Publications by authors named "Marion Jean"

60 Publications

Synthesis and Optical Resolution of Configurationally Stable Zwitterionic Pentacoordinate Silicon Derivatives.

Angew Chem Int Ed Engl 2021 Nov 12. Epub 2021 Nov 12.

Institut Parisien de Chimie Moléculaire, Sorbonne Université, CNRS, 4 Place Jussieu, CC 229, F-75252, Paris Cedex 05, France.

Stereogenic silicon centres in functionalised tetracoordinated organosilanes generally exhibit very high configurational stability under neutral conditions. This stability drops completely when higher coordination states of the silicon centre are reached due to rapid substituent exchange. Herein we describe the synthesis of chiral and neutral pentacoordinate silicon derivatives with high configurational stability. The zwitterionic nature of these air- and water-tolerant species allows for the first time their direct and efficient optical resolution using chiral HPLC techniques. By means of this method, pentacoordinate silicon compounds exhibiting high Si-inversion have been obtained as single enantiomers. A rationalisation of the enantiomerisation pathways has been also carried out using DFT calculations.
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http://dx.doi.org/10.1002/anie.202113836DOI Listing
November 2021

Transition metal complexes bearing atropisomeric saturated NHC ligands.

Chirality 2021 Nov 5. Epub 2021 Nov 5.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France.

From achiral imidazolinium salts, chiral transition metal complexes containing an N-heterocyclic carbene (NHC) ligand were prepared (metal = palladium, copper, silver, gold, rhodium). Axial chirality in these complexes results from the formation of the metal-carbene bond leading to the restriction of rotation of dissymmetric N-aryl substituents about the C-N bond. When these complexes exhibited a sufficient configurational stability, a resolution by chiral high-performance liquid chromatography (HPLC) on preparative scale enabled isolation of enantiomers with excellent enantiopurities (>99% ee) and good yields. A study of the enantiomerization barriers revealed the effect of the backbone nature as well as the type of transition metal on its values. Nevertheless, the evaluation of palladium-based complexes in asymmetric intramolecular α-arylation of amides demonstrated that the ability to induce an enantioselectivity cannot be correlated to the configurational stability of the precatalysts.
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http://dx.doi.org/10.1002/chir.23378DOI Listing
November 2021

Hemicryptophane Cages with a -Symmetric Cyclotriveratrylene Unit.

J Org Chem 2021 Nov 1;86(21):15055-15062. Epub 2021 Oct 1.

Aix Marseille Univ, CNRS, Centrale Marseille iSm2, 13284 Marseille, France.

Two new hemicryptophanes combining a cyclotriveratrylene unit with either an aminotrisamide or a tris(2-aminoethyl)amine (tren) moiety have been synthesized. Although a conventional synthesis approach was used, the molecular cages obtained are devoid of the expected symmetry. NMR analyses and X-ray crystal structure determination showed that these hemicryptophanes exhibited symmetry due to the unusual arrangement of the substituents of the cyclotriveratrylene unit. This unprecedented arrangement is related to a change in the regioselectivity of the Friedel-Crafts reactions that led to the CTV cap. This constitutes an original approach to access enantiopure chiral molecular cages with low symmetry.
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http://dx.doi.org/10.1021/acs.joc.1c01731DOI Listing
November 2021

Exciton coupling chirality in helicene-porphyrin conjugates.

Chem Commun (Camb) 2021 Oct 14;57(82):10743-10746. Epub 2021 Oct 14.

Univ Rennes, CNRS, ISCR - UMR 6226, F-35000 Rennes, France.

Enantiopure helicene-porphyrin conjugates were prepared. They show strong changes in their circular dichroic response as compared to classical helicene derivatives, with highly intense bisignate Exciton Coupling (EC) signal and Δ values up to 680 M cm for the Soret band. They also display circularly polarized fluorescence in the (far-)red region, with dissymmetry factors up to 7 × 10.
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http://dx.doi.org/10.1039/d1cc03314jDOI Listing
October 2021

Are the Physical Properties of [email protected] Complexes Easily Predictable? The Case of - and -Tris-aza-Cryptophanes.

J Org Chem 2021 Jun 25;86(11):7648-7658. Epub 2021 May 25.

