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1

Chemoselective synthesis of oligosaccharides of 2-deoxy-2-aminosugars  

PubMed Central

Along with the application of the S-benzoxazolyl glycosides to the high-yielding synthesis of disaccharides of the 2-amino-2-deoxy series, chemoselective assembly of oligosaccharides containing multiple residues of 2-amino-2-deoxyglycoses is reported. This modified armed-disarmed approach is relying on the observation that 2-N-trichloroethoxycarbonyl derivatives of S-benzoxazolyl glycosides are significantly more reactive than their 2-N-phthaloyl counterparts in MeOTf-promoted glycosylations. This allowed efficient chemoselective synthesis of 1,2-trans-linked oligosaccharides, the disarmed reducing end of which can be activated for immediate second step glycosidation in the presence of a more powerful activator AgOTf. As a result of this two-step activation, trans-trans-patterned trisaccharides could be assembled in a highly efficient manner. This result differs from the classic armed-disarmed technique, according to which usually cis-trans-patterned oligosaccharides are generated. PMID:17253751

Bongat, Aileen F. G.; Kamat, Medha N.; Demchenko, Alexei V.

2008-01-01

2

High chemoselectivity in the phenol synthesis  

PubMed Central

Summary Efforts to trap early intermediates of the gold-catalyzed phenol synthesis failed. Neither inter- nor intramolecularly offered vinyl groups, ketones or alcohols were able to intercept the gold carbenoid species. This indicates that the competing steps of the gold-catalyzed phenol synthesis are much faster than the steps of the interception reaction. In the latter the barrier of activation is higher. At the same time this explains the high tolerance of this very efficient and general reaction towards functional groups. PMID:21804874

Rudolph, Matthias; McCreery, Melissa Q; Frey, Wolfgang

2011-01-01

3

A chemoselective oxidation of monosubstituted ethylene glycol: facile synthesis of optically active ?-hydroxy acids.  

PubMed

A mild and efficient method for the synthesis of optically active ?-hydroxy acids through chemoselective oxidation of monosubstituted ethylene glycols using the TEMPO-NaOCl reagent system is described. It is evident from our studies that the solvent, pH and reaction temperature are very crucial for the success of this oxidation. The versatility of this method has been demonstrated with a variety of aliphatic, aromatic and carbohydrate substrates bearing various functional groups. PMID:24850510

Chinthapally, Kiran; Baskaran, Sundarababu

2014-07-01

4

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

PubMed

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

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

2014-09-26

5

Synthesis of 5,6-Dihydropyrazolo[1,5-c]quinazolines through Gold-Catalyzed Chemoselective Bicyclization of N-Propargylic Sulfonylhydrazones.  

PubMed

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

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

2015-01-16

6

Synthesis of ?,?-unsaturated ?'-haloketones through the chemoselective addition of halomethyllithiums to Weinreb amides.  

PubMed

A straightforward synthesis of variously functionalized ?,?-unsaturated ?'-haloketones has been achieved through the chemoselective addition of halomethyllithium carbenoids to Weinreb amides at -78 °C. A comparative study employing the corresponding esters under the same reaction conditions pointed out that the instability of the tetrahedral intermediate formed from the latter is responsible for the observed formation of carbinols instead of the desired haloketones. PMID:23805887

Pace, Vittorio; Castoldi, Laura; Holzer, Wolfgang

2013-08-01

7

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

PubMed Central

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

Smoot, James T.; Demchenko, Alexei V.

2009-01-01

8

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

PubMed Central

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

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

2012-01-01

9

Metabolic synthesis of clickable glutathione for chemoselective detection of glutathionylation.  

PubMed

Glutathionylation involves reversible protein cysteine modification that regulates the function of numerous proteins in response to redox stimuli, thereby altering cellular processes. Herein we developed a selective and versatile approach to identifying glutathionylation by using a mutant of glutathione synthetase (GS). GS wild-type catalyzes coupling of ?Glu-Cys to Gly to form glutathione. We generated a GS mutant that catalyzes azido-Ala in place of Gly with high catalytic efficiency and selectivity. Transfection of this GS mutant (F152A/S151G) and incubation of azido-Ala in cells efficiently afford the azide-containing glutathione derivative, ?Glu-Cys-azido-Ala. Upon H2O2 treatment, clickable glutathione allowed for selective and sensitive detection of glutathionylated proteins by Western blotting or fluorescence after click reaction with biotin-alkyne or rhodamine-alkyne. This approach affords the efficient metabolic tagging of intracellular glutathione with small clickable functionality, providing a versatile handle for characterizing glutathionylation. PMID:25079194

Samarasinghe, Kusal T G; Munkanatta Godage, Dhanushka N P; VanHecke, Garrett C; Ahn, Young-Hoon

2014-08-20

10

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

PubMed

The synthesis of highly negatively charged polyoxometalates with electrically and structurally controlled uniform basic sites can lead to the unique base catalysis. In this work, a ?-Keggin germanodecatungstate, [?-HGeW10 O36 ](7-) (A), having a -7 charge was, for the first time, successfully synthesized by the reaction of [?-H2 GeW10 O36 ](6-) with one equivalent of [(n-C4 H9 )4 N]OH under non-aqueous conditions. The activities of germanodecatungstates for base-catalyzed reactions dramatically increased with increase in the number negative charges from -6 to -7. In the presence of A, various combinations of acylating agents and primary alcohols including those with acid-sensitive functional groups chemoselectively gave the desired acylated products in high yields even under the stoichiometric conditions. PMID:25264017

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

2014-11-24

11

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

12

Chemoselective ligation  

DOEpatents

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

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

2011-12-13

13

Chemoselective ligation  

DOEpatents

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

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

2010-02-23

14

Chemoselective ligation  

DOEpatents

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

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

2011-05-10

15

Chemoselective ligation  

DOEpatents

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

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

2011-04-12

16

Chemoselective ligation  

DOEpatents

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

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

2003-05-27

17

Combined preconditioning and in vivo chemoselection with 6-thioguanine alone achieves highly efficient reconstitution of normal hematopoiesis with HPRT-deficient bone marrow  

PubMed Central

Purine analogs such as 6-thioguanine (6TG) cause myelotoxicity upon conversion into nucleotides by hypoxanthine-guanine phosphoribosyltransferase (HPRT). Here we have developed a novel and highly efficient strategy employing 6TG as a single agent for both conditioning and in vivo chemoselection of HPRT-deficient HSC. The dose-response and time course of 6TG myelotoxicity were first compared in HPRT-wild type mice and HPRT-deficient transgenic mice. Dosage and schedule parameters were optimized to employ 6TG for myelo-suppressive conditioning, immediately followed by in vivo chemoselection of HPRT-deficient transgenic donor bone marrow (BM) transplanted into syngeneic HPRT-wild type recipients. At appropriate doses, 6TG induced selective myelotoxicity without any adverse effects on extra-hematopoietic tissues in HPRT-wild type mice, while HSC deficient in HPRT activity were highly resistant to its cytotoxic effects. Combined 6TG conditioning and post transplant chemoselection consistently achieved ~95% engraftment of HPRT-deficient donor BM, with low overall toxicity. Long-term reconstitution of immunophenotypically normal BM was achieved in both primary and secondary recipients. Our results provide proof-of-concept that single-agent 6TG can be used both for myelo-suppressive conditioning without requiring irradiation, and for in vivo chemoselection of HPRT-deficient donor cells. Our results show that by applying the myelosuppressive effects of 6TG both before (as conditioning) and after transplantation (as chemoselection), highly efficient engraftment of HPRT-deficient hematopoietic stem cells can be achieved. PMID:22001673

Hacke, Katrin; Szakmary, Akos; Cuddihy, Andrew R; Rozengurt, Nora; Lemp, Nathan A; Aubrecht, Jiri; Lawson, Gregory W; Rao, Nagesh P; Crooks, Gay M; Schiestl, Robert H.; Kasahara, Noriyuki

2014-01-01

18

Synthesis of Hydrophilic Aminooxy Linkers and Multivalent Cores for Chemoselective Aldehyde/Ketone Conjugation.  

