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1

A mild, efficient and environmentally friendly method for the regio- and chemoselective synthesis of enaminones using Bi(TFA) 3 as a reusable catalyst in aqueous media  

Microsoft Academic Search

Bismuth(III) trifluoroacetate has been found to be an extremely efficient catalyst for the preparation of ?-enaminones in water. In addition, by employing this catalyst, high regio- and chemoselective enamination of carbonyl compounds was achieved.

Ahmad R. Khosropour; Mohammad M. Khodaei; Mehdi Kookhazadeh

2004-01-01

2

Chemoselective boronic ester synthesis by controlled speciation.  

PubMed

Control of boronic acid solution speciation is presented as a new strategy for the chemoselective synthesis of boronic esters. Manipulation of the solution equilibria within a cross-coupling milieu enables the formal homologation of aryl and alkenyl boronic acid pinacol esters. The generation of a new, reactive boronic ester in the presence of an active palladium catalyst also facilitates streamlined iterative catalytic C?C bond formation and provides a method for the controlled oligomerization of sp(2) -hybridized boronic esters. PMID:25267096

Fyfe, James W B; Seath, Ciaran P; Watson, Allan J B

2014-11-01

3

Chemoselective Suzuki coupling of diborylmethane for facile synthesis of benzylboronates.  

PubMed

The chemoselective Pd-catalyzed Suzuki-Miyaura cross-coupling reaction using a diborylmethane is reported. The use of an equimolar amount of base with a diborylmethane realized chemoselective coupling for the synthesis of various benzylboronate derivatives. Sterically hindered aryl bromides can give products in moderate to excellent yields. PMID:21644527

Endo, Kohei; Ohkubo, Takahiro; Shibata, Takanori

2011-07-01

4

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy  

PubMed Central

Summary A “stop-and-flow” strategy was developed for the chemoselective dioxygenation of alkenes with a PIFA-initiated cyclization. This method is conceived for the desymmetrization of seco-diene, and a series of substituted 5-hydroxymethyl-?-lactones were constructed after hydrolysis. This strategy also differentiates terminally substituted alkenes and constitutes a potentially novel synthetic approach for the efficient synthesis toward velbanamine. PMID:23766815

Liu, Huili; Zheng, Kuan; Lu, Xiang

2013-01-01

5

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

6

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

7

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

8

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 (Berkeley, CA)

2003-05-27

9

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

10

Chemoselective arylation of phenols with bromo-nitroarenes: synthesis of nitro-biaryl-ols and their conversion into benzofurans and carbazoles.  

PubMed

A series of electron withdrawing or donating group substituted phenols were chemoselectively arylated with various substituted bromo-nitroarenes using KO(t)Bu at room temperature via an SNAr pathway. The synthesis of natural alkaloids (carbazoles), dibenzofurans, and a biaryl-indole was achieved from the synthesized nitro-biaryl-ols. PMID:25007753

Kumar, Amit; Yadav, Abhimanyu; Verma, Ajay; Jana, Sadhan; Sattar, Moh; Kumar, Shailesh; Prasad, Ch Durga; Kumar, Sangit

2014-08-28

11

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

Leboeuf, David; Huang, Jie; Gandon, Vincent

2012-01-01

12

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

13

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, ...

14

Efficient, Divergent Synthesis of Cryptophycin Unit A Analogues  

PubMed Central

A flexible and divergent synthesis of cryptophycin unit A analogues is described. This method relies on iridium-catalysed stereo- and enantioselective crotylation and chemoselective one-pot oxidative olefination to access common intermediate 8. Heck, cross metathesis, and Suzuki-Miyaura reactions are illustrated for the generation of methyl ester unit A analogues 10a-d. PMID:22617820

Bolduc, Kyle L.; Larsen, Scott D.; Sherman, David H.

2012-01-01

15

Aminocyanation by the addition of N-CN bonds to arynes: chemoselective synthesis of 1,2-bifunctional aminobenzonitriles.  

PubMed

An efficient aminocyanation by the direct addition of aryl cyanamides to arynes is described, enabling incorporation of highly useful amino and cyano groups synchronously via cleavage of inert N-CN bonds, affording synthetically useful 1,2-bifunctional aminobenzonitriles. The postsynthetic functionalization of the aminocyanation products allows diverse formation of synthetically important derivatives such as drug molecule Ponstan and fused heterocycles. PMID:24325782

Rao, Bin; Zeng, Xiaoming

2014-01-01

16

Metal-free catalyst for the chemoselective methylation of amines using carbon dioxide as a carbon source.  

PubMed

N-methylation of amines is an important step in the synthesis of many pharmaceuticals and has been widely applied in the preparation of other key intermediates and chemicals. Therefore, the development of efficient methylation methods has attracted considerable attention. In this respect, carbon dioxide is an attractive C1 building block because it is an abundant, renewable, and nontoxic carbon source. Consequently, we developed a highly chemoselective, metal-free catalytic system that operates under ambient conditions for the N-methylation of amines. PMID:25256038

Das, Shoubhik; Bobbink, Felix D; Laurenczy, Gabor; Dyson, Paul J

2014-11-17

17

Prebiotically plausible oligoribonucleotide ligation facilitated by chemoselective acetylation  

PubMed Central

The recent synthesis of pyrimidine ribonucleoside-2?,3?-cyclic phosphates under prebiotically plausible conditions has strengthened the case for the involvement of RNA at an early stage in the origin of life. However, a prebiotic conversion of these weakly activated monomers, and their purine counterparts, to the 3?,5?-linked RNA polymers of extant biochemistry has been lacking – previous attempts leading only to short oligomers with mixed linkages. Here we show that the 2?-hydroxyl group of oligoribonucleotide-3?-phosphates can be chemoselectively acetylated in water under prebiotically credible conditions, allowing rapid and efficient template-directed ligation. The 2?-O-acetyl group at the ligation junction of the product RNA strand can be removed under conditions that leave the internucleotide bonds intact. Remarkably, acetylation of mixed oligomers possessing either 2?- or 3?-terminal phosphates is selective for the 2?-hydroxyl group of the latter. This newly discovered chemistry thus suggests a prebiotic route from ribonucleoside-2?,3?-cyclic phosphates to predominantly 3?,5?-linked RNA via partially 2?-O-acetylated-RNA. PMID:23609088

Bowler, Frank R.; Chan, Christopher K. W.; Duffy, Colm D.; Gerland, Beatrice; Islam, Saidul; Powner, Matthew W.; Sutherland, John D.; Xu, Jianfeng

2014-01-01

18

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

19

Total synthesis of (±)-gephyrotoxin by amide-selective reductive nucleophilic addition.  

PubMed

A chemoselective approach for the total synthesis of (±)-gephyrotoxin has been developed. The key to success was the utilization of N-methoxyamides, which enabled the direct coupling of the amide with an aldehyde and selective reductive nucleophilic addition to the amide in the presence of a variety of sensitive and electrophilic functional groups, such as a methyl ester. This chemoselective approach minimized the use of protecting-group manipulations and redox reactions, which resulted in the most concise and efficient total synthesis of (±)-gephyrotoxin described to date. PMID:24288230

Shirokane, Kenji; Wada, Takamasa; Yoritate, Makoto; Minamikawa, Ryo; Takayama, Nobuaki; Sato, Takaaki; Chida, Noritaka

2014-01-01

20

Short asymmetric synthesis of phenanthroindolizidines through chiral homoallylic sulfinamines.  

PubMed

An efficient stereocontrolled preparation of chiral phenanthroindolizidines is detailed. The synthesis relies on the stereoselective indium-mediated allylation of 2-(phenanthren-9-yl)acetaldehyde derivatives with chiral tert-butylsulfinamide. Chemoselective transformations from the corresponding homoallylic sulfinamine allow the synthesis of the phenanthroindolizidines in only three synthetic operations, without any detectable racemization. Following this procedure, the synthesis of natural (-)-tylophorine was successfully accomplished. PMID:25070561

Anton-Torrecillas, Cintia; Gonzalez-Gomez, Jose C

2014-09-28

21

A mild and efficient method for preparation of azides from alcohols using acidic ionic liquid [H-NMP]HSO 4  

Microsoft Academic Search

We report here an efficient method for the synthesis and characterization of [H-NMP]HSO4 and its application as an efficient catalyst and solvent for preparation of azides from corresponding alcohols under mild conditions. This processor showed high chemoselectivity for conversion of various alcohols to their corresponding azides.

Abdol R. Hajipour; Asiyeh Rajaei; Arnold E. Ruoho

2009-01-01

22

Convenient, efficient, and green method for synthesis of bis(indolyl)methanes with nano SIO2 under ultrasonic irradiation  

NASA Astrophysics Data System (ADS)

A green and efficient procedure for the preparation of bis(indolyl)methanes via the condensation of indoles with various carbonyl compounds in the presence of catalytic amount of nanosilica gel under ultrasonic irradiation in good to excellent yields (83% to 94% ) in solvent-free condition is described. Short reaction time, easy and quick isolation of the products, environmentally friendly procedure, excellent chemoselectivity, and excellent yields are the main advantages of this procedure. Native nanosilica gel was used as an inexpensive and readily available catalyst without any support of reagent or modification on it. The reaction is carried out in solvent-free condition in the absence of ultrasonic irradiation at 80°C, too. This methodology offers significant improvements for the synthesis of bis(indolyl)methanes with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents. Recovery and recycling of the silica nanoparticle catalyst were also described.

Ghodrati, Keivan; Hosseini, Saied Hosseine; Mosaedi, Rasol; Karami, Changiz; Maleki, Fariba; Farrokhi, Azita; Hamidi, Zohreh

2013-03-01

23

Chemoselective probes for metabolite enrichment and profiling  

Microsoft Academic Search

Chemical probes that target classes of proteins based on shared functional properties have emerged as powerful tools for proteomics. The metabolome rivals, if not surpasses, the proteome in terms of size and complexity, suggesting that efforts to profile metabolites would also benefit from targeted technologies. Here we apply the principle of chemoselective probes to the metabolome, creating a general strategy

Erin E Carlson; Benjamin F Cravatt

2007-01-01

24

Palladium-catalyzed chemoselective allylic substitution, Suzuki-Miyaura cross-coupling, and allene formation of bifunctional 2-B(pin)-substituted allylic acetate derivatives.  

PubMed

A formidable challenge at the forefront of organic synthesis is the control of chemoselectivity to enable the selective formation of diverse structural motifs from a readily available substrate class. Presented herein is a detailed study of chemoselectivity with palladium-based phosphane catalysts and readily available 2-B(pin)-substituted allylic acetates, benzoates, and carbonates. Depending on the choice of reagents, catalysts, and reaction conditions, 2-B(pin)-substituted allylic acetates and derivatives can be steered into one of three reaction manifolds: allylic substitution, Suzuki-Miyaura cross-coupling, or elimination to form allenes, all with excellent chemoselectivity. Studies on the chemoselectivity of Pd catalysts in their reactivity with boron-bearing allylic acetate derivatives led to the development of diverse and practical reactions with potential utility in synthetic organic chemistry. PMID:25077980

Kim, Byeong-Seon; Hussain, Mahmud M; Hussain, Nusrah; Walsh, Patrick J

2014-09-01

25

Palladium-catalyzed chemoselective decarboxylative ortho acylation of benzoic acids with ?-oxocarboxylic acids.  

PubMed

Palladium-catalyzed chemoselective decarboxylative cross coupling of benzoic acids with ?-oxocarboxylic acids was realized via an arene sp(2) C-H functionalization process. This work represents the first example of transition-metal-catalyzed cross-coupling reactions with two acids acting in different roles. The synthetic utility of this method was confirmed by the synthesis of pitofenone, an antispasmodic used in the combined drug Spasmalgon. PMID:23721458

Miao, Jinmin; Ge, Haibo

2013-06-21

26

Elucidation of the regio- and chemoselectivity of enzymatic allylic oxidations with Pleurotus sapidus - conversion of selected spirocyclic terpenoids and computational analysis  

PubMed Central

Summary Allylic oxidations of olefins to enones allow the efficient synthesis of value-added products from simple olefinic precursors like terpenes or terpenoids. Biocatalytic variants have a large potential for industrial applications, particularly in the pharmaceutical and food industry. Herein we report efficient biocatalytic allylic oxidations of spirocyclic terpenoids by a lyophilisate of the edible fungus Pleurotus sapidus. This ‘’mushroom catalysis’’ is operationally simple and allows the conversion of various unsaturated spirocyclic terpenoids. A number of new spirocyclic enones have thus been obtained with good regio- and chemoselectivity and chiral separation protocols for enantiomeric mixtures have been developed. The oxidations follow a radical mechanism and the regioselectivity of the reaction is mainly determined by bond-dissociation energies of the available allylic CH-bonds and steric accessibility of the oxidation site. PMID:24204436

Weidmann, Verena; Schaffrath, Mathias; Zorn, Holger

2013-01-01

27

Chemoselective reduction of ?-keto amides using nickel catalysts.  

PubMed

Ni-catalysts are used for the first time to synthesize highly important ?-hydroxy amides and ?-amino alcohols from ?-keto amides by chemoselective and complete reduction using hydrosilanes. Chemoselective complete reduction of ?-keto amides in the presence of a simple amide group is a key benefit of these Ni-catalysts. PMID:24911424

Mamillapalli, N Chary; Sekar, Govidasamy

2014-07-25

28

ZrCl4-mediated regio- and chemoselective Friedel-Crafts acylation of indole.  

PubMed

An efficient method for regio- and chemoselective Friedel-Crafts acylation of indole using acyl chlorides in the presence of ZrCl(4) has been discovered. It minimizes/eliminates common competing reactions that occur due to high and multiatom-nucleophilic character of indole. In this method, a wide range of aroyl, heteroaroyl alkenoyl, and alkanoyl chlorides undergo smooth acylation with various indoles without NH protection and afford 3-acylindoles in good to high yields. PMID:21526849

Guchhait, Sankar K; Kashyap, Maneesh; Kamble, Harshad

2011-06-01

29

Chemoselective benzylation of unprotected anthranilic acids with benzhydryl alcohols by water-soluble Au(III)/TPPMS in water.  

PubMed

A novel and efficient method for the benzylation of unprotected anthranilic acids with benzhydryl alcohols using water-soluble Au(III)/TPPMS in water is developed. Water plays an important role in our catalytic system. This new protocol could be used for not only N-benzylation, but also chemoselective C-benzylation by the Friedel-Crafts reaction. PMID:23745757

Hikawa, Hidemasa; Suzuki, Hideharu; Yokoyama, Yuusaku; Azumaya, Isao

2013-07-01

30

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

31

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

32

Chemoselective carbophilic addition of ?-diazoesters through ligand-controlled gold catalysis.  

PubMed

The chemoselective addition of arenes and 1,3-diketones to ?-aryldiazoesters was achieved through ligand-controlled gold catalysis. Unlike a dirhodium catalyst (which promotes C(sp3)-H insertion and cyclopropanation) and a copper catalyst (which catalyzes O-H and N-H insertions), the gold catalyst with an electron-deficient phosphite as the ancillary ligand exclusively gave the carbophilic addition product, thus representing a new and efficient approach to form "carbophilic carbocations", which selectively react with carbon nucleophiles. PMID:25056282

Xi, Yumeng; Su, Yijin; Yu, Zhaoyuan; Dong, Boliang; McClain, Edward J; Lan, Yu; Shi, Xiaodong

2014-09-01

33

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.

34

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

PubMed

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

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

2014-12-25

35

One-Pot Synthesis and Applications of N-Heteroaryl Iodonium Salts  

PubMed Central

An efficient one-pot synthesis of N-heteroaryl iodonium triflates from the corresponding N-heteroaryl iodide and arene has been developed. The reaction conditions resemble our previous one-pot syntheses, with suitable modifications to allow N-heteroaryl groups. The reaction time is only 30?min, and no anion exchange is required. The obtained iodonium salts were isolated in a protonated form, these salts can either be employed directly in applications or be deprotonated prior to use. The aryl groups were chosen to induce chemoselective transfer of the heteroaryl moiety to various nucleophiles. The reactivity and chemoselectivity of these iodonium salts were demonstrated by selectively introducing a pyridyl moiety onto both oxygen and carbon nucleophiles in good yields. PMID:24688890

Bielawski, Marcin; Malmgren, Joel; Pardo, Leticia M; Wikmark, Ylva; Olofsson, Berit

2014-01-01

36

Efficient synthesis of 2-(thiocyanomethylthio)benzothiazole  

Microsoft Academic Search

In the leather industry phenolic-based fungicides have been in use until recently. As a result of legislation limiting the content of pentachlorophenol (PCP) in leather, non-chlorophenolics based on 2-(thiocyanomethylthio)benzothiazole (TCMTB) have become more widely used in the leather industry for controlling the growth of fungi and sulphate-reducing bacteria. This paper reports a clean and simple method of synthesis of TCMTB,

Lakshmi Muthusubramanian; V. S. Sundara Rao; Rajat B Mitra

2001-01-01

37

Arylation with Unsymmetrical Diaryliodonium Salts: A Chemoselectivity Study  

PubMed Central

Phenols, anilines, and malonates have been arylated under metal-free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti-ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal-free reagents. PMID:23788251

Malmgren, Joel; Santoro, Stefano; Jalalian, Nazli; Himo*, Fahmi; Olofsson, Berit

2013-01-01

38

Chemoselective aromatic azido reduction with concomitant aliphatic azide employing Al/Gd triflates/NaI and ESI-MS mechanistic studies.  

PubMed

Aluminium and gadolinium triflates catalyze the chemoselective reduction of aromatic azides to the corresponding amines in combination with sodium iodide. This mild chemoselective method has been applied to the synthesis of various aryl amines, C2-azido-substituted pyrrolo[2,1-c][1,4]benzodiazepines, and fused[2,1-b]quinazolinones by an intramolecular azido reduction tandem cyclization reaction. Interestingly, this methodology selectively reduces aryl azides with enhanced yields and proceeds in shorter reaction times than previous strategies. The mechanistic aspects have been investigated and the intermediates associated with this selective transformation have been intercepted and characterized by online monitoring of the reaction by ESI-MS. PMID:19544509

Kamal, Ahmed; Markandeya, Nagula; Shankaraiah, Nagula; Reddy, C Ratna; Prabhakar, S; Reddy, C Sanjeeva; Eberlin, Marcos N; Silva Santos, Leonardo

2009-07-20

39

Efficient Synthesis of Ferrocenylcyclohexenone Under Solvent-Free Conditions  

Microsoft Academic Search

An efficient method for the synthesis of a series of ferrocenylcyclohexenones via tandem Michael–aldol reaction of ferrocenyl-substituted chalcones with dibenzyl ketone under solvent-free conditions is described. It was found that the factors including the electronic nature of chalcone, basicity of the base, reaction time, and temperature have effects on the formation of the ferrocenylcyclohexenones.

Zhi-Liang Shen; Wei-Juan Zhou; Jin-Ming Yang; Shun-Jun Ji

2009-01-01

40

Toward Efficient Enzymatic Glycan Synthesis: Directed Evolution and Enzyme Engineering  

Microsoft Academic Search

Enzymatic synthesis of oligosaccharides has traditionally employed glycosyltransferases, or glycosidases run in transglycosylation mode. Glycosynthases, mutant glycosidases in which the catalytic nucleophile has been removed, function as efficient transferases with glycosyl fluoride donors, frequently giving stoicheometric yields. Glycoligases, in which the acid\\/base catalyst has been mutated, synthesise sulfur-linked oligosaccharides when an activated donor is used in conjunction with a thiosugar

David H. Kwan; Stephen G. Withers

2011-01-01

41

Targeted and armed oncolytic adenovirus via chemoselective modification.  

PubMed

Oncolytic adenoviruses (Ads) are an emerging alternative therapy for cancer; however, clinical trial have not yet demonstrated sufficient efficacy. When oncolytic Ads are used in combination with taxoids a synergistic increase in both cytotoxicity and viral replication is observed. In order to generate a next generation oncolytic adenovirus, virion were physically conjugated to a highly potent taxoid, SB-T-1214, and a folate targeting motif. Conjugation was enabled via the metabolic incorporation of non-canonical monosaccharides (O-GlcNAz) and amino acids (homopropargylglycine), which served as sites for chemoselective modification. PMID:21669527

Banerjee, Partha S; Zuniga, Edison S; Ojima, Iwao; Carrico, Isaac S

2011-09-01

42

Energy efficiency in nanoscale synthesis using nanosecond plasmas  

PubMed Central

We report a nanoscale synthesis technique using nanosecond-duration plasma discharges. Voltage pulses 12.5?kV in amplitude and 40?ns in duration were applied repetitively at 30?kHz across molybdenum electrodes in open ambient air, generating a nanosecond spark discharge that synthesized well-defined MoO3 nanoscale architectures (i.e. flakes, dots, walls, porous networks) upon polyamide and copper substrates. No nitrides were formed. The energy cost was as low as 75?eV per atom incorporated into a nanostructure, suggesting a dramatic reduction compared to other techniques using atmospheric pressure plasmas. These findings show that highly efficient synthesis at atmospheric pressure without catalysts or external substrate heating can be achieved in a simple fashion using nanosecond discharges. PMID:23386976

Pai, David Z.; (Ken) Ostrikov, Kostya; Kumar, Shailesh; Lacoste, Deanna A.; Levchenko, Igor; Laux, Christophe O.

2013-01-01

43

Energy efficiency in nanoscale synthesis using nanosecond plasmas.  

PubMed

We report a nanoscale synthesis technique using nanosecond-duration plasma discharges. Voltage pulses 12.5?kV in amplitude and 40?ns in duration were applied repetitively at 30?kHz across molybdenum electrodes in open ambient air, generating a nanosecond spark discharge that synthesized well-defined MoO? nanoscale architectures (i.e. flakes, dots, walls, porous networks) upon polyamide and copper substrates. No nitrides were formed. The energy cost was as low as 75?eV per atom incorporated into a nanostructure, suggesting a dramatic reduction compared to other techniques using atmospheric pressure plasmas. These findings show that highly efficient synthesis at atmospheric pressure without catalysts or external substrate heating can be achieved in a simple fashion using nanosecond discharges. PMID:23386976

Pai, David Z; Ken Ostrikov, Kostya; Kumar, Shailesh; Lacoste, Deanna A; Levchenko, Igor; Laux, Christophe O

2013-01-01

44

Thermally robust Au99(SPh)42 nanoclusters for chemoselective hydrogenation of nitrobenzaldehyde derivatives in water.  

PubMed

We report the synthesis and catalytic application of thermally robust gold nanoclusters formulated as Au99(SPh)42. The formula was determined by electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry in conjunction with thermogravimetric analysis. The optical spectrum of Au99(SPh)42 nanoclusters shows absorption peaks at ~920 nm (1.35 eV), 730 nm (1.70 eV), 600 nm (2.07 eV), 490 nm (2.53 eV), and 400 nm (3.1 eV) in contrast to conventional gold nanoparticles, which exhibit a plasmon resonance band at 520 nm (for spherical particles). The ceria-supported Au99(SPh)42 nanoclusters were utilized as a catalyst for chemoselective hydrogenation of nitrobenzaldehyde to nitrobenzyl alcohol in water using H2 gas as the hydrogen source. The selective hydrogenation of the aldehyde group catalyzed by nanoclusters is a surprise because conventional nanogold catalysts instead give rise to the product resulting from reduction of the nitro group. The Au99(SPh)42/CeO2 catalyst gives high catalytic activity for a range of nitrobenzaldehyde derivatives and also shows excellent recyclability due to its thermal robustness. We further tested the size-dependent catalytic performance of Au25(SPh)18 and Au36(SPh)24 nanoclusters, and on the basis of their crystal structures we propose a molecular adsorption site for nitrobenzaldehyde. The nanocluster material is expected to find wide application in catalytic reactions. PMID:24568535

Li, Gao; Zeng, Chenjie; Jin, Rongchao

2014-03-01

45

Investigations Into The Chemoselective Modification Of THAM Directed Towards Biological Applications.  

E-print Network

?? Tris(hydroxymethyl)aminomethane (THAM) was a readily-available and economical amino-triol that was viewed as having a large untapped potential as a starting material. The full chemoselective… (more)

Calzavara, Janice L

2012-01-01

46

Transforming nonselective into chemoselective metal catalysts for the hydrogenation of substituted nitroaromatics.  

PubMed

It is generally accepted that good hydrogenation noble and nonnoble metal catalysts such as Pt, Ru, or Ni are not chemoselective for hydrogenation of nitro groups in substituted aromatic molecules. We have found that it is possible to transform nonchemoselective into highly chemoselective metal catalysts by controlling the coordination of metal surface atoms while introducing a cooperative effect between the metal and a properly selected support. Thus, highly chemoselective and general hydrogenation Pt, Ru, and Ni catalysts can be prepared by generating nanosized crystals of the metals on the surface of a TiO 2 support and decorating the exposed (111) and (100) crystal faces by means of a simple catalyst activation procedure. By doing this, it has been possible to change the relative rate for hydrogenating competitive groups present in the molecule by almost 2 orders of magnitude, increasing the chemoselectivity from less than 1% to more than 95%. PMID:18597431

Corma, Avelino; Serna, Pedro; Concepción, Patricia; Calvino, José Juan

2008-07-01

47

Efficient synthesis of polysubstituted olefins using stable palladium nanocatalyst: applications in synthesis of tamoxifen and isocombretastatin A4.  

PubMed

A phosphine-free stable palladium nanocatalyst was used for an efficient synthesis of polysubstituted olefins from N-tosylhydrazones and aryl iodides. This methodology was successfully utilized in the synthesis of biologically important tamoxifen and isocombretastatin A4. The nanocatalyst was easily recovered and reused without any apparent loss in size and catalytic activity. PMID:25036297

Ganapathy, Dhandapani; Sekar, Govindasamy

2014-08-01

48

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

49

Design and synthesis of constrained epothilone analogs: The efficient synthesis of eleven-membered rings by olefin metathesis  

Microsoft Academic Search

The efficient synthesis of both left- and right-hand halves of a constrained analog of the anticancer natural product epothilone is described. The eleven-membered rings common to both compounds are prepared by olefin metathesis.

Jeffrey D. Winkler; Joanne M. Holland; Jiri Kasparec; Paul H. Axelsen

1999-01-01

50

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

51

An efficient synthetic route to glycoamino acid building blocks for glycopeptide synthesis.  

PubMed

[reaction: see text] Chemical glycopeptide synthesis requires access to gram quantities of glycosylated amino acid building blocks. Hence, the efficiency of synthesis of such building blocks is of great importance. Here, we report a fast and highly efficient synthetic route to Fmoc-protected asparaginyl glycosides from unprotected sugars in three steps with high yields. The glycosylated amino acids were successfully incorporated into target glycopeptides 7 and 8 by standard Fmoc solid-phase peptide synthesis. PMID:15496084

Bejugam, Mallesham; Flitsch, Sabine L

2004-10-28

52

Nitrogen donor-controlled chemoselectivity of reaction in oxidation of sulfides with tetra-n-butylammonium hydrogen monopersulfate catalyzed by a partially ?-brominated meso-tetraphenylporphyrinatomanganese(III) acetate: a clue to the nature of active oxidant  

Microsoft Academic Search

Highly efficient and rapid oxidation of different sulfides to the corresponding sulfones with tetra-n- butylammonium hydrogen monopersulfate (TBAO) in the presence of catalytic amounts of Mn(TPPBr2)OAc at room temperature is reported. Contrary to other nitrogen donors, using 4-cyanopyridine as co-catalyst leads to an increase in the ratio of sulfoxide to sulfone in the products. Comparison of the chemoselectivity of reaction

Saeed Rayati; Saeed Zakavi; Vahid Noroozi

2010-01-01

53

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

54

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

55

Sulfated zirconia as an efficient catalyst for organic synthesis and transformation reactions  

Microsoft Academic Search

The efficacy of sulfated zirconia catalyst was investigated towards various acid-catalyzed organic syntheses and transformation reactions in the liquid phase. The SO42?\\/ZrO2 efficiently catalyzes synthesis of 1,5-benzodiazepine derivatives, electrophilic substitution of indoles with aldehydes to afford the corresponding bis(indolyl)methanes, synthesis of 3,4-dihydropyrimidinones, synthesis of diaryl sulfoxides, and tetrahydropyranylation of alcohols and phenols. Various advantages associated with these protocols include, simple

Benjaram M. Reddy; Pavani M. Sreekanth; Pandian Lakshmanan

2005-01-01

56

ROBUST SPLICING COSTS AND EFFICIENT SEARCH WITH BMM MODELS FOR CONCATENATIVE SPEECH SYNTHESIS  

E-print Network

to search for speech segments in a database that minimize some cost function [1, 2, 3]. The cost functionROBUST SPLICING COSTS AND EFFICIENT SEARCH WITH BMM MODELS FOR CONCATENATIVE SPEECH SYNTHESIS Ivan of corpus­based methods for con­ catenative speech synthesis, a large amount of interest has been placed

Bilmes, Jeff

57

ROBUST SPLICING COSTS AND EFFICIENT SEARCH WITH BMM MODELS FOR CONCATENATIVE SPEECH SYNTHESIS  

E-print Network

to search for speech segments in a database that minimize some cost function [1, 2, 3]. The cost functionROBUST SPLICING COSTS AND EFFICIENT SEARCH WITH BMM MODELS FOR CONCATENATIVE SPEECH SYNTHESIS Ivan of corpus-based methods for con- catenative speech synthesis, a large amount of interest has been placed

Washington at Seattle, University of

58

A new approach to asymmetric synthesis of infectocaryone.  

PubMed

A useful and flexible strategy for synthesis of (-)- and (+)-infectocaryone from commercial sugars is developed. The key step of the synthesis is a new-type Diels-Alder reaction with good chemoselectivity and stereoselectivity, in which a mixture of alkene regioisomers in a dynamic equilibrium is employed as chiral dienophiles for the first time. PMID:25141777

Liu, Xiubing; Hu, Lingling; Liu, Xiaojing; Jia, Junhao; Jiang, Lizhen; Lin, Jiangfeng; Chen, Xiaochuan

2014-10-14

59

Ionic liquid-regulated sulfamic acid: chemoselective catalyst for the transesterification of ?-ketoesters  

Microsoft Academic Search

1-Propyl-3-methylimidazolium chloride ([C3MIm]Cl) ionic liquid and sulfamic acid (NH2SO3H), as a synergetic catalytic medium, were used for the transesterification of acetoacetate with alcohols of different structures. It shows the good ability for the chemoselective transesterificatin of ?-ketoesters and maintains its catalytic activity in the reuse.

Wang Bo; Yang Li Ming; Suo Ji Shuan

2003-01-01

60

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.

61

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.

62

Chemoselective reduction of ?,?-unsaturated aldehydes using an unsupported nanoporous gold catalyst.  

PubMed

The remarkable effect of an unsupported nanoporous gold catalyst (AuNPore) on chemoselective hydrogenation of ?,?-unsaturated aldehydes using silane has been described. Enals can be reduced with excellent selectivity, giving the corresponding allylic alcohols in good to high chemical yields. PMID:25299948

Takale, Balaram S; Wang, Shanqiang; Zhang, Xuan; Feng, Xiujuan; Yu, Xiaoqiang; Jin, Tienan; Bao, Ming; Yamamoto, Yoshinori

2014-10-23

63

An efficient synthesis of chalcones based on the Suzuki reaction  

Microsoft Academic Search

A general method for the synthesis of chalcones based on the Suzuki reaction either between cinnamoyl chlorides and phenylboronic acids or between benzoyl chlorides and phenylvinylboronic acids is described.

Said Eddarir; Nicole Cotelle; Youssef Bakkour; Christian Rolando

2003-01-01

64

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

65

Observations on the interaction between coding and efficiency knowledge in the PSI Program Synthesis System  

Microsoft Academic Search

This paper discusses how the synthesis phase of the PSI system constructs programs from high level program models by using coding knowledge and efficiency knowledge. In our preliminary implementation, these knowledge bases are separated into distinct modules, the coding expert and the efficiency expert. We describe how the coding expert uses rule-based programming knowledge to produce alternative algorithm and data

David R. Barstow; Elaine Kant

1976-01-01

66

Efficient Dense Stereo with Occlusions for New View-Synthesis by Four-State Dynamic Programming  

Microsoft Academic Search

A new algorithm is proposed for efficient stereo and novel view synthesis. Given the video streams acquired by two synchronized cameras the proposed algorithm synthesises images from a virtual camera in arbitrary position near the physical cameras. The new technique is based on an improved, dynamic-programming, stereo algorithm for efficient novel view generation. The two main contributions of this paper

Antonio Criminisi; Andrew Blake; Carsten Rother; Jamie Shotton; Philip H. S. Torr

2007-01-01

67

Tandem Reactions for Streamlining Synthesis  

PubMed Central

CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

2009-01-01

68

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

69

A concise and efficient total synthesis of ?-mangostin and ?-mangostin from Garcinia mangostana.  

PubMed

The concise, efficient synthesis of alpha-mangostin is described in eight simple steps with 8.3% overall yield. Highlights include a practical approach to construct the isopentene groups and other diverse groups at C-2 and C-8 of the xanthene skeleton through Claisen rearrangement and Wittig reaction. Meanwhile the first total synthesis of beta-mangostin is presented with a similar approach. PMID:24079178

Xu, Dandan; Nie, Ying; Liang, Xizhou; Ji, Ling; Hu, Songyuan; You, Qidong; Wang, Fan; Ye, Hongchun; Wang, Jinxin

2013-08-01

70

Transglucosidases as efficient tools for oligosaccharide and glucoconjugate synthesis.  

PubMed

Transglucosidases are highly promising enzymatic tools for glucodiversification. Instead of involving nucleotide-activated sugars as d-glucosyl donor, they use the energy of simple osidic linkages to synthesize carbohydrate derivatives. The remarkable promiscuity of these enzymes regarding the acceptor substrate offers great opportunities for novel synthetic reactions. Glucansucrases that use sucrose as donor substrate are of particular interest and have been widely utilized to produce diverse structurally controlled molecules. Besides site-directed mutagenesis, recent developments in the combined use of computational protein design and molecular engineering have led to major achievements to create novel enzymes, in particular for the chemo-enzymatic synthesis of antigenic oligosaccharides. These promising results pave the way to the future development of tailored catalysts for the synthesis of glucoconjugates of pharmaceutical and nutritional interest. PMID:20362489

Monsan, Pierre; Remaud-Siméon, Magali; André, Isabelle

2010-06-01

71

Efficient synthesis of multifunctional furanoid C-glycoamino acid precursors  

Microsoft Academic Search

Ready access to constrained, multifunctionalized, hydrolytically stable amino acids has been established by the synthesis of their direct precursors using 2,5-anhydro-3-azido-3-deoxy-d-altrose (a ‘formyl azido-C-glycofuranoside’), or its readily available, stable synthetic equivalent [(1R) and (1S)-2,5-anhydro-3-azido-4,6-O-benzylidene-3-deoxy-1-fluoro-1-O-methyl-d-altritol], as novel molecular scaffolds.

Yolanda Vera-Ayoso; Pastora Borrachero; Francisca Cabrera-Escribano; Manuel Gómez-Guillén

2005-01-01

72

An efficient formal synthesis of the sesquiterpenoid longifolene.  

PubMed

Through a convenient ring expansion reaction of key intermediate 1, enone 5, containing the longifolene skeleton, was produced. Elaboration of 5 via hydrogenation, Wittig reaction, Simmons-Smith reaction, and subsequent hydrogenolysis led to ketone 9. Reductive debromination of 9 afforded 10, the penultimate precursor to longifolene. This formal total synthesis was accomplished in 13 steps using commercially available Wieland-Miescher ketone as the starting material. PMID:12713405

Karimi, Sasan; Tavares, Paula

2003-04-01

73

Chemoselective and direct functionalization of methyl benzyl ethers and unsymmetrical dibenzyl ethers by using iron trichloride.  

