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Generation of lignin-carbohydrate complex (LCC) between dehydrogenation polymer (DHP) and pulp fibers may have an important impact on the properties of pulp. In this work, the benzyl ester-type LCC was formed between oxidized cellulose and DHP. The effect of pH on the addition reaction of oxidized cellulose to quinone methide in the synthesis of DHP-cellulose complex (DHPCC) was investigated. The structure of the product was characterized by Fourier Transform Infrared (FTIR), Carbon 13-Nuclear Magnetic Resonance (13C-NMR), and 2-Dimensional Heteronuclear Single Quantum Coherence Nuclear Magnetic Resonance (2D HSQC NMR) analyses. The results indicated that cellulose was indeed oxidized and carboxyl groups were introduced into cellulose by the oxidation process. The formed DHPCC was connected by benzyl ester linkage. In addition, the pH of the reaction system had an important role in the formation of the benzyl ester bonds. The acidic condition (pH = 4.0) was conducive to the addition reaction of quinone methide with carboxyl groups of cellulose. Overall, this study provides helpful guidance for the generation of LCC between DHP and paper pulp fibers. [ABSTRACT FROM AUTHOR]

Enzymes play important roles not only in normal physiological processes but in the development of many diseases. In situ imaging of enzymes with high‐resolution in living systems would helpful for clinical diagnosis and treatment. However, many molecular fluorescent probes suffer from the drawback of diffusing away from the reaction site of enzymes even out of the cells, losing the in situ information and resulting in poor imaging resolution. Quinone methide (QM) based self‐immobilizing probes allow the fluorescent signal to be immobilized near the target for an extended period without deactivating the target enzymes, ensuring that it will provide amplified signals and in situ information of the target with high resolution. In this review, we summarized the recent progress of QM‐based self‐immobilizing probes including their design strategies, working mechanisms, classifications and applications in in situ enzyme imaging. This review calls for the development of more activatable QM‐based probe with the advantages of high stability in the absence of the target but very high labeling efficiency after activation. [ABSTRACT FROM AUTHOR]

Enzyme‐activatable near‐infrared (NIR) fluorescent probes and photosensitizers (PSs) have emerged as promising tools for molecular imaging and photodynamic therapy (PDT). However, in living organisms selective retention or even enrichment of these reagents after enzymatic activation at or near sites of interest remains a challenging task. Herein, we integrate non‐covalent and covalent retention approaches to introduce a novel "1‐to‐3" multi‐effect strategy—one enzymatic stimulus leads to three types of effects—for the design of an enzyme‐activatable NIR probe or PS. Using this strategy, we have constructed an alkaline phosphatase (ALP)‐activatable NIR fluorogenic probe and a NIR PS, which proved to be selectively activated by ALP to switch on NIR fluorescence or photosensitizing ability, respectively. Additionally, these reagents showed significant enrichment (over 2000‐fold) in ALP‐overexpressed tumor cells compared to the culture medium, accompanied by massive depletion of intracellular thiols, the major antioxidants in cells. The investigation of this ALP‐activatable NIR PS in an in vivo PDT model resulted in complete suppression of HeLa tumors and full recovery of all tested mice. Encouragingly, even a single administration of this NIR PS was sufficient to completely suppress tumors in mice, demonstrating the high potential of this strategy in biomedical applications. [ABSTRACT FROM AUTHOR]

An efficient approach towards the synthesis of substituted spirochromans and dihydrocoumarins from a three‐component reaction involving aromatic aldehydes, phenols and phenylene dithiolanes is described. This FeCl3 catalyzed reaction utilizes either aromatic aldehydes or their acetals for condensation with phenols to generate o‐quinone methides in situ which further undergo a formal [4+2] cyclization with phenylene dithiolanes. Careful control of temperature allows direct access to dihydrocoumarins by the removal of the thioacetal moiety. [ABSTRACT FROM AUTHOR]

Small-molecule crosslinkers are invaluable for probing biomolecular interactions and for crosslinking mass spectrometry. Existing chemical crosslinkers target only a small selection of amino acids, while conventional photo-crosslinkers target almost all residues non-specifically, complicating data analysis. Herein, we report photocaged quinone methide (PQM)-based crosslinkers that target nine nucleophilic residues through Michael addition, including Gln, Arg, and Asn, which are inaccessible to existing chemical crosslinkers. PQM crosslinkers were used in vitro, in Escherichia coli, and in mammalian cells to crosslink dimeric proteins and endogenous membrane receptors. The heterobifunctional crosslinker NHQM could crosslink proteins to DNA, for which few crosslinkers exist. The photoactivatable reactivity of these crosslinkers and their ability to target multiple amino acids will enhance the use of chemical crosslinking for studies of protein-protein and protein-DNA networks and for structural biology.

