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1

Asymmetric Synthesis of Sesaminone: Confirmation of Its Structure and Determination of Its Absolute Configuration.  

PubMed

An asymmetric synthesis of the naturally occurring antipode of the tetrahydrofuran lignan sesaminone ((-)-1) has been achieved. An X-ray crystal structure of the synthetic material validated the structure proposed in the literature for this lignan. Additionally, the absolute configuration of the natural product was established by correlation of the synthetic tetrahydrofuran with the known absolute configuration of L-Phe. The opening of the synthesis was a diastereoselective Evans aldol reaction between N-4-pentenoyloxazolidinone 6 and piperonal. Reduction of the major diastereomer of the aldol product provided enantiomerically pure diol 4. The primary and secondary hydroxyl groups of 4 were protected in tandem to generate silyl ether-MOM ether 9. The vinyl group contained in 9 was then elaborated, via a series of four steps, to aryl ketone 10. This aryl ketone was transformed to a mixture of silyl enol ether stereoisomers (11a,b); TiCl(4)-mediated activation of the MOM ethers contained in this mixture of enol ethers yielded tetrahydrofuran 12 as the major product. Treatment of 12 with fluoride provided synthetic (-)-1. PMID:11671858

Maioli, Andrew T.; Civiello, Rita L.; Foxman BM and, Bruce M.; Gordon, Dana M.

1997-10-17

2

Absolute asymmetric synthesis in enantioselective autocatalytic reaction networks: theoretical games, speculations on chemical evolution and perhaps a synthetic option.  

PubMed

The Soai reaction and the Viedma deracemization of racemic conglomerate crystal mixtures are experimental pieces of evidence of the ability of enantioselective autocatalytic coupled networks to yield absolute asymmetric synthesis. Thermodynamically open systems or systems with non-uniform energy distributions may lead to chiral final states and, in systems able to come into thermodynamic equilibrium with their surroundings, to kinetically controlled absolute asymmetric synthesis. The understanding of network parameters and of the thermodynamic scenarios that may lead to spontaneous mirror symmetry breaking (SMSB) could assist in the development of new methods for asymmetric synthesis and enantioselective polymerizations (e.g., replicators), and to frame reasonable speculations on the origin of biological homochirality. PMID:25352056

Ribó, Josep M; Blanco, Celia; Crusats, Joaquim; El-Hachemi, Zoubir; Hochberg, David; Moyano, Albert

2014-12-22

3

Asymmetric total synthesis and revision of the absolute configuration of 4-keto-clonostachydiol.  

PubMed

The first total synthesis of the 14-membered natural macrocyclic bislactone 4-keto-clonostachydiol, along with its enantiomer, has been accomplished in 13 steps with overall yields of 8.4% and 8.0%, respectively. The absolute configuration of 4-keto-clonostachydiol 1 has been revised as (5S,10S,13S). PMID:19382764

Han, Junjie; Su, Yingpeng; Jiang, Tuo; Xu, Yanfen; Huo, Xing; She, Xuegong; Pan, Xinfu

2009-05-15

4

Asymmetric Synthesis of Ageliferin  

PubMed Central

We describe herein an asymmetric synthesis of ageliferin. A Mn(III)-mediated oxidative radical cyclization reaction was used as the key step to construct the core skeleton of this pyrrole-imidazole dimer. This approach resembles the bio-genic [4+2] dimerization in an intramolecular fashion. PMID:21888421

Wang, Xiao; Ma, Zhiqiang; Lu, Jianming; Tan, Xianghui; Chen, Chuo

2011-01-01

5

Enantiomeric resolution and absolute configuration of asymmetric derivatives of 3,7-dimethylenebicyclo(3. 3. 1)nonane. Synthesis of chiral derivatives of adamantane  

SciTech Connect

A new method was developed for the enantiomeric resolution of asymmetric derivatives of 3,7-dimethylenebicyclo(3.3.1)nonane by liquid chromatography on a chiral sorbent, i.e., silica gel impregnated with silver d-camphor-10-sulfonate. During transannular electrophilic cyclization and photocyclization the enantiomeric dienes, the absolute configurations of which were determined by means of the circular dichromism spectra, form chiral derivatives of adamantane with full retention of the optical purity.

Krasutskii, P.A.; Rodionov, V.N.; Chesskaya, N.S.; Yurchenko, A.G.

1986-01-10

6

Synthesis and absolute configuration of hormone alpha1.  

PubMed

An important biological event in phytopathogens of the genus Phytophthora is sexual reproduction, which is conducted by two mating types, A1 and A2. A factor known as hormone alpha1 is secreted by the A1 mating type and induces the formation of sexual spores (oospores) in the A2 mating type. Here we describe the asymmetric synthesis and assignment of the absolute configuration of hormone alpha1 by oospore-inducing assays of the synthesized isomers. PMID:18297064

Yajima, Arata; Qin, Yong; Zhou, Xuan; Kawanishi, Naoki; Xiao, Xue; Wang, Jue; Zhang, Dan; Wu, Yi; Nukada, Tomoo; Yabuta, Goro; Qi, Jianhua; Asano, Tomoyo; Sakagami, Youji

2008-04-01

7

Hydroxamic Acids in Asymmetric Synthesis  

PubMed Central

Metal-catalyzed stereoselective reactions are a central theme in organic chemistry research. In these reactions, the stereoselection is achieved predominantly by introducing chiral ligands at the metal catalyst’s center. For decades, researchers have sought better chiral ligands for asymmetric catalysis and have made great progress. Nevertheless, to achieve optimal stereoselectivity and to catalyze new reactions, new chiral ligands are needed. Due to their high metal affinity, hydroxamic acids play major roles across a broad spectrum of fields from biochemistry to metal extraction. Dr. K. Barry Sharpless first revealed their potential as chiral ligands for asymmetric synthesis in 1977: He published the chiral vanadium-hydroxamic-acid-catalyzed, enantioselective epoxidation of allylic alcohols before his discovery of Sharpless Asymmetric Epoxidation, which uses titanium-tartrate complex as the chiral reagent. However, researchers have reported few highly enantioselective reactions using metal-hydroxamic acid as catalysts since then. This Account summarizes our research on metal-catalyzed asymmetric epoxidation using hydroxamic acids as chiral ligands. We designed and synthesized a series of new hydroxamic acids, most notably the C2-symmetric bis-hydroxamic acid (BHA) family. V-BHA-catalyzed epoxidation of allylic and homoallylic alcohols achieved higher activity and stereoselectivity than Sharpless Asymmetric Epoxidation in many cases. Changing the metal species led to a series of unprecedented asymmetric epoxidation reactions, such as (i) single olefins and sulfides with Mo-BHA, (ii) homoallylic and bishomoallylic alcohols with Zr- and Hf-BHA, and (iii) N-alkenyl sulfonamides and N-sulfonyl imines with Hf-BHA. These reactions produce uniquely functionalized chiral epoxides with good yields and enantioselectivities. PMID:23157425

Li, Zhi; Yamamoto, Hisashi

2012-01-01

8

Asymmetric synthesis of (-)-martinellic acid.  

PubMed

A high-yielding total asymmetric synthesis of (-)-martinellic acid is reported. The conjugate addition of lithium (R)-N-allyl-N-(?-methyl-4-methoxybenzyl)amide to tert-butyl (E)-3-[2'-(N,N-diallylamino)-5'-bromophenyl]propenoate and alkylation of the resultant ?-amino ester have been used as the key steps to install the C(9b) and C(3a) stereogenic centers, respectively, and a highly diastereoselective Wittig reaction/intramolecular Michael addition was then used to create the C(4) stereogenic center within this tricyclic molecular architecture. PMID:23556476

Davies, Stephen G; Fletcher, Ai M; Lee, James A; Lorkin, Thomas J A; Roberts, Paul M; Thomson, James E

2013-04-19

9

Quantifying Absolute Protein Synthesis Rates Reveals Principles Underlying  

E-print Network

Quantifying Absolute Protein Synthesis Rates Reveals Principles Underlying Allocation of Cellular present a genome-wide approach, based on ribosome profiling, for measuring absolute protein synthesis- lyses of protein synthesis. INTRODUCTION Protein biosynthesis is by far the largest consumer of energy

Zhang, Jianzhi

10

Asymmetric Synthesis of All the Known Phlegmarine Alkaloids  

PubMed Central

The asymmetric synthesis of all four of the known natural phlegmarines and one synthetic derivative has been accomplished in 19 to 22 steps from 4-methoxy-3-(triisopropylsilyl)pyridine. Chiral N-acylpyridinium salt chemistry was used twice to set the stereocenters at the C-9 and C-2? positions of the phlegmarine skeleton. Key reactions include the use of a mixed Grignard reagent for the second N-acylpyridinium salt addition, zinc/acetic acid reduction of a complex dihydropyridone, and a von Braun cyanogen bromide N-demethylation of a late intermediate. These syntheses confirmed the absolute stereochemistry of all the known phlegmarines. PMID:21077636

Wolfe, Bradley H.; Libby, Adam H.; Al-awar, Rima S.; Foti, Christopher J.; Comins, Daniel L.

2010-01-01

11

Asymmetric synthesis and sensory evaluation of sedanenolide.  

PubMed

The synthesis and sensory evaluation of enantiomeric sets of sedanenolide (1) and 3-butylphthalide (3) are described. The asymmetric synthesis was achieved via the intramolecular Diels-Alder reaction of chiral propargylester (5) which was prepared from optically active propargyl alcohol (4) and 2,4-pentadienoic acid. The sensory evaluation of these enantiomers revealed that there were distinct differences between their aroma character and odor threshold. PMID:21821949

Oguro, Daichi; Watanabe, Hidenori

2011-01-01

12

A Catalytic Asymmetric Total Synthesis of (-)-Perophoramidine.  

PubMed

We report a catalytic asymmetric total synthesis of the ascidian natural product perophoramidine. The synthesis employs a molybdenum-catalyzed asymmetric allylic alkylation of an oxindole nucleophile and a monosubstituted allylic electrophile as a key asymmetric step. The enantioenriched oxindole product from this transformation contains vicinal quaternary and tertiary stereocenters, and is obtained in high yield along with high levels of regio-, diastereo-, and enantioselectivity. To install the second quaternary stereocenter in the target, the route utilizes a novel regio- and diastereoselective allylation of a cyclic imino ether to deliver an allylated imino ether product in near quantitative yield and with complete regio- and diastereocontrol. Oxidative cleavage and reductive amination are used as final steps to access the natural product. PMID:25485074

Trost, B M; Osipov, M; Krüger, S; Zhang, Y

2015-01-01

13

A Catalytic Asymmetric Total Synthesis of (?)-Perophoramidine†  

PubMed Central

We report a catalytic asymmetric total synthesis of the ascidian natural product perophoramidine. The synthesis employs a molybdenum-catalyzed asymmetric allylic alkylation of an oxindole nucleophile and a monosubstituted allylic electrophile as a key asymmetric step. The enantioenriched oxindole product from this transformation contains vicinal quaternary and tertiary stereocenters, and is obtained in high yield along with high levels of regio-, diastereo-, and enantioselectivity. To install the second quaternary stereocenter in the target, the route utilizes a novel regio- and diastereoselective allylation of a cyclic imino ether to deliver an allylated imino ether product in near quantitative yield and with complete regio- and diastereocontrol. Oxidative cleavage and reductive amination are used as final steps to access the natural product. PMID:25485074

Osipov, M.; Krüger, S.; Zhang, Y.

2014-01-01

14

An efficient asymmetric synthesis of (-)-lupinine.  

PubMed

The asymmetric synthesis of (-)-lupinine was achieved in 8 steps, 15% overall yield and >99?:?1 dr from commercially available starting materials. The strategy used for the construction of the quinolizidine scaffold involved reaction of an enantiopure tertiary dibenzylamine via two sequential ring-closures which both occurred with concomitant N-debenzylation. PMID:24938152

Davies, Stephen G; Fletcher, Ai M; Foster, Emma M; Houlsby, Ian T T; Roberts, Paul M; Schofield, Thomas M; Thomson, James E

2014-08-01

15

Asymmetric Silver "Nanocarrot" Structures: Solution Synthesis and Their Asymmetric Plasmonic Resonances  

E-print Network

Asymmetric Silver "Nanocarrot" Structures: Solution Synthesis and Their Asymmetric Plasmonic the wet-chemical synthesis of asymmetric one-dimensional (1D) silver "nanocarrot" structures that exhibit of the longitudinal surface plasmon resonance peaks. The silver nanocarrots also show very high sensitivity

16

Asymmetric catalysis in organic synthesis  

SciTech Connect

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of the project was to prepare new catalyst systems, which would perform chemical reactions in an enantioselective manner so as to produce only one of the possible optical isomers of the product molecule. The authors have investigated the use of lanthanide metals bearing both diolate and Schiff-base ligands as catalysts for the enantioselective reduction of prochiral ketones to secondary alcohols. The ligands were prepared from cheap, readily available starting materials, and their synthesis was performed in a ''modular'' manner such that tailoring of specific groups within the ligand could be carried out without repeating the entire synthetic procedure. In addition, they have developed a new ligand system for Group IV and lanthanide-based olefin polymerization catalysts. The ligand system is easily prepared from readily available starting materials and offers the opportunity to rapidly prepare a wide range of closely related ligands that differ only in their substitution patterns at an aromatic ring. When attached to a metal center, the ligand system has the potential to carry out polymerization reactions in a stereocontrolled manner.

Reilly, S.D.; Click, D.R.; Grumbine, S.K.; Scott, B.L.; Watkins, J.G.

1998-11-01

17

Highly Efficient Asymmetric Synthesis of -Amino Acid Derivatives via  

E-print Network

Highly Efficient Asymmetric Synthesis of -Amino Acid Derivatives via Rhodium pure -amino acids and their deriva- tives are important building blocks for the synthesis of -peptides of -amino acids has attracted extensive interest. Although several stoichio- metric and catalytic methods

Zhang, Xumu

18

Recent Advances in Asymmetric Synthesis of ?-Stereogenic Phosphorus Compounds.  

PubMed

This chapter points out significant advances in the asymmetric synthesis of P-chiral organophosphorus compounds with many applications in stereoselective synthesis and in asymmetric catalysis, making reference to updated literature findings as well as the author's original research. Asymmetric addition and cycloaddition reactions, oxidation, including metal catalyzed and non-metal biocatalytic methods are described, in addition to synthetic approaches via nucleophilic substitution of appropriately substituted precursors. Use of chiral organophosphorus compounds in some asymmetric transformations such as hydrogenation and alkyl/arylation reactions is also discussed. PMID:25326833

Kolodiazhnyi, Oleg I

2014-10-19

19

New oxazoline-based ligands for application in asymmetric synthesis  

Microsoft Academic Search

Asymmetric catalysis is a powerful tool in the synthesis of optically pure compounds by providing excellent possibilities to introduce enantioselectivity using small amounts of an enantiomerically pure catalyst. Among the large variety of asymmetric ligands that have emerged since the start of aymmetric catalysis, enantiopure C2-symmetric bisoxazoline ligands have been identified as a 'privileged' class of ligands with applications in

H. L. van Lingen

2005-01-01

20

Ionic-liquid-supported (ILS) catalysts for asymmetric organic synthesis.  

PubMed

The asymmetric synthesis of compounds that contain new C-C and C-O bonds remains one of the most important types of synthesis in organic chemistry. Over the years, many different types of catalysts have been designed and used effectively to carry out such transformations. Ionic-liquid-supported (ILS) catalysts represent a new and very effective class of catalysts that are used to facilitate the asymmetric synthesis of such compounds. There are many advantages to using ILS catalysts; they are nontoxic, environmentally benign, and, most important, recyclable. An overview of the design, synthesis, mode of action, and effectiveness of this class of catalysts is reported. PMID:20235242

Ni, Bukuo; Headley, Allan D

2010-04-19

21

Assignment of Absolute Configuration to SCH 351448 via Total Synthesis?  

PubMed Central

The synthesis and absolute configuration of SCH 351448, an interesting ionophoric natural product, are reported herein. Mukaiyama aldol-Prins and segment-coupling Prins reactions were employed to construct the constituent tetrahydropyrans of SCH 351448. Efforts to assemble the C2-symmetric core of the natural product by a templated olefin metathesis strategy are described, however, a stepwise fragment assembly was ultimately utilized to complete the target molecule. PMID:18543942

Cheung, Lael L.; Marumoto, Shinji; Anderson, Christopher D.

2008-01-01

22

The asymmetric total synthesis of cinbotolide: a revision of the original structure.  

PubMed

The structure 3,4-dihydroxy-2,4,6,8-tetramethyldec-8-enolide (1) was assigned to a metabolite of Botrytis cinerea, but the spectra of several synthetic analogues had significant differences from that of 1. Examination of the constituents of a B. cinerea mutant that overproduces polyketides gave sufficient quantities of 1, now named cinbotolide, for chemical transformations. These led to a revised ?-butyrolactone structure for the metabolite. This structure has been confirmed by an asymmetric total synthesis, which also established its absolute configuration. PMID:25372296

Botubol, José Manuel; Durán-Peña, María Jesús; Macías-Sánchez, Antonio J; Hanson, James R; Collado, Isidro G; Hernández-Galán, Rosario

2014-12-01

23

First asymmetric total syntheses and determination of absolute configurations of (+)-eudesmadiene-12,6-olide and (+)-frullanolide.  

PubMed

The first asymmetric total syntheses of sesquiterpene lactones (+)-eudesmadiene-12,6-olide (1) and (+)-frullanolide (2) have been accomplished from 4-bromo-2-methoxyphenol (5) in 12 and 13 synthetic steps, respectively, and the absolute configurations of these two natural products were determined. PMID:23484913

Chou, Yu-Yu; Liao, Chun-Chen

2013-04-01

24

Synthesis of (+)-ambrisentan via chiral ketone-catalyzed asymmetric epoxidation.  

PubMed

The synthesis of optically pure (+)-ambrisentan has been achieved from 3,3-diphenylacrylate in four steps with 53% overall yield and >99% ee at the >100 g scale without column purification. The chiral epoxide intermediate was prepared via asymmetric epoxidation with a fructose-derived diacetate ketone as catalyst. PMID:22098088

Peng, Xianyou; Li, Peijun; Shi, Yian

2012-01-01

25

Pseudoephenamine: A Practical Chiral Auxiliary for Asymmetric Synthesis  

PubMed Central

Pseudoephenamine is shown to be a versatile chiral auxiliary for asymmetric synthesis. It is free from regulatory restrictions and exhibits remarkable stereocontrol in alkylation reactions, especially those that form quaternary carbon centers. Amides derived from pseudoephenamine exhibit a high propensity to be crystalline substances and provide sharp, well-defined peaks in NMR spectra. PMID:22461381

Morales, Marvin R.; Mellem, Kevin T.; Myers, Andrew G.

2013-01-01

26

Asymmetric Synthesis of the Aminocyclitol Pactamycin, a Universal Translocation Inhibitor  

PubMed Central

An asymmetric total synthesis of the aminocyclopentitol pactamycin is described, which delivers the title compound in 15 steps from 2,4-pentanedione. Critical to this approach was the exploitation of a complex symmetry-breaking reduction strategy to assemble the C1, C2, and C7 relative stereochemistry within the first four steps of the synthesis. Multiple iterations of this reduction strategy are described, and a thorough analysis of stereochemical outcomes is detailed. In the final case, an asymmetric Mannich reaction was developed to install a protected amine directly at the C2 position. Symmetry-breaking reduction of this material gave way to a remarkable series of stereochemical outcomes leading to the title compound without recourse to non-strategic downstream manipulations. This synthesis is immediately accommodating to the facile preparation of structural analogs. PMID:24245656

Sharpe, Robert J.; Malinowski, Justin T.; Johnson, Jeffrey S.

2014-01-01

27

Monosaccharides as Chiral Auxiliaries and Ligands for Asymmetric Synthesis  

NASA Astrophysics Data System (ADS)

This chapter summarizes some recent achievements in asymmetric synthesis, which have been accomplished using sugar derivatives as chiral environments . The use of sugar derivatives as chiral auxiliaries or as chiral ligands of transition-metal catalysts for realizing the asymmetric version of synthetically important organic reactions, such as carbon-carbon bond-forming reactions, the hydrogenation of the carbon-carbon double bond and hydrocyanation, is the focus of this chapter. Prominent studies on these subjects by several research groups are especially emphasized.

Totani, Kiichiro; Tadano, Kin-Ichi

28

Asymmetric synthesis of axially chiral anilides by Pd-catalyzed allylic substitutions with P/olefin ligands.  

PubMed

As an attractive class of non-biaryl atropisomeric compounds, C-N axially chiral anilides have received considerable attention, and several methods have been successfully developed for their synthesis. Pd-catalyzed asymmetric allylic amination was proved to be an effective approach for the chiral anilide synthesis, although only moderate enantioselectivity and relatively narrow substrate scope have been achieved in the previous work. Searching for highly efficient methods for the synthesis of axially chiral anilides is therefore of great interest in synthetic and pharmaceutical chemistry. In this paper, a palladium-catalyzed asymmetric allylic substitution of ortho-substituted anilides using phosphorus amidite-olefin ligands was successfully achieved to afford a variety of axially chiral anilides in high yields with up to 84% ee. The absolute configurations of chiral anilides were also determined from X-ray and CD spectra. PMID:25340871

Liu, Yilin; Feng, Xiangqing; Du, Haifeng

2015-01-01

29

Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes.  

PubMed

Allenes are molecules based on three carbons connected by two cumulated carbon-carbon double bonds. Given their axially chiral nature and unique reactivity, substituted allenes have a variety of applications in organic chemistry as key synthetic intermediates and directly as part of biologically active compounds. Although the demands for these motivated many endeavours to make axially chiral, substituted allenes by exercising asymmetric catalysis, the catalytic asymmetric synthesis of fully substituted ones (tetrasubstituted allenes) remained largely an unsolved issue. The fundamental obstacle to solving this conundrum is the lack of a simple synthetic transformation that provides tetrasubstituted allenes in the action of catalysis. We report herein a strategy to overcome this issue by the use of a phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates with N-arylsulfonyl imines and benzylic and allylic bromides. PMID:23422567

Hashimoto, Takuya; Sakata, Kazuki; Tamakuni, Fumiko; Dutton, Mark J; Maruoka, Keiji

2013-03-01

30

Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes  

NASA Astrophysics Data System (ADS)

Allenes are molecules based on three carbons connected by two cumulated carbon-carbon double bonds. Given their axially chiral nature and unique reactivity, substituted allenes have a variety of applications in organic chemistry as key synthetic intermediates and directly as part of biologically active compounds. Although the demands for these motivated many endeavours to make axially chiral, substituted allenes by exercising asymmetric catalysis, the catalytic asymmetric synthesis of fully substituted ones (tetrasubstituted allenes) remained largely an unsolved issue. The fundamental obstacle to solving this conundrum is the lack of a simple synthetic transformation that provides tetrasubstituted allenes in the action of catalysis. We report herein a strategy to overcome this issue by the use of a phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates with N-arylsulfonyl imines and benzylic and allylic bromides.

Hashimoto, Takuya; Sakata, Kazuki; Tamakuni, Fumiko; Dutton, Mark J.; Maruoka, Keiji

2013-03-01

31

The role of biocatalysis in the asymmetric synthesis of alkaloids  

PubMed Central

Alkaloids are not only one of the most intensively studied classes of natural products, their wide spectrum of pharmacological activities also makes them indispensable drug ingredients in both traditional and modern medicine. Among the methods for their production, biotechnological approaches are gaining importance, and biocatalysis has emerged as an essential tool in this context. A number of chemo-enzymatic strategies for alkaloid synthesis have been developed over the years, in which the biotransformations nowadays take an increasingly ‘central’ role. This review summarises different applications of biocatalysis in the asymmetric synthesis of alkaloids and discusses how recent developments and novel enzymes render innovative and efficient chemo-enzymatic production routes possible.

2013-01-01

32

The Development of the First Catalyzed Reaction of Ketenes and Imines: Catalytic, Asymmetric Synthesis of -Lactams  

E-print Network

The Development of the First Catalyzed Reaction of Ketenes and Imines: Catalytic, Asymmetric for the catalytic, asymmetric synthesis of -lactams resulting from the development of a catalyzed reaction resistance pressures,1 recently -lactams (especially nonnatural ones) have achieved many important

Lectka, Thomas

33

DNA-based hybrid catalysts for asymmetric organic synthesis.  

PubMed

Stereoselective hybrid systems based on metal-assisted catalysis with a chiral biomacromolecule form an attractive research area for the synthesis of enantiomerically pure compounds. Although various methods are available for this purpose, most rely on the use of enzymes, proteins, or RNA. The application of DNA-based hybrid catalysts for enantioselective synthesis emerged only a few years ago. DNA-based hybrid catalysts have been self-assembled from DNA and a metal complex with a specific ligand through supramolecular or covalent anchoring strategies and have demonstrated high stereoselectivity and rate enhancement in Lewis acid catalyzed reactions, such as Diels-Alder, Michael addition, and Friedel-Crafts reactions. For these reactions, cheap and commercially available salmon testes DNA has generally been used. In this Minireview, we summarize recent developments in the area of asymmetric catalysis with DNA-based hybrid catalysts. PMID:20455226

Park, Soyoung; Sugiyama, Hiroshi

2010-05-25

34

Chiral alkynylcarbinols from marine sponges: asymmetric synthesis and biological relevance.  

PubMed

Covering: up to March 2014. Previous review on the topic: B. W. Gung, C. R. Chim., 2009, 12, 489-505Chiral ?-functional lipidic propargylic alcohols extracted from marine sponges, in particular of the pacific genus Petrosia, constitute a class of acetylenic natural products exhibiting remarkable in vitro biological activities, especially anti-tumoral cytotoxicity. These properties, associated to functionalities that are uncommon among natural products, have prompted recent projects on asymmetric total synthesis. On the basis of a three-sector structural typology, three main sub-types of secondary alkynylcarbinols (with either alkyl, alkenyl, or alkynyl as the second substituent) can be identified as the minimal pharmacophoric units. Selected natural products containing these functionalities have been targeted using previously known or on purpose-designed procedures, where the stereo-determining step can be: (i) a C-C bond forming reaction (e.g. the Zn-mediated addition of alkynyl nucleophiles to aldehydes in the presence of chiral aminoalcohols), (ii) a functional layout (e.g. the asymmetric organo- or metallo-catalytic reduction of ynones), or (iii) an enantiomeric resolution (e.g. a lipase-mediated kinetic resolution via acetylation). The promising medicinal importance of these targets is finally surveyed, and future investigation prospects are proposed, such as: (i) further total synthesis of known or future extraction products; (ii) the synthesis of non-natural analogues, with simpler lipophilic environments of the alkynylcarbinol-based pharmacophoric units; (iii) the variation and optimization of both the pharmacophoric units and their lipophilic environment; and (iv) investigations into the biological mode of action of these unique structures. PMID:25275665

Listunov, Dymytrii; Maraval, Valérie; Chauvin, Remi; Génisson, Yves

2014-12-10

35

Asymmetric Synthesis of trans-2,5-Disubstituted Pyrrolidines from Enantiopure Homoallylic Amines. Synthesis of Pyrrolidine (?)-197B  

PubMed Central

Iodocyclization of sulfinimine-derived enantiopure homoallylic sulfonamides affords trans-2,5-disubstituted 3-iodopyrrolidines and represents valuable methodology for the asymmetric synthesis of this important heterocyclic ring system. PMID:16555832

Davis, Franklin A.; Song, Minsoo; Augustine, Alexander

2008-01-01

36

Total synthesis, proof of absolute configuration, and biosynthetic origin of stylopsal, the first isolated sex pheromone of strepsiptera.  

PubMed

The asymmetric total synthesis of the diastereomers of stylopsal establishes the absolute configuration of the first reported sex pheromone of the twisted-wing parasite Stylops muelleri as (3R,5R,9R)-trimethyldodecanal. The key steps for the diastereo- and enantiodivergent introduction of the methyl groups are two different types of asymmetric conjugate addition reactions of organocopper reagents to ?,?-unsaturated esters, whereas the dodecanal skeleton is assembled by Wittig reactions. The structure of the natural product was confirmed by chiral gas chromatography (GC) techniques, GC/MS and GC/electroantennography (EAD) as well as field tests. An investigation into the biosynthesis of the pheromone revealed that it is likely to be produced by decarboxylation of a 4,6,10-trimethyltridecanoic acid derivative, which was found in substantial amounts in the fat body of the female, but not in the host bee Andrena vaga. This triple-branched fatty acid precursor thus seems to be biosynthesized de novo through a polyketide pathway with two consecutive propionate-propionate-acetate assemblies to form the complete skeleton. The simplified, motionless and fully host-dependent female exploits a remarkable strategy to maximize its reproductive success by employing a relatively complex and potent sex pheromone. PMID:23630024

Lagoutte, Roman; Šebesta, Petr; Jiroš, Pavel; Kalinová, Blanka; Jirošová, Anna; Straka, Jakub; ?erná, Kate?ina; Šobotník, Jan; Cva?ka, Josef; Jahn, Ullrich

2013-06-24

37

A Catalytic Asymmetric Method for the Synthesis of -Unsaturated -Amino Acid Derivatives  

E-print Network

A Catalytic Asymmetric Method for the Synthesis of -Unsaturated -Amino Acid Derivatives Alice E for the synthesis of -unsaturated -amino acids and their corresponding 1,3-amino alcohol derivatives to the -unsaturated -amino acid derivatives of high enantiopurity. Introduction The development of synthetically

Walsh, Patrick J.

38

Synthesis of asymmetric tetracarboxylic acids and corresponding dianhydrides  

NASA Technical Reports Server (NTRS)

This invention relates to processes for preparing asymmetrical biphenyl tetracarboxylic acids and the corresponding asymmetrical dianhydrides, namely 2,3,3',4'-biphenyl dianhydride (a-BPDA), 2,3,3',4'-benzophenone dianhydride (a-BTDA) and 3,4'-methylenediphthalic anhydride (-MDPA). By cross-coupling reactions of reactive metal substituted o-xylenes or by cross-coupling o-xylene derivatives in the presence of catalysts, this invention specifically produces asymmetrical biphenyl intermediates that are subsequently oxidized or hydrolyzed and oxidized to provide asymmetric biphenyl tetracarboxylic acids in comparatively high yields. These asymmetrical biphenyl tetracarboxylic acids are subsequently converted to the corresponding asymmetrical dianhydrides without contamination by symmetrical biphenyl dianhydrides.

Chuang, Chun-Hua (Inventor)

2008-01-01

39

Determination by enantioselective synthesis of the absolute configuration of CPE, a potential intermediate in coronatine biosynthesis.  

PubMed

The first enantioselective synthesis of the methyl ester of CPE, a potential intermediate in coronatine (COR) biosynthesis, is described. Comparison of the specific rotation of the synthetic ester with that of the methyl ester of natural CPE established that the latter possesses the (R) configuration. This configuration is the same as that found at the corresponding asymmetric center of coronatine. Structure: see text. PMID:11554839

Tao, T; Parry, R J

2001-09-20

40

Roles of insulin, age, and asymmetric dimethylarginine on nitric oxide synthesis in vivo.  

PubMed

We tested the effects of insulin on production of nitrous oxide (NO)-related substances (nitrites and nitrates [NOx]) after (15)N-arginine intravenous infusion and on asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) concentrations in conditions reportedly associated with altered NO availability, i.e., aging, hypertension, hypercholesterolemia, and type 2 diabetes mellitus (T2DM). A total of 26 male subjects (age 23-71 years, BMI 23-33 kg/m(2)), some of whom were affected by mixed pathologic features, were enrolled. NOx fractional synthesis rate (FSR) was lower in elderly (P < 0.015) and T2DM subjects (P < 0.03) than in matched control subjects. Hyperinsulinemia generally increased both NOx FSR and absolute synthesis rate (ASR) and reduced NOx, ADMA, and SDMA concentrations. Insulin sensitivity was impaired only in T2DM. With use of simple linear regression analysis across all subjects, age was inversely correlated with both NOx FSR (R(2) = 0.23, P < 0.015) and ASR (R(2) = 0.21, P < 0.02). NOx FSR inversely correlated with both ADMA and SDMA. With use of multiple regression analysis and various models, NOx FSR remained inversely associated with age and ADMA, whereas ASR was inversely associated with age and diabetes. No association with insulin sensitivity was found. We conclude that whole-body NOx production is decreased in aging and T2DM. Age, ADMA concentration, and T2DM, but not insulin resistance, appear as negative regulators of whole-body NOx production. PMID:23474488

Tessari, Paolo; Cecchet, Diego; Artusi, Carlo; Vettore, Monica; Millioni, Renato; Plebani, Mario; Puricelli, Lucia; Vedovato, Monica

2013-08-01

41

A convergent rhodium-catalysed asymmetric synthesis of tetrahydroquinolines.  

PubMed

Rh-catalysed conjugate additions of 2-aminophenyl boronic acid derivatives were exploited in diastereoselective and asymmetric syntheses of tetrahydroquinolines. In both cases, combinatorial variation of the substitution of the tetrahydroquinoline ring system was possible. PMID:25052422

Li, Ho Yin; Horn, Joachim; Campbell, Amanda; House, David; Nelson, Adam; Marsden, Stephen P

2014-09-14

42

Asymmetric Total Synthesis of Alkaloid 223A and 6-epi-223A‡  

PubMed Central

A concise and asymmetric total synthesis of the title compound is described. The key ring system was constructed using an intramolecular Schmidt reaction on a norbornenone derivative, which was subsequently subjected to ring-opening metathesis followed by reduction. An unusual isomerization of the C-6 ethyl group afforded the desired stereochemistry of the natural product. The synthesis is readily adaptable to analogue production. PMID:19739687

Ghosh, Partha; Judd, Weston R.; Ribelin, Timothy; Aubé, Jeffrey

2009-01-01

43

Catalytic asymmetric assembly of octahydroindolones: divergent synthesis of lycorine-type amaryllidaceae alkaloids (+)-?-lycorane and (+)-lycorine.  

PubMed

We report the first catalytic asymmetric approach to octahydroindolones and a divergent enantioselective synthesis of perhydroindole alkaloids, as exemplified by lycorine-type Amaryllidaceae alkaloids (+)-?-lycorane and (+)-lycorine, from a common intermediate by using a highly concise route. The assembly of octahydroindolones employs a catalytic enantioselective 1,4-conjugate addition of nitro dienynes, followed by a TsOH-catalyzed cascade synthesis of highly functionalized enones, and a diastereoselective intramolecular Michael addition. PMID:24700723

Sun, Zhongwen; Zhou, Mingtao; Li, Xiang; Meng, Xueling; Peng, Fangzhi; Zhang, Hongbin; Shao, Zhihui

2014-05-12

44

Ru(CO)-salen-catalyzed synthesis of enantiopure aziridinyl ketones and formal asymmetric synthesis of (+)-PD 128907.  

PubMed

Aziridination of vinyl ketones using SESN(3) in the presence Ru(CO)-salen complex 1 provides the enantiopure aziridinyl ketones that can serve as useful chiral building blocks. A formal asymmetric synthesis of (+)-PD 128907 was achieved in an eight-step sequence via aziridination. PMID:22928558

Fukunaga, Yasuaki; Uchida, Tatsuya; Ito, Yutaro; Matsumoto, Kenji; Katsuki, Tsutomu

2012-09-01

45

Large-scale asymmetric synthesis of the bioprotective agent JP4-039 and analogs  

PubMed Central

JP4-039 is a novel nitroxide conjugate capable of crossing lipid bilayer membranes and scavenging reactive oxygen species (ROS). An efficient and scalable one-pot hydrozirconation-transmetalation-imine addition methodology has been developed for its asymmetric preparation. Furthermore, this versatile methodology allows for the synthesis of cyclopropyl and fluorinated analogs of the parent lead structure. PMID:21452836

Frantz, Marie-Céline; Pierce, Joshua G.; Pierce, Joan M.; Kangying, Li; Qingwei, Wan; Johnson, Matthew; Wipf, Peter

2011-01-01

46

Asymmetric Total Synthesis of (-)-Leuconoxine via Chiral Phosphoric Acid Catalyzed Desymmetrization of a Prochiral Diester.  

PubMed

The asymmetric total synthesis of (-)-leuconoxine has been achieved. The desymmetrization of a prochiral diester using a chiral phosphoric acid catalyst produced a highly enantioenriched lactam with excellent yield. The ring construction featuring an intramolecular N-acyliminium cyclization and the one-step pyrrolidone formation using Bestmann's ylide was successfully accomplished. PMID:25522825

Higuchi, Kazuhiro; Suzuki, Shin; Ueda, Reeko; Oshima, Norifumi; Kobayashi, Emiko; Tayu, Masanori; Kawasaki, Tomomi

2015-01-01

47

Asymmetric synthesis of trifluoromethylated amines via catalytic enantioselective isomerization of imines.  

PubMed

A new approach toward the asymmetric synthesis of optically active trifluoromethylated amines was enabled by an unprecedented, highly enantioselective catalytic isomerization of trifluoromethyl imines with a new chiral organic catalyst. Not only aryl but also alkyl trifluoromethylated amines could be obtained in high enantioselectivities. PMID:22906148

Wu, Yongwei; Deng, Li

2012-09-01

48

Chiral-Auxiliary-Mediated Asymmetric Synthesis of Tris-Heteroleptic Ruthenium Polypyridyl Complexes  

E-print Network

Chiral-Auxiliary-Mediated Asymmetric Synthesis of Tris-Heteroleptic Ruthenium Polypyridyl Complexes ruthenium polypyridyl complexes lacking additional chirality in the organic ligand sphere relies solely for a typical tris-heteroleptic ruthenium complex (Figure 1). This complex contains 2,2-bipyridine (bpy), 5

Meggers, Eric

49

Asymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido Complex  

E-print Network

Asymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido reaction. On the basis of the strong basicity and nucleophilicity of previously reported iron and ruthenium cationic phosphine complex 2-BPh4. Deprotonation of this complex with KHMDS afforded ruthenium phosphido

Toste, Dean

50

Asymmetric Total Synthesis of Dendrobatid Alkaloids: Preparation of Indolizidine 251F and Its 3-Desmethyl  

E-print Network

Asymmetric Total Synthesis of Dendrobatid Alkaloids: Preparation of Indolizidine 251F and Its 3-mail: jaube@ku.edu Abstract: Total syntheses of alkaloid 251F (1), a natural product detected from the skin array of natural product targets, particularly alkaloids, unprecedented in other biological systems.1

Taber, Douglass

51

The taumycin A macrocycle: asymmetric total synthesis and revision of relative stereochemistry.  

PubMed

The first asymmetric total synthesis and revision of the relative configuration of the 12-membered taumycin A macrocycle is described. Key to the success of this work was a novel ?-keto ketene macrocyclization that provided an efficient means by which to access two diastereomers of the desired macrolide without the need to employ additional coupling agents or unnecessary oxidation state adjustments. PMID:25248034

deGruyter, Justine N; Maio, William A

2014-10-01

52

Asymmetric Total Synthesis of Soraphen A: a Flexible Alkyne Strategy**  

PubMed Central

The alkyne functional group can be a valuable handle for organic synthesis since the alkyne can function both as a nucleophile or as an electrophile when activated with an appropriate metal catalyst. Herein, we exploit this dual nature of the alkyne moiety for the concise total synthesis of the natural product soraphen A. PMID:19554583

Trost, Barry M.; Sieber, Joshua D.; Qian, Wei; Dhawan, Rajiv; Ball, Zachary T.

2013-01-01

53

Chemoenzymatic asymmetric synthesis of pregabalin precursors via asymmetric bioreduction of ?-cyanoacrylate esters using ene-reductases.  

PubMed

The asymmetric bioreduction of a library of ?-cyanoacrylate esters using ene-reductases was studied with the aim to provide a biocatalytic route to precursors for GABA analogues, such as pregabalin. The stereochemical outcome could be controlled by substrate-engineering through size-variation of the ester moiety and by employing stereochemically pure (E)- or (Z)-isomers, which allowed to access both enantiomers of each product in up to quantitative conversion in enantiomerically pure form. In addition, stereoselectivities and conversions could be improved by mutant variants of OPR1, and the utility of the system was demonstrated by preparative-scale applications. PMID:23316696

Winkler, Christoph K; Clay, Dorina; Davies, Simon; O'Neill, Pat; McDaid, Paul; Debarge, Sebastien; Steflik, Jeremy; Karmilowicz, Mike; Wong, John W; Faber, Kurt

2013-02-15

54

Chemoenzymatic Asymmetric Synthesis of Pregabalin Precursors via Asymmetric Bioreduction of ?-Cyanoacrylate Esters Using Ene-Reductases  

PubMed Central

The asymmetric bioreduction of a library of ?-cyanoacrylate esters using ene-reductases was studied with the aim to provide a biocatalytic route to precursors for GABA analogues, such as pregabalin. The stereochemical outcome could be controlled by substrate-engineering through size-variation of the ester moiety and by employing stereochemically pure (E)- or (Z)-isomers, which allowed to access both enantiomers of each product in up to quantitative conversion in enantiomerically pure form. In addition, stereoselectivities and conversions could be improved by mutant variants of OPR1, and the utility of the system was demonstrated by preparative-scale applications. PMID:23316696

2013-01-01

55

Cinchona-based phase-transfer catalysts for asymmetric synthesis.  

PubMed

Phase-transfer catalysis is one of the most useful methodologies for practical syntheses given its operational simplicity and mild reaction conditions that enable its application in industrial processes. Cinchona alkaloids have been a popular, natural source of practical organocatalysts due largely to their excellent commercial availability and low cost. Since the first Cinchona alkaloid-derived phase-transfer catalysts was disclosed in 1981, diverse generations of Cinchona-derived phase-transfer catalysts have been developed and successfully applied to various asymmetric syntheses. In this feature article, we describe the generation of Cinchona-derived chiral phase-transfer catalysts according to the development stages and our efforts toward the design of polymeric Cinchona phase-transfer catalysts, the effects of the electronic functional group incorporated in the catalysts, and their application in asymmetric organic reactions. PMID:19920996

Jew, Sang-sup; Park, Hyeung-geun

2009-12-14

56

Asymmetric alkyldifluoroboranes and their use in secondary amine synthesis.  

PubMed

[reaction: see text] Asymmetric diol boronic esters with potassium bifluoride form the corresponding alkyltrifluoroborate and free diol under mild conditions. Defluoridation with tetrachlorosilane produces an alkyldifluoroborane intermediate. This conversion of relatively unreactive boronic esters to derivatives that are strong Lewis acids opens new synthetic opportunities, as illustrated by the preparation of (R)-2-phenylpyrrolidine in 98% ee from a pinanediol or 1,2-dicyclohexyl-1,2-ethanediol boronic ester via potassium (2-phenyl-4-azidobutyl)trifluoroborate. PMID:12074655

Matteson, Donald S; Kim, Gyung Youn

2002-06-27

57

Asymmetric multibranched conjugated molecules: Synthesis, structure and photophysical properties  

NASA Astrophysics Data System (ADS)

The symmetric multibranched ?-conjugated compounds with C3 or C6 configuration have been intensively studied. The reports on asymmetric multibranched compounds are very limited. In this work, we designed and synthesized two asymmetric multibranched ?-conjugated molecules using truxene as the central core, diphenylamino and thiophenyl (or thiophenylethynyl) groups as the different branches respectively: 2,7-di(N,N-diphenylamino)-12-(2-thiophenyl)-5,5?,10,10?,15,15?-hexaethyltruxene and 2,7-di(N,N-diphenylamino)-12-(2-thiophenylethynyl)-5,5?,10,10?,15,15?-hexaethyltruxene. Their photophysical properties have been explored combining with their theoretical calculation and X-ray single-crystal structure of a key intermediate. Though their different ?-conjugation length of branches, the two title compounds exhibit almost same absorption maxima. However, their emission peaks behave a gradual red-shift with the increase of the conjugation length. The theoretical calculation results indicate that the two asymmetric compounds behave a main transition from the HOMO - 1 to the LUMO or from the HOMO to the LUMO + 1 upon excited.

Zhao, Li; Wang, Wenji; Yuan, Mao-Sen

2015-01-01

58

Total synthesis and absolute configuration assignment of MRSA active garcinol and isogarcinol.  

PubMed

A short total synthesis of (±)-garcinol and (±)-isogarcinol, two endo-type?B PPAPs with reported activity against methiciline resistant Staphylococcus aureus (MRSA), is presented. The separation of framework-constructing from framework-decorating steps and the application of two highly regio- and stereoselective Pd-catalysed allylations, that is, the Pd-catalysed decarboxylative Tsuji-Trost allylation and the diastereoselective Pd-catalysed allyl-allyl cross-coupling, are key elements that allowed the total synthesis to be accomplished within 13 steps starting from acetylacetone. After separation of the enantiomers the absolute configurations of the four natural products (i.e., (-)-garcinol, (+)-guttiferone?E (i.e., ent-garcinol), (-)-isogarcinol, and (+)-isoxanthochymol (i.e., ent-isogarcinol)) were assigned based on ECD spectroscopy. PMID:25537962

Socolsky, Cecilia; Plietker, Bernd

2015-02-01

59

Inherently Chiral Calixarenes: Synthesis, Optical Resolution, Chiral Recognition and Asymmetric Catalysis  

PubMed Central

Inherently chiral calixarenes, whose chirality is based on the absence of a planar symmetry or an inversion center in the molecules as a whole through the asymmetric array of several achiral groups upon the three-dimensional calix-skeletons, are challenging and attractive chiral molecules, because of their potential in supramolecular chemistry. The synthesis and optical resolution of all varieties of inherently chiral calixarenes are systematically discussed and classified, and their applications in chiral recognition and asymmetric catalysis are thoroughly illustrated in this review. PMID:21339996

Li, Shao-Yong; Xu, Yao-Wei; Liu, Jun-Min; Su, Cheng-Yong

2011-01-01

60

The first asymmetric total synthesis of (+)-coriandrone A and B.  

PubMed

The first enantioselective total synthesis of (+)-coriandrone A and B, two bioactive natural products, has been achieved in 10 steps and 11 steps starting from commercially available methyl 2-hydroxy-4-methoxybenzoate. Key reactions include a Claison rearrangement, a Shi-type epoxidation-cyclization sequence and ortho-metallation of t-butylbenzamides with (S)-(-)-propylene oxide reaction. PMID:23986305

Wang, Wenjing; Xue, Jijun; Tian, Tian; Jiao, Yingdong; Li, Ying

2013-10-21

61

Rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles by enantioselective [2+2+2] cycloaddition.  

PubMed

A rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles has been developed through a [2+2+2] cycloaddition of silicon-containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germanium-stereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described. PMID:25491349

Shintani, Ryo; Takagi, Chihiro; Ito, Tomoaki; Naito, Masanobu; Nozaki, Kyoko

2015-01-26

62

Asymmetric Synthesis of gem-Difluoromethylenated Linear Triquinanes via Cascade gem-Difluoroalkyl Radical Cyclization.  

PubMed

An asymmetric synthesis of gem-difluoromethylenated linear triquinanes is described exploiting the synthetic utilities of PhSCF2TMS (5) as a "(•)CF2(-)'' building block. The strategy involves fluoride-catalyzed nucleophilic addition of PhSCF2TMS (5) to chiral ketocyclopentenes 6 to provide silylated adducts 9 or alcohol derivatives 10 and 11. Subsequent cascade radical cyclization of the gem-difluoroalkyl radical generated from silylated adducts 9 or alcohols 10 and 11 afforded gem-difluoromethylenated linear triquinanes 16 as an approximate 1:1 mixture of two diastereomers (16A and 16B). Alternatively, a convenient asymmetric synthesis of gem-difluoromethylenated linear triquinanes 16A can be accomplished by oxidation of 16a (R = H) to provide ketotriquinane 17 followed by a highly stereoselective nucleophilic addition to 17 employing DIBAL, NaBH4, and various Grignard reagents. PMID:25517014

Thaharn, Watcharaporn; Soorukram, Darunee; Kuhakarn, Chutima; Tuchinda, Patoomratana; Pakawatchai, Chaveng; Saithong, Saowanit; Reutrakul, Vichai; Pohmakotr, Manat

2015-01-16

63

Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of c7-functionalized indoles.  

PubMed

The first catalytic asymmetric cascade reaction of 7-vinylindoles has been established by the rational design of such substrates. Cascade reactions with isatin-derived 3-indolylmethanols in the presence of a chiral phosphoric acid derivative allow the diastereo- and enantioselective synthesis of C7-functionalized indoles as well as the construction of cyclopenta[b]indole and spirooxindole frameworks (all >95:5 d.r., 94->99?% ee). This approach not only addresses the great challenge of the catalytic asymmetric synthesis of C7-functionalized indoles, but also provides an efficient method for constructing biologically important cyclopenta[b]indole and spirooxindole scaffolds with excellent optical purity. Investigation of the reaction pathway and activation mode has suggested that this cascade reaction proceeds through a vinylogous Michael addition/Friedel-Crafts process, in which dual H-bonding activation of the two reactants plays a crucial role. PMID:25521722

Shi, Feng; Zhang, Hong-Hao; Sun, Xiao-Xue; Liang, Jing; Fan, Tao; Tu, Shu-Jiang

2015-02-16

64

Asymmetric Synthetic Access to the Hetisine Alkaloids: Total Synthesis of (+)-Nominine  

PubMed Central

A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cycloaddition of a 4-oxido-isoquinolinium betaine dipole with an ene–nitrile dipolarophile. Subsequent late-stage pyrrolidine-induced dienamine isomerization/Diels–Alder cascade allows for rapid construction of the carbon–nitrogen polycyclic skeleton within this class of C20-diterpenoid alkaloids. PMID:18046691

Peese, Kevin M.