PubMed

Methyl and benzyl ethers are widely utilized as protected alcohols due to their chemical stability, such as the low reactivity of the methoxy and benzyloxy groups as leaving groups under nucleophilic conditions. We have established the direct azidation of chemically stable methyl and benzyl ethers derived from secondary and tertiary benzyl alcohols. The present azidation chemoselectively proceeds at the secondary or tertiary benzylic positions of methyl benzyl ethers or unsymmetrical dibenzyl ethers and is also applicable to direct allylation, alkynylation, and cyanation reactions, as well as the azidation. The present methodologies provide not only a novel chemoselectivity but also the advantage of shortened synthetic steps, due to the direct process without the deprotection of the methyl and benzyl ethers. PMID:24459116

Sawama, Yoshinari; Goto, Ryota; Nagata, Saori; Shishido, Yuko; Monguchi, Yasunari; Sajiki, Hironao

2014-02-24

74

Chemoselective reduction of aromatic nitro and azo compounds in ionic liquids using zinc and ammonium salts  

Microsoft Academic Search

Nitroarenes were chemoselectively reduced to the corresponding amines using zinc and aqueous ammonium salts in ionic liquids as a safe and recyclable reaction medium. Our results specify the effect of ammonium salts in the process; the combination of Zn\\/NH4Cl in [bmim][PF6] or Zn\\/HCO2NH4 in [bmim][BF4] were the suitable conditions for the reduction of nitroarenes. Azobenzenes were also smoothly reduced to

Faiz Ahmed Khan; Jyotirmayee Dash; Ch Sudheer; Rakesh Kumar Gupta

2003-01-01

75

Chemoselective silyl transfer in the Mukaiyama aldol reaction promoted by super silyl Lewis acid.  

PubMed

In the silyl Lewis acid-promoted Mukaiyama aldol reaction, the steric and electronic properties of the silyl group on the silyl Lewis acid influence the reaction mechanism and product distribution. When super silyl triflates such as (TMS)3SiOTf and (TES)3SiOTf are used as Lewis acids, the silyl group of the silyl enol ether chemoselectively transfers to the product. The mechanistic details have been investigated using density functional theory (DFT) calculations. PMID:25338752

Sai, Masahiro; Akakura, Matsujiro; Yamamoto, Hisashi

2014-11-01

76

Highly chemoselective reduction of aromatic nitro compounds by copper nanoparticles/ammonium formate.  

PubMed

A highly chemoselective reduction of aromatic nitro compounds to the corresponding amino derivatives has been achieved by a combination of copper nanoparticles and ammonium formate in ethylene glycol at 120 degrees C. The reductions are successfully carried out in presence of a wide variety of other reducible functional groups in the molecule, such as Cl, I, OCH2Ph, NHCH2Ph, COR, COOR, CN, etc. The reactions are very clean and high yielding. PMID:18656983

Saha, Amit; Ranu, Brindaban

2008-09-01

77

Chemoselective tarantula toxins report voltage activation of wild-type ion channels in live cells.  

PubMed

Electrically excitable cells, such as neurons, exhibit tremendous diversity in their firing patterns, a consequence of the complex collection of ion channels present in any specific cell. Although numerous methods are capable of measuring cellular electrical signals, understanding which types of ion channels give rise to these signals remains a significant challenge. Here, we describe exogenous probes which use a novel mechanism to report activity of voltage-gated channels. We have synthesized chemoselective derivatives of the tarantula toxin guangxitoxin-1E (GxTX), an inhibitory cystine knot peptide that binds selectively to Kv2-type voltage gated potassium channels. We find that voltage activation of Kv2.1 channels triggers GxTX dissociation, and thus GxTX binding dynamically marks Kv2 activation. We identify GxTX residues that can be replaced by thiol- or alkyne-bearing amino acids, without disrupting toxin folding or activity, and chemoselectively ligate fluorophores or affinity probes to these sites. We find that GxTX-fluorophore conjugates colocalize with Kv2.1 clusters in live cells and are released from channels activated by voltage stimuli. Kv2.1 activation can be detected with concentrations of probe that have a trivial impact on cellular currents. Chemoselective GxTX mutants conjugated to dendrimeric beads likewise bind live cells expressing Kv2.1, and the beads are released by channel activation. These optical sensors of conformational change are prototype probes that can indicate when ion channels contribute to electrical signaling. PMID:25331865

Tilley, Drew C; Eum, Kenneth S; Fletcher-Taylor, Sebastian; Austin, Daniel C; Dupré, Christophe; Patrón, Lilian A; Garcia, Rita L; Lam, Kit; Yarov-Yarovoy, Vladimir; Cohen, Bruce E; Sack, Jon T

2014-11-01

78

An efficient total synthesis of ruprechstyril from Ruprechtia tangarana  

Microsoft Academic Search

A short total synthesis of natural isocarbostyril ruprechstyril (3-n-pentyl-6-methoxy-8-hydroxy-1(2H)-isoquinolinone) isolated from Ruprechtia tangarana is reported. 6,8-Dimethoxy-3-pentylisocoumarin obtained by condensation of 3,5-dimethoxyhomophthalic anhydride with hexanoyl chloride was smoothly converted to O-methylruprechstyril by refluxing with methanamide. Regioselective demethylation of the latter using anhydrous aluminium chloride in dichloromethane furnished the ruprechstyril. Complete demethylation to give (6-desmethoxyruprechstyril) was achieved using same reagent in ethanethiol.

Aamer Saeed

2012-01-01

79

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

80

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

E-print Network

to syn- thesis gas syngas , CO and H2, ideally in a 1:2 ratio. This is also a desirable feedstockApplied reaction dynamics: Efficient synthesis gas production via single collision partial dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO+2H2

Sibener, Steven

81

Thermal efficiency evaluation of HI synthesis\\/concentration procedures in the thermochemical water splitting IS process  

Microsoft Academic Search

Effects of operation parameters of HI synthesis and concentration procedures on thermal efficiency in the thermochemical hydrogen production IS process were investigated based on heat\\/mass balance. Concentration of HI was carried out by an electro-electrodialysis (EED) cell. Transport number of proton, electroosmosis coefficient and ratio of the flow rates at the inlets of the EED cell were considered as parameters

Seiji Kasahara; Shinji Kubo; Kaoru Onuki; Mikihiro Nomura

2004-01-01

82

A simple and efficient synthesis of fused morpholine pyrrolidines/piperdines with potential insecticidal activities.  

PubMed

A simple and efficient synthesis of fused morpholine pyrrolidine/piperdine core structures was accomplished via a Petasis-borono Mannich reaction of cyclic amino alcohols, glyoxal and arylboronic acids with moderate to good yields. The bioassay data showed that the synthesized compounds displayed selective insecticidal activities against armyworm and root-knot nematode. PMID:24927942

Wang, Jiayi; Xu, Beiling; Si, Shanyu; Li, Hui; Song, Gonghua

2014-11-01

83

Efficient Synthesis of a Novel Resorcyclide as Anticancer Agent Based on Hsp90 Inhibition  

PubMed Central

The highly efficient synthesis of a novel heat shock protein 90 (Hsp90)-based anticancer agent, triazole-cycloproparadicicol (5), is described. The key step involves a fragment coupling using “click chemistry.” The preliminary biological evaluation of triazole-cycloproparadicicol is also reported. PMID:21442009

Lei, Xiaoguang; Danishefsky, Samuel J.

2011-01-01

84

Tetrabutylammonium hydrogen sulfate catalyzed eco-friendly and efficient synthesis of glycosyl 1,4-dihydropyridines  

Microsoft Academic Search

An efficient and eco-friendly synthesis of glycosyl 1,4-dihydropyridines has been achieved by a three-component reaction of ?-keto esters or ketones, enamines and glycosyl aldehydes in the presence of tetrabutylammonium hydrogen sulfate as catalyst in diethylene glycol.

Neetu Tewari; Namrata Dwivedi; Rama P. Tripathi

2004-01-01

85

Simple and efficient synthesis of [MCI(NHC)] (M = Au, Ag) complexes.  

PubMed

A facile and efficient synthetic route leading to catalytically relevant N-heterocyclic carbene (NHC) gold complexes is described. The method consists of one pot synthesis starting from readily available imidazolium salts and [AuCl(tht)], in the presence of K2CO3. Using the same protocol NHC silver complexes have been synthesised starting from AgNO3. PMID:23685678

Visbal, Renso; Laguna, Antonio; Gimeno, M Concepción

2013-06-25

86

Efficient discovery of bioactive scaffolds by activity-directed synthesis.  

PubMed

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. PMID:25242481

Karageorgis, George; Warriner, Stuart; Nelson, Adam

2014-10-01

87

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

88

Efficient synthesis of natural polyphenolic stilbenes: resveratrol, piceatannol and oxyresveratrol.  

PubMed

The practical synthesis of important natural polyphenolic stilbenes, including resveratrol, piceatannol and oxyresveratrol, through Perkin methodology is described. Starting from 3,5-dihydoxyacetophenone (1), the common intermediate 3,5-dimethoxyphenylacetic acid (3) can be obtained via methylation and Willgerodt-Kindler reaction. Perkin condensations between (3) and substituted phenylaldehydes 4 furnished E-2,3-diarylacrylic acids 5, followed by decarboxylation in Cu/quinoline giving stilbene intermediates 6 which bear the Z-configuration. Finally, through a simultaneous demethylation/isomerization process in AlI?/CH?CN system, the target compounds 7a-c can be obtained respectively in good to high overall yields. The synthetic method proved to be more concise, trans-specific, mild, economical and commonly applicable. PMID:21048342

Sun, Hong-Yi; Xiao, Chun-Fen; Cai, Yu-Chen; Chen, Yu; Wei, Wen; Liu, Xian-Ke; Lv, Ze-Liang; Zou, Yong

2010-11-01

89

Efficient synthesis of (+)-1,8,8a-tri-epi-swainsonine, (+)-1,2-di-epi-lentiginosine, (+)-9a-epi-homocastanospermine and (-)-9-deoxy-9a-epi-homocastanospermine from a D-glucose-derived aziridine carboxylate, and study of their glycosidase inhibitory activities.  

PubMed

The utility of a D-glucose-derived aziridine carboxylate was demonstrated for the synthesis of polyhydroxylated quinolizidine and indolizidine alkaloids. The chemoselective reduction of 1 followed by two-carbon homologation by the Wittig reaction afforded gamma,delta-aziridino-alpha,beta-unsaturated ester 9, which on regioselective nucleophilic aziridine ring opening either by using water as a nucleophile or hydrogenation afforded delta-lactams 11/16--true synthons for the synthesis of four structurally different iminosugars, namely quinolizidine alkaloids 5b/5c, swainsonine 6b and lentiginosine 7b analogues. Glycosidase inhibitory activities of these iminosugars were investigated. PMID:18264570

Ajish Kumar, K S; Chaudhari, Vinod D; Dhavale, Dilip D

2008-02-21

90

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

91

The Cost-Efficiency Realization in the Escherichia coli-Based Cell-Free Protein Synthesis Systems.  

PubMed

A reliable and cost-efficient protein synthesis system is the prerequisite for both structural and functional proteomic studies. The last decades saw the great technological improvement in the development of different protein synthesis systems. The cell-free protein synthesis system, especially Escherichia coli-based cell-free protein synthesis system, has emerged as one of the most robust protocols which can meet the growing demand of protein synthesis. E. coli-based cell-free protein synthesis system has become a more complete system for protein synthesis over the last two decades. Here, we review the main development and modifications of the E. coli-based cell-free protein synthesis system. PMID:25185501

Lian, Qianqian; Cao, Hongzhi; Wang, Fengshan

2014-12-01

92

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

93

3-benzhydryl-4-piperidones as novel neurokinin-1 receptor antagonists and their efficient synthesis.  

PubMed

A series of novel 3-benzhydryl-4-piperidone derivatives were identified as potent tachykinin neurokinin-1 (NK(1)) receptor antagonists. An efficient and versatile synthesis of this series was achieved with a coupling reaction of 1-benzylpiperidones with benzhydryl bromides or benzhydrols in the presence of trifluoromethanesulfonate and a condensation reaction of piperidones with benzyl alcohols using ethyl o-phenylenephosphate. The 3-benzhydryl-4-piperidone skeleton, which has a 1,1-diphenylmethane moiety that is a known privileged substructure targeting G-protein coupled receptors, can be used for chemical library synthesis because of chemical accessibility and diversity. PMID:21807525

Shirai, Junya; Yamaoka, Masayoshi; Imamiya, Eikoh; Nakamura, Minoru; Tarui, Naoki; Hashimoto, Tadatoshi; Ikeura, Yoshinori

2011-09-01

94

Efficient control of electron localization by subcycle waveform synthesis  

NASA Astrophysics Data System (ADS)

We propose and demonstrate an efficient scheme for steering the electron localization of hydrogen molecules and their isotopes. Our scheme is based on the idea of subcycle waveform shaping by synthesizing coherent multicycle IR pulses of different wavelengths. This scheme leads to a good balance between the control of electronic and molecular motions. The results of a quantum model simulation indicate a substantial enhancement of the electron localization asymmetry compared with that of a few-cycle one-color pulse. Sixty-eight percent and 89% of the electrons in the dissociating fragments can be localized to one nucleus for H2+ and H2, respectively.

Lan, Pengfei; Takahashi, Eiji J.; Midorikawa, Katsumi

2012-07-01

95

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

96

Evaluating the coupling efficiency of phosphorylated amino acids for SPOT synthesis.  

PubMed

A high demand of interest concerning binding assays to study the consequences of posttranscriptional phosphorylation may be addressed by peptide array-based methods. A crucial factor for de novo chemical approaches to generate such arrays is the possibility to rationally permutate phosphorylation events along a huge number of sequences. The simple principle behind this advantage is the stepwise synthesis of peptides, which allows the incorporation of either phosphorylated or nonphosphorylated derivates at serine, threonine, and tyrosine positions. In spite of several reported applications of phosphopeptide arrays, there is, to our best knowledge, no reported analysis of the efficiency of the involved techniques. Here, we analyze different coupling conditions to introduce phosphoamino acids in standard SPOT synthesis. Our results clearly indicate that EEDQ is the preferable activator and can also be used in fully automated SPOT synthesis. PMID:18816512

Tapia, Victor; Ay, Bernhard; Triebus, Julia; Wolter, Eike; Boisguerin, Prisca; Volkmer, Rudolf

2008-12-01

97

Efficient ATP synthesis by thermophilic Bacillus FoF1-ATP synthase.  

PubMed

F(o)F(1)-ATP synthase (F(o)F(1)) synthesizes ATP in the F(1) portion when protons flow through F(o) to rotate the shaft common to F(1) and F(o). Rotary synthesis in isolated F(1) alone has been shown by applying external torque to F(1) of thermophilic origin. Proton-driven ATP synthesis by thermophilic Bacillus PS3 F(o)F(1) (TF(o)F(1)), however, has so far been poor in vitro, of the order of 1 s(-1) or less, hampering reliable characterization. Here, by using a mutant TF(o)F(1) lacking an inhibitory segment of the ?-subunit, we have developed highly reproducible, simple procedures for the preparation of active proteoliposomes and for kinetic analysis of ATP synthesis, which was driven by acid-base transition and K(+)-diffusion potential. The synthesis activity reached ? 16 s(-1) at 30 °C with a Q(10) temperature coefficient of 3-4 between 10 and 30 °C, suggesting a high level of activity at the physiological temperature of ? 60 °C. The Michaelis-Menten constants for the substrates ADP and inorganic phosphate were 13 ?M and 0.55 mM, respectively, which are an order of magnitude lower than previous estimates and are suited to efficient ATP synthesis. PMID:21605343

Soga, Naoki; Kinosita, Kazuhiko; Yoshida, Masasuke; Suzuki, Toshiharu

2011-08-01

98

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

99

An exceptionally simple and efficient synthesis of 6-methyl-6-vinylfulvene, and its oxidative transformations  

PubMed Central

A new efficient synthesis of 6-methyl-6-vinylfulvene was developed, starting from the 6-(2-hydroxyethyl)-6-methylfulvene. With larger quantities of the title compound in hand, its photooxygenation with singlet oxygen was studied. Cyclization of the cyclopropanone intermediate to both vinyl moieties in the unsaturated system was observed, whereas the saturated endoperoxide gave mostly the cyclopentenone derivative. m-CPBA attacks exclusively the endocyclic double bonds and gives the 3-cyclopentenones via the unstable epoxides. PMID:20161263

Erden, Ihsan; Gärtner, Christian

2009-01-01

100

Anhydrous tert-pentanol as a novel media for the efficient enzymatic synthesis of amoxicillin  

Microsoft Academic Search

The efficient enzymatic synthesis of amoxicillin using anhydrous tert-pentanol as a novel media has been demonstrated for the first time. p-OH-Phenylglycine methyl ester (HPGM) was selected as the activated acyl donor due to its good solubility in organic solvents. The screening results of 21 organic solvents showed that solvents with either strong polarity or poor substrate solubility were unfavorable. Remarkable

Chun-Xiu Chen; Qi Wu; Bo-Kai Liu; De-Shui Lv; Xian-Fu Lin

2008-01-01

101

Highly efficient and large-scale synthesis of graphene by electrolytic exfoliation  

Microsoft Academic Search

Highly efficient and large-scale synthesis of graphene from graphite was produced by electrolytic exfoliation using poly(sodium-4-styrenesulfonate) as an effective electrolyte. Scanning and transmission electron microscopy, and atomic force microscopy confirmed the existence of monolayer graphene sheets and stacks containing a few graphene sheets. Raman spectroscopy demonstrated that the as-prepared graphene sheets have low defect content. Based on the measurement of

Guoxiu Wang; Bei Wang; Jinsoo Park; Ying Wang; Bing Sun; Jane Yao

2009-01-01

102

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

103

Cycloaddition of 1,3-butadiynes: efficient synthesis of carbo- and heterocycles.  

PubMed

Cycloaddition reactions of alkynes are elegant, atom-efficient transformations for the synthesis of carbo- and heterocycles, mostly aromatic, involving the construction of challenging skeletons of complex molecules. Therefore significant efforts have recently been devoted to the development of novel methodologies, efficient strategies and different catalytic systems to broaden the scope of these reactions. We summarize in this review the recent advances in the cycloaddition reactions of 1,3-butadiynes to provide facile and reliable approaches to various functionalized carbo- and heterocycles. PMID:25191872

Nizami, Tauqir A; Hua, Ruimao

2014-01-01

104

Chemoselective Pd-catalyzed oxidation of polyols: synthetic scope and mechanistic studies.  

PubMed

The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate ?-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that ?-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle. PMID:23659308

Chung, Kevin; Banik, Steven M; De Crisci, Antonio G; Pearson, David M; Blake, Timothy R; Olsson, Johan V; Ingram, Andrew J; Zare, Richard N; Waymouth, Robert M

2013-05-22

105

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

106

Two-photon fluorescence imaging of intracellular hydrogen peroxide with chemoselective fluorescent probes  

PubMed Central

Abstract. We present the application of two-photon fluorescence (TPF) imaging to monitor intracellular hydrogen peroxide (H2O2) production in brain cells. For selective imaging of H2O2 over other reactive oxygen species, we employed small-molecule fluorescent probes that utilize a chemoselective boronate deprotection mechanism. Peroxyfluor-6 acetoxymethyl ester detects global cellular H2O2 and mitochondria peroxy yellow 1 detects mitochondrial H2O2. Two-photon absorption cross sections for these H2O2 probes are measured with a mode-locked Ti:sapphire laser in the wavelength range of 720 to 1040 nm. TPF imaging is demonstrated in the HT22 cell line to monitor both cytoplasmic H2O2 and localized H2O2 production in mitochondria. Endogenous cytoplasmic H2O2 production is detected with TPF imaging in rat astrocytes modified with d-amino acid oxidase. The TPF H2O2 imaging demonstrated that these chemoselective probes are powerful tools for the detection of intracellular H2O2. PMID:24084856

Guo, Hengchang; Aleyasin, Hossein; Howard, Scott S.; Dickinson, Bryan C.; Lin, Vivian S.; Haskew-Layton, Renee E.; Xu, Chris; Chen, Yu; Ratan, Rajiv R.

2013-01-01

107

Gold-catalyzed efficient synthesis of azepan-4-ones via a two-step [5 + 2] annulation†  

PubMed Central

A surprisingly efficient synthesis of azepan-4-ones via two-step [5 + 2] annulation is developed. This reaction involves a key gold catalysis and shows generally high regioselectivities and good to excellent diastereoselectivities. PMID:20442898

Cui, Li; Ye, Longwu; Zhang, Liming

2010-01-01

108

Enantio- and chemoselective Brønsted-acid/Mg(nBu)2 catalysed reduction of ?-keto esters with catecholborane.  

PubMed

The first enantio- and chemoselective Brønsted-acid catalysed reduction of ?-keto esters with catecholborane has been developed. The ?-hydroxy esters were obtained under mild reaction conditions in virtually quantitative yields and excellent enantioselectivities. With slight modifications both enantiomers can be obtained without any loss of selectivity. PMID:24643455

Enders, Dieter; Stöckel, Bianca A; Rembiak, Andreas

2014-05-01

109

Cyclometalated gold(III) complexes for chemoselective cysteine modification via ligand controlled C-S bond-forming reductive elimination.  

PubMed

Modular assembly of cyclometalated gold(III) complexes by choosing appropriate bidentate C,N-donor ligands and ancillary ligands for chemoselective cysteine modification of peptides and proteins via C-S bond-forming reductive elimination has been achieved. PMID:25154886

Kung, Karen Ka-Yan; Ko, Hok-Ming; Cui, Jian-Fang; Chong, Hiu-Chi; Leung, Yun-Chung; Wong, Man-Kin

2014-10-14

110

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

111

Chemoselective and regiospecific Suzuki coupling on a multisubstituted sp(3)-carbon in 1,1-diborylalkanes at room temperature.  

PubMed

The palladium-catalyzed Suzuki-Miyaura cross-coupling on a multisubstituted sp(3)-carbon in 1,1-diborylalkanes was achieved at room temperature. The generation of a monoborate intermediate by virtue of the adjacent B atom could result in the chemoselective coupling reaction under ambient conditions. PMID:20698667

Endo, Kohei; Ohkubo, Takahiro; Hirokami, Munenao; Shibata, Takanori

2010-08-18

112

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

113

Enantioselective total synthesis of marine diterpenoid clavulactone.  

PubMed

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

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

2012-06-25

114

One-pot synthesis of Pd@MOF composites without the addition of stabilizing agents.  

PubMed

In this work, the first example of a facile one-pot route for the synthesis of Pd@MOF composites without additional stabilizing agents is developed. The as-synthesized MOF composite shows high activity and chemoselectivity in the hydrogenation of cinnamaldehyde even under atmosphere pressure of H2 and at room temperature. PMID:25318046

Chen, Liyu; Chen, Huirong; Li, Yingwei

2014-10-30

115

Synthesis of a key intermediate for the preparation of FTY720 analogs.  

PubMed

A concise synthesis of a useful intermediate 10 for the preparation of fingolimod (FTY-720) analogs was achieved by utilizing a chemoselective Sonogashira reaction of trihalobenzene 12 with alkyne 13. The reaction proceeded with high selectivity to give alkyne 11 containing the dihalobenzene moiety in good yield. Compound 11 was converted into intermediate 10 by hydrogenation without reduction of the halogen atoms. PMID:23124563

Hamada, Maiko; Adachi, Kunitomo; Hikawa, Hidemasa; Yokoyama, Yuusaku

2012-01-01

116

Through the looking glass a new world of proteins enabled by chemical synthesis{  

E-print Network

' ­ the regioselective and chemoselective covalent condensation of unprotected peptide segments ­ has enabled that are the mirror images of proteins found in the natural world have been prepared by total chemical synthesis of the mirror-image protein will be used to systematically develop D-protein antagonists of this important

Bang, Duhee

117

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

E-print Network

of functionalized aromatics including heterocycles have been realized using TMP-cadmiate, (TMP)3CdLi (TMP = 2,2, and pyrrole derivatives) and even aromatic aza-heterocycles (pyridine, diazine compounds). Some heterocycles lithium 2,2,6,6-tetramethylpiperidide (LiTMP) and lithium diisopropylamide (LiDA)) have been largely

Boyer, Edmond

118

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

119

Regio- and chemoselective magnesiation of protected uracils and thiouracils using TMPMgCl x LiCl and TMP(2)Mg x 2 LiCl.  

PubMed

Two successive regio- and chemoselective magnesiations using TMPMgCl x LiCl and TMP(2)Mg x 2 LiCl enable the full functionalization of protected uracils and thiouracils in good to excellent yields. PMID:18802627

Mosrin, Marc; Boudet, Nadège; Knochel, Paul

2008-09-21

120

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

121

Efficient Utilization of Crude Glycerol as Fermentation Substrate in the Synthesis of Poly(3-hydroxybutyrate) Biopolymers  

Microsoft Academic Search

One refined and two crude glycerol (from biodiesel production) samples were utilized to produce poly(3-hydroxybutyrate) (PHB)\\u000a by Pseudomonas oleovorans NRRL B-14682. A batch culture fermentation protocol including 1% glycerol and an aeration rate of 3 standard liters per minute\\u000a proved best for PHB synthesis (av. yield = 1.0 ± 0.2 g\\/L at 48 h) and efficient glycerol utilization. PHB molecular weights\\u000a decreased as MeOH concentration increased.

Richard D. AshbyDaniel; Daniel K. Y. Solaiman; Gary D. Strahan

2011-01-01

122

Chemoselective hydrogenation of functionalized nitroarenes and imines by using carbon nanofiber-supported iridium nanoparticles.  

PubMed

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF-P, tubular: CNF-T, herringbone: CNF-H) with Ir4(CO)12 in mesitylene at 165 °C provided the corresponding CNF-supported iridium nanoparticles, Ir/CNFs (Ir content=2.3-2.6 wt.%). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size-controlled Ir nanoparticles (average particle size of 1.1-1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF-T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 tm of H2 , and the catalyst is reusable. Ir/CNF-T was also effective for the reductive N-alkylation of anilines with carbonyl compounds. PMID:24347068

Motoyama, Yukihiro; Taguchi, Masahiro; Desmira, Nelfa; Yoon, Seong-Ho; Mochida, Isao; Nagashima, Hideo

2014-01-01

123

Chemoselective Tryptophan Labeling with Rhodium Carbenoids at Mild pH  

PubMed Central

Significant improvements have been made to a previously reported tryptophan modification method using rhodium carbenoids in aqueous solution, allowing the reaction to proceed at pH 6–7. This technique is based on the discovery that tert-butylhydroxyl amine promotes indole modification with rhodium carbenoids over a broad pH range (2–7). This methodology was demonstrated on peptide and protein substrates, generally yielding 40–60% conversion with excellent tryptophan chemoselectivity. The solvent accessibility of the indole side chains was found to be a key factor in successful carbenoid addition, as demonstrated by conducting the reaction at temperatures high enough to cause thermal denaturation of the protein substrate. Progress toward the expression of proteins bearing solvent accessible tryptophan residues as reactive handles for modification with rhodium carbenoids is also reported. PMID:19366262

Antos, John M.; McFarland, Jesse M.; Iavarone, Anthony T.; Francis, Matthew B.

2009-01-01

124

Breaking the dichotomy of reactivity vs. chemoselectivity in catalytic S(N)1 reactions of alcohols.  

PubMed

The inability to decouple Lewis acid catalysis from undesirable Brønsted acid catalysed side reactions when water or other protic functional groups are necessarily present has forced chemists to choose between powerful but harsh catalysts or poor but mild ones, a dichotomy that restricts the substrate scope of dehydrative transformations such as the direct SN1 reaction of alcohols. A systematic survey of Lewis and Brønsted acids reveals that the strong non-hydrolyzable Lewis acid B(C6F5)3 leads to highly chemoselective alcohol substitution in the presence of acid-sensitive alkenes, protecting groups and other functional groups without the typical compromise in reaction rates, substrate scope and catalyst loading. PMID:24987941

Hellal, Malik; Falk, Florian C; Wolf, Eléna; Dryzhakov, Marian; Moran, Joseph

2014-08-21

125

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

PubMed

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

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

2014-08-15

126

Reduced Left Ventricular Compliance and Mechanical Efficiency after Prolonged Inhibition of NO Synthesis in Conscious Dogs  

PubMed Central

Acute inhibition of NO synthesis decreases left ventricular (LV) work and external efficiency, but it is unknown whether compensatory mechanisms can limit the alterations in LV mechanoenergetics after prolonged NO deficiency. Eight chronically instrumented male mongrel dogs received 35 mg kg?1 day?1 of N?-nitro-L-arginine methyl ester orally for 10 days to inhibit NO synthesis. At spontaneous beating frequency, heart rate, coronary blood flow, peak LV pressure, end-diastolic LV pressure and the maximum derivative of LV pressure (dP/dtmax) were not significantly different vs. baseline, whereas LV end-diastolic diameter (32.5 ± 1.0 vs. 37.6 ± 1.4 mm) and LV stroke work (515 ± 38 vs. 650 ± 44 mmHg mm), were reduced (all P < 0.05). The slope of the LV end-systolic pressure-diameter relationship was increased at 10 days vs. baseline (13.9 ± 1.0 vs. 9.6 ± 0.9 mmHg mm?1, P < 0.05), while the end-diastolic LV diameter was smaller at matched LV end-diastolic pressures. At fixed heart rate (130 beats min?1), cardiac oxygen consumption was increased (12.2 ± 1.5 vs. 9.9 ± 1.0 ml min?1), and the ratio between stroke work and oxygen consumption was decreased by 33 ±7 % (all P < 0.05) after NO inhibition. We conclude that sustained inhibition of NO synthesis in dogs causes a decrease in LV work despite an increased contractility, which is most probably due to reduced diastolic compliance and a decrease in external efficiency. Thus, prolonged NO deficiency is not compensated for on the level of LV mechanoenergetics in vivo. PMID:12878761

Post, Heiner; d'Agostino, Chiara; Lionetti, Vincenzo; Castellari, Michele; Kang, Elaine Y; Altarejos, Martin; Xu, Xiaobin; Hintze, Thomas H; Recchia, Fabio A

2003-01-01

127

Efficient Enantio- and Diastereo-divergent Synthesis of Poison-frog Alkaloids 251O and trans-223B  

PubMed Central

An efficient and flexible synthesis of poison-frog alkaloids 251O and trans-223B has been achieved using for both alkaloids an enantiodivergent process starting from the common lactam 1. The relative stereochemistry of 251O and trans-223B was determined to be 7 (R = n- C7H15, R’ = n-Pr) and 14 by the present enantioselective synthesis. PMID:19637860

Toyooka, Naoki; Zhou, Dejun; Nemoto, Hideo; Tezuka, Yasuhiro; Kadota, Shigetoshi; Andriamaharavo, Nirina R.; Garraffo, H. Martin; Spande, Thomas F.; Daly, John W.

2009-01-01

128

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

129

Efficient Synthesis of Eriodictyol from l-Tyrosine in Escherichia coli  

PubMed Central

The health benefits of flavonoids for humans are increasingly attracting attention. Because the extraction of high-purity flavonoids from plants presents a major obstacle, interest has emerged in biosynthesizing them using microbial hosts. Eriodictyol is a flavonoid with anti-inflammatory and antioxidant activities. Its efficient synthesis has been hampered by two factors: the poor expression of cytochrome P450 and the low intracellular malonyl coenzyme A (malonyl-CoA) concentration in Escherichia coli. To address these issues, a truncated plant P450 flavonoid, flavonoid 3?-hydroxylase (tF3?H), was functionally expressed as a fusion protein with a truncated P450 reductase (tCPR) in E. coli. This allowed the engineered E. coli to produce eriodictyol from l-tyrosine by simultaneously coexpressing the fusion protein with tyrosine ammonia lyase (TAL), 4-coumarate-CoA ligase (4CL), chalcone synthase (CHS), and chalcone isomerase (CHI). In addition, metabolic engineering was employed to enhance the availability of malonyl-CoA so as to achieve a new metabolic balance and rebalance the relative expression of genes to enhance eriodictyol accumulation. This approach made the production of eriodictyol 203% higher than that in the control strain. By using these strategies, the production of eriodictyol from l-tyrosine reached 107 mg/liter. The present work offers an approach to the efficient synthesis of other hydroxylated flavonoids from l-tyrosine or even glucose in E. coli. PMID:24610848

Zhu, Saijie; Wu, Junjun; Du, Guocheng

2014-01-01

130

Catalysis with inorganic cations. V. Intramolecular Hetero Diels-Alder versus ene reactions: Effect of magnesium perchlorate on chemoselectivity  

Microsoft Academic Search

The competition between Hetero Diels-Alder (HDA) and intramolecular ene reaction (IER) was tested on (E)1-acetyl-3-arylideneindolin-2-one (5). Under thermal conditions HDA products 6a,b are obtained in a quantitative yield stressing the importance of the configuration of the ?,?-unsaturated carbonyl system on the reactivity. Both reactivity and chemoselectivity are strongly influenced if the reaction is carried out in the presence of magnesium

Giovanni Desimoni; Giuseppe Faita; PierPaolo Righetti; Gianfranco Tacconi

1996-01-01

131

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

132

Synthesis and evaluation of tetramethylguanidinium-polyethylenimine polymers as efficient gene delivery vectors.  

PubMed

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

133

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

134

Efficient tandem synthesis of methyl esters and imines by using versatile hydrotalcite-supported gold nanoparticles.  

PubMed

Efficient basic hydrotalcite (HT)-supported gold nanoparticle (AuNP) catalysts have been developed for the aerobic oxidative tandem synthesis of methyl esters and imines from primary alcohols catalyzed under mild and soluble-base-free conditions. The catalytic performance can be fine-tuned for these cascade reactions by simple adjustment of the Mg/Al atomic ratio of the HT support. The one-pot synthesis of methyl esters benefits from high basicity (Mg/Al = 5), whereas moderate basicity greatly improves imine selectivity (Mg/Al = 2). These catalysts outperform previously reported AuNP catalysts by far. Kinetic studies show a cooperative enhancement between AuNP and the surface basic sites, which not only benefits the oxidation of the starting alcohol but also the subsequent steps of the tandem reactions. To the best of our knowledge, this is the first time that straightforward control of the composition of the support has been shown to yield optimum AuNP catalysts for different tandem reactions. PMID:22893610

Liu, Peng; Li, Can; Hensen, Emiel J M

2012-09-17

135

Amino acid assisted templating synthesis of hierarchical zeolitic imidazolate framework-8 for efficient arsenate removal.  

PubMed

We report the strategy of using the cationic surfactant cetyltrimethylammonium bromide (CTAB) and amino acid L-histidine (His) as co-templates to produce hierarchical ZIF-8 in an aqueous system at room temperature. The hierarchical ZIF-8 had both meso- and microporous structure, resulting in a high mesopore volume as well as specific surface area which can be controlled by the synthesis conditions. We put forward the hypothesis for the formation of a mesoporous structure and the enhancement of the porosity of ZIF-8 that the histidine plays a key role on the stabilization of CTAB micelles and avoiding the production of unexpected by-products therefore promotes the fabrication of pure phase ZIF-8 containing the mesopores interconnected with micropores. The prepared hierarchical ZIF-8 exhibited an excellent performance as a new kind of porous absorbent for efficient removal of the toxic arsenate. PMID:24296611

Wu, Yi-nan; Zhou, Meimei; Zhang, Bingru; Wu, Baozhen; Li, Jie; Qiao, Junlian; Guan, Xiaohong; Li, Fengting

2014-01-21

136

Nonlinear inverse synthesis for high spectral efficiency transmission in optical fibers  

E-print Network

In linear communication channels, spectral components (modes) defined by the Fourier transform of the signal propagate without interactions with each other. In certain nonlinear channels, such as the one modelled by the classical nonlinear Schr\\"odinger equation, there are nonlinear modes (nonlinear signal spectrum) that also propagate without interacting with each other and without corresponding nonlinear cross talk; effectively, in a linear manner. Here, we describe in a constructive way how to introduce such nonlinear modes for a given input signal. We investigate the performance of the nonlinear inverse synthesis (NIS) method, in which the information is encoded directly onto the continuous part of the nonlinear signal spectrum. This transmission technique, combined with the appropriate distributed Raman amplification, can provide an effective eigenvalue division multiplexing with high spectral efficiency, thanks to highly suppressed channel cross talk. The proposed NIS approach can be integrated with any...

