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

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.

Interaction between Spirosilanes and Lewis Bases: from Coordination to Frustration.

In this work, the interaction between Lewis bases, especially N-heterocyclic carbenes (NHCs), and hindered neutral silicon derivatives featuring high Lewis acidity is described. The formation of normal and abnormal Lewis adducts could be controlled by varying the acidity of the corresponding tetravalent spiro organosilane. Some DFT calculations permitted to gain insight into the thermodynamics of the NHC-spirosilane interaction featuring various NHCs differing in size and σ-donor capacity. Spirosilanes are introduced as new Lewis partners in frustrated Lewis pair (FLP) chemistry and some FLP-type reactivities are presented, in particular the activation of formaldehyde that could occur with both hindered NHCs and phosphines.

Enantioselective Brønsted Acid Catalysis as a Tool for the Synthesis of Natural Products and Pharmaceuticals.

Synthesis of biologically active molecules (whether at laboratory or industrial scale) remains a highly appealing area of modern organic chemistry. Nowadays, the need to access original bioactive scaffolds goes together with the desire to improve synthetic efficiency, while reducing the environmental footprint of chemical activities. Long neglected in the field of total synthesis, enantioselective organocatalysis has recently emerged as an environmentally friendly and indispensable tool for the construction of relevant bioactive molecules. Notably, enantioselective Brønsted acid catalysis has offered new opportunities in terms of both retrosynthetic disconnections and controlling stereoselectivity. The present report attempts to provide an overview of enantioselective total or formal syntheses designed around Brønsted acid-catalyzed transformations. To demonstrate the versatility of the reactions promoted and the diversity of the accessible motifs, this Minireview draws a systematic parallel between methods and retrosynthetic analysis. The manuscript is organized according to the main reaction types and the nature of newly-formed bonds.

An RNA editing/dsRNA binding-independent gene regulatory mechanism of ADARs and its clinical implication in cancer.

Adenosine-to-inosine (A-to-I) RNA editing, catalyzed by Adenosine DeAminases acting on double-stranded RNA(dsRNA) (ADAR), occurs predominantly in the 3' untranslated regions (3'UTRs) of spliced mRNA. Here we uncover an unanticipated link between ADARs (ADAR1 and ADAR2) and the expression of target genes undergoing extensive 3'UTR editing. Using METTL7A (Methyltransferase Like 7A), a novel tumor suppressor gene with multiple editing sites at its 3'UTR, we demonstrate that its expression could be repressed by ADARs beyond their RNA editing and double-stranded RNA (dsRNA) binding functions. ADARs interact with Dicer to augment the processing of pre-miR-27a to mature miR-27a. Consequently, mature miR-27a targets the METTL7A 3'UTR to repress its expression level. In sum, our study unveils that the extensive 3'UTR editing of METTL7A is merely a footprint of ADAR binding, and there are a subset of target genes that are equivalently regulated by ADAR1 and ADAR2 through their non-canonical RNA editing and dsRNA binding-independent functions, albeit maybe less common. The functional significance of ADARs is much more diverse than previously appreciated and this gene regulatory function of ADARs is most likely to be of high biological importance beyond the best-studied editing function. This non-editing side of ADARs opens another door to target cancer.

Dibenzazepinyl ureas as dual NMR and CD probes of helical screw-sense preference in conformationally equilibrating dynamic foldamers.

Conformationally mobile oligomers with helical structures, or 'dynamic foldamers', may populate a mixture of screw-sense conformers whose relative proportion has been used as a means of communicating information on a molecular scale. The dibenzazepinyl urea provides a means of quantifying both the sense and degree of this screw-sense preference through a combination of circular dichroism (CD) and NMR spectroscopy. The dibenzazepinyl urea probe is synthetically versatile, readily accessible, and easy to introduce to the terminus of an amide or a urea foldamer.

Stereospecific Intramolecular Arylation of 2- and 3-Pyridyl Substituted Alkylamines via Configurationally Stable α-Pyridyl Organolithiums.

Treatment of N'-aryl urea derivatives of enantiomerically enriched α-(2-pyridyl) and α-(3-pyridyl)alkylamines with a base leads to the migration of the N'-aryl substituent from N to C in a 'nonclassical' intramolecular nucleophilic aromatic substitution reaction. Both electron-rich and -poor rings migrate successfully. A new quaternary stereogenic center is formed adjacent to the pyridine ring with high stereospecificity, even when the intermediate anion is a presumably planar 2-picolyllithium. Base hydrolysis of the urea gives enantiomerically enriched α-pyridylalkylamines.

