Trimethyl lock: A trigger for molecular release in chemistry, biology, and pharmacology

Simple electrochemical synthesis of cyclic hydroxamic acids by reduction of nitroarenes

The electrochemical reduction of nitroarenes allows direct access to manifold nitrogen containing heterocycles. This work reports the simple and direct electro-organic synthesis of 18 different examples of 2H,4H-4-hydroxy-1,4-benzoxazin-3-ones in up to 81% yield. The scalability of the method was demonstrated on a gram-scale.

A chiral trimethyl lock based on the vicinal disubstituent effect: prolonged release of camptothecin into cancer cells

Synthesis and in vitro testing of a prodrug designed for the controlled delivery of the anticancer drug camptothecin within pancreatic cancer cells are reported. Our study reveals a non-conventional pharmacokinetic release characterized by an exponential pattern before reaching the half-life (t1/2) and a linear pattern thereafter. The release mechanism was triggered either by hydrolytic enzymes and/or by the acid microenvironment of cancer cells.

Enhancing SN38 prodrug delivery using a self-immolative linker and endogenous albumin transport

Enhancing the delivery and release efficiency of hydroxyl agents, constrained by high pKa values and issues of release rate or unstable linkage, is a critical challenge. To address this, a self-immolative linker, composed of a modifiable p-hydroxybenzyl ether and a fast cyclization adapter (N-(ortho-hydroxyphenyl)-N-methylcarbamate) was strategically designed, for the synthesis of prodrugs. The innovative linker not only provides a side chain modification but also facilitates the rapid release of the active payloads, thereby enabling precise drug delivery. Particularly, five prodrug model compounds (J1, J2, J3, J5 and J6) were synthesized to evaluate the release rates by using β-glucuronic acid as trigger and five hydroxyl compounds as model payloads. Significantly, all prodrug model compounds could efficiently release the hydroxyl payloads under the action of β-glucuronidase, validating the robustness of the linker. And then, to assess the drug delivery and release efficiency using endogenous albumin as a transport vehicle, J1148, a SN38 prodrug modified with maleimide side chain was synthesized. Results demonstrated that J1148 covalently bound to plasma albumin through in situ Michael addition, effectively targeting the tumor microenvironment. Activated by β-glucuronidase, J1148 underwent a classical 1, 6-elimination, followed by rapid cyclization of the adapter, thereby releasing SN38. Impressively, J1148 showed excellent therapeutic efficacy against human colonic cancer xenograft model, leading to a significant reduction or even disappearance of tumors (3/6 of mice cured). These findings underscore the potential of the designed linker in the delivery system of hydroxyl agents, positioning it at the forefront of advancements in drug delivery technology.

Design and Characterization of Prodrug-like Inhibitors for Preventing Glutamate Efflux through Reverse Transport

Glutamate transporters are responsible for active transport of the major excitatory neurotransmitter glutamate across the cell membrane, regulating the extracellular glutamate concentration in the mammalian brain. Extracellular glutamate levels in the brain are usually in the submicromolar range but can increase by exocytosis, inhibition of cellular uptake, or through glutamate release by reverse transport, as well as other mechanisms, which can lead to neurodegeneration and neuronal cell death. Such conditions can be encountered upon energy deprivation during an ischemic stroke. Here, we developed acetoxymethyl (AM) ester prodrug-like derivatives of excitatory amino acid transporter (EAAT) inhibitors that permeate the cell membrane and are activated, most likely through hydrolysis by endogenous cellular esterases, to form the active EAAT inhibitor. Upon increase in external K+ concentration, the inhibitors block glutamate efflux by EAAT reverse transport. Using a novel high-affinity fluorescent prodrug-like inhibitor, dl-threo-9-anthracene-methoxy-aspartate (TAOA) AM ester, we demonstrate that the precursor rapidly accumulates inside cells. Electrophysiological methods and fluorescence assays utilizing the iGluSnFR external glutamate sensor were used to demonstrate the efficacy of AM ester-protected inhibitors in inhibiting K+-mediated glutamate release. Together, our results provide evidence for a novel method to potentially prevent glutamate release by reverse transport under pathophysiological conditions in a model cell system, as well as in human astrocytes, while leaving glutamate uptake under physiological conditions operational. This method could have wide-ranging applications in the prevention of glutamate-induced neuronal cell death.

