Iridium-catalyzed intermolecular azide-alkyne cycloaddition of internal thioalkynes under mild conditions

Copper-catalyzed multicomponent polymerization of elemental selenium for regioselective synthesis of poly(5-diselenide-triazole)s

Herein, a unique multicomponent polymerization of elemental selenium, alkynes and azides was developed to prepare poly(5-diselenide-triazole)s with high regioselectivities and atom economy under mild conditions. Such selenium-containing triazoly polymers featured well-defined structures, high molecular weights (Mn up to 71 300 g mol-1) and yields (up to 90%), good solubility, high stability, and excellent redox-degradation properties.

Multicomponent Reaction Integrating Selenium(II)-Nitrogen Exchange (SeNEx) Chemistry and Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC)

Multicomponent reactions (MCRs) are powerful tools for rapidly constructing compound libraries with sufficient molecular diversity and complexity. Herein, to fully leverage a third aspect of molecular diversity enabled by the selenium-nitrogen exchange (SeNEx) reaction between alkynes and benzoselenazolones, a novel CuI-catalyzed three-component reaction has been successfully developed. This reaction integrates SeNEx with CuAAC click chemistry, enabling rapid and regioselective synthesis of 1,4,5-trisubstituted 5-seleno-1,2,3-triazoles with high atom economy and good to excellent yields (65 examples, 50%-95%). Notably, this MCR demonstrates excellent functional group tolerance and features modular, predictable, robust, mild reaction conditions, and operational simplicity (air and water compatibility). Extensive mechanism studies have revealed that this reaction proceeds by a unique SeNEx-CuAAC tandem reaction pathway, distinguishing it from conventional copper(I)-catalyzed interrupted click reactions. Importantly, a mononuclear σ-bound copper(I)-acetylide Cu1 was synthesized and confirmed to be an efficient catalyst for the SeNEx reaction. This discovery provides crucial mechanistic insights into the preferential reactivity of alkynyl groups toward SeNEx over CuAAC. Furthermore, preliminary biological activity screening identified compound 14 as a potent inhibitor of Escherichia coli β $\upbeta$ -glucuronidase (EcGUS), with an IC50 value of 3.16 µM. These findings underscore the significant potential of this MCR in synthetic chemistry, medical chemistry, and chemical biology.

Direct organocatalytic chemoselective synthesis of pharmaceutically active benzothiazole/benzoxazole-triazoles

Benzothiazole and benzoxazole heterocyclic ring-containing 1,4,5-trisubstituted-1,2,3-triazoles are well known for their wide range of applications in pharmaceutical and medicinal chemistry, but their high-yielding metal-free selective synthesis has always remained challenging as no comprehensive simple protocol has been outlined to date. Owing to their structural and medicinal importance, herein, we synthesized various benzothiazole and benzoxazole heterocyclic ring-containing 1,4,5-trisubstituted-1,2,3-triazoles in high to excellent yields with chemo-/regioselectivity from the library of benzothiazole/benzoxazole-ketones and aryl/alkyl-azides through an enolate-mediated organocatalytic azide-ketone [3 + 2]-cycloaddition under ambient conditions in a few hours. The commercial availability or quick synthesis of the starting materials and catalysts, a diverse substrate scope, chemo-/regioselectivity, quick synthesis of pharmaceutically active known compounds and their analogues, and numerous medicinal applications of functionalized benzothiazole/benzoxazole-triazoles are the key attractions of this metal-free organo-click reaction.

An updated review on 1,2,3-/1,2,4-triazoles: synthesis and diverse range of biological potential

The synthesis of triazoles has attracted a lot of interest in the field of organic chemistry because of its versatile chemical characteristics and possible biological uses. This review offers an extensive overview of the different pathways used in the production of triazoles. A detailed analysis of recent research indicates that triazole compounds have a potential range of pharmacological activities, including the ability to inhibit enzymes, and have antibacterial, anticancer, and antifungal activities. The integration of computational and experimental methods provides a thorough understanding of the structure-activity connection, promoting sensible drug design and optimization. By including triazoles as essential components in drug discovery, researchers can further explore and innovate in the synthesis, biological assessment, and computational studies of triazoles as drugs, exploring the potential therapeutic significance of triazoles.

