Thermally stable manganese(III) peroxido complexes with hindered N3 tripodal ligands: Structures and their physicochemical properties.

Mononuclear manganese(III) peroxido complexes are candidates for the reaction intermediates in manganese containing proteins, such as manganese superoxide dismutase (Mn-SOD) etc. In this study, manganese(III) peroxido complexes [Mn(O2)(L3)] and [Mn(O2)(L10)] ligated by anionic N3 type ligands with sterically hindered substituents, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (L3-) and hydrotris(3-adamantyl-5-isopropyl-1-pyrazolyl)borate (L10-), respectively, were structurally characterized. These complexes are the first examples of structurally characterized five-coordinate manganese(III) peroxido complexes. Their characteristic ν(OO) and ν(MnO) stretchings were determined by using H218O2 for the first time. Theoretical calculations were performed to obtain further insight into their structural parameters. The decomposed products were obtained as [{MnIII(µ-O)(L3)}2MnIV] and [MnIII(OH){L10(O)}] from [Mn(O2)(L3)] and [Mn(O2)(L10)], respectively.

Using a monocopper-superoxo complex to prepare multicopper-peroxo species relevant to proposed enzyme intermediates.

With the goal of generating a (peroxo)tricopper species analogous to the Peroxy Intermediate proposed for multicopper oxidases, solutions of the copper-superoxide complex [K(Krypt)][LCuO2] (L = N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Krypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) were reacted with the dicopper(I) complex [(TPBN)Cu2(MeCN)2][PF6]2 at -70 °C (TPBN = N,N,N',N'-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane). A metastable intermediate formed, which on the basis of UV-vis, EPR, and resonance Raman spectroscopy was proposed to derive from reaction of two equivalents of the copper-superoxide with one equivalent of the dicopper(I) complex to yield a complex with two (peroxo)dicopper moieties rather than the desired (peroxo)tricopper PI model. A similar intermediate formed upon reaction of [K(Krypt)][LCuO2] with [(BPMA)Cu(MeCN)][PF6] (BPMA = N,N-bis(2-pyridylmethyl)-methyl-amine), which contained the same donor set as provided by TPBN. Comparison of resonance Raman data and consideration of structural preferences for LCuX species led to hypothesis of a µ-η1:η2-peroxo structure for both intermediates.

Exploration of artemisinin derivatives and synthetic peroxides in antimalarial drug discovery research.

Malaria is a life-threatening infectious disease caused by protozoal parasites belonging to the genus Plasmodium. It caused an estimated 405,000 deaths and 228 million malaria cases globally in 2018 as per the World Malaria Report released by World Health Organization (WHO) in 2019. Artemisinin (ART), a "Nobel medicine" and its derivatives have proven potential application in antimalarial drug discovery programs. In this review, antimalarial activity of the most active artemisinin derivatives modified at C-10/C-11/C-16/C-6 positions and synthetic peroxides (endoperoxides, 1,2,4-trioxolanes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes) are systematically summarized. The developmental trend of ART derivatives, and cyclic peroxides along with their antimalarial activity and how the activity is affected by structural variations on different sites of the compounds are discussed. This compilation would be very useful towards scaffold hopping aimed at avoiding the unnecessary complexity in cyclic peroxides, and ultimately act as a handy resource for the development of potential chemotherapeutics against Plasmodium species.

Calcium peroxide-mediated in situ formation of multifunctional hydrogels with enhanced mesenchymal stem cell behaviors and antibacterial properties.