Multiplex immunohistochemistry/multiplex immunofluorescence (mIHC/mIF) enables the simultaneous detection of multiple markers in a single tissue section by visualizing the markers in different colors. Currently, tyramide signal amplification (TSA) is the most commonly used method because it is heat resistant to multiplexing. SPiDER-βGal (6′-(diethylamino)-4′-(fluoromethyl)spiro[isobenzofuran-1(3H),9′-[9H]xanthen]-3′-yl β-d-galactopyranoside), a novel fluorogenic substrate of β-galactosidase (β-gal) was reported recently. Its properties are favorable for application in sensitive mIF based on quinone methide chemistry. Combining SPiDER-βGal with its related substrates, a novel, sensitive fluorescent IHC method for formalin-fixed paraffin-embedded (FFPE) sections was developed, named the galactosidase-catalyzed fluorescence amplification method (GAFAM). Evaluation of GAFAM indicated the following characteristics: (1) the entire GAFAM procedure was complete within a few hours; (2) the optimal working concentration of the substrates was 20 μM; (3) the fluorescent product was heat resistant; (4) the GAFAM exhibited sensitivity comparable with that of TSA, which was higher than that of conventional IF; and (5) the GAFAM was applicable to mIF and multispectral imaging. GAFAM is expected to be applicable to IF (or mIF in combination with TSA), and is a promising tool for facilitating morphological research in various fields of life science. [ABSTRACT FROM AUTHOR]

Condensation of lignin is believed to interfere with delignification in alkaline pulping processes. The lack of clear evidence motivated us to quantitatively revisit it. This article evaluates the self-condensation of 4-hydroxymethyl-2-methoxyphenol (vanillyl alcohol, Va) in the simplest model system using Va and 2-methoxy-4-methylphenol (creosol, Cr) under the same soda cooking conditions employed in our previous paper. Dimeric and trimeric self-condensation products of Va consisting of the α-5 bond (VaVa, 2-(4-hydroxy-3-methoxybenzyl)-4-hydroxymethyl-6-methoxyphenol), α-1 bond (VaVa', bis(4-hydroxy-3-methoxyphenyl)methane), and α-5 & α-1 bonds (VaVaVa', 2,4-bis(4-hydroxy-3-methoxy-benzyl)-6-methoxyphenol) were identified and quantified. The formation rate of VaVa from Va was suggested to be about twice of that of VaVa', and to be similar to that of the condensation product between the α-carbon of Va and the aromatic C5-carbon of Cr (VaCr), which was identified in the first paper. Among all these detected condensation products, only VaVa that can be converted to the corresponding quinone methide (QM) readily underwent further condensation to be VaVaVa' and others. Only the monomers (Va and Cr) possessing the small steric factors condense with electrophilic QM's as nucleophiles. These results suggest that condensation of lignin in actual soda cooking processes, with steric factors much larger than the model system, progresses much less frequently than generally believed. [ABSTRACT FROM AUTHOR]

Chemoselective blocking of the phenolic hydroxyl (Ar-OH) group by methylation was found to suppress secondary repolymerization and charring during lignin depolymerization. Methylation of Ar-OH prevents formation of reactive quinone methide intermediates, which are partly responsible for undesirable secondary repolymerization reactions. Instead, this structurally modified lignin produces more relatively low molecular weight products from lignin depolymerization compared to unmodified lignin. This result demonstrates that structural modification of lignin is desirable for production of low molecular weight phenolic products. This approach could be directed toward alteration of natural lignification processes to produce biomass that is more amenable to chemical depolymerization.

