Click chemistry reactions in medicinal chemistry: applications of the 1,3-dipolar cycloaddition between azides and alkynes

1,5-Disubstituted 1,2,3-triazoles: Molecular scaffolds for medicinal chemistry and biomolecular mimetics

Ruthenium (II) catalyzed click chemistry enable the highly efficient and selective synthesis of 1,5-disubstituted 1,2,3-triazoles. This method provides exclusive formation of the desired 1,5-regioisomer. In the past twenty years, these reactions have become a valuable tool in organic synthesis. Similar to 1,4-regioisomer of 1,2,3-triazole, 1,5-disubstituted 1,2,3-triazole functions as biocompatible linkers and biologically active scaffolds. This review focuses on the synthesis and medicinal chemistry significance of these triazoles as versatile building blocks. Notably, they serve as bioisosteres of the cis-amide bond, conferring enhanced stability and mimicking constrained amino acids, making them crucial for peptidomimetic development. Hence, we are discussing their application in the development of peptidomimetics. 1,5-Disbstituted 1,2,3- triazoles mimic cis-amide bond in the peptides, altering their conformation and biological activity. Furthermore, we have discussed its application to create novel bioactive molecules, including mimics of natural products, nucleosides, nucleotides, glycoconjugates, and protein-protein interaction inhibitors. This review highlights their substantial potential in drug discovery, and provides a valuable resource for future research in this field.

Microwave-assisted click synthesis of levoglucosan triazolyl glycoconjugates using ascorbyl palmitate sodium salt (Asp-Na) as a green Co-catalyst

Ascorbyl palmitate sodium salt (Asp-Na) 2 has been found to be a highly effective co-catalyst in copper catalyzed azide-alkyne cycloaddition (CuAAC) reactions under microwave (MW) condition. This co-catalyst provides a more cost-efficient option compared to sodium ascorbate by reducing the stoichiometric amount of ascorbic acid required for the CuAAC reaction. With its palmitate side chain, Asp-Na 2 acts as a surfactant by improving the solubility of substrates, particularly the lipophilic compounds. Notably, it can be obtained in high purity by semi-synthesis from non-edible oils, aligning with the sustainable practices. Application of 2 in CuAAC reaction of levoglucosan based terminal alkyne (3) and azido-sugars (4) furnished the corresponding triazolyl glycoconjugates (5) in yields ranging between 70 and 90 %.

1,2,3-Triazole naphthaldehyde compounds and their oxime derivatives: in vitro and in silico DNA binding properties

In this work, we report the synthesis and DNA binding properties of a series of 1,2,3-triazole naphthaldehyde compounds and their oxime derivatives. The 1,2,3-triazole naphthaldehyde compounds (1a-1f) were prepared by the Cu(I) catalysed click reactions. The 1,2,3-triazole naphthaldehyde compounds (1a-1f) were then reacted with hydroxyl amine to yield 1,2,3-triazole oxime compounds (2a-2f). The structures of all compounds were characterized by Fourier-transform ınfrared spectroscopy, Nuclear magnetic resonance and elemental analysis. Crystal structures of compounds 1a, 1c, 1f, 2c and 2d were investigated by single crystal X-ray crystallography. The compounds were evaluated for their DNA binding properties via in vitro spectrophotometric and in silico molecular docking studies. The compounds were found to interact with DNA via a groove binding mode with considerable the binding constants. The groove binding mode of interactions were also suggested by fluorescence ethidium bromide replacement experiments and viscosity studies. Binding interactions of the compounds with DNA have also been studied by molecular docking studies.

Synthesis and anti-inflammatory activity of novel 1,2,3-triazole- derivatives from 7-Oxodehydroabietic acid

Dehydroabietic acid (DHA) is a naturally occurring diterpene with relevant biological activities. 7-Oxodehydroabietic acid as a highly oxidized state derivative from Dehydroabietic acid (DHA) showing good activities. However, the reported compounds did not include triazole derivatives. To discover novel potent anti-inflammatory diterpenoids, a series of hybrids of 7-Oxodehydroabietic acid containing 1,2,3-triazole moiety were designed and synthesized. The anti-inflammatory activity of the new compounds was assessed towards BV2 cell lines using L-NMMA (IC50 = 42.36 ± 2.47 µM) as a positive control. Compared with the L-NMMA, anti-inflammatory effect (NO inhibitory activities) was found in these novel molecules, especially compounds 9 (IC50 = 8.00 ± 0.83 µM), 10 (IC50 = 8.44 ± 0.89 µM), 15 (IC50 = 8.13 ± 0.97 µM) and 16 (IC50 = 8.84 ± 1.10 µM). The anti-inflammatory activity of compounds 9, 10, 15 and 16 in vivo are underway.

Polymeric Micellar Nanocatalysts for CuAAC Click Reaction in Water

Polymer-supported copper catalysts have attained a prominent status and continue to be a focal point of ongoing research and development due to their adaptable properties, which make them invaluable tools for diverse catalytic reactions in aqueous solutions. The objective of this investigation is to develop catalysts supported on a random copolymer that can be assembled in water. A series of random copolymer was prepared through postpolymerization modification of a polymer precursor, poly(pentafluorophenyl acrylate) (PPFPA), employing 1-amino-2-propanol and 1-(3-aminopropyl)imidazole via nucleophilic substitution. Following alkylation and copper insertion, it yielded a polymer-supported copper (Cu) catalyst on poly(N-(2-hydroxypropyl)acrylamide)-ran-poly(N-(3-(1-benzylimidazolium-3-yl)propyl)acrylamide) PHPAM76-ran-PILAM24(Cu(I)), capable of assembling into micellar catalysts in water with a diameter of 175 nm and low polydispersity. These developed self-assembled micelles can serve as nanocatalysts for the copper-catalyzed azide-alkyne cycloaddition (CuAAC) between alkyne and azide derivatives in an aqueous system. Employing PHPAM76-ran-PILAM24(Cu(I)) as the micellar catalyst with a 1 mol % Cu loading significantly enhances reaction yields (95-99%), achieving complete conversion at room temperature within 1-4 h, with minimal copper residue detected in the product (<0.06 ppm) after a straightforward extraction process. This research highlights the versatility of postpolymerization modification of the polymer precursor, PPFPA through nucleophilic substitution as a promising strategy for the development of tailored nanocatalysts for diverse chemical reactions in the future.