Three-step click assembly using trivalent platforms bearing azido, ethynyl, and fluorosulfonyl groups

Divergent synthesis of triazoles was achieved using newly designed platform molecules possessing azide, alkyne, and fluorosulfonyl moieties. Consecutive conjugations by the sulfur(VI) fluoride exchange and following consecutive triazole formations allowed us to prepare a wide variety of bis(triazole)s by virtue of selective transformations. One-pot triple-click assembly of easily accessible modules led to the facile synthesis of middle-molecular-weight triazoles with various functional moieties.

Diversity-oriented synthesis of stereodefined tetrasubstituted alkenes via a modular alkyne gem-addition strategy

Stereocontrolled construction of tetrasubstituted olefins has been an attractive issue yet remains challenging for synthetic chemists. In this manuscript, alkynyl selenides, when treated with ArBCl2, are subject to an exclusive 1,1-carboboration, affording tetrasubstituted alkenes with excellent levels of E-selectivity. Detailed mechanistic studies, supported by DFT calculations, elucidates the role of selenium in this 1,1-addition process. Coupled with subsequent C-B and C-Se bond transformations, this 1,1-addition protocol constitutes a modular access to stereodefined all-carbon tetrasubstituted alkenes. The merit of this approach is demonstrated by programmed assembly of diverse functionalized multi-arylated alkenes, especially enabling the stereospecific synthesis of all six possible stereoisomers of tetraarylethene (TAE) derived from the random permutation of four distinct aryl substituents around the double bond. The diversity-oriented synthesis is further utilized to explore different TAE luminogenic properties and potential Se-containing antitumor lead compounds.

1,3-Butadiynyl sulfide-based compact trialkyne platform molecule for sequential assembly of three azides

A compact trialkyne platform with a silyl-protected 1,3-butadiynyl sulfide moiety and a terminal alkyne group has been developed for sequential regioselective transition metal-catalyzed triazole formation reactions with three azides. This method enabled the facile construction of a low-molecular-weight triazole library and the synthesis of middle-molecular-weight trifunctional probes for protein modification.

Direct Organocatalytic Chemoselective Synthesis of Pharmaceutically Active 1,2,3-Triazoles and 4,5'-Bitriazoles

Carbonyl-containing 1,4,5-trisubstituted- and 1,4-disubstituted-1,2,3-triazoles are well-known for their wide range of applications in pharmaceutical and medicinal chemistry, but their high-yielding metal-free synthesis has always remained challenging, as no comprehensive protocol has been outlined to date. Owing to their structural and medicinal importance, herein, we synthesized various carbonyl-containing 1,4,5-trisubstituted- and 1,4-disubstituted-1,2,3-triazoles and unsymmetrical 4,5'-bitriazoles with high yields and chemo-/regioselectivity from the library of 2,4-diketoesters and azides in a sequential one-pot manner through the combination of organocatalytic enolization, in situ [3 + 2]-cycloaddition, and hydrolysis reactions. The commercial availability of the starting materials/catalysts, diverse substrate scope, performance in a one-pot manner, chemo-/regioselectivity of organo-click reaction, quick synthesis of unsymmetrical 4,5'-bitriazoles, a large number of synthetic applications, and numerous medicinal applications of carbonyl-containing 1,2,3-triazoles are the key attractions of this metal-free organo-click work.