Le, Son Thai; Turitsyn, Sergei K

2014-01-01

137

Efficient assembly of threaded molecular machines for sequence-specific synthesis.  

PubMed

We report on an improved strategy for the preparation of artificial molecular machines that can pick up and assemble reactive groups in sequence by traveling along a track. In the new approach a preformed rotaxane synthon is attached to the end of an otherwise fully formed strand of building blocks. This "rotaxane-capping" protocol is significantly more efficient than the "final-step-threading" method employed previously and enables the synthesis of threaded molecular machines that operate on extended oligomer, and potentially polymer, tracks. The methodology is exemplified through the preparation of a machine that adds four amino acid building blocks from a strand in sequence, featuring up to 20-membered ring native chemical ligation transition states. PMID:24678971

De Bo, Guillaume; Kuschel, Sonja; Leigh, David A; Lewandowski, Bartosz; Papmeyer, Marcus; Ward, John W

2014-04-16

138

Highly efficient total synthesis of the marine natural products (+)-avarone, (+)-avarol, (-)-neoavarone, (-)-neoavarol and (+)-aureol.  

PubMed

Biologically important and structurally unique marine natural products avarone (1), avarol (2), neoavarone (3), neoavarol (4) and aureol (5), were efficiently synthesized in a unified manner starting from (+)-5-methyl-Wieland-Miescher ketone 10. The synthesis involved the following crucial steps: i) Sequential BF(3)Et(2)O-induced rearrangement/cyclization reaction of 2 and 4 to produce 5 with complete stereoselectivity in high yield (2 --> 5 and 4 --> 5); ii) strategic salcomine oxidation of the phenolic compounds 6 and 8 to derive the corresponding quinones 1 and 3 (6 --> 1 and 8 --> 3); and iii) Birch reductive alkylation of 10 with bromide 11 to construct the requisite carbon framework 12 (10 + 11 --> 12). An in vitro cytotoxicity assay of compounds 1-5 against human histiocytic lymphoma cells U937 determined the order of cytotoxic potency (3 > 1 > 5 > 2 > 4) and some novel aspects of structure-activity relationships. PMID:17992684

Sakurai, Junji; Oguchi, Takamasa; Watanabe, Kazuhiro; Abe, Hideki; Kanno, Syu-ichi; Ishikawa, Masaaki; Katoh, Tadashi

2008-01-01

139

ACCESS 3. Approximation concepts code for efficient structural synthesis: User's guide  

NASA Technical Reports Server (NTRS)

A user's guide is presented for ACCESS-3, a research oriented program which combines dual methods and a collection of approximation concepts to achieve excellent efficiency in structural synthesis. The finite element method is used for structural analysis and dual algorithms of mathematical programming are applied in the design optimization procedure. This program retains all of the ACCESS-2 capabilities and the data preparation formats are fully compatible. Four distinct optimizer options were added: interior point penalty function method (NEWSUMT); second order primal projection method (PRIMAL2); second order Newton-type dual method (DUAL2); and first order gradient projection-type dual method (DUAL1). A pure discrete and mixed continuous-discrete design variable capability, and zero order approximation of the stress constraints are also included.

Fleury, C.; Schmit, L. A., Jr.

1980-01-01

140

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-Bregeot, Nicolas; Raushel, Jessica; Sandrock, Deidre L.

2012-01-01

141

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

142

Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in pigs.  

PubMed

From the observation that fasting heat production includes the cost of body protein resynthesis and the evidence that protein resynthesis is included in the regression estimate of protein retention efficiency it is conjectured that the estimate of maintenance from fasting heat production must be conceptually equal to the regression intercept estimate of maintenance plus the cost of body protein resynthesis. Experimental evidence for comparable situations shows an approximate observational equality in agreement with the conjectured conceptual equality. This approximate equality implies that the theoretical (stiochiometric) efficiency of protein synthesis should be used in conjunction with the estimate of maintenance from fasting heat production for the prediction of growth energy requirements. The approximate maintenance equalities suggest furthermore approximate equality of theoretical fat synthesis efficiency and regression fat retention efficiency. This conjecture is also supported by experimental evidence. Some practical nutrition and pig breeding implications of the foregoing conclusions are indicated. PMID:18684340

Roux, Carl Z

2009-03-01

143

Evaluation of silica-H2SO4 as an efficient heterogeneous catalyst for the synthesis of chalcones.  

PubMed

We report an efficient silica-H2SO4 mediated synthesis of a variety of chalcones that afforded the targeted compounds in very good yield compared to base catalyzed solvent free conditions as well as acid or base catalyzed refluxing conditions. PMID:23966089

Sultan, Aeysha; Raza, Abdul Rauf; Abbas, Muhammad; Khan, Khalid Mohammed; Tahir, Muhammad Nawaz; Saari, Nazamid

2013-01-01

144

Efficient synthesis of biscarbazoles by palladium-catalyzed twofold C-N coupling and C-H activation reactions.  

PubMed

A new and efficient strategy for the synthesis of 3,9'- and 2,9'-biscarbazoles was developed. Our strategy relies on the cyclization of 1,1'-biphenyl-2,2'-diyl bis(trifluoromethanesulfonate) with 4- or 3-anisidine, transformation of the methoxy to a triflate group and subsequent oxidative Pd-catalyzed cyclization with various anilines. PMID:24622946

Hung, Tran Quang; Thang, Ngo Ngoc; Hoang, Do Huy; Dang, Tuan Thanh; Villinger, Alexander; Langer, Peter

2014-04-28

145

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

146

Nonlinear inverse synthesis for high spectral efficiency transmission in optical fibers  

NASA Astrophysics Data System (ADS)

In linear communication channels, spectral components (modes) defined by the Fourier transform of the signal propagate without interactions with each other. In certain nonlinear channels, such as the one modelled by the classical nonlinear Schr\\"odinger equation, there are nonlinear modes (nonlinear signal spectrum) that also propagate without interacting with each other and without corresponding nonlinear cross talk; effectively, in a linear manner. Here, we describe in a constructive way how to introduce such nonlinear modes for a given input signal. We investigate the performance of the nonlinear inverse synthesis (NIS) method, in which the information is encoded directly onto the continuous part of the nonlinear signal spectrum. This transmission technique, combined with the appropriate distributed Raman amplification, can provide an effective eigenvalue division multiplexing with high spectral efficiency, thanks to highly suppressed channel cross talk. The proposed NIS approach can be integrated with any modulation formats. Here, we demonstrate numerically the feasibility of merging the NIS technique in a burst mode with high spectral efficiency methods, such as orthogonal frequency division multiplexing and Nyquist pulse shaping with advanced modulation formats (e.g., QPSK, 16QAM, and 64QAM), showing a performance improvement up to 4.5 dB, which is comparable to results achievable with multi-step per span digital back propagation.

Le, Son Thai; Prilepsky, Jaroslaw E.; Turitsyn, Sergei K.

2014-11-01

147

Formal Synthesis of 7-Methoxymitosene and Synthesis of its Analog via a Key PtCl2-Catalyzed Cycloisomerization  

PubMed Central

A formal synthesis of 7-methoxymitosene is achieved via a key platinum-catalyzed cycloisomerization. The precursor for the Pt catalysis, a fully functionalized benzene intermediate, was prepared via a regioselective electrophilic bromination followed by a chemoselective Sonogashira cross-coupling. It underwent the PtCl2-catalyzed cycloisomerization smoothly albeit its hindered and highly electron-rich nature. Analogs of 7-methoxymitosene can be accessed in an expedient manner by following a similar synthetic sequence. PMID:22765272

Liu, Lianzhu; Wang, Yanzhao

2012-01-01

148

Stereoselective, nitro-Mannich/lactamisation cascades for the direct synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles  

PubMed Central

Summary A versatile nitro-Mannich/lactamisation cascade for the direct stereoselective synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles has been developed. A highly enantioenriched substituted 5-nitropiperidin-2-one was synthesised in a four component one-pot reaction combining an enantioselective organocatalytic Michael addition with the diastereoselective nitro-Mannich/lactamisation cascade. Protodenitration and chemoselective reductive manipulation of the heterocycles was used to install contiguous and fully substituted stereocentres in the synthesis of substituted piperidines. PMID:22563355

Jakubec, Pavol; Cockfield, Dane M; Helliwell, Madeleine; Raftery, James

2012-01-01

149

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

150

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

151

Novel low temperature synthesis of ZnO nanostructures and its efficient field emission property  

SciTech Connect

We have developed a novel, simple and cost effective wet chemical synthetic route for the production of ZnO nanoneedles and nanoflowers at low temperature. The synthesis process does not require any surfactant, template or pre-seeding. The synthesized ZnO nanoneedles have very sharp tips with their lengths in the range 2-3 {mu}m, while for the case of nanoflowers, the nanoneedles were bunched together. X-ray diffraction study and X-ray photoelectron spectroscopic studies confirmed the formation of pure ZnO phase. Studies on the electron field emission property of the grown nanostructures showed that they are very efficient field emitter. The turn-on fields and the threshold fields are 3.6 V/{mu}m, 4.4 V/{mu}m and 5.4 V/{mu}m, 6.8 V/{mu}m for the ZnO nanoneedles and ZnO nanoflowers, respectively. The enhanced field emission property was attributed to the presence of sharp tips of the nanostructures.

Maiti, U.N.; Ahmed, Sk.F. [Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700032 (India); Mitra, M.K. [Nanoscience and Technology Center, Jadavpur University, Kolkata 700032 (India); Chattopadhyay, K.K. [Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700032 (India); Nanoscience and Technology Center, Jadavpur University, Kolkata 700032 (India)], E-mail: kalyan_chattopadhyay@yahoo.com

2009-01-08

152

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

153

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

154

Efficient synthesis of ferrocenylenones by Friedel–Crafts acylation with EtAlCl 2–Me 3Al  

Microsoft Academic Search

Efficient synthesis of ferrocenylenones using a Friedel–Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and ?-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2–Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method.

Özdemir Dogan; Volkan ?enol; Serhat Zeytinci; Hasan Koyuncu; Adnan Bulut

2005-01-01

155

Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes``Super-Growth''  

Microsoft Academic Search

We demonstrate an extremely efficient chemical vapour deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water [1]. Water-stimulated enhanced catalytic activity results in massive growth of super-dense 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

Kenji Hata

2005-01-01

156

Efficient and scalable one-pot synthesis of 2,4-dienols from cycloalkenones: optimized total synthesis of valerenic acid.  

PubMed

A mild and selective one-pot procedure to provide 2,4-dienols from simple cycloalkenones in high yields is described. This transformation is based on the in situ formation of acid-labile allylic alcohols, which on treatment with trifluoroacetic acid undergo a formal [1,3]-hydroxy migration to form diastereo- and enantiomerically enriched 2,4-dienols. The usefulness of this protocol is demonstrated in a short synthesis of valerenic acid. PMID:21894886

Ramharter, Juergen; Mulzer, Johann

2011-10-01

157

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

158

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

159

Scalable Synthesis of Cortistatin A and Related Structures  

PubMed Central

Full details are provided for an improved synthesis of cortistatin A and related structures as well as the underlying logic and evolution of strategy. The highly functionalized cortistatin A-ring embedded with a key heteroadamantane was synthesized by a simple and scalable 5-step sequence. A chemoselective, tandem geminal dihalogenation of an unactivated methyl group, a reductive fragmentation/trapping/elimination of a bromocyclopropane, and a facile chemoselective etherification reaction afforded the cortistatin A core, dubbed “cortistatinone”. A selective ?16-alkene reduction with Raney Ni provided cortistatin A. With this scalable and practical route, copious quantities of cortistatinone, ?16-cortistatin A-the equipotent direct precursor to cortistatin A, and its related analogs were prepared for further biological studies. PMID:21539314

Shi, Jun; Manolikakes, Georg; Yeh, Chien-Hung; Guerrero, Carlos A.; Shenvi, Ryan A.; Shigehisa, Hiroki

2011-01-01

160

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

161

Unique catalysis of gold nanoparticles in the chemoselective hydrogenolysis with H2: cooperative effect between small gold nanoparticles and a basic support.  

PubMed

Gold nanoparticles on hydrotalcite act as a heterogeneous catalyst for the chemoselective hydrogenolysis of various allylic carbonates to the corresponding terminal alkenes using H(2) as a clean reductant. The combination of gold nanoparticles and basic supports elicited significantly unique and selective catalysis in the hydrogenolysis. PMID:22641125

Noujima, Akifumi; Mitsudome, Takato; Mizugaki, Tomoo; Jitsukawa, Koichiro; Kaneda, Kiyotomi

2012-07-01

162

An understanding of chemoselective hydrogenation on crotonaldehyde over Pt(1 1 1) in the free energy landscape: The microkinetics study based on first-principles calculations  

Microsoft Academic Search

Microkinetic model is developed in the free energy landscape based on density functional theory (DFT) to quantitatively investigate the reaction mechanism of chemoselective partial hydrogenation of crotonaldehyde to crotyl alcohol over Pt(111) at the temperature of 353K. Three different methods (mobile, immobile and collision theory models) were carried out to obtain free energy barrier of adsorption\\/desorption processes. The results from

Xiao-Ming Cao; Robbie Burch; Chris Hardacre; P. Hu

2011-01-01

163

I. Development of Metal-Mediated SPOT-Synthesis Methods for the Efficient Construction of Small-Molecule Macroarrays. II. Design and Synthesis of Novel Bacterial Biofilm Inhibitors  

NASA Astrophysics Data System (ADS)

I. The use of small molecule probes to explore biological phenomena has become a valuable tool in chemical biology. As a result, methods that permit the rapid synthesis and biological evaluation of such compounds are highly sought-after. The small molecule macroarray represents one such approach for the synthesis and identification of novel bioactive agents. Macroarrays are readily constructed via the SPOT-synthesis technique on planar cellulose membranes, yielding spatially addressed libraries of ˜10-1000 unique compounds. We sought to expand the arsenal of chemical reactions compatible with this solid-phase platform, and developed highly efficient SPOT-synthesis protocols for the Mizoroki-Heck, Suzuki-Miyaura, and copper-catalyzed azide-alkyne cycloaddition reaction. We demonstrated that these metal-mediated reactions can be implemented, either individually or sequentially, for the efficient construction of small molecules in high purity on rapid time scales. Utilizing these powerful C-C and C-N bond forming coupling reactions, we constructed a series of macroarrays based on novel stilbene, phenyl-naphthalene, and triazole scaliblds. Subsequent biological testing of the stilbene and phenyl-naphthalene libraries revealed several potent antagonists and agonists, respectively, of the quorum sensing (QS) receptor LuxR in Vibrio fischeri. II. Bacteria living within biofilms are notorious for their resistance to known antibiotic agents, and constitute a major human health threat. Methods to attenuate biofilm growth would have a significant impact on the management of bacterial infections. Despite intense research efforts, small molecules capable of either inhibiting or dispersing biolilms remain scarce. We utilized natural products with purported anti-biofilm or QS inhibitory activity as sources of structural insight to guide the synthesis of novel biofilm modulators with improved activities. These studies revealed 2-aminobenzimidazole derivatives as highly potent biofilm inhibitors and dispersers in the opportunistic pathogen Pseudomonas aeruginosa. Studies of second-generation 2-aminobenzimidazoles revealed important structure-activity relationships that guided the design of yet more potent analogs. These compounds are amongst the most potent inhibitors of biofilm formation in wild-type P. aeruginosa to be reported. Mechanistic studies of the most active compounds suggest that QS inhibition is one pathway by which 2-aminobenzimidazoles modulate biofilm growth.

Frei, Reto

164

Zeolites. Efficient and Eco-friendly Catalysts for the Synthesis of Benzimidazoles  

Microsoft Academic Search

Summary.  A superior method of synthesis of 2-substituted benzimidazoles by means of the heterogeneous catalysis of synthetic and natural\\u000a zeolites in the reaction of 1,2-diaminobenzene with acid chlorides is described.

Majid M. Heravi; Mahmood Tajbakhsh; Amir N. Ahmadi; Bagher Mohajerani

2006-01-01

165

Lipases and (R)-oxynitrilases: useful tools in organic synthesis.  

PubMed

The use of enzymes in organic solvents is currently of special relevance for the preparation of products of high added value. Lipases are the enzymes that have shown the greatest utility through enzymatic transesterification reactions. Over the last few years, we have shown the value of the enzymatic aminolysis and ammonolysis reactions for the preparation of amides and for the resolution of esters and amines. We have shown that the enzymatic alkoxycarbonylation is also of great utility in chemoselective reactions of natural products. Lyases, enzymes much less exploited in organic synthesis, are proving increasingly interesting, especially the use of (R)-oxynitrilases for the synthesis of optically active cyanohydrins. PMID:12142141

Gotor, Vicente

2002-06-13

166

Effective Procedure for Selective Ammonolysis of Monosubstituted Oxiranes: Application to E7389 Synthesis.  

PubMed

A highly effective procedure is reported to synthesize 1,2-aminoalcohols by regio- and chemo-selective ammonolysis of monosubstituted epoxides. Additive- and concentration-effects were studied, revealing that: (1) methanesulfonic acid is most effective among the additives tested and (2) formation of bis-adducts is practically eliminated at [C] synthesis of potent anti-tumor compound E7389. PMID:19050739

Kaburagi, Yosuke; Kishi, Yoshito

2007-12-01

167

Effective Procedure for Selective Ammonolysis of Monosubstituted Oxiranes: Application to E7389 Synthesis  

PubMed Central

A highly effective procedure is reported to synthesize 1,2-aminoalcohols by regio- and chemo-selective ammonolysis of monosubstituted epoxides. Additive- and concentration-effects were studied, revealing that: (1) methanesulfonic acid is most effective among the additives tested and (2) formation of bis-adducts is practically eliminated at [C] ? 40 mM. The optimum condition thus identified was successfully applied to the final step of the synthesis of potent anti-tumor compound E7389. PMID:19050739

Kaburagi, Yosuke; Kishi, Yoshito

2007-01-01

168

Enzymatic resolution of racemates with a 'remote' stereogenic center as an efficient tool in drug, flavor and vitamin synthesis.  

PubMed

The enantioselective recognition of 'remote' stereogenic centers represents a scientific task in organic chemistry being also of current interest in the pharmaceutical industry. This is due to a range of pharmaceutically relevant molecules or intermediates thereof bearing a stereogenic center, which is separated from the functional group by a larger non-chiral moiety such as, for example, a longer sequence of bonds of at least three carbon or hetero-atoms or by a planar aromatic moiety. Notably, biocatalysis turned out to provide an excellent solution for a range of challenging syntheses in this field. For example, efficient enzymatic resolution processes of racemates with such a 'remote' stereogenic center were developed for the synthesis of pelitrexol, lasofoxifene and (S)-monastrol. In general, good yields accompanied by high enantioselectivities were obtained, thus underlining the tremendous potential of enzymes to recognize and enantioselectively transform enantiomers of racemates with 'remote' stereogenic centers. Such or similar types of stereoselective recognitions of 'remote' stereogenic centers by means of enzymes have been also reported in the field of flavor and vitamin synthesis. Thus, biocatalysis represents a promising solution for the efficient approach to enantiomerically pure complex chiral molecules with stereogenic centers being located apart from the functional group, and it can be expected that enzymatic resolution will be increasingly applied when searching for an efficient and also technically feasible process for also novel complex chiral molecules bearing a 'remote' stereogenic center. PMID:25082510

Alfaro Blasco, Maria; Gröger, Harald

2014-10-15

169

Surface-bound cytomimetic assembly based on chemoselective and biocompatible immobilization and further modification of intact liposome.  

PubMed

A surface-bound cytomimetic assembly based on chemically selective and biocompatible immobilization and further modification of intact liposome is described. Liposomes carrying PEG-triphenylphosphine were chemoselectively immobilized onto azide-modified glass slides through Staudinger ligation, followed by modification with azide-modified lactose as a model biomolecule through Staudinger ligation to afford the surface-bound cytomimetic assembly. The intact liposome immobilized and modified and its protein binding activity were confirmed by fluorescence imaging, fluorescent dye releasing kinetics, and AFM techniques. The resultant surface-bound cytomimetic assembly showed sustained stability and fluorescent dye releasing kinetics and specific protein binding activity. The reported method provides a robust platform for preparation of a complex immobilized liposome system with multifunctional components, which mimics the cell surface in both geographical and content features and thus will find important biomedical applications. PMID:20939526

Ma, Yong; Zhang, Hailong; Sun, Xue-Long

2010-11-17

170

Surface-Bound Cytomimetic Assembly Based on Chemoselective and Biocompatible Immobilization and Further Modification of Intact Liposome  

PubMed Central

A surface-bound cytomimetic assembly based on chemically selective and biocompatible immobilization and further modification of intact liposome is described. Liposome carrying PEG-triphenylphosphine was chemoselectively immobilized onto azide-modified glass slide through Staudinger ligation and followed by modification with azide-modified lactose as model biomolecule through Staudinger ligation to afford surface-bound cytomimetic assembly. The intact liposome immobilized and modified and its protein binding activity were confirmed by fluorescence imaging, fluorescent dye releasing kinetics and AFM techniques. The resultant surface-bound cytomimetic assembly showed sustained stability and fluorescent dye releasing kinetics and specific protein binding activity. The reported method provides a robust platform for preparation of complex immobilized liposome system with multifunctional components, which mimics cell surface in both geographical and content features and thus will find important biomedical applications PMID:20939526

Ma, Yong; Zhang, Hailong; Sun, Xue-Long

2010-01-01

171

Chemoselective Nitro Group Reduction and Reductive Dechlorination Initiate Degradation of 2-Chloro-5-Nitrophenol by Ralstonia eutropha JMP134  

PubMed Central

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. PMID:10347008

Schenzle, Andreas; Lenke, Hiltrud; Spain, Jim C.; Knackmuss, Hans-Joachim

1999-01-01

172

Synthesis and SAR of novel imidazoles as potent and selective cannabinoid CB2 receptor antagonists with high binding efficiencies.  

PubMed

The synthesis and structure-activity relationship studies of imidazoles are described. The target compounds 6-20 represent a novel chemotype of potent and CB(2)/CB(1) selective cannabinoid CB(2) receptor antagonists/inverse agonists with very high binding efficiencies in combination with favourable logP and calculated polar surface area values. Compound 12 exhibited the highest CB(2) receptor affinity (K(i)=1.03 nM) in this series, as well as the highest CB(2)/CB(1) subtype selectivity (>9708-fold). PMID:20031412

Lange, Jos H M; van der Neut, Martina A W; Wals, Henri C; Kuil, Gijs D; Borst, Alice J M; Mulder, Arie; den Hartog, Arnold P; Zilaout, Hicham; Goutier, Wouter; van Stuivenberg, Herman H; van Vliet, Bernard J

2010-02-01

173

Efficient synthesis of gluco-oligosaccharides and alkyl-glucosides by transglycosylation activity of ?-glucosidase from Sclerotinia sclerotiorum  

Microsoft Academic Search

An extracellular ?-glucosidase (?-glu x) from Sclerotinia sclerotiorum was used as catalyst for the synthesis of gluco-oligosaccharides (GOSs) and alkyl-glucosides. The purified ?-glu x was not\\u000a regiospecific for ?(1?4) linkages in either hydrolysis or transglycosylation catalysed-reactions. It efficiently synthesized\\u000a GOSs from cellobiose, gentiobiose and methyl ?-d-glucoside by transglycosylation. At optimal conditions, 119 mg\\/ml of GOSs (?\\u000a ?33%) were formed over 9 h

Issam Smaali; Thierry Maugard; Ferid Limam; Marie-Dominique Legoy; Nejib Marzouki

2007-01-01

174

A practical and efficient synthesis of the C-16-C-28 spiroketal fragment (CD) of the spongistatins.  

PubMed

A practical and efficient route to the CD spiroketal (C-16-C-28) of the spongistatins is reported. Two stereocenters are introduced from chiral building blocks with the remainder introduced by substrate-controlled transformations. The key beta-keto-1,3-dithiane intermediate is generated by a dithiol conjugate addition to an ynone and the 1,3-dithiane unit in the C-ring plays a key role in the spiroketalization and subsequent epimerization. The synthesis requires 24 steps, with a longest linear sequence of 19 steps in an overall yield of 14.5% (for the longest linear sequence). [reaction: see text] PMID:14653681

Gaunt, Matthew J; Hook, David F; Tanner, Huw R; Ley, Steven V

2003-12-11

175

Efficient Microwave-assisted One-pot Three-component Synthesis of 2,3-Disubstituted Benzofurans under Sonogashira Conditions  

PubMed Central

An efficient one-pot method for the synthesis of 2,3-disubstituted benzo[b]furans from commercially available 2-iodophenols, terminal acetylenes and aryl iodides has been developed utilizing Sonogashira reaction conditions. After an initial Sonogashira coupling of the 2-iodophenol with the terminal alkyne, cyclization involving the aryl iodide provides the 2,3-disubstituted benzo[b]furan in good to excellent yields. The use of microwave irradiation shortens the reaction times and minimizes the side products. This methodology is especially useful for the construction of libraries of highly substituted benzo[b]furans and their analogues. PMID:23504237

Markina, Nataliya A.; Chen, Yu; Larock, Richard C.

2013-01-01

176

An Efficient Synthesis of Dopamine Transporter Tracer [18F]FECNT1  

PubMed Central

A simple synthesis of the dopamine transporter ligand [18F]FECNT with high radiochemical yield and short synthesis time, suitable for routine production is reported. Reaction of 2?-carbomethoxy-3?-(4-chlorophenyl)nortropane with [18F]2-fluoroethyl triflate ([18F]FEtOTf) at room temperature for 4 min. provided [18F]FECNT in 84% decay corrected radiochemical yield. Since [18F]FEtOTf was prepared from [18F]2-fluoroethyl bromide that was isolated from its starting material, formation of unwanted side products and the amount of expensive precursor used could be greatly reduced. The overall radiochemical yields of [18F]FECNT were 40% (n=29) and the total synthesis time was ca. 100 min. The average specific activity of [18F]FECNT was 377.4 GBq/µmol (10.2 Ci/µmol). PMID:23208243

Murali, D.; Barnhart, T.E.; Vandehey, N.T.; Christian, B.T.; Nickles, R.J.; Converse, A.K.; Larson, J.A.; Holden, J.E.; Schneider, M.L.; DeJesus, O.T.

2012-01-01

177

An efficient synthesis of pyrazole chalcones under solvent free conditions at room temperature  

Microsoft Academic Search

An easy, safe, solvent free and effective method for the synthesis of pyrazole-substituted chalcones has been achieved by grinding pyrazole aldehydes and acetophenones in the presence of activated barium hydroxide (C-200) in high yield within short span of time. All reactions were carried out just by grinding the two reactants in the presence of activated barium hydroxide (C-200). Results are

Parvin Kumar; Sunil Kumar; Khalid Husain; Ashwani Kumar

2011-01-01

178

Efficient room-temperature synthesis of a highly strained carbon nanohoop fragment of buckminsterfullerene  

NASA Astrophysics Data System (ADS)

Warped carbon-rich molecules have captured the imagination of scientists across many disciplines. Owing to their promising materials properties and challenging synthesis, strained hydrocarbons are attractive targets that push the limits of synthetic methods and molecular design. Herein we report the synthesis and characterization of [5]cycloparaphenylene ([5]CPP), a carbon nanohoop that can be envisaged as an open tubular fragment of C60, the equator of C70 fullerene and the unit cycle of a [5,5] armchair carbon nanotube. Given its calculated 119 kcal mol-1 strain energy and severely distorted benzene rings, this synthesis, which employs a room-temperature macrocyclization of a diboronate precursor, single-electron reduction and elimination, is remarkably mild and high yielding (27% over three steps). Single-crystal X-ray diffraction data were obtained to confirm its geometry and previously disputed benzenoid character. First and second pseudoreversible oxidation and reduction events were observed via cyclic voltammetry. The ease of synthesis, high solubility and narrowest optical HOMO/LUMO gap of any para-polyphenylene synthesized make [5]CPP a desirable new material for organic electronics.

Evans, Paul J.; Darzi, Evan R.; Jasti, Ramesh

2014-05-01

179

Efficient synthesis of 1,3,7-substituted xanthines by a safety-catch protection strategy  

E-print Network

of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7 of pharmacologically active compounds with well-known ac- tivity as adenosine receptor antagonists, phosphodiesterase-, or 7-positions. Unfortunately, the synthesis of such compounds by the classic Traube4 method from 6

van Aalten, Daan

180

MIXSyn: An Efficient Logic Synthesis Methodology for Mixed XOR-AND/OR Dominated Circuits  

E-print Network

-intensive portions of the logic circuit. The second step is a library-free technology mapping that enhances design of the library is usually pre-determined by the standard cell full custom design carried out off-line. Instead, on the average, with respect to state-of-art academic and commercial synthesis tools, respectively. MIXSyn

De Micheli, Giovanni

181

Rapid microwave synthesis of indium filled skutterudites: An energy efficient route to high performance thermoelectric materials  

SciTech Connect

Graphical abstract: Filled skutterudites are promising thermoelectric materials. We report the microwave assisted synthesis of CoSb{sub 3} and In{sub 0.2}Co{sub 4}Sb{sub 12}. This method reduces the calcination time for skutterudite phase formation from 2 days to 2 min, thereby significantly reducing the time and energy needed to produce materials suitable for property and device testing. Highlights: Black-Right-Pointing-Pointer The microwave assisted solid state synthesis of CoSb{sub 3} and In{sub 0.2}Co{sub 4}Sb{sub 12} is reported. Black-Right-Pointing-Pointer This method allows the calcination time to be reduced from 2 days to 2 min. Black-Right-Pointing-Pointer Physical properties of microwave samples match those prepared conventionally. -- Abstract: Filled skutterudites are promising thermoelectric materials due to reduced thermal conductivity upon inserting a guest atom or 'rattler' into the CoSb{sub 3} structure. By using an indium rattler dimensionless Figure of Merit (ZT) values >1 at 650 K have been reported. The conventional synthesis of these compounds typically takes several days ({approx}3 days) to obtain the final well-sintered material for property measurements. We report here a microwave-assisted synthesis method that reduces the initial calcination time from 2 days to 2 min. This route significantly reduces the time needed to produce materials suitable for property and device testing.

Biswas, Krishnendu, E-mail: krishnendu.biswas@oregonstate.edu [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States)] [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States); Muir, Sean, E-mail: muirs@onid.orst.edu [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States)] [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States); Subramanian, M.A., E-mail: mas.subramanian@oregonstate.edu [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States)

2011-12-15

182

Controlled synthesis, growth mechanism and highly efficient solar photocatalysis of nitrogen-doped bismuth subcarbonate hierarchical nanosheets architectures.  

PubMed

The synthesis and self-assembly of hierarchical architectures from nanoscale building blocks with unique morphology, orientation and dimension have opened up new opportunities to enhance their functional performances and remain a great challenge. This work represents tunable synthesis of various types of 3D monodisperse in situ N-doped (BiO)(2)CO(3) hierarchical architectures composed of 2D single-crystal nanosheets with dominant (001) facets by a one-pot template-free hydrothermal method from bismuth citrate and ammonia solution. Depending on the concentration of ammonia solution, the morphology of N-doped (BiO)(2)CO(3), including dandelion-like, hydrangea-like and peony flower-like microspheres, can be selectively constructed due to different self-assembly patterns of nanosheets. It was revealed that the ammonia played dual roles in the formation of N-doped (BiO)(2)CO(3) architectures. One is to hydrolyze bismuth citrate, and the other is to behave as a nitrogen doping source. The in situ doped nitrogen substituted for oxygen in (BiO)(2)CO(3) and subsequently narrowed the band gap, making N-doped (BiO)(2)CO(3) visible light active. Due to the special nanosheets architectures, the prepared various N-doped (BiO)(2)CO(3) materials exhibited especially efficient photocatalytic activity and high durability for the removal of NO in air under both visible and UV light irradiation. Based on the direct observation of the growth process with respect to phase structure, chemical composition and morphological structure, a novel growth mechanism is revealed, which involves a unique multistep pathway, including reaction-nucleation, aggregation, crystallization, dissolution-recrystallization, and Ostwald ripening. The facile synthesis approach and the proposed growth mechanism could provide new insights into the design and controlled synthesis of inorganic hierarchical materials with new or enhanced properties. PMID:22622668

Dong, Fan; Sun, Yanjuan; Ho, Wing-Kei; Wu, Zhongbiao

2012-07-21

183

Rapid and efficient synthesis of soluble graphene nanosheets using N-methyl-p-aminophenol sulfate as a reducing agent  

NASA Astrophysics Data System (ADS)

Mass production of soluble graphene still remains a challenge, although several methodologies have been proposed. Here we report a rapid and efficient method for the synthesis of soluble graphene nanosheets (GNSs) with long-term dispersion stability in both aqueous and common organic solvents. Within only 12 min at 95?°C, exfoliated graphite oxide in ammonia solution (pH 10) was reduced to soluble GNSs using N-methyl-p-aminophenol sulfate (metol) as a reducing agent without external stabilizers. The prepared GNSs were characterized by different techniques and a comparison of metol and hydrazine hydrate as reducing agents was made. The results indicated that, with the advantages of being rapid, efficient, inexpensive and relatively environmentally friendly, the reduction of graphite oxide into soluble GNSs by metol is a promising substitute for hydrazine hydrate in the mass production of soluble GNSs.

Wang, Xialie; Wen, Xiaohong; Liu, Zhanpeng; Tan, Yi; Yuan, Ye; Zhang, Ping

2012-12-01

184

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

PubMed

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

2014-07-01

185

Efficient end-capping synthesis of neutral donor-acceptor [2]rotaxanes under additive-free and mild conditions.  

PubMed

Efficient end-capping synthesis of neutral donor-acceptor (D-A) [2]rotaxanes without loading any catalysts or activating agents was achieved by utilizing high reactivity of a pentacoordinated hydrosilane toward salicylic acid derivatives. As components of [2]rotaxanes, an electron-deficient naphthalenediimide-containing axle with a salicylic acid terminus and several electron-rich bis(naphthocrown) ether macrocycles were employed. End-capping reactions with the pentacoordinated hydrosilane underwent smoothly even at low temperature to afford the corresponding [2]rotaxanes in good yields. A [2]rotaxane containing bis-1,5-(dinaphtho)-38-crown-10 ether as a wheel molecule was synthesized and isolated in 84?% yield by the end-capping at -10?°C, presenting the highest yield ever reported for the end-capping synthesis of a neutral D-A [2]rotaxane. It was found that the yields of the [2]rotaxanes in the end-capping reactions were almost parallel to the formation ratios of the corresponding pseudo[2]rotaxanes estimated by utilizing model systems. These results indicate that the end-capping reaction using the pentacoordinated hydrosilane proceeded without perturbing the threading process, and most of the pseudo[2]rotaxanes underwent efficient end-capping reaction even at low temperature. PMID:25284148

Domoto, Yuya; Sase, Shohei; Goto, Kei

2014-11-24

186

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

PubMed

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

2015-02-01

187

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

188

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

189

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

PubMed

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

2014-09-01

190

An efficient, mild and solvent-free synthesis of benzene ring acylated harmalines.  