Abstract The condensation reaction of lignin is believed to interfere with delignification in alkaline pulping processes, without any clear evidence, which has motivated us to quantitatively revisit it. This paper is the first of a series, and hence we employed the simplest model system using 4-hydroxymethyl-2-methoxyphenol (vanillyl alcohol, Va) and 2-methoxy-4-methylphenol (creosol, Cr) under soda cooking conditions. The α-5-type condensation product between these compounds [VaCr, 2-(4-hydroxy-3-methoxybenzyl)-6-methoxy-4-methylphenol] was identified and quantified as exclusive. VaCr was yielded with a mole amount of 24%, 46%, 62%, or 72% based on that of disappearing Va at a reaction time of 120 min when the ratio of the initial concentration of Cr to that of Va was 1.0, 2.5, 5.0, or 7.5, respectively. These yields and an HPLC analysis of the reaction solution obtained by a treatment of Va as the sole compound under the same soda cooking conditions suggested the formation of self-condensation products of Va even in the treatments containing Cr. The obtained results comprehensively suggested that the self-condensation of Va progresses more readily than the condensation between Va and Cr. The factors behind this will be the topic of our next paper.

Single‐cell RNA sequencing (scRNA‐seq) has emerged as a powerful tool for profiling gene expression of distinct cell populations at the single‐cell level. However, the information of the positions of cells within the multicellular samples is missing in scRNA‐seq datasets. To overcome this limitation, we herein develop OpTAG (optical cell tagging) as a new chemical platform for attaching functional tags onto cell surfaces in a spatially resolved manner. With OpTAG, we establish OpTAG‐seq, which enables spatially resolved scRNA‐seq. We apply OpTAG‐seq to investigate the spatially defined transcriptional program in migrating cancer cells and identified a list of genes that are potential regulators for cancer cell migration and invasion. OpTAG‐seq provides a convenient method for mapping cellular heterogeneity with spatial information within multicellular biological systems. [ABSTRACT FROM AUTHOR]

The condensation reaction of lignin is believed to interfere with delignification in alkaline pulping processes, without any clear evidence, which has motivated us to quantitatively revisit it. This paper is the first of a series, and hence we employed the simplest model system using 4-hydroxymethyl-2-methoxyphenol (vanillyl alcohol, Va) and 2-methoxy-4-methylphenol (creosol, Cr) under soda cooking conditions. The α-5-type condensation product between these compounds [VaCr, 2-(4-hydroxy-3-methoxybenzyl)-6-methoxy-4-methylphenol] was identified and quantified as exclusive. VaCr was yielded with a mole amount of 24%, 46%, 62%, or 72% based on that of disappearing Va at a reaction time of 120 min when the ratio of the initial concentration of Cr to that of Va was 1.0, 2.5, 5.0, or 7.5, respectively. These yields and an HPLC analysis of the reaction solution obtained by a treatment of Va as the sole compound under the same soda cooking conditions suggested the formation of self-condensation products of Va even in the treatments containing Cr. The obtained results comprehensively suggested that the self-condensation of Va progresses more readily than the condensation between Va and Cr. The factors behind this will be the topic of our next paper. [ABSTRACT FROM AUTHOR]

Fucosidases are associated with several pathological conditions and play an important role in the health of the human gut. For example, fucosidases have been shown to be indicators and/or involved in hepatocellular carcinoma, breast cancer, and helicobacter pylori infections. A prerequisite for the detection and profiling of fucosidases is the formation of a specific covalent linkage between the enzyme of interest and the activity-based probe (ABP). The most commonly used fucosidase ABPs are limited to only one of the classes of fucosidases, the retaining fucosidases. New approaches are needed that allow for the detection of the second class of fucosidases, the inverting type. Here, we report an ortho-quinone methide-based probe with an azide mini-tag that selectively labels both retaining and inverting bacterial α-l-fucosidases. Mass spectrometry-based intact protein and sequence analysis of a probe-labeled bacterial fucosidase revealed almost exclusive single labeling at two specific tryptophan residues outside of the active site. Furthermore, the probe could detect and image extracellular fucosidase activity on the surface of live bacteria.