2008-01-01

65

Asymmetric Synthesis of Fully Substituted Cyclopentane-Oxindoles through an Organocatalytic Triple Michael Domino Reaction.  

PubMed

An efficient, highly stereoselective asymmetric synthesis of fully functionalized cyclopentanes bearing an oxindole moiety and several other functional groups in one pot has been developed. Key step is an organocatalytic triple Michael domino reaction forming three C?C bonds and six stereocenters, including a quaternary one. Starting from equimolar amounts of simple substrates, a high molecular complexity can be reached after a Wittig olefination in one pot. The new protocol can easily be scaled up to gram amounts. PMID:25470781

Zou, Liang-Hua; Philipps, Arne R; Raabe, Gerhard; Enders, Dieter

2015-01-12

66

Asymmetric synthesis of (+)-pyrido[3,4-b]homotropane.  

PubMed

(+)-pyrido[3,4- b]homotropane (PHT) was efficiently constructed in 12 steps from N, N-diisopropylisonicotinamide. The synthesis features (i) RCM reaction in installing the homotropane skeleton, (ii) Snieckus ortho-lithiation of N, N-diisopropylisonicotinamide followed by acylation, (iii) Myer reduction of bulky tertiary amide to alcohol with LiBH 3NH 2, and (iv) utilization of L-glutamic acid to introduce and establish the requisite stereogenic centers. PMID:18345639

Sang, Yingxia; Zhao, Jingrui; Jia, Xueshun; Zhai, Hongbin

2008-05-01

67

Asymmetric synthesis and effect of absolute stereochemistry of YCZ-2013, a brassinosteroid biosynthesis inhibitor.  

PubMed

The four stereoisomers of 2RS,4RS-1-[[2-(2,4-dichlorophenyl)-4-(2-(2-propenyloxy)phenoxymethyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole (YCZ-2013), a novel brassinosteroid biosynthesis inhibitor, were prepared. The diastereomers of 2RS,4R-5 and 2RS,4S-5 were prepared by using the corresponding optically pure R and S toluene-4-sulfonic acid 2,3-dihydroxypropyl ester (R-4,S-4). The enatiomerically and diastereomerically pure acetonide (5) was obtained by a method involving diastereoselective crystallisation of the tosylate salt, followed by re-equilibration with the mother liquor and chromatography. The optical purity of four target compounds (YCZ-2013) was confirmed by chiral high-performance liquid chromatography (HPLC) and NMR. The effects of these stereoisomers on Arabidopsis stem elongation indicated that the cis isomers of 2S,4R-YCZ-2013 and 2R,4S-YCZ-2013 exhibited potent inhibitory activity with IC50 values of approximately 24 ± 3 and 24 ± 2 nM, respectively. The IC50 values of the trans isomers of 2S,4S-YCZ-2013 and 2R,4R-YCZ-2013 are approximately 1510 ± 50 and 3900 ± 332 nM, respectively. Co-application of brassinolide (10nM), the most potent BR, and GA3 (1 ?M) to Arabidopsis seedlings grown in the dark with 2R,4S-YCZ-2013 and 2S,4R-YCZ-2013 revealed that brassinolide recovered the induced dwarfism of Arabidopsis seedlings, whereas GA3 showed no effect. PMID:24269478

Oh, Keimei; Yamada, Kazuhiro; Yoshizawa, Yuko

2013-12-15

68

Synthesis of Non-racemic ?-Hydroxy Phosphonates via Asymmetric Phospho-Aldol Reaction.  

PubMed

It has been more than 50 years since the first phospho-aldol reactions of dialkyl phosphites were reported. These efficient P-C bond-forming reactions have become the cornerstone of methods for the synthesis of ?-hydroxyphosphonates and, by numerous available substitution reactions, the synthesis of other ?- and ?-substituted phosphonates and phosphonic acids. Much of the interest in ?- and ?-substituted phosphonates and phosphonic acids has been stimulated by reports of their biological activity, which is often dependent upon their absolute and relative stereochemistry. In this chapter, we review diastereoselective and enantioselective additions of dialkyl phosphites to aldehydes and ketones, otherwise called the phospho-aldol, Pudovik or Abramov reactions. PMID:25467537

Spilling, Christopher D; Malla, Raj K

2014-12-01

69

Asymmetric Autocatalysis with Amplification of Chirality  

NASA Astrophysics Data System (ADS)

We found that chiral 5-pyrimidyl alkanols are highly enantioselective asymmetric autocatalysts for the addition of i-Pr2Zn to the corresponding aldehyde. Asymmetric autocatalysis with amplification of ee from extremely low (0.00005%) ee to >99.5% ee was realized for the first time by consecutive asymmetric autocatalysis. The chirality of CPL was directly correlated with the chirality of the pyrimidyl alkanol with high ee by asymmetric photodegradation of the racemic pyrimidyl alkanol in combination with asymmetric autocatalysis. Chiral inorganic crystals such as quartz act as chiral triggers and regulate the sense of the asymmetric autocatalysis. Chiral organic crystals composed of an achiral compound such as hippuric acid act as the initial source of chirality for asymmetric autocatalysis to produce the nearly enantiomerically pure product. Highly sensitive chiral discrimination of amino acids with low ee is described. Direct examination of extraterrestrial chirality was performed on meteorites by applying asymmetric autocatalysis as the chiral sensor. Spontaneous absolute asymmetric synthesis is described in the formation of enantiomerically enriched pyrimidyl alkanol from the reaction of pyrimidine-5-carbaldehyde and i-Pr2Zn without adding any chiral substance in combination with asymmetric autocatalysis. Asymmetric autocatalysis of a chiral pyrimidyl alkanol is the only possible method to discriminate a cryptochiral quaternary saturated hydrocarbon, whose chirality is not capable of determination by any current method. The discrimination of chirality due to deuterium substitution is also accessible by the highly sensitive asymmetric autocatalysis.

Soai, Kenso; Kawasaki, Tsuneomi

70

Asymmetric synthesis of tetrahydroisoquinolines by enzymatic Pictet-Spengler reaction.  

PubMed

Norcoclaurine synthase (NCS) catalyzes the stereoselective Pictet-Spengler reaction between dopamine and 4-hydroxyphenylacetaldehyde as the first step of benzylisoquinoline alkaloid synthesis in plants. Recent studies suggested that NCS shows relatively relaxed substrate specificity toward aldehydes, and thus, the enzyme can serve as a tool to synthesize unnatural, optically active tetrahydroisoquinolines. In this study, using an N-terminally truncated NCS from Coptis japonica expressed in Escherichia coli, we examined the aldehyde substrate specificity of the enzyme. Herein, we demonstrate the versatility of the enzyme by synthesizing 6,7-dihydroxy-1-phenethyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dihydroxy-1-propyl-1,2,3,4-tetrahydroisoquinoline in molar yields of 86.0 and 99.6% and in enantiomer excess of 95.3 and 98.0%, respectively. The results revealed the enzyme is a promising catalyst that functions to stereoselectively produce various 1-substituted-1,2,3,4-tetrahydroisoquinolines. PMID:25036970

Nishihachijo, Masakatsu; Hirai, Yoshinori; Kawano, Shigeru; Nishiyama, Akira; Minami, Hiromichi; Katayama, Takane; Yasohara, Yoshihiko; Sato, Fumihiko; Kumagai, Hidehiko

2014-01-01

71

Absolute configuration of arylglycerol- ? -aryl ethers obtained by asymmetric reduction of the corresponding ? -ketonic compound with intact Fusarium solani cells  

Microsoft Academic Search

When (±)-?-oxo-guaiacylglycerol-?-(vanillic acid) ether (1) is degraded byFusarium solani M-13-1, the?-ketone is initially reduced to giveerythro andthreo guaiacylglycerol-?-(vanillic acid) ethers (2), arylglycerol-?-aryl ethers, both of which are enantiomerically pure. The absolute configuration in each2 was determined by Mosher's method; the products were converted to?,?-di-(R)-?-methoxy-?-trifluoromethylphenylacetates (MTPA esters) (3?) oferythro (-)- andthreo (+)-veratrylglycerol-?-(methyl vanillate) ethers (3), whose1H nuclear magnetic resonance (NMR) spectra

Takeshi Katayama; Jyoji Tsutsui; Kazuo Tsueda; Takao Miki; Yasuhiro Yamada; Murao Sogo

2000-01-01

72

The origins of homochirality examined by using asymmetric autocatalysis.  

PubMed

Pyrimidyl alkanol was found to act as an asymmetric autocatalyst in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Asymmetric autocatalysis of 2-alkynylpyrimidyl alkanol with an extremely low enantiomeric excess (ca. 0.00005% ee) exhibits enormous asymmetric amplification to afford the same compound with >99.5% ee. This asymmetric autocatalysis with amplification of ee has been employed to examine the validity of proposed theories of the origins of homochirality. Circularly polarized light, quartz, sodium chlorate, cinnabar, chiral organic crystals and spontaneous absolute asymmetric synthesis were considered as possible candidates for the origin of chirality; each could act as a chiral source in asymmetric autocatalysis. Asymmetric autocatalysis can discriminate the isotope chirality arising from the small difference between carbon (carbon-13/carbon-12) and hydrogen (D/H) isotopes. Cryptochiral compounds were also discriminated by asymmetric autocatalysis. PMID:24449510

Soai, Kenso; Kawasaki, Tsuneomi; Matsumoto, Arimasa

2014-02-01

73

Toward a real synthesis of quantum and relativity theories: experimental evidence for absolute simultaneity  

E-print Network

We have demonstrated spatially-discontinuous jumps of electrons at a distance as long as about 1cm. The effect occurs in a modified integer quantum Hall system consisted of a great number of extended Laughlin-Halperin-type states. Our observations directly contradict the no-aether Einstein's interpretation of special relativity together with the Minkowski's model of spacetime. However they are consistent with the aether-related Lorentz-Poincare's interpretation that allows absolute simultaneity. We thus strongly challenge the fundamental status of Lorentz invariance and hence break the basic argument against de Broglie-Bohm realistic quantum theory. We argue that both de Broglie-Bohm and Lorentz-Poincare theories are capable of providing a real synthesis of quantum and relativity theories. The synthesis is of such kind that quantum theory appears the most fundamental physical theory for which relativity is only a limiting case. In accordance with this hierarchy, quantum theory naturally resolves the problem of aether in Lorentz-Poincare's relativity. The aether could be a deeper Bohm-type undivided quantum pre-space, the relevance of which directly follows from our observations.

S. A. Emelyanov

2013-01-16

74

Toward a real synthesis of quantum and relativity theories: experimental evidence for absolute simultaneity  

NASA Astrophysics Data System (ADS)

We have demonstrated spatially-discontinuous quantum jumps of electrons at a distance as long as about 1cm. The effect occurs in a modified integer quantum Hall system consisted of a great number of extended Laughlin-Halperin-type states. Our observations directly contradict the no-aether Einstein's interpretation of special relativity together with the Minkowski's model of spacetime. However they are consistent with the aether-related Lorentz-Poincare's interpretation that allows absolute simultaneity. We thus strongly challenge the fundamental status of Lorentz invariance and hence break the basic argument against de Broglie-Bohm realistic quantum theory. We argue that both de Broglie-Bohm and Lorentz-Poincare theories are capable of providing a real synthesis of quantum and relativity theories. This synthesis is of such kind that quantum theory appears the most fundamental physical theory for which relativity is only a limiting case. In accordance with this hierarchy, quantum theory naturally resolves the problem of aether in Lorentz-Poincare's relativity. The role of aether could be played by a deeper Bohm-type undivided quantum pre-space, the relevance of which at any lengthscale directly follows from our observations.

Emelyanov, S. A.

2013-06-01

75

Highly enantioselective catalytic asymmetric synthesis of a (R)-sibutramin precursor.  

PubMed

The first highly enantioselective, catalytic asymmetric synthesis of di-des-methylsibutramine 3 is described. Dienamide 10, prepared by acetic acid anhydride quenching of the condensation product of nitrile 4 with a methallyl magnesium chloride, proved to be an excellent substrate for ruthenium-catalyzed asymmetric hydrogenation with atropisomeric diphosphine ligands. Hydrogenation with a ruthenium/(R)- MeOBiPheP catalyst at S/C = 500, gave the chiral amide (R)-9 in 98.5% ee in almost quantitative yield. After acidic amide hydrolysis the desired amine (R)-3 was obtained without erosion of enantioselectivity. It is anticipated that the overall process will be amenable to large-scale production. PMID:21137687

Berens, Ulrich; Hafner, Andreas; Dosenbach, Oliver; Tritschler, Tanja; Schwarzenbach, Franz; Kirner, Hans-Jörg; Malan, Christophe; Mai-Huynh, Oanh

2010-01-01

76

Development of an Asymmetric Synthesis of a Chiral Quaternary FLAP Inhibitor.  

PubMed

A practical sequence involving a noncryogenic stereospecific boronate rearrangement followed by a robust formylation with an in situ generated DCM anion has been developed for the asymmetric construction of an all-carbon quaternary stereogenic center of a FLAP inhibitor. The key boronate rearrangement was rendered noncryogenic and robust by using LDA as the base and instituting an in situ trapping of the unstable lithiated benzylic carbamate with the boronic ester. A similar strategy was implemented for the DCM formylation reaction. It was found that the 1,2-boronate rearrangement for the formylation reaction could be temperature-controlled, thus preventing overaddition of the DCM anion and rendering the process reproducible. The robust stereospecific boronate rearrangement and formylation were utilized for the practical asymmetric synthesis of a chiral quaternary FLAP inhibitor. PMID:25562342

Fandrick, Keith R; Mulder, Jason A; Patel, Nitinchandra D; Gao, Joe; Konrad, Michael; Archer, Elizabeth; Buono, Frederic G; Duran, Adil; Schmid, Rolf; Daeubler, Juergen; Desrosiers, Jean-Nicolas; Zeng, Xingzhong; Rodriguez, Sonia; Ma, Shengli; Qu, Bo; Li, Zhibin; Fandrick, Daniel R; Grinberg, Nelu; Lee, Heewon; Bosanac, Todd; Takahashi, Hidenori; Chen, Zhidong; Bartolozzi, Alessandra; Nemoto, Peter; Busacca, Carl A; Song, Jinhua J; Yee, Nathan K; Mahaney, Paige E; Senanayake, Chris H

2015-02-01

77

Determination of absolute stereochemistry and an alternative synthesis of homopumiliotoxin 223G: identification on chiral GC columns with the natural alkaloid.  

PubMed

An alternative asymmetric synthesis of (+)-(lS,9aS)-homopumiliotoxin 223G (1) was accomplished via (1R,2R, 9aS)-1-(benzyloxy)-2-hydroxy-1-methyl-3[(E)-isobutylidene]++ +quinolizidi ne (4), which was synthesized according to the intramolecular nickel(II)/chromium(II)-mediated cyclization of the N-(iodoalkenyl)aldehyde 2. Compound 4 was converted to the acetate and subjected to reduction with lithium in ammonia, whereupon deprotection of the O-benzyl group and removal of the acetoxyl group occurred in a single operation to afford (+)-homopumiliotoxin 223G. The same sequence using (+/-)-4 was applied to the synthesis of racemic 223G. Gas chromatography of a sample of racemic 223G showed no separation into enantiomers on four different cyclodextrin-based chiral GC columns. We found, however, that the O-acetates of (+/-)-223G gave a nearly baseline separation on either a beta-cyclodextrin column or a permethylated beta-cyclodextrin column. The O-acetate of synthetic (+)-223G was identical on either of these two columns, with the first eluting O-acetate from acetylated (+/-)-223G and also with the acetylated 223G present in a frog skin extract, thus allowing us to confirm unambiguously the 1S,9aS absolute configurations of natural 223G. PMID:10978217

Kibayashi, C; Aoyagi, S; Wang, T C; Saito, K; Daly, J W; Spande, T F

2000-08-01

78

Highly enantioselective synthesis of ?-, ?-, and ?-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)–Cu- or Pd-catalyzed cross-coupling  

PubMed Central

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (?99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (?99% ee) and catalytic synthesis of various ?- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)–Cu- or Pd-catalyzed cross-coupling. ZACA–in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ?-alkene-1-ols produced both (R)- and (S)-?,?-dioxyfunctional intermediates (3) in 80–88% ee, which were readily purified to the ?99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These ?,?-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

2014-01-01

79

Asymmetric synthesis of ?-allyl-?-aryl ?-amino acids by tandem alkylation/?-allylation of ?-iminoesters.  

PubMed

The first asymmetric synthesis of ?-allyl-?-aryl ?-amino acids by means of a three-component coupling of ?-iminoesters, Grignard reagents, and cinnamyl acetate is reported. Notably, the enolate from the tandem process provides a much higher level of reactivity and selectivity than the same enolate generated via direct deprotonation, presumably due to differences in the solvation/aggregation state. A novel method for removal of a homoallylic amine protecting group delivers the free amine congeners. The ?-allyl group offers a means to generate further valuable ?-amino acid structures as exemplified by ring closing metathesis to generate a higher ring homologue of ?-aryl-proline. PMID:24666394

Curto, John M; Dickstein, Joshua S; Berritt, Simon; Kozlowski, Marisa C

2014-04-01

80

Multicomponent synthesis of chiral bidentate unsymmetrical unsaturated N-heterocyclic carbenes: copper-catalyzed asymmetric c?c bond formation.  

PubMed

A multicomponent strategy was applied to the synthesis of chiral bidentate unsaturated hydroxyalkyl- and carboxyalkyl-N-heterocyclic carbene (NHC) precursors. The newly developed low-cost chiral ligands derived from amino alcohols and amino acids were evaluated in copper-catalyzed asymmetric conjugated addition and asymmetric allylic alkylation, which afforded the desired tertiary and quaternary carbon stereocenters with excellent regio- and enantioselectivities (up to 99:1 e.r.). PMID:25421857

Jahier-Diallo, Claire; Morin, Marie S T; Queval, Pierre; Rouen, Mathieu; Artur, Isabelle; Querard, Pierre; Toupet, Loic; Crévisy, Christophe; Baslé, Olivier; Mauduit, Marc

2015-01-12

81

Asymmetric Synthesis of anti-?-Amino-?-Hydroxy Esters via Dynamic Kinetic Resolution of ?-Amino-?-Keto Esters  

PubMed Central

A method for the asymmetric synthesis of enantioenriched anti-?-hydroxy-?-amino acid derivatives by enantioconvergent reduction of the corresponding racemic ?-keto esters is presented. The requisite ?-keto esters are prepared via Mannich addition of ethyl diazoacetate to imines followed by oxidation of the diazo group with Oxone®. Implementation of a recently-developed dynamic kinetic resolution of ?-substituted-?-keto esters via Ru(II)-catalyzed asymmetric transfer hydrogenation provides the title motif in routinely high diastereo- and enantioselectivity. PMID:23631467

Goodman, C. Guy; Do, Dung T.

2013-01-01

82

Multi-component Cycloaddition Approaches in the Catalytic Asymmetric Synthesis of Alkaloid Targets†  

PubMed Central

Cycloaddition reactions are attractive strategies for rapid formation of molecular complexity in organic synthesis as multiple bonds are formed in a single process. To this end, several research groups have been actively involved in the development of catalytic methods to activate readily accessible ?-components to achieve cycloadditions. However, the use of C-N ?-components for the formation of heterocycles by these processes is less well developed. It has been previously demonstrated that the combination of different isocyanates with two alkynes yields pyridones of several types by metal-catalyzed [2+2+2] cycloadditions. The potential of this chemistry has been extended to alkenes as C-C ?-components, allowing the formation of sp3-stereocenters. In this tutorial review directed towards [n+2+2] cycloaddition of heterocumulenes, alkynes and alkenes, the recent advances in catalytic asymmetric synthesis of indolizidine, quinolizidine and azocine skeletons are discussed. PMID:19847348

Perreault, Stéphane; Rovis, Tomislav

2010-01-01

83

Enantioselective synthesis of cyclic amides and amines through mo-catalyzed asymmetric ring-closing metathesis.  

PubMed

First, an efficient method for the synthesis of optically enriched N-fused bicyclic structures is reported. Through Mo-catalyzed desymmetrization of readily available achiral polyene substrates, 5,6-, 5,7-, and 5,8-bicyclic amides can be synthesized in up to >98% ee. The effects of catalyst structure, olefin substitution, positioning of Lewis basic functional groups and ring size are examined and discussed in detail. In the second phase of investigations, a catalytic asymmetric method for highly enantioselective (up to 97% ee) synthesis of small- and medium-ring unsaturated cyclic amines is reported; optically enriched products bear a secondary amine or a readily removable Cbz or acetamide unit. Regio- and diastereoselective functionalizations of olefins within the optically enriched amine products have been carried out. Both catalytic asymmetric methods include transformations that lead to the formation of trisubstituted as well as disubstituted cyclic alkenes. The protocols outlined herein afford various cyclic amines of high optical purity; such products are not easily accessed by alternative protocols and can be used in enantioselective total syntheses of biologically active molecules. PMID:15941288

Sattely, Elizabeth S; Cortez, G Alexander; Moebius, David C; Schrock, Richard R; Hoveyda, Amir H

2005-06-15

84

Expedient asymmetric synthesis of all four isomers of N,N'-protected 2,3-diaminobutanoic acid.  

PubMed

2,3-Diaminobutanoic acid (DAB) is found in several peptide antibiotics, toxins, and biologically active molecules. This paper describes the practical and highly enantioselective synthesis of all four N,N'-protected DAB stereoisomers using an asymmetric Rh(I)-phosphine-catalyzed hydrogenation of isomeric enamides as the key step. Thermal and photochemical isomerization of the enamide hydrogenation substrates coupled with catalyst-geometric isomer pairing allows targeted synthesis of single DAB isomers in maximum yield. PMID:11397146

Robinson, A J; Stanislawski, P; Mulholland, D; He, L; Li, H Y

2001-06-15

85

Nickel-catalyzed asymmetric cross-couplings of secondary allylic chlorides and planar-chiral compounds in asymmetric synthesis  

E-print Network

In Part I, nickel-catalyzed asymmetric carbon-carbon bond-forming reactions are described. A nickel/Pybox system effectively catalyzes regio- and enantioselective cross-couplings between racemic secondary allylic chlorides ...

Son, Sunghee

2008-01-01

86

Asymmetric C-C Bond Formation between Chiral N-Phosphonyl Imines and Ni(II)-Complex of Glycine Schiff Base Provides a GAP Synthesis of ?,?-syn-Diamino Acid Derivatives.  

PubMed

The GAP asymmetric synthesis of ?,?-diamino acid derivatives has been achieved by reacting chiral N-phosphonyl imines with Ni(II)-complex of glycine ester-based enolate without the use of traditional purifications of chromatography and recrystallization. The successful control of synstereochemistry of vicinal diamino products complements our previous methods which afforded anti stereoisomers and enables all four individual isomers to be synthesized by simply changing enolate geometry. In contrast to our previous synthesis where required at least 5 equiv of glycine Schiff base enolate for complete conversion, the new synthesis only needs 1.1 equiv of glycine Schiff base enolate to give complete diastereoselectivity (>99% de) and yields (91% - 97%). The absolute stereochemistry has been unambiguously determined by X-ray structural analysis. PMID:25309122

Sun, Hao; Zhang, Haowei; Han, Jianlin; Pan, Yi; Li, Guigen

2013-08-01

87

Catalytic asymmetric synthesis of the pentacyclic core of (-)-nakadomarin A via oxazolidine as an iminium cation equivalent.  

PubMed

A facile and catalytic asymmetric synthesis of the pentacyclic core of (-)-nakadomarin A, containing all the stereogenic centers of the natural product was achieved. The key intermediate involves the oxazolidine moiety as an iminium cation equivalent. An efficient method for the removal of the N-hydroxyethyl group is also described. PMID:25216237

Tsuji, Nobuya; Stadler, Michael; Kazumi, Naoya; Inokuma, Tsubasa; Kobayashi, Yusuke; Takemoto, Yoshiji

2014-10-28

88

Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation  

SciTech Connect

An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

Tsai, Andy; Bergman, Robert; Ellman, Jonathan

2008-02-18

89

A facile process for the asymmetric synthesis of ?-trifluoromethylated ?-amino ketones via addition of ketone enolates to sulfinylimine.  

PubMed

An efficient method for the asymmetric synthesis of ?-trifluoromethylated ?-amino ketones via addition of ketone-derivative enolates to trifluoromethylated sulfinylimine has been developed, with good chemical yields and excellent diastereoselectivities. This practical method was also proved to be suitable for large-scale preparation. PMID:21210033

Mei, Haibo; Xiong, Yiwen; Han, Jianlin; Pan, Yi

2011-03-01

90

Asymmetric total synthesis of (-)-lingzhiol via a Rh-catalysed [3+2] cycloaddition.  

PubMed

The development of efficient reactions for the one-pot construction of bicyclic ring systems bearing two quaternary carbon centres at their bridgehead positions represents a significant challenge to synthetic chemistry. The development of new methods capable of overcoming this challenge is highly desirable, because this motif can be found in a wide range of natural products with significant biological activities. Herein, we report an efficient [3+2] cycloaddition reaction between an enal and an alleno rhodium species, which was generated in situ from the corresponding enynol via a retro metal-propargylation reaction, to give [3.3.0] and [3.4.0] bicyclic systems bearing two quaternary atoms at their bridgehead positions. The developed chemistry has been successfully applied to the asymmetric total synthesis of natural product (-)-lingzhiol (4) for the first time in 17 steps. PMID:25483390

Long, Rong; Huang, Jun; Shao, Wenbin; Liu, Song; Lan, Yu; Gong, Jianxian; Yang, Zhen

2014-01-01

91

Pyranophane transannular diels-alder approach to (+)-chatancin: a biomimetic asymmetric total synthesis.  

PubMed

An asymmetric total synthesis of (+)-chatancin was achieved via a transannular Diels-Alder (TADA) reaction of an in situ generated macrocyclic pyranophane pseudobase. The presented route constitutes the second of two proposed biosynthetic pathways that involves a TADA reaction. It links this diterpene biogenetically to the cembranoids. A set of TADA selection rules that rationalize the formation of (+)-chatancin from a dynamic equilibrium of four 2-hydroxy-2H-pyrane bicycles and their 16 potential TADA transition states are also outlined. Beyond the TADA reaction, highlights of the synthetic work include the assembly of a chiral acyclic macrocyclization substrate from (S)-citronellol and an efficient macrocyclization via a beta-ketosulfoxyde/enone Michael addition. PMID:14682691

Soucy, Pierre; L'Heureux, Alexandre; Toró, András; Deslongchamps, Pierre

2003-12-26

92

Haloperidol metabolite II prodrug: Asymmetric synthesis and biological evaluation on rat C6 glioma cells.  

PubMed

In a previous work we reported the antiproliferative effects of (±)-MRJF4, a novel haloperidol metabolite II (HP-mII) (a sigma-1 antagonist and sigma-2 agonist) prodrug, obtained through conjugation to 4-phenylbutyric acid (PhBA) [a histone deacetylase inhibitor (HDACi)] via an ester bond. As a continuation of this work, here we report the asymmetric synthesis of compounds (R)-(+)-MRJF4 and (S)-(-)-MRJF4 and the evaluation of their biological activity on rat C6 glioma cells, derived from glioblastoma multiforme (GBM), which is the most common and deadliest central nervous system (CNS) invasive malignancy. Favourable physicochemical properties, high permeability in the parallel artificial membrane permeability assay (PAMPA), good enzymatic and chemical stability, in vivo anticancer activity, associated with the capacity to reduce cell viability and to increase cell death by apoptosis, render compound (R)-(+)-MRJF4 a promising candidate for the development of a useful therapeutic for gliomas therapy. PMID:25461306

Sozio, Piera; Fiorito, Jole; Di Giacomo, Viviana; Di Stefano, Antonio; Marinelli, Lisa; Cacciatore, Ivana; Cataldi, Amelia; Pacella, Stephanie; Turkez, Hasan; Parenti, Carmela; Rescifina, Antonio; Marrazzo, Agostino

2015-01-27

93

Stereoselective synthesis of caffeic acid amides via enzyme-catalyzed asymmetric aminolysis reaction.  

PubMed

In this study, a new method was developed to prepare enantiopure caffeic acid amides by enzyme-catalyzed asymmetric aminolysis reaction. Methoxymethyl chloride (MOMCl) was first introduced as a protective and esterified reagent to obtain the MOM-protected caffeic acid MOM ester 1d. Aminolysis reaction occurred between 1d and (R, S)-?-phenylethylamine in the presence of an immobilized lipase (Novozym 435) from Candida antarctica. Compared with the methyl-protected caffeic acid methyl ester 1c, 1d as substrate improved the lipase-catalyzed reaction rate by 5.5-fold. After Novozym 435-catalyzed aminolysis reaction was established, we evaluated the effects of synthesis parameters on the catalytic activity and enantioselectivity of Novozym 435. A reaction conversion rate of 25.5% and an E value of >100 were achieved under the following optimum conditions: reaction solvent, anhydrous isooctane; reaction temperature, 70°C; reaction time, 24h; ester-to-amine substrate molar ratio, 1:40; and enzyme additive amount, 40 mg. Kinetic and thermodynamic analyses were conducted to determine the main factors affecting enantiomeric discrimination. Novozym 435 still showed 80% of its initial activity after recycling five times. Highly optically pure caffeic acid amides with an enantiomeric excess of 98.5% were finally obtained by HCl deprotection. The established enzyme-catalyzed asymmetric aminolysis method in this study might be used to prepare other caffeic acid amides. PMID:24056082

Xiao, Peiliang; Zhang, Suoqin; Ma, Huayu; Zhang, Aijun; Lv, Xiaoli; Zheng, Liangyu

2013-12-01

94

Asymmetric triple relay catalysis: enantioselective synthesis of spirocyclic indolines through a one-pot process featuring an asymmetric 6? electrocyclization.  

PubMed

A rare example of a one-pot process that involves asymmetric triple relay catalysis is reported. The key step is an asymmetric [1,5] electrocyclic reaction of functionalized ketimines. The substrates for this process were obtained in?situ in a two-step process that involved the hydrogenation of nitroarenes with a Pd/C catalyst to yield aryl amines and their subsequent coupling with isatin derivatives in a Brønsted acid catalyzed ketimine formation reaction. The electrocyclization was catalyzed by a bifunctional chiral Brønsted base/hydrogen bond donor catalyst. The one-pot process gave the desired products in good yields and with excellent enantioselectivity. PMID:25313907

Yin, Xiao-Ping; Zeng, Xing-Ping; Liu, Yun-Lin; Liao, Fu-Min; Yu, Jin-Sheng; Zhou, Feng; Zhou, Jian

2014-12-01

95

Asymmetric Total Synthesis of (?)-Plicatic Acid via a Highly Enantioselective and Diastereoselective Nucleophilic Epoxidation of Acyclic Trisubstitued Olefins  

PubMed Central

The first total synthesis of (?)-plicatic acid has been achieved by a concise and enantioselective route. In this synthesis, a conceptually new strategy featuring an asymmetric epoxidation-intramolecular epoxy-ring-opening Friedel-Crafts reaction sequence was developed for the stereoselective construction of the 2,7’-cyclolignane skeleton bearing contiguous quaternary-quaternary-tertiary stereocenters. The implementation of this strategy was enabled by the development of a modified protocol for the Seebach epoxidation with TADOOH, which affords an unprecedented, highly enantioselective and diastereoselective epoxidation with a range of ?-carbonyl-?-substituted acrylates 3. PMID:19601599

Sun, Bing-Feng; Hong, Ran; Kang, Yan-Biao; Deng, Li

2009-01-01

96

Total synthesis of (R,R,R)-?-tocopherol through asymmetric Cu-catalyzed 1,4-addition.  

PubMed

By introducing a disposable activating substituent at C-3, the asymmetric 1,4-addition to a notoriously unreactive 2-substituted chromenone was achieved with high levels of (2R)-stereoselectivity in the presence of a chiral Cu(I)-phosphoramidite complex as a catalyst. This paved the way for an efficient and conceptually novel synthesis of (R,R,R)-?-tocopherol from readily available starting materials. PMID:25088810

Termath, Andreas Ole; Sebode, Hanna; Schlundt, Waldemar; Stemmler, René T; Netscher, Thomas; Bonrath, Werner; Schmalz, Hans-Günther

2014-09-15

97

Synthesis of 2,5-asymmetrically substituted 3,4-diaminothieno[2,3-b]thiophenes by domino reaction.  

PubMed

A convenient one pot synthesis of 2,5-asymmetrically substituted thieno[2,3-b]thiophenes is developed. The method is based on consecutive domino reactions (SN2 reaction ? Thorpe-Ziegler reaction) using malononitrile and carbon disulfide as starting materials with the generation of potassium 2,2-dicyanoethene-1,1-bis(thiolate) in a solution. The high yield of the target thienothiophenes was achieved using the Ziegler dilution effect. PMID:24028177

Zubarev, Andrey A; Larionova, Natalia A; Rodinovskaya, Lyudmila A; Mortikov, Valery Yu; Shestopalov, Anatoliy M

2013-10-14

98

The synthesis and applications of a biaryl-based asymmetric phosphine ligand  

E-print Network

The asymmetric biaryl backbone of a dialkylbiphenyl phosphine ligand was developed, synthesized, and resolved. The application of the chiral phosphine ligand to the asymmetric Suzuki-Miyaura cross-coupling reaction was ...

Hirai, Satoko

2005-01-01

99

Synthesis of Side Chain Substituted 3-Butylisocoumarins and Absolute Configurations of Natural Isocoumarins from Artemisia dracunculus  

Microsoft Academic Search

Summary. A series of 3-hydroxy- and 3-bromobutyl-substituted isocoumarins was synthesized. The absolute configurations of three isocoumarin derivatives from Artemisia dracunculus, namely (-)-epoxyartemidin, (-)-2'-methoxydihydroartemidin, and (+)-3'-hydroxyartemidin were determined by chemical means via derivatization, kinetic racemate resolution ( Horeau method), and comparison of the circular dichroism (CD) spectra.

Gerda Lutz-Kutschera; Doris Engelmeier; Franz Hadacek; Andreas Werner; Harald Greger; Otmar Hofer

2003-01-01

100

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate  

PubMed Central

Summary Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane. PMID:21085513

Omedes-Pujol, Marta

2010-01-01

101

Molecular Models of Reactants and Products from an Asymmetric Synthesis of a Chiral Carboxylic Acid  

NSDL National Science Digital Library

Our JCE Featured Molecules for this month come from the paper by Thomas E. Smith, David P. Richardson, George A. Truran, Katherine Belecki, and Megumi Onishi (1). The authors describe the use of a chiral auxiliary, 4-benzyl-2-oxazolidinone, in the synthesis of a chiral carboxylic acid. The majority of the molecules used in the experiment, together with several of the pharmaceuticals mentioned in the paper, have been added to our molecule collection. In many instances multiple enantiomeric and diastereomeric forms of the molecules have been included. This experiment could easily be extended to incorporate various aspects of computation for use in an advanced organic or integrated laboratory. Here are some possible exercises using the R and S forms of the 4-benzyl-2-oxazolidinone as the authors point out that both forms are available commercially. Calculation of the optimized structures and energies of the enantiomers at the HF/631-G(d) level using Gaussian03 (2) produces the results shown in Table 1. Evaluation of the vibrational frequencies results in no imaginary frequencies and the 66 real frequencies are identical for the two forms. Examination of the computed IR spectra also shows them to be identical. Additionally, the Raman and NMR spectra can be calculated for the enantiomers and compared to experimental values and spectral patterns. A tool that is becoming increasingly important for assigning absolute configuration is vibrational circular dichroism (VCD). Although the vibrational spectra of an enantiomeric pair are identical, the VCD spectra show opposite signs, as shown in Figure 1. One can imagine a synthesis, using an unknown enantiomer of the chiral auxiliary, followed by calculations of the electronic and vibrational properties of all of the intermediates and the product, and determination of absolute configuration of reactants and products by comparison of experimental and computed VCD spectra. Using a viewer capable of displaying two molecules that can be moved independently, students could more easily visualize the origin of the enantiomeric preference in the reaction between the chelated enolate and allyl iodide.

102

Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of ?1 Receptors in the Brain  

PubMed Central

Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu2SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents. Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent ?1 ligands with high ?1/?2-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent ?1 ligand of this series of compounds, with a Ki value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[18F]F K222 carbonate complex. The radiochemical yield of [18F]-(R)-20 was 18%–20%, the radiochemical purity greater than 97% and the specific radioactivity 175–300 GBq/µmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the ?1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of ?1 receptors. PMID:24451404

Holl, Katharina; Schepmann, Dirk; Fischer, Steffen; Ludwig, Friedrich-Alexander; Hiller, Achim; Donat, Cornelius K.; Deuther-Conrad, Winnie; Brust, Peter; Wünsch, Bernhard

2014-01-01

103

New polymer-supported mono- and bis-cinchona alkaloid derivatives: synthesis and use in asymmetric organocatalyzed reactions.  

PubMed

The straightforward synthesis of polystyrene-supported Chinchona alkaloids and their application in the asymmetric dimerization of ketenes is reported. Six different immobilized derivatives, consisting of three dimeric and two monomeric 9-O ethers, were prepared by "click" anchoring of soluble alkaloid precursors on to azidomethyl resins. The resulting insoluble polymer-bound (IPB) organocatalysts were employed for promoting the dimerization of in-situ generated ketenes. After opening of the ketene dimer intermediates with N,O-dimethylhydroxylamine, valuable Weinreb amides were eventually obtained in good yield (up to 81?%) and excellent enantiomeric purity (up to 96?% ee). All of the IPB catalysts could be recycled effectively without significant loss of activity and enantioselectivity. The extension to other asymmetric transformations (meso-anhydride desymmetrization and ?-amination of 2-oxindoles) is also briefly discussed. PMID:25470334

Jumde, Ravindra P; Di Pietro, Anila; Manariti, Antonella; Mandoli, Alessandro

2015-02-01

104

Chiral N-phosphonyl imine chemistry: asymmetric synthesis of alpha-alkyl beta-amino ketones by reacting phosphonyl imines with ketone-derived enolates.  

PubMed

A series of new chiral syn-alpha-branched beta-amino ketones has been synthesized by reacting chiral phosphonyl imines with ketone-derived enolates. The N-protection group on imine auxiliary was found to be crucial to the asymmetric induction. The absolute stereochemistry has been unambiguously determined by converting a product to a known sample. PMID:19207422

Ai, Teng; Han, Jianlin; Chen, Zhong-Xiu; Li, Guigen

2009-02-01

105

An asymmetric synthesis of (+)-grandisol, a constituent of the aggregation pheromone of the cotton boll weevil, via a kinetic resolution.  

PubMed

A novel approach to the asymmetric synthesis of (+)-grandisol, (1R, 2S)-isopropenyl-1-methylcyclobutaneethanol, involves the use of catalytic kinetic resolution of a primary allylic alcohol, [(1RS, 5SR)-5-methylbicyclo[3.2.0]hept-2-en-2-yl] methanol. The allylic alcohol is prepared in four steps from simple achiral materials involving the use of a modified Shapiro reaction. The resolved alcohol (95% ee) is then reduced in two steps to the corresponding methyl alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene. This alkene is converted to (+)-grandisol (95% ee), in three steps, by modified literature procedures. PMID:11073589

Hamon, D P; Tuck, K L

2000-11-17

106

Highly enantioselective and efficient synthesis of flavanones including pinostrobin through the rhodium-catalyzed asymmetric 1,4-addition.  

PubMed

An efficient synthesis of bioactive chiral flavanones (1) was achieved through the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to chromone. The reaction in toluene proceeded smoothly at room temperature in the presence of 0.5% Rh catalyst with electron-poor chiral diphosphine MeO-F(12)-BIPHEP. In this reaction, the 1,2-addition to (S)-1 frequently occurred to yield (2S,4R)-2,4-diaryl-4-chromanol as a byproduct, which could be reduced by changing the reaction solvent to CH(2)Cl(2) to deactivate the Rh catalyst (3% required). PMID:21413690

Korenaga, Toshinobu; Hayashi, Keigo; Akaki, Yusuke; Maenishi, Ryota; Sakai, Takashi

2011-04-15

107

Preparation of anti-Vicinal Amino Alcohols: Asymmetric Synthesis of d-erythro-Sphinganine, (+)-Spisulosine, and d-ribo-Phytosphingosine  

PubMed Central

Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM ether-directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor d-erythro-sphinganine and the antitumor agent (+)-spisulosine, whereas the Overman rearrangement of chiral allylic trichloroacetimidates generated by the asymmetric reduction of an ?,?-unsaturated methyl ketone allowed rapid access both to d-ribo-phytosphingosine and l-arabino-phytosphingosine. PMID:23795558

2013-01-01

108

Simple synthesis of amorphous NiWO4 nanostructure and its application as a novel cathode material for asymmetric supercapacitors.  

PubMed

This study reports a simple synthesis of amorphous nickel tungstate (NiWO4) nanostructure and its application as a novel cathode material for supercapacitors. The effect of reaction temperature on the electrochemical properties of the NiWO4 electrode was studied, and results demonstrate that the material synthesized at 70 °C (NiW-70) has shown the highest specific capacitance of 586.2 F g(-1) at 0.5 A g(-1) in a three-electrode system. To achieve a high energy density, a NiW-70//activated carbon asymmetric supercapacitor is successfully assembled by use of NiW-70 and activated carbon as the cathode and anode, respectively, and then, its electrochemical performance is characterized by cyclic voltammetry and galvanostatic charge-discharge measurements. The results show that the assembled asymmetric supercapacitor can be cycled reversibly between 0 and 1.6 V with a high specific capacitance of 71.1 F g(-1) at 0.25 A g(-1), which can deliver a maximum energy density of 25.3 Wh kg(-1) at a power density of 200 W kg(-1). Furthermore, this asymmetric supercapacitor also presented an excellent, long cycle life along with 91.4% specific capacitance being retained after 5000 consecutive times of cycling. PMID:23910723

Niu, Lengyuan; Li, Zhangpeng; Xu, Ye; Sun, Jinfeng; Hong, Wei; Liu, Xiaohong; Wang, Jinqing; Yang, Shengrong

2013-08-28

109

Synthesis and asymmetric reactivity of enantiomerically pure cyclopentadienylmetal complexes derived from the chiral pool  

SciTech Connect

Starting from pulegone, camphor, and tartrate, three chiral cyclopentadienes were prepared efficiently. Metalation with Co/sub 2/(CO)/sub 8/ and TiCl/sub 3/ resulted in new chiral and enantiomerically pure substituted cyclopentadienyldicarbonylcobalt and -titanocene complexes. The latter were used in the quantitative catalytic asymmetric hydrogenation of 2-phenyl-1-butene in up to 34% optical yield. The former allowed the first asymmetric (2 + 2 + 2) cycloadditions promoted by chiral cyclopentadienylcobalt complexes to be observed.

Halterman, R.L.; Vollhardt, K.P.C.

1988-04-01

110

Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis  

PubMed Central

Summary For the first time, chiral sulfoximine derivatives have been applied as asymmetric organocatalysts. In combination with a thiourea-type backbone the sulfonimidoyl moiety leads to organocatalysts showing good reactivity in the catalytic desymmetrization of a cyclic meso-anhydride and moderate enantioselectivity in the catalytic asymmetric Biginelli reaction. Straightforward synthetic routes provide the newly designed thiourea-sulfoximine catalysts in high overall yields without affecting the stereohomogeneity of the sulfur-containing core fragment. PMID:23019479

Frings, Marcus; Thomé, Isabelle

2012-01-01

111

Synthesis of sheath voltage drops in asymmetric radio-frequency discharges  

NASA Astrophysics Data System (ADS)

A sheath voltage drop in asymmetric discharges is one of the most important parameters of radio-frequency capacitively coupled plasmas because it determines the kinetic energy of the ions incident on the target or substrate. In this study, we developed a numerical simulation code to estimate the sheath voltage drops and, consequently, the self-bias voltage. We roughly approximated general asymmetric rf discharges to one-dimensional spherical ones. The results obtained by using our simulation code are consistent with measurements and Lieberman's theory.

Yonemura, Shigeru; Nanbu, Kenichi; Iwata, Naoaki

2004-07-01

112

The synthesis and use in asymmetric epoxidation of metal salen complexes derived from enantiopure trans-cyclopentane- and cyclobutane-1,2-diamine  

Microsoft Academic Search

A complete synthesis of enantiopure trans-cyclopentane-1,2-diamine and trans-cyclobutane-1,2-diamine is described. These diamines have been used as components of novel chiral salen ligands whose chromium and manganese complexes were then evaluated as oxygen transfer agents in the asymmetric epoxidation of alkenes.

Adrian M. Daly; Declan G. Gilheany

2003-01-01

113

Directed orthometalation and the asymmetric total synthesis of N-deoxymilitarinone A and torrubiellone B.  

PubMed

A diverted total synthesis (DTS) approach to the total synthesis of pyridone alkaloids N-deoxymilitarinone A (8) and torrubiellone B (10) has been developed. The common intermediate 14 was first assembled by a dual directed orthometalation process using a methoxymethyl group as directed metalation group. Other crucial steps include the assembly of polyenes under aldol condensation for DTS using general and concise strategy and diastereoselective synthesis of the syn-dimethyl array by an Evans aldol reaction. PMID:24295075

Ding, Feiqing; William, Ronny; Leow, Min Li; Chai, Hua; Fong, Jacqueline Zi Mei; Liu, Xue-Wei

2014-01-01

114

Applications of helical-chiral pyridines as organocatalysts in asymmetric synthesis.  

PubMed

A new family of chiral pyridines has been designed and synthesized for use in asymmetric organocatalysis. Thus, helical-chiral pyridines induce high enantioselectivity in a range of mechanistically unrelated, synthetically significant transformations, including Friedel-Crafts alkylation with nitroalkenes, periselective Diels-Alder reactions with nitroalkenes, the ring-opening of epoxides with a chloride nucleophile, and the propargylation of aldehydes. PMID:23172849

Peng, Zhili; Takenaka, Norito

2013-02-01

115

Asymmetric Synthesis of Functionalized Tetrasubstituted ?-Aminophosphonates through Enantioselective Aza-Henry Reaction of Phosphorylated Ketimines.  

PubMed

Bifunctional Cinchona alkaloid thioureas efficiently catalyze asymmetric nucleophilic addition of nitromethane to ketimines derived from ?-aminophosphonic acids to afford tetrasubstituted ?-amino-?-nitro-phosphonates. Catalytic hydrogenation of (S)-?-amino-?-nitro-phosphonate 2d gives enantiopure (S)-?,?-diaminophosphonate 3. PMID:25422859

Vicario, Javier; Ortiz, Pablo; Ezpeleta, José M; Palacios, Francisco

2014-12-01

116

Catalytic asymmetric synthesis of mixed 3,3'-bisindoles and their evaluation as Wnt signaling inhibitors.  

PubMed

TOP class: The first efficient catalytic asymmetric coupling reaction of indoles with isatin-derived nitroalkenes was accomplished by using a complex consisting of a chiral imidazoline aminophenol ligand (1; see scheme) and Cu(OTf)(2). Biological activity of the newly formed chiral 3,3'-bisindoles was also confirmed in a Wnt signaling inhibitory assay. PMID:23355386

Arai, Takayoshi; Yamamoto, Yushi; Awata, Atsuko; Kamiya, Kentaro; Ishibashi, Masami; Arai, Midori A

2013-02-25

117

Organocatalytic asymmetric halogenation/semipinacol rearrangement: highly efficient synthesis of chiral ?-oxa-quaternary ?-haloketones.  

PubMed

A novel asymmetric halogenation/semipinacol rearrangement reaction catalyzed by cinchona alkaloid derivatives was developed. Two types of ?-haloketones (X = Br, Cl) were obtained with up to 95% yield and 99% enantiomeric excess. The desired (+) and (-) enantiomers of the ?-haloketones were readily obtained. PMID:21548637

Chen, Zhi-Min; Zhang, Qing-Wei; Chen, Zhi-Hua; Li, Hui; Tu, Yong-Qiang; Zhang, Fu-Min; Tian, Jin-Miao

2011-06-15

118

Highly efficient synthesis of beta-amino acid derivatives via asymmetric hydrogenation of unprotected enamines.  

PubMed

A direct asymmetric hydrogenation of unprotected enamino esters and amides is described. Catalyzed by Rh complexes with Josiphos-type chiral ligands, this method gives beta-amino esters and amides in high yield and high ee (93-97% ee). No acyl protection/deprotection is required. PMID:15303855

Hsiao, Yi; Rivera, Nelo R; Rosner, Thorsten; Krska, Shane W; Njolito, Eugenia; Wang, Fang; Sun, Yongkui; Armstrong, Joseph D; Grabowski, Edward J J; Tillyer, Richard D; Spindler, Felix; Malan, Christophe

2004-08-18

119

Baker's yeast-induced asymmetric reduction of ?-ketosulfides: synthesis of optically active 1-(benzothiazol-2-ylsulfanyl)-2-alkanols, 2-alkanols, and thiiranes  

Microsoft Academic Search

1-(Benzothiazol-2-ylsulfanyl)-2-alkanols 3 were prepared in very high enantiomeric excess by baker's yeast-induced asymmetric reduction of 1-(benzothiazol-2-ylsulfanyl)-2-alkanones 1. Conversion of 3 into optically active simple 2-alkanols 4 and thiiranes 2 by reductive desulfurization and base treatment, respectively, is also described. The absolute configuration of the new compounds synthesized has been established by chemical correlation and specific rotation comparison.

