Arnaud Chevalier

Bioconjugatable azo-based dark-quencher dyes: synthesis and application to protease-activatable far-red fluorescent probes.

We describe the efficient synthesis and one-step derivatization of novel, nonfluorescent azo dyes based on the Black Hole Quencher-3 (BHQ-3) scaffold. These dyes were equipped with various reactive and/or bioconjugatable groups (azido, α-iodoacetyl, ketone, terminal alkyne, vicinal diol). The azido derivative was found to be highly reactive in the context of copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions and allowed easy synthetic access to the first water-soluble (sulfonated derivative) and aldehyde-modified BHQ-3 dyes, the direct preparation of which failed by means of conventional azo-coupling reactions. The aldehyde- and α-iodoacetyl-containing fluorescence quenchers were readily conjugated to aminooxy- and cysteine-containing peptides by the formation of a stable oxime or thioether linkage, respectively. Further fluorescent labeling of the resultant peptide conjugates with red- or far-red-emitting rhodamine or cyanine dyes through sequential and/or one-pot bioconjugations, led to novel Förster resonance energy transfer (FRET) based probes suitable for the in vivo detection and imaging of urokinase plasminogen activator, a key protease in cancer invasion and metastasis.

Azo-Sulforhodamine Dyes: A Novel Class of Broad Spectrum Dark Quenchers

A rapid access to a novel class of water-soluble dark quencher dyes was achieved using an azo-coupling reaction between a fluorescent primary arylamine derived from a sulforhodamine 101 scaffold and a tertiary aniline equipped with different bioconjugatable groups. The thus obtained nonfluorescent azo-sulforhodamine hybrids display a broad quenching range spanning the visible to NIR regions. This was demonstrated through the preparation and enzymatic activation of FRET-based fluorogenic substrates of urokinase.

Synthesis, Biological Evaluation, and in Vivo Imaging of the first Camptothecin–Fluorescein Conjugate

The first synthesis and photophysical properties of a fluorecently labeled camptothecin derivative, namely, camptothecin-FI (CPT-FI), an antitumoral agent that targets topoisomerase I, are reported. The preparation of this fluorescent conjugate is based on a highly convergent and flexible approach which enables the rapid chemical modification of the AB ring system of this fragile pentacyclic alkaloid, aimed at introducing an anchoring point to graft the fluorophore. The selection of a fluorescein analogue as the reporter group has enabled us to get the first green-emitting CPT conjugate exhibiting valuable spectral properties and retaining biological properties of native CPT. Indeed, in biological models, i.e., glioma cell lines U87 and/or T98, the kinetics of cell endocytosis, as well as the efficacy of CPT-FI were compared to those of CPT. CPT-FI fluorescence was measured in the cytosolic compartment of T98 glioma cells from 5 min treatment and remained detectable until 48 h. As CPT, CPT-FI drastically inhibited glioma growth and cell cycle but exhibited a reduced affinity as compared to the native CPT. In vivo and ex vivo imaging studies of CPT-FI intratumoraly injected into a model of NIH-3T3 murine tumor xenografts in nude mice, showed accumulation around the injected site area, which is very promising to target tumors and follow biodistribution in vivo.

An optimized procedure for direct access to 1H-indazole-3-carboxaldehyde derivatives by nitrosation of indoles

Indazole derivatives are currently drawing more and more attention in medicinal chemistry as kinase inhibitors. 1H-indazole-3-carboxaldehydes are key intermediates to access to a variety of polyfunctionalized 3-substituted indazoles. We report here a general access to this motif, based on the nitrosation of indoles in a slightly acidic environment. These very mild conditions allow the conversion of both electron-rich and electron-deficient indoles into 1H-indazole-3-carboxaldehydes.

Total Synthesis and Structural Revision of Chaetoviridins A

The first synthesis of the proposed structures of chaetoviridins A 1-4 has been achieved in 10 steps by controlling the syn- or anti-aldol side chain. The angular lactone has been regioselectively introduced by condensation of a chiral dioxin-4-one to cazisochromene. Comparison of the NMR and circular dichroism data of the synthesized and reported natural products led to the complete reassignment and renaming of the chaetoviridins.