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1

Asymmetric synthesis of (+)-geranyllinaloisocyanide: assignment of absolute stereochemistry.  

PubMed

The first nonracemic synthesis of (+)-geranyllinaloisocyanide, starting with (-)-lactic acid methyl ester, has been accomplished by exploiting a [3.3] sigmatropic rearrangement of allyl cyanate. The synthesis enables assignment of the S configuration of the C(3) isocyano substituted, quaternary stereogenic center in natural geranyllinaloisocyanide. PMID:21491897

Ichikawa, Yoshiyasu; Matsuda, Yasunori; Okumura, Ken; Nakamura, Mitsuhiro; Masuda, Toshiya; Kotsuki, Hiyoshizo; Nakano, Keiji

2011-04-14

2

Absolute asymmetric synthesis of enantiopure organozinc reagents, followed by highly enantioselective chlorination.  

PubMed

We report the absolute asymmetric synthesis (AAS) of indenylzinc reagents by using total spontaneous resolution followed by enantiospecific conversion into 1-chloroindene. The chiral complex [Zn(dcp)(ind)(tmeda)] (dcp=2,6-dichlorophenoxy and tmeda=N,N,N',N'-tetramethylethylenediamine) (3) was prepared from the achiral starting materials indene, potassium, zinc chloride, TMEDA, and 2,6-dichlorophenol. The reagent resolved spontaneously on crystallization, and single crystals of 3 react with N-chlorosuccinimide in the presence of benzoquinone in 2-propanol to give 1-chloroindene in >98?% enantiomeric excess. It was found that (R)-3 gave (R)-1-chloroindene upon reaction, indicating an SE 2'-mechanism. Since bulk samples of 3 gave optically active product upon chlorination, total spontaneous resolution must have occurred. This demonstrates that enantiopure products can be obtained through the absolute asymmetric synthesis of organometallic reagents starting from achiral materials. The general absolute asymmetric synthesis (AAS) method offers easy access to both enantiomers and an almost limitless variation in the design of the product. PMID:23881740

Olsson, Susanne; Lennartson, Anders; Håkansson, Mikael

2013-07-23

3

Synthesis and determination of the absolute configuration of cavicularin by a symmetrization/asymmetrization approach.  

PubMed

Taking the strain: The asymmetric total synthesis and stereochemical assignment of (-)-cavicularin, which features a highly strained polycyclophane ring system, has been achieved. The key features of this synthesis are 1)?macrocyclization by an SN Ar reaction, 2)?group-selective reaction to induce planar chirality in a highly stereoselective manner, and 3)?radical transannulation to construct the highly strained ring system. PMID:23956143

Takiguchi, Hiromu; Ohmori, Ken; Suzuki, Keisuke

2013-08-16

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.

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

2011-01-01

5

Asymmetric Total Synthesis of Vindoline  

PubMed Central

A concise asymmetric total synthesis of (?)-vindoline (1) is detailed based on a tandem intramolecular [4+2]/[3+2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which the tether linking the initiating dienophile and oxadiazole bears a chiral substituent that controls the facial selectivity of the initiating Diels–Alder reaction and sets absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduces three rings and four C–C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. Implementation of the approach also required the development of a unique ring expansion reaction to provide a 6-membered ring suitably functionalized for introduction of the ?6,7-double bond found in the core structure of vindoline and defined our use of a protected hydroxymethyl group as the substituent used to control the stereochemical course of the cycloaddition cascade.

Kato, Daisuke; Sasaki, Yoshikazu; Boger, Dale L.

2010-01-01

6

Asymmetric Total Synthesis of Pyranicin  

PubMed Central

The asymmetric total synthesis of pyranicin (1) is reported. The butenolide ring was constructed via an asymmetric alkylation/ring-closing metathesis strategy. The three stereocenters in the left-hand tetrahydropyran ring were installed by sequential chiral auxiliary-mediated aldol reactions. Closure of the tetrahydropyran and fusion of the alkyl backbone were affected via a sequential ring-closing metathesis cross-metathesis strategy.

Crimmins, Michael T.; Jacobs, Danielle L.

2010-01-01

7

Spontaneous chiral crystallization of achiral materials and absolute asymmetric transformation in the chiral crystalline environment  

Microsoft Academic Search

Recently, the combination of chiral crystallization and the solid-state photoreaction has provided many successful examples\\u000a of absolute asymmetric synthesis.[1] In these reactions achiral materials adopted chiral arrangement only by spontaneous crystallization,\\u000a and optically active products are obtained from the topochemically controlled reaction with high ees (Figure 1).[2,3] This\\u000a method incurs a problem in crystallization of achiral molecules in chiral space

Masami Sakamoto

8

Asymmetric total synthesis of rollicosin.  

PubMed

[structure: see text] The first total synthesis of rollicosin, a member of a rare subgroup of Annonaceous acetogenins containing two terminal gamma-lactones, is reported. The approach features a highly regio- and stereoselective tandem ring-closing/cross-metathesis reaction for construction of the east-wing lactone and incorporation of the alkyl spacer. Establishment of the C4 stereocenter and addition of the west-wing lactone were achieved by Sharpless asymmetric dihydroxylation and enolate alkylation. PMID:15787477

Quinn, Kevin J; Isaacs, André K; DeChristopher, Brian A; Szklarz, Stephanie C; Arvary, Rebecca A

2005-03-31

9

Boronic esters in asymmetric synthesis.  

PubMed

The author's work on (?-haloalkyl)boronic esters as reagents for asymmetric synthesis is reviewed. Diastereomeric ratios exceeding 1000 can be achieved with this chemistry, and ratios around 100 are commonplace. The method allows sequential installation of a series of stereocenters and tolerates a wide variety of suitably protected functional substituents. (?-Amidoalkyl)boronic acids include biochemically significant serine protease inhibitors, one of which is the clinically successful proteasome inhibitor bortezomib, used for treatment of multiple myeloma and mantle cell lymphoma. PMID:23875690

Matteson, Donald S

2013-08-14

10

Synthesis and absolute configuration of (?)-chettaphanin II  

Microsoft Academic Search

An efficient synthesis of chettaphanin II has been achieved from ent-halimic acid. The absolute configuration of the natural product was established and corroborated by X-ray analysis of chettaphanin II.

I. S. Marcos; F. A. Hernández; M. J. Sexmero; D. D??ez; P. Basabe; A. B. Pedrero; N. Garc??a; F. Sanz; J. G. Urones

2002-01-01

11

Asymmetric Synthesis (by Garry Procter)  

NASA Astrophysics Data System (ADS)

Oxford University Press: New York, 1996. vi + 237 pp. ISBN 0 19 855726 4 (cloth); 85.00. ISBN 0 19 855725 6 (paper); 37.00. This ever-expanding area of organic chemistry is indeed a daunting challenge for a book, both in terms of the breadth of material and the rapid change of events relative to the publishing time line. I feel the author has done an admirable job juggling these two issues. Following an introductory chapter on the principles of asymmetric induction are seven chapters on individual classes of reactions: additions to carbonyl compounds, alpha-substitution using chiral enolates, asymmetric aldol reactions, additions to C-C double bonds, reduction and oxidation, rearrangements, and hydrolysis and esterification. The vast majority of the references are from the mid-80s through the early 90s, including both general and seminal references. In particular, I feel a very solid balance has been achieved between content and clarity. The chapter on "Principles" at the beginning was very well thought out and organized and is a wonderful overview of asymmetric synthesis. This is balanced nicely in subsequent chapters on specific methods where very useful, practical generalizations are presented, such as the "best alpha-hydroxylation" method or the "best alpha-bromination" procedure. The chapters also have nicely integrated examples that show the power of the particular bond construction being examined as it applies to published total syntheses, my favorite being the ones in the chapter on asymmetric aldol reactions.

Kesler, Brenda

1998-05-01

12

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

2013-04-04

13

Asymmetric synthesis employing chiral ketones as templates  

Microsoft Academic Search

Synthesis of optically active a-alkyl and a-arylthioglycolic acids from thioglycolic acid could be achieved by employing (1R)-(+)-camphor as the template. Asymmetric synthesis of D-daunosamine from thioglycolic acid through chiral 1,3-0xathiolan-5-one 5a was achieved in six synthetic steps. Asymmetric synthesis of optically active 1,2-diols from alkynes through camphor derived chiral allenes is described. Preparation and synthetic application of chiral three carbon

Biing-Jiun Uang; Shy-Yau Po; Shang-Cheng Hung; Hung-Hsin Liu; Chin-Yun Hsu; Yi-Sho Lin; Jia-Wen Chang

1997-01-01

14

A novel asymmetric synthesis of cinacalcet hydrochloride  

PubMed Central

Summary A novel route to asymmetric synthesis of cinacalcet hydrochloride by the application of (R)-tert-butanesulfinamide and regioselective N-alkylation of the naphthyl ethyl sulfinamide intermediate is described.

Gorentla, Laxminarasimhulu; Dubey, Pramod K

2012-01-01

15

A novel asymmetric synthesis of cinacalcet hydrochloride.  

PubMed

A novel route to asymmetric synthesis of cinacalcet hydrochloride by the application of (R)-tert-butanesulfinamide and regioselective N-alkylation of the naphthyl ethyl sulfinamide intermediate is described. PMID:23019473

Arava, Veera R; Gorentla, Laxminarasimhulu; Dubey, Pramod K

2012-08-24

16

Asymmetric synthesis of (+)-mequitazine from quinine.  

PubMed

The first asymmetric synthesis of the antihistaminic drug mequitazine is reported. Our approach started from quinine, a Cinchona alkaloid, whose chiral information was exploited for setting up the stereogenic center of (+)-mequitazine. PMID:21657243

Leroux, Sébastien; Larquetoux, Laurent; Nicolas, Marc; Doris, Eric

2011-06-09

17

Asymmetric synthesis of tetrabenazine and dihydrotetrabenazine.  

PubMed

The enantioselective synthesis of (+)-tetrabenazine (TBZ) and (+)-dihydrotetrabenazine (DTBZ), agents of significant interest for therapeutic and molecular imaging applications, has been completed in 21% (TBZ) and 16% (DTBZ) overall yield and in >97% ee from the starting dihydroisoquinoline. The synthesis utilizes Sodeoka's palladium-catalyzed asymmetric malonate addition to set the initial stereocenter followed by a number of diastereoselective transformations to incorporate the remaining asymmetric centers. PMID:19374381

Rishel, Michael J; Amarasinghe, Kande K D; Dinn, Sean R; Johnson, Bruce F

2009-05-15

18

A Concise Asymmetric Total Synthesis of (+)-Brevisamide  

PubMed Central

A new protecting-group-free synthesis of the marine monocyclic ether (+)-brevisamide is reported. The enantioselective synthesis utilizes a key asymmetric Henry reaction and an Achmatowicz rearrangement for the formation of the tetrahydropyran ring. A penultimate Stille cross-coupling allows for an efficient installation of the conjugated (E,E)-diene side chain ultimately delivering (+)-brevisamide.

Herrmann, Aaron T.; Martinez, Steven R.; Zakarian, Armen

2012-01-01

19

Asymmetric, stereocontrolled total synthesis of paraherquamide A.  

PubMed

The first total synthesis of paraherquamide A, a potent anthelmintic agent isolated from various Penicillium sp. with promising activity against drug-resistant intestinal parasites, is reported. Key steps in this asymmetric, stereocontrolled total synthesis include a new enantioselective synthesis of alpha-alkylated-beta-hydroxyproline derivatives to access the substituted proline nucleus and a highly diastereoselective intramolecular S(N)2' cyclization to generate the core bicyclo[2.2.2]diazaoctane ring system. PMID:14519003

Williams, Robert M; Cao, Jianhua; Tsujishima, Hidekazu; Cox, Rhona J

2003-10-01

20

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

2011-08-07

21

Fluorous Mixture Synthesis of Asymmetric Dendrimers  

PubMed Central

A divergent fluorous mixture synthesis (FMS) of asymmetric fluorinated dendrimers has been developed. Four generations of fluorinated dendrimers with the same fluorinated moiety were prepared with high efficiency, yield and purity. Comparison of the physicochemical properties of these dendrimers provided valuable information for their application and future optimization. This strategy has not only provided a practical method for the synthesis and purification of dendrimers, but also established the possibility of utilizing the same fluorinated moiety for FMS.

Jiang, Zhong-Xing; Yu, Yihua Bruce

2010-01-01

22

Asymmetric catalysis in complex target synthesis  

PubMed Central

This article describes three distinct strategies by which stereochemically complex molecules are synthesized and the ways asymmetric catalysis can impact on all three. The development of general methods to prepare synthetically useful building blocks leads to an expanded “chiral pool” of potential starting materials for asymmetric synthesis. The possibility of discovering new reactions to access new types of building blocks is particularly attractive and serves to help define the frontiers of the field. Asymmetric catalysis can also be applied to diastereoselective synthesis such that the stereochemistry of the catalyst, and not that of the substrate, determines the relative configuration of the product. Finally, in reactions where multiple stereocenters are generated simultaneously or in tandem, catalyst and substrate control can operate in a complementary manner to achieve one of many possible stereochemical outcomes selectively.

Taylor, Mark S.; Jacobsen, Eric N.

2004-01-01

23

Photochirogenesis: Photochemical models on the absolute asymmetric formation of amino acids in interstellar space  

Microsoft Academic Search

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical l-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar\\/circumstellar media. This

Cornelia Meinert; Pierre de Marcellus; Laurent Nahon; Nykola C. Jones; Søren V. Hoffmann; Jan Hendrik Bredehöft; Uwe J. Meierhenrich

2011-01-01

24

An Asymmetric Synthesis of Prozac  

Microsoft Academic Search

A total enantioselective synthesis of the SSRI (-)-Fluoxetine (Prozac?) is presented. Selective Serotonin Reuptake Inhibitors (SSRIs) work to prevent the reabsorption of serotonin, thus increasing the extracellular concentration of this important neurotransmitter. Low concentrations of serotonin are responsible for a variety of mental disorders, including depression, anxiety, and personality disorders. While Prozac is sold as a racemic drug, it has

Anders Eliasen

2010-01-01

25

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

26

An asymmetric formal synthesis of fasicularin.  

PubMed

An asymmetric formal synthesis of fasicularin (1) is described. This natural product, isolated from the extracts of the marine invertebrate Nephteis fasicularis, has shown modest cytotoxicity towards Vero cells. Fasicularin is among only two members of the cylindricine family of natural products, along with lepadiformine (2), to possess a trans A-B ring junction. Key steps of this approach to 1 involve a siloxy-epoxide semipinacol rearrangement of 5 to 6, a B-alkyl Suzuki-Miyaura coupling reaction by using enol trifluoromethanesulfonate 19 and a substrate-directed hydrogenation reaction of 24. This formal synthesis also highlights the difficulty in the incorporation of the thiocyanate functionality present in 1. PMID:15565724

Fenster, Michaël D B; Dake, Gregory R

2005-01-01

27

Microscale Synthesis of Chiral Alcohols via Asymmetric Catalytic Transfer Hydrogenation  

ERIC Educational Resources Information Center

|Synthesis of pure enantiomers is a key issue in industry, especially in areas connected to life sciences. Catalytic asymmetric synthesis has emerged as a powerful and practical tool. Here we describe an experiment on racemic reduction and asymmetric reduction via a catalytic hydrogen transfer process. Acetophenone and substituted acetophenones…

Peeters, Christine M.; Deliever, Rik; De Vos, Dirk

2009-01-01

28

Catalytic asymmetric synthesis of R207910.  

PubMed

The first asymmetric synthesis of a very promising antituberculosis drug candidate, R207910, was achieved by developing two novel catalytic transformations; a catalytic enantioselective proton migration and a catalytic diastereoselective allylation of an intermediate alpha-chiral ketone. Using 2.5 mol % of a Y-catalyst derived from Y(HMDS)(3) and the new chiral ligand 9, 1.25 mol % of p-methoxypyridine N-oxide (MEPO), and 0.5 mol % of Bu(4)NCl, alpha-chiral ketone 3 was produced from enone 4 with 88% ee. This reaction proceeded through a catalytic chiral Y-dienolate generation via deprotonation at the gamma-position of 4, followed by regio- and enantioselective protonation at the alpha-position of the resulting dienolate. Preliminary mechanistic studies suggested that a Y: 9: MEPO = 2: 3: 1 ternary complex was the active catalyst. Bu(4)NCl markedly accelerated the reaction without affecting enantioselectivity. Enantiomerically pure 3 was obtained through a single recrystallization. The second key catalytic allylation of ketone 3 was promoted by CuF.3PPh(3).2EtOH (10 mol %) in the presence of KO(t)Bu (15 mol %), ZnCl(2) (1 equiv), and Bu(4)PBF(4) (1 equiv), giving the desired diastereomer 2 in quantitative yield with a 14: 1 ratio without any epimerization at the alpha-stereocenter. It is noteworthy that conventional organometallic addition reactions did not produce the desired products due to the high steric demand and a fairly acidic alpha-proton in substrate ketone 3. This first catalytic asymmetric synthesis of R207910 includes 12 longest linear steps from commercially available compounds with an overall yield of 5%. PMID:20481617

Saga, Yutaka; Motoki, Rie; Makino, Sae; Shimizu, Yohei; Kanai, Motomu; Shibasaki, Masakatsu

2010-06-16

29

Asymmetric Synthesis of Diastereometric Diaminohepatanetetraols. A Proposal for the Configuration of (+)-Zwittermicin A  

PubMed Central

A proposed absolute configuration for the 7 stereocenters in (+)-zwittermicin A is described based on asymmetric synthesis of six diastereomeric 2,6-diamino-1,3,5,7-heptanetetraols corresponding to the C9-C15 segment, pair-wise 13C NMR chemical shift difference analysis of the models with the natural product, interpretation of enantiospecificity of serine loading domain of the zwittermicin A biosynthetic gene cluster, and degradation of the natural product.

Rogers, Evan W.; Molinski, Tadeusz F.

2008-01-01

30

A practical asymmetric synthesis of LTD4 antagonist  

Microsoft Academic Search

The asymmetric synthesis of L-699,392, a leukotriene antagonist, is reported. The main framework of the molecule is formed via a Heck reaction. The introduction of the asymmetric center was accomplished by the chiral reduction of prochiral ketone using B-chlorodiisopinocampheylborane. A very high asymmetric amplification was observed in which 95% ee product can be obtained from 70% optically pure a-pinene. A

I. Shinkai; A. O. King; R. D. Larsen

1994-01-01

31

Asymmetric Total Synthesis of Vindorosine, Vindoline and Key Vinblastine Analogues  

PubMed Central

Concise asymmetric total syntheses of vindoline (1) and vindorosine (2) are detailed based on a unique intramolecular [4+2]/[3+2] cycloaddition cascade of 1,3,4-oxadiazoles inspired by the natural product structures. A chiral substituent on the tether linking the dienophile and oxadiazole was used to control the facial selectivity of the initiating Diels–Alder reaction and set the absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduced three rings and four C–C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural products in a single step. Implementation of the approach for the synthesis of 1 and 2 required the development of a ring expansion reaction to provide a 6-membered ring suitably functionalized for introduction of the ?6,7-double bond found in the core structure of the natural products. Two unique approaches were developed that defined our use of a protected hydroxymethyl group as the substituent that controls the stereochemical course of the cycloaddition cascade. In the course of these studies, several analogues of vindoline were prepared containing deep-seated structural changes presently accessible only by total synthesis. These analogues, bearing key modifications at C6–C8, were incorporated into vinblastine analogues and used to probe the unusual importance (100-fold) and define the potential role of the vinblastine ?6,7-double bond.

Sasaki, Yoshikazu; Kato, Daisuke; Boger, Dale L.

2010-01-01

32

Asymmetric catalytic synthesis of the proposed structure of trocheliophorolide B.  

PubMed

A concise catalytic asymmetric synthesis of the proposed structure of trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, a Ru-catalyzed alder-ene reaction, and a Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a misassignment of the natural product structure. PMID:22913543

Trost, Barry M; Quintard, Adrien

2012-08-22

33

Asymmetric catalytic synthesis of the proposed structure of trocheliophorolide B  

PubMed Central

A concise catalytic asymmetric synthesis of the proposed structure of Trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, Ru-catalyzed alder-ene reaction and Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a miss-assignment of the natural product structure.

Quintard, Adrien

2012-01-01

34

Asymmetric Total Synthesis of the Epoxykinamycin FL-120B'**  

PubMed Central

Turn up the heat: An asymmetric total synthesis of the epoxykinamycin FL-120B’ is reported. The synthesis establishes a route to epoxide-containing diazobenzofluorenes which could potentially serve as monomers to the dimeric lomaiviticins. Key steps include Sharpless asymmetric epoxidation, Stille coupling, and intramolecular Friedel-Crafts acylation of atropisomeric carboxylic acids at elevated temperatures to construct the FL-120B’ core structure.

Scully, Stephen S.; Porco, John A.

2012-01-01

35

Synthesis and absolute configuration of demethyl (C-11) cezomycin.  

PubMed

The synthesis of (-)-demethyl (C-11) cezomycin was achieved through an efficient route that features the use of a Kulinkovich reaction to couple two multifunctionality-containing fragments and a cascade of ring opening of cyclopropanol/1,5-hydrogen shift/desilylation-oxidation. The hidden yet undeniable problem of irreproducible specific rotation for this family of compounds was solved by sufficient acidification. The absolute configuration for the natural product was thus established as the mirror image of the synthetic sample. PMID:23881716

Li, Shao-Gang; Wu, Yikang

2013-07-23

36

The first asymmetric synthesis of a dopamine D1 agonist, dihydrexidine, employing asymmetric conjugate addition technology  

Microsoft Academic Search

The first asymmetric synthesis of benzophenanthridine dopamine D1 full agonist, dihydrexidine, was accomplished employing three key processes, external chiral ligand-controlled conjugate addition of phenyllithium, Curtius conversion of a carboxylic group to an amino group, and finally Pictet–Spengler type cyclization completing skeleton construction.

Yasutomi Asano; Mitsuaki Yamashita; Kazushige Nagai; Masami Kuriyama; Ken-ichi Yamada; Kiyoshi Tomioka

2001-01-01

37

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

2011-11-29

38

A highly stereoselective asymmetric synthesis of (--)-lobeline and (--)-sedamine.  

PubMed

A highly stereoselective asymmetric synthesis of (--)-sedamine and (--)-lobeline is described from benzaldehyde in 16 and 17 steps with an overall yield of 20% and 14%, respectively. The key intermediate syn-3,4-epoxyalcohol was prepared in a highly diastereomeric fashion (>99% ee, dr) and served as a common intermediate for both alkaloids. PMID:12492320

Felpin, François-Xavier; Lebreton, Jacques

2002-12-27

39

Asymmetric total synthesis of ent-cyclooroidin  

PubMed Central

An enantiospecific total synthesis of the pyrrole-imidazole natural product cyclooroidin from histidine is described. The key N1-C9 bond is constructed through an intramolecular SN2-type of reaction of a chloro ester. Subsequent imidazole C2-azidation at the 2-position, pyrrole bromination, azide reduction and deprotection leads to the completion of the synthesis.

Mukherjee, Sabuj; Sivappa, Rasapalli; Yousufuddin, Muhammed; Lovely, Carl J.

2010-01-01

40

Asymmetric synthesis of amines using tert-butanesulfinamide.  

PubMed

Chiral amines are prevalent in many bioactive molecules, including amino acids and pharmaceutical agents. tert-Butanesulfinamide (tBS) is a chiral amine reagent that has enabled the reliable asymmetric synthesis of a very broad range of different amine structures from simple, readily available starting materials. Three steps are commonly applied to the asymmetric synthesis of amines: (i) condensation of tBS with a carbonyl compound, (ii) nucleophile addition and (iii) tert-butanesulfinyl group cleavage. Here we demonstrate these steps with the preparation of a propargylic tertiary carbinamine, one of a class of amines that have been used for many different biological purposes, including click chemistry applications, diversity-oriented synthesis, the preparation of peptide isosteres and the development of protease inhibitors as drug candidates and imaging agents. The process described here can be performed in 3-4 d. PMID:24157547

Xu, Hai-Chao; Chowdhury, Somenath; Ellman, Jonathan A

2013-10-24

41

Stereo and enantio-controlled synthesis of two naturally occurring polyoxygenated cyclohexenemethanols, (+)-epiepoxydon and (?)-phyllostine, via catalytic asymmetrization of a meso substrate  

Microsoft Academic Search

Two naturally occurring polyoxygenated cyclohexenemethanols, (+)-epiepoxydon and (?)-phyllostine, have been first synthesized in stereo- and enantio-controlled manner using a chiral cyclohexadienol synthon prepared by catalytic asymmetrization of a meso substrate. The synthesis has verified the proposed absolute structures of these natural products which have been deduced by CD measurements.

Takashi Kamikubo; Kou Hiroya; Kunio Ogasawara

1996-01-01

42

Asymmetric synthesis of the Japanese beetle pheromone via boronic esters  

Microsoft Academic Search

The pheromone of the Japanese beetle, [R-(Z)]-5-(1-decenyl)dihydro-2(3H)-furanone (7), has been synthesized efficiently in high enantiomeric purity via 1,2-dicyclohexyl-1,2-ethanediol boronic esters. The synthetic route involves reaction of an ?-chloro boronic ester with an alkynyllithium, and provides the first successful example of this substitution process in an asymmetric synthesis.

William C Hiscox; Donald S Matteson

2000-01-01

43

Catalytic asymmetric synthesis of ?-butenolides by direct vinylogous reactions.  

PubMed

The ?-butenolide structural motif is a prominent feature in many bioactive natural products and drugs. This short review summarizes catalytic asymmetric synthesis of ?-butenolides through direct vinylogous reactions by metal complexes and organocatalysts. In light of building chiral ?-tertiary and quaternary carbon centers of butenolides, three synthetic strategies are included: 1) the reactions with furanone derivatives as nucleophiles, 2) olefination of ?,?- disubstituted butenolides and 3) the reactions by using ?,?-disubstituted butenolides as nucleophiles. PMID:23544459

Yan, Lin; Wu, Xiaohong; Liu, Hongjun; Xie, Liangying; Jiang, Zhiyong

2013-05-01

44

Catalytic asymmetric total synthesis of (S)-(-)-zearalenone, a novel lipoxygenase inhibitor.  

PubMed

A catalytic asymmetric synthesis of (S)-(-)-zearalenone is reported using asymmetric allylic alkylation for the introduction of the stereocenter. (S)-(-)-Zearalenone turned out to be a novel lipoxygenase inhibitor. PMID:23867388

Baggelaar, Marc P; Huang, Yange; Feringa, Ben L; Dekker, Frank J; Minnaard, Adriaan J

2013-06-20

45

Asymmetric silver "nanocarrot" structures: solution synthesis and their asymmetric plasmonic resonances.  

PubMed

Here we report the wet-chemical synthesis of asymmetric one-dimensional (1D) silver "nanocarrot" structures that exhibit mixed twins and stacking fault domains along the <111> direction. Oriented attachment is the dominant mechanism for anisotropic growth. Multipolar plasmon resonances up to fourth order were measured by optical extinction spectroscopy and electron energy-loss spectroscopy (EELS) and are in agreement with theoretical calculations. Compared with those of symmetric 1D nanostructures of similar length, the dipole modes of the nanocarrots show a clear red shift, and the EELS maps show an asymmetric distribution of the resonant plasmonic fields and a compression of the resonance node spacing toward the tail. In addition, increasing the length of the nanocarrots causes an increase in the intensity and a steady red shift of the longitudinal surface plasmon resonance peaks. The silver nanocarrots also show very high sensitivity to the refractive index of their environment (890 ± 87 nm per refractive index unit). PMID:23758332

Liang, Hongyan; Rossouw, David; Zhao, Haiguang; Cushing, Scott K; Shi, Honglong; Korinek, Andreas; Xu, Hongxing; Rosei, Federico; Wang, Wenzhong; Wu, Nianqiang; Botton, Gianluigi A; Ma, Dongling

2013-06-19

46

Asymmetric synthesis of a selective endothelin A receptor antagonist.  

PubMed

An asymmetric synthesis of a selective endothelin A receptor antagonist 1b is described. Asymmetric conjugate addition of aryllithium derived from 18 to the chiral oxazoline 17 followed by hydrolysis afforded 15 in 96% ee via purification as (S)-(-)-1-phenylethylamine salt. Pd(OAc)(2)/dppf (1,1'-bis(diphenylphosphino)ferrocene) catalyzed carbonylation followed by chemoselective addition of aryllithium derived from 23 which gave ketone 24. Diastereoselective reduction of the ketone with catecholborane followed by concomitant activation of the resulting alcohol and cyclization gave the late intermediate 26. Introduction of amino moiety on the pyridine ring by imidoyl rearrangement followed by deprotection and purification by crystallization furnished the enantiomerically pure target molecule 1b in 8% overall yield from 16. PMID:12192138

Kato, Yoshiaki; Niiyama, Kenji; Jona, Hideki; Okada, Shigemitsu; Akao, Atsushi; Hiraga, Shouichi; Tsuchiya, Yoshimi; Tomimoto, Koji; Mase, Toshiaki

2002-08-01

47

Synthesis of novel metallocenes: Asymmetric hydrogenation catalysts to conductive polymers  

SciTech Connect

The goal of this research was to synthesize conductive polymers based on repeating ferrocene units. During the course of this study, the design of the conductive polymers evolved from the initial model based on [open quotes]stacked[open quotes] ferrocenes where ethano bridged cyclophentadienyl rings are linked by iron(II), to the latest ferrocene-diene model where ferrocene units were linked by double bonds. In the pursuit of these elusive monomers, attempts at their synthesis led down dead-end routes, even though new molecules were synthesized. Some of these dead-end routes, even though new molecules were synthesized. All the work reported in this dissertation had the eventual goal of synthesizing potential monomers for ferrocene conductive polymers. This dissertation is divided into three chapters. Chapter one describes the attempted synthesis of thiophene derivatives where a cyclopentadienyl ring is fused to the [c]-face. Although the target molecule was never synthesized, a convenient and safe new synthesis of 3,4-dibromo=2,5-dimethyl thiophene was developed along with the synthesis and full characterization of 3-bromo-4-trimethylsilyl-2,5-dimethylthiophene. Chapter two describes the design of asymmetric hydrogenation catalysts and the convenient synthesis of chiral titanocene derivatives. Chapter three summarizes the history of the attempts to prepare ferrocene containing conductive polymers and describes the synthesis of ferrocenophenes and diethano bridged bis(cyclophentadienyl) compounds for use as monomeric precursors to conductive polymers based on repeating ferrocene units.

Erickson, M.S.

1992-01-01

48

Asymmetric synthesis of ?-heterocycle substituted l-?-amino acids  

Microsoft Academic Search

A new efficient method of asymmetric synthesis of ?-heterocycle substituted l-?-amino acids through the addition of 3-amino-1,2,4-thiodiazole and 5-mercapto-1,2,4-triazoles, containing various substituents at the 3 and 4 positions, to the C?C bond of dehydroalanine in the Ni(II) complex of its Schiff base with (S)-2-N-(N?-benzylprolyl)aminobenzophenone has been elaborated upon. Under thermodynamic control, the stereoselectivity of the nucleophilic addition exceeded 94%. After

A. S. Saghiyan; A. V. Geolchanyan; S. G. Petrosyan; T. V. Ghochikyan; V. S. Haroutunyan; A. A. Avetisyan; Yu. N. Belokon’; K. Fisher

2004-01-01

49

Symmetrical and Asymmetrical Bisphosphonate Esters. Synthesis, Selective Hydrolysis, and Isomerization  

Microsoft Academic Search

Summary.  Two simple and efficient one-pot procedures for the synthesis of a series of ?-branched N-heterocycle-substituted methane-1,1-bisphosphonates\\u000a are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction\\u000a with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite\\u000a BPs. Partial

Wafaa M. Abdou; Neven A. Ganoub; Amin F. Fahmy; Abeer A. Shaddy

2006-01-01

50

Enantioselective synthesis of 5-epi-citreoviral using ruthenium-catalyzed asymmetric ring-closing metathesis.  

PubMed

Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in > or = 90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis. PMID:19785443

Funk, Timothy W

2009-11-01

51

Component mode synthesis for multibody systems with absolute coordinates  

Microsoft Academic Search

Abstract—In the present paper, the concept of the float- ing frame of reference is transformed to a description based on absolute coordinates. The equations are linearized for a certain configuration of the body based on a corotational strain tensor. Because of the transformation,to absolute coordinates, the mass matrix is constant and the stiffness matrix can be inverted efficiently. Pairs of

J. Gerstmayr

2007-01-01

52

Total synthesis of 1-deoxygulonojirimycin. Revision of the absolute configuration of the natural product  

Microsoft Academic Search

A concise, stereoselective synthesis of 1-deoxygulonojirimycin was achieved and the absolute configuration of the natural product was revised. Key features involve diastereoselective oxazoline formation catalyzed by palladium(0), RCM and dihydroxylation.

Sung-Jae Pyun; Kee-Young Lee; Chang-Young Oh; Jae-Eun Joo; Seung-Hoon Cheon; Won-Hun Ham

2005-01-01

53

Synthesis of asymmetric biphenyl derivatives for optoelectronic applications  

NASA Astrophysics Data System (ADS)

We report the synthesis and optical properties of a series of ten organic compounds with biphenyl as the backbone and asymmetrically modified by triphenylamines, carbazoles and tetraphenylsilanes (BP 1-10). BP 1-10 were synthesized mainly by Ullmann coupling reaction and Suzuki cross-coupling reaction and characterized by EA, NMR, MS, UV-Vis, DSC, TGA, fluorescence spectra and cyclic voltammetry. They exhibit reversible electrochemical behavior with low oxidation potentials and emit intense pure-blue light with high fluorescence quantum yields (up to 80%). BP 1 was fabricated into multi-layered light-emitting diodes as blue-emitting, host and hole transport materials. Based on the performance of BP 1 and the similarity in chemical structure to those compounds reported in literature, these compounds are expected to be good and versatile hole transport, host and blue emitting materials.

Zhu, Cai-Cai; Guo, Kun-Ping; Liu, Wang-Bo; He, Yan-Bo; Li, Zhi-Mei; Gao, Xi-Cun; Deng, Feng-Jie; Wei, Bin

2013-10-01

54

Chiral 1,3,2-oxazaborolidines in asymmetric synthesis: recent advances  

NASA Astrophysics Data System (ADS)

The use of chiral 1,3,2-oxazaborolidines in asymmetric organic synthesis, particularly, in enantioselective reduction of ketones, imines and oxime ethers, asymmetric Diels-Alder reactions, aldol condensation and atroposelective reduction of lactones is reviewed. Reactions of immobilised 1,3,2-oxazaborolidines are also considered.

Glushkov, Vladimir A.; Tolstikov, Alexander G.

2004-06-01

55

Total Synthesis and Absolute Stereochemical Assignment of Kibdelone C  

PubMed Central

The kibdelones are hexacyclic tetrahydroxanthones and potent anticancer agents isolated from an Australian microbe. Herein, we describe the synthesis of a chiral, non-racemic iodocyclohexene carboxylate EF ring fragment of the kibdelones employing an intramolecular iodo halo-Michael aldol reaction and its merger with an ABCD ring fragment to afford the congener kibdelone C.

Sloman, David L.; Bacon, Jeffrey W.; Porco, John A.

2011-01-01

56

A generic approach for the synthesis of dimer nanoclusters and asymmetric nanoassemblies.  

PubMed

Controlled assembly of nanoparticles into asymmetric configurations is of great interest due to their novel properties and promising applications. In this Article, we report a generic strategy for the synthesis of dimer nanoclusters and asymmetric nanoassemblies by using magnetic colloidal substrates, on which tailored surface modification and controlled physical confinement are applied. The modularity of our approach facilitates the fabrication of asymmetric nanostructures with varying sizes, shapes, compositions, surface chemistry, and surface hydrophobicity. Success in the syntheses sheds a light on the versatility of our strategy in rationally designing and synthesizing asymmetric nanostructures with tailored properties and functionalities. PMID:23346956

Hu, Yongxing; Sun, Yugang

2013-02-01

57

Recent advances in iridium-catalyzed asymmetric hydrogenation: new catalysts, substrates and applications in total synthesis.  

PubMed

Iridium-catalyzed asymmetric hydrogenation has emerged as a highly efficient method for the synthesis of enantiomerically pure compounds. This account summarizes our recent efforts in this field. We have developed a new type of P,O-ligand that was successfully applied to the asymmetric hydrogenation of ?,?-unsaturated carbonyl compounds. Furthermore we have demonstrated the potential of known iridium catalysts in the hydrogenation of ?,?-unsaturated boronic esters. And finally we could demonstrate the utility of iridium-catalyzed asymmetric hydrogenation in the formal synthesis of the natural product Platensimycin. PMID:22613146

Gani?, Adnan; Rageot, Denise; Tröndlin, Lars; Pfaltz, Andreas

2012-01-01

58

Enzyme-assisted asymmetric total synthesis of (-)-podophyllotoxin and (-)-picropodophyllin.  

PubMed

Described is the first catalytic, asymmetric synthesis of (-)-podophyllotoxin and its C(2)-epimer, (-)-picropodophyllin. Asymmetry is achieved via the enzymatic desymmetrization of advanced meso diacetate 20, through PPL-mediated ester hydrolysis. A second key feature of the synthesis is the strategically late introduction of the highly oxygenated natural ring E through an arylcopper species. The successful implementation of this approach augers well for the introduction of other functionalized rings E for future SAR work. The synthesis begins from piperonal, which is fashioned into isobenzofuran (IBF) precursor 14 in three steps (bromination, acetalization, and halogen-metal exchange/hydroxymethylation). Interestingly, treatment of 14 with HOAc in commerical dimethyl maleate (contains 5% dimethyl fumarate) leads to a nearly equimolar mixture of fumarate- (15) and maleate-IBF Diels-Alder adducts (16 and 17), indicating that IBF 11 reacts about 15 times faster with dimethyl fumarate than with dimethyl maleate. With scrupulously pure dimethyl maleate a 2.8:1 endo:exo mixture of maleate DA adducts is still obtained. On the other hand, the desired meso diester 16 is obtained pure and in nearly quantitative yield by employing neat dimethyl acetylene dicarboxylate as the dienophile, followed by catalytic hydrogenation. Reduction (LiAlH(4)) of 16 provides meso diol 19, which is then treated with Ac(2)O, BzCl, and PhCH(2)COCl to provide the corresponding meso diesters, 20-22. Screening of these meso benzoxabicyclo[2.2.1]heptyl substrate candidates across a battery of acyl transfer enzymes leads to an optimized match of diacetate 20 with PPL. Even on 10-20 g scales, asymmetry is efficiently introduced here, yielding the key chiral intermediate, monoacetate 25 (66% isolated yield, 83% corrected yield, 95% ee). Protecting group manipulation and oxidation (Swern) provide aldehyde 27b, which undergoes efficient retro-Michael ring opening to produce dihydronaphthalene 30, in which the C(3) and C(4) stereocenters are properly set. Following several unsuccessful approaches to the intramolecular delivery of ring E (via Claisen rearrangement, Heck-type cyclization, or radical cyclization), a highly diastereoselective, intermolecular conjugate addition of the arylcopper reagent derived from (3,4,5-trimethoxy)phenylmagnesium bromide and CuCN to acyl oxazolidinone 50 was developed (85% yield, only the required alpha-stereochemistry at C(1) is observed). The conjugate addition product is converted to (-)-picropodophyllin in two steps (lactonization, SEM deprotection) or to (-)-podophyllotoxin, in three steps, through the introduction of a C(2)-epimerization step, under Kende conditions, prior to the final conjugate addition. PMID:10814019

Berkowitz, D B; Choi, S; Maeng, J H

2000-02-11

59

Synthesis, resolution, and absolute stereochemistry of (-)-blestriarene C.  

PubMed

A naturally occurring 1,1'-biphenanthrene, blestriarene C (1), was prepared in 13 steps and 30% overall yield. The key steps are the ester-mediated nucleophilic aromatic substitution on 2,6-di-tert-butyl-4-methoxyphenyl 5-isopropoxy-2-methoxybenzoate (4) by 2-methoxy-4-methoxymethoxy-6-methylphenylmagnesium bromide (5) and a novel intramolecular cyclization of the resulting 4-isopropoxy-2'-methoxy-4'-methoxymethoxy-6'-methylbiphenyl-2-carboxylic ester 14 to 7-isopropoxy-4-methoxy-2-(methoxymethoxy)phenanthren-9-ol (15). The racemic blestriarene C was optically resolved by chiral HPLC on a preparative scale to give several 10-mg yields of both the enantiomers in up to 95% ee. The absolute stereochemistry was determined to be S(a)-(-) by the axial chirality recognition method, which was based on the stereospecific formation of a 12-membered cyclic diester containing two biaryl-o,o'-diyl unites joined by ester -CO(2)- linkages. The validity of the method was confirmed by an X-ray crystallographic analysis and ab initio conformational analyses of such 12-membered cyclic diesters. It was found that blestriarene C and its 7,7'-diisopropyl ether 2 underwent rapid photoracemization even under ambient light exposure. PMID:12636367

Hattori, Tetsutaro; Shimazumi, Yuhi; Goto, Hitoshi; Yamabe, Osamu; Morohashi, Naoya; Kawai, Wataru; Miyano, Sotaro

2003-03-21

60

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step  

PubMed Central

Summary The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed.

Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

2012-01-01

61

Asymmetric synthesis of the core structure of leucosceptroids A-D.  

PubMed

The asymmetric synthesis of the core structure of leucosceptroids A-D has been achieved. The key steps of the synthesis includes the formation of the cis-2,5-disubstituted THF ring by TPAP catalytic oxidative cyclization followed by a highly diastereoselective intramolecular Diels-Alder reaction to fashion the fused tricyclic hydrindane ring system. PMID:21644513

Xie, Jun; Ma, Yuelong; Horne, David A

2011-06-28

62

Establishing the absolute configuration of the asbestinins: enantioselective total synthesis of 11-acetoxy-4-deoxyasbestinin D.  

PubMed

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C-14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this subclass of the C-2-C-11-cyclized cembranoid natural products. PMID:16332064

Crimmins, Michael T; Ellis, J Michael

2005-12-14

63

Establishing the Absolute Configuration of the Asbestinins: Enantioselective Total Synthesis of 11-Acetoxy-4-deoxyasbestinin D  

PubMed Central

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this sub-class of the C2-C11-cyclized cembranoid natural products.

Crimmins, Michael T.; Ellis, J. Michael

2008-01-01

64

Asymmetric oxidation of sulfides catalyzed by titanium and vanadium complexes in the synthesis of biologically active sulfoxides  

NASA Astrophysics Data System (ADS)

Published data on the asymmetric synthesis of chiral biologically active sulfoxides by oxidation of appropriate sulfides catalyzed by titanium and vanadium complexes are generalized. Bibliography — 87 references.