Orthogonal Agent Comprising a Nitrile N-Oxide and a Phenylcarbamate for Facile Molecular Integration on Styrne-Butadiene Resin

The covalent attachment of poly(ethylene glycol) (PEGylation) to materials minimizes non-specific fouling of the material surface with biocomponents. While the PEGylation reaction on polar surfaces is widely used and regarded as a common technique, the PEGylation on less polar polymers and elastomers is extremely difficult due to the absence of reactive points with PEG terminus. Herein, the design and synthesis of an orthogonal agent with a nitrile N-oxide and a phenyl carbamate that can mediate between an alkene and an amine are reported. The ligation capacity of the orthogonal agent is demonstrated through the model reaction to connect between 1-hexene and 4-methoxybenzylamine and the grafting reaction of PEG onto poly(styrene-co-butadiene) (SB) resin. The surface characteristics of PEGylated SB film are evaluated by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Because SB resin is frequently used as a 3D-printing polymer, the present study indicates that the orthogonal agent can be applicable to the surface modification of 3D-printed objects precisely manufactured by using a computer-aided design (CAD) file in the future.

Click Reaction Inspired Enzyme Inhibitors in Diabetes Care: An Update in the Field of Chronic Metabolic Disorder

Diabetes is a chronic metabolic disorder that impacts all age groups and affects a large population worldwide. Humans receive glucose from almost every food source, and after absorption from the gut, it reaches the liver, which functions as the distribution center for it. The insulin-responsive glucose transporter type 4 (GLUT-4) is a major carrier of glucose to the various cells (majorly expressed in myocytes, adipocytes, and cardiomyocytes) in a well-fed state. In fasting periods, the glucose supply is maintained by glycogenolysis and gluconeogenesis. In diabetes, the distribution of glucose is hampered due to several reasons. Furthermore, to treat this disorder, several drugs have been synthesized, and click chemistry plays an important role. A more recent concept for producing pharmaceuticals with a click chemistry approach makes any reaction more practical and stereospecific, along with a higher yield of products and a smaller number of by-products. This approach comprises a compiled study of the activity of numerous compelling antidiabetic drugs containing 1,2,3-triazole derivatives supported by click chemistry. In this review, we discuss the synthetic antidiabetic drugs made via click chemistry and their commendable role in improving diabetes care.

Smiles-Rearrangement-Based One-Pot Synthesis of Diarylacetylenes from Benzylic Sulfones and Methyl Benzoates Mediated by LiN(SiMe3)2/KN(SiMe3)2

The one-pot synthesis of diphenylacetylene by the reaction of methyl benzoate with 1-(benzylsulfonyl)-3,5-di(trifluoromethyl)benzene was developed. The combination of LiN(SiMe3)2 and KN(SiMe3)2 is key to promoting the reaction. Simply combining methyl benzoate, 1-(benzylsulfonyl)-3,5-di(trifluoromethyl)benzene, LiN(SiMe3)2, and KN(SiMe3)2 can produce a variety of diaryl acetylenes (28 examples, 18-70% yields).

Benzene-1,3-disulfonyl fluoride and Benzene-1,3,5-trisulfonyl fluoride: Low-Cost, Stable, and Selective Reagents for SuFEx-Driven Deoxyazidation

The development of synthetic methods for the synthesis of organic azides is highly important, given their critical role in advancing click chemistry over the last twenty years. We report a reagent-economical, reliable, and scalable synthesis of alkyl azides from primary and secondary alcohols. This robust click method capitalizes on the synergistic interaction between Sulfur Fluoride Exchange (SuFEx) reagents-specifically, benzene-1,3-disulfonyl fluoride (BDSF) or benzene-1,3,5-trisulfonyl fluoride (BTSF)-and trimethylsilyl azide (TMSN3). The method offers procedural ease, accommodates a wide array of substrates, and enables late-stage functionalization. Additionally, we demonstrate the protocol's adaptability by validating a straightforward one-pot deoxyazidation-CuAAC sequence for drug discovery applications.

Recent advances in triazole synthesis via click chemistry and their pharmacological applications: A review

Click chemistry is a flexible method featuring only the most feasible and efficient chemical reactions. The synthesis of 1,2,3-triazole from azides and terminal acetylenes using copper(I) as a catalyst is an extremely powerful reaction due to the extreme dependability, good selectivity, and biocompatibility of the starting materials. Triazole molecules are more than simple passive linkers; through hydrogen bonding and dipole interactions, they rapidly bind with biological targets. Its applications in drug development are expanding, ranging from target-oriented in situ chemistry and combinatorial mechanisms for lead generation to bioconjugation methods to study proteins and DNA. The click chemistry has frequently been used to speed up drug discovery and optimization processes in the past few years. The click chemistry reaction based on copper-catalyzed azide-alkyne cycloaddition (CuAAC) is a biochemical process with applications in medicinal chemistry and chemical biology. Thus, click reactions are an essential component of the toolkit for medicinal chemistry and help medicinal chemists overcome the barriers in chemical reactions, increase throughput, and improve the standards of compound libraries. The review highlights the recent advancements in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry approach for synthesizing biologically important triazole moieties with a greater emphasis on synthesis methodologies and pharmacological applications. Additionally, the triazole-based FDA-approved drugs are also discussed with their mode of action to highlight the importance of the click chemistry approach in synthesizing the bioactive triazole compounds.

