Dynamic combinatorial/covalent chemistry: a tool to read, generate and modulate the bioactivity of compounds and compound mixtures

Adaptive Covalent Networks Enabled by Dual Reactivity: The Evolution of Reversible Covalent Bonds, Their Molecular Assemblies, and Guest Recognition

Adaptive chemistry allows transformation and selection within molecular networks, and adaptive systems composed of different types of dynamic covalent reactions (DCRs) are challenging. Herein, we demonstrate dual reactivity-based covalent networks encompassing the regulation of and switching between C-N- and C-S-based reversible covalent assemblies. The creation and exchange of C-N- or C-S-derived assemblies exhibiting diverse architectures, including linear structures, macrocycles, and cages, were achieved. The shift of reactivity then permitted the interconversion between C-N- and C-S-containing assemblies. Moreover, the adaption of intramolecular and intermolecular scaffolds was feasible via linker design. The latent hemiaminal chirality center offered a pathway for the induction of chirality within assemblies. Finally, switchable structural change and controlled extraction of ions were realized with Hg²⁺ as a guest for macrocycles. The remarkable complexity of networks described herein could open the door for the utility in sophisticated functional systems.

Tunable Structural Color Patterns Based on the Visible-Light-Responsive Dynamic Diselenide Metathesis

Structural color materials with reversible stimuli-responsiveness to external environment have been widely used in sensors, encryption, display, and other fields. Compared with other stimuli, visible light is highly controllable both temporally and spatially with less damage to materials, which is more suitable for structural color patterning. Herein, a new diselenide-containing shape memory material is prepared and used for creating patterns via visible light stimulus. In this system, the structural color originates from birefringence of stretched materials, whose shapes can be fixed while maintaining the mechanical stress. The fixed stress can be released by diselenide metathesis under visible light irradiation. By regulating the wavelength or irradiation time with a commercial projector, the pattern with tunable structural colors is realized and the structural color pattern can be erased and rewritten arbitrarily. During the patterning process, the optical signal is first stored as mechanical signal and then transformed back to optical signal. It is a new method for preparing visible-light-responsive structural color material and has great potential in display devices, anticounterfeiting labels, and data storage.

n → π* interactions as a versatile tool for controlling dynamic imine chemistry in both organic and aqueous media

The imine bond holds a prominent place in supramolecular chemistry and materials science, and one issue is the stability of imines due to their electrophilic nature. Here we introduced ortho-carboxylate groups into a series of aromatic aldehydes/imines for dictating imine dynamic covalent chemistry (DCC) through n → π* interactions, one class of widespread and yet underused non-covalent interactions. The thermodynamically stabilizing role of carboxylate-aldehyde/imine n → π* interactions in acetonitrile was elucidated by the movement of the imine exchange equilibrium and further supported by crystal analysis. Computational studies provided mechanistic insights for n → π* interactions, the strength of which can surpass that of CH hydrogen bonding and is dependent on the orientation of interacting sites based on natural bond orbital analysis. Moreover, the substituent effect and the combination of recognition sites allowed additional means for modulation. Finally, to show the relevance of our findings ortho-carboxylate containing aldehydes were used to regulate imine formation/exchange in water, and modification of the N-terminus of amino acids and peptides was achieved in a neutral buffer. This work represents the latest example of weak interactions governing DCC and sets the stage for assembly and application studies.

Noncovalent and Dynamic Covalent Chemistry Strategies for Driving Thermoresponsive Phase Transition with Multistimuli and Controlled Encapsulation/Release

