Key structural features to favour imines over hydrates in water: pyridoxal phosphate as a muse.

Imination reactions in water represent a challenge not only because of the high propensity of imines to be hydrolysed but also as a result of the competing hydrate formation through H2O addition to the aldehyde. In the present work we report a successful approach that allows for favouring imitation reactions while silencing hydrate formation. Such remarkable reactivity and selectivity can be attained by fine-tuning the electronic and steric structural features of the ortho-substituents of the carbonyl groups. It resulted from studying the structure-reactivity relationships in a series of condensation reactions between different amines and aldehydes, comparing the results to the ones obtained in the presence of the biologically-relevant pyridoxal phosphate (PLP). The key role of negatively-charged and sterically-crowding units (i.e., sulfonate groups) in disfavouring hydrate formation was corroborated by DFT and steric-hindrance calculations. Furthermore, the best-performing aldehyde leads to higher imine yields, selectivity and stability than those of PLP itself, allowing for the inhibition of a PLP-dependent enzyme (transaminase) through dynamic aldimine exchange. These results will increase the applicability of imine-based dynamic covalent chemistry (DCvC) under physiological conditions and will pave the way for the design of new carbonyl derivatives that might be used in the dynamic modification of biomolecules.

Constitutional adaptation to pKa modulation by remote ester hydrolysis.

The mechanisms through which environmental conditions affect the expression of interconnected species is a key step to comprehending the principles underlying complex chemical processes. In Nature, chemical modifications triggered by the environment have a major impact on the structure and function of biomolecules and regulate different reaction pathways. Yet, minimalistic artificial systems implementing related adaptation behaviours remain barely explored. The hydrolysis of amino acid methyl esters to their corresponding amino acids leads to a drastic change in pKa (ca. 7 and 9, respectively) that protonates the free amino group at physiological conditions. Dynamic covalent libraries (DCvLs) based on amino acid methyl esters and aldehydes respond to such hydrolysis and lead to constitutional adaptation. Each of the libraries studied experiences a DCvL conversion allowing for constituent selection due to the silencing of the zwitterionic amino acids towards imine formation. The selective action of different enzymes on the DCvLs results in states with simplified constitutional distributions and transient chirality. When additional components (i.e., scavengers) that are not affected by hydrolysis are introduced into the dynamic libraries, the amino acid methyl ester hydrolysis induces the up-regulation of the constituents made of these scavenging components. In these systems, the constituent distribution is resolved from a scrambled mixture of imines to a state characterized by the predominance of a single aldimine. Remarkably, although the final libraries display higher "simplexity", the different transient states present an increased complexity that allows for the emergence of organized structures [micelle formation] and distributions [up-regulation of two antagonistic constituents]. This reactive site inhibition by a remote chemical modification resembles the scenario found in some enzymes for the regulation of their activity through proximal post-translational modifications.

Triply Adaptive Libraries of Dynamic Covalent Macrocycles: Switching between Sorted and Unsorted States.

Dynamic noncovalent and covalent chemistries have enabled the constitutional modulation of chemical entities within chemical dynamic systems. The switching between order and disorder, i.e., self-sorted and unsorted states of constitutional dynamic libraries, remains challenging. Herein, we study the adaptive behaviors of a dynamic library of imine macrocycles generated from dialdehydes and diamines, seeking ways to exert control over sorting and unsorting processes. The distribution of constituents in the present library of dynamic macrocycles is modulated in response to internal and external effectors (e.g., time, metal cations, and chemical fuels), resulting in the transient amplification of self-sorted constituents in out-of-equilibrium states. The present study showcases higher complexity in systems subject to multiple adaptation through the dynamic interconversion between singularity/order and diversity/disorder.

Triple Adaptation of Constitutional Dynamic Networks of Imines in Response to Micellar Agents: Internal Uptake-Interfacial Localization-Shape Transition.

