Sterubin: Enantioresolution and Configurational Stability, Enantiomeric Purity in Nature, and Neuroprotective Activity in Vitro and in Vivo

Visualizing Intracellular Localization of Natural-Product-Based Chemical Probes Using Click-Correlative Light and Electron Microscopy

Flavonoids such as sterubin and fisetin─and derivatives thereof─show strong neuroprotective effects in vitro as well as in vivo, combined with negligible toxicity and can therefore be considered novel treatment options for neurodegenerative diseases such as Alzheimer's disease. However, their subcellular locations responsible for neuroprotection and exact modes of action still remain unclear. Here, we present chemical probes based on both flavonoids sterubin and fisetin that were utilized in fluorescence microscopy and click-correlative light and electron microscopy to detect and visualize the localization of specific intracellular targets. We successfully adapted the workflow of correlative light and electron microscopy to a click-chemistry-based approach in a murine hippocampal cell line (HT22) on ultrathin resin sections making visualization of a small molecule for the first time possible in this setup. Utilizing this newly adapted technique, we could demonstrate that sterubin and fisetin show specific enrichment in the endoplasmic reticulum.

Synthesis and structural modification of the natural product Ivesinol to discover novel autophagy activators

Autophagy is a lysosome-dependent cellular degradation pathway that responds to a variety of environmental and cellular stresses, which is defective in aging and age-related diseases, therefore, targeting autophagy with small-molecule activators has potential therapeutic benefits. In this study, we successfully completed the first total synthesis of Ivesinol, an identified antibacterial natural product, and efficiently constructed a library of its analogs. To measure the effect of Ivesinol analogs on autophagic activity, we performed cell imaging-based screening approach, and observed that several Ivesinol analogs exhibited potent autophagy-regulating activity. Specifically, the derivative B2 significantly activated autophagy activity in concentration- and time-dependent manners, and even outperformed the commonly used activator Torin1 in activating autophagy in MCF-7 cells at 0.5 μM. Bioinformatics analysis showed that B2 treatment significantly impacted ubiquitin mediated proteolysis and AMPK signaling pathway, with functionally related gene sets displaying strong correlations. Based on these findings, we proposed that B2 activates autophagy by mechanisms involved in downregulation of key HSP70 family members, activation of the UPR, and ultimately leading to autophagy. In conclusion, we suggest that B2 could be a promising and valuable autophagy activator with significant potential for further development.

Principles for Stereoselective Separation of Chiral Drug Compounds Enantiomers and Diastereomers in Pharmaceuticals and Biopharmaceuticals Using Liquid Chromatography

In the fields of pharmaceuticals and biopharmaceuticals, chiral liquid chromatography techniques including high-performance liquid chromatography and ultra-performance liquid chromatography are frequently used to isolate, identify, separate, and quantify chiral isomers, including enantiomers and diastereomers (stereoisomers), due to the significant differences in biological activity and therapeutic effects of stereoisomers. The authors have provided a comprehensive overview of the fundamental principles necessary for using liquid chromatography to separate and accurately estimate chiral compounds that exhibit stereoisomerism (both enantiomers and diastereomers). The development strategies outlined include the selection of chromatographic conditions, optimization of sample preparation, evaluation of degradation pathways, establishment of system suitability criteria, and execution of method validation studies. Additionally, this article supports the development of robust and stability-indicating methods by applying one factor at a time and design of experiments concepts for chiral drugs and their chiral impurities in pharmaceuticals and biopharmaceuticals. The method validation attributes essential to evaluate the characteristics of the developed method were discussed in this write-up. The validation parameters include specificity, linearity, detection limit, quantitation limit, accuracy, precision, solution stability.

