A C-H activation-based enantioselective synthesis of lower carbo[n]helicenes

The three-dimensional structure of carbohelicenes has fascinated generations of molecular chemists and has been exploited in a wide range of applications. Their strong circularly polarized luminescence has attracted considerable attention in recent years due to promising applications in new optical materials. Although the enantioselective synthesis of fused carbo- and heterohelicenes has been achieved, a direct catalytic enantioselective method allowing the synthesis of lower, non-fused carbo[n]helicenes (n = 4-6) is still lacking. We report here that Pd-catalysed enantioselective C-H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[n]helicenes. Computational mechanistic studies indicate that both the C-H activation and reductive elimination steps contribute to the overall enantioselectivity. The observed enantio-induction seems to arise from a combination of non-covalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. The photophysical and chiroptical properties of the synthesized scalemic [n]helicenes have been systematically studied

label free fluorescence detection of kinase activity using a gold nanoparticle based indicator displacement assay

A straightforward fluorescence indicator-displacement assay (IDA) has been developed for the quantitative analysis of ATP→ADP conversion

Synthesis, structural characterization, and chiroptical properties of planarly and axially chiral boranils

International audience2-Amino[2.2]paracyclophane reacts with salicylaldehyde or 2-hydroxyacetophenone to yield imines that then give access to a new series of boranils (8b–d) upon complexation with BF2. These novel boron-containing compounds display both planar and axial chiralities and were examined experimentally and computationally. In particular, their photophysical and chiroptical properties were studied and compared to newly prepared, simpler boranils (9a–d) exhibiting axial chirality only. Less sophisticated chiral architectures were shown to demonstrate overall stronger circularly polarized luminescence (CPL) activity

Circularly polarized-thermally activated delayed fluorescent materials based on chiral bicarbazole donors

G. P. thanks the SCBM, the “PTC du CEA” (POLEM) and the ANR (iChiralight, ANR-19-CE07-0040) for funding and David Buisson, Amélie Goudet and Sabrina Lebrequier. J. C. and L. Fa. acknowledge the Ministère de l’Education Nationale, de la Recherche et de la Technologie, the CNRS and the Spectroscopies-CDTP core facility is also acknowledged. The St. Andrews team thanks the China Scholarship Council, 201906250199 to W. S. and 202006250026 to J. W., E. Z.-C. is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089). We thank the EPSRC (EP/R035164/1) for funding.We describe herein a molecular design to generate circularly polarized thermally activated delayed fluorescence emitters in which chiral bicarbazole donors are connected to acceptor units via a rigid 8-membered cycle and how the nature of the donor and acceptor units affect the photophysical and chiroptical properties.Publisher PDFPeer reviewe

Amplification of Dissymmetry Factors in π-Extended [7]- and [9]Helicenes

π-Extended helicenes constitute an important class of polycyclic aromatic hydrocarbons with intrinsic chirality. Herein, we report the syntheses of π-extended [7]helicene 4 and π-extended [9]helicene 6 through regioselective cyclodehydrogenation in high yields, where a "prefusion" strategy plays a key role in preventing undesirable aryl rearrangements. The unique helical structures are unambiguously confirmed by X-ray crystal structure analysis. Compared to the parent pristine [7]helicene and [9]helicene, these novel π-extended helicenes display significantly improved photophysical properties, with a quantum yield of 0.41 for 6. After optical resolution by chiral high-performance liquid chromatography, the chiroptical properties of enantiomers 4-P/M and 6-P/M are investigated, revealing that the small variation in helical length from [7] to [9] can cause an approximately 10-fold increase in the dissymmetry factors. The circularly polarized luminescence brightness of 6 reaches 12.6 M⁻¹ cm⁻¹ as one of the highest among carbohelicenes

Squalene-Adenosine Nanoparticles: Ligands of Adenosine Receptors or Adenosine Prodrug?