Controlled Ring-Opening Polymerization of Macrocyclic Monomers Based on Ring-Opening/Ring-Closing Cascade Reaction

The development of a controlled ring-opening polymerization (ROP) method for synthesizing backbone-functionalized and sequence-controlled polymers with well-defined architectures from macrocyclic monomers is highly desirable in polymer chemistry. Herein, we developed a novel general controlled ROP of macrocycles for producing backbone functional and sequence-controlled polyurethanes and polyamides with controlled molecular weights and narrow dispersities (Đ < 1.1). The key to this method is the introduction of a trimethyl lock unit, an efficient cyclization-based self-immolative spacer, into the macrocyclic monomer ring as a "ring-opening trigger." ROP is initiated by the attack of a primary amine nucleophile on the ring-activated carbonate/ester group, leading to the ring opening of the macrocyclic monomer. Subsequently, spontaneous 6-exo-trig cyclization of the trimethyl lock unit occurs, detaching this ring-opening trigger and regenerating the primary amine end group. The regenerated primary amine group can then be used to propagate the polymer chain by iterating the ring-opening-ring-closing cascade reaction. The versatile ROP method can be applied in the synthesis of water-soluble polyurethanes, backbone-degradable polyurethanes and poly(ester amide)s, and sequence-controlled poly(amino acid)s with well-defined macromolecular architectures.

Self-Immolative Carbamate Linkers for CD19-Budesonide Antibody-Drug Conjugates

Antibody-drug conjugates consist of potent small-molecule payloads linked to a targeting antibody. Payloads must possess a viable functional group by which a linker for conjugation can be attached. Linker-attachment options remain limited for the connection to payloads via hydroxyl groups. A releasing group based on 2-aminopyridine was developed to enable stable attachment of para-aminobenzyl carbamate (PABC) linkers to the C21-hydroxyl group of budesonide, a glucocorticoid receptor agonist. Payload release involves a cascade of two self-immolative events that are initiated by the protease-mediated cleavage of the dipeptide-PABC bond. Budesonide release rates were determined for a series of payload-linker intermediates in buffered solution at pH 7.4 and 5.4, leading to the identification of 2-aminopyridine as the preferred releasing group. Addition of a poly(ethylene glycol) group improved linker hydrophilicity, thereby providing CD19-budesonide ADCs with suitable properties. ADC23 demonstrated targeted delivery of budesonide to CD19-expressing cells and inhibited B-cell activation in mice.

Siderophore conjugates to combat antibiotic-resistant bacteria

Antimicrobial resistance (AMR) is a global threat to society due to the increasing emergence of multi-drug resistant bacteria that are not susceptible to our last line of defence antibiotics. Exacerbating this issue is a severe gap in antibiotic development, with no new clinically relevant classes of antibiotics developed in the last two decades. The combination of the rapidly increasing emergence of resistance and scarcity of new antibiotics in the clinical pipeline means there is an urgent need for new efficacious treatment strategies. One promising solution, known as the 'Trojan horse' approach, hijacks the iron transport system of bacteria to deliver antibiotics directly into cells - effectively tricking bacteria into killing themselves. This transport system uses natively produced siderophores, which are small molecules with a high affinity for iron. By linking antibiotics to siderophores, to make siderophore antibiotic conjugates, the activity of existing antibiotics can potentially be reinvigorated. The success of this strategy was recently exemplified with the clinical release of cefiderocol, a cephalosporin-siderophore conjugate with potent antibacterial activity against carbapenem-resistant and multi-drug resistant Gram-negative bacilli. This review discusses the recent advancements in siderophore antibiotic conjugates and the challenges associated with the design of these compounds that need to be overcome to deliver more efficacious therapeutics. Potential strategies have also been suggested for new generations of siderophore-antibiotics with enhanced activity.

Mutual leveraging of proximity effects and click chemistry in chemical biology

Nature has the remarkable ability to realize reactions under physiological conditions that normally would require high temperature and other forcing conditions. In doing so, often proximity effects such as simultaneous binding of two reactants in the same pocket and/or strategic positioning of catalytic functional groups are used as ways to achieve otherwise kinetically challenging reactions. Though true biomimicry is challenging, there have been many beautiful examples of how to leverage proximity effects in realizing reactions that otherwise would not readily happen under near-physiological conditions. Along this line, click chemistry is often used to endow proximity effects, and proximity effects are also used to further leverage the facile and bioorthogonal nature of click chemistry. This review brings otherwise seemingly unrelated topics in chemical biology and drug discovery under one unifying theme of mutual leveraging of proximity effects and click chemistry and aims to critically analyze the biomimicry use of such leveraging effects as powerful approaches in chemical biology and drug discovery. We hope that this review demonstrates the power of employing mutual leveraging proximity effects and click chemistry and inspires the development of new strategies that will address unmet needs in chemistry and biology.

