Publications by authors named "Jean-Valère Naubron"

41 Publications

Fast interaction dynamics of G-quadruplex and RGG-rich peptides unveiled in zero-mode waveguides.

Nucleic Acids Res 2021 12;49(21):12348-12357

Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, 13013 Marseille, France.

G-quadruplexes (GQs), a non-canonical form of DNA, are receiving a huge interest as target sites for potential applications in antiviral and anticancer drug treatments. The biological functions of GQs can be controlled by specifically binding proteins known as GQs binding proteins. Some of the GQs binding proteins contain an arginine and glycine-rich sequence known as RGG peptide. Despite the important role of RGG, the GQs-RGG interaction remains poorly understood. By single molecule measurements, the interaction dynamics can be determined in principle. However, the RGG-GQs interaction occurs at micromolar concentrations, making conventional single-molecule experiments impossible with a diffraction-limited confocal microscope. Here, we use a 120 nm zero-mode waveguide (ZMW) nanoaperture to overcome the diffraction limit. The combination of dual-color fluorescence cross-correlation spectroscopy (FCCS) with FRET is used to unveil the interaction dynamics and measure the association and dissociation rates. Our data show that the RGG-GQs interaction is predominantly driven by electrostatics but that a specific affinity between the RGG sequence and the GQs structure is preserved. The single molecule approach at micromolar concentration is the key to improve our understanding of GQs function and develop its therapeutic applications by screening a large library of GQs-targeting peptides and proteins.
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http://dx.doi.org/10.1093/nar/gkab1002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8643622PMC
December 2021

Racemization mechanism of lithium tert-butylphenylphosphido-borane: A kinetic insight.

Chirality 2022 01 3;34(1):27-33. Epub 2021 Nov 3.

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

The racemization mechanism of tert-butylphenylphosphido-borane is investigated experimentally and theoretically. Based on this converging approach, it is shown, first, that several phosphido-borane molecular species coexist at the time of the reaction and, second, that one particular of both initially assumed reactive routes most significantly contribute to the overall racemization process. From our converging modeling and experimental measurement, it comes out that the most probable species to be here encountered is a phosphido-borane-Li (THF) neutral solvate, whose P-stereogenic center monomolecular inversion through a Y-shaped transition structure (Δ G° : 81 kJ mol ) brings the largest contribution to the racemization process.
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http://dx.doi.org/10.1002/chir.23383DOI Listing
January 2022

Breaking Symmetry Relaxes Structural and Magnetic Restraints, Suppressing QTM in Enantiopure Butterfly Fe Dy SMMs*.

Chemistry 2021 Nov 21;27(61):15102-15108. Epub 2021 Oct 21.

Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstr. 15, 76131, Karlsruhe, Germany.

The {Fe Dy } butterfly systems can show single molecule magnet (SMM) behaviour, the nature of which depends on details of the electronic structure, as previously demonstrated for the [Fe Dy (μ -OH) (Me-teaH) (O CPh) ] compound, where the [N,N-bis-(2-hydroxyethyl)-amino]-2-propanol (Me-teaH ) ligand is usually used in its racemic form. Here, we describe the consequences for the SMM properties by using enantiopure versions of this ligand and present the first homochiral 3d/4 f SMM, which could only be obtained for the S enantiomer of the ligand for [Fe Dy (μ -OH) (Me-teaH) (O CPh) ] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe Dy (μ -OH) (Me-teaH) (O CPh) (NO ) ] version, which could be obtained as the RS-, R- and S-compounds. Remarkably, the enantiopure versions show enhanced slow relaxation of magnetisation. The use of the enantiomerically pure ligand suppresses QTM, leading to the conclusion that use of enantiopure ligands is a "gamechanger" by breaking the cluster symmetry and altering the intimate details of the coordination cluster's molecular structure.
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http://dx.doi.org/10.1002/chem.202103360DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8596739PMC
November 2021

Chemically Fueled Three-State Chiroptical Switching Supramolecular Gel with Temporal Control.

J Am Chem Soc 2021 08 5;143(32):12650-12657. Epub 2021 Aug 5.