PubMed

A facile synthesis of a series of benzene ring acylated analogues of harmaline has been achieved by Friedel-Crafts acylation under solvent-free conditions at room temperature using acyl halides/acid anhydrides and AlCl3. The reaction afforded 10- and 12-acyl analogues of harmaline in good yield, along with minor quantities of N-acyl-tryptamines and 8-acyl analogues of N-acyltryptamines. PMID:20110872

Begum, Sabira; Zubair, Farhat; Nawazish, Ali Syed; Siddiqui, Bina Shaheen

2010-01-01

191

A highly efficient, simple, and ecofriendly microwave-induced synthesis of indolyl chalcones and pyrazolines  

Microsoft Academic Search

One-pot synthesis of indolyl chalcones (3a–c) employing indole-3-carboxaldehyde (1) and heteroaryl active methyl compounds (2a–c) under microwave irradiation is described. The indolyl chalcones (3a–c) are transformed into medicinally important pyrazolines (5a–f) using different hydrazines. Application of microwave irradiation leads to many remarkable advantages, such as solvent- and catalyst-free reaction conditions, simple work up procedure, shorter reaction time, in addition to

Zeba N. Siddiqui; Farheen Farooq; T. N. Mohammed Musthafa

2011-01-01

192

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

193

An Efficient Synthesis of (?)-Grandisol Featuring 1,5-Enyne Metathesis  

PubMed Central

An eight step synthesis of (±)-grandisol features a key sequence involving a high-yielding, microwave-assisted enyne metathesis to yield a 1-alkenylcyclobutene that is semihydrogenated to yield a silyl-protected grandisol. Metathesis catalyst screens revealed an intriguing trend whereby substrate conversion correlated strongly with the identity of the ligands on the catalyst. In addition, new reactivity of 1-alkenylcyclobutenes toward hydrogenation is described. PMID:19957923

Graham, Thomas J. A.; Gray, Erin E.; Burgess, James M.; Goess, Brian C.

2009-01-01

194

Synthesis of human growth hormone-releasing hormone via three-fragment serine/threonine ligation (STL).  

PubMed

The synthesis of human growth hormone-releasing hormone (hGH-RH), by the chemoselective serine/threonine ligations (STLs) of three unprotected peptide fragments, is reported. To allow for the multiple-fragment ligation, we chose the Msz (p-(methylsulfinyl)benzyloxycarbonyl) group, which is compatible with the preparation of peptide salicylaldehyde esters via Fmoc-SPPS and readily removed by reductive acidolysis, to protect the serine and threonine residue at the N-terminus. PMID:23884451

Zhang, Yinfeng; Li, Tianlu; Li, Xuechen

2013-09-14

195

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

196

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

197

Chemistry of polyhalogenated nitrobutadienes, 14: Efficient synthesis of functionalized (Z)-2-allylidenethiazolidin-4-ones  

PubMed Central

Summary The reaction of mercaptoacetic acid esters with pentachloro-2-nitro-1,3-butadiene (1) provides an appropriate precursor for the synthesis of special thiazolidin-4-ones. Applying different anilines as the second constituent for the requisite cyclization step, a series of (Z)-2-allylidenethiazolidin-4-ones was obtained in yields up to 81%. Some subsequent reactions have been examined too, such as the formation of perfunctionalized 1H-pyrazoles upon treatment with hydrazine. Thiazolidinones are as well known for their physiological activities as for their application in optoelectronics. PMID:25161721

Zapol'skii, Viktor A; Namyslo, Jan C; Gjikaj, Mimoza

2014-01-01

198

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

PubMed

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. PMID:25300279

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

2014-10-31

199

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

200

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

201

Highly efficient synthesis of sucrose monolaurate by alkaline protease Protex 6L.  

PubMed

An alkaline protease from Bacillus licheniformis, Protex 6L, was used for synthesis of sucrose monolaurate from sucrose and vinyl laurate in a tert-amyl alcohol/DMSO/water solvent mixture. Introducing sucrose as powder after mixing vinyl laurate with solvent mixture resulted in a higher reaction rate than when sucrose was added as a solution in DMSO. Response surface methodology (RSM) was applied to optimize the major reaction variables, water content, temperature and pH of the lyophilized enzyme. The optimal conditions derived from RSM (3.4% water content, 43 °C and pH of 10.1) provided a high initial reaction rate of 8.66 ± 0.3 mg/ml/h which agreed with the predicted value of 8.70 mg/ml/h. With 1.5 mg-enzyme/ml, 98.0% of the added sucrose was region-selectively converted to 1'-O-lauroylsucrose after 9h. Under the optimized conditions, Protex 6L exhibited a higher productivity for sucrose ester synthesis than Novozym 435 and three other commonly used enzymes. PMID:22305537

Wang, Xinran; Miao, Shida; Wang, Ping; Zhang, Songping

2012-04-01

202

A highly efficient magnetic solid acid catalyst for synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation.  

PubMed

Fe(3)O(4) nanoparticles were prepared by chemical coprecipitation method and subsequently coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction. Grafting of chlorosulfuric acid on the amino-functionalized Fe(3)O(4) nanoparticles afforded sulfamic acid-functionalized magnetic nanoparticles (SA-MNPs). SA-MNPs was found to be a mild and effective solid acid catalyst for the efficient, one-pot, three-component synthesis of 2,4,5-trisubstituted imidazoles under ultrasound irradiation. This protocol afforded corresponding imidazoles in shorter reaction durations, and in high yields. This green procedure has many obvious advantages compared to those reported in the previous literatures, including avoiding the use of harmful catalysts, easy and quick isolation of the products, excellent yields, short routine, and simplicity of the methodology. PMID:23137656

Safari, Javad; Zarnegar, Zohre

2013-03-01

203

Atom-Efficient, Solvent-Free, Green Synthesis of Chalcones by Grinding  

Microsoft Academic Search

An improved Claisen–Schmidt condensation reaction of methyl ketones and aromatic aldehydes can be achieved by grinding at room temperature in the absence of solvents. This process is simple, efficient, economical, and environmentally benign compared to classical reactions.

Nora M. Rateb; Hussein F. Zohdi

2009-01-01

204

The effect of cold exposure of sheep on digestion, rumen turnover time and efficiency of microbial synthesis.  

PubMed

1. Six closely shorn sheep were given brome grass (Bromus inermis) pellets at 1 h intervals and maintained at ambient temperatures of --I to Idegree and 18--21degrees for 28 d. Measurements of digestion were made during the last 10 d of temperature exposure. 2. Cold exposure resulted in a reduction in apparent dry matter (DM) digestibility from 0-482 to 0-450, and of apparent digestibility of organic matter (OM) from 0-511 to 0-477. Neither apparent digestibility nor retention of nitrogen was affected. 3. Apparent digestibility of OM in the rumen decreased from 0-300 to 0-242 with cold exposure, and was highly correlated with turnover time in the rumen of 103Ru, which was used as a particulate marker. 4. The efficiency of microbial synthesis (g N incorporated into microbial cells/kg OM apparently digested) was correlated with the dilution rate of the solute marker (51Cr) and with the turnover time of the particulate marker (103Ru) in the rumen. 5. Digestion in the intestine of DM and OM accounted for significantly more of apparent digestion in the whole gastrointestinal tract for sheep kept in the cold than for sheep kept in the warm. The apparent digestibilities of DM and OM entering the intestine were similar in sheep on both treatments, but significantly more non-ammonia-N was digested in the intestines of cold-exposed sheep. 6. The influence of dilution rate of rumen fluid on the efficiency of synthesis of microbial cells in the rumen is discussed. PMID:952836

Kennedy, P M; Christopherson, R J; Milligan, L P

1976-09-01

205

[BPy]HSO4 Acidic Ionic Liquid as a Novel, Efficient, and Environmentally Benign Catalyst for Synthesis of 1,5?Benzodiazepines under Mild Conditions  

Microsoft Academic Search

A novel and simple ionic liquid methodology for the synthesis of 1,5?benzodiazepines is described. 1?Butylpyridinium hydrogen sulphate ([BPy]HSO4), an acidic room?temperature ionic liquid, as a novel and efficient catalyst, was synthesized and used in the preparation of a series of 1,5?benzodiazepine derivatives by the reaction of o?phenylenediamine with chalcones under mild conditions. This method is easy, efficient, environmentally friendly, economical,

Yuying Du; Fuli Tian; Wenzhi Zhao

2006-01-01

206

Highly efficient and versatile synthesis of lactams and N-heterocycles via Al(OTf)3-catalyzed cascade cyclization and ionic hydrogenation reactions.  

PubMed

The discovery and development of an efficient and versatile method for the synthesis of N-substituted lactams is described. Pyrrolindinones, piperidones, and structurally related heterocycles were formed by Al(OTf)3-catalyzed cascade cyclization and ionic hydrogenation reactions of corresponding nitrogen substituted ketoamides in good yields. PMID:24313882

Qi, Jianguo; Sun, Chenbin; Tian, Yulin; Wang, Xiaojian; Li, Gang; Xiao, Qiong; Yin, Dali

2014-01-01

207

Rare-Earth Metal Chlorides as Efficient Catalysts for the Simple and Green Synthesis of 1,2-Disubstituted Benzimidazoles and 2-Substituted Benzothiazoles Under Ultrasound Irradiation  

Microsoft Academic Search

Under solvent-free and ultrasonic irradiation conditions, efficient methods for the synthesis of 1,2-disubstitued benzimidazoles and 2-substitued benzothiazoles by employing rare-earth metal chlorides as catalysts are described. The methods have the advantages of broad generality, economical catalysts, good yields, simple operation, solvent-free condition, and ambient temperature.

Li-Jun Zhang; Jing Xia; Yong-Qing Zhou; Hua Wang; Shao-Wu Wang

2012-01-01

208

Rare-Earth Metal Chlorides as Efficient Catalysts for the Simple and Green Synthesis of 1, 2-Disubstituted Benzimidazoles and 2-Substituted Benzothiazoles under Ultrasound Irradiation  

Microsoft Academic Search

Under solvent-free and ultrasonic irradiation conditions, efficient methods for the synthesis of 1, 2-disubstitued benzimidazoles and 2-substitued benzothiazoles by employing rare-earth metal chlorides as catalysts are described. The methods have the advantages of broad generality, economical catalysts, high yields, simple operation, solvent- free condition and ambient temperature.

Li-Jun Zhang; Jing Xia; Yong-Qing Zhou; Hua Wang; Shao-Wu Wang

2011-01-01

209

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

210

Reaction between isocyanides and chalcones: an efficient solvent-free synthesis of 5-hydroxy-3,5-diaryl-1,5-dihydro-2 H-pyrrol-2-ones  

Microsoft Academic Search

A simple and efficient synthesis of 5-hydroxy-3,5-diaryl-1,5-dihydro-2H-pyrrol-2-ones is described. Heating a mixture of an isocyanide and a 1,3-diaryl-2-propen-1-one under solvent-free conditions produces the title compounds in good to excellent yields.

Mehdi Adib; Mohammad Mahdavi; Mahsa Alizadeh Noghani; Hamid Reza Bijanzadeh

2007-01-01

211

Sulfamic Acid: An Efficient, Cost-Effective, and Reusable Solid Acid Catalyst for the Synthesis of 1,8-Naphthyridines Under Solvent-Free Heating and Microwave Irradiation  

Microsoft Academic Search

An efficient and convenient method is described for the synthesis of 1,8-naphthyridines in excellent yields by condensation of 2-aminonicotinaldehyde with various active methylene compounds in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

Y. Thirupathi Reddy; P. Raghotham Reddy; M. Nikhil Reddy; B. Rajitha; Peter A. Crooks

2008-01-01

212

Heteropolyacid: An efficient and eco-friendly catalyst for the synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthene  

Microsoft Academic Search

A simple and efficient catalytic procedure for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene is reported. Tungsten heteropoly acid catalysts are used both in bulk or supported on silica gel under solvent-free conditions at 100°C. Good yields and short reaction time are advantages of this new method.

Mostafa Mohammadpour Amini; Mozhdeh Seyyedhamzeh; Ayoob Bazgir

2007-01-01

213

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

214

Cis1,4Bis(triphenylphosphonium)-2Butene Peroxodisulfate as an Efficient Reagent for the Synthesis of Phenacyl Thiocyanates and Phenacyl Azides  

Microsoft Academic Search

Styrenes efficiently undergo thiocyanation and azidation with Cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate at ice temperature to furnish the corresponding thiocyanatoketones and azidoketones. This method is a direct, one-pot synthesis under mild condition using methanol as solvent.

Rashid Badri; Maryam Gorjizadeh

2011-01-01

215

Cis1,4-bis(triphenylphosphonium)-2-butene Peroxodisulfate as an Efficient Reagent for the Synthesis of Phenacyl Thiocyanates and Phenacyl Azides  

Microsoft Academic Search

Styrenes efficiently undergo thiocyanation and azidation with cis-1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate at 0 °C to furnish the corresponding thiocyanatoketones and azidoketones. This method is a direct, one-pot synthesis under mild condition using methanol as solvent.

Rashid Badri; Maryam Gorjizadeh

2012-01-01

216

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

217

A highly efficient in situ N-acetylation approach for solid phase synthesis.  

PubMed

We describe a new general N-acetylation method for solid phase synthesis. Malonic acid is used as a precursor and the reaction proceeds by in situ formation of a reactive ketene intermediate at room temperature. We have successfully applied this methodology to peptides and non-peptidic molecules containing a variety of functional groups. The reaction gave high yields compared to known acetylation methods, irrespective of the structure, conformation and sequence of the acetylated molecule. Computational studies revealed that the concerted mechanism via the ketene intermediate is kinetically favorable and leads to a thermodynamically stable acetylated product. In conclusion, our method can be easily applied to acetylation in a wide variety of chemical reactions performed on the solid phase. PMID:24526269

Chandra, Koushik; Roy, Tapta Kanchan; Naoum, Johnny N; Gilon, Chaim; Gerber, R Benny; Friedler, Assaf

2014-03-28

218

Simple and Efficient Procedure for the Friedel–Crafts Acylation of Aromatic Compounds with Carboxylic Acids in the Presence of P2O5\\/AL2O3 Under Heterogeneous Conditions  

Microsoft Academic Search

An efficient and chemoselective method for the Friedel–Crafts acylation of aromatic compounds using P2O5\\/Al2O3 and carboxylic acids. Both aromatic and aliphatic carboxylic acids reacted easily to afford the corresponding aromatic ketones in good yields.

Abdol R. Hajipour; Amin Zarei; Leila Khazdooz; Arnold E. Ruoho

2009-01-01

219

Acid-Promoted Chemoselective Introduction of Amide Functionality onto Aromatic Compounds Mediated by an Isocyanate Cation Generated from Carbamate.  

PubMed

Carbamates have been used as precursors of isocyanates, but heating in the presence of strong acids is required because cleavage of the C?O bond in carbamates is energy-demanding even in acid media. Direct amidation of aromatic compounds by isocyanate cations generated at room temperature from carbamoyl salicylates in trifluoromethanesulfonic acid (TfOH) was examined. Carbamates with ortho-salicylate as an ether group (carbamoyl salicylates) showed dramatically accelerated O?C bond dissociation in TfOH, which resulted in facile generation of the isocyanate cation. These chemoselective intermolecular aromatic amidation reactions proceeded even at room temperature and showed good compatibility with other electrophilic functionalities and high discrimination between N-monosubstituted carbamate and N,N-disubstituted carbamate. The reaction rates of secondary and tertiary amide formation were markedly different, and this difference was utilized to achieve successive (tandem) amidation reactions of molecules with an N-monosubstituted carbamate and an N,N-disubstituted carbamate with two kinds of aromatic compounds. PMID:25138062

Sumita, Akinari; Kurouchi, Hiroaki; Otani, Yuko; Ohwada, Tomohiko

2014-10-01

220

Synthesis of multifunctional PAMAM-aminoglycoside conjugates with enhanced transfection efficiency.  

PubMed

The development of multifunctional vectors for efficient and safe gene delivery is one of the major challenges for scientists working in the gene therapy field. In this context, we have designed a novel type of aminoglycoside-rich dendrimers with a defined structure based on polyamidoamine (PAMAM) in order to develop efficient, nontoxic gene delivery vehicles. Three different conjugates, i.e., PAMAM G4-neamine, -paromomycin, and -neomycin, were synthesized and characterized by nuclear magnetic resonance (NMR) and MALDI analysis. The conjugates were found to self-assemble electrostatically with plasmid DNA, and unlike neamine conjugate, each at its optimum showed increased gene delivery potency compared to PAMAM G4 dendrimer in three different cell lines, along with negligible cytotoxicity. These results all disclosed aminoglycosides as suitable functionalities for tailoring safe and efficient multifunctional gene delivery vectors. PMID:24147798

Ghilardi, Alessandra; Pezzoli, Daniele; Bellucci, Maria Cristina; Malloggi, Chiara; Negri, Armando; Sganappa, Aurora; Tedeschi, Gabriella; Candiani, Gabriele; Volonterio, Alessandro

2013-11-20

221

Synthesis and photopolymerization of propenyl ether and epoxy functionalized siloxanes  

NASA Astrophysics Data System (ADS)

The reactive precursors, 1-allyloxy-4(1-propenoxy)butane and allyl-epoxy-ester, were synthesized. The synthesis of propenyl ether and epoxy functionalized siloxanes has been achieved by the controlled, rhodium-catalyzed, chemoselective hydrosilation of allyl ether with various H-functional siloxanes. It was shown that the hydrosilation proceeds exclusively at the allyl ether group of allyloxy-propenoxybutane without participation at the propenyl ether group. The photoinduced cationic polymerization of these monomers was studied and found to be all highly reactive.

Kim, W. G.; Ahn, H. K.; Lee, H. W.; Kim, S. H.; Crivello, J. V.

2003-01-01

222

Synthesis of Application-Specific Highly Efficient Multi-Mode Cores for  

E-print Network

with efficiency in terms of power, perfor- mance, and area. The field programmable gate arrays (FPGAs) provide without fee provided that copies are not made or distributed for profit or direct commercial advantage component of this work in other works requires prior specific permission and/or a fee. Permissions may

Bhunia, Swarup

223

Montmorillonite K10 catalyzed efficient synthesis of amidoalkyl naphthols under solvent free conditions  

Microsoft Academic Search

An efficient green protocol for the preparation of amidoalkyl naphthols, employing a three-component one-pot condensation reaction of ?-naphthol, aromatic aldehyde, amides or urea in the presence of montmorillonite K10 clay under solvent free conditions has been described. The present procedure offers advantages such as shorter reaction time (<2h), simple workup, excellent yields, recovery and reusability of catalyst.

Srinivas Kantevari; Srinivasu V. N. Vuppalapati; Lingaiah Nagarapu

2007-01-01

224

Synthesis and Energy Transfer Efficiency of FRET Terminators Derived from Different Linkers  

Microsoft Academic Search

A number of different energy transfer dye labeled-cassettes were synthesized using aminoacid based trifunctional linkers and coupled to the propargylamino-substituted dideoxynucleoside-5?-triphosphates (ddNTPs). These terminators were evaluated for their energy transfer efficiency and DNA sequencing potential using thermostable DNA polymerase.

Shiv Kumar; Satyam Nampalli; Patrick J. Finn; T. Sudhakar Rao; Chung-Yuan Chen; Parke K. Flick; Carl W. Fuller

2003-01-01

225

Efficient Methodology for the Synthesis of 3-Amino-1,2,4-triazoles  

PubMed Central

A general and efficient method for the preparation of 3-amino-1,2,4-triazoles has been developed. The desired 3-amino-1,2,4-triazoles (1) were prepared in good overall yield via two convergent routes. The key intermediate within both routes is substituted hydrazinecarboximida-mide derivative 2. PMID:19731897

Noel, Romain; Song, Xinyi; Jiang, Rong; Chalmers, Michael J.; Griffin, Patrick R.; Kamenecka, Theodore M.

2010-01-01

226

Efficient methodology for the synthesis of 3-amino-1,2,4-triazoles.  

PubMed

A general and efficient method for the preparation of 3-amino-1,2,4-triazoles has been developed. The desired 3-amino-1,2,4-triazoles (1) were prepared in good overall yield via two convergent routes. The key intermediate within both routes is substituted hydrazinecarboximidamide derivative 2. PMID:19731897

Noël, Romain; Song, Xinyi; Jiang, Rong; Chalmers, Michael J; Griffin, Patrick R; Kamenecka, Theodore M

2009-10-01

227

N-heterocyclic carbene-catalyzed internal redox reaction of alkynals: an efficient synthesis of allenoates.  

PubMed

An efficient N-heterocyclic carbene (NHC)-catalyzed internal redox reaction of alkynals that bear a ? leaving group has been developed. This process provides a new access to a range of allenoates in good yields. Preliminary results demonstrate that the enantioselective variant can also be achieved. PMID:22352302

Zhao, Yu-Ming; Tam, Yik; Wang, Yu-Jie; Li, Zigang; Sun, Jianwei

2012-03-16

228

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

NASA Astrophysics Data System (ADS)

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 TiO2 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 TiO2'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 TiO2. The resulting green synthesized CdSe QDSCs with Cu2S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

Gao, Bing; Shen, Chao; Zhang, Bo; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia; Chen, Guorong

2014-05-01

229

DNA mismatch repair efficiency and fidelity are elevated during DNA synthesis in human cells  

PubMed Central

DNA mismatch repair (MMR) within human cells is hypothesized to occur primarily at the replication fork. However, experimental models measuring MMR activity at specific phases of the cell cycle and during genomic DNA synthesis are lacking. We have investigated MMR activity within the nuclear environment of HeLa cells after enriching for G1, S and G2/M phase of the cell cycle by centrifugal elutriation. This approach preserves physiologically normal MMR activity in cell populations subdivided into different phases of the cell cycle. Here we have shown that nuclear protein concentration of hMutS? and hMutL? increases as cells progress into S phase during routine cell culture. MMR activity, as measured by both in vitro and in vivo approaches, increases during S phase to the highest extent within normally growing cells. Both fidelity and activity of MMR are highest on actively replicating templates within intact cells during S phase. The MMR pathway however, is also active at lower levels at other phases of the cell cycle, and on nonreplicating templates. PMID:19138690

Edelbrock, Michael A.; Kaliyaperumal, Saravanan; Williams, Kandace J.

2009-01-01

230

The Efficient Synthesis and Biological Evaluation of Novel Bi-Functionalized Sarcophagine for 64Cu Radiopharmaceuticals  

PubMed Central

Purpose We and others have reported that Sarcophagine-based bifunctional chelators could be effectively used in the syntheses of 64Cu radiopharmaceuticals. The resulted 64Cu-Sarcophagine complexes demonstrated great in vivo stability. The goal of this study was to further derivatize Sarcophagine cage with amino and maleimide functional groups for conjugation with bioligands. Methods Starting from DiAmSar, three novel chelators (AnAnSar, BaMalSar, and Mal2Sar) with two functional groups have been synthesized. Among those, BaMalSar and Mal2Sar have been conjugated with cyclic peptide c(RGDyC) (denoted as RGD) and the resulted conjugates, BaMalSar-RGD and Mal2Sar-RGD2 have been labeled with 64Cu. The tumor targeting efficacy of 64Cu-labeled RGD peptides were evaluated in a subcutaneous U87MG glioblastoma xenograft model. Results The conjugates, BaMalSar-RGD and Mal2Sar-RGD2 could be labeled with 64CuCl2 in 10 min with high purity (>98%) and high radiochemical yield (>90%). Both 64Cu-BaMalSar-RGD and 64Cu-Mal2Sar-RGD2 exhibited high tumor uptake and tumor-to-normal tissue ratios. Conclusion Three novel chelators with two functional groups have been developed based on Sarcophagine cage. The platform developed in this study could have broad applications in the design and synthesis of 64Cu-radiopharmaceuticals. PMID:22737194

Liu, Shuanglong; Li, Dan; Huang, Chiun-Wei; Yap, Li-Peng; Park, Ryan; Shan, Hong; Li, Zibo; Conti, Peter S.

2012-01-01

231

A Highly Efficient Lucky Imaging Algorithm: Image Synthesis Based on Fourier Amplitude Selection  

NASA Astrophysics Data System (ADS)

We propose a new algorithm dramatically enhancing the efficiency of the lucky imaging technique for AO-corrected images in the visible range. It is achieved by a selection based on the relative strength of signal for each spatial frequency in the Fourier domain, making a more efficient use of information contained in each frame. Realistic simulations show that our algorithm allows us to reach the diffraction limit in the visible range on an AO-equipped 8 m telescope and enhances the Strehl ratio of an AO long exposure by a factor of up to 4. It outperforms the lucky imaging technique at an equivalent selection ratio. The fraction of selected data in simulation is also boosted from two to eight times for a given Strehl-ratio performance.

Garrel, Vincent; Guyon, Olivier; Baudoz, Pierre

2012-08-01

232

Efficient synthesis of large-scale heat exchanger networks using monogenetic algorithm  

Microsoft Academic Search

A promising method for the efficient design of large-scale heat exchanger networks is the genetic algorithm. The heat exchanger\\u000a network is divided into sub-networks which are optimized by a hybrid genetic algorithm. In additional steps these sub-networks\\u000a are optimized by a monogenetic algorithm. An example consisting of 39 process streams was considered in detail. Significant\\u000a improvements were made in reduction

Philipp Ernst; Georg Fieg; Xing Luo

2010-01-01

233

Copper-catalysed intramolecular O-arylation: a simple and efficient method for benzoxazole synthesis.  

PubMed

A wide range of 2-substituted benzoxazoles can be efficiently synthesized from N-(2-iodo-/bromo-phenyl)benzamides, and even the less reactive N-(2-chlorophenyl)benzamides, via Cu-catalysed intramolecular coupling cyclization reactions using methyl 2-methoxybenzoate as the ligand under mild reaction conditions. In addition, the benzoxazoles can be easily prepared from the primary amides coupling with o-dihalobenzenes in a single step. PMID:25350639

Wu, Fengtian; Zhang, Jie; Wei, Qianbing; Liu, Ping; Xie, Jianwei; Jiang, Haojie; Dai, Bin

2014-12-21

234

Efficient synthesis of polyethers from isosorbide by microwave-assisted phase transfer catalysis  

Microsoft Academic Search

Polyetherification of isosorbide with 1,8-dibromo or dimesyl octane was realized under phase transfer catalysis with increased efficiency when performed under microwave activation. In addition to rate increase in the reaction, microwave effects on polymer structures (as determined by MALDI-TOFMS) were observed. Polymers with higher molecular weights with the presence of ethylenic groups as chain terminations were thus obtained, unlike to

S. Chatti; M. Bortolussi; A. Loupy; J. C. Blais; D. Bogdal; M. Majdoub

2002-01-01

235

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

236

A Fast Graph-Searching Algorithm Enabling the Efficient Synthesis of Sub-Arrayed Planar Monopulse Antennas  

Microsoft Academic Search

An innovative approach in its different implementations for the synthesis of compromise sum and difference patterns of monopulse planar arrays is presented. The synthesis method is based on a sub-arraying technique aimed at generating the compromise patterns through an optimal excitation matching procedure. By exploiting some properties of the solution space, the synthesis problem is reformulated as a combinatorial one

Luca Manica; Paolo Rocca; Manuel Benedetti; Andrea Massa

2009-01-01

237

Efficient enzymatic systems for synthesis of novel ?-mangostin glycosides exhibiting antibacterial activity against Gram-positive bacteria.  

PubMed

Two enzymatic systems were developed for the efficient synthesis of glycoside products of ?-mangostin, a natural xanthonoid exhibiting anti-oxidant, antibacterial, anti-inflammatory, and anticancer activities. In these systems, one-pot reactions for the synthesis of UDP-?-D-glucose and UDP-?-D-2-deoxyglucose were modified and combined with a glycosyltransferase (GT) from Bacillus licheniformis DSM-13 to afford C-3 and C-6 position modified glucose and 2-deoxyglucose conjugated novel ?-mangostin derivatives. ?-Mangostin 3-O-?-D-glucopyranoside, ?-mangostin 6-O-?-D-glucopyranoside, ?-mangostin 3,6-di-O-?-D-glucopyranoside, ?-mangostin 3-O-?-D-2-deoxyglucopyranoside, ?-mangostin 6-O-?-D-2-deoxyglucopyranoside, and ?-mangostin 3,6-di-O-?-D-2-deoxyglucopyranoside were successfully produced in practical quantities and characterized by high-resolution quadruple time-of-flight electrospray ionization-mass spectrometry (HR-QTOF ESI/MS), (1)H and (13)C NMR analyses. In excess of the substrate, the maximum productions of three ?-mangostin glucopyranosides (4.8 mg/mL, 86.5 % overall conversion of ?-mangostin) and three ?-mangostin 2-deoxyglucopyronosides (4.0 mg/mL, 79 % overall conversion of ?-mangostin) were achieved at 4-h incubation period. All the ?-mangostin glycosides exhibited improved water solubility, and their antibacterial activity against three Gram-positive bacteria Micrococcus luteus, Bacillus subtilis, and Staphylococcus aureus was drastically enhanced by the glucosylation at C-3 position. In this study, diverse glycosylated ?-mangostin were produced in significant quantities by using inexpensive starting materials and recycling co-factors within a reaction vessel without use of expensive NDP-sugars in the glycosylation reactions. PMID:25038930

Le, Tuoi Thi; Pandey, Ramesh Prasad; Gurung, Rit Bahadur; Dhakal, Dipesh; Sohng, Jae Kyung

2014-10-01

238

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. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1005-1011, 2014. PMID:24891225

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

2014-09-01

239

Chemoselective one-step purification method for peptides synthesized by the solid-phase technique.  

PubMed Central

The specific reaction between SH and iodoacetamide groups has been explored as the basis of an affinity-type purification procedure for peptides synthesized by the solid-phase technique. For this affinity-type purification procedure, we synthesized an SH precursor reagent bearing an acid-labile S-protecting group, pMB-SCH2CONHCH2CH2-SO2CH2CH2OCO2pNP (compound I), in which pMB is p-methoxybenzyl and pNP is p-nitrophenyl. Using this reagent, the procedure involves the following sequence of four reactions: (i) attachment of the SH function of compound I to the alpha-amino group of a peptide-resin through a base-labile sulfonylethoxycarbonyl linkage in the final step of solid-phase peptide synthesis, (ii) acid treatment to remove the S-pMB and side-chain-protecting groups employed and cleave the modified peptide from the resin, (iii) immobilization of the derived SH-peptide on an iodoacetamide-resin column, and (iv) base (5% NH4OH) treatment to release the desired peptide from the resin in nearly pure form. To facilitate this purification procedure, unreacted amino groups were acetylated in each step during solid-phase synthesis. The usefulness of this method was demonstrated by the purification of several peptides (18 to approximately 44 amino acids in length) synthesized by the 9-fluorenylmethoxycarbonyl (Fmoc)-based solid-phase technique. The principle of this affinity-type purification procedure may also be applied to the tert-butoxycarbonyl (Boc)-based solid-phase technique. PMID:1871113

Funakoshi, S; Fukuda, H; Fujii, N

1991-01-01

240

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

PubMed

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

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

2011-08-01

241

Highly efficient synthesis of globular (bola)amphiphilic [5:1]hexakisadducts of C60.  

PubMed

We report on the very facile access of a new family of amphiphilic and bola-amphiphilic fullerene [5:1]hexakisadducts 9a-f and 11a-e. The key point for this successful approach is the use of C(2v)-symmetrical fullerene pentakisadduct precursors 2b-f allowing for the completely regioselective addition of a sixth malonate addend to complete the octahedral [5:1] addition pattern. For the synthesis of the new amphiphiles we first developed a new second-generation dendrimer containing 9 tert-butoxycarbonyl (Boc)-protected amino functions at the periphery and two new malonates containing 6 or 18 Boc-protected amino termini, respectively. The hexakisadducts contain up to 18 positive or negative charges at the dendritic moiety and either no or ten positive or negative charges at the unbranched malonate positions after deprotection with trifluoroacetic acid (TFA). The charge state at the termini is pH-dependent. Complete structural characterization of the new compounds was carried out by ESI mass spectrometry and by UV/Vis, FTIR, (1)H NMR and (13)C NMR spectroscopy. We were also able to obtain the first X-ray crystal structure of pentakisadduct (2a) with a C(2v)-symmetrical addition pattern. The new amphiphilic hexakisadducts show interesting solubility properties in water. Initial investigations on the aggregation properties of the amphiphilic hexakisadduct 12c by using dynamic light scattering (DLS) and conductivity measurements, show aggregates with a radius up to 200 nm and a critical micelle concentration (CMC) of approximately 8 mg L(-1). PMID:23307649

Hörmann, Frank; Brettreich, Michael; Donaubauer, Wolfgang; Hampel, Frank; Hirsch, Andreas

2013-02-18

242

Effects of chemical structure on the thermodynamic efficiency of radical chain carriers for organic synthesis.  

PubMed

The chain carrier index (CCI), defined as the ratio of the bond dissociation free energies (BDFE) of corresponding chain carrier halides and hydrides, is proposed as a measure of the thermodynamic efficiency of chain carriers for radical dehalogenation. The larger this value is relative to the corresponding value of the organic substrate, the more thermodynamically efficient the process. The chloride and bromide CCIs were evaluated at the G3(MP2)-RAD(+) level of theory for 120 different R-groups, covering a broad range of carbon-centered and noncarbon-centered species; the effects of solvent and temperature have also been studied. The broad finding from this work is that successful chain carriers generally maximize the strength of their halide (versus hydride bonds) through charge-shift bonding. As a result, the thermodynamic efficiency of a chain carrier tends to increase down the periodic table, and also with the inclusion of stronger electron donating substituents. The CCIs of carbon-centered species fall into a relatively narrow range so that, even when the CCI is maximized through inclusion of lone pair donor OMe or NMe(2) groups, the thermodynamic driving force for dehalogenation of other organic substrates is modest at best, and the process is likely to be kinetically hampered. Among the noncarbon-centered species studied, bismuth- and borane-centered compounds have some of the highest CCI values and, although their kinetics requires further optimization, these classes of compounds would be worth further investigation as tin-free radical reducing agents. PMID:21280598

Lin, Ching Yeh; Peh, Jessie; Coote, Michelle L

2011-03-18

243

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

244

Silver(I)-catalyzed deprotection of p-methoxybenzyl ethers: a mild and chemoselective method.  

PubMed

The p-methoxybenzyl protecting group (PMB) on various alcohols and an acid was efficiently and selectively cleaved by the action of a catalytic amount of silver(I) hexafluoroantimonate combined with 0.5 equiv of 1,3,5-trimethoxybenzene in dichloromethane at 40 °C. PMID:23002789

Kern, Nicolas; Dombray, Thomas; Blanc, Aurélien; Weibel, Jean-Marc; Pale, Patrick

2012-10-19

245

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

246

Efficient synthesis of boron-containing ?-acyloxyamide analogs via microwave irradiation.  

PubMed

In this report, a Passerini three-component reaction utilizing boron-containing carboxylic acids or aldehydes is discussed. The reaction was carried out in water and facilitated by the use of microwave irradiation. This methodology allowed for the efficient formation of a broad range of boron-containing ?-acyloxyamides under mild conditions within a short time. Two series of boron-containing ?-acyloxyamides were synthesized and subsequently screened for cytotoxicity using the MTT cell viability assay. Two potential lead compounds were found to have potent activity against the HepG2 cancer cell line, demonstrating the potential of this methodology for use in the development of novel pharmaceuticals. PMID:23966074

Chai, Chih-Cheng; Liu, Pin-Yi; Lin, Chia-Hung; Chen, Hsien-Chi; Wu, Yang-Chang; Chang, Fang-Rong; Pan, Po-Shen

2013-01-01

247

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

248

Efficient cyanoaromatic photosensitizers for singlet oxygen production: synthesis and characterization of the transient reactive species.  

