Rules of Chemospecificity of Nucleophilc Ring-opening of Dithia-/Oxathia-Phospholane Towards the Selective Synthesis of Nucleoside 5’-O-Pα-Thio/Dithio/Trithio-Phosphate Ester Conjugates

DBU-assisted nucleophilic ring-opening of both uridine-5’-(2-thio-1,3,2-dithia-phospholane), 3, and uridine-(2-thio-1,3,2-oxathia-phospholane), 8, lasted 2 min at RT and resulted in quantitative yields of uridine-5’-phosphoro-di/trithioate esters. Furthermore, it was selective for alcohol and thiol vs. amine nucleophiles. Yet, reaction of mercaptoethanol with 3, was chemo-specific for the oxygen vs. sulfur nucleophile, while for the reaction of mercaptoethanol with 8, the opposite chemo-specificity was observed, probably related to the steric hindrance in the former case. The observed chemospecificity opens facile avenue for the synthesis of nucleoside-5’-O-Pα-thio/dithio/trithio-phosphate ester derivative

Electrostatically Guided DynamicsThe Root of Fidelity in a Promiscuous Terpene Synthase?

Terpene cyclases are responsible for the initial cyclization cascade in the multistep synthesis of more than 60 000 known natural products. This abundance of compounds is generated using a very limited pool of substrates based on linear isoprenoids. The astounding chemodiversity obtained by terpene cyclases suggests a tremendous catalytic challenge to these often promiscuous enzymes. In the current study we present a detailed mechanistic view of the biosynthesis of the monoterpene bornyl diphosphate (BPP) from geranyl diphosphate by BPP synthase using state of the art simulation methods. We identify the bornyl cation as an enzyme-induced bifurcation point on the multidimensional free energy surface, connecting between the product BPP and the side product camphene. Chemical dynamics simulations suggest that the active site diphosphate moiety steers reaction trajectories toward product formation. Nonetheless, chemical dynamics is not precise enough for exclusive product formation, providing a rationale for the lack of fidelity in this promiscuous terpene cyclase

Phenyl-imidazolo-cytidine Analogues: Structure–Photophysical Activity Relationship and Ability To Detect Single DNA Mismatch

To expand the arsenal of fluorescent cytidine analogues for the detection of genetic material, we synthesized <i>para</i>-substituted phenyl-imidazolo-cytidine (^PhImC) analogues <b>5a</b>–<b>g</b> and established a relationship between their structure and fluorescence properties. These analogues were more emissive than cytidine (λ_em 398–420 nm, Φ 0.009–0.687), and excellent correlation was found between Φ of <b>5a</b>–<b>g</b> and σ_p^– of the substituent on the phenyl-imidazolo moiety (<i>R</i>² = 0.94). Calculations suggested that the dominant tautomer of ^PhImC in methanol solution is identical to that of cytidine. DFT calculations of the stable tautomer of selected ^PhImC analogues suggested a relationship between the HOMO–LUMO gap and Φ and explained the loss of fluorescence in the nitro analogue. Incorporation of the CF₃-^PhImdC analogue into a DNA probe resulted in 6-fold fluorescence quenching of the former. A <i>17-fold</i> reduction of fluorescence was observed for the <i>G-matched</i> duplex vs <b>ODN­(CF</b>_<b>3</b><b>-</b>^<b>Ph</b><b>ImdC)</b>, while for <i>A-mismatched</i> duplex, only a <i>2-fold</i> decrease was observed. Furthermore, since the quantum yield of <b>ODN­(CF</b>_<b>3</b><b>-</b>^<b>Ph</b><b>ImdC)</b>:<b>ODN­(G)</b> was reduced 17-fold vs that of a single strand, whereas that of <b>ODN­(CF</b>_<b>3</b><b>-</b>^<b>Ph</b><b>ImdC)</b>:<b>ORN­(G)</b> was reduced only 3.8-fold, <b>ODN­(CF</b>_<b>3</b><b>-</b>^<b>Ph</b><b>ImdC)</b> appears to be a DNA-selective probe. We conclude that the <b>ODN­(CF</b>_<b>3</b><b>-</b>^<b>Ph</b><b>ImdC)</b> probe, exhibiting emission sensitivity upon single nucleotide replacement, may be potentially useful for DNA single nucleotide polymorphism (SNP) typing

