Platform for Multiple Isotope Labeling via Carbon-Sulfur Bond Exchange.

In this work, we explore a nickel-catalyzed reversible carbon-sulfur (C-S) bond activation strategy to achieve selective sulfur isotope exchange. Isotopes are at the foundation of applications in life science, such as nuclear imaging, and are essential tools for the determination of pharmacokinetic and dynamic profiles of new pharmaceuticals. However, the insertion of an isotope into an organic molecule remains challenging, and current technologies are element-specific. Despite the ubiquitous presence of sulfur in many biologically active molecules, sulfur isotope labeling is an underexplored field, and sulfur isotope exchange has been overlooked. This approach enables us to move beyond standardized element-specific procedures and was applied to multiple isotopes, including deuterium, carbon-13, sulfur-34, and radioactive carbon-14. These results provide a unique platform for multiple isotope labeling and are compatible with a wide range of substrates, including pharmaceuticals. In addition, this technology proved its potential as an isotopic encryption device for organic molecules.

Exploration of the Copper-Catalyzed Sydnone and Sydnonimine-Alkyne Cycloaddition Reactions by High-Throughput Experimentation.

The reactivity of sydnones and sydnonimines toward terminal alkynes under copper catalysis has been explored using High-Throughput-Experimentation. A large panel of ligands and reaction conditions have been tested to optimize the copper-catalyzed sydnone click reaction discovered by our group ten years ago. This screening approach led to the identification of new ligands, which boosted the catalytic properties of copper and allowed the discovery of a new copper-catalyzed click-and-release reaction involving sydnonimines. This reaction allowed chemoselective ligation of terminal alkynes with sydnonimines and, simultaneously, the release of an isocyanate fragment molecule that can be used for further transformations.

Carbon Dioxide Radical Anion by Photoinduced Equilibration between Formate Salts and [11C, 13C, 14C]CO2: Application to Carbon Isotope Radiolabeling.

The need for carbon-labeled radiotracers is increasingly higher in drug discovery and development (carbon-14, ß-, t1/2 = 5730 years) as well as in positron emission tomography (PET) for in vivo molecular imaging applications (carbon-11, ß+, t1/2 = 20.4 min). However, the structural diversity of radiotracers is still systematically driven by the narrow available labeled sources and methodologies. In this context, the emergence of carbon dioxide radical anion chemistry might set forth potential unexplored opportunities. Based on a dynamic isotopic equilibration between formate salts and [13C, 14C, 11C]CO2, C-labeled radical anion CO2•- could be accessed under extremely mild conditions within seconds. This methodology was successfully applied to hydrocarboxylation and dicarboxylation reactions in late-stage carbon isotope labeling of pharmaceutically relevant compounds. The relevance of the method in applied radiochemistry was showcased by the whole-body PET biodistribution profile of [11C]oxaprozin in mice.

Fast and Bioorthogonal Release of Isocyanates in Living Cells from Iminosydnones and Cycloalkynes.

Bioorthogonal click-and-release reactions are powerful tools for chemical biology, allowing, for example, the selective release of drugs in biological media, including inside animals. Here, we developed two new families of iminosydnone mesoionic reactants that allow a bioorthogonal release of electrophilic species under physiological conditions. Their synthesis and reactivities as dipoles in cycloaddition reactions with strained alkynes have been studied in detail. Whereas the impact of the pH on the reaction kinetics was demonstrated experimentally, theoretical calculations suggest that the newly designed dipoles display reduced resonance stabilization energies compared to previously described iminosydnones, explaining their higher reactivity. These mesoionic compounds react smoothly with cycloalkynes under physiological, copper-free reaction conditions to form a click pyrazole product together with a released alkyl- or aryl-isocyanate. With rate constants up to 1000 M-1 s-1, this click-and-release reaction is among the fastest described to date and represents the first bioorthogonal process allowing the release of isocyanate electrophiles inside living cells, offering interesting perspectives in chemical biology.

PSL Chemical Biology Symposia Third Edition: A Branch of Science in its Explosive Phase.

This symposium is the third PSL (Paris Sciences & Lettres) Chemical Biology meeting (2016, 2019, 2023) held at Institut Curie. This initiative originally started at Institut de Chimie des Substances Naturelles (ICSN) in Gif-sur-Yvette (2013, 2014), under the directorship of Professor Max Malacria, with a strong focus on chemistry. It was then continued at the Institut Curie (2015) covering a larger scope, before becoming the official PSL Chemical Biology meeting. This latest edition was postponed twice for the reasons that we know. This has given us the opportunity to invite additional speakers of great standing. This year, Institut Curie hosted around 300 participants, including 220 on site and over 80 online. The pandemic has had, at least, the virtue of promoting online meetings, which we came to realize is not perfect but has its own merits. In particular, it enables those with restricted time and resources to take part in events and meetings, which can now accommodate unlimited participants. We apologize to all those who could not attend in person this time due to space limitation at Institut Curie.