Discovery and optimization of isoliquiritigenin as a death-associated protein kinase 1 inhibitor

Death-associated protein kinase 1 (DAPK1) is a phosphotransferase in the serine/threonine kinase family. Inhibiting DAPK1 is expected to be beneficial in treating Alzheimer's disease and protecting neuronal cells during cerebral ischemia. In this study, we demonstrated that the natural chalcone isoliquiritigenin inhibits DAPK1 in an ATP-competitive manner, and we synthesized halogen derivatives to amplify the inhibitory effect. Among the compounds tested, the chlorine, bromine, and iodine derivatives exhibited high DAPK1 inhibitory activity and binding affinity. Crystal structure analysis revealed that this improvement is attributable to the halogen atoms fitting well into the hydrophobic pocket formed by I77, L93, and I160. In particular, the chlorine derivative showed a significant enthalpic contribution to the interaction with DAPK1, suggesting its potential as a primary compound for new DAPK1 inhibitors.

The Neuroprotective Flavonoids Sterubin and Fisetin Maintain Mitochondrial Health under Oxytotic/Ferroptotic Stress and Improve Bioenergetic Efficiency in HT22 Neuronal Cells

The global increase in the aging population has led to a rise in many age-related diseases with continuing unmet therapeutic needs. Research into the molecular mechanisms underlying both aging and neurodegeneration has identified promising therapeutic targets, such as the oxytosis/ferroptosis cell death pathway, in which mitochondrial dysfunction plays a critical role. This study focused on sterubin and fisetin, two flavonoids from the natural pharmacopeia previously identified as strong inhibitors of the oxytosis/ferroptosis pathway. Here, we investigated the effects of the compounds on the mitochondrial physiology in HT22 hippocampal nerve cells under oxytotic/ferroptotic stress. We show that the compounds can restore mitochondrial homeostasis at the level of redox regulation, calcium uptake, biogenesis, fusion/fission dynamics, and modulation of respiration, leading to the enhancement of bioenergetic efficiency. However, mitochondria are not required for the neuroprotective effects of sterubin and fisetin, highlighting their diverse homeostatic impacts. Sterubin and fisetin, thus, provide opportunities to expand drug development strategies for anti-oxytotic/ferroptotic agents and offer new perspectives on the intricate interplay between mitochondrial function, cellular stress, and the pathophysiology of aging and age-related neurodegenerative disorders.

Protective effect of sterubin against neurochemical and behavioral impairments in rotenone-induced Parkinson's disease

This study was conducted to evaluate how sterubin affects rotenone-induced Parkinson's disease (PD) in rats. A total of 24 rats were distributed into 4 equal groups: normal saline control and rotenone control were administered saline or rotenone (ROT), respectively, orally; sterubin 10 received ROT + sterubin 10 mg/kg po; and sterubin alone was administered to the test group (10 mg/kg). Rats of the normal saline and sterubin alone groups received sunflower oil injection (sc) daily, 1 h after receiving the treatments cited above, while rats of the other groups received rotenone injection (0.5 mg/kg, sc). The treatment was continued over the course of 28 days daily. On the 29th day, catalepsy and akinesia were assessed. The rats were then euthanized, and the brain was extracted for estimation of endogenous antioxidants (MDA: malondialdehyde, GSH: reduced glutathione, CAT: catalase, SOD: superoxide dismutase), nitrative (nitrite) stress markers, neuroinflammatory cytokines, and neurotransmitter levels and their metabolites (3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), norepinephrine (NE), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA)). Akinesia and catatonia caused by ROT reduced the levels of endogenous antioxidants (GSH, CAT, and SOD), elevated the MDA level, and altered the levels of nitrites, neurotransmitters, and their metabolites. Sterubin restored the neurobehavioral deficits, oxidative stress, and metabolites of altered neurotransmitters caused by ROT. Results demonstrated the anti-Parkinson's activities of sterubin in ROT-treated rats.

Insights from molecular network analysis to docking of sterubin with potential targets

The use of a flavonoid compound sterubin in drug discovery is gaining momentum. Hence, it is of interest to document the molecular network analysis to docking of sterubin with potential targets to glean insights. We identified 32 target genes and (or) gene products for sterubin using DAVID tools for GO, KEGG pathway enrichment analyses and the STRING database. Further, molecular docking analysis data of sterubin with these targets is documented for further consideration in broad-spectrum drug discovery.