We report the development of multiresponsive thermally sensitive polymers through both supramolecular and reversible covalent strategies as well as their use in controlled encapsulation and release. Novel acylhydrazone-based dynamic covalent polymers displaying lower critical solution temperature (LCST) or upper critical solution temperature (UCST) were synthesized. A remarkable control over thermal phase transition can be tuned through multimodes, such as anions, cations, solvent, pH, and competing components. In particular, anion recognition allowed disassembly and thus led to a significant decrease of UCST in dimethyl sulfoxide, and the combination of anion and solvent effects offered additional handle for control. Moreover, the use of anions, cations, as well as pH change was employed for the modulation of LCST-type polymer in water. Furthermore, switching on/off thermoresponsiveness was readily achieved by dynamic covalent exchange. Mechanistic studies also shed light on stimuli-induced changes in aggregation behaviors. Finally, thermally controlled encapsulation and release of hydrophobic and hydrophilic dyes were realized with great repeatability and reversibility, respectively, showing potential in delivery and sensing. The results and strategies described should provide opportunities for many aspects, including dynamic assemblies, complex systems, and adaptive materials.

Emerging functional materials based on chemically designed molecular recognition

The specific interactions responsible for molecular recognition play a crucial role in the fundamental functions of biological systems. Mimicking these interactions remains one of the overriding challenges for advances in both fundamental research in biochemistry and applications in material science. However, current molecular recognition systems based on host–guest supramolecular chemistry rely on familiar platforms (e.g., cyclodextrins, crown ethers, cucurbiturils, calixarenes, etc.) for orienting functionality. These platforms limit the opportunity for diversification of function, especially considering the vast demands in modern material science. Rational design of novel receptor-like systems for both biological and chemical recognition is important for the development of diverse functional materials. In this review, we focus on recent progress in chemically designed molecular recognition and their applications in material science. After a brief introduction to representative strategies, we describe selected advances in these emerging fields. The developed functional materials with dynamic properties including molecular assembly, enzyme-like and bio-recognition abilities are highlighted. We have also selected materials with dynamic properties in contract to traditional supramolecular host–guest systems. Finally, the current limitations and some future trends of these systems are discussed.

The anionic recognition mechanism based on polyol and boronic acid receptors

Chloride, fluoride, dihydrogen phosphate, acetate, bromide, and hydrogen sulfate recognition from polyol and boronic acid receptors is elucidated.

Internal catalysis for dynamic covalent chemistry applications and polymer science

In this review, we provide a concise analysis of internal catalysis as an attractive design principle to combine chemical robustness with reactivity in dynamic covalent chemistry applications and a material context.

Using the dynamic behavior of macrocyclic monomers with a bis(hindered amino)disulfide linker for the preparation of end-functionalized polymers

End-functionalized polymers were synthesized by simply heating a mixture of a macrocyclic compound with one bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS) moiety and bifunctional acyclic BiTEMPS compounds as sources of repeat units and terminal groups, respectively.

Development of a multivalent acetylcholinesterase inhibitor via dynamic combinatorial chemistry

In this study, we report the generation of a polymer based dynamic combinatorial library (DCL) using aldehyde-functionalized linear poly(glycidol) and hydrazide derivatives as initial building blocks. In combination with tetrameric acetylcholinesterase (AChE), a certain type of amplified acylhydrazone side chain is identified and further used for the synthesis of a multivalent AChE inhibitor. The cytotoxicity and inhibition properties of the multivalent inhibitor are evaluated, and the results indicate superior bioactivity compared to the commercial reference Edrophonium chloride.

The Symbiotic Relationship Between Drug Discovery and Organic Chemistry

All pharmaceutical products contain organic molecules; the source may be a natural product or a fully synthetic molecule, or a combination of both. Thus, it follows that organic chemistry underpins both existing and upcoming pharmaceutical products. The reverse relationship has also affected organic synthesis, changing its landscape towards increasingly complex targets. This Review article sets out to give a concise appraisal of this symbiotic relationship between organic chemistry and drug discovery, along with a discussion of the design concepts and highlighting key milestones along the journey. In particular, criteria for a high-quality compound library design enabling efficient virtual navigation of chemical space, as well as rise and fall of concepts for its synthetic exploration (such as combinatorial chemistry; diversity-, biology-, lead-, or fragment-oriented syntheses; and DNA-encoded libraries) are critically surveyed.