Laboratoire de Chimie de l'ENS Lyon, (UMR 5182 CNRS-ENS-Université), Université Claude Bernard Lyon 1, F69342 Lyon, France.

We report the synthesis and optical resolution of -symmetrical tris-aza-cryptophanes - and -, as well as the study of their interaction with xenon hyperpolarized Xe NMR. These molecular cages are close structural analogues of the two well-known cryptophane-A (; chiral) and cryptophane-B (; achiral) diastereomers since these new compounds differ only by the presence of three nitrogen atoms grafted onto the same cyclotribenzylene unit. The assignment of their relative (syn vs anti) and absolute configurations was made possible, thanks to the combined use of quantum calculations at the density functional theory level and vibrational circular dichroism spectroscopy. More importantly, our results show that despite the large structural similarities with cryptophane-A () and -B (), these two new compounds show a very different behavior in the presence of xenon in organic solutions. These results demonstrate that prediction of the physical properties of the [email protected] complexes, only based on structural parameters, remains extremely difficult.
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http://dx.doi.org/10.1021/acs.joc.1c00701DOI Listing
June 2021

On the Enantioselective Phosphoric-Acid-Catalyzed Hantzsch Synthesis of Polyhydroquinolines.

Org Lett 2021 05 27;23(9):3394-3398. Epub 2021 Apr 27.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille 13397, France.

A reinvestigation of a chiral phosphoric-acid-catalyzed four-component Hantzsch enantioselective synthesis of polyhydroquinolines reported in 2009 is presented. In our hands, when the reaction was performed with fidelity to the original report using a chiral enantiopure phosphoric acid catalyst, no enantioselectivity was observed. Unlike in the original report, enantioselectivity results are backed by baseline separation of the enantiomers by HPLC analyses on chiral stationary phase with UV and chiroptical detection.
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http://dx.doi.org/10.1021/acs.orglett.1c00866DOI Listing
May 2021

Synthesis and Properties of Partially Saturated Fluorenyl-Derived [n]Helicenes Featuring an Overcrowded Alkene.

Chemistry 2021 May 30;27(28):7722-7730. Epub 2021 Apr 30.

LCC-CNRS, Université de Toulouse, CNRS, 31077, Toulouse, France.

The straightforward, multigram-scale synthesis of the partially saturated H -fluoreno[n]helicenes (n=5 or 7) featuring a central, overcrowded alkene is described. The key cyclization step was based on an intramolecular McMurry reaction from the corresponding 1,5-diketones. Chiral stationary phase HPLC analysis and isomer separation indicate that each helicenic compound is constituted of three diastereoisomers at room temperature, i. e. the configurationally stable (R,R,P)/(S,S,M) pair of enantiomers and an apparently achiral compound resulting from the rapid interconversion between the (R,S,P) and (S,R,M) enantiomers. The partially saturated H -fluoreno[n]helicenes are oxidatively aromatized to give an efficient access to the corresponding fluoreno[n]helicenes. The chiroptical properties (vibrational and electronic circular dichroism) of the chiral, enantiopure compounds have been measured and analyzed by quantum-chemical calculations, confirming their helicoidal nature.
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http://dx.doi.org/10.1002/chem.202100150DOI Listing
May 2021

Circularly Polarized Fluorescent Helicene-Boranils: Synthesis, Photophysical and Chiroptical Properties.

Chemistry 2021 May 22;27(29):7959-7967. Epub 2021 Apr 22.

Univ Rennes, CNRS, ISCR-UMR 6226, Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.

Mono- and di-boranil-substituted helicenes were prepared by BF -borylation of the corresponding anils, readily synthesized by condensation of 2-amino- and 2,15-diamino-helicenes with 4-(diethylamino)salicylaldehyde. After enantiomeric resolution using HPLC, their chiroptical properties including circularly polarized fluorescence in solution and in PMMA films were investigated and rationalized with the help of NMR, X-ray and quantum-chemical calculations.
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http://dx.doi.org/10.1002/chem.202100356DOI Listing
May 2021

Synthesis of Protected 3,4- and 2,3-Dimercaptophenylalanines as Building Blocks for -Peptide Synthesis and Incorporation of the 3,4-Analogue in a Decapeptide Using Solid-Phase Synthesis.

J Org Chem 2021 02 24;86(3):2210-2223. Epub 2021 Jan 24.

School of Applied and Interdisciplinary Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.