Development of an Allenyne-Alkyne [4+2] Cycloaddition and its Application to Total Synthesis of Selaginpulvilin A

A new [4+2] cycloaddition of allenyne-alkyne is developed. The reaction is believed to proceed with forming an α,3-dehydrotoluene intermediate. This species behaves as a σπ-diradical to react with a hydrogen atom donor, whereas it displays a zwitterionic reactivity toward weak nucleophiles. The efficiency of trapping α,3-dehydrotoluene depends not only on its substituents but also the trapping agents. Notable features of the reaction are the activating role of the extra alkyne of the 1,3-diyne that reacts with the allenyne moiety and the opposite mode of trapping with oxygen and nitrogen nucleophiles. Oxygen nucleophiles result in the oxygen-end incorporation at the benzylic position of the α,3-dehydrotoluene, whereas with amine nucleophiles the nitrogen-end is incorporated into the aromatic core. Relying on the allenyne-alkyne cycloaddition as an enabling strategy, a concise total synthesis of phosphodiesterase-4 inhibitory selaginpulvilin A is realized.

Water-Based Dynamic Depsipeptide Chemistry: Building Block Recycling and Oligomer Distribution Control Using Hydration-Dehydration Cycles

The high kinetic barrier to amide bond formation has historically placed narrow constraints on its utility in reversible chemistry applications. Slow kinetics has limited the use of amides for the generation of diverse combinatorial libraries and selection of target molecules. Current strategies for peptide-based dynamic chemistries require the use of nonpolar co-solvents or catalysts or the incorporation of functional groups that facilitate dynamic chemistry between peptides. In light of these limitations, we explored the use of depsipeptides: biorelevant copolymers of amino and hydroxy acids that would circumvent the challenges associated with dynamic peptide chemistry. Here, we describe a model system of N-(α-hydroxyacyl)-amino acid building blocks that reversibly polymerize to form depsipeptides when subjected to two-step evaporation-rehydration cycling under moderate conditions. The hydroxyl groups of these units allow for dynamic ester chemistry between short peptide segments through unmodified carboxyl termini. Selective recycling of building blocks is achieved by exploiting the differential hydrolytic lifetimes of depsipeptide amide and ester bonds, which we show are controllable by adjusting the solution pH, temperature, and time as well as the building blocks' side chains. We demonstrate that the polymerization and breakdown of the depsipeptides are facilitated by cyclic morpholinedione intermediates, and further show how structural properties dictate half-lives and product oligomer distributions using multifunctional building blocks. These results establish a cyclic mode of ester-based reversible depsipeptide formation that temporally separates the polymerization and depolymerization steps for the building blocks and may have implications for prebiotic polymer chemical evolution.

Convenient and Flexible Syntheses of gem-Dimethyl Carboxylic Triggers via Mono-Selective β-C(sp3)-H Arylation of Pivalic Acid with ortho-Substituted Aryl Iodides

This work presents a palladium(II)-catalyzed mono-selective C(sp3)-H arylation of pivalic acid for rapid construction of an important library of 3-aryl-2,2-dimethylpropanoic acids, especially those ortho-substituted-aryl compounds. The strategy greatly streamlines the...

Masked Amino Trimethyl Lock (H2 N-TML) Systems: New Molecular Entities for the Development of Turn-On Fluorophores and Their Application in Hydrogen Sulfide (H2 S) Imaging in Human Cells

Masked trimethyl lock (TML) systems as molecular moieties enabling the bioresponsive release of compounds or dyes in a controlled temporal and spatial manner have been widely applied for the development of drug conjugates, prodrugs or molecular imaging tools. Herein, we report the development of a novel amino trimethyl lock (H₂ N-TML) system as an auto-immolative molecular entity for the release of fluorophores. We designed Cou-TML-N₃ and MURh-TML-N₃ , two azide-masked turn-on fluorophores. The latter was demonstrated to selectively release fluorescent MURh in the presence of physiological concentrations of the redox-signaling molecule H₂ S in vitro and was successfully applied to image H₂ S in human cells.