PubMed

A series of three linear and two trivalent aminooxy-containing hydrophilic linkers and cores were synthesized. The five molecules contain from one to three aminooxy groups, and all but one contain an ether for enhanced aqueous solubility. These unique and versatile molecules can be utilized in the chemoselective conjugation of aldehyde/ketone-containing molecules, including reducing sugars, under mild aqueous conditions, and give rise to oxime-containing conjugates useful in a wide variety of applications and studies. The value of these aminooxy-based molecules and the ease and speed of preparation of both monovalent and multivalent oxime-linked molecules is demonstrated in two examples using the disaccharide cellobiose; one with a linear linker, and the second with a trivalent core. PMID:25382876

McReynolds, Katherine D; Dimas, Dustin; Le, Hoang

2014-04-01

19

Chemoselective synthesis of trifluoromethylated ?-butenolide derivatives via phosphine-promoted tandem reaction of allylic carbonates and trifluoromethyl ketones.  

PubMed

A novel chemoselective phosphine-mediated tandem reaction between nonsubstituted MBH carbonates and aryl trifluoromethyl ketones is described. The product selectivity of the reaction is easily tunable by changing the ratios of the two reactants, and mono- or bicyclic bistrifluoromethylated vinyl ?-butenolide products can be prepared with good chemoselectivity in modest-to-good yields and diastereoselectivities. The formation of the bicyclic ?-butenolide structures via a one-pot four-step sequence under phosphine catalysis is unprecedented. PMID:25296160

Xiao, Hua; Duan, Hong-yu; Ye, Jun; Yao, Ri-sheng; Ma, Juan; Yuan, Zhe-zhe; Zhao, Gang

2014-10-17

20

Novel Synthesis of 20 -O-methylguanosine  

E-print Network

and chemoselective synthesis of 20 -O-methylguanosine (6) has been accomplished in high yield without pro- tection 20 -O-methyl nucleosides, they are much less efficient in the case of the purine ana- logues.5 (chemoselectivity) and the need for selective pro- tection of the 30 - and 50 -OH groups (regioselectivity).6

Theodorakis, Emmanuel

21

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, ...

22

Efficient synthesis of pyrenylalanine.  

PubMed

An efficient synthesis of L-3-(1'-pyrenyl)alanine (Pya), a highly fluorescent amino acid, is described. The amino acid was obtained by the classical asymmetric hydrogenation of chiral 1-acetyl-3-pyrenemethylidene-6-methyl-piperazine-2,5-dione. In the proposed improved procedure mild conditions of the synthesis were applied and the final product--N-tertbutoxycarbonyl-pyrenylalanine--was obtained in good yield. Pyrenylalanine, due to its interesting photophysical properties, can be applied as a fluorescent probe in numerous biochemical and conformational studies. PMID:11764407

Szyma?ska, A; Wiczk, W; Lankiewicz, L

2001-01-01

23

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

24

The first chemoselective tandem acylation of the Blaise reaction intermediate: a novel method for the synthesis of alpha-acyl-beta-enamino esters, key intermediate for pyrazoles.  

PubMed

The Blaise reaction intermediate, a zinc bromide complex of beta-enamino ester, could be activated in situ by addition of a stoichiometric or catalytic amount of n-BuLi to allow chemoselective tandem C2-acylation providing alpha-acyl-beta-enamino esters, which are valuable intermediates for the syntheses of tri- and tetrasubstituted pyrazoles. PMID:18956034

Chun, Yu Sung; Lee, Ki Kon; Ko, Young Ok; Shin, Hyunik; Lee, Sang-gi

2008-11-01

25

Efficient synthesis of flavanone glucuronides.  

PubMed

The first efficient synthesis of flavanone glucuronides as potential human metabolites is described. The synthetic strategy is based on acetyl protection, followed by a combination of chemical and enzymatic deprotection steps. As an example, the method is applied to a synthesis of 7,4'-di-O-methyleriodictyol 3'-O-beta-d-glucuronide. The aglycone is a flavanone naturally present in tarragon spice ( Artemisia dracunculus ) as well as in various Chinese, Brazilian, and Malaysian medicinal plants. PMID:19653653

Boumendjel, Ahcene; Blanc, Madeleine; Williamson, Gary; Barron, Denis

2009-08-26

26

Mo(CO)6 catalysed chemoselective hydrosilylation of ?,?-unsaturated amides for the formation of allylamines.  

PubMed

Molybdenum hexacarbonyl (Mo(CO)6) was used as an efficient catalyst for the chemoselective reduction of the amide functionality in ?,?-unsaturated compounds, under hydrosilylation conditions using 1,1,3,3-tetramethyldisiloxane (TMDS) as the hydride source. PMID:25307061

Volkov, Alexey; Tinnis, Fredrik; Slagbrand, Tove; Pershagen, Ida; Adolfsson, Hans

2014-12-01

27

Development of highly chemoselective bulky zincate complex, tBu4ZnLi2: design, structure, and practical applications in small-/macromolecular synthesis.  

PubMed

We present full details of the unique reactivities of the newly developed dianion-type bulky zincate, dilithium tetra-tert-butylzincate (tBu(4)ZnLi(2)). With this reagent, halogen-zinc exchange reaction of variously functionalized haloaromatics and anionic polymerization of N-isopropylacrylamide (NIPAm)/styrene with excellent chemoselectivity were realized. Halogen-zinc exchange reaction followed by electrophilic trapping with propargyl bromide provided a convenient route to functionalized phenylallenes, particularly those with electrophilic functional groups (such as cyano, amide and halogens). Spectral and computational studies of the structure in the gas and liquid phases indicated extraordinary stabilization of this dianion-type zincate by its bulky ligands. PMID:18816554

Furuyama, Taniyuki; Yonehara, Mitsuhiro; Arimoto, Sho; Kobayashi, Minoru; Matsumoto, Yotaro; Uchiyama, Masanobu

2008-01-01

28

Prebiotically plausible oligoribonucleotide ligation facilitated by chemoselective acetylation  

NASA Astrophysics Data System (ADS)

The recent synthesis of pyrimidine ribonucleoside-2?,3?-cyclic phosphates under prebiotically plausible conditions has strengthened the case for the involvement of ribonucleic acid (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 led 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, which allows 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 that possess 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.

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

2013-05-01

29

Direct, regioselective, and chemoselective preparation of novel boronated tryptophans by Friedel-Crafts alkylation.  