3,4-Dimercaptophenylalanines and 2,3-dimercaptophenylalanines have been synthesized for the first time by nucleophilic substitution of a protected aminomalonate on 3,4- and 2,3-dimercaptobenzyl bromide derivatives. The dithiol functions were protected as thioketals, and the key precursors, diphenylthioketal-protected dimercaptobenzyl bromides, were synthesized via two distinct routes from either dihydroxy benzoates or toluene-3,4-dithiol. Racemic mixtures of the fully protected amino acids were separated by chiral HPLC into the corresponding enantiomers. The absolute configuration of both 3,4- and 2,3-analogues could be assigned based on X-ray crystallography and VCD/DFT measurements. Thioketal groups were deprotected upon reaction with mercury oxide and aqueous tetrafluoroboric acid followed by treatment with HS gas under an argon atmosphere to obtain the corresponding dimercapto amino acids. The optically pure l--protected 3,4-analogue (- enantiomer) was successfully incorporated into a decapeptide using standard solid-phase peptide synthesis. Therefore, dithiolene-functionalized peptides are now accessible from a simple synthetic procedure, and this should afford new molecular tools for research into the catalysis, diagnostic, and nanotechnology fields.
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http://dx.doi.org/10.1021/acs.joc.0c02359DOI Listing
February 2021

Epimerization-Free C-Term Activation of Peptide Fragments by Ball Milling.

Org Lett 2021 02 4;23(3):631-635. Epub 2021 Jan 4.

IBMM, Univ Montpellier, CNRS, ENSCM, Montpellier, France.

Peptides were produced in high yields and, if any, very low epimerization, by mechanochemical coupling of peptide fragments containing highly epimerization-prone and/or highly hindered amino acids at C-term. Ball milling was clearly identified as the key element enabling one to obtain such results.
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http://dx.doi.org/10.1021/acs.orglett.0c03209DOI Listing
February 2021

Two-Photon Absorbing AIEgens: Influence of Stereoconfiguration on Their Crystallinity and Spectroscopic Properties and Applications in Bioimaging.

ACS Appl Mater Interfaces 2020 Dec 20;12(49):55157-55168. Epub 2020 Nov 20.

Univ. Lyon, ENS Lyon, CNRS, Université Lyon 1, Laboratoire de Chimie, UMR 5182, 46 Allée d'Italie, 69364 Lyon, France.

This paper aims at designing chromophores with efficient aggregation-induced emission (AIE) properties for two-photon fluorescence microscopy (2PFM), which is one of the best-suited types of microscopy for the imaging of living organisms or thick biological tissues. Tetraphenylethylene (TPE) derivatives are common building blocks in the design of chromophores with efficient AIE properties. Therefore, in this study, extended TPE AIEgens specifically optimized for two-photon absorption (2PA) are synthesized and the resulting (/) isomers are separated using chromatography on chiral supports. Comparative characterization of the AIE properties is performed on the pure () and () isomers and the mixture, allowing us, in combination with powder X-ray diffraction and solid-state NMR, to document a profound impact of crystallinity on solid-state fluorescence properties. In particular, we show that stereopure AIEgens form aggregates of superior crystallinity, which in turn exhibit a higher fluorescence quantum yield compared to diastereoisomers mixtures. Preparation of stereopure organic nanoparticles affords very bright fluorescent contrast agents, which are then used for cellular and intravital two-photon microscopy on human breast cancer cells and on zebrafish embryos.
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http://dx.doi.org/10.1021/acsami.0c15810DOI Listing
December 2020

Axially and Helically Chiral Cationic Radical Bicarbazoles: SOMO-HOMO Level Inversion and Chirality Impact on the Stability of Mono- and Diradical Cations.

J Am Chem Soc 2020 Nov 17. Epub 2020 Nov 17.

Université Rennes, CNRS, ISCR-UMR 6226, Rennes F-35000, France.

