Synthesis of resveratrol using a direct decarbonylative Heck approach from resorcylic acid

Trends in the Potential of Stilbenes to Improve Plant Stress Tolerance: Insights of Plant Defense Mechanisms in Response to Biotic and Abiotic Stressors

Stilbenes belong to the naturally synthesized plant phytoalexins, produced de novo in response to various biotic and abiotic stressors. The importance of stilbenes in plant resistance to stress and disease is of increasing interest. However, the defense mechanisms and potential of stilbenes to improve plant stress tolerance have not been thoroughly reviewed. This work overviewed the pentose phosphate pathway, glycolysis pathway, shikimate pathway, and phenylalanine pathway occurred in the synthesis of stilbenes when plants are subjected to biotic and abiotic stresses. The positive implications and underlying mechanisms regarding defensive properties of stilbenes were demonstrated. Ten biomimetic chemosynthesis methods can underpin the potential of stilbenes to improve plant stress tolerance. The prospects for the application of stilbenes in agriculture, food, cosmetics, and pharmaceuticals industries are anticipated. It is hoped that some of the detailed ideas and practices may contribute to the development of stilbene-related products and improvement of plant resistance breeding.

Resveratrol-based biorefinery models for favoring its inclusion along the market value-added chains: A critical review

Resveratrol, a natural organic polyhydroxyphenolic compound, has gained significant attention in the last years given its potential health benefits, including antioxidant, anti-cancer, and anti-inflammatory properties. It can be directly extracted from plants, vegetables, and related products and waste resources, but also chemically/enzymatically/microbially synthesized. However, certain process strategies have some limitations, such as high costs, reduced yield or high energy demand, thus implying significant environmental loads. In this context, the search for more sustainable and circular process schemes is key to the integration of resveratrol into the market value chain of the food, cosmetic and pharmaceutical sectors. The extraction of resveratrol has traditionally been based on conventional methods such as solvent extraction, but advanced green extraction techniques offer more efficient and environmentally friendly alternatives. This review analyses both conventional and green alternative extraction technologies, as well as its bioproduction through microbial fermentation, in terms of production capacity, yield, purity and sustainability. It also presents alternative biorefinery models based on resveratrol bioproduction using by-products and waste streams as resources, specifically considering wine residues, peanut shells and wood bark as input resources, and also following a circular approach. This critical review provides some insight into the opportunities that resveratrol offers for promoting sustainable development and circularity in the related market value chains, and thus provides some criteria for decision making for biorefinery models in which resveratrol is one of the targeted high value-added products. It also identifies the future challenges to promote the inclusion of resveratrol in value chains, with the scale-up of green technologies and its demonstrated economic feasibility being the most prominent.

Denitrative Mizoroki–Heck reaction of unactivated alkenes

A general palladium-catalyzed denitrative Mizoroki–Heck reaction of unactivated alkenes has been developed with high E/Z selectivity.

Effect-directed analysis of estrogenic chemicals in sediments from an electronic-waste recycling area

Electronic waste (e-waste) pollution is of great concern due to the release of hazardous chemicals during the improper e-waste disposal. Many chemicals leached from e-waste were reported to pose estrogenic effects. To date, little is known regarding the occurrence and biological effects of estrogenic chemicals in sediments near an e-waste area. In this study, an effect-directed analysis (EDA) is applied to determine the estrogenic chemicals in sediments of four sites collected from a typical e-waste recycling city in China. Following screening with the ER-CALUX assay, the extract of sample with the most potent effect was subjected in fractionation using reverse phase liquid chromatography. Based on a target analysis for the active fractions, four compounds, including estrone, 17β-estradiol, 17α-ethinylestradiol and bisphenol A, were identified, and these contributed to 17% of the total toxic effects in the sample. A further nontarget analysis screened four candidates, namely diethylstilbestrol (DES), hexestrol (HES), nandrolone and durabolin, and the total contribution was found to be 48% from the active sample. Specifically, DES and HES were only detected in the active sample and were found to be the primary drivers of estrogenic effects. An examination of the identified chemicals in the four sites indicated that these estrogenic chemicals may originate from e-waste recycling, livestock excretion and domestic waste. These findings uncovered the estrogenic pollutants in sediments from an e-waste area. Considering single endpoint in biological assay is not abundant to screen chemicals with different toxic effects, further EDA studies with multiple endpoints are required to better understand the occurrence of representative or unknown chemicals in e-waste-polluted areas.