Synthesis and biological evaluation of chromanone-based derivatives as potential anti-neuroinflammatory agents

As a privileged scaffold, chromanone has been extensively introduced in the design of drug leads with diverse pharmacological features, particularly in the area of inflammatory diseases. Herein, the preparation of chromanone-based derivatives (4a-4i) was smoothly achieved, and their structures were characterized using 1H NMR, 13C NMR, and ESI-HRMS spectroscopy techniques. Out of them, analogue 4e exhibited the most potent inhibitory capacity against the NO release and iNOS expression, without apparent cytotoxicity. Our observations showed that 4e could dramatically prevent the translocation of NF-κB from the cytoplasm to nucleus, and decrease the production of proinflammatory cytokines TNF-α, IL-6 and IL-1β in LPS-induced BV-2 cells. Mechanistically, 4e significantly deactivated NF-κB by disturbing TLR4-mediated TAK1/NF-κB and PI3K/Akt signaling cascades. Consistent with the in vitro study, 4e could effectively mitigate the inflammation response of hippocampal tissue in LPS-induced mouse model by inhibiting microglial activation. Collectively, these results revealed 4e as a prospective neuroprotective candidate for the therapy of neuroinflammation-related disorders.

Dual-Acting Small Molecules: Subtype-Selective Cannabinoid Receptor 2 Agonist/Butyrylcholinesterase Inhibitor Hybrids Show Neuroprotection in an Alzheimer's Disease Mouse Model

We present the synthesis and characterization of merged human butyrylcholinesterase (hBChE) inhibitor/cannabinoid receptor 2 (hCB₂R) ligands for the treatment of neurodegeneration. In total, 15 benzimidazole carbamates were synthesized and tested for their inhibition of human cholinesterases, also with regard to their pseudoirreversible binding mode and affinity toward both cannabinoid receptors in radioligand binding studies. After evaluation in a calcium mobilization assay as well as a β-arrestin 2 (βarr2) recruitment assay, two compounds with balanced activities on both targets were tested for their immunomodulatory effect on microglia activation and regarding their pharmacokinetic properties and blood-brain barrier penetration. Compound 15d, containing a dimethyl carbamate motif, was further evaluated in vivo, showing prevention of Aβ_25-35-induced learning impairments in a pharmacological mouse model of Alzheimer's disease for both short- and long-term memory responses. Additional combination studies proved a synergic effect of BChE inhibition and CB₂R activation in vivo.

Synthesis, Structure Revision, and Anti-inflammatory Activity Investigation of Putative Blumeatin

Blumeatin, reported herein, bearing two hydroxyl groups at C3' and C5' of ring B, is isolated from the traditional Chinese medicine Blumea balsamifera. But the isolation procedure of blumeatin from plants has limitations of prolonged duration and high cost. A procedure featuring Lewis acid-catalyzed ring closure and chiral resolution via Schiff base intermediates is provided here to prepare optically pure blumeatin and its R-isomer efficiently. Furthermore, the structure revision of putative blumeatin based on a logically synthetic procedure and NMR spectroscopic analysis was conducted. The 1D and 2D NMR data analysis unambiguously confirmed our proposal that the reported blumeatin structure has been misassigned as it corresponds to sterubin, which contains two hydroxyl groups at C3' and C4' of ring B. Finally, the results of the ear-swelling test exhibited that synthetic (±)-blumeatin and (±)-sterubin had moderate anti-inflammatory activity which was less than that of (-)-sterubin.

