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1

Bifunctional Iminophosphorane Organocatalysts for Enantioselective Synthesis: Application to the Ketimine Nitro-Mannich Reaction  

PubMed Central

The design, synthesis, and development of a new class of modular, strongly basic, and tunable bifunctional Brønsted base/H-bond-donor organocatalysts are reported. These catalysts incorporate a triaryliminophosphorane as the Brønsted basic moiety and are readily synthesized via a last step Staudinger reaction of a chiral organoazide and a triarylphosphine. Their application to the first general enantioselective organocatalytic nitro-Mannich reaction of nitromethane to unactivated ketone-derived imines allows the enantioselective construction of ?-nitroamines possessing a fully substituted carbon atom. The reaction is amenable to multigram scale-up, and the products are useful for the synthesis of enantiopure 1,2-diamine and ?-amino acid derivatives. PMID:24107070

2013-01-01

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

A Catalytic Enantioselective Tandem Allylation Strategy for Rapid Terpene Construction: Application to the Synthesis of Pumilaside Aglycon  

PubMed Central

Catalytic enantioselective 1,2-diboration of 1,3-dienes followed by cascade allylborations with dicarbonyls provides rapid entry into carbocyclic reaction products. The stereochemical course of this reaction was studied along with its application in the synthesis of pumilaside aglycon. PMID:23390951

Ferris, Grace E.; Hong, Kai; Roundtree, Ian A.; Morken, James P.

2013-01-01

4

A catalytic enantioselective tandem allylation strategy for rapid terpene construction: application to the synthesis of pumilaside aglycon.  

PubMed

Catalytic enantioselective 1,2-diboration of 1,3-dienes followed by cascade allylborations with dicarbonyls provides rapid entry into carbocyclic reaction products. The stereochemical course of this reaction was studied along with its application in the synthesis of pumilaside aglycon. PMID:23390951

Ferris, Grace E; Hong, Kai; Roundtree, Ian A; Morken, James P

2013-02-20

5

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

PubMed Central

A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane with electron-deficient olefins has been developed. The synthesis of novel phosphoramidite ligands was critical in this effort, and the preparation and reactivity of these ligands is detailed. The evolution of the ligand design, commencing with acyclic amine-derived phosphoramidites and leading to cyclic pyrrolidine and azetidine structures is discussed. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of alkene acceptors, providing the desired methylenecyclopentanes with high levels of enantioselectivity. The donor scope was also explored and substituted systems were tolerated, including one bearing a nitrile moiety. These donors were reactive with unsaturated acylpyrroles, giving the product cyclopentane rings bearing three stereocenters in high enantioselectivity and complete diastereoselectivity. PMID:21936576

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

2011-01-01

6

A highly enantioselective benzothiepine synthesis  

PubMed

A highly enantioselective synthesis of benzothiepine 1a has been accomplished via an enantioenriched sulfoxide intermediate obtained by asymmetric oxidation with a chiral oxaziridine in 89:11 er. The key step is a thermodynamically controlled asymmetric cyclization reaction that produces two new stereogenic centers. The (4R,5R) isomer 1a was obtained in 98:2 er. PMID:10808444

Wang; Li; Huang; Lee; Reitz

2000-05-01

7

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

PubMed

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. PMID:25247276

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

2014-01-01

8

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

9

Enantioselective Total Synthesis of Aplyviolene  

PubMed Central

The enantioselective total synthesis of the rearranged spongian diterpene aplyviolene has been completed in 14 steps from the known hydroazulenone 8. The key junction of the hydrocarbon and oxygenated fragments to form the critical C8 quaternary carbon stereocenter and set the stage for elaborating the delicate bicyclic lactone functionality was accomplished in high yield and exquisite stereoselectivity by Michael addition of an enantioenriched hydroazulenone enolate to an enantiopure ?-bromocyclopentenone. PMID:21936525

Overman, Larry E.; Schnermann, Martin J.

2011-01-01

10

Enantioselective total synthesis of borrelidin.  

PubMed

The first total synthesis of the natural product borrelidin is described. The propionate fragment of the molecule was concisely synthesized through catalytic enantioselective reductive aldol reactions, a catalytic Negishi coupling, and a catalytic directed hydrogenation. The propionate segment was then fused to the vinyl iodide fragment through a catalytic Sonogashira coupling. Subsequent catalytic hydrostannylation and catalytic cyanation allowed access to the target structure. PMID:12568588

Duffey, Matthew O; LeTiran, Arnaud; Morken, James P

2003-02-12

11

Enantioselective synthesis of ( S)-dapoxetine  

Microsoft Academic Search

An efficient enantioselective synthesis leading directly to (+)-(S)-dapoxetine has been described for the first time using a Sharpless asymmetric dihydroxylation, Barton–McCombie deoxygention, and Mitsunobu reaction as the key steps.

Shafi A. Siddiqui; Kumar V. Srinivasan

2007-01-01

12

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

13

The Pauson-Khand Reaction as a New Entry to the Synthesis of Bridged Bicyclic Heterocycles: Application to the Enantioselective Total Synthesis of (?)-Alstonerine  

PubMed Central

The first application of the Pauson-Khand reaction (PKR) to the synthesis of azabridged bicyclic structures is described. Compounds containing azabicyclo[3.3.1]nonane and azabicyclo[3.2.1]octane rings fused to cyclopentenones were efficiently constructed via the PKR of cis-2,6-disubstituted N-acyl piperidine enyne substrates, many of which can be readily prepared from 4-methoxypyridine in a few steps. Moreover, the PKR of cis-2,6-disubstituted piperazine enynes allowed the preparation of diazabicyclo[3.3.1]nonanes fused to cyclopentenones. This new strategy for the synthesis of azabridged bicyclic frameworks was exploited as a key step in a concise, enantioselective total synthesis of the macroline alklaoid (?)-alstonerine. PMID:19122869

Miller, Kenneth A.; Shanahan, Charles S.; Martin, Stephen F.

2008-01-01

14

First enantioselective total synthesis of (-)-tejedine.  

PubMed

[structure: see text] The first enantioselective total synthesis of (-)-tejedine (1) is reported. Tejedine is a seco-bisbenzyltetrahydroisoquinoline isolated in 1998 as a minor component from Berberis vulgaris. The synthesis was achieved using a strategy employing four key steps, including a chiral auxiliary-assisted diastereoselective Bischler-Napieralski cyclization. PMID:12153207

Wang, You-Chu; Georghiou, Paris E

2002-08-01

15

Enantioselective biotransformations of nitriles in organic synthesis.  

PubMed

The hydration and hydrolysis of nitriles are valuable synthetic methods used to prepare carboxamides and carboxylic acids. However, chemical hydration and hydrolysis of nitriles involve harsh reaction conditions, have low selectivity, and generate large amounts of waste. Therefore, researchers have confined the scope of these reactions to simple nitrile substrates. However, biological transformations of nitriles are highly efficient, chemoselective, and environmentally benign, which has led synthetic organic chemists and biotechologists to study these reactions in detail over the last two decades. In nature, biological systems degrade nitriles via two distinct pathways: nitrilases catalyze the direct hydrolysis of nitriles to afford carboxylic acids with release of ammonia, and nitrile hydratases catalyze the conversion of nitriles into carboxamides, which then furnish carboxylic acids via hydrolysis in the presence of amidases. Researchers have subsequently developed biocatalytic methods into useful industrial processes for the manufacture of commodity chemicals, including acrylamide. Since the late 1990s, research by my group and others has led to enormous progress in the understanding and application of enantioselective biotransformations of nitriles in organic synthesis. In this Account, I summarize the important advances in enantioselective biotransformations of nitriles and amides, with a primary focus on research from my laboratory. I describe microbial whole-cell-catalyzed kinetic resolution of various functionalized nitriles, amino- and hydroxynitriles, and nitriles that contain small rings and the desymmetrization of prochiral and meso dinitriles and diamides. I also demonstrate how we can apply the biocatalytic protocol to synthesize natural products and bioactive compounds. These nitrile biotransformations offer an attractive and unique protocol for the enantioselective synthesis of polyfunctionalized organic compounds that are not readily obtainable by other methods. Nitrile substrates are readily available, and the mild reaction conditions are specific toward cyano and amido functional groups without interfering with other reactive functional groups. I anticipate that further advances in this field will lead to new and engineered nitrile-hydrolyzing enzymes or catalytic systems with improved activity and altered selectivity. These advances will broaden the scope of these transformations and their applications in organic synthesis. PMID:25699471

Wang, Mei-Xiang

2015-03-17

16

Enantioselective total synthesis of (-)-maoecrystal V.  

PubMed

The enantioselective synthesis of maoecrystal V, a cytotoxic polycyclic diterpene, is described. Key reactions in the synthesis include an intramolecular Heck reaction, an oxidative cycloetherification, and an intermolecular Diels-Alder reaction to forge the carbocyclic core in a concise and stereoselective manner. Late-stage amine and C-H oxidation is used to install the final functional groups required to complete the synthesis. PMID:25495370

Zheng, Changwu; Dubovyk, Igor; Lazarski, Kiel E; Thomson, Regan J

2014-12-24

17

Expedient enantioselective synthesis of cermizine D.  

PubMed

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

2012-03-16

18

Enantioselective total synthesis of the lignan (+)-linoxepin.  

PubMed

An enantioselective total synthesis of the natural (+)-linoxepin (1) was accomplished in eleven steps from bromovanin (24). Key steps are a domino carbopalladation/ Mizoroki-Heck reaction with the formation of a pentacyclic system, an asymmetric hydroboration as well as an oxidative lactonization. PMID:25345835

Tietze, Lutz F; Clerc, Jérôme; Biller, Simon; Duefert, Svenia-C; Bischoff, Matthias

2014-12-15

19

Short, enantioselective total synthesis of chatancin.  

PubMed

An enantioselective total synthesis of the polycyclic diterpene (+)-chatancin, a potent PAF antagonist, is reported. Proceeding in seven steps from dihydrofarnesal, this synthetic route was designed to circumvent macrocyclization-based strategies to complex, cyclized cembranoids. The described synthesis requires only six chromatographic purifications, is high yielding, and avoids protecting-group manipulations. An X-ray crystal structure of this fragile marine natural product was obtained. PMID:25470723

Zhao, Yu-Ming; Maimone, Thomas J

2015-01-19

20

Enantioselective synthesis of a dual orexin receptor antagonist.  

PubMed

A concise, enantioselective synthesis of the potent dual orexin inhibitor suvorexant (1) is reported. Key features of the synthesis include a mild copper-catalyzed amination, a highly chemoselective conjugate addition, and a tandem enantioselective transamination/seven-membered ring annulation. The synthesis requires inexpensive starting materials and only four linear steps for completion. PMID:22725839

Mangion, Ian K; Sherry, Benjamin D; Yin, Jingjun; Fleitz, Fred J

2012-07-01

21

Concise enantioselective synthesis of diospongins A and B  

PubMed Central

Ether transfer methodology is capable of stereoselectively generating 1,3-diol mono- and diethers in good yield. Surprisingly, allylic and benzylic substrates provide none of the desired products when exposed to previously optimized conditions of iodine monochloride. Herein, second-generation activation conditions for ether transfer have been developed that circumvents undesired side reactions for these substrates. The application of this chemistry to the enantioselective synthesis of diospongins A and B has now been accomplished. PMID:24058215

Stefan, Eric; Nalin, Ansel P.; Taylor, Richard E.

2013-01-01

22

Synthetic Studies on Borrelidin: Enantioselective Synthesis of the  

E-print Network

Synthetic Studies on Borrelidin: Enantioselective Synthesis of the C1-C12 Fragment Binh G. Vong February 11, 2003 ABSTRACT An efficient, enantioselective synthesis of the C1-C12 fragment 2 of borrelidin methodology. First isolated from Streptomyces rochei in 1949,1 borrelidin (1, Figure 1) is a macrolide

Theodorakis, Emmanuel

23

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

24

Enantioselective Total Synthesis of (?)-Jiadifenolide**  

PubMed Central

The first total synthesis of jiadifenolide (1), a potent neurotrophic modulator, has been reported. Highlights of the synthesis include: construction of the B ring via an asymmetric Robinson annulation; assembly of the E ring lactone via a novel acid-induced cascade reaction; and Pd(0)-mediated carbomethoxylation and methylation reactions for the construction of the C and A rings respectively. PMID:21400650

Xu, Jing; Trzoss, Lynnie; Chang, Weng K.; Theodorakis, Emmanuel. A.

2011-01-01

25

Catalytic enantioselective synthesis of quaternary carbon stereocentres  

NASA Astrophysics Data System (ADS)

Quaternary carbon stereocentres--carbon atoms to which four distinct carbon substituents are attached--are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

Quasdorf, Kyle W.; Overman, Larry E.

2014-12-01

26

Catalytic enantioselective synthesis of quaternary carbon stereocentres.  

PubMed

Quaternary carbon stereocentres-carbon atoms to which four distinct carbon substituents are attached-are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials. PMID:25503231

Quasdorf, Kyle W; Overman, Larry E

2014-12-11

27

Total Synthesis of (+)-Rishirilide B: Development and Application of General Processes for Enantioselective Oxidative Dearomatization of Resorcinol Derivatives  

PubMed Central

A concise synthesis of (+)-rishirilide B (2) is described. This is the first synthesis to be reported for the (+)-enantiomer of rishirilide B (2) as found in nature. The strategy accentuates the valuable combination of a method for o-quinone methide coupling with a method for enantioselective resorcinol dearomatization, which provides a densely functionalized chiral building block. The convergent synthesis illustrates several improvements and refinements to these methods and their supporting chemistries. Among these is the in situ generation of PhI[OTMS]OTf. Combination of this oxidant with phenol 31 constitutes the first example of a diastereoselective oxidative dearomatization of a resorcinol displaying a 2-alkyl substituent. In addition, the preparation of the cyclic sulfone 34 is reported. As a new dimethide precursor expressing a readily cleavable O-benzyl residue, sulfone 34 should prove useful in future endeavors. A protocol using the aluminum amide of dimethylhydrazine for opening and cleavage of a [1,4]-dioxan-2-one is also described. This procedure unmasks the hydroxy dione 36 by jettisoning the chiral directing group. Regioselective O-carbamylation of the 1,3-dione 36 enables the transformation of the remaining carbonyl into the ?-hydroxy carboxylic acid found in 2. The total synthesis of (+)-rishirilide B (2) requires 15 pots from benzaldehyde 17 and 13 pots from benzaldehyde 32. The final product emerges in yields of 12.5% and 20.3% from compounds 17 and 32, respectively. The longest linear sequence requires eight chromatographies. Important observations leading to the development of the principle asymmetric method are described within the context of the total synthesis. PMID:17147370

Mejorado, Lupe H.

2008-01-01

28

Enantioselective Total Synthesis of (?)-Acutumine  

PubMed Central

An account of the total synthesis of the tetracyclic alkaloid (?)-acutumine is presented. A first-generation approach to the spirocyclic subunit was unsuccessful due to incorrect regioselectivity in a radical cyclization. However, this work spawned a second-generation strategy in which the spirocycle was fashioned via a radical–polar crossover reaction. This process merged an intramolecular radical conjugate addition with an enolate hydroxylation, and created two stereocenters with excellent diastereoselectivity. The reaction was promoted by irradiation with a sunlamp, and a ditin reagent was required for aryl radical formation. These facts suggest that the substrate may function as a sensitizer, thereby facilitating homolytic cleavage of the ditin reagent. The propellane motif of the target was then installed via annulation of a pyrrolidine ring onto the spirocycle. The sequence of reactions used included a phenolic oxidation, an asymmetric ketone allylation mediated by Nakamura’s chiral allylzinc reagent, an anionic oxy-Cope rearrangement, a one-pot ozonolysis–reductive amination, and a Lewis acid promoted cyclization of an amine onto an ?,?-unsaturated dimethyl ketal. Further studies of the asymmetric ketone allylation demonstrated the ability of the Nakamura reagent to function well in a mismatched situation. A TiCl4-catalyzed regioselective methyl enol etherification of a 1,3-diketone completed the synthesis. PMID:19904909

Li, Fang; Tartakoff, Samuel S.; Castle, Steven L.

2009-01-01

29

Enantioselective Synthesis of -Hydroxyenones by Chiral Base-Catalyzed Kornblum DeLaMare Rearrangement  

E-print Network

are also viable substrates for the base- catalyzed enantioselective reaction. Thus, 23 was converted to 24Enantioselective Synthesis of -Hydroxyenones by Chiral Base-Catalyzed Kornblum De) are important building blocks for asym- metric organic synthesis.1 Enantioselective synthesis of this class

Toste, Dean

30

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

31

An enantioselective formal synthesis of montelukast sodium.  

PubMed

A formal synthesis of the antiasthma drug montelukast sodium is described, wherein the key chiral diol intermediate was accessed with greater convergence of the C-C bond-forming steps as compared to previous routes. Improved synthetic efficiency was achieved by deploying homogeneous metal-based catalysis in two pivotal steps. In the first, a tandem Mizoroki-Heck reaction and double-bond isomerization between a previously known allyl alcohol intermediate and a hindered 2-(2-halophenyl)propan-2-ol secured direct access to the 3-(2-(2-hydroxypropan-2-yl)phenyl)-1-phenylpropan-1-one moiety in the product. In the second step, asymmetric hydrogenation of the ketone functionality in the Mizoroki-Heck reaction product provided a convenient method to introduce the benzylic alcohol chiral center and obtain the desired chiral diol precursor of montelukast sodium. A detailed catalyst screening led to the identification of ((R)-Xyl-BINAP)((R,R)-DPEN)RuCl2 as a catalyst that afforded an enantioselectivity of 99% ee in the hydrogenation step on a multigram lab scale at a molar substrate:catalyst loading of 5000:1. PMID:25807000

Bollikonda, Satyanarayana; Mohanarangam, Saravanan; Jinna, Rajender Reddy; Kandirelli, Venkata Kiran Kumar; Makthala, Laxman; Sen, Saikat; Chaplin, David A; Lloyd, Richard C; Mahoney, Thomas; Dahanukar, Vilas Hareshwar; Oruganti, Srinivas; Fox, Martin E

2015-04-17

32

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

33

A Novel Synthesis of r-Amino Acid Derivatives through Catalytic, Enantioselective Ene Reactions of  

E-print Network

A Novel Synthesis of r-Amino Acid Derivatives through Catalytic, Enantioselective Ene Reactions variants are known.2 However, the corresponding catalytic, enantioselective ene reaction between alkenes, enantioselective imino ene reaction of R-imino ester 1 with alkenes 2a-f catalyzed by Lewis acid complex 3 and show

Lectka, Thomas

34

Facile synthesis of C 2-symmetric tridentate bis(thiazoline) and bis(oxazoline) ligands and their application in the enantioselective Henry reaction  

Microsoft Academic Search

A series of novel C2-symmetric bis(thiazoline) ligands with a diphenylamine backbone as a linkage between two thiazoline rings were synthesized by the use of the simple reagent phosphorus pentasulfide. Their application in the catalytic asymmetric Henry reaction of ?-keto esters was investigated with comparison to the corresponding bis(oxazoline) ligands. Cu(II)–bis(oxazoline) complexes furnished moderate enantioselectivities (up to 60% ee), while Cu(II)–bis(thiazoline)

Shao-Feng Lu; Da-Ming Du; Shi-Wei Zhang; Jiaxi Xu

2004-01-01

35

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 Central

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

2015-01-01

36

Enantioselective total synthesis of pinnaic acid and halichlorine.  

PubMed

The enantioselective total synthesis of the bioactive marine natural products pinnaic acid and halichlorine is reported in detail. Our total synthesis features the construction of the five-membered ring and C9 and C13 stereogenic centers through a palladium-catalyzed trimethylenemethane [3+2] cyclization; the installation of the nitrogen atom through a regioselective Beckmann rearrangement of a poorly reactive ketone; the stereoselective cyclization of the spiro ring through a four-step, one-pot hydrogenation-cyclization; and efficient connection of the sterically hindered lower chain through a reduced-pressure cross olefin metathesis reaction. PMID:24136879

Xu, Shu; Unabara, Daisuke; Uemura, Daisuke; Arimoto, Hirokazu

2014-01-01

37

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

38

Enantioselective Synthesis of (?)-Jiadifenin, a Potent Neurotrophic Modulator  

PubMed Central

The first enantioselective synthesis of (?)-jiadifenin (1), a potent neurite outgrowth promoter isolated from Illicium species, is described. The synthetic strategy builds upon bicyclic motif 6 that represents the AB ring of the natural product and proceeds in 19 steps and 1.1% overall yield. Key to our approach is a Mn(III)-mediated oxidation reaction of A ring that, following a regio- and diastereoselective ?-hydroxylation and methylation sequence, produces the desired functionalities of (?)-jiadifenin. The effect of synthetic 1 in NGF-mediated neurite outgrowth was also measured in PC-12 cells. PMID:21812392

Trzoss, Lynnie; Xu, Jing; Lacoske, Michelle H.; Mobley, William C.; Theodorakis, Emmanuel A.

2011-01-01

39

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

PubMed

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

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

2015-01-26

40

An Enantioselective Synthesis of (S)-4-Fluorohistidine  

PubMed Central

We report a new synthesis of enantiomerically pure (S)-4-fluorohisitidine based on diastereoselective alkylation of MOM-protected 4-fluoro-5-bromomethyl imidazole using the Schöllkopf bis-lactim amino acid synthesis. Improvements in procedures for preparation of key intermediates are also described. (S)-4-Fluorohisitidine prepared by this new method was identical in all respects to material prepared by previous procedures. PMID:19727329

Hajduch, Jan; Cramer, John C.; Kirk, Kenneth L.

2008-01-01

41

Enantioselective palladium-catalyzed dearomative cyclization for the efficient synthesis of terpenes and steroids.  

PubMed

A novel enantioselective palladium-catalyzed dearomative cyclization has been developed for the efficient construction of a series of chiral phenanthrenone derivatives bearing an all-carbon quaternary center. The effectiveness of this method in the synthesis of terpenes and steroids was demonstrated by a highly efficient synthesis of a kaurene intermediate, the facile construction of the skeleton of the anabolic steroid boldenone, and the enantioselective total synthesis of the antimicrobial diterpene natural product (-)-totaradiol. PMID:25631391

Du, Kang; Guo, Pan; Chen, Yuan; Cao, Zhen; Wang, Zheng; Tang, Wenjun

2015-03-01

42

Development of Ruthenium Catalysts for the Enantioselective Synthesis of P-Stereogenic Phosphines via Nucleophilic  

E-print Network

Development of Ruthenium Catalysts for the Enantioselective Synthesis of P-Stereogenic Phosphines the development of ruthenium(II) catalysts for the enantioselective alkylation of chiral racemic secondary asymmetric environment around the ruthenium center. The (R)-MeO- BiPHEP/dmpe (dmpe ) 1,2-bis

Toste, Dean

43

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.

44

Enantioselective total synthesis of (-)-xialenon A.  

PubMed

The first total synthesis of (-)-xialenon A (1) via conjugate allylation of a 1,5-cyclooctadiene-derived bicyclo[3.3.0]octenone 3 and an alpha'-hydroxylation on the more hinderd face of enone 9 using hypervalent iodine chemistry, is described. PMID:12430478

Hodgson, David M; Galano, Jean-Marie; Christlieb, Martin

2002-10-21

45

Organocatalytic Michael and Friedel-Crafts reactions in enantioselective synthesis of biologically active compounds  

NASA Astrophysics Data System (ADS)

Recent applications of organocatalytic Michael and Friedel-Crafts reactions in enantioselective synthesis of biologically active compounds: natural products, pharmaceutical agents and plant protection agents are reviewed. The key mechanisms of stereoinduction, types of organocatalysts and reagents used in these reactions are considered. The material is classified according to the type of newly formed bonds incorporating the asymmetric carbon atom, and the information for the most numerous C-C coupling reactions is systematized according to the natures of the electrophile and the nucleophile. The bibliography includes 433 references. Dedicated to Academician O M Nefedov on the occasion of his 80th birthday.

Maltsev, O. V.; Beletskaya, Irina P.; Zlotin, Sergei G.

2011-11-01

46

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

E-print Network

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

Lawson, Catherine L.

47

Aldehyde Coupling Reactions Enantioselective Organocatalytic  

E-print Network

Aldehyde Coupling Reactions Enantioselective Organocatalytic Direct Aldol Reactions of a upon carbohydrate architecture[2] as an important platform for reaction design and methodological advance- ment.[3] Application of the aldol reaction[4] to the synthesis of carbohydrates is well

MacMillan, David W. C.

48

O-Monoacyltartaric acid catalyzed enantioselective conjugate addition of a boronic acid to dienones: application to the synthesis of optically active cyclopentenones.  

PubMed

Enantioselective conjugate addition of styrylboronic acid to dienones was effectively catalyzed by an O-monoacyltartaric acid to afford monostyrylated products with good enantioselectivity. The RCM of the monostyrylated products using the Hoveyda-Grubbs II catalyst afforded optically active cyclopentenones, including a synthetic intermediate of the antitumor agent TEI-9826. The study shows that a diene additive such as 1,6-heptadiene or diallyl ether was essential for the RCM. PMID:25248134

Sugiura, Masaharu; Kinoshita, Ryo; Nakajima, Makoto

2014-10-01

49

Synthesis of 1-[bis(trifluoromethyl)phosphine]-1'-oxazolinylferrocene ligands and their application in regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates.  

PubMed

A class of novel, easily accessible and air-stable 1-[bis(trifluoromethyl)phosphine]-1'-oxazolinylferrocene ligands has been synthesized from ferrocene. It became apparent that these ligands can be used in the regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates in a highly efficient manner. Excellent regio- and enantioselectivity could be obtained for a wide range of substrates. PMID:24991277

Lai, Zeng-Wei; Yang, Rong-Fei; Ye, Ke-Yin; Sun, Hongbin; You, Shu-Li

2014-01-01

50

Synthesis of 1-[bis(trifluoromethyl)phosphine]-1’-oxazolinylferrocene ligands and their application in regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates  

PubMed Central

Summary A class of novel, easily accessible and air-stable 1-[bis(trifluoromethyl)phosphine]-1’-oxazolinylferrocene ligands has been synthesized from ferrocene. It became apparent that these ligands can be used in the regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates in a highly efficient manner. Excellent regio- and enantioselectivity could be obtained for a wide range of substrates. PMID:24991277

Lai, Zeng-Wei; Yang, Rong-Fei; Ye, Ke-Yin

2014-01-01

51

Enantioselective fluorination mediated by N-fluoroammonium salts of cinchona alkaloids: first enantioselective synthesis of BMS-204352 (MaxiPost).  

PubMed

We have employed a cinchona alkaloid/Selectfluor-mediated enantioselective fluorination of the oxindole 2 to achieve the first enantioslective synthesis of BMS-204352 (MaxiPost, S-1), an effective opener of maxi-K channels. Fluorination occurred to produce S-1 with 84% ee using the bis-cinchona alkaloid (DHQ)(2)AQN. Recrystallization produced enantiomerically pure (>99% ee) product. Quinidine-mediated fluorination of 2 gave the (R)-antipode of 1 with 68% ee. PMID:12636425

Shibata, Norio; Ishimaru, Takehisa; Suzuki, Emiko; Kirk, Kenneth L

2003-03-21

52

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A  

PubMed Central

Summary A concise enantioselective synthesis of the advanced intermediate 5 for the synthesis of pumiliotoxins (Gallagher’s intermediate) is described. The synthesis started from the regio- and trans-diastereoselective (dr = 98:2) reductive 3-butenylation of (R)-3-(tert-butyldimethylsilyloxy)glutarimide 14. After O-desilylation and Dess–Martin oxidation, the resulting keto-lactam 10 was subjected to a highly trans-stereoselective addition of the methylmagnesium iodide to give carbinol 11 as sole diastereomer. An efficient ring closure procedure consisting of ozonolysis and reductive dehydroxylation provided the indolizidine derivative 5, which completed the formal enantioselective total synthesis of pumiliotoxins 251D and 237A. PMID:24367400

Zhang, Jie

2013-01-01

53

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

54

Enantioselective total synthesis of (-)-nardoaristolone B via a gold(I)-catalyzed oxidative cyclization.  

PubMed

The first enantioselective total synthesis of (-)-nardoaristolone B is accomplished by the implementation of an enantio- and diastereoselective copper(I)-catalyzed conjugate addition/enolate trapping sequence and a gold(I)-catalyzed oxidative cyclization (intermolecular oxidant), employed for the first time in total synthesis. PMID:25563976

Homs, Anna; Muratore, Michael E; Echavarren, Antonio M

2015-02-01

55

Enantioselective Total Synthesis of (?)-Nardoaristolone B via a Gold(I)-Catalyzed Oxidative Cyclization  

PubMed Central

The first enantioselective total synthesis of (?)-nardoaristolone B is accomplished by the implementation of an enantio- and diastereoselective copper(I)-catalyzed conjugate addition/enolate trapping sequence and a gold(I)-catalyzed oxidative cyclization (intermolecular oxidant), employed for the first time in total synthesis. PMID:25563976

2015-01-01

56

Enantioselective Synthesis of cis-Fused Cyclooctanoids via Rhodium(I)-Catalyzed [4 + 2 + 2] Cycloadditions.  

PubMed

Catalytic multicomponent [m + n + o]-type cycloadditions offer efficient, atom-economical routes to diverse complex carbocycles. Recently, such transformations have emerged as unique strategies for medium ring carbocycle synthesis. Despite the important developments in this area, however, highly enantioselective [m + n + o]-type processes accessing medium ring carbocycles have yet to be developed. Herein, a rhodium-catalyzed [4 + 2 + 2] cycloaddition of allenedienes with allenes enabling the direct stereoselective synthesis of cis-fused cyclooctanoids is reported. These cycloadditions are successful with a diverse range of ?-components and demonstrate the potential for high levels of enantioselectivity in a [4 + 2 + 2] process. PMID:25692664

Lainhart, Brendan C; Alexanian, Erik J

2015-03-01

57

Enantioselective organocatalytic construction of hexahydropyrroloindole by means of ?-alkylation of aldehydes leading to the total synthesis of (+)-gliocladin C.  

PubMed

12-step program: The combined use of cinchona alkaloid based amine and chiral phosphoric acid enabled the asymmetric alkylation reaction of 3-hydroxyoxindoles with aldehydes to give 3,3'-disubstituted oxindoles in excellent enantioselectivities, which allows for the enantioselective total synthesis of (+)-gliocladin?C in 12?steps from 3-hydroxyoxindole with 19?% overall yield (see scheme; PMB = para-methoxybenzyl). PMID:23401076

Song, Jin; Guo, Chang; Adele, Arafate; Yin, Hao; Gong, Liu-Zhu

2013-03-01

58

Synthetic studies on borrelidin: enantioselective synthesis of the C1-C12 fragment.  

PubMed

[structure: see text] An efficient, enantioselective synthesis of the C1-C12 fragment 2 of borrelidin is presented. Construction of the "skipped" polymethylene chain of 2 was accomplished by iteration of Myers' alkylation, while formation of the C3 stereocenter was achieved by Roush's asymmetric allylboration methodology. PMID:12735735

Vong, Binh G; Abraham, Sunny; Xiang, Alan X; Theodorakis, Emmanuel A

2003-05-15

59

A Green, Enantioselective Synthesis of Warfarin for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

The enantioselective synthesis of drugs is of fundamental importance in the pharmaceutical industry. In this experiment, students synthesize either enantiomer of warfarin, a widely used anticoagulant, in a single step from inexpensive starting materials. Stereoselectivity is induced by a commercial organocatalyst, ("R","R")- or…

Wong, Terence C.; Sultana, Camille M.; Vosburg, David A.

2010-01-01

60

Synthesis of ?-amino acid derivatives and peptides via enantioselective addition of masked acyl cyanides to imines.  

PubMed

A general, asymmetric synthesis of amino acid derivatives is reported. Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective additions to N-Boc-aldimines. The reactions are catalyzed by a modified cinchona alkaloid, which can function as a bifunctional, hydrogen bonding catalyst, and afford adducts in excellent yields (90-98%) and high enantioselectivities (up to 97.5:2.5 er). Unmasking the addition products gives acyl cyanide intermediates that are intercepted by a variety of nucleophiles to afford ?-amino acid derivatives. Notably, the methodology provides an alternative method for peptide bond formation. PMID:25366558

Yang, Kin S; Rawal, Viresh H

2014-11-19

61

Rhodium catalysed conjugate addition of a chiral alkenyltrifluoroborate salt: the enantioselective synthesis of hermitamides A and B.  

PubMed

The concise enantioselective synthesis of hermitamides A and B is presented utilising a rhodium catalysed conjugate addition reaction to introduce the side chain and chiral information in a single step via an alkenyltrifluoroborate salt. PMID:19005593

Frost, Christopher G; Penrose, Stephen D; Gleave, Robert

2008-12-01

62

Enantioselective total synthesis of the potent antitumor agent (-)-mucocin using a temporary silicon-tethered ring-closing metathesis cross-coupling reaction.  

PubMed

The enantioselective total synthesis of the annonaceous acetogenin (-)-mucocin (1) was accomplished using a triply convergent 12-step sequence (longest linear sequence) in 13.6% overall yield. This represents the first application of the temporary silicon-tethered (TST) ring-closing metathesis (RCM) cross-coupling reaction and the enantioselective alkyne/aldehyde addition to the synthesis of a complex annonaceous acetogenin. Moreover, all three fragments required for the coupling reactions are conveniently prepared in 5-6 steps from two readily available enantiomerically enriched epoxides. Finally, this synthesis stimulated the development of a new approach for the construction of 3-hydroxy-2,6-disubstituted tetrahydropyrans, using the bismuth tribromide-mediated reductive etherification reaction, which represents a motif that is prevalent in a wide range of pharmacologically significant natural products. PMID:14640634

Evans, P Andrew; Cui, Jian; Gharpure, Santosh J; Polosukhin, Alexei; Zhang, Hai-Ren

2003-12-01

63

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

64

A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines  

PubMed Central

Summary A continuous-flow asymmetric organocatalytic photocyclization–transfer hydrogenation cascade reaction has been developed. The new protocol allows the synthesis of tetrahydroquinolines from readily available 2-aminochalcones using a combination of photochemistry and asymmetric Brønsted acid catalysis. The photocylization and subsequent reduction was performed with catalytic amount of chiral BINOL derived phosphoric acid diester and Hantzsch dihydropyridine as hydrogen source providing the desired products in good yields and with excellent enantioselectivities. PMID:24367413

2013-01-01

65

Enantioselective total synthesis of (?)-pseudophrynaminol through tandem olefination, isomerization and asymmetric Claisen rearrangement  

Microsoft Academic Search

A new and efficient total synthesis of (?)-pseudophrynaminol, the pyrrolo[2,3-b]indole alkaloid bearing the allylic moiety at the 3a-position, has been achieved by a sequence involving 3-allylindol-2-one 8 as a key intermediate. The enantioselective construction of the quaternary carbon in 8 was performed through a tandem cascade reaction of 2-allyloxyindolin-3-one 4, olefination, isomerization, and asymmetric Claisen rearrangement.

Tomomi Kawasaki; Atsuyo Ogawa; Yasuyuki Takashima; Masanori Sakamoto

2003-01-01

66

Catalytic chemo-, regio-, and enantioselective bromochlorination of allylic alcohols.  

PubMed

Herein we describe a highly chemo-, regio-, and enantioselective bromochlorination reaction of allylic alcohols, employing readily available halogen sources and a simple Schiff base as the chiral catalyst. The application of this interhalogenation reaction to a variety of substrates, the rapid enantioselective synthesis of a bromochlorinated natural product, and preliminary extension of this chemistry to dibromination and dichlorination are reported. PMID:25738419

Hu, Dennis X; Seidl, Frederick J; Bucher, Cyril; Burns, Noah Z

2015-03-25

67

H8-BINOL chiral imidodiphosphoric acids catalyzed enantioselective synthesis of dihydroindolo-/-pyrrolo[1,2-a]quinoxalines.  

PubMed

The first enantioselective synthesis of 5,6-dihydroindolo[1,2-a]quinoxalines is achieved by using a newly developed H8-BINOL-type imidodiphosphoric acid catalyst with low catalyst loading through efficient Pictet-Spengler-type reactions of indolyl anilines with ketones. This methodology also generates phenyl-4,5-dihydropyrrolo[1,2-a]quinoxalines with high yields and excellent enantioselectivities. Moreover, this method was utilized to synthesize an HIV-1 inhibitor with high yield and good enantioselectivity through a one-step procedure. PMID:25415871

Fan, Yan-Sen; Jiang, Yi-Jun; An, Dong; Sha, Di; Antilla, Jon C; Zhang, Suoqin

2014-12-01

68

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

69

Catalytic aerobic oxidation and tandem enantioselective cycloaddition in cascade multicomponent synthesis.  

