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1

Highly enantioselective bromocyclization of tryptamines and its application in the synthesis of (-)-chimonanthine.  

PubMed

A shorter path: A highly enantioselective bromocyclization of tryptamine has been developed using an anionic chiral phase-transfer catalyst. This method provides a direct approach for preparing chiral 3-bromopyrroloindoline from tryptamine, which enables a four-step enantioselective synthesis of (-)-chimonanthine. PG=protecting group. PMID:24123660

Xie, Weiqing; Jiang, Guangde; Liu, Huan; Hu, Jiadong; Pan, Xixian; Zhang, Hui; Wan, Xiaolong; Lai, Yisheng; Ma, Dawei

2013-12-01

2

Enantioselective cyclization of enamide-ynes and application to the synthesis of the kopsifoline core  

PubMed Central

We report the palladium-catalyzed enantioselective cyclization of 1,6-enamidynes to form spirocyclic ring systems. We applied this methodology to the concise synthesis of the skeletal core of the kopsifoline alkaloids. PMID:23772095

Corkey, Britton K.; Heller, Stephen T.; Wang, Yi-Ming

2013-01-01

3

Enantioselective total synthesis of (-)-laurenditerpenol.  

PubMed

A highly convergent total synthesis of (-)-laurenditerpenol has been accomplished through an organolithium to aldehyde nucleophilic addition. Preparation of the prerequisite key intermediates in optically pure form was based on an improved, short, and efficient synthesis of "wine lactone" from (S)-limonene and Corey's catalytic enantioselective Diels-Alder reaction of 2,5-dimethyl furan with diethyl fumarate. PMID:22905649

Pitsinos, Emmanuel N; Athinaios, Nikolaos; Vidali, Veroniki P

2012-09-01

4

Enantioselective Total Synthesis of (+)-Cassiol  

PubMed Central

An enantioselective total synthesis of (+)-cassiol is reported. The complex derived from Pd2(pmdba)3 and enantiopure t-BuPHOX ligand catalyzes enantioconvergent decarboxylative alkylation to generate the quaternary carbon stereocenter at an early stage. The overall synthetic strategy involves a convergent late-stage coupling of two fragments. The synthesis features a longest linear sequence of eight steps. PMID:19093836

Petrova, Krastina V.; Mohr, Justin T.; Stoltz, Brian M.

2009-01-01

5

Enantioselective Total Synthesis of (+)-Lithospermic Acid  

PubMed Central

An enantioselective synthesis of (+)-lithospermic acid, a potent anti-HIV agent, has been accomplished in a convergent manner in 9 steps. The synthesis features an enantioselective intramolecular oxa-Michael addition catalyzed by a quinidine derivative, a hypervalent iodine-mediated rearrangement of chromanone to dihydrobenzofuran, an enantioselective ?-oxyamination, and an intermolecular C-H olefination. PMID:22978790

Cheng, Xu; Zhou, Bing

2012-01-01

6

Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field  

NASA Astrophysics Data System (ADS)

Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine.

Xu, Yangyang; Yang, Guang; Xia, Hongyan; Zou, Gang; Zhang, Qijin; Gao, Jiangang

2014-09-01

7

Enantioselective Total Synthesis of (+)-Reserpine  

PubMed Central

A catalytic, enantioselective synthesis of (+)-reserpine is reported. The route features a highly diastereoselective, chiral catalyst-controlled formal aza-Diels–Alder reaction between a 6-methoxytryptamine-derived dihydro-?-carboline and an enantioenriched ?-substituted enone to form a key tetracyclic intermediate. This approach addresses the challenge of setting the C3 stereogenic center by using catalyst control. Elaboration of the tetracycle to (+)-reserpine includes an intramolecular aldol cyclization and a highly diastereoselective hydrogenation of a sterically hindered enoate. PMID:23331099

Rajapaksa, Naomi S.; McGowan, Meredeth A.; Rienzo, Matthew

2013-01-01

8

Enantioselective total synthesis of (+)-reserpine.  

PubMed

A catalytic, enantioselective synthesis of (+)-reserpine is reported. The route features a highly diastereoselective, chiral catalyst-controlled formal aza-Diels-Alder reaction between a 6-methoxytryptamine-derived dihydro-?-carboline and an enantioenriched ?-substituted enone to form a key tetracyclic intermediate. This approach addresses the challenge of setting the C3 stereogenic center by using catalyst control. Elaboration of the tetracycle to (+)-reserpine includes an intramolecular aldol cyclization and a highly diastereoselective hydrogenation of a sterically hindered enoate. PMID:23331099

Rajapaksa, Naomi S; McGowan, Meredeth A; Rienzo, Matthew; Jacobsen, Eric N

2013-02-01

9

Enantioselective C-C bond synthesis catalysed by enzymes.  

PubMed

The enantioselective synthesis of C-C bonds is often the pivotal step of a synthesis. Nature has made a variety of versatile enzymes available that catalyse this type of reaction very selectively under mild conditions. Cyanohydrins, acyloins (alpha-hydroxy ketones), alpha-hydroxy acids and aldols (beta-hydroxy ketones) are very efficiently synthesised enantioselectively with the aid of C-C bond forming enzymes, which we discuss in this tutorial review. In the case of the alpha-hydroxy acids the applications of nitrilases in a synthetic dkr even allows a disconnection that has no enantioselective chemical equivalent. PMID:16137165

Sukumaran, Joly; Hanefeld, Ulf

2005-06-01

10

Enantioselective Total Synthesis of (-)-Acylfulvene and (-)-Irofulven  

PubMed Central

We report our full account of the enantioselective total synthesis of (?)-acylfulvene (1) and (?)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor agents. We discuss (1) the application of an Evans’ Cu-catalyzed aldol addition reaction using a strained cyclopropyl ketenethioacetal, (2) an efficient enyne ring-closing metathesis (EYRCM) cascade reaction in a challenging setting, (3) the reagent IPNBSH for a late stage reductive allylic transposition reaction, and (4) the final RCM/dehydrogenation sequence for the formation of (?)-acylfulvene (1) and (?)-irofulven (2). PMID:19938810

Siegel, Dustin S.; Piizzi, Grazia; Piersanti, Giovanni; Movassaghi, Mohammad

2009-01-01

11

Enantioselective Total Synthesis of (?)-Acylfulvene and (?)- Irofulven  

E-print Network

We report our full account of the enantioselective total synthesis of (?)-acylfulvene (1) and (?)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor ...

Movassaghi, Mohammad

12

Enantioselective synthesis of endohedral metallofullerenes.  

PubMed

Endohedral metallofullerenes are promising materials in biomedical and material sciences. In particular, they are of interest as agents for magnetic resonance imaging (MRI), photovoltaic devices, and semimetallic components. The synthesis of chiral endofullerenes represents one step further in the potential use of these carbon allotropes; however, this step has not been addressed so far. In this regard, enantiopure endofullerenes are expected to open new avenues in fields in which chirality is a key issue. Here, the synthesis and characterization of the first chiral endohedral metallofullerenes, namely, chiral bis-adducts of La@C(72), are reported. Eight optically active isomers were obtained by enantioselective 1,3-dipolar cycloaddition of a N-metalated azomethine ylide onto a non-isolated-pentagon rule metallofullerene derivative, La@C(72)(C(6)H(3)Cl(2)), catalyzed by a copper chiral complex. The chiral bis-adducts of La@C(72), isolated by nonchiral HPLC, showed optical purities as high as 98% as revealed by the remarkable positive or negative Cotton effects observed in the circular dichroic spectra. PMID:21955273

Sawai, Koji; Takano, Yuta; Izquierdo, Marta; Filippone, Salvatore; Martín, Nazario; Slanina, Zdenek; Mizorogi, Naomi; Waelchli, Markus; Tsuchiya, Takahiro; Akasaka, Takeshi; Nagase, Shigeru

2011-11-01

13

Synthesis and Application of Polystyrene Nanospheres Supported Platinum Catalysts in Enantioselective Hydrogenations  

Microsoft Academic Search

\\u000a Abstract  Nearly monodisperse polystyrene nanospheres coated with platinum have been synthesized and applied successfully in the cinchona\\u000a alkaloid-modified enantioselective hydrogenation of ethyl pyruvate. During the catalyst preparation broadly varied experimental\\u000a conditions were used resulting in several catalysts with different properties. The effect of hydrogen pressure, solvent, modifier\\u000a and polystyrene nanoparticle size on the enantioselectivity was also studied. Based on the results

Béla Török; Aditya Kulkarni; Ryan DeSousa; Kalyani Satuluri; Marianna Török; G. K. Surya Prakash

14

Enantioselective formal synthesis of palmerolide A.  

PubMed

Enantioselective formal synthesis of macrolactone palmerolide A, a polyketide marine natural product, is described. Key strategies in the synthesis include the oxidative furan ring-opening of a chiral furyl carbinol for the installation of the 1,4-dienol core and a Jung nonaldol-aldol reaction for the dienamide core. PMID:21793548

Prasad, Kavirayani R; Pawar, Amit B

2011-08-19

15

Expedient Enantioselective Synthesis of Cermizine D  

PubMed Central

An efficient enantioselective synthesis of cermizine D has been developed that exploits the use of a common intermediate to access over 85% of the carbon backbone. Key steps include an organocatalyzed heteroatom Michael addition, a diastereoselective alkylation with ?-iodomethyl phenyl sulfide, a conjugate addition to a vinyl sulfone species and a sulfone coupling / desulfurization sequence to join the two major subunits. PMID:22372610

Veerasamy, Nagarathanam; Carlson, Erik C.; Carter, Rich G.

2012-01-01

16

A formal enantioselective total synthesis of FR901483.  

PubMed

A formal enantioselective total synthesis of the potent immunosuppressant FR901483 (1) has been accomplished. Our approach features the use of chiron 6 as the starting material, the application of the one-pot amide reductive bisalkylation method to construct the chiral aza-quaternary center (dr = 9:1), regio- and diastereoselective intramolecular aldol reaction to build the bridged ring, and ring closing metathesis to form the 3-pyrrolin-2-one ring. PMID:22937903

Huo, Hao-Hua; Zhang, Hong-Kui; Xia, Xiao-Er; Huang, Pei-Qiang

2012-09-21

17

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

2013-03-15

18

Scalable, enantioselective taxane total synthesis  

PubMed Central

Taxanes are a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel) — a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which possesses a suitable functional handle to access more oxidised members of its family. This route enabled a gram-scale preparation of the ”parent” taxane, taxadiene, representing the largest quantity of this naturally occurring terpene ever isolated or prepared in pure form. The taxane family’s characteristic 6-8-6 tricyclic system containing a bridgehead alkene is forged via a vicinal difunctionalisation/Diels–Alder strategy. Asymmetry is introduced by means of an enantioselective conjugate addition that forms an all-carbon quaternary centre, from which all other stereocentres are fixed via substrate control. This study lays a critical foundation for a planned access to minimally oxidised taxane analogs and a scalable laboratory preparation of Taxol itself. PMID:22169867

Mendoza, Abraham; Ishihara, Yoshihiro; Baran, Phil S.

2011-01-01

19

Enantioselective chemoenzymatic synthesis of trans-aziridines.  

PubMed

A straightforward, five-step procedure for the synthesis of enantiomerically pure 2,3-disubstituted trans-aziridines has been developed starting from commercially available aldehydes. Hydroxynitrile lyase-mediated cyanohydrin formation provided cyanohydrins in excellent enantioselectivities and good yields. Subsequent formation of diastereomerically pure anti-amino alcohols via a one-pot Grignard addition-reduction sequence, Cu(II)-catalyzed diazotransfer, and triphenylphosphine-mediated reductive cyclization provided the corresponding trans-aziridines in good yields and excellent diastereoselectivities. PMID:19743803

Ritzen, Bas; van Oers, Matthijs C M; van Delft, Floris L; Rutjes, Floris P J T

2009-10-01

20

Development of an Enantioselective Route towards the Lycopodium Alkaloids: Total Synthesis of Lycopodine  

PubMed Central

Synthesis of a C15-desmethyl tricycle core of lycopodine has been accomplished. Key steps in the synthetic sequence include organocatalytic, intramolecular Michael addition of a keto sulfone and a tandem 1,3-sulfonyl shift / Mannich cyclization to construct the tricyclic core ring system. Synthetic work towards this natural product family led to the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide – an organocatalyst which facilitiates enantioselective, intramolecular Michael additions. A detailed mechanistic discussion is provided for both the intramolecular Michael addition and the sulfone rearrangement. Finally, the application of these discoveries to the enantioselective total synthesis of alkaloid lycopodine is described. PMID:20586477

Yang, Hua; Carter, Rich G.

2010-01-01

21

Gold-catalyzed asymmetric allylic substitution of free alcohols: an enantioselective approach to chiral chromans with quaternary stereocenters for the synthesis of vitamin?e and analogues.  

PubMed

The enantioselective synthesis of ?- and ?-tocopherol (the most biologically active members of vitamin?E family) and analogues has been accomplished employing a new enantioselective gold catalyzed intramolecular allylic alkylation reaction followed by an olefin cross-metathesis as key steps. The methodology proved to be applicable to different olefins highlighting its potential for the synthesis of diverse libraries. PMID:25201099

Uria, Uxue; Vila, Carlos; Lin, Ming-Yuan; Rueping, Magnus

2014-10-20

22

Enantioselective synthesis of dityrosine and isodityrosine via asymmetric phase-transfer catalysis  

Microsoft Academic Search

Application of N-anthracenylmethyl cinchonidinium chloride quaternary ammonium phase-transfer catalysts to the enantio- and diastereoselective synthesis of dityrosine and isodityrosine is reported. Under liquid-liquid phase-transfer conditions the key ?-amino acid substituents are introduced with high enantioselectivity (?95%e.e.).

Barry Lygo

1999-01-01

23

Modular enantioselective synthesis of 8-aza-prostaglandin E1.  

PubMed

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-?-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based ?-amidalkylation protocol (dr = 6.8:1), with the chiral pre-?-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents. PMID:23957245

Wang, Xiao-Gang; Wang, Ai-E; Hao, Yi; Ruan, Yuan-Ping; Huang, Pei-Qiang

2013-09-20

24

Enantioselective synthesis of (+)-isolysergol via ring-closing metathesis.  

PubMed

The first enantioselective synthesis of (+)-isolysergol was completed in 12 steps from commercially available materials by a novel approach that features a late stage microwave-mediated, diastereomeric ring-closing metathesis catalyzed by a chiral molybdenum catalyst to simultaneously form the D ring and set the stereocenter at C(8). PMID:20462232

Deck, Jason A; Martin, Stephen F

2010-06-01

25

Enantioselective Synthesis of (+)-Isolysergol via Ring Closing Metathesis  

PubMed Central

The first enantioselective synthesis of (+)–isolysergol was completed in 12 steps from commercially available materials by a novel approach that features a late stage microwave-mediated, diastereomeric ring closing metathesis catalyzed by a chiral molybdenum catalyst to simultaneously form the D ring and set the stereocenter at C(8). PMID:20462232

Deck, Jason A.; Martin, Stephen F.

2010-01-01

26

Enantioselective total synthesis of (-)-blennolide?A.  

PubMed

Blennolide?A can be synthesized through an enantioselective domino-Wacker/carbonylation/methoxylation reaction of 7a with 96?% ee and an enantioselective Wacker oxidation of 7b with 89?% ee. Further transformations led to the ?,?-unsaturated ester (E)-17, which was subjected to a highly selective Michael addition, introducing a methyl group to give 18a. After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (-)-blennolide?A (ent-1) in a few steps. PMID:23649592

Tietze, Lutz F; Ma, Ling; Reiner, Johannes R; Jackenkroll, Stefan; Heidemann, Sven

2013-06-24

27

Enantioselective Total Synthesis of Avarol and Avarone.  

PubMed

Formation of the C11-C1' bond through application of Barton's radical decarboxylation and quinone addition is the cornerstone of a new convergent and concise synthesis of the marine metabolites avarol (1) and avarone (2; see scheme), for which antimitotic, antileukemic, and antiviral effects have been reported. PMID:10540432

Ling; Xiang; Theodorakis

1999-10-18

28

Enantioselective synthesis of primary 1-(aryl)alkylamines by nucleophilic 1,2-addition of organolithium reagents to hydroxyoxime ethers and application to asymmetric synthesis of G-protein-coupled receptor ligands.  

PubMed

(E)-Arylaldehyde oxime ethers bearing a (1S)-2-hydroxy-1-phenylethyl or (2R)-1-hydroxy-2-phenylethyl group as a chiral auxiliary, both derived from a single precursor, methyl (R)-mandelate, underwent nucleophilic addition with organolithium reagents via six-membered chelates to give the diastereomerically enriched (R)- and (S)-adducts, respectively, which, after chiral auxiliary removal by reductive N-O bond cleavage, led to the corresponding (R)- and (S)-1-(aryl)ethylamines. This organolithium addition protocol using methyllithium was applied in an enantiodivergent fashion to the preparation of both enantiomers of 1-(2-hydroxyphenyl)ethylamine, which has been previously used as an efficient chiral auxiliary for the synthesis of natural products in this laboratory. The synthetic utility of this methodology involving diastereoselective methyl addition was demonstrated by further application to the asymmetric synthesis of a new type of calcium receptor agonist (calcimimetics), (R)-(+)-NPS R-568 and its thio analogue. Furthermore, diastereoselective vinylation was accomplished by application of the hydroxy oxime ether-based protocol using vinyllithium, which allowed the development of the enantioselective synthesis of the NK-1 receptor antagonists, (+)-CP-99,994 and (+)-CP-122,721. PMID:15307728

Atobe, Masakazu; Yamazaki, Naoki; Kibayashi, Chihiro

2004-08-20

29

A broadly applicable NHC-Cu-catalyzed approach for efficient, site-, and enantioselective coupling of readily accessible (pinacolato)alkenylboron compounds to allylic phosphates and applications to natural product synthesis.  

PubMed

A set of protocols for catalytic enantioselective allylic substitution (EAS) reactions that allow for additions of alkenyl units to readily accessible allylic electrophiles is disclosed. Transformations afford 1,4-dienes that contain a tertiary carbon stereogenic site and are promoted by 1.0-5.0 mol % of a copper complex of an N-heterocyclic carbene (NHC). Aryl- as well as alkyl-substituted electrophiles bearing a di- or trisubstituted alkene may be employed. Reactions can involve a variety of robust alkenyl-(pinacolatoboron) [alkenyl-B(pin)] compounds that can be either purchased or prepared by various efficient, site-, and/or stereoselective catalytic reactions, such as cross-metathesis or proto-boryl additions to terminal alkynes. Vinyl-, E-, or Z-disubstituted alkenyl-, 1,1-disubstituted alkenyl-, acyclic, or heterocyclic trisubstituted alkenyl groups may be added in up to >98% yield, >98:2 SN2':SN2, and 99:1 enantiomeric ratio (er). NHC-Cu-catalyzed EAS with alkenyl-B(pin) reagents containing a conjugated carboxylic ester or aldehyde group proceed to provide the desired 1,4-diene products in good yield and with high enantioselectivity despite the presence of a sensitive stereogenic tertiary carbon center that could be considered prone to epimerization. In most instances, the alternative approach of utilizing an alkenylmetal reagent (e.g., an Al-based species) represents an incompatible option. The utility of the approach is illustrated through applications to enantioselective synthesis of natural products such as santolina alcohol, semburin, nyasol, heliespirone A, and heliannuol E. PMID:24467274

Gao, Fang; Carr, James L; Hoveyda, Amir H

2014-02-01

30

Perylenequinone Natural Products: Enantioselective Synthesis of the Oxidized Pentacyclic Core‡  

PubMed Central

An enantioselective approach to the perylenequinone core found in the mold perylenequinone natural products is outlined. Specifically, the first asymmetric syntheses of helical chiral perylenequinones absent any additional stereogenic centers are described. Key elements of the synthetic venture include a catalytic enantioselective biaryl coupling, a PIFA-induced naphthalene hydroxylation, and a palladium-mediated aromatic decarboxylation. Transfer of the binaphthalene axial stereochemistry to the perylenequinone helical stereochemistry proceeded with good fidelity. Furthermore, the resultant perylenequinones were shown to possess sufficient atropisomeric stability to be viable intermediates in the biogenesis of the perylenequinone natural products. This stability supports the use of the helical axis as a stereochemical relay in synthesis of the natural products containing additional stereochemical centers. PMID:19894746

Mulrooney, Carol A.; Morgan, Barbara J.; Li, Xiaolin; Kozlowski, Marisa C.

2009-01-01

31

Practical enantioselective synthesis of lamivudine (3TC ™) via a dynamic kinetic resolution  

Microsoft Academic Search

A practical enantioselective synthesis of lamivudine 1 is described. A highly effective dynamic kinetic resolution of the 5-hydroxyoxathiolane, followed by chlorination and introduction of cytosine provides an efficient synthesis of lamivudine.

Michael D. Goodyear; Malcolm L. Hill; Jono P. West; Andrew J. Whitehead

2005-01-01

32

Scalable enantioselective total synthesis of taxanes  

NASA Astrophysics Data System (ADS)

Taxanes form a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel), a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which has a suitable functional handle with which to access more oxidized members of its family. This route enables a gram-scale preparation of the ‘parent’ taxane—taxadiene—which is the largest quantity of this naturally occurring terpene ever isolated or prepared in pure form. The characteristic 6-8-6 tricyclic system of the taxane family, containing a bridgehead alkene, is forged via a vicinal difunctionalization/Diels-Alder strategy. Asymmetry is introduced by means of an enantioselective conjugate addition that forms an all-carbon quaternary centre, from which all other stereocentres are fixed through substrate control. This study lays a critical foundation for a planned access to minimally oxidized taxane analogues and a scalable laboratory preparation of Taxol itself.

Mendoza, Abraham; Ishihara, Yoshihiro; Baran, Phil S.

2012-01-01

33

Enantioselective Synthesis and Profiling of Two Novel Diazabicyclooctanone ?-Lactamase Inhibitors.  

PubMed

The enantioselective synthesis of two novel cyclopropane-fused diazabicyclooctanones is reported here. Starting from butadiene monoxide, the key enone intermediate 7 was prepared in six steps. Subsequent stereoselective introduction of the cyclopropane group and further transformation led to compounds 1a and 1b as their corresponding sodium salt. The great disparity regarding their hydrolytic stability was rationalized by the steric interaction between the cyclopropyl methylene and urea carbonyl. These two novel ?-lactamase inhibitors were active against class A, C, and D enzymes. PMID:25313328

Xiong, Hui; Chen, Brendan; Durand-Réville, Thomas F; Joubran, Camil; Alelyunas, Yun W; Wu, Dedong; Huynh, Hoan

2014-10-01

34

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis of Solanapyrone D  

E-print Network

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis the development of enantioselective catalytic variants of the Diels-Alder reaction.1 During this time, remarkable levels of enantiocontrol in the intramolecular Diels-Alder (IMDA) reaction,2,3 a notable deficiency

MacMillan, David W. C.

35

An Organocatalyzed enantioselective synthesis of (2S,3R,4S)-4-hydroxyisoleucine and its stereoisomers.  

PubMed

A concise enantioselective total synthesis of (2S,3R,4S)-4-hydroxyisoleucine and its stereoisomers is described. A key feature of this protocol is a catalytic enantioselective mannich reaction that is either anti- or syn-selective as genesis of chirality. PMID:20307090

Kumaraswamy, Gullapalli; Jayaprakash, Neerasa; Sridhar, Balasubramanian

2010-04-16

36

Total Synthesis of (S)-(+)-Tylophorine Via Enantioselective Intramolecular Alkene Carboamination  

PubMed Central

The enantioselective synthesis of (S)-(+)-tylophorine, a potent cancer cell growth inhibitor, has been accomplished in eight steps from commercially available 3,4-dimethoxybenzyl alcohol. A copper (II)-catalyzed enantioselective intramolecular alkene carboamination was employed as the key step to construct the chiral indolizidine ring. PMID:18588345

Zeng, Wei; Chemler, Sherry R.

2009-01-01

37

Enantioselective total synthesis of marine diterpenoid clavulactone.  

PubMed

The key steps in the synthesis of clavulactone are formation of an enantiopure cyclopentane precursor by epoxide rearrangement and intramolecular carbonyl-ene reaction, construction of the 3,4-dihydro-2H-pyran ring by intermolecular hetero-Diels-Alder reaction, closure of the eleven-membered ring, and finally generation of the lactone functionality by chemoselective allylic C(sp(3))-H oxidation. PMID:22644725

Yang, Zhen-Yu; Liao, Hong-Ze; Sheng, Kang; Chen, Yong-Fei; Yao, Zhu-Jun

2012-06-25

38

Enantioselective synthesis of a chiral nitrogen-doped buckybowl.  

PubMed

Bowl-shaped aromatic compounds, namely buckybowls constitute a family of curved polycyclic aromatic carbons along with fullerenes and carbon nanotubes. Doping of heteroatoms to the carbon frameworks of such aromatic compounds drastically modulates their physical and chemical properties. In contrast to nitrogen-doped azafullerenes or carbon nanotubes, synthesis of azabuckybowls, nitrogen-doped buckybowls, remains an unsolved challenging task. Here we report the first enantioselective synthesis of a chiral azabuckybowl, triazasumanene. X-ray crystallographic analysis confirmed that the doping of nitrogen induces a more curved and deeper bowl structure than in all-carbon buckybowls. As a result of the deeper bowl structure, the activation energy for the bowl inversion (thermal flipping of the bowl structure) reaches an extraordinarily high value (42.2?kcal per mol). As the bowl inversion corresponds to the racemization process for chiral buckybowls, this high bowl inversion energy leads to very stable chirality of triazasumanene. PMID:22692534

Tan, Qitao; Higashibayashi, Shuhei; Karanjit, Sangita; Sakurai, Hidehiro

2012-01-01

39

Enantioselective total synthesis of (+)-galbulin via organocatalytic domino Michael-Michael-aldol condensation.  

PubMed

A concise and practical enantioselective synthesis of (+)-galbulin has been achieved using organocatalytic domino Michael-Michael-aldol condensation and organocatalytic kinetic resolution as the key steps. PMID:22179766

Hong, Bor-Cherng; Hsu, Che-Sheng; Lee, Gene-Hsiang

2012-02-28

40

Enantioselective synthesis of a hydroxymethyl-cis-1,3-cyclopentenediol building block.  

PubMed

A brief, enantioselective synthesis of a hydroxymethyl-cis-1,3-cyclopentenediol building block is presented. This scaffold allows access to the cis-1,3-cyclopentanediol fragments found in a variety of biologically active natural and non-natural products. This rapid and efficient synthesis is highlighted by the utilization of the palladium-catalyzed enantioselective allylic alkylation of dioxanone substrates to prepare tertiary alcohols. PMID:23101616

Craig, Robert A; Roizen, Jennifer L; Smith, Russell C; Jones, Amanda C; Stoltz, Brian M

2012-11-16

41

Enantioselective Synthesis of a Hydroxymethyl-cis-1,3-cyclopentenediol Building Block  

PubMed Central

A brief, enantioselective synthesis of a hydroxymethyl-cis-1,3-cyclopentenediol building block is presented. This scaffold allows access to the cis-1,3-cyclopentanediol fragments found in a variety of biologically active natural and non-natural products. This rapid and efficient synthesis is highlighted by the utilization of the palladium-catalyzed enantioselective allylic alkylation of dioxanone substrates to prepare tertiary alcohols. PMID:23101616

Craig, Robert A.; Roizen, Jennifer L.; Smith, Russell C.; Jones, Amanda C.

2012-01-01

42

Enantioselective synthesis of ?-/?-alkoxy-?-hydroxy-?-alkyl-substituted Weinreb amides via DKR-ATH: application to the synthesis of advanced intermediate of (-)-brevisamide.  

PubMed

A method of preparing stereodefined ?-/?-alkoxy-?-hydroxy-?-alkyl-substituted Weinreb amides containing two successive hydroxyl-alkyl stereocenters has been developed. Further, this strategy coupled with organo-catalyzed asymmetric epoxidation culminates in the synthesis of a critical intermediate of (-)-brevisamide and its diastereomers. PMID:23994971

Kumaraswamy, Gullapalli; Narayana Murthy, Akula; Narayanarao, Vykunthapu; Vemulapalli, Sahithya Phani Babu; Bharatam, Jagadeesh

2013-10-21

43

Synthesis of Poly(Ethylene Glycol)–Supported (R)-BINOL Derivatives and Their First Application in Enantioselective Mukaiyama Aldol Reactions  

Microsoft Academic Search

The Mukaiyama aldol reaction of 2-styryl-oxazole-4-carbaldehyde (1) as model substrate with S-ketene silyl acetal 2 catalyzed by poly(ethylene glycol)-supported binaphthyl-derived chiral titanium(IV) complexes afforded the corresponding aldol product in good to excellent yields and enantioselectivities up to 94% ee. The chemical yields and\\/or the enantioselectivities are enhanced by generating the active catalyst from Ti(OiPr)4, polymer-supported ligands (R)-6 or (R)-8, and

Reinhold Zimmer; Vjekoslav Dekaris; Markus Knauer; Luise Schefzig; Hans-Ulrich Reissig

2009-01-01

44

Iterative direct aldol strategy for polypropionates: enantioselective total synthesis of (-)-membrenone a and B.  

PubMed

An iterative direct aldol reaction using a C3 propionate unit as an aldol donor offers expeditious access to polyketide assembly in a highly diastereo- and enantioselective manner. An all-syn polyketide array with four consecutive stereogenic centers was efficiently constructed by an aldol reaction of thiopropionamide via soft Lewis acid/hard Brønsted base cooperative catalysis. This iterative aldol strategy led to an enantioselective synthesis of (-)-membrenone A and B. PMID:25259628

Alagiri, Kaliyamoorthy; Lin, Shaoquan; Kumagai, Naoya; Shibasaki, Masakatsu

2014-10-17

45

An Intramolecular Diels-Alder Approach to the Eunicelins: Enantioselective Total Synthesis of Ophirin B  

E-print Network

An Intramolecular Diels-Alder Approach to the Eunicelins: Enantioselective Total Synthesis intramolecular Diels- Alder cycloaddition of tetraene 3. We report here the successful implementation ophirin B. Our strategy (Scheme 1) for the synthesis of the Diels-Alder substrate 3 was predicated on our

46

Concise and enantioselective total synthesis of 15-deoxy-?-(12,14)-prostaglandin J(2).  

PubMed

The concise and enantioselective synthesis of 15-deoxy-?(12,14)-prostaglandin J(2) (15d-PGJ(2)) has been accomplished in 11 steps from a known alcohol. The key step of the synthesis involves an asymmetric Rh-catalyzed cycloisomerization of ene-ynone, followed by an olefin isomerization. PMID:20929274

Kim, Nam-Jung; Moon, Hyunyoung; Park, Taesun; Yun, Hwayoung; Jung, Jong-Wha; Chang, Dong-Jo; Kim, Dae-Duk; Suh, Young-Ger

2010-11-01

47

Enantioselective synthesis of (R)-bufuralol via dynamic kinetic resolution in the key step.  

PubMed

An enantioselective synthesis of (R)-bufuralol via a ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR) has been achieved. The synthesis starts from readily available 2-ethylphenol and provides (R)-bufuralol in high ee and a good overall yield of 31%. PMID:20524620

Johnston, Eric V; Bogár, Krisztián; Bäckvall, Jan-E

2010-07-01

48

N-Heterocyclic carbene-catalyzed enantioselective synthesis of functionalized cyclopentenes via ?,?-unsaturated acyl azoliums.  

PubMed

Highly enantioselective NHC-organocatalyzed synthesis of functionalized cyclopentenes proceeding via ?,?-unsaturated acyl azolium intermediates is reported. The organocascade reaction of modified enals with malonic ester derivatives having a ?-benzoyl group involves the Michael-intramolecular aldol-?-lactonization-decarboxylation sequence to deliver cyclopentenes in good yields and excellent ee values. PMID:25307503

Mondal, Santigopal; Yetra, Santhivardhana Reddy; Patra, Atanu; Kunte, Sunita S; Gonnade, Rajesh G; Biju, Akkattu T

2014-10-28

49

Concise enantioselective synthesis of duloxetine via direct catalytic asymmetric aldol reaction of thioamide.  

PubMed

Direct catalytic asymmetric aldol reaction of thioamide offers a new entry to the concise enantioselective synthesis of duloxetine. The direct aldol protocol was scalable (>20 g) to afford the aldol product in 92% ee after LiAlH(4) reduction, and 84% of the chiral ligand was recovered after recrystallization. The following four steps of transformation delivered duloxetine. PMID:22494391

Suzuki, Yuta; Iwata, Mitsutaka; Yazaki, Ryo; Kumagai, Naoya; Shibasaki, Masakatsu

2012-05-01

50

Enantioselective synthesis of Janus kinase inhibitor INCB018424 via an organocatalytic aza-Michael reaction.  

PubMed

An enantioselective synthesis of INCB018424 via organocatalytic asymmetric aza-Michael addition of pyrazoles (16 or 20) to (E)-3-cyclopentylacrylaldehyde (23) using diarylprolinol silyl ether as the catalyst was developed. Michael adducts (R)-24 and (R)-27 were isolated in good yield and high ee and were readily converted to INCB018424. PMID:19385672

Lin, Qiyan; Meloni, David; Pan, Yongchun; Xia, Michael; Rodgers, James; Shepard, Stacey; Li, Mei; Galya, Laurine; Metcalf, Brian; Yue, Tai-Yuen; Liu, Pingli; Zhou, Jiacheng

2009-05-01

51

Toward the Synthesis of Cobyric Acid. Enantioselective Syntheses of Completely Differentiated Ring D Synthons  

PubMed Central

Alkyne acids 11 were prepared in an enantioselective fashion from allylic ester derivatives 18 or 20 by Ireland-Claisen rearrangement, followed by Si-assisted elimination of HBr. The title compounds are attractive ring D synthons for an ongoing synthesis of cobyric acid. PMID:18537250

Wang, Hui; Tassa, Carlos; Jacobi, Peter A.

2008-01-01

52

Pd-catalyzed enantioselective C-H iodination: asymmetric synthesis of chiral diarylmethylamines.  

PubMed

An enantioselective C-H iodination reaction using a mono-N-benzoyl-protected amino acid has been developed for the synthesis of chiral diarylmethylamines. The reaction uses iodine as the sole oxidant and proceeds at ambient temperature and under air. PMID:24151991

Chu, Ling; Wang, Xiao-Chen; Moore, Curtis E; Rheingold, Arnold L; Yu, Jin-Quan

2013-11-01

53

Catalytic amide allylation of ?-ketoesters: extremely high enantioselective synthesis of ester functionalised ?-methylene-?-butyrolactones.  

PubMed

This communication reports a significant breakthrough on the novel catalytic amide allylation to the acyclic ?-ketoester systems, achieving satisfactorily high yields and extremely high levels of the asymmetric induction to allow for highly enantioselective synthesis of ester functionalised ?-methylene-?-butyrolactones. PMID:25167094

Takahashi, Masaki; Murata, Yusuke; Ishida, Masahiro; Yagishita, Fumitoshi; Sakamoto, Masami; Sengoku, Tetsuya; Yoda, Hidemi

2014-10-21

54

Oxazoline-based organocatalyst for enantioselective strecker reactions: a protocol for the synthesis of levamisole.  

PubMed

A chiral oxazoline-based organocatalyst has been found to efficiently catalyze asymmetric Strecker reactions of various aromatic and aliphatic N-benzhydrylimines with trimethylsilyl cyanide (TMSCN) as a cyanide source at -20?°C to give ?-aminonitriles in high yield (96?%) with excellent chiral induction (up to 98?%?ee). DFT calculations have been performed to rationalize the enantioselective formation of the product with the organocatalyst in these reactions. The organocatalyst has been characterized by single-crystal X-ray diffraction analysis, as well as by other analytical methods. This protocol has been extended to the synthesis of the pharmaceutically important drug molecule levamisole in high yield and with high enantioselectivity. PMID:24009109

Sadhukhan, Arghya; Sahu, Debashis; Ganguly, Bishwajit; Khan, Noor-ul H; Kureshy, Rukhsana I; Abdi, Sayed H R; Suresh, E; Bajaj, Hari C

2013-10-11

55

Highly enantioselective synthesis of chiral cyclic amino alcohols and conhydrine by ruthenium-catalyzed asymmetric hydrogenation.  

PubMed

A highly efficient enantio- and diastereoselective synthesis of chiral cis-beta-N-alkyl/arylamino cyclic alcohols has been realized by asymmetric hydrogenation of racemic alpha-amino cyclic ketones via DKR catalyzed by [RuCl(2)((S)-Xyl-SDP)((R,R)-DPEN)]. The enantioselectivities of the reaction were up to 99.9% ee with 99:1 cis-selectivities. A practical catalytic asymmetric synthesis of all four isomers of conhydrine was also developed. PMID:19788265

Liu, Sheng; Xie, Jian-Hua; Li, Wei; Kong, Wei-Ling; Wang, Li-Xin; Zhou, Qi-Lin

2009-11-01

56

Hybrid gold/chiral Brønsted acid relay catalysis allows an enantioselective synthesis of (-)-5-epi-eupomatilone-6.  

PubMed

An enantioselective synthesis of (-)-5-epi-eupomatilone-6 has been accomplished by using relay catalytic cascade intramolecular hydrosiloxylation and Mukaiyama aldol reaction of 2,3,4-trimethoxy-6-(phenylethynyl)phenyl dimethylsilanol with fluorenylglyoxylate. PMID:24328038

Wu, Xiang; Li, Ming-Li; Wang, Pu-sheng

2014-01-01

57

Organocatalytic High Enantioselective Synthesis of ?-Formyl-?-hydroxyphosphonates.  

PubMed

The cross aldol reaction between enolizable aldehydes and ?-ketophosphonates was achieved for the first time by using 9-amino-9-deoxy-epi-quinine as the catalyst. ?-Formyl-?-hydroxyphosphonates were obtained in high to excellent enantioselectivities. The reaction works especially well with acetaldehyde, which is a tough substrate for organocatalyzed cross aldol reactions. The products were demonstrated to have anticancer activities. PMID:21918646

Perera, Sandun; Naganaboina, Vijaya Kumar; Wang, Long; Zhang, Bin; Guo, Qunsheng; Rout, Laxmidhar; Zhao, Cong-Gui

2011-06-30

58

Synthetic Studies on Norrisolide: Enantioselective Synthesis of the  

E-print Network

), efficient, and enantioselective. Norrisolide (1) is a marine natural product, initially isolated by Faulkner be attributed to their initially reported poor antimicrobial activity.2b Recent studies, however, have indicated Among the few natural products known to affect the Golgi organization, 1 distinguishes itself as being

Theodorakis, Emmanuel

59

Engineering an enantioselective amine oxidase for the synthesis of pharmaceutical building blocks and alkaloid natural products.  

PubMed

The development of cost-effective and sustainable catalytic methods for the production of enantiomerically pure chiral amines is a key challenge facing the pharmaceutical and fine chemical industries. This challenge is highlighted by the estimate that 40-45% of drug candidates contain a chiral amine, fueling a demand for broadly applicable synthetic methods that deliver target structures in high yield and enantiomeric excess. Herein we describe the development and application of a "toolbox" of monoamine oxidase variants from Aspergillus niger (MAO-N) which display remarkable substrate scope and tolerance for sterically demanding motifs, including a new variant, which exhibits high activity and enantioselectivity toward substrates containing the aminodiphenylmethane (benzhydrylamine) template. By combining rational structure-guided engineering with high-throughput screening, it has been possible to expand the substrate scope of MAO-N to accommodate amine substrates containing bulky aryl substituents. These engineered MAO-N biocatalysts have been applied in deracemization reactions for the efficient asymmetric synthesis of the generic active pharmaceutical ingredients Solifenacin and Levocetirizine as well as the natural products (R)-coniine, (R)-eleagnine, and (R)-leptaflorine. We also report a novel MAO-N mediated asymmetric oxidative Pictet-Spengler approach to the synthesis of (R)-harmicine. PMID:23808566

Ghislieri, Diego; Green, Anthony P; Pontini, Marta; Willies, Simon C; Rowles, Ian; Frank, Annika; Grogan, Gideon; Turner, Nicholas J

2013-07-24

60

Enantioselective synthesis of 2-methyl indolines by palladium catalysed asymmetric C(sp3)-H activation/cyclisation.  

PubMed

The first example of the enantioselective methyl C-H activation by an intramolecular ArPdX species and subsequent cyclisation was developed. Palladium catalysts using commercially available chiral diphosphines yield good ee's (up to 93% ee) in the synthesis of 2-methyl indolines from 2-halo N-isopropyl anilides. This approach was also employed for the synthesis of enantioenriched cyclohexyl fused indolines with moderate enantioselectivities. PMID:21927738

Anas, Saithalavi; Cordi, Alex; Kagan, Henri B

2011-11-01

61

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

E-print Network

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

Lee, Elaine C

2007-01-01

62

Enantioselective synthesis of ?-aryloxycarboxylic esters via asymmetric hydrogenation of ?-aryloxy-?,?-unsaturated esters.  

PubMed

A novel synthesis of ?-aryloxycarboxylic esters via asymmetric hydrogenation of the corresponding ?-aryloxy-?,?-unsaturated esters has been demonstrated. Bis(norbornadiene)rhodium(I) tetrafluoroborate (1 mol %) and Walphos W008-1 were used to generate the saturated products with high enantioselectivity and in high yield. The tolerability of the reaction to a diverse range of substituents on the aromatic ring was also explored. PMID:23072596

Stewart, Gavin W; Shevlin, Michael; Yamagata, Adam D Gammack; Gibson, Andrew W; Keen, Stephen P; Scott, Jeremy P

2012-11-01

63

Enantioselective synthesis of vicinal halohydrins via dynamic kinetic resolution.  

PubMed

[reaction: see text] Expanding the scope of enantioselective catalysis via DKR, transfer hydrogenation of a variety of cyclic alpha-halo ketones was accomplished using the Noyori/Ikariya (R,R)- or (S,S)-I catalysts and either HCO(2)H/Et(3)N or HCO(2)Na/n-Bu(4)NBr in H(2)O/CH(2)Cl(2) as the hydrogen sources. Good yields of vicinal bromo-, chloro-, and fluorohydrins with excellent de and ee levels were achieved in most cases after a simple tuning of reaction conditions. PMID:16381584

Ros, Abel; Magriz, Antonio; Dietrich, Hansjörg; Fernández, Rosario; Alvarez, Eleuterio; Lassaletta, José M

2006-01-01

64

Enantioselective total syntheses of acylfulvene, irofulven, and the agelastatins  

E-print Network

I. Enantioselective Total Synthesis of (-)-Acylfulvene, and (-)-Irofulven We report the enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven, which features metathesis reactions for the rapid assembly of ...

Siegel, Dustin S. (Dustin Scott), 1980-

2010-01-01

65

Enantioselective chemoenzymatic synthesis of cis- and trans-2,5-disubstituted morpholines.  

PubMed

A versatile synthesis of enantiomerically pure cis- and trans-2,5-disubstituted morpholines is described. Hydroxynitrile lyase-mediated cyanide addition onto aldehydes provided cyanohydrins in virtually quantitative yield and excellent enantioselectivity. Subsequent formation of diastereomerically pure amino esters via a three-step, one-pot reduction-transimination-reduction sequence followed by reduction and simultaneous protection provided cyclization precursors. Finally, cyclization and SmI(2)-mediated reductive detosylation completed the synthesis of cis- and trans-2,5-disubstituted morpholines in good yields and excellent diastereoselectivities. PMID:20384361

Ritzen, Bas; Hoekman, Steven; Verdasco, Elena Durán; van Delft, Floris L; Rutjes, Floris P J T

2010-05-21

66

Catalytic, Enantioselective Alkylation of r-Imino Esters: The Synthesis of Nonnatural r-Amino Acid Derivatives  

E-print Network

Catalytic, Enantioselective Alkylation of r-Imino Esters: The Synthesis of Nonnatural r-Amino Acid, 2001 Abstract: Methodology for the practical synthesis of nonnatural amino acids has been developed (up to 25:1/anti:syn), are protected nonnatural amino acids that represent potential precursors

Lectka, Thomas

67

Facile entry to an efficient and practical enantioselective synthesis of a polycyclic cholesteryl ester transfer protein inhibitor.  

PubMed

An efficient enantioselective synthesis of the chiral polycyclic cholesteryl ester transfer protein (CETP) inhibitor 1 has been developed. The synthesis was rendered practical for large scale via the development of a modified Hantzsch-type reaction to prepare the sterically hindered pyridine ring, enantioselective hydrogenation of hindered ketone 6 utilizing novel BIBOP-amino-pyridine derived Ru complex, efficient ICl promoted lactone formation, and a BF3 mediated hydrogenation process for diastereoselective lactol reduction. This efficient route was successfully scaled to produce multikilogram quantities of challenging CETP drug candidate 1. PMID:25084526

Han, Zhengxu S; Xu, Yibo; Fandrick, Daniel R; Rodriguez, Sonia; Li, Zhibin; Qu, Bo; Gonnella, Nina C; Sanyal, Sanjit; Reeves, Jonathan T; Ma, Shengli; Grinberg, Nelu; Haddad, Nizar; Krishnamurthy, Dhileep; Song, Jinhua J; Yee, Nathan K; Pfrengle, Waldemar; Ostermeier, Markus; Schnaubelt, Jürgen; Leuter, Zeno; Steigmiller, Sonja; Däubler, Jürgen; Stehle, Emanuel; Neumann, Lukas; Trieselmann, Thomas; Tielmann, Patrick; Buba, Annette; Hamm, Rainer; Koch, Gunter; Renner, Svenja; Dehli, Juan R; Schmelcher, Florian; Stange, Christian; Mack, Jürgen; Soyka, Rainer; Senanayake, Chris H

2014-08-15

68

Enantioselective total Synthesis of the agelastatin and trigonoliimine alkaloids  

E-print Network

I. Total Synthesis of the (-)-Agelastatin Alkaloids The pyrrole-imidazole family of marine alkaloids, derived from linear clathrodin-like precursors, constitutes a diverse array of structurally complex natural products. ...

Han, Sunkyu, 1982-

2012-01-01

69

Enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates via boron-mediated asymmetric aldol reaction.  

PubMed

A reagent-controlled, diastereo- and enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates has been achieved by the proper choice of solvent, temperature, alkoxy group, and amine for the diisopinocampheylboron-mediated asymmetric enolization-aldolization of phenylacetates. The pure diastereomers can be readily separated by column chromatography. PMID:23478288

Ramachandran, P Veeraraghavan; Chanda, Prem B

2013-04-18

70

Enantioselective synthesis of [9]- and [11]helicene-like molecules: double intramolecular [2+2+2] cycloaddition.  

