Discovering protein–protein interaction stabilisers by native mass spectrometry

Protein–protein interactions (PPIs) are key therapeutic targets. Most PPI-targeting drugs in the clinic inhibit these important interactions; however, stabilising PPIs is an attractive alternative in cases where a PPI is disrupted in a disease state. The discovery of novel PPI stabilisers has been hindered due to the lack of tools available to monitor PPI stabilisation. Moreover, for PPI stabilisation to be detected, both the stoichiometry of binding and the shift this has on the binding equilibria need to be monitored simultaneously. Here, we show the power of native mass spectrometry (MS) in the rapid search for PPI stabilisers. To demonstrate its capability, we focussed on three PPIs between the eukaryotic regulatory protein 14-3-3σ and its binding partners estrogen receptor ERα, the tumour suppressor p53, and the kinase LRRK2, whose interactions upon the addition of a small molecule, fusicoccin A, are differentially stabilised. Within a single measurement the stoichiometry and binding equilibria between 14-3-3 and each of its binding partners was evident. Upon addition of the fusicoccin A stabiliser, a dramatic shift in binding equilibria was observed with the 14-3-3:ERα complex compared with the 14-3-3:p53 and 14-3-3:LRRK2 complexes. Our results highlight how native MS can not only distinguish the ability of stabilisers to modulate PPIs, but also give important insights into the dynamics of ternary complex formation. Finally, we show how native MS can be used as a screening tool to search for PPI stabilisers, highlighting its potential role as a primary screening technology in the hunt for novel therapeutic PPI stabilisers.

Stabilising protein–protein interactions is challenging, yet therapeutically important. Native mass spectrometry can be used to monitor binding equilibria, allowing identification and measurement of novel protein–protein interaction stabilisers.     

Facile One‐Pot Synthesis of Tellurium Nanorods as Antioxidant and Anticancer Agents

Nanorods have been utilized in targeted therapy, controlled release, molecular diagnosis, and molecule imaging owing to their large surface area and optical, magnetic, electronic, and structural properties. However, low stability and complex synthetic methods have substantially limited the application of tellurium nanorods for use as antioxidant and anticancer agents. Herein, a facile one‐pot synthesis of functionalized tellurium nanorods (PTNRs) by using a hydrothermal synthetic system with a polysaccharide–protein complex (PTR), which was extracted from Pleurotus tuber‐regium, as a capping agent is described. PTNRs remained stable in water and in phosphate‐buffered saline and exhibited high hemocompatibility. Interestingly, these nanorods possessed strong antioxidant activity for scavenging 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid radical cation (ABTS^.+) and 2,2‐diphenyl‐1‐picrylhydrazylhydrate (DPPH) free radicals and demonstrated novel anticancer activities. However, these nanorods exhibited low cytotoxicity toward normal human cells. In addition, the PTNRs effectively induced a decrease in the mitochondrial membrane potential in a dose‐dependent manner, which indicated that mitochondrial dysfunction might play an important role in PTNR‐induced apoptosis. Therefore, this study provides a one‐pot strategy for the facile synthesis of tellurium nanorods with novel antioxidant and anticancer application potentials.     

Efficient approaches to S-alkyl-N-alkylisothioureas: syntheses of histamine H3 antagonist clobenpropit and its analogues

S-Alkyl-N-alkylisothioureas were efficiently synthesized via synthetic approach (A) using 3-phenylpropionyl isothiocyanate (PPI). The utility of the approach was proved by the syntheses of clobenpropit, a potent histamine H(3) antagonist, and its analogues. Alternatively, clobenpropit could be prepared via intramolecular amide cleavage (B) with use of 2-nitrophenylacetyl isothiocyanate (NPAI).     