PubMed

An efficient multicomponent cascade transformation for the highly diastereo- and enantioselective synthesis of complex natural product inspired polycyclic products from simple starting materials is described. The cascade is initiated by copper-catalyzed aerobic C?H oxidation of cyclopentadiene to cyclopentadienone followed by double catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The cascade synthesis efficiently yields structurally complex 5,5,5-tricyclic products with eight stereocenters with good yields and excellent diastereo- and enantiocontrol using one catalyst. PMID:25676025

Potowski, Marco; Merten, Christian; Antonchick, Andrey P; Waldmann, Herbert

2015-03-23

70

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

71

A General, Enantioselective Synthesis of 1-Azabicyclo[m.n.0]alkane Ring Systems  

PubMed Central

In this Letter, we describe a novel approach for the general and enantioselective synthesis of a diverse array of small to large 1-azabicyclo[m.n.0]alkyl ring systems with an embedded olefin handle for further functionalization. The stereochemistry is established via a highly diastereoselective indium-mediated allylation of an Ellman sulfinimine in greater than 9:1 dr., which is readily separable by column chromatography to afford a single diastereomer. This methodology allows for the rapid preparation of 1-azabicyclo[m.n.0]alkane ring systems that are not readily accessible through any other chemistry in excellent overall yields and, for many systems, the only enantioselective preparation reported to date. PMID:23459400

Senter, Timothy J.; Schulte, Michael L.; Konkol, Leah C.; Wadzinski, Tyler E.; Lindsley, Craig W.

2013-01-01

72

Enantioselective synthesis of both (+)- and (?)-derivatives of bicyclo[4.3.0]nonan-8-one and -3,8-diones from R-carvone  

Microsoft Academic Search

Enantioselective synthesis of both the enantiomeric forms of the hydrindane derivatives mentioned in the title, potential chiral precursors in terpenoid synthesis, starting from R-carvone employing two different cyclopentannulation methodologies is described.

Adusumilli Srikrishna; T. Jagadeeswar Reddy; Sankuratri Nagaraju

1996-01-01

73

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

PubMed Central

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

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

2009-01-01

74

Enantioselective synthesis of indoloquinolizidines via asymmetric catalytic hydrogenation/lactamization of imino diesters.  

PubMed

We have developed a highly efficient cascade sequence for asymmetric synthesis of indoloquinolizidines with absolute control of cis-H2/H12b relative geometry in good to excellent yields and excellent enantioselectivities. This cascade was triggered by the Ru(II)-TsDPEN-catalyzed asymmetric transfer hydrogenation of imino diesters, with subsequent spontaneous lactamization with discrimination between the two diastereotopic 2-alkoxy-2-oxoethyl groups. The synthetic utility of this strategy was demonstrated by the asymmetric preparation of dihydrocorynantheol, geissoschizol, and isogeissoschizol. PMID:24195678

Liu, Yong; Wang, Qun; Zhang, Ying; Huang, Jianbiao; Nie, Linlin; Chen, Jie; Cao, Weiguo; Wu, Xiaoyu

2013-12-01

75

Facile and highly enantioselective synthesis of (+)- and (-)-fluvastatin and their analogues.  

PubMed

A highly enantioselective synthesis of (+)- and (-)-fluvastatin and their analogues has been facilitated by the reaction of an aldehyde with diketene in the presence of Ti(O-i-Pr)4 and a chiral Schiff base ligand. Either enantiomer of the Schiff base could be employed to obtain (+)- or (-)-fluvastatin. Diastereoselective reductions of the resultant keto moiety of ?-hydroxy ketoesters provided the syn-1,3-diol esters (91% ee), which were subsequently recrystallized and saponified to afford (+)- and (-)-fluvastatin in >99.9% ee. PMID:20939538

Zacharia, James T; Tanaka, Takanori; Hayashi, Masahiko

2010-11-19

76

Enantioselective Total Synthesis of (?)-Citrinadin A and Revision of its Stereochemical Structure  

PubMed Central

The first enantioselective total synthesis of (?)-citrinadin A has been accomplished in 20 steps from commercially available materials via an approach that minimizes refunctionalization and protection/deprotection operations. The cornerstone of this synthesis features an asymmetric vinylogous Mannich addition of a dienolate to a chiral pyridinium salt to set the initial chiral center. A sequence of substrate-controlled reactions, including a highly stereoselective epoxidation/ring opening sequence and an oxidative rearrangement of an indole to furnish a spirooxindole, are then used to establish the remaining stereocenters in the pentacyclic core of (?)-citrinadin A. The successful synthesis of citrinadin A led to a revision of the stereochemical structure of the core substructure of the citrinadins. PMID:23837457

Bian, Zhiguo; Marvin, Christopher C.; Martin, Stephen F.

2013-01-01

77

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

78

A General, Highly Enantioselective Method for the Synthesis of D and L r-Amino Acids and Allylic Amines  

E-print Network

A General, Highly Enantioselective Method for the Synthesis of D and L r-Amino Acids and Allylic of amino acids is a subject of intense interest in the field of asymmetric catalysis. Traditionally. In this paper, we report on a different approach to amino acids based on an expeditious route to enantiopure

Walsh, Patrick J.

79

Enantioselective Total Synthesis of (?)-Minovincine in Nine Chemical Steps: An Approach to Ketone Activation in Cascade Catalysis  

PubMed Central

More cycling–fewer steps The first enantioselective total synthesis of (?)-minovincine has been accomplished in nine chemical steps and 13% overall yield. A novel, one-step Diels–Alder/?-elimination/conjugate addition organocascade sequence allowed rapid access to the central tetracyclic core in an asymmetric manner. PMID:24000234

Laforteza, Brian N.; Pickworth, Mark

2014-01-01

80

Bifunctional thiourea-catalyzed enantioselective double Michael reaction of ?,?-unsaturated ?-ketoester to nitroalkene: asymmetric synthesis of (?)-epibatidine  

Microsoft Academic Search

The asymmetric synthesis of 4-nitrocyclohexanone derivatives has been accomplished by enantioselective double Michael additions of ?,?-unsaturated ?-ketoesters to nitroalkenes using a catalytic amount of bifunctional thiourea and TMG. The three contiguous stereogenic centers of the obtained products were constructed with good to high diastereoselectivity and up to 92% ee. The biologically active natural product, (?)-epibatidine, has been synthesized from the

Yasutaka Hoashi; Takaya Yabuta; Yoshiji Takemoto

2004-01-01

81

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

PubMed Central

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

2011-01-01

82

Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of C7-functionalized indoles.  

PubMed

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

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

2015-02-16

83

Enantioselective synthesis of (S)-ibuprofen ester prodrug in cyclohexane by Candida rugosa lipase immobilized on Accurel MP1000.  

PubMed

An enantioselective esterification process was developed for the synthesis of 2-N-morpholinoethyl (S)-ibuprofen ester prodrug from racemic ibuprofen by using Candida rugosa lipase immobilized on Accurel MP1000 in cyclohexane. Compared with the performance of Lipase MY, the immobilized lipase possesses a higher enzyme activity and thermal stability, but with a slightly suppressed enantioselectivity. A kinetic model was proposed and confirmed from experiments, for the simulation of time-course conversions of both enantiomers at various combinations of substrate concentrations in a batch reactor. Preliminary results of employing the proposed model and the immobilized lipase in a continuous packed-bed reactor were also reported and discussed. PMID:11101325

Chen, J C; Tsai, S W

2000-01-01

84

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

85

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

PubMed

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

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

2014-12-22

86

Highly enantioselective synthesis and cellular evaluation of spirooxindoles inspired by natural products  

NASA Astrophysics Data System (ADS)

In biology-oriented synthesis the underlying scaffold classes of natural products selected in evolution are used to define biologically relevant starting points in chemical structure space for the synthesis of compound collections with focused structural diversity. Here we describe a highly enantioselective synthesis of natural-product-inspired 3,3'-pyrrolidinyl spirooxindoles-which contain an all-carbon quaternary centre and three tertiary stereocentres. This synthesis takes place by means of an asymmetric Lewis acid-catalysed 1,3-dipolar cycloaddition of an azomethine ylide to a substituted 3-methylene-2-oxindole using 1-3 mol% of a chiral catalyst formed from a N,P-ferrocenyl ligand and CuPF6(CH3CN)4. Cellular evaluation has identified a molecule that arrests mitosis, induces multiple microtubule organizing centres and multipolar spindles, causes chromosome congression defects during mitosis and inhibits tubulin regrowth in cells. Our findings support the concept that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry will be a rich source of compounds with diverse bioactivity.

Antonchick, Andrey P.; Gerding-Reimers, Claas; Catarinella, Mario; Schürmann, Markus; Preut, Hans; Ziegler, Slava; Rauh, Daniel; Waldmann, Herbert

2010-09-01

87

Direct, Enantioselective Synthesis of Pyrroloindolines and Indolines From Simple Indole Derivatives  

PubMed Central

The (R)-BINOL•SnCl4-catalyzed formal (3 + 2) cycloaddition between 3-substituted indoles and benzyl 2-trifluoroacetamidoacrylate is a direct, enantioselective method to prepare pyrroloindolines from simple starting materials. However, under the originally disclosed conditions, the pyrroloindolines are formed as mixtures of diastereomers, typically in the range of 3:1 to 5:1 favoring the exo-product. The poor diastereoselectivity detracts from the synthetic utility of the reaction. We report here that use of methyl 2-trifluoroacetamidoacrylate in conjunction with (R)-3,3'-dichloro-BINOL•SnCl4 provides the corresponding pyrroloindolines with improved diastereoselectivity (typically ?10:1). Guided by mechanistic studies, a one-flask synthesis of enantioenriched indolines by in situ reduction of a persistent iminium ion is also described. PMID:24039305

Ni, Jane; Wang, Haoxuan; Reisman, Sarah E.

2013-01-01

88

?-Hydroxy-?-lactones as nucleophiles in the Nicholas reaction for the synthesis of oxepene rings. Enantioselective formal synthesis of (-)-isolaurepinnacin and (+)-rogioloxepane A.  

PubMed

The enantioselective formal synthesis of (-)-isolaurepinnacin and (+)-rogioloxepane A has been achieved. The key steps are an intermolecular Nicholas reaction with a ?-hydroxy-?-lactone as the nucleophile, to form branched linear ethers, and an olefin ring-closing metathesis to obtain the oxepene core. PMID:24573686

Rodríguez-López, Julio; Ortega, Nuria; Martín, Victor S; Martín, Tomás

2014-04-11

89

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

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

90

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

91

Enantioselective Synthesis of Tryptophan Derivatives by a Tandem Friedel – Crafts Conjugate Addition/Asymmetric Protonation Reaction  

PubMed Central

The tandem Friedel–Crafts conjugate addition/asymmetric protonation reaction between 2-substituted indoles and methyl 2-acetamidoacrylate is reported. The reaction is catalyzed by (R)-3,3?-dibromo-BINOL in the presence of stoichiometric SnCl4, and is the first example of a tandem conjugate addition/asymmetric protonation reaction using a BINOL•SnCl4 complex as the catalyst. A range of indoles furnished synthetic tryptophan derivatives in good yields and high levels of enantioselectivity, even on preparative scale. The convergent nature of this transformation should lend itself to the preparation of unnatural tryptophan derivatives for use in a broad array of synthetic and biological applications. PMID:22390403

Kieffer, Madeleine E.; Repka, Lindsay M.; Reisman, Sarah E.

2012-01-01

92

Enantioselective template-directed [2+2] photocycloadditions of isoquinolones: scope, mechanism and synthetic applications.  

PubMed

A strategy for the enantioselective [2+2] photocycloaddition of isoquinolones with alkenes is presented, in which the formation of a supramolecular complex between a chiral template and the substrate ensures high enantioface differentiation by shielding one face of the substrate. Fifteen different electron-deficient alkenes and ten different substituted isoquinolones undergo efficient photocycloaddition, yielding the cyclobutane products in excellent yields and with outstanding regio-, diastereo- and enantioselectivities (up to 99?%?ee). The mechanism of the reaction is investigated by means of triplet sensitization/quenching and radical clock experiments, the results of which are consistent with the involvement of a triplet excited state and a 1,4-biradical intermediate. The variety of functionalized cyclobutanes obtained using this approach can be further increased by straightforward synthetic transformations of the photoadducts, allowing rapid access to libraries of compounds for various applications. PMID:25784615

Coote, Susannah C; Pöthig, Alexander; Bach, Thorsten

2015-04-27

93

Synthetic studies toward palau򡭩ne and enantioselective total synthesis of biogenetically related (+)-phakellin and (+)-monobromophakellin  

E-print Network

NITROGEN PROTECTING GROUP ? TOSYLVINYL (TSV) AND ITS APPLICATION IN PALAU?AMINE/AXINELLAMINE SYNTHESIS ............................ 19 A. Background ............................................................................... 19 B. Design... of an Electronically Switchable Protecting Group........ 23 C. Synthesis of Tsv-protected Diene.............................................. 25 D. The Diels-Alder Reaction and Tsv Reduction .......................... 27 E. Conclusion...

Wang, Shaohui

2009-05-15

94

Enantioselective synthesis of R-(?)-ligularenolide and the progesterone receptor ligand R-(?)PF1092C starting from S-(+)-carvone  

Microsoft Academic Search

A new enantioselective synthesis of eremophilane sesquiterpenes was developed starting from S-(+)-carvone 3, using a conjugate addition-annelation sequence. The synthesis of R-(?)-ligularenolide 1 was accomplished in a staightforward manner with the annelation of the lactone as the last step. For the synthesis of the progesterone receptor ligand R-(?)-PF1092C 2 a different strategy was followed in which first the lactone was

Louis H. D. Jenniskens; Aede de Groot

1998-01-01

95

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

96

Enantioselective synthesis of 3-substituted 1,2-oxazinanes via organocatalytic intramolecular aza-Michael addition.  

PubMed

A highly enantioselective intramolecular 6-exo-trig aza-Michael addition was developed to afford chiral 3-substituted 1,2-oxazinanes in high yields (up to 99% yield) and good enantioselectivities (up to 98/2 er). These reactions were enabled by a quinine-derived primary-tertiary diamine as a catalyst and pentafluoropropionic acid (PFP) as a co-catalyst. PMID:25272305

Cheng, Shuanghua; Yu, Shouyun

2014-11-21

97

Enantioselective synthesis of BMS-204352 (MaxiPost) using N-fluoroammonium salts of cinchona alkaloids (F-CA-BF4).  

PubMed

The enantioselective synthesis of a potent Maxi-K potassium channel opener (BMS-204352) mediated by N-fluoroammonium salts of cinchona alkaloids is described. Two synthetic pathways were evaluated. An ee as high as 88% was achieved (>99% after a single recrystallisation). PMID:12945759

Zoute, Ludivine; Audouard, Christophe; Plaquevent, Jean-Christophe; Cahard, Dominique

2003-06-01

98

Organocatalytic Enantioselective 1,3-Dipolar Cycloadditions between Seyferth-Gilbert Reagent and Isatylidene Malononitriles: Synthesis of Chiral Spiro-phosphonylpyrazoline-oxindoles.  

PubMed

A new method has been developed for the catalytic enantioselective 1,3-dipolar cycloaddition of the Seyferth-Gilbert reagent (SGR) to isatylidene malononitriles using a cinchona alkaloid derivative as a catalyst. This method allowed for the synthesis of a series of chiral spiro-phosphonylpyrazoline-oxindoles in good yields with excellent enantioselectivities. The synthetic utility of this method was further demonstrated by its use in a three-component domino reaction involving isatin, malononitrile, and SGR based on sequential Knoevenagel condensation and 1,3-dipolar cycloaddition reactions. PMID:25710384

Du, Taiping; Du, Fei; Ning, Yanqiang; Peng, Yungui

2015-03-01

99

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

100

The first enantioselective synthesis of imino-deoxydigitoxose and protected imino-digitoxose by using l-threonine aldolase-catalyzed aldol condensation  

Microsoft Academic Search

The first enantioselective synthesis of protected imino-digitoxose (?)-16 was attained starting with a synthetic intermediate of polyoxin C prepared by the l-threonine aldolase-catalyzed aldol condensation of (2S,3S)-2,3-O-isopropyriden-4-penten-1-al 8 and glycine. The strategy took advantage of an intramolecular nucleophilic attack by a Cbz-protected amino group on the hemiacetal carbon, a side reaction in the synthesis of natural products, for the formation

Toshihiro Nishiyama; Tetsuya Kajimoto; Swapnil S. Mohile; Noboru Hayama; Teppei Otsuda; Minoru Ozeki; Manabu Node

2009-01-01

101

Enantioselective synthesis of epoxides by alpha-deprotonation--electrophile trapping of achiral epoxides.  

PubMed

Enantioselective alpha-deprotonation of achiral epoxides 1, 21, and 26 using organolithiums in the presence of (-)-sparteine 2 and subsequent electrophile trapping gives access to enantioenriched trisubstituted epoxides 9-17, 22, 23, 27 and 28 (in up to 86% ee). PMID:14685333

Hodgson, David M; Buxton, Timothy J; Cameron, Iain D; Gras, Emmanuel; Kirton, Eirene H M

2003-12-01

102

Facile synthesis of magnetic homochiral metal-organic frameworks for "enantioselective fishing".  

PubMed

Magnetic functionalized homochiral metal-organic frameworks (MOFs) were prepared and applied to efficient enantioselective fishing of chiral drug intermediates. Under optimized conditions, the enantiomeric excess (ee) value as high as 85.2% was achieved for methyl phenyl sulfoxide (MPS) within 3 min. PMID:25634544

Chang, Cui-Lan; Qi, Xiao-Yue; Zhang, Jiang-Wei; Qiu, Ya-Ming; Li, Xian-Jiang; Wang, Xin; Bai, Yu; Sun, Jun-Liang; Liu, Hu-Wei

2015-02-12

103

Enantioselective Synthesis of Functionalized Pyrazoles by NHC-Catalyzed Reaction of Pyrazolones with ?,?-Unsaturated Aldehydes.  

PubMed

The N-heterocyclic carbene (NHC)-organocatalyzed enantioselective annulation reaction of pyrazolones with ?,?-unsaturated aldehydes proceeding via the chiral ?,?-unsaturated acyl azolium intermediates under oxidative conditions is presented. The reaction afforded dihydropyranone-fused pyrazoles in moderate to good yields and good er values under operationally simple and base-free conditions. PMID:25723547

Yetra, Santhivardhana Reddy; Mondal, Santigopal; Suresh, Eringathodi; Biju, Akkattu T

2015-03-20

104

Synthesis of chiral triazine coupling reagents based on esters of N-alkylproline and their application in the enantioselective incorporation of D or L amino acid residue directly from racemic substrate.  

PubMed

Esters of N-methylproline and N-allylproline were prepared and used as component for synthesis of chiral triazine based coupling reagents. N-Triazinylammonium tetrafluoroborate obtained from methylester of L-N-methylproline, 2-chloro-4,6-dimethozxy-1,3,5-triazine and tetrafluoroboric acid in the coupling of rac-Z- A1a-OH with glycine methylester preferred formation of D-Z-AlaGly-OMe with L/D ratio 21/79. Coupling reagent prepared from D enantiomer of N-methylproline gave L-Z-AlaGly-OMe with L/D ratio 75/25. PMID:25745772

Kasperowicz-Frankowska, Katarzyna; Gzik, Anna; Dziemidkiewicz, Micha?; Kolesi?ska, Beata; Kami?ski, Zbigniew J

2014-01-01

105

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

106

Enantioselective synthesis of (S)-2-cyano-2-methylpentanoic acid by nitrilase.  

PubMed

The nitrilase gene of Rhodococcus rhodochrous J1 was expressed in Escherichia coli using the expression vector, pKK223-3. The recombinant E. coli JM109 cells hydrolyzed enantioselectively 2-methyl-2-propylmalononitrile to form (S)-2-cyano-2-methylpentanoic acid (CMPA) with 96 % e.e. Under optimized conditions, 80 g (S)-CMPA l(-1) was produced with a molar yield of 97 % at 30 °C after a 24 h without any by-products. PMID:23288294

Yoshida, Toyokazu; Mitsukura, Koichi; Mizutani, Takuya; Nakashima, Ryo; Shimizu, Yasuyo; Kawabata, Hiroshi; Nagasawa, Toru

2013-05-01

107

Catalytic enantioselective construction of quaternary stereocenters: assembly of key building blocks for the synthesis of biologically active molecules.  

PubMed

The ever-present demand for drugs with better efficacy and fewer side effects continually motivates scientists to explore the vast chemical space. Traditionally, medicinal chemists have focused much attention on achiral or so-called "flat" molecules. More recently, attention has shifted toward molecules with stereogenic centers since their three-dimensional structures represent a much larger fraction of the chemical space and have a number of superior properties compared with flat aromatic compounds. Quaternary stereocenters, in particular, add greatly to the three-dimensionality and novelty of the molecule. Nevertheless, synthetic challenges in building quaternary stereocenters have largely prevented their implementation in drug discovery. The lack of effective and broadly general methods for enantioselective formation of quaternary stereocenters in simple molecular scaffolds has prompted us to investigate new chemistry and develop innovative tools and solutions. In this Account, we describe three approaches to constructing quaternary stereocenters: nucleophilic substitution of 3-halooxindoles, conjugate addition of boronic acids to cyclic enones, and allylic alkylation of enolates. In the first approach, malonic ester nucleophiles attack electrophilic 3-halooxindoles, mediated by a copper(II)-bisoxazoline catalyst. A variety of oxindoles containing a benzylic quaternary stereocenter can be accessed through this method. However, it is only applicable to the specialized 3,3-disubstituted oxindole system. To access benzylic quaternary stereocenters in a more general context, we turned our attention to the enantioselective conjugate addition of carbon nucleophiles to ?,?-unsaturated carbonyl acceptors. We discovered that in the presence of catalytic palladium-pyridinooxazoline complex, arylboronic acids add smoothly to ?-substituted cyclic enones to furnish ketones with a ?-benzylic quaternary stereocenter in high yields and enantioselectivities. The reaction is compatible with a wide range of arylboronic acids, ?-substituents, and ring sizes. Aside from benzylic quaternary stereocenters, a more challenging motif is a quaternary stereocenter not adjacent to an aromatic group. Such centers represent more general structures in chemical space but are more difficult to form by asymmetric catalysis. To address this greater challenge, and motivated by the greater reward, we entered the field of palladium-catalyzed asymmetric allylic alkylation of prochiral enolate nucleophiles about a decade ago. On the basis of Tsuji's work, which solved the issue of positional selectivity for unsymmetrical ketones, we discovered that the phosphinooxazoline ligand effectively rendered this reaction enantioselective. Extensive investigations since then have revealed that the reaction exhibits broad scope and accepts a range of substrate classes, each with its unique advantage in synthetic applications. A diverse array of carbonyl compounds bearing ?-quaternary stereocenters are obtained in excellent yields and enantioselectivities, and more possibilities have yet to be explored. As an alternative to palladium catalysis, we also studied iridium-catalyzed asymmetric allylic alkylations that generate vicinal quaternary and tertiary stereocenters in a single transformation. Overall, these methods provide access to small molecule building blocks with a single quaternary stereocenter, can be applied to various molecular scaffolds, and tolerate a wide range of functional groups. We envision that the chemistry reported in this Account will be increasingly useful in drug discovery and design. PMID:25715056

Liu, Yiyang; Han, Seo-Jung; Liu, Wen-Bo; Stoltz, Brian M

2015-03-17

108

Unprecedented 8,9'-neolignans: enantioselective synthesis of possible stereoisomers for structural determination.  

PubMed

(+)-Wutaienin (3) and its C-7 methyl ether (4), isolated from Zanthoxylum wutaiense, were found to be unprecedented 8,9'-neolignans containing an (S)-2-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydrobenzofuran skeleton. Wutaienin (3) was present in the plant as an inseparable 1:1 mixture of the (7,8)-syn-diastereoisomers. The diastereoisomeric mixture was characterized by comparison with four possible diastereoisomers, which were enantioselectively synthesized from (S)-5-bromo-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydrobenzofuran using Evans' oxazolidinone-assisted asymmetric aldol condensation to install the chiral centers at the C-7 and C-8 positions. PMID:25427159

Takahashi, Masato; Suzuki, Noriyuki; Ishikawa, Tsutomu; Huang, Hung-Yi; Chang, Hsun-Shuo; Chen, Ih-Sheng

2014-12-26

109

Enantioselective synthesis of ( S)-?-methylphenylalanine using ( S)-BINOLAMs as new phase-transfer catalysts  

Microsoft Academic Search

A series of (S)-bis(aminomethyl)binaphthols [(S)-BINOLAMs] 4 have been prepared and used as catalysts in the enantioselective C-alkylation reaction of the aldimine Schiff bases of alanine esters 5 under solid–liquid phase-transfer catalysis (PTC) conditions employing NaOH as base in toluene at room temperature. (S)-3,3?-Bis[(diethylamino)methyl]-2,2?-dihydroxy-1,1?-binaphthalene 4a gave the best e.e.s. (S)-?-Methylphenylalanine 7 was isolated, after hydrolysis of the iminoester, in 85% yield

Jesús Casas; Carmen Nájera; José M. Sansano; José González; José M. Saá; Manuel Vega

2001-01-01

110

(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

111

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

112

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

113

Enantioselective synthesis of macrocyclic heterobiaryl derivatives of molecular asymmetry by molybdenum-catalyzed asymmetric ring-closing metathesis.  

PubMed

Winding vine-shaped molecular asymmetry is induced by enantioselective ring-closing metathesis with a chiral molybdenum catalyst. The reaction proceeds under mild conditions through an E-selective ring-closing metathesis leading to macrocyclic bisazoles with enantioselectivities of up to 96?% ee. PMID:25706779

Okayama, Yoichi; Tsuji, Satoru; Toyomori, Yuka; Mori, Atsunori; Arae, Sachie; Wu, Wei-Yi; Takahashi, Tamotsu; Ogasawara, Masamichi

2015-04-13

114

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

115

Regio- and Enantioselective Catalytic Monoepoxidation of Conjugated Dienes: Synthesis of Chiral Allylic cis-Epoxides.  

PubMed

Ti(IV)-salan 4 catalyzes the diastereo- and enantioselective monoepoxidation of conjugated dienes using 30% H2O2 at rt or below even in the presence of other olefins and adjacent stereocenters. Its enantiomer, ent-4, provides access to the opposite diastereomer or enantiomer. The resultant chiral allylic epoxides, and the triols derived from them, are versatile synthetic intermediates as well as substructures present in many bioactive natural products. The epoxidation is highly specific for Z-olefins. For 1-acyl(silyl)oxypenta-2,4-dienes, epoxidation of the distal olefin is generally favored in contrast to the adjacent regioselectivity characteristic of Sharpless, peracid, and other directed epoxidations of hydroxylated dienes. PMID:25668127

Jat, Jawahar L; De, Saroj Ranjan; Kumar, Ganesh; Adebesin, Adeniyi Michael; Gandham, Shyam K; Falck, John R

2015-02-20

116

Kinetic investigation of a solvent-free, chemoenzymatic reaction sequence towards enantioselective synthesis of a ?-amino acid ester.  

PubMed

A solvent-free, chemoenzymatic reaction sequence for the enantioselective synthesis of ?-amino acid esters has been kinetically and thermodynamically characterized. The coupled sequence comprises a thermal aza-Michael addition of cheap starting materials and a lipase catalyzed aminolysis for the kinetic resolution of the racemic ester. Excellent ee values of >99% were obtained for the ?-amino acid ester at 60% conversion. Kinetic constants for the aza-Michael addition were obtained by straightforward numerical integration of second-order rate equations and nonlinear fitting of the progress curves. A different strategy had to be devised for the biocatalytic reaction. Initially, a simplified Michaelis-Menten model including product inhibition was developed for the reaction running in THF as an organic solvent. Activity based parameters were used instead of concentrations in order to facilitate the transfer of the kinetic model to the solvent-free system. Observed solvent effects not accounted for by the use of thermodynamic activities were incorporated into the kinetic model. Enzyme deactivation was observed to depend on the ratio of the applied substrates and also included in the kinetic model. The developed simple model is in very good agreement with the experimental data and allows the simulation and optimization of the solvent-free process. PMID:22275046

Strompen, Simon; Weiss, Markus; Ingram, Thomas; Smirnova, Irina; Gröger, Harald; Hilterhaus, Lutz; Liese, Andreas

2012-06-01

117

Enantioselective synthesis of chiral isotopomers of 1-alkanols by a ZACA-Cu-catalyzed cross-coupling protocol.  

PubMed

Chiral compounds arising from the replacement of hydrogen atoms by deuterium are very important in organic chemistry and biochemistry. Some of these chiral compounds have a non-measurable specific rotation, owing to very small differences between the isotopomeric groups, and exhibit cryptochirality. This particular class of compounds is difficult to synthesize and characterize. Herein, we present a catalytic and highly enantioselective conversion of terminal alkenes to various ? and more remote chiral isotopomers of 1-alkanols, with ?99?% enantiomeric excess (ee), by the Zr-catalyzed asymmetric carboalumination of alkenes (ZACA) and Cu-catalyzed cross-coupling reactions. ZACA-in?situ iodinolysis of allyl alcohol and ZACA-in?situ oxidation of TBS-protected ?-alkene-1-ols protocols were applied to the synthesis of both (R)- and (S)-difunctional intermediates with 80-90?% ee. These intermediates were readily purified to provide enantiomerically pure (?99?% ee) compounds by lipase-catalyzed acetylation. These functionally rich intermediates serve as very useful synthons for the construction of various chiral isotopomers of 1-alkanols in excellent enantiomeric purity (?99?% ee) by introducing deuterium-labeled groups by Cu-catalyzed cross-coupling reactions without epimerization. PMID:25351794

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

2014-12-01

118

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

119

Stereoselective synthesis of multisubstituted alkenes via ring opening reactions of cyclopropenes. Enantioselective copper catalysed asymmetric reduction of alkenylheteroarenes.   

E-print Network

heterocycles are able to provide effective activation of an adjacent alkene for highly enantioselective catalytic conjugate reduction reactions. Extension of the general concept to other classes of heteroarenes has been proven successful. Further manipulation...

Wang, Yi

2010-01-01

120

Enantioselective cyclopolymerization of 1,5-hexadiene catalyzed by chiral zirconocenes: A novel strategy for the synthesis of optically active polymers with chirality in the main chain  

SciTech Connect

Enantioselective cyclopolymerization represents a novel strategy for the synthesis of optically active main-chain chiral polymers. Cyclopolymerization of 1,5-hexadiene using the optically active catalyst precursor, (R,R)-(EBTHI)ZrBINOL ((R,R)-1) [EBTHI = ethylene-1,2-bis([eta][sup 5]-4,5,6,7-tetrahydro-1-indenyl); BINOL = 1,1[prime]-bi-2-naphtholate], yields optically active poly(methylene-1,3-cyclopentane) (PMCP) with a molar optical rotation of [[Phi

Coates, G.W.; Waymouth, R.M. (Stanford Univ., CA (United States))

1993-01-13

121

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

122

Highly enantioselective fluorination of unprotected 3-substituted oxindoles: one-step synthesis of BMS 204352 (MaxiPost).  

PubMed

The catalytic enantioselective fluorination of N-H-free 3-substituted oxindoles was accomplished by a Sc(III)/N,N'-dioxide complex. Under mild reaction conditions, a series of 3-aryl- and 3-alkyl-3-fluoro-2-oxindoles were obtained in excellent yields (up to 98%) and enantioselectivities (up to 99% ee) by using N-fluorobisbenzenesulfonimide (NFSI) as the fluorination agent. MaxiPost was synthesized efficiently in 81% yield with 96% ee. PMID:23030737

Li, Jun; Cai, Yunfei; Chen, Weiliang; Liu, Xiaohua; Lin, Lili; Feng, Xiaoming

2012-10-19

123

Enantioselective synthesis of benzoindolizidine derivatives using chiral phase-transfer catalytic intramolecular domino aza-Michael addition/alkylation.  

PubMed

An efficient and enantioselective strategy to synthesize benzoindolizidines from ?,?-unsaturated amino ketones via domino intramolecular aza-Michael addition/alkylation was developed. These reactions were enabled by cinchona alkaloid-derived quaternary ammonium salts as the phase-transfer catalyst. A variety of benzoindolizidines were prepared in good yields (up to 93%) and enantioselectivities (up to 92.8:7.2 er). PMID:25428596

Guo, Jiajia; Yu, Shouyun

2015-01-28

124

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

125

Enantioselective Total Synthesis and Biological Evaluation of (+)-Kibdelone A and a Tetrahydroxanthone Analogue  

PubMed Central

The total synthesis of kibdelone A has been accomplished using In(III)-catalyzed arylation of a heterocyclic quinone monoketal and iodine-mediated oxidative photochemical electrocyclization for construction of the ABCD ring moiety. Enzymatic dihydroxylation of methyl 2-halobenzoate substrates was employed for synthesis of activated 2-halo-cyclohexene F-ring fragments. A one pot oxa-Michael-Friedel-Crafts process allowed access to the first simplified analogues of the kibdelones PMID:23834060

Winter, Dana K.; Endoma-Arias, Mary Ann; Hudlicky, Tomas; Beutler, John A.; Porco, John A.

2013-01-01

126

Enantioselective Organocatalytic Transfer Hydrogenation  

E-print Network

Enantioselective Organocatalytic Transfer Hydrogenation Reactions using Hantzsch Esters STÃ?PHANE G catalysis reactions involving electron-deficient imines and olefin substrates. Enantioselective LUMO, including the invention of iminium activation, has led to the discovery of many new enantioselective

MacMillan, David W. C.

127

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

128

Cloning, overexpression, and characterization of a high enantioselective nitrilase from Sphingomonas wittichii RW1 for asymmetric synthesis of (R)-phenylglycine.  

PubMed

In this study, a high (R)-enantioselective nitrilase gene from Sphingomonas wittichii RW1 was cloned and overexpressed in Escherichia coli BL21 (DE3). The recombinant nitrilase was purified to homogeneity with a molecular weight of 40 kDa. The pH and temperature optima were shown to be pH 8.0 and 40 °C, respectively. The purified nitrilase was most active toward succinonitrile, approximately 30-fold higher than that for phenylglycinonitrile. Using the E. coli BL21/ReSWRW1 whole cells as biocatalysts, the kinetic resolution for asymmetric synthesis of (R)-phenylglycine was investigated at pH 6.0. A yield of 46 % was obtained with 95 % enantiomeric excess (ee), which made it a promising biocatalyst for synthesis of (R)-phenylglycine. PMID:24664232

Qiu, Jian; Su, Er-Zheng; Wang, Hua-Lei; Cai, Wen-Wen; Wang, Wei; Wei, Dong-Zhi

2014-05-01

129

Pd-Catalyzed Asymmetric Intramolecular Aryl C-O Bond Formation with SDP(O) Ligand: Enantioselective Synthesis of (2,3-Dihydrobenzo[b][1,4]dioxin-2-yl)methanols.  

PubMed

Employing a chiral spirodiphosphine monoxide ligand with 1,1'-spirobiindane backbone (SDP(O)), a desymmetrization strategy of Pd-catalyzed intramolecular asymmetric aryl C-O coupling of 2-(2-halophenoxy)propane-1,3-diols, was developed. The SDP(O) ligand shows much better results than its SDP counterpart. The protocol provides an efficient and highly enantioselective method for the synthesis of 2-hydroxymethyl-1,4-benzodioxanes. Density functional theory studies provide a model that accounts for the origin of the enantioselectivity. PMID:25656954

Shi, Jialing; Wang, Ting; Huang, Yusha; Zhang, Xinhao; Wu, Yun-Dong; Cai, Qian

2015-02-20

130

Enantioselective Synthesis of Tetrahydroquinolines, Tetrahydroquinoxalines, and Tetrahydroisoquinolines via Pd-Catalyzed Alkene Carboamination Reactions.  

PubMed

A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE provides excellent results in Pd-catalyzed alkene carboamination reactions between aniline derivatives bearing pendant alkenes and aryl or alkenyl halides. These transformations generate tetrahydroquinolines and tetrahydroquinoxalines that contain quaternary carbon stereocenters with high levels of asymmetric induction. In addition this catalyst also effects the asymmetric synthesis of tetrahydroisoquinolines via related transformations of 2-allylbenzylamines. In contrast to most other approaches to the asymmetric synthesis of these compounds, which frequently involve functional group interconversion or a single C-C or C-N bond-forming event, the carboamination reactions generate both a C-N bond, a C-C bond, and a stereocenter. PMID:25431650

Hopkins, B A; Wolfe, J P

2014-12-01

131

Enantioselective Synthesis of ?-Aminosilanes by Copper-Catalyzed Hydroamination of Vinylsilanes**  

PubMed Central

The synthesis of ?-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEG-PHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhydroxylamines as the electrophilic nitrogen source. This hydroamination reaction is compatible with differentially substituted vinylsilanes, thus providing access to amino acid mimics and other valuable chiral organosilicon compounds. PMID:25475991

Niljianskul, Nootaree; Zhu, Shaolin; Buchwald, Stephen L.

2015-01-01

132

Enantioselective synthesis of ?-aminosilanes by copper-catalyzed hydroamination of vinylsilanes.  

PubMed

The synthesis of ?-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEGPHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhydroxylamines as the electrophilic nitrogen source. This hydroamination reaction is compatible with differentially substituted vinylsilanes, thus providing access to amino acid mimics and other valuable chiral organosilicon compounds. PMID:25475991

Niljianskul, Nootaree; Zhu, Shaolin; Buchwald, Stephen L

2015-01-26

133

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

PubMed

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

Olsson, Susanne; Lennartson, Anders; Håkansson, Mikael

2013-09-01

134

Application of cyclodextrin-modified gold nanoparticles in enantioselective monolith capillary electrochromatography.  