Semi-Preparative Separation, Absolute Configuration, Stereochemical Stability and Effects on Human Neuronal Cells of MDPV Enantiomers

Synthetic cathinones, such as 3,4-methylenedioxypyrovalerone (MDPV), are widely abused due to their psychostimulant effects. As they are chiral molecules, studies of their stereochemical stability (racemization can occur in certain temperatures and acidic/basic environments) and of their biological and/or toxicity effects (enantiomers might display different properties) are of great relevance. In this study, the liquid chromatography (LC) semi-preparative enantioresolution of MDPV was optimized to collect both enantiomers with high recovery rates and enantiomeric ratio (e.r.) values. The absolute configuration of the MDPV enantiomers was determined by electronic circular dichroism (ECD) with the aid of theoretical calculations. The first eluted enantiomer was identified as S-(-)-MDPV and the second eluted enantiomer was identified as R-(+)-MDPV. A racemization study was performed by LC-UV, showing enantiomers' stability up to 48 h at room temperature and 24 h at 37 °C. Racemization was only affected by higher temperatures. The potential enantioselectivity of MDPV in cytotoxicity and in the expression of neuroplasticity-involved proteins-brain-derived neurotrophic factor (BDNF) and cyclin-dependent kinase 5 (Cdk5)-was also evaluated using SH-SY5Y neuroblastoma cells. No enantioselectivity was observed.

Sterubin protects against chemically-induced Alzheimer's disease by reducing biomarkers of inflammation- IL-6/ IL-β/ TNF-α and oxidative stress- SOD/MDA in rats

Sterubin, a flavanone is an active chemical compound that possesses neuroprotective activity. The current investigation was intended to assess the sterubin effect in scopolamine-activated Alzheimer's disease. The rats were induced with scopolamine (1.5 mg/kg) followed by treatment with sterubin (10 mg/kg) for 14 days. Behavioural analysis was predictable by the Y-maze test and Morris water test. Biochemical variables like nitric oxide acetylcholinesterase, Choline acetyltransferase, antioxidant markers like superoxide dismutase, glutathione transferase, malondialdehyde, catalase, and myeloperoxidase activity, neuroinflammatory markers such as tumor necrosis factor-alpha, nuclear factor kappa B, interferon-gamma, interleukin (IL-1β), and IL-6 were measured. The result stated that sterubin reversed the oxidative stress parameters, increased motor performance, and lowered the inflammatory markers in scopolamine-induced rats. The study demonstrated that sterubin possesses neuroprotective, anti-inflammatory, and antioxidant properties which can be used as a beneficial medication in AD.

Stereoselective Synthesis of Flavonoids: A Brief Overview

Stereoselective synthesis has been emerging as a resourceful tool because it enables the obtaining of compounds with biological interest and high enantiomeric purity. Flavonoids are natural products with several biological activities. Owing to their biological potential and aiming to achieve enantiomerically pure forms, several methodologies of stereoselective synthesis have been implemented. Those approaches encompass stereoselective chalcone epoxidation, Sharpless asymmetric dihydroxylation, Mitsunobu reaction, and the cycloaddition of 1,4-benzoquinone. Chiral auxiliaries, organo-, organometallic, and biocatalysis, as well as the chiral pool approach were also employed with the goal of obtaining chiral bioactive flavonoids with a high enantiomeric ratio. Additionally, the employment of the Diels-Alder reaction based on the stereodivergent reaction on a racemic mixture strategy or using catalyst complexes to synthesise pure enantiomers of flavonoids was reported. Furthermore, biomimetic pathways displayed another approach as illustrated by the asymmetric coupling of 2-hydroxychalcones driven by visible light. Recently, an asymmetric transfer hydrogen-dynamic kinetic resolution was also applied to synthesise (R,R)-cis-alcohols which, in turn, would be used as building blocks for the stereoselective synthesis of flavonoids.