PubMed

The enantioselective synthesis of completely ortho-fused [9]- and [11]helicene-like molecules has been achieved through a rhodium-mediated, intramolecular, double [2+2+2] cycloaddition of phenol- or 2-naphthol-linked hexaynes. Crystal structures and photophysical properties of these [9]- and [11]helicene-like molecules have also been disclosed. PMID:24964873

Kimura, Yuki; Fukawa, Naohiro; Miyauchi, Yuta; Noguchi, Keiichi; Tanaka, Ken

2014-08-01

71

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

PubMed

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

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

2005-06-15

72

Enantioselective synthesis of a chiral coordination polymer with circularly polarized visible laser.  

PubMed

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL-responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL-induced enantioselective synthesis. By irradiation with either left-handed or right-handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left-handed CPL resulted in crystals with a left-handed helical structure, and right-handed CPL led to crystals with a right-handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers. PMID:25251289

Wu, Shu-Ting; Cai, Zhen-Wen; Ye, Qiao-Yan; Weng, Chen-Hao; Huang, Xi-He; Hu, Xiao-Lin; Huang, Chang-Cang; Zhuang, Nai-Feng

2014-11-17

73

Developing novel organocatalyzed aldol reactions for the enantioselective synthesis of biologically active molecules.  

PubMed

Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered. PMID:21918584

Bhanushali, Mayur; Zhao, Cong-Gui

2011-06-01

74

Copper(I)-catalyzed enantioselective incorporation of ketones to cyclic hemiaminals for the synthesis of versatile alkaloid precursors.  

PubMed

A general catalytic enantioselective method that can produce five-, six-, and seven-membered N-heterocycles possessing various ketone moieties starting from stable and easily available cyclic hemiaminals and ketones was developed. The method involves three successive steps in one pot (aldol addition, dehydration, and enantioselective intramolecular aza-Michael reaction), all of which are promoted by a chiral copper(I)-conjugated Brønsted base catalyst. This method is useful for rapid access to versatile chiral building blocks for the synthesis of drug-lead alkaloids. PMID:23039221

Shi, Shi-Liang; Wei, Xiao-Feng; Shimizu, Yohei; Kanai, Motomu

2012-10-17

75

Catalytic enantioselective conjugate addition with Grignard reagents.  

PubMed

In this Account, recent advances in catalytic asymmetric conjugate addition of Grignard reagents are discussed. Synthetic methodology to perform highly enantioselective Cu-catalyzed conjugate addition of Grignard reagents to cyclic enones with ee's up to 96% was reported in 2004 from our laboratories. Excellent levels of stereocontrol were achieved with Cu(I) halides, alkylmagnesium bromides, and commercially available chiral ferrocenyl diphosphines. Studies carried out during the last 2 years demonstrated that these Cu-catalysts are very effective for the enantioselective conjugate addition of Grignard reagents to acyclic enones, alpha,beta-unsaturated esters, and thioesters. On the basis of this methodology, a diastereo- and enantioselective iterative route to deoxypropionate units was developed and applied to the synthesis of natural products. Finally, we summarize our recently conducted mechanistic investigations and the application of this catalytic system to the enantioselective SN2' substitution reactions of allylic bromides with Grignard reagents. PMID:17370989

López, Fernando; Minnaard, Adriaan J; Feringa, Ben L

2007-03-01

76

Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations  

E-print Network

I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand ...

Colby Davie, Elizabeth A. (Elizabeth Anne)

2005-01-01

77

Enantioselective Synthesis of (+)-Chamaecypanone C, a Novel Microtubule Inhibitor**  

PubMed Central

A number of bicyclo[2.2.2]octenone-containing natural products have been isolated from the heartwood of Chamaecyparis obtusa var. formosana (Figure 1) including the Diels-Alder adducts[1] obtunone (1),[2] chamaecypanone C (2),[3] and the [4+2] dimer (+)-3.[2],[4] Compound (+)-2 was shown to exhibit potent cytotoxicity against several human cancer cells including human oral epidermoid carcinoma (KB) (IC50 = 190 nM).[3] The biosynthesis of 2 was proposed[3] to occur via endo [4+2] cycloaddition between 1-hydroxymentha-3,5-dien-2-one 4 (Figure 2) and 1,3-bis-arylcyclopenta-1,3-diene 5, followed by oxidation to an enone in accord with literature reports of cyclopentadienes as biosynthetic precursors to natural products.[1b] An alternative possibility involving the corresponding cyclopentadienone 6 as dienophile may also be considered in light of known biosyntheses involving reactive cyclopentadienones.[5] Herein, we report a concise synthesis of both enantiomers of chamaecypanone C involving a retro-DA/DA cascade of dimer 3, obtained utilizing copper-mediated asymmetric oxidative dearomatization,[6] as well as biological studies documenting that the cytotoxic action of (+)-2 involves mitotic arrest as a consequence of its binding in the colchicine site of tubulin. PMID:19140149

Dong, Suwei; Hamel, Ernest; Bai, Ruoli; Covell, David G.; Beutler, John A.; Porco, John A.

2009-01-01

78

Dynamic kinetic asymmetric synthesis of five contiguous stereogenic centers by sequential organocatalytic stetter and Michael-aldol reaction: enantioselective synthesis of fully substituted cyclopentanols bearing a quaternary stereocenter.  

PubMed

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee). PMID:21348455

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou; Lee, Gene-Hsiang

2011-03-18

79

Development of ProPhenol ligands for the diastereo- and enantioselective synthesis of ?-hydroxy-?-amino esters.  

PubMed

A zinc-ProPhenol-catalyzed direct asymmetric aldol reaction between glycine Schiff bases and aldehydes is reported. The design and synthesis of new ProPhenol ligands bearing 2,5-trans-disubstituted pyrrolidines was essential for the success of this process. The transformation operates at room temperature and affords syn ?-hydroxy-?-amino esters in high yields with good to excellent levels of diastereo- and enantioselectivity. PMID:24502188

Trost, Barry M; Miege, Frédéric

2014-02-26

80

The enantioselective intramolecular aminative functionalization of unactivated alkenes, dienes, allenes and alkynes for the synthesis of chiral nitrogen heterocycles  

PubMed Central

The enantioselective intramolecular aminative functionalization of unactivated alkenes and related ?-systems is a straight-forward and atom economical strategy for the synthesis of chiral nitrogen heterocycles. These reactions can be categorized as oxidatively neutral, such as alkene hydroamination, or as oxidative reactions, such as alkene difunctionalization, e.g. aminooxygenation and carboamination. This perspective reviews the current work in the field and explores mechanistic trends that are common among the different catalysts and reaction types. PMID:20976023

Chemler, Sherry R.

2010-01-01

81

A Concise Enantioselective Synthesis and Cytotoxic Evaluation of the Anticancer Rotenoid Deguelin Enabled by a Tandem Knoevenagel/Conjugate Addition/Decarboxylation Sequence  

PubMed Central

(?)-Deguelin is a rotenoid natural product that possesses significant potential as a chemopreventive and chemotherapeutic agent. While several racemic syntheses of deguelin have been reported, a formal evaluation of the anticancer activity of both the natural and unnatural enantiomers remains lacking. We describe herein the successful application of a flexible and selective thiourea-catalyzed cyclization strategy toward the enantioselective total synthesis of deguelin, which allows access to either stereoisomer for biological studies. The synthesis was completed in six steps (longest linear) with no protecting groups. The evaluation of both enantiomers of the natural product demonstrated potent inhibition of several cancer cell lines by these compounds, but interestingly showed that the unnatural (+)-deguelin preferentially inhibited the growth of MCF-7 breast cancer and HepG2 liver carcinoma cells when compared to the natural product. PMID:24101971

Farmer, Rebecca L.

2013-01-01

82

Synthesis of (S)-7-amino-5-azaspiro[2.4]heptane via highly enantioselective hydrogenation of protected ethyl 1-(2-aminoaceto)cyclopropanecarboxylates.  

PubMed

Highly effective asymmetric hydrogenation of protected ethyl 1-(2-aminoaceto)cyclopropane carboxylates in the presence of [RuCl(benzene)(S)-SunPhos]Cl was realized, and high enantioselectivities (up to 98.7% ee) were obtained. This asymmetric hydrogenation provides a key intermediate for the enantioselective synthesis of (S)-7-amino-5-azaspiro[2.4]heptane moiety of quinolone antibacterial agents. PMID:21413753

Yao, Ying; Fan, Weizheng; Li, Wanfang; Ma, Xin; Zhu, Lvfeng; Xie, Xiaomin; Zhang, Zhaoguo

2011-04-15

83

Enantioselective Synthesis of Angularly Substituted 1-Azabicylic Rings: Coupled Dynamic Kinetic Epimerization and Chirality Transfer  

PubMed Central

A new strategy for enantioselective synthesis of azacyclic molecules in which dynamic kinetic equilibration of diastereomeric iminium ions precedes a stereochemistry-determining sigmatropic rearrangement is reported. The method is illustrated by the synthesis in high enantiomeric purity (generally 95–99% ee) of a variety of 1-azabicyclic molecules containing angular allyl or 3-substituted 2-propenyl side chains adjacent to nitrogen and up to three stereogenic centers. In these products, the size of the carbocyclic ring is varied widely (5–12 membered), however useful yields are obtained in forming 1-azabicyclic products containing only fused pyrrolidine and piperidine rings. Chi-rality transfer from substituents at carbons 1 and 2 of the 3-butenylamine fragment of the starting material is investigated, with methyl and phenyl substituents at the allylic position shown to provide exquisite stereocontrol (generally 98–99% chirality transfer). An attractive feature of the method is the ability to carry out the key transformation in the absence of solvent. Illustrated also is the high yielding conversion of four such products to a new family of bicyclic ?-amino acids of high enantiomeric purity. PMID:24090405

Aron, Zachary D.; Ito, Tatsuya; May, Tricia L.; Overman, Larry E.; Wang, Jocelyn

2013-01-01

84

Highly enantioselective organocatalytic trifluoromethyl carbinol synthesis--a caveat on reaction times and product isolation.  

PubMed

Aldol reactions with trifluoroacetophenones as acceptors yield chiral ?-aryl, ?-trifluoromethyl tertiary alcohols, valuable intermediates in organic synthesis. Of the various organocatalysts examined, Singh's catalyst [(2S)-N-[(1S)-1-hydroxydiphenylmethyl-3-methylbutyl]-2-pyrrolidinecarboxamide] was found to efficiently promote this organocatalytic transformation in a highly enantioselective manner. Detailed reaction monitoring ((19)F-NMR, HPLC) showed that, up to full conversion, the catalytic transformation proceeds under kinetic control and affords up to 95% ee in a time-independent manner. At longer reaction times, the catalyst effects racemization. For the product aldols, even weak acids (such as ammonium chloride) or protic solvents, can induce racemization, too. Thus, acid-free workup, at carefully chosen reaction time, is crucial for the isolation of the aldols in high (and stable) enantiomeric purity. As evidenced by (19)F-NMR, X-ray structural analysis, and independent synthesis of a stable intramolecular variant, Singh's catalyst reversibly forms a catalytically inactive ("parasitic") intermediate, namely a N,O-hemiacetal with trifluoroacetophenones. X-ray crystallography also allowed the determination of the product aldols' absolute configuration (S). PMID:22631871

Duangdee, Nongnaphat; Harnying, Wacharee; Rulli, Giuseppe; Neudörfl, Jörg-M; Gröger, Harald; Berkessel, Albrecht

2012-07-11

85

Enantioselective synthesis of tatanans A-C and reinvestigation of their glucokinase-activating properties  

PubMed Central

The tatanans are members of a novel class of complex sesquilignan natural products recently isolated from the rhizomes of Acorus tatarinowii Schott plants. Tatanans A, B and C have previously been reported to have potent glucokinase-activating properties that exceed the in vitro activity of known synthetic antidiabetic agents. Here, using a series of sequential [3,3]-sigmatropic rearrangements, we report the total synthesis of tatanan A in 13 steps and 13% overall yield. We also complete a concise enantioselective total synthesis of more complex, atropisomeric tatanans B and C via a distinct convergent strategy based on a palladium-catalysed diastereotopic aromatic group differentiation (12 steps, 4% and 8% overall yield, respectively). A plausible biosynthetic relationship between acyclic tatanan A and spirocyclic tatanans B and C is proposed and probed experimentally. With sufficient quantities of the natural products in hand, we undertake a detailed functional characterization of the biological activities of tatanans A–C. Contrary to previous reports, our assays utilizing pure recombinant human enzyme demonstrate that tatanans do not function as allosteric activators of glucokinase. PMID:23609092

Xiao, Qing; Jackson, Jeffrey J.; Basak, Ashok; Bowler, Joseph M.; Miller, Brian G.; Zakarian, Armen

2014-01-01

86

Memory of chirality (MOC) concept in imino-aldol reaction: enantioselective synthesis of ?,?-diamino esters and aziridines.  

PubMed

A simple strategy for the synthesis of chiral ?,?-diamino- and ?-amino,?-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies. PMID:23320819

Ghorai, Manas K; Ghosh, Koena; Yadav, A K; Nanaji, Y; Halder, Sandipan; Sayyad, Masthanvali

2013-03-15

87

Asymmetric Biomimetic Oxidations of Phenols: The Mechanism of the Diastereo- and Enantioselective Synthesis of Thomasidioic Acid  

Microsoft Academic Search

Enantiopure chiral amidic derivatives of sinapic acid were oxidised with hydrogen peroxide using horseradish peroxidase (HRP) as the catalyst to give the aryltetraline dilignol thomasidioic acid. Trans-diastereoselectivity and enantioselectivity in the formation of thomasidioic acid was observed. Computational methods show that the enantioselectivity is controlled by the ?-? oxidative coupling step, while the diastereoselectivity is controlled by the stability of

Luca Zoia; Maurizio Bruschi; Marco Orlandi; Eeva-Liisa Tolppa; Bruno Rindone

2008-01-01

88

Enantioselective synthesis of planar chiral ferrocenes via palladium-catalyzed annulation with diarylethynes  

PubMed Central

Summary When Boc-L-Val-OH was used as a ligand for the enantioselective Pd(II)-catalyzed annulation of N,N-substituted aminomethyl ferrocene derivatives with diarylethynes, ferrocenes with planar chirality could be achieved with excellent enantioselectivity (up to 99% ee). PMID:24062858

Shi, Yan-Chao; Yang, Rong-Fei; Gao, De-Wei

2013-01-01

89

Enantioselective Synthesis of anti- and syn-homopropargyl alcohols via Chiral Br?nsted Acid Catalyzed asymmetric Allenylboration reactions  

PubMed Central

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 triple asymmetric 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.

2012-01-01

90

Enantioselective synthesis of benzazepinoindoles bearing trifluoromethylated quaternary stereocenters catalyzed by chiral spirocyclic phosphoric acids.  

PubMed

The first highly enantioselective iso-Pictet-Spengler reaction of C-2-linked o-aminobenzylindoles with trifluoromethyl ketones was developed using chiral spirocyclic phosphoric acids as organocatalysts, which afforded optically active benzazepinoindoles bearing trifluoromethylated quaternary stereocenters. PMID:24890313

Li, Xuejian; Chen, Di; Gu, Haorui; Lin, Xufeng

2014-07-18

91

Asymmetric synthesis of amines by the catalytic enantioselective additions of hydrazoic acid to ketenes  

E-print Network

The development of a planar-chiral catalyst for the enantioselective additions of HN3 to hindered ketenes was investigated. It was demonstrated that a new planar-chiral catalyst (1.5) is an excellent catalyst for the ...

Nakai, Takashi, S.M. Massachusetts Institute of Technology

2007-01-01

92

Catalytic enantioselective conjugate addition of fluorobis(phenylsulfonyl)methane to enals: synthesis of chiral monofluoromethyl compounds.  

PubMed

A new highly catalytic enantioselective Michael addition of fluorobis(phenylsulfonyl)methane to alpha,beta-unsaturated aldehydes has been developed for the preparation of chiral monofluoromethyl compounds under mild reaction conditions. PMID:19652814

Zhang, Shilei; Zhang, Yinan; Ji, Yafei; Li, Hao; Wang, Wei

2009-08-28

93

Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies.  

PubMed

An enantioselective intramolecular chiral phosphoric acid-catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in?situ enantioenrichment through acetalization of the minor enantiomer. A new computational reaction exploration method was utilized to elucidate the mechanism and stereoselectivity of this transformation. Rather than confirming the originally postulated cyclization proceeding directly through a vinyl oxocarbenium ion, simulations identified an alternative two-step mechanism involving the formation of a mixed chiral phosphate acetal, which undergoes a concerted, asynchronous SN 2'-like displacement to yield the product with stereoselectivity in agreement with experimental observations. PMID:25196818

Sun, Zhankui; Winschel, Grace A; Zimmerman, Paul M; Nagorny, Pavel

2014-10-13

94

Enantioselective organocatalytic one-pot amination/aza-Michael/aldol condensation reaction sequence: synthesis of 3-pyrrolines with a quaternary stereocenter.  

PubMed

Primary amine-catalyzed direct conversion of ?,?-disubstituted aldehydes into 3-pyrrolines with a quaternary stereocenter is reported. The one-pot enantioselective sequence is based on a ?-amination, an aza-Michael addition of hydrazine, an aldol condensation dehydratation and proceeds with good yields and excellent levels of enantioselectivity. Synthetically attractive applications including the formation of aziridinopyrrolidine or epoxypyrrolidine derivatives with good yields and selectivities are also described. PMID:22927036

Desmarchelier, Alaric; Coeffard, Vincent; Moreau, Xavier; Greck, Christine

2012-10-01

95

Enantioselective nucleophile-catalyzed cycloadditions  

E-print Network

Chapter 1 describes the development of an asymmetric nucleophile-catalyzed [2+2] cycloaddition of ketenes with aldehydes. This is the first report of a catalytic enantioselective synthesis of trisubstituted [beta]-lactones. ...

Wilson, Jonathan E., Ph. D. Massachusetts Institute of Technology

2007-01-01

96

Enantioselective TADMAP-catalyzed carboxyl migration reactions for the synthesis of stereogenic quaternary carbon.  

PubMed

The chiral, nucleophilic catalyst TADMAP [1, 3-(2,2,2-triphenyl-1-acetoxyethyl)-4-(dimethylamino)pyridine] has been prepared from 3-lithio-4-(dimethylamino)pyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity. PMID:16417383

Shaw, Scott A; Aleman, Pedro; Christy, Justin; Kampf, Jeff W; Va, Porino; Vedejs, Edwin

2006-01-25

97

Asymmetric decarboxylative 1,4-addition of malonic acid half thioesters to vinyl sulfones: highly enantioselective synthesis of 3-monofluoromethyl-3-arylpropanoic esters.  

PubMed

An asymmetric decarboxylative 1,4-addition of malonic acid half thioesters (MAHTs) to 2-aryl-substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97?% ee). In view of tuning pKa values, a quinine-based benzyl-substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3-monofluorinated analogues of 3-methyl indanone and (+)-turmerone has been accomplished from decarboxylative 1,4-addition adducts with satisfactory results. PMID:24591040

Qiao, Baokun; Liu, Qian; Liu, Hongjun; Yan, Lin; Jiang, Zhiyong

2014-05-01

98

Brønsted acid catalyzed, conjugate addition of ?-dicarbonyls to in situ generated ortho-quinone methides--enantioselective synthesis of 4-aryl-4H-chromenes.  

PubMed

We describe herein a catalytic, enantioselective process for the synthesis of 4H-chromenes which are important structural elements of many natural products and biologically active compounds. A sequence comprising a conjugate addition of ?-diketones to in situ generated ortho-quinone methides followed by a cyclodehydration reaction furnished 4-aryl-4H-chromenes in generally excellent yields and high optical purity. A BINOL-based chiral phosphoric acid was employed as a Brønsted acid catalyst which converted ortho-hydroxy benzhydryl alcohols into hydrogen-bonded ortho-quinone methides and effected the carbon-carbon bond-forming event with high enantioselectivity. PMID:24938645

El-Sepelgy, Osama; Haseloff, Stefan; Alamsetti, Santosh Kumar; Schneider, Christoph

2014-07-21

99

Enantioselective Synthesis of Polycyclic Carbocycles via an Alkynylation-Allylation-Cyclization Strategy.  

PubMed

A new general three-stage strategy to access polycyclic ring systems bearing all-carbon quaternary centers with high enantioselectivity is reported. The required starting materials were readily accessed in racemic form through the ?-alkynylation of ketoesters with EBX (EthynylBenziodoXolone) hypervalent iodine reagents. A Pd-catalyzed asymmetric decarboxylation allylation was then achieved in high yields and enantioselectivities with Trost's biphosphine ligands. Finally, transition-metal catalyzed cyclization of the obtained chiral enynes gave access to fused and spiro polycyclic ring systems constituting the core of many bioactive natural products. PMID:25315421

Vita, Maria Victoria; Mieville, Pascal; Waser, Jerome

2014-11-01

100

A highly diastereoselective and enantioselective synthesis of polysubstituted pyrrolidines via an organocatalytic dynamic kinetic resolution cascade.  

PubMed

Highly functionalized pyrrolidine and piperidine analogues, with up to three stereogenic centers, were synthesized in good yield (50-95%), excellent dr (single isomer), and high ee (>90%) using a Cinchona alkaloid-derived carbamate organocatalyst. High stereoselective synergy was achieved by combining a reversible aza-Henry reaction with a dynamic kinetic resolution (DKR)-driven aza-Michael cyclization. Whereas both reactions proceed with moderate enantioselectivities (50-60% for each step), high enantioselectivities are obtained for the overall products devoid of dr sacrifice. PMID:23565748

Cheng, Tao; Meng, Sixuan; Huang, Yong

2013-04-19

101

A flexible enantioselective total synthesis of diospongins A and B and their enantiomers using catalytic hetero-Diels-Alder/Rh-catalyzed 1,4-addition and asymmetric transfer hydrogenation reactions as key steps.  

PubMed

A unified enantioselective route to total synthesis of diospongins A and B and their enantiomers has been developed employing achiral starting materials. All three stereocenters were introduced by means of catalytic reactions. PMID:19817354

Kumaraswamy, Gullapalli; Ramakrishna, Gajula; Naresh, Police; Jagadeesh, Bharatam; Sridhar, Balasubramanian

2009-11-01

102

Bioinspired total synthesis of katsumadain A by organocatalytic enantioselective 1,4-conjugate addition  

PubMed Central

Summary Katsumadain A, a naturally occurring in?uenza virus neuraminidase (NA) inhibitor, was synthesized by using a bioinspired, organocatalytic enantioselective 1,4-conjugate addition of styryl-2-pyranone with cinnamaldehyde, followed by a tandem Horner–Wadsworth–Emmons/oxa Michael addition. PMID:23946860

Wang, Yongguang; Bao, Ruiyang; Huang, Shengdian

2013-01-01

103

Enantioselective synthesis of succinic acids and ?-lactones via palladium catalysed allylic substitution reactions  

Microsoft Academic Search

The palladium catalysed reaction between non-symmetrical allyl acetates and sodiodimethylmalonate proceeds in high yields and enantioselectivities (up to 99% ee) using a diphenylphosphinoaryl oxazoline ligand. The so-formed substitution products are transformed into enantiomerically enriched succinic acids and also into enantiomerically enriched ?-lactones.

Steven J Coote

1995-01-01

104

Enantioselective synthesis in carbohydrate-based drug discovery: imino sugars, alkaloids and macrolide antibiotics.  

PubMed

This review is dedicated to enantioselective methods for the generation of carbohydrate-based lead compounds for drug research. Selected examples encompassing imino sugars, bicyclic imino sugar-type alkaloids such as castanospermine, swainsonine, or alexine, as well as macrolide glycosides are covered and discussed. PMID:24758433

Xavier, Nuno M; Rauter, Amélia P

2014-01-01

105

Phosphoric acid catalyzed diastereo- and enantioselective synthesis of substituted 1,3-diaminotetralins.  

PubMed

The reaction of anilines and phenylacetaldehydes in the presence of chiral phosphoric acid afforded optically active 1,2-trans, 2,3-cis 1,3-diaminotetralins in high yields with excellent diastereo- and enantioselectivities. The trans/cis product was readily isomerized to a trans/trans stereoisomer with no significant loss of enantiomeric purity. PMID:24762190

Dagousset, Guillaume; Erb, William; Zhu, Jieping; Masson, Géraldine

2014-05-01

106

Enantioselective microbial synthesis of the indigenous natural product (-)-?-bisabolol by a sesquiterpene synthase from chamomile (Matricaria recutita).  

PubMed

(-)-?-Bisabolol, a sesquiterpene alcohol, is a major ingredient in the essential oil of chamomile (Matricaria recutita) and is used in many health products. The current supply of (-)-?-bisabolol is mainly dependent on the Brazilian candeia tree (Eremanthus erythropappus) by distillation or by chemical synthesis. However, the distillation method using the candeia tree is not sustainable, and chemical synthesis suffers from impurities arising from undesirable ?-bisabolol isomers. Therefore enzymatic synthesis of (-)-?-bisabolol is a viable alternative. In the present study, a cDNA encoding (-)-?-bisabolol synthase (MrBBS) was identified from chamomile and used for enantioselective (-)-?-bisabolol synthesis in yeast. Chamomile MrBBS was identified by Illumina and 454 sequencing, followed by activity screening in yeast. When MrBBS was expressed in yeast, 8 mg of ?-bisabolol was synthesized de novo per litre of culture. The structure of purified ?-bisabolol was elucidated as (S,S)-?-bisabolol [or (-)-?-bisabolol]. Although MrBBS possesses a putative chloroplast-targeting peptide, it was localized in the cytosol, and a deletion of its N-terminal 23 amino acids significantly reduced its stability and activity. Recombinant MrBBS showed kinetic properties comparable with those of other sesquiterpene synthases. These data provide compelling evidence that chamomile MrBBS synthesizes enantiopure (-)-?-bisabolol as a single sesquiterpene product, opening a biotechnological opportunity to produce (-)-?-bisabolol. PMID:25048207

Son, Young-Jin; Kwon, Moonhyuk; Ro, Dae-Kyun; Kim, Soo-Un

2014-10-15

107

Asymmetric synthesis of metallocenes through enantioselective addition of organolithium reagents to 6-(dimethylamino)fulvene.  

PubMed

Enantioselective addition of aryllithiums 2a-d (Ar = Ph (a), 2-MeC(6)H(4) (b), 2-MeOC(6)H(4) (c), 1-naphthyl (d)) to 6-(dimethylamino)fulvene (1) in the presence of (-)-sparteine in toluene at -78 degrees C generated chiral cyclopentadienyllithiums (4) substituted with an N,N-dimethylamino(aryl)methyl group, where the enantioselectivities are 51, 91, 90, and 83% for 4a, 4b, 4c, and 4d, respectively. Treatment of the chiral cyclopentadienides 4 with FeCl(2) or Fe(acac)(2) gave ferrocenes, which contain an N,N-dimethylamino(aryl)methyl side chain on both of the cyclopentadienyl rings. The enantiomeric purity of the chiral ferrocenes 7 thus obtained is 99% ee or higher for those containing a 2-MeC(6)H(4) (7b) or a 2-MeOC(6)H(4) (7c) group. PMID:12003546

Suzuka, Toshimasa; Ogasawara, Masamichi; Hayashi, Tamio

2002-05-17

108

Enantioselective synthesis of hindered cyclic dialkyl ethers via catalytic oxa-Michael/Michael desymmetrization†  

PubMed Central

An asymmetric oxa-Michael/Michael cascade reaction of p-quinols and ?,?-unsaturated aldehydes provides access to hindered dialkyl ethers. A highly enantioselective oxa-Michael addition of a tertiary alcohol precedes an intramolecular cyclohexadienone desymmetrization, which allows for the concomitant formation of four contiguous stereocenters in a single step. The highly functionalized bicyclic frameworks are rapidly obtained from simple starting materials with good diastereoselection and serve as valuable precursors for further manipulation. PMID:24683449

Corbett, Michael T.; Johnson, Jeffrey S.

2014-01-01

109

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers  

PubMed Central

Summary Diaryl ethers carrying carbamoyloxymethyl groups may be desymmetrised enantio- and diastereoselectively by the use of the sec-BuLi–(?)-sparteine complex in diethyl ether. Enantioselective deprotonation of one of the two benzylic positions leads to atropisomeric products with ca. 80:20 e.r.; an electrophilic quench typically provides functionalised atropisomeric diastereoisomers in up to 97:3 d.r. PMID:22043243

Page, Abigail

2011-01-01

110

Enantioselective synthesis of ?-halo-?-alkylmalonates via phase-transfer catalytic ?-alkylation.  

PubMed

A new enantioselective synthetic method for ?-halo-?-alkylmalonates is reported. ?-Alkylation of diphenylmethyl tert-butyl ?-halomalonates under phase-transfer catalytic conditions (solid KOH, toluene, -40 °C) in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide (5 mol%) afforded diphenylmethyl tert-butyl ?-halo-?-alkylmalonates in very high chemical yields (up to 99%) and optical yields (up to 93% ee). PMID:24448720

Hong, Suckchang; Kim, Minsik; Jung, Myunggi; Ha, Min Woo; Lee, Myungmo; Park, Yohan; Kim, Mi-hyun; Kim, Taek-Soo; Lee, Jihoon; Park, Hyeung-geun

2014-03-01

111

Rhodium-Catalyzed Arylative Cyclization for the Enantioselective Synthesis of (Trifluoromethyl)cyclobutanols.  

PubMed

A rhodium-catalyzed cyclization of 1-(trifluoromethyl)-4-alkyn-1-ones with arylboronic acids is described to yield a novel class of small rings: (trifluoromethyl)cyclobutanols bearing an exocyclic double bond. The use of a rhodium/chiral diene complex allowed the reaction to proceed under mild conditions, often with high enantioselectivity. An X-ray crystal structure was obtained confirming the formation of the four-membered ring products. PMID:25233924

Johnson, Thomas; Choo, Ken-Loon; Lautens, Mark

2014-10-27

112

Catalytic enantioselective synthesis of atropisomeric biaryls: a cation-directed nucleophilic aromatic substitution reaction.  

PubMed

A catalytic enantioselective nucleophilic aromatic substitution reaction which yields axially chiral biaryl derivatives in excellent yields with e.r.?values of up to 97:3 has been developed. This process uses a chiral counterion to direct the addition of thiophenolate to a prochiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized to a range of atropisomeric structures without any reduction in enantioenrichment, thus offering access to unexplored chiral biaryl architectures. PMID:25257677

Armstrong, Roly J; Smith, Martin D

2014-11-17

113

S-(+)-carvone as starting material in the enantioselective synthesis of natural products  

Microsoft Academic Search

In this thesis the applicability of S-(+)-carvone as chiral starting material in the synthesis of biologically active compounds is examined. S-(+)-carvone is the major compound of caraway essential oil. The essential oil content of caraway seed may vary from 2-7% and it contains about 50-60% of S-(+)-carvoneS-(+)-carvone exhibits a number of interesting biological activities, eg., antifungal, insecticidal and plant growth

A. A. Verstegen-Haaksma

1994-01-01

114

Enantioselective synthesis of bis-?-amino acid esters via asymmetric phase-transfer catalysis  

Microsoft Academic Search

Application of N-anthracenylmethyl dihydrocinchonidinium bromide quaternary ammonium phase-transfer catalysts to the enantio- and diastereoselective synthesis of a series of bis-?-amino acid esters is reported. Under liquid-liquid phase-transfer conditions the target amino acid esters are obtained with high enantiomeric excess (?95%e.e.) via alkylation of two molecules of a benzophenone-derived glycine-imine with an appropriate dibromide.

Barry Lygo; John Crosby; Justine A. Peterson

1999-01-01

115

Enantioselective protonation  

Microsoft Academic Search

Enantioselective protonation is a common process in biosynthetic sequences. The decarboxylase and esterase enzymes that effect this valuable transformation are able to control both the steric environment around the proton acceptor (typically an enolate) and the proton donor (typically a thiol). Recently, several chemical methods for achieving enantioselective protonation have been developed by exploiting various means of enantiocontrol in different

Justin T. Mohr; Allen Y. Hong; Brian M. Stoltz

2009-01-01

116

Chiral gold(I) vs chiral silver complexes as catalysts for the enantioselective synthesis of the second generation GSK-hepatitis C virus inhibitor  

PubMed Central

Summary The synthesis of a GSK 2nd generation inhibitor of the hepatitis C virus, by enantioselective 1,3-dipolar cycloaddition between a leucine derived iminoester and tert-butyl acrylate, was studied. The comparison between silver(I) and gold(I) catalysts in this reaction was established by working with chiral phosphoramidites or with chiral BINAP. The best reaction conditions were used for the total synthesis of the hepatitis C virus inhibitor by a four step procedure affording this product in 99% ee and in 63% overall yield. The origin of the enantioselectivity of the chiral gold(I) catalyst was justified according to DFT calculations, the stabilizing coulombic interaction between the nitrogen atom of the thiazole moiety and one of the gold atoms being crucial. PMID:21915198

Martin-Rodriguez, Maria; de Cozar, Abel

2011-01-01

117

Synthesis and Use of Jacobsen's Catalyst: Enantioselective Epoxidation in the Introductory Organic Laboratory  

Microsoft Academic Search

Jacobsen's catalyst, N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, is a popular reagent for the enantioselective epoxidation of alkenes. This reagent is successfully prepared in three steps by beginning organic chemistry students. A mixture of 1,2-diaminocyclohexane isomers is purified and resolved by crystallization (and recrystallization) with L-tartaric acid; a diimine is formed between the resolved trans-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde to produce the Jacobsen ligand; and finally

John Hanson

2001-01-01

118

(Diisopinocampheyl)borane-Mediated Reductive Aldol Reactions of Acrylate Esters: Enantioselective Synthesis of Anti-Aldols  

PubMed Central

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). Results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R.

2013-01-01

119

(Diisopinocampheyl)borane-mediated reductive aldol reactions of acrylate esters: enantioselective synthesis of anti-aldols.  

PubMed

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). The results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R

2013-08-01

120

Enantioselective synthesis of cyclobutanes via sequential Rh-catalyzed bicyclobutanation/Cu-catalyzed homoconjugate addition.  

PubMed

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which t-butyl (E)-2-diazo-5-arylpent-4-enoates are treated with Rh2(S-NTTL)4 to provide enantiomerically enriched bicyclobutanes, which can subsequently engage in homoconjugate addition/enolate trapping sequence to give densely functionalized cyclobutanes with high diastereoselectivity. This three-component, two-catalyst procedure can be carried out in a single flask. Rh2(S-NTTL)4-catalyzed reaction of t-butyl (Z)-2-diazo-5-phenylpent-4-enoate gives the Büchner cyclization product in excellent enantioselectivity. PMID:23758288

Panish, Robert; Chintala, Srinivasa R; Boruta, David T; Fang, Yinzhi; Taylor, Michael T; Fox, Joseph M

2013-06-26

121

Enantioselective Synthesis of Cyclobutanes via Sequential Rh-catalyzed Bicyclobutanation/Cu-catalyzed Homoconjugate Addition  

PubMed Central

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which t-butyl (E)-2-diazo-5-arylpent-4-enoates are treated with Rh2(S-NTTL)4 to provide enantiomerically enriched bicyclobutanes, which can subsequently engage in homoconjugate addition/enolate trapping sequence to give densely functionalized cyclobutanes with high diastereoselectivity. This three-component, two-catalyst procedure can be carried out in a single flask. Rh2(S-NTTL)4–catalyzed reaction of t-butyl (Z)-2-diazo-5-phenylpent-4-enoate gives the Buchner cyclization product in excellent enantioselectivity. PMID:23758288

Panish, Robert; Chintala, Srinivasa R.; Boruta, David T.; Fang, Yinzhi; Taylor, Michael T.; Fox, Joseph M.

2013-01-01

122

Synthesis and Use of Jacobsen's Catalyst: Enantioselective Epoxidation in the Introductory Organic Laboratory  

NASA Astrophysics Data System (ADS)

Jacobsen's catalyst, N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, is a popular reagent for the enantioselective epoxidation of alkenes. This reagent is successfully prepared in three steps by beginning organic chemistry students. A mixture of 1,2-diaminocyclohexane isomers is purified and resolved by crystallization (and recrystallization) with L-tartaric acid; a diimine is formed between the resolved trans-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde to produce the Jacobsen ligand; and finally Jacobsen's catalyst is prepared from the ligand by treatment with manganese(II) acetate followed by oxidation with air. The students then use their Jacobsen catalyst to enantioselectively epoxidize one of the following alkenes: 1,2-dihydronaphthalene, styrene, or a-methylstyrene. After purifying their epoxides by flash chromatography, students determine the enantiopurity by GC using a chiral column. In this series of experiments students utilize a wide variety of laboratory techniques: running a reaction at reflux, aqueous workup with a separatory funnel, recrystallization, flash chromatography, TLC, polarimetry, IR and NMR spectroscopy, and chiral GC analysis. These labs also reinforce many important concepts related to chirality, stereochemistry, and optical activity.

Hanson, John

2001-09-01

123

Highly Enantioselective Catalytic Dynamic Resolution of N-Boc-2-lithiopiperidine: Synthesis of (R)-(+)-N-Boc-Pipecolic Acid, (S)-(?)-Coniine, (S)-(+)-Pelletierine, (+)-?-Conhydrine, (S)-(?)-Ropivacaine, and Formal Synthesis of (?)-Lasubine II and (+)-Cermizine C  

PubMed Central

The catalytic dynamic resolution (CDR) of rac-2-lithio-N-Boc-piperidine using chiral ligand 8 or its diastereomer 9, in the presence of TMEDA has led to the highly enantioselective syntheses of either enantiomer of 2-substituted piperidines using a wide range of electrophiles. The CDR has been applied to the synthesis of R- or S-pipecolic acid derivatives, (+)-?-conhydrine, (S)-(+)-pelletierine, (S)-(?)-ropivacaine, and formal synthesis of (?)-lasubine II and (+)-cermizine C. PMID:20806976

Beng, Timothy K.; Gawley, Robert E.

2010-01-01

124

Highly Enantioselective Syntheses of Functionalized r-Methylene--butyrolactones via Rh(I)-catalyzed Intramolecular Alder Ene  

E-print Network

(I)-catalyzed Intramolecular Alder Ene Reaction: Application to Formal Synthesis of (+)-Pilocarpine Aiwen Lei, Minsheng He -lactones has shown its potential efficiency.7 Extensive studies on transition metal-catalyzed Alder ene a highly enantioselective Rh-catalyzed intramolecular Alder ene reaction for the synthesis

Zhang, Xumu

125

Enantioselective Protonation  

PubMed Central

Enantioselective protonation is a common process in biosynthetic sequences. The decarboxylase and esterase enzymes that effect this valuable transformation are able to control both the steric environment around the proton acceptor (typically an enolate) and the proton donor (typically a thiol). Recently, several chemical methods to achieve enantioselective protonation have been developed by exploiting various means of enantiocontrol in different mechanisms. These laboratory transformations have proven useful for the preparation of a number of valuable organic compounds. PMID:20428461

Mohr, Justin T.; Hong, Allen Y.; Stoltz, Brian M.

2010-01-01

126

Enantioselective synthesis of diversely substituted quaternary 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones.  

PubMed

Benzodiazepines are privileged scaffolds in medicinal chemistry, but enantiopure examples containing quaternary stereogenic centers are extremely rare. We demonstrate that installation of the di(p-anisyl)methyl (DAM) group at N1 of 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones derived from enantiopure proteinogenic amino acids allows retentive replacement of the C3-proton via a deprotonation/trapping protocol. A wide variety of carbon and nitrogen electrophiles function well in this reaction, providing the corresponding quaternary benzodiazepines with excellent enantioselectivity. Deprotonation/trapping experiments on a pair of diastereomeric 1,4-benzodiazepine-2,5-diones provide evidence for a key role of conformational chirality in these enantioselective reactions. Acidic removal of the DAM group is fast and high-yielding and can be performed selectively in the presence of a N-Boc indole. Thus the synthesis of quaternary benzodiazepines with diverse N1 functionality can now be accomplished. PMID:17117873

Carlier, Paul R; Zhao, Hongwu; MacQuarrie-Hunter, Stephanie L; DeGuzman, Joseph C; Hsu, Danny C

2006-11-29

127

Palladium(II)-Catalyzed Enantioselective Synthesis of 2-Vinyl Oxygen Heterocycles  

PubMed Central

2-Vinylchromanes (1), 2-vinyl-1,4-benzodioxanes (2), and 2,3-dihydro-2-vinyl-2H-1,4-benzoxazines (3) can be prepared in high yields (90–98%) and excellent enantiomeric purities (87–98% ee) by [COP-OAc]2-catalyzed cyclization of phenolic (E)-allylic trichloroacetimidate precursors. Deuterium-labeling and computational experiments are consistent with these cyclization reactions taking place by an anti-oxypalladation/syn-deoxypalladation mechanism. 2-Vinylchromanes can be prepared also in good yields and high enantiomeric purities from analogous (E)-allylic acetate precursors, which constitutes the first report that acetate is a competent leaving group in COP-catalyzed enantioselective SN2? substitution reactions. PMID:22316285

Cannon, Jeffrey S.; Olson, Angela C.; Overman, Larry E.; Solomon, Nicole S.

2012-01-01

128

Enantioselective Total Synthesis of Ustiloxin D Hiroko Tanaka, Andrew M. Sawayama, and Thomas J. Wandless*  

E-print Network

in their synthesis include the use of a nucleophilic aromatic substitution reaction to construct the chiral tertiary alkyl- aryl ether,4b as well as Sharpless's asymmetric aminohydroxylation reaction to install the C10 reactions in the context of a total synthesis. A requirement for our synthesis was to develop a strategy

Wandless, Tom

129

From highly enantioselective catalytic reaction of 1,3-diynes with aldehydes to facile asymmetric synthesis of polycyclic compounds.  

PubMed

(S)-1,1'-Binaphth-2-ol (BINOL) in combination with ZnEt(2), Ti(O(i)Pr)(4), and biscyclohexylamine was found to catalyze the highly enantioselective (83-95% ee) addition of various 1,3-diynes to aldehydes of diverse structures. This method provides a convenient pathway to generate a number of optically active dienediynes as the acyclic precursors to polycyclic compounds. The chiral dienediynes undergo highly chemoselective Pauson-Khand (PK) cycloaddition in benzaldehyde by using [Rh(cod)Cl](2) as the catalyst in the presence of rac-BINAP. High diastereoselectivity (up to >20:1) has also been achieved with the chiral dienediyne substrates containing a bulky substituent adjacent to the chiral center. In the presence of the Grubbs II catalyst, ring-closing enyne metathesis of the PK cycloaddition products led to the formation of the desired 5,5,7- and 5,5,8-fused tricyclic compounds. Further highly diastereoselective Diels-Alder reaction of a 5,5,7-tricyclic compound with maleic anhydride produced a 5,5,7,6-polycyclic product. The asymmetric synthesis of polycyclic compounds from optically active dienediynes has established a novel and efficient synthetic route to the structural framework of many biologically significant molecules. PMID:21688803

Turlington, Mark; Du, Yuhao; Ostrum, Samuel G; Santosh, Vishaka; Wren, Kathryne; Lin, Tony; Sabat, Michal; Pu, Lin

2011-08-01

130

Simple Organic Molecules as Catalysts for Enantioselective Synthesis of Amines and Alcohols  

PubMed Central

The discovery of new catalysts that can generate complex organic compounds via enantioselective transformations is central to advances in the life sciences;i for this reason, many chemists try to discover catalysts that can be used to produce chiral molecules with a strong preference for one mirror image isomer.ii The ideal catalyst should be devoid of precious elementsiii and should bring reactions to completion in a few hours using operationally simple procedures. In this manuscript, we introduce a set of small organic molecules that can catalyze reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which can be used to synthesize more complex, biologically active molecules. A distinguishing feature of this new catalyst class is the presence of a 'key' proton embedded within their structure. The catalyst is derived from the abundant amino acid valine and was prepared in large quantities in four steps using inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mol % catalyst in less than six hours at room temperature to generate products in >85% yield and ?97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents render this advance vital to future progress in chemistry, biology and medicine. PMID:23407537

Silverio, Daniel L.; Torker, Sebastian; Pilyugina, Tatiana; Vieira, Erika M.; Snapper, Marc L.; Haeffner, Fredrik; Hoveyda, Amir H.

2012-01-01

131

Asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones via enantioselective tandem Michael-aldol reaction.  

PubMed

A simple and efficient method for the asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones and related natural products was developed on the basis of the catalytic asymmetric tandem Michael-aldol reaction and simple transformations. The synthetic utility of this method was illustrated by the facile synthesis of trisubstituted ?-butyrolactone natural products. PMID:23252990

Lee, Sung Il; Jang, Jin Hee; Hwang, Geum-Sook; Ryu, Do Hyun

2013-01-18

132

Enantioselective and regioselective pyrone Diels-Alder reactions of vinyl sulfones: total synthesis of (+)-cavicularin.  

PubMed

The total synthesis of (+)-cavicularin is described. The synthesis features an enantio- and regioselective pyrone Diels-Alder reaction of a vinyl sulfone to construct the cyclophane architecture of the natural product. The Diels-Alder substrate was prepared by a regioselective one-pot three-component Suzuki reaction of a non-symmetric dibromoarene. PMID:25082270

Zhao, Peng; Beaudry, Christopher M

2014-09-22

133

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

E-print Network

an intramolecular Diels-Alder cycloaddition.2k The total synthesis of 11-acetoxy-4-deoxyasbestinin D (1) was undertaken with the intent of validating the intramolecular Diels-Alder approach for the synthesis of the required Diels-Alder precursor. To this end, the benzyl ether was reductively cleaved, and the resultant

134

Enantioselective Synthesis of Axially Chiral Biaryls by the Pd- Catalyzed Suzuki-Miyaura Reaction: Substrate Scope and Quantum Mechanical Investigations  

E-print Network

We report efficient syntheses of axially chiral biaryl amides in yields ranging from 80?92%, and with enantioselectivity in the range 88?94% ee employing an asymmetric Suzuki?Miyaura process with Pd(OAc)[subscript 2] and ...