PubMed

?-cyclodextrin modified gold nanoparticles (CD-GNP) were employed as the stationary phase in monolith capillary electrochromatography (CEC) to facilitate enantioseparation. CD-GNP were covalently bound to the surface of the thiolated porous polymer monolithic column. The fabricated enantioselective monolithic column was characterized by a variety of spectroscopic methods. The column exhibited steady EOF mobility over pH values ranging from 4.6 to 9.7. Additionally, the column was stable under CEC separation conditions over 180 min. Moreover, the column exhibited good column-to-column reproducibility. The CD-GNP-modified monolithic column was employed in the efficient CEC separation of three pairs of drug enantiomers (chlorpheniramine, zopiclone and tropicamide). The results exhibit reproducible run-to-run enantioseparations and the monolith column can maintain its enantioselectivity for more than 1 month if the column is stored in a CD-GNP solution at 4°C. PMID:23618133

Li, Min; Tarawally, Musa; Liu, Xi; Liu, Xiaoling; Guo, Liping; Yang, Li; Wang, Guang

2013-05-15

135

Acid-base catalysis of chiral Pd complexes: development of novel catalytic asymmetric reactions and their application to synthesis of drug candidates.  

PubMed

Using the unique character of the chiral Pd complexes 1 and 2, highly efficient catalytic asymmetric reactions have been developed. In contrast to conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine and methylene compounds were activated to form chiral palladium enolates, which underwent enantioselective carbon-carbon bond-forming reactions such as Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid, formed concomitantly during the formation of the enolates to activate electrophiles, thereby promoting the C-C bond-forming reaction. This palladium enolate chemistry was also applicable to electrophilic enantioselective fluorination reactions, and various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, tert-butoxycarbonyl lactone/lactams, cyanoesters, and oxindole derivatives could be fluorinated in a highly enantioselective manner (up to 99% ee). Using this method, the catalytic enantioselective synthesis of BMS-204352, a promising anti-stroke agent, was achieved. In addition, the direct enantioselective conjugate addition of aromatic and aliphatic amines to alpha,beta-unsaturated carbonyl compound was successfully demonstrated. In this reaction, combined use of the Pd complex 2 having basic character and the amine salt was the key to success, allowing controlled generation of the nucleophilic free amine. This aza-Michael reaction was successfully applied to asymmetric synthesis of the CETP inhibitor torcetrapib. PMID:17015970

Hamashima, Yoshitaka

2006-10-01

136

A homochiral metal-organic porous material for enantioselective separation and catalysis  

NASA Astrophysics Data System (ADS)

Inorganic zeolites are used for many practical applications that exploit the microporosity intrinsic to their crystal structures. Organic analogues, which are assembled from modular organic building blocks linked through non-covalent interactions, are of interest for similar applications. These range from catalysis, separation and sensor technology to optoelectronics, with enantioselective separation and catalysis being especially important for the chemical and pharmaceutical industries. The modular construction of these analogues allows flexible and rational design, as both the architecture and chemical functionality of the micropores can, in principle, be precisely controlled. Porous organic solids with large voids and high framework stability have been produced, and investigations into the range of accessible pore functionalities have been initiated. For example, catalytically active organic zeolite analogues are known, as are chiral metal-organic open-framework materials. However, the latter are only available as racemic mixtures, or lack the degree of framework stability or void space that is required for practical applications. Here we report the synthesis of a homochiral metal-organic porous material that allows the enantioselective inclusion of metal complexes in its pores and catalyses a transesterification reaction in an enantioselective manner. Our synthesis strategy, which uses enantiopure metal-organic clusters as secondary building blocks, should be readily applicable to chemically modified cluster components and thus provide access to a wide range of porous organic materials suitable for enantioselective separation and catalysis.

Seo, Jung Soo; Whang, Dongmok; Lee, Hyoyoung; Jun, Sung Im; Oh, Jinho; Jeon, Young Jin; Kim, Kimoon

2000-04-01

137

Enantioselective synthesis of polycyclic coumarin derivatives catalyzed by an in situ formed primary amine-imine catalyst.  

PubMed

A facile in situ formed primary amine-imine organocatalyst was developed in the asymmetric Michael addition of substituted 4-hydroxycoumarins to cyclic enones. A series of optically active polycyclic coumarin derivatives were obtained in high yields with excellent enantioselectivities up to 97% ee. PMID:21770363

Zhu, Xi; Lin, Aijun; Shi, Yan; Guo, Jingyu; Zhu, Chengjian; Cheng, Yixiang

2011-08-19

138

Enantioselective synthesis of 2,3-disubstituted indanones via Pd-catalyzed intramolecular asymmetric allylic alkylation of ketones.  

PubMed

A Pd-catalyzed intramolecular asymmetric allylic alkylation (AAA) reaction with "hard" carbanions has been developed for the first time, affording 2,3-disubstituted indanones with high diastereo- and enantioselectivities. The transformation of these products into other core structures of natural products has been demonstrated. PMID:24206052

Li, Xiao-Hui; Zheng, Bao-Hui; Ding, Chang-Hua; Hou, Xue-Long

2013-12-01

139

Highly enantioselective catalytic 1,3-dipolar cycloadditions of ?-alkyl diazoacetates: efficient synthesis of functionalized 2-pyrazolines.  

PubMed

Highly enantioselective 1,3-dipolar cycloaddition reactions of ?-substituted diazoacetates are accomplished by catalysis of the chiral oxazaborolidinium ion. Functionalized 2-pyrazolines are synthesized in high to excellent enantiomeric ratios (up to >99?:?1). The synthetic utility of 2-pyrazoline was expanded via preparation of 2,4-diamino ester compounds bearing a chiral quaternary carbon center. PMID:25597984

Lee, Sung Il; Kim, Ka Eun; Hwang, Geum-Sook; Ryu, Do Hyun

2015-02-18

140

Iridium-catalyzed enantioselective allyl-allylsilane cross-coupling.  

PubMed

An enantioselective allyl-allylsilane cross-coupling involving racemic branched allylic alcohols and allylsilanes is reported. An iridium-(P,olefin) phosphoramidite complex enables the transformation with high regio- and stereoselectivity under operationally simple conditions. The utility of the coupling is demonstrated in a concise catalytic, enantioselective synthesis of a pyrethroid insecticide protrifenbute. PMID:25111443

Hamilton, James Y; Hauser, Nicole; Sarlah, David; Carreira, Erick M

2014-09-26

141

Molecular Bases of Enantioselectivity of Haloalkane Dehalogenase DbjA  

NASA Astrophysics Data System (ADS)

Enzymes are widely used for the synthesis of pharmaceuticals, agrochemicals, and food additives because they can catalyze high enantioselective transformations. In order to construct selective enzymes by protein engineering, it is important to understand the molecular basis of enzyme-substrate interactions that contribute to enantioselectivity. The haloalkane dehalogenase DbjA showed high enantioselectivity for two racemic mixtures: ?-bromoesters and ?-bromoalkanes. Thermodynamic analysis, protein crystallography, and computer simulations indicated that DbjA carries two bases for the enantiodiscrimination of each racemic mixture. This study helps us understand the molecular basis of the enantioselectivity and opens up new possibilities for constructing enantiospecific biocatalysts through protein engineering.

Sato, Yukari; Natsume, Ryo; Prokop, Zbynek; Brezovsky, Jan; Chaloupkova, Radka; Damborsky, Jiri; Nagata, Yuji; Senda, Toshiya

142

Cloning and characterization of a novel esterase from Rhodococcus sp. for highly enantioselective synthesis of a chiral cilastatin precursor.  

PubMed

A novel non-heme chloroperoxidase (RhEst1), with promiscuous esterase activity for enantioselective hydrolysis of ethyl (S)-2,2-dimethylcylopropanecarboxylate, was identified from the shot-gun library of Rhodococcus sp. ECU1013. RhEst1 was overexpressed in Escherichia coli BL21 (DE3), purified to homogeneity and functionally characterized. Fingerprinting analysis revealed that RhEst1 prefers to para-nitrophenyl (pNP) esters of short-chain acyl groups. pNP esters with a cyclic acyl moiety, especially that with a cyclobutanyl group, were also substrates for RhEst1. The Km values for methyl 2,2-dimethylcyclopropanecarboxylate (DmCpCm) and ethyl 2,2-dimethylcyclopropane carboxylate (DmCpCe) were 0.25 and 0.43 mM, respectively. RhEst1 could serve as an efficient hydrolase for the bioproduction of optically pure (S)-2,2-dimethyl cyclopropane carboxylic acid (DmCpCa) which is an important chiral building block for cilastatin. As much as 0.5 M of DmCpCe was enantioselectively hydrolyzed into (S)-DmCpCa with a molar yield of 47.8% and an enantiomeric excess (ee) of 97.5%, indicating an extremely high enantioselectivity (E = 240) of this novel and unique biocatalyst for green manufacturing of highly valuable chiral chemicals. PMID:25239898

Zhang, Yan; Pan, Jiang; Luan, Zheng-Jiao; Xu, Guo-Chao; Park, Sunghoon; Xu, Jian-He

2014-09-19

143

The Inner-Sphere Process in the Enantioselective Tsuji Allylation Reaction with (S)-t-Bu-phosphinooxazoline Ligands  

E-print Network

The Inner-Sphere Process in the Enantioselective Tsuji Allylation Reaction with (S in the enantioselectivity of the reaction.6 While this level of enantioselectivity is useful for many applications, it would enantioenriched R-quaternary ketones (e.g., 2). We reported a series of Pd catalysts that perform enantioselective

Goddard III, William A.

144

Organocatalytic, diastereo- and enantioselective synthesis of nonsymmetric cis-stilbene diamines: a platform for the preparation of single-enantiomer cis-imidazolines for protein-protein inhibition.  

PubMed

The finding by scientists at Hoffmann-La Roche that cis-imidazolines could disrupt the protein-protein interaction between p53 and MDM2, thereby inducing apoptosis in cancer cells, raised considerable interest in this scaffold over the past decade. Initial routes to these small molecules (i.e., Nutlin-3) provided only the racemic form, with enantiomers being enriched by chromatographic separation using high-pressure liquid chromatography (HPLC) and a chiral stationary phase. Reported here is the first application of an enantioselective aza-Henry approach to nonsymmetric cis-stilbene diamines and cis-imidazolines. Two novel mono(amidine) organocatalysts (MAM) were discovered to provide high levels of enantioselection (>95% ee) across a broad range of substrate combinations. Furthermore, the versatility of the aza-Henry strategy for preparing nonsymmetric cis-imidazolines is illustrated by a comparison of the roles of aryl nitromethane and aryl aldimine in the key step, which revealed unique substrate electronic effects providing direction for aza-Henry substrate-catalyst matching. This method was used to prepare highly substituted cis-4,5-diaryl imidazolines that project unique aromatic rings, and these were evaluated for MDM2-p53 inhibition in a fluorescence polarization assay. The diversification of access to cis-stilbene diamine-derived imidazolines provided by this platform should streamline their further development as chemical tools for disrupting protein-protein interactions. PMID:25017623

Vara, Brandon A; Mayasundari, Anand; Tellis, John C; Danneman, Michael W; Arredondo, Vanessa; Davis, Tyler A; Min, Jaeki; Finch, Kristin; Guy, R Kiplin; Johnston, Jeffrey N

2014-08-01

145

Enantioselective Synthesis of 1,2-Dihydronaphthalene-1-carbaldehydes by Addition of Boronates to Isochromene Acetals Catalyzed by Tartaric Acid.  

PubMed

Tartaric acid is an ideal asymmetric catalyst as it is abundant, cheap, and environmentally friendly. (+)-Tartaric acid was found to catalyze a novel enantioselective [4 + 2] cycloaddition of isochromene acetals and vinylboronates. A variety of substituted isochromene acetals were tolerated, furnishing the desired dihydronaphthalenes and dihydrobenzofluorene products in good yields. High enantiomeric ratios (up to 98.5:1.5) and excellent diastereoselectivities (all >99:1) were observed employing 10 mol % of (+)-tartaric acid as the catalyst, in combination with 5 mol % of Ho(OTf)3. PMID:25715172

Luan, Yi; Barbato, Keith S; Moquist, Philip N; Kodama, Tomohiro; Schaus, Scott E

2015-03-11

146

Enantioselective alkylative double ring-opening of epoxides derived from cyclic allylic ethers: synthesis of enantioenriched unsaturated diols.  

PubMed

A screen of external chiral ligands has led to enantioselective organolithium-induced alkylative double ring-opening of 3,4-epoxytetrahydrofuran 1 with n-BuLi to give 3-methyleneheptane-1,2-diol 3 in 75% yield and 55% ee in the presence of bisoxazoline 10, and in up to 60% ee in the presence of (-)-sparteine 2. Extending the alkylative double ring-opening reaction to epoxides derived from oxabicyclo[n.2.1]alkenes (n = 2.3) results in the formation of cycloalkenediols, which, when carried out in the presence of (-)-sparteine 2 affords products in up to 85% ee. PMID:12926388

Hodgson, David M; Stent, Matthew A H; Stefane, Bogdan; Wilson, Francis X

2003-04-01

147

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

PubMed

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

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

2014-07-01

148

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

PubMed

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

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

2014-12-01

149

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

150

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

PubMed Central

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

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

2014-01-01

151

Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade Strategies  

E-print Network

Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade in the enantioselective synthesis of spirooxindoles via organocascade strategies. Various organocatalysts with distinct on the enantioselective synthesis of spirooxindoles via organocascade strategies and is organized on the basis of three

Barbas III, Carlos F.

152

Enantioselective acylation of R-2-pentanol in a solid/gas reactor catalysed by lipase B from Candida antarctica.  

E-print Network

that there is no effect of the organic solvent on the enantioselectivity E of CALB for this reaction neither in the solid in enantioselective synthetic reactions. Among the most used lipases for synthesis or resolution of racemates, lipaseReview Copy Enantioselective acylation of R-2-pentanol in a solid/gas reactor catalysed by lipase B

Paris-Sud XI, Université de

153

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

154

Voice synthesis application  

SciTech Connect

Selection of a speech synthesis system as an augmentation for a perimeter security device is described. Criteria used in selection of a system are discussed. The final system is a speech 1000 speech synthesizer board that has a 2000 word speech lexicon, a first time charge of $75 for a 32 K EPROM of custom words, and extra features such as an alternate command to adjust desired listening level.

Lightstone, P.C.; Davidson, W.M.

1982-01-27

155

Copper-catalyzed propargylic substitution of dichloro substrates: enantioselective synthesis of trisubstituted allenes and formation of propargylic quaternary stereogenic centers.  

PubMed

An easy and versatile Cu-catalyzed propargylic substitution process is presented. Using easily prepared prochiral dichloro substrates, readily available Grignard reagents together with catalytic amount of copper salt and chiral ligand, we accessed a range of synthetically interesting trisubstituted chloroallenes. Substrate scope and nucleophile scope are broad, providing generally high enantioselectivity for the desired 1,3-substitution products. The enantioenriched chloroallenes could be further transformed into the corresponding trisubstituted allenes or terminal alkynes bearing all-carbon quaternary stereogenic centers, through the copper-catalyzed enantiospecific 1,1/1,3-substitutions. The two successive copper-catalyzed reactions could be eventually combined into a one-pot procedure and different desired allenes or alkynes were obtained respectively with high enantiomeric excesses. PMID:25327947

Li, Hailing; Grassi, David; Guénée, Laure; Bürgi, Thomas; Alexakis, Alexandre

2014-12-01

156

New phosphine-diamine and phosphine-amino-alcohol tridentate ligands for ruthenium catalysed enantioselective hydrogenation of ketones and a concise lactone synthesis enabled by asymmetric reduction of cyano-ketones  

PubMed Central

Enantioselective hydrogenation of ketones is a key reaction in organic chemistry. In the past, we have attempted to deal with some unsolved challenges in this arena by introducing chiral tridentate phosphine-diamine/Ru catalysts. New catalysts and new applications are presented here, including the synthesis of phosphine-amino-alcohol P,N,OH ligands derived from (R,S)-1-amino-2-indanol, (S,S)-1-amino-2-indanol and a new chiral P,N,N ligand derived from (R,R)-1,2-diphenylethylenediamine. Ruthenium pre-catalysts of type [RuCl2(L)(DMSO)] were isolated and then examined in the hydrogenation of ketones. While the new P,N,OH ligand based catalysts are poor, the new P,N,N system gives up to 98% e.e. on substrates that do not react at all with most catalysts. A preliminary attempt at realising a new delta lactone synthesis by organocatalytic Michael addition between acetophenone and acrylonitrile, followed by asymmetric hydrogenation of the nitrile functionalised ketone is challenging in part due to the Michael addition chemistry, but also since Noyori pressure hydrogenation catalysts gave massively reduced reactivity relative to their performance for other acetophenone derivatives. The Ru phosphine-diamine system allowed quantitative conversion and around 50% e.e. The product can be converted into a delta lactone by treatment with KOH with complete retention of enantiomeric excess. This approach potentially offers access to this class of chiral molecules in three steps from the extremely cheap building blocks acrylonitrile and methyl-ketones; we encourage researchers to improve on our efforts in this potentially useful but currently flawed process. PMID:23216944

2012-01-01

157

Enantioselective synthesis of ?-phenyl- and ?-(dimethylphenylsilyl)alkylboronic esters by ligand mediated stereoinductive reagent-controlled homologation using configurationally labile carbenoids.  

PubMed

Chain extension of boronic esters by the action of configurationally labile racemic lithium carbenoids in the presence of scalemic bisoxazoline ligands was explored for the enantioselective synthesis of the two title product classes. Enantioenriched 2° carbinols generated by oxidative work-up (NaOOH) of initial ?-phenylalkylboronate products were obtained in 35-83% yield and 70-96% ee by reaction of B-alkyl and B-aryl neopentyl glycol boronates with a combination of O-(?-lithiobenzyl)-N,N-diisopropylcarbamate and ligand 3,3-bis[(4S)-4,5-dihydro-4-isopropyloxazol-2-yl] pentane in toluene solvent (-78 °C to rt) with MgBr2·OEt2 additive. Enantioenriched ?-(dimethylsilylphenylsilyl)alkylboronates were obtained in 35-69% yield and 9-57% ee by reaction of B-alkyl pinacol boronates with a combination of lithio(dimethylphenylsilyl)methyl 2,4,6-triisopropylbenzoate and ligand 2,2-bis[(4S)-4,5-dihydro-4-isopropyloxazol-2-yl]propane in cumene solvent (-45 °C to -95 °C to rt). The stereochemical outcome of the second type of reaction depended on the temperature history of the organolithium·ligand complex indicating that the stereoinduction mechanism in this case involves some aspect of dynamic thermodynamic resolution. PMID:25695409

Barsamian, Adam L; Wu, Zhenhua; Blakemore, Paul R

2015-03-11

158

Enantioselective synthesis of d-?-amino amides from aliphatic aldehydes† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00064e Click here for additional data file. Click here for additional data file.  

PubMed Central

Peptides consisting of d-amino amides are highly represented among both biologically active natural products and non-natural small molecules used in therapeutic development. Chemical synthesis of d-amino amides most often involves approaches based on enzymatic resolution or fractional recrystallization of their diastereomeric amino acid salt precursors, techniques that produce an equal amount of the l-amino acid. Enantioselective synthesis, however, promises selective and general access to a specific ?-amino amide, and may enable efficient peptide synthesis regardless of the availability of the corresponding ?-amino acid. This report describes the use of a cinchona alkaloid-catalyzed aza-Henry reaction using bromonitromethane, and the integration of its product with umpolung amide synthesis. The result is a straightforward 3-step protocol beginning from aliphatic aldehydes that provides homologated peptides bearing an aliphatic side chain at the resulting d-?-amino amide. PMID:25838883

Schwieter, Kenneth E.

2015-01-01

159

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 Central

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 minutes. 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 seconds can be nearly entirely eroded within 30 minutes. 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.

2012-01-01

160

COMBUSTION SYNTHESIS OF ADVANCED MATERIALS: PRINCIPLESAND APPLICATIONS  

E-print Network

COMBUSTION SYNTHESIS OF ADVANCED MATERIALS: PRINCIPLESAND APPLICATIONS Arvind Varma, Alexander S. Gasless Combustion SynthesisFrom Elements B. Combustion Synthesis in Gas-Solid Systems C. Products of Thermite-vpe SHS D. Commercial Aspects IV. Theoretical Considerations A. Combustion Wave Propagation Theory

Mukasyan, Alexander

161

Enantioselective Decarboxylative Alkylation Reactions: Catalyst Development, Substrate Scope, and Mechanistic Studies  

PubMed Central

?-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursors: enol carbonates, enol silanes, and racemic ?-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. PMID:22083969

Behenna, Douglas C.; Mohr, Justin T.; Sherden, Nathaniel H.; Marinescu, Smaranda C.; Harned, Andrew M.; Tani, Kousuke; Seto, Masaki; Ma, Sandy; Novák, Zoltán; Krout, Michael R.; McFadden, Ryan M.; Roizen, Jennifer L.; Enquist, John A.; White, David E.; Levine, Samantha R.; Petrova, Krastina V.; Iwashita, Akihiko; Virgil, Scott C.; Stoltz, Brian M.

2012-01-01

162

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

163

Enantioselective total syntheses of several bioactive natural products based on the development of practical asymmetric catalysis.  

PubMed

I present herewith enantioselective total syntheses of several bioactive natural products, such as (-)-strychnine, (+)-decursin, (-)-cryptocaryolone diacetate, (-)-fluoxetine, and aeruginosin 298-A, based on practical asymmetric catalyses (Michael reaction, epoxidation, and phase-transfer reaction) that I developed with co-workers in Prof. Shibasaki's group over the past 5 years. In the first part of this review, I discuss the great improvement of catalyst efficiency in an ALB-catalyzed asymmetric Michael reaction of malonate and application to the pre-manufacturing scale (greater than kilogram scale) and enantioselective total synthesis of (-)-strychnine with the development of novel domino cyclization. To broaden the substrate generality of the Michael reaction, we developed a highly stable, storable, and reusable La-O-linked-BINOL complex. Further extension of the reaction using beta-keto ester as a Michael donor was achieved with the development of a La-NR-linked-BINOL complex, thereby improving indole alkaloid syntheses. In the second section, I discuss enantioselective total synthesis of (+)-decursin using catalytic asymmetric epoxidation. To achieve the synthesis, we developed a new La-BINOL-Ph(3)As = O (1:1:1) complex catalyst system, which has much higher reactivity and broader substrate generality than the previously developed catalyst systems. This allowed us to achieve catalytic asymmetric epoxidation of alpha,beta-unsaturated carboxylic acid derivatives with high enantioselectivity and broad substrate generality for the first time by changing the lanthanide metal and reaction conditions. Among them, catalytic asymmetric epoxidation of alpha,beta-unsaturated morpholinyl amides is quite useful in terms of synthetic utility of the corresponding alpha,beta-epoxy morpholinyl amides. Highly catalyst-controlled enantio- or diastereoselective epoxidation of the alpha,beta-unsaturated morpholinyl amides, coupled with diastereoselective reduction of beta-hydroxy ketones, enabled the synthesis of all possible stereoisomers of 1,3-polyol arrays with successful enantioselective total synthesis of several 1,3-polyol natural products, such as (-)-cryptocaryolone diacetate. In addition, the development of a new regioselective epoxide-opening reaction of alpha,beta-epoxy amides to the corresponding alpha- and beta-hydroxy amides enhanced the usefulness of the present epoxidation and was applied to the enantioselective total synthesis of (-)-fluoxetine. In the final section, I report the development of a new asymmetric two-center organocatalyst (TaDiAS) and its application to the enantioselective synthesis of aeruginosin 298-A and its analogues. Because of the remarkable structural diversity of TaDiAS, a practical asymmetric phase-transfer reaction with broad substrate generality was achieved. As a result, we succeeded in developing a highly versatile synthetic method for aeruginosin 298-A and its analogues. Inhibitory activity studies of the compounds against the serine protease trypsin provided preliminary information about their structure-activity relations. PMID:15340187

Ohshima, Takashi

2004-09-01

164

The First Enantioselective Organocatalytic Mukaiyama-Michael Reaction: A Direct Method for the Synthesis of Enantioenriched -Butenolide Architecture  

E-print Network

),6 further outlining the broad utility of the Mukaiyama-Aldol transform in asymmetric synthesis.7 Surpris anticipated that R, -unsaturated iminium ions arising from chiral amine 1 might be inert to silyloxy furan 1:anti, 85% ee); however, catalytic efficiency was poor (31% yield). On the basis of the assumption

MacMillan, David W. C.

165

Highly regio- and enantioselective synthesis of N-substituted 2-pyridones: iridium-catalyzed intermolecular asymmetric allylic amination.  

PubMed

The first iridium-catalyzed intermolecular asymmetric allylic amination reaction with 2-hydroxypyridines has been developed, thus providing a highly efficient synthesis of enantioenriched N-substituted 2-pyridone derivatives from readily available starting materials. This protocol features a good tolerance of functional groups in both the allylic carbonates and 2-hydroxypyridines, thereby delivering multifunctionalized heterocyclic products with up to 98?% yield and 99?%?ee. PMID:25504907

Zhang, Xiao; Yang, Ze-Peng; Huang, Lin; You, Shu-Li

2015-02-01

166

Enantioselective synthesis of nonphosphorus-containing phosphotyrosyl mimetics and their use in the preparation of tyrosine phosphatase inhibitory peptides  

Microsoft Academic Search

Three new L-amino acid analogues 12, 18 and 25 have been prepared in protected form suitable for incorporation into peptides by solid-phase synthesis using Fmoc protocols. These agents represent nonphosphorus-containing phosphotyrosyl (pTyr) mimetics, which utilize carboxylic groups to provide functionality normally afforded by the pTyr phosphate group. To demonstrate the utility of these analogues, the protein-tyrosine phosphatase-directed peptides Ac-D-A-D-E-X-L-amide (28

Zhu-Jun Yao; He Zhao; George W. A Milne; Li Wu; Zhong-Yin Zhang; Johannes H Voigt

1998-01-01

167

Enantioselective catalysis using lanthanide Schiff base complexes  

SciTech Connect

The use of lanthanide-based catalysts to facilitate organic transformations is currently an area of rapid growth, in particular the application of lanthanide alkoxide and triflate derivatives as effective Lewis-acidic catalysts for Michael additions and aldol reactions, and bis-pentamethylcyclopentadienyl derivatives as extremely active catalysts for hydrogenation and enantioselective hydroamination reactions. We have begun an investigation into the use of lanthanide complexes containing chiral alkoxide ligands as Lewis-acidic catalysts for enantioselective organic reactions. Since the large ionic radii of the lanthanide +III metal centers can often lead to oligomerization of simple alkoxide species, we have also examined the use of multidentate, chelating Schiff base ligands to provide an asymmetric environment about a lanthanide metal center. Structural investigations of the catalysts will be described, together with the use of these catalysts in enantioselective Meerwein-Ponndorf-Verley reduction of ketones and nitroaldol reactions.

Watkin, J.G. [Los Alamos National Laboratory, NM (United States)

1996-10-01

168

Enantioselective Synthesis of Allenylenol Silyl Ethers via Chiral Lithium Amide Mediated Reduction of Ynenoyl Silanes and Their Diels-Alder Reactions.  

PubMed

An enantioselective Meerwein-Ponndorf-Verley-type reduction of ynenoylsilanes by a chiral lithium amide followed by a Brook rearrangement and anti-mode protonation across conjugated 1,3-enynes provides allene derivatives bearing a 2-siloxyvinyl moiety in high enantioselectivity. The E/Z geometry of enol silyl ethers is controlled by the geometry of the starting enyne moiety. Thus, (E)- and (Z)-enol silyl ethers are obtained from (Z)- and (E)-ynenoylsilans, respectively. The 2-siloxyvinylallene products can participate in Diels-Alder reactions with reactive dienophiles such as PTAD, which can be achieved in a one-pot operation from ynenoylsilanes. PMID:25689472

Sasaki, Michiko; Kondo, Yasuhiro; Moto-Ishi, Ta-Ichi; Kawahata, Masatoshi; Yamaguchi, Kentaro; Takeda, Kei

2015-03-01

169

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

170

Enantioselective synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from ?-substituted ?-hydroxyaminoaldehydes.  

PubMed

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from ?-substituted ?-hydroxyaminoaldehydes is reported. The ?-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to ?,?-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected ?-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N-O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial ?-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available ?-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from ?-amino acids as the source of diversity and chirality. A broad substrate scope is possible because ?-aminoaldehydes can be prepared from ?,?-unsaturated aldehydes by an enantioselective organocatalytic process. PMID:24785413

Ranade, Adwait R; Georg, Gunda I

2014-02-01

171

Enantioselective Synthesis of 3,4-Dihydro-1,2-oxazepin-5(2H)-ones and 2,3-Dihydropyridin-4(1H)-ones from ?-Substituted ?-Hydroxyaminoaldehydes  

PubMed Central

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from ?-substituted ?-hydroxyaminoaldehydes is reported. The ?-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to ?,?-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected ?-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N–O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial ?-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available ?-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from ?-amino acids as the source of diversity and chirality. A broad substrate scope is possible because ?-aminoaldehydes can be prepared from ?,?-unsaturated aldehydes by an enantioselective organocatalytic process. PMID:24785413

2015-01-01

172

Crosslinked aggregates of Rhizopus oryzae lipase as industrial biocatalysts: preparation, optimization, characterization, and application for enantioselective resolution reactions.  

PubMed

Lipase from Rhizopus oryzae (ROL) was immobilized as crosslinked enzyme aggregate (CLEA) via precipitation with ammonium sulfate and simultaneous crosslinking with glutaraldehyde. The optimum conditions of the immobilization process were determined. Lipase CLEAs showed a twofold increase in activity when Tween 80-pretreated lipase was used for CLEA preparation. CLEAs were shown to have several advantages compared to free lipase. CLEAs were more stable at 50°C and 60°C as well as for a wide range of pH. After incubation at 50°C, CLEA showed 74% of initial activity whereas free enzyme was totally inactivated. Reduction of Schiff bases has been performed for the first time in the CLEA preparation process significantly improving the chemically modified CLEAs' reusability, thus providing an enzyme with high potential for recycling even under aqueous reaction conditions where enzyme leakage is, in general, one of the major problems. The CLEA retained 91% activity after 10 cycles in aqueous medium. The immobilized enzyme was used for kinetic resolution reactions. Results showed that immobilization had an enhancing effect on the conversion (c) as well as on the enantiomeric ratio (E). ROL CLEA displayed five times higher enantioselectivity for the hydrolysis of (R,S)-1-phenylethyl acetate and likewise 1.5 times higher enantioselectivity for the transesterification of racemic (R-S)-1-phenylethanol with vinylacetate. PMID:22685034

Kartal, Funda; Kilinc, Ali

2012-07-01

173

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

174

Enantioselective Synthesis of Homoallylic Amines through Reactions of (Pinacolato)allylborons with Aryl-, Heteroaryl-, Alkyl- or Alkene-Substituted Aldimines Catalyzed by Chiral C1-Symmetric NHC–Cu Complexes  

PubMed Central

A catalytic method for enantioselective synthesis of homoallylamides through Cu-catalyzed reactions of stable and easily accessible (pinacolato)allylborons with aryl-, heteroaryl-,alkyl- or alkenyl-substituted N-phosphinoylimines is disclosed. Transformations are promoted by 1–5 mol % of readily accessible NHC–Cu complexes, derived from C1-symmetric imidazolinium salts, which can be prepared in multi-gram quantities in four steps from commercially available materials. Allyl additions deliver the desired products in up to quantitative yield and 98.5:1.5 enantiomeric ratio and are amenable to gram-scale operations. A mechanistic model accounting for the observed selectivity levels and trends is proposed. PMID:21341657

Vieira, Erika M.; Snapper, Marc L.; Hoveyda, Amir H.

2011-01-01

175

Enantioselective Brønsted base catalysis with chiral cyclopropenimines.  

PubMed

Cyclopropenimines are shown to be a highly effective new class of enantioselective Brønsted base catalysts. A chiral 2,3-bis(dialkylamino)cyclopropenimine catalyzes the rapid Michael reaction of a glycine imine substrate with high levels of enantioselectivity. A preparative scale reaction to deliver 25 g of product is demonstrated, and a trivial large scale synthesis of the optimal catalyst is shown. In addition, the basicity of a 2,3-bis(dialkylamino)cyclopropenimine is measured for the first time and shown to be approximately equivalent to the P(1)-tBu phosphazene base. An X-ray crystal structure of the protonated catalyst is shown along with a proposed mechanistic and stereochemical rationale. PMID:22417078

Bandar, Jeffrey S; Lambert, Tristan H

2012-03-28

176

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

177

Development of magnetically separable immobilized lipase by using cellulose derivatives and their application in enantioselective esterification of ibuprofen.  

PubMed

Highly active, stable, and magnetically separable immobilized enzymes were developed using carboxymethyl cellulose (CMC) and diethylaminoethyl cellulose DEAE-C; hereafter designated "DEAE" as supporting materials. Iron oxide nanoparticles penetrated the micropores of the supporting materials, rendering them magnetically separable. Lipase (LP) was immobilized on the surface of the supporting materials by using cross-linked enzyme aggregation (CLEA) by glutaraldehyde. The activity of enzyme aggregates coated on DEAE was approximately 2 times higher than that of enzyme aggregates coated on CMC. This is explained by the fact that enzyme aggregates with amine residues are more efficient than those with carboxyl residues. After a 96-h enantioselective ibuprofen esterification reaction, 6% ibuprofen propyl ester was produced from the racemic mixture of ibuprofen by using DEAE-LP, and 2.8% using CMC-LP. PMID:18388463

Lee, Gowoun; Joo, Hongil; Kim, Jungbae; Lee, Jung-Heon

2008-03-01

178

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

179

Chiral linear polymers bonded alternatively with salen and 1,4-dialkoxy-2,6-diethynylbenzene: synthesis and application to diethylzinc addition to aldehydes  

Microsoft Academic Search

The synthesis of chiral polymers 1 bonded alternatively with salen and 1,4-dialkoxy-2,6-diethynylbenzene was accomplished. These polymers are recyclable and catalyze the Et2Zn addition to aldehydes with good enantioselectivity.

Suribabu Jammi; Laxmidhar Rout; Tharmalingam Punniyamurthy

2007-01-01

180

Enantioselective Synthesis of All-Carbon Quaternary Stereogenic Centers via Copper-Catalyzed Asymmetric Allylic Alkylation of (Z)-Allyl Bromides with Organolithium Reagents.  

PubMed

A copper/phosphoramidite catalyzed asymmetric allylic alkylation of Z?trisubstituted allyl bromides with organolithium reagents is reported. The reaction affords all-carbon quaternary stereogenic centers in high yields and very good regio- and enantioselectivity. This systematic study illustrates the crucial role of the olefin geometry of the allyl substrate on the outcome of the reaction and provides a viable alternative to access these important structural motifs. PMID:25631942

Fañanás-Mastral, Martín; Vitale, Romina; Pérez, Manuel; Feringa, Ben L

2015-03-01

181

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

182

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

183

Enantioselective Michael Addition of Water  

PubMed Central

The enantioselective Michael addition using water as both nucleophile and solvent has to date proved beyond the ability of synthetic chemists. Herein, the direct, enantioselective Michael addition of water in water to prepare important ?-hydroxy carbonyl compounds using whole cells of Rhodococcus strains is described. Good yields and excellent enantioselectivities were achieved with this method. Deuterium labeling studies demonstrate that a Michael hydratase catalyzes the water addition exclusively with anti-stereochemistry. PMID:25529526

Chen, Bi-Shuang; Resch, Verena; Otten, Linda G; Hanefeld, Ulf

2015-01-01

184

Enantioselective synthesis of dihydrocoumarin derivatives by chiral scandium(iii)-complex catalyzed inverse-electron-demand hetero-Diels-Alder reaction.  

PubMed

An asymmetric inverse-electron-demand hetero-Diels-Alder reaction between o-quinone methides and azlactones to generate potentially pharmacological active dihydrocoumarins has been achieved efficiently by using a chiral N,N'-dioxide-Sc(iii) complex as the catalyst. The desired products were obtained in high yields with excellent enantioselectivities and diastereoselectivities (up to 94% yield, 96% ee and >19?:?1 dr) under mild reaction conditions. A concerted reaction pathway was confirmed by Operando IR and control experiments. PMID:25649623

Hu, Haipeng; Liu, Yangbin; Guo, Jing; Lin, Lili; Xu, Yali; Liu, Xiaohua; Feng, Xiaoming

2015-02-17

185

Enantioselective Synthesis of 5,7-Bicyclic Ring Systems from Axially Chiral Allenes Using a Rh(I)-Catalyzed Cyclocarbonylation Reaction  

PubMed Central

A transfer of chirality in an intramolecular Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta[c]azepinones and dihydrocyclopenta[c]oxepinones enantioselectively (22 – 99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done. PMID:23485149

Grillet, Francois; Brummond, Kay M.

2013-01-01

186

Chemoselective and Enantioselective Oxidation of Indoles Employing Aspartyl Peptide Catalysts  

PubMed Central

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 enantioselective indole oxidation allows a rapid and biomimetic entry into several classes of alkaloid natural products. Despite this potentially high utility in the total synthesis, reports of catalytic enantioselective indole oxidation remain sparse. Here we report a highly chemoselective catalytic system for the indole oxidation that delivers 3-hydroxy-indolenines with good chemical yields and moderate to high levels of enantio- and diastereoselectivity (up to 95:5 er and up to 92:8 dr. These results represent, to our knowledge, the most selective values yet reported in the literature for catalytic asymmetric indole oxidation). Furthermore, the utility of enantioenriched hydroxy-indolenines in stereospecific rearrangements is demonstrated. PMID:21539386

Kolundzic, Filip; Noshi, Mohammad N.; Tjandra, Meiliana; Movassaghi, Mohammad; Miller, Scott J.

