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1

Versatile iridicycle catalysts for highly efficient and chemoselective transfer hydrogenation of carbonyl compounds in water.  

PubMed

Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include ?-substituted ketones (?-ether, ?-halo, ?-hydroxy, ?-amino, ?-nitrile or ?-ester), ?-keto esters, ?-keto esters and ?,?-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50?000 at pH?4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of ?-functionalised secondary alcohols, such as ?-hydroxyethers, ?-hydroxyamines and ?-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis. PMID:25124283

Talwar, Dinesh; Wu, Xiaofeng; Saidi, Ourida; Salguero, Noemí Poyatos; Xiao, Jianliang

2014-09-26

2

Synthesis of 5,6-dihydropyrazolo[1,5-c]quinazolines through gold-catalyzed chemoselective bicyclization of N-propargylic sulfonylhydrazones.  

PubMed

An efficient method for the preparation of 5,6-dihydropyrazolo[1,5-c]quinazolines via gold(I)-catalyzed chemoselective bicyclization of N-propargylic sulfonylhydrazones has been developed. This process relies on the chemoselective cyclization of the hydrazone nitrogen instead of the usually favored aniline nitrogen onto the alkyne. The synthetic utility of the current strategy is demonstrated through the synthesis of a potential Eg5/Kinesin spindle protein inhibitor. PMID:25544196

Tang, Hai-Tao; Xiong, Kai; Li, Ren-Hao; Ding, Zong-Cang; Zhan, Zhuang-Ping

2015-01-16

3

Synthesis of an enantiopure isoxazolidine monomer for ?3-aspartic acid in chemoselective ?-oligopeptide synthesis  

PubMed Central

The synthesis of an enantiopure isoxazolidine monomer for the incorporation of ?3-apartic acid residues into ?3-oligopeptides via chemoselective ?-ketoacid–hydroxylamine amide formation. This route involves nitrone cycloaddition of 3-thiophenylpropanal and circumvents limitations of other potential starting materials PMID:20161312

Ishida, Hiroshi; Carrillo, Nancy; Bode, Jeffrey W.

2009-01-01

4

Lanthanum(III) catalysts for highly efficient and chemoselective transesterification.  

PubMed

A facile, atom-economical, and chemoselective esterification is crucial in modern organic synthesis, particularly in the areas of pharmaceutical, polymer, and material science. However, a truly practical catalytic transesterification of carboxylic esters with various alcohols has not yet been well established, since, with many conventional catalysts, the substrates are limited to 1°- and cyclic 2°-alcohols. In sharp contrast, if we take advantage of the high catalytic activities of La(Oi-Pr)(3), La(OTf)(3), and La(NO(3))(3) as ligand-free catalysts, ligand-assisted or additive-enhanced lanthanum(III) catalysts can be highly effective acid-base combined catalysts in transesterification. A highly active dinuclear La(III) catalyst, which is prepared in situ from lanthanum(III) isopropoxide and 2-(2-methoxyethoxy)ethanol, is effective for the practical transesterification of methyl carboxylates, ethyl acetate, weakly reactive dimethyl carbonate, and much less-reactive methyl carbamates with 1°-, 2°-, and 3°-alcohols. As the second generation, nearly neutral "lanthanum(III) nitrate alkoxide", namely La(OR)(m)(NO(3))(3-m), has been developed. This catalyst is prepared in situ from inexpensive, stable, low-toxic lanthanum(III) nitrate hydrate and methyltrioctylphosphonium methyl carbonate, and is highly useful in the non-epimerized transesterification of ?-substituted chiral carboxylic esters, even under azeotropic reflux conditions. In these practical La(III)-catalyzed transesterifications, colorless esters can be obtained in small- to large-scale synthesis without the need for inconvenient work-up or careful purification procedures. PMID:23325290

Hatano, Manabu; Ishihara, Kazuaki

2013-03-11

5

TMP-cadmiate: A base for Efficient and Chemoselective Deprotonative Metallation Reactions of Aromatic Compounds  

E-print Network

1 TMP-cadmiate: A base for Efficient and Chemoselective Deprotonative Metallation Reactions are palladium-catalyzed cross-coupling reactions or simple quench with acid chlorides. Keywords: cadmium-shi, Saitama 351-0198, Japan. E-mail: uchi_yama@riken.jp Abstract: Efficient deprotonative cadmiation reactions

Boyer, Edmond

6

How the Arming Participating Moieties can Broaden the Scope of Chemoselective Oligosaccharide Synthesis by Allowing the Inverse Armed-Disarmed Approach  

PubMed Central

A new method for stereocontrolled glycosylation and chemoselective oligosaccharide synthesis has been developed. It has been determined that complete 1,2-trans selectivity can be achieved with the use of a 2-O-picolyl moiety, a novel neighboring group that is capable of efficient participation via a six-membered intermediate. The application of the picolyl concept to glycosidations of thioimidoyl, thioglycosyl, and trichloroacetimidoyl glycosyl donors is demonstrated. The picolyl moiety also retains the glycosyl donor in the armed state, as opposed to conventional acyl participating moieties. We name this new approach - “inverse armed-disarmed” strategy, because it allows for the chemoselective introduction of a 1,2-trans glycosidic linkage prior to other linkages. In the context of the oligosaccharide synthesis, the strategy provides trans-trans and trans-cis patterned oligosaccharides as opposed to classic Fraser-Reid’s armed-disarmed approach leading to cis-trans and cis-cis linkages. PMID:18939875

Smoot, James T.; Demchenko, Alexei V.

2009-01-01

7

Transfer hydrogenation using recyclable polyurea-encapsulated palladium: efficient and chemoselective reduction of aryl ketones.  

PubMed

A robust and recyclable palladium catalyst [Pd0EnCat] has been prepared by ligand exchange of polyurea-encapsulated palladium(II) acetate with formic acid, resulting in deposition of Pd(0) in the support material; Pd0EnCat is shown to be a highly efficient transfer hydrogenation catalyst for chemoselective reduction of a wide range of aryl ketones to benzyl alcohols. PMID:12703769

Yu, Jin-Quan; Wu, Hai-Chen; Ramarao, Chandrashekar; Spencer, Jonathan B; Ley, Steven V

2003-03-21

8

Highly efficient and chemoselective ?-iodination of acrylate esters through Morita-Baylis-Hillman-type chemistry.  

PubMed

The chemoselective ?-iodination of various simple and multi-functionalised acrylic esters is efficiently accomplished by a Morita-Baylis-Hillman protocol involving the use of N-iodophthalimide, 3-quinuclidinol and KF-Celite in acetonitrile. No degradation of the obtained compounds was observed under the optimized conditions thus, furnishing ?-iodoacrylates suitable for organometallic reactions (i.e. Nozaki-Kishi-Hiyama type coupling). PMID:23303274

Pace, Vittorio; Vilkauskait?, Gyt?; Ša?kus, Algirdas; Holzer, Wolfgang

2013-02-21

9

The chemoselective reduction of isoxazoline ?-lactams through iminium Aza-Diels-Alder reactions: a short-cut synthesis of aminols as valuable intermediates towards nucleoside derivatives.  

PubMed

Isoxazoline ?-lactams are prepared starting from the regioisomeric cycloadducts of benzonitrile oxide to the N-alkyl 2-azanorbornenes taking advantage of the efficient catalytic oxidation by RuO(4). The reduction of the amide groups is easily conducted in the presence of LiAlH(4) under mild conditions, which allowed for the chemoselective reduction of the amide moiety followed by ring opening to afford the desired conformationally locked isoxazoline-carbocyclic aminols, as valuable intermediates for nucleoside synthesis. PMID:22629174

Memeo, Misal Giuseppe; Mella, Mariella; Quadrelli, Paolo

2012-01-01

10

The Chemoselective Reduction of Isoxazoline ?-Lactams Through Iminium Aza-Diels-Alder Reactions: A Short-Cut Synthesis of Aminols as Valuable Intermediates towards Nucleoside Derivatives  

PubMed Central

Isoxazoline ?-lactams are prepared starting from the regioisomeric cycloadducts of benzonitrile oxide to the N-alkyl 2-azanorbornenes taking advantage of the efficient catalytic oxidation by RuO4. The reduction of the amide groups is easily conducted in the presence of LiAlH4 under mild conditions, which allowed for the chemoselective reduction of the amide moiety followed by ring opening to afford the desired conformationally locked isoxazoline-carbocyclic aminols, as valuable intermediates for nucleoside synthesis. PMID:22629174

Memeo, Misal Giuseppe; Mella, Mariella; Quadrelli, Paolo

2012-01-01

11

A basic germanodecatungstate with a -7 charge: efficient chemoselective acylation of primary alcohols.  

PubMed

The synthesis of highly negatively charged polyoxometalates with electrically and structurally controlled uniform basic sites can lead to the unique base catalysis. In this work, a ?-Keggin germanodecatungstate, [?-HGeW10O36](7-) (A), having a -7 charge was, for the first time, successfully synthesized by the reaction of [?-H2GeW10O36](6-) with one equivalent of [(n-C4H9)4N]OH under non-aqueous conditions. The activities of germanodecatungstates for base-catalyzed reactions dramatically increased with increase in the number negative charges from -6 to -7. In the presence of A, various combinations of acylating agents and primary alcohols including those with acid-sensitive functional groups chemoselectively gave the desired acylated products in high yields even under the stoichiometric conditions. PMID:25264017

Sugahara, Kosei; Satake, Naoto; Kamata, Keigo; Nakajima, Takahito; Mizuno, Noritaka

2014-11-24

12

Chemoselective ligation  

DOEpatents

The present invention features a chemoselective ligation reaction that can be carried out under physiological conditions. In general, the invention involves condensation of a specifically engineered phosphine, which can provide for formation of an amide bond between the two reactive partners resulting in a final product comprising a phosphine moiety, or which can be engineered to comprise a cleavable linker so that a substituent of the phosphine is transferred to the azide, releasing an oxidized phosphine byproduct and producing a native amide bond in the final product. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo (e.g. on the cell surface or intracellularly) and in vitro (e.g., synthesis of peptides and other polymers, production of modified (e.g., labeled) amino acids).

Saxon, Eliana (Albany, CA); Bertozzi, Carolyn R. (Berkeley, CA)

2010-02-23

13

Chemoselective ligation  

DOEpatents

The present invention features a chemoselective ligation reaction that can be carried out under physiological conditions. In general, the invention involves condensation of a specifically engineered phosphine, which can provide for formation of an amide bond between the two reactive partners resulting in a final product comprising a phosphine moiety, or which can be engineered to comprise a cleavable linker so that a substituent of the phosphine is transferred to the azide, releasing an oxidized phosphine byproduct and producing a native amide bond in the final product. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo (e.g., on the cell surface or intracellularly) and in vitro (e.g., synthesis of peptides and other polymers, production of modified (e.g., labeled) amino acids).

Saxon, Eliana (Albany, CA); Bertozzi, Carolyn Ruth (Berkeley, CA)

2010-11-23

14

Chemoselective ligation  

DOEpatents

The present invention features a chemoselective ligation reaction that can be carried out under physiological conditions. In general, the invention involves condensation of a specifically engineered phosphine, which can provide for formation of an amide bond between the two reactive partners resulting in a final product comprising a phosphine moiety, or which can be engineered to comprise a cleavable linker so that a substituent of the phosphine is transferred to the azide, releasing an oxidized phosphine byproduct and producing a native amide bond in the final product. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo (e.g., on the cell surface or intracellularly) and in vitro (e.g., synthesis of peptides and other polymers, production of modified (e.g., labeled) amino acids).

Saxon, Eliana (Albany, CA); Bertozzi, Carolyn R. (Berkeley, CA)

2011-04-12

15

Chemoselective ligation  

DOEpatents

The present invention features a chemoselective ligation reaction that can be carried out under physiological conditions. In general, the invention involves condensation of a specifically engineered phosphine, which can provide for formation of an amide bond between the two reactive partners resulting in a final product comprising a phosphine moiety, or which can be engineered to comprise a cleavable linker so that a substituent of the phosphine is transferred to the azide, releasing an oxidized phosphine byproduct and producing a native amide bond in the final product. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo (e.g., on the cell surface or intracellularly) and in vitro (e.g., synthesis of peptides and other polymers, production of modified (e.g., labeled) amino acids).

Saxon, Eliana (Albany, CA); Bertozzi, Carolyn Ruth (Berkeley, CA)

2011-12-13

16

Chemoselective ligation  

DOEpatents

The present invention features a chemoselective ligation reaction that can be carried out under physiological conditions. In general, the invention involves condensation of a specifically engineered phosphine, which can provide for formation of an amide bond between the two reactive partners resulting in a final product comprising a phosphine moiety, or which can be engineered to comprise a cleavable linker so that a substituent of the phosphine is transferred to the azide, releasing an oxidized phosphine byproduct and producing a native amide bond in the final product. The selectivity of the reaction and its compatibility with aqueous environments provides for its application in vivo (e.g., on the cell surface or intracellularly) and in vitro (e.g., synthesis of peptides and other polymers, production of modified (e.g., labeled) amino acids).

Saxon, Eliana (Albany, CA); Bertozzi, Carolyn R. (Berkeley, CA)

2011-05-10

17

Substrate-controlled chemoselective synthesis and potent cytotoxic activity of novel 5,6,7-triarylpyrido[2,3- d]pyrimidin-4-one derivatives  

Microsoft Academic Search

The substrate-controlled chemoselective synthesis of novel 5,6,7-triarylpyrido[2,3-d]pyrimidin-4-one derivatives has been successfully achieved via microwave-assisted three-component reactions of 2,6-diaminopyrimidin-4(3H)-one, aromatic aldehydes and 1,2-diphenylethanone. This approach has the prominent features of chemoselectivity, diasteroselectivity, atom economy, short reaction time, high yield as well as operational simplicity. Moreover, these novel compounds were subject to the test of in vitro cytotoxicity to carcinoma SW1116 and

Feng Shi; Jie Ding; Shu Zhang; Wen-Juan Hao; Chuang Cheng; Shujiang Tu

2011-01-01

18

An efficient and highly chemoselective N Boc protection of amines, amino acids, and peptides under heterogeneous conditions  

Microsoft Academic Search

\\u000a Abstract  A simple and efficient procedure for chemoselective mono-N-Boc protection of various structurally diverse amines, amino acids, and peptides with di-tert-butyl dicarbonate using Amberlyst-15 as catalyst in ethanol is described. The catalyst can be readily separated from the\\u000a reaction products with simple filtration and recovered for direct reuse. No competitive side-reactions such as formation of\\u000a isocyanate, urea, oxazolidinone, and N,N-di-Boc derivatives

Fatemeh Jahani; Mahmood Tajbakhsh; Samad Khaksar; Mohamad Reza Azizi

19

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

PubMed Central

The design and general synthesis of enantiopure isoxazolidinone monomers as precursors for the preparation of enantiopure N-terminal hydroxylamine—?3-oligopeptides, which may be used as reaction partners with ?-ketoacids in the decarboxylative amide ligation reaction, is described. PMID:21499500

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

2010-01-01

20

Using Nazarov Electrocyclization to Stage Chemoselective [1,2]-Migrations: Stereoselective Synthesis of Functionalized Cyclopentenones  

PubMed Central

Highly functionalized cyclopentenones are prepared stereospecifically based on a chemoselective copper(II)-mediated Nazarov/Wagner-Meerwein rearrangement sequence. After the initial 4? electrocyclization, this reaction involves two sequential [1,2]-migrations depending upon both migratory ability and steric bulk of the substituents at C1 and C5. This sequence can be achieved by using a catalytic quantity of copper(II) in combination with a weak Lewis acid. The mechanism of the reaction is also supported by DFT computations. PMID:21953873

Lebœuf, David; Huang, Jie; Gandon, Vincent

2012-01-01

21

Reagent control of [1,2]-Wagner-Meerwein shift chemoselectivity following the Nazarov cyclization: application to the total synthesis of enokipodin B.  

PubMed

An approach toward the carbon framework of various sesquiterpenes from the herbertane and cuparane families is described, including the concise total synthesis of enokipodin B. The key step is the construction of the vicinal quarternary centers of the skeleton through a tandem Nazarov cyclization/Wagner-Meerwein rearrangement mediated by a copper(II) complex. During this study, it was also found that changing the ligand architecture on the copper(II) promoter improved the chemoselectivity of the cationic rearrangement. PMID:23436444

Lebœuf, David; Wright, Christopher M; Frontier, Alison J

2013-04-01

22

Substrate-controlled chemoselective synthesis and potent cytotoxic activity of novel 5,6,7-triarylpyrido[2,3-d]pyrimidin-4-one derivatives.  

PubMed

The substrate-controlled chemoselective synthesis of novel 5,6,7-triarylpyrido[2,3-d]pyrimidin-4-one derivatives has been successfully achieved via microwave-assisted three-component reactions of 2,6-diaminopyrimidin-4(3H)-one, aromatic aldehydes and 1,2-diphenylethanone. This approach has the prominent features of chemoselectivity, diasteroselectivity, atom economy, short reaction time, high yield as well as operational simplicity. Moreover, these novel compounds were subject to the test of in vitro cytotoxicity to carcinoma SW1116 and SGC7901 cells. Most of the tested compounds showed significant cytotoxicity to SW1116 cells and compound 4b exhibited more potent and efficacious cytotoxicity to SGC7901 cells than doxorubicin hydrochloride as positive control. PMID:21296573

Shi, Feng; Ding, Jie; Zhang, Shu; Hao, Wen-Juan; Cheng, Chuang; Tu, Shujiang

2011-03-01

23

Sulfonic acid-functionalized ordered nanoporous Na+-montmorillonite as an efficient, eco-benign, and water-tolerant nanoreactor for chemoselective oxathioacetalization of aldehydes  

NASA Astrophysics Data System (ADS)

Sulfonic acid-functionalized ordered nanoporous sodium montmorillonite has been found to be a mild and efficient solid acid catalyst for the chemoselective protection of a variety of carbonyl compounds as oxathiolanes in good to excellent yields. The present method offers several advantages such as short reaction times, high yields, simple procedure and mild conditions. Also, the catalyst could be recycled and reused at least for five times without noticeably decreasing the catalytic activity.

Shirini, Farhad; Atghia, Seyyed Vahid; Mamaghani, Manouchehr

2013-01-01

24

AN EFFICIENT AND CHEMOSELECTIVE CBZ-PROTECTION OF AMINES USING SILICA-SULFURIC ACID AT ROOM TEMPERATURE  

EPA Science Inventory

A simple, facile, and chemoselective N-benzyloxycarbonylation of amines using silica-sulfuric acid that proceeds under solvent-free conditions at room temperature has been achieved. These reactions are applicable to a wide variety of primary (aliphatic, cyclic) secondary amines, ...

25

Highly efficient and chemoselective zinc-catalyzed hydrosilylation of esters under mild conditions.  

PubMed

A mild and highly efficient catalytic hydrosilylation protocol for room-temperature ester reductions has been developed using diethylzinc as the catalyst. The methodology is operationally simple, displays high functional group tolerance and provides for a facile access to a broad range of different alcohols in excellent yields. PMID:25524811

Kovalenko, Oleksandr O; Adolfsson, Hans

2015-02-01

26

Chemoselective Attachment of Biologically Active Proteins to Surfaces by Native Chemical Ligation  

SciTech Connect

The present work describes our ongoing efforts towards the creation of micro and nanoscaled ordered arrays of protein covalently attached to site-specific chemical linkers patterned by different microlithographic techniques. We present a new and efficient solid-phase approach for the synthesis of chemically modified long alkyl-thiols. These compounds can be used to introduce chemoselective reacting groups onto silicon-based surfaces. We show that these modified thiols can be used for creating nano- and micrometric chemical patterns by using different lithographic techniques. We show that these patterns can react chemoselectively with proteins which have been recombinantly modified to contain complementary chemical groups at specific positions thus resulting in the oriented attachment of the protein to the surface.

Cheung, C L; de Yoreo, J J; Coleman, M; Camarero, J A

2003-11-22

27

Assembly of Oriented Virus Arrays by Chemo-Selective Ligation Methods and Nanolithography Techniques  

SciTech Connect

The present work describes our ongoing efforts towards the creation of nano-scaled ordered arrays of protein/virus covalently attached to site-specific chemical linkers patterned by different nanolithograpy techniques. We will present a new and efficient solid-phase approach for the synthesis of chemically modified long alkyl-thiols. These compounds can be used to introduce chemoselective reacting groups onto gold and silicon-based surfaces. Furthermore, these modified thiols have been used to create nanometric patterns by using different nanolithography techniques. We will show that these patterns can react chemoselectively with proteins and/or virus which have been chemically or recombinantly modified to contain complementary chemical groups at specific positions thus resulting in the oriented attachment of the protein or virus to the surface.

Camarero, J A; Cheung, C L; Lin, T; Johnson, J E; Weeks, B L; Noy, A; De Yoreo, J J

2002-12-02

28

Chemoselective hydrosilylation of hydroxyketones  

PubMed Central

A chemoselective method for the hydrosilylation of ketones has been developed, using the combination of triphenylsilane and a catalyst prepared from Ni(COD)2 and the simple N-heterocyclic carbene IMes. The most notable feature of this method is that free hydroxyls are largely unaffected, thus providing a simple one-step procedure for the conversion of hydroxyketones to mono-protected diols, wherein the protecting group is exclusively installed on the ketone-derived hydroxyl. The process is typically high yielding with both simple ketones and more complex hydroxyketone substrates. PMID:23997314

Lage, Marta L.; Bader, Scott J.; Sa-ei, Kanicha; Montgomery, John

2013-01-01

29

Chemoselective hydrosilylation of hydroxyketones.  

PubMed

A chemoselective method for the hydrosilylation of ketones has been developed, using the combination of triphenylsilane and a catalyst prepared from Ni(COD)2 and the simple N-heterocyclic carbene IMes. The most notable feature of this method is that free hydroxyls are largely unaffected, thus providing a simple one-step procedure for the conversion of hydroxyketones to mono-protected diols, wherein the protecting group is exclusively installed on the ketone-derived hydroxyl. The process is typically high yielding with both simple ketones and more complex hydroxyketone substrates. PMID:23997314

Lage, Marta L; Bader, Scott J; Sa-Ei, Kanicha; Montgomery, John

2013-07-01

30

Remodelling glycoforms on proteins and cells by chemoselective ligation  

SciTech Connect

The chemoselective ligation strategy has found tremendous success in the synthesis of macromolecular protein conjugates. At the heart of this approach is the introduction of mutually and uniquely reactive functional groups onto unprotected fragments and the coupling of these fragments in an aqueous environment. We have extended the principle of chemoselective ligation to the generation of glycoproteins and cells with tailor-made glycoforms. New enzymatic and biosynthetic methods for introducing uniquely reactive functional groups onto protein-bound oligosaccharides will be presented, along with applications to glycoform engineering.

Bertozzi, C.R. [Univ. of California, Berkeley, CA (United States); [Lawrence Berkeley National Lab., CA (United States)

1997-12-31

31

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

32

Iridium-catalyzed synthesis of diaryl ethers by means of chemoselective C-F bond activation and the formation of B-F bonds.  

PubMed

Transition-metal-catalyzed C?F activation, in comparison with C?H activation, is more difficult to achieve and therefore less fully understood, mainly because carbon-fluorine bonds are the strongest known single bonds to carbon and have been very difficult to cleave. Transition-metal complexes are often more effective at cleaving stronger bonds, such as C(sp(2) )?X versus C(sp(3) )?X. Here, the iridium-catalyzed C?F activation of fluorarenes was achieved through the use of bis(pinacolato)diboron with the formation of the B?F bond and self-coupling. This strategy provides a convenient method with which to convert fluoride aromatic compounds into symmetrical diaryl ether compounds. Moreover, the chemoselective products of the C?F bond cleavage were obtained at high yields with the C?Br and C?Cl bonds remaining. PMID:25393610

Chen, Jianping; Zhao, Keyan; Ge, Bingyang; Xu, Chongying; Wang, Dawei; Ding, Yuqiang

2015-02-01

33

Reactions of difunctional electrophiles with functionalized aryllithium compounds: remarkable chemoselectivity by flash chemistry.  

PubMed

Flash chemistry using flow microreactors enables highly chemoselective reactions of difunctional electrophiles with functionalized aryllithium compounds by virtue of extremely fast micromixing. The approach serves as a powerful method for protecting-group-free synthesis using organolithium compounds and opens a new possibility in the synthesis of polyfunctional organic molecules. PMID:25504778

Nagaki, Aiichiro; Imai, Keita; Ishiuchi, Satoshi; Yoshida, Jun-ichi

2015-02-01

34

Chemoselective Reactions of Citral: Green Syntheses of Natural Perfumes for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

Chemoselectivity is a central concept in organic synthesis and may be readily appreciated in the context of the fragrant, polyfunctional natural product citral. We describe three single-step reactions students may perform on citral to synthesize other natural perfumes: citronellal, geraniol, nerol, or epoxycitral. Each of the reactions uses a…

Cunningham, Anna D.; Ham, Eun Y.; Vosburg, David A.

2011-01-01

35

Chemoselective ring opening of benzoxazaphosphinines  

Microsoft Academic Search

Cyclization of 2-[(4-chloroanilino)methyl]phenol (1) with thiophosphoryl chloride afforded 2-chloro-3-(4-chlorophenyl)-3,4-dihydro-2H-1,3,2?5-benzoxazaphosphinine-2-thione (2). Reaction of 2 with various heterocyclic amines (3) in the presence of Et3N\\/NaH gave 3-(4-chlorophenyl)-2-nitrogen heterocyclic substituted-3,4-dihydro-2H-1,3,2?5-benzoxaza-phosphinine-2-thiones (4). Further reaction of 4 with the N-sodium salt of amino heterocyclics in the presence of HCl at 50–60°C opened the benzoxazaphosphinine ring chemoselectively at the endocyclic P–O bond and yielded 2-[4-chloro(heterocyclic substituted-phosphorothioyl)anilino]methylphenols

K. R. Kishore Kumar Reddy; M. Anil Kumar; M. V. Narayana Reddy; C. Devendranath Reddy; C. Suresh Reddy

2008-01-01

36

A mild and highly convenient chemoselective alkylation of thiols using Cs 2CO 3–TBAI  

Microsoft Academic Search

A mild and improved method for the synthesis of thioethers has been developed. In the presence of cesium carbonate, tetrabutylammonium iodide, and DMF, various alkyl and aryl thiols underwent S-alkylation to afford structurally diverse sulfides in high yield. Unprotected mercaptoalcohols and thioamines reacted chemoselectively at the sulfur moiety exclusively. An example of a one-pot, solid-phase synthesis of a thioether is

Ralph Nicholas Salvatore; Robert A. Smith; Adam K. Nischwitz; Terrence Gavin

2005-01-01

37

Highly regioselective C-5 iodination of pyrimidine nucleotides and subsequent chemoselective sonogashira coupling with propargylamine.  

PubMed

An efficient C-5 iodination of pyrimidine-5'-triphosphates and subsequent palladium-catalyzed Sonogashira coupling reaction with propargylamine is described. The iodination reaction is highly regioselective and the coupling reaction is highly chemoselective that furnishes exclusive 5-(3-aminopropargyl)-pyrimidine-5'-triphosphate in good yield with high purity (>99%). PMID:25621703

Kore, Anilkumar R; Senthilvelan, Annamalai; Shanmugasundaram, Muthian

2015-02-01

38

Superarmed and Superdisarmed Building Blocks in Expeditious Oligosaccharide Synthesis  

PubMed Central

Traditional strategies for oligosaccharide synthesis often require extensive protecting and/or leaving group manipulations between each glycosylation step, thereby increasing the total number of synthetic steps while decreasing both the efficiency and yield. In contrast, expeditious strategies allow for the rapid chemical synthesis of complex carbohydrates by minimizing extraneous chemical manipulations. The armed–disarmed approach for chemoselective oligosaccharide synthesis is one such strategy that addresses these challenges. Herein, the significant improvements that have recently emerged in the area of chemoselective activation are discussed. These advancements have expanded the scope of the armed–disarmed methodology so that it can now be applied to a wider range of oligosaccharide sequences, in comparison to the original concept. Surveyed in this chapter are representative examples wherein these excellent innovations have already been applied to the synthesis of various oligosaccharides and glycoconjugates. PMID:21120713

Premathilake, Hemali D.

2011-01-01

39

An efficient total synthesis of (-)-huperzine A.  

PubMed

The total synthesis of Lycopodium alkaloid (-)-huperzine A has been accomplished in 10 steps with 17% overall yield from commercially abundant (R)-pulegone. The synthetic route features an efficient synthesis of 4 via a Buchwald-Hartwig coupling reaction, a dianion-mediated highly stereoselective alkylation of 4, and a rare example of an intramolecular Heck reaction of an enamine-type substrate. The stereoselective ?-elimination and the accompanying Wagner-Meerwein rearrangement are of particular interest. PMID:22900755

Ding, Rui; Sun, Bing-Feng; Lin, Guo-Qiang

2012-09-01

40

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

41

Synthesis of memory-efficient \\  

Microsoft Academic Search

We study synthesis of controllers for real-time systems, where the objective is to stay in a given safe set. The problem is solved by obtaining winning strategies in the setting of concurrent two-player timed automaton games with safety objectives. To prevent a player from winning by blocking time, we restrict each player to strategies that ensure that the player cannot

Krishnendu Chatterjee; Vinayak S. Prabhu

2011-01-01

42

Efficient Synthesis of Feature Models Nele Andersen  

E-print Network

- clude an e-commerce platform or not. The solution space model explains how the problem space decisions affect the realization--for example, how the e-commerce platform is woven into the implementationEfficient Synthesis of Feature Models Nele Andersen Krzysztof Czarnecki Steven She Andrzej W

Czarnecki, Krzysztof

43

Total Synthesis of Bryostatins. Development of Methodology for Atom-Economic and Stereoselective Synthesis of the C-ring Subunit  

PubMed Central

Bryostatins, a family of structurally complicated macrolides, exhibit an exceptional range of biological activities. The limited availability and structural complexity of these molecules makes development of an efficient total synthesis particularly important. This article describes our initial efforts towards the total synthesis of bryostatins, in which chemoselective and atom-economical methods for stereoselective assembly of the C-ring subunit were developed. A Pd-catalyzed tandem alkyne-alkyne coupling/6-endo-dig cyclization sequence was explored and successfully pursued in the synthesis of a dihydropyran ring system. Elaboration of this methodology ultimately led to a concise synthesis of the C-ring subunit of bryostatins. PMID:21793057

Trost, Barry M.; Frontier, Alison J.; Thiel, Oliver R.; Yang, Hanbiao; Dong, Guangbin

2012-01-01

44

A highly efficient diastereoselective synthesis of ?-isosalicin by maltase from Saccharomyces cerevisiae  

Microsoft Academic Search

In this report, ?-isosalicin, a potent anticoagulant and skin whitening agent, was synthesized by a highly efficient chemoselective and diastereoselective reaction, catalyzed by maltase from bakers’ yeast (Saccharomyces cerevisiae). The highest yield of this one-step transglucosylation reaction was achieved with 50mM of salicyl alcohol as a glucose acceptor. The key reaction factors were optimized using response surface methodology (RSM) with

Dušan Veli?kovi?; Aleksandra Dimitrijevi?; Filip Bihelovi?; Dejan Bezbradica; Ratko Jankov; Nenad Milosavi?

2011-01-01

45

The daphniphyllum alkaloids: total synthesis of (-)-calyciphylline N.  

PubMed

Presented here is a full account on the development of a strategy culminating in the first total synthesis of the architecturally complex daphniphyllum alkaloid, (-)-calyciphylline N. Highlights of the approach include a highly diastereoselective, intramolecular Diels-Alder reaction of a silicon-tethered acrylate; an efficient Stille carbonylation of a sterically encumbered vinyl triflate; a one-pot Nazarov cyclization/proto-desilylation sequence; and the chemoselective hydrogenation of a fully substituted diene ester. PMID:25756504

Shvartsbart, Artem; Smith, Amos B

2015-03-18

46

Approximation concepts for efficient structural synthesis  

NASA Technical Reports Server (NTRS)

It is shown that efficient structural synthesis capabilities can be created by using approximation concepts to mesh finite element structural analysis methods with nonlinear mathematical programming techniques. The history of the application of mathematical programming techniques to structural design optimization problems is reviewed. Several rather general approximation concepts are described along with the technical foundations of the ACCESS 1 computer program, which implements several approximation concepts. A substantial collection of structural design problems involving truss and idealized wing structures is presented. It is concluded that since the basic ideas employed in creating the ACCESS 1 program are rather general, its successful development supports the contention that the introduction of approximation concepts will lead to the emergence of a new generation of practical and efficient, large scale, structural synthesis capabilities in which finite element analysis methods and mathematical programming algorithms will play a central role.

Schmit, L. A., Jr.; Miura, H.

1976-01-01

47

An efficient synthesis of thiopyrano[5,6- c]coumarin\\/[6,5- c]chromones through intramolecular domino Knoevenagel hetero Diels–Alder reactions  

Microsoft Academic Search

The synthesis of novel polycyclic thiopyrano coumarin\\/chromone frameworks through intramolecular domino Knoevenagel hetero Diels–Alder reactions of 4-hydroxy coumarin and its benzo-analogous with S-prenylated aromatic aldehydes was studied. A high degree of chemoselectivity was achieved by the application of microwave irradiation and a solid support.

Jayadevan Jayashankaran; Rathna Durga R. S. Manian; Raghavachary Raghunathan

2006-01-01

48

Efficient Synthesis of Fluorescent Squaraine Rotaxane Dendrimers  

PubMed Central

A squaraine rotaxane scaffold with four alkynes groups is readily converted into a range of dendritic architectures using high yielding copper catalyzed alkyne azide cycloaddition (CuAAC) chemistry. A convergent synthesis approach is more efficient than a divergent pathway. Dendritic squaraine rotaxanes with peripheral amine groups can be further functionalized to produce multivalent deep-red fluorescent derivatives that exhibit high brightness and outstanding chemical stability in biological solution. The surface groups on these functionalized fluorescent dendrimers include guanidinium, mannose, and phosphatidylcholine. PMID:19957971

Xiao, Shuzhang; Fu, Na; Peckham, Kaitlin; Smith, Bradley D.

2009-01-01

49

Catalyst-Controlled Chemoselective Arylation of 2-Aminobenzimidazoles  

E-print Network

What N would you like? The chemoselective and complementary Pd- and Cu-catalyzed N-arylation of 2-aminobenzimidazoles is described. Selective N-arylation of the amino group was achieved with a Pd-catalyzed method, while ...

Ueda, Satoshi

50

Efficient Synthesis and Properties of Novel Near-Infrared Electrochromic  

E-print Network

Efficient Synthesis and Properties of Novel Near-Infrared Electrochromic Anthraquinone Imides@pku.edu.cn Received December 13, 2007 ABSTRACT An efficient synthesis of novel near-infrared electrochromic 6 are electrochromic and absorb intensely in the near-infrared range of 700-1600 nm upon electrochemical reduction

Wan, Xin-hua

51

Phenolic ester mediated oligopeptide synthesis promoted by HOBt.  

PubMed

Although substituted phenolic ester mediated peptide synthesis is an efficient and well established method, the same via totally unsubstituted phenyl ester is not preferred due to the extremely slow rate of aminolysis. We have investigated the scope of the unsubstituted phenyl ester as an intermediate in peptide bond formation and found that it may be useful for the design of chemoselective peptide ligation when HOBt is used as an acyl transfer catalyst. The scope of HOBt catalyzed, oxo ester mediated ligation is explored for the synthesis of oligopeptides containing a cysteine, serine and threonine at the N-terminus of the ligating peptide. PMID:24073626

Saha, Abhijit; Nadimpally, Krishna Chaitanya; Paul, Ashim; Kalita, Sourav; Mandal, Bhubaneswar

2014-01-01

52

Safe and Efficient Tetrazole Synthesis in a Continuous Flow Microreactor  

E-print Network

Safer flow: The synthesis of 5-substituted tetrazoles in flow (see scheme) is safe, efficient, scalable, requires no metal promoter, and uses a near-equimolar amount of NaN[subscript 3], yet nonetheless displays a broad ...

Palde, Prakash B.

53

Chemoselective silicification of synthetic peptides and polyamines  

PubMed Central

Summary Biosilicification sets the standard for the localized in vitro precipitation of silica at low orthosilicate concentrations in aqueous environment under ambient conditions. Numerous parameters must be controlled for the development of new technologies in designing inventive nanosilica structures, which are able to challenge the biological templates. A long neglected requirement that came into focus in the recent years are the cellular techniques of preventing unintentional lithification of cellular structures since numerous cellular components such as membranes, DNA, and proteins are known to precipitate nanosilica. The diatom metabolism makes use of techniques that restrict silicification to an armor of silica around the cell wall while avoiding the petrifying gaze of Medusa, which turns the whole cell into stone. Step by step, biochemistry unveils the hierarchical interplay of an arsenal of low-molecular weight molecules, proteins, and the cytoskeletal architecture and it becomes clearer why the organisms invest much metabolic effort for an obviously simple chemical reaction like the precipitation of amorphous silica. The discrimination between different soluble components in the silicification process (chemoselective silicification) is not only vitally important for the diatom but poses an interesting challenge for in vitro experiments. Until now, silica precipitation studies were mainly focused on the amount, the morphology, and composition of the precipitate while disregarding a quantitative analysis of the remaining soluble components. Here, we turn the tables and quantify the soluble components by 1H NMR in the progress of precipitation and present experiments which quantify the additivity, and potential cooperativity of long chain polyamines (LCPAs) and cationic peptides in the silicification process. PMID:25671155

Abacilar, Maryna; Daus, Fabian

2015-01-01

54

A Formal Total Synthesis of (?)-Brevisamide  

PubMed Central

A formal total synthesis of (?)-brevisamide has been achieved. The synthetic approach highlights a chemoselective asymmetric dihydroxylation and a one-pot Fraser-Reid epoxidation/PMB protection reaction sequence. PMID:21572531

Smith, Amos B.; Kutsumura, Noriki; Potuzak, Justin

2011-01-01

55

Fluorinated epoxides 6. Chemoselectivity in the preparation of  

E-print Network

Fluorinated epoxides 6. Chemoselectivity in the preparation of 2-[(heptafluoroisopropyl Fluorinated iodoacetate (CF3)2CFCH2CHICH2OAc (1) (prepared by radical addition of perfluoroisopropyl iodide to allyl acetate) and fluorinated iodohydrin (CF3)2CFCH2CHICH2OH (2) (prepared from 1) were converted

Cirkva, Vladimir

56

A chemoselective biomolecular template for assembling diverse nanotubular materials  

Microsoft Academic Search

We describe the design and production of a tobacco mosiac virus mutant that provides for specific and stoichiometric attachment of a wide variety of ligand-linker groups. As a result, specific ligands could be chemoselectively linked to the virion to produce highly diverse nanomolecular materials. These included semi-crystalline protein arrays and metallic 'nanopipes', as well as nanomolecular 'light sticks'. The method

Mukerrem Demir; Michael H. B. Stowell

2002-01-01

57

An efficient synthesis of a potent PPARpan agonist.  

PubMed

An efficient synthesis of 2-{4-[({4-{[4-(4-methoxyphenyl)piperazin-1-yl]methyl}-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl}methyl)thio]phenoxy}-2-methylpropanoic acid (1), a potent PPARpan agonist, is described. The seven-step synthesis, which afforded 1 in 30% overall yield, includes a highly regioselective carbon-sulfur bond formation via coupling of a bishydroxymethylthiazole (3) with 4-hydroxythiophenol, displacement of the remaining alcohol through a three-step telescoped sequence involving an efficient cleavage of an aryl mesylate, and an efficient and practical method of introducing an isobutyric acid fragment. PMID:17025332

Guo, Jiasheng; Erickson, Greg A; Fitzgerald, Russ N; Matsuoka, Richard T; Rafferty, Stephen W; Sharp, Matthew J; Sickles, Barry R; Wisowaty, James C

2006-10-13

58

An efficient synthesis of loline alkaloids  

NASA Astrophysics Data System (ADS)

Loline (1) is a small alkaloid that, in spite of its simple-looking structure, has posed surprising challenges to synthetic chemists. It has been known for more than a century and has been the subject of extensive biological investigations, but only two total syntheses have been achieved to date. Here, we report an asymmetric total synthesis of loline that, with less then ten steps, is remarkably short. Our synthesis incorporates a Sharpless epoxidation, a Grubbs olefin metathesis and an unprecedented transannular aminobromination, which converts an eight-membered cyclic carbamate into a bromopyrrolizidine. The synthesis is marked by a high degree of chemo- and stereoselectivity and gives access to several members of the loline alkaloid family. It delivers sufficient material to support a programme aimed at studying the complex interactions between plants, fungi, insects and bacteria brokered by loline alkaloids.

Cakmak, Mesut; Mayer, Peter; Trauner, Dirk

2011-07-01

59

An Efficient Microscale Procedure for the Synthesis of Aspirin  

NASA Astrophysics Data System (ADS)

The synthesis of aspirin is a part of many undergraduate organic synthesis labs and is frequently used in qualitative organic analysis laboratory for the identification of salicylic acid. We have found that aspirin can be synthesized on microscale by a simple and efficient procedure that eliminates the heating step employed in literature procedures and gives a pure, ferric-negative product (no purple color with alcoholic ferric chloride solution).

Pandita, Sangeeta; Goyal, Samta

1998-06-01

60

Oxidative Palladium(II) Catalysis: A Highly Efficient and Chemoselective Cross-Coupling Method for Carbon-Carbon Bond Formation under Base-Free and Nitrogenous-Ligand Conditions  

PubMed Central

We report herein the development of a general and mild protocol of oxygen promoted Pd(II) catalysis resulting in the selective cross-couplings of alkenyl- and arylboron compounds with various olefins. Unlike most cross-coupling reactions, this new methodology works well even in the absence of bases, consequently averting undesired homo-couplings. Nitrogen-based ligands including dimethyl-phenanathroline enhance reactivities and offer a highly efficient and stereoselective methodology to overcome challenging substrate limitations. For instance, oxidative palladium(II) catalysis is effective with highly substituted alkenes and cyclic alkenes, which are known to be incompatible with other known catalytic conditions. Most examined reactions progressed smoothly to completion at low temperatures and in short times. These interesting results provide mechanistic insights and utilities for a new paradigm of palladium catalytic cycles without bases. PMID:17165795

Yoo, Kyung Soo; Yoon, Cheol Hwan; Jung, Kyung Woon

2008-01-01

61

Enantioselective preparation and chemoselective cross-coupling of 1,1-diboron compounds  

NASA Astrophysics Data System (ADS)

The simplicity, efficiency and generality of the transition-metal-catalysed Suzuki-Miyaura cross-coupling reaction has led to its application in the preparation of a wide variety of organic compounds. Cross-coupling of alkylboron derivatives, however, remains a major challenge, in particular with regard to stereochemical control. Here, we describe the preparation and reaction of highly optically enriched 1,1-diboron compounds. A catalytic asymmetric conjugate borylation of ?-boronylacrylates provided geminal diboronate products that feature two distinct boronyl units, in 99% enantiomeric excess. Chemoselective cross-coupling of one-boronyl unit, a trifluoroborate salt, occurred stereospecifically via inversion of its configuration to generate enantioenriched benzylic or allylic boronates. The difficult transmetallation in the Suzuki-Miyaura catalytic reaction cycle is believed to be facilitated by a stabilization effect from the second boronyl unit, and internal coordination by the oxygen of the proximal carboxyester. We also explored subsequent functionalization of the second boronyl unit.

Lee, Jack Chang Hung; McDonald, Robert; Hall, Dennis G.

2011-11-01

62

Evolution of the Total Synthesis of (-)-Okilactomycin Exploiting a Tandem Oxy-Cope Rearrangement/Oxidation, the Petasis-Ferrier Union/Rearrangement and Ring Closing Metathesis  

PubMed Central

An effective, asymmetric total synthesis of the antitumor antibiotic (-)-okilactomycin (1) and assignment of the absolute configuration, has been achieved exploiting a convergent strategy. Highlights of the synthesis include: a diastereoselective oxy-Cope rearrangement/oxidation sequence to install the C(1) and C(13) stereogenic centers; a Petasis-Ferrier union/rearrangement to construct the highly functionalized tetrahydropyranone inscribed within the thirteen membered macrocycle ring, employing for the first time a sterically demanding acetal; an intramolecular chemoselective acylation to access an embedded bicyclic lactone; and an efficient ring closing metathesis (RCM) reaction to generate the macrocyclic ring. PMID:19170499

Smith, Amos B.; Bosanac, Todd; Basu, Kallol

2009-01-01

63

Optimal Decision Tree Synthesis for Efficient Neighborhood Computation  

NASA Astrophysics Data System (ADS)

This work proposes a general approach to optimize the time required to perform a choice in a decision support system, with particular reference to image processing tasks with neighborhood analysis. The decisions are encoded in a decision table paradigm that allows multiple equivalent procedures to be performed for the same situation. An automatic synthesis of the optimal decision tree is implemented in order to generate the most efficient order in which conditions should be considered to minimize the computational requirements. To test out approach, the connected component labeling scenario is considered. Results will show the speedup introduced using an automatically built decision system able to efficiently analyze and explore the neighborhood.

Grana, Costantino; Borghesani, Daniele

64

Diazo Groups Endure Metabolism and Enable Chemoselectivity in Cellulo  

PubMed Central

We introduce a stabilized diazo group as a reporter for chemical biology. ManDiaz, which is a diazo derivative of N-acetylmannosamine, is found to endure cellular metabolism and label the surface of a mammalian cell. There, its diazo group can undergo a 1,3-dipolar cycloaddition with a strained alkyne, providing a signal comparable to that from the azido congener, ManNAz. The chemoselectivity of diazo and alkynyl groups enables dual labeling of cells that is not possible with azido and alkynyl groups. Thus, the diazo group, which is approximately half the size of an azido group, provides unique opportunities for orthogonal labeling of cellular components. PMID:25658416

Andersen, Kristen A.; Aronoff, Matthew R.; McGrath, Nicholas A.; Raines, Ronald T.

2015-01-01

65

A highly chemoselective and practical alkynylation of thiols.  

PubMed

A thiol-alkynylation procedure utilizing the hypervalent iodine alkyne transfer reagent TIPS-ethynyl-benziodoxolone has been developed. This scalable reaction proceeds in five minutes at room temperature in an open flask using commercially available reagents. The scope of the reaction is broad, with a variety of phenolic, benzylic, heterocyclic, and aliphatic thiols undergoing alkynylation in excellent yield. The method is highly chemoselective as a vast array of functional groups are tolerated. The utility of the thiol-alkynylation in postsynthetic elaboration has been demonstrated through the facile installment of a fluorophore tag on a cysteine-containing peptide. PMID:23777551

Frei, Reto; Waser, Jérôme

2013-07-01

66

Regio- and Chemoselective Immobilization of Proteins on Gold Surfaces  

PubMed Central

Protein chips are powerful tools as analytical and diagnostic devices for detection of biomolecular interactions, where the proteins are covalently or noncovalently attached to biosensing surfaces to capture and detect target molecules or biomarkers. Thus, fabrication of biosensing surfaces for regio- and chemoselective immobilization of biomolecules is a crucial step for better biosensor performance. In our previous studies, a regio- and chemoselective immobilization strategy was demonstrated on glass surfaces. This strategy is now used to regioselectively attach proteins to self-assembled monolayers (SAMs) on gold surfaces. Recombinant green fluorescent protein (GFP), glutathione S-transferase (GST), and antibody-binding protein G, bearing a C-terminal CVIA motif, were prepared and a farnesyl analogue with an ?-alkyne moiety was attached to the sulfhydryl moiety in the cysteine side chain by protein farnesyltransferase. The proteins, modified with the bioorthogonal alkyne functional group, were covalently and regioselectively immobilized on thiol or dithiocarbamate (DTC) SAMs on a gold surface by a Huigsen [3 + 2] cycloaddition reaction with minimal nonspecific binding. A concentration-dependent increase of fluorescence intensity was observed in wells treated with GFP on both thiol- and DTC-SAMs. The highly ordered, densely packed layer allowed for a high loading of immobilized protein, with a concomitant increase in substrate binding capacity. The DTC-SAMs were substantially more resistant to displacement of the immobilized proteins from the gold surface by ?-mercaptoethanol than alkane-thiol SAMs. PMID:24437976

2015-01-01

67

Efficient synthesis and reactions of 1,2-dipyrrolylethynes  

PubMed Central

Various dipyrroles possess important motifs for construction of pyrrole-containing pigments. A series of 1,2-dipyrrolylethynes (4a–d) has been efficiently synthesized using an improved one-pot double Sonagashira coupling from trimethylsilylethyne and various 2-iodopyrroles. The resulting 1,2-dipyrrolylethynes were further transformed into novel indolyl-, ethenyl- and carboranyl-dipyrroles (5–7) using the Larock indole synthesis, stereoselective catalytic hydrogenation, or B10H14. Indolyl-dipyrroles were found to selectively bind fluoride ions using one pyrrolic and the indolyl NHs, whereas the carboranyl- and ethenyl-dipyrroles are potentially valuable precursors for the synthesis of porphyrin isomers and expanded pigments. PMID:21822371

Tanui, Hillary K.; Hao, Erhong; Ihachi, Moses I.; Fronczek, Frank R.; Smith, Kevin M.; Vicente, M. Graça H.

2011-01-01

68

Amino acid-functionalized dendrimers with heterobifunctional chemoselective peripheral groups for drug delivery applications  

PubMed Central

Dendrimers have emerged as multifunctional carriers for targeted drug delivery, gene delivery and imaging. Improving the functional versatility at the surface for carrying multiple conjugation reactions is becoming vital. Typically, generation four polyamidoamine (G4-PAMAM) dendrimers bear ~64 symmetrical end groups, often requiring different spacers to conjugate various functional groups (drugs and targeting moieties), increasing the synthetic steps. In the present study, a simple one-step synthesis to convert each symmetrical end group of G4-PAMAM dendrimers into two reactive, distinct orthogonal and chemoselective groups is described. A near-complete end-capping of the dendrimers (87–93%) with amino acids results in heterobifunctional G4-PAMAM dendrimers bearing a very high (? 110) diverse peripheral end groups (OH+NHBoc, OH+COOMe, SH+NHBoc, and COOH+NHBoc). Postfunctionalization ability of these dendrimers was evaluated. The heterbifunctional groups at the dendrimer periphery could be chemoselectively conjugated to multiple moieties such as drugs (indomethacin and dexamethasone) and drugs and imaging agents (dexamethasone and FITC). These conjugations could be achieved in immediate succession without functional group conversions, eliminating the additional elaborate synthetic steps traditionally required to append specific linkers. Furthermore, one of the two functional handles at periphery was used to develop in situ forming hydrogels, whereas the other handle could be used for conjugating the drugs (e.g., dexamethasone). The heterobifunctional dendrimers with either “NH2 or SH (thiopyridyl protected form)” terminations showed in situ hydrogel formation by cross-linking with N-hydroxysuccinimide or thiol-terminated multiarm polyethylene glycol (20 kDa). The choice of amino acids as versatile linkers would enable biocompatible dendrimer scaffolds for use in drug delivery. ?-potential measurements showed drastic lowering of the charge on G4-PAMAM-NH2 dendrimers by end-capping with amino acids, whereas in the case of neutral G4-PAMAM-OH dendrimers, the charge did not increase or decrease substantially. The in vitro cytotoxicity and hemolysis assay showed that the heterobifunctional dendrimers were noncytoxic in the 100 ng/mL to 1 mg/mL concentration range. With this study, we demonstrate the development of biocompatible dendrimers bearing multiple orthogonal surface groups, enabling the attachment of drugs, imaging agents, and gel formation using minimal synthetic steps. PMID:20415504

Navath, RS; Menjoge, AR; Wang, B; Romero, R; Kannan, S; Kannan, RM

2013-01-01

69

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

70

A simple, universal, efficient PCR-based gene synthesis method: sequential OE-PCR gene synthesis.  

PubMed

Herein we present a simple, universal, efficient gene synthesis method based on sequential overlap extension polymerase chain reactions (OE-PCRs). This method involves four key steps: (i) the design of paired complementary 54-mer oligonucleotides with 18 bp overlaps, (ii) the utilisation of sequential OE-PCR to synthesise full-length genes, (iii) the cloning and sequencing of four positive T-clones of the synthesised genes and (iv) the resynthesis of target genes by OE-PCR with correct templates. Mispriming and secondary structure were found to be the principal obstacles preventing successful gene synthesis and were easily identified and solved in this method. Compensating for the disadvantages of being laborious and time-consuming, this method has many attractive advantages, such as the ability to guarantee successful gene synthesis in most cases and good allowance for Taq polymerase, oligonucleotides, PCR conditions and a high error rate. Thus, this method provides an alternative tool for individual gene synthesis without strict needs of the high-specialised experience. PMID:23597923

Zhang, Pingping; Ding, Yingying; Liao, Wenting; Chen, Qiuli; Zhang, Huaqun; Qi, Peipei; He, Ting; Wang, Jinhong; Deng, Songhua; Pan, Tianyue; Ren, Hao; Pan, Wei

2013-07-25

71

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

72

Domino reaction involving the Bestmann-Ohira reagent and ?,?-unsaturated aldehydes: efficient synthesis of functionalized pyrazoles.  

PubMed

A mild, efficient and rapid domino reaction involving the Bestmann-Ohira reagent (BOR) and ?,?-unsaturated aldehydes has been developed for the synthesis of densely functionalized vinylpyrazoles. This reaction demonstrates the dual reactivity of BOR as a homologation reagent as well as a cycloaddition partner, thus constituting a domino reaction in an operationally simple procedure. The application of this efficient synthesis of pyrazoles has been demonstrated for the synthesis of phosphonyl analogues of pyrrolopyrazole alkaloids. PMID:25476791

Ahamad, Shakir; Gupta, Ashis Kumar; Kant, Ruchir; Mohanan, Kishor

2015-02-01

73

Engineering the elongation factor Tu for efficient selenoprotein synthesis  

PubMed Central

Selenocysteine (Sec) is naturally co-translationally incorporated into proteins by recoding the UGA opal codon with a specialized elongation factor (SelB in bacteria) and an RNA structural signal (SECIS element). We have recently developed a SECIS-free selenoprotein synthesis system that site-specifically—using the UAG amber codon—inserts Sec depending on the elongation factor Tu (EF-Tu). Here, we describe the engineering of EF-Tu for improved selenoprotein synthesis. A Sec-specific selection system was established by expression of human protein O6-alkylguanine-DNA alkyltransferase (hAGT), in which the active site cysteine codon has been replaced by the UAG amber codon. The formed hAGT selenoprotein repairs the DNA damage caused by the methylating agent N-methyl-N?-nitro-N-nitrosoguanidine, and thereby enables Escherichia coli to grow in the presence of this mutagen. An EF-Tu library was created in which codons specifying the amino acid binding pocket were randomized. Selection was carried out for enhanced Sec incorporation into hAGT; the resulting EF-Tu variants contained highly conserved amino acid changes within members of the library. The improved UTu-system with EF-Sel1 raises the efficiency of UAG-specific Sec incorporation to >90%, and also doubles the yield of selenoprotein production. PMID:25064855

Haruna, Ken-ichi; Alkazemi, Muhammad H.; Liu, Yuchen; Söll, Dieter; Englert, Markus

2014-01-01

74

Engineering the elongation factor Tu for efficient selenoprotein synthesis.  

PubMed

Selenocysteine (Sec) is naturally co-translationally incorporated into proteins by recoding the UGA opal codon with a specialized elongation factor (SelB in bacteria) and an RNA structural signal (SECIS element). We have recently developed a SECIS-free selenoprotein synthesis system that site-specifically--using the UAG amber codon--inserts Sec depending on the elongation factor Tu (EF-Tu). Here, we describe the engineering of EF-Tu for improved selenoprotein synthesis. A Sec-specific selection system was established by expression of human protein O(6)-alkylguanine-DNA alkyltransferase (hAGT), in which the active site cysteine codon has been replaced by the UAG amber codon. The formed hAGT selenoprotein repairs the DNA damage caused by the methylating agent N-methyl-N'-nitro-N-nitrosoguanidine, and thereby enables Escherichia coli to grow in the presence of this mutagen. An EF-Tu library was created in which codons specifying the amino acid binding pocket were randomized. Selection was carried out for enhanced Sec incorporation into hAGT; the resulting EF-Tu variants contained highly conserved amino acid changes within members of the library. The improved UTu-system with EF-Sel1 raises the efficiency of UAG-specific Sec incorporation to >90%, and also doubles the yield of selenoprotein production. PMID:25064855

Haruna, Ken-ichi; Alkazemi, Muhammad H; Liu, Yuchen; Söll, Dieter; Englert, Markus

2014-09-01

75

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids  

PubMed Central

Summary The near-unlimited availability of CO2 has stimulated a growing research effort in creating value-added products from this greenhouse gas. This paper presents the trends on the most important methods used in the electrochemical synthesis of carboxylic acids from carbon dioxide. An overview is given of different substrate groups which form carboxylic acids upon CO2 fixation, including mechanistic considerations. While most work focuses on the electrocarboxylation of substrates with sacrificial anodes, this review considers the possibilities and challenges of implementing other synthetic methodologies. In view of potential industrial application, the choice of reactor setup, electrode type and reaction pathway has a large influence on the sustainability and efficiency of the process. PMID:25383120

Matthessen, Roman; Fransaer, Jan; Binnemans, Koen

2014-01-01

76

Synthesis of heterocyclic [3.3.3]propellanes via a sequential four-component reaction.  