Shen, Xiaoqiang

135

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

PubMed Central

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

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

2009-01-01

136

Synthesis of (9 R)- and (9 S)-10-fluorodecan-9-olide (fluoro-phoracantholide I) first lipase-catalyzed enantioselective esterification of ?-fluoroalcohols  

Microsoft Academic Search

Synthesis of both enantiomers of fluoro-phoracantholide I, namely (9S)-10-fluorodecan-9-olide ((9S)-(?)-1 and (9R)-10-fluorodecan-9-olide (9R)-(+)-1, has been achieved through lipase-catalyzed enantioselective acetylation of methyl 10-fluoro-9-hydroxydecanoate (2a) with acetic anhydride in the presence of Lipase Amano PS (Pseudomonas cepacia). The higher homologue, methyl 11-fluoro-10-hydroxyundecanoate (2b) has also been resolved. These enzymatic resolutions by acetylation of ?-fluoro-(?-1)-hydroxyalkanoic acid esters of longchain fatty acids represent

Andreas Sattler; Günter Haufe

1995-01-01

137

Concise and enantioselective total synthesis of (-)-mehranine, (-)-methylenebismehranine, and related aspidosperma alkaloids.  

PubMed

We report an efficient and highly stereoselective strategy for the synthesis of Aspidosperma alkaloids based on the transannular cyclization of a chiral lactam precursor. Three new stereocenters are formed in this key step with excellent diastereoselectivity due to the conformational bias of the cyclization precursor, leading to a versatile pentacyclic intermediate. A subsequent stereoselective epoxidation followed by a mild formamide reduction enabled the first total synthesis of the Aspidosperma alkaloids (-)-mehranine and (+)-(6S,7S)-dihydroxy-N-methylaspidospermidine. A late-stage dimerization of (-)-mehranine mediated by scandium trifluoromethanesulfonate completed the first total synthesis of (-)-methylenebismehranine. PMID:25196158

Mewald, Marius; Medley, Jonathan William; Movassaghi, Mohammad

2014-10-20

138

Enantioselective total synthesis of (+)-lysergic acid, (+)-lysergol, and (+)-isolysergol by palladium-catalyzed domino cyclization of allenes bearing amino and bromoindolyl groups.  

PubMed

Enantioselective total synthesis of the biologically important indole alkaloids (+)-lysergol, (+)-isolysergol, and (+)-lysergic acid is described. Key features of these total synthesis include (1) a facile synthesis of a chiral 1,3-amino alcohol via the Pd(0)- and In(I)-mediated reductive coupling reaction between L-serine-derived 2-ethynylaziridine and formaldehyde; (2) the Cr(II)/Ni(0)-mediated Nozaki-Hiyama-Kishi (NHK) reaction of an indole-3-acetaldehyde with iodoalkyne; and (3) Pd(0)-catalyzed domino cyclization of an allene bearing amino and bromoindolyl groups. This domino cyclization enabled direct construction of the C/D ring system of the ergot alkaloids skeleton, as well as the creation of the C5 stereogenic center with transfer of the allenic axial chirality to the central chirality. PMID:21361331

Inuki, Shinsuke; Iwata, Akira; Oishi, Shinya; Fujii, Nobutaka; Ohno, Hiroaki

2011-04-01

139

New chiral derivatives of xanthones: synthesis and investigation of enantioselectivity as inhibitors of growth of human tumor cell lines.  

PubMed

A highly efficient and practical methodology for synthesis of new chiral derivatives of xanthones (CDXs) in enantiomerically pure form has been developed. According to this approach, thirty CDXs (3-32) were synthesized by coupling a carboxyxanthone (1) and a carboxymethoxyxanthone (2) with both enantiomers of commercially available chiral building blocks, namely six amino alcohols, one amine and one amino ester. The activation of the carboxylic acid group of the xanthonic scaffold was carried out with the coupling reagent O-(benzotriazol-1-yl)-N-N-N'-N'-tetramethyluronium tetrafluoroborate (TBTU), in the presence of a catalytic amount of TEA in anhydrous THF. The coupling reactions with the chiral blocks were performed at room temperature with short reactions times, excellent yields (ranging from 94% to 99%), and very high enantiomeric excess. The synthesized CDXs were evaluated for their effect on the in vitro growth of three human tumor cell lines, namely A375-C5 (melanoma), MCF-7 (breast adenocarcinoma), and NCI-H460 (non-small cell lung cancer). The most active compound was CDX 15 being active in all human tumor cell lines with values of GI50 of 32.15±2.03?M for A375-C5, 22.55±1.99?M for MCF-7, and 14.05±1.82?M for NCI-H460. Nevertheless, some CDXs showed cell-type selectivity. Furthermore, the growth inhibitory effects, in some cases, demonstrated to be depending on the stereochemistry of the CDXs. An interesting example was observed with the enantiomers 3 and 4, which demonstrated high enantioselectivity for MCF-7 and NCI-H460 cell lines. It can be inferred that the effects on the growth of the human tumor cell lines can be ascribed not only to the nature and positions of substituents on the xanthonic scaffold but also to the stereochemistry of the CDXs. Some considerations regarding structure-activity relationship within this class of compounds will be highlighted. PMID:24411197

Fernandes, Carla; Masawang, Kamonporn; Tiritan, Maria Elizabeth; Sousa, Emília; de Lima, Virgínia; Afonso, Carlos; Bousbaa, Hassan; Sudprasert, Wanwisa; Pedro, Madalena; Pinto, Madalena M

2014-02-01

140

Towards an Enantioselective Synthesis of (-)-Zampanolide: Preparation of the C9-C20 Region  

PubMed Central

Progress towards the synthesis of the microtubule-stabilizing agent, (?)-zampanolide, is reported. Construction of the 2,6-cis-tetrahydropyran ring was accomplished utilizing ether transfer methodology in conjunction with an intramolecular radical cyclization reaction. Efficient installation of the C16-C20 side chain relied on a one-pot cross-metathesis/olefination sequence, Sharpless epoxidation, and selective reduction of a vinyl epoxide. PMID:22720980

Wilson, Matthew R.; Taylor, Richard E.

2012-01-01

141

Recent advances on the enantioselective synthesis of C-nucleosides inhibitors of inosine monophosphate dehydrogenase (IMPDH).  

PubMed

This review will describe the recent advances in the synthesis of C-nucleosides with inhibitory activity of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the biosynthesis of guanine nucleotides. The review will cover synthetic approaches of structural analogues showing modifications in the furanose ring as well as in the heterocyclic base. Heterocyclic sugar nucleoside analogues in which the furanose ring has been replaced by a different heterocyclic ring including aza analogues, thioanalogues as well as dioxolanyl and isoxazolidinyl analogues are also considered. PMID:24758435

Merino, Pedro; Ghirardello, Mattia; Tejero, Tomas; Delso, Ignacio; Matute, Rosa

2014-01-01

142

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck-Iminium Ion Cyclization  

PubMed Central

A 1,2,3,4-tetrahydro-9a,4a-(iminoethano)-9H-carbazole (4) is a central structural feature of the Strychnos alkaloid minfiensine (1) and akuammiline alkaloids such as vincorine (5) and echitamine (6). A cascade catalytic asymmetric Heck-iminium cyclization was developed that rapidly provides 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazoles in high enantiomeric purity. Two sequences were developed for advancing 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazole 27 to (+)-minfiensine. In our first-generation approach, a reductive Heck cyclization was employed to form the fifth ring of (+)-minfiensine. In a second more concise total synthesis, an intramolecular palladium-catalyzed ketone enolate vinyl iodide coupling was employed to construct the final ring of (+)-minfiensine. This second-generation total synthesis of enantiopure (+)-minfiensine was accomplished in 6.5% overall yield and 15 steps from 1,2-cyclohexanedione and anisidine 13. A distinctive feature of this sequence is the use of palladium-catalyzed reactions to form all carbon–carbon bonds in the transformation of these simple precursors to (+)-minfiensine. PMID:18303837

Dounay, Amy B.; Humphreys, Philip G.; Overman, Larry E.; Wrobleski, Aaron D.

2010-01-01

143

Synthesis of Ferrocene Derivatives with Planar Chirality via Palladium-Catalyzed Enantioselective C-H Bond Activation.  

PubMed

The first catalytic and enantioselective C-H direct acylation of ferrocene derivatives has been developed. A series of 2-acyl-1-dimethylaminomethylferrocenes with planar chirality were provided under highly efficient and concise one-pot conditions with up to 85% yield and 98% ee. The products obtained could be easily converted to various chiral ligands via diverse transformations. PMID:25247387

Pi, Chao; Cui, Xiuling; Liu, Xiuyan; Guo, Mengxing; Zhang, Hanyu; Wu, Yangjie

2014-10-01

144

Organocatalytic cascade sulfa-Michael/aldol reaction of ?,?-disubstituted enones: enantioselective synthesis of tetrahydrothiophenes with a trifluoromethylated quaternary center.  

PubMed

A bifunctional squaramide-catalyzed sulfa-Michael/aldol cascade reaction initiated by sulfa-Michael addition of mercaptoacetaldehyde to ?-aryl-?-trifluoromethylated enones is successfully developed. The functionalized tetrahydrothiophenes with three continuous stereocenters including a trifluoromethylated quaternary carbon are readily obtained with moderate to good yields and high enantioselectivities. PMID:24079617

Su, Yu; Ling, Jun-Bing; Zhang, Shuang; Xu, Peng-Fei

2013-11-01

145

Enantioconvergent Hydroboration of a Racemic Allene: Enantioselective Synthesis of (E)-?-Stannyl-anti-Homoallylic Alcohols via Aldehyde Crotylboration  

PubMed Central

The enantioconvergent hydroboration of racemic allenylstannane (±)-1 with (dIpc)2BH converts both enantiomers of (±)-1 into the enantioenriched crotylborane (S)-E-3. Subsequent crotylboration of aldehydes with (S)-E-3 provides (E)-?-stannyl-homoallylic alcohols 5 in good yields and with excellent enantioselectivity. PMID:21449594

Chen, Ming; Roush, William R.

2011-01-01

146

Highly enantioselective synthesis of ?-azido-?-hydroxy methyl ketones catalyzed by a cooperative proline-guanidinium salt system.  

PubMed

The combined activity of (S)-proline and an achiral tetraphenylborate TBD-derived guanidinium salt permits the aldol reaction between azidoacetone and aromatic, or heteroaromatic aldehydes. The ?-azido-?-hydroxy methyl ketones obtained as products can be isolated in good yield, with high diastereo- and enantioselectivity. PMID:24468918

Martínez-Castañeda, Ángel; K?dziora, Kinga; Lavandera, Iván; Rodríguez-Solla, Humberto; Concellón, Carmen; del Amo, Vicente

2014-03-11

147

Exploring Nitrilase Sequence Space for Enantioselective Catalysis  

Microsoft Academic Search

Nitrilases are important in the biosphere as participants in synthesis and degradation pathways for naturally occurring, as well as xenobiotically derived, nitriles. Because of their inherent enantioselectivity, nitrilases are also attractive as mild, selective catalysts for setting chiral centers in fine chemical synthesis. Unfortunately, <20 nitrilases have been reported in the scientific and patent literature, and because of stability or

Dan E. Robertson; Jennifer A. Chaplin; Grace DeSantis; Mircea Podar; Mark Madden; Ellen Chi; Toby Richardson; Aileen Milan; Mark Miller; David P. Weiner; Kelvin Wong; Jeff McQuaid; Bob Farwell; Lori A. Preston; Xuqiu Tan; Marjory A. Snead; Martin Keller; Eric Mathur; Patricia L. Kretz; Mark J. Burk; Jay M. Short

2004-01-01

148

Using heteroaryl-lithium reagents as hydroxycarbonyl anion equivalents in conjugate addition reactions with (S,S)-(+)-pseudoephedrine as chiral auxiliary; enantioselective synthesis of 3-substituted pyrrolidines.  

PubMed

We have developed an efficient protocol for carrying out the stereocontrolled formal conjugate addition of hydroxycarbonyl anion equivalents to ?,?-unsaturated carboxylic acid derivatives using (S,S)-(+)-pseudoephedrine as chiral auxiliary, making use of the synthetic equivalence between the heteroaryl moieties and the carboxylate group. This protocol has been applied as key step in the enantioselective synthesis of 3-substituted pyrrolidines in which, after removing the chiral auxiliary, the heteroaryl moiety is converted into a carboxylate group followed by reduction and double nucleophilic displacement. Alternatively, the access to the same type of heterocyclic scaffold but with opposite absolute configuration has also been accomplished by making use of the regio- and diastereoselective conjugate addition of organolithium reagents to ?,?,?,?-unsaturated amides derived from the same chiral auxiliary followed by chiral auxiliary removal, ozonolysis, and reductive amination/intramolecular nucleophilic displacement sequence. PMID:23260037

Alonso, Beatriz; Ocejo, Marta; Carrillo, Luisa; Vicario, Jose L; Reyes, Efraim; Uria, Uxue

2013-01-18

149

Enantioselective synthesis of (1 S,2 S)-1,2-di- tert-butyl and (1 R,2 R)-1,2-di-(1-adamantyl)ethylenediamines  

Microsoft Academic Search

An enantioselective synthesis of sterically congested 1,2-di-tert-butyl and 1,2-di-(1-adamantyl)ethylenediamines has been developed. Thus, diastereomerically pure trans-1-apocamphanecarbonyl-4,5-dimethoxy-2-imidazolidinones 6 and 7 were successfully prepared by optical resolution of (±)-trans-4,5-dimethoxy-2-imidazolidinone using apocamphanecarbonyl chloride (MAC-Cl) followed by stereospecific and stepwise substitution of the dimethoxyl groups using tert-butyl or 1-adamantyl cuprates to provide (4S,5S)-4,5-di-tert-butyl and (4R,5R)-4,5-di-(1-adamantyl)-2-imidazolidinones 12 and 15, respectively. Furthermore, N-acetyl 4,5-di-tert-butyl and 4,5-di-(1-adamantyl)-2-imidazolidinones

Alaa A.-M. Abdel-Aziz; Serry A. A. El Bialy; Fatma E. Goda; Takehisa Kunieda

2004-01-01

150

Second-Generation DBFOX Ligands for the Synthesis of ?-Substituted ?-Amino Acids via Enantioselective Radical Conjugate Additions  

PubMed Central

A set of second-generation DBFOX ligands possessing extended aryl or benzyl-type groups was synthesized. The requisite amino alcohols were either commercially available (DBFOX/Bn) or constructed via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/t-BuPh, DBFOX/Pip) or phase-transfer-catalyzed asymmetric alkylation (DBFOX/MeNap). Complexes of the ligands with Mg(NTf2)2 were evaluated as promoters of enantioselective radical conjugate additions to ?,?-unsaturated ?-nitro amides and esters. Reactions employing the DBFOX/Nap ligand exhibited improved enantioselectivity relative to previously published additions mediated by DBFOX/Ph. However, the relatively modest increase in diastereomeric ratio suggests that our substrate–Lewis acid binding model, which was formulated based on results from DBFOX/Ph-promoted radical conjugate additions, is in need of revision. PMID:18947256

Banerjee, Biplab; Capps, Steven G.; Kang, Junghoon; Robinson, Joshua W.; Castle, Steven L.

2009-01-01

151

Asymmetric synthesis of chiral dihydrothiopyrans via an organocatalytic enantioselective formal thio [3 + 3] cycloaddition reaction with binucleophilic bisketone thioethers.  

PubMed

An unprecedented organocatalytic highly enantioselective approach to a 3,4-dihydro-2H-thiopyran scaffold with two contiguous stereogenic centers has been implemented through a formal thio [3 + 3] cycloaddition process involving a Michael-aldol condensation cascade sequence. Notably, a new class of binucleophilic bisketone thioethers is designed for the process. Furthermore, the fine-tuning of their reactivity enables the cascade process to proceed with highly regioselectively. PMID:24152030

Wang, Shengzheng; Zhang, Yongqiang; Dong, Guoqiang; Wu, Shanchao; Zhu, Shiping; Miao, Zhenyuan; Yao, Jianzhong; Li, Hao; Li, Jian; Zhang, Wannian; Sheng, Chunquan; Wang, Wei

2013-11-01

152

Palladium-catalysed enantioselective bis-alkoxycarbonylation of 1-olefins. Synthesis of optically active 2-substituted-butanedioates  

Microsoft Academic Search

Cationic palladium(II) complexes of the type [Pd(L^L?)(S2)]X2 (where L^L? is a chelate ligand with C2 symmetry, S is a solvent molecule, and X is an anion with low coordination properties) are able to catalyse the enantioselective bis-alkoxycarbonylation of 1-olefins to substituted succinates. Using atropisomeric fully aromatic ligands high enantio- and chemoselectivity have been obtained when styrene is the substrate. For

Martin Sperrle; Giambattista Consiglio

1999-01-01

153

Palladium-catalyzed enantioselective allylic alkylation of thiocarboxylate ions: asymmetric synthesis of allylic thioesters and memory effect/dynamic kinetic resolution of allylic esters.  

PubMed

The palladium-catalyzed allylic alkylation of KSAc and KSBz with racemic cyclic and acyclic allylic esters by using N,N'-(1R,2R)-1,2-cyclohexandiylbis[2-(diphenylphosphino)-benzamide] as ligand frequently gave the corresponding allylic thioesters with high ee values and yields. The reaction of the cyclic allylic carbonates with KSAc in the presence of H(2)O was accompanied by a partial palladium-catalyzed enantioselective "hydrolysis" of the substrates with formation of the corresponding enantioenriched allylic alcohols. The degree of the "hydrolysis" was strongly dependent on the solvent and the thiocarboxylate ion. Highly selective kinetic resolutions (KRs) were observed in the palladium-catalyzed reaction of the racemic cyclohexenyl and cycloheptenyl acetates with KSAc. While the KR of the cyclohexenyl acetate is characterized by a selectivity factor S = 72 +/- 19, that of the cycloheptenyl acetate afforded (R)-cycloheptenyl acetate of >or=99% ee in 48% yield and (S)-cycloheptenyl thioacetate of 98% ee in 50% yield. The palladium-catalyzed reaction of the racemic cyclopentenyl acetate with KSAc showed a strong "memory effect" (ME), that is, both enantiomers reacted with different enantioselectivities. The ME was probed by studying the palladium-catalyzed reactions of both the matched acetate of >or=99% ee and the mismatched acetate of >or=99% ee with KSAc. The acetates not only reacted with different enantioselectivities and rates but also suffered an unexpected and concomitant palladium-catalyzed racemization in the presence of the chiral ligand. This led in the case of the mismatched acetate to a temporary dynamic kinetic resolution (DKR) that featured a racemization of the mismatched acetate by the chiral catalyst. Studies of the palladium-catalyzed reaction of the racemic cyclopentenyl acetate, carbonate, and naphthoate with KSAc in the presence of the chiral ligand also showed the ME to be strongly dependent on the nucleofuge. This also allowed the synthesis of (S)-cyclopentenyl thioacetate of 92% ee in high yield from the racemic cyclopentenyl naphthoate. PMID:15176829

Lüssem, Bernhard J; Gais, Hans-Joachim

2004-06-11

154

Development of a nonchiral HPLC method with circular dichroism detection for chiral analysis of molybdenum-catalyzed enantioselective synthesis products.  

PubMed

The combination of a circular dichroism detector and nonchiral liquid chromatography was used for the chiral analysis of unresolved enantiomers to determine the enantioselectivity of a molybdenum-catalyzed asymmetric allylic alkylation reaction. The CD/UV peak area ratio of the unresolved enantiomers was calculated and compared with that of a reference standard to determine the enantiomeric purity. The limit of quantitation (LOQ) is 20 ng for the chiral ligand and 1 microg for the branched chiral product. The viability of the system depends on the limit of quantitation of the CD response and the linearity range of the CD and UV response. PMID:12125036

Miller, Michael T; Ge, Zhihong; Mao, Bing

2002-08-01

155

A general and enantioselective approach to pentoses: a rapid synthesis of PSI-6130, the nucleoside core of sofosbuvir.  

PubMed

An efficient route towards biologically relevant pentose derivatives is described. The de novo synthetic strategy features an enantioselective ?-oxidation reaction enabled by a chiral amine in conjunction with copper(II) catalysis. A subsequent Mukaiyama aldol coupling allows for the incorporation of a wide array of modular two-carbon fragments. Lactone intermediates accessed via this route provide a useful platform for elaboration, as demonstrated by the preparation of a variety of C-nucleosides and fluorinated pentoses. Finally, this work has facilitated expedient syntheses of pharmaceutically active compounds currently in clinical use. PMID:24670208

Peifer, Manuel; Berger, Raphaëlle; Shurtleff, Valerie W; Conrad, Jay C; MacMillan, David W C

2014-04-23

156

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

PubMed

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

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

2014-06-10

157

Application of capillary electrophoresis to study the enantioselective transformation of five chiral pesticides in aerobic soil slurries.  

PubMed

The enantiomers of five chiral pesticides of environmental interest, metalaxyl, imazaquin, fonofos (dyfonate), ruelene (cruformate), and dichlorprop, were separated analytically using capillary electrophoresis (CE) with cyclodextrin chiral selectors. For metalaxyl, imazaquin, and fonofos, aqueous slurries of soil samples from two sites in Georgia and one in Ohio were spiked with the racemate of each pesticide at 50-60 mg/L of aqueous phase of the slurry, and CE analyses were performed at various time intervals to determine enantiomer fractions (EF). Metalaxyl underwent enantioselective transformation; in one soil, the half-life of the target active R-(+)-enantiomer was 17 days while that for the S-(-)-enantiomer was 69 days. Transformation occurred more slowly in the other two soils but was still selective for the R-(+)-enantiomer. Imazaquin and fonofos exhibited nonselective enantiomer loss over their 3 months of incubation time; this could have been due to abiotic or nonselective microbial reactions. Ruelene and dichlorprop were transformed selectively in a variety of soils in a previously reported study (7) that showed the influence of environmental changes on the transformation of chiral pollutants in soils; analytical methods used in that study are reported here to further illustrate the application of CE. CE is shown to be a simple, efficient, and inexpensive way to follow the transformation of chiral pesticides in laboratory microcosms where concentrations can be made high enough (25-50 mg/L initial racemate concentration) for detection of residual parent enantiomers during most of the process. PMID:16076090

Jarman, Jessica L; Jones, W Jack; Howell, Lorrie A; Garrison, A Wayne

2005-08-10

158

Rhodium-catalyzed highly enantioselective arylation of cyclic diketimines: efficient synthesis of chiral tetrasubstituted 1,2,5-thiadiazoline 1,1-dioxides.  

PubMed

A highly enantioselective rhodium-catalyzed arylation of cyclic diketimines with arylboronic acids was achieved under mild conditions by employing a simple, sulfinamide-based branched olefin ligand. This protocol provides an efficient access to valuable chiral tetrasubstituted 1,2,5-thiadiazoline 1,1-dioxides in high yields with excellent enantioselectivities of up to 99% ee. PMID:25029275

Wang, Hui; Li, Yi; Xu, Ming-Hua

2014-08-01

159

Highly enantioselective synthesis of chiral 7-ring O- and N-heterocycles by a one-pot nitro-Michael-cyclization tandem reaction.  

PubMed

A concise enantioselective approach to synthesise medium-sized 7-ring O- and N-heterocycles has been developed. The synthetic strategy relies on an organocatalytic nitro-Michael-nitrile oxide cycloaddition tandem reaction, leading to the corresponding chiral benzoxe- and benzazepine derivatives containing an additional fused dihydroisoxazoline ring in good yields and excellent enantioselectivities (up to 97% ee). PMID:24190160

Rohlmann, Renate; Daniliuc, Constantin-Gabriel; Mancheño, Olga García

2013-12-25

160

Expression of a lipase on the cell-surface of Escherichia coli using the OmpW anchoring motif and its application to enantioselective reactions.  

PubMed

Microbial-surface display is the expression of proteins or peptides on the surface of cells by fusing an appropriate protein as an anchoring motif. Here, the outer membrane protein W (OmpW) was selected as a fusion partner for functional expression of Pseudomonas fluorescence SIK W1 lipase (TliA) on the cell-surface of Escherichia coli. Localization of the truncated OmpW-TliA fusion protein on the cell-surface was confirmed by immunoblotting and functional assay of lipase activity. Enantioselective hydrolysis of rac-phenylethyl butanoate by the displayed lipase resulted in optically active (R)-phenyl ethanol with 96% enantiomeric excess and 44% of conversion in 5 days. Thus, a small outer membrane protein OmpW, is a useful anchoring motif for displaying an active enzyme of ~50 kDa on the cell-surface and the surface-displayed lipase can be employed as an enantioselective biocatalyst in organic synthesis. PMID:23881313

Lee, Hyuk; Park, Si Jae; Han, Mee-Jung; Eom, Gyeong Tae; Choi, Min-Jung; Kim, Seong Ho; Oh, Young Hoon; Song, Bong Keun; Lee, Seung Hwan

2013-10-01

161

Total synthesis and study of myrmicarin alkaloids  

E-print Network

I. Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids An enantioselective gram-scale synthesis of a key dihydroindolizine intermediate for the preparation of myrmicarin alkaloids is described. Key transformations ...

Ondrus, Alison Evelynn, 1981-

2009-01-01

162

Enol ethers as substrates for efficient Z- and enantioselective ring-opening/cross-metathesis reactions promoted by stereogenic-at-Mo complexes: utility in chemical synthesis and mechanistic attributes.  

PubMed

The first examples of catalytic enantioselective ring-opening/cross-metathesis (EROCM) reactions that involve enol ethers are reported. Specifically, we demonstrate that catalytic EROCM of several oxa- and azabicycles, cyclobutenes and a cyclopropene with an alkyl- or aryl-substituted enol ether proceed readily in the presence of a stereogenic-at-Mo monopyrrolide-monoaryloxide. In some instances, as little as 0.15 mol % of the catalytically active alkylidene is sufficient to promote complete conversion within 10 min. The desired products are formed in up to 90% yield and >99:1 enantiomeric ratio (er) with the disubstituted enol ether generated in >90% Z selectivity. The enol ether of the enantiomerically enriched products can be easily differentiated from the terminal alkene through a number of functionalization procedures that lead to the formation of useful intermediates for chemical synthesis (e.g., efficient acid hydrolysis to afford the enantiomerically enriched carboxaldehyde). In certain cases, enantioselectivity is strongly dependent on enol ether concentration: larger equivalents of the cross partner leads to the formation of products of high enantiomeric purity (versus near racemic products with one equivalent). The length of reaction time can be critical to product enantiomeric purity; high enantioselectivity in reactions that proceed to >98% conversion in as brief a reaction time as 30 s can be nearly entirely eroded within 30 min. Mechanistic rationale that accounts for the above characteristics of the catalytic process is provided. PMID:22272931

Yu, Miao; Ibrahem, Ismail; Hasegawa, Masayuki; Schrock, Richard R; Hoveyda, Amir H

2012-02-01

163

One-pot chemoenzymatic synthesis of chiral 1,3-diols using an enantioselective aldol reaction with chiral Zn2+ complex catalysts and enzymatic reduction using oxidoreductases with cofactor regeneration.  

PubMed

We previously reported on enantioselective aldol reactions of acetone and some aldehydes catalyzed by chiral Zn(2+) complexes of L-prolyl-pendant [12]aneN(4) (L-ZnL(1)) and L-valyl-pendant [12]aneN(4) (L-ZnL(2)) in aqueous solution. Here, we report on the one-pot chemoenzymatic synthesis of chiral 1,3-diols in an aqueous solvent system at room temperature by a combination of enantioselective aldol reactions catalyzed by Zn(2+) complexes of L- and D-phenylalanyl-pendant [12]aneN(4) (L-ZnL(3) and D-ZnL(3) ) and the successive enantioselective reduction of the aldol products using oxidoreductases with the regeneration of the NADH (reduced form of nicotinamine adenine dinucleotide) cofactor. The findings indicate that all four stereoisomers of 1,3-diols can be produced by appropriate selection of a chiral Zn(2+)-complex and an oxidoreductase commercially available from the "Chiralscreen OH" kit. PMID:22174123

Sonoike, Shotaro; Itakura, Toshinari; Kitamura, Masanori; Aoki, Shin

2012-01-01

164

Enantioselective divergent syntheses of several polyhalogenated plocamium monoterpenes and evaluation of their selectivity for solid tumors.  

PubMed

The family of polyhalogenated monoterpenes from Plocamium counts over a hundred known members. Using glyceraldehyde acetonide as a chiral-pool precursor, an enantioselective and divergent strategy was developed that provides a blueprint for the synthesis of many of the small yet complex acyclic members of this family. The broad applicability of this approach is demonstrated with the short, eight-step synthesis of four natural products and three analogues. These syntheses are the first of any members of the acyclic polyhalogenated Plocamium monoterpenes and permitted the evaluation of their selectivity against a range of tumor cell lines. PMID:25220828

Vogel, Carl V; Pietraszkiewicz, Halina; Sabry, Omar M; Gerwick, William H; Valeriote, Frederick A; Vanderwal, Christopher D

2014-11-01

165

Catalytic enantioselective diversity-oriented synthesis of a small library of polyhydroxylated pyrans inspired from thiomarinol antibiotics.  

PubMed

A small library of 30 thiomarinol analogues was successfully synthesised using as a key step-a catalytic enantioselective tandem oxa[4+2] cycloaddition/aldehyde allylboration methodology. With this method, highly substituted [Formula: see text]-hydroxyalkyl dihydropyrans were assembled in a single three-component reaction utilizing three different enol ethers and a wide variety of aldehydes, such as aromatic, heteroaromatic, unsaturated and aliphatic aldehydes. In a second operation, a mild and direct method for reducing an acetal unit in the [Formula: see text]-hydroxyalkyl dihydropyrans was optimised without the need for protecting a nearby hydroxyl group. This procedure facilitated the synthetic sequence, which was completed by a dihydroxylation of the residual olefin of [Formula: see text]-hydroxyalkyl 2[Formula: see text]-pyrans to provide the desired library of dihydroxylated pyran analogues reminiscent of the thiomarinol antibiotics. The relative stereochemistry of the resulting library compounds was demonstrated by X-ray crystallography on one of the analogues. PMID:25151273

Al-Zoubi, Raed M; Hall, Dennis G

2014-11-01

166

Microbiological transformations 35: Enantioselective one-step preparative scale synthesis of 1,3-dithiane-1-oxide via whole-cell bacterial oxidation  

Microsoft Academic Search

This work describes the preparative scale enantioselective oxidation of 1,3-dithiane to the corresponding monosulfoxide using whole-cell cultures of two bacteria, i.e. Acinetobacter calcoaceticus NCIMB 9871 and Pseudomonas sp. NCIMB 9872.

Véronique Alphand; Nicoletta Gaggero; Stefano Colonna; Roland Furstoss

1996-01-01

167

Chiral phosphorus-based 1,3-dipoles: a modular approach to enantioselective 1,3-dipolar cycloaddition and polycyclic 2-pyrroline synthesis.  

PubMed

The design of a new class of chiral 1,3-dipoles for enantioselective cycloaddition reactions is reported. These phosphorus-based dipoles are easily formed (from imines, acid chlorides, and chiral phosphites), rigidly chiral, and undergo intramolecular alkene cycloaddition with high enantioselectivity. Overall, this provides a straightforward and modular approach to synthesize chiral 2-pyrrolines and pyrrolidines in up to 99% ee. PMID:24502319

Morin, Marie S T; Arndtsen, Bruce A

2014-02-21

168

Regiocontrol by remote substituents. An enantioselective total synthesis of frenolicin B via a highly regioselective Diels-Alder reaction  

SciTech Connect

The quinone subunit is contained in a broad range of biologically important natural products such as frenolicin B, which is a member of the pyranonaphthoquinone family. The diverse biological activity of quinones has led to the development of several new synthetic methods for quinones. Among the pathways featuring a cycloaddition reaction, one of the most general methods for the regiospecific synthesis of substituted quinones was pioneered by H.J. Rapoport and others. This method involves the Diels-Alder reaction of a substituted quinone. As part of a program to evaluate the directing effects of functional groups not directly attached to the atoms undergoing Diels-Alder cycloaddition, we now report that remote substituents on a dienophile can confer excellent regioselectivity in Diels-Alder reactions. This work has led to an extremely direct synthesis of the pyranonaphthoquinone framework and to the first synthesis of frenolicin B (1). 19 refs., 1 fig.

Kraus, G.A.; Li, J. (Iowa State Univ., Ames (United States)); Gordon, M.S.; Jensen, J.H. (Ames Lab. US-DOE, IA (United States))

1993-06-30

169

Enantioselective synthesis of polycyclic nitrogen heterocycles by Rh-catalyzed alkene hydroacylation: constructing six-membered rings in the absence of chelation assistance.  

PubMed

Catalytic, enantioselective hydroacylations of N-allylindole-2-carboxaldehydes and N-allylpyrrole-2-carboxaldehydes are reported. In contrast to many alkene hydroacylations that form six-membered rings, these annulative processes occur in the absence of ancillary functionality to stabilize the acylrhodium(III) hydride intermediate. The intramolecular hydroacylation reactions generate 7,8-dihydropyrido[1,2-a]indol-9(6H)ones and 6,7-dihydroindolizin-8(5H)-ones in moderate to high yields with excellent enantioselectivities. PMID:25020184

Du, Xiang-Wei; Ghosh, Avipsa; Stanley, Levi M

2014-08-01

170

Design of novel chiral N,N,O-tridentate phenanthroline ligands and their application to enantioselective addition of organozinc reagents to aldehydes.  

PubMed

The novel N,N,O-tridentate phenanthroline ligand (BinThro) bearing an axially chiral binaphthyl backbone prepared from BINOL was found to be an effective chiral catalyst for enantioselective addition of diethylzinc to aromatic aldehydes with high enantioselectivity (up to 95% ee). PMID:25080306

Naganawa, Yuki; Namba, Tomoya; Aoyama, Tomotaka; Shoji, Kentaro; Nishiyama, Hisao

2014-11-11

171

Phosphine-catalyzed asymmetric [4+1] annulation of activated ?,?-unsaturated ketones with Morita-Baylis-Hillman carbonates: enantioselective synthesis of spirooxindoles containing two adjacent quaternary stereocenters.  

PubMed

The asymmetric [4+1] annulation of activated ?,?-unsaturated ketones with MBH carbonates catalyzed by bifunctional thiourea-phosphine catalysts derived from an axially chiral binaphthyl scaffold has been developed, giving spirooxindoles with two adjacent quaternary stereocenters in good yields with high enantioselectivities and moderate diastereoselectivities under mild conditions. PMID:24976341

Hu, Fang-Le; Wei, Yin; Shi, Min

2014-08-18

172

Enantioselective Approach to Quinolizidines: Total Synthesis of Cermizine D and Formal Syntheses of Senepodine G & Cermizine C  

PubMed Central

The formal total syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselecetive, intramolecular amide Michael addition process. The total synthesis of cermizine D has been achieved through use of an organocatalyzed, heteroatom Michael addition to access a common intermediate. Additional key steps of this sequence include a matched, diastereoselective alkylation with an iodomethylphenyl sulfide and sulfone-aldehyde coupling/reductive desulfurization sequence to combine the major subunits. The utility of a Hartwig-style C-N coupling has been explored on functionally dense coupling partners. Diastereoselective conjugate additions to ?,?-unsaturated sulfones has been investigated which provided the key sulfone intermediate in just six steps from commercially available starting materials. The formal syntheses of senepodine G and cermizine C have been accomplished through an intramolecular cyclization process of a N-Boc protected piperidine sulfone. PMID:23627426

Veerasamy, Nagarathanam; Carlson, Erik C.; Collett, Nathan D.; Saha, Mrinmoy

2013-01-01

173

Chiral functionalization of graphene oxide by optically active helical-substituted polyacetylene chains and its application in enantioselective crystallization.  

PubMed

This article reports an original, versatile strategy to chirally functionalize graphene oxide (GO) with optically active helical-substituted polyacetylene. GO was first converted into alkynyl-GO containing polymerizable -C?C moieties, which took part in the polymerization of another chiral acetylenic monomer, yielding the expected GO hybrid covalently grafted with chiral helical polyacetylene chains. Transmission electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyses verified the successful attachment of substituted polyacetylene chains on GO by covalent chemical bonding. Moreover, circular dichroism effects and UV-vis absorption demonstrated that the GO hybrid possessed fascinating optical activity. It also largely improved the dispersibility of GO in tetrahydrofuran. The GO-derived hybrid was further used as a chiral inducer toward enantioselective crystallization of alanine enantiomers. l-Alanine was preferably induced to crystallize, forming rodlike crystals. PMID:24902050

Li, Weifei; Liang, Junya; Yang, Wantai; Deng, Jianping

2014-06-25

174

Enantioselective total syntheses of cyathane diterpenoids.  

PubMed

A Personal Account describing the enantioselective total syntheses of cyathane diterpenoids achieved in the Nakada group. A convergent approach to the cyathane scaffold, the [5-6-7] tricyclic carbon skeleton commonly found in cyathane diterpenoids, has been developed using the catalytic asymmetric intramolecular cyclopropanation (CAIMCP) and baker's yeast reduction. This approach has been successfully applied for the enantioselective total syntheses of (+)-allocyathin B2 , (-)-erinacine B, and (-)-erinacine E. The total synthesis of (-)-erinacine E has been achieved via the acyl group migratory intramolecular aldol reaction, which prevents the retro-aldol reaction and allows the construction of the strained structure. The highly efficient and stereoselective total syntheses of (-)-scabronines G, A, D, and (-)-episcabronine A have been achieved via the oxidative dearomatization/inverse electron demand Diels-Alder reaction cascade. Cascade reactions comprising three and five consecutive reactions were employed for the highly efficient total syntheses of (-)-scabronine A and (-)-episcabronine A, respectively. PMID:25065736

Nakada, Masahisa

2014-08-01

175

Germanium nanocrystals: Synthesis, characterization, and applications  

Microsoft Academic Search

The aim of this work was to demonstrate a simple synthesis route of Ge nanostructures (nanoparticles and nanowires), to characterize the physical and optical properties of Ge nanocrystal, and to demonstrate their biological and optoelectronics applications. The appropriate organometallic Ge 2+ precursors for the synthesis of Ge nanocrystals were identified. These precursors were used to develop a simple route that

Henry Gerung

2006-01-01

176

Enantioselective CuH-Catalyzed Anti-Markovnikov Hydroamination of 1,1-Disubstituted Alkenes.  

PubMed

Enantioselective synthesis of ?-chiral amines has been achieved via copper-catalyzed hydroamination of 1,1-disubstituted alkenes with hydroxylamine esters in the presence of a hydrosilane. This mild process affords a range of structurally diverse ?-chiral amines, including ?-deuterated amines, in excellent yields with high enantioselectivities. Furthermore, catalyst loading as low as 0.4 mol% could be employed to deliver product in undiminished yield and selectivity, demonstrating the practicality of this method for large-scale synthesis. PMID:25339089

Zhu, Shaolin; Buchwald, Stephen L

2014-11-12

177

Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(I) catalyst†  

PubMed Central

A racemic Au(I)-catalyzed three-component reaction has been developed to prepare cyclic carbamimidates from imines, terminal alkynes, and sulfonylisocyanates. This reaction exploits the carbophilic ?-acidity of gold catalysts to first activate an alkyne toward deprotonation and secondly, to activate the internal alkyne generated toward intramolecular O-cyclization. Unlike similar previously reported multicomponent gold-catalyzed reactions, the stereocenter generated during the alkynylation is preserved in the product. This trait was exploited by developing an enantioselective variant, using an unusual trans-1-diphenylphosphino-2-arylsulfamidocyclohexane ligand. Moderate to excellent levels of enantioselectivity were obtained using a variety of N-arylbenzylidene anilines (41–95% ee, 18 examples). PMID:22712050

Campbell, Matthew J.

2012-01-01

178

Enantioselective [4 + 2] cycloadditions of iminoacetonitriles : application to the total synthesis of (-)-quinolizidine 2071  

E-print Network

Iminoacetonitriles participate as reactive dienophiles in intramolecular Diels-Alder cycloadditions affording quinolizidines and indolizidines. The resulting a-amino nitrile cycloadducts are versatile intermediates that ...

Fontaine, Shaun D. (Shaun David)

2011-01-01

179

Asymmetric biomimetic oxidations of phenols: the mechanism of the diastereo- and enantioselective synthesis of dehydrodiconiferyl ferulate (DDF) and dehydrodiconiferyl alcohol (DDA)  

Microsoft Academic Search

Stereoselective bimolecular radical coupling of enantiopure phenylpropenoidic phenols are described, starting from enantiopure amidic derivatives of ferulic acid. The latter were prepared from ferulic acid by reaction with (S)-alanine or Oppolzer camphor sultam. The oxidation step was performed both enzymatically (HRP\\/H2O2) and chemically (Ag2O). The observed enantioselectivity in the oxidation step encompasses the range 65–84% and is consistent with the

Marco Orlandi; Bruno Rindone; Giorgio Molteni; Petteri Rummakko; Gösta Brunow

2001-01-01

180

Brønsted Acid catalyzed phosphoramidic Acid additions to alkenes: diastereo- and enantioselective halogenative cyclizations for the synthesis of C- and p-chiral phosphoramidates.  

PubMed

The first highly diastereo- and enantioselective additions of a halogen and phosphoramidic acid to unactivated alkenes have been developed, catalyzed by a chiral Brønsted acid. A unique feature of these additions is the opportunity for stereocontrol at two noncontiguous chiral centers, carbon and phosphorus, leading to cyclic P-chiral phosphoramidates. In addition to their inherent value, the phosphoramidates are precursors to enantioenriched epoxy allylamines. PMID:25336273

Toda, Yasunori; Pink, Maren; Johnston, Jeffrey N

2014-10-22

181

Asymmetric Catalysis Special Feature Part II: Development of an efficient, scalable, aldolase-catalyzed process for enantioselective synthesis of statin intermediates  

Microsoft Academic Search

A process is reported for efficient, enantioselective production of key intermediates for the common chiral side chain of statin-type cholesterol-lowering drugs such as Lipitor (atorvastatin) and Crestor (rosuvastatin). The process features a one-pot tandem aldol reaction catalyzed by a deoxyribose-5-phosphate aldolase (DERA) to form a 6-carbon intermediate with installation of two stereogenic centers from 2-carbon starting materials. An improvement of

William A. Greenberg; Alexander Varvak; Sarah R. Hanson; Kelvin Wong; Hongjun Huang; Pei Chen; Mark J. Burk

2004-01-01

182

Supporting Information for Levine, Krout, and Stoltz; Total Synthesis of (+)-Carissone SI 1 Catalytic Enantioselective Approach to the Eudesmane Sesquiterpenoids: Total Synthesis of (+)-  

E-print Network

of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, reactions were performed in flame-dried glassware under an argon or nitrogen atmosphere using dry Series HPLC utilizing a Chiralpak AD column (4.6 mm x 25 cm) obtained from Daicel Chemical Industries

Stoltz, Brian M.

183

A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

Bennett, George D.

2006-01-01

184

Enantioselective Total Syntheses of (-)-Palau'amine, (-)- Axinellamines, and (-)-Massadines  

PubMed Central

Dimeric pyrrole-imidazole alkaloids represent a rich and topologically unique class of marine natural products. This full account will follow the progression of efforts that culminated in the enantioselective total syntheses of the most structurally ornate members of this family: the axinellamines, the massadines, and palau’amine. A bio-inspired approach capitalizing on the pseudo-symmetry of the members of this class is recounted, delivering a deschloro derivative of the natural product core. Next, the enantioselective synthesis of the chlorocyclopentane core featuring a scalable, catalytic, enantioselective Diels–Alder reaction of a 1-siloxydiene is outlined in detail. Finally, the successful divergent conversion of this core to each of the aforementioned natural products, and the ensuing methodological developments are described. PMID:21861522

Seiple, Ian B.; Su, Shun; Young, Ian S.; Nakamura, Akifumi; Yamaguchi, Junichiro; J?rgensen, Lars; Rodriguez, Rodrigo A.; O'Malley, Daniel P.; Gaich, Tanja; Kock, Matthias; Baran, Phil S.

2011-01-01

185

Direct enantioselective aldol-Tishchenko reaction catalyzed by chiral lithium diphenylbinaphtholate.  

PubMed

Chiral lithium diphenylbinaphtholate is an effective catalyst for the enantioselective aldol-Tishchenko reaction, affording 1,3-diol derivatives with three contiguous chiral centers and high stereoselectivities. Successive aldol-aldol-Tishchenko reactions gave a triol derivative with five consecutive chiral centers. The present reaction was applicable to highly enantioselective Evans-Tishchenko reduction. PMID:21355567

Ichibakase, Tomonori; Nakajima, Makoto

2011-04-01

186

Enantioselective halocyclization using reagents tailored for chiral anion phase-transfer catalysis.  

PubMed

A chiral anion phase-transfer system for enantioselective halogenation is described. Highly insoluble, ionic reagents were developed as electrophilic bromine and iodine sources, and application of this system to o-anilidostyrenes afforded halogenated 4H-3,1-benzoxazines with excellent yield and enantioselectivity. PMID:22830953

Wang, Yi-Ming; Wu, Jeffrey; Hoong, Christina; Rauniyar, Vivek; Toste, F Dean

2012-08-01

187

Development of new methods in organic synthesis and their applications to the synthesis of biologically interesting natural products.  

PubMed

2,6-Dimethyl-9-Aryl-9-phosphabicyclo[3.3.1]nonanes (9-PBN and 9-NapBN) and the chiral diaminophosphine oxides (DIAPHOXs) derived from aspartic acid have been introduced as useful ligands and preligands, respectively, for transition metal-catalyzed asymmetric synthesis. anti-Selective asymmetric hydrogenation of ?-amino-?-ketoesters using Ru-, Rh-, Ir-, and Ni-catalysts through dynamic kinetic resolution have been developed for the first time, producing efficiently important anti ?-hydroxy-?-amino acids. The total synthesis of several biologically active natural products was achieved by use of the transition metal-catalyzed reaction using DIAPHOX, anti-selective asymmetric hydrogenation, and reactions developed by us. Synthesis of tangutorine, an antitumor indole alkaloid, has been enantioselectively achieved for the first time. Enantioselective synthesis of a martinelline chiral core was accomplished using the asymmetric tandem Michael-Aldol reaction as a key step developed by us. This synthesis represents the formal total synthesis of martinelline and martinellic acid. Papuamide B was synthesized through the elucidation of unknown stereostructures by using the anti-selective asymmetric hydrogenation and reactions developed by us. PMID:22223369

Hamada, Yasumasa

2012-01-01

188

Enantioselective Hydroformylation of Aniline Derivatives  

PubMed Central

We have developed a ligand that reversibly binds to aniline substrates allowing for the control of regioselectivity and enantioselectivity in hydroformylation. In this paper we address how the electronics of the aniline ring affect both binding of the substrate to the ligand and the enantioselectivity in this reaction. PMID:21842847

Joe, Candice L.; Tan, Kian L.

