Sunday, March 24, 2013

Clip chemistry

Oxidation-Accelerated Hydrolysis of the Ortho Ester-Containing
Acid-Labile Polymers
Cheng-Cheng Song, Ran Ji, Fu-Sheng Du, De-Hai Liang, and Zi-Chen Li

An interesting example of "clip" chemistry: cleavage of 4-(pinacolboryl)-benzyl ester using H2O2, resulting in a carboxylic acid and p-quinone methide (which eventually undergoes hydration).

Speaking of Chromatography..

The presentation today on GPC and HPLC reminded me of a Baran Lab blog post I read not too long ago about moving bed chromatography and this paper specifically.
This type of chromatography was developed to better separate enantiomers by moving the stationary phase of a column in the opposite direction of the mobile phase as shown in the diagram below.
It's tough to move the stationary phase though without causing mixing and other problems and so they designed a simulated moving bed system. This is comprised of four sections of regular columns with various ports for feeding and extracting solvent in and out of. By rotating the ports at which you feed mobile phase into and extract products in the direction with the mobile phase flow, you simulate the solid moving in the opposite direction. This process is widely used in industry, the separation of fructose being a notable example.
Of course this requires tons of optimization which you can read about in that paper. 

C-H activation

Palladium(0)-Catalyzed Alkynylation of C(sp3)−H Bonds
Jian He, Masayuki Wasa, Kelvin S. L. Chan, and Jin-Quan Yu
An important transformation for building carbon skeletons. 
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C-H activation

Iridium-Catalyzed C–H Borylation of Cyclopropanes

Carl W. Liskey and John F. Hartwig

This reaction might allow easy synthesis of substrates poised for Suzuki cross-coupling.

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NHC complexes

NHC Ligands as Modulators of Luminescence in Three-
Coordinate Gold(I) Complexes with Spectacular Quantum Yields
Renso Visbal, Isaura Ospino, Jose Maria Lopez-De-Luzuriaga, Antonio Laguna, and M. Concepción Gimeno
Solution- and solid-state- stable three-coordinate gold complexes with NHC/carborane-diphosphine ligands have been prepared and they display very high quantum yield for phosphorescence.
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Gold complexes

A Golden Ring: Molecular Gold Carbido Complexes
Elliot S Borren, Anthony Francis Hill, Rong Shang, Manab Sharma, and Anthony Creswick Willis
This paper reports an interesting complex containing 4 gold atoms arranged in a ring spaced by single carbon atoms

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Efficient C-Ar bond formation

Nickel-Catalyzed Cross-Couplings of Benzylic Pivalates with Arylboroxines: Stereospecific Formation of Diarylalkanes and Triarylmethanes

Qi Zhou , Harathi D. Srinivas , Srimoyee Dasgupta , and Mary P. Watson *

"We have developed a stereospecific nickel-catalyzed cross-coupling of benzylic pivalates with arylboroxines. The success of this reaction relies on the use of Ni(cod)2 as the catalyst and NaOMe as a uniquely effective base. This reaction has broad scope with respect to the arylboroxine and benzylic pivalate, enabling the synthesis of a variety of diarylalkanes and triarylmethanes in good to excellent yields and ee’s."

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Bio-inspired networks

A Continuous Network of Lipid Nanotubes Fabricated from the
Gliding Motility of Kinesin Powered Microtubule Filaments
Nathan F. Bouxsein, Amanda Carroll-Portillo, Marlene Bachand, Darryl Y. Sasaki, and George D. Bachand
"Taxol-stabilized microtubules taxol-stabilized MTs, in constant 2D motion via surface absorbed kinesin, extracted and extended lipid nanotube networks from large Lα phase multilamellar liposomes... Interactions between MTs and extended lipid nanotubes resulted in bifurcation of the nanotubes and ultimately the generation of highly branched networks of fluidically connected nanotubes...The ability of these networks to capture nanomaterials at the membrane surface with high fidelity was subsequently demonstrated using quantum dots as a model system."
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Precision polymers, dendrimers

Extending the Limits of Precision Polymer Synthesis: Giant Polyphenylene Dendrimers in the Mega Dalton Mass Range Approaching Structural Perfection

Thi-Thanh-Tam Nguyen , Martin Baumgarten , Ali Rouhanipour , Hans Joachim Raeder , Ingo Lieberwirth , and Klaus Mullen

This paper reports the synthesis and characterization of the first megadalton polyaromatic dendrimer (and earlier generation dendrimers).  They got beautiful, albeit broad, MALDI spectra, narrow GPC traces (remarkably, even for late-generation species), and TEM images of these gigantic molecules.  The synthesis was achieved via D.A. chemistry/deprotection of alkynes.

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Synthesis and Properties of Multicleavable Amphiphilic Dendritic Comblike and Toothbrushlike Copolymers Comprising Alternating PEG and PCL Grafts

A polymerization scheme to obtain hyperbranched and dendritic functional copolymers is described here. Through the use of self-condensing vinyl polymerization, sequence controlled copolymerization, and RAFT, this lab was able to create alternating AB copolymer "combs," and further functionalize the ends of these combs to make "toothbrushes." Near perfect AB sequencing was achieved by RAFT copolymerization with a styrene derivative and a maleimide derivative. Maleimides have a very low tendency to self-polymerize, but a rapid rate of polymerization with other vinyl monomers.

Stepwise Click Functionalization of DNA through a Bifunctional Azide with a Chelating and a Nonchelating Azido Group

This paper utilizes cool click chemistry to make heterodimers of nucleosides and oligonucleotides. The bis-azide linker used features a copper coordinating azide site and a regular azide site. The coordinating site will react selectively with an alkyne in the presence of Cu(II)acetate and in the absence of an external reducing agent like sodium ascorbate. The other azide site can then be "clicked" to a different alkyne in the presence of Cu(II)acetate and sodium ascorbate. 

Ultrasound, pH, and Magnetically Responsive Crown-Ether-Coated Core/Shell Nanoparticles as Drug Encapsulation and Release Systems

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This paper outlines the synthesis and thorough characterization of core-shell nanoparticles to be used in pH and ultrasound drug delivery. These particles feature an iron oxide core surrounded by a mesopourous silica shell that is capable of harboring a payload of drug molecules. The drugs are held inside by an outer layer of crown ethers that chelate metal ions such as Cs+. This outer layer also helps reduce cytotoxicity in addition to protecting the particles in vivo. These nanoparticles also displayed high r2 relaxivity.  

Radiolabeled Nanogels for Nuclear Molecular Imaging

This paper outlines synthesis of gallium chelating nanogels. These nanogels are prepared from thiol crosslinked "prepolymer" chains composed of PLa and PEG. Gallium chelating ligands are also incorporated via thiol Michael addition.

Supramolecular Nanostructures Formed by Anticancer Drug Assembly

Supramolecular Nanostructures Formed by Anticancer Drug Assembly





The load of CPT on peptide via disulfylbutyrate linker and the assembly of these peptides to form nanoparticles for drug delivery. The kinetic release of CPT and in vitro dose-response relationship were studied.