PubMed

A highly chemoselective heteroannulation protocol for the synthesis of unreported polysubstituted heterocyclic [3.3.3]propellanes has been developed by sequential four-component reaction of ninhydrin, malononitrile, primary amines, and dialkyl acetylenedicarboxylates under mild conditions in water. To the best of our knowledge, there are no previous reports for the synthesis of these classes of heterocyclic [3.3.3]propellanes. The merit of this sequential Knoevenagel condensation/enamine formation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, the use of water as reaction media, and the efficiency of production without the use of any activator or metal promoters. This synthesis serves as a nice addition to group-assistant-purification (GAP) chemistry in which purification via chromatography and recrystallization can be avoided, and the pure products were obtained simply by washing the crude products with 95% ethanol. PMID:22480382

Alizadeh, Abdolali; Rezvanian, Atieh; Zhu, Long-Guan

2012-05-01

77

General Chemoselective and Redox-Responsive Ligation and Release Strategy  

PubMed Central

We report a switchable redox click and cleave reaction strategy for conjugating and releasing a range of molecules on demand. This chemoselective redox-responsive ligation (CRRL) and release strategy is based on a redox switchable oxime linkage that is controlled by mild chemical or electrochemical redox signals and can be performed at physiological conditions without the use of a catalyst. Both conjugation and release reactions are kinetically well behaved and quantitative. The CRRL strategy is synthetically modular and easily monitored and characterized by routine analytical techniques. We demonstrate how the CRRL strategy can be used for the dynamic generation of cyclic peptides and the ligation of two different peptides that are stable but can be selectively cleaved upon changes in the redox environment. We also demonstrate a new redox based delivery of cargoes to live cells strategy via the CRRL methodology by synthesizing a FRET redox-responsive probe that is selectively activated within a cellular environment. We believe the ease of the CRRL strategy should find wide use in a range of applications in biology, tissue engineering, nanoscience, synthetic chemistry, and material science and will expand the suite of current conjugation and release strategies. PMID:24559434

2015-01-01

78

Metal-free activation of H 2 O 2 by synergic effect of ionic liquid and microwave: chemoselective oxidation of benzylic alcohols to carbonyls and unexpected formation of anthraquinone in aqueous condition  

Microsoft Academic Search

H2O2 mediated oxidation of alcohols in ionic liquid is revisited, wherein, ionic liquids under the influence of microwave irradiation\\u000a have been found to facilitate activation of H2O2 without any metal catalyst in aqueous condition. The method utilizes a neutral ionic liquid [hmim]Br both as catalyst and\\u000a solvent for efficient and chemoselective oxidation of benzyl alcohol derivatives on aromatic (?, ?)

Rakesh Kumar; Nandini Sharma; Naina Sharma; Abhishek Sharma; Arun K. Sinha

79

Protecting group free synthesis of urea-linked glycoconjugates: efficient synthesis of ?-urea glycosides in aqueous solution.  

PubMed

A method for the protecting group free synthesis of ?-urea-linked glycoconjugates has been developed. The one step process, involving reactions between urea and D-glucose, N-acetyl-D-glucosamine or D-xylose in acidic aqueous solution, furnishes the corresponding ?-urea glycosides in modest yields. This simple and efficient procedure is applicable to the synthesis of ?-urea tethered amino acid-carbohydrate conjugates. PMID:24796538

Ichikawa, Yoshiyasu; Minami, Takahiro; Kusaba, Shohei; Saeki, Nobuyoshi; Tonegawa, Yuta; Tomita, Yumiko; Nakano, Keiji; Kotsuki, Hiyoshizo; Masuda, Toshiya

2014-06-21

80

An efficient approach for monosulfide bridge formation in solid-phase peptide synthesis  

Microsoft Academic Search

An efficient approach for the synthesis of cyclic peptides containing unnatural thioether side-chain bridges, based on the use of (2S)-9-fluorenylmethyl-2-[(tert-butoxycarbonyl)amino]-4-iodobutanoate and its homologue 5-iodopentanoate, derived from Boc-l-Asp-OFm and Boc-l-Glu-OFm, respectively, is reported. The synthesis was performed by a tandem combination of solid-phase peptide synthesis and microwave-assisted cyclization strategy.

Pietro Campiglia; Isabel Gomez-Monterrey; Luigi Longobardo; Teresa Lama; Ettore Novellino; Paolo Grieco

2004-01-01

81

Hypervalent iodine reagents enable chemoselective deboronative/decarboxylative alkenylation by photoredox catalysis.  

PubMed

Chemoselective C(sp(3))-C(sp(2)) coupling reactions under mild reaction conditions are useful for synthesizing alkyl-substituted alkenes having sensitive functional groups. Reported here is a visible-light-induced chemoselective alkenylation through a deboronation/decarboxylation sequence under neutral aqueous reaction conditions at room temperature. This reaction represents the first hypervalent-iodine-enabled radical decarboxylative alkenylation reaction, and a novel benziodoxole-vinyl carboxylic acid reaction intermediate was isolated. This C(sp(3))-C(sp(2)) coupling reaction leads to aryl-and acyl-substituted alkenes containing various sensitive functional groups. The excellent chemoselectivity, stable reactants, and neutral aqueous reaction conditions of the reaction suggest future biomolecule applications. PMID:25504966

Huang, Hanchu; Jia, Kunfang; Chen, Yiyun

2015-02-01

82

Chemical Protein Synthesis by Solid Phase Ligation of Unprotected Peptide Segments  

E-print Network

Chemical Protein Synthesis by Solid Phase Ligation of Unprotected Peptide Segments Lynne E. Canne capabilities for total chemical protein synthesis. Introduction Chemical ligation,1 the chemoselective reaction solid phase protein synthesis approach uses the chemical ligation of unprotected peptide segments,1

Dennis, Edward A.

83

Efficient synthesis of anacardic acid analogues and their antibacterial activities.  

PubMed

Anacardic acid derivatives exhibit a broad range of biological activities. In this report, an efficient method for the synthesis of anacardic acid derivatives was explored, and a small set of salicylic acid variants synthesised retaining a constant hydrophobic element (a naphthyl tail). The naphthyl side chain was introduced via Wittig reaction and the aldehyde installed using directed ortho-metalation reaction of the substituted o-anisic acids. The failure of ortho-metalation using unprotected carboxylic acid group compelled us to use directed ortho-metalation in which a tertiary amide was used as a strong ortho-directing group. In the initial route, tertiary amide cleavage during final step was challenging, but cleaving the tertiary amide before Wittig reaction was beneficial. The Wittig reaction with protected carboxylic group (methyl ester) resulted in side-products whereas using sodium salt resulted in higher yields. The novel compounds were screened for antibacterial activity and cytotoxicity. Although substitution on the salicylic head group enhanced antibacterial activities they also enhanced cytotoxicity. PMID:23416004

Mamidyala, Sreeman K; Ramu, Soumya; Huang, Johnny X; Robertson, Avril A B; Cooper, Matthew A

2013-03-15

84

An Efficient and Highly Diastereoselective Synthesis of GSK1265744, a Potent HIV Integrase Inhibitor.  

PubMed

A novel synthesis of GSK1265744, a potent HIV integrase inhibitor, is described. The synthesis is highlighted by an efficient construction of the densely functionalized pyridinone core as well as a highly diastereoselective formation of the acyl oxazolidine moiety. The latter exploits the target molecule's ability to chelate to Mg(2+), a key feature in the integrase inhibitor's mechanism of action. PMID:25615910

Wang, Huan; Kowalski, Matthew D; Lakdawala, Ami S; Vogt, Frederick G; Wu, Lianming

2015-02-01

85

An efficient synthesis of daidzein, dimethyldaidzein, and isoformononetin  

Microsoft Academic Search

Synthesis of the soy isoflavone, daidzein, and its derivatives, isoformononetin and dimethyldaidzein, through utilization of a novel synthetic pathway is reported. This synthesis employs an enamine addition and O-methylation of 2,4-dihydroxyacetophenone, a subsequent ring closure and iodination, followed by a Suzuki coupling with PEG 10000. Demethylation of either isoformononetin or dimethyldaidzein afforded daidzein.

Kyle F. Biegasiewicz; Jeffrey D. St. Denis; Vincent M. Carroll; Ronny Priefer

2010-01-01

86

Chemoselective C-benzylation of unprotected anilines with benzyl alcohols using Re2O7 catalyst.  

PubMed

An unprecedented dehydrative C-C bond formation between unprotected anilines with benzyl alcohols is disclosed. Re2O7 catalyst (5 mol %) at elevated reaction temperature (80 °C) provided C-benzylanilines with high to excellent yields and with good chemoselectivities (over N-alkylation). A probable mechanism has been proposed based on mechanistic studies. PMID:24601671

Nallagonda, Rajender; Rehan, Mohammad; Ghorai, Prasanta

2014-04-01

87

Lipase active site covalent anchoring of Rh(NHC) catalysts: towards chemoselective artificial metalloenzymes.  

PubMed

A Rh(NHC) phosphonate complex reacts with the lipases cutinase and Candida antarctica lipase B resulting in the first (soluble) artificial metalloenzymes formed by covalent active site-directed hybridization. When compared to unsupported complexes, these new robust hybrids show enhanced chemoselectivity in the (competitive) hydrogenation of olefins over ketones. PMID:25786894

Basauri-Molina, M; Riemersma, C F; Würdemann, M A; Kleijn, H; Klein Gebbink, R J M

2015-04-01

88

The Use of pH to Influence Regio-and Chemoselectivity in the Asymmetric  

E-print Network

- S1 - The Use of pH to Influence Regio- and Chemoselectivity in the Asymmetric Aminohydroxylation-Hoover Capillary Melting Point Apparatus and are uncorrected. The pH of solutions was measured by AquemetTM Research AR15 pH meter equipped with Corning semimicrocombo electrode (#476156), which was standardized

Hergenrother, Paul J.

89

The Use of pH to Influence Regio-and Chemoselectivity in the Asymmetric  

E-print Network

The Use of pH to Influence Regio- and Chemoselectivity in the Asymmetric Aminohydroxylation, 2002 ABSTRACT The pH-controlled Sharpless asymmetric aminohydroxylation (AA) of styrenes provides 1 inversely correlated with enantiselectivity.3a We now report a method utilizing pH control to override other

Hergenrother, Paul J.

90

Efficient synthesis of ethisterone glycoconjugate via bis-triazole linkage.  

PubMed

Synthesis of sugar based triazolyl azido-alcohols was accomplished via one pot click reaction of glycosyl alkynes with epichlorohydrin in aqueous medium. All the developed triazolyl azido-alcohols were further utilized for the synthesis of bis-triazolyl ethisterone glycoconjugates using CuAAC reaction. The developed triazole-linked ethisterone glycoconjugates would be crucial in androgen receptor pharmacology and chemical biology. PMID:25369262

Mishra, Kunj B; Mishra, Bhuwan B; Tiwari, Vinod K

2014-11-18

91

Origin of chemoselectivity in N-heterocyclic carbene catalyzed cross-benzoin reactions: DFT and experimental insights.  

PubMed

An exploration into the origin of chemoselectivity in the NHC-catalyzed cross-benzoin reaction reveals several key factors governing the preferred pathway. In the first computational study to explore the cross-benzoin reaction, a piperidinone-derived triazolium catalyst produces kinetically controlled chemoselectivity. This is supported by (1)H NMR studies as well as a series of crossover experiments. Major contributors include the rapid and preferential formation of an NHC adduct with alkyl aldehydes, a rate-limiting carbon-carbon bond formation step benefiting from a stabilizing ?-stacking/?-cation interaction, and steric penalties paid by competing pathways. The energy profile for the analogous pyrrolidinone-derived catalyst was found to be remarkably similar, despite experimental data showing that it is less chemoselective. The chemoselectivity could not be improved through kinetic control; however, equilibrating conditions show substantial preference for the same cross-benzoin product kinetically favored by the piperidinone-derived catalyst. PMID:25734574

Langdon, Steven M; Legault, Claude Y; Gravel, Michel

2015-04-01

92

A Subsystem Synthesis Method for Efficient Vehicle Multibody Dynamics  

Microsoft Academic Search

A subsystem synthesis method has been proposed for dynamicanalysis of a vehicle multibody system that consists of severalsubsystems. In this method, each subsystem can be independently analyzedwith a virtual reference body. For overall vehicle system analysis,subsystems can be synthesized to the chassis with effective inertiamatrix and force vector from the virtual reference body of eachsubsystem. Using this matrix and vector,

Sung-Soo Kim

2002-01-01

93

Total synthesis of the proposed structure of a polyketide from Phialomyces macrosporus.  

PubMed

Total synthesis of the proposed structure of a polyketide isolated from Phialomyces macrosporus is described. The synthesis involved chemoselective epoxidation, regioselective epoxide ring opening, chemo- and diastereoselective dihydroxylation, and vinylation of lactone accompanied by the formation of a furan ring. PMID:25634478

Abe, Hideki; Itaya, Satoko; Sasaki, Kei; Kobayashi, Toyoharu; Ito, Hisanaka

2015-02-12

94

Rapid synthesis of oligodeoxyribonucleotides VI. Efficient, mechanised synthesis of heptadecadeoxyribonucleotides by an improved solid phase phosphotriester route.  

PubMed Central

Efficient mechanised synthesis of heptadecadeoxyribonucleotides has been achieved on an economically small scale by an improved solid phase phosphotriester method on a polydimethylacrylamide resin. Improvements were made in the preparation of dinucleotide building blocks, reaction conditions for oligonucleotide assembly and in purification of deprotected oligonucleotides by h.p.l.c. Several milligrams of pure heptadecamers were obtained. Two of the heptadecamers were designed for sequencing in opposite directions of DNA cloned in phage M13mp2. Images PMID:7232224

Duckworth, M L; Gait, M J; Goelet, P; Hong, G F; Singh, M; Titmas, R C

1981-01-01

95

Automatic Synthesis of Efficient Intrusion Detection Systems on FPGAs  

Microsoft Academic Search

This paper presents a methodology and a tool for automatic synthesis of highly ecien t intrusion detection systems using a high-level, graph-based parti- tioning methodology and tree-based lookahead architectures. Intrusion detection for network security is a compute-intensive application demanding high system performance. The tools implement and automate a customizable o w for the creation of ecien t Field Programmable Gate

Zachary K. Baker; Viktor K. Prasanna

2004-01-01

96

An efficient synthesis of the plant growth hormone 1-triacontanol  

Microsoft Academic Search

A high yield synthesis of 1-triacontanol was based on the cheap and easily available starting materials 1-octadecanol and 1,12-dodecanediol. The first one was converted to octadecanal using a phase transfer system, whereas the second one after phase transfer bromination and reaction with triphenylphosphine provided 1-hydroxy-12-triphenylphosphonium bromide.Wittig reaction of these two synthons and subsequent hydrogenation furnished the desired product.

N. H. Tran-Thi; H. Falk

1995-01-01

97

Efficiency, error and yield in light-directed maskless synthesis of DNA microarrays  

PubMed Central

Background Light-directed in situ synthesis of DNA microarrays using computer-controlled projection from a digital micromirror device--maskless array synthesis (MAS)--has proved to be successful at both commercial and laboratory scales. The chemical synthetic cycle in MAS is quite similar to that of conventional solid-phase synthesis of oligonucleotides, but the complexity of microarrays and unique synthesis kinetics on the glass substrate require a careful tuning of parameters and unique modifications to the synthesis cycle to obtain optimal deprotection and phosphoramidite coupling. In addition, unintended deprotection due to scattering and diffraction introduce insertion errors that contribute significantly to the overall error rate. Results Stepwise phosphoramidite coupling yields have been greatly improved and are now comparable to those obtained in solid phase synthesis of oligonucleotides. Extended chemical exposure in the synthesis of complex, long oligonucleotide arrays result in lower--but still high--final average yields which approach 99%. The new synthesis chemistry includes elimination of the standard oxidation until the final step, and improved coupling and light deprotection. Coupling Insertions due to stray light are the limiting factor in sequence quality for oligonucleotide synthesis for gene assembly. Diffraction and local flare are by far the largest contributors to loss of optical contrast. Conclusions Maskless array synthesis is an efficient and versatile method for synthesizing high density arrays of long oligonucleotides for hybridization- and other molecular binding-based experiments. For applications requiring high sequence purity, such as gene assembly, diffraction and flare remain significant obstacles, but can be significantly reduced with straightforward experimental strategies. PMID:22152062

2011-01-01

98

Size and support-dependent silver cluster catalysis for chemoselective hydrogenation of nitroaromatics  

Microsoft Academic Search

Silver clusters on ?-Al2O3 support catalyze highly chemoselective reduction of a nitro group for the reduction of substituted nitroaromatics such as nitrostyrene. These catalysts show higher selectivity than conventional platinum-group metal-based heterogeneous catalysts. Systematic studies on the influence of the metal particle size and support oxides show that the intrinsic activity increases with decrease in the silver particle size, and

Ken-ichi Shimizu; Yuji Miyamoto; Atsushi Satsuma

2010-01-01

99

Chemoselection of allogeneic HSC after murine neonatal transplantation without myeloablation or post-transplant immunosuppression.  

PubMed

The feasibility of allogeneic transplantation, without myeloablation or post-transplant immunosuppression, was tested using in vivo chemoselection of allogeneic hematopoietic stem cells (HSCs) after transduction with a novel tricistronic lentiviral vector (MGMT(P140K)-2A-GFP-IRES-TK (MAGIT)). This vector contains P140K-O(6)-methylguanine-methyltransferase (MGMT(P140K)), HSV-thymidine kinase (TK(HSV)), and enhanced green fluorescent protein (eGFP) enabling (i) in vivo chemoselection of HSC by conferring resistance to benzylguanine (BG), an inhibitor of endogenous MGMT, and to chloroethylating agents such as 1,3-bis(2-chloroethyl)nitrosourea (BCNU) and, (ii) depletion of proliferating cells such as malignant clones or transduced donor T cells mediating graft versus host disease (GVHD), by expression of the suicide gene TK(HSV) and Ganciclovir (GCV) administration. Non-myeloablative transplantation of transduced, syngeneic, lineage-depleted (Lin(-)) BM in neonates resulted in 0.67% GFP(+) mononuclear cells in peripheral blood. BG/BCNU chemoselection, 4 and 8 weeks post-transplant, produced 50-fold donor cell enrichment. Transplantation and chemoselection of major histocompatibility complex (MHC)-mismatched MAGIT-transduced Lin(-) BM also produced similar expansion for >40 weeks. The efficacy of this allotransplant approach was validated in Hbb(th3) heterozygous mice by correction of ?-thalassemia intermedia, without toxicity or GVHD. Negative selection, by administration of GCV resulted in donor cell depletion without graft ablation, as re-expansion of donor cells was achieved with BG/BCNU treatment. These studies show promise for developing non-ablative allotransplant approaches using in vivo positive/negative selection. PMID:22871662

Falahati, Rustom; Zhang, Jianqing; Flebbe-Rehwaldt, Linda; Shi, Yimin; Gerson, Stanton L; Gaensler, Karin Ml

2012-11-01

100

Assimilation efficiencies of chemical contaminants in aquatic invertebrates: A synthesis  

SciTech Connect

Assimilation efficiencies of contaminants from ingested food are critical for understanding chemical accumulation and trophic transfer in aquatic invertebrates. Assimilation efficiency is a first-order physiological parameter that can be used to systematically compare the bioavailability of different contaminants from different foods. The various techniques used to measure contaminant assimilation efficiencies are reviewed. Pulse-chase feeding techniques and the application of gamma-emitting radiotracers have been invaluable in measuring metal assimilation efficiencies in aquatic animals. Uniform radiolabeling of food is required to measure assimilation, but this can be difficult when sediments are the food source. Biological factors that influence contaminant assimilation include food quantity and quality, partitioning of contaminants in the food particles, and digestive physiology of the animals. Other factors influencing assimilation include the behavior of the chemical within the animal's gut and its associations with different geochemical fractions of food particles. Assimilation efficiency is a critical parameter to determine (and to make predictions of) bioaccumulation of chemicals from dietary exposure. Robust estimates of assimilation efficiency coupled with estimates of aqueous uptake can be used to determine the relative importance of aqueous and dietary exposures. For bioaccumulation of metals from sediments, additional studies are required to test whether metals bound to the acid-volatile sulfide fraction of sediments can be available to benthic deposit-feeding inverterbrates. Most assimilation efficiency studies have focused on chemical transfer in organisms at the bottom of the food chain; additional studies are required to examine chemical transfer at higher trophic levels.

Wang, W.X.; Fisher, N.S.

1999-09-01

101

Scanning droplet cell for chemoselective patterning through local electroactivation of protected quinone monolayers.  

PubMed

A reagentless strategy for template-free patterning of uniformly inert surfaces is suggested. A layer of p-hydroquinone (HQ) protected by the tert-butyldimethylsilyl (TBDMS) group is electrografted onto glassy carbon electrodes. Chemoselective activation is performed through electrochemically controlled cleavage of the TBDMS group, which yields the redox-active surface-confined quinone moieties. The latter are shown to undergo electrochemically induced Michael addition, which serves for subsequent functionalization of the electrode surface. Patterning of the TBDMS-quinone-modified surface is accomplished by using selective localized cleavage of the protecting group. State-of-the-art direct-mode scanning electrochemical microscopy (SECM) patterning fails to yield the anticipated interfacial reaction; however, the electrochemical scanning droplet cell (SDC) is capable of conducting the localized chemoselective reaction. In a small area, dictated by the dimensions of the droplet, electrochemically induced cleavage of the protecting group can be performed locally to give rise to arrays of active quinone spots. Upon deprotection, the redox signals, attributed to the hydroquinone/benzoquinone couple, provide the first direct evidence for chemoselective electrochemical patterning of sensitive functionalities. Subsequent SECM studies of the resulting modified areas demonstrate spatial control of the proposed patterning technique. PMID:24353197

Clausmeyer, Jan; Henig, Jörg; Schuhmann, Wolfgang; Plumeré, Nicolas

2014-01-13

102

Gold-catalyzed oxidative ring expansion of 2-alkynyl-1,2-dihydropyridines or -quinolines: highly efficient synthesis of functionalized azepine or benzazepine scaffolds.  

PubMed

A gold-catalyzed highly regio- and chemoselective oxidative ring expansion of 2-alkynyl-1,2-dihydropyridines and its analogues using pyridine-N-oxide as the oxidant has been developed. Ring expansion proceeds through exclusive 1,2-migration of a vinyl or phenyl group, whereas no 1,2-H and 1,2-N migration take place. The reaction provides an efficient and attractive route to various types of medium-sized azepine derivatives in generally high to excellent yields with a broad functional group tolerance. DFT studies indicate that the reaction proceeds through the formation of a cyclopropyl gold intermediate, and no gold carbene species is involved. PMID:25424452

Chen, Ming; Chen, Yifeng; Sun, Ning; Zhao, Jidong; Liu, Yuanhong; Li, Yuxue

2015-01-19

103

Efficient formal synthesis of oseltamivir phosphate (Tamiflu) with inexpensive D-ribose as the starting material.  

PubMed

An efficient formal synthesis of oseltamivir phosphate (Tamiflu) has been achieved in 12 steps with use of the inexpensive and highly abundant D-ribose as the starting material. This concise alternative route does not utilize protecting groups and features the introduction of 3-pentylidene ketal as the latent 3-pentyl ether, the use of a highly efficient RCM reaction to form the Tamiflu skeleton, and selective functional group manipulations. PMID:19938847

Osato, Hiroshi; Jones, Ian L; Chen, Anqi; Chai, Christina L L

2010-01-01

104

General and Efficient Synthesis of O-Sulfonylhydroxylamine Derivatives  

Microsoft Academic Search

A general and efficient synthetic route to O-sulfonylhydroxylamine derivatives is described. The approach involves acylation of hydroxylamine with benzyl chloroformate to give N-carbobenzoxy hydroxylamine, followed by sulfonation and hydrogenolysis to give products.

Liqiong Qin; Zhiming Zhou; Jia Wei; Ting Yan; Hongliang Wen

2010-01-01

105

An efficient formal synthesis of ( S)-dapoxetine from enantiopure 3-hydroxy azetidin-2-one  

Microsoft Academic Search

An efficient formal synthesis of S-(+) dapoxetine starting from 3-hydroxy azetidin-2-one is described. The intermediate (S)-3-(dimethyl amino)-3-phenylpropan-1-ol was synthesized in enantiopure form starting with 3-hydroxy azetidin-2-one in seven steps.

Pinak M. Chincholkar; Ajaykumar S. Kale; Vikas K. Gumaste; Abdul Rakeeb A. S. Deshmukh

2009-01-01

106

Magnesium bis(monoperoxyphthalate) hexahydrate as mild and efficient oxidant for the synthesis of selenones  

PubMed Central

Summary A new, efficient and mild method for the direct oxidation of selenides to selenones using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) has been developed. Noteworthy this transformation proceeds at room temperature, employs a cheap and safety oxidant and has a broad functional group tolerance. Moreover, the produced selenones could be useful intermediates for the synthesis of different heterocyclic compounds. PMID:24991278

Curini, Massimo; Rosati, Ornelio; Minuti, Lucio

2014-01-01

107

An efficient synthesis of loline alkaloids Mesut Cakmak, Peter Mayer and Dirk Trauner*  

E-print Network

An efficient synthesis of loline alkaloids Mesut Cakmak, Peter Mayer and Dirk Trauner* Loline (1) is a small alkaloid that, in spite of its simple-looking structure, has posed surprising challenges alkaloid family. It delivers sufficient material to support a programme aimed at studying the complex

Trauner, Dirk

108

ACCESS-2: Approximation Concepts Code for Efficient Structural Synthesis, user's guide  

NASA Technical Reports Server (NTRS)

A user's guide is presented for the ACCESS-2 computer program. ACCESS-2 is a research oriented program which implements a collection of approximation concepts to achieve excellent efficiency in structural synthesis. The finite element method is used for structural analysis and general mathematical programming algorithms are applied in the design optimization procedure.

Miura, H.; Schmit, L. A., Jr.

1978-01-01

109

An efficient single-enzymatic cascade for asymmetric synthesis of chiral amines catalyzed by ?-transaminase.  

PubMed

An efficient single-enzymatic cascade approach for the asymmetric synthesis of chiral amines has been developed, which applies the amino donor 3-aminocyclohexa-1,5-dienecarboxylic acid spontaneously tautomerizing to reach reaction completion with excellent ee values. PMID:23169388

Wang, Bo; Land, Henrik; Berglund, Per

2013-01-01

110

Solvent-free microwave organic synthesis as an efficient procedure for green chemistry  

Microsoft Academic Search

Solvent-free methods are especially adapted to organic synthesis under Green Chemistry conditions. When coupled to microwave (MW) irradiation, it results in very efficient and clean procedures with noticeable improvements over classical methods. To take advantage of MW specific effects, the most suitable cases involve reactions with polar mechanisms with increase of the polarity during the progress of the reaction and

André Loupy

2004-01-01

111

Efficient discovery of bioactive scaffolds by activity-directed synthesis  

NASA Astrophysics Data System (ADS)

The structures and biological activities of natural products have often provided inspiration in drug discovery. The functional benefits of natural products to the host organism steers the evolution of their biosynthetic pathways. Here, we describe a discovery approach—which we term activity-directed synthesis—in which reactions with alternative outcomes are steered towards functional products. Arrays of catalysed reactions of ?-diazo amides, whose outcome was critically dependent on the specific conditions used, were performed. The products were assayed at increasingly low concentration, with the results informing the design of a subsequent reaction array. Finally, promising reactions were scaled up and, after purification, submicromolar ligands based on two scaffolds with no previous annotated activity against the androgen receptor were discovered. The approach enables the discovery, in tandem, of both bioactive small molecules and associated synthetic routes, analogous to the evolution of biosynthetic pathways to yield natural products.

Karageorgis, George; Warriner, Stuart; Nelson, Adam

2014-10-01

112

Improvement of efficiency in the enzymatic synthesis of lactulose palmitate.  

PubMed

Sugar esters are considered as surfactants due to its amphiphilic balance that can lower the surface tension in oil/water mixtures. Enzymatic syntheses of these compounds are interesting both from economic and environmental considerations. A study was carried out to evaluate the effect of four solvents, temperature, substrate molar ratio, biocatalyst source, and immobilization methodology on the yield and specific productivity of lactulose palmitate monoester synthesis. Lipases from Pseudomonas stutzeri (PsL) and Alcaligenes sp. (AsL), immobilized in porous silica functionalized with octyl groups (adsorption immobilization, OS) and with glyoxyl-octyl groups (both adsorption and covalent immobilization, OGS), were used. The highest lactulose palmitate yields were obtained at 47 °C in acetone, for all biocatalysts, while the best lactulose:palmitic acid molar ratio differed according to the immobilization methodology, being 1:1 for AsL-OGS biocatalyst (20.7 ± 3%) and 1:3 for the others (30-50%). PMID:25797166

Bernal, Claudia; Illanes, Andres; Wilson, Lorena

2015-04-15

113

Ultrasound assisted synthesis of imidazolium salts: an efficient way to ionic liquids.  

PubMed

In this study a straightforward and efficient approach concerning synthesis of 1,3-diazole derivatives under ultrasound (US) irradiation as well as under conventional thermal heating (TH) is presented. N-alkylation under US irradiation may be considered environmentally friendly in terms of higher yields, smaller amounts of solvent used and an overall energy efficiency due to a substantial reduction of reaction times. A comparative study of ultrasound vs. conventional conditions has been performed. Overall, the use of US proved to be more efficient than TH. A possible explanation concerning the different behavior of imidazole and benzimidazole in the N1-alkylation reactions under US irradiation was proposed. PMID:25465880

Zbancioc, Gheorghita; Mangalagiu, Ionel I; Moldoveanu, Costel

2015-03-01

114

Facile, efficient, and diastereoselective synthesis of heterohelicene-like molecules.  

PubMed

A concise and efficient route to new and interesting heterohelicene-like molecules has been developed through the one-pot, cascade reductive coupling reaction of o-hydroxydiimines or o-nitrodiimines and triphosgene in the presence of TiCl4/Sm. Purification of the final products only required a single recrystallization leading to high purity. High diastereoselectivity was also achieved, and two structures of the final products were confirmed by X-ray diffraction analysis. PMID:23451838

Lin, Wei; Dou, Guo-Lan; Hu, Ming-Hua; Cao, Cheng-Pao; Huang, Zhi-Bin; Shi, Da-Qing

2013-03-15

115

An efficient prebiotic synthesis of cytosine and uracil  

NASA Technical Reports Server (NTRS)

In contrast to the purines, the routes that have been proposed for the prebiotic synthesis of pyrimidines from simple precursors give only low yields. Cytosine can be synthesized from cyanoacetylene and cyanate; the former precursor is produced from a spark discharge in a CH4/N2 mixture and is an abundant interstellar molecule. But this reaction requires relatively high concentrations of cyanate (> 0.1 M), which are unlikely to occur in aqueous media as cyanate is hydrolysed rapidly to CO2 and NH3. An alternative route that has been explored is the reaction of cyanoacetaldehyde (formed by hydrolysis of cyanoacetylene) with urea. But at low concentrations of urea, this reaction produces no detectable quantities of cytosine. Here we show that in concentrated urea solution--such as might have been found in an evaporating lagoon or in pools on drying beaches on the early Earth--cyanoacetaldehyde reacts to form cytosine in yields of 30-50%, from which uracil can be formed by hydrolysis. These reactions provide a plausible route to the pyrimidine bases required in the RNA world.

Robertson, M. P.; Miller, S. L.

1995-01-01

116

New mono- and diethynylsiloxysilsesquioxanes--efficient procedures for their synthesis.  

PubMed

Ethynyl-substituted siloxysilsesquioxanes are promising building blocks for a wide range of substances based on a POSS/DDSQ core, especially for (oligo-)polymer syntheses and modifications (the formation of hybrid materials with interesting photophysical and mechanical properties). In this study, we report on a series of new mono- and diethynylsiloxysilsesquioxanes formed via an efficient and highly selective one-pot process from silsesquioxanes with reactive Si-OH groups based on sequential condensation, hydrolysis, chlorination and substitution reactions. All newly synthesized compounds were isolated and characterized by spectroscopic methods. PMID:25047114

Dudziec, Beata; Rzonsowska, Monika; Marciniec, Bogdan; Brz?kalski, Dariusz; Wo?niak, Bartosz

2014-09-21

117

An Efficient, Optimized Synthesis of Fentanyl and Related Analogs  

PubMed Central

The alternate and optimized syntheses of the parent opioid fentanyl and its analogs are described. The routes presented exhibit high-yielding transformations leading to these powerful analgesics after optimization studies were carried out for each synthetic step. The general three-step strategy produced a panel of four fentanyls in excellent yields (73–78%) along with their more commonly encountered hydrochloride and citric acid salts. The following strategy offers the opportunity for the gram-scale, efficient production of this interesting class of opioid alkaloids. PMID:25233364

Valdez, Carlos A.; Leif, Roald N.; Mayer, Brian P.

2014-01-01

118

An efficient, optimized synthesis of fentanyl and related analogs.  

PubMed

The alternate and optimized syntheses of the parent opioid fentanyl and its analogs are described. The routes presented exhibit high-yielding transformations leading to these powerful analgesics after optimization studies were carried out for each synthetic step. The general three-step strategy produced a panel of four fentanyls in excellent yields (73-78%) along with their more commonly encountered hydrochloride and citric acid salts. The following strategy offers the opportunity for the gram-scale, efficient production of this interesting class of opioid alkaloids. PMID:25233364

Valdez, Carlos A; Leif, Roald N; Mayer, Brian P

2014-01-01

119

Efficient enzymatic synthesis of ampicillin by mutant Alcaligenes faecalis penicillin G acylase.  

PubMed

Semi-synthetic ?-lactam antibiotics (SSBAs) are one of the most important antibiotic families in the world market. Their enzymatic synthesis can be catalyzed by penicillin G acylases (PGAs). In this study, to improve enzymatic synthesis of ampicillin, site-saturating mutagenesis was performed on three conserved amino acid residues: ?F24, ?R146, and ?F147 of thermo-stable penicillin G acylase from Alcaligenes faecalis (Af PGA). Four mutants ?F24G, ?F24A, ?F24S, and ?F24P were recovered by screening the mutant bank. Kinetic analysis of them showed up to 800-fold increased kcat/Km value for activated acyl donor D-phenylglycine methyl ester (D-PGME). When ?F24G was used for ampicillin synthesis under kinetic control at industrially relevant conditions, 95% of nucleophile 6-aminopenicillanic acid (6-APA) was converted to ampicillin in aqueous medium at room temperature while 12% process time is needed to reach maximum product accumulation at 25% enzyme concentration compared with the wild-type Af PGA. Consequently, process productivity of enzymatic synthesis of ampicillin catalyzed by Af PGA was improved by more than 130 times, which indicated an enzyme viable for efficient SSBAs synthesis. PMID:25681630

Deng, Senwen; Su, Erzheng; Ma, Xiaoqiang; Yang, Shengli; Wei, Dongzhi

2015-04-10

120

ACCESS 1: Approximation Concepts Code for Efficient Structural Synthesis program documentation and user's guide  

NASA Technical Reports Server (NTRS)

The program documentation and user's guide for the ACCESS-1 computer program is presented. ACCESS-1 is a research oriented program which implements a collection of approximation concepts to achieve excellent efficiency in structural synthesis. The finite element method is used for structural analysis and general mathematical programming algorithms are applied in the design optimization procedure. Implementation of the computer program, preparation of input data and basic program structure are described, and three illustrative examples are given.

Miura, H.; Schmit, L. A., Jr.

1976-01-01

121

Silica-ZnCl2: An Efficient Catalyst for the Synthesis of 4-Methylcoumarins  

PubMed Central

Silica-ZnCl2 has been found to be an efficient and eco-friendly catalyst for the synthesis of substituted 4-methylcoumarins from ethyl acetoacetate and substituted phenols under “neat” conditions in an oil bath at 80°C. The experimental procedure is simple, includes shorter reaction times (15–65?min), compatible with sensitive functional groups, and results in excellent yield of the products. PMID:24455295

Datta, Bandita; Pasha, Mohamed Afzal

2013-01-01

122

Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes  

Microsoft Academic Search

We demonstrate the efficient chemical vapor deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above

Kenji Hata; Don N. Futaba; Kohei Mizuno; Tatsunori Namai; Motoo Yumura; Sumio Iijima

2004-01-01

123

Efficient microwave-assisted synthesis of novel 3-aminohexahydrocoumarin derivatives and evaluation on their cytotoxicity  

Microsoft Academic Search

The efficient synthesis of novel 3-aminohexahydrocoumarin derivatives with high diastereoselectivity, wide applicability, short reaction time, high yields as well as operational simplicity was achieved via microwave-assisted reactions of dimedone or cyclohexane-1,3-dione with 4-arylidene-2-phenyloxazol-5(4H)-ones. Moreover, these novel compounds were subject to the test of in vitro cytotoxicity to carcinoma SW1116 and SGC7901 cells. Seven compounds showed stronger cytotoxicity to carcinoma SW1116

Feng Shi; An-Xiao Dai; Shu Zhang; Xiao-Hong Zhang; Shu-Jiang Tu

2011-01-01

124

Effect of Peptides and Amino Acids on Efficiency of Rumen Bacterial Protein Synthesis in Continuous Culture  

Microsoft Academic Search

Five species of rumen bacteria were grown in continuous culture to study effects of peptides and amino acids on efficiency of energy utilization for micro- bial protein synthesis. Decreasing the source of amino acids from .5 g\\/liter to 0 g\\/liter with glucose at .5 g\\/liter caused the yield of bacterial protein to decrease, but the most dramatic effects were from

Michael A. Cotta; James B. Russell

1982-01-01

125

Calorimetrically obtained information about the efficiency of ectoine synthesis from glucose in Halomonas elongata.  

PubMed

Compatible solutes are becoming more and more attractive commercially. Thus, knowledge of the efficiency of synthesis of compatible solutes from different carbon substrates is very important. As the growth rate and rates of formation of compatible solutes correspond to the heat flux, calorimetric measurements are particularly suitable for providing this information. By growing microorganisms continuously in a calorimeter, and generating a feeding stream with gradually increasing salinity without changing any other growth conditions, we were able to determine the efficiency of growth-associated synthesis of compatible solutes. This was shown for Halomonas elongata DMSZ 2581(T) growing on glucose, which synthesizes (at 25 degrees C) 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) as its main osmotic counterweight. The requirement of biologically usable energy for its growth-associated synthesis was found to be very low: a 100% efficiency of the conversion of the substrate-carbon into ectoine is both theoretically possible and was reached approximately in practice. The growth rate and yield coefficient were essentially independent of the ectoine formation rate, and the rate of substrate-carbon assimilation was far greater than the rate of dissimilation. The specific maximum growth rate was limited by the rate of formation of ectoine. PMID:11420137

Maskow, T; Babel, W

2001-07-01

126

Information and Efficiency in the Nervous System—A Synthesis  

PubMed Central

In systems biology, questions concerning the molecular and cellular makeup of an organism are of utmost importance, especially when trying to understand how unreliable components—like genetic circuits, biochemical cascades, and ion channels, among others—enable reliable and adaptive behaviour. The repertoire and speed of biological computations are limited by thermodynamic or metabolic constraints: an example can be found in neurons, where fluctuations in biophysical states limit the information they can encode—with almost 20–60% of the total energy allocated for the brain used for signalling purposes, either via action potentials or by synaptic transmission. Here, we consider the imperatives for neurons to optimise computational and metabolic efficiency, wherein benefits and costs trade-off against each other in the context of self-organised and adaptive behaviour. In particular, we try to link information theoretic (variational) and thermodynamic (Helmholtz) free-energy formulations of neuronal processing and show how they are related in a fundamental way through a complexity minimisation lemma. PMID:23935475

Sengupta, Biswa; Stemmler, Martin B.; Friston, Karl J.

2013-01-01

127

Efficient synthesis of hexahydroindenopyridines and their potential as melatoninergic ligands.  

PubMed

Hexahydroindenopyridine (HHIP) is an interesting tricyclic piperidine nucleus that is structurally related to melatonin, a serotonin-derived neurohormone. Melatonin receptor ligands have applications in several cellular, neuroendocrine and neurophysiological disorders, including depression and/or insomnia. We report herein an efficient two-step method to prepare new HHIP via enamine C-alkylation-cyclization. The influence of substituents on the benzene ring and the nitrogen atom on melatoninergic receptors has been studied. Among the 25 synthesized HHIPs, some of them containing methylenedioxy (series 2) and 8-chloro-7-methoxy substituents (series 4) on the benzene ring revealed affinity for the MT1 and/or the MT2 receptors within the nanomolar range or low micromolar. Similar activities were also encountered for those presenting urea (4g), N-aryl (2e) and N-alkyl (2f) acetamide functions. Therefore, new synthesized compounds with a HHIP nucleus have emerged as new promising leads towards the discovery of melatoninergic ligands which could provide new therapeutic agents. PMID:25232966

Párraga, Javier; Moreno, Laura; Diaz, Amelia; El Aouad, Noureddine; Galán, Abraham; Sanz, María Jesús; Caignard, Daniel-Henri; Figadère, Bruno; Cabedo, Nuria; Cortes, Diego

2014-10-30

128

Chemoselective cross-linking and functionalization of alginate via Staudinger ligation  

PubMed Central

In this study, we demonstrate the applicability of functionalized alginate to serve as a platform for the covalent cross-linking or immobilization of complimentary phosphine functionalized groups via the chemoselective Staudinger ligation scheme. Azide groups were covalently linked to alginate through a heterobifunctional polyethylene glycol (PEG) linker and carbodiimide. Degree of azide functionalization was varied as a function of carbodiimide concentration and determined by proton nuclear magnetic resonance (1H NMR) and infrared spectroscopy. Spontaneous and covalently cross-linked alginate-PEG gels were generated via the Staudinger ligation scheme upon incubation of the azide functionalized alginate with PEG chains having 1-methyl-2-diphenylphosphino-terephthalate (MDT) as end groups. Modulation of the MDT to N3 ratio resulted in variability of gel characteristics. In addition, azide functionalized alginate retained its capacity to instantaneously form hydrogels via electrostatic interaction with multivalent cations such as Ca2+ and Ba2+. Subsequently, covalent linkage of phosphine functionalized agents post-gelation of the alginate was feasible, as illustrated via linkage of MDT-PEG-carboxyfluorescein. Capitalization of the chemoselective and cell compatible Staudinger ligation scheme for covalent cross-linking of alginate hydrogels may enhance the utility of this polymer for the stable encapsulation of various cell types, in addition to their use in the immobilization of labeling agents, proteins, and other bioactive molecules. PMID:19848408

Gattás-Asfura, Kerim M.; Stabler, Cherie L.

2010-01-01

129

Chemoselective small molecules that covalently modify one lysine in a non-enzyme protein in plasma  

SciTech Connect

A small molecule that could bind selectively to and then react chemoselectively with a non-enzyme protein in a complex biological fluid, such as blood, could have numerous practical applications. Herein, we report a family of designed stilbenes that selectively and covalently modify the prominent plasma protein transthyretin in preference to more than 4,000 other human plasma proteins. They react chemoselectively with only one of eight lysine {epsilon}-amino groups within transthyretin. The crystal structure confirms the expected binding orientation of the stilbene substructure and the anticipated conjugating amide bond. These covalent transthyretin kinetic stabilizers exhibit superior amyloid inhibition potency compared to their noncovalent counterparts, and they prevent cytotoxicity associated with amyloidogenesis. Though there are a few prodrugs that, upon metabolic activation, react with a cysteine residue inactivating a specific non-enzyme, we are unaware of designed small molecules that react with one lysine {epsilon}-amine within a specific non-enzyme protein in a complex biological fluid.

Choi, Sungwook; Connelly, Stephen; Reixach, Natàlia; Wilson, Ian A.; Kelly, Jeffery W. (Scripps)

2010-02-19

130

A protecting group-free synthesis of the Colorado potato beetle pheromone  

PubMed Central

Summary A novel synthesis of the aggregation pheromone of the Colorado potato beetle, Leptinotarsa decemlineata, has been developed based on a Sharpless asymmetric epoxidation in combination with a chemoselective alcohol oxidation using catalytic [(neocuproine)PdOAc]2OTf2. Employing this approach, the pheromone was synthesized in 3 steps, 80% yield and 86% ee from geraniol. PMID:24367402

Wu, Zhongtao; Jäger, Manuel; Buter, Jeffrey

2013-01-01

131

A protecting group-free synthesis of the Colorado potato beetle pheromone.  

PubMed

A novel synthesis of the aggregation pheromone of the Colorado potato beetle, Leptinotarsa decemlineata, has been developed based on a Sharpless asymmetric epoxidation in combination with a chemoselective alcohol oxidation using catalytic [(neocuproine)PdOAc]2OTf2. Employing this approach, the pheromone was synthesized in 3 steps, 80% yield and 86% ee from geraniol. PMID:24367402

Wu, Zhongtao; Jäger, Manuel; Buter, Jeffrey; Minnaard, Adriaan J

2013-01-01

132

Novelties of kinetics of chemoselective reduction of citronellal to citronellol by sodium borohydride under liquid–liquid phase transfer catalysis  

Microsoft Academic Search

Borohydride reductions, although common, have not been studied from kinetic and mechanistic view points due to complex chemistry and more so, there is no report on kinetics and mechanism of such reductions under phase transfer catalysis. The novelties of phase transfer catalysed chemoselective reduction of citronellal to citronellol using sodium borohydride were studied in detail in liquid–liquid phase transfer catalysis

Ganapati D. Yadav; Sharad V. Lande

2006-01-01

133

Reversing the Role of the Metal-Oxygen -Bond. Chemoselective Catalytic Reductions with a Rhenium(V)-Dioxo Complex  

E-print Network

Reversing the Role of the Metal-Oxygen -Bond. Chemoselective Catalytic Reductions with a Rhenium addition of the Si-H bond to a metal ligand -bond (eq 2). The overall effect of this process is to convert- and moisture-tolerant catalytic one-step reduction-protection of carbonyl groups employing rhenium

Toste, Dean

134

Simple and Efficient Purification Protocol of 9-(Trifluoroacetyl)anthracene from Anthracene  

Microsoft Academic Search

A protocol has been developed to purify 9-(trifluoroacetyl)anthracene from anthracene, the major impurity associated in its synthesis. The protocol utilizes a chemoselective thermal Diels–Alder reaction, employing maleic anhydride as the dienophile. The resulting Diels–Alder adduct can then be removed by extractive workup followed by recrystallization to give 9-(trifluoroacetyl)anthracene with ?99% chemical purity.

Justin R. Denton

2011-01-01

135

Efficient synthesis of silver nanoparticles from Prosopis juliflora leaf extract and its antimicrobial activity using sewage  

NASA Astrophysics Data System (ADS)

In this paper, aqueous extract of fresh leaves of Prosopis juliflora was used for the synthesis of silver (Ag) nanoparticles. UV-Vis spectroscopy studies were carried out to asses silver nanoparticles formation within 5 min, scanning electron microscopic was used to characterize shape of the Ag nanoparticles, X-ray diffraction analysis confirms the nanoparticles as crystalline silver and facecentered cubic type and Fourier transform infra-red assed that shows biomolecule compounds which are responsible for reduction and capping material of silver nanoparticles. The anti microbial activity of silver nanoparticle was performed using sewage. The approach of plant-mediated synthesis appears to be cost efficient, eco-friendly and easy methods.

Raja, K.; Saravanakumar, A.; Vijayakumar, R.

2012-11-01

136

Robust and efficient, yet uncatalyzed, synthesis of trialkylsilyl-protected cyanohydrins from ketones.  

PubMed

High-yielding cyanosilylation of ketones with NaCN and various chlorotrialkylsilanes in DMSO proceeds smoothly without catalysis to give silyl-protected ketone cyanohydrins. The unique role of DMSO consists in rendering naked cyanide anions that reversibly add to the C double bond O bond at the rate-determining step followed by fast trapping of the transient tertiary sodium cyanoalcoholates with chlorotrialkylsilanes or in situ generated cyanotrialkylsilanes. Preparatively, the reaction matches the best known catalytic cyanosilylation systems applying expensive Me(3)SiCN and demonstrates unprecedented efficiency in the synthesis of sterically congested trialkylsilyl-protected cyanohydrins. PMID:18307356

Cabirol, Fabien L; Lim, Angela E C; Hanefeld, Ulf; Sheldon, Roger A; Lyapkalo, Ilya M

2008-03-21

137

Efficient Synthesis of (P-Chirogenic) o-Boronated Phosphines from sec-Phosphine Boranes.  

PubMed

An efficient synthesis of boronated phosphines with an o-phenylene-bridge prepared from sec-phosphine boranes and using benzyne chemistry is reported. Successive reactions of sec-phosphine boranes with n-BuLi and 1,2-dibromobenzene, and then with boron reagents, afford the o-boronatophenylphosphine derivatives in 71% yields. The use of P-chirogenic sec-phosphine boranes leads to the free boronated phosphines with retention of configuration at the P-center after decomplexation. The reaction of P-chirogenic o-boronatophenylphosphine with KHF2 affords the corresponding trifluoroborated phosphine with ee >98%. PMID:25680028

Bayardon, Jérôme; Bernard, Julie; Rémond, Emmanuelle; Rousselin, Yoann; Malacea-Kabbara, Raluca; Jugé, Sylvain

2015-03-01

138

A highly efficient green synthesis of 1, 8-dioxo-octahydroxanthenes  

PubMed Central

SmCl3 (20 mol%) has been used as an efficient catalyst for reaction between aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione at 120°C to give 1,8-dioxo-octahydroxanthene derivatives in high yield. The same reaction in water, at room temperature gave only the open chain analogue of 1,8-dioxo-octahydroxanthene. Use of eco-friendly green Lewis acid, readily available catalyst and easy isolation of the product makes this a convenient method for the synthesis of either of the products. PMID:22152051

2011-01-01

139

Efficient lipase-selective synthesis of dilauryl mannoses by simultaneous reaction–extraction system  

Microsoft Academic Search

An efficient method for enzymatic-selective synthesis of dilauryl mannoses was developed using lipase-catalyzed condensation\\u000a of d-mannose and lauric acid in a simultaneous reaction–extraction system. The highest equilibrium conversion of diesters of 51%\\u000a (1,6-diester: 14%; 3,6-diester: 18%; 4,6-diester: 19%) and the total conversion of mono and dilauryl mannoses of 76% were\\u000a achieved at the n-hexane\\/acetonitrile ratio of 1:1, the molar ratio

Wenbin Zhang; Yinjiao Wang; Khizar Hayat; Xiaoming Zhang; Abbas Shabbar; Biao Feng; Chengsheng Jia

2009-01-01

140

Air-stable gold nanoparticles ligated by secondary phosphine oxides for the chemoselective hydrogenation of aldehydes: crucial role of the ligand.  

PubMed

The synthesis of air-stable and homogeneous gold nanoparticles (AuNPs) employing tert-butyl(naphthalen-1-yl)phosphine oxide as supporting ligand is described via NaBH4 reduction of a Au(I) precursor, [(tert-butyl(naphthalen-1-yl)phosphine oxide)AuCl]2. This highly reproducible and simple procedure furnishes small (1.24 ± 0.16 nm), highly soluble nanoparticles that are found to be highly active catalysts for the hydrogenation of substituted aldehydes, giving high conversions and chemoselectivities for a wide variety of substrates. In addition to catalytic studies the role of the novel stabilizer in the remarkable activity and selectivity exhibited by this system was interrogated thoroughly using a wide range of techniques, including ATR FT-IR, HRMAS NMR, XPS, and EDX spectroscopy. In particular, isotopic labeling experiments enabled us to probe the coordination mode adopted by the SPO ligand bound to the nanoparticle surface by ATR FT-IR spectroscopy. In combination with a series of control experiments we speculate that the SPO ligand demonstrates ligand-metal cooperative effects and plays a seminal role in the heterolytic hydrogenation mechanism. PMID:24444462

Cano, Israel; Chapman, Andrew M; Urakawa, Atsushi; van Leeuwen, Piet W N M

2014-02-12

141

Sodium tetrachloroaurate(III) dihydrate-catalyzed efficient synthesis of 1,5-benzodiazepine and quinoxaline derivatives*  

PubMed Central

Both 1,5-benzodiazepine and quinoxaline derivatives are important heterocycles in pharmaceuticals. We describe an efficient and clean method for the synthesis of 1,5-benzodiazepines from o-phenylenediamine and ketones catalyzed by sodium tetrachloroaurate(III) dihydrate under mild conditions. The catalyst was shown to be equally effective for the synthesis of quinoxalines from o-phenylenediamine and ?-bromo ketones under the similar reaction conditions. This method produced good yields. PMID:20104644

Shi, Ren-xin; Liu, Yun-kui; Xu, Zhen-yuan

2010-01-01

142

Unusual chemoselective Rh(II)-catalysed transformations of ?-diazocarbonyl piperidine cores.  

PubMed

The reactivity of various ?-diazocarbonyl piperidine scaffolds, characterised by an increased molecular complexity, was tested with various Rh(II) catalysts. The structure of the starting reagent is of relevance to the synthetic results. An unexpected dimerisation took place, starting from the simple piperidine scaffold, to give the hexahydrotetrazine ring system. Products derived from a nitrogen ylide intermediate or aromatic substitution (1,3,4,5-tetrahydro-2,5-methanobenzo[c]azepine and 1,2,3,3a-tetrahydrocyclopenta[de]isoquinolin-4(5?H)-one rings, respectively) were obtained from tetrahydroisoquinoline derivatives. The chemoselectivity of the reaction could be controlled by the choice of starting reagent, Rh(II) catalyst and the reaction conditions. Finally, it was found that the azepino heterocycle could coordinate to the catalyst to give new Rh(II) complexes. PMID:25421441

Bonetti, Andrea; Beccalli, Egle; Caselli, Alessandro; Clerici, Francesca; Pellegrino, Sara; Gelmi, Maria Luisa

2015-01-19

143

A coenzyme-independent decarboxylase/oxygenase cascade for the efficient synthesis of vanillin.  

