The impact of click chemistry in medicinal chemistry

Synthesis, SAR, and application of JQ1 analogs as PROTACs for cancer therapy

JQ1 is a wonder therapeutic molecule that selectively inhibits the BRD4 signaling pathway and is thus widely used in the anticancer drug discovery program. Due to its unique selective BRD4 binding property, its applications are further extended in the design and synthesis of bi-functional PROTAC molecules. This BRD4 targeting PROTAC molecule selectively degrades the protein by proteolysis. There are several modifications of JQ1 known to date and extensively explored for their applications in PROTAC technology by several research groups in academia as well as industry for targeting oncogenic genes. In this review, we have covered the discovery and synthesis of the JQ1 molecule. The SAR of the JQ1 analogs will help researchers develop potent JQ1 compounds with improved inhibitory properties against malignant cells. Furthermore, we explored the potential application of JQ1 analogs in PROTAC technology. The brief history of the bromodomain family of proteins, as well as the obstacles connected with PROTAC technology, can help comprehend the context of the current research, which has the potential to improve the drug development process. Overall, this review comprehensively appraises JQ1 molecules and their prior implementation in PROTAC technology and cancer therapy.

Radical-Chain Hydrosilylation of Alkenes Enabled by Triplet Energy Transfer

Development of mild, robust and metal-free catalytic approach for the hydrosilylation of alkenes is critical to the advancement of modern organosilicon chemistry given their powerful capacity in the construction of various C-Si bonds. Herein, we wish to disclose a visible light-triggered organophotocatalytic strategy, which proceeds via a triplet energy transfer (EnT)-enabled radical chain pathway. Notably, this redox-neutral protocol is capable of accommodating a broad spectrum of electron-deficient and -rich alkenes with excellent functional group compatibility. Electron-deficient alkenes are more reactive and the reaction could be finished within a couple of minutes even in PBS solution with extremely low concentration, which suggests its click-like potential in organic synthesis. The preparative power of the transformations has been further highlighted in a number of complex settings, including the late-stage functionalization and scale-up experiments. Furthermore, although only highly reactive (TMS)3SiH is suitable hydrosilane substrate, our studies revealed the great reactivity and versatility of (TMS)3Si- group in diverse C-Si and Si-Si bond cleavage-based transformations, enabling the rapid introduction of diverse functional groups and the facile construction of valuable quaternary silicon architectures.

Electron Donor-Acceptor Complex-Enabled Autoinductive Conversion of Acylnitromethanes to Acylnitrile Oxides in a Photochemical Machetti-De Sarlo Reaction: Synthesis of 5-Substituted 3-Acylisoxazoles

A photochemical Machetti-De Sarlo reaction has been developed for preparing 5-substituted 3-acylisoxazoles from acylnitromethanes and terminal alkynes. This photochemical protocol utilizes an innovative electron donor-acceptor complex, generated in situ from acylnitromethanes, catalytic LiOtBu, and 1,1,1,3,3,3-hexafluoro-2-propanol, as a photosensitizer to promote rapid conversion with a broad substrate scope in up to 80% efficiency. A sigmoidal autoinductive kinetic profile is revealed, demonstrating the novel and unique dual catalysis in the first photochemical approach of this reaction.

Chromatography Scrutiny, Molecular Docking, Clarifying the Selectivities and the Mechanism of [3 + 2] Cycloloaddition Reaction between Linallol and Chlorobenzene-Nitrile-oxide

Employing the Molecular Electron Density Theory, [3 + 2] cycloaddition processes between 4-chlorobenzenenitrileoxide and linalool, have been applied using the DFT/B3LYP/6-311(d,p) method, activation, reaction energies and the reactivity indices are calculated. In an investigation of conceptual DFT indices, LIL-1 will contribute to this reaction as a nucleophile, whilst NOX-2 will participate as an electrophile. This cyclization is regio, chemo and stereospecific, as demonstrated by the reaction and activation energies, in clear agreement with the experiment's results, in addition, ELF analysis revealed that the mechanism for this cycloaddition occurs in two steps. Furthermore, a docking study was conducted on the products studied, and the interaction with the protein protease COVID-19 (PDB ID: 6LU7), our results indicate that the presence of the -OH group increases the affinity of these products, moreover, adsorption study by chromatography was made on silica gel as support; our outcome reveals that the -OH group creates an intramolecular hydrogen bond in the product P2, while in the product P3 will create a hydrogen bond with the silica gel which makes the two products P2 and P3 are very easy to separate by chromatography, this result is in excellent agreement with the Rf retention value. The study might provide a fundamental for developing natural anti-viral compound in promoting human health.