Pd-, Cu-, and Ni-Catalyzed Reactions: A Comprehensive Review of the Efficient Approaches towards the Synthesis of Antibacterial Molecules

A strong synthetic tool for many naturally occurring chemicals, polymers, and pharmaceutical substances is transition metal-catalyzed synthesis. A serious concern to human health is the emergence of bacterial resistance to a broad spectrum of antibacterial medications. The synthesis of chemical molecules that are potential antibacterial candidates is underway. The main contributions to medicine are found to be effective in transition metal catalysis and heterocyclic chemistry. This review underlines the use of heterocycles and certain effective transition metals (Pd, Cu, and Ni) as catalysts in chemical methods for the synthesis of antibacterial compounds. Pharmaceutical chemists might opt for clinical exploration of these techniques due to their potential.

Exploring Triazole-Connected Steroid-Pyrimidine Hybrids: Synthesis, Spectroscopic Characterization, and Biological Assessment

Molecules originating from natural sources are physicochemically and biologically diverse. The conjugation of two active biomolecules has become the foundation for medical and pharmaceutical sciences. An effective synthesis of 11 new steroid-pyrimidine conjugates containing 1,2,3-triazole rings was carried out. The group of 3α-OH bile acids (lithocholic, deoxycholic, cholic) and 3β-OH sterols (cholesterol, cholestanol) were respectively modified to azidoacetates. 2-thiouracil was converted into N(1)S and N(3)S dipropargyl derivatives. Azide-alkyne cycloaddition in the presence of copper(I) of the obtained compounds led to the preparation of 1,2,3-triazole derivatives. Based on a series of spectroscopic (1H NMR, 13C NMR, Fourier-transform infrared (FT-IR)), spectrometric analyses (Electrospray ionization-mass spectrometry (ESI-MS), electron impact-mass spectrometry (EI-MS)), and semiempirical calculations, the structures of all compounds were confirmed. In silico biological tests and molecular docking (for domain 1KZN, 2H94, 5V5Z, 1EZF, 2Q85) were performed for selected compounds. The tests performed indicate the theoretical antimicrobial potential of the obtained ligands.

Design and synthesis of 1,2-dihydroquinoline/chromene fused sugar triazole frameworks by copper-catalyzed one-pot click and intramolecular arylation reactions

Expedient copper-catalyzed one-pot click and intramolecular arylation reactions have been developed for the synthesis of 1,2-dihydroquinoline/chromene-fused triazoles with varying sugar functionalities. It has been observed that the additive TMEDA greatly facilitates this copper-catalyzed cyclization. This reaction involves two mechanistically distinct reactions i.e. an atom-economical click reaction and a direct arylation of a sugar triazole. This method provides rapid and simple access to fused sugar triazoles in moderate to good yields. All the key products were characterized using 1H and 13C NMR and HRMS data.

Halogen-Atom Transfer Enabled Catalytic Enantioselective Coupling to Chiral Trifluoromethylated Alkynes via Dual Nickel and Photocatalysis

With halogen-atom transfer as an effective tool, a novel catalytic enantioselective protocol to generate chiral trifluoromethylated alkynes has been established by a cooperative photoredox and nickel catalysis system, providing a straightforward and modular route to access this type of product in good yields and enantioselectivities. The halogen-atom transfer process is essential for the reaction and this novel strategy offers another promising way to utilize alkyl halides with highly negative reduction potentials. It firstly expands nickel-catalyzed asymmetric reductive cross-couplings of organohalides from the traditional single-electron transfer to halogen-atom transfer.

Ferrocenyl Azoles: Versatile N-Containing Heterocycles and their Anticancer Activities

The medicinal chemistry of ferrocene has gained its momentum after the discovery of biological activities of ferrocifen and ferroquine. These ferrocenyl drugs have been designed by replacing the aromatic moiety of the organic drugs, tamoxifen and chloroquine respectively, with a ferrocenyl unit. The promising biological activities of these ferrocenyl drugs have paved a path to explore the medicinal applications of several ferrocenyl conjugates. In these conjugates, the ferrocenyl moiety has played a vital role in enhancing or imparting the anticancer activity to the molecule. The ferrocenyl conjugates induce the cytotoxicity by generating reactive oxygen species and thereby damaging the DNA. In medicinal chemistry, the five membered nitrogen heterocycles (azoles) play a significant role due to their rigid ring structure and hydrogen bonding ability with the biomolecules. Several potent drug candidates with azole groups have been in use as chemotherapeutics. Considering the importance of ferrocenyl moiety and azole groups, several ferrocenyl azole conjugates have been synthesized and screened for their biological activities. Hence, in the view of a wide scope in the development of potent drugs based on ferrocenyl azole conjugates, herein we present the details of synthesis and the anticancer activities of ferrocenyl compounds bearing azole groups such as imidazole, triazoles, thiazole and isoxazoles.

