Synthesis and characterization of bimodal probes for MRI and optical imaging

L’Imagerie par Résonance Magnétique (IRM) offre une excellente résolution à l’échelle macroscopique alors que l’imagerie optique lui est parfaitement complémentaire car elle dispose d’une haute résolution à l’échelle microscopique ainsi que d’une forte sensibilité. Les complexes de gadolinium(III) ont déjà prouvé leur efficacité en tant qu’agents de contraste IRM et d’autres lanthanides luminescents émettant dans le proche infrarouge conviennent pour l’imagerie optique. Des complexes de lanthanides bishydratés à motif pyridine montrant des résultats très prometteurs pour les deux types d’imagerie ont été développés précédemment au laboratoire. Afin d’améliorer leurs propriétés optiques, des ligands à motifs isoquinoléines ont été synthétisés. Leurs complexes de lanthanides montrent des propriétés magnétiques prometteuses et des constantes thermodynamiques qui démontrent leur faible toxicité in vitro. La longueur d’onde d’excitation et les rendements quantiques des complexes d’Yb3+ et de Nd3+ ont été augmentés pour permettre d’obtenir des images de luminescence et d’envisager des applications in vivo.Afin d’améliorer davantage ces propriétés optiques, la synthèse de ligands à motif 2-azaanthraquinone a été entreprise mais l’instabilité chimique de ces molécules n’a pas permis d’isoler les ligands désirés.Cette approche bimodale a été appliquée à la conception de sondes sensibles au zinc. La synthèse de complexes de Gd3+ à motifs pyridines adaptés permet une detection relaxométrique qualitative et sélective de ce cation. Cependant, l’absence de variation du nombre d’hydratation ne permet pas la détection par luminescence. De légères modifications chimiques sur les ligands devraient permettre d’atteindre cet objectif.Among the state-of-the-art imaging techniques, Magnetic Resonance Imaging (MRI) offers an excellent macroscopic scale resolution whereas optical imaging shows high microscopic scale resolution and great sensitivity. Gadolinium complexes have already proved their efficiency as MRI contrast agents whereas other lanthanide cations emitting in the near infrared may suit for optical imaging purposes. Pyridine-based lanthanide complexes which showed promising results as bimodal probes have previously been developed. In the objective of improving their optical properties, isoquinoline-based ligands have been synthesized. The lanthanide complexes show promising magnetic properties and their thermodynamic stability presumes in vitro low toxicity. Excitation wavelengths and quantum yields of both Nd3+ and Yb3+ complexes have been improved to obtain luminescence images and to foresee in vivo applications. In order to further improve the optical properties, attempts to synthesize 2-azaanthraquinone-based ligands have been made.The desired ligands could not have been isolated due to their chemical instability. This bimodal approach has been applied to the design of smart probes sensitive to zinc. The qualitative and selective detection of the latter has been realized thanks to Gd3+ complexes with adapted pyridine-based ligands. However, the detection by luminescence could not be achieved. Slight chemical modifications on the ligands should allow reaching this goal