An immunomodulator from Tinospora cordifolia with antioxidant activity in cell-free systems

Several plant products are known to exhibit immense medicinal value against human diseases. Our earlier studies showed that dry stem crude extract (DSCE) ofTinospora cordifolia contained a polyclonal B cell mitogen, G1-4A. DSCE as well as G1-4A also enhanced immune response in mice. In order to explore the possibility of using G1-4A/PPI (partially purified immunomodulator) to modulate radiation induced immunosuppression, the antioxidant effect of PPI from this plant was examined against reactive oxygen and nitrogen species (ROS/RNS), generated by photosensitization/peroxynitrite. Levels of lipid peroxidation products, superoxide dismutase (SOD) and catalase in liver/spleen homogenate from mouse were monitored. Photosensitization induced significant increase in thiobarbituric acid reactive substances (TBARS) in liver. The activities of SOD and catalase were reduced considerably. PPI, present during photosensitisation, prevented lipid peroxidation and restored the activities of both the enzymes. Likewise, oxidative damage induced by peroxynitrite was inhibited by PPI. The degradation of proteins due to photosensitization as assessed by SDS-PAGE was effectively reduced by simultaneous treatment with PPI during photosensitization. Selective inhibitors of ROS like mannitol, SOD, sodium azide and antioxidants, GSH and vitamin C brought about significant inhibition of formation of TBARS suggesting possible involvement of O₂ ^•,^•OH and¹O₂. Photosensitization in deuterated buffer enhanced formation of TBARS thus indicating generation of¹O₂. Thus, the action of PPI may be against oxidative damage through Type I and II photosensitization mechanisms. Therefore, the immunomodulator fromTinospora cordifolia may also be beneficial as an antioxidant.     

MC8 Peptide-Mediated Her-2 Receptor Targeting Based on PEI-β-CyD as Gene Delivery Vector

A novel vector with high gene delivery efficiency and special cell targeting ability was developed using a good strategy that utilized low molecular weight polyethylenimine (PEI; molecular weight, 600 KDa [PEI600]) cross-linked to β-cyclodextrin (β-CyD) via a facile synthetic route. Human epidermal growth factor receptor 2 (Her-2) are highly expressed in a variety of human cancer cells and are potential targets for cancer therapy. MC8 peptides, which have been proven to combine especially with Her-2 on cell membranes were coupled to PEI-β-CyD using N-succinimidyl-3-(2-pyridyldithio) propionate as a linker. The ratios of PEI600, β-CyD, and peptide were calculated based on proton integral values obtained from the ¹H-NMR spectra of the resulting products. Electron microscope observations showed that MC8-PEI-β-CyD can efficiently condense plasmid DNA (pDNA) into nanoparticles of about 200 nm, and MTT assays suggested the decreased toxicity of the polymer. Experiments on gene delivery efficiency in vitro showed that MC8-PEI-β-CyD/pDNA polyplexes had significantly greater transgene activities than PEI-β-CyD/pDNA in the Skov3 and A549 cells, which positively expressed Her-2, whereas, no such effect was observed in the MCF-7 cells, which negatively expressed Her-2. Our current research indicated that the synthesized nonviral vector shows improved gene delivery efficiency and targeting specificity in Her-2 positive cells.     

Natural Cryoprotective and Cytoprotective Agents in Cryopreservation: A Focus on Melatonin

Cryoprotective and cytoprotective agents (Cytoprotective Agents) are fundamental components of the cryopreservation process. This review presents the essentials of the cryopreservation process by examining its drawbacks and the role of cytoprotective agents in protecting cell physiology. Natural cryoprotective and cytoprotective agents, such as antifreeze proteins, sugars and natural deep eutectic systems, have been compared with synthetic ones, addressing their mechanisms of action and efficacy of protection. The final part of this article focuses melatonin, a hormonal substance with antioxidant properties, and its emerging role as a cytoprotective agent for somatic cells and gametes, including ovarian tissue, spermatozoa and spermatogonial stem cells.     

Synthesis,characterization and antioxidant,antibacterial activity Zn2+, Cu2+, Ni2+ and Co2+, complexes of ligand [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole]

New metal complexes of (Zn(II), Co(II), Ni(II) and Cu(II)) based on the ligand 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] were synthesized, whose structures were determined with the different spectroscopic techniques ¹H NMR,¹³C NMR, FT-IR, UV–Visible and by mass spectrometry. The thermal analysis was performed by TG-DTA. The antioxidant activity of the ligand and its complexes was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, in comparison with the synthetic antioxidant, ascorbic acid. The results obtained showed that the antioxidant activity of the ligand and its complexes is moderate and that the copper complex has a high activity that exceeds that of ascorbic acid. Antimicrobial activity of the ligand and its metal complexes was studied against two Gram-positive bacteria: Bacillus subtilis ILP1428B, Staphylococcus aureus CIP543154 and two Gram-negative bacteria: Pseudomonas aeruginosa ATCC27653, Escherichia coli CIP5412 (American Type Culture Collection)the activity data show that the metal complexes are more potent than the free ligand.     

