Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

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.

Mechanoredox/Nickel Co-Catalyzed Cross Electrophile Coupling of Benzotriazinones with Alkyl (Pseudo)halides

An air-tolerant mechanoredox/nickel cocatalyzed cross electrophile coupling of benzotriazinones with alkyl (pseudo)halides is developed by liquid-assisting grinding in the presence of manganese powders and strontium titanate as a reductant and a cocatalyst, respectively. Mechanical activation of metal surfaces via ball milling eliminates the chemical activator for manganese, while mechanoredox cocatalysis of strontium titanate remarkably improves the aryl/alkyl cross electrophile coupling via piezoelectricity-mediated radical generation from alkyl halides. Both benzotriazinones and alkyl (pseudo)halides display reactivities in the mechanoredox/nickel cocatalysis different from those of conventional thermal chemistry in solution. The scope of the reaction is demonstrated with 26 examples, showing a high chemoselectivity of bromides vs chlorides.

Cu ions anchored in the porphyrin center act as transient metal centers of 2D-MOFs to enhance photocatalytic hydrogen production

To improve charge transfer efficiency, non-noble metal Cu anchored in the porphyrin center can realize a new ligand-to-linker metal charge-transfer (LLMCT) process in 2D Ti-based porphyrin MOFs.

Advancing mechanochemical synthesis by combining milling with different energy sources

Owing to its efficiency and unique reactivity, mechanochemical processing of bulk solids has developed into a powerful tool for the synthesis and transformation of various classes of materials. Nevertheless, mechanochemistry is primarily based on simple techniques, such as milling in comminution devices. Recently, mechanochemical reactivity has started being combined with other energy sources commonly used in solution-based chemistry. Milling under controlled temperature, light irradiation, sound agitation or electrical impulses in newly developed experimental setups has led to reactions not achievable by conventional mechanochemical processing. This Perspective describes these unique reactivities and the advances in equipment tailored to synthetic mechanochemistry. These techniques - thermo-mechanochemistry, sono-mechanochemistry, electro-mechanochemistry and photo-mechanochemistry - represent a notable advance in modern mechanochemistry and herald a new level of solid-state reactivity: mechanochemistry 2.0.

Mechanochemical Approach towards Multi-Functionalized 1,2,3-Triazoles and Anti-Seizure Drug Rufinamide Analogs Using Copper Beads

Highly regiospecific, copper-salt-free and neat conditions have been demonstrated for the 1,3-dipolar azide-alkyne cycloaddition (AAC) reactions under mechanochemical conditions. A group of structurally challenging alkynes and heterocyclic derivatives was efficiently implemented to achieve highly functionalized 1,4-disubstituted-1,2,3-triazoles in good to excellent yield by using the Cu beads without generation of unwanted byproducts. Furthermore, the high-speed ball milling (HSBM) strategy has also been extended to the synthesis of the commercially available pharmaceutical agent, Rufinamide, an antiepileptic drug (AED) and its analogues. The same strategy was also applied for the synthesis of the Cl-derivative of Rufinamide. Analysis of the single crystal XRD data of the triazole was also performed for the final structural confirmation. The Cu beads are easily recoverable from the reaction mixture and used for the further reactions without any special treatment.

The Direct Mechanocatalytic Suzuki–Miyaura Reaction of Small Organic Molecules

The molecular Suzuki cross‐coupling reaction was conducted mechanochemically, without solvents, ligands, or catalyst powders. Utilizing one catalytically active palladium milling ball, products could be formed in quantitative yield in as little as 30 min. In contrast to previous reports, the adjustment of milling parameters led to the complete elimination of abrasion from the catalyst ball, thus enabling the first reported systematic catalyst analysis. XPS, in situ XRD, and reference experiments provided evidence that the milling ball surface was the location of the catalysis, allowing a mechanism to be proposed. The versatility of the approach was demonstrated by extending the substrate scope to deactivated and even sterically hindered aryl iodides and bromides.