Stiffness-switchable DNA-based constitutional dynamic network hydrogels for self-healing and matrix-guided controlled chemical processes

Constitutional dynamic networks (CDNs) attract interest as signal-triggered reconfigurable systems mimicking natural networks. The application of CDNs to control material properties is, however, a major challenge. Here we report on the design of a CDN consisting of four toehold-modified constituents, two of which act as bidentate units for chain-elongating, while the other two form a tetradentate structure acting as a crosslinking unit. Their hybridization yields a hydrogel of medium stiffness controlled by the balance between bidentate and tetradentate units. Stabilization of the tetradentate constituent by an auxiliary effector up-regulates the crosslinking unit, yielding a high-stiffness hydrogel. Conversely, stabilization of one of the bidentate constituents by an orthogonal effector enriches the chain-elongation units leading to a low-stiffness hydrogel. Using appropriate counter effectors, the hydrogels are reversibly switched across low-, medium- and high-stiffness states. The hydrogels are used to develop self-healing and controlled drug-release matrices and functional materials for operating biocatalytic cascades.

Dynamic hydrogels with controllable properties are of interest for a range of applications. Here, the authors report on a DNA hydrogel system which can be tailored to have reversible mechanical changes, reversible shape changes, is self-healing and can be used for controlled release applications.

Dynamic Covalent Switches and Communicating Networks for Tunable Multicolor Luminescent Systems and Vapor-Responsive Materials

Molecular switches are an intensive area of research, and in particular, the control of multistate switching is challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and both permitted the activation of optical switches. The variation in electron-withdrawing competition between the fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling patterns. The combination of switches in situ further enabled the creation of communicating networks for multistate color switching, including white emission, through the delicate control of DCRs in complex mixtures. Finally, reversible and recyclable multiresponsive luminescent materials were achieved with molecular networks on the solid support, allowing visualization of different types of vapors and quantification of primary amine vapors with high sensitivity and wide detection range. The results reported herein should be appealing for future studies of dynamic assemblies, molecular sensing, intelligent materials, and biological labeling.

Self-Healing Hydrogels: The Next Paradigm Shift in Tissue Engineering?

Given their durability and long-term stability, self-healable hydrogels have, in the past few years, emerged as promising replacements for the many brittle hydrogels currently being used in preclinical or clinical trials. To this end, the incompatibility between hydrogel toughness and rapid self-healing remains unaddressed, and therefore most of the self-healable hydrogels still face serious challenges within the dynamic and mechanically demanding environment of human organs/tissues. Furthermore, depending on the target tissue, the self-healing hydrogels must comply with a wide range of properties including electrical, biological, and mechanical. Notably, the incorporation of nanomaterials into double-network hydrogels is showing great promise as a feasible way to generate self-healable hydrogels with the above-mentioned attributes. Here, the recent progress in the development of multifunctional and self-healable hydrogels for various tissue engineering applications is discussed in detail. Their potential applications within the rapidly expanding areas of bioelectronic hydrogels, cyborganics, and soft robotics are further highlighted.

Cell-Penetrating Dynamic-Covalent Benzopolysulfane Networks

Cyclic oligochalcogenides (COCs) are emerging as promising systems to penetrate cells. Clearly better than and different to the reported diselenolanes and epidithiodiketopiperazines, we introduce the benzopolysulfanes (BPS), which show efficient delivery, insensitivity to inhibitors of endocytosis, and compatibility with substrates as large as proteins. This high activity coincides with high reactivity, selectively toward thiols, exceeding exchange rates of disulfides under tension. The result is a dynamic-covalent network of extreme sulfur species, including cyclic oligomers, from dimers to heptamers, with up to nineteen sulfurs in the ring. Selection from this unfolding adaptive network then yields the reactivities and selectivities needed to access new uptake pathways. Contrary to other COCs, BPS show high retention on thiol affinity columns. The identification of new modes of cell penetration is important because they promise new solutions to challenges in delivery and beyond.

