Absorption​ of free radicals in the body cannot be done by antioxidant compounds originating from the human body, so exogenous antioxidants are required to help in their natural antioxidant action. Oxidative stress can be caused by an imbalance of free radical inhibitors and the accumulation of free radicals that enter cellular structures. Synthetic antioxidants found in external antioxidants are not the primary choice because they are harmful and carcinogenic. Therefore, using natural ingredients provides a necessary alternative to constructing novel natural antioxidants. Recent studies have highlighted critical analysis and evaluation that flavonoids are a unique class of secondary metabolites found in plants and used in communities as traditional therapeutics with proven bioactivity. This could support new discoveries based on various herbal medicines and in addition, the functional effectiveness of flavonoids as antioxidants against free radicals. In this review, there are several strengths in the discussion. First, the study takes a comprehensive approach by covering various aspects, including the properties and sources of free radicals, oxidative stress in relation to different diseases, antioxidant defense mechanisms, and the specific antioxidant mechanisms of flavonoids. Second, the focus on natural antioxidants, especially flavonoids, and also discussion about clinical applications and human studies, limitations, global perspectives, and future research directions of flavonoids compounds become references in the selection of natural medicines. But, several constraints should be considered when interpreting the findings of this review. First, the discussion about the mechanism of antioxidant compounds is only discussed in general and only takes one example of a compound (flavonoid) that has the potential as an antioxidant. Second, the lack of findings regarding the relationship between several diseases discussed with free radicals. Third, a limited number of studies investigated regarding clinical applications and human studies of some of the diseases discussed.

Shiga toxin (Stx) is one of the most critical factors in the development of hemolytic uremic syndrome and other systemic complications following enterohemorrhagic Escherichia coli (EHEC) infection. Substances neutralizing Stx by interfering with toxin‐receptor binding have been explored as therapeutic candidates for EHEC infection. In this study, we examined globotriaosyl (Gb₃), galabiosyl (Gb₂) and galacto‐trehalose, each of which was synthetically conjugated with a polyacrylamide backbone, for Stx‐neutralizing activity. Galacto‐trehalose was designed as a Gb₂ mimicking, unnatural Stx‐ligand that was expected to show tolerance to enzymatic degradation in vivo. Galacto‐trehalose copolymer showed neutralizing activity against Stx‐1 but not Stx‐2 in a HeLa cell cytotoxicity assay. It was thought that galacto‐trehalose copolymer could be a lead compound for the treatment of Stx‐mediated diseases, although it requires modification to show neutralizing activity to Stx‐2. The Gb₃ copolymer with high sugar unit density showed stronger neutralizing activity against Stx‐2 than those with lower density. However, the density‐dependency of the neutralizing activity was less obvious against Stx‐1. Intravenous administration of the Gb3 copolymer prevented death in mice lethally infected with Stx‐1‐ and Stx‐2‐producing E. coli O157:H7. Thus, we demonstrated that the artificial Gb₃ copolymer could neutralize Stx‐1 and the more clinically relevant Stx‐2 in vitro and effectively inhibit Stx toxicity in vivo.

Glycerol is a symmetrical, small biomolecule with high flexibility in molecular conformations. Using a ¹H-NMR spectroscopic Karplus analysis in our way, we analyzed a rotational isomerism in the glycero backbone which generates three kinds of staggered conformers, namely gt (gauche-trans), gg (gauche-gauche), and tg (trans-gauche), at each of sn-1,2 and sn-2,3 positions. The Karplus analysis has disclosed that the three rotamers are consistently equilibrated in water keeping the relation of ‘gt:gg:tg = 50:30:20 (%)’ at a wide range of concentrations (5 mM~540 mM). The observed relation means that glycerol in water favors those symmetric conformers placing 1,2,3-triol groups in a gauche/gauche geometry. We have found also that the rotational isomerism is remarkably changed when the solvent is replaced with DMSO-d₆ or dimethylformamide (DMF-d₇). In these solvents, glycerol gives a relation of ‘gt:gg:tg = 40:30:30 (%)’, which means that a remarkable shift occurs in the equilibrium between gt and tg conformers. By this shift, glycerol turns to also take non-symmetric conformers orienting one of the two vicinal diols in an antiperiplanar geometry.