PubMed

In order to graft cyanoaromatic molecules onto various inert supports, we designed two new cyanoanthracene derivatives of benzo[b]triphenylene-9,14-dicarbonitrile (DBTP, 1), which already demonstrated good photosensitizing properties. We synthesized 3-(N-hydroxypropyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 3 and 3-(N-N0-Boc-aminohexyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 4 and compared their photophysical properties in acetonitrile relative to those of the parent compound 1 and its carboxylic derivative 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, 2. The transient species were analysed and the quantum yields of singlet oxygen production (??) determined in acetonitrile. The effect of chemical functionalization can be considered negligible, since absorption spectra, fluorescence emission spectra and fluorescence lifetimes do not significantly change with the substituent. The triplet-triplet absorption spectra and the triplet excited state lifetimes are similar for the whole series. For compounds 1-4 high values of ??, close to that of the standard sensitizer 1H-phenalen-1-one (PN, ?? ? 1), and higher than that of the well-known photosensitizer 9,10-dicyanoanthracene (DCA), are due to very efficient intersystem crossing from the singlet to the triplet excited state and subsequent energy transfer to ground state oxygen ((3)O2). They belong to a class of very efficient photosensitizers, absorbing visible light and stable under irradiation, they may be functionalized without significant changes to their photophysical behaviour, and grafted onto various supports. PMID:24013434

Ronzani, Filippo; Arzoumanian, Emmanuel; Blanc, Sylvie; Bordat, Patrice; Pigot, Thierry; Cugnet, Cyril; Oliveros, Esther; Sarakha, Mohamed; Richard, Claire; Lacombe, Sylvie

2013-10-28

249

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

2014-10-01

250

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

251

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.

252

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

253

An efficient synthesis of a hydroxyethylamine (HEA) isostere and its ?-aminophosphonate and phosphoramidate derivatives as potential anti-HIV agents.  

PubMed

HIV protease is a promising drug target for AIDS therapy, and several potent HIV-1 protease inhibitors have been reported to date. Although existing inhibitors exhibit high selectivity, they have also been associated with severe side effects and the possible emergence of therapeutic resistance. As HIV protease cleaves the peptide bond via a tetrahedral intermediate, various transition-state models such as hydroxyethylamine (HEA) have been designed. We therefore pursued an efficient synthesis of an HEA isostere; this was performed with a novel one-pot reduction-transimination-reduction reaction sequence as a key step. ?-Aminophosphonate and phosphoramidate derivatives of the HEA isostere were designed and synthesized, and all of the synthesized derivatives were assayed for their anti-HIV activities against wild-type and mutant HIV strains. Phosphoramidate derivative 15 a was found to be the most active of all synthesized compounds against the III(B) and RES056 strains. As phosphonates are known to exhibit physiological stability, good cell permeability, and other promising pharmacokinetic characteristics, our newly synthesized compounds have the potential as alternatives to existing therapeutics and diagnostics. PMID:22786810

Bhattacharya, Asish K; Rana, Kalpeshkumar C; Pannecouque, Christophe; De Clercq, Eric

2012-09-01

254

Efficient formation of luminescent lanthanide(III) complexes by solid-phase synthesis and on-resin screening.  

PubMed

Time-resolved luminescence measurements of luminescent lanthanide complexes have advantages in biological assays and high-throughput screening, owing to their high sensitivity. In spite of the recent advances in their energy-transfer mechanism and molecular-orbital-based computational molecular design, it is still difficult to estimate the quantum yields of new luminescent lanthanide complexes. Herein, solid-phase libraries of luminescent lanthanide complexes were prepared through amide-condensation and Pd-catalyzed coupling reactions and their luminescent properties were screened with a microplate reader. Good correlation was observed between the time-resolved luminescence intensities of the solid-phase libraries and those of the corresponding complexes that were synthesized by using liquid-phase chemistry. This method enabled the rapid and efficient development of new sensitizers for Sm(III), Eu(III), and Tb(III) luminescence. Thus, solid-phase combinatorial synthesis combined with on-resin screening led to the discovery of a wide variety of luminescent sensitizers. PMID:23946082

Nakamura, Tatsuya; Mizukami, Shin; Tanaka, Miho; Kikuchi, Kazuya

2013-11-01

255

Synthesis efficiency of heavy carbon clusters from ETFE ablated by different numbers of laser pulse in vacuum  

NASA Astrophysics Data System (ADS)

We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [?CH 2?CH 2?CF 2?CF 2?] n) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions C n+ with n?30 were observed in the mass spectra. The fractional abundance of heavy clusters in the mass spectrum decreased with the number of laser pulse. On the other hand, carbon became rich in the atomic composition of the laser-irradiated surface, and the eroded area on the surface increased with the number of laser pulse. From these results, it is suggested that the carbon-rich material surface results in the less efficient production of heavy carbon clusters. In addition, it is also suggested that clustering reactions in eroded craters do not contribute to the synthesis of heavy clusters.

Shibagaki, K.; Takada, N.; Sasaki, K.; Kadota, K.

2002-09-01

256

Efficient one-step synthesis of 4-amino substituted phthalimides and evaluation of their potential as fluorescent probes.  

PubMed

The phthalimide scaffold is recognized from bioactive compounds and marketed drugs, but can also be used as fluorescent probes by introducing a 4-amino substituent. Unfortunately, a general and convenient method to synthesize various 4-amino substituted phthalimides has been lacking. To overcome this, an atom efficient one-step synthesis of 4-amino substituted phthalimides in good to excellent yields that tolerate a wide range of substituents has been developed. Several of the generated compounds display interesting solvatochromic properties with high quantum yield of fluorescence in non-polar solvents that are significantly reduced in polar protic solvents. Many of these compounds displayed non-toxic properties and non-detectable unspecific binding and can thus potentially be linked to a substrate and used as fluorescent probes. Furthermore, bioactive and fluorescent 4-amino substituted phthalimides with IC50-values in the low micromolar range in cell-based assays have been identified and could be used to study uptake and distribution. The developed convenient synthetic method is thus valuable not only to construct fluorescent probes and fluorescent bioactive compounds to gain information about target binding, but also from a structure activity point of view in the various areas where the phthalimides have displayed activity. PMID:24849574

Kindahl, Tomas; Chorell, Erik

2014-07-01

257

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

258

Comparison of three efficient-detail-synthesis methods for modeling using under-sampled data  

NASA Astrophysics Data System (ADS)

Synthetic scene generation models depend on the repeated evaluation or iteration of often computationally expensive functions to create 'texture' or structure in a modeled natural scene. The computational burden of 'texture' function evaluation is dependent upon the spatial frequency response characteristics of the optical system through which the modeled scene is to be 'propagated.' All real 'cameras' utilize detector elements of finite size to transduce the resulting MXN pixels of the image. Two general situations arise in modeling the effects of cameras (sensors) on the imaged scene. The first is the 'oversampled' case where the Nyquist frequency of the detector spacing exceeds the cutoff of the optics transfer (aperture) function. The 'undersampled' case is when such Nyquist frequency is below the aperture cutoff spatial frequency, which results in aliasing. The application of brute force in the oversampled case results in MXN scene 'texture' function evaluations, while for the undersampled case, (mM)X(nN) (m, n > 1) points are required. Several computationally efficient methods significantly reduce the stated brute force computational burden for these two cases. This paper discusses three such methods. For the oversampled case, a correct and efficient method is 2D sample 'interpolation,' in the multirate digital signal processing sense. This method expressly avoids signal aliasing caused by simpler but inappropriate bilinear interpolation of the sparser set of (mM)+(nN) (m, n fractions < 1) scene samples onto the MXN imaged scene. The second and third techniques discussed are applicable to the undersampled case. Each relies upon MXN scene 'texture' function evaluations. The second technique extrapolates the frequency spectrum of the MXN grid with a synthetic spectrum beyond Nyquist which follows the 1/f(beta ) decrease in power typical of natural (fractal) textures. The third technique, 'fractal interpolation,' operates in the spatial domain where spatial detail, generated from the computed ('texture' function) MXN grid onto a larger (nM)X(nN) grid, is synthesized at the same local fractal dimension as that of the MXN 'undersampled' data. In both cases, the synthesized frequencies above the camera Nyquist are 'folded back' in the spectral domain to approximate the aliasing of spatial frequencies into the transduced image.

Iannarilli, Frank J., Jr.; Wohlers, Martin R.

1991-07-01

259

Synthesis, structural characterisation, bio-potential efficiency and DNA cleavage applications of nicotinamide metal complexes  

NASA Astrophysics Data System (ADS)

Mixed ligand complexes were synthesised using nicotinamide as the primary ligand and nitrite as the secondary ligand were characterised by FT-IR, UV-Vis, 1H NMR, TG-DTA-DTG, X-ray powder diffraction and physical analytical studies. From the molar conductance, magnetic moment and electronic spectral data of the synthesised complexes a general formula of [M(ONO)2(NA)2] where M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) and [Cr2(ONO)6(NA)2] with a distorted octahedral structure were proposed. Thermal analyses show that the complexes lose molecules of hydration initially and subsequently expel anionic and organic ligands in continuous steps. The kinetic parameter values, such as, E*, ?H*, ?S* and ?G* illustrate the spontaneous association of the metal and ligands in the formation of the complexes. The antimicrobial efficacy of the ligand and its complexes were examined by in vitro method against various pathogenic bacterial and fungal strains. The metal complexes were found to posses efficient antimicrobial properties compared to nicotinamide and a few of these complexes could turn out to be excellent models for the design of effective antibiotic drug substances. The intercalating interaction of Cu(II) complex with CT-DNA was inspected by absorption spectral and viscosity studies, thermal denaturation and electro-analytical experiments.

Surendra Dilip, C.; Siva Kumar, V.; John Venison, S.; Vetha potheher, I.; Rajalaxmi (a) Subahashini, D.

2013-05-01

260

Synthesis, spectral, SHG efficiency and computational studies of some newly synthesized unsymmetrical azines of 4-biphenylcarboxaldehyde.  

PubMed

A series of novel unsymmetrical azines 2-8 are prepared and characterized by FT-IR, (1)H, (13)C NMR, Mass and UV spectral studies. The Gaussian-03 B3LYP/6-311+G(d,p) calculations on these azines are used to evaluate the heat of formation of the different conformers, identify the stable conformation, to determine dipole moment (?), polarizability (?0), first hyperpolarizability (?tot), selected geometrical parameters, MEP surface, frontier molecular orbital energies (HOMO-LUMO) and their energy gap. The ?, ?0, ?tot values clearly depict that the unsymmetrical azine 8 is found to have a good NLO property compared to other azines 1-7. The SHG measurement of unsymmetrical azine 8 was performed by Kurtz and Perry powder method and the results indicated that the azine 8 is having comparable efficiency as that of potassium dihydrogen phosphate (KDP) crystal. The natural bond orbital (NBO) analysis of the unsymmetrical azines 2-8 are also made using B3LYP/6-31G(d,p) basis set. PMID:24755639

Arulmani, R; Sankaran, K R

2014-08-14

261

Synthesis of copper hydroxide and oxide nanostructures via anodization technique for efficient photocatalytic application.  

PubMed

We have demonstrated a facile protocol for synthesizing CuO and Cu2O mixed-phase nanostructures by anodization of copper hydroxide (Cu(OH)2) nanoneedles and their heat treatment in different atmospheres, which affect photocatalytic degradation efficiency. The oxygen annealed sample had relatively small (100 nm) lamellar, spherical nanoparticulate structures on the substrate surface, which showed better photocatalytic degradation of reactive black 5 dye resulting from the appropriate morphology and phase formation, compared to the samples annealed in different atmospheres and vacuum. The pseudo first-order rate constant (k) of the oxygen annealed sample was 0.0054/min, which was relatively high due to the formation of a CuO-Cu2O heterojunction with matching band potentials. Air, nitrogen, argon and vacuum annealing resulted in bigger particles and different morphologies, which led to pseudo first-order rate constants (k) of 0.0032/min (air-annealed); 0.0021/min (N2-annealed); 0.0033/min (Ar-annealed); and 0.0027/min (vacuum-annealed), which resulted in poor photocatalytic degradation of the reactive black 5 dye. PMID:23421221

Hyam, Rajeshkumar Shankar; Lee, Jongseok; Cho, Eunju; Khim, Jeehyeong; Lee, Haigun

2012-11-01

262

Gold(I)-catalyzed furan-yne cyclizations involving 1,2-rearrangement: efficient synthesis of functionalized 1-naphthols and its application to the synthesis of wailupemycin?G.  

PubMed

Gold-catalyzed cascade cyclization/1,2-rearrangement of 1-(2-furanyl)phenyl propargyl alcohols has been developed, which provides a rapid and efficient access to multisubstituted 1-naphthols bearing an enal or enone moiety with high stereoselectivity. The (Z)- or (E)-stereochemistry can be easily controlled by choosing protected- or non-protected substrates. The utility of the methodology has been illustrated in the first total synthesis of wailupemycin?G. PMID:25080016

Chen, Yifeng; Wang, Lu; Sun, Ning; Xie, Xin; Zhou, Xiaobo; Chen, Haoyi; Li, Yuxue; Liu, Yuanhong

2014-09-15

263

Eco-efficient one-pot synthesis of quinazoline-2,4(1H,3H)-diones at room temperature in water.  

PubMed

An efficient one-pot synthesis of quinazoline-2,4(1H,3H)-diones was developed. First, the reactions of anthranilic acid derivatives with potassium cyanate afforded the corresponding urea derivatives. Then, cyclization of the urea derivatives with NaOH afforded the monosodium salts of benzoylene urea. Finally, HCl treatment afforded the desired products in near-quantitative yields. This is an eco-efficient method because all the reactions were carried out in water, and the desired products were obtained simply by filtration. The aqueous filtrate was the only waste generated from the reaction. We scaled up the reaction to 1 kg starting material, thus establishing an alternative approach for the green synthesis of quinazoline-2,4(1H,3H)-diones in the chemical and pharmaceutical industries. PMID:24920051

Tian, Xin-Chuan; Huang, Xing; Wang, Dan; Gao, Feng

2014-01-01

264

Sulfamic acid: An efficient and cost-effective solid acid catalyst for the synthesis of ?-aminophosphonates at ambient temperature  

Microsoft Academic Search

Sulfamic acid catalyzed solvent-free protocol has been developed for the synthesis of ?-aminophosphonates by three component condensation between aldehydes, amines and diethyl phosphite at ambient temperature.

S. D. Mitragotri; D. M. Pore; U. V. Desai; P. P. Wadgaonkar

2008-01-01

265

Total Synthesis of (+)-11,11'-Dideoxyverticillin A  

PubMed Central

The fungal metabolite (+)-11,11'-dideoxyverticillin A, a cytotoxic alkaloid isolated from a marine Penicillium sp., belongs to a fascinating family of densely functionalized, stereochemically complex, and intricate dimeric epidithiodiketopiperazine natural products. Although the dimeric epidithiodiketopiperazines have been known for nearly four decades, none has succumbed to total synthesis. We report a concise enantioselective total synthesis of (+)-11,11'-dideoxyverticillin A via a strategy inspired by our biosynthetic hypothesis for this alkaloid. Highly stereo- and chemoselective advanced stage tetrahydroxylation and tetrathiolation reactions, as well as a mild strategy for the introduction of the epidithiodiketopiperazine core in the final step were developed to address this highly sensitive substructure. Our rapid functionalization of the advanced molecular framework aims to mimic plausible biosynthetic steps and offers an effective strategy for the chemical synthesis of other members of this family of alkaloids. PMID:19359584

Kim, Justin; Ashenhurst, James A.; Movassaghi, Mohammad

2014-01-01

266

Ferric sulfate [Fe 2(SO 4) 3· xH 2O]: an efficient heterogeneous catalyst for the synthesis of tetrahydroquinoline derivatives using Povarov reaction  

Microsoft Academic Search

Fe2(SO4)3·xH2O can be used as an efficient and reusable catalyst for the synthesis of pyrano- and furanotetrahydroquinolines via one-pot three-component Povarov reaction involving aromatic aldehydes, aromatic amines, and cyclic enol ethers. The catalyst is recyclable, economically viable, and environmentally benign. This protocol provides good yields and diastereoselectivity as well as applicability on a wide range of substrates.

Abu T. Khan; Deb Kumar Das

2011-01-01

267

Efficient synthesis of styrene carbonate from CO 2 and styrene oxide using zinc catalysts immobilized on soluble imidazolium–styrene copolymers  

Microsoft Academic Search

Preparation of zinc catalysts (Zn\\/PS-IL[X], X=Br?, Cl?, BF4?, and PF6?) supported on imidazolium–styrene copolymers, as well as their catalytic use for the solvent-free synthesis of styrene carbonate from CO2 and styrene oxide, are described. Among the catalysts examined, Zn\\/PS-IL[Br] was proved to be the most efficient. When used in a homogeneous system during the reaction process, Zn\\/PS-IL[Br] gave a 97.5%

Kun Qiao; Fumitaka Ono; Quanxi Bao; Daisuke Tomida; Chiaki Yokoyama

2009-01-01

268

Adenovirus type 5 early region 1b gene product is required for efficient shutoff of host protein synthesis.  

PubMed Central

To determine the role adenovirus 5 early region 1b-encoded 21- and 55-kilodalton proteins play in adenovirus productive infection, mutants have been isolated which were engineered to contain small deletions or insertions at 5.8, 7.9, or 9.6 map units. By using an overlap recombination procedure involving H5dl314 (delta 3.7 to 4.6 map units) DNA cleaved at 2.6 map units with ClaI and the adenovirus 5 XhoI-C (0 to 15.5 map units) fragment containing the desired mutation, viral mutants were isolated by their ability to produce plaques on KB cell line 18, which constitutively expresses only viral early region 1b functions (Babiss et al., J. Virol. 46:454-465, 1983). DNA sequence analysis of the viral mutants isolated (H5dl118, H5dl110, H5in127, and H5dl163) indicates that all of the viruses contain mutations which affect the 55-kilodalton protein, whereas dl118 should also produce a truncated form of the 21-kilodalton protein. When analyzed for their replication characteristics in HeLa cells, all of the mutant viruses exhibited extended eclipse periods and effected yields that were reduced to 10% or less of that produced by H5sub309 (parent virus of the mutants which is phenotypically identical to wild-type adenovirus 5). When compared with characteristics of sub309, the early and late transcription and DNA replication of the mutants were similar, but synthesis of late polypeptides and late cytoplasmic mRNAs was greatly reduced. Quantitation of mutant virus-specific late mRNAs associated with polysomes revealed a threefold reduction when compared with that of sub309. Analysis of infected cell extracts further revealed that these mutants were incapable of efficiently shutting off host cell protein synthesis, suggesting that the 55-kilodalton protein plays a role in this process. These data suggest that early region 1b products may function by interacting with additional viral or host cell macromolecules to modulate host cell shutoff or that some late viral mRNA or polypeptide may potentiate this reaction. Images PMID:6142122

Babiss, L E; Ginsberg, H S

1984-01-01

269

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available: Experimental details and Fig. S1-S7 as mentioned in the text. See DOI: 10.1039/c4nr03040k

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

2014-10-01

270

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

271

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst  

Microsoft Academic Search

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)2O using sulfamic acid as catalyst (5mol%) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter

Dharita J. Upadhyaya; Alessandro Barge; Rachele Stefania; Giancarlo Cravotto

2007-01-01

272

Silver nanoparticles supported on alumina--a highly efficient and selective nanocatalyst for imine reduction.  

PubMed

Silver nanoparticles supported on alumina were prepared and tested in the catalytic reduction of various imines to primary and secondary amines and were shown to be exceptionally active and chemoselective. Furthermore, the catalytic activity of the prepared nanocatalyst was also tested in the synthesis of secondary amines from primary amines in a tandem reaction protocol (oxidation-imination-reduction) using air and molecular hydrogen as oxidizing and reducing agents, respectively. The reported synthesis is performed under mild reaction conditions, which complies with the demands of modern organic synthesis. Due to the mild reaction conditions and high conversion as well as high selectivity, we consider that the utilization of silver nanoparticles supported on alumina represents an attractive and environmentally friendly alternative to the current synthesis of N-alkyl amines. PMID:24323249

Poreddy, Raju; García-Suárez, Eduardo J; Riisager, Anders; Kegnæs, Søren

2014-03-21

273

ZnO Nanoparticles as an Efficient, Heterogeneous, Reusable, and Ecofriendly Catalyst for Four-Component One-Pot Green Synthesis of Pyranopyrazole Derivatives in Water  

PubMed Central

An extremely efficient catalytic protocol for the synthesis of a series of pyranopyrazole derivatives developed in a one-pot four-component approach in the presence of ZnO nanoparticles as heterogeneous catalyst using water as a green solvent is reported. Greenness of the process is well instituted as water is exploited both as reaction media and medium for synthesis of catalyst. The ZnO nanoparticles exhibited excellent catalytic activity, and the proposed methodology is capable of providing the desired products in good yield (85–90%) and short reaction time. After reaction course, ZnO nanoparticles can be recycled and reused without any apparent loss of activity which makes this process cost effective and hence ecofriendly. All the synthesized compounds have been characterized on the basis of elemental analysis, IR, 1H NMR, and 13C NMR spectral studies. PMID:24282386

Sachdeva, Harshita; Saroj, Rekha

2013-01-01

274

Highly chemoselective reduction of amides (primary, secondary, tertiary) to alcohols using SmI2/amine/H2O under mild conditions.  

PubMed

Highly chemoselective direct reduction of primary, secondary, and tertiary amides to alcohols using SmI2/amine/H2O is reported. The reaction proceeds with C-N bond cleavage in the carbinolamine intermediate, shows excellent functional group tolerance, and delivers the alcohol products in very high yields. The expected C-O cleavage products are not formed under the reaction conditions. The observed reactivity is opposite to the electrophilicity of polar carbonyl groups resulting from the n(X) ? ?*(C?O) (X = O, N) conjugation. Mechanistic studies suggest that coordination of Sm to the carbonyl and then to Lewis basic nitrogen in the tetrahedral intermediate facilitate electron transfer and control the selectivity of the C-N/C-O cleavage. Notably, the method provides direct access to acyl-type radicals from unactivated amides under mild electron transfer conditions. PMID:24460078

Szostak, Michal; Spain, Malcolm; Eberhart, Andrew J; Procter, David J

2014-02-12

275

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

276

Total synthesis of diptoindonesin G via a highly efficient domino cyclodehydration/intramolecular Friedel-Crafts acylation/regioselective demethylation sequence.  

PubMed

A highly efficient total synthesis of diptoindonesin G is described employing a domino dehydrative cyclization/intramolecular Friedel-Crafts acylation/regioselective demethylation reaction of aryloxyketone 7 by the action of BCl(3) wherein the tetracyclic 6H-anthra[1,9-bc]furan-6-one skeleton was constructed via the 3-arylbenzofuran in a one-pot manner. This is the first example of the strategic combination of these three reactions in a cascade fashion. The routes presented here allow for direct access to diptoindonesin G and its analogues. PMID:21033722

Kim, Kyungsun; Kim, Ikyon

2010-11-19

277

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

278

Copper ferrite nanoparticles: an efficient and reusable nanocatalyst for a green one-pot, three-component synthesis of spirooxindoles in water.  

PubMed

A green reaction of isatins, active cyanomethanes, and cyclic 1,3-dicarbonyl derivatives for the efficient and simple one-pot three-component synthesis of spirooxindole fused heterocycles in refluxing water by use of magnetically recoverable and reusable catalyst is reported. The features of this procedure are, the use of magnetically recoverable and reusable catalyst, mild reaction conditions, high to excellent product yields, operational simplicity, and easy workup procedures. Most importantly of all, easy magnetic separation of the catalyst eliminates the requirement of catalyst filtration after completion of the reaction. Furthermore, the catalyst remained highly active even after 5 repeated uses. PMID:24050156

Bazgir, Ayoob; Hosseini, Ghaffar; Ghahremanzadeh, Ramin

2013-10-14

279

Design, synthesis and antiviral potential of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes using an efficient polymer-supported catalyst.  

PubMed

Polyethyleneglycol bound sulfonic acid (PEG-OSO?H), a chlorosulphonic acid-modified polyethylene glycol was successfully used as an efficient and eco-friendly polymeric catalyst in the synthesis of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes obtained from the reaction of 2-naphthol and carbonyl compounds under solvent-free conditions with short reaction times and excellent yields. The biological properties of these synthesized title compounds revealed that compounds 3b, 3c, 3f and 3i showed highly significant anti-viral activity against tobacco mosaic virus. PMID:22710828

Reddi Mohan Naidu, Kalla; Satheesh Krishna, Balam; Anil Kumar, Mungara; Arulselvan, Palanisamy; Ibrahim Khalivulla, Shaik; Lasekan, Ola

2012-01-01

280

Titanocene(III)-catalyzed 6-exo versus 7-endo cyclizations of epoxypolyprenes: efficient control and synthesis of versatile terpenic building blocks.  

PubMed

In this article, a complete study on the selectivity of titanocene(III) cyclization of epoxypolyprenes is presented. The requirements for the formation of six- or seven-membered rings during these cyclizations are determined, taking into account the different substitution pattern in the epoxypolyprene precursor. Thus, a complete selectivity to 6-exo or 7-endo cyclization process has been achieved, yielding mono-, bi-, and even tricyclic compounds, constituting a new and efficient access to this type of derivative. Additionally, this procedure opens the possibility to prepare excellent building blocks for the synthesis of polycyclic compounds with a trisubstituted oxygenated function, which is present in several natural terpenes. PMID:24105753

Justicia, José; Jiménez, Tania; Miguel, Delia; Contreras-Montoya, Rafael; Chahboun, Rachid; Alvarez-Manzaneda, Enrique; Collado-Sanz, Daniel; Cárdenas, Diego J; Cuerva, Juan M

2013-10-18

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

Simple and efficient biomimetic synthesis of Mn3O4 hierarchical structures and their application in water treatment.  

PubMed

Biotemplate synthesis of functional materials is interesting owing to low cost, high yield and easy way of preparation. Recently, we have developed a simple and cost effective biomimetic synthesis of hierarchical network like nanostructures of manganese oxide (Mn3O4). Readily available eggshell membrane with nucleating and capping sites were used as a template in our synthesis. The prepared material was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis and X-ray Diffraction (XRD). The surface area was calculated using the Brunauer-Emmett-Teller (BET) theory, and pore size distribution was obtained by Barrett-Joyner-Helenda (BJH) method. The prepared Mn3O4 showed good ability to remove organic pollutants from water and expected to be useful in effluent treatment in textile industry. PMID:22524029

Mallampati, Ramakrishna; Valiyaveettil, Suresh

2012-01-01

283

A strategy utilizing a recyclable macrocycle transporter for the efficient synthesis of a triazolium-based [2]rotaxane.  

PubMed

A general synthesis of triazolium-containing [2]rotaxanes, which could not be accessed by other methods, is reported. It is based on a sequential strategy starting from a well-designed macrocycle transporter which contains a template for dibenzo-24-crown-8 and a N-hydroxysuccinimide (NHS) moiety. The sequence is: 1)?synthesis by slippage of a [2]rotaxane building-block; 2)?its elongation at its NHS end; 3)?the delivery of the macrocycle to the elongated part of the axle by an induced translational motion; 4)?the contraction process to yield the targeted [2]rotaxane and recycle the initial transporter. PMID:24910397

Chao, Sovy; Romuald, Camille; Fournel-Marotte, Karine; Clavel, Caroline; Coutrot, Frédéric

2014-07-01

284

Efficient dibenzo[c]acridine helicene-like synthesis and resolution: scaleup, structural control, and high chiroptical properties.  

PubMed

Herein, we describe our recent expeditious synthesis of dibenzo[c]acridine helicene-like compounds on a large scale in pure enantiomeric form. This flexible synthesis allows for variation at several positions on the skeleton. Geometrical parameters related to these compounds have been obtained from monocrystal X-ray structure resolution. Additionally, chiroptical parameters have been recorded, highlighting the versatility of this family showing for example optical rotation at 589 nm varying between 135 and 150 deg g(-1)cm(2). PMID:22176157

Jierry, Loïc; Harthong, Steven; Aronica, Christophe; Mulatier, Jean-Christophe; Guy, Laure; Guy, Stéphan

2012-01-01

285

An efficient and versatile synthesis of GlcNAcstatins-potent and selective O-GlcNAcase inhibitors built on the tetrahydroimidazo[1,2-a]pyridine scaffold.  

PubMed

We report a novel approach to the synthesis of GlcNAcstatins-members of an emerging family of potent and selective inhibitors of peptidyl O-GlcNAc hydrolase build upon tetrahydroimidazo[1,2-a]pyridine scaffold. Making use of a streamlined synthetic sequence featuring de novo synthesis of imidazoles from glyoxal, ammonia and aldehydes, a properly functionalised linear GlcNAcstatin precursor has been efficiently prepared starting from methyl 3,4-O-(2',3'-dimethoxybutane-2',3'-diyl)-?-d-mannopyranoside. Subsequent ring closure of the linear precursor in an intramolecular S(N)2 process furnished the key fused d-mannose-imidazole GlcNAcstatin precursor in excellent yield. Finally, a sequence of transformations of this key intermediate granted expeditious access to a variety of the target compounds bearing a C(2)-phenethyl group and a range of N(8) acyl substituents. The versatility of the new approach stems from an appropriate choice of a set of acid labile permanent protecting groups on the monosaccharide starting material. Application was demonstrated by the synthesis of GlcNAcstatins containing polyunsaturated and thiol-containing amido substituents. PMID:20976183

Borodkin, Vladimir S; van Aalten, Daan M F

2010-09-25

286

Immobilized Cu (II)—Amino Acid Complexes as Prospective Highly Efficient Catalytic Materials: Synthesis, Structural Characterization and Catalytic Activities  

NASA Astrophysics Data System (ADS)

In this work the covalent anchoring of N-or C-protected Cu(II)—L-tyrosine complexes onto a swellable resin or surface-modified silica gel is described. Experimental conditions (solvents, the availability of ligands) of the synthesis were varied; the structures (by IR spectroscopy) and the superoxide dismutase activities of the anchored complexes were studied.

Pálinkó, István; Ordasi, Adrien; Kiss, János T.; Labádi, Imre

2008-11-01

287

Efficient Dense Stereo and Novel-view Synthesis for Gaze Manipulation in One-to-one Teleconferencing  

Microsoft Academic Search

A new algorithm is proposed for novel-view synthesis, with particular application to teleconferencing. Given the video streams acquired by two cameras placed on either side of a computer monitor, the proposed algorithm synthesises images from a virtual camera in arbitrary position (typically located within the monitor area) to facilitate eye contact. The new technique is based on an improved, dynamic-programming,

Antonio Criminisi; Jamie Shotton; Andrew Blake; Carsten Rother; Philip H. S. Torr

2003-01-01

288

Efficient metal-free synthesis of various pyrido[2',1':2,3]imidazo- [4,5-b]quinolines.  

PubMed

Dancing with diversity: The synthesis of diverse pyrido[2',1':2,3]imidazo[4,5-b]quinolines bearing several substitution patterns was developed based on combining a multicomponent reaction (Groebke-Blackburn-Bienaymé reaction) with an original cyclization as a secondary transformation (see scheme; DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). PMID:23955568

Arnould, Mathieu; Hiebel, Marie-Aude; Massip, Stéphane; Léger, Jean Michel; Jarry, Christian; Berteina-Raboin, Sabine; Guillaumet, Gérald

2013-09-01

289

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

290

Silver-catalyzed oxidative coupling of aniline and ene carbonyl/acetylenic carbonyl compounds: an efficient route for the synthesis of quinolines.  

PubMed

An efficient silver-mediated coupling of aniline with ene carbonyl/acetylenic carbonyl compounds for the synthesis of quinolines is reported. The transformation is effective for a broad range of substrates, thus enabling the expansion of substituent architectures on the heterocyclic framework. The electronic properties of the substituents on the amine have been investigated. It was found that molecules with both electron-donating and electron-withdrawing substituents were suitable substrates for this transformation, and the expected products were obtained in moderate to excellent yields. The use of a single catalytic system to mediate chemical transformations in a synthetic operation is important for the development of new atom-economic strategies and this strategy is efficient in building complex structures from simple starting materials in an environmentally benign fashion. PMID:25195503

Zhang, Xu; Xu, Xuefeng

2014-11-01

291

Lewis acid promoted construction of chromen-4-one and isoflavone scaffolds via regio- and chemoselective domino Friedel-Crafts acylation/Allan-Robinson reaction.  

PubMed

A facile and efficient synthesis of chromen-4-one and isoflavone frameworks is achieved by the domino C-acylation/O-acylation/aldolization sequence. This operationally simple one-pot elegant strategy provides structurally unique chromen-4-ones and isoflavones directly from phenols via concomitant formation of multiple C-C and C-O bonds in a single operation. The outcomes of the buttressing effect, substituent dependence, and catalyst and solvent specificity during the course of the Friedel-Crafts acylation reactions are demonstrated and supported by fitting experiments. PMID:25299841

Chanda, Tanmoy; Chowdhury, Sushobhan; Koley, Suvajit; Anand, Namrata; Singh, Maya Shankar

2014-10-29

292

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

293

Novel Protocol for the Chemical Synthesis of Crustacean Hyperglycemic Hormone Analogues -- An Efficient Experimental Tool for Studying Their Functions  

PubMed Central

The crustacean Hyperglycemic Hormone (cHH) is present in many decapods in different isoforms, whose specific biological functions are still poorly understood. Here we report on the first chemical synthesis of three distinct isoforms of the cHH of Astacus leptodactylus carried out by solid phase peptide synthesis coupled to native chemical ligation. The synthetic 72 amino acid long peptide amides, containing L- or D-Phe3 and (Glp1, D-Phe3) were tested for their biological activity by means of homologous in vivo bioassays. The hyperglycemic activity of the D-isoforms was significantly higher than that of the L-isoform, while the presence of the N-terminal Glp residue had no influence on the peptide activity. The results show that the presence of D-Phe3 modifies the cHH functionality, contributing to the diversification of the hormone pool. PMID:22253873

Mosco, Alessandro; Zlatev, Vientsislav; Guarnaccia, Corrado; Pongor, Sandor; Campanella, Antonella; Zahariev, Sotir; Giulianini, Piero G.

2012-01-01

294

Novel protocol for the chemical synthesis of crustacean hyperglycemic hormone analogues--an efficient experimental tool for studying their functions.  

PubMed

The crustacean Hyperglycemic Hormone (cHH) is present in many decapods in different isoforms, whose specific biological functions are still poorly understood. Here we report on the first chemical synthesis of three distinct isoforms of the cHH of Astacus leptodactylus carried out by solid phase peptide synthesis coupled to native chemical ligation. The synthetic 72 amino acid long peptide amides, containing L- or D-Phe³ and (Glp¹, D-Phe³) were tested for their biological activity by means of homologous in vivo bioassays. The hyperglycemic activity of the D-isoforms was significantly higher than that of the L-isoform, while the presence of the N-terminal Glp residue had no influence on the peptide activity. The results show that the presence of D-Phe³ modifies the cHH functionality, contributing to the diversification of the hormone pool. PMID:22253873

Mosco, Alessandro; Zlatev, Vientsislav; Guarnaccia, Corrado; Pongor, Sándor; Campanella, Antonella; Zahariev, Sotir; Giulianini, Piero G

2012-01-01

295

An efficient colorimetric assay for RNA synthesis by viral RNA-dependent RNA polymerases, using thermostable pyrophosphatase.  

PubMed

RNA-dependent RNA polymerase (RdRp) is essential for the replication of RNA genome-containing positive-strand RNA viruses. We developed a simple colorimetric assay to quantify the RNA synthesis activity of RdRp by measuring the pyrophosphates released during nascent RNA synthesis. RNA polymerase reaction was quenched by heating at 70 °C for 5 min, during which thermostable inorganic pyrophosphatase converted the accumulated pyrophosphates into inorganic phosphates. Subsequently, the amount of inorganic phosphate was measured using a color-developing reagent. Using RdRp's from hepatitis C virus and foot-and-mouth disease virus, we demonstrate that this colorimetric assay facilitates the measurement of RNA polymerase activity. PMID:23219564

Nguyen, Hanh Thi Dieu; Chong, Youhoon; Oh, Deok-Kun; Heo, Yong-Seok; Viet, Pham Tan; Kang, Lin-Woo; Jeon, Sung-Jong; Kim, Dong-Eun

2013-03-15

296

Highly efficient four-component synthesis of 4(3H)-quinazolinones: palladium-catalyzed carbonylative coupling reactions.  

