Stilbenes of Gnetum ula

Gnetin, a new stilbene isolated from Gnetum ula is assigned the structure 3,4-methylenedioxy-4′-methoxy-trans-stilbene, 3 on the basis of spectroscopic data and synthesis. The structure 3,3′,4-trihydroxy-2-methoxy-trans-stilbene, 1a earlier assigned to a trihydroxymonomethoxy stilbene is now revised to 3,4,5′-trihydroxy-3′-methoxy-trans-stilbene, 1b.     

Synthesis, in vitro and in silico evaluation of novel trans-stilbene analogues as potential COX-2 inhibitors

25 new trans-stilbene and trans-stilbazole derivatives were investigated using in vitro and in silico techniques. The selectivity and potency of the compounds were assessed using commercial ELISA test. The obtained results were incorporated into 2D QSAR assay. The most promising compound 4-nitro-3′,4′,5′-trihydroxy-trans-stilbene (N1) was synthetized and its potency and selectivity were confirmed. N1 was classified as preferential COX-2 inhibitor. Its ability to inhibit COX-2 in MCF-7 cell line was established and its cytotoxicity by MTT test was assessed. The compound was more cytotoxic than celecoxib within studied concentration range. Finally, the investigated trans-stilbene was docked into COX-1 and COX-2 active sites using “CDOCKER” protocol.     

A DFT method for the study of the antioxidant action mechanism of resveratrol derivatives

Quantum-chemical calculations using DFT, have been performed to explain the molecular structure antioxidant activity relationship of resveratrol (RSV) (1) analogues: 3,4-dihydroxy-trans-stilbene (3,4-DHS) (2); 4,4′-dihydroxy-trans-stilbene (4,4′-DHS) (3); 4-hydroxy-trans-stilbene (4-HS) (4); 3,5-dihydroxy-trans-stilbene (3,5-DHS) (5); 3,3′-dimethoxy-4,4′-dihydroxy-trans-stilbene (3,3′-DM-4,4′-DHS) (6); 2,4-dihydroxy-trans-stilbene (2,4-DHS) (7) and 2,4,4′-trihydroxy-trans-stilbene (2,4,4′-THS) (8). It was found that all compounds studied were effective antioxidants with the exception of 3, 5-DHS. The high antioxidant activity of both 3, 3′-DM-4, 4′-DHS and 3, 4-DHS may be due to the abstraction of the two hydrogen atoms of the para and ortho-position hydroxyls respectively, to form a quinone structure. Our results revealed that the antioxidant pharmacophore of 2,4-DHS and 2,4,4′-THS, exhibiting higher antioxidant activity than resveratrol, is the 2-hydroxystilbene, rather than 4-hydroxystilbene. Experimental observations were satisfactorily explained and commented.     

Cytotoxic,tubulin-interfering and proapoptotic activities of 4′-methylthio-<Emphasis Type="Italic">trans</Emphasis>-stilbene derivatives,analogues of <Emphasis Type="Italic">trans</Emphasis>-resveratrol

The aim of this study was to evaluate the cytotoxicity of a series of seven 4′-methylthio-trans-stilbene derivatives against cancer cells: MCF7 and A431 in comparison with non-tumorigenic MCF12A and HaCaT cells. The mechanism of anti-proliferative activity of the most cytotoxic trans-resveratrol analogs: 3,4,5-trimethoxy-4′-methylthio-trans-stilbene (3,4,5-MTS) and 2,4,5-trimethoxy-4′-methylthio-trans-stilbene (2,4,5-MTS) was analyzed and compared with the effect of trans-resveratrol. All the compounds that were studied exerted a stronger cytotoxic effect than trans-resveratrol did. MCF7 cells were the most sensitive to the cytotoxic effect of trans-resveratrol analogs with IC₅₀ in the range of 2.1–6.0 µM. Comparing the cytotoxicity of 3,4,5-MTS and 2,4,5-MTS, a significantly higher cytotoxic activity of these compounds against MCF7 versus MCF12A was observed, whereas no significant difference was observed in cytotoxicity against A431 and HaCaT. In the series of 4′-methylthio-trans-stilbenes, 3,4,5-MTS and 2,4,5-MTS were the most promising compounds for further mechanistic studies. The proapoptotic activity of 3,4,5-MTS and 2,4,5-MTS, estimated with the use of annexin-V/propidium iodide assay, was comparable to that of trans-resveratrol. An analysis of cell cycle distribution showed a significant increase in the percentage of apoptotic cells and G2/M phase arrest in MCF7 and A431 as a result of treatment with 3,4,5-MTS, whereas trans-resveratrol tended to increase the percentage of cells in S phase, particularly in epithelial breast cells MCF12A and MCF7. Both trans-stilbene derivatives enhanced potently tubulin polymerization in a dose-dependent manner with sulfur atom participating in the interactions with critical residues of the paclitaxel binding site of β-tubulin.     