2011-01-01

187

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

PubMed Central

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

Lathrop, Stephen P.

2013-01-01

188

Enantioselective magnetochiral photochemistry  

PubMed

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the 'homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy--an effect linking chirality and magnetism--can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life. PMID:10879530

Rikken, G L; Raupach, E

2000-06-22

189

Enantioselective magnetochiral photochemistry  

NASA Astrophysics Data System (ADS)

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the `homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy-an effect linking chirality and magnetism-can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life.

Rikken, G. L. J. A.; Raupach, E.

2000-06-01

190

Automatic Platform Synthesis and Application Mapping for  

E-print Network

Platform and Code Generation . . . . . . . . . . 34 3.4 Project Generation for Xilinx Platform StudioAutomatic Platform Synthesis and Application Mapping for Multiprocessor Systems On-Chip MASTER, including photocopy- ing, recording or by any information storage and retrieval system, without permission

Stefanov, Todor Plamenov

191

Chapter 1Catalytic, Enantioselective Construction of Pyrroloindolines 1 Recent Developments in the Catalytic, Enantioselective Construction of  

E-print Network

products. Catalytic, enantioselective reactions to prepare pyrroloindolines can be categorized primarily succeeded by several enantioselective organocatalytic - alkylation reactions of oxindoles.11 Recently, LuoChapter 1­Catalytic, Enantioselective Construction of Pyrroloindolines 1 CHAPTER 1 Recent

Winfree, Erik

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

Synthesis, characterisation and application of inherently conducting polymer nanoparticles  

Microsoft Academic Search

Synthesis of inherently conducting polymers (ICPs) nanoparticles is an option to improve the processability and conductivity of ICPs. In this thesis, the synthesis and application of ICPs nanoparticles has been demonstrated. Various polymerisation methods, such as emulsion polymerisation, use of steric stabiliser and synthesis in ionic liquid (IL) media, have been used to synthesise polymer nanoparticles. These synthesis methods render

Orawan Ngamna

2006-01-01

194

Enantioselective damage of diclofop acid mediated by oxidative stress and acetyl-CoA carboxylase in nontarget plant Arabidopsis thaliana.  

PubMed

Diclofop-methyl (DM) is a widely used chiral herbicide, which rapidly hydrolyzes to its major metabolite diclofop acid (DC) after application. With a carbon chiral center, DC not only is an important ingredient of herbicidal activity, but also has a long half-life in soil. Studies so far have only considered the activity of racemic DM in target organisms, and the enantioselective toxicity in nontarget plants of DM and DC has yet to be explored. In this study, the enantioselective phytotoxicity of DC mediated by oxidative stress and the key enzyme ACCase in the fatty acid synthesis system on the model plant Arabidopsis thaliana was investigated. Significant differences between the two enantiomers were observed in phytotoxicity including growth inhibition, oxidative damage and alteration of key genes expression of ACCase, with R-DC showing greater toxicity to Arabidopsis thaliana than S-DC. The results of molecular docking showed that there was a stronger affinity between R-DC and the target enzyme carboxyltransferase domain of ACCase, likely leading to the enantioselective phytotoxicity of DC. This study suggested that chirality of both parent compounds and metabolites should be considered to improve our understanding of the environmental fate and risks of chiral pesticides. PMID:22770422

Zhang, Qiong; Zhao, Meirong; Qian, Haifeng; Lu, Tao; Zhang, Quan; Liu, Weiping

2012-08-01

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

Enantioselective separation and phytotoxicity on rice seedlings of paclobutrazol.  

PubMed

The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(-)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(-)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(-)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance. PMID:21395310

Zhang, Anping; Xie, Xuemei; Liu, Weiping

2011-04-27

198

MICROWAVE TECHNOLOGY CHEMICAL SYNTHESIS APPLICATIONS  

EPA Science Inventory

Microwave-accelerated chemical syntheses in various solvents as well as under solvent-free conditions have witnessed an explosive growth. The technique has found widespread application predominantly exploiting the inexpensive unmodified household microwave (MW) ovens although th...

199

Radiation synthesis and fabrication for biomedical applications  

NASA Astrophysics Data System (ADS)

Radiation synthesis and fabrication techniques can make various specific forms and structures of materials enhancedly which are useful for biomedical applications. Those materials are a porous gel and membrane, an interpenetrating networked(IPN) hydrogel, a heterogeneous surface phase membrane, an ultra-thin membrane, a biofunctional laminate and an ultra-fine particle. Radiation techniques can attach various biofunctionalities to those materials effectively by means of immobilization of biofunctional components such as enzymes, proteins, hormones, drugs, microbial cells and tissue cells. It is convenient that the immobilization can be finished at the same time as the synthesis and fabrication in many cases. The applications to bioreactors, biosensors, artificial organs, drug delivery systems and recently to signal responsive chemical delivery systems, have been studied and developed based on those techniques.

Kaetsu, Isao

1995-09-01

200

Ethylene glycol: properties, synthesis, and applications.  

PubMed

Ethylene glycol (EG) is an important organic compound and chemical intermediate used in a large number of industrial processes (e.g. energy, plastics, automobiles, and chemicals). Indeed, owing to its unique properties and versatile commercial applications, a variety of chemical systems (e.g., catalytic and non-catalytic) have been explored for the synthesis of EG, particularly via reaction processes derived from fossil fuels (e.g., petroleum, natural gas, and coal) and biomass-based resources. This critical review describes a broad spectrum of properties of EG and significant advances in the prevalent synthesis and applications of EG, with emphases on the catalytic reactivity and reaction mechanisms of the main synthetic methodologies and applied strategies. We also provide an overview regarding the challenges and opportunities for future research associated with EG. PMID:22488259

Yue, Hairong; Zhao, Yujun; Ma, Xinbin; Gong, Jinlong

2012-06-01

201

Enantioselective effects in coordination compounds  

NASA Astrophysics Data System (ADS)

The information that has appeared during the last 15 years relating to enantioselectivity in the formation and reactions of kinetically inert and kinetically labile complexes is classified in the present review. Attention is mainly given to chiral discrimination of ligands that are exchanged in the internal or external coordination spheres of the complexes. The occurrence of enantioselective effects has also been recorded in reactions of coordination compounds that occur without ligand exchange, in particular, in photochemical processes. The variety of forms in which enantioselectivity is displayed is shown and methods for studying it are described. The bibliography includes 223 references.

Kurganov, Alexander A.; Ponomareva, T. M.; Davankov, Vadim A.

1990-02-01

202

Synthesis, Properties, and Applications Of Boron Nitride  

NASA Technical Reports Server (NTRS)

Report describes synthesis, properties, and applications of boron nitride. Especially in thin-film form. Boron nitride films useful as masks in x-ray lithography; as layers for passivation of high-speed microelectronic circuits; insulating films; hard, wear-resistant, protective films for optical components; lubricants; and radiation detectors. Present status of single-crystal growth of boron nitride indicates promising candidate for use in high-temperature semiconductor electronics.

Pouch, John J.; Alterovitz, Samuel A.

1993-01-01

203

Dynamic control of chirality in phosphine ligands for enantioselective catalysis  

PubMed Central

Chirality plays a fundamental role in biology and chemistry and the precise control of chirality in a catalytic conversion is a key to modern synthesis most prominently seen in the production of pharmaceuticals. In enantioselective metal-based catalysis, access to each product enantiomer is commonly achieved through ligand design with chiral bisphosphines being widely applied as privileged ligands. Switchable phosphine ligands, in which chirality is modulated through an external trigger signal, might offer attractive possibilities to change enantioselectivity in a catalytic process in a non-invasive manner avoiding renewed ligand synthesis. Here we demonstrate that a photoswitchable chiral bisphosphine based on a unidirectional light-driven molecular motor, can be used to invert the stereoselectivity of a palladium-catalysed asymmetric transformation. It is shown that light-induced changes in geometry and helicity of the switchable ligand enable excellent selectivity towards the racemic or individual enantiomers of the product in a Pd-catalysed desymmetrization reaction. PMID:25806856

Zhao, Depeng; Neubauer, Thomas M.; Feringa, Ben L.

2015-01-01

204

Colloidosomes: Synthesis, properties and applications.  

PubMed

Colloidosomes represent a rapidly expanding field with various applications in microencapsulation, including the triggered release of cargoes. With self-assembled shells comprising colloidal particles, they offer significant flexibility with respect to microcapsule functionality. This review explores the various types of particles and techniques that have been employed to prepare colloidosomes. The relative advantages and disadvantages of these routes are highlighted and their potential as microcapsules for both small molecule and macromolecular actives is evaluated. PMID:25533538

Thompson, Kate L; Williams, Mark; Armes, Steven P

2015-06-01

205

Amphiphilic conetworks: Definition, synthesis, applications  

Microsoft Academic Search

The emerging field of amphiphilic conetworks (APCNs) is critically reviewed. A definition of APCNs is proposed and discussed in depth. The field of APCN science, born in 1988, is delineated and differentiated from similar constructs (e.g. interpenetrating networks, grafted networks). Among the justifications for sustained scientific\\/technological interest in APCNs are hosts of high-technology applications, some in commercial use and some

Gabor Erdodi; Joseph P. Kennedy

2006-01-01

206

Screening-engineered Field-effect Photovoltaics and Synthesis, Characterization, and Applications of Carbon-based and Related Nanomaterials  

E-print Network

Photovoltaics and Synthesis, Characterization, and Applications of Carbon-Photovoltaics and Synthesis, Characterization, and Applications of Carbon-Photovoltaics and Synthesis, Characterization, and Applications of Carbon-

Regan, William Raymond

2012-01-01

207

Highly enantioselective nickel-catalyzed intramolecular reductive cyclization of alkynones.  

PubMed

The first asymmetric nickel-catalyzed intramolecular reductive cyclization of alkynones is reported. A P-chiral monophosphine and triethylsilane were used as the ligand and the reducing reagent, respectively, to form a series of tertiary allylic alcohols bearing furan/pyran rings in excellent yields and enantioselectivities. This reaction has a broad substrate scope and enabled the efficient synthesis of dehydroxycubebin and chiral dibenzocyclooctadiene skeletons. PMID:25597850

Fu, Wenzhen; Nie, Ming; Wang, Aizhen; Cao, Ziping; Tang, Wenjun

2015-02-16

208

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

209

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

210

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

211

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

212

Synthesis, characterization and applications of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic materials (Co, Ni, and Fe), the magnetite (Fe3O 4) is least toxic and hence most promising for applications in medical diagnostics. Microemulsion-based synthesis utilizes the local aqueous environment within a reverse micelle as a nano-scale reactor and allows synthesizing nanoparticles with a hydrophilic surface for subsequent functionalization. By controlling the water-to-surfactant ratio, the type of surfactants, and the ionic strength of the aqueous core, one can control the size and shape of the resulting particles. We developed such a system that allows the multi-step synthesis of surface-functionalized, magnetic nanoparticles in a one-pot synthesis reaction. By altering the system chemistry, we were further able to produce either spheres or cylinders of controlled dimension in the size range of 5 nm to 30 nm. Using standard bio-conjugation techniques, we successfully immobilized an enzyme onto the nanoparticles. We also developed a theoretical model for the separation and fractionation of nanoparticles based on their size and magnetic properties. Using the multiphysics and finite element modeling capabilities of FEMLAB(TM), we solved the coupled system of PDEs describing the interaction of magnetic particles within a magnetic field for either static (cylindrical beaker) or convective flow (capillary) conditions. A net retention time as high as 310 s is achieved for 200 nm particles at field strength of 1250 kA/m. The model allows the design of a magnetic, field-flow fractionation (MFFF) system to separate nanoparticles by size.

Kanmukhla, Vikram Kumar

213

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

214

Immobilization of epoxide hydrolase from Aspergillus niger onto DEAE-cellulose: enzymatic properties and application for the enantioselective resolution of a racemic epoxide  

Microsoft Academic Search

Recombinant epoxide hydrolase (EH) from Aspergillus niger can be a very promising tool for the resolution of various racemic epoxides by enantioselective hydrolysis. The enzyme was successfully immobilized by ionic adsorption onto DEAE-cellulose (99% yield, 70% of retention activity). The temperature for maximal activity (40°C) and the activation energy (38.8kJ\\/mol) were similar for both the immobilized and free EHs, whereas

S. Karboune; A. Archelas; R. Furstoss; J. Baratti

2005-01-01

215

Highly enantioselective ring-opening reactions of aziridines with indole and its application in the building of C3-halogenated pyrroloindolines.  

PubMed

A magnesium-catalyzed asymmetric ring-opening reaction of aziridine with indole has been realized by employing commercially available chiral ligands. Both of the enantiomers of the ring-opening product could be obtained with good yields and a high level of enantioselectivity. The corresponding ring-opening product could be further transformed to various types of enantioenriched C3 -halogenated-pyrroloindolines. PMID:25351884

Yang, Dongxu; Wang, Linqing; Han, Fengxia; Li, Dan; Zhao, Depeng; Cao, Yiming; Ma, Yunxia; Kong, Weidong; Sun, Quantao; Wang, Rui

2014-12-01

216

Highly Enantioselective Rhodium-Catalyzed Hydrogenation of  

E-print Network

been invented to facili- tate enantioselective catalytic reactions, and unique properties of chiralHighly Enantioselective Rhodium-Catalyzed Hydrogenation of Dehydroamino Acids with New Chiral is the key for the development of highly enantioselective reac- tions. In contrast to many chiral phosphines

Zhang, Xumu

217

Characterization, crystallization and preliminary X-­ray diffraction analysis of an (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767: enantioselectivity for potential industrial applications  

PubMed Central

The structures and reaction mechanisms of enantioselective hydrolases, which can be used in industrial applications such as biotransformations, are largely unknown. Here, the X-ray crystallographic study of a novel (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767, which can be used in the production of (S)-ketoprofen, is described. Multiple sequence alignments with other hydrolases revealed that pfEstA contains a conserved Ser67 within the S-­X-X-K motif as well as a highly conserved Tyr156. Recombinant protein containing an N-terminal His tag was expressed in Escherichia coli, purified to homogeneity and characterized using SDS–PAGE, MALDI-TOF MS and enantioselective analysis. pfEstA was crystallized using a solution consisting of 1?M sodium citrate, 0.1?M CHES pH 9.5, and X-ray diffraction data were collected to a resolution of 1.9?Å with an R merge of 7.9%. The crystals of pfEstA belonged to space group P212121, with unit-cell parameters a = 65.31, b = 82.13, c = 100.41?Å, ? = ? = ? = 90°. PMID:23143253

Kim, Seulgi; Duc Ngo, Tri; Kim, Kyeong Kyu; Kim, T. Doohun

2012-01-01

218

APPLICATIONS OF CAPILLARY ELECTROPHORESIS TO THE STUDY OF CHIRAL ENVIRONMENTAL POLLUTANTS: ENANTIOMER SEPARATION AND MEASUREMENTS OF ENANTIOSELECTIVITY  

EPA Science Inventory

CE is rarely used for routine environmental analysis of organic pollutants -- certainly not to the extent of gas chromatography or high pressure liquid chromatography. There are advantages to CE, however, that belie this lack of application. For example, CE is preferred over GC f...

219

One-dimensional nanomaterials: Synthesis and applications  

NASA Astrophysics Data System (ADS)

My research mainly covers three types of one-dimensional (1D) nanomaterials: metal oxide nanowires, transition metal oxide core-shell nanowires and single-walled carbon nanotubes. This new class of nanomaterials has generated significant impact in multiple fields including electronics, medicine, computing and energy. Their peculiar, fascinating properties are promising for unique applications on electronics, spintronics, optical and chemical/biological sensing. This dissertation will summarize my research work on these three 1D nanomaterials and propose some ideas that may lead to further development. Chapter 1 will give a brief introduction of nanotechnology journey and 1D nanomaterials. Chapter 2 and 3 will discuss indium oxide nanowires, as the representative of metal oxide nanwires. More specifically, chapter 2 is focused on the synthesis, material characterization, transport studies and doping control of indium oxide nanowires; Chapter 3 will give a comprehensive review of our systematic studies on molecular memory applications based on molecule/indium oxide nanowire heterostructures. Chapter 4 will introduce another 1D nanomaterial-transition metal oxide (TMO) core-shell nanowires. The discuss will focus on the synthesis of TMO nanowires, material analysis and their electronic properties as a function of temperature and magnetic field. Chapter 5 is dedicated to aligned single-walled carbon nanotubes (SWNTs) on synthesis with rational control of position and orientation, detailed characterization and construction of scaled top-gated transistors. This chapter presents a way to produce the p- and n-type nanotube transistors based on gate voltage polarity control during electrical breakdown. Finally, chapter 6 summarizes the above discussions and proposes some suggestions for future studies.

Lei, Bo

220

Absolute enantioselective separation: optical activity ex machina.  

PubMed

The paper describes methodology of using three independent macroscopic factors affecting molecular orientation to accomplish separation of a racemic mixture without the presence of any other chiral compounds, i. e., absolute enantioselective separation (AES) which is an extension of a concept of applying these factors to absolute asymmetric synthesis. The three factors may be applied simultaneously or, if their effects can be retained, consecutively. The resulting three mutually orthogonal or near orthogonal directors constitute a true chiral influence and their scalar triple product is the measure of the chirality of the system. AES can be executed in a chromatography-like microfluidic process in the presence of an electric field. It may be carried out on a chemically modified flat surface, a monolithic polymer column made of a mesoporous material, each having imparted directional properties. Separation parameters were estimated for these media and possible implications for the natural homochirality are discussed. PMID:16342798

Bielski, Roman; Tencer, Michal

2005-11-01

221

Studies towards total synthesis of borrelidin, stereoselective synthesis of the polysubstituted macrolidic part  

Microsoft Academic Search

Enantioselective synthesis of the polysubstituted macrolidic part of borrelidin (1) is presented. Six out of the nine stereogenic centers in 12 and 13 were achieved in >99.2 %ee in seven steps from meso-diol 4. The synthesis is based on enantioselective formation of bis-epoxide 10 followed by regioselective alkylation of the epoxide functionalities.

Nizar Haddad; Michael Grishko; Ashraf Brik

1997-01-01

222

Widely Applicable Synthesis of Enantiomerically Pure (?99% ee) Tertiary Alkyl-containing 1-Alkanols via ZACA–Pd- or Cu-Catalyzed Cross-Coupling  

PubMed Central

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

Xu, Shiqing; Lee, Ching-Tien; Wang, Guangwei

2013-01-01

223

Electroconductive hydrogels: synthesis, characterization and biomedical applications.  

PubMed

Electroconductive hydrogels (ECHs) are composite biomaterials that bring together the redox switching and electrical properties of inherently conductive electroactive polymers (CEPs) with the facile small molecule transport, high hydration levels and biocompatibility of cross-linked hydrogels. General methods for the synthesis of electroconductive hydrogels as polymer blends and as polymer co-networks via chemical oxidative, electrochemical and/or a combination of chemical oxidation followed by electrochemical polymerization techniques are reviewed. Specific examples are introduced to illustrate the preparation of electroconductive hydrogels that were synthesized from poly(HEMA)-based hydrogels with polyaniline and from poly(HEMA)-based hydrogels with polypyrrole. The key applications of electroconductive hydrogels; as biorecognition membranes for implantable biosensors, as electro-stimulated drug release devices for programmed delivery, and as the low interfacial impedance layers on neuronal prostheses are highlighted. These applications provide great new horizons for these stimuli responsive, biomimetic polymeric materials. PMID:20060580

Guiseppi-Elie, Anthony

2010-04-01

224

Facile route to 3,5-disubstituted morpholines: enantioselective synthesis of O-protected trans-3,5-bis(hydroxymethyl)morpholines.  

PubMed

[reaction: see text] (3R,5R)-1 R1 & R2 = TBDPS, (3S,5R)-2 R1 = Bn,R2 = TBDPS, (3S,5S)-3 R2 & R2 = Bn. trans-3,5-Bis(benzyl/tert-butyldiphenylsilyloxymethyl)morpholines, promising candidates for the C(2)-symmetric class of chiral reagents, were prepared with excellent optical purity. A key step in the synthesis is the coupling of a serinol derivative with 2,3-O-isopropylideneglycerol triflate or its equivalent. This methodology was extended to the synthesis of chiral trans-3-(benzyloxymethyl)-5-(tert-butyldiphenylsilyloxymethyl)morpholine, a potentially useful chiral building block. PMID:14703339

Dave, Rajesh; Sasaki, N André

2004-01-01

225

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

226

Enantioselective Total Syntheses of (?)-Taiwaniaquinone H and (?)-Taiwaniaquinol B by Iridium-Catalyzed Borylation and Palladium-Catalyzed Asymmetric ?-Arylation  

PubMed Central

We report a concise, enantioselective total synthesis of (?)-taiwaniaquinone H and the first enantioselective total synthesis of (?)-taiwaniaquinol B by a route that includes enantioselective, palladium-catalyzed ?-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C–H borylation. This asymmetric ?-arylation creates the benzylic, quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic, quaternary, stereogenic centers, even those lacking a carbonyl group in the ?-position, by asymmetric ?-arylation. PMID:21268578

Liao, Xuebin; Stanley, Levi M.; Hartwig, John F.

2011-01-01

227

Development of (trimethylsilyl)ethyl ester protected enolates and applications in palladium-catalyzed enantioselective allylic alkylation: intermolecular cross-coupling of functionalized electrophiles.  

PubMed

The development of (trimethylsilyl)ethyl ester protected enolates is reported. The application of this class of compounds in palladium-catalyzed asymmetric allylic alkylation is explored, yielding a variety of ?-quaternary six- and seven-membered ketones and lactams. Independent coupling partner synthesis engenders enhanced allyl substrate scope relative to traditional ?-ketoester substrates; highly functionalized ?-quaternary ketones generated by the union of (trimethylsilyl)ethyl ?-ketoesters and sensitive allylic alkylation coupling partners serve to demonstrate the utility of this method for complex fragment coupling. PMID:24724872

Reeves, Corey M; Behenna, Douglas C; Stoltz, Brian M

2014-05-01

228

Highly enantioselective organocatalytic Biginelli reaction.  

PubMed

A series of binol- and H8-binol-based phosphoric acids have for the first time been evaluated for their ability to catalyze Biginelli reactions of aldehydes, thiourea or urea, and beta-keto esters. A new chiral phosphoric acid, derived from 3,3'-diphenyl-H8-binol, exhibited superior catalytic activity and enantioselectivity compared to its structural analogues, affording high enantioselectivities ranging from 85 to 97% ee with a wide scope of substrates. A metal-free preparation of optically active monastrol was achieved on the basis of the current process. PMID:17105279

Chen, Xiao-Hua; Xu, Xiao-Ying; Liu, Hua; Cun, Lin-Feng; Gong, Liu-Zhu

2006-11-22

229

An enantioselective formal synthesis of 4-demethoxydaunomycin using the catalytic asymmetric ring opening reaction of meso-epoxide with p-anisidine  

Microsoft Academic Search

A catalytic asymmetric formal synthesis of 4-demethoxydaunomycin (3) was achieved using a catalytic asymmetric ring opening reaction of meso-epoxide 9 as a key step. The epoxide opening reaction was promoted by 10mol% of Pr-(R)-BINOL–Ph3P?O complex to give the ?-amino alcohol 11 in 80% yield with 65% enantiomeric excess (ee). Single recrystallization enhanced the enantiomeric purity of the ?-amino alcohol 11

Akihiro Sekine; Takashi Ohshima; Masakatsu Shibasaki

2002-01-01

230

Highly Enantioselective Catalytic Phenylation of Ketones with a  

E-print Network

with high enantioselectivities.1,2 In contrast, analogous addition reactions to ketones have provenHighly Enantioselective Catalytic Phenylation of Ketones with a Constrained Geometry Titanium, gives good to excellent enantioselectivities with a range of substrates. The asymmetric addition

Walsh, Patrick J.

231

Optical nanoparticles: synthesis and biomedical application  

NASA Astrophysics Data System (ADS)

This paper presents a summary of our results on studies of synthesis and biomedical application of optical nanoparticles. Gold, dye-doped silica based and core–shell multifunctional multilayer (SiO2/Au, Fe3O4/SiO2, Fe3O4/SiO2/Au) water-monodispersed nanoparticles were synthesized by chemical route and surface modified with proteins and biocompatible chemical reagents. The particles were conjugated with antibody or aptamer for specific detecting and imaging bacteria and cancer cells. The photothermal effects of gold nanoshells (SiO2/Au and Fe3O4/SiO2/Au) on cells and tissues were investigated. The nano silver substrates were developed for surface enhanced Raman scattering (SERS) spectroscopy to detect melamine.

Nhung Tran, Hong; Nghiem, Thi Ha Lien; Thuy Duong Vu, Thi; Chu, Viet Ha; Huan Le, Quang; Nhung Hoang, Thi My; Thanh Nguyen, Lai; Pham, Duc Minh; Thuan Tong, Kim; Hoa Do, Quang; Vu, Duong; Nghia Nguyen, Trong; Tan Pham, Minh; Nguyen Duong, Cao; Thuy Tran, Thanh; Son Vu, Van; Thuy Nguyen, Thi; Nguyen, Thi Bich Ngoc; Tran, Anh Duc; Thuong Trinh, Thi; Nguyen, Thi Thai An

2015-01-01

232

Tetracalcium phosphate: Synthesis, properties and biomedical applications.  

PubMed

Monoclinic tetracalcium phosphate (TTCP, Ca(4)(PO(4))(2)O), also known by the mineral name hilgenstockite, is formed in the (CaO-P(2)O(5)) system at temperatures>1300 degrees C. TTCP is the only calcium phosphate with a Ca/P ratio greater than hydroxyapatite (HA). It appears as a by-product in plasma-sprayed HA coatings and shows moderate reactivity and concurrent solubility when combined with acidic calcium phosphates such as dicalcium phosphate anhydrous (DCPA, monetite) or dicalcium phosphate dihydrate (DCPD, brushite). Therefore it is widely used in self-setting calcium phosphate bone cements, which form HA under physiological conditions. This paper aims to review the synthesis and properties of TTCP in biomaterials applications such as cements, sintered ceramics and coatings on implant metals. PMID:20438869

Moseke, C; Gbureck, U

2010-10-01

233

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

234

Highly enantioselective synthesis of 2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-ones via catalytic asymmetric intramolecular cascade imidization-nucleophilic addition-lactamization.  

PubMed

Highly enantioselective catalytic asymmetric intramolecular cascade imidization-nucleophilic addition-lactamization of N(1)-alkylethane-1,2-diamine with methyl 2-formylbenzoate catalyzed by a chiral phosphoric acid represents the first efficient method for the preparation of medicinally interesting chiral 2,3-dihydro-1H-imidazo[2,1-a]isoindol-5(9bH)-ones with high yields and excellent enantioselectivities. This strategy has been shown to be quite general toward various methyl 2-formylbenzoates. PMID:25468078

He, Yuwei; Cheng, Chuyu; Chen, Bin; Duan, Kun; Zhuang, Yue; Yuan, Bo; Zhang, Meisan; Zhou, Yougui; Zhou, Zihong; Su, Yu-Jun; Cao, Rihui; Qiu, Liqin

2014-12-19

235

Palladium-catalyzed regio-, diastereo-, and enantioselective allylation of nitroalkanes with monosubstituted allylic substrates.  

PubMed

Pd-catalyzed asymmetric allylic alkylation of nitroalkanes and monosubstituted allylic substrates was performed to afford products with two adjacent chiral centers and with excellent regio-, diastereo-, and enantioselectivities. The usefulness of the protocol in organic synthesis was demonstrated by transformation of the product to an optically active homoallylamine, a 2,3-disubstituted tetrahydropyridine, and an ?,?-disubstituted amino acid derivative. PMID:23741970

Yang, Xiao-Fei; Yu, Wei-Hua; Ding, Chang-Hua; Ding, Qiu-Ping; Wan, Shi-Li; Hou, Xue-Long; Dai, Li-Xin; Wang, Pin-Jie

2013-07-01

236

Enantioselective gold catalyzed dearomative [2+2]-cycloaddition between indoles and allenamides.  

PubMed

The highly enantioselective synthesis of densely functionalized 2,3-indoline-cyclobutanes by means of chiral gold catalysis is presented. Intermolecular formal [2+2]-cycloaddition reactions between substituted indoles and allenamides enabled direct access to methylenecyclobutane-fused indolines, featuring two consecutive quaternary stereogenic centers with excellent stereochemical control (dr > 20?:?1, ee up to 99%). PMID:25562811

Jia, Minqiang; Monari, Magda; Yang, Qing-Qing; Bandini, Marco

2015-02-11

237

The lack of methods available for installing functionalities or structural motifs during chemical synthesis can at first be frustrating. However,  

E-print Network

of enantioselective reactions in total synthesis are highlighted in Fig. 1. In each of these cases, the target the need for enantioselective variants. Following the devel- opment of the [4+2] cycloaddition reaction7 Lewis acids, culminating in a report of the first highly enantioselective catalytic Diels­Alder reaction

Cai, Long

238

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

239

Organocatalytic enantioselective multicomponent reactions (OEMCRs)  

Microsoft Academic Search

The achieved level of expertise in organocatalytic processes has allowed synthetic chemists to apply this useful synthetic strategy to enantioselective multicomponent reactions. Although, this new methodology is still in its infancy, the reported results show the possibilities and versatility of this type of reaction, with an extraordinary level of atom efficiency being reached. All examples, from classical Mannich, Biginelli, Michael,

Gabriela Guillena; Diego J. Ramón; Miguel Yus

2007-01-01

240

New doubly orthogonal functions and their application to pattern synthesis  

NASA Astrophysics Data System (ADS)

A new eigenintegral equation to construct doubly orthogonal function systems is proposed and applied to pattern synthesis under constraints. Both weighting functions and integral domains are arbitrarily defined in the construction of the systems. The applications include fan-beam synthesis under beam power constraint and optimization of the product of (gain) (S,N). Kernel expansion for basic pattern function is discussed.

Tokumaru, S.; Nakahara, M.; Yamamoto, S.

1981-08-01

241

Palladium-catalyzed enantioselective decarboxylative cycloaddition of vinylethylene carbonates with isocyanates.  

PubMed

An efficient method for the enantioselective construction of ?-substituted ?-vinylglycinol derivatives through palladium-catalyzed decarboxylative cycloaddition of vinylethylene carbonates with isocyanates was developed. By using a palladium complex generated in situ from [Pd2 (dba)3]?CHCl3 (dba=dibenzylideneacetone) and (S)-Segphos as a catalyst under mild reaction conditions, the process provided 4-substituted-4-vinyloxazolidin-2-ones in high yields with a high level of enantioselectivity. The stereochemical outcome of the reaction was explained by DFT calculations and the synthetic utility of the process was demonstrated by the gram-scale transformation and formal synthesis of MK-0731 as a kinesin spindle protein inhibitor. PMID:25400207

Khan, Ajmal; Xing, Juxiang; Zhao, Jingming; Kan, Yuhe; Zhang, Wanbin; Zhang, Yong Jian

2015-01-01

242

Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams  

NASA Astrophysics Data System (ADS)

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 Article, we describe the highly enantioselective palladium-catalysed 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 envisage 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 used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

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

2012-02-01

243

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

244

Assembly intermediates in polyketide biosynthesis: enantioselective syntheses of beta-hydroxycarbonyl compounds.  

PubMed

A versatile approach for the enantioselective synthesis of functionalised beta-hydroxy N-acetylcysteamine thiol esters has been developed which allows the facile incorporation of isotopic labels. It has been shown that a remarkable reversal of selectivity occurs in the titanium mediated aldol reaction of acyloxazolidinone using either (S)- or (R)-tert-butyldimethylsilyloxybutanal. The aldol products are valuable intermediates in the synthesis of 4-hydroxy-6-substituted delta-lactones. PMID:15858656

Le Sann, Christine; Munoz, Dulce M; Saunders, Natalie; Simpson, Thomas J; Smith, David I; Soulas, Florilène; Watts, Paul; Willis, Christine L

2005-05-01

245

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

246

Synthesis and applications of heterostructured semiconductor nanocrystals  

NASA Astrophysics Data System (ADS)

Semiconductor nanocrystals (NCs) have been of great interest to researchers for several decades due to their unique optoelectronic properties. These nanoparticles are widely used for a variety of different applications. However, there are many unresolved issues that lower the efficiency and/or stability of devices which incorporate these NCs. Our research is dedicated to addressing these issues by identifying potential problems and resolving them, improving existing systems, generating new synthetic strategies, and/or building new devices. The general strategies for the synthesis of different nanocrystals were established in this work, one of which is the colloidal growth of gold domains onto CdS semiconductor nanocrystals. Control of shape and size was achieved simply by adjusting the temperature and the time of the reaction. Depending on the exact morphology of Au and CdS domains, fabricated nano-composites can undergo evaporation-induced self-assembly onto a substrate, which is very useful for building devices. CdS/Au heterostructures can assemble in two different ways: through end-to-end coupling of Au domains, resulting in the formation of one-dimensional chains; and via side-by-side packing of CdS nanorods, leading to the onset of two-dimensional superlattices. We investigated the nature of exciton-plasmon interactions in Au-tipped CdS nanorods using femtosecond transient absorption spectroscopy. The study demonstrated that the key optoelectronic properties of electrically coupled metal and semiconductor domains are significantly different from those observed in systems with weak inter-domain coupling. In particular, strongly-coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton carrier excitations. Colloidal QDs are starting to replace organic molecules in many different applications, such as organic light emmiting diods (OLEDs), due to their light emmision tunability. We reported a general strategy for the assembly of all-inorganic light-emitting nanocrystal films with an emission quantum yield in the 30-52% range. Our methodology relies on solution-processing of CdSe nanocrystals into a crystalline matrix of a wide band gap semiconductor (CdS, ZnS). As a result, we replace original organic ligands on nanocrystal surfaces with an inorganic medium which efficiently preserves the quantum confinement of electrical charges in CdSe NCs. In addition to strong emission, fabricated films demonstrated excellent thermal and chemical stability, and a large refractive index, which avails their integration into emerging solid-state nanocrystal devices. The ability to control size and shape of NCs is essential as it automatically affects the optoelectronic properties of the crystals. Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of NCs, but some nanoparticle morphologies require alternative processing strategies. We have shown that chemical etching of colloidal nanoparticles can facilitate the realization of desirable nanocrystal geometries. This methodology allows both CdSe and CdS composed semiconductor domains be exposed to the external environment, while maintaining a structural design that is highly desirable for catalytic applications. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers. We expect that the demonstrated application will become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticle architectures for applications in the areas of photocatalysis, photovoltaics, and light detection.

Khon, Elena

247

Enantioselective changes in oxidative stress and toxin release in Microcystis aeruginosa exposed to chiral herbicide diclofop acid.  

PubMed

Enantioselective oxidative stress and toxin release from Microcystis aeruginosa after exposure to the chiral herbicide diclofop acid were investigated. Racemic diclofop acid, R-diclofop acid and S-diclofop acid induced reactive oxygen species (ROS) generation, increased the concentration of malondialdehyde (MDA), enhanced the activity of superoxide dismutase (SOD) and triggered toxin release in M. aeruginosa to varying degrees. The increase in MDA concentration and SOD activity in M. aeruginosa occurred sooner after exposure to diclofop acid than when the cyanobacteria was exposed to either the R- and the S-enantiomer. In addition, enantioselective toxicity of the enantiomers was observed. The R-enantiomer trigged more ROS generation, more SOD activity and more toxin synthesis and release in M. aeruginosa cells than the S-enantiomer. Diclofop acid and its R-enantiomer may collapse the transmembrane proton gradient and destroy the cell membrane through lipid peroxidation and free radical oxidation, whereas the S-enantiomer did not demonstrate such action. R-diclofop acid inhibits the growth of M. aeruginosa in the early stage, but ultimately induced greater toxin release, which has a deleterious effect on the water column. These results indicate that more comprehensive study is needed to determine the environmental safety of the enantiomers, and application of chiral pesticides requires more direct supervision and training. Additionally, lifecycle analysis of chiral pollutants in aquatic system needs more attention to aide in the environmental assessment of chiral pesticides. PMID:24240105

Ye, Jing; Zhang, Ying; Chen, Shengwen; Liu, Chaonan; Zhu, Yongqiang; Liu, Weiping

2014-01-01

248

Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric Aminocatalysis  

NASA Astrophysics Data System (ADS)

The concept of combining heterogeneous transition metal and amine catalysis for enantioselective cascade reactions has not yet been realized. This is of great advantage since it would allow for the recycling of expensive and non-environmentally friendly transition metals. We disclose that the use of a heterogeneous Pd-catalyst in combination with a simple chiral amine co-catalyst allows for highly enantioselective cascade transformations. The preparative power of this process has been demonstrated in the context of asymmetric cascade Michael/carbocyclization transformations that delivers cyclopentenes bearing an all carbon quaternary stereocenters in high yields with up to 30:1 dr and 99% ee. Moreover, a variety of highly enantioselective cascade hetero-Michael/carbocyclizations were developed for the one-pot synthesis of valuable dihydrofurans and pyrrolidines (up to 98% ee) by using bench-stable heterogeneous Pd and chiral amines as co-catalysts.