PubMed

Vanillin is one of the most widely used flavor compounds in the world as well as a promising versatile building block. The biotechnological production of vanillin from plant-derived ferulic acid has attracted much attention as a new alternative to chemical synthesis. One limitation of the known metabolic pathway to vanillin is its requirement for expensive coenzymes. Here, we developed a novel route to vanillin from ferulic acid that does not require any coenzymes. This artificial pathway consists of a coenzyme-independent decarboxylase and a coenzyme-independent oxygenase. When Escherichia coli cells harboring the decarboxylase/oxygenase cascade were incubated with ferulic acid, the cells efficiently synthesized vanillin (8.0 mM, 1.2 g?L(-1) ) via 4-vinylguaiacol in one pot, without the generation of any detectable aromatic by-products. The efficient method described here might be applicable to the synthesis of other high-value chemicals from plant-derived aromatics. PMID:25164030

Furuya, Toshiki; Miura, Misa; Kino, Kuniki

2014-10-13

144

Suppression of HLA Expression by Lentivirus-mediated Gene Transfer of siRNA Cassettes and In Vivo Chemoselection to Enhance Hematopoietic Stem Cell Transplantation  

PubMed Central

Current approaches for hematopoietic stem cell (HSC) and organ transplantation are limited by donor and host-mediated immune responses to allo-antigens. Application of these therapies is limited by the toxicity of preparative and post-transplant immunosuppressive regimens and a shortage of appropriate HLA-matched donors. We have been exploring two complementary approaches for genetically modifying donor cells that achieve long-term suppression of cellular proteins that elicit host immune responses to mismatched donor antigens, and provide a selective advantage to genetically engineered donor cells after transplantation. The first approach is based on recent advances that make feasible targeted down-regulation of HLA expression. Suppression of HLA expression could help to overcome limitations imposed by extensive HLA polymorphisms that restrict the availability of suitable donors. Accordingly, we have recently investigated whether knockdown of HLA by RNA interference (RNAi) enables allogeneic cells to evade immune recognition. For efficient and stable delivery of short hairpin-type RNAi constructs (shRNA), we employed lentivirus-based gene transfer vectors that integrate into genomic DNA, thereby permanently modifying transduced donor cells. Lentivirus-mediated delivery of shRNA targeting pan-Class I and allele-specific HLA achieved efficient and dose-dependent reduction in surface expression of HLA in human cells, and enhanced resistance to allo-reactive T lymphocyte-mediated cytotoxicity, while avoiding non-MHC restricted killing. Complementary strategies for genetic engineering of HSC that would provide a selective advantage for transplanted donor cells and enable successful engraftment with less toxic preparative and immunosuppressive regimens would increase the numbers of individuals to whom HLA suppression therapy could be offered. Our second strategy is to provide a mechanism for in vivo selection of genetically modified HSC and other donor cells. We have uniquely combined transplantation during the neonatal period, when tolerance may be more readily achieved, with a positive selection strategy for in vivo amplification of drug-resistant donor HSC. This model system enables the evaluation of mechanisms of tolerance induction to neo-antigens, and allogeneic stem cells during immune ontogeny. HSC are transduced ex vivo by lentivirus-mediated gene transfer of P140K-O6-methylguanine-methyltransferase (MGMTP140K). The MGMTP140K DNA repair enzyme confers resistance to benzylguanine, an inhibitor of endogenous MGMT, and to chloroethylating agents such as BCNU. In vivo chemoselection enables enrichment of donor cells at the stem cell level. Using complementary approaches of in vivo chemoselection and RNAi-induced silencing of HLA expression may enable the generation of histocompatibility-enhanced, and eventually, perhaps “universally” compatible cellular grafts. PMID:19048410

Hacke, Katrin; Falahati, Rustom; Flebbe-Rehwaldt, Linda; Kasahara, Noriyuki; Gaensler, Karin M. L.

2010-01-01

145

Synthesis and Evaluation of Tetramethylguanidinium-Polyethylenimine Polymers as Efficient Gene Delivery Vectors  

PubMed Central

Previously, we demonstrated that 6-(N,N,N?,N?-tetramethylguanidinium chloride)-hexanoyl-polyethylenimine (THP) polymers exhibited significantly enhanced transfection efficiency and cell viability. Here, in the present study, we have synthesized a series of N,N,N?,N?-tetramethylguanidinium-polyethylenimine (TP1-TP5) polymers via a single-step reaction involving peripheral primary amines of bPEI and varying amounts of 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU). These polymers were found to interact efficiently with negatively charged pDNA and formed stable complexes in the size range of ~240–450?nm. Acid-base titration profiles revealed improved buffering capacity of TP polymers as compared to bPEI. Transfection and cytotoxicity assays performed with TP/pDNA complexes on HEK293, CHO, and HeLa cells showed significantly higher transfection efficiency and cell viability with one of the complexes, TP2/pDNA complex, exhibited the highest transfection efficiency (~1.4–2.3-fold) outcompeting native bPEI and the commercially available transfection reagent, Lipofectamine 2000. Compared to previously reported THP polymers, the transfection efficiency of TP/pDNA complexes was found to be lower, as examined by flow cytometry. These results highlight the importance of the hydrophobic C-6 linker in THP polymers in forming compact nanostructures with pDNA, which might lead to efficient uptake and internalization of the complexes; however, the projected TP polymers offer an advantage of their rapid and economical one-step synthesis. PMID:24864245

Mahato, Manohar; Yadav, Santosh; Kumar, Pradeep; Sharma, Ashwani Kumar

2014-01-01

146

Solvent-controlled halo-selective selenylation of aryl halides catalyzed by Cu(II) supported on Al2O3. A general protocol for the synthesis of unsymmetrical organo mono- and bis-selenides.  

PubMed

Alumina-supported Cu(II) efficiently catalyzes selenylation of aryl iodides and aryl bromides by diaryl, dialkyl, and diheteroaryl diselenides in water and PEG-600, respectively, leading to a general route toward synthesis of unsymmetrical diaryl, aryl-alkyl, aryl-heteroaryl, and diheteroaryl selenides. A sequential reaction of bromoiodobenzene with one diaryl/diheteroaryl/dialkyl diselenide in water and another diaryl/diheteroaryl/dialkyl diselenide in PEG-600 in the second step produces unsymmetrical diaryl, diheteroaryl, or aryl-alkyl bis-selanyl benzene. A library of functionalized organo mono- and bis-selenides, including a potent biologically active molecule and a couple of analogues of bioactive selenides, were obtained in high yields by this protocol. The reactions are chemoselective and high yielding. The Cu-Al2O3 catalyst is recycled for seven runs without any appreciable loss of activity. PMID:23786642

Chatterjee, Tanmay; Ranu, Brindaban C

2013-07-19

147

Nickel nanoparticles catalyzed chemoselective Knoevenagel condensation of Meldrum’s acid and tandem enol lactonizations via cascade cyclization sequence  

Microsoft Academic Search

A novel protocol has been reported wherein, polyethylene glycol (PEG) stabilized nickel nanoparticles have been used as catalyst for chemoselective Knoevenagel condensation of aromatic aldehydes and Meldrum’s acid to give 5-arylidene Meldrum’s acid which underwent tandem enol lactonization by Michael addition\\/cyclization sequence with active methylene compounds in the presence of Ni nanoparticles to give corresponding enol lactone derivatives.

Jitender M. Khurana; Kanika Vij

2011-01-01

148

Design and Synthesis of Novel Block Copolymers for Efficient Opto-Electronic Applications  

NASA Technical Reports Server (NTRS)

It has been predicted that nano-phase separated block copolymer systems containing electron rich donor blocks and electron deficient acceptor blocks may facilitate the charge carrier separation and migration in organic photovoltaic devices due to improved morphology in comparison to polymer blend system. This paper presents preliminary data describing the design and synthesis of a novel Donor-Bridge-Acceptor (D-B-A) block copolymer system for potential high efficient organic optoelectronic applications. Specifically, the donor block contains an electron donating alkyloxy derivatized polyphenylenevinylene (PPV), the acceptor block contains an electron withdrawing alkyl-sulfone derivatized polyphenylenevinylene (PPV), and the bridge block contains an electronically neutral non-conjugated aliphatic hydrocarbon chain. The key synthetic strategy includes the synthesis of each individual block first, then couple the blocks together. While the donor block stabilizes and facilitates the transport of the holes, the acceptor block stabilizes and facilitates the transport of the electrons, the bridge block is designed to hinder the probability of electron-hole recombination. Thus, improved charge separation and stability are expected with this system. In addition, charge migration toward electrodes may also be facilitated due to the potential nano-phase separated and highly ordered block copolymer ultra-structure.

Sun, Sam-Shajing; Fan, Zhen; Wang, Yiqing; Taft, Charles; Haliburton, James; Maaref, Shahin

2002-01-01

149

Phosphinoyl and Thiophosphinoylcarbodithioates: Synthesis, Molecular Structure, and Application as New Efficient Mediators for RAFT Polymerization.  

PubMed

New phosphinoyl and thiophosphinoylcarbodithioates were synthesized in a one-pot reaction from the corresponding phosphinochalcogenides. Compounds of this new generation of thiocarbonylthio derivatives have been fully characterized by IR as well as (1) H, (31) P, and (13) C?NMR spectroscopy and by mass spectrometry. Their solid-state structures reveal that they are isostructural but crystallize in different space groups. These new compounds are highly efficient reversible chain-transfer agents for the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St) and n-butyl acrylate (nBA), with controlled number-average molecular weights (Mn ) and narrow dispersity values (Ð<1.3). The controlled character of the polymerization was further exemplified by MALDI-TOF mass spectrometry and the synthesis of PSt-P(nBA) diblock copolymers. PMID:25476265

Mazières, Stéphane; Kulai, Ihor; Geagea, Roland; Ladeira, Sonia; Destarac, Mathias

2015-01-19

150

Efficient microwave-assisted synthesis of novel 3-aminohexahydrocoumarin derivatives and evaluation on their cytotoxicity.  

PubMed

The efficient synthesis of novel 3-aminohexahydrocoumarin derivatives with high diastereoselectivity, wide applicability, short reaction time, high yields as well as operational simplicity was achieved via microwave-assisted reactions of dimedone or cyclohexane-1,3-dione with 4-arylidene-2-phenyloxazol-5(4H)-ones. Moreover, these novel compounds were subject to the test of in vitro cytotoxicity to carcinoma SW1116 and SGC7901 cells. Seven compounds showed stronger cytotoxicity to carcinoma SW1116 cells than doxorubicin hydrochloride at the concentration of 10 ug/mL. Nearly all the tested compounds exhibited strong or moderate cytotoxicity to SGC7901 cells with IC(50) values from 5.127 to 0.158 ug/mL. PMID:21247667

Shi, Feng; Dai, An-Xiao; Zhang, Shu; Zhang, Xiao-Hong; Tu, Shu-Jiang

2011-03-01

151

Synthesis and Cross-Coupling of Secondary Ammoniomethyltrifluoroborates: Rapid and Efficient Access to Secondary Arylmethylamines  

PubMed Central

Ammoniomethyl trifluoroborates are very powerful reagents that can be used to access biologically relevant aryl- and heteroaryl-methylamine motifs via Suzuki-Miyaura cross-couplings. Until now, this method was limited to the production of tertiary and primary amines. The synthesis of a large array of secondary ammoniomethyltrifluoroborates has been achieved via a one step nucleophilic substitution reaction on the potassium bromomethyltrifluoroborate. Smooth cross-coupling conditions have been designed, based on the use of an aminobiphenyl palladium precatalyst, to couple these trifluoroborates efficiently with aryl bromides. This strategy offers a new way to access biologically relevant motifs and allows, with the previously developed methods, access to all three classes of aminomethylarenes. PMID:22767518

Fleury-Brégeot, Nicolas; Raushel, Jessica; Sandrock, Deidre L.

2012-01-01

152

Micelle-Template Synthesis of Nitrogen-Doped Mesoporous Graphene as an Efficient Metal-Free Electrocatalyst for Hydrogen Production  

PubMed Central

Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications. PMID:25523276

Huang, Xiaodan; Zhao, Yufei; Ao, Zhimin; Wang, Guoxiu

2014-01-01

153

Micelle-Template Synthesis of Nitrogen-Doped Mesoporous Graphene as an Efficient Metal-Free Electrocatalyst for Hydrogen Production  

NASA Astrophysics Data System (ADS)

Synthesis of mesoporous graphene materials by soft-template methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micelle-template strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications.

Huang, Xiaodan; Zhao, Yufei; Ao, Zhimin; Wang, Guoxiu

2014-12-01

154

The total synthesis of (-)-nitidasin.  

PubMed

Nitidasin is a pentacyclic sesterterpenoid with a rare 5-8-6-5 carbon skeleton that was isolated from the Peruvian folk medicine "Hercampuri". It belongs to a small class of sesterterpenoids that feature an isopropyl trans-hydrindane moiety fused to a variety of other ring systems. As a first installment of our general approach toward these natural products, we report the total synthesis of the title compound. Our stereoselective, convergent route involves the addition of a complex alkenyl lithium compound to a trans-hydrindanone, followed by chemoselective epoxidation, ring-closing olefin metathesis, and redox adjustment. PMID:24962933

Hog, Daniel T; Huber, Florian M E; Mayer, Peter; Trauner, Dirk

2014-08-01

155

Cyanuric Chloride as an Efficient Catalyst for the Synthesis of 2,3-Unsaturated O-Glycosides by Ferrier Rearrangement  

PubMed Central

Cyanuric chloride has been found to be an efficient catalyst for the synthesis of 2,3-unsaturated O-glycosides from the reaction of 3,4,6-tri-O-acetyl-D-glucal and a wide range of alcohols in dichloromethane at room temperature. The experimental procedure is simple, and the products are obtained in high yields. PMID:24574881

Yang, Xiaojuan; Li, Na

2014-01-01

156

AN EFFICIENT AND SIMPLE AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES  

EPA Science Inventory

An efficient and clean synthesis of N-aryl azacycloalkanes from alkyl dihalides and aniline derivatives has been achieved using microwave irradiation in an aqueous potassium carbonate medium. The phase separation can simplify the product isolation and reduce usage of vol...

157

Efficient Nazarov cyclization/Wagner-Meerwein rearrangement terminated by a Cu(II)-promoted oxidation: synthesis of 4-alkylidene cyclopentenones.  

PubMed

The discovery and elucidation of a new Nazarov cyclization/Wagner-Meerwein rearrangement/oxidation sequence is described that constitutes an efficient strategy for the synthesis of 4-alkylidene cyclopentenones. DFT computations and EPR experiments were conducted to gain further mechanistic insight into the reaction pathways. PMID:23436470

Lebœuf, David; Theiste, Eric; Gandon, Vincent; Daifuku, Stephanie L; Neidig, Michael L; Frontier, Alison J

2013-04-01

158

Efficient Nazarov Cyclization/Wagner-Meerwein Rearrangement Terminated by a Cu(II)-Promoted Oxidation: Synthesis of 4-Alkylidene Cyclopentenones  

PubMed Central

The discovery and elucidation of a novel Nazarov cyclization/Wagner-Meerwein rearrangement/oxidation sequence is described, which constitutes an efficient strategy for the synthesis of 4-alkylidene cyclopentenones. DFT computations and EPR experiments were conducted to gain further mechanistic insight into the reaction pathways. PMID:23436470

Lebœuf, David; Theiste, Eric; Gandon, Vincent; Daifuku, Stephanie L.; Neidig, Michael L.

2013-01-01

159

Ceric Ammonium Nitrate (CAN): An Efficient Catalyst for the Coumarin Synthesis via Pechmann Condensation using Conventional Heating and Microwave Irradiation  

Microsoft Academic Search

An efficient and convenient method for the synthesis of substituted coumarins via Pechmann condensation of different phenols with ethylacetoacetate in the presence of ammonium cerium(IV) nitrate as the catalyst in a solvent- free media using both conventional heating and microwave irradiation.

Y. Thirupathi Reddy; Vijayakumar N. Sonar; Peter A. Crooks; Pavan K. Dasari; P. Narsimha Reddy; B. Rajitha

2008-01-01

160

Effects of nitric oxide and its synthesis inhibitor on neuron efficiency detected by a fiber-optic-based multisensor  

NASA Astrophysics Data System (ADS)

Sodium nitroprusside (SNP) as an exogenous nitric oxide (NO) donor and N(omega) -nitro-L-arginine methyl ester(L-NAME) as NO synthesis inhibitor was driven into monkey cortex by iontophoresis, their effects on face recognition of monkey were observed, and neuron firing as well as neuron efficiency were monitored by fiberoptic-based multisensor during face recognition. The results show that L-NAME and low dose of SNP(5 nM) did not have any significant effect on face recognition and neuron efficiency, however high dose of SNP(50 nM) increased simultaneously both correct rate of face recognition and neuron efficiency, but not neuron firing. The results were discussed according to NO and its synthesis mechanism.

Shen, Zheng; Hua, Jun; Lin, Shuzhi; Liu, Xiangfeng

1998-01-01

161

A Highly Practical Copper(I)/TEMPO Catalyst System for Chemoselective Aerobic Oxidation of Primary Alcohols  

PubMed Central

Aerobic oxidation reactions have been the focus of considerable attention, but their use in mainstream organic chemistry has been constrained by limitations in their synthetic scope and by practical factors, such as the use of pure O2 as the oxidant or complex catalyst synthesis. Here, we report a new (bpy)CuI/TEMPO catalyst system that enables efficient and selective aerobic oxidation of a broad range of primary alcohols, including allylic, benzylic and aliphatic derivatives, to the corresponding aldehydes using readily available reagents, at room temperature with ambient air as the oxidant. The catalyst system is compatible with a wide range of functional groups and the high selectivity for 1° alcohols enables selective oxidation of diols that lack protecting groups. PMID:21861488

Hoover, Jessica M.; Stahl, Shannon S.

2011-01-01

162

Multifunctional organoboron compounds for scalable natural product synthesis  

NASA Astrophysics Data System (ADS)

Efficient catalytic reactions that can generate C-C bonds enantioselectively, and ones that can produce trisubstituted alkenes diastereoselectively, are central to research in organic chemistry. Transformations that accomplish these two tasks simultaneously are in high demand, particularly if the catalysts, substrates and reagents are inexpensive and if the reaction conditions are mild. Here we report a facile multicomponent catalytic process that begins with a chemoselective, site-selective and diastereoselective copper-boron addition to a monosubstituted allene; the resulting boron-substituted organocopper intermediates then participate in a similarly selective allylic substitution. The products, which contain a stereogenic carbon centre, a monosubstituted alkene and an easily functionalizable Z-trisubstituted alkenylboron group, are obtained in up to 89 per cent yield, with more than 98 per cent branch-selectivity and stereoselectivity and an enantiomeric ratio greater than 99:1. The copper-based catalyst is derived from a robust heterocyclic salt that can be prepared in multigram quantities from inexpensive starting materials and without costly purification procedures. The utility of the approach is demonstrated through enantioselective synthesis of gram quantities of two natural products, namely rottnestol and herboxidiene (also known as GEX1A).

Meng, Fanke; McGrath, Kevin P.; Hoveyda, Amir H.

2014-09-01

163

Efficient synthesis of tension modulation in strings and membranes based on energy estimation.  

PubMed

String and membrane vibrations cannot be considered as linear above a certain amplitude due to the variation in string or membrane tension. A relevant special case is when the tension is spatially constant and varies in time only in dependence of the overall string length or membrane surface. The most apparent perceptual effect of this tension modulation phenomenon is the exponential decay of pitch in time. Pitch glides due to tension modulation are an important timbral characteristic of several musical instruments, including the electric guitar and tom-tom drum, and many ethnic instruments. This paper presents a unified formulation to the tension modulation problem for one-dimensional (1-D) (string) and two-dimensional (2-D) (membrane) cases. In addition, it shows that the short-time average of the tension variation, which is responsible for pitch glides, is approximately proportional to the system energy. This proportionality allows the efficient physics-based sound synthesis of pitch glides. The proposed models require only slightly more computational resources than linear models as opposed to earlier tension-modulated models of higher complexity. PMID:22280712

Avanzini, Federico; Marogna, Riccardo; Bank, Balázs

2012-01-01

164

Miniemulsion as efficient system for enzymatic synthesis of acid alkyl esters.  

PubMed

The aim of this work is to devise an efficient enzymatic process for the production of linear alkyl esters in aqueous miniemulsion systems. The esterification reactions of linear alcohols and carboxylic acids were performed with three different enzymes, commercial Amano lipase PS from Pseudomonas cepacia, Lipase type VII from Candida rugosa, and lyophilized Fusarium solani pisi cutinase expressed in Saccharomyces cerevisiae SU50. The miniemulsion system shows a high potential for the synthesis of linear alkyl esters, for example, hexyl octanoate, which could be synthesized with an ester yield of 94% using Amano lipase PS. Even with hydrophilic alcohols as ethanol, ethyl decanoate could be obtained with a concentration of 0.45 M and a yield of 62% using F. s. pisi cutinase as catalyst. High esterification rates for ethyl- and hexyloleate in miniemulsion showed a significant shift in cutinase selectivity towards longer chain length carboxylic acids. The stepwise addition of the alcohol led to an increase of the esterification yield. Moreover, increasing the amount of dispersed organic phase, mainly consisting of the substrates, led to a significant increase of the final ester concentration (e.g., concentration of 1.4 M for ethyl decanoate for the esterification with Amano Lipase PS). PMID:20503297

de Barros, Dragana P C; Fonseca, Luís P; Cabral, Joaquim M S; Aschenbrenner, Eugen M; Weiss, Clemens K; Landfester, Katharina

2010-07-01

165

Biochemical Characterization of a First Fungal Esterase from Rhizomucor miehei Showing High Efficiency of Ester Synthesis  

PubMed Central

Background Esterases with excellent merits suitable for commercial use in ester production field are still insufficient. The aim of this research is to advance our understanding by seeking for more unusual esterases and revealing their characterizations for ester synthesis. Methodology/Principal Findings A novel esterase-encoding gene from Rhizomucor miehei (RmEstA) was cloned and expressed in Escherichia coli. Sequence analysis revealed a 975-bp ORF encoding a 324-amino-acid polypeptide belonging to the hormone-sensitive lipase (HSL) family IV and showing highest similarity (44%) to the Paenibacillus mucilaginosus esterase/lipase. Recombinant RmEstA was purified to homogeneity: it was 34 kDa by SDS-PAGE and showed optimal pH and temperature of 6.5 and 45°C, respectively. The enzyme was stable to 50°C, under a broad pH range (5.0–10.6). RmEstA exhibited broad substrate specificity toward p-nitrophenol esters and short-acyl-chain triglycerols, with highest activities (1,480 U mg?1 and 228 U mg?1) for p-nitrophenyl hexanoate and tributyrin, respectively. RmEstA efficiently synthesized butyl butyrate (92% conversion yield) when immobilized on AOT-based organogel. Conclusion RmEstA has great potential for industrial applications. RmEstA is the first reported esterase from Rhizomucor miehei. PMID:24204998

Liu, Yu; Xu, Haibo; Yan, Qiaojuan; Yang, Shaoqing; Duan, Xiaojie; Jiang, Zhengqiang

2013-01-01

166

Ultrasonic irradiation assisted efficient regioselective synthesis of CF3-containing pyrazoles catalyzed by Cu(OTf)2/Et3N  

PubMed Central

Background Most of the known approaches to the synthesis of CF3-containing organic compounds suffer from serious drawbacks. For example the starting materials required for these methods are rather difficult to obtain, or they are fairly toxic and inconvenient to work with and methods for direct fluorination and trifluoromethylation do not always allow the introduction of the CF3-group at the required position of a molecule. Results An efficient and attractive regioselective synthesis of a series of novel pyrazoles containing the trifluromethyl moiety was achieved using Cu(OTf)2/Et3N as an efficient catalytic system under ultrasonic irradiation. Conclusions Cu(OTf)2/Et3N catalyst showed a great advantage over all the investigated catalysts, and the ultrasonic irradiation method offered high yields of pyrazoles in short reaction time compared with classical conditions. gHMBC spectra of the product were used to rationalize the observed regioselectivity. PMID:23764261

2013-01-01

167

An Efficient Solution-Phase Synthesis of 4,5,7-Trisubstituted Pyrrolo[3,2-d]pyrimidines  

PubMed Central

We have developed an efficient and robust route to synthesize 4,5,7-trisubstituted pyrrolo[3,2-d]pyrimidines as potent kinase inhibitors. This solution-phase synthesis features a SNAr substitution reaction, cross-coupling reaction, one-pot reduction/reductive amination and N-alkylation reaction. These reactions occur rapidly with high yields and have broad substrate scopes. A variety of groups can be selectively introduced into the N5 and C7 positions of 4,5,7-trisubstituted pyrrolopyrimidines at a late stage of the synthesis, thereby providing a highly efficient approach to explore the structure-activity relationships of pyrrolopyrimidine derivatives. Four synthetic analogs have been profiled against a panel of 48 kinases and a new and selective FLT3 inhibitor 9 is identified. PMID:23181516

Zhang, Weihe; Liu, Jing; Stashko, Michael A.; Wang, Xiaodong

2013-01-01

168

Tandem chain walking polymerization and atom transfer radical polymerization for efficient synthesis of dendritic nanoparticles for bioconjugation.  

PubMed

A tandem polymerization methodology, chain walking polymerization (CWP) followed by atom transfer radical polymerization, was developed for efficient synthesis of nanoparticles for bioconjugation. Using the chain walking palladium-alpha-diimine catalyst (catalyst 1), dendritic polymers bearing multiple initiation sites were synthesized and used as macroinitiators for subsequent Cu(I)-mediated ATRP. Control of molecular weight and size of the water-soluble core-shell polymeric nanoparticles was achieved by tuning reaction conditions. Addition of an N-acryloyloxysuccinamide (NAS) monomer at the end of the ATRP afforded NHS-activated polymer nanoparticles. Conjugation with both small dye molecules and protein (ovalbumin) yielded nanoparticle conjugates with relatively high dye or protein per particle ratio. With the efficient synthesis and good biocompatibility, these nanoparticles may find many potential applications in bioconjugation. PMID:16569005

Chen, Guanghui; Huynh, Devan; Felgner, Philip L; Guan, Zhibin

2006-04-01

169

Efficient Synthesis of Poly(hydroxyethyl Methacrylate)-b-Poly(dimethylaminoethyl Methacrylate) Block Copolymer by Atom Transfer Radical Polymerization.  

NASA Astrophysics Data System (ADS)

Polymers containing hydroxyethyl methacrylate (HEMA) and dimethylaminoethyl methacrylate (DMAEMA) have found wide applications in areas such as bioseparation, tissue engineering and controlled drug delivery. The controlled synthesis of block copolymers of PDMAEMA-b-PHEMA from PDMAEMA macroinitiator by atom transfer radical polymerization (ATRP), however, has not been successful due to the loss of chain end functionality during polymerization. We report an ATRP system that affords efficient chain extension from PDMAEMA to HEMA using Cu(0)/1,1,4,7,10,10-hexamethyltriethylenetetramine as the catalyst, 2-chloropropionitrile as the initiator in methanol at room temperature. A clear peak shift in the gel permeation chromatography trace towards shorter elution times indicates chain growth on HEMA addition. The chain end functionalities of PDMAEMA are thus retained and can be used to efficiently initiate chain extension reaction of HEMA. This new synthetic route opens new possibilities for the synthesis of pH- and temperature-responsive systems containing DMAEMA.

Tang, Wei; Loo, Yueh-Lin

2009-03-01

170

An efficient synthesis for a new class antimalarial agent, 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaborole  

Microsoft Academic Search

Efficient synthesis is essential for antimalarial therapeutics. A four-step route has been established for the synthesis of 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaborole 1 that is a potent new class boron-containing antimalarial agent in preclinical development with IC50=26nM against the malaria parasite Plasmodium falciparum.

Yong-Kang Zhang; Jacob J. Plattner; Eric E. Easom; David Waterson; Min Ge; Zhiya Li; Lingchao Li; Yong Jian

2011-01-01

171

A Simple, Efficient Synthesis of 2-Aryl Benzimidazoles Using Silica Supported Periodic Acid Catalyst and Evaluation of Anticancer Activity  

PubMed Central

A new, efficient method for the synthesis of 2-aryl substituted benzimidazole by using silica supported periodic acid (H5IO6-SiO2) as a catalyst has been developed. The salient feature of the present method includes mild reaction condition, short reaction time, high yield and easy workup procedure. The synthesized benzimidazoles exhibited potent anticancer activity against MCF7 and HL60 cell lines. PMID:24052861

Sontakke, Vyankat A.; Ghosh, Sougata; Lawande, Pravin P.; Chopade, Balu A.; Shinde, Vaishali S.

2013-01-01

172

Ionic Liquid as Catalyst and Reaction Medium: A Simple and Efficient Procedure for Paal–Knorr Furan Synthesis  

Microsoft Academic Search

The ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulfate, [bmim]HSO4, efficiently catalyzes Paal–Knorr furan synthesis without any organic solvent. A wide range of aliphatic and aromatic 1,4-diketones easily undergo condensations to form furan derivatives, providing a general and convenient procedure. The Paal–Knorr reaction of ester-substituted 1,4-diketones is first reported. The ionic liquid can be recovered and reused for subsequent runs without any appreciable

Gangqiang Wang; Zhi Guan; Rongchang Tang; Yanhong He

2010-01-01

173

Size Dependence of Atomically Precise Gold Nanoclusters in Chemoselective Hydrogenation and Active Site Structure  

SciTech Connect

We here investigate the catalytic properties of water-soluble Aun(SG)m nanocluster catalysts (H-SG = glutathione) of different sizes, including Au15(SG)13, Au18(SG)14, Au25(SG)18, Au38(SG)24, and captopril-capped Au25(Capt)18 nanoclusters. These Aun(SR)m nanoclusters (-SR represents thiolate generally) are used as homogeneous catalysts (i.e., without supports) in the chemoselective hydrogenation of 4-nitrobenzaldehyde (4-NO2PhCHO) to 4-nitrobenzyl alcohol (4-NO2PhCH2OH) in water with H2 gas (20 bar) as the hydrogen source. These nanocluster catalysts, except Au18(SG)14, remain intact after the catalytic reaction, evidenced by UV-vis spectra which are characteristic of each sized nanoclusters and thus serve as spectroscopic fingerprints . We observe a drastic size-dependence and steric effect of protecting ligands on the gold nanocluster catalysts in the hydrogenation reaction. Density functional theory (DFT) modeling of the 4-nitrobenzaldehyde adsorption shows that both the CHO and NO2 groups are in close interact with the S-Au-S staples on the gold nanocluster surface; the adsorption of the 4-nitrobenzaldehyde molecule on the four different sized Aun(SR)m nanoclusters are moderately strong and similar in strength. The DFT results suggest that the catalytic activity of the Aun(SR)m nanoclusters is primarily determined by the surface area of the Au nanocluster, consistent with the observed trend of the conversion of 4-nitrobenzaldehyde versus the cluster size. Overall, this work offers the molecular insight into the hydrogenation of 4-nitrobenzaldehyde and the catalytically active site structure on gold nanocluster catalysts.

Li, Gao [Carnegie Mellon University (CMU); Jiang, Deen [ORNL; Kumar, Santosh [Carnegie Mellon University (CMU); Chen, Yuxiang [Carnegie Mellon University (CMU); Jin, Rongchao [Carnegie Mellon University (CMU)

2014-01-01

174

Cysteinyl Peptide Capture for Shotgun Proteomics: Global Assessment of Chemoselective Fractionation  

PubMed Central

The complexity of cell and tissue proteomes presents one of the most significant technical challenges in proteomic biomarker discovery. Multidimensional liquid chromatography?tandem mass spectrometry (LC?MS/MS)-based shotgun proteomics can be coupled with selective enrichment of cysteinyl peptides (Cys-peptides) to reduce sample complexity and increase proteome coverage. Here we evaluated the impact of Cys-peptide enrichment on global proteomic inventories. We employed a new cleavable thiol-reactive biotinylating probe, N-(2-(2-(2-(2-(3-(1-hydroxy-2-oxo-2-phenylethyl)phenoxy)acetamido)ethoxy)-ethoxy)ethyl)-5-(2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl)pentanamide (IBB), to capture Cys-peptides after digestion. Treatment of tryptic digests with the IBB reagent followed by streptavidin capture and mild alkaline hydrolysis releases a highly purified population of Cys-peptides with a residual S-carboxymethyl tag. Isoelectric focusing (IEF) followed by LC?MS/MS of Cys-peptides significantly expanded proteome coverage in Saccharomyces cerevisiae (yeast) and in human colon carcinoma RKO cells. IBB-based fractionation enhanced detection of Cys-proteins in direct proportion to their cysteine content. The degree of enrichment typically was 2?8-fold but ranged up to almost 20-fold for a few proteins. Published copy number annotation for the yeast proteome enabled benchmarking of MS/MS spectral count data to yeast protein abundance and revealed selective enrichment of cysteine-rich, lower abundance proteins. Spectral count data further established this relationship in RKO cells. Enhanced detection of low abundance proteins was due to the chemoselectivity of Cys-peptide capture, rather than simplification of the peptide mixture through fractionation. PMID:20731415

2010-01-01

175

Partially reduced iridium oxide clusters dispersed on titania as efficient catalysts for facile synthesis of dimethylformamide from CO2, H2 and dimethylamine.  

PubMed

A novel bifunctional catalyst based on partially reduced iridium oxide supported on TiO2 was found to be exceedingly efficient for the organic-solvent-free synthesis of dimethylformamide from CO2, H2 and dimethylamine. PMID:24990297

Bi, Qing-Yuan; Lin, Jian-Dong; Liu, Yong-Mei; Xie, Song-Hai; He, He-Yong; Cao, Yong

2014-08-21

176

Direct formation of small Cu2O nanocubes, octahedra, and octapods for efficient synthesis of triazoles  

NASA Astrophysics Data System (ADS)

In most studies describing the preparation of Cu2O crystals of various morphologies, the particle sizes are normally hundreds of nanometers to micrometers due to rapid particle growth, so they are not exactly nanocrystals. Here we report surfactant-free formation of sub-100 nm Cu2O nanocrystals with systematic shape evolution from cubic to octahedral structures by preparing an aqueous mixture of Cu(OAc)2, NaOH, and N2H4 solution. Adjustment of the hydrazine volume enables the particle shape control. Uniform nanocubes and octahedra were synthesized with edge lengths of 37 and 67 nm, respectively. Novel Cu2O octapods with an edge length of 135 nm were also produced by mixing CuCl2 solution, SDS surfactant, NaOH solution, and NH2OH.HCl reductant solution. All of them are nearly the smallest Cu2O nanocrystals of the same shapes ever reported. These small cubes, octahedra, and octapods were employed as catalysts in the direct synthesis of 1,2,3-triazoles from the reaction of alkynes, organic halides, and NaN3 at 55 °C. All of them displayed high product yields in short reaction times. The octahedra enclosed by the {111} facets are the best catalysts, and can catalyze this cycloaddition reaction with high yields in just 2 h when different alkynes were used to make diverse triazole products. Hence, the small Cu2O particles provide time-saving, energy-efficient, and high product yield benefits to organocatalysis.In most studies describing the preparation of Cu2O crystals of various morphologies, the particle sizes are normally hundreds of nanometers to micrometers due to rapid particle growth, so they are not exactly nanocrystals. Here we report surfactant-free formation of sub-100 nm Cu2O nanocrystals with systematic shape evolution from cubic to octahedral structures by preparing an aqueous mixture of Cu(OAc)2, NaOH, and N2H4 solution. Adjustment of the hydrazine volume enables the particle shape control. Uniform nanocubes and octahedra were synthesized with edge lengths of 37 and 67 nm, respectively. Novel Cu2O octapods with an edge length of 135 nm were also produced by mixing CuCl2 solution, SDS surfactant, NaOH solution, and NH2OH.HCl reductant solution. All of them are nearly the smallest Cu2O nanocrystals of the same shapes ever reported. These small cubes, octahedra, and octapods were employed as catalysts in the direct synthesis of 1,2,3-triazoles from the reaction of alkynes, organic halides, and NaN3 at 55 °C. All of them displayed high product yields in short reaction times. The octahedra enclosed by the {111} facets are the best catalysts, and can catalyze this cycloaddition reaction with high yields in just 2 h when different alkynes were used to make diverse triazole products. Hence, the small Cu2O particles provide time-saving, energy-efficient, and high product yield benefits to organocatalysis. Electronic supplementary information (ESI) available: SEM images of Cu2O nanocrystals with shape evolution, XRD patterns, calculations for the determination of volumes needed for the catalysis experiment, spectral characterization of the triazole products synthesized and their NMR spectra. See DOI: 10.1039/c4nr02076f

Tsai, Ya-Huei; Chanda, Kaushik; Chu, Yi-Ting; Chiu, Chun-Ya; Huang, Michael H.

2014-07-01

177

Direct formation of small Cu2O nanocubes, octahedra, and octapods for efficient synthesis of triazoles.  

PubMed

In most studies describing the preparation of Cu2O crystals of various morphologies, the particle sizes are normally hundreds of nanometers to micrometers due to rapid particle growth, so they are not exactly nanocrystals. Here we report surfactant-free formation of sub-100 nm Cu2O nanocrystals with systematic shape evolution from cubic to octahedral structures by preparing an aqueous mixture of Cu(OAc)2, NaOH, and N2H4 solution. Adjustment of the hydrazine volume enables the particle shape control. Uniform nanocubes and octahedra were synthesized with edge lengths of 37 and 67 nm, respectively. Novel Cu2O octapods with an edge length of 135 nm were also produced by mixing CuCl2 solution, SDS surfactant, NaOH solution, and NH2OH · HCl reductant solution. All of them are nearly the smallest Cu2O nanocrystals of the same shapes ever reported. These small cubes, octahedra, and octapods were employed as catalysts in the direct synthesis of 1,2,3-triazoles from the reaction of alkynes, organic halides, and NaN3 at 55 °C. All of them displayed high product yields in short reaction times. The octahedra enclosed by the {111} facets are the best catalysts, and can catalyze this cycloaddition reaction with high yields in just 2 h when different alkynes were used to make diverse triazole products. Hence, the small Cu2O particles provide time-saving, energy-efficient, and high product yield benefits to organocatalysis. PMID:24947435

Tsai, Ya-Huei; Chanda, Kaushik; Chu, Yi-Ting; Chiu, Chun-Ya; Huang, Michael H

2014-08-01

178

Chitosan-DNA nanoparticles as gene carriers: synthesis, characterization and transfection efficiency.  

PubMed

Chitosan-DNA nanoparticles were prepared using a complex coacervation process. The important parameters for the nanoparticle synthesis were investigated, including the concentrations of DNA, chitosan and sodium sulfate, temperature of the solutions, pH of the buffer, and molecular weights of chitosan and DNA. At an amino group to phosphate group ratio (N/P ratio) between 3 and 8 and a chitosan concentration of 100 microg/ml, the size of particles was optimized to approximately 100--250 nm with a narrow distribution, with a composition of 35.6 and 64.4% by weight for DNA and chitosan, respectively. The surface charge of these particles was slightly positive with a zeta potential of +12 to +18 mV at pH lower than 6.0, and became nearly neutral at pH 7.2. The chitosan-DNA nanoparticles could partially protect the encapsulated plasmid DNA from nuclease degradation as shown by electrophoretic mobility analysis. The transfection efficiency of chitosan-DNA nanoparticles was cell-type dependent. Typically, it was three to four orders of magnitude, in relative light units, higher than background level in HEK293 cells, and two to ten times lower than that achieved by LipofectAMINE-DNA complexes. The presence of 10% fetal bovine serum did not interfere with their transfection ability. Chloroquine could be co-encapsulated in the nanoparticles at 5.2%, but with negligible enhancement effect despite the fact that chitosan only showed limited buffering capacity compared with PEI. The present study also developed three different schemes to conjugate transferrin or KNOB protein to the nanoparticle surface. The transferrin conjugation only yielded a maximum of four-fold increase in their transfection efficiency in HEK293 cells and HeLa cells, whereas KNOB conjugated nanoparticles could improve gene expression level in HeLa cells by 130-fold. Conjugation of PEG on the nanoparticles allowed lyophilization without aggregation, and without loss of bioactivity for at least 1 month in storage. The clearance of the PEGylated nanoparticles in mice following intravenous administration was slower than unmodified nanoparticles at 15 min, and with higher depositions in kidney and liver. However, no difference was observed at the 1-h time point. PMID:11182210

Mao, H Q; Roy, K; Troung-Le, V L; Janes, K A; Lin, K Y; Wang, Y; August, J T; Leong, K W

2001-02-23

179

Synthesis of Proteins by Native Chemical Ligation  

NASA Astrophysics Data System (ADS)

A simple technique has been devised that allows the direct synthesis of native backbone proteins of moderate size. Chemoselective reaction of two unprotected peptide segments gives an initial thioester-linked species. Spontaneous rearrangement of this transient intermediate yields a full-length product with a native peptide bond at the ligation site. The utility of native chemical ligation was demonstrated by the one-step preparation of a cytokine containing multiple disulfides. The polypeptide ligation product was folded and oxidized to form the native disulfide-containing protein molecule. Native chemical ligation is an important step toward the general application of chemistry to proteins.

Dawson, Philip E.; Muir, Tom W.; Clark-Lewis, Ian; Kent, Stephen B. H.

1994-11-01

180

Iridium-Catalyzed Selective Hydrogenation of 3-Hydroxypyridinium Salts: A Facile Synthesis of Piperidin-3-ones.  

PubMed

The selective hydrogenation of 3-hydroxypyridinium salts has been achieved using a homogeneous iridium catalyst, providing a direct access to 2- and 4-substituted piperidin-3-one derivatives with high yields, which are important organic synthetic intermediates and the prevalent structural motifs in pharmaceutical agents. Mild reaction conditions, high chemoselectivity, and easy scalability make this reaction highly practical for the synthesis of piperidin-3-ones. PMID:25803488

Huang, Wen-Xue; Wu, Bo; Gao, Xiang; Chen, Mu-Wang; Wang, Baomin; Zhou, Yong-Gui

2015-04-01

181

Asymmetric Synthesis of 1,2-dioxanes: Approaches to the Peroxyplakoric Acids  

PubMed Central

The stereospecific intramolecular alkylation of a hydroperoxyacetal provides the basis for the first asymmetric synthesis of the dioxane propionate core of the peroxyplakorates. Chemoselective hydrometallation of an alkyne in the presence of a peroxide is used to introduce a synthon for the polyunsaturated side chains of the peroxyplakorates. The route suggests a general solution for the 1,2-dioxane unit in many peroxide natural products. PMID:20160918

Xu, Chunping; Schwartz, Chris; Raible, Joseph; Dussault, Patrick H.

2009-01-01

182

Simple and efficient synthesis of novel glycosyl thiourea derivatives as potential antitumor agents  

Microsoft Academic Search

The practical synthesis of pseudonucleosides incorporating thiourea derivative by coupling of monosaccharides (d-galactose, d-glucose and d-xylose) per-O-acetylated glycosyl isothiocyanates and different heterocyclic hydrazide derivatives is reported. The method involves the preparation of per-O-acetylated glycosyl isothiocyanates from per-O-acetylated sugars (two-step synthesis), which couple with heterocyclic hydrazides from amines to give thiourea-linked pseudonucleosides. All newly synthesized pseudonucleosides were assayed against human lung

Zhang Shusheng; Zhan Tianrong; Cheng Kun; Xia Youfeng; Yang Bo

2008-01-01

183

Efficient and green synthesis of tetrasubstituted pyrroles promoted by task-specific basic ionic liquids as catalyst in aqueous media.  

PubMed

Synthesis of tetrasubstituted pyrroles by the three-component condensation reaction of acid chlorides, dialkyl acetylenedicarboxylates, and amino acids in the presence of various room-temperature ionic liquids (RTILs) as catalysts in water is reported. Among the ionic liquids used, the basic functionalized ionic liquid, butyl methyl imidazolium hydroxide [bmim]OH, was the most effective catalyst. The influence of reaction temperature, reaction time, and amount of ionic liquid on the reaction was investigated. The [bmim]OH/H(2)O catalyst system could be reused for at least five recycles without appreciable loss of efficiency. PMID:19381850

Yavari, Issa; Kowsari, Elaheh

2009-11-01

184

Supported and non-supported ruthenium(II)/phosphine/[3-(2-aminoethyl)aminopropyl]trimethoxysilane complexes and their activities in the chemoselective hydrogenation of trans-4-phenyl-3-butene-2-al.  

PubMed

Syntheses of four new ruthenium(II) complexes of the [RuCl(2)(P)(2)(N)(2)] type using 2-(diphenylphosphino)ethyl methyl ether (P-O) as ether-phosphine and triphenylphosphine (PPh(3)) as monodentate phosphine ligands in the presence of [3-(2-aminoethyl)aminopropyl]trimethoxysilane as diamine co-ligand are presented for the first time. The reactions were conducted at room temperature and under an inert atmosphere. Due to the presence of the trimethoxysilane group in the backbone of complexes 1 and 2 they were subjected to an immobilization process using the sol-gel technique in the presence of tetraethoxysilane as cross-linker. The structural behavior of the phosphine ligands in the desired complexes during synthesis were monitored by (31)P{(1)H}-NMR. Desired complexes were deduced from elemental analyses, Infrared, FAB-MS and (1)H-, (13)C- and (31)P-NMR spectroscopy, xerogels X1 and X2 were subjected to solid state, (13)C-, (29)Si- and (31)P-NMR spectroscopy, Infrared and EXAF. These complexes served as hydrogenation catalysts in homogenous and heterogeneous phases, and chemoselective hydrogenation of the carbonyl function group in trans-4-phenyl-3-butene-2-al was successfully carried out under mild basic conditions. PMID:20657383

Warad, Ismail

2010-07-01

185

Air- and moisture-stable amphoteric molecules: enabling reagents in synthesis.  

PubMed

Researchers continue to develop chemoselective synthesis strategies with the goal of rapidly assembling complex molecules. As one appealing approach, chemists are searching for new building blocks that include multiple functional groups with orthogonal chemical reactivity. Amphoteric molecules that possess nucleophilic and electrophilic sites offer a versatile platform for the development of chemoselective transformations. As part of a program focused on new methods of synthesis, we have been developing this type of reagents. This Account highlights examples of amphoteric molecules developed by our lab since 2006. We have prepared and evaluated aziridine aldehydes, a class of stable unprotected ?-amino aldehydes. Structurally, aziridine aldehydes include both a nucleophilic amine nitrogen and an electrophilic aldehyde carbon over the span of three atoms. Under ambient conditions, these compounds exist as homochiral dimers with an aziridine-fused five-membered cyclic hemiaminal structure. We have investigated chemoselective reactions of aziridine aldehydes that involve both the aziridine and aldehyde functionalities. These transformations have produced a variety of densely functionalized nitrogen-containing compounds, including amino aldehydes, 1,2-diamines, reduced hydantoins, C-vinyl or alkynyl aziridines, and macrocyclic peptides. We have also developed air- and moisture-stable ?-boryl aldehydes, another class of molecules that are kinetically amphoteric. The ?-boryl aldehydes contain a tetracoordinated N-methyliminodiacetyl (MIDA) boryl substituent, which stabilizes the ?-metalloid carbonyl system and prevents isomerization to its O-bond enolate form. Primarily taking advantage of chemoselective transformations at the aldehyde functionality, these ?-boryl aldehydes have allowed us to synthesize a series of new functionalized boron-containing compounds that are difficult or impossible to prepare using established protocols, such as ?-borylcarboxylic acids, boryl alcohols, enol ethers, and enamides. Using ?-borylcarboxylic acids as starting materials, we have also prepared several new amphoteric borylated reagents, such as ?-boryl isocyanates, isocyanides, and acylboronates. These compounds are versatile building blocks in their own right, enabling the rapid synthesis of other boron-containing molecules. PMID:24495255

He, Zhi; Zajdlik, Adam; Yudin, Andrei K

2014-04-15

186

Unusual pyrimidine participation: efficient stereoselective synthesis of potent dual orexin receptor antagonist MK-6096.  

PubMed

An asymmetric synthesis of dual orexin receptor antagonist MK-6096 (1) is described. Key steps for the trans-2,5-disubstituted piperidinyl ether fragment include a biocatalytic transamination, a trans-selective Mukaiyama aldol, and a regioselective pyridyl SNAr process. The pyrimidyl benzoic acid was synthesized via a Negishi coupling and a nitrile hydrolysis. Coupling of the two fragments via a catalytic T3P-mediated amidation completed the synthesis. Unusual behaviors in the hydrolysis of pyrimidyl benzonitrile and the amide coupling of the pyrimidyl benzoic acid are also described. PMID:25365229

Chung, John Y L; Zhong, Yong-Li; Maloney, Kevin M; Reamer, Robert A; Moore, Jeffrey C; Strotman, Hallena; Kalinin, Alexei; Feng, Ronnie; Strotman, Neil A; Xiang, Bangping; Yasuda, Nobuyoshi

2014-11-21

187

Short and Efficient Synthesis of Alkyl- and Aryl-Ortho-Hydroxy-Anilides and their Antibiotic Activity  

PubMed Central

Abstract Ortho-hydroxy-anilides are part of natural products like the new antibiotics platencin (A) and platensimycin (B). An important step in the total synthesis of these antibiotics or their derivatives is the preparation of the o-hydroxy-anilide partial structure. The presented method allows the preparation of o-hydroxy-anilides and o-dihydroxy-anilides from 2-nitrophenol esters in a one-step synthesis without protecting the hydroxy group. Aryl- and alkyl-anilides were prepared following this method as simple analogues of platensimycin (A). The resulting compounds were tested in an agar diffusion assay for their antibiotic potency.

Krauß, Jürgen; Plesch, Eva; Clausen, Sabine; Bracher, Franz

2014-01-01

188

Chemoselective nitro group reduction and reductive dechlorination initiate degradation of 2-chloro-5-nitrophenol by Ralstonia eutropha JMP134  

SciTech Connect

Ralstonia eutropha JMP134 utilizes 2-chloro-5-nitrophenol as a sole source of nitrogen, carbon, and energy. The initial steps for degradation of 2-chloro-5-nitrophenol are analogous to those of 3-nitrophenol degradation in R. eutropha JMP134, 2-chloro-5-nitrophenol is initially reduced to 2-chloro-5-hydroxylaminophenol, which is subject to an enzymatic Bamberger rearrangement yielding 2-amino-5-chlorohydroquinone. The chlorine of 2-amino-5-chlorohydroquinone is removed by a reductive mechanism, and aminohydroquinone is formed. 2-Chloro-5-nitrophenol and 3-nitrophenol induce the expression of 3-nitrophenol nitroreductase, of 3-hydroxylaminophenol mutase, and of the dechlorinating activity. 3-Nitrophenol nitroreductase catalyzes chemoselective reduction of aromatic nitro groups to hydroxylamino groups in the presence of NADPH. 3-Nitrophenol nitroreductase is active with a variety of mono-, di-, and trinitroaromatic compounds, demonstrating a relaxed substrate specificity of the enzyme. Nitrosobenzene serves as a substrate for the enzyme and is converted faster than nitrobenzene.

Schenzle, A.; Lenke, H.; Knackmuss, H.J. [Univ. Stuttgart (Germany); Spain, J.C. [AFRL/MRLQ, Tyndall AFB, FL (United States). Armstrong Lab.

1999-06-01

189

Rapid and efficient ultrasound-assisted method for the combinatorial synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives.  

PubMed

An efficient one-pot synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives by four-component reaction of hydrazine, ?-keto ester, isatin, and malononitrile or ethyl cyanoacetate catalyzed by piperidine under ultrasound irradiation is described. This synthesis was confirmed to follow the group-assistant-purification chemistry (GAP) chemistry process, which can avoid traditional chromatography and recrystallization purifications. PMID:22141731

Zou, Yi; Hu, Yu; Liu, Hai; Shi, Daqing

2012-01-01

190

SpeedyGenes: an improved gene synthesis method for the efficient production of error-corrected, synthetic protein libraries for directed evolution  

PubMed Central

The de novo synthesis of genes is becoming increasingly common in synthetic biology studies. However, the inherent error rate (introduced by errors incurred during oligonucleotide synthesis) limits its use in synthesising protein libraries to only short genes. Here we introduce SpeedyGenes, a PCR-based method for the synthesis of diverse protein libraries that includes an error-correction procedure, enabling the efficient synthesis of large genes for use directly in functional screening. First, we demonstrate an accurate gene synthesis method by synthesising and directly screening (without pre-selection) a 747 bp gene for green fluorescent protein (yielding 85% fluorescent colonies) and a larger 1518 bp gene (a monoamine oxidase, producing 76% colonies with full catalytic activity, a 4-fold improvement over previous methods). Secondly, we show that SpeedyGenes can accommodate multiple and combinatorial variant sequences while maintaining efficient enzymatic error correction, which is particularly crucial for larger genes. In its first application for directed evolution, we demonstrate the use of SpeedyGenes in the synthesis and screening of large libraries of MAO-N variants. Using this method, libraries are synthesised, transformed and screened within 3 days. Importantly, as each mutation we introduce is controlled by the oligonucleotide sequence, SpeedyGenes enables the synthesis of large, diverse, yet controlled variant sequences for the purposes of directed evolution. PMID:25108914

Currin, Andrew; Swainston, Neil; Day, Philip J.; Kell, Douglas B.

2014-01-01

191

Concise formal synthesis of (-)-7-deoxyloganin via N-heterocyclic carbene catalysed rearrangement of ?,?-unsaturated enol esters.  

PubMed

NHC catalysed rearrangement of ?,?-unsaturated enol esters derived from formyl acetates and cyclopentyl annulated ?,?-unsaturated acids provides the cyclopentapyranone core of (-)-7-deoxyloganin (1) with diastereo- and chemoselectivity in 6 steps starting from (-)-citronellal. The elaboration to the natural product has been investigated using two new approaches. The most successful intercepts our previous work on (-)-7-deoxyloganin (1) allowing completion of a formal total synthesis in 10-steps. PMID:22024770

Candish, Lisa; Lupton, David W

2011-12-01

192

Retention of OsNMD3 in the cytoplasm disturbs protein synthesis efficiency and affects plant development in rice  

PubMed Central

The ribosome is the basic machinery for translation, and biogenesis of ribosomes involves many coordinated events. However, knowledge about ribosomal dynamics in higher plants is very limited. This study chose a highly conserved trans-factor, the 60S ribosomal subunit nuclear export adaptor NMD3, to characterize the mechanism of ribosome biogenesis in the monocot plant Oryza sativa (rice). O. sativa NMD3 (OsNMD3) shares all the common motifs and shuttles between the nucleus and cytoplasm via CRM1/XPO1. A dominant negative form of OsNMD3 with a truncated nuclear localization sequence (OsNMD3?NLS) was retained in the cytoplasm, consequently interfering with the release of OsNMD3 from pre-60S particles and disturbing the assembly of ribosome subunits. Analyses of the transactivation activity and cellulose biosynthesis level revealed low protein synthesis efficiency in the transgenic plants compared with the wild-type plants. Pharmaceutical treatments demonstrated structural alterations in ribosomes in the transgenic plants. Moreover, global expression profiles of the wild-type and transgenic plants were investigated using the Illumina RNA sequencing approach. These expression profiles suggested that overexpression of OsNMD3?NLS affected ribosome biogenesis and certain basic pathways, leading to pleiotropic abnormalities in plant growth. Taken together, these results strongly suggest that OsNMD3 is important for ribosome assembly and the maintenance of normal protein synthesis efficiency. PMID:24723395

Shi, Yanyun; Liu, Xiangling; Li, Rui; Gao, Yaping; Xu, Zuopeng; Zhang, Baocai; Zhou, Yihua

2014-01-01

193

Applied reaction dynamics: Efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh(111)  

NASA Astrophysics Data System (ADS)

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh(111) catalytic substrate, CH4+(1/2)O2?CO +2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam's translational energy, and approaches unity for energies greater than ˜1.3eV. Comparison with a simplified model of the methane-Rh(111) reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO +2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C-H bond activation with subsequent thermal heterogeneous reactions.

Gibson, K. D.; Viste, M.; Sibener, S. J.

2006-10-01

194

The methyltransferase domain of dengue virus protein NS5 ensures efficient RNA synthesis initiation and elongation by the polymerase domain  

PubMed Central

Viral RNA-dependent RNA polymerases (RdRps) responsible for the replication of single-strand RNA virus genomes exert their function in the context of complex replication machineries. Within these replication complexes the polymerase activity is often highly regulated by RNA elements, proteins or other domains of multi-domain polymerases. Here, we present data of the influence of the methyltransferase domain (NS5-MTase) of dengue virus (DENV) protein NS5 on the RdRp activity of the polymerase domain (NS5-Pol). The steady-state polymerase activities of DENV-2 recombinant NS5 and NS5-Pol are compared using different biochemical assays allowing the dissection of the de novo initiation, transition and elongation steps of RNA synthesis. We show that NS5-MTase ensures efficient RdRp activity by stimulating the de novo initiation and the elongation phase. This stimulation is related to a higher affinity of NS5 toward the single-strand RNA template indicating NS5-MTase either completes a high-affinity RNA binding site and/or promotes the correct formation of the template tunnel. Furthermore, the NS5-MTase increases the affinity of the priming nucleotide ATP upon de novo initiation and causes a higher catalytic efficiency of the polymerase upon elongation. The complex stimulation pattern is discussed under the perspective that NS5 adopts several conformations during RNA synthesis. PMID:25209234

Potisopon, Supanee; Priet, Stéphane; Collet, Axelle; Decroly, Etienne; Canard, Bruno; Selisko, Barbara

2014-01-01

195

De Novo Asymmetric Synthesis of all D-, all L- and D-/L-Oligosaccharides Using Atom-less Protecting Groups  

PubMed Central

Oligosaccharide synthesis is hindered by the need for multiple steps as well as numerous selective protections and deprotections. Herein we report a highly efficient de novo route to various oligosaccharide motifs, of use for biological and medicinal structure activity studies. The key to the overall efficiency is the judicious use of asymmetric catalysis and synthetic design. These green principles include the bidirectional use of highly stereoselective catalysis (Pd(0)-glycosylation/post-glycosylation). In addition, the chemoselective use of C-C and C-O ?-bonds functionality, as atom-less protecting groups as well as an anomeric directing group (via a Pd-?-allyl), highlights the atom economical aspects of the route to a divergent set of natural and unnatural oligosaccharides (i.e., various D-/L-diastereomers of oligosaccharide as well as deoxysugars which lack C-2 anomeric directing groups). For example, in only 12 steps, the construction of a highly branched hepta-saccharide with 35 stereocenters was accomplished from an achiral acylfuran. PMID:22780712

Babu, Ravula Satheesh; Chen, Qian; Kang, Sang-Woo; Zhou, Maoquan; O’Doherty, George A.