PubMed

A facile synthetic approach to the direct preparation of various novel unnatural boronated protected tryptophans using a regio- and chemoselective electrophilic substitution of 4- and 5-boronated indoles with N-protected dehydroalanine is described. The gram-scale synthesis of two free tryptophan boronic acids is also reported. PMID:22208950

Bartolucci, Silvia; Bartoccini, Francesca; Righi, Marika; Piersanti, Giovanni

2012-01-20

30

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

31

An Assessment of Chemoselective Neoglycosylation Methods Using Chlorambucil as a Model  

PubMed Central

To systematically assess the impact of glycosylation and the corresponding chemoselective linker upon the anticancer activity/selectivity of the drug chlorambucil, herein we report the synthesis and anticancer activities of a 63-member library of chlorambucil-based neoglycosides. A comparison of N-alkoxyamine-, N-acyl hydrazine- and N-hydroxyamine-based chemoselective glycosylation of chlorambucil revealed sugar-and linker-dependent partitioning among open and closed-ring neoglycosides and corresponding sugar-dependent variant biological activity. Cumulatively, this study represents the first neoglycorandomization of a synthetic drug and expands our understanding of the impact of sugar structure upon product distribution/equilibria in the context of N-alkoxyamino-, N-hydroxyamino- and N-acyl hydrazine-based chemoselective glycosylation. This study also revealed several analogs with increased in vitro anticancer activity, most notably D-threoside 60 (NSC 748747), which displayed much broader tumor specificity and notably increased potency over the parent drug. PMID:20973561

Goff, Randal D.; Thorson, Jon S.

2010-01-01

32

PPh(3)·HBr-DMSO mediated expedient synthesis of ?-substituted ?,?-unsaturated ?-ketomethylthioesters and ?-bromo enals: application to the synthesis of 2-methylsulfanyl-3(2H)-furanones.  

PubMed

An efficient chemoselective general procedure for the synthesis of ?-substituted ?,?-unsaturated ?-ketomethylthioesters from ?,?-unsaturated ketones has been achieved through an unprecedented PPh3 ?HBr-DMSO mediated oxidative bromination and Kornblum oxidation sequence. The newly developed reagent system serves admirably for the synthesis of ?-bromoenals from enals. Furthermore, AuCl3 -catalyzed efficient access to 3(2H)-furanones from the above intermediates under extremely mild conditions are described. PMID:24339245

Mal, Kanchan; Sharma, Abhinandan; Maulik, Prakas R; Das, Indrajit

2014-01-13

33

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

Microsoft Academic Search

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

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

2005-01-01

34

Short and efficient synthesis of fluorinated ?-lactams.  

PubMed

The diastereoselective synthesis of fluorinated ?-lactams has been achieved through an efficient five step process. The route can tolerate a range of functionalities, and provides a quick route for the generation of new fluorinated medicinal building blocks. PMID:25247464

Cogswell, Thomas J; Donald, Craig S; Long, De-Liang; Marquez, Rodolfo

2015-01-21

35

EFFICIENT SYNTHESIS OF CYTOTOXIC FURONAPHTHOQUINONE NATURAL PRODUCTS  

Microsoft Academic Search

An efficient synthesis of furonaphthoquinone natural products 1 and 4 has been carried out starting from 2-hydroxy-1, 4-naphthoquinone (10) and 2,3-dimethoxy-1,3-butadiene (11) in the presence of CAN.

Yong Rok Lee; Byung So Kim

2001-01-01

36

Dearomatization Strategies in the Synthesis of Complex Natural Products  

PubMed Central

Evolution in the field of the total synthesis of natural products has led to exciting developments over the last decade. Numerous chemo-selective and enantioselective methodologies have emerged from total syntheses, resulting in efficient access to many important natural product targets. This Review highlights recent developments concerning dearomatization, a powerful strategy for the total synthesis of architecturally complex natural products wherein planar, aromatic scaffolds are converted to three-dimensional molecular architectures. PMID:21506209

Roche, Stéphane P.; Porco, John A.

2014-01-01

37

An Efficient, Second-Generation Synthesis of the Signature Dioxabicyclo[3.2.1]octane Core of (+)-Sorangicin A and Elaboration of the (Z,Z,E)-Triene Acid System  

PubMed Central

An efficient, second-generation synthesis of the signature dioxabicyclo[3.2.1]octane core of (+)-sorangicin A (1), in conjunction with an effective, stereocontrolled protocol to arrive at the requisite Z,Z,E triene acid system has been developed. Highlights of the core construction entail a three-component union, a KHMDS-promoted epoxide ring formation-ring opening cascade, a Takai olefination and a chemoselective Sharpless dihydroxylation. Assembly of the triene acid system was then achieved via Stille cross-coupling with the ethyl ester of (Z,Z)-5-tributylstannyl-2,4- pentadienoic acid, followed by mild hydrolysis preserving the triene configuration. PMID:19182995

Smith, Amos B.; Dong, Shuzhi

2010-01-01

38

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

PubMed

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

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

2012-09-01

39

An efficient total synthesis of (-)-epothilone B.  

PubMed

An efficient total synthesis of (-)-epothilone B has been achieved in ca. 8% yield over 11 steps from 9 (or 10 steps from 7/8), which features a bissiloxane-tethered ring closing metathesis reaction to approach the trisubstituted (Z) double bond and forms a new basis for further development of an industrial process for epothilone B and ixabepilone. PMID:23214997

Wang, Jie; Sun, Bing-Feng; Cui, Kai; Lin, Guo-Qiang

2012-12-21

40

An efficient catalytic method for fulvene synthesis  

PubMed Central

The effects of the nature and amount of base, substrate structure, amount of added water and solvent on the condensation of carbonyl compounds with cyclopentadiene in the presence of secondary amines were investigated. Based on these studies, a new efficient and green synthesis of fulvenes was developed. PMID:22021940

Co?kun, Necdet; Erden, Ihsan

2011-01-01

41

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

42

Highly Efficient Asymmetric Synthesis of -Amino Acid Derivatives via  

E-print Network

Highly Efficient Asymmetric Synthesis of -Amino Acid Derivatives via Rhodium pure -amino acids and their deriva- tives are important building blocks for the synthesis of -peptides of -amino acids has attracted extensive interest. Although several stoichio- metric and catalytic methods

Zhang, Xumu

43

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

44

The effect of substrate structure on the chemoselectivity of Candida1 antarctica lipase B-catalyzed acylation of amino-alcohols2  

E-print Network

interesting products with many applications in food, cosmetic and14 pharmaceutical industries, but it is real antarctica lipase B; Organic solvent;32 Chemoselectivity33 34 hal-00789681,version1-18Feb2013 #12;3 1 pharmaceutics and cosmetics, through the synthesis of ceramides [1, 2] as potential anti-viral37 or anti

Boyer, Edmond

45

Chemoselective reduction of nitroaromatics to anilines using decaborane in methanol  

Microsoft Academic Search

Nitrobenzenes were chemoselectively reduced to the corresponding anilines using decaborane (B10H14) in the presence of Pd\\/C and two drops of acetic acid at reflux under nitrogen atmosphere in high yields.

Jong Woo Bae; Young Jin Cho; Seung Hwan Lee; Cheol Min Yoon

2000-01-01

46

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

47

Mechanistic origin of chemoselectivity in thiolate-catalyzed Tishchenko reactions.  