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

The recent discovery of temporally controlled gels opens broad perspectives to the field of smart functional materials. However, to obtain fully operative systems, the design of simple and robust gels displaying complex functions is desirable. Herein, we fuel dissipative gelating materials through iterative additions of trichloroacetic acid (TCA). This simple fuel enables to switch over time an acid/base-dependent commercially available amino acid gelator/DBU combination between three distinct states (anionic, cationic, and neutral), while liberating volatile CO and CHCl upon fuel consumption. Of interest, the anionic resting state of the system is obtained through trapping of 1 equiv of CO through the formation of a carbamate. The system is tunable, robust, and resilient over time with over 25 consecutive sol-gel-sol cycles possible without significant loss of properties. Most importantly, because of the chiral nature of the amino acid gelator, the system features chiroptical switching properties moving reversibly between three distinct states as observed by ECD. The described system considerably enhances the potential of smart molecular devices for logic gates or data storage by adding a time dimension based on three states to the gelating materials. It is particularly simple in terms of chemical components involved, but it enables sophisticated functions.
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http://dx.doi.org/10.1021/jacs.1c05183DOI Listing
August 2021

Allosteric Guest Binding in Chiral Zirconium(IV) Double Decker Porphyrin Cages.

European J Org Chem 2021 Jan 5;2021(4):607-617. Epub 2021 Jan 5.

Radboud University Institute for Molecules and Materials Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands.

Chiral zirconium(IV) double cage sandwich complex has been synthesized in one step from porphyrin cage was obtained as a racemate, which was resolved by HPLC and the enantiomers were isolated in >99.5 % ee. Their absolute configurations were assigned on the basis of X-ray crystallography and circular dichroism spectroscopy. Vibrational circular dichroism (VCD) experiments on the enantiomers of revealed that the chirality around the zirconium center is propagated throughout the whole cage structure. The axial conformational chirality of the double cage complex displayed a VCD fingerprint similar to the one observed previously for a related chiral cage compound with planar and point chirality. shows fluorescence, which is quenched when viologen guests bind in its cavities. The binding of viologen and dihydroxybenzene derivatives in the two cavities of occurs with negative allostery, the cooperativity factors α (=4 K/K) being as low as 0.0076 for the binding of -dimethylviologen. These allosteric effects are attributed to a pinching of the second cavity as a result of guest binding in the first cavity.
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http://dx.doi.org/10.1002/ejoc.202001392DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7898692PMC
January 2021

Quinolizidine Alkaloids from .

J Nat Prod 2021 04 19;84(4):1198-1202. Epub 2021 Feb 19.

USR CNRS-Pierre Fabre No. 3388 ETaC, Centre de Recherche et Développement Pierre Fabre, 31035 Toulouse, France.

Five new quinolizidine alkaloids were isolated from the leaves of (Urb.) Urb. (Caricaceae) and named cylicomorphins A-E (-). They all are ester derivatives of the same basic quinolizidine skeleton bearing hydroxy, methyl, and ethanoic acid substituents. Their structures were mainly established by NMR spectroscopy, and the absolute configuration is proposed on the basis of VCD data and Mosher ester derivatization. Compound displayed cytotoxicity in the 10 μM range against an HCT-116 cell line.
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http://dx.doi.org/10.1021/acs.jnatprod.0c01261DOI Listing
April 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

Absolute configuration and host-guest binding of chiral porphyrin-cages by a combined chiroptical and theoretical approach.

Nat Commun 2020 09 22;11(1):4776. Epub 2020 Sep 22.

Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. The chiral porphyrin-cages form complexes with achiral and chiral viologen-guests and upon binding one of the axial enantiomorphs of the guest is bound selectively, as is indicated by induced-electronic-dichroism-spectra in combination with calculations. This host-guest binding also leads to unusual enhanced vibrational circular dichroism, which is the result of a combination of phenomena, such as rigidification of the host and guest structures, charge transfer, and coupling of specific vibration modes of the host and guest. The results offer insights in how the porphyrin cage-compounds may be used to construct a future molecular Turing machine that can write chiral information onto polymer chains.
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http://dx.doi.org/10.1038/s41467-020-18596-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7508876PMC
September 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

Stereoselective Syntheses, Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes.

Angew Chem Int Ed Engl 2020 Feb 8;59(8):3264-3271. Epub 2020 Jan 8.

