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1. New 1,2,3-Triazoles from (R)-Carvone: Synthesis, DFT Mechanistic Study and In Vitro Cytotoxic Evaluation

   https://doi.org/10.3390/molecules27030769  

   Oubella, Ali; Bimoussa, Abdoullah; N’ait Oussidi, Abdellah; Fawzi, Mourad; Auhmani, Aziz; Morjani, Hamid; Riahi, Abdelkhalek; Esseffar, M’hamed; Parish, Carol; Ait Itto, Moulay Youssef (February 2022, Molecules)

   Aseries of novel 1,4-disubstituted 1,2,3-triazoles were synthesized from an (R)-carvone terminal alkyne derivative via a Cu (I)-catalyzed azide–alkyne cycloaddition reaction using CuSO4,5H2O as the copper (II) source and sodium ascorbate as a reducing agent which reduces Cu (II) into Cu (I). All the newly synthesized 1,2,3-triazoles 9a–h were fully identified on the basis of their HRMS and NMR spectral data and then evaluated for their cell growth inhibition potential by MTS assay against HT-1080 fibrosarcoma, A-549 lung carcinoma, and two breast adenocarcinoma (MCF-7 and MDA-MB-231) cell lines. Compound 9d showed notable cytotoxic effects against the HT-1080 and MCF-7 cells with IC50 values of 25.77 and 27.89 µM, respectively, while compound 9c displayed significant activity against MCF-7 cells with an IC50 value of 25.03 µM. Density functional calculations at the B3LYP/6-31G* level of theory were used to confirm the high reactivity of the terminal alkyne as a dipolarophile. Quantum calculations were also used to investigate the mechanism of both the uncatalyzed and copper (I)-catalyzed azide–alkyne cycloaddition reaction (CuAAC). The catalyzed reaction gives complete regioselectivity via a stepwise mechanism streamlining experimental observations. The calculated free-energy barriers 4.33 kcal/mol and 29.35 kcal/mol for the 1,4- and 1,5-regioisomers, respectively, explain the marked regioselectivity of the CuAAC reaction. 

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2. Photoswitchable Sol–Gel Transitions and Catalysis Mediated by Polymer Networks with Coumarin‐Decorated Cu ₂₄ L ₂₄ Metal–Organic Cages as Junctions

   https://doi.org/10.1002/anie.201913297  

   Oldenhuis, Nathan J.; Qin, K. Peter; Wang, Shu; Ye, Hong‐Zhou; Alt, Eric A.; Willard, Adam P.; Van Voorhis, Troy; Craig, Stephen L.; Johnson, Jeremiah A. (January 2020, Angewandte Chemie International Edition)

   Abstract Photoresponsive materials that change in response to light have been studied for a range of applications. These materials are often metastable during irradiation, returning to their pre‐irradiated state after removal of the light source. Herein, we report a polymer gel comprising poly(ethylene glycol) star polymers linked by Cu₂₄L₂₄metal–organic cages/polyhedra (MOCs) with coumarin ligands. In the presence of UV light, a photosensitizer, and a hydrogen donor, this “polyMOC” material can be reversibly switched between Cu^II, Cu^I, and Cu⁰. The instability of the MOC junctions in the Cu^Iand Cu⁰states leads to network disassembly, forming Cu^I/Cu⁰solutions, respectively, that are stable until re‐oxidation to Cu^IIand supramolecular gelation. This reversible disassembly of the polyMOC network can occur in the presence of a fixed covalent second network generated in situ by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC), providing interpenetrating supramolecular and covalent networks. 

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3. Biocompatible photoinduced CuAAC using sodium pyruvate

   https://doi.org/10.1039/D1CC05566F  

   Jeong, Jaepil; Szczepaniak, Grzegorz; Yerneni, Saigopalakrishna S.; Lorandi, Francesca; Jafari, Hossein; Lathwal, Sushil; Das, Subha R.; Matyjaszewski, Krzysztof (November 2021, Chemical Communications)

   Sodium pyruvate, a natural intermediate produced during cellular metabolism, is commonly used in buffer solutions and media for biochemical applications. Here we show the use of sodium pyruvate (SP) as a reducing agent in a biocompatible aqueous photoinduced azide–alkyne cycloaddition (CuAAC) reaction. This copper( i )-catalyzed 1,3-dipolar cycloaddition is triggered by SP under UV light irradiation, exhibits oxygen tolerance and temporal control, and provides a convenient alternative to current CuAAC systems, particularly for biomolecular conjugations. 

