128 research outputs found
Synthesis and Star/Linear Topology Transformation of a Mechanically Linked ABC Terpolymer
The synthesis of
an ABC star terpolymer containing one polymer
chain connected mechanically through a rotaxane linkage and its topology
transformation to a linear structure are reported. Pseudo[2]Ârotaxane,
which was designed as the key trifunctional species for the star polymer
synthesis, comprised a <i>sec</i>-ammonium axle with ethynyl
and hydroxy groups and a crown ether wheel with a trithiocarbonate
group. Stepwise polymer connections to the pseudo[2]Ârotaxane using
the three groups afforded a rotaxane-linked ABC star terpolymer. The
topology transformation from star to linear by the removal of the
attractive interaction between the axle and wheel components yielded
a linear ABC terpolymer via the wheel shifting to the axle end. The
spectroscopic and solution property changes clearly indicated the
occurrence of the polymer topology change
Iron-Catalyzed Remote Arylation of Aliphatic CâH Bond via 1,5-Hydrogen Shift
Catalytic amounts of an ironÂ(III)
salt and a N-heterocyclic carbene
ligand catalyze the arylation of 2-iodoalkylarenes with diphenylzinc
selectively at the Îł CâH bond of the alkyl side chain.
Several lines of evidence suggest that the iron catalyst reacts with
the aryl iodide moiety of the substrate to generate an aryliron intermediate
that behaves in a radical manner and cleaves the aliphatic CâH
bond through 1,5-hydrogen transfer; the resulting alkyliron intermediate
undergoes reductive elimination to give the arylated product
Diols, αâKetols, and Diones as 2<sub>2Ï</sub> Components in [2+2+2] Cycloadditions of 1,6-Diynes via Ruthenium(0)-Catalyzed Transfer Hydrogenation
The
first use of vicinal diols, ketols, or diones as 2<sub>2Ï</sub> components in metal-catalyzed [2+2+2] cycloaddition is described.
Using ruthenium(0) catalysts, 1,6-diynes form ruthenaÂcycloÂpentaÂdienes
that engage transient diones in successive carbonyl addition. Transfer
hydrogenolysis of the resulting rutheniumÂ(II) diolate mediated by
the diol or ketol reactant releases the cycloadduct with regeneration
of ruthenium(0) and the requisite dione
Osmium(0)-Catalyzed CâC Coupling of Ethylene and αâOlefins with Diols, Ketols, or Hydroxy Esters via Transfer Hydrogenation
OsmiumÂ(0) complexes derived from
Os<sub>3</sub>(CO)<sub>12</sub> and XPhos (2-dicyclohexylphosphino-2âČ,4âČ,6âČ-triisopropylbiphenyl)
catalyze the CâC coupling of α-hydroxy esters <b>1a</b>â<b>1i</b>, α-ketols <b>1j</b>â<b>1o</b>, or 1,2-diols <i>dihydro</i>-<b>1j</b>â<b>1o</b> with ethylene <b>2a</b> to form ethylated tertiary
alcohols <b>3a</b>â<b>3o</b>. As illustrated in
couplings of 1-octene <b>2b</b> with vicinally dioxygenated
reactants <b>1a</b>, <b>1b</b>, <b>1i</b>, <b>1j</b>, <b>1k</b>, <b>1m</b>, higher α-olefins
are converted to adducts <b>4a</b>, <b>4b</b>, <b>4i</b>, <b>4j</b>, <b>4k</b>, <b>4m</b> with complete
levels of branched regioselectivity. Oxidation level independent CâC
coupling is demonstrated by the reaction of 1-octene <b>2b</b> with diol <i>dihydro</i>-<b>1k</b>, α-ketol <b>1k</b>, and dione <i>dehydro</i>-<b>1k</b>. Functionalized
olefins <b>2c</b>â<b>2f</b> react with ethyl mandelate <b>1a</b> to furnish adducts <b>5a</b>â<b>8a</b> as single regioisomers. The collective data, including deuterium
labeling studies, are consistent with a catalytic mechanism involving
olefinâdione oxidative coupling to form an oxa-osmacyclopentane,
which upon reductive cleavage via hydrogen transfer from the secondary
alcohol reactant releases the product of carbinol <i>C</i>-alkylation with regeneration of the ketone. Single-crystal X-ray
diffraction data of the dinuclear complex Os<sub>2</sub>(CO)<sub>4</sub>(O<sub>2</sub>CR)<sub>2</sub>(XPhos)<sub>2</sub> and the trinuclear
complex Os<sub>3</sub>(CO)<sub>11</sub>(XPhos) are reported. These
studies suggest increased Ï-backbonding at the stage of the
metalâolefin Ï-complex plays a critical role in facilitating
alkeneâcarbonyl oxidative coupling, as isostructural ruthenium(0)
complexes, which are weaker Ï-donors, do not catalyze the transformations
reported herein
Epithelial-Mesenchymal Transition Stimulates Human Cancer Cells to Extend Microtubule-based Invasive Protrusions and Suppresses Cell Growth in Collagen Gel
<div><p>Epithelial-mesenchymal transition (EMT) is a crucial event in tumor invasion and metastasis. However, most of past EMT studies have been conducted in the conventional two-dimensional (2D) monolayer culture. Therefore, it remains unclear what invasive phenotypes are acquired by EMT-induced cancer cells. To address this point, we attempted to characterize EMT cells in more physiological, three-dimensional (3D) collagen gel culture. EMT was induced by treating three human carcinoma cell lines (A549, Panc-1 and MKN-1) with TGF-Ă. The TGF-Ă treatment stimulated these cells to overexpress the invasion markers laminin Îł2 and MT1-MMP in 2D culture, in addition to the induction of well-known morphological change and EMT marker expression. EMT induction enhanced cell motility and adhesiveness to fibronectin and collagen in 2D culture. Although EMT cells showed comparable cell growth to control cells in 2D culture, their growth rates were extremely suppressed in soft agar and collagen gel cultures. Most characteristically, EMT-induced cancer cells commonly and markedly extended invasive protrusions in collagen gel. These protrusions were mainly supported by microtubules rather than actin cytoskeleton. Snail-introduced, stable EMT cells showed similar protrusions in 3D conditions without TGF-Ă. Moreover, these protrusions were suppressed by colchicine or inhibitors of heat shock protein 90 (HSP-90) and protein phosphatase 2A. However, MMP inhibitors did not suppress the protrusion formation. These data suggest that EMT enhances tumor cell infiltration into interstitial stroma by extending microtubule-based protrusions and suppressing cell growth. The elevated cell adhesion to fibronectin and collagen and high cell motility also seem important for the tumor invasion.</p> </div
Effects of various inhibitors on protrusion formation of MKN-1 cells in 3D collagen gel.