DNA damage induced by resveratrol and its synthetic analogues in the presence of Cu (II) ions: Mechanism and structure-activity relationship

The prooxidant effect of resveratrol (3,5,4′-trihydroxy-trans-stibene) and its synthetic analogues (ArOH), that is, 3,4,4′-trihydroxy-trans-stibene (3,4,4′-THS), 3,4,5-trihydroxy-trans-stibene (3,4,5-THS), 3,4-dihydroxy-trans-stibene (3,4-DHS), 4,4′-dihydroxy-trans-stibene (4,4′-DHS), 2,4-dihydroxy-trans-stilbene (2,4-DHS), 3,5-dihydroxy-trans-stilbene (3,5-DHS) and 3,5,4′-trimethoxy-trans-stibene (3,5,4′-TMS), on supercoiled pBR322 plasmid DNA strand breakage and calf thymus DNA damage in the presence of Cu (II) ions has been studied. It was found that the compounds bearing ortho-dihydroxyl groups (3,4-DHS, 3,4,4′-THS, and 3,4,5-THS) or bearing 4-hydroxyl groups (2,4-DHS, 4,4′-DHS, and resveratrol) exhibit remarkably higher activity in the DNA damage than the ones bearing no such functionalities. Kinetic analysis by UV-visible spectra demonstrates that the formation of ArOH-Cu (II) complexes, the stabilization of oxidative intermediate derived from ArOH and Cu (II)/Cu (I) redox cycles, might be responsible for the DNA damage. This study also reveals a good correlation between antioxidant and prooxidant activity, as well as cytotoxicity against human leukemia (HL-60 and Jurkat) cell lines. The mechanisms and implications of these observations are discussed.     

Isolation and Characterization of a Stilbene-degrading Strain of Pseudomonas fluorescens,and Production of Antioxidant Compounds by Stilbene Metabolism

In this study, we consider the use of hydrocarbon-degrading bacteria that degrade trans-stilbene as a novel approach for synthesizing potentially bioactive hydroxylated stilbenes. A trans-stilbene-degrading bacterium, MN2, was isolated from activated sludge through enrichment culture, and identified as Pseudomonas fluorescens using conventional techniques. Degradation of trans-stilbene by this strain yielded two metabolites that had significant antioxidant activity.     

Antioxidant effects and hepatoprotective activity of 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene from Morus bombycis Koidzumi roots on CCl4-induced liver damage

We investigated hepatoprotective activity and antioxidant effect of the 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene that purified from Morus bombycis Koidzumi roots against CCl₄-induced liver damage in rats. The 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene displayed dose-dependent superoxide radical scavenging activity (IC₅₀ = 430.2 μg/ml), as assayed by the electron spin resonance (ESR) spin-trapping technique. The increase in aspartate aminotransferase (AST) activities in serum associated with carbon tetrachloride (CCl₄)-induced liver injury was inhibited by 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene and at a dose of 400 ～ 600 mg/kg samples had hepatoprotective activity comparable to the standard agent, silymarin. The biochemical assays were confirmed by histological observations showing that the 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene decreased cell ballooning in response to CCl₄ treatment. These results demonstrate that the 2,5-dihydroxy-4,3′-di(β-d-glucopyranosyloxy)-trans-stilbene is a potent antioxidant with a liver protective action against CCl₄-induced hepatotoxicity.     

Rat liver DT-diaphorase: regulation of functional mRNA levels by 3-methylcholanthrene, trans-stilbene oxide, and phenobarbital

Total liver poly(A⁺)-RNA isolated from untreated, and 3-methylcholanthrene-, trans-stilbene oxide-, and phenobarbital-treated rats has been translated in the rabbit reticulocyte lysate system in order to determine the effect of these xenobiotics on the level of translationally active DT-diaphorase mRNA. The in vitro translation systems were subjected to immunoprecipitation with rabbit IgG raised against purified DT-diaphorase and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The identity of the radiolabeled, immunoprecipitated product as DT-diaphorase was confirmed by limited peptide mapping using Staphylococcus aureus V-8 protease. These quantitation results demonstrate that 3-methylcholanthrene leads to an eightfold elevation in functional DT-diaphorase mRNA at 8 h after a single administration of 3-methylcholanthrene; whereas, trans-stilbene oxide and phenobarbital produced only a modest elevation, two- to three-fold, in the functional DT-diaphorase mRNA level. These data indicate that the increase in the level of DT-diaphorase after 3-methylcholanthrene administration noted previously [B. Höjeberg, K. Blomberg, S. Stenberg, and C. Lind (1981)Arch. Biochem. Biophys.207, 205–216] can be totally accounted for by an elevation in the mRNA level specific for this protein.     