Peptide-Assisted Nucleic Acid Delivery Systems on the Rise

Concerns associated with nanocarriers' therapeutic efficacy and side effects have led to the development of strategies to advance them into targeted and responsive delivery systems. Owing to their bioactivity and biocompatibility, peptides play a key role in these strategies and, thus, have been extensively studied in nanomedicine. Peptide-based nanocarriers, in particular, have burgeoned with advances in purely peptidic structures and in combinations of peptides, both native and modified, with polymers, lipids, and inorganic nanoparticles. In this review, we summarize advances on peptides promoting gene delivery systems. The efficacy of nucleic acid therapies largely depends on cell internalization and the delivery to subcellular organelles. Hence, the review focuses on nanocarriers where peptides are pivotal in ferrying nucleic acids to their site of action, with a special emphasis on peptides that assist anionic, water-soluble nucleic acids in crossing the membrane barriers they encounter on their way to efficient function. In a second part, we address how peptides advance nanoassembly delivery tools, such that they navigate delivery barriers and release their nucleic acid cargo at specific sites in a controlled fashion.

Bioresponsive nanomedicines based on dynamic covalent bonds

Trends in the development of modern medicine necessitate the efficient delivery of therapeutics to achieve the desired treatment outcomes through precise spatiotemporal accumulation of therapeutics at the disease site. Bioresponsive nanomedicine is a promising platform for this purpose. Dynamic covalent bonds (DCBs) have attracted much attention in studies of the fabrication of bioresponsive nanomedicines with an abundance of combinations of therapeutic modules and carrier function units. DCB-based nanomedicines could be designed to maintain biological friendly synthesis and site-specific release for optimal therapeutic effects, allowing the complex to retain an integrated structure before accumulating at the disease site, but disassembling into individual active components without compromising function in the targeted organs or tissues. In this review, we focus on responsive nanomedicines containing dynamic chemical bonds that can be cleaved by various specific stimuli, enabling achievement of targeted drug release for optimal therapy in various diseases.

Geminal Repulsion Disrupts Diels-Alder Reactions of Geminally Substituted Cyclopentadienes and 4H-Pyrazoles

We have experimentally and computationally explored the sluggish Diels-Alder reactivities of the geminally substituted 5,5-dimethylcyclopentadiene and 5,5-dimethyl-2,3-diazacyclopentadiene (4,4-dimethyl-4H-pyrazole) scaffolds. We found that geminal dimethylation of 1,2,3,4-tetramethylcyclopentadiene to 1,2,3,4,5,5-hexamethylcyclopentadiene decreases the Diels-Alder reactivity towards maleimide by 954-fold. Quantum mechanical calculations revealed that the decreased Diels-Alder reactivities of gem-dimethyl substituted cyclopentadienes and 2,3-diazacyclopentadienes are not a consequence of unfavorable steric interactions between the diene and dienophile as reported previously, but a consequence of the increased repulsion within the gem-dimethyl group in the transition state. The findings have implications for the use of cyclopentadienes in "click" chemistry.

Click, release, and fluoresce: In-vivo generation of CO with concomitant synthesis of a fluorescent reporter

Delivering a therapeutically active gaseous molecule represents very unique challenges in terms of both precise dosing and concentration assessment. To overcome these obstacles, there have been recent reports of using prodrug approaches for the in-vitro and in-vivo generation of carbon monoxide (CO), which is an endogenous signaling molecule with validated therapeutic efficacy in a range of animal models. Some key components of these approaches include the use of a hydrophobicity-driven Diels-Alder reaction under physiological conditions followed by a cheletropic reaction of the corresponding norbornadien-7-one intermediate, leading to extrusion of CO. With proper design, the same approach also leads to the formation of a fluorescent reporter, allowing for quantitative assessment of the amount of CO released. All these allow for a strategy of "click, release, and fluoresce" in delivering a precise dose of carbon monoxide with the ability to "self-report" delivery quantity and efficiency. This strategy has also been further refined to construct a CO delivery platform with additional functionalities such as bioorthogonal labeling, targeting, triggered release, and simultaneously delivery of more than one payload. This review highlights recent developments in this area.