Injectable hydrogels can serve as therapeutic vehicles and implants for the treatment of various diseases as well as for tissue repair/regeneration. In particular, the horseradish peroxidase (HRP) and hydrogen peroxide (H2O2)-catalyzed hydrogelation system has attracted much attention, due to its ease of handling and controllable gel properties. In this study, we introduce calcium peroxide (CaO2) as a H2O2-generating reagent to gradually supply a radical source for the HRP-catalyzed crosslinking reaction. This novel therapy can create stiff hydrogels without compromising the cytocompatibility of the hydrogels due to the use of initially high concentrations of H2O2. The physico-chemical properties of the hydrogels can be controlled by varying the concentrations of HRP and CaO2. In addition, the controlled and sustained release of bioactive molecules, including H2O2, O2, and Ca2+ ions, from the hydrogels could stimulate the cellular behaviors (attachment, migration, and differentiation) of human mesenchymal stem cells. Moreover, the hydrogels exhibited killing efficacy against both Gram-negative and Gram-positive bacteria, dependent on the H2O2 and Ca2+ release amounts. These positive results suggest that hydrogels formed by HRP/CaO2 can be used as potential matrices for a wide range of biomedical applications, such as bone regeneration and infection treatment.

Cyclic Synthetic Peroxides Inhibit Growth of Entomopathogenic Fungus Ascosphaera apis without Toxic Effect on Bumblebees.

In recent years, the number of pollinators in the world has significantly decreased. A possible reason for this is the toxic effects of agrochemicals reducing the immunity of insects that leads to their increased susceptibility to pathogens. Ascosphaera apis is a dangerous entomopathogenic fungus, afflicting both honeybees and bumblebees. We investigated fungicide activity of cyclic synthetic peroxides against A. apis isolated from Bombus terrestris L. The peroxides exhibited high mycelium growth inhibition of A. apis up to 94-100% at concentration 30 mg/L. EC50 values were determined for the most active peroxides. Two peroxides showed higher antifungal activity against A. apis than the commercial fungicide Triadimefon. The studied peroxides did not reduce the ability of bumblebees to fly and did not lead to the death of bumblebees. A new field of application for peroxides was disclosed.

Synthetic Peroxides Promote Apoptosis of Cancer Cells by Inhibiting P-Glycoprotein ABCB5.

This article discloses a new horizon for the application of peroxides in medical chemistry. Stable cyclic peroxides are demonstrated to have cytotoxic activity against cancer cells; in addition a mechanism of cytotoxic action is proposed. Synthetic bridged 1,2,4,5-tetraoxanes and ozonides were effective against HepG2 cancer cells and some ozonides selectively targeted liver cancer cells (the selectivity indexes for compounds 11 b and 12 a are 8 and 5, respectively). In some cases, tetraoxanes and ozonides were more selective than paclitaxel, artemisinin, and artesunic acid. Annexin V flow-cytometry analysis revealed that the active ozonides 22 a and 23 a induced cell death of HepG2 by apoptosis. Further study showed that compounds 22 a and 23 a exhibited a strong inhibitory effect on P-glycoprotein (P-gp/ABCB5)-overexpressing HepG2 cancer cells. ABCB5 is a key player in the multidrug-resistant phenotype of liver cancer. Peroxides failed to demonstrate a direct correlation between oxidative potential and their biological activity. To our knowledge this is the first time that peroxide diastereoisomers have been found to show stereospecific antimalarial action against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum. Stereoisomeric ozonide 12 b is 11 times more active than stereoisomeric ozonide 12 a (IC50 =5.81 vs 65.18 µm). Current findings mean that ozonides merit further investigation as potential therapeutic agents for drug-resistant hepatocellular carcinoma.

Design, synthesis and biological evaluation of novel 5α, 8α-endoperoxide steroidal derivatives with hybrid side chain as anticancer agents.

A series of novel 5α, 8α-endoperoxide steroidal hybrid derivatives containing isatin or indole substituents on the C-17 side chain were synthesized and characterized. The preliminary anti-proliferative activity of the compounds against HepG2, MCF-7, HT-29 and HeLa cell lines were investigated. Compounds 7g and 7l displayed significant anti-proliferative activity in vitro against HepG2 and Hela cells, with IC50 values lower than 8 µM. Furthermore, the biological functions of 7g were examined by flow cytometry and colony analysis. The results showed that 7g could induce HepG2 cell apoptosis, inhibited cell cycle progression, and colony growth. The studies indicated that structural modification at C-17 position could be a promising launch point for design steroidal anticancer agents.

