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Inhibitors of human β-N-acetyl-D-hexosaminidase (hHEX) A and human O-GlcNAcase (hOGA) reportedly play roles in multiple diseases, suggesting their potential for pharmacological chaperone (PC) therapy of Sandhoff disease (SD) and Tay-Sachs disease (TSD), as lysosomal storage diseases, and Alzheimer's disease and progressive supranuclear palsy, respectively. In particular, hHEXA inhibitors as PCs have been shown to successfully enhance hHEXA levels, leading to the chronic form of SD and TSD. In the diagnosis of enzyme deficiencies in SD and TSD, artificial hHEXA substrates based on 4-methylumbelliferone as a fluorophore are available and generally used; however, they do not have sufficient performance to screen for potential inhibitors for a PC therapy from compound libraries. Further, there are currently few fluorogenic substrates for hHEXA suitable for such requirements and there are no substrates ideal for cell-based inhibitor screening. Here, we clarified the difference in enzyme active site structure between hHEXA and hOGA from their tertiary structures. To develop lysosome-localized hHEXA-specific fluorogenic substrates based on the difference in their active site structures, our developed quinone methide cleavage substrate design platform was applied for the molecular design of substrates. Thereafter, we synthesized via the shortest route and evaluated novel three-color fluorogenic substrates for hHEXA that exhibited excellent specificity and sensitivity in three human cell lines. The designed substrates represent the first-in-a class of new substrates that can be utilized to screen hHEXA inhibitors in adherent human cultured cells.

This study describes an investigation into polybromocatechol conjugates isolated from a marine red alga, Symphyocladia latiuscula (Harvey) Yamada, collected from coastal waters off Qingdao, China. We report on the isolation and characterisation of eight undescribed aconitic acid conjugates, symphyocladins R-X, including a likely solvolysis artifact of symphyocladin S, and an undescribed furanoyl conjugate, symphyocladin Y. Structure elucidation was achieved by detailed spectroscopic analysis. A plausible biosynthetic pathway linking all these co-metabolites through a cascade of quinone methide additions is proposed.

Eumelanin is responsible for photoprotection in living organisms. It is made of 5,6‐dihydroxyindole (DHI) oligomers. However, lack of detailed structural knowledge limits understanding its function and exploiting its potential in material science. To uncover the relationship between structural stability and optical properties, we have studied a virtual library of 830 DHI dimers. We find a preference for oxidized, polycyclic structures which speaks in favor of graphite‐like structures for the larger oligomers, and propose an electrocyclic formation mechanism. Besides widely considered quinone oxidation patterns, also structures with interfragment double bonds and zwitterionic resonance structures are stable. Future theoretical melanine models will have to cover this diversity, and we introduce a new representative set of 49 stable dimers. Some stable oxidized dimers have absorption energies as low as 1.3 eV. They may be present as substructures in the naturally found oligomers and contribute to the absorption spectrum of the biopolymer., To understand the details of eumelanin structure and relate the stability of its components with optical properties, we have studied a library of 830 minimal models of eumelanin components, dimers of 5,6‐dihydroxy indole (DHI), with density functional theory. Our library considers all possible chemical diversity. The most stable dimers have polycyclic, oxidized structures and absorb as low as 1.3 eV (λ>900 nm).

Hydrogen sulfide (H2S) is an important biomolecule that plays key signaling and protective roles in different physiological processes. With goals of advancing both the available research tools and the associated therapeutic potential of H2S, researchers have developed different methods to deliver H2S on demand in different biological contexts. A recent approach to develop such donors has been to design compounds that release carbonyl sulfide (COS), which is quickly converted to H2S in biological systems by the ubiquitous enzyme carbonic anhydrase (CA). Although highly diversifiable, many approaches using this general platform release quinone methides or related electrophiles after donor activation. Many such electrophiles are likely scavenged by water, but recent efforts have also expanded alternative approaches that minimize the formation of electrophilic byproducts generated after COS release. This mini-review focuses specifically on recent examples of COS-based H2S donors that do no generate quinone methide byproducts after donor activation.

The reversible generation and capture of certain electrophilic quinone methide intermediates support dynamic reactions with DNA that allow for migration and transfer of alkylation and cross-linking. This reversibility also expands the possible consequences that can be envisioned when confronted by DNA repair processes and biological machines. To begin testing the response to such an encounter, quinone methide-based modification of DNA has now been challenged with a helicase (T7 bacteriophage gene protein four, T7gp4) that promotes 5' to 3' translocation and unwinding. This model protein was selected based on its widespread application, well characterized mechanism and detailed structural information. Little over one-half of the cross-linking generated by a bisfunctional quinone methide remained stable to T7gp4 and did not suppress its activity. The helicase likely avoids the topological block generated by this fraction of cross-linking by its ability to shift from single- to double-stranded translocation. The remaining fraction of cross-linking was destroyed during T7gp4 catalysis. Thus, this helicase is chemically competent to promote release of the quinone methide from DNA. The ability of T7gp4 to act as a Brownian ratchet for unwinding DNA may block recapture of the QM intermediate by DNA during its transient release from a donor strand. Most surprisingly, T7gp4 releases the quinone methide from both the translocating strand that passes through its central channel and the excluded strand that was typically unaffected by other lesions. The ability of T7gp4 to reverse the cross-link formed by the quinone methide does not extend to that formed irreversibly by the nitrogen mustard mechlorethamine.

Tyrosinase catalyzes the oxidation of phenols and catechols (o-diphenols) to o-quinones. The reactivities of o-quinones thus generated are responsible for oxidative browning of plant products, sclerotization of insect cuticle, defense reaction in arthropods, tunichrome biochemistry in tunicates, production of mussel glue, and most importantly melanin biosynthesis in all organisms. These reactions also form a set of major reactions that are of nonenzymatic origin in nature. In this review, we summarized the chemical fates of o-quinones. Many of the reactions of o-quinones proceed extremely fast with a half-life of less than a second. As a result, the corresponding quinone production can only be detected through rapid scanning spectrophotometry. Michael-1,6-addition with thiols, intramolecular cyclization reaction with side chain amino groups, and the redox regeneration to original catechol represent some of the fast reactions exhibited by o-quinones, while, nucleophilic addition of carboxyl group, alcoholic group, and water are mostly slow reactions. A variety of catecholamines also exhibit side chain desaturation through tautomeric quinone methide formation. Therefore, quinone methide tautomers also play a pivotal role in the fate of numerous o-quinones. Armed with such wide and dangerous reactivity, o-quinones are capable of modifying the structure of important cellular components especially proteins and DNA and causing severe cytotoxicity and carcinogenic effects. The reactivities of different o-quinones involved in these processes along with special emphasis on mechanism of melanogenesis are discussed.