Green solvent-free synthesis of new N-heterocycle-L-ascorbic acid hybrids and their antiproliferative evaluation

Aim: The authors' aim was to improve the application of copper-catalyzed azide-alkyne cycloaddition in the synthesis of hybrids containing biologically significant nucleobases and L-ascorbic acid scaffolds by introducing an environmentally friendly and waste-free ball mill. Results: Two series of hybrids with a purine, pyrrolo[2,3- d]pyrimidine or 5-substituted pyrimidine attached to 2,3-dibenzyl-L-ascorbic acid via a hydroxyethyl- (15a–23a) or ethylidene-1,2,3-triazolyl (15b–23b) bridge were prepared by ball milling and conventional synthesis. The unsaturated 6-chloroadenine L-ascorbic acid derivative 16b can be highlighted as a lead compound and showed strong antiproliferative activity against HepG2 (hepatocellular carcinoma) and SW620 (colorectal adenocarcinoma) cells. Conclusion: Mechanochemical synthesis was superior in terms of sustainability, reaction rate and yield, highlighting the advantageous applications of ball milling over classical reactions.

A guide to direct mechanocatalysis

Direct mechanocatalysis (DM) describes solvent-free catalytic reactions that are initiated by mechanical forces in mechanochemical reactors such as ball mills. The distinctive feature of DM is that the milling materials, e.g. the milling balls themselves are the catalyst of the reaction. In this article we follow the historical evolution of this novel concept and give a guide to this emerging, powerful synthesis tool. Within this perspective we seek to highlight the impact of the relevant milling parameters, the nature of the catalyst and potential additives, the scope of reactions that are currently accessible by this method, and the thus far raised hypotheses on the underlying mechanisms of direct mechanochemical transformations.

Development of sustainable synthesis of glucuronic acid glycodendrimers using ball milling and microwave-assisted CuAAC reaction

Two green strategies for CuAAC reaction based on two activation pathways, solvent free mechanochemistry and microwave irradiation using a recycable biosolvent, are reported for the synthesis of glucuronic acid glycodendrimers with good conversión.

Monitoring Solid-Phase Reactions in Self-Assembled Monolayers by Surface-Enhanced Raman Spectroscopy

Nanopatterned surfaces enhance incident electromagnetic radiation and thereby enable the detection and characterization of self-assembled monolayers (SAMs), for instance in surface-enhanced Raman spectroscopy (SERS). Herein, Au nanohole arrays, developed and characterized as SERS substrates, are exemplarily used for monitoring a solid-phase deprotection and a subsequent copper(I)-catalyzed azide-alkyne cycloaddition "click" reaction, performed directly on the corresponding SAMs. The SERS substrate was found to be highly reliable in terms of signal reproducibility and chemical stability. Furthermore, the intermediates and the product of the solid-phase synthesis were identified by SERS. The spectra of the immobilized compounds showed minor differences compared to spectra of the microcrystalline solids. With its uniform SERS signals and the high chemical stability, the platform paves the way for monitoring molecular manipulations in surface functionalization applications.

Novel Bis- and Mono-Pyrrolo[2,3-d]pyrimidine and Purine Derivatives: Synthesis, Computational Analysis and Antiproliferative Evaluation

Novel symmetrical bis-pyrrolo[2,3-d]pyrimidines and bis-purines and their monomers were synthesized and evaluated for their antiproliferative activity in human lung adenocarcinoma (A549), cervical carcinoma (HeLa), ductal pancreatic adenocarcinoma (CFPAC-1) and metastatic colorectal adenocarcinoma (SW620) cells. The use of ultrasound irradiation as alternative energy input in Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) shortened the reaction time, increased the reaction efficiency and led to the formation of exclusively symmetric bis-heterocycles. DFT calculations showed that triazole formation is exceedingly exergonic and confirmed that the presence of Cu(I) ions is required to overcome high kinetic requirements and allow the reaction to proceed. The influence of various linkers and 6-substituted purine and regioisomeric 7-deazapurine on their cytostatic activity was revealed. Among all the evaluated compounds, the 4-chloropyrrolo[2,3-d]pyrimidine monomer 5f with 4,4′-bis(oxymethylene)biphenyl had the most pronounced, although not selective, growth-inhibitory effect on pancreatic adenocarcinoma (CFPAC-1) cells (IC₅₀ = 0.79 µM). Annexin V assay results revealed that its strong growth inhibitory activity against CFPAC-1 cells could be associated with induction of apoptosis and primary necrosis. Further structural optimization of bis-chloropyrrolo[2,3-d]pyrimidine with aromatic linker is required to develop novel efficient and non-toxic agent against pancreatic cancer.