1,5-disubstituted 1,2,3-triazolylated carbohydrates and nucleosides

In general, 1,5-disubstituted 1,2,3-triazolyl moiety is much less common in the synthesis and applications in comparison to its regioisomeric counterpart. Moreover, the synthesis of 1,5-disubstituted 1,2,3-triazoles are not so straightforward as is the case for copper catalyzed strategy of 1,4-disubstituted 1,2,3-triazoles. The preparation of 1,5-triazolylated carbohydrates and nucleosides are even more complex because of the difficulties in accessing the appropriate starting materials as well as the compatibility of reaction conditions with the various protecting groups. 1,5-Disubstitution regioisomeric triazoles of carbohydrates and nucleosides were traditionally obtained as minor products through straightforward heating of the mixture of azides and terminal alkynes. However, the separation of isomers was tedious or in some cases futile. On the other hand, regioselective synthesis using ruthenium catalysis triggered serious concern of residual metal content in therapeutically important ingredients. Therefore, serious efforts are being made by several groups to develop non-toxic metal based or completely metal-free synthesis of 1,5-disubstituted 1,2,3-triazoles. This article strives to summarize the pre-Click era as well as the post-2001 reports on the synthesis and potential applications of 1,5-disubstituted 1,2,3-triazoles in biological systems.

Design and Synthesis of Novel Antioxidant 2-Substituted-5,7,8-Trimethyl-1,4-Benzoxazine Hybrids: Effects on Young and Senescent Fibroblasts

The exponential growth of the aged population worldwide is followed by an increase in the prevalence of age-related disorders. Oxidative stress plays central role in damage accumulation during ageing and cell senescence. Thus, a major target of today's anti-ageing research has been focused on antioxidants counteracting senescence. In the current work, six novel 5,7,8-trimethyl-1,4-benzoxazine/catechol or resorcinol hybrids were synthesized connected through a methoxymethyl-1,2,3-triazolyl or a 1,2,3-triazoly linker. The compounds were evaluated for their antioxidant capacity in a cell-free system and for their ability to reduce intracellular ROS levels in human skin fibroblasts, both young (early-passage) and senescent. The most efficient compounds were further tested in these cells for their ability to induce the expression of the gene heme oxygenase-1 (ho-1), known to regulate redox homeostasis, and cellular glutathione (GSH) levels. Overall, the two catechol derivatives were found to be more potent than the resorcinol analogues. Furthermore, these two derivatives were shown to act coordinately as radical scavengers, ROS inhibitors, ho-1 gene expression inducers, and GSH enhancers. Interestingly, one of the two catechol derivatives was also found to enhance human skin fibroblast viability. The properties of the synthesized compounds support their potential use in cosmetic applications, especially in products targeting skin ageing.

Copper-Catalyzed Enantioselective Synthesis of Spirohydroindoles by Ethoxyformylmethylene Oxindole and Iminoester 1,3-Dipole Cycloaddition: An Examination of Associated Biological Activities

A highly enantioselective 1,3-dipolar cycloaddition of ethoxyformylmethylene oxindole with iminoesters has been achieved using the Cu(I)-(S,Sp)-Ph Phosferrox catalytic system, generating a series of chiral spiro[pyrrolidin-3,3'-oxindole] compounds with four consecutive stereocenters, including a spirocycle quaternary center (71%-99% yield, up to >20:1 dr and 95:5 er). The compounds exhibited good inhibitory activity against Valsa mali (V.m.), Fusarium oxysporium (F.o.), and Alternaria brassicae (A.b.).

Each Interruption is an Opportunity: Novel Synthetic Strategies Explored Through Interrupted Click Reactions

The particular and unique mechanism of the copper-catalyzed reaction between azides and alkynes (CuAAC) has not only allowed for the efficient synthesis of 1,2,3-trisubstituted 1,4-triazoles in excellent yields and under mild conditions, becoming the quintessential click reaction, but it has also enabled the straightforward formation of a metallocycle intermediate, the copper triazolyl. This, under suitable reaction conditions able to suppress its protonolysis, can be used either for the creation of new bicyclic triazolyl structures or for the generation of novel three or four-component reactions. The aim of this review is to rationalize and unify all these transformations, which are collectively referred to as "interrupted click reactions".

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.

Sustainable production of triazoles from lignin major motifs

An efficiently catalyzed synthesis of pharmaceutically relevant 1,2,3-trazoles from renewable resources is highly desirable. However, due to incompatible catalysis conditions, this endeavor remained challenging so far. Herein, a practical access protocol to 1,2,3-triazoles, starting from lignin phenolic β-O-4 with γ-OH group utilizing a vanadium-based catalyst is presented. A broad substrate scope reaching up to 97 % yield of 1,2,3-triazoles are obtained. The reaction pathway includes selective cleavage of double C-O bonds, cycloaddition, and dehydrogenation. Mechanistic studies and density-functional theory (DFT) calculations suggest that the V-based complex acts as a bifunctional catalyst for both selective C-O bonds cleavage and dehydrogenation. This synthetic pathway has been applied for the synthesis of pharmacological and biological active carbohydrate derivatives starting from biomass components as feedstock, enabling a potential sustainable route to triazolyl carbohydrate derivatives, which paves the way for lignin-based heterocyclic aromatics in the pharmaceutical applications.

Antifungal and Antiparasitic Activities of Metallocene-Containing Fluconazole Derivatives

The search for new anti-infectives based on metal complexes is gaining momentum. Among the different options taken by researchers, the one involving the use of organometallic complexes is probably the most successful one with a compound, namely, ferroquine, already in clinical trials against malaria. In this study, we describe the preparation and in-depth characterization of 10 new (organometallic) derivatives of the approved antifungal drug fluconazole. Our rationale is that the sterol 14α-demethylase is an enzyme part of the ergosterol biosynthesis route in Trypanosoma and is similar to the one in pathogenic fungi. To demonstrate our postulate, docking experiments to assess the binding of our compounds with the enzyme were also performed. Our compounds were then tested on a range of fungal strains and parasitic organisms, including the protozoan parasite Trypanosoma cruzi (T. cruzi) responsible for Chagas disease, an endemic disease in Latin America that ranks among some of the most prevalent parasitic diseases worldwide. Of high interest, the two most potent compounds of the study on T. cruzi that contain a ferrocene or cobaltocenium were found to be harmless for an invertebrate animal model, namely, Caenorhabditis elegans (C. elegans), without affecting motility, viability, or development.