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

We report a molecular design and concept using π-system elongation and steric effects from helicenes surrounding a triphenylene core toward stable chiral polycyclic aromatic hydrocarbons (PAHs) with a maximal π-distortion to tackle their aromaticity, supramolecular and molecular properties. The selective syntheses, and the structural, conformational and chiroptical properties of two diastereomeric large multi-helicenes of formula C H having a triphenylene core and embedding three [5]helicene units on their inner edges and three [7]helicene units at their periphery are reported based on diastereoselective and, when applicable, enantiospecific Yamamoto-type cyclotrimerizations of racemic or enantiopure 9,10-dibromo[7]helicene. Both molecules have an extremely distorted triphenylene core, and one of them exhibits the largest torsion angle recorded so far for a benzene ring (twist=36.9°).
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http://dx.doi.org/10.1002/anie.201913200DOI Listing
February 2020

Strategic Stereoselective Halogen (F, Cl) Insertion: A Tool to Enhance Supramolecular Properties in Polyols.

Chemistry 2019 Nov 30;25(66):15098-15105. Epub 2019 Oct 30.

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

To improve the supramolecular properties of organic compounds, chemists continuously need to identify new tools. Herein, the influence of the stereoselective insertion of halogen atoms (F or Cl) on different supramolecular properties is analyzed. Inserting anti-halohydrins in polyols considerably strengthens the H-bonding networks and other supramolecular interactions. This behavior resulted in improved anion binding, H-bonding catalysis, or organogel properties of the designed polyols with strong perspectives for applications in other classes of substrates.
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http://dx.doi.org/10.1002/chem.201902983DOI Listing
November 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

Structural Elucidation and Cytotoxicity of a New 17-Membered Ring Lactone from Algerian .

Molecules 2018 Dec 8;23(12). Epub 2018 Dec 8.

Laboratoire Chimie des Produits Naturels (CPN), Campus Grimaldi, Université de Corse, UMR CNRS 6134 SPE, BP 52, 20250 Corte, France.

The chemical composition of a hexanic extract of , obtained from its aerial parts, was investigated by GC-FID, GC/MS, HRMS, NMR and VCD analyses. The main compounds were germacrene D (23.6%), eudesma-4(15)-7-dien-1-β-ol (8.2%) and falcarindiol (9.4%), which are associated with a new uncommon and naturally found 17-membered ring lactone. This 17-membered ring features conjugated acetylenic bonds, named campestrolide (23.0%). The crude extract showed moderate antitrypanosomal (), antileishmanial () and anticancer (cancerous macrophage-like murine cells) activities, and also displayed cytotoxicity, (human normal fibroblasts) in similar concentration ranges (IC = 3.0, 3.9, 4.0 and 4.4 µg/mL respectively). Likewise, campestrolide displayed low activity on all tested cells (IC: 12.5⁻19.5 µM) except on , on which it was very active and moderately selective (IC = 2.2 µM. SI= 8.9). In conclusion, the new compound that has been described, displaying a singular structure, possesses interesting antitrypanosomal activity that should be further investigated and improved.
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http://dx.doi.org/10.3390/molecules23123250DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6321439PMC
December 2018

Atropisomerism in a 10-Membered Ring with Multiple Chirality Axes: (3 Z,9 Z)-1,2,5,8-Dithiadiazecine-6,7(5 H,8 H)-dione Series.

J Org Chem 2018 08 13;83(15):7566-7573. Epub 2018 Jun 13.

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

For the first time, chirality in (3 Z,9 Z)-1,2,5,8-dithiadiazecine-6,7(5 H,8 H)-dione series was recognized. Enantiomers of the 4,9-dimethyl-5,8-diphenyl analogue were isolated at room temperature, and their thermal stability was determined. X-ray crystallography confirmed the occurrence of a pair of enantiomers in the crystal. Absolute configurations were assigned by comparing experimental and calculated vibrational/electronic circular dichroism spectra of isolated enantiomers. A distorted tesseract (four-dimensional hypercube) was used to visualize the calculated enantiomerization process, which requires the rotation around four chirality axes. Conformers of higher energy as well as several concurrent pathways of similar energies were revealed.
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http://dx.doi.org/10.1021/acs.joc.8b01009DOI Listing
August 2018

Chiral Nanographene Propeller Embedding Six Enantiomerically Stable [5]Helicene Units.