Mechanical metal activation for Ni-catalyzed, Mn-mediated cross-electrophile coupling between aryl and alkyl bromides

Liquid-assisted grinding enables nickel-catalyzed, manganese-mediated cross-electrophile coupling between aryl and alkyl bromides under chemical activator-free and non-anhydrous conditions.

Direct Mechanocatalysis: Using Milling Balls as Catalysts

Direct mechanocatalysis describes catalytic reactions under the involvement of mechanical energy with the distinct feature of milling equipment itself being the catalyst. This novel type of catalysis features no solubility challenges of the catalysts nor the substrate and on top offering most facile way of separation.

A retrievable implant for the long-term encapsulation and survival of therapeutic xenogeneic cells

The long-term function of transplanted therapeutic cells typically requires systemic immune suppression. Here, we show that a retrievable implant comprising of a silicone reservoir and a porous polymeric membrane protects human cells encapsulated in it after implant transplantation in the intraperitoneal space of immunocompetent mice. Membranes with pores 1 µm in diameter allowed host macrophages to migrate into the device without the loss of transplanted cells, whereas membranes with pore sizes under 0.8 µm prevented their infiltration by immune cells. A synthetic polymer coating prevented fibrosis and was necessary for the long-term function of the device. For over 130 days the device supported human cells engineered to secrete erythropoietin in immunocompetent mice as well as transgenic human cells carrying an inducible gene circuit for the on-demand secretion of erythropoietin. Pancreatic islets from rats encapsulated in the device and implanted in diabetic mice restored normoglycaemia in the mice for over 75 days. The biocompatible device provides a retrievable solution for the transplantation of engineered cells in the absence of immunosuppression.

Harmicines - harmine and cinnamic acid hybrids as novel antiplasmodial hits

Harmicines constitute novel hybrid compounds that combine two agents with reported antiplasmodial properties, namely β-carboline harmine and a cinnamic acid derivative (CAD). Cu(I) catalyzed azide-alkyne cycloaddition was employed for the preparation of three classes of hybrid molecules: N-harmicines 6a-i, O-harmicines 7a-i and N,O-bis-harmicines 8a-g,i. In vitro antiplasmodial activities of harmicines against the erythrocytic stage of Plasmodium falciparum (chloroquine-sensitive Pf3D7 and chloroquine-resistant PfDd2 strains) and hepatic stage of P. berghei, as well as cytotoxicity against human liver hepatocellular carcinoma cell line (HepG2), were evaluated. Remarkably, most of the compounds exerted significant activities against both stages of the Plasmodium life cycle. The conjugation of various CADs to harmine resulted in the increased antiplasmodial activity relative to harmine. In general, O-harmicines 7 exhibited the highest activity against the erythrocytic stage of both P. falciparum strains, whereas N,O-bis harmicines 8 showed the most pronounced activity against P. berghei hepatic stages. For the latter compound, molecular dynamics simulations confirmed binding within the ATP binding site of PfHsp90, while the weaker binders, namely 6b and harmine, were found to be positioned away from this structural element. In addition, decomposition of the computed binding free energies into contributions from individual residues suggested guidelines for further derivatization of harmine towards more efficient compounds. Cytotoxicity screening revealed N-harmicines 6 as the least, and O-harmicines 7 as the most toxic compounds. Harmicines 6g, 8b and 6d exerted the most selective action towards Plasmodium over human cells, respectively. These results establish harmicines as hits for future optimisation and development of novel antiplasmodial agents.

Mechanochemical amorphization of chitin: impact of apparatus material on performance and contamination

Herein, we present a study of the impact of the jar and ball medium on the performance in the mechanochemical amorphization of chitin. We measured the crystallinity index of chitin after milling it in a vibration mill in an apparatus made of copper, aluminum, brass, tungsten carbide, zirconia, stainless steel, polytetrafluoroethylene (PTFE), or poly(methyl methacrylate) (PMMA). These materials offer a range of Vickers hardness values and the impact of these parameters is discussed. The role of the size and mass of the balls is also studied in the case of stainless steel. This study also highlights one of the major challenges during milling, which is contamination of the studied samples.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.