An Osmium(III)/Osmium(V) Redox Couple Generating Os^V(O)(OH) Center for <i>cis</i>-1,2-Dihydroxylation of Alkenes with H₂O₂: Os Complex with a Nitrogen-Based Tetradentate Ligand

For the synthesis of the 1,2-diols, <i>cis</i>-1,2-dihydroxylation of alkenes catalyzed by osmium­(VIII) tetroxide (OsO₄) is a powerful method. However, OsO₄ is quite toxic due to its highly volatile and sublimable nature. Thus, the development of alternative catalysts for <i>cis</i>-1,2-dihydroxylation of alkenes is highly challenging. Our approach involves the use of a nitrogen-based tetradentate ligand, tris­(2-pyridylmethyl)­amine (tpa), for an osmium center to develop a new osmium catalyst and hydrogen peroxide (H₂O₂) as a cheap and environmentally benign oxidant. The new Os–tpa complex acts as a very efficient turnover catalyst for <i>syn</i>-selective dihydroxylation of various alkenes (turnover number ∼1000) in aqueous media, and H₂O₂ oxidant is formally incorporated into the products quantitatively (100% atom efficiency). The reaction intermediates involved in the catalytic cycle have been isolated and characterized crystallographically as [Os^III(OH)­(H₂O)­(tpa)]²⁺ and [Os^V(O)­(OH)­(tpa)]²⁺ complexes. The observed <i>syn</i>-selectivity, structural characteristics of the intermediates, and kinetic studies have suggested a concerted [3 + 2]-cycloaddition mechanism between [Os^V(O)­(OH)­(tpa)]²⁺ and alkenes, which is strongly supported by DFT calculations

Experimental and Theoretical Studies on the Platinum-Mediated Selective C(sp)–Si Bond Cleavage of Alkynylsilanes

A series of <i>cis</i>-alkynyl­(silyl)­platinum­(II) complexes was prepared via the chemoselective C­(sp)–Si bond cleavage of alkynylsilanes by a platinum(0) complex ligated with the P–N hemilabile bidentate ligand. The coordination of the triple bond to the platinum center triggers selective C­(sp)–Si bond cleavage. Hammett plots of the ³¹P­{¹H} NMR spectroscopic properties (δ and <i>J</i> values) reflect an electronic effect on platinum­(II) complexes; trans substituents of arylethynyl groups are influenced, but cis-positioned silyl groups are not affected, as evidenced by ²⁹Si­{¹H} NMR. In comparison, Hammett plots show that C­(sp)–Si bond cleavage rates are accelerated by electron-rich alkynylsilanes, which is opposite to the ordinary oxidative addition of aryl halides to transition metals often observed in catalytic cross-coupling reactions. A DFT calculation reveals that intermediates and transition states are stabilized by electron-rich alkynylsilanes and that the five-membered hemilabile P–N ligand is essential, in which a reactive electron-deficient 14-electron platinum(0) species is produced via the dissociation of nitrogen, giving rise to a monodentate phosphine coordination. Electron-rich alkynylsilanes allow decreased π back-donation from the platinum center to the ligand, accelerating the dissociation of the more labile nitrogen. Steric congestion between diisopropylphosphino and silyl groups thermodynamically disfavors C­(sp)–Si bond cleavage

Facile Estimation of Catalytic Activity and Selectivities in Copolymerization of Propylene Oxide with Carbon Dioxide Mediated by Metal Complexes with Planar Tetradentate Ligand

Mechanistic studies were conducted to estimate (1) catalytic activity for PPC, (2) PPC/CPC selectivity, and (3) PPC/PPO selectivity for the metal-catalyzed copolymerization of propylene oxide with carbon dioxide [PPC: poly­(propylene carbonate); CPC = cyclic propylene carbonate; PPO: poly­(propylene oxide)]. Density functional theory (DFT) studies demonstrated that the Δ<i>G</i>_crb – Δ<i>G</i>_epx value should be an effective indicator for the catalytic activities [Δ<i>G</i>_epx: dissociation energy of ethylene oxide from the epoxide-coordinating metal complex; Δ<i>G</i>_crb: dissociation energy of methyl carbonate from the metal–carbonate complex]. In addition, metal complexes with a subthreshold Δ<i>G</i>_epx value were found to show low PPC/CPC selectivity. The PPC/PPO selectivity was related to the Δ<i>G</i>_alk – Δ<i>G</i>_epx value and steric environment around the metal center (Δ<i>G</i>_alk: dissociation energy of alkoxide ligand from the metal center). Based on the mechanistic studies, two metal complexes were designed and applied to the copolymerization to support validity of these indicators. The results presented here should be useful for brand-new catalyst candidates since these indicators can be easily calculated by DFT method without computing transition states