2012-01-01

196

Efficient synthesis of C-N-coupled heterobiaryls by sequential N-h functionalization reactions.  

PubMed

C-N-coupled heterobiaryls were synthesized by sequential N-H functionalization reactions: stereoselective rhodium-catalyzed N-H insertion, followed by regioselective palladium-catalyzed C-H amination. Because of the good substrate scope and excellent selectivity, the developed method presents a novel approach for the synthesis of heterobiaryls, which are potent antibiotics. PMID:25830922

Lee, Dong Jin; Yoo, Eun Jeong

2015-04-17

197

Convenient and efficient protocols for coumarin synthesis via Pechmann condensation in neutral ionic liquids  

Microsoft Academic Search

Neutral ionic liquids with catalytic amount of acid have been employed for coumarin synthesis via Pechmann condensation of phenols and ethyl acetoacetate under ambient conditions. The reaction was also successfully carried out at high temperature in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid, without the use of any acid catalyst. The possibility of Brönsted acidic ionic liquids catalysing this reaction has also been

Mahesh K. Potdar; Meghana S. Rasalkar; Swapnil S. Mohile; Manikrao M. Salunkhe

2005-01-01

198

Efficient Synthesis and Electronic Studies of Core-Shell Nanowires Based on Colossal Magnetoresistive Manganites  

E-print Network

on this powerful technique in the synthesis of 1-D heterostructures is still in a preliminary stage despite and successfully synthesized single crystalline MgO/LCMO and MgO/LSMO core-shell nanowires by de- positing such as metal-insulator phase transitions and colossal magnetoresistance (CMR) at the nano- scale. This paper

Zhou, Chongwu

199

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

200

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

201

A practical and efficient synthesis of quinoxaline derivatives catalyzed by task-specific ionic liquid  

Microsoft Academic Search

A cheap and recyclable task-specific ionic liquid N, N, N-trimethyl-N-propanesulfic acid ammonium hydrogen sulfate [TMPSA]·HSO4 was used as the catalyst for the synthesis of quinoxaline derivatives. The reaction could be accomplished in water as well as organic solvent, and the satisfactory results were obtained under the mild conditions. The products could be separated from the catalyst simply by filtration and

Fang Dong; Gong Kai; Fei Zhenghao; Zhou Xinli; Liu Zuliang

2008-01-01

202

Cerium ammonium nitrate-catalyzed multicomponent reaction for efficient synthesis of functionalized tetrahydropyridines.  

PubMed

A highly atom-economic one-pot synthesis of functionalized tetrahydropyridines by a multicomponent condensation reaction of ?-keto ester, two equivalents of aromatic aldehyde, and two equivalents of amine in the presence of a catalytic amount of cerium ammonium nitrate (CAN) is reported. In this way, a series of pharmacologically interesting substituted piperidine derivatives were obtained in moderate to good yields at room temperature. PMID:21395344

Wang, Hong-Juan; Mo, Li-Ping; Zhang, Zhan-Hui

2011-03-14

203

Chitosan-DNA nanoparticles as gene carriers: synthesis, characterization and transfection efficiency  

Microsoft Academic Search

Chitosan-DNA nanoparticles were prepared using a complex coacervation process. The important parameters for the nanoparticle synthesis were investigated, including the concentrations of DNA, chitosan and sodium sulfate, temperature of the solutions, pH of the buffer, and molecular weights of chitosan and DNA. At an amino group to phosphate group ratio (N\\/P ratio) between 3 and 8 and a chitosan concentration

Hai-Quan Mao; Krishnendu Roy; Vu L. Troung-Le; Kevin A. Janes; Kevin Y. Lin; Yan Wang; J. Thomas August; Kam W. Leong

2001-01-01

204

Simple enzymatic procedure for l?carnosine synthesis: whole?cell biocatalysis and efficient biocatalyst recycling  

PubMed Central

Summary ??Peptides and their derivates are usually stable to proteolysis and have an increased half?life compared with ??peptides. Recently, ??aminopeptidases were described as a new enzyme class that enabled the enzymatic degradation and formation of ??peptides. As an alternative to the existing chemical synthesis routes, the aim of the present work was to develop a whole?cell biocatalyst for the synthesis and production of ??peptides using this enzymatic activity. For the optimization of the reaction system we chose the commercially relevant ?,??dipeptide l?carnosine (??alanine?l?histidine) as model product. We were able to show that different recombinant yeast and bacteria strains, which overexpress a ??peptidase, could be used directly as whole?cell biocatalysts for the synthesis of l?carnosine. By optimizing relevant reaction conditions for the best?performing recombinant Escherichia coli strain, such as pH and substrate concentrations, we obtained high l?carnosine yields of up to 71%. Long?time as well as biocatalyst recycling experiments indicated a high stability of the developed biocatalyst for at least five repeated batches. Application of the recombinant E. coli in a fed?batch process enabled the accumulation of l?carnosine to a concentration of 3.7?g?l?1. PMID:21255308

Heyland, Jan; Antweiler, Nicolai; Lutz, Jochen; Heck, Tobias; Geueke, Birgit; Kohler, Hans?Peter E.; Blank, Lars M.; Schmid, Andreas

2010-01-01

205

Efficient utilization of greenhouse gases in a gas-to-liquids process combined with CO2/steam-mixed reforming and Fe-based Fischer-Tropsch synthesis.  

PubMed

Two process models for carbon dioxide utilized gas-to-liquids (GTL) process (CUGP) mainly producing light olefins and Fischer-Tropsch (F-T) synthetic oils were developed by Aspen Plus software. Both models are mainly composed of a reforming unit, an F-T synthesis unit and a recycle unit, while the main difference is the feeding point of fresh CO2. In the reforming unit, CO2 reforming and steam reforming of methane are combined together to produce syngas in flexible composition. Meanwhile, CO2 hydrogenation is conducted via reverse water gas shift on the Fe-based catalysts in the F-T synthesis unit to produce hydrocarbons. After F-T synthesis, the unreacted syngas is recycled to F-T synthesis and reforming units to enhance process efficiency. From the simulation results, it was found that the carbon efficiencies of both CUGP options were successfully improved, and total CO2 emissions were significantly reduced, compared with the conventional GTL processes. The process efficiency was sensitive to recycle ratio and more recycle seemed to be beneficial for improving process efficiency and reducing CO2 emission. However, the process efficiency was rather insensitive to split ratio (recycle to reforming unit/total recycle), and the optimum split ratio was determined to be zero. PMID:24933030

Zhang, Chundong; Jun, Ki-Won; Ha, Kyoung-Su; Lee, Yun-Jo; Kang, Seok Chang

2014-07-15

206

Templated synthesis of nickel nanoparticles: Toward heterostructured nanocomposites for efficient hydrogen storage  

NASA Astrophysics Data System (ADS)

The world is currently facing an energy and environmental crisis for which new technologies are needed. Development of cost-competitive materials for catalysis and hydrogen storage on-board motor vehicles is crucial to lead subsequent generations into a more sustainable and energy independent future. This thesis presents work toward the scalable synthesis of bimetallic heterostructures that can enable hydrogen to compete with carbonaceous fuels by meeting the necessary gravimetric and volumetric energy densities and by enhancing hydrogen sorption/desorption kinetics near ambient temperatures and pressures. Utilizing the well-known phenomenon of hydrogen spillover, these bimetallic heterostructures could work by lowering the activation energy for hydrogenation and dehydrogenation of metals. Herein, we report a novel method for the scalable synthesis of silica templated zero-valent nickel particles (Ni?SiO2) that hold promise for the synthesis of nickel nanorods for use in bimetallic heterostructures for hydrogen storage. Our synthesis proceeds by chemical reduction of a nickel-hydrazine complex with sodium borohydride followed by calcination under hydrogen gas to yield silica encapsulated nickel particles. Transmission electron microscopy and powder X-ray diffraction were used to characterize the general morphology of the resultant nanocapsules as well as the crystalline phases of the incorporated Ni0 nanocrystals. The structures display strong magnetic behavior at room temperature and preliminary data suggests nickel particle size can be controlled by varying the amount of nickel precursor used in the synthesis. Calcination under different environments and TEM analysis provides evidence for an atomic migration mechanism of particle formation. Ni?SiO2 nanocapsules were used as seeds to induce heterogeneous nucleation and subsequent growth within the nanocapsule via electroless nickel plating. Nickel nanoparticle growth occurs under high temperature alkaline conditions, however silica nanocapsule integrity is not maintained due to the incompatibility of silica with the growth conditions. Silica nanocapsule integrity is maintained under low temperature neutral conditions, but nickel particle growth is not observed. Through FTIR and UV/Vis analysis, we show the degree of crosslinking and condensation increases in calcined silica compared to as-synthesized silica. We propose the increased density of the silica nanocapsule hinders mass transfer of the bulky nickel precursor complex from solution and onto the surface of the "catalytic" zero-valent nickel seed within the nanocapsule cavity. Decreasing the density of the silica nanocapsule can be achieved through co-condensation of tetraethylorthosilicate with an alkyl functionalized silane followed by calcination to remove the organic component or by chemical etching in alkaline solution, but will not be addressed in this thesis.

Nelson, Nicholas Cole

207

Templated synthesis of nickel nanoparticles: Toward heterostructured nanocomposites for efficient hydrogen storage  

SciTech Connect

The world is currently facing an energy and environmental crisis for which new technologies are needed. Development of cost-competitive materials for catalysis and hydrogen storage on-board motor vehicles is crucial to lead subsequent generations into a more sustainable and energy independent future. This thesis presents work toward the scalable synthesis of bimetallic heterostructures that can enable hydrogen to compete with carbonaceous fuels by meeting the necessary gravimetric and volumetric energy densities and by enhancing hydrogen sorption/desorption kinetics near ambient temperatures and pressures. Utilizing the well-known phenomenon of hydrogen spillover, these bimetallic heterostructures could work by lowering the activation energy for hydrogenation and dehydrogenation of metals. Herein, we report a novel method for the scalable synthesis of silica templated zero-valent nickel particles (Ni?SiO{sub 2}) that hold promise for the synthesis of nickel nanorods for use in bimetallic heterostructures for hydrogen storage. Our synthesis proceeds by chemical reduction of a nickel-hydrazine complex with sodium borohydride followed by calcination under hydrogen gas to yield silica encapsulated nickel particles. Transmission electron microscopy and powder X-ray diffraction were used to characterize the general morphology of the resultant nanocapsules as well as the crystalline phases of the incorporated Ni{sup 0} nanocrystals. The structures display strong magnetic behavior at room temperature and preliminary data suggests nickel particle size can be controlled by varying the amount of nickel precursor used in the synthesis. Calcination under different environments and TEM analysis provides evidence for an atomic migration mechanism of particle formation. Ni?SiO{sub 2} nanocapsules were used as seeds to induce heterogeneous nucleation and subsequent growth within the nanocapsule via electroless nickel plating. Nickel nanoparticle growth occurs under high temperature alkaline conditions, however silica nanocapsule integrity is not maintained due to the incompatibility of silica with the growth conditions. Silica nanocapsule integrity is maintained under low temperature neutral conditions, but nickel particle growth is not observed. Through FTIR and UV/Vis analysis, we show the degree of crosslinking and condensation increases in calcined silica compared to as-synthesized silica. We propose the increased density of the silica nanocapsule hinders mass transfer of the bulky nickel precursor complex from solution and onto the surface of the “catalytic” zero-valent nickel seed within the nanocapsule cavity. Decreasing the density of the silica nanocapsule can be achieved through co-condensation of tetraethylorthosilicate with an alkyl functionalized silane followed by calcination to remove the organic component or by chemical etching in alkaline solution, but will not be addressed in this thesis.

Nelson, Nicholas Cole [Ames Laboratory

2013-05-07

208

Switching between reaction pathways by an alcohol cosolvent effect: SmI2-ethylene glycol vs SmI2-H2O mediated synthesis of uracils.  

PubMed

A chemoselective switch between reaction pathways by an alcohol cosolvent effect in a general SmI2-mediated synthesis of uracil derivatives is described. The method relies on the use of coordinating solvents to increase the redox potential of Sm(II) and results in a chemoselective 1,2-reduction (SmI2-H2O) or 1,2-migration via in situ generated N-acyliminium ions (SmI2-ethylene glycol, EG). This work exploits the mild conditions of the SmI2-mediated monoreduction of barbituric acids and offers an attractive protocol for the synthesis of uracil derivatives with biological activity from readily accessible building blocks. PMID:25343692

Szostak, Michal; Spain, Malcolm; Sautier, Brice; Procter, David J

2014-11-01

209

The hepatitis C virus internal ribosome entry site facilitates efficient protein synthesis in blood vessel endothelium during tumour angiogenesis.  

PubMed

The development of gene delivery systems for therapeutic use involves vectors (often retrovirus or adenovirus) which typically encode one target protein, but the use of internal ribosome entry sites (IRES) can confer the ability to express more than one protein from bi- or polycistronic mRNAs. IRES elements can display tissue-specific expression, so it is necessary to determine suitable IRES for specific clinical applicability. Blood vessel endothelial cells are important clinically since many different conditions involve neo-vascularisation (angiogenesis). We have demonstrated that the viral hepatitis C IRES element is a powerful mediator of protein synthesis in angiogenesis, such as found in solid tumours. Homologous recombination was used to introduce IRES-lacZ sequences into the Lmo2 gene, which is expressed in endothelial cells. beta-Galactosidase expression was determined during vascular remodelling in mouse embryos and in sprouting endothelium during growth of solid tumours, and showed that the hepatitis C IRES is used efficiently for protein synthesis in endothelial cells. This IRES element can provide the means to express two or more therapeutic genes in blood vessel endothelium in clinical conditions, such as cancer, which depend on angiogenesis. PMID:12682381

Chung, Grace T Y; Yamada, Yoshihiro; Pannell, Richard; Forster, Alan; Rabbitts, Terence H

2003-04-15

210

Highly efficient enzymatic synthesis of an ascorbyl unstaturated fatty acid ester with ecofriendly biomass-derived 2-methyltetrahydrofuran as cosolvent.  

PubMed

Enzymatic synthesis of ascorbyl undecylenate, an unsaturated fatty acid ester of ascorbic acid, was reported with biomass-derived 2-methyltetrahydrofuran (MeTHF) as the cosolvent. Of the immobilized lipases tested, Candida antarctica lipase B (CAL-B) showed the highest activity for enzymatic synthesis of ascorbyl undecylenate. Effect of reaction media on the enzymatic reaction was studied. The cosolvent mixture, t-butanol-MeTHF (1:4, v/v) proved to be the optimal medium, in which not only ascorbic acid had moderate solubility, but also CAL-B showed a high activity, thus addressing the major problem of the solvent conflict for dissolving substrate and keeping satisfactory enzyme activity. In addition, the enzyme was much more stable in MeTHF and t-butanol-MeTHF (1:4) than in previously widely used organic solvents, t-butanol, 2-methyl-2-butanol, and acetone. The much higher initial reaction rate in this cosolvent mixture may be rationalized by the much lower apparent activation energy of this enzymatic reaction (26.6 vs. 38.1-39.1 kJ/mol) and higher enzyme catalytic efficiency (Vmax /Km , 8.4 vs. 1.3-1.4 h(-1) ). Ascorbyl undecylenate was obtained with the yields of 84-89% and 6-regioselectivity of >99% in t-butanol-MeTHF (1:4) at supersaturated substrate concentrations (60 and 100 mM) after 5-8 h. PMID:24891225

Hu, Ying-Dan; Qin, Ye-Zhi; Li, Ning; Zong, Min-Hua

2014-01-01

211

Efficient synthesis of chloro-derivatives of sialosyllactosylceramide, and their enhanced inhibitory effect on epidermal growth factor receptor activation  

PubMed Central

Glycosphingolipids are components of essentially all mammalian cell membranes and are involved in a variety of significant cellular functions, including proliferation, adhesion, motility and differentiation. Sialosyllactosylceramide (GM3) is known to inhibit the activation of epidermal growth factor receptor (EGFR). In the present study, an efficient method for the total chemical synthesis of monochloro- and dichloro-derivatives of the sialosyl residue of GM3 was developed. The structures of the synthesized compounds were fully characterized by high-resolution mass spectrometry and nuclear magnetic resonance. In analyses of EGFR autophosphorylation and cell proliferation ([3H]-thymidine incorporation) in human epidermoid carcinoma A431 cells, two chloro-derivatives exhibited stronger inhibitory effects than GM3 on EGFR activity. Monochloro-GM3, but not GM3 or dichloro-GM3, showed a significant inhibitory effect on ?EGFR, a splicing variant of EGFR that lacks exons 2–7 and is often found in human glioblastomas. The chemical synthesis of other GM3 derivatives using approaches similar to those described in the present study, has the potential to create more potent EGFR inhibitors to block cell growth or motility of a variety of types of cancer that express either wild-type EGFR or ?EGFR. PMID:24944646

KAWASHIMA, NAGAKO; QU, HUANHUAN; LOBATON, MARLIN; ZHU, ZHENYUAN; SOLLOGOUB, MATTHIEU; CAVENEE, WEBSTER K.; HANDA, KAZUKO; HAKOMORI, SEN-ITIROH; ZHANG, YONGMIN

2014-01-01

212

An efficient synthesis of substituted 2-iminothiazolidin-4-one and thiadiazoloquinazolinone derivatives.  

PubMed

A convenient synthesis of functionalized 2-iminothiazolidin-4-ones and thiadiazoloquinazolinones has been achieved by the reaction of dialkyl acetylenedicarboxylates (DAAD) with 1-pheny-3-pyridin-2-yl-thiourea (1) and 3-amino-2-mercapto-3H-quinazolin-4-one (8), respectively. The starting materials for these processes were prepared from phenyl isothiocyanate, 2-aminopyridine for (1) and anthranilic acid, carbon disulfide, hydrazine for (8). Treatment of these compounds with DAAD resulted in the formation of an intermediate that readily underwent intramolecular cyclization to afford functionalized five membered heterocyclic rings was formed. PMID:19219556

Ahmadi, Ali; Saidi, Kazem; Khabazzadeh, Hojattollah

2009-08-01

213

One pot, rapid and efficient synthesis of water dispersible gold nanoparticles using alpha-amino acids  

NASA Astrophysics Data System (ADS)

A detailed study on the synthesis of spherical and monodispersed gold nanoparticles (AuNPs) using all of the 20 naturally occurring ?-amino acids has been reported. The synthesized nanoparticles have been further characterized using various techniques such as absorbance spectroscopy, transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance. Size control of the nanoparticles has been achieved by varying the ratio of the gold ion to the amino acid. These monodispersed water soluble AuNPs synthesized using non-toxic, naturally occurring ?-amino acids as reducing and capping/stabilizing agents serve as a remarkable example of green chemistry.

Wangoo, Nishima; Kaur, Sarabjit; Bajaj, Manish; Jain, D. V. S.; Sharma, Rohit K.

2014-10-01

214

Facile and efficient one-pot synthesis of 2-arylbenzoxazoles using hydrogen tetrachloroaurate as catalyst under oxygen atmosphere*  

PubMed Central

In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl4·4H2O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show that this method could bring excellent yields as high as 96%. THF was proven to be the best choice among several solvents screened and the reaction was tolerated with a variety of aromatic aldehydes possessing electron-donating or withdrawing groups. The advantages of the present method lie in catalytic process using economic and environmentally benign dioxygen as oxidant. PMID:19489113

Liu, Yun-kui; Mao, Da-jie; Lou, Shao-jie; Qian, Jian-qiang; Xu, Zhen-yuan

2009-01-01

215

Polyoxometalate-mediated one-pot synthesis of pd nanocrystals with controlled morphologies for efficient chemical and electrochemical catalysis.  

PubMed

Polyoxometalates (POMs), as inorganic ligands, can endow metal nanocrystals (NCs) with unique reactivities on account of their characteristic redox properties. In the present work, we present a facile POM-mediated one-pot aqueous synthesis method for the production of single-crystalline Pd NCs with controlled shapes and sizes. The POMs could function as both reducing and stabilizing agents in the formation of NCs, and thus gave a fine control over the nucleation and growth kinetics of NCs. The prepared POM-stabilized Pd NCs exhibited excellent catalytic activity and stability for electrocatalytic (formic acid oxidation) and catalytic (Suzuki coupling) reactions compared to Pd NCs prepared without the POMs. This shows that the POMs play a pivotal role in determining the catalytic performance, as well as the growth, of NCs. We envision that the present approach can offer a convenient way to develop efficient NC-based catalyst systems. PMID:25684660

Kim, Dongheun; Seog, Ji Hyun; Kim, Minjune; Yang, MinHo; Gillette, Eleanor; Lee, Sang Bok; Han, Sang Woo

2015-03-27

216

Efficient Solid-Phase Synthesis of 2-Substituted-3-Hydroxy-4(1H)-Quinolinone-7-Carboxamides with Two Diversity Positions  

PubMed Central

Highly efficient solid-phase synthesis of 2-substituted-3-hydroxy-4(1H)-quinolinone-7-carboxamides was developed using anthranilates and bromoketones as the key synthons. Primary amines immobilized to acid-cleavable BAL linker were acylated with 1-methyl-2-aminoterephtalate. Following cleavage of the methyl ester, bromoketones were used to form resin-bound phenacyl esters. Acid-mediated cleavage and subsequent cyclization in solution afforded 3-hydroxy-4(1H)-quinolinones in high purity and yield. Highly efficient solid-phase synthesis (purity >90%, yield >80%, synthetic time 2 days using commercially available synthons) is amenable to high throughput/combinatorial synthesis to match the high throughput screening capability. PMID:17676809

Soural, Miroslav; Krch?ák, Viktor

2008-01-01

217

A General and Efficient Synthesis of 2-Phenylbenzothiazoles From Diphenyl Disulfides  

Microsoft Academic Search

Benzothiazoles containing a substituted-phenyl at the 2 position can be synthesized cleanly and efficiently from the corresponding bis(2-aminophenyl) disulfide. Bis(2-aminophenyl) disulfides represent a stable source of 2-aminobenzenethiols.

Yi-Hua Chang; John D. Peak; Scott W. Wierschke; William A. Feld

1993-01-01

218

Highly efficient synthesis of enantiomerically enriched 2-hydroxymethylaziridines by enzymatic desymmetrization.  

PubMed

Both enantiomers of protected and unprotected 2-hydroxymethylaziridines are efficiently and enantiospecifically synthesized by using a combination of enzymatic and synthetic methods. PPL was used for lipase-catalyzed desymmetrization of N-protected serinol. [reaction: see text]. PMID:17217268

Choi, Jun Young; Borch, Richard F

2007-01-18

219

Highly Efficient Synthesis of Enantiomerically Enriched 2-Hydroxymethylaziridines by Enzymatic Desymmetrization  

PubMed Central

Both enantiomers of protected and unprotected 2-hydroxymethylaziridines are efficiently and enantiospecifically synthesized using a combination of enzymatic and synthetic methods. PPL was used for lipase-catalyzed desymmetrization of N-protected serinol. PMID:17217268

Choi, Jun Young; Borch, Richard F.

2008-01-01

220

Bifunctionalized allenes. Part XIII. A convenient and efficient method for regioselective synthesis of phosphorylated ?-hydroxyallenes with protected and unprotected hydroxy group.  

PubMed

The paper describes a convenient and efficient method for regioselective synthesis of phosphorylated ?-hydroxyallenes using an atom economical [2,3]-sigmatropic rearrangement of intermediate propargyl phosphites or phosphinites. These can be readily prepared via reaction of protected alkynols with dimethyl chlorophosphite or chlorodiphenyl phosphine respectively in the presence of a base. PMID:24840901

Ismailov, Ismail E; Ivanov, Ivaylo K; Christov, Valerij Ch

2014-01-01

221

Sequential rearrangement of 1,2,4Z,7-tetraenes involving [1,5]-hydrogen migration and electrocyclization: an efficient synthesis of eight-membered cyclic compounds.  

PubMed

An efficient protocol for the synthesis of eight-membered bicyclic compounds from the cycloisomerization of 1,2,4Z,7-tetraenes has been established. The possible intermediate for this transformation was trapped by its Diels-Alder reaction with N-ethyl maleimide. Thus the reaction may proceed via the sequential processes involving [1,5]-hydrogen migration and electrocyclization. PMID:16608314

Ma, Shengming; Gu, Zhenhua

2006-04-19

222

Bismuth Subnitrate Catalyzed Efficient Synthesis of 3,4?Dihydropyrimidin?2(1H)?Ones: An Improved Protocol for the Biginelli Reaction  

Microsoft Academic Search

An efficient synthesis of 3,4?dihydropyrimidinones (DHPMs) using bismuth subnitrate as the catalyst for the first time from an aldehyde, ??ketoester, and urea in acetonitrile is described. This new method consistently has the advantage of excellent yields (88–96%) and short reaction times (1.5–4 h) than do classical Biginelli reaction conditions.

Y. Thirupathi Reddy; B. Rajitha; P. Narsimha Reddy; B. Sunil Kumar; V. P. Rao G

2004-01-01

223

Efficient catalysis by MgCl2 in hydrogen generation via hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis.  

PubMed

Magnesium chloride efficiently catalyzed the hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis. Hydrogen yield of 1635 mL g(-1) was obtained (MgH(2)), i.e. with 96% conversion in 30 min at 303 K. PMID:22538836

Zhao, Zelun; Zhu, Yunfeng; Li, Liquan

2012-06-01

224

Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors.  

PubMed

Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations. PMID:25733848

Yu, Xinge; Smith, Jeremy; Zhou, Nanjia; Zeng, Li; Guo, Peijun; Xia, Yu; Alvarez, Ana; Aghion, Stefano; Lin, Hui; Yu, Junsheng; Chang, Robert P H; Bedzyk, Michael J; Ferragut, Rafael; Marks, Tobin J; Facchetti, Antonio

2015-03-17

225

Rational Design and Synthesis of Freestanding Photoelectric Nanodevices as Highly Efficient Photocatalysts  

PubMed Central

Photocatalysts are of significant interest for solar energy harvesting and conversion into chemical energy. However, the photocatalysts available to date are limited by either poor efficiency in the visible light range or insufficient photoelectrochemical stability. Here we report the rational design of a new generation of freestanding photoelectric nanodevices as highly efficient and stable photocatalysts by integrating a nanoscale photodiode with two redox catalysts in a single nanowire heterostructure. We show that a platinum-silicon-silver nanowire heterostructure can be synthesized to integrate a nanoscale metal-semiconductor Schottky diode encased in a protective insulating shell with two exposed metal catalysts. We further demonstrated that the Schottky diodes exhibited pronounced photovoltaic effect with nearly unity internal quantum efficiency, and that the integrated nanowire heterostructures could be used as highly efficient photocatalysts for a wide range of thermodynamically downhill and uphill reactions including photocatalytic degradation of organic dyes, reduction of metal ions and carbon dioxide using visible light. Our studies for the first time demonstrated the integration of multiple distinct functional components into a single nanostructure to form a standalone active nanosystem, and for the first time successfully realized a photoelectric nanodevice that is both highly efficient and highly stable throughout the entire solar spectrum. It thus opens a rational avenue to design and synthesize a new generation of photoelectric nanosystems with unprecedented efficiency and stability, and will impact broadly in areas including environmental remediation and solar fuel production. PMID:20373781

Qu, Yongquan; Liao, Lei; Cheng, Rui; Wang, Yue; Lin, Yung-chen; Huang, Yu; Duan, Xiangfeng

2010-01-01

226

Chemoselective Multicomponent One-Pot Assembly of Purine Precursors in Water  

PubMed Central

The recent development of a sequential, high-yielding route to activated pyrimidine nucleotides, under conditions thought to be prebiotic, is an encouraging step toward the greater goal of a plausible prebiotic pathway to RNA and the potential for an RNA world. However, this synthesis has led to a disparity in the methodology available for stepwise construction of the canonical pyrimidine and purine nucleotides. To address this problem, and further explore prebiotically accessible chemical systems, we have developed a high-yielding, aqueous, one-pot, multicomponent reaction that tethers masked-sugar moieties to prebiotically plausible purine precursors. A pH-dependent three-component reaction system has been discovered that utilizes key nucleotide synthons 2-aminooxazole and 5-aminoimidazoles, which allows the first divergent purine/pyrimidine synthesis to be proposed. Due to regiospecific aminoimidazole tethering, the pathway allows N9 purination only, thus suggesting the first prebiotically plausible mechanism for regiospecific N9 purination. PMID:21043502

2010-01-01

227

Synthesis of homogeneous Pt-bimetallic nanoparticles as highly efficient electrocatalysts.  

SciTech Connect

Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

Wang, C.; Chi, M.; Li, D.; van der Vliet, D.; Wang, G.; Lin, Q.; Mitchell, J.; More, K. L.; Markovic, N. M.; Stamenkovic, V. R. (Materials Science Division); (Oak Ridge Nat. Lab.); (Brown Univ.); (Univ. Pittsburgh)

2011-01-01

228

Synthesis and evaluation of RNA transesterification efficiency using stereospecific serinol-terpyridine conjugates.  

PubMed

Six novel artificial ribonucleases were synthesized employing a stereochemically pure abasic serinol backbone residue for attachment of the RNA transesterification agent copper(II) terpyridine. These stereochemically pure abasic residues were synthesized as phosphoramidite building blocks from the parent L-serine and D-serine starting building blocks and incorporated into oligonucleotides via solid-phase DNA synthesis. These artificial ribonucleases were constructed to determine if the stereochemistry of the alpha carbon of an abasic serinol residue has influence over RNA transesterification through selective placement of a pendant transesterification agent in either the major or minor groove. The novel artificial ribonucleases and previously synthesized artificial ribonucleases were challenged with a 28-mer and 159-mer RNA substrate. It was determined that the stereochemistry of the carbon atom derived from the alpha-carbon of serine did not influence the extent of cleavage in these studies using copper(II) terpyridine conjugated artificial ribonucleases. PMID:16252668

Putnam, William C; Bashkin, James K

2005-01-01

229

Effects of solids and liquid flows on fermentation in continuous cultures. II. Nitrogen partition and efficiency of microbial synthesis.  

PubMed

The effects of varying solids retention time (SRT) and liquid dilution rate (D) on N partition and microbial efficiency were studied in vitro with a dual flow continuous culture system. SRT's of 14.3, 22.0 and 29.7 hr and D's of .07, .11 and .15 volumes/hr were used. Ammonia N accounted for 2.69 to 7.30% of total effluent N. Highest values were observed with 29.7-hr SRT at .11 and .15/hr D's, and were associated with a slight decrease in microbial N. Between 1.17 and 2.50 g microbial N were produced per 24 hr, accounting for 31.34 to 50.49% of total effluent N. Daily output of microbial N increased (P less than .05) with increasing D at the lowest SRT but showed little or no change at the 22.0- and 29.7-hr SRT's. Feed bypass N was inversely related to microbial N and accounted for 44.91 to 65.10% of total effluent N. Microbial cell yields per mole ATP (YATP) ranged from 10.40 to 24.41 and tended to increase with decreased SRT more than with increased D, although responses were variable. Efficiency of microbial N synthesis ranged from 15.75 to 23.91 g microbial N/kg digested dry matter (DDM), with trends similar to those seen for YATP. PMID:7193203

Crawford, R J; Hoover, W H; Junkins, L L

1980-10-01

230

High-resolution analysis of DNA synthesis start sites and nucleosome architecture at efficient mammalian replication origins  

PubMed Central

DNA replication origins are poorly characterized genomic regions that are essential to recruit and position the initiation complex to start DNA synthesis. Despite the lack of specific replicator sequences, initiation of replication does not occur at random sites in the mammalian genome. This has lead to the view that DNA accessibility could be a major determinant of mammalian origins. Here, we performed a high-resolution analysis of nucleosome architecture and initiation sites along several origins of different genomic location and firing efficiencies. We found that mammalian origins are highly variable in nucleosome conformation and initiation patterns. Strikingly, initiation sites at efficient CpG island-associated origins always occur at positions of high-nucleosome occupancy. Origin recognition complex (ORC) binding sites, however, occur at adjacent but distinct positions marked by labile nucleosomes. We also found that initiation profiles mirror nucleosome architecture, both at endogenous origins and at a transgene in a heterologous system. Our studies provide a unique insight into the relationship between chromatin structure and initiation sites in the mammalian genome that has direct implications for how the replication programme can be accommodated to diverse epigenetic scenarios. PMID:23995398

Lombraña, Rodrigo; Almeida, Ricardo; Revuelta, Isabel; Madeira, Sofia; Herranz, Gonzalo; Saiz, Néstor; Bastolla, Ugo; Gómez, María

2013-01-01

231

Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells  

SciTech Connect

Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30?nm, and absorption peak from 475?nm to 510?nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO{sub 2} electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO{sub 2}'s to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn; Chen, Guorong, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Zhang, Bo [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China)

2014-05-21

232

Direct synthesis of high-density lead sulfide nanowires on metal thin films towards efficient infrared light conversion  

NASA Astrophysics Data System (ADS)

We report chemical-vapor-deposition (CVD) synthesis of high-density lead sulfide (PbS) nanowire arrays and nano pine trees directly on Ti thin films, and the fabrication of photovoltaic devices based upon the PbS nanowires. The as-grown nanowire arrays are largely vertically aligned to the substrates and are uniformly distributed over a relatively large area. Field effect transistors incorporating single PbS nanowires show p-type conduction and high mobilities. These catalytic metal thin films also serve as photocarrier collection electrodes and greatly facilitate device integration. For the first time, we have fabricated Schottky junction photovoltaic devices incorporating PbS nanowires, which demonstrate the capability of converting near-infrared light to electricity. The PbS nanowire devices are stable in air and their external quantum efficiency shows no significant decrease over a period of 3 months in air. We have also compared the photocurrent direction and quantum efficiencies of photovoltaic devices made with different metal electrodes, and the results are explained by band bending at the Schottky junction. Our research shows that PbS nanowires are promising building blocks for collecting near-infrared solar energy.

Wu, Hengkui; Yang, Yiming; Oh, Eunsoon; Lai, Fachun; Yu, Dong

2012-07-01

233

A Methodology for Synthesis of Efficient Intrusion Detection Systems on FPGAs  

Microsoft Academic Search

Intrusion detection for network security is a computa- tion intensive application demanding high system perfor- mance. System level design, a relatively unexplored field in this area, allows more efficient communication and ex- tensive reuse of hardware components for dramatic in- creases in area-time performance. By applying optimiza- tion strategies to the entire database, we reduce hardware requirements compared to architectures

Zachary K. Baker; Viktor K. Prasanna

2004-01-01

234

An Efficient Synthesis of the Fully Elaborated Isoindolinone Unit of Muironolide A  

PubMed Central

An efficient stereocontrolled construction of the fully substituted isoindolone subunit of muironolide A is described. The approach is centered on the intramolecular Diels-Alder reaction between the enol form of the ?-keto amide and an ? ? ? ?-unsaturated ester, followed by the installation of the cyclohexene double bond. PMID:23826676

Xiao, Qing; Young, Kyle

2013-01-01

235

Dhvar5 antimicrobial peptide (AMP) chemoselective covalent immobilization results on higher antiadherence effect than simple physical adsorption.  

PubMed

Bacterial colonization and subsequent biofilm formation is still one of the major problems associated with medical devices. Antimicrobial peptides (AMP) immobilization onto biomaterials surface is a promising strategy to avoid bacterial colonization. However, a correct peptide orientation and exposure from the surface is essential to maintain AMP antimicrobial activity. This work aims to evaluate the effect of the immobilization on antibacterial activity of Dhvar5 (LLLFLLKKRKKRKY), an AMP with a head-to-tail amphipathicity. Dhvar5 was linked to thin chitosan coatings in i) a controlled orientation and exposure, testing covalent immobilization of its N- or C-terminus and using spacers with different lengths and flexibilities or in ii) a random orientation by physical adsorption. Chitosan coating was chosen due to its antimicrobial properties and readiness to be functionalized. Surface characterization demonstrated the chemoselective immobilization of the peptide with different spacers in a similar concentration (?2 ng/cm(2)). Efficacy assays demonstrated that covalent immobilization of Dhvar5 exposing its cationic end, improves the chitosan coating antimicrobial effect by decreasing Methicillin-resistant Staphylococcus aureus (MRSA) colonization. This effect was enhanced when longer spacers were used independently of their flexibility. In opposite, immobilized Dhvar5 exposing its hydrophobic end has no effect on bacterial adhesion to chitosan, and when adsorbed in a random orientation even induces bacterial adhesion to chitosan coating. PMID:25818458

Costa, Fabíola M T A; Maia, Sílvia R; Gomes, Paula A C; Martins, M Cristina L

2015-06-01

236

Design and efficient synthesis of novel GM2 analogues with respect to the elucidation of the function of GM2 activator  

Microsoft Academic Search

To elucidate the mechanism underlying the hydrolysis of the GalNAc?1?4Gal linkage in ganglioside GM2 [GalNAc?1?4(NeuAc?2?3)Gal?1?4Glc?1?1?\\u000a Cer] by ?-hexosaminidase A (Hex A) with GM2 activator protein, we designed and synthesized two kinds of GM2 linkage analogues—6?-NeuAc-GM2\\u000a and ?-GalNAc-GM2. In this paper, the efficient and systematic synthesis of these GM2 analogues was described. The highlight\\u000a of our synthesis process is that the

Tatsuya Komori; Takayuki Ando; Akihiro Imamura; Yu-Teh Li; Hideharu Ishida; Makoto Kiso

2008-01-01

237

Engineering of a 129-residue tripod protein by chemoselective ligation of proline-II helices  

Microsoft Academic Search

A 129-residue tripod protein was designed, synthesized, and biophysically characterized. This receptor-adhesive modular protein contained three 30-residue proline-II helices linked to a 9-residue proline-II helix through thioether bonds. Coupling of 6-maleimidohexanoic acid succinimido ester to cis-N?-Boc-4-amino-L-proline furnished in 77% yield the maleimido acid cis-N-Boc-4-(6-maleimidohexanamido)-L-proline (Boc-Prm), which was used in the solid-phase synthesis of the linker peptide CH3-CO-Pro3-Prm3-Pro3-***NH2. The leg peptide,

Dewey G. McCafferty; Cheryl A. Slate; Bassam M. Nakhle; Harold D. Graham; Todd L. Austell; Richard W. Vachet; Brian H. Mullis; Bruce W. Erickson

1995-01-01

238

A facile low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells  

NASA Astrophysics Data System (ADS)

Titania (TiO2) nanorods have been synthesized with controlled size for dye-sensitized solar cells (DSSCs) via hydrothermal route at low hydrothermal temperature of 100 °C for 24 h. The titania nanorods were characterized using XRD, SEM, TEM/HRTEM, UV-vis Spectroscopy, FTIR and BET specific surface area ( S BET), as well as pore-size distribution by BJH. The results indicated that the bulk traps and the surface states within the TiO2 nanorods films have enhanced the efficiency of DSSCs. The size of the titania nanorods was 6.7 nm in width and 22 nm in length. The high surface area can provide more sites for dye adsorption, while the fast photoelectron-transfer channel can enhance the photogenerated electron transfer to complete the circuit. The specific surface area S BET was 77.14 m2 g-1 at the synthesis conditions. However, the band gap energy of the obtained titania nanorods was 3.2 eV. The oriented nanorods with appropriate lengths are beneficial in improving the electron transport property and thus leading to the increase of photocurrent, together enhancing the power conversion efficiency. A nearly quantitative absorbed photon-to-electrical current conversion achieved upon excitation at wave length of 550 nm and the power efficiency was enhanced from 5.6 % for commercial TiO2 nanoparticles Degussa (P25) cells to 7.2 % for TiO2 nanorods cells under AM 1.5 illumination (100 mW cm-2). The TiO2 cells performance was improved due to their high surface area, hierarchically mesoporous structures and fast electron-transfer rate compared with the Degussa (P25).

Shalan, A. E.; Rashad, M. M.; Yu, Youhai; Lira-Cantú, Mónica; Abdel-Mottaleb, M. S. A.

2013-01-01

239

Click mechanochemistry: quantitative synthesis of "ready to use" chiral organocatalysts by efficient two-fold thiourea coupling to vicinal diamines.  

PubMed

Mechanochemical methods of neat grinding and liquid-assisted grinding have been applied to the synthesis of mono- and bis(thiourea)s by using the click coupling of aromatic and aliphatic diamines with aromatic isothiocyanates. The ability to modify the reaction conditions allowed the optimization of each reaction, leading to the quantitative formation of chiral bis(thiourea)s with known uses as organocatalysts or anion sensors. Quantitative reaction yields, combined with the fact that mechanochemical reaction conditions avoid the use of bulk solvents, enabled solution-based purification methods (such as chromatography or recrystallization) to be completely avoided. Importantly, by using selected model reactions, we also show that the described mechanochemical reaction procedures can be readily scaled up to at least the one-gram scale. In that way, mechanochemical synthesis provides a facile method to fully transform valuable enantiomerically pure reagents into useful products that can immediately be applied in their designed purpose. This was demonstrated by using some of the mechanochemically prepared reagents as organocatalysts in a model Morita-Baylis-Hillman reaction and as cyanide ion sensors in organic solvents. The use of electronically and sterically hindered ortho-phenylenediamine revealed that mechanochemical reaction conditions can be readily optimized to form either the 1:1 or the 1:2 click-coupling product, demonstrating that reaction stoichiometry can be more efficiently controlled under these conditions than in solution-based syntheses. In this way, it was shown that excellent stoichiometric control by mechanochemistry, previously established for mechanochemical syntheses of cocrystals and coordination polymers, can also be achieved in the context of covalent-bond formation. PMID:22648998

Štrukil, Vjekoslav; Igrc, Marina D; Eckert-Maksi?, Mirjana; Friš?i?, Tomislav

2012-07-01

240

Peptide arrays on cellulose support: SPOT synthesis, a time and cost efficient method for synthesis of large numbers of peptides in a parallel and addressable fashion  

Microsoft Academic Search

Peptide synthesis on cellulose using SPOT technology allows the parallel synthesis of large numbers of addressable peptides in small amounts. In addition, the cost per peptide is less than 1% of peptides synthesized conventionally on resin. The SPOT method follows standard fluorenyl-methoxy-carbonyl chemistry on conventional cellulose sheets, and can utilize more than 600 different building blocks. The procedure involves three

Dirk FH Winkler; Robert EW Hancock; Kai Hilpert

2007-01-01

241

Efficient and facile synthesis of acrylamide libraries for protein-guided tethering.  

PubMed

A kinetic template-guided tethering (KTGT) strategy has been developed for the site-directed discovery of fragments that bind to defined protein surfaces, where acrylamide-modified fragments can be irreversibly captured in a protein-templated conjugate addition reaction. Herein, an efficient and facile method is reported for the preparation of acrylamide libraries from a diverse range of amine fragments using a solid-supported quaternary amine base. PMID:25582165

Allen, Charlotte E; Curran, Peter R; Brearley, Andrew S; Boissel, Valerie; Sviridenko, Lilya; Press, Neil J; Stonehouse, Jeffrey P; Armstrong, Alan

2015-02-01

242

A new and efficient method for the synthesis of Ulipristal acetate.  

PubMed

In this study, we describe another new and efficient route for preparing Ulipristal acetate. The 1,4-addition compound 5 was greatly improved after the starting material ketone 1 was underwent epoxidation, cyanation, hydroxyl group protection and Grignard addition. The synthetic procedure is only 6 steps and the total yield is about 27.4%, which is much suitable for industrial process. PMID:24686204

Cheng, Xu; Li, Xiaocen; Duan, Yanjun; Yu, Yongguo; Hai, Li; Wu, Yong

2014-06-01

243

Facile synthesis of nanostructured vanadium oxide as cathode materials for efficient Li-ion batteries  

E-print Network

-ion batteries Yanyi Liu,a Evan Uchaker,a Nan Zhou,ab Jiangang Li,ac Qifeng Zhanga and Guozhong Cao*a Received 23 and VO2 (B) nanorods were tested as active cathode materials for Li-ion batteries. The V2O5 sheet for efficient Li-ion batteries. Introduction The expansion and demands for energy use in the past several

Cao, Guozhong

244

Highly efficient and regioselective synthesis of dihydromyricetin esters by immobilized lipase.  

PubMed

Dihydromyricetin is the principle component of the Chinese herbal tea Teng-cha and a promising ingredient for functional food and nutraceuticals, but its low solubility limits its application potentials. This study explored enzymatic acylation of dihydromyricetin to improve its solubility in lipid systems. Acylation was achieved with several lipases with the synthesis of a major (>86%) product and a minor product. Isolation and purification of the products by preparative HPLC followed by LC-MS, (13)C NMR, (1)H NMR and 2 D-HSQC NMR analyses showed that the major product was a dihydromyricetin monoester with the acylation site at the 3-OH group of C ring. Quantum chemical calculations revealed that the 3-OH had the lowest antioxidant activity, and therefore acylation at this site was expected to have minimum impact on the antioxidant activity. Several factors, including solvent, acyl donor, enzyme origin, molar ratio of substrates and reaction temperature and time, exhibited significant effects on the initial rate, conversion yield and regioselectivity of the reaction. Acylation occurred only with vinyl acetate as the acyl donor, and highest conversion yields were achieved with immobilized Penicillium expansum lipase and Novozyme 435 with DMSO and acetonitrile being the best solvents. In general, the acylation results were found to be superior to previous reports on acylation of aglycone flavonoids with respects to conversion yield and regioselectivity. PMID:25701177

Li, Wei; Wu, Huan; Liu, Benguo; Hou, Xuedan; Wan, Duanji; Lou, Wenyong; Zhao, Jian

2015-04-10

245

Dispersion-precipitation synthesis of nanosized magnetic iron oxide for efficient removal of arsenite in water.  

PubMed

Nanosized magnetic iron oxide was facilely synthesized by a dispersion-precipitation method, which involved acetone-promoted precipitation of colloidal hydrous iron oxide nanoparticles and subsequent calcination of the precipitate at 250°C. Characterization by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, nitrogen sorption, and vibrating-sample magnetometry revealed that the material was a composite of ?-Fe2O3 and ?-Fe2O3 with primary particle size of 15-25nm and specific surface area of 121m(2)/g, as well as superparamagnetic property. The material was used as adsorbent for the removal of arsenite in water. Batch experiments showed that the adsorption isotherms at pH 3.0-11.0 fit the Langmuir equation and the adsorption obeys pseudo-second-order kinetics. Its maximum sorption capability for arsenite is 46.5mg/g at pH 7.0. Coexisting nitrate, carbonate, sulfate, chloride, and fluoride have no significant effect on the removal efficiency of arsenite, while phosphate and silicate reduce the removal efficiency to some extent. The As(III) removal mechanism is chemisorption through forming inner-sphere surface complexes. The efficiency of arsenic removal is still maintained after five cycles of regeneration-reuse. PMID:25612934

Cheng, Wei; Xu, Jing; Wang, Yajie; Wu, Feng; Xu, Xiuyan; Li, Jinjun

2015-05-01

246

Marine Sponge/CuO Nanocrystal: A Natural and Efficient Catalyst for Sulfonamides Synthesis  

PubMed Central

Background Marine sponge/nano-CuO as a natural catalyst efficiently catalyzed the Sulfonylation reaction of p-chlorobenzene sulfonyl chlorides with amines in order to prepare sulfonamides. The advantages included use of a natural catalyst, ease of handling, requirement of a very small amount of catalyst, mild reaction condition and appropriateness to high yield. Objectives The current study aimed to look for a solid support reaction and to develop a general, mild and novel method in order to synthesize sulfonamides in the absence of a strong base, it was found that marine sponge/nano-CuO is a natural and efficient catalyst for this method at room temperature. Materials and Methods The reaction was carried out simply by addition of amine and p -chlorobenzene sulfonyl chloride to the mixture of Marine sponge powder/nano-CuO in acetonitrile at room temperature. Then the reaction mixture was extracted by CH2Cl2 and was dried over anhydrous magnesium sulfate. Evaporation of the solvent afforded the products. Results In this method several derivatives of sulfonamide underwent the reaction of different amines with p-chlorobenzene sulfonyl chloride in the presence of marine sponge/nano-CuO in CH3CN are synthesized. Conclusions In conclusion, a new, natural and efficient marine catalyst, and a marine sponge/nano-CuO were developed to synthesize sulfonamide derivatives in CH3CN in 75–93% yields. This method was applied to a wide range of aromatic and aliphatic amines under mild conditions. PMID:24624171

Shushizadeh, Mohamad Reza; Mostoufi, Azar; Fakhrian, Marjan

2012-01-01

247

A new and efficient approach to isoxazolines. First synthesis of 3-aryl-5-dichloromethyl-2-isoxazolines  

Microsoft Academic Search

An efficient synthetic method for 3-aryl-5-dichloromethyl-2-isoxazolines has been established. Reactions between anhydrous chloral and acetophenones in hot acetic acid lead to 1-aryl-4,4,4-trichloro-3-hydroxybutan-1-ones (chloralacetophenones), which provided 1-aryl-4,4-dichlorobut-3-en-1-ones (2,2-dichlorovinylacetophenones) by dehydration and subsequent electrochemical reduction. These ?,?-unsaturated enones reacted with hydroxylamine yielding oxime intermediates whose treatment with aqueous sodium hydroxide gave novel 3-aryl-5-dichloromethyl-2-isoxazolines in fair to high yields. The molecular structure of

Antonio Guirado; Bruno Martiz; Raquel Andreu; Delia Bautista

2011-01-01

248

Inhibitors of sterol synthesis. A highly efficient and specific side-chain oxidation of  

Microsoft Academic Search

As part of a program directed towards the chemi- cal syntheses of potential metabolites and analogs of 3p- hydroxy-5a-cholest-8( 14)en-15-one (I), a potent regulator of cholesterol metabolism, several routes have been ex- plored for the preparation of 3&hydroxy-l5keto-5a-chol- 8(14)en-24-oic acid (IV). These investigations led to a remarkably specific and efficient side-chain oxidation of I. For example, treatment of the acetate

George J. Schroepfer

249

Design and synthesis of molecular donors for solution-processed high-efficiency organic solar cells.  

PubMed

Organic semiconductors incorporated into solar cells using a bulk heterojunction (BHJ) construction show promise as a cleaner answer to increasing energy needs throughout the world. Organic solar cells based on the BHJ architecture have steadily increased in their device performance over the past two decades, with power conversion efficiencies reaching 10%. Much of this success has come with conjugated polymer/fullerene combinations, where optimized polymer design strategies, synthetic protocols, device fabrication procedures, and characterization methods have provided significant advancements in the technology. More recently, chemists have been paying particular attention to well-defined molecular donor systems due to their ease of functionalization, amenability to standard organic purification and characterization methods, and reduced batch-to-batch variability compared to polymer counterparts. There are several critical properties for efficient small molecule donors. First, broad optical absorption needs to extend towards the near-IR region to achieve spectral overlap with the solar spectrum. Second, the low lying highest occupied molecular orbital (HOMO) energy levels need to be between -5.2 and -5.5 eV to ensure acceptable device open circuit voltages. Third, the structures need to be relatively planar to ensure close intermolecular contacts and high charge carrier mobilities. And last, the small molecule donors need to be sufficiently soluble in organic solvents (?10 mg/mL) to facilitate solution deposition of thin films of appropriate uniformity and thickness. Ideally, these molecules should be constructed from cost-effective, sustainable building blocks using established, high yielding reactions in as few steps as possible. The structures should also be easy to functionalize to maximize tunability for desired properties. In this Account, we present a chronological description of our thought process and design strategies used in the development of highly efficient molecular donors that achieve power conversion efficiencies greater than 7%. The molecules are based on a modular D(1)-A-D(2)-A-D(1) architecture, where A is an asymmetric electron deficient heterocycle, which allowed us to quickly access a library of compounds and develop structure-property-performance relationships. Modifications to the D1 and D2 units enable spectral coverage throughout the entire visible region and control of HOMO energy levels, while adjustments to the pendant alkyl substituents dictate molecular solubility, thermal transition temperatures, and solid-state organizational tendencies. Additionally, we discuss regiochemical considerations that highlight how individual atom placements can significantly influence molecular and subsequently device characteristics. Our results demonstrate the utility of this architecture for generating promising materials to be integrated into organic photovoltaic devices, call attention to areas for improvement, and provide guiding principles to sustain the steady increases necessary to move this technology forward. PMID:23984626

Coughlin, Jessica E; Henson, Zachary B; Welch, Gregory C; Bazan, Guillermo C

2014-01-21

250

Efficient synthesis and reaction kinetics of readily water soluble esters containing sulfonic groups.  

PubMed

A series of various readily water soluble esters were synthesized by a very efficient procedure. These compounds can be useful as thermosensitive tracers for studying the cooling progress in a low enthalpy georeservoir exploitable by double flash geothermal power plant systems. The kinetics of their hydrolysis was investigated. Acylation of primary alcohols or phenols was carried out by a method based on a single-phase solvent system consisting of ethyl acetate acting as an organic solvent and triethylamine acting as a catalyst. Products were characterized by 1H-NMR, and 13C-NMR. PMID:25517341

Idzik, Krzysztof R; Nödler, Karsten; Maier, Friedrich; Licha, Tobias

2014-01-01

251

Macrocyclic amine-linked oligocarbazole hollow microspheres: facile synthesis and efficient lead sorbents.  

PubMed

Novel macrocyclic amine-linked oligocarbazole hollow microspheres are synthesized via a one-step oxidative method in aqueous solution. Upon altering the oxidants and acidic media, the average diameters of the obtained hollow microspheres are tunable from 0.23 to 2.0 ?m. With attractive amine and carbazole functionalities, exposed surface area, thermostability, and photoluminescent properties, the amine-linked oligocarbazole hollow microspheres are directly assembled to yield heavy metal sorbents with excellent selectivity and recyclability, shown to efficiently remove lead from contaminated water. PMID:25228586

Liao, Yaozu; Cai, Sisi; Huang, Shaojun; Wang, Xia; Faul, Charl F J

2014-11-01

252

Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows  

NASA Astrophysics Data System (ADS)

Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism.

Batista, Carlos; Ribeiro, Ricardo M.; Teixeira, Vasco

2011-12-01

253

Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows.  

PubMed

Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism. PMID:21711813

Batista, Carlos; Ribeiro, Ricardo M; Teixeira, Vasco

2011-01-01

254

Design synthesis and optimization of permanent magnet synchronous machines based on computationally-efficient finite element analysis  

NASA Astrophysics Data System (ADS)

In this dissertation, a model-based multi-objective optimal design of permanent magnet ac machines, supplied by sine-wave current regulated drives, is developed and implemented. The design procedure uses an efficient electromagnetic finite element-based solver to accurately model nonlinear material properties and complex geometric shapes associated with magnetic circuit design. Application of an electromagnetic finite element-based solver allows for accurate computation of intricate performance parameters and characteristics. The first contribution of this dissertation is the development of a rapid computational method that allows accurate and efficient exploration of large multi-dimensional design spaces in search of optimum design(s). The computationally efficient finite element-based approach developed in this work provides a framework of tools that allow rapid analysis of synchronous electric machines operating under steady-state conditions. In the developed modeling approach, major steady-state performance parameters such as, winding flux linkages and voltages, average, cogging and ripple torques, stator core flux densities, core losses, efficiencies and saturated machine winding inductances, are calculated with minimum computational effort. In addition, the method includes means for rapid estimation of distributed stator forces and three-dimensional effects of stator and/or rotor skew on the performance of the machine. The second contribution of this dissertation is the development of the design synthesis and optimization method based on a differential evolution algorithm. The approach relies on the developed finite element-based modeling method for electromagnetic analysis and is able to tackle large-scale multi-objective design problems using modest computational resources. Overall, computational time savings of up to two orders of magnitude are achievable, when compared to current and prevalent state-of-the-art methods. These computational savings allow one to expand the optimization problem to achieve more complex and comprehensive design objectives. The method is used in the design process of several interior permanent magnet industrial motors. The presented case studies demonstrate that the developed finite element-based approach practically eliminates the need for using less accurate analytical and lumped parameter equivalent circuit models for electric machine design optimization. The design process and experimental validation of the case-study machines are detailed in the dissertation.