2011-01-01

189

Synthesis and application of phosphinoferrocenylaminophosphine ligands for asymmetric catalysis.  

PubMed

A new class of bidentate ligands utilizing a phosphine-aminophosphine structure has been prepared on a ferrocenylethyl backbone in a straightforward and scalable fashion from acetylferrocene. The unique property of the alpha-ferrocenyl carbonium ion that allows the replacement of a variety of "leaving groups" with retention of configuration greatly facilitates the synthesis, and a number of ligands have been prepared by varying the nitrogen and phosphorus substituents on the aminophosphine. These readily prepared phosphinoferrocenylaminophosphines, known as BoPhoz ligands, show surprising hydrolytic and air stability, with no degradation after 3 years open to the air. The rhodium complexes of these ligands show exceedingly high enantioselectivities (generally >95% ee) and activities often in excess of 50,000 catalyst turnovers per hour for the asymmetric hydrogenation of a wide variety of dehydro-alpha-amino acid and itaconic acid derivatives. They also show high activity and good to excellent enantioselectivity for the hydrogenation of a number of alpha-ketoesters. PMID:15730312

Boaz, Neil W; Mackenzie, Elaine B; Debenham, Sheryl D; Large, Shannon E; Ponasik, James A

2005-03-01

190

Dinuclear Zinc-Prophenol-Catalyzed Enantioselective ?-Hydroxyacetate Aldol Reaction with Activated Ester Equivalents  

PubMed Central

An enantioselective ?-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc Prophenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting ?,?-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Trost, Barry M.; Michaelis, David J.; Truica, Mihai I.

2013-01-01

191

Dinuclear zinc-ProPhenol-catalyzed enantioselective ?-hydroxyacetate aldol reaction with activated ester equivalents.  

PubMed

An enantioselective ?-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc-ProPhenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting ?,?-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Trost, Barry M; Michaelis, David J; Truica, Mihai I

2013-09-01

192

Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation  

PubMed Central

Summary Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of “classic” natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge. PMID:25383121

Liu, Yiyang; Liniger, Marc; McFadden, Ryan M; Roizen, Jenny L; Malette, Jacquie; Reeves, Corey M; Behenna, Douglas C; Seto, Masaki; Kim, Jimin; Mohr, Justin T; Virgil, Scott C

2014-01-01

193

Applications of Bartoli indole synthesis.  

PubMed

In 1989, the reaction of vinyl magnesium halides with ortho-substituted nitroarenes leading to indoles was discovered. This reaction is now frequently reported as the "Bartoli reaction" or the "Bartoli indole synthesis" (BIS). It has rapidly become the shortest and most flexible route to 7-substituted indoles, because the classical indole syntheses generally fail in their preparation. The flexibility of the Bartoli reaction is great as it can be extended to heteroaromatic nitro derivatives and can be run on solid support. This review will focus on the use of the Bartoli indole synthesis as the key step in preparations of complex indoles, which appeared in the literature in the last few years. PMID:24718836

Bartoli, Giuseppe; Dalpozzo, Renato; Nardi, Monica

2014-07-01

194

Synthesis, characterization and optical applications of nanomaterials  

Microsoft Academic Search

Nanomaterials have been studied extensively due to their potential application in electronics, photonics and nanodevices. There are a wide variety of methods developed to create the nano-scale materials. Chemical colloidal synthesis is the way most used since it is reproducible and high efficiency. Nanoparticles lie at the heart of nanoscience for their novel electronic, magnetic and optical properties. In this

Fen Xu

2010-01-01

195

Synthesis of chiral N-phosphoryl aziridines through enantioselective aziridination of alkenes with phosphoryl azide via Co(II)-based metalloradical catalysis  

PubMed Central

Summary The Co(II) complex of a new D 2-symmetric chiral porphyrin 3,5-DiMes-QingPhyrin, [Co(P6)], can catalyze asymmetric aziridination of alkenes with bis(2,2,2-trichloroethyl)phosphoryl azide (TcepN3) as a nitrene source. This new Co(II)-based metalloradical aziridination is suitable for different aromatic olefins, producing the corresponding N-phosphorylaziridines in good to excellent yields (up to 99%) with moderate to high enantioselectivities (up to 85% ee). In addition to mild reaction conditions and generation of N2 as the only byproduct, this new metalloradical catalytic system is highlighted with a practical protocol that operates under neutral and non-oxidative conditions. PMID:24991280

Tao, Jingran; Jin, Li-Mei

2014-01-01

196

A Preparation of (-)-Nutlin-3 Using Enantioselective Organocatalysis at Decagram Scale  

PubMed Central

Chiral nonracemic cis-4,5-bis(aryl) imidazolines have emerged as a powerful platform for the development of cancer chemotherapeutics, stimulated by the Hoffmann-La Roche discovery that Nutlin-3 can restore apoptosis in cells with wild-type p53. The lack of efficient methods for the enantioselective synthesis of cis-imidazolines, however, has limited their more general use. Our disclosure of the first enantioselective synthesis of (?)-Nutlin-3 provided a basis to prepare larger amounts of this tool used widely in cancer biology. Key to the decagram-scale synthesis described here was the discovery of a novel bis(amidine) organocatalyst that provides high enantioselectivity at warmer reaction temperature (?20 °C) and low catalyst loadings. Further refinements to the procedure led to the synthesis of (?)-Nutlin-3 in a 17 gram batch, and elimination of all but three chromatographic purifications. PMID:24127627

Davis, Tyler A.; Vilgelm, Anna E.; Richmond, Ann; Johnston, Jeffrey N.

2013-01-01

197

Gold(I)-Catalyzed Enantioselective Intramolecular Hydroamination of Allenes Rebecca L. LaLonde, Benjamin D. Sherry, Eun Joo Kang, and F. Dean Toste*  

E-print Network

Gold(I)-Catalyzed Enantioselective Intramolecular Hydroamination of Allenes Rebecca L. La on the utility of gold(I) complexes as homogeneous catalysts for organic synthesis has recently dramati- cally reported.2 Within this handful of reactions, the most well-developed enantioselective gold- (I

Toste, Dean

198

Enantioselective Dichlorination of Allylic Alcohols  

PubMed Central

The development of an enantioselective allylic alcohol dichlorination catalyzed by dimeric cinchona alkaloid derivatives and employing aryl iododichlorides as chlorine sources is reported. Reaction optimization, exploration of the substrate scope, and a model for stereoinduction are presented. PMID:21542622

Nicolaou, K. C.; Simmons, Nicholas L.; Ying, Yongcheng; Heretsch, Philipp M.; Chen, Jason S.

2011-01-01

199

BIOINSPIRED CATALYSTS: SYNTHESIS, CHARACTERISATION AND SOME APPLICATIONS  

Microsoft Academic Search

Our recent work concerning the synthesis, characterisation and some applications of bioinspired electron-transfer catalysts is reviewed in this contribution. The catalysts were various mono- or heterobimetallic complexes having either Cu(II) or Cu(II) and Zn(II) as central ions and amino acids, their derivatives or various N- containing organic molecules as ligands. Emphasis was based upon the solid support immobilised versions of

István Pálinkó

200

Enzymatic enantioselective C-C-bond formation in microreactors.  

PubMed

We have demonstrated that multiple crude enzyme lysates containing a hydroxynitrile lyase can be used for the enantioselective synthesis of cyanohydrins from aldehydes in microchannels. Using a microreactor setup, two important parameters were efficiently screened consuming only minute amounts of reagents. More importantly, results from the continuous flow reaction were fully consistent with results obtained from larger batchwise processes in which a stable emulsion was formed. PMID:17879309

Koch, K; van den Berg, R J F; Nieuwland, P J; Wijtmans, R; Schoemaker, H E; van Hest, J C M; Rutjes, F P J T

2008-03-01

201

Tetrabenzotriazaporphyrins: synthesis, properties and application  

NASA Astrophysics Data System (ADS)

Synthetic approaches to tetrabenzotriazaporphyrins and their complexes with metals and semimetals (P, Si) are considered. Methods for complexation of free-base tetrabenzotriazaporphyrin ligands and the preparation of water-soluble derivatives via the introduction of a sulfo group are analyzed. Particular attention is given to investigations of this class of compounds by electronic absorption spectroscopy and possibilities of their practical application. The bibliography includes 80 references.

Kalashnikov, V. V.; Pushkarev, V. E.; Tomilova, L. G.

2014-07-01

202

Nanoceria as antioxidant: Synthesis and biomedical applications  

NASA Astrophysics Data System (ADS)

The therapeutic application of nanomaterials has been a focus of numerous studies in the past decade. Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by the reactive oxygen intermediates (ROI). The radical-scavenging role of ceria nanoparticles (nanoceria) have been established, as well as the autocatalytic ability of nanoceria to regenerate under various environmental conditions. The synthesis of nanoceria in biocompatible media has also been reported along with cell viability in order to determine the potential use of nanoceria in biomedical applications.

Karakoti, A. S.; Monteiro-Riviere, N. A.; Aggarwal, R.; Davis, J. P.; Narayan, R. J.; Self, W. T.; McGinnis, J.; Seal, S.

2008-03-01

203

Enol Ethers as Substrates for Efficient Z- and Enantioselective Ring-Opening/Cross-Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes: Utility in Chemical Synthesis and Mechanistic Attributes  

E-print Network

The first examples of catalytic enantioselective ring-opening/cross-metathesis (EROCM) reactions that involve enol ethers are reported. Specifically, we demonstrate that catalytic EROCM of several oxa- and azabicycles, ...

Yu, Miao

204

Dendrimers: synthesis, applications, and properties  

PubMed Central

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications. PMID:24994950

2014-01-01

205

Dendrimers: synthesis, applications, and properties  

NASA Astrophysics Data System (ADS)

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications.

Abbasi, Elham; Aval, Sedigheh Fekri; Akbarzadeh, Abolfazl; Milani, Morteza; Nasrabadi, Hamid Tayefi; Joo, Sang Woo; Hanifehpour, Younes; Nejati-Koshki, Kazem; Pashaei-Asl, Roghiyeh

2014-05-01

206

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

PubMed

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

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

2014-07-25

207

Application of Catalytic Dynamic Resolution of N-Boc-2-lithiopiperidine to the Asymmetric Synthesis of 2-Aryl and 2-Vinyl Piperidines  

PubMed Central

The highly enantioselective synthesis of 2-aryl- and 2-vinyl-piperidines has been accomplished through a catalytic dynamic resolution (CDR) of N-Boc-2-lithiopiperidine. The method has been applied to the synthesis of both enantiomers of the tobacco alkaloid anabasine. PMID:21174392

Beng, Timothy K.; Gawley, Robert E.

2011-01-01

208

DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications  

E-print Network

DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications Jenifer L. Lawrie for improving the sensitivity of label-free optical biosensors based on in-situ synthesis of DNA probes within was utilized as the sensor structure. Synthesis of DNA probe, as well as sensing of target DNA, was verified

Weiss, Sharon

209

Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application  

E-print Network

Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application.................................................................................................................20 1.10.1. Administration of antioxidant enzymes................................................................................20 1.10. 2. Administration of enzyme mimics

Amrhein, Valentin

210

Exploring Nitrilase Sequence Space for Enantioselective Catalysis†  

PubMed Central

Nitrilases are important in the biosphere as participants in synthesis and degradation pathways for naturally occurring, as well as xenobiotically derived, nitriles. Because of their inherent enantioselectivity, nitrilases are also attractive as mild, selective catalysts for setting chiral centers in fine chemical synthesis. Unfortunately, <20 nitrilases have been reported in the scientific and patent literature, and because of stability or specificity shortcomings, their utility has been largely unrealized. In this study, 137 unique nitrilases, discovered from screening of >600 biotope-specific environmental DNA (eDNA) libraries, were characterized. Using culture-independent means, phylogenetically diverse genomes were captured from entire biotopes, and their genes were expressed heterologously in a common cloning host. Nitrilase genes were targeted in a selection-based expression assay of clonal populations numbering 106 to 1010 members per eDNA library. A phylogenetic analysis of the novel sequences discovered revealed the presence of at least five major sequence clades within the nitrilase subfamily. Using three nitrile substrates targeted for their potential in chiral pharmaceutical synthesis, the enzymes were characterized for substrate specificity and stereospecificity. A number of important correlations were found between sequence clades and the selective properties of these nitrilases. These enzymes, discovered using a high-throughput, culture-independent method, provide a catalytic toolbox for enantiospecific synthesis of a variety of carboxylic acid derivatives, as well as an intriguing library for evolutionary and structural analyses. PMID:15066841

Robertson, Dan E.; Chaplin, Jennifer A.; DeSantis, Grace; Podar, Mircea; Madden, Mark; Chi, Ellen; Richardson, Toby; Milan, Aileen; Miller, Mark; Weiner, David P.; Wong, Kelvin; McQuaid, Jeff; Farwell, Bob; Preston, Lori A.; Tan, Xuqiu; Snead, Marjory A.; Keller, Martin; Mathur, Eric; Kretz, Patricia L.; Burk, Mark J.; Short, Jay M.

2004-01-01

211

Total synthesis of pseudodehydrothyrsiferol.  

PubMed

An enantioselective total synthesis of pseudodehydrothyrsiferol has been accomplished. The synthetic sequence highlights formation of the highly strained tetrahydropyran C-ring by a Mitsunobu-type S(N)2 reaction with an oxygen nucleophile. PMID:19113900

Hioki, Hideaki; Motosue, Masatoshi; Mizutani, Yasuhiko; Noda, Akira; Shimoda, Tomoaki; Kubo, Miwa; Harada, Kenichi; Fukuyama, Yoshiyasu; Kodama, Mitsuaki

2009-02-01

212

Synthesis, characterization and applications of different nanostructures  

NASA Astrophysics Data System (ADS)

There has been a growing interest in the field of nanoscience for the last several decades including the use in optical, electrical, biological and medicinal applications. This thesis focuses on the synthesis of different nanoparticles for their potential uses in drug delivery and antimicrobial agents as well as porous alumina membranes as surface enhanced Raman scattering or SERS substrates. The synthesis of nanocomposites (NCs) composed of silica and poly(4-vinyl pyridine) (P4VP) in a basic ethanol solution is presented in chapter 2. The composition of the NCs appears to be homogenous after synthesis and is greatly affected by heat and pH changes. When the NCs are heated, a core-shell nanostructure is produced with silica forming a shell around a P4VP core. At lower pHs, the NCs form a silica core with a P4VP shell while at higher pHs the silica is etched away causing the NC to decompose. A novel synthesis method of growing stable copper oxide nanoparticles with poly(acrylic acid) (PAA) is presented in chapter 3. Insoluble copper (I) oxide is dissolved with ammonium hydroxide and reduced using sodium borohydride to form metallic copper nanoparticles that oxidize overtime to form copper oxide nanoparticles stable in an aqueous environment. In addition to copper oxide nanoparticles, copper (I) iodide and copper (II) sulfide particles were also synthesized in the presence of PAA. In chapter 4, alumina membranes with 100nm and 200nm pores were coated with silver and used as SERS substrates to detect small molecules. The alumina membranes are coated with silver by reducing silver (I) oxide with ethanol. The thickness of the silver layer depends primarily on the length of time the substrate comes into contact with the Ag2O in solution with longer exposure times producing thicker films. Raman scattering of 10-100nM adenine concentrations were collected.

Snyder, Whitney Elaine

213

Synthesis of complex fluorides for optical applications  

NASA Astrophysics Data System (ADS)

Large single crystals of alkali metal fluorides are desirable for many reasons. Fluoride laser crystals have a wide transmission range and on account of their low phonon energies, many efficient laser emissions have been obtained from 285 nm to 4.34 microm.1,2 Inorganic fluoride single crystals feature large bandgaps, very wide optical transmittance ranges from vacuum-ultraviolet (VUV) to mid-IR wavelength regions, lower refractive indices than those of oxides, and typically lower phonon energies (which drastically reduce multiphonon relaxation rates of rare earth ions).3 The main goal of this work was to investigate the hydrothermal synthesis of alkali metal fluorides. Melt techniques have been used thoroughly to research a variety of fluoride systems and showed many phases that were inaccessible due to incongruent melting or phase stability. The existence of these phases was shown but never characterized or grown as a crystalline material. Solution growth in supercritical water was an ideal way to attempt the synthesis of novel compounds and phases. New synthetic routes to known phases and compounds also arose as a part of this work. Optically clear colorless crystals of K2BeF4 were synthesized up to 2 mm in size, and showed no phase transitions up to 1029 K, which suggests paraelectricitys at room temperature, contradicting previous reports.4 Attempts to incorporate a rare earth ion into the fluoroberyllate lattice proved unsuccessful however reactions between beryllium fluoride and lanthanide fluorides could be exploited as a synthetic route to single crystal rare earth fluorides. Hydrothermal reactions with KF produced crystals of three different phases: hexagonal KY2F7, trigonal KYF4 and orthorhombic K2YF5. All were optically clear, colorless crystals, with the K2YF5 crystals growing the largest. This compound is beneficial due to its application as a radiation dosimeter and laser host. 5,6 Optical quality colorless crystals of RbY2F7 and CsY2F7 up to 4 mm in size were produced, and many spectroscopically active rare earth elements were doped into both hosts. A novel synthetic pathway to the hexagonal beta-RbGd3F 10, was discovered which led to the novel compound, beta-RbHo 3F10. The hydrothermal synthesis of hexafluoroelpasolites and lanthanide sesquioxides is also investigated. The hydrothermal synthesis described in this work has furthered the study of complex fluorides for optical applications. Novel synthetic pathways were discovered to known optical materials. Novel materials were also discovered. 1Takashima, M. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 176. 2Fouassier, C. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 316. 3Capper, P. In Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials, John Wiley and Sons: Great Britain, 2005. 4Solans, X.; Gonzalez-Silgo, C.; Calvet, T.; Ruiz-Perez, C.; Martinez-Sarrion, M. L.; Mestres, L. Phys. Rev. B 1998, 57(9), 5122-5125. 5Azorin-Nieto, J.; Khaidukov, N.M.; Sanchez-Rodriguez, A.; Azorin-Vega, J.C. Nuclear Instruments and Methods in Physics Research, 2007, B263, 36-40. 6Wang, D.; Min, Y.; Xia, S.; Makhov, V.N.; Khaidukov, N.M.; J.C. Krupa, J.C. Journal of Alloys and Compounds, 2003, 361, 294-298.

Stepleton, Seth Eugene

214

Enantioselective iron-catalysed O-H bond insertions  

NASA Astrophysics Data System (ADS)

The ready availability, low price and environmentally benign character of iron mean that it is an ideal alternative to precious metals in catalysis. Recent growth in the number of iron-catalysed reactions reported reflects an increasing demand for sustainable chemistry. Only a limited number of chiral iron catalysts have been reported and these have, in general, proven less enantioselective than other transition-metal catalysts, thus limiting their appeal. Here, we report that iron complexes of spiro-bisoxazoline ligands are highly efficient catalysts for asymmetric O-H bond insertion reactions. These complexes catalyse insertions into the O-H bond of a wide variety of alcohols and even water, with exceptional enantioselectivities under mild reaction conditions. The selectivities surpass those obtained with other transition-metal catalysts. This study should inspire and encourage the use of iron instead of traditional precious metals in the development of greener catalysts for catalytic asymmetric synthesis.

Zhu, Shou-Fei; Cai, Yan; Mao, Hong-Xiang; Xie, Jian-Hua; Zhou, Qi-Lin

2010-07-01

215

Efficient, highly enantioselective synthesis of selina-1,3, 7(11)-trien-8-one, a major component of the essential oil of Eugenia uniflora.  

PubMed

The first synthesis of selina-1,3,7(11)-trien-8-one (1), a major constituent of the essential oil from the leaves of Eugenia uniflora, has been accomplished, with excellent stereo- and regiocontrol, in eight steps and in 12% overall yield from the known octalone derivative 2a. PMID:11000042

Kanazawa, A; Patin, A; Greene, A E

2000-09-01

216

Separation of racemic mixture by ultrafiltration of enantioselective micelles 2. (De)complexation kinetics  

Microsoft Academic Search

The application of enantioselective micelles in ultrafiltration systems can be an alternative route to meet the increasing demand for enantiopure products. We have studied the separation of D,L-phenylalanine (Phe) by cholesteryl-L-glutamate:CuII (CLG:CuII) anchored in nonionic micelles (intrinsic enantioselectivity D\\/L,int = 1.9). A cascaded system is needed to complete the separation, as a single stage is insufficient to obtain >99?ptically pure

Pieter E. M. Overdevest; Maarten A. I. Schutyser; Bruin de T. J. M; Klaas van't Riet; Jos T. F. Keurentjes; Albert van der Padt

2001-01-01

217

NSF/Tokyo Report: US-Japan Workshop: Nanoparticle Synthesis and Applications  

NSF Publications Database

... Workshop: Nanoparticle Synthesis and Applications Date: 5/21/97 The National Science Foundation's ... Workshop: Nanoparticle Synthesis and Applications The following report was submitted by Dr. James R ...

218

Synthesis, characterization and application of electrode materials  

SciTech Connect

It has been known that significant advances in electrochemistry really depend on improvements in the sensitivity, selectivity, convenience, and/or economy of working electrodes, especially through the development of new working electrode materials. The advancement of solid state chemistry and materials science makes it possible to provide the materials which may be required as satisfactory electrode materials. The combination of solid state techniques with electrochemistry expands the applications of solid state materials and leads to the improvement of electrocatalysis. The study of Ru-Ti{sub 4}O{sub 7} and Pt-Ti{sub 4}O{sub 7} microelectrode arrays as introduced in paper 1 and paper 4, respectively, focuses on their synthesis and characterization. The synthesis is described by high temperature techniques for Ru or Pt microelectrode arrays within a conductive Ti{sub 4}O{sub 7} ceramic matrix. The characterization is based on the data obtained by x-ray diffractometry, scanning electron microscopy, voltammetry and amperometry. These microelectrode arrays show significant enhancement in current densities in comparison to solid Ru and Pt electrodes. Electrocatalysis at pyrochlore oxide Bi{sub 2}Ru{sub 2}O{sub 7.3} and Bi{sub 2}Ir{sub 2}O{sub 7} electrodes are described in paper 2 and paper 3, respectively. Details are reported for the synthesis and characterization of composite Bi{sub 2}Ru{sub 2}O{sub 7.3} electrodes. Voltammetric data are examined for evidence that oxidation can occur with transfer of oxygen to the oxidation products in the potential region corresponding to anodic discharge of H{sub 2}O with simultaneous evolution of O{sub 2}. Paper 3 includes electrocatalytic activities of composite Bi{sub 2}Ir{sub 2}O{sub 7} disk electrodes for the oxidation of I{sup -} and the reduction of IO{sub 3}{sup -}.

He, L.

1995-07-07

219

Enantioselective, desymmetrizing bromolactonization of alkynes.  

PubMed

Asymmetric bromolactonizations of alkynes are possible using a desymmetrization approach. The commercially available catalyst (DHQD)2PHAL promotes these cyclizations in combination with cheap NBS as a bromine source to give bromoenol lactones in high yield and with high enantioselectivity. The bromoenol lactone products, containing a tetrasubstituted alkene and a quaternary stereocenter, are valuable building blocks for synthetic chemistry. PMID:23679927

Wilking, Michael; Mück-Lichtenfeld, Christian; Daniliuc, Constantin G; Hennecke, Ulrich

2013-06-01

220

Cyclopalladated complexes in enantioselective catalysis  

NASA Astrophysics Data System (ADS)

The results of the use of optically active palladacycles in enantioselective catalysis of [3,3]-sigmatropic rearrangements, aldol condensation, the Michael reaction and cross-coupling are analyzed. Reactions with allylic substrates or reagents and some other transformations are considered.

Dunina, Valeria V.; Gorunova, Olga N.; Zykov, P. A.; Kochetkov, Konstantin A.

2011-01-01

221

Highly enantioselective electrophilic ?-bromination of enecarbamates: chiral phosphoric acid and calcium phosphate salt catalysts.  

PubMed

Metal-free chiral phosphoric acids and chiral calcium phosphates both catalyze highly enantio- and diastereoselective electrophilic ?-bromination of enecarbamates to provide an atom-economical synthesis of enantioenriched vicinal haloamines. Either enantiomer can be formed in good yield with excellent diastereo- and enantioselectivity simply by switching the catalyst from a phosphoric acid to its calcium salt. PMID:22686436

Alix, Aurélien; Lalli, Claudia; Retailleau, Pascal; Masson, Géraldine

2012-06-27

222

Gold(I)-Catalyzed Enantioselective [4+2]-Cycloaddition of Allene-Dienes  

PubMed Central

An enantioselective gold(I)-catalyzed intramolecular [4+2]-cycloaddition of allenes and dienes is reported. The reactions allows for the asymmetric synthesis of trans-hexahydroindenes and pyrrolidine products using C3-symmetric phosphitegold(I) and ortho-arylphosphoramiditegold(I) complexes as catalysts, respectively. PMID:19961192

Gonzalez, Ana Z.; Toste, F. Dean

2009-01-01

223

Nanostructured metal foams: synthesis and applications  

SciTech Connect

Fabrication of monolithic metallic nanoporous materials is difficult using conventional methodology. Here they report a relatively simple method of synthesizing monolithic, ultralow density, nanostructured metal foams utilizing self-propagating combustion synthesis of novel metal complexes containing high nitrogen energetic ligands. Nanostructured metal foams are formed in a post flame-front dynamic assembly with densities as low as 0.011 g/cc and surface areas as high as 270 m{sup 2}/g. They have produced metal foams via this method of titanium, iron, cobalt, nickel, zirconium, copper, palladium, silver, hafnium, platinum and gold. Microstructural features vary as a function of composition and process parameters. Applications for the metal foams are discussed including hydrogen absorption in palladium foams. A model for the sorption kinetics of hydrogen in the foams is presented.

Luther, Erik P [Los Alamos National Laboratory; Tappan, Bryce [Los Alamos National Laboratory; Mueller, Alex [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Volz, Heather [Los Alamos National Laboratory; Cardenas, Andreas [Los Alamos National Laboratory; Papin, Pallas [Los Alamos National Laboratory; Veauthier, Jackie [Los Alamos National Laboratory; Stan, Marius [Los Alamos National Laboratory

2009-01-01

224

Asymmetric Synthesis of 1,3-anti-Diol Containing Subunits using Phosphorus-Based Tethers: Application in the Total Synthesis of Dolabelide C  

E-print Network

-854. (b) Gauthier, D. R.; Zandi, K. S.; Shea, K. J.; "Disposable Tethers in Synthetic Organic Chemistry," Tetrahedron 1998, 54, 2289-2338. (2) (a) White, J. D.; Carter R. G. In Science of Synthesis: Houben-Weyl Methods of Molecular Transformations...; Fleming, I., Ed.; Georg Thieme Verlag: New York, 2001; Vol. 4, pp 371-412 and references cited therein. (b) Evans, P. A. ; Cui, J.; Gharpure, S. J.; Polosukhin, A.; Zhang, H. R. "Enantioselective Total Synthesis of the Potent Antitumor Agent (–)-Mucocin...

Thomas, Christopher Daniel

2010-12-16

225

Squaramide-Catalyzed Enantioselective Michael Addition of Masked Acyl Cyanides to Substituted Enones  

PubMed Central

Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective Michael addition to substituted enones. The reactions are catalyzed by chiral squaramides and afford adducts in high yields (90–99%) and with excellent enantioselectivities (85–98%). The addition products are unmasked to produce dicyanohydrins that, upon treatment with a variety of nucleophiles, provide ?-keto acids, esters, and amides. The use of this umpolung synthon has enabled, in enantiomerically enriched form, the first total synthesis of the prenylated polyphenol (+)-fornicin C. PMID:24090310

Yang, Kin S.; Nibbs, Antoinette E.; Türkmen, Yunus E.; Rawal, Viresh H.

2014-01-01

226

Diastereo- and enantioselective three-component coupling approach to highly substituted pyrrolidines.  

PubMed

The enantioselective synthesis of substituted pyrrolidines through a mild Lewis-acid catalyzed three-component coupling reaction between picolinaldehyde, amino acids, and activated olefins is reported. The reaction uses low catalyst loadings of commercially available chiral diamines and copper triflate proposed to self-assemble in conjunction with the chelating aldehydes, 4-substituted-2-picolinaldehydes or 4-methylthiazole-2-carboxaldehyde, to generate a catalyst complex. A model is provided to explain how this complex directs enantioselectivity. This work represents a significant advance in the ease, scope, and cost of producing highly substituted, enantioenriched pyrrolidines. PMID:23952564

Chaulagain, Mani Raj; Felten, Albert E; Gilbert, Kevin; Aron, Zachary D

2013-09-20

227

Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams  

PubMed Central

The enantioselective synthesis of Nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines including the total synthesis of natural products and medicinal chemistry. In this manuscript, we describe the highly enantioselective palladium-catalyzed decarboxylative allylic alkylation of readily available lactams to form 3,3,-disubstituted pyrrolidinones, piperidinones, caprolactams, and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envision that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. PMID:22270628

Behenna, Douglas C.; Liu, Yiyang; Yurino, Taiga; Kim, Jimin; White, David E.; Virgil, Scott C.; Stoltz, Brian M.

2011-01-01

228

Synthesis, Characterization and Catalytic Applications of Organized Mesoporous Aluminas  

Microsoft Academic Search

The synthesis of organized mesoporous aluminas has opened a very interesting area for application of this type of materials, particularly as catalysts or catalyst supports. This review focuses on the individual synthesis routes to produce organized mesoporous aluminas with large surface areas and narrow pore size distributions, and on the evaluation of their textural, chemical and thermal properties and outlines

Nad?žda Žilková; Ji?í ?ejka

2008-01-01

229

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

ii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Florida Emergy Database for Standardized National Emergy Synthesis Sharlynn Sweeney, Matthew J. Cohen, Danielle

Slatton, Clint

230

Enantioselective recognition at mesoporous chiral metal surfaces  

PubMed Central

Chirality is widespread in natural systems, and artificial reproduction of chiral recognition is a major scientific challenge, especially owing to various potential applications ranging from catalysis to sensing and separation science. In this context, molecular imprinting is a well-known approach for generating materials with enantioselective properties, and it has been successfully employed using polymers. However, it is particularly difficult to synthesize chiral metal matrices by this method. Here we report the fabrication of a chirally imprinted mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and chiral template molecules. The porous platinum retains a chiral character after removal of the template molecules. A matrix obtained in this way exhibits a large active surface area due to its mesoporosity, and also shows a significant discrimination between two enantiomers, when they are probed using such materials as electrodes. PMID:24548992

Wattanakit, Chularat; Come, Yemima Bon Saint; Lapeyre, Veronique; Bopp, Philippe A.; Heim, Matthias; Yadnum, Sudarat; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

2014-01-01

231

Synthesis, characterization and optical applications of nanomaterials  

NASA Astrophysics Data System (ADS)

Nanomaterials have been studied extensively due to their potential application in electronics, photonics and nanodevices. There are a wide variety of methods developed to create the nano-scale materials. Chemical colloidal synthesis is the way most used since it is reproducible and high efficiency. Nanoparticles lie at the heart of nanoscience for their novel electronic, magnetic and optical properties. In this dissertation, there are two parts where researches have been performed based on the synthesis of metal and semiconductor nanoparticles. In part I, Semiconductor type-II core-shell quantum dots (QDs) ZnO-CdS have been synthesized by chemical colloidal method which was carried out in a two-step process. We initially synthesized ZnO core nanoparticles and overcoat them with CdS shell. UV-Visible spectra, photoluminescence spectra (PL), high resolution TEM images and X-ray microanalysis for composition studies of the core-shell nanoparticles were characterized. PL lifetime measurements showed this type-II ZnO-CdS core-shell QDs presented extended exciton lifetime due to the spatial separation of electrons and holes between the core and the shell, which opens various useful applications in biosensors and photovoltaic devices. In part II, normal Raman (NR) and surface enhanced Raman scattering (SERS) spectra of 3-hydroxyflavone (3-HF) have been measured. The SERS spectra were obtained both on a Ag electrode surface and on Ag colloidal nanoparticles. The experimental results support the DFT geometry calculations, which show that an adatom site at the vertex of Ag20 cluster binding with the 3-HF molecular plane tilted at an angle of about 53° to the surface is a low-energy structure. This is consistent with the enhancement of in-plane vibrational modes. Furthermore, the effect of fluence level on the discoloration of marble surfaces after the removal of the encrustation by 355 nm laser pulses was comparatively studied. Considering the thermochemical reaction possibly occurring in the encrustation during laser irradiation, the mechanism responsible for the discoloration of the cleaned marble surface was analyzed. The reduction of iron oxides by graphite plays a key role in determining the final color of the cleaned marble surface. The marble surfaces before and after laser irradiation were characterized in terms of the chemical components through surface enhanced Raman spectroscopy on Ag colloidal nanoparticles. To analyze the working mechanism of the liquid layer covering the marble encrustation, distilled water, ethanol and acetone were used in marble cleaning to compare the cleaning efficiency at different fluence levels. Surface-enhanced Raman spectroscopy (SERS) on silver colloidal nanoparticles was also used to identify the chemical constituents of the cleaned marble with these three different liquids.

Xu, Fen

232

Efficient synthesis of ?-extended phenazasilines for optical and electronic applications.  

PubMed

The rhodium-catalyzed synthesis of phenazasilines from readily achievable biarylhydrosilanes is presented. This highly efficient method offers opportunities for preparing ?-extended phenazasilines with enhanced optoelectronic properties for device applications in organic electronics. PMID:25370829

Li, Huanhuan; Wang, Yang; Yuan, Kai; Tao, Ye; Chen, Runfeng; Zheng, Chao; Zhou, Xinhui; Li, Junfeng; Huang, Wei

2014-12-25

233

Synthesis of highly quenching fullerene derivatives for biosensor applications  

E-print Network

This dissertation examines the synthesis of fullerene-based fluorescence quenchers for numerous biosensor applications. The Introduction describes the need for biosensors in our society, what they are and various biosensing ...

Pérez, Vanessa Virginia, 1981-

2004-01-01

234

Semiconductor nanocrystals : synthesis, mechanisms of formation, and applications in biology  

E-print Network

The primary focus of this thesis is the synthesis and applications of semiconductor nanocrystals, or quantum dots (QDs). Novel synthetic routes to ternary 1-III-VI QDs are presented, and we report the first highly luminescent ...

Allen, Peter M. (Peter Matthew)

2010-01-01

235

Nitroxides: applications in synthesis and in polymer chemistry.  

PubMed

This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures. PMID:21538729

Tebben, Ludger; Studer, Armido

2011-05-23

236

Synthesis and characterization of advanced materials for Navy applications  

NASA Technical Reports Server (NTRS)

The synthesis of ceramics and ceramic coatings through the sol-gel process has extensive application with the United States Navy and a broad range of potential commercial applications as well. This paper surveys seven specific applications for which the Navy is investigating these advanced materials. For each area, the synthetic process is described and the characteristics of the materials are discussed.

Covino, J.; Lee, I.

1994-01-01

237

Enantioselective ligand exchange in modern separation techniques  

Microsoft Academic Search

As a follow-up to a series of review articles on enantioselective ligand exchange chromatography, the present contribution critically evaluates achievements in this area of active and successful research which have been reported in the scientific literature since 1992. Also discussed is enantioselective ligand exchange in electromigration techniques which have developed especially fruitfully during the last decade.

Vadim A. Davankov

2003-01-01

238

Directed evolution of an enantioselective lipase  

Microsoft Academic Search

Background: The biocatalytic production of enantiopure compounds is of steadily increasing importance to the chemical and biotechnological industry. In most cases, however, it is impossible to identify an enzyme that possesses the desired enantioselectivity. Therefore, there is a strong need to create by molecular biological methods novel enzymes which display high enantioselectivity.Results: A bacterial lipase from Pseudomonas aeruginosa (PAL) was

Klaus Liebeton; Albin Zonta; Klaus Schimossek; Marco Nardini; Dietmar Lang; Bauke W. Dijkstra; Manfred T. Reetz; Karl-Erich Jaeger

2000-01-01

239

COMBUSTION SYNTHESIS OF ADVANCED MATERIALS: PRINCIPLESAND APPLICATIONS  

E-print Network

. Gasless Combustion SynthesisFrom Elements B. Combustion Synthesis in Gas-Solid Systems C. Products Density for Gasless Systems D. Green Mixture Density and Initial Gas Pressure for Gas-Solid Systems E). This review article summarizes the state of the art in combustion syn- thesis,from both the scientijc

Mukasyan, Alexander

240

Studies toward the total synthesis of glycinoeclepin A  

E-print Network

Studies directed toward the synthesis of the A-ring portion of glycinoeclepin A are described. The enantioselective synthesis of key diketone intermediate 128 in four steps from 2,2-dimethyl-1,3-cyclohexanedione (5) has ...

Thongsornkleeb, Charnsak

2006-01-01

241

Concise total synthesis of (+)-gliocladins B and C  

E-print Network

The first total synthesis of (+)-gliocladin B is described. Our concise and enantioselective synthesis takes advantage of a new regioselective Friedel–Crafts-based strategy to provide an efficient multigram-scale access ...

Movassaghi, Mohammad

242

One-pot organocatalytic enantioselective Michael-Michael-aldol-Henry reaction cascade. A facile entry to the steroid system with six contiguous stereogenic centers.  

PubMed

An expedited method has been developed for the enantioselective synthesis of highly functionalized steroid systems containing six contiguous stereogenic centers with high enantioselectivities (99% ee). The one-pot methodology comprises a cascade of organocatalytic Michael-Michael-aldol-Henry reactions of 7-nitrohept-3-en-2-one and 5-(1-methyl-2,5-dioxocyclopentyl)pent-2-enal. The structure and absolute configuration of the products were confirmed by X-ray analyses of appropriate products. PMID:24796861

Jhuo, Dai-Huei; Hong, Bor-Cherng; Chang, Chun-Wei; Lee, Gene-Hsiang

2014-05-16

243

Highly diastereo- and enantioselective organocatalytic domino Michael/aldol reaction of acyclic 3-halogeno-1,2-diones to ?,?-unsaturated aldehydes.  

PubMed

The first organocatalytic diastereo- and enantioselective domino Michael/aldol reaction of 3-halogeno-1,2-diones to ?,?-unsaturated aldehydes has been achieved. This transformation tolerates a large variety of electronically different substituents on both reactive partners and allows the synthesis of challenging cyclopentanone derivatives with four contiguous stereogenic centers in excellent diastereoselectivities (>20:1 dr) as well as good yields (69-97%), and enantioselectivities (up to 94% ee). PMID:23607321

Lefranc, Alice; Guénée, Laure; Alexakis, Alexandre

2013-05-01

244

Enantioselective Diels-Alder reactions catalyzed by hydrogen bonding.  

PubMed

Like molecules of life (e.g., proteins and DNA), many pharmaceutical drugs are also asymmetric (chiral); they are not superimposable on their mirror images. One mirror image form (enantiomer) of a drug can have desirable activity, the other not. Consequently, the development of methods for the selective synthesis of one enantiomer is of great scientific and economic importance. We report here that a simple, commercially available chiral alcohol, alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), catalyzes the all-carbon Diels-Alder reactions of aminosiloxydienes and substituted acroleins to afford the products in good yields and high enantioselectivities (up to 92% enantiomeric excess). It is remarkable that the reactions are promoted by hydrogen bonding, the ubiquitous "glue" that helps to keep water molecules together and holds up the 3D structures of proteins. Hydrogen bond catalysis is little used in chemical synthesis, wherein most reactions are promoted by complexes of Lewis acidic metal salts coordinated to chiral ligands. As it does for enzymes, hydrogen bonding not only organizes TADDOL into a well defined conformation, but, functioning as a Brønsted acid catalyst, it also activates the dienophile toward reaction with the diene. The gross structure of the TADDOL has been found to have a profound influence on both the rate and the enantioselectivity of the cycloadditions. These structure-function effects are rationalized by evaluating the conformation adopted by the TADDOLs in the crystal state. It is suggested that pi,pi-stacking plays an central role in the overall catalytic cycle, in particular, the enantioselective step. PMID:15069185

Thadani, Avinash N; Stankovic, Ana R; Rawal, Viresh H

2004-04-20

245

Synthesis and applications of metal oxide nanowires  

NASA Astrophysics Data System (ADS)

The one-dimensional nanostructured materials have attracted much attention because of their superior properties from the deducing size in the nanometer range. Among them, metal oxide materials provide a wide diversity and functionality in both theoretical study and applications. This work focused on the synthesis of metal oxide nanowires, and further investigated possible applications of nanostructured metal oxide materials. High quality ZnO nanowires have been synthesized by catalyst-assisted molecular beam epitaxy. The control of initial Au or Ag film thickness and subsequent annealing conditions is shown to provide an effective method for controlling the size and density of nucleation sites for catalyst-driven growth of ZnO nanowires. For gas sensing applications, it is found that the sensitivity for detecting hydrogen is greatly enhanced by sputter-depositing metal catalysts (Pt and Pt) on surface. The sensors are shown to detect ppm hydrogen at room temperature using <0.4 mW of power when using multiple nanowires. A comparison study of the hydrogen-sensing characteristics of ZnO thin films with different thickness and ZnO nanowires was studied. The Pt-coated single nanowires show a current response by approximately a factor of 3 larger at room temperature. Both types of sensors are shown to be capable of the detection of ppm hydrogen at room temperature with nW power levels, but the nanowires show different recovery characteristics, consistent with the expected higher surface coverage of adsorbed hydrogen. The feasibility of a number of metal oxide nanowires has been synthesized by a high-pressure assisted pulsed laser deposition. The high density well-aligned metal oxide nanowires can be directly grown on substrate without metal catalysts. The results suggest the possibility of growing complex metal oxide nanostructures, including tailored heterostructures and aligned heterojunction arrays with PLD technique. The growth of epitaxial SnO2 on c-sapphire using pulsed laser deposition is examined. X-ray diffraction analysis shows that the films are highly a-axis oriented SnO2 with the rutile structure. The effects of Ga doping on SnO2 films were studied. The Hall data showed p-type behavior occurs only at specific growth condition, but converted back to n-type and degraded as time proceeds.

Tien, Li-Chia

246

Cell-Free Protein Synthesis: Applications Come of Age  

PubMed Central

Cell-free protein synthesis has emerged as a powerful technology platform to help satisfy the growing demand for simple and efficient protein production. While used for decades as a foundational research tool for understanding transcription and translation, recent advances have made possible cost-effective microscale to manufacturing scale synthesis of complex proteins. Protein yields exceed grams protein produced per liter reaction volume, batch reactions last for multiple hours, costs have been reduced orders of magnitude, and reaction scale has reached the 100-liter milestone. These advances have inspired new applications in the synthesis of protein libraries for functional genomics and structural biology, the production of personalized medicines, and the expression of virus-like particles, among others. In the coming years, cell-free protein synthesis promises new industrial processes where short protein production timelines are crucial as well as innovative approaches to a wide range of applications. PMID:22008973

Carlson, Erik D.; Gan, Rui; Hodgman, C. Eric; Jewett, Michael C.

2014-01-01

247

Two Wheeled Vehicle Dynamics Synthesis for Real-Time Applications  

E-print Network

Two Wheeled Vehicle Dynamics Synthesis for Real-Time Applications Salim Hima and Hichem Arioui into a two wheeled vehicles real-time applications such as driving simulators. The synthesized model takes dynamics, Recursive Newton-Euler algorithm. 1. INTRODUCTION IN the two last decades, the safety of ground

Paris-Sud XI, Université de

248

Organocatalytic enantioselective hydrophosphonylation of aldehydes.  

PubMed

We report our results concerning the first squaramide-catalysed hydrophosphonylation of aldehydes. In all cases, the reactions proceeded smoothly and cleanly under mild reaction conditions rendering final ?-hydroxy phosphonates in very good yields and high enantioselectivities. It is one of the few organocatalytic examples of this reaction using aldehydes. It is the first time that diphenylphosphite (1e) has been successfully employed in a chiral Pudovik reaction with aldehydes, in contrast to the dialkylphosphites used in previously published procedures, extending the generality of this asymmetric methodology. PMID:24413980

Alegre-Requena, Juan V; Marqués-López, Eugenia; Sanz Miguel, Pablo J; Herrera, Raquel P

2014-02-28

249

Hydroxynitrile lyase catalyzed cyanohydrin synthesis at high pH-values.  

PubMed

The application of unusual high pH-values within enzymatic cyanohydrin synthesis has been investigated. Usually enzymatic cyanohydrin synthesis in two-phase systems requires low pH-values within the aqueous phase to suppress the non-enzymatic side reaction. In contrast, we investigated the usage of pH-values above pH 6 by using the highly enantioselective (S)-selective hydroxynitrile lyase from Manihot esculenta. With these unusual reaction conditions also the unfavorable substrate 3-phenoxy-benzaldehyde can be converted by the wild type enzyme with excellent conversion and enantiomeric excess yielding pure (S)-3-phenoxy-benzaldehyde cyanohydrin with an enantiomeric excess of 97%. Although the variant MeHNL-W128A shows a higher activity with respect to this reaction, the enantioselectivity was reduced (85% e.e.(S)). Additionally, a new continuous spectroscopic cyanohydrin assay monitoring the formation of 3-phenoxy-benzaldehyde cyanohydrin was developed. PMID:18204865

von Langermann, Jan; Guterl, Jan-Karl; Pohl, Martina; Wajant, Harald; Kragl, Udo

2008-04-01

250

Enantioselective Total Synthesis of (+)-Rogioloxepane A  

E-print Network

structural unit of many ladder ether marine toxins and simpler Laurencia acetogenin metabolites.1 The chal of the Laurencia-derived C15 acetogenins containing an R,R-trans- disubstituted oxepene ring. As part ethers. Rogioloxepane A (1) was isolated from Laurencia micro- cladia off the Torrent II Rogiolo

251

Catalytic enantioselective synthesis of chiral ?-butyrolactones.  

PubMed

A tandem catalytic asymmetric aldol reaction/cyclization of ?,?-didehydro-?-lactones with aldehydes was achieved using chiral tin dibromide as a chiral precatalyst and sodium alkoxide as a base precatalyst. Optically active trans-?,?-disubstituted ?-butyrolactones were selectively obtained in moderate to high yields with up to 99% ee from ?-aryl-substituted ?,?-didehydro-?-butyrolactones and bulky aliphatic aldehydes. PMID:21348475

Yanagisawa, Akira; Kushihara, Naoyuki; Yoshida, Kazuhiro

2011-03-18

252

Enantioselective, transition metal catalyzed cycloisomerizations.  