Leonardo Di Nunno; Carlo Franchini; Angelo Nacci; Antonio Scilimati; Maria Stefania Sinicropi

1999-01-01

120

Asymmetric synthesis of chiral 9,10-dihydrophenanthrenes using Pd-catalyzed asymmetric intramolecular Friedel-Crafts allylic alkylation of phenols.  

PubMed

We developed a novel asymmetric synthetic method for multisubstituted 9,10-dihydrophenanthrenes based on the Pd-catalyzed asymmetric intramolecular Friedel-Crafts allylic alkylation of phenols, which produces 10-vinyl or 10-isopropenyl chiral 9,10-dihydrophenanthrene derivatives in high yield with up to 94% ee. PMID:22509956

Suzuki, Yuta; Nemoto, Tetsuhiro; Kakugawa, Kazumi; Hamajima, Akinari; Hamada, Yasumasa

2012-05-01

121

Palladium-Catalyzed Asymmetric Alkylation in the Synthesis of Cyclopentanoid and Cycloheptanoid Core Structures Bearing All-Carbon Quaternary Stereocenters  

PubMed Central

General catalytic asymmetric routes toward cyclopentanoid and cycloheptanoid core structures embedded in numerous natural products have been developed. The central stereoselective transformation in our divergent strategies is the enantioselective decarboxylative alkylation of seven-membered ?-ketoesters to form ?-quaternary vinylogous esters. Recognition of the unusual reactivity of ?-hydroxyketones resulting from the addition of hydride or organometallic reagents enabled divergent access to ?-quaternary acylcyclopentenes through a ring contraction pathway or ?-quaternary cycloheptenones through a carbonyl transposition pathway. Synthetic applications of these compounds were explored through the preparation of mono-, bi-, and tricyclic derivatives that can serve as valuable intermediates for the total synthesis of complex natural products. This work complements our previous work with cyclohexanoid systems. PMID:22347731

Hong, Allen Y.; Bennett, Nathan B.; Krout, Michael R.; Jensen, Thomas; Harned, Andrew. M.

2011-01-01

122

Synthesis and characterisation of self-assembled and self-adjuvanting asymmetric multi-epitope lipopeptides of ovalbumin.  

PubMed

Designing a lipopeptide (LP) vaccine with a specific asymmetric arrangement of epitopes may result in an improved display of antigens, increasing host-cell recognition and immunogenicity. This study aimed to synthesise and characterise the physicochemical properties of a library of asymmetric LP-based vaccine candidates that contained multiple CD4(+) and CD8(+) T-cell epitopes from the model protein antigen, ovalbumin. These fully synthetic vaccine candidates were prepared by microwave-assisted solid phase peptide synthesis. The C12 or C16 lipoamino acids were coupled to the N or C?terminus of the OVA CD4 peptide epitope. The OVA CD4 LPs and OVA CD8 peptide constructs were then conjugated using azide-alkyne Huisgen cycloaddition to give multivalent synthetic vaccines. Physiochemical characterisation of these vaccines showed a tendency to self-assemble in aqueous media. Changes in lipid length and position induced self-assembly with significant changes to their morphology and secondary structure as shown by transmission electron microscopy and circular dichroism. PMID:25399845

Eskandari, Sharareh; Stephenson, Rachel J; Fuaad, Abdullah Ahmad; Apte, Simon H; Doolan, Denise L; Toth, Istvan

2015-01-12

123

Total Synthesis of Gobiusxanthin Stereoisomers and Their Application to Determination of Absolute Configurations of Natural Products: Revision of Reported Absolute Configuration of Epigobiusxanthin  

PubMed Central

(3R)-Gobiusxanthin stereoisomers (1a–d) were synthesized by stereoselective Wittig reaction of the (3R)-C15-acetylenic tri-n-butylphosphonium salt 7 with C25-apocarotenal stereoisomers 5a,b and 14a,b bearing four kinds of 3,6-dihydroxy-?-end groups. The validity of the reported stereochemistry of gobiusxanthin was demonstrated by the fact that the reported spectral data of natural gobiusxanthin were in agreement with those of synthetic (3R,3'S,6'R)-gobiusxanthin (1a). On the other hand, the reported CD spectral data of natural epigobiusxanthin, which has been assigned as (3R,3'R,6'R)-isomer (3'-epigobiusxanthin), were identical with those of synthetic (3R,3'S,6'S)-isomer 1d (6'-epigobiusxanthin) rather than those of the corresponding synthetic 3'-epi-isomer 1b. It was found that the stereochemistry at C3-position has little effect on the shape of their CD spectra. Thus, in order to reinforce the validity of the absolute configurations at C3-position of natural specimens, (3S,3'S,6'R)- and (3S,3'S,6'S)-stereoisomers 1e and 1f were also synthesized and a HPLC analytical method for four stereoisomers was established by using a column carrying a chiral stationary phase. The HPLC analysis has proven that the stereochemistry of the natural epigobiusxanthin is 3R,3'S,6'S. PMID:25561412

Yamano, Yumiko; Ematsu, Kotaro; Kurimoto, Hiromasa; Maoka, Takashi; Wada, Akimori

2014-01-01

124

Asymmetric Synthesis of Medium-Sized Rings by Intramolecular Au(I)-Catalyzed Cyclopropanation  

PubMed Central

An efficient method for the asymmetric gold(I)-catalyzed preparation of medium sized rings has been developed. The method provides 7- to 9-membered rings in excellent yield. High enantioselectivities can be achieved for 7- and 8-membered ring products employing chiral gold(I) complexes. The results provide insight into the mechanism, showing the fluxional nature of gold(I)-stabilized vinyl carbenoid intermediates. PMID:19161306

Watson, Iain D. G.; Ritter, Stefanie; Toste, F. Dean

2009-01-01

125

One-Pot Synthesis of New Symmetric and Asymmetric Xanthene Dyes.  

PubMed

Symmetric and asymmetric xanthene dyes have been prepared by a convenient one-step procedure from aldehyde and diol or m-aminophenol precursors using concentrated phosphoric acid as a solvent. This protocol provides access to water-soluble dyes with large Stoke's shifts and far-red fluorescence emission. These compounds are envisioned as components of fluorescence-based sensors for a variety of imaging applications. PMID:19834587

Hilderbrand, Scott A; Weissleder, Ralph

2007-06-18

126

One-Pot Synthesis of New Symmetric and Asymmetric Xanthene Dyes  

PubMed Central

Symmetric and asymmetric xanthene dyes have been prepared by a convenient one-step procedure from aldehyde and diol or m-aminophenol precursors using concentrated phosphoric acid as a solvent. This protocol provides access to water-soluble dyes with large Stoke’s shifts and far-red fluorescence emission. These compounds are envisioned as components of fluorescence-based sensors for a variety of imaging applications. PMID:19834587

Hilderbrand, Scott A.; Weissleder, Ralph

2009-01-01

127

Efficient asymmetric synthesis of silanediol precursors from 1,5-dihydrosiloles.  

PubMed

Dihydrosiloles are easily prepared from 1,3-dienes and dichlorosilanes, even on kilogram scale. Asymmetric hydroboration of a 3-alkyl-1,5-dihydrosilole, prepared from a 2-alkyl-1,3-diene, followed by treatment with aqueous HF results in Peterson fragmentation, forming optically active 3-alkyl-4-fluorosilyl-1-butenes. The fluorosilanes are stable to moisture but very reactive toward nucleophiles. In addition, they can be converted to nucleophilic silyllithium reagents. PMID:17967032

Sen, Sushmita; Purushotham, Madhusudhan; Qi, Yingmei; Sieburth, Scott McN

2007-11-22

128

Facile asymmetric synthesis of the core nuclei of xanthanolides, guaianolides, and eudesmanolides.  

PubMed

[reaction: see text] Bicyclic and tricyclic gamma-butyrolactones with 5,7-, 5,6,5-, 5,6,6-, or 5,7,5-fused ring systems, being found in xanthanolides, eudesmanolides, and guaianolides, were readily synthesized from methyl furan-2-carboxylic acid. Key steps were a copper(I)-catalyzed asymmetric cyclopropanation, Sakurai allylations, intramolecular ene reactions, and ring-closing metathesis reactions. PMID:12633111

Nosse, Bernd; Chhor, Rakeshwar B; Jeong, Won Boo; Böhm, Claudius; Reiser, Oliver

2003-03-20

129

Influence of aromatic substituents on metal(II)salen catalysed, asymmetric synthesis of ?-methyl ?-amino acids  

Microsoft Academic Search

The influence of substituents on both the aromatic rings of the catalyst, and the benzylidene unit of the substrate are investigated in the (salen)copper(II) catalysed asymmetric benzylation of alanine derivatives. Catalysts with electron-donating, and electron-withdrawing substituents of various sizes and at various locations on the aromatic rings of the salen ligand were prepared, but all exhibited inferior enantioselectivity to the

Thierry Achard; Jose A Fuentes; Michael North; Teresa Parsons

2004-01-01

130

Asymmetric reduction of 4-hydroxy-2-butanone to (R)-1,3-butanediol with absolute stereochemical selectivity by a newly isolated strain of Pichia jadinii.  

PubMed

In this study, a novel strain of Pichia jadinii, HBY61, capable of the biocatalysis of 4-hydroxy-2-butanone (4H2B) to (R)-1,3-BD was isolated. HBY61 produced (R)-1,3-BD with high activity and absolute stereochemical selectivity (100 % e.e). Glucose and beef extract were found to be the key factors governing the fermentation, and their optimal concentrations were determined to be 84.2 and 43.7 g/L, respectively. The optimal bioconversion conditions of 4H2B catalyzed by HBY61 were pH 7.4, 30 °C, and 250 rpm with 6 % (v/v) glucose as the co-substrate. Accordingly, when 45 g/L of 4H2B was divided into three equal parts and added successively into the system at set time intervals, the maximum (R)-1,3-BD concentration reached 38.3 g/L with high yield (85.1 %) and strict 100 % enantioselectivity. Compared with previously reported yields for the biocatalytic production of (R)-1,3-BD, the use of strain HBY61 provided a high yield with excellent stereoselectivity. PMID:25306883

Yang, Taowei; Man, Zaiwei; Rao, Zhiming; Xu, Meijuan; Zhang, Xian; Xu, Zhenghong

2014-12-01

131

Flexible and Asymmetric Ligand in Constructing Coordinated Complexes: Synthesis, Crystal Structures and Fluorescent Characterization  

PubMed Central

Flexible and asymmetric ligand L [L = 1-((pyridin-3-yl)methyl)-1H-benzotriazole], is used as a basic backbone to construct complicated metal-organic frameworks. Two new polymers, namely, [Ag2(L)2(NO3)2]n (1) and [Ag(L)(ClO4)]n (2), were synthesized and characterized by X-ray structure analysis and fluorescent spectroscopy. The complex 1 gives an “S” type double helical conformation, whereas complex 2 exhibits a 1D zigzag configuration. Different anions affect the silver coordination geometry and crystal packing topology. PMID:21339976

Chen, Peng; Lin, Jianhua

2011-01-01

132

Diastereoselective synthesis of dihydropyrans via Prins cyclization of enol ethers: total asymmetric synthesis of (+)-civet cat compound.  

PubMed

Trimethylsilyl trifluoromethanesulfonate (TMSOTf) can be efficiently used for Prins cyclization of acrylyl enol ethers to 5,6-dihydro-2H-pyran-2-acetates stereo- and regioselectively in good yields. The methodology was used for the total synthesis of natural product (+)-civet. PMID:24245586

Sultana, Sabera; Indukuri, Kiran; Deka, Manash J; Saikia, Anil K

2013-12-01

133

cis-Decahydroquinolines via asymmetric organocatalysis: application to the total synthesis of lycoposerramine Z.  

PubMed

A concise synthesis of the Lycopodium alkaloid lycoposerramine Z is reported. Key to the strategy is a one-pot organocatalyzed Michael reaction followed by a domino Robinson annulation/intramolecular aza-Michael reaction promoted by LiOH, leading to enantiopure cis-decahydroquinolines. PMID:23270499

Bradshaw, Ben; Luque-Corredera, Carlos; Bonjoch, Josep

2013-01-18

134

Asymmetric epoxidation of cis-alkenes mediated by iminium salts: highly enantioselective synthesis of levcromakalim.  

PubMed

[reaction: see text] A range of cis-substituted olefins has been epoxidized with a new dihydroisoquinolinium salt catalyst, using tetraphenylphosphonium monoperoxysulfate as the stoichiometric oxidant, giving ee's of up to 97%. The reaction has been used as the key step in an enantioselective synthesis of the antihypertensive agent levcromakalim. PMID:15673243

Page, Philip C Bulman; Buckley, Benjamin R; Heaney, Harry; Blacker, A John

2005-02-01

135

Synthesis and use of an asymmetric transfer hydrogenation catalyst based on iron(II) for the synthesis of enantioenriched alcohols and amines.  

PubMed

The catalytic hydrogenation of prochiral ketones and imines is an advantageous approach to the synthesis of enantioenriched alcohols and amines, respectively, which are two classes of compounds that are highly prized in pharmaceutical, fragrance and flavoring chemistry. This hydrogenation reaction is generally carried out using ruthenium-based catalysts. Our group has developed an alternative synthetic route that is based on the environmentally friendlier iron-based catalysis. This protocol describes the three-part synthesis of trans-[amine(imine)diphosphine]chlorocarbonyliron(II) tetrafluoroborate templated by iron salts and starting from commercially available chemicals, which provides the precatalyst for the efficient asymmetric transfer hydrogenation of ketones and imines. The use of the enantiopure (S,S) catalyst to reduce prochiral ketones to the (R)-alcohol in good to excellent yields and enantioenrichment is also detailed, as well as the reduction to the amine in very high yield and enantiopurity of imines substituted at the nitrogen with the N-(diphenylphosphinoyl) group (-P(O)Ph2). Although the best ruthenium catalysts provide alcohols in higher enantiomeric excess (ee) than the iron complex catalyst used in this protocol, they do so on much longer time scales or at higher catalyst loadings. This protocol can be completed in 2 weeks. PMID:25569331

Zuo, Weiwei; Morris, Robert H

2015-02-01

136

Highly enantioselective synthesis of alpha,beta-diaminopropanoic acid derivatives using a catalytic asymmetric hydrogenation approach.  

PubMed

Rh-DuPhos-catalyzed asymmetric hydrogenation of alpha,beta-diamidoacrylates provides a highly efficient and enantioselective route to chiral alpha,beta-diaminopropanoic acid derivatives. The mechanistic course of the hydrogenation was studied using isotopically enriched enamide complexes and phosphorus and carbon NMR. Addition of methyl alpha-N-benzoyl-beta-N-acetyl-diaminopropenoate to the solvated catalyst gave a single 1:1 enamide complex and demonstrated the binding of the olefin and alpha-amide carbonyl group; the carboxylate and beta-N-acyl groups did not bind to the metal. Changes to the electronic and steric properties of the beta-N-acyl group were well tolerated; however, small changes to the binding alpha-N-acyl group were found to significantly affect hydrogenation yields. PMID:11397145

Robinson, A J; Lim, C Y; He, L; Ma, P; Li, H Y

2001-06-15

137

Steric control of the asymmetric synthesis of N-substituted 2-methyl-4-piperidones  

SciTech Connect

Transmission of the iodomethylate of 1,2-dimethyl-4-piperidone by (S)-sec-butylamine gives 1-(S-sec-butyl)-2S-methyl-4-piperidone in 33% optical yield while transamination by (S)-1-methyl-2-phenylethylamine gives a 1:1 diastereomeric mixture of 1-(1-methyl-2-phenylethyl)-2-methyl-4-piperidone. The decrease in the optical yield is related to the facile opening of the piperidone ring at the C-N bond with subsequent recyclization. The /sup 13/C NMR data indicate that all the diastereomers of the 4-piperidones obtained are in the chain conformation with predominantly equatorial orientation of the methyl group at C/sub (2)/. The chiral optical properties were studied and the absolution configurations of the 4-piperidones obtained were established.

Grishina, G.V.; Potapov, V.M.; Abdulganeeva, S.A.; Korchagina, E.Yu.

1986-06-01

138

Asymmetric synthesis of trans-2,3-piperidinedicarboxylic acid and trans-3,4-piperidinedicarboxylic acid derivatives.  

PubMed

Asymmetric syntheses of (2S,3S)-3-(tert-butoxycarbonyl)-2-piperidinecarboxylic acid (1b), (3R,4S)-4-(tert-butoxycarbonyl)-3-piperidinecarboxylic acid (2b), and their corresponding N-Boc and N-Cbz protected analogues 8a,b and 17a,b are described. Enantiomerically pure 1b has been synthesized in five steps starting from L-aspartic acid beta-tert-butyl ester. Tribenzylation of the starting material followed by alkylation with allyl iodide using KHMDS produces the key intermediate 5a in a 6:1 diastereomeric excess. Upon hydroboration, the alcohol 6a is oxidized, and the resulting aldehyde 7 is subjected to a ring closure via reductive amination, providing 1b in an overall yield of 38%. Optically pure 2b has been synthesized beginning with N-Cbz-beta-alanine. The synthesis involves the induction of the first stereogenic center using Evans's chemistry and sequential LDA-promoted alkylations with tert-butyl bromoacetate and allyl iodide. Further elaboration by ozonolysis and reductive amination affords 2b in an overall yield of 28%. PMID:11856030

Xue, Chu-Biao; He, Xiaohua; Roderick, John; Corbett, Ronald L; Decicco, Carl P

2002-02-01

139

A short stereoselective synthesis of prepiscibactin using a SmI2-mediated Reformatsky reaction and Zn2+-induced asymmetric thiazolidine formation.  

PubMed

Prepiscibactin (1) is a possible intermediate in the biosynthesis of piscibactin, the siderophore responsible for the iron uptake of the bacterium Photobacterium damselae subsp. piscicida, the aethiological agent of fish pasteurellosis. Compound 1 was synthesized by a convergent approach starting from L-/D-cysteine and 2-hydroxybenzonitrile. The key steps were a highly diastereoselective SmI2-mediated Reformatsky reaction and Zn(2+)-induced asymmetric thiazolidine formation followed by lactamization. The absolute configuration 9R,10S,12R,13S was established for 1, and this confirmed the previous relative stereochemistry proposed on the basis of NOE and computational methods. PMID:25343747

Segade, Yuri; Montaos, Marcos A; Rodríguez, Jaime; Jiménez, Carlos

2014-11-01

140

Stereoselective Synthesis of ?-Hydroxy Enamines, Amino Cyclopropanes and 1,3-Amino Alcohols via Asymmetric Catalysis  

PubMed Central

Tandem methods for the catalytic asymmetric preparation of enantioenriched ?-hydroxy (E)-enamines and cyclopropylamines are presented. The diastereoselective hydrogenation of enantioenriched (E)-trisubstituted hydroxy enamines to generate 1,2-disubstituted 1,3-amino alcohols is also outlined. These methods are initiated by highly regioselective hydroboration of N-tosyl substituted ynamides with diethylborane to generate ?-amino alkenyl boranes. In situ boron to zinc transmetalation generates ?-amino alkenyl zinc reagents. These functionalized vinylzinc intermediates were subsequently added to aldehydes in the presence of catalyst derived from an enantioenriched amino alcohol (morpholino isoborneol, MIB). The catalyst promotes highly enantioselective C–C bond-formation to provide ?-hydroxy enamines in good isolated yields (68–86%) with 54–98% enantioselectivity. The intermediate zinc ?-alkoxy enamines can be subjected to a tandem cyclopropanation to afford amino cyclopropyl carbinols with three continuous stereocenters in a one-pot procedure with good yields (72–82%), enantioselectivities of 76–94% and diastereomeric ratios >20:1. Diastereoselective hydrogenation of isolated enantioenriched ?-hydroxy enamines over Pd/C furnished syn-1,2-disubstituted-1,3-amino alcohols with high yields (82–90%) and moderate to excellent diastereoselectivities. These methods were used in an efficient preparation of the enantioenriched precursor to PRC200-SS derivatives, which are potent serotonin-norepinephrine-dopamine reuptake inhibitors. PMID:20853837

Valenta, Petr; Carroll, Patrick J.; Walsh, Patrick J.

2010-01-01

141

Synthesis of Enantiomerically Pure Anthracyclinones  

NASA Astrophysics Data System (ADS)

The anthracycline antibiotics are among the most important clinical drugs used in the treatment of human cancer. The search for new agents with improved therapeutic efficacy and reduced cardiotoxicity stimulated considerable efforts in the synthesis of new analogues. Since the biological activity of anthracyclines depends on their natural absolute configuration, various strategies for the synthesis of enantiomerically pure anthracyclinones (aglycones) have been developed. They comprise: resolution of racemic intermediate, incorporation of a chiral fragment derived from natural and non-natural chiral pools, asymmetric synthesis with the use of a chiral auxiliary or a chiral reagent, and enantioselective catalysis. Synthetic advances towards enantiopure anthracyclinones reported over the last 17 years are reviewed.

Achmatowicz, Osman; Szechner, Barbara

142

Asymmetric synthesis of highly substituted azapolycyclic compounds via 2-alkenyl sulfoximines: potential scaffolds for peptide mimetics.  

PubMed

The application of metalated, enantiomerically pure acyclic and cyclic 2-alkenyl sulfoximines for the synthesis of highly substituted aza(poly)cyclic ring systems is described. The method relies on a one-pot combination of a reagent-controlled allyl transfer reaction to alpha- or beta-amino aldehydes, followed by a Michael-type cyclization of the intermediate vinyl sulfoximines generated in the first step. The sulfur-free target compounds are preferentially obtained by samarium iodide treatment of the sulfonimidoyl substituted heterocycles. In addition to this methodological work, initial results on the biological activity of selected examples are reported. Furthermore, a concept for the transformation of peptidic lead structures into non-peptide mimetics is described, and the relevance of the new approach to highly substituted azaheterocycles in this context is discussed. PMID:16551111

Reggelin, Michael; Junker, Bernd; Heinrich, Timo; Slavik, Stefan; Bühle, Philipp

2006-03-29

143

Asymmetric synthesis from terminal alkenes by cascades of diboration and cross-coupling  

NASA Astrophysics Data System (ADS)

Terminal, monosubstituted alkenes are ideal prospective starting materials for organic synthesis because they are manufactured on very large scales and can be functionalized via a broad range of chemical transformations. Alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic ?-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of ?-olefins, none of these catalytic enantioselective processes results in chain-extending carbon-carbon bond formation to the terminal carbon. Here we describe a strategy that directly addresses this gap in synthetic methodology, and present a single-flask, catalytic enantioselective conversion of terminal alkenes into a number of chiral products. These reactions are facilitated by a neighbouring functional group that accelerates palladium-catalysed cross-coupling of 1,2-bis(boronates) relative to non-functionalized alkyl boronate analogues. In tandem with enantioselective diboration, this reactivity feature transforms alkene starting materials into a diverse array of chiral products. We note that the tandem diboration/cross-coupling reaction generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), uses low loadings (1-2 mol per cent) of commercially available catalysts and reagents, offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology.

Mlynarski, Scott N.; Schuster, Christopher H.; Morken, James P.

2014-01-01

144

One-pot asymmetric synthesis of seven-membered carbocycles cyclohepta[b]indoles via a sequential organocatalytic Michael/double Friedel-Crafts alkylation reaction.  

PubMed

A new method has been developed for the enantioselective synthesis of highly functionalized cyclohepta[b]indoles with high enantioselectivity (up to 96% ee). The process combines an enantioselective organocatalytic Michael addition and a highly efficient double Friedel-Crafts reaction sequence in one pot with good yields and stereoselectivity. The structures and absolute configurations of the products were confirmed by X-ray analysis. PMID:23848568

Dange, Nitin S; Hong, Bor-Cherng; Lee, Chih-Ching; Lee, Gene-Hsiang

2013-08-01

145

A new dinuclear chiral salen complexes for asymmetric ring opening and closing reactions: Synthesis of valuable chiral intermediates  

Microsoft Academic Search

A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H2O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to

Santosh Singh Thakur; Shu-Wei Chen; Wenji Li; Chang-Kyo Shin; Seong-Jin Kim; Yoon-Mo Koo; Geon-Joong Kim

2006-01-01

146

Catalytic Asymmetric Synthesis Using Feedstocks. An Enantioselective Route to 2-Arylpropionic Acids and 1-Arylethyl Amines via Hydrovinylation of Vinyl Arenes  

PubMed Central

A three-step procedure for the synthesis of 2-arylpropionic acids (profens) from vinyl arenes in nearly enantiomerically pure form has been developed. Excellent yields (>97%), regioselectivities (>99%), and enantioselectivities (>97% ee) for the desired branched products were obtained in the asymmetric hydrovinylation reactions of vinyl arenes, and the products from these reactions were transformed into 2-arylpropionic acids via oxidative degradation. Subsequent Curtius or Schmidt rearrangements of these acids provided highly valued 1-arylethyl amines, including a prototypical primary amine with an ?-chiral tertiary N-alkyl group, in very good yields. PMID:19317393

Smith, Craig R.; RajanBabu, T. V.

2009-01-01

147

Concomitant Determination of Absolute Values of Cellular Protein Amounts, Synthesis Rates, and Turnover Rates by Quantitative Proteome Profiling  

Microsoft Academic Search

Two-dimensional gel electrophoresis of protein fractions isolated from 35S-radiolabeled cells provides qualitative information on intracellular amounts, 35S incorporation rates, protein modifications, and subcellular localizations of up to thousands of individual proteins. In this study we extended proteome profiling to provide quantitative data on synthesis rates of individual proteins. We combined fluorescence detection of radiolabeled proteins with SYPRO ruby™ staining and

Christopher Gerner; Susanne Vejda; Dieter Gelbmann; Editha Bayer; Josef Gotzmann; Rolf Schulte-Hermann; Wolfgang Mikulits

2002-01-01

148

Asymmetric synthesis of indole homo-Michael adducts via dynamic kinetic Friedel-Crafts alkylation with cyclopropanes.  

PubMed

An enantioconvergent Friedel-Crafts alkylation of indoles with donor-acceptor cyclopropanes is described. The reaction is catalyzed by pybox•MgI2 and proceeds via a type I dynamic kinetic asymmetric transformation (DyKAT). PMID:23654283

Wales, Steven M; Walker, Morgan M; Johnson, Jeffrey S

2013-05-17

149

Synthesis of 3,3-Disubstituted Oxindoles by Palladium-Catalyzed Asymmetric Intramolecular ?-Arylation of Amides: Reaction Development and Mechanistic Studies.  

PubMed

Palladium complexes incorporating chiral N-heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular ?-arylation of amides producing 3,3-disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate-determining and reductive elimination to be enantioselectivity-determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8, containing a tBu and a 1-naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro-oxindoles and three azaspiro-oxindoles often in high yields (up to 99?%) and enantioselectivities (up to 97?%?ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X-ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency. PMID:23893893

Katayev, Dmitry; Jia, Yi-Xia; Sharma, Akhilesh K; Banerjee, Dipshikha; Besnard, Céline; Sunoj, Raghavan B; Kündig, E Peter

2013-07-25

150

A gram-scale route to phlegmarine alkaloids: rapid total synthesis of (-)-cermizine B.  

PubMed

The synthesis of the Lycopodium alkaloid (-)-cermizine B (1), which establishes its absolute configuration, is achieved by combining asymmetric organocatalysis and an uninterrupted eight-step reaction sequence, followed by a final reduction step. This "pot-economy" strategy provides access to the cis-phlegmarine stereoparent embedded in 1 for the first time, rapidly and on a gram-scale. PMID:24727855

Bradshaw, Ben; Luque-Corredera, Carlos; Bonjoch, Josep

2014-07-11

151

Absolute Zero  

NASA Astrophysics Data System (ADS)

Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book “Absolute Zero and the Conquest of Cold” by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

Donnelly, Russell J.; Sheibley, D.; Belloni, M.; Stamper-Kurn, D.; Vinen, W. F.

2006-12-01

152

Catalytic asymmetric synthesis of trans-configured beta-lactones: cooperation of Lewis acid and ion pair catalysis.  

PubMed

The development of the first trans-selective catalytic asymmetric [2+2] cyclocondensation of acyl halides with aliphatic aldehydes furnishing 3,4-disubstituted beta-lactones is described. This work made use of a new strategy within the context of asymmetric dual activation catalysis: it combines the concepts of Lewis acid and organic aprotic ion pair catalysis in a single catalyst system. The methodology could also be applied to aromatic aldehydes and offers broad applicability (29 examples). The utility was further demonstrated by nucleophilic ring-opening reactions that provide highly enantiomerically enriched anti-aldol products. PMID:20602368

Kull, Thomas; Cabrera, José; Peters, René

2010-08-01

153

Enantioselective synthesis of syn- and anti-1,3-aminoalcohols via ?-aminoketones and subsequent reduction/dynamic kinetic asymmetric transformation.  

PubMed

?-Aminoketones obtained from imines in an organocatalytic Mannich reaction were transformed to enantio- and diastereomerically pure 1,3-aminoalcohols with two stereogenic centers via a combined reduction/dynamic kinetic asymmetric transformation. Both syn and anti diastereomers were obtained in high yield, dr, and ee. PMID:20942403

Millet, Renaud; Träff, Annika M; Petrus, Michiel L; Bäckvall, Jan-E

2010-11-01

154

One-Pot Asymmetric Nitro-Mannich/Hydroamination Cascades for the Synthesis of Pyrrolidine Derivatives: Combining Organocatalysis and Gold Catalysis  

PubMed Central

The highly enantioselective preparation of trisubstituted pyrrolidine derivatives employing a one-pot nitro-Mannich/hydroamination cascade is reported. This cascade approach utilizes an asymmetric bifunctional organocatalytic nitro-Mannich reaction followed by a gold-catalyzed allene hydroamination reaction. The products are afforded in good yields and excellent diastereo- and enantioselectivities. PMID:24563809

2014-01-01

155

Influence of the metal and chiral diamine on metal(II)salen catalysed, asymmetric synthesis of ?-methyl ?-amino acids  

Microsoft Academic Search

The influence of the metal ion and chiral diamine used to form a metal(salen) complex on the catalytic activity of the complex in the asymmetric benzylation of an alanine enolate was investigated. Only metal ions which could form square-planar complexes gave catalytically active complexes, and best results were obtained with metal ions from the first row of transition metals, particularly

Yuri N Belokon; Jose Fuentes; Michael North; Jonathan W Steed

2004-01-01

156

Part I. Asymmetric Diels-Alder reaction of cyclic Isoimidium salts Part II. Total synthesis of a camphor derived dimer Part III. Asymmetric cyclopropanation catalyzed by chiral camphor-based Dirhodium(II) complex.  

E-print Network

??Part I. Asymmetric Diels-Alder Reaction of Cyclic Isoimidium Salts The asymmetric Diels-Alder reaction of cyclic isoimidium salts are described. The corresponding cycloadducts are obtained with… (more)

Miller, Yan (1982 - )

2010-01-01

157

Asymmetric synthesis of ?-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 3: Michael addition reactions and miscellaneous transformations.  

PubMed

The major goal of this review is a critical discussion of the literature data on asymmetric synthesis of ?-amino acids via Michael addition reactions involving Ni(II)-complexes of amino acids. The material covered is divided into two conceptually different groups dealing with applications of: (a) Ni(II)-complexes of glycine as C-nucleophiles and (b) Ni(II)-complexes of dehydroalanine as Michael acceptors. The first group is significantly larger and consequently subdivided into four chapters based on the source of stereocontrolling element. Thus, a chiral auxiliary can be used as a part of nucleophilic glycine Ni(II) complex, Michael acceptor or both, leading to the conditions of matching vs. mismatching stereochemical preferences. The particular focus of the review is made on the practical aspects of the methodology under discussion and mechanistic considerations. PMID:24888480

Aceña, José Luis; Sorochinsky, Alexander E; Soloshonok, Vadim

2014-09-01

158

Catalytic and asymmetric Friedel–Crafts alkylation of indoles with nitroacrylates. Application to the synthesis of tryptophan analogues  

Microsoft Academic Search

An asymmetric Friedel–Crafts alkylation of indoles with nitroacrylates catalyzed by chiral (4R,5S)-DiPh-BOX (L1)–Cu(OTf)2 complex (10mol%) has been developed. The reactions provide tryptophan nitro-precursors in moderate diastereoselectivities (anti\\/syn up to 72:28) and good to excellent enantioselectivities (up to 99% ee). The alkylation products could be easily reduced to optically active tryptophan analogues with Zn\\/H+.

Yong Sui; Li Liu; Jun-Ling Zhao; Dong Wang; Yong-Jun Chen

2007-01-01

159

Improved and efficient synthesis of chiral N,P-ligands via cyclic sulfamidates for asymmetric addition of butyllithium to benzaldehyde.  

PubMed

A robust and scaleable route to chiral 1-isopropylamino-2-(diphenylphosphino)ethanes is described via the ring-opening of chiral, cyclic sulfamidates with potassium diphenylphosphide (KPPh(2)). The novel protocol offers a robust access to gram quantities of chiral amino phosphinoethanes in high yields. The Li-amides of the chiral aminophosphines were evaluated as chiral ligands in the asymmetric addition of n-butyllithium (BuLi) to benzaldehyde, yielding 1-phenylpentanol up to 98% ee. PMID:17696545

Rönnholm, Petra; Södergren, Mikael; Hilmersson, Göran

2007-09-13

160

Synthesis of an azido precursor to (2S,5R)-5-hydroxylysine using an asymmetric organocatalytic chlorination/reduction sequence.  

PubMed

An efficient, robust, and scalable synthesis of an azido precursor to the modified amino acid (2S,5R)-5-hydroxylysine was developed on the basis of the use of a highly stereoselective organocatalytic ?-chlorination-reduction protocol. The final Fmoc-protected (2S,5R)-6-azido-5-hydroxylysine derivative can be used in solid-phase peptide synthesis, providing access to proteins that contain large quantities of post-translationally modified lysine (e.g., collagens). PMID:24175670

Johannes, Manuel; Brimble, Margaret A

2013-12-20

161

A Double Asymmetric Hydrogenation Strategy for the Reduction of 1,1-Diaryl Olefins Applied to an Improved Synthesis of CuIPhEt, a C2-Symmetric N-Heterocyclic Carbenoid  

PubMed Central

A library of iridium and rhodium phosphine catalysts have been screened for the double asymmetric hydrogenation of 2,6-di-(1-phenylethenyl)-4-methyl aniline to produce the C2-symmetric aniline precursor of the N-heterocyclic carbenoid CuIPhEt. The best catalyst produced the desired enantiomer in 98.6% selectivity. This rare example of a highly selective hydrogenation of a 1,1-diaryl olefin enables a 4 step asymmetric synthesis of the C2-symmetric phenylethyl imidazolium ion (IPhEt) from p-toluidine and phenylacetylene, and its conversion to the hydrosilylation catalyst CuIPhEt. PMID:23383707

Spahn, Elizabeth; Albright, Abigail; Shevlin, Michael; Pauli, Larissa; Pfaltz, Andreas; Gawley, Robert E.

2013-01-01

162

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity  

PubMed Central

Despite over three decades of research into asymmetric phase transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with a libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation. A two part synthetic strategy comprised of: (1) preparation of enantioenriched scaffolds and (2) development of parallel synthesis procedures is described. The strategy allows for the facile introduction of four variable groups in the vicinity of a stereogenic quaternary ammonium ion. The quaternary ammonium ions exhibited a wide range of activity and to a lesser degree enantioselectivity. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion. PMID:21446721

Denmark, Scott E.; Gould, Nathan D.; Wolf, Larry M.

2011-01-01

163

Asymmetric Ion-Pairing Catalysis  

PubMed Central

Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction. PMID:23192886

Brak, Katrien

2014-01-01

164

One-step synthesis of graphene nanoribbon-MnO2 hybrids and their all-solid-state asymmetric supercapacitors  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) hierarchical hybrid nanomaterials (GNR-MnO2) of graphene nanoribbons (GNR) and MnO2 nanoparticles have been prepared via a one-step method. GNR, with unique features such as high aspect ratio and plane integrity, has been obtained by longitudinal unzipping of multi-walled carbon nanotubes (CNTs). By tuning the amount of oxidant used, different mass loadings of MnO2 nanoparticles have been uniformly deposited on the surface of GNRs. Asymmetric supercapacitors have been fabricated with the GNR-MnO2 hybrid as the positive electrode and GNR sheets as the negative electrode. Due to the desirable porous structure, excellent electrical conductivity, as well as high rate capability and specific capacitances of both the GNR and GNR-MnO2 hybrid, the optimized GNR//GNR-MnO2 asymmetric supercapacitor can be cycled reversibly in an enlarged potential window of 0-2.0 V. In addition, the fabricated GNR//GNR-MnO2 asymmetric supercapacitor exhibits a significantly enhanced maximum energy density of 29.4 W h kg-1 (at a power density of 12.1 kW kg-1), compared with that of the symmetric cells based on GNR-MnO2 hybrids or GNR sheets. This greatly enhanced energy storage ability and high rate capability can be attributed to the homogeneous dispersion and excellent pseudocapacitive performance of MnO2 nanoparticles and the high electrical conductivity of the GNRs.Three-dimensional (3D) hierarchical hybrid nanomaterials (GNR-MnO2) of graphene nanoribbons (GNR) and MnO2 nanoparticles have been prepared via a one-step method. GNR, with unique features such as high aspect ratio and plane integrity, has been obtained by longitudinal unzipping of multi-walled carbon nanotubes (CNTs). By tuning the amount of oxidant used, different mass loadings of MnO2 nanoparticles have been uniformly deposited on the surface of GNRs. Asymmetric supercapacitors have been fabricated with the GNR-MnO2 hybrid as the positive electrode and GNR sheets as the negative electrode. Due to the desirable porous structure, excellent electrical conductivity, as well as high rate capability and specific capacitances of both the GNR and GNR-MnO2 hybrid, the optimized GNR//GNR-MnO2 asymmetric supercapacitor can be cycled reversibly in an enlarged potential window of 0-2.0 V. In addition, the fabricated GNR//GNR-MnO2 asymmetric supercapacitor exhibits a significantly enhanced maximum energy density of 29.4 W h kg-1 (at a power density of 12.1 kW kg-1), compared with that of the symmetric cells based on GNR-MnO2 hybrids or GNR sheets. This greatly enhanced energy storage ability and high rate capability can be attributed to the homogeneous dispersion and excellent pseudocapacitive performance of MnO2 nanoparticles and the high electrical conductivity of the GNRs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06650a

Liu, Mingkai; Tjiu, Weng Weei; Pan, Jisheng; Zhang, Chao; Gao, Wei; Liu, Tianxi

2014-03-01

165

Diastereomeric aziridine carbinol catalyzed enantioselective arylation reaction: toward the asymmetric synthesis of both enantiomers of chiral 3-aryl phthalide.  

PubMed

The diastereomeric aziridine carbinols are applied, respectively, as efficient chiral ligand in the catalysis of asymmetric arylation and sequential arylation-lactonization cascade. The two diastereomers, which are facilely synthesized from the same chiral source, function as pseudo enantiomers in arylation of aromatic aldehydes providing the different enantiomers of the diarylmethanols with almost the same excellent enantioselectivities. The arylation method is also carried out in tandem with lactonization process to afford a concise synthetic approach to both enantiomers of optically active 3-aryl phthalide. PMID:24912109

Song, Xixi; Hua, Yuan-Zhao; Shi, Jing-Guo; Sun, Ping-Ping; Wang, Min-Can; Chang, Junbiao

2014-07-01

166

Asymmetric synthesis of 2,3-dihydropyrroles by ring-opening/cyclization of cyclopropyl ketones using primary amines.  

PubMed

The asymmetric ring-opening/cyclization of cyclopropyl ketones with primary amine nucleophiles was catalyzed by a chiral N,N'-dioxide/scandium(III) complex through a kinetic resolution process. A broad range of cyclopropyl ketones and primary amines are suitable substrates of this reaction. The corresponding products were afforded in excellent enantioselectivities and yields (up to 97?%?ee and 98?% yield) under mild reaction conditions. This method provides a promising access to chiral 2,3-dihydropyrroles as well as an effective procedure for the kinetic resolution of 2-substituted cyclopropyl ketones. PMID:25363459

Xia, Yong; Liu, Xiaohua; Zheng, Haifeng; Lin, Lili; Feng, Xiaoming

2015-01-01

167

Asymmetric synthesis and catalytic activity of 3-methyl-?-proline in enantioselective anti-Mannich-type reactions.  

PubMed

Enantiomerically pure 3-methyl-?-proline was synthesized using an asymmetric phase-transfer-catalyzed alkylation of a cyanopropanoate to establish the all-carbon stereogenic center. The catalytic activity of 3-methyl-?-proline in the Mannich-type reaction between a glyoxylate imine and ketones/aldehydes was subsequently investigated. The catalyst was designed and found to be more soluble in nonpolar organic solvents relative to the unsubstituted ?-proline catalyst, and as a result allowed for added flexibility during optimization efforts. This work culminated in the development of a highly anti-diastereo- and enantioselective process employing low catalyst loading. PMID:23808600

Nagata, Kazuhiro; Kuga, Yasushi; Higashi, Akinori; Kinoshita, Atsushi; Kanemitsu, Takuya; Miyazaki, Michiko; Itoh, Takashi

2013-07-19

168

A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (?)-cephalimysin A  

PubMed Central

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(?)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A. PMID:24224080

Lathrop, Stephen P.

2013-01-01

169

Heck cyclization strategy for preparation of erythrinan alkaloids: asymmetric synthesis of unnatural (-)-erysotramidine from L-tartaric Acid.  

PubMed

With an imide derived from l-tartaric acid as the starting material, ent-erysotramidine was synthesized for the first time. The synthesis features the use of the enantiopure synthon, prepared in a set of highly stereoselective reactions, including N-acyliminium cyclization, dihydrofuranyl ring formation via silver-catalyzed intramolecular alcohol addition to acetylene, and vinyl ether catalytic hydrogen reduction. The crucial step of the synthesis, assembly of ring A, was achieved by using Heck cyclization of (Z)-iodoolefin. PMID:25569446

Mostowicz, Danuta; Dygas, Miros?aw; Ka?u?a, Zbigniew

2015-02-01

170

Asymmetric Synthesis of Allylic Sulfonic Acids: Enantio- and Regioselective Iridium-Catalyzed Allylations of Na2 SO3.  

PubMed

An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well. PMID:25367779

Liu, Wei; Zhao, Xiao-Ming; Zhang, Hong-Bo; Zhang, Liang; Zhao, Ming-Zhu

2014-12-15

171

Asymmetric domino synthesis of indanes bearing four contiguous stereocentres catalyzed by sub-mol% loadings of a squaramide in minutes.  

PubMed

An efficient diastereo- and enantioselective synthesis of polyfunctionalized indanes bearing four contiguous stereogenic centres in generally very short reaction times and sub-mol% squaramide catalyst loadings has been developed. The novel methodology creates a maximum of two stereocentres per bond formation via an organocatalytic Michael-Henry domino reaction. PMID:24064746

Loh, Charles C J; Hack, Daniel; Enders, Dieter

2013-11-11

172

Effect of high pressure on the organocatalytic asymmetric Michael reaction: highly enantioselective synthesis of ?-nitroketones with quaternary stereogenic centers.  

PubMed

The significant effect of hydrostatic pressure on the difficult organocatalytic 1,4-conjugate addition of nitroalkanes to prochiral sterically congested ?,?-disubstituted enones is demonstrated. This approach allows for the synthesis of ?-nitroketones containing quaternary stereogenic centers with good yields, excellent enantioselectivity, and low loading (1-5 mol %) of simple chiral primary amine catalysts. PMID:21671564

Kwiatkowski, Piotr; Dudzi?ski, Krzysztof; ?y?wa, Dawid

2011-07-15

173

Asymmetric total synthesis of paecilomycin E, 10'-epi-paecilomycin E and 6'-epi-cochliomycin C.  

PubMed

The asymmetric total syntheses of naturally occurring resorcylic acid lactone paecilomycin E and two of its structural congeners have been reported in this article. The major highlight of the synthetic venture is the application of the late stage Mitsunobu macrolactonization method (as it is difficult to achieve the desired products through the standard carboxyl activation method) of a properly functionalized seco-acid. The macrolactonization precursor was synthesized by applying an "E"-selective Julia-Kocienski olefination of a highly functionalized aromatic aldehyde and a sulphone, which constitutes all the stereocenters (C4', C5', C6' and C10'; 3S,7R,8R,9S) in the target molecule. PMID:25204742

Pal, Pratik; Jana, Nandan; Nanda, Samik

2014-11-01

174

Asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units: synthesis, optical and electrochemical properties.  

PubMed

Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been efficiently synthesized and characterized by FT-IR, (1)H NMR, (13)C NMR, mass spectrometry and elemental analysis. The UV-vis absorption maximum wavelength, fluorescence excitation wavelength, fluorescence emission wavelength and fluorescence quantum yield were measured in dilute tetrahydrofuran solution. The solvent effect was also studied. The HOMO and LUMO levels of these compounds were calculated by density functional theory (DFT) (B3LYP, 6-31G(*)) method and cyclic voltammetry. They emit bright violet to blue emission with high fluorescence quantum yields (0.23-0.94) and large Stokes shifts (53-102 nm). These compounds possess high HOMO levels (-5.03 to -5.17 eV) and suitable band gaps, indicating that they could be benefit for hole injection. The results show that they have a potential for application in optoelectronic materials. PMID:24463245

Lu, Huixiong; He, Daohang

2014-04-24

175

The mimic of type II aldolases chemistry: asymmetric synthesis of beta-hydroxy ketones by direct aldol reaction.  

PubMed

An efficient direct aldol reaction has been developed for the synthesis of chiral beta-hydroxy ketone using a combination of C(1)-symmetric chiral prolinamides based on o-phenylenediamine and zinc triflate as catalyst. The reaction was convenient to carry out in aqueous media with up to 98% chemical yields and up to 94% ee values. The current strategy can be regarded as the analogue of aldolase type II, which suggests a new pathway for the designing of new organocatalysts. PMID:20572810

Lu, Zhijin; Mei, Haibo; Han, Jianlin; Pan, Yi

2010-08-01

176

Synthesis of axially chiral biaryls through sulfoxide-directed asymmetric mild C-H activation and dynamic kinetic resolution.  

PubMed

A mild and robust direct C-H functionalization strategy has been applied to the synthesis of axially chiral biaryls. Such an efficient and stereoselective transformation occurs through an original dynamic kinetic resolution pathway enabling the conversion of diastereomeric mixtures of non-prefunctionalized substrates into atropisomerically pure, highly substituted biaryl scaffolds. The main feature of this transformation is the use of an enantiopure sulfoxide as both chiral auxiliary and traceless directing group. The potential of newly synthesized biaryls as valuable building blocks is further illustrated. PMID:25302823

Hazra, Chinmoy Kumar; Dherbassy, Quentin; Wencel-Delord, Joanna; Colobert, Françoise

2014-12-01

177

PEG mediated synthesis and biological evaluation of asymmetrical pyrazole curcumin analogues as potential analgesic, anti-inflammatory and antioxidant agents.  

PubMed

The new series of asymmetrical pyrazole curcumin analogues 4a-g were synthesized by using polyethylene glycol (PEG-400) as a green reaction medium and evaluated for their in vivo analgesic and in vitro antioxidant (H2 O2 , DPPH, Ferrous reducing power and Nitric oxide scavenging activity) and anti-inflammatory activities. All the compounds synthesized 4a-g showed the potential to demonstrate analgesic activity as compared to the standard ibuprofen. Among the tested series, compounds 4e and 4b exhibited good hydrogen peroxide scavenging activity as compared to the standard butylated hydroxy toluene (BHT). Compounds 4b, 4d, 4f, and 4g showed good DPPH free radical scavenging activity. Compounds 4b, 4c, 4d, 4e and 4g showed excellent ferrous-reducing power activity, whereas all the compounds showed better nitric oxide scavenging activity than standard ascorbic acid. Additionally, all the synthesized compounds were also screened for their in vitro anti-inflammatory activity. Compounds 4b, 4d, 4f and 4g showed good anti-inflammatory activity as compared to standard diclofenac sodium. PMID:25130070

Jadhav, Shravan Y; Bhosale, Raghunath B; Shirame, Sachin P; Patil, Sandeep B; Kulkarni, Suresh D

2015-03-01

178

1: Mass asymmetric fission barriers for {sup 98}Mo; 2: Synthesis and characterization of actinide-specific chelating agents  

SciTech Connect

Excitation functions have been measured for complex fragment emission from the compound nucleus {sup 98}Mo, produced by the reaction of {sup 86}Kr with {sup 12}C. Mass asymmetric fission barriers have been obtained by fitting the excitation functions with a transition state formalism. The extracted barriers are {approximately} 5.7 MeV higher, on average, than the calculations of the Rotating Finite Range Model (RFRM). These data clearly show an isospin dependence of the conditional barriers when compared with the extracted barriers from {sup 90}Mo and {sup 94}Mo. Eleven different liquid/liquid extractants were synthesized based upon the chelating moieties 3,2-HOPO and 3,4-HOPO; additionally, two liquid/liquid extractants based upon the 1,2-HOPO chelating moiety were obtained for extraction studies. The Pu(IV) extractions, quite surprisingly, yielded results that were very different from the Fe(III) extractions. The first trend remained the same: the 1,2-HOPOs were the best extractants, followed closely by the 3,2-HOPOs, followed by the 3,4-HOPOs; but in these Pu(IV) extractions the 3,4-HOPOs performed much better than in the Fe(III) extractions. 129 refs.