PubMed

The thiolate-catalyzed Tishchenko reaction has shown high chemoselectivity for the formation of double aromatic-substituted esters. In the present study, the detailed reaction mechanism and, in particular, the origin of the observed high chemoselectivity, have been studied with DFT calculations. The catalytic cycle mainly consisted of three steps: 1,2-addition, hydride transfer, and acyl transfer steps. The calculation results reproduce the experimental observations that 4-chlorobenzaldehyde acts as the hydrogen donor (carbonyl part in the ester product), while 2-methoxybenzaldehyde acts as the hydrogen acceptor (alcohol part in the product). The two main factors are responsible for such chemoselectivity: 1) in the rate-determining hydride transfer step, the para-chloride substituent facilitates the hydride-donating process by weakening the steric hindrance, and 2) the ortho-methoxy substituent facilitates the hydride-accepting process by stabilizing the magnesium center (by compensating for the electron deficiency). PMID:25213329

Yu, Hai-Zhu; Tian, Xue-Jiao; Lin, Xiang; Hu, Guo-Hua; Dang, Zhi-Min

2014-12-01

48

Highly Efficient Synthesis of Chiral -Amino Acid Derivatives via  

E-print Network

Highly Efficient Synthesis of Chiral -Amino Acid Derivatives via Asymmetric Hydrogenation Wenjun-TangPhos complex is an efficient hydrogenation catalyst for making chiral -amino acid derivatives. With the Rh -amino acids has drawn a great deal of attention due to its importance in biomedical research

Zhang, Xumu

49

An efficient synthesis of loline alkaloids  

NASA Astrophysics Data System (ADS)

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

Cakmak, Mesut; Mayer, Peter; Trauner, Dirk

2011-07-01

50

An efficient asymmetric synthesis of (-)-lupinine.  

PubMed

The asymmetric synthesis of (-)-lupinine was achieved in 8 steps, 15% overall yield and >99?:?1 dr from commercially available starting materials. The strategy used for the construction of the quinolizidine scaffold involved reaction of an enantiopure tertiary dibenzylamine via two sequential ring-closures which both occurred with concomitant N-debenzylation. PMID:24938152

Davies, Stephen G; Fletcher, Ai M; Foster, Emma M; Houlsby, Ian T T; Roberts, Paul M; Schofield, Thomas M; Thomson, James E

2014-08-01

51

Chemoselective silicification of synthetic peptides and polyamines  

PubMed Central

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

Abacilar, Maryna; Daus, Fabian

2015-01-01

52

Monomers for preparation of amide linked RNA: Synthesis of C3’-homologated nucleoside amino acids from d-xylose  

PubMed Central

Amides as neutral and hydrophobic internucleoside linkages in RNA are highly interesting modifications for RNA interference. However, testing amides in siRNAs is hampered by the shortage of efficient methods to synthesize the monomeric building blocks, the nucleoside amino acid equivalents. This paper reports an efficient synthesis of protected ribonucleoside 5'-amino 3'-carboxylic acids from d-xylose in 14 steps 7% overall yield. The key features that ensure efficiency and ease of operations are chemoselective reduction of the ester and minimization of protecting group manipulation. PMID:20725640

Tanui, Paul; Kullberg, Martin; Song, Ni; Chivate, Yashodhan

2010-01-01

53

Efficient synthesis of cis-2,6-di-(2- quinolylpiperidine)  

PubMed Central

An efficient synthesis of cis-2,6-di-(2-quinolylpiperidine) has been developed. The key steps involve Wittig reaction of N-Cbz-protected cis-piperidine-2,6-dicarboxaldehyde (3) with 2-(triphenylphosphinyl- methyl)quinoline bromide (4) and sequential removal of the N-Cbz group and double bond reduction. This synthetic procedure provides an efficient preparation for this useful norlobelane analogue. PMID:24511163

Ding, Derong; Dwoskin, Linda P.; Crooks, Peter A.

2013-01-01

54

Efficient Synthesis of Enantiopure -Amino--Keto Acids from  

E-print Network

Efficient Synthesis of Enantiopure -Amino--Keto Acids from L-Homoserine Anil K. Sharma and Paul J hergenro@uiuc.edu Received March 26, 2003 ABSTRACT A variety of -amino--keto acids were prepared in four-catalyzed Grignard addition to a N-protected derivative of L-homoserine. One of the -amino--keto acids was then used

Hergenrother, Paul J.

55

Smart Memory Synthesis for Energy-Efficient Computed Tomography Reconstruction  

E-print Network

Smart Memory Synthesis for Energy-Efficient Computed Tomography Reconstruction Qiuling Zhu, Larry mandate greater pat- tern regularity and commonality for logic and memory circuits, new opportunities are created to affordably synthesize more powerful smart memory blocks for specific applications. Leveraging

Franchetti, Franz

56

Efficient synthesis of OTA network for linear analog functions  

Microsoft Academic Search

This paper reports a general methodology and a computer-aided design (CAD) tool (BECAS 1.0) for synthesis of linear analog functions with a network of operational transconductance amplifiers (OTAs). Efficient analog circuits have been synthesized with the CAD tool and reported along with the simulation results. SPICE simulated results of the synthesized circuit match closely with those derived theoretically from the

Baidya Nath Ray; Parimal Pal Chaudhuri; Prasanta Kumar Nandi

2002-01-01

57

Continuous chemoselective methylation of functionalized amines and diols with supercritical methanol over solid acid and acid-base bifunctional catalysts.  

PubMed

The selective N-methylation of bifunctionalized amines with supercritical methanol (scCH(3)OH) promoted by the conventional solid acids (H-mordenite, beta-zeolite, amorphous silica-alumina) and acid-base bifunctional catalysts (Cs-P-Si mixed oxide and gamma-alumina) was investigated in a continuous-flow, fixed-bed reactor. The use of scCH(3)OH in the reaction of 2-aminoethanol with methanol (amine/CH(3)OH = 1/10.8) over the solid catalysts led to a significant improvement in the chemoselectivity of the N-methylation. Among the catalysts examined, the Cs-P-Si mixed oxide provided the most efficient catalyst performance in terms of selectivity and reactivity at 300 degrees C and 8.2 MPa; the N-methylation selectivity in the products reaching up to 94% at 86% conversion. The present selective methylation was successfully applied to the synthesis of N-methylated amino alcohols and diamines as well as O-methylated ethylene glycol. Noticeably, ethoxyethylamine was less reactive, suggesting that the hydroxy group of the amino alcohols is a crucial structural factor in determining high reactivity and selectivity, possibly because of the tethering effect of another terminus, a hydroxo group, to the catalyst surface. The magic-angle-spinning NMR spectroscopy and X-ray diffraction analysis of the Cs-P-Si mixed oxide catalyst revealed that the acidic and basic sites originate from P(2)O(5)/SiO(2) and Cs/SiO(2), respectively, and the weak acid-base paired sites are attributed to three kinds of cesium phosphates on SiO(2). The weak acid-base sites on the catalyst surface might be responsible for the selective dehydrative methylation. PMID:15186176

Oku, Tomoharu; Arita, Yoshitaka; Tsuneki, Hideaki; Ikariya, Takao

2004-06-16

58

Chemoselective Polymerization Control: From Mixed-Monomer Feedstock to Copolymers**  

PubMed Central

A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents. PMID:24453135

Romain, Charles; Williams, Charlotte K

2014-01-01

59

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

60

Efficient total synthesis of novel bioactive microbial metabolites.  

