Advances in the development of pharmaceutical antioxidants

Azobisisobutyronitrile loaded on mesoporous silica particles: A new stressor for solid-state oxidative forced degradation studies

A new approach for testing drug sensitivity to autooxidative degradation in the solid state is demonstrated in this work. A novel solid-state form of stressing agent for autooxidation has been proposed, based on azobisisobutyronitrile loaded into mesoporous silica carrier particles. The new solid-state form of the stressing agent was applied in degradation studies of two active pharmaceutical ingredients: bisoprolol and abiraterone acetate. The effectiveness and predictivity of the method were evaluated by comparing impurity profiles with those obtained by traditional stability testing of commercial tablets containing the investigated APIs. The results obtained by the new solid-state stressor were also compared with those obtained by an existing method for testing peroxide oxidative degradation in the solid state using a complex of polyvinylpyrrolidone with hydrogen peroxide. It was found that the new silica particle-based stressor was able to effectively predict which impurities could be formed by autooxidation in tablets and that this new approach is complementary to methods for testing peroxide oxidative degradation known from the literature.

Recent Developments and Perspectives in the C-Se Cross Coupling Reactions

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The C-Se bond forming reactions are attractive synthetic strategies for biochemists and synthetic chemists alike for the synthesis of various molecules that are of biological, pharmaceutical and material interest. Therefore, the design and synthesis of organoselenium compounds currently constitute engaging fundamental problems in applied chemistry both in pharmaceutical and academic laboratories. This review discusses the recent works reported in carbon–selenium cross-coupling reactions with the emphasis on the mechanistic aspects of the reactions. The reacting species, the addition of ligands, selection of catalysts, use of suitable solvents, proper setting of reaction time, are well discussed to understand the detailed mechanism. Various simple, economical and environmentally friendly protocols are demonstrated, which ensured product stability, low toxicity, environmentally benign and excellent reactivity for the synthesis of organoselenium compounds. This review covers the scientific literature from 2010 to 2019.

Crystal structure and Hirshfeld surface analysis of (2E,2'E)-1,1'-[seleno-bis-(4,1-phenyl-ene)]bis-[3-(4-chloro-phen-yl)prop-2-en-1-one]

In the title com-pound, C30H20Cl2O2Se, the C-Se-C angle is 99.0 (2)°, with the dihedral angle between the planes of the attached benzene rings being 79.1 (3)°. The average endocyclic angles (Se-C-C) facing the Se atom are 122.1 (5) and 122.2 (5)°. The Se atom is essentially coplanar with the attached benzene rings, deviating by 0.075 (1) and 0.091 (1) Å. In the two phenyl-ene(4-chloro-phen-yl)prop-2-en-1-one units, the benzene rings are inclined to each other by 44.6 (3) and 7.8 (3)°. In the crystal, the mol-ecules stack up the a axis, forming layers parallel to the ac plane. There are no significant classical inter-molecular inter-actions present. Hirshfeld surface analysis, two-dimensional fingerprint plots and the mol-ecular electrostatic potential surface were used to analyse the crystal packing. The Hirshfeld surface analysis suggests that the most significant contributions to the crystal packing are by C⋯H/H⋯C contacts (17.7%).

EASI Transformation: An Efficient Transient Expression Method for Analyzing Gene Function in Catharanthus roseus Seedlings