Polyhydroxybenzoic acid derivatives as potential new antimalarial agents

With more than 200 million cases and 400,000 related deaths, malaria remains one of the deadliest infectious diseases of 2021. Unfortunately, despite the availability of efficient treatments, we have observed an increase in people infected with malaria since 2015 (from 211 million in 2015 to 229 million in 2019). This trend could partially be due to the development of resistance to all the current drugs. Therefore, there is an urgent need for new alternatives. We have, thus, selected common natural scaffolds, polyhydroxybenzoic acids, and synthesized a library of derivatives to better understand the structure-activity relationships explaining their antiplasmodial effect. Only gallic acid derivatives showed a noticeable potential for further developments. Indeed, they showed a selective inhibitory effect on Plasmodium (IC₅₀ ~20 µM, SI > 5) often associated with interesting water solubility. Moreover, this has confirmed the critical importance of free phenolic functions (pyrogallol moiety) for the antimalarial effect. Methyl 4-benzoxy-3,5-dihydroxybenzoate (39) has, for the first time, been recognized as a potential lead for future research because of its marked inhibitory activity against Plasmodium falciparum and its significant hydrosolubility (3.72 mM).

Pd-Catalyzed Cross-Coupling of Organostibines with Styrenes to Give Unsymmetric (E)-Stilbenes and (1E,3E)-1,4-Diarylbuta-1,3-dienes and Fluorescence Properties of the Products

A general and effective palladium-catalyzed cross-coupling of organostibines with styrenes to give (E)-olefins was disclosed. By the use of an organostibine reagent, this method can produce unsymmetric (E)-1,2-diarylethylenes and (1E,3E)-1,4-diarylbuta-1,3-dienes in good yields with high E/Z selectivity and good functional group tolerance. Resveratrol and DMU-212 were synthesized in high yield. The protocol can be extended to the synthesis of (1E,3E,5E)-1,6-diphenylhexa-1,3,5-triene in 40% yield. Products 5e, 5f, and 7a showed good photoluminescence quantum yields ranging from 72 to 99%.

Resveratrol: a review of plant sources, synthesis, stability, modification and food application

Resveratrol, a stilbene molecule belonging to the polyphenol family, is usually extracted from a great many natural plants. The technologies of preparation and extraction methods are developing rapidly. As resveratrol has many beneficial properties, it has been widely utilized in food and medicine industry. In terms of its structure, it is susceptible to degradation and can undergo chemical changes during food processing. Different studies have therefore given more attention to various aspects of resveratrol, including anti-aging, anti-oxidant, and anti-cancer activity. This review classifies the study of resveratrol, considers plant sources, synthesis, stability, common reactions, and food applications, and provides references to boost its food and medical utilization. © 2019 Society of Chemical Industry.

A Biocompatible Heterogeneous MOF-Cu Catalyst for In Vivo Drug Synthesis in Targeted Subcellular Organelles

As a typical bioorthogonal reaction, the copper-catalyzed azide-alkyne cycloaddition (CuAAC) has been used for drug design and synthesis. However, for localized drug synthesis, it is important to be able to determine where the CuAAC reaction occurs in living cells. In this study, we constructed a heterogeneous copper catalyst on a metal-organic framework that could preferentially accumulate in the mitochondria of living cells. Our system enabled the localized synthesis of drugs through a site-specific CuAAC reaction in mitochondria with good biocompatibility. Importantly, the subcellular catalytic process for localized drug synthesis avoided the problems of the delivery and distribution of toxic molecules. In vivo tumor therapy experiments indicated that the localized synthesis of resveratrol-derived drugs led to greater antitumor efficacy and minimized side effects usually associated with drug delivery and distribution.