Neuritogenic glycosaminoglycan hydrogels promote functional recovery after severe traumatic brain injury

Objective.Severe traumatic brain injury (sTBI) induced neuronal loss and brain atrophy contribute significantly to long-term disabilities. Brain extracellular matrix (ECM) associated chondroitin sulfate (CS) glycosaminoglycans promote neural stem cell (NSC) maintenance, and CS hydrogel implants have demonstrated the ability to enhance neuroprotection, in preclinical sTBI studies. However, the ability of neuritogenic chimeric peptide (CP) functionalized CS hydrogels in promoting functional recovery, after controlled cortical impact (CCI) and suction ablation (SA) induced sTBI, has not been previously demonstrated. We hypothesized that neuritogenic (CS)CP hydrogels will promote neuritogenesis of human NSCs, and accelerate brain tissue repair and functional recovery in sTBI rats.Approach.We synthesized chondroitin 4-Osulfate (CS-A)CP, and 4,6-O-sulfate (CS-E)CP hydrogels, using strain promoted azide-alkyne cycloaddition (SPAAC), to promote cell adhesion and neuritogenesis of human NSCs,in vitro; and assessed the ability of (CS-A)CP hydrogels in promoting tissue and functional repair, in a novel CCI-SA sTBI model,in vivo. Main results.Results indicated that (CS-E)CP hydrogels significantly enhanced human NSC aggregation and migration via focal adhesion kinase complexes, when compared to NSCs in (CS-A)CP hydrogels,in vitro. In contrast, NSCs encapsulated in (CS-A)CP hydrogels differentiated into neurons bearing longer neurites and showed greater spontaneous activity, when compared to those in (CS-E)CP hydrogels. The intracavitary implantation of (CS-A)CP hydrogels, acutely after CCI-SA-sTBI, prevented neuronal and axonal loss, as determined by immunohistochemical analyses. (CS-A)CP hydrogel implanted animals also demonstrated the significantly accelerated recovery of 'reach-to-grasp' function when compared to sTBI controls, over a period of 5-weeks.Significance.These findings demonstrate the neuritogenic and neuroprotective attributes of (CS)CP 'click' hydrogels, and open new avenues for the development of multifunctional glycomaterials that are functionalized with biorthogonal handles for sTBI repair.

Conjugates of 3,5-Bis(arylidene)-4-piperidone and Sesquiterpene Lactones Have an Antitumor Effect via Resetting the Metabolic Phenotype of Cancer Cells

In recent years, researchers have often encountered the significance of the aberrant metabolism of tumor cells in the pathogenesis of malignant neoplasms. This phenomenon, known as the Warburg effect, provides a number of advantages in the survival of neoplastic cells, and its application is considered a potential strategy in the search for antitumor agents. With the aim of developing a promising platform for designing antitumor therapeutics, we synthesized a library of conjugates of 3,5-bis(arylidene)-4-piperidone and sesquiterpene lactones. To gain insight into the determinants of the biological activity of the prepared compounds, we showed that the conjugates of 3,5-bis(arylidene)-4-piperidone and sesquiterpene lactones, which are cytotoxic agents, demonstrate selective activity toward a number of tumor cell lines with glycolysis-inhibiting ability. Moreover, the results of molecular and in silico screening allowed us to identify these compounds as potential inhibitors of the pyruvate kinase M2 oncoprotein, which is the rate-determining enzyme of glycolysis. Thus, the results of our work indicate that the synthesized conjugates of 3,5-bis(arylidene)-4-piperidone and sesquiterpene lactones can be considered a promising platform for designing selective cytotoxic agents against the glycolysis process, which opens new possibilities for researchers involved in the search for antitumor therapeutics among compounds containing piperidone platforms.

Triazoles in Medicinal Chemistry: Physicochemical Properties, Bioisosterism, and Application

Triazole demonstrates distinctive physicochemical properties, characterized by weak basicity, various dipole moments, and significant dual hydrogen bond acceptor and donor capabilities. These features are poised to play a pivotal role in drug-target interactions. The inherent polarity of triazole contributes to its lower logP, suggesting the potential improvement in water solubility. The metabolic stability of triazole adds additional value to drug discovery. Moreover, the metal-binding capacity of the nitrogen atom lone pair electrons of triazole has broad applications in the development of metal chelators and antifungal agents. This Perspective aims to underscore the unique physicochemical attributes of triazole and its application. A comparative analysis involving triazole isomers and other heterocycles provides guiding insights for the subsequent design of triazoles, with the hope of offering valuable considerations for designing other heterocycles in medicinal chemistry.

In vitro α-glucosidase, docking and density functional theory studies on novel azide metal complexes

Aim: The goal of this study is to synthesize new metal complexes containing N-methyl-1-(pyridin-2-yl)methanimine and azide ligands as α-glucosidase inhibitors for Type 2 diabetes. Materials & methods: The target complexes (12-16) were synthesized by reacting N-methyl-1-(pyridin-2-yl)methanimine (L1) with sodium azide in the presence of corresponding metal salts. The investigation of target protein interactions, vibrational, electronic and nonlinear optical properties for these complexes was performed by molecular docking and density functional theory studies. Results: Among these complexes, complex 13 (IC50 = 0.2802 ± 0.62 μM) containing Hg ion showed the highest α-glucosidase inhibitory property. On the other hand, significant results were detected for complexes containing Cu and Ag ions. Conclusion: Complex 13 may be an alternate anti-diabetic inhibitor according to in vitro/docking results.