Catalyst Development for the Synthesis of Ozonides and Tetraoxanes Under Heterogeneous Conditions: Disclosure of an Unprecedented Class of Fungicides for Agricultural Application.

The catalyst H3+x PMo12-x +6 Mox +5 O40 supported on SiO2 was developed for peroxidation of 1,3- and 1,5-diketones with hydrogen peroxide with the formation of bridged 1,2,4,5-tetraoxanes and bridged 1,2,4-trioxolanes (ozonides) with high yield based on isolated products (up to 86 and 90 %, respectively) under heterogeneous conditions. Synthesis of peroxides under heterogeneous conditions is a rare process and represents a challenge for this field of chemistry, because peroxides tend to decompose on the surface of a catalyst . A new class of antifungal agents for crop protection, that is, cyclic peroxides: bridged 1,2,4,5-tetraoxanes and bridged ozonides, was discovered. Some ozonides and tetraoxanes exhibit a very high antifungal activity and are superior to commercial fungicides, such as Triadimefon and Kresoxim-methyl. It is important to note that none of the fungicides used in agricultural chemistry contains a peroxide fragment.

Bioactive Natural and Synthetic Peroxides for the Treatment of Helminth and Protozoan Pathogens: Synthesis and Properties.

The significant spread of helminth and protozoan infections, the uncontrolled intake of the known drugs by a large population, the emergence of resistant forms of pathogens have prompted people to search for alternative drugs. In this review, we have focused attention on structures and synthesis of peroxides active against parasites causing neglected tropical diseases and toxoplasmosis. To date, promising active natural, semi-synthetic and synthetic peroxides compounds have been found.

Ultrasound-Assisted Green Synthesis of Dialkyl Peroxides under Phase-Transfer Catalysis Conditions.

The dialkyl peroxides, which contain a thermally unstable oxygen-oxygen bond, are an important source of radical initiators and cross-linking agents. New efficient and green methods for their synthesis are still being sought. Herein, ultrasound-assisted synthesis of dialkyl peroxides from alkyl hydroperoxides and alkyl bromides in the presence of an aqueous solution of an inorganic base was systematically studied under phase-transfer catalysis (PTC) conditions. The process run in a tri-liquid system in which polyethylene glycol as a phase-transfer catalyst formed a third liquid phase between the organic and inorganic phases. The use of ultrasound provided high yields of organic peroxides (70-99%) in significantly shorter reaction times (1.5 h) in comparison to reaction with magnetic stirring (5.0 h). In turn, conducting the reaction in the tri-liquid PTC system allowed easy separation of the catalyst and its multiple use without significant loss of activity.

Novel Peroxides as Promising Anticancer Agents with Unexpected Depressed Antimalarial Activity.

Twenty six peroxides belonging to bridged 1,2,4,5-tetraoxanes, bridged 1,2,4-trioxolanes (ozonides), and tricyclic monoperoxides were evaluated for their in vitro antimalarial activity against Plasmodium falciparum (3D7) and for their cytotoxic activities against immortalized human normal fibroblast (CCD19Lu), liver (LO2 ), and lung (BEAS-2B) cell lines as well as human liver (HepG2) and lung (A549) cancer-cell lines. Synthetic ozonides were shown to have the highest cytotoxicity on HepG2 (IC50 =0.19-0.59 µm), and some of these compounds selectively targeted liver cancer (selectivity index values for compounds 13 a and 14 a are 20 and 28, respectively) at levels that, in some cases, were higher than those of paclitaxel, artemisinin, and artesunic acid. In contrast some ozonides showed only moderate antimalarial activity against the chloroquine-sensitive 3D7 strain of P. falciparum (IC50 from 2.76 to 24.2 µm; 12 b, IC50 =2.76 µm; 13 a, IC50 =20.14 µm; 14 a, IC50 =6.32 µm). These results suggest that these derivatives have divergent mechanisms of action against cancer cells and malaria-infected cells. A cyclic voltammetry study of the peroxides was performed, but most of the compounds did not show direct correlation in oxidative capacity-activity. Our findings offer a new source of antimalarial and anticancer agents through structural modification of peroxide compounds.