Volcho, Konstantin P.; Salakhutdinov, Nariman F.

2009-05-01

65

Asymmetric synthesis of 2,4,5-trisubstituted ?2-thiazolines.  

PubMed

?(2)-Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5-trisubstituted ?(2)-thiazolines. These ?(2)-thiazolines were synthesized from readily accessible/commercially available ?,?-unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an O?N acyl migration reaction as key steps. The final products were obtained in good yields with up to 97?% enantiomeric excess. PMID:23776083

Bengtsson, Christoffer; Nelander, Hanna; Almqvist, Fredrik

2013-06-17

66

Asymmetric Synthesis of 2,4,5-Trisubstituted ?2-Thiazolines  

PubMed Central

?2-Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5-trisubstituted ?2-thiazolines. These ?2-thiazolines were synthesized from readily accessible/commercially available ?,?-unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an O?N acyl migration reaction as key steps. The final products were obtained in good yields with up to 97% enantiomeric excess.

Bengtsson, Christoffer; Nelander, Hanna; Almqvist, Fredrik

2013-01-01

67

A facile method of synthesis of asymmetric hollow silica spheres.  

PubMed

This paper presents a "one-step" method to synthesize asymmetric hollow silica spheres. In this method, when positively charged polystyrene particles were blended with mercaptopropyltriethoxysilane and stirred at 50 °C in alkaline ethanol/water medium for a period of time, Janus or lobed asymmetric hollow silica spheres could be directly obtained, just changing the ratio of ethanol to water in the reaction medium. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the morphology and topography of the asymmetric hollow silica spheres. The formation mechanism was described in detail. PMID:21722911

Yuan, Junjie; Wang, Zhengqi

2011-06-14

68

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

2013-03-08

69

Enantioconvergent Synthesis of (+)-Aphanorphine via Asymmetric Pd-Catalyzed Alkene Carboamination  

PubMed Central

A concise asymmetric synthesis of (+)-aphanorphine has been achieved via a new enantioconvergent strategy. A racemic ?-aminoalkene derivative is transformed into a 1:1 mixture of enantiomerically enriched diastereomers using an asymmetric Pd-catalyzed carboamination. This mixture is then converted to an enantiomerically enriched protected aphanorphine derivative by a Friedel-Crafts reaction, which generates a quaternary all-carbon stereocenter. The natural product is obtained in three additional steps.

Mai, Duy N.; Rosen, Brandon R.; Wolfe, John P.

2011-01-01

70

Practical asymmetric synthesis of a selective endothelin A receptor (ETA) antagonist.  

PubMed

[structure: see text]. A practical, chromotography-free asymmetric synthesis was developed for the large scale preparation of an endothelin receptor antagonist 2. This synthesis includes a new efficient process for the preparation of 6-bromo-2,3-dihydrobenzofuran, a stereoselective conjugate addition of an aryllithium followed by stereospecific addition of the Grignard reagent of the top aryl bromide, and an aminophosphate-mediated sterospecific intramolecular enolate alkylation, which led to the formation of the five-membered ring bearing three contiguous asymmetric centers. PMID:11594833

Song, Z J; Zhao, M; Frey, L; Li, J; Tan, L; Chen, C Y; Tschaen, D M; Tillyer, R; Grabowski, E J; Volante, R; Reider, P J; Kato, Y; Okada, S; Nemoto, T; Sato, H; Akao, A; Mase, T

2001-10-18

71

Total synthesis of (-)-hippodamine by stereocontrolled construction of azaphenalene skeleton based on extended one-pot asymmetric azaelectrocyclization.  

PubMed

The first asymmetric total synthesis of (-)-hippodamine has been accomplished via the concise construction of its azaphenalene core, which is featured by the 2,4,6-chiral piperidine synthesis based on one-pot asymmetric azaelectrocyclization in the partially activated substituent system and the subsequent intramolecular Mannich reaction. PMID:23688061

Fujita, Shintaro; Sakaguchi, Taku; Kobayashi, Toyoharu; Tsuchikawa, Hiroshi; Katsumura, Shigeo

2013-05-21

72

Enantioselective Total Synthesis of (+)-Gliocladin C  

PubMed Central

The first total synthesis of gliocladin C, a fungal-derived marine alkaloid containing a rare trioxopiperazine fragment, is reported. This asymmetric synthesis establishes the absolute configuration of this structurally novel natural product.

Overman, Larry E.; Shin, Youseung

2008-01-01

73

Asymmetric total synthesis of (-)-amphidinolide V through effective combinations of catalytic transformations.  

PubMed

An asymmetric total synthesis of (-)-amphidinolide V was accomplished. The synthesis features a base-catalyzed alkynyl silane alcoholysis/ring-closing enyne metathesis sequence for facile construction of a 1,3-diene motif. A diene RCM followed by a ring-contractive allylic transposition of cyclic silyl ethers was incorporated for the stereoselective installation of a functionalized 1,5-diene subunit. An efficient proline-mediated direct cross-aldol condensation of two advanced aldehyde intermediates was utilized for the construction of a key ?,?-unsaturated epoxyaldehyde. This total synthesis demonstrates the prowess of metal-catalyzed transformations in complex molecule synthesis. PMID:23514007

Volchkov, Ivan; Lee, Daesung

2013-03-28

74

Asymmetric bioreductions: application to the synthesis of pharmaceuticals  

Microsoft Academic Search

Selected examples of asymmetric bioreductions of pharmaceutically relevant prochiral ketones are reviewed. These data show that microbial screens lead to the identification of appropriate biocatalysts, and that the use of miniaturized and semi-automated technology can greatly reduce both labor and lead times. The same data also highlight the need to evaluate a relatively large and\\/or diverse microbial population (highlighting biodiversity).

Michel Chartrain; Randolph Greasham; Jeffrey Moore; Paul Reider; David Robinson; Barry Buckland

2001-01-01

75

Efficient asymmetric synthesis of lamivudine via enzymatic dynamic kinetic resolution.  

PubMed

The anti-HIV nucleoside lamivudine was asymmetrically synthesized in only three steps via a novel surfactant-treated subtilisin Carlsberg-catalyzed dynamic kinetic resolution protocol. The enantiomer of lamivudine could also be accessed using the same protocol catalyzed by Candida antarctica lipase B. PMID:24071972

Hu, Lei; Schaufelberger, Fredrik; Zhang, Yan; Ramström, Olof

2013-10-10

76

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.

2013-01-01

77

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.

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

2011-01-01

78

N-silyl oxyketene imines are underused yet highly versatile reagents for catalytic asymmetric synthesis  

Microsoft Academic Search

The reactions of acyl anion equivalents (d1 synthons) with carbonyl electrophiles allow for the construction of a wide range of molecules useful for the synthesis of biologically active compounds, natural products and chiral ligands. Despite their utility, significant challenges still exist for developing catalytic, enantioselective variants of these reactions. For example, the asymmetric benzoin process, arguably the most characteristic reaction

Tyler W. Wilson; Scott E. Denmark

2010-01-01

79

Asymmetric catalytic alkynylation of acetaldehyde and its application to the synthesis of (+)-tetrahydropyrenophorol  

PubMed Central

By controlling the kinetics of alkynylation over aldolisation (by slowing adding the acceptor), the challenging asymmetric catalytic alkynylation of acetaldehyde has been realized. This protocol yields the corresponding attractive synthons in good to excellent enantiocontrol and shows broad tolerance and applicability. This was highlighted by its application to the synthesis of several natural products such as the rapid construction of the macrocyclic diolide (+)-tetrahydropyrenophorol.

Trost, Barry. M.; Quintard, Adrien

2012-01-01

80

?-Transaminase-catalyzed asymmetric synthesis of unnatural amino acids using isopropylamine as an amino donor.  

PubMed

Isopropylamine is an ideal amino donor for reductive amination of carbonyl compounds by ?-transaminase (?-TA) owing to its cheapness and high volatility of a ketone product. Here we developed asymmetric synthesis of unnatural amino acids via ?-TA-catalyzed amino group transfer between ?-keto acids and isopropylamine. PMID:23897436

Park, Eul-Soo; Dong, Joo-Young; Shin, Jong-Shik

2013-09-25

81

DNA vs. Mirror-Image DNA: A Universal Approach to Tune the Absolute Configuration in DNA-Based Asymmetric Catalysis.  

PubMed

Mirror mirror on the wall: By taking advantage of the unique structural features of L-DNA, the first examples of left-helical enantioselective induction in the field of DNA-based asymmetric catalysis were realized. Most importantly, this approach is the only one that allows a reliable and predictable access to both enantiomers for any given reaction. PMID:24030985

Wang, Jocelyn; Benedetti, Erica; Bethge, Lucas; Vonhoff, Stefan; Klussmann, Sven; Vasseur, Jean-Jacques; Cossy, Janine; Smietana, Michael; Arseniyadis, Stellios

2013-09-12

82

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.

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

2013-01-01

83

A series of asymmetrical phthalocyanines: synthesis and near infrared properties.  

PubMed

We report here the preparation of asymmetrical phthalocyanine dimers 1a-3a, which are endowed with novel charge transfer bands at 1,151-1,154 nm and strong NIR luminescences at 840-860 nm and 1,600-1,650 nm. Through H-bonding interaction, 1a-3a are inclined to self-assemble into hexrod nanotubes at the interface of CHCl? and CH?H. Our results provide further insights into the interaction in molecular dimers, and suggest that 1a-3a have potential application in magnets and supramolecular architectures. PMID:23603946

Huang, Guoqing; Li, Jianxi; Cong, Fangdi; Li, Chao; Chu, Xixi; Meng, Yanyan; Du, Guotong; Du, Xiguang

2013-04-19

84

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

2013-08-29

85

?-Vinylic amino acids: occurrence, asymmetric synthesis, and biochemical mechanisms  

Microsoft Academic Search

This report presents an overview of the family of naturally occurring ‘vinylic’ amino acids, namely those that feature a C–C double bond directly attached to the ?-carbon, along the side chain. Strategies that have been brought to bear on the stereocontrolled synthesis of these olefinic amino acids are surveyed. The mechanistic diversity by which such ‘vinylic triggers’ can be actuated

David B. Berkowitz; Bradley D. Charette; Kannan R. Karukurichi; Jill M. McFadden

2006-01-01

86

Catalytic asymmetric synthesis of beta-hydroxyacids and their esters  

Microsoft Academic Search

Data on the catalytic methods for the reduction of beta-ketoacids and their esters to the corresponding optically active hydroxyacids and hydroxyesters with the aid of enzymes and chiral heterogeneous and metal complex catalysts are surveyed. The application of optically active hydroxyesters as chiral synthons and monomers for the synthesis of biodegradable polymers is examined. Procedures for increasing the optical purity

Evgenii I. Klabunovskii

1996-01-01

87

Asymmetric synthesis of pent-3-yl ( R)-6-methyl-cyclohex-1-ene carboxylate  

Microsoft Academic Search

An expeditious asymmetric synthesis of pent-3-yl (R)-6-methyl-cyclohex-1-enecarboxylate has been achieved in four steps in 42% overall yield employing as the key step a domino reaction initiated by a highly diastereoselective lithium amide 1,4-conjugate addition to a nona-2,7-diendioic diester followed by a 6-exo-trig cyclisation of the thus formed enolate. Cope elimination protocol of the cyclic adduct affords, depending on the lithium

Narciso M. Garrido; David Díez; Sara H. Domínguez; Mercedes García; M. Rosa Sánchez; Stephen G. Davies

2006-01-01

88

Hydroxynitrile lyase from Passiflora edulis: Purification, characteristics and application in asymmetric synthesis of ( R)-mandelonitrile  

Microsoft Academic Search

A hydroxynitrile lyase from leaves of Passiflora edulis (PeHNL) was purified and characterized for the first time. The enzyme is a monomer of 15kDa and 18kDa by SDS-PAGE, and gel filtration, respectively. Asymmetric synthesis of (R)-mandelonitrile from benzaldehyde and acetone cyanohydrin in a biphasic system employing the PeHNL from rinds of P. edulis was carried out. Several parameters influenced the

Techawaree Ueatrongchit; Ken’ichirou Tamura; Tohru Ohmiya; Aran H-Kittikun; Yasuhisa Asano

2010-01-01

89

Asymmetric synthesis of organometallic reagents using enzymatic methods  

Microsoft Academic Search

The use of enzymatic catalysis in the synthesis and resolution of organometallic complexes is reviewed and discussed. Examples\\u000a show the potential of biological catalysts for oxidation, reduction, hydrolysis, and esterification of both transition metal\\u000a and main group organometallic substrates. Chirality in organometallic complexes caused by the presence of chiral carbon centers\\u000a in substituent groups, tetrahedral or pseudotetrahedral metal centers, and

D. E. Bergbreiter; M. Momongan

1992-01-01

90

Stereocontrolled synthesis of trisubstituted cyclopropanes: expedient, atom-economical, asymmetric syntheses of (+)-Bicifadine and DOV21947.  

PubMed

[reaction: see text] An expedient, atom-economical, asymmetric synthesis of 1-aryl-3-azabicyclo[3.1.0]hexanes, including (+)-Bicifadine and DOV21947, in a single-stage through process without isolation of any intermediates has been developed. The key of this synthesis is the in-depth mechanistic understanding of the complicated epoxy nitrile coupling at each reaction stage. Therefore, the desired trisubstituted cyclopropane can be prepared in high ee and yield by controlling the reaction pathway through manipulating the nitrile anion aggregation state. PMID:16898842

Xu, Feng; Murry, Jerry A; Simmons, Bryon; Corley, Edward; Fitch, Kenneth; Karady, Sandor; Tschaen, David

2006-08-17

91

Studies Toward the Asymmetric Synthesis of the Right Part of the Mycalamides  

PubMed Central

Described herein is the asymmetric synthesis of a functionalized, trioxadecalin unit that comprises the right-hand part of the mycalamides and related natural products. The synthetic route involves a 16-step sequence that accomplishes the formation of two heterocyclic rings and the generation of five stereocenters. The synthesis commenced with a C2 symmetric starting material, diethyl D-tartrate, and took advantage of a relay of diastereoselective reactions to extend this four-carbon chain and introduce new chiral centers. Subsequent electrophile mediated cyclization afforded the desired pyran ring, which was then transformed into the desired, functionalized trioxadecalin skeleton.

Zhong, H. Marlon; Sohn, Jeong-Hun; Rawal, Viresh H.

2008-01-01

92

Concise, Asymmetric, Stereocontrolled Total Synthesis of Stephacidins A, B and Notoamide B  

PubMed Central

Concise asymmetric total syntheses of the fungal metabolites (?)-stephacidin A, (+)-stephacidin B, and (+)-notoamide B are described. Key features of these total syntheses include (1) a facile synthesis of (R)-allyl proline methyl ester, (2) a revised route toward the pyranoindole ring system, (3) a novel cross-metathesis strategy for the introduction of important functional groups, and (4) an SN2? cyclization to form the [2.2.2] bridged bicyclic ring system. Furthermore, our synthesis has taken advantage of microwave heating to shorten reaction times as well as increase yields for the preparation of vital intermediates.

Artman, Gerald D.; Grubbs, Alan W.; Williams, Robert M.

2007-01-01

93

Reflections on spontaneous asymmetric synthesis by amplifying autocatalysis.  

PubMed

Spontaneous generation of chirality was observed in the course of studying the mechanism of asymmetric autocatalysis by NMR in ZnR2 alkylation of pyrimidin-5-aldehydes. A systematic study was carried out in order to discover its origins. Even in clean fresh non-glass reaction vessels spontaneous ee was clearly observed, and was not dependent on any single reaction parameter. For comparison it was demonstrated that enantiomerically pure Zn alkoxide catalyst could control the configuration of the reaction product even when present at below micromolar concentrations. The high propensity of the Soai reaction system to produce an enantiomerically enriched product without initial bias is suggested to result from stochastic effects. These are especially important in autocatalysis because all the final products can be derived by breeding from a small number of initial events. The statistical excess of one enantiomer in that set is sufficient to generate a measurable ee in the product. The process is aided by the requirement for dimerisation before the product is an active catalyst. An enumeration that rationalises these observations is provided. PMID:14649913

Gridnev, Ilya D; Serafimov, Joerg M; Quiney, Harry; Brown, John M

2003-11-01

94

Synthesis and spectroscopic properties of novel asymmetric Schiff bases.  

PubMed

Three novel diimine Schiff bases including two asymmetric imines (2-OH)R-CHN-C(6)H(4)-CHN-R'(2-OH) type [where R=R'=phenyl for H(2)L(1); R=naphthyl, R'=phenyl for H(2)L(2) and R=R'=naphthyl for H(2)L(3)] have been synthesized with a new two step method. For this purpose, the starting Schiff bases 4-nitrobenzylidene-2-hydroxyaniline (SB(1)-NO(2)) and 4-nitrobenzylidene-2-hydroxy-3-naphthylamine (SB(2)-NO(2)) have been synthesized, previously. Nitro groups of them have been reduced into their amino derivatives (SB(1)-NH(2) and SB(2)-NH(2)) with sodium dithionite as selective reductant and the other imino groups have been formed by adding salicylaldehyde or 2-hydroxy-1-naphthaldehyde to the same solutions. The structures of the diimine Schiff bases were confirmed by elemental analyses, ESI-MS, FT-IR, (1)H NMR and (13)C NMR spectroscopy. The phenol-imine and keto-amine tautomerism of the Schiff bases were investigated by FT-IR, (1)H NMR, (13)C NMR techniques and UV-vis spectra in different solvents (DMSO, methanol, chloroform, toluene and cyclohexane). The effects of acidic and basic media on the tautomeric equilibria were discussed. PMID:20541456

Güngör, Ozlem; Gürkan, Perihan

2010-05-24

95

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl- and Diheteroarylmethanols  

PubMed Central

Enantioenriched diaryl-, aryl heteroaryl- and diheteroarylmethanols exhibit important biological and medicinal properties. One-pot catalytic asymmetric syntheses of these compounds beginning from readily available aryl bromides are introduced. Thus, lithium-bromide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with ZnCl2 to generate ArZnCl. A second equivalent of n-BuLi was added to form the mixed organozinc, ArZnBu. In the presence of enantioenriched amino alcohol-based catalysts, ArZnBu adds to aldehydes to afford essentially racemic diarylmethanols. The low enantioselectivities were attributed to a LiCl-promoted background reaction. To inhibit this background reaction, the chelating diamine TEEDA (tetraethylethylene diamine) was introduced prior to aldehyde addition. Under these conditions, enantioenriched diarylmethanols were obtained with >90% ee. Arylations of enals generated allylic alcohols with 81–90% ee. This procedure was unsuccessful, however, when applied to heteraryl bromides, which was attributed to decomposition of the heteroaryl lithium under the salt metathesis conditions. To avoid this problem, the metathesis was conducted with EtZnCl, which enabled the salt metathesis to proceed at low temperatures. The resulting EtZn(ArHetero) intermediates (ArHetero=2- and 3-thiophenyl, 2-benzothiophenyl, 3-furyl, and 5-indolyl) were successfully added to aldehydes and heteroaryl aldehydes with enantioselectivities between 81–99%. These are the first examples of catalytic and highly enantioselective syntheses of diheteroarylmethanols. In a similar fashion, ferrocenyl bromide was used to generate FcZnEt and the ferrocenyl group added to benzaldehyde and heteroaromatic aldehydes to form ferrocene-based ligand precursors in 86–95% yield with 96–98% ee. It was also found that the arylation and heteroarylation of enals could be followed by diastereoselective epoxidations to provide epoxy alcohols with high enantio- and diastereoselectivities in a one-pot procedure.

Salvi, Luca; Kim, Jeung Gon; Walsh, Patrick J.

2009-01-01

96

Synthesis of three asymmetric N-confused tetraarylporphyrins.  

PubMed

Two monosubstituted and one tetrasubstituted N-confused porphyrins (1-3) were prepared in ca. 3-5% yields using a [2 + 2] synthesis. The monosubstituted porphyrins have carbomethoxy (1) or nitro (2) substituents on one of the meso-phenyl groups, while the meso-phenyl groups of the third NCP (3) are substituted with nitro, bromo, and methyl groups in an AB(2)C pattern. The specific regiochemistry of the aryl rings around the macrocycle in each porphyrin was definitively determined using a combination of 1D ((1)H and (13)C) and 2D (gHMBC, gHSQC and ROESY) NMR spectroscopy. The absorption spectra of 1-3 in CH(2)Cl(2) are similar to those of N-confused tetraphenylporphyrin (NCTPP) but have Soret and Q bands that are shifted to lower energies with smaller extinction coefficients in comparison to those for NCTPP. PMID:22730896

Acharya, Rajendra; Paudel, Liladhar; Joseph, Jojo; McCarthy, Claire E; Dudipala, Venkat R; Modarelli, Jody M; Modarelli, David A

2012-07-06

97

Total synthesis and absolute stereochemical assignment of (+)- and (-)-galbulimima alkaloid 13.  

PubMed

We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13. The absolute stereochemistry of natural (-)-galbulimima alkaloid 13 is revised to 2S. Sequential use of catalytic cross-coupling and cross-metathesis reactions followed by an intramolecular Diels-Alder reaction provided the required trans-decalin AB-ring system and masked the C16 carbonyl as an N-vinyl carbamate for late-stage unveiling in the form of the necessary C16 enone. A vinyl radical cyclization secured the C-ring, while successful execution of our strategy for introduction of the CDE-ring system in complex galbulimima alkaloids provided the target pentacycle with complete diastereoselection. PMID:16787063

Movassaghi, Mohammad; Hunt, Diana K; Tjandra, Meiliana

2006-06-28

98

Enantioselective total synthesis and confirmation of the absolute and relative stereochemistry of streptorubin B.  

PubMed

The enantioselective total synthesis of the pyrrolophane natural product streptorubin B is described. Key steps in the concise route include the application of a one-pot enantioselective aldol cyclization/Wittig reaction and an anionic oxy-Cope rearrangement to forge the crucial 10-membered ring. Comparisons between CD spectra of synthetic and natural samples of streptorubin B coupled with X-ray crystallography allowed for the determination of the absolute stereochemistry of this natural product for the first time. These studies also provided unambiguous proof of the relative configuration between the butyl side chain and the bispyrrole subunit. Additional studies revealed a novel atropstereoselective Paal-Knorr pyrrole condensation and provided fundamental experimental insight into the barrier for atropisomerization of the natural product. PMID:21166419

Hu, Dennis X; Clift, Michael D; Lazarski, Kiel E; Thomson, Regan J

2010-12-17

99

Asymmetric Palladium-Catalyzed Carboamination Reactions for the Synthesis of Enantiomerically Enriched 2-(Arylmethyl)- and 2-(Alkenylmethyl) pyrrolidines  

PubMed Central

The enantioselective synthesis of 2-(arylmethyl)- and 2-(alkenylmethyl)pyrrolidine derivatives via Pd-catalyzed alkene carboamination reactions is described. These transformations generate enantiomerically enriched products with up to 94% ee from readily available alkenyl or aryl bromides and N-boc-pent-4-enylamines. The application of this method to a concise asymmetric synthesis of (?)-tylophorine is also discussed.

Mai, Duy N.; Wolfe, John P.

2010-01-01

100

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D.  

PubMed

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction. PMID:16104734

Wilson, Rebecca M; Jen, Wendy S; Macmillan, David W C

2005-08-24

101

The first enantiospecific synthesis of (+)-10,11-epoxythapsan-10-ol: revision of the absolute stereochemistry of thapsanes  

Microsoft Academic Search

The first enantiospecific synthesis of (+)-cis,anti,cis-1,8,12,12-tetramethyl-4-oxatricyclo[6.4.0.02,6]dodecan-3-ol (+)-1g, an enantiomer of natural thapsane isolated from Thapsia villosa var minor, is accomplished starting from (R)-carvone, which revises the absolute stereochemistry of natural thapsanes.

A Srikrishna; K Anebouselvy

2002-01-01

102

The first synthesis of a 12-membered macrolide natural product via a RCM protocol: determination of absolute stereochemistry  

Microsoft Academic Search

The first synthesis of (10S,12R)-10-hydroxy-12-methyl-1-oxacyclododecane-2,5-dione and its C12 epimer is reported, thereby assigning the absolute stereochemistry of the natural product. The strategy utilizes a syn selective reduction, Yamaguchi esterification, and ring-closing metathesis as the key steps.

Palakodety Radha Krishna; Ravula Srinivas

2008-01-01

103

Total synthesis of (+)-( S)-angustureine and the determination of the absolute configuration of the natural product angustureine  

Microsoft Academic Search

Angustureine, isolated from the bark of Galipea officinalis Hancock, is a novel quinoline alkaloid with a n-pentyl side chain at the 2-position. The total synthesis of (+)-(S)-angustureine and a determination of the absolute configuration of the natural product angustureine were achieved using ring-closing metathesis (RCM) and the Mitsunobu reaction as key steps.

Chumpol Theeraladanon; Mitsuhiro Arisawa; Masako Nakagawa; Atsushi Nishida

2005-01-01

104

Total synthesis and determination of the absolute configuration of 5,6-dihydro-?-pyrone natural product synargentolide B.  

PubMed

Enantiospecific total synthesis and determination of the absolute stereochemistry of the ?-pyrone-containing natural product synargentolide B were accomplished. The absolute stereochemistry of the natural product was established by synthesizing the possible diastereomers and comparison of the data with those reported for the natural product. During the process, total synthesis of the putative structure of related natural product 6R-[1S,2R,5R,6S-(tetraacetyloxy)-3E-heptenyl]-5,6-dihydro-2H-pyran-2-one was also accomplished and confirmed by X-ray crystal structure analysis. Wittig-Horner reaction of a chiral phosphonate derived from (S)-lactic acid and ring-closing metathesis were the key reactions during the course of the total synthesis. PMID:23477705

Prasad, Kavirayani R; Gutala, Phaneendra

2013-03-27

105

Asymmetric synthesis of cyclic hydroxy ketones derived from enol ethers via sharpless asymmetric dihydroxylation. A study in the correlation of the enol ether chain length and enantioselectivity.  

PubMed

The Sharpless asymmetric dihydroxylation reaction of enol ethers derived from their corresponding cyclic ketones, gave alpha-hydroxyketones with high enantioselectivity. The enantiomeric excess was found to be proportional to the length of the unbranched enol ether chain with a maximum ee for the pentyl enol ether. An efficient synthesis of alpha-hydroxy chromanone in >90% ee was demonstrated using this method. PMID:14535787

Marcune, Benjamin F; Karady, Sandor; Reider, Paul J; Miller, Ross A; Biba, Mirlinda; DiMichele, Lisa; Reamer, Robert A

2003-10-17

106

Enantioselective total synthesis of (+)-ibophyllidine via an asymmetric phosphine-catalyzed [3 + 2] annulation†  

PubMed Central

In this study we performed the total synthesis of the terpene indole alkaloid (+)-ibophyllidine through a pathway involving asymmetric phosphine catalysis, with our novel l-4-hydroxyproline–derived chiral phosphine mediating the key [3 + 2] annulation. Hydrogenation of the [3 + 2] adduct allowed the rapid formation of the stereochemically dense pyrrolidine ring of (+)-ibophyllidine in excellent yield with exceptionally high levels of both diastereo- and enantioselectivity. We constructed the remainder of the pentacyclic skeleton through an intramolecular alkylation and an intramolecular aza-Morita–Baylis–Hillman reaction.

Andrews, Ian P.

2012-01-01

107

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

PubMed

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; Johnson, Jeffrey S

2013-04-30

108

Investigation of Lewis acid versus Lewis base catalysis in asymmetric cyanohydrin synthesis.  

PubMed

The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}(2)] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X=EtOSO(3) or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}(2)O] and triphenylphosphine oxide, a non-linear Hammett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron-deficient. These results suggested that the aluminium complex/triphenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ketones and this was found to be the case. PMID:20715204

North, Michael; Omedes-Pujol, Marta; Williamson, Courtney

2010-10-01

109

Engineering methylaspartate ammonia lyase for the asymmetric synthesis of unnatural amino acids  

NASA Astrophysics Data System (ADS)

The redesign of enzymes to produce catalysts for a predefined transformation remains a major challenge in protein engineering. Here, we describe the structure-based engineering of methylaspartate ammonia lyase (which in nature catalyses the conversion of 3-methylaspartate to ammonia and 2-methylfumarate) to accept a variety of substituted amines and fumarates and catalyse the asymmetric synthesis of aspartic acid derivatives. We obtained two single-active-site mutants, one exhibiting a wide nucleophile scope including structurally diverse linear and cyclic alkylamines and one with broad electrophile scope including fumarate derivatives with alkyl, aryl, alkoxy, aryloxy, alkylthio and arylthio substituents at the C2 position. Both mutants have an enlarged active site that accommodates the new substrates while retaining the high stereo- and regioselectivity of the wild-type enzyme. As an example, we demonstrate a highly enantio- and diastereoselective synthesis of threo-3-benzyloxyaspartate (an important inhibitor of neuronal excitatory glutamate transporters in the brain).

Raj, Hans; Szyma?ski, Wiktor; de Villiers, Jandré; Rozeboom, Henriëtte J.; Veetil, Vinod Puthan; Reis, Carlos R.; de Villiers, Marianne; Dekker, Frank J.; de Wildeman, Stefaan; Quax, Wim J.; Thunnissen, Andy-Mark W. H.; Feringa, Ben L.; Janssen, Dick B.; Poelarends, Gerrit J.

2012-06-01

110

Engineering methylaspartate ammonia lyase for the asymmetric synthesis of unnatural amino acids.  

PubMed

The redesign of enzymes to produce catalysts for a predefined transformation remains a major challenge in protein engineering. Here, we describe the structure-based engineering of methylaspartate ammonia lyase (which in nature catalyses the conversion of 3-methylaspartate to ammonia and 2-methylfumarate) to accept a variety of substituted amines and fumarates and catalyse the asymmetric synthesis of aspartic acid derivatives. We obtained two single-active-site mutants, one exhibiting a wide nucleophile scope including structurally diverse linear and cyclic alkylamines and one with broad electrophile scope including fumarate derivatives with alkyl, aryl, alkoxy, aryloxy, alkylthio and arylthio substituents at the C2 position. Both mutants have an enlarged active site that accommodates the new substrates while retaining the high stereo- and regioselectivity of the wild-type enzyme. As an example, we demonstrate a highly enantio- and diastereoselective synthesis of threo-3-benzyloxyaspartate (an important inhibitor of neuronal excitatory glutamate transporters in the brain). PMID:22614383

Raj, Hans; Szyma?ski, Wiktor; de Villiers, Jandré; Rozeboom, Henriëtte J; Veetil, Vinod Puthan; Reis, Carlos R; de Villiers, Marianne; Dekker, Frank J; de Wildeman, Stefaan; Quax, Wim J; Thunnissen, Andy-Mark W H; Feringa, Ben L; Janssen, Dick B; Poelarends, Gerrit J

2012-04-29

111

[Asymmetric synthesis of aromatic L-amino acids catalyzed by transaminase].  

PubMed

Aromatic L-Amino acids are important chiral building blocks for the synthesis of many drugs, pesticides, fine chemicals and food additives. Due to the high activity and steroselectivity, enzymatic synthesis of chiral building blocks has become the main research direction in asymmetric synthesis field. Guided by the phylogenetic analysis of transaminases from different sources, two representative aromatic transaminases TyrB and Aro8 in type I subfamily, from the prokaryote Escherichia coli and eukaryote Saccharomyces cerevisia, respectively, were applied for the comparative study of asymmetric transamination reaction process and catalytic efficiency of reversely converting keto acids to the corresponding aromatic L-amino acid. Both TyrB and Aro8 could efficiently synthesize the natural aromatic amino acids phenylalanine and tyrosine as well as non-natural amino acid phenylglycine. The chiral HPLC analysis showed the produced amino acids were L-configuration and the e.e value was 100%. L-alanine was the optimal amino donor, and the transaminase TyrB and Aro8 could not use D-amino acids as amino donor. The optimal molar ratio of amino donor (L-alanine) and amino acceptor (aromatic alpha-keto acids) was 4:1. Both of the substituted group on the aromatic ring and the length of fatty acid carbon chain part in the molecular structure of aromatic substrate alpha-keto acid have the significant impact on the enzyme-catalyzed transamination efficiency. In the experiments of preparative-scale transamination synthesis of L-phenylglycine, L-phenylalanine and L-tyrosine, the specific production rate catalyzed by TryB were 0.28 g/(g x h), 0.31 g/(g x h) and 0.60 g/(g x h) and the specific production rate catalyzed by Aro8 were 0.61 g/(g x h), 0.48 g/(g x h) and 0.59 g/(g x h). The results obtained here were useful for applying the transaminases to asymmetric synthesis of L-amino acids by reversing the reaction balance in industry. PMID:23457787

Xia, Wenna; Sun, Yu; Min, Cong; Han, Wei; Wu, Sheng

2012-11-01

112

Synthesis, optical resolution, absolute configuration, and osteogenic activity of cis-pterocarpans.  

PubMed

A convenient synthesis of natural and synthetic pterocarpans was achieved in three steps. Optical resolution of the respective enantiomers was accomplished by analytical and semi-preparative HPLC on a chiral stationary phase. For medicarpin and its synthetic derivative 9-demethoxymedicarpin, the absolute configuration was confirmed by a combination of experimental LC-ECD coupling and quantum-chemical ECD calculations. (-)-Medicarpin and (-)-9-demethoxymedicarpin are both 6aR,11aR-configured, and consequently the corresponding enantiomers, (+)-medicarpin and (+)-9-demethoxymedicarpin, possess the 6aS,11aS-configuration. A comparative mechanism study for osteogenic (bone forming) activity of medicarpin (racemic versus enantiomerically pure material) revealed that (+)-(6aS,11aS)-medicarpin (6a) significantly increased the bone morphogenetic protein-2 (BMP2) expression and the level of the bone-specific transcription factor Runx-2 mRNA, while the effect was opposite for the other enantiomer, (-)-(6aR,11aR)-medicarpin (6a), and for the racemate, (±)-medicarpin, the combined effect of both the enantiomers on transcription levels was observed. PMID:22955848

Goel, Atul; Kumar, Amit; Hemberger, Yasmin; Raghuvanshi, Ashutosh; Jeet, Ram; Tiwari, Govind; Knauer, Michael; Kureel, Jyoti; Singh, Anuj K; Gautam, Abnish; Trivedi, Ritu; Singh, Divya; Bringmann, Gerhard

2012-09-06

113

Asymmetric, stereocontrolled total synthesis of (+) and (?)-spirotryprostatin B via a diastereoselective azomethine ylide [1,3]-dipolar cycloaddition reaction  

Microsoft Academic Search

The asymmetric, stereocontrolled total syntheses of (+) and (?)-spirotryprostatin B (2) are described. Formation of the core pyrrolidine ring was accomplished via a diastereoselective asymmetric [1,3]-dipolar cycloaddition reaction. Addition of 3-methoxy-3-methylbutanal to (5R,6S)-2,3,5,6-tetrahydro-5,6-diphenyl-1,4-oxazin-2-one generated an azomethine ylide that reacted with ethyl oxindolylidene acetate to furnish the desired cycloadduct (11) that possessed the correct relative and absolute stereochemistry of natural spirotryprostatin

Paul R Sebahar; Hiroyuki Osada; Takeo Usui; Robert M Williams

2002-01-01

114

Stereocontrolled synthesis of substituted chiral piperidines via one-pot asymmetric 6?-azaelectrocyclization: asymmetric syntheses of (-)-dendroprimine, (+)-7-epidendroprimine, (+)-5-epidendroprimine, and (+)-5,7-epidendroprimine.  

PubMed

The asymmetric one-pot 6?-azaelectrocyclization of alkenyl vinyl stannane, ethyl (Z)-2-iodo-4-oxobutenoate, and (-)-7-isopropyl-cis-aminoindanol in the presence of a Pd(0) catalyst stereoselectively produced the tetracyclic aminoacetal compounds, resulting from the four-bond formation accompanying by controlling the stereochemistry at the two asymmetric centers. The produced cyclic aminoacetals can be regarded as synthetic precursors of substituted chiral piperidines, and the syntheses of 2,4- and 2,4,6-substituted piperidines were realized from the obtained aminoacetals by the stereoselective hydrogenation of the double bond conjugated with the C-4 ester group and alkylation at the aminoacetal moiety. In addition, the stereoselective synthesis of an indolizidine alkaloid, (-)-dendroprimine, and its three stereoisomers, (+)-7-epidendroprimine, (+)-5-epidendroprimine, and (+)-5,7-epidendroprimine, were achieved. PMID:22263723

Kobayashi, Toyoharu; Hasegawa, Futoshi; Hirose, Yoshikatsu; Tanaka, Katsunori; Mori, Hajime; Katsumura, Shigeo

2012-02-08

115

Asymmetric synthesis and anti-protozoal activity of the 8,4'-oxyneolignans virolin, surinamensin and analogues.  

PubMed

The asymmetric synthesis of 8,4'-oxyneolignans (-)-virolin, (-)-surinamensin and a number of analogues has been achieved. A divergent synthesis was used, with all compounds being elaborated from a single chiral aldehyde derived from ethyl lactate. In the 15 compounds that were tested, the level of substitution on the A-ring was found to directly influence the activity against Leishmania donovani whilst the activity against Plasmodium falciparum was influenced by numerous substitution and stereochemical factors. PMID:23313632

Rye, Claire E; Barker, David

2012-12-16

116

Palladium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles via enantioselective C-H bond functionalization.  

PubMed

A Pd-catalyzed asymmetric synthesis of Si-stereogenic dibenzosiloles is developed through enantioselective C-H bond functionalization of prochiral 2-(arylsilyl)aryl triflates. High chemo- and enantioselectivities are achieved by employing a Josiphos-type ligand under mild conditions. PMID:22506681

Shintani, Ryo; Otomo, Haruka; Ota, Kensuke; Hayashi, Tamio

2012-04-19

117

Asymmetric Synthesis of Methylenetetrahydrofurans by Palladium-Catalyzed [3+2] Cycloaddition of Trimethylenemethane with Aldehydes - A Novel Ligand Design  

PubMed Central

The palladium-catalyzed [3+2] cycloaddition of trimethylenemethane (TMM) with aldehydes is a direct and efficient route to methylenetetrahydrofurans. Herein we describe the first asymmetric synthesis of methylenetetrahydrofurans utilizing a palladium-TMM complex in the presence of a novel phosphoramidite ligand possessing a stereogenic phophorus. The method allows for the formation of chiral disubstituted tetrahydrofurans in good yields and enantioselectivies.

Trost, Barry M.; Bringley, Dustin A.; Silverman, Steven M.

2011-01-01

118

Active versus passive substituent participation in the auxiliary-mediated asymmetric synthesis of an octahedral metal complex.  

PubMed

Ambiguous chirality transfer: A surprising reversal of chirality transfer from carbon to metal is reported in the asymmetric synthesis of a chiral ruthenium complex, affording the metal-centered configuration ? or ? depending only on the chemical composition of the side chain of a chiral salicyloxazoline auxiliary. PMID:22915359

Chen, Liang-An; Ma, Jiajia; Celik, Mehmet Ali; Yu, Hong-Lang; Cao, Zexing; Frenking, Gernot; Gong, Lei; Meggers, Eric

2012-08-22

119

Asymmetric Synthesis of alpha-Amino Phosphonic Acids by Diastereoselective Addition of Trimethyl Phosphite onto Chiral Oxazolidines(1).  

PubMed

A simple and general asymmetric synthesis of alpha-amino phosphonic acids is described. The method involves the highly selective addition of trialkyl phosphite onto various chiral oxazolidines. Oxazaphosphorinanes thus obtained with an excellent diastereoselectivity furnish the corresponding (S)-alpha-substituted amino phosphonic acids in good overall yields and high ee (77-->97%) after simple deprotection. PMID:11667216

Maury, Catherine; Gharbaoui, Tawfik; Royer, Jacques; Husson, Henri-Philippe

1996-05-31

120

Asymmetric synthesis of enantiopure isoxazolidinone monomers for the synthesis of ?3-oligopeptides by chemoselective amide ligation  

PubMed Central

The design and general synthesis of enantiopure isoxazolidinone monomers as precursors for the preparation of enantiopure N-terminal hydroxylamine—?3-oligopeptides, which may be used as reaction partners with ?-ketoacids in the decarboxylative amide ligation reaction, is described.

Juarez-Garcia, M. Elisa; Yu, Shouyun; Bode, Jeffrey W.

2010-01-01

121

Development of an Asymmetric Trimethylenemethane Cycloaddition Reaction: Application in the Enantioselective Synthesis of Highly Substituted Carbocycles  

PubMed Central

A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane with electron-deficient olefins has been developed. The synthesis of novel phosphoramidite ligands was critical in this effort, and the preparation and reactivity of these ligands is detailed. The evolution of the ligand design, commencing with acyclic amine-derived phosphoramidites and leading to cyclic pyrrolidine and azetidine structures is discussed. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of alkene acceptors, providing the desired methylenecyclopentanes with high levels of enantioselectivity. The donor scope was also explored and substituted systems were tolerated, including one bearing a nitrile moiety. These donors were reactive with unsaturated acylpyrroles, giving the product cyclopentane rings bearing three stereocenters in high enantioselectivity and complete diastereoselectivity.

Trost, Barry M.; Silverman, Steven M.; Stambuli, James P.

2011-01-01

122

An advance on exploring N-tert-butanesulfinyl imines in asymmetric synthesis of chiral amines.  