Synthesis of resveratrol derivatives as new analgesic drugs through desensitization of the TRPA1 receptor

A series of 31 resveratrol derivatives was designed, synthesized and evaluated for activation and inhibition of the TRPA1 channel. Most acted as activators and desensitizers of TRPA1 channels like resveratrol or allyl isothiocyanate (AITC). Compound 4z (HUHS029) exhibited higher inhibitory activity than resveratrol with an IC₅₀ value of 16.1μM. The activity of 4z on TRPA1 was confirmed in TRPA1-expressing HEK293 cells, as well as in rat dorsal root ganglia neurons by a whole cell patch clamp recording. Furthermore, pretreatment with 4z exhibited an analgesic effect on AITC-evoked TRPA1-related pain behavior in vivo.

A facile and rapid access to resveratrol derivatives and their radioprotective activity

A facile and rapid access to resveratrol derivatives has been achieved based on palladium-catalyzed oxidative Heck reaction of aryl boronic acids with styrenes followed by demethylation in moderate to good yields. A series of resveratrol derivatives with various functional groups has been synthesized easily. The radioprotective activity of synthesized compounds has also been evaluated using rat thymocytes. The results revealed that some resveratrol derivatives efficiently protected the thymocytes from radiation-induced apoptosis.

The Application of Template Selectophores for the Preparation of Molecularly Imprinted Polymers

Molecularly imprinted polymers are versatile materials with wide application scope for the detection, capture and separation of specific compounds present in complex feed stocks. A major challenge associated with their preparation has been the need to sacrifice one mole equivalent of the template molecule to generate the complementary polymer cavities that selectively bind the target molecule. Moreover, template molecules can often be difficult to synthesise, expensive or lack stability. In this study, we describe a new approach, directed at the use of synthetic selectophores, chosen as readily prepared and low cost structural analogues with recognition groups in similar three-dimensional arrangements as found in the target molecule. To validate the approach, a comparative study of selectophores related to the polyphenolic compound (E)-resveratrol has been undertaken using traditional and green chemical synthetic approaches. These molecular mimic compounds were employed as polymer templates and also as binding analytes to interrogate the recognition sites associated with the molecularly imprinted polymers. Importantly, the study confirms that the use of selectophores has the potential to confer practical advantages, including access to more efficient methods for selection and preparation of suitable template molecules with a broader range of molecular diversity, as well as delivering imprinted polymers capable of recognizing the target compound and structurally related products.

Translating endoplasmic reticulum biology into the clinic: a role for ER-targeted natural products?

ER stress has been identified as a hallmark, and sometimes trigger, of several pathologies, notably cancer, inflammation and neurodegenerative diseases like Alzheimer's and Parkinson's. Among the molecules described in literature known to affect ER function, the majority are natural products, suggesting that natural molecules may constitute a significant arsenal of chemical entities for modulating this cellular target. In this review, we will start by presenting the current knowledge of ER biology and the hallmarks of ER stress, thus paving the way for presenting the natural products that have been described as being ER modulators, either stress inducers or ER protectors. The chemistry, distribution and mechanism of action of these compounds will be presented and discussed.

Olefins from biomass feedstocks: catalytic ester decarbonylation and tandem Heck-type coupling

Catalytic method employs “masked” carboxylic acids to yield alkenes, via decarbonylation and/or C–C coupling of activated esters.

FeCl3-promoted and ultrasound-assisted synthesis of resveratrol O-derived glycoside analogs

Phenol derived O-glycosides were synthesized using a direct and convenient O-glycosidation, starting from acetylated sugars in the presence of FeCl3, an inexpensive, mild and benign Lewis acid catalyst. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with conventional conditions leading to the corresponding β-O-glycosides as the major anomer. Post-synthetic transformations of iodophenol intermediates led to new resveratrol O-glycoside analogs in good overall yields.

