Chemoenzymatic synthesis of chiral 2,2 '-bipyridine ligands and their N-oxide derivatives: applications in the asymmetric aminolysis of epoxides and asymmetric allylation of aldehydes

A series of enantiopure 2,2'-bipyridines have been synthesised from the corresponding cis-dihydrodiol metabolites of 2-chloroquinolines. Several of the resulting hydroxylated 2,2'-bipyridines were found to be useful chiral ligands for the asymmetric aminolysis of meso-epoxides leading to the formation of enantioenriched amino alcohols (-> 84%ee). N-oxide and N,N'-dioxide derivatives of these 2,2'-bipyridines, including separable atropisomers, have been synthesised and used as enantioselective organocatalysts in the asymmetric allylation of aldehydes to give allylic alcohols (-> 86%ee).

The influence of the relative phase between the driving voltages on electron heating in asymmetric dual frequency capacitive discharges

The influence of the relative phase between the driving voltages on electron heating in asymmetric phase-locked dual frequency capacitively coupled radio frequency plasmas operated at 2 and 14 MHz is investigated. The basis of the analysis is a nonlinear global model with the option to implement a relative phase between the two driving voltages. In recent publications it has been reported that nonlinear electron resonance heating can drastically enhance the power dissipation to electrons at moments of sheath collapse due to the self-excitation of nonlinear plasma series resonance (PSR) oscillations of the radio frequency current. This work shows that depending on the relative phase of the driving voltages, the total number and exact moments of sheath collapse can be influenced. In the case of two consecutive sheath collapses a substantial increase in dissipated power compared with the known increase due to a single PSR excitation event per period is observed. Phase resolved optical emission spectroscopy (PROES) provides access to the excitation dynamics in front of the driven electrode. Via PROES the propagation of beam-like energetic electrons immediately after the sheath collapse is observed. In this work we demonstrate that there is a close relation between moments of sheath collapse, and thus excitation of the PSR, and beam-like electron propagation. A comparison of simulation results to experiments in a single and dual frequency discharge shows good agreement. In particular the observed influence of the relative phase on the dynamics of a dual frequency discharge is described by means of the presented model. Additionally, the analysis demonstrates that the observed gain in dissipation is not accompanied by an increase in the electrode’s dc-bias voltage which directly addresses the issue of separate control of ion flux and ion energy in dual frequency capacitively coupled radio frequency plasmas.

A distributed contention-vector division multiple access (D-CVDMA) protocol for wireless networks

Traditional Time Division Multiple Access (TDMA) protocol provides deterministic periodic collision free data transmissions. However, TDMA lacks flexibility and exhibits low efficiency in dynamic environments such as wireless LANs. On the other hand contention-based MAC protocols such as the IEEE 802.11 DCF are adaptive to network dynamics but are generally inefficient in heavily loaded or large networks. To take advantage of the both types of protocols, a D-CVDMA protocol is proposed. It is based on the k-round elimination contention (k-EC) scheme, which provides fast contention resolution for Wireless LANs. D-CVDMA uses a contention mechanism to achieve TDMA-like collision-free data transmissions, which does not need to reserve time slots for forthcoming transmissions. These features make the D-CVDMA robust and adaptive to network dynamics such as node leaving and joining, changes in packet size and arrival rate, which in turn make it suitable for the delivery of hybrid traffic including multimedia and data content. Analyses and simulations demonstrate that D-CVDMA outperforms the IEEE 802.11 DCF and k-EC in terms of network throughput, delay, jitter, and fairness.