J Am Chem Soc 2017 12 25;139(51):18508-18511. Epub 2017 Oct 25.

Aix Marseille Université , CNRS, CINAM, 13288 Marseille, France.

A one-step synthesis of a nanographene propeller with a D-symmetry was obtained starting from 7,8-dibromo[5]helicene by Yamamoto nickel(0) couplings. It afforded a chiral polyaromatic hydrocarbon (PAH) embedding six enantiomerically stable [5]helicene units. This dense accumulation of helical strain resulted in a distorted geometry, but stable stereochemistry. The conformational, structural, chiroptical, and photophysical properties of the molecule are reported.
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http://dx.doi.org/10.1021/jacs.7b07622DOI Listing
December 2017

Racemization and transesterification of alkyl hydrogeno-phenylphosphinates.

J Mol Model 2017 May 27;23(5):168. Epub 2017 Apr 27.

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

In this article, we explore, both theoretically and experimentally, the general reactivity of alkyl hydrogeno-phenylphosphinates with alcohols. We show that alcohol molecules act exclusively as nucleophilic species, and add to alkyl hydrogeno-phenylphosphinates, leading to pentacoordinated intermediates. These intermediates are shown to subsequently competitively undergo alcohol eliminations and/or Berry pseudorotations. This offers several possible routes for racemizations and/or alcohol exchange reactions. Transition standard Gibbs free energies predicted from DFT calculations for the overall alcohol exchange mechanism are shown to be compatible with those experimentally measured in case ethanol reacts with ethyl hydrogeno-phenylphosphinate (134.5∼136.0 kJ mol at 78 °C). Graphical abstract ᅟ.
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http://dx.doi.org/10.1007/s00894-017-3343-7DOI Listing
May 2017

Frozen Chirality of Tertiary Aromatic Amides: Access to Enantioenriched Tertiary α-Amino Acid or Amino Alcohol without Chiral Reagent.

Chemistry 2017 Apr 12;23(24):5787-5798. Epub 2017 Apr 12.

Univ. Paris-Sud, Laboratoire de Méthodologie, Synthèse et Molécules Thérapeutiques, ICMMO, UMR 8182, CNRS, Université Paris-Saclay, Bât 410, 91405, Orsay, France.

One of the fundamental and intriguing aspects of life is the homochirality of the essential molecules. In this field, the absolute asymmetric synthesis of α-amino acids is a major challenge. Herein, we report access, by chemical means, to tertiary α-amino acid derivatives in up to 96 % ee without using any chiral reagent. In our strategy, the dynamic axial chirality of tertiary aromatic amides is frozen in a crystal and is responsible for the stereoselectivity of the subsequent steps. Furthermore, we could control the configuration of the final product by manually sorting and selecting the initial crystals. Based on vibrational circular dichroism studies, we could rationalize the observed stereoselectivity.
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http://dx.doi.org/10.1002/chem.201700110DOI Listing
April 2017

Isolation of the major chiral compounds from Bubonium graveolens essential oil by HPLC and absolute configuration determination by VCD.

Chirality 2017 Feb 26;29(2):70-79. Epub 2016 Dec 26.

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

The chirality issues in the essential oils (EOs) of leaves and flowers from Bubonium graveolens were addressed by chiral high-performance liquid chromatography (HPLC) with polarimetric detection and vibrational circular dichroism (VCD). The chemical compositions of the crude oils of three samples were established by gas chromatography / mass spectrometry (GC/MS). The well-known cis-chrysanthenyl acetate (1), oxocyclonerolidol (2), and the recently disclosed cis-acetyloxychrysanthenyl acetate (3), the three major chiral compounds, were isolated by preparative HPLC. The naturally occurring oxocycloneroledol (2), mostly found in the leaf oil (49.4-55.6%), presents a (+) sign in the mobile phase during HPLC on a chiral stationary phase (CSP) with a Jasco polarimetric detection. The naturally occurring cis-chrysanthenyl acetate (1) and cis-acetyloxychrysanthenyl acetate (3), mostly found in the flower EO (35.9-74.9% and 10.0-34.3%, respectively), both present a (-) sign. HPLC on a CSP with polarimetric detection is an unprecedented approach to readily differentiate the flower and leaf EOs according to their chiral signature. The comparison of the experimental and calculated VCD spectra of pure isolated 1, 2, and 3 provided their absolute configuration as being (1S,5R,6S)-(-)-2,7,7-trimethylbicyclo[3.1.1]hept-2-en-6-yl acetate 1, (2R,6R)-(+)-6-ethenyl-2,6-dimethyl-2-(4-methylpent-3-en-1-yl)dihydro-2H-pyran-3(4H)-one) 2 and (1S,5R,6R,7S)-(-)-7-(acetyloxy)-2,6-dimethylbicyclo[3.1.1]hept-2-en-6-yl]methyl acetate 3. Compounds 1, 2, and 3 were already known in B. graveolens but this is the first report of the absolute configuration of (+)-2 and (-)-3. The VCD chiral signatures of the crude oils were also recorded.
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http://dx.doi.org/10.1002/chir.22672DOI Listing
February 2017