We report persistent chiral organic mono- and diradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the type of chirality, namely, axial versus helical. An unusual chemical stability was observed for sterically unprotected axial bicarbazole radical in comparison with monocarbazole and helical bicarbazole ones. Such results were experimentally and theoretically investigated, revealing an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest (doubly) occupied molecular orbital (HOMO) in both axial and helical bicarbazole monoradicals along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings allowed us to explore in depth the SOMO-HOMO inversion (SHI) in chiral radical molecular systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare a persistent, intrinsically chiral, diradical which notably displayed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by magnetometry experiments.
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http://dx.doi.org/10.1021/jacs.0c08948DOI Listing
November 2020

Simultaneous Control of Central and Helical Chiralities: Expedient Helicoselective Synthesis of Dioxa[6]helicenes.

J Am Chem Soc 2020 09 8;142(38):16199-16204. Epub 2020 Sep 8.

Aix Marseille Université, CNRS, Centrale Marseille, iSm2, Marseille, France.

An expedient synthesis of a new family of configurationally stable dioxa[6]helicenes was established using a sequential helicoselective organocatalyzed heteroannulation/eliminative aromatization via enantioenriched fused 2-nitro dihydrofurans featuring both central and helical chiralities. Starting from simple achiral precursors, a broad range of these previously unknown chiral heterocyclic scaffolds were obtained with good efficiency, and their aromatization proceeded with very high enantiopurity retention in most cases.
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http://dx.doi.org/10.1021/jacs.0c07995DOI Listing
September 2020

Chiral Diketopyrrolopyrrole-Helicene Polymer With Efficient Red Circularly Polarized Luminescence.

Front Chem 2020 9;8:237. Epub 2020 Apr 9.

Univ Rennes, CNRS, Institut des Sciences Chimiques de Rennes, ISCR-UMR 6226, Rennes, France.

Chiral diketopyrrolopyrrole (DPP)-helicene polymers were synthesized to develop efficient red circularly polarized (CP) light emitters. These original chiral dyes display intense electronic circular dichroism (ECD) and CP luminescence (CPL) in the far-red spectral region owing to the presence of excitonic coupling between achiral DPPs within the chiral environment of the polymeric structure. This work affords an interesting example illustrating the potential of π-conjugated helical polymers for chiral optoelectronic applications.
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http://dx.doi.org/10.3389/fchem.2020.00237DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7160364PMC
April 2020

Enantio- and Substrate-Selective Recognition of Chiral Neurotransmitters with -Symmetric Switchable Receptors.

Org Lett 2020 02 27;22(3):891-895. Epub 2020 Jan 27.

Aix Marseille Univ., CNRS, Centrale Marseille, iSm2 , Marseille 13397 , France.

We report on the synthesis of -symmetric enantiopure cage molecules , which exhibit remarkable to exclusive enantioselective recognition properties toward chiral ammonium neurotransmitters. Strong changes in the substrate selectivity are also observed when different stereoisomers of are used. Furthermore, protonation/deprotonation induces a reversible modification of the conformation of , which switches from an imploded to an inflated form, leading to ejection and reuptake of the guest initially encaged inside the cavity.
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http://dx.doi.org/10.1021/acs.orglett.9b04440DOI Listing
February 2020

Enantiopure encaged Verkade's superbases: Synthesis, chiroptical properties, and use as chiral derivatizing agent.

Chirality 2020 02 17;32(2):139-146. Epub 2019 Dec 17.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France.

Verkade's superbases, entrapped in the cavity of enantiopure hemicryptophane cages, have been synthesized with enantiomeric excess (ee) superior to 98%. Their absolute configuration has been determined by using electronic circular dichroism (ECD) spectroscopy. These enantiopure encaged superbases turned out to be efficient chiral derivatizing agents for chiral azides, underlining that the chirality of the cycloveratrylene (CTV) macrocycle induces different magnetic and chemical environments around the phosphazide functions.
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http://dx.doi.org/10.1002/chir.23156DOI Listing
February 2020

From Prochiral N-Heterocyclic Carbenes to Optically Pure Metal Complexes: New Opportunities in Asymmetric Catalysis.

J Am Chem Soc 2020 01 23;142(1):93-98. Epub 2019 Dec 23.

Aix Marseille Univ , CNRS, Centrale Marseille, iSm2 , Marseille , France.

