Bioorthogonal regulation of DNA circuits for smart intracellular microRNA imaging

Catalytic DNA circuits represent a versatile toolbox for tracking intracellular biomarkers yet are constrained with low anti-interference capacity originating from their severe off-site activation. Herein, by introducing an unprecedented endogenous DNA repairing enzyme-powered pre-selection strategy, we develop a sequential and specific on-site activated catalytic DNA circuit for achieving the cancer cell-selective imaging of microRNA with high anti-interference capacity. Initially, the circuitry reactant is firmly caged by an elongated stabilizing duplex segment with a recognition/cleavage site of a cell-specific DNA repairing enzyme, which can prevent undesired signal leakage prior to its exposure to target cells. Then, the intrinsic DNA repairing enzyme of target cells can liberate the DNA probe for efficient intracellular microRNA imaging via the multiply guaranteed molecular recognition/activation procedures. This bioorthogonal regulated DNA circuit presents a modular and programmable amplification strategy for highly reliable assays of intracellular biomarkers, and provides a pivotal molecular toolbox for living systems.

An on-site bioorthogonal regulated DNA circuit was developed by introducing an endogenous DNA repairing enzyme-mediated sequential activation strategy to achieve cancer cell-selective microRNA imaging with high anti-interference ability.     

Polyvalent spherical aptamer engineered macrophages: X-ray-actuated phenotypic transformation for tumor immunotherapy

Spatiotemporally activatable immune cells are promising for tumor immunotherapy owing to their potential high specificity and low side effects. Herein, we developed an X-ray-induced phenotypic transformation (X-PT) strategy through macrophage engineering for safe and efficient tumor immunotherapy. Without complex genetic engineering, the cell membranes of M0-type macrophages were chemically engineered with AS1411 aptamer-based polyvalent spherical aptamer (PSA) via the combination of metabolic glycan labelling and bioorthogonal click reaction. Owing to the superior specificity, affinity and polyvalent binding effects of the high-density AS1411 aptamers, the engineered macrophages could easily recognize and adhere to tumor cells. With further X-ray irradiation, reactive oxygen species (ROS) generated by the Au-based PSA could efficiently transform the accumulated macrophages in situ from biocompatible M0 into antitumoral M1 phenotype via activating the nuclear factor κB signaling pathway, thereby achieving tumor-specific killing. In vitro and in vivo experiments confirmed the high tumor recognition and X-ray-induced polarization effect of the engineered macrophages. Compared to natural macrophages, our engineered macrophages significantly inhibited tumor growth in mice even if the radiation dose was reduced by three-fold. We believe this X-PT strategy will open a new avenue for clinical immune cell-based therapy.

An X-ray-induced phenotypic transformation strategy (X-PT) through macrophage engineering was developed for safe and effective immunotherapy.     

Direct decarboxylation of ten-eleven translocation-produced 5-carboxylcytosine in mammalian genomes forms a new mechanism for active DNA demethylation

DNA cytosine methylation (5-methylcytosine, 5mC) is the most important epigenetic mark in higher eukaryotes. 5mC in genomes is dynamically controlled by writers and erasers. DNA (cytosine-5)-methyltransferases (DNMTs) are responsible for the generation and maintenance of 5mC in genomes. Active demethylation of 5-methylcytosine (5mC) is achieved by ten-eleven translocation (TET) dioxygenase-mediated oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). 5fC and 5caC are further processed by thymine DNA glycosylase (TDG)-initiated base excision repair (BER) to restore unmodified cytosines. The TET-TDG-BER pathway could cause the production of DNA strand breaks and therefore jeopardize the integrity of genomes. Here, we investigated the direct decarboxylation of 5caC in mammalian genomes by using metabolic labeling with 2′-fluorinated 5caC (F-5caC) and mass spectrometry analysis. Our results clearly demonstrated the decarboxylation of 5caC occurring in mammalian genomes, which unveiled that, in addition to the TET-TDG-BER pathway, the direct decarboxylation of TET-produced 5caC constituted a new pathway for active demethylation of 5mC in mammalian genomes.

We demonstrated that the ten-eleven translocation (TET) dioxygenase-mediated oxidation of 5-methylcytosine followed by direct decarboxylation of 5-carboxylcytosine constitutes a novel pathway for active DNA demethylation in mammalian genomes.     