PubMed

Although catalytic asymmetric synthesis has undergone tremendous growth in the last 30 years, chiral auxiliary-aided asymmetric synthesis continues to attract considerable attention. Chiral N- tert-butanesulfinamide, as pioneered by Ellman and co-workers, is undoubtedly one of the most efficient auxiliaries developed to date; it allows the preparation, through simple conversion, of a diverse range of enantiopure amines, which are ubiquitous in natural products and biologically active molecules. Following on from our studies of the SmI(2)-mediated asymmetric syntheses of alpha,gamma-substituted gamma-butyrolactones, we found that simple homocoupling of chiral N- tert-butanesulfinyl imines in the presence of SmI(2) produced enantiopure vicinal C2-symmetric diamines in high yield. In addition, C2-unsymmetric chiral diamines are readily prepared through SmI(2)-mediated cross-couplings of N- tert-butanesulfinyl imines and nitrones; these transformations represented the first successful examples of asymmetric cross-coupling between two different imine species. Subsequently, we discovered another useful reaction induced by SmI(2), the efficient cross-coupling of N- tert-butanesulfinyl imines and aldehydes, which provides ready access to enantiopure anti-1,2-amino alcohols. The synthetic applicability of this reaction was demonstrated through its use in the facile total syntheses of (3R,4S)-statine, d- erythro-sphinganine, (+)-CP-99,994, and (+)-L-733,060. The Zn/In-mediated allylation of chiral N- tert-butanesulfinyl imines yields homoallylic amines. After pondering the reaction mechanism, we developed optimal reaction conditions for reversing the stereogenic outcome, thereby allowing the preparation of enantiopure homoallylic amines of either handedness from single enantiomers of the (R)- or (S)-sulfinyl imine. When a benzoyl-substituted allyl bromide is used for allylation, the reaction proceeds smoothly to give 2-vinyl-substituted anti-1,2-amino alcohols in high yields and diastereoselectivities, another simple method for preparing enantiopure amino alcohols. We employed these reactions in the syntheses of enantiopure allylglycine, 3-allyl-isoindolinones, and (-)-cytoxazone. Further studies led to the discovery that the allylations of N- tert-butanesulfinyl aldimines can be performed in water. The reactions described in this Account are among the simplest and most efficient synthetic methods available for preparing enantio-enriched diamines, amino alcohols, homoallylic amines, and other amine derivatives. These reactions are additionally attractive because of the ready availability of the starting materials, the simplicity of the reaction conditions, and the high degree of stereochemical control. Their applications in the total syntheses of several biologically interesting molecules illustrate the versatility of these transformations; we hope that they will stimulate the development of new synthetic methods. PMID:18533688

Lin, Guo-Qiang; Xu, Ming-Hua; Zhong, Yu-Wu; Sun, Xing-Wen

2008-06-06

123

Transition metal complexes — A new class of catalysts of interfacial alkylation for the asymmetrical synthesis of ?-amino acids  

Microsoft Academic Search

A new class of catalysts of interfacial asymmetrical alkylation is suggested for the synthesis of a-amino acids — positively charged complexes of the transition metals Cu(II), Ni(II), and Pd(II). These complexes consist of several fragments, by variation of which the structure of the catalysts can readily be modified. The complexes are chiral on account of (S)proline derivatives contained in them

V. I. Maleev; S. O. Videnskaya; M. B. Saporovskaya; V. A. Tsyryapkin; V. M. Belikov

1991-01-01

124

Collagen synthesis, nitric oxide and asymmetric dimethylarginine in diabetic subjects undergoing hyperbaric oxygen therapy.  

PubMed

The main pathological condition in patients with impaired wound healing is diabetes mellitus. These patients have significantly low circulating nitric oxide (NO) levels because the stimulatory action of insulin on NO synthesis is absent. Additionally, asymmetric dimethylarginine (ADMA), an inhibitor of NO synthase, is increased owing to the generation of oxidative stress. NO was thought to contribute to wound healing. Hyperbaric oxygen (HBO) treatment is generally used in order to accelerate the healing of wounds. The aim of this study was to determine the changes in plasma procollagen type I and III N-terminal peptides (PINP and PIIINP), total nitrite/nitrate (NO(x)) and ADMA levels; and to evaluate their relation to healing during the HBO treatment of foot ulcers. Data obtained from 18 diabetic patients before and after the HBO therapy were compared statistically by the Wilcoxon test. NO(x) was increased in 11 and ADMA was decreased in 12 patients following HBO treatment. Both PINP (32.6 +/- 29.4 microg/l vs 44.3 +/- 33.4 microg/l) and PIIINP (6.97 +/- 3.01 microg/l vs 7.92 +/- 2.49 microg/l) were significantly increased (p < 0.05). Progressive reductions were observed in wound areas, as assessed by the digital wound imaging. In 12 patients, wounds healed by 50% or higher; whereas only two subjects had minimal improvements (15% or less healing). The duration of diabetes correlated negatively with wound healing (r = -498, p < 0.05). This study suggests that increased collagen synthesis is associated with wound healing during hyperbaric oxygen therapy. Nitric oxide generation may also contribute to the healing process. PMID:19681664

Gurdol, F; Cimsit, M; Oner-Iyidogan, Y; Kocak, H; Sengun, S; Yalcinkaya-Demirsoz, S

2009-08-12

125

[Development of asymmetric synthesis of optically active compounds including fluoroorganic molecules].  

PubMed

The synthesis of chiral fluorinated molecules is important in the biological and medicinal chemistry fields in view of the influence of fluorine's unique properties on biological activity. In recent years, we have studied asymmetric synthesis focussing on such optically active compounds. This review describes 1) diastereoselective trifluoromethylation of chiral N-acyloxazolidinones, 2) catalytic enantioselective aldol reactions of fluorine-substituted ketene silyl acetals, and 3) catalytic enantioselective allylation of aldehydes mediated by chiral Lewis bases. The trifluoromethylation of lithium enolates of N-acyloxazolidinones with iodotrifluoromethane is mediated by triethylborane to give the corresponding trifluoromethylated products with up to 86% diastereomeric excess. The stereoselective reaction is considered to proceed through the attack of the trifluoromethyl radical on the less hindered face of the lithium imide. Difluoroketene and bromofluoroketene trimethylsilyl ethyl acetals react with various aldehydes in the presence of chiral Lewis acids to afford the corresponding desired aldols with up to 99% enantiomeric excess (ee). It is noteworthy that the aldol reactions of the fluorine-substituted acetals at -78 degrees C and at higher temperatures (-45 or -20 degrees C) provide the (+)- and (-)-aldols, respectively, with excellent-to-good enantioselectivity. Chiral phosphoramides newly prepared from (S)-proline were found to catalyze the allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes in good enantioselective yields (up to 90% ee). (S,S)-Bis(alpha-methylbenzyl)formamide developed as an efficient catalyst for the allylation and crotylation of aliphatic aldehydes mediates the enantioselective addition with the assistance of hexamethylphosphoramide (HMPA) to afford the corresponding homoallylic alcohols in up to 98% ee. PMID:10590709

Iseki, K

1999-11-01

126

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.

Omedes-Pujol, Marta

2010-01-01

127

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.

128

Asymmetric synthesis and CD investigation of the 1,4-benzodioxane lignans eusiderins A, B, C, G, L, and M.  

PubMed

The enantioselective synthesis of (-)-eusiderins A (1), B (2), G (25), L (23), M (5) and (+)-eusiderin C (20) and a range of analogues was undertaken using an efficient, divergent synthesis all from a single chiral aldehyde 15, which was derived from (S)-ethyl lactate 9. A comprehensive set of NMR data along with ECD spectra and optical rotation measurements of the synthesized natural products and analogues were then obtained. This data confirmed the absolute stereochemistry of eusiderins A (1) and C (20) and for the first time gives the ECD and optical rotation for eusiderins B (2), G (25), L (23), and M (5) and a range of other substituted 1,4-benzodioxanes. This data will now allow for the determination of absolute stereochemistry of other members in this class of compound. PMID:22913812

Pilkington, Lisa I; Barker, David

2012-08-30

129

Stereodivergent strategy for neurofuran synthesis via palladium-catalyzed asymmetric allylic cyclization: total synthesis of 7-epi-ST-?(8)-10-neurofuran.  

PubMed

Neurofurans are formed in vivo in the human brain as a consequence of an increased oxidative stress, and they could be valuable biomarkers of the neuronal oxidative stress. In this paper, an enantioselective stereodivergent approach to two key neurofuran precursors, belonging to the AC and ST classes, has been developed starting from a single achiral precursor, the meso-diol 11. The absolute configuration of the THF cores was secured by a Pd-catalyzed asymmetric allylic alkylation using (S,S)-L1 and (R,R)-L2 ligands, respectively. PMID:23641720

Valli, Matteo; Bruno, Paolo; Sbarbada, Davide; Porta, Alessio; Vidari, Giovanni; Zanoni, Giuseppe

2013-05-14

130

A facile asymmetric synthesis of either enantiomer of 2-substituted pyrrolidines.  

PubMed

A new and general method for asymmetric synthesis of either enantiomer of 2-substituted pyrrolidines from a single starting material is described. Reductive cyclization of (S(S))-gamma-chloro-N-tert-butanesulfinyl ketimines with LiBHEt(3) in THF at -78 to 23 degrees C afforded (S(S),R)-N-tert-butanesulfinyl-2-substituted pyrrolidines in excellent yields (88-98%) and with high diastereoselectivity (99:1). The diastereoselectivity is controlled effectively by the choice of reducing agent. Thus, the corresponding epimers of (S(S),S)-2-substituted pyrrolidines were synthesized in good yields (87-98%) and with high diastereoslectivity (1:99) by simply switching the reducing agent from LiBHEt(3) to DIBAL-H/LiHMDS. Deprotection of N-tert-butanesulfinyl-2-substituted pyrrolidines using 4 N HCl in dioxane and MeOH gave the corresponding enantiomers of 2-substituted pyrrolidines in quantative yield. This method was found to be effective for a variety of substrates including aromatic, heteroaromatic, and aliphatic substituents. Extension of this methodology to the formation of 2-substituted piperidines is also illustrated. Reductive cyclization of (S(S))-delta-chloro-N-tert-butanesulfinyl ketimine with LiBHEt(3) in THF at -78 to 23 degrees C or DIBAL-H/LiHMDS in toluene at -78 to 0 degrees C afforded the (S(S),R)-N-tert-butanesulfinyl-2-substituted piperidines in excellent yield (98%) and with high diastereoselectivity (99:1) or (S(S),S)-N-tert-butanesulfinyl-2-substituted piperidines in good yield (98%) and with high diastereoselectivity (1:99), respectively. PMID:20201593

Rajender Reddy, Leleti; Das, Sonia G; Liu, Yugang; Prashad, Mahavir

2010-04-01

131

Radical addition approach to asymmetric amine synthesis: design, implementation, and comparison of chiral N-acylhydrazones.  

PubMed

Intermolecular radical addition to C=N bonds with acyclic stereocontrol offers excellent potential as a mild, nonbasic carbon-carbon bond construction approach to chiral amines. Here, complete details of the first radical additions to chiral N-acylhydrazones as an approach to asymmetric amine synthesis are disclosed. Novel N-acylhydrazones were designed as chiral C=N radical acceptors with Lewis acid activation, restriction of conformational mobility, and commercial availability of precursors. Amination of 4-alkyl-2-oxazolidinones with O-(mesitylenesulfonyl)hydroxylamine or O-(p-nitrobenzoyl)hydroxylamine afforded N-aminooxazolidinones which were condensed with aldehydes to afford N-acylhydrazones 3-8. Three synthetic methods were developed, implementing these N-acylhydrazones in Lewis acid-promoted intermolecular radical additions to C=N bonds. First, additions of various secondary and tertiary alkyl iodides to propionaldehyde and benzaldehyde hydrazones (3 and 7) under tin hydride radical chain conditions in the presence of ZnCl2 gave N-acylhydrazine adducts with diastereomeric ratios ranging from 93:7 to 99:1. Radical additions to a series of N-acylhydrazones with different substituents on the oxazolidinone revealed that benzyl and diphenylmethyl were more effective stereocontrol elements than those with the aromatic ring directly attached to the oxazolidinone. Second, a tin-free method, exploiting dual functions of triethylborane for both initiation and chain propagation, enabled improved yields in addition of secondary alkyl iodides. Third, under photolytic conditions with hexamethylditin, primary radical addition could be achieved with ethyl iodide in the presence of diethyl ether as cosolvent; the 1-ethoxyethyl adduct was observed as a minor product. Chloromethyl addition was achieved under both the tin-free and photolytic conditions; in this case, the adduct bears alkyl chloride functionality with potential for further elaboration. PMID:16050694

Friestad, Gregory K; Draghici, Cristian; Soukri, Mustapha; Qin, Jun

2005-08-01

132

Disulfonimide-Catalyzed Asymmetric Synthesis of ?(3)-Amino Esters Directly from N-Boc-Amino Sulfones.  

PubMed

An asymmetric Mannich reaction of silyl ketene acetals with N-Boc-amino sulfones has been developed. A chiral disulfonimide efficiently catalyzes both the in situ generation of the corresponding N-Boc imines and the asymmetric Mannich reaction with excellent yields and enantioselectivities. Kinetic studies confirm a proposed stepwise mechanism. PMID:24090068

Wang, Qinggang; Leutzsch, Markus; van Gemmeren, Manuel; List, Benjamin

2013-10-03

133

Synthesis of hollow asymmetrical silica dumbbells with a movable inner core  

Microsoft Academic Search

Hollow asymmetrical silica dumbbells containing a movable inner core were fabricated by a template-assisted method. Three different templates were employed for the fabrication of the hollow asymmetrical dumbbells. For the preparation of the first template, silica particles were uniformly covered with a cross-linked polymethylmethacrylate (PMMA) shell and the polymerization of styrene was conducted to induce a protrusion of polystyrene (PSt)

Daisuke Nagao; Carlos M. van Kats; Kentaro Hayasaka; Maki Sugimoto; Mikio Konno; Arnout Imhof; Alfons van Blaaderen

2010-01-01

134

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

2011-03-17

135

Enantioselective synthesis induced by tetrathia-[7]-helicenes in conjunction with asymmetric autocatalysis  

Microsoft Academic Search

Highly enantioenriched 5-pyrimidyl alkanol was formed using tetrathia-[7]-helicenes as a chiral initiator in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, in conjunction with asymmetric autocatalysis.

Tsuneomi Kawasaki; Kenta Suzuki; Emanuela Licandro; Alberto Bossi; Stefano Maiorana; Kenso Soai

2006-01-01

136

Synthesis of hollow asymmetrical silica dumbbells with a movable inner core.  

PubMed

Hollow asymmetrical silica dumbbells containing a movable inner core were fabricated by a template-assisted method. Three different templates were employed for the fabrication of the hollow asymmetrical dumbbells. For the preparation of the first template, silica particles were uniformly covered with a cross-linked polymethylmethacrylate (PMMA) shell and the polymerization of styrene was conducted to induce a protrusion of polystyrene (PSt) from the PMMA shell. Anisotropic colloids composed of silica, PMMA, and PSt were used as templates, coated with a silica shell, and held at 500 degrees C for 2 h to remove the polymer interior components of the template colloid. The heat treatment successfully produced hollow asymmetrical silica dumbbells containing an inner silica core. After being dried, approximately 50% of the inner silica particles that were originally coated with PMMA ended up in the other hollow sphere in which the PSt component existed before heat treatment, indicating that the inner silica particles could pass through the hollow asymmetrical dumbbells' necks and were free to move in the interior. In the preparation of the second and third asymmetrical dumbbell templates, magnetic silica particles and titania particles, respectively, were covered with a PMMA shell to incorporate externally responsive particles into the hollow silica shells as above. The successful syntheses demonstrated the generality of our approach. The passage of the responsive particles through the dumbbell's neck enabled active control of the position of the responsive particles inside the asymmetrical dumbbells by external fields. PMID:20073531

Nagao, Daisuke; van Kats, Carlos M; Hayasaka, Kentaro; Sugimoto, Maki; Konno, Mikio; Imhof, Arnout; van Blaaderen, Alfons

2010-04-01

137

Synthesis of PDE IVb inhibitors. 1. Asymmetric synthesis and stereochemical assignment of (+)- and (-)-7-[3-(cyclopentyloxy)-4-methoxyphenyl]hexahydro-3H-pyrrolizin-3-one.  

PubMed

Asymmetric synthesis of GlaxoSmithKline's highly potent phosphodiesterase inhibitor 1 has been accomplished in nine steps and 16% overall yield. The original strategy suggested involves as a key step the silylation of enantiopure six-membered cyclic nitronates 4 obtained by a highly stereoselective [4 + 2]-cycloaddition of an appropriate nitroalkene 5 to trans-1-phenyl-2-(vinyloxy)cyclohexane. Functionalization of the resulting 5,6-dihydro-4H-1,2-oxazine and subsequent stereoselective reduction of 1,2-oxazine ring in intermediate 2 furnished the pyrrolizidinone framework with the recovery of chiral auxiliary alcohol. PMID:21866916

Sukhorukov, Alexey Yu; Boyko, Yaroslav D; Ioffe, Sema L; Khomutova, Yulia A; Nelyubina, Yulia V; Tartakovsky, Vladimir A

2011-09-16

138

Synthesis and characterization of asymmetric polymer/inorganic nanocomposites with pH/temperature sensitivity  

NASA Astrophysics Data System (ADS)

An easy, comprehensive and inexpensive method is demonstrated to produce asymmetric polymer/inorganic nanocomposites in a large quantity. With the aid of Pickering emulsion, unmodified particles aggregate on the surface of emulsion droplets and are fixed in place when the wax solidifies. The exposed surfaces of immobilized SiO2 particles are modified chemically by 2-(dimethylamino) ethylmethacrylate (DMAEMA). With the removal of wax, the exposed side of particles can be further modified chemically by N-isopropylacrylamide (NIPAAm). Based on these procedures, dual responsive asymmetric nanocomposite particles are achieved with both pH and temperature sensitivities. Due to their dual-stimuli and asymmetric structure, these particles have potential applications in molecule targeting, drug delivery and as building blocks for the assembly of complex nanostructure.

Zhang, Xinjie; Gao, Chunmei; Liu, Mingzhu; Huang, Yinjuan; Yu, Xiyong; Ding, Enyong

2013-01-01

139

A room-temperature catalytic asymmetric synthesis of allenes with ECNU-Phos.  

PubMed

Three-carbon axial chirality has been asymmetrically established from racemic one-carbon central chirality efficiently at room temperature: we report here the discovery of the first catalytic asymmetric carbonylation of readily available racemic propargylic carbonates to access optically active 2,3-allenoates with fairly high ee. The combination of [(?-allyl)PdCl]2 with [(R)-ECNU-Phos], a new chiral bisphosphine ligand based on a biphenyl skeleton, demonstrates high enantioselectivity. Both enantiomers of allenoates can be obtained at room temperature by applying either (R)- or (S)-ECNU-Phos. PMID:23869750

Wang, Yuli; Zhang, Wanli; Ma, Shengming

2013-07-29

140

Spiroborate esters in the borane-mediated asymmetric synthesis of pyridyl and related heterocyclic alcohols  

PubMed Central

The effectiveness of several spiroborate ester catalysts was investigated in the asymmetric borane reduction of 2-, 3-, 4-acetylpyridines under different reaction conditions. Highly enantiomerically enriched 1-(2-, 3- and 4-pyridyl)ethanols and 1-(heterocyclic)ethanols were obtained using 1 to 10% catalytic loads of the spiroborate 5 derived from diphenylprolinol and ethylene glycol.

Stepanenko, Viatcheslav; De Jesus, Melvin; Correa, Wildeliz; Guzman, Irisbel; Vazquez, Cindybeth; Ortiz, Lymaris; Ortiz-Marciales, Margarita

2009-01-01

141

Asymmetric Synthesis of Hydrobenzofuranones via Desymmetrization of Cyclohexadienones using the Intramolecular Stetter Reaction  

PubMed Central

Dearomatization of phenols followed by oxidation affords cyclohexadienyloxyacetaldehydes, which produce hydrobenzofuranones via asymmetric intramolecular Stetter reaction in good to excellent yield. Quaternary as well as up to three contiguous stereocenters may be formed in good to excellent enantioselectivities and high diastereoselectivities.

Liu, Qin; Rovis, Tomislav

2008-01-01

142

Enantioselective Synthesis of Hydrobenzofuranones Using an Asymmetric Desymmetrizing Intramolecular Stetter Reaction of Cyclohexadienones  

PubMed Central

A series of cyclohexadienones were synthesized by dearomatization of phenols followed by Dess-Martin oxidation. Asymmetric intramolecular Stetter reactions of these substrates provide hydrobenzofuranones in good to excellent yields and excellent stereoselectivities. Up to three stereocenters as well as quaternary stereocenter are formed from polysubstituted substrates. A scale up experiment demonstrates the utility of this transformation.

Liu, Qin; Rovis, Tomislav

2008-01-01

143

Absolute Zero  

Microsoft Academic Search

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

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

2006-01-01

144

An efficient asymmetric synthesis of the potent beta-blocker ICI-118,551 allows the determination of enantiomer dependency on biological activity.  

PubMed

A highly efficient, practical and flexible two-step asymmetric synthesis of the beta(2)-selective beta-blocker ICI 118,551 is reported, allowing an unambiguous determination of the dependency of biological activity with optical activity, revealing the S,S-enantiomer to be the most potent. PMID:20431838

Baker, James R; Hothersall, J Daniel; Fitzmaurice, Richard J; Tucknott, Matthew; Vinter, Andy; Tinker, Andrew; Caddick, Stephen

2010-04-30

145

Construction of vicinal all-carbon quaternary stereocenters by catalytic asymmetric alkylation reaction of 3-bromooxindoles with 3-substituted indoles: total synthesis of (+)-perophoramidine.  

PubMed

Highly congested vicinal all-carbon quaternary stereocenters were generated via catalytic asymmetric alkylation reaction of 3-bromooxindoles with 3-substituted indoles. These catalytic reactions proceeded in excellent yields with a broad scope on either reaction partner, and with outstanding diastereo- and enantiocontrol. The newly developed method led to the total synthesis of (+)-perophoramidine in a highly efficient manner. PMID:24032694

Zhang, Hailong; Hong, Liang; Kang, Hong; Wang, Rui

2013-09-13

146

Gold meets rhodium: tandem one-pot synthesis of ?-disubstituted ketones via Meyer-Schuster rearrangement and asymmetric 1,4-addition.  

PubMed

An asymmetric one-pot tandem Au/Rh-catalyzed synthesis of highly enantioenriched ?-disubstituted ketones starting from racemic propargyl alcohols is disclosed. The compatibility of the two metal complexes (Au/Rh) and their orthogonal ligand systems (NHC/diene) in this bimetallic catalytic system is investigated. PMID:23777565

Hansmann, Max M; Hashmi, A Stephen K; Lautens, Mark

2013-06-18

147

Two Remarkable Epimerizations Imperative for the Success of an Asymmetric Total Synthesis of (+)-Aigialospirol.  

PubMed

Two remarkable epimerization processes were uncovered during our pursuit of an enantioselective synthesis of (+)-aigialospirol featuring a cyclic acetal tethered ring-closing metathesis. Through modeling, we were able to turn these two unexpected epimerizations to our advantage via modeling to ensure a successful and concise total synthesis, thereby firmly establishing cyclic acetal tethered RCM as a powerful strategy in natural product synthesis. Most importantly, calculations allowed us to fully understand the nature and the mechanistic course of these two epimerizations that were imperative to the total synthesis efforts. PMID:21221423

Figueroa, Ruth; Feltenberger, John B; Guevarra, Christle C; Hsung, Richard P

2011-01-01

148

Asymmetric Synthesis of ?-Amino 1,3-Dithianes via Chiral N-Phosphonyl Imine-based Umpolung Reaction  

PubMed Central

A series of ?-amino-1,3-dithianes have been synthesized via the asymmetric Umpolung reaction of 2-lithio-1,3-dithianes with chiral N-phosphonyl imines in good chemical yields (up to 82%) and good to excellent diastereoselectivities (>99:1). The addition manner by which chiral N-phosphonyl imines are slowly added into the solution of 2-lithio-1,3-dithiane was found to be crucial for achieving excellent diastereoselectivity. The current synthesis was proven to follow the GAP chemistry (Group-Assistant-Purification chemistry) process which avoids traditional purification techniques of chromatography or recrystallization, i.e., the pure chiral ?-amino-1,3-dithianes attached with the chiral N-phosphonyl group were readily obtained by washing the solid crude products with hexane or the mixture of hexane-ethyl acetate.

Kattamuri, Padmanabha V.; Ai, Teng; Pindi, Suresh; Sun, Yinwei; Gu, Peng; Shi, Min; Li, Guigen

2011-01-01

149

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.

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

2011-01-01

150

Studies on the Biosynthesis of Cholesterol. XVII. The Asymmetric Synthesis of a Symmetrical Molecule  

Microsoft Academic Search

The differentiation between two identical chemical groups in the Ca'a' 'bd molecule in enzymic reactions is discussed first. It is then shown that squalene biosynthesized from two molecules of [1-D2]farnesyl pyrophosphate is asymmetrically labelled at one of its central methylene carbon atoms, one of the deuterium atoms at C-1 of one of the two farnesyl residues having been replaced stereospecifically

J. W. Cornforth; Rita H. Cornforth; C. Donninger; G. Popjak; G. Ryback; G. J. Schroepfer

1966-01-01

151

Asymmetric Synthesis of Apio Fluoroneplanocin a Analogs as Potential AdoHcy Hydrolase Inhibitor  

Microsoft Academic Search

Apio fluoroneplanocin A (apio F-NPA, 3) and its uracil analogue 4 have been designed and asymmetrically synthesized starting from D-ribose. Introduction of fluoro group into vinylic position of 5 was accomplished successfully over 5 steps employing key reactions such as iodination according to an addition-elimination reaction mechanism, stereo- and regioselective reduction of ?,? -unsaturated ketone, and electrophilic fluorination. This methodology

Ah-Young Park; Hyung Ryong Moon; Kyung Ran Kim; Jin-Ah Kang; Moon Woo Chun; Lak Shin Jeong

2007-01-01

152

Asymmetric synthesis of diverse glycolic acid scaffolds via dynamic kinetic resolution of ?-keto esters.  

PubMed

The dynamic kinetic resolution of ?-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse ?-substituted-?-hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective ?-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of ?-aryl- and ?-chloro-?-keto esters. PMID:23186551

Steward, Kimberly M; Corbett, Michael T; Goodman, C Guy; Johnson, Jeffrey S

2012-11-27

153

Analytical synthesis algorithm of dual-band filters with asymmetric pass bands and generalized topology  

Microsoft Academic Search

A straightforward method for the synthesis of dual-passband filters is proposed. The method reduces the synthesis algorithm to the computation of only two coefficients, that completely determine the dual-band response as long as it is adequately normalized in frequency. The resulting network is built by attaching an additional resonator to each existing one, being all the new resonators identical. This

Alejandro Garcia Lamperez

2007-01-01

154

Synthesis and application of a new bisphosphite ligand collection for asymmetric hydroformylation of allyl cyanide.  

PubMed

A series of mono- and bidentate phosphites was prepared with (S)-5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-biphenyl-2,2'-dioxy [(S)-BIPHEN] as a chiral auxiliary and screened in the asymmetric hydroformylation of allyl cyanide. These hydroformylation results were compared with those of two existing chiral ligands, Chiraphite and BINAPHOS, whose utility in asymmetric hydroformylation has been previously demonstrated. Bisphosphite 11 with a 2,2'-biphenol bridge was found to be the best overall ligand for asymmetric hydroformylation of allyl cyanide with up to 80% ee and regioselectivities (branch-to-linear ratio, b/l) of 20 with turnover frequency of 625 [h(-)(1)] at 35 degrees C. BINAPHOS gave enantioselectivities up to 77% ee when the reaction was conducted in either acetone or neat but with poor regioselectivity (b/l 2.8) and activities 7 times lower than that of 11. The product of allyl cyanide hydroformylation using (R,R)-11 was subsequently transformed into (R)-2-methyl-4-aminobutanol, a useful chiral building block. Single-crystal X-ray structures of (S,S)-11 and its rhodium complex 19 were determined. PMID:15176828

Cobley, Christopher J; Gardner, Kelli; Klosin, Jerzy; Praquin, Céline; Hill, Catherine; Whiteker, Gregory T; Zanotti-Gerosa, Antonio; Petersen, Jeffrey L; Abboud, Khalil A

2004-06-11

155

Asymmetric synthesis of pyrimidyl alkanol without adding chiral substances by the addition of diisopropylzinc to pyrimidine-5-carbaldehyde in conjunction with asymmetric autocatalysis  

Microsoft Academic Search

Enantiomerically enriched pyrimidyl alkanol with either S or R configuration was obtained stochastically from the reaction between pyrimidine-5-carbaldehyde and diisopropylzinc without adding chiral substances in conjunction with subsequent asymmetric autocatalysis, leading to amplification of the enantiomeric excess.

Kenso Soai; Itaru Sato; Takanori Shibata; Soichiro Komiya; Masanobu Hayashi; Yohei Matsueda; Hikaru Imamura; Tadakatsu Hayase; Hiroshi Morioka; Hayami Tabira; Jun Yamamoto; Yasunori Kowata

2003-01-01

156

Asymmetric syntheses and transformations--tools for chirality multiplication in drug synthesis.  

PubMed

A review of currently used methods for the synthesis and resolution of enantiomers of drugs and their precursors is presented. For the synthesis part the methods of diastereoselective as well as enantioselective synthesis are discussed, with particular consideration given to enantioselective catalysis with either metal complexes or biocatalysts. Desymmetrization processes are also included as methods to access enantiomerically pure compounds. Racemate resolution still remains an important method to obtain pure enantiomers and methods involving kinetic resolution in enzymatic or chemical systems, and particularly in connection with racemization (dynamic kinetic resolution) are on the rise in fine chemical industry, when applicable. PMID:17357583

Gawro?ski, Jacek

157

Stereoselective synthesis of norephedrine and norpseudoephedrine by using asymmetric transfer hydrogenation accompanied by dynamic kinetic resolution.  

PubMed

Each of the enantiomers of both norephedrine and norpseudoephedrine were stereoselectively prepared from the common, prochiral cyclic sulfamidate imine of racemic 1-hydroxy-1-phenyl-propan-2-one by employing asymmetric transfer hydrogenation (ATH) catalyzed by the well-defined chiral Rh-complexes, (S,S)- or (R,R)-Cp*RhCl(TsDPEN), and HCO(2)H/Et(3)N as the hydrogen source. The ATH processes are carried out under mild conditions (rt, 15 min) and are accompanied by dynamic kinetic resolution. PMID:22621372

Lee, Hyeon-Kyu; Kang, Soyeong; Choi, Eun Bok

2012-05-31

158

One step synthesis of a new asymmetric water-soluble phosphine  

Microsoft Academic Search

The new asymmetric water-soluble phosphine (S)-(?)-(3-diphenylphosphino-2-hydroxypropyl)trimethylammonium chloride was synthesised from the accessible (S)-(?)-(3-chloro-2-hydroxypropyl)trimethylammonium chloride by means of a one pot reaction between this ionic compound and sodium diphenylphosphide in liquid ammonia. The palladium complex (L)PdCl3 (L=(S)-(?)-(3-diphenylphosphino-2-hydroxypropyl)trimethylammonium) was prepared by reaction between this ligand and PdCl2(PhCN)2 and was characterised by spectroscopic methods.

Mireia Condom; Joan Suades

2005-01-01

159

Synthesis, structure and magnetic properties of an asymmetric dinuclear oxocitratovanadate(IV) complex  

Microsoft Academic Search

Evaporation of an aqueous solution containing VO2+, citric acid and neocuproine (2,9-dimethyl-1,10-phenanthroline=neo) produces blue crystals of (Hneo)3[(VO)2(cit)(Hcit)]·4H2O (1). An X-ray structural analysis showed that 1 consists of a discrete, asymmetric, dinuclear oxocitratovanadate(IV) complex and three neocuproinium cations. The complex contains one six-coordinate V(IV) atom with a distorted octahedral geometry and one five-coordinate V(IV) atom with a distorted square pyramidal geometry.

Suzana Burojevic; Itzhak Shweky; Avi Bino; David A. Summers; Robert C. Thompson

1996-01-01

160

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.

Chen, Peng; Lin, Jianhua

2011-01-01

161

Flexible and asymmetric ligand in constructing coordinated complexes: synthesis, crystal structures and fluorescent characterization.  

PubMed

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, [Ag(2)(L)(2)(NO(3))(2)](n) (1) and [Ag(L)(ClO(4))](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

2010-12-27

162

The asymmetric synthesis of terminal aziridines by methylene transfer from sulfonium ylides to imines.  

PubMed

A new ylide-based protocol for the asymmetric aziridination of imines via methylene transfer has been developed involving the use of a simple chiral sulfonium salt and an organic strong base. A systematic study identified triisopropylphenyl sulfonylimines as optimal substrates for the process. Unexpectedly, hindered C2-symmetric sulfonyl salts incorporating bulky ethers at C-2 and C-5--which had previously been useful in the corresponding epoxidation chemistry--decomposed in these aziridination reactions via competing elimination pathways. Under optimised conditions it was found that a simple salt derived from (2R,5R)-2,5-diisopropyl thiolane could mediate asymmetric methylene transfer to a range of imines with uniformly excellent yields with 19-30% ee. Since this is a similar level of enantiomeric excess to that obtained using these same salts in epoxidation chemistry, it was concluded that if more bulky sulfonium salts could be devised which were resistant to decomposition under the reaction conditions, that highly enantioselective aziridine formation by methylene transfer would be possible. PMID:23598787

Kavanagh, Sarah A; Piccinini, Alessandro; Connon, Stephen J

2013-04-18

163

Asymmetric autocatalysis: crystallization-induced highly enantioselective synthesis of a conglomerating oxo-rhenium(V) complex  

Microsoft Academic Search

Experiments designed to elucidate the mechanistic foundation and origins of enantioselectivity in a symmetry breaking synthesis are described. The autocatalytic enantioselective preparation of the title complex cis-[ReOCl2(P?O)py] [py=pyridine; P?O=(OCMe2CMe2O)POCMe2CMe2O(1?)], either C or A handed, from optically inactive substrates can be controlled by catalytic quantities of the non-racemic conglomerating product. The synthesis can be accomplished due to enantioselective complex formation and

Witold K. Rybak

2008-01-01

164

Highly Efficient Synthesis of Heterocyclic and Alicyclic ?(2) -Amino Acid Derivatives by Catalytic Asymmetric Hydrogenation.  

PubMed

A valuable class of new heterocyclic and alicyclic prochiral ?-aminomethylacrylates has been conveniently synthesized through a three-step transformation involving a Baylis-Hillman reaction, O-acetylation, and a subsequent allylic amination. The corresponding novel ?(2) -amino acid derivatives were prepared with excellent enantioselectivities and high yields by catalytic asymmetric hydrogenation using the catalyst rhodium(Et-Duphos) (Et-Duphos=2',5',2'',5''-tetraethyl-1,2-bis(phospholanyl)benzene)) under mild reaction conditions (up to 99?% ee and S/C=1000). The influence of the substrate on the enantioselectivity and reactivity is investigated, and the most suitable substrate configuration for the highly efficient enantioselective hydrogenation of ?-substituted ?-aminomethylacrylates under the Rh-Duphos system is reported. The current protocol provides a very practical, facile, and scalable method for the preparation of heterocyclic and alicyclic ?(2) -amino acids and their derivatives. PMID:23776190

Li, Lanning; Chen, Bin; Ke, Yuanyuan; Li, Qing; Zhuang, Yue; Duan, Kun; Huang, Yichun; Pang, Jiyan; Qiu, Liqin

2013-06-17

165

Asymmetric synthesis of the balanol heterocycle via a palladium-mediated epimerization and olefin metathesis.  

PubMed

[formula: see text] The enantioselective formal synthesis of balanol, a potent protein kinase C inhibitor, was accomplished from D-serine utilizing a Pd-catalyzed equilibration of diastereomeric 5-vinyloxazolines to set the stereochemistry of the vicinal amino and hydroxyl groups. A ruthenium-catalyzed ring-closing metathesis was employed to form the seven-membered nitrogen heterocyle. PMID:10823189

Cook, G R; Shanker, P S; Peterson, S L

1999-08-26

166

Chiral enol oxazolines and thiazolines as auxiliary ligands for the asymmetric synthesis of ruthenium-polypyridyl complexes.  

PubMed

Various ligands, such as (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl]ethen-1-ol ((S)-) and (Z)-1-phenyl-2-[(4S)-4-phenyl-4,5-dihydro-1,3-thiazol-2-yl]ethen-1-ol ((S)-), were investigated as auxiliaries for the asymmetric synthesis of chiral ruthenium(II) complexes. The reaction of these chiral auxiliary ligands with [RuCl2 (dmso)4 ], 2,2'-bipyridine (bpy, 2.2?equiv), and triethylamine (10?equiv) in DMF/PhCl (1:8) at 140?°C for several hours diastereoselectively provided the complexes ?-[Ru(bpy)2 {(S)-?H}] (?-(S)-, 52?% yield, 56:1 d.r.) and ?-[Ru(bpy)2 {(S)-?H}] (?-(S)-, 48?% yield, >100:1 d.r.) in a single step after purification. Both ?-(S)- and ?-(S)- could be converted into ?-[Ru(bpy)3 ](PF6 )2 by replacing the bidentate enolato ligands with bpy, under retention of configuration, induced by either NH4 PF6 as a weak acid (from ?-(S)-: 73?% yield, 22:1 e.r.; from ?-(S)-: 77?% yield, 22:1 e.r.), TFA as a strong acid (from ?-(S)-: 72?% yield, 52:1 e.r.; from ?-(S)-: 85?% yield, 25:1 e.r.), methylation with Meerwein's salt (from ?-(S)-: 59?% yield, 46:1 e.r.; from ?-(S)-: 86?% yield, 37:1 e.r.), ozonolysis (from ?-(S)-: 56?% yield, 22:1 e.r.; from ?-(S)-: 43?% yield, 6.3:1 e.r.), or oxidation with a peroxy acid (from ?-(S)-: 72?% yield, 45:1 e.r.; from ?-(S)-: 79?% yield, 8.5:1 e.r.). This study shows that, except for the reaction with NH4 PF6 , oxazoline-enolato complex ?-(S)- provides ?-[Ru(bpy)3 ](PF6 )2 with higher enantioselectivities than analogous thiazoline-enolato complex ?-(S)-, which might be due to the higher coordinative stability of the thiazoline-enolato complex, thus requiring more prolonged reaction times. Thus, this study provides attractive new avenues for the asymmetric synthesis of non-racemic ruthenium(II)-polypyridyl complexes without the need for using a strong acid or a strong methylating reagent, as has been the case in all previously reported auxiliary methods from our group. PMID:23818279

Huang, Biao; Wang, Lun; Gong, Lei; Meggers, Eric

2013-07-01

167

Scalable, efficient process for the synthesis of ( R)-3,5-bistrifluoromethylphenyl ethanol via catalytic asymmetric transfer hydrogenation and isolation as a DABCO inclusion complex  

Microsoft Academic Search

(R)-3,5-Bistrifluoromethylphenyl ethanol 2, a key building block in the synthesis of aprepitant, has been synthesized from ketone 5 via catalytic asymmetric transfer hydrogenation using a simplified catalyst generation procedure. The process uses (1S,2R)-cis-1-aminoindan-2-ol 10 and dichloro(p-cymene)Ru(II)dimer 9 as the chiral ligand and metal source for the reduction. While the reduction provides 2 in 90–92% ee, an isolation of 2 as

Karl B. Hansen; Jennifer R. Chilenski; Richard Desmond; Paul N. Devine; Edward J. J. Grabowski; Richard Heid; Michele Kubryk; David J. Mathre; Richard Varsolona

2003-01-01

168

Asymmetric catalysis of the Strecker amino acid synthesis by a cyclic dipeptide  

Microsoft Academic Search

A novel cyclic dipeptide —cyclo[(S)-His-(S)-NorArg] — has been prepared which catalyzes an enantioselective version of the Strecker amino acid synthesis. The catalyst, when present in 2 mol % quantity in methanol solution, catalyzes the addition of hydrogen cyanide toN-alkylimines to afforda-amino nitriles in high yield and high enantiomeric excess. Furthermore, acid hydrolysis ofN-benzhydryl-a-amino nitriles afforded the correspondinga-amino acids directly. This

M. S. Iyer; K. M. Gigstad; N. D. Namdev; M. Lipton

1996-01-01

169

"One-pot" reductive lactone alkylation provides a concise asymmetric synthesis of chiral isoprenoid targets.  

PubMed

An efficient method, based on nucleophilic addition to lactones followed by modified in situ Clemmensen reduction, provides a short synthetic route to chiral isoprenoid targets. The efficacy of this method has been exemplified through the synthesis of several targets including the commercial fragrance Rosaphen, the side chain of Zaragozic acid C, the cotton leaf sex pheromone, and the side chains of vitamin E. PMID:23957629

Cao, Jia; Perlmutter, Patrick

2013-08-19

170

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

171

Full stereochemical determination of ajudazols A and B by bioinformatics gene cluster analysis and total synthesis of ajudazol B by an asymmetric ortholithiation strategy.  

PubMed

The stereochemical determination of the potent respiratory chain inhibitors ajudazols A and B and the total synthesis of ajudazol B are reported. Configurational assignment was exclusively based on biosynthetic gene cluster analysis of both ketoreductase domains for hydroxyl-bearing stereocenters and one of the first predictive enoylreductase alignments for methyl-bearing stereocenters. The expedient total synthesis resulting in unambiguous proof of the predicted stereochemistry involves a short stereoselective approach to the challenging isochromanone stereotriad by an innovative asymmetric ortholithiation strategy, a modular oxazole formation, and a late-stage Z,Z-selective Suzuki coupling. PMID:23127125

Essig, Sebastian; Bretzke, Sebastian; Müller, Rolf; Menche, Dirk

2012-11-14

172

Synthesis of enantiopure phthalides including 3-butylphthalide, a fragrance component of celery oil, and determination of their absolute configurations.  

PubMed

Enantiopure phthalides 2 and 5-8 were synthesized via enantioresolution of the corresponding alcohols with a chiral auxiliary of camphorsultam dichlorophthalic acid, (1S,2R,4R)-(-)-CSDP acid 3, followed by solvolysis with KOH in MeOH and the catalytic oxidation of chiral glycols with iridium complex 28. The absolute configurations of phthalides 2 and 5-8 were determined by applying the (1)H-NMR anisotropy method of MalphaNP acid (4), 2-methoxy-2-(1-naphthyl)propionic acid, to the chiral synthetic precursory alcohols. In the case of 3-phenylphthalide (R)-(-)-7, the absolute configuration determined by the (1)H-NMR anisotropy method using MalphaNP acid 4 agreed with that by the X-ray crystallographic method. By applying these methods, 3-butylphthalide (S)-(-)-2, a fragrance component of essential oil of celery, has been synthesized in an enantiopure form, and its absolute configuration was unambiguously determined. PMID:15830406

Kosaka, Masashi; Sekiguchi, Satoshi; Naito, Junpei; Uemura, Makoto; Kuwahara, Shunsuke; Watanabe, Masataka; Harada, Nobuyuki; Hiroi, Kunio

2005-05-01

173

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.