In vivo tissue distribution and safety of polyacrylic acid-modified titanium peroxide nanoparticles as novel radiosensitizers.

Polyacrylic acid (PAA)-modified titanium peroxide nanoparticles (PAA-TiOx NPs) are promising radiosensitizers. PAA-TiOx NPs were synthesized from commercial TiO2 nanoparticles that were modified with PAA and functionalized by H2O2 treatment. To realize practical clinical uses for PAA-TiOx NPs, their tissue distribution and acute toxicity were evaluated using healthy mice and mice bearing tumors derived from xenografted MIAPaCa-2 human pancreatic cancer cells. Healthy mice were injected with PAA-TiOx NPs at 25 mg/kg body weight via the tail vein, and tumor-bearing mice were injected either into the tumor locally or via the tail vein. The concentration of PAA-TiOx NPs in major organs was determined over time using inductively coupled-plasma atomic emission spectrometry. After 1 h, 12% of the PAA-TiOx NP dose had accumulated in the tumor, and 2.8% of the dose remained after 1 week. Such high accumulation could be associated with enhanced permeability and retention effects of the tumor, as PAA-TiOx NPs are composed of inorganic particles and polymers, without tumor-targeting molecules. The liver accumulated the largest proportion of the injected nanoparticles, up to 42% in tumor-bearing mice. Blood biochemical parameters were also investigated after intravenous injection of PAA-TiOx NPs in healthy mice. PAA-TiOx NPs invoked a slight change in various liver-related biochemical parameters, but no liver injury was observed over the practical dose range. In the future, PAA-TiOx NPs should be modified to prevent accumulation in the liver and minimize risk to patients.

Hydroperoxyl radical and formic acid formation from common DNA stabilizers upon low energy electron attachment.

2-Amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) and ethylenediaminetetraacetic acid (EDTA) are key components of biological buffers and are frequently used as DNA stabilizers in irradiation studies. Such surface or liquid phase studies are done with the aim to understand the fundamental mechanisms of DNA radiation damage and to improve cancer radiotherapy. When ionizing radiation is used, abundant secondary electrons are formed during the irradiation process, which are able to attach to the molecular compounds present on the surface. In the present study we experimentally investigate low energy electron attachment to TRIS and methyliminodiacetic acid (MIDA), an analogue of EDTA, supported by quantum chemical calculations. The most prominent dissociation channel for TRIS is through hydroperoxyl radical formation, whereas the dissociation of MIDA results in the formation of formic and acetic acid. These compounds are well-known to cause DNA modifications, like strand breaks. The present results indicate that buffer compounds may not have an exclusive protecting effect on DNA as suggested previously.

Iron-Catalyzed Batch/Continuous Flow C-H Functionalization Module for the Synthesis of Anticancer Peroxides.

Iron-catalyzed dehydrogenative cross-coupling of carbonyl compounds with aliphatic peroxide was developed under mild conditions. A library of linear alkylated and arylated peroxides are synthesized in good to excellent yield. This method is highly selective and general for a range of biologically important derivatives of 2-oxindole, barbituric acid, and 4-hydroxy coumarin with a good functional group tolerance and without the cleavage of the peroxide bond. This peroxidation reaction is upscalable to grams and also synthesizable in continuous flow with increased safety in short duration. Mechanistic investigation reveals Fe-(II) undergoes redox type process to generate the radical intermediates, which subsequently recombine selectively to form the stable peroxides. The potential of peroxides is evaluated by cell viability assay and found to exhibit the good anticancer activity with minimum IC50= 5.3 µM.