Veeck, A.C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; [Lawrence Livermore National Lab., CA (United States). Glenn T. Seaborg Inst. for Transactinium Science; [Lawrence Berkeley National Lab., CA (United States). Nuclear Science Div.

1996-08-01

179

Asymmetric Synthesis and Evaluation of Danshensu-Cysteine Conjugates as Novel Potential Anti-Apoptotic Drug Candidates  

PubMed Central

We have previously reported that the danshensu-cysteine conjugate N-((R)-3-benzylthio-1-methoxy-1-oxo-2-propanyl)-2-acetoxy-3-(3,4-diacetoxyphenyl) propanamide (DSC) is a potent anti-oxidative and anti-apoptotic agent. Herein, we further design and asymmetrically synthesize two diastereoisomers of DSC and explore their potential bioactivities. Our results show that DSC and its two diastereoisomers exert similar protective effects in hydrogen peroxide (H2O2)-induced cellular injury in SH-SY5Y cells, as evidenced by the increase of cell viability, superoxide dismutase (SOD), and reduced glutathione (GSH) activity, and glutathione peroxidase (GPx) expression, and the decrease of cellular morphological changes and nuclear condensation, lactate dehydrogenase (LDH) release, and malondialdehyde (MDA) production. In H2O2-stimulated human umbilical vein endothelial cells (HUVEC), DSC concentration-dependently attenuates H2O2-induced cell death, LDH release, mitochondrial membrane potential collapse, and modulates the expression of apoptosis-related proteins (Bcl-2, Bax, caspase-3, and caspase-9). Our results provide strong evidence that DSC and its two diastereoisomers have similar anti-oxidative activity and that DSC exerts significant vascular-protective effects, at least in part, through inhibition of apoptosis and modulation of endogenous antioxidant enzymes. PMID:25551606

Pan, Li-Long; Wang, Jie; Jia, Yao-Ling; Zheng, Hong-Ming; Wang, Yang; Zhu, Yi-Zhun

2014-01-01

180

Asymmetric synthesis and evaluation of danshensu-cysteine conjugates as novel potential anti-apoptotic drug candidates.  

PubMed

We have previously reported that the danshensu-cysteine conjugate N-((R)-3-benzylthio-1-methoxy-1-oxo-2-propanyl)-2-acetoxy-3-(3,4-diacetoxyphenyl) propanamide (DSC) is a potent anti-oxidative and anti-apoptotic agent. Herein, we further design and asymmetrically synthesize two diastereoisomers of DSC and explore their potential bioactivities. Our results show that DSC and its two diastereoisomers exert similar protective effects in hydrogen peroxide (H2O2)-induced cellular injury in SH-SY5Y cells, as evidenced by the increase of cell viability, superoxide dismutase (SOD), and reduced glutathione (GSH) activity, and glutathione peroxidase (GPx) expression, and the decrease of cellular morphological changes and nuclear condensation, lactate dehydrogenase (LDH) release, and malondialdehyde (MDA) production. In H2O2-stimulated human umbilical vein endothelial cells (HUVEC), DSC concentration-dependently attenuates H2O2-induced cell death, LDH release, mitochondrial membrane potential collapse, and modulates the expression of apoptosis-related proteins (Bcl-2, Bax, caspase-3, and caspase-9). Our results provide strong evidence that DSC and its two diastereoisomers have similar anti-oxidative activity and that DSC exerts significant vascular-protective effects, at least in part, through inhibition of apoptosis and modulation of endogenous antioxidant enzymes. PMID:25551606

Pan, Li-Long; Wang, Jie; Jia, Yao-Ling; Zheng, Hong-Ming; Wang, Yang; Zhu, Yi-Zhun

2014-01-01

181

Synthesis and characterization of mesoporous spinel NiCo2O4 using surfactant-assembled dispersion for asymmetric supercapacitors  

NASA Astrophysics Data System (ADS)

A simple and scalable process has been developed for synthesizing spinel NiCo2O4 nanocrystals through a thermal decomposition method. The introduction of hexadecyltrimethylammonium bromide (CTAB, (C16H33)N(CH3)3Br) into precursor solutions significantly enhances the homogeneity and porosity of spinel NiCo2O4. The porosity and high specific surface area of NiCo2O4 preserves the brilliant pseudo-capacitive performances due to providing smooth paths for electrolyte penetration and ion diffusion into inner active sites. Morphologies and microstructures of the active materials are examined by transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses. Thermogravimetric analysis (TGA) is used to evaluate the thermal properties of precursor solutions. The electrochemical performances of NiCo2O4 are systematically characterized by cyclic voltammetry and charge-discharge tests. Asymmetric supercapacitors are assembled with these brilliant binary oxides as the positive electrode and activated carbon as the negative electrode. The highly porous NiCo2O4 exhibits superior capacitive performances, i.e., high specific capacitance (764 F g-1 at 2 mV s-1) and long cycle life.

Hsu, Chun-Tsung; Hu, Chi-Chang

2013-11-01

182

Teaching Absolute Value Meaningfully  

ERIC Educational Resources Information Center

What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

Wade, Angela

2012-01-01

183

[Asymmetric synthesis of multi-substituted ?-lactams via C-N axially chiral enolates in intramolecular conjugate addition].  

PubMed

The synthesis of ?-lactams with contiguous tetra- and trisubstituted carbon centers has been accomplished via the 4-exo-trig intramolecular conjugate addition of C-N axially chiral enolates generated from ?-amino acid derivatives. Use of a metal carbonate in a protic solvent (i.e., Cs(2)CO(3) in EtOH) was found to be critical for the success of the reaction. Under optimized reaction conditions, axially chiral enolates were generated in very low concentration, thereby favoring intramolecular conjugate addition while minimizing intermolecular side reactions. The highly strained ?-lactam enolates formed through this reversible intramolecular conjugate addition were rapidly protonated by EtOH in the reaction media to afford ?-lactams in up to 97% ee. PMID:23123721

Yoshimura, Tomoyuki

2012-01-01

184

Direct amino acid-catalyzed cascade biomimetic reductive alkylations: application to the asymmetric synthesis of Hajos-Parrish ketone analogues.  

PubMed

A direct amino acid-catalyzed chemo- and enantioselective process for the double cascade synthesis of highly substituted 2-alkyl-cyclopentane-1,3-diones, 2-alkyl-3-methoxy-cyclopent-2-enones and Hajos-Parrish (H-P) ketone analogs is presented via reductive alkylation chemistry. For the first time, we have developed a single-step alkylation of cyclopentane-1,3-dione with aldehydes/ketones and a Hantzsch ester through an organocatalytic reductive alkylation strategy. A direct combination of amino acid-catalyzed cascade olefination-hydrogenation and cascade Robinson annulations of cyclopentane-1,3-dione, aldehydes/ketones, a Hantzsch ester and methyl vinyl ketone furnished the highly functionalized H-P ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products have shown direct applications in pharmaceutical chemistry. PMID:18972048

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2008-11-21

185

Origin of Stereocontrol in Guanidine-Bisurea Bifunctional Organocatalyst That Promotes ?-Hydroxylation of Tetralone-Derived ?-Ketoesters: Asymmetric Synthesis of ?- and ?-Substituted Tetralone Derivatives via Organocatalytic Oxidative Kinetic Resolution.  

PubMed

The mechanism of asymmetric ?-hydroxylation of tetralone-derived ?-ketoesters with guanidine-bisurea bifunctional organocatalyst in the presence of cumene hydroperoxide (CHP) was examined by means of DFT calculations to understand the origin of the stereocontrol in the reaction. The identified transition-state model was utilized to design an enantioselective synthesis of ?- or ?-substituted tetralones by catalytic oxidative kinetic resolution reaction of tetralone-derived ?-ketoesters. This kinetic resolution reaction proceeded with high selectivity, and selectivity factors (s value) of up to 99 were obtained. The potential utility of this oxidative kinetic resolution method for synthesis of natural products was confirmed by applying it to achieve an enantioselective synthesis of (+)-linoxepin (13) from ?-substituted tetralone rac-7 in only six steps. PMID:25580909

Odagi, Minami; Furukori, Kota; Yamamoto, Yoshiharu; Sato, Makoto; Iida, Keisuke; Yamanaka, Masahiro; Nagasawa, Kazuo

2015-02-11

186

Asymmetric catalysis activated by visible light.  

PubMed

Visible light driven organic chemistry has sparked much excitement over the last several years. This review summarizes recent progress in combining visible light activation with asymmetric catalysis, processes that are either mediated by photoinduced electron or energy transfer. The tasks of photoactivation and asymmetric catalysis are typically accomplished by dual catalyst systems but several recent reports demonstrate that they can also be effectively executed by single catalysts. Beyond the discovery of novel asymmetric transformations under mild reaction conditions, this contemporary area of organic chemistry holds promise for the development of economical and environmentally friendly methods for the asymmetric synthesis of chiral compounds. PMID:25572775

Meggers, Eric

2015-02-10

187

Synthesis and determination of the absolute configuration of Armatol A through a polyepoxide cyclization cascade : revision of the proposed structures of Armatols A-F  

E-print Network

Cyclization Cascades Leading to the Tricyclic Fragment of Armatol A The synthesis of the fused 6,7,7-tricycle of armatol A was investigated. Fragments containing both a ketone and an aldehyde for subsequent fragment coupling ...

Underwood, Brian Saxton

2011-01-01

188

C2-Symmetric enantiopure ethanotethered bis(alpha,beta-butenolides) as templates for asymmetric synthesis. Application to the synthesis of (+)-grandisol.  

PubMed

Starting from D-mannitol, we have prepared several C(2)-symmetric ethanotethered bis(alpha,beta-butenolides) and studied their [2+2] photocycloaddition reaction with ethylene. The protective groups of the central diol unit have a noticeable influence on the facial selectivity of the cycloaddition, the bis(trimethylsilyloxy) derivatives showing the highest diastereoselectivity. A theoretical conformational analysis of the substrates in the ground state is in good agreement with the diastereofacial selectivity experimentally observed. The bis(photocycloadducts) have been converted into the enantiopure cyclobutanes formally derived from the photoreaction of ethylene with gamma-hydroxymethyl-alpha,beta-butenolide, in which only a moderate facial selectivity had been previously found. As an application of these studies, we have developed a highly efficient and stereoselective synthesis of (+)-grandisol. PMID:12636414

de March, Pedro; Figueredo, Marta; Font, Josep; Raya, Javier; Alvarez-Larena, Angel; Piniella, Juan F

2003-03-21

189

Asymmetric conjugate reductions with samarium diiodide: asymmetric synthesis of (2S,3R)- and (2S,3S)-[2-2H,3-2H]-leucine-(S)-phenylalanine dipeptides and (2S,3R)-[2-(2)H,3-2H]-phenylalanine methyl ester.  

PubMed

The highly diastereoselective samarium diiodide and D(2)O-promoted conjugate reduction of homochiral (E)- and (Z)-benzylidene and isobutylidene diketopiperazines (E)-5,7 and (Z)-6,8 has been demonstrated. This methodology allows the asymmetric synthesis of methyl (2S,3R)-dideuteriophenylalanine 27 in > or = 95% de and >98% ee, and (2S,3R)- or (2S,3S)-dideuterioleucine-(S)-phenylalanine dipeptides 37 and 38 in moderate de, 66% and 74% respectively. A mechanism is proposed to account for this process. PMID:15827639

Davies, Stephen G; Rodriguez-Solla, Humberto; Tamayo, Juan A; Cowley, Andrew R; Concellon, Carmen; Garner, A Christopher; Parkes, Alastair L; Smith, Andrew D

2005-04-21

190

Synthesis of new Schiff base-camphorsulfonyl amide ligands and in situ screening in the asymmetric additions of organozinc reagents to aldehydes  

Microsoft Academic Search

We have designed and synthesized a new library of highly modular Schiff base-camphorsulfonyl amide ligands from readily available starting materials. These ligands have been used in the asymmetric addition of diethyl zinc to aldehydes in good yields (up to 91%) and high enantioselectivities (up to 93%). Moreover, when the ligands were used in the asymmetric addition of phenylacetylene to aldehydes,

Jiangtao Sun; Xu Pan; Zhenya Dai; Chengjian Zhu

2008-01-01

191

Applications of organocatalytic asymmetric synthesis to drug prototypes--dual action and selective inhibitors of n-nitric oxide synthase with activity against the 5-HT1D/1B subreceptors.  

PubMed

The scope of MacMillan's organocatalytic asymmetric conjugate addition reaction of indoles and electron-rich aromatics to ?,?-unsaturated aldehydes has been extended to the use of 3-amino crotonaldehydes as substrates. The aromatics used include indoles as well as an aniline and a furan. The scope and effect of the groups on nitrogen (R, R') has also been studied. The method has been applied to the concise synthesis of an advanced precursor to S-(+)-1, a drug prototype for the treatment of migraine headaches. PMID:21271688

Hanessian, Stephen; Stoffman, Eli; Mi, Xueling; Renton, Paul

2011-03-01

192

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres  

NASA Astrophysics Data System (ADS)

The development of a general catalytic method for the direct and stereoselective construction of contiguous all-carbon quaternary stereocentres remains a formidable challenge in chemical synthesis. Here, we report a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalysed by a palladium complex bearing a newly devised phosphine ligand with a chiral ammonium salt component, which enables the single-step construction of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, in a five-membered heterocyclic framework. This stereoselective cycloaddition protocol relies on the remarkable ability of the chiral ligand to rigorously control the absolute stereochemistry of each chiral centre associated with the multiple bond-forming events, and provides a reliable catalytic process for the asymmetric synthesis of densely functionalized pyrrolidines.

Ohmatsu, Kohsuke; Imagawa, Naomichi; Ooi, Takashi

2014-01-01

193

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres.  

PubMed

The development of a general catalytic method for the direct and stereoselective construction of contiguous all-carbon quaternary stereocentres remains a formidable challenge in chemical synthesis. Here, we report a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalysed by a palladium complex bearing a newly devised phosphine ligand with a chiral ammonium salt component, which enables the single-step construction of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, in a five-membered heterocyclic framework. This stereoselective cycloaddition protocol relies on the remarkable ability of the chiral ligand to rigorously control the absolute stereochemistry of each chiral centre associated with the multiple bond-forming events, and provides a reliable catalytic process for the asymmetric synthesis of densely functionalized pyrrolidines. PMID:24345946

Ohmatsu, Kohsuke; Imagawa, Naomichi; Ooi, Takashi

2014-01-01

194

Absolute nuclear material assay  

DOEpatents

A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

Prasad, Manoj K. (Pleasanton, CA); Snyderman, Neal J. (Berkeley, CA); Rowland, Mark S. (Alamo, CA)

2012-05-15

195

Synthesis of (3S,3?S)- and meso-Stereoisomers of Alloxanthin and Determination of Absolute Configuration of Alloxanthin Isolated from Aquatic Animals  

PubMed Central

In order to determine the absolute configuration of naturally occurring alloxanthin, a HPLC analytical method for three stereoisomers 1a–c was established by using a chiral column. Two authentic samples, (3S,3?S)- and meso-stereoisomers 1b and 1c, were chemically synthesized according to the method previously developed for (3R,3?R)-alloxanthin (1a). Application of this method to various alloxanthin specimens of aquatic animals demonstrated that those isolated from shellfishes, tunicates, and crucian carp are identical with (3R,3?R)-stereoisomer 1a, and unexpectedly those from lake shrimp, catfish, biwa goby, and biwa trout are mixtures of three stereoisomers of 1a–c. PMID:24862182

Yamano, Yumiko; Maoka, Takashi; Wada, Akimori

2014-01-01

196

Absolute airborne gravimetry  

Microsoft Academic Search

This work consists of a feasibility study of a first stage prototype airborne absolute gravimeter system. In contrast to relative systems, which are using spring gravimeters, the measurements acquired by absolute systems are uncorrelated and the instrument is not suffering from problems like instrumental drift, frequency response of the spring and possible variation of the calibration factor. The major problem

Henri Baumann

2005-01-01

197

Isolation and complete structural assignment of Lycopodium alkaloid cernupalhine A: theoretical prediction and total synthesis validation.  

PubMed

Cernupalhine A (1) is a trace Lycopodium alkaloid (0.7 mg) possessing a new C17N skeleton with an unusual hydroxydihydrofuranone motif newly isolated from Palhinhaea cernua L. Its complete structural assignment, including absolute stereochemistry, was established through a combination of high-field NMR techniques and computational methods and further unequivocal confirmation by the first asymmetric total synthesis. Following the first total synthesis of lobscurinine (3), 1 was achieved via regio- and stereoselective cyanide ion addition and subsequent acid treatment. PMID:24779557

Dong, Liao-Bin; Wu, Ya-Nan; Jiang, Shi-Zhi; Wu, Xing-De; He, Juan; Yang, Yu-Rong; Zhao, Qin-Shi

2014-05-16

198

Diversity-oriented asymmetric catalysis (DOAC): stereochemically divergent synthesis of thiochromanes using an imidazoline-aminophenol-nickel-catalyzed Michael/Henry reaction.  

PubMed

The (S,S)-diphenylethylenediamine-derived imidazoline-aminophenol-Ni complex catalyzed tandem asymmetric Michael/Henry reaction of 2-mercaptobenzaldehydes with ?-nitrostyrenes to give the corresponding (2S,3R,4R)-2-aryl-3-nitrothiochroman-4-ols in up to 99% diastereoselectivity with 95% ee was demonstrated in diversity-oriented asymmetric catalysis. Reduction of the nitro group of the chiral thiochromanes gave a new series of (2S,3R,4R)-3-amino-2-arylthiochroman-4-ols with retention of the strereoselectivity. PMID:24601640

Arai, Takayoshi; Yamamoto, Yushi

2014-03-21

199

Simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition for controlled synthesis of asymmetric axial ZnO nanospindles  

NASA Astrophysics Data System (ADS)

Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the <0002> direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures.Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the <0002> direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures. Electronic supplementary information (ESI) available: XRD pattern, TEM, and SEM images of ZnO nanospindles. See DOI: 10.1039/c4nr01888e

Yang, Hong-Jie; He, Sheng-Yan; Tuan, Hsing-Yu

2014-07-01

200

Simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition for controlled synthesis of asymmetric axial ZnO nanospindles.  

PubMed

Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the ?0002? direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures. PMID:24970315

Yang, Hong-Jie; He, Sheng-Yan; Tuan, Hsing-Yu

2014-08-01

201

Efficient rhodium-catalyzed asymmetric hydrogenation for the synthesis of a new class of N-aryl beta-amino acid derivatives.  

PubMed

[reaction: see text] N-Aryl beta-amino esters were obtained by asymmetric hydrogenation of a new class of N-aryl beta-enamino esters. High conversions and up to 96.3% ee values were achieved with a Rh-TangPhos catalyst. PMID:16268574

Dai, Qian; Yang, Weiran; Zhang, Xumu

2005-11-10

202

Dynamic kinetic resolution based asymmetric transfer hydrogenation of ?-alkoxy-?-ketophosphonates. Diastereo- and enantioselective synthesis of monoprotected 1,2-dihydroxyphosphonates.  

PubMed

Dynamic kinetic resolution driven, asymmetric transfer hydrogenation reactions of a wide range of 2-substituted ?-alkoxy-?-ketophosphonates 3 were observed to proceed efficiently to give the corresponding 2-substituted ?-alkoxy-?-hydroxy phosphonates 4 with excellent levels of diastereo- and enantioselectivity. These processes are promoted by using well-defined, commercially available, chiral transition metal catalysts and a 0.2:1 mixture of formic acid and triethylamine as the hydrogen source and solvent. PMID:24568588

Son, Se-Mi; Lee, Hyeon-Kyu

2014-03-21

203

Absolute and relative blindsight.  

PubMed

The concept of relative blindsight, referring to a difference in conscious awareness between conditions otherwise matched for performance, was introduced by Lau and Passingham (2006) as a way of identifying the neural correlates of consciousness (NCC) in fMRI experiments. By analogy, absolute blindsight refers to a difference between performance and awareness regardless of whether it is possible to match performance across conditions. Here, we address the question of whether relative and absolute blindsight in normal observers can be accounted for by response bias. In our replication of Lau and Passingham's experiment, the relative blindsight effect was abolished when performance was assessed by means of a bias-free 2AFC task or when the criterion for awareness was varied. Furthermore, there was no evidence of either relative or absolute blindsight when both performance and awareness were assessed with bias-free measures derived from confidence ratings using signal detection theory. This suggests that both relative and absolute blindsight in normal observers amount to no more than variations in response bias in the assessment of performance and awareness. Consideration of the properties of psychometric functions reveals a number of ways in which relative and absolute blindsight could arise trivially and elucidates a basis for the distinction between Type 1 and Type 2 blindsight. PMID:25305691

Balsdon, Tarryn; Azzopardi, Paul

2015-03-01

204

Improved synthesis and application of planar-chiral nucleophilic catalysts in asymmetric reactions and copper-catalyzed enantioselective N-H insertion reactions  

E-print Network

The development of an improved synthesis of nucleophilic planar-chiral catalysts is described in Chapter 1. This route is amenable to scale-up and preparative chiral HPLC is unnecessary to resolve the racemic catalysts. ...

Lee, Elaine C

2007-01-01

205

Asymmetric transfer hydrogenation of 2-tosyloxy-1-(4-hydroxyphenyl)ethanone derivatives: synthesis of ( R)-tembamide, ( R)-aegeline, ( R)-octopamine, and ( R)-denopamine  

Microsoft Academic Search

Catalytic transfer hydrogenation of 2-tosyloxy-1-(4-hydroxyphenyl)ethanone derivatives leads to efficient synthesis of ?-adrenergic agonists, (R)-tembamide, (R)-aegeline, (R)-octopamine, and (R)-denopamine.

Do-Min Lee; Jong-Cheol Lee; Nakcheol Jeong; Kee-In Lee

2007-01-01

206

Absolute pitch may not be so absolute.  

PubMed

Most people cannot name the musical note that corresponds to a particular pitch without being provided a reference note, but those people with absolute pitch (AP) can do this accurately. Early experience during a developmental period is often thought to convey identity and stability of the note categories in people with AP, but the plasticity of these categories has not been investigated. Here we provide the first evidence that the note categories of adults with AP can change with listening experience. Participants with AP showed shifts in perception in direct accord with prior exposure to music detuned by a fraction of a semitone. This suggests that the apparent stability of AP categories is conferred not by early experience but rather by the cultural norms adopted for tuning music. PMID:23757308

Hedger, Stephen C; Heald, Shannon L M; Nusbaum, Howard C

2013-08-01

207

Asymmetric dark matter  

SciTech Connect

We review the theoretical framework underlying models of asymmetric dark matter, describe astrophysical constraints which arise from observations of neutron stars, and discuss the prospects for detecting asymmetric dark matter.

Kumar, Jason [Department of Physics and Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

2014-06-24

208

Symmetric Cryptography Asymmetric Cryptography  

E-print Network

Outline Symmetric Cryptography Asymmetric Cryptography Key Management Network Security Cryptography Symmetric Cryptography Asymmetric Cryptography Key Management Network Security 1 Symmetric Cryptography Symmetric Cryptography Overview Block Cipher Modes Multiple Encryption Hash Functions Message Authentication

Ramkumar, Mahalingam

209

Symmetric Cryptography Asymmetric Cryptography  

E-print Network

Outline Trust Symmetric Cryptography Asymmetric Cryptography Key Management Network Security Cryptography - A Review Mahalingam Ramkumar Mississippi State University, MS September 22, 2006 Ramkumar Review #12;Outline Trust Symmetric Cryptography Asymmetric Cryptography Key Management Network Security 1

Ramkumar, Mahalingam

210

Relative and Absolute Directions  

NSDL National Science Digital Library

The purpose of this resource is to learn about latitude and longitude while developing math skills. Students begin by asking the simple question: 'Where Am I?' Then they learn about the magnetic Earth and the use of compasses and angles. Students also learn about the difference between relative and absolute locations. Throughout this activity, students practice using a variety of math skills.

The GLOBE Program, University Corporation for Atmospheric Research (UCAR)

2003-08-01

211

Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures.  

PubMed

Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln(3+) (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln(3+) nanorods, whereas the stipe is composed of over layered ZnO:Ln(3+) nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln(3+) mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light. PMID:25293373

Yue, Dan; Lu, Wei; Jin, Lin; Li, Chunyang; Luo, Wen; Wang, Mengnan; Wang, Zhenling; Hao, Jianhua

2014-11-21

212

Bifunctional Asymmetric Catalysis  

PubMed Central

CONSPECTUS In the field of catalytic, asymmetric synthesis, there is a growing emphasis on multifunctional systems, in which multiple parts of a catalyst or multiple catalysts work together to promote a specific reaction. These efforts, in part, are result-driven, and they are also part of a movement toward emulating the efficiency and selectivity of nature’s catalysts, enzymes. In this Account, we illustrate the importance of bifunctional catalytic methods, focusing on the cooperative action of Lewis acidic and Lewis basic catalysts by the simultaneous activation of both electrophilic and nucleophilic reaction partners. For our part, we have contributed three separate bifunctional methods that combine achiral Lewis acids with chiral cinchona alkaloid nucleophiles, for example, benzoylquinine (BQ), to catalyze highly enantioselective cycloaddition reactions between ketene enolates and various electrophiles. Each method requires a distinct Lewis acid to coordinate and activate the electrophile, which in turn increases the reaction rates and yields, without any detectable influence on the outstanding enantioselectivities inherent to these reactions. To place our results in perspective, many important contributions to this emerging field are highlighted and our own reports are chronicled. PMID:18402470

PAULL, DANIEL H.; ABRAHAM, CIBY J.; SCERBA, MICHAEL T.; ALDEN-DANFORTH, ETHAN; LECTKA, THOMAS

2008-01-01

213

Divergent total synthesis of the Lycopodium alkaloids huperzine A, huperzine B, and huperzine U.  

PubMed

Huperzine A, huperzine B, and huperzine U are congeners isolated from the Chinese herb Huperzia serrata (= Lycopodium serratum ) in minuscule amounts. The most efficient total synthesis of huperzine A, the first asymmetric total syntheses of huperzine B, and the first total synthesis of huperzine U have been achieved efficiently in overall yields of 17%, 10%, and 9%, respectively, each spanning 10-13 steps from (R)-pulegone. The featured steps include palladium-catalyzed Buchwald-Hartwig coupling and Heck cyclization reactions and an Ir-catalyzed olefin isomerization reaction. This work has established the absolute configurations of huperzine B and huperzine U and revealed that natural huperzine A, huperzine B, and huperzine U possess the same set of absolute stereochemistries, thus providing support for the potential role of huperzine B and huperzine U in the biosynthesis of huperzine A. PMID:24299147

Ding, Rui; Fu, Jian-Guo; Xu, Guang-Qiang; Sun, Bing-Feng; Lin, Guo-Qiang

2014-01-01

214

A highly efficient asymmetric synthesis of quaternary stereocenter-containing indolizidine and quinolizidine alkaloids using aldehydes, nitroalkenes, and unactivated cyclic ketimines.  

PubMed

A highly efficient approach for the construction of indolizidines and quinolizidines bearing a bridged quaternary stereocenter has been established in a one-pot fashion using aldehydes, nitroalkenes, and cyclic ketimines with excellent enantioselectivities and in high yields. Moreover, this method could be applied to the synthesis of indolizidines in the gram scale. PMID:25379636

Tan, Yu; Chen, Yong-Jian; Lin, Hua; Luan, Han-Lin; Sun, Xing-Wen; Yang, Xiao-Di; Lin, Guo-Qiang

2014-12-28

215

Fluorine effects in organocatalysis - asymmetric Brønsted acid assisted Lewis base catalysis for the synthesis of trifluoromethylated heterocycles exploiting the negative hyperconjugation of the CF3-group.  

PubMed

An efficient Brønsted acid assisted Lewis base catalysis protocol for the synthesis of enantiomerically pure trifluoromethylated dihydropyridazines starting from readily available hydrazones and ?,?-unsaturated aldehydes has been developed. The reaction exhibits high tolerance towards many functional groups and is applicable to various aliphatic, aromatic and hetero-aromatic ?,?-unsaturated aldehydes, and provides the products in good yields and with excellent enantioselectivities. PMID:24911934

Volla, Chandra M R; Das, Arindam; Atodiresei, Iuliana; Rueping, Magnus

2014-07-25

216

The Direct Catalytic Asymmetric Aldol Reaction  

PubMed Central

Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets PMID:20419212

Brindle, Cheyenne S.

2013-01-01

217

Absolute configuration of neostenine  

NASA Astrophysics Data System (ADS)

Heavy atoms bromine and iodine were incorporated into the neostenine ( 1) skeleton through reductive cleavage of the lactone ring, followed by acylation with 4-bromobenzoyl chloride, and salt formation with methyl iodide, respectively. The absolute configuration of the seven chiral centers C1, C9, C9a, C10, C11, C1 and C13 in 1 were assigned as S, S, R, R, R, R, and S, respectively, based on the Flack parameters in X-ray structure refinement, and results from the two heavy atom derivatives are consistent with each other. As many Stemona alkaloids share the same lactone and pyrrolo[1,2-?]azepine nucleus as those in 1, the facile method reported in this paper can be applied for the determination of absolute configurations of similar alkaloids.

Jiang, Ren-Wang; Ye, Wencai; Shaw, Pang-Chui; But, Paul Pui-Hay; Mak, Thomas C. W.

2010-03-01

218

Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures  

NASA Astrophysics Data System (ADS)

Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln3+ (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln3+ nanorods, whereas the stipe is composed of over layered ZnO:Ln3+ nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln3+ mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light.Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln3+ (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln3+ nanorods, whereas the stipe is composed of over layered ZnO:Ln3+ nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln3+ mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light. Electronic supplementary information (ESI) available: STEM-SEI image and EDS elemental mapping of an individual ZnO: Eu3+ mushroom. See DOI: 10.1039/c4nr04359f

Yue, Dan; Lu, Wei; Jin, Lin; Li, Chunyang; Luo, Wen; Wang, Mengnan; Wang, Zhenling; Hao, Jianhua

2014-10-01

219

Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity  

NASA Astrophysics Data System (ADS)

New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, 1H NMR, 13C NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL2A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.

?ahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, U?ur

2013-02-01

220

Total synthesis of Class II and Class III Galbulimima Alkaloids  

E-print Network

I. Total Synthesis of All Class III Galbulimima Alkaloids We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13, (-)-himgaline anad (-)-himbadine. The absolute stereochemistry of natural (-)-galbulimima ...

Tjandra, Meiliana

2010-01-01

221

Biomimetic asymmetric synthesis of (R)-GTRI-02 and (3S,4R)-3,4-dihydroxy-3,4-dihydronaphthalen-1(2H)-ones.  

PubMed

The NADPH-dependent tetrahydroxynaphthalene reductase (T4HNR) from Magnaporthe grisea was used for the biomimetic synthesis of (R)-GTRI-02 by stereoselective reduction of 1-(3,6,8-trihydroxy-1-methylnaphthalen-2-yl)ethanone. This also led to the isolation of a (3S,4R)-cis-ketodiol formed by T4HNR-catalyzed reduction of the corresponding hydroxynaphthoquinone. Flaviolin and lawsone also reduced to corresponding cis-ketodiols in good yields. PMID:22738326

Husain, Syed Masood; Schätzle, Michael A; Röhr, Caroline; Lüdeke, Steffen; Müller, Michael

2012-07-20

222

Formal total synthesis of cyanolide A.  

PubMed

Formal total synthesis of cyanolide A, aglycosidic dimeric macrolide is accomplished. The key reactions involved are asymmetric acetate aldol reaction, CBS reduction, and Shiina's lactonization. PMID:21280592

Pabbaraja, Srihari; Satyanarayana, K; Ganganna, B; Yadav, J S

2011-03-18

223

Absolute airborne gravimetry  

NASA Astrophysics Data System (ADS)

This work consists of a feasibility study of a first stage prototype airborne absolute gravimeter system. In contrast to relative systems, which are using spring gravimeters, the measurements acquired by absolute systems are uncorrelated and the instrument is not suffering from problems like instrumental drift, frequency response of the spring and possible variation of the calibration factor. The major problem we had to resolve were to reduce the influence of the non-gravitational accelerations included in the measurements. We studied two different approaches to resolve it: direct mechanical filtering, and post-processing digital compensation. The first part of the work describes in detail the different mechanical passive filters of vibrations, which were studied and tested in the laboratory and later in a small truck in movement. For these tests as well as for the airborne measurements an absolute gravimeter FG5-L from Micro-G Ltd was used together with an Inertial navigation system Litton-200, a vertical accelerometer EpiSensor, and GPS receivers for positioning. These tests showed that only the use of an optical table gives acceptable results. However, it is unable to compensate for the effects of the accelerations of the drag free chamber. The second part describes the strategy of the data processing. It is based on modeling the perturbing accelerations by means of GPS, EpiSensor and INS data. In the third part the airborne experiment is described in detail, from the mounting in the aircraft and data processing to the different problems encountered during the evaluation of the quality and accuracy of the results. In the part of data processing the different steps conducted from the raw apparent gravity data and the trajectories to the estimation of the true gravity are explained. A comparison between the estimated airborne data and those obtained by ground upward continuation at flight altitude allows to state that airborne absolute gravimetry is feasible and has a spatial resolution comparable to the one of the relative airborne gravimetry. For a wavelength on the order of 11 km the mean value of the resolution of the estimated gravity is 9.7 mGal. Finally some suggestions are formulated for the improvement of the system which should simplify its use, increase the accuracy and reduce its price.

Baumann, Henri

224

Electronic Absolute Cartesian Autocollimator  

NASA Technical Reports Server (NTRS)

An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the mirror is slightly tilted. Hence, one can determine the amount and direction of tilt from the coordinates of the target image on the viewing plane.

Leviton, Douglas B.

2006-01-01

225

Synthesis, crystal structures, and properties of two novel cadmium(II)-organic frameworks based on asymmetric dicarboxylate and N-donor ligands  

NASA Astrophysics Data System (ADS)

Two novel cadmium(II)-organic frameworks with asymmetric dicarboxylate and N-donor ligands, namely [Cd(cpa)(phen)]n (1) and {[Cd2(cpa)2(bpy)1.5]·0.5H2O}n (2) (H2cpa = 3-(4-benzoic)propionic acid, phen = 1,10-phenanthroline, bpy = 4,4";-bipyridine) have been hydrothermally synthesized and characterized by elemental analyses, FT-IR spectra, single-crystal X-ray diffraction analyses, TGA, powder XRD and fluorescent measurements. 1 displays a double zigzag chain structure containing 8-number and 22-number circles. 2 Shows a 6-connected 3D polymer network based on tetranuclear cadmium cluster units. The most striking feature of 2 is that a pair of identical 3D networks are interlocked with each other to the form a 2-fold interpenetrated 3D ?-Po structural topology. The diverse structures of two complexes indicate that the skeleton of N-donor ligands plays a great role in the assembly of such different frameworks. In addition, the thermal stabilities, XRD and photoluminescence properties of 1-2 were also studied.

Chen, Xiaoli; Gao, Loujun; Zhang, Xiaoge; Han, Xuhua; Wang, Yao; Sun, Rong

2014-08-01

226

Synthesis and characterization of new chiral Cu(ii)-N4 complexes and their application in the asymmetric aza-Henry reaction.  

PubMed

Cu(ii) Schiff base complexes Cu(ii)- and Cu(ii)- based on 2-acetyl pyridine with both (1R,2R)-1,2-diaminocyclohexane and (1S,2S)-1,2-diaminocyclohexane were synthesized in a single step. Subsequent reduction of ligands and with NaBH4 followed by complexation with Cu(OTf)2 resulted in generation of two more additional chiral centers in complexes Cu(ii)- and Cu(ii)-. The ligands and their corresponding complexes were well characterized by several spectral techniques like (1)H-NMR, (13)C-NMR, LC-MS, CD, UV-Vis spectroscopy and microanalysis. The respective Cu(ii) complexes derived from ligands and were investigated using both the solution and solid state EPR spectra. The particular orientation of the reduced complex with Cu(OTf)2 was confirmed by the X-ray crystal structure of the corresponding complex. All the catalytic protocols were applied in the asymmetric aza-Henry reaction to evaluate the catalytic properties of the Cu(ii) complexes in the present study. PMID:24988542

Das, Anjan; Kureshy, Rukhsana I; Maity, Nabin Ch; Subramanian, P S; Khan, Noor-ul H; Abdi, Sayed H R; Suresh, E; Bajaj, Hari C

2014-08-28

227

A new copper(II) Schiff base complex containing asymmetrical tetradentate N2O2 Schiff base ligand: Synthesis, characterization, crystal structure and DFT study  

NASA Astrophysics Data System (ADS)

A new copper (II) Schiff base complex, CuL1, was prepared from the reaction of asymmetrical Schiff base ligand of L1 and Cu(OAC)2 (L1 = salicylidene imino-ethylimino-pentan-2-one). The Schiff base ligand, L1, and its copper (II) complex, CuL1, have been characterized by elemental analysis (CHN) and FT-IR and UV-vis spectroscopy. In addition, 1H NMR was employed for characterization of the ligand. Thermogrametric analysis of the CuL1 reveals its thermal stability and its decomposition pattern shows that it is finally decomposed to the copper oxide (CuO). The crystal structure of CuL1 was determined by the single crystal X-ray analysis. The CuL1 complex crystallizes in the monoclinic system, with space group P21/n and distorted square planar coordination around the metal ion. The Schiff base ligand of L1 acts as a chelating ligand and coordinates via two nitrogen and two oxygen atoms to the copper (II) ion with C1 symmetry. The structure of the CuL1 complex was also studied theoretically at different levels of DFT and basis sets. According to calculated results the Csbnd O bond length of the salicylate fragment is slightly higher than that in the acetylacetonate fragment of ligand, which could be interpreted by resonance increasing between phenyl and chelated rings in ligand in relative to the acetylacetonate fragment.

Grivani, Gholamhossein; Baghan, Sara Husseinzadeh; Vakili, Mohammad; Khalaji, Aliakbar Dehno; Tahmasebi, Vida; Eigner, Václav; Dušek, Michal

2015-02-01

228

Facile synthesis of hierarchical Co3O4@MnO2 core-shell arrays on Ni foam for asymmetric supercapacitors  

NASA Astrophysics Data System (ADS)

Hierarchical Co3O4@MnO2 core-shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core-shell arrays on Ni foam have exhibited a high specific capacitance (560 F g-1 at a current density of 0.2 A g-1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg-1 and a maximum power density of 158 kW kg-1. The rational design of the unique core-shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.

Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Wen, Zhiyu; Liu, Qing

2014-04-01

229

Synthesis and characterization of xanthene-bridged Schiff-base dimanganese(III) complexes: bimetallic catalysts for asymmetric oxidation of sulfides.  

PubMed

Dimanganese(III) complexes of salen-type ligands anchored by 9,9-dimethylxanthene-4,5-diyl spacers were synthesized. Two types of structures, cyclic and acyclic forms, are presented. The 2 + 2 Schiff-base condensation of 5,5'-(9,9-dimethylxanthene-4,5-diyl)bis(salicylaldehyde) and 1,2-diaminobenzene gave a macrocyclic ligand, from which a cyclic dimanganese(III) complex was synthesized. A similar dimanganese(III) complex with stereogenic centers was synthesized by the metal-assisted condensation reaction using (1R,2R)-1,2-diaminocyclohexane. Acyclic dimanganese(III) complexes anchored by one xanthene spacer were obtained by metal-assisted stepwise condensation reactions using the xanthene-bridged bis(salicylaldehyde), (1R,2R)-1,2-diaminocyclohexane monohydrochloride, and salicylaldehydes. X-Ray crystal structure analysis confirmed that both cyclic and acyclic complexes have two cofacially oriented salen-type manganese(III) units in a complex cation, showing an Mn...Mn distance of ca. 5.1 A. Asymmetric oxidation of sulfides was performed by using the chiral dimeric complexes as catalysts, which showed enantiomeric excesses ranging from 5 to 19%. The addition of 4-(dimethylamino)pyridine to the reaction system improved the enantioselectivity up to 39% ee. This effect was not observed for the corresponding mononuclear catalyst. PMID:20023944

Hirotsu, Masakazu; Ohno, Naoki; Nakajima, Takashi; Kushibe, Chie; Ueno, Keiji; Kinoshita, Isamu

2010-01-01

230

The information as Absolute  

E-print Network

This article presents and grounds (i.e. presents proof of the existence, the truth, the self-consistence and the completeness of)the informational conception ("the Information as Absolute" conception)in physics and philosophy. the conception defines the information as an ultimately common, real and fundamental concept/phenomenon - "Absolute", which exists as anabsolutely infinite set ("Information" Set) of elements (members) and informational (e.g., logical) linksbetween the elements; where any element itself is some informational structure also. Correspondingly, for example, Matter as the substence, radiation, etc., is some development or realization of informational patterns, constituting a specific - and practically infinitesimal comparing to the Set - subset of the "Information" Set. The conception allows for the resolution, or at least for a consideration on a higher level of comprehension, of the basic ontological and epistemological problems in philosophy and natural sciences; in physics it allows to suggest reasonable model, which makes more clear basic phisical notions,such as space, time, matter, etc.

Sergey V. Shevchenko; Vladimir V. Tokarevsky

2010-04-20

231

NOVA: Absolute Zero  

NSDL National Science Digital Library

On a hot day, some might wish they could get the temperature down a bit. They might not wish it to be as cold as, say absolute zero, but there are many scientists who are interested in doing just that. For those who are curious, absolute zero clocks in at around minus 460 degrees Fahrenheit. This engaging website is meant to serve as a complementary resource to the two-part series that recently aired on NOVA on this engaging topic. Visitors can start by watching a short preview of the program, and then continuing on to look over some of the special interactive features on the site. All told, there are ten different features, including "A Sense of Scale", "How Low Can You Go?", and "Milestones in Cold Research". The "Milestones in Cold Research" is a great place to start, as it's an interactive timeline that chronicles the "netherworld of extraordinarily low temperatures" as investigated by everyone from Galileo to current researchers. Of course, there are also more playful features here, such as "The Ice Trade", which asks users to dispatch ships loaded with natural ice to Florida, Brazil, and India.

232

Improved synthesis of structural analogues of (?)-epicatechin gallate for modulation of staphylococcal ?-lactam resistance?  

PubMed Central

The high-yielding synthesis of enantiomerically pure epicatechin gallate analogues where the A and/or B-ring hydroxylation is reduced or altered has been achieved by optimising routes to the catechin stereochemistry. The B-ring analogues were synthesised by using an electrophilic ring closure onto an enantiomerically enriched epoxide as a key step. The A and B-ring hydroxyl-deleted analogues were synthesised through a Mitsunobu cyclisation. For the B-ring analogues, the anti- (catechin) stereochemistry was converted to the syn- (epicatechin) stereochemistry by a known oxidation/reduction protocol. Absolute stereochemistry was derived from either a Sharpless epoxidation or asymmetric dihydroxylation. PMID:24876661

Anderson, James C.; Grounds, Helen; Reeves, Suzanna; Taylor, Peter W.

2014-01-01

233

Asymmetric Cryptographic Algorithms  

Microsoft Academic Search

The concept of asymmetric cryptographic algorithms introduced by W. Diffie and M. Hellman in 1976 is considered. The problems of factorization of large integers and finding discrete logarithms for elements of finite large-order groups are presented. It is proved that asymmetric cryptographic algorithms based on the problem of finding a discrete logarithm for points of an elliptic curve over a

I. N. Kovalenko; A. I. Kochubinskii

2003-01-01

234

January 2004 Asymmetric Cell  

E-print Network

January 2004 Asymmetric Cell Division By Pamela J. Hines and Suzanne Kadereit Asymmetric cell cell" is one of the fates. In the case of the stem cell, the cell's first step must be to divide and to produce one daughter like itself, able to continue as a stem cell, and one daughter unlike itself, able

Extavour, Cassandra

235

Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases.  

PubMed

Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of beta-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCl under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2'-amino-1,1'-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8'-amino-1,1'-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to alpha-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The (1)H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed. PMID:14558835

Belokon, Yuri N; Bespalova, Natalia B; Churkina, Tatiana D; Císarová, Ivana; Ezernitskaya, Marina G; Harutyunyan, Syuzanna R; Hrdina, Radim; Kagan, Henri B; Kocovský, Pavel; Kochetkov, Konstantin A; Larionov, Oleg V; Lyssenko, Konstantin A; North, Michael; Polásek, Miroslav; Peregudov, Alexander S; Prisyazhnyuk, Vladimir V; Vyskocil, Stepán

2003-10-22

236

Synthesis and crystal structure determination of some asymmetrical and symmetrical CR-type macrocyclic Schiff base complexes, with a single pendant coordinating 2-aminoethyl arm.  

PubMed

A novel, totally asymmetrical tripodal 2,3',4"-tetraamine ligand, N((CH2)2NH2)((CH2)3NH2)((CH2)4NH2), epb, has been synthesized. In the presence of copper(II) and nickel(II) ions it condenses with 2,6-diacetylpyridine in 1:1 ethanol-water solution, producing some new CR-type complexes with a pendant primary amino group. The X-ray crystal structure of the resulting copper(II) complex, [Cu(3,4(2)-CR)](PF6)2 (1), and two other related complexes, [Cu(2,4(2)-CR)](ClO4)2 (2) and [Cu(3,3(2)-CR)](ClO4)2 (3), are reported. Crystal data: complex 1, monoclinic, P2(1)/n, a = 8.366(3) A, b = 15.549(3) A, c = 20.283(2) A, beta = 98.73(2) degrees, V = 2607.8(11) A3, Z = 4, R1 = 0.0621, wR2 = 0.1615; complex 2, monoclinic, P2(1)/c, a = 7.981(10) A, b = 18.882(3) A, c = 15.185(3) A, beta = 96.40(2) degrees, V = 2275.7(6) A3, Z = 4, R1 = 0.0773, wR2 = 0.1635; complex 3, monoclinic, P2(1)/n, a = 7.8764(10) A, b = 15.361(2) A, c = 19.370(2) A, beta = 100.330(10) degrees, V = 2305.7(5) A3, Z = 4, R1 = 0.0537, wR2 = 0.1397. In all of these, copper atoms are bonded to four nitrogens of a macrocyclic ring and a nitrogen of the pendant arm. The arrangements are slightly distorted square-pyramidal in which the primary amino groups occupy apical positions and have the longest Cu-N distances. For all isomers, copper(II) ions are somewhat above the plane of the imino-pyridine system of the macrocylic ring in the direction of the pendant coordinated primary amino group. PMID:11153507

Keypour, H; Salehzadeh, S; Pritchard, R G; Parish, R V

2000-12-11

237

Synthesis, structure, magnetism, and spectroscopic properties of heterobinuclear copper(II)-zinc(II) complexes and their copper(II)-copper(II) analogues in asymmetric ligand environments.  

PubMed

Heterobinuclear copper(II)-zinc(II) complexes and their homobinuclear dicopper(II) counterparts (1-4) of two asymmetric ligands (H2L1 and H2L2), based on 2-aminocyclopent-1-ene-1-dithiocarboxylate, are reported. The ligands are capable of providing both donor set and coordination number asymmetry in tandem. Metal centers in these complexes are connected by a micro-alkoxo and a bridging pyrazolate moiety, as confirmed by X-ray structure analyses of 1, 3, and 4. The Cu(1) site in the dicopper complex (1) is square planar and so are the copper sites in the Cu-Zn complexes 3 and 4. The pentacoordinated Zn sites in the latter complexes have distorted TBP geometry (tau = 0.74), while the corresponding Cu site in 1 has a highly distorted square pyramidal structure (tau = 0.54). The Cu...Zn separations in 3 and 4 are 3.3782 and 3.3403 angstroms, respectively, while the Cu...Cu distance in 1 is 3.3687 angstroms. The dicopper complexes are EPR silent at 77 K, in which the copper(II) centers are coupled by strong antiferromagnetic coupling (J = ca. -290 cm(-1)) as confirmed by variable-temperature (4-300 K) magnetic measurements. These compounds (1 and 2) undergo two one-electron reductions and a single step two-electron oxidation at ca. -0.26, -1.40, and 1.0 V vs Ag/AgCl reference, respectively, as indicated by cyclic and differential pulse voltammetry done at subambient temperatures. EPR spectra of 3 and 4 display axial anisotropy at 77 K with the gperpendicular region being split into multiple lines due to N-superhyperfine coupling (AN = 15.3 x 10(-4) cm(-1)). The observed trend in the spin-Hamiltonian parameters, gparallel > gperpendicular > 2.04 and |Aperpendicular| < |Aparallel| approximately (120-150) x 10(-4) cm(-1), indicates a d(x2-y2)-based ground state with tetragonal site symmetry for the Cu(II) center in these molecules. PMID:15360251

Ghosh, Dipesh; Kundu, Nabanita; Maity, Goutam; Choi, Ki-Young; Caneschi, Andrea; Endo, Akira; Chaudhury, Muktimoy

2004-09-20

238

Determination of the Absolute Stereochemistry of Secondary Alcohols: An Advanced Organic Chemistry Experiment for Undergraduate Students.  

ERIC Educational Resources Information Center

Describes experiments which can be completed in five four-hour laboratory sessions, including two synthesis (alpha-phenylbutyric and alpha-phenylbutyric acid anhydride) and determining the absolute stereochemistry of secondary alcohols using the synthetic products. (JN)

Bandaranayake, Wickramasinghe M.