Interplay between n→π* Interactions and Dynamic Covalent Bonds: Quantification and Modulation by Solvent Effects

Orbital donor-acceptor interactions play critical roles throughout chemistry, and hence, their regulation and functionalization are of great significance. Herein we demonstrate for the first time the investigation of n→π* interactions through the strategy of dynamic covalent chemistry (DCC), and we further showcase its use in the stabilization of imine. The n→π* interaction between donor X and acceptor aldehyde/imine within 2-X-2'-formylbiphenyl derivatives was found to significantly influence the thermodynamics of imine exchange. The orbital interaction was then quantified through imine exchange, the equilibrium of which was successfully correlated with the difference in natural bond orbital stabilization energy of n→π* interactions of aldehyde and its imine. Moreover, the examination of solvent effects provided insights into the distinct feature of the modulation of n→π* interaction with aprotic and protic solvents. The n→π* interaction involving imine was enhanced in protic solvents due to hydrogen bonding with the solvent. This finding further enabled the stabilization of imine in purely aqueous solution. The strategies and results reported should find application in many fields, including molecular recognition, biological labeling, and asymmetric catalysis.

QCM sensing of multivalent interactions between lectins and well-defined glycosylated nanoplatforms

Quartz crystal microbalance (QCM) methodology has been adopted to unravel important factors contributing to the "cluster glycoside effect" observed in carbohydrate-lectin interactions. Well-defined, glycosylated nanostructures of precise sizes, geometries and functionalization patterns were designed and synthesized, and applied to analysis of the interaction kinetics and thermodynamics with immobilized lectins. The nanostructures were based on Borromean rings, dodecaamine cages, and fullerenes, each of which carrying a defined number of carbohydrate ligands at precise locations. The synthesis of the Borromeates and dodecaamine cages was easily adjustable due to the modular assembly of the structures, resulting in variations in presentation mode. The binding properties of the glycosylated nanoplatforms were evaluated using flow-through QCM technology, as well as hemagglutination inhibition assays, and compared with dodecaglycosylated fullerenes and a monovalent reference. With the QCM setup, the association and dissociation rate constants and the associated equilibrium constants of the interactions could be estimated, and the results used to delineate the multivalency effects of the lectin-nanostructure interactions.

Mechanochemistry of supramolecules

The urge to use alternative energy sources has gained significant attention in the eye of chemists in recent years. Solution-based traditional syntheses are extremely useful, although they are often associated with certain disadvantages like generation of waste as by-products, use of large quantities of solvents which causes environmental hazard, etc. Contrastingly, achieving syntheses through mechanochemical methods are generally time-saving, environmentally friendly and more economical. This review is written to shed some light on supramolecular chemistry and the synthesis of various supramolecules through mechanochemistry.

Organogelating and narcissistic self-sorting behaviour of non-preorganized oligoamides

Depending on the length (n) and the nature of the end group (X), structurally flexible oligoamides OAT and OATe were found to be good organogelators and their mixtures showed narcissistic self-sorting in both the xerogel and wet gel states.

Several series of structurally flexible, non-preorganized oligoamides with carboxylic acid, hydride, N-propargyl amide and N-propyl amide end groups were synthesized and characterized. They were found to be strong organogelators for aromatic solvents. Both the number and density of the amide units, and the nature of the end group were found to influence the gel strength as well as the kinetics of gel formation. Oligomers with a higher number and density of amide units were found to form stronger gels. Rather unexpectedly, a slight change of the end group could significantly affect the enthalpy and entropy of formation of the resulting self-assembly. Oligomers with the N-propargyl amide end group were found to be kinetically trapped in the melted state, which devoid them of forming crystalline zone upon cooling. On the other hand, the corresponding saturated N-propyl amide analog did not show the same effect. Upon mixing of these oligomers, narcissistic self-sorting could be observed in both the wet gel and xerogel states if (i) the difference in the number of amide units is greater than one or (ii) the amide unit densities are different. A semi-quantitative assessment of the extent of self-sorting could be achieved by constructing the corresponding phase diagram of the mixed gel systems. It is concluded that narcissistic self-sorting does not just prevail in mixtures making up of structurally different molecules, but appears to be fairly general even in mixtures of structurally similar molecular homologs.