Phenylfuropyridone natural products from fungi exhibit a range of antibacterial and cytotoxicity activities, and can potentiate azole antifungal compounds. We elucidated the biosynthetic pathway of compounds in the citridone family through heterologous reconstitution of the pfp pathway. We demonstrate that multiple members of this family can be accessed from a reactive ortho-quinone methide (o-QM) intermediate through electrocyclization, cycloisomerization, or conjugate addition. Formation of the quaternary carbon center in citridone B is catalyzed by an epoxide-forming P450 enzyme, followed by carbon skeletal rearrangement. Our results showcase how nature harvests the reactivities of an o-QM intermediate to biosynthesize complex natural products.

Neurogenerative diseases, such as Parkinson’s disease, are associated, not only with the selective loss of dopamine (DA), but also with the accumulation of reactive catechol-aldehyde, 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is formed as the immediate oxidation product of cytoplasmic DA by monoamine oxidase. DOPAL is well known to exhibit toxic effects on neuronal cells. Both catecholic and aldehyde groups seem to be associated with the neurotoxicity of DOPAL. However, the exact cause of toxicity caused by this compound remains unknown. Since the reactivity of DOPAL could be attributed to its immediate oxidation product, DOPAL-quinone, we examined the potential reactions of this toxic metabolite. The oxidation of DOPAL by mushroom tyrosinase at pH 5.3 produced conventional DOPAL-quinone, but oxidation at pH 7.4 produced the tautomeric quinone-methide, which gave rise to 3,4-dihydroxyphenylglycolaldehyde and 3,4-dihydroxybenzaldehyde as products through a series of reactions. When the oxidation reaction was performed in the presence of ascorbic acid, two additional products were detected, which were tentatively identified as the cyclized products, 5,6-dihydroxybenzofuran and 3,5,6-trihydroxybenzofuran. Physiological concentrations of Cu(II) ions could also cause the oxidation of DOPAL to DOPAL-quinone. DOPAL-quinone exhibited reactivity towards the cysteine residues of serum albumin. DOPAL-oligomer, the oxidation product of DOPAL, exhibited pro-oxidant activity oxidizing GSH to GSSG and producing hydrogen peroxide. These results indicate that DOPAL-quinone generates several toxic compounds that could augment the neurotoxicity of DOPAL.

Natural pentacyclic triterpenoids (PTs) have been often reported to exhibit a wide range of biological activities. Among them, the anticancer and anti-inflammatory activities are the most studied. Over the last two decades, the number of publications reporting the anticancer effects of PTs has risen exponentially, reflecting the increasing interest in these natural products for the development of new antineoplastic drugs. Among of the most investigated PTs regarding their anticancer properties are oleanane-, ursane and friedelane-types, including oleanolic, glycyrrhetinic, ursolic and asiatic acids, and celastrol, among others. The extensive research in this field shows that the anticancer effects of PTs are mediated by several mechanisms, as they modulate a diverse range of molecular targets and signaling pathways, involved in cancer cell proliferation and survival. Considering the anticancer potential of this class of compounds, a number of semisynthetic derivatives has been synthetized aiming to improve their therapeutic activity and pharmacokinetic properties, and decrease their toxicity. Some of these new semisynthetic derivatives have shown improved anticancer activity in various cancer cell lines and animal models compared with the parent compound. Moreover, some of these compounds have been assessed in clinical trials, proving to be safe for human use. This review updates the most recent findings on the semisynthetic derivatives of oleanane-, ursane- and quinone methide friedelane-type PTs with anticancer activity. A brief introduction concerning the PTs and their anticancer activity is given, and the main semisynthetic modifications that have been performed between 2012 and early 2017 are reviewed and discussed.

Polymeric nanoreactors (NRs) have distinct advantages to improve chemical reaction efficiency, but the in vivo applications are limited by lack of tissue-specificity. Herein, novel glucose oxidase (GOD)-loaded therapeutic vesicular NRs (theraNR) are constructed based on a diblock copolymer containing poly(ethylene glycol) (PEG) and copolymerized phenylboronic ester or piperidine-functionalized methacrylate (P(PBEM-co-PEM)). Upon systemic injection, theraNR are inactive in normal tissues. At a tumor site, theraNR are specifically activated by the tumor acidity via improved permeability of the membranes. Hydrogen peroxide (H2O2) production by the catalysis of GOD in theraNR increases tumor oxidative stress significantly. Meanwhile, high levels of H2O2 induce self-destruction of theraNR releasing quinone methide (QM) to deplete glutathione and suppress the antioxidant ability of cancer cells. Finally, theraNR efficiently kill cancer cells and ablate tumors via the synergistic effect.

Quinone methide (QM) formation induced by endogenously generated H2O2 is attractive for biological and biomedical applications. To overcome current limitations due to low biological activity of H2O2-activated QM precursors, we are introducing herein several new arylboronates with electron donating substituents at different positions of benzene ring and/or different neutral leaving groups. The reaction rate of the arylboronate esters with H2O2 and subsequent bisquinone methides formation and DNA cross-linking was accelerated with the application of Br as a leaving group instead of acetoxy groups. Additionally, a donating group placed meta to the nascent exo-methylene group of the quinone methide greatly improves H2O2-induced DNA interstrand cross-link formation as well as enhances the cellular activity. Multiple donating groups decrease the stability and DNA cross-linking capability, which lead to low cellular activity. A cell-based screen demonstrated that compounds 2a and 5a with a OMe or OH group dramatically inhibited the growth of various tissue-derived cancer cells while normal cells were less affected. Induction of H2AX phosphorylation by these compounds in CLL lymphocytes provide evidence for a correlation between cell death and DNA damage. The compounds presented herein showed potent anticancer activities and selectivity, which represent a novel scaffold for anticancer drug development.

