reaction system, and a higher temperature thus will be needed.

Exploring the Diversity and Regulation of Apocarotenoid Metabolic Pathways in Plants.

In plants, carotenoids are subjected to enzyme-catalyzed oxidative cleavage reactions as well as to non-enzymatic degradation processes, which produce various carbonyl products called apocarotenoids. These conversions control carotenoid content in different tissues and give rise to apocarotenoid hormones and signaling molecules, which play important roles in plant growth and development, response to environmental stimuli, and in interactions with surrounding organisms. In addition, carotenoid cleavage gives rise to apocarotenoid pigments and volatiles that contribute to the color and flavor of many flowers and several fruits. Some apocarotenoid pigments, such as crocins and bixin, are widely utilized as colorants and additives in food and cosmetic industry and also have health-promoting properties. Considering the importance of this class of metabolites, investigation of apocarotenoid diversity and regulation has increasingly attracted the attention of plant biologists. Here, we provide an update on the plant apocarotenoid biosynthetic pathway, especially highlighting the diversity of the enzyme carotenoid cleavage dioxygenase 4 (CCD4) from different plant species with respect to substrate specificity and regioselectivity, which contribute to the formation of diverse apocarotenoid volatiles and pigments. In addition, we summarize the regulation of apocarotenoid metabolic pathway at transcriptional, post-translational, and epigenetic levels. Finally, we describe inter- and intraspecies variation in apocarotenoid production observed in many important horticulture crops and depict recent progress in elucidating the genetic basis of the natural variation in the composition and amount of apocarotenoids. We propose that the illustration of biochemical, genetic, and evolutionary background of apocarotenoid diversity would not only accelerate the discovery of unknown biosynthetic and regulatory genes of bioactive apocarotenoids but also enable the identification of genetic variation of causal genes for marker-assisted improvement of aroma and color of fruits and vegetables and CRISPR-based next-generation metabolic engineering of high-value apocarotenoids.

Mechanism-Based Approach to Reagent Selection for Oxidative Carbon-Hydrogen Bond Cleavage Reactions.

Numerous hydride-abstracting agents generate the same cationic intermediate, but substrate features such as intermediate cation stability, oxidation potential, and steric environment can influence reaction rates in an oxidant-dependent manner. This manuscript provides experimental data to illustrate the role that structural features play in the kinetics of hydride abstraction reactions with commonly used quinone-, oxoammonium ion-, and carbocation- based oxidants. Computational studies of the transition state structures and energies explain these results and energy decomposition analysis calculations reveal unique sensitivities to electrostatic attraction and steric repulsions. Rigorous rate studies of select reactions validated the capacity of the calculations to predict reactivity trends. Additionally, kinetics studies demonstrate the potential for product inhibition in DDQ-mediated reactions. These studies provide a clear guide to select the optimal oxidant for structurally disparate substrates and lead to predictions of reactivity that were validated experimentally.