Understanding the behavior of complex chemical reaction networks and how environmental conditions can modulate their organization as well as the associated outcomes may take advantage of the design of related artificial systems. Microenvironments with defined boundaries are of particular interest for their unique properties and prebiotic significance. Dynamic covalent libraries (DCvLs) and their underlying constitutional dynamic networks (CDNs) have been shown to be appropriate for studying adaptation to several processes, including compartmentalization. However, microcompartments (e.g., micelles) provide specific environments for the selective protection from interfering reactions such as hydrolysis and an enhanced chemical promiscuity due to the interface, governing different processes of network modulation. Different interactions between the micelles and the library constituents lead to dynamic sensing, resulting in different expressions of the network through pattern generation. The constituents integrated into the micelles are protected from hydrolysis and hence preferentially expressed in the network composition at the cost of constitutionally linked members. In the present work, micellar integration was observed for two processes: internal uptake based on hydrophobic forces and interfacial localization relying on attractive electrostatic interactions. The latter drives a complex triple adaptation of the network with feedback on the shape of the self-assembled entity. Our results demonstrate how microcompartments can enforce the expression of constituents of CDNs by reducing the hydrolysis of uptaken members, unravelling processes that govern the response of reactions networks. Such studies open the way toward using DCvLs and CDNs to understand the emergence of complexity within reaction networks by their interactions with microenvironments.

Supramolecular Polymers: Inherently Dynamic Materials.

ConspectusSince its inception in the early 1990s, the field of supramolecular polymers (SPs) has grown into an interdisciplinary field of chemistry. It expanded from the self-assembly of molecular building blocks based on H-bonding into the realm of complex dynamic material, encompassing both supramolecular noncovalent and molecular covalent regimes. It has paved the path for a more diverse field of research into a new class of polymeric materials, coined dynamic polymers or dynamers. Dynamers are bringing a paradigm shift not only in material science research but also in a broad field of applications from self-healing materials to biocompatible polymeric materials. The present Account presents the evolution of supramolecular polymer chemistry from simple linear polymeric chains to complex dynamic polymers imparting novel functional properties, such as component exchange and self-healing. We explore how SPs led to materials of increasing complexity, starting from simple main-chain polymers to the formation of more complex columnar SPs and lateral SPs. The field has experienced three partially overlapping periods. The main goal was first the generation of polymeric entities from various molecular components connected through noncovalent interactions, especially complementary hydrogen bonding recognition patterns as well as stacked columnar SPs. Thereafter, attention was directed in parallel to the exploration of the properties of SPs and their applications as novel materials. In a third period, the dynamic properties of supramolecular polymers were explored, taking advantage of the lability of noncovalent interactions to perform component rearrangement and exchange. We illustrate how the field of SPs has emerged as a multidisciplinary field of chemistry, biology, and materials science with selected examples from the literature. The SPs, specifically dynamic owing to their inherent reversibility, also pave the path to easier sorting and recycling, as desired in the plastics industry.One of the biggest challenges that the plastics industry is facing today is the end-of-life fate of plastics. Plastics that cannot be recycled end up in landfills or are improperly disposed of in rivers and oceans, polluting and damaging the environmental balance irreversibly. Dynamic polymeric materials presenting inherent dynamicity could pave the way for addressing this long-standing challenge of nonrecyclability of plastics. Dynamers formed via noncovalent interactions or reversible covalent bonds can be broken into components that could be easily recycled and reused. Therefore, dynamers could play a pivotal role toward closing the loop for the plastics industry and provide a solution to an elusive circular economy with plastics being an integral part.

"The Sulfur Dance" Around Arenes and Heteroarenes - the Reversible Nature of Nucleophilic Aromatic Substitutions.

We disclose the features of a category of reversible nucleophilic aromatic substitutions in view of their significance and generality in dynamic aromatic chemistry. Exchange of sulfur components surrounding arenes and heteroarenes may occur at 25 °C, in a process that one may call a "sulfur dance". These SN Ar systems present their own features, apart from common reversible reactions utilized in dynamic covalent chemistry (DCC). By varying conditions, covalent dynamics may operate to provide libraries of thiaarenes with some selectivity, or conversion of a hexa(thio)benzene asterisk into another one. The reversible nature of SN Ar is confirmed by three methods: a convergence of the products distribution in reversible SN Ar systems, a related product redistribution between two per(thio)benzenes by using a thiolate promoter, and from kinetic/thermodynamic data. A four-component dynamic covalent system further illustrates the thermodynamically-driven formation of a thiacalix[2]arene[2]pyrimidine by sulfur component exchanges. This work stimulates the implementation of reversible SN Ar in aromatic chemistry and in DCC.