trans-Stilbene degradation by Arthrobacter sp. SL3 cells

trans-Stilbene degradation was examined by the reaction using resting cells of microorganisms isolated through the enrichment culture using trans-stilbene. The strain SL3, showing the highest trans-stilbene-degrading activity, was identified as Arthrobacter sp. One of the reaction products was identified to be cis,cis-muconic acid. Arthrobacter sp. SL3 cells also transformed benzaldehyde, benzoic acid and catechol into cis,cis-muconic acid, suggesting that one benzene ring of trans-stilbene was converted into cis,cis-muconic acid via benzaldehyde formed by its C_α=C_β bond cleavage.     

Cloning and characterization of a microsomal epoxide hydrolase from Heliothis virescens

Epoxide hydrolases (EHs) are α/β-hydrolase fold superfamily enzymes that convert epoxides to 1,2-trans diols. In insects EHs play critical roles in the metabolism of toxic compounds and allelochemicals found in the diet and for the regulation of endogenous juvenile hormones (JHs). In this study we obtained a full-length cDNA, hvmeh1, from the generalist feeder Heliothis virescens that encoded a highly active EH, Hv-mEH1. Of the 10 different EH substrates that were tested, Hv-mEH1 showed the highest specific activity (1180 nmol min^?1 mg^?1) for a 1,2-disubstituted epoxide-containing fluorescent substrate. This specific activity was more than 25- and 3900-fold higher than that for the general EH substrates cis-stilbene oxide and trans-stilbene oxide, respectively. Although phylogenetic analysis placed Hv-mEH1 in a clade with some lepidopteran JH metabolizing EHs (JHEHs), JH III was a relatively poor substrate for Hv-mEH1. Hv-mEH1 showed a unique substrate selectivity profile for the substrates tested in comparison to those of MsJHEH, a well-characterized JHEH from Manduca sexta, and hmEH, a human microsomal EH. Hv-mEH1 also showed unique enzyme inhibition profiles to JH-like urea, JH-like secondary amide, JH-like primary amide, and non-JH-like primary amide compounds in comparison to MsJHEH and hmEH. Although Hv-mEH1 is capable of metabolizing JH III, our findings suggest that this enzymatic activity does not play a significant role in the metabolism of JH in the caterpillar. The ability of Hv-mEH1 to rapidly hydrolyze 1,2-disubstituted epoxides suggests that it may play roles in the metabolism of fatty acid epoxides such as those that are commonly found in the diet of Heliothis.     

Synthesis and biological evaluation of cis-restrained carbocyclic combretastatin A-4 analogs: Influence of the ring size and saturation on cytotoxic properties

Combretastatin A-4 (CA-4) is a highly cytotoxic natural product and several derivatives have been prepared which underwent clinical trial. These investigations revealed that the cis-stilbene moiety of the natural product is prone to undergo cis/trans isomerization under physiological conditions, reducing the overall activity of the drug candidates. Herein, we report the preparation of cis-restrained carbocyclic analogs of CA-4. The compounds, which differ by the size and hybridization of the carbocyclic ring have been evaluated for their cytotoxic properties and their ability to inhibit tubulin polymerization. Biological data, supported by molecular docking studies, identified cyclobutenyl and cyclobutyl derivatives of the natural product as highly promising drug candidates.     

4,4′-Dihydroxy-trans-stilbene,a resveratrol analogue,exhibited enhanced antioxidant activity and cytotoxicity

Resveratrol (3,5,4′-trans-trihydroxystibene) is a natural phytoalexin present in grapes and red wine, which possesses a variety of biological activities including antioxidant activity. In order to find more active antioxidant with resveratrol as the lead compound we synthesized 4,4′-dihydroxy-trans-stilbene (4,4′-DHS). The antioxidant activities of resveratrol and 4,4′-DHS were evaluated by the reaction kinetics with galvinoxyl radical or Cu(II) ions, and the inhibition effects against free-radical-induced peroxidation of human erythrocyte ghosts. It was found that 4,4′-DHS exhibits remarkably higher antioxidant activity than resveratrol. The oxidative products of resveratrol and 4,4′-DHS in the presence of Cu(II) in acetonitrile were identified as the dihydrofuran dimers by spectroscopic method, and the antioxidant mechanism for 4,4′-DHS was proposed. In addition, 4,4′-DHS exhibits remarkably higher cytotoxicity against human promyelocytic leukemia (HL-60) cells than resveratrol.     

