Novel stereoselective synthesis of functionalized oxazolidinones from chiral aziridines

Enantiomerically pure N-(R)-alpha-methylbenzyl-4(R)-(chloromethyl)oxazolidinones (4R)-5a-k were synthesized in one step and high yields from various aziridine-2-methanols (S)-2a-k by intramolecular cyclization with phosgene. The alpha-methylbenzyl substituent on the nitrogen was easily cleaved to give both enanatiomers of 4-(chloromethyl)oxazolidinones (R)-7a and (S)-7a. (R)-7a was used for the efficient syntheses of (L)-homophenylalaninol analogues (S)-12a-j. We also applied the same methodology to prepare oxazolidinones 9a-c containing a heteroatom-substituted alkyl group at C-4 in high yields.     

Quantitative analysis of ephedrine analogues from ephedra species using 1H-NMR

Four ephedrine analogues such as ephedrine, pseudoephedrine, methylephedrine, and methylpseudoephedrine were determined by (1)H-NMR from Ephedra species. In the region of delta 5.0-4.0, the signals of H-1 attached to the same carbon with a hydroxyl, were well separated from each other in CDCl(3). The amount of each alkaloid was calculated by the relative ratio of the intensity of H-1 signal to the known amount of internal standard, 200 microg of anthracene. This method allows rapid determination of the quantity of four ephedrine alkaloids from Ephedra species. The amount of these alkaloids was in the range of 1.0-2.0% of dry weight depending on the plant materials.     

Lugdunomycin,an Angucycline‐Derived Molecule with Unprecedented Chemical Architecture

The angucyclines form the largest family of polycyclic aromatic polyketides, and have been studied extensively. Herein, we report the discovery of lugdunomycin, an angucycline‐derived polyketide, produced by Streptomyces species QL37. Lugdunomycin has unique structural characteristics, including a heptacyclic ring system, a spiroatom, two all‐carbon stereocenters, and a benzaza‐[4,3,3]propellane motif. Considering the structural novelty, we propose that lugdunomycin represents a novel subclass of aromatic polyketides. Metabolomics, combined with MS‐based molecular networking analysis of Streptomyces sp. QL37, elucidated 24 other rearranged and non‐rearranged angucyclines, 11 of which were previously undescribed. A biosynthetic route for the lugdunomycin and limamycins is also proposed. This work demonstrates that revisiting well‐known compound families and their producer strains still is a promising approach for drug discovery.     

Synthesis and characterization of multiblock copolymers based on hydrophilic disulfonated poly(arylene ether sulfone) and hydrophobic partially fluorinated poly(arylene ether ketone) for fuel cell applications

Sulfonated fluorinated multiblock copolymers based on high performance polymers were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers consist of fully disulfonated poly(arylene ether sulfone) and partially fluorinated poly(arylene ether ketone) as hydrophilic and hydrophobic segments, respectively. Synthesis of the multiblock copolymers was achieved by a condensation coupling reaction between controlled molecular weight hydrophilic and hydrophobic oligomers. The coupling reaction could be conducted at relatively low temperatures (e.g., 105 °C) by utilizing highly reactive hexafluorobenzene (HFB) as a linkage group. The low coupling reaction temperature could prevent a possible trans‐etherification, which can randomize the hydrophilic‐hydrophobic sequences. Tough ductile membranes were prepared by solution casting and their membrane properties were evaluated. With similar ion exchange capacities (IECs), proton conductivity and water uptake were strongly influenced by the hydrophilic and hydrophobic block sequence lengths. Conductivity and water uptake increased with increasing block length by developing nanophase separated morphologies. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments revealed that the connectivity of the hydrophilic segments was enhanced by increasing the block length. The systematic synthesis and characterization of the copolymers are reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 214–222, 2010     

Water purification by membranes: The role of polymer science

Two of the greatest challenges facing the 21st century involve providing sustainable supplies of clean water and energy, two highly interrelated resources, at affordable costs. Membrane technology is expected to continue to dominate the water purification technologies owing to its energy efficiency. However, there is a need for improved membranes that have higher flux, are more selective, are less prone to various types of fouling, and are more resistant to the chemical environment, especially chlorine, of these processes. This article summarizes the nature of the global water problem and reviews the state of the art of membrane technology. Existing deficiencies of current membranes and the opportunities to resolve them with innovative polymer chemistry and physics are identified. Extensive background is provided to help the reader understand the fundamental issues involved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Novel itaconic acid-based superabsorbent polymer with improved gel strength and salt resistance using 2-acrylamido-2-methyl-1-propanesulfonic acid

The synthesis of novel superabsorbent polymers (SAPs) based on itaconic acid (IA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is described for application in personal hygiene products such as disposable diapers. The AMPS is introduced to improve the low absorption performance of the existing IA-based SAPs. The salt-resistant properties of AMPS are shown to improve the absorption performance of SAP with respect to aqueous salt solutions. Further, the high ionization constant of the sulfonic acid group of AMPS contributes to the increase of the centrifugation retention capacity (CRC) of the SAP. Meanwhile, the amide group of AMPS improves the gel strength of the SAP by forming hydrogen bonds between the polymer chains. This increase in gel strength is demonstrated by the enhanced absorbency under load (AUL) and rheological analysis. The degree of neutralization affect the absorption properties of SAP, and the SAP exhibits maximum CRC and AUL of 57.3 and 14.4 g/g at 60% neutralization, respectively. As a crosslinking agent content increased, AUL increased but CRC significantly decreased. Additionally, soil pH evaluation confirms that SAP do not cause soil acidification.     