Along with the increasing resistance of Candida spp. to some antibiotics, it is necessary to find new antifungal drugs, one of which is from the medicinal plant Red Betel (Piper crocatum). The purpose of this research is to isolate antifungal constituents from P. crocatum and evaluate their activities as ergosterol biosynthesis inhibitors via an in silico study of ADMET and drug-likeness analysis. Two new active compounds 1 and 2 and a known compound 3 were isolated, and their structures were determined using spectroscopic methods, while their bioactivities were evaluated via in vitro and in silico studies, respectively. Antifungal compound 3 was the most active compared to 1 and 2 with zone inhibition values of 14.5, 11.9, and 13.0 mm, respectively, at a concentration of 10% w/v, together with MIC/MFC at 0.31/1.2% w/v. Further in silico study demonstrated that compound 3 had a stronger ΔG than the positive control and compounds 1 and 2 with −11.14, −12.78, −12.00, and −6.89 Kcal/mol against ERG1, ERG2, ERG11, and ERG24, respectively, and also that 3 had the best Ki with 6.8 × 10⁻³, 4 × 10⁻⁴, 1.6 × 10⁻³, and 8.88 μM. On the other hand, an ADMET analysis of 1–3 met five parameters, while 1 had one violation of Ro5. Based on the research data, the promising antifungal constituents of P. crocatum allow P. crocatum to be proposed as a new antifungal candidate to treat and cure infections due to C. albicans.

Glycosyl-[60]fullerenes were first used as decontaminants against ricin, a lactose recognition proteotoxin in the Ricinus communis family. A fullerene glycoconjugate carrying two lactose units was synthesized by a [3 + 2] cycloaddition reaction between C₆₀ and the azide group in 6-azidohexyl β-lactoside per-O-acetate. A colloidal aqueous solution with brown color was prepared from deprotected bis(lactosyl)-C₆₀ and was found stable for more than 6 months keeping its red color. Upon mixing with an aqueous solution of Ricinus communis agglutinin (RCA₁₂₀), the colloidal solution soon caused precipitations, while becoming colorless and transparent. In contrast, a solution of concanavalin A (Con A) caused no apparent change, indicating that the precipitation was caused specifically by carbohydrate–protein interactions. This notable phenomenon was quantified by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and the results were discussed in terms of detection and decontamination of the deadly biological toxin in the Ricinus communis family.

Piper betle is an edible plant known for its potent antioxidant activity. Among its phenolic constituents, cinnamic acid has been identified as a key compound contributing to this bioactivity. Although cinnamic acid is a well‐known molecule, this study is the first to report its isolation from P. betle leaves, contributing valuable insights into the chemotaxonomy and phytochemical profile of the species. The aim of this research is to isolate cinnamic acid from the methanol extract of betel leaves and evaluate its antioxidant activity using DPPH and nonenzymatic mimic superoxide dismutase (mSOD) assays. Furthermore, computational analyses were performed using density functional theory (DFT) to assess the antioxidant properties, and molecular docking studies were conducted to investigate the interaction mechanisms of cinnamic acid and its derivatives with several enzymes. The results obtained that cinnamic acid had a strong antioxidant activity with IC ₅₀ value using the DPPH and mSOD methods of 76.46 and 36 μg/mL, respectively. The analysis used DFT studies of reactive cinnamic acid as seen from the values of several global descriptive parameters. The deviation in the energy gap from E _HOMO and E _LUMO is quite small, which is 0.0205 eV. Based on the molecular docking results, cinnamic acid ligands and its derivatives act on the amino acid active sites against xanthine oxidase (XO), NADPH oxidase (NO), cytochrome P450 (CP450), and lipoxygenase (LO) receptors although the binding affinity values are not stronger than the positive control for these four receptors. Therefore, cinnamic acid and its derivatives can be used as a compound to counteract free radicals or as an antioxidant.