The Catharanthus roseus plant is the exclusive source of the valuable anticancer terpenoid indole alkaloids, vinblastine (VB) and vincristine (VC). The recent availability of transcriptome and genome resources for C. roseus necessitates a fast and reliable method for studying gene function. In this study, we developed an Agrobacterium-mediated transient expression method to enable the functional study of genes rapidly in planta, conserving the compartmentalization observed in the VB and VC pathway. We focused on (1) improving the transformation method (syringe versus vacuum agroinfiltration) and cultivation conditions (seedling age, Agrobacterium density, and time point of maximum transgene expression), (2) improving transformation efficiency through the constitutive expression of the virulence genes and suppressing RNA silencing mechanisms, and (3) improving the vector design by incorporating introns, quantitative and qualitative reporter genes (luciferase and GUS genes), and accounting for transformation heterogeneity across the tissue using an internal control. Of all the parameters tested, vacuum infiltration of young seedlings (10-day-old, harvested 3 days post-infection) resulted in the strongest increase in transgene expression, at 18 - 57 fold higher than either vacuum or syringe infiltration of other seedling ages. Endowing the A. tumefaciens strain with the mutated VirGN54D or silencing suppressors within the same plasmid as the reporter gene further increased expression by 2 - 10 fold. For accurate measurement of promoter transactivation or activity, we included an internal control to normalize the differences in plant mass and transformation efficiency. Including the normalization gene (Renilla luciferase) on the same plasmid as the reporter gene (firefly luciferase) consistently yielded a high signal and a high correlation between RLUC and FLUC. As proof of principle, we applied this approach to investigate the regulation of the CroSTR1 promoter with the well-known activator ORCA3 and repressor ZCT1. Our method demonstrated the quantitative assessment of both the activation and repression of promoter activity in C. roseus. Our efficient Agrobacterium-mediated seedling infiltration (EASI) protocol allows highly efficient, reproducible, and homogenous transformation of C. roseus cotyledons and provides a timely tool for the community to rapidly assess the function of genes in planta, particularly for investigating how transcription factors regulate terpenoid indole alkaloid biosynthesis.

Efficient Heterogeneous Copper-Catalysed C–Se Coupling of Aryl Iodides with Symmetrical Diselenides towards Unsymmetrical Monoselenides

A highly efficient heterogeneous copper(I)-catalysed C–Se coupling of aryl iodides with diaryl diselenides was achieved in dimethylformamide at 110 °C under neutral conditions by using a 10 mol% of bipyridine-functionalised MCM-41-supported copper(I) complex [bpy-MCM-41-CuI] as the catalyst and magnesium as the reductive reagent, yielding a variety of unsymmetrical diaryl selenides in good to excellent yields. This heterogeneous copper catalyst can be easily recovered by a simple filtration of the reaction solution and recycled at least seven times without significant loss of activity.

Crystal structure of 1,1'-[selanediyl-bis(4,1-phenyl-ene)]bis-(2-chloro-ethan-1-one)

In the title mol-ecule, C16H12Cl2O2Se, the C-Se-C angle is 100.05 (14)°, with the dihedral angle between the planes of the benzene rings being 69.92 (17)°. The average endocyclic angles (Se-Car-Car; ar = aromatic) facing the Se atom are 120.0 (3) and 119.4 (3)°. The Se atom is essentially coplanar with the benzene rings, with Se-Car-Car-Car torsion angles of -179.2 (3) and -179.7 (3)°. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds forming chains propagating along the a-axis direction. The chains are linked via C-H⋯π inter-actions, forming a three-dimensional network.

Metal-free sp3C–H functionalization: a novel approach for the syntheses of selenide ethers and thioesters from methyl arenes

A DTBP-promoted, operationally simple, metal-free and solvent-free formation of C–Se and C–S bonds through sp³C–H functionalization of methyl arenes with diselenides and disulfides is described.

Bis(4-acetyl-phen-yl) selenide

In the title compound, C₁₆H₁₄O₂Se, the dihedral angle between the benzene rings is 87.08 (11)°. In the crystal, mol­ecules are linked into layers parallel to the bc plane by inter­molecular C—H⋯O hydrogen bonds.

Copper oxide nanoparticle-catalyzed coupling of diaryl diselenide with aryl halides under ligand-free conditions

A new, efficient and ligand-free cross-coupling reaction of aryl halides and diaryl diselenides using a catalytic amount of nanocrystalline CuO as a recyclable catalyst with KOH as the base in DMSO at 110 degrees C is reported. This protocol has been utilized for the synthesis of a variety of aryl selenides in excellent yields from the readily available aryl halides and diaryl diselenides.

Targeting antioxidants to mitochondria by conjugation to lipophilic cations

Mitochondrial oxidative damage contributes to a range of degenerative diseases. Consequently, the selective inhibition of mitochondrial oxidative damage is a promising therapeutic strategy. One way to do this is to invent antioxidants that are selectively accumulated into mitochondria within patients. Such mitochondria-targeted antioxidants have been developed by conjugating the lipophilic triphenylphosphonium cation to an antioxidant moiety, such as ubiquinol or alpha-tocopherol. These compounds pass easily through all biological membranes, including the blood-brain barrier, and into muscle cells and thus reach those tissues most affected by mitochondrial oxidative damage. Furthermore, because of their positive charge they are accumulated several-hundredfold within mitochondria driven by the membrane potential, enhancing the protection of mitochondria from oxidative damage. These compounds protect mitochondria from damage following oral delivery and may therefore form the basis for mitochondria-protective therapies. Here we review the background and work to date on this class of mitochondria-targeted antioxidants.