Dansylated Nitrile N-Oxide as the Fluorescent Dye Clickable to Unsaturated Bonds without Catalyst

Fluorescent polymeric materials have been exploited in the fields of aesthetical purposes, biomedical engineering, and three-dimensional printing applications. While the fluorescent materials are prepared by the polymerization of fluorescent monomer or the blending a fluorescent dye with common polymer, the covalent immobilization of fluorescent dye onto common polymers is not the practical technique. In this paper, dansylated nitrile N-oxide (Dansyl-NO) has been designed and synthesized to be a stable nitrile N-oxide as the derivative of 2-hydroxy-1-naphthaldehyde. While Dansyl-NO shows good reactivity to an alkene and an alkyne to give fluorescent Dansyl-Ene and Dansyl-Yne, respectively, it hardly reacts to a nitrile. The results indicate that Dansyl-NO serves as a fluorescent dye clickable to alkenes and alkynes. To know the effects of solvent on the fluorescent properties, the UV-vis and fluorescence spectra of Dansyl-Ene are measured in three solvents. Dansyl-Ene shows fluorescent solvatochromism, which appears to be red-shifted along with the increase in solvent polarity. Poly(styrene-co-butadiene) directly reacts with Dansyl-NO to give fluorescent modified SB. The emission spectrum of modified SB is blue-shifted compared with that of Dansyl-Ene. The blue-shift could be possibly attributed to the presence of less polar polymer skeleton around the dansyl moieties of modified SB.

Design, synthesis, in silico molecular docking, and ADMET studies of quinoxaline-isoxazole-piperazine conjugates as EGFR-targeting agents

In this paper, we report the synthesis of quinoxaline-isoxazole-piperazine conjugates. The anticancer activity was evaluated against three human cancer cell lines, including MCF-7 (breast), HepG-2 (liver), and HCT-116 (colorectal). The outcomes of the tested compounds 5d, 5e, and 5f have shown more potent activity when compared to the standard drug erlotinib. In a cell survivability test (MCF-10A), three potent compounds (5d, 5e, and 5f) were evaluated against the normal breast cell line, although neither of them displayed any significant cytotoxicity with IC50 values greater than 84 μM. Furthermore, the compounds 5d, 5e, and 5f were tested for tyrosine kinase EGFR inhibitory action using erlotinib as the reference drug and compound 5e was shown to be more potent in inhibiting the tyrosine kinase EGFR than sorafenib. In addition to this, molecular docking studies of compounds 5d, 5e, and 5f demonstrated that these compounds had more EGFR-binding interactions. The potent compounds 5d, 5e, and 5f were subjected to in silico pharmacokinetic assessment by SWISS, ADME, and pkCSM. While the compounds 5d, 5e, and 5f followed Lipinski, Veber, Egan, and Muegge rules without any deviation.

Colorectal anticancer activity of a novel class of triazolic triarylmethane derivatives

Triarylmethanes and triazoles constitute privileged structures extensively used in drug discovery programs. In this work, 12 novel triarylmethanes linked to a triazole ring were designed, synthesized, and chemically characterized aiming to target colorectal cancer. The synthetic strategy for triarylmethanes mono- and bi-substituted by a functionalized triazole ring involved a 1,3-dipolar cycloaddition. A preliminary screening in human colorectal cancer cells (HT-29 and HCT116) and murine primary fibroblasts (L929) allowed the selection of the best candidate 9b based on its high inhibition of cancer cell proliferation with an IC50 of 11 μM on HT-29 and 14 μM on HCT116 and its non-cytotoxic effects on murine fibroblasts (<100 μM). A deep mechanistic study on various pathways showed that compound 9b induces caspase-3 cleavage, and its inhibitory effect on PARP activity is correlated with the increase of DNA fragmentation in cancer cells. Moreover, 9b induced apoptosis promoted by the inhibition of anti-apoptotic cell survival signaling pathways demonstrated via the downregulation of phosphorylated Akt and ERK proteins. Finally, the predicted binding modes of compounds 8c and 9b to five potential biological targets (i.e., AKT, ERK-1 and ERK-2, PARP and caspase-3) was evaluated using molecular modeling, and the predictions of the SuperPred webserver identified ERK2 as the most remarkable target. Also predicted in silico, 9b displayed appropriate drug-likeness and good absorption, distribution, metabolism and excretion (ADME) profiles.

Cassia fistula galactomannan stabilized copper nanocatalyst as an efficient, recyclable heterogeneous catalyst for the fast clickable [3+2] Huisgen cycloadditions in water

In this study, we have first time investigated the synthesis of copper nanocatalyst by using biopolymer galactomannan, naturally extracted from Cassia fistula pods. The methodology involved for the preparation of copper nanocatalyst is economical, efficient, environment friendly, and did not involve further processing for stabilization or reduction of copper nanoparticles. The morphology and structural characterization of the nanocatalyst was performed by using different techniques such as FT-IR, 1H NMR, SEM, EDX, HR-TEM, XRD, XPS, ICP-MS, BET, and TGA analysis. The prepared copper nanocatalyst is applied for the click [3+2] Huisgen cycloadditions of various azides and alkynes, employing water as environmentally benign solvent. In comparison to earlier reported methods, our method requires lowest catalyst loading, less reaction time, excellent yields and have wide substrate scope. Additionally, the catalyst was easily recovered by simple filtration and recycled at least ten consecutive times without any appreciable loss of efficiency and selectivity. The effect of mannose and galactose (Man/Gal) ratio of Cassia fistula galactomannan on the catalytic activity were also investigated.