PubMed

This review illustrates enantioselective transition-metal promoted skeletal rearrangements of polyunsaturated substrates possessing olefin, alkyne or allene functions. These processes are classified according to the number of carbon atoms involved in the cyclization, from (1C+1C) to (2C+2C+2C) or (2C+5C) cyclizations. Thus, for instance, (1C+1C) processes are typified notably by Alder-ene type reactions taking place mainly under palladium and rhodium catalysis, in the presence of chiral phosphorus ligands. Also, rhodium, platinum, and gold promoted insertions of unsaturated carbon-carbon bonds into C-H bonds belong to this class. For each class of reactions or substrate type the best ligand-metal pairs are highlighted. Unfortunately, unlike other transition metal promoted reactions, the mechanisms of chiral induction and stereochemical pathways have not been established so far in any of these reactions. In only a few instances, qualitative heuristic models have been tentatively proposed. Although the available stereochemical information is systematically given here, the paper focuses mainly on synthetic aspects of enantioselective cycloisomerizations. PMID:22674143

Marinetti, Angela; Jullien, Hélène; Voituriez, Arnaud

2012-07-21

253

Enantioselective Sensing by Luminescence  

Microsoft Academic Search

\\u000a \\u000a Abstract  Enantiomeric analysis is one of the crucial points for the sensor technology, due to the increasing importance that enantiomerically\\u000a pure compounds and drugs have in pharmaceutic and agrochemical applications. Enantiomeric luminescent sensors give different\\u000a responses by interaction or reaction with chiral molecules, allowing one to assess their optical purity by spectroscopic measurements.\\u000a Moreover, chemosensors have been developed to perform enantiomeric

Alessandro Accetta; Roberto Corradini; Rosangela Marchelli

254

Application of variable metric methods to structural synthesis  

NASA Technical Reports Server (NTRS)

Powell (1977, 1978), Biggs (1972, 1975), and Han (1976, 1977) have developed a class of variable metric methods which create an explicit, quadratic, subproblem which is to be solved for finding a search direction for design improvement. A one-dimensional search is then performed. The present paper has the objective to present this variable metric approach in the context of structural synthesis. The variable metric algorithm is modified for application to the structural synthesis problem. The application of the new procedure is illustrated with the aid of examples, taking into account a 10-bar planar truss, a 17-bar planar tower, and a cantilever beam.

Vanderplaats, G. N.; Sugimoto, H.

1985-01-01

255

Catalytic enantioselective decarboxylative reactions using organocatalysts.  

PubMed

Catalytic decarboxylative reactions are attractive as biomimetic reactions and environmentally friendly reaction processes. In this review, the origin and recent development of organocatalytic enantioselective decarboxylative reactions of malonic acid half oxy- or thioesters, or ?-ketoacids are summarized. PMID:24270735

Nakamura, Shuichi

2014-01-21

256

Catalytic enantioselective bromoamination of allylic alcohols.  

PubMed

An enantioselective bromoamination of allylic alcohols has been developed for the first time using a newly designed cinchona-derived thiourea as the catalyst and N,N-dibromo-4-nitrobenzenesulfonamide as a bromine and amine source. PMID:25259372

Qi, Juan; Fan, Guo-Tao; Chen, Jie; Sun, Ming-Hui; Dong, Yu-Ting; Zhou, Ling

2014-10-14

257

ENANTIOSELECTIVITY IN THE BIODEGRADATION OF PCB ATROPISOMERS  

EPA Science Inventory

Microcosms inoculated with sediment from two locations in a contaminated reservoir, Lake Hartwell, SC, USA, degraded certain PCB atropisomers enantioselectively while other atropisomers were degraded in racemic proportions. The microcosms were spiked with either 234-236 PCB (PCB...

258

Zinc Oxide Nanoparticles for Revolutionizing Agriculture: Synthesis and Applications  

PubMed Central

Nanotechnology is the most innovative field of 21st century. Extensive research is going on for commercializing nanoproducts throughout the world. Due to their unique properties, nanoparticles have gained considerable importance compared to bulk counterparts. Among other metal nanoparticles, zinc oxide nanoparticles are very much important due to their utilization in gas sensors, biosensors, cosmetics, drug-delivery systems, and so forth. Zinc oxide nanoparticles (ZnO NPs) also have remarkable optical, physical, and antimicrobial properties and therefore have great potential to enhance agriculture. As far as method of formation is concerned, ZnO NPs can be synthesized by several chemical methods such as precipitation method, vapor transport method, and hydrothermal process. The biogenic synthesis of ZnO NPs by using different plant extracts is also common nowadays. This green synthesis is quite safe and ecofriendly compared to chemical synthesis. This paper elaborates the synthesis, properties, and applications of zinc oxide nanoparticles.

Sabir, Sidra; Arshad, Muhammad

2014-01-01

259

Total synthesis and study of myrmicarin alkaloids  

E-print Network

The myrmicarins are a family of air- and temperature-sensitive alkaloids that possess unique structural features. Our concise enantioselective synthesis of the tricyclic myrmicarins enabled evaluation of a potentially ...

Ondrus, Alison E.

260

77 FR 8324 - Applications for the Environment: Real-Time Information Synthesis (AERIS) User Needs Workshop...  

Federal Register 2010, 2011, 2012, 2013

...TRANSPORTATION Applications for the Environment: Real-Time Information Synthesis...to discuss the Applications for the Environment: Real- Time Information Synthesis...environmental benefits in a connected vehicle environment. For more information on the...

2012-02-14

261

Engineering homochiral metal-organic frameworks for heterogeneous asymmetric catalysis and enantioselective separation.  

PubMed

Owing to the potential applications in technological areas such as gas storage, catalysis, separation, sensing and nonlinear optics, tremendous efforts have been devoted to the development of porous metal-organic frameworks (MOFs) over the past ten years. Homochiral porous MOFs are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds due to the lack of homochiral inorganic porous materials such as zeolites. In this review, we summarize the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and latest advances in asymmetric heterogeneous catalysis and enantioselective separation. PMID:20799372

Liu, Yan; Xuan, Weimin; Cui, Yong

2010-10-01

262

Organocatalytic enantioselective tandem aldol-cyclization reaction of ?-isothiocyanato imides and activated carbonyl compounds.  

PubMed

The organocatalytic enantioselective tandem aldol-cyclization reactions of ?-isothiocyanato imides and activated carbonyl compounds, such as isatins, an ?-ketolactone and a 1,2-dione, have been studied with cinchona alkaloid-derived thiourea-catalysts. This methodology provided an easy way to access enantiomerically enriched spirobicyclic thiocarbamates with high yields and good to excellent stereoselectivity, which have been demonstrated to be useful precursors for the synthesis of biologically active molecules. PMID:21921975

Guang, Jie; Zhao, Cong-Gui

2011-06-15

263

Enantioselective Cycloaddition of Münchnones onto [60]Fullerene: Organocatalysis versus Metal Catalysis  

PubMed Central

Novel chiral catalytic systems based on both organic compounds and metal salts have been developed for the enantioselective [3 + 2] cycloaddition of münchnones onto fullerenes and olefins. These two different approaches proved to be efficient and complementary in the synthesis of optically active pyrrolino[3,4:1,2][60]fullerenes with high levels of enantiomeric excess and moderate to good conversions. Further functionalization of the pyrrolinofullerene carboxylic acid derivatives has been carried out by esterification and amidation reactions. PMID:24483247

2014-01-01

264

Synthesis and Applications of Mixed Oxide Nanotubes  

NASA Astrophysics Data System (ADS)

Metal oxide nanotube is one of the nanostructured materials. Templates method, which is the technique in which templates are covered with metal oxides and the templates were removed to form metal oxide nanotubes, is a typical synthesis method for metal oxide nanotubes. In this section, synthesis of mixed oxide nanotubes using carbon nanofibers (CNFs) as templates is described. Because CNFs with various shapes were used as templates, oxide nanotubes with various shapes such as straight and helical were formed. Successive adsorption of metal oxide precursors on CNFs resulted in the formation of mixed oxide nanotubes with specific composition. In addition, a nano-macrostructured material, silica fiber-immobilized nanofibrous LaMnO3, was fabricated using this template process. In propane oxidation, the nano-macrostructured material showed superior activity to the conventional powder catalysts.

Ogihara, Hitoshi; Sadakane, Masahiro; Ueda, Wataru

265

Enantioselective Functionalization of Allylic C-H Bonds Following a Strategy of Functionalization and Diversification  

PubMed Central

We report the enantioselective functionalization of allylic C-H bonds in terminal alkenes by a strategy involving the installation of a temporary functional group at the terminal carbon atom by C-H bond functionalization, followed by diversification of this intermediate with a broad scope of reagents. The method consists of a one-pot sequence of palladium-catalyzed allylic C-H bond oxidation under neutral conditions to form linear allyl benzoates, followed by iridium-catalyzed allylic substitution. This overall transformation forms a variety of chiral products containing a new C-N, C-O, C-S or C-C bond at the allylic position in good yield with high branched-to-linear selectivity and excellent enantioselectivity (ee ? 97%). The broad scope of the overall process results from separating the oxidation and functionalization steps; by doing so, the scope of nucleophile encompasses those sensitive to direct oxidative functionalization. The high enantioselectivity of the overall process is achieved by developing an allylic oxidation that occurs without acid to form the linear isomer with high selectivity. These allylic functionalization processes are amenable to an iterative sequence leading to (1,n)-functionalized products with catalyst-controlled diastereo- and enantioselectivity. The utility of the method in the synthesis of biologically active molecules has been demonstrated. PMID:24156776

Sharma, Ankit; Hartwig, John F.

2013-01-01

266

On the enantioselective hydrogenation of isomeric methyl 3-acetamidobutenoates with RhI complexes.  

PubMed

The enantioselective hydrogenation of E- and Z-methyl 3-acetamidobutenoate, key intermediates in the synthesis of a pharmaceutically important chiral beta-amino acid, with RhI catalysts in MeOH as solvent has been investigated in detail. As chiral ligands, Et-DuPHOS, Me4-BASPHOS, DI-PAMP, DIOP, HO-DIOP and Et-Ferro-TANE have been employed. The particular role of oxyfunctionalization in some diphosphine catalysts is addressed in relation to the E/Z geometry of the substrate and the dependency of the ee on the H2 pressure. Kinetic investigations with [Rh(diphosphane)(MeOH)2]-BF4, taking into consideration the special nature of the precatalyst [[Rh-(cod)2]BF4/ligand versus [Rh(cod)ligand)]BF4], NMR spectroscopic measurements and the H2 pressure dependence of the observed enantioselectivity provide evidence that the reaction proceeds via an "unsaturated route" mechanism. This mechanism correlates to catalytic features found in the past for the hydrogenation of related unsaturated alpha-amino acid precursors. The influence of the temperature was similarly investigated. A nonlinear dependency of the enantiomeric ratio as a function of the reciprocal of the temperature has been found. The correlation between temperature and H2 pressure and their effects on the enantioselectivity is discussed. In general, the highest enantioselectivities for the hydrogenation of both isomeric substrates can be achieved at room temperature and below, whereas the fastest conversion takes place at 30-50 degrees C. PMID:12613038

Heller, Detlef; Drexler, Hans-Joachim; You, Jingsong; Baumann, Wolfgang; Drauz, Karlheinz; Krimmer, Hans-Peter; Börner, Armin

2002-11-15

267

Highly enantioselective aldol reactions between acetaldehyde and activated acyclic ketones catalyzed by chiral primary amines.  

PubMed

Highly enantioselective cross-aldol reactions between acetaldehyde and activated acyclic ketones are reported for the first time. Various acyclic ketones, such as saturated and unsaturated keto esters, reacted with acetaldehyde in the presence of a chiral primary amine and a Brønsted acid to afford optically enriched tertiary alcohols in good yields and with excellent enantioselectivities. Trifluoromethyl ketones were tolerable under the reaction conditions, thereby affording the trifluoromethyl carbinol in good-to-excellent yields and enantioselectivities. Structural modification of the chiral amines from the same chiral source switched the stereoselectivity of the products. The utility of aldol chemistry was demonstrated in the brief synthesis of functionally enriched ?-lactones. Theoretical calculations on the transition-state structure indicated that the protonated tertiary amine could effectively activate the carbonyl group of a keto ester to promote the addition process through hydrogen-bonding interaction and, simultaneously, provide an appropriate attacking pattern for the approach of the keto ester to the enamine, which is formed from acetaldehyde and the chiral catalyst, on a particular face, resulting in high enantioselectivity. PMID:23559455

Deng, Yu-Hua; Chen, Jin-Quan; He, Long; Kang, Tai-Ran; Liu, Quan-Zhong; Luo, Shi-Wei; Yuan, Wei-Chen

2013-05-27

268

Synthesis and applications of non-racemic cyanohydrins  

Microsoft Academic Search

Methods for the catalytic asymmetric synthesis of cyanohydrins derived from both aldehydes and ketones are reviewed. Successful catalysts based on enzymes, peptides and transitional metal complexes are included, and mechanistic detail is included where appropriate. Illustrations of the many synthetic applications of non-racemic cyanohydrins are given.

Michael North

2003-01-01

269

Mediated Intergroup Contact: Concept Explication, Synthesis, and Application  

Microsoft Academic Search

This article had an overarching goal of paving a foundation for the scholarship on intergroup contact in the field of media research. This goal was approached from three different directions: concept explication, synthesis, and application. First, selective reviews of literature on intergroup contact research and media effects research were conducted to identify a term that can best represent existing terminology

Sung-Yeon Park

2012-01-01

270

Synthesis and photovoltaic application of coper (I) sulfide nanocrystals  

SciTech Connect

We present the rational synthesis of colloidal copper(I) sulfide nanocrystals and demonstrate their application as an active light absorbing component in combination with CdS nanorods to make a solution-processed solar cell with 1.6percent power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period.

Wu, Yue; Wadia, Cyrus; Ma, Wanli; Sadtler, Bryce; Alivisatos, A.Paul

2008-06-24

271

Synthesis, Characterization and Application of Single and Mixed Oxides Nanomaterials  

Microsoft Academic Search

Single and mixed oxides have been widely used for various applications such as a semiconductor in dye-sensitized solar cell, catalysts, fuel cells, resistors, gas sensors, transparent optical device, optical coatings and so on. The efficiency of materials is influenced by many factors such as crystallinity of structure, particle size, surface area, and the method of preparation. The sol-gel synthesis is

Sorapong Pavasupree; Supachai Ngamsinlapasathian; Sommai Pivsa-art; Yoshikazu Suzuki; Susumu Yoshikawa

272

The heuristic synthesis of applications-oriented microcode  

Microsoft Academic Search

This paper describes an algorithm for the synthesis of applications-oriented microcode for a dynamically microprogrammable computer. The need for such an algorithm is expressed by Reigel, Faber, and Fisher as an integral step in the solution of the tuning problem, or the problem of modifying a system architecture in order to optimally solve a given problem. This modification of architecture

A. M. Abd-alla; D. C. Karlgaard

1973-01-01

273

Synthesis of Fire-Safe Polymers For Aerospace Applications  

Microsoft Academic Search

The proposed project will focus on the synthesis of new poly- mers that are suitable as fire resistant materials in aerospace applications. The increased utilization of polymeric materials in aircrafts interiors and passenger seats represents the largest source of potentially combustible materials. The success of this research will advance efforts to construct desirable fire- safe materials. S YNTHESIS OF FUNCTIONAL

Jack Y. Lu

274

PERCEPTUAL CATEGORIZATION OF MOVING SOUNDS FOR SYNTHESIS APPLICATIONS  

E-print Network

to the physics of moving sound sources. In practice, the following phys- ical phenomena were simulated: Doppler effect, air ab- sorption, reverb rate (for propagation inside a room). We tested if sound transformationsPERCEPTUAL CATEGORIZATION OF MOVING SOUNDS FOR SYNTHESIS APPLICATIONS Adrien Merer, Sølvi Ystad

Paris-Sud XI, Université de

275

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

ii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Florida-renewable emergy use per capita, were compared to social, political, economic, and environmental indicators

Slatton, Clint

276

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

ii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Florida basis. Converting each flow to macroeconomic flows (using the global emergy money ratio) suggests

Slatton, Clint

277

Catalytic enantioselective reactions driven by photoinduced electron transfer.  

PubMed

Photoinduced electron transfer is an essential step in the conversion of solar energy into chemical energy in photosystems I and II (ref. 1), and is also frequently used by chemists to build complex molecules from simple precursors. During this process, light absorption generates molecules in excited electronic states that are susceptible to accepting or donating electrons. But although the excited states are straightforward to generate, their short lifetimes makes it challenging to control electron transfer and subsequent product formation-particularly if enantiopure products are desired. Control strategies developed so far use hydrogen bonding, to embed photochemical substrates in chiral environments and to render photochemical reactions enantioselective through the use of rigid chiral complexing agents. To go beyond such stoichiometric chiral information transmission, catalytic turnover is required. Here we present a catalytic photoinduced electron transfer reaction that proceeds with considerable turnover and high enantioselectivity. By using an electron accepting chiral organocatalyst that enforces a chiral environment on the substrate through hydrogen bonding, we obtain the product in significant enantiomeric excess (up to 70%) and in yields reaching 64%. This performance suggests that photochemical routes to chiral compounds may find use in general asymmetric synthesis. PMID:16121176

Bauer, Andreas; Westkämper, Felix; Grimme, Stefan; Bach, Thorsten

2005-08-25

278

[Application of levansucrase in levan synthesis--a review].  

PubMed

Levan is a fructan mainly linked by beta-(2,6)-glycosidic bonds with some beta-(2,1)-linked branch chains. Some microbial levan exhibit biological activities such as antitumor, antidiabetic and immunostimulating activities. hypolipidemic effect, and function as prebiotics, which has a wide and potential application in the pharmaceutical and food industry. Because of low extraction yields from microbial fermentation and a very complex process for chemical synthesis of levan, enzymatic synthesis of levan has attracted tremendous interest. Levansucrase (EC 2. 4. 1. 10), a beta-propeller protein belonging to the glycoside hydrolase family 68 (GH68) with reaction mechanism of non-Leloir glycosyltransferase, catalyzes the synthesis of levan by transferring the fructosyl group of non-activated sucrose into the fructan chain. The molecular structure and regulation of gene expression of some microbial levansucrases have been elucidated. Meanwhile, the enzymatic synthesis of levan by levansucrase is widely studied. In this review, catalytic mechanism of levansucrase, molecular structure and regulation of gene expression of some microbial levansucrases, and the application of levansucrases in enzymatic synthesis of levan were summarized. PMID:25272807

Lu, Juan; Lu, Lili; Xiao, Min

2014-06-01

279

Aperture synthesis polarimetry: Application to the Dominion Radio Astrophysical Observatory synthesis telescope  

Microsoft Academic Search

Aperture synthesis is a powerful technique for imaging the radio sky and can be used to make images in all four Stokes parameters, providing a complete measurement of the polarization state of the received radiation. In centimeter-wavelength continuum astronomy the received signals are generally partially linearly polarized, with a negligibly small fraction of circular polarization. For this application the preferred

R. J. Smegal; T. L. Landecker; J. F. Vaneldik; D. Routledge; P. E. Dewdney

1997-01-01

280

Homogeneous and heterogeneous asymmetric reactions. Part 13. Clay-supported noble metal catalysts in enantioselective hydrogenations  

Microsoft Academic Search

The preparation, characterization and application of new clay-supported Pt and Pd catalysts containing cinchonidine as chiral modifier are described. The preparation was carried out by deposition of the metal by impregnation followed by the immobilization of the modifier. The catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The samples were tested in enantioselective hydrogenation of ethyl

Béla Török; Katalin Balázsik; Istvá Kun; György Szöllösi; Gerda Szakonyi; Mihály Bartók

1999-01-01

281

Pristine nanomaterials: synthesis, stability and applications.  

PubMed

Capping-free and linker-free nanostructures/hybrids possess superior properties due to the presence of pristine surfaces and interfaces. In this review, various methods for synthesizing pristine nanomaterials are presented along with the general principles involved in their morphology control. In wet chemical synthesis, the interplay between various reaction parameters results in diverse morphology. The fundamental principles behind the evolution of morphology including nanoporous aggregates of metals and other inorganic materials, 2D nanocrystals of metals is elucidated by capping-free methods in aqueous medium. In addition, strategies leading to the attachment of bare noble metal nanoparticles to functional oxide supports/reduced graphene oxide has been demonstrated which can serve as a simple solution for obtaining thermally stable and efficient supported catalysts with free surfaces. Solution based synthesis of linker-free oxide-semiconductor hybrids and capping-free metal nanowires on substrates are also discussed in this context with ZnO/CdS and ultrathin Au nanowires as examples. A simple and rapid microwave-assisted method is highlighted for obtaining such hybrids which can be employed for high-yield production of similar materials. PMID:23674238

Kundu, Paromita; Anumol, E A; Ravishankar, N

2013-06-21

282

Asymmetric synthesis of cis-2,5-disubstituted pyrrolidine, the core scaffold of ?3-AR agonists.  

PubMed

A practical, enantioselective synthesis of cis-2,5-disubstituted pyrrolidine is described. Application of an enzymatic DKR reduction of a keto ester, which is easily accessed through a novel intramolecular N?C benzoyl migration, yields syn-1,2-amino alcohol in >99% ee and >99:1 dr. Subsequent hydrogenation of cyclic imine affords the cis-pyrrolidine in high diastereoselectivity. By integrating biotechnology into organic synthesis and isolating only three intermediates over 11 steps, the core scaffold of ?3-AR agonists is synthesized in 38% overall yield. PMID:23451898

Xu, Feng; Chung, John Y L; Moore, Jeffery C; Liu, Zhuqing; Yoshikawa, Naoki; Hoerrner, R Scott; Lee, Jaemoon; Royzen, Maksim; Cleator, Ed; Gibson, Andrew G; Dunn, Robert; Maloney, Kevin M; Alam, Mahbub; Goodyear, Adrian; Lynch, Joseph; Yasuda, Nobuyashi; Devine, Paul N

2013-03-15

283

Hydroxynitrile lyase catalyzed cyanohydrin synthesis at high pH-values  

Microsoft Academic Search

The application of unusual high pH-values within enzymatic cyanohydrin synthesis has been investigated. Usually enzymatic\\u000a cyanohydrin synthesis in two-phase systems requires low pH-values within the aqueous phase to suppress the non-enzymatic side\\u000a reaction. In contrast, we investigated the usage of pH-values above pH 6 by using the highly enantioselective (S)-selective hydroxynitrile lyase from Manihot esculenta. With these unusual reaction conditions

Jan von Langermann; Jan-Karl Guterl; Martina Pohl; Harald Wajant; Udo Kragl

2008-01-01

284

Controllable synthesis and biomedical applications of silver nanomaterials.  

PubMed

Silver nanomaterials have lots of peculiar and exciting physical and chemical properties that are different from massive silver, so the synthesis and applications of silver nanomaterials have attracted a great deal of attention in the last decade. Currently, all kinds of silver nanomaterials having different shapes and sizes have been synthesized by many ingenious methods, and silver nanomaterials have exhibited extensive application prospects in many fields especially in biomedical aspect. In this article, the controllable synthesis of silver nanomaterials including nanorods, nanowires, nanotubes, nanoprisms, nanoplates, nanodisks, nanospheres, and nanopolyhedrons, etc. are reviewed. Silver nanomaterials are most utilized in the form of nanoparticles, so the main biomedical applications of silver nanoparticles, such as antibacterial and antiviral applications, antitumor applications, biosensors and biological labels, optical imaging and imaging intensifier, are discussed. Although antibacterial applications are still the most important aspects of silver nanomaterials at present, antitumor, optical sensors and imaging applications of silver nanomaterials have also shown good potential perspectives. More biomedical applications of silver nanomaterials still need to be exploited for the future, and the biological safety of silver nanomaterials also should be paid enough attention before their practical applications. PMID:22413219

Huang, Zhihai; Jiang, Xiaoli; Guo, Dawei; Gu, Ning

2011-11-01

285

Catalytic asymmetric synthesis of allylic alcohols and derivatives and their applications in organic synthesis.  

PubMed

Allylic alcohols represent an important and highly versatile class of chiral building blocks for organic synthesis. This Review summarizes the plethora of methods developed for the catalytic asymmetric synthesis of enantioenriched allylic alcohols. These include: dynamic kinetic resolution (DKR/DKAT), nucleophilic 1,2-addition to carbonyl groups, allylic substitution, oxidation of C-H bonds, the addition of O nucleophiles to ? systems, reduction of unsaturated carbonyl compounds, and an alternative route from enantioenriched propargylic alcohols. Furthermore, these catalytic asymmetric processes are exemplified by their applications in the syntheses of complex molecules such as natural products and potential therapeutic agents. PMID:23319206

Lumbroso, Alexandre; Cooke, Michael L; Breit, Bernhard

2013-02-11

286

Nanosilver particles in medical applications: synthesis, performance, and toxicity  

PubMed Central

Nanosilver particles (NSPs), are among the most attractive nanomaterials, and have been widely used in a range of biomedical applications, including diagnosis, treatment, drug delivery, medical device coating, and for personal health care. With the increasing application of NSPs in medical contexts, it is becoming necessary for a better understanding of the mechanisms of NSPs’ biological interactions and their potential toxicity. In this review, we first introduce the synthesis routes of NSPs, including physical, chemical, and biological or green synthesis. Then the unique physiochemical properties of NSPs, such as antibacterial, antifungal, antiviral, and anti-inflammatory activity, are discussed in detail. Further, some recent applications of NSPs in prevention, diagnosis, and treatment in medical fields are described. Finally, potential toxicology considerations of NSPs, both in vitro and in vivo, are also addressed. PMID:24876773

Ge, Liangpeng; Li, Qingtao; Wang, Meng; Ouyang, Jun; Li, Xiaojian; Xing, Malcolm MQ

2014-01-01

287

Application of optimality criteria in structural synthesis  

NASA Technical Reports Server (NTRS)

The rational use of optimality criteria was investigated for a class of structural synthesis problems where materials, configuration and applied load conditions are specified, and the minimum weight design is to be determined. The potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored. The reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm. Optimality criteria methods for obtaining design vectors associated with displacement, system buckling and natural frequency constraints are presented. A stress ratio method was used to generate a basis design vector representing the stress constraints. The finite element displacement method was used as the basic structural analysis tool. Results for several examples of truss systems subject to stress, displacement and minimum size constraints are presented. An assessment of these results indicates the effectiveness of the hybrid method developed.

Terai, K.

1974-01-01

288

High-Yield Synthesis and Applications of Anisotropic Gold Nanoparticles  

NASA Astrophysics Data System (ADS)

This work will describe research directed towards the synthesis of anisotropic gold nanoparticles as well as their functionalization and biological applications. The thesis will begin by describing a new technique for the high-yield synthesis of gold nanorods using hydroquinone as a reducing agent. This addresses important limitations of the traditional nanorod synthesis including low yield of gold ions conversion to metallic form and inability to produce rods with longitudinal surface plasmon peak above 850 nm. The use of hydroquinone was also found to improve the synthesis of gold nanowires via the nanorod-seed mediated procedure developed in our lab. The thesis will next present the synthesis of novel starfruitshaped nanorods, mesorods, and nanowires using a modified nanorod-seed mediated procedure. The starfruit particles displayed increased activity as surfaceenhanced Raman spectroscopy (SERS) substrates as compared to smooth structures. Next, a method for the functionalization of gold nanorods using a cationic thiol, 16-mercaptohexadecyltrimethylammonium bromide (MTAB), will be described. By using this thiol, we were able to demonstrate the complete removal of toxic surfactant from the nanorods and were also able to precisely quantify the grafting density of thiol molecules on the nanorod surface through a combination of several analytical techniques. Finally, this thesis will show that MTABfunctionalized nanorods are nontoxic and can be taken up in extremely high numbers into cancer cells. The thesis will conclude by describing the surprising uptake of larger mesorods and nanowires functionalized with MTAB into cells in high quantities.

Vigderman, Leonid

289

Enantioselective biomimetic total syntheses of kuwanons I and J and brosimones A and B.  

PubMed

The first enantioselective total syntheses of prenylflavonoid Diels-Alder natural products (-)-kuwanon?I, (+)-kuwanon?J, (-)-brosimone?A, and (-)-brosimone?B have been accomplished from a common intermediate based on a concise synthetic strategy. Key elements of the synthesis include a biosynthesis-inspired asymmetric Diels-Alder cycloaddition mediated by a chiral ligand/boron Lewis acid, as well as a process involving regioselective Schenck ene reaction, reduction, and dehydration to realize a biomimetic dehydrogenation for generation of the required diene precursor. Furthermore, a remarkable tandem inter-/intramolecular asymmetric Diels-Alder cycloaddition process was applied for the synthesis of (-)-brosimone?A. PMID:25044511

Han, Jianguang; Li, Xia; Guan, Yong; Zhao, Wenjun; Wulff, William D; Lei, Xiaoguang

2014-08-25

290

SPEECH PRODUCTION AND PERCEPTION MODELS AND THEIR APPLICATIONS TO SYNTHESIS, RECOGNITION, AND CODING  

E-print Network

SPEECH PRODUCTION AND PERCEPTION MODELS AND THEIR APPLICATIONS TO SYNTHESIS, RECOGNITION andperception mechanismsandleadtohigh- quality computer synthesis of speech, robust automatic speech recognition performance, reliability,andwide-spread use of speech-processing devices. Using mathematical modelsof

Alwan, Abeer

291

A formal, one-pot ?-chlorination of primary alcohols and its utilization in the transformation of terpene feedstock and the synthesis of a C2-symmetrical terminal bis-epoxide.  

PubMed

A one-pot transformation of alkan-1-ols into 2-chloroalkan-1-ols is described. As a practical application, terpene-derived primary alcohols were converted into semiochemicals such as olfactory lactones (aerangis lactone, whisky lactone, and cognac lactone) and pheromones (cruentol and ferrugineol). Using heptane-1,7-diol as a bifunctional substrate, the corresponding bis-epoxide was synthesized by bidirectional synthesis in good yield and high enantioselectivity. PMID:24437547

Swatschek, Jörg; Grothues, Lydia; Bauer, Jonathan O; Strohmann, Carsten; Christmann, Mathias

2014-02-01

292

Large-scale de novo DNA synthesis: technologies and applications.  

PubMed

For over 60 years, the synthetic production of new DNA sequences has helped researchers understand and engineer biology. Here we summarize methods and caveats for the de novo synthesis of DNA, with particular emphasis on recent technologies that allow for large-scale and low-cost production. In addition, we discuss emerging applications enabled by large-scale de novo DNA constructs, as well as the challenges and opportunities that lie ahead. PMID:24781323

Kosuri, Sriram; Church, George M

2014-05-01

293

The application of micro reactors for organic synthesis.  

PubMed

This tutorial review describes how micro reactors are being applied to synthetic chemistry covering a wide range of applications, from the preparation of nanograms of material for drug discovery and screening to the multi-tonne production of fine chemicals. This article explores how miniaturisation may revolutionise chemical synthesis and demonstrates that products are generated in higher yield and purity compared to the equivalent bulk reactions, in much shorter periods of time. PMID:15726160

Watts, Paul; Haswell, Stephen J

2005-03-01

294

Carbon Nanotubes: Synthesis, Properties and Pharmaceutical Applications  

Microsoft Academic Search

Carbon nanotubes (CNTs) are unique cylindrical forms of carbon that have carved a niche in the field of nanomedicine. The possibility of incorporating functionalized carbon nanotubes into cells and the biological milieu offers numerous advantages for potential applications in biology, pharmacology and drug delivery. One of the most promising is the utilization of CNTs as a new carrier system for

Inderbir Singh; Ashish K. Rehni; Pradeep Kumar; Manoj Kumar

2009-01-01

295

Enantioselective degradation of the chiral fungicides metalaxyl and furalaxyl by Brevibacillus brevis.  

PubMed

For almost four decades, the chiral fungicides metalaxyl and furalaxyl have been in use in plant protection on a global scale. Both substances are distributed as racemic mixtures, yet the desirable interference in nucleic acid synthesis of harmful fungi only occurs by the (-)-R-enantiomer. As enantioselective degradation in Scheyern (Germany) and Yaoundé (Cameroon) soils has been documented, the influence of 50 isolated microorganisms on the R/S ratio was investigated. A high-pressure liquid chromatography method with a chiral column to separate enantiomers of metalaxyl and furalaxyl, and subsequent detection by tandem mass spectrometry, was employed. Only one of these microorganisms, a strain of Brevibacillus brevis, showed an enantioselective degradation pattern in liquid culture; the respective (-)-R-enantiomers were preferably degraded. Moreover, (-)-R-furalaxyl was degraded faster in cultures supplemented simultaneously with both fungicides of the same concentration. PMID:23716265

Sulimma, Lutz; Bullach, Anke; Kusari, Souvik; Lamshöft, Marc; Zühlke, Sebastian; Spiteller, Michael

2013-06-01

296

Enantioselective disposition of albuterol in humans.  

PubMed

The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers of beta 2-agonists previously thought of as "inactive" may be associated with toxic effects is a further compelling reason to study the enantioselective pharmacokinetics of this class of drugs. In addition, the role of enantiomers in producing side effects, such as tremor and reduction in renal function, needs to be reassessed. The beta 2-agonists can be looked on as textbook examples of the inherent danger of ignoring chirality in the study of pharmacokinetics and pharmacodynamics. The growing body of information on the enantioselective disposition of beta 2-agonists in humans will enhance the rational use of these drugs in the future management of patients. PMID:8866176

Boulton, D W; Fawcett, J P

1996-01-01

297

Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications  

SciTech Connect

The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic and mechanical properties from those of the bulk material. Nanoparticles synthesis can be grouped into 3 broad approaches. The first one is wet phase synthesis (sol-gel processing), the second is mechanical attrition, and the third is gas-phase synthesis (aerosol). The properties of the final product may differ significantly depending on the fabrication route. Currently, there are no economical large-scale production processes for nanoparticles. This hinders the widespread applications of nanomaterials in products. The Idaho National Laboratory (INL) is engaging in research and development of advanced modular hybrid plasma reactors for low cost production of nanoparticles that is predicted to accelerate application research and enable the formation of technology innovation alliances that will result in the commercial production of nanocomposites for alternative energy production devices such as fuel cells, photovoltaics and electrochemical double layer capacitors.

Peter C. Kong; Alex W. Kawczak

2008-09-01

298

Synthesis, properties, and applications of iron nanoparticles.  

SciTech Connect

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earths crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Irons reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of irons potential, and work in this field appears to be blossoming.

Huber, Dale L.

2005-01-01

299

Norbornene based polybetaines: Synthesis and biological applications  

NASA Astrophysics Data System (ADS)

Polymeric betaines gain considerable attention for their interesting solution properties, but even more so, for their favorable bio- and haemocompatible properties. When incorporated into materials or used as surface coatings, some of these zwitterionic polymers strongly resist protein absorption due to their hygroscopic nature, making betaines promising candidates for medical diagnostics, drug delivery, and tissue engineering applications. This dissertation introduces novel norbornene-based polybetaines as foundational materials for biological applications, including non-fouling coatings and antimicrobial macromolecules. Sulfo- and carboxybetaines, composed of backbones that do not contain hydrolyzable units under physiological conditions, as well as new polymers that carry a dual functionality at the repeat unit level, coupling a zwitterionic functionality with an alkyl moiety varied to adjust the amphiphilicity of the overall system, are introduced. How structural changes, backbone chemistry, hydrophilicity/amphiphilicity, and coating surface roughness impact their non-fouling properties is investigated.

Colak, Semra

300

Chiral catalysts dually functionalized with amino acid and Zn2+ complex components for enantioselective direct aldol reactions inspired by natural aldolases: design, synthesis, complexation properties, catalytic activities, and mechanistic study.  

PubMed

Aldolases are enzymes that catalyze stereospecific aldol reactions in a reversible manner. Naturally occurring aldolases include class I aldolases, which catalyze aldol reactions via enamine intermediates, and class II aldolases, in which Zn(2+) enolates of substrates react with acceptor aldehydes. In this work, Zn(2+) complexes of L-prolyl-pendant[15]aneN(5) (ZnL(3)), L-prolyl-pendant[12]aneN(4) (ZnL(4)), and L-valyl-pendant[12]aneN(4) (ZnL(5)) were designed and synthesized for use as chiral catalysts for enantioselective aldol reactions. The complexation constants for L(3) to L(5) with Zn(2+) [logK(s)(ZnL)] were determined to be 14.1 (for ZnL(3)), 7.6 (for ZnL(4)), and 9.6 (for ZnL(5)), indicating that ZnL(3) is more stable than ZnL(4) and ZnL(5). The deprotonation constants of Zn(2+)-bound water [pK(a)(ZnL) values] for ZnL(3), ZnL(4), and ZnL(5) were calculated to be 9.2 (for ZnL(3)), 8.2 (for ZnL(4)), and 8.6 (for ZnL(5)), suggesting that the Zn(2+) ions in ZnL(3) is a less acidic Lewis acid than in ZnL(4) and ZnL(5). These values also indicated that the amino groups on the side chains weakly coordinate to Zn(2+). We carried out aldol reactions between acetone and 2-chlorobenzaldehyde and other aldehydes in the presence of catalytic amounts of the chiral Zn(2+) complexes in acetone/H(2)O at 25 and 37 degrees C. Whereas ZnL(3) yielded the aldol product in 43% yield and 1% ee (R), ZnL(4) and ZnL(5) afforded good chemical yields and high enantioselectivities of up to 89% ee (R). UV titrations of proline and ZnL(4) with acetylacetone (acac) in DMSO/H(2)O (1:2) indicate that ZnL(4) facilitates the formation of the ZnL(4)(acac)(-) complex (K(app)=2.1x10(2) M(-1)), whereas L-proline forms a Schiff base with acac with a very small equilibrium constant. These results suggest that the amino acid components and the Zn(2+) ions in ZnL(4) and ZnL(5) function in a cooperative manner to generate the Zn(2+)-enolate of acetone, thus permitting efficient enantioselective C-C bond formation with aldehydes. PMID:19746465

Itoh, Susumu; Kitamura, Masanori; Yamada, Yasuyuki; Aoki, Shin

2009-10-12

301

[Progress in synthesis technologies and application of aviation biofuels].  

PubMed

Development of aviation biofuels has attracted great attention worldwide because that the shortage of fossil resources has become more and more serious. In the present paper, the development background, synthesis technologies, current application status and existing problems of aviation biofuels were reviewed. Several preparation routes of aviation biofuels were described, including Fischer-Tropsch process, catalytic hydrogenation and catalytic cracking of bio-oil. The status of flight tests and commercial operation were also introduced. Finally the problems for development and application of aviation biofuels were stated, and some accommodation were proposed. PMID:23789270

Sun, Xiaoying; Liu, Xiang; Zhao, Xuebing; Yang, Ming; Liu, Dehua

2013-03-01

302

Plasma assisted synthesis of WS2 for gas sensing applications  

NASA Astrophysics Data System (ADS)

We report the plasma assisted synthesis of WS2 thin films and demonstrate their suitability for sensing applications. This was achieved by using a H2S plasma to sulphurise WO3 films at temperatures as low as 500 °C. This is a significant step towards semiconductor compatible growth of transition metal dichalcogenide (TMD) thin films without the need for highly elevated temperatures. We found that the electrical transport in thin films is highly sensitive to the presence of NH3. A sensitivity of 1.4 ppm NH3 in nitrogen at room temperature has been achieved, demonstrating the potential of 2D TMD films for sensing applications.

O'Brien, Maria; Lee, Kangho; Morrish, Rachel; Berner, Nina C.; McEvoy, Niall; Wolden, Colin A.; Duesberg, Georg S.

2014-11-01

303

Synthesis and applications of silver nanoparticles  

NASA Astrophysics Data System (ADS)

Due to their unique properties, silver nanoparticles are used in a wide range of applications, like electronics, optics, catalysis, biology, etc. The preferred route for their preparation has been, and still is, the reduction of silver salts in solutions. While dedicated reducing agents, solvents, and dispersants are typically used in this approach, in some cases, the same additive (ex: polyols) may play multiple roles. Such dual-function additives are particularly interesting alternatives as they offer the possibility of replacing the undesirable reductants often used in conventional precipitation methods. In the current research, an environmentally friendly route to prepare stable concentrated aqueous dispersions of silver nanoparticles is investigated experimentally. It was found that Arabic gum, a well known stabilizing agent, can also rapidly and completely reduce Ag 2O to metallic silver in alkaline solutions (pH >12.0) and elevated temperature (65 °C). The average size of the silver nanoparticles could be tailored from 13 to 30 nm by varying the experimental conditions. To prepare stable metal colloids by chemical precipitation methods requires in most cases a high concentration of polymeric dispersants. Consequently, the particles are embedded in the organic matrix, which can not be removed without affecting the properties of the particles and/or the dispersion stability. This can have a negative effect in many applications. In this work, an enzymatic hydrolysis method for isolating the silver particles from dispersions containing high concentrations of polymer was identified. In addition, a chemical hydrolysis method yielding dispersed silver nanoparticles with low content of residual polymer for printable electronics applications is investigated. The low sintering temperature of silver nanoparticles and high electrical conductivity make them very attractive for the fabrication of conductive patterns especially for flexible electronic applications. In the final section of this thesis, the silver nanoparticles are deposited using inkjet printing technology with a Dimatix printer DMP -2831. Silver nanoparticles of 13 nm, 80 nm, and mixtures of the two sizes were used to evaluate the effect of particle size and size distribution on the electrical properties of sintered films. The silver layers deposited with a 'drop-on-demand' inkjet printer were heated at temperatures ranging from 125°C to 200°C. The small particles formed less resistive films at 125°C, while the larger ones provided better electrical conductivity above 150°C. The inks containing mixed small and large particles yielded the most conductive silver films over the entire investigated temperature range. A mechanism explaining these results is proposed based on the evolution of film microstructure with temperature.

Balantrapu, Krishna Chaitanya

304

Doped Carbon Nanotubes: Synthesis, Characterization and Applications  

Microsoft Academic Search

\\u000a Various applications of carbon nanotubes require their chemical modification in\\u000a order to tune\\/control their physicochemical properties. One way for achieving this\\u000a control is by carrying out doping processes through which atoms and molecules\\u000a interact (covalently or noncovalently) with the nanotube surfaces. The aim of this\\u000a chapter is to emphasize the importance of different types of doping in carbon\\u000a nanotubes (single-,

Mauricio Terrones; Antonio G. Souza Filho; Apparao M. Rao

305

Exchange-coupled nanocomposites: chemical synthesis, characterization and applications.  

PubMed

Nanocomposites containing soft and hard magnetic phases have attracted immense attention for energy-related and biomedical applications. With exchange coupling between nanoscale grains in the composites, magnetization of the soft magnetic phase can rotate coherently with that of the hard magnetic phase. In particular, good control of the soft and hard phases at the nanoscale in the composites is of great importance for effective exchange coupling, allowing us to make the best of the strengths of soft and hard magnetic phases and to optimize the magnetic properties for targeted applications. In this review, we present the recent progress in the chemical synthesis and applications of exchange-coupled nanocomposites. Firstly, the principle of nanomagnetism and exchange coupling is introduced. Secondly, the characterization of exchange-coupled nanocomposites is summarized. Thirdly, the chemical methods for the production of different exchange-coupled nanocomposites are presented. Finally, applications of exchange-coupled nanocomposites in magnetic energy storage and biomedicine are addressed. PMID:25130706

Liu, Fei; Hou, Yanglong; Gao, Song

2014-12-01

306

Biomedical Nanocrystal Agents: Design, Synthesis, and Applications  

NASA Astrophysics Data System (ADS)

In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2 ) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T 1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2˜22 nm) and iron based magnetic nanocrystals (4 ˜33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3˜4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.

Cho, Minjung

307

One-dimensional zinc oxide nanomaterials synthesis and photovoltaic applications  

NASA Astrophysics Data System (ADS)

As humanly engineered materials systems approach the atomic scale, top-down manufacturing approaches breakdown and following nature's example, bottom-up or self-assembly methods have the potential to emerge as the dominant paradigm. Synthesis of one-dimensional nanomaterials takes advantage of such self-assembly manufacturing techniques, but until now most efforts have relied on high temperature vapor phase schemes which are limited in scalability and compatibility with organic materials. The solution-phase approach is an attractive low temperature alternative to overcome these shortcomings. To this end, this thesis is a study of the rationale solution-phase synthesis of ZnO nanowires and applications in photovoltaics. The following thesis goals have been achieved: rationale synthesis of a single ZnO nanowire on a polymer substrate without seeding, design of a wafer-scale technique to control ZnO nanowire array density using layer-by-layer polymers, determination of optimal nanowire field emitter density to maximize the field enhancement factor, design of bridged nanowires across metal electrodes to order to circumvent post-synthesis manipulation steps, electrical characterization of bridged nanowires, rationale solution-phase synthesis of long ZnO nanowires on optical fibers, fabrication of ZnO nanowire dye-sensitized solar cells on optical fibers, electrical and optical characterization of solar cell devices, comparison studies of 2-D versus 3-D nanowire dye-sensitized solar cell devices, and achievement of 6-fold solar cell power conversion efficiency enhancement using a 3-D approach. The thesis results have implications in nanomanufacturing scale-up and next generation photovoltaics.

Weintraub, Benjamin A.

308

Enantioselective organocatalytic epoxidation using hypervalent iodine reagents  

E-print Network

Enantioselective organocatalytic epoxidation using hypervalent iodine reagents Sandra Lee and David Abstract--A rare example of a hypervalent iodine reagent participating in a 1,4-heteroconjugate addition imidazolidinone catalyst 1. Development of an `internal syringe pump' effect via the slow release of iodosobenzene

MacMillan, David W. C.

309

Synthesis and catalytic applications of combined zeolitic/mesoporous materials  

PubMed Central

Summary In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials. PMID:22259762

Vernimmen, Jarian; Cool, Pegie

2011-01-01

310

A Catalytic, Asymmetric Formal Synthesis of (+)-Hamigeran B  

PubMed Central

A concise asymmetric, formal synthesis of (+)-hamigeran B is reported. A Pd-catalyzed, decarboxylative allylic alkylation, employing a trifluoromethylated derivative of t-BuPHOX, is utilized as the enantioselective step to form the critical quaternary carbon center in excellent yield and enantioselectivity. The product is converted in three steps to a late-stage intermediate previously used in the synthesis of hamigeran B. PMID:21271716

Mukherjee, Herschel; McDougal, Nolan T.; Virgil, Scott C.