Controlling the absolute and relative stereochemistry of a seven-membered oxepane in the formation of HIV integrase inhibitor MK-1376 was accomplished through a strategy involving the use of asymmetric allylation and stereoconvergent, substrate-directed installation of an amine fragment. Surprising reactivity was demonstrated during the asymmetric allylation in which the allyl-pyrimidone product was formed reversibly. The stereoconvergent amine addition was accomplished through an elimination/addition sequence involving a quinone methide reactive intermediate, and nucleophilic trapping of the reactive quinone methide intermediate with methylamine. This novel approach delivered MK-1376, offering 100-fold greater productivity and 50-fold less waste than the initial synthetic chemistry route. [ABSTRACT FROM AUTHOR]

A formal [4+2] propargylic annulation of indoles and pyrrole with ethynyl benzoxazinanones was described. This protocol provides a concise synthesis of tetrahydro‐5H‐indolo[2,3‐b]quinolines and tetrahydro‐3H‐pyrrolo[3,2‐b]quinoline, the core structures of alkaloid frameworks, featuring excellent yields, high diastereoselectivity, mild conditions and wide substrate scope. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine how differences in the type of aromatic nucleus, side-chain structure and type of solvent affect the formation rate of quinone methide (QM) in the alkaline reaction of lignin. The reaction was done at a NaOH concentration of 1.0 mol l−1 and temperature of 75–140°C under an anaerobic condition. The formation rates of QM were in the order: syringyl > guaiacyl > p-hydroxyphenyl, when model compounds with lignin-type aromatic nuclei were compared. This and other results on various phenolic compounds suggested that the formation of QM is rapid from compounds having a high electron density in the aromatic π-electron system. The formation of QM was faster from a C6-C2-type than from a C6-C1-type lignin model compound, which was attributed to the fact that QM is an alkene and hence more stable when an unsaturated carbon in QM has an alkyl substituent, like the C6-C2-type compound. When aqueous 1,4-dioxane solutions with different 1,4-dioxane contents were used, the formation of QM became slower with increasing 1,4-dioxane content. This can be explained by the variation in the negative charge density in the rate-determining step, where the density is larger at the transition than at the initial state and consequently the activation energy is lower in a solvent with higher polarity. [ABSTRACT FROM AUTHOR]

Selective suicide inhibitors represent a seductively attractive approach for inactivation of therapeutically relevant enzymes since they are generally devoid of off-target toxicity in vivo. While most suicide inhibitors are converted to reactive species at enzyme active sites, theoretically bioactivation can also occur in ectopic (secondary) sites that have no known function. Here, we report an example of such an "ectopic suicide inhibition", an unprecedented bioactivation mechanism of a suicide inhibitor carried out by a non-catalytic site of thioredoxin glutathione reductase (TGR). TGR is a promising drug target to treat schistosomiasis, a devastating human parasitic disease. Utilizing hits selected from a high throughput screening campaign, time-resolved X-ray crystallography, molecular dynamics, mass spectrometry, molecular modeling, protein mutagenesis and functional studies, we find that 2-naphtholmethylamino derivatives bound to this novel ectopic site of Schistosoma mansoni (Sm)TGR are transformed to covalent modifiers and react with its mobile selenocysteine-containing C-terminal arm. In particular, one 2-naphtholmethylamino compound is able to specifically induce the pro-oxidant activity in the inhibited enzyme. Since some 2-naphtholmethylamino analogues show worm killing activity and the ectopic site is not conserved in human orthologues, a general approach to development of novel and selective anti-parasitic therapeutics against schistosoma is proposed. Image 1 • Thioredoxin glutathione reductase (TGR) is a promising drug-target for schistosomiasis. • 2-naphtholmethylamino compounds are transformed into quinone methide by a unique ectopic site of TGR. • Quinone methide alkylates the functional redox sites of TGR. • A new mechanism for TGR inhibition is proposed and called "ectopic suicide inhibition". • The selective inhibition of TGR from schistosoma is attainable. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new type of chemical warhead bearing trifluoromethyl groups based on quinone methide (QM) has been developed for efficient biomolecule labeling in living cells. • "Decaging-to-labeling" strategy on proteins based on the QM warhead has been evaluated. • Computational studies revealed that the generation rate of QM, rather than its reactivity, contributes more to labeling efficacy. Biomolecule labeling in living systems is crucial for understanding biological processes and discovering therapeutic targets. A variety of labeling warheads have been developed for multiple biological applications, including proteomics, bioimaging, sequencing, and drug development. Quinone methides (QMs), a class of highly reactive Michael receptors, have recently emerged as prominent warheads for on-demand biomolecule labeling. Their highly flexible functionality and tunability allow for diverse biological applications, but remain poorly explored at present. In this regard, we designed, synthesized, and evaluated a series of new QM probes with a trifluoromethyl group at the benzyl position and substituents on the aromatic ring to manipulate their chemical properties for biomolecule labeling. The engineered QM warhead efficiently labeled proteins both in vitro and under living cell conditions, with significantly enhanced activity compared to previous QM warheads. We further analyzed the labeling efficacy with the assistance of density functional theory (DFT) calculations, which revealed that the QM generation process, rather than the reactivity of QM, contributes more predominantly to the labeling efficacy. Noteworthy, twelve nucleophilic residues on the BSA were labeled by the probe, including Cys, Asp, Glu, His, Lys, Asn, Gln, Arg, Ser, Thr, Trp and Tyr. Given their high efficiency and tunability, these new QM warheads may hold great promise for a broad range of applications, especially spatiotemporal proteomic profiling for in-depth biological studies. [ABSTRACT FROM AUTHOR]