Electrooxidative dearomatization of biaryls: synthesis of tri- and difluoromethylated spiro[5.5]trienones

Radical spirocyclization via dearomatization has emerged as an attractive strategy for the rapid synthesis of structurally diverse spiro molecules. We report the use of electrochemistry to perform an oxidative dearomatization of biaryls leading to tri- and difluoromethylated spiro[5.5]trienones in a user friendly undivided cell set-up and a constant current mode. The catalyst- and chemical oxidant-free dearomatization procedure features ample scope, and employs electricity as the green and sole oxidant.

Radical spirocyclization via dearomatization has emerged as an attractive strategy for the rapid synthesis of structurally diverse spiro molecules.     

Cell–cell interactions via non-covalent click chemistry

Metabolic glycoengineering with unnatural sugars became a valuable tool for introducing recognition markers on the cell membranes via bioorthogonal chemistry. By using this strategy, we functionalized the surface of tumor and T cells using complementary artificial markers based on both β-cyclodextrins (β-CDs) and adamantyl trimers, respectively. Once tied on cell surfaces, the artificial markers induced cell–cell adhesion through non-covalent click chemistry. These unnatural interactions between A459 lung tumor cells and Jurkat T cells triggered the activation of natural killer (NK) cells thanks to the increased production of interleukin-2 (IL-2) in the vicinity of cancer cells, leading ultimately to their cytolysis. The ready-to-use surface markers designed in this study can be easily inserted on the membrane of a wide range of cells previously submitted to metabolic glycoengineering, thereby offering a simple way to investigate and manipulate intercellular interactions.

We designed complementary artificial markers that were introduced on the surface of cells previously modified by metabolic glycoengineering. These recognition markers enable unnatural cell–cell adhesion through non-covalent click chemistry.     

Enabling chemical protein (semi)synthesis via reducible solubilizing tags (RSTs)

Chemical synthesis of proteins with poor solubility presents a challenging task. The existing solubilizing tag strategies are not suitable for the expressed protein segment. To address this issue, we report herein that solubilizing tags could be introduced at the side chain of the peptide and C-terminal peptide salicylaldehyde esters via a disulfide linker. Such reducible solubilizing tags (RSTs) are compatible with peptide salicylaldehyde ester-mediated Ser/Thr ligation and Cys/Pen ligation for purifying and ligating peptides with poor solubility. This strategy features operational simplicity and readily accessible materials. Both the protein 2B4 cytoplasmic tail and FCER1G protein have been successfully synthesized via this strategy. Of particular note, the RST strategy could be used for solubilizing the expressed protein segment for protein semi-synthesis of the HMGB1 protein.

The reducible solubilizing tag strategy served as a simple and powerful method for the chemical synthesis and semi-synthesis via Ser/Thr ligation and Cys/Pen ligation of extensive self-assembly peptides, membrane proteins with poor solubility.     

The Morita–Baylis–Hillman reaction for non-electron-deficient olefins enabled by photoredox catalysis

A strategy for overcoming the limitation of the Morita–Baylis–Hillman (MBH) reaction, which is only applicable to electron-deficient olefins, has been achieved via visible-light induced photoredox catalysis in this report. A series of non-electron-deficient olefins underwent the MBH reaction smoothly via a novel photoredox-quinuclidine dual catalysis. The in situ formed key β-quinuclidinium radical intermediates, derived from the addition of olefins with quinuclidinium radical cations, are used to enable the MBH reaction of non-electron-deficient olefins. On the basis of previous reports, a plausible mechanism is suggested. Mechanistic studies, such as radical probe experiments and density functional theory (DFT) calculations, were also conducted to support our proposed reaction pathways.

A strategy for overcoming the limitation of the Morita–Baylis–Hillman (MBH) reaction, which is only applicable to electron-deficient olefins, has been achieved via visible-light induced photoredox catalysis in this report.     