1980-01-01

239

Asymmetric Synthesis, Structure, and Reactivity of Unexpectedly Stable Spiroepoxy-?-Lactones Including Facile Conversion to Tetronic Acids: Application to (+)-Maculalactone A  

PubMed Central

A novel class of small spirocyclic heterocycles, spiroepoxy-?-lactones (1,4-dioxaspiro[2.3]-hexan-5-ones), is described that exhibit a number of interesting reactivity patterns. These spiroheterocycles, including an optically active series, are readily synthesized by epoxidation of ketene dimers (4-alkylidene-2-oxetanones) available from homo- or heteroketene dimerization. An analysis of bond lengths in these systems by X-ray crystallography and comparison to data for known spirocycles and those determined computationally, suggest that anomeric effects in these systems may be more pronounced due to their rigidity and may contribute to their surprising stability. The synthetic utility of spiroepoxy-?-lactones was explored and one facile rearrangement identified under several conditions provides a 3-step route from acid chlorides to optically active tetronic acids, ubiquitous heterocycles in bioactive natural products. The addition of various nucleophiles to these spirocycles leads primarily to addition at C5 and C2. The utility of an optically active spiroepoxy-?-lactone was demonstrated in the concise, enantioselective synthesis of the anti-fouling agent, (+)-maculalactone A, which proceeds in 5 steps from hydrocinnamoyl chloride by way of a tetronic acid intermediate. PMID:19453152

Duffy, Richard J.; Morris, Kay A.; Vallakati, Ravikrishna; Zhang, Wei; Romo, Daniel

2009-01-01

240

Prediction of multi-target networks of neuroprotective compounds with entropy indices and synthesis, assay, and theoretical study of new asymmetric 1,2-rasagiline carbamates.  

PubMed

In a multi-target complex network, the links (L(ij)) represent the interactions between the drug (d(i)) and the target (t(j)), characterized by different experimental measures (K(i), K(m), IC50, etc.) obtained in pharmacological assays under diverse boundary conditions (c(j)). In this work, we handle Shannon entropy measures for developing a model encompassing a multi-target network of neuroprotective/neurotoxic compounds reported in the CHEMBL database. The model predicts correctly >8300 experimental outcomes with Accuracy, Specificity, and Sensitivity above 80%-90% on training and external validation series. Indeed, the model can calculate different outcomes for >30 experimental measures in >400 different experimental protocolsin relation with >150 molecular and cellular targets on 11 different organisms (including human). Hereafter, we reported by the first time the synthesis, characterization, and experimental assays of a new series of chiral 1,2-rasagiline carbamate derivatives not reported in previous works. The experimental tests included: (1) assay in absence of neurotoxic agents; (2) in the presence of glutamate; and (3) in the presence of H2O2. Lastly, we used the new Assessing Links with Moving Averages (ALMA)-entropy model to predict possible outcomes for the new compounds in a high number of pharmacological tests not carried out experimentally. PMID:25255029

Romero Durán, Francisco J; Alonso, Nerea; Caamaño, Olga; García-Mera, Xerardo; Yañez, Matilde; Prado-Prado, Francisco J; González-Díaz, Humberto

2014-01-01

241

Direct organocatalytic asymmetric heterodomino reactions: the Knoevenagel/Diels-Alder/epimerization sequence for the highly diastereoselective synthesis of symmetrical and nonsymmetrical synthons of benzoannelated centropolyquinanes.  

PubMed

Amino acids and amines have been used to catalyze three component hetero-domino Knoevenagel/Diels-Alder/epimerization reactions of readily available various precursor enones (1a-l), aldehydes (2a-p), and 1,3-indandione (3). The reaction provided excellent yields of highly substituted, symmetrical and nonsymmetrical spiro[cyclohexane-1,2'-indan]-1',3',4-triones (5) in a highly diastereoselective fashion with low to moderate enantioselectivity. The Knoevenagel condensation of arylaldehydes (2a-p) and 1,3-indandione (3) under organocatalysis provided arylidene-1,3-indandiones (17) in very good yields. We demonstrate for the first time amino acid- and amine-catalyzed epimerization reactions of trans-spiranes (6) to cis-spiranes (5). The mechanism of conversion of trans-spiranes (6) to cis-spiranes 5 was shown to proceed through a retro-Michael/Michael reaction rather than deprotonation/reprotonation by isolation of the morpholine enamine intermediate of cis-spirane (22). Prochiral cis-spiranes (5ab) and trans-spiranes (6ab) are excellent starting materials for the synthesis of benzoannelated centropolyquinanes. Under amino acid and amine catalysis, the topologically interesting dispirane 24 was prepared in moderate yields. Organocatalysis with pyrrolidine catalyzed a series of four reactions, namely the Michael/retro-Michael/Diels-Alder/epimerization reaction sequence to furnish cis-spirane 5ab in moderate yield from enone 1a and 1,3-indandione 3. PMID:15373469

Ramachary, D B; Anebouselvy, K; Chowdari, Naidu S; Barbas, Carlos F

2004-09-01

242

Absolute configuration of isoeichlerialactone  

PubMed Central

The title seco-dammarane triterpenoid, C27H42O4 (systematic name: 3-{(3S,3aR,5aR,6S,7S,9aR,9bR)-6,9a,9b-trimethyl-3-[(R)-2-methyl-5-oxotetra­hydro­furan-2-yl]-7-(prop-1-en-2-yl)dodeca­hydro-1H-cyclo­penta­[a]naphthalen-6-yl}propanoic acid), has been isolated for the first time from the seeds of Aglaia forbesii. The mol­ecule has three fused rings and all rings are in trans-fused. The two cyclo­hexane rings are in standard chair conformations and the cyclo­pentane ring adopts an envelope conformation. Its absolute configuration was determined by the refinement of the Flack parameter to 0.26?(17). In the crystal, mol­ecules are linked into chains along [010] by O—H?O hydrogen bonds. PMID:21580698

Fun, Hoong-Kun; Joycharat, Nantiya; Voravuthikunchai, Supayang Piyawan; Chantrapromma, Suchada

2010-01-01

243

The Absolute Relativity Theory  

E-print Network

This paper is a first presentation of a new approach of physics that we propose to refer as the Absolute Relativity Theory (ART) since it refutes the idea of a pre-existing space-time. It includes an algebraic definition of particles, interactions and Lagrangians. It proposed also a purely algebraic explanation of the passing of time phenomenon that leads to see usual Euler-Lagrange equations as the continuous version of the Knizhnik-Zamolodchikov monodromy. The identification of this monodromy with the local ones of the Lorentzian manifolds gives the Einstein equation algebraically explained in a quantized context. A fact that could lead to the unification of physics. By giving an algebraic classification of particles and interactions, the ART also proposes a new branch of physics, namely the Mass Quantification Theory, that provides a general method to calculate the characteristics of particles and interactions. Some examples are provided. The MQT also predicts the existence of as of today not yet observed particles that could be part of the dark matter. By giving a new interpretation of the weak interaction, it also suggests an interpretation of the so-called dark energy.

Jean-Marc Oury; Bruno Heintz

2009-08-18

244

Absolute induction angiometer.  

PubMed

The objective of this method is the continuous recording of vascular diameters and their measurement in absolute terms. This can be accomplished by percutaneously introduced intravascular sensors (IVS) or surgically implanted perivascular sensors (PVS). Both types of sensor are made of bifilar insulated wires forming a bifilar loop. One wire of the bifilar loop acts as a transformer primary inducing an electromotive force (EMF) in the secondary loop wire. The latter EMF is a measure of the vascular diameter. The IVS loop is made of resilient wire and is disposed across a vascular diameter in the central plane of a blood vessel. The sensitivity is such that phasic variations of a few micrometers in the diameter of a major blood vessel (such as the aorta or a coronary artery) can be measured and recorded. The surgically implanted perivascular loop sensor permits observation of vasomotion in a conscious, unrestrained animal. Both IVS and PVS permit observation of coronary vasomotion in the beating heart. Unlike the relative induction angiometer, the present device does not require an extracorporeal magnet. PMID:7362877

Kolin, A

1980-01-01

245

Asymmetric reductive amination.  

PubMed

Asymmetric reductive amination (ARA) affords synthetically valuable chiral amines straightforwardly. This chapter reviews the recent advances made in the area, focusing on ARA by hydrogenation, transfer hydrogenation, organocatalytic reduction, and biocatalytic reduction. PMID:24158548

Wang, Chao; Xiao, Jianliang

2014-01-01

246

Asymmetric hydrogenation of imines.  

PubMed

Homogeneous catalytic asymmetric hydrogenation has evolved into a significantly useful methodology for the preparation of enantiopure compounds. Significant advances in asymmetric hydrogenation of imines have enabled a straightforward and powerful approach to various chiral amines. An overview of the many variants of the chiral transition metal catalysts, illustrations of synthetic applications, and discussions of emerging and future strategies from a mechanistic perspective are presented. PMID:24197774

Li, Wei; Zhang, Xumu

2014-01-01

247

Organocatalytic asymmetric fluorination of ?-chloroaldehydes involving kinetic resolution  

PubMed Central

Summary In a previous study it was shown that the enantioselective ?-fluorination of racemic ?-chloroaldehydes with a chiral organocatalyst yielded the corresponding ?-chloro-?-fluoroaldehydes with high enantioselectivity. It was also revealed that kinetic resolution of the starting aldehydes was involved in this asymmetric fluorination. This paper describes the determination of the absolute stereochemistry of a resulting ?-chloro-?-fluoroaldehyde. Some information about the substrate scope and a possible reaction mechanism are also described which shed more light on the nature of this asymmetric fluorination reaction. PMID:24605153

Okimi, Takuya; Abe, Yoshiyuki; Narayama, Akira; Nakamura, Nami; Iwasa, Seiji

2014-01-01

248

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation  

E-print Network

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation Inauguraldissertation. Parts of this work have been previously published: ,,Proline-Based P,O Ligands/Iridium Complexes in Iridium-Catalyzed Asymmetric Hydrogenation: New Catalysts, Substrates and Applications in Total Synthesis

Amrhein, Valentin

249

Recent progress in asymmetric bifunctional catalysis using multimetallic systems.  

PubMed

The concept of bifunctional catalysis, wherein both partners of a bimolecular reaction are simultaneously activated, is very powerful for designing efficient asymmetric catalysts. Catalytic asymmetric processes are indispensable for producing enantiomerically enriched compounds in modern organic synthesis, providing more economical and environmentally benign results than methods requiring stoichiometric amounts of chiral reagents. Extensive efforts in this field have produced many asymmetric catalysts, and now a number of reactions can be rendered asymmetric. We have focused on the development of asymmetric catalysts that exhibit high activity, selectivity, and broad substrate generality under mild reaction conditions. Asymmetric catalysts based on the concept of bifunctional catalysis have emerged as a particularly effective class, enabling simultaneous activation of multiple reaction components. Compared with conventional catalysts, bifunctional catalysts generally exhibit enhanced catalytic activity and higher levels of stereodifferentiation under milder reaction conditions, attracting much attention as next-generation catalysts for prospective practical applications. In this Account, we describe recent advances in enantioselective catalysis with bifunctional catalysts. Since our identification of heterobimetallic rare earth-alkali metal-BINOL (REMB) complexes, we have developed various types of bifunctional multimetallic catalysts. The REMB catalytic system is effective for catalytic asymmetric Corey-Chaykovsky epoxidation and cyclopropanation. A dinucleating Schiff base has emerged as a suitable multidentate ligand for bimetallic catalysts, promoting catalytic syn-selective nitro-Mannich, anti-selective nitroaldol, and Mannich-type reactions. The sugar-based ligand GluCAPO provides a suitable platform for polymetallic catalysts; structural elucidation revealed that their higher order polymetallic structures are a determining factor for their function in the catalytic asymmetric Strecker reaction. Rational design identified a related ligand, FujiCAPO, which exhibits superior performance in catalytic asymmetric conjugate addition of cyanide to enones and a catalytic asymmetric Diels-Alder-type reaction. The combination of an amide-based ligand with a rare earth metal constitutes a unique catalytic system: the ligand-metal association is in equilibrium because of structural flexibility. These catalytic systems are effective for asymmetric amination of highly coordinative substrate as well as for Mannich-type reaction of alpha-cyanoketones, in which hydrogen bonding cooperatively contributes to substrate activation and stereodifferentiation. Most of the reactions described here generate stereogenic tetrasubstituted carbons or quaternary carbons, noteworthy accomplishments even with modern synthetic methods. Several reactions have been incorporated into the asymmetric synthesis of therapeutics (or their candidate molecules) such as Tamiflu, AS-3201 (ranirestat), GRL-06579A, and ritodrine, illustrating the usefulness of bifunctional asymmetric catalysis. PMID:19435320

Shibasaki, Masakatsu; Kanai, Motomu; Matsunaga, Shigeki; Kumagai, Naoya

2009-08-18

250

Asymmetric Spindle Positioning  

PubMed Central

Summary When a spindle is positioned asymmetrically in a dividing cell, the resulting daughter cells are unequal in size. Asymmetric spindle positioning can be driven by regulated forces that can pull or push a spindle. The physical and molecular mechanisms that can position spindles asymmetrically have been studied in a number of systems, and some themes have begun to emerge from recent research. Recent work in budding yeast has presented a model for how cytoskeletal motors and cortical capture molecules can function in orienting and positioning a spindle. The temporal regulation of microtubule-based pulling forces that move a spindle has been examined in one animal system. Although the spindle positioning force generators have not been identified in most animal systems, the forces have been found to be regulated by both PAR polarity proteins and by G-protein signaling pathways in more than one animal system. PMID:16361093

McCarthy, Erin K.; Goldstein, Bob

2007-01-01

251

Asymmetric ion trap  

DOEpatents

An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity.

Barlow, Stephan E. (Richland, WA); Alexander, Michael L. (Richland, WA); Follansbee, James C. (Pasco, WA)

1997-01-01

252

Dynamic kinetic asymmetric transformations of ?-stereogenic ?-ketoesters by direct aldolization.  

PubMed

Dynamic kinetic asymmetric transformations (DyKAT) of racemic ?-bromo-?-keto esters by direct aldolization of nitromethane and acetone provide access to fully substituted ?-glycolic acid derivatives bearing a ?-stereocenter. The aldol adducts are obtained in excellent yield with high relative and absolute stereocontrol under mild reaction conditions. Mechanistic studies determined that the reactions proceed through a facile catalyst-mediated racemization of the ?-bromo-?-keto esters under a DyKAT Type I manifold. PMID:24222195

Corbett, Michael T; Johnson, Jeffrey S

2014-01-01

253

Absolute configuration of naturally occurring glabridin.  

PubMed

The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-dihydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH-H2O mixture (95:5?v/v) to yield colorless crystals containing one molecule per asymmetric unit (Z' = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantiopurity of any isolated or synthetic glabridin sample. PMID:24192160

Simmler, Charlotte; Fronczek, Frank R; Pauli, Guido F; Santarsiero, Bernard D

2013-11-01

254

Global relative and absolute quantitation in microbial proteomics.  

PubMed

Proteomic studies are designed to yield either qualitative information on proteins (identification, distribution, posttranslational modifications, interactions, structure and function) or quantitative information (abundance, distribution within different localizations, temporal changes in abundance due to synthesis and degradation or both). To this end these studies can draw upon a wide range of qualitative and quantitative gel-based and gel-free techniques. This review summarizes current proteomic workflows for global relative or absolute protein quantitation and their application in microbial physiology. PMID:22445110

Otto, Andreas; Bernhardt, Jörg; Hecker, Michael; Becher, Dörte

2012-06-01

255

Asymmetrically Warped Spacetimes  

Microsoft Academic Search

We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates (``asymmetrically warped'' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause

Csaba Csaki

2001-01-01

256

Absolute instability in a TWT  

NASA Astrophysics Data System (ADS)

There is renewed interest in the traveling wave tube (TWT) because of the recent advances in microwave power module (D. R. Whaley et al., IEEE Trans. Plasma Sci. 26, 912 (1998)) and of the significant growth in satellite communication. A serious threat to the operation of TWT is bandedge oscillation, occurring at the ?-mode of the slow wave circuit. A candidate for bandedge oscillation is the excitation of absolute instability. In this paper, we approximate the circuit mode by a parabola in the dispersion diagram (?-k plane). We use the Briggs-Bers criterion to determine the threshold value of C (C = Pierce parameter) for the onset of absolute instability. The stabilizing effect of a distributed resistive loss, and of velocity detune, is included. The differences in absolute instabilities between fast wave and slow wave devices are discussed.

Lau, Y. Y.; Ang, L. K.

1998-11-01

257

Database applicaton for absolute spectrophotometry  

NASA Astrophysics Data System (ADS)

32-bit database application with multidocument interface for Windows has been developed to calculate absolute energy distributions of observed spectra. The original database contains wavelength calibrated observed spectra which had been already passed through apparatus reductions such as flatfielding, background and apparatus noise subtracting. Absolute energy distributions of observed spectra are defined in unique scale by means of registering them simultaneously with artificial intensity standard. Observations of sequence of spectrophotometric standards are used to define absolute energy of the artificial standard. Observations of spectrophotometric standards are used to define optical extinction in selected moments. FFT algorithm implemented in the application allows performing convolution (deconvolution) spectra with user-defined PSF. The object-oriented interface has been created using facilities of C++ libraries. Client/server model with Windows Socket functionality based on TCP/IP protocol is used to develop the application. It supports Dynamic Data Exchange conversation in server mode and uses Microsoft Exchange communication facilities.

Bochkov, Valery V.; Shumko, Sergiy

2002-12-01

258

Absolute reflectances from reflectometer readings.  

PubMed

Equations have been derived that allow differences in reflectometer readings of the same sample with various reflectometers to be minimized by placing all reflectances on an absolute basis. For pigmented vehicle films the Fresnel reflectances and transmittances at the air-vehicle interface can be calculated for an arbitrary incident angular light distribution. The form of the reflected and transmitted angular distributions can also be calculated. The equations have been used to determine absolute reflectances of titanium dioxide pigmented films from meter readings of two reflectometers-the General Electric Recording and the Colormaster. PMID:20111160

Sullivan, W F

1971-07-01

259

Multipartite asymmetric quantum cloning  

SciTech Connect

We investigate the optimal distribution of quantum information over multipartite systems in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example, if the clones are partitioned into a set of M{sub A} clones with fidelity F{sup A} and another set of M{sub B} clones with fidelity F{sup B}, the trade-off between these fidelities is analyzed, and particular cases of optimal N{yields}M{sub A}+M{sub B} cloning machines are exhibited. We also present an optimal 1{yields}1+1+1 cloning machine, which is an example of a tripartite fully asymmetric cloner. Finally, it is shown how these cloning machines can be optically realized.

Iblisdir, S.; Gisin, N. [GAP-Optique, University of Geneva, 20 rue de l'Ecole-de-Medecine, CH-1211 (Switzerland); Acin, A. [ICFO-Institut de Ciencies Fotoniques, Jordi Girona 29, 08034 Barcelona (Spain); Cerf, N.J. [QUIC, Ecole Polytechnique, CP 165, Universite Libre de Bruxelles, 1050 Brussels (Belgium); Filip, R. [Department of Optics, Palacky University, 17. listopadu 50, 77200 Olomouc (Czech Republic); Fiurasek, J. [QUIC, Ecole Polytechnique, CP 165, Universite Libre de Bruxelles, 1050 Brussels (Belgium); Department of Optics, Palacky University, 17. listopadu 50, 77200 Olomouc (Czech Republic)

2005-10-15

260

Asymmetrical Quantum Cryptographic Algorithm  

E-print Network

A cryptographic algorithm is proposed based on fully quantum mechanical keys and ciphers. Encryption and decryption are carried out via an appropriate measurement process on entangled states as governed by a quantum mechanical, asymmetrical and dynamical public key distribution. The use of public keys leads to a high availability of our scheme, while their quantum nature is shown to ensure unconditional security of the proposed algorithm.

Guihua Zeng; Carlos Saavedra; Christoph H. Keitel

2002-02-04

261

Asymmetric information and economics  

NASA Astrophysics Data System (ADS)

We present an expression of the economic concept of asymmetric information with which it is possible to derive the dynamical laws of an economy. To illustrate the utility of this approach we show how the assumption of optimal information flow leads to a general class of investment strategies including the well-known Q theory of Tobin. Novel consequences of this formalism include a natural definition of market efficiency and an uncertainty principle relating capital stock and investment flow.

Frieden, B. Roy; Hawkins, Raymond J.

2010-01-01

262

Classical Mechanics without Absolute Space  

E-print Network

A relative mechanics with no absolute space is shown to be equivalent to Newtonian mechanics applied in a universe of zero net angular momentum. Closed spaces in General Relativity have no angular momentum and shrivel to one point as the mass-energy contained tends to zero, so obeying Mach's principle on the origin of inertia.

D. Lynden-Bell; J. Katz

1995-10-01

263

Absolute configuration of amphidinin A.  

PubMed

The absolute configurations at six stereogenic centers in amphidinin A (1), a cytotoxic linear polyketide isolated from a symbiotic marine dinoflagellate, Amphidinium sp., were elucidated to be 2R, 4R, 6S, 9R 11R, and 12S by the combination of J-based configuration analysis, modified Mosher's method, and density-functional theory calculations. PMID:24836179

Iwai, Takahiro; Kubota, Takaaki; Kobayashi, Jun'ichi

2014-06-27

264

Absolute transition probabilities of phosphorus.  

NASA Technical Reports Server (NTRS)

Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

Miller, M. H.; Roig, R. A.; Bengtson, R. D.

1971-01-01

265

Absolute Pitch and Planum Temporale  

Microsoft Academic Search

An increased leftward asymmetry of the planum temporale (PT) in absolute-pitch (AP) musicians has been previously reported, with speculation that early exposure to music influences the degree of PT asymmetry. To test this hypothesis and to determine whether a larger left PT or a smaller right PT actually accounts for the increased overall PT asymmetry in AP musicians, anatomical magnetic

Julian Paul Keenan; Ven Thangaraj; Andrea R. Halpern; Gottfried Schlaug

2001-01-01

266

TOLUENE DIOXYGENASE-MEDIATED OXIDATION OF BROMO(METHYLSULFANYL)BENZENES. ABSOLUTE  

E-print Network

sulfone 3 offers unique opportunities for ap- plication in asymmetric synthesis, Fig. 1. Sulfones additions, cycloadditions of the vinyl (dienyl) sulfone, and intramolecular cycloadditions. Both the sulfur stereogenic centers. Diol 2 thus serves as an equivalent for a "prochiral" butadiene. In this paper we report

Hudlicky, Tomas

267

The Absolute Spectrum Polarimeter (ASP)  

NASA Technical Reports Server (NTRS)

The Absolute Spectrum Polarimeter (ASP) is an Explorer-class mission to map the absolute intensity and linear polarization of the cosmic microwave background and diffuse astrophysical foregrounds over the full sky from 30 GHz to 5 THz. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r much greater than 1O(raised to the power of { -3}) and Compton distortion y < 10 (raised to the power of{-6}). We describe the ASP instrument and mission architecture needed to detect the signature of an inflationary epoch in the early universe using only 4 semiconductor bolometers.

Kogut, A. J.

2010-01-01

268

Absolute configurations of monoesters produced by enzyme catalyzed hydrolysis of diethyl 3-hydroxyglutarate  

Microsoft Academic Search

Biocatalytic asymmetrizations of diethyl 3-hydroxyglutarate furnish a route to the enantiomers of ethyl 4-cyano-3-hydroxybutanoate. The enantiopreference of different enzymes has been established by chiral chromatography. Conclusive evidence for absolute configurations has been provided by X-ray crystallographic structure determination of co-crystals of the predominant monoester with (R)-phenylethylamine. The predominant enantiopure monoester produced by ammonolysis of diethyl 3-hydroxyglutarate catalyzed by immobilized lipase

Anders Riise Moen; Bård Helge Hoff; Lars Kristian Hansen; Thorleif Anthonsen; Elisabeth Egholm Jacobsen

2004-01-01

269

Optimal Asymmetric Quantum Cloning  

E-print Network

While the no-cloning theorem, which forbids the perfect copying of quantum states, is well-known as one of the defining features of quantum mechanics, the question of how well the theory allows a state to be cloned is yet to be completely solved. In this paper, rigorous solutions to the problem of M to N asymmetric cloning of qudits are obtained in a number of interesting cases. The central result is the solution to the 1 to N universal asymmetric qudit cloning problem for which the exact trade-off in the fidelities of the clones for every N and d is derived. Analogous results are proven for qubits when M=N-1. We also consider state-dependent 1 to N qubit cloning, providing a general parametrization in terms of a Heisenberg star Hamiltonian. In all instances, we determine the feasibility of implementing the cloning economically, i.e., without an ancilla, and determine the dimension of the ancilla when an economic implementation is not possible.

Alastair Kay; Ravishankar Ramanathan; Dagomir Kaszlikowski

2012-08-28

270

SpinPhox/iridium(I)-catalyzed asymmetric hydrogenation of cyclic ?-alkylidene carbonyl compounds.  

PubMed

Optically active medium-sized cyclic carbonyl compounds bearing an ?-chiral carbon center are of interest in pharmaceutical sciences and asymmetric synthesis. Herein, SpinPhox/Ir(I) catalysts have been demonstrated to be highly enantioselective in the asymmetric hydrogenation of the C?C bonds in the exocyclic ?,?-unsaturated cyclic carbonyls, including a broad range of ?-alkylidene lactams, unsaturated cyclic ketones, and lactones. It is noteworthy that the procedure can be successfully used in the asymmetric hydrogenation of the challenging ?-alkylidenelactam substrates with six- or seven-membered rings, thus affording the corresponding optically active carbonyl compounds with an ?-chiral carbon center in generally excellent enantiomeric excesses (up to 98?%?ee). Synthetic utility of the protocol has also been demonstrated in the asymmetric synthesis of the anti-inflammatory drug loxoprofen and its analogue, as well as biologically important ?-aminocaproic acid derivatives. PMID:24446418

Liu, Xu; Han, Zhaobin; Wang, Zheng; Ding, Kuiling

2014-02-10

271

The Asymmetric Drift of the Thick Disk Population  

E-print Network

We investigate the kinematics of the intermediate population using the photometric and astrometric sample surveys towards two opposite directions (galactic centre and anticentre) at intermediate latitude. A multivariate discriminant analysis (MDA) is used to distinguish the `Thick Disk' from other populations with the help of the Besan\\c con model of population synthesis. The data constrain the asymmetric drift of the intermediate population, which is found to be 40$\\pm$10 km sec$^{-1}$ and does not depend on the galactic radius.

Devendra Ojha; Annie C. Robin; Olivier Bienayme

1994-08-21

272

Absolute calibration of a spherical reference surface for a Fizeau interferometer with the shift-rotation method of iterative algorithm  

NASA Astrophysics Data System (ADS)

We present an absolute testing of a spherical reference surface of a Fizeau interferometer with the method of shift-rotation, which relies on the decomposition of the surface deviation into rotationally asymmetric and symmetric components. With a new procedure to measure the rotationally asymmetric component and an iterative algorithm to calculate the symmetric component, the method can calibrate the spherical reference surface with high accuracy. An experiment is presented to verify the validity of the absolute testing method. The reference surface deviation measured with the absolute testing method agrees well with that of random-ball-averaging testing method; the root mean square of the residual figure between them is ˜0.8 nm.

Song, Weihong; Wu, Fan; Hou, Xi; Wu, Gaofeng; Liu, Bin; Wan, Yongjian

2013-03-01

273

Asymmetrical Ventricular Enlargement in Parkinson's  

E-print Network

Asymmetrical Ventricular Enlargement in Parkinson's Disease Xuemei Huang, MD, PhD,1 * Yueh Z. Lee, Chapel Hill, North Carolina, USA; 3 Department of Medicine (Neurology), Pacific Parkinson's Research, Bethesda, Maryland, USA Abstract: Parkinson's disease (PD) typically manifests with asymmetric motor

Utah, University of

274

Asymmetrically warped R=0 braneworlds  

Microsoft Academic Search

A new family of five dimensional, R=0 braneworlds with asymmetric warp factors is proposed. Beginning with the invariance of the Ricci scalar for the general class of asymmetrically warped spacetimes we, subsequently specialise to the R=0 case. Solutions are obtained by choosing a particular relation (involving a parameter $\\\

Sayan Kar

2002-01-01

275

Expanding the toolbox of asymmetric organocatalysis by continuous-flow process.  

PubMed

Despite all the organic chemistry reaction methodologies already developed for the continuous-flow process, asymmetric synthesis is one that has gained less attention. Since the pioneering work of Barbas and MacMillan, organocatalysis has emerged as the third pillar of asymmetric catalysis. In this review, we present a survey of literature regarding the use of organocatalysis under continuous-flow conditions. PMID:25585518

Finelli, Fernanda G; Miranda, Leandro S M; de Souza, Rodrigo O M A

2015-02-17

276

Asymmetric photoredox transition-metal catalysis activated by visible light  

NASA Astrophysics Data System (ADS)

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-01

277

Annihilating asymmetric dark matter  

NASA Astrophysics Data System (ADS)

The relic abundance of particle and antiparticle dark matter (DM) need not be vastly different in thermal asymmetric dark matter (ADM) models. By considering the effect of a primordial asymmetry on the thermal Boltzmann evolution of coupled DM and anti-DM, we derive the requisite annihilation cross section. This is used in conjunction with cosmic microwave background and Fermi-LAT gamma-ray data to impose a limit on the number density of anti-DM particles surviving thermal freeze-out. When the extended gamma-ray emission from the Galactic Center is reanalyzed in a thermal ADM framework, we find that annihilation into ? leptons prefer anti-DM number densities 1%-4% that of DM while the b -quark channel prefers 50%-100%.

Bell, Nicole F.; Horiuchi, Shunsaku; Shoemaker, Ian M.

2015-01-01

278

Asymmetrically warped spacetimes  

SciTech Connect

We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates ('asymmetrically warped' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause apparent violations of Lorentz invariance and of causality from the brane observer's point of view. An important experimentally verifiable consequence of this is that gravitational waves may travel with a speed different from the speed of light on the brane, and possibly even faster. We find the most general spacetimes of this sort, which are given by certain types of black hole spacetimes characterized by the m a s and the charge of the black hole. We show how to satisfy the junction conditions and analyze the properties of these space-times.

Csaki, C. (Csaba)

2001-01-01

279

Asymmetric inheritance of cytoophidia in Schizosaccharomyces pombe.  

PubMed

A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our time-lapse studies suggest that cytoophidia are dynamic. Once the mother cell divides, the cytoplasmic and nuclear cytoophidia independently partition into one of the two daughter cells. Although the two daughter cells differ from one another morphologically, they possess similar chances of inheriting the cytoplasmic cytoophidium from the mother cell, suggesting that the partition of cytoophidium is a stochastic process. Our findings on asymmetric inheritance of cytoophidia in S. pombe offer an exciting opportunity to study the inheritance of metabolic enzymes in a well-studied model system. PMID:25361577

Zhang, Jing; Hulme, Lydia; Liu, Ji-Long

2014-01-01

280

Mechanochemical organic synthesis.  

PubMed

Recently, mechanical milling using a mixer mill or planetary mill has been fruitfully utilized in organic synthesis under solvent-free conditions. This review article provides a comprehensive overview of various solvent-free mechanochemical organic reactions, including metal-mediated or -catalyzed reactions, condensation reactions, nucleophilic additions, cascade reactions, Diels-Alder reactions, oxidations, reductions, halogenation/aminohalogenation, etc. The ball milling technique has also been applied to the synthesis of calixarenes, rotaxanes and cage compounds, asymmetric synthesis as well as the transformation of biologically active compounds. PMID:23660585

Wang, Guan-Wu

2013-09-21

281

Apparatus for absolute pressure measurement  

NASA Technical Reports Server (NTRS)

An absolute pressure sensor (e.g., the diaphragm of a capacitance manometer) was subjected to a superimposed potential to effectively reduce the mechanical stiffness of the sensor. This substantially increases the sensitivity of the sensor and is particularly useful in vacuum gauges. An oscillating component of the superimposed potential induced vibrations of the sensor. The phase of these vibrations with respect to that of the oscillating component was monitored, and served to initiate an automatic adjustment of the static component of the superimposed potential, so as to bring the sensor into resonance at the frequency of the oscillating component. This establishes a selected sensitivity for the sensor, since a definite relationship exists between resonant frequency and sensitivity.

Hecht, R. (inventor)

1969-01-01

282

Alkaline earth metal catalysts for asymmetric reactions.  

PubMed

The group 2 alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) are among the most common elements on Earth, abundant in both the sea and the Earth's crust. Although they are familiar in our daily lives, their application to organic synthesis has, so far, been limited. Some particularly useful properties of these elements include (i) low electronegativity, (ii) a stable oxidation state of +2, meaning that they can potentially form two covalent bonds with anions, and (iii) the ability to occupy a variety of coordination sites due to their large ionic radius. Furthermore, the alkaline earth metals, found between the group 1 and group 3 elements, show mild but significant Lewis acidity, which can be harnessed to control coordinative molecules via a Lewis acid-base interaction. Taken together, these characteristics make the metals Ca, Sr, and Ba very promising components of highly functionalized acid-base catalysts. In this Account, we describe the development of chiral alkaline earth metal catalysts for asymmetric carbon-carbon bond-forming reactions. Recently prepared chiral alkaline earth metal complexes have shown high diastereo- and enantioselectivities in fundamental and important chemical transformations. We chose chiral bisoxazoline (Box) derivatives bearing a methylene tether as a ligand for chiral modification. These molecules are very useful because they can covalently coordinate to alkaline earth metals in a bidentate fashion through deprotonation of the tether portion. It was found that chiral calcium-Box complexes could successfully promote catalytic asymmetric 1,4-addition and [3 + 2] cycloaddition reactions with high diastereo- and enantioselectivities. Both the calcium-Box complexes and chiral strontium-bis-sulfonamide and chiral barium-BINOLate complexes could catalyze asymmetric 1,4-addition reactions with high enantioselectivities. Furthermore, we designed a calcium-neutral coordinative ligand complex as a new type of chiral alkaline earth metal catalyst. We found that pyridinebisoxazolines (Pybox) worked well: they served as excellent ligands for calcium compounds in 1,4-addition reactions and Mannich reactions. Moreover, they were successful in 1,4-additions in concert with enantioselective protonation, affording the desired products in good to high enantioselectivities. Our results demonstrate that alkaline earth metals are very useful and attractive catalysts in organic synthesis. Moreover, their ubiquity in the environment is a distinct advantage over rare metals for large-scale processes, and their minimal toxicity is beneficial in both handling and disposal. PMID:20979379

Kobayashi, Sh?; Yamashita, Yasuhiro

2011-01-18

283

Extremal asymmetric universal cloning machines  

E-print Network

The trade-offs among various output fidelities of asymmetric universal cloning machines are investigated. First we find out all the attainable optimal output fidelities for the 1 to 3 asymmetric universal cloning machine and it turns out that there are two kinds of extremal asymmetric cloning machines which have to cooperate in order to achieve some of the optimal output fidelities. Second we construct a family of extremal cloning machines that includes the universal symmetric cloning machine as well as an asymmetric 1 to $1+N$ cloning machine for qudits with two different output fidelities such that the optimal trade-off between the measurement disturbance and state estimation is attained in the limit of infinite $N$.

Jiang, Mingming

2012-01-01

284

Extremal asymmetric universal cloning machines  

E-print Network

The trade-offs among various output fidelities of asymmetric universal cloning machines are investigated. First we find out all the attainable optimal output fidelities for the 1 to 3 asymmetric universal cloning machine and it turns out that there are two kinds of extremal asymmetric cloning machines which have to cooperate in order to achieve some of the optimal output fidelities. Second we construct a family of extremal cloning machines that includes the universal symmetric cloning machine as well as an asymmetric 1 to $1+N$ cloning machine for qudits with two different output fidelities such that the optimal trade-off between the measurement disturbance and state estimation is attained in the limit of infinite $N$.

Mingming Jiang; Sixia Yu

2012-02-08

285

Near threshold absolute TDCS: first results  

NASA Astrophysics Data System (ADS)

A new method, and first results for an impact energy 2 eV above the threshold of ionisation of helium, are presented for the measurement of absolute triple differential cross sections (TDCS) in a crossed beam experiment. The method is based upon measurement of beam/target overlap densities using known absolute total ionisation cross sections and of detection efficiencies using known absolute double differential cross sections (DDCS). For the present work the necessary absolute DDCS for 1 eV electrons had also to be measured. Results are presented for several different coplanar kinematics and are compared with recent DWBA calculations.

Rösel, T.; Schlemmer, P.; Röder, J.; Frost, L.; Jung, K.; Ehrhardt, H.

1992-12-01

286

Synthesis and Suzuki-Miyaura Cross-Coupling of Enantioenriched Secondary Potassium ?-Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to ?,?-Unsaturated Carbonyl Compounds  

PubMed Central

Enantioenriched potassium ?-trifluoroboratoamides have been synthesized via an asymmetric, copper-catalyzed 1,4-addition of tetrahydroxydiboron (BBA) and tetrakis(dimethylamino)diboron to ?,?-unsaturated amides. These dibora reagents provide access to the desired organotrifluoroborates using effective and atom economical sources of boron. The copper-catalyzed ?-boration is extended to ?,?-unsaturated ketones and esters. Desired potassium organotrifluoroborates are synthesized with yields up to 92% and enantiomeric ratios up to 98:2. The enantioenriched potassium ?-trifluoroboratoamides are successfully cross-coupled with an array of aryl and heteroaryl chlorides in high yield with complete stereochemical fidelity as the transmetalation proceeds through an SE2 mechanism via an open transition state. PMID:24741373

Wisniewski, Steven R.; Hosseini-Sarvari, Mona

2014-01-01

287

Nonracemic synthesis of GK-GKRP disruptor AMG-3969.  

PubMed

A nonracemic synthesis of the glucokinase-glucokinase regulatory protein disruptor AMG-3969 (5) is reported. Key features of the synthetic approach are an asymmetric synthesis of the 2-alkynyl piperazine core via a base-promoted isomerization and a revised approach to the synthesis of the aminopyridinesulfonamide with an improved safety profile. PMID:24678849

Bourbeau, Matthew P; Ashton, Kate S; Yan, Jie; St Jean, David J

2014-04-18

288

Nonequilibrium equalities in absolutely irreversible processes  

NASA Astrophysics Data System (ADS)

We generalize nonequilibrium integral equalities to situations involving absolutely irreversible processes for which the forward-path probability vanishes and the entropy production diverges, rendering conventional integral fluctuation theorems inapplicable. We identify the mathematical origins of absolute irreversibility as the singularity of probability measure. We demonstrate the validity of the obtained equalities for several models.

Murashita, Yûto; Funo, Ken; Ueda, Masahito

2014-10-01

289

Absolute optical metrology : nanometers to kilometers  

NASA Technical Reports Server (NTRS)

We provide and overview of the developments in the field of high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.

Dubovitsky, Serge; Lay, O. P.; Peters, R. D.; Liebe, C. C.

2005-01-01

290

Investigating Absolute Value: A Real World Application  

ERIC Educational Resources Information Center

Making connections between various representations is important in mathematics. In this article, the authors discuss the numeric, algebraic, and graphical representations of sums of absolute values of linear functions. The initial explanations are accessible to all students who have experience graphing and who understand that absolute value simply…

Kidd, Margaret; Pagni, David

2009-01-01

291

Enantioselective synthesis of 12-amino alkylidenecyclopentenone prostaglandins.  

PubMed

An enantioselective synthesis of new 12-amino alkylidenecyclopentenone prostaglandins is reported. The key step of the synthesis involved a [3.3] sigmatropic rearrangement of an asymmetric allylic cyanate to elaborate an asymmetric 5-amino-1,6-diene which was further transformed into cyclopentenone by successive ring-closing metathesis reaction catalyzed by the Grubbs reagent and one-pot oxidation. A palladium-catalyzed cross-coupling reaction on a 5-iodo-1,5-diene allowed the synthesis of prostanoids with variable Rw side chains. These new compounds exhibit high cytotoxic activities. PMID:12076134

Roulland, Emmanuel; Monneret, Claude; Florent, Jean-Claude; Bennejean, Caroline; Renard, Pierre; Léonce, Stéphane

2002-06-28

292

Chiral (Acyclic Diaminocarbene)Gold(I)-Catalyzed Dynamic Kinetic Asymmetric Transformation of Propargyl Esters  

PubMed Central

A highly enantioselective transformation catalyzed by chiral (acyclic diaminocarbene)gold(I) complexes is reported. The enantioselective synthesis of 2-substituted chromenyl pivalates from racemic phenol-substituted propargyl pivalates was developed. Rearrangement of the substrates in the presence of cationic gold gave allene intermediates, whose cyclization resulted in formation of enantioenriched product through a dynamic kinetic asymmetric transformation. PMID:21797265

Wang, Yi-Ming; Kuzniewski, Christian N.; Rauniyar, Vivek; Hoong, Christina; Toste, F. Dean

2013-01-01

293

A Biomimetic Route for the Construction of the [4+2] and [3+2] Core Skeletons of the Dimeric Pyrrole-Imidazole Alkaloids and the Asymmetric Synthesis of Ageliferins  

PubMed Central

The pyrrole-imidazole alkaloids have fascinated chemists for decades because of their unique structures. The high nitrogen and halogen contents and the densely functionalized skeletons make their laboratory synthesis challenging. We describe herein an oxidative method for accessing the core skeletons of two classes of pyrrole-imidazole dimers. This synthetic strategy was inspired by the putative biosynthesis pathways and its development was facilitated by computational studies. Using this method, we have successfully prepared ageliferin, bromoageliferin, and dibromoageliferin in their natural enantiomeric form. PMID:23072663

Wang, Xiao; Wang, Xiaolei; Tan, Xianghui; Lu, Jianming; Cormier, Kevin W.; Ma, Zhiqiang

2012-01-01

294

Absolute pitch twin study and segregation analysis.  

PubMed

Absolute pitch is a rare pitch-naming ability with unknown etiology. Some scientists maintain that its manifestation depends solely on environmental factors, while others suggest that genetic factors contribute to it. We sought to further investigate the hypothesis that genetic factors support the acquisition of absolute pitch and to better elucidate the inheritance pattern of this trait. To this end, we conducted a twin study and a segregation analysis using data collected from a large population of absolute pitch possessors. The casewise concordance rate of 14 monozygotic twin pairs, 78.6%, was significantly different from that of 31 dizygotic twin pairs, 45.2%, assuming single ascertainment (x(2) = 5.57, 1 df, p = .018), supporting a role for genetics in the development of absolute pitch. Segregation analysis of 1463 families, assuming single ascertainment, produced a segregation ratio p(D) = .089 with SEp(D) = 0.006. Unlike an earlier segregation analysis on a small number of absolute pitch probands from musically educated families, our study indicates that absolute pitch is not inherited in a simple Mendelian fashion. Based on these data, absolute pitch is likely genetically heterogeneous, with environmental, epigenetic, and stochastic factors also perhaps contributing to its genesis. These findings are in agreement with the results of our recent linkage analysis. PMID:21425900

Theusch, Elizabeth; Gitschier, Jane

2011-04-01

295

Asymmetric retinal growth in the adult teleost green sunfish (Lepomis cyanellus).  

PubMed

Previous studies on fish retina have suggested that a curved, non-fused embryonic fissure is associated with, and perhaps caused by, asymmetric growth along the retina's marginal germinal zone (where neurons and Müller glia are added appositionally throughout life). In this report retinal growth was measured directly in adult green sunfish (Lepomis cyanellus), which has a curved, non-fused embryonic fissure. Growth was asymmetric in both small and large fish: ventral and nasal retina grew more than temporal and dorsal retina. This asymmetry was due to different net rates of cellular addition, rather than differential passive expansion. The absolute rates of retinal growth in the centroperipheral direction were roughly exponential functions of fish size--smaller fish grow faster than large fish--but the area of new retina added per unit time did not vary with fish size. Visual implications of asymmetric retinal growth are evaluated. PMID:7718505

Cameron, D A

1995-01-01

296

Recent progress in asymmetric fluorination and trifluoromethylation reactions.  

PubMed

All domains of society are impacted by fluorine chemistry. In particular, fluorine plays a key role in medicinal, pharmaceutical and agrochemical sciences in which the synthesis and evaluation of molecules featuring one or more fluorine atoms is nowadays routine in every new discovery and development program. Since the beginning of this century, enantiopure fluorinated molecules are at the forefront of innovation of the tremendous achievements in fluorine chemistry. This review introduces the reader to the recent progress in asymmetric installation of one fluorine and a trifluoromethyl group via nucleophilic, electrophilic and radical diastereo- and enantioselective reactions. PMID:24484424

Bizet, Vincent; Besset, Tatiana; Ma, Jun-An; Cahard, Dominique

2014-01-01

297

Asymmetric Organocatalysis at the Service of Medicinal Chemistry  

PubMed Central

The application of the most representative and up-to-date examples of homogeneous asymmetric organocatalysis to the synthesis of molecules of interest in medicinal chemistry is reported. The use of different types of organocatalysts operative via noncovalent and covalent interactions is critically reviewed and the possibility of running some of these reactions on large or industrial scale is described. A comparison between the organo- and metal-catalysed methodologies is offered in several cases, thus highlighting the merits and drawbacks of these two complementary approaches to the obtainment of very popular on market drugs or of related key scaffolds. PMID:24971178

2014-01-01

298

A facile stereoselective total synthesis of (R)-rugulactone.  

PubMed

An efficient and novel synthesis of (R)-rugulactone has been achieved employing Sharpless asymmetric epoxidation of allyl alcohols followed by selective hydride reduction of epoxy alcohols and olefin cross metathesis reactions. PMID:24971179

Reddy, B Narasimha; Singh, R P

2014-01-01

299

A Facile Stereoselective Total Synthesis of (R)-Rugulactone  

PubMed Central

An efficient and novel synthesis of (R)-rugulactone has been achieved employing Sharpless asymmetric epoxidation of allyl alcohols followed by selective hydride reduction of epoxy alcohols and olefin cross metathesis reactions. PMID:24971179

Reddy, B. Narasimha; Singh, R. P.

2014-01-01

300

Time delay control of absolute negative mobility and multiple current reversals in an inertial Brownian motor  

NASA Astrophysics Data System (ADS)

The phenomena of absolute negative mobility (ANM) and multiple current reversals (MCR) are investigated numerically in an inertial Brownian motor with time-delayed feedback under the influence of a time-periodic and a constant, biasing driving force. Within tailored parameter regimes, the increasing delay time diminishes the noise-induced ANM and the deterministic ANM while it induces the ANM in a normal transport regime. When an asymmetric parameter is added in the periodic potential, the presence and absence of MCR are controlled by manipulating the delay time.

Du, Lu-Chun; Mei, Dong-Cheng

2011-11-01

301

Measurement of the absolute branching fraction of D0-->K-pi+.  