Skeletal Rearrangement of Cyano-Substituted Iminoisobenzofurans into Alkyl 2‑Cyanobenzoates Catalyzed by B(C₆F₅)₃

An efficient method for the direct conversion of cyano-substituted iminoisobenzofurans into their corresponding alkyl 2-cyanobenzoates has been developed. This transformation proceeds via cleavage of C–C, C–O, and C–N bonds in starting iminoisobenzofurans. DFT study revealed that intermediate α-iminonitriles are produced in situ via C–C bond formation between 2-iminium benzoates and a cyanide ion. Generation of isocyanide as the byproduct in a more thermodynamic manner in DFT calculations also supports the experimental results

Incorporation of fallow weed increases phosphorus availability in a farmer’s organic rice fields on allophanic Andosol in eastern Japan

<p>We investigated the amount of soil phosphorus (P) in a farmer’s paddy fields under organic farming (OF) for various periods from 0 to 22 years as well as other farmers’ fields under conventional farming. All the fields are located in allophanic Andosol with long history of P fertilizer application, and some of them have been converted to OF across years. After conversion to OF, P was supplied only with winter fallow weeds mainly Foxtail (<i>Alopecurus aequalis</i>), rice residues (rice bran and straw), and guano. We determined total-P (Tot-P) and plant-available P (Av-P), which consists of Truog-P (Tru-P) and Bray-2-P under reducing condition with ascorbic acid (Asc-P), in soils of each field. For both Av-Ps, the ratio to Tot-P increased across years under OF following quadratic functions with both linear and quadratic terms being statistically significant. The ratios showed little changes for the initial 15 (Tru-P) or 10 (Asc-P) years and increased rapidly thereafter. These temporal changes in Av-P were consistent with the rapid increase of the amount of P accumulated in the winter fallow weeds and incorporated in the fields after beginning of OF. These results led us to the hypothesis that the incorporation of winter weeds has contributed to the increase of Av-P in the organic fields across years. We tested this hypothesis by investigating temporal changes of Av-P after suspending the weed incorporation for 2 consecutive years in plots of the organic fields. Both Av-Ps were significantly greater in plots with continued weed incorporation (CWI) than those in plots with its suspension. We further found that the increase of Asc-P in plots with CWI was 4.9-fold the input of total P in the incorporated weeds. This suggests that the incorporation of winter fallow weeds enhanced soil-P availability beyond the supply of P accumulated in the weeds.</p

R50E is a dominant-negative inhibitor of FGF signaling.

<p>A.R50E competed with WT FGF1 for binding to the FGFR1 D2D3 fragment. Biotinylated FGF1 and increasing concentrations of unlabelled FGF1 or FGF1 mutants were incubated with the immobilized FGFR1 D2D3 fragment and bound biotinylated FGF1 was measured with HRP-conjugated avidin. The 3xA mutation located at the predicted FGF-FGFR binding site <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010273#pone.0010273-Presta1" target="_blank">[1]</a> was used as a negative control. The results indicate that R50E competitively blocked the binding of biotinylated WT FGF1 to FGFR fragment to the same extent as WT FGF1. * P<0.0001, ** P = 0.0002 (n = 3) compared to +3A. There is no significant difference between WT and R50E at 10 µg/ml. B. R50E suppressed the DNA synthesis in BaF3-FGFR1c cells induced by WT FGF1. We cultured BaF3-FGFR1c cells in the presence of 1 ng/ml WT FGF1 and 25 or 50 ng/ml R50E for 24 h instead of IL-3 and measured incorporation of BrdU. Results are shown as means +/−SEM. * P<0.0001, ** P = 0.0003 by t-test (n = 4) compared to No R50E. C. R50E suppressed the proliferation of BaF3-FGFR1c cells induced by WT FGF1. We cultured BaF3-FGFR1c cells in the presence of 1 ng/ml WT FGF1 and 100 or 200 ng/ml R50E for 24 h instead of IL-3 and measured cell proliferation by MTS assays. Results are shown as means +/− SEM. * P<0.0025, ** P = 0.0093 by t-test (n = 3) compared to No R50E.</p

R50E is less effective in inducing sustained ERK1/2 activation in NIH3T3 cells.