In vivo metal-catalyzed SeCT therapy by a proapoptotic peptide

Selective cell tagging (SeCT) therapy is a strategy for labeling a targeted cell with certain chemical moieties via a catalytic chemical transformation in order to elicit a therapeutic effect. Herein, we report a cancer therapy based on targeted cell surface tagging with proapoptotic peptides (Ac-GGKLFG-X; X = reactive group) that induce apoptosis when attached to the cell surface. Using either Au-catalyzed amidation or Ru-catalyzed alkylation, these proapoptotic peptides showed excellent therapeutic effects both in vitro and in vivo. In particular, co-treatment with proapoptotic peptide and the carrier–Ru complex significantly and synergistically inhibited tumor growth and prolonged survival rate of tumor-bearing mice after only a single injection. This is the first report of Ru catalyst application in vivo, and this approach could be used in SeCT for cancer therapy.

The combination of a proapoptotic peptide with covalent tagging and a carrier-Ru-complex inhibited tumor growth in mice after a single injection.     

A crosslinked colloidal network of peptide/nucleic base amphiphiles for targeted cancer cell encapsulation

The use of peptide amphiphiles (PAs) is becoming increasingly popular, not only because of their unique self-assembly properties but also due to the versatility of designs, allowing biological responsiveness, biocompatibility, and easy synthesis, which could potentially contribute to new drug design and disease treatment concepts. Oligonucleotides, another major functional bio-macromolecule class, have been introduced recently as new functional building blocks into PAs, further enriching the tools available for the fabrication of bio-functional PAs. Taking advantage of this, in the present work, two nucleic base-linked (adenine, A and thymine, T) RGD-rich peptide amphiphiles (NPAs) containing the fluorophores naphthalimide and rhodamine (Nph-A and Rh-T) were designed and synthesized. The two NPAs exhibit distinctive assembly behaviours with spherical (Rh-T) and fibrous (Nph-A) morphologies, and mixing Nph-A with Rh-T leads to a densely crosslinked colloidal network (Nph-A/Rh-T) via mutually promoted supramolecular polymerization via nucleation-growth assembly. Because of the RGD-rich sequences in the crosslinked network, further research on in situ targeted cancer cell (MDA-MB-231) encapsulation via RGD–integrin recognition was performed, and the modulation of cell behaviours (e.g., cell viability and migration) was demonstrated using both confocal laser scanning microscopy (CLSM) imaging and a scratch wound healing assay.

A cross-linking of peptide–nucleic base amphiphiles leads to a dense colloidal network that can perform targeted cancer cell encapsulation in situ.     

A general strategy for in situ assembly of light-up fluorophores via bioorthogonal Suzuki-Miyaura cross-coupling

Herein we presented a general strategy for in situ assembly of intramolecular charge-transfer (ICT)-based light-up fluorophores via bioorthogonal Suzuki-Miyaura cross-coupling reaction. By introducing iodo group at the appropriate position, five fluorophores with different scaffolds including naphthalimide, coumarin, naphthalene sulfonate, nitrobenzoxadiazole, and acetonaphthone, were designed as bioorthogonal multicolor fluorogenic probes, which could produce significant fluorescence enhancement and high fluorescence quantum yield after Suzuki-Miyaura reaction with aryl boronic acid or boronate. Manipulating the substituents and π scaffold in the fluorophores allows fine-tuning of their photophysical properties. With this strategy, we succeeded in peptide conjugation, no-wash fluorogenic protein labeling, and mitochondria-selective bioorthogonal imaging in live cells.     

Linking metal–organic cages pairwise as a design approach for assembling multivariate crystalline materials

Using metal–organic cages (MOCs) as preformed supermolecular building-blocks (SBBs) is a powerful strategy to design functional metal–organic frameworks (MOFs) with control over the pore architecture and connectivity. However, introducing chemical complexity into the network via this route is limited as most methodologies focus on only one type of MOC as the building-block. Herein we present the pairwise linking of MOCs as a design approach to introduce defined chemical complexity into porous materials. Our methodology exploits preferential Rh-aniline coordination and stoichiometric control to rationally link Cu₄L₄ and Rh₄L₄ MOCs into chemically complex, yet extremely well-defined crystalline solids. This strategy is expected to open up significant new possibilities to design bespoke multi-functional materials with atomistic control over the location and ordering of chemical functionalities.