Synthesis and characterization of highly magnetized nanocrystalline Co(30)Fe(70) alloy by chemical reduction

Co(30)Fe(70) nanoparticles with mean particle size of about 8 nm were successfully synthesized by the chemical reduction of cobalt chloride and iron chloride with borohydride as a reducing agent in aqueous solution. The composition and size of the Co(30)Fe(70) nanoparticles were optimized by controlling the molar ratio of starting materials, reaction time, and dropping rate of aqueous reducing agent. As alloy powders prepared by chemical reduction tend to be amorphous in the as-synthesized state, the as-precipitated Co(30)Fe(70) nanoparticles were heat-treated to achieve crystallinity at the different temperatures for 1 h. The Co(30)Fe(70) nanocrystallite by chemical reduction shows excellent soft magnetic behavior, such as high permeability, negligible coercivity, and high saturation magnetization like that of Co(30)Fe(70) bulk.     

Conformational preferences of proline oligopeptides

A conformational study on the terminally blocked proline oligopeptides, Ac-(Pro)(n)()-NMe(2) (n = 2-5), is carried out using the ab initio Hartree-Fock level of theory with the self-consistent reaction field method in the gas phase and in solutions (chloroform, 1-propanol, and water) to explore the preference and transition between polyproline II (PPII) and polyproline I (PPI) conformations depending on the chain length, the puckering, and the solvent. The mean differences in the free energy per proline of the up-puckered conformations relative to the down-puckered conformations for both diproline and triproline increases for the PPII-like conformations and decreases for the PPI-like conformations as the solvent polarity increases. These calculated results indicate that the PPII-like structures have preferentially all-down puckerings in solutions, whereas the PPI-like structures have partially mixed puckerings. The free energy difference per proline residue between the PPII- and PPI-like structures decreases as the proline chain becomes longer in the gas phase but increases as the proline chain becomes longer in solutions and the solvent polarity increases. In particular, our calculated results indicate that each of the proline oligopeptides can exist as an ensemble of conformations with the trans and cis peptide bonds in solutions, although the PPII-like structure with all-trans peptide bonds is dominantly preferred, which is reasonably consistent with the previously observed results. In diproline Ac-(Pro)(2)-NMe(2), the rotational barrier to the cis-to-trans isomerization for the first prolyl peptide bond increases as the solvent polarity increases, whereas the rotational barrier for the second prolyl peptide bond does not show the monotonic increase as the solvent polarity increases. When the rotational barriers for these two prolyl peptide bonds were compared, it could be deduced that the conformational transition from PPI with the cis peptide bond to PPII with the trans peptide bond is initiated at the C-terminus and proceeds to the N-terminus in water. This is consistent with the results from NMR experiments on polyproline in D(2)O but opposite to the results from enzymatic hydrolysis kinetics experiments on polyproline.     

Determination of zearalenone by liquid chromatography/tandem mass spectrometry and application to a pharmacokinetic study

Zearalenone, a mycotoxin biosynthesized by various Fusarium fungi, is widely found as a contaminant in grains and animal feeds. This study describes a rapid and sensitive LC/MS/MS assay method for the quantification of zearalenone in rat serum. The assay was validated to demonstrate the specificity, linearity, recovery, lower limit of quantification (LLOQ), accuracy and precision. The multiple reaction monitoring was based on the transition of m/z 317.0 → 130.9 for zearalenone and 319.0 → 204.8 for zearalanone (internal standard). The assay utilized a single liquid–liquid extraction with t‐butyl methyl ether and isocratic elution, and the LLOQ was 0.5 ng/mL using 0.1 mL rat serum. The assay was linear over a concentration range from 0.5 to 200 ng/mL, with correlation coefficients >0.9996. The mean intra‐ and inter‐day assay accuracy was 101.2–112.9 and 96.3–108.0%, respectively. The mean intra‐ and inter‐day precision was between 1.3–7.6 and 3.6–10.6%, respectively. The developed assay was applied to a pharmacokinetic study after a bolus intravenous injection of zearalenone in rats. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of functional groups on the solubilities of coumarin derivatives in supercritical carbon dioxide

Summary Solubilities in supercritical CO₂ of coumarin, four monosubstituted coumarin derivatives (4-hydroxycoumarin, 7-hydroxycoumarin, 7-methoxycoumarin, and 7-methylcoumarin) and four disubstituted derivatives, (6,7-dihydroxycoumarin, 7-hydroxycoumarin-4-acetic acid, 7-methoxycoumarin-4-acetic acid, and 7-hydroxy-4-methylcoumarin) were measured in the temperature range 35–50 °C and the pressure range 8.5–25 MPa. In general, the substituted coumarin derivatives were less soluble than simple coumarin. It was also found that substitution at the C-4 position of coumarin tended to reduce the solubility more than substitution at the C-7 position. These solubility data are essential for the systematic application of SFE and SFC of coumarin derivatives from plant sources.