Well-defined optically pure transition metal (TM) complexes bearing - and -symmetric N-heterocyclic carbene (NHC) ligands were prepared from prochiral NHC precursors. As predicted by DFT calculations, our strategy capitalizes on the formation of a metal-carbene bond which induces an axis of chirality. Configurationally stable atropisomers of various NHC-containing TM complexes were isolated by preparative HPLC on a chiral stationary phase in good yields and excellent optical purities (up to 99.5% ee). The carbene transfer from an optically pure Cu complex to a gold or palladium center reveals, for the first time, a full stereoretentivity, supporting the hypothesis of an associative mechanism for the transmetalation. The potential of these new chiral TM complexes was illustrated in asymmetric catalysis with up to 98% ee.
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http://dx.doi.org/10.1021/jacs.9b12698DOI Listing
January 2020

Synthesis and chiroptical properties of organometallic complexes of helicenic N-heterocyclic carbenes.

Chirality 2019 12 31;31(12):1005-1013. Epub 2019 Oct 31.

Intitut des Sciences Chimiques de Rennes, ISCR-UMR 6226, Rennes, France.

Novel [4, 6]helicenes (4a,b) bearing a fused imidazolium unit have been prepared from [4, 6]helicene-2,3-di-n-propyl-amines 3a,b. The in situ formation of N-heterocyclic carbene (NHC) derivatives followed by their complexation to iridium(I) or rhodium(I) gave access to complexes 1a, 1'a, and 1b, containing mono-coordinated helicene-NHC, chloro and COD (COD = 1,5-cyclooctadiene) ligands. Ir and Rh complexes 1a and 1'a were characterized by X-ray crystallography. HPLC and NMR analyses showed that Ir(I) complex 1b existed as a mixture of two diastereomeric complexes corresponding to enantiomeric pairs M-(-)/P-(+)-1b and M-(-)/P-(+)-1b which differ by the position of COD through space. The chiroptical properties (electronic circular dichroism and optical rotation) of the four stereoisomers were measured. These complexes were also tested as catalysts in a transfer hydrogenation reaction.
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http://dx.doi.org/10.1002/chir.23143DOI Listing
December 2019

Chiroptical fingerprints to characterize lavender and lavandin essential oils.

J Chromatogr A 2020 Jan 24;1610:460568. Epub 2019 Sep 24.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France. Electronic address:

Polarimetric HPLC detector was used to acquire chromatograms for lavender/lavandin essentials oils (EOs) on different chiral stationary phases. Amylose tris-(3,5-dichloro-phenylcarbamate) immobilized on silica allowed the best separation of the numerous chiral phytomarkers and was thus used to obtain a chiroptical fingerprint for 158 samples of French lavender/lavandin EOs. Samples from different varieties (Abrial, Fine, Grosso, Maillette, Matherone, Sumian and Super) were collected over three crop years (2012, 2013 and 2014), from four different locations in France (``Alpes-de-Haute-Provence'', ``Ardèche'', ``Drôme'' and ``Vaucluse'') to take into account seasonal and geographic origin variations. The combination of the polarimetric fingerprints and chemometrics was tested for varietal discrimination. We assessed the ability to discriminate the EOs samples and their variety by partial least squares-discriminant analysis (PLS-DA). This case study showed that liquid chromatography with polarimetric detector in tandem with chemometric analysis was efficient to differentiate the varietal origins of French lavender/lavandin EOs.
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http://dx.doi.org/10.1016/j.chroma.2019.460568DOI Listing
January 2020

Synthesis, resolution, and chiroptical properties of hemicryptophane cage controlling the chirality of propeller arrangement of a C triamide unit.

Chirality 2019 Nov 2;31(11):910-916. Epub 2019 Sep 2.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France.

The five-steps synthesis of a hemicryptophane cage combining a benzene-1,3,5-tricarboxamide unit and a cyclotriveratrylene (CTV) moiety is described. Chiral high-performance liquid chromatography (HPLC) was used to resolve the racemic mixture. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental electronic circular dichroism (ECD) spectra with the calculated ones. X-ray molecular structures reveal that the capped benzene-1,3,5-tricarboxamide unit adopts a structurally chiral conformation in solid state: the chirality of CTV moiety controls the Λ or Δ orientation of the three amides.
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http://dx.doi.org/10.1002/chir.23131DOI Listing
November 2019

Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties.

Chemistry 2019 Nov 9;25(63):14364-14369. Epub 2019 Oct 9.

Aix Marseille Univ, CNRS, Centrale Marseille, ISM2, 13397, Marseille, France.