PubMed

Given the importance of quinazolinones and carbonylative transformations, a palladium-catalyzed four-component carbonylative coupling system for the synthesis of diverse 4(3H)-quinazolinone in a concise and convergent fashion has been developed. Starting from 2-bromoanilines (1?mmol), trimethyl orthoformate (2?mmol), and amines (1.1?mmol), under 10?bar of CO, the desired products were isolated in good yields in the presence of Pd(OAc)2 (2?mol?%), BuPAd2 (6?mol?%) in 1,4-dioxane (2?mL) at 100?°C, using N,N-diisopropylethylamine (2?mmol) as the base. Notably, the process tolerates the presence of various reactive functional groups and is very selective for quinazolinones, and was used in the synthesis of the precursor to the bioactive dihydrorutaempine. PMID:24338922

He, Lin; Li, Haoquan; Neumann, Helfried; Beller, Matthias; Wu, Xiao-Feng

2014-01-27

297

Palladium-catalyzed carbonylation of 2-bromoanilines with 2-formylbenzoic Acid and 2-halobenzaldehydes: efficient synthesis of functionalized isoindolinones.  

PubMed

A concise and highly versatile method for the synthesis of functionalized isoindolinones is reported. Various 2-bromoanilines undergo palladium-catalyzed carbonylation with 2-formylbenzoic acid under a convenient and mild procedure to give good to excellent yields of the corresponding isoindolinones. Additionally, 2-halobenzaldehydes can be applied as substrates in palladium-catalyzed double-carbonylation to provide identical compounds in moderate to good yields. PMID:25212125

Natte, Kishore; Chen, Jianbin; Li, Haoquan; Neumann, Helfried; Beller, Matthias; Wu, Xiao-Feng

2014-10-27

298

A short and efficient synthesis of 1-deoxy-castanospermine and 1-deoxy-8a- epi-castanospermine  

Microsoft Academic Search

A new route for the synthesis of 1-deoxy-castanospermine 2 and 1-deoxy-8a-epi-castanospermine 3 has been developed via a sequential triple reductive amination process of a suitably protected d-gluco-oct-5-ulo-1,8-dialdose, which was easily prepared by three carbon homologation of readily available ?-d-xylo-pentodialdose using an appropriate Grignard reagent followed by oxidation.

Nitin T Patil; Jayant N Tilekar; Dilip D Dhavale

2001-01-01

299

Efficient synthesis of 3-(4,5-dihydro-1 H-imidazole-2-yl)-1 H-indoles  

Microsoft Academic Search

A simple method for the synthesis of various 3-(4,5-dihydro-1H-imidazole-2-yl)-1H-indoles is described. Treatment of different substituted indoles with 1-acetyl-imidazolidin-2-one in the presence of phosphorus oxychloride afforded after hydrolysis in ethanol the corresponding 3-(4,5-dihydro-1H-imidazole-2-yl)-1H-indoles in moderate to good yields.

Ulrike Hary; Ulrike Roettig; Michael Paal

2001-01-01

300

Abnormalities in exercising skeletal muscle in congestive heart failure can be explained in terms of decreased mitochondrial ATP synthesis, reduced metabolic efficiency, and increased glycogenolysis.  

PubMed Central

OBJECTIVE: To distinguish between the effects of reduced oxidative capacity and reduced metabolic efficiency on skeletal muscle bioenergetics during exercise in patients with congestive heart failure. DESIGN AND PATIENTS: Patients were studied by 31P magnetic resonance spectroscopy during aerobic exercise and recovery, and results compared with controls. RESULTS: In flexor digitorum superficialis muscle (26 patients) there was a 30% decrease in oxidative capacity compared with control (mean (SE) 36 (2) v 51 (4) mM/min) and also a 40% decrease in "effective muscle mass" (5 (1) v 9 (1) arbitrary units), probably at least partly the result of reduced metabolic efficiency. Both contribute to increased phosphocreatine depletion and intracellular acidosis during exercise. However, an increased concentration of ADP (an important mitochondrial regulator) during exercise permitted near-normal rates of oxidative ATP synthesis. Results were similar in gastrocnemius muscle (20 patients), with a 30% decrease in maximum oxidative capacity (29 (4) v 39 (3) mM/min) and a 65% decrease in effective muscle mass (5 (1) v 13 (2) arbitrary units). Exercise training improved maximum oxidative capacity in both muscles, and in gastrocnemius effective muscle mass also. CONCLUSIONS: Skeletal muscle exercise abnormalities in patients with congestive heart failure results more from decreased metabolic efficiency than from the abnormalities in mitochondrial oxidation. Both decreased efficiency and defective mitochondrial oxidation result in an increased activation of glycogen phosphorylase, and may be improved by exercise training. PMID:8774325

Kemp, G. J.; Thompson, C. H.; Stratton, J. R.; Brunotte, F.; Conway, M.; Adamopoulos, S.; Arnolda, L.; Radda, G. K.; Rajagopalan, B.

1996-01-01

301

An efficient microwave-assisted synthesis method for the production of water soluble amine-terminated Si nanoparticles  

NASA Astrophysics Data System (ADS)

Silicon nanoparticles can be considered a green material, especially when prepared via a microwave-assisted method without the use of highly reactive reducing agents or hydrofluoric acid. A simple solution synthesis of hydrogen-terminated Si- and Mn-doped Si nanoparticles via microwave-assisted synthesis is demonstrated. The reaction of the Zintl salt, Na4Si4, or Mn-doped Na4Si4, Na4Si4(Mn), with ammonium bromide, NH4Br, produces small dispersible nanoparticles along with larger particles that precipitate. Allylamine and 1-amino-10-undecene were reacted with the hydrogen-terminated Si nanoparticles to provide water solubility and stability. A one-pot, single-reaction process and a one-pot, two-step reaction process were investigated. Details of the microwave-assisted process are provided, with the optimal synthesis being the one-pot, two-step reaction procedure and a total time of about 15 min. The nanoparticles were characterized by transmission electron microscopy (TEM), x-ray diffraction, and fluorescence spectroscopies. The microwave-assisted method reliably produces a narrow size distribution of Si nanoparticles in solution.

Atkins, Tonya M.; Y Louie, Angelique; Kauzlarich, Susan M.

2012-07-01

302

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

PubMed

DNA polymerase ? (Pol?) is the only known Y-family DNA polymerase that bypasses the 10S (+)-trans-anti-benzo[a]pyrene diol epoxide (BPDE)-N(2)-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-N(2)-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 PGM2(52-516) but not PGM1(52-516) 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

2014-02-01

303

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

304

Preparation of Au/CeO2 exhibiting strong surface plasmon resonance effective for selective or chemoselective oxidation of alcohols to aldehydes or ketones in aqueous suspensions under irradiation by green light.  

PubMed

Au/CeO(2) samples with various Au contents were prepared by the multistep (MS) photodeposition method. Their properties including Au particle size, particle dispersion, and photoabsorption were investigated and compared with properties of samples prepared by using the single-step (SS) photodeposition method. The MS- and SS-Au/CeO(2) samples were used for selective oxidation of benzyl alcohols to corresponding benzaldehydes in aqueous suspensions under irradiation by visible light from a green LED, and the correlations between reaction rates and physical properties of the MS- and SS-Au/CeO(2) samples were investigated. Difference in the two photodeposition methods was reflected in the average size and number of Au nanoparticles, for example, 92 nm and 1.3 × 10(12) (g-Au/CeO(2))(-1) for MS photodeposition and 59 nm and 4.8 × 10(12) (g-Au/CeO(2))(-1) for SS photodeposition in the case of 1.0 wt % Au samples. Fixation of larger Au particles resulted in strong photoabsorption of the MS-Au/CeO(2) samples at around 550 nm due to the surface plasmon resonance, and the Kubelka-Munk function of the photoabsorption linearly increased with increase in Au content up to 2.0 wt %, in contrast to the photoabsorption of SS-Au/CeO(2) samples, which was weak and was saturated even at around 0.5 wt %. Due to the strong photoabsorption, the MS-Au/CeO(2) samples exhibited reaction rates approximately twice larger than those of SS-Au/CeO(2) samples with the same Au contents, and apparent quantum efficiency of MS-Au/CeO(2) reached 4.9% at 0.4 mW cm(-2). Linear correlations were observed between reaction rates (r) and surface area of Au nanoparticles (S) in both MS- and SS-Au/CeO(2) samples, though the two slopes of r versus S plots were different, suggesting that oxidation of benzyl alcohol occurred on the Au surface and that S was one of the important factors controlling the reaction rate. Photocatalytic oxidation of benzyl alcohol having an amino group revealed that the Au/CeO(2) photocatalyst exhibited high chemoselectivity toward the hydroxyl group of alcohol, i.e, the Au/CeO(2) photocatalyst almost quantitatively converted aminobenzyl alcohol to aminobenzaldehyde with 99% yield. PMID:22876761

Tanaka, Atsuhiro; Hashimoto, Keiji; Kominami, Hiroshi

2012-09-01

305

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

306

Synthesis of fluorene- and anthracene-based ?-conjugated polymers and dependence of emission range and luminous efficiency on molecular weight  

Microsoft Academic Search

In the present work poly[9,9-dioctylfluorene-co-2-pentyl-9,10-bis(4-vinylphenyl)anthracene], a fluorene- and anthracene-based copolymer, is synthesized through a Heck coupling reaction. In order to synthesize polymers with high-molecular weight, DMF (P1), DMF\\/p-Xylene=1\\/1 (P2), p-Xylene (P3), and 1,4-Dioxane (P4) are used as solvents, which are an important factor in the synthesis process. The number of average molecular weights (Mn) of the synthesized polymers P1–P4 do

Jang Yong Lee; Min Hee Choi; Doo Kyung Moon; Jung Rim Haw

2010-01-01

307

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; Vazquez, Patricia G.; Romanelli, Gustavo P.

2012-01-01

308

Carbohydrate-Binding Module-Cyclodextrin Glycosyltransferase Fusion Enables Efficient Synthesis of 2-O-d-Glucopyranosyl-l-Ascorbic Acid with Soluble Starch as the Glycosyl Donor  

PubMed Central

In this study, we achieved the efficient synthesis of 2-O-d-glucopyranosyl-l-ascorbic acid (AA-2G) from soluble starch by fusing a carbohydrate-binding module (CBM) from Alkalimonas amylolytica ?-amylase (CBMAmy) to cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans. One fusion enzyme, CGT-CBMAmy, was constructed by fusing the CBMAmy to the C-terminal region of CGTase, and the other fusion enzyme, CGT?E-CBMAmy, was obtained by replacing the E domain of CGTase with CBMAmy. The two fusion enzymes were then used to synthesize AA-2G from soluble starch as a cheap and easily soluble glycosyl donor. Under the optimal conditions, the AA-2G yields produced using CGT?E-CBMAmy and CGT-CBMAmy were 2.01 g/liter and 3.03 g/liter, respectively, which were 3.94- and 5.94-fold of the yield from the wild-type CGTase (0.51 g/liter). The reaction kinetics of the two fusion enzymes were analyzed and modeled to confirm the enhanced specificity toward soluble starch. It was also found that, compared to the wild-type CGTase, the two fusion enzymes had relatively high hydrolysis and disproportionation activities, factors that favor AA-2G synthesis. Finally, it was speculated that the enhancement of soluble starch specificity may be related to the changes of substrate binding ability and the substrate binding sites between the CBM and the starch granule. PMID:23503312

Han, Ruizhi; Li, Jianghua; Shin, Hyun-Dong; Chen, Rachel R.; Du, Guocheng

2013-01-01

309

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

310

Base-assisted one-pot synthesis of N,N',N"-triaryltriazatriangulenium dyes: enhanced fluorescence efficiency by steric constraints.  

PubMed

In this paper we report the first synthesis of cationic N,N',N"-triaryltriazatriangulenium dyes (Ar(3)-TATA(+)). Previously, only alkyl-substituted triazatriangulenium derivatives (R(3)-TATA(+)) were known, a consequence of the low reactivity of anilines in the aromatic nucleophilic substitution reaction leading to the formation of the TATA(+) core. The synthesis of Ar(3)-TATA(+) was achieved by heating the tris(2,6-dimethoxyphenyl)methylium ion (DMP(3)C(+)) in various anilines in the presence of NaH. In the solvent-free reaction all three aryl substituents could be introduced despite the low reactivity of the anilines. The symmetric Ar(3)-TATA(+) derivatives with Ar = phenyl (2), 4-methoxyphenyl (3), and 4-bromophenyl (4) were synthesized. Single crystal structures of 2 and 4 were obtained as BF(4)(-) salts, where torsional angles larger than 80° were observed between the TATA(+) chromophore and the aryl substituents. The photophysical properties were studied in solution and in thin films. The results show that the Ar(3)-TATA(+) dyes have a surprising 3-fold increase in fluorescence quantum yields when compared to the parent alkyl-substituted R(3)-TATA(+) salts. With a high quantum yield (>50%) and emission in the red (?(fl) = 560 nm) the Ar(3)-TATA(+) dyes represent a promising new addition to the family of superstable cationic triangulenium dyes. Additionally, the synthesized tribromo derivative 4 is shown to be a potential triagonal synthon for polymers and other macromolecules. PMID:22616844

Hammershøj, Peter; Sørensen, Thomas Just; Han, Bao-Hang; Laursen, Bo W

2012-07-01

311

Simple Synthesis and Biological Evaluation of Some Benzimidazoles Using Sodium Hexafluroaluminate, Na 3 AlF 6 , as an Efficient Catalyst  

PubMed Central

Considerable attention has been focused on the synthesis of benzimidazoles due to having a broad spectrum of biological activities such as anti-parasitic, fungicidal, anti-thelemintic and anti-inflammatory activities. As a part of our research work in this area, a series of benzimidasole derivatives (3a-n) were synthesized in good to high yields by reaction of o-phenylenediamine and different aromatic aldehydes in the presence of sodium hexafluroaluminate, Na3AlF6, as an efficient catalyst at 50 ?C. This environmentally benign and practical method offers several advantages, such as high yields, use of available catalyst, mild reaction conditions and easy workup. The antibacterial activity of these benzimidasoles was also evaluated using Staphylococcus aureus (mm) and Escherichia coli (mm) bacterial strain. All synthesized materials were characterized using IR and NMR spectroscopy as well as microanalyses data. PMID:24734060

Mobinikhaledi, Akbar; Hamta, Ahmad; Kalhor, Mehdi; Shariatzadeh, Mehdi

2014-01-01

312

Synthesis of POSS-based ionic conductors with low glass transition temperatures for efficient solid-state dye-sensitized solar cells.  

PubMed

Replacing liquid-state electrolytes with solid-state electrolytes has been proven to be an effective way to improve the durability of dye-sensitized solar cells (DSSCs). We report herein the synthesis of amorphous ionic conductors based on polyhedral oligomeric silsesquioxane (POSS) with low glass transition temperatures for solid-state DSSCs. As the ionic conductor is amorphous and in the elastomeric state at the operating temperature of DSSCs, good pore filling in the TiO2 film and good interfacial contact between the solid-state electrolyte and the TiO2 film can be guaranteed. When the POSS-based ionic conductor containing an allyl group is doped with only iodine as the solid-state electrolyte without any other additives, power conversion efficiency of 6.29% has been achieved with good long-term stability under one-sun soaking for 1000 h. PMID:24933357

Zhang, Wei; Wang, Zhong-Sheng

2014-07-01

313

Aqueous SDS micelle-promoted acid-catalyzed domino ABB' imino Diels-Alder reaction: a mild and efficient synthesis of privileged 2-methyl-tetrahydroquinoline scaffolds.  

PubMed

A new green protocol for the efficient synthesis of pharmacologically relevant 4-amidyl-2-methyl-1,2,3,4-tetrahydroquinolines (THQs) through the domino type ABB' imino Diels-Alder reaction in acidified water in the presence of sodium dodecyl sulphate (SDS) surfactant was developed for the first time. The influence of the SDS micelles and their different concentrations (5.0, 8.2 and 12.0 mM) on reactivity of the imino Diels-Alder reaction was studied. It was found that the best THQ yields (70-99%) are achieved above the critical micellar concentration (12 mM) using pH 1.0-2.5. This procedure resulted in a general and clean environmentally benign protocol to obtain the privileged diastereospecific cis 2,4-disubstituted THQ molecules of highest biological interest. PMID:23615634

Merchán Arenas, Diego R; Martínez Bonilla, Carlos A; Kouznetsov, Vladimir V

2013-06-14

314

Efficient continuous-flow synthesis of novel 1,2,3-triazole-substituted ?-aminocyclohexanecarboxylic acid derivatives with gram-scale production  

PubMed Central

Summary The preparation of novel multi-substituted 1,2,3-triazole-modified ?-aminocyclohexanecarboxylic acid derivatives in a simple and efficient continuous-flow procedure is reported. The 1,3-dipolar cycloaddition reactions were performed with copper powder as a readily accessible Cu(I) source. Initially, high reaction rates were achieved under high-pressure/high-temperature conditions. Subsequently, the reaction temperature was lowered to room temperature by the joint use of both basic and acidic additives to improve the safety of the synthesis, as azides were to be handled as unstable reactants. Scale-up experiments were also performed, which led to the achievement of gram-scale production in a safe and straightforward way. The obtained 1,2,3-triazole-substituted ?-aminocyclohexanecarboxylates can be regarded as interesting precursors for drugs with possible biological effects. PMID:23946850

Ötvös, Sándor B; Georgiádes, Ádám; Mándity, István M; Kiss, Lóránd

2013-01-01

315

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

316

[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

317

A Brønsted acidic ionic liquid as an efficient and environmentally benign catalyst for biodiesel synthesis from free fatty acids and alcohols.  

PubMed

Biodiesel could be synthesized using Brønsted acidic ionic liquid N-methyl-2-pyrrolidonium methyl sulfonate ([NMP][CH(3)SO(3)]) as a catalyst, specially with free long-chain fatty acids or their mixtures, as well as with low-molecular weight alcohols as substrates. This catalyst showed good catalytic and reusable performance under mild conditions and without any additional organic solvent. The ionic liquid could be reused eight times after the water in the ionic liquid was removed. The yields of fatty acid alkyl esters could reach between 93.6% and 95.3% after the esterifications were carried out at 70 degrees C for 8h. Therefore, an efficient and environmentally friendly catalyst was provided for the synthesis of biodiesel from low-cost feedstocks such as waste oils. PMID:19427782

Zhang, Lei; Xian, Mo; He, Yucai; Li, Liangzhi; Yang, Jianming; Yu, Shitao; Xu, Xin

2009-10-01

318

Synthesis of Graphite Oxide-Fe3O4 Nanocomposites for Rapid and Efficient Removal of Environmental Contaminants.  

E-print Network

??I. Combined Tween 20-stabilized Gold Nanoparticles and Reduced Graphite Oxide-Fe3O4 Nanoparticle Composites for Rapid and Efficient Removal of Mercury Species in Environmental Water This study… (more)

Shih, Ya-Chen

2014-01-01

319

Deposition of Cryptosporidium parvum oocysts in porous media: a synthesis of attachment efficiencies measured under varying environmental conditions.  

PubMed

An extensive set of column experiments was performed with freshly harvested Cryptosporidium parvum oocysts to evaluate the effects of solution chemistry, surface coatings, interactions with other suspended particles, and pore fluid velocity on the fate and transport of this widely occurring waterborne pathogen in sandy porous media. We synthesized our data set with a comprehensive literature survey of similar experiments, to compute attachment (collision) efficiencies (?) used in colloid filtration theory (CFT) using three models for the single collector efficiency (?) across a wide range of experimental conditions. Most prior experiments have observed the transport of surface-treated, sterile C. parvum oocyst in porous media. Our column data confirm for freshly harvested oocysts that the presence of iron coatings on the sand medium and the presence of suspended illite clay drastically enhance oocyst deposition. Increasing ionic strength and decreasing pH also systematically enhance the attachment efficiency. Attachment efficiency decreases only at a very high ionic strength, most likely as a result of steric repulsion and possibly other changes in oocyst surface properties. Attachment efficiencies vary with fluid flow rate but without showing specific trends. We found that the computed attachment efficiency across all reported experiments could be reliably estimated using a regression model based on parameters related to ionic strength and pH. The regression model performed better with the Nelson-Ginn ? model and Tufenkji-Elimelech ? model than with the Rajagopalan-Tien ? model. When CFT is used in environmental assessments, the proposed regression model provides a practical estimator for attachment efficiencies of C. parvum oocyst deposition in porous media for a variety of environmental conditions unfavorable to attachment. PMID:22861686

Park, Yeonjeong; Atwill, E Robert; Hou, Lingling; Packman, Aaron I; Harter, Thomas

2012-09-01

320

In-line coupling of a reversed-phase column to cope with limited chemoselectivity of a quinine carbamate-based anion-exchange type chiral stationary phase.  

PubMed

A chiral stationary phase based on tert-butylcarbamoyl quinine has shown remarkable enantiomer separation capability for the thyroid hormone thyroxine (T(4)) and its structural analogue triiodothyronine (T(3)) employing hydroorganic buffered mobile phases (typical RP conditions). To overcome the problem of a somehow limited chemoselectivity for the critical peak pair between adjacent L-thyroxine (L-T(4)) and D-thyroxine (D-T(4)) peaks on the chiral anion-exchanger CSP when all four compounds need to be analysed simultaneously like in impurity profiling of L-T(4 )drug products, an RP column (Gemini C18) was serially coupled with the chiral anion-exchanger column to add a hydrophobic selectivity increment and to improve thereby the critical resolution between L-T(3) and D-T(4). Various parameters such as organic modifier content, pH, buffer concentration and type, type of achiral column as well as sequence of achiral and chiral column have been investigated with individual and tandem columns. With the optimized conditions and use of the tandem column a significantly improved separation, as compared to the chiral anion-exchanger column alone, with a critical resolution as high as 3.7 and an almost equal band spacing of the four components of the test mixture could be obtained. The sequence of the columns (achiral-chiral or chiral-achiral) had no significant effect on the separation performance. PMID:18428182

Sardella, Roccaldo; Lämmerhofer, Michael; Natalini, Benedetto; Lindner, Wolfgang

2008-06-01

321

An Eco-Friendly Improved Protocol for the Synthesis of Bis(3-indolyl)methanes Using Poly(4-vinylpyridinium)hydrogen Sulfate as Efficient, Heterogeneous, and Recyclable Solid Acid Catalyst  

PubMed Central

Highly efficient and eco-friendly protocol for the synthesis of bis(3-indolyl)methanes by the electrophilic substitution reaction of indole with aldehydes catalyzed by poly(4-vinylpyridinium)hydrogen sulfate was described. Excellent yields, shorter reaction times, simple work-up procedure, avoiding hazardous organic solvents, and reusability of the catalyst are the most obvious advantages of this method. PMID:24052864

Banothu, Janardhan; Gali, Rajitha; Velpula, Ravibabu; Bavantula, Rajitha; Crooks, Peter A.

2013-01-01

322

A novel and efficient synthesis of pyrimido[4,5- d]pyrimidine-2,4,7-trione and pyrido[2,3- d:6,5- d] dipyrimidine-2,4,6,8-tetrone derivatives  

Microsoft Academic Search

An efficient and direct procedure for the synthesis of pyrimido[4,5-d]pyrimidine-2,4,7-trione derivatives has been described under microwave-assisted conditions. Reaction of 6-amino-1,3-dimethyluracil with aromatic aldehydes resulted in the formation of pyrido[2,3-d:6,5-d] dipyrimidine-2,4,6,8-tetrone derivatives.

Minoo Dabiri; Hamid Arvin-Nezhad; Hamid Reza Khavasi; Ayoob Bazgir

2007-01-01

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

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

325

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; Kahlig, Hanspeter

2014-01-01

326

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

327

Efficient removal of methylene blue over composite-phase BiVO4 fabricated by hydrothermal control synthesis  

E-print Network

Efficient removal of methylene blue over composite-phase BiVO4 fabricated by hydrothermal control of methylene blue under visible light. It was found that composite-phase BiVO4 with hmono > 60% presented% of the 10 mg LÃ?1 methylene blue was degraded within 120 min catalyzed by the best catalyst BiVO4 with hmono

Cao, Guozhong

328

2-Diazoacetoacetic acid, an efficient and convenient reagent for the synthesis of a-diazo-b-ketoesters{  

E-print Network

of the esterification with a number of alcohols.13 As shown in Table 1, esterification occurs efficiently for a variety-ketoesters in good yields (entries 1, 2, 9­11).14 As shown in entry 8, 3-methoxyphenol undergoes esterification

Stoltz, Brian M.

329

Investigation of facet effects on the catalytic activity of Cu2O nanocrystals for efficient regioselective synthesis of 3,5-disubstituted isoxazoles.  

PubMed

Cubic, octahedral, and rhombic dodecahedral Cu2O nanocrystals bound by respectively {100}, {111}, and {110} facets were successfully employed to catalyze the [3 + 2] cycloaddition reaction for the regioselective synthesis of 3,5-disubstituted isoxazoles. Surfactant-free nanocrystals having the same total surface area were used for the catalysis. Strongly facet-dependent organocatalytic activity has been observed. Rhombic dodecahedra with fully exposed surface copper atoms on the (110) planes are the most efficient catalysts, followed by octahedra and the least active nanocubes. The particles are also recyclable catalysts. Cu2O rhombic dodecahedra were also used for the syntheses of 3,5-disubstituted isoxazoles from a wide variety of aromatic imidoyl chlorides and terminal alkynes in ethanol at 50 °C with excellent yields. Furthermore, a one-pot multi-component synthetic approach was demonstrated to form isoxazoles directly from readily available aldehyde precursors. This work clearly shows that precise facet engineering of Cu2O crystals can lead to significantly improved organocatalytic efficiency. PMID:24165690

Chanda, Kaushik; Rej, Sourav; Huang, Michael H

2013-12-21

330

Synthesis and characterization of cesium molybdo vanado phosphate immobilized on platelet SBA-15: An efficient inorganic composite ion-exchanger for gadolinium ion sorption  

NASA Astrophysics Data System (ADS)

A series of cesium molybdo vanado phosphate (CsMVP) supported on platelet SBA-15 (SBA-15-%xCsMVP, x = 20, 30, 40 and 50 wt.%) was synthesized to develop an efficient inorganic composite ion-exchanger for gadolinium ion removal from aqueous solution. The preparation has been carried out using two-step aqueous impregnation methods. The obtained products were characterized by inductively coupled plasma (ICP), XRD, N2 adsorption-desorption isotherms, scanning electron microscopy (SEM) and FT-IR. In order to examine adsorption behavior of this compound on gadolinium removal, the effect of heteropoly metalate loading, pH, contact time, concentration of metal ion and temperature were investigated under batch system conditions. The SBA-15-30%CsMVP showed maximum adsorption capacity toward gadolinium removal. The results suggested that this methodology provides the general synthesis of supported heteropolymetalate with large surface areas, and ordered nano porous structures that can be used as inorganic composite ion-exchanger for efficient removal of gadolinium ions from aqueous solution.

Aghayan, H.; Khanchi, A. R.; Mahjoub, A. R.

2013-06-01

331

Efficient Synthesis, Liquid-Chromatography Purification, and Tandem Mass Spectrometric Characterization of Estrogen-Modified DNA Bases  

PubMed Central

Estrogens are metabolized to active quinones that modify DNA and may lead to various cancers. To extend the analytical methodology for estrogen-modified purine bases, we report here a simple modification to existing synthetic procedures that use 2-iodoxybenzoic acid (IBX) as the oxidizing agent for the reference material and putative biomarker, 4-hydroxyestrone-1-N3Adenine (4-OH-E1-1-N3Ade). The reaction leads to two catechol estrogen quinones, CE1-2,3-Q and CE1-3,4-Q, both of which react via Michael additions to afford 4-OH-E1-1-N3Ade and other DNA adducts. LC separation permits the isolation of high-purity 4-OH-E1-1-N3Ade. With this method, we also prepared single-13C and uniformly-15N (U-15N) labeled 4-OH-E1-1-N3Ade with 8-13C-labeled Ade and U-15N-labeled adenosine 5?-monophosphate (AMP). The approach is also effective for the synthesis of 4-hydroxyestradiol-1-N3Adenine, 4-OH-E2-1-N3Ade, and 4-hydroxyestrone(estradiol)-1-N7Guanine, 4-OH-E1(E2)-1-N7Gua. The tandem mass spectra (MS2 and MS3) of 4-OH-E1-(unlabeled, 8-13C-, and U-15N-labeled)1-N3Ade and accurate mass measurements for MS2 product ions allow us to assign unambiguously the formula of fragments and delineate the fragmentation pathways. One important reaction is dehydration, which occurs at the ketone oxygen in C-17 position of estrone. Another is loss of NH3, a ubiquitous process for purines and modified purines, which is affected by the steroid modification. Evidence from MS/MS supports the migration of H-atom(s) from estrone in the loss of NH3. An interesting interaction occurs between the steroid and Ade in the modified base, promoting loss of CH2NH, a loss that distinguishes modified Ade from unmodified Ade. The synthesis of a stable-isotope-labeled 4-OH-E1-1-N3Ade and the understanding of the fragmentation processes will enable studies aimed at detection of naturally occurred 4-OH-E1-1-N3Ade in biological samples. PMID:18512969

Zhang, Qiang; Gross, Michael L.

2009-01-01

332

RACK1 depletion in a mouse model causes lethality, pigmentation deficits and reduction in protein synthesis efficiency.  

PubMed

The receptor for activated C-kinase 1 (RACK1) is a conserved structural protein of 40S ribosomes. Strikingly, deletion of RACK1 in yeast homolog Asc1 is not lethal. Mammalian RACK1 also interacts with many nonribosomal proteins, hinting at several extraribosomal functions. A knockout mouse for RACK1 has not previously been described. We produced the first RACK1 mutant mouse, in which both alleles of RACK1 gene are defective in RACK1 expression (?F/?F), in a pure C57 Black/6 background. In a sample of 287 pups, we observed no ?F/?F mice (72 expected). Dissection and genotyping of embryos at various stages showed that lethality occurs at gastrulation. Heterozygotes (?F/+) have skin pigmentation defects with a white belly spot and hypopigmented tail and paws. ?F/+ have a transient growth deficit (shown by measuring pup size at P11). The pigmentation deficit is partly reverted by p53 deletion, whereas the lethality is not. ?F/+ livers have mild accumulation of inactive 80S ribosomal subunits by polysomal profile analysis. In ?F/+ fibroblasts, protein synthesis response to extracellular and pharmacological stimuli is reduced. These results highlight the role of RACK1 as a ribosomal protein converging signaling to the translational apparatus. PMID:23212600

Volta, Viviana; Beugnet, Anne; Gallo, Simone; Magri, Laura; Brina, Daniela; Pesce, Elisa; Calamita, Piera; Sanvito, Francesca; Biffo, Stefano

2013-04-01

333

Synthesis and efficient blue-emitting of Eu2+-activated borate fluoride BaAlBO3F2  

NASA Astrophysics Data System (ADS)

Eu2+-doped borate fluoride BaAlBO3F2 was synthesized by the conventional high temperature solid state reaction. The crystal phase formations were confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence (PL) excitation and emission spectra, and the decay curves were investigated. Eu2+-doped BaAlBO3F2 phosphor can be efficiently excited by near-UV light and presents narrow blue luminescence band centered at 450 nm. The maximum absolute quantum efficiency (QE) of BaAlBO3F2:0.05Eu2+ phosphor was measured to be 76% excited at 398 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability with high thermal activation-energy on temperature quenching effects because of the rigid crystal lattices.

Tao, Zhengxu; Huang, Yanlin; Cai, Peiqing; Kim, Sun Il; Seo, Hyo Jin

2014-11-01

334

Efficient chemoenzymatic synthesis of biotinylated human serum albumin-sialoglycoside conjugates containing O-acetylated sialic acids  

PubMed Central

Sialyl Tn (STn) and sialyl lactoside derivatives containing O-acetylated sialic acid residues have been synthesized using a one-pot three-enzyme system and conjugated to biotinylated human serum albumin (HSA) using an adipic acid para-nitrophenyl ester coupling reagent. This approach has been proven to be efficient for preparing carbohydrate-protein conjugates containing base-sensitive O-acetyl groups. PMID:17637967

Yu, Hai; Chokhawala, Harshal A.; Varki, Ajit; Chen, Xi

2008-01-01

335

Efficient and General Synthesis of 3-Aminoindolines and 3-Aminoindoles via Copper-Catalyzed Three Component Coupling Reaction  

PubMed Central

An efficient three component coupling (TCC) reaction toward a variety of 3-aminoindoline and 3-aminoindole derivatives has been developed. This cascade transformation proceeds via the copper-catalyzed coupling reaction between 2-aminobenzaldehyde, secondary amine, and alkyne leading to propargylamine intermediate, which, under the reaction conditions, undergoes cyclization into the indoline core. The latter, upon treatment with a base, smoothly isomerizes into indole. Alternatively, indole can directly be synthesized in a one-pot sequential reaction. PMID:23620715

Chernyak, Dmitri; Chernyak, Natalia

2013-01-01

336

Efficient and General Synthesis of 3-Aminoindolines and 3-Aminoindoles via Copper-Catalyzed Three Component Coupling Reaction.  

PubMed

An efficient three component coupling (TCC) reaction toward a variety of 3-aminoindoline and 3-aminoindole derivatives has been developed. This cascade transformation proceeds via the copper-catalyzed coupling reaction between 2-aminobenzaldehyde, secondary amine, and alkyne leading to propargylamine intermediate, which, under the reaction conditions, undergoes cyclization into the indoline core. The latter, upon treatment with a base, smoothly isomerizes into indole. Alternatively, indole can directly be synthesized in a one-pot sequential reaction. PMID:23620715

Chernyak, Dmitri; Chernyak, Natalia; Gevorgyan, Vladimir

2010-04-19

337

Ionic Liquid Promoted Eco-friendly and Efficient Synthesis of 2,3-Dihydroquinazolin-4(1 H )-ones  

Microsoft Academic Search

Summary.  2,3-Dihydroquinazolin-4(1H)-ones were efficiently synthesised by the reaction of isatoic anhydride, a primary amine or ammonium acetate, and different\\u000a aromatic aldehydes in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) without using any acidic catalyst. Also a bis-derivative of the title compound as a polyheterocyclic system was synthesised\\u000a successfully in high yield.

Minoo Dabiri; Peyman Salehi; Mostafa Baghbanzadeh

2007-01-01

338

Solid-Phase Synthesis and Kinetic Characterization of Fluorogenic Enzyme-Degradable Hydrogel Crosslinkers  

PubMed Central

Of critical importance in drug delivery and tissue engineering applications is the degradabilty of implanted polymeric materials. The use of peptide-derived crosslinkers in hydrogel design is a valuable approach by which polymeric carriers can be endowed with enzymatic degradability in a predictable, ‘programmable’ fashion. The solid-phase synthesis strategy described herein allows for an expeditious, flexible synthesis of bis-acrylamide-derivatized peptides with complex modifications, as exemplified by the incorporation of fluorophore and quencher moieties into a matrix metalloprotease (MMP)-degradable crosslinker. The crude synthetic product was obtained in high yield and purity, and purified by standard methods; it was then used directly for polymerization without the need for tedious and often non-chemoselective solution-phase modifications. Functional appendages incorporated for detection provided a direct, quantitative link between enzymatic activity and hydrogel degradation using routine methods for identification of optimal enzyme-specific degradability. PMID:16602715

Moss, Jason A.; Stokols, Shula; Hixon, Mark; Ashley, Fawn; Chang, Jason Y.; Janda, Kim D.

2008-01-01

339

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction.  