Identification of thetrans-stilbene oxide-active glutathione transferase in human mononuclear leukocytes and in liver as GST1

A glutathione transferase from human mononuclear leukocytes with a high activity towardtrans-stilbene oxide (GT-tSBO) has been studied in liver and blood from fetus and adults and in blood from neonates. Using starch gel electrophoresis, different phenotypes of GST1 have been determined, GST1 0, GST1 1, and GST1 2. As judged from activity measurements and the fact that only those individuals who express the null allele of GST1, the GST1 0, which has a low activity towardtrans-stilbene oxide, it is concluded that the hepatic transferase GST1 is identical to GT-tSBO, as well as to hepatic transferase μ. In addition, it has been shown that the different genotypes of GST1 1 (GST1 1-1, GST1 1-0) and GST1 2 (GST1 2-2, GST1 2-0) can be separated by measuring the GT-tSBO activity in whole blood from the same individual. It is also demonstrated that GT-tSBO activity is much lower in fetal liver, approximately 10 times, compared with adult liver, while this activity seems to be unchanged in the blood from fetus and adults, as well as in neonates.     

Radiometric assays for mammalian epoxide hydrolases and glutathione S-transferase

A number of epoxides, including cis- and trans-stilbene oxides, were assayed as substrates for epoxide hydrolases (EHs) by gas-liquid chromatography. Radiolabeled stilbene oxides were prepared by sodium borotritide reduction of desyl chloride followed by ring closure with base treatment. Rapid radiometric assays for EHs were performed by differential partitioning of the epoxide into dodecane, while the product diol remained in the aqueous phase. Glutathione (GSH) transferase was similarly assayed by partitioning the epoxide and diol, if formed metabolically, into 1-hexanol, while the GSH conjugate was retained in the aqueous phase. The cytosolic EH rapidly hydrates the trans isomer while the cis is very poorly hydrated. In contrast, the cis is a better substrate for the microsomal EH than the trans. GSH transferase utilized both epoxides as substrates, but conjugation is faster with the cis isomer. Cytosolic EH activity is high in mouse but very low in rat and guinea pig. Microsomal EH activity, in contrast, is highest in guinea pig, intermediate in rat, and the lowest in mouse. GSH transferase activity, which is high in all three species, can be inhibited by chalcone, with an I₅₀ of 3.1 × 10^?5m. These assays facilitate the rapid evaluation and direct comparison of epoxide-metabolizing systems in cell homogenates used in short-term mutagenicity assays, cell or organ culture, and possibly in vivo.     

C-N-palladacyclic-catalyzed Heck reaction in EGME/water: Rate and regioselectivity controlled by the solvents ratio

Novel as well as known C,N-palladacyclic neutral complexes were tested as precatalyst in the Heck reaction between bromobenzene and styrene under aerobic conditions. The catalytic system Pd(II) complex/K₂CO₃/EGME-H₂O (EGME = ethylene glycol monomethyl ether) showed to be highly efficient. Best performances of the catalysts were achieved by controlling the amount of water: generally a H₂O content within the 25-50% v/v range resulted in the highest conversion of the substrates into trans-stilbene. As a matter of fact, bromobenzene and styrene can be converted quantitatively using only 0.01 mol% of precatalyst with very high regioselectivity for the trans product and with a TOF of 10 000 h⁻¹. In the absence of water, all complexes were less efficient and differences in their activity were found, while such a differentiation disappeared when water was added.     

Tubulin-interactive stilbene derivatives as anticancer agents

Microtubules are dynamic polymers that occur in eukaryotic cells and play important roles in cell division, motility, transport and signaling. They form during the process of polymerization of α- and β-tubulin dimers. Tubulin is a significant and heavily researched molecular target for anticancer drugs. Combretastatins are natural cis-stilbenes that exhibit cytotoxic properties in cultured cancer cells in vitro. Combretastatin A-4 (3′-hydroxy-3,4,4′, 5-tetramethoxy-cis-stilbene; CA-4) is a potent cytotoxic cis-stilbene that binds to β-tubulin at the colchicine-binding site and inhibits tubulin polymerization. The prodrug CA-4 phosphate is currently in clinical trials as a chemotherapeutic agent for cancer treatment. Numerous series of stilbene analogs have been studied in search of potent cytotoxic agents with the requisite tubulin-interactive properties. Microtubule-interfering agents include numerous CA-4 and transresveratrol analogs and other synthetic stilbene derivatives. Importantly, these agents are active in both tumor cells and immature endothelial cells of tumor blood vessels, where they inhibit the process of angiogenesis. Recently, computer-aided virtual screening was used to select potent tubulin-interactive compounds. This review covers the role of stilbene derivatives as a class of antitumor agents that act by targeting microtubule assembly dynamics. Additionally, we present the results of molecular modeling of their binding to specific sites on the α- and β-tubulin heterodimer. This has enabled the elucidation of the mechanism of stilbene cytotoxicity and is useful in the design of novel agents with improved anti-mitotic activity. Tubulin-interactive agents are believed to have the potential to play a significant role in the fight against cancer.     