PubMed

Bioactive natural products produced by microbes have almost limitless potential in pharmaceutical applications, and the organic synthesis of such products as lead compounds will result in the creation of new and widely useful pharmaceutical products. A program of discovery of naturally occurring bioactive microbial metabolites has been ongoing at the Kitasato Institute. We have also developed efficient, rational, and highly flexible production methods for generation of target compounds, synthesis of related compounds, elucidation of their structure-activity relationships, and the possible creation of improved bioactive compounds. In this Account, the isolation and total synthesis of naturally occurring bioactive microbial metabolites in order to create novel medicines for specific illnesses is described. This covers diseases and conditions such as atherosclerosis, Alzheimer's disease, cancer, inflammation, and osteoporosis, among others, and focuses on six specific compounds. Pyripyropenes were discovered from Aspergillus fumigatus FO-1289 through our screening of microbial metabolites that strongly inhibit acyl-CoA cholesterol acyltransferase (ACAT) in order to develop a new class of cholesterol-lowering agents. These novel polyoxygenated mixed polyketide-terpenoid (meroterpenoid) metabolites contain a fused pyridyl alpha-pyrone moiety. We carried out the first total synthesis of (+)-pyripyropene A via a flexible, concise, and highly efficient route and also clarified the structure-activity relationships. Arisugacins were discovered from Penicillium sp. FO-4259 by our screening of microbial metabolites that strongly inhibit acetylcholinesterase (AChE) in order to create novel medicines for Alzheimer's disease (AD). Arisugacins are also meroterpenoids. We have achieved the first convergent total synthesis of arisugacins A and B. Lactacystin was isolated from Streptomyces sp. OM-6519 via our screening of microbial metabolites that promote the differentiation of the neuroblastoma cell to further discover new AD medicines. Lactacystin has a novel gamma-lactam thioester structure and is also a selective and strong proteasome inhibitor. We have developed a concise approach to synthesize lactacystin designed to afford easy access to the original compound and a variety of analogs. Macrosphelides were isolated from Microsphaeropsis sp. FO-5050 from our screening of microbial metabolites that inhibit the adhesion of HL-60 cells to human umbilical vein endothelial cells (HUVEC). Macrosphelides are the first 16-membered macrotriolides. Macrosphelides prevent cell-cell adhesion by inhibiting the binding of sialyl Lewis X to E-selectin. We have accomplished the first efficient total synthesis of macrosphelides. Madindolines were isolated from Streptomyces nitrosporeus K93-0711 by our program to discover new interleukin 6 (IL-6) modulators. Madindolines are comprised of a 3a-hydroxyfuroindoline ring connected at nitrogen via a methylene bridge to a cyclopentene-1,3-dione ring. We have developed an efficient and practical total synthesis of madindolines. Madindoline A binds to gp130 selectively and inhibits IL-6 activity. Neoxaline was isolated from Aspergillus japonicus Fg-551. Neoxaline is a member of a novel class of biologically active indole alkaloids characterized by a unique indoline spiroaminal framework and binds to tubulin, which results in inhibition of tubulin polymerization. We have developed a concise stereoselective synthesis of the indoline spiroaminal framework of neoxaline. PMID:18217720

Sunazuka, Toshiaki; Hirose, Tomoyasu; Omura, Satoshi

2008-02-01

61

Efficient synthesis and reactions of 1,2-dipyrrolylethynes  

PubMed Central

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

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

2011-01-01

62

Regio- and Chemoselective Immobilization of Proteins on Gold Surfaces  

PubMed Central

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

2015-01-01

63

Introducing deep eutectic solvents to polar organometallic chemistry: chemoselective addition of organolithium and Grignard reagents to ketones in air.  

PubMed

Despite their enormous synthetic relevance, the use of polar organolithium and Grignard reagents is greatly limited by their requirements of low temperatures in order to control their reactivity as well as the need of dry organic solvents and inert atmosphere protocols to avoid their fast decomposition. Breaking new ground on the applications of these commodity organometallics in synthesis under more environmentally friendly conditions, this work introduces deep eutetic solvents (DESs) as a green alternative media to carry out chemoselective additions of ketones in air at room temperature. Comparing their reactivities in DES with those observed in pure water suggest that a kinetic activation of the alkylating reagents is taking place, favoring nucleophilic addition over the competitive hydrolysis, which can be rationalized through formation of halide-rich magnesiate or lithiate species. PMID:24771680

Vidal, Cristian; García-Álvarez, Joaquín; Hernán-Gómez, Alberto; Kennedy, Alan R; Hevia, Eva

2014-06-01

64

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

65

Exploiting Orthogonally Reactive Functionality: Synthesis and Stereochemical Assignment of (?)-Ushikulide A  

PubMed Central

In spite of the tremendous advances in modern spectroscopic methods, organic synthesis continues to play a pivotal role in elucidating the full structures of complex natural products. This method has the advantage that even in the absence of a firm structural assignment, a combination of logic and spectroscopic comparison can arrive at the correct structure. Herein, we report execution of this strategy with respect to ushikulide A, a newly isolated and previously stereochemically-undefined member of the oligomycin-rutamycin family. To maximize synthetic efficiency, we envisioned chemoselective manipulation of orthogonally reactive functional groups, notably alkenes and alkynes as surrogates for certain carbonyl and hydroxyl functionalities. This approach has the dual effect of minimizing the number of steps and protecting groups required for our synthetic route. This strategy culminated in the efficient synthesis and stereochemical assignment of ushikulide A. PMID:18989964

Trost, Barry M.; O’Boyle, Brendan M.

2009-01-01

66

Glycoprotein Synthesis: An Update David P. Gamblin, Eoin M. Scanlan, and Benjamin G. Davis*  

E-print Network

in the `quality control' of protein synthesis.7-9 In the absence of correct glycosylation, many proteins foldGlycoprotein Synthesis: An Update David P. Gamblin, Eoin M. Scanlan, and Benjamin G. Davis Synthesis 143 3.1. Indiscriminate Convergent Glycosylation 143 3.2. Chemoselective and Site

Davis, Ben G.

67

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

68

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

69

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

PubMed

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

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

2015-02-01

70

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

PubMed

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

Huang, Hanchu; Jia, Kunfang; Chen, Yiyun

2015-02-01

71

An efficient green MCR protocol for the stereoselective synthesis of ?-acetamido ketones catalyzed by Selectfluor™  

Microsoft Academic Search

An efficient, green, room temperature process for the stereoselective synthesis of ?-amido ketones employing a one-pot multi-component reaction of aromatic aldehydes, ?-substituted or ?-unsubstituted ketones, an acid chloride, and a nitrile in presence of catalytic amount of Selectfluor™ is described. The process offers advantages such as high anti-selectivity, shorter reaction time, energy efficiency, and simple work-up.

V. S. Shinu; B. Sheeja; E. Purushothaman; D. Bahulayan

2009-01-01

72

Efficient regimes of butadiene rubber synthesis on separate supply of feedstock to cascade reactors  

NASA Astrophysics Data System (ADS)

Mathematical simulation of the synthesis of butadiene rubber on the basis of a neodymium-containing catalytic system in a cascade of continuously operating reactors is carried out. Expressions for the characteristics of the branching of the synthesized polymer macromolecules have been derived. Efficient regimes of rubber synthesis on separate supply of feedstock to the cascade reactors allowing one to obtain rubber with specified parameters without losing the cascade capacity have been determined.

Manuiko, G. V.; Bashkirov, D. V.; Aminova, G. A.; Bronskaya, V. V.; Ignashina, T. V.; Ismagilova, A. I.; Diyakonov, G. S.; Sakhabutdinov, A. G.

2011-09-01

73

Microwave assisted convenient one-pot synthesis of coumarin derivatives via Pechmann condensation catalyzed by FeF3 under solvent-free conditions and antimicrobial activities of the products.  

