Synthesis, Structure and Antioxidant Activity of Cyclohexene-Fused Selenuranes and Related Derivatives

Design, synthesis, pharmacological evaluation, and in silico studies of the activity of novel spiro pyrrolo[3,4-d]pyrimidine derivatives

In the present study, spiro compounds are shown to have distinctive characteristics because of their interesting conformations and their structural impacts on biological systems. A new family of functionalized spiro pyrrolo[3,4-d]pyrimidines is prepared via the one-pot condensation reaction of amino cyclohexane derivatives with benzaldehyde to prepare fused azaspiroundecanedione and azaspirodecenone/thione derivatives. A series of synthesized spiro compounds were scanned against DPPH and evaluated for their ability to inhibit COX-1 and COX-2. All compounds exhibit significant antiinflammatory activity, and they inhibited both COX-1 and COX-2 enzymes with a selectivity index higher than celecoxib as a reference drug. The most powerful and selective COX-2 inhibitor compounds were 11 and 6, with selectivity indices of 175 and 129.21 in comparison to 31.52 of the standard celecoxib. However, candidate 14 showed a very promising antiinflammatory activity with an IC50 of 6.00, while celecoxib had an IC50 of 14.50. Our findings are promising in the area of medicinal chemistry for further optimization of the newly designed and synthesized compounds regarding the discussed structure-activity relationship study (SAR), in order to obtain a superior antioxidant lead compound in the near future. All chemical structures of the novel synthesized candidates were unequivocally elucidated and confirmed utilizing spectroscopic and elemental investigations.

Tetravalent Spiroselenurane Catalysts: Intramolecular Se···N Chalcogen Bond-Driven Catalytic Disproportionation of H2O2 to H2O and O2 and Activation of I2 and NBS

Chalcogen-bonding interactions have recently gained considerable attention in the field of synthetic chemistry, structure, and bonding. Here, three organo-spiroselenuranes, having a Se(IV) center with a strong intramolecular Se···N chalcogen-bonded interaction, have been isolated by the oxidation of the respective bis(2-benzamide) selenides derived from an 8-aminoquinoline ligand. Further, the synthesized spiroselenuranes, when assayed for their antioxidant activity, show disproportionation of hydrogen peroxide into H₂O and O₂ with first-order kinetics with respect to H₂O₂ for the first time by any organoselenium molecules as monitored by ¹H NMR spectroscopy. Electron-donating 5-methylthio-benzamide ring-substituted spiroselenurane disproportionates hydrogen peroxide at a high rate of 15.6 ± 0.4 × 10³ μM min^-1 with a rate constant of 8.57 ± 0.50 × 10^-3 s^-1, whereas 5-methoxy and unsubstituted-benzamide spiroselenuranes catalyzed the disproportionation of H₂O₂ at rates of 7.9 ± 0.3 × 10³ and 2.9 ± 0.3 × 10³ μM min^-1 with rate constants of 1.16 ± 0.02 × 10^-3 and 0.325 ± 0.025 × 10^-3 s^-1, respectively. The evolved oxygen gas from the spiroselenurane-catalyzed disproportion of H₂O₂ has also been confirmed by a gas chromatograph-thermal conductivity detector (GCTCD) and a portable digital polarographic dissolved O₂ probe. Additionally, the synthesized spiroselenuranes exhibit thiol peroxidase antioxidant activities for the reduction of H₂O₂ by a benzenethiol co-reductant monitored by UV-visible spectroscopy. Next, the Se···N bonded spiroselenuranes have been explored as catalysts in synthetic oxidation iodolactonization and bromination of arenes. The synthesized spiroselenurane has activated I₂ toward the iodolactonization of alkenoic acids under base-free conditions. Similarly, efficient chemo- and regioselective monobromination of various arenes with NBS catalyzed by chalcogen-bonded synthesized spiroselenuranes has been achieved. Mechanistic insight into the spiroselenuranes in oxidation reactions has been gained by ⁷⁷Se NMR, mass spectrometry, UV-visible spectroscopy, single-crystal X-ray structure, and theoretical (DFT, NBO, and AIM) studies. It seems that the highly electrophilic nature of the selenium center is attributed to the presence of an intramolecular Se···N interaction and a vacant coordination site in spiroselenuranes is crucial for the activation of H₂O₂, I₂, and NBS. The reaction of H₂O₂, I₂, and NBS with tetravalent spiroselenurane would lead to an octahedral-Se(VI) intermediate, which is reduced back to Se(IV) due to thermodynamic instability of selenium in its highest oxidation state and the presence of a strong intramolecular N-donor atom.