A new strategy to design atomically precise multivariate metal–organic frameworks is presented. This is achieved by linking two preformed metal–organic cages via a precisely tuned Rh–aniline interaction.     

Hypervalent iodine promoted the synthesis of cycloheptatrienes and cyclopropanes

A new strategy is reported for intramolecular Buchner-type reactions using PIDA as a promotor. Traditionally, the Buchner reaction is achieved via Rh-carbenoids derived from Rh^II catalysts with diazo compounds. Herein, the first metal-free Buchner-type reaction to construct highly strained cycloheptatriene- and cyclopropane-fused lactams is presented. The advantage of these transformations is in their mild reaction conditions, simple operation, broad functional group compatibility and rapid synthetic protocol. In addition, scaled-up experiments and a series of follow-up synthetic procedures were performed to clarify the flexibility and practicability of this method. DFT calculations were carried out to clarify the mechanism.

A new strategy is reported for intramolecular Buchner-type reactions using PIDA as a promotor.     

Real-time imaging of cell-surface proteins with antibody-based fluorogenic probes

Cell-surface proteins, working as key agents in various diseases, are the targets for around 66% of approved human drugs. A general strategy to selectively detect these proteins in a real-time manner is expected to facilitate the development of new drugs and medical diagnoses. Although brilliant successes were attained using small-molecule probes, they could cover a narrow range of targets due to the lack of suitable ligands and some of them suffer from selectivity issues. We report herein an antibody-based fluorogenic probe prepared via a two-step chemical modification under physiological conditions, to fulfill the selective recognition and wash-free imaging of membrane proteins, establishing a modular strategy with broad implications for biochemical research and for therapeutics.

A modular strategy to convert commercially available antibodies into fluorogenic probes has been developed, enabling selective recognition and wash-free imaging of endogenous membrane proteins.      

Visible-light-induced transition metal and photosensitizer free decarbonylative addition of amino-arylaldehydes to ketones

The decarbonylative-coupling reaction is generally promoted by transition metals (via organometallic complexes) or peroxides (via radical intermediates), often at high temperatures to facilitate the CO release. Herein, a visible-light-induced, transition metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes at room temperature is reported. Tertiary/secondary alcohols were obtained in moderate to excellent yields promoted by using CsF under mild conditions. The detailed mechanistic investigation showed that the reaction proceeded through photoexcitation–decarbonylation of the aldehyde to generate an aromatic anion, followed by its addition to ketones/aldehydes. The reaction mechanism was verified by the density functional theory (DFT) calculations.

A visible-light-induced, transition-metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes via anion intermediates at room temperature is developed.     

CO/light dual-activatable Ru(ii)-conjugated oligomer agent for lysosome-targeted multimodal cancer therapeutics

Stimuli-activatable and subcellular organelle-targeted agents with multimodal therapeutics are urgently desired for highly precise and effective cancer treatment. Herein, a CO/light dual-activatable Ru(ii)-oligo-(thiophene ethynylene) (Ru-OTE) for lysosome-targeted cancer therapy is reported. Ru-OTE is prepared via the coordination-driven self-assembly of a cationic conjugated oligomer (OTE-BN) ligand and a Ru(ii) center. Upon the dual-triggering of internal gaseous signaling molecular CO and external light, Ru-OTE undergoes ligand substitution and releases OTE-BN followed by dramatic fluorescence recovery, which could be used for monitoring drug delivery and imaging guided anticancer treatments. The released OTE-BN selectively accumulates in lysosomes, physically breaking their integrity. Then, the generated cytotoxic singlet oxygen (¹O₂) causes severe lysosome damage, thus leading to cancer cell death via photodynamic therapy (PDT). Meanwhile, the release of the Ru(ii) core also suppresses cancer cell growth as an anticancer metal drug. Its significant anticancer effect is realized via the multimodal therapeutics of physical disruption/PDT/chemotherapy. Importantly, Ru-OTE can be directly photo-activated using a two-photon laser (800 nm) for efficient drug release and near-infrared PDT. Furthermore, Ru-OTE with light irradiation inhibits tumor growth in an MDA-MB-231 breast tumor model with negligible side effects. This study demonstrates that the development of an activatable Ru(ii)-conjugated oligomer potential drug provides a new strategy for effective subcellular organelle-targeted multimodal cancer therapeutics.