The isothiourea-catalyzed enantioselective 1,6-conjugate addition of para-nitrophenyl esters to 2,6-disubstituted para-quinone methides is reported. para-Nitrophenoxide, generated in situ from initial N-acylation of the isothiourea by the para-nitrophenyl ester, is proposed to facilitate catalyst turnover in this transformation. A range of para-nitrophenyl ester products can be isolated, or derivatized in situ by addition of benzylamine to give amides at up to 99% yield. Although low diastereocontrol is observed, the diastereoisomeric ester products are separable and formed with high enantiocontrol (up to 94:6 er).

A series of tripeptides TrpTrpPhe (1), TrpTrpTyr (2), and TrpTrpTyr[CH2N(CH3)2] (3) were synthesized, and their photophysical properties and non-covalent binding to polynucleotides were investigated. Fluorescent Trp residues (quantum yield in aqueous solvent ΦF = 0.03–0.06), allowed for the fluorometric study of non-covalent binding to DNA and RNA. Moreover, high and similar affinities of 2×HCl and 3×HCl to all studied double stranded (ds)-polynucleotides were found (logKa = 6.0–6.8). However, the fluorescence spectral responses were strongly dependent on base pair composition: the GC-containing polynucleotides efficiently quenched Trp emission, at variance to AT- or AU-polynucleotides, which induced bisignate response. Namely, addition of AT(U) polynucleotides at excess over studied peptide induced the quenching (attributed to aggregation in the grooves of polynucleotides), whereas at excess of DNA/RNA over peptide the fluorescence increase of Trp was observed. The thermal denaturation and circular dichroism (CD) experiments supported peptides binding within the grooves of polynucleotides. The photogenerated quinone methide (QM) reacts with nucleophiles giving adducts, as demonstrated by the photomethanolysis (quantum yield ΦR = 0.11–0.13). Furthermore, we have demonstrated photoalkylation of AT oligonucleotides by QM, at variance to previous reports describing the highest reactivity of QMs with the GC reach regions of polynucleotides. Our investigations show a proof of principle that QM precursor can be imbedded into a peptide and used as a photochemical switch to enable alkylation of polynucleotides, enabling further applications in chemistry and biology.

A simple arylamine-catalyzed Mannich-cyclization cascade reaction was developed for facile synthesis of substituted 2H-benzo[h]chromenes. The notable feature of the process included the efficient generation of ortho-quinone methides (o-QMs) catalyzed by a simple aniline. The mild reaction conditions allowed for a broad spectrum of 1- and 2-naphthols and trans-cinnamaldehydes to engage in the cascade sequence with high efficiency.