Small molecule cross-linkers are invaluable for probing biomolecular interactions and for cross-linking mass spectrometry (CXMS) in addressing large protein complexes and intrinsically disordered proteins. Existing chemical cross-linkers target only a small selection of amino acid residues, limiting the number and type of cross-links, while conventional photocross-linkers target virtually all residues non-selectively, complicating data analysis. Here we report photocaged quinone methide (PQM)-based cross-linkers that are able to multitarget nine nucleophilic residues through specific Michael addition. In addition to Asp, Glu, Lys, Ser, Thr, and Tyr, PQM cross-linkers notably cross-linked Gln, Arg, and Asn hitherto untargetable by existing chemical cross-linkers, markedly increasing the number of residues targetable with a single cross-linker. Such multiplicity of cross-links will increase the abundance of cross-linked peptides for CXMS identification and afford ample constraints to facilitate structural deciphering. PQM cross-linkers were used in vitro, in E. coli, and in mammalian cells to cross-link dimeric proteins and endogenous membrane receptors. The cross-linker NHQM could directly cross-link proteins to DNA, for which few cross-linkers exist. The photoactivatable and multitargeting reactivity of these PQM cross-linkers will substantially enhance chemical cross-linking based technologies for studies of protein-protein and protein-DNA networks and for structural biology.

Made available in DSpace on 2020-12-12T01:45:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-11-01 The native Brazilian plant Maytenus ilicifolia accumulates a set of quinone methide triterpenoids with important pharmacological properties, of which maytenin, pristimerin and celastrol accumulate exclusively in the root bark of this medicinal plant. The first committed step in the quinone methide triterpenoid biosynthesis is the cyclization of 2,3-oxidosqualene to friedelin, catalyzed by the oxidosqualene cyclase friedelin synthase (FRS). In this study, we produced heterologous friedelin by the expression of M. ilicifolia FRS in Nicotiana benthamiana leaves and in a Saccharomyces cerevisiae strain engineered using CRISPR/Cas9. Furthermore, friedelin-producing N. benthamiana leaves and S. cerevisiae cells were used for the characterization of CYP712K4, a cytochrome P450 from M. ilicifolia that catalyzes the oxidation of friedelin at the C-29 position, leading to maytenoic acid, an intermediate of the quinone methide triterpenoid biosynthesis pathway. Maytenoic acid produced in N. benthamiana leaves was purified and its structure was confirmed using high-resolution mass spectrometry and nuclear magnetic resonance analysis. The three-step oxidation of friedelin to maytenoic acid by CYP712K4 can be considered as the second step of the quinone methide triterpenoid biosynthesis pathway, and may form the basis for further discovery of the pathway and heterologous production of friedelanes and ultimately quinone methide triterpenoids. Department of Plant Biotechnology and Bioinformatics Ghent University VIB Center for Plant Systems Biology Department of Organic Chemistry Institute of Chemistry so Paulo State University (UNESP) Department of Biological Sciences School of Pharmaceutical Sciences so Paulo State University (UNESP) VIB Metabolomics Core Department of Organic Chemistry Institute of Chemistry so Paulo State University (UNESP) Department of Biological Sciences School of Pharmaceutical Sciences so Paulo State University (UNESP)

Many herbal medicines such as epimedium have been reported to cause adverse effects, and icaritin is the common aglycone of many glucosides in epimedium. Our present work aimed at the clarification of the metabolic activation of icaritin possibly responsible for the adverse effects of epimedium. A quinone methide metabolite (M1) was detected in icaritin-fortified microsomal incubations. A glutathione (GSH) conjugate (M2) and N-acetyl-l-cysteine (NAC) conjugate (M3) derived from icaritin were observed in GSH/NAC-supplemented rat/human liver microsomal incubations. CYP3A family was the predominant enzyme catalyzing the bioactivation of icaritin. In conclusion, sufficient evidence indicates the metabolic activation of icaritin to quinone methide metabolite.

[Image: see text] Quinone methides are reactive electrophiles that are generated during metabolism of various drugs, natural products, and food additives. Their chemical properties and cellular effects have been described previously, and now their response to packaging DNA in a nucleosome core is described. A model bisquinone methide precursor (bisQMP) was selected based on its ability to form reversible adducts with guanine N7 that allow for their redistribution and transfer after quinone methide regeneration. Assembly of Widom’s 601 DNA with the histone octamer of H2A, H2B, H3, and H4 from Xenopus laevis significantly suppressed alkylation of the DNA. This result is a function of DNA packaging since addition of the octamer without nucleosome reconstitution only mildly protected DNA from alkylation. The lack of competition between nucleophiles of DNA and the histones was consistent with the limited number of adducts formed by the histones as detected by tryptic digestion and ultraperformance liquid chromatography–mass spectrometry. Only three peptide adducts were observed after reaction with a monofunctional analogue of bisQMP, and only two peptide adducts were observed after reaction with bisQMP. Histone reaction was also suppressed when reconstituted into the nucleosome core particle. However, bisQMP was capable of cross-linking the DNA and histones in moderate yields (~20%) that exceeded expectations derived from reaction of cisplatin, nitrogen mustards, and diepoxybutane. The core histones also demonstrated a protective function against dynamic alkylation by trapping the reactive quinone methide after its spontaneous regeneration from DNA adducts.

12 páginas.- 13 figuras.- 1 tabla.- 41 referencias.- Supporting information: Cartesian coordinates for low energy conformation of all compounds, optimized using M06-2X/6-311++G(d,p)., Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a monomeric unit in the lignification of palm fruit endocarp tissues. Results indicated that piceatannol homo-couples and cross-couples with monolignols through radical reactions and is integrally incorporated into the lignin polymer. The current work reports on the thermodynamics of the proposed reactions using density functional theory calculations. The results indicated that, in general, the energetics of both homo-coupling and cross-coupling are not dissimilar from those of the monolignol coupling, demonstrating the compatibility of piceatannol with the lignification process. Moreover, the DFT methods appear to predict the correct courses of post-coupling rearomatization reactions. © 2019, This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562 . Specifically, it used the Bridges system at the Pittsburgh Supercomputing Center (PSC) and Stampede2 at the Texas Advanced Computing Center ( TACC ), both via MCB-090159 to GTB. JR and HK Were funded by the DOE Great Lakes Bioenergy Research Center (DOE Office of Science BER DE-FC02-07ER64494 and DE-SC0018409 ). JRe and JCdR were funded by the Spanish Projects CTQ2014-60764-JIN and AGL2017-83036-R (financed by Agencia Estatal de Investigación, AEI and Fondo Europeo de Desarrollo Regional, FEDER). GTB acknowledges support from the US Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office under Contract No. DE-AC36-08GO28308 to the National Renewable Energy Laboratory.