2'-Modified Thymidines with Bioorthogonal Cyclopropene or Sydnone as Building Blocks for Copper-Free Postsynthetic Functionalization of Chemically Synthesized Oligonucleotides.

The development of facile methods for conjugating relevant probes, ligands, or delivery agents onto oligonucleotides (ONs) is highly desirable both for fundamental studies in chemical biology and for improving the pharmacology of ONs in medicinal chemistry. Numerous efforts have been focused on the introduction of bioorthogonal groups onto phosphoramidite building blocks, allowing the controlled chemical synthesis of reactive ONs for postsynthetic modifications. Among these building blocks, alkyne, cyclooctynes, trans-cyclooctene, and norbornene have been proved to be compatible with automated solid-phase chemistry. Herein, we present the development of novel 2'-functionalized nucleoside phosphoramidite monomers comprising bioorthogonal methylcyclopropene or sydnone moieties and their introduction for the first time to ON solid-phase synthesis. Traceless ON postsynthetic modifications with reactive complementary probes were successfully achieved through either inverse electron-demand Diels-Alder (iEDDA) reactions or strain-promoted sydnone-alkyne cycloaddition (SPSAC). These results expand the set of bioorthogonal phosphoramidite building blocks to generate ONs for postsynthetic labeling.

Radiation-Responsive Benzothiazolines as Potential Cleavable Fluorogenic Linkers for Drug Delivery.

Radiosensitive compounds can be useful for the detection of radiations and also as prodrugs that can be activated during a radiotherapy. Herein we describe the use of benzothiazolines, which upon treatment with 137 Cs produced γ-irradiation in water give rise to fluorescent benzothiazoles and concomitant release of amines or carboxylic acids. In a proof of concept study, we showed that benzothiazolines may be used as new cleavable linkers that can be triggered upon irradiation.

Bioorthogonal Drug Release from Nanometric Micelles in Living Cells.

We explored a bioorthogonal approach to release drugs from stimuli-responsive micelles inside tumor cells. The concept relies on sydnonimine-based micelles that undergo quantitative cleavage in presence of cyclooctynes, hence releasing their content within living cells. Four cleavable micelles were developed to allow massive burst release of Entinostat, a potent histone deacetylase inhibitor, following their internalization inside cancer cells. A comparative study on the influence of the bioorthogonal-mediated versus passive drug release from micelles was carried out. The results indicated that a fast release of the drug triggered a stronger antiproliferative activity on tumor cells compared to the passive diffusion of the drug from the micelles core. These finding may be of great interest for the development of new nanomedicines.

Click and Bio-Orthogonal Reactions with Mesoionic Compounds.

Click and bio-orthogonal reactions are dominated by cycloaddition reactions in general and 1,3-dipolar cycloadditions in particular. Among the dipoles routinely used for click chemistry, azides, nitrones, isonitriles, and nitrile oxides are the most popular. This review is focused on the emerging click chemistry that uses mesoionic compounds as dipole partners. Mesoionics are a very old family of molecules, but their use as reactants for click and bio-orthogonal chemistry is quite recent. The facility to derivatize these dipoles and to tune their reactivity toward cycloaddition reactions makes mesoionics an attractive opportunity for future click chemistry development. In addition, some compounds from this family are able to undergo click-and-release reactions, finding interesting applications in cells, as well as in animals. This review covers the synthetic access to main mesoionics, their reaction with dipolarophiles, and recent applications in chemical biology and heterocycle synthesis.

Modern Strategies for Carbon Isotope Exchange.

In contrast to stable and natural abundant carbon-12, the synthesis of organic molecules with carbon (radio)isotopes must be conceived and optimized in order to navigate through the hurdles of radiochemical requirements, such as high costs of the starting materials, harsh conditions and radioactive waste generation. In addition, it must initiate from the small cohort of available C-labeled building blocks. For long time, multi-step approaches have represented the sole available patterns. On the other side, the development of chemical reactions based on the reversible cleavage of C-C bonds might offer new opportunities and reshape retrosynthetic analysis in radiosynthesis. This review aims to provide a short survey on the recently emerged carbon isotope exchange technologies that provide effective opportunity for late-stage labeling. At present, such strategies have relied on the use of primary and easily accessible radiolabeled C1-building blocks, such as carbon dioxide, carbon monoxide and cyanides, while the activation principles have been based on thermal, photocatalytic, metal-catalyzed and biocatalytic processes.

Direct Carbon Isotope Exchange of Pharmaceuticals via Reversible Decyanation.

The incorporation of carbon-14 allows tracking of organic molecules and provides vital knowledge on their fate. This information is critical in pharmaceutical development, crop science, and human food safety evaluation. Herein, a transition-metal-catalyzed procedure enabling carbon isotope exchange on aromatic nitriles is described. By utilizing the radiolabeled precursor Zn([14C]CN)2, this protocol allows the insertion of the desired carbon tag without the need for structural modifications, in a single step. By reducing synthetic costs and limiting the generation of radioactive waste, this procedure will facilitate the labeling of nitrile containing drugs and accelerate 14C-based ADME studies supporting drug development.