Quinone methide (QM) as a latent trapping unit has been widely explored in activity‐based self‐immobilizing reagents. However, further application of this strategy has been largely hampered by the limited labeling efficiency to proteins. In this study, a thorough investigation on the labeling efficiency and the structure of QM‐based trapping unit is presented, from which a QM with multiple leaving groups was identified as an optimal trapping unit. An alkaline phosphatase (ALP) immobilizing reagent featured with this multiple‐labeling trapping unit exhibited lower nonspecific binding and, remarkably, a significantly higher labeling efficiency over other immobilizing reagents upon enzymatic activation. The utility of this imaging reagent was further demonstrated with the in vitro and in vivo visualization of the ALP activities. Furthermore, the multiple functional trapping unit may find greater value in the other activity‐based immobilizing probes. [ABSTRACT FROM AUTHOR]

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. Free energy of dehydrogenation of piceatanol and the unpaired electron density for the resultant free radical. Image 105537 • Piceatannol can act as lignin monomer. • The coupling reactions of piceatannol are thermodynamically similar to those of monolignols. • Dehydrogenation reactions of coupled piceatannol products are thermodynamically feasible. [ABSTRACT FROM AUTHOR]

New bifunctional quinone methide (QM) precursors, bisphenols 2a-2e, and monofunctional QM precursor 7 were synthesized. Upon treatment with fluoride, desilylation triggers formation of reactive intermediates, QMs, which was demonstrated by trapping QM with azide or methanol. The ability of QMs to alkylate and cross-link DNA was assayed by investigation of the effects of QMs to DNA denaturing, but without conclusive evidence. Furthermore, treatment of a plasmid DNA with compounds 2a-2e and KF, followed by the analysis by alkaline denaturing gel electrophoresis, did not provide evidence for the DNA cross-linking. MTT test performed on two human cancer cell lines (MCF7 breast adenocarcinoma and SUM159 pleomorphic breast carcinoma), with and without fluoride, indicated that 2a-2e or the corresponding QMs did not exhibit cytotoxic activity, in line with the lack of ability to cross-link DNA. The lack of reactivity with DNA and biological activity were explained by sequential formation of QMs where bifunctional cytotoxic reagent is probably never produced. Instead, the sequential generation of monofunctional QM followed by a faster hydrolysis leads to the destruction of biologically active reagent. The findings described here are particularly important for the rational design of new generation of QM precursor molecules that will attain desirable DNA reactivity and cytotoxicity. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Seven aconitic acid conjugates, symphyocladins R-X, and the furanoyl conjugate, symphyocladin Y, were isolated from a Chinese marine red alga, Symphyocladia latiuscula. Image 1 Highlights • Marine red alga Symphyocladia latiuscula produced 9 previously undescribed polybromocatechol conjugates. • Structure elucidations were achieved by detailed spectroscopic analysis (2D NMR). • A plausible biosynthetic pathway linking these compounds through a cascade of quinone methide is proposed. [ABSTRACT FROM AUTHOR]

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.

Quinone methides (QMs) are highly reactive compounds that have been defined as “elusive” intermediates, or even as a “synthetic enigma” in organic chemistry. Indeed, there were just a handful of examples of their utilization in catalytic asymmetric settings until some years ago. This review collects organocatalytic asymmetric reactions that employ QMs as substrates and intermediates, from the early examples, mostly based on stabilized QMs bearing specific substitution patterns, to more recent contributions, which have dramatically expanded the scope of QM chemistry. In fact, it was only very recently that the generation of QMs in situ through strategies compatible with organocatalytic methodologies has been realized. This tactic has finally opened the gate to the full exploitation of these unstable intermediates, leading to a series of remarkable disclosures. Several types of synthetically powerful asymmetric addition and cycloaddition reactions, applicable to a broad range of QMs, are now available.

The Escherichia coli lacZ gene encoding β‐galactosidase is a widely used reporter, but few synthetic substrates are available for detecting its activity with single‐cell resolution in living samples. Our recently reported fluorogenic substrate SPiDER‐βGal is suitable for this purpose, but its hydrolysis product shows green fluorescence emission, and a red‐shifted analogue is therefore required for use in combination with green fluorescent protein (GFP) markers. Herein, we describe the development of a red‐shifted fluorogenic substrate for β‐galactosidase, SPiDER‐Red‐βGal, based on a silicon rhodol scaffold and a carboxylic group as the intramolecular nucleophile. LacZ‐positive cells were successfully labeled with SPiDER‐Red‐βGal at single‐cell resolution in living samples, which enabled us to visualize different cell types in combination with GFP markers. SPiDER and the fly: A new fluorogenic β‐galactosidase substrate, SPiDER‐Red‐βGal, based on a silicon rhodol scaffold and a carboxylic group as the intramolecular nucleophile, exhibited simultaneous activation of red fluorescence and labeling ability for intracellular proteins via a quinone methide intermediate. The probe can label lacZ‐positive cells at single‐cell resolution in vivo with perfect orthogonality to green fluorescent protein (GFP) markers. [ABSTRACT FROM AUTHOR]