Telomerase reverse transcriptase promotes cancer cell proliferation by augmenting tRNA expression.

Transcriptional reactivation of telomerase reverse transcriptase (TERT) reconstitutes telomerase activity in the majority of human cancers. Here, we found that ectopic TERT expression increases cell proliferation, while acute reductions in TERT levels lead to a dramatic loss of proliferation without any change in telomere length, suggesting that the effects of TERT could be telomere independent. We observed that TERT determines the growth rate of cancer cells by directly regulating global protein synthesis independently of its catalytic activity. Genome-wide TERT binding across 5 cancer cell lines and 2 embryonic stem cell lines revealed that endogenous TERT, driven by mutant promoters or oncogenes, directly associates with the RNA polymerase III (pol III) subunit RPC32 and enhances its recruitment to chromatin, resulting in increased RNA pol III occupancy and tRNA expression in cancers. TERT-deficient mice displayed marked delays in polyomavirus middle T oncogene-induced (PyMT-induced) mammary tumorigenesis, increased survival, and reductions in tRNA levels. Ectopic expression of either RPC32 or TERT restored tRNA levels and proliferation defects in TERT-depleted cells. Finally, we determined that levels of TERT and tRNA correlated in breast and liver cancer samples. Together, these data suggest the existence of a unifying mechanism by which TERT enhances translation in cells to regulate cancer cell proliferation.

α-Quaternary Proline Derivatives by Intramolecular Diastereoselective Arylation of N-Carboxamido Proline Ester Enolates.

Pyrrolidine-2-carboxylate esters substituted in the 3-, 4- or 5-positions were converted to their N'-aryl urea derivatives. Deprotonation at the 2-position to form a potassium enolate led to migration of the N'-aryl substituent to the 2 position of the pyrrolidine ring, followed by cyclization of the resulting urea to give bicyclic α-aryl hydantoin derivatives of substituted prolines. Depending on the substitution pattern of the starting material, high diastereoselectivity was observed in the aryl migration, allowing formation of the products in enantiomerically enriched form, despite the intermediacy of a planar enolate. The hydrolysis of the bicyclic hydantoins under basic conditions gave a range of enantiopure and enantioenriched quaternary α-aryl proline derivatives.

Depression, family and cellular immunity: Influence of family relationships and cellular immunity on the severity of depression.

BACKGROUND: Exposure to stress activates the hypothalamic-pituitary-adrenal axis through the release of catecholamines, which modify humoral and cellular immunity. On the one hand, this psycho-immunological theory makes it possible to forge links between immunity and depression. On the other hand, we know that family determinants are an important variable in the model of vulnerability to depression. Our study weighs the influence of cellular immunity and family relations on the severity of depression. SUBJECTS AND METHOD: 498 inpatients with major depressive disorder were enrolled in an open-label trial. In addition to a socio-demographic questionnaire, they completed Olsen's FACES III and the Beck Depression Inventory (BDI). Flow cytometry was used to assess lymphocyte subsets. RESULTS: In terms of immunity, there are correlations between the BDI and percentages of CD3 (p=0.015; r=-0.112), CD4 (p<0.000; r=-0.175), CD4/CD8 (p=0.045; r=-0.093) and CD16 and 56 (p=0.014; r=0.113). In terms of family relationships, there is a correlation between the BDI and family of origin, both for cohesion (p=0.007; r=-0.169) and adaptability (p=0.035; r=-0.133) measures. With respect to the relationship between family dynamics and immunity, there are correlations between adaptability in the family of origin and CD3 (p=0.04; r=0.094) and CD4 (p=0.044; r=0.093). A logistic regression model for family variables explained 11.4% of the BDI, compared to 12.7% for immune variables, while a model including the two explained 16%. CONCLUSIONS: While both the family and immunity can explain the BDI, it is surprising they have a greater effect in combination than individually. This suggests that the psycho-immunological theory should look at the relation between immunity and family life, notably in relation to the family of origin.

RING1B O-GlcNAcylation regulates gene targeting of polycomb repressive complex 1 in human embryonic stem cells.