Unveiling the anticancer mechanism of 1,2,3-triazole-incorporated thiazole-pyrimidine-isoxazoles: insights from docking and molecular dynamics simulations

Cancer is a major global health concern, and the constant search for novel, selective anticancer compounds with low toxicity is never ending. Nitrogen heterocyclic compounds such as pyrimidine and triazole have been identified as potential candidates for cancer treatment. A novel series of 1,2,3-triazole incorporated thiazole-pyrimidine-isoxazole derivatives 10 (a-j) were designed, synthesized and evaluated for antitumorigenic activities against human breast cancer (MCF-7), human lung cancer (A549) and human prostate (PC3 & DU-145) various cell-lines by employing MTT assay using etoposide as the positive control. The synthesized hybrids yielded decent efficacy, which was further compared with the standard drug. Among all the molecules, 10h revealed the more potent anticancerous activities, having IC50 values ranging from 0.011 ± 0.0017 µM; 0.063 ± 0.0012 µM; 0.017 ± 0.0094 µM and 0.66 ± 0.072 µM with DU145, PC3, A549, and MCF7 cell-lines, respectively. Tubulin, being a major protein involved with diverse biological actions, also serves, as a crucial target for several clinically practiced anticancer drugs, was utilized for docking analyses to evaluate the binding affinity of ligands. Docking results demonstrates that the selected hybrids 10 (g-j) exhibited good binding affinities with protein. Subsequently, drug likeness studies were carried out on the synthesized compounds to evaluate and analyze their drug like properties such as absorption, distribution, metabolism, excretion, and toxicity (ADMET) for toxicity prediction. Based on these analyses, the selected complexes were further employed for molecular dynamic simulations to analyze stability via an exhaustive cumulative 200 nanoseconds simulation. These results suggest that the selected compounds are stable and might serve as potential inhibitors to tubulin complex. In conclusion, we propose these synthesized compounds 10 (g-j) might provide new insights into cancer treatment and have potential for future development.Communicated by Ramaswamy H. Sarma.

"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.

Proof of concept: Pull down assay using bovine serum albumin and an immunomodulator small molecule

In the past decade, there has been increasing interest in use of small molecules for immunomodulation. The affinity-based pull-down purification is an essential tool for target identification of small molecules and drug discovery. This study presents our recent efforts to investigate the cellular target(s) of Compound A, a small molecule with demonstrated immunomodulatory properties in human peripheral blood mononuclear cells (PBMCs). While we have previously observed the immunomodulatory activity of Compound A in PBMCs, the specific molecular targets underlying its effects remains elusive. To address this challenge, we synthesized a trifluoromethyl phenyl diazirine (TPD)-bearing trifunctional Probe 1 based on the chemical structure of Compound A, which could be used in a pull-down assay to efficiently bind to putative cellular targets via photoaffinity labelling. In this report, we utilized bovine serum albumin (BSA) as a model protein to establish a proof-of-concept in order to assess the suitability of Probe 1 for binding to an endogenous target. By the successful synthesis of Probe 1 and demonstrating the efficient binding of Probe 1 to BSA, we propose that this method can be used as a tool for further identification of potential protein targets of small molecules in living cells. Our findings provide a valuable starting point for further investigations into the molecular mechanisms underlying the immunomodulatory effects of Compound A.

Click chemistry as a method for the synthesis of steroid bioconjugates of bile acids derivatives and sterols

Six steroid conjugates of bile acids and sterol derivatives have been synthesized using the click chemistry method. The azide-alkyne Huisgen cycloaddition of the propionyl ester of lithocholic, deoxycholic and cholic acid with azide derivatives of cholesterol and cholestanol gave new bile acid-sterol conjugates linked with a 1,2,3-triazole ring. Previously, sterols were converted to bromoacetate substituted derivatives by reaction with bromoacetic acid bromide in anhydrous dichloromethane. These compounds were then converted to azide derivatives using sodium azide. The propiolic esters of lithocholic, deoxycholic and cholic acids were obtained by reaction with propiolic acid in the presence of p-toluenesulfonic acid. Additionally, two of these steroids: methyl 3α-propynoyloxy-12α-acetoxy-5β-cholane-24-oate and methyl 3α-propynoyloxy-7 α,12α-diacetoxy-5β-cholane-24-oate were also obtained and characterized for the first time. All conjugates were obtained in good yields using an efficient synthesis method. The structures of all conjugates and the four substrates were confirmed by spectral (1H- and 13C NMR, FT-IR) analysis, mass spectrometry (ESI-MS), and PM5 semiempirical methods. The pharmacotherapeutic potential of the synthesized compounds was estimated based on the in silico Prediction of Activity Spectra for Substances (PASS) method. The cytotoxicity of the compounds was in vitro evaluated in a hemolytic assay using human erythrocytes as a cell model. The in silico and in vitro study results indicate that the selected compound possesses an interesting biological activity and can be considered as potential drug design agent. Additionally, molecular docking was performed for the selected conjugate.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

N2 modified cap analogues as translation inhibitors and substrates for preparation of therapeutic mRNA

In recent years many scientists have begun to focus on the mRNA molecule's emeregence as a new type of drug. Its fast-moving and successful career as a vaccine technology cannot be underestimated. mRNA provides new opportunities and allows for the rapid preparation of effective drugs at low cost. These extensive possibilities stem from a number of factors, but the small cap structure located at the 5' end of the mRNA is one contributing factor. Cap protects mRNA and ensures efficient recruitment to the biosynthesis machinery. Furthermore, it allows for the easy introduction of various modifications that influence the activity of the entire mRNA. Among the many different cap analogues that have been reported, those modified at the N2 position of guanosine have been systematically developed. N2-modified caps in the form of nucleoside monophosphates or dinucleotides show favorable biological properties, as well as a high capacity to inhibit the translation process in the cell-free RRL system. Modified N2 dinucleotides are efficiently incorporated into the structure of the mRNA transcript, and in specific circumstances with the correct orientation, making them an interesting alternative for ARCA-type analogues. Moreover, mRNA transcripts containing cap structures modified within the exocyclic amino group show very high translational activity. Therefore, analogues modified at the N2 position may have future applications as therapeutics against various manifestations of cancer and as desirable tools in RNA engineering.

