A multicomponent reaction platform towards multimodal near-infrared BODIPY dyes for STED and fluorescence lifetime imaging.

We report a platform combining multicomponent reaction synthesis and automated cell-based screening to develop biocompatible NIR-BODIPY fluorophores. From a library of over 60 fluorophores, we optimised compound NIRBD-62c as a multimodal probe with suitable properties for STED super-resolution and fluorescence lifetime imaging. Furthermore, we employed NIRBD-62c for imaging trafficking inside cells and to examine how pharmacological inhibitors can alter the vesicular traffic between intracellular compartments and the plasma membrane.

Multiple Multicomponent Reactions: Unexplored Substrates, Selective Processes, and Versatile Chemotypes in Biomedicine.

Multiple multicomponent reactions rapidly assemble complex structures. Despite being very productive, the lack of selectivity and the reduced number of viable transformations restrict their general application in synthesis. Hereby, we describe a rationale for a selective version of these processes based in the preferential generation of intermediates which are less reactive than the initial substrates. In this way, applying the Groebke-Blackburn-Bienaymé reaction on a range of α-polyamino-polyazines, we prepared a family compact heterocyclic scaffolds with relevant applications in medicinal and biological chemistry (live cell imaging probes, selective binders for DNA quadruplexes, and antiviral agents against human adenoviruses). The approach has general character and yields complex molecular targets in a selective, tunable and direct manner.

Tetrasubstituted Imidazolium Salts as Potent Antiparasitic Agents against African and American Trypanosomiases.

Imidazolium salts are privileged compounds in organic chemistry, and have valuable biological properties. Recent studies show that symmetric imidazolium salts with bulky moieties can display antiparasitic activity against T. cruzi. After developing a facile methodology for the synthesis of tetrasubstituted imidazolium salts from propargylamines and isocyanides, we screened a small library of these adducts against the causative agents of African and American trypanosomiases. These compounds display nanomolar activity against T. brucei and low (or sub) micromolar activity against T. cruzi, with excellent selectivity indexes and favorable molecular properties, thereby emerging as promising hits for the treatment of Chagas disease and sleeping sickness.

Modern Synthetic Avenues for the Preparation of Functional Fluorophores.

Biomedical research relies on the fast and accurate profiling of specific biomolecules and cells in a non-invasive manner. Functional fluorophores are powerful tools for such studies. As these sophisticated structures are often difficult to access through conventional synthetic strategies, new chemical processes have been developed in the past few years. In this Minireview, we describe the most recent advances in the design, preparation, and fine-tuning of fluorophores by means of multicomponent reactions, C-H activation processes, cycloadditions, and biomolecule-based chemical transformations.

Electrophilic, Activation-Free Fluorogenic Reagent for Labeling Bioactive Amines.

Herein we report the preparation of BODIPY mesoionic acid fluorides through a short sequence involving an isocyanide multicomponent reaction as the key synthetic step. These novel BODIPY acid fluorides are water-stable electrophilic reagents that can be used for the fluorescent derivatization of amine-containing biomolecules using mild and activation-free reaction conditions. As a proof of principle, we have labeled the antifungal natamycin and generated a novel fluorogenic probe for imaging a variety of human and plant fungal pathogens, with excellent selectivity over bacterial cells.

Insertion of Isocyanides into N-Si Bonds: Multicomponent Reactions with Azines Leading to Potent Antiparasitic Compounds.

Trimethylsilyl chloride is an efficient activating agent for azines in isocyanide-based reactions, which then proceed through a key insertion of the isocyanide into a N-Si bond. The reaction is initiated by N activation of the azine, followed by nucleophilic attack of an isocyanide in a Reissert-type process. Finally, a second equivalent of the same or a different isocyanide inserts into the N-Si bond leading to the final adduct. The use of distinct nucleophiles leads to a variety of α-substituted dihydroazines after a selective cascade process. Based on computational studies, a mechanistic hypothesis for the course of these reactions was proposed. The resulting products exhibit significant activity against Trypanosoma brucei and T. cruzi, featuring favorable drug-like properties and safety profiles.