Enzyme-Catalyzed Regioselective Synthesis of 4-Hetero-Functionalized 1,5-Disubstituted 1,2,3-Triazoles

Enzyme-catalyzed novel protocols for the regioselective construction of fully substituted 1,2,3-triazoles by employing 2-azido-1,3,5-triazine (ADT) as a 1,3-dipole for the cycloaddition reaction with the activated alkene in an aqueous medium have been developed. Various 4-heterosubstituted-1,2,3-triazoles were readily assembled in good to excellent yields with high regioselectivity. This reaction also features wide substrate scope, strong functional group tolerance, gram-scale synthesis, and an environmentally friendly process.

Practice of green chemistry strategies in synthetic organic chemistry: a glimpse of our sincere efforts in green chemistry research

This feature article summarises our recent contributions (2019-2023) in designing and developing a handful of promising organic transformations for accessing several diversely functionalised biologically relevant organic scaffolds, following the green chemistry principles, particularly focusing on the application of low-energy visible light, electrochemistry, ball-milling, ultrasound, and catalyst- and additive-free synthetic strategies.

Regiodivergent Synthesis of 4- and 5-Sulfenyl Oxazoles from Alkynyl Thioethers

The regiodivergent synthesis of 4- and 5-sulfenyl oxazoles from 1,4,2-dioxazoles and alkynyl thioethers has been achieved. Gold-catalysed conditions are used to favour the formation of 5-sulfenyl oxazoles via β-selective attack of the nitrenoid relative to the sulfenyl group. In contrast, 4-sulfenyl oxazoles are formed by α-selective reaction under Brønsted acid conditions from the same substrates. The nature of stabilising gold-sulfur interactions have been investigated by natural bond orbital analysis, showing that the S→Au interactions are significantly stronger in the intermediate that favours the 5-sulfenyl oxazoles. A kinetic survey identifies catalyst inhibition processes. This study into the regiodivergent methods includes the development of telescoped annulation-oxidation protocols for regioselective access to oxazole sulfoxides and sulfones.

Lewis Acid-Catalyzed Formal [4 + 2] Reaction of Alkynyl Sulfides and 2-Pyrones To Access Polysubstituted Aryl Sulfides

A practical and efficient method to access polysubstituted aryl sulfides has been discovered via a Lewis acid-catalyzed reaction between alkynyl sulfide and 2-pyrone, involving a Diels-Alder/retro-Diels-Alder pathway. Alkynyl sulfide as an electron-rich dienophile and 2-pyrones as electron-poor dienes are conjunctively transformed into a series of polysubstituted aryl sulfides with broad functional group compatibility in good to excellent yields (40 examples, 43-88% yield). The robustness and practicality of the protocol has been demonstrated through gram-scale synthesis and the ease of transformation of the resulting products.

Synthesis of alkynyl sulfides via base-promoted nucleophilic ring-opening of α-bromostyrene sulfonium salt

An efficient method for the synthesis of alkynyl sulfides via a C(sp3)-S bond cleavage of α-bromostyrene sulfonium salts has been developed. This base-promoted nucleophilic ring-opening pathway allows the preparation of diverse alkynyl sulfide compounds using tetramethylene sulfoxide as the sulfur source. The reaction proceeds with good functional group tolerance and could be applied to the late-stage functionalization of bioactive molecules and drugs. Furthermore, the synthetic utility of this method was demonstrated by a one-pot synthesis, scale-up reaction and further modification of various alkynyl sulfide products.

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".

Emerging Aspects of Triazole in Organic Synthesis: Exploring its Potential as a Gelator

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) - commonly known as the "click reaction" - serves as the most effective and highly reliable tool for facile construction of simple to complex designs at the molecular level. It relates to the formation of carbon heteroatomic systems by joining or clicking small molecular pieces together with the help of various organic reactions such as cycloaddition, conjugate addition, ring-opening, etc. Such dynamic strategy results in the generation of triazole and its derivatives from azides and alkynes with three nitrogen atoms in the five-membered aromatic azole ring that often forms gel-assembled structures having gelating properties. These scaffolds have led to prominent applications in designing advanced soft materials, 3D printing, ion sensing, drug delivery, photonics, separation, and purification. In this review, we mainly emphasize the different mechanistic aspects of triazole formation, which includes the synthesis of sugar-based and non-sugar-based triazoles, and their gel applications reported in the literature for the past ten years, as well as the upcoming scope in different branches of applied sciences.