Quercetin and Related Analogs as Therapeutics to Promote Tissue Repair

Quercetin is a polyphenol of the flavonoid class of secondary metabolites that is widely distributed in the plant kingdom. Quercetin has been found to exhibit potent bioactivity in the areas of wound healing, neuroprotection, and anti-aging research. Naturally found in highly glycosylated forms, aglycone quercetin has low solubility in aqueous environments, which has heavily limited its clinical applications. To improve the stability and bioavailability of quercetin, efforts have been made to chemically modify quercetin and related flavonoids so as to improve aqueous solubility while retaining bioactivity. In this review, we provide an updated overview of the biological properties of quercetin and proposed mechanisms of actions in the context of wound healing and aging. We also provide a description of recent developments in synthetic approaches to improve the solubility and stability of quercetin and related analogs for therapeutic applications. Further research in these areas is expected to enable translational applications to improve ocular wound healing and tissue repair.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

Probing the structure of human tRNA3Lys in the presence of ligands using docking, MD simulations and MSM analysis

The tRNA3Lys, which acts as a primer for human immunodeficiency virus type 1 (HIV-1) reverse transcription, undergoes structural changes required for the formation of a primer-template complex. Small molecules have been targeted against tRNA3Lys to inhibit the primer-template complex formation. The present study aims to understand the kinetics of the conformational landscape spanned by tRNA3Lys in apo form using molecular dynamics simulations and Markov state modeling. The study is taken further to investigate the effect of small molecules like 1,4T and 1,5T on structural conformations and kinetics of tRNA3Lys, and comparative analysis is presented. Markov state modeling of tRNA3Lys apo resulted in three metastable states where the conformations have shown the non-canonical structures of the anticodon loop. Based on analyses of ligand-tRNA3Lys interactions, crucial ion and water mediated H-bonds and free energy calculations, it was observed that the 1,4-triazole more strongly binds to the tRNA3Lys compared to 1,5-triazole. However, the MSM analysis suggest that the 1,5-triazole binding to tRNA3Lys has brought rigidity not only in the binding pocket (TΨC arm, D-TΨC loop) but also in the whole structure of tRNA3Lys. This may affect the easy opening of primer tRNA3Lys required for HIV-1 reverse transcription.

Synthesis, α-Glucosidase inhibitory activity and docking studies of Novel Ethyl 1,2,3-triazol-4-ylmethylthio-5,6-diphenylpyridazine-4-carboxylate derivatives

In this work, a novel series of pyridazine-triazole hybrid molecules were prepared and evaluated as inhibitors of rat intestinal α-glucosidase enzyme. Amongst all newly synthesized compounds, 10k showed good inhibition in the series with IC₅₀ value of 1.7 µM which is 100 folds stronger than positive control, acarbose. The cytotoxicity revealed that this compound is not toxic against normal cell line, HDF. The docking studies showed that triazole ring plays an important role in the binding interactions with the active site. The insertion of compound 10k into the active pocket of α-glucosidase and formation of hydrogen bonds with Leu677 was observed from docking studies. The kinetic studies revealed that this compound has uncompetitive mode of inhibition against α-glucosidase enzyme.

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.

Design, synthesis, anticancer evaluation and molecular docking studies of 1,2,3-triazole incorporated 1,3,4-oxadiazole-Triazine derivatives

A new library of 1,2,3-triazole-incorporated 1,3,4-oxadiazole-triazine derivatives (9a-j) was designed, synthesized, and tested in vitro for anticancer activity against PC3 and DU-145 (prostate cancer), A549 (lung cancer), and MCF-7 (breast cancer) cancer cell lines using the MTT assay with etoposide as the control drug. The compounds exhibited remarkable anticancer activity, with IC50 values ranging from 0.16 ± 0.083 μM to 11.8 ± 7.46 μM, whereas the positive control ranged from 1.97 0.45 μM to 3.08 0.135 μM. Compound 9 d with a 4-pyridyl moiety shown exceptional anticancer activity against PC3, A549, MCF-7, and DU-145 cell lines, with IC50 values of 0.17 ± 0.063 μM, 0.19 ± 0.075 μM, 0.51 ± 0.083 μM, and 0.16 ± 0.083 μM, respectively.

Design principles of the use of alkynes in radical cascades

One of the simplest organic functional groups, the alkyne, offers a broad canvas for the design of cascade transformations in which up to three new bonds can be added to each of the two sterically unencumbered, energy-rich carbon atoms. However, kinetic protection provided by strong π-orbital overlap makes the design of new alkyne transformations a stereoelectronic puzzle, especially on multifunctional substrates. This Review describes the electronic properties contributing to the unique utility of alkynes in radical cascades. We describe how to control the selectivity of alkyne activation by various methods, from dynamic covalent chemistry with kinetic self-sorting to disappearing directing groups. Additionally, we demonstrate how the selection of reactive intermediates directly influences the propagation and termination of the cascade. Diverging from a common departure point, a carefully planned reaction route can allow access to a variety of products.