Two Synthetic Replicators Compete To Process a Dynamic Reagent Pool

Complementary building blocks, comprising a set of four aromatic aldehydes and a set of four nucleophiles-three anilines and one hydroxylamine-combine through condensation reactions to afford a dynamic covalent library (DCL) consisting of the eight starting materials and 16 condensation products. One of the aldehydes and, consequently, all of the DCL members derived from this compound bear an amidopyridine recognition site. Exposure of this DCL to two maleimides, M^p and M^m, each equipped with a carboxylic acid recognition site, results in the formation of a series of products through irreversible 1,3-dipolar cycloaddition reactions with the four nitrones present in the DCL. However, only the two cycloadducts in the product pool that incorporate both recognition sites, T^p and T^m, are self-replicators that can harness the DCL as feedstock for their own formation, facilitating their own synthesis via autocatalytic and cross-catalytic pathways. The ability of these replicators to direct their own formation from the components present in the dynamic reagent pool in response to the input of instructions in the form of preformed replicators is demonstrated through a series of quantitative ¹⁹F{¹H} NMR spectroscopy experiments. Simulations establish the critical relationships between the kinetic and thermodynamic parameters of the replicators, the initial reagent concentrations, and the presence or absence of the DCL and their influence on the competition between T^p and T^m. Thus, we establish the rules that govern the behavior of the competing replicators under conditions where their formation is coupled tightly to the processing of a DCL.

Growing Prospects of Dynamic Covalent Chemistry in Delivery Applications

Delivery remains a major obstacle restricting the potential action of small molecular drugs as well as novel biologics which cannot readily enter cells without the help of a vector. A successful active delivery process involves three steps: (a) tagging the drug with a vector, (b) effective trafficking of this [drug-vector] conjugate through biological barriers, and finally (c) controlled drug release. While covalent bond formation and/or supramolecular association is involved in the making of the [drug-vector] conjugate, the final step requires precisely a controlled dissociation in order to trigger drug release. Therefore, in pursuit of smart, effective, and nontoxic delivery systems, it has become widely recognized that control over dynamic self-assembly could unleash the efficacy of artificial vectors. In this Account, I discuss our endeavors, and those of colleagues, in the recent implementation of Dynamic Covalent Chemistry (DCvC) in delivery applications. DCvC exploits reversible covalent reactions to generate covalent systems that can self-fabricate, adapt, respond, and fall apart in a controlled fashion. A privileged set of reversible covalent reactions has emerged in the community working on delivery applications and is based on condensation reactions (imine, acylhydrazone, oxime), and disulfide and boronate ester formations. The latest developments making this chemistry particularly attractive for such a DCvC approach are discussed. The rational justifying the potential of DCvC in delivery is based on the principle that using such reversible covalent reactions afford transient [drug-vector] conjugates which form spontaneously and chemoselectively, then adapt and self-correct their structure during self-assembly and trafficking thanks to the dynamic nature of the reversible covalent bonds, and finally respond to physicochemical stimuli such as pH and redox changes, thereby enabling controlled dissociation and concomitant drug release. For these reasons, DCvC has recently emerged as a leverage tool with growing prospects for advancing toward smarter delivery systems. The implementation of DCvC can follow three approaches that are discussed herein: (1) dynamic covalent bioconjugates, involving the transient covalent conjugation with a vector, (2) dynamic covalent vectors, involving the controlled dynamic and adaptive assembly and disassembly of vectors that complex drugs through supramolecular association, and (3) dynamic covalent targeting, involving the transient chemoselective formation of covalent bonds with the constituents of cell membranes. While DCvC has already attracted interest in material sciences, the recent results described in this Account showcase the vast potential of DCvC in biological sciences, and in particular in delivery applications where self-fabricated, adaptive, and responsive devices are of utmost importance.

