Rodolfo Lavilla

Heterocycles as Key Substrates in Multicomponent Reactions: The Fast Lane towards Molecular Complexity

Heterocycles display an intrinsic reactivity which enables rich, versatile and productive transformations. Taking into account their ubiquitous presence in natural products and drugs, the development of new, fast and efficient preparative protocols for these structures remains an urgent task in Organic Synthesis. Multicomponent reactions using heterocyclic chemistry offer new possibilities to exploit this exclusive reactivity. Recent results show relevant examples of such transformations. Several approaches which allow the construction of complex heterocyclic compounds from simple starting materials using this principle have been analyzed.

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.

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.

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.

Constrained Cyclopeptides: Biaryl Formation through Pd-Catalyzed C−H Activation in Peptides—Structural Control of the Cyclization vs. Cyclodimerization Outcome

A series of short tryptophan-phenylalanine peptides containing an iodo substituent on the phenyl ring was subjected to Pd-catalyzed CH activation reactions to give the corresponding aryl-indole coupled products. Two types of adducts were generated: cyclomonomer and cyclodimeric peptides; no evidence of oligo- or polymerization products was detected. Contrary to standard peptide macrocyclizations, the factors controlling the fate of the reaction are the number of amino acids between the aromatic residues and the regiochemistry of the parent iodo derivative, independent of both the concentration and the cyclization mode. The method is general and allows access to novel biaryl peptidic topologies, which have been fully characterized.

A trifluorinated thiazoline scaffold leading to pro-apoptotic agents targeting prohibitins.

A new class of small molecules, with an unprecedented trifluorothiazoline scaffold, were synthesized and their pro-apoptotic activity was evaluated. With an EC50 in the low micromolar range, these compounds proved to be potent inducers of apoptosis in a broad spectrum of tumor cell lines, regardless of the functional status of p53. Fast structure-activity relationship studies allowed the preparation of the strongest apoptosis-inducing candidate. Using a high performance affinity purification approach, we identified prohibitinsu20051 and 2, key proteins involved in the maintenance of cell viability, as the targets for these compounds.

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 Nu2005activation 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 Trypanosomau2005brucei and T.u2005cruzi, featuring favorable drug-like properties and safety profiles.

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.

Polythiazole linkers as functional rigid connectors: a new RGD cyclopeptide with enhanced integrin selectivity

Polythiazole amino acids clasp linear peptides to generate cyclic derivatives, however, the resulting species are not merely stapled peptides but bear a complex heterocyclic moiety displaying its intrinsic set of interactions. As a proof of concept, a bisthiazole moiety has been grafted onto an RGD sequence to deliver a new cilengitide analogue with improved integrin selectivity and remarkable in vivo antiangiogenic activity.

Evolution of a multicomponent system: computational and mechanistic studies on the chemo- and stereoselectivity of a divergent process.

The evolution of a ternary molecular system (imine, diene and nitrile) is analyzed to disclose the pathways leading to a divergent synthetic outcome. The Lewis acid catalyzed reaction between cyclohexadiene, 2-phenyl-indol-3-one and acetonitrile yields the imino-Diels-Alder adduct as the major product together with minor amounts of the Mannich-Ritter-amidine product. The experimental and computational data show that the relative orientation of the initial reactants dictates the synthetic outcome. The exo approach between imine and diene leads to the Diels-Alder adduct in a concerted process, whereas the endo mode leads to a polarized intermediate, which is trapped by acetonitrile to yield the multicomponent adduct.