2011-01-01

311

APPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH  

E-print Network

, extrapolated from DNA synthesis measurements, and 14C02 primary production on a transect of the equatorialAPPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH AND PRODUCTION. Stroup Tom Humphreys #12;ABSTRACT The rate of nucleic acid synthesis was used as a measure of growth

Luther, Douglas S.

312

Synthesis and Applications of Carbon Nanotubes and Graphene carbon nanotube, graphene, CVD growth, application  

E-print Network

Synthesis and Applications of Carbon Nanotubes and Graphene carbon nanotube, graphene, CVD growth] SWNT ACCVD CVD SWNT CVD SWNT #12; SWNT CVD SWNT CVD SWNT nm SWNT CVD CVD Co Fe 900 1100 C SWNT MWNT SWNT SWNT HiPco [5] CoMoCAT [6] ACCVD ACCVD 500900 C SWNT CVD [1] 1

Maruyama, Shigeo

313

Controlled synthesis of porous platinum nanostructures for catalytic applications.  

PubMed

Porous platinum, that has outstanding catalytic and electrical properties and superior resistant characteristics to corrosion, has been widely applied in chemical, petrochemical, pharmaceutical, electronic, and automotive industries. As the catalytic activity and selectivity depend on the size, shape and structure of nanomaterials, the strategies for controlling these factors of platinum nanomaterials to get excellent catalytic properties are discussed. Here, recent advances in the design and preparation of various porous platinum nanostructures are reviewed, including wet-chemical synthesis, electro-deposition, galvanic replacement reaction and de-alloying technology. The applications of various platinum nanostructures are also discussed, especially in fuel cells. PMID:24749422

Cao, Yanqin; Zhang, Junwei; Yang, Yong; Huang, Zhengren; Long, Nguyen Viet; Nogami, Masayuki

2014-02-01

314

Enantioselective three-component Kabachnik-Fields reaction catalyzed by chiral scandium(III)-N,N'-dioxide complexes.  

PubMed

The N,N'-dioxide-Sc(III) complex has been applied in the three-component Kabachnik-Fields reaction of aldehydes, 2-aminophenol, and diphenyl phosphite, giving the corresponding alpha-amino phosphonates in good yields with high enantioselectivities (up to 87% ee). The direct Kabachnik-Fields reaction proceeded with extremely high reactivity under mild reaction conditions and could be used for large-scale synthesis of the alpha-amino phosphonates. PMID:19226133

Zhou, Xin; Shang, Deju; Zhang, Qi; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming

2009-03-19

315

Organocatalytic, enantioselective, intramolecular oxa-Michael reaction of alkoxyboronate: a new strategy for enantioenriched 1-substituted 1,3-dihydroisobenzofurans.  

PubMed

An unprecedented strategy for the synthesis of enantioenriched 1-substituted 1,3-dihydroisobenzofurans via an enantioselective oxa-Michael reaction of o-alkoxyboronate containing chalcone (II) has been accomplished employing cinchona alkaloid based squaramide bifunctional organocatalyst in the presence of proton source. The corresponding alkoxyboronate intermediates have been readily prepared in situ from o-formyl chalcones using neutral borane as hydride source and a tertiary amine moiety which is a counterpart of the catalyst. PMID:25337660

Ravindra, Barnala; Das, Braja Gopal; Ghorai, Prasanta

2014-11-01

316

Synthesis and catalytic applications of novel mesoporous aluminosilicate molecular sieves  

SciTech Connect

This paper reports on the synthesis of 4 series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different Al compounds were examined as Al source in the hydrothermal synthesis, including pseudo boehmite (alumina), Al sulfate, Al isopropoxide, and Na aluminate. Each Al source was examined at 3 different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the d{sub 100}-spacings for the samples prepared with different Al sources: Na aluminate > Al isopropoxide < Na aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. {sup 27}Al NMR and {sub 29}Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and Na aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. They also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.

Reddy, K.M.; Song, C. [Pennsylvania State Univ., University Park, PA (United States)

1997-12-31

317

Analysis of enantioselective biochemical, physiological, and transcriptional effects of the chiral herbicide diclofop methyl on rice seedlings.  

PubMed

Diclofop methyl (DM) is a chiral herbicide that is widely used as a racemic mixture. This study analyzed the enantioselective effects of R- and S-DM on rice at the physiological and molecular levels. DM exerts an enantioselective effect on rice growth, reactive oxygen substance (ROS) formation, and antioxidant gene expression, with R-DM acting as a more potent stressor than S-DM. An analysis of chlorophyll fluorescence demonstrated that photosynthesis process was more strongly inhibited by R-DM than by S-DM. Microarray results showed that many metabolic pathways, including starch and sucrose metabolism, oxidative phosphorylation, and amino acid biosynthesis and metabolism, were affected by DM in an enantioselective manner. These results suggest that R-DM is more active to plant growth than S-DM and that this activity is induced not only by repression of fatty acid synthesis but also by R-DM affecting the transcription of genes in other metabolic pathways in an enantioselective manner. PMID:22612386

Qian, Haifeng; Wang, Ruiqin; Chen, Jun; Ding, Haiyan; Yong, Wei; Songlin, Ruan; Fu, Zhengwei

2012-06-01

318

Enantioselective Total Syntheses of Plectosphaeroic Acids B and C  

PubMed Central

Evolution of the synthetic strategy that culminated in the first total syntheses of the structurally unique plectosphaeroic acids B (2) and C (3) is described. The successful enantioselective route to (+)-2 and (+)-3 proceeds in 6 and 11 steps from the known hexahydro-2H-pyrazinopyrrolo[2,3-b]indole-1,4-dione 39, which in turn are available in enantiomerically pure form by chemical synthesis. The central challenge in this synthesis endeavor was uniting the hexahydro-2H-pyrazinopyrrolo[2,3-b]indole-1,4-dione and cinnabarinic acid fragments of these marine alkaloids. Critical for achieving this successful C–N bond formation was the use of an iodocinnabarinic acid diester in which the amino group was masked with two Boc substituents, a Cu(I) carboxylate complex, and the weak base KOAc. The highly congested C–N bond generated in this coupling, in conjunction with the delicate nature of the densely functionalized coupling partners, provide striking testament to the power of modern copper-mediated amination methods. Two approaches, one stereoselective, for introducing the methylthio substituents of (+)-plectosphaeroic acid B were developed. The epitrisulfide ring of (+)-plectosphaeroic acid C was formed by ring expansion of an epidisulfide precursor. PMID:24007470

Jabri, Salman Y.

2013-01-01

319

Upconversion Nanoparticles: Synthesis, Surface Modification, and Biological Applications  

PubMed Central

New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a non-linear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photo-bleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this review, we discuss the recent progress in the synthesis and surface modification of rare earth doped UCNPs with a specific focus on their biological applications. PMID:21419877

Wang, Meng; Abbineni, Gopal; Clevenger, April; Mao, Chuanbin; Xu, Shukun

2011-01-01

320

Boronic acid-containing hydrogels: synthesis and their applications.  

PubMed

Boronic acid-containing hydrogels are important intelligent materials. With the introduction of boronic acid functionality, these hydrogels exhibit a lot of interesting properties, such as glucose-sensitivity, reversibility and self-healing. These materials have found important applications in many areas, especially in biomedical areas. This paper aims to provide an overview of the current state of the art of the study in this area. We review the synthesis and properties of various boronic acid-containing hydrogels, including macroscopic hydrogels, microgels and layer-by-layer self-assembled films. Their applications were described, with an emphasis on the design of various glucose sensors and self-regulated insulin delivery devices. New development in this area was highlighted. Problems and the new directions were discussed. PMID:23860617

Guan, Ying; Zhang, Yongjun

2013-10-21

321

Nanocrystal-micelle: synthesis, self-assembly and application.  

PubMed

Nanocrystals (NCs) are one of the important building blocks for fabrication of nanostructured arrays for wide range of optical, electronic, magnetic, catalytic and biosensing applications. Here, our recent advances in the synthesis, self-assembly and application of NC-micelles are highlighted. The NCs are encapsulated inside the core of surfactant micelles in a rapid, interfacially driven micro-emulsion process. The flexible surface chemistry of the NC-micelles causes them to be water-soluble and allows further self-assembly into two- and three-dimensional ordered arrays. The NC-micelles are biocompatible, of interest for bio-labeling. Finally, integration of the ordered arrays and charge transport property are discussed. PMID:18338033

Fan, Hongyou

2008-03-28

322

Enantioselective total syntheses of (-)-FR901483 and (+)-8-epi-FR901483.  

PubMed

The enantioselective total syntheses of the potent immunosuppressant FR901483 (1) and its 8-epimer (47) have been accomplished. Our approach features the use of building block 6 as the chiron, the application of the one-pot amide reductive bis-alkylation method to construct the chiral aza-quaternary center (dr = 9:1), regio- and diastereoselective intramolecular aldol reaction to build the bridged ring, and RCM to form the 3-pyrrolin-2-one ring. PMID:23214918

Huo, Hao-Hua; Xia, Xiao-Er; Zhang, Hong-Kui; Huang, Pei-Qiang

2013-01-18

323

Voice Modification for Applications in Speech Synthesis Juergen Schroeter, AT&T Labs Research  

E-print Network

- 1 - Voice Modification for Applications in Speech Synthesis Juergen Schroeter, AT&T Labs modifications. We conclude by assessing the prospects of voice modification in speech synthesis in light of now for somewhat narrow applications, such as travel reservations, weather reports, etc. [24]. This high quality

Greenberg, Albert

324

Enantioselective Construction of Remote Quaternary Stereocenters  

PubMed Central

Summary Molecules containing all-carbon quaternary stereocenters – carbon atoms bonded to four distinct carbon substituents – are prevalent in Nature. However, the construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for forging quaternary stereocenters that are remote from other functional groups are underdeveloped. Herein we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. The reported method allows direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ? aryl carbonyl compounds, as the unsaturation of the alkene is relayed to the alcohol resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocenters along the alkyl chain, which links the alkene and the alcohol, wherein the stereocenter is preserved. The described method is flexible, allowing access to diverse building blocks containing an enantiomerically enriched, quaternary center. PMID:24717439

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-01-01

325

Inter- and intramolecular enantioselective carbolithiation reactions  

PubMed Central

Summary In this review we summarize recent developments in inter- and intramolecular enantioselective carbolithiation reactions carried out in the presence of a chiral ligand for lithium, such as (?)-sparteine, to promote facial selection on a C=C bond. This is an attractive approach for the construction of new carbon–carbon bonds in an asymmetric fashion, with the possibility of introducing further functionalization on the molecule by trapping the reactive organolithium intermediates with electrophiles. PMID:23504613

Gómez-SanJuan, Asier; Sotomayor, Nuria

2013-01-01

326

Gold(I)-catalyzed enantioselective cycloaddition reactions  

PubMed Central

Summary In recent years there have been extraordinary developments of gold(I)-catalyzed enantioselective processes. This includes progress in the area of cycloaddition reactions, which are of particular interest due to their potential for the rapid construction of optically active cyclic products. In this article we will summarize some of the most remarkable examples, emphasizing reaction mechanisms and key intermediates involved in the processes. PMID:24204438

2013-01-01

327

Catalytic enantioselective difluoroalkylation of aldehydes.  

PubMed

Copper-catalyzed bond scission of pentafluorobutane-1,3-diones generates difluoroenolates that react with aldehydes to give a wide range of chiral ?,?-difluoro-?-hydroxy ketones within a few hours in up to 99?% yield and 92?%?ee. The synthetic utility of this reaction is demonstrated with the stereoselective synthesis of a chiral anti-1,3-diol exhibiting a central difluoromethylene unit and efficient conversion to a 2,2-difluoro-3-hydroxy carboxylic acid. PMID:23780866

Zhang, Peng; Wolf, Christian

2013-07-22

328

Utilization of maltodextrin based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-perindopril.  

PubMed

Enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins {dextrose equivalent (DE) 4.0-7.0 (I), 13.0-17.0 (II) and 16.5-19.5 (III)} as chiral selectors for the assay of S-perindopril is described. The proposed electrodes could be reliably employed in the assay of S-perindopril raw material and from its pharmaceutical formulation, Coversyl((R)) tablets. The electrode based on maltodextrin (I) showed the best enantioselectivity and time-stability. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper. PMID:18969348

Ozoemena, Kenneth I; Stefan, Raluca-Ioana; van Staden, Jacobus F; Aboul-Enein, Hassan Y

2004-03-10

329

Dual catalysis in enantioselective oxidopyrylium-based [5 + 2] cycloadditions.  

PubMed

A new method for effecting catalytic enantioselective intramolecular [5 + 2] cycloadditions based on oxidopyrylium intermediates is reported. The dual catalyst system consists of a chiral primary aminothiourea and a second achiral thiourea. Experimental evidence points to a new type of cooperative catalysis with each species being necessary to generate a reactive pyrylium ion pair that undergoes subsequent cycloaddition with high enantioselectivity. PMID:21848300

Burns, Noah Z; Witten, Michael R; Jacobsen, Eric N

2011-09-21

330

Asymmetric sonochemical reactions. Enantioselective hydrogenation of ?-ketoesters over platinum catalysts  

Microsoft Academic Search

The sonochemical enantioselective hydrogenation of different ?-ketoesters to the corresponding hydroxy derivatives over cinchona modified Pt catalysts is described. Ultrasonic irradiation was found to be beneficial in improving the optical yields. Besides studying the reaction rates and enantioselectivities, the effect of ultrasonics on the catalyst–modifier system and the scale-up of the process will also be considered.

B Török; K Balázsik; M Török; Gy Szöllösi; M Bartók

2000-01-01

331

Chiral separation by enantioselective liquid-liquid extraction.  

PubMed

The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid-liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid-liquid extraction including host-guest chemistry, extraction and phase transfer mechanisms, and multistage liquid-liquid extraction processing. Then the literature on enantioselective liquid-liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants. PMID:21107491

Schuur, Boelo; Verkuijl, Bastiaan J V; Minnaard, Adriaan J; de Vries, Johannes G; Heeres, Hero J; Feringa, Ben L

2011-01-01

332

Synthesis of gold nanoparticles for application as biosensors in engineering  

NASA Astrophysics Data System (ADS)

This paper presents the synthesis of gold nanoparticles (AuNPs) suitable to the construction of engineering biosensors. The phenomenon of Localized Surface Plasmons Resonance (LSPR) and Surface Plasmon Polarization are explored in these sensors. AuNPs allow developing nanoscale devices that interacts with chemical and biological systems. The LSPR is the main operation principle explored in these nanosystems that promote electromagnetic wave oscillation on such small metallic structures. Our results have shown that the resonance is directly linked to the size of the nanoparticles, the nature of the dielectric material and support environment where the device is being studied, previously reported for Zhao et al. [1]. Nanoparticles with size of 56 to 88 nm was obtained this work. The Turkevich method was to used to make AuNP's with spherical morphology, this system is it possible to application in biosensor because your strong interation with light and environment.

Prado, Adilson R.; Oliveira, Jairo P.; Milaneze, Bárbara A.; Nogueira, Breno V.; Guimarães, Marco C. C.; Almeida, Luiz C. P.; Neto, Anselmo Frizera; Pontes, Maria J.; Ribeiro, Moisés. R. N.

2014-08-01

333

Nickel(0)-Catalyzed Enantioselective Annulations of Alkynes and Arylenoates Enabled by a Chiral NHC Ligand: Efficient Access to Cyclopentenones.  

PubMed

Cyclopentenones are versatile structural motifs of natural products as well as reactive synthetic intermediates. The nickel-catalyzed reductive [3+2] cycloaddition of ?,?-unsaturated aromatic esters and alkynes constitutes an efficient method for their synthesis. Here, nickel(0) catalysts comprising a chiral bulky C1 -symmetric N-heterocyclic carbene ligand were shown to enable an efficient asymmetric synthesis of cyclopentenones from mesityl enoates and internal alkynes under mild conditions. The bulky NHC ligand provided the cyclopentenone products in very high enantioselectivity and led to a regioselective incorporation of unsymmetrically substituted alkynes. PMID:25258104

Ahlin, Joachim S E; Donets, Pavel A; Cramer, Nicolai

2014-11-24

334

Crystalline colloidal array hydrogel materials: From synthesis to applications  

NASA Astrophysics Data System (ADS)

This dissertation is focused on the synthesis, characterization, and applications of crystalline colloidal array (CCA) hydrogel materials. CCA are three dimensional periodic structures formed by the electrostatic self-assembly of monodisperse macroionic colloidal spheres in an aqueous medium. CCA dispersions efficiently Bragg diffract light in the near UV to near IR spectral region, and are useful in areas of optical device fabrication, chemical sensing devices, and novel separation materials. We developed methodologies to synthesize monodisperse colloidal silica spheres via hydrolysis and condensation of tetraethoxysilane in nonionic reverse microemulsion systems. We examined the effects of reaction parameters and surfactant hydrophilic-lipophilic-balance (HLB) number on the final particle size and size distribution. We developed a unique multi-step growth technique by which the final particle diameter can be continuously selected with extremely narrow size distributions over a broad size range. We also developed methodologies to surface functionalize silica spheres to increase the particle surface charge density by two orders of magnitude. The resulting dispersions readily self-assemble into CCA and Bragg diffract light over a broad concentration range. In addition, we discovered an anomalously intense secondary diffraction phenomenon from CCA which occurs due to the superimposed Bragg diffraction from numerous lattice planes. This was quantitatively modeled by using dynamical diffraction and light scattering theory. We extended the microemulsion synthesis methodologies to fabricate monodisperse SiOsb2/CdS composite spheres with well-controlled and complex morphologies. By controlling the co-precipitation process, CdS could be incorporated into silica spheres as quantum dots, as large inclusions, as surface patches and welds, or as shells or cores. Further processing of these materials by selectively etching out CdS templates also generated a series of porous silica spheres with controlled pore characteristics. We also developed the synthesis of a novel hydrogel material with an embedded mesoscopic periodic array of water voids. These voids, much larger than the average mesh spacing of the hydrogel matrix, serve as "entropic traps" in which macromolecules preferentially partition to maximize their conformational entropy. We examined the partitioning of model chain polymers between the voids and the gel medium by probing the Bragg diffraction from the void array. Our results are the first experimental verification of the entropic trapping phenomenon. The materials developed here may be useful for applications in optical filters, nonlinear optics, catalyst supports, and macromolecular separation materials.

Liu, Lei

335

Synthesis of ribo-hexopyranoside- and altrose-based azacrown ethers and their application in an asymmetric Michael addition.  

PubMed

The synthesis of four new ribo-hexopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type and two altropyranoside-based crown ethers were elaborated. Our syntheses utilized the regioselective ring opening of the oxiran moiety of the 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. The reaction of methyl-2,3-anhydro-4,6-O-benzylidene-?-D-mannopyranoside with ethanolamine is especially of interest to afford a 3-substituted altropyranoside. One of the ribo-hexopyranoside-based lariat ethers with a 4-methoxyphenyl substituent induced an enantioselectivity of 80% when used as catalyst in the Michael addition of diethyl acetamidomalonate to trans-?-nitrostyrene under phase transfer catalytic conditions. PMID:23220061

Rapi, Zsolt; Bakó, Péter; Keglevich, György; Szöll?sy, Áron; Drahos, László; Heged?s, László

2013-01-10

336

Solution synthesis, optical properties, and bioimaging applications of silicon nanocrystals.  

PubMed

Conspectus Understanding and unlocking the potential of semiconductor nanocrystals (NCs) is important for future applications ranging from biomedical imaging contrast agents to the next generation of solar cells and LEDs. Silicon NCs (Si NCs) have key advantages compared with other semiconductor NCs due to silicon's high natural abundance, low toxicity and strong biocompatibility, and unique size, and surface dependent optical properties. In this Account, we review and discuss the synthesis, surface modification, purification, optical properties, and applications of Si NCs. The synthetic methods used to make Si NCs have improved considerably in the last 5-10 years; highly monodisperse Si NCs can now be produced on the near gram scale. Scaled-up syntheses have allowed scientists to drive further toward the commercial utilization of Si NCs. The synthesis of doped Si NCs, through addition of a simple elemental precursor to a reaction mixture or by the production of a single source precursor, has shown great promise. Doped Si NCs have demonstrated unique or enhanced properties compared with pure Si NCs, for example, magnetism due to the presence of magnetic metals like Fe and Mn. Surface reactions have reached a new level of sophistication where organic (epoxidation and diol formation) and click (thiol based) chemical reactions can be carried out on attached surface molecules. This has led to a wide range of biocompatible functional groups as well as a degree of emission tuneability. The purification of Si NCs has been improved through the use of size separation columns and size selective precipitation. These purification approaches have yielded highly monodisperse and pure Si NCs previously unachieved. This has allowed scientists to study the size and surface dependent properties and toxicity and enabled the use of Si NCs in biomedical applications. The optical properties of Si NCs are complex. Using a combination of characterization techniques, researchers have explored the relation between the optical properties and the size, surface functionalization, and preparation method. This work has led to a greater fundamental understanding of the unique optical properties of Si NCs. Si NCs are being studied for a wide range of important applications, including LEDS with tunable electroluminescence ranging from NIR to yellow, the encapsulation of Si NCs within micelles terminated with proteins to allow targeted in vivo imaging of cells, Si NC-polymer hybrid solar cells, and the use of Si NCs in battery anodes with high theoretical capacity and good charge retention. PMID:25252604

McVey, Benjamin F P; Tilley, Richard D

2014-10-21

337

Umpolung Amide Synthesis Using Substoichiometric N-Iodosuccinimide (NIS) and Oxygen as a Terminal Oxidant.  

PubMed

Umpolung Amide Synthesis (UmAS) provides direct access to amides from an ?-bromo nitroalkane and an amine. Based on its mechanistic bifurcation after convergent C-N bond formation, depending on the absence or presence of oxygen, UmAS using substoichiometric N-iodosuccinimide (NIS) under aerobic conditions has been developed. In combination with the enantioselective preparation of ?-bromo nitroalkane donors, this protocol realizes the goal of enantioselective ?-amino amide and peptide synthesis based solely on catalytic methods. PMID:25198239

Schwieter, Kenneth E; Shen, Bo; Shackleford, Jessica P; Leighty, Matthew W; Johnston, Jeffrey N

2014-09-19

338

Enantioselective Henry reaction catalyzed by "ship in a bottle" complexes.  

PubMed

Two chiral Schiff-base complexes of copper(II) have been successfully encapsulated inside the cavity of zeolite-NaY via a "ship in a bottle" synthesis method. The presence of the two complexes inside the cages of zeolite-Y has been confirmed based on various spectrochemical and physicochemical techniques, viz. FTIR, UV-vis/DRS, ESR, XPS, CV, EDX, SEM, and TGA. Zeolite-encapsulated chiral copper(II) Schiff-base complexes are found to give a high-enantioselective (84% ee, R conformation) nitro-aldol product at -20 °C. The encapsulated copper complexes are found to show higher catalytic efficiency than their homogeneous counterparts under identical conditions. Density functional theory (DFT) calculation has been implemented to understand the effect of the zeolite matrix on structural, electronic, and reactivity properties of the synthesized complexes. Theoretical calculation predicts that upon encapsulation into the zeolite matrix the Cu center becomes more susceptible to nucleophilic attack, favoring a nitro-aldol reaction. A plausible mechanism is suggested based on the experimental and theoretical results. The structures of reaction intermediates and transition state(s) involved in the catalytic cycle are derived using DFT. PMID:23848182

Bania, Kusum K; Karunakar, Galla V; Goutham, Kommuru; Deka, Ramesh C

2013-07-15

339

Synthesis of internally functionalized silica nanoparticles for theranostic applications  

NASA Astrophysics Data System (ADS)

This thesis addresses the synthesis and characterization of novel inorganic silica nanoparticle hybrids. It focuses in large part on their potential applications in the medical field. Silica acts as a useful carrier for a variety of compounds and this thesis silica will demonstrate its use as a carrier for boron or gadolinium. Boron-10 and gadolinium-157 have been suggested for the radiological treatment of tumor cells through the process called neutron capture therapy (NCT). Gadolinium is also commonly used as a Magnetic Resonance Imaging (MRI) contrast agent. Particles that carry it have potential theranostic applications of both imaging and treating tumors. Chapter 1 presents a background on synthetic strategies and usages of silica nanoparticles, and NCT theory. Chapter 2 describes a procedure to create mesoporous metal chelating silica nanoparticles, mDTTA. This is achieved via a co-condensation of tetraethoxysilane (TEOS) and 3-trimethoxysilyl-propyl diethylenetriamine (SiDETA) followed by a post-synthesis modification step with bromoacetic acid (BrAA). These particles have a large surface area and well-defined pores of ~2 nm. The mDTTA nanoparticles were used to chelate the copper(II), cobalt(II) and gadolinium(III). The chelating of gadolinium is the most interesting since it can be used as a MRI contrast agent and a neutron capture therapeutic. The synthetic procedure developed also allows for the attachment of a fluorophore that gives the gadolinium chelating mDTTA nanoparticles a dual imaging modality. Chapter 3 presents the synthetic method used to produce two classes of large surface area organically modified silica (ORMOSIL) nanoparticles. Condensating the organosilane vinyltrimethoxysilane in a micellar solution results in nanoparticles that are either surface rough (raspberry-like) or mesoporous nanoparticles, which prior to this thesis has not been demonstrated in ORMOSIL chemistry. Furthermore, the vinyl functionalities are modified, using hydroboration, to make the nanoparticles into water-dispersible boron carriers that also have potential boron neutron capture therapy (BNCT) applications. Lastly, Chapter 4 provides a general description of NCT, specifically that involving boron-10 and gadolinium-157. It further describes the synthetic methodology used in producing fatty acid coated boron nanoparticles (BNPs). The BNPs are encapsulated with silica to add a hydrophilic shell so that they can potentially be used in biological systems as BNCT agents. The silica shell is also modified with a fluorophore, dansyl chloride, so that the particle hybrid could be imaged during cell studies.

Walton, Nathan Isaac

340

Recent progress in the synthesis and selected applications of MCM-41: a short review  

Microsoft Academic Search

Recent progress in the synthesis and applications of MCM-41 based mesoporous materials is reviewed. Since the independent discovery in the early 1990s by groups in the Japan and USA of the formation of mesostructured silica using surfactants as structure directing agents, a variety of alternative synthesis routes have been proposed. These include the use of ionic (both cationic and anionic)

S. Bhattacharyya; G. Lelong; M.-L. Saboungi

2006-01-01

341

Application of -Synthesis based H-Control for Adaptive Optics in Laser Material Processing  

E-print Network

Application of µ-Synthesis based H-Control for Adaptive Optics in Laser Material Processing Steffen Mauch1 and Johann Reger1 Abstract-- An adaptive optics system is used for the con- trolled attenuation-- adaptive optics, robust control, H-control, material processing, µ-synthesis I. INTRODUCTION As the costs

Knobloch,Jürgen

342

Chemo- and regioselective functionalization of uracil derivatives. Applications to the synthesis of oxypurinol and emivirine.  

PubMed

[reaction: see text] A novel route for the synthesis of 4,5-difunctionalized uracils using a chemo- and regioselective bromine/magnesium exchange reaction on 5-bromo-4-halogeno-2,6-dimethoxypyrimidines has been developed. Applications to the synthesis of pharmaceuticals such as oxypurinol and emivirine are reported. PMID:16898805

Boudet, Nadège; Knochel, Paul

2006-08-17

343

Nanostructured organic electronic materials: Synthesis and sensor applications  

NASA Astrophysics Data System (ADS)

This study is an investigation into (a) the process by which one obtains bulk quantities of nanofibers of parent polythiophene, (b) in-situ deposition of nanofibers of polythiophene on flexible substrate and its application in vapor sensing, and (c) inkjet printing of graphene on flexible substrate and its application as a detector. (a) The 2 nd chapter of the thesis is an extension of "seeding" method from aqueous to organic solvents to synthesize parent polythiophene nanofibers. Bulk quantities of parent polythiophene nanofibers were synthesized in one step using catalytic amounts of freeze dried V2O5. This work is published in Chemistry Letters 2008 37(5), 526--527. (b) The 3rd chapter deals with in-situ films of polythiophene nanofibers on plastic substrates. In this a one step method to directly deposit nanofibers of parent polythiophene on flexible substrate is discussed. These films show a reversible detection of highly oxidizing vapors such as NO2, Cl2 and SO 2 at ppb levels under ambient conditions. This work is published in Macromolecules 2009, 42, 5414--5415. (c) The 4 th chapter describes the synthesis of reduced graphene oxide (RGO) using a mild reducing agent ascorbic acid (Vitamin C) rather than traditionally used harsh reducing agents (N2H4). Dispersions of RGO were inkjet printed on flexible substrate and has been shown to detect aggressive vapors NO2 and Cl2 at ambient conditions. This work is accepted for publication in Angewandte Chemie (Nov 2009).

Dua, Vineet

344

Development of a Double Allylboration Reagent Targeting 1,5-syn-(E)-Diols: Application to the Synthesis of the C(23)-C(40) Fragment of Tetrafibricin  

PubMed Central

Interest in the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin prompted us to develop a new method for the synthesis of 1,5-syn-(E)-diols. Toward this end, the kinetically controlled hydroboration of allenes 6, 33, ent-39, 42 and 45 with the Soderquist borane 25R were studied. Tetrabutylammonium allenyltrifluoroborate 45 gave superior results and was utilized in a double allylboration sequence with two different aldehydes to provide the targeted 1,5-syn-(E)-diols in generally high yields (72–98%), and with high enantioselectivity (>95% e.e.), diastereoselectivity (d.r. >20:1), and (E)/(Z) selectivity (>20:1). This new method was applied to the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin. PMID:21857752

Nuhant, Philippe; Kister, Jeremy; Lira, Ricardo; Sorg, Achim; Roush, William R.

2011-01-01

345

Organocatalytic enantioselective construction of multi-functionalized spiro oxindole dienes.  

PubMed

A diastereo- and enantio-selective domino Michael-cyclization-tautomerization reaction of isatylidene malononitriles with ?,?-dicyanoalkenes catalyzed by a cinchona alkaloid-derived bifunctional thiourea catalyst has been developed. A series of multi-functionalized spiro oxindole diene derivatives have been obtained in good to excellent yields (up to 97%) with good to excellent enantioselectivities (up to 96%) as well as good diastereoselectivities (up to 7.9?:?1). In addition, an anomalous temperature effect on the enantioselectivity has also been studied for this transformation. PMID:24840651

Huang, Xiao-Fei; Zhang, Ya-Fei; Qi, Zheng-Hang; Li, Nai-Kai; Geng, Zhi-Cong; Li, Kun; Wang, Xing-Wang

2014-07-01

346

Enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones.  

PubMed

Two approaches have been developed for the enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones to form a quaternary carbon centre using (1R,2S)-1-phenyl-2-(1-pyrrolidinyl)-1-propanol as the chiral ligand. Good yields and high enantioselectivities (80-91% ee) were achieved with a range of alkyl aryl ketones in a convenient one-pot protocol using ethyl iododifluoroacetate and diethylzinc to form the difluorinated Reformatsky reagent homogeneously. In the traditional two-step Reformatsky reaction using the preformed Reformatsky reagent generated from ethyl iododifluoroacetate and zinc dust, good yields and good enantioselectivities (75-84% ee) were also obtained. PMID:22421710

Fornalczyk, Michal; Singh, Kuldip; Stuart, Alison M

2012-04-28

347

Sustainable synthesis, characterization, and applications of metal oxide nanostructures  

NASA Astrophysics Data System (ADS)

Nanomaterials have attracted significant research focus due to their advantageous and unique properties (i.e. electronic, magnetic, optical, and mechanical) as compared with the bulk. Metal oxide nanostructures are of particular interest, as they are very robust and display high chemical and thermal stability, while offering a diverse array of fascinating properties. By reliably controlling the size, morphology, composition, and crystallinity of these nanostructures, their properties can be tuned for a specific purpose. These advantageous tailorable properties render them as ideal candidates for many applications such as catalysis, sensing, electronics, optoelectronics, energy storage, and even medicine. Driven by their increased popularity and potential applications, efforts to synthesize nanomaterials have moved toward environmentally-friendly methodologies, such as wet-chemical, molten-salt, hydrothermal, and sol-gel methods. We will discuss the green synthesis of strontium ruthenate (SrRuO 3), the yttrium manganese oxides (YMnO3 and YMn2O 5), and the magnetic spinel ferrites (MFe2O4 where 'M' is Mg, Fe, Co, Ni, Cu, and Zn) and our ability to reliably tune their properties for various applications. The effects of the molten salt parameters on the resulting particle size and morphology were explored for SrRuO 3 and the yttrium manganese oxides. For example, rapid cooling rates and the use of surfactants allowed us to produced faceted octahedra of SrRuO 3, which resulted in a 4-fold enhancement of their activity towards methanol oxidation with respect to smooth rounded particles. Similarly, using the hydrothermal method, we generated ferrite nanoparticles of different compositions and sizes. We investigated their potential as contrast agents for magnetic resonance imaging (MRI) and as photocatalysts, and observed significant differences as a function of both size and composition. Similarly, we will also examine surface and structural effects upon the electronic properties of V2O 3 nanowires.

Tiano, Amanda Lyn

348

Metal containing mesoporous silica materials: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

The work presented here comprises the development of a new route for the incorporation of transition metals (TM = Mn, V, Cr) into the pores of mesoporous silica materials, the characterization, and the applications of the resulting materials. The mesoporous silica material used in this work is of the M41S family, known as MCM-48. The first part of the work is going to be focused on in the incorporation of manganese species. Characterization of the resulting materials will be sub-divided in two major parts: (1) Structural and textural properties and (2) Analysis of the Mn oxidation state, coordination and location in the mesoporous host. The process of incorporation of Mn into the mesoporous materials takes place by using high valence metal precursor anions. Then a mechanism to describe the process of loading the Mn species will be proposed. The method developed makes possible the incorporation of high loadings of transition metals while maintaining the properties of the host material, MCM-48. In the second part of the research the synthesis method developed in the first part is used to incorporate other transition metals such as vanadium and chromium. As in the first part, the nature of the TM species is investigated and their catalytic application in oxidation of styrene is also studied. The materials show good activity towards styrene oxidation with conversions as high as 100%. The catalysts can also be recycled without significant loss of activity. Finally, the last part of the research deals with the incorporation of tin oxide into mesoporous silica. A similar approach to the one used for transition metals was used to load tin in MCM-48, however, discrete tin oxide nanoparticles were formed on the surface of the mesoporous structure rather than inside of the pores. The sensing properties towards reducing gases such as hydrogen of these materials were tested, and the Sn containing mesoporous silica show promising properties for gas sensing applications.

Gomez, Sinue

349

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules.  

PubMed

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules. PMID:25001884

Ben-Moshe, Assaf; Wolf, Sharon Grayer; Bar Sadan, Maya; Houben, Lothar; Fan, Zhiyuan; Govorov, Alexander O; Markovich, Gil

2014-01-01

350

Colloidal-sized metal-organic frameworks: synthesis and applications.  

PubMed

Colloidal metal-organic frameworks (CMOFs), nanoporous colloidal-sized crystals that are uniform in both size and polyhedral shape, are crystals composed of metal ions and organic bridging ligands, which can be used as building blocks for self-assembly in organic and aqueous liquids. They stand in contrast to conventional metal-organic frameworks (MOFs), which scientists normally study in the form of bulk crystalline powders. However, powder MOFs generally have random crystal size and shape and therefore do not possess either a definite mutual arrangement with adjacent particles or uniformity. CMOFs do have this quality, which can be important in vital uptake and release kinetics. In this Account, we present the diverse methods of synthesis, pore chemistry control, surface modification, and assembly techniques of CMOFs. In addition, we survey recent achievements and future applications in this emerging field. There is potential for a paradigm shift, away from using just bulk crystalline powders, towards using particles whose size and shape are regulated. The concept of colloidal MOFs takes into account that nanoporous MOFs, conventionally prepared in the form of bulk crystalline powders with random crystal size, shape, and orientation, may also form colloidal-sized objects with uniform size and morphology. Furthermore, the traditional MOF functions that depend on porosity present additional control over those MOF functions that depend on pore interactions. They also can enable controlled spatial arrangements between neighboring particles. To begin, we discuss progress regarding synthesis of MOF nano- and microcrystals whose crystal size and shape are well regulated. Next, we review the methods to modify the surfaces with dye molecules and polymers. Dyes are useful when seeking to observe nonluminescent CMOFs in situ by optical microscopy, while polymers are useful to tune their interparticle interactions. Third, we discuss criteria to assess the stability of CMOFs for various applications. In another section of this Account, we give examples of supracrystal assembly in liquid, on substrates, at interfaces, and under external electric fields. We end this Account with discussion of possible future developments, both conceptual and technological. PMID:24328052

Sindoro, Melinda; Yanai, Nobuhiro; Jee, Ah-Young; Granick, Steve

2014-02-18

351

Stop-flow lithography for complex particle synthesis and application in directed assembly  

E-print Network

The synthesis of complex microparticles is an important objective. These particles can find use in a number of applications ranging from tissue engineering to ceramics and assembly. Tuned assembly of anisotropic particles ...

Panda, Priyadarshi

2012-01-01

352

Low dimensional silver nanostructures : synthesis, growth mechanism, properties and applications.  

E-print Network

??Synthesis of metal nanoparticles has recently attracted extensive research interest because of the importance of these materials' specific properties such as optical, electronic, magnetic, mechanical,… (more)

Xiong, Shixian

2011-01-01

353

Enantioselective construction of remote quaternary stereocentres  

NASA Astrophysics Data System (ADS)

Small molecules that contain all-carbon quaternary stereocentres--carbon atoms bonded to four distinct carbon substituents--are found in many secondary metabolites and some pharmaceutical agents. The construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for synthesizing quaternary stereocentres that are remote from other functional groups are underdeveloped. Here we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. This method provides direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ?-aryl carbonyl compounds, because the unsaturation of the alkene is relayed to the alcohol, resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocentres along the alkyl chain, which links the alkene and the alcohol, in which the stereocentre is preserved. The method described allows access to diverse molecular building blocks containing an enantiomerically enriched quaternary centre.

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-04-01

354

Catalytic, Enantioselective Bifunctional Inverse Electron Demand Hetero-Diels-Alder Reactions of Ketene Enolates and o-Benzoquinone  

E-print Network

Catalytic, Enantioselective Bifunctional Inverse Electron Demand Hetero-Diels-Alder Reactions@jhu.edu Catalytic, enantioselective Diels-Alder reactions ([4 + 2] cycloadditions) constitute a vital part

Lectka, Thomas

355

Synthesis and applications of quantum dots and magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and Zn 1-xCd xSe alloyed QDs derived are tunable in fluorescence emissions between 360 nm and 700 nm. They show high quantum yields (QYs) of up to 50%, with narrow bandwidths of 19-55 nm. The synthesis of glutathione-capped QDs is simple and cost-effective compared to the conventional organometallic approaches. It can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions. We have also demonstrated the fabrication of magnetic quantum dots (MQDs) through a seed-mediated approach. The formation and assembly of these bifunctional nanocomposites have been elucidated by high-resolution transmission electron microscopy (HRTEM). The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components in this hybrid system. We have created biocompatible silica-coated MQDs that effectively target the cell membranes.

Ying, Jackie Y.; Zheng, Yuangang; Selvan, S. Tamil

2008-02-01

356

Synthesis and Characterization of Dyes with Solar Energy Applications  

NASA Astrophysics Data System (ADS)

The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis.

Brennan, Bradley J.

357

Synthesis and characterization of advanced nanomaterials for energy applications  

NASA Astrophysics Data System (ADS)

Energy is essential for life. It is thus important to continue understanding how to reduce energy consumption, and increase energy generation. The use of nanoscale materials (nanomaterials) are expected to reduce resources and energy needed in fabricating electrical and electronic devices and help in reducing energy consumption. For example, boron nitride nanotubes (BNNTs) which have uniform band structures, are expected to find application in nanoscale electronic and optoelectronic devices. These devices will have smaller dimension, cost fewer resources and less energy to fabricate, and consume less energy due to minimum electron scattering in their ideally defect-free tubular structures. On the other hand, nanomaterials are also expected to improve the performance of thermoelectric devices that can convert heat into energy. In this thesis, we first investigated low-temperature synthesis of BNNTs (Chapter 1). Effects of substrate temperatures, bias voltages, and catalysts are discussed and a selective-phase growth model is proposed. During the course of this investigation, we discovered Si nanotubes (SiNTs) by catalytic plasma treatment (Chapter 2). The detailed growth parameters and characterizations are presented and a modified growth model is discussed. In addition, electronic properties are measured by AFM. Since Si has exceptional thermoelectric properties, the newly discovered SiNTs are prospects for related applications. We have thus evaluated the potential conversion efficiency and production cost of various nanostructured thermoelectric materials (Chapter 3 and 4). Based on state-of-the-art dish-stirling systems, we evaluate the feasibility of replacing stirling engines by thermoelectric modules. Finally, we have decided to investigate the properties of boron-nanocarbon ensembles (Chapter 5 and 6) as prospective thermoelectric materials. Detailed characterizations includes SEM, HRTEM, Raman, XRD are presented. Seebeck coefficient and electrical conductivity are both measured with various temperatures. Induction quenching confirms that boron-doping help improve power factor of nanocarbon ensembles.

Xie, Ming

358

Chemoselective and Enantioselective Oxidation of Indoles Employing Aspartyl Peptide Catalysts  

E-print Network

Catalytic enantioselective indole oxidation is a process of particular relevance to the chemistry of complex alkaloids, as it has been implicated in their biosynthesis. In the context of synthetic methodology, catalytic ...

Movassaghi, Mohammad

359

BIOACCUMULATION AND ENANTIOSELECTIVE BIOTRANSFORMATION OF FIPRONIL AND SELECTED CONAZOLE FUNGICIDES  

EPA Science Inventory

In this research, dietary accumulation and enantioselective biotransformation were determined for rainbow trout (Oncorhynchus mykiss) exposed separately to the phenylpyrazole insecticide fipronil and to a series of selected conazole fungicides. Bioaccumulation of each pesticide ...

360

Fine-Tuning Monophosphine Ligands for Enhanced Enantioselectivity. Influence  

E-print Network

Fine-Tuning Monophosphine Ligands for Enhanced Enantioselectivity. Influence of Chiral Hemilabile of this as a control element in asymmetric catalysis. As a test case, we chose a commercially relevant substrate, 4

RajanBabu, T. V. "Babu"

361

Progress in transition metal-based enantioselective catalysis  

E-print Network

In Chapter 1, the first enantioselective cross-coupling reactions of racemic secondary benzylic halides are described (eq 1). This method was applied to the syntheses of intermediates employed by other groups in the ...

Arp, Forrest O

2008-01-01

362

Patterns in Organometallic Chemistry with Application in Organic Synthesis.  

ERIC Educational Resources Information Center

Of interest in this discussion of organometallic complexes are stoichiometric or catalytic reagents for organic synthesis in the complex transformations observed during synthesis for transition metal organometallic complexes. Detailed are general reaction types from which the chemistry or many transition metal organometallic complexes can be…

Schwartz, Jeffrey; Labinger, Jay A.

1980-01-01

363

Threshold network synthesis and optimization and its application to nanotechnologies  

Microsoft Academic Search

We propose an algorithm for efficient threshold network synthesis of arbitrary multioutput Boolean functions. Many nanotechnologies, such as resonant tunneling diodes, quantum cellular automata, and single electron tunneling, are capable of implementing threshold logic efficiently. The main purpose of this work is to bridge the current wide gap between research on nanoscale devices and research on synthesis methodologies for generating

Rui Zhang; Pallav Gupta; Lin Zhong; Niraj K. Jha

2005-01-01

364

Threshold network synthesis and optimization and its application to nanotechnologies  

Microsoft Academic Search

We propose an algorithm for efficient threshold network synthesis of arbitrary multi-output Boolean functions. Many nanotechnologies, such as resonant tunneling diodes (RTDs), quantum cellular automata (QCA), and single electron tunneling (SET), are capable of implementing threshold logic efficiently. The main purpose of this work is to bridge the current wide gap between research on nanoscale devices and research on synthesis

Rui Zhang; Pallav Gupta; Lin Zhong; Niraj K. Jha

2005-01-01

365

Toward Practical Applications of Software Synthesis \\Lambda Douglas R. Smith  

E-print Network

methods are usually conceived as a way to obtain verifiably correct soft­ ware, so many researchers have paths to the ultimate success of formal methods. We argue that mechanized synthesis tools can have on the synthesis of transportation scheduling algorithms. 1 Introduction We have been exploring automated tools

Smith, Douglas R.

366

Catalytic enantioselective addition of thioacids to trisubstituted nitroalkenes.  