Target-Specific Bioorthogonal Reactions for Precise Biomedical Applications

Bioorthogonal chemistry is a promising toolbox for dissecting biological processes in the native environment. Recently, bioorthogonal reactions have attracted considerable attention in the medical field for treating diseases, since this approach may lead to improved drug efficacy and reduced side effects via in situ drug synthesis. For precise biomedical applications, it is a prerequisite that the reactions should occur in the right locations and on the appropriate therapeutic targets. In this minireview, we highlight the design and development of targeted bioorthogonal reactions for precise medical treatment. First, we compile recent strategies for achieving target-specific bioorthogonal reactions. Further, we emphasize their application for the precise treatment of different therapeutic targets. Finally, a perspective is provided on the challenges and future directions of this emerging field for safe, efficient, and translatable disease treatment.

Mechanochemical Solvent-Free One-Pot Synthesis of Poly-Functionalized 5-(Arylselanyl)-1H-1,2,3-triazoles Through a Copper(I)-Catalyzed Click Reaction

A mechanochemistry-driven practical and efficient synthetic protocol for accessing diverse series of biologically relevant poly-functionalized 5-(arylselanyl)-1H-1,2,3-triazoles through copper(I)-catalyzed click reaction between aryl/heteroaryl acetylenes, diaryl diselenides, benzyl bromides, and sodium azide has been accomplished under high-speed ball-milling. Advantages of this method include operational simplicity, avoidance of using solvent and external heating, one-pot synthesis, short reaction time in minutes, good to excellent yields, broad substrate scope, and gram-scale applications. Furthermore, synthesized organoselenium compounds were synthetically diversified to biologically promising selenones.

Organic Base-Facilitated Thiol-Thioalkyne Reaction with Exclusive Regio- and Stereoselectivity

Here, we report the regiospecific hydrothiolation of electron-rich thioalkynes with exclusive stereoselectivity facilitated by an organic base, which could proceed exceedingly fast under ambient atmosphere and room temperature, affording β trans addition products in up to nearly quantitative yields. The dual nature of the sulfur atom in attracting and donating electrons is supposed to be pivotal in determining the regio- and stereoselectivity. This system tolerates a wide range of thiols and thioalkynes and shows great potential in polymer synthesis.

Multicomponent cyclization with azides to synthesize N-heterocycles

Heterocyclic compounds, both naturally derived and synthetically produced, constitute a wide variety of biologically active and industrially important compounds. The synthesis and application of heterocyclic compounds have garnered significant attention and experienced rapid growth in recent decades. Organic azides, due to their unique properties and distinctive reactivity, have become a convenient chemical tool for achieving a wide range of heterocycles such as triazoles and tetrazoles. Importantly, the field of multicomponent reaction (MCR) chemistry provides a convergent approach to access various N-heterocyclic scaffolds, offering novelty, diversity, and complexity. However, the exploration of MCR pathways to N-heterocyclic compounds remains incomplete. Here, we review the use of multicomponent reactions for the preparation of N-heterocycles. A wide range of reactions based on azides for the synthesis of various types of N-heterocyclic systems have been developed.

Asymmetric rhodium-catalyzed click cycloaddition to access C-N axially chiral N-triazolyl indoles

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is regarded as a prime example of "click chemistry", but the asymmetric click cycloaddition of internal alkynes still remains challenging. A new asymmetric Rh-catalyzed click cycloaddition of N-alkynylindoles with azides was developed, providing atroposelective access to C-N axially chiral triazolyl indoles, a new type of heterobiaryl, with excellent yields and enantioselectivity. This asymmetric approach is efficient, mild, robust and atom-economic, and features very broad substrate scope with easily available Tol-BINAP ligands.