Spacer-free BODIPY fluorogens in antimicrobial peptides for direct imaging of fungal infection in human tissue.

Fluorescent antimicrobial peptides are promising structures for in situ, real-time imaging of fungal infection. Here we report a fluorogenic probe to image Aspergillus fumigatus directly in human pulmonary tissue. We have developed a fluorogenic Trp-BODIPY amino acid with a spacer-free C-C linkage between Trp and a BODIPY fluorogen, which shows remarkable fluorescence enhancement in hydrophobic microenvironments. The incorporation of our fluorogenic amino acid in short antimicrobial peptides does not impair their selectivity for fungal cells, and enables rapid and direct fungal imaging without any washing steps. We have optimized the stability of our probes in human samples to perform multi-photon imaging of A. fumigatus in ex vivo human tissue. The incorporation of our unique BODIPY fluorogen in biologically relevant peptides will accelerate the development of novel imaging probes with high sensitivity and specificity.

New peptide architectures through C-H activation stapling between tryptophan-phenylalanine/tyrosine residues.

Natural peptides show high degrees of specificity in their biological action. However, their therapeutical profile is severely limited by their conformational freedom and metabolic instability. Stapled peptides constitute a solution to these problems and access to these structures lies on a limited number of reactions involving the use of non-natural amino acids. Here, we describe a synthetic strategy for the preparation of unique constrained peptides featuring a covalent bond between tryptophan and phenylalanine or tyrosine residues. The preparation of such peptides is achieved in solution and on solid phase directly from the corresponding sequences having an iodo-aryl amino acid through an intramolecular palladium-catalysed C-H activation process. Moreover, complex topologies arise from the internal stapling of cyclopeptides and double intramolecular arylations within a linear peptide. Finally, as a proof of principle, we report the application to this new stapling method to relevant biologically active compounds.

Highly active aluminium catalysts for the formation of organic carbonates from CO2 and oxiranes.

Al(III) complexes of amino-tris(phenolate) ligand scaffolds have been prepared to attain highly Lewis acidic catalysts. Combination of the aforementioned systems with ammonium halides provides highly active catalysts for the synthesis of organic carbonates through addition of carbon dioxide to oxiranes with initial turnover frequencies among the highest reported to date within the context of cyclic carbonate formation. Density functional theory (DFT) studies combined with kinetic data provides a rational for the relative high activity found for these Al(III) complexes, and the data are consistent with a monometallic mechanism. The activity and versatility of these Al(III) complexes has also been evaluated against some state-of-the-art catalysts and the combined results compare favorably in terms of catalyst construction, stability, activity, and applicability.

Multicomponent reactions for de novo synthesis of BODIPY probes: in vivo imaging of phagocytic macrophages.

Multicomponent reactions are excellent tools to generate complex structures with broad chemical diversity and fluorescent properties. Herein we describe the adaptation of the fluorescent BODIPY scaffold to multicomponent reaction chemistry with the synthesis of BODIPY adducts with high fluorescence quantum yields and good cell permeability. From this library we identified one BODIPY derivative (PhagoGreen) as a low-pH sensing fluorescent probe that enabled imaging of phagosomal acidification in activated macrophages. The fluorescence emission of PhagoGreen was proportional to the degree of activation of macrophages and could be specifically blocked by bafilomycin A, an inhibitor of phagosomal acidification. PhagoGreen does not impair the normal functions of macrophages and can be used to image phagocytic macrophages in vivo.

A powerful aluminum catalyst for the synthesis of highly functional organic carbonates.

An aluminum complex based on an amino triphenolate ligand scaffold shows unprecedented high activity (initial TOFs up to 36,000 h(-1)), broad substrate scope, and functional group tolerance in the formation of highly functional organic carbonates prepared from epoxides and CO(2). The developed catalytic protocol is further characterized by low catalyst loadings and relative mild reaction conditions using a cheap, abundant, and nontoxic metal.

