Antioxidative capacities of stilbenoid Suaveolensone A and Flavonoid Suaveolensone B: A detailed analysis of structural-electronic properties and mechanisms

Computational Chemistry Strategies to Investigate the Antioxidant Activity of Flavonoids-An Overview

Despite several decades of research, the beneficial effect of flavonoids on health is still enigmatic. Here, we focus on the antioxidant effect of flavonoids, which is elementary to their biological activity. A relatively new strategy for obtaining a more accurate understanding of this effect is to leverage computational chemistry. This review systematically presents various computational chemistry indicators employed over the past five years to investigate the antioxidant activity of flavonoids. We categorize these strategies into five aspects: electronic structure analysis, thermodynamic analysis, kinetic analysis, interaction analysis, and bioavailability analysis. The principles, characteristics, and limitations of these methods are discussed, along with current trends.

Selective Structural Derivatization of Flavonoid Acetamides Significantly Impacts Their Bioavailability and Antioxidant Properties

Flavonoids show abundant favorable physicochemical and drug related properties, leading to substantial biological applications which are limited by undesirable properties such as poor solubility, high polarity, low bioavailability, and enzymatic degradations. Chemical modification with bioisosteres can be used to address some of these challenges. We report the synthesis and characterization of partial flavonoid acetamide derivatives from quercetin, apigenin and luteolin and the evaluation of their structure-activity relationships based on antioxidant, bioavailability, drug likeness, and toxicity properties. The sequential synthesis was achieved with 76.67-87.23% yield; the structures of the compounds were confirmed using ¹H & ¹³C NMR characterizations. The purity of each compound was determined by HPLC while the molecular weights were determined by mass spectrometry. The % bioavailability was determined using the dialysis tubing procedure and the values were in the range 15.97-38.12%. The antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and expressed as the IC₅₀ values which were in the range 31.52-198.41 µM. The drug likeness and the toxicity properties of compounds 4, 5, 7, 11 and 15 were predicted using computational tools and showed satisfactory results. A structure-activity relationship evaluation reveals that hydroxyl and methylene groups attached on the 2-phenylchromen-4-one structure of the flavonoid play a colossal role in the overall antioxidant and bioavailability properties. The improved bioavailability and excellent drug relevance and toxicity properties present flavonoid acetamide derivatives as prospective drug candidates for further evaluations.

Current Trends in Computational Quantum Chemistry Studies on Antioxidant Radical Scavenging Activity

The antioxidative nature of chemicals is now routinely studied using computational quantum chemistry. Scientists are constantly proposing new approaches to investigate those methods, and the subject is evolving at a rapid pace. The goal of this review is to collect, consolidate, and present current trends in a clear, methodical, and reference-rich manner. This paper is divided into several sections, each of which corresponds to a different stage of elaborations: preliminary concerns, electronic structure analysis, and general reactivity (thermochemistry and kinetics). The sections are further subdivided based on methodologies used. Concluding remarks and future perspectives are presented based on the remaining elements.

Improving the antioxidant activity of natural antioxidant honokiol by introducing the amino group

Exploring and synthesizing the compounds with stronger antioxidant activity have always been the goal of researchers. Herein, the substitution effects of the amino (NH₂-) group with the excellent electron-donating ability in different positions on the antioxidant activity of Honokiol (Hon) were systematically explored by using the quantum chemistry calculation based on the density functional theory method. The three possible antioxidant mechanisms of Hon and its four NH₂-substituted derivatives (Hon1-Hon4), containing the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were explored in depth considering the gas and solvent phases. In addition, the frontier molecular orbital energies, natural bond orbital (NBO) charge population, and global descriptive parameters were used to study their antioxidant activity. The results indicate that compared with the original molecule Hon, the NH₂ substituents would have the stronger antioxidant activity. Moreover, the radical scavenging process of Hon and its derivatives has a disposition to the HAT and SPLET mechanisms in the gas and solvent phases, respectively. Meaningfully, owing to the lowest bond dissociation enthalpy and proton affinity values, Hon4 would show the most prominent antioxidant activity by comparison with the other compounds. In conclusion, this work will provide the purposeful reference for designing and synthesizing the antioxidants with more outstanding performance.

Quo vadis Cardiac Glycoside Research?