Asymmetric synthesis of an N-acylpyrrolidine for inhibition of HCV polymerase

A practical asymmetric synthesis of a highly substituted N-acylpyrrolidine on multi-kilogram scale is described. The key step in the construction of the three stereocenters is a [3+2] cycloaddition of methyl acrylate and an imino ester prepared from L-leucine t-butyl ester hydrochloride and 2-thiazolecarboxaldehyde. The cycloaddition features novel asymmetric catalysis via a complex of silver acetate and a cinchona alkaloid, particularly hydroquinine, with complete diastereomeric control and up to 87% enantiomeric control. The alkaloid serves as a ligand as well as a base for the formation of the azomethine ylide or 1,3-dipole. Experiments have shown that the hydroxyl group of hydroquinine is a critical element for the enantioselectivities observed. The cycloaddition methodology is also applicable to methylvinyl ketone, providing access to either alpha- or beta-epimers of 4-acetylpyrrolidine depending on the reaction conditions utilized. The synthesis also highlights an efficient N-acylation, selective O- versus N-methylation, and a unique ester reduction with NaBH4-MeOH catalyzed by NaB(OAc)(3)H that not only achieves excellent chemoselectivity but also avoids formation of the undesired but thermodynamically favored epimer. The highly functionalized target is synthesized in seven linear steps from L-leucine t-butyl ester hydrochloride with all three isolated intermediates being highly crystalline.

Asymmetric rhodium carbene insertion into the Si-H bond: identification of new dirhodium(II) carboxylate catalysts using parallel synthesis techniques

Decomposition of methyl 2-diazophenylacetate in the presence of silanes and a chiral dirhodium(11) catalyst results in Si-H insertion of the intermediate carbenoid with varying degrees of enantioselectivity. New chiral dirhodium(11) carboxylate catalysts were identified using solution phase parallel synthesis techniques. (C) 2003 Elsevier Science Ltd. All rights reserved.

Non-thiazolidinedione antihyperglycemic agents. Part 5: asymmetric aldol synthesis of (S)-(-)-2-oxy-3-arylpropanoic acids.

Haigh, David; Birrell, Helen C.; Cantello, Barrie C. C.; Eggleston, Drake S.; Haltiwanger, R. Curtis; Hindley, Richard M.; Ramaswamy, Anantha; Stevens, Nicola C. Department of Medicinal Chemistry, SmithKline Beecham Pharmaceuticals, Essex, UK. Tetrahedron: Asymmetry (1999), 10(7), 1353-1367. Publisher: Elsevier Science Ltd., CODEN: TASYE3 ISSN: 0957-4166. Journal written in English. CAN 131:144537 AN 1999:369514 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) Abstract Boron-mediated asym. aldol reactions of 4-[2-(2-benzoxazolylmethylamino)ethoxy]benzaldehyde with 2-oxyethanoyloxazolidinones contg. electron withdrawing, chelating, and bulky alkoxy and aryloxy groups, gave variable yields of syn-aldol adducts in high diastereoisomeric excess. These adducts were dehydroxylated in a sequence which complements the traditional Evans asym. alkylation strategy. Cleavage of the auxiliary from these intermediates afforded antihyperglycemic (S)-(-)-2-oxy-3-arylpropanoic acids in excellent enantiomeric excess. The target compds. were ?-alkoxy-4-[2-[(benzoxazolyl)amino]ethoxy]benzenepropanoic acid derivs. The biol. activity of the compds. thus prepd. was not reported here.

Asymmetric rhodium carbenoid insertion into the Si-H bond.

Buck, Richard T.; Doyle, Michael P.; Drysdale, Martin J.; Ferris, Leigh; Forbes, David C.; Haigh, David; Moody, Christopher J.; Pearson, Neil D.; Zhou, Qi-Lin. Dep. Chemistry, Loughborough Univ., Loughborough, Leicestershire, UK. Tetrahedron Letters (1996), 37(42), 7631-7634. Publisher: Elsevier, CODEN: TELEAY ISSN: 0040-4039. Journal written in English. CAN 125:328854 AN 1996:644681 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) Abstract Decompn. of Me 2-diazophenylacetate in the presence of dimethylphenylsilane and a chiral dirhodium(II) catalyst results in Si-H insertion of the intermediate carbenoid to give PhCH(SiMe2Ph)CO2Me with varying degrees of enantioselectivity (up to 47% ee; 47% using (S)-Rh2L4, LH = I).