Average Electron Density: A Quantitative Tool for Evaluating Non-Classical Bioisosteres of Amides

Bioisosterism is strategically used in drug design to enhance the pharmacokinetic and pharmacodynamic properties of therapeutic molecules. The average electron density (AED) tool has been used in several studies to quantify similarities among nonclassical bioisosteres of carboxylic acid. In this study, the AED tool is used to quantify the similarities among nonclassical bioisosteres of an amide group. In particular, amide-to-1,2,3-triazole bioisosterism is considered. To evaluate the AED differences exhibited by isomers of nonclassical bioisosteres, both isomers of amide (cis and trans) and 1,2,3-triazole (1,4 and 1,5 disubstituted moieity) were considered. The amide and 1,2,3-triazole bioisosteric moieties were capped with various R groups (R= methyl, hydrogen, and chloro) to account for changes in their environment. Amide-to-triazole bioisosteric substitutions were then explored in a more realistic environment, that is, within the FDA-approved anticancer imatinib drug. The AED tool effectively identified similarities between substantially different moieties, 1,2,3-triazole and amide, showing AED differences of no more than 4%. The AED tool was also proven to be useful in evaluating the contribution of various factors affecting triazole-amide bioisosterism including isomerism and changes in their environment. The AED values of each bioisostere were transferable within a maximum difference of 2.6%, irrespective of the change in environment. The 1,4- and 1,5-disubstituted isomers of 1,2,3-triazole have AED values that differ by less than unity, 0.52%. Similarly, the AED values of the cis- and trans-amide isomers differ by only 1.31%. Overall, the AED quantitative tool not only replicated experimental observations regarding similarities in bioisosteres, but also explained and quantified each contributing factor. This demonstrates the extended utility of the AED tool from nonclassical carboxylic acid bioisosteres to amide equivalents.On the contrary, electrostatic potential maps, usually used in the literature to qualitatively evaluate bioisosterism, were not similar for the 1,2,3-triazole and amide bioisosteres, under different environments. Overall, the AED tool proves to be powerful in quantitatively evaluating and predicting bioisosterism across diverse moieties considering structural and environmental variations, making it valuable in drug design.

What is the future of click chemistry in drug discovery and development?

INTRODUCTION

The concept of click chemistry was introduced in 2001 as an effective, efficient, and sustainable approach to making functional groups harnessing the thermodynamic properties of a set of known chemical reactions that are based on nature. Some of the most common examples include reactions that produce 1,2,3-triazoles, which have been used with great success in drug discovery and development, and in chemical biology. The reactions unite two molecules quickly and irreversibly, and the reactions can be performed inside living cells, without harming the cell.

AREAS COVERED

The main focus of this perspective is the future of click chemistry in drug discovery and development, exemplified by novel click chemistry approaches and other aspects of the drug development enterprise, like SPAAC and analogous techniques, PROTACs, as well as diversity-oriented click chemistry.

EXPERT OPINION

Drug discovery and development has benefited enormously from the amazing advances that have been made in the field of click chemistry since 2001. The methods most likely to have the most future applications include metal-catalyzed azide-alkyne cycloadditions giving 1,2,3-triazoles, SPAAC for medical diagnostics and vaccine development, other congeners, Sulfur-Fluoride Exchange (SuFEx) and Diversity-Oriented Clicking (DOC), a concept with diverse molecular methodology with the potential for obtaining extensive molecular diversity.

Recent advances in the application of alkynes in multicomponent reactions

Alkynes have two active positions to carry out chemical reactions: C[triple bond, length as m-dash]C and C-H. These two positions are involved and activated in different reactions using different reagents. In this study, we investigated the reactions of alkynes that are involved in multi-component reactions through the C-C and C-H positions and examined the progress and gaps of each reaction by carefully studying the mechanism of the reactions. Firstly, we investigated and analyzed the reactions involving the C[triple bond, length as m-dash]C position of alkynes, including the reactions between derivatives of alkynes with RN3, sulfur compounds (RSO2R', DMSO, S8, DABCO(SO2)2 and DABSO), barbituric acids, aldehydes and amines, COOH, α-diazoesters or ketones, and isocyanides. Then, we examined and analyzed the important reactions involving the C-H position of alkynes and the progress and gaps in these reactions, including the reaction between alkyne derivatives with amines and aldehydes for the synthesis of propargylamines, the reaction between alkynes with CO2 and the reaction between alkynes with CO.

"Click Chemistry": An Emerging Tool for Developing a New Class of Structural Motifs against Various Neurodegenerative Disorders

Click chemistry is a set of easy, atom-economical reactions that are often utilized to combine two desired chemical entities. Click chemistry accelerates lead identification and optimization, reduces the complexity of chemical synthesis, and delivers extremely high yields without undesirable byproducts. The most well-known click chemistry reaction is the 1,3-dipolar cycloaddition of azides and alkynes to form 1,2,3-triazoles. The resulting 1,2,3-triazoles can serve as both bioisosteres and linkers, leading to an increase in their use in the field of drug discovery. The current Review focuses on the use of click chemistry to identify new molecules for treating neurodegenerative diseases and in other areas such as peptide targeting and the quantification of biomolecules.

Click Chemistry and Targeted Degradation: A Winning Combination for Medicinal Chemists?