Structural Requirements for the Neuroprotective and Anti-Inflammatory Activities of the Flavanone Sterubin

Alzheimer's disease (AD) is the most frequent age-associated disease with no treatments that can prevent, delay, slow, or stop its progression. Thus, new approaches to drug development are needed. One promising approach is the use of phenotypic screening assays that can identify compounds that have therapeutic efficacy in target pathways relevant to aging and cognition, as well as AD pathology. Using this approach, we identified the flavanone sterubin, from Yerba santa (Eriodictyon californicum), as a potential drug candidate for the treatment of AD. Sterubin is highly protective against multiple initiators of cell death that activate distinct death pathways, potently induces the antioxidant transcription factor Nrf2, and has strong anti-inflammatory activity. Moreover, in a short-term model of AD, it was able to prevent decreases in short- and long-term memory. In order to better understand which key chemical functional groups are essential to the beneficial effects of sterubin, we compared the activity of sterubin to that of seven closely related flavonoids in our phenotypic screening assays. Surprisingly, only sterubin showed both potent neuroprotective activity against multiple insults as well as strong anti-inflammatory activity against several distinct inducers of inflammation. These effects correlated directly with the ability of sterubin to strongly induce Nrf2 in both nerve and microglial cells. Together, these results define the structural requirements underlying the neuroprotective and anti-inflammatory effects of sterubin and they provide the basis for future studies on new compounds based on sterubin.

Novel benzimidazole-based pseudo-irreversible butyrylcholinesterase inhibitors with neuroprotective activity in an Alzheimer's disease mouse model

As levels of acetylcholinesterase (AChE) decrease while levels of butyrylcholinesterase (BChE) increase in later stages of Alzheimer's disease (AD), BChE stands out as a promising target for treatment of AD. Therefore, several benzimidazole-carbamates were designed based on docking studies to inhibit BChE selectively over AChE, while retaining a reasonable solubility. Synthesized molecules exhibit IC50 values from 2.4 μM down to 3.7 nM with an overall highly hBChE-selective profile of the designed compound class. After evaluation of potential neurotoxicity, the most promising compound was further investigated in vivo. Compound 11d attenuates Aβ25-35-induced learning impairments in both spontaneous alternation and passive avoidance responses at a very low dosage of 0.03 mg kg-1, proving selective BChE inhibition to lead to effective neuroprotectivity in AD.

Synthesis and Biological Evaluation of Flavonoid‐Cinnamic Acid Amide Hybrids with Distinct Activity against Neurodegeneration in Vitro and in Vivo

Flavonoids are polyphenolic natural products and have shown significant potential as disease‐modifying agents against neurodegenerative disorders like Alzheimer's disease (AD), with activities even in vivo. Hybridization of the natural products taxifolin and silibinin with cinnamic acid led to an overadditive effect of these compounds in several phenotypic screening assays related to neurodegeneration and AD. Therefore, we have exchanged the flavonoid part of the hybrids with different flavonoids, which show higher efficacy than taxifolin or silibinin, to improve the activity of the respective hybrids. Chemical connection between the flavonoid and cinnamic acid was realized by an amide instead of a labile ester bond to improve stability towards hydrolysis. To investigate the influence of a double bond at the C‐ring of the flavonoid, the dehydro analogues of the respective hybrids were also synthesized. All compounds obtained show neuroprotection against oxytosis, ferroptosis and ATP‐depletion, respectively, in the murine hippocampal cell line HT22. Interestingly, the taxifolin and the quercetin derivatives are the most active compounds, whereby the quercetin derivate shows even more pronounced activity than the taxifolin one in all assays applied. As aimed for, no hydrolysis product was found in cellular uptake experiments after 4 h whereas different metabolites were detected. Furthermore, the quercetin‐cinnamic acid amide showed pronounced activity in an in vivo AD mouse model at a remarkably low dose of 0.3 mg/kg.