NAD(P)H Quinone Oxidoreductase-1 in Organ and Tumor Tissues: Distinct Activity Levels Observed with a Benzo-rosol-Based Dual-Excitation and Dual-Emission Probe

NAD(P)H quinone oxidoreductase-1 (NQO1), a protective enzyme against cellular oxidative stress, is expressed abnormally high in solid tumors and thus recognized as a cancer biomarker. To develop a fluorescent NQO1 probe with practicality, we investigated benzo-rosol fluorophores linked with a known self-immolative quinone substrate. Four probe candidates exhibited ratiometric sensing behavior toward the enzyme, satisfying our orbital mismatch stratagem proposed before, under dual-excitation and dual-emission conditions that alleviate the spectral overlap issue commonly observed with the ratiometric probes based on intramolecular charge-transfer change. Among the candidates, two ester-linked compounds exhibited hydrolytic instability to water or an esterase, discouraging us to develop such ester-linked probes. One ether-linked, hydrolytically stable probe provided brighter cellular fluorescence than the other and thus was applied to ratiometric imaging of NQO1 in cells and tissues. We found that the enzyme activity levels are much different in organ tissues: stomach (56), kidney (22), colon (9.8), testis (7.8), bladder (5.6), lung (1.2), and muscle (1.0). Furthermore, a markedly high enzyme level (14.6-fold) was observed in a xenograft tumor tissue compared with that in a normal tissue, which suggests that such an NQO1 probe is promising for cancer diagnosis and for studying the enzyme-associated biology.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Prodrugs of Persulfides, Sulfur Dioxide, and Carbon Disulfide: Important Tools for Studying Sulfur Signaling at Various Oxidation States

Significance: Bioactive sulfur species such as hydrogen sulfide (H₂S), persulfide species (R-S_nSH, n ≥ 1), hydrogen polysulfide (H₂S_n, n ≥ 2), sulfur dioxide (SO₂), and carbon disulfide (CS₂) participate in various physiological and/or pathological pathways such as vasodilation, apoptosis, inflammation, and energy metabolism regulation. The oxidation state of the individual sulfur species endows them unique biological activities. Recent Advances: There have been great strides made in achieving molecular understanding of the sulfur-signaling processes. Critical Issues: The development of various chemical tools that deliver reactive sulfur species in a controllable manner has played an important role in understanding the different roles of various sulfur species. In this review, we focus on three types of sulfur species, including persulfide, SO₂, and CS₂. Starting with a brief introduction of their physiological functions, we will then assess the various drug delivery strategies to generate persulfide species, SO₂, and CS₂ as research tools and potentially as therapeutic agents. Future Directions: Development of donors of various sulfur species that respond to distinct stimulus is critical for this field. Another key to the long-term success of this field is the identification of an area of unmet medical need that can be addressed with these sulfur species.

The Different Faces of [Ru(bpy)3Cl2] and fac[Ir(ppy)3] Photocatalysts: Redox Potential Controlled Synthesis of Sulfonylated Fluorenes and Pyrroloindoles from Unactivated Olefins and Sulfonyl Chlorides

A cascade alkene sulfonylation that simultaneously forges C-S and C-C bonds is a highly efficient and powerful approach for directly accessing structurally diverse sulfonylated compounds in a single operation. The reaction was enabled by visible-light-mediated regioselective radical addition of sulfonyl chlorides to 2-arylstyrenes using fac[Ir(ppy)₃] as a photocatalyst, demonstrating its unique role in a photocascade process to execute atom transfer radical addition (ATRA) followed by photocyclization. A new class of sulfonyl-substituted fluorenes and pyrroloindoles, which are useful in the field of photoelectronic materials and medicinal chemistry, was produced in excellent yields by this photocascade reaction. In contrast, the cyclization was interrupted when using the [Ru(bpy)₃Cl₂] catalyst having lower reduction potential, leading only to the formation of a C-S bond and the production of acyclic sulfonylated 2-arylstyrenes under identical reaction conditions. The synthetic utility of the present room-temperature photocatalysis is enhanced by the broad availability of bench-stable sulfonyl chlorides and unactivated olefins, thereby providing a cost-effective and broad-scope protocol.