Single-molecule analysis of interaction between p53TAD and MDM2 using aerolysin nanopores

Protein–protein interactions (PPIs) are regarded as important, but undruggable targets. Intrinsically disordered p53 transactivation domain (p53TAD) mediates PPI with mouse double minute 2 (MDM2), which is an attractive anticancer target for therapeutic intervention. Here, using aerolysin nanopores, we probed the p53TAD peptide/MDM2 interaction and its modulation by small-molecule PPI inhibitors or p53TAD phosphorylation. Although the p53TAD peptide showed short-lived (<100 ms) translocation, the protein complex induced the characteristic extraordinarily long-lived (0.1 s ∼ tens of min) current blockage, indicating that the MDM2 recruitment by p53TAD peptide almost fully occludes the pore. Simultaneously, the protein complex formation substantially reduced the event frequency of short-lived peptide translocation. Notably, the addition of small-molecule PPI inhibitors, Nutlin-3 and AMG232, or Thr18 phosphorylation of p53TAD peptide, were able to diminish the extraordinarily long-lived events and restore the short-lived translocation of the peptide rescued from the complex. Taken together, our results elucidate a novel mechanism of single-molecule sensing for analyzing PPIs and their inhibitors using aerolysin nanopores. This novel methodology may contribute to remarkable improvements in drug discovery targeted against undruggable PPIs.

Using aerolysin nanopores, we probed protein–protein interaction (PPI) between p53TAD and MDM2 and its modulation by small-molecule PPI inhibitors and p53TAD phosphorylation.     

Fabrication and Characterization of Chitosan–Pea Protein Isolate Nanoparticles

Chitosan (CS) and pea protein isolate (PPI) were used as raw materials to prepare nanoparticles. The structures and functional properties of the nanoparticles with three ratios (1:1, 1:2 1:3, CS:PPI) were evaluated. The particle sizes of chitosan–pea protein isolate (CS–PPI) nanoparticles with the ratios of 1:1, 1:2, and 1:3 were 802.95 ± 71.94, 807.10 ± 86.22, and 767.75 ± 110.10 nm, respectively, and there were no significant differences. Through the analysis of turbidity, endogenous fluorescence spectroscopy and Fourier transform infrared spectroscopy, the interaction between CS and PPI was mainly caused by electrostatic mutual attraction and hydrogen bonding. In terms of interface properties, the contact angles of nanoparticles with the ratio of 1:1, 1:2, and 1:3 were 119.2°, 112.3°, and 107.0°, respectively. The emulsifying activity (EAI) of the nanoparticles was related to the proportion of protein. The nanoparticle with the ratio of 1:1 had the highest potential and the best thermal stability. From the observation of their morphology by transmission electron microscopy, it could be seen that the nanoparticles with a ratio of 1:3 were the closest to spherical. This study provides a theoretical basis for the design of CS–PPI nanoparticles and their applications in promoting emulsion stabilization and the delivery of active substances using emulsions.     

Design of Drug-Like Protein–Protein Interaction Stabilizers Guided By Chelation-Controlled Bioactive Conformation Stabilization

Protein–protein interactions (PPIs) of 14-3-3 proteins are a model system for studying PPI stabilization. The complex natural product Fusicoccin A stabilizes many 14-3-3 PPIs but is not amenable for use in SAR studies, motivating the search for more drug-like chemical matter. However, drug-like 14-3-3 PPI stabilizers enabling such studies have remained elusive. An X-ray crystal structure of a PPI in complex with an extremely low potency stabilizer uncovered an unexpected non-protein interacting, ligand-chelated Mg²⁺ leading to the discovery of metal-ion-dependent 14-3-3 PPI stabilization potency. This originates from a novel chelation-controlled bioactive conformation stabilization effect. Metal chelation has been associated with pan-assay interference compounds (PAINS) and frequent hitter behavior, but chelation can evidently also lead to true potency gains and find use as a medicinal chemistry strategy to guide compound optimization. To demonstrate this, we exploited the effect to design the first potent, selective, and drug-like 14-3-3 PPI stabilizers.     