Iridium-Catalyzed Synthesis of Chiral 1,2,3-Triazoles Units and Precise Construction of Stereocontrolled Oligomers

Iridium-catalyzed azide-thioalkyne cycloaddition reaction (IrAAC) has proved to be a powerful tool for the synthesis of fully substituted 1,2,3-triazole compounds with exclusive regioselectivity. Here we report its successful use in the precise construction of stereocontrolled oligomers that have great potential in diverse applications. Starting with the azide derived from L-prolinol and different functionalized thioalkynes, chiral 1,2,3-triazole units were fabricated with high efficiency under the IrAAC condition, which were further assembled into stereocontrolled oligotriazoles through metal-free exponential growth strategies. The structure and uniformity of these oligomers were well identified by ¹H NMR, size-exclusion chromatography, and mass spectrometry, the stereoregularity of which were studied through circular dichroism and circular polarized luminescence analysis.

Copper-Catalyzed Cascade Multicomponent Reaction of Azides, Alkynes, and Selenium: Synthesis of Ditriazolyl Diselenides

A copper-catalyzed cascade multicomponent reaction for synthesizing ditriazolyl diselenides from azides, terminal alkynes, and elemental selenium has been developed. The present reaction features utilizing readily available and stable reagents, high atom-economy, and mild reaction conditions. A possible mechanism is proposed.

Process-Divergent Syntheses of 4- and 5-Sulfur-Functionalized 1,2,3-Triazoles via Copper-Catalyzed Azide-Alkyne Cycloadditions of 1-Phosphinyl-2-sulfanylethynes

4-Sulfanyl-substituted 1,2,3-triazoles were provided regioselectively with good yields and broad scope via consecutive t-BuOK-promoted dephosphinylation of 1-phosphinyl-2-sulfanylethynes and copper-catalyzed azide-alkyne cycloadditions (CuAAC) with alkyl azides. Unsymmetrically substituted ditriazoles were successfully obtained using a tandem dephosphinylative CuAAC protocol with diazides. Direct CuAAC of the 1-phosphinyl-2-sulfanylethynes with azides afforded regioisomeric mixtures of 4-phosphinyl-5-sulfanyl- and 5-phosphinyl-4-sulfanyl-1,2,3-triazoles that were easily separable from one another. When the phosphinyl- and sulfanyl-substituted triazoles were treated with t-BuOK, the dephosphination proceeded smoothly, yielding the corresponding 5- and 4-sulfanyltriazoles, respectively. 5-(1-Aryl-1-hydroxymethyl)-4-sulfanyltriazoles were synthesized by stepwise treatment of 5-phosphinyl-4-sulfanyltriazole with MeMgBr and arylaldehydes. Additionally, Ph₂P(O) and RS groups in the triazoles were easily converted to Ph₂P and RSO₂ by PhSiH₃-reduction and m-CPBA-oxidation, respectively. Following the dephosphinylative CuAAC of 1-phosphinyl-2-(4-t-butylphenylsulfanyl)ethyne with aryl azides and m-CPBA-oxidation, potent antagonists of pregnane X receptor LC-58 and LC-59 were successfully produced.

Iridium-catalysed thioether-directed regioselective cycloaddition of internal alkynes with azides

We report herein a cationic iridium-catalysed thioether-directed alkyne-azide cycloaddition reaction. Diverse 2-alkynyl phenyl sulfides can undergo cycloaddition with different azides in a regioselective fashion. The reaction features high efficiency, a short reaction time, and a broad substrate scope, providing modular access to complex S-containing triazoles.