Consecutive feedback-driven constitutional dynamic networks

Cellular transformations are driven by environmentally triggered complex dynamic networks, which include signal-triggered feedback processes, cascaded reactions, and switchable transformations. We apply the structural and functional information encoded in the sequences of nucleic acids to construct signal-triggered constitutional dynamic networks (CDNs) that mimic the functions of natural networks. Using predesigned hairpin structures as triggers, the network generates functional strands, which stabilize one or the other of the constituents of the network, leading to feedback-driven reconfiguration and time-dependent equilibration of the networks. Using structurally designed hairpins, positive-feedback or negative-feedback mechanisms operated by the CDNs are demonstrated. With two predesigned hairpins, the coupled consecutive operations of negative/positive- or positive/positive- feedback cascades are accomplished. The time-dependent composition changes of the networks are well reproduced by chemical kinetics simulations that provide predictive behaviors of the network, under variable auxiliary conditions. Beyond mimicking natural network properties and functions by means of the synthetic nucleic-acid-based CDNs, the systems introduce versatile perspectives for the design of amplified sensors (sensing of miRNA-376a) and the development of logic gate circuits.

The transcription factor STAT5 catalyzes Mannich ligation reactions yielding inhibitors of leukemic cell proliferation

Protein-templated fragment ligations have been established as a powerful method for the assembly and detection of optimized protein ligands. Initially developed for reversible ligations, the method has been expanded to irreversible reactions enabling the formation of super-additive fragment combinations. Here, protein-induced Mannich ligations are discovered as a biocatalytic reaction furnishing inhibitors of the transcription factor STAT5. STAT5 protein catalyzes multicomponent reactions of a phosphate mimetic, formaldehyde, and 1H-tetrazoles yielding protein ligands with greatly increased binding affinity and ligand efficiency. Reactions are induced under physiological conditions selectively by native STAT5 but not by other proteins. Formation of ligation products and (auto-)inhibition of the reaction are quantified and the mechanism is investigated. Inhibitors assembled by STAT5 block specifically the phosphorylation of this protein in a cellular model of acute myeloid leukemia (AML), DNA-binding of STAT5 dimers, expression of downstream targets of the transcription factor, and the proliferation of cancer cells in mice.

The oncogene STAT5 is involved in cancer cell proliferation. Here, the authors use STAT5 protein to assemble its own small molecule inhibitors via Mannich ligation (three-component-reactions) and show that the resultant ligands can inhibit the proliferation of cancer cells in a mouse model.

Multiple adaptation of constitutional dynamic networks and information storage in constitutional distributions of acylhydrazones

We report a study of the behavior of four dynamic covalent libraries (DCLs) based on acylhydrazones aAbB and of the corresponding square constitutional dynamic networks (CDNs) NA-ND under the effect of three agents, namely, metal cations, base + metal cations and light irradiation; in particular, the successful switching of the CDN NB between two orthogonal distributions results, respectively, from metallo-selection and photo-selection. The four DCLs undergo triple adaptation when subjected to the three agents with the generation of specific CDN distributions characteristic of each of the four DCLs. The ternary outputs displayed by the DCLs present three states (-1, 0 and 1) related to three different constitutional distributions expressed in response to the triple inputs applied. This latter process amounts to the storage of molecular information in dynamic distributions rather than in selective interactions between complementary entities undergoing molecular recognition.

The canonical behavior of the entropic component of thermodynamic effective molarity. An attempt at unifying covalent and noncovalent cyclizations

The statistically corrected entropic component of effective molarity (EM_S*) complies with the “canonical” values expressed by the log plot of EM_S* vs. the number n of single bonds in the ring product.

Quadruple hydrogen bonds and thermo-triggered hydrophobic interactions generate dynamic hydrogels to modulate transplanted cell retention

Supramolecular dynamic hydrogels with quadruple hydrogen bonds and thermo-triggered hydrophobic interactions demonstrate a promising capability of modulating transplanted cell retention.

