Application of high pressure induced by water-freezing to the direct catalytic asymmetric three-component List-Barbas-Mannich reaction

High pressure induced by water-freezing has been successfully applied to the direct catalytic asymmetric-three component List-Barbas-Mannich reaction, in which higher yield and better enantioselectivity can be realized than those from the reaction at room temperature under 0.1 MPa.     

New avenues in dinitrogen fixation research

The present article focuses on a recent finding concerning dinitrogen fixation by using titanium oxide/conducting polymer composite systems and its comparison with an earlier fixation method (Schrauzer process) that makes use of a powdered titanium oxide. Both processes work under the stimulus of light at room temperature and pressure, but dinitrogen is fixed to a solid ammonium salt crystal in the former and to a gaseous ammonia molecule in the latter process. Differences in the physicochemical concepts between the two processes are discussed.     

An elementary construction of tilting complexes

Let A be an artin algebra and e∈A an idempotent with add(eA_A)=add(D(_AAe)). Then a projective resolution of Ae_eAe gives rise to tilting complexes for A, where P(l)^• is of term length l+1. In particular, if A is self-injective, then is self-injective and has the same Nakayama permutation as A. In case A is a finite dimensional algebra over a field and eAe is a Nakayama algebra, a projective resolution of eAe over the enveloping algebra of eAe gives rise to two-sided tilting complexes {T(2l)^•}_l?1 for A, where T(2l)^• is of term length 2l+1. In particular, if eAe is of Loewy length two, then we get tilting complexes {T(l)^•}_l?1 for A, where T(l)^• is of term length l+1.     

Rapid large-scale magnetic-field dissipation in a collisionless current sheet via coupling between Kelvin-Helmholtz and lower-hybrid drift instabilities

Rapid large-scale magnetic-field dissipation is observed in a full kinetic simulation of cross-field current instabilities in a current sheet even when the thickness of the current sheet is at ion scale. The Kelvin-Helmholtz instability caused by the velocity shear between the current-carrying ions and the cold background ions excites the lower-hybrid drift instability at the edges of the undulated current sheet. We show that the nonlinear coupling between these two instabilities is responsible for the observed rapid dissipation. The simulation result presents a new route for magnetic-field dissipation in an ion-scale current sheet and demonstrates the general significance of nonlinear cross-scale coupling in collisionless plasmas.     

Characterization of resulting network polymer precursors in stepwise crosslinking diepoxide/diamine polymerization

Our previous mechanistic discussion of network formation in chainwise crosslinking multiallyl polymerization was extended to stepwise crosslinking diepoxide/diamine polymerization, typically including bisphenol‐A diglycidyl ether (BADGE) and 4,4′‐diaminodiphenylmethane (DDM). In allyl polymerization a monomer chain transfer is an essential termination reaction, providing only oligomeric primary polymer chains. Therefore, crosslinking multiallyl polymerization could be in the category of a classical gelation theory. Thus, the gelation behavior was discussed by comparing the actual gel point with the theoretical one. Then the resulting network polymer precursors (NPPs) were characterized by size‐exclusion chromatography‐multiangle laser light scattering‐viscometry to clarify the stepwise crosslinking BADGE/DDM polymerization mechanism. Notably, the intrinsic viscosity ratio [η]_NPP/[η]_Linear tended to decrease with the progress of crosslinking and finally, it reached less than 0.2. This suggests that the structure of resulting NPP becomes dendritic at a conversion close to the gel point. These dendritic NPPs can collide with each other to form crosslinks between NPPs, eventually leading to gelation as a reflection of the high concentration of NPP. The dilution effect on gelation was marked in polar solvent; no gelation was observed at a dilution of 1/5. However, in nonpolar solvent the gelation was promoted by dilution; this is ascribed to enhanced crosslink formation between NPPs through hydrogen bonding due to abundant hydroxyl groups in the NPP generated by the polyaddition reaction. Finally, the subject of “Is cured epoxy resin inhomogeneous?” is briefly discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Structures of the Reactive Intermediates in Organocatalysis with Diarylprolinol Ethers