Sizov, Gennadi Y.

255

Regulation of 6S RNA by pRNA synthesis is required for efficient recovery from stationary phase in E. coli and B. subtilis  

PubMed Central

6S RNAs function through interaction with housekeeping forms of RNA polymerase holoenzyme (E?70 in Escherichia coli, E?A in Bacillus subtilis). Escherichia coli 6S RNA accumulates to high levels during stationary phase, and has been shown to be released from E?70 during exit from stationary phase by a process in which 6S RNA serves as a template for E?70 to generate product RNAs (pRNAs). Here, we demonstrate that not only does pRNA synthesis occur, but it is an important mechanism for regulation of 6S RNA function that is required for cells to exit stationary phase efficiently in both E. coli and B. subtilis. Bacillus subtilis has two 6S RNAs, 6S-1 and 6S-2. Intriguingly, 6S-2 RNA does not direct pRNA synthesis under physiological conditions and its non-release from E?A prevents efficient outgrowth in cells lacking 6S-1 RNA. The behavioral differences in the two B. subtilis RNAs clearly demonstrate that they act independently, revealing a higher than anticipated diversity in 6S RNA function globally. Overexpression of a pRNA-synthesis-defective 6S RNA in E. coli leads to decreased cell viability, suggesting pRNA synthesis-mediated regulation of 6S RNA function is important at other times of growth as well. PMID:22102588

Cavanagh, Amy T.; Sperger, Jamie M.; Wassarman, Karen M.

2012-01-01

256

Autographa californica multiple nucleopolyhedrovirus ac66 is required for the efficient egress of nucleocapsids from the nucleus, general synthesis of preoccluded virions and occlusion body formation  

SciTech Connect

Although orf66 (ac66) of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is conserved in all sequenced lepidopteran baculovirus genomes, its function is not known. This paper describes generation of an ac66 knockout AcMNPV bacmid mutant and analyses of the influence of ac66 deletion on the virus replication in Sf-9 cells so as to determine the role of ac66 in the viral life cycle. Results indicated that budded virus (BV) yields were reduced over 99% in ac66-null mutant infected cells in comparison to that in wild-type virus infected cells. Optical microscopy revealed that occlusion body synthesis was significantly reduced in the ac66 knockout bacmid-transfected cells. In addition, ac66 deletion interrupted preoccluded virion synthesis. The mutant phenotype was rescued by an ac66 repair bacmid. On the other hand, real-time PCR analysis indicated that ac66 deletion did not affect the levels of viral DNA replication. Electron microscopy revealed that ac66 is not essential for nucleocapsid assembly, but for the efficient transport of nucleocapsids from the nucleus to the cytoplasm. These results suggested that ac66 plays an important role for the efficient exit of nucleocapsids from the nucleus to the cytoplasm for BV synthesis as well as for preoccluded virion and occlusion synthesis.

Ke Jianhao [State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, 510275 Guangzhou (China)], E-mail: kejhkejh@yahoo.cn; Wang Jinwen; Deng Riqiang [State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, 510275 Guangzhou (China); Wang Xunzhang [State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, 510275 Guangzhou (China)], E-mail: wxz@mail.sysu.edu.cn

2008-05-10

257

Enantioselective Organocatalytic Reduction of ?-Trifluoromethyl Nitroalkenes: An Efficient Strategy for the Synthesis of Chiral ?-Trifluoromethyl Amines.  

PubMed

An efficient organocatalytic stereoselective reduction of ?-trifluoromethyl-substituted nitroalkenes, mediated by 3,5-dicarboxylic ester-dihydropyridines (Hantzsch ester type), has been successfully developed. A multifunctional thiourea-based (S)-valine derivative was found to be the catalyst of choice, promoting the reaction in up to 97?%?ee. The methodology has been applied to a wide variety of substrates, leading to the formation of differently substituted precursors of enantiomerically enriched ?-trifluoromethyl amines. The mechanism of the reaction and the mode of action of the metal-free catalytic species were computationally investigated; on the basis of DFT transition-state (TS) analysis, a model of stereoselection was also proposed. PMID:25573847

Massolo, Elisabetta; Benaglia, Maurizio; Orlandi, Manuel; Rossi, Sergio; Celentano, Giuseppe

2015-02-23

258

Pullulan-protamine as efficient haemocompatible gene delivery vector: synthesis and in vitro characterization.  

PubMed

Biodegradable non-viral vectors with good transfection efficiency is essential for successful gene delivery. The purpose of this study was to design a non-viral vector by conjugating protamine to pullulan and elucidate the potential use of pullulan protamine conjugate (PPA) as an effective, non toxic and haemocompatible gene delivery system. The particle size and surface charge were measured using Nanosizer. Derivatization was confirmed by NMR, FTIR and DSC analyses. Acid base titration revealed the buffering behaviour of the conjugate. The protection of DNA from nuclease enzyme and interaction of plasma components on the stability of nanoplexes were also analysed. The uptake studies confirmed the plasmid delivery into the nucleus and the inhibitor studies determined the uptake mechanism. Transfection experiments revealed the capability of PPA to cellular uptake in C6 cells and facilitate high gene expression. Thus, PPA proves to be a promising non-viral vector. PMID:24507274

Priya, S S; Rekha, M R; Sharma, Chandra P

2014-02-15

259

Highly efficient solvent-free synthesis of 1,3-diacylglycerols by lipase immobilised on nano-sized magnetite particles.  

PubMed

Recently, 1,3-DAGs (1,3-diacylglycerols) have attracted considerable attention as healthy components of food, oil and pharmaceutical intermediates. Generally, 1,3-DAG is prepared by lipase-mediated catalysis in a solvent free system. However, the system's high reaction temperature (required to reach the reactants' melting point), high substrate concentration and high viscosity severely reduce the lipase's activity, selectivity and recycling efficiency. In this report, MjL (Mucor javanicus lipase) was found to have the best performance in the solvent-free synthesis of 1,3-DAGs of several common commercial lipases. By covalent binding to amino-group-activated NSM (nano-sized magnetite) particles and cross-linking to form an enzyme aggregate coat, MjL's specific activity increased 10-fold, and was able to be reused for 10 cycles with 90% residual activity at 55°C. 1,3-DAGs of lauric, myristic, palmitic, stearic, oleic and linoleic acid were prepared using the resulting immobilised enzyme, all with yields greater than 90%, and the reaction time was also greatly reduced. PMID:24054246

Meng, Xiao; Xu, Gang; Zhou, Qin-Li; Wu, Jian-Ping; Yang, Li-Rong

2014-01-15

260

Multifunctional "clickates" as versatile extended heteroaromatic building blocks: efficient synthesis via click chemistry, conformational preferences, and metal coordination.  

PubMed

Click chemistry has been utilized to access 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridines (BTPs) as versatile extended heteroaromatic building blocks for their exploitation in supramolecular chemistry, in particular foldamer and ligand design. In addition to their high-yielding synthesis using Cu(I)-catalyzed Huisgen-type 1,3-dipolar cycloaddition reactions the formed triazole moieties constitute an integral part of the BTP framework and encode both its pronounced conformational preferences as well as its chelating ability. A diverse set of symmetrical and non-symmetrical BTPs carrying electron-donating and -withdrawing substituents at both terminal aryl and the central pyridine moieties has efficiently been synthesized and could furthermore readily be postfunctionalized with amphiphilic side chains and porphyrin chromophores. In both solution and solid state, the BTP scaffold adopts a highly conserved horseshoe-like anti-anti conformation. Upon protonation or metal coordination, the BTP scaffold switches to the chelating syn-syn conformation. Iron and europium complexes have been prepared, successfully characterized by single-crystal X-ray diffraction analysis, and investigated with regard to their spin state and luminescent properties. The extended heteroaromatic BTP scaffold should prove useful for the design of responsive foldamer backbones and the preparation of new magnetic and emissive materials. PMID:17948330

Meudtner, Robert M; Ostermeier, Marc; Goddard, Richard; Limberg, Christian; Hecht, Stefan

2007-01-01

261

Efficient Synthesis and Anti-Tubercular Activity of a Series of Spirocycles: An Exercise in Open Science  

PubMed Central

Tuberculosis afflicts an estimated 2 billion people worldwide and causes 1.3 million deaths annually. Chemotherapeutic solutions rely on drugs developed many years ago, with only one new therapeutic having been approved in the last 40 years. Given the rise of drug-resistant strains, there is an urgent need for the development of a more robust drug development pipeline. GlaxoSmithKline recently placed the structures and activities of 177 novel anti-tubercular leads in the public domain, as well as the results of ongoing optimisation of some of the series. Since many of the compounds arose from screening campaigns, their provenance was unclear and synthetic routes were in many cases not reported. Here we present the efficient synthesis of several novel analogues of one family of the GSK compounds—termed “Spiros”—using an oxa-Pictet–Spengler reaction. The new compounds are attractive from a medicinal chemistry standpoint and some were potent against the virulent strain, suggesting this class is worthy of further study. The research was carried out using open source methodology, providing the community with full access to all raw experimental data in real time. PMID:25493550

Badiola, Katrina A.; Quan, Diana H.; Triccas, James A.; Todd, Matthew H.

2014-01-01

262

Hydrothermal synthesis of rutile-anatase TiO2 nanobranched arrays for efficient dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Rutile-anatase TiO2 nanobranched arrays were prepared in two sequential hydrothermal-synthesis steps. The morphologies and crystalline nanostructures of the samples were investigated by controlling growth time and the concentration of the titanium precursor. All samples were characterized by field-emission scanning electron microscopy and X-ray diffraction analysis. It was found that treating the surfaces of rutile TiO2 nanorods with aqueous TiCl4 solutions allows the anatase TiO2 nanobranches to grow perpendicular to the main rutile TiO2 nanorods attached to the FTO glass. Irregularly shaped, dense TiO2 structures formed in the absence of TiCl4 treatment. A light-to-electricity conversion efficiency of 3.45% was achieved using 2.3 ?m tall TiO2 nanobranched arrays in a dye-sensitized solar cell. This value is significantly higher than that observed for pure rutile TiO2 nanorods.

Kwon, Soon Jin; Im, Hyo Been; Nam, Jung Eun; Kang, Jin Kyu; Hwang, Taek Sung; Yi, Kwang Bok

2014-11-01

263

Chemoselectivity-induced multiple interfaces in MWCNT/Fe3O4@ZnO heterotrimers for whole X-band microwave absorption.  

PubMed

A chemoselective route to induce Fe3O4@ZnO core-shell nanoparticles decorating carbon nanotubes to form MWCNT/Fe3O4@ZnO heterotrimers has been developed. Charges are redistributed in the heterotrimers through C-O-Zn, C-O-Fe and Fe-O-Zn bondings, giving rise to multiple electronic phases. The generated significant interfacial polarization and synergetic interaction between dielectric and magnetic absorbers result in the MWCNT/Fe3O4@ZnO heterotrimers with high-performance microwave absorption in an entire X band. PMID:25080205

Wang, Zhijiang; Wu, Lina; Zhou, Jigang; Jiang, Zhaohua; Shen, Baozhong

2014-11-01

264

Chemoselective hydroamination of vinyl arenes catalyzed by an NHC-amidate-alkoxide Pd(II) complex and p-TsOH  

PubMed Central

The hydroamination of various substituted vinyl arenes with benzenesulfonamide was explored using an NHC-amidate-alkoxide palladium catalyst in conjunction with p-TsOH. Utilizing halide-substituted and electron-rich vinyl arenes, this methodology selectively furnished the cross-coupled hydroamination products in moderate to excellent yields in a Markovnikov fashion while greatly reducing undesired acid-catalyzed homocoupling of the vinyl arenes. Electron-rich vinyl arenes typically required milder conditions than electron-poor ones. While most effective for para-substituted substrates, the catalyst system also furnished the desired products from ortho- and meta-substituted vinyl arenes with high chemoselectivities. PMID:24039309

Giles, Richard; O'Neill, Justin; Lee, Joo Ho; Chiu, Michael K.

2013-01-01

265

Efficient synthesis of functionalized dihydro-1H-indol-4(5H)-ones via one-pot three-component reaction under catalyst-free conditions.  

PubMed

A facile and efficient one-pot procedure for the preparation of functionalized dihydro-1H-indol-4(5H)-ones by a catalyst-free, three-component reaction of 1,3-dicarbonyl compounds, arylglyoxal monohydrate and enaminones under mild conditions in excellent yield is reported. This synthesis was confirmed to follow the group-assisted-purification (GAP) chemistry process, which can avoid traditional purifications, chromatography, and recrystallization. PMID:23597107

Wang, Hui-Yan; Shi, Da-Qing

2013-05-13

266

ONE-POT SYNTHESIS OF 2,4,5TRISUBSTITUTED IMIDAZOLES USING [BPy]H2PO4, AN EFFICIENT AND RECYCLABLE CATALYST  

Microsoft Academic Search

[BPy]H2PO4 was easily prepared and used as efficient and recyclable catalyst for the one-pot synthesis of 2,4,5-trisubstituted imidazoles under solvent-free conditions in good to excellent yields. Solvent-free conditions, simple experimental and work-up procedures, along with the use of non-toxic, recyclable catalyst of an environmentally benign nature are remarkable features of the procedure.

Yuliang Zhang; Zhongqiang Zhou

2012-01-01

267

A highly efficient and robust cell-free protein synthesis system prepared from wheat embryos: Plants apparently contain a suicide system directed at ribosomes  

Microsoft Academic Search

Current cell-free protein synthesis systems can synthesize proteins with high speed and accuracy, but produce only a low yield because of their instability over time. Here we describe the preparation of a highly efficient but also robust cell-free system from wheat embryos. We first investigated the source of the instability of existing systems in light of endogenous ribosome-inactivating proteins and

Kairat Madin; Tatsuya Sawasaki; Tomio Ogasawara; Yaeta Endo

2000-01-01

268

Water-soluble aminocurdlan derivatives by chemoselective azide reduction using NaBH4.  

PubMed

Water-solubility can often enhance the utility of polysaccharide derivatives, for example in pharmaceutical and biomedical applications. Synthesis of water-soluble aminopolysaccharides, particularly those bearing other sensitive functional groups, can be a challenging endeavor. Curdlan is a bioactive ?-1,3-glucan with considerable promise for biomedical applications. Aminocurdlans are intriguing target molecules for study of, for example, their interactions with the proteins that form tight junctions between enterocytes. Herein we report the preparation of two water-soluble 6-aminocurdlans starting from 6-bromo-6-deoxycurdlan. The 6-bromide was first displaced by nucleophilic substitution with sodium azide in dimethyl sulfoxide. The O-2 groups were acylated with hydrophilic oligo (ethylene oxide) esters, so as to enhance aqueous solubility. The resultant 6-azido-6-deoxy-2,4-di-O-trioxadecanoylcurdlan was then treated with excess sodium borohydride to reduce the azide; unexpectedly, the water-soluble product proved to be the amide, 6-trioxadecanamido-6-deoxycurdlan. Regioselectivity and degree of substitution (DS) of those derivatives were characterized by means of (1)H NMR, (13)C NMR and FTIR-spectroscopy, elemental analysis, and titration. Alternatively, direct borohydride reduction of the parent 6-azido-6-deoxycurdlan afforded 6-amino-6-deoxycurdlan that was also water-soluble. PMID:25817646

Zhang, Ruoran; Edgar, Kevin J

2015-05-20

269

Efficient synthesis and characterization of ergosterol laurate in a solvent-free system.  

PubMed

Ergosterol and its derivatives have attracted much attention for a variety of health benefits, such as anti-inflammatory and antioxidant activities. However, ergosterol esters are advantageous because this compound has better solubility than the free ergosterol. In this work, ergosterol laurate was efficiently synthesized for the first time by direct esterification in a solvent-free system. The desired product was purified, characterized by Fourier transform infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance, and finally confirmed to be ergosterol laurate. Meanwhile, the effect of various catalysts, catalyst dose, reaction temperature, substrate molar ratio, and reaction time were studied. Both the conversion of ergosterol and the selectivity of the desired product can reach above 89% under the selected conditions: sodium dodecyl sulfate + hydrochloric acid as the catalyst, 2:1 molar ratio of lauric acid/ergosterol, catalyst dose of 4% (w/w), 120 °C, and 2 h. The oil solubility of ergosterol and its laurate was also compared. The results showed that the solubility of ergosterol in oil was significantly improved by direct esterification with lauric acid, thus greatly facilitating the incorporation into a variety of oil-based systems. PMID:25405492

He, Wen-Sen; Yin, Ji; Xu, Han-Shan; Qian, Qiu-Ying; Jia, Cheng-Sheng; Ma, Hai-Le; Feng, Biao

2014-12-01

270

A simple, efficient and environmentally benign synthetic protocol for the synthesis of spirooxindoles using choline chloride-oxalic acid eutectic mixture as catalyst/solvent system.  

PubMed

An efficient and environmentally benign domino protocol has been presented for the synthesis of structurally diverse spirooxindoles spiroannulated with pyranopyridopyrimidines, indenopyridopyrimidines, and chromenopyridopyrimidines involving three-component reaction of aminouracils, isatins and cyclic carbonyl compounds in deep eutectic solvent (choline chloride-oxalic acid: 1:1) which acts as efficient catalyst and environmentally benign reaction medium. The present protocol offers several advantages such as operational simplicity with easy workup, shorter reaction times excellent yields with superior atom economy and environmentally benign reaction conditions with the use of cost-effective, recyclable, non-toxic and bio-degradable DES as catalyst/solvent. PMID:25329839

Khandelwal, Sarita; Rajawat, Anshu; Tailor, Yogesh Kumar; Kumar, Mahendra

2014-01-01

271

Trifluoroacetic Acid as an Efficient Catalyst for One-Pot, Four-Component Synthesis of 1,2,4,5Tetrasubstituted Imidazoles Under Microwave-Assisted, Solvent-Free Conditions  

Microsoft Academic Search

An efficient method for synthesis of various tetrasubstituted imidazoles, using trifluoroacetic acid (TFA) as a catalytic support, by four-component condensation of benzil, aldehydes, amines, and ammonium acetate under microwave-irradiated, solvent-free conditions is described.

Mohammad R. Mohammadizadeh; Alireza Hasaninejad; M. Bahramzadeh

2009-01-01

272

Rational design and synthesis of efficient Carbon and/or Silica functional nanomaterials for electrocatalysis and nanomedicine  

NASA Astrophysics Data System (ADS)

In nanomaterials there is a strong correlation between structure and properties. Thus, the design and synthesis of nanomaterials with well-defined structures and morphology is essential in order to produce materials with not only unique but also tailorable properties. The unique properties of nanomaterials in turn can be taken advantage of to create materials and nanoscale devices that can help address important societal issues, such as meeting renewable energy sources and efficient therapeutic and diagnostic methods to cure a range of diseases. In this thesis, the different synthetic approaches I have developed to produce functional nanomaterials composed of earth-abundant elements (mainly carbon and silica) at low cost in a very sustainable manner are discussed. In Chapter 1, the fundamental properties of nanomaterials and their properties and potential applications in many areas are introduced. In chapter 2, a novel synthetic method that allows polymerization of polyaniline (PANI), a conducting polymer, inside cylindrical channel pores of nanoporous silica (SBA-15) is discussed. In addition, the properties of the III resulting conducting polymer in the confined nanochannel spaces of SBA-15, and more importantly, experimental demonstration of the use of the resulting hybrid material (PANI/SBA-15 material) as electocatalyst for electrooxidation reactions with good overpotential, close to zero, are detailed. In chapter 3, the synthetic approach discussed in Chapter 2 is further extended to afford nitrogen- and oxygen-doped mesoporous carbons. This is possible by pyrolysis of the PANI/SBA-15 composite materials under inert atmosphere, followed by etching away their silica framework. The high catalytic activity of resulting carbon-based materials towards oxygen reduction reaction despite they do not possess any metal dopants is also included. The potential uses of nanomaterials in areas such as nanomedicine need deep understanding of the biocompatibility/ toxicity of the materials. In Chapter 4, comparative in vitro and in vivo assessments of the biological properties and murine lung toxicity (biocompatibility) of the carbon-based nanomaterials synthesized above and in core-shell architectures containing carbon, silica and cobalt is presented. The results indicate that silica shell is essential for biocompatibility. Furthermore, cobalt oxide is the preferred phase over the zero valent Co(0) phase to impart biocompatibility to cobalt-based nanoparticles. This study is a result of collaboration between Asefa's research group at Rutgers University and Souid's research group at United Arab Emirates University. In Chapter 5, a new synthetic method to carbon nanoneedles (or a new class of carbon nanomaterials with high aspect ratios) is presented. In the work, cellulose nanocrystals are prepared and used as precursor for carbon nanostructures. Unlike other types of carbon nanomaterials, carbon IV nanoneedles possess high surface area and large proportion of edge planes, which have outstanding charge transfer and catalytic properties. The resulting metal-free, carbon nanoneedles are shown to serve as effective electrocatalysts for oxidation of hydrazine. In Chapter 6, the synthesis of amorphous carbon nanoneedles containing cobalt and their catalytic activities for oxygen reduction reaction is discussed. Even though the activity of the materials is lower than the one discussed in Chapter 3 for polyaniline-derived mesoporous carbons, the result and discussion in this chapter provides new insights on the effects and advantages of carbon nanoneedles on the electrocatalytic activity of the materials. In addition, the effects of cobalt content and nanoneedles' structures on the catalytic activity of the materials are described. In chapter 7, the synthesis of very small Au nanoparticles within SBA-15 mesoporous silica host materials by galvanic exchange reactions is described. The resulting Au/SBA-15 materials with different size Au nanoparticles are shown to have very interesting surface plasmon resonance (SPR) activity as a result of

Da Silva, Rafael

273

Witting Reaction Using a Stabilized Phosphorus Ylid: An Efficient and Stereoselective Synthesis of Ethyl Trans-Cinnamate  

ERIC Educational Resources Information Center

An instructive experiment for the synthesis of ethyl trans-cinnamate, a pleasant smelling ester used in perfumery and flavoring by the reaction of benzaldehyde with the stable ylid triphenylphosphorane is described. The synthesis, workup and characterization of trans-cinnamate may be accomplished in a single laboratory session with commonly…

Speed, Traci J.; Mclntyre, Jean P.; Thamattoor, Dasan M.

2004-01-01

274

Efficient Solid-Phase Synthesis of 3-Substituted-5-Oxo-5H-Thiazolo[2,3-b]Quinazoline-8-Carboxamide under Mild Conditions with Two Diversity Positions  

PubMed Central

Highly efficient solid-phase synthesis of thiazolo[2,3,b]quinazolines under mild conditions was developed using resin-bound 2-amino-terephthalamic acid, Fmoc-NCS, and bromoketones. Primary amines immobilized to an acid-cleavable backbone amide linker were acylated with 1-methyl-2-aminoterephtalate. Following cleavage of the methyl ester, Fmoc-NCS was used to form a resin-bound thiourea. Bromoketones were subsequently added to form an aminothiazole ring and the cyclization was performed using DIC/HOBt to afford thiazolo[2,3,b]quinazolines. Highly efficient solid-phase synthesis is amenable to high throughput/combinatorial synthesis. PMID:17907790

Bouillon, Isabelle; Krch?ák, Viktor

2008-01-01

275

Organic-inorganic hybrid supermicroporous iron(III) phosphonate nanoparticles as an efficient catalyst for the synthesis of biofuels.  

PubMed

Here we report a novel family of crystalline, supermicroporous iron(III) phosphonate nanomaterials (HFeP-1-3, HFeP-1-2, and HFeP-1-4) with different Fe(III)-to-organophosphonate ligand mole ratios. The materials were synthesized by using a hydrothermal reaction between benzene-1,3,5-triphosphonic acid and iron(III) chloride under acidic conditions (pH ? 4.0). Powder X-ray diffraction, N2 sorption, transmission and scanning electron microscopy (TEM and SEM) image analysis, thermogravimetric and differential thermal analysis (TGA-DTA), and FTIR spectroscopic tools were used to characterize the materials. The triclinic crystal phase [P1(2) space group] of the hybrid iron phosphonate was established by a Rietveld refinement of the PXRD analysis of HFeP-1-3 by using the MAUD program. The unit cell parameters are a = 8.749(1), b = 8.578(1), c = 17.725(3)?Å; ? = 104.47(3), ? = 97.64(1), ? = 113.56(3)°; and V = 1013.41?Å(3). With these crystal parameters, we proposed an 24-membered-ring open framework structure for HFeP-1. Compound HFeP-1-3, with an starting Fe/ligand molar ratio of 3.0, shows the highest Brunauer-Emmett-Telller (BET) surface area of 556?m(2) g(-1) and uniform supermicropores of approximately 1.1?nm. The acidic surface of the porous iron(III) phosphonate nanoparticles was used in a highly efficient and recyclable catalytic transesterification reaction for the synthesis of biofuels under mild reaction conditions. PMID:23650095

Pramanik, Malay; Bhaumik, Asim

2013-06-24

276

ZrCl4\\/NaI and ZrOCl2 · 8H2O\\/NaI as effective systems for reductive coupling of sulfonyl chlorides and chemoselective deoxygenation of sulfoxides  

Microsoft Academic Search

Zirconium tetrachloride\\/sodium iodide (ZrCl4\\/NaI) and ZrOCl2 · 8H2O\\/NaI conduct effective reductive coupling of sulfonyl chlorides to their corresponding disulfides and chemoselective reduction of sulfoxides to their thioethers in high yields.

H. Firouzabadi; N. Iranpoor; M. Jafarpour

2005-01-01

277

Chemical Synthesis of a Hyaluronic Acid Decasaccharide  

PubMed Central

The chemical synthesis of a hyaluronic acid decasaccharide using the pre-activation based chemoselective glycosylation strategy is described. Assembly of large oligosaccharides is generally challenging due to the increased difficulties in both glycosylation and deprotection. Indeed, the same building blocks previously employed for hyaluronic acid hexasaccharide syntheses failed to yield the desired decasaccharide. After extensive experimentation, the decasaccharide backbone was successfully constructed with an overall yield of 37% from disaccharide building blocks. The trichloroacetyl group was used as the nitrogen protective group for the glucosamine units and the addition of TMSOTf was found to be crucial to suppress the formation of trichloromethyl oxazoline side-product and enable high glycosylation yield. For deprotections, the combination of a mild basic condition and the monitoring methodology using 1H-NMR allowed the removal of all base-labile protective groups, which facilitated the generation of the fully deprotected HA decasaccharide. PMID:19764799

Lu, Xiaowei; Kamat, Medha N.; Huang, Lijun; Huang, Xuefei

2009-01-01

278

Rapid Chemoselective Bioconjugation Through the Oxidative Coupling of Anilines and Aminophenols  

PubMed Central

A highly efficient protein bioconjugation method is described involving the addition of anilines to o-aminophenols in the presence of sodium periodate. The reaction takes place in aqueous buffer at pH 6.5 and can reach high levels of completion in 2–5 min. The product of the reaction has been characterized using X-ray crystallography, which revealed that an unprecedented oxidative ring contraction occurs after the coupling step. The compatibility of the reaction with protein substrates has been demonstrated through the attachment of small molecules, polymer chains, and peptides to p-aminophenylalanine residues introduced into viral capsids through amber stop codon suppression. The coupling of anilines to o-aminophenol groups derived from tyrosine residues is also described. The compatibility of this method with thiol modification chemistry is shown through the attachment of a near-IR fluorescent chromophore to cysteine residues inside the viral capsid shells, followed by the attachment of integrin-targeting RGD peptides to anilines on the exterior surface. PMID:21919497

Behrens, Christopher R.; Hooker, Jacob M.; Obermeyer, Allie C.; Romanini, Dante W.; Katz, Elan M.; Francis, Matthew B.

2012-01-01

279

Efficient Synthesis of the Cyclopentanone Fragrances (Z)-3-(2-oxopropyl)-2-(pent-2-en-1-yl)cyclopentanone and Magnolione.  

PubMed

This paper describes the selective syntheses of two cis-isomer enriched cyclopentanone fragrances: (Z)-3-(2-oxopropyl)-2-(pent-2-en-1-yl)cyclopentanone (4 steps, 62% overall yield, 67% cis) and Magnolione(®) (5 steps, 60% overall yield, 55% cis). In addition, the asymmetric synthesis of (3aR,7aS)-5-methyl-2,3,3a,4,7,7a-hexahydro-1H-inden-1-one as well as (3a'R,7a'S)-5'-methyl-2',3',3a',4',7',7a'-hexahydrospiro[[1,3]dioxolane-2,1'-indene]) has been realized by an efficient kinetic resolution, which enables the selective synthesis of the 2S,3R-isomer-enriched 3 and 4. PMID:24729640

Pan, Guojun; Williams, Robert M

2014-01-14

280

Efficient Synthesis of the Cyclopentanone Fragrances (Z)-3-(2-oxopropyl)-2-(pent-2-en-1-yl)cyclopentanone and Magnolione  

PubMed Central

This paper describes the selective syntheses of two cis-isomer enriched cyclopentanone fragrances: (Z)-3-(2-oxopropyl)-2-(pent-2-en-1-yl)cyclopentanone (4 steps, 62% overall yield, 67% cis) and Magnolione® (5 steps, 60% overall yield, 55% cis). In addition, the asymmetric synthesis of (3aR,7aS)-5-methyl-2,3,3a,4,7,7a-hexahydro-1H-inden-1-one as well as (3a'R,7a'S)-5'-methyl-2',3',3a',4',7',7a'-hexahydrospiro[[1,3]dioxolane-2,1'-indene]) has been realized by an efficient kinetic resolution, which enables the selective synthesis of the 2S,3R-isomer-enriched 3 and 4. PMID:24729640

Pan, Guojun; Williams, Robert M.

2014-01-01

281

Key Building Blocks via Enzyme-Mediated Synthesis  

NASA Astrophysics Data System (ADS)

Biocatalytic approaches to valuable building blocks in organic synthesis have emerged as an important tool in the last few years. While first applications were mainly based on hydrolases, other enzyme classes such as oxidoreductases or lyases moved into the focus of research. Nowadays, a vast number of biotransformations can be found in the chemical and pharmaceutical industries delivering fine chemicals or drugs. The mild reaction conditions, high stereo-, regio-, and chemoselectivities, and the often shortened reaction pathways lead to economical and ecological advantages of enzymatic conversions. Due to the enormous number of enzyme-mediated syntheses, the present chapter is not meant to be a complete review, but to deliver comprehensive insights into well established enzymatic systems and recent advances in the application of enzymes in natural product synthesis. Furthermore, it is focused on the most frequently used enzymes or enzyme classes not covered elsewhere in the present volume.

Fischer, Thomas; Pietruszka, Jörg

282

Sulfonic Acid Functionalized Nano-?-Al2O3: A New, Efficient, and Reusable Catalyst for Synthesis of 3-Substituted-2H-1,4-Benzothiazines  

PubMed Central

A simple and efficient synthetic protocol has been developed for the synthesis of 3-substituted-2H-1,4-benzothiazines by using a novel sulfonic acid functionalized nano-?-Al2O3 catalyst, devoid of corrosive acidic, and basic reagents. The developed method has the advantages of good to excellent yields, short reaction times, operational simplicity, and a recyclable catalyst. The catalyst can be prepared by a simple procedure from inexpensive and readily available nano-?-Al2O3 and has been shown to be recoverable and reusable up to six cycles without any loss of activity. PMID:23935435

Li, Wei Lin; Tian, Shuan Bao; Zhu, Feng

2013-01-01

283

Ultrasonic activated efficient synthesis of chromenes using amino-silane modified Fe3O4 nanoparticles: A versatile integration of high catalytic activity and facile recovery  

NASA Astrophysics Data System (ADS)

An efficient synthesis of 2-amino-4H-chromenes is achieved by one pot three component coupling reaction of aldehyde, malononitrile, and resorcinol using amino-silane modified Fe3O4 nanoparticles (MNPs-NH2) heterogeneous nanocatalyst under sonic condition. The attractive advantages of the present process are mild reaction conditions, short reaction times, easy isolation of products, good yields and simple operational procedures. Combination of the advantages of ultrasonic irradiation and magnetic nanoparticles provides important methodology to carry out catalytic transformations.

Safari, Javad; Zarnegar, Zohre

2014-08-01

284

Sulfonic acid functionalized nano-?-Al2O3: a new, efficient, and reusable catalyst for synthesis of 3-substituted-2H-1,4-benzothiazines.  

PubMed

A simple and efficient synthetic protocol has been developed for the synthesis of 3-substituted-2H-1,4-benzothiazines by using a novel sulfonic acid functionalized nano-?-Al2O3 catalyst, devoid of corrosive acidic, and basic reagents. The developed method has the advantages of good to excellent yields, short reaction times, operational simplicity, and a recyclable catalyst. The catalyst can be prepared by a simple procedure from inexpensive and readily available nano-?-Al2O3 and has been shown to be recoverable and reusable up to six cycles without any loss of activity. PMID:23935435

Li, Wei Lin; Tian, Shuan Bao; Zhu, Feng

2013-01-01

285

Synthesis of a naphthyridone p38 MAP kinase inhibitor.  

PubMed

Compound 1 is a p38 MAP kinase inhibitor potentially useful for the treatment of rheumatoid arthritis and psoriasis. A novel six-step synthesis suitable for large-scale preparation was developed in support of a drug development program at Merck Research Laboratories. The key steps include a tandem Heck-lactamization, N-oxidation, and a highly chemoselective Grignard addition of 4-(N-tert-butylpiperidinyl)magnesium chloride to a naphthyridone N-oxide. The N-oxide exerted complete chemoselectivity via chelation in directing the Grignard addition to the alpha position as opposed to 1,4-addition on the ene-lactam. The dihydropyridyl adduct was in situ aromatized with isobutylchloroformate followed by heating in pyridine. Syntheses of Grignard precursor, N-tert-butyl-4-chloro-piperidine, were accomplished via transamination with a quaternary ammonium piperidone or via addition of methylmagnesium chloride to an iminium ion. Utilizing this chemistry, multi-kilogram preparation of compound 1 was successfully demonstrated. PMID:17064039

Chung, John Y L; Cvetovich, Raymond J; McLaughlin, Mark; Amato, Joseph; Tsay, Fuh-Rong; Jensen, Mark; Weissman, Steve; Zewge, Daniel

2006-10-27

286

High chemoselectivity of an advanced iron catalyst for the hydrogenation of aldehydes with isolated C?C bond: a computational study.  

PubMed

Knölker's iron complex is a "green" catalyst that exhibits low toxicity and is abundant in nature. Density functional theory (DFT) was used to explore the highly chemoselective nature of the catalytic hydrogenation of CH2?CHCH2CHO. An outer-sphere concerted hydrogen transfer was found to be the most reasonable kinetic route for the hydrogenation of the olefin. However, the C?C hydrogenation reaction has a high free energy barrier of 28.1 kcal/mol, requiring a high temperature to overcome. By comparison, the CH?O bond concerted hydrogen-transfer reaction catalyzed using Knölker's iron catalyst has an energy barrier of only 14.0 kcal/mol. Therefore, only the CH?O of CH2?CHCH2CHO can be hydrogenated in the presence of Knölker's catalyst at room temperature, due to kinetic domination. All computational results were in good agreement with experimental results. PMID:25222376

Lu, Xi; Cheng, Runjiao; Turner, Nicholas; Liu, Qian; Zhang, Mingtao; Sun, Xiaomin

2014-10-01

287

Efficient and green synthesis of 4H-pyrans and 4H-pyrano[2,3-c] pyrazoles catalyzed by task-specific ionic liquid [bmim]OH under solvent-free conditions  

Microsoft Academic Search

A facile and convenient procedure for the synthesis of 4H-pyrans from aldehydes, malononitrile, and ethyl acetoacetate\\/acetylacetone and also synthesis of 4H-pyrano[2,3-c]pyrazoles from three-component condensation of aldehydes, malononitrile, and pyrazolone or four-component condensation of aldehydes, malononitrile, ethyl acetoacetate, and hydrazine monohydrate using [bmim]OH as task-specific ionic liquid has been described. The protocol proves to be efficient and environmentally benign in terms

Jitender M. Khurana; Ankita Chaudhary

2012-01-01

288

Cell-free protein synthesis from a release factor 1 deficient Escherichia coli activates efficient and multiple site-specific nonstandard amino acid incorporation.  

PubMed

Site-specific incorporation of nonstandard amino acids (NSAAs) into proteins enables the creation of biopolymers, proteins, and enzymes with new chemical properties, new structures, and new functions. To achieve this, amber (TAG codon) suppression has been widely applied. However, the suppression efficiency is limited due to the competition with translation termination by release factor 1 (RF1), which leads to truncated products. Recently, we constructed a genomically recoded Escherichia coli strain lacking RF1 where 13 occurrences of the amber stop codon have been reassigned to the synonymous TAA codon (rEc.E13.?prfA). Here, we assessed and characterized cell-free protein synthesis (CFPS) in crude S30 cell lysates derived from this strain. We observed the synthesis of 190±20 ?g/mL of modified soluble superfolder green fluorescent protein (sfGFP) containing a single p-propargyloxy-L-phenylalanine (pPaF) or p-acetyl-L-phenylalanine. As compared to the parent rEc.E13 strain with RF1, this results in a modified sfGFP synthesis improvement of more than 250%. Beyond introducing a single NSAA, we further demonstrated benefits of CFPS from the RF1-deficient strains for incorporating pPaF at two- and five-sites per sfGFP protein. Finally, we compared our crude S30 extract system to the PURE translation system lacking RF1. We observed that our S30 extract based approach is more cost-effective and high yielding than the PURE translation system lacking RF1, ?1000 times on a milligram protein produced/$ basis. Looking forward, using RF1-deficient strains for extract-based CFPS will aid in the synthesis of proteins and biopolymers with site-specifically incorporated NSAAs. PMID:24328168

Hong, Seok Hoon; Ntai, Ioanna; Haimovich, Adrian D; Kelleher, Neil L; Isaacs, Farren J; Jewett, Michael C

2014-06-20

289

Cell-free Protein Synthesis from a Release Factor 1 Deficient Escherichia coli Activates Efficient and Multiple Site-specific Nonstandard Amino Acid Incorporation  

PubMed Central

Site-specific incorporation of nonstandard amino acids (NSAAs) into proteins enables the creation of biopolymers, proteins, and enzymes with new chemical properties, new structures, and new functions. To achieve this, amber (TAG codon) suppression has been widely applied. However, the suppression efficiency is limited due to the competition with translation termination by release factor 1 (RF1), which leads to truncated products. Recently, we constructed a genomically recoded Escherichia coli strain lacking RF1 where 13 occurrences of the amber stop codon have been reassigned to the synonymous TAA codon (rEc.E13.?prfA). Here, we assessed and characterized cell-free protein synthesis (CFPS) in crude S30 cell lysates derived from this strain. We observed the synthesis of 190 ± 20 ?g/mL of modified soluble superfolder green fluorescent protein (sfGFP) containing a single p-propargyloxy-l-phenylalanine (pPaF) or p-acetyl-l-phenylalanine. As compared to the parent rEc.E13 strain with RF1, this results in a modified sfGFP synthesis improvement of more than 250%. Beyond introducing a single NSAA, we further demonstrated benefits of CFPS from the RF1-deficient strains for incorporating pPaF at two- and five-sites per sfGFP protein. Finally, we compared our crude S30 extract system to the PURE translation system lacking RF1. We observed that our S30 extract based approach is more cost-effective and high yielding than the PURE translation system lacking RF1, ?1000 times on a milligram protein produced/$ basis. Looking forward, using RF1-deficient strains for extract-based CFPS will aid in the synthesis of proteins and biopolymers with site-specifically incorporated NSAAs. PMID:24328168

2014-01-01

290

Efficient routes toward the synthesis of the D-rhamno-trisaccharide related to the A-band polysaccharide of Pseudomonas aeruginosa  

PubMed Central

Summary The present work describes efficient avenues for the synthesis of the trisaccharide repeating unit [?-D-Rhap-(1?3)-?-D-Rhap-(1?3)-?-D-Rhap] associated with the A-band polysaccharide of Pseudomonas aeruginosa. One of the key steps involved 6-O-deoxygenation of either partially or fully acylated 4,6-O-benzylidene-1-thiomannopyranoside by radical-mediated redox rearrangement in high yields and regioselectivity. The D-rhamno-thioglycosides so obtained allowed efficient access to the trisaccharide target via stepwise glycosylation as well as a one-pot glycosylation protocol. In a different approach, a 4,6-O-benzylidene D-manno-trisaccharide derivative was synthesized, which upon global 6-O-deoxygenation followed by deprotection generated the target D-rhamno-trisaccharide. The application of the reported regioselective radical-mediated deoxygenation on 4,6-O-benzylidene D-manno thioglycoside (hitherto unexplored) has potential for ramification in the field of synthesis of oligosaccharides based on 6-deoxy hexoses. PMID:25161705

Chaudhury, Aritra; Maity, Sajal K

2014-01-01

291

Efficient synthesis of the tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain.  

PubMed

The tetrasaccharide repeating unit of the O-antigen of Escherichia coli O174 strain was synthesized applying sequential glycosylations of suitably functionalized monosaccharide intermediates. Activation of glycosyl trichloroacetimidate derivatives using nitrosyl tetrafluoroborate (NOBF4) has been used during the synthesis. The glycosylation steps were high yielding with satisfactory stereo outcome. PMID:25318901

Bhaumik, Ishani; Ghosh, Tamashree; Misra, Anup Kumar

2014-11-18

292

Controllable synthesis of mesoporous carbon nanospheres and Fe-N/carbon nanospheres as efficient oxygen reduction electrocatalysts.  

PubMed

The synthesis of mesoporous carbon nanospheres (MCNs), especially with diameters below 200 nm remains a great challenge due to weak interactions between the carbon precursors and soft templates, as well as the uncontrollable cross-linking rate of carbon precursors. Herein, we demonstrate a simple acid-assisted, hydrothermal synthesis approach to synthesizing such uniform MCNs with well controlled diameters ranging from 20 to 150 nm under highly acidic conditions (2 M HCl). Both the carbon precursor and the template are partly protonated under such conditions and show additional Coulombic interactions with chloride ions (acts as mediators). This kind of enhanced interaction is similar to that of the "I(+)X(-)S(+)" mechanism in the synthesis of mesoporous metal oxide, which can effectively retard the cross-linking rate of resol molecules and avoid macroscopic phase separation during the hydrothermal synthesis. Due to their uniform spherical morphology, small diameter, and high surface areas, MCNs can be modified with Fe and N species via impregnation of cheap precursors (ferric nitrate and dicyandiamide), which are further converted into nonprecious electrocatalysts for oxygen reduction reactions. The resulting Fe-N/MCNs exhibit high catalytic activities, long-term stability and improved methanol tolerance under alkaline conditions, which can be potentially used in direct methanol fuel cells and metal-air batteries. PMID:25779978

Wei, Jing; Liang, Yan; Zhang, Xinyi; Simon, George P; Zhao, Dongyuan; Zhang, Jin; Jiang, Sanping; Wang, Huanting

2015-03-26

293

Iodine catalyzed efficient synthesis of symmetrical diaryl sulfoxides from arenes and thionyl chloride under solvent-free conditions  

Microsoft Academic Search

Synthesis of symmetrical diaryl sulfoxides from arenes and thionyl chloride in the presence of a catalytic amount of iodine at room temperature under solvent-free conditions is described. Mild reaction conditions, easy workup, high yield, and easily available catalyst are important features of this method.

Hong She Wang; Jun E. Zeng

2007-01-01

294

Simultaneous sonication assistance for the synthesis of pyrroloacridinones and its efficient catalyst HBF4 supported on uniform spherical silica nanoparticles.  

PubMed

Fluoroboric acid (HBF4) adsorbed on mesoporous silica nanoparticles of 600nm dimension was synthesized and characterized by N2 adsorption, HRTEM, EDX, XPS. The applicability of silica-HBF4 was probed through the sonication assisted synthesis of pyrroloacridinones in ecofriendly solvent ethanol. Standard leaching experiment was performed to show that the reaction was heterogeneous with this recyclable catalyst. PMID:25023825

Ray, Suman; Manna, Priyabrata; Mukhopadhyay, Chhanda

2015-01-01

295

An efficient synthesis of pyrido[1,2-a]indoles through aza-Nazarov type cyclization.  

PubMed

Transition metal free Brønsted acid mediated synthesis of biologically important pyrido[1,2-a]indole scaffolds through aza-Nazarov type cyclization of readily available diaryl(2-pyridyl)methanol using formic acid has been developed. This methodology has been successfully extended to synthesize atropisomers. PMID:25516921

Karthikeyan, Iyyanar; Arunprasath, Dhanarajan; Sekar, Govindasamy

2015-01-31

296

Organocatalysis in heterocyclic synthesis: DABCO as a mild and efficient catalytic system for the synthesis of a novel class of quinazoline, thiazolo [3,2-a]quinazoline and thiazolo[2,3-b] quinazoline derivatives  

PubMed Central

Background There are only limited publications devoted to the synthesis of especially thiazolo[3,2-a]quinazoline which involved reaction of 2-mercaptopropargyl quinazolin-4-one with various aryl iodides catalyzed by Pd-Cu or by condensation of 2-mercapto-4-oxoquinazoline with chloroacetic acid, inspite of this procedure was also reported in the literature to afford the thiazolo [2,3-b] quinazoline. So the multistep synthesis of the thiazolo[3,2-a]- quinazoline suffered from some flaws and in this study we have synthesized a novel class of thiazoloquinazolines by a simple and convenient method involving catalysis by 1,4-diazabicyclo[2.2.2]octane (DABCO). Results A new and convenient one-pot synthesis of a novel class of 2-arylidene-2H-thiazolo[3,2-a]quinazoline-1,5-diones 9a-i was established through the reaction between methyl-2-(2-thio-cyanatoacetamido)benzoate (4) and a variety of arylidene malononitriles 8a-i in the presence of DABCO as a mild and efficient catalytic system via a Michael type addition reaction and a mechanism for formation of the products observed is proposed. Moreover 4 was converted to ethyl-2-[(4-oxo-3,4-dihydroquinazolin-2-yl)thio]acetate (10) upon reflux in ethanol containing DABCO as catalyst. The latter was reacted with aromatic aldehydes and dimethylformamide dimethylacetal (DMF-DMA) to afford a mixture of two regioselectively products with identical percentage yield, these two products were identified as thiazolo[3,2-a]quinazoline 9,13 and thiazolo[2,3-b]quinazoline 11,12 derivatives respectively. The structure of the compounds prepared in this study was elucidated by different spectroscopic tools of analyses also the X-ray single crystal technique was employed in this study for structure elucidation, Z/E potential isomerism configuration determination and to determine the regioselectivity of the reactions. Conclusion A simple and efficient one-pot synthesis of a novel class of 2-arylidene-2H-thiazolo[3,2-a]quinazoline-1,5-diones 9a-i was established through DABCO catalyzed Michael type addition reaction. In addition many fused quinazoline and quinazoline derivatives were synthesized which appeared as valuable precursors in synthetic and medicinal chemistry. PMID:23651877

2013-01-01

297

Significant enhancement in the efficiency and selectivity of iron-catalyzed oxidative cross-coupling of phenols by fluoroalcohols.  

PubMed

Significant enhancement of both the rate and the chemoselectivity of iron-catalyzed oxidative coupling of phenols can be achieved in fluorinated solvents, such as 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), 2,2,2-trifluoroethanol (TFE), and 1-phenyl-2,2,2-trifluoroethanol. The generality of this effect was examined for the cross-coupling of phenols with arenes and polycyclic aromatic hydrocarbons (PAHs) and of phenol with ?-dicarbonyl compounds. The new conditions were utilized in the synthesis of 2'''-dehydroxycalodenin?B in only four synthetic steps. PMID:25655277

Gaster, Eden; Vainer, Yulia; Regev, Almog; Narute, Sachin; Sudheendran, Kavitha; Werbeloff, Aviya; Shalit, Hadas; Pappo, Doron

2015-03-27

298

Robinson's landmark synthesis of tropinone.  

PubMed

The 1917 total synthesis of tropinone by Sir Robert Robinson represents a landmark achievement in organic synthesis. Decades ahead of its time in terms of its retrosynthetic logic and biomimetic approach, the elegant combination of these two elements in this synthesis continues to serve as an inspiration for the development of new and efficient strategies for complex molecule synthesis. PMID:24116374

Medley, Jonathan William; Movassaghi, Mohammad

2013-11-28

299

Variants of mouse DNA polymerase ? reveal a mechanism of efficient and accurate translesion synthesis past a benzo[a]pyrene dG adduct  

PubMed Central

DNA polymerase ? (Pol?) is the only known Y-family DNA polymerase that bypasses the 10S (+)-trans-anti-benzo[a]pyrene diol epoxide (BPDE)-N2-deoxyguanine adducts efficiently and accurately. The unique features of Pol?, a large structure gap between the catalytic core and little finger domain and a 90-residue addition at the N terminus known as the N-clasp, may give rise to its special translesion capability. We designed and constructed two mouse Pol? variants, which have reduced gap size on both sides [Pol? Gap Mutant (PGM) 1] or one side flanking the template base (PGM2). These Pol? variants are nearly as efficient as WT in normal DNA synthesis, albeit with reduced accuracy. However, PGM1 is strongly blocked by the 10S (+)-trans-anti-BPDE-N2-dG lesion. Steady-state kinetic measurements reveal a significant reduction in efficiency of dCTP incorporation opposite the lesion by PGM1 and a moderate reduction by PGM2. Consistently, Pol?-deficient cells stably complemented with PGM1 GFP-Pol? remained hypersensitive to BPDE treatment, and complementation with WT or PGM2 GFP-Pol? restored BPDE resistance. Furthermore, deletion of the first 51 residues of the N-clasp in mouse Pol? (mPol?52–516) leads to reduced polymerization activity, and the mutant PGM252–516 but not PGM152–516 can partially compensate the N-terminal deletion and restore the catalytic activity on normal DNA. However, neither WT nor PGM2 mPol?52–516 retains BPDE bypass activity. We conclude that the structural gap physically accommodates the bulky aromatic adduct and the N-clasp is essential for the structural integrity and flexibility of Pol? during translesion synthesis. PMID:24449898

Liu, Yang; Yang, Yeran; Tang, Tie-Shan; Zhang, Hui; Wang, Zhifeng; Friedberg, Errol; Yang, Wei; Guo, Caixia

2014-01-01

300

Multifunctional “Clickates” as Versatile Extended Heteroaromatic Building Blocks: Efficient Synthesis via Click Chemistry, Conformational Preferences, and Metal Coordination  

Microsoft Academic Search

Click chemistry has been uti- lized to access 2,6-bis(1-aryl-1,2,3-tri- ACHTUNGTRENNUNGazol-4-yl)pyridines (BTPs) as versatile extended heteroaromatic building blocks for their exploitation in supra- molecular chemistry, in particular fol- damer and ligand design. In addition to their high-yielding synthesis using CuI- catalyzed Huisgen-type 1,3-dipolar cy- cloaddition reactions the formed tri- ACHTUNGTRENNUNGazole moieties constitute an integral part of the BTP framework and encode

Marc Ostermeier; Richard Goddard; Christian Limberg; Stefan Hecht

2007-01-01

301

Highly Efficient Enzymatic Synthesis of 2-Monoacylglycerides and Structured Lipids and their Production on a Technical Scale  

Microsoft Academic Search

We report here a two-step process for the high-yield enzymatic synthesis of 2-monoacylglycerides (2-MAG) of saturated as well\\u000a as unsaturated fatty acids with different chain lengths. The process consists of two steps: first the unselective esterification\\u000a of fatty acids and glycerol leading to a triacylglyceride followed by an sn1,3-selective alcoholysis reaction yielding 2-monoacylglycerides. Remarkably, both steps can be catalyzed by

Jan Pfeffer; Andreas Freund; Rachid Bel-Rhlid; Carl-Erik Hansen; Matthias Reuss; Rolf D. Schmid; Steffen C. Maurer

2007-01-01

302

An efficient route for the preparation of activated carbon supported ruthenium catalysts with high performance for ammonia synthesis  

Microsoft Academic Search

An impregnation–precipitation method was developed for the preparation of activated carbon supported ruthenium-based catalysts for ammonia synthesis. The ammonia concentration in the outlet of reactor for the Ba–Ru–K\\/AC catalysts prepared via impregnation–precipitation method is as high as 20.4vol% at 648K, pressure of 10MPa and with a space velocity of 10,000h?1, which is much higher than that of catalysts obtained via

Ying Li; Chonggen Pan; Wenfeng Han; Haifang Chai; Huazhang Liu

2011-01-01

303

Highly efficient and clean synthesis of verbenone over well ordered two-dimensional mesoporous chromium silicate catalysts  

Microsoft Academic Search

Two-dimensional mesoporous SBA-15 catalysts synthesized by different hydrothermal methods have been used, for the first time, in the liquid-phase oxidation of ?-pinene with t-butyl hydrogen peroxide (TBHP) for the synthesis of verbenone (VO). The recyclable CrSBA-15 catalysts have also been reused in this reaction to find their catalytic activities. To investigate the leaching of chromium species on the silica surface,

M. Selvaraj; M. Kandaswamy; D. W. Park; C. S. Ha

2010-01-01

304

The role of ?6-desaturase acyl-carrier specificity in the efficient synthesis of long-chain polyunsaturated fatty acids in transgenic plants.  

PubMed

The role of acyl-CoA-dependent ?6-desaturation in the heterologous synthesis of omega-3 long-chain polyunsaturated fatty acids was systematically evaluated in transgenic yeast and Arabidopsis thaliana. The acyl-CoA ?6-desaturase from the picoalga Ostreococcus tauri and orthologous activities from mouse (Mus musculus) and salmon (Salmo salar) were shown to generate substantial levels of ?6-desaturated acyl-CoAs, in contrast to the phospholipid-dependent ?6-desaturases from higher plants that failed to modify this metabolic pool. Transgenic plants expressing the acyl-CoA ?6-desaturases from either O. tauri or salmon, in conjunction with the two additional activities required for the synthesis of C20 polyunsaturated fatty acids, contained higher levels of eicosapentaenoic acid compared with plants expressing the borage phospholipid-dependent ?6-desaturase. The use of acyl-CoA-dependent ?6-desaturases almost completely abolished the accumulation of unwanted biosynthetic intermediates such as ?-linolenic acid in total seed lipids. Expression of acyl-CoA ?6-desaturases resulted in increased distribution of long-chain polyunsaturated fatty acids in the polar lipids of transgenic plants, reflecting the larger substrate pool available for acylation by enzymes of the Kennedy pathway. Expression of the O. tauri?6-desaturase in transgenic Camelina sativa plants also resulted in the accumulation of high levels of ?6-desaturated fatty acids. This study provides evidence for the efficacy of using acyl-CoA-dependent ?6-desaturases in the efficient metabolic engineering of transgenic plants with high value traits such as the synthesis of omega-3 LC-PUFAs. PMID:21902798

Sayanova, Olga; Ruiz-Lopez, Noemi; Haslam, Richard P; Napier, Johnathan A

2012-02-01

305

High-Efficiency Synthesis of Human ?-Endorphin and Magainin in the Erythrocytes of Transgenic Mice: A Production System for Therapeutic Peptides  

NASA Astrophysics Data System (ADS)

Chemical synthesis of peptides, though feasible, is hindered by considerations of cost, purity, and efficiency of synthesizing longer chains. Here we describe a transgenic system for producing peptides of therapeutic interest as fusion proteins at low cost and high purity. Transgenic hemoglobin expression technology using the locus control region was employed to produce fusion hemoglobins in the erythrocytes of mice. The fusion hemoglobin contains the desired peptide as an extension at the C end of human ?-globin. A protein cleavage site is inserted between the C end of the ?-globin chain and the N-terminal residue of the desired peptide. The peptide is recovered after cleavage of the fusion protein with enzymes that recognize this cleavage signal as their substrate. Due to the selective compartmentalization of hemoglobin in the erythrocytes, purification of the fusion hemoglobin is easy and efficient. Because of its compact and highly ordered structure, the internal sites of hemoglobin are resistant to protease digestion and the desired peptide is efficiently released and recovered. The applicability of this approach was established by producing a 16-mer ?-endorphin peptide and a 26-mer magainin peptide in transgenic mice. Transgenic animals and their progeny expressing these fusion proteins remain healthy, even when the fusion protein is expressed at >25% of the total hemoglobin in the erythrocytes. Additional applications and potential improvements of this methodology are discussed.