Click chemistry is universally recognized as a powerful strategy for the fast and precise assembly of diverse building blocks. Targeted Protein Degradation (TPD) is a new therapeutic modality based on heterobifunctional small-molecule degraders that provides new opportunities to medicinal chemists dealing with undruggable targets and incurable diseases. Here, we highlight how very recently the TPD field and that of click chemistry have merged, opening up the possibility for fine-tuning the properties of a degrader, chemically assembled through a "click" synthesis. By reviewing concrete examples, we want to provide the reader with the insight that the application of click and bioorthogonal chemistry in the TDP field may be a winning combination.

An insight on medicinal attributes of 1,2,3- and 1,2,4-triazole derivatives as alpha-amylase and alpha-glucosidase inhibitors

Diabetes Mellitus (DM) is the globe's common leading disease which is caused by high consumption of glucose. DM compiles groups of metabolic disorders which are characterized by inadequate secretion of insulin from pancreas, resulting in hyperglycemia condition. Many enzymes play a vital role in the metabolism of carbohydrate known as α-amylase and α-glucosidase which is calcium metalloenzyme that leads to breakdown of complex polysaccharides into glucose. To tackle this problem, search for newer antidiabetic drugs is the utmost need for the treatment and/or management of increasing diabetic burden. The inhibition of α-amylase and α-glucosidase is one of the effective therapeutic approaches for the development of antidiabetic therapeutics. The exhaustive literature survey has shown the importance of medicinally privileged triazole specifically 1,2,3-triazol and 1,2,4-triazoles scaffold tethered, fused and/or clubbed with other heterocyclic rings structures as promising agents for designing and development of novel antidiabetic therapeutics. Molecular hybrids namely pyridazine-triazole, pyrazoline-triazole, benzothiazole-triazole, benzimidazole-triazole, curcumin-triazole, (bis)coumarin-triazole, acridine-9-carboxamide linked triazole, quinazolinone-triazole, xanthone-triazole, thiazolo-triazole, thiosemicarbazide-triazole, and indole clubbed-triazole are few examples which have shown promising antidiabetic activity by inhibiting α-amylase and/or α-glucosidase. The present review summarizes the structure-activity relationship (SAR), enzyme inhibitory activity including IC50 values, percentage inhibition, kinetic studies, molecular docking studies, and patents filed of the both scaffolds as alpha-amylase and alpha-glucosidase inhibitors, which may be used for further development of potent inhibitors against both enzymes.

The Certainty of a Few Good Reactions

The impact of click chemistry was recently recognized with the 2022 Nobel Prize in Chemistry. The breadth of areas where click chemistry has accelerated discovery is prodigal. In one of the most written about subjects in chemistry over recent years, this short perspective zones in on a small fragment of what we, the authors, consider are some of the most critical developments in synthetic chemistry, which have expanded access to the click chemistry toolbox. In addition, we touch upon areas within medicinal chemistry and novel approaches to drug discovery enabled by click chemistry, where we believe there is untapped potential for biological function to be found and exploited.

Lipidated variants of the antimicrobial peptide nisin produced via incorporation of methionine analogs for click chemistry show improved bioactivity

The increase in antibiotic resistance calls for accelerated molecular engineering strategies to diversify natural products for drug discovery. The incorporation of non-canonical amino acids (ncAAs) is an elegant strategy for this purpose, offering a diverse pool of building blocks to introduce desired properties into antimicrobial lanthipeptides. We here report an expression system using Lactococcus lactis as a host for non-canonical amino acid incorporation with high efficiency and yield. We show that incorporating the more hydrophobic analog ethionine (instead of methionine) into nisin improves its bioactivity against several Gram-positive strains we tested. New-to-nature variants were further created by click chemistry. By azidohomoalanine (Aha) incorporation and subsequent click chemistry, we obtained lipidated variants at different positions in nisin or in truncated nisin variants. Some of them show improved bioactivity and specificity against several pathogenic bacterial strains. These results highlight the ability of this methodology for lanthipeptide multi-site lipidation, to create new-to-nature antimicrobial products with diverse features, and extend the toolbox for (lanthi)peptide drug improvement and discovery.

Click inspired synthesis of piperazine-triazolyl sugar-conjugates as potent anti-Hela activity

To imbibe the aim of synthesizing water-soluble and biocompatible motif, a click-inspired piperazine glycoconjugate has been devised up. In this report, we present a focused approach to design and synthesis of versatile sugar-appended triazoles through 'Click Chemistry' along with their pharmacological studies on cyclin-dependent kinases (CDKs) and cell cytotoxicity on cancer cells using in silico and in vitro approaches, respectively. The study has inclusively recognized the galactose- and mannose-derived piperazine conjugates as the promising motifs. The findings suggested that the galactosyl bis-triazolyl piperazine analogue 10b is the most CDK interactive derivative and also possess significant anticancer activity.

Advances of bioorthogonal coupling reactions in drug development

Currently, bioorthogonal coupling reactions have garnered considerable interest due to their high substrate selectivity and less restrictive reaction conditions. During recent decades, bioorthogonal coupling reactions have emerged as powerful tools in drug development. This review describes the current applications of bioorthogonal coupling reactions in compound library building mediated by the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and in situ click chemistry or conjunction with other techniques; druggability optimization with 1,2,3-triazole groups; and intracellular self-assembly platforms with ring tension reactions, which are presented from the viewpoint of drug development. There is a reasonable prospect that bioorthogonal coupling reactions will accelerate the screening of lead compounds, the designing strategies of small molecules and expand the variety of designed compounds, which will be a new trend in drug development in the future.