Formation, Characterization, and Reactivity of a Nonheme Oxoiron(IV) Complex Derived from the Chiral Pentadentate Ligand asN4Py.

Inorg Chem 2016 Oct 26;55(20):10090-10093. Epub 2016 Sep 26.

Department of Chemistry, University of Pannonia , 8201 Veszprém, Hungary.

The chiral pentadentate low-spin (S = 1) oxoiron(IV) complex [Fe(O)(asN4Py)] (2) was synthesized and spectroscopically characterized. Its formation kinetics, reactivity, and (enantio)selectivity in an oxygen-atom-transfer reaction was investigated in detail and compared to a similar pentadentate ligand-containing system.
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http://dx.doi.org/10.1021/acs.inorgchem.6b01089DOI Listing
October 2016

A switchable self-assembling and disassembling chiral system based on a porphyrin-substituted phenylalanine-phenylalanine motif.

Nat Commun 2016 09 1;7:12657. Epub 2016 Sep 1.

Aix Marseille Univ, CNRS, Centrale Marseille, Institut des Sciences Moléculaires de Marseille (iSm2), UMR 7313, Chirosciences, Avenue Escadrille Normandie Niemen, Service 442, F-13397 Marseille, France.

Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.
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http://dx.doi.org/10.1038/ncomms12657DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5025786PMC
September 2016

A switchable dual organocatalytic system and the enantioselective total synthesis of the quadrane sesquiterpene suberosanone.

Chem Commun (Camb) 2016 May;52(39):6565-8

Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR7313, F-13397 Marseille, France.

The combination of aminocatalysis with N-heterocyclic carbene catalysis has been extended to a switchable dual catalytic system, which allowed a direct enantioselective entry to bridged bicyclo[3.n.1] ring systems and the total synthesis of the natural product (1R)-suberosanone.
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http://dx.doi.org/10.1039/c6cc01689hDOI Listing
May 2016

Analysis of the major chiral compounds of Artemisia herba-alba essential oils (EOs) using reconstructed vibrational circular dichroism (VCD) spectra: En route to a VCD chiral signature of EOs.

Anal Chim Acta 2016 Jan 2;903:121-30. Epub 2015 Dec 2.

Aix-Marseille Université, Centrale Marseille, CNRS, ISM2 UMR 7313, Marseille, France. Electronic address:

An unprecedented methodology was developed to simultaneously assign the relative percentages of the major chiral compounds and their prevailing enantiomeric form in crude essential oils (EOs). In a first step the infrared (IR) and vibrational circular dichroism (VCD) spectra of the crude essential oils were recorded and in a second step they were modelized as a linear weighted combination of the IR and VCD spectra of the individual spectra of pure enantiomer of the major chiral compounds present in the EOs. The VCD spectra of enantiomer of known enantiomeric excess shall be recorded if they are not yet available in a library of VCD spectra. For IR, the spectra of pure enantiomer or racemic mixture can be used. The full spectra modelizations were performed using a well known and powerful mathematical model (least square estimation: LSE) which resulted in a weighting of each contributing compound. For VCD modelization, the absolute value of each weighting represented the percentage of the associate compound while the attached sign addressed the correctness of the enantiomeric form used to build the model. As an example, a model built with the non-prevailing enantiomer will show a negative sign of the weighting value. For IR spectra modelization, the absolute value of each weighting represented the percentage of the compounds without of course accounting for the chirality of the prevailing enantiomers. Comparison of the weighting values issuing from IR and VCD spectra modelizations is a valuable source of information: if they are identical, the EOs are composed of nearly pure enantiomers, if they are different the chiral compounds of the EOs are not in an optically pure form. The method was applied on four samples of essential oil of Artemisia herba-alba in which the three major compounds namely (-)-α-thujone, (+)-β-thujone and (-)-camphor were found in different proportions as determined by GC-MS and chiral HPLC using polarimetric detector. In order to validate the methodology, the modelization of the VCD spectra was performed on purpose using the individual VCD spectra of (-)-α-thujone, (+)-β-thujone and (+)-camphor instead of (-)-camphor. During this work, the absolute configurations of (-)-α-thujone and (+)-β-thujone were confirmed by comparison of experimental and calculated VCD spectra as being (1S,4R,5R) and (1S,4S,5R) respectively.
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http://dx.doi.org/10.1016/j.aca.2015.11.010DOI Listing
January 2016

On-Demand Cyclophanes: Substituent-Directed Self-Assembling, Folding, and Binding.

J Org Chem 2016 Jan 6;81(2):654-61. Epub 2016 Jan 6.

Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, UMR 5246 CNRS - Université Claude Bernard Lyon 1 - CPE Lyon, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.

A family of p-cyclophanes based on bis- or tetrafunctionalized 1,4-bisthiophenol units linked by disulfide bridges was obtained by self-assembly on a gram scale and without any chromatographic purification. The nature of the functionalities borne by these so-called dyn[4]arenes plays a crucial role on their structural features as well as their molecular recognition abilities. Tuning these functions on demand yields tailored receptors for cations, anions, or zwitterions in organic or aqueous media.
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http://dx.doi.org/10.1021/acs.joc.5b02605DOI Listing
January 2016

A forgotten chiral spiro compound revisited: 3,3'-dimethyl-3H,3'H-2,2'-spirobi[[1,3]benzothiazole].

Chirality 2015 Oct 25;27(10):716-21. Epub 2015 Aug 25.

Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397, Marseille, France.

The title compound was obtained as a side product during dimerization-oxidation steps of the carbene generated from N-methylbenzothiazolium iodide. Chromatography on (S,S)-Whelk O1 column showed on cooling a typical plateau shape chromatogram indicating an exchange between two enantiomers on the column. The thermal barrier to racemization was determined (85 kJ.mol(-1) at 10 °C) by dynamic high-performance liquid chromatography (DHPLC).The absolute configuration of the first (M) and second eluted (P) enantiomers on the (S, S)-Whelk O1 column was established by comparing the reconstructed circular dichroism (CD) spectra from the CD detector signal and the calculated CD spectrum of the (P) enantiomer. Mass spectrometry revealed that 3,3'-dimethyl-3H,3'H-2,2'-spirobi[[1,3]benzothiazole] can be viewed as a masked thiophenate attached to a benzothiazolium framework.
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http://dx.doi.org/10.1002/chir.22492DOI Listing
October 2015

Stereospecific Synthesis of α- and β-Hydroxyalkyl P-Stereogenic Phosphine-Boranes and Functionalized Derivatives: Evidence of the P=O Activation in the BH3 -Mediated Reduction.

Chemistry 2015 Oct 14;21(44):15607-21. Epub 2015 Sep 14.

Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397, Marseille (France).

Access to hydroxy-functionalized P-chiral phosphine-boranes has become an important field in the synthesis of P-stereogenic compounds used as ligands in asymmetric catalysis. A family of optically pure α and β-hydroxyalkyl tertiary phosphine-boranes has been prepared by using a three-step procedure from readily accessible enantiopure adamantylphosphinate, obtained by semi-preparative HPLC on multigram scale. Firstly, a two-step one-pot transformation affords the enantiopure hydroxyalkyl tertiary phosphine oxides in good yields and enantioselectivities. The third step, BH3 -mediated reduction, allows the formation of the desired phosphine-boranes with excellent stereospecifity. The mechanistic study of this reduction provides new evidence to elucidate the crucial role of the pendant hydroxy group and the subsequent activation of the P=O bond by the boron atom.
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http://dx.doi.org/10.1002/chem.201502647DOI Listing
October 2015

Absolute Configuration Determination of Azulenyl Diols Isolated From Asymmetric Pinacol Coupling.