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

2010-01-01

174

Synthesis, Structural, and Electrochemical Stability Studies of Nanocrystalline 5V Lithiated Oxides for Asymmetric Supercapacitor  

NASA Astrophysics Data System (ADS)

For the development of asymmetric (hybrid) supercapacitor, we have synthesized nanoscale double substituted LiNi YCo1-2 YMn1+ YO4 (Y=0.05, 0.1, 0.25 and 0.45) spinels using mechanochemical, hydrothermal, microwave assisted combustion aided procedures. The samples have been characterized by XRD, TEM, and XAFS. Lattice parameter of the spinels increased with nickel content, and decreased from 400 to 600 C, at which temperature the particle size is 20nm. The sample with composition LiNi0.45Co0.1Mn1.45O4 has shown the best electrochemical performance, with redox potential of 4.6V, capacity of 129.6mAhg-1, cyclability of 99.6% per cycle, and retained the capacity up to 1 C rate. The XANES of Mn and M as a function of x showed that the high voltage (˜5 V) in the cathode materials of an Li secondary battery is due to the oxidation of M^3+ to M^4+ (M=Co) and M^2+ to M^4+ (in the case of M=Ni). The EXAFS analysis revealed that Ni^2+ is oxidized to Ni^4+ via the Ni^3+ state with a Jahn--Teller distorted Ni^3+--O octahedron. A hybrid device employing nanostructured LiNi YCo1-2 YMn1+ YO4 /polymer electrolyte/nanoporous carbon black (NCB) powders was assembled. grant # W911NF-07-1-0426

Parker, William; Wu, Huiming; Bobba, Rambabu

2008-04-01

175

Chiral Ditopic Cyclophosphazane (CycloP) Ligands: Synthesis, Coordination Chemistry, and Application in Asymmetric Catalysis.  

PubMed

A series of dichlorocyclophosphazanes [{ClP(?-NR)}2 ] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl3 . Their condensation reactions with axially chiral biaryl diols yielded ansa-bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single-crystal X-ray diffraction. These studies show that all of the ditopic CycloP ligands are C2 symmetric, rendering their metal coordination sites symmetry equivalent. Two well-established enantioselective reactions were explored by using late-transition metal CycloP complexes as catalysts; the gold-catalyzed hydroamination of ?-allenyl sulfonamides and the asymmetric nickel-catalyzed three-component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold-catalyzed reaction and 92:8 in the nickel-catalyzed bis-homoallylation reaction were observed. PMID:24038171

Roth, Torsten; Wadepohl, Hubert; Wright, Dominic S; Gade, Lutz H

2013-08-28

176

Asymmetric synthesis and antimicrobial activity of some new mono and bicyclic beta-lactams.  

PubMed

Reaction of the amino acid D-phenylalanine ethyl ester (4) with cinnamaldehyde gave chiral Schiff base 5, which underwent an asymmetric Staudinger [2+2] cycloaddition reaction with phthalimidoacetyl chloride to give the monocyclic beta-lactam 6 as a single stereoisomer. Ozonolysis of 6 followed by reduction with lithium aluminum tri(tert-butoxy) hydride afforded the hydroxymethyl beta-lactam 8. Treatment of 8 with methansulfonyl chloride gave the mesylated monocyclic beta-lactam 9, which was converted to the bicyclic beta-lactam 10 upon treatment with 1,8-diazabicyclo[5,4.0] undec-7-ene (DBU). Deprotection of the phthalimido group in beta-lactams 6 and 10 by methylhydrazine and subsequent acylation of the free amino beta-lactams with different acyl chlorides in the presence of pyridine afforded mono and bicyclic beta-lactams 14a-d and 15a-d respectively. The compounds prepared were tested against Escherichia coli, Staphilococcus citrus, Klebsiella pneumanie and Bacillus subtillis. Some of these compounds showed potential antimicrobial activities. PMID:18007494

Jarrahpour, A A; Shekarriz, M; Taslimi, A

2004-11-30

177

Synthesis and Transistor Properties of Asymmetric Oligothiophenes: Relationship between Molecular Structure and Device Performance.  

PubMed

A series of three thiophene-naphthalene-based asymmetric oligomers-5-decyl-2,2':5',2'':5'',2'''-quaterthiophene (DtT), 5-decyl-5''-(naphthalen-2-yl)-2,2':5',2''-terthiophene (D3TN), and 5-(4-decylphenyl)-5'-(naphthalen-2-yl)-2,2'-bithiophene (DP2TN)-was synthesized by Suzuki cross-coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self-assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H-type aggregates with a face-to-face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing-incidence wide-angle X-ray scattering. These oligomers were used as the active layers of p-type organic field-effect transistors, and the resulting devices showed field-effect mobilities of 3.3×10(-3) ?cm(2) ?V(-1) ?s(-1) for DtT, 1.6×10(-2) ?cm(2) ?V(-1) ?s(-1) for D3TN, and 3.7×10(-2) ?cm(2) ?V(-1) ?s(-1) for DP2TN. The differences in transistor performances were attributed to the degree of ? overlap and the morphological differences determined by the molecular structures. PMID:24108597

An, Tae Kyu; Jang, Sang Hun; Kim, Seul-Ong; Jang, Jaeyoung; Hwang, Jihun; Cha, Hyojung; Noh, Young Ri; Yoon, Soon Byung; Yoon, Yong Jin; Kim, Lae Ho; Chung, Dae Sung; Kwon, Soon-Ki; Kim, Yun-Hi; Lee, Sang-Gyeong; Park, Chan Eon

2013-09-17

178

In vivo nitric oxide synthesis, insulin sensitivity, and asymmetric dimethylarginine in obese subjects without and with metabolic syndrome.  

PubMed

Metabolic syndrome (MetSyn) is associated with impaired endothelial function. Here the association between nitric oxide (NO) production and insulin sensitivity (Si) in obese subjects with and without MetSyn was evaluated. The relationship between NO production and asymmetric dimethylarginine (ADMA) was also explored. Seven healthy normal-weight subjects (male/female [M/F], 3/4; age, 27.4 ± 10.9 years; body mass index [BMI], 21.9 ± 2.2 kg/m(2)), 7 obese subjects without MetSyn (M/F, 1/6; age, 48.0 ± 8.0 years; BMI, 34.5 ± 2.3 kg/m(2)), and 7 with MetSyn (M/F, 3/4; age, 48.0 ± 10.7 years; BMI, 33.4 ± 2.9 kg/m(2)) were recruited. Body composition and cardiometabolic functions (blood pressure, glucose, insulin, triglycerides, total cholesterol, high-density lipoprotein, ADMA) were measured. A frequent sampling intravenous glucose tolerance test was performed to measure Si. A novel stable isotopic method was used to measure in vivo rates of NO production. The NO production was lower in obese subjects with MetSyn compared with normal-weight subjects and obese subjects without MetSyn. Similarly, Si was significantly lower in obesity, both without and with MetSyn, compared with the control group. A significant direct association was found between NO synthesis and Si (? = 0.47, P = .03). Circulating levels of ADMA were significantly higher in the obese group with MetSyn. A nonsignificant negative trend between ADMA and NO synthesis was observed. The association between Si and NO production suggests a close mechanistic link between endothelial function and insulin signaling. The results may be highly informative for the development of controlled longitudinal interventions to improve endothelial and metabolic regulation. PMID:22146092

Siervo, Mario; Bluck, Les J C

2011-12-05

179

Enantioselective synthesis of anti- and syn-homopropargyl alcohols via chiral Brønsted acid catalyzed asymmetric allenylboration reactions.  

PubMed

Chiral Brønsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in highly diastereoselective syntheses of a variety of anti, anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R

2012-06-25

180

Asymmetric Synthesis of 3-Substituted 4-Oxoesters Using the SAMP\\/RAMP-Hydrazone Method  

Microsoft Academic Search

. Based on aldehydes 1a-f or ketone 1g, 3-substituted 4-oxo esters 6a-g were synthesized in three steps in moderate to good overall yield (12-50%) and in excellent enantiomeric excesses ($ee >90\\\\to 95$%) by an Umpolung-strategy employing the SAMP-\\/RAMP-hydrazone method. The key step in the synthesis is the highly diastereoselective alkylation of lithiated SAMP-hydrazones 3a-g (chiral d$^2$-nucleophiles) with tert-butyl bromoacetate (4)

D. Enders; U. Baus; P. Müller; K. C. Nicolaou; B. Jandeleit

1998-01-01

181

Stereoselective synthesis of unsymmetrical ?,?-diarylacrylates by a Heck-Matsuda reaction: versatile building blocks for asymmetric synthesis of ?,?-diphenylpropanoates, 3-aryl-indole, and 4-aryl-3,4-dihydro-quinolin-2-one and formal synthesis of (-)-indatraline.  

PubMed

?,?-Disubstituted ?,?-unsaturated esters may serve as valuable derivatives for the preparation of other highly functionalized systems found in many natural products and marketed drugs. The stereoselective synthesis of unsymmetrical ?,?-diarylacrylate compounds possessing two similar aromatic groups remains a substantial challenge. A simple and convenient stereoselective protocol for the preparation of ?,?-disubstituted acrylates via a Heck-Matsuda reaction is reported. Good to high yields were accomplished by a "ligand-free" Pd-catalyzed arylation reaction of cinnamate esters with arenediazonium tetrafluoroborates. Both electron-deficient and electron-rich arenediazonium salts could be employed as arylating reagents, and cinnamate esters were generally more reactive when substituted with an electron-donating group. The overall methodology is highly stereoselective, and this attribute was taken advantage of in the asymmetric Cu-catalyzed 1,4 reduction reaction to provide ?,?-diarylpropanoates in high enantioselectivities. The synthesis of a 3-aryl indole and a chiral 4-aryl-2-quinolone from ?,?-diarylacrylates was achieved by cyclization in the presence of a diphosphine ligated CuH catalyst. A convenient route for the asymmetric formal synthesis of the psychoactive compound (-)-Indatraline is also presented. PMID:21241065

Taylor, Jason G; Correia, Carlos Roque D

2011-01-11

182

Asymmetric chemoenzymatic synthesis of miconazole and econazole enantiomers. The importance of chirality in their biological evaluation.  

PubMed

A simple and novel chemoenzymatic route has been applied for the first time in the synthesis of miconazole and econazole single enantiomers. Lipases and oxidoreductases have been tested in stereoselective processes; the best results were attained with oxidoreductases for the introduction of chirality in an adequate intermediate. The behaviors of a series of ketones and racemic alcohols in bioreductions and acetylation procedures, respectively, have been investigated; the best results were found with alcohol dehydrogenases A and T, which allowed the production of (R)-2-chloro-1-(2,4-dichlorophenyl)ethanol in enantiopure form under very mild reaction conditions. Final chemical modifications have been performed in order to isolate the target fungicides miconazole and econazole both as racemates and as single enantiomers. Biological evaluation of the racemates and single enantiomers has shown remarkable differences against the growth of several microorganisms; while (R)-miconazole seemed to account for most of the biological activity of racemic miconazole on all the strains tested, both enantiomers of econazole showed considerable biological activities. In this manner, (R)-econazole showed higher values against Candida krusei , while higher values were observed for (S)-econazole against Cryptococcus neoformans, Penicillium chrysogenum, and Aspergillus niger. PMID:21384803

Mangas-Sánchez, Juan; Busto, Eduardo; Gotor-Fernández, Vicente; Malpartida, Francisco; Gotor, Vicente

2011-03-08

183

Stereoselective Synthesis of Highly Functionalized Cyclopropanes. Application to the Asymmetric Synthesis of (1S,2S)-2,3-Methanoamino Acids.  

PubMed

One-pot palladium(0)-catalyzed alkylation and S(N)(') cyclization of 1,4-dichlorobut-2-ene 1 by the anion of alpha-substituted carbonitriles 2a-d can provide highly functionalized cyclopropanes (E)-4a-d, diastereoselectivity, (de 88-100%). Several attempts to achieve the asymmetric synthesis of the 1-amino-2-ethenylcyclopropanecarbonitrile (E)-9, by means of this new procedure, i.e., using chiral palladium ligands, chiral aminoacetonitriles (-)- and (+)-12 (from 1-hydroxypinanone) or chiral allyl chlorides (4S)-20b-d and (4R)-20e (from (2S) ethyl lactate) have pointed up the reversibility of the palladium-catalyzed cyclization step, responsible for the low enantioselectivity observed (ee 88%) and provided the enantiomerically enriched 1-amino-2-propenylcyclopropanecarbonitrile (E)-22 (ee > 83%) suitable precursor of (1S,2S)-2,3-methanoamino acids. PMID:11674544

Dorizon, Philippe; Su, Guifa; Ludvig, Gitte; Nikitina, Lilyia; Paugam, Renée; Ollivier, Jean; Salaün, Jacques

1999-06-25

184

Catalytic asymmetric Henry reaction  

Microsoft Academic Search

The classical Henry reaction, the coupling of a nitroalkane with a carbonyl compound in the presence of a base, is an important C–C bond forming reaction in organic chemistry giving ?-nitroalcohols, which are useful synthons in organic synthesis. However, an asymmetric version of the reaction, that has been developed recently, gives a new dimension to the classical Henry reaction whereby

Joshodeep Boruwa; Naminita Gogoi; Partha Pratim Saikia; Nabin C. Barua

2006-01-01

185

Catalytic asymmetric diaziridination.  

PubMed

The first catalytic enantio- and diastereoselective synthesis of diaziridines is presented. Aziridination of N-tosyl aldimines applying modified hydroxylamine under asymmetric phase-transfer catalysis furnished optically active diaziridines. The diaziridines are formed as a single diastereomer in up to 96% ee, containing two orthogonal N-protecting groups, which can be deprotected selectively. PMID:23488989

Lykke, Lennart; Halskov, Kim Søholm; Carlsen, Bjørn Dreiø; Chen, Victor X; Jørgensen, Karl Anker

2013-03-18

186

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

187

Enantioselective desymmetrization of meso bicyclic hydrazines: a novel approach to the asymmetric synthesis of polysubstituted amino cyclopentanic cores.  

PubMed

Catalytic asymmetric hydroboration can be successfully applied to meso bicyclic hydrazines. The resulting alcohols are of great synthetic interest and can lead in a straightforward manner to cyclopentanic diamino alcohols with good enantiomeric purity. PMID:12003572

Pérez Luna, A; Ceschi, M-A; Bonin, M; Micouin, L; Husson, H-P; Gougeon, S; Estenne-Bouhtou, G; Marabout, B; Sevrin, M; George, P

2002-05-17

188

Responsive helical self-assembly of AgNO3 and melamine through asymmetric coordination for Ag nanochain synthesis.  

PubMed

Responsive nanohelices can be self-assembled via asymmetric coordination bonding between AgNO3 and melamine. Silver nanochains composed of nanoparticles can be synthesized simply by photo-reduction of the above complex. PMID:23148050

Fei, Jinbo; Gao, Liang; Zhao, Jie; Du, Cuiling; Li, Junbai

2012-11-13

189

Asymmetric syntheses of pipecolic acid and derivatives  

Microsoft Academic Search

Summary Results in the field of asymmetric synthesis of pipecolic acid derivatives are reviewed. Three sections describe the asymmetric syntheses of the title compounds (i) from the chiral pool (a-amino acids or carbohydrates) (ii) using a chiral auxiliary either derived from terpenes,a-amino acids, tartaric acid, an amine orß-amino alcohols (iii) by means of asymmetric catalysis.

François Couty

1999-01-01

190

Total synthesis of (+)-crotogoudin.  

PubMed

Fellowship of the ring: The first total synthesis of (+)-crotogoudin, a 3,4-seco-atisane diterpenoid natural product, is reported. Asymmetric access to the bicyclo[2.2.2]octane core is achieved through a desymmetrization of a meso-diketone with baker's yeast (LG=leaving group, PG=protecting group). A SmI2 -induced radical cyclopropane-opening/annulation/elimination cascade affords the suitably decorated tetracyclic structure of (+)-crotogoudin. The synthesis led to revision of the reported optical rotation of the natural product and to assignment of its absolute configuration as an ent-atisane (5R,10R). PMID:24039092

Breitler, Simon; Carreira, Erick M

2013-08-26

191

Asymmetric synthesis of ?,?-diamino acid derivates via Mannich-type reactions of a chiral Ni(II) complex of glycine with N-tosyl imines.  

PubMed

A practical procedure composed of an asymmetric Mannich-type reaction between N-tosyl imine and a Ni(II) complex of glycine with (R)-o-[N-(N-benzylprolyl)amino]bezaophenone (BPB) as a chiral auxiliary catalyzed by Et(3)N in DMF to (R,2R,3S)-complexes, and decomposition of products with HCl to offer syn-(2R,3S)-?,?-diamino acids, was developed. Stereochemical mechanism of the Mannich reaction was proposed and supported by determining the absolute configuration of the product of the Mannich reaction relying on X-ray analysis. This two-step approach to amino acids was a general method and adapted to large-scale preparation. PMID:21858319

Song, Guowei; Jin, Meihong; Li, Zhenjiang; Ouyang, Pingkai

2011-08-22

192

Chemo-enzymatic asymmetric synthesis of S-citalopram by lipase-catalyzed cyclic resolution and stereoinversion of quaternary stereogenic center.  

PubMed

A chemo-enzymatic synthesis method of S-citalopram was developed to overcome the disadvantage of relatively low selectivity of enzyme towards tertiary alcohols. The combination of kinetic resolution, cyclic resolution and stereoinversion synthesis was successfully applied in the asymmetric synthesis of the S-citalopram. Using the kinetic model to predict the cyclic resolution, R-diol with high ee value was obtained by controlling the conversion rate. Subsequently, the unwanted R-diol was inverted to S-citalopram by stereoinversion of chiral quaternary center with 98.0% yield and ee value of 91.0%. Based on dynamic simulation and experiments, the kinetic resolution was scaled up from 10 mL to 1 L and 14 L, gradually. There was no significant scale-up effect and the dynamic simulation result fitted the experimental data well, with an error of 12.5 and 14.0%, respectively. This chemo-enzymatic synthesis route is a promising model system for the production of pharmaceuticals with the chiral tertiary alcohols intermediate. PMID:23135492

Wang, Shi-Zhen; Wu, Jian-Ping; Xu, Gang; Yang, Li-Rong

2012-11-08

193

Relay catalysis: combined metal catalyzed oxidation and asymmetric iminium catalysis for the synthesis of bi- and tricyclic chromenes.  

PubMed

A catalytic asymmetric oxidative iminium-allenamine cascade allows the use of propargyl alcohols as stable substrates and yields valuable chiral bicyclic 4H-chromenes. A subsequent Michael addition-condensation domino reaction provides complex tricyclic 4H-chromenes in a highly enantioselective fashion. PMID:22363938

Rueping, Magnus; Dufour, Jeremy; Maji, Modhu Sudan

2012-02-23

194

Asymmetric synthesis of 2-alkyl-3-thiazoline carboxylates: stereochemistry of the MnO 2-mediated oxidation of cis- and trans-2-alkyl-thiazolidine-(4 R)-carboxylates  

Microsoft Academic Search

The asymmetric synthesis of a series of 3-thiazoline carboxylates, 2, was effected by MnO2 oxidation of the corresponding cis\\/trans thiazolidines, 1. The stereochemistry of the oxidation reaction was studied using NMR and chiral GC analyses. Compounds 2 were obtained with enantiomeric excesses (e.e.s) in the range of 40–100%.

Xavier Fernandez; Elisabet Duñach

2001-01-01

195

Asymmetric synthesis of ?-chloro-?,?-diamino- and ?,?-aziridino-?-aminoacylpyrrolidines and -piperidines via stereoselective Mannich-type additions of N-(diphenylmethylene)glycinamides across ?-chloro-N-sulfinylimines  

PubMed Central

Summary The asymmetric synthesis of new chiral ?-chloro-?,?-diaminocarboxylamide derivatives by highly diastereoselective Mannich-type reactions of N-(diphenylmethylene)glycinamides across chiral ?-chloro-N-p-toluenesulfinylaldimines was developed. The resulting (S S,2S,3S)-?-chloro-?,?-diaminocarboxylamides were formed with the opposite enantiotopic face selectivity as compared to the (S S,2R,3R)-?-chloro-?,?-diaminocarboxyl esters obtained via Mannich-type addition of analogous N-(diphenylmethylene)glycine esters across a chiral ?-chloro-N-p-toluenesulfinylaldimine. Selective deprotection under different acidic reaction conditions and ring closure of the ?-chloro-?,?-diaminocarboxylamides was optimized, which resulted in N?-deprotected syn-?-chloro-?,?-diaminocarboxylamides, N-sulfinyl-?,?-aziridino-?-aminocarboxylamide derivatives, a trans-imidazolidine, and an N?,N?-deprotected syn-?-chloro-?,?-diaminocarboxylamide.

Callebaut, Gert; Mangelinckx, Sven; Van der Veken, Pieter; Tornroos, Karl W; Augustyns, Koen

2012-01-01

196

Stereoselective Rh2(S-IBAZ)4-catalyzed cyclopropanation of alkenes, alkynes, and allenes: asymmetric synthesis of diacceptor cyclopropylphosphonates and alkylidenecyclopropanes.  

PubMed

A mild and highly stereoselective rhodium(II)-catalyzed cyclopropanation of alkenes, alkynes, and allenes with diacceptor diazo compounds is reported. Using the phosphonate moiety as an efficient trans-directing group, the first catalytic asymmetric route to diacceptor cycloprop(en)ylphosphonates was developed by employing an ?-cyano diazophosphonate and Rh(2)(S-IBAZ)(4) as chiral catalyst. The isosteric character of phosphonic and carboxylic acid derivatives allowed the alternative use of an ?-cyano diazo ester in the process, leading to ?-cyano cycloprop(en)ylcarboxylates in high yields and stereoselectivities. Taking advantage of the particular reactivity of the cyanocarbene intermediates involved in this system, the scope of compatible substrates could be extended to substituted allenes, leading to the development of the first catalytic enantioselective method for the synthesis of diacceptor alkylidenecyclopropanes. PMID:23289770

Lindsay, Vincent N G; Fiset, Dominic; Gritsch, Philipp J; Azzi, Soula; Charette, André B

2013-01-15

197

P-Chiral ferrocenephospholanes: synthesis, reactivity, metal complex chemistry and application in the asymmetric hydrogenation of olefins.  

PubMed

Starting from (R)-N,N-dimethyl-1-ferrocenylethylamine, a diastereoselective ortho-lithiation procedure and a stereoconvergent intramolecular hydrophosphination gave access to P-chiral ferrocenephospholanes. These mono- or bidentate ligands were converted to the corresponding rhodium and iridium complexes, including a chiral version of Crabtree's catalyst, and tested in the asymmetric hydrogenation of functionalized and unfunctionalized olefins. A significant reactivity difference between the rhodium-1,5-cyclooctadiene and the rhodium-norbornadiene complex was observed during catalyst activation. PMID:19894235

Gschwend, Björn; Pugin, Benoît; Bertogg, Andreas; Pfaltz, Andreas

2009-12-01

198

The Synthesis of Some New Sulfur-Bearing Various Heterocyclic Systems Derived from Asymmetrical N,N?-Disubstituted Thiourea Derivatives  

Microsoft Academic Search

The heterocyclization of an asymmetrical N,N?-disubstituted thiourea (1a–d) in ring closure reactions with Br2\\/AcOH, ethyl chloroacetate, diethyl oxalate, diethyl malonate, and hydrazine hydrate led to the direct formation of sulfur-bearing various heterocyclic systems (2–8) in which the thiaenolization is toward the aryl group. The synthetic work and reactivity investigations have been well supported by standard modern spectroscopic techniques (IR, H

Hosam Saad

2006-01-01

199

Stereoselective synthesis of ( R )-3-quinuclidinol through asymmetric reduction of 3-quinuclidinone with 3-quinuclidinone reductase of Rhodotorula rubra  

Microsoft Academic Search

A novel nicotinamide adenine dinucleotide phosphate-dependent carbonyl reductase, 3-quinuclidinone reductase, was isolated\\u000a from Rhodotorula rubra JCM3782. The enzyme catalyzes the asymmetric reduction of 3-quinuclidinone to (R)-3-quinuclidinol. The gene encoding the enzyme was also cloned and sequenced. A 819-bp nucleotide fragment was confirmed\\u000a to be the gene encoding the 3-quinuclidinone reductase by agreement of the internal amino acid sequences of the

Atsuko Uzura; Fumiki Nomoto; Akiko Sakoda; Yukifumi Nishimoto; Michihiko Kataoka; Sakayu Shimizu

2009-01-01

200

Synthesis and Crystal Structure of New Chiral Ferrocenyl Schiff Base Ligands and Application in the Asymmetric Transfer Hydrogenation of Acetophenone  

Microsoft Academic Search

Novel ferrocenyl?imine ligands 5 (5a-5c) have been synthesized for the iridium catalyzed asymmetric transfer hydrogenation of acetophenone. Ferrocenyl?2?thiopheneformaldehyde?imine ligand 5c was characterized by single crystal X?ray diffraction analysis. Single crystal X?ray diffraction analysis reveals that the molecular structure of the title compound is enantiomerically pure and crystallizes in the noncentrosymmetric P4(1) space group, orthorhombic. The two phenyl group adopts a

Peng Liu

2007-01-01

201

Synthesis of Polymer-supported Chiral Lithium Amide Bases and Application in Asymmetric Deprotonation of Prochiral Cyclic Ketones  

PubMed Central

Polymer-supported chiral amines were effectively prepared from amino acid derivatives and Merrifield resin. Treatment of polymer-supported amines with n-butyllithium gave the corresponding polymer-suppported chiral lithium amide bases, which were tested in the asymmetric deprotonation reactions of prochiral ketones. The trimethylsilyl enol ethers were obtained in up to 82% ee at room temperature. The polymer-supported chiral lithium amides can be readily recycled and reused without any significant loss of reactivity or selectivity.

Ma, Lili; Williard, Paul G.

2007-01-01

202

A Casein Kinase 1 and PAR Proteins Regulate Asymmetry of a PIP 2 Synthesis Enzyme for Asymmetric Spindle Positioning  

Microsoft Academic Search

SUMMARY Spindle positioning is an essential feature of asym- metric cell division. The conserved PAR proteins to- gether with heterotrimeric G proteins control spindle positioning inanimalcells,buthowthesearelinked is not known. In C. elegans, PAR protein activity leads to asymmetric spindle placement through cortical asymmetry of Ga regulators GPR-1\\/2. Here, we es- tablish that the casein kinase 1 gamma CSNK-1 and a

Costanza Panbianco; David Weinkove; Esther Zanin; David Jones; Nullin Divecha; Monica Gotta; Julie Ahringer

2008-01-01

203

Asymmetric synthesis of ?-adrenergic blockers through multistep one-pot transformations involving in situ chiral organocatalyst formation.  

PubMed

Two birds one stone: A new atom-economical one-pot approach to enantioselective chiral drug synthesis, involving in situ multistep organocatalyst formation and the application of the reaction for multistep sequential synthesis of ?-adrenergic blockers is disclosed (see scheme). PMID:22113987

Wei, Shengwei; Messerer, Regina; Tsogoeva, Svetlana B

2011-11-23

204

Highly active catalysts of bisphosphine oxides for asymmetric Heck reaction.  

PubMed

Bisphosphine oxides formed highly active asymmetric Heck catalysts, which were applied in asymmetric synthesis of pharmacologically active azacycles. Olefin insertion proceeded via cis pathways, different from P,N-ligands. PMID:24005808

Hu, Jian; Lu, Yunpeng; Li, Yongxin; Zhou, Jianrong Steve

2013-10-21

205

Asymmetric synthesis of the mC 7N core of the manumycin family: Preparation of (+)MT 35214 and a formal total synthesis of (?)-alisamycin  

Microsoft Academic Search

An asymmetric approach to the mC7N epoxyquinone central unit of the manumycin antibiotics is described based on the enantioselective (89% ee) chiral phase transfer epoxidation of a substituted cyclohexenone. The chiral epoxide is employed in the first syntheses of the title compounds in enantiomerically pure form.

Gregor Macdonald; Lilian Alcaraz; Norman J Lewis; Richard J. K Taylor

1998-01-01

206

Improved asymmetric synthesis of 3,4-dihydro-2-[3-(1,1,2,2-tetrafluoroethoxy)phenyl]-5-[3-(trifluoromethoxy)phenyl]-alpha-(trifluoromethyl)-1(2H)-quinolineethanol, a potent cholesteryl ester transfer protein inhibitor.  

PubMed

The asymmetric synthesis of 3,4-dihydro-2-[3-(1,1,2,2-tetrafluoroethoxy)phenyl]-5-[3-(trifluoromethoxy)phenyl]-alpha-(trifluoromethyl)-1(2H)-quinolineethanol (compound 11), a cholesteryl ester transfer protein inhibitor, is accomplished. The asymmetric center is established via the chiral reduction of ketone 4 employing Corey's (R)-Me CBS oxazaborolidine reagent. The tetrahydroquinoline core of the molecule is established via a Cu-mediated intramolecular amination reaction. The preparation of the prochiral ketone 4 has also been improved by eliminating the use of a hazardous aryltin reagent. PMID:19507869

Rano, Thomas A; Kuo, Gee-Hong

2009-07-01

207

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization  

Microsoft Academic Search

A new asymmetric H-shaped block copolymer (PS)2–PEO–(PMMA)2 has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl–PS)2–CHCOOCH2CH2OH with an active hydroxyl group. The chlorine was removed to yield the (PS)2–CHCOOCH2CH2OH

Xifei Yu; Tongfei Shi; Guo Zhang; Lijia An

2006-01-01

208

The synthesis of chiral ?-aryl-?,?-unsaturated amino alcohols via a Pd-catalyzed asymmetric allylic amination.  

PubMed

Chiral ?-aryl-?,?-unsaturated amino alcohols were synthesized via a Pd-catalyzed asymmetric allylic amination of 4-aryl-1,3-dioxolan-2-one using planar chiral 1,2-disubstituted ferrocene-based phosphinooxazolines as ligands. Under the optimized reaction conditions, a series of substrates were examined and the products were obtained in good to excellent yields (up to 92%) and enantioselectivities (up to 98% ee) under mild reaction conditions. The desired products were determined to be of (R)-configuration and could subsequently be transformed into compounds with interesting biological activity using simple transformations. PMID:24077558

Quan, Mao; Butt, Nicholas; Shen, Jiefeng; Shen, Kaiji; Liu, Delong; Zhang, Wanbin

2013-10-01

209

Synthesis of asymmetric difunctional initiators and their use in the preparation of block copolymers via ATRP and SFRP  

Microsoft Academic Search

Novel asymmetric difunctional initiators 2-phenyl-2-[(2,2,6,6-tetramethylpiperidino)oxy]ethyl 2-bromo-2-methyl propanoate and of 2-phenyl-2-[(2,2,6,6-tetramethylpiperidino)oxy]ethyl 2-bromo propanoate were synthesized in a three-step reaction sequence and used in atom transfer radical polymerization (ATRP) of methyl methacrylate or tert-butyl acrylate leading to corresponding polymer with tempo moiety as chain end. These polymers were found to be efficient initiators for stable free radical polymerization (SFRP) of styrene. 1H

U Tunca; B Karl?ga; S Ertekin; A. L Ugur; O Sirkecioglu; G Hizal

2001-01-01

210

Enantioselective synthesis of 2,2-disubstituted terminal epoxides via catalytic asymmetric Corey-Chaykovsky epoxidation of ketones.  

PubMed

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li(3)-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%-91% ee) and yield ( > 99%-88%) from a broad range of methyl ketones with 1-5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%-67% ee). PMID:22314382

Sone, Toshihiko; Yamaguchi, Akitake; Matsunaga, Shigeki; Shibasaki, Masakatsu

2012-02-07

211

Synthesis, structures, electrochemistry and catalytic activities of copper(II) and palladium(II) complexes with asymmetric tetraazacycloannulenes  

Microsoft Academic Search

Copper(II) and palladium(II) complexes with 15-membered asymmetric 5,9-dihydro-2,4,10,12-tetramethyl-1,5,9,13-monobenzotetraazacyclo[15]tetradecine have been synthesized and characterized. The electrochemical behaviors of the complexes showed a reduction and two one-electron irreversible oxidation waves in given potential ranges due to the metal ion and macrocycle ring, respectively. The electrocatalytic reduction of dioxygen on glassy carbon electrodes electropolymerized by such 15-membered and 14-membered tetraazaannulene complexes occurred at

E. H. Kim; D. I. Kim; H. S. Lee; H. G. Na; J. C. Byun; J. H. Choi; Y. C. Park

2007-01-01

212

Synthesis and resolution of the biaryl-like diphosphine (S)-Me2-CATPHOS, preparation of a derived rhodium precatalyst and applications in asymmetric hydrogenation.  

PubMed

This protocol describes the synthesis of a representative example of the enantiopure biaryl-like CATPHOS class of diphosphines, (S)-9,9'-dimethyl-9,9',10,10'-tetrahydro-9,10,9',10'-biethenobianthracene-11,11'-bis(diphenylphosphino)-12,12'-diyl ((S)-Me(2)-CATPHOS), and its derived cationic rhodium-based hydrogenation precatalyst. The C(2)-symmetric framework of Me(2)-CATPHOS is the result of a regioselective Diels-Alder cycloaddition between 1,4-bis(diphenylphosphinoyl)buta-1,3-diyne and 9-methylanthracene, such that the bulky methyl-substituted bridgehead carbon atoms are attached to C2 and C3 of the 1,3-butadiene tether. Enantiopure Me(2)-CATPHOS is obtained in an operationally straightforward three-step procedure and isolated in ?50-60% overall yield and <99% enantiopurity, after diastereoselective resolution with (2R,3R)-(-)-2,3-O-dibenzoyltartaric acid. The derived rhodium complex forms a highly effective catalyst for the asymmetric hydrogenation of a range of dehydroamino acid derivatives, as well as (E)-?-aryl-(enamido)phosphonates, giving ee values in excess of 99%, the highest to be reported for the latter class of substrate. The total time required for the synthesis of (S)-Me(2)-CATPHOS, including resolution, reduction and crystallizations, is 130 h and preparation of the corresponding rhodium precatalyst requires an additional 24-26 h. PMID:23018192

Doherty, Simon; Smyth, Catherine H

2012-09-20

213

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.

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

2011-01-01

214

A new asymmetric synthesis of 2,6- cis-disubstituted 4-methylenepiperidines: total synthesis of (+)-alkaloid 241D and (+)-isosolenopsin A  

Microsoft Academic Search

A highly diastereoselective synthesis of 2,6-cis-disubstituted-4-methylenepiperidines based on a Mannich type intramolecular cyclization of an allylsilane on an iminium ion is described. The synthetic potential of this methodology is demonstrated by the enantioselective synthesis of two natural piperidine alkaloids: (+)-alkaloid 241D and (+)-isosolenopsin A.

Jérémy Monfray; Yvonne Gelas-Mialhe; Jean-Claude Gramain; Roland Remuson

2005-01-01

215

Stereoselective synthesis of (R)-3-quinuclidinol through asymmetric reduction of 3-quinuclidinone with 3-quinuclidinone reductase of Rhodotorula rubra.  

PubMed

A novel nicotinamide adenine dinucleotide phosphate-dependent carbonyl reductase, 3-quinuclidinone reductase, was isolated from Rhodotorula rubra JCM3782. The enzyme catalyzes the asymmetric reduction of 3-quinuclidinone to (R)-3-quinuclidinol. The gene encoding the enzyme was also cloned and sequenced. A 819-bp nucleotide fragment was confirmed to be the gene encoding the 3-quinuclidinone reductase by agreement of the internal amino acid sequences of the purified enzyme. The gene encodes a total of 272 amino acid residues, and the deduced amino acid sequence shows similarity to those of several short-chain dehydrogenase/reductase family proteins. An expression vector, pWKLQ, which contains the full length 3-quinuclidinone reductase gene was constructed. Using Escherichia coli cells coexpressing the 3-quinuclidinone reductase and glucose dehydrogenase (cofactor regeneration enzyme) genes, 618 mM 3-quinuclidinone was almost stiochiometrically converted to (R)-3-quinuclidinol with an >99.9% enantiomeric excess within 21 h of reaction. PMID:19234697

Uzura, Atsuko; Nomoto, Fumiki; Sakoda, Akiko; Nishimoto, Yukifumi; Kataoka, Michihiko; Shimizu, Sakayu

2009-02-21

216

Synthesis, one and two-photon optical properties of two asymmetrical and symmetrical carbazole derivatives containing quinoline ring  

NASA Astrophysics Data System (ADS)

The carbazole derivatives are suitable for two-photon absorption optical storage and photoluminescence material. Two carbazole derivatives, asymmetrical and symmetrical type molecules containing quinoline rings as electron acceptors and an N-ethylcarbazole group as electron donor, 9-ethyl-3-(2-quinolin)viny-carbazole (4) and 9-ethyl-3,6-bis(2-(quinolin)vinyl)-carbazole (5), had been synthesized by the Vilsmeier reaction of formylation and Knoevenagel condensation. The one-photon properties including absorption, fluorescence emission spectra, fluorescence quantum yields and fluorescence decay behaviors were investigated in N,N-dimethylformamide. Meanwhile, these compounds were theoretically surveyed by the density functional theory (DFT) and the time-dependent functional theory (TD-DFT). The two-photon excited fluorescence and two-photon absorption cross-sections were measured for the compounds by 120 fs pulse at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate. The results showed that both of the two compounds 4 and 5 had higher fluorescence quantum yield (?) of 0.77 and 0.81 comparing with carbazole. Compounds 5 with symmetric ? conjugated structure possessed longer fluorescence lifetime (?) of 21.4 ns and larger two-photon absorption cross-sections (?TPA) of 364 × 10-50 cm4 s/photon than those of compounds 4 with asymmetric ? conjugated structure (? = 10.03 ns and ?TPA = 81 × 10-50 cm4 s/photon). It was indicated that the one and two-photon optical properties of carbazole derivatives are influenced strongly by the symmetry and length of ? conjugated structure.

Li, Liang; Wang, Ping; Zhang, Yichi; Wu, Yiqun; Chen, Zhimin; He, Chunying

2013-11-01

217

Engineering Acyclic Stereocontrol in the Alkylation of Vinylglycine-Derived Dianions:  Asymmetric Synthesis of Higher ?-Vinyl Amino Acids  

Microsoft Academic Search

A generalizable synthesis of higher L-R-vinyl amino acids is presented. The strategy pursued here involves the introduction of the amino acid side chain via the alkylation of a chiral, vinylglycine- derived dianionic dienolate, bearing the (-)-8-(‚-naphthyl)menthyl (d'Angelo) auxiliary. A model is presented that postulates a favored \\

David B. Berkowitz; Jill M. McFadden; Marianne K. Sloss

2000-01-01

218

Towards novel amide-modified oligonucleotides: asymmetric synthesis of 5?-( S)-methyl-3?-carboxymethylene-3?-deoxythymidine  

Microsoft Academic Search

The synthesis of novel 5?-(S)-methyl-3?-carboxymethylene-3?-deoxythymidine is reported. Key steps involve diastereoselective lactonization, enantioselective enzymatic ester hydrolysis and diastereoselective glycosidation of a key intermediate with thymine with 100% ?-selectivity via Lewis acid mediated cleavage of a [3.2.1] oxabicyclic lactone.

Sebastian Wendeborn; Hannes Nussbaumer; Frédéric Robert; Mario Jörg; Johannes Paul Pachlatko

2002-01-01

219

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

2013-10-01

220

Creation of novel chiral synthons with enzymes: application to enantioselective synthesis of antibiotics.  

PubMed

Retrosynthesis was carried out to generate, from a target molecule, a symmetric diester in the prochiral or meso form. The symmetric diester was subjected to asymmetric hydrolysis with pig liver esterase to create the corresponding chiral half-ester. The chiral half-ester was converted into the target molecule by organic synthesis. Thus, various types of carbapenem antibiotics, negamycin, showdomycin, 6-azapseudouridine, cordycepin, aristeromycin, neplanocin A, and precursors of fortimicin were efficiently synthesized with the desired absolute configuration. The methods for asymmetric synthesis starting from substrates with sigma-symmetry have been extensively developed. PMID:3874758

Ohno, M

1985-01-01

221

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

222

Base-dependent stereodivergent intramolecular aza-Michael reaction: asymmetric synthesis of 1,3-disubstituted isoindolines.  

PubMed

The nucleophilic addition (AN ) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2 -symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may allow for the orthogonal synthesis of ?,?'-dipeptides using a single nitrogen atom as a linchpin. PMID:23852920

Fustero, Santos; Herrera, Lidia; Lázaro, Ruben; Rodríguez, Elsa; Maestro, Miguel A; Mateu, Natalia; Barrio, Pablo

2013-07-12

223

Glucogenic blood sugar formation in an insect Manduca sexta L.: asymmetric synthesis of trehalose from 13C enriched pyruvate  

Microsoft Academic Search

Gluconeogenesis and blood sugar formation were examined in Manduca sexta, fed carbohydrate- and fat-free diets with varying levels of casein. De novo carbohydrate synthesis was examined by nuclear magnetic resonance spectroscopy of the 13C enrichment in blood trehalose and alanine derived from (2-13C)pyruvate and (2,3-13C2)pyruvate administered to 5th instar larvae. Gluconeogenic flux and blood trehalose concentration were positively correlated with

S. N. Thompson; D. B. Borchardt

2003-01-01

224

Efficient asymmetric synthesis of P-chiral phosphine oxides via properly designed and activated benzoxazaphosphinine-2-oxide agents.  

PubMed

A general, efficient, and highly diastereoselective method for the synthesis of structurally and sterically diverse P-chiral phosphine oxides was developed. The method relies on sequential nucleophilic substitution on the versatile chiral phosphinyl transfer agent 1,3,2-benzoxazaphosphinine-2-oxide, which features enhanced and differentiated P-N and P-O bond reactivity toward nucleophiles. The reactivities of both bonds are fine-tuned to allow cleavage to occur even with sterically hindered nucleophiles under mild conditions. PMID:23369026

Han, Zhengxu S; Goyal, Navneet; Herbage, Melissa A; Sieber, Joshua D; Qu, Bo; Xu, Yibo; Li, Zhibin; Reeves, Jonathan T; Desrosiers, Jean-Nicolas; Ma, Shengli; Grinberg, Nelu; Lee, Heewon; Mangunuru, Hari P R; Zhang, Yongda; Krishnamurthy, Dhileep; Lu, Bruce Z; Song, Jinhua J; Wang, Guijun; Senanayake, Chris H

2013-02-06

225

Concise asymmetric synthesis of a (1R,2S)-1-amino- 2-vinylcyclopropanecarboxylic acid-derived sulfonamide and ethyl ester.  