Engineering exosome-based biomimetic nanovehicles for wound healing

Complexity and difficulties in wound management are pressing concerns that affect patients' quality of life and may result in tissue infection, necrosis, and loss of local and systemic functions. Hence, novel approaches to accelerate wound healing are being actively explored over the last decade. Exosomes as important mediators of intercellular communications are promising natural nanocarriers due to their biocompatibility, low immunogenicity, drug loading and targeting capacities, and innate stability. More importantly, exosomes are developed as a versatile pharmaceutical engineering platform for wound repair. This review provides an overview of the biological and physiological functions of exosomes derived from a variety of biological origins during wound healing phases, strategies for exosomal engineering, and therapeutic applications in skin regeneration.

Nonhydrolyzable d‑phenylalanine-benzoxazole derivatives retain antitubercular activity

The emergence of drug resistant Mycobacterium tuberculosis, the causative agent of tuberculosis, demands the development of new drugs and new drug targets. We have recently reported that the d-phenylalanine benzoxazole Q112 has potent antibacterial activity against this pathogen with a distinct mechanism of action from other antimycobacterial agents. Q112 and previously reported derivatives were unstable in plasma and no free compound could be observed. Here we expand the structure-activity relationship for antimycobacterial activity and find nonhydrolyzable derivatives with decreased plasma binding. We also show that there is no correlation between antibacterial activity and inhibition of PanG, a putative target for these compounds.

Copper-Based Metal–Organic Frameworks (MOFs) as an Emerging Catalytic Framework for Click Chemistry

In the extensive terrain of catalytic procedures for the synthesis of organic molecules, metal–organic frameworks (MOFs) as heterogenous catalysts have been investigated in a variety of chemical processes, including Friedel–Crafts reactions, condensation reactions, oxidations, and coupling reactions, and utilized owing to their specific properties such as high porosity, tuneability, extraordinary catalytic activity, and recyclability. The eminent copper-tailored MOF materials can be exceptionally dynamic and regioselective catalysts for click reactions (1,3-dipolar cycloaddition reaction). Considering the fact that Cu(I)-catalyzed alkyne–azide cycloaddition (CuAAC) reactions can be catalyzed by several other copper catalysts such as Cu (II)-β-cyclodextrin, Cu(OAc)2, Fe3O4@SiO2, picolinimidoamide–Cu(II) complex, and Cu(II) porphyrin graphene, the properties of sorption and reusability, as well as the high density of copper-MOFs, open an efficient and robust pathway for regimented catalysis of this reaction. This review provides a comprehensive description and analysis of the relevant literature on the utilization of Cu-MOFs as catalysts for CuAAC ‘click’ reactions published in the past decade.

Green Hydrogel Synthesis: Emphasis on Proteomics and Polymer Particle-Protein Interaction

The field of drug discovery has seen significant progress in recent years. These advances drive the development of new technologies for testing compound's effectiveness, as well as their adverse effects on organs and tissues. As an auxiliary tool for drug discovery, smart biomaterials and biopolymers produced from biodegradable monomers allow the manufacture of multifunctional polymeric devices capable of acting as biosensors, of incorporating bioactives and biomolecules, or even mimicking organs and tissues through self-association and organization between cells and biopolymers. This review discusses in detail the use of natural monomers for the synthesis of hydrogels via green routes. The physical, chemical and morphological characteristics of these polymers are described, in addition to emphasizing polymer-particle-protein interactions and their application in proteomics studies. To highlight the diversity of green synthesis methodologies and the properties of the final hydrogels, applications in the areas of drug delivery, antibody interactions, cancer therapy, imaging and biomarker analysis are also discussed, as well as the use of hydrogels for the discovery of antimicrobial and antiviral peptides with therapeutic potential.

The 1,2,3-triazole 'all-in-one' ring system in drug discovery: a good bioisostere, a good pharmacophore, a good linker, and a versatile synthetic tool

INTRODUCTION

The 1,2,3-triazole ring occupies an important space in medicinal chemistry due to its unique structural properties, synthetic versatility and pharmacological potential making it a critical scaffold. Since it is readily available through click chemistry for creating compound collections against various diseases, it has become an emerging area of interest for medicinal chemists.

AREAS COVERED

This review article addresses the unique properties of the1,2,3-triazole nucleus as an intriguing ring system in drug discovery while focusing on the most recent medicinal chemistry strategies exploited for the design and development of 1,2,3-triazole analogs as inhibitors of various biological targets.

EXPERT OPINION

Evidently, the 1,2,3-triazole ring with unique structural features has enormous potential in drug design against various diseases as a pharmacophore, a bioisoster or a structural platform. The most recent evidence indicates that it may be more emerging in drug molecules in near future along with an increasing understanding of its prominent roles in drug structures. The synthetic feasibility and versatility of triazole chemistry make it certainly ideal for creating compound libraries for more constructive structure-activity relationship studies. However, more comparative and target-specific studies are needed to gain a deeper understanding of the roles of the 1,2,3-triazole ring in molecular recognition.[Figure: see text].