Extraction and Identification of Two Flavonoids in Phlomoides hyoscyamoides as an Endemic Plant of Iran: The Role of Quercetin in the Activation of the Glutathione Peroxidase, the Improvement of the Hydroxyproline and Protein Oxidation in Bile Duct-Ligated Rats

BACKGROUND

Cholestatic liver disease, a serious chronic condition that develops progressive hepatic degeneration through free radicals.

OBJECTIVE

The present study was designed to extract and identify two flavonoids in Phlomoides hyoscyamoides plant, native to Iran and evaluate the role of quercetin identified on the liver injury among bile ductligated rats.

METHODS

This study was conducted on 25 male Wistar rats within three groups of sham control, mere bile duct-ligated, and bile duct-ligated with quercetin. The bile duct-ligated animals received quercetin at a dose of 50 mg/kg/day for 10 days, followed by biochemical tests, oxidative stress markers, activity of antioxidant enzymes and hematoxylin and eosin staining. Molecular docking was used to explore the interactive behavior of quercetin with glutathione peroxidase.

RESULTS

According to analyses of the obtained extract, two main active ingredients of P. hyoscyamoides were rutin and quercetin. Bile duct-ligated group showed a significant liver necrosis, a clear increase in plasma and tissue oxidative stress parameters, and a decrease in glutathione peroxidase activity as compared to sham control group. Quercetin injection in bile duct-ligated rats resulted in significant decrease in hydroxyproline, protein carbonyl and histopathologic indexes and significant increase in glutathione peroxidase activity (P-value≤0.05). Based on the molecular docking, the quercetin was able to regulate the glutathione peroxidase activity.

CONCLUSION

The quercetin acts as an enzyme inducer by renewing the glutathione peroxidase activity and inhibiting the oxidation of proteins and hence decreases the oxidative stress. These results could be a sign of confirming the positive role of quercetin in attenuating the liver damage and degeneration.

Zero-, one-, two- and three-dimensional supramolecular architectures sustained by Se…O chalcogen bonding: A crystallographic survey

The Cambridge Structural Database was evaluated for crystals containing Se…O chalcogen bonding interactions. These secondary bonding interactions are found to operate independently of complementary intermolecular interactions in about 13% of the structures they can potentially form. This number rises significantly when more specific interactions are considered, e.g. Se…O(carbonyl) interactions occur in 50% of cases where they can potentially form. In about 55% of cases, the supramolecular assemblies sustained by Se…O(oxygen) interactions are one-dimensional architectures, with the next most prominent being zero-dimensional assemblies, at 30%.

Chemistry and Chemical Biology of Selenenyl Sulfides and Thioseleninic Acids

Significance: Selenenyl sulfides (RSeSRs) and thioseleninic acids (RSeSHs) are the monoselenium (Se) analogs of disulfides and persulfides that contain Se-S bonds. These bonds are found in several antioxidant-regenerating enzymes as derivatives of selenocysteine, making them an important player in redox biology as it pertains to sulfur redox regulation. Recent Advances: Mechanistic studies of redox-regulating selenoenzymes such as thioredoxin reductase and glutathione peroxidase suggest crucial Se-S bonds in the active sites. Peptide models and small-molecule mimics of these active sites have been prepared to study their fundamental chemistry. These advances help pave the road to better understand the functions of the Se-S bond in the body. Critical Issues: The Se-S bond is unstable at atmospheric temperatures and pressures. Therefore, studying their properties proposes a major challenge. Currently, there are no trapping reagents specific to RSeSRs or RSeSHs, making their presence, identity, and fates in biological environments difficult to track. Future Directions: Further understanding of the fundamental chemistry/biochemistry of RSeSRs and RSeSHs is needed to understand what their intracellular targets are and to what extent they impact signaling. Besides antioxidant regeneration and peroxide radical reduction, the roles of RSeSR and RSeSHs in other systems need to be further explored.

Organoselenium small molecules as catalysts for the oxidative functionalization of organic molecules

This perspective highlights the critical analysis of the challenges, in the past decade, which led to the development of organoselenium compounds and their use as versatile catalysts in organic synthesis towards the oxidation of olefins and C–H bonds. Furthermore, the emphasis here differs from previous reviews of the field by classifying the various types of catalyses and the diverse strategies.