PubMed

The development and demonstration of short, robust and chromatography-free sequences for the preparation of a (1R,2S)-1-amino-2-vinylcyclopropane-carboxylic acid-derived sulfonamide and ethyl ester in ?99% ee are described. Both compounds are common building blocks in multiple preparations of potent HCV NS3 protease inhibitors. The robustness of the asymmetric cyclopropanation of (E)-N-benzylideneglycine ethyl ester under phase transfer catalysis conditions is significantly improved based on a detailed mechanistic investigation that included an analysis of the catalyst decomposition pathway, a postulated model for the stereo-selectivity that was guided by calculations and rigorous quality control of the starting materials and reagents. Wet milling has been demonstrated to dramatically accelerate this phase transfer reaction. A bench stable benzylidene-protected primary 1-amino-2-vinylcyclopropane amide intermediate was isolated and its reliable enantiomeric enrichment was achieved by a controlled crystallization process. A chemical resolution procedure was identified using di-p-toluoyl-(D)-tartaric acid to access (1R,2S)-1-amino-2-vinyl-cyclopropanecarboxylic ester in high ee. PMID:24175327

Lou, Sha; Cuniere, Nicolas; Su, Bao-Ning; Hobson, Lindsay A

2013-10-21

226

Synthesis and biological evaluation of asymmetric indole curcumin analogs as potential anti-inflammatory and antioxidant agents.  

PubMed

Abstract A series of asymmetric indole curcumin analogs were synthesized and evaluated as possible inhibiters of pro-inflammatory enzymes such as COX-2, pro-inflammatory cytokines as TNF-? and IL-6, trypsin and ?-glucuronidase. They were also tested for antioxidant activities. The results showed that compounds 5e and 5h were found to be the most potent inhibitors of COX-2 (83.33%, 82.50%) and ?-glucuronidase (67.80%, 64.12%). All the synthesized compounds exhibited promising activity against IL-6 in a range of 71-100% at 10?µM concentration. Compounds 5f, 5h, 5e, 5c and 5d showed significant inhibition against TNF-? (28-51%) and IL-6 (87-98%) with low toxicity (45-51%) against CCK-8 cells. With few exceptions, all other compounds were found to be good to excellent inhibitors of IL-6 and moderate inhibitors of TNF-?; however, the toxicity profiles of these compounds need to be ameliorated in further optimization studies. Amongst the tested compounds, 5c, 5b, 5j and 5g were found to possess excellent reducing activity and 5b, 5c and 5h were moderate DPPH (1,1-diphenyl-2-picryl hydrazine) radical scavengers. PMID:23356406

Bandgar, Babasaheb P; Kinkar, Santosh N; Chavan, Hemant V; Jalde, Shivkumar S; Shaikh, Rafik U; Gacche, Rajesh N

2013-01-28

227

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

228

Asymmetric synthesis and conformational analysis by NMR spectroscopy and MD of Aba- and ?-MeAba-containing dermorphin analogues.  

PubMed

Dermorphin analogues, containing a (S)- and (R)-4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one scaffold (Aba) and the ?-methylated analogues as conformationally constrained phenylalanines, were prepared. Asymmetric phase-transfer catalysis was unable to provide the (S)-?-Me-o-cyanophenylalanine precursor for (S)-?-MeAba in acceptable enantiomeric purity. However, by using a Schöllkopf chiral auxiliary, this intermediate was obtained in 88?% ee. [(S)-Aba?3-Gly?4]dermorphin retained ?-opioid affinity but displayed an increased ?-affinity. The corresponding R?epimer was considerably less potent. In contrast, the [(R)-?-MeAba?3-Gly?4]dermorphin isomer was more potent than its S?epimer. Tar-MD simulations of both non-methylated [Aba?3-Gly?4]dermorphin analogues showed a degree of folding at the C-terminal residues toward the N?terminus of the peptide, without however, adopting a stabilized ?-turn conformation. The ?-methylated analogues, on the other hand, exhibited a type?I/I' ?-turn conformation over the ?-MeAba?3 and Gly?4 residues, which was stabilized by a hydrogen bond involving Tyr?5-HN and D-Ala?2-CO. PMID:21990068

Vandormael, Bart; De Wachter, Rien; Martins, José C; Hendrickx, Pieter M S; Keresztes, Attila; Ballet, Steven; Mallareddy, Jayapal R; Tóth, Fanni; Tóth, Géza; Tourwé, Dirk

2011-08-29

229

Synthesis of C1-symmetric chiral secondary diamines and their applications in the asymmetric copper(II)-catalyzed Henry (nitroaldol) reactions.  

PubMed

A small library of C(1)-symmetric chiral diamines (L1-L9) was constructed via condensing exo-(-)-bornylamine or (+)-(1S,2S,5R)-menthylamine with various Cbz-protected amino acids. Among them, ligand L1/CuCl(2)·2H(2)O complex (2.5 mol %) shows outstanding catalytic efficiency for Henry reaction between a variety of aldehydes and nitroalkanes to afford the expected products in high yields (up to 98%) with excellent enantioselectivities (up to 99%) and moderate to good diastereoselectivities (up to 90:10). This process is air- and moisture tolerant and has been applied to the synthesis of (S)-2-amino-1-(3,4-dimethoxyphenyl)ethanol (9), a key intermediate for (S)-epinephrine and (S)-norepinephrine. On the basis of HRMS and X-ray diffraction analysis of the L1/CuCl(2) complex, a transition-state model was proposed to explain the origin of asymmetric induction. The low catalyst loading, excellent yields and enantioselectivities, inexpensive copper salt, and mild reaction conditions make our catalytic system to be practically useful. PMID:21190323

Zhou, Yirong; Dong, Junfang; Zhang, Fanglin; Gong, Yuefa

2010-12-29

230

Asymmetric synthesis of optically active 2,3-diarylsuccinic acids by oxidative homocoupling of chiral 3-(arylacetyl)-2-oxazolidones  

Microsoft Academic Search

Oxidative homocoupling of chiral 3-(arylacetyl)-2-oxazolidones 1 was achieved by treatment with DABCO-TiCl4 or DMAP-TiCl4 and afforded the corresponding dimers stereospecifically. The reaction of (4S)- and (4R)-substituted 1 gave (S,S)- and (R,R)-dimers respectively. The obtained dimers were easily transformed to the corresponding 2,3-diaryl succinic acids. This reaction therefore provides a useful method for the synthesis of optically pure 2,3-diarylsuccinic acids. The

Naoki Kise; Kimikage Kumada; Yuichi Terao; Nasuo Ueda

1998-01-01

231

Synthesis of novel GABA uptake inhibitors. Part 6: preparation and evaluation of N-Omega asymmetrically substituted nipecotic acid derivatives.  

PubMed

In a previous series of potent GABA uptake inhibitors published from this laboratory, we noticed that asymmetry in the substitution pattern of the bis-aromatic moiety in known GABA uptake inhibitors such as 4 [1-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid] and 5 [(R)-1-(4,4-bis(3-methyl-2-thienyl)-3-butenyl)-3-piperidinecarboxylic acid] was beneficial for high affinity. This led us to investigate asymmetric analogues of known symmetric GABA uptake inhibitors in which one of the aryl groups has been exchanged with an alkyl, alkylene or cycloalkylene moiety as well as other modifications in the lipophilic part. The in vitro values for inhibition of [(3)H]-GABA uptake in rat synaptosomes was determined for each compound, and it was found that several of the novel compounds inhibit GABA uptake as potently as their known symmetrical reference analogues. Several of the novel compounds were also evaluated for their ability to inhibit clonic seizures induced by a 15 mg/kg (ip) dose of methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) in vivo. Some of the compounds, for example 18 [(R)-1-(2-(((1,2-bis(2-fluorophenyl)ethylidene)amino)oxy)ethyl)-3-piperidinecarboxylic acid], show a high in vivo potency and protective index comparable with that of our recently launched anticonvulsant product, 5 [(R)-1-(4,4-bis(3-methyl-2-thienyl)-3-butenyl)-3-piperidinecarboxylic acid], and may therefore serve as second-generation drug candidates. PMID:11597457

Andersen, K E; Lau, J; Lundt, B F; Petersen, H; Huusfeldt, P O; Suzdak, P D; Swedberg, M D

2001-11-01

232

Discovery and application of new bacterial strains for asymmetric synthesis of L-tert-butyl leucine in high enantioselectivity.  

PubMed

Discovery of new bacterial strains with fast identification in a miniaturized system was performed for the synthesis of optically active L-tert-butyl leucine. With tert-butyl leucine amide as nitrogen source, one bacterial strain with high conversion and high enantioselectivity was discovered among 120 isolated microorganisms from local soils and identified as Mycobacterium sp. JX009. Glucose and ammonium chloride were examined as the good carbon source and nitrogen source for the cells' growth separately. The cells grew better at 30 °C and at pH 7.5 with higher activity of 2,650 U/l in comparison with other conditions. Cells' stability was improved by immobilization on synthetic resin 0730 without pretreatment. Tert-butyl leucine amide (30 mM) was successfully hydrolyzed by immobilized cells and examined as the highest chemical concentration that cells could endure. After six reaction cycles, the immobilized cells retained 90% activity with production of L-tert-butyl leucine in 98% ee. The results firstly reported the application of new bacterial strain in the hydrolysis of tert-butyl leucine amide to produce optically active L-tert-butyl leucine in an efficient way with investigation in detail. PMID:21153891

Jin, Jian-Zhong; Chang, Dong-Liang; Zhang, Jie

2010-12-14

233

Asymmetric synthesis of chiral organofluorine compounds: use of nonracemic fluoroiodoacetic acid as a practical electrophile and its application to the synthesis of monofluoro hydroxyethylene dipeptide isosteres within a novel series of HIV protease inhibitors.  

PubMed

Two stereoselective routes to a series of diastereomeric inhibitors of HIV protease, monofluorinated analogues of the Merck HIV protease inhibitor indinavir, are described. The two routes feature stereoselective construction of the fluorinated core subunits by asymmetric alkylation reactions. The first-generation syntheses were based on the conjugate addition of the lithium enolate derived from pseudoephedrine alpha-fluoroacetamide to nitroalkene 12, a modestly diastereoselective transformation. A more practical second-generation synthetic route was developed that is based on a novel method for the asymmetric synthesis of organofluorine compounds, by enolate alkylation using optically active fluoroiodoacetic acid as the electrophile in combination with a chiral amide enolate. Resolution of fluoroiodoacetic acid with ephedrine provides either enantiomeric form of the electrophile in > or = 96% ee. Alkylation reactions with this stable and storable chiral fluorinated precursor are shown to proceed in a highly stereospecific manner. With the development of substrate-controlled syn- or anti-selective reductions of alpha-fluoro ketones 44 and 45 (diastereomeric ratios 12:1-84:1), efficient and stereoselective routes to each of the four targeted inhibitors were achieved. The optimized synthetic route to the most potent inhibitor (syn,syn-4, K(i) = 2.0 nM) proceeded in seven steps (87% average yield per step) from aminoindanol hydrocinnamide 40 and (S)-fluoroiodoacetic acid, and allowed for the preparation of more than 1 g of this compound. The inhibition of HIV-1 protease by each of the fluorinated inhibitors was evaluated in vitro, and the variation of potency as a function of inhibitor stereochemistry is discussed. PMID:11472148

Myers, A G; Barbay, J K; Zhong, B

2001-08-01

234

Asymmetric synthesis of nonracemic primary amines via spiroborate-catalyzed reduction of pure (E)- and (Z)-O-benzyloximes: applications toward the synthesis of calcimimetic agents.  

PubMed

Highly enantiopure (1-aryl)- and (1-naphthyl)-1-ethylamines were synthesized by the borane-mediated reduction of single-isomeric (E)- and (Z)-O-benzyloxime ethers using the stable spiroborate ester derived from (S)-diphenyl valinol and ethylene glycol as the chiral catalyst. Primary (R)-arylethylamines were prepared by the reduction of pure (Z)-ethanone oxime ethers in up to 99% ee using 15% of catalyst. Two convenient and facile approaches to the synthesis of new and known calcimimetic analogues employing enantiopure (1-naphthalen-1-yl)ethylamine as chiral precursor are described. PMID:23638707

Ou, Wenhua; Espinosa, Sandraliz; Meléndez, Héctor J; Farré, Silvia M; Alvarez, Jaime L; Torres, Valerie; Martínez, Ileanne; Santiago, Kiara M; Ortiz-Marciales, Margarita

2013-05-13

235

Shedding light on Brønsted acid catalysis--a photocyclization-reduction reaction for the asymmetric synthesis of tetrahydroquinolines from aminochalcones in batch and flow.  

PubMed

A new asymmetric photocyclization-reduction cascade employing readily available aminochalcones has been developed. The reaction sequence has been achieved by unifying photochemistry and asymmetric Brønsted acid catalysis and involves photocyclization followed by Brønsted acid catalyzed enantioselective hydrogenation in batch and flow. PMID:23903260

Liao, Hsuan-Hung; Hsiao, Chien-Chi; Sugiono, Erli; Rueping, Magnus

2013-07-31

236

Thioether-based anchimeric assistance for asymmetric coordination chemistry with ruthenium(II) and osmium(II).  

PubMed

(R)-4-(alkylthiomethyl)-5,5-dimethyl-2-(2'-hydroxyphenyl)-2-oxazolines are demonstrated to be highly suitable chiral auxiliaries for the two-step conversion of the half-sandwich complex [Ru(?(6)-C6H6)(bpy)Cl]Cl, bpy = 2,2'-bipyridine, into ?-configured ruthenium polypyridyl complexes. The tailored thioether substituent at the oxazoline ring is essential for this conversion and not only promotes the removal of the benzene moiety but also controls the absolute metal-centered configuration. Applied to osmium, this strategy resulted in the first highly asymmetric synthesis of ?-[Os(bpy)3](PF6)2. PMID:23503568

Chen, Liang-An; Ding, Xiaobing; Gong, Lei; Meggers, Eric

2013-04-28

237

Negative Absolute Temperatures  

Microsoft Academic Search

It is pointed out that there are a few physical systems whose temperature when measured on an absolute scale can assume negative values. Such temperatures are not colder than absolute zero; a system with a negative temperature can give heat to one at an infinite temperature and is therefore hotter. The mechanism for such negative temperatures is described, the main

Warren G. Proctor

1978-01-01

238

Absolute Lipschitz extendability  

Microsoft Academic Search

A metric space X is said to be absolutely Lipschitz extendable if every Lipschitz function f from X into any Banach space Z can be extended to any containing space Y?X, where the loss in the Lipschitz constant in the extension is independent of Y,Z, and f. We show that various classes of natural metric spaces are absolutely Lipschitz extendable.

James R. Lee; Assar Naor

2004-01-01

239

Synthesis, absolute configuration and biological activities of both enantiomers of 2-(5,7-Dichloro-3-indolyl)propionic acid: a novel dichloroindole auxin and antiauxin.  

PubMed

Racemic 2-(5,7-dichloro-3-indolyl)propionic acid (5,7-Cl(2)-2-IPA) was synthesized from 5,7-dichloroindole-3-acetic acid by successive esterification, methoxycarbonylation, methylation, and double hydrolysis. The racemate was converted to diastereomeric esters of l-menthol; these were separated by recycling HPLC into two optically active diastereomers that were then hydrolyzed with p-TsOH to two optically active enantiomers of 5,7-Cl(2)-2-IPA. The absolute configurations of both these enantiomers were determined by comparing the (1)H-NMR spectra of their diastereomeric l-menthyl esters with those of the diastereomeric l-menthyl esters of 2-(3-indolyl)propionic acid (2-IPA) of known absolute configurations.An assay by the coleoptile elongation of Avena sativa showed the (S)-(+)-enantiomer of 5,7-Cl(2)-2-IPA to have weak auxin activity, whereas the (R)-(-)-antipode had no auxin activity at any concentration tested. Interestingly, the (R)-(-)-enantiomer had antiauxin activity very close to that of 2-(5,7-dichloro-3-indolyl)isobutyric acid (5,7-Cl(2)-IIBA), a strong antiauxin. These data indicate that, of the two methyl groups in its molecule, the antiauxin activity of 5,7-Cl(2)-IIBA was due only to the (R)-methyl group. PMID:15215593

Katayama, Masato; Kato, Yasuhito; Marumo, Shingo

2004-06-01

240

Asymmetric Differentiation  

NASA Astrophysics Data System (ADS)

Asymmetric Differentiation is the name I have given to a novel method of looking for the point of no variation of a function defined by an integral (summation). The simplest example is that of the definite integral of F(x,p) from x = a to x = b where p is some parameter. Unlike the usual method of differentiation, this technique dis-continuously breaks the range of integration into two parts and considers p goes to p + Dp for x within [a,c] and p goes to p - Dp for x within [c,b] where a < c < b. What this process reveals about the underlying function depends on the context. For example, for a normalized probability distribution it produces the median. I further illustrate via a circle (compressed/expanded with a fixed area), an ellipse (stretched/tightened perimeter of fixed arc length), and a sphere (compressed/expanded surface of fixed area). The symmetry of these figures portends the result. Several conservative physical problems are solved by considering the variation of the action---a ball thrown off a building in a constant gravitational field, the simple harmonic oscillator, the spherical pendulum, a charged particle in a constant magnetic field, and the two-body problem. Finally, the financial engineering problem for which this method was invented is presented too.

Taff, L. G.

2001-04-01

241

Antineoplastic Agents 561. Total Synthesis of Respirantin1a  

PubMed Central

Total synthesis of the eighteen-membered ring cyclodepsipeptide believed to be respirantin (1b) has been achieved. The key step in the synthesis is an intramolecular transesterification of the ?-ketoester alcohol 6 to afford the protected macrocycle 5. The synthetic product was shown to be identical to a natural product presumed to be respirantin (1b) and the absolute stereochemistry of 6 of the 7 asymmetric centers of cyclodepsipeptide 1b was unequivocally established. Respirantin (1b) was found to be a remarkable inhibitor of cancer cell growth and related to the antimycin family of antibiotics.

Pettit, George R.; Smith, Thomas H.; Feng, Song; Knight, John C.; Tan, Rui; Pettit, Robin K.; Hinrichs, Peter A.

2008-01-01

242

Asymmetric catalysis in organic synthesis  

Microsoft Academic Search

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

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

1998-01-01

243

New androst-4-en-17-spiro-1,3,2-oxathiaphospholanes. Synthesis, assignment of absolute configuration and in vitro cytotoxic and antimicrobial activities.  

PubMed

The reactions of 17?-hydroxyprogesterone with Lawesson's reagent (LR) in toluene, CH(2)Cl(2) and/or CCl(4) gave, depending on the duration of the reaction, two diastereoisomeric androst-4-en-17-spiro-1,3,2-oxathiaphospholane-2-sulfide pairs 2a,b and 3a,b in approximately 7:3 ratio, differing in configuration at the phosphorus atom. A parallel analysis of heteronuclear 2D (1)H-(13)C spectra (HSQC and HMBC) and homonuclear 2D spectra (NOESY) enabled complete (1)H and (13)C assignments of each isomer. Also, analysis of NOESY correlations provided evidence for the preferred conformation. X-ray analysis of 3a confirmed the structure and absolute configuration on phosphorus. A pathway for the formation of 1,3,2-oxathiaphospholane ring was proposed. Cytotoxic activity in vitro was tested against three tumor cell lines (human cervix carcinoma HeLa cells and two human breast carcinoma MDA-MB-361 and MDA-MB-453 cells). Compound 3a and mixture 3a,b showed a moderate activity against HeLa and MDA-MB-453 cell lines while against MDA-MB-361 cell line all tested compounds exerted very weak cytotoxic effect. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, toxicity to brine shrimp Artemia salina, were evaluated. All tested compounds showed strong antifungal activity. PMID:22342468

Krsti?, Natalija M; Bjelakovi?, Mira S; Pavlovi?, Vladimir D; Robeyns, Koen; Jurani?, Zorica D; Mati?, Ivana; Novakovi?, Irena; Sladi?, Dušan M

2012-02-09

244

Asymmetric synthesis of L-azetidine-2-carboxylic acid and 3-substituted congeners—conformationally constrained analogs of phenylalanine, naphthylalanine, and leucine  

Microsoft Academic Search

Enantiopure L-azetidine-2-carboxylic acid, the (3R)-phenyl, (3R)-naphthyl and (3S)-isopropyl analogs were prepared based on a zinc-mediated asymmetric addition of allylic halides to the camphor sultam derivative of glyoxylic acid O-benzyl oxime.

Stephen Hanessian; Naomy Bernstein; Rui-Yang Yang; Robert Maguire

1999-01-01

245

?,?-CHF- and ?,?-CHCl-dGTP diastereomers: synthesis, discrete 31P NMR signatures and absolute configurations of new stereochemical probes for DNA polymerases  

PubMed Central

Deoxynucleoside 5?-triphosphate analogues in which the ?,?-bridging oxygen has been replaced with a CXY group are useful chemical probes to investigate DNA polymerase catalytic and base selection mechanisms. A limitation of such probes has been that conventional synthetic methods generate a mixture of diastereomers when the bridging carbon substitution is non-equivalent (X ? Y). We report here a general solution to this long-standing problem with four examples of individual ?,?-CXY dNTP diastereomers: (S)- and (R)-?,?-CHCl dGTP (12a-1, 12a-2) and (S)- and (R)-?,?-CHF dGTP (12b-1, 12b-2). Central to their preparation was conversion of the achiral parent bisphosphonic acids to P,C-dimorpholinamide derivatives (7) of their (R)-mandelic acid monoesters (6), which provided access to the individual diastereomers 7a-1, 7a-2, 7b-1, and 7b-2 by preparative HPLC. Selective acidic hydrolysis of the P-N bond then afforded the “ portal ” diastereomers 10, which were readily coupled to morpholine-activated dGMP. Removal of the chiral auxiliary by H2 (Pd/C) afforded the four individual diastereomeric nucleotides (12), which were characterized by 31P, 1H and 19F NMR, and by MS. After treatment with Chelex®-100 to remove traces of paramagnetic ions, at pH ~10 the diastereomer pairs 12a and 12b exhibit discrete P? and P? 31P resonances. The more upfield P? and more downfield P? resonances (and also the more upfield 19F NMR resonance in 12b) are assigned to the (R) configuration at the P?-CHX-P? carbons, based on the absolute configurations of the individual diastereomers as determined by X-ray crystallographic structures of their ternary complexes with DNA-pol ?.

Wu, Yue; Zakharova, Valeria M.; Kashemirov, Boris A.; Goodman, Myron F.; Batra, Vinod K.; Wilson, Samuel H.; McKenna, Charles E.

2012-01-01

246

?,?-CHF- and ?,?-CHCl-dGTP diastereomers: synthesis, discrete 31P NMR signatures, and absolute configurations of new stereochemical probes for DNA polymerases.  

PubMed

Deoxynucleoside 5'-triphosphate analogues in which the ?,?-bridging oxygen has been replaced with a CXY group are useful chemical probes to investigate DNA polymerase catalytic and base-selection mechanisms. A limitation of such probes has been that conventional synthetic methods generate a mixture of diastereomers when the bridging carbon substitution is nonequivalent (X ? Y). We report here a general solution to this long-standing problem with four examples of ?,?-CXY dNTP diastereomers: (S)- and (R)-?,?-CHCl-dGTP (12a-1/12a-2) and (S)- and (R)-?,?-CHF-dGTP (12b-1/12b-2). Central to their preparation was conversion of the prochiral parent bisphosphonic acids to the P,C-dimorpholinamide derivatives 7 of their (R)-mandelic acid monoesters, which provided access to the individual diastereomers 7a-1, 7a-2, 7b-1, and 7b-2 by preparative HPLC. Selective acidic hydrolysis of the P-N bond then afforded "portal" diastereomers, which were readily coupled to morpholine-activated dGMP. Removal of the chiral auxiliary by H(2) (Pd/C) gave the four individual diastereomeric nucleotides 12, which were characterized by (31)P, (1)H, and (19)F NMR spectroscopy and by mass spectrometry. After treatment with Chelex-100 to remove traces of paramagnetic ions, at pH ~10 the diastereomer pairs 12a,b exhibit discrete P(?) and P(?)(31)P resonances. The more upfield P(?) and more downfield P(?) resonances (and also the more upfield (19)F NMR resonance in 12b) are assigned to the R configuration at the P(?)-CHX-P(?) carbons on the basis of the absolute configurations of the individual diastereomers as determined from the X-ray crystallographic structures of their ternary complexes with DNA and polymerase ?. PMID:22397499

Wu, Yue; Zakharova, Valeria M; Kashemirov, Boris A; Goodman, Myron F; Batra, Vinod K; Wilson, Samuel H; McKenna, Charles E

2012-05-18

247

Absolute neutrino mass scale  

NASA Astrophysics Data System (ADS)

Neutrino oscillation experiments firmly established non-vanishing neutrino masses, a result that can be regarded as a strong motivation to extend the Standard Model. In spite of being the lightest massive particles, neutrinos likely represent an important bridge to new physics at very high energies and offer new opportunities to address some of the current cosmological puzzles, such as the matter-antimatter asymmetry of the Universe and Dark Matter. In this context, the determination of the absolute neutrino mass scale is a key issue within modern High Energy Physics. The talks in this parallel session well describe the current exciting experimental activity aiming to determining the absolute neutrino mass scale and offer an overview of a few models beyond the Standard Model that have been proposed in order to explain the neutrino masses giving a prediction for the absolute neutrino mass scale and solving the cosmological puzzles.

Capelli, Silvia; Di Bari, Pasquale

2013-04-01

248

Absolute radiation detector  

NASA Astrophysics Data System (ADS)

An absolute radiation detector (a cryogenic radiometer) is being developed to replace the existing UK primary national standard cryogenic radiometer with an improved uncertainty. The cryogenic radiometer will be capable of measuring black body radiation and laser radiation with an uncertainty approaching 10 ppm. From these measurements it will be possible to determine the fundamental constant, the Stefan Boltzmann constant, confirming the radiometer as an absolute detector, and link this determination to the SI unit of luminous intensity, the candela. Thus detector and source based scales/standards will be tied to an invariant physical quantity ensuring their long-term stability.

Martin, John E.

1996-11-01

249

Gas Transport Properties of Asymmetric Block Copolyimide Membranes  

Microsoft Academic Search

We have synthesized fluorinated block copolyimides with different block chain lengths by chemical imidization in a two-pot procedure and prepared the asymmetric coployimide membranes using the dry-wet phase inversion process. The gas transport properties of the asymmetric membranes were measured using a high vacuum apparatus equipped with a Baratron absolute pressure gauge at 76 cmHg and 35 °C. We demonstrated

Yumi Kashimura; Satoshi Aoyama; Hiroyoshi Kawakami

2009-01-01

250

NOVA: Absolute Zero  

NSDL National Science Digital Library

This NOVA website contains information about the scientific quest to utilize cold and to achieve the lowest temperature possible. Several interactive simulations present topics such as the states of matter, the anatomy of a refrigerator, and a virtual lab to achieve low temperatures. The site also includes articles on absolute hot, ultra-cold atoms, and milestones in cold research.

2008-04-06

251

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

252

Absolute configuration of franganine.  

PubMed

The absolute configuration of franganine (1), a cyclopeptide alkaloid isolated from the methanol root bark extract of Discaria americana, was established on the basis of detailed NMR spectroscopic data and X-ray diffraction analysis of its salt (2). PMID:22680778

Caro, Miguel S B; de Oliveira, Leonardo H; Ilha, Vinicius; Burrow, Robert A; Dalcol, Ionara I; Morel, Ademir F

2012-06-08

253

[Absolute configuration and enantiomeric purity of celiprolol].  

PubMed

The absolute configuration of (+)-celiprolol ([alpha]D = +6.3 degrees in CHCl3) was established by a 9-step synthesis via the (+) (R)-acetonide of (R)-glyceraldehyde. This result was confirmed by the Cupra-A CD-spectra of the isopropyl and hydroxy analogs. The enantiomeric purity was determined by NMR analysis of the diastereomeric amide esters obtained by reaction of celiprolol with 2 mol of alpha-methoxy-alpha-trifluoromethyl-phenylacetic acid chloride (Mosher's reagent). PMID:2946303

Hofer, O; Schlögl, K

1986-08-01

254

Asymmetric synthesis of ?-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: Aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of ?-amino acids.  

PubMed

This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of ?-amino-?-hydroxy and ?,?-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of ?-amino acids Schiff bases for deracemization of racemic ?-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure ?-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed. PMID:24043459

Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim

2013-09-17

255

Efficient synthesis of optically pure alcohols by asymmetric hydrogen-transfer biocatalysis: application of engineered enzymes in a 2-propanol–water medium  

Microsoft Academic Search

We describe an efficient method for producing both enantiomers of chiral alcohols by asymmetric hydrogen-transfer bioreduction\\u000a of ketones in a 2-propanol (IPA)–water medium with E. coli biocatalysts expressing phenylacetaldehyde reductase (PAR: wild-type and mutant enzymes) from Rhodococcus sp. ST-10 and alcohol dehydrogenase from Leifsonia sp. S749 (LSADH). We also describe the detailed properties of mutant PARs, Sar268, and HAR1, which

Nobuya Itoh; Kentaro Isotani; Masatoshi Nakamura; Kousuke Inoue; Yasuhiro Isogai; Yoshihide Makino

256

Rotational features of carbon-nitrogen bonds in axially chiral o- tert-butyl anilides and related molecules. Potential substrates for the ‘prochiral auxiliary’ approach to asymmetric synthesis  

Microsoft Academic Search

A new strategy for asymmetric induction termed the ‘prochiral auxiliary’ approach is introduced. Reactions of acylating agents with prochiral N-methyl-o-tert-butyl aniline provide anilides that are axially chiral by virtue of restricted rotation about the N?Ar bond. Rotamer populations about the amide bond (E\\/Z) were studied by 1H NMR. Several pairs of enantiomeric o-tert-butyl anilides were separated by chiral chromatography and

Dennis P. Curran; Gregory R. Hale; Steven J. Geib; Aaron Balog; Quezia B. Cass; Ana Luiza G. Degani; Marcelo Z. Hernandes; Luiz Carlos G. Freitas

1997-01-01

257

Dynamic kinetic resolution in the stereoselective synthesis of 4,5-diaryl cyclic sulfamidates by using chiral rhodium-catalyzed asymmetric transfer hydrogenation.  

PubMed

The dynamic kinetic resolution of 4,5-diaryl cyclic sulfamidate imines was achieved via asymmetric transfer hydrogenation using a HCO(2)H/Et(3)N mixture as the hydrogen source and chiral Rh catalysts (R,R)- or (S,S)-RhCl(TsDPEN)Cp* affording the corresponding cyclic sulfamidates in good yields with up to >20 : 1 dr and up to >99% ee. PMID:21331420

Han, Juae; Kang, Soyeong; Lee, Hyeon-Kyu

2011-02-18

258

Absolute beam brightness detector  

SciTech Connect

In generally accepted emittance measurement, main attention is concentrated on emittance areas {epsilon}{sub x}, {epsilon}{sub y} occupied by desired part of ion beam in transverse phase space and shape of these areas. The absolute beam phase density (brightness) as usually is not measured directly and the average beam brightness B is calculated from a beam intensity I and the transverse emittances. In the ion source and low energy beam transport (LEBT) optimization, it is important to preserve the beam brightness because some aberration of ion optic and beam instabilities can decrease the brightness of the central part of ion beam significantly. For these brightness measurements, it is convenient to use an absolute beam brightness detector with the brightness determination from one short considered in this article.

Dudnikov, Vadim [Muons, Inc., Batavia, Illinois 60510 (United States)

2012-02-15

259

Absolute E-rings  

Microsoft Academic Search

A ring R with 1 is called an E-ring if EndZR is ring-isomorphic to R under the canonical homomorphism taking the value 1? for any ??EndZR. Moreover R is an absolute E-ring if it remains an E-ring in every generic extension of the universe. E-rings are an important tool for algebraic topology as explained in the introduction. The existence of

Rüdiger Göbel; Daniel Herden; Saharon Shelah

2011-01-01

260

Asymmetric catalytic epoxidation of styrene by dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes synthesis and physicochemical studies  

Microsoft Academic Search

Some dissymmetric Mn(III) and Ru(III) chiral Schiff base complexes derived from 1R,2R(?)1,2-diaminocyclohexane with 3-acetyl-4-hydroxy-6-methyl-2-pyrone and salicylaldehyde, 5-chloro-5-methoxy-and 5-nitrosalicylaldehyde have been synthesized. The characterization of the complexes was accomplished by microanalysis, IR, UV-Vis, CD spectroscopy, conductance measurements, magnetic susceptibility, optical rotation and electrochemical studies. The asymmetric epoxidations catalyzed by the complexes were examined with styrene using the terminal oxidant, iodosylbenzene to

R. I. Kureshy; N. H. Khan; S. H. R. Abdi; A. K. Bhatt

1996-01-01

261

Synthesis and structural characterization of a carboxylate bridged tetranuclear copper complex derived from reduced Schiff base asymmetric compartmental ligand containing an amino acid side arm  

Microsoft Academic Search

The dinucleating asymmetric reduced Schiff base compartmental ligand H2L {2-[5-bromo-2-hydroxy-3-(4-methyl-piperazin-1-ylmethyl)-benzylamino]-propionic acid} (see Scheme 1 for H2L) gives the tetracopper(II) complex [Cu4L2(CH3COO)4]·2CH3CN·2H2O (1) on reaction with (CH3COO)2Cu·H2O. The single crystal X-ray structure of 1 reveals that this complex is a carboxylate bridged dimer of dinuclear copper(II) subunits, in which the copper(II) centers adopt different geometries, resulting in a {Cu4} complex.

Chullikkattil P. Pradeep; Panthapally S. Zacharias; Samar K. Das

2006-01-01

262

Solvent-free synthesis, DNA-topoisomerase II activity and molecular docking study of new asymmetrically N,N'-substituted ureas.  

PubMed

A new series of asymmetrically N,N'-substituted ureas 20–25 was prepared using solvent free conditions, which is an eco-friendly methodology, starting with Schiff bases derived from cinnamaldehyde and p-substituted anilines, which are subsequently submitted to reduction reactions that afford the corresponding asymmetric secondary amines. All of the intermediates were prepared using solvent free reactions, which were compared to traditional methodologies. All of the reactions required a remarkably short amount of time and provided good yields when solvent free conditions were employed compared to other methodologies. The DNA-topoisomerase II-? (topo II-?) activity was evaluated in relaxation assays, which showed that all of the compounds inhibited the enzyme activity at 10 ?M, except for urea 24. Furthermore, a molecular docking study indicated that the compounds 20–25 binding to the topo II-? are able to interact with the same binding site as the anticancer drug etoposide, suggesting that the ureas could inhibit the enzyme by the same mechanism of action observed for etoposide, which prevents re-ligation of the DNA strands. PMID:23117429

Esteves-Souza, Andressa; Rodrigues-Santos, Claudio E; Del Cistia, Catarina de Nigris; Silva, Daniel Rosa da; Sant'anna, Carlos Maurício R; Echevarria, Aurea

2012-11-01

263

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

264

Absolute configuration of odorine  

PubMed Central

The title compound, known as odorine or roxburghiline {systematic name: (S)-N-[(R)-1-cinnamoylpyrrolidin-2-yl]-2-methyl­butanamide}, C18H24N2O2, is a nitro­genous compound isolated from the leaves of Aglaia odorata. The absolute configuration was determined by refinement of the Flack parameter with data collected using Cu K? radiation showing positions 2 and 2? to be S and R, respectively. The pyrrolidine ring adopts an envelope conformation. In the crystal, mol­ecules are linked into chains along [010] by inter­molecular N—H?O hydrogen bonds.

Fun, Hoong-Kun; Chantrapromma, Suchada; Yodsaoue, Orapun; Karalai, Chatchanok

2010-01-01

265

Absolute configuration of odorine.  

PubMed

The title compound, known as odorine or roxburghiline {systematic name: (S)-N-[(R)-1-cinnamoylpyrrolidin-2-yl]-2-methyl-butanamide}, C(18)H(24)N(2)O(2), is a nitro-genous compound isolated from the leaves of Aglaia odorata. The absolute configuration was determined by refinement of the Flack parameter with data collected using Cu K? radiation showing positions 2 and 2' to be S and R, respectively. The pyrrolidine ring adopts an envelope conformation. In the crystal, mol-ecules are linked into chains along [010] by inter-molecular N-H?O hydrogen bonds. PMID:21588760

Fun, Hoong-Kun; Chantrapromma, Suchada; Yodsaoue, Orapun; Karalai, Chatchanok

2010-08-28

266

ABSOLUTE POLARIMETRY AT RHIC.  

SciTech Connect

Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy Of {Delta}P{sub beam}/P{sub beam} < 5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {Delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of AN in the CNI region (four-momentum transfer squared 0.001 < -t < 0.032 (GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

OKADA; BRAVAR, A.; BUNCE, G.; GILL, R.; HUANG, H.; MAKDISI, Y.; NASS, A.; WOOD, J.; ZELENSKI, Z.; ET AL.

2007-09-10

267

Synthesis, spectral, photolysis and electrochemical studies of mononuclear copper(II) complex with a new asymmetric tetradentate ligand: application as copper nanoparticle precursor.  

PubMed

A copper(II) complex with asymmetric tetradentate Schiff base ligand, obtained by the single condensation of 1,2-diaminopropane with 2-hydroxy-5-methoxy benzaldehyde was prepared. The ligand and complex were characterized by their IR, UV-Vis, FT-IR, NMR spectra and CV. Crystal structures of the mononuclear copper complex have been obtained by X-ray diffraction studies which revealed to be distorted square planner coordination geometry. The spectral data confirm coordination of ligand to copper ion center. The redox properties of complex at different scan rates exhibit grossly similar features consisting of an electrochemically pseudo-reversible Cu(II)/Cu(I) reduction at ca. -0.97 V and pseudo-reversible Cu(I)/Cu(II) oxidation at ca. -0.81 V. The copper nanoparticles with average size of 73 nm were formed by thermal reduction of copper complex in the presence of triphenylphosphine. PMID:22728968

Habibi, Mohammad Hossein; Mikhak, Maryam

2012-06-06

268

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

PubMed

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, (1)H NMR, (13)C 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 ZnL(2)A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain. PMID:23274224

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

2012-11-15

269

Catalytic asymmetric synthesis of 3-(alpha-hydroxy-beta-carbonyl) oxindoles by a Sc(III)-catalyzed direct aldol-type reaction.  

PubMed

A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) (Tf = trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93% yield, 99:1 diastereomeric ratio (dr), and >99% enantiomeric excess (ee)) under mild conditions, to deliver 3-(alpha-hydroxy-beta-carbonyl) oxindoles with vicinal quaternary-tertiary or quaternary-quaternary stereocenters. Even with 1 mol % catalyst loading or on scaleup (10 mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and Sc(III)-based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. PMID:20175165

Shen, Ke; Liu, Xiaohua; Zheng, Ke; Li, Wei; Hu, Xiaolei; Lin, Lili; Feng, Xiaoming

2010-03-22

270

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

271

Asymmetric cell division  

Microsoft Academic Search

Asymmetric cell division is a conserved mechanism for partitioning information during mitosis. Over the past several years, significant progress has been made in our understanding of how cells establish polarity during asymmetric cell division and how determinants, in the form of localized proteins and mRNAs, are segregated. In particular, genetic studies in Drosophila and Caenorhabditis elegans have linked cell polarity,

Fabrice Roegiers; Yuh Nung Jan

2004-01-01

272

Pd-catalyzed asymmetric allylic etherification using chiral biphenol-based diphosphinite ligands and its application for the formal total synthesis of (-)-galanthamine.  

PubMed

A library of novel chiral biphenol-based diphosphinite (BOP) ligands was designed and created. These BOP ligands were applied to a Pd-catalyzed intermolecular allylic etherification reaction, which provided a key intermediate for the formal total synthesis of (-)-galanthamine with 97% ee in 97% yield. PMID:23472673

Zang, Yang; Ojima, Iwao

2013-03-29

273

Optimized absolute testing method of shift-rotation.  

PubMed

The absolute testing method of shift-rotation that combines the traditional N-position method and Zernike polynomial fitting has been commonly employed in surface metrology. It preserves the high spatial frequency of the surface deviation with the N-position method to obtain the rotationally asymmetric surface deviation, but it suffers the kN? order angular terms errors missed by the N-position method when it calculates the rotationally symmetric surface deviation with the Zernike rotationally symmetric polynomial fitting method. An optimized absolute testing method of shift-rotation is presented in this paper. It considers the missing kN? order errors when the equations of the rotationally symmetric surface deviation are solved. As a result, it is more accurate than the traditional method. Experimental absolute results of spherical surfaces are given. PMID:24085219

Song, Weihong; Wu, Fan; Hou, Xi; Wan, Yongjian

2013-10-01

274

Per-6-amino-?-cyclodextrin as a chiral base catalyst promoting one-pot asymmetric synthesis of 2-aryl-2,3-dihydro-4-quinolones.  

PubMed

A highly efficient one-pot synthesis of enantiomerically enriched 2-aryl-2,3-dihydroquinolin-4(1H)-ones has been carried out for the first time using per-6-ABCD as a supramolecular host, chiral base catalyst, and a reusable promoter to give the corresponding scaffold with high yield (up to 99%) and enantiomeric excess (up to 99%). The catalyst is recovered and reused without loss in its activity. PMID:23245355

Kanagaraj, Kuppusamy; Pitchumani, Kasi

2012-12-27

275

Synthesis of 6,6?- and 6MeO–PEG–BINOL-Ca soluble polymer bound ligands and their application in asymmetric Michael and epoxidation reactions  

Microsoft Academic Search

Design and synthesis of a flexible spacer attached 6-MeO–PEG–BINOL ligand has been described. The enantioenriched Ca soluble polymer bound ligand (SPB-II) was generated utilizing easily available, eco-friendly CaCl2, and applied for CC as well as CO bond forming reactions. The ligand was precipitated adding diethylether, and the same ligand was used with equal efficiency for two more cycles.

G. Kumaraswamy; Nivedita Jena; M. N. V. Sastry; G. Venkata Rao; K. Ankamma

2005-01-01

276

Asymmetric synthesis of ( S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: Enantioselectivity and enzyme–substrate docking studies  

Microsoft Academic Search

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form

Jihye Jung; Hyun Joo Park; Ki-Nam Uhm; Dooil Kim; Hyung-Kwoun Kim

2010-01-01

277

Heterometallic Cu/Co and Cu/Co/Zn complexes bearing rare asymmetric tetranuclear cores: synthesis, structures, and magnetic and catalytic properties toward the peroxidative oxidation of cycloalkanes.  