Bioorthogonal Reactions in Animals.

The advent of bioorthogonal chemistry has led to the development of powerful chemical tools that enable increasingly ambitious applications. In particular, these tools have made it possible to achieve what is considered to be the holy grail of many researchers involved in chemical biology: to perform unnatural chemical reactions within living organisms. In this minireview, we present an update of bioorthogonal reactions that have been carried out in animals for various applications. We outline the advances made in the understanding of fundamental biological processes, and the development of innovative imaging and therapeutic strategies using bioorthogonal chemistry.

Click and Release Chemistry for Activity-Based Purification of ß-Lactam Targets.

ß-Lactams, the cornerstone of antibiotherapy, inhibit multiple and partially redundant targets referred to as transpeptidases or penicillin-binding proteins. These enzymes catalyze the essential cross-linking step of the polymerization of cell wall peptidoglycan. The understanding of the mechanisms of action of ß-lactams and of resistance to these drugs requires the development of reliable methods to characterize their targets. Here, we describe an activity-based purification method of ß-lactam targets based on click and release chemistry. We synthesized alkyne-carbapenems with suitable properties with respect to the kinetics of acylation of a model target, the Ldtfm L,D-transpeptidase, the stability of the resulting acylenzyme, and the reactivity of the alkyne for the cycloaddition of an azido probe containing a biotin moiety for affinity purification and a bioorthogonal cleavable linker. The probe provided access to the fluorescent target in a single click and release step.

Transition-Metal-Free Carbon Isotope Exchange of Phenyl Acetic Acids.

A transition-metal-free carbon isotope exchange procedure on phenyl acetic acids is described. Utilizing the universal precursor CO2 , this protocol allows the carbon isotope to be inserted into the carboxylic acid position, with no need of precursor synthesis. This procedure enabled the labeling of 15 pharmaceuticals and was compatible with carbon isotopes [14 C] and [13 C]. A proof of concept with [11 C] was also obtained with low molar activity valuable for distribution studies.

Dynamic Carbon Isotope Exchange of Pharmaceuticals with Labeled CO2.

A copper-catalyzed procedure enabling dynamic carbon isotope exchange is described. Utilizing the universal precursor [14C]CO2, this protocol allows to insert, in one single step, the desired carbon tag into carboxylic acids with no need of structural modifications. Reducing synthetic costs and limiting the generation of radioactive waste, this procedure will facilitate the access to carboxylic acids containing drugs and accelerate early 14C-based ADME studies supporting drug development.

Sydnone-Based Approach to Heterohelicenes through 1,3-Dipolar-Cycloadditions.

The first approach to pyrazole-containing helicenes via sydnone-aryne [3 + 2]-cycloaddition is described. An unprecedented regioselectivity in the cycloaddition step toward the more sterically constrained product was observed in the presence of extended aromatic scaffolds. DFT calculations enabled understanding the origin of this unexpected selectivity.

2nd PSL Chemical Biology Symposium (2019): At the Crossroads of Chemistry and Biology.

Chemical Biology is the science of designing chemical tools to dissect and manipulate biology at different scales. It provides the fertile ground from which to address important problems of our society, such as human health and environment.

Controlled Release of a Micelle Payload via Sequential Enzymatic and Bioorthogonal Reactions in Living Systems.

A bioorthogonal approach is explored to release the content of nanoparticles on demand. Exploiting our recently described click-and-release technology, we developed a new generation of cleavable micelles able to disassemble through a sequential enzymatic and bioorthogonal activation process. Proof-of-concept experiments showed that this new approach could be successfully used to deliver the substances encapsulated into micelles in living cells as well as in mice by two complementary targeted strategies.

Strain-Promoted 1,3-Dithiolium-4-olates-Alkyne Cycloaddition.

Reported here is the reactivity of mesoionic 1,3-dithiolium-4-olates towards strained alkynes, leading to thiophene cycloaddition products. In the process, the potential of these dipoles towards orthogonal reaction with azides, allowing efficient double ligation reactions, was discovered. A versatile process to access benzo[c]thiophenes, in an unprecedented divergent fashion, was developed and provides a new entry to unconventional polyaromatic thiophenes.

Design and Synthesis of Iminosydnones for Fast Click and Release Reactions with Cycloalkynes.

Emerging applications in the field of chemical biology are currently limited by the lack of bioorthogonal reactions allowing both removal and linkage of chemical entities on complex biomolecules. We recently discovered a novel reaction between iminosydnones and strained alkynes leading to two products resulting from ligation and fragmentation of iminosydnones under physiological conditions. We now report the synthesis of a panel of substituted iminosydnones and the structure reactivity relationship between these compounds and strained alkyne partners. This study identified the most relevant substituents, which allow to increase the rate of the transformation and to develop a bifunctional cleavable linker with improved kinetics.