Activatable cell-penetrating peptides: 15 years of research

An important hurdle for the intracellular delivery of large cargo is the cellular membrane, which protects the cell from exogenous substances. Cell-penetrating peptides (CPPs) can cross this barrier but their use as drug delivery vehicles is hampered by their lack of cell type specificity. Over the past years, several approaches have been explored to control the activity of CPPs that can be primed for cellular uptake. Since the first report on such activatable CPPs (ACPPs) in 2004, various methods of activation have been developed. Here, we provide an overview of the different ACPPs strategies known to date and summarize the benefits, drawbacks, and future directions.

Prodrug Strategies to Improve the Solubility of the HCV NS5A Inhibitor Pibrentasvir (ABT-530)

A research program to discover solubilizing prodrugs of the HCV NS5A inhibitor pibrentasvir (PIB) identified phosphomethyl analog 2 and trimethyl-lock (TML) prodrug 9. The prodrug moiety is attached to a benzimidazole nitrogen atom via an oxymethyl linkage to allow for rapid and complete release of the drug for absorption following phosphate removal by intestinal alkaline phosphatase. These prodrugs have good hydrolytic stability properties and improved solubility compared to PIB, both in aqueous buffer (pH 7) and FESSIF (pH 5). TML prodrug 9 provided superior in vivo performance, delivering high plasma concentrations of PIB in PK studies conducted in mice, dogs, and monkeys. The improved dissolution properties of these phosphate prodrugs provide them the potential to simplify drug dosage forms for PIB-containing HCV therapy.

Pharmacological inhibition of PRMT7 links arginine monomethylation to the cellular stress response

Protein arginine methyltransferases (PRMTs) regulate diverse biological processes and are increasingly being recognized for their potential as drug targets. Here we report the discovery of a potent, selective, and cell-active chemical probe for PRMT7. SGC3027 is a cell permeable prodrug, which in cells is converted to SGC8158, a potent, SAM-competitive PRMT7 inhibitor. Inhibition or knockout of cellular PRMT7 results in drastically reduced levels of arginine monomethylated HSP70 family stress-associated proteins. Structural and biochemical analyses reveal that PRMT7-driven in vitro methylation of HSP70 at R469 requires an ATP-bound, open conformation of HSP70. In cells, SGC3027 inhibits methylation of both constitutive and inducible forms of HSP70, and leads to decreased tolerance for perturbations of proteostasis including heat shock and proteasome inhibitors. These results demonstrate a role for PRMT7 and arginine methylation in stress response.

Protein arginine methyltransferases (PRMTs) are increasingly recognized as potential therapeutic targets but PRMT7 remains an understudied member of this enzyme family. Here, the authors develop a chemical probe for PRMT7 and apply it to elucidate the role of PRMT7 in the cellular stress response.

Mass spectrometric analysis of acid-assisted photochemical release of the trimethyl lock system on the monolayers on gold

We report the acid-assisted photolysis of the trimethyl lock system which has long been harnessed for a variety of applications such as drug delivery, cellular imaging, enzyme activity assays, and surface patterning. By mass spectrometric analysis, we found that photoinduced intramolecular cyclization and the ensuing release of the pendant groups of the trimethyl lock on the self-assembled monolayers proceeded cleanly in the presence of HCl, to give a high yield.

The acid-assisted photolysis of the trimethyl lock on the surface was characterized by mass spectrometry.

Development of Chemical Biology Tools Focusing on Peptide/Amide Bond Cleavage Reaction

Peptides and proteins are involved in almost all biological events. In this review, three chemical biology tools, which were developed for peptide/protein sciences from a viewpoint of peptide/amide bond cleavage, are overviewed. First, study on an artificial amino acid that enables stimulus-responsive functional control of peptides/proteins is briefly described. Two N-S acyl transfer reaction-based tools, one a linker molecule for facile identification of target proteins of bioactive compounds and the other a reagent for selective labeling of proteins of interest, are then discussed.

A chemical probe of CARM1 alters epigenetic plasticity against breast cancer cell invasion

CARM1 is a cancer-relevant protein arginine methyltransferase that regulates many aspects of transcription. Its pharmacological inhibition is a promising anti-cancer strategy. Here SKI-73 (6a in this work) is presented as a CARM1 chemical probe with pro-drug properties. SKI-73 (6a) can rapidly penetrate cell membranes and then be processed into active inhibitors, which are retained intracellularly with 10-fold enrichment for several days. These compounds were characterized for their potency, selectivity, modes of action, and on-target engagement. SKI-73 (6a) recapitulates the effect of CARM1 knockout against breast cancer cell invasion. Single-cell RNA-seq analysis revealed that the SKI-73(6a)-associated reduction of invasiveness acts by altering epigenetic plasticity and suppressing the invasion-prone subpopulation. Interestingly, SKI-73 (6a) and CARM1 knockout alter the epigenetic plasticity with remarkable difference, suggesting distinct modes of action for small-molecule and genetic perturbations. We therefore discovered a CARM1-addiction mechanism of cancer metastasis and developed a chemical probe to target this process.