Deiana, Luca; Afewerki, Samson; Palo-Nieto, Carlos; Verho, Oscar; Johnston, Eric V.; Córdova, Armando

2012-11-01

249

A simplified catalytic system for direct catalytic asymmetric aldol reaction of thioamides; application to an enantioselective synthesis of atorvastatin  

Microsoft Academic Search

A new catalytic system was developed for the direct catalytic asymmetric aldol reaction of thioamides. The new lithium-free Cu catalyst (second-generation catalyst) exhibited enhanced catalytic efficiency over the previously developed catalyst comprising [Cu(CH3CN)4]PF6\\/Ph-BPE\\/LiOAr (first-generation catalyst), which required a tedious catalyst preparation process. In the reaction with the second-generation catalyst, the intermediate Cu-aldolate functioned as a Brønsted base to generate thioamide

Yuji Kawato; Mitsutaka Iwata; Ryo Yazaki; Naoya Kumagai; Masakatsu Shibasaki

2011-01-01

250

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

251

Mechanochemical synthesis of advanced nanomaterials for catalytic applications.  

PubMed

Mechanochemical synthesis emerged as the most advantageous, environmentally sound alternative to traditional routes for nanomaterials preparation with outstanding properties for advanced applications. Featuring simplicity, high reproducibility, mild/short reaction conditions and often solvent-free condition (dry milling), mechanochemistry can offer remarkable possibilities in the development of advanced catalytically active materials. The proposed contribution has been aimed to provide a brief account of remarkable recent findings and advances in the mechanochemical synthesis of solid phase advanced catalysts as opposed to conventional systems. The role of mechanical energy in the synthesis of solid catalysts and their application is critically discussed as well as the influence of the synthesis procedure on the physicochemical properties and the efficiency of synthesized catalysts is studied. The main purpose of this feature article is to highlight the possibilities of mechanochemical protocols in (nano)materials engineering for catalytic applications. PMID:25713819

Xu, Chunping; De, Sudipta; Balu, Alina M; Ojeda, Manuel; Luque, Rafael

2015-04-01

252

Asymmetric total synthesis of apocynaceae hydrocarbazole alkaloids (+)-deethylibophyllidine and (+)-limaspermidine.  

PubMed

An unprecedented asymmetric catalytic tandem aminolysis/aza-Michael addition reaction of spirocyclic para-dienoneimides has been designed and developed through organocatalytic enantioselective desymmetrization. A unified strategy based on this key tandem methodology has been divergently explored for the asymmetric total synthesis of two natural Apocynaceae alkaloids, (+)-deethylibophyllidine and (+)-limaspermidine. The present studies not only enrich the tandem reaction design concerning the asymmetric catalytic assembly of a chiral all-carbon quaternary stereocenter contained in the densely functionalized hydrocarbazole synthons but also manifest the potential for the application of the asymmetric catalysis based on the para-dienone chemistry in asymmetric synthesis of natural products. PMID:25767939

Du, Ji-Yuan; Zeng, Chao; Han, Xiao-Jie; Qu, Hu; Zhao, Xian-He; An, Xian-Tao; Fan, Chun-An

2015-04-01

253

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; Côme, Yémima Bon Saint; Lapeyre, Veronique; Bopp, Philippe A.; Heim, Matthias; Yadnum, Sudarat; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

2014-01-01

254

Enantioselective recognition at mesoporous chiral metal surfaces  

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

255

Enantioselective catalysis of photochemical reactions.  

PubMed

The nature of the excited state renders the development of chiral catalysts for enantioselective photochemical reactions a considerable challenge. The absorption of a 400?nm photon corresponds to an energy uptake of approximately 300?kJ?mol(-1) . Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual catalysis). PMID:25728854

Brimioulle, Richard; Lenhart, Dominik; Maturi, Mark M; Bach, Thorsten

2015-03-23

256

Enantioselective Ring-Opening DOI: 10.1002/anie.200804415  

E-print Network

substrates, the enantioselectivity in the TMSN3-mediated reactions exceed the highest values reported to dateEnantioselective Ring-Opening DOI: 10.1002/anie.200804415 Enantioselective Desymmetrization of meso for the enantioselective opening of meso-epoxides with trimethylsilyl azide (TMSN3),[1] such desymmetrization reac- tions

RajanBabu, T. V. "Babu"

257

Chiral Brønsted acid from a cationic gold(I) complex: catalytic enantioselective protonation of silyl enol ethers of ketones.  

PubMed

A chiral Brønsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the ?-position. Furthermore, the application of this Brønsted acid was extended to the first Brønsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio. PMID:21815666

Cheon, Cheol Hong; Kanno, Osamu; Toste, F Dean

2011-08-31

258

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides  

PubMed Central

Summary Enantioselective desymmetrization of meso-aziridines and meso-epoxides with various nucleophiles by organocatalysis has emerged as a cutting-edge approach in recent years. This review summarizes the origin and recent developments of enantioselective desymmetrization of meso-aziridines and meso-epoxides in the presence of organocatalysts. PMID:24062828

2013-01-01

259

Practical and highly selective sulfur ylide-mediated asymmetric epoxidations and aziridinations using a cheap and readily available chiral sulfide: extensive studies to map out scope, limitations, and rationalization of diastereo- and enantioselectivities.  

PubMed

The chiral sulfide, isothiocineole, has been synthesized in one step from elemental sulfur, ?-terpinene, and limonene in 61% yield. A mechanism involving radical intermediates for this reaction is proposed based on experimental evidence. The application of isothiocineole to the asymmetric epoxidation of aldehydes and the aziridination of imines is described. Excellent enantioselectivities and diastereoselectivities have been obtained over a wide range of aromatic, aliphatic, and ?,?-unsaturated aldehydes using simple protocols. In aziridinations, excellent enantioselectivities and good diastereoselectivities were obtained for a wide range of imines. Mechanistic models have been put forward to rationalize the high selectivities observed, which should enable the sulfide to be used with confidence in synthesis. In epoxidations, the degree of reversibility in betaine formation dominates both the diastereoselectivity and the enantioselectivity. Appropriate tuning of reaction conditions based on understanding the reaction mechanism enables high selectivities to be obtained in most cases. In aziridinations, betaine formation is nonreversible with semistabilized ylides and diastereoselectivities are determined in the betaine forming step and are more variable as a result. PMID:23902598

Illa, Ona; Namutebi, Mariam; Saha, Chandreyee; Ostovar, Mehrnoosh; Chen, C Chun; Haddow, Mairi F; Nocquet-Thibault, Sophie; Lusi, Matteo; McGarrigle, Eoghan M; Aggarwal, Varinder K

2013-08-14

260

An overview of quantumquantum dotdot synthesis, applications  

E-print Network

? Control AntiHER2 #12;Quantum dots ~2 - 6 nm #12;How are they made? #12;Synthesis Movie http? Michalet et al. Science, 307, 2005 Gao et al. Nat.Biotech., 22, 2004Green, Angew. Chem., 43, 2004 Sapsford

261

Supramolecular dendritic polymers: from synthesis to applications.  

PubMed

CONSPECTUS: Supramolecular dendritic polymers (SDPs), which perfectly combine the advantages of dendritic polymers with those of supramolecular polymers, are a novel class of non-covalently bonded, highly branched macromolecules with three-dimensional globular topology. Because of their dynamic/reversible nature, unique topological structure, and exceptional physical/chemical properties (e.g., low viscosity, high solubility, and a large number of functional terminal groups), SDPs have attracted increasing attention in recent years in both academic and industrial fields. In particular, the reversibility of non-covalent interactions endows SDPs with the ability to undergo dynamic switching of structure, morphology, and function in response to various external stimuli, such as pH, temperature, light, stress, and redox agents, which further provides a flexible and robust platform for designing and developing smart supramolecular polymeric materials and functional supramolecular devices. The existing SDPs can be systematically classified into the following six major types according to their topological features: supramolecular dendrimers, supramolecular dendronized polymers, supramolecular hyperbranched polymers, supramolecular linear-dendritic block copolymers, supramolecular dendritic-dendritic block copolymers, and supramolecular dendritic multiarm copolymers. These different types of SDPs possess distinct morphologies, unique architectures, and specific functions. Benefiting from their versatile topological structures as well as stimuli-responsive properties, SDPs have displayed not only unique characteristics or advantages in supramolecular self-assembly behaviors (e.g., controllable morphologies, specific performance, and facile functionalization) but also great potential to be promising candidates in various fields. In this Account, we summarize the recent progress in the synthesis, functionalization, and self-assembly of SDPs as well as their potential applications in a wide range of fields. A variety of synthetic methods using non-covalent interactions have been established to prepare different types of SDPs based on varied mono- or multifunctionalized building blocks (e.g., monomer, dendron, dendrimer, and hyperbranched polymer) with homo- or heterocomplementary units. In addition, SDPs can be further endowed with excellent functionalities by employing different modification approaches involving terminal, focal-point, and backbone modification. Similar to conventional dendritic polymers, SDPs can self-assemble into diverse supramolecular structures such as micelles, vesicles, fibers, nanorings, tubes, and many hierarchical structures. Finally, we highlight some typical examples of recent applications of SDP-based systems in biomedical fields (e.g., controlled drug/gene/protein delivery, bioimaging, and biomimetic chemistry), nanotechnology (e.g., nanoreactors, catalysis, and molecular imprinting), and functional materials. The current research on SDPs is still at the very early stage, and much more work needs to be done. We anticipate that future studies of SDPs will focus on developing multifunctional, hierarchical supramolecular materials toward their practical applications by utilization of cooperative non-covalent interactions. PMID:24779892

Dong, Ruijiao; Zhou, Yongfeng; Zhu, Xinyuan

2014-07-15

262

Chemoselective and Enantioselective Hydrogenations on Immobilized Complexes  

NASA Astrophysics Data System (ADS)

Homogeneous catalysts, which are mixed with the reactants at the molecular level, typically show the highest activity and selectivity as they offer chemically well-defined active sites and are not limited by heat and mass transport. However, an inherent disadvantage of the homogeneous catalysis is the need to separate the catalyst from a product after the reaction. Therefore, solid or immobilized homogeneous catalysts are preferred in industry. In this contribution we pay attention to chemoselectivity, regioselectivity and enantioselectivity in the synthesis of fine chemicals by means of hydrogenation reactions with immobilised homogeneous complexes. Preferential hydrogenation of one functional group in a molecule over another is the chemoselective process, while regioselective hydrogenation is the preferential formation of one constitutional isomer of the product in a reaction in which other isomers may also be formed, and the stereoselective hydrogenation is the formation of an excess of one stereoisomer over others. Homogeneous and heterogeneous catalytic transfer hydrogenations (CTH) were additionally introduced as alternative methods to the classical hydrogenation processes. They utilise a different hydrogen source from molecular hydrogen and can find their use for reduction of any type of groups.

Zsigmond, Agnes; Notheisz, Ferenc; Kluson, Petr; Floris, Tomas

263

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

PubMed

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

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

2013-08-01

264

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

Federal Register 2010, 2011, 2012, 2013, 2014

...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

265

Design and synthesis of mixed oxides nanoparticles for biofuel applications  

SciTech Connect

The work in this dissertation presents the synthesis of two mixed metal oxides for biofuel applications and NMR characterization of silica materials. In the chapter 2, high catalytic efficiency of calcium silicate is synthesized for transesterfication of soybean oil to biodisels. Chapter 3 describes the synthesis of a new Rh based catalyst on mesoporous manganese oxides. The new catalyst is found to have higher activity and selectivity towards ethanol. Chapter 4 demonstrates the applications of solid-state Si NMR in the silica materials.

Chen, Senniang

2010-05-15

266

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.

267

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. PMID:25436235

Sabir, Sidra; Arshad, Muhammad

2014-01-01

268

Combinatorial evolution of site- and enantioselective catalysts for polyene epoxidation  

NASA Astrophysics Data System (ADS)

Selectivity in the catalytic functionalization of complex molecules is a major challenge in chemical synthesis. The problem is magnified when there are several possible stereochemical outcomes and when similar functional groups occur repeatedly within the same molecule. Selective polyene oxidation provides an archetypical example of this challenge. Historically, enzymatic catalysis has provided the only precedents. Although non-enzymatic catalysts that meet some of these challenges became known, a comprehensive solution has remained elusive. Here, we describe low molecular weight peptide-based catalysts, discovered through a combinatorial synthesis and screening protocol, that exhibit site- and enantioselective oxidation of certain positions of various isoprenols. This diversity-based approach, which exhibits features reminiscent of the directed evolution of enzymes, delivers catalysts that compare favourably to the state-of-the-art for the asymmetric oxidation of these compounds. Moreover, the approach culminated in catalysts that exhibit alternative-site selectivity in comparison to oxidation catalysts previously described.

Lichtor, Phillip A.; Miller, Scott J.

2012-12-01

269

A Lewis acid activated reaction of Zn with EtI to promote highly enantioselective alkyne additions to aldehydes.  

PubMed

An easily available BINOL-Ti(O(i)Pr)4 catalyst system is found to activate the reaction of Zn powder with EtI for the asymmetric alkyne addition to aldehydes at room temperature. It allows the synthesis of a number of synthetically useful chiral propargylic alcohols with both high yields and high enantioselectivity (up to >96% ee). PMID:25407055

Chen, Shan-yong; Liu, Winnie; Wu, Xuedan; Ying, Jun; Yu, Xiaoqi; Pu, Lin

2015-01-01

270

Enantioselective Synthesis of Axial Chiral Allenes  

E-print Network

Noyes b C C C y z a Orthogonal Bonding C OO O OAc OAc NPh PhPh NPhHO D-camphorsulphonic acid BenzenePh NPhHO D-camphorsulphonic acid Benzene, heat C Ph NPhPh NPh []5461 = +437º 1952?: First cyclic allenes. Their intermediacy has been determined through trapping/degradation studies. M. Regitz and coworkers have described

Stoltz, Brian M.

271

Activation of pig liver esterase in organic media with organic polymers: application to the enantioselective acylation of racemic functionalized secondary alcohols.  

PubMed

Pig liver esterase (PLE) shows practically no activity in acylation of alcohols with vinylic esters in organic solvents. However, addition of methoxypoly(ethylene glycol) (MPEG), bovine serum albumin (BSA), TentaGelAmino resin (TGA), or aminomethyl polystyrene (AMPS) confers activity to PLE in acylation of alcohols with vinyl propionate in organic solvents of low water content. Polymer-activated PLE showed high enantioselectivities (E > 100) in the acylation of racemic 1-alkoxy-, 1-ethylsulfanyl-, and 1-fluoro-3-aryl-2-propanols as well as racemic 1-phenoxy-2-propanol and racemic 1-methoxy-2-phenoxy-2-propanol. The synthetic utility of polymer-activated PLE has been demonstrated by the gram-scale resolution of 1-methoxy-3-phenyl-2-propanol, 1-ethylsulfanyl-3-phenyl-2-propanol, 1-methoxy-3-p-methoxyphenyl-2-propanol, 1-fluoro-3-phenyl-2-propanol, and 1-methoxy-3-phenoxy-2-propanol. In PLE-catalyzed acylation of alcohols with vinyl propionate, acetaldehyde and propionic acids, both being detrimental to the enzyme, are formed as byproducts. In addition, the water content of the system, which is critical for the activity of pig liver esterase, is lowered because of a competing enzymatic hydrolysis of the acyl donor. The polymers TGA, BSA, and AMPS not only scavenge the aldehyde and the acid through imine formation and neutralization, respectively, but replenish at least in part also the water consumed in the competing hydrolysis of the acyl donor. A recovery of PLE together with the polymer was achieved without major loss of activity through their immobilization on a water-saturated polyaramide membrane, which occurs spontaneously in organic solvents. PMID:11348121

Gais, H J; Jungen, M; Jadhav, V

2001-05-18

272

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

273

Enantioselective inhibition of microbial lipolytic enzymes by nonracemic monocyclic enolphosphonate analogues of cyclophostin.  

PubMed

Four nonracemic enolphosphonate analogues of Cyclophostin were obtained by asymmetric synthesis, and their absolute configurations at both phosphorus and C-5 carbon chiral centers were unambiguously assigned. The influence of chirality was studied by testing the inhibitory effects of these four stereoisomers toward the lipolytic activity of three microbial lipases: Fusarium solani cutinase, Rv0183, and LipY from Mycobacterium tuberculosis . Cutinase was highly diastereoselective for the (Sp) configuration using (Sc) inhibitors, whereas no obvious stereopreference at phosphorus was observed with (Rc) compounds. Conversely, Rv0183 exhibited strong enantioselective discrimination for (Sp) configuration regardless of the chirality at the asymmetric carbon atom. Lastly, LipY discriminated only the unusual diastereoisomeric configuration (Rc, Rp) leading to the most potent inhibitor. This work, which provides a fundamental premise for the understanding of the stereoselective relationships between nonracemic enolphosphonates and their inhibitory activity, also opens new prospects on the design and synthesis of highly specific enantioselective antimicrobial agents. PMID:23651298

Point, Vanessa; Malla, Raj K; Carrière, Frederic; Canaan, Stéphane; Spilling, Christopher D; Cavalier, Jean-François

2013-06-13

274

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

275

Synthesis and photovoltaic application of copper(I) sulfide nanocrystals.  

PubMed

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 1.6% power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period. PMID:18651779

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

2008-08-01

276

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

277

Parameter Synthesis in Nonlinear Dynamical Systems: Application to Systems Biology  

E-print Network

. The dynamics of biological processes are often modeled as systems of nonlinear ordinary differential equations problem for nonlinear dynamical systems. That is, for systems of nonlinear ordinary differential equationsParameter Synthesis in Nonlinear Dynamical Systems: Application to Systems Biology Alexandre Donz

Langmead, Christopher James

278

Enantioselective environmental toxicology of chiral pesticides.  

PubMed

The enantioselective environmental toxic effect of chiral pesticides is becoming more important. As the industry develops, increasing numbers of chiral insecticides and herbicides will be introduced into use, potentially posing toxic effects on nontarget living beings. Chiral pesticides, including herbicides such as acylanilides, phenoxypropanoic acids, and imidazolinones, and insecticides such as synthetic pyrethroids, organophosphates, and DDT often behave enantioselectively during agricultural use. These compounds also pose unpredictable enantioselective ecological threats to nontarget living beings and/or humans, affecting the food chain and entire ecosystems. Thus, to investigate the enantioselective toxic effects of chiral insecticides and herbicides is necessary during environmental protection. The environmental toxicology of chiral pesticides, especially the findings obtained from studies conducted in our laboratory during the past 10 years, is reviewed. PMID:25643169

Ye, Jing; Zhao, Meirong; Niu, Lili; Liu, Weiping

2015-03-16

279

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

2014-11-18

280

Enantioselective aldol reaction between isatins and cyclohexanone catalyzed by amino Acid sulphonamides.  

PubMed

Sulphonamides derived from primary ?-amino acid were successfully applied to catalyze the aldol reaction between isatin and cyclohexanone under neat conditions. More interestingly, molecular sieves, as privileged additives, were found to play a vital role in achieving high enantioselectivity. Consequently, high yields (up to 99%) along with good enantioselectivities (up to 92% ee) and diastereoselectivities (up to 95:5 dr) were obtained. In addition, this reaction was also conveniently scaled up, demonstrating the applicability of this protocol. Chirality 27:314-319, 2015. © 2015 Wiley Periodicals, Inc. PMID:25691447

Wang, Jun; Liu, Qi; Hao, Qing; Sun, Yanhua; Luo, Yiming; Yang, Hua

2015-04-01

281

Highly enantioselective adsorption of small prochiral molecules on a chiral intermetallic compound.  

PubMed

Intrinsically chiral surfaces of intermetallic compounds are shown to be novel materials for enantioselective processes. Their advantage is the significantly higher thermal and chemical stability, and therefore their extended application range for catalyzed chiral reactions compared to surfaces templated with chiral molecular modifiers or auxiliaries. On the Pd1 -terminated PdGa(111) surface, room-temperature adsorption of a small prochiral molecule (9-ethynylphenanthrene) leads to exceptionally high enantiomeric excess ratios of up to 98?%. Our findings highlight the great potential of intrinsically chiral intermetallic compounds for the development of novel, enantioselective catalysts that can be operated at high temperatures and potentially also in harsh chemical environments. PMID:25655521

Prinz, Jan; Gröning, Oliver; Brune, Harald; Widmer, Roland

2015-03-23

282

Spontaneous mirror symmetry breaking via enantioselective autocatalysis  

SciTech Connect

The conditions for spontaneous generation of optically active product under autocatalytic type reactions is considered on the base of the general kinetic model of enantioselective autocatalytic stages. It is shown that the spontaneous generation of optical activity mostly depends on the enantioselectivity of catalytic transformations. The properties of autocatalytic reactions, which are needed for an experiment, as well as the necessary chemical conditions, are discussed. {copyright} {ital 1996 American Institute of Physics.}

Avetisov, V.A. [N. N. Semenov Institute of Chemical Physics of the Russian Academy of Sciences, ul.Kossvgina 4, 11-7977 Moscow (Russia)

1996-07-01

283

Spontaneous mirror symmetry breaking via enantioselective autocatalysis  

NASA Astrophysics Data System (ADS)

The conditions for spontaneous generation of optically active product under autocatalytic type reactions is considered on the base of the general kinetic model of enantioselective autocatalytic stages. It is shown that the spontaneous generation of optical activity mostly depends on the enantioselectivity of catalytic transformations. The properties of autocatalytic reactions, which are needed for an experiment, as well as the necessary chemical conditions, are discussed.

Avetisov, Vladik A.

1996-07-01

284

SignSynth: A Sign Language Synthesis Application Using Web3D and Perl  

Microsoft Academic Search

Development of sign synthesis (also known as text-to-sign) can benefit from studying the history of its older cousin, speech synthesis. As Klatt (1) outlines the basic a rchitecture of a speech synthesis application, I will discuss the architecture of a sign synthesis application and mention some of the applications and p rototypes currently available. I will focus on SignSynth, a

Angus B. Grieve-smith

2001-01-01

285

Scope and Mechanistic Analysis of the Enantioselective Synthesis of Allenes by Rhodium-Catalyzed Tandem Ylide Formation/[2, 3]-Sigmatropic Rearrangement between Donor/Acceptor Carbenoids and Propargylic Alcohols  

PubMed Central

Rhodium-catalyzed reactions of tertiary propargylic alcohols with methyl aryl- and styryldiazoacetates result in tandem reactions, consisting of oxonium ylide formation followed by [2, 3]-sigmatropic rearrangement. This process competes favorably with the standard O—H insertion reaction of carbenoids. The resulting allenes are produced with high enantioselectivity (88–98% ee) when the reaction is catalyzed by the dirhodium tetraprolinate complex, Rh2(S-DOSP)4. Kinetic resolution is possible when racemic tertiary propargylic alcohols are used as substrates. Under the kinetic resolution conditions, the allenes are formed with good diastereoselectivity and enantioselectivity (up to 6.1:1 dr, 88–93% ee) and the unreacted alcohols are enantioenriched to 65–95% ee. Computational studies reveal that the high asymmetric induction is obtained via an organized transition states involving a two-point attachment: ylide formation between the alcohol oxygen and the carbenoid and hydrogen bonding of the alcohol to a carboxylate ligand. The 2,3-sigmatropic rearrangement proceeds through initial cleavage of the O-–H bond to generate an intermediate with close-lying open-shell singlet, triplet and closed-shell singlet electronic states. This intermediate would have significant diradical character, which is consistent with the observation that the 2,3-sigmatropic rearrangement is favored with donor/acceptor carbenoids and more highly functionalized propargylic alcohols. PMID:22924394

Li, Zhanjie; Boyarskikh, Vyacheslav; Hansen, Jørn H.; Autschbach, Jochen; Musaev, Djamaladdin G.; Davies, Huw M. L.

2012-01-01

286

Enantioselective functionalization of allylic C-H bonds following a strategy of functionalization and diversification.  

PubMed

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 the catalytic 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 a 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

2013-11-27

287

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

288

Aerosol synthesis and application of folded graphene-based materials  

NASA Astrophysics Data System (ADS)

Graphene oxide colloid has been widely used in the synthesis of various graphene-based materials. Graphene oxide sheets, with a low bending rigidity, can be folded when assembled in aqueous phase. A simple but industrial scalable way, aerosol processing, can be used to fabricate folded graphene-based materials. These folded materials can carry various cargo materials and be used in different applications such as time-controlled drug release, medical imaging enhancement, catalyst support and energy related areas. The aerosol synthesis of folded graphene-based materials can also be easily extended to fabricate hybrid nanomaterials without any complicated chemistries.

Chen, Yantao; Wang, Zhongying; Qiu, Yang

2015-12-01

289

Synthesis and Characterization of Polymers for Fuel Cells Application  

NASA Technical Reports Server (NTRS)

The goal of this summer research is to prepare Polymer Exchange Membranes (PEM s) for fuel cell application. Several high temperature polymers such as polybenzimidazoles and polyether ketones were known to possess good high temperature stability and had been investigated by post-sulfonation to yield sulfonated polymers. The research project will involve two approaches: 1. Synthesis of polybenzimidazoles and then react with alkyl sultonse to attach an aliphatic sulfonic groups. 2. Synthesis of monomers containing sulfonic acid units either on a aromatic ring or on an aliphatic chain and then polymerize the monomers to form high molecular weight sulfonate polymers.

Tytko, Stephen F.

2003-01-01

290

Multipore zeolites: synthesis and catalytic applications.  

PubMed

In the last few years, important efforts have been made to synthesize so-called "multipore" zeolites, which contain channels of different dimensions within the same crystalline structure. This is a very attractive subject, since the presence of pores of different sizes would favor the preferential diffusion of reactants and products through those different channel systems, allowing unique catalytic activities for specific chemical processes. In this Review we describe the most attractive achievements in the rational synthesis of multipore zeolites, containing small to extra-large pores, and the improvements reported for relevant chemical processes when these multipore zeolites have been used as catalysts. PMID:25664421

Moliner, Manuel; Martínez, Cristina; Corma, Avelino

2015-03-16

291

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

292

Pristine nanomaterials: synthesis, stability and applications  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

293

Nanoparticles: synthesis and applications in life science and environmental technology  

NASA Astrophysics Data System (ADS)

This work focuses on the synthesis, functionalization, and application of gold and silver nanoparticles, magnetic nanoparticles Fe3O4, combination of 4-ATP-coated silver nanoparticles and Fe3O4 nanoparticles. The synthesis methods such as chemical reduction, seeding, coprecipitation,and inverse microemulsion will be outlined. Silica- and amino-coated nanoparticles are suitable for several applications in biomedicine and the environment. The applications of the prepared nanoparticles for early detection of breast cancer cells, basal cell carcinoma, antibacterial test, arsenic removal from water, Herpes DNA separation, CD4+ cell separation and isolation of DNA of Hepatitis virus type B (HBV) and Epstein–Barr virus (EBV) are discussed. Finally, some promising perspectives will be pointed out. Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

Luong Nguyen, Hoang; Nguyen, Hoang Nam; Hai Nguyen, Hoang; Quynh Luu, Manh; Hieu Nguyen, Minh

2015-03-01

294

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

295

Cathedral-III : architecture-driven high-level synthesis for high throughput DSP applications  

Microsoft Academic Search

The goal of this paper is to extend the synthesis of real time digital signal processing (DSP) algorithms towards the domain of high throughput applications. A novel architectural style specifically suited for this application domain is presented. Furthermore, a synopsis of a novel synthesis script typically oriented towards this architecture is described (architecture-driven synthesis). The emphasis in the script is

Werner Geurts; F. Catthoor; H. De Man

1991-01-01

296

Cathedral-III: Architecture-driven high-level synthesis for high throughput DSP applications  

Microsoft Academic Search

The goal of this paper is to extend the synthesis of real time digital signal processing (DSP) algorithms towards the domain of high throughput applications. A novel architectural style specitlcally suited for this application domain is presented. Furthermore, a synopsis of a novel synthesis script typically oriented towards this architecture is described (architecture-driven synthesis). The emphasis in the script is

Stefaan Notel; Werner Geurts; Francky Catthoori; Hugo De Man

1991-01-01

297

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

298

Synthesis of boron nitride nanotubes and their applications.  

PubMed

Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed. PMID:25671154

Kalay, Saban; Yilmaz, Zehra; Sen, Ozlem; Emanet, Melis; Kazanc, Emine; Çulha, Mustafa

2015-01-01

299

Synthesis of boron nitride nanotubes and their applications  

PubMed Central

Summary Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed. PMID:25671154

Kalay, Saban; Yilmaz, Zehra; Sen, Ozlem; Emanet, Melis; Kazanc, Emine

2015-01-01

300

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

301

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides  

E-print Network

Catalytic Enantioselective Negishi Reactions of Racemic Secondary Benzylic Halides Forrest O. Arp with excellent enantioselectivity (eqs 3 and 4). Table 1. Catalytic Enantioselective Negishi Reactions of Racemic in developing nickel-catalyzed cross-coupling reactions of secondary alkyl electrophiles.1 To fully exploit

Fu, Gregory C.

302

Highly Enantioselective Cyclocarbonylation of Allylic Alcohols Catalyzed by Novel  

E-print Network

the first enantioselective variant of this reaction using commercially available chiral bisphosphine ligands enantioselectivity in a number of Rh-BICP and Ru-BICP catalyzed asymmetric hydrogenation reactions.7 These resultsHighly Enantioselective Cyclocarbonylation of Allylic Alcohols Catalyzed by Novel Pd-1

Zhang, Xumu

303

The Construction of All-Carbon Quaternary Stereocenters by Use of Pd-Catalyzed Asymmetric Allylic Alkylation Reactions in Total Synthesis  

PubMed Central

All-carbon quaternary stereocenters have posed significant challenges in the synthesis of complex natural products. These important structural motifs have inspired the development of broadly applicable palladium-catalyzed asymmetric allylic alkylation reactions of unstabilized non-biased enolates for the synthesis of enantioenriched ?-quaternary products. This microreview outlines key considerations in the application of palladium-catalyzed asymmetric allylic alkylation reactions and presents recent total syntheses of complex natural products that have employed these powerful transformations for the direct, catalytic, enantioselective construction of all-carbon quaternary stereocenters. PMID:24944521

Hong, Allen Y.

2014-01-01

304

Conducting Polymer Nanostructures: Template Synthesis and Applications in Energy Storage  

PubMed Central

Conducting polymer nanostructures have received increasing attention in both fundamental research and various application fields in recent decades. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in energy storage because of the unique properties arising from their nanoscaled size: high electrical conductivity, large surface area, short path lengths for the transport of ions, and high electrochemical activity. Template methods are emerging for a sort of facile, efficient, and highly controllable synthesis of conducting polymer nanostructures. This paper reviews template synthesis routes for conducting polymer nanostructures, including soft and hard template methods, as well as its mechanisms. The application of conducting polymer mesostructures in energy storage devices, such as supercapacitors and rechargeable batteries, are discussed. PMID:20717527

Pan, Lijia; Qiu, Hao; Dou, Chunmeng; Li, Yun; Pu, Lin; Xu, Jianbin; Shi, Yi

2010-01-01

305

Synthesis of Fluorosurfactants for Emulsion-Based Biological Applications  

PubMed Central

Microemulsion represents an attractive platform for fundamental and applied biomedical research because the emulsified droplets can serve as millions of compartmentalized micrometer-sized reactors amenable to high-throughput screening or online monitoring. However, establishing stable emulsions with surfactants that are compatible with biological applications remains a significant challenge. Motivated by the lack of commercially available surfactants suitable for microemulsion-based biological assays, this study describes the facile synthesis of a biocompatible fluorosurfactant with nonionic tris(hydroxymethyl)methyl (Tris) polar head groups. We have further demonstrated compatibility of the developed surfactant with diverse emulsion-based applications, including DNA polymeric nanoparticle synthesis, enzymatic activity assay, and bacterial or mammalian cell culture, in the setup of both double- and multiphases of emulsions. PMID:24646088

2015-01-01

306

Waveform synthesis for imaging and ranging applications  

DOEpatents

Frequency dependent corrections are provided for quadrature imbalance and Local Oscillator (LO) feed-through. An operational procedure filters imbalance and LO feed-through effects without prior calibration or equalization. Waveform generation can be adjusted/corrected in a synthetic aperture radar system (SAR), where a rolling phase shift is applied to the SAR's QDWS signal where it is demodulated in a receiver; unwanted energies, such as LO feed-through and/or imbalance energy, are separated from a desired signal in Doppler; the separated energy is filtered from the receiver leaving the desired signal; and the separated energy in the receiver is measured to determine the degree of imbalance that is represented by it. Calibration methods can also be implemented into synthesis. The degree of LO feed-through and imbalance can be used to determine calibration values that can then be provided as compensation for frequency dependent errors in components, such as the QDWS and SSB mixer, affecting quadrature signal quality.

Doerry, Armin W.; Dudley, Peter A.; Dubert, Dale F.; Tise, Bertice L.

2004-12-07

307

Synthesis of software programs for embedded control applications  

Microsoft Academic Search

Software components for embedded reactive real-time applications must satisfy tight code size and run- time constraints. Cooperating finite state machines provide a convenient intermediate format for embedded system co-synthesis, between high-level specification languages and software or hardware implementations. We propose a software generation methodology that takes advantage of a restricted class of specifications and allows for tight control over the

Felice Balarin; Massimiliano Chiodo; Paolo Giusto; Harry Hsieh; Attila Jurecska; Luciano Lavagno; Alberto L. Sangiovanni-vincentelli; Ellen M. Sentovich; Kei Suzuki

1999-01-01

308

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

309

Enantioselective cyclopropanation of indoles: construction of all-carbon quaternary stereocenters.  

PubMed

The first enantioselective copper-catalyzed cyclopropanation of N-acyl indoles is described. Using carbohydrate-based bis(oxazoline) ligands (glucoBox), the products were obtained in up to 72% ee. Cyclopropanation of N-Boc 3-methyl indole yielded a product with an all-carbon quaternary stereocenter, which is a valuable building block for the synthesis of indole alkaloids: Deprotection and rearrangement gave a tricyclic hemiaminal ester in 96% ee, which was subsequently employed as a key intermediate for the synthesis of (-)-desoxyeseroline. PMID:23009104

Özüduru, Gülsüm; Schubach, Thea; Boysen, Mike M K

2012-10-01

310

Magnetic Nanotubes: Synthesis, Properties, and Applications  

Microsoft Academic Search

This article presents a comprehensive review of recent progress of research dedicated to magnetic nanotubes (MNTs). The review mainly covers the recent achievements in the syntheses, properties, and applications of MNTs. After introducing the significance of MNTs and the magnetic characteristics of elements in the periodic table, the article starts with a brief overview of the existing fabrication pathways for

Yixing Ye; Baoyou Geng

2012-01-01

311

Nanoceria as Antioxidant: Synthesis and Biomedical Applications  

Technology Transfer Automated Retrieval System (TEKTRAN)

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 rol...

312

[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

313

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

314

Synthesis and Anticancer Activity of All Known (?)-Agelastatin Alkaloids  

E-print Network

The full details of our enantioselective total syntheses of (?)-agelastatins A–F (1–6), the evolution of a new methodology for synthesis of substituted azaheterocycles, and the first side-by-side evaluation of all known ...

Han, Sunkyu

315

Temperature-controlled bidirectional enantioselectivity in a dynamic catalyst for asymmetric hydrogenation.  

PubMed

Asymmetric catalysis using enantiomerically pure catalysts is one of the most widely used methods for the preparation of enantiomerically pure compounds. The separate synthesis of both enantiomerically pure compounds requires tedious and time-consuming preparation of both enantiomerically pure catalysts or chiral separation of the racemic products. Here, we report a stereochemically flexible diastereomeric rhodium(I) catalyst for asymmetric hydrogenations of prochiral (Z)-?-acetamidocinnamates and ?-substituted acrylates, which changes its enantioselectivity depending on the temperature to produce each enantiomerically pure compound in high yield with constant high enantioselectivity over time. The same axially chiral rhodium(I) catalyst produces (R)-phenylalanine derivatives in enantiomeric ratios of up to 87:13 (R/S) at low temperature and up to 3:97 (R/S) of the corresponding S?enantiomers after re-equilibration of the same catalyst at elevated temperature. PMID:25708097

Storch, Golo; Trapp, Oliver

2015-03-16

316

Enantioselective Desymmetrization of Prochiral Cyclohexanones by Organocatalytic Intramolecular Michael Additions to ?,?-Unsaturated Esters.  

PubMed

A new catalytic asymmetric desymmetrization reaction for the synthesis of enantioenriched derivatives of 2-azabicyclo[3.3.1]nonane, a key motif common to many alkaloids, has been developed. Employing a cyclohexanediamine-derived primary amine organocatalyst, a range of prochiral cyclohexanone derivatives possessing an ?,?-unsaturated ester moiety linked to the 4-position afforded the bicyclic products, which possess three stereogenic centers, as single diastereoisomers in high enantioselectivity (83-99?%?ee) and in good yields (60-90?%). Calculations revealed that stepwise C?C bond formation and proton transfer via a chair-shaped transition state dictate the exclusive endo selectivity and enabled the development of a highly enantioselective primary amine catalyst. PMID:25727215

Gammack Yamagata, Adam D; Datta, Swarup; Jackson, Kelvin E; Stegbauer, Linus; Paton, Robert S; Dixon, Darren J

2015-04-13

317

L-proline-catalyzed enantioselective one-pot cross-Mannich reaction of aldehydes.  