PubMed

We measure the absolute branching fraction for D(0)-->K(-)pi(+) using partial reconstruction of B(0)-->D(*+)Xl(-)nu(l) decays, in which only the charged lepton and the pion from the decay D(*+)-->D(0)pi(+) are used. Based on a data sample of 230 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D(0)-->K(-)pi(+)) = (4.007+/-0.037+/-0.072)%, where the first uncertainty is statistical and the second is systematic. PMID:18352359

Aubert, B; Bona, M; Boutigny, D; Karyotakis, Y; Lees, J P; Poireau, V; Prudent, X; Tisserand, V; Zghiche, A; Garra Tico, J; Grauges, E; Lopez, L; Palano, A; Eigen, G; Ofte, I; Stugu, B; Sun, L; Abrams, G S; Battaglia, M; Brown, D N; Button-Shafer, J; Cahn, R N; Groysman, Y; Jacobsen, R G; Kadyk, J A; Kerth, L T; Kolomensky, Yu G; Kukartsev, G; Lopes Pegna, D; Lynch, G; Mir, L M; Orimoto, T J; Pripstein, M; Roe, N A; Ronan, M T; Tackmann, K; Wenzel, W A; Del Amo Sanchez, P; Hawkes, C M; Watson, A T; Held, T; Koch, H; Lewandowski, B; Pelizaeus, M; Schroeder, T; Steinke, M; Cottingham, W N; Walker, D; Asgeirsson, D J; Cuhadar-Donszelmann, T; Fulsom, B G; Hearty, C; Knecht, N S; Mattison, T S; McKenna, J A; Khan, A; Saleem, M; Teodorescu, L; Blinov, V E; Bukin, A D; Druzhinin, V P; Golubev, V B; Onuchin, A P; Serednyakov, S I; Skovpen, Yu I; Solodov, E P; Todyshev, K Yu; Bondioli, M; Curry, S; Eschrich, I; Kirkby, D; Lankford, A J; Lund, P; Mandelkern, M; Martin, E C; Stoker, D P; Abachi, S; Buchanan, C; Foulkes, S D; Gary, J W; Liu, F; Long, O; Shen, B C; Zhang, L; Paar, H P; Rahatlou, S; Sharma, V; Berryhill, J W; Campagnari, C; Cunha, A; Dahmes, B; Hong, T M; Kovalskyi, D; Richman, J D; Beck, T W; Eisner, A M; Flacco, C J; Heusch, C A; Kroseberg, J; Lockman, W S; Schalk, T; Schumm, B A; Seiden, A; Williams, D C; Wilson, M G; Winstrom, L O; Chen, E; Cheng, C H; Dvoretskii, A; Fang, F; Hitlin, D G; Narsky, I; Piatenko, T; Porter, F C; Mancinelli, G; Meadows, B T; Mishra, K; Sokoloff, M D; Blanc, F; Bloom, P C; Chen, S; Ford, W T; Hirschauer, J F; Kreisel, A; Nagel, M; Nauenberg, U; Olivas, A; Smith, J G; Ulmer, K A; Wagner, S R; Zhang, J; Gabareen, A M; Soffer, A; Toki, W H; Wilson, R J; Winklmeier, F; Zeng, Q; Altenburg, D D; Feltresi, E; Hauke, A; Jasper, H; Merkel, J; Petzold, A; Spaan, B; Wacker, K; Brandt, T; Klose, V; Lacker, H M; Mader, W F; Nogowski, R; Schubert, J; Schubert, K R; Schwierz, R; Sundermann, J E; Volk, A; Bernard, D; Bonneaud, G R; Latour, E; Lombardo, V; Thiebaux, Ch; Verderi, M; Clark, P J; Gradl, W; Muheim, F; Playfer, S; Robertson, A I; Xie, Y; Andreotti, M; Bettoni, D; Bozzi, C; Calabrese, R; Cecchi, A; Cibinetto, G; Franchini, P; Luppi, E; Negrini, M; Petrella, A; Piemontese, L; Prencipe, E; Santoro, V; Anulli, F; Baldini-Ferroli, R; Calcaterra, A; de Sangro, R; Finocchiaro, G; Pacetti, S; Patteri, P; Peruzzi, I M; Piccolo, M; Rama, M; Zallo, A; Buzzo, A; Contri, R; Lo Vetere, M; Macri, M M; Monge, M R; Passaggio, S; Patrignani, C; Robutti, E; Santroni, A; Tosi, S; Chaisanguanthum, K S; Morii, M; Wu, J; Dubitzky, R S; Marks, J; Schenk, S; Uwer, U; Bard, D J; Dauncey, P D; Flack, R L; Nash, J A; Nikolich, M B; Panduro Vazquez, W; Behera, P K; Chai, X; Charles, M J; Mallik, U; Meyer, N T; Ziegler, V; Cochran, J; Crawley, H B; Dong, L; Eyges, V; Meyer, W T; Prell, S; Rosenberg, E I; Rubin, A E; Gritsan, A V; Guo, Z J; Lae, C K; Denig, A G; Fritsch, M; Schott, G; Arnaud, N; Béquilleux, J; Davier, M; Grosdidier, G; Höcker, A; Lepeltier, V; Le Diberder, F; Lutz, A M; Pruvot, S; Rodier, S; Roudeau, P; Schune, M H; Serrano, J; Sordini, V; Stocchi, A; Wang, W F; Wormser, G; Lange, D J; Wright, D M; Chavez, C A; Forster, I J; Fry, J R; Gabathuler, E; Gamet, R; Hutchcroft, D E; Payne, D J; Schofield, K C; Touramanis, C; Bevan, A J; George, K A; Di Lodovico, F; Menges, W; Sacco, R; Cowan, G; Flaecher, H U; Hopkins, D A; Jackson, P S; McMahon, T R; Salvatore, F; Wren, A C; Brown, D N; Davis, C L; Allison, J; Barlow, N R; Barlow, R J; Chia, Y M; Edgar, C L; Lafferty, G D; West, T J; Yi, J I; Anderson, J; Chen, C; Jawahery, A; Roberts, D A; Simi, G; Tuggle, J M; Blaylock, G; Dallapiccola, C; Hertzbach, S S; Li, X; Moore, T B; Salvati, E; Saremi, S; Cowan, R; Fisher, P H; Sciolla, G; Sekula, S J; Spitznagel, M; Taylor, F; Yamamoto, R K; McLachlin, S E; Patel, P M; Robertson, S H; Lazzaro, A; Palombo, F; Bauer, J M; Cremaldi, L; Eschenburg, V; Godang, R; Kroeger, R; Sanders, D A; Summers, D J; Zhao, H W; Brunet, S; Côté, D; Simard, M; Taras, P; Viaud, F B; Nicholson, H; De Nardo, G; Fabozzi, F; Lista, L; Monorchio, D; Sciacca, C; Baak, M A; Raven, G; Snoek, H L; Jessop, C P; Losecco, J M; Benelli, G; Corwin, L A; Gan, K K; Honscheid, K; Hufnagel, D; Kagan, H; Kass, R; Morris, J P; Rahimi, A M; Regensburger, J J; Ter-Antonyan, R; Wong, Q K; Blount, N L; Brau, J; Frey, R; Igonkina, O; Kolb, J A; Lu, M; Rahmat, R; Sinev, N B; Strom, D; Strube, J; Torrence, E; Gagliardi, N; Gaz, A; Margoni, M; Morandin, M; Pompili, A; Posocco, M; Rotondo, M; Simonetto, F; Stroili, R; Voci, C; Ben-Haim, E; Briand, H; Chauveau, J; David, P; Del Buono, L; de la Vaissière, Ch; Hamon, O; Hartfiel, B L; Leruste, Ph; Malclès, J; Ocariz, J; Perez, A; Gladney, L; Biasini, M; Covarelli, R; Manoni, E; Angelini, C; Batignani, G; Bettarini, S; Calderini, G; Carpinelli, M; Cenci, R; Cervelli, A; Forti, F

2008-02-01

302

Asymmetric perturbations of signalling oligomers.  

PubMed

This review focuses on rapid and reversible noncovalent interactions for symmetric oligomers of signalling proteins. Symmetry mismatch, transient symmetry breaking and asymmetric perturbations via chemical (ligand binding) and physical (electric or mechanic) effects can initiate the signalling events. Advanced biophysical methods can reveal not only structural symmetries of stable membrane-bound signalling proteins but also asymmetric functional transition states. Relevant techniques amenable to distinguish between symmetric and asymmetric architectures are discussed including those with the capability of capturing low-populated transient conformational states. Typical examples of signalling proteins are overviewed for symmetry breaking in dimers (GPCRs, growth factor receptors, transcription factors); trimers (acid-sensing ion channels); tetramers (voltage-gated cation channels, ionotropic glutamate receptor, CNG and CHN channels); pentameric ligand-gated and mechanosensitive channels; higher order oligomers (gap junction channel, chaperonins, proteasome, virus capsid); as well as primary and secondary transporters. In conclusion, asymmetric perturbations seem to play important functional roles in a broad range of communicating networks. PMID:24650570

Maksay, Gábor; T?ke, Orsolya

2014-05-01

303

Synthesis, characterization and X-ray crystal structures of Vanadium(IV), Cobalt(III), Copper(II) and Zinc(II) complexes derived from an asymmetric bidentate Schiff-base ligand at ambient temperature  

NASA Astrophysics Data System (ADS)

An asymmetric bidentate Schiff-base ligand (HL: 2-((allylimino)methyl)phenol) was prepared from reaction of salicylaldehyde and Allylamine. Vanadium(IV), Cobalt(III), Copper(II) and Zinc(II) complexes, VOL2, CoL3, CuL2 and ZnL2 were synthesized from the reaction of VO(acac)2, CoCl2·6H2O, CuCl2·2H2O and Zn(NO3)2·6H2O with the bidentate Schiff base ligand (HL: 2-allyliminomethyl-phenol) in methanol at ambient temperature. The ligand and its metal complexes were characterized by elemental analysis (CHN), FT-IR spectroscopy. In addition, 1H and 13C NMR techniques were employed for characterization of the ligand (HL) and diamagnetic complex ZnL2. The molecular structures of all complexes were determined by single crystal X-ray diffraction technique. In the ZnL2 and CuL2 complexes, the metal ion is coordinated by two nitrogen and two oxygen atoms from two Schiff base ligands in an approximately square planar trans-[MN2O2] coordination geometry. In the Vanadium(IV) complex, VOL2, the vanadium center in this structure has a distorted tetragonal pyramidal N2O3 coordination sphere and for Cobalt(III) complex, CoL3, the CoIII ion is six coordinated by three bidentate Schiff base ligands in a distorted octahedral environment.

Khorshidifard, Mahsa; Amiri Rudbari, Hadi; Kazemi-Delikani, Zahra; Mirkhani, Valiollah; Azadbakht, Reza

2015-02-01

304

Efficient synthesis of pyrenylalanine.  

PubMed

An efficient synthesis of L-3-(1'-pyrenyl)alanine (Pya), a highly fluorescent amino acid, is described. The amino acid was obtained by the classical asymmetric hydrogenation of chiral 1-acetyl-3-pyrenemethylidene-6-methyl-piperazine-2,5-dione. In the proposed improved procedure mild conditions of the synthesis were applied and the final product--N-tertbutoxycarbonyl-pyrenylalanine--was obtained in good yield. Pyrenylalanine, due to its interesting photophysical properties, can be applied as a fluorescent probe in numerous biochemical and conformational studies. PMID:11764407

Szyma?ska, A; Wiczk, W; Lankiewicz, L

2001-01-01

305

Absolute colorimetric characterization of a DSLR camera  

NASA Astrophysics Data System (ADS)

A simple but effective technique for absolute colorimetric camera characterization is proposed. It offers a large dynamic range requiring just a single, off-the-shelf target and a commonly available controllable light source for the characterization. The characterization task is broken down in two modules, respectively devoted to absolute luminance estimation and to colorimetric characterization matrix estimation. The characterized camera can be effectively used as a tele-colorimeter, giving an absolute estimation of the XYZ data in cd=m2. The user is only required to vary the f - number of the camera lens or the exposure time t, to better exploit the sensor dynamic range. The estimated absolute tristimulus values closely match the values measured by a professional spectro-radiometer.

Guarnera, Giuseppe Claudio; Bianco, Simone; Schettini, Raimondo

2014-03-01

306

Absolute, high-resolution optical position encoder  

NASA Astrophysics Data System (ADS)

Modern computer-controlled manufacturing machinery requires the absolute and highly accurate measurement of the linear position. Such an absolute, optical linear position encoder is described here. It is based on the transilluminance of a glass scale with an inexpensive light-emitting diode. The scale has two code tracks, one based on a pseudo-random binary sequence for the coarse determination of position and another periodic code for accurate fine-position measurement. A single-lens telecentric optical system images the code tracks in a mechanically insensitive way onto a custom photodetector. This special detector IC is capable of determining the components of the (complex) Fourier transform for the spatial frequency of the periodic code. The absolute optical position encoder shows a resolution of 10 nm andan absolute accuracy of better than 100 nm over short distances, verified with a commercial laser interferometer.

Engelhardt, Kai; Seitz, Peter

1996-01-01

307

Absolute, high-resolution optical position encoder.  

PubMed

Modern computer-controlled manufacturing machinery requires the absolute and highly accurate measurement of the linear position. Such an absolute, optical linear position encoder is described here. It is based on the transilluminance of a glass scale with an inexpensive light-emitting diode. The scale has two code tracks, one based on a pseudo-random binary sequence for the coarse determination of position and another periodic code for accurate fine-position measurement. A single-lens telecentric optical system images the code tracks in a mechanically insensitive way onto a custom photodetector. This special detector IC is capable of determining the components of the (complex) Fourier transform for the spatial frequency of the periodic code. The absolute optical position encoder shows a resolution of 10 nm and an absolute accuracy of better than 100 nm over short distances, verified with a commercial laser interferometer. PMID:21069000

Engelhardt, K; Seitz, P

1996-01-01

308

Magnifying absolute instruments for optically homogeneous regions  

SciTech Connect

We propose a class of magnifying absolute optical instruments with a positive isotropic refractive index. They create magnified stigmatic images, either virtual or real, of optically homogeneous three-dimensional spatial regions within geometrical optics.

Tyc, Tomas [Institute of Theoretical Physics and Astrophysics, Masaryk University, Kotlarska 2, CZ-61 137 Brno (Czech Republic)

2011-09-15

309

Absolute Continuous Bivariate Generalized Exponential Distribution  

E-print Network

Absolute Continuous Bivariate Generalized Exponential Distribution Debasis Kundu and Rameshwar D. Gupta Abstract Generalized exponential distribution has been used quite effectively to model posi- tively skewed lifetime data as an alternative to the well known Weibull or gamma distributions

Kundu, Debasis

310

Emission trading with absolute and intensity caps  

E-print Network

The Kyoto Protocol introduced emission trading to help reduce the cost of compliances for the Annex B countries that have absolute caps. However, we need to expand the emission trading to cover developing countries in order ...

Song, Jaemin

2005-01-01

311

Organocatalytic sequential one-pot double cascade asymmetric synthesis of Wieland-Miescher ketone analogues from a Knoevenagel/hydrogenation/Robinson annulation sequence: scope and applications of organocatalytic biomimetic reductions.  

PubMed

A practical and novel organocatalytic chemo- and enantioselective process for the cascade synthesis of highly substituted 2-alkyl-cyclohexane-1,3-diones and Wieland-Miescher (W-M) ketone analogs is presented via reductive alkylation as a key step. First time, we developed the one-step alkylation of dimedone and 1,3-cyclohexanedione with aldehydes and Hantzsch ester through an organocatalytic reductive alkylation strategy. Direct combination of l-proline-catalyzed cascade Knoevenagel/hydrogenation and cascade Robinson annulation of CH acids (dimedone and 1,3-cyclohexanedione), aldehydes, Hantzsch ester, and methyl vinyl ketone furnished the highly functionalized W-M ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products show a direct application in pharmaceutical chemistry. PMID:17552564

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2007-07-01

312

The absolute magnitudes of Type IA supernovae  

Microsoft Academic Search

Absolute magnitudes in the B, V, and I bands are derived for nine well-observed Type Ia supernovae, using host galaxy distances estimated via the surface brightness fluctuations or Tully-Fisher methods. These data indicate that there is a significant intrinsic dispersion in the absolute magnitudes at maximum light of Type Ia supernovae, amounting to +\\/- 0.8 mag in B, +\\/- 0.6

M. M. Phillips

1993-01-01

313

Absolute and relative quantification of RNA modifications via biosynthetic isotopomers.  

PubMed

In the resurging field of RNA modifications, quantification is a bottleneck blocking many exciting avenues. With currently over 150 known nucleoside alterations, detection and quantification methods must encompass multiple modifications for a comprehensive profile. LC-MS/MS approaches offer a perspective for comprehensive parallel quantification of all the various modifications found in total RNA of a given organism. By feeding (13)C-glucose as sole carbon source, we have generated a stable isotope-labeled internal standard (SIL-IS) for bacterial RNA, which facilitates relative comparison of all modifications. While conventional SIL-IS approaches require the chemical synthesis of single modifications in weighable quantities, this SIL-IS consists of a nucleoside mixture covering all detectable RNA modifications of Escherichia coli, yet in small and initially unknown quantities. For absolute in addition to relative quantification, those quantities were determined by a combination of external calibration and sample spiking of the biosynthetic SIL-IS. For each nucleoside, we thus obtained a very robust relative response factor, which permits direct conversion of the MS signal to absolute amounts of substance. The application of the validated SIL-IS allowed highly precise quantification with standard deviations<2% during a 12-week period, and a linear dynamic range that was extended by two orders of magnitude. PMID:25129236

Kellner, Stefanie; Ochel, Antonia; Thüring, Kathrin; Spenkuch, Felix; Neumann, Jennifer; Sharma, Sunny; Entian, Karl-Dieter; Schneider, Dirk; Helm, Mark

2015-01-01

314

Jasminum flexile flower absolute from India--a detailed comparison with three other jasmine absolutes.  

PubMed

Jasminum flexile flower absolute from the south of India and the corresponding vacuum headspace (VHS) sample of the absolute were analyzed using GC and GC-MS. Three other commercially available Indian jasmine absolutes from the species: J. sambac, J. officinale subsp. grandiflorum, and J. auriculatum and the respective VHS samples were used for comparison purposes. One hundred and twenty-one compounds were characterized in J. flexile flower absolute, with methyl linolate, benzyl salicylate, benzyl benzoate, (2E,6E)-farnesol, and benzyl acetate as the main constituents. A detailed olfactory evaluation was also performed. PMID:19831037

Braun, Norbert A; Kohlenberg, Birgit; Sim, Sherina; Meier, Manfred; Hammerschmidt, Franz-Josef

2009-09-01

315

Enantioselective Synthesis of SNAP-7941  

PubMed Central

An enantioselective synthesis of SNAP-7941, a potent melanin concentrating hormone receptor antagonist, was achieved using two organocatalytic methods. The first method utilized to synthesize the enantioenriched dihydropyrimidone core was the Cinchona alkaloid-catalyzed Mannich reaction of ?-keto esters to acyl imines and the second was chiral phosphoric acid-catalyzed Biginelli reaction. Completion of the synthesis was accomplished via selective urea formation at the N3 position of the dihydropyrimidone with the 3-(4-phenylpiperidin-1-yl)propyl amine side chain fragment. The synthesis of SNAP-7921 highlights the utility of asymmetric organocatalytic methods in the construction of an important class of chiral heterocycles. PMID:18767801

Goss, Jennifer M.; Schaus, Scott E.

2009-01-01

316

Asymmetric diffusion in heterogeneous media  

NASA Astrophysics Data System (ADS)

Diffusion in heterogeneous media (i.e., layers with discontinuous values of the diffusivity parameter) is found in different situations, including geology, catalyst, physiology and separation processes. This work considers an array of rectangular layers of different diffusivity as a simple model for studying diffusivity in heterogeneous media. Random walk simulations adapted for transport across interfaces between different materials are used for showing that heterogeneous media exhibit asymmetric transport in the sense that the diffusive flux depends of the transport direction. It is shown that Brownian particles run preferentially along the direction of decreasing diffusivity. An uphill diffusion effect is found when particles move from high to low diffusivity layers. In terms of Fick’s modeling, asymmetric transport is explained from the presence of a jump in the particle density at layer interfaces.

Alvarez-Ramirez, J.; Dagdug, L.; Meraz, M.

2014-02-01

317

Dividend Policy under Asymmetric Information  

Microsoft Academic Search

ABSTRACT We extend the standard finance model of the firm's dividend\\/investment\\/financing decisions by allowing the firm's managers,to know,more than outside investors about the true state of the firm's current earnings. The extension endogenizes the dividend (and financing) announcement,effects amply documented,in recent research. But once trading of shares is admitted to the model along with asymmetric information, the familiar Fisherian criterion

Merton H. Miller; Kevin Rock

1985-01-01

318

Asymmetric fingerprinting for larger collusions  

Microsoft Academic Search

. Fingerprinting schemes deter people from illegallyredistributing digital data by enabling the original merchant ofthe data to identify the original buyer of a redistributed copy.So-called traitor-tracing schemes have the same goal for keysused to decrypt information that is broadcast in encryptedform. Recently, asymmetric fingerprinting and traitor-tracingschemes were introduced. Here, only the buyer knows thefingerprinted copy after a sale, and if

Birgit Pfitzmann; Michael Waidner

1997-01-01

319

Asymmetric gold nanoparticle reduction into polydimethylsiloxane thin films  

NASA Astrophysics Data System (ADS)

Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log10-scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

Dunklin, Jeremy R.; Forcherio, Gregory T.; Berry, Keith R.; Roper, D. Keith

2014-09-01

320

New absolute magnitude calibrations for detached binaries  

NASA Astrophysics Data System (ADS)

Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% (??/??0.15). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: -0.18<(B-V)0<0.91, -1.6absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit.

Bilir, S.; Ak, T.; Soydugan, E.; Soydugan, F.; Yaz, E.; Filiz Ak, N.; Eker, Z.; Demircan, O.; Helvaci, M.

2008-10-01

321

New absolute magnitude calibrations for detached binaries  

E-print Network

Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% ($\\sigma_{\\pi}/\\pi\\leq0.15$). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: $-0.18<(B-V)_{0}<0.91$, $-1.6absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit.

S. Bilir; T. Ak; E. Soydugan; F. Soydugan; E. Yaz; N. Filiz Ak; Z. Eker; O. Demircan; M. Helvaci

2008-06-07

322

Asymmetric Wettability Directs Leidenfrost Droplets  

SciTech Connect

Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

Agapov, Rebecca L [ORNL] [ORNL; Boreyko, Jonathan B [ORNL] [ORNL; Briggs, Dayrl P [ORNL] [ORNL; Srijanto, Bernadeta R [ORNL] [ORNL; Retterer, Scott T [ORNL] [ORNL; Collier, Pat [ORNL] [ORNL; Lavrik, Nickolay V [ORNL] [ORNL

2014-01-01

323

Total synthesis of (+/-)-pentacycloanammoxic acid.  

PubMed

The first total synthesis of (+/-)-pentacycloanammoxic acid/methyl ester (1), an unusual naturally occurring fatty acid from Candidatus Brocadia anammoxidans, has been accomplished by the sequence of reactions shown in Scheme 1. The C20-structure of 1 was assembled with stereocontrol from three building blocks: cyclooctatetraene, 2-cyclopentenone, and 7-bromoheptanoic acid. The synthesis of 1 confirms the proposed structure of 1. The mode of biosynthesis and absolute configuration have yet to be clarified. PMID:15571387

Mascitti, Vincent; Corey, E J

2004-12-01

324

Absolute Zero: Community Education Outreach Guide  

NSDL National Science Digital Library

This guide provides curricular resources for study of the history and science of the quest for ever colder temperature. Designed for teachers and informal educators of middle school students. this guide offers hands-on demonstrations, questions to encourage student participation, suggestions for class activities, and ways to encourage students to continue studying the science. Topics include low-temperature physics and the impact of technologies such as air conditioning, refrigeration and liquefied gases. This material is related to a two-part public broadcasting special, Absolute Zero, produced by Meridian Productions and Windfall Films. Absolute Zero is underwritten by the National Science Foundation and the Alfred P. Sloan Foundation and is based largely on Tom Shachtmanâs acclaimed book, Absolute Zero and the Conquest of Cold.

2008-09-18

325

Precise Measurement of the Absolute Fluorescence Yield  

SciTech Connect

We present preliminary results of the absolute yield of fluorescence emission in atmospheric gases. Measurements were performed at the Fermilab Test Beam Facility with a variety of beam particles and gases. Absolute calibration of the fluorescence yield to 5% level was achieved by comparison with two known light sources - the Cherenkov light emitted by the beam particles, and a calibrated nitrogen laser. The uncertainty of the energy scale of current Ultra-High Energy Cosmic Rays experiments will be significantly improved by the AIRFLY measurement.

Ave, M.; Daumiller, K.; Keilhauer, B.; Klages, H.; Salamida, F.; Smida, R. [Karlsruhe Institute of Technology, IK, Postfach 6980, D - 76021 Karlsruhe (Germany); Bohacova, M.; Nozka, L.; Palatka, M.; Ridky, J.; Schovanek, P. [Institute of Physics of the Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Praha 8 (Czech Republic); Di Carlo, P.; Iarlori, M.; Petrera, S.; Rizi, V. [Dipartimento di Fisica dell'Universita de l'Aquila and INFN, Via Vetoio, I-67010 Coppito, Aquila (Italy); Di Giulio, C.; Verzi, V. [Dipartimento di Fisica dell'Universita di Roma Tor Vergata and Sezione INFN, Via della Ricerca Scientifica, I-00133 Roma (Italy); San Luis, P. Facal; Monasor, M.; Privitera, P. [University of Chicago, Enrico Fermi Institute and Kavli Institute for Cosmological Physics, 5640 S. Ellis Ave., Chicago, IL 60637 (United States)

2011-09-22

326

New absolute magnitude calibrations for detached binaries  

E-print Network

Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% ($\\sigma_{\\pi}/\\pi\\leq0.15$). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: $-0.18<(B-V)_{0}<0.91$, $-1.6

Bilir, S; Soydugan, E; Soydugan, F; Yaz, E; Ak, N Filiz; Eker, Z; Demircan, O; Helvaci, M

2008-01-01

327

Absolute rate theories of epigenetic stability  

Microsoft Academic Search

Spontaneous switching events in most characterized genetic switches are rare, resulting in extremely stable epigenetic properties. We show how simple arguments lead to theories of the rate of such events much like the absolute rate theory of chemical reactions corrected by a transmission factor. Both the probability of the rare cellular states that allow epigenetic escape and the transmission factor

Aleksandra M. Walczak; José N. Onuchic; Peter G. Wolynes

2005-01-01

328

High-accuracy absolute distance metrology Proefschrift  

E-print Network

High-accuracy absolute distance metrology Proefschrift ter verkrijging van de graad van doctor aan and controls the formation with high accuracy is an essential component to enable the science measurement with high accuracy. For Darwin, the required accuracy would be 70 micrometers over a distance of up to 250

329

Absolute partial photoionization cross sections of ozone.  

SciTech Connect

Despite the current concerns about ozone, absolute partial photoionization cross sections for this molecule in the vacuum ultraviolet (valence) region have been unavailable. By eclectic re-evaluation of old/new data and plausible assumptions, such cross sections have been assembled to fill this void.

Berkowitz, J.; Chemistry

2008-04-01

330

An Absolute Electrometer for the Physics Laboratory  

ERIC Educational Resources Information Center

A low-cost, easy-to-use absolute electrometer is presented: two thin metallic plates and an electronic balance, usually available in a laboratory, are used. We report on the very good performance of the device that allows precise measurements of the force acting between two charged plates. (Contains 5 footnotes, 2 tables, and 6 figures.)

Straulino, S.; Cartacci, A.

2009-01-01

331

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications  

PubMed Central

Bridged bicyclic sulfide 1 was originally found to provide high levels of asymmetric induction in sulfur ylide-mediated epoxidations. This sulfide possesses chirality in the [2.2.1] thioether moiety and the [2.2.1] camphor-derived carbocyclic moiety. To determine whether the optimal sulfide had been used, a diastereomer of sulfide 1 in which the stereochemistry of the [2.2.1] carbocycle was reversed (sulfide 5) was prepared and studied as an epoxidation catalyst. This diastereomer gave considerably lower levels of asymmetric induction than the original sulfide 1. From computational and x-ray studies it was found that sulfide 5 gave rise to a more hindered ylide, which reacted more reversibly with aldehydes leading to lower enantioselectivity. Conditions that reduced reversibility were also tested and high enantioselectivities were returned for sulfide 5 (similar to sulfide 1). The implications for the synthesis of chiral sulfides for asymmetric epoxidations are discussed. PMID:15034181

Aggarwal, Varinder K.; Charmant, Jonathan; Dudin, Leo; Porcelloni, Marina; Richardson, Jeffery

2004-01-01

332

LG tools for asymmetric wargaming  

NASA Astrophysics Data System (ADS)

Asymmetric operations represent conflict where one of the sides would apply military power to influence the political and civil environment, to facilitate diplomacy, and to interrupt specified illegal activities. This is a special type of conflict where the participants do not initiate full-scale war. Instead, the sides may be engaged in a limited open conflict or one or several sides may covertly engage another side using unconventional or less conventional methods of engagement. They may include peace operations, combating terrorism, counterdrug operations, arms control, support of insurgencies or counterinsurgencies, show of force. An asymmetric conflict can be represented as several concurrent interlinked games of various kinds: military, transportation, economic, political, etc. Thus, various actions of peace violators, terrorists, drug traffickers, etc., can be expressed via moves in different interlinked games. LG tools allow us to fully capture the specificity of asymmetric conflicts employing the major LG concept of hypergame. Hypergame allows modeling concurrent interlinked processes taking place in geographically remote locations at different levels of resolution and time scale. For example, it allows us to model an antiterrorist operation taking place simultaneously in a number of countries around the globe and involving wide range of entities from individuals to combat units to governments. Additionally, LG allows us to model all sides of the conflict at their level of sophistication. Intelligent stakeholders are represented by means of LG generated intelligent strategies. TO generate those strategies, in addition to its own mathematical intelligence, the LG algorithm may incorporate the intelligence of the top-level experts in the respective problem domains. LG models the individual differences between intelligent stakeholders. The LG tools make it possible to incorporate most of the known traits of a stakeholder, i.e., real personalities involved in the conflict with their specific individual style.

Stilman, Boris; Yakhnis, Alex; Yakhnis, Vladimir

2002-07-01

333

Reynolds number effects on supersonic asymmetrical flows over a cone at high angle of attack  

NASA Technical Reports Server (NTRS)

The supersonic viscous flow over a 5-degree half-angle cone at an angle of attack of four times the cone half-angle is studied computationally using both the conical and the three-dimensional Navier-Stokes equations. The numerical solutions were obtained with an implicit, upwind-biased algorithm. Asymmetrical flowfields of the absolute-instability type are found using the conical-flow equations which agree with published results. However, the absolute instabilities of the originally symmetric flow found with the conical equations do not occur in the three-dimensional simulations, although spurious asymmetric three-dimensional flows for symmetric bodies arise if the grid resolution is insufficient in the nose region. The asymmetric flows computed with the three-dimensional equations are convective instabilities and are possible if the local Reynolds number exceeds a critical value and a fixed geometric asymmetry is imposed. A continuous range of asymmetries can be developed, depending on the size of the disturbance and the Reynolds number. As the Reynolds number is increased, the asymmetries demonstrate a bistable behavior at levels of side force consistent with those predicted using the conical equations. Below a certain critical Reynolds number, any flow asymmetries arising from a geometrical asymmetry are damped with increasing distance downstream from the geometrical asymmetry.

Thomas, J. L.

1991-01-01

334

Catalysis for total synthesis Prof. Dr Alois FRSTNER  

E-print Network

#12;Catalysis for total synthesis Prof. Dr Alois F�RSTNER Director, Max-Planck-Institut für are privileged substrates in gold- and platinum catalysis. Recent mechanistic studies in this field and the development of asymmetric variants will be discussed. Selected applications to the total synthesis

Halazonetis, Thanos

335

Target-directed synthesis of antibacterial drug candidate GSK966587.  

PubMed

An efficient enantioselective total synthesis of the potent antibiotic GSK966587 was accomplished. Highlights of the synthesis include two innovative Heck reactions, a highly selective zincate base directed ortho-metalation, Sharpless asymmetric epoxidation, and a fully convergent final step fragment coupling. PMID:20670007

Voight, Eric A; Yin, Hao; Downing, Susan V; Calad, Stacie A; Matsuhashi, Hayao; Giordano, Ilaria; Hennessy, Alan J; Goodman, Richard M; Wood, Jeffery L

2010-08-01

336

Asymmetric hydroxylative phenol dearomatization promoted by chiral binaphthylic and biphenylic iodanes.  

PubMed

The long-standing quest for chiral hypervalent organoiodine compounds (i.e., iodanes) as metal-free reagents for asymmetric synthesis continues. Although remarkable progress has recently been made in organoiodine-catalyzed reactions using a terminal oxidant in stoichiometric amounts, there is still a significant need for "flaskable" chiral iodane reagents. Herein, we describe the synthesis of new iodobinaphthyls and iodobiphenyls, their successful and selective DMDO-mediated oxidation into either ?(3)- or ?(5)-iodanes, and the evaluation of their capacity to promote asymmetric hydroxylative phenol dearomatization (HPD) reactions. Most notably, a C2-symmetrical biphenylic ?(5)-iodane promoted the HPD-induced conversion of the monoterpene thymol into the corresponding ortho-quinol-based [4+2] cyclodimer (i.e., bis(thymol)) with enantiomeric excesses of up to 94%. PMID:25047148

Bosset, Cyril; Coffinier, Romain; Peixoto, Philippe A; El Assal, Mourad; Miqueu, Karinne; Sotiropoulos, Jean-Marc; Pouységu, Laurent; Quideau, Stéphane

2014-09-01

337

Geometry-induced asymmetric diffusion  

E-print Network

Past work has shown that ions can pass through a membrane more readily in one direction than the other. We demonstrate here in a model and an experiment that for a mixture of small and large particles such asymmetric diffusion can arise solely from an asymmetry in the geometry of the pores of the membrane. Our deterministic simulation considers a two-dimensional gas of elastic disks of two sizes diffusing through a membrane, and our laboratory experiment examines the diffusion of glass beads of two sizes through a metal membrane. In both experiment and simulation, the membrane is permeable only to the smaller particles, and the asymmetric pores lead to an asymmetry in the diffusion rates of these particles. The presence of even a small percentage of large particles can clog a membrane, preventing passage of the small particles in one direction while permitting free flow of the small particles in the other direction. The purely geometric kinetic constraints may play a role in common biological contexts such as membrane ion channels.

Robert S. Shaw; Norman Packard; Matthias Schröter; Harry L. Swinney

2007-04-28

338

Scatterometry measurement of asymmetric gratings  

NASA Astrophysics Data System (ADS)

Scatterometry has been used extensively for the characterization of critical dimensions (CD) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. So far the majority of applications are for symmetric gratings. In most cases devices are designed to be symmetric although errors could occur during fabrication process and result in undesired asymmetry. The problem with conventional optical scatterometry techniques lies in the lack of capability to distinguish between left and right asymmetries. In this work we investigate the possibility of measuring grating asymmetry using Mueller matrix spectroscopic ellipsometry (MM-SE). A patterned hard disk prepared by nano-imprint technique is used for the study. The relief image on the disk sometimes has asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. The undesired tilting resist profile causes difficulties to the downstream processes or even makes them fail. Cross-section SEM reveals that the asymmetrical resist lines are typically tilted towards the outer diameter direction. The simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration method. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes, such as lithography and etch processing, for which symmetric structures are desired.

Li, Jie; Hwu, Justin J.; Liu, Yongdong; Rabello, Silvio; Liu, Zhuan; Hu, Jiangtao

2009-12-01

339

Active matter on asymmetric substrates  

NASA Astrophysics Data System (ADS)

For collections of particles in a thermal bath interacting with an asymmetric substrate, it is possible for a ratchet effect to occur where the particles undergo a net dc motion in response to an ac forcing. Ratchet effects have been demonstrated in a variety of systems including colloids as well as magnetic vortices in type-II superconductors. Here we examine the case of active matter or self-driven particles interacting with asymmetric substrates. Active matter systems include self-motile colloidal particles undergoing catalysis, swimming bacteria, artificial swimmers, crawling cells, and motor proteins. We show that a ratchet effect can arise in this type of system even in the absence of ac forcing. The directed motion occurs for certain particle-substrate interaction rules and its magnitude depends on the amount of time the particles spend swimming in one direction before turning and swimming in a new direction. For strictly Brownian particles there is no ratchet effect. If the particles reflect off the barriers or scatter from the barriers according to Snell's law there is no ratchet effect; however, if the particles can align with the barriers or move along the barriers, directed motion arises. We also find that under certain motion rules, particles accumulate along the walls of the container in agreement with experiment. We also examine pattern formation for synchronized particle motion. We discuss possible applications of this system for self-assembly, extracting work, and sorting as well as future directions such as considering collective interactions and flocking models.

Olson Reichhardt, C. J.; Drocco, J.; Mai, T.; Wan, M. B.; Reichhardt, C.

2011-10-01

340

ASYMMETRIC SOLAR POLAR FIELD REVERSALS  

SciTech Connect

The solar polar fields reverse because magnetic flux from decaying sunspots moves toward the poles, with a preponderance of flux from the trailing spots. If there is a strong asymmetry, in the sense that most activity is in the northern hemisphere, then that excess flux will move toward the north pole and reverse that pole first. If there is more activity in the south later on, then that flux will help to reverse the south pole. In this way, two humps in the solar activity and a corresponding difference in the time of reversals develop (in the ideal case). Such a difference was originally noted in the very first observation of polar field reversal just after the maximum of the strongly asymmetric solar cycle 19, when the southern hemisphere was most active before sunspot maximum and the south pole duly reversed first, followed by the northern hemisphere more than a year later, when that hemisphere became most active. Solar cycles since then have had the opposite asymmetry, with the northern hemisphere being most active before solar maximum. We show that polar field reversals for these cycles have all happened in the north first, as expected. This is especially noteworthy for the present solar cycle 24. We suggest that the association of two or more peaks of solar activity when separated by hemispheres with correspondingly different times of polar field reversals is a general feature of the cycle, and that asymmetric polar field reversals are simply a consequence of the asymmetry of solar activity.

Svalgaard, Leif [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)] [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Kamide, Yohsuke, E-mail: leif@leif.org [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi (Japan)] [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi (Japan)

2013-01-20

341

Recent Developments in the Catalytic, Asymmetric Construction of Pyrroloindolines Bearing All-Carbon Quaternary Stereocenters  

PubMed Central

Pyrroloindoline alkaloids constitute a large family of natural products that has inspired the development of an impressive array of new reactions to prepare the key heterocyclic motif. This synopsis will address catalytic, asymmetric reactions developed to synthesize pyrroloindolines bearing C3a all-carbon quaternary stereocenters. The methods described herein include both transition metal-catalyzed and organocatalyzed reactions that have been demonstrated suitable for the synthesis of the pyrroloindoline framework. PMID:24295135

Repka, Lindsay M.; Reisman, Sarah E.

2014-01-01

342

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in renal failure patients  

Microsoft Academic Search

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in renal failure patients.BackgroundNitric oxide (NO) synthesis is inhibited by the ADMA that accumulates in the plasma of patients with renal failure; however, the concentration of SDMA also is enhanced. Therefore, it has been hypothesized that ADMA and SDMA may contribute to hypertension in these patients.MethodsWe measured the concentrations of ADMA,

CHRISTIAN FLECK; ALEXANDER JANZ; FRANK SCHWEITZER; ELKE KARGE; MARKUS SCHWERTFEGER; GÖNTER STEIN

2001-01-01

343

Heterogeneous asymmetric epoxidation of unfunctionalized olefins catalyzed by polymer-bound (salen)manganese complexes  

Microsoft Academic Search

The synthesis of three different polymer-bound chiral Mn-salen complexes (Poly-1, -2a, -2b) is reported, along with their application as recyclable catalysts in heterogeneous asymmetric epoxidation with mCPBA\\/NMO of several unfunctionalized olefins. The introduction of a spacing group between the polymeric chain and the metal centre (Poly-2a and -2b) considerably increased the enantioselectivity of the process.

Filippo Minutolo; Dario Pini; Antonella Petri; Piero Salvadori

1996-01-01

344

Testing for Asymmetric Dynamic Oligopoly Models  

Microsoft Academic Search

In this paper, we specify a theoretical dynamic oligopoly model with regard to asymmetric firms. We then estimate a structural dynamic model of demand and pricing relations for the semiconductor industry. Using quarterly firm-level output and cost data as well as industry prices from 1974 to 1996, we estimate whether market conduct is symmetric or asymmetric, and how different groups

2001-01-01

345

VIBRATIONAL RESONANCE IN AN ASYMMETRIC DUFFING OSCILLATOR  

E-print Network

VIBRATIONAL RESONANCE IN AN ASYMMETRIC DUFFING OSCILLATOR S. JEYAKUMARI, V. CHINNATHAMBI Department of the high-frequency forces at which vibrational resonance occurs. Furthermore, we observe that an additional: Vibrational resonance; asymmetric Duffing oscillator; biperiodic force. 1 #12;I. INTRODUCTION The study

Rey Juan Carlos, Universidad

346

Defect-free ultrahigh flux asymmetric membranes  

DOEpatents

Defect-free, ultrahigh flux integrally-skinned asymmetric membranes having extremely thin surface layers (<0.2 .mu.m) comprised of glassy polymers are disclosed. The membranes are formed by casting an appropriate drope followed by forced convective evaporation of solvent to obtain a dry phase separated asymmetrical structure. The structure is then washed in a precipitation liquid and dried.

Pinnau, Ingo (Austin, TX); Koros, William J. (Austin, TX)

1990-01-01

347

Branching Cells for Asymmetric Event Structures  

E-print Network

Branching Cells for Asymmetric Event Structures Samy Abbes December 2012 Abstract We introduce branching cells for Asymmetric Event Structures. They provide a way to decompose maximal configuration-prefixes. . . . . . . . . . . . . . . . . . . . 9 4 Defining Branching Cells for AES 11 Informal Description of Branching Cells on an Example. . 11

Boyer, Edmond

348

Multipartite asymmetric quantum cloning S. Iblisdir,1  

E-print Network

Multipartite asymmetric quantum cloning S. Iblisdir,1 A. Acín,2 N. J. Cerf,3 R. Filip,4 J. Fiurásek in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example

Cerf, Nicolas

349

Directing cell migration with asymmetric micropatterns  

E-print Network

Directing cell migration with asymmetric micropatterns Xingyu Jiang*, Derek A. Bruzewicz*, Amy P This report shows that the direction of polarization of attached mammalian cells determines the direction constrain individual cells to asymmetric geometries (for example, a teardrop); these geometries polarize

Prentiss, Mara

350

Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach  

PubMed Central

Summary Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques. PMID:23243475

Chauhan, Pankaj

2012-01-01

351

cybersecurity.pnnl.gov Asymmetric Resilient Cybersecurity  

E-print Network

cybersecurity.pnnl.gov Asymmetric Resilient Cybersecurity Cyber attacks are persistent Cyber attack have disastrous consequences on the rest of the system. The Asymmetric Resilient Cybersecurity altering how cybersecurity is implemented today. These capabilities will be driven by and measured by real

352

An absolute measure for a key currency  

NASA Astrophysics Data System (ADS)

It is generally considered that the US dollar and the euro are the key currencies in the world and in Europe, respectively. However, there is no absolute general measure for a key currency. Here, we investigate the 24-hour periodicity of foreign exchange markets using a recurrence plot, and define an absolute measure for a key currency based on the strength of the periodicity. Moreover, we analyze the time evolution of this measure. The results show that the credibility of the US dollar has not decreased significantly since the Lehman shock, when the Lehman Brothers bankrupted and influenced the economic markets, and has increased even relatively better than that of the euro and that of the Japanese yen.

Oya, Shunsuke; Aihara, Kazuyuki; Hirata, Yoshito

353

From Hubble's NGSL to Absolute Fluxes  

NASA Technical Reports Server (NTRS)

Hubble's Next Generation Spectral Library (NGSL) consists of R-l000 spectra of 374 stars of assorted temperature, gravity, and metallicity. Each spectrum covers the wavelength range, 0.18-1.00 microns. The library can be viewed and/or downloaded from the website, http://archive.stsci.edu/prepds/stisngsll. Stars in the NGSL are now being used as absolute flux standards at ground-based observatories. However, the uncertainty in the absolute flux is about 2%, which does not meet the requirements of dark-energy surveys. We are therefore developing an observing procedure that should yield fluxes with uncertainties less than 1 % and will take part in an HST proposal to observe up to 15 stars using this new procedure.

Heap, Sara R.; Lindler, Don

2012-01-01

354

Absolute and relative dosimetry for ELIMED  

NASA Astrophysics Data System (ADS)

The definition of detectors, methods and procedures for the absolute and relative dosimetry of laser-driven proton beams is a crucial step toward the clinical use of this new kind of beams. Hence, one of the ELIMED task, will be the definition of procedures aiming to obtain an absolute dose measure at the end of the transport beamline with an accuracy as close as possible to the one required for clinical applications (i.e. of the order of 5% or less). Relative dosimetry procedures must be established, as well: they are necessary in order to determine and verify the beam dose distributions and to monitor the beam fluence and the energetic spectra during irradiations. Radiochromic films, CR39, Faraday Cup, Secondary Emission Monitor (SEM) and transmission ionization chamber will be considered, designed and studied in order to perform a fully dosimetric characterization of the ELIMED proton beam.

Cirrone, G. A. P.; Cuttone, G.; Candiano, G.; Carpinelli, M.; Leonora, E.; Lo Presti, D.; Musumarra, A.; Pisciotta, P.; Raffaele, L.; Randazzo, N.; Romano, F.; Schillaci, F.; Scuderi, V.; Tramontana, A.; Cirio, R.; Marchetto, F.; Sacchi, R.; Giordanengo, S.; Monaco, V.

2013-07-01

355

Absolute calibration of TFTR helium proportional countersa)  

NASA Astrophysics Data System (ADS)

The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 and 50 ms depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments.

Strachan, J. D.; Barnes, Cris W.; Diesso, M.; Jassby, D.; Johnson, L.; Loughlin, M.; McCauley, S.; Munsat, T.; Roquemore, A. L.

1995-02-01

356

Probing absolute spin polarization at the nanoscale.  

PubMed

Probing absolute values of spin polarization at the nanoscale offers insight into the fundamental mechanisms of spin-dependent transport. Employing the Zeeman splitting in superconducting tips (Meservey-Tedrow-Fulde effect), we introduce a novel spin-polarized scanning tunneling microscopy that combines the probing capability of the absolute values of spin polarization with precise control at the atomic scale. We utilize our novel approach to measure the locally resolved spin polarization of magnetic Co nanoislands on Cu(111). We find that the spin polarization is enhanced by 65% when increasing the width of the tunnel barrier by only 2.3 Å due to the different decay of the electron orbitals into vacuum. PMID:25423049

Eltschka, Matthias; Jäck, Berthold; Assig, Maximilian; Kondrashov, Oleg V; Skvortsov, Mikhail A; Etzkorn, Markus; Ast, Christian R; Kern, Klaus

2014-12-10

357

Absolute and relative dosimetry for ELIMED  

SciTech Connect

The definition of detectors, methods and procedures for the absolute and relative dosimetry of laser-driven proton beams is a crucial step toward the clinical use of this new kind of beams. Hence, one of the ELIMED task, will be the definition of procedures aiming to obtain an absolute dose measure at the end of the transport beamline with an accuracy as close as possible to the one required for clinical applications (i.e. of the order of 5% or less). Relative dosimetry procedures must be established, as well: they are necessary in order to determine and verify the beam dose distributions and to monitor the beam fluence and the energetic spectra during irradiations. Radiochromic films, CR39, Faraday Cup, Secondary Emission Monitor (SEM) and transmission ionization chamber will be considered, designed and studied in order to perform a fully dosimetric characterization of the ELIMED proton beam.

Cirrone, G. A. P.; Schillaci, F.; Scuderi, V. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic); Cuttone, G.; Candiano, G.; Musumarra, A.; Pisciotta, P.; Romano, F. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy); Carpinelli, M. [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy)] [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy); Leonora, E.; Randazzo, N. [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Presti, D. Lo [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Raffaele, L. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Tramontana, A. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Cirio, R.; Sacchi, R.; Monaco, V. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy); Marchetto, F.; Giordanengo, S. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)

2013-07-26

358

Robust control design with real parameter uncertainty using absolute stability theory. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

The purpose of this thesis is to investigate an extension of mu theory for robust control design by considering systems with linear and nonlinear real parameter uncertainties. In the process, explicit connections are made between mixed mu and absolute stability theory. In particular, it is shown that the upper bounds for mixed mu are a generalization of results from absolute stability theory. Both state space and frequency domain criteria are developed for several nonlinearities and stability multipliers using the wealth of literature on absolute stability theory and the concepts of supply rates and storage functions. The state space conditions are expressed in terms of Riccati equations and parameter-dependent Lyapunov functions. For controller synthesis, these stability conditions are used to form an overbound of the H2 performance objective. A geometric interpretation of the equivalent frequency domain criteria in terms of off-axis circles clarifies the important role of the multiplier and shows that both the magnitude and phase of the uncertainty are considered. A numerical algorithm is developed to design robust controllers that minimize the bound on an H2 cost functional and satisfy an analysis test based on the Popov stability multiplier. The controller and multiplier coefficients are optimized simultaneously, which avoids the iteration and curve-fitting procedures required by the D-K procedure of mu synthesis. Several benchmark problems and experiments on the Middeck Active Control Experiment at M.I.T. demonstrate that these controllers achieve good robust performance and guaranteed stability bounds.

How, Jonathan P.; Hall, Steven R.

1993-01-01

359

The absolute bioavailability of caffeine in man  

Microsoft Academic Search

The absolute bioavailability of orally administered caffeine was investigated in 10 healthy adult male volunteers, aged 18.8 to 30.0 years. The subjects were administered a 5 mg\\/kg dose of caffeine as either an aqueous oral solution or an intravenous infusion, on separate occasions about 1 week apart, in a randomized crossover fashion. Plasma samples were collected over the 24-h period

J. Blanchard; S. J. A. Sawers

1983-01-01

360

PROJECTIVE ABSOLUTENESS UNDER SACKS DAISUKE IKEGAMI  

E-print Network

M), to construct the transitive model M[G] of ZFC (called a generic extension). M[G] is the smallest transitive model of ZFC such that M M[G] and G M[G]. Furthermore M[G] is a model on whose properties we-generic filter G over M, is true in M is true in M[G]. If a statement is absolute under some forcing extension

Amsterdam, University of

361

Measurement of absolute thermoelectric power by photoemission  

NASA Astrophysics Data System (ADS)

It is pointed out that a determination of the temperature dependence of the Fermi cutoff in the conduction band of a metal provides a means of measuring the thermal emf of a single metal, as well as the absolute thermoelectric power, without use of a reference substance. The energy of the Fermi cutoff is determined by photoemission. The method is illustrated by a crude determination of the thermal emfs of copper and constantan.

Wertheim, G. K.; Buchanan, D. N. E.

1991-12-01

362

Designing asymmetric multiferroics with strong magnetoelectric coupling  

NASA Astrophysics Data System (ADS)

Multiferroics offer exciting opportunities for electric-field control of magnetism. Single-phase multiferroics suitable for such applications at room temperature need much more study. Here, we propose the concept of an alternative type of multiferroics, namely, the "asymmetric multiferroic." In asymmetric multiferroics, two locally stable ferroelectric states are not symmetrically equivalent, leading to different magnetic properties between these two states. Furthermore, we predict from first principles that a Fe-Cr-Mo superlattice with the LiNbO3-type structure is such an asymmetric multiferroic. The strong ferrimagnetism, high ferroelectric polarization, and significant dependence of the magnetic transition temperature on polarization make this asymmetric multiferroic an ideal candidate for realizing electric-field control of magnetism at room temperature. Our study suggests that the asymmetric multiferroic may provide an alternative playground for voltage control of magnetism and find its applications in spintronics and quantum computing.