The anticancer therapeutics of lysosome disruption/PDT/chemotherapy based on Ru-OTE complex was achieved, which provides a new strategy for developing multimodal and effective stimuli-activatable subcellular organelle-targeted cancer therapeutics.     

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4–8 transition metal catalysts

In this Perspective, we discuss recent syntheses of 5- and 6-membered aromatic heterocycles via multicomponent reactions (MCRs) that are catalyzed by group 4–8 transition metals. These MCRs can be categorized based on the substrate components used to generate the cyclized product, as well as on common mechanistic features between the catalyst systems. These particular groupings are intended to highlight mechanistic and strategic similarities between otherwise disparate transition metals and to encourage future work exploring related systems with otherwise-overlooked elements. Importantly, in many cases these early- to mid-transition metal catalysts have been shown to be as effective for heterocycle syntheses as the later (and more commonly implemented) group 9–11 metals.

In this Perspective, we discuss recent syntheses of 5- and 6-membered aromatic heterocycles via multicomponent reactions (MCRs) catalyzed by group 4–8 transition metals, with a focus on common mechanisms and synthetic strategies across the series.     

Rhodium-catalysed ortho-alkynylation of nitroarenes

The ortho-alkynylation of nitro-(hetero)arenes takes place in the presence of a Rh(iii) catalyst to deliver a wide variety of alkynylated nitroarenes regioselectively. These interesting products could be further derivatized by selective reduction of the nitro group or palladium-catalysed couplings. Experimental and computational mechanistic studies demonstrate that the reaction proceeds via a turnover-limiting electrophilic C–H metalation ortho to the strongly electron-withdrawing nitro group.

Rh(iii)-catalyzed ortho-alkynylation of nitro-(hetero)arenes leads to a wide variety of alkynylated nitroarenes via a turnover-limiting electrophilic C–H ortho-metalation.     

Synthesis of tryptophan-containing 2,5-diketopiperazines via sequential C–H activation: total syntheses of tryprostatin A,maremycins A and B

Indole 2,5-diketopiperazines (DKPs) are an important type of metabolic cyclic dipeptides containing a tryptophan (Trp) unit possessing a range of interesting biological activities. The intriguing structural features and divergent activities have stimulated tremendous efforts towards their efficient synthesis. Herein, we report the development of a unified strategy for the synthesis of three Trp-containing DKPs, namely tryprostatin A, and maremycins A and B, via a sequential C–H activation strategy. The key Trp skeletons were synthesized from the inexpensive, readily available alanine via a Pd(ii)-catalyzed β-methyl C(sp³)–H monoarylation. A subsequent C2-selective prenylation of the resulting 6-OMe-Trp by Pd/norbornene-promoted C–H activation led to the total synthesis of tryprostatin A in 12 linear steps from alanine with 25% overall yield. Meanwhile, total syntheses of maremycins A and B were successfully accomplished using a sequential Pd-catalyzed methylene C(sp³)–H methylation as the key step in 15 linear steps from alanine.

Indole 2,5-diketopiperazines (DKPs) are an important type of metabolic cyclic dipeptides containing a tryptophan (Trp) unit possessing a range of interesting biological activities.     

Regiodivergent sulfonylarylation of 1,3-enynes via nickel/photoredox dual catalysis

Catalytic difunctionalization of 1,3-enynes represents an efficient and versatile approach to rapidly assemble multifunctional propargylic compounds, allenes and 1,3-dienes. Controlling selectivity in such addition reactions has been a long-standing challenging task due to multiple reactive centers resulting from the conjugated structure of 1,3-enynes. Herein, we present a straightforward method for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis. Hinging on the nature of 1,3-enynes, diverse reaction pathways are feasible: synthesis of α-allenyl sulfones via 1,4-sulfonylarylation, or preparation of (E)-1,3-dienyl sulfones with high chemo-, regio- and stereoselectivity through 3,4-sulfonylarylation. Notably, this is the first example that nickel and photoredox catalysis are merged to achieve efficient and versatile difunctionalization of 1,3-enynes.

A mild reaction protocol for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis has been developed, which led to efficient synthesis of α-allenyl sulfones or 1,3-dienyl sulfones.