New 3- and 4-hydroxyfuranones as anti-oxidants and anti-inflammatory agents

Two series of new furanones substituted by methylsulfonylphenyl or methylsulfamidophenyl moieties were found to protect against oxidation damage by inhibiting or quenching free radicals and reactive oxygen species in in vitro experiments. The effect on lipid peroxidation was also examined. In addition, we investigated the activity of products in two models of inflammation: phorbol ester-induced ear edema in mice and carrageenan-induced paw edema in rat. The most powerful compounds and with reducing activity against DPPH (IC50=1779 and 57 microM, respectively), superoxide anion quenching capacity (IC50=511 and 49 microM, respectively), lipid peroxidation inhibitory effect and anti-inflammatory properties (about 50-65% inhibition of edema at 200 mg/kg ip in both tests used) were selected for further pharmacological and toxicological tests because of their attractive profile for the treatment of inflammatory diseases.

Oxidative stress in viral hepatitis and AIDS

Dominant types of viral hepatitis are presently A, B, and C with prophylactic immunization available only for A and B. Hepatitis B and C and human immunodeficiency virus (HIV) infection constitute a worldwide scourge and treatment is far from satisfactory. Each produces severe oxidative stress (OS) and secondary cellular damage of varying severity and, as in toxic hepatitis, progression and regression are dependent on redox balance between oxidation and antioxidation. Experimental and clinical studies suggest that xenobiotics and co-infections exert cumulative, detrimental effects on their pathogeneses and further deplete antioxidants. It is proposed therefore that in the clinical management of these infections and especially in their early stages, considerable benefit should accrue from antioxidant repletion at dosages substantially above recommended daily allowances (RDAs) in conjunction with a nutritious high protein diet. Because plasma zinc and selenium concentrations are very low, their replenishment by high dosages is urgent and mandatory particularly in advanced HIV infections bordering on acrodermatitis enteropathica. Also recommended is their long-term continuance at high normal levels.

Oxidative stress, toxic hepatitis, and antioxidants with particular emphasis on zinc

Hepatic metabolism of biological toxins, industrial poisons, and medicinal agents involves disturbed hepatic cell biochemistry with augmented generation of reactive oxygen species and free radicals and redox imbalance with secondary damage to proteins, nucleic acids, lipids, and carbohydrates. The xenobiotic hepatotoxicity ranging from a subclinical anicteric state to severe necroinflammatory hepatitis (acute, recurrent or chronic) and cirrhosis depends on the nature, dosage, and duration of exposure to the xenobiotic, the antioxidant defence, and concomitant exposure to other diseases or xenobiotics. Experimental and clinical studies suggest that xenobiotic hepatotoxicity with variable depletion of antioxidants can be avoided or ameliorated by administration of an unusually high dosage of zinc or by a combination of antioxidants above normal daily requirements. Therefore reassessment of optimal prophylactic and therapeutic nutritional requirements of antioxidants (particularly zinc) to defend humans against xenobiotic induced oxidative stress is advocated.

Antioxidative components of Psoralea corylifolia (Leguminosae)

A meroterpene and four flavonoids were isolated from the seeds of Psoralea corylifolia as antioxidative components. Their structures were elucidated by spectral data and identified as bakuchiol (1), bavachinin (2), bavachin (3), isobavachin (4) and isobavachalcone (5). In particular, meroterpene 1 and flavonoids 4 and 5 showed broad antioxidative activities in rat liver microsomes and mitochondria. They inhibited NADPH-, ascorbate-, t-BuOOH- and CCl(4)-induced lipid peroxidation in microsomes. They also prevented NADH-dependent and ascorbate-induced mitochondrial lipid peroxidation. Bakuchiol (1) was the most potent antioxidant in microsomes and the inhibition of oxygen consumption induced by lipid peroxidation was time-dependent. Furthermore, bakuchiol (1) protected human red blood cells against oxidative haemolysis. These phenolic compounds in P. corylifolia were shown to be effective in protecting biological membranes against various oxidative stresses.