Breaking the photoswitch speed limit.

The forthcoming generation of materials, including artificial muscles, recyclable and healable systems, photochromic heterogeneous catalysts, or tailorable supercapacitors, relies on the fundamental concept of rapid switching between two or more discrete forms in the solid state. Herein, we report a breakthrough in the "speed limit" of photochromic molecules on the example of sterically-demanding spiropyran derivatives through their integration within solvent-free confined space, allowing for engineering of the photoresponsive moiety environment and tailoring their photoisomerization rates. The presented conceptual approach realized through construction of the spiropyran environment results in ~1000 times switching enhancement even in the solid state compared to its behavior in solution, setting a record in the field of photochromic compounds. Moreover, integration of two distinct photochromic moieties in the same framework provided access to a dynamic range of rates as well as complementary switching in the material's optical profile, uncovering a previously inaccessible pathway for interstate rapid photoisomerization.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy.

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Supramolecular multivalency effects enhance imine formation in aqueous medium allowing for dynamic modification of enzymatic activity.

Imine formation under physiological conditions represents a challenging reaction due to the strong propensity of aldimines to be hydrolyzed. Herein we disclose the remarkable effect of supramolecular multivalency on increasing imine stability. A family of reactive aldehydes was synthesized bearing supramolecularly-active sites within their structure. The imine formation activity for such aldehydes was evaluated and compared with model aldehydes. The reaction of the best-performing species - containing two carboxylate groups-with a set of amines showed a significant decrease in imine yields as the degree of supramolecular multivalency between sidechains decreased. The reversible conjugation of amino acid derivatives and small peptides was also assayed, with excellent selectivities for the imine formation at the Nα position even in substrates containing competing sites. Preliminary results on protein bioconjugation revealed that a model enzyme could be dynamically inhibited upon reaction with the aldehyde, with its native activity being recovered by displacing the imine bonds with a suitable chemical effector (i.e., acylhydrazide).

Behavior of a Dynamic Covalent Library Driven by Combined Pd(II) and Biphasic Effectors for Metal Transport between Phases.

This work reports the effect of Pd(II) as chemical effector on an acylhydrazone-based dynamic covalent library (DCL) in biphasic systems (water/chloroform). The constituents of the DCL are self-built and distributed in the two phases, two of them are lipophilic enough to play the role of a carrier agent that may transfer Pd(II) from the aqueous phase to the organic phase. Upon addition of Pd(II), the DCL of components exhibits a strong amplification of the constituent that is the most adapted to stabilize Pd(II) in chloroform as well as its agonist in water. This evolution is driven by the combination of the interaction of the DCL with Pd(II) and the presence of the two phases. This study paves the way to a novel approach for liquid/liquid extraction and metal recovery by means of adaptive extractant species generated in situ by a DCL.

Dynamic covalent self-assembly and self-sorting processes in the formation of imine-based macrocycles and macrobicyclic cages.

Investigating the self-assembly and self-sorting behaviour of dynamic covalent organic architectures makes possible the parallel generation of multiple discrete products in a single one pot procedure. We here report the self-assembly of covalent organic macrocycles and macrobicyclic cages from dialdehyde and polyamine components via multiple [2 + 2] and [3 + 2] polyimine condensations. Furthermore, component self-sorting processes have been monitored within the dynamic covalent libraries formed by these macrocycles and macrobicyclic cages. The progressive assembly of the final structures involves intermediates which undergo component selection and self-correction to generate the final thermodynamic constituents. The homo-self-sorting observed seems to involve entropic factors, as the homoleptic species present a higher symmetry than the competing heteroleptic ones. This study not only emphasizes the importance of an adequate design of the components of complex self-sorting systems, but also verifies the conjecture that systems of higher complexity may generate simpler outputs through the operation of competitive self-sorting.

The Effect of Acidic and Alkaline Seawater on the F-Actin-Dependent Ca2+ Signals Following Insemination of Immature Starfish Oocytes and Mature Eggs.