Lu, X. Z.; Xiang, H. J.

2014-09-01

363

Measurement of absolute gravity acceleration in Firenze  

NASA Astrophysics Data System (ADS)

This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) ?Gal and (980 492 048.3 ± 3.0) ?Gal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.

de Angelis, M.; Greco, F.; Pistorio, A.; Poli, N.; Prevedelli, M.; Saccorotti, G.; Sorrentino, F.; Tino, G. M.

2011-01-01

364

Asymmetric autocatalysis of pyrimidyl alkanol and its application to the study on the origin of homochirality.  

PubMed

Conspectus Amplification of enantiomeric excess (ee) is a key feature for the chemical evolution of biological homochirality from the origin of chirality. We describe the amplification of ee in the asymmetric autocatalysis of 5-pyrimidyl alkanols in the reaction between diisopropylzinc (i-Pr2Zn) and pyrimidine-5-carbaldehydes. During the reaction, an extremely low ee (ca. 0.00005% ee) can be amplified to >99.5% ee, and therefore, the initial slightly major enantiomer is automultiplied by a factor of ca. 630000, while the initial slightly minor enantiomer is automultiplied by a factor of less than 1000. In addition, pyrimidyl alkanols with various substituents at the 2-position of the pyrimidine ring, 3-quinolyl alkanol, 5-carbamoyl-3-pyridyl alkanol, and large multifunctionalized pyrimidyl alkanols also act as highly efficient asymmetric autocatalysts in the addition of i-Pr2Zn to the corresponding aldehydes. The asymmetric autocatalysis of pyrimidyl alkanol can discriminate the chirality of various compounds. Chiral substances such as alcohols, amino acids, hydrocarbons, metal complexes, and heterogeneous chiral materials can act as chiral triggers for asymmetric autocatalysis to afford pyrimidyl alkanols with the corresponding absolute configuration of the initiator. This recognition ability of chiral compounds is extremely high, and chiral discrimination of a cryptochiral quaternary saturated hydrocarbon was established by applying asymmetric autocatalysis. By using the large amplification effect of the asymmetric autocatalysis, we can link various proposed origins of chirality with highly enantioenriched organic compounds in conjunction with asymmetric autocatalysis. Thus, a statistical fluctuation in ee of racemic compounds can be amplified to high ee by using asymmetric autocatalysis. Enantiomeric imbalance induced by irradiation of circularly polarized light can affect the enantioselectivity of asymmetric autocatalysis. The asymmetric autocatalysis was also triggered by the morphology of inorganic chiral crystals such as quartz, sodium chlorate, and cinnabar. Chiral organic crystals of achiral compounds also act as chiral initiators, and during the study of a crystal of cytosine, enantioselective chiral crystal phase transformation of the cytosine crystal was achieved by removal of the water of crystallization in an achiral monohydrate crystal. Enantioselective C-C bond formation was realized on the surfaces of achiral single crystals based on the oriented prochirality of achiral aldehydes. Furthermore, asymmetric autocatalysis of pyrimidyl alkanols is a highly sensitive reaction that can recognize and amplify the significantly small effect of a chiral compound arising solely from isotope substitution of hydrogen, carbon, and oxygen (D/H, (13)C/(12)C, and (18)O/(16)O). These examples show that asymmetric autocatalysis with an amplification of chirality is a powerful tool for correlating the origin of chirality with highly enantioenriched organic compounds. Asymmetric autocatalysis using two ?-amino alcohols reveals a reversal of enantioselectivity in the addition of i-Pr2Zn to aldehyde and is one approach toward understanding the mechanism of asymmetric dialkylzinc addition, where heteroaggregates act as the catalytic species. PMID:25511374

Soai, Kenso; Kawasaki, Tsuneomi; Matsumoto, Arimasa

2014-12-16

365

Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses  

SciTech Connect

A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200?ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (?), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as ? increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as ? increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.

Diomede, Paola, E-mail: padiomede@gmail.com; Economou, Demetre J., E-mail: economou@uh.edu [Plasma Processing Laboratory, Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004 (United States)

2014-06-21

366

Condensation on Slippery Asymmetric Bumps  

E-print Network

Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena including anti-reflective structures and contact time of impacting droplets, the effect of the detailed bump topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric convex topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared...

Park, Kyoo-Chul; He, Neil; Aizenberg, Joanna

2015-01-01

367

$?$ meson decay on asymmetrical lattices  

E-print Network

We present a lattice QCD calculation of the characteristics of the $\\rho$ meson decay. The study is carried out on spatially asymmetric boxes using nHYP-smeared clover fermions in the quenched approximation. The resonance mass and coupling constant are calculate using the P-wave scattering phaseshifts, of the isospin I=1 two-pion system. We use pion masses m_{\\pi}= 418 MeV and m_{\\pi}=312 MeV. In both cases, the $\\rho$ decay is kinematically feasible. We work on lattice sizes N_z X 24^2 X 48 with lattice spacing a=0.1 fm and N_z=24,30,34,48.

Craig Pelissier; Andrei Alexandru; Frank X. Lee

2011-11-09

368

Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from a Deprotonated -Aminonitrile  

E-print Network

Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from for the preparation of various alkaloids. Here, the preparation of the benzylisoquinolines (+)-laudanidine and (-)-tetrahydropseudoepiberberine using Noyori's asymmetric transfer hydrogenation are described. The dimeric alkaloids (+)-O

Lawson, Catherine L.

369

Total Synthesis of (?)-Normalindine via Addition of Metallated 4-Methyl-3-cyanopyridine to an Enantiopure Sulfinimine  

PubMed Central

A concise total asymmetric synthesis of the tetrahydronaphthridine alkaloid (?)-normalindine has been accomplished via the addition of a laterally metallated 4-methyl-3-cyanopyridine to a sulfinimine (N-sulfinyl imine) as the key step. PMID:17081004

Davis, Franklin A.; Melamed, Jeffrey Y.; Sharik, Steve S.

2008-01-01

370

Scaleable catalytic asymmetric Strecker syntheses of unnatural alpha-amino acids.  

PubMed

Alpha-amino acids are the building blocks of proteins and are widely used as components of medicinally active molecules and chiral catalysts. Efficient chemo-enzymatic methods for the synthesis of enantioenriched alpha-amino acids have been developed, but it is still a challenge to obtain non-natural amino acids. Alkene hydrogenation is broadly useful for the enantioselective catalytic synthesis of many classes of amino acids, but it is not possible to obtain alpha-amino acids bearing aryl or quaternary alkyl alpha-substituents using this method. The Strecker synthesis-the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis-is an especially versatile chemical method for the synthesis of racemic alpha-amino acids. Asymmetric Strecker syntheses using stoichiometric amounts of a chiral reagent have been applied successfully on gram-to-kilogram scales, yielding enantiomerically enriched alpha-amino acids. In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent could provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen limited use on preparative scales (more than a gram). The limited utility of existing catalytic methods may be due to several important factors, including the relatively complex and precious nature of the catalysts and the requisite use of hazardous cyanide sources. Here we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-natural amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. This catalyst is robust, without sensitive functional groups, so it is compatible with aqueous cyanide salts, which are safer and easier to handle than other cyanide sources; this makes the method adaptable to large-scale synthesis. We have used this new method to obtain enantiopure amino acids that are not readily prepared by enzymatic methods or by chemical hydrogenation. PMID:19829379

Zuend, Stephan J; Coughlin, Matthew P; Lalonde, Mathieu P; Jacobsen, Eric N

2009-10-15

371

Determination of the absolute contours of optical flats  

NASA Technical Reports Server (NTRS)

Emersons procedure is used to determine true absolute contours of optical flats. Absolute contours of standard flats are determined and a comparison is then made between standard and unknown flats. Contour differences are determined by deviation of Fizeau fringe.

Primak, W.

1969-01-01

372

Concise Total Synthesis and Stereochemical Revision of all (?)-Trigonoliimines  

PubMed Central

The concise and enantioselective total syntheses of (?)-trigonoliimines A, B, and C are described. Our unified strategy to all three natural products is based on asymmetric oxidation and reorganization of a single bistryptamine, a sequence of transformations with possible biogenetic relevance. We revise the absolute stereochemistry of (?)-trigonoliimines A, B, and C. PMID:21667943

Han, Sunkyu

2012-01-01

373

Synthesis of proposed aglycone of mandelalide A.  

PubMed

A highly convergent synthesis of the proposed mandelalide A aglycone is reported. The cornerstones of the synthetic strategy include the following: E-selective intramolecular Heck cyclization, Masamune-Roush olefination, Stork-Zhao-Wittig olefination, modified Prins cyclization; Sharpless asymmetric dihydroxylation followed by Williamson-type etherification, Julia-Kocienski olefination, Brown crotylation, and Brown allylation reactions. PMID:24738830

Reddy, Karla Mahender; Yamini, Vanipenta; Singarapu, Kiran K; Ghosh, Subhash

2014-05-16

374

Stereoselective Synthesis of Quaternary Proline Analogues  

PubMed Central

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of ?-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton. PMID:19655047

Calaza, M. Isabel

2009-01-01

375

A stereoselective synthesis of (+)-gonyautoxin 3.  

PubMed

An asymmetric synthesis of the paralytic shellfish poison (PSP), (+)-gonyautoxin 3, is described. A unique, Rh-catalyzed amination reaction provides rapid access to the heteratom-rich, tricyclic core of the toxin, which is common to more than 30 related natural products. The completed route should facilitate the preparation of other naturally occurring PSPs and designed analogues thereof. PMID:18759394

Mulcahy, John V; Du Bois, J

2008-09-24

376

Correlated effects of noise on symmetry of an asymmetric bistable system  

NASA Astrophysics Data System (ADS)

The effects of correlation between additive and multiplicative noises on the symmetry of an asymmetric bistable system are investigated. The steady-state probability distribution function of the system was calculated by using analytical and numerical methods. Results indicate that i) for the case of positive correlation between noises, as the correlation strength between additive and multiplicative noises, ?, increases, the symmetry of the system is restored; ii) for the case of negative correlation between noises, as the absolute value of ? increases, the symmetry of the system is destroyed; and iii) the analytic prediction agrees well with the stochastic simulation result.

Li, Chun; Long, Fei; Mei, Dong-Cheng

2015-01-01

377

Asymmetric Methods for the Synthesis of Flavanones, Chromanones, and Azaflavanones  

PubMed Central

Flavanones, chromanones, and related structures are privileged natural products that display a wide variety of biological activities. Although flavanoids are abundant in nature, there are a limited number of available general and efficient synthetic methods for accessing molecules of this class in a stereoselective manner. Their structurally simple architectures belie the difficulties involved in installation and maintenance of the stereogenic configuration at the C2 position, which can be sensitive and can undergo epimerization under mildly acidic, basic, and thermal reaction conditions. This review presents the methods currently used to access these related structures. The synthetic methods include manipulation of the flavone/flavanone core, carbon-carbon bond formation, and carbon–heteroatom bond formation. PMID:22876166

Nibbs, Antoinette E.

2012-01-01

378

Asymmetric synthesis of the azabicyclic core of the Stemona alkaloids.  

PubMed

A general strategy for the construction of the 1-azabicyclo[5.3.0]decane core of Stemona alkaloids is developed. Our diversity-oriented approach exploits 1,3-dipolar cycloaddition of five-membered cyclic nitrones to C(6) olefins, followed by N-O reductive cleavage and azepine closure. The use of various enantiopure pyrroline N-oxides allows for a practical, stereoselective preparation of several putative precursors of different Stemona alkaloids. PMID:15822978

Alibés, Ramon; Blanco, Pilar; Casas, Eva; Closa, Montserrat; de March, Pedro; Figueredo, Marta; Font, Josep; Sanfeliu, Elena; Alvarez-Larena, Angel

2005-04-15

379

Catalytic Asymmetric Synthesis of Hydroxy Enol Ethers: Approach to a  

E-print Network

. Vagelos Laboratories, UniVersity of PennsylVania, Philadelphia, PennsylVania 19104 pwalsh@sas.upenn.edu Received February 7, 2005 ABSTRACT Hydroboration of ethoxy acetylene, transmetalation to zinc, and addition to -Hydroxy Aldehydes ORGANIC LETTERS 2005 Vol. 7, No. 9 1729-1732 10.1021/ol050255n CCC: $30.25 © 2005

Walsh, Patrick J.

380

From Bi-immunity to Absolute Undecidability Laurent Bienvenu  

E-print Network

From Bi-immunity to Absolute Undecidability Laurent Bienvenu , Adam R. Day , Rupert H¨olzl October- pute A on a set of positions of positive upper density. Absolute undecidability is a weakening of bi-immunity. Downey, Jockusch and Schupp [2] asked whether, unlike the case for bi-immunity, there is an absolutely

Paris-Sud XI, Université de

381

Absolute Radiometric Calibration of EUNIS-06  

NASA Technical Reports Server (NTRS)

The Extreme-Ultraviolet Normal-Incidence Spectrometer (EUNIS) is a soundingrocket payload that obtains imaged high-resolution spectra of individual solar features, providing information about the Sun's corona and upper transition region. Shortly after its successful initial flight last year, a complete end-to-end calibration was carried out to determine the instrument's absolute radiometric response over its Longwave bandpass of 300 - 370A. The measurements were done at the Rutherford-Appleton Laboratory (RAL) in England, using the same vacuum facility and EUV radiation source used in the pre-flight calibrations of both SOHO/CDS and Hinode/EIS, as well as in three post-flight calibrations of our SERTS sounding rocket payload, the precursor to EUNIS. The unique radiation source provided by the Physikalisch-Technische Bundesanstalt (PTB) had been calibrated to an absolute accuracy of 7% (l-sigma) at 12 wavelengths covering our bandpass directly against the Berlin electron storage ring BESSY, which is itself a primary radiometric source standard. Scans of the EUNIS aperture were made to determine the instrument's absolute spectral sensitivity to +- 25%, considering all sources of error, and demonstrate that EUNIS-06 was the most sensitive solar E W spectrometer yet flown. The results will be matched against prior calibrations which relied on combining measurements of individual optical components, and on comparisons with theoretically predicted 'insensitive' line ratios. Coordinated observations were made during the EUNIS-06 flight by SOHO/CDS and EIT that will allow re-calibrations of those instruments as well. In addition, future EUNIS flights will provide similar calibration updates for TRACE, Hinode/EIS, and STEREO/SECCHI/EUVI.

Thomas, R. J.; Rabin, D. M.; Kent, B. J.; Paustian, W.

2007-01-01

382

Achieving Climate Change Absolute Accuracy in Orbit  

NASA Technical Reports Server (NTRS)

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Système Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5-50 micron), the spectrum of solar radiation reflected by the Earth and its atmosphere (320-2300 nm), and radio occultation refractivity from which accurate temperature profiles are derived. The mission has the ability to provide new spectral fingerprints of climate change, as well as to provide the first orbiting radiometer with accuracy sufficient to serve as the reference transfer standard for other space sensors, in essence serving as a "NIST [National Institute of Standards and Technology] in orbit." CLARREO will greatly improve the accuracy and relevance of a wide range of space-borne instruments for decadal climate change. Finally, CLARREO has developed new metrics and methods for determining the accuracy requirements of climate observations for a wide range of climate variables and uncertainty sources. These methods should be useful for improving our understanding of observing requirements for most climate change observations.

Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C. O.; Bantges, R.; Best, F.; Bowman, K.; Brindley, H.; Butler, J. J.; Collins, W.; Dykema, J. A.; Doelling, D. R.; Feldman, D. R.; Fox, N.; Huang, X.; Holz, R.; Huang, Y.; Jennings, D.; Jin, Z.; Johnson, D. G.; Jucks, K.; Kato, S.; Kratz, D. P.; Liu, X.; Lukashin, C.; Mannucci, A. J.; Phojanamongkolkij, N.; Roithmayr, C. M.; Sandford, S.; Taylor, P. C.; Xiong, X.

2013-01-01

383

Asymmetric transmission for linearly polarized electromagnetic radiation.  

PubMed

Metamaterials have shown to support the intriguing phenomenon of asymmetric electromagnetic transmission in the opposite propagation directions, for both circular and linear polarizations. In the present article, we propose a criterion on the relationship among the elements of transmission matrix, which allows asymmetrical transmission for linearly polarized electromagnetic radiation only while the reciprocal transmission for circularly one. Asymmetric hybridized metamaterials are shown to satisfy this criterion. The influence from the rotation of the sample around the radiation propagation direction is discussed. A special structure design is proposed, and its characteristics are analyzed by using numerical simulation. PMID:21643086

Kang, Ming; Chen, Jing; Cui, Hai-Xu; Li, Yongnan; Wang, Hui-Tian

2011-04-25

384

Viscous effects in the absolute convective instability of the Batchelor vortex  

NASA Astrophysics Data System (ADS)

The effects of viscosity on the instability properties of the Batchelor vortex are investigated. The characteristics of spatially amplified branches are first documented in the convectively unstable regime for different values of the swirl parameter q and the co-flow parameter a at several Reynolds numbers Re. The absolute convective instability transition curves, determined by the Briggs Bers zero-group velocity criterion, are delineated in the (a, q)-parameter plane as a function of Re. The azimuthal wavenumber m of the critical transitional mode is found to depend on the magnitude of the swirl q and on the jet (a > [minus sign]0.5) or wake (a < [minus sign]0.5) nature of the axial flow. At large Reynolds numbers, the inviscid results of Olendraru et al. (1999) are recovered. As the Reynolds number decreases, the pocket of absolute instability in the (a, q)-plane is found to shrink gradually. At Re = 667; the critical transitional modes for swirling jets are m = [minus sign]2 or m = [minus sign]3 and absolute instability prevails at moderate swirl values even in the absence of counterflow. For higher swirl levels, the bending mode m = [minus sign]1 becomes critical. The results are in good overall agreement with those obtained by Delbende et al. (1998) at the same Reynolds number. However, a bending (m = +1) viscous mode is found to partake in the outer absolute convective instability transition for jets at very low positive levels of swirl. This asymmetric branch is the spatial counterpart of the temporal viscous mode isolated by Khorrami (1991) and Mayer & Powell (1992). At Re = 100, the critical transitional mode for swirling jets is m = [minus sign]2 at moderate and high swirl values and, in order to trigger an absolute instability, a slight counterflow is always required. A bending (m = +1) viscous mode again becomes critical at very low swirl values. For wakes (a < [minus sign]0.5) the critical transitional mode is always found to be the bending mode m = [minus sign]1, whatever the Reynolds number. However, above q = 1.5, near-neutral centre modes are found to define a tongue of weak absolute instability in the (a, q)-plane. Such modes had been analytically predicted by Stewartson & Brown (1985) in a strictly temporal inviscid framework.

Olendraru, C.; Sellier, A.

2002-05-01

385

Absolute calibration of the Auger fluorescence detectors  

SciTech Connect

Absolute calibration of the Pierre Auger Observatory fluorescence detectors uses a light source at the telescope aperture. The technique accounts for the combined effects of all detector components in a single measurement. The calibrated 2.5 m diameter light source fills the aperture, providing uniform illumination to each pixel. The known flux from the light source and the response of the acquisition system give the required calibration for each pixel. In the lab, light source uniformity is studied using CCD images and the intensity is measured relative to NIST-calibrated photodiodes. Overall uncertainties are presently 12%, and are dominated by systematics.

Bauleo, P.; Brack, J.; Garrard, L.; Harton, J.; Knapik, R.; Meyhandan, R.; Rovero, A.C.; /Buenos Aires, IAFE; Tamashiro, A.; Warner, D.

2005-07-01

386

Characterization of the DARA solar absolute radiometer  

NASA Astrophysics Data System (ADS)

The Davos Absolute Radiometer (DARA) prototype is an Electrical Substitution Radiometer (ESR) which has been developed as a successor of the PMO6 type on future space missions and ground based TSI measurements. The DARA implements an improved thermal design of the cavity detector and heat sink assembly to minimize air-vacuum differences and to maximize thermal symmetry of measuring and compensating cavity. The DARA also employs an inverted viewing geometry to reduce internal stray light. We will report on the characterization and calibration experiments which were carried out at PMOD/WRC and LASP (TRF).

Finsterle, W.; Suter, M.; Fehlmann, A.; Kopp, G.

2011-12-01

387

Distances and absolute magnitudes from trigonometric parallaxes  

E-print Network

We first review the current knowledge of Hipparcos systematic and random errors, in particular small-scale correlations. Then, assuming Gaussian parallax errors and using examples from the recent Hipparcos literature, we show how random errors may be misinterpreted as systematic errors, or transformed into systematic errors. Finally we summarise how to get unbiased estimates of absolute magnitudes and distances, using either Bayesian or non-parametrical methods. These methods may be applied to get either mean quantities or individual estimates. In particular, we underline the notion of astrometry-based luminosity, which avoids the truncation biases and allows a full use of Hipparcos samples.

F. Arenou; X. Luri

1998-12-04

388

Absolute Priority for a Vehicle in VANET  

NASA Astrophysics Data System (ADS)

In today's world, traffic jams waste hundreds of hours of our life. This causes many researchers try to resolve the problem with the idea of Intelligent Transportation System. For some applications like a travelling ambulance, it is important to reduce delay even for a second. In this paper, we propose a completely infrastructure-less approach for finding shortest path and controlling traffic light to provide absolute priority for an emergency vehicle. We use the idea of vehicular ad-hoc networking to reduce the imposed travelling time. Then, we simulate our proposed protocol and compare it with a centrally controlled traffic light system.

Shirani, Rostam; Hendessi, Faramarz; Montazeri, Mohammad Ali; Sheikh Zefreh, Mohammad

389

Continuum limit of electrostatic gyrokinetic absolute equilibrium  

SciTech Connect

Electrostatic gyrokinetic absolute equilibria with continuum velocity field are obtained through the partition function and through the Green function of the functional integral. The new results justify and explain the prescription for quantization/discretization or taking the continuum limit of velocity. The mistakes in the Appendix D of our earlier work [J.-Z. Zhu and G. W. Hammett, Phys. Plasmas 17, 122307 (2010)] are explained and corrected. If the lattice spacing for discretizing velocity is big enough, all the invariants could concentrate at the lowest Fourier modes in a negative-temperature state, which might indicate a possible variation of the dual cascade picture in 2D plasma turbulence.

Zhu Jianzhou [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-06-15

390

Absolute method of measuring magnetic susceptibility  

USGS Publications Warehouse

An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacement versus distance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved. ?? 1959 The American Institute of Physics.

Thorpe, A.; Senftle, F.E.

1959-01-01

391

Ammonia synthesis  

Microsoft Academic Search

In a process for producing ammonia in a synthesis loop in which fresh synthesis gas containing hydrogen, nitrogen and, lesser amounts of argon and methane is combined with a hydrogen enriched recycle gas to provide combined synthesis gas, the combined synthesis is introduced to and reacted over ammonia synthesis catalyst under synthesis conditions to provide converted gas containing ammonia, hydrogen,

B. G. Mandelik; J. R. Cassata; P. J. S. Katy; C. P. Van Dijk

1986-01-01

392

Measurement of the Absolute Branching Fraction of D0 to K- pi+  

SciTech Connect

The authors measure the absolute branching fraction for D{sup 0} {yields} K{sup -} {pi}{sup +} using partial reconstruction of {bar B}{sup 0} {yields} D*{sup +}X{ell}{sup -}{bar {nu}}{sub {ell}} decays, in which only the charged lepton and the pion from the decay D*{sup +} {yields} D{sup 0}{pi}{sup +} are used. Based on a data sample of 230 million B{bar B} pairs collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, they obtain {Beta}(D{sup 0} {yields} K{sup -}{pi}{sup +}) = (4.007 {+-} 0.037 {+-} 0.070)%, where the first error is statistical and the second error is systematic.

Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J.P.; Poireau, V.; Prudent, X.; Tisserand, V.; Zghiche, A.; /Annecy, LAPP; Garra Tico, J.; Grauges, E.; /Barcelona U., ECM; Lopez, L.; Palano, A.; /Bari U.; Eigen, G.; Ofte, I.; Stugu, B.; Sun, L.; /Bergen U.; Abrams, G.S.; Battaglia, M.; Brown, D.N.; Button-Shafer, J.; /LBL, Berkeley

2007-04-25

393

Asymmetrical division of Saccharomyces cerevisiae.  

PubMed Central

The unequal division model proposed for budding yeast (L. H. Hartwell and M. W. Unger, J. Cell Biol. 75:422-435, 1977) was tested by bud scar analyses of steady-state exponential batch cultures of Saccharomyces cerevisiae growing at 30 degrees C at 19 different rates, which were obtained by altering the carbon source. The analyses involved counting the number of bud scars, determining the presence or absence of buds on at least 1,000 cells, and independently measuring the doubling times (gamma) by cell number increase. A number of assumptions in the model were tested and found to be in good agreement with the model. Maximum likelihood estimates of daughter cycle time (D), parent cycle time (P), and the budded phase (B) were obtained, and we concluded that asymmetrical division occurred at all growth rates tested (gamma, 75 to 250 min). D, P, and B are all linearly related to gamma, and D, P, and gamma converge to equality (symmetrical division) at gamma = 65 min. Expressions for the genealogical age distribution for asymmetrically dividing yeast cells were derived. The fraction of daughter cells in steady-state populations is e-alpha P, and the fraction of parent cells of age n (where n is the number of buds that a cell has produced) is (e-alpha P)n-1(1-e-alpha P)2, where alpha = IN2/gamma; thus, the distribution changes with growth rate. The frequency of cells with different numbers of bud scars (i.e., different genealogical ages) was determined for all growth rates, and the observed distribution changed with the growth rate in the manner predicted. In this haploid strain new buds formed adjacent to the previous buds in a regular pattern, but at slower growth rates the pattern was more irregular. The median volume of the cells and the volume at start in the cell cycle both increased at faster growth rates. The implications of these findings for the control of the cell cycle are discussed. PMID:6991494

Lord, P G; Wheals, A E

1980-01-01

394

Measurement of the rate of cholesterol synthesis in various organs of the rat in vivo.  

E-print Network

Measurement of the rate of cholesterol synthesis in various organs of the rat in vivo. T. MAGOT F. Summary. A method to measure the absolute values of the rate of cholesterol synthesis in vivo in each organ being corrected for cholesterol transfer. The rate of cholesterol synthesis in the intact

Paris-Sud XI, Université de

395

Ultrahigh-resolution Cartesian absolute optical encoder  

NASA Astrophysics Data System (ADS)

A new optical encoder which measures absolute, true-Cartesian displacement with ultra-high sensitivity and linearity has been developed at NASA"s Goddard Space Flight Center. The device is the two-dimensional analog of recently developed linear and rotary encoders based on optical pattern recognition. In this encoder, a glass scale carrying absolute Cartesian position information travels with the payload in an X-Y motion system. Because the scale comprises the entire measurement coordinate system in a monolithic form, motion control axes can be skew to one another to an arbitrary degree and can exhibit substantial lateral drift with no effect on the correctness of X-Y readout, thus eliminating challenges of orthogonal mounting for motion axes and challenges of mounting independent encoders parallel to the directions of travel for each constituent X and Y axis. Prototype devices with ranges of 30 x 30 mm and 150 x 150 mm with 5 nm and 50 nm resolutions, respectively, have been built in the laboratory. Performance data from the Cartesian encoder in the Point Target Assembly for the optical calibration stimulus for Hubble Space Telescope"s Wide Field Camera 3 are presented.

Leviton, Douglas B.; Kirk, Jeff; Lobsinger, Luke

2003-11-01

396

The absolute threshold of cone vision.  

PubMed

We report measurements of the absolute threshold of cone vision, which has been previously underestimated due to suboptimal conditions or overly strict subjective response criteria. We avoided these limitations by using optimized stimuli and experimental conditions while having subjects respond within a rating scale framework. Small (1' fwhm), brief (34 ms), monochromatic (550 nm) stimuli were foveally presented at multiple intensities in dark-adapted retina for 5 subjects. For comparison, 4 subjects underwent similar testing with rod-optimized stimuli. Cone absolute threshold, that is, the minimum light energy for which subjects were just able to detect a visual stimulus with any response criterion, was 203 ± 38 photons at the cornea, ~0.47 log unit lower than previously reported. Two-alternative forced-choice measurements in a subset of subjects yielded consistent results. Cone thresholds were less responsive to criterion changes than rod thresholds, suggesting a limit to the stimulus information recoverable from the cone mosaic in addition to the limit imposed by Poisson noise. Results were consistent with expectations for detection in the face of stimulus uncertainty. We discuss implications of these findings for modeling the first stages of human cone vision and interpreting psychophysical data acquired with adaptive optics at the spatial scale of the receptor mosaic. PMID:21270115

Koenig, Darren; Hofer, Heidi

2011-01-01

397

Experimental results for absolute cylindrical wavefront testing  

NASA Astrophysics Data System (ADS)

Applications for Cylindrical and near-cylindrical surfaces are ever-increasing. However, fabrication of high quality cylindrical surfaces is limited by the difficulty of accurate and affordable metrology. Absolute testing of such surfaces represents a challenge to the optical testing community as cylindrical reference wavefronts are difficult to produce. In this paper, preliminary results for a new method of absolute testing of cylindrical wavefronts are presented. The method is based on the merging of the random ball test method with the fiber optic reference test. The random ball test assumes a large number of interferograms of a good quality sphere with errors that are statistically distributed such that the average of the errors goes to zero. The fiber optic reference test utilizes a specially processed optical fiber to provide a clean high quality reference wave from an incident line focus from the cylindrical wave under test. By taking measurements at different rotation and translations of the fiber, an analogous procedure can be employed to determine the quality of the converging cylindrical wavefront with high accuracy. This paper presents and discusses the results of recent tests of this method using a null optic formed by a COTS cylindrical lens and a free-form polished corrector element.

Reardon, Patrick J.; Alatawi, Ayshah

2014-09-01

398

Twisted absolute instability in lifted flames  

NASA Astrophysics Data System (ADS)

The theory of resonant modes is extended to finite length systems containing pinch points of complex axial wavenumber k0 and frequency ?0 with arbitrary ?kk0=?2? /?k2. The quantity ?kk0 is shown to be an important indicator of how streamwise boundary conditions modify the local absolute mode at (k0,?0). In particular, when Im(?kk0)>0, the pinch point is twisted, and resonant modes owing to streamwise boundary conditions may then have growth rates greater than that of the unbounded absolute mode. In this case, global instability may occur while the flow is only convectively unstable. The premixing zone between the nozzle and a lifted flame on a variable-density jet is an example of a streamwise-confined system containing a twisted pinch point. For this system, linear stability analysis is employed to locate resonant modes along a solution curve in the complex k and ? planes. The orientation of the solution curve predicts destabilization owing to streamwise confinement as well as increasing global frequency with decreasing lift-off height as observed in previous direct numerical simulations. The theory also suggests that low-frequency fluctuations observed in the simulations may be explained by beating between two resonant modes of slightly differing frequencies.

Nichols, Joseph W.; Chomaz, Jean-Marc; Schmid, Peter J.

2009-01-01

399

Quantum key distribution with asymmetric channel noise  

SciTech Connect

We show that, one may take advantage of the asymmetry of channel noise. With appropriate modifications to the standard protocols, both the key rate and the tolerable total channel noise can be increased if the channel noise is asymmetric.

Wang Xiangbin [Imai Quantum Computation and Information Project, ERATO, JST, Hongo White Building 201, 5-28-3, Hongo, Bunkyo, Tokyo 113-0033 (Japan)

2005-05-15

400

Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov  

E-print Network

Asymmetric Abelian Avalanches and Sandpiles Andrei Gabrielov Mathematical Sciences Institute consider two classes of threshold failure models, Abel- ian avalanches and sandpiles, with the redistribution matrices satisfying nat- ural conditions guaranteeing absence of infinite avalanches. We

Gabrielov, Andrei

401

Asymmetric wave propagation in planar chiral fibers  

E-print Network

We demonstrate the realization of a two-dimensional chiral optical waveguide with an infinite translational symmetry that exhibits asymmetric wave propagation. The low-symmetry geometry of the cross-section that lacks any ...

Shemuly, Dana

402

Asymmetric transmission and optical rotation of a quasi-3D asymmetric metallic structure.  

PubMed

Three-dimensional (3D) asymmetric plasmonic structures possessing asymmetric optical transmission properties have been widely studied. However, these structures have limitations for application due to fabrication techniques. Here, a quasi-3D asymmetric structure built up by a metallic rod-shaped particles layer and a metallic L-shaped holes layer was fabricated by the sputtering and the focused ion beam (FIB) milling. A broadband (1000-1600 nm) asymmetric transmission and optical rotation have been demonstrated experimentally. Numerical calculations show that the coupling between the cavity and particle plasmonic resonances contributes to this effect. PMID:25490485

Wu, Shan; Xu, Su; Zhang, Yi; Wu, Yanning; Jiang, Jianjuan; Wang, Qianjin; Zhang, Xuejin; Zhu, Yongyuan

2014-11-15

403

Transformation of America's Military and Asymmetric War  

Microsoft Academic Search

In the post–Cold War and post–9\\/11 era, the need for broadening the focus of military transformation to include asymmetric warfare capabilities has been given lip service. The U.S. military did not feel the necessity to widen the scope, if not to change the focus, of transformation to include asymmetric warfare until 2003 and 2004. During Operation Iraqi Freedom, the Iraqi

Ehsan Ahrari

2010-01-01

404

Stereoselective synthesis of (+)-loline alkaloid skeleton.  

PubMed

The loline alkaloids present a compact polycyclic pyrrolizidine skeleton and contain a strained five-membered ethereal bridge, structural features that have proven challenging for synthetic chemists to incorporate since the discovery of this natural product family more than 100 years ago. These alkaloids are produced by mutualistic fungal symbionts (endophytes) living on certain species of pasture grasses and protect the host plant from insect herbivory. The asymmetric total synthesis of loline alkaloids is reported and extends our first-generation (racemic) synthesis of this alkaloid family. Key to the synthesis is a diastereoselective tethered aminohydroxylation of a homoallylic carbamate function and a Petasis Borono-Mannich addition. PMID:25611615

Miller, Kelsey E; Wright, Anthony J; Olesen, Margaret K; Hovey, M Todd; Scheerer, Jonathan R

2015-02-01

405

Asymmetric Solar Polar Field Reversals  

NASA Astrophysics Data System (ADS)

The solar polar fields reverse because magnetic flux from decaying sunspots moves towards the poles, with a preponderance of flux from the trailing spots. Let us assume that there is a strong asymmetry in the sense that all activity is in the Northern Hemisphere, then that excess flux will move to the North Pole and reverse that pole, while nothing happens in the South. If later on, there is a lot of activity in the South, then that flux will help reverse the South Pole. In this way, we get two humps in solar activity and a corresponding difference in time of reversals. Such difference was first noted by Babcock in 1959 from the very first observation of polar field reversal just after the maximum of strongly asymmetric solar cycle 19. At that time, the Southern Hemisphere was most active in the beginning of the cycle and the South Pole duly reversed first, followed by the Northern Hemisphere more than a year later. Babcock noted that "For more than a year, the unexpected peculiarity was presented of two poles with the same sign". Solar cycles since then have had the opposite asymmetry, with the Northern Hemisphere being most active early in the cycle. Polar field reversals for these cycles have as expected happened first in the North. This is especially noteworthy for the present solar cycle 24. We suggest that the association of two peaks of solar activity when separated by hemispheres with correspondingly different times of polar field reversals is a general feature of the cycle.

Svalgaard, L.; Kamide, Y.

2012-12-01

406

Asymmetric Bessel-Gauss beams.  

PubMed

We propose a three-parameter family of asymmetric Bessel-Gauss (aBG) beams with integer and fractional orbital angular momentum (OAM). The aBG beams are described by the product of a Gaussian function by the nth-order Bessel function of the first kind of complex argument, having finite energy. The aBG beam's asymmetry degree depends on a real parameter c?0: at c=0, the aBG beam is coincident with a conventional radially symmetric Bessel-Gauss (BG) beam; with increasing c, the aBG beam acquires a semicrescent shape, then becoming elongated along the y axis and shifting along the x axis for c?1. In the initial plane, the intensity distribution of the aBG beams has a countable number of isolated optical nulls on the x axis, which result in optical vortices with unit topological charge and opposite signs on the different sides of the origin. As the aBG beam propagates, the vortex centers undergo a nonuniform rotation with the entire beam about the optical axis (c?1), making a ?/4 turn at the Rayleigh range and another ?/4 turn after traveling the remaining distance. At different values of the c parameter, the optical nulls of the transverse intensity distribution change their position, thus changing the OAM that the beam carries. An isolated optical null on the optical axis generates an optical vortex with topological charge n. A vortex laser beam shaped as a rotating semicrescent has been generated using a spatial light modulator. PMID:25401437

Kotlyar, V V; Kovalev, A A; Skidanov, R V; Soifer, V A

2014-09-01

407

Absolute instability of a viscous hollow jet.  

PubMed

An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail. Asymptotic analyses for low and high Reynolds numbers are provided, showing that old and well-established limiting dispersion relations [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945); S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Dover, New York, 1961)] should be used with caution. In the creeping flow limit, the analysis shows that, if the hollow jet is filled with any finite density and viscosity fluid, a steady jet could be made arbitrarily small (compatible with the continuum hypothesis) if the coflowing liquid moves faster than a critical velocity. PMID:17358457

Gañán-Calvo, Alfonso M

2007-02-01

408

Absolute instability of a viscous hollow jet  

NASA Astrophysics Data System (ADS)

An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail. Asymptotic analyses for low and high Reynolds numbers are provided, showing that old and well-established limiting dispersion relations [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945); S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Dover, New York, 1961)] should be used with caution. In the creeping flow limit, the analysis shows that, if the hollow jet is filled with any finite density and viscosity fluid, a steady jet could be made arbitrarily small (compatible with the continuum hypothesis) if the coflowing liquid moves faster than a critical velocity.

Gañán-Calvo, Alfonso M.

2007-02-01

409

Absolute radiometric calibration of the Thematic Mapper  

NASA Technical Reports Server (NTRS)

Calibration data for the solar reflective bands of the Landsat-5 TM obtained from five in-flight absolute radiometric calibrations from July 1984-November 1985 at White Sands, New Mexico are presented and analyzed. Ground reflectance and atmospheric data were utilized to predict the spectral radiance at the entrance pupil of the TM and the average number of digital counts in each TM band. The calibration of each of the TM solar reflective bands was calculated in terms of average digital counts/unit spectral radiance for each band. It is observed that for the 12 reflectance-based measurements the rms variation from the means as a percentage of the mean is + or - 1.9 percent; for the 11 measurements in the IR bands, it is + or - 3.4 percent; and the rms variation for all 23 measurements is + or - 2.8 percent.

Slater, P. N.; Biggar, S. F.; Holm, R. G.; Jackson, R. D.; Mao, Y.

1986-01-01

410

Absolute beam current monitoring in endstation c  

SciTech Connect

The first few experiments at CEBAF require approximately 1% absolute measurements of beam currents expected to range from 10-25{mu}A. This represents errors of 100-250 nA. The initial complement of beam current monitors are of the non intercepting type. CEBAF accelerator division has provided a stripline monitor and a cavity monitor, and the authors have installed an Unser monitor (parametric current transformer or PCT). After calibrating the Unser monitor with a precision current reference, the authors plan to transfer this calibration using CW beam to the stripline monitors and cavity monitors. It is important that this be done fairly rapidly because while the gain of the Unser monitor is quite stable, the offset may drift on the order of .5{mu}A per hour. A summary of what the authors have learned about the linearity, zero drift, and gain drift of each type of current monitor will be presented.

Bochna, C.

1995-04-01

411

In vivo absorption spectroscopy for absolute measurement  

PubMed Central

In in vivo spectroscopy, there are differences between individual subjects in parameters such as tissue scattering and sample concentration. We propose a method that can provide the absolute value of a particular substance concentration, independent of these individual differences. Thus, it is not necessary to use the typical statistical calibration curve, which assumes an average level of scattering and an averaged concentration over individual subjects. This method is expected to greatly reduce the difficulties encountered during in vivo measurements. As an example, for in vivo absorption spectroscopy, the method was applied to the reflectance measurement in retinal vessels to monitor their oxygen saturation levels. This method was then validated by applying it to the tissue phantom under a variety of absorbance values and scattering efficiencies. PMID:23082298

Furukawa, Hiromitsu; Fukuda, Takashi

2012-01-01

413

Construction of contiguous tetrasubstituted chiral carbon stereocenters via direct catalytic asymmetric aldol and Mannich-type reactions.  

PubMed

Catalytic asymmetric synthesis of unnatural amino acids with vicinal tetrasubstituted chiral carbon stereocenters is described. In the first part, direct catalytic asymmetric aldol reaction of simple non-activated ketone electrophiles with ?-substituted ?-isothiocyanato ester donors was realized. A Mg/Schiff base catalyst promoted the aldol reaction, and ?-amino-?-hydroxy esters were obtained in up to 98% ee and 98:2 d.r. In the second part, the Mg/Schiff base catalyst and a Sr/Schiff base catalyst were utilized for stereodivergent direct asymmetric Mannich-type reaction of ketimines. The Mg/Schiff base catalyst gave syn-?,?-diamino esters, while the Sr/Schiff base catalyst produced anti-?,?-diamino esters in good to high enantioselectivity, up to 97% ee. PMID:21898777

Matsunaga, Shigeki; Yoshino, Tatsuhiko

2011-09-01

414

A sampling theory for asymmetric communities.  

PubMed

We introduce the first analytical model of asymmetric community dynamics to yield Hubbell's neutral theory in the limit of functional equivalence among all species. Our focus centers on an asymmetric extension of Hubbell's local community dynamics, while an analogous extension of Hubbell's metacommunity dynamics is deferred to an appendix. We find that mass-effects may facilitate coexistence in asymmetric local communities and generate unimodal species abundance distributions indistinguishable from those of symmetric communities. Multiple modes, however, only arise from asymmetric processes and provide a strong indication of non-neutral dynamics. Although the exact stationary distributions of fully asymmetric communities must be calculated numerically, we derive approximate sampling distributions for the general case and for nearly neutral communities where symmetry is broken by a single species distinct from all others in ecological fitness and dispersal ability. In the latter case, our approximate distributions are fully normalized, and novel asymptotic expansions of the required hypergeometric functions are provided to make evaluations tractable for large communities. Employing these results in a bayesian analysis may provide a novel statistical test to assess the consistency of species abundance data with the neutral hypothesis. PMID:21182847

Noble, Andrew E; Temme, Nico M; Fagan, William F; Keitt, Timothy H

2011-03-21

415

The asymmetric gait toenail unit sign.  

PubMed

The aim of this investigation was to resolve a diagnostic problem and report toenail unit changes attributable to shoe friction that resemble onychomycosis, but that are fungus-negative, and identify common skeletal causes in patients with an asymmetric walking gait. X-ray and clinical feet inspections were performed to evaluate skeletal components that change normal foot biodynamics. Forty-nine patients, all dermatophyte-negative, were reviewed. All patients were those seen in our private practice who demonstrated skeletal and toenail unit abnormalities such as onycholysis, nail bed keratosis resembling distal subungual onychomycosis, nail plate surface abnormalities, distal toe skin keratosis, a diagnostic nail plate shape, as well as several skeletal abnormalities. The clinical abnormalities of the asymmetric gait syndrome include onycholysis, nail bed keratosis, nail plate surface abnormalities, and a diagnostic nail plate shape. By the patient's history, the skeletal findings that were present worsened with age and, in many patients, they were familial. Onychomycosis does not lead to an asymmetric gait nail problem, asymmetric gait toenail does not favor dermatophyte infection, and not all nail dystrophies are the result of an asymmetric walking gait. PMID:23008938

Zaias, Nardo; Rebell, Gerbert; Casal, German; Appel, Jason

2012-01-01

416

Absolute nuclear material assay using count distribution (LAMBDA) space  

DOEpatents

A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

Prasad, Manoj K. (Pleasanton, CA); Snyderman, Neal J. (Berkeley, CA); Rowland, Mark S. (Alamo, CA)

2012-06-05

417

Advances in transition metal-catalyzed asymmetric hydrogenation of heteroaromatic compounds.  

PubMed

Transition metal-catalyzed asymmetric hydrogenation of heteroaromatic compounds is undoubtedly a straightforward and environmentally friendly method for the synthesis of a wide range of optically active heterocyclic compounds, which are widespread and ubiquitous in naturally occurring and artificial bioactive molecules. Over the past decade, a number of transition metal (Ir, Rh, Ru, and Pd) catalysts bearing chiral phosphorus ligands, amine-tosylamine ligands, and N-heterocyclic carbene ligands have been developed for such challenging transformation. This review will describe the significant contributions concerning the transition metal-catalyzed asymmetric hydrogenation of N-, O-, and S-containing heteroaromatic compounds, with emphasis on the evolution of different chiral ligands, related catalyst immobilization, and mechanism investigations. PMID:24173671

He, Yan-Mei; Song, Feng-Tao; Fan, Qing-Hua

2014-01-01

418

Asymmetric organic-inorganic hybrid membrane formation via block copolymer-nanoparticle co-assembly.  

PubMed

A facile method for forming asymmetric organic-inorganic hybrid membranes for selective separation applications is developed. This approach combines co-assembly of block copolymer (BCP) and inorganic nanoparticles (NPs) with non-solvent induced phase separation. The method is successfully applied to two distinct molar mass BCPs with different fractions of titanium dioxide (TiO2) NPs. The resulting hybrid membranes exhibit structural asymmetry with a thin nanoporous surface layer on top of a macroporous fingerlike support layer. Key parameters that dictate membrane surface morphology include the fraction of inorganics used and the length of time allowed for surface layer development. The resulting membranes exhibit both good selectivity and high permeability (3200 ± 500 Lm(-2) h(-1) bar(-1)). This fast and straightforward synthesis method for asymmetric hybrid membranes provides a new self-assembly platform upon which multifunctional and high-performance organic-inorganic hybrid membranes can be formed. PMID:24102154

Gu, Yibei; Dorin, Rachel M; Wiesner, Ulrich

2013-01-01

419

Catalytic asymmetric aldol reactions in aqueous media--a 5 year update.  

PubMed

Asymmetric reactions in water and in aqueous solutions have become an area of fast growing interest recently. Although for a long time neglected as a medium for organic reactions, water has attracted attention as the most widely distributed solvent in the world. Indeed, water is the solvent used by nature for biological chemistry including aldol reactions being essential for glycolysis, gluconeogenesis and related processes. Consequently, artificial catalysts designed and used for aldol reactions in water can be promising for the synthesis of enantiopure molecules and are also important for the understanding of complex chemistry of life. This tutorial review summarizes recent developments in the area of aqueous asymmetric aldol reactions highlighting two fundamental directions--development of water compatible chiral Lewis acids and amine-based organocatalysts. PMID:24150484

Mlynarski, Jacek; Ba?, Sebastian

2014-01-21

420

Asymmetric Dihydroxylation of Cinnamonitrile to trans-3-[(5S,6R)-5,6-Dihydroxycyclohexa-1,3-dienyl]-acrylonitrile  

E-print Network

]-acrylonitrile using Chlorobenzene Dioxygenase in Escherichia coli (pTEZ30) Selcuk Yildirim,a Josef Zezula,b Tomas purposes. We characterized the cis-dihy- droxylation of cinnamonitrile by chlorobenzene dioxy- genase (CDO: asymmetric synthesis; biocatalysis; bio- transformations; chlorobenzene dioxygenase; dihy- droxylation; scale

Hudlicky, Tomas

421

Asymmetric soft-error resistant memory  

NASA Technical Reports Server (NTRS)

A memory system is provided, of the type that includes an error-correcting circuit that detects and corrects, that more efficiently utilizes the capacity of a memory formed of groups of binary cells whose states can be inadvertently switched by ionizing radiation. Each memory cell has an asymmetric geometry, so that ionizing radiation causes a significantly greater probability of errors in one state than in the opposite state (e.g., an erroneous switch from '1' to '0' is far more likely than a switch from '0' to'1'. An asymmetric error correcting coding circuit can be used with the asymmetric memory cells, which requires fewer bits than an efficient symmetric error correcting code.

Buehler, Martin G. (inventor); Perlman, Marvin (inventor)

1991-01-01

422

Reversal modes in asymmetric Ni nanowires  

NASA Astrophysics Data System (ADS)

We have investigated the evolution of the magnetization reversal mechanism in asymmetric Ni nanowires as a function of their geometry. Circular nanowires are found to reverse their magnetization by the propagation of a vortex domain wall, while in very asymmetric nanowires the reversal is driven by the propagation of a transverse domain wall. The effect of shape asymmetry of the wire on coercivity and remanence is also studied. Angular dependence of the remanence and coercivity is also addressed. Tailoring the magnetization reversal mechanism in asymmetric nanowires can be useful for magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls. Finally, an alternative method to detect the presence of magnetic drops is proposed.

Leighton, B.; Pereira, A.; Escrig, J.

