Ruthenium‐catalyzed synthesis of quinolines via reductive heteroannulation of nitroarenes with 3‐amino‐1‐propanols

Nitroarenes are reductively cyclized with 3‐amino‐1‐propanols in dioxane/H₂O in the presence of a ruthenium catalyst and tin(II) chloride dihydrate together with isopropanol to afford the corresponding quinolines. A reaction pathway involving initial reduction of nitroarenes to anilines, propanol group transfer from 3‐amino‐1‐propanols to anilines, N‐alkylation of anilines by 3‐anilino‐1‐propanols and heteroannulation of 1,3‐dianilinopropanes is proposed.     

Multidimensional high performance liquid chromatography--capillary electrophoresis separation of a protein digest: an update

The trypsin digest of a mixture of two proteins, namely cytochrome c and myoglobin, was first separated in the first dimension by high-performance liquid chromatography (HPLC). Fractions from the HPLC were collected every 30s with the aid of a fraction collector into a 96-well microtiter plate. After concentration, all the collected fractions were analyzed simultaneaosly in the second dimension by a 96-array capillary electrophoresis system. The labeled peptides were detected by laser-induced fluorescence. An internal standard, allura red, was added to all the fractions, prior to capillary electrophoretic analysis. The internal standard serves two functions, migration time correction and signal intensity correction. The data are presented in two different formats, as an electropherogram of all the fractions and in a two-dimensional (2-D) format. The 2-D plot of the data shows the density of each spot, which corresponds to the concentration of the migrating peptides. The total experimental time for the HPLC and capillary electrophoretic analyses ist less than 1 h, which ist much faster than using 2-D slab-gel electrophoresis or single-capillary capillary electrophoresis.     

From crown ethers to zeolites: Reaction of EtAlCl2 with crown ethers

In contrast to aluminum alkyls, alkyl aluminum halides such as EtAlCl₂ react with crown ethers to form cation-anion pairs which exhibit the liquid clathrate effect. Specifically, [12-C-4·AlCl₂][AlCl₃Et] and [18-C-6·AlCl₂][AlCl₃Et] have been isolated and characterized by X-ray diffraction techniques. The cations show aluminum in an octahedral environment made up of four of the oxygen atoms from the crown and two chlorine atoms. The 12-C-4 derivative crystallizes in the monoclinic space group P2₁/c with cell constants of a=7.497(4), b=22.121(8), c=12.339(5) Å, =94.99(3)^o, and Z=4 for =1.43 g cm^–3. Least-squares refinement based on 1413 observed reflections led to a final conventional R value of 0.093. The 18-C-6 complex belongs to the triclinic space group P1 with a=8.414(4), b=12.193(6), c=12.394(6) Å, =73.14(4), =86.07(4), =81.52(4)^o, and Z=2 for =1.45 g cm^–3. Refinement based on 2605 observed reflections led to R=0.063. The complex aluminum-containing species are related to a class of compounds called aluminoxanes.     

Efficient synthesis of N-benzyl-3-aminopyrrolidine-2,5-dione and N-benzyl-3-aminopyrrolidin-2-one

Reaction of N-tert-butyloxycarbonylasparagine (Boc-Asn) with 2 equiv of benzyl bromide in presence of cesium carbonate led to N-benzyl-3-Boc-amino-pyrrolidin-2,5-dione 1a (N-benzyl-3-Boc-aminosuccinimide). Borane dimethylsulfide reduced 3-Boc-aminopyrrolidine-2,5-dione 1a into 3-Boc-aminopyrrolidin-2-one 2a. The same procedure could also be used to prepare derivatives 1 and 2 substituted on the aromatic ring.     

SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS*

Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m~2/g) andpore volumes (e.g. 0.6 cm~3/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, porevolumes and pore diameters of the hybrid materials increase.     