Cyclobis[n]helicenes (n=3 or 5) are chiral D -symmetric π-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five different cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (>200 kJ mol ). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their unusual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.
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http://dx.doi.org/10.1002/chem.201902637DOI Listing
November 2019

Chiroptical study of cryptophanes subjected to self-encapsulation.

Chirality 2019 Jul 28;31(7):481-491. Epub 2019 May 28.

Univ Lyon, Ens de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie, Lyon, France.

In 1,1,2,2-tetrachloroethane-d , the Xe NMR spectrum of the [email protected] complex bearing seven acetate groups ([email protected] complex) shows an unusually broad signal compared with that of its congeners (Chapellet, LL. et al. J. Org. Chem. 2015;80:6143-6151). To interpret this unexpected behaviour, a H NMR analysis and a thorough study of the chiroptical properties of 1 as a function of the nature of the solvent have been performed. The H NMR spectra of 1 reveal that a self-encapsulation phenomenon takes place in DMSO-d and 1,1,2,2-tetrachloroethane-d solvents. Thanks to the separation of the two enantiomers of 1 by HPLC on chiral stationary phase, the two enantiomers of 1 have been studied in detail by polarimetry, electronic (ECD), and vibrational (VCD) circular dichroism spectroscopies. Except for ECD spectroscopy, these chiroptical techniques reveal spectroscopic changes as a function of the nature of the solvent. For instance, in DMSO and 1,1,2,2-tetrachloroethane, in which the self-encapsulation phenomenon takes place, the sign of the specific optical rotation of [CD(-) ]-1 and [CD(+) ]-1 is changed. These results have then been compared with those obtained with cryptophane-223 bearing only one acetate group on the propylenedioxy linker (compound 2) and with cryptophane-223 bearing six acetate groups (compound 3). A self-encapsulation phenomenon is also observed with compound 2. Finally, compounds 2 and 3 show different chiroptical properties compared with those obtained with the two enantiomers of compound 1.
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http://dx.doi.org/10.1002/chir.23079DOI Listing
July 2019

Bis-4-aza[6]helicene: A Bis-helicenic 2,2'-Bipyridine with Chemically Triggered Chiroptical Switching Activity.

J Org Chem 2019 May 18;84(9):5383-5393. Epub 2019 Apr 18.

Université Rennes, Institut des Sciences Chimiques de Rennes, UMR CNRS , 6226 Campus de Beaulieu , 35042 Rennes Cedex , France.

A novel enantiopure bis-helicenic 2,2'-bipyridine system was prepared using a Negishi coupling. Thanks to the bipyridine unit, the coordination with Zn and protonation processes were studied, revealing efficient tuning of photophysical (UV/visible and emission) and chiroptical properties (electronic circular dichroism and circularly polarized emission) of the system. The coordination/decoordination and protonation/deprotonation processes appeared reversible, thus constituting novel chiroptical switches.
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http://dx.doi.org/10.1021/acs.joc.9b00389DOI Listing
May 2019

Effect of substituents on the configurational stability of the stereogenic nitrogen in metal(II) complexes of α-amino acid Schiff bases.

Chirality 2019 05 27;31(5):401-409. Epub 2019 Mar 27.

Department of Organic Chemistry I, Faculty of Chemistry, University of the Basque Country, San Sebastián, Spain.

Herein, we report a general method for quantitative measurement of the configurational stability of the stereogenic nitrogen coordinated to M (II) in the corresponding square planar complexes. This stereochemical approach is quite sensitive to steric and electronic effects of the substituents and shown to work well for Ni(II), Pd(II), and Cu(II) complexes. Structural simplicity of the compounds used, coupled with high sensitivity and reliability of experimental procedures, bodes well for application of this approach in evaluation of chemical stability and stereochemical properties of newly designed chiral ligands for general asymmetric synthesis of tailor-made amino acids.
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http://dx.doi.org/10.1002/chir.23066DOI Listing
May 2019

High-Relaxivity Gd(III)-Hemicryptophane Complex.

Org Lett 2019 04 11;21(7):1999-2003. Epub 2019 Mar 11.

Aix Marseille Univ , CNRS, Centrale Marseille, iSm2 , Marseille , France.