In starfish, the addition of the hormone 1-methyladenine (1-MA) to immature oocytes (germinal vesicle, GV-stage) arrested at the prophase of the first meiotic division induces meiosis resumption (maturation), which makes the mature eggs able to respond to the sperm with a normal fertilization response. The optimal fertilizability achieved during the maturation process results from the exquisite structural reorganization of the actin cytoskeleton in the cortex and cytoplasm induced by the maturing hormone. In this report, we have investigated the influence of acidic and alkaline seawater on the structure of the cortical F-actin network of immature oocytes of the starfish (Astropecten aranciacus) and its dynamic changes upon insemination. The results have shown that the altered seawater pH strongly affected the sperm-induced Ca2+ response and the polyspermy rate. When immature starfish oocytes were stimulated with 1-MA in acidic or alkaline seawater, the maturation process displayed a strong dependency on pH in terms of the dynamic structural changes of the cortical F-actin. The resulting alteration of the actin cytoskeleton, in turn, affected the pattern of Ca2+ signals at fertilization and sperm penetration.

Hypoxia, a Targetable Culprit to Counter Pancreatic Cancer Resistance to Therapy.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and it is a disease of dismal prognosis. While immunotherapy has revolutionized the treatment of various solid tumors, it has achieved little success in PDAC. Hypoxia within the stroma-rich tumor microenvironment is associated with resistance to therapies and promotes angiogenesis, giving rise to a chaotic and leaky vasculature that is inefficient at shuttling oxygen and nutrients. Hypoxia and its downstream effectors have been implicated in immune resistance and could be contributing to the lack of response to immunotherapy experienced by patients with PDAC. Paradoxically, increasing evidence has shown hypoxia to augment genomic instability and mutagenesis in cancer, suggesting that hypoxic tumor cells could have increased production of neoantigens that can potentially enable their clearance by cytotoxic immune cells. Strategies aimed at relieving this condition have been on the rise, and one such approach opts for normalizing the tumor vasculature to reverse hypoxia and its downstream support of tumor pathogenesis. An important consideration for the successful implementation of such strategies in the clinic is that not all PDACs are equally hypoxic, therefore hypoxia-detection approaches should be integrated to enable optimal patient selection for achieving improved patient outcomes.

Grid-Type Quaternary Metallosupramolecular Compounds Inhibit Human Cholinesterases through Dynamic Multivalent Interactions.

We report the implementation of coordination complexes containing two types of cationic moieties, i. e. pyridinium and ammonium quaternary salt, as potential inhibitors of human cholinesterase enzymes. Utilization of ligands containing NNO-coordination site and binding zinc metal ion allowed mono- and tetra-nuclear complexes to be obtained with corner and grid structural type, respectively, thus affecting the overall charge of the compounds (from +1 to +8). We were able to examine for the first time the multivalency effect of metallosupramolecular species on their inhibitory abilities towards acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Importantly, resolution of the crystal structures of the obtained enzyme-substrate complexes provided a better understanding of the inhibition process at the molecular level.

Toward in Silico Modeling of Dynamic Combinatorial Libraries.

Dynamic combinatorial libraries (DCLs) display adaptive behavior, enabled by the reversible generation of their molecular constituents from building blocks, in response to external effectors, e.g., protein receptors. So far, chemoinformatics has not yet been used for the design of DCLs-which comprise a radically different set of challenges compared to classical library design. Here, we propose a chemoinformatic model for theoretically assessing the composition of DCLs in the presence and the absence of an effector. An imine-based DCL in interaction with the effector human carbonic anhydrase II (CA II) served as a case study. Support vector regression models for the imine formation constants and imine-CA II binding were derived from, respectively, a set of 276 imines synthesized and experimentally studied in this work and 4350 inhibitors of CA II from ChEMBL. These models predict constants for all DCL constituents, to feed software assessing equilibrium concentrations. They are publicly available on the dedicated website. Models rationally selected two amines and two aldehydes predicted to yield stable imines with high affinity for CA II and provided a virtual illustration on how effector affinity regulates DCL members.

Superalkali Coated Rydberg Molecules.

A series of complexes of Na, K, NH4, and H3O with [bpy.bpy.bpy]cryptand, [2.2.2]cryptand, and spherical cryptand were investigated via DFT and ab initio methods. We found that by coating Rydberg molecules with the "organic skin" one could further decrease their ionization potential energy, reaching the values of ∼1.5 eV and a new low record of 1.3 eV. The neutral cryptand complexes in this sense possess a weakly bounded electron and may be considered as very strong reducing agents. Moreover, the presence of an organic cage increases the thermodynamic stability of Rydberg molecules making them stable toward the proton detachment.