Sharma, Ajay; Khoury-Christianson, Anastasia M.; White, Steven P.; Dhanjal, Nirpal K.; Huang, Wen; Paulhiac, Clara; Friedman, Eric J.; Manjula, Belur N.; Kumar, Ramesh

1994-09-01

306

Efficient Synthesis and In Vivo Incorporation of Acridon-2-ylalanine, a Fluorescent Amino Acid for Lifetime and FRET/LRET Studies  

PubMed Central

The amino acid acridon-2-ylalanine (Acd) can be a valuable probe of protein conformational change because it is a long lifetime, visible wavelength fluorophore that is small enough to be incorporated during ribosomal biosynthesis. Incorporation of Acd into proteins expressed in E. coli requires efficient chemical synthesis to produce large quantities of the amino acid and the generation of a mutant aminoacyl tRNA synthetase that can selectively charge the amino acid onto a tRNA. Here, we report the synthesis of Acd in 87 % yield over five steps from Tyr, and the identification of an Acd synthetase by screening candidate enzymes previously evolved from M. janaschii Tyr synthetase for unnatural amino acid incorporation. Furthermore, we characterize the photophysical properties of Acd, including quenching interactions with select natural amino acids and Förster resonance energy transfer (FRET) interactions with common fluorophores such as methoxycoumarin (Mcm). Finally, we demonstrate the value of incorporation of Acd into proteins, using changes in Acd fluorescence lifetimes, Mcm/Acd FRET, or energy transfer to Eu3+ to monitor protein folding and binding interactions. PMID:24303933

Speight, Lee C.; Muthusamy, Anand K.; Goldberg, Jacob M.; Warner, John B.; Wissner, Rebecca F.; Willi, Taylor S.; Woodman, Bradley F.; Mehl, Ryan A.; Petersson, E. James

2014-01-01

307

Alkyne Elementometalation–Pd-Catalyzed Cross-Coupling. Towards Synthesis of Various Types of Acyclic Alkenes in High Yields, Efficiently, Selectively, Economically, and Safely—“Green” Way  

PubMed Central

Palladium-catalyzed cross-coupling reactions, especially those involving Zn, Al, Zr (Negishi coupling) and B (Suzuki coupling), collectively have brought about “revolutionary” changes in organic synthesis. Thus, two regio- and stereodefined carbon groups generated as R1M (M = Zn, Al, B, Cu, Zr, etc.) and R2X (X = I, Br, OTs, etc.) may now be cross-coupled to give R1–R2 with essentially full retention of all structural features. For alkene syntheses, alkyne elementometalation reactions including hydrometalation (B, Al, Zr, etc.), carbometalation (Cu, Al–Zr, etc.), and haloboration (BX3 where X is Cl, Br, and I) have proven to be critically important. Some representative examples of highly efficient and selective (?98%) syntheses of di-, tri- and oligoenes containing regio- and stereodefined di- and trisubstituted alkenes of all conceivable types will be discussed with emphasis on those of natural products. Some interesting but undesirable cases involving loss of the initial structural identities of the alkenyl groups are attributable to the formation of allylpalladium species, which must be either tamed or avoided. Some such examples involving the synthesis of 1,3-, 1,4-, and 1,5-dienes will also be discussed. PMID:20465291

Wang, Guangwei; Rao, Honghua; Xu, Zhaoqing

2010-01-01

308

Contribution of RpoS to metabolic efficiency and ectoines synthesis during the osmo- and heat-stress response in the halophilic bacterium Chromohalobacter salexigens.  

PubMed

Chromohalobacter salexigens is a halophilic ?-proteobacterium that responds to osmotic and heat stresses by accumulating ectoine and hydroxyectoine respectively. Evolution has optimized its metabolism to support high production of ectoines. We analysed the effect of an rpoS mutation in C.?salexigens metabolism and ectoines synthesis. In long-term adapted cells, the rpoS strain was osmosensitive but not thermosensitive and showed unaltered ectoines content, suggesting that RpoS regulates ectoine(s)-independent osmoadaptive mechanisms. RpoS is involved in the regulation of C.?salexigens metabolic adaptation to stress, as early steps of glucose oxidation through the Entner-Doudoroff pathway were deregulated in the rpoS mutant, leading to improved metabolic efficiency at low salinity. Moreover, a reduced pyruvate (but not acetate) overflow was displayed by the rpoS strain at low salt, probably linked to a slowdown in gluconate production and/or subsequent metabolism. Interestingly, RpoS does not seem to be the main regulator triggering the immediate transcriptional response of ectoine synthesis to osmotic or thermal upshifts. However, it contributed to the expression of the ect genes in cells previously adapted to low or high salinity. PMID:25417903

Salvador, Manuel; Argandoña, Montserrat; Pastor, Jose M; Bernal, Vicente; Cánovas, Manuel; Csonka, Laszlo N; Nieto, Joaquín J; Vargas, Carmen

2015-04-01

309

An Efficient Protocol for the Synthesis of Quinoxaline Derivatives at Room Temperature Using Recyclable Alumina-Supported Heteropolyoxometalates  

PubMed Central

We report a suitable quinoxaline synthesis using molybdophosphovanadates supported on commercial alumina cylinders as catalysts. These catalysts were prepared by incipient wetness impregnation. The catalytic test was performed under different reaction conditions in order to know the performance of the synthesized catalysts. The method shows high yields of quinoxaline derivatives under heterogeneous conditions. Quinoxaline formation was obtained using benzyl, o-phenylenediamine, and toluene as reaction solvent at room temperature. The CuH2PMo11VO40 supported on alumina showed higher activity in the tested reaction. Finally, various quinoxalines were prepared under mild conditions and with excellent yields. PMID:22536123

Ruiz, Diego M.; Autino, Juan C.; Quaranta, Nancy; Vázquez, Patricia G.; Romanelli, Gustavo P.

2012-01-01

310

[11C]PR04.MZ, a promising DAT ligand for low concentration imaging: synthesis, efficient 11C-0-methylation and initial small animal PET studies  

SciTech Connect

PR04.MZ was designed as a highly selective dopamine transporter inhibitor, derived from natural cocaine. Its binding profile indicates that [{sup 11}C]PR04.MZ may be suited as a PET radioligand for the non-invasive exploration of striatal and extrastriatal DAT populations. As a key feature, its structural design facilitates both, labelling with fluorine-18 at its terminally fluorinated butynyl moiety and carbon-11 at its methyl ester function. The present report concerns the efficient [{sup 11}C]MeI mediated synthesis of [{sup 11}C]PR04.MZ from an O-desmethyl precursor trifluoroacetic acid salt with Rb{sub 2}CO{sub 3} in DMF in up to 95 {+-} 5% labelling yield. A preliminary {mu}PET-experiment demonstrates the reversible, highly specific binding of [{sup 11}C]PR04.MZ in the brain of a male Sprague-Dawley rat.

Riss, P.J.; Hooker, J.; Alexoff, D.; Kim, Sung-Won; Fowler, J.S.; Roesch, F.

2009-05-01

311

Task-specific nitrite and azide ionic liquids for the efficient one-pot synthesis of 1,2,3-triazoles from the aniline derivatives.  

PubMed

An efficient, fast, and straightforward procedure for the synthesis of aromatic azides and in situ preparation of 1,2,3-triazoles under mild conditions is described. Aniline derivatives have been treated with task-specific [bmim]NO(2) and [bmim]N(3) ionic liquids to give the related phenyl azides which, on further in situ reaction with 1,3-diketones and ethylacetoacetate, afforded 1,2,3-triazoles in very good to excellent yields in very short reaction time. This procedure, which generates azides followed by azide in situ cycloaddition with diketone, has become an attractive option. In this protocol, [bmim]N(3) is used instead of the highly toxic reagent NaN(3). PMID:22466931

Valizadeh, Hassan; Amiri, Mohammad; Khalili, Elham

2012-05-01

312

Translation of microwave methodology to continuous flow for the efficient synthesis of diaryl ethers via a base-mediated SNAr reaction  

PubMed Central

Summary Whilst microwave heating has been widely demonstrated as a synthetically useful tool for rapid reaction screening, a microwave-absorbing solvent is often required in order to achieve efficient reactant heating. In comparison, microreactors can be readily heated and pressurised in order to “super-heat” the reaction mixture, meaning that microwave-transparent solvents can also be employed. To demonstrate the advantages associated with microreaction technology a series of SNAr reactions were performed under continuous flow by following previously developed microwave protocols as a starting point for the investigation. By this approach, an automated microreaction platform (Labtrix® S1) was employed for the continuous flow synthesis of diaryl ethers at 195 °C and 25 bar, affording a reduction in reaction time from tens of minutes to 60 s when compared with a stopped-flow microwave reactor. PMID:22043247

Watts, Paul

2011-01-01

313

Biomolecule-assisted synthesis of carbon nitride and sulfur-doped carbon nitride heterojunction nanosheets: An efficient heterojunction photocatalyst for photoelectrochemical applications  

PubMed Central

Summary A biomolecule-assisted pyrolysis method has been developed to synthesize sulfur-doped graphitic carbon nitride (CNS) nanosheets. During the synthesis, sulfur could be introduced as a dopant into the lattice of carbon nitride (CN). Sulfur doping changed the texture as well as relative band positions of CN. By growing CN on preformed sulfur-doped CN nanosheets, composite CN/CNS heterojunction nanosheets were constructed, which significantly enhanced the photoelectrochemical performance as compared with various control counterparts including CN, CNS and physically mixed CN and CNS (CN+CNS). The enhanced photoelectrochemical performance of CN/CNS heterojunction nanosheets could be ascribed to the efficient separation of photoexcited charge carriers across the heterojunction interface. The strategy of designing and preparing CN/CNS heterojunction photocatalysts in this work can open up new directions for the construction of all CN-based heterojunction photocatalysts. PMID:24991514

Tao, Hua Bing; Chen, Jiazang; Miao, Jianwei

2014-01-01

314

Chemical Synthesis of Circular Proteins*  

PubMed Central

Circular proteins, once thought to be rare, are now commonly found in plants. Their chemical synthesis, once thought to be difficult, is now readily achievable. The enabling methodology is largely due to the advances in entropic chemical ligation to overcome the entropy barrier in coupling the N- and C-terminal ends of large peptide segments for either intermolecular ligation or intramolecular ligation in end-to-end cyclization. Key elements of an entropic chemical ligation consist of a chemoselective capture step merging the N and C termini as a covalently linked O/S-ester intermediate to permit the subsequent step of an intramolecular O/S-N acyl shift to form an amide. Many ligation methods exploit the supernucleophilicity of a thiol side chain at the N terminus for the capture reaction, which makes cysteine-rich peptides ideal candidates for the entropy-driven macrocyclization. Advances in desulfurization and modification of the thiol-containing amino acids at the ligation sites to other amino acids add extra dimensions to the entropy-driven ligation methods. This minireview describes recent advances of entropy-driven ligation to prepare circular proteins with or without a cysteinyl side chain. PMID:22700959

Tam, James P.; Wong, Clarence T. T.

2012-01-01

315

The general application of immobilized proteins and enzymes has played a central role in the expansion of biotechnology and synthesis-related industries. As the efficiency, selectivity and maximum attainable loading of enzymes upon commercially produced s  

E-print Network

in the expansion of biotechnology and synthesis-related industries. As the efficiency, selectivity and maximum of biotechnology, particularly in situations where enzymes are used to mediate synthetic transformations. Although of the industry. Once considered a relatively crude and non-specific method, modern immobilization protocols

Taralp, Alpay

316

Efficient, Green, Solvent-Free Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones via Biginelli Reaction Catalyzed by Cu(NO3)2·3H2O  

Microsoft Academic Search

The synthesis of 3,4-dihydropyrimidin-2-(1H)-ones derivatives via a three-component Biginelli reaction using copper nitrate as a catalyst under solventless conditions is reported, providing a green, rapid, efficient, and convenient method for the preparation of Biginelli compounds in good yields.

Dong-Chao Wang; Hai-Ming Guo; Gui-Rong Qu

2010-01-01

317

Methanobactin-Mediated Synthesis of Gold Nanoparticles Supported over Al2O3 toward an Efficient Catalyst for Glucose Oxidation  

PubMed Central

Methanobactin (Mb) is a copper-binding peptide that appears to function as an agent for copper sequestration and uptake in methanotrophs. Mb can also bind and reduce Au(III) to Au(0). In this paper, Au/Al2O3 catalysts prepared by a novel incipient wetness-Mb-mediated bioreduction method were used for glucose oxidation. The catalysts were characterized, and the analysis revealed that very small gold nanoparticles with a particle size <4 nm were prepared by the incipient wetness-Mb-mediated bioreduction method, even at 1.0% Au loading (w/w). The influence of Au loading, calcination temperature and calcination time on the specific activity of Au/Al2O3 catalysts was systematically investigated. Experimental results showed that decomposing the Mb molecules properly by calcinations can enhance the specific activity of Au/Al2O3 catalysts, though they acted as reductant and protective agents during the catalyst preparation. Au/Al2O3 catalysts synthesized by the method exhibited optimum specific activity under operational synthesis conditions of Au loading of 1.0 wt % and calcined at 450 °C for 2 h. The catalysts were reused eight times, without a significant decrease in specific activity. To our knowledge, this is the first attempt at the preparation of Au/Al2O3 catalysts by Mb-mediated in situ synthesis of gold nanoparticles. PMID:25429424

Xin, Jia-Ying; Lin, Kai; Wang, Yan; Xia, Chun-Gu

2014-01-01

318

Methanobactin-mediated synthesis of gold nanoparticles supported over Al2O3 toward an efficient catalyst for glucose oxidation.  

PubMed

Methanobactin (Mb) is a copper-binding peptide that appears to function as an agent for copper sequestration and uptake in methanotrophs. Mb can also bind and reduce Au(III) to Au(0). In this paper, Au/Al2O3 catalysts prepared by a novel incipient wetness-Mb-mediated bioreduction method were used for glucose oxidation. The catalysts were characterized, and the analysis revealed that very small gold nanoparticles with a particle size <4 nm were prepared by the incipient wetness-Mb-mediated bioreduction method, even at 1.0% Au loading (w/w). The influence of Au loading, calcination temperature and calcination time on the specific activity of Au/Al2O3 catalysts was systematically investigated. Experimental results showed that decomposing the Mb molecules properly by calcinations can enhance the specific activity of Au/Al2O3 catalysts, though they acted as reductant and protective agents during the catalyst preparation. Au/Al2O3 catalysts synthesized by the method exhibited optimum specific activity under operational synthesis conditions of Au loading of 1.0 wt % and calcined at 450 °C for 2 h. The catalysts were reused eight times, without a significant decrease in specific activity. To our knowledge, this is the first attempt at the preparation of Au/Al2O3 catalysts by Mb-mediated in situ synthesis of gold nanoparticles. PMID:25429424

Xin, Jia-Ying; Lin, Kai; Wang, Yan; Xia, Chun-Gu

2014-01-01

319

Efficient solar-driven synthesis, carbon capture, and desalinization, STEP: solar thermal electrochemical production of fuels, metals, bleach.  

PubMed

STEP (solar thermal electrochemical production) theory is derived and experimentally verified for the electrosynthesis of energetic molecules at solar energy efficiency greater than any photovoltaic conversion efficiency. In STEP the efficient formation of metals, fuels, chlorine, and carbon capture is driven by solar thermal heated endothermic electrolyses of concentrated reactants occuring at a voltage below that of the room temperature energy stored in the products. One example is CO(2) , which is reduced to either fuels or storable carbon at a solar efficiency of over 50% due to a synergy of efficient solar thermal absorption and electrochemical conversion at high temperature and reactant concentration. CO(2) -free production of iron by STEP, from iron ore, occurs via Fe(III) in molten carbonate. Water is efficiently split to hydrogen by molten hydroxide electrolysis, and chlorine, sodium, and magnesium from molten chlorides. A pathway is provided for the STEP decrease of atmospheric carbon dioxide levels to pre-industial age levels in 10 years. PMID:22025216

Licht, S

2011-12-15

320

A practical and benign synthesis of primary amines through ruthenium-catalyzed reduction of nitriles.  

PubMed

The catalytic hydrogenation of nitriles represents an atom-economic and valuable route to amines. In the present study, the ruthenium-catalyzed hydrogenation of various organic nitriles to give primary amines has been examined in detail. Straightforward ruthenium complexes modified by cheap and widely available triphenylphosphine allow for the efficient and general reduction of various aryl, alkyl, and heterocyclic nitriles. By using a practical in situ catalyst composed of [Ru(cod)(methylallyl(2))] and PPh(3), excellent yields and chemoselectivity were achieved. Moreover, the catalyst system displays broad functional group tolerance. PMID:19034895

Enthaler, Stephan; Junge, Kathrin; Addis, Daniele; Erre, Giulia; Beller, Matthias

2008-01-01

321

Template-free synthesis of hollow nitrogen-doped carbon as efficient electrocatalysts for oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

In this paper, we report a template-free method to fabricate hollow nitrogen-doped carbon (HNC) by pyrolysis of hollow polyaniline microspheres, which were synthesized by suspension polymerization method. The entire synthesis is simple, environmentally benign, and economic. The oxygen reduction reaction (ORR) activity of the as-prepared HNC catalyst is close to that of the commercial Pt/C catalyst in alkaline media with four electron pathway. Moreover, the HNC shows much better fuel crossover resistance and long-term durability than the commercial Pt/C in alkaline medium. All these features make HNC a potentially promising and suitable substitute for the expensive noble metal catalysts in the next generation alkaline fuel cells.

Wu, Rui; Chen, Siguo; Zhang, Yuanliang; Wang, Yao; Ding, Wei; Li, Li; Qi, Xueqiang; Shen, Xiu; Wei, Zidong

2015-01-01

322

In situ synthesis of CdS decorated titanate nanosheets with highly efficient visible-light-induced photoactivity  

NASA Astrophysics Data System (ADS)

Appropriately dispersed CdS nanoparticles were intimately embedded into titanate nanosheets (TNS) through ion-exchange and in situ sulfurization process. The sheet-like intermediates of titanate during the transforming process into nanotubes were firstly used as substrate for the decoration of CdS nanoparticles, and the synthesis route was achieved by ion-exchange process between titanate precursor and Cd2+ ions solution, and the following sulfuration process by using Na2S solutions. The catalytic activity of the photocatalyst was investigated by photodegradation of Rhodamine B under visible light irradiation. With an optimal Cd/Ti molar ratio of 15%, the CdS/TNS composite exhibits the highest photocatalytic performance, which is approximately 5.4 times greater than that of pure TNS. The mechanism of the separation behavior of the photogenerated charges was also discussed.

Liu, Zhi; Fang, Pengfei; Liu, Fuwei; Zhang, Yupeng; Liu, Xinzhao; Lu, Dingze; Li, Delong; Wang, Shaojie

2014-06-01

323

Synthesis of carbon embedded MFe2O4 (M = Ni, Zn and Co) nanoparticles as efficient hydrogenation catalysts.  

PubMed

Successful synthesis of stable MFe2O4 nanoparticles@C has been realized by applying the novel concept of using levulinic acid possessing carboxyl and carbonyl groups to facilitate the interaction with metal ions (M(2+) and Fe(3+)) and the carbon source (phloroglucinol) in the sol-gel polymerization method. All the samples have been characterized by XRD, SEM, FT-IR, TEM, HRTEM, ICP-AES, CHNS, and N2 adsorption-desorption, and were studied for their performance towards hydrogenation reaction of styrene. Out of three samples NiFe2O4 gave excellent selective hydrogenation activity of styrene to ethyl benzene (100% conversion and 100% selectivity). Optimal production of ethyl benzene over NiFe2O4 nanoparticles@C has been established at 80 °C reaction temperature after 24 h reaction time under 40 bar hydrogen pressure. PMID:24983775

Nandan, Devaki; Sreenivasulu, Peta; Viswanadham, Nagabhatla; Chiang, Ken; Newnham, Jarrod

2014-08-21

324

Efficient Synthesis of Frutinone?A and Its Derivatives through Palladium-Catalyzed C?H Activation/Carbonylation.  

PubMed

Frutinone?A, a biologically active ingredient of an antimicrobial herbal extract, demonstrates potent inhibitory activity towards the CYP1A2 enzyme. A three-step total synthesis of frutinone?A with an overall yield of 44?% is presented. The construction of the chromone-annelated coumarin core was achieved through palladium-catalyzed C?H carbonylation of 2-phenolchromones. The straightforward synthetic route allowed facile substitutions around the frutinone?A core and thus rapid exploration of the structure-activity relationship (SAR) profile of the derivatives. The inhibitory activity of the synthesized frutinone?A derivatives were determined for CYP1A2, and ten compounds exhibited one-to-two digit nanomolar inhibitory activity towards the CYP1A2 enzyme. PMID:25252104

Shin, Yongje; Yoo, Changho; Moon, Youngtaek; Lee, Yunho; Hong, Sungwoo

2015-04-01

325

Nano scale magnetically recoverable supported heteropoly acid as an efficient catalyst for the synthesis of benzimidazole derivatives in water.  

PubMed

12-Tungstophosphoric acid supported on silica-coated magnetic nano particles was prepared and characterized by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction and inductively coupled plasma atomic emission spectroscopy. Acidity of the catalysts was measured by potentiometric titration with n-butylamine. Catalytic activity of the prepared sample was evaluated in the model synthesis of 1,2-disubstituted benzimidazole derivatives in water. The catalyst showed excellent catalytic activity and the corresponding products were obtained in good to excellent yields under mild reaction conditions. Furthermore, the catalyst could be easily recovered using an external magnet and reused several times. The leaching and surface acidity of the recovered catalyst were also investigated. PMID:24664342

Rafiee, Ezzat; Rahpeima, Nasibeh; Eavani, Sara

2014-01-01

326

Indium-mediated allylation in carbohydrate synthesis: A short and efficient approach towards higher 2-acetamido-2-deoxy sugars  

PubMed Central

Summary Higher aminosugars are interesting targets in carbohydrate synthesis since these compounds play important roles in biological systems. However, their availability from natural sources is limited. Thus, in order to investigate their biological function, the development of facile and adaptable routes to this class of compounds is of fundamental importance. Our synthetic route towards these target molecules makes use of readily accessible pentoses and hexoses, which are subjected to indium-mediated two-carbon chain elongation. Subsequent ozonolysis and treatment with base yields ?,?-unsaturated aldehydes, which are stereoselectively epoxidized using Jørgenson’s protocol. After Wittig chain elongation the obtained allylic epoxides were regio- and stereoselectively opened with trimethylsilyl azide under palladium catalysis. Finally, a suitable deprotection protocol, starting with acidic acetate cleavage and ozonolysis was established. Peracetylation of the products simplifies purification and subsequent azide reduction followed by final deacetylation using methanolic sodium methoxide furnishes the title compounds. PMID:25246982

Albler, Christopher; Hollaus, Ralph; Kählig, Hanspeter

2014-01-01

327

Graphite oxide-mediated synthesis of porous CeO{sub 2} quadrangular prisms and their high-efficiency adsorptive performance  

SciTech Connect

Graphical abstract: - Highlights: • Porous CeO{sub 2} quadrangular prisms have been prepared via graphite oxide-mediated synthesis. • Dual-pore hierarchical systems are formed with the pore distributions around 4 nm and 30 nm. • Porous CeO{sub 2} exhibits a rapid adsorption to Rhodamine B with a removal efficiency of ?99%. • Porous CeO{sub 2} retains the same performances in different pH solutions. - Abstract: We report a graphite oxide-mediated approach for synthesizing porous CeO{sub 2} through a facile hydrothermal process followed by thermal annealing in air. The phase structure, morphology, microstructure and porosity of the products have been revealed by a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N{sub 2} adsorption. The as-prepared CeO{sub 2} products show well-defined quadrangular prism morphology, and they are composed of interconnected nanoparticles with diameters around 30–100 nm. In particular, the dual-pore hierarchical systems are created in the CeO{sub 2} quadrangular prisms with the pore distributions around 4 nm and 30 nm. The dye sorption capacity of the porous CeO{sub 2} is investigated, which exhibits a rapid adsorption to rhodamine B with a high removal efficiency of ?99%. Moreover, the CeO{sub 2} absorbent retains the same performances in different pH solutions.

Chang, Ling; Wang, Fengxian; Xie, Dong; Zhang, Jun; Du, Gaohui, E-mail: gaohuidu@zjnu.edu.cn

2013-10-15

328

Synthesis of ultrathin CdS nanosheets as efficient visible-light-driven water splitting photocatalysts for hydrogen evolution.  

PubMed

Ultrathin CdS nanosheets with a thickness of ~4 nm have been synthesized through an ultrasonic-induced aqueous exfoliation method involving lamellar CdS-DETA hybrid nanosheets as starting materials and L-cysteine as a stabilizing agent. The as-obtained CdS ultrathin nanosheets exhibit efficient photocatalytic activity and good stability for hydrogen production. PMID:24029921

Xu, You; Zhao, Weiwei; Xu, Rui; Shi, Yanmei; Zhang, Bin

2013-10-28

329

AN EFFICIENT AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES  

EPA Science Inventory

N-aryl azacycloalkanes, an important class of building blocks in natural product and pharmaceuticals, are synthesized via an efficient and simple eco-friendly protocol that involves double N-alkylation of aniline derivatives. The reaction is accelerated by exposure to microwaves ...

330

Efficient synthesis of spironaphthopyrano [2,3-d]pyrimidine-5,3'-indolines under solvent-free conditions catalyzed by SBA-Pr-SO3H as a nanoporous acid catalyst.  

PubMed

A green, simple one-pot synthesis of spironaphthopyrano[2,3-d]pyrimidine-5,3'-indoline derivatives by a three-component reaction of isatins, 2-naphthol, and barbituric acids under solvent-free conditions in the presence of SBA-Pr-SO(3)H has been accomplished. Sulfonic acid functionalized SBA-15 (SBA-Pr-SO(3)H) as a heterogeneous nanoporous solid acid catalyst was found to be an efficient and recyclable acid catalyst in this synthesis. PMID:25286212

Ziarani, Ghodsi Mohammadi; Lashgari, Negar; Faramarzi, Sakineh; Badiei, Alireza

2014-01-01

331

Fast and highly chemoselective alkynylation of thiols with hypervalent iodine reagents enabled through a low energy barrier concerted mechanism.  

PubMed

Among all functional groups, alkynes occupy a privileged position in synthetic and medicinal chemistry, chemical biology, and materials science. Thioalkynes, in particular, are highly useful, as they combine the enhanced reactivity of the triple bond with a sulfur atom frequently encountered in bioactive compounds and materials. Nevertheless, general methods to access these compounds are lacking. In this article, we describe the mechanism and full scope of the alkynylation of thiols using ethynyl benziodoxolone (EBX) hypervalent iodine reagents. Computations led to the discovery of a new, three-atom concerted transition state with a very low energy barrier, which rationalizes the high reaction rate. On the basis of this result, the scope of the reaction was extended to the synthesis of aryl- and alkyl-substituted alkynes containing a broad range of functional groups. New sulfur nucleophiles such as thioglycosides, thioacids, and sodium hydrogen sulfide were also alkynylated successfully to lead to the most general and practical method yet reported for the synthesis of thioalkynes. PMID:25365776

Frei, Reto; Wodrich, Matthew D; Hari, Durga Prasad; Borin, Pierre-Antoine; Chauvier, Clément; Waser, Jérôme

2014-11-26

332

Fast and Highly Chemoselective Alkynylation of Thiols with Hypervalent Iodine Reagents Enabled through a Low Energy Barrier Concerted Mechanism  

PubMed Central

Among all functional groups, alkynes occupy a privileged position in synthetic and medicinal chemistry, chemical biology, and materials science. Thioalkynes, in particular, are highly useful, as they combine the enhanced reactivity of the triple bond with a sulfur atom frequently encountered in bioactive compounds and materials. Nevertheless, general methods to access these compounds are lacking. In this article, we describe the mechanism and full scope of the alkynylation of thiols using ethynyl benziodoxolone (EBX) hypervalent iodine reagents. Computations led to the discovery of a new, three-atom concerted transition state with a very low energy barrier, which rationalizes the high reaction rate. On the basis of this result, the scope of the reaction was extended to the synthesis of aryl- and alkyl-substituted alkynes containing a broad range of functional groups. New sulfur nucleophiles such as thioglycosides, thioacids, and sodium hydrogen sulfide were also alkynylated successfully to lead to the most general and practical method yet reported for the synthesis of thioalkynes. PMID:25365776

2014-01-01

333

Highly efficient and chemo selective catalyst system for the synthesis of blossom orange fragrance and flavoring compounds  

Microsoft Academic Search

Acetal and acylal formation reactions of organic compounds are efficiently catalyzed by zirconia-supported mixed oxide systems under liquid-phase reaction conditions. 15WZ-750 (where, W=WO3 and Z=ZrO2) was the most active catalyst, which could be recyclable without loss in its activities. This study reports the use of a non zeolitic solid acid catalyst systems based on zirconia-supported isopoly and heteropoly acids, which

Josena Justus; Ajayan Vinu; Biju M. Devassy; Veerappan V. Balasubramanian; Walter Bohringer; Jack Fletcher; S. B. Halligudi

2008-01-01

334

Efficient carbazole synthesis via Pd/Cu-cocatalyzed cross-coupling/isomerization of 2-allyl-3-iodoindoles and terminal alkynes.  

PubMed

The Pd/Cu-cocatalyzed one-pot reaction of 2-allyl-3-iodo-1-tosyl-1H-indoles and terminal alkynes afforded carbazoles highly efficiently via sequential carbon-carbon coupling, isomerization, cyclization, and aromatization forming a benzene ring. Both Pd and Cu are responsible for the coupling step, while K2CO3 was observed to be critical for the subsequent cyclization. PMID:24617639

Zhu, Can; Ma, Shengming

2014-03-21

335

Synthesis of highly efficient antibacterial agent Ag doped ZnO nanorods: Structural, Raman and optical properties  

SciTech Connect

Here, synthesis, structural, morphological, Raman, optical properties and antibacterial activity of undoped and Ag doped ZnO nanorods by chemical co-precipitation technique have been reported. Structural analysis has revealed that Ag doping cannot deteriorate the structure of ZnO and wurtzite phase is maintained. Lattice constants are found to be decreased with the Ag doping. Fourier transform infrared and Raman spectroscopy also confirm the X-ray diffraction results. Scanning electron microscopy results have demonstrated the formation of ZnO nanorods with average diameter and length of 96?nm and 700?nm, respectively. Raman spectroscopy results suggest that the Ag doping enhances the number of defects in ZnO crystal. It has been found from optical study that Ag doping results in positional shift of band edge absorption peak. This is attributed to the successful incorporation of Ag dopant into ZnO host matrix. The antibacterial activity of prepared nanorods has been determined by two different methods and compared to that of undoped ZnO nanorods. Ag doped ZnO nanorods exhibit excellent antibacterial activity as compared to that of undoped ZnO nanorods. This excellent antibacterial activity may be attributed to the presence of oxygen vacancies and Zn{sup 2+} interstitial defects. Our preliminary findings suggest that Ag doped ZnO nanorods can be used externally to control the spreading of infections related with tested bacterial strains.

Jan, Tariq; Iqbal, Javed, E-mail: javed.saggu@iiu.edu.pk [Laboratory of Nanoscience and Technology, Department of Physics, International Islamic University Islamabad (Pakistan); Ismail, Muhammad [Institute of Biomedical and Genetic Engineering (IBGE), Islamabad (Pakistan); Mahmood, Arshad [Nano Devices Labs, National Institute of Lasers and Optronics, Islamabad (Pakistan)

2014-04-21

336

Highly efficient synthesis of exopolysaccharides by Lactobacillus curvatus DPPMA10 during growth in hydrolyzed wheat flour agar.  

PubMed

The aim of this study was to optimize the production of exopolysaccharides (EPS) by sourdough Lactobacillus curvatus DPPMA10 for industrial application. The effects of pH, temperature, planktonic or attached cells and of some food matrices as substrates were studied. Wheat flour hydrolysate (WFH), reconstituted skimmed milk (RSM) and whey milk were supplemented with fresh yeast extract, mineral salts, and/or molasses. Non-controlled pH, starting from 5.6 to 3.5, was the optimal condition for L. curvatus DPPMA10. Temperature of 30 degrees C was also found to be optimal. Solid surfaces (agar culture media) stimulated attached bacteria to synthesize EPS (> or = of two-fold, P<0.05) with respect to planktonic cells (broth media). The highest production of EPS (ca. 46-50 g/kg of wet medium) was found during growth as attached cells in WFH agar supplemented with glucose, sucrose or molasses, mineral salts and fresh yeast extract at 30 degrees C for 48 h. As shown by high-performance liquid chromatography analysis, glucose was the only hydrolysis end-product for EPS synthesized during 48 h of incubation. The EPS synthesized by L. curvatus DPPMA10 improved the quality of bread and was utilized as carbon course by intestinal strains of lactobacilli and bifidobacteria. The synthesis of EPS by L. curvatus DPPMA10 under the conditions of this study may open new perspectives for their industrial applications. PMID:20398955

Minervini, F; De Angelis, M; Surico, R F; Di Cagno, R; Gänzle, M; Gobbetti, M

2010-06-30

337

Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel extract  

NASA Astrophysics Data System (ADS)

In the present study, the biosynthesis of rutile TiO2 nanoparticles (TiO2 NPs) was achieved by a novel, biodegradable and convenient procedure using fruit peel Annona squamosa aqueous extract. This is the first report on the new, simple, rapid, eco-friendly and cheaper methods for the synthesis of rutile TiO2 NPs at lower temperature using agricultural waste. Rutile TiO2 NPs were characterized by UV, XRD, SEM, TEM and EDS studies. The UV-Vis spectrophotometer results were promising and showed a rapid production of TiO2 NPs with a surface plasmon resonance occurring at 284 nm. The formation of the TiO2 NPs as observed from the XRD spectrum is confirmed to be TiO2 particles in the rutile form as evidenced by the peaks at 2? = 27.42°, 36.10°, 41.30° and 54.33° when compared with the literature. The TEM images showed polydisperse nanoparticles with spherical shapes and size 23 ± 2 nm ranges.

Roopan, Selvaraj Mohana; Bharathi, A.; Prabhakarn, A.; Abdul Rahuman, A.; Velayutham, K.; Rajakumar, G.; Padmaja, R. D.; Lekshmi, Mohan; Madhumitha, G.

2012-12-01

338

Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel extract.  

PubMed

In the present study, the biosynthesis of rutile TiO(2) nanoparticles (TiO(2) NPs) was achieved by a novel, biodegradable and convenient procedure using fruit peel Annona squamosa aqueous extract. This is the first report on the new, simple, rapid, eco-friendly and cheaper methods for the synthesis of rutile TiO(2) NPs at lower temperature using agricultural waste. Rutile TiO(2) NPs were characterized by UV, XRD, SEM, TEM and EDS studies. The UV-Vis spectrophotometer results were promising and showed a rapid production of TiO(2) NPs with a surface plasmon resonance occurring at 284 nm. The formation of the TiO(2) NPs as observed from the XRD spectrum is confirmed to be TiO(2) particles in the rutile form as evidenced by the peaks at 2?=27.42°, 36.10°, 41.30° and 54.33° when compared with the literature. The TEM images showed polydisperse nanoparticles with spherical shapes and size 23±2 nm ranges. PMID:22983203

Roopan, Selvaraj Mohana; Bharathi, A; Prabhakarn, A; Rahuman, A Abdul; Velayutham, K; Rajakumar, G; Padmaja, R D; Lekshmi, Mohan; Madhumitha, G

2012-12-01

339

New, efficient synthesis of oseltamivir phosphate (Tamiflu) via enzymatic desymmetrization of a meso-1,3-cyclohexanedicarboxylic acid diester.  

PubMed

A new, enantioselective synthesis of the influenza neuraminidase inhibitor prodrug oseltamivir phosphate 1 (Tamiflu) and its enantiomer ent-1 starting from cheap, commercially available 2,6-dimethoxyphenol 10 is described. The main features of this approach comprise the cis-hydrogenation of 5-(1-ethyl-propoxy)-4,6-dimethoxy-isophthalic acid diethyl ester (6a) and the desymmetrization of the resultant all-cis meso-diesters 7a and 7b, respectively. Enzymatic hydrolysis of the meso-diester 7b with pig liver esterase afforded the (S)-monoacid 8b, which was converted into cyclohexenol 17 via a Curtius degradation and a base-catalyzed decarboxylative elimination of the Boc-protected oxazolidinone 14. Introduction of the second amino function via S(N)2 substitution of the corresponding triflate 18 with NaN3 followed by azide reduction, N-acetylation, and Boc-deprotection gave oseltamivir phosphate 1 in a total of 10 steps and an overall yield of approximately 30%. The enantiomer ent-1 was similarly obtained via an enzymatic desymmetrization of meso-diester 7a with Aspergillus oryzae lipase, providing the (R)-monoacid ent-8a. PMID:18517254

Zutter, Ulrich; Iding, Hans; Spurr, Paul; Wirz, Beat

2008-07-01

340

An efficient rhythmic component expression and weighting synthesis strategy for classifying motor imagery EEG in a brain computer interface  

NASA Astrophysics Data System (ADS)

The recognition of mental states during motor imagery tasks is crucial for EEG-based brain computer interface research. We have developed a new algorithm by means of frequency decomposition and weighting synthesis strategy for recognizing imagined right- and left-hand movements. A frequency range from 5 to 25 Hz was divided into 20 band bins for each trial, and the corresponding envelopes of filtered EEG signals for each trial were extracted as a measure of instantaneous power at each frequency band. The dimensionality of the feature space was reduced from 200 (corresponding to 2 s) to 3 by down-sampling of envelopes of the feature signals, and subsequently applying principal component analysis. The linear discriminate analysis algorithm was then used to classify the features, due to its generalization capability. Each frequency band bin was weighted by a function determined according to the classification accuracy during the training process. The present classification algorithm was applied to a dataset of nine human subjects, and achieved a success rate of classification of 90% in training and 77% in testing. The present promising results suggest that the present classification algorithm can be used in initiating a general-purpose mental state recognition based on motor imagery tasks.

Wang, Tao; He, Bin

2004-03-01

341

Synthesis and evaluation of diethylethylamine-chitosan for gene delivery: composition effects on the in vitro transfection efficiency.  

PubMed

Chitosan has been indicated as a safe and promising polycation vector for gene delivery. However its low transfection efficiency has been a challenging obstacle for its application. To address this limitation, we synthesized chitosan derivatives which had increasing amounts of diethylethylamine groups (DEAE) attached to the chitosan main chain. The plasmid DNA VR1412 (pDNA), encoding the ß-galactosidase (ß-gal) reporter gene was used to prepare nanoparticles with the chitosan derivatives, and the transfection studies were performed with HeLa cells. By means of dynamic light scattering and zeta potential measurements, it was shown that diethylethylamine-chitosan derivatives (DEAE(x)-CH) were able to condense DNA into small particles having a surface charge depending on the polymer/DNA ratio (N/P ratio). Nanoparticles prepared with derivatives containing 15 and 25% of DEAE groups (DEAE(15)-CH and DEAE(25)-CH) exhibited transfection efficiencies ten times higher than that observed with deacetylated chitosan (CH). For derivatives with higher degrees of substitution (DS), transfection efficiency decreased. The most effective carriers showed low cytotoxicity and good transfection activities at low charge ratios (N/P). Vectors with low DS were easily degraded in the presence of lysozyme at physiological conditions in vitro and the nontoxicity displayed by these vectors opens up new opportunities in the design of DEAE-chitosan-based nanoparticles for gene delivery. PMID:23306549

de Paula Pansani Oliveira, Franciele; Dalla Picola, Isadora Pfeifer; Shi, Qin; Barbosa, Hellen Franciane Gonçalves; Tiera, Vera Aparecida de Oliveira; Fernandes, Júlio Cesar; Tiera, Marcio José

2013-02-01

342

Integrated lipase production and in situ biodiesel synthesis in a recombinant Pichia pastoris yeast: an efficient dual biocatalytic system composed of cell free enzymes and whole cell catalysts  

PubMed Central

Background Lipase-catalyzed biotransformation of acylglycerides or fatty acids into biodiesel via immobilized enzymes or whole cell catalysts has been considered as one of the most promising methods to produce renewable and environmentally friendly alternative liquid fuels, thus being extensively studied so far. In all previously pursued approaches, however, lipase enzymes are prepared in an independent process separated from enzymatic biodiesel production, which would unavoidably increase the cost and energy consumption during industrial manufacture of this cost-sensitive energy product. Therefore, there is an urgent need to develop novel cost-effective biocatalysts and biocatalytic processes with genuine industrial feasibility. Result Inspired by the consolidated bioprocessing of lignocellulose to generate bioethanol, an integrated process with coupled lipase production and in situ biodiesel synthesis in a recombinant P. pastoris yeast was developed in this study. The novel and efficient dual biocatalytic system based on Thermomyces lanuginosus lipase took advantage of both cell free enzymes and whole cell catalysts. The extracellular and intracellular lipases of growing yeast cells were simultaneously utilized to produce biodiesel from waste cooking oils in situ and in one pot. This integrated system effectively achieved 58% and 72% biodiesel yield via concurrent esterified-transesterified methanolysis and stepwise hydrolysis-esterification at 3:1 molar ratio between methanol and waste cooking oils, respectively. Further increasing the molar ratio of methanol to waste cooking oils to 6:1 led to an 87% biodiesel yield using the stepwise strategy. Both water tolerance and methanol tolerance of this novel system were found to be significantly improved compared to previous non-integrated biodiesel production processes using separately prepared immobilized enzymes or whole cell catalysts. Conclusion We have proposed a new concept of integrated biodiesel production. This integrated system couples lipase production to lipase-catalyzed biodiesel synthesis in one pot. The proof-of-concept was established through construction of a recombinant P. pastoris yeast strain that was able to grow, overexpress T. lanuginosus lipase, and efficiently catalyze biodiesel production from fed waste cooking oils and methanol simultaneously. This simplified single-step process represents a significant advance toward achieving economical production of biodiesel at industrial scale via a ‘green’ biocatalytic route. PMID:24713071

2014-01-01

343

Ethyl Cinnamate Derivatives as Promising High-Efficient Acaricides against Psoroptes cuniculi: Synthesis, Bioactivity and Structure-Activity Relationship.  

PubMed

This paper reported the synthesis, structure-activity relationship (SAR) and acaricidal activity in vitro against Psoroptes cuniculi, a mange mite, of 25 ethyl cinnamate derivatives. All target compounds were synthesized and elucidated by means of MS, (1)H- and (13)C-NMR analysis. The results showed that 24 out of 25 tested compounds at 1.0?mg/mL demonstrated acaricidal activity in varying degrees. Among them, 6, 15, 26, 27 and 30 showed significant activity with median lethal concentration values (LC50) of 89.3, 119.0, 39.2, 29.8 and 41.2?µg/mL, respectively, which were 2.1- to 8.3-fold the activity of ivermectin (LC50=247.4?µg/mL), a standard drug in the treatment of Psoroptes cuniculi. Compared with ivermectin, with a median lethal time value (LT50) of 8.9?h, 27 and 30 showed smaller LT50 values of 7.9 and 1.3?h, respectively, whereas 6, 15 and 26 showed slightly larger LT50 values of 10.6, 11.0 and 10.4?h at 4.5?µmol/mL. SARs showed that the presence of o-NO2 or m-NO2 on the benzene ring significantly improved the activity, whereas the introduction of a hydroxy, methoxy, acetoxy, methylenedioxy, bromo or chloro group reduced the activity. (E)-Cinnamates were more effective than their (Z)-isomer. Nevertheless, the carbon-carbon double bond in the acrylic ester moiety was proven not to be essential to improve the activity of cinnamic acid esters. Thus, the results strongly indicate that cinnamate derivatives, especially their dihydro derivatives, should be promising candidates or lead compounds for the development of novel acaricides for the effective control of animal or human acariasis. PMID:25739666

Zhang, Bingyu; Lv, Chao; Li, Weibo; Cui, Zhiming; Chen, Dongdong; Cao, Fangjun; Miao, Fang; Zhou, Le

2015-04-01

344

One-step synthesis of xanthones catalyzed by a highly efficient copper-based magnetically recoverable nanocatalyst.  

PubMed

A versatile and highly efficient strategy to construct a xanthone skeleton via a ligand-free intermolecular catalytic coupling of 2-substituted benzaldehydes and a wide range of phenols has been developed. For this purpose, a novel and magnetically recoverable catalyst consisting of copper nanoparticles on nanosized silica coated maghemite is presented. The reaction proceeds smoothly with easy recovery and reuse of the catalyst. The methodology is compatible with various functional groups and provides an attractive protocol for the generation of a small library of xanthones in very good yield. PMID:24869459

Menéndez, Cintia A; Nador, Fabiana; Radivoy, Gabriel; Gerbino, Darío C

2014-06-01

345

An efficient synthesis of bridged heterocycles from an Ir(I) bis-amination/ring-closing metathesis sequence.  

PubMed

The amination of bis-allylic imidates using an Iridium(I) catalyst leads to the efficient formation of 2,6-divinyl heterocycles. Careful screening of amines, solvents, and conditions has led to the discovery of a system that favors formation of the desired cis products with synthetically useful levels of diastereoselectivity, and these results are further explained by computer based transition state energy calculations. Exposure of the heterocycles to ring-closing metathesis catalysts leads to the desired bridged heterocyclic systems. PMID:22953715

Brawn, Ryan A; Guimarães, Cristiano R W; McClure, Kim F; Liras, Spiros

2012-09-21

346

Metal-organic framework-templated synthesis of magnetic nanoporous carbon as an efficient absorbent for enrichment of phenylurea herbicides.  

PubMed

Nanoporous carbon with a high specific surface area and unique porous structure represents an attractive material as an adsorbent in analytical chemistry. In this study, a magnetic nanoporous carbon (MNC) was fabricated by direct carbonization of Co-based metal-organic framework in nitrogen atmosphere without using any additional carbon precursors. The MNC was used as an effective magnetic adsorbent for the extraction and enrichment of some phenylurea herbicides (monuron, isoproturon, diuron and buturon) in grape and bitter gourd samples prior to their determination by high performance liquid chromatography with ultraviolet detection. Several important experimental parameters that could influence the extraction efficiency were investigated and optimized. Under the optimum conditions, a good linearity was achieved in the concentration range of 1.0-100.0ngg(-1) for monuron, diuron and buturon and 1.5-100.0ngg(-1) for isoproturon with the correlation coefficients (r) larger than 0.9964. The limits of detection (S/N=3) of the method were in the range from 0.17 to 0.46ngg(-1). The results indicated that the MNC material was stable and efficient adsorbent for the magnetic solid-phase extraction of phenylurea herbicides and would have a great application potential for the extraction and preconcentration of more organic pollutants from real samples. PMID:25819788

Liu, Xingli; Wang, Chun; Wu, Qiuhua; Wang, Zhi

2015-04-22

347

Feed array synthesis for reflector antennas in contoured beam applications via an efficient and novel Gaussian beam technique  

NASA Astrophysics Data System (ADS)

A relatively rapid procedure is developed, which combines a novel Gaussian beam approach for the fast analysis of reflector antenna radiation patterns with an iterative optimization method, to synthesize feed array distributions for parabolic reflectors in contoured beam applications. Here, relatively few Gaussian beams are employed as electromagnetic basis functions to represent the field radiated by the feed array in a highly efficient manner. Closed form expressions are used to find the reflection and diffraction of each of these Gaussian beams when they are incident on the parabolic reflector after they are launched from appropriate locations on the feed array plane. The coefficients (or initial launching amplitudes) of the Gaussian beams used in this expansion for the radiation from the feed array are found via an efficient iterative optimization procedure based on the method of successive projections. These coefficients are then directly related to the strengths of the array element source distributions (or array weights). Numerical examples of practical interest are presented to illustrate the utility and the speed of the present approach, which is found to be substantially faster than conventional approaches for these cases.

Chou, Hsi-Tseng; Pathak, Prabhakar H.; Burkholder, Robert J.

2001-01-01

348

Highly efficient diglycolamide-based task-specific ionic liquids: synthesis, unusual extraction behaviour, irradiation, and fluorescence studies.  

PubMed

Two new diglycolamide-based task-specific ionic liquids (DGA-TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA-TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am(3+), and even higher extraction of the lanthanide ion, Eu(3+) (about 5-10 fold). Dilution of the DGA-TSILs in an ionic liquid, C(4)mim(+)·NTf(2)(-), afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO(3)(-) anion, along with the participation of two DGA-TSIL molecules. Time-resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner-sphere water molecule in the Eu(III)-DGA-TSIL complexes in the presence and absence of C(4)mim(+)·NTf(2)(-) as the diluent. The very high radiolytic stability of DGA-TSIL 6 makes it one of the most-efficient solvent systems for the extraction of actinides under acidic feed conditions. PMID:23319409

Mohapatra, Prasanta K; Sengupta, Arijit; Iqbal, Mudassir; Huskens, Jurriaan; Verboom, Willem

2013-02-25

349

Facile synthesis of Ag-ZnO hybrid nanospindles for highly efficient photocatalytic degradation of methyl orange.  

PubMed

Highly photocatalytically active Ag nanoparticle decorated ZnO nanospindles were synthesized by a facile wet chemical method. The structural and optical properties of the as-synthesized materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive X-ray spectroscopy, UV-visible absorption spectroscopy and Raman spectroscopy. The photocatalytic activity of these nanostructures was evaluated by analyzing sunlight driven degradation of methyl orange (MO) dye and it was observed that Ag nanoparticle modified ZnO nanospindles show significantly enhanced photocatalytic activity for degradation of MO, as compared to ZnO nanospindles. We attribute the observed enhanced photocatalytic activity of Ag nanoparticle decorated ZnO nanospindles to their improved sunlight utilization efficiency and the efficient suppression of recombination of photogenerated charge carriers due to the electron scavenging action of Ag nanoparticles and the interfacial electron transfers due to the Schottky junction between Ag nanoparticles and ZnO nanospindles. PMID:25025425

Kuriakose, Sini; Choudhary, Vandana; Satpati, Biswarup; Mohapatra, Satyabrata

2014-09-01

350

Characterization of Halomonas sp. Strain H11 ?-Glucosidase Activated by Monovalent Cations and Its Application for Efficient Synthesis of ?-d-Glucosylglycerol  

PubMed Central

An ?-glucosidase (HaG) with the following unique properties was isolated from Halomonas sp. strain H11: (i) high transglucosylation activity, (ii) activation by monovalent cations, and (iii) very narrow substrate specificity. The molecular mass of the purified HaG was estimated to be 58 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). HaG showed high hydrolytic activities toward maltose, sucrose, and p-nitrophenyl ?-d-glucoside (pNPG) but to almost no other disaccharides or malto-oligosaccharides higher than trisaccharides. HaG showed optimum activity to maltose at 30°C and pH 6.5. Monovalent cations such as K+, Rb+, Cs+, and NH4+ increased the enzymatic activity to 2- to 9-fold of the original activity. These ions shifted the activity-pH profile to the alkaline side. The optimum temperature rose to 40°C in the presence of 10 mM NH4+, although temperature stability was not affected. The apparent Km and kcat values for maltose and pNPG were significantly improved by monovalent cations. Surprisingly, kcat/Km for pNPG increased 372- to 969-fold in their presence. HaG used some alcohols as acceptor substrates in transglucosylation and was useful for efficient synthesis of ?-d-glucosylglycerol. The efficiency of the production level was superior to that of the previously reported enzyme Aspergillus niger ?-glucosidase in terms of small amounts of by-products. Sequence analysis of HaG revealed that it was classified in glycoside hydrolase family 13. Its amino acid sequence showed high identities, 60%, 58%, 57%, and 56%, to Xanthomonas campestris WU-9701 ?-glucosidase, Xanthomonas campestris pv. raphani 756C oligo-1,6-glucosidase, Pseudomonas stutzeri DSM 4166 oligo-1,6-glucosidase, and Agrobacterium tumefaciens F2 ?-glucosidase, respectively. PMID:22226947

Saburi, Wataru; Yamamoto, Takeshi; Kudo, Toshiaki

2012-01-01

351

Efficient 11C-carbonylation of isolated aryl palladium complexes for PET: application to challenging radiopharmaceutical synthesis.  

PubMed

We describe the successful implementation of palladium-aryl oxidative addition complexes as stoichiometric reagents in carbonylation reactions with (11)CO to produce structurally challenging, pharmaceutically relevant compounds. This method enables the first (11)C-carbonyl labeling of an approved PET tracer, [(11)C]raclopride, for the dopamine D2/D3 receptor by carbonylation with excellent radiochemical purity and yield. Two other molecules, [(11)C]olaparib and [(11)C]JNJ 31020028, were efficiently labeled in this manner. The technique distinguishes itself from existing methods by the markedly improved purity profiles of the tracer molecules produced and provides access to complex structures in synthetically useful yields, hereby offering a viable alternative to other (11)C-labeling strategies. PMID:25569730

Andersen, Thomas L; Friis, Stig D; Audrain, Hélène; Nordeman, Patrik; Antoni, Gunnar; Skrydstrup, Troels

2015-02-01

352

Synthesis and in vitro transfection efficiency of spermine-based cationic lipids with different central core structures and lipophilic tails.  

PubMed

Twelve spermine-based cationic lipids with four different central core structures (di(oxyethyl)amino, di(oxyethyl)amino carboxy, 3-amino-1,2-dioxypropyl and 2-amino-1,3-dioxypropyl) and three hydrophobic tails (lauric acid, myristic acid and palmitic acid) were synthesized. The liposomes containing lipids and DOPE showed moderate to good in vitro DNA delivery into HeLa cells. GFP expression experiments revealed that liposomes composed of lipids with 3-amino-1,2-dioxypropyl as a central core structure exhibited highest transfection efficiency under serum-free condition. Whereas, lipid with 2-amino-1,3-dioxypropyl core structure showed highest transfection under 10% serum condition. Moreover, the liposomes and lipoplexes composted of these cationic lipids exhibited low cytotoxicity. PMID:25556091

Niyomtham, Nattisa; Apiratikul, Nuttapon; Suksen, Kanoknetr; Opanasopit, Praneet; Yingyongnarongkul, Boon-Ek

2015-02-01

353

An efficient N-heterocyclic carbene-ruthenium complex: application towards the synthesis of polyesters and polyamides.  

PubMed

The ruthenium benzimidazolylidene-based N-heterocyclic carbene (NHC) complex 4 catalyzes the direct dehydrogenative condensation of primary alcohols into esters and primary alcohols in the presence of amines to the corresponding amides in high yields. This efficient new catalytic system shows a high selectivity towards the conversion of diols to polyesters and of a mixture of diols and diamines to polyamides. The only side product formed in this reaction is molecular hydrogen. Remarkable is the conversion of hydroxytelechelic polytetrahydrofuran (M¯n = 1000 g mol(-1) )-a polydispers starting material-into a hydrolytically degradable polyether with ester linkages (M¯n = 32 600 g mol(-1) ) and, in the presence of aliphatic diamines, into a polyether with amide linkages in the back bone (M¯n = 16 000 g mol(-1) ). PMID:25653190

Malineni, Jagadeesh; Keul, Helmut; Möller, Martin

2015-03-01

354

Synthesis of efficient TiO2-based photocatalysts by phosphate surface modification and the activity-enhanced mechanisms  

NASA Astrophysics Data System (ADS)

A simple strategy to greatly increase the thermal stability of nanocrystalline anatase has been put forward to fabricate efficient TiO2-based photocatalysts under ultraviolet irradiation, via the surface modification with phosphate anions. The results show that the increased anatase thermal stability is attributed to the roles of the phosphate modification effectively inhibiting the contacts among anatase nanocrystals. Compared to un-modified TiO2, the modified TiO2 calcined at high temperature (over 700 °C) exhibits much high photocatalytic activity for degrading Rhodamine B (or phenol) solution, even superior to the commercial P25 TiO2. The activity enhancement is mainly attributed to the increased separation rate of photogenerated charge carriers on the basis of the measurements of steady state- and transient state-surface photovoltage spectroscopy. This work would provide a practical route to reasonably design and synthesize high-performance TiO2-based nanostructured photocatalysts with high anatase thermal stability.

Jing, Liqiang; Qin, Xu; Luan, Yunbo; Qu, Yichun; Xie, Mingzheng

2012-02-01

355

An efficient ionic liquid mediated synthesis, cholinesterase inhibitory activity and molecular modeling study of novel piperidone embedded ?,?-unsaturated ketones.  