The polytopic hemicryptophane cage HC1 combining a cyclotriveratrylene (CTV) unit and a tris(2-aminoethyl)amine (tren) moiety connected by three 2-hydroxyisophthalamide linkers was synthesized in 12 steps. The resulting highly functionalized covalent host is soluble in aqueous medium and has been used to complex Gd(III) ion. The Gd(III)@HC1 complex presents promising relaxivity properties when compared to the clinically used Dotarem MRI agent.
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http://dx.doi.org/10.1021/acs.orglett.9b00081DOI Listing
April 2019

Umpolung Reactivity of in Situ Generated Phosphido-Boranes: An Entry to P-Stereogenic Aminophosphine-Boranes.

J Org Chem 2019 Apr 12;84(7):4551-4557. Epub 2019 Mar 12.

Aix Marseille Univ, CNRS, Centrale Marseille, iSm2 , Marseille 13397 , France.

The synthesis of P-stereogenic aminophosphine-boranes has been developed on the basis of umpolung reactivity of in situ generated alkylarylphosphido-boranes, which are normally configurationally unstable intermediates. In our case, their high configurational stability was due to the slow release of the hydroxyalkyl protecting group, together with the fast formation of the iodophosphanylborane in the presence of N-iodosuccinimide. The subsequent substitution reaction was found to proceed in moderate to good yields and in a very high stereospecifity (es) using a variety of amines as nucleophiles.
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http://dx.doi.org/10.1021/acs.joc.9b00333DOI Listing
April 2019

Unique Class of Enantiopure N-Heterocyclic Carbene Half-Sandwich Iridium(III) Complexes with Stable Configurations: Probing Five-Membered versus Six-Membered Iridacycles.

Inorg Chem 2019 Mar 18;58(5):2930-2933. Epub 2019 Feb 18.

Sorbonne Université, Campus Pierre et Marie Curie, Institut Parisien de Chimie Moléculaire (IPCM), UMR, CNRS 8232 , 4 place Jussieu , 75252 Paris, Cedex 05 , France.

A unique class of enantiopure N-heterocyclic carbene half-sandwich iridium complexes is reported. These compounds display stable configurations at the metal center, as demonstrated by their chiroptical properties. Remarkably, because of the nature of the naphthalimide molecule, two regioisomers containing five-membered [( R)-2a and ( S)-2a] and six-membered [( R)-2b and ( S)-2b] iridacycles were obtained. Density functional theory calculations are advanced to rationalize their relative stability.
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http://dx.doi.org/10.1021/acs.inorgchem.8b03469DOI Listing
March 2019

Chromatographic approach to study the configurational stability of Ni(II) complexes of amino-acid Schiff bases possessing stereogenic nitrogen.

Chirality 2019 04 31;31(4):328-335. Epub 2019 Jan 31.

Department of Organic Chemistry I, Faculty of Chemistry, University of the Basque Country UPV/EHU, San Sebastián, Spain.

Herein, we disclose the design of a model Ni(II) complex of glycine Schiff base possessing single-nitrogen stereogenic center, which was successfully used for high-performance liquid chromatography (HPLC)-assisted assessment of its configurational stability. The major finding is that the configurational stability of the Ni(II)-coordinated nitrogen is profoundly dependent on the reaction conditions used, in particular the solvent, and can range from inconsequential (t less than 5 min) to virtually completely stable (t 90 y). The discovery reported in this study most likely to be of certain theoretical and synthetic value.
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http://dx.doi.org/10.1002/chir.23059DOI Listing
April 2019

Improved synthesis, resolution, absolute configuration determination and biological evaluation of HLM006474 enantiomers.

Bioorg Med Chem Lett 2019 02 17;29(3):380-382. Epub 2018 Dec 17.

UNIV. NIMES, EA7352 CHROME, Rue du Dr G. Salan, 30021 Nîmes Cedex 1, France. Electronic address:

An improved green synthesis of the E2F inhibitor HLM0066474 is described, using solvent-free and microwave irradiation conditions. The two enantiomers are separated using semi-preparative separation on Chiralpak ID and their absolute configuration is determined by vibrational circular dichroism (VCD) analysis. Biological evaluation of both enantiomers on E2F1 transcriptional activity reveals that the (+)-R, but not the (-)-S enantiomer is biologically active in repressing E2F1 transcriptional activity.
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http://dx.doi.org/10.1016/j.bmcl.2018.12.037DOI Listing
February 2019
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