Tailoring of new Ni(II), Hg(II) and UO2(II)–hydrazide complexes: characterization,studies in-vitro and in-silico as well as the Hartree-Fock modeling

A new hydrazide ligand was prepared to synthesize Ni(II), Hg(II) and UO₂(II) complexes, which elucidated by all possible tools. Accordingly, 1M:2L molar ratio was suggested for Ni(II) and Hg(II) complexes, while UO₂(II) complex close to 1:1 ratio. The ligand binds as a bidentate or tridentate mode either as a monobasic via deprotonation of azomethine group or as a neutral with Hg(II) complex. A square-planer geometry was suggested for [Ni(L)₂], while the other complexes reveal octahedral geometry. The antimicrobial screening was performed as well as the antioxidant and cytotoxic activity test towards Ehrlich ascites cells. The ligand and its Ni(II) complex produce a notable inhibition for microorganisms, while their antioxidant and cytotoxicity are up to the standards themselves. The DFT/B3LYP and Hartree-Fock (HF) methods were used to optimize the structures under suitable basis sets to obtain essential parameters and 3D-maps. Utilizing Swiss-ADME link reveals the positive response of the ligand to blood brain barrier and human intestinal absorption. Moreover, other silico tests were performed via Pharmacophore and Molecular Operating Environmental module (MOE) against different proteins. Finally, the agreement between vitro and silico results was noticed with the ligand and its Ni(II)complex.     

Antioxidant and spectroscopic studies of crosslinked polymers synthesized by grafting polymerization of ferulic acid

A novel, simple synthetic strategy for the preparation of crosslinked polymers with significant antioxidant properties is proposed. Ferulic acid (FA), a well‐known antioxidant compound, due to its reactivity toward free radical process, was inserted into a polymeric network with methacrylic acid (MAA) and ethylene glycole dimethacrylate acting as comonomer and crosslinker, respectively. All the reactants were simultaneously mixed in the polymerization feed and one‐pot radical reaction was carried out. Irregular microparticles were prepared by bulk polymerization and microspheres by precipitation polymerization. The materials were characterized by nuclear magnetic resonance–magic angle spinning (NMR‐MAS) studies, to verify effective FA insertion into polymeric networks, and by morphological, dimensional analyses, and water absorption measurement to study their superficial and swelling properties, respectively. Antioxidant properties of materials were evaluated by linoleic acid emulsion system–thiocyanate assay, determination of scavenging activity on DPPH radicals, determination of available phenolic groups in polymeric matrices, and determination of total antioxidant capacity. Copyright © 2009 John Wiley & Sons, Ltd.     

Adhesion and proliferation of cells on new polymers modified biomaterials

Up to today, several techniques have been used to maintain cells in culture for studying many aspects of cell biology and physiology. More often, cell culture is dependent on proper anchorage of cells to the growth surface. Poly-l-lysine is commonly used as adhesive molecule. In this study, we present, as an alternative to poly-l-lysine, new polymer film substrates, realized by electropolymerization of different monomers on fluorine-doped tin oxide (FTO) surfaces since electropolymerization is a good method to coat selectively metallic or semiconducting electrodes with polymer films. So, the adhesion, proliferation and morphology of rat neuronal cell lines were investigated on polymer treated surfaces. Several amine-based biocompatible polymers were tested: polyethyleneimine (PEI), polypropyleneimine (PPI), polypyrrole (PPy) and poly(p-phenylenediamine) (PPPD). These polymer films were coated on FTO surfaces by electrochemical oxidation. After 8 h in a culture medium, a high percentage of cells was found to be attached to PEI and PPI compared to the other polymers and to the reference surfaces (glass and FTO uncovered). After 24 and 72 h in the culture medium, cells were found to proliferate faster on PEI and PPI than on other polymers and reference surfaces. Consequently, cells have a greater fold expansion on PEI and PPI than on PPPD, PPy or glass and FTO uncoated. From these results, we deduce that PEI and PPI can be useful as coating surface to cultivate neuronal cells.     