We report herein a method for the recovery, purification, and application of OX063, a costly, commercially available nontoxic spin probe widely used for electron paramagnetic resonance (EPR) imaging, as well as its corresponding quinone methide (QM) form. This precious probe can be successfully recovered after use in animal model experiments (25–47% recovery from crude lyophilizate with 98.5% purity), even from samples that are >2 years old. Significantly, the recovered trityl can be reused in further animal model EPR imaging experiments. The work also describes support for the observed formation of an air-sensitive radical derived from the QM under reducing conditions.

International audience; Ferrociphenols (FCs) and their oxidized, electrophilic quinone methide metabolites (FC-QMs) are organometallic compounds related to tamoxifen that exhibit strong antiproliferative properties. To evaluate the reactivity of FC-QMs towards cellular nucleophiles, we studied their reaction with selected thiols. A series of new compounds resulting from the addition of these nucleophiles, the FC-SR adducts, were thus synthesized and completely characterized. Such conjugates are formed upon metabolism of FCs by liver microsomes in the presence of NADPH and thiols. Some of them exhibit antiproliferative properties comparable to those of their FC precursors. Under oxidizing conditions they either lead to their FC-QM precursors or to new quinone methides containing the SR moiety, FC-SR-QM. These results not only provide interesting data about the reactivity and mechanism of antiproliferative effects of FCs, but also open the way towards new series of organometallic anti-tumor compounds.

Nevirapine (NVP) is a non-nucleoside reverse transcriptase-inhibitor, which is associated with severe idiosyncratic skin rash and hepatotoxicity. These adverse drug reactions are believed to be mediated by the formation of epoxides and/or quinone methide formed by oxidative metabolism by P450s and 12-sulfoxyl-NVP formed by sequential 12-hydroxylation and O-sulfonation. Although different GSH-conjugates and corresponding mercapturic acids have been demonstrated previously in vitro and in vivo, the role of the glutathione S-transferases in the inactivation of the different reactive metabolites has not been studied so far. In the present study the activity of 10 recombinant human glutathione S-transferases (GSTs) in the detoxification of the different reactive metabolites of NVP was studied. The results show that GSTP1-1 is a highly active catalyst of GSH-conjugation of the oxidative metabolites of NVP, even at high GSH-concentration. Experiments with trideuterated NVP suggest involvement of a reactive epoxide rather than quinone methide in the formation of the GSH-conjugate formed after oxidative bioactivation. GSH-conjugation of 12-sulfoxyl-NVP forming NVP-12-GSH was only catalyzed by GSTM1-1, GSTA1-1, and GSTA3-3. Although the exact expression levels of these enzymes in the skin is unknown, the relatively low activity of this catalysis makes it unlikely that GSTs can provide significant protection against this metabolite. However, since NVP-12-GSH is specifically formed via the 12-sulfoxyl-NVP, its corresponding urinary mercapturic acid can be considered as a biomarker for recent internal exposure to this protein-reactive sulfate. However, it has to be taken into account that 12-sulfoxyl-NVP is not completely trapped by GSH and that rates of bioinactivation will differ between patients due to variability in expression of GSTM1, GSTA1, and GSTA3.

A simple method for the dimerization of phenylpropenoid derivatives is reported. It leverages electrochemical oxidation of p-unsaturated phenols to access the dimeric materials in a biomimetic fashion. The mild nature of the transformation provides excellent functional group tolerance, resulting in a unified approach for the synthesis of a range of natural products and related analogues with excellent regiocontrol. The operational simplicity of the method allows for greater efficiency in the synthesis of complex natural products. Interestingly, the quinone methide dimer intermediates are potent radical-trapping antioxidants; more so than the phenols from which they are derived – or transformed to – despite the fact that they do not possess a labile H-atom for transfer to the peroxyl radicals that propagate autoxidation.

Pharmacologic arm-selective unfolded protein response (UPR) signaling pathway activation is emerging as a promising strategy to ameliorate imbalances in endoplasmic reticulum (ER) proteostasis implicated in diverse diseases. The small molecule N-(2-hydroxy-5-methylphenyl)-3-phenylpropanamide (147) was previously identified (Plate et al., 2016) to preferentially activate the ATF6 arm of the UPR, promoting protective remodeling of the ER proteostasis network. Here we show that 147-dependent ATF6 activation requires metabolic oxidation to form an electrophile that preferentially reacts with ER proteins. Proteins covalently modified by 147 include protein disulfide isomerases (PDIs), known to regulate ATF6 activation. Genetic depletion of PDIs perturbs 147-dependent induction of the ATF6-target gene, BiP, implicating covalent modifications of PDIs in the preferential activation of ATF6 afforded by treatment with 147. Thus, 147 is a pro-drug that preferentially activates ATF6 signaling through a mechanism involving localized metabolic activation and selective covalent modification of ER resident proteins that regulate ATF6 activity.

International audience; The synthesis and chemical oxidation profile of a new generation of ferrocifen derivatives with strong anti-proliferative behavior in vitro is reported. In particular, the hydroxypropyl derivative HO(CH2)(3)C(Fc)= C(C6H4OH)(2) (3b) exhibited exceptional antiproliferative activity against the cancer cell lines HepG2 and MDA-MB-231 TNBC, with IC50 values of 0.07 and 0.11 mu m, respectively. Chemical oxidation of 3b yielded an unprecedented tetrahydrofuran-substituted quinone methide (QM) via internal cyclization of the hydroxyalkyl chain, whereas the corresponding alkyl analogue CH3CH2-C(Fc)= C(C6H4OH)(2) merely formed a vinyl QM. The ferrocenyl group in 3b plays a key role, not only as an intramolecular reversible redox ``antenna'', but also as a stabilized carbenium ion ``modulator''. The presence of the oxygen heterocycle in 3b-QM enhances its stability and leads to a unique chemical oxidation profile, thus revealing crucial clues for deciphering its mechanism of action in vivo.