Cardiac glycosides (CGs), toxins well-known for numerous human and cattle poisoning, are natural compounds, the biosynthesis of which occurs in various plants and animals as a self-protective mechanism to prevent grazing and predation. Interestingly, some insect species can take advantage of the CG’s toxicity and by absorbing them, they are also protected from predation. The mechanism of action of CG’s toxicity is inhibition of Na⁺/K⁺-ATPase (the sodium-potassium pump, NKA), which disrupts the ionic homeostasis leading to elevated Ca²⁺ concentration resulting in cell death. Thus, NKA serves as a molecular target for CGs (although it is not the only one) and even though CGs are toxic for humans and some animals, they can also be used as remedies for various diseases, such as cardiovascular ones, and possibly cancer. Although the anticancer mechanism of CGs has not been fully elucidated, yet, it is thought to be connected with the second role of NKA being a receptor that can induce several cell signaling cascades and even serve as a growth factor and, thus, inhibit cancer cell proliferation at low nontoxic concentrations. These growth inhibitory effects are often observed only in cancer cells, thereby, offering a possibility for CGs to be repositioned for cancer treatment serving not only as chemotherapeutic agents but also as immunogenic cell death triggers. Therefore, here, we report on CG’s chemical structures, production optimization, and biological activity with possible use in cancer therapy, as well as, discuss their antiviral potential which was discovered quite recently. Special attention has been devoted to digitoxin, digoxin, and ouabain.

Antioxidative and α-glucosidase inhibitory constituents of Polyscias guilfoylei: experimental and computational assessments

Searching for bioactive agents from medicinal plants, eleven constituents were isolated from Polyscias guilfoylei stem for the first time, including a nucleoside uracil (1), two sterols β-sitosterol (2) and daucosterol (3), a saponin androseptoside A (4), two lignans (+)-pinoresinol (5) and (+)-syringaresinol (6), four phenolic acids protocatechuic acid (7), methyl protocatechuate (8), caffeic acid (9), and 5-O-caffeoylquinic acid (10), and a flavonoid quercitrin (11). Metabolites 1, 4, and 6-11 have never been observed in genus Polyscias before. Phenolic compounds 7 and 9 possessed the respective IC₅₀ values of 21.33 and 13.88 µg/mL in DPPH (2,2-diphenyl-1-picrylhydrazyl) antioxidative assay, as compared with that of the positive control resveratrol (IC₅₀ = 13.21 µg/mL). From density functional theory (DFT) calculated approach, the DPPH free radical scavenging capacity of two compounds 7 and 9 can be explained by the role of OH groups at carbons C-3 and C-4. Antioxidative actions of these two potential agents are followed HAT (H atom transfer) mechanism by OH bond disruption in gas, but SPLET (sequential proton loss electron transfer) mechanism in solvents water and methanol. Compared to 4-OH group, 3-OH group showed better bond disruption enthalpies and better kinetic energies since it reacted with HOO^• and DPPH radicals. Sterols 2-3 and flavonoid 11 induced the IC₅₀ values of < 2.0 µg/mL better than the positive control acarbose (IC₅₀ = 184.0 µg/mL) in α-glucosidase inhibitory assay. Their interactions with human intestinal C- and N-terminal domains of α-glucosidase were explored using molecular docking study. The obtained results proved that compounds 2, 3, and 11 bind relatively stronger with the C-terminal domain than to the N-terminal domain through pivotal residues in the binding site and could be hypothesized as mixed inhibitors.

Antioxidant of Trans-Resveratrol: A Comparison between OH and CH Groups Based on Thermodynamic Views

Trans-resveratrol establishes the planarity in its structure which makes it an interesting compound in both experimental and theoretical examinations. The current study, using the density functional method (DFT), attempts to compare the antioxidative capacities between hydroxyl (OH) and aromatic methine (CH) groups of this molecule. Becke’s exchange-correlation B3LYP functional together with 6-311++G(d, p) basis set was used to reveal the effects of structural geometry and electronic feature on the antioxidative results of OH and CH groups. The antioxidative action of trans-resveratrol has followed the HAT mechanism in gas, but the SPLET pathway in liquids. OH bond breaking is easier than CH bond disruption. 4-OH bond breaking induces the lowest BDE values of 74.4–77.9 kcal/mol in gas, acetone, methanol, and water, as well as the lowest PA values of 37.2–46.2 kcal/mol in acetone, methanol, and water. From the kinetic view, 4-OH is also an active center to capture laboratory radical DPPH, ROS radicals HOO• and CH3O•, and RNS radical •NO2.