Peroxides with Anthelmintic, Antiprotozoal, Fungicidal and Antiviral Bioactivity: Properties, Synthesis and Reactions.

The biological activity of organic peroxides is usually associated with the antimalarial properties of artemisinin and its derivatives. However, the analysis of published data indicates that organic peroxides exhibit a variety of biological activity, which is still being given insufficient attention. In the present review, we deal with natural, semi-synthetic and synthetic peroxides exhibiting anthelmintic, antiprotozoal, fungicidal, antiviral and other activities that have not been described in detail earlier. The review is mainly concerned with the development of methods for the synthesis of biologically active natural peroxides, as well as its isolation from natural sources and the modification of natural peroxides. In addition, much attention is paid to the substantially cheaper biologically active synthetic peroxides. The present review summarizes 217 publications mainly from 2000 onwards.

Chemical antagonism between photodynamic agents and chemotherapeutics: mechanism and avoidance.

We report a photochemical reaction-induced antagonism between the photodynamic agent (PS) and anti-cancer drugs during combined therapy. The annihilation of singlet oxygen and alkene-containing drugs into inactive drug hydroperoxides is responsible for the antagonism, and results in decreased efficacy against several cancer cell lines. Experimental and simulation results reveal that the annihilation abates with increasing distance between the PS and drugs via confining the PS and drugs into separated vehicles. As a result, antagonism can be switched to synergism in treating both drug sensitive and resistant cancer cells.

Geometric effects on OO bond scission of copper(II)-alkylperoxide complexes.

Copper(II) complexes supported by N3-tridentate ligands, consisting of a rigid cyclic diamine (8-membered cyclic-diamine; L8 or 7-membered cyclic-diamine; L7) and a 2-(2-pyridyl)ethyl (-CH2CH2Py) group, were synthesized and structurally characterized. Reaction of the copper(II) complexes and cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH3CN gave the corresponding cumylperoxide complexes L8CuIIOOCm and L7CuIIOOCm. The UV-vis and EPR spectra suggested that L8CuIIOOCm takes a tetrahedrally distorted structure, whereas L7CuIIOOCm has a planar geometry in solution. Resonance Raman spectra of these alkylperoxide complexes indicated that the O-O stretching vibration energy of L8CuIIOOCm (νO-O=878cm-1) is somewhat lower than that of L7CuIIOOCm (νO-O=881cm-1). Such a difference in O-O bond strength is reflected to the reactivity difference of these two alkylperoxide complexes. Namely, the reactivity L8CuIIOOCm toward CHD (1,4-cyclohexadiene) as well as solvent molecule (CH3CN) is higher than that of L7CuIIOOCm due to the weaker O-O bond of the former complex as compared to that of the latter complex. Geometric effects on the reactivity induced by the supporting ligands are discussed.

Synthesized zinc peroxide nanoparticles (ZnO2-NPs): a novel antimicrobial, anti-elastase, anti-keratinase, and anti-inflammatory approach toward polymicrobial burn wounds.