Chirality 2015 Nov 14;27(11):826-34. Epub 2015 Sep 14.

Institute of Organic Chemistry "C. D. Nenitzescu" of the Romanian Academy, Splaiul Independentei, Bucharest, Romania.

A convenient enantioselective approach for the pinacol coupling of 1-acetylazulene involving easily accessible (R)- or (S)-BINOLs as chiral additive is reported. This supposes the preformation of the chiral titanium-BINOL complex in 1:2 ratio and subsequent reduction with zinc when, 2,3-di(azulen-1-yl)butane-2,3-diol can be isolated in around 60% enantiomeric excess. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental and Boltzmann-weighted calculated VCD and ECD spectra and assigned as (+)-(2S;3S)-di(azulen-1-yl)butane-2,3-diol. Chirality 27:826-834, 2015. © 2015 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/chir.22523DOI Listing
November 2015

Origin of the enantioselectivity in organocatalytic Michael additions of β-ketoamides to α,β-unsaturated carbonyls: a combined experimental, spectroscopic and theoretical study.

Chemistry 2015 Jan 7;21(2):778-90. Epub 2014 Nov 7.

Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397, Marseille (France). Fax: (+33) 491-289-187.

The organocatalytic enantioselective conjugate addition of secondary β-ketoamides to α,β-unsaturated carbonyl compounds is reported. Use of bifunctional Takemoto's thiourea catalyst allows enantiocontrol of the reaction leading either to simple Michael adducts or spirocyclic aminals in up to 99 % ee. The origin of the enantioselectivity has been rationalised based on combined DFT calculations and kinetic analysis. This study provides a deeper understanding of the reaction mechanism, which involves a predominant role of the secondary amide proton, and clarifies the complex interactions occurring between substrates and the catalyst.
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http://dx.doi.org/10.1002/chem.201404481DOI Listing
January 2015

Double transfer of chirality in organocopper-mediated bis(alkylating) cycloisomerization of enediynes.

Angew Chem Int Ed Engl 2014 Mar 19;53(12):3227-31. Epub 2014 Feb 19.

Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire UMR7273, 13390 Marseille (France).

An original synthesis of chiral benzofulvenes triggered by organocopper reagents is reported. These enantiopure products are available through a highly chemo-, regio-, diastereo-, and enantioselective bis(alkylating) cycloisomerization process. A double chirality transfer (central-to-axial-to-central) is observed.
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http://dx.doi.org/10.1002/anie.201310530DOI Listing
March 2014

Cooperative use of VCD and XRD for the determination of tetrahydrobenzoisoquinolines absolute configuration: a reliable proof of memory of chirality and retention of configuration in enediyne rearrangements.

Chirality 2013 Dec 13;25(12):832-9. Epub 2013 Aug 13.

Aix-Marseille Université, CNRS ICR UMR7273, Marseille, France.

The absolute configurations (AC) of azaheterocylic compounds resulting from the cascade rearrangement of enediynes involving only light atoms were unambiguously assigned by the joint use of vibrational circular dichroism (VCD) and copper radiation single crystal X-ray diffraction (XRD). These AC determinations proved that the rearrangements of enediynes proceeded with memory of chirality and retention of configuration.
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http://dx.doi.org/10.1002/chir.22221DOI Listing
December 2013

Electron cryo-microscopy of TPPS4⋅2HCl tubes reveals a helical organisation explaining the origin of their chirality.

Chemphyschem 2013 Oct 31;14(14):3209-14. Epub 2013 Jul 31.

Division of Structural Studies, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB1 0QH (UK).

A widely studied achiral porphyrin, which is highly soluble in aqueous solutions (TPPS4), is shown to self-assemble into helical nanotubes. These were imaged by electron cryo-microscopy and a state-of-the-art image analysis allows building a map at ∼5 Å resolution, one of the highest obtained so far for molecular materials. The authors were able to trace the apparent symmetry breaking to existing nuclei in the "as received samples", while carefully purified samples show that both handnesses occur in equal amounts.
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http://dx.doi.org/10.1002/cphc.201300606DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4281918PMC
October 2013
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