PubMed

This protocol describes a procedure for the synthesis of syn-beta-amino alpha-substituted aldehydes, versatile intermediates in synthetic organic chemistry, via asymmetric, direct, one-pot, three-component, cross-Mannich reaction of two different aldehydes. The reaction consists of two steps; one is the formation of imine by the reaction of aldehyde and p-anisidine in the presence of Pro, and the second step is the enantioselective addition reaction of enamine generated from the other aldehyde and Pro with the imine generated in the first step. As the aldehyde easily racemizes, gamma-amino alcohol was isolated and characterized after reduction. The yield and diastereo- and enantioselectivities are generally excellent. It will take approximately 26 h to complete the protocol: 0.5 h to set up the reaction, 20.5 h for the reaction and 5 h for the isolation and purification. PMID:17401345

Hayashi, Yujiro; Urushima, Tatsuya; Tsuboi, Wataru; Shoji, Mitsuru

2007-01-01

318

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

319

Total Synthesis of (?)-Mucocin  

PubMed Central

An enantioselective total synthesis of (?)-mucocin has been completed. A combination of asymmetric glycolate aldol additions and ring closing metathesis reactions were exploited to construct the C18-C34 and C7-C17 fragments. A selective cross metathesis reaction was employed as the key step to couple two complex fragments. PMID:16706528

Crimmins, Michael T.; Zhang, Yan; Diaz, Frank A.

2008-01-01

320

Total synthesis of (-)-mucocin.  

PubMed

[reaction: see text] An enantioselective total synthesis of (-)-mucocin has been completed. A combination of asymmetric glycolate aldol additions and ring closing metathesis reactions were exploited to construct the C18-C34 and C7-C17 fragments. A selective cross-metathesis reaction was employed as the key step to couple two complex fragments. PMID:16706528

Crimmins, Michael T; Zhang, Yan; Diaz, Frank A

2006-05-25

321

Synthesis of (+)-Coronafacic Acid  

PubMed Central

An enantioselective synthesis of (+)-coronafacic acid has been achieved. Rhodium catalyzed cyclization of an ?-diazoester provided the intermediate cyclopentanone in high enantiomeric purity. Subsequent Fe-mediated cyclocarbonylation of a derived alkenyl cyclopropane gave a bicyclic enone, that then was hydrogenated and carried on to the natural product. PMID:19231870

Taber, Douglass F.; Sheth, Ritesh B.; Tian, Weiwei

2009-01-01

322

Engineering and Applications of fungal laccases for organic synthesis  

PubMed Central

Laccases are multi-copper containing oxidases (EC 1.10.3.2), widely distributed in fungi, higher plants and bacteria. Laccase catalyses the oxidation of phenols, polyphenols and anilines by one-electron abstraction, with the concomitant reduction of oxygen to water in a four-electron transfer process. In the presence of small redox mediators, laccase offers a broader repertory of oxidations including non-phenolic substrates. Hence, fungal laccases are considered as ideal green catalysts of great biotechnological impact due to their few requirements (they only require air, and they produce water as the only by-product) and their broad substrate specificity, including direct bioelectrocatalysis. Thus, laccases and/or laccase-mediator systems find potential applications in bioremediation, paper pulp bleaching, finishing of textiles, bio-fuel cells and more. Significantly, laccases can be used in organic synthesis, as they can perform exquisite transformations ranging from the oxidation of functional groups to the heteromolecular coupling for production of new antibiotics derivatives, or the catalysis of key steps in the synthesis of complex natural products. In this review, the application of fungal laccases and their engineering by rational design and directed evolution for organic synthesis purposes are discussed. PMID:19019256

Kunamneni, Adinarayana; Camarero, Susana; García-Burgos, Carlos; Plou, Francisco J; Ballesteros, Antonio; Alcalde, Miguel

2008-01-01

323

Boron nitride nanotube: synthesis and applications  

NASA Astrophysics Data System (ADS)

Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA/JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800°C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

2014-04-01

324

Boron Nitride Nanotube: Synthesis and Applications  

NASA Technical Reports Server (NTRS)

Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800 C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha I.; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

2014-01-01

325

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

326

Hollow-structured mesoporous materials: chemical synthesis, functionalization and applications.  

PubMed

Hollow-structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft-templating and hard-templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented. PMID:24687906

Li, Yongsheng; Shi, Jianlin

2014-05-28

327

Synthesis, characterization, and applications of nanocomposite membranes  

NASA Astrophysics Data System (ADS)

In the present work polymer nanocomposites (PCN) derived from synthetic lithium hectorite clay (SLH) and polyethylene oxide (PEO) have been prepared and characterized for use as polymer electrolytes in lithium ion secondary batteries and as catalytic membranes for fuel cell applications. PCNs are prepared by intercalating polyethylene oxide in the clay layers of SLH. The resulting films are physically and electrochemically evaluated. In situ small-angle X-ray scattering (SAXS) studies have been conducted to monitor the structural changes of polymer nanocomposites upon heating. These nanocomposites are made of different mass ratios of PEO and SLH. On the basis of the in situ SAXS results, it was found that the polymer matrix losses its crystallinity at about 60°C and the composite is stable up to 150°C. Conductivity values, activation energies, and lithium transference numbers indicate that the PCNs are single ion conductors with transference numbers close to unity. The activation energies are in the range of 0.02 eV, two orders of magnitude higher than the conventional polymer electrolytes. A synthetic hectorite was also ion-exchanged with Pt(II) and suspended in a solution containing PEO for the fuel cell applications. The resulting membrane was subsequently reduced under H2 at 200°C for 2--3 hr. The final membrane contains Pt(0) at 2.4 wt% loading levels. XRD shows development of Pt(0) by the appearance of crystalline peaks upon reduction. A lineshape analysis using the Scherrer equation of the (220) peak shows Pt(0) particles of 3.8 nm or 7.5 nm depending upon processing conditions. These values are confirmed by TEM, and a high dispersion of the metal is evident. XRD and TGA confirm that PEO is stable to the processing conditions. In situ SAXS measurements of the reduction process were also performed. Under a reducing atmosphere, the shape of the scattering curves visually changes between 100--120°C. Analysis of the scattering curves using the general unified fit equation yields particles with diameters of 4.8--5.1 nm, and is assumed to arise from the reduced Pt(0) nanoparticles. Later, the membranes were used in an actual setup for the oxidation and separation of CO from the H2-rich gas. The spacing of the membrane helps to reduce the CO concentration level by preventing CO gas to penetrate. Poor CO stream, which goes through the membrane, reacts with O2 and then is converted to CO2 catalytically.

Kizilel, Riza

328

Enantioselective -Vinylation of Aldehydes via the Synergistic Combination of Copper and Amine Catalysis  

E-print Network

Enantioselective -Vinylation of Aldehydes via the Synergistic Combination of Copper and Amine the enantioselective - trifluoromethylation and -arylation of aldehydes via the synergistic combination of copper the enantioselective construction of a wide variety of - substituted-,-unsaturated aldehydes without olefin isomer

MacMillan, David W. C.

329

Automatic Single View-Based 3-D Face Synthesis for Unsupervised Multimedia Applications  

Microsoft Academic Search

Various 3-D face synthesis techniques have been proposed and extensively used in many applications. Compared with others, single view-based face synthesis technology allows unsupervised 3-D face reconstruction without any offline operations. Although many algorithms have been published, automatic and robust single view-based 3-D face synthesis still remains unsolved. In contrast to other methods, the single view-based 3-D face synthesis algorithm

Yun Sheng; Abdul H. Sadka; Ahmet M. Kondoz

2008-01-01

330

Enantioselective stable isotope analysis (ESIA) of polar herbicides.  

PubMed

Assessing the environmental fate of chiral micropollutants such as herbicides is challenging. The complexity of aquatic systems often makes it difficult to obtain hydraulic mass balances, which is a prerequisite when assessing degradation based on concentration data. Elegant alternatives are concentration-independent approaches like compound-specific isotope analysis or enantiospecific concentration analysis. Both detect degradation-induced changes from ratios of molecular species, either isotopologues or enantiomers. A combination of both-enantioselective stable isotope analysis (ESIA)-provides information on (13)C/(12)C ratios for each enantiomer separately. Recently, Badea et al. demonstrated for the first time ESIA for the insecticide ?-hexachlorocyclohexane. The present study enlarges the applicability of ESIA to polar herbicides such as phenoxy acids: 4-CPP ((RS)-2-(4-chlorophenoxy)-propionic acid), mecoprop (2-(4-chloro-2-methylphenoxy)-propionic acid), and dichlorprop (2-(2,4-dichlorophenoxy)-propionic acid). Enantioselective gas chromatography-isotope ratio mass spectrometry was accomplished with derivatization prior to analysis. Precise carbon isotope analysis (2????0.5‰) was obtained with ?7 ng C on column. Microbial degradation of dichlorprop, 2-(2,4-dichlorophenoxy)-propionic acid by Delftia acidovorans MC1 showed pronounced enantiomer fractionation, but no isotope fractionation. In contrast, Badea et al. observed isotope fractionation, but no enantiomeric fractionation. Hence, the two lines of evidence appear to complement each other. They may provide enhanced insight when combined as ESIA. PMID:23377114

Maier, Michael P; Qiu, Shiran; Elsner, Martin

2013-03-01

331

Hierarchical layered double hydroxide nanocomposites: structure, synthesis and applications.  

PubMed

Layered double hydroxide (LDH)-based nanocomposites, constructed by interacting LDH nanoparticles with other nanomaterials (e.g. silica nanoparticles and magnetic nanoparticles) or polymeric molecules (e.g. proteins), are an emerging yet active area in healthcare, environmental remediation, energy conversion and storage. Combining advantages of each component in the structure and functions, hierarchical LDH-based nanocomposites have shown great potential in biomedicine, water purification, and energy storage and conversion. This feature article summarises the recent advances in LDH-based nanocomposites, focusing on their synthesis, structure, and application in drug delivery, bio-imaging, water purification, supercapacitors, and catalysis. PMID:25562489

Gu, Zi; Atherton, John James; Xu, Zhi Ping

2015-02-01

332

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

333

Applications of C–H Functionalization Logic to Cyclobutane Synthesis  

PubMed Central

The application of C–H functionalization logic to target-oriented synthesis provides an exciting new venue for the development of new and useful strategies in organic chemistry. In this article, C–H functionalization reactions are explored as an alternative approach to access pseudodimeric cyclobutane natural products, such as the dictazole and the piperarborenine families. The use of these strategies in a variety of complex settings highlights the subtle geometric, steric, and electronic effects at play in the auxiliary guided C–H functionalization of cyclobutanes. PMID:24548142

2015-01-01

334

Enantioselective iron-catalyzed intramolecular cyclopropanation reactions.  

PubMed

An iron-catalyzed asymmetric intramolecular cyclopropanation was realized in high yields and excellent enantioselectivity (up to 97%?ee) by using the iron complexes of chiral spiro-bisoxazoline ligands as catalysts. The superiority of iron catalysts exhibited in this reaction demonstrated the potential abilities of this sustainable metal in asymmetric carbenoid transformation reactions. PMID:25283384

Shen, Jun-Jie; Zhu, Shou-Fei; Cai, Yan; Xu, Huan; Xie, Xiu-Lan; Zhou, Qi-Lin

2014-11-24

335

Titanium-Catalyzed Enantioselective Additions of  

E-print Network

Titanium-Catalyzed Enantioselective Additions of Alkyl Groups to Aldehydes: Mechanistic Studies by zinc- or titanium- based catalysts. While the mechanism of the zinc/amino alcohol catalysts has received significant attention, the titanium-based catalysts have been less studied. This Account

Walsh, Patrick J.

336

Perfluorophenyl Azides: New Applications in Surface Functionalization and Nanomaterial Synthesis  

PubMed Central

Conspectus A major challenge in materials science is the ongoing search for coupling agents that are readily synthesized, capable of versatile chemistry, able to easily functionalize materials and surfaces, and efficient in covalently linking organic and inorganic entities. A decade ago, we began a research program investigating perfluorophenylazides (PFPAs) as the coupling agents in surface functionalization and nanomaterial synthesis. The p-substituted PFPAs are attractive heterobifunctional coupling agents because of their two distinct and synthetically distinguishable reactive centers: (i) the fluorinated phenylazide, which is capable of forming stable covalent adducts, and (ii) the functional group R, which can be tailored through synthesis. Two approaches have been undertaken for material synthesis and surface functionalization. The first method involves synthesizing PFPA bearing the first molecule or material with a functional linker R, and then attaching the resulting PFPA to the second material by activating the azido group. In the second approach, the material surface is first functionalized with PFPA via functional center R, and coupling of the second molecule or material is achieved with the surface azido groups. In this Account, we review the design and protocols of the two approaches, providing examples in which PFPA derivatives were successfully used in material surface functionalization, ligand conjugation, and the synthesis of hybrid nanomaterials. The methods developed have proved to be general and versatile, and they are applicable to a wide range of materials (especially those that lack reactive functional groups or are difficult to derivatize) and to various substrates of polymers, oxides, carbon materials, and metal films. The coupling chemistry can be initiated by light, heat, and electrons. Patterned structures can be generated by selectively activating the areas of interest. Furthermore, the process is easy to perform, and light activation occurs in minutes, greatly facilitating the efficiency of the reaction. PFPAs indeed demonstrate many benefits as versatile surface coupling agents and offer opportunities for further exploration. PMID:20690606

Liu, Li-Hong; Yan, Mingdi

2010-01-01

337

Enantioselective toxicities of chiral ionic liquids 1-alkyl-3-methylimidazolium lactate to aquatic algae.  

PubMed

With the wide application of chiral ionic liquids (CILs) as green solvents, their threats to the aquatic environment cannot be ignored. Thus, risk assessment and the prospective design of inherently safe CILs have become more urgent. However, whether enantioselectivity is a feature of the aquatic toxicity of CILs is poorly understood. Herein, we describe the first investigation into the ecotoxicities of CILs toward green algae Scenedesmus obliquus and Euglena gracilis. A series of methylimidazolium lactic ionic liquids, which cation parts with different alkyl chains and anion part is enantiomers of lactate, are used as representative CILs. The results of S. obliquus showed that the EC50 value of L-(+)-1-ethyl-3-methylimidazolium lactate (L-(+)-EMIM L) was more than 5000 ?M, while the EC50 value of D-(-)-1-ethyl-3-methylimidazolium lactate (D-(-)-EMIM L) was 2255.21 ?M. Such a distinct difference indicates the enantioselective toxicity of CILs to algae. This enantioselectivity initially persisted with increasing carbon chain length, but no longer exhibited when with greater carbon chain lengths, due to changes in the toxicity weightings of the cation parts. Further research showed that the enantioselective effects of CILs resulted from the differences in the production of reactive oxygen species, the damage to cell membrane integrity and cell wall after exposure to CILs. Results from this study showed that monitoring for the racemate CILs will give an inadequate or misleading environmental risk assessment. Thus, we should improve our ability to predict their effects in natural environments. In the meantime, non-selective use of CILs will do harm to aquatic organisms. Therefore, to minimize their potential for environmental impact, the enantioselective toxicities of CILs with short alkyl chains should be taken into consideration. PMID:24880783

Chen, Hui; Zou, Yuqin; Zhang, Lijuan; Wen, Yuezhong; Liu, Weiping

2014-09-01

338

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

339

Highly enantioselective hydrogenation of alpha-arylmethylene cycloalkanones catalyzed by iridium complexes of chiral spiro aminophosphine ligands.  

PubMed

The highly efficient asymmetric hydrogenation of alpha-arylmethylene cycloalkanones catalyzed by Ir-complexes of chiral spiro aminophosphine ligands was developed, providing chiral exo-cyclic allylic alcohols at high yields with excellent enantioselectivities (up to 97% ee) and high turnover numbers (S/C up to 10,000). This new reaction provided an efficient method for the synthesis of the key intermediate of the active form of the anti-inflammatory loxoprofen. PMID:20232874

Xie, Jian-Bo; Xie, Jian-Hua; Liu, Xiao-Yan; Kong, Wei-Ling; Li, Shen; Zhou, Qi-Lin

2010-04-01

340

Nanocrystals-Related Synthesis, Assembly, and Energy Applications  

SciTech Connect

During the past decades, nanocrystals have attracted broad attention due to their unique shape- and size-dependent physical and chemical properties that differ drastically from their bulk counterparts. Hitherto, much effort has been dedicated to achieving rational controlling over the morphology, assembly, and related energy applications of the nanomaterials. Therefore, the ability to manipulate the morphology, size, and size distribution of inorganic nanomaterials is still an important goal in modern materials physics and chemistry. Especially, the world s demand for energy supply is causing a dramatic escalation of social and political unrest. Likewise, the environmental impact of the global climate change due to the combustion of fossil fuel is becoming increasingly alarming. These problems compel us to search for effective routes to build devices that can supply sustainable energy, with not only high efficiency but also environmental friendship. One of ways to relieve the energy crisis is to exploit devices based on renewable energy sources, such as solar energy and water power. Aiming at this exploration, the primary stage requires the design of appropriate strategies for the synthesis of high-quality nanocrystals with respect to size uniformity and superior electrochemical performances. As a consequence, we organize the current special issue for Journal of Nanomaterials to provide the authors with a platform and readers with the latest achievements of nanocrystals-related synthesis, assembly, and energy applications.

Zou, Bo [Jilin University, Changchun; Yu, Williams [Worcester Polytechnic Institute; Seo, Jaetae [Hampton University; Zhu, Ting [Philips Lumileds Lighting Company; Hu, Michael Z. [ORNL

2012-01-01

341

Zirconium-catalyzed desymmetrization of aminodialkenes and aminodialkynes through enantioselective hydroamination.  

PubMed

The catalytic addition of alkenes and amines (hydroamination) typically provides ?- or ?-amino stereocenters directly through C-N or C-H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C-N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the ?-amino stereocenter generated by C-N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H2NR vs D2NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselective processes in aminodialkene cyclization and the peripheral stereocenter in aminodialkyne desymmetrization/cyclization. PMID:25560913

Manna, Kuntal; Eedugurala, Naresh; Sadow, Aaron D

2015-01-14

342

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

343

Semiconducting black phosphorus: synthesis, transport properties and electronic applications.  

PubMed

Phosphorus is one of the most abundant elements preserved in earth, and it comprises a fraction of ?0.1% of the earth crust. In general, phosphorus has several allotropes, and the two most commonly seen allotropes, i.e. white and red phosphorus, are widely used in explosives and safety matches. In addition, black phosphorus, though rarely mentioned, is a layered semiconductor and has great potential in optical and electronic applications. Remarkably, this layered material can be reduced to one single atomic layer in the vertical direction owing to the van der Waals structure, and is known as phosphorene, in which the physical properties can be tremendously different from its bulk counterpart. In this review article, we trace back to the research history on black phosphorus of over 100 years from the synthesis to material properties, and extend the topic from black phosphorus to phosphorene. The physical and transport properties are highlighted for further applications in electronic and optoelectronics devices. PMID:25307017

Liu, Han; Du, Yuchen; Deng, Yexin; Ye, Peide D

2014-10-13

344

Synthesis of enantiomerically enriched 3-amino-2-oxindoles through a palladium-mediated asymmetric intramolecular arylation of ?-ketimino amides.  

PubMed

A highly efficient and enantioselective synthesis of 3-amino-2-oxindoles through a palladium-catalyzed asymmetric intramolecular arylation of ?-ketimino amides using (R)-DiFluorPhos as the coordinating ligand is reported. This report constitutes the first enantioselective palladium-catalyzed arylation of ketimines. PMID:22946713

Tolstoy, Päivi; Lee, Samantha X Y; Sparr, Christof; Ley, Steven V

2012-09-21

345

Enantioselective oxidative gold catalysis enabled by a designed chiral P,N-bidentate ligand.  

PubMed

A newly developed P,N-bidentate ligand enables enantioselective intramolecular cyclopropanation by a reactive ?-oxo gold carbene intermediate generated in situ. The ligand design is based on our previously proposed structure (with a well-organized triscoordinated gold center) of the carbene intermediate in the presence of a P,N-bidentate ligand. A C2-symmetric piperidine ring was incorporated in the ligand as the nitrogen-containing moiety. A range of racemic transformations of ?-oxo gold carbene intermediates have been developed recently, and this new class of chiral ligands could enable their modification for asymmetric synthesis, as demonstrated in this study. PMID:25431180

Ji, Kegong; Zheng, Zhitong; Wang, Zhixun; Zhang, Liming

2015-01-19

346

A carbohydrate approach for the formal total synthesis of (?)-aspergillide C  

PubMed Central

Summary An enantioselective formal total synthesis of aspergillide C is accomplished using commercially available tri-O-acetyl-D-galactal employing a Ferrier-type C-glycosylation, utilizing a Trost hydrosilylation and protodesilylation as key reactions. PMID:25670981

Hari Krishna, Namballa; Sridhar, Ydhyam; Kamal, Ahmed

2014-01-01

347

Enzymatic enantioselective decarboxylative protonation of heteroaryl malonates.  

PubMed

The enzyme aryl/alkenyl malonate decarboxylase (AMDase) catalyses the enantioselective decarboxylative protonation (EDP) of a range of disubstituted malonic acids to give homochiral carboxylic acids that are valuable synthetic intermediates. AMDase exhibits a number of advantages over the non-enzymatic EDP methods developed to date including higher enantioselectivity and more environmentally benign reaction conditions. In this report, AMDase and engineered variants have been used to produce a range of enantioenriched heteroaromatic ?-hydroxycarboxylic acids, including pharmaceutical precursors, from readily accessible ?-hydroxymalonates. The enzymatic method described here represents an improvement upon existing synthetic chemistry methods that have been used to produce similar compounds. The relationship between the structural features of these new substrates and the kinetics associated with their enzymatic decarboxylation is explored, which offers further insight into the mechanism of AMDase. PMID:25766433

Lewin, Ross; Goodall, Mark; Thompson, Mark L; Leigh, James; Breuer, Michael; Baldenius, Kai; Micklefield, Jason

2015-04-20

348

Vancomycin Molecular Interactions: Antibiotic and Enantioselective Mechanisms  

NASA Astrophysics Data System (ADS)

Medical studies established that vancomycin and other related macrocyclic antibiotics have an enhanced antimicrobial activity when they are associated as dimers. The carbohydrate units attached to the vancomycin basket have an essential role in the dimerization reaction. Covalently synthesized dimers were found active against vancomycin-resistant bacterial strains. A great similarity between antibiotic potential and enantioselectivity was established. A covalent vancomycin dimer was studied in capillary electrophoresis producing excellent chiral separation of dansyl amino acids. Balhimycin is a macrocyclic glycopeptide structurally similar to vancomycin. The small differences are, however, responsible for drastic differences in enantioselectivity in the same experimental conditions. Contributions from studies examining vancomycin's mechanism for antimicrobial activity have substantially aided our understanding of its mechanism in chiral recognition.

Ward, Timothy J.; Gilmore, Aprile; Ward, Karen; Vowell, Courtney

349

Oligothiophene semiconductors: synthesis, characterization, and applications for organic devices.  

PubMed

Oligothiophenes provide a highly controlled and adaptable platform to explore various synthetic, morphologic, and electronic relationships in organic semiconductor systems. These short-chain systems serve as models for establishing valuable structure-property relationships to their polymer analogs. In contrast to their polymer counterparts, oligothiophenes afford high-purity and well-defined materials that can be easily modified with a variety of functional groups. Recent work by a number of research groups has revealed functionalized oligothiophenes to be the up-and-coming generation of advanced materials for organic electronic devices. In this review, we discuss the synthesis and characterization of linear oligothiophenes with a focus on applications in organic field effect transistors and organic photovoltaics. We will highlight key structural parameters, such as crystal packing, intermolecular interactions, polymorphism, and energy levels, which in turn define the device performance. PMID:24641239

Zhang, Lei; Colella, Nicholas S; Cherniawski, Benjamin P; Mannsfeld, Stefan C B; Briseno, Alejandro L

2014-04-23

350

Design, synthesis, and application of stimulus-sensing biohybrid hydrogels.  

PubMed

A key feature of any living system is the ability to sense and react to the environmental stimuli. The biochemical characterization of the underlying biological sensors combined with advances in polymer chemistry has enabled the development of stimulus-sensitive biohybrid materials that translate most diverse chemical and biological input into a precise change in material properties. In this review article, we first describe synthesis strategies of how biological and chemical polymers can functionally be interconnected. We then provide a comprehensive overview of how the different properties of biological sensor molecules such as competitive target binding and allosteric modulation can be harnessed to develop responsive materials with applications in tissue engineering and drug delivery. PMID:23982955

Hotz, Natascha; Wilcke, Louisa; Weber, Wilfried

2013-10-01

351

Framed carbon nanostructures: synthesis and applications in functional SPM tips.  

PubMed

We present a synthesis method to fabricate framed carbon-based nanostructures having highly anisotropic shapes, in particular, the nanofork and nanoscalpel structures which are obtained systematically under optimized growth conditions. A theoretical model is developed to explain the formation of such nanostructures on Si cantilevers and W etched wires exposed to a focused electron beam. We then demonstrate the potentials of these nanostructures as functional tips for scanning probe microscopy. Owing to their anisotropic shapes, such tips can be very useful for nanolithography, nanosurgery of biological objects, and precise manipulation with surface particles. Overall, our method provides a simple and robust way to produce functional scanning probe microscopy tips with variable shapes and enhanced capabilities for different applications compared to standard cantilevers. PMID:25461592

Mukhin, I S; Fadeev, I V; Zhukov, M V; Dubrovskii, V G; Golubok, A O

2015-01-01

352

Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma  

PubMed Central

Glioblastoma multiforme (GBM) is the most common and most aggressive malignant primary brain tumor in humans. Current GBM treatment includes surgery, radiation therapy, and chemotherapy, sometimes supplemented with novel therapies. Despite recent advances, survival of GBM patients remains poor. Major challenges in GBM treatment are drug delivery across the blood–brain barrier, restriction of damage to healthy brain tissues, and limitation of resistance to therapies. This article reviews recent advances in the application of magnetic nanoparticles (MNPs), gold nanorods (GNRs), and carbon nanotubes (CNTs) for hyperthermia ablation of GBM. First, the article introduces GBM, its current treatment, and hyperthermia as a potential modality for the management of GBM. Second, it introduces MNPs, GNRs, and CNTs as inorganic agents to induce hyperthermia in GBM. Third, it discusses different methodologies for synthesis of each inorganic agent. Finally, it reviews in vitro and in vivo studies in which MNPs, GNRs, and CNTs have been applied for hyperthermia ablation and drug delivery in GBM. PMID:24959075

Verma, Jyoti; Lal, Sumit; Van Noorden, Cornelis JF

2014-01-01

353

Design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates.  

PubMed

Paclitaxel (1a), a well known antitumor agent adopted mainly for the treatment of breast and ovarian cancer, suffers from significant disadvantages such as low solubility, certain toxicity and specific drug-resistance of some tumor cells. To overcome these problems extensive research has been carried out. Among the various proposed strategies, the conjugation of paclitaxel (1a) to a biocompatible polymer, such as hyaluronic acid (HA, 2), has also been considered. Coupling a bioactive compound to a biocompatible polymer offers, in general, many advantages such as better drug solubilization, better stabilization, specific localization and controlled release. Hereafter the design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates are reviewed. An overview of HA-paclitaxel combinations is also given. PMID:18305424

Leonelli, Francesca; La Bella, Angela; Migneco, Luisa Maria; Bettolo, Rinaldo Marini

2008-01-01

354

Structure, Synthesis, and Applications of TiO2 Nanobelts.  

PubMed

TiO2 semiconductor nanobelts have unique structural and functional properties, which lead to great potential in many fields, including photovoltaics, photocatalysis, energy storage, gas sensors, biosensors, and even biomaterials. A review of synthetic methods, properties, surface modification, and applications of TiO2 nanobelts is presented here. The structural features and basic properties of TiO2 nanobelts are systematically discussed, with the many applications of TiO2 nanobelts in the fields of photocatalysis, solar cells, gas sensors, biosensors, and lithium-ion batteries then introduced. Research efforts that aim to overcome the intrinsic drawbacks of TiO2 nanobelts are also highlighted. These efforts are focused on the rational design and modification of TiO2 nanobelts by doping with heteroatoms and/or forming surface heterostructures, to improve their desirable properties. Subsequently, the various types of surface heterostructures obtained by coupling TiO2 nanobelts with metal and metal oxide nanoparticles, chalcogenides, and conducting polymers are described. Further, the charge separation and electron transfer at the interfaces of these heterostructures are also discussed. These properties are related to improved sensitivity and selectivity for specific gases and biomolecules, as well as enhanced UV and visible light photocatalytic properties. The progress in developments of near-infrared-active photocatalysts based on TiO2 nanobelts is also highlighted. Finally, an outline of important directions of future research into the synthesis, modification, and applications of this unique material is given. PMID:25800706

Zhao, Zhenhuan; Tian, Jian; Sang, Yuanhua; Cabot, Andreu; Liu, Hong

2015-04-01

355

Anisotropic gold nanoparticles: synthesis, properties, applications, and toxicity.  

PubMed

Anisotropic gold nanoparticles (AuNPs) have attracted the interest of scientists for over a century, but research in this field has considerably accelerated since 2000 with the synthesis of numerous 1D, 2D, and 3D shapes as well as hollow AuNP structures. The anisotropy of these nonspherical, hollow, and nanoshell AuNP structures is the source of the plasmon absorption in the visible region as well as in the near-infrared (NIR) region. This NIR absorption is especially sensitive to the AuNP shape and medium and can be shifted towards the part of the NIR region in which living tissue shows minimum absorption. This has led to crucial applications in medical diagnostics and therapy ("theranostics"), especially with Au nanoshells, nanorods, hollow nanospheres, and nanocubes. In addition, Au nanowires (AuNWs) can be synthesized with longitudinal dimensions of several tens of micrometers and can serve as plasmon waveguides for sophisticated optical devices. The application of anisotropic AuNPs has rapidly spread to optical, biomedical, and catalytic areas. In this Review, a brief historical survey is given, followed by a summary of the synthetic modes, variety of shapes, applications, and toxicity issues of this fast-growing class of nanomaterials. PMID:24421264

Li, Na; Zhao, Pengxiang; Astruc, Didier

2014-02-10

356

Synthesis and characterization of aqueous quantum dots for biomedical applications  

NASA Astrophysics Data System (ADS)

Quantum Dots (QDs) are semiconductor nanocrystals (1˜20 nm) exhibiting distinctive photoluminescence (PL) properties due to the quantum confinement effect. Having many advantages over organic dyes, such as broad excitation and resistance to photobleaching, QDs are widely used in bioapplications as one of most exciting nanobiotechnologies. To date, most commercial QDs are synthesized through the traditional organometallic method and contain toxic elements, such as cadmium, lead, mercury, arsenic, etc. The overall goal of this thesis study is to develop an aqueous synthesis method to produce nontoxic quantum dots with strong emission and good stability, suitable for biomedical imaging applications. Firstly, an aqueous, simple, environmentally friendly synthesis method was developed. With cadmium sulfide (CdS) QDs as an example system, various processing parameters and capping molecules were examined to improve the synthesis and optimize the PL properties. The obtained water soluble QDs exhibited ultra small size (˜5 nm), strong PL and good stability. Thereafter, using the aqueous method, the zinc sulfide (ZnS) QDs were synthesized with different capping molecules, i.e., 3-mercaptopropionic acid (MPA) and 3-(mercaptopropyl)trimethoxysilane (MPS). Especially, via a newly developed capping molecule replacement method, the present ZnS QDs exhibited bright blue emission with a quantum yield of 75% and more than 60 days lifetime in the ambient conditions. Two cytotoxicity tests with human endothelial cells verified the nontoxicity of the ZnS QDs by cell counting with Trypan blue staining and fluorescence assay with Alamar Blue. Taking advantage of the versatile surface chemistry, several strategies were explored to conjugate the water soluble QDs with biomolecules, i.e., antibody and streptavidin. Accordingly, the imaging of Salmonella t. cells and biotinylated microbeads has been successfully demonstrated. In addition, polyethylenimine (PEI)-QDs complex was formed and delivered into PC12 neuronal cells for intracellular imaging with uniform distribution. The water soluble QDs were also embedded in electrospun polymer fibers as fluorescent nanocomposite. In summary, the ease of aqueous processing and the excellent PL properties of the nontoxic water soluble ZnS QDs provide great potential for various in vivo applications.

Li, Hui

357

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

358

High enantioselective novozym 435-catalyzed esterification of (r,s)-flurbiprofen monitored with a chiral stationary phase.  

PubMed

Lipases form Candida rugosa and Candida antarctica were tested for their application in the enzymatic kinetic resolution of (R,S)-flurbiprofen by enantioselective esterification. Successful chromatographic separation with well-resolved peaks of (R)- and (S)-flurbiprofen and their esters was achieved in one run on chiral stationary phases by high-performance liquid chromatography (HPLC). In this study screening of enzymes was performed, and Novozym 435 was selected as an optimal catalyst for obtaining products with high enantiopurity. Additionally, the influence of organic solvents (dichloromethane, dichloroethane, dichloropropane, and methyl tert-butyl ether), primary alcohols (methanol, ethanol, n-propanol, and n-butanol), reaction time, and temperature on the enantiomeric ratio and conversion was tested. The high values of enantiomeric ratio (E in the range of 51.3-90.5) of the esterification of (R,S)-flurbiprofen were obtained for all tested alcohols using Novozym 435, which have a great significance in the field of biotechnological synthesis of drugs. The optimal temperature range for the performed reactions was from 37 to 45 °C. As a result of the optimization, (R)-flurbiprofen methyl ester was obtained with a high optical purity, eep?=?96.3 %, after 96 h of incubation. The enantiomeric ratio of the reaction was E?=?90.5 and conversion was C?=?35.7 %. PMID:25561056

Siódmiak, Tomasz; Mangelings, Debby; Heyden, Yvan Vander; Ziegler-Borowska, Marta; Marsza??, Micha? Piotr

2015-03-01

359

Enantioselective biotransformation of chiral PCBs in whole poplar plants.  

PubMed

Chiral PCBs have been used as molecular probes of biological metabolic processes due to their special physical, chemical, and biological properties. Many animal studies showed the enantioselective biotransformation of chiral PCBs, but it is unclear whether plants can enantioselectively biotransform chiral PCBs. In order to explore the enantioselectivity of chiral PCBs in whole plants, poplars (Populus deltoides × nigra, DN34), a model plant with complete genomic sequence, were hydroponically exposed to 2,2',3,5',6-pentachlorobiphenyl (PCB95) and 2,2',3,3',6,6'-hexachlorobiphenyl (PCB136) for 20 days. PCB95 and PCB136 were shown to be absorbed, taken-up and translocated in whole poplars, and they were detected in various tissues of whole poplars. However, the enantioselectivity of poplar for PCB95 and PCB136 proved to be quite different. The first eluting enantiomer of PCB95 was enantioselectively removed in whole poplar, especially in the middle and bottom xylem. It was likely enantioselectively metabolized inside poplar tissues, in contrast to racemic mixtures of PCB95 remaining in hydroponic solutions in contact with plant roots of whole and dead poplars. Unlike PCB95, PCB136 remained nearly racemic in most parts of whole poplars after 20 days exposure. These results suggest that PCB136 is more difficult to be enantioslectively biotransformed than PCB95 in whole poplars. This is the first evidence of enantioselectivity of chiral PCBs in whole plants, and suggests that poplars can enantioselectively biotransform at least one chiral PCB. PMID:21329345

Zhai, Guangshu; Hu, Dingfei; Lehmler, Hans-Joachim; Schnoor, Jerald L

2011-03-15

360

Breaking news on the enantioselective intermolecular Heck reaction.  

PubMed

Glowing results with less phosphorus: Tremendous progress has been made recently in asymmetric intermolecular Heck chemistry. Previously unprecedented enantioselective Heck-Matsuda reactions have been accomplished, and mixed phosphine/phosphine oxides have been shown to be superior ligands in enantioselective Mizoroki-Heck reactions. All of this was achieved with chiral ligands containing few or even no phosphorus donors (see scheme). PMID:24481834

Oestreich, Martin

2014-02-24

361

Studies on Rhizopus arrhizus mediated enantioselective reduction of arylalkanones  

Microsoft Academic Search

The effect of substitution on the biotransformation of various arylalkanones using Rhizopus arrhizus was investigated. The organism was found to be promising for the reduction of phenylalkanones and arylethanones with good to excellent enantioselectivity. The reduction followed Prelog's rule giving the (S)-carbinols in all the cases. The enantioselectivity of the reaction improved with increasing size of the groups flanking the

Neeta A Salvi; Subrata Chattopadhyay

2001-01-01

362

Organocatalytic enantioselective addition of thiols to ketimines derived from isatins.  

PubMed

The first catalytic enantioselective addition of thiols to ketimines derived from isatins has been developed. Excellent yields and enantioselectivities were observed for the reaction of various ketimines and thiols using a cinchona alkaloid sulfonamide catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. PMID:25526427

Nakamura, Shuichi; Takahashi, Shun; Nakane, Daisuke; Masuda, Hideki

2015-01-01

363

Enantioselective Addition of Diethylzinc to Aldehydes Catalyzed by a Titanate  

E-print Network

Enantioselective Addition of Diethylzinc to Aldehydes Catalyzed by a Titanate Complex with a Chiral to aldehydes is one of the most widely studied carbon-carbon bond-forming reac- tions. Many systems reported of diethylzinc to aldehydes (Figure 1).5 Herein we report the scope of this enantioselective reaction

Zhang, Xumu

364

Highly Enantioselective Organocatalytic r-Amination Reactions of Aryl  

E-print Network

Highly Enantioselective Organocatalytic r-Amination Reactions of Aryl Oxindoles: Developing States carlos@scripps.edu Received October 18, 2010 ABSTRACT An enantioselective r-amination of aryl oxindoles catalyzed by a dimeric quinidine has been developed. The reaction is general, broad in substrate

Barbas III, Carlos F.