Ir-Catalyzed Regioselective Dihydroboration of Thioalkynes toward Gem-Diboryl Thioethers

While 1,1-diboryl (gem-diboryl) compounds are valuable synthetic building blocks, currently, related studies have mainly focused on those 1,1-diboryl alkanes without a hetero functional group in the α-position. gem-Diboryl compounds with an α-hetero substituent, though highly versatile, have been limitedly accessible and thus rarely utilized. Herein, we have developed the first α-dihydroboration of heteroalkynes leading to the efficient construction of gem-diboryl, hetero-, and tetra-substituted carbon centers. This straightforward, practical, mild, and atom-economic reaction is an attractive complement to the conventional multistep synthetic strategy relying on deprotonation of gem-diborylmethane by a strong base. Specifically, [Ir(cod)(OMe)]₂ was found to be uniquely effective for this process of thioalkynes, leading to excellent α-regioselectivity when delivering the two boryl groups, which is remarkable in view of the many competitive paths including monohydroboration, 1,2-dihydroboration, dehydrodiboration, triboration, tetraboration, etc. Control experiments combined with DFT calculations suggested that this process involves two sequential hydroboration events. The second hydroboration requires a higher energy barrier due to severe steric repulsion in generating the highly congested α-sulfenyl gem-diboryl carbon center, a structural motif that was almost unknown before.

Base-mediated ketenimine formation from N-sulfonylthioimidates for the synthesis of 5-amino-1-vinyl/aryl-1,2,3-triazoles

N-Sulfonylthioimidate was converted to ketenimine under basic conditions. The reaction with vinyl/aryl azides was induced to cause dipolar cycloaddition to form 5-amino-1-vinyl/aryl-1,2,3-triazoles. The advantages of this method are high efficiency, structural diversity of products favorable yields and applicability to gram-scale operations.

Versatile Synthetic Platform for 1,2,3-Triazole Chemistry

1,2,3-Triazole scaffolds are not obtained in nature, but they are still intensely investigated by synthetic chemists in various fields due to their excellent properties and green synthetic routes. This review will provide a library of all synthetic routes used in the past 21 years to synthesize 1,2,3-triazoles and their derivatives using various metal catalysts (such as Cu, Ni, Ru, Ir, Rh, Pd, Au, Ag, Zn, and Sm), organocatalysts, metal-free as well as solvent- and catalyst-free neat syntheses, along with their mechanistic cycles, recyclability studies, solvent systems, and reaction condition effects on regioselectivity. Constant developments indicate that 1,2,3-triazoles will help lead to future organic synthesis and are useful for creating molecular libraries of various functionalized 1,2,3-triazoles.

Biomacromolecule-Assisted Screening for Reaction Discovery and Catalyst Optimization

Reaction discovery and catalyst screening lie at the heart of synthetic organic chemistry. While there are efforts at de novo catalyst design using computation/artificial intelligence, at its core, synthetic chemistry is an experimental science. This review overviews biomacromolecule-assisted screening methods and the follow-on elaboration of chemistry so discovered. All three types of biomacromolecules discussed─enzymes, antibodies, and nucleic acids─have been used as "sensors" to provide a readout on product chirality exploiting their native chirality. Enzymatic sensing methods yield both UV-spectrophotometric and visible, colorimetric readouts. Antibody sensors provide direct fluorescent readout upon analyte binding in some cases or provide for cat-ELISA (Enzyme-Linked ImmunoSorbent Assay)-type readouts. DNA biomacromolecule-assisted screening allows for templation to facilitate reaction discovery, driving bimolecular reactions into a pseudo-unimolecular format. In addition, the ability to use DNA-encoded libraries permits the barcoding of reactants. All three types of biomacromolecule-based screens afford high sensitivity and selectivity. Among the chemical transformations discovered by enzymatic screening methods are the first Ni(0)-mediated asymmetric allylic amination and a new thiocyanopalladation/carbocyclization transformation in which both C-SCN and C-C bonds are fashioned sequentially. Cat-ELISA screening has identified new classes of sydnone-alkyne cycloadditions, and DNA-encoded screening has been exploited to uncover interesting oxidative Pd-mediated amido-alkyne/alkene coupling reactions.