PubMed

The first example of a catalytic enantioselective addition to and nitronate protonation of trisubstituted nitroalkenes to produce highly enantioenriched products with a tetrasubstituted carbon is reported. Thioacids added in excellent yields and with high enantioselectivities to both activated and unactivated nitroalkenes. The 1,2-nitrothioacetate products can be readily converted in two steps to biomedically relevant 1,2-aminosulfonic acids without loss of enantiopurity. PMID:25196997

Phelan, James P; Patel, Evan J; Ellman, Jonathan A

2014-10-13

367

Synthesis, assembly, and applications of single-walled carbon nanotube  

NASA Astrophysics Data System (ADS)

This dissertation presents the synthesis and assembly of aligned carbon nanotubes, and their applications in both nano-electronics such as transistor and integrated circuits and macro-electronics in energy conversion devices as transparent conducting electrodes. Also, the high performance chemical sensor using metal oxide nanowire has been demonstrated. Chapter 1 presents a brief introduction of carbon nanotube, followed by discussion of a new synthesis technique using nanosphere lithography to grow highly aligned single-walled carbon nanotubes atop quartz and sapphire substrates. This method offers great potential to produce carbon nanotube arrays with simultaneous control over the nanotube orientation, position, density, diameter and even chirality. Chapter 3 introduces the wafer-scale integration and assembly of aligned carbon nanotubes, including full-wafer scale synthesis and transfer of massively aligned carbon nanotube arrays, and nanotube device fabrication on 4 inch Si/SiO2 wafer to yield submicron channel transistors with high on-current density ˜ 20 muA/mum and good on/off ratio and CMOS integrated circuits. In addition, various chemical doping methods for n-type nanotube transistors are studied to fabricate CMOS integrated nanotube circuits such as inverter, NAND and NOR logic devices. Furthermore, defect-tolerant circuit design for NAND and NOR is proposed and demonstrated to guarantee the correct operation of logic circuit, regardless of the presence of mis-aligned or mis-positioned nanotubes. Carbon nanotube flexible electronics and smart textiles for ubiquitous computing and sensing are demonstrated in chapter 4. A facile transfer printing technique has been introduced to transfer massively aligned single-walled carbon nanotubes from the original sapphire/quartz substrates to virtually any other substrates, including glass, silicon, polymer sheets, and even fabrics. The characterization of transferred nanotubes reveals that the transferred nanotubes are highly conductive, transparent, and flexible as well. Based on transferred nanotube arrays on fabric, we have successfully demonstrated nanotube transistors with on/off ratios ˜ 105, and chemical sensors for low-concentration NO2 and 2,4,6-trinitrotoluene (TNT). In Chapter 5, I present the study of transparent conductive thin films made with two kinds of commercial carbon nanotubes: HiPCO and arc-discharge nanotubes. These films have been further exploited as hole-injection electrodes for organic light emitting diodes (OLEDs) on both rigid glass and flexible substrates. Our experiments reveal that films based on arc discharge nanotubes are overwhelmingly better than HiPCO-nanotube-based films in all the critical aspects, including the surface roughness, sheet resistance, and transparency. The optimized films show a typical sheet resistance of ˜160O/? at 87% transparency and have been successfully used to make OLEDs with high stability and long lifetime. Lastly, I present the fast and scalable integration of nanowire chemical sensors with micromachined hotplates built on SiN membranes. These hotplates allowed nanowire chemical sensors to operate at elevated temperatures in order to enhance the sensitivity of chemical sensors to target gases. By applying different current through the platinum heating filament, we can easily vary the device temperature from room temperature to 350°C. These nanosensors with integrated hot plates have been exploited for the detection of ethanol, CO and hydrogen down to concentrations of 1 ppm, 10 ppm and 50 ppm, respectively.

Ryu, Koungmin

368

Remarkable Enhancement of Enantioselectivity in the Asymmetric Conjugate Addition of Dimethylzinc to (Z)-Nitroalkenes with a Catalytic [(MeCN)4 Cu]PF6 -Hoveyda Ligand Complex.  

PubMed

An enantioselective copper-catalyzed asymmetric conjugate addition of Me2 Zn to (Z)-nitroalkenes led to the formation of all-carbon quaternary stereogenic centers with high stereoselectivity. The key features of the new method are the unprecedented use of [(MeCN)4 Cu]PF6 in conjunction with the Hoveyda ligand L1 and the use of (Z)-nitroalkene substrates so that undesired nitroalkene isomerization is minimized and enantioselectivity is enhanced dramatically. We also describe a novel, practical, and highly (Z)-selective nitroalkene synthesis. PMID:25225113

Zeng, Xingzhong; Gao, Joe J; Song, Jinhua J; Ma, Shengli; Desrosiers, Jean-Nicolas; Mulder, Jason A; Rodriguez, Sonia; Herbage, Melissa A; Haddad, Nizar; Qu, Bo; Fandrick, Keith R; Grinberg, Nelu; Lee, Heewon; Wei, Xudong; Yee, Nathan K; Senanayake, Chris H

2014-11-01

369

Concise Synthesis of the Bacterial DNA Primase Inhibitor (+)-Sch 642305  

E-print Network

Concise Synthesis of the Bacterial DNA Primase Inhibitor (+)-Sch 642305 Erica M. Wilson and Dirk@cchem.berkeley.edu Received January 23, 2007 ABSTRACT A highly convergent, enantioselective synthesis of (+)-Sch 642305-closing metathesis. Bacterial DNA primase is an integral component of the prokaryotic DNA replication machinery

Trauner, Dirk

370

Synthesis of (-)-Tetrodotoxin: Preparation of an Advanced Cyclohexenone Intermediate  

E-print Network

Synthesis of (-)-Tetrodotoxin: Preparation of an Advanced Cyclohexenone Intermediate Douglass F the enantioselective synthesis of tetrodotoxin is outlined. The enantiomerically pure cyclopentene 15 was generated. Introduction Tetrodotoxin 1, a potent blocker of sodium ion channels originally isolated from the puffer fish,1

Taber, Douglass

371

Synthesis, characterization and potential applications of iron-platinum nanoparticles  

NASA Astrophysics Data System (ADS)

Monodisperse FePt nanoparticles with controlled size and geometry have drawn great attention in the last decade for fundamental scientific studies and for their potential applications in advanced materials and devices such as ultra-high-density magnetic recording media, exchange-coupled nanocomposite magnets, biomedicines and nanodevices. This dissertation focuses on the synthesis and characterization of FePt nanoparticles and their use in potential applications. The FePt nanoparticles of different size (2 to 16 nm) and shape (spherical, cubic, rod) were synthesized by a chemical solution method. The size and shape of these particles were controlled by adjusting reaction parameters. The as-synthesized FePt nanoparticles have chemically disordered fcc structure and are superparamagnetic at room temperature. Upon heat treatment the nanoparticles were transformed into ordered L10 structure, and high coercivity up to 27 kOe was achieved. Magnetic properties of annealed FePt nanoparticles including magnetization and coercivity were strongly dependent on particle size, shape, composition and annealing temperature. FePt/Fe3O4 bimagnetic nanoparticles with two different morphologies, core/shell and heterodimer, were prepared by coating or attaching Fe3O4 on surface of FePt nanoparticles. The size of FePt and Fe3O4 was tuned very finely to obtain most effective exchange coupling. The heterodimer nanoparticles resulted in relatively poor magnetic properties compared to the core/shell nanoparticles due to insufficient exchange coupling. By optimizing the dimensions of the FePt and Fe3O 4 in core/shell bimagnetic nanoparticles, energy products up to 17.8 MGOe were achieved. FePt/Fe3O4 core/shell and FePt+Fe3O 4 mixed nanoparticles with similar magnetic properties were compacted under 2.0 GPa at 400°C, 500°C and 600°C. A density up to 84% of the full density was achieved. After annealing at 650°C in forming gas, the FePt/Fe3O4 compacted samples were converted into L10 FePt/Fe3Pt magnetic nanocomposite. The nanoscale morphology was retained before and after annealing for bulk samples made from both core/shell and mixed nanoparticles. After annealing, the highest energy product in the bulk samples was 18.1 MGOe based on the theoretical density. The core/shell nanoparticle compacted samples had more effective exchange coupling than the mixed nanoparticle compacted samples. FePt/Au core/shell nanoparticles were successfully synthesized where Au shell was coated by reduction of gold acetate on surface of FePt nanoparticles. The FePt/Au core/shell nanoparticles show ferromagnetism after annealing at optimum temperature without any significant sintering. Also, FePtAu nanoparticles were prepared by doping Au into FePt nanoparticles during the synthesis. By tuning right stoichiometry of the FexPtyAu100-x-y nanoparticles, the phase transition temperature from fcc to L1 0 was reduced by more than 200°C. After annealing at 500°C, the highest coercivity of 18 kOe was obtained from the Fe51Pt 36Au13 nanoparticles compared to 2 kOe from Fe51Pt 49 nanoparticles without any sacrifice in saturation magnetization.

Nandwana, Vikas

372

Polyclonal antibodies: a cheap and efficient tool for screening of enantioselective catalysts.  

PubMed

Enantioselective polyclonal antibodies have been produced and characterized to develop a high-throughput screening method for lipase activity fingerprinting, with a view to the enantioselective hydrolysis of azlactones. PMID:22441296

Macovei, Cristian; Vicennati, Paola; Quinton, Julia; Nevers, Marie-Claire; Volland, Hervé; Créminon, Christophe; Taran, Frédéric

2012-05-11

373

Rhodium/phospholane-phosphite catalysts give unusually high regioselectivity in the enantioselective hydroformylation of vinyl arenes.  

PubMed

Using the phospholane-phosphite ligand, BOBPHOS, almost perfect regioselectivities and high enantioselectivities (up to 92% ee) are observed in Rh catalysed enantioselective hydroformylation of vinyl arenes. This can be achieved under solvent-free conditions. PMID:24362887

Noonan, Gary M; Cobley, Christopher J; Mahoney, Thomas; Clarke, Matthew L

2014-02-11

374

Synthesis, characterization and applications of a perdeuterated amphipol.  

PubMed

Amphipols are short amphipathic polymers that can substitute for detergents at the hydrophobic surface of membrane proteins (MPs), keeping them soluble in the absence of detergents while stabilizing them. The most widely used amphipol, known as A8-35, is comprised of a polyacrylic acid (PAA) main chain grafted with octylamine and isopropylamine. Among its many applications, A8-35 has proven particularly useful for solution-state NMR studies of MPs, for which it can be desirable to eliminate signals originating from the protons of the surfactant. In the present work, we describe the synthesis and properties of perdeuterated A8-35 (perDAPol). Perdeuterated PAA was obtained by radical polymerization of deuterated acrylic acid. It was subsequently grafted with deuterated amines, yielding perDAPol. The number-average molar mass of hydrogenated and perDAPol, ~4 and ~5 kDa, respectively, was deduced from that of their PAA precursors, determined by size exclusion chromatography in tetrahydrofuran following permethylation. Electrospray ionization-ion mobility spectrometry-mass spectrometry measurements show the molar mass and distribution of the two APols to be very similar. Upon neutron scattering, the contrast match point of perDAPol is found to be ~120 % D2O. In (1)H-(1)H nuclear overhauser effect NMR spectra, its contribution is reduced to ~6 % of that of hydrogenated A8-35, making it suitable for extended uses in NMR spectroscopy. PerDAPol ought to also be of use for inelastic neutron scattering studies of the dynamics of APol-trapped MPs, as well as small-angle neutron scattering and analytical ultracentrifugation. PMID:24652511

Giusti, Fabrice; Rieger, Jutta; Catoire, Laurent J; Qian, Shuo; Calabrese, Antonio N; Watkinson, Thomas G; Casiraghi, Marina; Radford, Sheena E; Ashcroft, Alison E; Popot, Jean-Luc

2014-10-01

375

Nonenzymatic dynamic kinetic resolution of secondary alcohols via enantioselective acylation: synthetic and mechanistic studies.  

PubMed

Because of the ubiquity of the secondary carbinol subunit, the development of new methods for its enantioselective synthesis remains an important ongoing challenge. In this report, we describe the first nonenzymatic method for the dynamic kinetic resolution (DKR) of secondary alcohols (specifically, aryl alkyl carbinols) through enantioselective acylation, and we substantially expand the scope of this approach, vis-à-vis enzymatic reactions. Simply combining an effective process for the kinetic resolution of alcohols with an active catalyst for the racemization of alcohols did not lead to DKR, due to the incompatibility of the ruthenium-based racemization catalyst with the acylating agent (Ac(2)O) used in the kinetic resolution. A mechanistic investigation revealed that the ruthenium catalyst is deactivated through the formation of a stable ruthenium-acetate complex; this deleterious pathway was circumvented through the appropriate choice of acylating agent (an acyl carbonate). Mechanistic studies of this new process point to reversible N-acylation of the nucleophilic catalyst, acyl transfer from the catalyst to the alcohol as the rate-determining step, and carbonate anion serving as the Brønsted base in that acyl-transfer step. PMID:22934603

Lee, Sarah Yunmi; Murphy, Jaclyn M; Ukai, Atsushi; Fu, Gregory C

2012-09-12

376

Non-Enzymatic Dynamic Kinetic Resolution of Secondary Alcohols via Enantioselective Acylation: Synthetic and Mechanistic Studies  

PubMed Central

Because of the ubiquity of the secondary carbinol subunit, the development of new methods for its enantioselective synthesis remains an important ongoing challenge. In this report, we describe the first non-enzymatic method for the dynamic kinetic resolution (DKR) of secondary alcohols (specifically, aryl alkyl carbinols) through enantioselective acylation, and we substantially expand the scope of this approach, vis-à-vis enzymatic reactions. Simply combining an effective process for the kinetic resolution of alcohols with an active catalyst for the racemization of alcohols did not lead to DKR, due to the incompatibility of the ruthenium-based racemization catalyst with the acylating agent (Ac2O) used in the kinetic resolution. A mechanistic investigation revealed that the ruthenium catalyst is deactivated through the formation of a stable ruthenium-acetate complex; this deleterious pathway was circumvented through the appropriate choice of acylating agent (an acyl carbonate). Mechanistic studies of this new process point to reversible N-acylation of the nucleophilic catalyst, acyl transfer from the catalyst to the alcohol as the rate-determining step, and carbonate anion serving as the Brønsted base in that acyl-transfer step. PMID:22934603

Lee, Sarah Yunmi; Murphy, Jaclyn M.; Ukai, Atsushi; Fu, Gregory C.

2012-01-01

377

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation  

PubMed Central

The catalytic asymmetric aminooxygenation of alkenes provides an efficient and straightforward approach to prepare chiral vicinal amino alcohols. We have reported a copper(II)-catalyzed enantioselective intramolecular alkene aminooxygenation, using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as the oxygen source, which results in the synthesis of chiral indolines and pyrrolidines. Herein we disclose that kinetics studies indicate the reaction is first order both in substrate and the [Cu(R,R)-Ph-bis(oxazoline)]OTf2 catalyst, and zero order in TEMPO. Furthermore, kinetic isotope effect studies support that the cis aminocupration step, the addition of N-Cu across the alkene, is the rate-limiting step. Subsequent formation of a carbon radical intermediate, and direct carbon radical trapping with TEMPO is the indicated mechanism for the C-O bond formation as suggested by a deuterium labeling experiment. A ligand screen revealed that C(4)-phenyl substitution on the bis(oxazoline) is optimal for high asymmetric induction. The size of the substrate’s N-sulfonyl group also influences the enantioselectivity of the reaction. The preparative scale catalytic aminooxygenation reaction (gram scale) was demonstrated and an unexpected dependence on reaction temperature was uncovered on the larger scale reaction. PMID:23244027

Paderes, Monissa C.; Keister, Jerome B.; Chemler, Sherry R.

2013-01-01

378

Rational control of hydrothermal nanowire synthesis and its applications  

E-print Network

Hydrothermal nanowire synthesis is a rapidly emerging nanowire discipline that enables low temperature growth and batch process. It has a major impact on the development of novel energy conversion devices, high density ...

Joo, Jaebum

2010-01-01

379

Marketing: Exploring Applications for Educational Dissemination. Literature Synthesis.  

National Technical Information Service (NTIS)

This synthesis of information about marketing and information dissemination of education-related products is divided into three parts: an overview of major writings, specific marketing strategies, and resources for further study. The first part opens with...

L. Reed

1978-01-01

380

Nanocrystals: Solution-based synthesis and applications as nanocatalysts  

Microsoft Academic Search

Nanocrystals are emerging as key materials due to their novel shape- and size-dependent chemical and physical properties that\\u000a differ drastically from their bulk counterparts. The main challenges in this field remain rationally controlled synthesis\\u000a and large scale production. This article reviews recent progress in our laboratory related to solution-based synthesis of\\u000a various nanostructures, including zero-dimensional (0-D) nanocrystals, 1-D nanowires and

Dingsheng Wang; Ting Xie; Yadong Li

2009-01-01

381

Enantioselective disposition of clenbuterol in rats.  

PubMed

Clenbuterol is a long-acting ?2-adrenoceptor agonist and bronchodilator that is used for the treatment of asthma, but the desired activities reside almost exclusively in the (-)-R-enantiomer. This study examined enantioselectivity in the disposition of clenbuterol following administration of clenbuterol racemate to rats. Concentrations of clenbuterol enantiomers in plasma, urine and bile were determined by LC-MS/MS assay with a Chirobiotic T column. This method was confirmed to show high sensitivity, specificity and precision, and clenbuterol enantiomers in 0.1 ml volumes of plasma were precisely quantified at concentrations as low as 0.25 ng/ml. The pharmacokinetic profiles of clenbuterol enantiomers following intravenous and intraduodenal administration of clenbuterol racemate (2 mg/kg) in rats were significantly different. The distribution volume of (-)-R-clenbuterol (9.17 l/kg) was significantly higher than that of (+)-S-clenbuterol (4.14 l/kg). The total body clearance of (-)-R-clenbuterol (13.5 ml/min/kg) was significantly higher than that of the (+)-S-enantiomer (11.5 ml/min/kg). An in situ absorption study in jejunal loops showed no difference in the residual amount between the (-)-R- and (+)-S-enantiomers. Urinary clearance was the same for the two enantiomers, but biliary excretion of (-)-R-clenbuterol was higher than that of the (+)-S-enantiomer. The fractions of free (non-protein-bound) (-)-R- and (+)-S-clenbuterol in rat plasma were 48.8% and 33.1%, respectively. These results indicated that there are differences in the distribution and excretion of the clenbuterol enantiomers, and these may be predominantly due to enantioselective protein binding. PMID:24323748

Hirosawa, Iori; Ishikawa, Mai; Ogino, Mio; Ito, Hiroshi; Hirao, Takuya; Yamada, Harumi; Asahi, Mariko; Kotaki, Hajime; Sai, Yoshimichi; Miyamoto, Ken-Ichi

2014-05-01

382

One-Dimensional Metal Oxide Nanotubes, Nanowires, Nanoribbons, and Nanorods: Synthesis, Characterizations, Properties and Applications  

Microsoft Academic Search

One dimensional nanomaterials have attracted much attention from academia and industry. A large series of devices have been created on the basis of 1D nanomaterials. Their applications have changed and will continuously change our daily life. In this paper, we will present a comprehensive review on the synthesis, structure characterization, properties and actual and future potential applications of one dimensional

Yu Li; Xiao-Yu Yang; Yi Feng; Zhong-Yong Yuan; Bao-Lian Su

2012-01-01

383

Enantioselective Construction of 2,3-Dihydrofuro[2,3-b]quinolines through Supramolecular Hydrogen Bonding Interactions.  

PubMed

The first asymmetric synthesis of 2,3-dihydrofuro[2,3-b]quinolines has been achieved by a cascade asymmetric aziridination/intramolecular ring-opening process of differently substituted 3-alkenylquinolones. Good yields and high enantioselectivities (up to 78?% yield and 95?% ee) were recorded when employing 2,2,2-trichloroethoxysulfonamide as the nitrene source, PhI(OCOtBu)2 as the oxidant, and a chiral C2 -symmetric Rh(II) complex as the catalyst (1?mol?%). The catalyst bears two lactam motifs, which serve as binding sites for substrate coordination through supramolecular hydrogen-bonding interactions. PMID:25196199

Zhong, Fangrui; Bach, Thorsten

2014-10-13

384

[2+2] Photocycloaddition of 3-Alkenyloxy-2-cycloalkenones: Enantioselective Lewis Acid Catalysis and Ring Expansion.  

PubMed

By application of substoichiometric amounts (50?mol?%) of a chiral Lewis acid, the intramolecular [2+2] photocycloaddition of the title compounds was achieved with high enantioselectivity (up to 94?%?ee). Upon cleavage of the cyclobutane ring the resulting tricyclic products underwent ring-expansion reactions under acidic conditions and formed anellated seven- or eight-membered-ring systems without racemization. The ring expansion could be combined with a diastereoselective reduction (triethylsilane) or allylation (allyltrimethylsilane) upon BF3 catalysis (48-87?% yield). PMID:25251714

Brimioulle, Richard; Bach, Thorsten

2014-11-17

385

Controlled Synthesis of Monolayer Graphene Toward Transparent Flexible Conductive Film Application  

Microsoft Academic Search

We demonstrate the synthesis of monolayer graphene using thermal chemical vapor deposition and successive transfer onto arbitrary\\u000a substrates toward transparent flexible conductive film application. We used electron-beam-deposited Ni thin film as a synthetic\\u000a catalyst and introduced a gas mixture consisting of methane and hydrogen. To optimize the synthesis condition, we investigated\\u000a the effects of synthetic temperature and cooling rate in

Byeong-Joo Lee; Han-Young Yu; Goo-Hwan Jeong

2010-01-01

386

Recent Applications of Vinyl Sulfones and Vinyl Sulfoxides in Asymmetric Synthesis  

Microsoft Academic Search

Herein we present some new synthetic applications based on the use of functionalized ?,?-unsaturated sulfones and ?,?-unsaturated sulfoxides. In particular, we have developed a stereodivergent approach to the synthesis of castanospermine stereoisomers from ?-amino-?-oxygenated-?.?-unsaturated sulfones as well as a stereoselective synthesis of substituted dihydrofurans by Pd(0) catalyzed reaction of the carbonate derivatives of ?-oxygenated-?.?-unsaturated sulfones with methylene active ketones. Additionally,

Juan C. Carretero; RamóN GóMez Arrayás; Nuria Diaz Buezo; José Luis Garrido; Inés Alonso; Javier Adrio

1999-01-01

387

New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels-Alder  

E-print Network

New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels-Alder transformations. In this context, we document the first highly enantioselective organocatalytic Diels-Alder this hypothesis we investigated the capacity of chiral amines to enantioselectively catalyze the Diels-Alder

MacMillan, David W. C.

388

Chiral Lewis base-assisted Brønsted acid (LBBA)-catalyzed enantioselective cyclization of 2-geranylphenols.  

PubMed

Chiral Lewis base-assisted Brønsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimetic enantioselective cyclization. A salt of a chiral phosphonous acid diester with FSO(3)H catalyzes the enantioselective cyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee). PMID:21591803

Sakakura, Akira; Sakuma, Masayuki; Ishihara, Kazuaki

2011-06-17

389

Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards  

E-print Network

1 Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towardsW) on Candida antarctica lipase B (CALB) activity and enantioselectivity towards secondary alcohols was assessed that water has many effects on Candida antarctica lipase B (CALB) catalyzed enantioselective reactions

Paris-Sud XI, Université de

390

Synthesis, characterization and application of functional carbon nano materials  

NASA Astrophysics Data System (ADS)

The synthesis, characterizations and applications of carbon nanomaterials, including carbon nanorods, carbon nanosheets, carbon nanohoneycombs and carbon nanotubes were demonstrated. Different growth techniques such as pulsed laser deposition, DC/RF sputtering, hot filament physical vapour deposition, evaporative casting and vacuum filtration methods were introduced or applied for synthesizing carbon nanomaterials. The morphology, chemical compositions, bond structures, electronic, mechanical and sensing properties of the obtained samples were investigated. Tilted well-aligned carbon micro- and nano- hybrid rods were fabricated on Si at different substrate temperatures and incident angles of carbon source beam using the hot filament physical vapour deposition technique. The morphologic surfaces and bond structures of the oblique carbon rod-like structures were investigated by scanning electron microscopy, field emission scanning electron microscopy, transmission electron diffraction and Raman scattering spectroscopy. The field emission behaviour of the fabricated samples was also tested. Carbon nanosheets and nanohoneycombs were also synthesized on Si substrates using a hot filament physical vapor deposition technique under methane ambient and vacuum, respectively. The four-point Au electrodes are then sputtered on the surface of the nanostructured carbon films to form prototypical humidity sensors. The sensing properties of prototypical sensors at different temperature, humidity, direct current, and alternative current voltage were characterized. Linear sensing response of sensors to relative humidity ranging from 11% to 95% is observed at room temperature. Experimental data indicate that the carbon nanosheets based sensors exhibit an excellent reversible behavior and long-term stability. It also has higher response than that of the humidity sensor with carbon nanohoneycombs materials. Conducting composite films containing carbon nanotubes (CNTs) were prepared in two different ways of evaporative casting and vacuum filtration methods using the biopolymer kappa-carrageenan (KC) as a dispersant. Evaporative casting and vacuum filtration film-formation processes were compared by testing electrical properties. Results showed that films produced using vacuum filtration had higher electrical properties than those prepared using the evaporative casting method. The evaporative casted multi walled carbon nanotubes composite films also performed as the best humidity sensor over all other films measured.

Chu, Jin

391

Chemically functionalized gold nanoparticles: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

This thesis focuses on the development and application of gold nanoparticle based detection systems and biomimetic structures. Each class of modified nanoparticle has properties that are defined by its chemical moieties that interface with solution and the gold nanoparticle core. In Chapter 2, a comparison of the biomolecular composition and binding properties of various preparations of antibody oligonucleotide gold nanoparticle conjugates is presented. These constructs differed significantly in terms of their structure and binding properties. Chapter 3 reports the use of electroless gold deposition as a light scattering signal enhancer in a multiplexed, microarray-based scanometric immunoassay using the gold nanoparticle probes evaluated in Chapter 2. The use of gold development results in greater signal enhancement than the typical silver development, and multiple rounds of metal development were found to increase the resulting signal compared to one development. Chapter 4 describes an amplified scanometric detection method for human telomerase activity. Gold nanoparticles functionalized with specific oligonucleotide sequences can efficiently capture telomerase enzymes and subsequently be elongated. Both the elongated and unmodified oligonucleotide sequences are simultaneously measured. At low telomerase concentrations, elongated strands cannot be detected, but the unmodified sequences, which come from the same probe particles, can be detected because their concentration is higher, providing a novel form of amplification. Chapter 5 reports the development of a novel colorimetric nitrite and nitrate ion assay based upon gold nanoparticle probes functionalized with Griess reaction reagents. This assay takes advantage of the distance-dependent plasmonic properties of the gold nanoparticles and the ability of nitrite ion to facilitate the cross coupling of novel nanoparticle probes. The assay works on the concept of a kinetic end point and can be triggered at the EPA limit for this ion in drinking water. Finally, Chapter 6 describes the synthesis of high density lipoprotein biomimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL and bind free cholesterol with a Kd of 4 nM.

Daniel, Weston Lewis

392

Highly efficient, enantioselective syntheses of (S)-(+)- and (R)-(-)-dapoxetine starting with 3-phenyl-1-propanol.  

PubMed

A highly efficient, enantioselective sequence has been developed for the synthesis of (S)- and (R)-dapoxetine. The pathways involve the intermediacy of the 6-membered-ring sulfamate esters 4, which were generated by Du Bois asymmetric C-H amination reactions of the prochiral sulfamate 3, catalyzed by the chiral dirhodium(II) complexes. During the course of our research, the absolute configuration of the enantiomer of 4-pheny[1,2,3]oxathiazinane 2,2-dioxide (4r), prepared by the Du Bois asymmetric C-H amination reaction of 3 and the Rh(2)(S-nap)(4) catalyst, is determined to be R and not S as was originally reported. PMID:19957926

Kang, Soyeong; Lee, Hyeon-Kyu

2010-01-01

393

Toward Practical Applications of Software Synthesis Douglas R. Smith  

E-print Network

are usually conceived as a way to obtain veri ably correct soft- ware, so many researchers have focused to the ultimate success of formal methods. We argue that mechanized synthesis tools can have an impact of transportation scheduling algorithms. 1 Introduction We have been exploring automated tools for transforming

Green, Cordell

394

Review on the progress in synthesis and application of magnetic carbon nanocomposites  

NASA Astrophysics Data System (ADS)

This review focuses on the synthesis and application of nanostructured composites containing magnetic nanostructures and carbon-based materials. Great progress in fabrication of magnetic carbon nanocomposites has been made by developing methods including filling process, template-based synthesis, chemical vapor deposition, hydrothermal/solvothermal method, pyrolysis procedure, sol-gel process, detonation induced reaction, self-assembly method, etc. The applications of magnetic carbon nanocomposites expanded to a wide range of fields such as environmental treatment, microwave absorption, magnetic recording media, electrochemical sensor, catalysis, separation/recognization of biomolecules and drug delivery are discussed. Finally, some future trends and perspectives in this research area are outlined.

Zhu, Maiyong; Diao, Guowang

2011-07-01

395

Asymmetric Synthesis of Functionalized Dihydro- and Tetrahydropyrans via an Organocatalytic Domino Michael-Hemiacetalization Reaction  

PubMed Central

Starting from ?-hydroxymethyl nitroalkenes and various 1,3-dicarbonyl compounds, a one-pot organocatalyzed diastereo- and enantioselective synthesis of polyfunctionalized dihydro- and tetrahydropyran derivatives via a domino Michael-hemiacetalization sequence is reported. The title compounds bearing a variety of functional groups can be synthesized in this way in good yields (59–91%) and with moderate to excellent diastereoselectivities (26–98% de) and enantioselectivities (71–99% ee).

Urbanietz, Gregor; Atodiresei, Iuliana; Enders, Dieter

2014-01-01

396

Natural compounds in the synthesis of chiral organophosphorous ligands  

NASA Astrophysics Data System (ADS)

Methods for the synthesis of chiral organophosphorus compounds based on natural optically active compounds (hydroxy acids, amino acids and their derivatives, mono- and disaccharides, mono- and diterpenoids, steroids) are discussed. Particular attention is given to the synthesis of bisphosphines and bisphosphinites. These compounds serve as ligands for transition metal complexes, which catalyse asymmetric hydrogenation. Data on the enantioselectivity of hydrogenation of unsaturated precursors of amino acids and unsaturated prochiral acids as well as on information on the enantioselectivity of hydrosilylation of ketones are surveyed.

Tolstikov, Alexander G.; Khlebnikova, Tatiana B.; Tolstikova, Olga V.; Tolstikov, Genrikh A.

2003-09-01

397

A stereoselective switch: enantiodivergent approach to the synthesis of isoflavanones.  

PubMed

A modular six-step asymmetric synthesis of two naturally occurring and three non-natural isoflavanones containing tertiary ?-aryl carbonyls is reported. This synthetic route, utilising a Pd-catalyzed decarboxylative asymmetric protonation, produces isoflavanones in excellent enantioselectivities from 76-97?%. A switch in the sense of stereoinduction was observed when different H(+) sources were employed, showing the first example of dual stereocontrol in an asymmetric protonation reaction. The first enantioselective synthesis of the naturally occurring isoflavanones sativanone and 3-o-methylviolanone has been accomplished. PMID:25314579

Doran, Robert; Carroll, Michael P; Akula, Ramulu; Hogan, Bryan F; Martins, Marta; Fanning, Séamus; Guiry, Patrick J

2014-11-17

398

Anisotropic Hexagonal Boron Nitride Nanomaterials - Synthesis and Applications  

SciTech Connect

Boron nitride (BN) is a synthetic binary compound located between III and V group elements in the Periodic Table. However, its properties, in terms of polymorphism and mechanical characteristics, are rather close to those of carbon compared with other III-V compounds, such as gallium nitride. BN crystallizes into a layered or a tetrahedrally linked structure, like those of graphite and diamond, respectively, depending on the conditions of its preparation, especially the pressure applied. Such correspondence between BN and carbon readily can be understood from their isoelectronic structures [1, 2]. On the other hand, in contrast to graphite, layered BN is transparent and is an insulator. This material has attracted great interest because, similar to carbon, it exists in various polymorphic forms exhibiting very different properties; however, these forms do not correspond strictly to those of carbon. Crystallographically, BN is classified into four polymorphic forms: Hexagonal BN (h-BN) (Figure 1(b)); rhombohedral BN (r-BN); cubic BN (c-BN); and wurtzite BN (w-BN). BN does not occur in nature. In 1842, Balmain [3] obtained BN as a reaction product between molten boric oxide and potassium cyanide under atmospheric pressure. Thereafter, many methods for its synthesis were reported. h-BN and r-BN are formed under ambient pressure. c-BN is synthesized from h-BN under high pressure at high temperature while w-BN is prepared from h-BN under high pressure at room temperature [1]. Each BN layer consists of stacks of hexagonal plate-like units of boron and nitrogen atoms linked by SP{sup 2} hybridized orbits and held together mainly by Van der Waals force (Fig 1(b)). The hexagonal polymorph has two-layered repeating units: AA'AA'... that differ from those in graphite: ABAB... (Figure 1(a)). Within the layers of h-BN there is coincidence between the same phases of the hexagons, although the boron atoms and nitrogen atoms are alternatively located along the c-axis. The rhombohedral system consists of three-layered units: ABCABC..., whose honeycomb layers are arranged in a shifted phase, like as those of graphite. Reflecting its weak interlayer bond, the h-BN can be cleaved easily along its layers, and hence, is widely used as a lubricant material. The material is stable up to a high temperature of 2300 C before decomposition sets in [2] does not fuse a nitrogen atmosphere of 1 atm, and thus, is applicable as a refractory material. Besides having such properties, similar to those of graphite, the material is transparent, and acts as a good electric insulator, especially at high temperatures (10{sup 6} {Omega}m at 1000 C) [1]. c-BN and w-BN are tetrahedrally linked BN. The former has a cubic sphalerite-type structure, and the latter has a hexagonal wurtzite-type structure. c-BN is the second hardest known material (the hardest is diamond), the so-called white diamond. It is used mainly for grinding and cutting industrial ferrous materials because it does not react with molten iron, nickel, and related alloys at high temperatures whereas diamond does [1]. It displays the second highest thermal conductivity (6-9 W/cm.deg) after diamond. This chapter focuses principally upon information about h-BN nanomaterials, mainly BN nanotubes (BNNTs), porous BN, mono- and few-layer-BN sheets. There are good reviews book chapters about c-BN in [1, 4-6].

Han,W.Q.

2008-08-01

399

Organocatalytic enantioselective synthesis of 2,3-dihydropyridazines.  

PubMed

We have developed an efficient procedure for the easy and straightforward preparation of functionalized dihydropyridazines as highly enantiopure materials by reaction of pyruvaldehyde 2-tosyl hydrazone with a variety of ?,?-unsaturated aldehydes using a chiral secondary amine as catalyst. The overall process consists of a cascade reaction involving an initial aza-Michael reaction, in which the stereocentre is installed, followed by an intramolecular aldol reaction/dehydration step. PMID:22245768

Fernández, Maitane; Vicario, Jose L; Reyes, Efraím; Carrillo, Luisa; Badía, Dolores

2012-02-18

400

Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)  

DOEpatents

A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-[alpha]-benzoylamino-4boronocinnamic acid, asymmetrically hydrogenating the z-[alpha]-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA. 3 figs.

Samsel, E.G.

1992-10-20

401

Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)  

DOEpatents

A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-.alpha.-benzoylamino-4-boronocinnamic acid, asymmetrically hydrogenating the z-.alpha.-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA.

Samsel, Edward G. (Baton Rouge, LA)

1992-01-01

402

Enantioselective Synthesis of the Antiinflammatory Agent (-)-Acanthoic Acid  

E-print Network

used in folkloric medicines.3 Notable examples of such successful endeavors are the plant-derived me on this subject, see: Kinghorn, A. D., Balandrin, M. F., Eds. Human Medicinal Agents from Plants; ACS Symposium For thousands of years, mankind has known about the benefit of drugs from nature. Among them, plants

Theodorakis, Emmanuel

403

Synthesis of high purity metal oxide nanoparticles for optical applications  

NASA Astrophysics Data System (ADS)

In this paper we present our recent research results in synthesizing various metal oxide nanoparticles for use as laser gain media (solid state as well as fiber lasers) and transparent ceramic windows via two separate techniques, co-precipitation and flame spray pyrolysis. The nanoparticles were pressed into ceramic discs that exhibited optical transmission approaching the theoretical limit and showed very high optical-to-optical lasing slope efficiency. We have also synthesized sesquioxide nanoparticles using a Flame Spray Pyrolysis (FSP) technique that leads to the synthesis of a metastable phase of sesquioxide which allows fabricating excellent optical quality transparent windows with very fine grain sizes. Finally, we present our research in the synthesis of rare earth doped boehmite nanoparticles where the rareearth ion is encased in a cage of aluminum and oxygen to prevent ion-ion proximity and energy transfer. The preforms have been drawn into fibers exhibiting long lifetimes and high laser efficiencies.

Baker, C.; Kim, W.; Friebele, E. J.; Villalobos, G.; Frantz, J.; Shaw, L. B.; Sadowski, B.; Fontana, J.; Dubinskii, M.; Zhang, J.; Sanghera, J.

2014-09-01

404

Nanoporous Silica Matrices and Their Application in Synthesis of Nanostructures  

NASA Astrophysics Data System (ADS)

The effect of the presence of I-4 Me-Ph ionene in the supramolecular template (cetyltrimethylammonium bromide) on formation of porous structure of silicas was studied. We also studied the peculiarities of template synthesis of mesoporous silicas inside of large pores of silica gel. Mesoporous silicas with chemically modified surface were applied in synthesis of metallic nanostructures. Porous silicas with grafted layer of hydridepolysiloxane were used for in situ preparation of supported nanoparticles of gold and silver by reduction of metal ions from chloroauric acid and silver nitrate solutions, respectively. Nitrogen adsorption-desorption, X-ray powder diffraction analysis, scanning and transmission electron microscopies, IR-, UV-visible, and laser correlation spectroscopies were applied for characterization of adsorbents and nanostructures obtained.

Tertykh, V. A.; Yanishpolskii, V. V.; Katok, K. V.; Berezovska, I. S.

405

A General Approach for Preparing Epidithiodioxopiperazines from Trioxopiperazine Precursors. Enantioselective Total Syntheses of (+)- and (?)- Gliocladine C, (+)-Leptosin D, (+)-T988C, Bionectin A and (+)-Gliocladin A  

PubMed Central

A common strategy for preparing tryptophan-derived epidithiodioxopiperazine (ETP) natural product containing a hydroxyl substituent adjacent to a quaternary carbon stereocenter is reported. This strategy is exemplified by enantioselective total syntheses of four heptacyclic ETP natural products — gliocladine C (6), leptosin D (7), T988C (8), and bionectin A (9)—starting with the di-(tertbutoxycarbonyl) derivative 17 of the trioxopiperazine natural product gliocladin C, which is readily available by enantioselective chemical synthesis. In addition, total syntheses of the enantiomer of gliocladine C (ent-6) and gliocladin A (11), the di(methylthio) congener of bionectin A, are reported. These syntheses illustrate a synthetic strategy wherein diversity in the dioxopiperazine unit of ETP natural products is introduced at a late stage in a synthetic sequence. In vitro cytotoxicity of compounds in this series against invasive human prostrate (DU145) and melanoma (A2058) cancer cell lines is described and compared to that of chaetocin A (4). PMID:23452236

DeLorbe, John E.; Horne, David; Jove, Richard; Mennen, Steven M.; Nam, Sangkil; Zhang, Fang-Li; Overman, Larry E.

2013-01-01

406

Rh2(S-PTTL)3TPA--A Mixed Ligand Dirhodium(II) Catalyst for Enantioselective Reactions of ?-Alkyl-?-Diazoesters  

PubMed Central

Herein we report the synthesis of the mixed ligand paddlewheel complex dirhodium(II) tris[N-phthaloyl-(S)-tert-leucinate] triphenylacetate, Rh2(S-PTTL)3TPA, the structure of which bears similarity to the chiral crown complex Rh2(S-PTTL)4. Rh2(S-PTTL)3TPA engages substrate classes (aliphatic alkynes, silylacetylenes, ?-olefins) that are especially challenging in intermolecular reactions of ?-alkyl-?-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh2(S-PTTL)4. Mixing ligands on paddlewheel complexes offers a versatile handle for diversifying catalyst structure and reactivity. The results described herein illustrate how mixed ligand catalysts can create new opportunities for the optimization of catalytic asymmetric processes. PMID:23125912

Boruta, David T.; Dmitrenko, Olga; Yap, Glenn P. A.

2012-01-01

407

Rh(2)(S-PTTL)(3)TPA-A Mixed Ligand Dirhodium(II) Catalyst for Enantioselective Reactions of ?-Alkyl-?-Diazoesters.  

PubMed

Herein we report the synthesis of the mixed ligand paddlewheel complex dirhodium(II) tris[N-phthaloyl-(S)-tert-leucinate] triphenylacetate, Rh(2)(S-PTTL)(3)TPA, the structure of which bears similarity to the chiral crown complex Rh(2)(S-PTTL)(4). Rh(2)(S-PTTL)(3)TPA engages substrate classes (aliphatic alkynes, silylacetylenes, ?-olefins) that are especially challenging in intermolecular reactions of ?-alkyl-?-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh(2)(S-PTTL)(4). Mixing ligands on paddlewheel complexes offers a versatile handle for diversifying catalyst structure and reactivity. The results described herein illustrate how mixed ligand catalysts can create new opportunities for the optimization of catalytic asymmetric processes. PMID:23125912

Boruta, David T; Dmitrenko, Olga; Yap, Glenn P A; Fox, Joseph M

2012-05-01

408

A Fluorous Phosphate Protecting Group with Applications to Carbohydrate Synthesis  

PubMed Central

The first fluorous protecting group for phosphate is reported. This group can be used as a facile tag for purification and be removed under mild reducing conditions using zinc and ammonium formate. Synthesis of a disaccharide from Leishmania using this fluorous protecting group demonstrated the group's stability to the acidic conditions necessary for glycosylation as well as its orthogonality to several other common protecting groups. PMID:21384825

Liu, Lin

2011-01-01

409

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two ? position(s) of a carbonyl group) with high diastereo- and enantioselectivities. PMID:23828817

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-08-01

410

Synthesis, Characterization, and Applications of Hemifluorinated Dibranched Amphiphiles  

PubMed Central

Here we describe the synthesis, the physicochemical and preliminary pharmaceutical assessment of a novel class of hemifluorinated dibranched derivatives (M1diHxFy). These novel compounds have the remarkable ability of completely stopping the Ostwald ripening commonly associated with nanoemulsions. The developed synthesis is modular and it allows easy incremental structural variations in the fluorophilic (fluorous chains)-, lipophilic (alkyl spacer head)- and hydrophilic (polar head) domains. Furthermore, the synthesis can be easily scaled-up and highly pure compounds can be readily obtained through silica gel and fluoro-silica gel column chromatography, without any need to use HPLC or other time-consuming techniques. Surface properties like micelle formation, critical aggregation concentration (CAC) and emulsion stability studies demonstrated the different behavior of dibranched hemifluorinated surfactant (M1diHxFy) with respect to that of single chain semifluorinated analogues (MzFy). Remarkably, the new polymer M1diH3F8 drastically slowed the ripening of nanoemulsions of the commonly used fluorinated anesthetic sevoflurane over a period of more than one year. During this time, the nanodroplet size did not increase to more than 400 nm. This result is very promising for inducing and maintaining general anesthesia through intravenous delivery of volatile anesthetics, eliminating the need for the use of large and costly vaporizers in the operating room. PMID:21736353

Parlato, Maria Cristina; Jee, Jun-Pil; Teshite, Motti; Mecozzi, Sandro

2011-01-01

411

Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects  

NASA Astrophysics Data System (ADS)

Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative. The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles. The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

Prabhu, Sukumaran; Poulose, Eldho K.

2012-10-01

412

Synthesis of binaphthyl based phosphine and phosphite ligands.  

PubMed

The development of large scale synthesis of enantiopure and thermally stable (R)- and (S)-BINOL molecules constitutes a key milestone in the field of asymmetric catalysis. Particularly, a great variety of chiral binaphthyl-based phosphorus compounds, herein represented by phosphite and phosphine classes, have earned considerable relevance due to their versatility as ligands in enantioselective metal-catalysed reactions, allowing the preparation of optically active products with the desired enantiopurity. This review highlights the most relevant concepts and accounts regarding general synthetic procedures for binaphthyl-based mono- and bidentate phosphites and phosphines. Furthermore, the search for environmentally benign chemical catalytic processes compelled us to also give special attention to the functionalisation of binaphthyl-based phosphorus ligands for use in alternative reaction media. When available, a critical selection of their applications in catalysis is briefly assessed. PMID:23783506

Pereira, Mariette M; Calvete, Mário J F; Carrilho, Rui M B; Abreu, Artur R

2013-08-21

413

Asymmetric bromine-lithium exchange: application toward the synthesis of natural product.  

PubMed

Asymmetric bromine-lithium exchange has been successfully employed to synthesize bicoumarin chiral building blocks of (+)-isokotanin A and (-)-kotanin in good yields and with an excellent level of enantioselectivity. This is the first reported example of formal syntheses, using this direct methodology, leading to the single (M)-atropoisomer of (+)-isokotanin A and (-)-kotanin building blocks, without any resolution step. PMID:23919304

Graff, Julien; Debande, Thibaut; Praz, Jézabel; Guénée, Laure; Alexakis, Alexandre

2013-08-16

414

Advances in hypersonic vehicle synthesis with application to studies of advanced thermal protection system  

Microsoft Academic Search

This report summarizes the work entitled 'Advances in Hypersonic Vehicle Synthesis with Application to Studies of Advanced Thermal Protection Systems.' The effort was in two areas: (1) development of advanced methods of trajectory and propulsion system optimization; and (2) development of advanced methods of structural weight estimation. The majority of the effort was spent in the trajectory area.

Mark D. Ardema

1995-01-01

415

Design and synthesis of perfluorinated amphiphilic copolymers: Smart nanomicelles for theranostic applications  

Microsoft Academic Search

Since decades, varieties of amphiphilic polymers have been widely investigated for improving aqueous solubility and bioavailability of the hydrophobic drugs. The upcoming approach is to develop more efficient advanced nano-carrier molecules capable of more than drug delivery. Herein, we report the design and synthesis of some novel carrier molecules with multiple applications including drug encapsulation, drug delivery and diagnosis (imaging).

Mukesh K. Pandey; Rahul Tyagi; Ke Yang; Robert J. Fisher; Clark K. Colton; Jayant Kumar; Virinder S. Parmar; Eric Aiazian; Arthur C. Watterson

2011-01-01

416

ON THE APPLICABILITY OF DISTRIBUTED MODE LOUDSPEAKER PANELS FOR WAVE FIELD SYNTHESIS BASED SOUND REPRODUCTION  

Microsoft Academic Search

The applicability of distributed mode loudspeaker (DML) panels for Wave Field Synthesis based sound reproduction is investigated. For WFS a large number of closely spaced loudspeakers is necessary. DML panels are light-weight and can be placed directly on the walls. Results are reported of a research project to test the objective and subjective performance of these speaker panels for WFS.

Marinus M. Boone; Werner P. J. de Bruijn

417

A specialised speech synthesis technique for application to automatic reverse directory service  

Microsoft Academic Search

This paper describes a specialised version of Eloquens, the CSELT's text-to-speech synthesiser, which has been conceived to achieve a substantial improvement for what concerns not only intelligibility, but also speech naturalness in the synthesis of messages in an automatic reverse directory service. This result has been obtained taking advantage of the peculiarities of the application domain, namely the possibility, or

Luciano Nebbia; Silvia Quazza; Pier Luigi Salza

1998-01-01

418

Application-layer Connector Synthesis Paola Inverardi, Romina Spalazzese, and Massimo Tivoli  

E-print Network

Application-layer Connector Synthesis Paola Inverardi, Romina Spalazzese, and Massimo Tivoli Dipartimento di Informatica - Universit`a degli Studi dell'Aquila, Italy {paola.inverardi,romina--190" DOI : 10.1007/978-3-642-21455-4_5 #12;2 Paola Inverardi, Romina Spalazzese, and Massimo Tivoli

Paris-Sud XI, Université de

419

Overview of cell-free protein synthesis: historic landmarks, commercial systems, and expanding applications.  