Structures of the reactive intermediates (enamines and iminium ions) of organocatalysis with diarylprolinol derivatives have been determined. To this end, diarylprolinol methyl and silyl ethers, 1 , and aldehydes, Ph? CH₂? CHO, ^tBu? CH₂? CHO, Ph? CH=CH? CHO, are condensed to the corresponding enamines, A and 3 (Scheme 2), and cinnamoylidene iminium salts, B and 4 (Scheme 3). These are isolated and fully characterized by melting/decomposition points, [α]_D, elemental analysis, IR and NMR spectroscopy, and high‐resolution mass spectrometry (HR‐MS). Salts with BF₄, PF₆, SbF₆, and the weakly coordinating Al[OC(CF₃)₃]₄ anion were prepared. X‐Ray crystal structures of an enamine and of six iminium salts have been obtained and are described herein (Figs. 2 and 4–8, and Tables 2 and 7) and in a previous preliminary communication (Helv. Chim. Acta 2008 , 91, 1999). According to the NMR spectra (in CDCl₃, (D₆)DMSO, (D₆)acetone, or CD₃OD; Table 1), the major isomers 4 of the iminium salts have (E)‐configuration of the exocyclic N?C(1′) bond, but there are up to 11% of the (Z)‐isomer present in these solutions (Fig. 1). In all crystal structures, the iminium ions have (E)‐configuration, and the conformation around the exocyclic N‐C? C‐O bond is synclinal‐exo (cf. C and L ), with one of the phenyl groups over the pyrrolidine ring, and the RO group over the π‐system. One of the meta‐substituents (Me in 4b , CF₃ in 4c and 4e ) on a 3,5‐disubstituted phenyl group is also located in the space above the π‐system. DFT Calculations at various levels of theory (Tables 3–6) confirm that the experimentally determined structures (cf. Fig. 10) are by far (up to 8.3 kcal/mol) the most stable ones. Implications of the results with respect to the mechanism of organocatalysis by diarylprolinol derivatives are discussed.     

A new method for the high performance liquid chromatographic determination of TA-870, a dopamine prodrug (catechol ester compound)

A new method for the high performance liquid chromatographic (HPLC) determination of N-(N-acetyl-L-methionyl)-O,O-bis(ethoxycarbonyl)dopamine (TA-870), a dopamine prodrug, in biological fluid has been developed. In order to measure with an electrochemical detector (ECD), TA-870 was passed first through an immobilized carboxylesterase column to be converted to the electrochemically active deethoxycarbonylated TA-870 (DEC-TA-870). The properties of this carboxylesterase immobilized on Sepharose 4B were examined by this flow injection system. Hydrolysis of TA-870 with this immobilized carboxylesterase was a maximum at pH 7-8 and 50 degrees C, and the activity decreased in the presence of organic solvent such as acetonitrile. For the determination of TA-870 in biological fluids, an HPLC-immobilized enzyme-ECD system using a column-switching technique was developed. The blood was deproteinized with ethanol, and TA-870 in the ethanol extracts was adsorbed in Bond Elut C18. The dichloromethane eluate from Bond Elut C18 was injected into the HPLC system. The HPLC apparatus was composed of three pumps, two separation columns (LiChrosorb Si 60 and mu Bondasphere), a trap column (Bond Elut), an enzyme column, ECD and the column-switching system. The calibration curve for TA-870 in blood was linear in the range from 2 to 200 ng/mL. This new assay method might be useful also for the determination of other catechol ester compounds.     

Enantioselective preparation of C-ring fragment of cotylenin A via catalytic asymmetric intramolecular cyclopropanation of α-diazo β-keto ester

A synthetic pathway to the C-ring fragment of cotylenin A which emerged from our retrosynthetic analysis of cotylenin A is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of the α-diazo-β-keto ester bearing 2,4,6-trimethylphenyl group as the ester part has been found to afford the crystalline product with high ee, which allowed to establish the approach to the C-ring fragment which required ten-pot operations. The developed approach would be beneficial to a large scale synthesis of the C-ring fragment for the total synthesis of cotylenin A.