Drugs that are small molecules have the potential to block the individual proteins that drive the spread of cancer, but their design is a challenge. This is because they need to get inside the cell and find their target without binding to other proteins on the way. However, small molecule drugs often have an electric charge, which makes it hard for them to cross the cell membrane. Additionally, most proteins are not completely unique, making it harder for the drugs to find the correct target.

CARM1 is a protein that plays a role in the spread of breast cancer cells, and scientists are currently looking for a small molecule that will inhibit its action. The group of enzymes that CARM1 belongs to act by taking a small chemical group, called a methyl group, from a molecule called SAM, and transferring it to proteins that switch genes on and off. In the case of CARM1, this changes cell behavior by turning on genes involved in cell movement. Genetically modifying cells so they will not produce any CARM1 stops the spread of breast cancer cells, but developing a drug with the same effects has proved difficult. Existing drugs that can inhibit CARM1 in a test tube struggle to get inside cells and to distinguish between CARM1 and its related enzymes.

Now, Cai et al. have modified and tested a CARM1 inhibitor to address these problems, and find out how these small molecules work. At its core, the inhibitor has a structure very similar to a SAM molecule, so it can fit into the SAM binding pocket of CARM1 and its related enzymes. To stop the inhibitor from binding to other proteins, Cai et al. made small changes to its structure until it only interacted with CARM1.Then, to get the inhibitor inside breast cancer cells, Cai et al. cloaked its charged area with a chemical shield, allowing it to cross the cell membrane. Inside the cell, the chemical shield broke away, allowing the inhibitor to attach to CARM1. Analysis of cells showed that this inhibition only affected the cancer cells most likely to spread. Blocking CARM1 switched off genes involved in cell movement and stopped cancer cells from travelling through 3D gels.

This work is a step towards making a drug that can block CARM1 in cancer cells, but there is still further work to be done. The next stages will be to test whether the new inhibitor works in other types of cancer cells, in living animals, and in human patient samples.

Gold-Catalyzed Aromatizations of 3-Ene-5-siloxy-1,6-diynes with Nitrosoarenes To Enable 1,4-N,O-Functionalizations: One-Pot Construction of 4-Hydroxy-3-aminobenzaldehyde Cores

This work describes gold-catalyzed aromatizations of 3-ene-5-siloxy-1,6-diynes with nitrosoarenes to form 4-hydroxy-3-aminobenzaldehyde derivatives, manifesting the use of nitrosoarenes as 1,4-N,O-functionalization sources. Various 3-ene-5-siloxy-1,6-diynes in benzoid and nonbenzoid types are applicable substrates. A series of ¹⁸O- and ²H-labeling experiments have been conducted to exclude gold-π-alkyne intermediates. We postulate a mechanism of dual gold catalysis involving initial formation of gold-π-alkynylgold species that activates a 1,5-hydrogen shift to form reactive 1,6-dipoles, thus furnishing intramolecular Michael-type reactions with nitrosonium electrophiles.

Design, Synthesis, and Cellular Uptake of Oligonucleotides Bearing Glutathione-Labile Protecting Groups

Glutathione-labile protecting groups for phosphodiester moieties in oligonucleotides were designed, synthesized, and incorporated into oligonucleotides. The protecting groups on the phosphodiester moieties were cleaved in a buffer containing 10 mM glutathione, which was used as a model of intracellular fluid. Cellular uptake of oligonucleotides bearing glutathione-labile protecting groups was strongly affected by the location and number of the protecting groups.