Self-templated synthesis of an orthoformate in,in-cryptand and its bridgehead inversion by dynamic covalent exchange

We report the template-free dynamic covalent self-assembly of a small orthoformate cryptand, which appears to be driven by the formation of two sets of intramolecular, four-centre hydrogen bonds.

A pillar[5]arene with an amino-terminated arm stabilizes the formation of aliphatic hemiaminals and imines

A self-included mono-amino substituted pillar[5]arene efficiently stabilizes the hemiaminal and imine formation from the reaction of aliphatic amines and aldehydes.

Visible-light-induced metathesis reaction between diselenide and ditelluride

A visible-light-responsive metathesis reaction between diselenide and ditelluride proceeding through a radical mechanism without catalysts.

Controlling the Catalytic and Optical Properties of Aggregated Nanoparticles or Semiconductor Quantum Dots Using DNA-Based Constitutional Dynamic Networks

Nucleic acid-based constitutional dynamic networks (CDNs) attract growing interest as a means to mimic complex biological networks. The triggered stabilization of the CDNs allows the dictated guided reversible reconfiguration and re-equilibration of the CDNs to other CDN configurations, where some of the constituents are up-regulated, while other constituents are down-regulated. Although substantial progress in controlling the adaptive dynamic control of the compositions of networks by means of auxiliary triggers was demonstrated, the use of CDNs as active ensembles for controlling chemical functionalities is still a challenge. We report on the assembly of signal-triggered CDN systems that guide the switchable aggregation of Au nanoparticles (NPs), thereby controlling their plasmonic properties and their catalytic functions (Au NPs-catalyzed oxidation of l-DOPA to dopachrome). In addition, we demonstrate that the triggered and orthogonal up-regulation and down-regulation of the constituents of the CDNs leads to the dictated aggregation of different-sized CdSe/ZnS quantum dots (QDs), cross-linked by K⁺-ion-stabilized G-quadruplex units. The incorporation of hemin into the G-quadruplex cross-linking units yields horseradish peroxidase-mimicking DNAzyme units that catalyze the generation of chemiluminescence via the oxidation of luminol by H₂O₂. The resulting chemiluminescence stimulates the chemiluminescence resonance energy transfer (CRET) process to the QDs, resulting in the luminescence of the two-sized QDs. By the application of appropriate triggers, the CDN-dictated up-regulation and down-regulation of the different-sized QDs aggregates are demonstrated, and the control over the photophysical functions of the different-sized QDs, by means of the CDNs, is highlighted.

Discovery of a Biologically Active Bromodomain Inhibitor by Target-Directed Dynamic Combinatorial Chemistry

Target-directed dynamic combinatorial chemistry (DCC) has emerged as a strategy for the identification of inhibitors of relevant therapeutic targets. In this contribution, we use this strategy for the identification of a high-affinity binder of a parasite target, the Trypanosoma cruzi bromodomain-containing protein TcBDF3. This protein is essential for viability of T. cruzi, the protozoan parasite that causes Chagas disease. A small dynamic library of acylhydrazones was prepared from aldehydes and acylhydrazides at neutral pH in the presence of aniline. The most amplified library member shows (a) high affinity for the template, (b) interesting antiparasitic activity against different parasite forms, and (c) low toxicity against Vero cells. In addition, parasites are rescued from the compound toxicity by TcBDF3 overexpression, suggesting that the toxicity of this compound is due to the TcBDF3 inhibition, i.e., the binding event that initially drives the molecular amplification is reproduced in the parasite, leading to selective toxicity.

Dynamic covalent bond-based hydrogels with superior compressive strength, exceptional slice-resistance and self-healing properties

A novel dynamic-covalent bond-based single network hydrogel was developed, of which the failure compressive stress and strain as well as the failure tensile stress and strain could exceed 27.3 MPa and 98.4% as well as 0.23 MPa and 282.3%, respectively. In addition, the gel shows remarkable slice-resistance and self-healing properties.