PubMed

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method. PMID:12371868

Ling, Taotao; Poupon, Erwan; Rueden, Erik J; Kim, Sun H; Theodorakis, Emmanuel A

2002-10-16

340

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

341

Chemoselective Protection and Deprotection of Aldehydes Using Solid Supported Reagent (Silica Chloride) Under Solvent-Free Conditions  

Microsoft Academic Search

Silica chloride, a heterogeneous catalyst, has been found to be an efficient catalyst for the protection of aldehydes as acylals under solvent-free conditions, and deprotection of acylals to aldehydes in methanol as a solvent occurred. The reaction takes a shorter time and ensures good to excellent yield of the products.

Bandita Datta; M. A. Pasha

2011-01-01

342

Facile and selective synthesis of oligothiophene-based sensitizer isomers: an approach toward efficient dye-sensitized solar cells.  

PubMed

Two sets of isomeric organic dyes with n-hexyl (DH and AH) or 2-ethylhexyl (DEH and AEH) groups substituted at the spacer part have been designed and straightforwardly synthesized via a facile and selective synthetic route. The structure difference between the isomers stands at the position of the incorporated alkyl chains which are introduced into the terthiophene spacer close to the donor (D) or anchor (A) side. The relationship between the isomeric structures and the optoelectronic properties are systematically investigated. It is found that, in the D series dyes, the alkyl group is much closer to the aromatic donor moiety, which brings about strong steric hindrance and therefore causes a remarkable twist in the molecular skeleton. In contrast, a more planar chemical structure and more effective ?-conjugation are realized in the A series dye isomers. Consequently, the A series isomeric dyes demonstrate bathochromically shifted absorption bands, resulting in the improved light-harvesting capability and enhanced photo-generated current. However, the D series isomeric dyes with more twisted molecular skeleton have suppressed the intermolecular interactions and retarded the charge recombination more efficiently, which induces higher open-circuit photovoltage. Combining the two effects on the performance of the fabricated dye-sensitized solar cells (DSSC), the influence from the short-circuit photocurrent plays a more significant role on the power conversion efficiency (?). As a result, isomer AEH-based DSSC with quasi-solid-state electrolyte displays the highest ? of 7.10% which remained at 98% of the initial value after continuous light soaking for 1000 h. Promisingly, a ? of 8.66% has been achieved for AEH-based DSSC with liquid electrolyte containing Co(II)/(III) redox couple. This work presents the crucial issue of molecular engineering and paves a way to design organic sensitizers for highly efficient and stable DSSCs. PMID:23981089

Feng, Quanyou; Zhang, Qian; Lu, Xuefeng; Wang, Hong; Zhou, Gang; Wang, Zhong-Sheng

2013-09-25

343

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

344

Efficient and modular synthesis of new structurally diverse functionalized [n]paracyclophanes by a ring-distortion strategy.  

PubMed

With the goal of synthesizing new [n]paracyclophanes, the expansion of the scope of a strategy originally disclosed by Winterfeldt et?al., was investigated. This approach involves sequential Diels-Alder/retro-Diels-Alder reactions, the applications of which have been constrained so far to steroid derivatives. An efficient access to new functionalized [9]-, [10]-, and [16]paracyclophanes, including original cage architectures, was developed from readily available building blocks using thermal electrocyclization and a cycloaddition/cycloreversion sequence as the key steps. PMID:24981087

Krieger, Jean-Philippe; Ricci, Gino; Lesuisse, Dominique; Meyer, Christophe; Cossy, Janine

2014-08-11

345

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

346

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

347

A high activity adsorbent of ZnO-Al2O3 nanocomposite particles: Synthesis, characterization and dye removal efficiency  

NASA Astrophysics Data System (ADS)

In order to stabilize the ZnO species on surfaces of Al2O3 particles, the ZnO-Al2O3 nanocomposite particles with different ZnO contents were prepared by heterogeneous precipitation method using bayerite seed particles. The as-prepared nanocomposites were characterized in terms of crystal structure, morphology and surface area. The results indicated the formation of wurtzite-type ZnO nanoflakes (thickness of 40-80 nm) on surfaces of ?-Al2O3 particles, which led to nanocomposite particles with high surface areas depending on Al2O3 content. The obtained nanocomposites were used as promising adsorbents in adsorption of methyl orange (MO) from aqueous solution as an anionic dye and were compared with pure ZnO and Al2O3 adsorbents. The nanocomposite adsorbents showed a superior MO removal efficiency than pure adsorbents, which was attributed to unique morphology of ZnO active sites with activated surface charge and also high surface area obtained in nanocomposite adsorbents. Moreover, it was found that there is an optimum between the amount of ZnO active sites and Al2O3 for the maximum of percentage removal of MO, which was obtained for 40%ZnO-Al2O3 adsorbent with 98% efficiency and low equilibrium time of 20 min with a fixed adsorbent concentration of 500 ppm and a fixed dye concentration of 50 ppm.

Tajizadegan, Hamid; Jafari, Majid; Rashidzadeh, Mehdi; Saffar-Teluri, Ali

2013-07-01

348

A Stilbene that Binds Selectively to Transthyretin in Cells and Remains Dark Until it Undergoes a Chemoselective Reaction to Create a Bright Blue Fluorescent Conjugate  

PubMed Central

We describe a non-fluorescent, second generation stilbene that very selectively binds to transthyretin in complex biological environments and remains dark until it chemoselectively reacts with the pKa perturbed Lys-15 ?-amino group of transthyretin to form a bright blue fluorescent conjugate. Stilbene A2 is mechanistically unusual in that it remains non-fluorescent in cell lysates lacking transthyretin, even though there is likely some proteome binding. Thus, it is especially useful for cellular imaging, as background fluorescence is undetectable until A2 reacts with transthyretin. The mechanistic basis for the effective lack of environment-sensitive fluorescence of A2 when bound to, but before reacting with, transthyretin is reported. Stilbene A2 exhibits sufficiently rapid transthyretin conjugation kinetics at 37 °C to enable pulse-chase experiments to be performed, in this case demonstrating that transthyretin is secreted from HeLa cells. As the chase compound, we employed C1–a cell permeable, highly selective, non-covalent, transthyretin binding dihydrostilbene that cannot become fluorescent. The progress reported is viewed as a first and necessary step toward our long-term goal of creating a one-chain, one-binding-site transthyretin tag, whose fluorescence can be regulated by adding A2, or an analogous molecule. Fusing proteins of interest to a one-chain, one-binding-site transthyretin tag regulated by A2 should be useful for studying folding, trafficking and degradation in the cellular secretory pathway, utilizing pulse-chase experiments. Immediate applications of A2 include utilizing its conjugate fluorescence to quantify transthyretin concentration in human plasma, reflecting nutritional status, and determining the binding stoichiometry of kinetic stabilizer drugs to transthyretin in plasma. PMID:20964336

Choi, Sungwook; Ong, Derrick Sek Tong; Kelly, Jeffery W.

2010-01-01

349

Synthesis of dimethyl derivatives of imidazolinone herbicides: their use in efficient gas chromatographic methods for the determination of these herbicides.  

PubMed

The dimethyl derivatives of imazaquin, imazapyr, imazmethapyr, imazethapyr, 2-[4,5 dihydro-1, 4-dimethyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methoxymethyl- 3-pyridine carboxylic acid, 2-[4,5-dihydro-1,4 -dimethyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4-methyl benzoic acid, and 2-[4,5-dihydro-1,4-dimethyl-4-(1-methyl ethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl benzoic acid were prepared and fully characterized. The availability of these derivatives has led to the development of efficient and multiresidue gas chromatographic methods for trace level analysis of imidazolinone herbicides in matrixes such as water, soybean, and soil. PMID:11141261

Anisuzzaman, A K; Amin, M; Ogg, N; Hoq, F; Kanithi, M R; Jenkins, R E

2000-12-01

350

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

351

Controlled synthesis of CuInS2/reduced graphene oxide nanocomposites for efficient dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

A nanocomposite comprised CuInS2 and reduced graphene oxide have been successfully synthesized via a facile two-step hydrothermal route using graphene oxide, thiourea, Indium chloride tetrahydrate and cuprous chloride as the raw materials, and L-Ascorbic acid as the reductant. Compared with pristine CuInS2, CuInS2 and reduced graphene oxide nanocomposites exploited as counter electrodes have exhibited outstanding electrocatalytic activity for the reduction of triiodide and excellent chemical stability due to the introduction of reduced graphene oxide. The characterization measurements indicate that the power conversion efficiency of dye-sensitized solar cell fabricated with CuInS2 and reduced graphene oxide nanocomposites counter electrode achieves 6.96%, which is higher than that of device using pristine CuInS2 counter electrode (5.49%), and comparable to the conventional platinum counter electrode (6.92%) under the same test conditions.

Zhou, Lei; Yang, Xiao; Yang, Bo; Zuo, Xueqin; Li, Guang; Feng, Ali; Tang, Huaibao; Zhang, Haijun; Wu, Mingzai; Ma, Yongqing; Jin, Shaowei; Sun, Zhaoqi; Chen, Xiaoshuang

2014-12-01

352

A scalable graphene sulfur composite synthesis for rechargeable lithium batteries with good capacity and excellent columbic efficiency.  

PubMed

Sulfur nanoparticles wrapped with a conductive graphene framework was synthesized with a high sulfur loading through a scalable one-step process. The graphene-coated sulfur nanostructured composite, when used as cathode for lithium sulfur battery, shows a reversible capacity of 808 mAh g(-1) at a rate of 210 mA g(-1) and an average columbic efficiency of ?98.3% over 100 cycles. It is found that graphene oxide (GO) with a porous structure offers flexible confinement function that helps prevent the loss of active materials, thus extending the cycling life of the electrode. Moreover, reduced graphene oxide provides a conductive network surrounding the sulfur particles, which facilitates both electron transport and ion transportation. This novel one-step, all-solution-based process is scalable and provides a promising approach for potential industrial applications. PMID:24555988

Gao, Xianfeng; Li, Jianyang; Guan, Dongsheng; Yuan, Chris

2014-03-26

353

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

354

Mechanistically Diverse Copper-, Silver-, and Gold- Catalyzed Acyloxy and Phosphatyloxy Migrations: Efficient Synthesis of Heterocycles via Cascade Migration/Cycloisomerization Approach  

PubMed Central

A set of cycloisomerizaton methodologies of alkynyl ketones and imines with concurrent acyloxy, phosphatyloxy, or sulfonyloxy group migration, which allow for the efficient synthesis of multisubstituted furans and N-fused heterocycles has been developed. Investigation of the reaction course by way of employing 17O-labelled substrates allowed for elucidation of the mechanisms behind these diverse transformations. It was found that, while the phosphatyloxy migration in conjugated alkynyl imines in their cycloisomerization to N-fused pyrroles proceeded via a [3,3]-sigmatropic rearrangement, the analogous cycloisomerization of skipped alkynyl ketones proceeds through two consecutive 1,2-migrations, resulting in an apparent 1,3-shift, followed by a subsequent 1,2-migration through competitive oxirenium and dioxolenylium pathways. Investigations of the 1,2-acyloxy migration of conjugated alkynyl ketones en route to furans demonstrated the involvement of a dioxolenylium intermediate. The mechanism of cycloisomerization of skipped alkynyl ketones containing an acyloxy group was found to be catalyst dependent; Lewis and Brønsted acid catalysts caused an ionization/SN1' isomerization to the allene, followed by cycloisomerization to the furan, while transition metal-catalysts evoked a Rautenstrauch-type mechanistic pathway. Furthermore, control experiments in the cycloisomerization of skipped alkynyl ketones under transition metal catalysis revealed that, indeed, these reactions were catalyzed by transition metal complexes as opposed to Brønsted acids resulting from hydrolysis of these catalysts with eventual water. Further synthetic utility of the obtained phosphatyloxy-substituted heterocycles was demonstrated through their efficient employment in the Kumada cross-coupling reaction with various Grignard reagents. PMID:17658805

Schwier, Todd; Sromek, Anna W.; Yap, Dahrika M. L.; Chernyak, Dmitri; Gevorgyan, Vladimir

2008-01-01

355

Two-step electrochemical synthesis of polypyrrole/reduced graphene oxide composites as efficient pt-free counter electrode for plastic dye-sensitized solar cells.  

PubMed

Polypyrrole/reduced graphene oxide (PPy/RGO) composites on the rigid and plastic conducting substrates were fabricated via a facile two-step electrochemical process at low temperature. The polypyrrole/graphene oxide (PPy/GO) composites were first prepared on the substrate with electrochemical polymerization method, and the PPy/RGO composites were subsequently obtained by electrochemically reducing the PPy/GO. The resultant PPy/GO and PPy/RGO composites were porous, in contrast to the dense and flat pristine PPy films. The cyclic voltammetry measurement revealed that resultant composites exhibited a superior catalytic performance for triiodide reduction in the order of PPy/RGO > PPy/GO > PPy. The catalytic activity of PPy/RGO was comparable to that of Pt counter electrode (CE). Under the optimal conditions, an energy conversion efficiency of 6.45% was obtained for a rigid PPy/RGO-based dye-sensitized solar cell, which is 90% of that for a thermally deposited Pt-based device (7.14%). A plastic counter electrode was fabricated by depositing PPy/RGO composites on the plastic ITO/PEN substrate, and then an all-plastic device was assembled and exhibited an energy conversion efficiency of 4.25%, comparable to that of the counterpart using a sputtered-Pt CE (4.83%) on a plastic substrate. These results demonstrated that electrochemical synthesis is a facile low-temperature method to fabricate high-performance RGO/polymer composite-based CEs for plastic DSCs. PMID:25162375

Liu, Wantao; Fang, Yanyan; Xu, Peng; Lin, Yuan; Yin, Xiong; Tang, Guangshi; He, Meng

2014-09-24

356

Efficient methods for sample processing and cDNA synthesis by RT-PCR for the detection of grapevine viruses and viroids.  

PubMed

Template preparation is important in reverse-transcription polymerase chain reaction (RT-PCR)-based detection methods. A TissueLyser with tungsten carbide beads was used for simultaneous processing of up to 48 samples under the same conditions in the development of a simple and rapid procedure to prepare a plant extract for RT reaction. A sandpaper method was also developed by which wood tissue of dormant cuttings could be macerated easily to process with minimal time and effort. It was also demonstrated that the combination use of random primers and oligo dT primer in an RT reaction was efficient for simultaneous cDNA synthesis of viral and viroid RNAs in plant extracts. These template preparation methods were used for the amplification of Grapevine leafroll-associated virus-1,-2, and -3; Grapevine virus A and B; Grapevine rupestris stem pitting-associated virus; Grapevine fleck virus; and Grapevine fanleaf virus. All these viruses tested in this study were reliably detected up to a 10(3)-fold or higher dilution of the original extract. Besides, Hop stunt viroid and Grapevine yellow speckle viroid 1 were well amplified in the same manner as the template preparation and following PCR for virus detection. These methods would contribute to cost-effective testing of a large number of samples through the year and help to detect viral pathogens in grapevine. PMID:16510197

Nakaune, Ryoji; Nakano, Masaaki

2006-06-01

357

High yield production of a soluble bifidobacterial ?-galactosidase (BbgIV) in E. coli DH5? with improved catalytic efficiency for the synthesis of prebiotic galactooligosaccharides.  

PubMed

The bifidobacterial ?-galactosidase (BbgIV) was produced in E. coli DH5? at 37 and 30 °C in a 5 L bioreactor under varied conditions of dissolved oxygen (dO2) and pH. The yield of soluble BbgIV was significantly (P < 0.05) increased once the dO2 dropped to 0-2% and remained at such low values during the exponential phase. Limited dO2 significantly (P < 0.05) increased the plasmid copy number and decreased the cells growth rate. Consequently, the BbgIV yield increased to its maximum (71-75 mg per g dry cell weight), which represented 20-25% of the total soluble proteins in the cells. In addition, the specific activity and catalytic efficiency of BbgIV were significantly (P < 0.05) enhanced under limited dO2 conditions. This was concomitant with a change in the enzyme secondary structure, suggesting a link between the enzyme structure and function. The knowledge generated from this work is very important for producing BbgIV as a biocatalyst for the development of a cost-effective process for the synthesis of prebiotic galactooligosaccharides from lactose. PMID:23383752

Osman, Ali; Tzortzis, George; Rastall, Robert A; Charalampopoulos, Dimitris

2013-03-01

358

Two-dimensional mesoporous carbon nanosheets and their derived graphene nanosheets: synthesis and efficient lithium ion storage.  

PubMed

We report a new solution deposition method to synthesize an unprecedented type of two-dimensional ordered mesoporous carbon nanosheets via a controlled low-concentration monomicelle close-packing assembly approach. These obtained carbon nanosheets possess only one layer of ordered mesopores on the surface of a substrate, typically the inner walls of anodic aluminum oxide pore channels, and can be further converted into mesoporous graphene nanosheets by carbonization. The atomically flat graphene layers with mesopores provide high surface area for lithium ion adsorption and intercalation, while the ordered mesopores perpendicular to the graphene layer enable efficient ion transport as well as volume expansion flexibility, thus representing a unique orthogonal architecture for excellent lithium ion storage capacity and cycling performance. Lithium ion battery anodes made of the mesoporous graphene nanosheets have exhibited an excellent reversible capacity of 1040 mAh/g at 100 mA/g, and they can retain at 833 mAh/g even after numerous cycles at varied current densities. Even at a large current density of 5 A/g, the reversible capacity is retained around 255 mAh/g, larger than for most other porous carbon-based anodes previously reported, suggesting a remarkably promising candidate for energy storage. PMID:23282081

Fang, Yin; Lv, Yingying; Che, Renchao; Wu, Haoyu; Zhang, Xuehua; Gu, Dong; Zheng, Gengfeng; Zhao, Dongyuan

2013-01-30

359

Numerical Optimization of Quenching Efficiency and Particle Size Control in Flame Synthesis of ZrO2 Nanoparticles  

NASA Astrophysics Data System (ADS)

The development of a new quenching design combining rapid cooling with an expansion for controlling the size of nanoparticles synthesized at industrial scale by flame spray pyrolysis was investigated. The design of the quenching device was supported by simulations using a coupled computational fluid dynamics-monodisperse aerosol model to reduce the size of the primary particles and their agglomerate diameters while conserving the production yield at the filter above the burner. The results showed that quenching the spray flame in an open environment led to lower production yield due to the negative velocity of quenching gas which diverted the particles to the bottom of reactor. An additional upstream air flow could help to increase the particle production yield at high air flow rates, while it had a negative effect on the penetration depth of quenching gas inside the main flame which resulted in higher flame heights. The new design showed that adding an enclosure around the burner and quenching ring can significantly increase the quenching efficiency and reduce the particle size. The technique to control the particle size was also studied in this paper.

Torabmostaedi, Hosein; Zhang, Tao

2014-09-01

360

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

361

Palladium-catalyzed one-pot three- or four-component coupling of aryl iodides, alkynes, and amines through C-N bond cleavage: efficient synthesis of indole derivatives.  

PubMed

An efficient synthesis of N-substituted indole derivatives was realized by combining the Pd-catalyzed one-pot multicomponent coupling approach with cleavage of the C(sp(3))-N bonds. Three or four components of aryl iodides, alkynes, and amines were involved in this coupling process. The cyclopentadiene-phosphine ligand showed high efficiency. A variety of aryl iodides, including cyclic and acyclic tertiary amino aryl iodides, and substituted 1-bromo-2-iodobenzene derivatives could be used. Both symmetric and unsymmetric alkynes substituted with alkyl, aryl, or trimethylsilyl groups could be applied. Cyclic secondary amines such as piperidine, morpholine, 4-methylpiperidine, 1-methylpiperazine, 2-methylpiperidine, and acyclic amines including secondary and primary amines all showed good reactivity. Further application of the resulting indole derivatives was demonstrated by the synthesis of benzosilolo[2,3-b]indole. PMID:24449487

Hao, Wei; Geng, Weizhi; Zhang, Wen-Xiong; Xi, Zhenfeng

2014-02-24

362

Simple and Efficient Synthesis of 2Aryl2,3-Dihydroquinolin-4(1H)-ones Using Silica Chloride as a New Catalyst Under Solvent-Free Conditions  

Microsoft Academic Search

A mild, efficient, and high-yielding method for the synthesis of 2-aryl-2,3-dihydroquinolin-4(1H)-ones from their corresponding 2-amino chalcones using silica chloride (SiO2Cl) under solvent-free conditions is described. A series of 2-aryl-2,3-dihydroquinolin-4(1H)-ones containing both electron-donating and electron-withdrawing substituents were synthesized.

M. Muthukrishnan; M. Mujahid; V. Punitharasu; D. A. Dnyaneshwar

2010-01-01

363

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

364

?-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

365

Facile synthesis of yolk-shell magnetic mesoporous carbon microspheres for efficient enrichment of low abundance peptides.  

PubMed

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 m(2) g(-1)), a large pore volume (0.31 cm(3) 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. PMID:24061763

Wan, Hao; Qin, Hongqiang; Xiong, Zhichao; Zhang, Weibing; Zou, Hanfa

2013-11-21

366

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

367

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

2014-10-29

368

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

369

Cycloisomerization of 1,6-enynes in organoaqueous medium: an efficient and eco-friendly access to furan derivatives. Synthesis of a key intermediate of podophyllotoxin  

Microsoft Academic Search

The first cycloisomerization of enynes catalyzed by Pd(TPPTS)3 catalyst in aqueous medium to give functionalized furans is described. This new reaction has been applied to the synthesis of podophyllotoxin analog.

Jean-Christophe Galland; Sonia Dias; Monique Savignac; Jean-Pierre Genêt

2001-01-01

370

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...

371

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

372

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

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, (13)C NMR, and (1)HNMR spectroscopy. PMID:24288503

Sachdeva, Harshita; Dwivedi, Diksha; Saroj, Rekha

2013-01-01

373

Fast Analog Circuit Synthesis Using Sensitivity Based Near Neighbor Searches  

Microsoft Academic Search

We present an efficient analog synthesis algorithm employing regression models of circuit matrices. Circuit matrix models achieve accurate and speedy synthesis of analog circuits. In this paper, synthesis is accelerated by eliminating numerous computations of the matrix elements during a synthesis run. Computations are avoided by reusing exact or nearby design points visited during previous synthesis iterations. Hashing and multidimensional

Almitra Pradhan; Ranga Vemuri

2008-01-01

374

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

375

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

376

Highly chemoselective hydrogenolysis of iodoarenes.  

PubMed

The catalytic hydrodehalogenation reaction using molecular hydrogen and Pd/C has been revisited. It is shown that the speed of removal of halogen increases with increasing electronegativity I < Br < Cl. Nevertheless, selective dehydrohalogenation in compounds containing other reducible functions can be achieved only with iodine and not with bromine or chlorine. Selective deiodination of iodobenzophenone could be accomplished without reducing the carbonyl group. Hydrogenolysis of azidoiodoaromatic compounds to the corresponding azido compounds is high yielding. This selectivity was exploited for the labeling of benzophenone- and azido-containing compounds by deuterium and tritium. PMID:11856040

Faucher, Nicolas; Ambroise, Yves; Cintrat, Jean-Christophe; Doris, Eric; Pillon, Florence; Rousseau, Bernard

2002-02-01

377

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

378

An efficient green protocol for the synthesis of chalcones by a Claisen–Schmidt reaction using bismuth(III)chloride as a catalyst under solvent-free condition  

Microsoft Academic Search

An environmentally benign protocol for the synthesis of chalcones by the Claisen–Schmidt condensation of aldehydes with ketones using eco-friendly non-toxic bismuth(III)chloride catalyst under solvent-free condition is reported. In this protocol, the reaction time is very short, yields are high, and there are no other pollutants formed.

Dhruva Kumar; Jagir S. Sandhu

2010-01-01

379

Sulfamic acid: a novel and efficient catalyst for the synthesis of aryl-14 H-dibenzo[ a. j]xanthenes under conventional heating and microwave irradiation  

Microsoft Academic Search

A simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a.j]xanthenes is described through a one-pot condensation of ?-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

B. Rajitha; B. Sunil Kumar; Y. Thirupathi Reddy; P. Narsimha Reddy; N. Sreenivasulu

2005-01-01

380

Sulfamic Acid as a Novel, Efficient, Cost?Effective, and Reusable Solid Acid Catalyst for the Synthesis of Pyrroles under Solvent?Free Conditions  

Microsoft Academic Search

Paal–Knorr condensation of 2,5?hexadione with primary amines in the presence of a catalytic amount of sulfamic acid under solvent?free conditions has been accomplished with an excellent yield. This is a very easy, rapid, and high?yielding reaction for the synthesis N?substituted pyrrole derivatives.

Surya K. De

2008-01-01

381

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

382

Activation of disarmed 2- O-alkoxycarbonylated glycosyl trichloroacetimidates with lanthanide triflates: an efficient approach for the synthesis of 1,2- trans glycosides  

Microsoft Academic Search

Disarmed glycosyl trichloroacetimidates can be activated by Yb(OTf)3 in the synthesis of 1,2-trans glycosides involving primary and secondary acceptors. Concurrent formation of orthoester side products can be avoided by the use of alkoxycarbonyl groups for the protection of the donor 2-hydroxyl.

Matteo Adinolfi; Gaspare Barone; Alfonso Iadonisi; Lorenzo Mangoni; Marialuisa Schiattarella

2001-01-01

383

ZnO nanoparticles: An efficient nanocatalyst for the synthesis of ?-acetamido ketones\\/esters via a multi-component reaction  

Microsoft Academic Search

A convenient one-pot multi-component reaction of aromatic aldehydes, enolizable ketones or ?-keto esters and acetonitrile in the presence of acetyl chloride and 10mol% ZnO nanoparticles for the synthesis of ?-acetamido ketones\\/esters at room temperature is described.

Zohreh Mirjafary; Hamdollah Saeidian; Azam Sadeghi; Firouz Matloubi Moghaddam

2008-01-01

384

Triflic acid controlled successive annelation of aromatic sulfonamides: An efficient one-pot synthesis of N-sulfonyl pyrroles, indoles and carbazoles  

PubMed Central

A novel one-pot synthesis of N-substituted heterocycles via successive cyclization/annelation starting from primary sulfonamides is described. This process leads directly to N-sulfonyl pyrroles, indoles and carbazoles. The selection of appropriate reactant/triflic acid ratio successfully controls the formation of the desired product. PMID:19629194

Abid, Mohammed; Teixeira, Liliana; Torok, Bela

2009-01-01

385

Triflic acid controlled successive annelation of aromatic sulfonamides: an efficient one-pot synthesis of N-sulfonyl pyrroles, indoles and carbazoles  

Microsoft Academic Search

A novel one-pot synthesis of N-substituted heterocycles via successive cyclization\\/annelation starting from primary sulfonamides is described. This process directly leads to N-sulfonyl pyrroles, indoles and carbazoles. The selection of an appropriate reactant\\/triflic acid ratio successfully controls the formation of the desired product.

Mohammed Abid; Liliana Teixeira; Béla Török

2007-01-01

386

New and efficient technique for the synthesis of ?-caprolactone using KHSO 5 as an oxidising agent in the presence of a phase transfer catalyst  

Microsoft Academic Search

A new method for the synthesis of ?-caprolactone based on the Baeyer–Villiger oxidation of cyclohexanone was developed. In the proposed reaction, potassium peroxomonosulphate was used as an oxidising agent under phase transfer catalysis conditions. The effects of the reaction parameters, including the type of phase transfer catalyst, the concentration of the oxidising agent, the type of organic solvent and temperature,

Stefan Baj; Anna Chrobok; Agnieszka Siewniak

2011-01-01

387

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

PubMed

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

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

2000-09-01

388

Rapid synthesis of new block copolyurethanes derived from l -leucine cyclodipeptide in reusable molten ammonium salts: novel and efficient green media for the synthesis of new hydrolysable and biodegradable copolyurethanes  

Microsoft Academic Search

This study concerns the synthesis of novel multi block polyurethane (PU) copolymers containing cyclodipeptide, taking the\\u000a advantage of ionic liquids (ILs) under microwave irradiation. For this, l-leucine anhydride cyclodipeptide (LACP) was prepared and then a new class of poly(ether-urethane-urea)s (PEUUs) was synthesized\\u000a in molten ammonium type ILs. ILs were used as reaction media and PUs were prepared via two-step polymerization

Fatemeh Rafiemanzelat; Elahe Abdollahi

389

Organic reactions in water: a distinct novel approach for an efficient synthesis of alpha-amino phosphonates starting directly from nitro compounds.  

PubMed

A distinct approach for high-yielding synthesis of alpha-amino phosphonates has been discovered through three-component reaction of nitro compounds, aldehydes, or ketones and dialkyl or trialkyl phosphites using indium in dilute aqueous HCl at room temperature. This one-pot conversion consists of the following steps: (i) reduction of nitro compounds to amines, (ii) formation of imines from amines and carbonyl compounds, and (iii) hydrophosphonylation of imines. PMID:19775086

Das, Biswanath; Satyalakshmi, Gandham; Suneel, Kanaparthy; Damodar, Kongara

2009-11-01

390

TiO 2–SO 4 2? as a novel solid acid catalyst for highly efficient, solvent free and easy synthesis of chalcones under microwave irradiation  

Microsoft Academic Search

TiO2–SO42? has been prepared by the sol–gel method using H2SO4 and used for the synthesis of chalcones under microwave irradiation. Sulfate loading by H2SO4 increases the Lewis acidity of TiO2. This catalyst gives an excellent yield with less reaction time and is an inexpensive, easily recyclable catalyst for this reaction.

B. Krishnakumar; R. Velmurugan; M. Swaminathan

2011-01-01

391

Intramolecular 5-endo-trig aminomercuration of beta-hydroxy-gamma-alkenylamines: efficient route to a pyrrolidine ring and its application for the synthesis of (+)-castanospermine and analogues.  

PubMed

The intramolecular aminomercuration reaction of sugar-derived beta-hydroxy-gamma-alkenylamines 8a-c undergoes 5-endo-trig cyclization in high yield. The sugar-substituted pyrrolidines thus obtained were elaborated to the synthesis of polyhydroxylated indolizidine alkaloids, namely, castanospermine 1a, 1-epi-castanospermine 1b, and 8a-epi-castanospermine 1c, having promising glycosidase inhibitory activities. PMID:16749803

Karanjule, Narayan S; Markad, Shankar D; Shinde, Vaishali S; Dhavale, Dilip D

2006-06-01

392

Enantioselective total synthesis of (-)-laurenditerpenol.  

PubMed

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

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

2012-09-01

393

BiCl3 Catalyzed Thiolyzation Reaction of 1,2-Epoxides with Diaryl Disulfides in the Presence of Zinc Powder and Ionic Liquid  

Microsoft Academic Search

A new and efficient method has been developed for the regio- and chemoselective synthesis of ? -hydroxysulfides with the ring-opening reaction of 1,2-epoxides by diaryl disulfides and zinc powder in the presence of a catalytic amount of BiCl3 in molten tetrabutyl phosphonium bromide as an ionic liquid.

A. R. Khosropour; M. M. Khodaei; K. Ghozati

2005-01-01

394

Metal-free aerobic oxidative C-N bond cleavage of tertiary amines for the synthesis of N-heterocycles with high atom efficiency.  

PubMed

An efficient metal-free aerobic oxidative C-N bond cleavage of tertiary amines has been developed to construct N-heterocycles using molecular oxygen as the sole oxidant with high atom efficiency, in which all of the three alkyl groups in tertiary amines can be utilized and transformed into N-heterocycles. PMID:24788750

Chen, Xiuling; Chen, Tieqiao; Zhou, Yongbo; Han, Daoqing; Han, Li-Biao; Yin, Shuang-Feng

2014-06-21

395

Tunable and Chemoselective Syntheses of Dihydroisobenzofurans and Indanones via Rhodium-Catalyzed Tandem Reactions of 2-Triazole-benzaldehydes and 2-Triazole-alkylaryl Ketones.  

PubMed

Two novel rhodium(II)-catalyzed tandem reactions were developed for the synthesis of dihydroisobenzofuran and indanone derivatives from 2-triazole-benzaldehydes and 2-triazole-alkylaryl ketones. Dihydroisobenzofuran derivatives were obtained in good yields with high regioselectivities when alcohols were used as nuclophiles in these reactions, whereas the replacement of the alcohol with water resulted in the diastereoselective formation of highly functionalized indanone derivatives. PMID:25327974

Shen, Hongjuan; Fu, Junkai; Gong, Jianxian; Yang, Zhen

2014-11-01

396

Synthesis of 2,6-disubstituted dihydropyrans via an efficient BiBr3-initiated three component, one-pot cascade  

PubMed Central

The rapid synthesis of cis-2,6-disubstituted dihydropyrans is achieved in a three-component, one-pot cascade reaction. BiBr3-ediated addition of ketene silyl acetals or silyl enol ethers to ?,?-unsaturated cis-4-trimethylsilyl-3-butenal provides a Mukaiyama aldol adduct containing a vinylsilane moiety tethered to a silyl ether. Addition of a second aldehyde initiates a domino sequence involving intermolecular addition followed by an intramolecular silyl-modified Sakurai (ISMS) reaction. Isolated yields of this one-pot reaction vary from 44 to 80% and all compounds were isolated as the cis-diastereomers (10 examples). PMID:20161364

Lian, Yajing; Speight, Lee C.; Stevenson, Heather E.; Sprachman, Melissa M.; Katkish, Lauren A.; Mattern, M. Christa

2009-01-01

397

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

398

Aperture synthesis  

Microsoft Academic Search

The article reviews the principles of aperture synthesis theory, with emphasis on earth rotation aperture synthesis, and the main data processing techniques for aperture synthesis telescope systems. A derivation is given for the formula giving the brightness distribution recorded by a continuum aperture synthesis system which samples the complex autocorrelation function of the electric field. The basic formulas are presented

W. N. Brouw

1975-01-01

399

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

400

Investigation of post-synthesis heat treatment of strontium gallium selenium:europium phosphor for improving quantum efficiency and suitable phosphor integration methods for enhancing the overall performance of white LEDs  

NASA Astrophysics Data System (ADS)

A high-quality white light source requires high luminous efficacy (lumens per input watt) and good color qualities. Theoretically, in the "yellow-green" spectral region (with peak wavelength around 555 nm), the luminous efficiency (lumens per radiant watt) reaches a maximum based on the luminous efficiency function, V(lambda), and can potentially generate high luminous efficacy. Unfortunately, the light-emitting diode (LED) suffers from low external quantum efficiency in the "yellow-green" region, and therefore the luminous efficacy value becomes low. An alternative to generating green light is to use phosphor down-conversion by exciting a green-emission phosphor with a near-UV or blue LED of higher external quantum efficiency. A simulation study was carried out to understand how the phosphor emission spectrum affects the phosphor-converted (PC) white LED performance, including both luminous efficacy and color properties. Based on the findings of the simulation study, an ideal emission spectrum of the PC white LED is proposed. The ideal emission spectrum includes: (1) a blue LED with excitation in the range from 440 to 470 nm; (2) a yellow-green phosphor emission with a peak at 555 nm and full-width at half-maximum (FWHM) of 60 nm; (3) a red phosphor emission with a peak at 640 nm and FWHM of 70 nm. To achieve a high luminous efficacy, the external quantum efficiency of the blue LED, the yellow-green phosphor and the red phosphor should be high. As a start, a SrGa2Se4:Eu2+ phosphor with a peak at 555 nm and FWHM of approximately 60 nm was investigated in this study. The SrGa2Se4:Eu2+ phosphor was initially synthesized and followed by a systematic study of the post-synthesis annealing process. The purpose of this study was to investigate how the post-synthesis annealing conditions, including the annealing temperature, annealing duration, and the annealing ambient atmosphere, can affect the phosphor performance. The phosphor performance was characterized in terms of quantum efficiency and emission properties. The mechanism of how various annealing conditions affect the phosphor performance was analyzed, based on the analyses of the phosphor material and optical properties. In the second part of this study, the optical properties of the phosphor were carefully analyzed to understand the behavior of the phosphor-converted photons. Different phosphor density, phosphor thickness, and geometric configurations of PC white LED packages were studied to maximize the photon extraction. Based on the simulation results, a secondary "red" phosphor is important for color properties improvement. The performance of a PC white LED, consisting of two types of phosphor ("yellow" and "red") was therefore investigated. It was found that the combined performance of "yellow" and "red" phosphors is influenced by their application as a mixture or stacked layers, the specific layer order, the phosphor densities, the phosphor external quantum efficiencies, the overall spectral power distribution (SPD), and the phosphor excitation and emission spectra and their efficiencies.