PubMed

The three novel heterometallic complexes [CuCo(III)Co(II)(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.55)(H(2)O)(0.45)](H(2)O)(0.45) (1), [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.74)(H(2)O)(0.26)](H(2)O)(0.26) (2), and [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(DMF)] (3) have been prepared using a one-pot reaction of copper powder with cobalt chloride (1) and zinc nitrate (2, 3) in a methanol (1, 2) or dimethylformamide (3) solution of N-methyldiethanolamine. A search of the Cambridge Structural Database shows that the tetranuclear asymmetric cores M(4)(?(3)-X)(?-X)(5) of 1-3 represent an extremely rare case of M(4)X(6) arrays. The magnetic investigations of 1 disclose antiferromagnetic coupling in a Co(II)-Cu(II)-Co(II) exchange fragment with J(Co-Cu)/hc = -4.76 cm(-1), J(Co-Co)/hc = -2.76 cm(-1), and D(Co)/hc = +34.3 cm(-1). Compounds 1-3 act as precursors for the mild peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone with overall yields up to 23%. The synthetic and structural features as well as the thermogravimetric behavior and electrospray ionization mass spectrometry data are discussed. PMID:21506552

Nesterov, Dmytro S; Kokozay, Volodymyr N; Jezierska, Julia; Pavlyuk, Oleksiy V; Bo?a, Roman; Pombeiro, Armando J L

2011-04-20

278

Asymmetric synthesis of alpha-amino acids: preparation and alkylation of monocyclic iminolactones derived from alpha-methyl trans-cinnamaldehyde.  

PubMed

Two novel chiral monocyclic iminolactones 14a and 14b have been prepared. The chiral auxiliary 12 was obtained from alpha-methyl-trans-cinnamaldehyde through reduction, methylation, Sharpless asymmetric dihydroxylation, and oxidation in 87% overall yield. Esterification of compound 12 with the respective protected amino acids followed by deprotection and cyclization provided the corresponding iminolactones, each in 82% overall yield. Alkylation of the iminolactone 14a afforded the alpha-methyl-alpha,alpha-disubstituted products 15 and 16 in good yields (78-99%) and excellent diastereoselectivity (de >98%). Alkylations of the iminolactone 14b furnished the alpha-benzyl-alpha,alpha-disubstituted products 15a, 16b, 17, and 18 in good yields (51-86%) but moderate diastereoselectivities (43-56%). When HMPA or DMPU was used as a cosolvent, the rate of alkylation of the iminolactone 14b was accelerated with improved yields (56-99%) and diastereoselectivities (50-83%). Hydrolysis of the dialkylated iminolactones yielded the alpha,alpha-disubstituted alpha-amino acids in good yields (80-98%) and high enantiomeric excesses (98-99%) with good recovery of compound 12 (83-92%). PMID:18783273

Lu, Ta-Jung; Lin, Cheng-Kun

2008-12-19

279

Two 2D Cd(II) coordination polymers based on asymmetrical Schiff-base ligand: Synthesis, crystal structures and luminescent properties  

NASA Astrophysics Data System (ADS)

Two new two-dimensional coordination polymers [Cd3L2(SCN)6]n (1) and [CdLI2]n (2) have been synthesized and characterized by IR spectroscopy, elemental analysis, TG technique, XRPD and complete single crystal structure analysis, where L is 4-(pyridine-2-yl)methyleneamino-1,2,4-trizaole. Asymmetrical Schiff-base ligand L with five- and six-membered N-containing heterocyclic rings acts as a tridentate bridging ligand to bind two Cd(II) centers through one terminal Ntriazolyl and one pyridylimine chelate unit in 1 and 2. For polymer 1, tridentate bridging ligands link Cd-(1,3-?-SCN-) 1D inorganic chains to form a 2D layer network. The existence of Csbnd H⋯? and ?sbnd ? stacking interactions between 2D hybrid layers further gives rise to a 3D supramolecular network. In comparison with 1, polymer 2 shows a 2D layer network containing hexanuclear macrometallacyclic units. The 2D layers are staggered together through the combination of Csbnd H⋯? and ?sbnd ? stacking interactions and forming a 3D supramolecular structure. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

Dang, Dong-Bin; Li, Meng-Meng; Bai, Yan; Zhou, Rui-Min

2013-02-01

280

Recent developments in asymmetric multicomponent reactions.  

PubMed

Multicomponent reactions (MCRs) receive increasing attention because they address both diversity and complexity in organic synthesis. Thus, in principle diverse sets of relatively complex structures can be generated from simple starting materials in a single reaction step. The ever increasing need for optically pure compounds for pharmaceutical and agricultural applications as well as for catalysis promotes the development of asymmetric multicomponent reactions. In recent years, asymmetric multicomponent reactions have been applied to the total synthesis of various enantiopure natural products and commercial drugs, reducing the number of required reaction steps significantly. Although many developments in diastereoselective MCRs have been reported, the field of catalytic enantioselective MCRs has just started to blossom. This critical review describes developments in both diastereoselective and catalytic enantioselective multicomponent reactions since 2004. Significantly broadened scopes, new techniques, more environmentally benign methods and entirely novel MCRs reflect the increasingly inventive paths that synthetic chemist follow in this field. Until recently, enantioselective transition metal-catalyzed MCRs represented the majority of catalytic enantioselective MCRs. However, metal contamination is highly undesirable for drug synthesis. The emergence of organocatalysis greatly influences the quest for new asymmetric MCRs. PMID:22546840

de Graaff, Corien; Ruijter, Eelco; Orru, Romano V A

2012-05-21

281

Widely applicable synthesis of enantiomerically pure tertiary alkyl-containing 1-alkanols by zirconium-catalyzed asymmetric carboalumination of alkenes and palladium- or copper-catalyzed cross-coupling.  

PubMed

A highly enantioselective and widely applicable method for the synthesis of various chiral 2-alkyl-1-alkanols, especially those of feeble chirality, has been developed. It consists of zirconium-catalyzed asymmetric carboalumination of alkenes (ZACA), lipase-catalyzed acetylation, and palladium- or copper-catalyzed cross-coupling. By virtue of the high selectivity factor (E) associated with iodine, either (S)- or (R)-enantiomer of 3-iodo-2-alkyl-1-alkanols (1), prepared by ZACA reaction of allyl alcohol, can be readily purified to the level of ?99% ee by lipase-catalyzed acetylation. A variety of chiral tertiary alkyl-containing alcohols, including those that have been otherwise difficult to prepare, can now be synthesized in high enantiomeric purity by Pd- or Cu-catalyzed cross-coupling of (S)-1 or (R)-2 for introduction of various primary, secondary, and tertiary carbon groups with retention of all carbon skeletal features. These chiral tertiary alkyl-containing alcohols can be further converted into the corresponding acids with full retention of the stereochemistry. The synthetic utility of this method has been demonstrated in the highly enantioselective (?99% ee) and efficient syntheses of (R)-2-methyl-1-butanol and (R)- and (S)-arundic acids. PMID:23670801

Xu, Shiqing; Lee, Ching-Tien; Wang, Guangwei; Negishi, Ei-ichi

2013-05-13

282

An improved asymmetric total synthesis of (+)-biotin via the enantioselective desymmetrization of a meso-cyclic anhydride mediated by cinchona alkaloid-based sulfonamide  

Microsoft Academic Search

The highly enantioselective total synthesis of (+)-biotin 1 via the Hoffmann–Roche lactone–thiolactone strategy has been achieved starting from cis-1,3-dibenzyl-2-imidazolidone-4,5-dicarboxylic acid 2 with an overall yield of 35%. Two contiguous stereogenic centers at C-3a and C-6a were established through a rapid cinchona alkaloid-based sulfonamide-mediated enantioselective alcoholysis of meso-cyclic anhydride 3 to afford (4S,5R)-cinnamyl hemiester 4h, the direct precursor to (3aS,6aR)-lactone 5

Fei Xiong; Xu-Xiang Chen; Fen-Er Chen

2010-01-01

283

Absolute and other tolerances  

SciTech Connect

In a production process it is necessary to specify tolerances for characteristics such as dimensions, within which the measured characteristic must fall in order for the part to be acceptable. This tolerance can be based on both functional requirements and an allowance for measurement error. Sandia National Laboratories has provided general guidance for setting tolerances for its parts in Sandia General Requirements Specification 9900000, Sec. 3.3.2, titled Absolute Tolerance Concept. Implementing this guidance, particularly for parts other than Sandia's, has been a source of controversy, so in 1986 a Working Group of DOE statisticians undertook a study of statistical aspects of tolerance specification. This report presents the Group's analysis and findings. Several measures of consumer's risk were defined and then evaluated with respect to computational convenience, information requirement, rationale, and economic considerations. As an aid in setting tolerances, several cost models were considered and the optimum tolerances derived and compared. Because cost considerations have a major effect on the choice of tolerances, it is recommended that design and production personnel attempt to realistically model the cost of nonconformance in jointly arriving at appropriate measurement tolerances. 9 refs., 4 figs., 4 tabs.

Easterling, R.G.; Johnson, M.E.; Bement, T.R.; Nachtsheim, C.J.

1989-02-01

284

Absolute configuration of isoeichlerialactone.  

PubMed

The title seco-dammarane triterpenoid, C(27)H(42)O(4) (systematic name: 3-{(3S,3aR,5aR,6S,7S,9aR,9bR)-6,9a,9b-trimethyl-3-[(R)-2-methyl-5-oxotetra-hydro-furan-2-yl]-7-(prop-1-en-2-yl)dodeca-hydro-1H-cyclo-penta-[a]naphthalen-6-yl}propanoic acid), has been isolated for the first time from the seeds of Aglaia forbesii. The mol-ecule has three fused rings and all rings are in trans-fused. The two cyclo-hexane rings are in standard chair conformations and the cyclo-pentane ring adopts an envelope conformation. Its absolute configuration was determined by the refinement of the Flack parameter to 0.26?(17). In the crystal, mol-ecules are linked into chains along [010] by O-H?O hydrogen bonds. PMID:21580698

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

2010-03-20

285

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.

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

2010-01-01

286

Absolute neutrino mass measurements  

SciTech Connect

The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2{beta}) searches, single {beta}-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy.Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium {beta}-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope ({sup 137}Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R and D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2{beta} decay and single {beta}-decay.

Wolf, Joachim [Karlsruhe Institute of Technology (KIT), IEKP, Postfach 3640, 76021 Karlsruhe (Germany)

2011-10-06

287

Absolute Zero: Science Educator's Guide  

NSDL National Science Digital Library

This guide provides recommendations for curricular modules on low temperature physics. Designed for teachers and informal educators of middle school students. this guide complements the Absolute Zero Community Education Outreach Guide. Suggestions on leading discussions, increasing student participation, and the use of inquiry are included. 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

288

Synthesis of the C(21)-C(26) fragment of superstolide A: concerning the stereochemistry of (E)-crotylboration reactions of alaninal derivatives.  

PubMed

A stereoselective synthesis of the C(21)-C(26) fragment of superstolide A has been completed. The absolute and relative stereochemistry of intermediate 14 has been conclusively proven by NMR and X-ray diffraction methods. In the course of this work, it was found that the stereochemistry of 3 had been misassigned in our previously reported synthesis of the C(18)-C(26) segment. This error stems from the unexpected diastereoselectivity in the double asymmetric reaction of N-acetyl-d-alaninal 1 and the tartrate ester modified (E)-crotylboronate (R,R)-2. PMID:12737561

Yakelis, Neal A; Roush, William R

2003-05-16

289

Stereocontrolled synthesis of (?)-5,11-dideoxytetrodotoxin  

Microsoft Academic Search

Asymmetric synthesis of (?)-5,11-dideoxytetrodotoxin, an analog of puffer fish toxin, was accomplished from a common key intermediate through a novel hydroxylation at the C-8 position with neighboring group participation of trichloroacetamide, a highly stereoselective addition of acetylide as an equivalent of carboxylic acid, and a new guanidine synthesis from trichloroacetamide as key steps. This study presents the first asymmetric synthesis

Masanori Asai; Toshio Nishikawa; Norio Ohyabu; Noboru Yamamoto; Minoru Isobe

2001-01-01

290

Synthesis of asymmetric peroxides: transition metal (Cu, Fe, Mn, Co) catalyzed peroxidation of beta-dicarbonyl compounds with tert-butyl hydroperoxide.  

PubMed

The transition metal (Cu, Fe, Mn, Co) catalyzed peroxidation of beta-dicarbonyl compounds at the alpha position by tert-butyl hydroperoxide was discovered. A selective, experimentally convenient, and gram-scale method was developed for the synthesis of alpha-peroxidated derivatives of beta-diketones, beta-keto esters, and diethyl malonate. Virtually stoichiometric (2-3/1) molar ratios of tert-butyl hydroperoxide and a dicarbonyl compound were used in the reactions with beta-diketones and beta-keto esters. The target compounds were synthesized in the highest yields from beta-keto esters (45-90%) and in somewhat lower yields from beta-diketones (46-75%) and malonates (37-67%). PMID:20586497

Terent'ev, Alexander O; Borisov, Dmitry A; Yaremenko, Ivan A; Chernyshev, Vladimir V; Nikishin, Gennady I

2010-08-01

291

Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: enantioselectivity and enzyme-substrate docking studies.  

PubMed

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form alcohol. The homology models and docking models with ECOB and NADPH elucidated their substrate specificities and enantioselectivities. A glucose dehydrogenase-coupling reaction was used as NADPH recycling system to perform continuously the reduction reaction. Recombinant E. coli cell co-expressing YDL124W and Bacillus subtilis glucose dehydrogenase produced (S)-ECHB exclusively. PMID:20601218

Jung, Jihye; Park, Hyun Joo; Uhm, Ki-Nam; Kim, Dooil; Kim, Hyung-Kwoun

2010-06-20

292

Absolute Realizability of Predicate Formulas  

NASA Astrophysics Data System (ADS)

The concept of an absolutely realizable predicate formula is introduced. It can be regarded as a certain refinement of the concept of a constructively generally valid formula in predicate logic. It is proved that the class of all absolutely realizable formulas is a \\Pi^1_1-complete set.Bibliography: 16 titles.

Plisko, V. E.

1984-04-01

293

Absolute Identification by Relative Judgment  

ERIC Educational Resources Information Center

In unidimensional absolute identification tasks, participants identify stimuli that vary along a single dimension. Performance is surprisingly poor compared with discrimination of the same stimuli. Existing models assume that identification is achieved using long-term representations of absolute magnitudes. The authors propose an alternative…

Stewart, Neil; Brown, Gordon D. A.; Chater, Nick

2005-01-01

294

Synthesis and characterization of group 4 metal amides with new C2-symmetric binaphthyldiamine-based ligands and their use as catalysts for asymmetric hydroamination/cyclization.  

PubMed

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe(2))(4) (M = Ti, Zr) and chiral ligands, (R)-2,2'-bis(p-toluenesulfonylamino)-1,1'-binaphthyl (1H(2)), (R)-2,2'-bis(diphenylphosphinoylamino)-1,1'-binaphthyl (2H(2)), (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (3H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(pyrrol-2-ylmethyleneamino)-1,1'-binaphthyl (4H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (5H(2)), and (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitylenesulfonylamino)-1,1'-binaphthyl (6H(2)), which are derived from (R)-2,2'-diamino-1,1'-binaphthyl. Reaction of M(NMe(2))(4) with 1 equiv of arylsulfonylamides 1H(2) and 6H(2), diphenylphosphoramide 2H(2), mesitoylamides 3H(2) and 5H(2), or Schiff base ligand 4H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the chiral titanium amides (1)Ti(NMe(2))(2).3C(6)H(6) (7.3C(6)H(6)), (4)Ti(NMe(2))(2) (11), (5)Ti(NMe(2))(2) (13) and (6)Ti(NMe(2))(2) (15), and zirconium amides (1)Zr(NMe(2))(2) (8), (2)Zr(NMe(2))(2) (9), (3)Zr(NMe(2))(2) (10), (4)Zr(NMe(2))(2) (12), (5)Zr(NMe(2))(2) (14) and (6)Zr(NMe(2))(2).C(7)H(8) (16.C(7)H(8)) respectively, in good yields. These amides are stable below 90 degrees C in toluene solution, but they degrade via ligand redistribution at a higher temperature. For example, treatment of (1)Zr(NMe(2))(2) (8) or (5)Zr(NMe(2))(2) (14) in refluxing toluene for three days leads to the isolation of the complexes (1)(2)Zr.C(7)H(8) (17.C(7)H(8)) and (5)(2)Zr.3C(7)H(8) (18.3C(7)H(8)) respectively, in moderate yields. These new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 7-9, 11-13, and 15-18 have further been confirmed by X-ray diffraction analyses. The titanium amide 13 and all the zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to excellent yields with moderate to excellent ee values (up to 93%). Theoretical studies reveal the interaction between the carbon chain of the substrate and the sterically demanding ligand groups plays a key role in the stereodirection of the enantioselection during the Zr=N bond approaches to the C=C bond. PMID:20390168

Zi, Guofu; Zhang, Furen; Xiang, Li; Chen, Yue; Fang, Weihai; Song, Haibin

2010-02-23

295

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.

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

2009-01-01

296

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

297

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

298

Enantioselective synthesis of levomilnacipran.  

PubMed

A novel approach for the asymmetric synthesis of the active (1S,2R)-enantiomer of the antidepressant milnacipran is reported. The two stereogenic centers borne by the cyclopropane ring were sequentially installed starting from phenylacetic acid. PMID:22767143

Alliot, Julien; Gravel, Edmond; Pillon, Florence; Buisson, David-Alexandre; Nicolas, Marc; Doris, Eric

2012-07-06

299

Motion Parallax and Absolute Distance.  

National Technical Information Service (NTIS)

The accuracy of absolute distance estimation based on monocular motion parallax was determined both before and after specific training. With the usual distance information eliminated, subjects either held their heads stationary or rhythmically rotated the...

S. H. Ferris

1971-01-01

300

Measurement of the Absolute Branching Fraction of D0?K-?+  

NASA Astrophysics Data System (ADS)

We measure the absolute branching fraction for D0?K-?+ using partial reconstruction of B¯0?D*+X?-?¯? decays, in which only the charged lepton and the pion from the decay D*+?D0?+ are used. Based on a data sample of 230×106 BB¯ pairs collected at the ?(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D0?K-?+)=(4.007±0.037±0.072)%, where the first uncertainty is statistical and the second is systematic.

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.

2008-02-01

301

Palladium-catalyzed asymmetric benzylation of azlactones.  

PubMed

Asymmetric benzylation of prochiral azlactone nucleophiles enables the catalytic introduction of a benzyl group towards the synthesis of ?,?-disubstituted amino acids. Herein, we report an enantioselective palladium-catalyzed process using chiral bis(diphenylphosphinobenzoyl)diamine (dppba) ligands. Naphthalene- and heterocycle-based methyl carbonates react with a number of azlactones derived from both natural and unnatural amino acids. Monocyclic benzylic electrophiles, for which the barrier to ionization is higher, must employ a phosphate leaving group in order to react. Reaction conditions for electron-rich and -neutral benzylic electrophiles have been developed, and the scope of the reaction has been explored with respect to both reaction partners. The high levels of asymmetric induction, as well as the reactivity pattern of the electrophiles, suggest an ?(3) -benzyl intermediate that arises through two distinct pathways. PMID:24115047

Trost, Barry M; Czabaniuk, Lara C

2013-09-25

302

Asymmetric information and economics  

Microsoft Academic Search

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

B. Roy Frieden; Raymond J. Hawkins

2010-01-01

303

Asymmetric Conflict 2010.  

National Technical Information Service (NTIS)

The objective of this task was to evaluate how the challenges of asymmetric conflict will have changed over the two-decade period from the wake- up call provided by the Persian Gulf War to 2010. As a result of investments made under the Defense Counterpro...

B. Roberts

2000-01-01

304

Globalization and Asymmetrical Warfare.  

National Technical Information Service (NTIS)

Globalization is having a tremendous effect on the ability of terrorist and criminal organizations to act on a global scale. These organizations are using asymmetrical means to target U.S. interests at home and abroad. The events of September 11th were th...

W. J. Hartman

2002-01-01

305

CLINES WITH ASYMMETRIC MIGRATION  

Microsoft Academic Search

The consequences of asymmetric dispersion on the maintenance of an allele in a one-dimensional environmental pocket are examined. The diffusion model of migration and selection is restricted to a single diallelic locus in a monoe- cious population in the absence of mutation and random drift. It is further supposed that migration is homogeneous and independent of genotype, the population density

THOMAS NAGYLAKI

306

Payout and asymmetric information  

Microsoft Academic Search

This article investigates the effects of payout policy on the level of asymmetric information in the market for common equity shares. The results suggest that higher dividend levels are associated with lower price impact, both as a percentage of economic value and as a percentage of the spread. And greater share repurchase ratios are associated with lower price impacts as

Michel T. J. Rakotomavo

2010-01-01

307

Asymmetric cell division  

Microsoft Academic Search

With the recent identification of intrinsic cell-fate determinants for asymmetric cell division in several systems, biologists have begun to gain insight into the cellular mechanisms by which these determinants are preferentially segregated into one of the two daughter cells during mitosis so that the daughter cells acquire different fates.

Yuh Nung Jan; Lily Yeh Jan

1998-01-01

308

Asymmetric dimethylarginine in children with homocystinuria or phenylketonuria  

Microsoft Academic Search

Plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis from l-arginine and a cardiovascular risk factor, was found to be elevated in plasma of homocysteinemic adults. Enhanced cardiovascular\\u000a risk due to homocystinuria and impaired renal function has been found in patients with phenylketonuria (PKU) on protein-restricted\\u000a diet. However, it is still unknown whether ADMA synthesis

Nele Kanzelmeyer; Dimitrios Tsikas; Kristine Chobanyan-Jürgens; Bibiana Beckmann; Bernhard Vaske; Sabine Illsinger; Anibh M. Das; Thomas Lücke

309

Highly asymmetric rice genomes  

PubMed Central

Background Individuals in the same species are assumed to share the same genomic set. However, it is not unusual to find an orthologous gene only in small subset of the species, and recent genomic studies suggest that structural rearrangements are very frequent between genomes in the same species. Two recently sequenced rice genomes Oryza sativa L. var. Nipponbare and O. sativa L. var. 93-11 provide an opportunity to systematically investigate the extent of the gene repertoire polymorphism, even though the genomic data of 93-11 derived from whole-short-gun sequencing is not yet as complete as that of Nipponbare. Results We compared gene contents and the genomic locations between two rice genomes. Our conservative estimates suggest that at least 10% of the genes in the genomes were either under presence/absence polymorphism (5.2%) or asymmetrically located between genomes (4.7%). The proportion of these "asymmetric genes" varied largely among gene groups, in which disease resistance (R) genes and the RLK kinase gene group had 11.6 and 7.8 times higher proportion of asymmetric genes than housekeeping genes (Myb and MADS). The significant difference in the proportion of asymmetric genes among gene groups suggests that natural selection is responsible for maintaining genomic asymmetry. On the other hand, the nucleotide diversity in 17 R genes under presence/absence polymorphism was generally low (average nucleotide diversity = 0.0051). Conclusion The genomic symmetry was disrupted by 10% of asymmetric genes, which could cause genetic variation through more unequal crossing over, because these genes had no allelic counterparts to pair and then they were free to pair with homologues at non-allelic loci, during meiosis in heterozygotes. It might be a consequence of diversifying selection that increased the structural divergence among genomes, and of purifying selection that decreased nucleotide divergence in each R gene locus.

Ding, Jing; Araki, Hitoshi; Wang, Qiang; Zhang, Pengfei; Yang, Sihai; Chen, Jian-Qun; Tian, Dacheng

2007-01-01

310

Asymmetric pyrene derivatives for organic field-effect transistors.  

PubMed

For the synthesis of an ortho-dithienylpyrene, a K-region bromination of pyrene was developed which enabled the first reported, non-statistical asymmetric functionalization of pyrene at the 4, 5, 9 and 10 positions. Crystal structures, optical and electronic properties and FET characteristics have been investigated. PMID:21594241

Zöphel, Lukas; Beckmann, Dirk; Enkelmann, Volker; Chercka, Dennis; Rieger, Ralph; Müllen, Klaus

2011-05-18

311

An asymmetric aminohydroxylation approach to the azepine core of (-)-balanol.  

PubMed

[reaction: see text]An efficient formal synthesis of the potent protein kinase C inhibitor (-)-balanol that relies on a modified asymmetric aminohydroxylation of the alpha,beta-unsaturated aryl ester (1) is reported. The aryl ester functionality and the dihydroquinyl alkaloid ligand system (DHQ)2-AQN are used to control the regio- and enantioselectivity of the process. PMID:10990399

Masse, C E; Morgan, A J; Panek, J S

2000-08-24

312

Searching for asymmetric inductions in chiral smectic mesophases  

Microsoft Academic Search

Searching for asymmetric synthesis in smectic phases is, to our knowledge, reported for the first time in this paper. Two different reactions able to lead to optical enrichment were carried out in smectic phases (S) composed of chiral molecules. The first was a thermally promoted 1,3 dipolar cycloaddition of a diazo compound to a prochiral thiocarbonyl derivative run in a

L. Finzi; G. Maccagnani; S. Masiero; B. Samorí; P. Zani

1989-01-01

313

Asymmetric MRI Magnet Design Using a Hybrid Numerical Method  

Microsoft Academic Search

This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to

Huawei Zhao; Stuart Crozier; David M. Doddrell

1999-01-01

314

Asymmetric mineral mining plough  

SciTech Connect

A mineral mining plough for use in asymmetric ploughing, and movable to and fro alongside a conveyor, has a plough body provided with cutter means at its two ends. A first cutter means is arranged to win material when the plough is on the uphill run (That is to say when the plough moves in the opposite direction as the conveyor). A second cutter means is arranged to win material when the plough is on the downhill run. The second cutter means is mounted on the plough body for vertical movement relative to the plough body. This enables the second cutter means to be swung out of its working position (On the downhill run) to lie in a rest position (On the uphill run) in which it is in the path of travel of the first cutter means. This vertical movement of the second cutter means results in a plough of shorter length than known asymmetric ploughs.

Hauschopp, A.; Huss, H.; Rassmann, C.; Schwolow, G.

1981-07-28

315

JWST Absolute Flux Calibration Plan  

NASA Astrophysics Data System (ADS)

The plan for the absolute flux calibration of all JWST instruments will be described. The science goal is to be able to predict the absolute flux of stars for all JWST instruments to sub-1% accuracy. A set of A0V, solar, and hot stars have been picked as a preliminary calibration sample. This calibration sample has been chosen specifically to provide at least 5 stars of each type in all the observing modes of each JWST instrument. In addition to existing Hubble and Spitzer observations, ground-based high-resolution spectroscopy will be obtained to provide strong, independent constraints on the best fitting model stellar atmospheres for each star.

Gordon, Karl D.; Bohlin, R.

2013-01-01

316

Asymmetric WIMP dark matter  

Microsoft Academic Search

In existing dark matter models with global symmetries the relic abundance of dark matter is either equal to that of anti-dark matter (thermal WIMP), or vastly larger, with essentially no remaining anti-dark matter (asymmetric dark matter). By exploring the consequences of a primordial asymmetry on the coupled dark matter and anti-dark matter Boltzmann equations we find large regions of parameter

Michael L. Graesser; Ian M. Shoemaker; Luca Vecchi

2011-01-01

317

Asymmetric acoustic gratings  

NASA Astrophysics Data System (ADS)

The unidirectional transmission of acoustic waves is realized by a simple geometrically asymmetric steel grating structure. This exotic phenomenon stems from the one-way diffraction effect induced by the different periods of the slits on the both surfaces of the sample. And the frequency range of unidirectional transmission is simply determined by the structure periods. The experimental results agree well with the theoretical simulation. This remarkable effect is expected potential applications in ultrasonic devices, such as acoustic rectifiers and acoustic diodes.

He, Zhaojian; Peng, Shasha; Ye, Yangtao; Dai, Zhongwei; Qiu, Chunyin; Ke, Manzhu; Liu, Zhengyou

2011-02-01

318

Motion parallax and absolute distance  

Microsoft Academic Search

Determined the accuracy of absolute distance estimation based on monocular motion parallax both before and after specific training. With the usual distance information eliminated, 70 Navy enlisted men either held their heads stationary or rhythmically rotated their heads about a vertical axis while judging the distance of stimuli placed 1.22-4.57 m. away. Although distance perception was poor before training, head

Steven H. Ferris

1972-01-01

319

JWST Absolute Flux Calibration Planning  

Microsoft Academic Search

The planning for the absolute flux calibration of all four JWST science instruments will be described. The main goal is to provide a uniform calibration (photometric and spectrophotometric) across all instruments using a common set of calibration stars. These stars will include white dwarfs, A0V, and solar type stars. The combination of these different types of stars will serve to

Karl D. Gordon; R. Bohlin

2011-01-01

320

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

2012-03-21

321

An asymmetric total synthesis of (?)-fumagillol  

Microsoft Academic Search

(?)-Fumagillol (2), a hydrolysis product of fumagillin (1), has been synthesized in a highly stereoselective manner utilizing a glycolate Claisen rearrangement and an intramolecular ester enolate alkylation as key steps starting from carbohydrate-based precursor 5.

Deukjoon Kim; Soon Kil Ahn; Hoon Bae; Won Jun Choi; Hak Sung Kim

1997-01-01

322

Asymmetric Synthesis of Tertiary Benzylic Alcohols  

PubMed Central

Vinyl, aryl and alkynyl organometallics add to ketones containing a stereogenic sulfoxide. Tertiary alcohols are generated in diastereomerically and enantiomerically pure form. Reductive lithiation converts the sulfoxide into a variety of useful functional groups.

Antczak, Monika I.; Cai, Feng; Ready, Joseph M.

2010-01-01

323

Total synthesis of (-)-histrionicotoxin.  

PubMed

A total synthesis of (-)-histrionicotoxin was achieved. Our synthesis features preparation of a pseudosymmetrical dienyne through chirality transfer from an allenylsilane, a dienyne metathesis to produce the bicyclo [5.4.0] system in optically active form, selective functionalization of a diene via a 5-exo-trig iodoetherification, and an asymmetric propargylation. PMID:21793562

Adachi, Yohei; Kamei, Noriyuki; Yokoshima, Satoshi; Fukuyama, Tohru

2011-07-27

324

Three dimensional asymmetric model of the magnetopause  

NASA Astrophysics Data System (ADS)

We identify 542 magnetopause crossings from Interball, Geotail, Wind, Cluster, LANL and GOES for normal and extreme solar wind conditions. The magnetopause crossings cover the global region in the near-Earth space, and corresponding upstream solar wind parameters, including the density ratio of helium to hydrogen, are identified from ACE or Wind with 5-min resolution by shifting time to maximize the correlation between the clock angle of the IMF and that of magnetosheath field. Based on these data, a three dimensional asymmetric model of the magnetopause is developed for GSM coordinates by Levenberg Marquardt (LM) method for nonlinear parameter fitting. This model can describe the possible structures of the magnetopause shape (MPS), including east-west asymmetry in the YGSM direction, south-north asymmetry in the ZGSM direction, asymmetry between the east-west direction and the southnorth direction, and indentations in the vicinity of the north and south cusps. In order to give the appropriate initial values for the fitting coefficients and get the reasonable relationship between the interplanetary solar wind parameters and the MPS, we separate the fitting regions into three parts by the divided-fitting method: the sub solar region, the low-middle latitude region and the high latitude region. According to the decrease in the standard deviation from fitting, the asymmetric model of MPS is optionally parameterized by solar wind dynamic pressure (DP), interplanetary magnetic field (BZ), and dipole tilt angle (?). Considering saturation effects of IMF BZ and DP on the MPS, we use multinomial functions first and then select the saturated functions to replace them. The preliminary result in the investigation show that the standard deviation and the absolute deviation of this model are decreased to 0.908RE and 0.665RE, and that this asymmetric model is appropriate to predict the MPS for both normal and extreme solar wind conditions.

Lin, Ruilin

325

Entropy equation and absolute temperature  

Microsoft Academic Search

In this paper we consider the equivalence between the heat and the entropy balance laws. These two equations are related by\\u000a an integrating factor, which defines the absolute temperature. This result is obtained applying the thermodynamic laws to\\u000a a perfect fluid. So that, by means of the entropy equation we introduce the Second Law of Thermodynamics. Two particular cases\\u000a of

Giovambattista Amendola; Carlo Banfi; Mauro Fabrizio

2010-01-01

326

Least Absolute Relative Error Estimation  

PubMed Central

Multiplicative regression model or accelerated failure time model, which becomes linear regression model after logarithmic transformation, is useful in analyzing data with positive responses, such as stock prices or life times, that are particularly common in economic/financial or biomedical studies. Least squares or least absolute deviation are among the most widely used criterions in statistical estimation for linear regression model. However, in many practical applications, especially in treating, for example, stock price data, the size of relative error, rather than that of error itself, is the central concern of the practitioners. This paper offers an alternative to the traditional estimation methods by considering minimizing the least absolute relative errors for multiplicative regression models. We prove consistency and asymptotic normality and provide an inference approach via random weighting. We also specify the error distribution, with which the proposed least absolute relative errors estimation is efficient. Supportive evidence is shown in simulation studies. Application is illustrated in an analysis of stock returns in Hong Kong Stock Exchange.

CHEN, Kani; GUO, Shaojun; YING, Zhiliang

2013-01-01

327

Asymmetrically modified nucleosomes.  

PubMed

Mononucleosomes, the basic building blocks of chromatin, contain two copies of each core histone. The associated posttranslational modifications regulate essential chromatin-dependent processes, yet whether each histone copy is identically modified in vivo is unclear. We demonstrate that nucleosomes in embryonic stem cells, fibroblasts, and cancer cells exist in both symmetrically and asymmetrically modified populations for histone H3 lysine 27 di/trimethylation (H3K27me2/3) and H4K20me1. Further, we obtained direct physical evidence for bivalent nucleosomes carrying H3K4me3 or H3K36me3 along with H3K27me3, albeit on opposite H3 tails. Bivalency at target genes was resolved upon differentiation of ES cells. Polycomb repressive complex 2-mediated methylation of H3K27 was inhibited when nucleosomes contain symmetrically, but not asymmetrically, placed H3K4me3 or H3K36me3. These findings uncover a potential mechanism for the incorporation of bivalent features into nucleosomes and demonstrate how asymmetry might set the stage to diversify functional nucleosome states. PMID:23021224

Voigt, Philipp; LeRoy, Gary; Drury, William J; Zee, Barry M; Son, Jinsook; Beck, David B; Young, Nicolas L; Garcia, Benjamin A; Reinberg, Danny

2012-09-28

328

New methodology for the asymmetric reduction of ketones.  

PubMed

This review highlights recent reports, between 2000 and early 2002, of new methodologies for the asymmetric reduction of ketones, leading to the formation of alcohols. Since ketone reduction is a pivotal reaction in organic chemistry, and since its enantioselective variant constitutes an increasing fraction of this widely reported reaction, we have been highly selective in the choice of material. Emphasis will be placed on the application of asymmetric reduction of ketones to drug synthesis, on unusually novel applications and on new classes of reagents for these applications, the majority of which involve catalytic processes. The rapid rise of asymmetric transfer hydrogenation to prominence in recent years will be reflected by a high level of coverage in this review, while other more established methods (oxazaborolidines, hydrogenation) will also be featured. PMID:12478719

Wills, Martin; Hannedouche, Jerome

2002-11-01

329

Asymmetric Divisions of Germline Cells  

Microsoft Academic Search

In most vertebrates and invertebrates, germ cells produce female and male gametes after one or several rounds of asymmetric cell division. Germline-specific features are used for the asymmetric segregation of fates, chromosomes and size during gametogenesis. In Drosophila females, for example, a germline-specific organelle called the fusome is used repeatedly to polarize the divisions of germline stem cells for their

Pierre Fichelson; Jean-René Huynh

330

Preparation of asymmetric porous materials  

SciTech Connect

A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.

Coker, Eric N. (Albuquerque, NM)

2012-08-07

331

Competitive Equilibria with Asymmetric Information  

Microsoft Academic Search

This paper studies competitive equilibria in economies where agents trade in markets for standardized, non-exclusive financial contracts, under conditions of asymmetric information (both of the moral hazard and the adverse selection type). The problems for the existence of competitive equilibria in this framework are identified, and shown to be essentially the same under different forms of asymmetric information. We then

Alberto Bisin; Piero Gottardi

1999-01-01

332

Collateralized assets and asymmetric information  

Microsoft Academic Search

Introducing assets backed by physical collateral, we extend the [Cornet, B., De Boisdeffre, L., 2002. Arbitrage and price revelation with asymmetric information and incomplete markets. Journal of Mathematical Economics 38, 393–490.] model of asymmetric information to allow for default. We show that, independently of the financial-informational structure, equilibrium exists.

Myrian Petrassi; Juan Pablo Torres-Martínez

2008-01-01

333

Asymmetrical switch costs in children  

Microsoft Academic Search

Switching between tasks produces decreases in performance as compared to repeating the same task. Asymmetrical switch costs occur when switching between two tasks of unequal difficulty. This asymmetry occurs because the cost is greater when switching to the less difficult task than when switching to the more difficult task. Various theories about the origins of these asymmetrical switch costs have

Michelle R. Ellefson; Laura R. Shapiro; Nick Chater

2006-01-01

334

Identification of an Asymmetrically Localized Determinant, Ash1p, Required for Lineage-Specific Transcription of the Yeast HO Gene  

Microsoft Academic Search

S. cerevisiae cells exhibit asymmetric determination of cell fate. Cell division yields a mother cell, which is competent to transcribe the HO gene and switch mating type, and a daughter cell, which is not. We have isolated a mutant in which daughters transcribe HO and switch mating type. This mutation defines the ASH1 gene (asymmetric synthesis of HO). Deletion and

Anita Sil; Ira Herskowitz

1996-01-01

335

Mean-absolute deviation portfolio optimization for mortgage-backed securities  

Microsoft Academic Search

We develop an integrated simulation\\/optimization model for managing portfolios of mortgage-backed securities. The mortgage portfolio problem is viewed in the same spirit of models used for the management of portfolios of equities. That is, it trades off rates of return with a suitable measure of risk. In this respect we employ amean-absolute deviation model which is consistent with the asymmetric

Stavros A. Zenios; Pan Kang

1993-01-01

336

Absolute calibration of optical tweezers  

SciTech Connect

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB ('geometrical optics') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and 'jump' effects are also confirmed.

Viana, N.B.; Mazolli, A.; Maia Neto, P.A.; Nussenzveig, H.M.; Rocha, M.S.; Mesquita, O.N. [LPO-COPEA and Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 (Brazil); Departamento de Fisica, Instituto de Ciencias ExatasUniversidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 (Brazil)

2006-03-27

337

Asymmetric MRI Magnet Design Using a Hybrid Numerical Method  

NASA Astrophysics Data System (ADS)

This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries.

Zhao, Huawei; Crozier, Stuart; Doddrell, David M.

1999-12-01

338

Absolute Gravity Changes In Alaska  

NASA Astrophysics Data System (ADS)

Visco-elastic deformation models such as that of Soldati et al. [1999] predict time varying gravity signals associated with post-seismic deformation following the 1964 Prince William Sound earthquake (Mw=9.2). The rates of change are a function of the upper mantle viscosity. Aseismic creep is also a candidate mechanism for the deformation. The models differ in the spatial distribution of gravity changes; visco-elastic signals span a much larger region. Previous absolute gravity measurements have been made in Fairbanks, Alaska and Palmer, Alaska, during 1990-1991. Estimated uncertainties are in the 3-5 uGal range Visco-elastic gravity changes for Palmer are predicted to range from zero to tens of uGal, depending on the model viscosity and thickness parameters. New absolute gravity measurements at these sites are scheduled for September 2001, with 2 uGal estimated uncertainty. We hope to present initial results of the new measurements, with discussion of their implications for model testing. Different time series and instruments will be merged, and necessary corrections will be discussed

Sasagawa, G. S.

2001-12-01

339

Chlorine, an atom economical auxiliary for asymmetric aldol reactions.  

PubMed

An auxiliary strategy has been developed for asymmetric reactions of aldehydes in which the auxiliary itself is not chiral, but a single chlorine atom introduced via organocatalytic ?-chlorination. The stereodirecting influence of the chlorine atom is then exploited prior to its removal by radical reduction. This strategy is demonstrated in the synthesis of several aldols (92-99% ee) and the natural products (+)-dihydroyashabushiketol and (+)-solistatin. PMID:23370443

Halperin, Shira D; Britton, Robert

2013-02-13

340

Efficient and selective synthesis of (S,R,R,S,R,S)-4,6,8,10,16,18-hexamethyl-docosane via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction).  

PubMed

(S,R,R,S,R,S)-4,6,8,10,16,18-Hexamethyldocosane (1) was synthesized in 11% yield in 11 steps in the longest linear sequence from > or =98% pure (S)-beta-citronellal and 6 additional steps for the preparation of 11 in 23% yield from propene. Five of the six asymmetric carbon centers were generated catalytically and stereoselectively by the ZACA reaction (5 times), one lipase-catalyzed acetylation, and two chromatographic operations. PMID:18275210

Zhu, Gangguo; Liang, Bo; Negishi, Ei-ichi

2008-02-15

341

Bounded variation, absolute continuity and absolute integrability for fuzzy-number-valued functions  

Microsoft Academic Search

In this paper, the concepts of bounded variation and absolute continuity for the fuzzy-number-valued functions are presented and discussed by means of the representation of the absolute value for fuzzy numbers. The relations among bounded variation, absolute continuity, Kaleva's integral and fuzzy Henstock integral are characterized. Especially, the representation of absolute continuous fuzzy valued functions is given by Henstock (Kaleva)

Zengtai Gong; Wu Congxin

2002-01-01

342

Absolute configuration of xerophenone A.  