A visible light photoredox-catalyzed and radical-mediated strategy for the in situ generation of aza-ortho-quinone methides from readily accessible alkenylanilines and alkyl radical precursors has been accomplished for the first time. This protocol enables an efficient multicomponent cascade reaction of alkenylanilines, halides and sulfur ylides, and shows wide substrate scope and high functional group tolerance with respect to each component. Treatment of the initially formed cycloaddition products with a base leads to a convergent and streamlined synthesis of densely functionalized indoles in a single flask operation.

The total syntheses of medicarpin, sophoracarpan A, and kushecarpin A from a common intermediate are achieved by using ortho- and para-quinone methide chemistry. Additionally, the relative stereochemistry of sophoracarpan A and B have been reassigned.

Over the last 30 years, the quinone-methide elimination has served as a valuable tool for achieving various important molecular functions. Molecular adaptors based on quinone-methide or aza-quinone-methide reactivity have been designed, synthesized, and used in diagnostic probes, molecular amplifiers, drug delivery systems, and self-immolative dendritic/polymeric molecular systems. These unique adaptors function as stable spacers between an enzyme- or reagent-responsive group and a reporter moiety and can undergo 1,4-, 1,6-, or 1,8-type elimination reactions upon cleavage of the triggering group. Such reactivity results in the release of the reporter group through formation of a quinone-methide species. This type of elimination was applied to design distinct molecular adaptors capable of multiple quinone-methide eliminations. Using this chemistry, we have developed unique molecular structures that are known today as self-immolative dendrimers. These dendrimers disassemble upon a single triggering event in a domino-like manner from the focal point to their periphery with the consequent release of multiple end-groups. Such molecular structures are used in self-immolative dendritic prodrugs and in diagnostic probes to obtain a significant amplification effect. To further enhance amplification, we have developed the dendritic chain reaction, which uses simple molecules to achieve functionality of high-generation virtual self-immolative dendrimers. In addition, we harnessed the quinone-methide elimination reactivity to design polymers that disassemble from head-to-tail initiated by an analyte-responsive event. Following this example, other chemical reactivities were demonstrated by scientists to design such polymeric molecules. In a manner analogous to the quinone-methide elimination, electron rearrangement can lead to formation of conjugated quinone-methide-type dyes with long-wavelength emission of fluorescence. We have recently applied an intramolecular charge transfer to form a unique kind of quinone-methide type derivative based on a donor-two-acceptors molecular structure. This intramolecular charge transfer produces a new fluorochrome with an extended conjugation of π-electron system that is used for the design of long-wavelength fluorogenic probes with a turn-ON option. The rapidly expanding use of quinone-methide species, reflected in the increased number of examples reported in the literature, indicates the importance of this tool in chemistry. These species provide a useful gateway to functional molecular structures with distinct reactivities and spectroscopic characteristics.

A large variety of phenolic compounds, including phenolic acids (hydroxybenzoic acids, hydroxycinnamic acids, and their esters), stilbenes (trans-resveratrol and trans-piceatannol), flavan-3-ols (e.g., (-)-epicatechin, (+)-catechin, and their polymers {the proanthocyanidins, PACs}), other flavonoids (e.g., isoflavones, flavanols, and flavones, etc.) and biflavonoids (e.g., morelloflavone), were identified in dry-blanched peanut skins (PS) by this study. High-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry (ESI-MS(n)) was applied to separate and identify the phenolic constituents. Reversed-phase HPLC was employed to separate free phenolic compounds as well as PAC monomers, dimers, and trimers. PACs with a degree of polymerization (DP) of >4 were chromatographed via hydrophilic interaction liquid chromatography (HILIC). Tentative identification of the separated phenolics was based solely on molecular ions and MS(n) fragmentation patterns acquired by ESI-MS in the negative-ion mode. The connection sequence of PAC oligomers (DP

The present study characterized the products formed from the reaction of amino acids and in turn, proteins, with lignin resulting in cross-coupling. When added to reaction mixtures containing coniferyl alcohol, horseradish peroxidase and H2O2, three amino acids (Cys, Tyr, and Thr) are able to form adducts. The low molecular weight products were analyzed by HPLC and from each reaction mixture, one product was isolated and analyzed by LC/MS. LC/MS results are consistent with bond formation between the polar side-chain of these amino acids with Cα. These results are consistent with the cross-coupling of Cys, Tyr and Thr through a quinone methide intermediate. In addition to the free amino acids, it was found that the cross-coupling of proteins with protolignin through Cys or Tyr residues. The findings provide a mechanism by which proteins and lignin can cross-couple in the plant cell wall.

Nevirapine (NVP) can cause serious skin rashes and hepatotoxicity. It also causes an immune-mediated skin rash in rats but not hepatotoxicity. This rash is caused by a metabolite of NVP; specifically, NVP is oxidized in the liver to a benzylic alcohol (12-OH-NVP), which travels to the skin where it forms a reactive benzylic sulfate. This could both act as a hapten and induce a danger signal. In contrast, most of the covalent binding in the liver involves oxidation of the methyl group leading to a reactive quinone methide. In this study, we examined the effects of NVP and 12-OH-NVP on gene expression in the liver and skin. Both NVP and 12-OH-NVP induced changes in the liver, but the list of genes was different, presumably reflecting different bioactivation pathways. In contrast, many more genes were up-regulated in the skin by 12-OH-NVP than by NVP, which is consistent with the fact that 12-OH-NVP is an obligate intermediate in the formation of the reactive sulfate in the skin. Genes up-regulated by 12-OH-NVP in the skin included TRIM63 (18-fold increase), S100a7a (7-fold increase), IL22-RA2 (4-fold increase), and DAPK1 (3-fold increase). TRIM63 acts as a ubiquitin ligase, which is consistent with protein damage leading to an increase in protein turnover. In addition, TRIM proteins are involved in inflammasome activation, and it appears that inflammasome activation is an essential step in the induction of NVP-induced skin rash. S100A7 is considered a danger signal, and its upregulation supports the danger hypothesis. Upregulation of the IL-22 RA2 gene marks an immune response. DAPK1 is involved with inflammasome assembly through binding directly to NLRP3, a NOD-like receptor expressed in keratinocytes. These results provide important clues to how NVP causes the induction of an immune response, in this case leading to skin rash.