Synthèse et caractérisation de sondes bimodales pour l'IRM et l'imagerie optique

Among the state-of-the-art imaging techniques, Magnetic Resonance Imaging (MRI) offers an excellent macroscopic scale resolution whereas optical imaging shows high microscopic scale resolution and great sensitivity. Gadolinium complexes have already proved their efficiency as MRI contrast agents whereas other lanthanide cations emitting in the near infrared may suit for optical imaging purposes. Pyridine-based lanthanide complexes which showed promising results as bimodal probes have previously been developed. In the objective of improving their optical properties, isoquinoline-based ligands have been synthesized. The lanthanide complexes show promising magnetic properties and their thermodynamic stability presumes in vitro low toxicity. Excitation wavelengths and quantum yields of both Nd3+ and Yb3+ complexes have been improved to obtain luminescence images and to foresee in vivo applications. In order to further improve the optical properties, attempts to synthesize 2-azaanthraquinone-based ligands have been made.The desired ligands could not have been isolated due to their chemical instability. This bimodal approach has been applied to the design of smart probes sensitive to zinc. The qualitative and selective detection of the latter has been realized thanks to Gd3+ complexes with adapted pyridine-based ligands. However, the detection by luminescence could not be achieved. Slight chemical modifications on the ligands should allow reaching this goal.L’Imagerie par Résonance Magnétique (IRM) offre une excellente résolution à l’échelle macroscopique alors que l’imagerie optique lui est parfaitement complémentaire car elle dispose d’une haute résolution à l’échelle microscopique ainsi que d’une forte sensibilité. Les complexes de gadolinium(III) ont déjà prouvé leur efficacité en tant qu’agents de contraste IRM et d’autres lanthanides luminescents émettant dans le proche infrarouge conviennent pour l’imagerie optique. Des complexes de lanthanides bishydratés à motif pyridine montrant des résultats très prometteurs pour les deux types d’imagerie ont été développés précédemment au laboratoire. Afin d’améliorer leurs propriétés optiques, des ligands à motifs isoquinoléines ont été synthétisés. Leurs complexes de lanthanides montrent des propriétés magnétiques prometteuses et des constantes thermodynamiques qui démontrent leur faible toxicité in vitro. La longueur d’onde d’excitation et les rendements quantiques des complexes d’Yb3+ et de Nd3+ ont été augmentés pour permettre d’obtenir des images de luminescence et d’envisager des applications in vivo.Afin d’améliorer davantage ces propriétés optiques, la synthèse de ligands à motif 2-azaanthraquinone a été entreprise mais l’instabilité chimique de ces molécules n’a pas permis d’isoler les ligands désirés.Cette approche bimodale a été appliquée à la conception de sondes sensibles au zinc. La synthèse de complexes de Gd3+ à motifs pyridines adaptés permet une detection relaxométrique qualitative et sélective de ce cation. Cependant, l’absence de variation du nombre d’hydratation ne permet pas la détection par luminescence. De légères modifications chimiques sur les ligands devraient permettre d’atteindre cet objectif

New Catalytic Reactions using CO2_2 for Radiolabeling of Tracers

International audienceCO$_2$, well known as a greenhouse gas responsible for global warming and considered as a cheap, non-toxic, renewable C1 building block, is by far the most accessible primary source of carbon for all radiolabeled compounds. However, its kinetic and thermodynamic stability significantly restrains potential applications. Broader availability of secondary labeled carbon sources would therefore grant access to a wide array of highly functionalized bioactive tracers. Indeed, $^{14}$C labelled compounds are commonly required during the development process of drugs where as $^{11}$C molecules are key radiotracers for positron emission tomography (PET) imaging.In this context, we have been investigating CO$_2$ reduction into methoxy derivatives followed by a Suzuki cross-coupling to generate anisoles moieties. Selective borane mediated organocatalytic CO2 reduction into OMe synthons has been previously disclosed by our group. However, very few couplings between methanol derivatives and aryl halides have been reported to date. Inspired by Novak’s work, an innovative, efficient palladium catalyzed cross-coupling between methoxyboranes and aryl bromides has been developed under mild conditions. Working in a double chamber set-up allows both reactions to becompatible. This strategy is further expected to be tested on therapeutic targets and ideally transposed to $^{14}$C and $^{11}$C isotope

Zinc-Mediated Double Addition on Functionalized Nitriles

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Catalytic methoxylation of aryl halides using 13^{13}C- and 14^{14}C-labeled CO2_2

International audienceThe functionalization of carbon dioxide (CO$_2$) into high-value building blocks is a relevant topic in carbon isotope labeling, where CO$_2$ is the primary carbon source. A catalytic methoxylation of aryl halides directly from [$^{13}$C] and [$^{14}$C]CO$_2$ is reported. Relying on the intermediacy of the methoxyborane BBN-OCH$_3$, as new secondary nucleophilic labeled source, this strategy allowed labeling of a series of substrates, including challenging pharmaceuticals containing tertiary alkyl amine substituents

11 C-glyburide PET imaging unveils the negligible brain penetration of glyburide in humans

International audienceKimberly and coworkers reported the beneficial effects of intravenous glyburide on the clinical outcome of brain edema. We developed the carbon-11 radiolabeled analogue of glyburide to study the body distribution of this compound using PET imaging. In a healthy subject, the brain distribution of 11C-glyburide matched the cerebral blood volume suggesting negligible blood-brain barrier (BBB) penetration. This clinical observation corroborates preclinical findings suggesting that local changes in BBB structure and function are required for targeted delivery and favorable effects of glyburide to the injured brain tissue while minimizing potential side effects to the healthy brain