Synthesis of Asebogenin and Balsacone A Precursor by a Novel Synthetic Strategy: Recent Opportunities for and Challenges of Total Synthesis of Balsacone A

One of the main areas of interest of synthetic organic chemistry is the rapid construction of small molecules with proven diverse biological activities for the development of new strategies to cure human health. In particular, the development of novel synthetic strategies is the most important option for reaching the molecular scaffolds of active molecules of natural origin. Balsacone A and asebogenin are compounds that exhibit a wide variety of important biological activities. In this respect, it has become very important to develop new strategies for the construction of biologically active natural and synthetic balsacone analogues. In particular, balsacone derivatives with hydroxy-substituted dihydrochalcone skeletons can be isolated from plant sources or obtained by hemi-syntheses using bio-sourced precursors. An efficient synthetic strategy to synthetically obtain balsacone A is the aim of the present study that considers the limited natural availability of these molecules as well as other factors, such as cost and time. Starting with phloroglucinol, a nine-step synthesis of the precursor of balsacone A was achieved at a 10% overall yield. Furthermore, asebogenin, which has a dihydrochalcone structure and plays a key role in the synthesis of balsacone A, was synthesised with a good yield.

Merging bioresponsive release of insulin-like growth factor I with 3D printable thermogelling hydrogels

3D printing of biomaterials enables spatial control of drug incorporation during automated manufacturing. This study links bioresponsive release of the anabolic biologic, insulin-like growth factor-I (IGF-I) in response to matrix metalloproteinases (MMP) to 3D printing using the block copolymer of poly(2-methyl-2-oxazoline) and thermoresponsive poly(2-n-propyl-2-oxazine) (POx-b-POzi). For that, a chemo-enzymatic synthesis was deployed, ligating IGF-I enzymatically to a protease sensitive linker (PSL), which was conjugated to a POx-b-POzi copolymer. The product was blended with the plain thermogelling POx-b-POzi hydrogel. MMP exposure of the resulting hydrogel triggered bioactive IGF-I release. The bioresponsive IGF-I containing POx-b-POzi hydrogel system was further detailed for shape control and localized incorporation of IGF-I via extrusion 3D printing for future applications in biomedicine and biofabrication.

The Regulatory Effects and the Signaling Pathways of Natural Bioactive Compounds on Ferroptosis

Natural bioactive compounds abundantly presented in foods and medicinal plants have recently received a remarkable attention because of their various biological activities and minimal toxicity. In recent years, many natural compounds appear to offer significant effects in the regulation of ferroptosis. Ferroptosis is the forefront of international scientific research which has been exponential growth since the term was coined. This type of regulated cell death is driven by iron-dependent phospholipid peroxidation. Recent studies have shown that numerous organ injuries and pathophysiological processes of many diseases are driven by ferroptosis, such as cancer, arteriosclerosis, neurodegenerative disease, diabetes, ischemia-reperfusion injury and acute renal failure. It is reported that the initiation and inhibition of ferroptosis plays a pivotal role in lipid peroxidation, organ damage, neurodegeneration and cancer growth and progression. Recently, many natural phytochemicals extracted from edible plants have been demonstrated to be novel ferroptosis regulators and have the potential to treat ferroptosis-related diseases. This review provides an updated overview on the role of natural bioactive compounds and the potential signaling pathways in the regulation of ferroptosis.

Current developments in the synthesis of 4-chromanone-derived compounds

The chroman-4-one framework is a significant structural entity that belongs to the class of oxygen-containing heterocycles. It acts as a major building block in a large class of medicinal compounds, and synthetic compounds exhibit a broad variety of remarkable biological and pharmaceutical activities. Several studies have been performed to improve the methodologies of 4-chromanone-derived compounds. This review focuses on the major synthetic methods of preparation reported on chroman-4-one derivatives from 2016 to 2021.

An overview of chiral separations of pharmaceutically active substances by HPLC (2018-2020)

This review provides a brief survey of chiral separation of pharmaceutically active substances published over the last 3 years (2018-2020). Chiral separation of drugs is an important area of research. The control of enantiomeric purity and determination of individual enantiomeric drug molecules is a necessity especially for clinical, analytical, and regulatory purposes. Among chromatographic resolution methods, high-performance liquid chromatography based on chiral stationary phases remains the most popular and effective method used for chiral separation of various drugs. In this review, attention is paid to several classes of chiral stationary phases that have been the most frequently used for drug enantioseparation during this period.