365

One-Pot Enantioselective Syntheses of Iminosugar Derivatives Using Organocatalytic  

E-print Network

-catalyzed intermolecular aldol reaction7 and other related reactions,8 enantioselective syntheses of a number of compoundOne-Pot Enantioselective Syntheses of Iminosugar Derivatives Using Organocatalytic anti-Michael-anti-Aza-Henry Reactions Ritsuo Imashiro, Hisatoshi Uehara, and Carlos F. Barbas III* The Skaggs Institute for Chemical

Barbas III, Carlos F.

366

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

367

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

368

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

369

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

370

Application of ASP for Automatic Synthesis of Flexible Multiprocessor Systems from Parallel Programs  

E-print Network

Application of ASP for Automatic Synthesis of Flexible Multiprocessor Systems from Parallel. However, as the synthesis problem usually exhibits structure, Answer Set Programming (ASP), for which be effectively employed. This pa- per presents a design flow based on ASP that uses the solver clasp as back

Schaub, Torsten

371

Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis  

E-print Network

Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis Revision of TCAD synthesis which relies on alphabetic tree construction is presented. Alphabetic trees are trees which any internal edge crossing. First, a mechanism for generating all alphabetic trees on a given number

Pedram, Massoud

372

Synthesis and Application of a 5-Aldehyde Phosphoramidite for Covalent Attachment of  

E-print Network

Synthesis and Application of a 5-Aldehyde Phosphoramidite for Covalent Attachment of DNA of the duplex DNA constraint to RNA, utilizing an aldehyde tethered to the 5-terminus of the DNA. Here we describe the synthesis of a thymidine phosphora- midite that has the 5-tethered aldehyde masked as a 1

Silverman, Scott K.

373

Applications of total synthesis to problems in neurodegeneration: Fascinating chemistry along the way.  

PubMed

The possibility for the application of organic synthesis to the discovery of new agents in combating neurodegenerative disorders is described. Our focus has been on agents derived from natural-product leads and natural products themselves prepared through total synthesis. Herein, we describe some of the chemistry as well as interesting observations made along the way. PMID:16906750

Wilson, Rebecca M; Danishefsky, Samuel J

2006-08-01

374

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

E-print Network

APPLICATION 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 grown under controlled conditions. These studies demonstrated that accurate rates of nucleic acid

Luther, Douglas S.

375

Enzymatic routes for the synthesis of ursodeoxycholic acid.  

PubMed

Ursodeoxycholic acid, a secondary bile acid, is used as a drug for the treatment of various liver diseases, the optimal dose comprises the range of 8-10mg/kg/day. For industrial syntheses, the structural complexity of this bile acid requires the use of an appropriate starting material as well as the application of regio- and enantio-selective enzymes for its derivatization. Most strategies for the synthesis start from cholic acid or chenodeoxycholic acid. The latter requires the conversion of the hydroxyl group at C-7 from ?- into ?-position in order to obtain ursodeoxycholic acid. Cholic acid on the other hand does not only require the same epimerization reaction at C-7 but the removal of the hydroxyl group at C-12 as well. There are several bacterial regio- and enantio-selective hydroxysteroid dehydrogenases (HSDHs) to carry out the desired reactions, for example 7?-HSDHs from strains of Clostridium, Bacteroides or Xanthomonas, 7?-HSDHs from Clostridium, Collinsella, or Ruminococcus, or 12?-HSDH from Clostridium or from Eggerthella. However, all these bioconversion reactions need additional steps for the regeneration of the coenzymes. Selected multi-step reaction systems for the synthesis of ursodeoxycholic acid are presented in this review. PMID:25131646

Eggert, Thorsten; Bakonyi, Daniel; Hummel, Werner

2014-12-10

376

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

377

Green synthesis and applications of Au-Ag bimetallic nanoparticles.  

PubMed

This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenolapplication. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field. PMID:25218228

Meena Kumari, M; Jacob, John; Philip, Daizy

2015-02-25

378

Green synthesis and applications of Au-Ag bimetallic nanoparticles  

NASA Astrophysics Data System (ADS)

This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol < k2-nitrophenol < k3-nitrophenol. Thermal conductivity is measured as a function of volume fraction and it is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

Meena Kumari, M.; Jacob, John; Philip, Daizy

2015-02-01

379

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

380

Enantioselective Construction of Pyrrolidines by Palladium-Catalyzed Asymmetric [3+2] Cycloaddition of Trimethylenemethane with Imines  

PubMed Central

A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane (TMM) with imines has been developed. Central to this effort were the novel phosphoramidite ligands developed in our laboratories. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of imine acceptors to provide the corresponding pyrrolidine cycloadducts with excellent yields and selectivities. Use of a bis-2-naphthyl phosphoramidite allowed the successful cycloaddition of the parent TMM with N-Boc imines, and has further permitted the reaction of substituted donors with N-tosyl aldimines and ketimines in high regio-, diastereo-, and enantioselectivity. Use of a diphenylazetidine ligand allows the complimentary synthesis of the exocyclic nitrile product shown, and we demonstrate control of the regioselectivity of the product based on manipulation of the reaction parameters. PMID:22309214

Trost, Barry M.; Silverman, Steven M.

2012-01-01

381

SYNTHESIS AND CHARACTERIZATION OF SILICON NANOROD ARRAYS FOR SOLAR CELL APPLICATIONS  

E-print Network

- tentially allowing for novel multijunction solar cells. Nanowires can be grown in a variety of differentSYNTHESIS AND CHARACTERIZATION OF SILICON NANOROD ARRAYS FOR SOLAR CELL APPLICATIONS Brendan M

Atwater, Harry

382

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

383

Synthesis, characterization and biosensing application of photon upconverting nanoparticles  

NASA Astrophysics Data System (ADS)

Phosphor/fluorescent molecules/particles have been widely used in various applications for quite some time. Typically, light with longer wavelength(s) is emitted when excited by shorter wavelength light. The opposite effect also exists, where a phosphor particle is excited with an infrared or red light and emits color(s) of shorter wavelengths, a process called up-conversion. Materials with upconverting properties have narrower absorption and line emission spectra than their down-converting counterparts. Because most non-target materials in a complex mixture do not possess such photon up-conversion properties, a dramatically improved S/N ratio is expected in sensing and luminescence reporting applications. This makes photon upconverting materials ideal for identification of trace amounts of target molecules. Here we report the synthesis, characterization and DNA detection application based on NaYF4:Yb3+, Er3+ photon upconverting nanoparticles. The design of a nucleotide sensor for the detection of point mutation associated with sickle cell disease is described. The underlying principle for the detection is luminescence resonance energy transfer (LRET), with the photon upconverting nanoparticle as the donor and a dye, N,N,N',N'-tetramethyl-6-carboxyrhodamine (TAMRA), as the acceptor. The detection scheme is based on a sandwich-type hybridization format. The presence of the target DNA is indicated by the increase of the normalized acceptor's emission. Based on photon upconverting nanoparticles, which display high S/N ratio and no photobleaching, the DNA sensor demonstrates high sensitivity and specificity. The results demonstrate great potential of such nanomaterials as oligonucleotide sensors.

Kumar, Manoj; Zhang, Peng

2009-02-01

384

Synthesis and Applications of Inorganic/Organic-Polymer Nanocomposites  

NASA Astrophysics Data System (ADS)

This research work focuses on developing new synthesis routes to fabricate polymer nanocomposites tailored towards different applications. A simple, one-step method has been devised for synthesizing free-standing, flexible metal nanoparticle-polydimethylsiloxane films. This process simplifies prevalent methods to synthesize nanocomposites, in that here nanoparticles are created in situ while curing the polymer. This route circumvents the need for pre-synthesized nanoparticles, external reducing agents and stabilizers, thereby significantly reducing processing time and cost. The resulting nanocomposite also demonstrates enhancement in mechanical and antibacterial properties, with other envisaged applications in biomedical devices and catalysis. Applying the same mechanism as that used for the formation of bulk metalsiloxane nanocomposites, metal core-siloxane shell nanoparticles and siloxane nanowires were synthesized, with octadecylsilane as the precursor and in situ formed metal nanoparticles (gold, silver) as the catalyst. This method offers some unique advantages over the previously existing methods. This is a room temperature route which does not require high temperature refluxing or the use of pre-synthesized nanoparticles. Furthermore, this synthesis process gives a control over the shape of resulting nanocomposite structures (1-D wires or 0-D spherical particles). High thermal stability of polydimethylsiloxane (PDMS) makes it viable to alternatively synthesize metal nanoparticles in the polymer matrix by thermal decomposition process. This technique is generic across a range of metals (palladium, iron, nickel) and results in nanoparticles with a very narrow size distribution. Membranes with palladium nanoparticles demonstrate catalytic activity in ethylene hydrogenation reaction. Additionally, a new nanocomposite electrode has been developed for flexible and light-weight Li-ion batteries. Flexible films were prepared by the integration of the poly(vinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer electrolyte with the three-dimensional (3D), nanostructured electrode composed of aligned carbon nanotube (CNT)-copper oxide hybrid. This hybrid electrode was fabricated by a combination of chemical vapor deposition and electrodeposition techniques. Embedding it in PVDF polymer results in a flexible system and also renders an external separator redundant. This new design shows an improvement in electrochemical performance over pure CNTs as both CNTs and Cu2O contribute towards electrochemical activity. Efforts have also been undertaken towards synthesizing synthetic adhesives by mimicking the design principles found in nature. Aligned patterned CNTs have been used to replicate the fibrillar structure found in geckos' toes which generates adhesion through van der Waals forces. The adhesive forces in CNTs were found to be higher than in geckos and the key to this phenomenon lies in the extensive side-wall contact obtained on compressing CNTs against a surface.

Goyal, Anubha

385

Enhancing the Enantioselectivity of CALB by substrate imprinting: an1 experimental and molecular dynamics simulation study.2  

E-print Network

to catalyze esterification29 and transesterification reactions. Furthermore, they are enantioselectiveEnhancing the Enantioselectivity of CALB by substrate imprinting: an1 experimental and molecular enantioselective transesterification, with various alkyl-9 propanoate acyl donors, was studied in a solid

Boyer, Edmond

386

Synthesis of Boron Nitride Nanotubes for Engineering Applications  

NASA Technical Reports Server (NTRS)

Boron Nitride nanotubes (BNNT) are of interest to the scientific and technical communities for many of the same reasons that carbon nanotubes (CNT) have attracted large amounts of attention. Both materials have potentially unique and significant properties which may have important structural and electronic applications in the future. However of even more interest than their similarities may be the differences between carbon and boron nanotubes. Whilt boron nitride nanotubes possess a very high modulus similaar to CNT, they are also more chemically and thermally inert. Additionally BNNT possess more uniform electronic properties, having a uniform band gap of approximately 5.5 eV while CNT vary from semi-conductin to conductor behavior. Boron Nitride nanotubes have been synthesized by a variety of methods such as chemical vapor deposition, arc discharge and reactive milling. Consistently producing a reliable product has proven difficult. Progress in synthesis of 1-2 gram sized batches of Boron Nitride nanotubes will be discussed as well as potential uses for this unique material.

Hurst, Janet; Hull, David; Gorican, Dan

2005-01-01

387

Silver nanoparticles: synthesis, properties, toxicology, applications and perspectives  

NASA Astrophysics Data System (ADS)

In recent years the outbreak of re-emerging and emerging infectious diseases has been a significant burden on global economies and public health. The growth of population and urbanization along with poor water supply and environmental hygiene are the main reasons for the increase in outbreak of infectious pathogens. Transmission of infectious pathogens to the community has caused outbreaks of diseases such as influenza (A/H5N1), diarrhea (Escherichia coli), cholera (Vibrio cholera), etc throughout the world. The comprehensive treatments of environments containing infectious pathogens using advanced disinfectant nanomaterials have been proposed for prevention of the outbreaks. Among these nanomaterials, silver nanoparticles (Ag-NPs) with unique properties of high antimicrobial activity have attracted much interest from scientists and technologists to develop nanosilver-based disinfectant products. This article aims to review the synthesis routes and antimicrobial effects of Ag-NPs against various pathogens including bacteria, fungi and virus. Toxicology considerations of Ag-NPs to humans and ecology are discussed in detail. Some current applications of Ag-NPs in water-, air- and surface- disinfection are described. Finally, future prospects of Ag-NPs for treatment and prevention of currently emerging infections are discussed.

Tran, Quang Huy; Quy Nguyen, Van; Le, Anh-Tuan

2013-09-01

388

Surfactantless synthesis of silver nanoplates and their application in SERS.  

SciTech Connect

Silver nanoplates with thicknesses of 50-70 nm and edge lengths ranging from 200 nm to 1 mm are grown on semiconductor waters at room temperature through a simple galvanic reaction between an aqueous solution of silver nitrate and n-type GaAs. The as-grown silver structures have chemically clean surfaces because no surfactant or coordinating molecules are involved in the synthesis. Electron microscopy characterization indicates that each silver plate has rough surfaces and a half-moon morphology with one straight edge and on arclike edge. Systematic studies on varying reaction conditions reveal that the oxide (i.e., Ga{sub 2}O{sub 3} and As{sub 2}O{sub 3}) layers of GaAs, generated in situ in the reactions, play an important role in assisting the growth of anisotropic nanoplates. The cleanliness of the surfaces of the silver nanoplates is beneficial to attachment of interesting molecules on their surfaces for various applications, such as plasmonic-enhanced photophysical and photochemical processes and surface-enhanced spectroscopies.

Sun, Y.; Wiederrecht, G.; Center for Nanoscale Materials

2007-11-01

389

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

390

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

391

Electrochemically mediated enantioselective reduction of chiral sulfoxides.  

PubMed

The respiratory DMSO reductase from Rhodobacter capsulatus catalyzes the reduction of dimethyl sulfoxide to dimethyl sulfide. Herein, we have utilized this Mo enzyme as an enantioselective catalyst to generate optically pure sulfoxides (methyl p-tolyl sulfoxide, methyl phenyl sulfoxide and phenyl vinyl sulfoxide) from racemic starting materials. A hexaaminecobalt coordination compound in its divalent oxidation state was employed as the mediator of electron transfer between the working electrode and DMSO reductase to continually reactivate the enzyme after turnover. In all cases, chiral HPLC analysis of the reaction mixture revealed that the S-sulfoxide was reduced more rapidly leading to enrichment or isolation of the R isomer. PMID:25410832

Chen, Kuan-I; Challinor, Victoria L; Kielmann, Linda; Sharpe, Philip C; De Voss, James J; Kappler, Ulrike; McEwan, Alastair G; Bernhardt, Paul V

2015-03-01

392

Synthesis, characterizations, and applications of carbon nanotubes and silicon nanowires  

NASA Astrophysics Data System (ADS)

Carbon nanotubes (CNTs) have received great attention because of their unique structure and promising applications in microelectronic devices such as field electron emitters. Silicon nanowires (SiNWs) are also very popular because Si is a well established electronic material. This thesis will present my effort on synthesis, characterizations, and applications of CNTs and SiNWs by thermal chemical vapor deposition (CVD) method. For CNTs growth, block copolymer micelles were used as a template to create large area arrays of metal nanoclusters as catalysts for patterned arrays, and Fe/Al/Fe sandwich film on single crystal magnesium oxide (MgO) substrate was used as the catalyst for growth of long length aligned CNTs by CVD. The factors that affect the structure and length of CNTs have been investigated. CNTs were also grown on etched Si substrate by PECVD method. Continuous dropwise condensation was achieved on a biomimetic two-tier texture with short CNTs deposited on micromachined pillars. Superhydrophobic condensation model was studied. For SiNWs growth, hydrogen gold tetrachloride was uniformly mixed into the salt and decomposed into gold nanoparticles at the growth temperature and acted as the catalyst particles to start the growth of Si nanowires. The as-grown Si nanowires are about 70--90 nm in diameter and up to 200 micrometers long. The salt was completely removed by water rinse after growth. Field emission of aligned CNTs grown on Si substrates and SiNWs on Si substrates and carbon clothes has been studied. A post growth annealing procedure has been found to drastically improve the field emission performance of these CNTs and SiNWs.

Xiong, Guangyong

393

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

394

(S)-(-)-(2-MeBu)N(Pr)?MeI salt as template in the enantioselective synthesis of the enantiopure two-dimensional (S)-(-)-(2-MeBu)N(Pr)?Me[?Mn?Cr(C?O?)?] ferromagnet.  

PubMed

We describe herein the synthesis of (rac)- or enantiopure (S)-(-)-(2-MeBu)N(Pr)?MeI ammonium salts. These racemic and enantiopure ammonium salts were used as cationic templates to obtain new two-dimensional (2D) ferromagnets [(rac)-(2-MeBu)N(Pr)?Me][MnCr(C?O?)?] and [(S)-(-)-(2-MeBu)N(Pr)?Me][?Mn? nCr(C?O?)?]. The absolute configuration of the hexacoordinated Cr(III) metallic ion in the enantiopure 2D network was determined by a circular dichroism measurement. The structure of [(2-MeBu)N(Pr)?Me][MnCr(C?O?)?], established by single crystal X-ray diffraction, belongs to the chiral P63 space group. According to direct current (dc) magnetic measurements, these compounds are ferrromagnets with a temperature Tc = 6°K. PMID:23798358

Gruselle, Michel; Li, Yanling; Ovanesyan, Nikolay; Makhaev, Viktor; Shilov, Gennadi; Mushenok, Fedor; Train, Cyrille; Aldoshin, Serguey

2013-08-01

395

DNA Synthesis, Assembly and Applications in Synthetic Biology  

PubMed Central

The past couple of years saw exciting new developments in microchip-based gene synthesis technologies. Such technologies hold the potential for significantly increasing the throughput and decreasing the cost of gene synthesis. Together with more efficient enzymatic error correction and genome assembly methods, these new technologies are pushing the field of synthetic biology to a higher level. PMID:22633067

Ma, Siying; Tang, Nicholas; Tian, Jingdong

2012-01-01

396

VLSI architectural synthesis for an acoustic echo cancellation application  

Microsoft Academic Search

An architectural synthesis tool dedicated to Digital Signal Processing, GAUT, is presented. Synthesis is achieved under both real time and silicon cost constraints. The algorithm is first described using a high level behavioral language. The control and data flow graph (CDFG) obtained is synthesized into processing control, memorization and communication units. These specifications are in VHDL, thus enabling the interconnection

Olivier SENTIEYS; Eric MARTIN; J.-L. Philippe

1993-01-01

397

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

398

Gradual Relaxation Techniques with Applications to Behavioral Synthesis  

Microsoft Academic Search

Heuristics are widely used for solving computational intractablesynthesis problems. However, until now, there has been limitedeffort to systematically develop heuristics that can be applied to avariety of synthesis tasks. We focus on development of generaloptimization principles so that they can be applied to a wide rangeof synthesis problems. In particular, we propose a new way torealize the most constraining principle

Zhiru Zhang; Yiping Fan; Miodrag Potkonjak; Jason Cong

2003-01-01

399

Natural-product synthesis: Stitching together palau'amine  

NASA Astrophysics Data System (ADS)

The long-awaited first total synthesis of the structurally intriguing natural product palau'amine has now been achieved. The synthesis features cascade reactions and an 'across ring' stitching of a 'macropalau'amine', and sets the bar for future efforts towards an enantioselective variant.

Romo, Daniel

2010-03-01

400

Nanomanufacturing of silica nanowires: Synthesis, characterization and applications  

NASA Astrophysics Data System (ADS)

In this research, selective and bottom-up manufacturing of silica nanowires on silicon (Si) and its applications has been investigated. Localized synthesis of these nanowires on Si was achieved by metal thin film catalysis and metal ion implantation based seeding approach. The growth mechanism of the nanowires followed a vapor-liquid-solid (VLS) mechanism. Mass manufacturing aspects such as growth rate, re-usability of the substrate and experimental growth model were also investigated. Further, silica nanowires were explored as surface enhanced Raman (SER) substrate and immunoassay templates towards optical and electrochemical detection of cancer biomarkers respectively. Investigating their use in photonic applications, optically active silica nanowires were synthesized by erbium implantation after nanowire growth and implantation of erbium as a metal catalyst in Si to seed the nanowires. Ion implantation of Pd in Si and subsequent annealing in Ar at 1100 0 C for 60 mins in an open tube furnace resulted in silica nanowires of diameters ranging from 15 to 90 nm. Similarly, Pt was sputtered on to Si and further annealed to obtain silica nanowires of diameters ranging from 50 to 500 nm. Transmission electron microscopy studies revealed the amorphous nature of the wires. In addition, nano-sized Pd catalyst was found along the body of the nanowires seeded by Pd implantation into Si. After functionalization of the wires with 3 - AminoPropylTriMethoxySilane (APTMS), the Pd decorated silica nanowires served as an SER substrate exhibiting a sensitivity of 10 7 towards the detection of interleukin-10 (IL-10, a cancer biomarker) with higher spatial resolution. Voltammetric detection of IL-10 involved silica nanowires synthesized by Pd thin film catalysis on Si as an immunoassay template. Using the electrochemical scheme, the presence of IL-10 was detected down to 1fg/mL in ideal pure solution and 1 pg/mL in clinically relevant samples. Time resolved photoluminescence (PL) results from the Er doped silica nanowires indicate a sharp emission around 1.54 microm representative of the I13/2 to I15/2 transition in Erbium. Also, a five-fold increase in the PL intensity and 30% augment in luminescence life time have been observed in nanowires when compared to fused silica sample prepared under similar conditions. The experimental results indicate the potential of silica nanowires in a wide variety of applications such as the development of orthogonal biosensors, fabrication of metallic nanowires, and environmental sensing probes.

Sekhar, Praveen Kumar

401

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

402

Synthesis of 1-substituted tetrahydroisoquinolines by lithiation and electrophilic quenching guided by in situ IR and NMR spectroscopy and application to the synthesis of salsolidine, carnegine and laudanosine.  

PubMed

The lithiation of N-tert-butoxycarbonyl (N-Boc)-1,2,3,4-tetrahydroisoquinoline was optimized by in situ IR (ReactIR) spectroscopy. Optimum conditions were found by using n-butyllithium in THF at -50?°C for less than 5?min. The intermediate organolithium was quenched with electrophiles to give 1-substituted 1,2,3,4-tetrahydroisoquinolines. Monitoring the lithiation by IR or NMR spectroscopy showed that one rotamer reacts quickly and the barrier to rotation of the Boc group was determined by variable-temperature NMR spectroscopy and found to be about 60.8?kJ?mol(-1), equating to a half-life for rotation of approximately 30?s at -50?°C. The use of (-)-sparteine as a ligand led to low levels of enantioselectivity after electrophilic quenching and the "poor man's Hoffmann test" indicated that the organolithium was configurationally unstable. The chemistry was applied to N-Boc-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline and led to the efficient synthesis of the racemic alkaloids salsolidine, carnegine, norlaudanosine and laudanosine. PMID:23677770

Li, Xiabing; Leonori, Daniele; Sheikh, Nadeem S; Coldham, Iain

2013-06-10

403

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 ...

404

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

405

Enantioselective Copper-Catalyzed Reductive Coupling of Alkenylazaarenes with Ketones   

E-print Network

nucleophilic additions, the enantioselective reductive coupling of alkenylazaarenes with ketones has been developed. The process is tolerant of a wide variety of azaarenes and ketones, and provides aromatic heterocycles bearing tertiary-alcohol-containing side...

Saxena, Aakarsh; Choi, Bonnie; Hon, Lam Wai

2012-05-23

406

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

407

Organocatalytic Enantioselective ?-Hydroxymethylation of Aldehydes: Mechanistic Aspects and Optimization.  

PubMed

Further studies of the direct enantioselective ?-hydroxymethylation of aldehydes employing the ?,?-diarylprolinol trimethylsilyl ether class of organocatalysts are described. This process has proven efficient for access to ?-hydroxycarboxylic acids and ?-hydroxy-?,?-unsaturated esters from aldehydes in generally good yields, excellent enantioselectivity, and compatibility with a broad range of functional groups in the aldehyde. The goal of these studies was to identify the critical reaction variables that influence the yield and enantioselectivity of the ?-hydroxymethylation process such as catalyst structure, pH of the medium, purity of the reactants and reagents particularly with respect to the presence of acidic impurities, and the nature of the buffer, along with the standard variables including solvent, time, temperature and mixing efficiency. The previously identified intermediate lactol has been further characterized and its reactivity examined. These studies have led to identification of the most critical variables translating directly into improved substrate scope, reproducibility, enantioselectivity, and yields. PMID:25793648

Boeckman, Robert K; Biegasiewicz, Kyle F; Tusch, Douglas J; Miller, John R

2015-04-17

408

The upside of downsizing: asymmetric trifunctional organocatalysts as small enzyme mimics for cooperative enhancement of both rate and enantioselectivity with regulation.  

PubMed

Small molecule organic catalysts (organocatalysts) are widely used in asymmetric catalysis and synthesis. Compared to their enzymatic and transition-metal counterparts, organocatalysts have advantages in catalytic scope and efficiency but are more limited in proficiency. Chiral trifunctional organocatalysts, in which multiple catalytic motifs act cooperatively on a chiral scaffold, are an emerging class of organocatalysts with improved proficiency. Cooperativity design that enables both enantioselectivity and rate enhancement is essential to developing future generations of organocatalysts in biomimetic asymmetric catalysis. PMID:23966336

Liu, Fei

2013-11-01

409

An NHC-Catalyzed In Situ Activation Strategy to ?-Functionalize Saturated Carboxylic Acid: An Enantioselective Formal [3+2] Annulation for Spirocyclic Oxindolo-?-butyrolactones.  

PubMed

An in situ NHC-catalyzed activation strategy to ?-functionalize saturated carboxylic acid was developed. This asymmetric formal [3+2] annulation could deliver spirocyclic oxindolo-?-butyrolactones from saturated carboxylic acid and isatin in good yields with high to excellent enantioselectivities. The easy availability of the starting materials, direct installation of functional units at unreactive carbon atom and the convergent assembly make this protocol attractive in the field of organic synthesis. PMID:25689040

Xie, Yuanwei; Yu, Chenxia; Li, Tuanjie; Tu, Shujiang; Yao, Changsheng

2015-03-27

410

Bifunctional amino sulfonohydrazide catalyzed direct asymmetric Mannich reaction of cyclic ketimines with ketones: highly diastereo- and enantioselective construction of quaternary carbon stereocenters.  

PubMed

A bifunctional amino sulfonohydrazide which contains multiple sites for hydrogen bonding with substrates was found to enhance reactivity and enantioselectivity in the direct asymmetric Mannich reaction of N-sulfonyl cyclic ketimines with ketones. In this efficient transformation, not only methyl ketones but also cyclic ketones can be employed to provide a general methodology to construct tetrasubstituted ?-amino ester in a stereoselective manner. The synthetic utility of a substituted amino ester product is demonstrated by the synthesis of biologically active spirotetrahydrofuran. PMID:25664888

Zhang, Sheng; Li, Lijun; Hu, Yanbin; Zha, Zhenggen; Wang, Zhiyong; Loh, Teck-Peng

2015-02-20

411

Adaptation of a Small-Molecule Hydrogen-Bond Donor Catalyst to an Enantioselective Hetero-Diels–Alder Reaction Hypothesized for Brevianamide Biosynthesis  

PubMed Central

Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels–Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis. PMID:25697748

2015-01-01

412

Application of lean manufacturing concepts to drug discovery: rapid analogue library synthesis.  

PubMed

The application of parallel synthesis to lead optimization programs in drug discovery has been an ongoing challenge since the first reports of library synthesis. A number of approaches to the application of parallel array synthesis to lead optimization have been attempted over the years, ranging from widespread deployment by (and support of) individual medicinal chemists to centralization as a service by an expert core team. This manuscript describes our experience with the latter approach, which was undertaken as part of a larger initiative to optimize drug discovery. In particular, we highlight how concepts taken from the manufacturing sector can be applied to drug discovery and parallel synthesis to improve the timeliness and thus the impact of arrays on drug discovery. PMID:16961404

Weller, Harold N; Nirschl, David S; Petrillo, Edward W; Poss, Michael A; Andres, Charles J; Cavallaro, Cullen L; Echols, Martin M; Grant-Young, Katherine A; Houston, John G; Miller, Arthur V; Swann, R Thomas

2006-01-01

413

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

414

Perspective view of GSC: How to realize the industrial application of artificial photo synthesis?  

NASA Astrophysics Data System (ADS)

Artificial photo synthesis is one of the dream reactions, which can contribute to the industrial application from a view point of green sustainable chemistry. Considering the hardness of subjects to obtain the enough performance on artificial photo synthesis and the difference between the current infrastructure and required ones, which can fit to this application, we have to solve these subjects one by one from a strategic view point. Diversification of chemical resource and compatibility of process technologies will be the keys for industrial application.

Setoyama, T.

2013-12-01

415

Enantioselective aza-Henry reaction using cinchona organocatalysts  

Microsoft Academic Search

The aza-Henry reaction of imines with nitromethane was promoted by cinchona alkaloids and modified cinchona bases to give optically active ?-nitroamines. Various N-protected imines were examined as substrates. N-Boc, N-Cbz, and N-Fmoc protected imines gave the best results in terms of chemical yields and enantioselectivities. After a careful screening of a series of chiral bases, very good enantioselectivities up to

Luca Bernardi; Francesco Fini; Raquel P. Herrera; Alfredo Ricci; Valentina Sgarzani

2006-01-01

416

Enantioselective hydrogenation of ethyl acetoacetate on asymmetric Raney Ni catalysts  

SciTech Connect

The properties of Raney nickel catalysts modified by (+)-tartaric acid and active in enantioselective hydrogenation of ethyl acetoacetate depend on the chemical and phase compositions of the starting Ni-Al alloys. A decrease of the Ni content in the Ni-Al alloy specimens which corresponds to an increase of the fraction of the NiAl/sub 3/ intermetallic compound in them contributes to an increase of the catalytic activity and enantioselectivity of the action of the obtained catalysts.

Zubareva, N.D.; Chernysheva, V.V.; Grigor'ev, Yu.A.; Klabunovskii, E.I.

1987-09-10

417

Salen Promoted Enantioselective Nazarov Cyclizations of Activated and Unactivated Dienones  

PubMed Central

A novel class of chiral 5,5?-di(2,4,6-trialkyl)aryl salen-metal complexes have been developed and shown to catalyze highly enantioselective Nazarov cyclization reactions, giving rise to cyclopentenoids in 90:10–98:2 er. Significantly, the catalysts also promote, for the first time, highly enantioselective Nazarov reactions of “unactivated” dienones, producing hydrindenone products having in place three contiguous chiral centers. PMID:23506509

Hutson, Gerri E.; Türkmen, Yunus E.; Rawal, Viresh H.

2014-01-01

418

Salen promoted enantioselective Nazarov cyclizations of activated and unactivated dienones.  

PubMed

A novel class of chiral 5,5'-di(2,4,6-trialkyl)aryl salen-metal complexes have been developed and shown to catalyze highly enantioselective Nazarov cyclization reactions, giving rise to cyclopentenoids in 90:10-98:2 er. Significantly, the catalysts also promote, for the first time, highly enantioselective Nazarov reactions of "unactivated" dienones, producing hydrindenone products having in place three contiguous chiral centers. PMID:23506509

Hutson, Gerri E; Türkmen, Yunus E; Rawal, Viresh H

2013-04-01

419

Enantioselective organocatalytic oxidation of functionalized sterically hindered disulfides.  

PubMed

[structure: see text]. The first study on enantioselective oxidation of functionalized sterically hindered disulfides is reported. This study shows that the Shi organocatalytic system using carbohydrate-derived ketone with oxone is superior to the Ellman-Bolm vanadium catalyst in terms of chemical yield and enantioselectivity. Whereas the latter system afforded mostly racemic thiosulfinates in low to moderate yields, the former one afforded thiosulfinates with up to 96% ee. PMID:17341090

Khiar, Noureddine; Mallouk, Siham; Valdivia, Victoria; Bougrin, Khalid; Soufiaoui, Mohammed; Fernández, Inmaculada

2007-03-29

420

Synthesis of an Application-Specific Soft Multiprocessor Jason Cong, Guoling Han and Wei Jiang  

E-print Network

System-on-a-Chip on FPGA platforms. In particular, soft processors on FPGAs (e.g., MicroBlaze from XilinxSynthesis of an Application-Specific Soft Multiprocessor System Jason Cong, Guoling Han and Wei ABSTRACT The application-specific multiprocessor System-on-a-Chip is a promising design alternative because

Cong, Jason "Jingsheng"

421

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

422

Anisotropic nanomaterials: Synthesis, optical and magnetic properties, and applications  

NASA Astrophysics Data System (ADS)

As nanoscience and nanotechnology mature, anisotropic metal nanostructures are emerging in a variety of contexts as valuable class of nanostructures due to their distinctive attributes. With unique properties ranging from optical to magnetic and beyond, these structures are useful in many new applications. Chapter two discusses the nanodisk code: a linear array of metal disk pairs that serve as surface-enhanced Raman scattering substrates. These multiplexing structures employ a binary encoding scheme, perform better than previous nanowires designs (in the context of SERS) and are useful for both convert encoding and tagging of substrates (based both on spatial disk position and spectroscopic response) as well as biomolecule detection (e.g. DNA). Chapter three describes the development of improved, silver-based nanodisk code structures. Work was undertaken to generate structures with high yield and reproducibility and to reoptimize the geometry of each disk pair for maximum Raman enhancement. The improved silver structures exhibit greater enhancement than Au structures (leading to lower DNA detection limits), convey additional flexibility, and enable trinary encoding schemes where far more unique structures can be created. Chapter four considers the effect of roughness on the plasmonic properties of nanorod structures and introduces a novel method to smooth the end-surfaces of nanorods structures. The smoothing technique is based upon a two-step process relying upon diffusion control during nanowires growth and selective oxidation after each step of synthesis is complete. Empirical and theoretical work show that smoothed nanostructures have superior and controllable optical properties. Chapter five concerns silica-encapsulated gold nanoprisms. This encapsulation allows these highly sensitive prisms to remain stable and protected in solution, enabling their use as class-leading sensors. Theoretical study complements the empirical work, exploring the effect of encapsulation on the SPR of these structures. Chapter six focuses on the magnetic properties of Au-Ni heterostructures. In addition to demonstration of nanoconfinement effects based upon the anisotropy of the nanorods/nanodisk structure, the magnetic coupling of rod-disk heterostructures is examined. Subsequent investigations suggest that the magnetic behavior of disks can be influenced by nearby rod segments, leading to the creation of a three-state spin system that may prove useful in device applications.

Banholzer, Matthew John

423

Synthesis and characterization of iron based nanoparticles for novel applications  

NASA Astrophysics Data System (ADS)

The work in this thesis has been focused on the fabrication and characterization of iron based nanoparticles with controlled size and morphology with the aim: (i) to investigate their properties for potential applications in MICR toners and biomedical field and (ii) to study finite size effects on the magnetic properties of the nanoparticles. For the biomedical applications, core/shell structured iron/iron-oxide and hollow shell nanoparticles were synthesized by thermal decomposition of iron organometallic compounds [Fe(CO)5] at high temperature. Core/shell structured iron/iron-oxide nanoparticles have been prepared in the presence of oleic acid and oleylamine. Particle size and composition was controlled by varying the reaction parameters during synthesis. The as-made particles are hydrophobic and not dispersible in water. Water dispersibility was achieved by ligand exchange a with double hydrophilic diblock copolymer. Relaxometery measurements of the transverse relaxation time T2 of the nanoparticles solution at 3 Tesla confirm that the core/shell nanoparticles are an excellent MRI contrast agent using T2 weighted imaging sequences. In comparison to conventionally used iron oxide nanoparticles, iron/iron-oxide core/shell nanoparticles offer four times stronger T2 shortening effect at comparable core size due to their higher magnetization. The magnetic properties were studied as a function of particle size, composition and morphology. Hollow nanostructures are composed of randomly oriented grains arranged together to make a shell layer and make an interesting class of materials. The hollow morphology can be used as an extra degree of freedom to control the magnetic properties. Owing to their hollow morphology, they can be used for the targeted drug delivery applications by filling the drug inside their cavity. For the magnetic toners applications, particles were synthesized by chemically reducing iron salt using sodium borohydride and then coated with polyethylene glycol. Parameters such as the reactant concentrations and their flow rate were varied to study the effect of particle size, structure and crystallinity on the magnetic nanoparticles. Many different hydrophilic surfactants and polymers electrolytes were investigated for the particles' stability in water. PSSNa was found to be the best coating agent among all the other investigated polymer and surfactants for particles stability in water. Particles have an average size of 50 nm and magnetization above 150 emu/g. It is anticipated that owing to their high saturation magnetization and magneto crystalline anisotropy, the incorporations of PSSNa coated nanoparticles into the MICR toner can reduce the pigment loading and hence optimize the toner quality. The magnetic properties were studied as a function of particle size, composition and morphology. The saturation magnetization and coercivity was found to be strongly dependent on the particle size and morphology. The estimated effective anisotropy of the particles was found to be much higher than their bulk values because of their morphology and finite size effects. Core/shell particles below an average size of 12 nm display superparamagnetism and exchange bias phenomenon. The hollow morphology can be used as an extra degree of freedom to control magnetic properties. The enormously large number of pinned spins at the inner and outer surface and at the interface between the grain boundaries in hollow nanoparticles, gives rise to a very large value of effective anisotropy in these nanoparticles and measured hyteresis loops are minor loops. The surface spin disorder contribution to magnetic behavior is strongly influenced by the cooling field magnitude.