2012-11-01

423

An Apparatus for Absolute Neutron Flux Measurement  

NASA Astrophysics Data System (ADS)

A fully-absorbing neutron detector is being developed to measure the absolute flux (s-1) of a cold neutron beam at the level of 0.1,%. The device will be used to calibrate a neutron flux monitor used in an in-beam neutron lifetime measurement performed at NIST (?n= (886.3 ±3.4) s). The precision of the measurement was limited by the uncertainty in the efficiency of the neutron flux monitor (0.3,%). The flux monitor operates by counting charged particles produced when neutrons impinge on a ^6Li (or ^10B) foil. Its efficiency was calculated from the cross section, the solid angle subtended by the charged particle detectors, and the amount of neutron-absorbing material present on the foil. Successful calibration would reduce the neutron lifetime uncertainty to approximately 0.25,%. In addition, using the measured solid angle and amount of material on the deposit, a new experimental value for the ^6Li or (^10B) capture cross section will be obtained. Details of the apparatus and the measurement technique along with the status of the experiment will be discussed.

Yue, A.; Greene, G.; Dewey, M. S.; Gilliam, D.; Nico, J.; Laptev, A.

2007-10-01

424

Absolute quantum energy inequalities in curved spacetime  

E-print Network

Quantum Energy Inequalities (QEIs) are results which limit the extent to which the smeared renormalised energy density of the quantum field can be negative, when averaged along a timelike curve or over a more general timelike submanifold in spacetime. On globally hyperbolic spacetimes the minimally-coupled massive quantum Klein--Gordon field is known to obey a `difference' QEI that depends on a reference state chosen arbitrarily from the class of Hadamard states. In many spacetimes of interest this bound cannot be evaluated explicitly. In this paper we obtain the first `absolute' QEI for the minimally-coupled massive quantum Klein--Gordon field on four dimensional globally hyperbolic spacetimes; that is, a bound which depends only on the local geometry. The argument is an adaptation of that used to prove the difference QEI and utilises the Sobolev wave-front set to give a complete characterisation of the singularities of the Hadamard series. Moreover, the bound is explicit and can be formulated covariantly under additional (general) conditions. We also generalise our results to incorporate adiabatic states.

Christopher J. Fewster; Calvin J. Smith

2007-02-09

425

Absolute calibration of forces in optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are highly versatile laser traps for neutral microparticles, with fundamental applications in physics and in single molecule cell biology. Force measurements are performed by converting the stiffness response to displacement of trapped transparent microspheres, employed as force transducers. Usually, calibration is indirect, by comparison with fluid drag forces. This can lead to discrepancies by sizable factors. Progress achieved in a program aiming at absolute calibration, conducted over the past 15 years, is briefly reviewed. Here we overcome its last major obstacle, a theoretical overestimation of the peak stiffness, within the most employed range for applications, and we perform experimental validation. The discrepancy is traced to the effect of primary aberrations of the optical system, which are now included in the theory. All required experimental parameters are readily accessible. Astigmatism, the dominant effect, is measured by analyzing reflected images of the focused laser spot, adapting frequently employed video microscopy techniques. Combined with interface spherical aberration, it reveals a previously unknown window of instability for trapping. Comparison with experimental data leads to an overall agreement within error bars, with no fitting, for a broad range of microsphere radii, from the Rayleigh regime to the ray optics one, for different polarizations and trapping heights, including all commonly employed parameter domains. Besides signaling full first-principles theoretical understanding of optical tweezers operation, the results may lead to improved instrument design and control over experiments, as well as to an extended domain of applicability, allowing reliable force measurements, in principle, from femtonewtons to nanonewtons.

Dutra, R. S.; Viana, N. B.; Maia Neto, P. A.; Nussenzveig, H. M.

2014-07-01

426

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules  

PubMed Central

Summary A review of the synthesis of natural products and bioactive compounds adopting phosphonamide anion technology is presented highlighting the utility of phosphonamide reagents in stereocontrolled bond-forming reactions. Methodologies utilizing phosphonamide anions in asymmetric alkylations, Michael additions, olefinations, and cyclopropanations will be summarized, as well as an overview of the synthesis of the employed phosphonamide reagents. PMID:25246946

Focken, Thilo

2014-01-01

427

Asymmetric Position-Based Quantum Cryptography  

E-print Network

A large number of quantum location verification protocols have been proposed. All existing protocols in this field are based on symmetric cryptography where verifiers and the prover use the same secret key. The prover obtains secret key from different verifiers, in pieces through public channels, which may result in security compromise. In this paper, we give a formulism to prove information-theoretic position-based quantum cryptography is possible in asymmetric quantum setting. We propose a quantum location verification protocol based on asymmetric quantum cryptographic where two different keys will be used.

Muhammad Nadeem

2014-03-27

428

Total absorption in asymmetric hyperbolic media  

PubMed Central

Finite-thickness slabs of hyperbolic media with tilted optical axes exhibit asymmetry properties for waves propagating upward and downward with respect to slab interfaces. Under certain conditions, asymmetric hyperbolic media acquire extreme permittivity parameters and the difference between upward and downward propagating waves becomes very large. Furthermore, both waves can be perfectly matched with the free space; such a feature makes possible the development of optically ultra thin perfect absorbers. The proposed approach is unified and allows the use of different -negative materials. Of particular interest is the asymmetric hyperbolic medium, made of silicon nanowires, since it can be directly applicable to solar cell systems. PMID:24036519

Nefedov, Igor S.; Valagiannopoulos, Constantinos A.; Hashemi, Seed M.; Nefedov, Evgeny I.

2013-01-01

429

Determination of Absolute Zero Using a Computer-Based Laboratory  

ERIC Educational Resources Information Center

We present a simple computer-based laboratory experiment for evaluating absolute zero in degrees Celsius, which can be performed in college and undergraduate physical sciences laboratory courses. With a computer, absolute zero apparatus can help demonstrators or students to observe the relationship between temperature and pressure and use…

Amrani, D.

2007-01-01

430

Absolute calibration of analog detectors using stimulated parametric down conversion  

Microsoft Academic Search

Spontaneous parametric down conversion has been largely exploited as a tool for absolute calibration of photon counting detectors, photomultiplier tubes or avalanche photodiodes working in Geiger regime. In this work we investigate the extension of this technique from very low photon flux of photon counting regime to the absolute calibration of analog photodetectors at higher photon flux. Moving toward higher

G. Brida; M. Chekhova; M. Genovese; M.-L. Rastello; I. Ruo-Berchera

2009-01-01

431

Safety Logics I: Absolute Safety Zhisheng Huang and John Bell #  

E-print Network

medical safety­critical system would consider states in which the patient dies as a result of treatmentSafety Logics I: Absolute Safety Zhisheng Huang and John Bell # Applied Logic Group Department}@dcs.qmw.ac.uk Abstract In this paper we distinguish between absolute safety and normative safety, and develop a formal

Huang, Zhisheng

432

Asymmetric Rh-Catalyzed Hydrogenation of Enamides with a Chiral  

E-print Network

for this asymmetric catalytic system. Higher pressure gave slightly better enantioselectivities and reactivities (e compounds from prochiral precur- sors, enantioselective catalytic hydrogenation of dehydro precursors has asymmetric catalytic hydrogenation systems only hydrogenate electron-deficient olefins with high enanti

Zhang, Xumu

433

Terahertz Optical Asymmetric Demultiplexer Switch with a Symmetrical Switching Window  

E-print Network

asymmetrical demultiplexer (TOAD) switch. This is achieved by saturating the semiconductor optical amplifier (SOA), located within the TOAD loop, from both directions. So that, both clockwise (CW) and counter], terahertz optical asymmetric demultiplexer (TOAD) [2], ultrafast nonlinear interferometer (UNI) [3

Haddadi, Hamed

434

Evaluation of the Absolute Regional Temperature Potential  

NASA Technical Reports Server (NTRS)

The Absolute Regional Temperature Potential (ARTP) is one of the few climate metrics that provides estimates of impacts at a sub-global scale. The ARTP presented here gives the time-dependent temperature response in four latitude bands (90-28degS, 28degS-28degN, 28-60degN and 60-90degN) as a function of emissions based on the forcing in those bands caused by the emissions. It is based on a large set of simulations performed with a single atmosphere-ocean climate model to derive regional forcing/response relationships. Here I evaluate the robustness of those relationships using the forcing/response portion of the ARTP to estimate regional temperature responses to the historic aerosol forcing in three independent climate models. These ARTP results are in good accord with the actual responses in those models. Nearly all ARTP estimates fall within +/-20%of the actual responses, though there are some exceptions for 90-28degS and the Arctic, and in the latter the ARTP may vary with forcing agent. However, for the tropics and the Northern Hemisphere mid-latitudes in particular, the +/-20% range appears to be roughly consistent with the 95% confidence interval. Land areas within these two bands respond 39-45% and 9-39% more than the latitude band as a whole. The ARTP, presented here in a slightly revised form, thus appears to provide a relatively robust estimate for the responses of large-scale latitude bands and land areas within those bands to inhomogeneous radiative forcing and thus potentially to emissions as well. Hence this metric could allow rapid evaluation of the effects of emissions policies at a finer scale than global metrics without requiring use of a full climate model.

Shindell, D. T.

2012-01-01

435

Absolute optical surface measurement with deflectometry  

NASA Astrophysics Data System (ADS)

Deflectometry utilises the deformation and displacement of a sample pattern after reflection from a test surface to infer the surface slopes. Differentiation of the measurement data leads to a curvature map, which is very useful for surface quality checks with sensitivity down to the nanometre range. Integration of the data allows reconstruction of the absolute surface shape, but the procedure is very error-prone because systematic errors may add up to large shape deviations. In addition, there are infinitely many combinations for slope and object distance that satisfy a given observation. One solution for this ambiguity is to include information on the object's distance. It must be known very accurately. Two laser pointers can be used for positioning the object, and we also show how a confocal chromatic distance sensor can be used to define a reference point on a smooth surface from which the integration can be started. The used integration algorithm works without symmetry constraints and is therefore suitable for free-form surfaces as well. Unlike null testing, deflectometry also determines radius of curvature (ROC) or focal lengths as a direct result of the 3D surface reconstruction. This is shown by the example of a 200 mm diameter telescope mirror, whose ROC measurements by coordinate measurement machine and deflectometry coincide to within 0.27 mm (or a sag error of 1.3?m). By the example of a diamond-turned off-axis parabolic mirror, we demonstrate that the figure measurement uncertainty comes close to a well-calibrated Fizeau interferometer.

Li, Wansong; Sandner, Marc; Gesierich, Achim; Burke, Jan

436

P-Phos: a family of versatile and effective atropisomeric dipyridylphosphine ligands in asymmetric catalysis.  

PubMed

This Account outlines our efforts in the design and synthesis of a family of highly effective atropisomeric dipyridylphosphine ligands (P-Phos and its variants) and in the development of their widespread applications in transition-metal-catalyzed asymmetric reactions including hydrogenation, hydrosilylation, and C-C bond formation. Desirable attributes, such as air stability, broad substrate scope, fast rates of reaction, excellent enantioselectivities, low catalyst loading, and mild conditions, make the catalyst systems highly attractive and thus may provide excellent opportunities for practical applications. PMID:17042471

Wu, Jing; Chan, Albert S C

2006-10-01

437

Asymmetric bioreduction of activated alkenes to industrially relevant optically active compounds  

PubMed Central

Ene-reductases from the ‘Old Yellow Enzyme’ family of flavoproteins catalyze the asymmetric reduction of various ?,?-unsaturated compounds at the expense of a nicotinamide cofactor. They have been applied to the synthesis of valuable enantiopure products, including chiral building blocks with broad industrial applications, terpenoids, amino acid derivatives and fragrances. The combination of these highly stereoselective biocatalysts with a cofactor recycling system has allowed the development of cost-effective methods for the generation of optically active molecules, which is strengthened by the availability of stereo-complementary enzyme homologues. PMID:22498437

Winkler, Christoph K.; Tasnádi, Gábor; Clay, Dorina; Hall, Mélanie; Faber, Kurt

2012-01-01

438

Stochastic Differential Games with Asymmetric Information  

SciTech Connect

We investigate a two-player zero-sum stochastic differential game in which the players have an asymmetric information on the random payoff. We prove that the game has a value and characterize this value in terms of dual viscosity solutions of some second order Hamilton-Jacobi equation.

Cardaliaguet, Pierre, E-mail: Pierre.Cardaliaguet@univ-brest.fr; Rainer, Catherine [Universite de Brest, Laboratoire de Mathematique (UMR CNRS 6205) (France)], E-mail: Catherine.Rainer@univ-brest.fr

2009-02-15

439

Cascading failures on networks with asymmetric dependence  

NASA Astrophysics Data System (ADS)

Networks with mutual dependence have been shown to be much more vulnerable to random failures and targeted attacks than those without. However, in real networks, the dependence between two nodes is not always mutual. Periphery nodes may depend on hub nodes, yet the converse is not necessarily true. Considering this asymmetric dependence, we propose a model of cascading dynamics of networks, where the dependence between nodes is determined by their degrees. We find that the asymmetric dependence makes networks more robust than the symmetric one, and the percolation transition point is not sensitive to the number of the asymmetric dependence nodes. Furthermore, scale-free networks with asymmetric dependence can still be very robust to random failures, rather than extremely fragile as the one with mutual dependence. We also develop an approach to analyse this model and obtain the exact solutions for the size of the giant component and the critical point. Both simulation and analytical results reveal the existence of the crossover between the first- and the second-order percolation transitions in our model.

Li, Ming; Liu, Run-Ran; Jia, Chun-Xiao; Wang, Bing-Hong

2014-12-01

440

Mach bands change asymmetrically during solar eclipses.  

PubMed

Observations made during two partial eclipses of the Sun show that the Mach bands on shadows cast by the Sun disappear and reappear asymmetrically as an eclipse progresses. These changes can be explained as due to changes in the shape of the penumbras of shadows as the visible portion of the Sun forms crescents of different orientation. PMID:12892435

Ross, John; Diamond, Mark R; Badcock, David R

2003-01-01

441

Polarization of Drosophila Neuroblasts During Asymmetric Division  

E-print Network

Polarization of Drosophila Neuroblasts During Asymmetric Division Kenneth E. Prehoda Department by their polarization into separate apical and basal cortical domains during mitosis. Neuroblast symmetry breaking kinase C (aPKC) is a broad regulator of polarity that localizes to the neuroblast apical cortical region

Prehoda, Ken

442

Asymmetric volatility transmission in international stock markets  

Microsoft Academic Search

The transmission mechanism of price and volatility spillovers across the New York, Tokyo and London stock markets is investigated. The asymmetric impact of good news (market advances) and bad news (market declines) on volatility transmission is described by an extended multivariate Exponential Generalized Autoregressive Conditionally Heteroskedastic (EGARCH) model. Using daily open-to-close returns, we find strong evidence that volatility spillovers in

G. Geoffrey Booth

1995-01-01

443

Asymmetrical Path Interference Test of Light  

E-print Network

The asymmetrical path interference test of light is put forward in the paper. In the test, two different results would arise under the same experimental conditions if light is regarded as wave or particle. Therefore, the test can help us to comprehend which concept, wave or particle, is more essential for micro-particles.

Mei Xiaochun

2006-03-05

444

Artificial surface with asymmetric reflection properties  

Microsoft Academic Search

An artificial surface with asymmetric reflection properties is presented. By covering a metal ground plane with periodic metal-dielectric composite textures, the electromagnetic reflection properties can be altered. By tuning the individual lattice of a periodic mushroom-type texture to vary the surface impedance, a surface with graded reflection phases as a function of position can be designed. Applying a linear gradient

Kihun Chang; Jihwan Ahn; Young Joong Yoon

2008-01-01

445

External combustion engine having an asymmetrical CAM  

Microsoft Academic Search

An external combustion engine having an asymmetrical cam is the focus of this patent. The engine includes a combustion chamber for generating a high-pressure, energized gas from a monopropellant fuel and an even number of cylinders for receiving sequentially the energized gas through the rotary valve, the gas performing work on a piston disposed within each cylinder. The pistons transfer

Anthony W. Duva

1994-01-01

446

Asymmetric Information, Financing Constraints, and Investment  

Microsoft Academic Search

The results of a number of theoretical papers lead to the hypothesis that financial variables affect capital sp ending because of asymmetric information in capital markets. The auth ors review the relevant theory and test this hypothesis with a large sample of firm data. The results show that financial variables such a s cash flow and interest expense add significant

Steven M Fazzari; Michael J Athey

1987-01-01

447

Asymmetric hindwing foldings in rove beetles.  

PubMed

Foldable wings of insects are the ultimate deployable structures and have attracted the interest of aerospace engineering scientists as well as entomologists. Rove beetles are known to fold their wings in the most sophisticated ways that have right-left asymmetric patterns. However, the specific folding process and the reason for this asymmetry remain unclear. This study reveals how these asymmetric patterns emerge as a result of the folding process of rove beetles. A high-speed camera was used to reveal the details of the wing-folding movement. The results show that these characteristic asymmetrical patterns emerge as a result of simultaneous folding of overlapped wings. The revealed folding mechanisms can achieve not only highly compact wing storage but also immediate deployment. In addition, the right and left crease patterns are interchangeable, and thus each wing internalizes two crease patterns and can be folded in two different ways. This two-way folding gives freedom of choice for the folding direction to a rove beetle. The use of asymmetric patterns and the capability of two-way folding are unique features not found in artificial structures. These features have great potential to extend the design possibilities for all deployable structures, from space structures to articles of daily use. PMID:25368178

Saito, Kazuya; Yamamoto, Shuhei; Maruyama, Munetoshi; Okabe, Yoji

2014-11-18

448

The truncated mean of an asymmetric distribution  

Microsoft Academic Search

This paper investigates a simple procedure to estimate robustly the mean of an asymmetric distribution. The procedure removes the observations which are larger or smaller than certain limits and takes the arithmetic mean of the remaining observations, the limits being determined with the help of a parametric model, e.g., the Gamma, the Weibull or the Lognormal distribution. The breakdown point,

A. Marazzi; C. Ruffieux

1999-01-01

449

Asymmetric Information Warfare: Cyberterrorism Critical Infrastructures  

Microsoft Academic Search

Terrorist attacks in recent years, particularly those of October 12, 2000 and September 11, 2001, along with war games such as Millennium Challenge have demonstrated forcefully that asymmetric warfare [THO01] with conventional weapons poses a challenge to existing defense and homeland security structures that have not been addressed satisfactorily. It appears only prudent to assume that such attacks, whether by

Stephen D. Wolthusen

2003-01-01

450

Spectral response of asymmetrical random oscillators  

Microsoft Academic Search

An analytical procedure to estimate the power spectral density (PSD) response of a weakly damped oscillator with a nonlinear asymmetrical restoring force under external stochastic wide-band excitation is presented. An equivalent linear system with random parameters is derived, from which the PSD is deduced. The use of corrective terms yields an approximation of the PSD in the region of the

S. Bellizzi; R. Bouc

1996-01-01

451

Total Synthesis of Piericidin A1 and B1 and Key Analogues  

PubMed Central

Full details of the total synthesis of piericidin A1 and B1 and its extension to the preparation of a series of key analogues are described including ent-piericidin A1 (ent-1), 4'-deshydroxypiericidin A1 (58), 5'-desmethylpiericidin A1 (73), 4'-deshydroxy-5'-desmethylpiericidin A1 (75), and the corresponding analogues 51, 59, 76, and 77 bearing a simplified farnesyl side chain. The evaluation of these key analogues, along with those derived from their further functionalizations, permitted a scan of the key structural features providing new insights into the role of the substituents found in both the pyridyl core as well as the side chain. A strategic late stage heterobenzylic Stille cross-coupling reaction of the pyridyl core with the fully elaborated side chain permitted ready access to the analogues in which each half of the molecule could be systematically and divergently modified. The pyridyl cores were assembled enlisting inverse electron demand Diels–Alder reactions of N-sulfonyl-1-azabutadienes while key elements of side chain syntheses include an anti selective asymmetric aldol to install the C9 and C10 relative and absolute stereochemistry (for natural and ent-1) and a modified Julia olefination for formation of the C5–C6 trans double bond with convergent assemblage of the side chains. PMID:16953619

Schnermann, Martin J.; Romero, F. Anthony; Hwang, Inkyu; Nakamaru-Ogiso, Eiko; Yagi, Takao; Boger, Dale L.

2008-01-01

452

Charge asymmetric cosmic rays as a probe of flavor violating asymmetric dark matter  

SciTech Connect

The recently introduced cosmic sum rules combine the data from PAMELA and Fermi-LAT cosmic ray experiments in a way that permits to neatly investigate whether the experimentally observed lepton excesses violate charge symmetry. One can in a simple way determine universal properties of the unknown component of the cosmic rays. Here we attribute a potential charge asymmetry to the dark sector. In particular we provide models of asymmetric dark matter able to produce charge asymmetric cosmic rays. We consider spin zero, spin one and spin one-half decaying dark matter candidates. We show that lepton flavor violation and asymmetric dark matter are both required to have a charge asymmetry in the cosmic ray lepton excesses. Therefore, an experimental evidence of charge asymmetry in the cosmic ray lepton excesses implies that dark matter is asymmetric.

Masina, Isabella [Dipartimento di Fisica, Università di Ferrara and INFN Sez. di Ferrara, Via Saragat 1, I-44100 Ferrara (Italy); Sannino, Francesco, E-mail: masina@fe.infn.it, E-mail: sannino@cp3-origins.net [CP3-Origins and DIAS, University of Southern Denmark, Campusvej 55, DK-5230 Odense M (Denmark)

2011-09-01

453

Asymmetric Bulkheads for Cylindrical Pressure Vessels  

NASA Technical Reports Server (NTRS)

Asymmetric bulkheads are proposed for the ends of vertically oriented cylindrical pressure vessels. These bulkheads, which would feature both convex and concave contours, would offer advantages over purely convex, purely concave, and flat bulkheads (see figure). Intended originally to be applied to large tanks that hold propellant liquids for launching spacecraft, the asymmetric-bulkhead concept may also be attractive for terrestrial pressure vessels for which there are requirements to maximize volumetric and mass efficiencies. A description of the relative advantages and disadvantages of prior symmetric bulkhead configurations is prerequisite to understanding the advantages of the proposed asymmetric configuration: In order to obtain adequate strength, flat bulkheads must be made thicker, relative to concave and convex bulkheads; the difference in thickness is such that, other things being equal, pressure vessels with flat bulkheads must be made heavier than ones with concave or convex bulkheads. Convex bulkhead designs increase overall tank lengths, thereby necessitating additional supporting structure for keeping tanks vertical. Concave bulkhead configurations increase tank lengths and detract from volumetric efficiency, even though they do not necessitate additional supporting structure. The shape of a bulkhead affects the proportion of residual fluid in a tank that is, the portion of fluid that unavoidably remains in the tank during outflow and hence cannot be used. In this regard, a flat bulkhead is disadvantageous in two respects: (1) It lacks a single low point for optimum placement of an outlet and (2) a vortex that forms at the outlet during outflow prevents a relatively large amount of fluid from leaving the tank. A concave bulkhead also lacks a single low point for optimum placement of an outlet. Like purely concave and purely convex bulkhead configurations, the proposed asymmetric bulkhead configurations would be more mass-efficient than is the flat bulkhead configuration. In comparison with both purely convex and purely concave configurations, the proposed asymmetric configurations would offer greater volumetric efficiency. Relative to a purely convex bulkhead configuration, the corresponding asymmetric configuration would result in a shorter tank, thus demanding less supporting structure. An asymmetric configuration provides a low point for optimum location of a drain, and the convex shape at the drain location minimizes the amount of residual fluid.

Ford, Donald B.

2007-01-01

454

ASYMMETRIC SPECIALIZATION: A PERVASIVE FEATURE OF PLANT–POLLINATOR INTERACTIONS  

Microsoft Academic Search

Although specialization in species interactions has usually been equated to reciprocal specialization, asymmetric specialization (i.e., a specialist interacting with a generalist) is also likely. Recent studies have suggested that asymmetric specialization in species interactions could be more common than previously thought. We contrasted patterns of asymmetric specialization observed in 18 plant-pollinator interaction webs with pre- dictions based on null models.

Diego P. Vázquez; Marcelo A. Aizen

2004-01-01

455

The Hebrew University of Jerusalem Lecture 9 Asymmetric Cryptography  

E-print Network

The Hebrew University of Jerusalem Lecture 9 ­ Asymmetric Cryptography The Public Key Model Asymmetric Cryptography (also called Public­Key Cryptography) was a real breakthrough in cryptography. The major change between asymmetric cryptography and the `traditional' symmetric cryptography is that

Porat, Ely

456

The Minimization Method of Measuring Errors for Balancing Asymmetrical Rotors  

Microsoft Academic Search

The accuracy of rotor balancing is influenced by measuring errors essentially. The conventional influence coefficient method considering measurement errors is able to improve the balancing accuracy of symmetrical rotors. However, the balancing accuracy of asymmetrical rotors cannot be improved by using conventional method. Since asymmetrical rotors are axis-asymmetrical, the balancing result is affected by inequality of rotary inertia and bending

Yuan Kang; Chih-Pin Chiang; Chun-Chieh Wang; Tzu-Wei Lin; Yi-Jui Chui

2003-01-01

457

Asymmetric Punishment as an Instrument of Corruption Control  

E-print Network

-post incentives for agents to report the crime and thereby stop colluding. The idea of asymmetric punishment. If asymmetric punishment is quite widespread in the case of ...nancial and organized crime, it is relativelyAsymmetric Punishment as an Instrument of Corruption Control Karna Basu, Kaushik Basu, and Tito

Bandyopadhyay, Antar

458

Disposition Effect andAsymmetric Volatility of Individual Stocks  

Microsoft Academic Search

We investigate asymmetric volatility effect (the negative partial correlation between volatility and lagged return), conditioning volatility changes to the sign of cumulative return over the past ten days. We find that negative cumulative past returns are fundamental to understand asymmetric volatility. However we also find that asymmetric volatility can not be interpreted as simply a response to cumulative returns instead

Claudio M. P. Cunha

2011-01-01

459

Optimization of Asymmetric Catalysts Using Achiral Ligands: Metal  

E-print Network

by Katsuki2,3 in the asymmetric epoxidation with achiral manganese salen complexes resulted in highOptimization of Asymmetric Catalysts Using Achiral Ligands: Metal Geometry-Induced Ligand Asymmetry becomes asymmetric, a concept termed Metal Geometry-Induced Ligand Asymmetry. The enantioselectivity

Walsh, Patrick J.

460

Absolute instability in viscoelastic mixing layers  

NASA Astrophysics Data System (ADS)

The spatiotemporal linear stability of viscoelastic planar mixing layers is investigated. A one-parameter family of velocity profiles is used as the base state with the parameter, S, controlling the amount of shear and backflow. The influence of viscoelasticity in dilute polymer solutions is modeled with the Oldroyd-B and FENE-P constitutive equations. Both models require the specification of the ratio of the polymer-relaxation and convective time scales (the Weissenberg number, We) and the ratio of solvent and solution viscosities (?). The maximum polymer extensibility, L, must also be specified for the FENE-P model. We examine how the variation of these parameters along with the Reynolds number, Re, affects the minimum value of S at which the flow becomes locally absolutely unstable. With the Oldroyd-B model, the influence of viscoelasticity is shown to be almost fully captured by the elasticity, E^* equiv (1-? ) We/Re, and Scrit decreases as elasticity is increased, i.e., elasticity is destabilizing. A simple approximate dispersion relation obtained via long-wave asymptotic analysis is shown to accurately capture this destabilizing influence. Results obtained with the FENE-P model exhibit a rich variety of behavior. At large values of the extensibility, L, results are similar to those for the Oldroyd-B fluid as expected. However, when the extensibility is reduced to more realistic values (L ? 100), one must consider the scaled shear rate, ? _c equiv We S/2L, in addition to the elasticity. When ?c is large, the base-state polymer stress obtained by the FENE-P model is reduced, and there is a corresponding reduction in the overall influence of viscoelasticity on stability. Additionally, elasticity exhibits a stabilizing effect which is driven by the streamwise-normal perturbation polymer stress. As ?c is reduced, the base-state and perturbation normal polymer stresses predicted by the FENE-P model move towards the Oldroyd-B values, and the destabilizing influence of elasticity observed with the Oldroyd-B model is again present.

Ray, Prasun K.; Zaki, Tamer A.

2014-01-01

461

Transition-Metal Catalyzed Synthesis of Aspergillide B: An Alkyne Addition Strategy  

PubMed Central

A catalytic enantioselective formal total synthesis of aspergillide B is reported. This linchpin synthesis was enabled by the development of new conditions for Zn-ProPhenol catalyzed asymmetric alkyne addition. This reaction was used in conjunction with ruthenium-catalyzed trans-hydrosilylation to affect the rapid construction of a late-stage synthetic intermediate of aspergillide B to complete a formal synthesis of aspergillide B in a highly efficient manner. PMID:22356535

Bartlett, Mark J.

2012-01-01

462

Asymmetric Dimethylarginine (ADMA): a promising biomarker for cardiovascular disease?  

PubMed

Asymmetric Dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) production. ADMA is generated from methylation of arginine residues by protein arginine methyltransferases (PRMTs) and subsequent proteolysis, while its elimination is achieved mainly by degradation with dimethylarginine dimethylaminohydrolase (DDAH). Oxidative stress, endothelial nitric oxide synthase (eNOS) inhibition, eNOS uncoupling, inflammation and shear stress play a pivotal role in ADMA pathophysiology by managing PRMT/DDAH expression and NO synthesis and leading to a common result - endothelial dysfunction. Endothelial dysfunction seems to be the common finding in studies investigating the role of ADMA in cardiovascular disease (CVD). High-performance liquid chromatography (HPLC), mass spectrometry (MS) and enzyme-linked immunosorbent assay (ELISA) are the existing methods for ADMA quantification. However, none of them fulfils all the criteria to be characterized as "gold standard". ADMA is significantly associated with risk factors for CVD and almost with every disease of the cardiovascular system; showing an independent, strong prognostic value for mortality and future cardiovascular events. This article aims to review the current knowledge about ADMA biology and metabolism, pathophysiological mechanisms implicating ADMA in CVD, methods for the determination of ADMA and its association with CVD risk factors and established CVDs. PMID:23470077

Bouras, Georgios; Deftereos, Spyridon; Tousoulis, Dimitrios; Giannopoulos, Georgios; Chatzis, Georgios; Tsounis, Dimitrios; Cleman, Michael W; Stefanadis, Christodoulos

2013-01-01

463

Homo-Roche Ester Derivatives By Asymmetric Hydrogenation and Organocatalysis  

PubMed Central

Asymmetric hydrogenation routes to homologs of The Roche ester tend to be restricted to hydrogenations of itaconic acid derivatives, ie substrates that contain a relatively unhindered, 1,1-disubstituted, alkene. This is because in hydrogenations mediated by RhP2 complexes, the typical catalysts, it is difficult to obtain high conversions using the alternative substrate for the same product, the isomeric trisubstituted alkenes (D in the text). However, chemoselective modification of the identical functional groups in itaconic acid derivatives are difficult, hence it would be favorable to use the trisubstituted alkene. Trisubstituted alkene substrates can be hydrogenated with high conversions using chiral analogs of Crabtree’s catalyst of the type IrN(carbene). This paper demonstrates such reactions are scalable (tens of grams) and can be manipulated to give optically pure homo-Roche ester chirons. Organocatalytic fluorination, chlorination, and amination of the homo-Roche building blocks was performed to demonstrate that they could be easily transformed into functionalized materials with two chiral centers and ?,?-groups that provide extensive scope for modifications. A synthesis of (S,S)- and (R,S)-?-hydroxyvaline was performed to illustrate one application of the amination product. PMID:24219839

Khumsubdee, Sakunchai; Zhou, Hua; Burgess, Kevin

2013-01-01

464

Transition to Absolute Instability for (not so) Dummies  

E-print Network

These notes are intended as an elementary introduction to the concept of absolute instability. The transition from convective instability to absolute instability is an important issue when the stability of stationary flow solutions is investigated. The arguments here described were first developed in the framework of plasma physics and later applied to the hydrodynamics of mixing layers and shear flows. Far from being a comprehensive analysis of this complicated subject, the aim of these notes is just to sketch a rudimentary and quite elementary ground for physicists or engineers which have a familiarity with the basic features of linear stability in fluid dynamics, but are new to the concept of absolute instability.

Barletta, Antonio

2014-01-01

465

ABSOLUTE PROPERTIES OF THE ECCENTRIC ECLIPSING BINARY STAR FT ORIONIS  

SciTech Connect

Accurate absolute properties are determined for the first time for the 3.15 day period eccentric eclipsing binary star FT Ori based on new absolute photometry, five differential light curves, and a radial velocity curve. The stars appear to be normal for their spectral types, A0 + A2. The orbit is highly eccentric (e = 0.409) and shows apsidal motion with a period of 536 years. The absolute properties and the degree of central mass concentration of the stars are consistent with current theoretical models at an age of 190 Myr.

Sabby, Jeffrey A. [Physics Department, Southern Illinois University Edwardsville, Edwardsville, IL 62025 (United States); Lacy, Claud H. Sandberg [Physics Department, University of Arkansas, Fayetteville, AR 72701 (United States); Ibanoglu, Cafer [Astronomy and Space Sciences Department, Science Faculty, Ege University, 35100 Boronova, Izmir (Turkey); Claret, Antonio, E-mail: jsabby@siue.edu, E-mail: clacy@uark.edu, E-mail: cafer.ibanoglu@ege.edu.tr, E-mail: claret@iaa.es [Instituto de Astrofisica de Andalucia, CSIC, Apdo. Postal 3004, E-18080 Granada (Spain)

2011-06-15

466

Measurement of Disintegration Rates and Absolute {gamma}-ray Intensities  

SciTech Connect

The majority of practical radioactive materials decay by modes that include {gamma}-ray emission. For questions of 'how much' or 'how pure', one must know the absolute intensities of the major radiations. We are using liquid scintillation counting (LSC) to measurements of disintegration rates, coupled with {gamma}-ray spectroscopy to measure absolute {gamma}-ray emission probabilities. Described is a study of the 227Th chain yielding absolute {gamma}-ray intensities with {approx}0.5% accuracy and information on LSC efficiencies.

DeVries, Daniel J.; Griffin, Henry C. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109 (United States)

2006-03-13

467

Niobium-mediated synthesis of phosphorus-rich molecules  

E-print Network

The use of a sterically demanding enolate ligand -OC[2Ad]Mes supported by niobium has allowed for the synthesis of (Mes[2Ad]CO) 3Nb=PP7Nb(OC [2Ad]Mes)3 through P4 coupling by a low-valent niobium intermediate. This asymmetric ...

Cossairt, Brandi M. (Brandi Michelle)

2010-01-01

468

Highly Efficient Synthesis of Chiral -Amino Acid Derivatives via  

E-print Network

Highly Efficient Synthesis of Chiral -Amino Acid Derivatives via Asymmetric Hydrogenation Wenjun-TangPhos complex is an efficient hydrogenation catalyst for making chiral -amino acid derivatives. With the Rh -amino acids has drawn a great deal of attention due to its importance in biomedical research

Zhang, Xumu

469

Enantio- and diastereoselective synthesis of spiro-epoxyoxindoles.  

PubMed

An asymmetric synthesis of epoxyoxindoles from isatins has been developed by employing chiral sulfur ylides generated in situ from camphor-derived sulfonium salts. This reaction allows an efficient access to enantioenriched spiro-epoxyoxindoles under mild reaction conditions, featuring high yields and excellent enantio- and diastereoselectivities. PMID:24730463

Boucherif, Amina; Yang, Qing-Qing; Wang, Qiang; Chen, Jia-Rong; Lu, Liang-Qiu; Xiao, Wen-Jing

2014-05-01

470

Total synthesis of aphadilactones A-D.  

PubMed

The first total synthesis of aphadilactones A-D, diastereomeric natural products recently isolated from the Meliaceae plant Aphanamixis grandifolia by Yue and co-workers, which possess an unprecedented carbon skeleton, has been achieved. The synthesis features a catalytic asymmetric hetero-Diels-Alder reaction to form the dihydropyran ring, concurrent installation of the lactone and furan moieties via a tandem acid-catalyzed acetal cleavage, oxidation, and cyclization process, and an intermolecular Diels-Alder reaction to forge the target products. PMID:24959931

Yin, Jian-Peng; Gu, Min; Li, Ying; Nan, Fa-Jun

2014-07-01

471

Organocatalytic asymmetric assembly reactions for the syntheses of carbohydrate derivatives by intermolecular Michael-Henry reactions  

PubMed Central

Given the significance of carbohydrates in life, medicine, and industry, the development of simple and efficient de novo methods to synthesize carbohydrates are highly desirable. Organocatalytic asymmetric assembly reactions are powerful tools to rapidly construct molecules with stereochemical complexity from simple precursors. Here, we present a simple and robust methodology for the asymmetric synthesis of pyranose derivatives with talo- and manno- configurations from simple achiral precursors through organocatalytic asymmetric intermolecular Michael–Henry reaction sequences. In this process, (tert-butyldimethylsilyloxy)acetaldehyde 1 was successfully utilized in two ways: as a donor in a highly selective anti-Michael reaction and as an acceptor in a consecutive Henry reaction. Varied nitroolefins served as Michael acceptors and varied aldehydes substituted for 1 as Henry acceptors providing for the construction of a wide range of carbohydrates with up to 5 stereocenters. In these reactions, a catalyst-controlled Michael reaction followed by a substrate-controlled Henry reaction provided 3,4-dideoxytalose derivatives 6 in a highly stereoselective manner. The Henry reaction was affected by addition of a simple base such as triethylamine: A complex chiral base was not necessary. 3,4-Dideoxymannose derivatives 7 were produced by simply changing the base from triethylamine to 1,8-diazabicyclo[5.4.0]undec-7-ene. Extension of this methodology to a syn-Michael initiated sequence was also successful. A mechanistic discussion is provided to explain the unusual substrate-induced stereoselectivity of the Henry reaction. PMID:20639468

Uehara, Hisatoshi; Imashiro, Ritsuo; Hernández-Torres, Gloria; Barbas, Carlos F.

2010-01-01

472

Mini-implants and miniplates generate sub-absolute and absolute anchorage  

PubMed Central

The functional demand imposed on bone promotes changes in the spatial properties of osteocytes as well as in their extensions uniformly distributed throughout the mineralized surface. Once spatial deformation is established, osteocytes create the need for structural adaptations that result in bone formation and resorption that happen to meet the functional demands. The endosteum and the periosteum are the effectors responsible for stimulating adaptive osteocytes in the inner and outer surfaces.Changes in shape, volume and position of the jaws as a result of skeletal correction of the maxilla and mandible require anchorage to allow bone remodeling to redefine morphology, esthetics and function as a result of spatial deformation conducted by orthodontic appliances. Examining the degree of changes in shape, volume and structural relationship of areas where mini-implants and miniplates are placed allows us to classify mini-implants as devices of subabsolute anchorage and miniplates as devices of absolute anchorage. PMID:25162561

Consolaro, Alberto

2014-01-01

473

Brønsted acid activation strategy in transition-metal catalyzed asymmetric hydrogenation of N-unprotected imines, enamines, and N-heteroaromatic compounds.  

PubMed

Asymmetric hydrogenation plays an important role in organic synthesis, but that of the challenging substrates such as N-unprotected imines, enamines, and N-heteroaromatic compounds (1H-indoles, 1H-pyrroles, pyridines, quinolines, and quinoxalines) has only received increased attention in the past three years. Considering the interaction modes of a Brønsted acid with a Lewis base, Brønsted acids may be used as the ideal activators of C=N bonds. This Minireview summarizes the recent advances in transition-metal-catalyzed, Brønsted acid activated asymmetric hydrogenation of these challenging substrates, thus offering a promising substrate activation strategy for transformations involving C=N bonds. PMID:22577004

Yu, Zhengkun; Jin, Weiwei; Jiang, Quanbin

2012-06-18

474

Direct comparisons between absolute and relative geomagnetic paleointensities: Absolute calibration of a relative paleointensity stack  

NASA Astrophysics Data System (ADS)

Absolute geomagnetic paleointensities (APIs) have been estimated from igneous rocks, while relative paleomagnetic intensities (RPIs) have been reported from sediment cores. These two datasets have been treated separately, as correlations between APIs and RPIs are difficult on account of age uncertainties. High-resolution RPI stacks have been constructed from globally distributed sediment cores with high sedimentation rates. Previous studies often assumed that the RPI stacks have a linear relationship with geomagnetic axial dipole moments, and calibrated the RPI values to API values. However, the assumption of a linear relationship between APIs and RPIs has not been evaluated. Also, a quantitative calibration method for the RPI is lacking. We present a procedure for directly comparing API and RPI stacks, thus allowing reliable calibrations of RPIs. Direct comparisons between APIs and RPIs were conducted with virtually no associated age errors using both tephrochronologic correlations and RPI minima. Using the stratigraphic positions of tephra layers in oxygen isotope stratigraphic records, we directly compared the RPIs and APIs reported from welded tuffs contemporaneously extruded with the tephra layers. In addition, RPI minima during geomagnetic reversals and excursions were compared with APIs corresponding to the reversals and excursions. The comparison of APIs and RPIs at these exact points allowed a reliable calibration of the RPI values. We applied this direct comparison procedure to the global RPI stack PISO-1500. For six independent calibration points, virtual axial dipole moments (VADMs) from the corresponding APIs and RPIs of the PISO-1500 stack showed a near-linear relationship. On the basis of the linear relationship, RPIs of the stack were successfully calibrated to the VADMs. The direct comparison procedure provides an absolute calibration method that will contribute to the recovery of temporal variations and distributions of geomagnetic axial dipole moments from RPI stacks for the past several million years.

Mochizuki, N.; Yamamoto, Y.; Hatakeyama, T.; Shibuya, H.

2013-12-01

475

Diastereodivergent organocatalytic asymmetric vinylogous Michael reactions.  

PubMed

One of the major challenges of modern asymmetric catalysis is the ability to selectively control the formation of all diastereoisomers of reaction products possessing multiple stereocenters. Pioneers of such diastereodivergent catalytic asymmetric processes have focused on reactions where the newly formed stereogenic centres are proximal to the active carbonyl group. To date, however, diastereodivergent reactions at remote positions remain an unmet challenge. Herein, we describe a catalyst-controlled diastereodivergence in the formation of remote stereocenters in the direct vinylogous Michael reactions of ?, ?-unsaturated butenolides to ?, ?-unsaturated ketones. The reactions are enabled by two complementary, non-enantiomeric multifunctional catalysts, which mutually activate and organise both reactants, affording either the syn- or anti-adduct with high diastereo- and enantioselectivity. These two catalytic systems are also applicable in the Mukaiyama-Michael reactions and tandem Michael-Michael reactions. PMID:25057788

Li, Xin; Lu, Min; Dong, Yun; Wu, Wenbin; Qian, Qingqing; Ye, Jinxing; Dixon, Darren J

2014-01-01

476

Asymmetric twins in rhombohedral boron carbide  

SciTech Connect

Superhard materials consisting of light elements have recently received considerable attention because of their ultrahigh specific strength for a wide range of applications as structural and functional materials. However, the failure mechanisms of these materials subjected to high stresses and dynamic loading remain to be poorly known. We report asymmetric twins in a complex compound, boron carbide (B{sub 4}C), characterized by spherical-aberration-corrected transmission electron microscopy. The atomic structure of boron-rich icosahedra at rhombohedral vertices and cross-linked carbon-rich atomic chains can be clearly visualized, which reveals unusual asymmetric twins with detectable strains along the twin interfaces. This study offers atomic insights into the structure of twins in a complex material and has important implications in understanding the planar defect-related failure of superhard materials under high stresses and shock loading.

Fujita, Takeshi, E-mail: tfujita@wpi-aimr.tohoku.ac.jp; Guan, Pengfei; Madhav Reddy, K.; Hirata, Akihiko; Guo, Junjie [WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Chen, Mingwei, E-mail: mwchen@wpi-aimr.tohoku.ac.jp [WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China)

2014-01-13

477

On Asymmetric Distributions of Satellite Galaxies  

NASA Astrophysics Data System (ADS)

We demonstrate that the asymmetric distribution of M31 satellites cannot be produced by tides from the Milky Way as such effects are too weak. However, loosely bound associations and groups of satellites can fall into larger halos and give rise to asymmetries. We compute the survival times for such associations. We prove that the survival time is always shortest in Keplerian potentials, and can be ~3 times longer in logarithmic potentials. We provide an analytical formula for the dispersal time in terms of the size and velocity dispersion of the infalling structure. We show that, if an association of ~10 dwarfs fell into the M31 halo, its present aspect would be that of an asymmetric disk of satellites. We also discuss the case of cold substructure in the Andromeda II and Ursa Minor dwarfs.

Bowden, A.; Evans, N. W.; Belokurov, V.

2014-10-01

478

On Asymmetric Classifier Training for Detector Cascades  

SciTech Connect

This paper examines the Asymmetric AdaBoost algorithm introduced by Viola and Jones for cascaded face detection. The Viola and Jones face detector uses cascaded classifiers to successively filter, or reject, non-faces. In this approach most non-faces are easily rejected by the earlier classifiers in the cascade, thus reducing the overall number of computations. This requires earlier cascade classifiers to very seldomly reject true instances of faces. To reflect this training goal, Viola and Jones introduce a weighting parameter for AdaBoost iterations and show it enforces a desirable bound. During their implementation, a modification to the proposed weighting was introduced, while enforcing the same bound. The goal of this paper is to examine their asymmetric weighting by putting AdaBoost in the form of Additive Regression as was done by Friedman, Hastie, and Tibshirani. The author believes this helps to explain the approach and adds another connection between AdaBoost and Additive Regression.

Gee, Timothy Felix [ORNL

2006-01-01

479

Deformation of an asymmetric thin film  

E-print Network

Experiments have investigated shape changes of polymer films induced by asymmetric swelling by a chemical vapor. Inspired by recent work on the shaping of elastic sheets by non-Euclidean metrics [Y. Klein, E. Efrati, and E. Sharon, Science 315, 1116 (2007)], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike that earlier work, the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may be curvature into a partial cylinder or a partial sphere. We calculate the elastic energy for each of these shapes, and show that the sphere is favored for films smaller than a critical size, which depends on the film thickness, while the cylinder is favored for larger films.

Jun Geng; Jonathan V. Selinger

2011-11-03

480

Asymmetric quantum channel for quantum teleportation  

E-print Network

There are a few obstacles, which bring about imperfect quantum teleportation of a continuous variable state, such as unavailability of maximally entangled two-mode squeezed states, inefficient detection and imperfect unitary transformation at the receiving station. We show that all those obstacles can be understood by a combination of an {\\it asymmetrically-decohered} quantum channel and perfect apparatuses for other operations. For the asymmetrically-decohered quantum channel, we find some counter-intuitive results; one is that teleportation does not necessarily get better as the channel is initially squeezed more and another is when one branch of the quantum channel is unavoidably subject to some imperfect operations, blindly making the other branch as clean as possible may not result in the best teleportation result. We find the optimum strategy to teleport an unknown field for a given environment or for a given initial squeezing of the channel.

M. S. Kim; Jinhyoung Lee

2000-05-04

481

The use of MPA amide for the assignment of absolute configuration of a sterically hindered cyclic secondary amine by 'mix and shake' NMR method.  

PubMed

We present here a new method using methoxyphenylacetic acid (MPA) as the chiral derivatizing agent (CDA) for the assignment of absolute configuration of cyclic secondary amines. The MPA amides were prepared using the purification-free 'mix and shake' method. A detailed conformational analysis for the two diastereomeric amides was conducted by 2D NMR experiments and molecular mechanics calculations. We have established that, in the most stable conformation of each syn rotamer of MPA amides, the H-alpha in the MPA moiety is oriented toward the bulky substituent group at the asymmetric carbon in the chiral amine, presumably to avoid steric and/or electrostatic interactions. The observed NMR data were correlated with the conformational model to allow unambiguous assignment of absolute configuration of secondary amines. The results demonstrate that the MPA can be used as a useful CDA in the case of sterically crowded cyclic secondary amines from which the MTPA amides are usually difficult to make. PMID:18098224

Gao, Jinhai; Haas, Hansjoerg; Wang, Kate Yaping; Chen, Zhuoliang; Breitenstein, Werner; Rajan, Srinivasan

2008-01-01

482

Absolute Value Boundedness, Operator Decomposition, and Stochastic Media and Equations  

NASA Technical Reports Server (NTRS)

The research accomplished during this period is reported. Published abstracts and technical reports are listed. Articles presented include: boundedness of absolute values of generalized Fourier coefficients, propagation in stochastic media, and stationary conditions for stochastic differential equations.

Adomian, G.; Miao, C. C.

1973-01-01

483

Temporal Dynamics of Microbial Rhodopsin Fluorescence Reports Absolute Membrane Voltage  

PubMed Central

Plasma membrane voltage is a fundamentally important property of a living cell; its value is tightly coupled to membrane transport, the dynamics of transmembrane proteins, and to intercellular communication. Accurate measurement of the membrane voltage could elucidate subtle changes in cellular physiology, but existing genetically encoded fluorescent voltage reporters are better at reporting relative changes than absolute numbers. We developed an Archaerhodopsin-based fluorescent voltage sensor whose time-domain response to a stepwise change in illumination encodes the absolute membrane voltage. We validated this sensor in human embryonic kidney cells. Measurements were robust to variation in imaging parameters and in gene expression levels, and reported voltage with an absolute accuracy of 10 mV. With further improvements in membrane trafficking and signal amplitude, time-domain encoding of absolute voltage could be applied to investigate many important and previously intractable bioelectric phenomena. PMID:24507604