Unsymmetrical octanuclear Schiff base clusters: synthesis, characterization and catalysis.

The synthesis and characterization of nonsymmetrical octanuclear Schiff base clusters derived from nonsymmetrical diamine precursors is reported. These cluster complexes, typically assemblies comprising of four bimetallic salphen units, are isolated as a mixture of geometrical isomers as a result of different relative positions of the peripheral groups present in the diamine connectors within each cluster compound. A variety of peripheral groups can be installed including aryl bromides, protected carboxylic acids and pyridyl functionalities. The analysis of these octanuclear systems has been challenging, though mass spectrometric analysis provides a useful and diagnostic tool for the straightforward determination of the mono-disperse nature of these products. The presence of various electron-withdrawing and -donating groups on the peripheral aryl fragment allows for electronic modulation as supported by the application of these cluster derivatives in the homogeneous catalytic conversion of epoxides into their respective cyclic carbonates.

Imaging histamine in live basophils and macrophages with a fluorescent mesoionic acid fluoride.

Histamine is a biogenic amine with fundamental roles in circulatory and immune systems. We report a fluorescent small molecule (Histamine Blue) for imaging intracellular histamine in live basophils and macrophages. Histamine Blue is a fluorescent mesoionic acid fluoride that turns on upon reaction with histamine. The selective response of Histamine Blue enabled the visualization of intracellular histamine under different physiological conditions.

Synthesis and properties of oligonucleotides carrying isoquinoline imidazo[1,2-a]azine fluorescent units.

Oligonucleotides carrying novel fluorescent compounds with a dipolar isoquinoline imidazo[1,2-a]azine core were prepared. Analysis of the melting curves demonstrates that DNA duplexes carrying these fluorescent labels at their ends have a slight increase in DNA duplex stability. The UV absorption and fluorescent properties of the oligonucleotide conjugates were analyzed. The fluorescent label is sensitive to duplex formation, as cooperative melting curves are also observed at 366 nm and fluorescence has a large increase upon denaturation. Cell uptake studies allow observation of these fluorescently labeled oligonucleotides internalized into HeLa cells.

Boron-based dipolar multicomponent reactions: simple generation of substituted aziridines, oxazolidines and pyrrolidines.

New multicomponent reactions of aldehydes, isocyanides, trialkylboron reagents and dipolarophiles have been developed as an efficient route to diverse scaffolds, including aziridines, oxazolidines and poly-substituted pyrrolidines. This chemistry, inspired by a report by Hesse in 1965, is simple and involves mild conditions. Computational studies provide a basis to investigate the stereochemical features observed in the formation of oxazolidines and four-component adducts, and permit identification of potential factors that might influence the outcome of the multicomponent reaction. Thus, a rational screening of all the components and reaction parameters is made to examine the manifold mechanistic pathways and establish the practical limits for standard applications. Finally, intramolecular and solid-supported versions of these reactions bring new synthetic possibilities and practical protocols. Overall, the results describe a new family of multicomponent reactions valuable not only for organic reactivity, but also for combinatorial chemistry and drug discovery.

Ugi multicomponent reaction followed by an intramolecular nucleophilic substitution: convergent multicomponent synthesis of 1-sulfonyl 1,4-diazepan-5-ones and of their benzo-fused derivatives.

A short, two-step approach to the synthesis of diazepane or diazocane systems, based on a Ugi multicomponent reaction followed by a subsequent intramolecular SN2 reaction was studied. 1-sulfonyl tetrahydrobenzo[e]-1,4-diazepin-1-ones 1 were obtained in very high yield through a Ugi multicomponent reaction followed by Mitsunobu cyclization. On the other hand, aliphatic 1-sulfonyl 1,4-diazepan-5-ones 2 could be obtained employing different cyclization conditions (sulfuryl diimidazole). A similar approach toward diazocane rings using hydroxamates as nucleophiles was less successful, affording only O-cyclized adducts or unexpected side products. A mechanistic explanation of the observed outcomes is proposed.