In chemico methods, based on the assessment of a hapten's reactivity toward peptides, have been proposed as alternative methods for the assessment of the skin sensitizing potential of chemicals. However, even with these approaches showing promise, a major drawback is the activation of prohaptens, i.e. molecules needing a metabolic activation to become reactive and therefore sensitizing. Recently, it has been proposed to couple an enzymatic activation step based on horseradish peroxidase (HRP)/hydrogen peroxide to such peptide reactivity assays. To evaluate this approach, the behavior of 2-methoxy-4-methylphenol (2M4MP), reported as a moderate sensitizer according to the Local Lymph Node Assay (LLNA), has been investigated in this assay. To follow the reaction with the peptides and characterize more easily intermediates and adducts, the molecule was first (13)C isotopically substituted at the most probable reactive position. When 2M4MP was incubated with HRP/H2O2 in a mixture PBS (pH 7.4, 0.1M)/acetonitrile 2:1, two main products were formed deriving from the formation of a quinone methide 2M4MQ subsequently trapped by either H2O2 or H2O to form a benzylic hydroperoxide or alcohol, respectively. When nucleophiles such as GSH or a peptide containing a cysteine residue (Pep-Cys) were present in the reaction medium, the quinone methide 2M4MQ was trapped by the more nucleophilic thiol function to form thio-adducts. No modifications of 2M4MP were observed when the same reactions were carried out without HRP confirming that the activation of the molecule was enzyme related. Amino nucleophiles were shown to be far less reactive towards the quinone methide 2M4MQ with only tiny formation of adducts with lysine or arginine side chains. In addition we demonstrated that the same enzymatic activation could also take place in a microemulsion based on sodium dodecyl sulfate/tert-butanol/chloroform/buffer.

A general protocol for the synthesis of benzylic amines via side-chain amination of alkylquinones is reported. The reactions are initiated by the tautomerization of an alkylquinone to the corresponding quinone methide, which is subsequently trapped in situ by an amine nucleophile. This process is promoted by tertiary amines in protic solvents under mild conditions and is compatible with many functional groups. 1,2- and 1,4-benzoquinones, as well as naphthoquinones, participate in this reaction using a wide range of primary and secondary amines/anilines. The synthetic utility of this transformation is also explored.

Aspergillus fumigatus is an opportunistic fungal pathogen and the most common causative agent of fatal invasive mycoses. The flavin-dependent monooxygenase siderophore A (SidA) catalyzes the oxygen and NADPH dependent hydroxylation of l-ornithine (l-Orn) to N5-l-hydroxyornithine in the biosynthetic pathway of hydroxamate-containing siderophores in A. fumigatus. Deletion of the gene that codes for SidA has shown that it is essential in establishing infection in mice models. Here, a fluorescence polarization high-throughput assay was used to screen a 2320 compound library for inhibitors of SidA. Celastrol, a natural quinone methide, was identified as a noncompetitive inhibitor of SidA with a MIC value of 2 μM. Docking experiments suggest that celastrol binds across the NADPH and l-Orn pocket. Celastrol prevents A. fumigatus growth in blood agar. The addition of purified ferric-siderophore abolished the inhibitory effect of celastrol. Thus, celastrol inhibits A. fumigatus growth by blocking siderophore biosy...

Electrophilic reactive intermediates resulting from drug metabolism have been associated with toxicity and off-target effects and in some drug discovery programs trigger NO-GO decisions. Many botanicals and dietary supplements are replete with such reactive electrophiles, notably Michael acceptors, which have been demonstrated to elicit chemo-preventive mechanisms; and Michael acceptors are gaining regulatory approval as contemporary cancer therapeutics. Identifying protein targets of these electrophiles is central to understanding potential therapeutic benefit and toxicity risk. NO-donating NSAID prodrugs (NO-NSAIDs) have been the focus of extensive clinical and preclinical studies in inflammation and cancer chemoprevention and therapy: a subset exemplified by pNO-ASA, induces chemopreventive mechanisms following bioactivation to an electrophilic quinone methide (QM) Michael acceptor. Having previously shown that these NO-independent, QM-donors activated Nrf2 via covalent modification of Keap-1, we demonstrate that components of canonical NF-κB signaling are also targets, leading to the inhibition of NF-κB signaling. Combining bio-orthogonal probes of QM-donor ASA prodrugs with mass spectrometric proteomics and pathway analysis, we proceeded to characterize the quinonome: the protein cellular targets of QM-modification by pNO-ASA and its ASA pro-drug congeners. Further comparison was made using a biorthogonal probe of the “bare-bones”, Michael acceptor, and clinical anti-inflammatory agent, dimethyl fumarate, which we have shown to inhibit NF-κB signaling. Identified quinonome pathways include post-translational protein folding, cell-death regulation, protein transport, and glycolysis; and identified proteins included multiple heat shock elements, the latter functionally confirmed by demonstrating activation of heat shock response.

Methyleugenol (ME), an alkenylbenzene compound, is a constituent of many foods and is used as flavoring agent in foodstuffs and as fragrance in cosmetics. It has been reported that exposure to ME can cause carcinogenicity, cytotoxicity, and genotoxicity. Metabolic activation is suggested to play an important role in ME-induced toxicities. Electrophilic metabolites of ME have been reported to covalently bind to proteins and nucleic acids. The objective of this study was to identify GSH and related cysteine conjugates derived from these reactive metabolites in vivo. Five biliary GSH (M1-M5) and four urinary cysteine conjugates (M6-M9) were detected in rats given ME. M1 and M2 were GSH conjugates derived from the epoxide of ME. M3, M4, and M5 were GSH conjugates possibly generated from the corresponding α,β-unsaturated aldehyde, carbonium ion, and quinone methide, respectively. The structures of the GSH conjugates were verified by chemical synthesis. Cysteine conjugates M6, M7, M8, and M9 were found to correspond to the respective M1/M2, M3, M4, and M5. The data obtained from the present in vivo work facilitate the understanding of mechanism action of ME toxicities and may provide information suitable for use as biomarkers of exposure to ME.