Exploiting the vicinal disubstituent effect on the diastereoselective synthesis of γ and δ lactones

Trifluoroacetic acid catalysed lactonization of vicinal disubstituted γ-hydroxyesters was investigated in different solvents. The reaction kinetics, monitored by NMR spectroscopy, showed that: (i) the vic-disubstituent effect is stereoselective since the anti diastereoisomer ring closes substantially more rapidly than the syn isomer ring; (ii) the anti-vic effect is much stronger than the classical Thorpe-Ingold effect (known also as the gem-disubstituent effect), instead the syn diastereoisomers have rate constants comparable to that of the gem-disubstituted ester; (iii) the vic-effect can be enhanced by increasing the steric hindrance of one of the two substituents or carrying out the reaction in non-polar solvents. DFT computations of energy barriers (ΔG‡) were in good agreement with the experimental data. The distortion/interaction-activation strain model together with the Winstein-Holness kinetic scheme gave more insights into the origin of the vic-effect. An application of this effect consists of the diastereomeric resolution of disubstituted γ and δ lactones, among which are the naturally occurring Nicotiana t. lactone, the whisky and cognac oak lactones, and the Aerangis lactone. Both cis and trans diastereoisomers of these lactones were isolated in good yield and with high diastereomeric excess (de >92%). The selectivities of the diastereomeric resolution process, determined by NMR spectroscopy, are reported as well.

A general strategy for visible-light decaging based on the quinone cis-alkenyl lock

Combining the fast thermal cyclization of o-coumaric acid derivatives with the intramolecular photoreduction of quinones gives new visible-light photoremovable protecting groups absorbing well above 450 nm.

Boronic acids as building blocks for the construction of therapeutically useful bioconjugates

This review summarizes boronic acid's contribution to the development of bioconjugates with a particular focus on the molecular mechanisms underlying its role in the construction and function of the bioconjugate, namely as a bioconjugation warhead, as a payload and as part of a bioconjugate linker.

Development of Protecting Groups for Prodrug-Type Oligonucleotide Medicines

In recent years, nucleic acid-based drug therapeutics have gained considerable attention for their potential in the treatment of various diseases. However, their therapeutic value is greatly hindered by the challenge of delivering them into cells. One possible strategy to improve cellular uptake is the use of "prodrug-type oligonucleotide medicine" in which negatively charged phosphodiester moieties are masked by bio-labile protecting groups. In this review, we describe our recent studies related to bio-labile protecting groups for phosphodiester moieties in the development of prodrug-type oligonucleotide medicines.

Orally Absorbed Derivatives of the β-Lactamase Inhibitor Avibactam. Design of Novel Prodrugs of Sulfate Containing Drugs

Only one FDA-approved β-lactamase inhibitor has ever been orally available: clavulanic acid, approved in 1984. Avibactam, approved by FDA in 2015, is the first of a new class of BLIs called diazabicyclooctanes, or "DBOs". This class has much broader coverage than clavulanic acid but can only be administered by intravenous injection. Herein, we describe the synthesis and testing of the first approved BLI to be rendered orally bioavailable since clavulanic acid (1984).

Advances in redox-responsive drug delivery systems of tumor microenvironment

With the improvement of nanotechnology and nanomaterials, redox-responsive delivery systems have been studied extensively in some critical areas, especially in the field of biomedicine. The system constructed by redox-responsive delivery can be much stable when in circulation. In addition, redox-responsive vectors can respond to the high intracellular level of glutathione and release the loaded cargoes rapidly, only if they reach the site of tumor tissue or targeted cells. Moreover, redox-responsive delivery systems are often applied to significantly improve drug concentrations in targeted cells, increase the therapeutic efficiency and reduce side effects or toxicity of primary drugs. In this review, we focused on the structures and types of current redox-responsive delivery systems and provided a comprehensive overview of relevant researches, in which the disulfide bond containing delivery systems are of the utmost discussion.

Enzyme-Activated Fluorogenic Probes for Live-Cell and in Vivo Imaging

Fluorogenic probes, small-molecule sensors that unmask brilliant fluorescence upon exposure to specific stimuli, are powerful tools for chemical biology. Those probes that respond to enzymatic catalysis illuminate the complex dynamics of biological processes at a level of spatiotemporal detail and sensitivity unmatched by other techniques. Here, we review recent advances in enzyme-activated fluorogenic probes for biological imaging. We organize our survey by enzyme classification, with emphasis on fluorophore masking strategies, modes of enzymatic activation, and the breadth of current and future applications. Key challenges such as probe selectivity and spectroscopic requirements are described alongside therapeutic, diagnostic, and theranostic opportunities.