Inhibition of cancer derived cell lines proliferation by synthesized hydroxylated stilbenes and new ferrocenyl-stilbene analogs. Comparison with resveratrol

Further advances in understanding the mechanism of action of resveratrol and its application require new analogs to identify the structural determinants for the cell proliferation inhibition potency. Therefore, we synthesized new trans-resveratrol derivatives by using the Wittig and Heck methods, thus modifying the hydroxylation and methoxylation patterns of the parent molecule. Moreover, we also synthesized new ferrocenylstilbene analogs by using an original protective group in the Wittig procedure. By performing cell proliferation assays we observed that the resveratrol derivatives show inhibition on the human colorectal tumor SW480 cell line. On the other hand, cell viability/cytotoxicity assays showed a weaker effects on the human hepatoblastoma HepG2 cell line. Importantly, the lack of effect on non-tumor cells (IEC18 intestinal epithelium cells) demonstrates the selectivity of these molecules for cancer cells. Here, we show that the numbers and positions of hydroxy and methoxy groups are crucial for the inhibition efficacy. In addition, the presence of at least one phenolic group is essential for the antitumoral activity. Moreover, in the series of ferrocenylstilbene analogs, the presence of a hidden phenolic function allows for a better solubilization in the cellular environment and significantly increases the antitumoral activity.

Improved synthesis of bioactive stilbene derivatives applying design of experiments to the Heck–Matsuda reaction

Design of experiments (DOE) was instrumental to optimize reaction conditions which allowed the efficient synthesis of key bioactive stilbenes.

Scope and limitations of the Heck-Matsuda-coupling of phenol diazonium salts and styrenes: a protecting-group economic synthesis of phenolic stilbenes

4-Phenol diazonium salts undergo Pd-catalyzed Heck reactions with various styrenes to 4'-hydroxy stilbenes. In almost all cases higher yields and fewer side products were observed, compared to the analogous 4-methoxy benzene diazonium salts. In contrast, the reaction fails completely with 2- and 3-phenol diazonium salts. For these substitution patterns the methoxy-substituted derivatives are superior.

A new synthesis of 4'-resveratrol esters and evaluation of the potential for anti-depressant activity

The 4'-ester analog of the disease preventative resveratrol 1 (RV), 4'-acetyl-RV 2 along with 4'-pivaloate 13 and benzoate 14 RV were synthesized. The previously developed palladium catalyzed decarbonylative Heck coupling was used to assemble the stilbene core together with 3,5-dibenzyl protected phenol intermediates that allowed for efficient coupling and deprotection using boron trifluoride etherate. Studies with Long-Evans rats were performed to establish safety, toxicity, and behavioral parameters. In addition, the Porsalt forced-swim test was used to demonstrate anti-depressant activity.

Immobilization of laccase for oxidative coupling of trans-resveratrol and its derivatives

Trametes Villosa Laccase (TVL) was immobilized through physical adsorption on SBA-15 mesoporous silica and the immobilized TVL was used in the oxidative coupling of trans-resveratrol. Higher loading and activity of the immobilized enzyme on SBA-15 were obtained when compared with the free enzyme. The effects of reaction conditions, such as buffer type, pH, temperature and substrate concentration were investigated, and the optimum conditions were screened and resulted in enzyme activity of up to 10.3 μmol/g·h. Furthermore, the oxidative couplings of the derivatives of trans-resveratrol were also catalyzed by immobilized TVL. The immobilized TVL was recyclable and could maintain 78% of its initial activity after reusing it four times.

Enrichment of (E)-resveratrol from peanut byproduct with molecularly imprinted polymers

Molecularly imprinted solid phase extraction (MISPE) has been employed to isolate and concentrate bioactive polyphenols from peanut press waste. To this end, a molecularly imprinted polymer (MIP) templated with the phytoalexin (E)-resveratrol has been prepared via self-assembly with the functional monomer 4-vinylpyridine (4VP) in a 1:3 molar ratio. Subsequent molecular interrogation of the MIP binding sites demonstrated preferential structural selectivity for (E)-resveratrol with respect to other structurally related naturally occurring compounds. This selectivity was subsequently exploited to achieve substantial sample cleanup of peanut press waste under aqueous conditions with significant enrichment of (E)-resveratrol (>60 fold) requiring minimal sample preparation.