The radiosensitizing effects of naturally occurring triterpenes were investigated in human lung cancer cells. Several quinone methide-containing triterpenes (QMTs) enhanced the cytotoxic effect of ionizing radiation (IR) and of these QMTs, celastrol (CE) had the greatest enhancing effect on IR-induced cell death in vitro. Additionally, the quinone methide moiety of CE was shown to be essential for CE-mediated radiosensitization; in contrast, dihydrocelastrol (DHCE), does not contain this moiety. Reactive oxygen species (ROS) production by IR was augmented in combination with CE, which was responsible for CE-mediated radiosensitization. CE induced the thiol reactivity and inhibited the activities of antioxidant molecules, such as thioredoxin reductase and glutathione. In vivo, nude mouse xenografting data also revealed that tumor growth delay was greater in mice treated with CE plus IR, compared with those treated with CE or IR alone. When DHCE, instead of CE, was combined with IR, tumor growth delay was similar to that in IR alone-treated mice. These results demonstrate that CE synergistically enhances the effects of IR and suggest the novel anticancer therapeutic use of CE in combination with radiation therapy.

Proanthocyanidins (PAs) are the most important and valuable polyphenolic compounds of Terminalia species (family Combretaceae) used for the treatment of several diseases. This study aims to seek identification and characterization of PAs in the ethanolic extracts of bark and fruit of six Terminalia species viz T. arjuna, T. bellerica, T. catappa, T. chebula, T. elliptica and T. paniculata. A high performance liquid chromatography with quadrupole time-of-flight tandem mass spectrometry (HPLC/ESI-QTOF-MS/MS) method was developed for the simultaneous identification and characterization of PAs. The chromatographic separation was carried on a Thermo Betasil C8 column (250 mmx4.5 mm, 5μm) operated with 0.1% formic acid aqueous solution and acetonitrile as the mobile phase. The MS/MS fragmentation study of [M-H]- ions obtained from these PAs showed distinguishable fragment ions with high mass accuracy. Heterocyclic ring fission (HRF), retro-Diels-Alder (RDA) fragmentation, quinone methide (QM) fragmentation and benzofuran formation (BFF) have been identified as the characteristic fragments. Total of 51 PAs were tentatively identified which include 28 dimers, 15 trimers and 8 other flavan-3-ols.

Lucidin-3-O- primeveroside (LuP) is one of the components of madder root (Rubia tinctorum L.; MR) which is reported to be carcinogenic in the kidney and liver of rats. Since metabolism of LuP generates genotoxic compounds such as lucidin (Luc) and rubiadin (Rub), it is likely that LuP plays a key role in MR carcinogenesis. In the present study, the chemical structures of Luc-specific 2'-deoxyguanosine (dG) and 2'-deoxyadenosine (dA) adducts following the reactions of dG and dA with a Luc carbocation or quinone methide intermediate derived from Acetoxy-Luc were determined by liquid chromatography with photodiode array and electron spray ionizaion-mass spectrometry (LC-PDA-ESI/MS). The identification of the two measurable adducts as Luc-N(2)-dG and Luc-N(6)-dA was confirmed by NMR analysis. Subsequently, using a newly developed quantitative analytical method using LC-ESI/MS, the formation of Luc-N(2)-dG and Luc-N(6)-dA from the reaction of calf thymus DNA with Luc in the presence of S9 mixture was observed. The fact that this reaction with Rub also gave rise to the same dG and dA adducts strongly suggests that Rub genotoxicity involves a metabolic conversion to Luc. The precise determination of the modified DNA bases generated by LuP and the method for their analysis may contribute to further comprehension of the mode of action underlying carcinogenesis by MR and related anthraquinones.

Dihydrofolate reductase (DHFR) is the subject of intensive investigation since it appears to be the primary target enzyme for antifolate drugs. Fluorescence quenching experiments show that the ester bond-containing tea polyphenols (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) are potent inhibitors of DHFR with dissociation constants (K(D))of 0.9 and 1.8 microM, respectively, while polyphenols lacking the ester bound gallate moiety [e.g., (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)] did not bind to this enzyme. To avoid stability and bioavailability problems associated with tea catechins we synthesized a methylated derivative of ECG (3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin; TMECG), which effectively binds to DHFR (K(D) = 2.1 microM). In alkaline solution, TMECG generates a stable quinone methide product that strongly binds to the enzyme with a K(D) of 8.2 nM. Quercetin glucuronides also bind to DHFR but its effective binding was highly dependent of the sugar residue, with quercetin-3-xyloside being the stronger inhibitor of the enzyme with a K(D) of 0.6 microM. The finding that natural polyphenols are good inhibitors of human DHFR could explain the epidemiological data on their prophylactic effects for certain forms of cancer and open a possibility for the use of natural and synthetic polyphenols in cancer chemotherapy.

Summary Tailoring steps in aromatic polyketide antibiotic biosynthesis are an important source of structural diversity and, consequently, an intriguing focal point for enzymological studies. PgaE and PgaM from Streptomyces sp. PGA64 are representatives of flavoenzymes catalyzing early post-PKS reactions in angucycline biosynthesis. This in vitro study illustrates that the chemoenzymatic conversion of UWM6 into the metabolite, gaudimycin C, requires multiple closely coupled reactions to prevent intermediate degradation. The NMR structure of gaudimycin C confirms that the reaction cascade involves C12- and C12b-hydroxylation, C2,3-dehydration, and stereospecific ketoreduction at C6. Enzymatic 18 O incorporation studies verify that the oxygens at C12 and C12b derive from O 2 and H 2 O, respectively. The results indicate that PgaM deviates mechanistically from flavoprotein monooxygenases, and suggest an alternative catalytic mechanism involving a quinone methide intermediate.

The syntheses of four totarane diterpenes-totarol, 8,11,13-totaratriene-12,13-diol, 6-deoxymaytenoquinone and maytenoquinone-are described. Totarol was synthesized via cyclization of a modified polyene. 8,11,13-Totaratriene-12,13-diol was prepared from natural totarol by ortho-oxidation with mCBPO (m-chlorobenzoyl peroxide). Maytenoquinone and 6-deoxymaytenoquinone were synthesized from 8,11,13-totaratriene-12,13-diol. 1 H-NMR analysis showed that tautomeric isomerization between 6-deoxymaytenoquinone (2-hydroxy-4-quinone methide) and the ortho-quinone was very slow.