The 4′-hydroxy group is responsible for the in vitro cytogenetic activity of resveratrol

We previously reported that 3,5,4′-trihydroxy-trans-stilbene (resveratrol), a polyphenolic phytoalexin found in grapes, induces a high frequency of sister chromatid exchanges (SCEs) in vitro. In this study, to investigate structure activity relationships, we synthesized six analogues of resveratrol differing in number and position of hydroxy groups, and we investigated their activity in chromosomal aberration (CA), micronucleus (MN) and sister chromatid exchange (SCE) tests in a Chinese hamster cell line (CHL). Two of the six analogues (3,4′-dihydroxy-trans-stilbene and 4-hydroxy-trans-stilbene) showed clear positive responses in a concentration-dependent manner in all three tests. Both were equal to or stronger than resveratrol in genotoxicity. The 4′-hydroxy (OH) analogue had the simplest chemical structure and was the most genotoxic. The other analogues did not have a 4′-hydroxy group. These results suggested that a 4′-hydroxy group is essential to the genotoxicity of stilbenes.     

Synthesis of metabolic intermediates of diethylstilbestrol

This report details the synthesis of 1) 3,4,4′-trihydroxy-α,α′-diethyl-trans-stilbene; 2) 3,4-bis-(p-hydroxyphenyl)-trans-3-hexenol; 3) 3,4-bis-(p-hydroxyphenyl)-2,4-cis,cis-hexadienol; 4) 3,4-bis-(3′-methoxy-4′-hydroxyphenyl)-trans-3-hexene; 5) 3,4-bis-(3′, 4′-dimethoxyphenyl)-trans-3-hexene. These compounds are suspected metabolites of diethylstilbestrol.     

3,4,4′-Trihydroxy-trans-stilbene,an analogue of resveratrol,is a potent antioxidant and cytotoxic agent

Abstract

Resveratrol (3,5,4′-trihydroxy-trans-stilbene) is a naturally occurring polyphenol widely distributed in food and dietary plants. This phytochemical has been intensively studied as an efficient antioxidant and anticancer agent, and a variety of substituted stilbenes have been developed in order to improve the potency of resveratrol. In this work, we described the synthesis of 3,4,4 -trihydroxy-trans-stilbene (3,4,4′-THS), an analogue of resveratrol, and studied its antioxidant and cytotoxic activity in vitro. 3,4,4 -THS was much more efficient than resveratrol in protecting against free radical-induced lipid peroxidation, photo-sensitized DNA oxidative damage, and free radical-induced hemolysis of human red blood cells. More potent growth inhibition in cultured human leukemia cells (HL-60) was also observed for 3,4,4 -THS. The relationship between the antioxidant efficiency and cytotoxic activity was discussed, with the emphasis on inhibition of the free radical enzyme ribonucleotide reductase by antioxidants. The result that this subtle structure modification of resveratrol drastically improves its bioactivity provides important strategy to develop novel resveratrol-based molecules.     

Stereocontrolled synthesis of (E)-stilbene derivatives by palladium-catalyzed Suzuki-Miyaura cross-coupling reaction

A general procedure for the stereocontrolled synthesis of (E)-stilbene derivatives by palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of (E)-2-phenylethenylboronic acid pinacol ester with aryl bromides was investigated. (E)-2-Phenylethenylboronic acid pinacol ester was prepared by 9-BBN-catalyzed hydroboration of phenylacetylene with pinacolborane. This reagent undergoes facile palladium-catalyzed cross-coupling with a diverse set of aryl bromides to provide the corresponding (E)-stilbene derivatives in moderate to good yield. The use of the sterically bulky t-Bu₃PHBF₄ ligand was crucial to the successful coupling of electron-rich and electron-poor aryl bromides. Complete stereochemical retention of the (E)-2-phenylethenylboronic acid pinacol ester alkene geometry was observed in all of the (E)-stilbene derivatives synthesized.