PubMed

A rapid and efficient solvent-free one-pot synthesis of coumarin derivatives by Pechmann condensation reactions of phenols with ethyl acetoacetate using FeF3 as a catalyst under microwave irradiation is described. This one-pot synthesis on a solid inorganic support provides the products in good yields. The newly synthesized compounds were systematically characterized by IR, 1H-NMR, 13C-NMR, MS and elemental CHN analyses. The proposed solvent-free microwave irradiation method using the environmentally friendly catalyst FeF3 offers the unique advantages of high yields, shorter reaction times, easy and quick isolation of the products, excellent chemoselectivity, and a one-pot, green synthesis. The products were screened for antimicrobial activity, and the results showed that the compounds reacted against all the tested bacteria. PMID:25255747

Vahabi, Vahid; Hatamjafari, Farhad

2014-01-01

74

Chemoselective per-O-trimethylsilylation and homogeneous N-functionalisation of amino sugars.  

PubMed

A highly efficient CH3CN-promoted hexamethyldisilazane per-O-trimethylsilylation of amino sugars was developed. Its applications in homogenous N-functionalisation and a concise synthesis of glucosamine 6-phosphate are described. PMID:25384128

Joseph, A Abragam; Dhurandhare, Vijay M; Chang, Chun-Wei; Verma, Ved Prakash; Mishra, Girija Prasad; Ku, Chiao-Chu; Lin, Chun-Cheng; Wang, Cheng-Chung

2015-01-01

75

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

PubMed

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

Nallagonda, Rajender; Rehan, Mohammad; Ghorai, Prasanta

2014-04-01

76

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective  

E-print Network

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective% head-to-tail (HT) couplings1,2 has led to the discovery of materials that self-assemble both aggregation is precursive to a microcrystalline, self-assembled structure which has been characterized by X

McCullough, Richard D.

77

Substrate-directable electron transfer reactions. Dramatic rate enhancement in the chemoselective reduction of cyclic esters using SmI2-H2O: mechanism, scope, and synthetic utility.  

PubMed

Substrate-directable reactions play a pivotal role in organic synthesis, but are uncommon in reactions proceeding via radical mechanisms. Herein, we provide experimental evidence showing dramatic rate acceleration in the Sm(II)-mediated reduction of cyclic esters that is enabled by transient chelation between a directing group and the lanthanide center. This process allows unprecedented chemoselectivity in the reduction of cyclic esters using SmI2-H2O and for the first time proceeds with a broad substrate scope. Initial studies on the origin of selectivity and synthetic application to form carbon-carbon bonds are also disclosed. PMID:24079360

Szostak, Michal; Spain, Malcolm; Choquette, Kimberly A; Flowers, Robert A; Procter, David J

2013-10-23

78

Ascorbic acid efficiently enhances neuronal synthesis of norepinephrine from dopamine.  

PubMed

Ascorbic acid enhances synthesis of norepinephrine from dopamine in adrenal chromaffin cells by serving as a co-factor for chromaffin granule dopamine ?-hydroxylase (D?H). However, there is controversy regarding in situ kinetics of the ascorbate effect in chromaffin cells, as well as whether they apply to neuronal cells. In this study we evaluated the stimulation of norepinephrine synthesis from dopamine in cultured SH-SY5Y neuroblastoma cells. These cells contained neither ascorbate nor norepinephrine in culture, but when provided with dopamine, they generated intracellular norepinephrine at rates that were stimulated several-fold by intracellular ascorbate. Ascorbate-induced increases in norepinephrine synthesis in dopamine-treated cells were linear over 60 min, despite saturation of intracellular ascorbate. Norepinephrine accumulation after 60 min of incubation with 100 ?M dopamine was half-maximal at intracellular ascorbate concentrations of 0.2-0.5 mM, which fits well with the literature K(m) for ascorbate of D?H using dopamine as a substrate. Moreover, these ascorbate concentrations were generated by initial extracellular ascorbate concentrations of less than 25 ?M due to concentrative accumulation by the ascorbate transporter. Treatment with 100 ?M dopamine acutely increased cellular superoxide generation, which was prevented by ascorbate loading, but associated with a decrease in intracellular ascorbate when the latter was present at concentrations under 1 mM. These results show that ascorbate promptly enhances norepinephrine synthesis from dopamine by neuronal cells that it does so at physiologic intracellular concentrations in accord with the kinetics of D?H, and that it both protects cells from superoxide and by providing electrons to D?H. PMID:23022576

May, James M; Qu, Zhi-Chao; Nazarewicz, Rafal; Dikalov, Sergey

2013-01-01

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

Thiopyran route to polypropionates: an efficient synthesis of serricornin.  

PubMed

The synthesis of serricornin [(4S,6S,7S)-7-hydroxy-4,6-dimethylnonan-3-one], a sex pheromone produced by the female cigarette beetle (Lasioderma serricorne F.), in seven steps from readily available racemic 1,4-dioxa-8-thiaspiro[4.5]decane-6-carboxaldehyde (6) is described. The key steps include enantioselective aldol reaction of 6 with tetrahydrothiopyran-4-one catalyzed by 5-[(2S)-pyrrolidine-2-yl]-1H-tetrazole to fabricate the tetrapropionate skeleton, stereoselective Li(s)Bu(3)BH reduction of the resulting aldol adduct, Barton-McCombie deoxygenation, and Raney nickel desulfurization. PMID:17081039

Ward, Dale E; Jheengut, Vishal; Beye, Garrison E

2006-11-10

81

Gold-Catalyzed Oxidative Ring Expansion of 2-Alkynyl-1,2-Dihydropyridines or -quinolines: Highly Efficient Synthesis of Functionalized Azepine or Benzazepine Scaffolds.  

PubMed

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

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

2015-01-19

82

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

83

Efficient synthesis of nevirapine analogs to study its metabolic profile by click fishing  

Microsoft Academic Search

Knowledge of the biotransformation and pharmacokinetics of the antiretroviral agent nevirapine is still insufficient. In order to trace rash inducing metabolites of nevirapine, we devised a short and efficient multi-gram synthesis of a nevirapine analog that can be coupled to azide containing compounds by click chemistry.

Sylvain Bernard; Daniel Defoy; Yves L. Dory; Klaus Klarskov

2009-01-01

84

Efficient Automata-Based Assertion-Checker Synthesis of SEREs for Hardware Emulation  

E-print Network

Efficient Automata-Based Assertion-Checker Synthesis of SEREs for Hardware Emulation Marc Boul allows the adoption of ABV in hardware emulation. Towards that goal, we introduce the algorithms violations. As circuits become more complex, hardware emulation is becoming an increasingly important asset

Zilic, Zeljko

85

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

E-print Network

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

Trauner, Dirk

86

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

PubMed Central

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

Curini, Massimo; Rosati, Ornelio; Minuti, Lucio

2014-01-01

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 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

89

An efficient synthesis of pyridoxal oxime derivatives under microwave irradiation.  