Successive addition of two different Grignard reagents to nitriles: access to α,α-disubstituted propargylamine derivatives

International audienceThe successive addition of two different Grignard reagents to acyl cyanohydrins was performed with success by taking advantage of the low reactivity of alkynyl Grignard reagents. The experimental conditions were adjusted so that they were not reactive during the first addition step, but reactive only in the second one. The synthetic utility of the prepared compounds was validated by the preparation of chiral quaternary α-amino acids

An original radio-biomimetic approach to synthesize radiometabolites for PET imaging

International audienceTo fully exploit the potential of positron emission tomography (PET) imaging to assess drug distribution and pharmacokinetics in the central nervous system, the contribution of radiometabolites to the PET signal has to be determined for correct interpretation of data. However, radiosynthesis and extensive study of radiometabolites are rarely investigated and very challenging for complex drugs. Therefore, an original radio-biomimetic (RBM) approach was developed to rapidly synthesize radiometabolites and non-invasively investigate their kinetics with PET imaging. This method enabled the challenging radiosynthesis of [11C]nor-buprenorphine ([11C]nor-BUP), the main metabolite of buprenorphine (BUP) which has been identified as a substrate of the P-glycoprotein (P-gp) transport function at the blood-brain barrier (BBB). Biomimetic conditions using cytochromes P450 3A4 to convert BUP into nor-BUP were optimized taking into account the short half-life of carbon-11 (t1/2 = 20.4 min). Those conditions afforded 32% of conversion within 20 min and were applied to the biomimetic radiosynthesis of [11C]nor-BUP from [11C]BUP. Automated radiosynthesis of [11C]BUP according to a procedure described in the literature followed by optimized RBM conditions afforded [11C]nor-BUP in 1.5% decay-corrected radiochemical yield within 90 min and 90 ± 15 GBq/μmol molar activity. HPLC quality control showed chemical and radiochemical purities above 98%. To demonstrate the applicability of the RBM approach to preclinical studies, brain PET images in rats showed a drastic lower uptake of [11C]nor-BUP (0.067 ± 0.023%ID/cm-3) compared to [11C]BUP (0.436 ± 0.054%ID/cm-3). P-gp inhibition using Tariquidar increased the brain uptake of [11C]nor-BUP (0.557 ± 0.077%ID/cm-3)

Automated two-step manufacturing of [11C]glyburide radiopharmaceutical for PET imaging in humans

International audienceIntroduction: Glyburide is an approved anti-diabetes drug binding to the sulfonylurea receptors-1 (SUR-1) and substrate of solute carrier (SLC) transporters, which can be isotopically radiolabelled with carbon-11 for PET imaging. The aim of this work is to present an original and reproducible automated radiosynthesis of [11C]glyburide and a full European Pharmacopeia 9.7 compliant quality control to use [11C]glyburide in PET imaging clinical trials.Methods: Different conditions were explored to afford non-radioactive glyburide by one or two-step methylation. These experiments were monitored by UPLC-MS. The optimized process was applied to the automated radiosynthesis of [11C]glyburide using a TRACERlab® FX C Pro. A complete quality control according to Pharmacopeia guidelines was realized.Results: One-step methylation revealed regioselectivity issues as methylation occurred preferentially on the sulfonylurea moiety. Two-step approach by methylation followed by reaction with cyclohexyl isocyanate afforded glyburide without formation of methylated side products. Ready-to-inject [11C]glyburide was obtained in 5% non-decay corrected radiochemical yield and 110 ± 20 GBq/μmol molar activity within 40 min (n = 8). [11C]Glyburide quality control was compliant with the Pharmacopeia requirements.Conclusions: We have described a highly reproducible and automated two-step radiosynthesis of [11C]glyburide which was qualified as a radiopharmaceutical for human injection. This whole manufacturing process is currently being used to conduct a clinical trial to elucidate the hepatic transport of drugs.Advances in knowledge: Compared to previously reported radiosynthesis of [11C]glyburide, this work provides an original and reproducible approach which can be transferred to any PET centre interested in using this radiotracer for preclinical or clinical imaging.Implication for patient care: This work provides a method to manufacture [11C]glyburide for human PET imaging. This radiopharmaceutical could be used to elucidate the role of transporters in drug exposure of different organs or to monitor brain recovery after central nervous system (CNS) injuries