<p>A. Time-course of ERK1/2 activation and FRS2α activation induced by WT FGF1- or R50E-stimulated cells. We stimulated serum-starved cells with 5 ng/ml WT FGF1 or R50E at indicated time points and analyzed cell lysates by Western blotting using anti phospho-FRS2α, phospho-ERK1/2, total-FRS2α, or ERK1/2 antibody. A representative data is shown from several independent experiments. B. Time-course of WT FGF1 or R50E induced FGFR1 phosphorylation. We stimulated serum starved cells with 5 ng/ml WT FGF1 or R50E in the presence of 5 µg/ml heparin, and analyzed cell lysates by Western blotting. A representative data is shown from several independent experiments. C. ERK1/2 activation levels more rapidly reduced in cells stimulated with R50E than cells stimulated with WT FGF1. Lysates of cells stimulated with R50E or WT FGF1 were analyzed by Western blotting using anti phospho- or total FRS2α antibody. Fold increase of ERK1/2 signals (phosphorylated protein/total protein) is shown with control “time 0” as 1. Data are shown as means +/− SEM of triplicate experiments. ERK1/2 activation at 6 h with R50E is significantly lower in than with WT FGF1 (* P<0.05, n = 3). D. FRS2α phosphorylation levels reduced more rapidly in cells stimulated with R50E than in cells stimulated with WT FGF1. Lysates of cells stimulated with R50E or WT FGF1 were analyzed by Western blotting using anti phospho- or total FRS2α antibody. Relative intensity of FRS2α signals is shown with density at 15 min as 100. The level of total FRS2α in each lane was comparable using anti-FRS2α (data not shown). FRS2α phosphorylation at 6 h with R50E is significantly lower in than with WT FGF1 (* P<0.05, n = 3). E. Time-course of ERK1/2 activation induced by WT FGF1-or R50E-stimulated human umbilical endothelial cells (HUVECs). Experiments were performed as described in A except that HUVEC was used.</p

WT FGF1 induced FGFR1-FGF-αvβ3 ternary complex formation, but R50E was defective in this function.

<p>We immunoprecipitated the FGFR1-αvβ3 complex from cell lysates with anti-FGFR1 (A) or anti-β3 mAb (B), and analyzed the immuno-purified materials by Western blot analysis. A. WT FGF1 induced co-immunoprecipitation of integrin β3 and SHP-1 with FGFR1 using anti-FGFR1, but R50E was defective in this function. B. WT FGF1 induced co-immunoprecipitation of FGFR1 with integrin β3 using anti-integrin β3, but R50E was defective in this function. We stimulated serum-starved NIH 3T3 cells with 5 ng/ml WT FGF1 or R50E for 1 h in the presence of 5 µg/ml heparin. C. Co-precipitation of integrin β3 and FGFR1 upon FGF1 stimulation in HUVEC. Serum-starved HUVEC were stimulated by 5 ng/ml WT FGF1 or R50E with 5 µg/ml heparin for 1 h. Cell lysates were immunoprecipitated with anti-FGFR1 or anti-β3 monoclonal antibody, and the immunoprecipitates were analyzed by Western blotting. D. WT FGF and R50E similarly activated c-Src. We stimulated serum starved NIH 3T3 cells with WT FGF1 or R50E, and cell lysates were analyzed by Western blotting using antibodies specific to phospho-c-Src or c-Src. E. Time-course of embryonic fibroblasts from SHP-2 (−/−) or control mice. Serum starved cells were treated with WT FGF1 or R50E (5 ng/ml) for the time indicated and cell lysates were analyzed by Western blotting.</p

FGFR and ERK signaling is required for FGF1 to mediate TGF-β1 induced EMT in MCF10A cells.

<p><i>A and B</i>, Starved MCF10A cells were stimulated with 5 ng/ml TGF-β1 and 50 ng/ml FGF1 in the presence of 1 μM PD173074 specific inhibitor of FGFR1 (A) or 10 μM U0126 specific inhibitor of MEK1 (B) for 48 h. DMSO was used as a solvent control for the chemicals. Cells were then lysed, and protein levels were analyzed by Western blotting with the indicated antibodies. Bands intensity was measured by densitometry.</p