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4. Biotin-Conjugated Cellulose Nanofibers Prepared via Copper-Catalyzed Alkyne-Azide Cycloaddition (CuAAC) “Click” Chemistry

   https://doi.org/10.3390/nano10061172  

   Goodge, Katarina; Frey, Margaret (June 2020, Nanomaterials)

   null (Ed.)

   As potential high surface area for selective capture in diagnostic or filtration devices, biotin-cellulose nanofiber membranes were fabricated to demonstrate the potential for specific and bio-orthogonal attachment of biomolecules onto nanofiber surfaces. Cellulose acetate was electrospun and substituted with alkyne groups in either a one- or two-step process. The alkyne reaction, confirmed by FTIR and Raman spectroscopy, was dependent on solvent ratio, time, and temperature. The two-step process maximized alkyne substitution in 10/90 volume per volume ratio (v/v) water to isopropanol at 50 °C after 6 h compared to the one-step process in 80/20 (v/v) at 50 °C after 48 h. Azide-biotin conjugate “clicked” with the alkyne-cellulose via copper-catalyzed alkyne-azide cycloaddition (CuAAC). The biotin-cellulose membranes, characterized by FTIR, SEM, Energy Dispersive X-ray spectroscopy (EDX), and XPS, were used in proof-of-concept assays (HABA (4′-hydroxyazobenzene-2-carboxylic acid) colorimetric assay and fluorescently tagged streptavidin assay) where streptavidin selectively bound to the pendant biotin. The click reaction was specific to alkyne-azide coupling and dependent on pH, ratio of ascorbic acid to copper sulfate, and time. Copper (II) reduction to copper (I) was successful without ascorbic acid, increasing the viability of the click conjugation with biomolecules. The surface-available biotin was dependent on storage medium and time: Decreasing with immersion in water and increasing with storage in air. 

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5. Tetranuclear and trinuclear copper( i ) pyrazolates as catalysts in copper mediated azide–alkyne cycloadditions (CuAAC)

   https://doi.org/10.1039/d1dt04026j  

   Patterson, Monika R.; Dias, H. V. (December 2021, Dalton Transactions)

   Homoleptic, tetranuclear copper( i ) pyrazolates {[3,5-( t -Bu) 2 Pz]Cu} 4 , {[3-(CF 3 )-5-( t -Bu)Pz]Cu} 4 , and {[4-Br-3,5-( i -Pr) 2 Pz]Cu} 4 are excellent stand-alone catalysts for azide–alkyne cycloaddition reactions (CuAAC). This work demonstrates that a range of pyrazolates, including those with electron donating and electron-withdrawing groups to sterically demanding substituents on the pyrazolyl backbones, can serve as effective ligand supports on tetranuclear copper catalysts. However, in contrast to the tetramers and also highly fluorinated {[3,5-(CF 3 ) 2 Pz]Cu} 3 , trinuclear copper( i ) complexes such as {[3,5-( i -Pr) 2 Pz]Cu} 3 and {[3-(CF 3 )-5-(CH 3 )Pz]Cu} 3 supported by relatively electron rich pyrazolates display poor catalytic activity in CuAAC. The behavior and degree of aggregation of several of these copper( i ) pyrazolates in solution were examined using vapor pressure osmometry. Copper( i ) complexes such as {[3,5-(CF 3 ) 2 Pz]Cu} 3 and {[3-(CF 3 )-5-( t -Bu)Pz]Cu} 4 with electron withdrawing pyrazolates were found to break up in solution to different degrees producing smaller aggregates while those such as {[3,5-( i -Pr) 2 Pz]Cu} 3 and {[3,5-( t -Bu) 2 Pz]Cu} 4 with electron rich pyrazolates remain intact. In addition, kinetic experiments were performed to understand the unusual activity of tetranuclear copper( i ) pyrazolate systems. 

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