Synthesis of C-carbamoyl-1,2,3-triazoles by microwave-induced 1,3-dipolar cycloaddition of organic azides to acetylenic amides

1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides under "Non-Conventional" Conditions: Green Solvents, Irradiation, and Continuous Flow

The 1,3-dipolar cycloaddition reactions (DCs) of nitrile oxides (NOs) to alkenes and alkynes are useful methods for the synthesis of 2-isoxazolines and isoxazoles respectively, which are important classes of heterocyclic compounds in organic and medicinal chemistry. Most of these reactions are carried out in organic solvents and under thermal activation. Nevertheless the use of supercritical carbon dioxide (scCO₂ ) and ionic liquids (Ils) as alternative solvents and the application of microwave (MW) and ultrasound (US) as alternative activation procedures have evident advantages from the "Green Chemistry" point of view. The critical discussion on the applications of these "unconventional" activation methods and reaction conditions in the 1,3-DCs of NOs is the objective of the present Review.

1,3-Dipolar cycloaddition of nitrones to oxa(aza)bicyclic alkenes

A new 1,3-dipolar cycloaddition of oxa(aza)bicyclic alkenes with nitrones has been developed without any catalyst and additive under mild conditions. The proposed concerted mechanism is investigated by DFT calculations of the reaction pathways.

Base-Promoted Synthesis of N-Substituted 1,2,3-Triazoles via Enaminone-Azide Cycloaddition Involving Regitz Diazo Transfer

The domino reactions between NH-based secondary enaminones and tosyl azide have been developed for the synthesis of various N-substituted 1,2,3-triazoles by employing t-BuONa as the base promoter. Through a key Regitz diazo-transfer process with tosyl azide, the reactions proceed efficiently at room temperature with good substrate tolerance.

Copper immobilized onto a triazole functionalized magnetic nanoparticle: a robust magnetically recoverable catalyst for “click” reactions

A novel magnetic heterogeneous copper catalyst was synthesized by immobilization of copper ions onto triazole functionalized Fe₃O₄.

Synthesis of triazolo-fused benzoxazepines and benzoxazepinones via Passerini reactions followed by 1,3-dipolar cycloadditions

Azidobenzaldehydes can be used in Passerini three-component condensations to synthesize small collections of triazolo-fused heterocycles in an efficient and combinatorial fashion upon post-condensation azide-alkyne cycloadditions. Triazolo-fused benzoxazepinones were obtained in moderate to good overall yields with a concise two-step protocol. Triazolo-fused benzoxazepines were instead prepared by means of a longer, yet straightforward route comprising a Passerini reaction, hydrolysis of the ester moiety, O-alkylation with propargylic bromides, and 1,3-dipolar cycloaddition.

Cathepsin L silencing enhances arsenic trioxide mediated in vitro cytotoxicity and apoptosis in glioblastoma U87MG spheroids

Despite improved treatment options, glioblastoma multiforme (GBM) remains the most aggressive brain tumour with the shortest post-diagnostic survival. Arsenite (As2O3) is already being used in the treatment of acute promyelocytic leukaemia (APL), yet its effects on GBM have not been evaluated in detail. In U87MG cell monolayers, we have previously shown that arsenite cytotoxicity significantly increases upon transient inhibition of lysosomal protease Cathepsin L (CatL). As multicellular spheroids more closely represent in vivo tumours, we aimed to evaluate the impact of permanent CatL silencing on arsenite treatment in U87MG spheroids. CatL was stably silenced using shRNA expression plasmid packed lentiviruses. By using metabolic- and cell viability assays, we demonstrated that long-term CatL silencing significantly increased arsenite cytotoxicity in U87MG spheroids. Silenced CatL also increased arsenite-mediated apoptosis in spheroids via elevated p53 expression, Bax/Bcl2 ratio and caspase 3/7 activity, though with lower efficacy than in monolayers. Arsenite cytotoxicity was enhanced by lower CatL activity, since similar cytotoxicity increase was also observed using the novel CatL inhibitor AT094. The results have significant translational impact, since stable CatL silencing would enable the application of lower systemic doses of arsenite to achieve the desired cytotoxic effects on GBMs in vivo.

Triazole bridges as versatile linkers in electron donor-acceptor conjugates

Aromatic triazoles have been frequently used as π-conjugated linkers in intramolecular electron transfer processes. To gain a deeper understanding of the electron-mediating function of triazoles, we have synthesized a family of new triazole-based electron donor-acceptor conjugates. We have connected zinc(II)porphyrins and fullerenes through a central triazole moiety--(ZnP-Tri-C(60))--each with a single change in their connection through the linker. An extensive photophysical and computational investigation reveals that the electron transfer dynamics--charge separation and charge recombination--in the different ZnP-Tri-C(60) conjugates reflect a significant influence of the connectivity at the triazole linker. Except for the m4m-ZnP-Tri-C(60)17, the conjugates exhibit through-bond photoinduced electron transfer with varying rate constants. Since the through-bond distance is nearly the same for all the synthesized ZnP-Tri-C(60) conjugates, the variation in charge separation and charge recombination dynamics is mainly associated with the electronic properties of the conjugates, including orbital energies, electron affinity, and the energies of the excited states. The changes of the electronic couplings are, in turn, a consequence of the different connectivity patterns at the triazole moieties.

N-Benzyl-2-propynamide

Pale-yellow crystals of the title compound, C(10)H(9)NO, have been obtained by the reaction of benzyl-amine and methyl propiolate. Weak inter-molecular hydrogen bonding is observed between acetyl-enic H and carbonyl O atoms. The crystal packing is stabilized by these C-H⋯O and by N-H⋯O inter-molecular hydrogen-bonding inter-actions.

"Flash" solvent-free synthesis of triazoles using a supported catalyst

A solvent-free synthesis of 1,4-disubstituted-1,2,3-triazoles using neat azides and alkynes and a copper(I) polymer supported catalyst (Amberlyst) A21*CuI) is presented herein. As it provides the products in high yields and purities within minutes, this method thus being characterized as a "flash" synthesis, and was exemplified through the synthesis of a 24-compound library on a small scale.

Organic azides: an exploding diversity of a unique class of compounds

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aubé rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.