PubMed

Quaternary salts of pyridoxal oxime have been synthesized by the quaternization of pyridoxal oxime with substituted phenacyl bromides using microwave heating. Microwave-assisted rapid synthesis was done both in solvent (acetone) and under solvent-free conditions. Good to excellent yields (58%-94%) were obtained in acetone in very short reaction times (3-5 min) as well as in the solvent-free procedure (42%-78%) in very short reaction times (7-10 min) too. Effective metodologies for the preparation of pyridoxal oxime quaternary salts, having the advantagies of being eco-friendly, easy to handle, and performed in shorter reactions time are presented. The structure of compound 7, in which a 4-fluorophenacyl moiety is bonded to the pyridinium ring nitrogen atom, was unequivocally confirmed by the single-crystal X-ray diffraction method. PMID:24914903

Gašo-Soka?, Dajana; Buši?, Valentina; Cetina, Mario; Juki?, Marijana

2014-01-01

90

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

91

Efficient Synthesis of Fmoc-Protected Phosphinic Pseudodipeptides: Building Blocks for the Synthesis of Matrix Metalloproteinase Inhibitors  

PubMed Central

A convenient route for the synthesis of Fmoc-protected phosphinic dipeptide building blocks is described. The protected amino acid isosteres benzyloxycarbonyl aminomethyl phosphinic acid (glycine surrogate), benzyl ?-isopropyl acrylate (valine surrogate), and benzyl ?-isobutyl acrylate (leucine surrogate) were synthesized starting from commercially available materials. Reaction of either the valine or leucine surrogate with bis(trimethylsilyl) phosphonite generated the pseudodipeptide bond. The synthesis concluded with an efficient one-pot three-step procedure involving a bis-deprotection of the N- and C-termini under catalytic hydrogenation conditions followed by selective capping of the N-terminus with an Fmoc group to yield either Fmoc-NHCH2PO(OAd)CH2CH(Pri)CO2H or Fmoc-NHCH2PO(OAd)CH2CH(Bui)CO2H. PMID:20225219

Bhowmick, Manishabrata; Sappidi, Ravinder R.; Fields, Gregg B.; Lepore, Salvatore D.

2012-01-01

92

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

PubMed

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

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

2015-03-01

93

Efficient synthesis of dichlorodenafil, an unapproved sildenafil analogue appearing in non-prescription supplements.  

PubMed

We have developed an efficient synthesis of dichlorodenafil (4), an unapproved sildenafil analogue isolated from dietary supplements. Our sequence employs POCl(3)-mediated chlorination of readily available chloroacetyl compound 7 followed by selective hydrolysis of the chloro-heterocycle function. Our synthesis confirms the structure of the illegal additive, and will provide regulatory agencies with ready access to authentic standard samples of dichlorodenafil (4) to aid in their mission to protect the public from unapproved and potentially harmful erectile dysfunction (ED) drug analogues that are added to herbal and dietary supplements without providing users with appropriate toxicological or pharmacological information. PMID:23649199

Kim, Jong Yup; Hwang, In Gyun; Oh, Jae Ho; Kang, Il Hyun; Kwon, Sung Won; Kim, Deukjoon

2013-01-01

94

Ultrasound promoted clay catalyzed efficient and one pot synthesis of substituted oxindoles.  

PubMed

A simple facile, one-pot synthesis of oxindoles in reasonable purity is reported via intramolecular Friedal-Craft cyclization. Clay KSF is an inexpensive, efficient and mild catalyst for the synthesis of substituted oxindoles by the reaction of chloroacetyl chloride and various anilines under the influence of ultrasonic irradiation under solvent-free conditions. The remarkable advantages of this method are the simple experimental procedures, short reaction times, high yields of products, suitability for a wide variety of substituents, and the green aspects through the avoidance of toxic catalyst and solvents. PMID:21504851

Dandia, A; Bhati, D S; Jain, A K; Sharma, G N

2011-09-01

95

Liquid-phase synthesis of block copolymers containing sequence-ordered segments.  

PubMed

Monodisperse sequence-defined oligomers have been synthesized in solution in the absence of protecting groups. These structures have been prepared stepwise using two consecutive chemoselective reactions: 1,3-dipolar cycloaddition of terminal alkynes and azides and amidification of carboxylic acids with primary amines. These oligomers were efficiently constructed on either a conventional solid support (commercial Wang resin) or tailor-made soluble polystyrene supports synthesized by atom-transfer radical polymerization. The latter approach was found to be very versatile. Indeed, well-defined soluble macromolecular supports allowed not only the synthesis and cleavage of defined oligomers (i.e., sacrificial support) but also the preparation of noncleavable block copolymers containing sequence-defined segments. PMID:19522508

Pfeifer, Sebastian; Zarafshani, Zoya; Badi, Nezha; Lutz, Jean-François

2009-07-01

96

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

97

Remarkable biomimetic chemoselective aerobic oxidation of flavano-ellagitannins found in oak-aged wine.  

PubMed

Under the auspices of Bacchus! Acutissimins, natural flavano-ellagitannins, occur in oak-aged wine as a result of a diastereoselective condensation reaction of the flavan-3-ol catechin, a component of grapes, with the C-glucosidic ellagitannin vescalagin, found in oak. The acutissimins are further converted into natural mongolicains and analogues of camelliatannin?G in a remarkably chemoselective fashion by simple aerobic oxidation. PMID:24039115

Petit, Emilie; Lefeuvre, Dorothée; Jacquet, Rémi; Pouységu, Laurent; Deffieux, Denis; Quideau, Stéphane

2013-10-25

98

Chemoselection of Allogeneic HSC After Murine Neonatal Transplantation Without Myeloablation or Post-transplant Immunosuppression  

PubMed Central

The feasibility of allogeneic transplantation, without myeloablation or post-transplant immunosuppression, was tested using in vivo chemoselection of allogeneic hematopoietic stem cells (HSCs) after transduction with a novel tricistronic lentiviral vector (MGMTP140K-2A-GFP-IRES-TK (MAGIT)). This vector contains P140K-O6-methylguanine-methyltransferase (MGMTP140K), HSV-thymidine kinase (TKHSV), and enhanced green fluorescent protein (eGFP) enabling (i) in vivo chemoselection of HSC by conferring resistance to benzylguanine (BG), an inhibitor of endogenous MGMT, and to chloroethylating agents such as 1,3-bis(2-chloroethyl)nitrosourea (BCNU) and, (ii) depletion of proliferating cells such as malignant clones or transduced donor T cells mediating graft versus host disease (GVHD), by expression of the suicide gene TKHSV and Ganciclovir (GCV) administration. Non-myeloablative transplantation of transduced, syngeneic, lineage-depleted (Lin?) BM in neonates resulted in 0.67% GFP+ mononuclear cells in peripheral blood. BG/BCNU chemoselection, 4 and 8 weeks post-transplant, produced 50-fold donor cell enrichment. Transplantation and chemoselection of major histocompatibility complex (MHC)-mismatched MAGIT-transduced Lin? BM also produced similar expansion for >40 weeks. The efficacy of this allotransplant approach was validated in Hbbth3 heterozygous mice by correction of ?-thalassemia intermedia, without toxicity or GVHD. Negative selection, by administration of GCV resulted in donor cell depletion without graft ablation, as re-expansion of donor cells was achieved with BG/BCNU treatment. These studies show promise for developing non-ablative allotransplant approaches using in vivo positive/negative selection. PMID:22871662

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

2012-01-01

99

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

PubMed

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

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

2012-11-01

100

Tertiary amide-based Knoevenagel-type reactions: a direct, general, and chemoselective approach to enaminones.  