Internally Functionalized Dendrimers Based on Fully Substituted 1,2,3-Triazoles

Being one important class in dendrimer chemistry, internally functionalized dendrimers (IFDs) are still exiguous. Here we demonstrate the first construction of IFDs involving fully substituted 1,2,3-triazole rings as interior functionality carriers. Through divergent or convergent synthetic protocols established on the efficient iridium-catalyzed annulation of internal 1-thioalkynes with organic azides (IrAAC), sequence-controlled heterolayered dendrimers with different branched structures are achieved in a convenient manner. ¹ H NMR, MS and SEC characterizations well identify their architecture and high purity. This article is protected by copyright. All rights reserved.

Azido-type-selective triazole formation by iridium-catalyzed cycloaddition with thioalkynes

The iridium-catalyzed azide-thioalkyne cycloaddition was found to proceed much faster with benzyl azide than with phenyl azide. The high azido-type selectivity was also observed in other combinations of azides with different steric environments. This finding enabled the efficient assembly of three azidophilic molecules to triazido platforms by three sequential triazole-forming reactions.

Asymmetric Azide-Alkyne Cycloaddition with Ir(I)/Squaramide Cooperative Catalysis: Atroposelective Synthesis of Axially Chiral Aryltriazoles

An Ir(I)/squaramide cooperative catalytic strategy for atroposelective synthesis of axially chiral aryltriazoles has been developed for the first time. Diverse structurally novel aryltriazole skeletons that cannot be accessed by traditional click reactions were synthesized in good yields with excellent enantioselectivity. Both enantiomers were easily obtained from a pair of diastereoisomeric natural quinidine- and quinine-derived squaramides. A significant Ir(I)/squaramide coordination activation, but no self-quenching phenomenon was observed in this metal/organo cooperative catalytic system.

Organocatalytic synthesis and antitumor activity of novel 1,2,3-triazoles derived from fatty β-ketoesters

Background:

Developing methods to synthesize highly functionalized and complex 1,2,3-triazoles from various combinations of substrates remains a significant challenge in organic synthesis. Thus, to the best of our knowledge, an organocatalytic approach to synthesize 1,2,3-triazoles derived from fatty acids has not been explored.

Objective:

In this sense, we describe here the organocatalyzed synthesis and preliminary results of antitumor and cytotoxic activity of a range of 1,2,3-triazoles derived from fatty esters.

Methods:

To synthesize 1,2,3-triazoles 3 derived from fatty β-ketoesters, we performed the reaction of appropriate aryl azides 2a-j with β-ketoesters 1a-c in the presence of 5 mol% of DBU using DMSO as a solvent at 70 °C for 24 h. The viability of 5637 cells was determined by measuring the reduction of soluble MTT to water-insoluble formazan. The IC50 concentration that inhibits 50% of cell growth and the results were obtained by at least three independent experiments in triplicate for each test.

Results:

Through enolate-mediated organocatalysis, 1,2,3-triazoles 3 derived from fatty β-ketoesters were synthesized in moderate to excellent yields by reacting fatty esters 1 with aryl azides 2 in the presence of a catalytic amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (5 mol%). All compounds derived from palmitic acetoacetate 1a were evaluated regarding induced cytotoxicity in vitro in a human bladder cancer cell line, and compounds 3a, 3d, 3e, and 3g were shown to be promising alternatives for bladder cancer treatment and presented the lowest inhibitory concentration of IC50.

Conclusion:

We described a synthetic procedure to prepare 1,2,3-triazoles derived from fatty β-ketoesters by DBU-catalyzed 1,3-dipolar cycloaddition reactions of fatty esters with different aryl azides. Compounds derived from palmitic acetoacetate were screened for antitumor and cytotoxic activity in vitro in human bladder cancer cell lines, and compounds 3a, 3d, 3e, and 3g showed potential to treat bladder cancer.

Synthesis of sulfamoyl-triazolyl-carboxamides as pharmacological myeloperoxidase inhibitors

Sulfamoyl-triazolyl-carboxamides were synthesized using DBU as a catalyst, and their molecular docking and MPO activity analyses were performed.