Asymmetric profiles observed in the recombination of Bi79+: A benchmark for relativistic theories involving interference

Asymmetric profiles have been observed in the recombination cross section of Be-like Bi obtained by measuring the electron energy dependence of the ion abundance ratio in an electron-beam ion trap. In contrast to the previous x-ray measurements, the present measurement gives the integrated recombination cross section with higher statistical quality, which provides a benchmark to test the relativistic theory involving the interference between the resonant and continuum states. The comparison with our theoretical study shows that the Breit interaction plays an important role in this case.

Promoting mental health in Northern Ireland: addressing division, inequality and stigma

This article provides an overview of the literature on the impact of ‘the Troubles’ on mental health in Nor thern Ireland. It identifies three main phases of professional and policy response from concerns about the effects of the violence in the early 1970s, through many years of collective denial and neglect, until acknowledgment, following the Good Friday Agreement in 1998 (Nor thern Ireland Office, 1998), of high levels of trauma and unmet need. The issues of inequality and stigma are also considered and it is argued that peace is necessary but insufficient for promoting mental health. The development of mental health services in Nor thern Ireland and the relatively recent focus on promoting mental health are also outlined and examined. It is suggested that attempts to address the needs arising as a result of ‘the Troubles’ and more general mental health promotion strategies have, to some extent, developed in parallel and that it may be impor tant to integrate these effor ts. The relative under-development of mental health services, the comprehensive Bamford Review of Mental Health and Learning Disability (2005; 2006) and the positive approach of the Public Health Agency mean that, even in the current economic climate, there are great oppor tunities for progress. Routine screening, in primary care and mental health services for trauma, including Troubles-related trauma, is recommended to identify and address these issues on an individual level. It is also argued, however, that more substantial political change is needed to effectively address societal division, inequality and stigma to the benefit of all.

Notes on the Asymmetric Hydrogenation of Methyl Acetoacetate in Neoteric Solvents

Asymmetric hydrogenation of methyl acetoacetate to methyl (R)-3-hydroxybutyrate by [(R)-RuCl(binap)( p-cymen)] Cl has been studied in methanol-ionic liquid and methanol-dense CO(2) solvent systems. The ionic pairs triethylhexylammonium and 1-methylimidazolium with bis(trifluoromethane sulfonyl) imide and hexafluorophosphates were used. The role of ionic pairs on the kinetic parameters and (enantio) selectivity has been demonstrated. Although the CO(2) expanded methanol system suffered from a reduction in both reaction rate and product selectivity, this changed in the presence of water. The high selectivity of the optimized methanol-CO(2)-water-halide system was designed as a consequence of observed additive effects.

Sexual division of antibacterial resource defence in breeding burying beetles, Nicrophorus vespilloides

A key component of parental care involves defending resources destined for offspring from a diverse array of potential interspecific competitors, such as social parasites, fungi and bacteria. 2. Just as with other aspects of parental care, such as offspring provisioning or brood defence, sexual conflict between parents may arise over how to share the costs of this form of care. There has been little previous work, however, to investigate how this particular burden might be shared. 3. Here, we describe a hitherto uncharacterized form of parental care in burying beetles Nicrophorus vespilloides, a species which prepares carrion for its young and faces competition from microbes for this resource. We found that parents defend the carcass with antibacterial anal exudates, and that the antibacterial activity of these exudates is only upregulated following the discovery of a corpse. At the same time, phenoloxidase activity in the anal exudates is downregulated, indicating parallels with the internal insect immune system. 4. In unmanipulated breeding pairs, females had higher antibacterial activity in their anal exudates than males, suggesting sex-specific roles in this aspect of parental care. 5. When we experimentally widowed males, we found that they increased levels of antibacterial activity in their anal exudates. Experimentally widowing females, however, led them to decrease levels of antibacterial activity in their anal exudates. Widowed beetles of each sex thus produced anal exudates of comparable antibacterial activity. We suggest that this flexible division of antibacterial activity may be coordinated by Juvenile Hormone. © 2009 British Ecological Society.