In Vitro Antioxidant and Pancreatic Anticancer Activity of Novel 5-Fluorouracil-Coumarin Conjugates

Molecular hybridization consists of the combination of two or more non-identical pharmacophores in a single molecule. It has emerged as a promising strategy that allows the design of molecular frameworks with enhanced activity and affinity compared to their parent drugs. In this work, two novel hybrids that combine the well-known anticancer chemotherapeutic agent 5-fluorouracil with antioxidant coumarin derivatives have been synthesized and characterized by means of a copper-catalyzed azide-alkyne cycloaddition (CuAAC). The conjugates showed good antioxidant properties and a high tendency to aggregate and form stable nanoparticles in aqueous media, with regular shape and uniform size. These materials have proven to be preferential cytotoxic agents in vitro against human pancreatic cancer cells PANC-1, with an activity superior to free 5-fluorouracil. These results open up the possibility of exploiting the synergistic combination between 5-fluorouracil and coumarin derivatives and warrant further investigation of these hybrids as promising pancreatic anticancer agents.

Synthesis of 4-Hydroxycoumarin-Based Triazoles/Oxadiazoles as Novel Anticancer Agents

A series of novel 3-substituted-4-hydroxycoumarins 7 and 8 containing (5-aryl-1,3,4-oxadiazol-2-yl)thio or (4-amino-5-aryl-4H-1,2,4-triazol-3-yl)thio moieties have been synthesized and evaluated as anticancer agents. The in vitro MTT assay of compounds against hepatocellular carcinoma (HepG2), breast cancer (MCF7) cells, and a human colorectal adenocarcinoma cell line with epithelial morphology (HT29) indicated that the HepG2 cells had more susceptibility to the tested compounds. Indeed, all compounds (with the exception of 7b, 7c, 7g, and 8g) were more potent than the standard drug doxorubicin against HepG2 cells (IC₅₀ values=1.65-3.83 μM). Although, the better result was obtained with the oxadiazole analog 7h against HepG2 (IC₅₀ =1.65 μM), the N-amino-triazole derivatives 8c, 8e, 8f and, 8h with IC₅₀ values of 1.78-6.34 μM showed potent activity against all tested cell lines. The good drug-like properties and in vitro potency and selectivity of 4-hydroxycoumarins 8 make them as good leads for the development of new anticancer agents.

Synthesis of (E)-2-(1H-tetrazole-5-yl)-3-phenylacrylenenitrile derivatives catalyzed by new ZnO nanoparticles embedded in a thermally stable magnetic periodic mesoporous organosilica under green conditions

ZnO nanoparticles embedded in a magnetic isocyanurate-based periodic mesoporous organosilica (Fe3O4@PMO-ICS-ZnO) were prepared through a modified environmentally-benign procedure for the first time and properly characterized by appropriate spectroscopic and analytical methods or techniques used for mesoporous materials. The new thermally stable Fe3O4@PMO-ICS-ZnO nanomaterial with proper active sites and surface area as well as uniform particle size was investigated for the synthesis of medicinally important tetrazole derivatives through cascade condensation and concerted 1,3-cycloaddition reactions as a representative of the Click Chemistry concept. The desired 5-substituted-1H-tetrazole derivatives were smoothly prepared in high to quantitative yields and good purity in EtOH under reflux conditions. Low catalyst loading, short reaction time and the use of green solvents such as EtOH and water instead of carcinogenic DMF as well as easy separation and recyclability of the catalyst for at least five consecutive runs without significant loss of its activity are notable advantages of this new protocol compared to other recent introduced procedures.

Consecutive Alkylation, "Click", and "Clip" Reactions for the Traceless Methionine-Based Conjugation and Release of Methionine-Containing Peptides

"Click" reactions have revolutionized research in many areas of science. However, a disadvantage of the high stability of the Click product is that identifying simple treatments for cleanly dissociating the latter under the same guiding principles, i.e., a "Clip" reaction, remains a challenge. This study demonstrates that electron-deficient alkynes, conveniently installed on methionine residues, can participate in well-known Click (nucleophilic thiol-allene addition) and subsequent Clip reactions (radical thiol-ene addition). To illustrate this concept, a variety of bioconjugates (peptide-peptide; peptide-fluorophore; peptide-polymer; and peptide-protein) were prepared. Interestingly, the Clip reaction of these bioconjugates releases the original peptides concurrent with regeneration of their unmodified methionine residue, in minutes. Moreover, the conjugates demonstrate substantial stability toward endogenous levels of reactive species in bacteria, illustrating the potential for this chemistry in the biosciences. The reaction conditions employed in the Click and Clip steps are compatible with the preservation of the integrity of biomolecules/fluorophores and involve readily accessible reagents and the natural functional groups on peptides/proteins.

Radical Oxyazidation of Alkenes in Pure Water

Compared to universal radical difunctionalizations of alkenes that are performed with organic solvents, such reactions with water as the sole solvent are rarely reported. Concerning the global consensus on environmental issues, we have developed herein a method for the radical oxyazidation of alkenes in pure water. This reaction allows the construction of C–N and C–O bonds in a one-pot process. Styrenes, 1,3-dienes, and unactivated alkenes react smoothly under mild and environmentally benign conditions to afford a wide scope of functionalized azides in excellent yields and selectivities.