PubMed

A series of hitherto unreported piperidone embedded ?,?-unsaturated ketones were synthesized efficiently in ionic solvent and evaluated for cholinesterase inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. Most of the synthesized compounds displayed good enzyme inhibition; therein compounds 7i and 7f displayed significant activity against AChE with IC50 values of 1.47 and 1.74 µM, respectively. Compound 6g showed the highest BChE inhibitory potency with IC50 value of 3.41 µM, being 5 times more potent than galanthamine. Molecular modeling simulation was performed using AChE and BChE receptors extracted from crystal structure of human AChE and human BChE to determine the amino acid residues involved in the binding interaction of synthesized compounds and their relevant receptors. PMID:24138113

Kia, Yalda; Osman, Hasnah; Kumar, Raju Suresh; Murugaiyah, Vikneswaran; Basiri, Alireza; Khaw, Kooi Yeong; Rosli, Mohd Mustaqim

2014-01-01

356

Confined-space alloying of nanoparticles for the synthesis of efficient PtNi fuel-cell catalysts.  

PubMed

The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0?A?mgPt(-1). Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined-space alloying of the nanoparticles in a controlled manner in the pores of the support. PMID:25354360

Baldizzone, Claudio; Mezzavilla, Stefano; Carvalho, Hudson W P; Meier, Josef Christian; Schuppert, Anna K; Heggen, Marc; Galeano, Carolina; Grunwaldt, Jan-Dierk; Schüth, Ferdi; Mayrhofer, Karl J J

2014-12-15

357

Highly efficient synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate and its derivatives by a robust NADH-dependent reductase from E. coli CCZU-K14.  

PubMed

An NADH-dependent reductase (CmCR) from Candida magnoliae was discovered by genome mining for carbonyl reductases. After CmCR was overexpressed in Escherichia coli BL21, a robust reductase-producing strain, recombinant E. coli CCZU-K14, was employed for the efficient synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE) from the reduction of ethyl 4-chloro-3-oxobutanoate (COBE). After the optimization, the optimum reaction conditions were obtained. Notably, E. coli CCZU-K14 had broad substrate specificity in reducing both aliphatic and aromatic substrates, and excellent enantioselectivity of CCZU-K14 was observed for most of the tested substrates, resulting in chiral alcohols of over 99.9% ee. Moreover, COBE at a high concentration of (3000mM) could be asymmetrically reduced to (S)-CHBE in the high yield (>99.0%) and high enantiometric excess value (>99.9% ee) after 14h. Significantly, E. coli CCZU-K14 shows high potential in the industrial production of (S)-CHBE and its derivatives (>99.9% ee). PMID:24745897

He, Yu-Cai; Tao, Zhi-Cheng; Zhang, Xian; Yang, Zhen-Xing; Xu, Jian-He

2014-06-01

358

Facile one-step synthesis of N-doped ZnO micropolyhedrons for efficient photocatalytic degradation of formaldehyde under visible-light irradiation  

NASA Astrophysics Data System (ADS)

N-doped ZnO micropolyhedrons were fabricated by calcining the mixture of commercial ZnO (analytical grade) and NH4NO3 at 600 °C for 1.5 h, in which NH4NO3 was utilized as the nitrogen source. The structure, composition, BET specific surface area and optical properties of N-doped ZnO sample were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, wavelength dispersive X-ray fluorescence spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption-desorption isotherms, and UV-vis diffuse reflectance spectroscopy. The photocatalytic results demonstrated that the as-synthesized N-doped ZnO microcrystals possessed much higher photocatalytic activity than N-doped TiO2 (which was synthesized by calcining the mixture of P25 TiO2 and NH4NO3 at 600 °C for 1.5 h) and commercial pure ZnO in the decomposition of formaldehyde under visible-light (? > 420 nm) irradiation. The present work suggests that NH4NO3 is a promising nitrogen source for one-step calcination synthesis of microcrystalline N-doped ZnO, which can be applied as a visible-light-activated photocatalyst in efficient utilization of solar energy for treating formaldehyde wastewater.

Wu, Changle

2014-11-01

359

An efficient and convenient synthesis of ethyl 1-(4-methoxyphenyl)-5-phenyl-1H-1,2,3-triazole-4-carboxylate.  

PubMed

The "click chemistry" of using organic azides and terminal alkynes is arguably the most efficient and straightforward route to the synthesis of 1,2,3-triazoles. In this paper, an alternative and direct access to ethyl 1-(4-methoxyphenyl)-5-phenyl-1H-1,2,3-triazole-4-carboxylate is described. Treatment of ethyl diazoacetate with 4-methoxyaniline derived aryl imines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene provided fully substituted 1,2,3-triazoles in good to high chemical yields. The base-mediated reaction tolerates various substituted phenyl imines as well as ethyl diazoacetate or the more bulky diazoacetamide. A reasonable mechanism is proposed that involves the addition of an imine nitrogen atom to the terminal nitrogen atom of the diazo compound, followed by aromatization to give the 1,2,3-triazole. The presence of the 4-carboxy group is advantageous as it can be easily transformed into other functional groups. PMID:20029887

Chen, Jung-Hsuan; Liu, Shuan-Ru; Chen, Kwunmin

2010-02-01

360

Structure of the Human Angiotensin II Type 1 (AT1) Receptor Bound to Angiotensin II from Multiple Chemoselective Photoprobe Contacts Reveals a Unique Peptide Binding Mode*  

PubMed Central

Breakthroughs in G protein-coupled receptor structure determination based on crystallography have been mainly obtained from receptors occupied in their transmembrane domain core by low molecular weight ligands, and we have only recently begun to elucidate how the extracellular surface of G protein-coupled receptors (GPCRs) allows for the binding of larger peptide molecules. In the present study, we used a unique chemoselective photoaffinity labeling strategy, the methionine proximity assay, to directly identify at physiological conditions a total of 38 discrete ligand/receptor contact residues that form the extracellular peptide-binding site of an activated GPCR, the angiotensin II type 1 receptor. This experimental data set was used in homology modeling to guide the positioning of the angiotensin II (AngII) peptide within several GPCR crystal structure templates. We found that the CXC chemokine receptor type 4 accommodated the results better than the other templates evaluated; ligand/receptor contact residues were spatially grouped into defined interaction clusters with AngII. In the resulting receptor structure, a ?-hairpin fold in extracellular loop 2 in conjunction with two extracellular disulfide bridges appeared to open and shape the entrance of the ligand-binding site. The bound AngII adopted a somewhat vertical binding mode, allowing concomitant contacts across the extracellular surface and deep within the transmembrane domain core of the receptor. We propose that such a dualistic nature of GPCR interaction could be well suited for diffusible linear peptide ligands and a common feature of other peptidergic class A GPCRs. PMID:23386604

Fillion, Dany; Cabana, Jérôme; Guillemette, Gaétan; Leduc, Richard; Lavigne, Pierre; Escher, Emanuel

2013-01-01

361

Rhodium catalyzed arylation of diazo compounds with aryl boronic acids.  

PubMed

A general and efficient synthesis of diarylacetate, a diarylmethine derivative, was accomplished through rhodium catalyzed direct arylation of diazo compounds with arylboronic acids. The reaction tolerates various boronic acid derivatives and functional groups. Notably, chemoselective arylation of diazo compounds over other electrophiles were demonstrated. The efficacy of the developed methodology is shown by the expeditious synthesis of the core structure of diclofensine. PMID:25759939

Ghorai, Jayanta; Anbarasan, Pazhamalai

2015-04-01

362

Rapid and efficient one-pot synthesis of spiro[indoline-3,4'-pyrano[2, 3-c]pyrazole] derivatives catalyzed by l-proline under ultrasound irradiation.  

PubMed

A rapid and efficient ultrasound-promoted one-pot synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives is described here. The reaction of substituted phenylhydrazine and dialkyl acetylenedicarboxylate with substituted isatin and malononitrile is catalyzed by l-proline to give good-to-excellent yields in water/ethanol (v/v, 1:1) at room temperature. PMID:24931425

Liju, Wang; Ablajan, Keyume; Jun, Feng

2015-01-01

363

Task-specific ionic liquid catalyzed efficient microwave-assisted synthesis of 12-alkyl or aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones under solvent-free conditions  

Microsoft Academic Search

The green, mild, and efficient synthesis of 12-alkyl or aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones has been achieved by a three-component coupling of 2-naphthol, aldehydes, and cyclic1,3-dicarbonyl compounds in the presence of a sulfonic acid functionalized ionic liquid without any solvent under microwave irradiation. The catalyst can be reused at least eight times without any noticeable decrease in catalytic activity.

Dhiman Kundu; Adinath Majee; Alakananda Hajra

2011-01-01

364

An efficient and expedient method for the synthesis of 11C-labeled ?-aminoisobutyric acid: A tumor imaging agent potentially useful for cancer diagnosis  

Microsoft Academic Search

We describe the synthesis of 11C-labeled ?-aminoisobutyric acid 2 from iodo[11C]methane and methyl N-(diphenylmethylen)-d,l-alaniate (5). The tetrabutylammonium fluoride (TBAF)-promoted ?-[11C]methylation of sterically hindered analog 5 was a key step in our synthesis process. Total radiochemical conversion of 2 was high and a remote-controlled synthesis was carried out. A comparative tumor positron emission tomography (PET) imaging study using the same model

Koichi Kato; Atsushi B. Tsuji; Tsuneo Saga; Ming-Rong Zhang

2011-01-01

365

High-Yield Synthesis of Sub-10 nm Pt Nanotetrahedra with Bare ?111? Facets for Efficient Electrocatalytic Applications.  

PubMed

Unlike other shapes, the design of tetrahedral Pt nanocrystals (Pt-NTd), which have the largest number of Pt(111) surface atoms and highest catalytic activities toward the electron transfer reactions, has widely been considered a synthetic challenge due to their thermodynamic instability. Here, we show that, by inducing their nucleation on functionalized carbon, Pt NTds can be obtained with tunable sizes and high yields. The carbon support anchors the nanocrystals early and prevents their oriented attachment leading to nanowire formation. Therein, an in situ generated amine is crucial for stabilization of Pt-NTds, which can later be removed to expose the Pt(111) facets for higher catalytic efficiency. The bare nanocrystals exhibit much improved stability and electrocatalytic activity characteristic of Pt(111) toward oxygen reduction reaction (ORR) and methanol and formic acid oxidation reactions. For example, ?90% of their activity was retained after 5000 potential cycles, while the ORR onset potential was recorded to be very high, 1.01 V vs reversible hydrogen electrode (RHE). PMID:25660263

Rana, Moumita; Chhetri, Manjeet; Loukya, B; Patil, Pramod K; Datta, Ranjan; Gautam, Ujjal K

2015-03-01

366

An efficient synthesis of five-membered cyclic ethers from 1,3-diols using molecular iodine as a catalyst.  

PubMed

Intramolecular cyclic etherification of 1,3-diols was investigated using iodine as a catalyst under solution reaction conditions. Compounds containing five-membered ether rings were obtained. Propella ether (11-oxatricyclo[4.4.3.0(1,6)]tridecane) was conveniently synthesized from 1,3-diol (6-(2-hydroxyethyl)spiro[4.5]decan-6-ol) in 97% yield via carbon skeleton rearrangement. Spiroethers and bicyclic ethers were also obtained from the corresponding 1,3-diols in yields of over 77%. The most suitable reaction conditions were a temperature of 80 degrees C, a 1:0.2 molar ratio of 1,3-diol:iodine, and a time period of 8 h. In addition, terpenoic ethers were efficiently synthesized from the corresponding 1,3-diols, derived from (+)-camphor and (-)-fenchone, via skeleton rearrangement. In particular, the reaction of the 1,3-diol derived from (+)-camphor proceeded smoothly at room temperature with a yield of 91%. The yield of the cyclic ether using iodine as a catalyst was comparable to the method using sulfuric acid. PMID:18622127

Kasashima, Yoshio; Fujimoto, Hiroshi; Mino, Takashi; Sakamoto, Masami; Fujita, Tsutomu

2008-01-01

367

Synthesis of CdS/ZnO/graphene composite with high-efficiency photoelectrochemical activities under solar radiation  

NASA Astrophysics Data System (ADS)

A novel ternary CdS/ZnO/graphene composite has been successfully prepared by loading ZnO and CdS nanoparticles in graphene nanosheets via a facile one-step hydrothermal method. The microstructures and properties have been examined by X-ray diffraction (XRD), scanning electron microscopy with an energy dispersive spectroscope (EDS), transmission electron microscopy, Raman and UV-vis diffuse reflectance spectra (DRS). The characterization results reveal that the crystalline of the composite is very well, the graphene sheets were tightly coated with ZnO and CdS nanoparticles, and the light-harvesting was effectively strengthened. Taking photoelectrochemical test, the ternary CdS/ZnO/graphene composite exhibits enhanced photocatalytic activity compared with its foundation matrix binary composites and pure ZnO and CdS. The improved photocatalytic performance can be attributed to the enhanced light absorption, the extremely efficient charge separation, as well as superior durability of the ternary composite. It is proposed that graphene-based composites by coupling graphene to suitable, multiple semiconductors can not only greatly improve the capacity for photocatalytic, but also expand the exploration and utilization of graphene-based nanocomposites for energy conversion.

Han, Weijia; Ren, Long; Qi, Xiang; Liu, Yundan; Wei, Xiaolin; Huang, Zongyu; Zhong, Jianxin

2014-04-01

368

Synthesis of highly phosphonic acid functionalized benzene-bridged periodic mesoporous organosilicas for use as efficient dye adsorbents.  

PubMed

Periodic mesoporous organosilicas (PMOs) with benzene bridging groups in the silica wall were functionalized with a tunable content of phosphonic acid groups. These bifunctional materials were synthesized by co-condensation of two different organosilane precursors, that is, 1,4-bis(triethoxysilyl)benzene (BTEB) and sodium 3-(trihydroxysilyl)propyl methyl phosphate (SPMP), under acidic conditions using nonionic surfactant Brij-S10 as template. The materials exhibited well-ordered mesostructures and were characterized by X-ray diffraction, nitrogen sorption, TEM, TGA, FTIR, and solid-state NMR measurements. The materials thus obtained were employed as adsorbents to remove different types of dyes, for example, cationic dyes methylene blue and phenosafranine, anionic orange II, and amphoteric rhodamine B, from aqueous solutions. The materials exhibited a remarkably high adsorption capacity than activated carbon due to their ordered mesostructures, a large number of phosphonic acid groups, and high surface areas. The adsorption was mainly governed by electrostatic interaction, but also involved ?-? stacking interaction as well as hydrogen bonding. The adsorption kinetics can be better fitted by the pseudo-second order model. The adsorption process was controlled by the mechanisms of external mass transfer and intraparticle diffusion. The materials retained more than 97% dye removal efficiency after use for five consecutive cycles. PMID:25010459

Deka, Juti Rani; Liu, Chia-Ling; Wang, Tzu-Hua; Chang, Wei-Chieh; Kao, Hsien-Ming

2014-08-15

369

Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction  

PubMed Central

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO32? to form graphene, but also sulfur in SO42? from its highest (+6) to lowest valence which was hybridized into the carbon sp2 framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites. PMID:25790856

Wang, Jiacheng; Ma, Ruguang; Zhou, Zhenzhen; Liu, Guanghui; Liu, Qian

2015-01-01

370

Efficient one-pot synthesis of peapod-like hollow carbon nanomaterials for utrahigh drug loading capacity.  

PubMed

In this paper, peapod-like hollow carbon nanomaterial was fabricated via an efficient one-pot hydrothermal route. The carbon-silica composite was employed as the precursor and cetyltrimethylammonium bromide (CTAB) as the morphology-controlled agent. SEM and TEM results indicated that the carbon shell and the silica core in the precursor were not closely linked but rattle-type structure. After removing the silica template, the obtained carbon product had uniform peapod-like morphology, interconnected pores and high specific surface areas (above 800.0 m(2)/g). We found that CTAB played an important role in the formation of the products with peapod-like morphology. The particle sizes of the hollow carbon nanospheres were readily adjusted by varying the dosage of tetraethoxysilane (TEOS) and the volume ratio of ethanol and water. Based on the experimental results, the formation mechanism of the hollow carbon nanomaterial was also discussed. By virtue of their unique nanostructure and porous properties, the peapod-like hollow carbon nanomaterial exhibited ultrahigh drug loading capacity above 98.4% for doxorubicin hydrochloride (DOX). PMID:25313471

Guo, Jingxin; Zhang, Haijiao; Geng, Hongya; Mi, Xianqiang; Ding, Guoji; Jiao, Zheng

2015-01-01

371

Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction.  

PubMed

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO3(2-) to form graphene, but also sulfur in SO4(2-) from its highest (+6) to lowest valence which was hybridized into the carbon sp(2) framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites. PMID:25790856

Wang, Jiacheng; Ma, Ruguang; Zhou, Zhenzhen; Liu, Guanghui; Liu, Qian

2015-01-01

372

Efficient synthesis of [¹¹C]ramelteon as a positron emission tomography probe for imaging melatonin receptors involved in circadian rhythms.  

PubMed

Ramelteon (TAK-375) is a novel melatonin receptor agonist that is used for clinical treatment of insomnia. The present report describes radiolabeling of ramelteon with the short-lived positron-emitter ¹¹C (T(1/2)=20.4 min) by 2 methods. One method was [¹¹C]methylation of an acetoamide precursor and the other was [¹¹C]acylation of the corresponding amine precursor. First, [¹¹C]methylation method showed the low reproducibility together with the production of many kinds of side products from which the [¹¹C-methyl]Ramelteon was separated with chemical purity of <28% and radiochemical purity of >98%. Whereas, the [¹¹C]acylation method showed high efficiency and reproducibility with a good radiochemical yield (22-43%, decay corrected), high chemical and radiochemical purities (>99% each), and high specific activity (43-162 GBq/µmol) (n=5) after HPLC purification. [¹¹C]Ramelteon is a potential positron emission tomography (PET) probe for imaging the melatonin receptor. PMID:21804256

Takashima-Hirano, Misato; Tazawa, Syusaku; Takahashi, Kazuhiro; Doi, Hisashi; Suzuki, Masaaki

2011-01-01

373

?-Keto esters from ketones and ethyl chloroformate: a rapid, general, efficient synthesis of pyrazolones and their antimicrobial, in silico and in vitro cytotoxicity studies  

PubMed Central

Background Pyrazolones are traditionally synthesized by the reaction of ?-keto esters with hydrazine and its derivatives. There are methods to synthesize ?-keto esters from esters and aldehydes, but these methods have main limitation in varying the substituents. Often, there are a number of methods such as acylation of enolates in which a chelating effect has been employed to lock the enolate anion using lithium and magnesium salts; however, these methods suffer from inconsistent yields in the case of aliphatic acylation. There are methods to synthesize ?-keto esters from ketones like caboxylation of ketone enolates using carbon dioxide and carbon monoxide sources in the presence of palladium or transition metal catalysts. Currently, the most general and simple method to synthesize ?-keto ester is the reaction of dimethyl or ethyl carbonate with ketone in the presence of strong bases which also requires long reaction time, use of excessive amount of reagent and inconsistent yield. These factors lead us to develop a simple method to synthesize ?-keto esters by changing the base and reagent. Results A series of ?-keto esters were synthesized from ketones and ethyl chloroformate in the presence of base which in turn are converted to pyrazolones and then subjected to cytotoxicity studies towards various cancer cell lines and antimicrobial activity studies towards various bacterial and fungal strains. Conclusion The ?-keto esters from ethyl chloroformate was successfully attempted, and the developed method is simple, fast and applicable to the ketones having the alkyl halogens, protecting groups like Boc and Cbz that were tolerated and proved to be useful in the synthesis of fused bicyclic and tricyclic pyrazolones efficiently using cyclic ketones. Since this method is successful for different ketones, it can be useful for the synthesis of pharmaceutically important pyrazolones also. The synthesized pyrazolones were subjected to antimicrobial, docking and cytotoxicity assay against ACHN (human renal cell carcinoma), Panc-1 (human pancreatic adenocarcinoma) and HCT-116 (human colon cancer) cell line, and lead molecules have been identified. Some of the compounds are found to have promising activity against different bacterial and fungal strains tested. PMID:23870758

2013-01-01

374

Interactions at the Dimer Interface Influence the Relative Efficiencies for Purine Nucleotide Synthesis and Pyrophosphorolysis in a Phosphoribosyltransferase  

SciTech Connect

Enzymes that salvage 6-oxopurines, including hypoxanthine phosphoribosyltransferases (HPRTs), are potential targets for drugs in the treatment of diseases caused by protozoan parasites. For this reason, a number of high-resolution X-ray crystal structures of the HPRTs from protozoa have been reported. Although these structures did not reveal why HPRTs need to form dimers for catalysis, they revealed the existence of potentially relevant interactions involving residues in a loop of amino acid residues adjacent to the dimer interface, but the contributions of these interactions to catalysis remained poorly understood. The loop, referred to as active-site loop I, contains an unusual non-proline cis-peptide and is composed of residues that are structurally analogous with Leu67, Lys68, and Gly69 in the human HPRT. Functional analyses of site-directed mutations (K68D, K68E, K68N, K68P, and K68R) in the HPRT from Trypanosoma cruzi, etiologic agent of Chagas disease, show that the side-chain at position 68 can differentially influence the K{sub m} values for all four substrates as well as the k{sub cat} values for both IMP formation and pyrophosphorolysis. Also, the results for the K68P mutant are inconsistent with a cis-trans peptide isomerization-assisted catalytic mechanism. These data, together with the results of structural studies of the K68R mutant, reveal that the side-chain of residue 68 does not participate directly in reaction chemistry, but it strongly influences the relative efficiencies for IMP formation and pyrophosphorolysis, and the prevalence of lysine at position 68 in the HPRT of the majority of eukaryotes is consistent with there being a biological role for nucleotide pyrophosphorolysis.

Canyuk, Bhutorn; Medrano, Francisco J.; Wenck, MaryAnne; Focia, Pamela J.; Eakin, Ann E.; Craig III, Sydney P. (UNC); (Connecticut)

2010-03-05

375

Rapid efficient synthesis and characterization of silver, gold, and bimetallic nanoparticles from the medicinal plant Plumbago zeylanica and their application in biofilm control  

PubMed Central

Background Nanoparticles (NPs) have gained significance in medical fields due to their high surface-area-to-volume ratio. In this study, we synthesized NPs from a medicinally important plant – Plumbago zeylanica. Materials and methods Aqueous root extract of P. zeylanica (PZRE) was analyzed for the presence of flavonoids, sugars, and organic acids using high-performance thin-layer chromatography (HPTLC), gas chromatography-time of flight-mass spectrometry (GC-TOF-MS), and biochemical methods. The silver NPs (AgNPs), gold NPs (AuNPs), and bimetallic NPs (AgAuNPs) were synthesized from root extract and characterized using ultraviolet-visible spectra, X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The effects of these NPs on Acinetobacter baumannii, Staphylococcus aureus, and Escherichia coli biofilms were studied using quantitative biofilm inhibition and disruption assays, as well as using fluorescence, scanning electron microscopy, and atomic force microscopy. Results PZRE showed the presence of phenolics, such as plumbagin, and flavonoids, in addition to citric acid, sucrose, glucose, fructose, and starch, using HPTLC, GC-TOF-MS, and quantitative analysis. Bioreduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) were confirmed at absorbances of 440 nm (AgNPs), 570 nm (AuNPs), and 540 nm (AgAuNPs), respectively. The maximum rate of synthesis at 50°C was achieved with 5 mM AgNO3 within 4.5 hours for AgNPs; and with 0.7 mM HAuCl4 within 5 hours for AuNPs. The synthesis of AgAuNPs, which completed within 90 minutes with 0.7 mM AgNO3 and HAuCl4, was found to be the fastest. Fourier-transform infrared spectroscopy confirmed bioreduction, while EDS and XRD patterns confirmed purity and the crystalline nature of the NPs, respectively. TEM micrographs and DLS showed about 60 nm monodispersed Ag nanospheres, 20–30 nm Au nanospheres adhering to form Au nanotriangles, and about 90 nm hexagonal blunt-ended AgAuNPs. These NPs also showed antimicrobial and antibiofilm activity against E. coli, A. baumannii, S. aureus, and a mixed culture of A. baumannii and S. aureus. AgNPs inhibited biofilm in the range of 96%–99% and AgAuNPs from 93% to 98% in single-culture biofilms. AuNPs also showed biofilm inhibition, with the highest of 98% in S. aureus. AgNPs also showed good biofilm disruption, with the highest of 88% in A. baumannii. Conclusion This is the first report on rapid and efficient synthesis of AgNPs, AuNPs and AgAuNPs from P. zeylanica and their effect on quantitative inhibition and disruption of bacterial biofilms. PMID:24920901

Salunke, Gayatri R; Ghosh, Sougata; Santosh Kumar, RJ; Khade, Samiksha; Vashisth, Priya; Kale, Trupti; Chopade, Snehal; Pruthi, Vikas; Kundu, Gopal; Bellare, Jayesh R; Chopade, Balu A

2014-01-01

376

Facile synthesis of yolk-shell magnetic mesoporous carbon microspheres for efficient enrichment of low abundance peptides  

NASA Astrophysics Data System (ADS)

Magnetic mesoporous carbon microspheres with a yolk-shell structure (YSMMCS) have been prepared via a new in situ carbon source strategy. The material was fabricated by two shells coated onto the Fe3O4 particles; the inner dense and thick silica shell could protect the magnetic core from harsh acidic solvents as well as induce the void between the core and the outer shell for the yolk-shell structure, while the outer organosilica shell was used as the template and carbon source for in situ preparation of a carbon shell with mesoporous structure. A C18-alkyl chain was incorporated in situ as the carbon precursor efficiently, avoiding the conventional infiltration step, which was very difficult to manipulate and time-consuming with the possibility of losing the carbon precursor. The resulting yolk-shell magnetic mesoporous carbon microspheres exhibited a high surface area (273.15 m2 g-1), a large pore volume (0.31 cm3 g-1), and a strong magnetic response (a saturation magnetization value of 34.57 emu g-1). As a result of the void between the core and the outer shell and the ?-? stacking effect, adsorption capacity reached 191.64 mg g-1 by using Rhodamine B as a standard analyte, indicating the great potential application of the material as drug carriers. Owing to the inherent hydrophobicity and high surface area, the composite material showed better performance in the enrichment of peptides than a magnetic mesoporous silica material (Fe2O3@nSiO2@mSiO2). According to the LC-MS/MS results, about 51 and 29 nonredundant peptides were identified from tryptic digests of 5 nM BSA. Additionally, taking advantage of the mesoporous structure and strong magnetic response, the material was utilized to selectively extract low abundance endogenous peptides from human serum in the presence of high abundance proteins. Based on the LC-MS/MS results, 962 endogenous peptides were obtained by 2.5 mg YSMMCS relative to 539 endogenous peptides by 5 mg Fe2O3@nSiO2@mSiO2, confirming the outstanding performance of YSMMCS in peptidome analysis.Magnetic mesoporous carbon microspheres with a yolk-shell structure (YSMMCS) have been prepared via a new in situ carbon source strategy. The material was fabricated by two shells coated onto the Fe3O4 particles; the inner dense and thick silica shell could protect the magnetic core from harsh acidic solvents as well as induce the void between the core and the outer shell for the yolk-shell structure, while the outer organosilica shell was used as the template and carbon source for in situ preparation of a carbon shell with mesoporous structure. A C18-alkyl chain was incorporated in situ as the carbon precursor efficiently, avoiding the conventional infiltration step, which was very difficult to manipulate and time-consuming with the possibility of losing the carbon precursor. The resulting yolk-shell magnetic mesoporous carbon microspheres exhibited a high surface area (273.15 m2 g-1), a large pore volume (0.31 cm3 g-1), and a strong magnetic response (a saturation magnetization value of 34.57 emu g-1). As a result of the void between the core and the outer shell and the ?-? stacking effect, adsorption capacity reached 191.64 mg g-1 by using Rhodamine B as a standard analyte, indicating the great potential application of the material as drug carriers. Owing to the inherent hydrophobicity and high surface area, the composite material showed better performance in the enrichment of peptides than a magnetic mesoporous silica material (Fe2O3@nSiO2@mSiO2). According to the LC-MS/MS results, about 51 and 29 nonredundant peptides were identified from tryptic digests of 5 nM BSA. Additionally, taking advantage of the mesoporous structure and strong magnetic response, the material was utilized to selectively extract low abundance endogenous peptides from human serum in the presence of high abundance proteins. Based on the LC-MS/MS results, 962 endogenous peptides were obtained by 2.5 mg YSMMCS relative to 539 endogenous peptides by 5 mg Fe2O3@nSiO2@mSiO2, confirming the outstanding performance of YSMMCS in peptido

Wan, Hao; Qin, Hongqiang; Xiong, Zhichao; Zhang, Weibing; Zou, Hanfa

2013-10-01

377

Synthesis of Na-zeolites from fly ash  

Microsoft Academic Search

The present study focuses on the synthesis of zeolites after fly ash activation, the major objectives being: (a) to study the activation processes; (b) to elucidate the activation conditions for maximum synthesis efficiency; (c) to optimize the conditions for the monomineral synthesis; and (d) to test synthesis efficiencies for different fly ash types. Fly ash was activated by NaOH and

Xavier Querol; Felicià Plana; Andrés Alastuey; Angel López-Soler

1997-01-01

378

Towards novel efficient and stable nuclear import signals: synthesis and properties of trimethylguanosine cap analogs modified within the 5',5'-triphosphate bridge.  

PubMed

A trimethylguanosine (TMG) cap is present at the 5' end of several small nuclear and nucleolar RNAs. Recently, it has been reported that the TMG cap is a potential nuclear import signal for nucleus-targeting therapeutic nucleic acids and proteins. The import is mediated by recognition of the TMG cap by the snRNA transporting protein, snurportin1. This work describes the synthesis and properties of a series of dinucleotide TMG cap (m3(2,2,7)GpppG) analogs modified in the 5',5'-triphosphate bridge as tools to study TMG cap-dependent biological processes. The bridge was altered at different positions by introducing either bridging (imidodiphosphate, O to NH and methylenebisphosphonate, O to CH2) or non-bridging (phosphorothioate, O to S and boranophosphate, O to BH3) modifications, or by elongation to tetraphosphate. The stability of novel analogs in blood serum was studied to reveal that the ?,?-bridging O to NH substitution (m3(2,2,7)GppNHpG) confers the highest resistance. Short RNAs capped with analogs containing ?,?-bridging (m3(2,2,7)GppNHpG) or ?-non-bridging (m3(2,2,7)GppSpG D2) modifications were resistant to decapping pyrophosphatase, hNudt16. Preliminary studies on binding by human snurportin1 revealed that both O to NH and O to S substitutions support this binding. Due to favorable properties in all three assays, m3(2,2,7)GppNHpG was selected as a promising candidate for further studies on the efficiency of the TMG cap as a nuclear import signal. PMID:25296894

Zytek, Malgorzata; Kowalska, Joanna; Lukaszewicz, Maciej; Wojtczak, Blazej A; Zuberek, Joanna; Ferenc-Mrozek, Aleksandra; Darzynkiewicz, Edward; Niedzwiecka, Anna; Jemielity, Jacek

2014-12-01

379

Parallel synthesis and screening of peptide conjugates.  

PubMed

Peptide conjugates represent an emerging class of therapeutics. However, in contrast to that of small molecules and peptides, the discovery and optimization of peptide conjugates is low in throughput, resource intensive, time-consuming, and based on educated decisions rather than screening. A strategy for the parallel synthesis and screening of peptide conjugates is presented that (1) reduces variability in the conjugation steps; (2) provides a new method to rapidly and quantitatively measure conversion in crude conjugation mixtures; (3) introduces a purification step using an immobilized chemical scavenger that does not rely on protein-specific binding; and (4) is supported by robust analytical methods to characterize the large number of end products. Copper-free click chemistry is used as the chemoselective ligation method for conjugation and purification. The productivity in the generation and screening of peptide conjugates is significantly improved by applying this strategy as is demonstrated by the optimization of the anti-Angiopoietin-2 (Ang2) CovX-body, CVX-060, a peptide-antibody scaffold conjugate that has advanced in clinical trials for oncology indications. PMID:24824568

Dirksen, Anouk; Madsen, Mark; Dello Iacono, Giuseppe; Matin, Marla J; Bacica, Michael; Stankovi?, Nebojša; Callans, Sherri; Bhat, Abhijit

2014-06-18

380

Total synthesis of marinomycin A using salicylate as a molecular switch to mediate dimerization  

NASA Astrophysics Data System (ADS)

Antibiotics play a significant role in human health because of their ability to treat life-threatening bacterial infections. The growing problems with antibiotic resistance have made the development of new antibiotics a World Health Organization priority. Marinomycin A is a member of a new class of bis-salicylate-containing polyene macrodiolides, which have potent antibiotic activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Herein, we describe a triply convergent synthesis of this agent using the salicylate as a novel molecular switch for the chemoselective construction of the macrodiolide. This strategy raises new questions regarding the biosynthetic role of the salicylate and its potential impact on the mechanism of action of these types of agents. For instance, in contrast to penicillin, which enhances the electrophilicity of the cyclic amide through ring strain, salicylates reduce the electrophilicity of the aryl ester through an intramolecular resonance-assisted hydrogen bond to provide an amide surrogate.

Evans, P. Andrew; Huang, Mu-Hua; Lawler, Michael J.; Maroto, Sergio

2012-08-01

381

An efficient and expedient method for the synthesis of 11C-labeled ?-aminoisobutyric acid: a tumor imaging agent potentially useful for cancer diagnosis.  

PubMed

We describe the synthesis of (11)C-labeled ?-aminoisobutyric acid 2 from iodo[(11)C]methane and methyl N-(diphenylmethylen)-d,l-alaniate (5). The tetrabutylammonium fluoride (TBAF)-promoted ?-[(11)C]methylation of sterically hindered analog 5 was a key step in our synthesis process. Total radiochemical conversion of 2 was high and a remote-controlled synthesis was carried out. A comparative tumor positron emission tomography (PET) imaging study using the same model mouse showed higher uptake of 2 than with (11)C-labeled methionine and [(18)F] fluorodeoxyglucose (FDG). PMID:21392981

Kato, Koichi; Tsuji, Atsushi B; Saga, Tsuneo; Zhang, Ming-Rong

2011-04-15

382

Alum Catalyzed Simple, Efficient, and Green Synthesis of 2-[3-Amino-5-methyl-5-(pyridin-3-yl)-1,5-dihydro-4H-1,2,4-triazol-4-yl]propanoic Acid Derivatives in Aqueous Media  

PubMed Central

Alum (KAl(SO4)2·12H2O) is an inexpensive, efficient, and nontoxic catalyst used for the synthesis of 2-[3-amino-5-methyl-5-(pyridin-3-yl)-1,5-dihydro-4H-1,2,4-triazol-4-yl]propanoic acid derivatives in aqueous media by the reaction of 3-acetyl pyridine (1), amino acids (2)/(6), and thiosemicarbazide (4) at 80°C. This methodology offers significant improvements for the synthesis of products with regards to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts which uphold the motto of green chemistry. Synthesized compounds have been characterized by FT-IR, 13C NMR, and 1HNMR spectroscopy. PMID:24288503

Sachdeva, Harshita; Dwivedi, Diksha; Saroj, Rekha

2013-01-01

383

Iodine as a novel and efficient reagent for the synthesis of ?-aminonitriles by a three-component condensation of carbonyl compounds, amines, and trimethylsilyl cyanide  

Microsoft Academic Search

A straightforward and general method has been developed for the synthesis of ?-aminonitriles by simply combining aldehydes or ketones, amines, and trimethylsilyl cyanides in the presence of a catalytic amount of molecular iodine at room temperature.

Laurel Royer; Surya K. De; Richard A. Gibbs

2005-01-01

384

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin–West reaction: Isolation of some 5-succinyloxyoxazole intermediates  

Microsoft Academic Search

A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction of these anhydrides with N-Fmoc-protected dipeptides under the modified Dakin–West reaction affords mainly the corresponding 5-succinyloxyoxazoles.

Joseph Richard Casimir; Laurent Ettouati; Joëlle Paris

1998-01-01

385

Rapid and efficient synthesis of peptide fragments containing ?-aminoisobutyric acid using Fmoc-amino acid chlorides\\/potassium salt of 1-hydroxybenzotriazole  

Microsoft Academic Search

The synthesis of peptides containing multiple Aib residues was accomplished using Fmoc-Aib-Cl in presence of KOBt. As no additional base was added, the duration of coupling reactions could be extended. Thus, the synthesis of the alamethicin 1–4 fragment, Aib-Pro-Aib-Ala, the emerimicin 2–6 fragment, Aib-Aib-Aib-Val-Gly and the Aib tetramer, Fmoc-(Aib)4-OBzl were accomplished in good yield and purity.

Vommina V. Suresh Babu; Hosahudya N. Gopi

1998-01-01

386

EFFICIENT CHEMICAL SYNTHESIS USING MICROWAVES  

EPA Science Inventory

Synthetic organic transformations performed under non-traditional conditions are becoming popular primarily to circumvent the growing environmental concerns. A solvent-free approach that involves microwave (MW) exposure of neat reactants catalyzed by the surfaces of less-expensiv...

387

Monosaccharides as Scaffolds for the Synthesis of Novel Compounds  

NASA Astrophysics Data System (ADS)

This chapter focuses on monosaccharides and scaffolds their derivatives as scaffolds for the synthesis of primarily bioactive compounds. Such carbohydrate derivatives have been designed to modulate mainly protein-protein and peptide-protein interactions although modulators of carbohydrate-protein and carbohydrate-nucleic acid interactions have also been of interest. The multiple hydroxyl groups that are present on saccharides have made pyranose, furanose and iminosugars ideal templates or scaffolds to which recognition or pharmacophoric groups can be grafted to generate novel compounds for medicinal chemistry. The synthesis of compounds for evaluations require strategies for regioselective reactions of saccharide hydroxyl groups and use of orthogonally stable protecting groups. Syntheses have been carried out on the solid phase and in solution. Also the use of uronic acids, amino sugars and sugar amino acids has facilitated the synthesis of peptidomimetics and prospecting libraries as they enable, through presence of amino or carboxylic acid groups, chemoselective approaches to be employed in solution and on solid phase. Sugar amino acids are readily incorporated, as peptide isosteres, to generate sugar-peptide hybrids or for the synthesis of novel carbopeptoids . The synthesis of new cyclic compounds, derived in part from saccharides, and their application as scaffolds is an emerging area and recent examples include spirocyclic compounds, benzodiazepine-saccharide hybrids and macrolide-saccharide hybrids. Potent bioactive saccharide derivatives have been identified that include enzyme inhibitors , somatostatin receptor ligands, integrin ligands, anti-viral compounds, shiga toxin inhibitors and cell growth inhibitors. Some saccharide derivatives have demonstrated improved cellular permeability when compared with peptides and are in clinical trials.

Murphy, Paul V.; Velasco-Torrijos, Trinidad

388

An Efficient One-Pot Green Protocol for the Synthesis of 5-Unsubstituted 3,4-Dihydropyrimidin-2(1H)-Ones Using Recyclable Amberlyst 15 DRY as a Heterogeneous Catalyst via Three-Component Biginelli-Like Reaction  

PubMed Central

An environmentally benign green protocol for the synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones using Amberlyst 15 DRY as a recyclable catalyst has been developed. The use of resinous, nontoxic, thermally stable, and inexpensive Amberlyst 15 DRY, as a recyclable heterogeneous catalyst, makes the process simple with negligible chemical waste. Among the various solid acid catalysts Amberlyst 15 DRY was found to be the most efficient catalyst with regard to reaction time, yield, and ease of work-up procedure. PMID:24052845

Jetti, Srinivasa Rao; Verma, Divya; Jain, Shubha

2012-01-01

389

An eco-friendly procedure for the efficient synthesis of arylidinemalononitriles and 4,4?-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ols) in aqueous media  

Microsoft Academic Search

Commercially available lithium hydroxide monohydrate (LiOH·H2O) was found to be a novel “dual activation” catalyst for Knoevenagel condensation between malononitrile (1) or 3-methyl 1-phenyl-1H-pyrazol-5-(4H)-one (6) with aromatic aldehydes 2a–e leading to an efficient and easy synthesis of arylidenemalononitriles 3a–d and 4,4?-(arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ols) 7a–c in short times. The reaction of aryl aldehydes with malononitrile afforded excellent yields after 1–6 min in aqueous

Moustafa A. Gouda; Ameen A. Abu-Hashem

2012-01-01

390

An efficient and novel one-pot synthesis of 2,4,5-triaryl-1 H -imidazoles catalyzed by UO 2 (NO 3 ) 2 ·6H 2 O under heterogeneous conditions  

Microsoft Academic Search

An efficient, convenient, and novel one-pot method of 2,4,5-triaryl-1H-imidazoles synthesis using benzil, arene carbaldehydes, and ammonium acetate, catalyzed by uranyl nitrate hexahydrate [UO2(NO3)2·6H2O] supported on acidic alumina and resulting in good to excellent yields under heterogeneous conditions, is reported. Formation\\u000a of a reactants-catalyst complex was confirmed by UV-VIS spectral data. Antibacterial (MIC) and antioxidant activity of the\\u000a synthesized compounds was

Vardhineedi Sri Venkata Satyanarayana; Amaravadi Sivakumar

2011-01-01

391

Wells–Dawson heteropolyacid supported on silica: a highly efficient catalyst for synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles  

Microsoft Academic Search

Heteropolyacid H6P2W18O62·24H2O (WD) supported on silica (WD\\/SiO2) has been used as an effective catalytic system for the synthesis of various 1,2,4,5-tetrasubstituted imidazoles by four-component\\u000a condensation of benzil, aldehydes, amines and ammonium acetate under solvent-free conditions. This approach can be useful\\u000a for three-component synthesis of 2,4,5-trisubstituted imidazoles. The same reactions were repeated by using benzoin instead\\u000a of benzil.

Ali Reza Karimi; Zahra Alimohammadi; Mostafa M. Amini

2010-01-01

392

Separating the isomers—Efficient synthesis of the N-hydroxysuccinimide esters of 5 and 6-carboxyfluorescein diacetate and 5 and 6-carboxyrhodamine B  

PubMed Central

Diacetate protection of 5 and 6-carboxyfluorescein followed by synthesis of the N-hydroxysuccinimide esters allowed ready separation of the two isomers on a multi-gram scale. The 5 and 6-carboxyrhodamine B N-hydroxysuccinimide esters were also readily synthesised and separated. PMID:24856065

Brunet, Aurélie; Aslam, Tashfeen; Bradley, Mark

2014-01-01

393

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin-West reaction: Isolation of some 5-succinyloxyoxazole intermediates  

Microsoft Academic Search

Summary  A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction\\u000a of these anhydrides withN-Fmoc-protected dipeptides under the modified Dakin-West reaction affords mainly the corresponding 5-succinyloxyoxazoles.

Joseph Richard Casimir; Laurent Ettouati; Joëlle Paris

1998-01-01

394

Synthesis of (+)-spirolaxine methyl ether.  

PubMed

A short and efficient synthesis of (+)-spirolaxine methyl ether, a metabolite of the fungus Sporotrichum laxum with inhibitory activity against Helicobacter pylori, is described. The synthesis has been carried out by a Prins cyclization, to obtain the [6,5]-spiroketal system, and a Wadsworth-Emmons condensation, applied for the installation of the polymethylene chain on the phthalide moiety. PMID:16872220

Nannei, Raffaella; Dallavalle, Sabrina; Merlini, Lucio; Bava, Adriana; Nasini, Gianluca

2006-08-01

395

Nano-CuFe2O4 as a magnetically separable and reusable catalyst for the synthesis of diaryl/aryl alkyl sulfides via cross-coupling process under ligand-free conditions.  

PubMed

An efficient protocol was developed for the CuFe(2)O(4) nanopowder-catalyzed aryl-sulfur bond formation between aryl halide and thiol/disulfide. A variety of aryl sulfides were synthesized in impressive yields with good chemoselectivity and functional group tolerance in the presence of a catalytic amount of CuFe(2)O(4), Cs(2)CO(3) as base, in nitrogen atmosphere, under ligand-free conditions, in DMSO as solvent at 100 °C. The catalyst is air-stable, inexpensive, magnetically separable and recyclable up to four cycles. PMID:21769376

Swapna, Kokkirala; Murthy, Sabbavarapu Narayana; Jyothi, Mocharla Tarani; Nageswar, Yadavalli Venkata Durga

2011-09-01

396

Vanillin Synthesis from 4-Hydroxybenzaldehyde  

ERIC Educational Resources Information Center

A regioselective, safe and efficient method for the synthesis of vanillin from 4-hydroxybenzaldehyde is being described. The vanillin derived from the process is cheap and can be used as a flavor or in the paper industry.

Taber, Douglass F.; Patel, Shweta; Hambleton, Travis M.; Winkel, Emma E.

2007-01-01

397

Transition-metal-free cross-coupling of thioethers with aryl(cyano)iodonium triflates: a facile and efficient method for the one-pot synthesis of thiocyanates.  

PubMed

A novel transition-metal-free cross-coupling method for the one-step synthesis of thiocyanates via the C-S bond cleavage of readily available thioethers with aryl(cyano)-iodonium triflates as the cyanating agent is developed. This process features relatively broad substrate scopes, less-toxic hypervalent iodine reagents, mild operating conditions, excellent functional group compatibilities, and affords various thiocyanates in moderate to good yields. PMID:25811416

Zhu, Dan; Chang, Denghu; Shi, Lei

2015-04-01

398

An efficient tandem approach for the synthesis of functionalized 2-pyridone-3-carboxylic acids using three-component reaction in aqueous media.  

PubMed

Novel analogs of 2-pyridone-3-carboxylic acids 4a-l have been prepared by the three-component reaction of 3-formyl chromone, Meldrum's acid, and primary amines in the presence of a catalytic amount of diammonium hydrogen phosphate in water. Good-to-high yields, easy work-up, and an environmentally friendly profile are the advantages of this method for the synthesis of 2-pyridone-3-carboxylic acid derivatives. PMID:24792225

Mehrparvar, Saber; Balalaie, Saeed; Rabbanizadeh, Mahnaz; Ghabraie, Elmira; Rominger, Frank

2014-08-01

399

Efficient and Green Approaches for the Synthesis of 4H-Benzo[g]chromenes in Water, Under Neat Conditions, and Using Task-Specific Ionic Liquid  

Microsoft Academic Search

Facile and convenient procedures have been described for the synthesis of 4H-benzo[g]chromenes by one-pot condensation of aromatic aldehydes, malononitrile\\/ethyl cyanoacetate, and 2-hydroxy-1,4-naphthoquinone. The reaction has been accomplished using catalytic cetyltrimethylammonium bromide (CTAB) in water under reflux or under neat conditions at 110 °C. A task-specific ionic liquid, 1-butyl-3-methyl imidazolium hydroxide ([bmim]OH), has also been found to be an effective catalyst for

Jitender M. Khurana; Devanshi Magoo; Ankita Chaudhary

2012-01-01

400

Efficient combination of task-specific ionic liquid and microwave dielectric heating applied to one-pot three component synthesis of a small library of 4-thiazolidinones  

Microsoft Academic Search

The first report of the use of task-specific ionic liquid as synthetic equivalent of ionic liquid-phase matrice for the preparation of a small library of 4-thiazolidinones is reported in this paper. The starting (ethyleneglycol)ionic liquid-phase is functionalized in good yields with 4-(formylphenoxy)butyric acid by using usual esterification reaction conditions (DCC\\/DMAP as catalyst). The synthesis of the ionic liquid-phase bound 4-thiazolidinones

Joan Fraga-Dubreuil; Jean Pierre Bazureau

2003-01-01

401

Efficient and Green Approaches for the Synthesis of 4H-Benzo[g]chromenes in Water, Neat Conditions and Using Task-Specific Ionic Liquid  

Microsoft Academic Search

Facile and convenient procedures have been described for the synthesis of 4H-benzo[g]chromenes by one-pot condensation of aromatic aldehydes, malononitrile\\/ethyl cyanoacetate and 2-hydroxy-1,4-naphthoquinone. The reaction has been accomplished using catalytic cetyltrimethylammonium bromide (CTAB) in water under reflux or under neat conditions at 110 °C. Task-specific ionic liquid, 1-butyl-3-methyl imidazolium hydroxide ([bmim]OH), has also been found as an effective catalyst towards this transformation.

Jitender M. Khurana; Devanshi Magoo; Ankita Chaudhary

2012-01-01

402

At the same hepatic amino acid load, portal infusion of amino acids is more efficient than peripheral infusion in stimulating liver protein synthesis in the dog  

PubMed Central

Background Hepatic glucose uptake is enhanced by portal delivery of glucose which creates a negative arterio-portal substrate gradient. Hepatic amino acid (AA) utilization may be regulated by the same phenomenon, but this has not been proven. Objective We aimed to assess hepatic AA balance and protein synthesis with or without a negative arterio-portal AA gradient. Design Somatostatin was infused IV, and insulin and glucagon were replaced intraportally at 4- and 3-fold basal rates, respectively, in 3 groups (n=9 each) of conscious dogs with catheters for hepatic balance measurement. Arterial glucose concentrations were clamped at 9 mM. An AA mixture was infused IV to maintain basal concentrations (EuAA), intraportally to mimic the post-meal AA increase (PoAA), or IV (PeAA) to match the hepatic AA load in PoAA. Protein synthesis was assessed with a primed, continuous [14C]leucine infusion. Results Net hepatic glucose uptake in PoAA was ?50% of that in EuAA and PeAA (P<0.05). The hepatic intracellular leucine concentration was 2- to 2.5-fold greater in PoAA and PeAA than EuAA (P<0.05); net hepatic leucine uptake and 14C leucine utilization were ?2-fold greater (P<0.05) and albumin synthesis was 30% greater (P<0.05) in PoAA than EuAA and PeAA, Phosphorylation of ribosomal protein S6 (downstream of the mammalian target of Rapamycin complex 1 [mTORC1]) was significantly increased in PoAA, but not PeAA, vs EuAA. Conclusions Portal, but not peripheral, AA delivery significantly enhanced hepatic protein synthesis under conditions where AA, glucose, insulin and glucagon did not differ at the liver, an effect apparently mediated by mTORC1 signalling. PMID:18842785

Dardevet, Dominique; Kimball, Scot R; Jefferson, Leonard S; Cherrington, Alan D; Rémond, Didier; DiCostanzo, Catherine A; Moore, Mary Courtney

2009-01-01

403

Aerobic iron-based cross-dehydrogenative coupling enables efficient diversity-oriented synthesis of coumestrol-based selective estrogen receptor modulators.  

PubMed

An iron-based cross-dehydrogenative coupling (CDC) approach was applied for the diversity-oriented synthesis of coumestrol-based selective estrogen receptor modulators (SERMs), representing the first application of CDC chemistry in natural product synthesis. The first stage of the two-step synthesis of coumestrol involved a modified aerobic oxidative cross-coupling between ethyl 2-(2,4-dimethoxybenzoyl)acetate and 3-methoxyphenol, with FeCl3 (10 mol%) as the catalyst. The benzofuran coupling product was then subjected to sequential deprotection and lactonization steps, affording the natural product in 59% overall yield. Based on this new methodology other coumestrol analogues were prepared, and their effects on the proliferation of the estrogen receptor (ER)-dependent MCF-7 and of the ER-independent MDA-MB-231 breast cancer cells were tested. As a result, new types of estrogen receptor ligands having an acetamide group instead of the 9-hydroxyl group of coumestrol were discovered. Both 9-acetamido-coumestrol and 8-acetamidocoumestrol were found more active than the natural product against estrogen-dependent MCF-7 breast cancer cells, with IC50 values of 30 and 9 nM, respectively. PMID:23946113

Kshirsagar, Umesh A; Parnes, Regev; Goldshtein, Hagit; Ofir, Rivka; Zarivach, Raz; Pappo, Doron

2013-09-27

404

Total synthesis of fentanyl  

Microsoft Academic Search

Fentanyl of a potent anilidopiperidine analgesic has been synthesized from a simple phenyle-thylamine by four step sequence.\\u000a The key part of this synthesis involves an efficient construction of phenylethylpiperidone skeleton via aminomethano desilyation-cyclization\\u000a followed by Swern oxidation.

Young-Ger Suh; Kyung-Ho Cho; Dong-Yoon Shin

1998-01-01

405

Synthesis of mimics of pramanicin from pyroglutamic Acid and their antibacterial activity.  

PubMed

Epoxypyrrolidinones are available by epoxidation of carboxamide-activated bicyclic lactam substrates derived from pyroglutamate using aqueous hydrogen peroxide and tertiary amine catalysis. In the case of an activating Weinreb carboxamide, further chemoselective elaboration leads to the efficient formation of libraries of epoxyketones. Deprotection may be achieved under acidic conditions to give epoxypyroglutaminols, although the ease of this process can be ameliorated by the presence of internal hydrogen bonding. Bioassay against S. aureus and E. coli indicated that some compounds exhibit antibacterial activity. These libraries may be considered to be structural mimics of the natural products pramanicin and epolactaene. More generally, this outcome suggests that interrogation of bioactive natural products is likely to permit the identification of "privileged" structural scaffolds, providing frameworks suitable for optimization in a short series of chemical steps that may accelerate the discovery of new antibiotic chemotypes. Further optimization of such systems may permit the rapid identification of novel systems suitable for antibacterial drug development. PMID:25647715

Tan, Song Wei Benjamin; Chai, Christina L L; Moloney, Mark G; Thompson, Amber L

2015-03-01

406

All-catalytic, efficient, and asymmetric synthesis of alpha,omega-diheterofunctional reduced polypropionates via "one-pot" Zr-catalyzed asymmetric carboalumination-Pd-catalyzed cross-coupling tandem process.  

PubMed

A highly efficient method for the synthesis of stereochemically pure (>/=99% ee and >50/1 dr) alpha,omega-diheterofunctional reduced polypropionates has been developed. The essential features of the method are represented by the conversion of inexpensive styrene into 2-methyl-4-phenyl-1-pentanol (1) in 50% yield over two steps from styrene via Zr-catalyzed asymmetric carboalumination (ZACA) reaction in the presence of (NMI)2ZrCl2 and Pd-catalyzed vinylation of the in situ generated isoalkylalanes in the presence of Zn(OTf)2 and a catalytic amount of Pd(DPEphos)Cl2. This ZACA-Pd-catalyzed vinylation may be repeated as needed without purification. After the final ZACA reaction, oxidation with O2 provides alpha-hydroxy-omega-phenyl reduced polypropionates, which can be fully or partially purified by chromatography. After acetylation, Ru-catalyzed oxidative cleavage of the Ph ring, and reduction with BH3.THF, the second chromatographic purification provides stereoisomerically pure alpha,omega-diheterofunctional reduced polypropionates (e.g., 9 and 11) that can be further converted to key intermediates 6 and 7 for the synthesis of ionomycin (4) and borrelidin (5), respectively, by known reactions. PMID:15740104

Novak, Tibor; Tan, Ze; Liang, Bo; Negishi, Ei-Ichi

2005-03-01

407

Total synthesis of 12-methoxydihydrochelerythrine and anti-tumour activity of its quaternary base: toward an efficient synthetic route for 12-alkoxybenzo[c]phenanthridine bases via naphthoquinone monooxime from 2-benzofuranyl-1-tetralone derivative.  

PubMed

A concise total synthesis of 12-methoxydihydrochelerythrine (6), isolated from Bocconia integrifolia, is described. The synthesis features an efficient route to a 12-alkoxybenzo[c]phenanthridine skeleton via naphthoquinone monooxime 11 as a key compound. Starting from 7-methoxy-2-methylbenzo[b]furan (9), 3-aryl-1-tetralone 10 was synthesised, followed by aromatisation to 3-aryl-1-naphthol 17. After oxidative cleavage of the furan ring, basic nitrosation of naphthol 22 gave the naphthoquinone 11. The benzo[c]phenanthridine skeleton was formed by reductive cyclisation of 11. Deoxygenation of the lactam moiety in 23 afforded nor-base 32 and methylation of 32 under reductive conditions gave the target dihydro base 6 (23 steps from benzofuran 9 in 10% overall yield). The corresponding quaternary base 7 showed moderate anti-tumour activity against cancer cell lines; on NCI-H460: IC50 4.5 microM and on MDA-MB-231: IC50 1.2 microM. Introduction of a methoxy group into the 12-position of the benzo[c]phenanthridine skeleton could cause enhanced activity against MDA-MB-231 by comparison of 7 with chelerythrine (35) (IC50 5.3 microM). PMID:14518124

Watanabe, Toshiko; Ohashi, Yoshiaki; Yoshino, Rie; Komano, Naoko; Eguchi, Miyuki; Maruyama, Sakiko; Ishikawa, Tsutomu

2003-09-01

408

Cyclic 1,2-Diketones as Core Building Blocks: A Strategy for the Total Synthesis of (?)-Terpestacin  

PubMed Central

We report a full account of our work towards the total synthesis of (?)-terpestacin (1), a sesterterpene originally isolated from fungal strain Arthrinium sp. FA1744. Its promising anti-HIV/anti-cancer activity as well as its novel structure make terpestacin an attractive synthetic target. A strategy based on the unique reactivity of cyclic 1,2-diketones (diosphenol) was developed, and total synthesis of 1 was achieved in 20 steps in the longest linear sequence from commercially available 3-methyl-1,2-cyclopentanedione (19). The key feature of our synthesis is represented by double usage of a “Pd AAA-Claisen” protocol, first in the early stage to generate the C1 quaternary center and second in the late stage to install the side chain. In addition, a rather unusual ene-1,2-dione moiety was synthesized and utilized as an excellent Michael acceptor to attach the C15 substituent. Several possible routes towards the total synthesis have been examined and carefully evaluated. During our exploration, many interesting chemoselectivity issues have also been addressed, such as a highly selective ring-closing metathesis (RCM) and a challenging oxidation of a disubstituted olefin in the presence of three trisubstiuted ones. PMID:20411537

Dong, Guangbin; Vance, Jennifer A.