<p>MKN-1 cells were incubated with 10 ng/ml TGF-Ă in serum-containing medium in 3D collagen gel culture, as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053209#pone-0053209-g005" target="_blank">Figures 5</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053209#pone-0053209-g006" target="_blank">6</a>. To the collagen culture were added various inhibitors, and the protrusion formation was quantified 24 h later (A, C and D) or 3 h later (B). (A) The indicated concentrations of cytochalasin B and colchicine were added into the culture medium at the same time as the TGF-Ă addition. (B) Cytochalasin B (5 ”M) and colchicine (1 ”M) were added into the culture medium after incubation with TGF-Ă for 24 h. (C) MKN-1 cells were treated without (Control) or with cantharidin (1 ”M) and/or radicicol (1 ”M) as described in (A). (D) MKN-1 cells were pretreated with 10 ”g/ml of each neutral antibody at 37°C for 30 min, and the pretreated cells were embedded into collagen gel containing 10 ”g/ml of the indicated anti-integrin antibody and 10 ng/ml TGF-Ă. All these inhibitors were not cytotoxic at least under the above experimental conditions, as analyzed by the trypan blue staining. However, cytotoxic effects became evident when the cells were incubated with 5 ”M cytochalasin B or 1 ”M colchicine for 24 h.</p
Cell adhesion activity of Lm332-ECM and purified Lm332 toward NHK cells.
<p>ECMs from Ă3Îł2-HEK and Lm332-HEK cultures and Lm332-coated plates were prepared as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035546#pone-0035546-g004" target="_blank">Figure 4</a>. (A) Phase-contrast microscopic images of NHK cells after 10 min incubation. Original magnification, Ă300. Lm332 protein was coated at 1.0 ”g/ml on the plate. (B) NHK cells suspended in KGM growth medium were inoculated into each well and then incubated at 37°C for 10 min. After the incubation, non-adherent cells were removed, and adherent cells were quantified. Numerical values under three right columns indicate the concentration at ”g/ml of coated Lm332 protein. Each bar represents the mean ± S.D. of the fluorescent intensity (FI) for adherent cells in triplicate assays. The data shown are representative of at least three independent experiments performed.</p
A Metallacycle Fragmentation Strategy for Vinyl Transfer from Enol Carboxylates to Secondary Alcohol CâH Bonds via Osmium- or Ruthenium-Catalyzed Transfer Hydrogenation
A strategy
for catalytic vinyl transfer from enol carboxylates
to activated secondary alcohol CâH bonds is described. Using
XPhos-modified ruthenium(0) or osmium(0) complexes, enol carboxylateâcarbonyl
oxidative coupling forms transient ÎČ-acyloxy-oxametallacycles,
which eliminate carboxylate to deliver allylic rutheniumÂ(II) or osmiumÂ(II)
alkoxides. Reduction of the metalÂ(II) salt via hydrogen transfer from
the secondary alcohol reactant releases the product of carbinol CâH
vinylation and regenerates ketone and zero-valent catalyst
Fine structures of Lm332-ECM (left), Ă3Îł2-ECM (center) and purified Lm332 (right) were analyzed by TEM at a magnification of Ă 50,000.
<p>Bars indicate 100 nm.</p
Effect of sodium selenate on Lm332 deposition by NHK cells.
<p>(A) Immunoblotting analysis. NHK cells were inoculated in serum-free medium at a density of 4Ă10<sup>5</sup> cells per 35-mm dish, incubated overnight, and treated with (+) or without (â) 0.1 mM sodium selenate (Sigma) at 37°C for 24 h. After the incubation, the ECM and CM were prepared from each culture and analyzed for the laminin α3 chain by immunoblotting as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035546#pone-0035546-g001" target="_blank">Figure 1</a>. (B) The ECMs from the control (none) and selenate-treated cultures (+selenate) were subjected to immunofluorescence staining with the anti-laminin α3 chain antibody BG5. (C) Phase-contrast micrographs of control and selenate-treated cultures. Other experimental conditions are described in â<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035546#s4" target="_blank">Materials and Methods</a>â.</p
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