GRAPHIC ABSTRACT

A Food Supplement with Antioxidative Santa Herba Extract Modulates Energy Metabolism and Contributes to Weight Management

The plant Santa herba (Eriodictyon californicum) contains high flavonoids, thus potentially exerting beneficial effects in context of obesity, often accompanied by inflammation and metabolic imbalance. The study assessed the impact of Santa herba on oxidative stress, energy metabolism, weight reduction, and eating behavior, combining in vitro models with clinical data. Santa herba binding of the adenosine receptor A2A (ADORA2A) was assessed using a radioligand binding assay. A Caenorhabditis elegans model was used to determine mobility boosting effects, and Santa herba oxygen radical absorbance capacity (ORAC) values were determined in comparison to antioxidative plants. Clinical data, that is, body weight and appetite-related parameters, were obtained from overweight and obese women receiving either Santa herba or placebo for 12 weeks. Results showed that Santa herba extract binds to ADORA2A, stimulates C. elegans motility (+7.5%) and locomotion, and yields high antioxidative capacities (ORAC: 819 trolox equivalent). Clinical data, obtained from 24 overweight and 25 obese women (mean: 47.5 years), demonstrated a reduced body weight (P = .042) and body fat (P = .044), and by trend reduced leptin levels (P = .065) in women with obesity after Santa herba consumption compared to placebo. In conclusion, Santa herba extract has energizing and antioxidative properties and may aid in weight management of people with obesity. ClinicalTrials.gov Identifier: NCT03853603.

Modulation of the Neuroprotective and Anti-inflammatory Activities of the Flavonol Fisetin by the Transition Metals Iron and Copper

Alterations occur in the homeostasis of the transition metals iron (Fe2+) and copper (Cu2+) during aging and these are further amplified in neurodegenerative diseases, including Alzheimer's disease (AD). These observations suggest that the most effective drug candidates for AD might be those that can reduce these alterations. The flavonoid fisetin has both neuroprotective and anti-inflammatory activity both in vitro and in vivo and can bind both iron and copper suggesting that its chelating activity might play a role in its beneficial effects. To test this idea, the effects of iron and copper on both the neuroprotective and anti-inflammatory activities of fisetin were examined. It is shown that while fisetin can reduce the potentiation of cell death by iron and copper in response to treatments that lower glutathione levels, it is much less effective when the metals are combined with other inducers of oxidative stress. In addition, iron but not copper reduces the anti-inflammatory effects of fisetin in a dose-dependent manner. These effects correlate with the ability of iron but not copper to block the induction of the antioxidant transcription factor, Nrf2, by fisetin. In contrast, although the flavanone sterubin also binds iron, the metal has no effect on sterubin's ability to induce Nrf2 or protect cells from toxic or pro-inflammatory insults. Together, these results suggest that while iron and copper binding could contribute to the beneficial effects of neuroprotective compounds in the context of neurodegenerative diseases, the consequences of this binding need to be fully examined for each compound.

Sterubin: Enantioresolution and Configurational Stability, Enantiomeric Purity in Nature, and Neuroprotective Activity in Vitro and in Vivo

Alzheimer's disease (AD) is a neurological disorder with still no preventive or curative treatment. Flavonoids are phytochemicals with potential therapeutic value. Previous studies described the flavanone sterubin isolated from the Californian plant Eriodictyon californicum as a potent neuroprotectant in several in vitro assays. Herein, the resolution of synthetic racemic sterubin (1) into its two enantiomers, (R)-1 and (S)-1, is described, which has been performed on a chiral chromatographic phase, and their stereochemical assignment online by HPLC-ECD coupling. (R)-1 and (S)-1 showed comparable neuroprotection in vitro with no significant differences. While the pure stereoisomers were configurationally stable in methanol, fast racemization was observed in the presence of culture medium. We also established the occurrence of extracted sterubin as its pure (S)-enantiomer. Moreover, the activity of sterubin (1) was investigated for the first time in vivo, in an AD mouse model. Sterubin (1) showed a significant positive impact on short- and long-term memory at low dosages.