PubMed

During the early days of molecular biology, cell-free protein synthesis played an essential role in deciphering the genetic code and contributed to our understanding of translation of protein from messenger RNA. Owing to several decades of major and incremental improvements, modern cell-free systems have achieved higher protein synthesis yields at lower production costs. Commercial cell-free systems are now available from a variety of material sources, ranging from "traditional" E. coli, rabbit reticulocyte lysate, and wheat germ extracts, to recent insect and human cell extracts, to defined systems reconstituted from purified recombinant components. Although each cell-free system has certain advantages and disadvantages, the diversity of the cell-free systems allows in vitro synthesis of a wide range of proteins for a variety of downstream applications. In the post-genomic era, cell-free protein synthesis has rapidly become the preferred approach for high-throughput functional and structural studies of proteins and a versatile tool for in vitro protein evolution and synthetic biology. This unit provides a brief history of cell-free protein synthesis and describes key advances in modern cell-free systems, practical differences between widely used commercial cell-free systems, and applications of this important technology. Curr. Protoc. Mol. Biol. 108:16.30.1-16.30.11. © 2014 by John Wiley & Sons, Inc. PMID:25271714

Chong, Shaorong

2014-01-01

420

Synthetic studies on the icetexones: enantioselective formal syntheses of icetexone and epi-icetexone  

PubMed Central

Two strategies for the synthesis of the icetexane diterpenoids icetexone and epi-icetexone that rely on Ga(III)-catalyzed cycloisomerization of alkynyl indene substrates to yield fused [6-7-6] tricycles have been explored. In the first approach, access to a tricycle bearing a gem-dimethyl group paved the way for explorations of C–H functionalization of one of the methyl groups in close proximity to a hydroxyl-directing group. This approach was ultimately unsuccessful and led only to ring cleaved products. In the second approach, an alkynyl indene substrate bearing a cyano substituent was utilized, which was effective in providing a functional handle to access the icetexone subclass of diterpenoids. A key epoxide opening/diazene rearrangement sequence was utilized to complete a formal synthesis of icetexone and epi-icetexone, which is discussed in detail. Furthermore, the cyano-containing substrate has been prepared in enantioenriched form using a Rh-catalyzed conjugate addition reaction, which now provides a route to the enantioselective synthesis of these natural products. PMID:24249921

de Jesus Cortez, Felipe; Lapointe, David; Hamlin, Amy M.; Simmons, Eric M.; Sarpong, Richmond

2013-01-01

421

Synthesis of pipelined memory access controllers for streamed data applications on FPGA-based computing engines  

Microsoft Academic Search

Commercially available behavioral synthesis tools do not adequately support FPGA vendor-specific external memory interfaces making it extremely difficult to exploit pipelined memory access modes as well as application specific memory operations scheduling critical for high-performance solutions. This lack of support substantially increases the complexity and the burden on designers in the mapping of applications to FPGA-based computing engines. In this

Pedro C. Diniz

2001-01-01

422

Magnetic nanoparticles: synthesis, functionalization, and applications in bioimaging and magnetic energy storage  

PubMed Central

This tutorial review summarizes the recent advances in the chemical synthesis and potential applications of monodisperse magnetic nanoparticles. After a brief introduction to nanomagnetism, the review focuses on recent developments in solution phase syntheses of monodisperse MFe2O4, Co, Fe, CoFe, FePt and SmCo5 nanoparticles. The review further outlines the surface, structural, and magnetic properties of these nanoparticles for biomedicine and magnetic energy storage applications. PMID:19690734

Frey, Natalie A.; Peng, Sheng; Cheng, Kai; Sun, Shouheng

2009-01-01

423

Magnetic nanoparticles: synthesis, functionalization, and applications in bioimaging and magnetic energy storage.  

PubMed

This tutorial review summarizes the recent advances in the chemical synthesis and potential applications of monodisperse magnetic nanoparticles. After a brief introduction to nanomagnetism, the review focuses on recent developments in solution phase syntheses of monodisperse MFe(2)O(4), Co, Fe, CoFe, FePt and SmCo(5) nanoparticles. The review further outlines the surface, structural, and magnetic properties of these nanoparticles for biomedicine and magnetic energy storage applications. PMID:19690734

Frey, Natalie A; Peng, Sheng; Cheng, Kai; Sun, Shouheng

2009-09-01

424

Synthesis and assembly of magnetic nanoparticles for information and energy storage applications  

NASA Astrophysics Data System (ADS)

This mini-review summarizes the recent advances in chemical synthesis and assembly of monodisperse magnetic nanoparticles for magnetic applications. After a brief introduction to nanomagnetism, the review focuses on recent developments in solution phase syntheses and assemblies of monodisperse Fe, CoFe, FePt and SmCo5 nanoparticles. The review further outlines the structural and magnetic properties of these nanoparticles for magnetic information and energy storage applications.

Zhang, Hong-Wang; Liu, Yi; Sun, Shou-Heng

2010-12-01

425

Combustion synthesis of tin dioxide nanocomposites for gas sensing applications  

NASA Astrophysics Data System (ADS)

The current work focuses on understanding the mechanisms controlling tin dioxide (SnO2) nanoparticle morphology in combustion synthesis systems and how nanoarchitecture affects performance of solid-state gas sensors. A range of analytical methods (including transmission and scanning electron microscopy, x-ray diffraction, nitrogen absorption, and XEDS) were used to characterize the materials properties as a function of the combustion synthesis conditions. A novel method of generating tin dioxide materials was developed which provides a new degree of control over SnO2 morphology; including spherical, nanorod and encapsulated particle architectures. A simplified model for particle formation based on characteristic times was developed to identify the physical and chemical processes affecting the morphologies observed using transmission electron microscope imaging. The SnO2 nanoparticles evolve from primary particles sizes of 7 nm to 14 nm through the synthesis region, and the results indicate interparticle collision and sintering are the dominant mechanisms in determining particle size and morphology for the flame conditions studied. Metal acetates were used to create metal/SnO 2 nanocomposite materials, and the processes controlling gold acetate decomposition in particular were explored. The results of the studies suggest a relationship between the precursor crystallite size and the product nanoparticles. The well-characterized SnO2 particles were evaluated as the active materials for gas-sensing. Sensor sensitivity and time response to carbon monoxide in dry air was used to investigate microstructure-performance links. Excellent sensitivity (3 7, based on the ratio of the resistance of the sensor in air to the resistance in the target gas) and time response (4--20 seconds) were demonstrated for the thin film gas sensors. Fabrication studies demonstrated the sensor performance was a strong function of the film deposition method. A novel method for manufacturing sensors with outstanding consistency and performance was developed. This method was used to explore the effects of microstructure and composition on sensor performance. Gold and palladium doped SnO2 gas sensors indicated the introduction of dopants has potential to improve sensor performance; however, the effects are dependent on the additive distribution and location. The combustion synthesis and sensor fabrication methods that are the results of these studies will dramatically accelerate the design of new sensors and sensor optimization.

Bakrania, Smitesh Dhirajlal

426

The application of microwaves to rapid chemical synthesis  

SciTech Connect

The synthesis of a wide variety of organic and organometallic compounds can be carried out conveniently and rapidly using microwave heating. The dramatic rate enhancements which result from microwave irradiation of reactants in sealed vessels are attributed mainly to the superheating of the solvent due to the high pressures generated. However there is considerable evidence that the rates of some reactions are enhanced by microwave heating in open vessels, suggesting localized superheating or some specific microwave effect. While microwave irradiation does not usually alter the product composition of a reaction appreciably, there have been a few reports in which some product selectivity has been observed.

Gedye, R.; Westaway, K.; Smith, F. [Laurentian Univ., Sudbury, Ontario (Canada)

1995-12-31

427

Synthesis and application of a new fluorous-tagged ammonia equivalent.  

PubMed

A novel fluorous-tagged ammonia equivalent has been developed. It is based on a nitrogen-oxygen bond, which can be cleaved in a traceless manner by a molybdenum complex or samarium diiodide. The application in the synthesis of ureas, amides, sulfonamides, and carbamates is described. The scope of the fluorous N-O linker is exemplified by the synthesis of itopride, a drug used for the treatment of functional dyspepsia. Itopride was synthesized with the aid of fluorous purification methods and the product was isolated in good overall yield, with high purity. PMID:20333716

Nielsen, Simon D; Smith, Garrick; Begtrup, Mikael; Kristensen, Jesper L

2010-04-19

428

[3,3]-Sigmatropic rearrangements: recent applications in the total synthesis of natural products†  

PubMed Central

Among the fundamental chemical transformations in organic synthesis, the [3,3]-sigmatropic rearrangement occupies a unique position as a powerful, reliable, and well-defined method for the stereoselective construction of carbon–carbon or carbon–heteroatom bonds. While many other reactions can unite two subunits and create a new bond, the strengths of sigmatropic rearrangements derive from their ability to enable structural reorganization with unmatched build-up of complexity. Recent applications that illustrate [3,3]-sigmatropic processes as a key concept in the synthesis of complex natural products are described in this tutorial review, covering literature from about 2001 through early 2009. PMID:19847347

Ilardi, Elizabeth A.; Stivala, Craig E.

2014-01-01

429

Novel 7-substituted coumarin compounds and an improved method for their synthesis. [Patent application  

SciTech Connect

Novel substituted coumarin compounds and an improved method for their synthesis are disclosed. The preferred class of compounds are substituted at the 7-position. The method of synthesis comprises reacting a polyhydroxy benzene or a substituted phenol, with a ..beta..-alkoxy acrylic acid or nitrile, in the presence of a Lewis acid catalyst. By the inclusion of the catalyst in the reaction mixture, the reaction can be carried out under much milder experimental conditions and in increased yields. The method is also applicable to the preparation of substituted amino phenols.

Bissell, E.R.

1982-01-20

430

Application of Modified Least Squares Method to a Space Curve Generating Mechanism for Optimum Synthesis  

NASA Astrophysics Data System (ADS)

Synthesis of mechanisms for generation of space curve is a challenging task for designers of the mechanical systems. Least squares method (LSM) has been extensively used for optimization of both planar and spatial mechanisms. Modified least squares method is applied for optimum synthesis of a slotted link mechanism with flexibly attached slider for space curve generation to show the scope of the modified method for optimum design. An example problem is included to illustrate the application of the method. Results are compared with conventional LSM.

Baishya, N. J.; Sharma, D.; Dixit, U. S.

2014-11-01

431

Proposed study to determine potential flight applications and human factors design guidelines of voice recognition/synthesis systems  

NASA Technical Reports Server (NTRS)

An effort to evaluate the human factors aspects and potential of voice recognition/synthesis techniques and the application of present and near-future (5 years) voice recognition/synthesis systems as a pilot/aircraft cockpit interface capability in an operational environment is discussed. The analysis will emphasize applications for single pilot instrument flight rules operations but will also include applications for other categories of aircraft with various levels of complexity.

Bergeron, H. P.

1983-01-01

432

Synthesis and characterization of semiconductor nanomaterials for thermoelectric applications  

NASA Astrophysics Data System (ADS)

In this dissertation, I explore simple chemical means to produce various nanomaterials. In Chapter 2, the synthesis of size-tuned bismuth telluride nanoparticles is discussed. The solution phase synthesis of bismuth telluride nanoparticles has been accomplished in the presence of a library of thiols as the capping ligand. These crystalline nanostructures range in size from ˜20 to ˜100nm with a relatively narrow size dispersity. Size and shape of the resulting nanostructures has been investigated as a function of chain length of the thiol and temperature. An investigation into the thermoelectric properties of the nanostructures shows promising electrical conductivity, thermopower, and thermal conductivity for undoped bismuth telluride. In Chapter 3, a soluble precursor for antimony telluride is described. This precursor was used to fabricate semiconductor nanowires of varying diameter and thin films through simple templating methods. Electrical conductivity and thermoelectric power measurements of these films are only slightly lower than for antimony telluride films fabricated by vacuum deposition. In Chapter 4, the polytetrafluoroethylene (PTFE)/metal nanocomposites are discussed. Palladium and nickel PTFE nanocomposites were made by impregnation of the polymer with metal acetates. Annealing and jet blowing of these materials form PTFE nanofiber/metal nanoparticle composites.

Dirmyer, Matthew R.

433

Synthesis and energy applications of oriented metal oxide nanoporous films  

NASA Astrophysics Data System (ADS)

This dissertation mainly addresses the synthesis of well-ordered mesoporous titania thin films by dip coating with PEO-PPO-PEO triblock copolymer surfactant template P123. Because P123 is composed of poly(ethylene oxide) [PEO] and poly(propylene oxide) [PPO] blocks, concentrations of ingredients are adjusted to tune the films' wall thickness, pore size and mesophase. Structural changes are consistent with partitioning of species among PEO blocks, PPO blocks, and the PEO/PPO interface. Titanates localize near PEO and increase wall thickness (by 5 nm to 7 nm). Depending on aging temperature, PPG either swells the PPO cores (when it is hydrophobic) or introduces large (>200 nm) voids (when it is hydrophilic but phase separates during heating). 1-butanol localizes at the PEO/PPO interface to favor a 3D hexagonal mesostructure. In another approach, anodizing Ti foils yields vertically aligned titania nanotubes arrays with exceptional stabilities as anodes in lithium ion batteries; they maintain capacities of 130-230 mAhg-1 over 200 cycles. No microstructural changes are induced by battery cycling and good electrical contact is maintained. A diffusion induced stress model suggests that thin-walled nanotubes arrays should be stable under testing conditions, and that ordered hexagonal columnar pore arrays should have both high charge/discharge rates and low stress development. KEY WORDS: materials synthesis, porous, thin film, alternative energy, self-assembly

Wu, Qingliu

434

Enantioselective toxicity and bioaccumulation of fipronil in fathead minnows (Pimephales promelas) following water and sediment exposures.  

PubMed

Fipronil is a widely used, broad-spectrum pesticide that is applied as an equal mixture of two enantiomers. As regulations on older pesticides become more stringent, production and application of fipronil is expected to grow, leading to increased inputs into aquatic environments and complex exposures to biota. To better understand the potential exposures introduced by fipronil contamination, we conducted subchronic toxicity tests with larval fathead minnows (Pimephales promelas) and waterborne fipronil and its enantiomers and exposed juvenile fathead minnows to fipronil-spiked sediment. Enantioselective toxicity was observed in fish after the 7-d subchronic exposure, with increased toxicity of the racemate and (+) enantiomer observed compared with the (-) enantiomer. Curiously, toxicities of the racemate and (+) enantiomer were not significantly different, even though the racemate contains 50% of the (+) enantiomer and 50% of the less toxic (-) enantiomer. During the sediment exposure, racemic fipronil in sediment was transformed primarily to fipronil sulfide, while exposed fish rapidly accumulated fipronil and/or fipronil sulfide and transformed the majority to fipronil sulfone. Using the results of the sediment-exposure experiment, the authors explored a mechanism that may contribute to the interesting trends in enantioselective toxicity observed during the waterborne exposures. In tandem, the aquatic toxicity experiment and the spiked sediment exposure demonstrate the potentially complex behavior of fipronil in sediment and fish. PMID:23109279

Baird, Suzanne; Garrison, Arthur; Jones, Jack; Avants, Jimmy; Bringolf, Robert; Black, Marsha

2013-01-01

435

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides  

E-print Network

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides Forrest O. Arp of reaction partners, racemic secondary benzylic halides, can be coupled with organozinc reagents in very good (a benzylic bromide). Fourth, the process is stereoconvergent; both enantiomers of the racemic

Fu, Gregory C.

436

Carbohydrate-based N-heterocyclic carbenes for enantioselective catalysis.  

PubMed

Versatile syntheses of C2-linked and C2-symmetric carbohydrate-based imidazol(in)ium salts from functionalised amino-carbohydrate derivatives are reported. The novel NHCs were ligated to [Rh(COD)Cl]2 and evaluated in Rh-catalysed asymmetric hydrosilylation of ketones with good yields and promising enantioselectivities. PMID:25296562

Henderson, Alexander S; Bower, John F; Galan, M Carmen

2014-10-29

437

The Enantioselective Addition of Alkyne Nucleophiles to Carbonyl Groups  

PubMed Central

Over the past decade, large strides have been achieved in the invention of methods for the direct enantioselective addition of alkynes and metal alkynylide nucleophiles into prochiral aldehydes, ketones, and imines. This review highlights and compares the available methods for these transformations. PMID:24353484

Trost, Barry M.; Weiss, Andrew H.

2013-01-01

438

A Hybrid Phosphorus Ligand for Highly Enantioselective Asymmetric Hydroformylation  

E-print Network

with relatively low reaction rate and low conversion. This limits the utilities of this important transformation derivatives and vinyl acetate. Introduction Hydroformylation is the reaction of alkenes with carbon monoxide an acceptable reaction rate. However, high enantioselectivities are generally observed at low temperature

Zhang, Xumu

439

Lanthanide Lewis acid-mediated enantioselective conjugate radical additions.  

PubMed

[reaction: see text] Lanthanide triflates along with proline-derived ligands have been found to be efficient catalysts for enantioselective conjugate addition of nucleophilic radicals to enoates. N-Acyl oxazolidinones, when used as achiral additives, gave meaningful enhancements in the ees for the product. PMID:12182591

Sibi, Mukund P; Manyem, Shankar

2002-08-22

440

Microgel-supported Oxazaborolidines: Novel Catalysts for Enantioselective Reductions  

Microsoft Academic Search

Microgel-bound oxazaborolidines have been prepared and used as catalysts in the enantioselective reduction of prochiral ketones. The preparation of these soluble, crosslinked polymer molecules was accomplished by solution polymerisation. The approach involved the preparation of microgels bearing free boronic acid functionalities and their subsequent conversion to oxazaborolidines. The selectivities of these supported catalysts are in most cases comparable to those

C. Schunicht; A. Biffis; G. Wulff

2000-01-01

441

CHLORDANE AND HEPTACHLOR ARE METABOLIZED ENANTIOSELECTIVELY BY RAT LIVER MICROSOMES  

PubMed Central

Chlordane, heptachlor and their metabolites are chiral persistent organic pollutants that undergo enantiomeric enrichment in the environment. This study investigated the enantioselective metabolism of both chlordane isomers and heptachlor, major components of technical chlordane, by liver microsomes prepared from male rats treated with corn oil (CO) or inducers of CYP2B (PB; Phenobarbital) and CYP3A enzymes (DX; dexamethasone), isoforms induced by chlordane treatment. The extent of the metabolism of all three parent compounds was dependent on the microsomal preparation used, and followed the rank order PB > DX > CO. The mass balances ranged from 49-130 % of the parent compound added to the microsomal incubations. Both cis- and trans-chlordane were enantioselectively metabolized to oxychlordane (EF=0.45-0.89) and 1,2-dichlorochlordene (EF=0.42-0.90). Heptachlor was metabolized enantioselectively, with heptachlor epoxide B (EF=0.44-0.54) being the only metabolite. Interestingly, the direction on the enrichment for oxychlordane, 1,2-dichlorochlordene and heptachlor epoxide differed depending on the microsomal preparation. These findings demonstrate that the direction and extent of the enantioselective metabolism of both chlordane isomers and heptachlor is P450 isoform-dependent and can be modulated by the induction of P450 enzymes. PMID:23799267

Kania-Korwel, Izabela; Lehmler, Hans-Joachim

2013-01-01

442

Enantioselective diamination with novel chiral hypervalent iodine catalysts.  

PubMed

Vicinal diamines constitute one the most important functional motif in organic chemistry because of its wide occurrence in a variety of biological and pharmaceutical molecules. We report an efficient metal-free, highly stereoselective intramolecular diamination using a novel chiral hypervalent iodine reagent together with its application as an efficient catalyst for the synthesis of diamines. PMID:25042733

Mizar, Pushpak; Laverny, Aragorn; El-Sherbini, Mohammad; Farid, Umar; Brown, Michael; Malmedy, Florence; Wirth, Thomas

2014-08-01

443

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step.  

PubMed

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. PMID:23019438

Enders, Dieter; Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

2012-01-01

444

Asymmetric synthesis of aryloxypropanolamines via OsO 4-catalyzed asymmetric dihydroxylation  

Microsoft Academic Search

A simple and effective procedure for the enantioselective synthesis of several ?-adrenergic blocking agents incorporating the first asymmetric synthesis of celiprolol, is described. The key steps are (i) sharpless asymmetric dihydroxylation of aryl allyl ethers to introduce chirality into the molecules and (ii) conversion of cyclic sulfates into the corresponding epoxides using a three-step procedure.

Iliyas A. Sayyed; Vinay V. Thakur; Milind D. Nikalje; Gajanan K. Dewkar; S. P. Kotkar; A. Sudalai

2005-01-01

445

Synthesis of the tetracyclic core of Illicium sesquiterpenes using an organocatalyzed asymmetric Robinson annulation  

PubMed Central

Summary An enantioselective synthesis of the core framework of neurotrophic Illicium majucin-type sesquiterpenes is described here. This strategy is based on an organocatalyzed asymmetric Robinson annulation and provides an efficient approach for a diversity-oriented synthesis of Illicium natural products that holds remarkable therapeutic potential for neurodegenerative diseases. PMID:23843905

Trzoss, Lynnie; Xu, Jing; Lacoske, Michelle H

2013-01-01

446

Silyl Ketene Imines: Highly Versatile Nucleophiles for Catalytic, Asymmetric Synthesis  

PubMed Central

This Minireview provides an overview on the development of silyl ketene imines and their recent applications in catalytic, enantioselective reactions. The unique structure of the ketene imine allows a diverse range of reactivity patterns and provides solutions to existing challenges in the enantioselective construction of quaternary stereogenic carbon centers and cross-benzoin adducts. A variety of reactions for which silyl ketene imines have been applied are presented with an overall goal of inspiring new uses for these underutilized nucleophiles. PMID:22968901

Denmark, Scott E.; Wilson, Tyler W.

2012-01-01

447

Polyacrolein containing microspheres: Synthesis, properties and possible medical applications  

Microsoft Academic Search

Polymeric microspheres are used in medical diagnostics, therapy, and as supports for enzymes and other proteins in biotechnology. These particles have also found application in fundamental studies in the life-sciences as useful tools for separation of the living cells and subcellular fragments. This article presents comprehensive information on polyacrolein containing microspheres suitable for medical applications. Various synthetic procedures (radical, anionic,

Stanislaw Slomkowski

1998-01-01

448

Nanostructured organic electronic materials: Synthesis and sensor applications  

Microsoft Academic Search

This study is an investigation into (a) the process by which one obtains bulk quantities of nanofibers of parent polythiophene, (b) in-situ deposition of nanofibers of polythiophene on flexible substrate and its application in vapor sensing, and (c) inkjet printing of graphene on flexible substrate and its application as a detector. (a) The 2 nd chapter of the thesis is

Vineet Dua

2009-01-01

449

The application of spinors to pulse synthesis and analysis.  

PubMed

We show how spinors may be used to solve many problems in pulse synthesis and analysis. They provide an elegant simple notation for many problems. We show how one can specify the component of a spinor and then, by exactly solving the Bloch equations, synthesize a hard pulse sequence or a soft pulse which will yield the desired spinor. This is done by generalizing our previous approach to inverting the Bloch equations. This can be applied to synthesizing refocusing pulses. Finally, some simple consequences about symmetric pulses are derived. It is shown that given a symmetric inversion pulse, one can always synthesize an asymmetric inverting pulse of the same duration, which, as an inversion, is better. PMID:2607966

Shinnar, M; Leigh, J S

1989-10-01

450

Synthesis and characterization of peptide nanostructures designed for sensing applications  

NASA Astrophysics Data System (ADS)

We report the design and the synthesis of membrane-active peptide nanostructures, as well as their use as signal transducer in a fluorimetric assay for biologically relevant analytes. Addition of hydrophobic 21-residue peptides bearing six crown ether side chains to a solution of small unilamellar vesicles loaded with a pH-sensitive fluorophore induces a rapid fluorescence increase associated with Na+/H+ transport across the bilayer membrane. To demonstrate the usefulness of these peptide nanostructures in the development of simple, rapid, and sensitive detection assays for a wide range of analytes, peptide nanostructures bearing a biotin at the N-terminal position were prepared. Addition of avidin to the assay employing these modified peptides resulted in a significant change in the time-dependent fluorescence profile. Control experiments with a non-binding proteins and saturated avidin showed that the observed changes are indeed due to specific binding of avidin to biotin modified nanostructures.

Voyer, Normand; Arseneault, Mathieu; Otis, Francois

2005-09-01

451

Integration and Application of Radio Telemetry Data Collected on a Mobile Fish Species: a Synthesis of Bull Trout Movement Research  

E-print Network

Integration and Application of Radio Telemetry Data Collected on a Mobile Fish Species: a Synthesis of the research on bull trout has involved the use of radio telemetry to monitor the movements of this highly telemetry studies as a predicate to a synthesis of the state of knowledge about bull trout movement

452

Synthesis and applications of electron deficient conjugated polymers  

E-print Network

Chapter 1. In this introductory chapter, we present the general properties of conjugated polymers for sensory and electronic applications, with a special emphasis placed on electron-deficient materials. Chapter 2. In this ...

Kim, Youngmi, Ph. D

2005-01-01

453

Design and synthesis of nanocrystal heterostructures for optoelectronic applications  

E-print Network

Colloidal semiconductor nanocrystals can be used for a variety of optoelectronic applications including light emitting devices (LEDs) and photovoltaics. Their narrow emission spectra make them excellent fluorophors for use ...

Halpert, Jonathan E

2008-01-01

454

Phosphine oxide-catalyzed enantioselective intramolecular aldol reaction via regioselective enolization of unsymmetrical diketones with tetrachlorosilane.  

PubMed

The phosphine oxide-catalyzed asymmetric intramolecular aldol reactions of diketones were investigated. The combination of tetrachlorosilane and a chiral phosphine oxide catalyst promoted the acetyl-selective enolization of diketones, and the subsequent intramolecular aldol reaction occurred in an enantioselective manner. The introduction of two trimethylsilyl groups at the 4- and 4'-positions in BINAP dioxide catalyst improved the enantioselectivity. This reaction provides an effective synthetic method to access ?-tertiary-hydroxy cyclohexanones in high yields and with high enantioselectivity. PMID:25192225

Kotani, Shunsuke; Aoki, Shohei; Sugiura, Masaharu; Ogasawara, Masamichi; Nakajima, Makoto

2014-09-19

455

Enantioselective Intramolecular Openings of Oxetanes Catalyzed by (salen)Co(III) Complexes: Access to Enantioenriched Tetrahydrofurans  

PubMed Central

The catalytic enantioselective intramolecular ring-opening of oxetanes with alcohols is catalyzed by (salen)Co(III) complexes. Either a monomeric or oligomeric catalyst can be used successfully in this transformation, providing 3-substituted tetrahydrofurans in both high yield and enantioselectivity. This methodology extends the range of electrophiles that can be activated toward highly enantioselective addition reactions by (salen)metal catalysts to an important new class. PMID:19199427

Loy, Rebecca N.; Jacobsen, Eric N.

2009-01-01

456

Enantioselective electrophilic trifluoromethylthiolation of ?-ketoesters: a case of reactivity and selectivity bias for organocatalysis.  

PubMed

A chiral Lewis base or a phase-transfer catalyst (PTC) can mediate the highly enantioselective trifluoromethylthiolation of ?-ketoesters with the previously developed SCF3 reagent. Reactions of indanone-derived ?-ketoesters occurred with high yield and excellent enantioselectivity with quinine as catalyst. Reactions of tetralone- or 1-benzosuberone-derived ?-ketoesters occurred with moderate to good enantioselectivity with a quinine-derived PTC. PMID:24000200

Wang, Xueqiang; Yang, Tao; Cheng, Xiaolin; Shen, Qilong

2013-12-01

457

Synthesis and application of new polymer bound catalysts  

SciTech Connect

Nitric acid has been shown to be a weak acid in acetonitrile. It is conceivable that a nitrate salt of a weakly Lewis acidic cation could furnish a ''naked'' nitrate anion as a basic catalyst in a variety of reactions in non-aqueous solvents. Such a nitrate salt could also be bound to a polymeric support via the cation, thereby allowing for reclamation and recycling of the nitrate ion. This subject is dealt with in Chapter 2, wherein my contributions consisted of performing all the reactions with the polymer supported catalyst and carrying out the experiments necessary to shed light on the reaction mechanisms. Chapter 3 contains a description of the structure and catalytic properties of an azidoproazaphosphatrane. This compound is an air-stable versatile catalyst that has proven useful not only homogeneously, but also when bound to a solid support. The synthesis of a polymer bound proazaphosphatrane containing a trivalent phosphorus is presented in Chapter 4. Such a compound has been sought after by our group for a number of years. Not only does the synthesis I have accomplished for it allow for easier separation of proazaphosphatrane catalysts from reaction mixtures, but recycling of the base is made much simpler. Proazaphosphatranes are useful homogeneous catalysts that activate atoms in other reagents, thus enhancing their reactivity. The next chapters deal with two such reactions with aldehydes and ketones, namely silylcyanations with trialkylsilylcyanides (Chapters 5 and 6) and reductions with poly(methylhydrosiloxane), in Chapter 7. In Chapter 5, Zhigang Wang performed the initial optimization and scoping of the reaction, while repetitions of the scoping experiments for reproducibility, determination of diastereomeric ratios, and experiments aimed at elucidating aspects of the mechanism were performed by me. The proazaphosphatrane coordinates to the silicon atom in both cases, thereby allowing the aforementioned reactions to proceed under much milder conditions. Proazaphosphatranes are also effective Broensted-Lowry bases. This is illustrated in Chapter 8 wherein a wide variety of conjugate addition reactions are catalyzed by proazaphosphatranes. In that chapter, repetitions of the nitroalkane addition reactions for reproducibility, improved spectral data for the products and comparisons of literature yields of all reactions were performed by the author.

Fetterly, Brandon Michael

2005-08-01

458

Synthesis, NMR characterization, and a simple application of lithium borotritide  

SciTech Connect

LiBH{sub 4} is a powerful and selective reagent for regiospecific reduction reactions. A simple synthesis of LiB{sup 3}H{sub 4} at near theoretical specific radioactivity is reported. The authors have treated Li{sup 3}H synthesized from tritium gas ({sup 3}H{sub 2}, {approximately}98%) with BBr{sub 3} to produce LiB{sup 3}H{sub 4} (specific activity = 4120 GBq/mmol = 110 Ci/mmol. The maximum theoretical specific activity of LiB{sup 3}H{sub 4} is 4252 GBq/mmol = 115.04 Ci/mmol; 1 matom of {sup 3}H = 1063 GBq = 28.76 Ci.) The tritium labeling performance of the reagent was tested by an exemplary reduction of 2-naphthaldehyde to 2-naphthalenemethanol. LiB{sup 3}H{sub 4} and the reduction products were characterized by a combination of {sup 1}H, {sup 3}H, and {sup 11}B NMR techniques, as appropriate. 35 refs., 1 fig.

Than, Chit; Morimoto, Hiromi [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); Andres, H. [Sandoz Pharma Ltd., Basle (Switzerland)] [and others] [Sandoz Pharma Ltd., Basle (Switzerland); and others

1996-12-13

459

Synthesis and Characterization of Nanostructured Catalysts for Photovoltaic Applications  

NASA Astrophysics Data System (ADS)

The objective of this project was to investigate the effect of the morphology of titanium dioxide (TiO2) nanoparticles on the electron transport properties and light harvesting potential in a dye sensitized solar cell (DSSC). Particular attention was given to develop synthetic methods to produce metal oxide photocatalysts with similar crystallite size, with different morphologies (spheres, fibers, hierarchical spheres, and globular structures) with the aim of studying the relationship between morphology and photocatalytic activity. The addition of CNTs to the synthesis showed that they acted as nucleation sites and altered the morphology. Materials were fully characterized using Raman, SEM, XRD, BET, and FTIR. The photocatalytic activity of the as-synthesized materials was tested in a DSSC configuration and characterized using electrochemical impedance spectroscopy. It was found that the different morphologies had different light scattering properties which influenced the efficiencies. Based on these preliminary results, the nanofibres prepared in heptane performed the best, with good dye loading, electron lifetime and diffusion coefficient. The addition of a scattering layer using hierarchical spheres showed promising results in decreased transparency and increased efficiency. The addition of CNTs had an adverse effect, this could be due to light blocking by the black CNTs and increased recombination with the electrolyte.

McGillivray, Donald

460

Synthesis and characterization of pillared stevensites: application to chromate adsorption.  

PubMed

The purpose of this work was to study the synthesis of pillared interlayered clays from Moroccan stevensite called locally 'Ghassoul'. This clay has been intercalated with cetyltrimethylammonium surfactant (CTA-Stv) and aluminium hydroxypolycation (Al13-Stv). Characterization studies were performed using XRF, XRD, FTIR and DTA/TG analysis. Basal spacing values of Al13-Stv and CTA-Stv increased respectively from 13.5 A for natural stevensite to 17.5 and 17.6 A with increasing Al13(7+)/clay and CTA+/clay ratios. The DTA/TG results showed that Al13-Stv has a relatively high thermal stability compared with CTA-Stv. A quasi-irreversible intercalation by exchanging the interlayer inorganic cations with voluminous pillars Al13(7+) or CTA+ was observed. Batch adsorption of chromate anions from aqueous solutions was investigated and the results showed that both pillared clays had great affinity for the chromate compared with untreated stevensite. The Dubinin-Kaganer-Radushkevich (DKR) model was selected to describe the adsorption isotherms. The maximum adsorption capacities for natural stevensite, Al13-Stv and CTA-Stv are 13.7, 75.4 and 195.6 mmol/kg, respectively. PMID:21780704

Benhammou, A; Yaacoubi, A; Nibou, L; Bonnet, J P; Tanouti, B

2011-01-01

461

Nanoparticle-polymer composite membranes: Synthesis, characterization, and environmental applications  

NASA Astrophysics Data System (ADS)

Advances in nanotechnology and materials science offer new possibilities for the development of novel water treatment technologies A salient example is the emergence of a new generation of nanostructured membranes with improved separation properties and, in some cases, multifunctional capabilities. The present work explores different aspects of the formation of nanoparticle-enabled membranes, focusing on the dependence between synthetic methods, nanoparticle properties, and the performance of the obtained membranes. The effects of nanoparticle loading, size and morphology, and methods of nanoparticle incorporation on the functional properties of the resulting nanocomposite membranes are studied. Additionally, empirical predictors of membrane performance for the rational design of nanocomposite membranes and novel strategies for the manufacture of membrane-based sensors and biofouling resistant membrane spacers are presented. The first chapter of the dissertation provides an overview of the theory of phase inversion in polymer blends -- one of the main methods for the fabrication of ultrafiltration membranes. The second chapter describes the study of the effect of shape and loading of carbon nanoparticle fillers on the hydraulic properties of nanocomposite membranes. In the third chapter, the effects of casting mixture composition and nanoparticle incorporation route on the morphological structure and separation performance of nanocomposite membranes are described and the potential use of these nanocomposites for the mitigation of membrane biofouling is discussed. Finally, in the last chapter, a method for the synthesis of a nanoparticle-enabled, membrane-based sensor for water quality control is presented.

Taurozzi, Julian S.

462

Palladium- and Ruthenium-Catalyzed Decarboxylative Allylations and Michael Addition-Allylation Reactions. Applications in Nitrogen Heterocycle Synthesis  

E-print Network

of dihydroquinoline derivatives. Once again, reaction in the presence of Michael acceptors led to a formal decarboxylative [4+2] cycloaddition. The analogous reaction in the presence of nonracemic palladium catalysts led to a highly enantioselective reaction. Lastly...

Wang, Chao

2008-08-21

463

A microfluidic tubing method and its application for controlled synthesis of polymeric nanoparticles.  

PubMed

This report describes a straightforward but robust tubing method for connecting polydimethylsiloxane (PDMS) microfluidic devices to external equipment. The interconnection is irreversible and can sustain a pressure of up to 4.5 MPa that is characterized experimentally and theoretically. To demonstrate applications of this high-pressure tubing technique, we fabricate a semicircular microfluidic channel to implement a high-throughput, size-controlled synthesis of poly(lactic-co-glycolic acid) (PLGA) nanoparticles ranging from 55 to 135 nm in diameter. This microfluidic device allows for a total flow rate of 410 mL h(-1), resulting in enhanced convective mixing which can be utilized to precipitate small size nanoparticles with a good dispersion. We expect that this tubing technique would be widely used in microfluidic chips for nanoparticle synthesis, cell manipulation, and potentially nanofluidic applications. PMID:24675980

Wang, Jidong; Chen, Wenwen; Sun, Jiashu; Liu, Chao; Yin, Qifang; Zhang, Lu; Xianyu, Yunlei; Shi, Xinghua; Hu, Guoqing; Jiang, Xingyu

2014-05-21

464

Synthesis and characterization of ZnO nanowires for nanosensor applications  

SciTech Connect

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 {sup o}C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H{sub 2} of a gas nanosensor based on an individual ZnO nanowire is also reported.

Lupan, O., E-mail: lupan@physics.ucf.edu [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Department of Microelectronics and Semiconductor Devices, Technical University of Moldova, 168 Stefan cel Mare Blvd., MD-2004 Chisinau, Republic of Moldova (Moldova, Republic of); Emelchenko, G.A. [Institute of Solid State Physics, Russian Academy of Science, 142432 Chernogolovka, Moscow District (Russian Federation)] [Institute of Solid State Physics, Russian Academy of Science, 142432 Chernogolovka, Moscow District (Russian Federation); Ursaki, V.V. [Institute of Applied Physics of the Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova (Moldova, Republic of) [Institute of Applied Physics of the Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova (Moldova, Republic of); National Center for Materials Study and Testing, Technical University of Moldova, Chisinau 2004, Republic of Moldova (Moldova, Republic of); Chai, G. [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States)] [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Redkin, A.N.; Gruzintsev, A.N. [Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District (Russian Federation)] [Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District (Russian Federation); Tiginyanu, I.M. [Institute of Applied Physics of the Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova (Moldova, Republic of) [Institute of Applied Physics of the Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova (Moldova, Republic of); National Center for Materials Study and Testing, Technical University of Moldova, Chisinau 2004, Republic of Moldova (Moldova, Republic of); Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova (Moldova, Republic of); Chow, L. [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States) [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Ono, L.K. [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States)] [Department of Physics, University of Central Florida, Orlando, FL 32816-2385 (United States); and others

2010-08-15

465

An Overview of Stereoselective Synthesis of ?-Aminophosphonic Acids and Derivatives  

PubMed Central

An overview of all methodologies published during the last few years focused to the stereoselective (diastereoselective or enantioselective) synthesis of ?-aminophosphonic acids and derivatives is reported. The procedures have been classified according a retrosynthetic strategy and taking into account the formation of each one of the bonds connected to the chiral centre. PMID:20871799

Ordonez, Mario; Rojas-Cabrera, Haydee; Cativiela, Carlos

2009-01-01

466

Chiral Synthesis on Catalysts Immobilized in Microporous and Mesoporous Materials  

Microsoft Academic Search

This paper reviews the recent progress made in the asymmetric synthesis on chiral catalysts in porous materials and discusses the effects of surface and pores on enantioselectivity (confinement effect). This paper also summarizes various approaches of immobilization of the chiral catalysts onto surfaces and into pores of solid inorganic supports such as microporous and mesoporous materials. The most important reactions

2004-01-01

467

First asymmetric synthesis of planar chiral [2.2]metacyclophanes.  

PubMed

A general three step asymmetric synthesis of planar chiral [2.2]metacyclophanes utilizing selective benzylic and aryl metalations is described. The final enantioselective step is achieved using a (-)-sparteine mediated aryl metalation, following which electrophile reaction gives planar chiral cyclophanes with enantiomeric ratios (er) above 90?:?10. PMID:23615867

Blangetti, Marco; Müller-Bunz, Helge; O'Shea, Donal F

2013-07-14

468

Efficient, Divergent Synthesis of Cryptophycin Unit A Analogues  

PubMed Central

A flexible and divergent synthesis of cryptophycin unit A analogues is described. This method relies on iridium-catalysed stereo- and enantioselective crotylation and chemoselective one-pot oxidative olefination to access common intermediate 8. Heck, cross metathesis, and Suzuki-Miyaura reactions are illustrated for the generation of methyl ester unit A analogues 10a-d. PMID:22617820

Bolduc, Kyle L.; Larsen, Scott D.; Sherman, David H.

2012-01-01

469

A genomic search approach to identify carbonyl reductases in Gluconobacter oxydans for enantioselective reduction of ketones.  

PubMed

The versatile carbonyl reductases from Gluconobacter oxydans in the enantioselective reduction of ketones to the corresponding alcohols were exploited by genome search approach. All purified enzymes showed activities toward the tested ketoesters with different activities. In the reduction of 4-phenyl-2-butanone with in situ NAD(P)H regeneration system, (S)-alcohol was obtained with an e.e. of up to 100% catalyzed by Gox0644. Under the same experimental condition, all enzymes catalyzed ethyl 4-chloroacetoacetate to give chiral products with an excellent e.e. of up to 99%, except Gox0644. Gox2036 had a strict requirement for NADH as the cofactor and showed excellent enantiospecificity in the synthesis of ethyl (R)-4-chloro-3-hydroxybutanoate. For the reduction of ethyl 2-oxo-4-phenylbutyrate, excellent e.e. (>99%) and high conversion (93.1%) were obtained by Gox0525, whereas the other enzymes showed relatively lower e.e. and conversions. Among them, Gox2036 and Gox0525 showed potentials in the synthesis of chiral alcohols as useful biocatalysts. PMID:25130736

Chen, Rong; Liu, Xu; Lin, Jinping; Wei, Dongzhi

2014-01-01

470

Development of catalysts and ligands for enantioselective gold catalysis.  

PubMed

During the past decade, the use of Au(I) complexes for the catalytic activation of C-C ?-bonds has been investigated intensely. Over this time period, the development of homogeneous gold catalysis has been extraordinarily rapid and has yielded a host of mild and selective methods for the formation of carbon-carbon and carbon-heteroatom bonds. The facile formation of new bonds facilitated by gold naturally led to efforts toward rendering these transformations enantioselective. In this Account, we survey the development of catalysts and ligands for enantioselective gold catalysis by our research group as well as related work by others. We also discuss some of our strategies to address the challenges of enantioselective gold(I) catalysis. Early on, our work with enantioselective gold-catalyzed transformations focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, the careful choice of the weakly coordinating ligand (or counterion) was necessary to obtain high levels of enantioselectivity for the case of allene hydroamination. These counterion effects led us to use the anion itself as a source of chirality, which was successful in the case of allene hydroalkoxylation. In general, these tactics enhance the steric influence around the reactive gold center beyond the two-coordinate ligand environment. The use of binuclear complexes allowed us to use the second gold center and its associated ligand (or counterion) to exert a further steric influence. In a similar vein, we employed a chiral anion (in place of or in addition to a chiral ligand) to move the chiral information closer to the reactive center. In order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, we also developed a new class of mononuclear phosphite and phosphoramidite ligands to supplement the previously widely utilized phosphines. However, we needed to judiciously design the steric environment to create "walls" that enclose the gold center. We also successfully applied these same considerations to the development of binuclear carbene ligands for gold. Finally, we describe the design of bifunctional urea-monophosphine ligands used in a gold-catalyzed three-component coupling. PMID:24228794

Wang, Yi-Ming; Lackner, Aaron D; Toste, F Dean

2014-03-18

471

Highly enantioselective aldol reaction of acetone with ?,?-unsaturated ?-keto esters promoted by simple chiral primary-tertiary diamine catalysts.  

PubMed

A series of primary-tertiary diamine catalysts were successfully applied to promote the enantioselective aldol reaction of acetone with ?,?-unsaturated ?-keto esters in excellent yields (up to 99%) and enantioselectivities (up to 96% ee). PMID:21614388

Peng, Lin; Wang, Liang-Liang; Bai, Jian-Fei; Jia, Li-Na; Guo, Yun-Long; Luo, Xi-Ya; Wang, Fei-Ying; Xu, Xiao-Ying; Wang, Li-Xin

2011-07-01

472

Recent Research on One-Dimensional Silicon-Based Semiconductor Nanomaterials: Synthesis, Structures, Properties and Applications  

Microsoft Academic Search

The field of silicon nanowires (SiNWs) and silicon-based 1D nanostructured heterostructures represent one of the most important research subjects within the nanomaterials family. A series of synthesis approaches of SiNWs and silicon-based 1D nanostructured heterostructures have been developed, and have garnered the greatest attention in the past decades for a variety of applications. This article provides an overview on recent

Zhenyu Zhang; Rujia Zou; Li Yu; Junqing Hu

2011-01-01

473

Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers  

Microsoft Academic Search

We report the synthesis and characterization of nanosized zinc oxide particles and their application on cotton and wool fabrics\\u000a for UV shielding. The nanoparticles were produced in different conditions of temperature (90 or 150 °C) and reacting medium\\u000a (water or 1,2-ethanediol). A high temperature was necessary to obtain small monodispersed particles. Fourier transformed infrared\\u000a spectroscopy (FTIR), transmission electron microscopy (TEM), and

Alessio Becheri; Maximilian Dürr; Pierandrea Lo Nostro; Piero Baglioni

2008-01-01

474

Green synthesis of (?)-isopulegol from (+)-citronellal: application to essential oil of citronella  

Microsoft Academic Search

A simple green and efficient method has been developed for the synthesis of (?)-isopulegol from (+)-citronellal in the presence of a solid supported catalyst (SiO2\\/ZnCl2), under solvent-free conditions and MW irradiation. It was also found that the same technology is applicable to the direct preparation of (?)-isopulegol from the essential oil of citronella (Cymbopogon nardus, growing in southern Brazil) in

Raquel G. Jacob; Gelson Perin; Leticia N. Loi; Claudia S. Pinno; Eder J. Lenardão

2003-01-01

475

Robust Controller Synthesis in Automatic Guided Vehicles Applications  

Microsoft Academic Search

We are interested in AGV applications since a long time, particularly in the fleld of car vehicles and agricultural machines. This paper deals with the design of robust lateral controllers expressed directly in the sensor space. We use the camera sensor to extract an image of the position and orientation of the vehicle in regard with the white band, and

P. Martinet; C. Thibaud; B. Thuilot; J. Gallice

1998-01-01