Effects of Dithiothreitol on Fertilization and Early Development in Sea Urchin.

The vitelline layer (VL) of a sea urchin egg is an intricate meshwork of glycoproteins that intimately ensheathes the plasma membrane. During fertilization, the VL plays important roles. Firstly, the receptors for sperm reside on the VL. Secondly, following cortical granule exocytosis, the VL is elevated and transformed into the fertilization envelope (FE), owing to the assembly and crosslinking of the extruded materials. As these two crucial stages involve the VL, its alteration was expected to affect the fertilization process. In the present study, we addressed this question by mildly treating the eggs with a reducing agent, dithiothreitol (DTT). A brief pretreatment with DTT resulted in partial disruption of the VL, as judged by electron microscopy and by a novel fluorescent polyamine probe that selectively labelled the VL. The DTT-pretreated eggs did not elevate the FE but were mostly monospermic at fertilization. These eggs also manifested certain anomalies at fertilization: (i) compromised Ca2+ signaling, (ii) blocked translocation of cortical actin filaments, and (iii) impaired cleavage. Some of these phenotypic changes were reversed by restoring the DTT-exposed eggs in normal seawater prior to fertilization. Our findings suggest that the FE is not the decisive factor preventing polyspermy and that the integrity of the VL is nonetheless crucial to the egg's fertilization response.

Constitutional Dynamic Selection at Low Reynolds Number in a Triple Dynamic System: Covalent Dynamic Adaptation Driven by Double Supramolecular Self-Assembly.

A triple dynamic complex system has been designed, implementing a dynamic covalent process coupled to two supramolecular self-assembly steps. To this end, two dynamic covalent libraries (DCLs), DCL-1 and DCL-2, have been established on the basis of dynamic covalent C═C/C═N organo-metathesis between two Knoevenagel derivatives and two imines. Each DCL contains a barbituric acid-based Knoevenagel constituent that may undergo a sequential double self-organization process involving first the formation of hydrogen-bonded hexameric supramolecular macrocycles that subsequently undergo stacking to generate a supramolecular polymer SP yielding a viscous gel state. Both DCLs display selective self-organization-driven amplification of the constituent that leads to the SP. Dissociation of the SP on heating causes reversible randomization of the constituent distributions of the DCLs as a function of temperature. Furthermore, diverse distribution patterns of DCL-2 were induced by modulation of temperature and solvent composition. The present dynamic systems display remarkable self-organization-driven constitutional adaption and tunable composition by coupling between dynamic covalent component selection and two-stage supramolecular organization. In more general terms, they reveal dynamic adaptation by component selection in low Reynolds number conditions of living systems where frictional effects dominate inertial behavior.

Phase Ib dose-escalation study of the hypoxia-modifier Myo-inositol trispyrophosphate in patients with hepatopancreatobiliary tumors.

Hypoxia is prominent in solid tumors and a recognized driver of malignancy. Thus far, targeting tumor hypoxia has remained unsuccessful. Myo-inositol trispyrophosphate (ITPP) is a re-oxygenating compound without apparent toxicity. In preclinical models, ITPP potentiates the efficacy of subsequent chemotherapy through vascular normalization. Here, we report the results of an unrandomized, open-labeled, 3 + 3 dose-escalation phase Ib study (NCT02528526) including 28 patients with advanced primary hepatopancreatobiliary malignancies and liver metastases of colorectal cancer receiving nine 8h-infusions of ITPP over three weeks across eight dose levels (1'866-14'500 mg/m2/dose), followed by standard chemotherapy. Primary objectives are assessment of the safety and tolerability and establishment of the maximum tolerated dose, while secondary objectives include assessment of pharmacokinetics, antitumor activity via radiological evaluation and assessment of circulatory tumor-specific and angiogenic markers. The maximum tolerated dose is 12,390 mg/m2, and ITPP treatment results in 32 treatment-related toxicities (mostly hypercalcemia) that require little or no intervention. 52% of patients have morphological disease stabilization under ITPP monotherapy. Following subsequent chemotherapy, 10% show partial responses while 60% have stable disease. Decreases in angiogenic markers are noted in ∼60% of patients after ITPP and tend to correlate with responses and survival after chemotherapy.