O-linked-N-acetylglucosamine (O-GlcNAc) post-translationally modifies and regulates thousands of proteins involved in various cellular mechanisms. Recently, O-GlcNAc has been linked to human embryonic stem cells (hESC) differentiation, however the identity and function of O-GlcNAc proteins regulating hESC remain unknown. Here, we firstly identified O-GlcNAc modified human stem cell regulators such as hnRNP K, HP1γ, and especially RING1B/RNF2. Thereafter, we focused our work on RING1B which is the catalytic subunit of the polycomb repressive complex 1 (PRC1) a major epigenetic repressor essential for pluripotency maintenance and differentiation. By point-mutation, we show that T(250)/S(251) and S(278) RING1B residues are bearing O-GlcNAc, and that T(250)/S(251) O-GlcNAcylation decreases during differentiation. O-GlcNAc seems to regulate RING1B-DNA binding as suggested by our ChIP-sequencing results. Non-O-GlcNAcylated RING1B is found to be enriched near cell cycle genes whereas O-GlcNAcylated RING1B seems preferentially enriched near neuronal genes. Our data suggest that during hESC differentiation, the decrease of RING1B O-GlcNAcylation might enable PRC1 to switch its target to induce neuron differentiation. Overall, we demonstrate that O-GlcNAc modifies and regulates an essential epigenetic tool, RING1B, which may contribute to hESC pluripotency maintenance and differentiation.

Conformational cooperativity between helical domains of differing geometry in oligoamide-oligourea foldamer chimeras.

Linking together an oligourea and an oligoamide foldamer gives rise to a conformationally well-defined structure, despite the different hydrogen-bonding patterns in the two domains, provided the oligomers are ligated amide C terminus to urea N terminus. A powerful screw-sense preference induced at the N terminus of the resulting chimeric structure provides evidence for cooperative conformational interactions within the 'block co-foldamer'.

Inducing achiral aliphatic oligoureas to fold into helical conformations.

The ability of urea-linked oligomers of achiral diamines (achiral analogues of the well-established chiral oligourea foldamers) to adopt helical conformations was explored spectroscopically. Up to four achiral units were ligated either to a well-formed helical trimer or to a single chiral diamine, and the extent to which they adopted a screw-sense preference was determined by NMR and CD. In the best performing cases, a trimeric chiral oligourea and even a single cis-cyclohexanediamine monomer induced folding into a helical conformation.

Multiple reaction monitoring mass spectrometry for the discovery and quantification of O-GlcNAc-modified proteins.

O-linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification regulating proteins involved in a variety of cellular processes and diseases. Unfortunately, O-GlcNAc remains challenging to detect and quantify by shotgun mass spectrometry (MS) where it is time-consuming and tedious. Here, we investigate the potential of Multiple Reaction Monitoring Mass Spectrometry (MRM-MS), a targeted MS method, to detect and quantify native O-GlcNAc modified peptides without extensive labeling and enrichment. We report the ability of MRM-MS to detect a standard O-GlcNAcylated peptide and show that the method is robust to quantify the amount of O-GlcNAcylated peptide with a method detection limit of 3 fmol. In addition, when diluted by 100-fold in a trypsin-digested whole cell lysate, the O-GlcNAcylated peptide remains detectable. Next, we apply this strategy to study glycogen synthase kinase-3 beta (GSK-3ß), a kinase able to compete with O-GlcNAc transferase and modify identical site on proteins. We demonstrate that GSK-3ß is itself modified by O-GlcNAc in human embryonic stem cells (hESC). Indeed, by only using gel electrophoresis to grossly enrich GSK-3ß from whole cell lysate, we discover by MRM-MS a novel O-GlcNAcylated GSK-3ß peptide, bearing 3 potential O-GlcNAcylation sites. We confirm our finding by quantifying the increase of O-GlcNAcylation, following hESC treatment with an O-GlcNAc hydrolase inhibitor. This novel O-GlcNAcylation could potentially be involved in an autoinhibition mechanism. To the best of our knowledge, this is the first report utilizing MRM-MS to detect native O-GlcNAc modified peptides. This could potentially facilitate rapid discovery and quantification of new O-GlcNAcylated peptides/proteins.

Intramolecular trapping of allenylzincs by carbonyl groups.

Allenylzinc formed via oxygen-promoted zinc/iodine exchange between propargyl iodides and diethylzinc can be trapped by intramolecular reaction with various electrophiles such as aldehydes, ketones, esters, carbamates, and imides. Potentially useful building blocks were obtained in high yields.

Intramolecular arylation of amino acid enolates.

Dianionic enolates formed from N'-aryl urea derivatives of amino acids undergo intramolecular C-arylation by attack of the enolate anion on the N'-aryl ring, leading to a hydantoin derivative of a quaternary amino acid. In situ IR studies allow identification of four intermediates on the reaction pathway.

Excess of O-linked N-acetylglucosamine modifies human pluripotent stem cell differentiation.