Ex situ generation of stoichiometric and substoichiometric 12CO and 13CO and its efficient incorporation in palladium catalyzed aminocarbonylations

A new technique for the ex situ generation of carbon monoxide (CO) and its efficient incorporation in palladium catalyzed carbonylation reactions was achieved using a simple sealed two-chamber system. The ex situ generation of CO was derived by a palladium catalyzed decarbonylation of tertiary acid chlorides using a catalyst originating from Pd(dba)(2) and P(tBu)(3). Preliminary studies using pivaloyl chloride as the CO-precursor provided an alternative approach for the aminocarbonylation of 2-pyridyl tosylate derivatives using only 1.5 equiv of CO. Further design of the acid chloride CO-precursor led to the development of a new solid, stable, and easy to handle source of CO for chemical transformations. The synthesis of this CO-precursor also provided an entry point for the late installment of an isotopically carbon-labeled acid chloride for the subsequent release of gaseous [(13)C]CO. In combination with studies aimed toward application of CO as the limiting reagent, this method provided highly efficient palladium catalyzed aminocarbonylations with CO-incorporations up to 96%. The ex situ generated CO and the two-chamber system were tested in the synthesis of several compounds of pharmaceutical interest and all of them were labeled as their [(13)C]carbonyl counterparts in good to excellent yields based on limiting CO. Finally, palladium catalyzed decarbonylation at room temperature also allowed for a successful double carbonylation. This new protocol provides a facile and clean source of gaseous CO, which is safely handled and stored. Furthermore, since the CO is generated ex situ, excellent functional group tolerance is secured in the carbonylation chamber. Finally, CO is only generated and released in minute amounts, hence, eliminating the need for specialized equipment such as CO-detectors and equipment for running high pressure reactions.

Natural stilbenes: an overview

Natural stilbenes have been a hot research topic due to their intricate structures and diverse biological activities. Although their molecular backbone consists only of 1,2-diphenylethylene units, stilbenes show an enormous diversity with regard to the different units present, the degree of polymerisation, and the pattern of oligomer construction. From January 1995 to the end of 2008, more than 400 new naturally occurring stilbenes were isolated and identified, and this review focuses on their structural diversity, distribution, and bioactivity.

Biotransformation of piceid in Polygonum cuspidatum to resveratrol by Aspergillus oryzae

Biotransformation of piceid in Polygonum cuspidatum to resveratrol by Aspergillus oryzae was investigated in this study. Resveratrol is widely used in medicine, food, and cosmetic because of its pharmacological properties. However, it has a much lower content in plants compared with its glucoside piceid, which has a much lower bioavailability. Traditionally, the aglycone is acquired by acid or enzymatic hydrolysis of its glucoside, but the violent condition and the acid pollution in hydrolytic reaction and the high cost of the enzyme limit their industrial development. In this paper, fermentation of P. cuspidatum by A. oryzae was successfully performed, during which, piceid was converted to resveratrol with the highest yield of trans-resveratrol 1.35%, 3.6 times higher than that obtained from raw herb by microwave-assisted extraction. Scale-up production was also performed and the yield of trans-resveratrol was 3.1 times higher after 24 h incubation. Therefore, biotransformation is a better method to increase the yield of resveratrol because of its high yield and mild conditions.

Design and synthesis of compounds that extend yeast replicative lifespan

This past decade has seen the identification of numerous conserved genes that extend lifespan in diverse species, yet the number of compounds that extend lifespan is relatively small. A class of compounds called STACs, which were identified as activators of Sir2/SIRT1 NAD+-dependent deacetylases, extend the lifespans of multiple species in a Sir2-dependent manner and can delay the onset of age-related diseases such as cancer, diabetes and neurodegeneration in model organisms. Plant-derived STACs such as fisetin and resveratrol have several liabilities, including poor stability and relatively low potency as SIRT1 activators. To develop improved STACs, stilbene derivatives with modifications at the 4' position of the B ring were synthesized using a Horner-Emmons-based synthetic route or by hydrolyzing deoxyrhapontin. Here, we describe synthetic STACs with lower toxicity toward human cells, and higher potency with respect to SIRT1 activation and lifespan extension in Saccharomyces cerevisiae. These studies show that it is possible to improve upon naturally occurring STACs based on a number of criteria including lifespan extension.