Chemical Control in the Battle against Fidelity in Promiscuous Natural Product Biosynthesis: The Case of Trichodiene Synthase

Terpene cyclases catalyze the highly stereospecific molding of polyisoprenes into terpenes, which are precursors to most known natural compounds. The isoprenoids are formed via intricate chemical cascades employing rich, yet highly erratic, carbocation chemistry. It is currently not well understood how these biocatalysts achieve chemical control. Here, we illustrate the catalytic control exerted by trichodiene synthase, and in particular, we discover two features that could be general catalytic tools adopted by other terpenoid cyclases. First, to avoid formation of byproducts, the enzyme raises the energy of bisabolyl carbocation, which is a general mechanistic branching point in many sesquiterpene cyclases, resulting in an essentially concerted cyclization cascade. Second, we identify a sulfur–carbocation dative bonding interaction that anchors the bisabolyl cation in a reactive conformation, avoiding tumbling and premature deprotonation. Specifically, Met73 acts as a chameleon, shifting from an initial sulfur−π interaction in the Michaelis complex to a sulfur–carbocation complex during catalysis

Rules for the Design of Highly Fluorescent Nucleoside Probes: 8‑(Substituted Cinnamyl)-Adenosine Analogues

Currently, there are no tools that can help the design of useful fluorescent analogues. Hence, we synthesized a series of 8-(substituted cinnamyl)-adenosine analogues, <b>5</b>–<b>17</b>, and established a relationship between their structure and fluorescence properties. We attempted to find a correlation between maximum emission wavelengths (λ_em) of <b>5</b>–<b>17</b> or their quantum yields (φ), and Hammett constants (σ<i>_p</i> and σ<i>_m</i>) of the substituent on the cinnamyl moiety. A linear correlation was observed at low-medium σ values, but not at high σ values (≥0.7). Next, we explored correlation between λ_em and φ of <b>5</b>–<b>17</b> and computed HOMO and LUMO energy levels of fragments of <b>5</b>–<b>17</b>, i.e., 8-vinyl 9-Me-adenine (fluorescent molecule), <b>18</b>, and substituted toluene rings (fluoresence modulators), <b>19</b>–<b>30</b>. High φ correlated with relatively close LUMO levels of <b>19</b>–<b>30</b> and <b>18</b> (−0.076 to −0.003 eV). The electron density of LUMO of nitro analogues <b>9</b> and <b>15</b> is localized on the aryl ring only, which explains their low φ. Calculation of HOMO–LUMO gap of <b>5</b>–<b>17</b> enables accurate prediction of the λ_abs for a planned analogue, and LUMO levels of an aryl moiety vs 8-vinyl 9-Me-adenine, allows the prediction of high or low φ. These findings lay the ground for prediction of fluorescence properties of additional analogues having a similar structure

Developing Effective Electrodes for Supercapacitors by Grafting of Trihydroxybenzene onto Activated Carbons

International audienceThe specific capacity of activated carbon electrodes for supercapacitors may be enhanced with additional faradaic redox reactions by grafting of electroactive aromatic molecules with heteroatoms that act as redox centers. Such enrichment was demonstrated recently with anthraquinone and catechol using diazonium chemistry. Here, trihydroxybenzene, which has obvious advantages, was successfully grafted, yielding a mass enrichment of 25%. Electrochemical characterization in acidic aqueous solution after in situ methoxy deprotection demonstrated an initial specific capacity of 65 mAh g(-1), which faded only slightly to 55 mAh g(-1) after about 2000 cycles and remained stable for over 4500 cycles