Khurshid, Hafsa

424

Discovery of an Escherichia coli Esterase with High Activity and Enantioselectivity toward 1,2-O-Isopropylideneglycerol Esters?†  

PubMed Central

Escherichia coli has been widely used as an expression host for the identification of desired biocatalysts through screening or selection assays. We have previously used E. coli in growth selection and screening assays for identification of Bacillus subtilis lipase variants (located in the periplasm) with improved activity and enantioselectivity toward 1,2-O-isopropylideneglycerol (IPG) esters. In the course of these studies, we discovered that E. coli itself exhibits significant cytoplasmic esterase activity toward IPG esters. In order to identify the enzyme (or enzymes) responsible for this esterase activity, we analyzed eight E. coli knockout strains, in which single esterase genes were deleted, for their ability to hydrolyze IPG butyrate. This approach led to the identification of esterase YbfF as the major E. coli enzyme responsible for the hydrolytic activity toward IPG esters. The gene coding for YbfF was cloned and overexpressed in E. coli, and the corresponding protein was purified and characterized for its biocatalytic performance. YbfF displays a high level of activity toward IPG butyrate and IPG caprylate and prefers the R-enantiomer of these substrates, producing the S-enantiomer of the IPG product with high enantiomeric excess (72 to 94% ee). The enantioselectivity of YbfF for IPG caprylate (E = 40) could be significantly enhanced when using dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) as cosolvents in kinetic resolution experiments. The enzyme also shows high enantioselectivity toward 1-phenylethyl acetate (E ? 200), giving the chiral product (R)-1-phenylethanol with >99% ee. The high activity and enantioselectivity of YbfF make it an attractive enzyme for organic synthesis. PMID:21764964

Godinho, Luis F.; Reis, Carlos R.; Tepper, Pieter G.; Poelarends, Gerrit J.; Quax, Wim J.

2011-01-01

425

Enantioselective Intramolecular Aldehyde Alkylation with Simple Olefins: Direct Access to Homo-Ene Products  

E-print Network

Enantioselective Intramolecular Aldehyde Alkylation with Simple Olefins: Direct Access to Homo. Conceptually, this novel mechanism allows direct access to "homo-ene"- type products. Carbocyclic transformations, including direct enantioselective - allylic alkylation,7 -enolation,8 -vinylation,9 -chlorination

MacMillan, David W. C.

426

Enantioselective Direct Amination of Aldehydes via a Photoredox Mechanism: A Strategy for Asymmetric Amine Fragment Coupling  

E-print Network

Enantioselective Direct Amination of Aldehydes via a Photoredox Mechanism: A Strategy States *S Supporting Information ABSTRACT: The direct, asymmetric -amination of aldehydes has been enantioselective -addition to catalytically formed chiral enamines to directly produce stable -amino aldehyde

MacMillan, David W. C.

427

Enediolate-Dilithium Amide Mixed Aggregates in the Enantioselective Alkylation of Arylacetic Acids: Structural  

E-print Network

enantioselective organolithium reactions scrutinized through structural and mechanistic studies12 has demonstratedEnediolate-Dilithium Amide Mixed Aggregates in the Enantioselective Alkylation of Arylacetic Acids studies implicate the non-dimerized trilithiated mixed aggregate. Reaction of the dilithiated amide

Collum, David B.

428

Enantioselective Rhodium-Catalyzed Nucleophilic Allylation of Cyclic Imines with Allylboron Reagents   

E-print Network

The highly diastereo- and enantioselective title reaction of a range of cyclic imines with various potassium allyltrifluoroborates most likely proceeds via allylrhodium(I) intermediates, and represents the first rhodium-catalyzed enantioselective...

Luo, Yunfei; Hepburn, Hamish B.; Chotsaeng, Nawasit; Lam, Hon Wai

429

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

430

First total synthesis of (-)-sinularianin B.  

PubMed

The first enantioselective total synthesis of (-)-sinularianin B, a structurally unique sesquiterpenoid isolated from the Formosan soft coral Sinularia sp., has been accomplished in 16 steps with 39.5% overall yield. Key transformations include formation of a cyclopentane possessing a tertiary hydroxy group via a tandem intermolecular-intramolecular alkylation involving a 5-endo cyclization. PMID:23877353

Ota, Koichiro; Miyaoka, Hiroaki

2013-09-25

431

Enantioselective redox-neutral rh-catalyzed coupling of terminal alkynes with carboxylic acids toward branched allylic esters.  

PubMed

We report on the first enantioselective variant of the atom-economic and redox-neutral coupling of carboxylic acids with terminal alkynes under rhodium catalysis utilizing the chiral, bidentate (R,R)-Cp-DIOP ligand. This represents the first example of this convenient asymmetric access to valuable branched allylic esters. The utility of this methodology is demonstrated by both a reaction performed on large scale and a short three-step synthesis of two naturally occurring ?-butyrolactones. A stereochemical model explaining the observed absolute configuration of the products based on DFT calculations is given. PMID:25667963

Koschker, Philipp; Kähny, Matthias; Breit, Bernhard

2015-03-01

432

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

433

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

434

Synthesis of application-level utility functions for autonomic self-assessment  

Microsoft Academic Search

We present an approach to self-assessment for Autonomic Computing, based on the synthesis of utility functions, at the level\\u000a of an autonomic application, or even a single task or feature performed by that application. This paper describes the fundamental\\u000a steps of our approach: instrumentation of the application; collection of exhaustive samples of runtime data about relevant\\u000a quality attributes of the

Giuseppe Valetto; Paul deGrandis; Dale Seybold

435

Enantioselective pharmacokinetics of ibuprofen and involved mechanisms.  

PubMed

Although dexibuprofen (S-ibuprofen) was marketed in Austria and Switzerland, the racemate at various formulations is still extensively used worldwide, and there are no indications that the racemate will be replaced by the single enantiomer. Thus, elucidation of the characteristics and involved mechanisms of the chiral pharmacokinetics of racemic ibuprofen is of special importance for the understanding of the pharmacological and toxicological consequences, and for prediction of the clinically potential drug interactions and influence of the pathological states. Stereoselective pharmacokinetics and metabolism are common features for chiral nonsteroidal antiinflammatory drugs (NSAIDs) and especially for 2-arylpropionic acid derivatives characterized with a chiral center adjacent to the carboxyl group. Although the enantioselective pharmacokinetic characteristics of different NSAIDs should be treated case by case, they share similar mechanisms underlying the protein binding, metabolism and chiral inversion. Ibuprofen was the most extensively researched drug in terms of chiral characteristics and mechanisms. Therefore, elucidation of the mechanisms derived from research on ibuprofen may provide better understanding and prediction of other chiral drugs. This article attempts to elucidate the chiral pharmacokinetics and involved mechanisms of ibuprofen in comparison with other NSAIDs based on recent developments. Topics on history of ibuprofen, enantioselective analysis method, absorption, protein binding, conventional metabolism, metabolic chiral inversion, gene polymorphism, and biochemical developments were included. It is worth mentioning that some underlying biochemical mechanisms, especially for the metabolic chiral inversion and ethnic differences still remain to be seen. Further research is required to develop human-resourced researching model and to provide more evidence concerning the site of inversion, species variation, CYP450 gene polymorphisms, and biochemical mechanisms. PMID:15747501

Hao, Haiping; Wang, Guangji; Sun, Jianguo

2005-01-01

436

Enantioselective effects of chiral herbicide diclofop acid on rice Xiushui 63 seedlings.  

PubMed

In this study, the acute toxicity (72-h EC50 values) of chiral diclofop acid towards rice Xiushui 63 seedlings and its effects on the Hill reaction activities of chloroplasts were determined. Significant differences were observed between the two enantiomers in 72-h EC50 values and in both in vivo and in vitro relative Hill reaction activities. These observations indicate that the enantiomers of diclofop acid pose different toxicities to rice seedlings: the S-enantiomer is more toxic to leaves and the R-enantiomer is more toxic to roots. These enantioselective toxic effects on rice seedlings should be taken into account in chiral herbicide application. PMID:19452112

Ye, Jing; Zhang, Qiong; Zhang, Anping; Wen, Yuezhong; Liu, Weiping

2009-07-01

437

[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

438

Synthesis of N-arylated oxazolidinones via a palladium catalyzed cross coupling reaction. Application to the synthesis of the antibacterial agent Dup-721  

Microsoft Academic Search

A method for the intermolecular coupling of aryl bromides and oxazolidinones is described. Application to intermediates useful for the preparation of a known class of antibacterial agent and the synthesis of the known antibacterial oxazolidinone Dup-721 are described.

David J Madar; Hana Kopecka; Daisy Pireh; Jonathan Pease; Marina Pliushchev; Richard J Sciotti; Paul E Wiedeman; Stevan W Djuric

2001-01-01

439

A Computational Model Relating Structure and Reactivity in Enantioselective Oxidations of Secondary Alcohols by  

E-print Network

with the associated anion. The enantioselectivities observed under base-rich reaction conditions follow directly from of these reactions is the enantioselective oxidation of secondary alcohols to ketones by a (-)-sparteine-PdX2A Computational Model Relating Structure and Reactivity in Enantioselective Oxidations of Secondary

Goddard III, William A.

440

Catalytic Enantioselective Conia-Ene Reaction Britton K. Corkey and F. Dean Toste*  

E-print Network

Catalytic Enantioselective Conia-Ene Reaction Britton K. Corkey and F. Dean Toste* Department enantioselective Conia-ene reaction. To this end, treatment of -ketoester 1 with 5% of cationic chiral gold of -dicarbonyl compounds undergo the Pd(II)/ Yb(III)-catalyzed enantioselective Conia-ene reaction (Table 2

Toste, Dean

441

Highly Enantioselective Rh-Catalyzed Hydrogenations with a New Chiral 1,4-Bisphosphine  

E-print Network

rigidity leads to high enantioselectivity in asymmetric reactions. The four stereogenic carbon centers. The extent to which the quadrants are blocked has a strong influence on the reaction enantioselectivity reactions.1 The enantioselectivity with DIOP, however, is not as good in many asymmetric reactions as some

Zhang, Xumu

442

The First General Enantioselective Catalytic Diels-Alder Reaction with Simple r, -Unsaturated Ketones  

E-print Network

The First General Enantioselective Catalytic Diels-Alder Reaction with Simple r, -Unsaturated of enantioselective carbon-carbon bond-forming reactions. In this communication, we extend this organocatalytic, we document the first enantioselective catalytic Diels-Alder reaction with simple ketone dienophiles

MacMillan, David W. C.

443

Highly Enantioselective Rh-Catalyzed Intramolecular AlderEne Reactions for the  

E-print Network

Highly Enantioselective Rh-Catalyzed Intramolecular Alder±Ene Reactions for the Syntheses of Chiral, the enantioselective processes of metal-catalyzed Alder±ene reactions are relatively unex- plored and the development intramolecular Alder±ene reactions of enynes using a [{Rh(diphos)Cl}2] precursor.[4] Enantioselectivities between

Zhang, Xumu

444

Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards  

E-print Network

of reaction [5-7], thermodynamic activity of water (aW) [6-9] and temperature [10,11] on enantioselectivity that water has many effects on Candida antarctica lipase B (CALB) catalyzed enantioselective reactions1 Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards

Paris-Sud XI, Université de

445

LETTER 1169 Highly Enantioselective Hydrogenation of a-Keto Esters Catalyzed by  

E-print Network

bisphospines on the reactivity and enantioselectivity of asymmetric hydrogenation reactions. For exampleLETTER 1169 Highly Enantioselective Hydrogenation of a-Keto Esters Catalyzed by Ru-Tunephos Complexes HighlyEnantioselectiveHydrogenationofa-KetoEstersChun-Jiang Wang, Xianfeng Sun, Xumu Zhang

Zhang, Xumu

446

A general approach to the enantioselective a-oxidation of aldehydes via synergistic catalysis  

E-print Network

addition etc.).4 A number of enantioselective aldehyde a-oxidation reactions have recently been reported; however, there are no direct methods that demonstrate high reaction efficiency and enantioselectivityA general approach to the enantioselective a-oxidation of aldehydes via synergistic catalysis Scott

MacMillan, David W. C.

447

?-Conjugated Aromatics Based on Truxene: Synthesis, Self-Assembly, and Applications.  

PubMed

Recently, many efforts have been devoted to developing novel polycyclic aromatics due to their unique optical and electronic properties and broad applications, such as in organic field-effect transistors, organic photovoltaics, and organic light-emitting diodes. Among various ?-conjugated molecules, many truxene derivatives have interesting characteristics such as C3 -symmetry, strong blue emission, and a planar rigid structure. Moreover, compared with many other ?-conjugated aromatics, the synthesis and modification of truxene are particularly facile and diverse. In this account, we summarize investigations into truxene derivatives from synthesis and physical properties to applications in organic electronics. PMID:25474741

Shi, Ke; Wang, Jie-Yu; Pei, Jian

2015-02-01

448

Design, synthesis, and characterization of new materials for thermoelectric applications  

NASA Astrophysics Data System (ADS)

Currently, the best known material for thermoelectric refrigeration at room temperature is and alloy of Bi2Te3 and Sb 2Te3. This material has been the basis for room temperature thermoelectric cooling for over 40 years, but its low cooling efficiency (?10% of Carnot Efficiency) has limited its adaptation to small-market specialty applications. Since Bi2Te3 and its alloys have been studied so extensively, it is doubtful that large improvements in efficiency can be made by further modifications of Bi2Te3 (ie. by changing doping or processing of the material). Therefore, this dissertation deals with the discovery and exploration of completely new systems of compounds. The most important parameter for characterizing the efficiency of a thermoelectric material is the dimensionless quantity ZT, where ZT = S2T/rhokappa. Here, S is the thermopower, T is the temperature, kappa is the thermal conductivity, and rho is the electrical resistivity. These variables are not independent of each other, and usually if one of the values is altered by changing composition or doping, the others change as well. Understanding these parameters in depth leads us to several guidelines for searching for better thermoelectric materials and these are discussed in the dissertation. The concept of obtaining highly symmetric crystal structures and also its relation to increasing the value of ZT is discussed. The synthesis of several new quaternary compounds by starting with highly symmetric tetrahedral anion building blocks is presented. While some of these compounds did in fact have high symmetry structures, none were suitable for further studies because they all had large bandgaps. Further systems we explored include heavy metal telluride compounds and compounds that have multiple ordered anions. These systems were chosen based on the concept of minimizing thermal conductivity. A brief chapter on skutterudite materials explores a few new compounds discovered in this highly researched area. The skutterudites are potentially good thermoelectric materials at temperatures above room temperature, however, the compounds discovered were metals and unsuitable for thermoelectric applications. Perhaps the most promising area of research in thermoelectrics presented in this dissertation involves the use of thallium as an alkali metal-like cation. It is shown here that thallium chalcogenides form a wide variety of structures that in many ways mimic the chemistry of alkali metal chalcogenides, yet often form different structures. We present 18 new compounds in that chapter, one of which (Tl1-xSn3+2 xBi7-xSe 14) has an estimated ZT of 0.2--0.3 at room temperature. Since this is not an optimized value, the value of ZT may be able to be increased considerably by carefully adjusting the carrier density. Finally, we present a chapter on measuring the various important thermoelectric parameters (S, rho, and kappa). The construction of a new apparatus for such measurements is presented, along with a new method for measuring kappa, which is much more rapid than steady-state methods.

Reynolds, Thomas Kent

449

Enantioselective Recognition in Solution: The Case of Countercurrent Chromatography  

NASA Astrophysics Data System (ADS)

Countercurrent chromatography (CCC) is a preparative separation technique that works with a liquid stationary phase. Biphasic liquid systems are needed to perform a separation. Since a chiral selector is required to perform enantiomer separations, special requirements are imposed in CCC. The chiral selector (CS) must be located in the stationary phase since partitioning with the mobile phase would cause losses of the valuable chiral selector in the mobile phase. Sulfated cyclodextrins and proteins were used as polar CS located in the polar stationary phase (reversed phase mode). Apolar CSs such as N-dodecyl-L-proline 3,5-dimethylanilide or Whelk-O selectors, quinine and quinidine derivatives, cellulose or amylose apolar derivatives were used located in the apolar stationary phase (normal phase mode). The special CCC displacement method called pH-zone refining was found useful in the increase of the loading capacity for cellulose, quinine, quinidine, and proline-derived selectors. Dual and multidual mode uses of CCC could produce an increase in peak separation thereby broadening the applicability of moderately enantioselective CSs.

Rubio, Núria; Minguillón, Cristina

450

Arthrobacter sp. lipase immobilization for improvement in stability and enantioselectivity.  

PubMed

Arthrobacter sp. lipase (ABL, MTCC no. 5125) is being recognized as an efficient enzyme for the resolution of drugs and their intermediates. The immobilization of ABL on various matrices for its enantioselectivity, stability, and reusability has been studied. Immobilization by covalent bonding on sepharose and silica afforded a maximum of 380 and 40 IU/g activity, respectively, whereas sol-gel entrapment provided a maximum of 150 IU/g activity in dry powder. The immobilized enzyme displayed excellent stability in the pH range of 4-10 and even at higher temperature, i.e., 50-60 degrees C, compared to free enzyme, which is unstable under extreme conditions. The resolution of racemic auxiliaries like 1-phenyl ethanol and an intermediate of antidepressant drug fluoxetine, i.e., ethyl 3-hydroxy-3-phenylpropanoate alkyl acylates, provided exclusively R-(+) products ( approximately 99% ee, E=646 and 473), compared to cell free extract/whole cells which gave a product with approximately 96% ee (E=106 and 150). The repeated use (ten times) of covalently immobilized and entrapped ABL resulted in no loss in activity, thus demonstrating its prospects for commercial applications. PMID:16896604

Chaubey, Asha; Parshad, Rajinder; Koul, Surrinder; Taneja, Subhash C; Qazi, Ghulam N

2006-12-01

451

Highly Efficient Synthesis of Chiral ?-CF3 Amines via Rh-Catalyzed Asymmetric Hydrogenation.  

PubMed

Highly enantioselective catalytic asymmetric hydrogenation of ?-CF3-enamides has been achieved by employing rhodium-DuanPhos as the catalyst, which provides a readily accessible method for the synthesis of chiral trifluoromethylated amines. The reaction has a broad substrate scope; both aryl- and alkyl-substituted ?-CF3-enamides worked smoothly and afford the corresponding chiral amines in high yields and excellent enantioselectivities (up to 99% ee). PMID:25685874

Jiang, Jun; Lu, Wenxin; Lv, Hui; Zhang, Xumu

2015-03-01

452

Microwave-Assisted Synthesis ? Catalytic Applications in Aqueous Media  

EPA Science Inventory

The development of sustainable methods directed towards the synthesis of molecules is due to the heightened awareness and recognition of alternative eco-friendly and economical protocols that have minimum impact on environment. Among others, microwave (MW)-assisted methodology ha...

453

Applications in Synthesis of Commodities and Fine Chemicals  

NASA Astrophysics Data System (ADS)

Channels and cages of microporous and mesoporous materials can be considered as nanoreactors whose properties (topology, morphology, nature of the active site and chemical surroundings) can be finely tuned and fitted to the synthesis of functionalised high-added value molecules, such as commodities and fine chemicals.

Guisnet, Michel; Guidotti, Matteo

454

Synthesis of an array antenna for hyperthermia applications  

Microsoft Academic Search

In the present work the synthesis of an array antenna for hyperthermia treatment is developed. The selected antenna is an array antenna surrounded by a semicircular reflector which has shown to ease the penetration and focalization in malignant biological tissues. A bolus is introduced as a protection in order to avoid an increasing heat hazard of superficial healthy tissues. The

Ruth V. Sabariego; Luis Landesa; Fernando Obelleiro

2000-01-01

455

Applications of Ultrasound to the Synthesis of Nanostructured Materials  

E-print Network

Cavitation Chemistry deals with the interaction between energy and matter, and chemical reactions require some form of energy (e.g., heat, REVIEW www.MaterialsViews.com www.advmat.de [*] Prof. K. S. Suslick synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive

Suslick, Kenneth S.

456

Wet Chemical Synthesis of Aluminum Nanoparticles for UV Plasmonics Applications  

E-print Network

GP-A-12 Wet Chemical Synthesis of Aluminum Nanoparticles for UV Plasmonics, Texas, U.S.A. Aluminum nanoparticles are a promising plasmonic material because aluminum is highly fluorescence, and SERS. In this work, shape and size control of aluminum metal nanoparticles is achieved

457

Immobilization and Characterization of a New Regioselective and Enantioselective Lipase Obtained from a Metagenomic Library  

PubMed Central

In previous work, a new lipase and its cognate foldase were identified and isolated from a metagenomic library constructed from soil samples contaminated with fat. This new lipase, called LipG9, is a true lipase that shows specific activities that are comparable to those of well-known industrially-used lipases with high activity against long-chain triglycerides. In the present work, LipG9 was co-expressed and co-immobilized with its foldase, on an inert hydrophobic support (Accurel MP1000). We studied the performance of this immobilized LipG9 (Im-LipG9) in organic media, in order to evaluate its potential for use in biocatalysis. Im-LipG9 showed good stability, maintaining a residual activity of more than 70% at 50°C after incubation in n-heptane (log P 4.0) for 8 h. It was also stable in polar organic solvents such as ethanol (log P -0.23) and acetone (log P -0.31), maintaining more than 80% of its original activity after 8 h incubation at 30°C. The synthesis of ethyl esters was tested with fatty acids of different chain lengths in n-heptane at 30 °C. The best conversions (90% in 3 h) were obtained for medium and long chain saturated fatty acids (C8, C14 and C16), with the maximum specific activity, 29 U per gram of immobilized preparation, being obtained with palmitic acid (C16). Im-LipG9 was sn-1,3-specific. In the transesterification of the alcohol (R,S)-1-phenylethanol with vinyl acetate and the hydrolysis of the analogous ester, (R,S)-1-phenylethyl acetate, Im-LipG9 showed excellent enantioselectivity for the R-isomer of both substrates (E> 200), giving an enantiomeric excess (ee) of higher than 95% for the products at 49% conversion. The results obtained in this work provide the basis for the development of applications of LipG9 in biocatalysis. PMID:25706996

Alnoch, Robson Carlos; Martini, Viviane Paula; Glogauer, Arnaldo; Costa, Allen Carolina dos Santos; Piovan, Leandro; Muller-Santos, Marcelo; de Souza, Emanuel Maltempi; de Oliveira Pedrosa, Fábio; Mitchell, David Alexander; Krieger, Nadia

2015-01-01

458

Immobilization and characterization of a new regioselective and enantioselective lipase obtained from a metagenomic library.  

PubMed

In previous work, a new lipase and its cognate foldase were identified and isolated from a metagenomic library constructed from soil samples contaminated with fat. This new lipase, called LipG9, is a true lipase that shows specific activities that are comparable to those of well-known industrially-used lipases with high activity against long-chain triglycerides. In the present work, LipG9 was co-expressed and co-immobilized with its foldase, on an inert hydrophobic support (Accurel MP1000). We studied the performance of this immobilized LipG9 (Im-LipG9) in organic media, in order to evaluate its potential for use in biocatalysis. Im-LipG9 showed good stability, maintaining a residual activity of more than 70% at 50 °C after incubation in n-heptane (log P 4.0) for 8 h. It was also stable in polar organic solvents such as ethanol (log P -0.23) and acetone (log P -0.31), maintaining more than 80% of its original activity after 8 h incubation at 30 °C. The synthesis of ethyl esters was tested with fatty acids of different chain lengths in n-heptane at 30 °C. The best conversions (90% in 3 h) were obtained for medium and long chain saturated fatty acids (C8, C14 and C16), with the maximum specific activity, 29 U per gram of immobilized preparation, being obtained with palmitic acid (C16). Im-LipG9 was sn-1,3-specific. In the transesterification of the alcohol (R,S)-1-phenylethanol with vinyl acetate and the hydrolysis of the analogous ester, (R,S)-1-phenylethyl acetate, Im-LipG9 showed excellent enantioselectivity for the R-isomer of both substrates (E> 200), giving an enantiomeric excess (ee) of higher than 95% for the products at 49% conversion. The results obtained in this work provide the basis for the development of applications of LipG9 in biocatalysis. PMID:25706996

Alnoch, Robson Carlos; Martini, Viviane Paula; Glogauer, Arnaldo; Costa, Allen Carolina dos Santos; Piovan, Leandro; Muller-Santos, Marcelo; de Souza, Emanuel Maltempi; de Oliveira Pedrosa, Fábio; Mitchell, David Alexander; Krieger, Nadia

2015-01-01

459

Synthesis of Enantiomerically Pure Anthracyclinones  

NASA Astrophysics Data System (ADS)

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

Achmatowicz, Osman; Szechner, Barbara

460

Enantioselective intramolecular oxidative aminocarbonylation of alkenylureas catalyzed by palladium-spiro bis(isoxazoline) complexes.  

PubMed

An enantioselective synthesis of tetrahydropyrrolo[1,2-c]pyrimidine-1,3-diones via a palladium-catalyzed intramolecular oxidative aminocarbonylation is described. The carbon-carbon double bond of alkenylurea substrates has been shown to react intramolecularly with a nitrogen nucleophile in the presence of a palladium catalyst under a carbon monoxide atmosphere. The use of a chiral spiro bis(isoxazoline) ligand (SPRIX) is essential to obtain the desired products in optically active forms. In comparison with the coordination ability of other known ligands, this peculiar character of SPRIX originates from two structural characteristics: low sigma-donor ability of the isoxazoline coordination site and rigidity of the spiro skeleton. PMID:19925006

Tsujihara, Tetsuya; Shinohara, Toshio; Takenaka, Kazuhiro; Takizawa, Shinobu; Onitsuka, Kiyotaka; Hatanaka, Minoru; Sasai, Hiroaki

2009-12-18

461

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

462

Enantioselective resolution of 2-(1-hydroxy-3-butenyl)-5-methylfuran by immobilized lipase.  

PubMed

An efficient and convenient strategy for synthesis of enantiomerically pure S-2-(1-hydroxy-3-butenyl)-5-methylfuran was for the first time described utilizing a lipase-mediated asymmetric acylation in organic solvents. Rhizopus arrhizus lipase was chosen as the biocatalyst, and different immobilization methods including sol-gel encapsulation and covalent attachment were adopted to improve its catalytic characteristics. Various influential factors of the reaction were also investigated. Finally, the results showed that the lipase covalently attached onto epoxy resin exhibited the highest enantioselectivity and operational stability. Under optimized reaction conditions, i.e., n-hexane as the solvent, 5/1 (mol/mol) of vinyl acetate to 2-(1-hydroxy-3-butenyl)-5-methylfuran and 30 degrees C, the ee value of S-1 reached up to above 98% at 52% conversion with an E value of 99. PMID:18815782

Yang, Guang; Wu, Jianping; Xu, Gang; Yang, Lirong

2009-01-01

463

Enantioselective syntheses and sensory properties of 2-methyl-tetrahydrofuran-3-thiol acetates.  

PubMed

The enantioselective synthesis of four stereoisomers of 2-methyl-tetrahydrofuran-3-thiol acetate was achieved. The two enantiomers of the important intermediate cis-2-methyl-3-hydroxy-tetrahydrofuran were obtained by Sharpless asymmetric dihydroxylation (AD), whereas the two enantiomers of trans-2-methyl-3-hydroxy-tetrahydrofuran were derived from the corresponding optically active cis-isomers by Mitsunobu reaction. Each stereoisomer of 2-methyl-3-hydroxy-tetrahydrofuran went through mesylation and nucleophilic substitution to afford the corresponding product with specific configuration. (2R,3S)- and (2R,3R)-2-methyl-tetrahydrofuran-3-thiol acetate were obtained in 80% ee, whereas the (2S,3R)- and (2S,3S)-isomers were in 62% ee. The odor properties of the synthesized four stereoisomers were evaluated by gas chromatography-olfactometry (GC-O), which revealed perceptible differences among stereoisomers both in odor features and in intensities. PMID:25560460

Dai, Yifeng; Shao, Junqiang; Yang, Shaoxiang; Sun, Baoguo; Liu, Yongguo; Ning, Ting; Tian, Hongyu

2015-01-21

464

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

465

Development of Catalysts and Ligands for Enantioselective Gold Catalysis  

PubMed Central

CONSPECTUS The use of Au(I) complexes for the catalytic activation of C-C ?-bonds has been the subject of intense investigation in the last decade or so. The facile formation of carbon-carbon and carbon-heteroatom bonds facilitated by gold naturally led to efforts to render these transformations enantioselective. Early examples of enantioselective gold-catalyzed transformations have focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, careful choice of the weakly coordinating ligand (or counterion) was needed 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 order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, a new class of mononuclear phosphite and phosphoramidite ligands was developed to supplement the previously widely utilized phosphines. Finally carbene ligands, in particular, the acyclic diaminocarbenes, have also been successfully applied to enantioselective transformations. PMID:24228794

Wang, Yi-Ming; Lackner, Aaron D.; Toste, F. Dean

2014-01-01

466

Manganese-Substituted ?-Carbonic Anhydrase as an Enantioselective Peroxidase  

NASA Astrophysics Data System (ADS)

Carbonic anhydrase binds a zinc ion in a hydrophobic active site using the imidazole groups of three histidine residues. The natural role of carbonic anhydrase is to catalyze the reversible hydration of carbon dioxide to bicarbonate, but it also catalyzes hydrolysis of esters with moderate enantioselectivity. Replacing the active-site zinc with manganese yielded manganese-substituted carbonic anhydrase (CA[Mn]), which shows peroxidase activity with a bicarbonate-dependent mechanism. In the presence of bicarbonate and hydrogen peroxide, CA[Mn] catalyzed the efficient oxidation of o-dianisidine with k cat /K M = 1.4 × 106 M-1s-1, which is comparable to that for horseradish peroxidase, k cat /K M = 57 × 106 M-1s-1. CA[Mn] also catalyzed the moderately enantioselective epoxidation of olefins to epoxides (E = 5 for p-chlorostyrene). This enantioselectivity is similar to that for natural heme-based peroxidases, but has the advantage that CA[Mn] avoids formation of aldehyde side products. CA[Mn] degrades during the epoxidation, limiting the yield of the epoxidations to <12%. Replacement of active-site residues Asn62, His64, Asn67, Gln92, or Thr200 with alanine by site-directed mutagenesis decreased the enantioselectivity showing that the active site controls enantioselectivity of the epoxidation.

Jing, Qing; Okrasa, Krzysztof; Kazlauskas, Romas J.

467

Recent Applications of Alkene Metathesis in Fine Chemical Synthesis  

NASA Astrophysics Data System (ADS)

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions serve, inter alia, as key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. The present chapter is aiming at illustrating the great synthetic potential of metathesis reactions. Shortcomings, such as the control of olefin geometry and the unpredictable effect of substituents on the reacting olefins, will also be addressed. Examples to be presented include epothilones, amphidinolides, spirofungin A, and archazolid. Synthetic approaches involving silicon-tethered ring-closing metathesis, relay ring-closing metathesis, sequential reactions, domino as well as tandem metathesis reactions will also be illustrated.

Bicchielli, Dario; Borguet, Yannick; Delaude, Lionel; Demonceau, Albert; Dragutan, Ileana; Dragutan, Valerian; Jossifov, Christo; Kalinova, Radostina; Nicks, François; Sauvage, Xavier

468

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

469

Plasma synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications  

Microsoft Academic Search

Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous\\u000a synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal\\u000a plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration;\\u000a particles can be electrostatically confined in a reactor

Uwe Kortshagen; Lorenzo Mangolini; Ameya Bapat

2007-01-01

470

Plasma synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications  

Microsoft Academic Search

Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous\\u000a synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal\\u000a plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration;\\u000a particles can be electrostatically confined in a reactor

Uwe Kortshagen; Lorenzo Mangolini; Ameya Bapat

471

One-dimensional zinc oxide nanomaterials synthesis and photovoltaic applications  

Microsoft Academic Search

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

Benjamin A. Weintraub

2010-01-01

472

The application of green chemistry methods in organophosphorus synthesis  

NASA Astrophysics Data System (ADS)

Data concerning the synthesis of organophosphorus compounds in ionic liquids, in water and under solvent-free conditions are considered and summarized. It is shown that this strategy, which complies with the definition of green chemistry, has advantages in terms of the rate of the process and the yields of target products as compared with syntheses in common organic solvents. The Wittig, Horner-Wadsworth-Emmons, Kabachnik-Fields, Arbuzov and Michaelis reactions are considered as examples. The bibliography includes 178 references.

Odinets, Irina L.; Matveeva, E. V.

2012-03-01

473

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

474

Advances in hypersonic vehicle synthesis with application to studies of advanced thermal protection system  

NASA Technical Reports Server (NTRS)

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.

Ardema, Mark D.

1995-01-01

475

Carbon Nanotubes Advanced Topics in the Synthesis, Structure, Properties and Applications  

E-print Network

Carbon Nanotubes · Advanced Topics in the Synthesis, Structure, Properties and Applications Jorio 48824, USA tomanek@pa.msu.edu http://www.pa.msu.edu/~tomanek/ 1 The story behind the Nanotube Rush Nanotubes have evolved into one of the most intensively studied materials and are held responsible for co

476

Synthesis and Optimization of Threshold Logic Networks with Application to Nanotechnologies  

E-print Network

Synthesis and Optimization of Threshold Logic Networks with Application to Nanotechnologies Rui Zhang, Pallav Gupta, Lin Zhong, and Niraj K. Jha Department of Electrical Engineering Princeton networks are well-balanced, and hence delay-optimized. I. INTRODUCTION The Semiconductor Industries

Zhong, Lin

477

Shape Memory RGD-Containing Networks: Synthesis, Characterization, and Application in Cell Culture  

E-print Network

Shape Memory RGD-Containing Networks: Synthesis, Characterization, and Application in Cell Culture the development of a biodegradable and biocompatible hydrogel with tailored shape memory as well as desirable on the hydrogel surface. This hydrogel, tailored to exhibit shape memory behavior in the cell culture compatible

Mather, Patrick T.

478

M-type barium hexaferrite synthesis and characterization for phase shifter applications  

E-print Network

M-type barium hexaferrite synthesis and characterization for phase shifter applications A. T. Wise; published online 13 April 2011) M-type barium hexaferrite films have been grown by liquid phase epitaxy half a percent. VC 2011 American Institute of Physics. [doi:10.1063/1.3559471] Since M-type barium

McHenry, Michael E.

479

M-type barium hexaferrite synthesis and characterization for phase shifter applications  

E-print Network

M-type barium hexaferrite synthesis and characterization for phase shifter applications A. T. Wise subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions #12;M-type barium-type barium hexaferrite films have been grown by liquid phase epitaxy and examined by x-ray diffraction

Laughlin, David E.

480

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 performance, reliability,andwide-spread use of speech-processing devices. Using mathematical modelsof of these devices. In this tutorial paper, we review recent advances in speech production and perception modeling

Alwan, Abeer

481

Enantioselectivity of racemic metolachlor and S-metolachlor in maize seedlings.  

PubMed

Chiral herbicides may have enantioselective effects on plants. In this study, we assessed and compared the enantioselectivity of the chiral herbicides rac-metolachlor and S-metolachlor to maize seedlings. The superoxide dismutase activity (SOD) activity of roots and stem leaves treated by rac-metolachlor was 1.38 and 1.99 times that of roots and stem leaves treated by S-metolachlor. The peroxidase activity (POD) activity of roots and stem leaves was 1.48 and 2.79 times that of roots and stem leaves treated by S-metolachlor, respectively, while the catalase activity (CAT) activity was 4.77 and 8.37 times greater, respectively. The Hill reaction activity of leaves treated by rac-metolachlor were 1.45, 1.33, and 1.14 times those treated by S-metolachlor with treatments of 18.6, 37.2, and 74.4 ?M. The differences observed between treatments of rac- and S-metolachlor were significant. Significant differences in maize seedling morphology were also observed between rac- and S-metolachlor treatments. The degradation rate of S-metolachlor in roots was greater than that of rac-metolachlor. The half-lives of rac- and S-metolachlor were 80.6 and 60.3 h at 18.6 ?M; 119.5 and 90 h at 37.2 ?M; and 169 and 164.8 h at 74.4 ?M, respectively. Using the liquid chromatography-mass spectrometry method, hydroxymetolachlor, deschlorometolachlor and deschlorometolachlor propanol were considered to be possible metabolites. We determined the enantioselective toxicity of rac- and S-metolachlor to maize and speculated on the proposed metabolic pathway of metolachlor in maize roots. These results will help to develop an understanding of the proper application of rac- and S-metolachlor in crops, and give some information for environmental safety evaluation of rac- and S-metolachlor. PMID:20954044

Xie, Fei; Liu, Hui J; Cai, Wei D

2010-11-01

482