PubMed

The title compound, C(33)H(42)O(5), known as xerophenone A {systematic name: (1R,3R,4R,6S,8E,10R)-10-hy-droxy-8-[hy-droxy(phen-yl)methyl-ene]-4-methyl-1,6-bis-(3-methyl-but-2-en-1-yl)-3-(3-methyl-but-3-en-1-yl)-11-oxatricyclo-[4.3.1.1(4,10)]undecane-7,9-dione} is a naturally occurring rearranged benzophenone compound which was isolated from the twigs of Garcinia propinqua. The absolute configuration was determined by refining the Flack parameter to 0.18?(16). The absolute configurations at positions 1, 3, 4, 6 and 10 of the xerophenone A are R, R, R, S and R. In the mol-ecule, the cyclo-hexane-1,3-dione, tetra-hydro-2H-pyran and tetra-hydro-furan rings adopt twisted boat, standard chair and envelope conformations, respectively. The 3-methyl-but-3-en-1-yl substituent is disordered over two sets of sites in a 0.771?(11):0.229?(11) ratio. An intra-molecular O-H?O hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked by O-H?O and weak C-H?O inter-actions into a chain along the a axis. A very weak C-H?? inter-action and C?O short contact [2.989?(2)?Å] are also present. PMID:22590330

Fun, Hoong-Kun; Tantapakul, Cholpisut; Laphookhieo, Surat; Boonnak, Nawong; Chantrapromma, Suchada

2012-04-21

343

Absolute configuration of xerophenone A  

PubMed Central

The title compound, C33H42O5, known as xerophenone A {systematic name: (1R,3R,4R,6S,8E,10R)-10-hy­droxy-8-[hy­droxy(phen­yl)methyl­ene]-4-methyl-1,6-bis­(3-methyl­but-2-en-1-yl)-3-(3-methyl­but-3-en-1-yl)-11-oxatricyclo­[4.3.1.14,10]undecane-7,9-dione} is a naturally occurring rearranged benzophenone compound which was isolated from the twigs of Garcinia propinqua. The absolute configuration was determined by refining the Flack parameter to 0.18?(16). The absolute configurations at positions 1, 3, 4, 6 and 10 of the xerophenone A are R, R, R, S and R. In the mol­ecule, the cyclo­hexane-1,3-dione, tetra­hydro-2H-pyran and tetra­hydro­furan rings adopt twisted boat, standard chair and envelope conformations, respectively. The 3-methyl­but-3-en-1-yl substituent is disordered over two sets of sites in a 0.771?(11):0.229?(11) ratio. An intra­molecular O—H?O hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked by O—H?O and weak C—H?O inter­actions into a chain along the a axis. A very weak C—H?? inter­action and C?O short contact [2.989?(2)?Å] are also present.

Fun, Hoong-Kun; Tantapakul, Cholpisut; Laphookhieo, Surat; Boonnak, Nawong; Chantrapromma, Suchada

2012-01-01

344

Some noise properties of 2DFT MR images from asymmetrically sampled data.  

PubMed

This report describes noise statistics in 2DFT MR images, expanding the earlier work of Henkelman and others to include variably asymmetric sampling and conjugate synthesis reconstruction. The effects of low-order polynomial and Fourier phase correction used with conjugate synthesis are also explicitly considered. This analysis shows that complex images obtained by conjugate synthesis have an elliptical noise distribution, with the smaller axis corresponding to the imaginary image channel. Derivations and simulations predict a ratio of mean to standard deviation in the background of magnitude images varying from the known value of square root of pi/(4 - pi) (approximately 1.91) for full symmetry to square root of 2/(pi - 2) (approximately 1.32) at fully asymmetric or half-echo sampling; these predictions are validated over a range of asymmetry by experimental measurements. These results are important for predicting and interpreting image noise when using asymmetric sampling. PMID:1435597

Hua, J; Hurst, G C; Duerk, J L

345

Hereditarily Unicoherent Continua and Their Absolute Retracts  

Microsoft Academic Search

We investigate absolute retracts for classes of hereditarily unicoherent continua, tree-like continua, ?- dendroids, dendroids and some other related ones. The main results are: (1) the inverse limits of trees with confluent bond- ing mappings are absolute retracts of hereditarily unicoherent continua; (2) each tree-like continuum is embeddable in a spe- cial way in a tree-like absolute retract for the

Janusz J. Charatonik; W? odzimierz J. Charatonik; Janusz R. Prajs

2004-01-01

346

Synthesis of 2,3-Dihydro-1-phenylbenzo[b]phosphole (1-Phenylphosphindane) and Its Use as a Mechanistic Test in the Asymmetric Appel Reaction: Decisive Evidence against Involvement of Pseudorotation in the Stereoselecting Step.  

PubMed

Racemic 2,3-dihydro-1-phenylbenzo[b]phosphole was obtained by reduction of 1-phenylbenzo[b]phosphole-1-oxide, itself derived by ring-closing metathesis of phenylstyrylvinylphosphine oxide. The title compound was then reoxidized under asymmetric Appel conditions. Comparison of the sense and degree of the stereoselectivity to those obtained with an open-chain analogue indicated that the ring system does not affect the selectivity of the process. This in turn strongly suggests that the stereoselection is not related to pseudorotamer preferences in putative phosphorane intermediates. PMID:24079276

Carr, Damien J; Kudavalli, Jaya Satyanarayana; Dunne, Katherine S; Müller-Bunz, Helge; Gilheany, Declan G

2013-09-30

347

Enantioselective synthesis of 1-nitrotricyclo[5,2,2,0 2,6]undeca-3,8-dienes via tandem consecutive asymmetric Diels–Alder reaction–Cope rearrangement  

Microsoft Academic Search

The 1-glyco-2-nitrocyclohexa-2,4-dienes 1a and 5a react with cyclopentadiene to yield, almost exclusively, the 10-glyco-1-nitrotricyclo[5,2,2,02,6]undeca-3,8-dienes 4a and 8a. Formation of these products is explained as the result of a tandem consecutive asymmetric Diels–Alder reaction–Cope rearrangement. Periodate oxidation of deprotected sugar side-chains, followed by sodium borohydride reduction yielded enantiomerically pure 10-formyl- and 10-hydroxymethyl-1-nitrotricyclo[5,2,2,02,6]undeca-3,8-dienes. Structures have been determined by X-ray crystallographic and spectroscopic

E. Román; M. Baños; F. J. Higes; J. A. Serrano

1998-01-01

348

Synthesis and biodistribution of new oxo and nitrido 99mTc complexes with asymmetrical potentially dianionic or trianionic tetradentate SNNO ligands derived from methyl-2-aminocyclopentene-1-dithiocarboxylic acid.  

PubMed

In this work, 10 new asymmetrical tetradentate SNNO ligands were prepared by reaction of the amine function of methyl 2-[(beta-aminoethyl)amino]cyclopentene-1-dithiocarboxylate with various bifunctional substituents bearing hydroxyl/ketone and hydroxyl/aldehyde functional groups and with diethyl oxalate. 99mTc labeling efficiency was optimized by adjusting temperature and pH conditions. Seven nitrido and two oxo 99mTc complexes were isolated. Six of them proved to be stable near physiological conditions. Biodistribution studies in the rat showed a significant heart uptake for four of them and strong kidney and liver uptake for the other two. PMID:9466364

Belhadj-Tahar, H; Ouhayoun, E; Cros, G; Darbieu, M H; Tafani, J A; Fabre, J; Esquerre, J P; Coulais, Y

1998-01-01

349

Measurement of Absolute Magnetic Moment  

NASA Astrophysics Data System (ADS)

In the past NIST has issued a number of magnetic moment and magnetic susceptibility standards. One of the most popular has been the Ni magnetic moment standard in the form a 2.38 mm diameter sphere of annealed, high-purity nickel, issued in 1978. However, the supply of all the magnetic standards has been exhausted for several years now and the equipment used for their certification no longer exists. Currently, NIST is assembling a precision absolute magnetometer closely resembling the force-based system used earlier by Candela and Mundy (G.A. Candela and R.E. Mundy, Rev. Sci. Instr. 32, 1056 (1959).), but which will have improved accuracy. This magnetometer will be used to certify a new series of magnetic standards, the first of which will be a replacement nickel sphere. A sphere has the advantage that it has uniform magnetization and a known demagnetizing factor, and approximates a point dipole. Nickel has the advantage of saturation at low field, a small temperature dependence at room temperature, and a relatively small field dependence. Other standards with smaller moments and other geometries are also being considered. These, and the current state of the equipment development will be described.

Shull, R. D.; Swartzendruber, L. J.

1998-03-01

350

Absolute configuration of strictosidinic acid.  

PubMed

The absolute configuration of strictosidinic acid, (2S,3R,4S)-3-ethenyl-2-(?-D-glucopyranosyloxy)-4-{[(1S)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-1-yl]methyl}-3,4-dihydro-2H-pyran-5-carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2S,3R,4S)-3-ethenyl-2-(?-D-glucopyranosyloxy)-4-{[(1S)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-2-ium-1-yl]methyl}-3,4-dihydro-2H-pyran-5-carboxylate)sodium] chloride monohydrate], {[Na(C(26)H(32)N(2)O(9))(H(2)O)(2)]Cl·H(2)O}(n). The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O-H...O and O-H...Cl types. The solid-state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation. PMID:22476143

Castro, Rosane de P; Matos, Carolina da S; do Nascimento, Cláudia A; Oliveira, Cecília M A; Kato, Lucília; Lião, Luciano M; Sabino, José R

2012-03-14

351

Emphatic Visual Speech Synthesis  

Microsoft Academic Search

The synthesis of talking heads has been a flourishing research area over the last few years. Since human beings have an uncanny ability to read people's faces, most related applica- tions (e.g., advertising, video-teleconferencing) require absolutely realistic photometric and behavioral synthesis of faces. This paper proposes a person-specific facial synthesis framework that allows high realism and includes a novel way

Javier Melenchon; Elisa Martinez; Fernando De La Torre; José A. Montero

2009-01-01

352

MSTAR: a submicrometer absolute metrology system  

NASA Astrophysics Data System (ADS)

The Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor permits absolute distance measurement with subnanometer accuracy, an improvement of 4 orders of magnitude over current techniques. The system uses fast phase modulators to resolve the integer cycle ambiguity of standard interferometers. The concept is described and demonstrated over target distances up to 1 m. The design can be extended to kilometer-scale separations.

Lay, O. P.; Dubovitsky, S.; Peters, R. D.; Burger, J. P.; Ahn, S.-W.; Steier, W. H.; Fetterman, H. R.; Chang, Y.

2003-06-01

353

What is wrong with absolute individual fitness?  

Microsoft Academic Search

One of the most basic facts about evolution is that fitness is a relative concept. It does not matter how well an organism survives and reproduces, only that it does so better than other organisms bearing alternative traits. Nevertheless, many evolutionary arguments are framed in terms of absolute individual fitness. The absolute fitness criterion (AFC) can be justified in terms

David Sloan Wilson

2004-01-01

354

Indistinguishability of absolutely continuous and singular distributions  

Microsoft Academic Search

It is shown that there are no consistent decision rules for the hypothesis testing problem of distinguishing between absolutely continuous and purely singular probability distributions on the real line. In fact, there are no consistent decision rules for distinguishing between absolutely continuous distributions and distributions supported by Borel sets of Hausdorff dimension 0. It follows that there is no consistent

Steven P. Lalley; Andrew Nobel

2003-01-01

355

Absolute fission rates in the FFTF  

Microsoft Academic Search

The part of the FFTF Reactor Characterization Program reported in this paper is a measurement of absolute fission rates of eight major fuel isotopes at two different positions within the reactor. The instruments employed in these tests were fission ionization chambers for which the absolute efficiency and fissionable deposit mass assay have been rigorously established.

D. M. Gilliam; J. L. Fuller; J. A. Grundl; J. A. Rawlins; J. W. Daughtry

1981-01-01

356

Absolute Income, Relative Income, and Happiness  

ERIC Educational Resources Information Center

|This paper uses data from the World Values Survey to investigate how an individual's self-reported happiness is related to (i) the level of her income in absolute terms, and (ii) the level of her income relative to other people in her country. The main findings are that (i) both absolute and relative income are positively and significantly…

Ball, Richard; Chernova, Kateryna

2008-01-01

357

Enzymatic desymmetrization of 2-amino-2-methyl-1,3-propanediol: asymmetric synthesis of ( S)- N-Boc- N, O-isopropylidene-?-methylserinal and (4 R)-methyl-4-[2-(thiophen-2-yl)ethyl]oxazolidin-2-one  

Microsoft Academic Search

We report herein, the novel enzymatic desymmetrization of 2-tert-butoxycarbonylamino-2-methyl-1,3-propanediol 1. This method makes it possible to prepare (S)-N-Boc-N,O-isopropylidene-?-methylserinal 3, which is a chiral building block for the synthesis of a variety of ?-substituted alanine derivatives. Moreover, optically active (4R)-methyl-4-[2-(thiophen-2-yl)ethyl]oxazolidin-2-one 4, one of the key intermediates in the synthesis of a novel immunosuppressant, has been prepared by this methodology.

Takashi Tsuji; Yukiko Iio; Toshiyasu Takemoto; Takahide Nishi

2005-01-01

358

ASYMMETRIC SOLAR WIND ELECTRON DISTRIBUTIONS  

SciTech Connect

The present paper provides a possible explanation for the solar wind electron velocity distribution functions possessing asymmetric energetic tails. By numerically solving the electrostatic weak turbulence equations that involve nonlinear interactions among electrons, Langmuir waves, and ion-sound waves, it is shown that different ratios of ion-to-electron temperatures lead to the generation of varying degrees of asymmetric tails. The present finding may be applicable to observations in the solar wind near 1 AU and in other regions of the heliosphere and interplanetary space.

Yoon, Peter H.; Kim, Sunjung; Lee, Junggi; Lee, Junhyun; Park, Jongsun; Park, Kyungsun; Seough, Jungjoon [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Hong, Jinhy [Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701 (Korea, Republic of)

2012-08-20

359

Review of Asymmetric Dark Matter  

NASA Astrophysics Data System (ADS)

Asymmetric dark matter models are based on the hypothesis that the present-day abundance of dark matter has the same origin as the abundance of ordinary or "visible" matter: an asymmetry in the number densities of particles and antiparticles. They are largely motivated by the observed similarity in the mass densities of dark and visible matter, with the former observed to be about five times the latter. This review discusses the construction of asymmetric dark matter models, summarizes cosmological and astrophysical bounds, and touches on direct detection prospects and collider signatures.

Petraki, Kalliopi; Volkas, Raymond R.

2013-07-01

360

Suction performance and internal flow of a 2-bladed helical inducer with inlet asymmetric plate  

NASA Astrophysics Data System (ADS)

It has been found in our past studies that the installation of asymmetric plate at the inlet of inducer is effective for the suppression of cavitation surge phenomenon. In the present study, the suction performance of 2-bladed helical inducer with an inlet asymmetric plate is experimentally investigated. It is observed that the suction performance in large flow rate conditions is not significantly influenced by the asymmetric plate, whereas the head of inducer with the asymmetric plate increases just before the head breakdown in partial flow conditions. To understand the mechanism of this additional head, the flow measurements and the numerical simulations are carried out. It is found that the circumferential component of absolute velocity at the exit of inducer slightly increases with the development of cavitation in both cases with and without the inlet asymmetric plate, indicating the increase of the theoretical head. The theoretical head increase with the inlet asymmetric plate is also confirmed by the unsteady numerical simulations, suggesting that the additional head is achieved through the increase of the theoretical head with the change of the exiting flow from the inducer associated with some amount of cavitation.

Watanabe, S.; Uchinono, Y.; Ishizaka, K.; Furukawa, A.; Kim, J.-H.

2013-10-01

361

Numb Expression and Asymmetric versus Symmetric Cell Division in Distal Embryonic Lung Epithelium  

PubMed Central

Proper balance between self-renewal and differentiation of lung-specific progenitors is absolutely required for normal lung morphogenesis/regeneration. Therefore, understanding the behavior of lung epithelial stem/progenitor cells could identify innovative solutions for restoring normal lung morphogenesis and/or regeneration. The Notch inhibitor Numb is a key determinant of asymmetric or symmetric cell division and hence cell fate. Yet Numb proximal-distal expression pattern and symmetric versus asymmetric division are uncharacterized during lung epithelial development. Herein, the authors find that the cell fate determinant Numb is highly expressed and asymmetrically distributed at the apical side of distal epithelial progenitors and segregated to one daughter cell in most mitotic cells. Knocking down Numb in MLE15 epithelial cells significantly increased the number of cells expressing the progenitor cell markers Sox9/Id2. Furthermore, cadherin hole analysis revealed that most distal epithelial stem/progenitor cells in embryonic lungs divide asymmetrically; with their cleavage, planes are predicted to bypass the cadherin hole, resulting in asymmetric distribution of the cadherin hole to the daughter cells. These novel findings provide evidence for asymmetric cell division in distal epithelial stem/progenitor cells of embryonic lungs and a framework for future translationally oriented studies in this area.

El-Hashash, Ahmed H. K.

2012-01-01

362

Enantioselective synthesis of (+)-malbrancheamide B.  

PubMed

The asymmetric total synthesis of the chlorinated [2.2.2]-diazabicyclic indole alkaloid (+)-malbrancheamide B is reported. Key to the synthesis is a domino reaction sequence that employs an aldol condensation, alkene isomerization, and intramolecular Diels-Alder cycloaddition. Diastereofacial selection between the azadiene stereofaces is enforced with a chiral aminal auxiliary. A formal 7-step (longest linear route) synthesis of (±)-malbrancheamide B is also reported. PMID:23360221

Laws, Stephen W; Scheerer, Jonathan R

2013-02-08

363

Asymmetrical Switch Costs in Children  

ERIC Educational Resources Information Center

|Switching between tasks produces decreases in performance as compared to repeating the same task. Asymmetrical switch costs occur when switching between two tasks of unequal difficulty. This asymmetry occurs because the cost is greater when switching to the less difficult task than when switching to the more difficult task. Various theories about…

Ellefson, Michelle R.; Shapiron, Laura R.; Chater, Nick

2006-01-01

364

Asymmetric spasms in west syndrome  

Microsoft Academic Search

We studied 6 patients with asymmetric spasms who comprised 16.2% of 37 patients with West syndrome (WS) who demonstrated clusters of tonic spasms on simultaneous video-EEG recordings. Neuroimaging studies showed diffuse cerebral abnormalities in 3 of 6 patients and unilateral hemispheric lesions in the remaining 3. In 3, the clusters of spasms occurred soon after a preceding partial seizure. Lateral

Yoshiko Haga; Kazuyoshi Watanabe; Tamiko Negoro; Kosaburo Aso; Masao Kitoh; Norihide Maeda; Takashi Ohki

1995-01-01

365

Stable walking with asymmetric legs  

Microsoft Academic Search

Asymmetric leg function is often an undesired side-effect in artificial legged systems and may reflect functional deficits or variations in the mechanical construction. It can also be found in legged locomotion in humans and animals such as after an accident or in specific gait patterns. So far, it is not clear to what extent differences in the leg function of

Andreas Merker; Juergen Rummel; Andre Seyfarth

2011-01-01

366

Generalized Asymmetrical Bidirectional Associative Memory  

Microsoft Academic Search

A classical bidirectional associative memory (BAM) suffers from low storage capacity and abundance of spurious memories though it has the properties of good generalization and noise immunity. In this paper, Ham- ming distance in recall procedure of usual asymmetrical BAM is replaced with modified Hamming distance by introducing weighting matrix into connection matrix. This generalization is validated to increase storage

Tae-Dok Eom; Changkyu Choi; Ju-Jang Lee

367

Asymmetric Information in Financial Markets  

Microsoft Academic Search

Asymmetric information (the fact that borrowers have better information than their lenders) and its theoretical and practical evidence now forms part of the basic tool kit of every financial economist. It is a phenomenon that has major implications for a number of economic and financial issues ranging from both micro and macroeconomic level - corporate debt, investment and dividend policies,

Ricardo N. Bebczuk; N Ricardo

368

Asymmetric information and financial markets  

Microsoft Academic Search

This paper aims to explore the relevance of the Asymmetric Information and the Theory of Argumentation TA in the complex area of financial crises. Specifically, we investigated the scope of the phenomenon of persuasion in advertising. It examines advertisements in publications notable economic movement in Colombia. The financial communication is important to distinguish how to run the models of behavior

Fernando Estrada

2012-01-01

369

The Brokerage of Asymmetric Information  

Microsoft Academic Search

In this paper we oversee the logic of information sets, firstly handling information and markets in perfect environments and, secondly, dealing with information and markets in imperfect environments, in the context of bounded rationality. Further on, asymmetric information is addressed together with the role of opportunistic behaviour through hidden action, hidden information, the free-rider problem and signaling, expanding on financial

Rodolfo Apreda

2001-01-01

370

Variable angle asymmetric cut monochromator.  

National Technical Information Service (NTIS)

A variable incident angle, asymmetric cut, double crystal monochromator was tested for use on beamlines at the Advanced Photon Source (APS). For both undulator and wiggler beams the monochromator can expand area of footprint of beam on surface of the crys...

R. K. Smither P. B. Fernandez

1993-01-01

371

Three-phase asymmetrical load-flow  

Microsoft Academic Search

This paper deals with the three-phase asymmetrical load-flow problem. It presents a solution of this problem in the sequence domain, which is more efficient than standard solutions in both the phase and the sequence domain. It specially copes with the asymmetrical states of unbalanced power systems. The efficiency is achieved by introducing the following basic advancements of the standard asymmetrical

V. C. Strezoski; L. D. Trpezanovski

2000-01-01

372

Challenging the absence of observable hydrogens in the assignment of absolute configurations by NMR: application to chiral primary alcohols.  

PubMed

The absolute configuration of beta-chiral primary alcohols devoid of observable hydrogens on one of the beta-substituents at the asymmetric carbon (L(1)/L(2)) can be determined by comparison of the (1)H NMR of their (R)- and (S)-9-AMA ester derivatives and analysis of the Deltadelta(RS) for the L substituent and the Cbeta-H. PMID:17389991

Freire, Félix; Seco, José Manuel; Quiñoá, Emilio; Riguera, Ricardo

2007-01-30

373

There is Neither Classical Bug with a Superluminal Shadow Nor Quantum Absolute Collapse Nor (Subquantum) Superluminal Hidden Variable  

Microsoft Academic Search

In this work we analyse critically Griffiths's example of the classical superluminal motion of a bug shadow. Griffiths considers that this example is conceptually very close to quantum nonlocality or superluminality,i.e. quantum breaking of the famous Bell inequality. Or, generally, he suggests implicitly an absolute asymmetric duality (subluminality vs. superluminality) principle in any fundamental physical theory.It, he hopes, can be

Vladan Pankovic; Milan Predojevic; Miodrag Krmar; Milan Radovanovic

2005-01-01

374

Catalytic asymmetric carbon-carbon bond formation via allylic alkylations with organolithium compounds  

Microsoft Academic Search

Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general

Manuel Pérez; Martín Fañanás-Mastral; Pieter H. Bos; Alena Rudolph; Syuzanna R. Harutyunyan; Ben L. Feringa

2011-01-01

375

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.

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

2013-01-01

376

Nucleophilic addition of methyllithium to chiral oxime ethers: asymmetric preparation of 1-(aryl)ethylamines and application to a synthesis of calcimimetics (+)NPS R-568 and its thio analogue  

Microsoft Academic Search

Chiral (E)-arylaldehyde oxime ethers, prepared using (R)-1-phenyl-1,2-ethanediol as a chiral auxiliary, undergo nucleophilic addition with methyllithium to give diastereomerically enriched O-alkyl hydroxylamines which, after reductive N?O bond cleavage, lead to the corresponding (R)-1-(aryl)ethylamines. This methodology has been applied to the enantioselective synthesis of a new type of arylalkylamine calcimimetics (R)-(+)-NPS R-568 and its thio analogue.

Naoki Yamazaki; Masakazu Atobe; Chihiro Kibayashi

2001-01-01

377

The Simplicity Argument and Absolute Morality  

ERIC Educational Resources Information Center

|In this paper the author has maintained that there is a similarity of thought to be found in the writings of Cudworth, Emerson, and Husserl in his investigation of an absolute system of morality. (Author/RK)|

Mijuskovic, Ben

1975-01-01

378

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

379

Absolute calibration technique for spontaneous fission sources  

SciTech Connect

An absolute calibration technique for a spontaneously fissioning nuclide (which involves no arbitrary parameters) allows unique determination of the detector efficiency for that nuclide, hence of the fission source strength.

Zucker, M.S.; Karpf, E.

1984-01-01

380

A New Gimmick for Assigning Absolute Configuration.  

ERIC Educational Resources Information Center

|A five-step procedure is provided to help students in making the assignment absolute configuration less bothersome. Examples for both single (2-butanol) and multi-chiral carbon (3-chloro-2-butanol) molecules are included. (JN)|

Ayorinde, F. O.

1983-01-01

381

A New Gimmick for Assigning Absolute Configuration.  

ERIC Educational Resources Information Center

A five-step procedure is provided to help students in making the assignment absolute configuration less bothersome. Examples for both single (2-butanol) and multi-chiral carbon (3-chloro-2-butanol) molecules are included. (JN)

Ayorinde, F. O.

1983-01-01

382

Sensor of Ratios of Absolute Gas Pressures.  

National Technical Information Service (NTIS)

The article describes a sensor of ratios of absolute gas pressures containing elastic sensitive elements picking up pressures and acting on a compensation spring system transmitting the force onto a tensometric converter which for the purpose of improving...

G. I. Tyukel L. A. Pletnev

1967-01-01

383

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

2008-02-06

384

MSTAR: a submicrometer absolute metrology system.  

PubMed

The Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor permits absolute distance measurement with subnanometer accuracy, an improvement of 4 orders of magnitude over current techniques. The system uses fast phase modulators to resolve the integer cycle ambiguity of standard interferometers. The concept is described and demonstrated over target distances up to 1 m. The design can be extended to kilometer-scale separations. PMID:12816236

Lay, O P; Dubovitsky, S; Peters, R D; Burger, J P; Ahn, S W; Steier, W H; Fetterman, H R; Chang, Y

2003-06-01

385

Nonlinear constraints in the absolute coordinate formulation  

Microsoft Academic Search

Summary  The modeling of deformation in flexible multibody systems is still under intensive investigation. While the floating frame\\u000a of reference formulation has become a standard for the modeling of deformable moving bodies, formulations based on absolute\\u000a coordinates are comparatively new. The recently developed absolute nodal coordinate formulation uses solely nodal position\\u000a and slopes as degrees of freedom for structural elements. The

J. Gerstmayr

2007-01-01

386

Kelvin and the absolute temperature scale  

NASA Astrophysics Data System (ADS)

This paper describes the absolute temperature scale of Kelvin (William Thomson). Kelvin found that Carnot's axiom about heat being a conserved quantity had to be abandoned. Nevertheless, he found that Carnot's fundamental work on heat engines was correct. Using the concept of a Carnot engine Kelvin found that Q1/Q2 = T1/T2. Thermometers are not used to obtain absolute temperatures since they are calculated temperatures.

Erlichson, Herman

2001-07-01

387

New 'side-off' coordination asymmetric homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes as models for hydrolysis of p-nitrophenylphosphate: synthesis, characterization and electrochemical studies.  

PubMed

A series of new phenol based coordination asymmetric side-off homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. The electronic spectra of all the complexes show "Red shift" in LMCT band, for the ligand H(2)L(2) having electron donating C(2)H(5) groups as N-substituents in the free side arms compared to ligand H(2)L(1) having relatively lower electron donating CH(3) groups. Electrochemical studies of the complexes reveal that all the binuclear complexes show two irreversible one-electron transfer reduction waves in the cathodic region. There is an "anodic shift" in the first reduction potential of the complexes of the ligand H(2)L(1) when compared to that of the complexes of the ligand H(2)L(2) due to the presence of higher electron donating C(2)H(5) N-substituents in the later case than the relatively lower electron donating N-substituents in the former case. Hydrolysis of p-nitrophenylphosphate using homobinuclear Ni(II) and heterobinuclear Ni(II)-Zn(II) complexes as catalysts showed that the homobinuclear complexes have higher rate constant values than that of the corresponding heterobinuclear complexes. A comparison of the spectral, electrochemical and catalytic behavior of the complexes of the ligands is discussed on the basis of the electron donating nature of the N-substituents at the free side arms. PMID:23314389

Shanmuga Bharathi, K; Sreedaran, S; Kalilur Rahiman, A; Narayanan, Vengidusamy

2012-12-20

388

Asymmetric contests with general technologies  

Microsoft Academic Search

Summary. We investigate the pure-strategy Nash equilibria of asymmetric, winner-take-all, imperfectly discriminating contests, focussing on existence, uniqueness and rent dissipation. When the contest success function is determined by a production function with decreasing returns for each contestant, there is a unique pure-strategy equilibrium. If marginal product is also bounded, limiting total expenditure is equal to the value of the prize

Richard Cornes; Roger Hartley

2005-01-01

389

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

390

Nonlinear Resonance in Asymmetric Oscillators  

Microsoft Academic Search

We study the periodic solutions of equations with asymmetric nonlinearities “at resonance” with the Fu???k spectrum. We compute the associated topological degree and prove existence, multiplicity, and stability of large-amplitude oscillations for equations with a small friction term. Such equations can be viewed, e.g., as simple models for investigating vertical oscillations of long-span suspension bridges. The results are typically of

Christian Fabry; Alessandro Fonda

1998-01-01

391

Deformation of an asymmetric film  

NASA Astrophysics Data System (ADS)

Recent 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 [1,2], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike Refs. [1,2], the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may be Gaussian curvature into a sphere or mean curvature into a cylinder. 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. We compare the formalism for asymmetric films with previous theoretical work on symmetric films, and compare the predictions with experimental results. [4pt] [1] Y. Klein, E. Efrati, and E. Sharon, Science 315, 1116 (2007).[0pt] [2] E. Efrati, E. Sharon, and R. Kupferman, J. Mech. Phys. Solids 57, 762 (2009).

Geng, Jun; Selinger, Jonathan

2010-03-01

392

Asymmetric dimethylarginine (ADMA) accelerates cell senescence.  

PubMed

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and its accumulation has been associated with cardiovascular disease. We aimed to investigate the role of ADMA in endothelial cell senescence. Endothelial cells were cultured until the tenth passage. ADMA was replaced every 48 hours starting at the fourth passage. ADMA significantly accelerated senescence-associated beta-galactosidase activity. Additionally, the shortening of telomere length was significantly speeded up and telomerase activity was significantly reduced. This effect was associated with an increase of oxidative stress: both allantoin, a marker of oxygen free radical generation, and intracellular reactive oxygen species increased significantly after ADMA treatment compared with control, whereas nitric oxide synthesis decreased. Furthermore, ADMA-increased oxidative stress was accompanied by a decrease in the activity of dimethylarginine dimethylaminohydrolase, the enzyme that degrades ADMA, which could be prevented by the antioxidant pyrrolidine dithiocarbamate. Exogenous ADMA also stimulated secretion of monocyte chemotactic protein-1 and interleukin-8. Co-incubation with the methyltransferase inhibitor S-adenosylhomocysteine abolished the effects of ADMA. These data suggest that ADMA accelerates senescence, probably via increased oxygen radical formation by inhibiting nitric oxide elaboration. This study provides evidence that modest changes of intracellular ADMA levels are associated with significant effects on slowing down endothelial senescence. PMID:16444871

Bode-Böger, Stefanie M; Scalera, Fortunato; Martens-Lobenhoffer, Jens

2005-07-01

393

Absolute dimensions and masses of eclipsing binaries. V. IQ Persei  

SciTech Connect

New photometric and spectroscopic observations of the 1.7 day eclipsing binary IQ Persei (B8 + A6) have been analyzed to yield very accurate fundamental properties of the system. Reticon spectroscopic observations obtained at McDonald Observatory were used to determine accurate radial velocities of both stars in this slightly eccentric large light-ratio binary. A new set of VR light curves obtained at McDonald Observatory were analyzed by synthesis techniques, and previously published UBV light curves were reanalyzed to yield accurate photometric orbits. Orbital parameters derived from both sets of photometric observations are in excellent agreement. The absolute dimensions, masses, luminosities, and apsidal motion period (140 yr) derived from these observations agree well with the predictions of theoretical stellar evolution models. The A6 secondary is still very close to the zero-age main sequence. The B8 primary is about one-third of the way through its main-sequence evolution. 27 references.

Lacy, C.H.; Frueh, M.L.

1985-08-01

394

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

395

Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.  

PubMed

An efficient catalytic asymmetric synthesis of chiral ?-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid. PMID:21268603

Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

2011-01-26

396

Asymmetric Aminolytic Kinetic Resolution of Racemic Epoxides Using Recyclable Chiral Polymeric Co(III)-Salen Complexes: A Protocol for Total Utilization of Racemic Epoxide in the Synthesis of (R)-Naftopidil and (S)-Propranolol.  

PubMed

Chiral polymeric Co(III) salen complexes with chiral ((R)/(S)-BINOL, diethyl tartrate) and achiral (piperazine and trigol) linkers with varying stereogenic centers were synthesized for the first time and used as catalysts for aminolytic kinetic resolution (AKR) of a variety of terminal epoxides and glycidyl ethers to get enantio-pure epoxides (ee, 99%) and N-protected ?-amino alcohols (ee, 99%) with quantitative yield in 16 h at RT under optimized reaction conditions. This protocol was also used for the synthesis of two enantiomerically pure drug molecules (R)-Naftopidil (?1-blocker) and (S)-Propranolol (?-blocker) as a key step via AKR of single racemic naphthylglycidyl ether with Boc-protected isoproylamine with 100% epoxide utilization at 1 g level. The catalyst 1 was successfully recycled for a number of times. PMID:23899243

Kumar, Manish; Kureshy, Rukhsana I; Shah, Arpan K; Das, Anjan; Khan, Noor-Ul H; Abdi, Sayed H R; Bajaj, Hari C

2013-08-28

397

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

398

Molecular iodine absolute frequencies. Final report  

SciTech Connect

Fifty specified lines of {sup 127}I{sub 2} were studied by Doppler-free frequency modulation spectroscopy. For each line the classification of the molecular transition was determined, hyperfine components were identified, and one well-resolved component was selected for precise determination of its absolute frequency. In 3 cases, a nearby alternate line was selected for measurement because no well-resolved component was found for the specified line. Absolute frequency determinations were made with an estimated uncertainty of 1.1 MHz by locking a dye laser to the selected hyperfine component and measuring its wave number with a high-precision Fabry-Perot wavemeter. For each line results of the absolute measurement, the line classification, and a Doppler-free spectrum are given.

Sansonetti, C.J. [National Inst. of Standards and Technology, Gaithersburg, MD (United States)

1990-06-25

399

Absolute distance measurement with the MSTAR sensor  

NASA Astrophysics Data System (ADS)

The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard intrferometers, and making it possible to measure distance with sub-nanometer accuracy. The sensor uses a single laser in conjugation with fast phase modulators and low-frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beam-launching optics, and signal processing - and show results for target distance up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances.

Lay, Oliver P.; Dubovitsky, Serge; Peters, Robert D.; Burger, Johan; Ahn, Seh-Won; Steier, William H.; Fetterman, Harold R.; Chang, Yian

2003-11-01

400

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

401

Biocatalytic asymmetric amination of carbonyl functional groups - a synthetic biology approach to organic chemistry.  

PubMed

Transaminases catalyze amino transfer reactions from amino donors such as amino acids or amines to keto acids or ketones to give chiral amino acid or amines in optically pure form. alpha-Amino acid dehydrogenases catalyze the asymmetric reductive amination of alpha-keto acids using ammonia as amino donor to furnish L-amino acids. The distinct features and synthetic application of these two enzymes are reviewed in an effort to illustrate their promising and challenging aspects in serving as approaches to the direct asymmetric synthesis of optically pure amines from the corresponding keto compounds, a formidable problem in organic chemistry. PMID:19757497

Zhu, Dunming; Hua, Ling

2009-10-01

402

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

403

Asymmetric cell division during animal development.  

PubMed

Although most cells produce two equal daughters during mitosis, some can divide asymmetrically by segregating protein determinants into one of their two daughter cells. Interesting parallels exist between such asymmetric divisions and the polarity established in epithelial cells, and heterotrimeric G proteins might connect these aspects of cell polarity. The discovery of asymmetrically segregating proteins in vertebrates indicates that the results obtained in invertebrate model organisms might also apply to mammalian stem cells. PMID:11413461

Knoblich, J A

2001-01-01

404

Enantioselective Total Synthesis of Pladienolide B: A Potent Spliceosome Inhibitor  

PubMed Central

An enantioselective and convergent total synthesis of pladienolide B (1) is described. Pladienolide B binds to the SF3b complex of a spliceosome and inhibits mRNA splicing activity. The synthesis features an epoxide opening reaction, an asymmetric reduction of a ?-keto ester, and a cross metathesis strategy for the side chain synthesis.

Anderson, David D.

2012-01-01

405

A Concise Enantioselective Synthesis of (-)-Ranirestat  

PubMed Central

A concise, enantioselective synthesis of the potent aldose reductase inhibitor ranirestat (1) is reported. The synthesis was accomplished employing inexpensive, commercially available starting materials. A palladium-catalyzed asymmetric allylic alkylation (Pd-AAA) of malonate 4 was utilized as a key transformation to construct the tetrasubstituted chiral center in the target.

Trost, Barry M.; Osipov, Maksim; Dong, Guangbin

2010-01-01

406

Total synthesis of brevisamide and herboxidiene  

Microsoft Academic Search

Brevisamide is a recently discovered natural product. It is believed to play an important role in the biosynthesis of marine polyether toxins, such as brevenal. We have accomplished an asymmetric total synthesis of brevisamide. The synthesis is convergent and involves the efficient sp2-sp 3 type coupling of fragments via Suzuki reaction. The stereogenic tetrahydropyran ring was synthesized via a highly

Jianfeng Li

2011-01-01

407

Total synthesis of chaetoquadrins A-C.  

PubMed

The first total synthesis of the monoamine oxidase inhibitors chaetoquadrins A-C has been accomplished. Key steps in the synthesis include an aromatic Claisen rearrangement, asymmetric boron aldol reaction and acid-mediated spiroketalization. Comparison of spectral data for the synthetic spiroketals confirmed the proposed structure for these natural products. PMID:23327616

Kim, U Bin; Furkert, Daniel P; Brimble, Margaret A

2013-01-17

408

Symmetric mortality and asymmetric suicide cycles.  

PubMed

In this investigation, tests were performed to determine whether mortality cycles are asymmetric. Results from an asymmetry test of U.S. time-series data from 1951 to 2005 provide no evidence that all-cause mortality or mortality caused by disease causes asymmetric cycles. However, the rate of fatalities from suicide exhibits the pattern of an asymmetric cycle. The evidence for asymmetric suicide cycles is statistically significant for men and working-age groups but not for women and non-working-age groups. PMID:20378221

Wu, Wen-Chieh; Cheng, Hui-Pei

2010-03-16

409

Enantioselective total synthesis of macrolide (+)-neopeltolide.  

PubMed

The asymmetric total synthesis of the anti-proliferative macrolide (+)-neopeltolide has been completed. The stereochemically defined trisubstituted tetrahydropyran ring was constructed via a catalytic hetero-Diels-Alder reaction creating two new chiral centers in a highly diastereoselective manner. The other key features of this synthesis included Brown's asymmetric allylation to install the requisite C-11 and C-13 stereocenters. The synthesis of the oxazole side chain consisted of a hydrozirconation of an alkynyl stannane to establish the Z stereochemistry, followed by a palladium catalyzed cross coupling to introduce the desired Z olefin in the oxazole side chain. PMID:24121457

Ghosh, Arun K; Shurrush, Khriesto A; Dawson, Zachary L

2013-10-11

410

Enantioselective synthesis of (-)-pentalenene.  

PubMed

A short, enantioselective synthesis of (-)-pentalenene is described. Catalytic enantioselective cyclopropenation with (R,R)-Rh2(OAc)(DPTI)3 was used to set the absolute stereochemistry, and an intramolecular Pauson-Khand reaction of the resulting cyclopropenyne was used to establish the quaternary center. PMID:18031057

Pallerla, Mahesh K; Fox, Joseph M

2007-11-22

411

On Stationary Strategies for Absolutely Continuous Houses  

Microsoft Academic Search

Whether stationary families of strategies are uniformly adequate for a leavable, analytically measurable, nonnegative gambling problem whose optimal return function is everywhere finite is a question which remains open. It is, however, given an affirmative answer if, for example, the fortune space is Euclidean and all nontrivial, available gambles are absolutely continuous with respect to Lebesgue measure.

Lester E. Dubins; William D. Sudderth

1979-01-01

412

Precision absolute positional measurement of laser beams.  

PubMed

We describe an instrument which, coupled with a suitable coordinate measuring machine, facilitates the absolute measurement within the machine frame of the propagation direction of a millimeter-scale laser beam to an accuracy of around ±4 ?m in position and ±20 ?rad in angle. PMID:23669658

Fitzsimons, Ewan D; Bogenstahl, Johanna; Hough, James; Killow, Christian J; Perreur-Lloyd, Michael; Robertson, David I; Ward, Henry

2013-04-20

413

On the Measurement of Absolute Velocities  

Microsoft Academic Search

Inertial observers can not only measure their absolute velocities but that of light as well, thereby being able to shed insight into the principle of the constancy of light velocity. The light speeds c±v, though considered to conflict with this principle, are shown herein to not be true physical entities. Keywords: special relativity theory, time, coordinate systems, relative velocity. Consider

A. C. V. Ceapa

414

Conditions for Equilibrium at Negative Absolute Temperatures  

Microsoft Academic Search

In the classical phenomenological thermodynamic theory of Gibbs, equilibrium is defined as the state of maximum entropy at constant energy, and a theorem is proved (the energy theorem) which asserts that the equilibrium state is the state of minimum energy at fixed entropy. This theorem is not true for systems at negative absolute temperatures. By examining a familiar statistical model

Bernard D. Coleman; Walter Noll

1959-01-01

415

Negative absolute temperatures and rotating temperatures  

Microsoft Academic Search

Although negative absolute temperatures, and rotating temperatures, only arise in certain special situations it is of interest to consider what, if any, changes have to be made in traditional thermodynamics in order to accommodate them. It is found that about the only change required is a slight modification of the Kelvin-Planck formulation of the second law. The terms, hotter, colder,

J. G. Powles

1963-01-01

416

On the absolute configuration of matricin.  

PubMed

The assignment of the absolute configuration of matricin rests on indirect evidence. On the basis of synthetic, NMR and CD studies with its decomposition product, chamazulene carboxylic acid, we were able to firmly establish the accepted 3S,3aR,4S,9R,9aS,9bS configuration of matricin. PMID:11345709

Goeters, S; Imming, P; Pawlitzki, G; Hempel, B

2001-04-01

417

It's Not All Relative: Relative Versus Absolute  

NSDL National Science Digital Library

Learning about the sizes of things and scale engages students in thinking about conceptual benchmarks for sizes. In this investigation, students learn to order objects on a relative scale, as well as to accurately label actual or absolute sizes. In additi

Taylor, Amy R.; Jones, M. G.; Falvo, Michael R.

2009-04-01

418

Absolute Measurement of exp 152 Eu.  

National Technical Information Service (NTIS)

A new method of the absolute measurement for exp 152 Eu was established based on the 4 pi beta - gamma spectroscopic anti-coincidence method. It is a coincidence counting method consisting of a 4 pi beta -counter and a Ge(Li) gamma -ray detector, in which...