Structure-hepatoprotective activity relationship of 3,4-dihydroxycinnamic acid (caffeic acid) derivatives

3,4-Dihydroxycinnamic acid (caffeic acid, CAF) is a natural product containing a catechol group with an alpha,beta-unsaturated carboxylic acid chain that has shown hepatoprotective properties. The aim of this work was to determine the importance of the 4-hydroxy, 3-hydroxy, 3,4-dihydroxy substituents and the double bond moiety on the hepatic pharmacological effects of the molecule. We compared the ability of the caffeic, 4-hydroxycinnamic, 3-hydroxycinnamic, cinnamic and 3,4-dihydroxyhydrocinnamic (a caffeic acid analogue without the double bond) acids at a dose of 50 mg kg(-1), p.o., to reduce the liver damage produced by CCl(4) (4 g kg(-1), p.o.) intoxication in the rat. Cinnamic acid, the non-hydroxylated analogue, only modestly protected the experimental animals challenged with CCl(4), suggesting that hydroxyl groups participate in the pharmacological properties of CAF. The 3,4-dihydroxyhydrocinnamic derivative did not show any significant differences when compared with the CAF effect in this model, suggesting that the double bond does not account for the liver pharmacological properties of CAF. In contrast, the 4-hydroxy substituent seems to be very important for hepatoprotective activity because the 4-hydroxy analogue improved almost every hepatic injury marker altered by CCl(4), and in a better way than CAF did.

The effects of carbamazepine and valproic acid on the erythrocyte glutathione, glutathione peroxidase, superoxide dismutase and serum lipid peroxidation in epileptic children

Some epileptic drugs may change antioxidant enzyme activities in humans and experimental animals. Recent studies suggest that membrane lipid peroxidation may be causally involved in some forms of epilepsy, and the differences are reported in free radical scavenging enzyme levels. GSHpX, SOD, GSH are important parameters of antioxidant defence mechanisms. This study was undertaken to evaluate the effects of valproic acid and carbamazepine (CBZ) therapy on erythrocyte glutathione (GSH), glutathione peroxidase (GSHpX), superoxide dismutase (SOD) and lipid peroxidation. During the treatment with VPA or CBZ, the erythrocyte GSHpX and GSH levels of epileptic children were significantly changed as compared to those of health control subjects. The mean levels of serum lipid peroxidation and erythrocyte superoxide dismutase were not statistically different from controls. The methods used for investigation of glutathione peroxidase, superoxide dismutase, glutathione and serum lipid peroxidation were all based on spectrophotometric measurement.

Antioxidative properties of organotellurium compounds in cell systems

The protective/antioxidative properties of diaryl tellurides were demonstrated in cellular systems of increasing complexity. In the presence of glutathione, bis(4-hydroxyphenyl) telluride (1a), bis(4-aminophenyl) telluride (1d) and bis(2-carboxyphenyl) telluride (1h) reduced by more than 50% t-butyl hydroperoxide-induced cell death in lung fibroblast cultures at concentrations below 2 microM. Bis(2,6-dimethyl-4-hydroxyphenyl) telluride (2b) reduced by more than 50% leukocyte-mediated and phorbol-12-myristate-13-acetate-stimulated damage to Caco-2 cells at 0.1 microM concentration. As judged by their abilities to reduce formation of thiobarbituric acid reactive substances at concentrations close to 1 microM, diaryl tellurides 1a, 1d and 2b protected rat kidney tissue against oxidative damage caused by anoxia and reoxygenation. The organotellurium compounds also offered protection after systemic administration. In the presence of diaryl telluride 2b (0.1-1 microM), the ischemia/reperfusion-induced vascular permeability increase in the hamster cheek pouch was significantly reduced as compared with the control. Some of the most active organotellurium cell protectants were evaluated for their ability to inhibit formation of the inflammatory mediators leukotriene B4 and interleukin-1beta. An inhibitory effect on the secretion of these species was seen for compounds 1a and 2b at or above 10 microM concentrations. The protective effects of diaryl tellurides against t-butyl hydroperoxide-induced cell injury can be ascribed mainly to the peroxide-decomposing, glutathione peroxidase-like capacity of the compounds. The chain-breaking, electron- or hydrogen atom-donating ability of diaryl tellurides seems to be the main reason for their protection against leukocyte-mediated cell damage in Caco-2 cells and in the oxidatively challenged rat kidney and hamster cheek pouch.