2010-01-01

409

An Atom-Economic and Selective Ruthenium-Catalyzed Redox Isomerization of Propargylic Alcohols. An Efficient Strategy for the Synthesis of Leukotrienes  

PubMed Central

Catalytic ruthenium complexes in conjunction with an indium cocatalyst and Bronsted acid isomerize primary and secondary propargylic alcohols in good yields to provide trans enals and enones exclusively. Readily available indenylbis(triphenylphosphine)ruthenium chloride in the presence of indium triflate and camphorsulfonic acid give the best turnover numbers and reactivity with the broadest range of substrates. Deuterium labeling experiments suggest that the process occurs through propargylic hydride migration followed by protic cleavage of the resultant vinylruthenium intermediate. Application of this method to the synthesis of leukotriene B4 demonstrates its utility and extraordinary selectivity. PMID:18702463

Trost, Barry M.; Livingston, Robert C.

2008-01-01

410

Three Component Reaction: An Efficient Synthesis and Reactions of 3,4-Dihydropyrimidin-2(1H)-Ones and Thiones Using New Natural Catalyst  

PubMed Central

Synthesis of 3,4-dihydropyrimidin-2(1H)-one and 3,4-dihydropyrimidin-2(1H)-thione derivatives from aldehydes, 1,3-dicarbonyl derivatives and urea or thiourea using granite and quartz as new, natural and reusable catalysts. Some of the 3,4-dihydropyrimidin-2(1H)-thione derivatives were used to prepare new heterocyclic compounds. The antimicrobial activity of selected examples of the synthesized compounds was tested and showed moderate activity. PMID:24052868

Elmaghraby, A. M.; Mousa, I. A.; Harb, A. A.; Mahgoub, M. Y.

2013-01-01

411

An efficient catalytic system based on 7,8-dihydroxy-4-methylcoumarin and copper(II) for the click synthesis of diverse 1,4-disubstituted-1,2,3-triazoles under green conditions.  

PubMed

In this work, the combination of 7,8-dihydroxy-4-methyl coumarin (DHMC) as a novel bidentate O,O-chelating agent and copper(II) acetate monohydrate (2:1 molar ratio) has been found to form an efficient catalytic system. This catalyst provided good to excellent yields in the multi-component click synthesis of 1,4-disubstituted-1,2,3-triazoles by using various structurally diverse organic halides, different non-activated terminal alkynes, and sodium azide. This catalytic system eliminates the need for the isolation of the hazardous azide intermediates which are generated in situ. The reaction is carried out in aqueous phase at room temperature and it can be accelerated by sonication or by increasing the reaction temperature. Moreover, the reaction can be performed in large scale. It is noteworthy that DHMC is commercially available and that it can be easily synthesized with low cost materials. PMID:24866914

Sharghi, Hashem; Shiri, Pezhman; Aberi, Mahdi

2014-08-01

412

A novel sodium iodide and ammonium molybdate co-catalytic system for the efficient synthesis of 2-benzimidazoles using hydrogen peroxide under ultrasound irradiation.  

PubMed

The reaction of aldehydes and o-phenylenediamine for the preparation of 2-benzimidazoles has been studied using hydrogen peroxide as an oxidant under ultrasound irradiation at room temperature in this paper. The combination of substoichiometric sodium iodide and ammonium molybdate as co-catalysts, together with using small amounts of hydrogen peroxide, makes this transformation very efficient and attractive under ultrasound. Thus, a mild, green and efficient method is established to carry out this reaction in high yield. PMID:24074960

Bai, Guo-Yi; Lan, Xing-Wang; Chen, Guo-Feng; Liu, Xiao-Fang; Li, Tian-Yu; Shi, Ling-Juan

2014-03-01

413

An efficient synthesis of 3-OBn-6?,14-epoxy-bridged opiates from naltrexone and identification of a related dual MOR inverse agonist/KOR agonist.  

PubMed

In an effort to better understand the conformational preferences that inform the biological activity of naltrexone and related naltrexol derivatives, a new synthesis of the restricted analog 3-OBn-6?,14-epoxymorphinan 4 is described. 4 was synthesized starting from naltrexone in 50% overall yield, proceeding through the OBn-6?-triflate intermediate 8. Key steps to the synthesis include benzylation (96% yield), reduction (90% yield, ?:?:3:2), followed by a one-pot triflation/displacement sequence (96% yield) to yield the desired bridged epoxy derivative 4. X-ray crystallographic analysis of intermediate 3-OBn-6?-naltrexol 7a supports population of the key boat conformation required for the epoxy ring closure. We also report that the 6?-mesylate 10-a high affinity opioid receptor ligand, the epimeric derivative of 11, and an analog of 12-functions as an inverse agonist at the mu opioid receptor using herkinorin pre-conditioned cells and an agonist at the kappa opioid receptor when evaluated in independent in vitro [(35)S]-GTP-?-S assays. PMID:22771010

Martin, David J; FitzMorris, Paul E; Li, Bo; Ayestas, Mario; Sally, Ellicott J; Dersch, Christina M; Rothman, Richard B; Deveau, Amy M

2012-11-15

414

From protein total synthesis to peptide transamidation and metathesis: playing with the reversibility of N,S-acyl or N,Se-acyl migration reactions.  

PubMed

Amide forming reactions are central to the field of peptide and protein synthesis and are considered to be poorly reversible reactions owing to the high stability of peptide bonds. One amide-forming reaction is native chemical ligation (NCL) which is driven by a sulfur to nitrogen acyl migration process from a transient thioester intermediate. However, recent studies have revealed the reversibility of the S,N-acyl shift reaction or of the related Se,N-acyl shift process using mild aqueous conditions. Such chemical processes have great potential for the chemoselective formation of peptide bonds to cysteine or selenocysteine, and open novel avenues in the field of peptide transamidation and metathesis reactions. PMID:25438800

Melnyk, Oleg; Agouridas, Vangelis

2014-10-01

415

An efficient solid-phase strategy for total synthesis of naturally occurring amphiphilic marine siderophores: amphibactin-T and moanachelin ala-B.  

PubMed

Microorganisms such as bacteria, fungi and some plants secrete an abundance of suites of low molecular weight, high-affinity iron(iii)-chelating acylated siderophores. The peptide composition of a suite of amphiphilic siderophores generated by a Vibrio species, isolated from oligotrophic open ocean water, contained the same iron(iii)-scavenging polar head group and is attached to a fatty acid. In the present study, we report the first total synthesis of the naturally obtainable marine siderophores amphibactin-T and moanachelin ala-B on solid-phase using standard Fmoc-chemistry. Furthermore, we discuss the preparation of orthogonal protected Orn amino acid 'N(?)-Fmoc-N(?)-(acetyl)-N(?)-(benzoyloxy)-ornithine' [Fmoc-Orn(Ac,OBz)-OH], which is the most important constructive building block for amphibactin and moanachelin siderophores syntheses. The applications of this Orn unit on solid-phase have also been discussed. PMID:25806414

Cherkupally, Prabhakar; Ramesh, Suhas; Govender, Thavendran; Kruger, Hendrik G; de la Torre, Beatriz G; Albericio, Fernando

2015-04-01

416

Efficient synthesis and utilization of phenyl-substituted heteroaromatic carboxylic acids as aryl diketo acid isosteres in the design of novel HIV-1 integrase inhibitors.  

PubMed

Three new types of aryl diketo acid (ADK) isosteres were designed by conversion of the biologically labile 1,3-diketo unit into heteroaromatic motif such as isoxazole, isothiazole, or 1H-pyrazole to improve the physicochemical property of ADK-based HIV-1 integrase (IN) inhibitors. The synthesis of the heteroaromatic carboxylic acids was established by employing phenyl beta-diketoester or benzaldehyde as the starting material and 1,3-dipolar cycloaddition as the key reaction. Of the compounds tested, the 3-benzyloxyphenyl-substituted isoxazole carboxylic acid displayed the best IN inhibitory and antiviral activities, with N-hydroxylamidation enhancing the in vitro and in vivo potency. These findings are important for further optimization of ADK-based IN inhibitors. PMID:18662877

Zeng, Li-Fan; Zhang, Hu-Shan; Wang, Yun-Hua; Sanchez, Tino; Zheng, Yong-Tang; Neamati, Nouri; Long, Ya-Qiu

2008-08-15

417

Sulphamic Acid (H2NSO3H): A Low Cost, Mild and an Efficient Catalyst for the Synthesis of Substituted N-Phenylpyrazoles Under Solvent-Free Conditions  

Microsoft Academic Search

N-phenylpyrazoles are synthesized by condensing phenylhydrazine and 1,3-diketones in the presence of catalytic amount of sulphamic acid, a mild and an efficient solid acid catalyst, under solvent-free conditions. This condensation proceeds smoothly in shorter reaction time.

Mohan R. Shetty; Shriniwas D. Samant

2011-01-01

418

Sulfamic Acid (H2NSO3H): A Low-Cost, Mild, and Efficient Catalyst for the Synthesis of Substituted N-Phenylpyrazoles Under Solvent-Free Conditions  

Microsoft Academic Search

N-Phenylpyrazoles are synthesized by condensing phenylhydrazine and 1,3-diketones in the presence of a catalytic amount of sulfamic acid, a mild and an efficient solid acid catalyst, under solvent-free conditions. This condensation proceeds smoothly in shorter reaction time.

Mohan R. Shetty; Shriniwas D. Samant

2012-01-01

419

Convenient and Efficient Synthesis of 1,1?Bis?(4?alkylthiophenyl)?1?alkenes via Tandem Friedel–Crafts Acylation and Alkylation of Sulfides and Acyl Chlorides  

Microsoft Academic Search

1,1?Bis(4?alkylthiophenyl)?1?alkenes were conveniently and efficiently prepared from alkyl phenyl sulfides and acyl chlorides via a tandem Friedel–Crafts acylation and alkylation in the presence of anhydrous aluminum chloride. The scope, limitation, and mechanism of the tandem reaction were also discussed.

Jiaxi Xu; Jiakun Xia; Yu Lan

2005-01-01

420

INTERNATIONAL JOURNAL OF EMBEDDED SYSTEMS, VOL. X, NO. XX, JUNE 2004 1 Energy-Efficient Hardware/Software Co-Synthesis  

E-print Network

INTERNATIONAL JOURNAL OF EMBEDDED SYSTEMS, VOL. X, NO. XX, JUNE 2004 1 Energy-Efficient Hardware, etc., onto a single chip. They are being used to implement many wireless embedded systems, where chip. An example of these RSoCs is the Triscend A7 CSoC device [19], which integrates a 32- bit ARM7

Prasanna, Viktor K.

421

One-pot synthesis of nitrogen and sulfur co-doped graphene as efficient metal-free electrocatalysts for the oxygen reduction reaction.  

PubMed

Novel N, S co-doped graphene (NSG) was prepared by annealing graphene oxide with thiourea as the single N and S precursor. The NSG electrodes, as efficient metal-free electrocatalysts, show a direct four-electron reaction pathway, high onset potential, high current density and high stability for the oxygen reduction reaction. PMID:24687131

Wang, Xin; Wang, Jie; Wang, Deli; Dou, Shuo; Ma, Zhaoling; Wu, Jianghong; Tao, Li; Shen, Anli; Ouyang, Canbin; Liu, Qiuhong; Wang, Shuangyin

2014-05-14

422

Highly Efficient and Selective Synthesis of Conjugated Triynes and Higher Oligoynes of Biological and Materials Chemical Interest via Palladium-Catalyzed Alkynyl-Alkenyl Coupling†  

PubMed Central

Iteration of Pd-catalyzed reaction of alkynyl- and oligoynylzincs with (E)-ICH=CHCl followed by metalation-termination with electrophiles(E) has provided a linear route to conjugated tri- and tetraynes, while Pd-catalyzed monoalkynylation of 1,1-dibromoenynes accompanied by dehydrobromination has provided a convergent route to conjugated tri-, tetra-, and pentaynes. Both display unprecedent high efficiency and selectivity. PMID:17134269

Métay, Estelle; Hu, Qian

2013-01-01

423

A new hypercrosslinked supermicroporous polymer, with scope for sulfonation, and its catalytic potential for the efficient synthesis of biodiesel at room temperature.  

PubMed

We have designed a new hypercrosslinked supermicroporous polymer (HMP-1) with a BET surface area of 913 m(2) g(-1) by FeCl3via a catalyzed Friedel-Crafts alkylation reaction between carbazole and ?,?'-dibromo-p-xylene. Upon sulfonation HMP-1 yielded a very efficient solid acid catalyst for the production of biodiesels via esterification/transesterification of free fatty acids (FFA)/esters at room temperature. PMID:25702885

Bhunia, Subhajit; Banerjee, Biplab; Bhaumik, Asim

2015-03-10

424

A Simple and Efficient Synthesis of an Acid-labile Polyphosphoramidate by Organobase-catalyzed Ring-Opening Polymerization and Transformation to Polyphosphoester Ionomers by Acid Treatment  

PubMed Central

The direct synthesis of an acid-labile polyphosphoramidate by organobase-catalyzed ring-opening polymerization and an overall two-step preparation of polyphosphodiester ionomers (PPEI) by acid-assisted cleavage of the phosphoramidate bonds along the backbone of the polyphosphoramidate were developed in this study. The ultrafast organobase-catalyzed ring-opening polymerization of a cyclic phospholane methoxyethyl amidate monomer initiated by benzyl alcohol allowed for the preparation of well-defined polyphosphoramidates (PPA) with predictable molecular weights, narrow molecular weight distributions (PDI<1.10), and well-defined chain ends. Cleavage of the acid-labile phosphoramidate bonds on the polyphosphoramidate repeat units was evaluated under acidic conditions over a pH range of 1–5, and the complete hydrolysis produced polyphosphodiesters. The thermal properties of the resulting polyphosphoester ionomer acid and polyphosphoester ionomer sodium salt exhibited significant thermal stability. The parent PPA and both forms of the PPEIs showed low cytotoxicities toward HeLa cells and RAW 264.7 mouse macrophage cells. The synthetic methodology developed here has enriched the family of water-soluble polymers prepared by rapid and convenient organobase-catalyzed ring-opening polymerizations and straightforward chemical medication reactions, which are designed to be hydrolytically degradable and have promise for numerous biomedical and other applications. PMID:23997276

Zhang, Shiyi; Wang, Hai; Shen, Yuefei; Zhang, Fuwu; Seetho, Kellie; Zou, Jiong; Taylor, John-Stephen A.; Dove, Andrew P.; Wooley, Karen L.

2013-01-01

425

Template-free synthesis of cube-like Ag/AgCl nanostructures via a direct-precipitation protocol: highly efficient sunlight-driven plasmonic photocatalysts.  

PubMed

In this paper, we report that cube-like Ag/AgCl nanostructures could be facilely fabricated in a one-pot manner through a direct-precipitation protocol under ambient conditions, wherein no additional issues such as external energy (e.g., high temperature or high pressure), surfactants, or reducing agents are required. In terms of using sodium chloride (NaCl) as chlorine source and silver acetate (CH?COOAg) as silver source, it is disclosed that simply by adding an aqueous solution of NaCl into an aqueous solution of CH?COOAg, Ag/AgCl nanostructures with a cube-like geometry, could be successfully formulated. We show that thus-formulated cube-like Ag/AgCl nanospecies could be used as high-performance yet durable visible-light-driven or sunlight-driven plasmonic photocatalysts for the photodegradation of methyl orange (MO) and 4-chlorophenol (4-CP) pollutants. Compared with the commercially available P25-TiO?, and the Ag/AgCl nanospheres previously fabricated via a surfactant-assisted method, our current cube-like Ag/AgCl nanostructures could exhibit much higher photocatalytic performance. Our template free protocol might open up new and varied opportunities for an easy synthesis of cube-like Ag/AgCl-based high-performance sunlight-driven plasmonic photocatalysts for organic pollutant elimination. PMID:23138343

Zhu, Mingshan; Chen, Penglei; Ma, Wanhong; Lei, Bin; Liu, Minghua

2012-11-01

426

A general catalytic hydroamidation of 1,3-dienes: atom-efficient synthesis of N-allyl heterocycles, amides, and sulfonamides.  

PubMed

Transition-metal-catalyzed hydroamination reactions are sustainable and atom-economical C?N bond-forming processes. Although remarkable progress has been made in the inter- and intramolecular amination of olefins and 1,3-dienes, related intermolecular reactions of amides are still much less known. Control of the regioselectivity without analogous telomerization is the particular challenge in the catalytic hydroamidation of alkenes and 1,3-dienes. Herein, we report a general protocol for the hydroamidation of electron-deficient N-heterocyclic amides and sulfonamides with 1,3-dienes and vinyl pyridines in the presence of a catalyst derived from [{Pd(?-cinnamyl)Cl}2 ] and ligand L7 or L10. The reactions proceeded in good to excellent yield with high regioselectivity. The practical utility of our method is demonstrated by the hydroamidation of functionalized biologically active substrates. The high regioselectivity for linear amide products makes the procedure useful for the synthesis of a variety of allylic amides. PMID:24452993

Banerjee, Debasis; Junge, Kathrin; Beller, Matthias

2014-02-01

427

Synthesis of aminoacylated N6,N6-dimethyladenosine solid support for efficient access to hydrolysis-resistant 3?-charged tRNA mimics  

PubMed Central

RNA-amino acid and RNA-peptide conjugates that mimic charged tRNA 3?-ends are valuable substrates for structural and functional investigations of ribosomal complexes. To obtain such conjugates, most synthetic approaches that are found in the literature make use of puromycin. This well available aminonucleoside antibiotic contains a dimethylamino group at the nucleobase and a methylated tyrosine that is connected via an amide linkage to the ribose moiety. To increase structural diversity, we present the synthesis of a N6,N6-dimethylated 3?-azido-3?-deoxyadenosine precursor that can be coupled to any amino acid. Further derivatization results in the solid support that is eligible for the preparation of stable 3?-aminoacyl- or 3?-peptidyl-tRNA termini with an amide instead of the natural ester linkage. The present work expands our previously established route that delivered a broad range of peptidyl-tRNA mimics to the corresponding counterparts with N6,N6-dimethylation pattern of the terminal adenosine (A76). This aspect is of significance to modulate the binding preferences of the mimics for ribosomal A- versus P-site. PMID:25457127

Neuner, Sandro; Micura, Ronald

2014-01-01

428

Synthesis of aminoacylated N(6),N(6)-dimethyladenosine solid support for efficient access to hydrolysis-resistant 3'-charged tRNA mimics.  

PubMed

RNA-amino acid and RNA-peptide conjugates that mimic charged tRNA 3'-ends are valuable substrates for structural and functional investigations of ribosomal complexes. To obtain such conjugates, most synthetic approaches that are found in the literature make use of puromycin. This well available aminonucleoside antibiotic contains a dimethylamino group at the nucleobase and a methylated tyrosine that is connected via an amide linkage to the ribose moiety. To increase structural diversity, we present the synthesis of a N(6),N(6)-dimethylated 3'-azido-3'-deoxyadenosine precursor that can be coupled to any amino acid. Further derivatization results in the solid support that is eligible for the preparation of stable 3'-aminoacyl- or 3'-peptidyl-tRNA termini with an amide instead of the natural ester linkage. The present work expands our previously established route that delivered a broad range of peptidyl-tRNA mimics to the corresponding counterparts with N(6),N(6)-dimethylation pattern of the terminal adenosine (A76). This aspect is of significance to modulate the binding preferences of the mimics for ribosomal A- versus P-site. PMID:25457127

Neuner, Sandro; Micura, Ronald

2014-12-15

429

Synthesis, optical and electrochemical properties of the A-?-D-?-A porphyrin and its application as an electron donor in efficient solution processed bulk heterojunction solar cells  

NASA Astrophysics Data System (ADS)

A conjugated acceptor-donor-acceptor (A-?-D-?-A) with the Zn-porphyrin core and the di-cyanovinyl substituted thiophene (A) connected at meso positions denoted as VC62 was designed and synthesized. The optical and electrochemical properties of VC62 were investigated. This new porphyrin exhibits a broad and intense absorption in the visible and near infrared regions. Bulk-heterojunction (BHJ) solution processed organic solar cells based on this porphyrin, as electron donor material, and PC71BM ([6,6]-phenyl C71 butyric acid methyl ester), as electron acceptor material, were fabricated using THF and a pyridine-THF solvent exhibiting a power conversion efficiency of 3.65% and 5.24%, respectively. The difference in efficiencies is due to the enhancement of the short circuit current Jsc and FF of the solar cell, which is ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and a better balanced charge transport in the device processed with the pyridine-THF solvent.

Vijay Kumar, Challuri; Cabau, Lydia; Koukaras, Emmanuel N.; Sharma, Ganesh D.; Palomares, Emilio

2014-11-01

430

One-step synthesis of highly efficient three-dimensional Cd1-xZnxS photocatalysts for visible light photocatalytic water splitting  

PubMed Central

Visible light accounts for about 43% of the solar spectrum, and developing highly efficient visible-light-driven photocatalyst is of special significance. In this work, highly efficient three-dimensional (3D) Cd1?xZnxS photocatalysts for hydrogen generation under the irradiation of visible light were synthesized via one-step solvothermal pathway. Scanning electron microscope, X-ray diffractometer, Raman spectrometer, and X-ray photoelectron spectrometer were utilized to characterize the morphology, crystal structure, vibrational states, and surface composition of the obtained 3D Cd1?xZnxS. UV-Vis spectra indicated that the as-synthesized Cd1?xZnxS had appropriate bandgap and position of the conduction band that is beneficial for visible light absorption and photo-generated electron-hole pair separation. Moreover, the 3D structure offers a larger surface area thus supplying more surface reaction sites and better charge transport environment, and therefore, the efficiency of water splitting was improved further. PMID:23883429

2013-01-01

431

Total synthesis of (+)-vibsanin A.  

PubMed

The first total synthesis of (+)-vibsanin A, an 11-membered vibsane diterpenoid, was achieved, unambiguously establishing its relative and absolute stereochemistry. Highlights of the synthesis include the stereoselective formation of an all-carbon quaternary stereocenter by a zinc-mediated Barbier-type allylation in an aqueous medium, and the efficient construction of an 11-membered ring skeleton by a combination of an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction and a Mitsunobu reaction. PMID:25622000

Takao, Ken-ichi; Tsunoda, Kohei; Kurisu, Takuya; Sakama, Akihiro; Nishimura, Yoshiyasu; Yoshida, Keisuke; Tadano, Kin-ichi

2015-02-01

432

Total Synthesis of (+)-Irciniastatin A (a.k.a. Psymberin) and (?)-Irciniastatin B  

PubMed Central

A unified synthetic strategy to access (+)-irciniastatin A (a.k.a. psymberin) and (?)- irciniastatin B, two cytotoxic secondary metabolites, has been achieved. Highlights of the convergent strategy comprise a boron-mediated aldol union to set the C(15)–C(17) syn-syn triad, reagent control to set the four stereocenters of the tetrahydropyran core, and a late-stage Curtius rearrangement to install the acid-sensitive stereogenic N,O-aminal. Having achieved the total synthesis of (+)-irciniastatin A, we devised an improved synthetic route to the tetrahydropyran core (13 steps) compared to the first-generation synthesis (22 steps). Construction of the structurally similar (?)-irciniastatin B was then achieved via modification of a late-stage (?)-irciniastatin A intermediate to implement a chemoselective deprotection/oxidation sequence to access the requisite oxidation state at C(11) of the tetrahydropyran core. Of particular significance, the unified strategy will permit late-stage diversification for analogue development, designed to explore the biological role of substitution at the C(11) position of these highly potent tumor cell growth inhibitory molecules. PMID:23510264

An, Chihui; Jurica, Jon A.; Walsh, Shawn P.; Hoye, Adam T.; Smith, Amos B.

2013-01-01

433

One pot aqueous synthesis of nanoporous Au85Pt15 material with surface bound Pt islands: an efficient methanol tolerant ORR catalyst  

NASA Astrophysics Data System (ADS)

For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the `Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm-2) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm-2) as the anode material performed better (38 mW cm-2) than the HiSPEC Pt/C cathode material (16 mW cm-2).For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the `Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm-2) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm-2) as the anode material performed better (38 mW cm-2) than the HiSPEC Pt/C cathode material (16 mW cm-2). Electronic supplementary information (ESI) available: Materials, characterization, catalyst and MEA preparation, Fig. S1-S9. See DOI: 10.1039/c4nr04712e

Anandha Ganesh, P.; Jeyakumar, D.

2014-10-01

434

Microwave-assisted solvothermal synthesis of flower-like Ag/AgBr/BiOBr microspheres and their high efficient photocatalytic degradation for p-nitrophenol  

SciTech Connect

Flower-like Ag/AgBr/BiOBr microspheres were successfully fabricated by the approach of microwave-assisted solvothermal and in situ photo-assisted reduction. A reactive ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C{sub 16}mim]Br) was employed as Br source in the presence of surfactant polyvinylpyrrolidone (PVP). The photocatalytic activity of Ag/AgBr/BiOBr towards the decomposition of p-nitrophenol under visible light irradiation was evaluated. The results indicated that Ag/AgBr/BiOBr showed enhanced photocatalytic activity towards p-nitrophenol, comparing with P25, BiOBr and Ag/AgBr. More than 96% of p-nitrophenol was decomposed in 3.5 h under visible-light irradation. The excellent photocatalytic activity of flower-like Ag/AgBr/BiOBr microspheres can be attributed to the large specific surface area, strong visible-light absorption, suitable energy band structure and surface plasmon resonance effect of Ag nanoparticles. The possible photocatalytic mechanism was proposed based on the active species test and band gap structure analysis. - Graphical abstract: The photocatalytic reaction mechanisms of the as-prepared Ag/AgBr/BiOBr. Display Omitted - Highlights: • Successful synthesis of flower-like Ag/AgBr/BiOBr microspheres. • The Ag/AgBr/BiOBr showed much higher photocatalytic activity towards p-nitrophenol as compared to BiOBr and Ag/AgBr. • The reasons for the excellent photocatalytic activity are the large specific surface area, strong visible-light absorption and surface plasmon resonance effect of Ag nanoparticles. • The O{sub 2}·{sup ?}, Br{sup 0} and photogenerated h{sup +} play key roles in the photocatalytic degradation process.

Li, Tingting, E-mail: tingtingli1983@hotmail.com [Department of Chemistry and Chemical Engineering, Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Changsha 410082 (China); State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha 410082 (China); Department of Environment and Chemical Engineering, Key Laboratory of Jiangxi Province for Ecological Diagnosis, Remediation and Pollution Control, Nanchang Hangkong University, Nanchang 330063 (China); Luo, Shenglian, E-mail: sllou@hnu.edu.cn [Department of Chemistry and Chemical Engineering, Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Changsha 410082 (China); State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha 410082 (China); Department of Environment and Chemical Engineering, Key Laboratory of Jiangxi Province for Ecological Diagnosis, Remediation and Pollution Control, Nanchang Hangkong University, Nanchang 330063 (China); Yang, Lixia [Department of Environment and Chemical Engineering, Key Laboratory of Jiangxi Province for Ecological Diagnosis, Remediation and Pollution Control, Nanchang Hangkong University, Nanchang 330063 (China)

2013-10-15

435

Magnetic Cross-Linked Enzyme Aggregates (mCLEAs) of Candida antarctica Lipase: An Efficient and Stable Biocatalyst for Biodiesel Synthesis  

PubMed Central

Enzyme-catalyzed production of biodiesel is the object of extensive research due to the global shortage of fossil fuels and increased environmental concerns. Herein we report the preparation and main characteristics of a novel biocatalyst consisting of Cross-Linked Enzyme Aggregates (CLEAs) of Candida antarctica lipase B (CALB) which are covalently bound to magnetic nanoparticles, and tackle its use for the synthesis of biodiesel from non-edible vegetable and waste frying oils. For this purpose, insolubilized CALB was covalently cross-linked to magnetic nanoparticles of magnetite which the surface was functionalized with –NH2 groups. The resulting biocatalyst combines the relevant catalytic properties of CLEAs (as great stability and feasibility for their reutilization) and the magnetic character, and thus the final product (mCLEAs) are superparamagnetic particles of a robust catalyst which is more stable than the free enzyme, easily recoverable from the reaction medium and reusable for new catalytic cycles. We have studied the main properties of this biocatalyst and we have assessed its utility to catalyze transesterification reactions to obtain biodiesel from non-edible vegetable oils including unrefined soybean, jatropha and cameline, as well as waste frying oil. Using 1% mCLEAs (w/w of oil) conversions near 80% were routinely obtained at 30°C after 24 h of reaction, this value rising to 92% after 72 h. Moreover, the magnetic biocatalyst can be easily recovered from the reaction mixture and reused for at least ten consecutive cycles of 24 h without apparent loss of activity. The obtained results suggest that mCLEAs prepared from CALB can become a powerful biocatalyst for application at industrial scale with better performance than those currently available. PMID:25551445

Cruz-Izquierdo, Álvaro; Picó, Enrique A.; López, Carmen; Serra, Juan L.; Llama, María J.

2014-01-01

436

One-pot synthesis of C18-functionalized core-shell magnetic mesoporous silica composite as efficient sorbent for organic dye.  

PubMed

In this work, a facile one-pot strategy was proposed for the synthesis of C18-functionalized core-shell magnetic mesoporous silica composite (Fe3O4/mSiO2-C18). The Fe3O4/mSiO2-C18 composite, with an average size of 80nm and a functionalized mesoporous silica shell of about 30nm in thickness, has excellent adsorption ability toward methylene blue dye (MB) due to the large surface area (303m(2)g(-1)) and the abundant hydrophobic C18 groups. The adsorption equilibrium was achieved within 20min and the adsorption behavior of MB on Fe3O4/mSiO2-C18 composite fitted the pseudo-second-order kinetic model well (k2=1.29×10(-2)gmg(-1)min(-1), qe=144.72mgg(-1), ho=270.27mgg(-1)min(-1) under 25°C and an initial MB concentration of 10mgL(-1)). Langmuir and Freundlich isothermal adsorption models can both be used to describe the adsorption process and the maximum Langmuir adsorption capacity of MB on Fe3O4/mSiO2-C18 at 25°C and pH 7.5 is 363.64mgg(-1). Thermodynamic parameters show that the adsorption reaction is exothermic and spontaneous (?H(0)=-63.49kJmol(-1), ?G(0)=-7.80kJmol(-1)). Ionic strength and pH affected the adsorption slightly. In addition, the MB adsorbed sorbent can be readily separated from water solution by an external magnet because of the high magnetic saturation value (22.62emug(-1)). After being regenerated by treatment with acidic methanol, the sorbent could be reused for at least 5 cycles with a little decrease in adsorption capacity. PMID:25734221

Zhang, Xiaole; Zeng, Tao; Wang, Saihua; Niu, Hongyun; Wang, Xiaoke; Cai, Yaqi

2015-06-15

437

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination.  

PubMed

Heteroleptic silylamido complexes of the heavier alkaline earth elements calcium and strontium containing the highly fluorinated 3-phenyl hydrotris(indazolyl)borate {F12 -Tp(4Bo,?3Ph) }(-) ligand have been synthesized by using salt metathesis reactions. The homoleptic precursors [Ae{N(SiMe3 )2 }2 ] (Ae=Ca, Sr) were treated with [Tl(F12 -Tp(4Bo,?3Ph) )] in pentane to form the corresponding heteroleptic complexes [(F12 -Tp(4Bo,?3Ph) )Ae{N(SiMe3 )2 }] (Ae=Ca (1); Sr (3)). Compounds 1 and 3 are inert towards intermolecular redistribution. The molecular structures of 1 and 3 have been determined by using X-ray diffraction. Compound 3 exhibits a Sr???MeSi agostic distortion. The synthesis of the homoleptic THF-free compound [Ca{N(SiMe2 H)2 }2 ] (4) by transamination reaction between [Ca{N(SiMe3 )2 }2 ] and HN(SiMe2 H)2 is also reported. This precursor constitutes a convenient starting material for the subsequent preparation of the THF-free complex [(F12 -Tp(4Bo,?3Ph) )Ca{N(SiMe2 H)2 }] (5). Compound 5 is stabilized in the solid state by a Ca????-Si?H agostic interaction. Complexes 1 and 3 have been used as precatalysts for the intramolecular hydroamination of 2,2-dimethylpent-4-en-1-amine. Compound 1 is highly active, converting completely 200?equivalents of aminoalkene in 16?min with 0.50?mol?% catalyst loading at 25?°C. PMID:25620111

Romero, Nuria; Ro?ca, Sorin-Claudiu; Sarazin, Yann; Carpentier, Jean-François; Vendier, Laure; Mallet-Ladeira, Sonia; Dinoi, Chiara; Etienne, Michel

2015-03-01

438

An efficient synthesis of new caffeine-based chalcones, pyrazolines and pyrazolo[3,4-b][1,4]diazepines as potential antimalarial, antitrypanosomal and antileishmanial agents.  

PubMed

A new series of chalcones 5a-f were synthesized from caffeine-based aldehyde 3 and substituted acetophenones 4a-f. Treatment of compounds 5a-f with hydrazine hydrate led to pyrazolines 6a-f, and their subsequent reaction with acetic anhydride or formic acid afforded the corresponding N-substituted pyrazolines 7a-f and 8a-f respectively. Additionally, the regioselective cyclocondensation reaction of chalcones 5a-f with 4,5-diaminopyrazole 9 afforded the diazepine derivatives 10a-f. Synthesis of the above novel compounds was carried out through a simple procedure involving an easy work-up and mild reaction conditions. In vitro antimalarial activity against Plasmodium falciparum was evaluated for the obtained compounds. Among of them, just pirazoline 6a showed an outstanding growth inhibition percentage 85.2 ± 5.4%, while diazepines 10a-f showed remarkable growth inhibitions in the range of 80.3 ± 13.5 to 94.2 ± 0.2% when were tested at 20 ?g/mL. Compounds 5b, 5e, 7c and 7f showed remarkable activities against Leishmania panamensis with growth inhibition of 88.3 ± 1.5, 82.6 ± 2.2, 82.8 ± 1.7 and 87.6 ± 0.5% respectively, at 20 ?g/mL. In vitro assays against Trypanozoma cruzi showed that pyrazoline 6d displayed a growth inhibition of 61.9 ± 7.8% at 20 ?g/mL while chalcone 5f was considered especially active with a growth inhibition of 9.7 ± 1.5% for a very low concentration of 1.0 ?g/mL. PMID:25725376

Insuasty, Braulio; Ramírez, Juan; Becerra, Diana; Echeverry, Carlos; Quiroga, Jairo; Abonia, Rodrigo; Robledo, Sara M; Vélez, Iván Darío; Upegui, Yulieth; Muñoz, July A; Ospina, Victoria; Nogueras, Manuel; Cobo, Justo

2015-03-26

439

Synthesis of Mn-intercalated layered titanate by exfoliation-flocculation approach and its efficient photocatalytic activity under visible-light  

SciTech Connect

A novel Mn-intercalated layered titanate as highly active photocatalyst in visible-light region has been synthesized via a convenient and efficient exfoliation-flocculation approach with divalent Mn ions and monolayer titanate nanosheets. The 0.91 nm interlayer spacing of obtained photocatalyst is in accordance with the sum of the thickness of titanate nanosheet and the diameter of Mn ions. The yellow photocatalyst shows a spectral response in visible-light region and the calculated band gap is 2.59 eV. The photocatalytic performance of this material was evaluated by degradation and mineralization of an aqueous dye methylene blue under visible-light irradiation, and an enhanced photocatalytic activity in comparison with protonated titanate as well as the P25 TiO{sub 2} and N-doped TiO{sub 2} was obtained. Additionally, the layered structure is retained, no dye ions intercalating occurs during the photocatalysis process, and a {approx}90% photocatalytic activity can be remained after reusing 3 cycles. - Graphical abstract: Mn-intercalated layered titanate as a novel and efficient visible-light harvesting photocatalyst was synthesized via a convenient and efficient exfoliation-flocculation approach in a mild condition. Highlights: Black-Right-Pointing-Pointer Mn-intercalated titanate has been prepared by exfoliation-flocculation approach. Black-Right-Pointing-Pointer The as-prepared catalyst shows spectral response in the visible-light region. Black-Right-Pointing-Pointer Heat treatment at certain temperature enables formation of Mn-doped TiO{sub 2}. Black-Right-Pointing-Pointer Dye can be degradated effectively by the catalyst under visible light irradiation.

Fu, Jie; Tian, Yanlong; Chang, Binbin; Li, Gengnan; Xi, Fengna [Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 5 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018 (China)] [Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 5 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018 (China); Dong, Xiaoping, E-mail: xpdong@zstu.edu.cn [Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 5 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018 (China)] [Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 5 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018 (China)

2012-12-15

440

Borax: An Ecofriendly and Efficient Catalyst for One-Pot Synthesis of 3,4-Dihydropyrimidine-2(1H)-ones under Solvent-Free Conditions  

Microsoft Academic Search

Borax in the presence of a very small amount of 5 M sulfuric acid efficiently catalyses the three-component condensation of an aldehyde, ?-ketoester, and urea or thiourea to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones or 3,4-dihydropyrimidin-2(1H)-thiones in good to excellent yields under solvent-free conditions at 80 °C. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yield, short

Jayashree Nath; Mihir K. Chaudhuri

2010-01-01

441

Highly efficient click labeling using 2-[18F]fluoroethyl azide and synthesis of an 18F N-hydroxysuccinimide ester as conjugation agent  

PubMed Central

Introduction Click labeling using 2-[18F]fluoroethyl azide has been proven to be promising methods of radiolabeling small molecules and peptides, some of which are undergoing clinical evaluations. However, the previously reported method afforded low yield, poor purities and under desirable reproducibility. Methods A vacuum distillation method was used to isolate 2-[18F]fluoroethyl azide, and the solvent effect of acetonitrile (ACN) and dimethylformamide (DMF) on the click labeling using Cu(I) from copper sulfate/sodium ascorbate was studied. The labeling conditions were optimized to radiosynthesize a hydroxysuccinimide ester (NHS). Results 2-[18F]fluoroethyl azide was isolated by the vacuum distillation method with > 80% yield within 10 min in a “pure” and click-ready form. It was found that the amount of DMF was critical for maintaining high levels of Cu(I) from copper sulfate/sodium ascorbate in order to rapidly complete the click labeling reaction. The addition of bathophenanthrolinedisulfonic acid disodium salt (BPDS) to the mixture of copper sulfate/sodium ascorbate also greatly improved the click labeling efficiency. Through exploiting these optimizations, a base-labile N-hydroxysuccinimide (NHS) ester was rapidly radiosynthesized in 90% isolated yield with good chemical and radiochemical purities. Conclusions We have developed a general method to click-label small molecules efficiently using [18F]2 for research and clinical use. This NHS ester can be used for conjugation chemistry to label antibodies, peptides and small molecules as PET tracers. PMID:22770647

Zhou, Dong; Chu, Wenhua; Dence, Carmen S.; Mach, Robert H.; Welch, Michael J.

2012-01-01

442

Synthesis of biodegradable cross-linked poly(beta-amino ester) for gene delivery and its modification, inducing enhanced transfection efficiency and stepwise degradation.  

PubMed

Biodegradable cross-linked poly(beta-amino ester) (CLPAE) was synthesized by Michael addition of pentaerythritol triacrylate and N,N-dimethylethylenediamine and modified with aminohexanoic acid and lysine to CLPAE-Ahx and CLPAE-Lys, respectively, for a gene delivery system. They could self-assemble with plasmid DNA, forming nanosized polyplexes, and CLPAE-Ahx polyplex released plasmid DNA slowly during a week through stepwise degradation. The polymers showed minimal cytotoxicity on 293 cells due to their biodegradability and biocompatibility. Transfection efficiencies of CLPAE-Ahx and CLPAE-Lys were comparable to that of PEI in 293 cells and C2C12 cells. Additionally, high transfection of CLPAE-Ahx on primary rat aorta vascular smooth muscle cells (SMC) and primary mouse embryonic fibroblast cells (MEF) shows a potential for a gene delivery system on primary cells, restenosis treatment of human SMC, and MEF cell function research. In conclusion, CLPAE-Ahx could be used as a nontoxic and highly efficient gene delivery system. PMID:16173791

Kim, Tae-Il; Seo, Hyo Jung; Choi, Joon Sig; Yoon, Jae Keun; Baek, Jung-Un; Kim, Kwan; Park, Jong-Sang

2005-01-01

443

Synthesis of iron oxide/partly graphitized carbon composites as a high-efficiency and low-cost cathode catalyst for microbial fuel cells.  

PubMed

Waste cornstalks and pomelo skins are used as carbon resources for preparing nanocomposites of iron oxide and partly graphitized carbon (Fe3O4/PGC-CS and Fe3O4/PGC-PS). The results showed that Fe3O4 with a face-centered cubic structure is uniformly dispersed on the skeleton of Fe3O4/GC, and the highest SBET values of Fe3O4/PGC-CS (476.5 m(2) g(-1)) and Fe3O4/PGC-PS (547.7 m(2) g(-1)) are obtained at 1000 °C. The electrical conductivity and density of catalytic active sites are correspondingly improved by the introduction of Fe species. Microbial fuel cells (MFCs) with a mixed composite (Fe3O4/PGC-CS:Fe3O4/PGC-PS = 1:1) cathode (three-dimensional structures) generate the highest power density of 1502 ± 30 mW m(-2), which is 26.01% higher than that of Pt/C (1192 ± 33 mW m(-2)) and only declines by 7.12% after 18 cycles. The Fe3O4/PGC-CS cathode has the highest Coulombic efficiency (24.3 ± 0.7%). The Fe3O4/PGC composites exhibit high oxygen reduction reactivity, low charge transfer resistances, and long-term stability and can be used as a low-cost and high-efficiency catalyst for MFCs. PMID:25084054

Ma, Ming; Dai, Ying; Zou, Jin-long; Wang, Lei; Pan, Kai; Fu, Hong-gang

2014-08-27

444

In situ ion exchange synthesis of strongly coupled Ag@AgCl/g-C?N? porous nanosheets as plasmonic photocatalyst for highly efficient visible-light photocatalysis.  

PubMed

A novel efficient Ag@AgCl/g-C3N4 plasmonic photocatalyst was synthesized by a rational in situ ion exchange approach between exfoliated g-C3N4 nanosheets with porous 2D morphology and AgNO3. The as-prepared Ag@AgCl-9/g-C3N4 plasmonic photocatalyst exhibited excellent photocatalytic performance under visible light irradiation for rhodamine B degradation with a rate constant of 0.1954 min(-1), which is ?41.6 and ?16.8 times higher than those of the g-C3N4 (?0.0047 min(-1)) and Ag/AgCl (?0.0116 min(-1)), respectively. The degradation of methylene blue, methyl orange, and colorless phenol further confirmed the broad spectrum photocatalytic degradation abilities of Ag@AgCl-9/g-C3N4. These results suggested that an integration of the synergetic effect of suitable size plasmonic Ag@AgCl and strong coupling effect between the Ag@AgCl nanoparticles and the exfoliated porous g-C3N4 nanosheets was superior for visible-light-responsive and fast separation of photogenerated electron-hole pairs, thus significantly improving the photocatalytic efficiency. This work may provide a novel concept for the rational design of stable and high performance g-C3N4-based plasmonic photocatalysts for unique photochemical reaction. PMID:25427293

Zhang, Shouwei; Li, Jiaxing; Wang, Xiangke; Huang, Yongshun; Zeng, Meiyi; Xu, Jinzhang

2014-12-24

445

Regulation and function of local protein synthesis in neuronal dendrites  

Microsoft Academic Search

It has long been shown that protein synthesis can occur in neuronal dendrites, but its significance remained unclear until relatively recently. Studies suggest that local protein synthesis has crucial roles in synaptic plasticity, the change in neuronal communication efficiency that is probably a cellular basis of learning and memory. Induced by neuronal activity, local protein synthesis provides key factors for

Changan Jiang; Erin M. Schuman

2002-01-01

446

Synthesis of high efficient Ca{sub 2}SiO{sub 4}:Eu{sup 2+} green emitting phosphor by a liquid phase precursor method  

SciTech Connect

Green emitting Eu{sup 2+}-doped Ca{sub 2}SiO{sub 4} phosphors were synthesized by three different methods (a conventional solid state reaction (SSR) method, a novel liquid phase precursor approach using SiO{sub 2} sol (LPP-SiO{sub 2}(sol)) and water-soluble silicon compound (LPP-WSS)). The obtained phosphors exhibited a broad excitation spectrum ranging from 225 to 450 nm and a strong green emission peak at 502 nm due to the 4f{sup 6}5d{sup 1}{yields}4f{sup 7}({sup 8}S{sub 7/2}) transition of Eu{sup 2+}. The highest luminescent intensity was obtained for the samples fired at 1100 Degree-Sign C. The dependence of luminescence properties on Eu{sup 2+} concentration for the phosphors synthesized using LPP-WSS method was also examined from 0.1 to 5.0 mol% and the maximum emission intensity was observed at 3.0 mol% Eu{sup 2+}. A detailed analysis using various characterizations revealed that phosphors produced by the LPP-WSS process exhibited more homogenous phase distribution and higher luminescence intensity than those from the other two processes, which suggested the potential application of Ca{sub 2}SiO{sub 4}:Eu{sup 2+} in white light-emitting diodes and fluorescence lamps. - Graphical abstract: The synthesis of Eu{sup 2+} doped Ca{sub 2}SiO{sub 4} green emitting phosphors were carried out using LPP-SiO{sub 2}(sol), LPP-WSS and SSR methods. The adequate reaction of starting materials base on solution mixing and cellulose impregnating during LPP-WSS procedure resulted in single crystalline structure as well as fine morphology, and finally determined a superior luminescent intensity. Highlights: Black-Right-Pointing-Pointer Ca{sub 2}SiO{sub 4}:Eu{sup 2+} phosphor was synthesized by three methods (SSR, LPP-SiO{sub 2} and LPP-WSS). Black-Right-Pointing-Pointer Effect of different processes on the property of phosphor was studied. Black-Right-Pointing-Pointer Phosphor produced by LPP-WSS showed better homogenous phase and fluorescent property. Black-Right-Pointing-Pointer LPP-WSS approach was identified as the best method among these three approaches.

Luo, Y.Y.; Jo, D.S.; Senthil, K. [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Tezuka, S.; Kakihana, M. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577 (Japan); Toda, K. [Department of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University, Ikarashi 2 nocho 8050, Niigata 950-2181 (Japan); Masaki, T. [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Yoon, D.H., E-mail: dhyoon@skku.edu [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2012-05-15

447

Single-crystalline Bi2Te3 nanosheets with uniform morphology via a simple, efficient, and high-yield microwave-assisted synthesis  

NASA Astrophysics Data System (ADS)

A simple but efficient microwave-assisted method with high-yield products was applied to synthesize regular hexagon Bi2Te3 nanosheets. Rhombohedral Bi2Te3 with pure single crystalline phase was demonstrated by XRD patterns, HRTEM images, and SAED figures. The SEM and TEM images showed that the Bi2Te3 nanosheets were uniform, and that the average lengths of the hexagon sides were approximately 320 nm. The growth mechanisms and morphological transformations were systematically studied by controlling the reaction time, KOH concentration, and polyvinylpyrrolidone (PVP) dosage. This work has indicated that abundant KOH benefited the formation of uniform Bi2Te3 nanosheets without Te nanorods. Meanwhile, long reaction time and abundant PVP favored the formation of regular hexagon nanosheets with smooth surfaces.

Li, Zhiliang; Teng, Renyuan; Zheng, Shuqi; Zhang, Yuzhuo; Huang, Ting; Lu, Guiwu

2014-11-01

448

A versatile cyclic 2,2'-azobenzenophane with a functional handle and its polymers: efficient synthesis and effect of topological structure on chiroptical properties.  

PubMed

Two novel cyclic azobenzenophanes (SC, RC) with functional handles have been synthesized efficiently by a Glaser coupling reaction. Through a Suzuki coupling reaction, alternating ring/linear polymers with rigid (conjugated)/flexible (unconjugated) bridges were obtained from the resultant cyclic azobenzenophanes. The optical activities of linear, cyclic, and macromolecular binaphethyl-azobenzene derivatives were investigated by UV/Vis and circular dichroism (CD) spectra and the time-dependent (TD)-DFT method. Experimental results and theoretical analyses indicated that the cyclic configurations exhibited better chiroptical features than the others, and the reverse conformation and difference of dextro-/levo-rotation of azobenzenophanes were detected by comparing linear and cyclic structures, which provides an opportunity for the optical-rotation-controlled "smart" materials systems in future. PMID:25510346

Lu, Jinjie; Xia, Aiyou; Zhou, Nianchen; Zhang, Wei; Zhang, Zhengbiao; Pan, Xiangqiang; Yang, Yonggang; Wang, Yong; Zhu, Xiulin

2015-02-01

449

Novel two-step synthesis of NiS nanoplatelet arrays as efficient counter electrodes for dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Platinum-free (Pt-free) counter electrodes (CEs) can reduce the cost of dye-sensitized solar cells (DSCs). In this study, a general strategy is proposed to construct Pt-free CEs, namely direct growth of electrocatalytic active nanostructures (metal sulfide, etc.) on conductive substrates via low temperature solution routes. As an implementation, nickel sulfide (NiS) nanoarray film composed of interconnected nanoplatelets is successfully fabricated by a two-step solution route. The as-grown NiS nanoarray film follows the sulfurization process in a thiourea aqueous solution from the precursor of hydrothermally deposited Ni(OH)2 nanoplatelet arrays on FTO substrates. When applied as a Pt-free CE in DSCs, a maximum power conversion efficiency of 7.10% is achieved, comparable to that of Pt CE (7.35%).

Zhao, Wei; Zhu, Xiaolong; Bi, Hui; Cui, Houlei; Sun, Shengrui; Huang, Fuqiang

2013-11-01

450

An efficient access to the synthesis of novel 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives.  

PubMed

An efficient access to the tetracyclic-fused quinoline systems, 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives 4a-l, is described, involving the intramolecular Friedel-Crafts acylation reaction of 2-(phenoxymethyl)-4-phenylquinoline-3-carboxylic acid derivatives 3a-l aided by the treatment with PPA (polyphosphoric acid) or Eaton's reagent. The required starting compound (2) was obtained by Friedländer reaction of 2-aminobenzophenone (1) with 4-chloroethylacetoacetate by using CAN (cerium ammonium nitrate, 10 mol %) as catalyst at room temperature. The substrates 3a-l were prepared through one-pot reaction of ethyl 2-(chloromethyl)-4-phenylquinoline-3-carboxylate (2) and substituted phenols. Our developed strategy, involving a three-step route, offers easy access to tetracyclic-fused quinoline systems in short reaction times, and the products are obtained in moderate to good yields. PMID:23209522

Gao, Wentao; Lin, Guihai; Li, Yang; Tao, Xiyue; Liu, Rui; Sun, Lianjie

2012-01-01

451

Highly efficient and site-selective [3 + 2] cycloaddition of carbene-derived ambident dipoles with ketenes for a straightforward synthesis of spiro-pyrrolidones.  

PubMed

The [3 + 2] cycloaddition reaction of 2-arylthiocarbamoyl benzimidazolium, -imidazolinium, and -triazolium inner salts (the ambident C-C-N and C-C-S 1,3-dipoles derived from carbenes) with ketenes proceeded efficiently in a highly site-selective manner to produce the C-C-N cycloaddition products benzimidazoline-, imidazolidine-, or triazoline spiro-pyrrolidones in 58-93% yields. Theoretical calculation suggests a stepwise mechanism for the reaction and indicates that the C-C-N cycloaddition of the dipoles with ketenes is both a dynamically and thermodynamically favored reaction pathway. Their easy availability, high reactivity, and reaction selectivity render the benzimidazolium, -imidazolinium, and -triazolium inner salts powerful and versatile 1,3-dipoles in the construction of novel spiro heterocyclic systems, which are not easily accessible by other methods. PMID:17629341

Li, Jia-Qi; Liao, Rong-Zhen; Ding, Wan-Jian; Cheng, Ying

2007-08-01

452

Comment on Gao, W., et al. "Efficient one-pot synthesis of 5-chloromethyl-furfural (CMF) from carbohydrates in mild biphasic systems", Molecules 2013, 18, 7675-7685.  

PubMed

In a recent paper entitled "Efficient One-Pot Synthesis of 5-Chloromethyl-furfural (CMF) from Carbohydrates in Mild Biphasic Systems," published in Molecules [1], Gao and coworkers describe the use of a biphasic aq. HCl-H3PO4/CHCl3 reagent for the preparation of CMF from various feedstocks. The maximum yield (46.8%) was obtained from fructose by reaction at 45 °C for 20 h. While sucrose gave a similar yield, the same reaction with glucose and cellulose gave 7.3% and 7.8% yields, respectively. Remarkably, the same process applied to Kraft pulp and powdered wood samples gave between 16.0% and 31.4% CMF, based on sugar content. Looking to the Experimental section for insight into this unusual outcome, the statement, "the procedure of treating lignocellulose sample (Table 6) was almost the same as the carbohydrate, except adding the selected simple 1.0 mg each trial " [sic] appears, which is difficult to interpret. PMID:24451255

Mascal, Mark

2013-01-01

453

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

454

Effects of sol-gel synthesis on 5Fe-15Mn-40Zn-40Ti-O mixed oxide structure and its H2S removal efficiency from industrial gas streams.  

PubMed

A novel Fe-Mn-Zn-Ti-O mixed metal oxide has been developed for efficient low-temperature (25-50 degrees C) removal of H2S from a gas mixture containing 600 ppm H2S, 25 vol% H2, 7.5 vol % CO2, and 1-3 vol% H2O that simulates typical conditions experienced at the outlet of a bioreactor loaded with sulfate metal reducing bacteria (SMRB) that converts toxic Cr6+ and As5+ present in ground and surface waters and soils into nontoxic elements. During the latter conversion H2S gas is produced and has to be treated. In the present work it is demonstrated for the first time that by using the sol-gel synthesis route at given experimental conditions (e.g., metal precursor salts, solvent system, and solution pH), optimum structural properties for the Fe-Mn-Zn-Ti-O solid can be obtained for maximization of H2S uptake. In particular, at 25 degrees C an H2S uptake (0.085 g H2S/g solid) larger by at least a factor of 3 compared to a commercial Ni-based H2S absorbent material was obtained. PMID:19603648

Polychronopoulou, Kyriaki; Efstathiou, Angelos M

2009-06-15

455

One-pot synthesis of nitrogen and sulfur co-doped onion-like mesoporous carbon vesicle as an efficient metal-free catalyst for oxygen reduction reaction in alkaline solution  

NASA Astrophysics Data System (ADS)

Nitrogen and sulfur co-doped onion-like mesoporous carbon vesicle (NS-MCV) with multilayer lamellar structure is synthesized as a metal-free catalyst through a convenient and economical procedure. The synthesized materials are systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrate that N and S atoms can be successfully doped into the framework of MCV with little impact on the morphology and structure. The NS-MCV manifests a remarkably high electrocatalytic activity as a metal-free electrocatalyst for the oxygen reduction reaction (ORR) with mainly a four-electron transfer pathway. Moreover, in contrast to the commercially available Pt/C catalyst, the NS-MCV shows much better long-term stability and tolerance toward methanol crossover in an alkaline medium. Such excellent performances can be mainly attributed to the synergistic effect arising from the addition of N and S heteroatom, optimized S content and high surface area. The NS-MCV with a simple synthesis method may further exploited as potentially efficient and inexpensive metal-free ORR catalyst materials.

Han, Ce; Bo, Xiangjie; Zhang, Yufan; Li, Mian; Guo, Liping

2014-12-01