One-Bond-Nucleophilicity and -Electrophilicity Parameters: An Efficient Ordering System for 1,3-Dipolar Cycloadditions

Diazoalkanes are ambiphilic 1,3-dipoles that undergo fast Huisgen cycloadditions with both electron-rich and electron-poor dipolarophiles but react slowly with alkenes of low polarity. Frontier molecular orbital (FMO) theory considering the 3-center-4-electron π-system of the propargyl fragment of diazoalkanes is commonly applied to rationalize these reactivity trends. However, we recently found that a change in the mechanism from cycloadditions to azo couplings takes place due to the existence of a previously overlooked lower-lying unoccupied molecular orbital. We now propose an alternative approach to analyze 1,3-dipolar cycloaddition reactions, which relies on the linear free energy relationship lg k₂(20 °C) = s_N(N + E) (eq 1) with two solvent-dependent parameters (N, s_N) to characterize nucleophiles and one parameter (E) for electrophiles. Rate constants for the cycloadditions of diazoalkanes with dipolarophiles were measured and compared with those calculated for the formation of zwitterions by eq 1. The difference between experimental and predicted Gibbs energies of activation is interpreted as the energy of concert, i.e., the stabilization of the transition states by the concerted formation of two new bonds. By linking the plot of lg k₂ vs N for nucleophilic dipolarophiles with that of lg k₂ vs E for electrophilic dipolarophiles, one obtains V-shaped plots which provide absolute rate constants for the stepwise reactions on the borderlines. These plots furthermore predict relative reactivities of dipolarophiles in concerted, highly asynchronous cycloadditions more precisely than the classical correlations of rate constants with FMO energies or ionization potentials. DFT calculations using the SMD solvent model confirm these interpretations.

Synthesis of vanillin derivatives with 1,2,3-triazole fragments and evaluation of their fungicide and fungistatic activities

Vanillin is the main component of natural vanilla extract and is responsible for its flavoring properties. Besides its well-known applications as an additive in food and cosmetics, it has also been reported that vanillin can inhibit fungi of clinical interest, such as Candida spp., Cryptococcus spp., Aspergillus spp., as well as dermatophytes. Thus, the present work approaches the synthesis of a series of vanillin derivatives with 1,2,3-triazole fragments and the evaluation of their antifungal activities against Candida albicans, Candida glabrata, Candida parapsilosis, Candida tropicalis, Cryptococcus neoformans, Cryptococcus gattii, Trichophyton rubrum, and Trichophyton interdigitale strains. Twenty-two vanillin derivatives were obtained, with yields in the range of 60%-91%, from copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction between two terminal alkynes prepared from vanillin and different benzyl azides. In general, the evaluated compounds showed moderate activity against the microorganisms tested, with minimum inhibitory concentration (MIC) values ranging from 32 to >512 µg mL^-1 . Except for compound 3b against the C. gattii R265 strain, all vanillin derivatives showed fungicidal activity for the yeasts tested. The predicted physicochemical and ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties for the compounds indicated favorable profiles for drug development. In addition, a four-dimensional structure-activity relationship (4D-SAR) analysis was carried out and provided useful insights concerning the structures of the compounds and their biological profile. Finally, molecular docking calculations showed that all compounds bind favorably at the lanosterol 14α-demethylase enzyme active site with binding energies ranging from -9.1 to -12.2 kcal/mol.

Synthesis of Benzothiazole Linked Triazole Conjugates and Their Evaluation Against Cholinesterase Enzymes

In this paper we report the synthesis, in‐silico and in‐vitro evaluations of a new series of benzothiazole linked triazole conjugates. The synthesized compounds have been evaluated as the inhibitor of cholinesterase enzymes using Ellman's method. The benzothiazole and triazole derivatives were synthesized separately and further combined through covalent amide bond linkage.The compounds showed good to excellent results towards butyryl cholinesterase (BuChE) inhibition. Docking studies revealed that the hydrophobic aromatic part of N‐benzothiazole binds to the PAS and the 1,2,4‐triazole residue binds to the CAS of BuChE. The in‐silico docking results for BuChE are consistent with the in‐vitro results. Also, the molecular dynamics simulation studies of the best docked molecule 8 a had shown similar binding stability as the reference drug donepezil. Good molecular interaction was also observed for acetylcholinesterase (AChE). The molecular modelling and evaluations against cholinesterase enzyme provided novel lead molecule which with further modifications in their structure have potential for the treatment of Alzheimer disease (AD) in future.

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].

Application of "Click" Chemistry in Biomedical Hydrogels

Since "click" chemistry was first reported in 2001, it has remained a popular research topic in the field of chemistry due to its high yield without byproducts, fast reaction rate, simple reaction, and biocompatibility. It has achieved good applications in various fields, especially for the preparation of hydrogels. The development of biomedicine presents new challenges and opportunities for hydrogels, and "click" chemistry provides a library of chemical tools for the preparation of various innovative hydrogels, including cell culture, 3D bioprinting, and drug release. This article summarizes several common "click" reactions, including copper-catalyzed azide-alkyne cycloaddition reactions, strain-promoted azide-alkyne cycloaddition (SPAAC) reaction, thiol-ene reaction, the Diels-Alder reaction, and the inverse electron demand Diels-Alder (IEDDA) reaction. We introduce the "click" reaction in the nucleic acid field to expand the concept of "click" chemistry. This article focuses on the application of "click" chemistry for preparing various types of biomedical hydrogels and highlights the advantages of "click" reactions for cross-linking to obtain hydrogels. This review also discusses applications of "click" chemistry outside the field of hydrogels, such as drug synthesis, targeted delivery, and surface modification, hydrogels have great application potential in these fields in the future and hopefully inspire other applications of hydrogels.