Adhesives that selectively debond from a surface by stimuli-induced head-to-tail continuous depolymerization of poly(benzyl ether) macro-cross-linkers within a poly(norbornene) matrix are described. Continuous head-to-tail depolymerization provides faster rates of response than can be achieved using a small-molecule cross-linker, as well as responses to lower stimulus concentrations. Shear-stress values for glass held together by the adhesive reach 0.51±0.10 MPa, whereas signal-induced depolymerization via quinone methide intermediates reduces the shear stress values to 0.05±0.02 MPa. Changing the length of the macro-cross-linkers alters the time required for debonding, and thus enables the programmed sequential release of specific layers in a glass composite material.

Metal, oxidant and other additive-free novel methods for direct C–H aryloxylation of aliphatic amines are developed. In the presence of excess amine, the course of the reaction was diverted, producing various arylmethylamines via hydride-free formal reductive amination. Involvement of a quinone methide intermediate was revealed from mechanistic studies.

The synthesis of fluorinated compounds as well as the use of these products as building blocks for the preparation of complex molecules are fast growing research areas. Herein we highlight recent progress in the activation of allylic and benzylic C–F bonds for the synthesis of functionalized molecules. SN2′ reactions of allylic difluoro and trifluoro compounds as well as transition-metal-catalyzed (nickel, palladium, platinum and copper) processes are described. The C–F bond activation of 3-fluoropropenes was achieved with platinum- or organocatalysis. Benzylic C–F bond activation was realized with magnesium by deprotonation leading to the formation of reactive quinone methide intermediates and with hydrogen bond donors by forming strong F⋯H interactions.

Since its first observation in 1907, ortho-quinone methide (o-QM) has occupied a strategic place within the framework of reactive intermediates in organic synthesis. In recent years, o-QM has enhanced its importance as a versatile reactive intermediate, and its applications in organic synthesis, material chemistry, fine chemicals, and pharmaceuticals are increasing rapidly. This critical review summarizes the key concepts behind o-QMs and provides an overview of current applications in organic synthesis to provide an appropriate background for synthetic, medicinal and combinatorial developments. This review covers the literature from its origin to the mid of 2014 (112 references).

Although quinone methides are often postulated as intermediates in the biosynthesis of many polyphenolic natural products, deploying their power in a laboratory setting to achieve similar bond constructions has sometimes proven challenging. Herein, a total synthesis of the resveratrol trimer vaticanol A has been achieved through three instances of quinone methide chemistry. These operations, one of which succeeded only under very specific conditions, expediently generated its [7,5]-carbocyclic core, afforded a unique sequence for dihydrobenzofuran formation, and concurrently generated, in addition to the target molecule, a series of diastereomers reflective of many other isolates.

Natural terpene quinone methides (QM) and their derivatives have been investigated as therapeutics due to their broad antifungal, antibacterial, and antitumor activities. Recently, we reported that a terpene QM was formed from the catechol precursor through the disproportionation of Cu(II)/(I) redox cycle, and extensive DNA damage was observed throughout the oxidation process. In this paper, we investigate DNA damage with a series of terpene catechols as analogues of natural QM precursors and suggest that reactive oxygen species (ROS) are responsible for the observed DNA damage in the Cu(2+)-induced oxidation despite the stereo- and structural difference of these catechol or subsequent oxidation products. In addition, the presence of NADH significantly enhanced the extent of DNA damage by oxidation of these catechols. Especially with alkene catechols 6-7, the extent of DNA damage was independent of the concentration of catechols, implying that NADH enables the continuous production of ROS through the redox cycle of catechols/quinones.

A quinone methide diterpene: abietaquinone methide, which possesses potent anti-methicillin-resistant Staphylococcus aureus (MRSA) and anti-vancomycin-resistant Enterococcus (VRE) activities, was synthesized via efficiently ortho-oxidation of ferruginol derived from industrially available dehydroabietic acid. ortho-Oxidation of phenols was developed to give mono esters of catechols using a stable diacyl peroxide, bis(4-chlorobenzoyl) peroxide (m-chlorobenzoyl peroxide: mCBPO) which was synthesized from meta-chlorobenzoic acid. Efficient one pot ortho-oxidation reaction of phenol with an adduct of meta-chloroperbenzoic acid (mCPBA) with dicyclohexylcarbodiimide (DCC) was also reported.

Highly electrophilic quinone methide (QM) intermediates often express a surprising selectivity for weak nucleophiles of DNA even when proximity effects do not guide reaction. On the basis of model studies with an unsubstituted ortho-QM, these observations can now be explained by the reversibility of QM alkylation and the time-dependent shift from kinetic to thermodynamic products. The persistent and most commonly identified QM adducts represent thermodynamic products that typically form in low yield by irreversible reaction with weak nucleophiles such as the N1 and N2 of dG and the N6 of dA under neutral conditions. In contrast, strong nucleophiles such as the N1 of dA and the N3 of dC generate relatively high yields of their QM adducts. However, these products dissipate over time as the QM is repeatedly regenerated and repartitioned over the available nucleophiles. The adduct formed by the N7 of dG undergoes a similar release of QM as well as deglycosylation at comparable rates. The kinetic products of QM alkylation serve as a reservoir for QM regeneration and transfer that are likely to prolong the cellular activity of an otherwise highly transient intermediate.

Terpene quinone methides have been isolated from natural resources and exhibit broad biological activities against bacteria, fungi, and tumor cells through the reactive quinone methide (QM) moiety. The biological potential of the oxidation of terpene QM precursors, however, has not been assessed even though Cu(2+)-induced oxidation of catechol shows detrimental effects on cells. In this study, a diterpenone catechol was investigated as a precursor of terpene QM under aqueous conditions in the presence of Cu2+. Direct QM formation was implied in the Cu(2+)-induced oxidation through the study of thiol addition using HPLC and ESI-MS analysis. In addition, oxidation of the initial QM adduct to a second-QM intermediate was observed. The direct QM oxidation pathway may be unique for diterpenone catechol in the Cu(2+)-induced oxidation and is an addition to the reported isomerization pathway of o-quinones to QMs. The DNA damage by the Cu(2+)-induced oxidation of diterpenone catechol was assessed on a short duplex DNA target. Both direct DNA cleavage and nucleobase oxidation were observed extensively by in situ-generated hydroxyl radicals.