Structural and Thermal Characterization of Halogenated Azidopyridines: Under-Reported Synthons for Medicinal Chemistry

Owing to their participation in Click reactions, bifunctional azides are valuable intermediates in the preparation of medicines and biochemical tool compounds. Despite the privileged nature of pyridines among pharmaceutical scaffolds, reports of the synthesis and characterization of azidopyridines bearing a halogen substituent for further elaboration are almost completely unknown in the literature. As azidopyridines carry nearly equal numbers of nitrogen and carbon atoms, we hypothesized that safety concerns limited the application of these useful bifunctional building blocks in medicinal and biological chemistry. To address this concern, we prepared and characterized nine azidopyridines bearing a single fluorine, chlorine, or bromine atom. All were examined by differential scanning calorimetry (DSC), in which they demonstrated exotherms of 228-326 kJ/mol and onset temperatures between 119 and 135 °C. Selected azidopyridines were advanced to mechanical stress testing, in which impact sensitivity was noted for one regioisomer of C5H3FN4. The utility of these versatile intermediates was demonstrated through their use in a variety of Click reactions and the diversification of the halogen handles.

Recent advances in the synthesis of naturally occurring tetronic acids

During the last decades the interest towards natural products containing the tetronic acid moiety augmented significantly, due to their challenging structures and to the wide range of biological activities they display. This increasing enthusiasm has led to noteworthy advances in the development of innovative methodologies for the construction of the butenolide nucleus. This review provides an overview of the progress in the synthesis of tetronic acid as a structural key motif of natural compounds, covering the last 15 years. Herein, the most representative synthetic pathways towards structurally diverse natural tetronic acids are grouped according to the strategy followed. The first part describes the functionalization of a preformed tetronic acid core by intermolecular reactions (cross-coupling reactions, nucleophilic substitution, multicomponent reactions) whereas the second part deals with intramolecular approaches (Dieckmann, cycloaddition or ring expansion reactions) to construct the heterocyclic core. This rational subcategorization allowed us to make some considerations about the best approaches for the synthesis of specific substrates, including modern intriguing methodologies such as microwave irradiation, solid phase anchoring, bio-transformations and continuous flow processes.

An Overview of Recent Advances in Biomedical Applications of Click Chemistry

Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is a modular and bio-orthogonal approach that is being adopted for the efficient synthesis of organic and bioorganic compounds. It leads to the selective formation of 1,4-disubstituted 1,2,3-triazole units connecting readily accessible building blocks via a stable and biocompatible linkage. The vast array of the bioconjugation applications of click chemistry has been attributed to its fast reaction kinetics, quantitative yields, minimal byproducts, and high chemospecificity and regioselectivity. These combined advantages make click reactions quite suitable for the lead identification and the development of pharmaceutical agents in the fields of medicinal chemistry and drug discovery. In this review, we have outlined the key aspects, the mechanistic details and merits and demerits of the click reaction. In addition, we have also discussed the recent pharmaceutical applications of click chemistry, ranging from the development of anticancer, antibacterial, and antiviral agents to that of biomedical imaging agents and clinical therapeutics.

Advances in Functionalized Photosensitive Polymeric Nanocarriers

The synthesis of light-responsive nanocarriers (LRNs) with a variety of surface functional groups and/or ligands has been intensively explored for space-temporal controlled cargo release. LRNs have been designed on demand for photodynamic-, photothermal-, chemo-, and radiotherapy, protected delivery of bioactive molecules, such as smart drug delivery systems and for theranostic duties. LRNs trigger the release of cargo by a light stimulus. The idea of modifying LRNs with different moieties and ligands search for site-specific cargo delivery imparting stealth effects and/or eliciting specific cellular interactions to improve the nanosystems’ safety and efficacy. This work reviews photoresponsive polymeric nanocarriers and photo-stimulation mechanisms, surface chemistry to link ligands and characterization of the resultant nanosystems. It summarizes the interesting biomedical applications of functionalized photo-controlled nanocarriers, highlighting the current challenges and opportunities of such high-performance photo-triggered delivery systems.

Squaric Acid-Based Radiopharmaceuticals for Tumor Imaging and Therapy

Targeting vectors bound to a chelator represent a significant fraction of radiopharmaceuticals used nowadays for diagnostic and therapeutic purposes in nuclear medicine. The use of squaramides as coupling units for chelator and targeting vector helps to circumvent the disadvantages of several common coupling methods. This review gives an overview of the use of squaric acid diesters (SADE) as linking agents. It focuses on the conjugation of cyclic chelators, e.g., DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), as well as hybrid chelators like AAZTA⁵ (6-pentanoic acid-6-amino-1,4-diazepine tetracetic acid) or DATA^5m (6-pentanoic acid-6-amino-1,4-diazapine-triacetate) to different targeting vectors, e.g., prostate-specific membrane antigen inhibitors (KuE; PSMAi), fibroblast activation protein inhibitors (FAPi), and monoclonal antibodies (mAbs). An overview of the synthesis, radiolabeling, and in vitro and in vivo behavior of the described structures is given. The unique properties of SADE enable a fast and simple conjugation of chelators to biomolecules, peptides, and small molecules under mild conditions. Furthermore, SA-containing conjugates could not only display similar in vitro characteristics in terms of binding affinity when compared to reference compounds, but may even induce beneficial effects on the pharmacokinetic properties of these radiopharmaceuticals.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