O-linked-N-acetylglucosamine (O-GlcNAc), a post translational modification, has emerged as an important cue in controlling key cell mechanisms. Here, we investigate O-GlcNAc's role in the maintenance and differentiation of human pluripotent stem cells (hPSC). We reveal that protein expression of O-GlcNAc transferase and hydrolase both decreases during hPSC differentiation. Upregulating O-GlcNAc with O-GlcNAc hydrolase inhibitors has no significant effect on either the maintenance of pluripotency in hPSC culture, or the loss of pluripotency in differentiating hPSC. However, in spontaneously differentiating hPSC, excess O-GlcNAc alters the expression of specific lineage markers: decrease of ectoderm markers (PAX6 by 53-88%, MSX1 by 26-49%) and increase of adipose-related mesoderm markers (PPARγ by 28-100%, C/EBPα by 46-135%). All other lineage markers tested (cardiac, visceral-endoderm, trophectoderm) remain minimally affected by upregulated O-GlcNAc. Interestingly, we also show that excess O-GlcNAc triggers a feedback mechanism that increases O-GlcNAc hydrolase expression by 29-91%. To the best of our knowledge, this is the first report demonstrating that excess O-GlcNAc does not affect hPSC pluripotency in undifferentiated maintenance cultures; instead, it restricts the hPSC differentiation towards specific cell lineages. These data will be useful for developing targeted differentiation protocols and aid in understanding the effects of O-GlcNAc on hPSC differentiation.

EPR investigation of zinc/iodine exchange between propargyl iodides and diethylzinc: detection of propargyl radical by spin trapping.

The production of propargyl radicals in the reaction of dialkylzincs with propargyl iodides in nondegassed medium was investigated by EPR using tri-tert-butylnitrosobenzene (TTBNB) as a spin trap. The radical mechanism and the nature of the observed species were confirmed by the trapping of propargyl radicals generated by an alternative pathway: i.e., upon irradiation of propargyl iodides in the presence of hexa-n-butyldistannane. In dialkylzinc-mediated experiments a high concentration of adduct was instantaneously observed, whereas no spontaneous production of spin adduct was detected in a blank experiment performed with the propargylic iodide and TTBNB in the absence of diethylzinc. Under irradiation in the presence of distannane, two different species were observed at the very beginning of the irradiation; the nitroxide resulting from the trapping of propargyl radical at the propargyl carbon remained the only species detected after irradiating for several minutes. The absence of adducts resulting from the trapping of allenyl canonical forms was supported by DFT calculations and by the preparation of an authentic sample.

Aminomethylation of Michael acceptors: complementary radical and polar approaches mediated by dialkylzincs.

Phtalimidomethyl iodide and substituted maleimidomethyl iodide were used as radical precursors in dialkylzinc-mediated radical addition to diethyl fumarate. The reactions led stereoselectively to functionalized pyrrolizidines. The radical mechanism was supported by spin-trapping experiments and rationalized by theoretical calculations. Radical additions, on the one hand, and carbozincation followed by transmetalation with copper(I), on the other, were shown to be complementary methods to achieve the formal aminomethylation of activated unsaturated compounds.

Technical advances to genetically engineering human embryonic stem cells.

Human embryonic stem cells (hESC) are important to basic scientific research as an in vitro model system for the study of human development and to clinical research as an invaluable cell source for regenerative medicine. The ability to genetically engineer hESC is a critical resource as it facilitates many fundamental studies to understand gene regulation and cell development. These techniques include (1) unidirectional or reversible; (2) non-, pseudo- or completely site-specific; and (3) endogenous and/or pre-engineered DNA sequences modification; where each has its own strengths and limitations. This article reviews the various methodologies to genetically engineer hESC to achieve a stable gene insertion or deletion. We discuss the existing challenges of the well-established methodologies (lentivirus and Cre/loxP system), and further examine recent advances in this field, such as the latest genetic modifying tools (phiC31 integrase, PiggyBac transposase and zinc finger nucleases). We also propose new opportunities for future developments to aid genetic modifications of hESC, and new applications for future basic and therapeutic research in hESC.

Unprecedented noncatalyzed anti-carbozincation of diethyl acetylenedicarboxylate through alkylzinc group radical transfer.

The radical carbozincation of diethyl acetylenedicarboxylate, performed at room temperature in the presence of air, leads to fumaric derivatives through a selective alkylzinc group radical transfer controlled by coordination. The total trans stereocontrol is unprecedented, carbocupration is well-known to give the reversal selectivity at low temperature, while classical radical addition methodologies lead to mixtures of isomers.