Adenosine receptors (ARs) represent key drug targets in many human pathologies, including cardiovascular, neurologic, and inflammatory diseases. To overcome the very rapid metabolization of adenosine, metabolically stable AR agonists and antagonists were developed. However, few of these molecules have reached the market due to efficacy and safety issues. Conjugation of adenosine to squalene to form squalene-adenosine (SQAd) nanoparticles (NPs) dramatically improved the pharmacological efficacy of adenosine, especially for neuroprotection in stroke and spinal cord injury. However, the mechanism by which SQAd NPs displayed therapeutic activity remained totally unknown. In the present study, two hypotheses were discussed: 1) SQAd bioconjugates, which constitute the NP building blocks, act directly as AR ligands; or 2) adenosine, once released from intracellularly processed SQAd NPs, interacts with these receptors. The first hypothesis was rejected, using radioligand displacement assays, as no binding to human ARs was detected, up to 100 µM SQAd, in the presence of plasma. Hence, the second hypothesis was examined. SQAd NPs uptake by HepG2 cells, which was followed using radioactive and fluorescence tagging, was found to be independent of equilibrative nucleoside transporters but rather mediated by low-density lipoprotein receptors. Interestingly, it was observed that after cell internalization, SQAd NPs operated as an intracellular reservoir of adenosine, followed by a sustained release of the nucleoside in the extracellular medium. This resulted in a final paracrine-like activation of the AR pathway, evidenced by fluctuations of the second messenger cAMP. This deeper understanding of the SQAd NPs mechanism of action provides a strong rational for extending the pharmaceutical use of this nanoformulation.Medicinal Chemistr

Synthèse et propriétés de nouvelles architectures moléculaires hélicoïdales

VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

Catalytic self-assembled monolayers on gold nanoparticles

none2This review describes the attractiveness of catalytic self-assembled monolayers (SAMs) on gold nanoparticles as catalytic systems. The hybrid inorganic–organic catalytic systems combine the advantages of homogeneous and heterogeneous catalysis (higher activity and catalyst recycling, respectively). The high fidelity process of SAM formation on gold nanoparticles, together with the possibility of making mixed SAMs composed of different thiols, provides an unprecedented route to stable, complex catalytic systems. Insertion of catalysts in a mixed monolayer can improve the catalytic performances, due to catalyst orientation, changes in the local chemical environment, or through the steering effect of neighbouring thiols. Alternatively, insertion of catalytic units in a monolayer may be an essential prerequisite in the case when catalysis requires cooperation between two catalytic units (for instance two metal ions). Finally, the multivalent nature of these systems is an important feature especially in the case when the substrate contains multiple reactive sites. Catalytic SAMs on gold nanoparticles also find applications beyond the field of catalysis, for instance in diagnostics and nanotechnology.noneG. Pieters; L.J. PrinsPieters, Gregory; Prins, LEONARD JA

Excited State Intramolecular Proton Transfer Based Fluorophores with Circularly Polarized Luminescence Emission

International audienceAbstract Herein, the first molecular design allowing the combination of circularly polarized luminescence (CPL) and excited state intramolecular proton transfer (ESIPT) fluorescence is described. In this novel class of emitters, the chiroptical activity originates from a chiral excitonic coupling induced by the tethering of two ESIPT fluorophores via a readily accessible trans ‐1,2‐diaminocyclohexane scaffold. This approach has notably allowed the synthesis in a single step of a CPL‐active molecule displaying a very large Stokes shift (up to 12 087 cm −1 in toluene solution) and the synthesis in three steps of one of the rare examples of CPL‐active purely organic dual‐emission materials

Chiral perturbation on single benzene‐based fluorophores: A structure/(chir)optical activity relationship study

International audienceAbstract In this paper, we describe the synthesis and the (chir)optical properties of a novel series of circularly polarized luminescent emitters. These molecules involve a compact single benzene‐based donor‐acceptor fluorophore composed of two cyclic alkylamines as electron donors and a phthalonitrile moiety as electron acceptor linked to a configurationally stable BINOL acting as a chiral perturbation unit. These new compounds display fair quantum yields (up to 66%) with emission maxima around 500 nm in toluene solutions, and the study of their chiroptical properties has shown that the cyclic alkylamine's ring size affects significantly the luminescence dissymmetry factors, reaching 2.2 × 10 −3 for the larger cyclic alkylamine moieties