DNA-Encoded Chemistry: Drug Discovery from a Few Good Reactions

Click chemistry, proposed nearly 20 years ago, promised access to novel chemical space by empowering combinatorial library synthesis with a "few good reactions". These click reactions fulfilled key criteria (broad scope, quantitative yield, abundant starting material, mild reaction conditions, and high chemoselectivity), keeping the focus on molecules that would be easy to make, yet structurally diverse. This philosophy bears a striking resemblance to DNA-encoded library (DEL) technology, the now-dominant combinatorial chemistry paradigm. This review highlights the similarities between click and DEL reaction design and deployment in combinatorial library settings, providing a framework for the design of new DEL synthesis technologies to enable next-generation drug discovery.

Alkaloids in Contemporary Drug Discovery to Meet Global Disease Needs

An overview is presented of the well-established role of alkaloids in drug discovery, the application of more sustainable chemicals, and biological approaches, and the implementation of information systems to address the current challenges faced in meeting global disease needs. The necessity for a new international paradigm for natural product discovery and development for the treatment of multidrug resistant organisms, and rare and neglected tropical diseases in the era of the Fourth Industrial Revolution and the Quintuple Helix is discussed.

Modified Nucleosides, Nucleotides and Nucleic Acids via Click Azide-Alkyne Cycloaddition for Pharmacological Applications

The click azide = alkyne 1,3-dipolar cycloaddition (click chemistry) has become the approach of choice for bioconjugations in medicinal chemistry, providing facile reaction conditions amenable to both small and biological molecules. Many nucleoside analogs are known for their marked impact in cancer therapy and for the treatment of virus diseases and new targeted oligonucleotides have been developed for different purposes. The click chemistry allowing the tolerated union between units with a wide diversity of functional groups represents a robust means of designing new hybrid compounds with an extraordinary diversity of applications. This review provides an overview of the most recent works related to the use of click chemistry methodology in the field of nucleosides, nucleotides and nucleic acids for pharmacological applications.

Dextran based amphiphilic self-assembled biopolymeric macromolecule synthesized via RAFT polymerization as indomethacin carrier

This work demonstrates a facile pathway to develop a biopolymer based amphiphilic macromolecule through reversible addition-fragmentation chain transfer (RAFT) polymerization, using dextran (a biopolymer) as starting material. Also, a new hydrophobic monomer [2-methyl-acrylic acid 1-benzyl-1H-[1,2,3] triazol-4-ylmethyl ester (MABTE)] has been synthesized using methacrylic acid via "click" approach. The resultant copolymer displays controlled radical polymerization characteristics: narrow polydispersity (Ð) and controlled molecular weight as obtained through advanced polymer chromatography (APC) analysis. In aqueous solution, the copolymer can proficiently be self-assembled to provide micellar structure, which has been evidenced from field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses. The in-vitro cytotoxicity study illustrates the nontoxic nature of the copolymer up to 100 μg/mL polymer concentration. The copolymer has been found to be worthy as an efficient carrier for the sustained release of hydrophobic drug: Indomethacin (IND).

An insight in anti-malarial potential of indole scaffold: A review

Malaria is a major parasitic disease in tropical and sub-tropical regions. Pertaining to the sustaining resistance in malarial parasite against the available drugs, novel treatment options are the need of the hour. In this resolve recently, focus has shifted to finding the natural alternatives that possess anti-plasmodial activity for combatting malaria. Drawing on the text written in ancient scriptures and Ayurveda, natural compounds are now being screened for their therapeutic properties. Indole is one such natural compound, present in all living organisms, it displays a range of therapeutic activities including anticancer, anti-inflammatory, antimalarial etc. In this review, we have discussed various indole scaffold as well as the semi-synthetic drugs containing indole moiety that have been synthesized for malaria treatment.

Ionogels Obtained by Thiol-ene Photopolymerization-Physicochemical Characterization and Application in Electrochemical Capacitors

Flexible ionogels with good mechanical properties were obtained in situ by thiol-ene photopolymerization of trimethylolpropane tris(3-mercaptopropionate) (TMPTP) and 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATT) (with C=C: SH ratio 1:1) in four imidazolium ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide—EMImNTf₂, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-EMImOTf, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-BMImNTf₂, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate—BMImOTf) used in the range 50 to 70 wt.%. The mechanical and electrochemical properties of obtained ionogels were examined. Ionogels with ionic liquids (ILs) with NTf₂⁻ anion are more puncture resistant than with OTf⁻ anion. Moreover, ionogels with the NTF₂⁻ anion have better electrochemical properties than those with the OTf⁻ anion. Although it should be noted that ionogels with the EMIm⁺ cation have a higher conductivity than the BMIm⁺. This is connected with intermolecular interactions between polymer matrix and IL related to the polarity of IL described by the Kamlet-Taft parameters. These parameters influence the morphology of the polymer matrix (as shown by the SEM micrograph), which is formed by interconnected polymer spheres.