Gold-Catalyzed Annulations with Nucleophilic Nitrenoids Enabled by Heteroatom-Substituted Alkynes

The combination of a nucleophilic nitrene equivalent, a triple bond and a π-acid catalyst has underpinned numerous efficient transformations for the preparation of azacycles. This personal account details our efforts in developing an annulation strategy. Adding a nucleophilic nitrenoid to an activated alkyne can generate carbenoid character that is then quenched by a cyclisation onto the nitrenoid substituent. The use and development of N-acyl and N-heterocyclic pyridinium-N-aminides as 1,3-N,O and 1,3-N,N-dipole equivalents is discussed in the context of oxazole and heterocycle-fused imidazole formation, respectively. The resulting processes are highly efficient, practically straightforward, and tolerate considerable structural and functional group variation. Our use of heteroatom-substituted alkynes as enabling tools for reaction discovery is discussed. The reactivity accessed from the strong donor-like properties of ynamides is complemented by that obtained from alkynyl thioethers, which are emerging as interesting substrates for π-acid catalysis.

In situ activation of therapeutics through bioorthogonal catalysis

Bioorthogonal chemistry refers to any chemical reactions that can occur inside of living systems without interfering with native biochemical processes, which has become a promising strategy for modulating biological processes. The development of synthetic metal-based catalysts to perform bioorthogonal reactions has significantly expanded the toolkit of bioorthogonal chemistry for medicinal chemistry and synthetic biology. A wide range of homogeneous and heterogeneous transition metal catalysts (TMCs) have been reported, mediating different transformations such as cycloaddition reactions, as well as bond forming and cleaving reactions. However, the direct application of 'naked' TMCs in complex biological media poses numerous challenges, including poor water solubility, toxicity and catalyst deactivation. Incorporating TMCs into nanomaterials to create bioorthogonal nanocatalysts can solubilize and stabilize catalyst molecules, with the decoration of the nanocatalysts used to provide spatiotemporal control of catalysis. This review presents an overview of the advances in the creation of bioorthogonal nanocatalysts, highlighting different choice of nano-scaffolds, and the therapeutic and diagnostic applications.

Synthesis of homochiral sulfanyl- and sulfoxide-substituted naphthyltriazoles and study of the conformational stability

The preparation of a series of novel homochiral atropisomeric sulfanyl- and sulfoxide-substituted naphthyltriazoles is described. The triazolization methodology used presents a new way towards novel and highly stable 1,2,3-triazole-based atropisomers, and introduces a new and complementary synthetic pathway towards 4-sulfanyl substituted 1,2,3-triazoles. Starting from sulfanyl-substituted naphthyl ketones, enantiopure amines, and 4-nitrophenyl azide, a collection of 16 sulfanyl-substituted naphthyltriazoles were obtained via the triazolization reaction in which the homochiral diastereomers are readily isolated. Subsequent monooxidation results in the preparation of several sulfoxide-substituted naphthyltriazoles. The absolute configuration of a set of diastereomeric sulfanyl- and sulfoxide-appended naphthyltriazoles was deduced via X-ray crystallography. Furthermore, the conformational stability of the atropisomers was determined experimentally, and further confirmed and analyzed with the aid of computational DFT calculations.

Bioorthogonal Azide-Thioalkyne Cycloaddition Catalyzed by Photoactivatable Ruthenium(II) Complexes

Tailored ruthenium sandwich complexes bearing photoresponsive arene ligands can efficiently promote azide-thioalkyne cycloaddition (RuAtAC) when irradiated with UV light. The reactions can be performed in a bioorthogonal manner in aqueous mixtures containing biological components. The strategy can also be applied for the selective modification of biopolymers, such as DNA or peptides. Importantly, this ruthenium-based technology and the standard copper-catalyzed azide-alkyne cycloaddition (CuAAC) proved to be compatible and mutually orthogonal.