Zhu, Yiting

401

Total synthesis of asterredione.  

PubMed

The first total synthesis of asterredione was efficiently accomplished over five linear steps and in 21.5% overall yield. As the crucial step, the 2-quaternary 1,3-cyclopentenedione skeleton of asterredione was readily achieved using the Darzens/ring-expansion strategy developed in our laboratory. The structure of synthesized asterredione was fully confirmed by X-ray crystallography. PMID:24517486

Gai, Sinan; Zhang, Qing; Hu, Xiangdong

2014-03-01

402

Gas-assisted growth of boron-doped nickel nanotube arrays: rapid synthesis, growth mechanisms, tunable magnetic properties, and super-efficient reduction of 4-nitrophenol  

NASA Astrophysics Data System (ADS)

Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (~70 s) for the reduction of 4-nitrophenol.Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (~70 s) for the reduction of 4-nitrophenol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00411b

Li, Xiang-Zi; Wu, Kong-Lin; Ye, Yin; Wei, Xian-Wen

2013-04-01

403

Designed synthesis of SiO2/TiO2 core/shell structure as light scattering material for highly efficient dye-sensitized solar cells.  

PubMed

SiO2/TiO2 core/shell nanoparticles (STCS-NPs) with diameters of 110, 240, and 530 nm were fabricated to investigate the influence of the size and refractive index of light-scattering particles on light-scattering properties. The optical properties of STCS-NPs were evaluated and compared with SiO2-NPs and TiO2-NPs. The structure of STCS-NPs, consisting of a low refractive index core and high refractive index shell, provides efficient light scattering. The optimized anode film with STCS-NPs had ca. 20% improved power conversion efficiency (PCE). PMID:23635382

Son, Suim; Hwang, Sun Hye; Kim, Chanhoi; Yun, Ju Young; Jang, Jyongsik

2013-06-12

404

Solid-phase synthesis of 4,8-disubstituted-8,9-dihydropyrazino[2,3-g]quinazolin-7(6H)-ones.  

PubMed

An approach for the solid-phase synthesis of 4,8-disubstituted-8,9-dihydropyrazino[2,3-g]quinazolin-7(6H)-ones from 4-chloro-7-fluoro-6-nitroquinazoline scaffold is described. A chemoselective reaction of resin-bound arylamines (3) with 4-chloro-7-fluoro-6-nitroquinazoline (8) yielded resin-bound 4-arylamino-7-fluoro-6-nitroquinazolines (4), which were reacted with amino acid methyl esters to afford the corresponding resin-bound compound (5). Following the reduction of nitro group and intramolecular cyclization of 5, resin-bound 4,8-disubstituted-8,9-dihydropyrazino[2,3-g]quinazolin-7(6H)-one (6) was yielded. The desired products (7) were obtained in good yields and purities after cleavage from the resin. PMID:17849477

Zhang, Yandong; Yao, Chao; Houghten, Richard A; Yu, Yongping

2008-01-01

405

Aziridines from intramolecular alkene aziridination of sulfamates: reactivity toward carbon nucleophiles. application to the synthesis of spisulosine and its fluoro analogue.  

PubMed

Catalytic intramolecular alkene aziridination of sulfamate is an emerging methodology for the asymmetric synthesis of chiral functionalized amines involving the formation of bicyclic aziridines. This study demonstrates the ability of the latter to undergo ring-opening with various carbon nucleophiles: Grignard reagents, lithium salts of terminal alkynes, dithiane, malonate. These S(N)2-type reactions occur with high levels of regio- and chemoselectivity to generally afford seven-membered cyclic sulfamidates in good yields. Carbon nucleophiles have also been found to react with these sulfamidates provided that the sulfamate ester has been previously activated by introduction of a tosyl substituent on the NH group. The versatility of this strategy has been illustrated with the syntheses of spisulosine and its fluoro analogue. PMID:21812488

Malik, Guillaume; Estéoule, Audrey; Retailleau, Pascal; Dauban, Philippe

2011-09-16

406

Mild and Highly Efficient Stereoselective Synthesis of 2,3-Unsaturated Glycopyranosides using La(NO3)3 ? 6H2O as a Catalyst: Ferrier Rearrangement  

PubMed Central

A mild and highly efficient stereoselective reaction of 3,4,6-tri-O-acetyl-D-glucal with a variety of nucleophiles, viz. alcohols, phenols, thiols, thiophenols, and allyl trimethyl silane (TMS), in the presence of 5 mol% of lanthanum(III) nitrate hexahydrate under solvent-free conditions yielded the corresponding 2,3-unsaturated glycopyranosides (pseudoglycals) in excellent yields.

Suryakiran, N.; Reddy, S. Malla; Srinivasulu, M.; Venkateswarlu, Y.

2007-01-01

407

Facile Synthesis of Bis(indolyl)methanes Using LaCl3 · 7H2O as a Mild and Efficient Catalyst in Molten Salt Media  

Microsoft Academic Search

Efficient electrophilic substitution reaction of indole with various carbonyl compounds were carried out using a catalytic amount of LaCl3 · 7H2O in molten tetraethylammonium chloride as an ionic liquid to afford the corresponding bis(indolyl)methanes in excellent yields.

Neda Seyedi; Kazem Saidi; Hojatollah Khabazzadeh

2009-01-01

408

An efficient green catalyst comprising 12-tungstophosphoric acid and MCM-41: synthesis characterization and diesterification of succinic acid, a potential bio-platform molecule  

Microsoft Academic Search

An efficient green catalyst comprising 12-tungstophosphoric acid (TPA) and MCM-41 was synthesized. The catalytic activity was evaluated for liquid phase solvent free diesterification of succinic acid. The support and the synthesized catalyst were characterized by various physico-chemical techniques. Fourier transform infrared, diffuse reflectance spectroscopy, and P NMR spectra indicate that the Keggin structure of TPA was not destroyed after anchoring

Varsha Brahmkhatri; Anjali Patel

2012-01-01

409

An efficient green catalyst comprising 12-tungstophosphoric acid and MCM-41: synthesis characterization and diesterification of succinic acid, a potential bio-platform molecule  

Microsoft Academic Search

An efficient green catalyst comprising 12-tungstophosphoric acid (TPA) and MCM-41 was synthesized. The catalytic activity was evaluated for liquid phase solvent free diesterification of succinic acid. The support and the synthesized catalyst were characterized by various physico-chemical techniques. Fourier transform infrared, diffuse reflectance spectroscopy, and P NMR spectra indicate that the Keggin structure of TPA was not destroyed after anchoring

Varsha Brahmkhatri; Anjali Patel

2011-01-01

410

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

PubMed

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

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

2014-08-01

411

Bismuth (III) Salts Promoted and Ionic Liquid Assisted an Efficient and Environmentally Benign One-Pot Synthesis of 1,5-Benzodiazepine Derivatives  

PubMed Central

1,5-Benzodiazepine derivatives were synthesized by the condensation reactions of o-phenylenediamine and ketones catalyzed by bismuth (III) salts under mild conditions. This method is easy, efficient, environment and eco-friendly, free of toxic catalysts, and gives good to excellent yields of 1, 5-benzodiazepines. PMID:24052827

Chaskar, Atul; Patil, Latika; Phatangare, Kiran; Padalkar, Vikas; Takale, Santosh

2011-01-01

412

Silica sulfuric acid: an efficient and reusable catalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2(1 H)-ones  

Microsoft Academic Search

Silica sulfuric acid efficiently catalyzes the three-component Biginelli reaction between an aldehyde, a ?-dicarbonyl compound and urea or thiourea in refluxing ethanol to afford the corresponding dihydropyrimidinones in high yields. The catalyst is reusable and can be applied several times without any decrease in the yield of the reactions.

Peyman Salehi; Minoo Dabiri; Mohammad Ali Zolfigol; Mohammad Ali Bodaghi Fard

2003-01-01

413

One?Pot, Three?Component Synthesis of 2,3?Dihydro?4(1H)?quinazolinones by Montmorillonite K?10 as an Efficient and Reusable Catalyst  

Microsoft Academic Search

A wide range of mono? and disubstituted dihydroquinazolinones were synthesised via condensation of isatoic anhydride, primary amines, or ammonium salts with aromatic aldehydes in the presence of montmorillonite K?10. The catalyst is reusable and could be recycled for several runs without any decrease in its efficiency.

Peyman Salehi; Minoo Dabiri; Mostafa Baghbanzadeh; Mahboobeh Bahramnejad

2006-01-01

414

Application of N,N-dimethylformamide dineopentyl acetal for efficient anchoring of N alpha-9-fluorenylmethyloxycarbonylamino acids as p-alkoxybenzyl esters in solid-phase peptide synthesis.  

PubMed

The attachment of Fmoc-amino acids onto p- alkoxybenzyl alcohol resins via DCC-DMAP coupling suffers from two different problems: formation of dimers and racemization. The use of N,N-dimethylformamide dineopentyl acetal for the preparation of Fmoc- aminoacyloxybenzyl handles is the basis of a safe and efficient anchoring method that avoids both problems. PMID:6547115

Albericio, F; Barany, G

1984-04-01

415

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

E-print Network

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

Movassaghi, Mohammad

416

Endo-Selective Enyne Ring-Closing Metathesis Promoted by Stereogenic-at-Mo Monoalkoxide and Monoaryloxide Complexes. Efficient Synthesis of Cyclic Dienes Not Accessible through Reactions with Ru Carbenes  

PubMed Central

Stereogenic-at-Mo monoalkoxide and monoaryloxide complexes promote enyne ring-closing metathesis (RCM) reactions, affording the corresponding endo products with high selectivity (typically >98:<2 endo:exo). All catalysts can be prepared and used in situ. Five-, six-, and seven-membered rings are obtained through reactions with enyne substrates that bear all-carbon tethers as well as those that contain heteroatom substituents. The newly developed catalytic protocols complement the related exo-selective Ru-catalyzed processes. In cases where Ru-based complexes deliver exo and endo products nondiscriminately, such as when tetrasubstituted cyclic alkenes are generated, Mo-catalyzed reactions afford the endo product exclusively. The efficiency of synthesis of N- and O-containing endo diene heterocycles can be improved significantly through structural modification of Mo catalysts. The modularity of Mo-based monopyrrolides is thus exploited in the identification of the most effective catalyst variants. Through alteration of O-based monodentate ligands, catalysts have been identified that promote enyne RCM with improved efficiency. The structural attributes of three Mo complexes are elucidated through X-ray crystallography. The first examples of catalytic enantioselective enyne RCM reactions are reported (up to 98:2 enantiomer ratio and >98% endo). PMID:19580318

Lee, Yeon-Ju; Schrock, Richard R.; Hoveyda, Amir H.

2010-01-01

417

Eco-friendly methodology for efficient synthesis and scale-up of 2-ethylhexyl-p-methoxycinnamate using Rhizopus oryzae lipase and its biological evaluation.  

PubMed

Lipase-mediated synthesis of phenolic acid esters is a green and economical alternative to current chemical methods. Octyl methoxycinnamate, an important UVB-absorbing compound, was synthesized by the esterification of p-methoxycinnamic acid with 2-ethyl hexanol using Rhizopus oryzae lipase. A molar ratio of 1:2 of p-methoxycinnamic acid and 2-ethyl hexanol was found to give an optimum yield using cyclo-octane (50 ml) as reaction solvent, at a temperature of 45 °C, and 750 U of lipase, resulting in a yield of 91.3 % in 96 h. This reaction was successfully scaled up to 400-ml reaction size where 88.6 %bioconversion was achieved. The synthesized compound was found to have superior antioxidant activity as compared to ascorbic acid. The synthesized compound also exhibited good antimicrobial activity against Escherichia coli, Klebsiella pneumonia, Salmonella typhi, Staphylococcus aures, Candida albicans (yeast), Aspergillus niger, Alternaria solani, and Fussarium oxysporum by well diffusion method in terms of zone of inhibitions (in mm). PMID:24668019

Kumar, Vinod; Jahan, Firdaus; Kameswaran, Karthikeya; Mahajan, Richi V; Saxena, Rajendra Kumar

2014-06-01

418

One pot aqueous synthesis of nanoporous Au85Pt15 material with surface bound Pt islands: an efficient methanol tolerant ORR catalyst.  

PubMed

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)). PMID:25241856

Anandha Ganesh, P; Jeyakumar, D

2014-10-01

419

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

420

Solution-phase synthesis of single-crystal Cu3Si nanowire arrays on diverse substrates with dual functions as high-performance field emitters and efficient anti-reflective layers  

NASA Astrophysics Data System (ADS)

There is strong and growing interest in applying metal silicide nanowires as building blocks for a new class of silicide-based applications, including spintronics, nano-scale interconnects, thermoelectronics, and anti-reflective coating materials. Solution-phase environments provide versatile materials chemistry as well as significantly lower production costs compared to gas-phase synthesis. However, solution-phase synthesis of silicide nanowires remains challenging due to the lack of fundamental understanding of silicidation reactions. In this study, single-crystalline Cu3Si nanowire arrays were synthesized in an organic solvent. Self-catalyzed, dense single-crystalline Cu3Si nanowire arrays were synthesized by thermal decomposition of monophenylsilane in the presence of copper films or copper substrates at 420 to 475 °C and 10.3 MPa in supercritical benzene. The solution-grown Cu3Si nanowire arrays serve dual functions as field emitters and anti-reflective layers, which are reported on copper silicide materials for the first time. Cu3Si nanowires exhibit superior field-emission properties, with a turn-on-voltage as low as 1.16 V ?m-1, an emission current density of 8 mA cm-2 at 4.9 V ?m-1, and a field enhancement factor (?) of 1500. Cu3Si nanowire arrays appear black with optical absorption less than 5% between 400 and 800 nm with minimal reflectance, serving as highly efficient anti-reflective layers. Moreover, the Cu3Si nanowires could be grown on either rigid or flexible substrates (PI). This study shows that solution-phase silicide reactions are adaptable for high-quality silicide nanowire growth and demonstrates their promise towards fabrication of metal silicide-based devices.There is strong and growing interest in applying metal silicide nanowires as building blocks for a new class of silicide-based applications, including spintronics, nano-scale interconnects, thermoelectronics, and anti-reflective coating materials. Solution-phase environments provide versatile materials chemistry as well as significantly lower production costs compared to gas-phase synthesis. However, solution-phase synthesis of silicide nanowires remains challenging due to the lack of fundamental understanding of silicidation reactions. In this study, single-crystalline Cu3Si nanowire arrays were synthesized in an organic solvent. Self-catalyzed, dense single-crystalline Cu3Si nanowire arrays were synthesized by thermal decomposition of monophenylsilane in the presence of copper films or copper substrates at 420 to 475 °C and 10.3 MPa in supercritical benzene. The solution-grown Cu3Si nanowire arrays serve dual functions as field emitters and anti-reflective layers, which are reported on copper silicide materials for the first time. Cu3Si nanowires exhibit superior field-emission properties, with a turn-on-voltage as low as 1.16 V ?m-1, an emission current density of 8 mA cm-2 at 4.9 V ?m-1, and a field enhancement factor (?) of 1500. Cu3Si nanowire arrays appear black with optical absorption less than 5% between 400 and 800 nm with minimal reflectance, serving as highly efficient anti-reflective layers. Moreover, the Cu3Si nanowires could be grown on either rigid or flexible substrates (PI). This study shows that solution-phase silicide reactions are adaptable for high-quality silicide nanowire growth and demonstrates their promise towards fabrication of metal silicide-based devices. Electronic supplementary information (ESI) available: Additional SEM, TEM images, and FTIR spectrum of Cu3Si nanowires. See DOI: 10.1039/c3nr03045h

Yuan, Fang-Wei; Wang, Chiu-Yen; Li, Guo-An; Chang, Shu-Hao; Chu, Li-Wei; Chen, Lih-Juann; Tuan, Hsing-Yu

2013-09-01

421

An efficient one-pot synthesis of 3-glyoxylic acids of electron-deficient substituted azaindoles by ionic liquid imidazolium chloroaluminate-promoted Friedel–Crafts acylation  

Microsoft Academic Search

An efficient, one-pot Friedel–Crafts acylation\\/hydrolysis reaction promoted by the acidic ionic liquid 1-ethyl-3-methylimidazolium chloroaluminate (generated from 1-ethyl-3-methylimidazolium chloride (EmimCl) and aluminum chloride (X(AlCl3), mole fraction X=0.75) for the formation of 3-glyoxylic acid derivatives of electron-deficient, substituted 4- and 6-azaindoles is described.

Kap-Sun Yeung; Zhilei Qiu; Michelle E. Farkas; Qiufen Xue; Alicia Regueiro-Ren; Zhong Yang; John A. Bender; Andrew C. Good; John F. Kadow

2008-01-01

422

An asymmetric [3+2] cycloaddition of alkynes with oxiranes by selective C-C bond cleavage of epoxides: highly efficient synthesis of chiral furan derivatives.  

PubMed

An efficient enantioselective [3+2] cycloaddition of alkynes with oxiranes via selective C-C bond cleavage of epoxides was developed. A number of optically active 2,5-dihydrofurans were obtained in excellent yields (up to 99%) and enantioselectivities (up to 95% ee) under mild reaction conditions. Moreover, chiral tetrahydrofuran could also be obtained by cycloaddition of alkene and oxirane or hydrogenation of chiral 2,5-dihydrofuran. PMID:25133274

Chen, Weiliang; Fu, Xuan; Lin, Lili; Yuan, Xiao; Luo, Weiwei; Feng, Juhua; Liu, Xiaohua; Feng, Xiaoming

2014-10-01

423

In situ silver nanoparticles synthesis in agarose film supported on filter paper and its application as highly efficient SERS test stripes.  

PubMed

Highly efficient multifunctional agarose SERS test stripes has been fabricated by a convenient facile approach. SERS stripes were found to be highly sensitive, robust, and capable to alleviate the two major drawbacks of filter paper based SERS substrate i.e. the weak adhesion of plasmonic nanoparticles and the diffusion of analyte into the paper surface. The fabricated stripes have been used successfully for the ultra-trace detection of analytes of forensic interest including a dye, pesticide and explosive. PMID:24582080

Raza, Ali; Saha, Basudeb

2014-04-01

424

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

Microsoft Academic Search

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

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

425

Al2O3 nanoparticles: an efficient and recyclable nanocatalyst for the rapid synthesis of N-heteroaryl formamides under solvent-free conditions.  

PubMed

A series of N-heteroaryl formamides were efficiently synthesized from heteroarylamines and formic acid using Al2O3 nanoparticles as a heterogeneous catalyst under solvent-free conditions. The smaller size of Al2O3 nanoparticles with a higher surface to volume ratio has a promising catalytic activity, resulting in a short reaction times and high reaction yields under mild reaction conditions. The catalyst could be recycled and reused four times without a noticeable decrease in its activity. PMID:24664345

Olyaei, Abolfazl; Bagheri, Hasan; Sadeghpour, Mahdieh; Razeghi, Reza; Vaziri, Mohsen

2014-01-01

426

Eco-friendly and efficient one-pot synthesis of alkyl- or aryl-14 H-dibenzo[ a, j]xanthenes in water  

Microsoft Academic Search

Alkyl- or aryl-14H-dibenzo[a,j]xanthene derivatives are synthesized efficiently by the reaction of ?-naphthol and aliphatic and aromatic aldehydes in the presence of KAl(SO4)2·12H2O (alum) under aqueous condition at 100°C. Different types of aromatic and aliphatic aldehydes are used in the reaction and in all cases the products synthesized successfully. Several solvents were examined for this reaction; however, in terms of reaction

Minoo Dabiri; Mostafa Baghbanzadeh; Maryam Shakouri Nikcheh; Elham Arzroomchilar

2008-01-01

427

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

Microsoft Academic Search

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

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

2004-01-01

428

An extremely efficient three-component reaction of aldehydes/ketones, amines, and phosphites (Kabachnik-Fields reaction) for the synthesis of alpha-aminophosphonates catalyzed by magnesium perchlorate.  

PubMed

Commercially available magnesium perchlorate is reported as an extremely efficient catalyst for the synthesis of alpha-aminophosphonates. A three-component reaction (3-CR) of an amine, an aldehyde or a ketone, and a di-/trialkyl phosphite (Kabachnik-Fields reaction) took place in one pot under solvent-free conditions to afford the corresponding alpha-aminophosphonates in high yields and short times. The use of solvent retards the rate of the reaction and requires a much longer reaction time than that for neat conditions. The reactions involving an aldehyde, an aromatic amine without any electron-withdrawing substituent, and a phosphite are carried out at rt. The reactions involving cyclic ketones, aromatic amines with an electron-withdrawing substituent, and aryl alkyl ketone (e.g., acetophenone) require longer reaction times at rt or heating. Magnesium perchlorate was found to be superior to other metal perchlorates and metal triflates during the reaction of 4-methoxybenzaldehyde, 2,4-dinitroaniline, and dimethyl phosphite. The catalytic activity of various magnesium compounds was influenced by the counteranion, and magnesium perchlorate was found to be the most effective. The reaction was found to be general with di-/trialkyl phosphites and diaryl phosphite. The Mg(ClO4)2-catalyzed alpha-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or alpha-hydroxy phosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine, and the phosphite in the transition state. PMID:17253748

Bhagat, Srikant; Chakraborti, Asit K

2007-02-16

429

Solution-phase synthesis of single-crystal Cu3Si nanowire arrays on diverse substrates with dual functions as high-performance field emitters and efficient anti-reflective layers.  

PubMed

There is strong and growing interest in applying metal silicide nanowires as building blocks for a new class of silicide-based applications, including spintronics, nano-scale interconnects, thermoelectronics, and anti-reflective coating materials. Solution-phase environments provide versatile materials chemistry as well as significantly lower production costs compared to gas-phase synthesis. However, solution-phase synthesis of silicide nanowires remains challenging due to the lack of fundamental understanding of silicidation reactions. In this study, single-crystalline Cu3Si nanowire arrays were synthesized in an organic solvent. Self-catalyzed, dense single-crystalline Cu3Si nanowire arrays were synthesized by thermal decomposition of monophenylsilane in the presence of copper films or copper substrates at 420 to 475 °C and 10.3 MPa in supercritical benzene. The solution-grown Cu3Si nanowire arrays serve dual functions as field emitters and anti-reflective layers, which are reported on copper silicide materials for the first time. Cu3Si nanowires exhibit superior field-emission properties, with a turn-on-voltage as low as 1.16 V ?m(-1), an emission current density of 8 mA cm(-2) at 4.9 V ?m(-1), and a field enhancement factor (?) of 1500. Cu3Si nanowire arrays appear black with optical absorption less than 5% between 400 and 800 nm with minimal reflectance, serving as highly efficient anti-reflective layers. Moreover, the Cu3Si nanowires could be grown on either rigid or flexible substrates (PI). This study shows that solution-phase silicide reactions are adaptable for high-quality silicide nanowire growth and demonstrates their promise towards fabrication of metal silicide-based devices. PMID:23979254

Yuan, Fang-Wei; Wang, Chiu-Yen; Li, Guo-An; Chang, Shu-Hao; Chu, Li-Wei; Chen, Lih-Juann; Tuan, Hsing-Yu

2013-10-21

430

Duplex formation between the sRNA DsrA and rpoS mRNA is not sufficient for efficient RpoS synthesis at low temperature.  

PubMed

At low temperatures the Escherichia coli rpoS mRNA, encoding the stationary phase sigma factor RpoS, forms an intramolecular secondary structure (iss) that impedes translation initiation. Under these conditions the small RNA DsrA, which is stabilzed by Hfq, forms a duplex with rpoS mRNA sequences opposite of the ribosome-binding site (rbs). Both the DEAD box helicase CsdA and Hfq have been implicated in DsrA·rpoS duplex formation. Hfq binding to A-rich sequences in the rpoS leader has been suggested to restructure the mRNA, and thereby to accelerate DsrA·rpoS duplex formation, which, in turn, was deemed to free the rpoS rbs and to permit ribosome loading on the mRNA. Several experiments designed to elucidate the role of Hfq in DsrA-mediated translational activation of rpoS mRNA have been conducted in vitro. Here, we assessed RpoS synthesis in vivo to further study the role of Hfq in rpoS regulation. We show that RpoS synthesis was reduced when DsrA was ectopically overexpressed at 24 °C in the absence of Hfq despite of DsrA·rpoS duplex formation. This observation indicated that DsrA·rpoS annealing may not be sufficient for efficient ribosome loading on rpoS mRNA. In addition, a HfqG29A mutant protein was employed, which is deficient in binding to A-rich sequences present in the rpoS leader but proficient in DsrA binding. We show that DsrA·rpoS duplex formation occurs in the presence of the HfqG29A mutant protein at low temperature, whereas synthesis of RpoS was greatly diminished. RNase T1 footprinting studies of DsrA·rpoS duplexes in the absence and presence of Hfq or HfqG29A indicated that Hfq is required to resolve a stem-loop structure in the immediate coding region of rpoS mRNA. These in vivo studies corroborate the importance of the A-rich sequences in the rpoS leader and strongly suggest that Hfq, besides stabilizing DsrA and accelerating DsrA·rpoS duplex formation, is also required to convert the rpoS mRNA into a translationally competent form. PMID:24448230

Hämmerle, Hermann; Ve?erek, Branislav; Resch, Armin; Bläsi, Udo

2013-12-01

431

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

432

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

433

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

434

Cu(II) Schiff base complex as a highly efficient catalyst for the synthesis of polyhydroquinoline derivatives via Hantzsch condensation in water.  

PubMed

In the present study, Cu(II) Schiff-base complex is introduced as a highly efficient and green solid catalyst for the unsymmetrical Hantzsch condensation through a four-component coupling of various aldehydes, dimedone, ethyl acetoacetate and ammonium acetate to form polyhydroquinoline derivatives in good to excellent yields. This reaction was carried out in the presence of 1 mol% of catalysts in water at room temperature. The reusability of the catalysts was demonstrated by a five-run test. Remarkable features of this new procedure are cleaner reaction profiles, shorter reactiontimes, simple experimental and work-up procedures. PMID:23701007

Vahdat, Seyed Mohammad

2013-12-01

435

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

436

Mild and Efficient Synthesis of Benzoxazoles, Benzothiazoles, Benzimidazoles, and Oxazolo[4,5- b ]pyridines Catalyzed by Bi(III) Salts Under Solvent-Free Conditions  

Microsoft Academic Search

Summary.  A series of benzoxazoles, benzothiazoles, benzimidazoles, and oxazolo[4,5-b]pyridines was efficiently synthesized from the reactions of o-aminophenols, o-aminothiophenol, o-phenylenediamines, and 2-amino-3-hydroxypyridine with orthoesters in the presence of catalytic amounts of Bi(III) salts,\\u000a such as Bi(TFA)3, Bi(OTf)3, and BiOClO4 xH2O under solvent-free conditions. The remarkable features of this new protocol are high conversion, very short reaction times,\\u000a cleaner reaction profiles under solvent-free

Iraj Mohammadpoor-Baltork; Ahmad R. Khosropour; Seyedeh F. Hojati

2007-01-01

437

Catalyst assisted synthesis of initiator attached silica monolith particles via isocyanate-hydroxyl reaction for production of polystyrene bound chromatographic stationary phase of excellent separation efficiency.  

PubMed

Dibutyltin dichloride (DBTDC) was used as a catalyst to chemically bind 4-chloromehtylphenylisocynate (4-CPI) to porous monolithic silica particles via isocyanate-hydroxyl reaction, and the reaction product was reacted with sodium diethyldithiocarbamate (SDDC) to yield initiator attached silica monolith particles. Reversible addition-fragmentation transfer (RAFT) polymerization was taken place on them to result in polystyrene attached silica particles that showed excellent separation efficiency when packed in a chromatographic column (1.0 mm × 300 mm). The numbers of theoretical plates (N) of 56,500 is better than those of any commercially available HPLC or UHPLC column yet. PMID:24290766

Ali, Faiz; Kim, Yune Sung; Lee, Jin Wook; Cheong, Won Jo

2014-01-10

438

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

439

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

440

A versatile strategy for the synthesis of N-linked glycoamino acids from glycals.  

PubMed

A versatile route for the synthesis of N-linked glycoamino acids from readily available glycals is reported. A variety of glycals possessing different carbohydrate templates (mono-, di- and trisaccharide glycals) were shown to undergo a novel iodine catalyzed stereoselective diamination reaction with chloramine-T. Taking advantage of the difference in the reactivity between the anomeric and C2 sulfonamido groups of these diamines 7, 13, 15, 17 and 19, they could be protected differentially at the C2 and anomeric nitrogen atoms. Thus, chemoselective acetylation of these diamines installed the C2 acetamido group, an essential functionality that plays a crucial role in inducing a beta-turn in N-linked glycoproteins. Subsequent protection of the anomeric nitrogens of 20a,b,e as their Alloc (allyloxycarbonyl) derivatives followed by SmI(2) mediated facile didetosylation afforded 24a-c. Deprotection of the Alloc group of 24a and 24c and coupling of the liberated free amine with a variety of protected amino acids provided N-linked glycoamino acids 25 and 27 in high yields. An illustrative synthesis of an N-linked glycopeptide 29 is also reported. PMID:18004466

Kumar, Vipin; Ramesh, Namakkal G

2007-12-01

441

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

442

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

443

An efficient access to the synthesis of novel 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives  

PubMed Central

Summary 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

Lin, Guihai; Li, Yang; Tao, Xiyue; Liu, Rui; Sun, Lianjie

2012-01-01

444

Highly efficient Yb3+/Tm3+ co-doped NaYF4 nanotubes: Synthesis and intense ultraviolet to infrared up-conversion luminescence  

NASA Astrophysics Data System (ADS)

Nanocrystals of up-conversion (UC) phosphor Yb3+/Tm3+ co-doped NaYF4 are prepared by a facile hydrothermal method using oleic acid as a stabilizing agent. The as-prepared nanocrystals are of hexagonal phase, and have tube-like morphology and strong ultraviolet (UV) and blue UC fluorescence intensity, which have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectroscopy. The effect of Yb3+ concentration on the UC emission properties is also analyzed. Our results reveal that the intensity of emission peaks can be controlled by varying the Yb3+ concentration and these NaYF4 nanotubes are highly efficient host material. The as-prepared NaYF4 nanotubes show potential applications in UV compact solid state lasers and multi-channel fluorescent label.

Zhang, Y. Y.; Wang, Y.; Deng, J. Q.; Wang, J.; Ni, S. C.

2014-02-01

445

Lipophilic pyrylium salts in the synthesis of efficient pyridinium-based cationic lipids, gemini surfactants, and lipophilic oligomers for gene delivery.  

PubMed

Several new classes of pyridinium cationic lipids were synthesized and tested as gene delivery agents. They were obtained through a procedure that generates simultaneously the heterocyclic ring and the positively charged nitrogen atom, using lipophilic pyrylium salts as key intermediates that react with primary amines, yielding pyridinium salts. The choice of the appropriately substituted primary amine, diamine or polyamine, allows the design of the shape of the final lipids, gemini surfactants, or lipophilic polycations. We report also a comprehensive structure-activity relationship study that identified the most efficient structural variables at the levels of the hydrophobic anchor, linker, and counterion for these classes of pyridinium cationic lipids. This study was also aimed at finding the best liposomal formulation for the new transfection agents. PMID:16789743

Ilies, Marc Antoniu; Seitz, William A; Johnson, Betty H; Ezell, Edward L; Miller, Aaron L; Thompson, E Brad; Balaban, Alexandru T

2006-06-29

446

Synthesis of Honeycomb-like Mesoporous Pyrite FeS2 Microspheres as Efficient Counter Electrode in Quantum Dots Sensitized Solar Cells.  

PubMed

Honeycomb-like mesoporous pyrite FeS2 microspheres, with diameters of 500-800 nm and pore sizes of 25-30 nm, are synthesized by a simple solvothermal approach. The mesoporous FeS2 microspheres are demonstrated to be an outstanding counter electrode (CE) material in quantum dot sensitized solar cells (QDSSCs) for electrocatalyzing polysulfide electrolyte regeneration. The cell using mesoporous FeS2 microspheres as CE shows 86.6% enhancement in power conversion efficiency (PCE) than the cell using traditional noble Pt CE. Furthermore, it also shows 11.4% enhancement in PCE than the cell using solid FeS2 microspheres as CE, due to the mesoporous structure facilitating better contact with polysulfide electrolyte and fast diffusion of redox couple species in electrolyte. PMID:24986216

Xu, Jun; Xue, Hongtao; Yang, Xia; Wei, Huaixin; Li, Wenyue; Li, Zhangpeng; Zhang, Wenjun; Lee, Chun-Sing

2014-11-01

447

Selective uptake of cholesteryl esters from apolipoprotein-E-free high-density lipoproteins by rat parenchymal cells in vivo is efficiently coupled to bile acid synthesis.  

PubMed Central

[3H]Cholesteryl ester-labelled human high-density lipoprotein (HDL) was injected into rats and its decay, intrahepatic cellular distribution and the kinetics of biliary secretion were determined. At 10 min after injection the hepatic uptake of cholesteryl esters from HDL was 3-fold higher as compared with the apolipoprotein. Selective uptake was exerted only by parenchymal cells (5.6-fold more cholesteryl esters than apolipoprotein) and not by liver endothelial or Kupffer cells. The kinetics of biliary secretion of processed cholesteryl esters initially associated with HDL or low-density lipoprotein (LDL) were compared in unrestrained rats, equipped with permanent catheters in bile duct, duodenum and heart. At 72 h after injection of [3H]cholesteryl oleate-labelled HDL, 51.0 +/- 2.5% of the injected dose was recovered as bile acids, which is about twice as high as the secretion of biliary radioactivity after injection of [3H]cholesteryl oleate-labelled LDL. Oestradiol treatment stimulated only liver uptake of LDL cholesteryl esters, and resulted in a 2-fold higher liver uptake than with HDL. However, the rate of radioactive bile acid formation from [3H]cholesteryl oleate-labelled HDL was still more rapid than for LDL. It is concluded that the selective uptake pathway for cholesteryl esters from HDL in parenchymal cells is more efficiently coupled to the formation of bile acids than is the cholesteryl ester uptake from LDL. This efficient coupling may facilitate the role of HDL in reverse cholesterol transport. PMID:1747108

Pieters, M N; Schouten, D; Bakkeren, H F; Esbach, B; Brouwer, A; Knook, D L; van Berkel, T J

1991-01-01

448

Facile synthesis of V(4+) self-doped, [010] oriented BiVO4 nanorods with highly efficient visible light-induced photocatalytic activity.  

PubMed

Monodispersed monoclinic BiVO4 nanorods grown along the [010] direction were prepared using a one-step low temperature hydrothermal method in the presence of the low-cost, nontoxic sodium oleate serving as a chelating agent. The BiVO4 nanorods with diameters of 15-20 nm possess a huge specific surface area as large as 28.2 m(2) g(-1), which can endow them with high photocatalytic activity and strong adsorption of reactants. Meanwhile, the specific [010] growth direction is capable of facilitating efficient electron-hole separation by accumulating electrons on {010} facets. Thus, the highly efficient photocatalytic activity of the as-prepared BiVO4 nanorods under visible light, which far surpasses that of commercial P25, is demonstrated by the degradation of rhodamine B and phenol. Plentiful V(4+) species, which can create oxygen vacancies, is detected implying that the as-obtained nanorods are self-doped BiVO4. Significantly, 61% of rhodamine B is