2D TiS2 Flakes for Tetracycline Hydrochloride Photodegradation under Solar Light

Here, we report a simple route of synthesizing bulk layered TiS2 via chemical vapor transport (CVT) using non-toxic inorganic precursors, followed by successful isolation of few-layered TiS2 flakes using high-frequency-based liquid-phase exfoliation. Exfoliated TiS2 flakes exhibit significantly enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride (TCH) under simulated solar light irradiation, achieving ~ 95% degradation efficiency with its reaction rate constants six times higher than that of the bulk counterpart. The underlying degradation mechanism can be attributed to the fully exposed reactive sites originating from the well-defined layered structure. Trapping experiments coupled with electron paramagnetic resonance (EPR) measurements confirm the generation of electrons and hydroxyl radicals as major active species. The photodegradation pathway and intermediates of TCH were studied in-depth through liquid chromatography-mass spectrometry (LC-MS). The current work provides new insight into using exfoliated TiS2 for environmental remediation

Catechol-Modified Carbon Cloth as Hybrid Electrode for Energy Storage Devices

International audienc

Structure-function analysis of ceTIR-1/hSARM1 explains the lack of Wallerian axonal degeneration in C. elegans

Summary: Wallerian axonal degeneration (WD) does not occur in the nematode C. elegans, in contrast to other model animals. However, WD depends on the NADase activity of SARM1, a protein that is also expressed in C. elegans (ceSARM/ceTIR-1). We hypothesized that differences in SARM between species might exist and account for the divergence in WD. We first show that expression of the human (h)SARM1, but not ceTIR-1, in C. elegans neurons is sufficient to confer axon degeneration after nerve injury. Next, we determined the cryoelectron microscopy structure of ceTIR-1 and found that, unlike hSARM1, which exists as an auto-inhibited ring octamer, ceTIR-1 forms a readily active 9-mer. Enzymatically, the NADase activity of ceTIR-1 is substantially weaker (10-fold higher Km) than that of hSARM1, and even when fully active, it falls short of consuming all cellular NAD+. Our experiments provide insight into the molecular mechanisms and evolution of SARM orthologs and WD across species

The Therapeutic Potential of AN-7, a Novel Histone Deacetylase Inhibitor, for Treatment of Mycosis Fungoides/Sezary Syndrome Alone or with Doxorubicin.

The 2 histone deacetylase inhibitors (HDACIs) approved for the treatment of cutaneous T-cell lymphoma (CTCL) including mycosis fungoides/sezary syndrome (MF/SS), suberoylanilide hydroxamic acid (SAHA) and romidepsin, are associated with low rates of overall response and high rates of adverse effects. Data regarding combination treatments with HDACIs is sparse. Butyroyloxymethyl diethylphosphate (AN-7) is a novel HDACI, which was found to have selective anticancer activity in several cell lines and animal models. The aim of this study was to compare the anticancer effects of AN-7 and SAHA, either alone or combined with doxorubicin, on MF/SS cell lines and peripheral blood lymphocytes (PBL) from patients with Sezary syndrome (SPBL). MyLa cells, Hut78 cells, SPBL, and PBL from healthy normal individuals (NPBL) were exposed to the test drugs, and the findings were analyzed by a viability assay, an apoptosis assay, and Western blot. AN-7 was more selectively toxic to MyLa cells, Hut78 cells, and SPBL (relative to NPBL) than SAHA and also acted more rapidly. Both drugs induced apoptosis in MF/SS cell lines, SAHA had a greater effect on MyLa cell line, while AN-7 induced greater apoptosis in SPBL; both caused an accumulation of acetylated histone H3, but AN-7 was associated with earlier kinetics; and both caused a downregulation of the HDAC1 protein in MF/SS cell lines. AN-7 acted synergistically with doxorubicin in both MF/SS cell lines and SPBL, and antagonistically with doxorubicin in NPBL. By contrast, SAHA acted antagonistically with doxorubicin on MF/SS cell lines, SPBL, and NPBL, leaving <50% viable cells. In conclusion, AN-7 holds promise as a therapeutic agent in MF/SS and has several advantages over SAHA. Our data provide a rationale for combining AN-7, but not SAHA, with doxorubicin to induce the cell death in MF/SS