Design and Synthesis of Bioisosteres of Acylhydrazones as Stable Inhibitors of the Aspartic Protease Endothiapepsin

Acylhydrazone‐based dynamic combinatorial chemistry (DCC) is a powerful strategy for the rapid identification of novel hits. Even though acylhydrazones are important structural motifs in medicinal chemistry, their further progression in development may be hampered by major instability and potential toxicity under physiological conditions. It is therefore of paramount importance to identify stable replacements for acylhydrazone linkers. Herein, we present the first report on the design and synthesis of stable bioisosteres of acylhydrazone‐based inhibitors of the aspartic protease endothiapepsin as a follow‐up to a DCC study. The most successful bioisostere is equipotent, bears an amide linker, and we confirmed its binding mode by X‐ray crystallography. Having some validated bioisosteres of acylhydrazones readily available might accelerate hit‐to‐lead optimization in future acylhydrazone‐based DCC projects.

Multiprotein Dynamic Combinatorial Chemistry: A Strategy for the Simultaneous Discovery of Subfamily-Selective Inhibitors for Nucleic Acid Demethylases FTO and ALKBH3

Dynamic combinatorial chemistry (DCC) is a powerful supramolecular approach for discovering ligands for biomolecules. To date, most, if not all, biologically templated DCC systems employ only a single biomolecule to direct the self-assembly process. To expand the scope of DCC, herein, a novel multiprotein DCC strategy has been developed that combines the discriminatory power of a zwitterionic "thermal tag" with the sensitivity of differential scanning fluorimetry. This strategy is highly sensitive and could differentiate the binding of ligands to structurally similar subfamily members. Through this strategy, it was possible to simultaneously identify subfamily-selective probes against two clinically important epigenetic enzymes: FTO (7; IC₅₀ =2.6 μm) and ALKBH3 (8; IC₅₀ =3.7 μm). To date, this is the first report of a subfamily-selective ALKBH3 inhibitor. The developed strategy could, in principle, be adapted to a broad range of proteins; thus it is of broad scientific interest.

Three Switchable Orthogonal Dynamic Covalent Reactions and Complex Networks Based on the Control of Dual Reactivity

Achieving complexity is central to the creation of chemical systems, inspired by natural systems. Herein we introduce a strategy of switchable orthogonal dynamic covalent chemistry (DCC) toward the regulation of complex dynamic networks. The control of dual reactivity of tautomers and resulting pathways allowed reversible covalent bonding of a large scope of primary amines, secondary amines, alcohols, and thiols with high efficiency. The selection of reaction pathways next enabled the realization of orthogonal but switchable dynamic covalent reactions (DCRs) with nucleophile pairs of amine/alcohol, alcohol/thiol, and amine/thiol by varying protonation and oxidation states. Control experiments confirmed the crucial role of dual reactivity on the stability and switchability of DCRs. The specificity toward amines, alcohols, and thiols, as well as interconversion between their corresponding assemblies, was further accomplished in one vessel, thus creating tunable communicating networks with three types of DCRs. Moreover, the switchable orthogonality combined with differential reactivity of multiple sulfonamides and nucleophiles enhanced the complexity within dynamic libraries. The generality and versatility of our approaches should facilitate their incorporation into many aspects of chemistry endeavors.

Fluorescent "keep-on" type pharmacophore obtained from dynamic combinatorial library of Schiff bases

We established a novel principle for fluorescence detection of a target protein. A low-molecular-weight fluorescent pharmacophore, as a targeted probe, was selected from a dynamic combinatorial library of Schiff bases. The pharmacophore retains its fluorescence when bound to the hydrophobic site of the target, whereas it loses it because of hydrolysis when unbound. Graphical abstract We describe a novel concept for detection of a target protein (i.e., HSA) by using a keep-on-type fluorescent pharmacophore which is discovered from a dynamic combinatorial library of Schiff bases. When the target is absent, the keep-on-pharmacophore is degraded by hydrolysis, with the result that we can see no fluorescence.