Simultaneous total antioxidant capacity assay of lipophilic and hydrophilic antioxidants in the same acetone-water solution containing 2% methyl-β-cyclodextrin using the cupric reducing antioxidant capacity (CUPRAC) method

Antioxidants are health beneficial compounds that can protect cells from the damage caused by unstable molecules known as reactive oxygen species (ROS). This work reports the capacity assay of both lipophilic and hydrophilic antioxidants simultaneously, by making use of their ‘host-guest’ complexes with methyl-β-cyclodextrin (M-β-CD), a cyclic oligosaccharide, in acetonated aqueous medium using the cupric reducing antioxidant capacity (CUPRAC) method. Thus the order of antioxidant potency of various compounds irrespective of their lipophilicity could be established in the same solvent medium. M-β-CD was introduced as the water solubility enhancer for lipophilic antioxidants. Two percent M-β-CD (w/v) in an acetone-H₂O (9:1, v/v) mixture was found to sufficiently solubilize β-carotene, lycopene, vitamin E, vitamin C, synthetic antioxidants and other phenolic antioxidants. This assay was validated through linearity, additivity, precision, and recovery. The validation results demonstrate that the CUPRAC assay is reliable and robust. In acetonated aqueous solution of M-β-CD, only CUPRAC and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays were capable of measuring carotenoids together with hydrophilic antioxidants. The CUPRAC antioxidant capacities of a wide range of polyphenolics and flavonoids were experimentally reported in this work as trolox equivalent antioxidant capacity (TEAC) in the CUPRAC assay, and compared to those found by reference methods, ABTS/horseradish peroxidase (HRP)-H₂O₂ and ferric reducing antioxidant power (FRAP) assays.     

A Small‐Molecule Protein–Protein Interaction Inhibitor of PARP1 That Targets Its BRCT Domain

Poly(ADP‐ribose)polymerase‐1 (PARP1) is a BRCT‐containing enzyme (BRCT=BRCA1 C‐terminus) mainly involved in DNA repair and damage response and a validated target for cancer treatment. Small‐molecule inhibitors that target the PARP1 catalytic domain have been actively pursued as anticancer drugs, but are potentially problematic owing to a lack of selectivity. Compounds that are capable of disrupting protein–protein interactions of PARP1 provide an alternative by inhibiting its activities with improved selectivity profiles. Herein, by establishing a high‐throughput microplate‐based assay suitable for screening potential PPI inhibitors of the PARP1 BRCT domain, we have discovered that (±)‐gossypol, a natural product with a number of known biological activities, possesses novel PARP1 inhibitory activity both in vitro and in cancer cells and presumably acts through disruption of protein–protein interactions. As the first known cell‐permeable small‐molecule PPI inhibitor of PAPR1, we further established that (?)‐gossypol was likely the causative agent of PARP1 inhibition by promoting the formation of a 1:2 compound/PARP1 complex by reversible formation of a covalent imine linkage.     

Hydroxytyrosol Acyl Esters: Biosynthesis and Activities

We previously reported the production of high yields of hydroxytyrosol through the bioconversion of tyrosol. In the present work, hydroxytyrosol was subjected to the lipase catalyzed acylation aiming for the recovery of more lipophilic esters that might be easily incorporated in cosmetic and food preparations. Hydroxytyrosyl acetate and hydroxytyrosyl oleate were produced with respective molar esterification yields of 98% and 78%. DPPH free radical quenching potency demonstrated that the acylation of hydroxytyrosol did not alter its antioxidant activity. The acylated esters were shown to be more effective than the natural antioxidant: caffeic acid and two synthetic ones as BHA and BHT. Antiproliferative activity on human cervical cells (HeLa) resulted in IC₅₀ values of 0.46, 0.42 and 0.33 mM for hydroxytyrosol and its acetyl and oleyl esters, respectively. Additionally, when used at a non-cytotoxic concentration (100 μM), these compounds showed significant effectiveness in preventing iron-induced oxidative stress, resulting in a reduction of 30%, 36% and 38% in thiobarbituric acid-reactive substance production, respectively.     