Self-assembled morphologies of monotethered polyhedral oligomeric silsesquioxane nanocubes from computer simulation

Self-assembly of functionalized nanoscale building blocks is a promising strategy for "bottom-up" materials design. Recent experiments have demonstrated that the self-assembly of polyhedral oligomeric silsesquioxane (POSS) "nanocubes" functionalized with organic tethers can be utilized to synthesize novel materials with highly ordered, complex nanostructures. We have performed molecular simulations for a simplified model of monotethered POSS nanocubes to investigate systematically how the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tether lengths, and solvent conditions, can be manipulated to achieve useful structures via self-assembly. We report conventional lamellar and cylindrical structures that are typically found in block copolymer and surfactant systems, including a thermotropic order-order transition, but with interesting stabilization of the lamellar phase caused by the bulkiness and cubic geometry of the POSS nanocubes.     

Application of solid phase microextraction in the determination of paralytic shellfish poisoning toxins

A SPME-HPLC-post-column fluorescent derivatization method for the direct determination of saxitoxin (STX), the most potent paralytic shellfish poisoning (PSP) toxin, in water has been developed. Commercially available SPME devices with 50 microm Carbowax templated resin (CW/TPR) coating was found to be able to pre-concentrate STX from aqueous media. A special pre-conditioning treatment of soaking the SPME coating in 0.1 M NaOH solution significantly improved the extraction efficiency. The optimal pH for the SPME process is 8.1 and the equilibration time is 40 min. The partition coefficient, K, of the distribution of STX between the SPME coating and the aqueous media was measured to be 2.99 +/- 0.04 x 10(3). Extracted toxin on the SPME stationary phase was difficult to be desorbed by the HPLC mobile phase under dynamic desorption mode. A static ion-pairing desorption technique using a desorption solvent mixture of 20 mM sodium 1-heptanesulfonate in 30% aqueous acetonitrile acidified with 50 mM sulfuric acid was developed to overcome this problem. The method detection limit and repeatability achieved by this SPME-HPLC method were 0.11 ng ml(-1) and 3.7%, respectively, with a sample volume of just 5 ml of water. This analytical method is adequate for the monitoring of the PSP toxin in fresh/drinking waters. However, serious interference was observed when this technique was applied to saline water samples. This is probably due to competition of sodium ions with the cationic STX for absorption into the SPME stationary phase.     

Synthesis of a highly hindered hydrindanone via alpha-carbonyl radical cyclization: enantiospecific formal syntheses of (-)-pinguisenol and (-)-alpha-pinguisene

An enantiospecific synthesis of Schinzer's ketone 3 from (R)-(+)-pulegone via alpha-carbonyl radical cyclization was accomplished. This work also constitutes an enantiospecific formal syntheses of (-)-pinguisenol and (-)-alpha-pinguisene. The intermediate ketone 4 would be useful for the synthesis of other pinguisane-type sesquiterpenes.     

Eliminating positively charged lysine epsilon-NH3+ groups on the surface of carbonic anhydrase has no significant influence on its folding from sodium dodecyl sulfate

This study compares the folding of two polypeptides--bovine carbonic anhydrase (BCA) and peracetylated BCA (BCA-Ac(18))--having the same sequence of amino acids but differing by 18 formal units of charge, from a solution containing denaturing concentrations of sodium dodecyl sulfate (SDS). Acetylation of BCA with acetic anhydride converts all 18 lysine-epsilon-NH(3)(+) groups to lysine-epsilon-NHCOCH(3) groups and generates BCA-Ac(18). Both BCA and BCA-Ac(18) are catalytically active, and circular dichroism spectroscopy (CD) suggests that they have similar secondary and tertiary structures. SDS at concentrations above approximately 10 mM denatured both proteins. When the SDS was removed by dialysis, both proteins were regenerated in native form. This study suggests that large differences in the net charge of the polypeptide have no significant influence on the structure, the ability to refold, or the rate of refolding of this protein from solutions containing SDS. This study reinforces the idea that charged residues on the surface of BCA do not guide protein folding and raises the broader question of why proteins have charged residues on their surface, outside of the region of the active site.