H. Baba S. Baba S. Ichikawa T. Sekine I. Ishikawa

1981-01-01

419

Investigation of Absolute Light Output Measurement Techniques  

Microsoft Academic Search

The recently published works on new measurement techniques of the scintillators' absolute light yield triggered our response in the attempt to find out a way to resolve the disagreements between the old, established technique and the emerging, new one. Authors of the new approach argue that the conditions in which the photomultipliers photocathodes quantum efficiencies' characteristics are being determined differ

Marek Moszynski; Antoni Nassalski; Agnieszka Syntfeld-Kazuch; Tomasz Szczesniak; L. Swiderski

2007-01-01

420

Investigation of Absolute Light Output Measurement Techniques  

Microsoft Academic Search

The recently published works on new measurement techniques of the scintillators' absolute light yield triggered our response in the attempt to find out a way to resolve the disagreements between the old, established technique and the emerging, new one. Authors of the new approach argue that the conditions in which the photomultipliers photocathodes quantum efficiencies' characteristics are being determined differ

M. Gierlik; M. Moszynski; A. Nassalski; A. Syntfeld-Kazuch; T. Szczesniak; L. Swiderski

2006-01-01

421

Global absolute sea level: The Hawaiian network  

Microsoft Academic Search

NOAA has begun work on a pilot absolute sea level network in Hawaii. Tide gauge stations on the islands of Hawaii, Maui, Oahu, and Kauai have been upgraded by installing Next Generation Water Level Measurements Systems (NGWLMS). A regular program of monitoring the stability of each tide gauge in the International Earth Rotation Service (IERS) conventional terrestrial reference frame has

William E. Carter; Miranda Chin; J. Ross Mackay; George Peter; Wolfgang Scherer; John Diamante

1988-01-01

422

Asymmetric low back loading in asymmetric lifting movements is not prevented by pelvic twist  

Microsoft Academic Search

Asymmetric lifting is associated with an increased risk of low back disorders. Especially in lifting movements, characterized by a small amount of asymmetry, it is still the question if asymmetric lumbosacral torques occur, or if subjects try to avoid asymmetric back loading by twisting their pelvis with respect to the feet. An increase of the lifting speed or the box

Idsart Kingma; Jaap H van Dieën; Michiel de Looze; Huub M Toussaint; Patricia Dolan; Chris T. M Baten

1998-01-01

423

The Asymmetric Current Mirror Probe  

NASA Astrophysics Data System (ADS)

The difference in floating potential, between two closely spaced probe tips, is often used as a measure of the electric field in plasmas. This technique assumes a thermal Maxwellian distribution for plasma electrons and is unreliable in the presence of a fast non-Maxwellian electron tail. The influence of fast-tail electrons on floating potential measurements can be mitigated by using emissive probes or probes of unbalanced collection area. These probes have floating potentials that are closer to plasma potential than the floating potential of a standard Langmuir probe. An example of an unbalanced area probe is the ball-pen probe [Schrittwieser, et al., Rom. Journ. Phys., Vol. 50, 2005], in which the ion collection area is substantially larger than the electron collection area. The asymmetric current mirror probe achieves the effect of unbalanced collection area electronically, by amplification of the current drawn to the ion tip. Comparisons of radial profiles of floating potential in the LAPD at UCLA, measured using a Langmuir probe, ball-pen probe and asymmetric mirror probe are presented. The effects of using differences in floating potential, measured by these various probes, to determine the electric field is discussed.

Maggs, J. E.; Carter, T. A.

2008-11-01

424

Asymmetric dark matter from leptogenesis  

NASA Astrophysics Data System (ADS)

We present a new realization of asymmetric dark matter in which the dark matter and lepton asymmetries are generated simultaneously through two-sector leptogenesis. The right-handed neutrinos couple both to the Standard Model and to a hidden sector where the dark matter resides. This framework explains the lepton asymmetry, dark matter abundance and neutrino masses all at once. In contrast to previous realizations of asymmetric dark matter, the model allows for a wide range of dark matter masses, from keV to 10 TeV. In particular, very light dark matter can be accommodated without violating experimental constraints. We discuss several variants of our model that highlight interesting phenomenological possibilities. In one, late decays repopulate the symmetric dark matter component, providing a new mechanism for generating a large annihilation rate at the present epoch and allowing for mixed warm/cold dark matter. In a second scenario, dark matter mixes with the active neutrinos, thus presenting a distinct method to populate sterile neutrino dark matter through leptogenesis. At late times, oscillations and dark matter decays lead to interesting indirect detection signals.

Falkowski, Adam; Ruderman, Joshua T.; Volansky, Tomer

2011-05-01

425

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.

2011-09-01

426

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

427

Asymmetrical membranes and surface tension.  

PubMed Central

The (31)P-nuclear magnetic resonance chemical shift of phosphatidic acid in a membrane is sensitive to the lipid head group packing and can report qualitatively on membrane lateral compression near the aqueous interface. We have used high-resolution (31)P-nuclear magnetic resonance to evaluate the lateral compression on each side of asymmetrical lipid vesicles. When monooleoylphosphatidylcholine was added to the external monolayer of sonicated vesicles containing dioleoylphosphatidylcholine and dioleoylphosphatidic acid, the variation of (31)P chemical shift of phosphatidic acid indicated a lateral compression in the external monolayer. Simultaneously, a slight dilation was observed in the inner monolayer. In large unilamellar vesicles on the other hand the lateral pressure increased in both monolayers after asymmetrical insertion of monooleoylphosphatidylcholine. This can be explained by assuming that when monooleoylphosphatidylcholine is added to large unilamellar vesicles, the membrane bends until the strain is the same in both monolayers. In the case of sonicated vesicles, a change of curvature is not possible, and therefore differential packing in the two layers remains. We infer that a variation of lipid asymmetry by generating a lateral strain in the membrane can be a physiological way of modulating the conformation of membrane proteins.

Traikia, Mounir; Warschawski, Dror E; Lambert, Olivier; Rigaud, Jean-Louis; Devaux, Philippe F

2002-01-01

428

Cost Calculation for Incremental Hardware Synthesis.  

National Technical Information Service (NTIS)

The incremental estimation of layout area for logic circuits is considered. The estimates are to be used during the automated synthesis of hardware structures. These estimates are used to compare circuits on their efficiency. The absolute accuracy of the ...

R. J. Vanengelshoven R. Vandenborn

1988-01-01

429

Total Synthesis of (-)-Aplaminal  

PubMed Central

The total synthesis and assignment of absolute configuration of (?)-aplaminal (1), a cytotoxic metabolite from a sea hare possessing a triazobicyclo[3.2.1]octane skeleton, has been achieved. The synthesis entailed condensation of a monoprotected diamine (3) with dimethyl 2-oxomalonate (4) to generate the imidazolidine core (2). Introduction of the third nitrogen via Mitsunobu activation and azide displacement, followed by reduction and lactam formation (AlMe3) furnished (?)-aplaminal (1). Overall, the synthesis entailed 9 steps and proceeded in 17% overall yield.

Smith, Amos B.; Liu, Zhuqing

2009-01-01

430

Stereoselective total synthesis of furofuran lignans through dianion aldol condensation  

Microsoft Academic Search

Highly stereoselective total synthesis of (+)-eudesmin, (+)-yangambin, (?)-eudesmin, and (?)-yangambin is described. This method is useful to generate the core skeleton of furofuran rings utilizing modification of Evans asymmetric aldol condensation.

Jae-Chul Jung; Ju-Cheun Kim; Hyung-In Moon; Oee-Sook Park

2006-01-01

431

Chemoenzymatic synthesis of the alarm pheromone (+)-verbenone from geranyl diphosphate.  

PubMed

The enzyme-guided asymmetric synthesis of (+)-verbenone from geranyl diphosphate in a simple two-step, one pot transformation highlights the potential of chemoenzymatic procedures for the generation of high-value terpenoids. PMID:22684271

Yoosuf-Aly, Zulfa; Faraldos, Juan A; Miller, David J; Allemann, Rudolf K

2012-06-11

432

Determination of the absolute stereostructure of seco-macrosphelide E produced by a fungal strain from a sea hare.  

PubMed

seco-Macrosphelide E has been isolated from a strain of Periconia byssoides originally separated from the sea hare Aplysia kurodai. Its absolute stereostructure, with the same configuration as that of macrosphelide E, have been elucidated on the basis of spectroscopic analyses and unambiguous synthesis. PMID:11848230

Nakamura, Hiroshi; Ono, Machiko; Yamada, Takeshi; Numata, Atsushi; Akita, Hiroyuki

2002-02-01

433

Spindle orientation during asymmetric cell division  

Microsoft Academic Search

Development of a multicellular organism from a fertilized egg depends on a precise balance between symmetric cell divisions to expand the pool of similar cells, and asymmetric cell divisions to create cell-type diversity. Spindle orientation can influence the generation of symmetric or asymmetric cell fates depending on how it is coupled to cell-intrinsic polarity cues, or how it is positioned

Karsten H. Siller; Chris Q. Doe

2009-01-01

434

Contemporary Asymmetric Conflict Theory in Historical Perspective  

Microsoft Academic Search

This article offers an intellectual history of theoretical work devoted to explaining asymmetric conflict outcomes since World War II. Three factors are critical to understanding how the literature has evolved. First, the concept of “asymmetric conflict” encompasses a number of overlapping literatures, including insurgency, terrorism, counterinsurgency, and most recently, civil wars. Second, and interrelated, the field of inquiry has been

Ivan Arreguín-Toft

2012-01-01

435

The Catalytic Asymmetric Intramolecular Stetter Reaction  

PubMed Central

This account chronicles our efforts at the development of a catalytic asymmetric Stetter reaction using chiral triazolium salts as small molecule organic catalysts. Advances in the mechanistically related azolium-catalyzed asymmetric benzoin reaction are discussed, particularly as they apply to catalyst design. A chronological treatise of reaction discovery, catalyst optimization and reactivity extension follows.

de Alaniz, Javier Read; Rovis, Tomislav

2010-01-01

436

A NEW SECURITY PROBLEM: THE ASYMMETRICAL WARFARE  

Microsoft Academic Search

Welcome to the world of asymmetrical warfare, a place high on the anxiety list of military planners. In the asymmetrical realm, mi litary experts say, a small band of commandos might devastate the United States and leave no clue about who ordered the attack.\\

József Németh

437

Gauge symmetries in heterotic asymmetric orbifolds  

NASA Astrophysics Data System (ADS)

We study heterotic asymmetric orbifold models. By utilizing the lattice engineering technique, we classify (22,6)-dimensional Narain lattices with right-moving non-Abelian group factors which can be starting points for Z3 asymmetric orbifold construction. We also calculate gauge symmetry breaking patterns.

Beye, Florian; Kobayashi, Tatsuo; Kuwakino, Shogo

2013-10-01

438

Redetermination and absolute configuration of pruniflorone M monohydrate  

PubMed Central

The title xanthone known as pruniflorone M (systematic name: (2R)-5,10-dihy­droxy-2-hy­droxy­methyl-1,1-dimethyl-1H-furo[2,3-c]xanthen-6-one), crystallized in a monohydrate form, C18H16O6·H2O. It was isolated from the green fruits of Cratoxylum formosum ssp. pruniflorum. The structure of the title compound has been reported previously [Boonnak et al. (2010 ?). Aust. J. Chem. 63, 1550–1556], but we report here the absolute configuration determined using Cu K? radiation. There are two crystallograpically independent mol­ecules in the asymmetric unit, which differ slightly in the bond angles. The hy­droxy­methyl substituents at position 2 of the furan rings of both pruniflorone M mol­ecules adopt R configurations. In both mol­ecules, the three rings of the xanthone skeleton are approximately coplanar, with an r.m.s. deviation of 0.0124?(2)?Å for one mol­ecule and 0.0289?(2)?Å for the other, and the furan ring adopts an envelope conformation. In the crystal, mol­ecules of pruniflorone M and water are linked into a two-dimensional network by O—H?O hydrogen bonds and weak C—H?O inter­actions. The crystal structure is further consolidated by ?–? inter­actions with centroid–centroid distances in the range 3.5987?(13)–3.7498?(14)?Å. Short C?C [3.378?(3)?Å] and O?O [2.918?(3)?Å] contacts are also observed.

Fun, Hoong-Kun; Chantrapromma, Suchada; Boonnak, Nawong; Karalai, Chatchanok; Chantrapromma, Kan

2011-01-01

439

Superfluidity in asymmetric nuclear matter  

SciTech Connect

The onset of superfluidity in isospin-asymmetric nuclear matter is investigated within the BCS theory. A neutron-proton superfluid state in the channel {sup 3}S{sub 1}-{sup 3}D{sub 1} comes about from the interplay between thermal excitations and separation {delta}{mu} of the two Fermi surfaces. The superfluid state disappears above the threshold value of the density-asymmetry parameter {alpha}=(n{sub n}{minus}n{sub p})/n{approx_equal}0.35. For large enough shift between the two Fermi surfaces {delta}{mu}=(1)/(2)({mu}{sub n}{minus}{mu}{sub p}) the transition to the normal state becomes a first-order transition and a second gap solution develops. This solution, however, corresponds to a metastable superfluid state which is unstable with respect to the transition to the normal state. {copyright} {ital 1997} {ital The American Physical Society}

Sedrakian, A.; Alm, T. [Max-Planck-Gesellschaft, AG Theoretische Vielteilchenphysik, Universitaet Rostock, D-18051 Rostock (Germany); Lombardo, U. [Dipartimento di Fisica and INFN, 57 Corso Italia, I-95129 Catania (Italy)

1997-02-01

440

Quantum simulators at negative absolute temperatures  

NASA Astrophysics Data System (ADS)

We propose that negative absolute temperatures in ultracold atomic clouds in optical lattices can be used to simulate quantum systems in new regions of phase diagrams. First we discuss how the attractive SU(3) Hubbard model in three dimensions can be realized using repulsively interacting 173Yb atoms, then we consider how an antiferromagnetic S=1 spin chain could be simulated using spinor 87Rb or 23Na atoms. The general idea to achieve negative absolute temperatures is to reverse the sign of the external harmonic potential. Energy conservation in a deep optical lattice imposes a constraint on the dynamics of the cloud, which can relax toward a T<0 state. As the process is strongly nonadiabatic, we estimate the change of the entropy.

Rapp, Ákos

2012-04-01

441

Absolute calibration of TFTR helium proportional counters  

SciTech Connect

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, C.W.; Diesso, M.; Jassby, D.; Johnson, L.; Loughlin, M.; McCauley, S.; Munsat, T.; Roquemore, A.L. (Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 (United States))

1995-02-01

442

Absolute calibration of TFTR helium proportional counters  

SciTech Connect

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 msec and 50 msec 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.; Diesso, M.; Jassby, D.; Johnson, L.; McCauley, S.; Munsat, T.; Roquemore, A.L. [Princeton Univ., NJ (United States). Plasma Physics Lab.; Barnes, C.W. [Princeton Univ., NJ (United States). Plasma Physics Lab.]|[Los Alamos National Lab., NM (United States); Loughlin, M. [Princeton Univ., NJ (United States). Plasma Physics Lab.]|[JET Joint Undertaking, Abingdon (United Kingdom)

1995-06-01

443

Quantifying absolute carbon isotope ratios by AMS  

NASA Astrophysics Data System (ADS)

Our AMS produced a ratio of instrument transmissions for 14C and 13C equal to 13/14 to 0.22 ± 0.06% accuracy at a specific charge-changing energy of 235 keV and giving absolute isotope ratios with that mass correction. The ratio for 13C and 12C transmissions was 12/13 at 215 keV. A differential equation model of energetic ion and atom transport through the gas collision cell was constructed with functions representing experimental cross-sections for all collision effects. This model showed cation yield dependencies that were linear with energy for the monoenergetic isotopic ions at the energies that we measured, explaining the inverse mass dependence. The model predicted multiple lower energies that have this dependence and, more importantly, two low energies at which cation yields were equal for pairs of isotopes, presaging potential absolute isotope ratio measurements at low MS energies.

Vogel, John S.; Giacomo, Jason A.; Dueker, Stephen R.

2013-01-01

444

FOC Absolute Sensitivity (F/48 Relay)  

NASA Astrophysics Data System (ADS)

The absolute DQE for the f/48 camera has not yet been directly measured in orbit. This has been in part due to the absence of faint enough standards. This proposal will attempt to correct this deficiency by observations of UV standard stars with combinations of filters and small formats to achieve count rates that are not seriously nonlinear. Because of the use of small formats, interactive acquisitions will be required as well as special commanding for nonstandard formats. Internal LED exposures will also be necessary to geometrically calibrate the nonstandard format and to tie its absolute response to those of other formats (there is a significant format- dependent response variation for f/48).

Paresce, Francesco

1993-07-01

445

Absolute pitch in autism: A case study  

Microsoft Academic Search

We present the case study of QC, a low-functioning adolescent with autism, who possesses the special ability of absolute pitch. QC participated in an in-depth assessment of pitch perception and processing systems relevant for current cognitive models of autism. Her performance was compared to that of mental age-and chronological age-matched groups of persons with average intelligence, or to that of

L. Mottron; I. Peretz; S. Belleville; N. Rouleau

1999-01-01

446

Absolute Ultraviolet Stellar Irradiances from SORCE SOLSTICE  

Microsoft Academic Search

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) spacecraft is a grating spectrometer that has been measuring both solar and stellar fluxes in the 115-300 nm range since 2003. Preflight instrument calibration using the SURF III synchrotron source yields an uncertainty in the absolute stellar irradiances of just a few percent.The SOLSTICE program stars

Martin Snow; W. E. McClintock; T. N. Woods; G. Rottman

2006-01-01

447

The absolute isotopic composition of europium  

NASA Astrophysics Data System (ADS)

Calibrated mass spectrometric measurements on highly enriched isotopes of europium in the form of 99.96% pure sesquioxide were carried out with a thermal ionization mass spectrometer, yielding an absolute isotopic composition of 47.810(42) at.% 151Eu and 52.190(42) at.% 153Eu, and the atomic weight of europium as 151.9644(9) with error given as 2[sigma]. No isotopic fractionation was found in terrestrial normal europium materials.

Chang, Tsing Lien; Qian, Qiu-Yu; Zhao, Mo-Tian; Wang, Jun

1994-11-01

448

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

449

Clock retardation, absolute space, and special relativity  

Microsoft Academic Search

We consider a sequence of absolute-space kinematical theories which differ more or less from the special theory of relativity (STR) in the amount of clock retardation which they predict, but which agree with STR with respect to roundtrip light experiments, such as Michelson-Morley and Kennedy-Thorndike. This sequence of theories is imbedded in the synchrony-free formulation of STR developed by Winnie

Carlo Giannoni

1979-01-01

450

Training the absolute identification of pitch  

Microsoft Academic Search

Two methods for training the absolute judgment of pitch, reference training and series training, were studied. Reference training\\u000a concentrated during training on the identification of three reference tones in a set of nine pure tones, while series training\\u000a gave equal weight during training to the identification of all nine tones. Results of pre- and posttraining tests, scored\\u000a for the number

Lola L. Cuddy

1970-01-01

451

Absolute absorption of ozone in the midinfrared  

SciTech Connect

The absolute absorption of ozone in the midinfrared has been measured relative to 253.7-nm ultraviolet absorption to an accuracy of 1% using a Bruker Fourier transform spectrometer. These new results agree with previous measurements by diode laser measurements after the latter are corrected for more recent infrared calculations and ultraviolet cross sections. They also agree with a determination based on refractive index measurements in the infrared. 16 refs., 4 figs., 3 tabs.

Pickett, H.M.; Peterson, D.B.; Margolis, J.S. (California Inst. of Technology, Pasadena (United States))

1992-12-20

452

A Cryogenic Radiometer for Absolute Radiometric Measurements  

NASA Astrophysics Data System (ADS)

The adoption in 1979 of a new definition of the candela, which permitted a detector-based approach to the realization of the unit, has emphasized the importance of high-accuracy absolute radiation detectors. This paper describes a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant-power measurements. The principal advantages of operating the radiometer at liquid helium temperatures are that the detector can be a large, highly absorbing cavity (absorptivity 99.998%) and that exact equivalence of electrical and radiant heating can be clearly demonstrated. It will be the primary absolute detector for a new realization of the candela at NPL and will provide the basis for the development of a wider range of radiometric and spectroradiometric standards. The use of the radiometer to measure the radiant power of an intensity-stabilized laser source at the milliwatt level with an uncertainty of 4 parts in 105 is also described, together with its application in the determination of the responsivity of transfer-standard detectors, such as silicon photodiodes.

Martin, J. E.; Fox, N. P.; Key, P. J.

1985-01-01

453

Chemical composition of French mimosa absolute oil.  

PubMed

Since decades mimosa (Acacia dealbata) absolute oil has been used in the flavor and perfume industry. Today, it finds an application in over 80 perfumes, and its worldwide industrial production is estimated five tons per year. Here we report on the chemical composition of French mimosa absolute oil. Straight-chain analogues from C6 to C26 with different functional groups (hydrocarbons, esters, aldehydes, diethyl acetals, alcohols, and ketones) were identified in the volatile fraction. Most of them are long-chain molecules: (Z)-heptadec-8-ene, heptadecane, nonadecane, and palmitic acid are the most abundant, and constituents such as 2-phenethyl alcohol, methyl anisate, and ethyl palmitate are present in smaller amounts. The heavier constituents were mainly triterpenoids such as lupenone and lupeol, which were identified as two of the main components. (Z)-Heptadec-8-ene, lupenone, and lupeol were quantified by GC-MS in SIM mode using external standards and represents 6%, 20%, and 7.8% (w/w) of the absolute oil. Moreover, odorant compounds were extracted by SPME and analyzed by GC-sniffing leading to the perception of 57 odorant zones, of which 37 compounds were identified by their odorant description, mass spectrum, retention index, and injection of the reference compound. PMID:20070087

Perriot, Rodolphe; Breme, Katharina; Meierhenrich, Uwe J; Carenini, Elise; Ferrando, Georges; Baldovini, Nicolas

2010-02-10

454

Formal synthesis of (±)-morphine.  

PubMed

The pain ends here: A novel synthetic strategy for the construction of (±)-morphine rings?B and E was developed, in which SmI2 -promoted reductive coupling/desulfurization and tandem alcoholysis/oxa-Michael addition featured as the key steps for the assembly of the C9-C14 and C5-O bonds, respectively. Asymmetric tandem alcoholysis/oxa-Michael addition was also feasible for the enantiocontrolled synthesis of morphine. PMID:23509056

Li, Jing; Liu, Guo-Liang; Zhao, Xian-He; Du, Ji-Yuan; Qu, Hu; Chu, Wen-Dao; Ding, Ming; Jin, Cong-Yang; Wei, Meng-Xue; Fan, Chun-An

2013-03-18

455

Total synthesis of ochnaflavone  

PubMed Central

Summary The first total syntheses of ochnaflavone, an asymmetric biflavone consisting of apigenin and luteolin moieties, and the permethyl ether of 2,3,2'',3''-tetrahydroochnaflavone have been achieved. The key steps in the synthesis of ochnaflavone were the formation of a diaryl ether and ring cyclization of an ether-linked dimeric chalcone to assemble the two flavone nuclei. Optimal experimental conditions for the oxidative cyclization to form ochnaflavone were established.

Ndoile, Monica M

2013-01-01

456

Absolute Calibration of AXAF Effective Area  

NASA Astrophysics Data System (ADS)

In order to measure the absolute x-ray flux from objects observed by AXAF, the absolute effective area of the telescope must be known. Because there are no standard candles in the x-ray sky, a prelaunch calibration must be done. The overall effective area of the combined optic and focal plane detectors requires a knowledge of the absolute flux in the incident x-ray beam that illuminates them in the X-ray Calibration Facility at Marshall Space Flight Center. In order to calibrate the beam, a standard detector is needed. We report on the approach being developed to calibrate standard detectors to 1% in effective area. Basic data on physical properties of materials, such as the Henke tables, are not adequate. This is true both because of imprecision in the data, and difficulties with designing detectors whose overall efficiency can be synthesized from a knowledge of constituent properties. Therefore, we resort to calibrating the detector against a standard source, the PTB beam lines at the BESSY synchrotron. The PTB white beam line is calibrated to 0.3%, and the monochromatic line to 1% over the lower portion of the AXAF energy range, and to a few percent over the higher energy range. Special precautions are taken to assure that the detectors are stable following calibration at BESSY. These include dealing with condensation of frozen water vapor on a germanium detector, and providing a built-in radioactive source to check stability. The AXAF effective area is sensitive to small changes in particulate and molecular contamination on its x-ray optics. Therefore, the absolute standard established on the ground must be transferred to orbit. To accomplish this, AXAF employs radioactive sources mounted forward of the optic. X-rays from these sources reflected from the optic are detected by a flight focal plane detector. The counting rates from before and after launch can be used to measure any change in the effective area, establishing the on-orbit absolute effective area.

Kellogg, E.; Tsiang, E.; Schwartz, D.; Hughes, J.; Gaetz, T.; Wargelin, B.; Kolodziejczak, J.; Scholze, F.; Ulm, G.; O'dell, S.; Elsner, R.

1995-12-01

457

Luminescent neutral platinum complexes bearing an asymmetric N(^) N(^) N ligand for high-performance solution-processed OLEDs.  

PubMed

The synthesis and full characterization of new platinum complexes bearing a bulky asymmetric dianionic tridentate ligand is reported. The hindrance of the ligand prevents detrimental intermolecular interactions yielding to highly emitting species in both crystalline state and thin-film. Such properties prompted their successful use in solution-processed OLEDs, showing remarkable external quantum efficiency up to 5.6%. PMID:22972396

Cebrián, Cristina; Mauro, Matteo; Kourkoulos, Dimitrios; Mercandelli, Pierluigi; Hertel, Dirk; Meerholz, Klaus; Strassert, Cristian A; De Cola, Luisa

2012-09-13

458

A heterogeneous layered bifunctional catalyst for the integration of aerobic oxidation and asymmetric C-C bond formation.  

PubMed

The design and synthesis of a heterogeneous bifunctional chiral catalyst for the sequential aerobic oxidation-asymmetric Michael reactions between primary allylic alcohols and dibenzyl malonate are described. Interestingly, we found that layering bimetallic nanoparticles over the organocatalyst, within the chiral composite material, is crucial for catalytic activity. PMID:24036576

Miyamura, Hiroyuki; Choo, Gerald C Y; Yasukawa, Tomohiro; Yoo, Woo-Jin; Kobayashi, Shu

2013-10-01

459

Improvement in Central Arterial Pressure Waveform during Hemodialysis Is Related to a Reduction in Asymmetric Dimethylarginine (ADMA) Levels  

Microsoft Academic Search

Background: Cardiovascular mortality is high in hemodialysis (HD) patients. Early arterial pressure wave reflections, reflecting arterial stiffness and the endogenous nitric oxide synthesis inhibitor asymmetric dimethylarginine (ADMA) levels predict mortality in HD patients. Therefore, we aimed to study changes in ADMA levels and central arterial pressure waveform during HD. Methods: Thirty-two chronic HD patients were studied before and after a

Inga Soveri; Lars Lind; Björn Wikström; Mihkel Zilmer; Kersti Zilmer; Bengt Fellström

2007-01-01

460

Three-Dimensional Quantitative Optical Measurement of Asymmetrically Focused Ultrasound Pressure Field  

NASA Astrophysics Data System (ADS)

High-intensity focused ultrasound (HIFU) is used for the treatment of tumors such as prostate cancer. In the development of this technique, an accurate and fast measurement of the HIFU pressure field is important. A hydrophone is generally used for the measurement, but it might disturb the pressure field and scanning it in the field takes a long time. On the other hand, optical ultrasonic field mapping has the advantages of speed and its nature of not by interfering with the acoustic field. In this study, we reconstructed an asymmetric ultrasound field by optical measurement using a computed tomography (CT) algorithm. The asymmetric field was generated by a focused transducer with four elements. Also, the absolute measurement of ultrasonic pressure was checked by measuring the center of the field of the charge-coupled device (CCD) camera. The results showed overall agreement with those of hydrophone measurement.

Shimazaki, Yuta; Harigane, Soichiro; Yoshizawa, Shin; Umemura, Shin-ichiro

2012-07-01

461

Dynamic Kinetic Resolution of Biaryl Atropisomers via Peptide-Catalyzed Asymmetric Bromination  

Microsoft Academic Search

Despite the widespread use of axially chiral, or atropisomeric, biaryl ligands in modern synthesis and the occurrence of numerous natural products exhibiting axial chirality, few catalytic methods have emerged for the direct asymmetric preparation of this compound class. Here, we present a tripeptide-derived small-molecule catalyst for the dynamic kinetic resolution of racemic biaryl substrates. The reaction proceeds via an atropisomer-selective

Jeffrey L. Gustafson; Daniel Lim; Scott J. Miller

2010-01-01

462

A new asymmetric diamide from the seed cake of Jatropha curcas L.  

PubMed

A new asymmetric diamide (E)-N-(3-acetamidopropyl)-cinnamamide named curcamide (1) has been isolated from the ethanol extract of the seed cake of Jatropha curcas L. along with 7 known compounds identified as isoamericanin (2), isoprincepin (3), caffeoylaldehyde (4), isoferulaldehyde (5), glycerol monooleate (6), syringaldehyde (7), and ?-ethyl-d-glucopyranoside (8). The synthesis and antibacterial activity of the new compound have been also studied. PMID:22516541

Yao, Licheng; Han, Changri; Chen, Guangying; Song, Xiaoping; Chang, Yonghui; Zang, Wenxia

2012-04-11

463

Optimal asymmetric economical state-dependent cloners  

NASA Astrophysics Data System (ADS)

We present the optimal asymmetric economical 1-3 phase-covariant and real state cloning in two-dimensions. The fidelity distributions of copies of two state-dependent cloners are the same, and higher than that of the optimal asymmetric universal quantum cloning. Using a quantum network, we calculate the single-qubit rotation angles to implement two symmetric economical state-dependent cloners. We also propose an experimentally feasible scheme to implement the optimal asymmetric economical 1-3 phase-covariant cloner. The scheme can be realized with the success probability of 100%.

Zhang, Wen-Hai; Ye, Liu

2009-07-01

464

In-Flight Absolute Radiometric Calibration of the Thematic Mapper.  

National Technical Information Service (NTIS)

The TM multispectral scanner system was calibrated in an absolute manner before launch. To determine the temporal changes of the absolute radiometric calibration of the entire system, spectroradiometric measurements of the ground and the atmosphere were m...

K. R. Castle R. G. Holm C. J. Kastner J. M. Palmer P. N. Slater

1983-01-01

465

A new absolute magnitude calibration for red clump stars  

NASA Astrophysics Data System (ADS)

We present a new MV absolute magnitude calibration for the red clump stars.We used the red clump stars in open and globular clusters.Precise absolute magnitudes can be estimated from the calibration formula.

Bilir, S.; Ak, T.; Ak, S.; Yontan, T.; Bostanc?, Z. F.

2013-10-01

466

Cosmological Frames for Theories with Absolute Parallelism  

NASA Astrophysics Data System (ADS)

The vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker cosmologies are hard to work out in most of the theories featuring absolute parallelism. The difficulty is traced in the fact that these theories are not invariant under local Lorentz transformations of the vierbein. We illustrate this issue in the framework of f(T) theories and Born-Infeld determinantal gravity. In particular, we show that the early Universe as described by the Born-Infeld scheme is singularity free and naturally inflationary as a consequence of the very nature of Born-Infeld gravitational action.

Fiorini, Franco; Ferraro, Rafael

2011-05-01

467

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

468

Telescope alignment with the absolute distance interferometer  

NASA Astrophysics Data System (ADS)

Achieving optimal performance from a multiple element telescope is critically dependent on an element position sensing and control system. We first discuss the design of a novel absolute distance measuring interferometer with performance suitable for such a sensing system, and secondly describe how it can be simply integrated into the telescope. Features of the interferometer include an extended ambiguity range, high temporal bandwidth, and very high accuracy. The concept for the overall optical alignment system is expected to compensate in part for local atmospheric distortions as well as mechanical vibrations while not interfering with the optical performance of the telescope.

Massie, N. A.; Dunn, M. R.

1982-10-01

469

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

470

Absolute entropies from molecular dynamics simulation trajectories  

NASA Astrophysics Data System (ADS)

A heuristic formula for calculating absolute entropies from the covariance matrix of atom-positional fluctuations was extensively tested. Because of its heuristic nature, the results obtained are compared to analytical expressions for an ensemble of harmonic oscillators, for the ideal gas, and to numerical results obtained from the equation of state for the Lennard-Jones fluid as a means of validation of the approximate formula for the entropy. The formula yields rather accurate results. The removal of translational and rotational rigid body motion and the effect of the various fitting procedures involved are discussed for the more realistic system of a ?-heptapeptide in solution.

Schäfer, Heiko; Mark, Alan E.; van Gunsteren, Wilfred F.

2000-11-01

471

Inviscid axisymmetric absolute instability of swirling jets  

NASA Astrophysics Data System (ADS)

The propagation characteristics of inviscid axisymmetric linearized disturbances to swirling jets are investigated for two families of model velocity profiles. Briggs' method is applied to dispersion relations to determine when the basic swirling jets are absolutely or convectively unstable. The method is also applied to the neutral inertial waves used by Benjamin to characterize the subcritical or supercritical nature of the flow. Although these waves are neutral, Briggs' method nonetheless indicates a qualitative change in behaviour at Benjamin's criticality condition. The first model jet has uniform axial velocity, rigid-body rotation and issues into still fluid. A known difficulty in the application of Briggs' method to the analytical dispersion relation for inviscid waves in this flow is resolved. The difficulty is that the pinch point can cross into the left half of the complex-wavenumber plane, where waves grow exponentially with radius and fail to satisfy homogeneous boundary conditions. In this paper the physical consequences of this behaviour are explained. It is shown that if the still fluid is of infinite extent in the radial direction, then the jet is convectively unstable to axisymmetric waves, but if the jet is confined by an outer cylinder concentric with the jet axis, then it becomes absolutely unstable to axisymmetric waves provided that the swirl (ratio of azimuthal to axial velocity) is large enough. This destabilizing effect of confinement occurs however large the radius of the outer cylinder. A second family of model swirling jets with smooth profiles and a finite thickness shear layer at the jet edge is also studied. The inviscid stability equations are solved numerically in this case. The results from the analytical dispersion relations are reproduced as the shear layer thickness tends to zero. However, increasing this thickness acts to destabilize the absolute instability of axisymmetric waves, apparently due to the centrifugal instability present in the shear layer. It is suggested that the transition from convective to absolute instability could be associated with the onset of an unsteady vortex breakdown. The swirl required to produce this transition can be either greater, or less, than the swirl required to produce the transition from supercritical to subcritical flow, depending on the details of the basic velocity profiles. A codimension-two point in parameter space can exist where the unsteady bifurcation associated with the convectivesubcritical transition. Such codimension-two points can control a rich variety of nonlinear dynamical behaviour.

Healey, J. J.

472

Computing absolute and essential spectra using continuation  

NASA Astrophysics Data System (ADS)

A continuation approach to the computation of essential and absolute spectra of differential operators on the real line is presented. The advantages of this approach, compared with direct eigenvalue computations for the discretized operator, are the efficient and accurate computation of selected parts of the spectrum (typically those near the imaginary axis) and the option to compute nonlinear travelling waves and selected eigenvalues or other stability indicators simultaneously in order to locate accurately the onset to instability. We also discuss the implementation and usage of this approach with the software package AUTO and provide example computations for the FitzHugh Nagumo and the complex Ginzburg Landau equation.

Rademacher, Jens D. M.; Sandstede, Björn; Scheel, Arnd

2007-05-01

473

Stereocontrol in Asymmetric ?-Lactam Syntheses from Imines and Cyanosuccinic Anhydrides.  

PubMed

Computations (SCS-MP2//B3LYP) reveal that the asymmetric synthesis of highly substituted ?-lactams with three stereogenic centers, including one quaternary center, proceeds through a Mannich reaction between the enol form of the anhydride and the E-imine, followed by a transannular acylation. This new mechanistic picture accounts for both the observed reactivity and stereoselectivity. CH-O and hydrogen bonding interactions in the Mannich step and torsional steering effects in the acylation step are responsible for stereocontrol. It is demonstrated that this new mechanistic picture applies to the related reactions of homophthalic anhydrides with imines and presents new vistas for the design of a new reaction to access complex molecular architectures. PMID:24070216

Pattawong, Ommidala; Tan, Darlene Q; Fettinger, James C; Shaw, Jared T; Cheong, Paul Ha-Yeon

2013-09-26

474

Contrast sensitivity in asymmetric glaucoma.  

PubMed

We measured central contrast sensitivity in both eyes of 27 patients with asymmetric glaucomatous visual field loss or optic disc cupping. In 15 patients contrast sensitivity was less in the eye that by perimetry or ophthalmoscopy was the more severely damaged. In 10 patients contrast sensitivity was the same in the two eyes. In two patients, it was impaired more in the eye with the normal visual field. However, the latter two patients had ophthalmoscopic evidence of optic nerve damage (disc hemorrhage or large cup) in the eye with the lower contrast sensitivity, even though the visual field was normal. Asymmetry of contrast sensitivity was not found in normal control subjects. These results suggest that glaucoma does alter central vision, even when visual acuity remains normal and visual field defects are far from fixation. Contrast sensitivity may be impaired by a different mechanism than that which leads to visual dield loss. Although the two types of visual dysfunction often occur together, some patients may have more severe impairment of central vision (as measured by contrast sensitivity testing) in one eye and more severe loss of peripheral vision (as measured by perimetry) in the other eye. PMID:6706474

Motolko, M A; Phelps, C D

1984-01-01

475

Fracture Recess: Asymmetric Continuum Approach  

NASA Astrophysics Data System (ADS)

This presentation is based on the Asymmetric Continuum Theory, which could be applied both for the solids, fluids and extreme motions: fractures, vortices, turbulence and shock waves. This theoretical approach is based on the papers concerning the solid and fluid continua (Teisseyre, 2009, publ. in "Bull. Seismol. Soc. Am." ; Teisseyre, 2010: publ. in "Acta Geophys."; Teisseyre, 2011, publ. in "Bull. Seismol. Soc. Am." and Teisseyre, 2012, publ. in "Acta Geophys."). These papers lead us also to the fracture processes situated in a kind of fracture recess, where the continuum might contain both solid and fluid elements. A similarity to the solid-fluid debris-flow models by Hutter and Schneider (2010, publ. in "Continuum Mech. Thermodyn.", parts 1,2) is underlined. In this approach the deformations and thus also strains are treated as the independent fields governed by the respective equations of motion. We derive such basic motion relations by an uniform approach; we extend our considerations to include also the extreme motions; a role of the release-rebound processes is underline. Our aim is to present a new attempt to describe the fracture processes which may appear inside a kind of fracture recess in a solid body; here such a recess is considered as a mixed continuum with both the solid and fluid phases.

Teisseyre, R.

2012-04-01

476

Optimal Farm Credit Pricing under Asymmetric Information.  

National Technical Information Service (NTIS)

Lenders cannot determine any farmer's exact ability at the time of loan initiation. The asymmetric information can prevent fully efficient loan pricing by lenders. The resulting losses can be mitigated by nonuniform loan pricing where Loan size is used as...

H. Lee R. G. Chambers

1988-01-01

477

Multispecies Decompression Model Using Asymmetrical Gas Kinetics.  

National Technical Information Service (NTIS)

This project developed and evaluated a new mathematical decompression model with asymmetrical gas kinetics. The intended application was to support U.S. Navy diving operations involving surface decompression with oxygen (02) following air diving (Sur-D 02...

K. A. Gault R. S. Lillo D. J. Temple P. K. Weathersby

2003-01-01

478

Guided modes in asymmetric graphene waveguides  

NASA Astrophysics Data System (ADS)

An asymmetric quantum well in graphene can act as a slab waveguide for electron waves in a manner analogous to the electromagnetic waves in dielectrics. Guided modes and the probability current density are analyzed in the graphene electron waveguide induced by asymmetric electrostatic potential. The modes in an asymmetric graphene waveguide include guided modes, "cover modes", "substrate modes" and "radiation modes". The conditions for a guided mode are quantified. It is found that the fundamental mode is absent when both the Klein tunneling and classical motion are present. The confinement of electrons for lower order mode is stronger than for higher order mode. We hope that these characteristics in asymmetric graphene waveguide can provide potential applications in graphene-based waveguide devices.

He, Ying; Xu, Yi; Yang, Yanfang; Huang, Weide

2013-08-01

479

The centrosome and asymmetric cell division  

PubMed Central

Asymmetric stem cell division is a mechanism widely employed by the cell to maintain tissue homeostasis, resulting in the production of one stem cell and one differentiating cell. However, asymmetric cell division is not limited to stem cells and is widely observed even in unicellular organisms as well as in cells that make up highly complex tissues. In asymmetric cell division, cells must organize their intracellular components along the axis of asymmetry (sometimes in the context of extracellular architecture). Recent studies have described cell asymmetry in many cell types and in many cases such asymmetry involves the centrosome (or spindle pole body in yeast) as the center of cytoskeleton organization. In this review, I summarize recent discoveries in cellular polarity that lead to an asymmetric outcome, with a focus on centrosome function.

2009-01-01

480

Asymmetric flow events in a VEER 1000.  

National Technical Information Service (NTIS)

This paper describes the simulation of asymmetric loss of flow events in Russian designed VVER-1000 reactors using the RETRAN-02 Mod4 computer code. VVER-1000 reactors have significant differences from United States pressurized water reactors including mu...

W. C. Horak R. J. Kennett W. Shier J. G. Guppy

1992-01-01

481

Suzuki-Miyaura approach to JNJ-26076713, an orally active tetrahydroquinoline-containing alphaVbeta3/alphaVbeta5 integrin antagonist. enantioselective synthesis and stereochemical studies.  

PubMed

An improved scale-up synthesis was required for the alpha(V)beta(3)/alpha(V)beta(5) integrin antagonist 1, which had demonstrated oral efficacy in eye disease models of angiogenesis and vascular permeability. A stereodefined, quinoline-substituted, unsaturated ester was conveniently prepared by a Suzuki-Miyaura coupling to facilitate exploration of multiple methods of asymmetric reduction. The catalytic chiral hydrogenation of the corresponding unsaturated acid (Z-5b) with a ruthenium-based metal precursor and the (R)-XylPhanePhos ligand proved particularly efficient and economical. The resulting (3S)-quinoline-containing intermediate was reduced to an equal mixture of tetrahydroquinoline diastereomers. The undesired diastereomer could be recycled to the desired one by an oxidation/reduction protocol. The absolute stereochemistry of 1 was established as 3S,3'S by a combination of X-ray diffraction and chemical means. PMID:1827