Increasing of multidrug resistance (MDR) remains an intractable challenge for burn patients. Innovative nanomaterials are also in high demand for the development of new antimicrobial biomaterials that inevitably have opened new therapeutic horizons in medical approaches and lead to many efforts for synthesizing new metal oxide nanoparticles (NPs) for better control of the MDR associated with the polymicrobial burn wounds. Recently, it seems that metal oxides can truly be considered as highly efficient inorganic agents with antimicrobial properties. In this study, zinc peroxide NPs (ZnO2-NPs) were synthesized using the co-precipitation method. Synthesized ZnO2-NPs were characterized by X-ray diffraction, Fourier transformed infrared, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and ultraviolet-visible spectroscopy. The characterization techniques revealed synthesis of the pure phase of non-agglomerated ZnO2-NPs having sizes in the range of 15-25 nm with a transition temperature of 211°C. Antimicrobial activity of ZnO2-NPs was determined against MDR Pseudomonas aeruginosa (PA) and Aspergillus niger (AN) strains isolated from burn wound infections. Both strains, PA6 and AN4, were found to be more susceptible strains to ZnO2-NPs. In addition, a significant decrease in elastase and keratinase activities was recorded with increased concentrations of ZnO2-NPs until 200 µg/mL. ZnO2-NPs revealed a significant anti-inflammatory activity against PA6 and AN4 strains as demonstrated by membrane stabilization, albumin denaturation, and proteinase inhibition. Moreover, the results of in vivo histopathology assessment confirmed the potential role of ZnO2-NPs in the improvement of skin wound healing in the experimental animal models. Clearly, the synthesized ZnO2-NPs have demonstrated a competitive capability as antimicrobial, anti-elastase, anti-keratinase, and anti-inflammatory candidates, suggesting that the ZnO2-NPs are promising metal oxides that are potentially valued for biomedical applications.

Exploring the Sponge Consortium Plakortis symbiotica-Xestospongia deweerdtae as a Potential Source of Antimicrobial Compounds and Probing the Pharmacophore for Antituberculosis Activity of Smenothiazole A by Diverted Total Synthesis.

Fractionation of the bioactive CHCl3-MeOH (1:1) extracts obtained from two collections of the sponge consortium Plakortis symbiotica-Xestospongia deweerdtae from Puerto Rico provided two new plakinidone analogues, designated as plakinidone B (2) and plakinidone C (3), as well as the known plakinidone (1), plakortolide F (4), and smenothiazole A (5). The structures of 1-5 were characterized on the basis of 1D and 2D NMR spectroscopic, IR, UV, and HRMS analysis. The absolute configurations of plakinidones 2 and 3 were established through chemical correlation methods, VCD/ECD experiments, and spectroscopic data comparisons. When assayed in vitro against Mycobacterium tuberculosis H37Rv, none of the plakinidones 1-3 displayed significant activity, whereas smenothiazole A (5) was the most active compound, exhibiting an MIC value of 4.1 µg/mL. Synthesis and subsequent biological screening of 8, a dechlorinated version of smenothiazole A, revealed that the chlorine atom in 5 is indispensable for anti-TB activity.

Synthetic Approaches to Mono- and Bicyclic Perortho-Esters with a Central 1,2,4-Trioxane Ring as the Privileged Lead Structure in Antimalarial and Antitumor-Active Peroxides and Clarification of the Peroxide Relevance.

The synthesis of 4-styryl-substituted 2,3,8-trioxabicyclo[3.3.1]nonanes, peroxides with the core structure of the bioactive 1,2,4-trioxane ring, was conducted by a multistep route starting from the aryl methyl ketones 1a-1c. Condensation and reduction/oxidation delivered enals 4a-4c that were coupled with ethyl acetate and reduced to the 1,3-diol substrates 6a-6c. Highly diastereoselective photooxygenation delivered the hydroperoxides 7a-7c and subsequent PPTS (pyridinium-p-toluenesulfonic acid)-catalyzed peroxyacetalization with alkyl triorthoacetates gave the cyclic peroxides 8a-8e. These compounds in general show only moderate antimalarial activities. In order to extend the repertoire of cyclic peroxide structure, we aimed for the synthesis of spiro-perorthocarbonates from orthoester condensation of ß-hydroxy hydroperoxide 9 but could only realize the monocyclic perorthocarbonate 10. That the central peroxide moiety is the key structural motif in anticancer active GST (glutathione S-transferase)-inhibitors was elucidated by the synthesis of a 1,3-dioxane 15-with a similar substitution pattern as the pharmacologically active peroxide 11-via a singlet oxygen ene route from the homoallylic alcohol 12.