Anticarcinogenic and Antioxidant Action of an Edible Aquatic Flora Jussiaea repens L. Using In Vitro Bioassays and In Vivo Zebrafish Model

Oxidative stress is the major cause of many health conditions, and regular consumption of antioxidants helped to encounter and prevent such oxidative stress-related diseases. Due to safety concerns over long-term uses of synthetic antioxidants, natural antioxidants are more preferred. The purpose of this study is to investigate the antioxidant and anticancer activities of Jussiaea repens L., a wild edible flora found in Manipur, India. The antioxidant activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), Ferric reducing antioxidant power (FRAP) assay and DNA-nicking assay. The anticancer activity was tested using five cancer lines viz., SKOV3 cells (ovarian), HeLa (cervical), MDA-MB-231 (breast), PANC-1 (pancreatic), and PC3 (prostate). The toxicity, developmental effect, antiproliferative activity was further tested using zebrafish embryos. The methanolic plant extract had higher polyphenol content than flavonoids. The in vitro study demonstrated a promising antioxidant capacity and DNA protection ability of this plant. The extract also showed cytotoxic activity against SKOV3, HeLa, MDA-MB-23, and PANC-1 cancer cell lines. The in vivo studies on zebrafish embryos demonstrated the extract’s ability to suppress the developmental process and elicited more cytotoxicity to cancer cells than developing zebrafish embryos. Moreover, the in vivo studies on zebrafish embryos also indicated the antiproliferative activity of J. repens L. extract.     

Protective effect of mitochondrially targeted antioxidant MitoQ on oxidatively stressed fibroblasts

3T3 and VH10 cells were subjected to oxidative damage by hydroxyl radicals generated from Cu(II) ions and ascorbate. The presence of reactive oxygen and nitrogen species in cells was determined using fluorescent dyes. MitoQ—a mitochondrially targeted antioxidant—was examined to prevent cell death and was compared with trolox as a reference standard serving as an antioxidant. MitoQ at lower concentrations (up to 500 nM) prevented damage of mitochondria and thereby increased viability of cells. However, at higher concentrations (over 500 nM) MitoQ decreased the viability of both strains of cells. The last observation indicates that the application of MitoQ should be evaluated also from the point of its cell-destructive potential.     

New coumarin derivative with potential antioxidant activity: Synthesis,DNA binding and in silico studies (Docking,MD, ADMET)

A new coumarin derivative, 7-((8-(4-benzylpiperidin-1-yl)octyl)oxy)-4-methyl-2H-chromen-2-one (C3), was synthesized by two-step alkylation reaction of 7-hydroxy-4-methyl coumarin. The structure and purity of the compound were characterized by its ¹H and ¹³C NMR, FT-IR and LC-MS spectral data. The DNA binding interaction of C3 was evaluated using UV–vis spectrophotometric and viscosimetric methods. These experiments showed that C3 was bound in intercalative mode. The antioxidant activity of C3 was evaluated by the DPPH method, the antioxidant activity results displayed that C3 had DPPH radical scavenging effect. The possible mechanism of antioxidant and anticancer activity of C3 was investigated via molecular docking by using two enzymes CYP450 and EGFR as receptors. The C3 also tended a good antioxidant ability based on the result of the molecular docking analysis, with good binding affinity values (-7.82 kcal/mol) and binding site interactions. Molecular Dynamics (MD) simulation was implemented to elucidate the interactions with the protein–ligand complex in 20 ns. The ADMET analyzes which paved the way for us to predict C3 as a drug candidate were also performed. All experimental and theoretical results showed that the compound C3 was a potential drug candidate as an antioxidant and anticancer agent.     

New samarium(III) complex of 5‐aminoorotic acid with antioxidant activity

A samarium(III) complex (SmAOA) of 5‐aminoorotic acid (HAOA) was synthesized by reaction of the respective inorganic salt and ligand in a molar ratio of 1:3. The structure of the complex was determined by means of elemental analysis and UV–visible, NMR, Fourier transform infrared (FT‐IR) and FT Raman spectroscopies. Significant differences in the FT‐IR and FT Raman spectra of the complex were observed as compared to the spectra of the free ligand. Detailed vibrational analysis of HAOA and Sm(III)–AOA systems revealed that the binding mode in the complex was bidentate through the carboxylic oxygen atoms. The newly synthesized SmAOA showed antioxidant properties. The antioxidant activities of both HAOA and SmAOA were related to their electron donor properties. Copyright © 2015 John Wiley & Sons, Ltd.