Abstract Quinone methides are important reactive intermediates in photobiology and photochemistry, with little known regarding the photo-induces generation of reactive quinone methides species from relevant precursors in aqueous solutions. Here, the time-resolved spectroscopy methods including the transient absorption experiments and time-resolved Resonance Raman were employed to directly study the photophysics and photochemical processes of 6,6′-Bis(hydroxymethyl)-1,1′-binaphthyl-2,2′-diol (BQMP-a) in neat MeCN and 1:1 MeCN:H 2 O aqueous solutions. In aqueous solution, the intramolecular excited state proton transfer (ESIPT) process was observed where the water molecules help deliver the proton on the hydroxyl group to the naphthol ring within 125 ps in the singlet excited state of BQMP-a. This solvent mediated ESIPT will then lead to the leaving of the H 2 O group in 906 ps followed by the generation of the binol quinone methide (BQM-a) intermediate with a lifetime of 1.7 μs. As a result, the BQMP-a provides a different production rate of quinone methides compared with the 1,1′-(2,2′-Dihydroxy-1,1′-binaphthyl-6,6′-diyl) bis( N,N,N -trimethylmethanaminium) bromide system, which indicates the leaving group is an important factor in the generation of the reactive DNA alkylated intermediates. [ABSTRACT FROM AUTHOR]

Prodrug-based stimuli-responsive vectors have emerged as highly promising platform. Inspired by the fact that antioxidant systems including glutathione (GSH) make cancer cells adapt to oxidative stress and play a role in the inactivation of alkylating agents like chlorambucil (CHL) inside tumor cells, while arylboronic acid could transform into GSH depleting agent quinone methide (QM) upon degradation by reactive oxygen species (ROS) over-expressed in tumor cells, a ROS-responsive nanoprodrug (denoted by PPAHC) of CHL was established by integrating CHL into diols-containing hydrophilic polymer with self-immolative linker 4-(hydroxymethyl)phenylboronic acid (HPBA). The prodrug could form core-shell nanoparticle and possess high stability during storage. Drug release profile of PPAHC nanoprodrug demonstrated that nature CHL could be quickly released from PPAHC nanoprodrug in the presence of hydrogen peroxide (H 2 O 2 ). Moreover, PPAHC nanoprodrug showed improved therapeutic efficiency compared to CHL via anti-proliferative study and cell apoptosis assay. Further measurement of GSH content and ROS levels in tumor cells suggested that the synergistic impact resulted from QM-mediated GSH reduction and CHL-induced further oxidative stress insults to tumor cells. In vivo tumor suppression effect and biocompatibility indicated the superiorities of PPAHC nanoprodrug. Accordingly, PPAHC provides a new approach as a ROS-responsive CHL delivery system and has a great potential for cancer therapy. [ABSTRACT FROM AUTHOR]

We describe a complete account of our total synthesis and biological evaluation of (−)-berkelic acid and analogs. We delineate a synthetic strategy inspired by a potentially biomimetic union between the natural products spicifernin and pulvilloric acid. After defining optimal parameters, we executed a one-pot silver-mediated in situ dehydration of an isochroman lactol to methyl pulvillorate, the cycloisomerization of a spicifernin-like alkynol to the corresponding exocyclic enol ether, and a subsequent cycloaddition to deliver the tetracyclic core of berkelic acid. Our studies confirm that the original assigned berkelic acid structure is not stable and equilibrates into a mixture of 4 diastereomers, fully characterized by X-ray crystallography. In addition to berkelic acid, C22- epi -berkelic acid, and nor -berkelic acids, we synthesized C26-oxoberkelic acid analogs that were evaluated against human cancer cell lines. In contrast to data reported for natural berkelic acid, our synthetic material and analogs were found to be devoid of activity. [ABSTRACT FROM AUTHOR]