Organoselenium compounds as mimics of selenoproteins and thiol modifier agents

Selenium is an essential trace element for animals and its role in the chemistry of life relies on a unique functional group: the selenol (-SeH) group. The selenol group participates in critical redox reactions. The antioxidant enzymes glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) exemplify important selenoproteins. The selenol group shares several chemical properties with the thiol group (-SH), but it is much more reactive than the sulfur analogue. The substitution of S by Se has been exploited in organic synthesis for a long time, but in the last 4 decades the re-discovery of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the demonstration that it has antioxidant and therapeutic properties has renovated interest in the field. The ability of ebselen to mimic the reaction catalyzed by GPx has been viewed as the most important molecular mechanism of action of this class of compound. The term GPx-like or thiol peroxidase-like reaction was previously coined in the field and it is now accepted as the most important chemical attribute of organoselenium compounds. Here, we will critically review the literature on the capacity of organoselenium compounds to mimic selenoproteins (particularly GPx) and discuss some of the bottlenecks in the field. Although the GPx-like activity of organoselenium compounds contributes to their pharmacological effects, the superestimation of the GPx-like activity has to be questioned. The ability of these compounds to oxidize the thiol groups of proteins (the thiol modifier effects of organoselenium compounds) and to spare selenoproteins from inactivation by soft-electrophiles (MeHg⁺, Hg²⁺, Cd²⁺, etc.) might be more relevant for the explanation of their pharmacological effects than their GPx-like activity. In our view, the exploitation of the thiol modifier properties of organoselenium compounds can be harnessed more rationally than the use of low mass molecular structures to mimic the activity of high mass macromolecules that have been shaped by millions to billions of years of evolution.

Computational Modeling of the Catalytic Cycle of Glutathione Peroxidase Nanomimic

To elucidate the role of a derivative of ebselen as a mimic of the antioxidant selenoenzyme glutathione peroxidase, density functional theory and solvent-assisted proton exchange (SAPE) were applied to model the reaction mechanism in a catalytic cycle. This mimic plays the role of glutathione peroxidase through a four-step catalytic cycle. The first step is described as the oxidation of 1 in the presence of hydrogen peroxide, while selenoxide is reduced by methanthiol at the second step. In the third step of the reaction, the reduction of selenenylsulfide occurs by methanthiol, and the selenenic acid is dehydrated at the final step. Based on the kinetic parameters, step 4 is the rate-determining step (RDS) of the reaction. The bond strength of the atoms involved in the RDS is discussed with the quantum theory of atoms in molecules (QTAIM). Low value of electron density, ρ(r), and positive Laplacian values are the evidence for the covalent nature of the hydrogen bonds rupture (O₃₀-H₃₁, O₃₃-H₃₄). A change in the sign of the Laplacian, L(r), from the positive value in the reactant to a negative character at the transition state indicates the depletion of the charge density, confirming the N₅-H₁₀ and O₁₁-Se₁ bond breaking. The analysis of electron location function (ELF) and localized orbital locator (LOL) of the Se₁-N₅ and Se₁-O₁₁ bonds have been done by multi-WFN program. High values of ELF and LOL at the transition state regions between the Se, N, and O atoms display the bond formation. Finally, the main donor-acceptor interaction energies were analyzed using the natural bond orbital analysis for investigation of their stabilization effects on the critical bonds at the RDS.

Computational kinetic modeling of the selenol catalytic activity as the glutathione peroxidase nanomimic

Density functional theory and solvent-assisted proton exchange methods have been applied for computational modeling of the catalytic cycle of selenol zwitterion anion from the kinetic and thermodynamic viewpoints. Selenol zwitterion anion has been represented as an effective glutathione peroxidase nanomimic. It reduces peroxides through a three-step pathway. In the first step, seleninic acid is produced through deprotonating of the selenol zwitterion anion in the presence of the hydrogen peroxide. Seleninic acid reacts with a thiol to form selenylsulfide in the second step. In the last step, selenylsulfide is reduced by the second thiol and regenerates selenolate anion through disulfide formation. Selenol zwitterion anion in comparison to more widely studied compounds such as ebselen has a good activity to react with hydrogen peroxide and producing seleninic acid. The energy barrier of this reaction is 11.7kcalmol^-1 which is smaller than the reported enzyme mimics. Moreover, the reactions of seleninic acid and selenylsulfide with methanethiol, which is used as a nucleophile, are exothermic by -18.4 or -57.0kcalmol^-1, respectively. Based on the global electron density transfer value of -0.507 e from the natural atomic charge analysis, an electronic charge depletion at the transition state (TS), electron-donor substitutions on the selenolate facilitates the reduction reaction, effectively. Finally, the nature of the bond formation/cleavage at the TS has been quantitatively described by using the topological analyses.