PubMed

We report one-pot and chemoselective Knoevenagel-type reactions using highly stable amides and lactams as the electrophilic substrates. The method is based on the in situ activation of amide carbonyl with triflic anhydride and a subsequent reaction with carbanions generated in situ from carbonyl compounds. The amide-based method is an alternative to the versatile thioamide-based Eschenmoser sulfide contraction. PMID:24967872

Huang, Pei-Qiang; Ou, Wei; Xiao, Kai-Jiong; Wang, Ai-E

2014-08-14

101

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

102

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

103

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

104

Efficient ATP synthesis by thermophilic Bacillus FoF1-ATP synthase  

PubMed Central

FoF1-ATP synthase (FoF1) synthesizes ATP in the F1 portion when protons flow through Fo to rotate the shaft common to F1 and Fo. Rotary synthesis in isolated F1 alone has been shown by applying external torque to F1 of thermophilic origin. Proton-driven ATP synthesis by thermophilic Bacillus PS3 FoF1 (TFoF1), 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 TFoF1 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 Q10 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

2011-01-01

105

Tandem Chain Walking Polymerization and ATRP for Efficient Synthesis of Dendritic Nanoparticles for Bioconjugation  

PubMed Central

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

Chen, Guanghui; Huynh, Devan; Felgner, Phil L.; Guan, Zhibin

2012-01-01

106

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

107

Highly efficient, enantioselective synthesis of (+)-grandisol from a C2-symmetric bis(alpha,beta-butenolide).  

PubMed

[reaction: see text] A new, very efficient, enantioselective synthesis of the sexual attracting insect pheromone (+)-grandisol has been developed, in which the key step is the double [2 + 2] photocycloaddition of ethylene to a bis(alpha,beta-butenolide) readily available from D-mannitol. The C2 symmetry of the substrate and the appropriate protection of the central diol unit are the crucial features for the high diastereofacial discrimination during the cycloaddition process. PMID:10814272

de March, P; Figueredo, M; Font, J; Raya, J

2000-01-27

108

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

PubMed

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

2009-05-20

109

Efficient synthesis of fatty monoglyceride sulfates from fatty acids and fatty acid methyl esters  

Microsoft Academic Search

An efficient high yield synthesis of fatty monoglyceride sulfates from fatty acids or fatty acid methyl esters, glycerine\\u000a and chlorosulfuric acid in chloroform using stoichiometric amounts of reagents was developed. Sodium coco monoglyceride sulfate\\u000a was prepared in 79% yield with 93% purity from coco fatty acids. Similarly, sodium palm kernel monoglyceride sulfate in 57%\\u000a yield and sodium palm monoglyceride sulfate

Fahim U. Ahmed

1990-01-01

110

Efficient Realization of Wave Digital Components for Physical Modeling and Sound Synthesis  

Microsoft Academic Search

Wave digital filters (WDFs) were originally developed for robust discrete-time simulation of analog filters, but recently they have been applied successfully to modeling of physical systems such as musical instruments and to model-based sound synthesis. While basic WDF elements are sufficient to implement arbitrary passive lumped-element models, the computational efficiency of such models is not optimal. In this paper, we

Matti Karjalainen

2008-01-01

111

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

Microsoft Academic Search

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

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

2004-01-01

112

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

Microsoft Academic Search

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

Michael A. Cotta; James B. Russell

1982-01-01

113

Information and Efficiency in the Nervous System—A Synthesis  

PubMed Central

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

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

2013-01-01

114

Efficient synthesis of [18F]trifluoromethane and its application in the synthesis of PET tracers.  

PubMed

A new strategy towards [(18)F]trifluoromethyl-containing compounds is developed. [(18)F]trifluoromethane is synthesised in a fast and efficient manner and subsequently used in the reaction with aldehydes and ketones forming [(18)F]trifluoromethyl carbinols in good yields. PMID:23563284

van der Born, Dion; Herscheid, J Koos D M; Orru, Romano V A; Vugts, Danielle J

2013-05-11

115

Aerobic dehydrogenation of cyclohexanone to cyclohexenone catalyzed by Pd(DMSO)2(TFA)2: evidence for ligand-controlled chemoselectivity.  

PubMed

The dehydrogenation of cyclohexanones affords cyclohexenones or phenols via removal of 1 or 2 equiv of H2, respectively. We recently reported several Pd(II) catalyst systems that effect aerobic dehydrogenation of cyclohexanones with different product selectivities. Pd(DMSO)2(TFA)2 is unique in its high chemoselectivity for the conversion of cyclohexanones to cyclohexenones, without promoting subsequent dehydrogenation of cyclohexenones to phenols. Kinetic and mechanistic studies of these reactions reveal the key role of the dimethylsulfoxide (DMSO) ligand in controlling this chemoselectivity. DMSO has minimal kinetic influence on the rate of Pd(TFA)2-catalyzed dehydrogenation of cyclohexanone to cyclohexenone, while it strongly inhibits the second dehydrogenation step, conversion of cyclohexenone to phenol. These contrasting kinetic effects of DMSO provide the basis for chemoselective formation of cyclohexenones. PMID:23662700

Diao, Tianning; Pun, Doris; Stahl, Shannon S

2013-06-01

116

Aerobic Dehydrogenation of Cyclohexanone to Cyclohexenone Catalyzed by Pd(DMSO)2(TFA)2: Evidence for Ligand-Controlled Chemoselectivity  

PubMed Central

The dehydrogenation of cyclohexanones affords cyclohexenones or phenols via removal of one or two equivalents of H2, respectively. We recently reported several PdII catalyst systems that effect aerobic dehydrogenation of cyclohexanones with different product selectivities. Pd(DMSO)2(TFA)2 is unique in its high chemoselectivity for the conversion of cyclohexanones to cyclohexenones, without promoting subsequent dehydrogenation of cyclohexenones to phenols. Kinetic and mechanistic studies of these reactions reveal the key role of the dimethylsulfoxide (DMSO) ligand in controlling this chemoselectivity. DMSO has minimal kinetic influence on the rate of Pd(TFA)2-catalyzed dehydrogenation of cyclohexanone to cyclohexenone, while it strongly inhibits the second dehydrogenation step, conversion of cyclohexenone to phenol. These contrasting kinetic effects of DMSO provide the basis for chemoselective formation cyclohexenones. PMID:23662700

Diao, Tianning; Pun, Doris; Stahl, Shannon S.

2013-01-01

117

Facile and efficient one-pot synthesis of benzimidazoles using lanthanum chloride  

PubMed Central

Background We report the synthesis of benzimidazoles using lanthanum chloride as an efficient catalyst. One-pot synthesis of 2-substituted benzimidazole derivatives from o-phenylenediamine and a variety of aldehydes were developed under mild reaction conditions. Results We have examined the effect of different solvents using the same reaction conditions. The yield of the product varied with the nature of the solvents, and better conversion and easy isolation of products were found with acetonitrile. In a similar manner, the reaction with o-phenylenediamine and 3,4,5-trimethoxybenzaldehyde was carried out without any solvents. The observation shows that the reaction was not brought into completion, even after starting for a period of 9 h, and the reaction mixture showed a number of spots in thin-layer chromatography. Conclusions In conclusion, lanthanum chloride has been employed as a novel and efficient catalyst for the synthesis of benzimidazoles in good yields from o-phenylenediamine and a wide variety of aldehydes. All of the reactions were carried out in the presence of lanthanum chloride (10 mol%) in acetonitrile at room temperature. PMID:23919542

2013-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

119

Efficient synthesis of exo-N-carbamoyl nucleosides: application to the synthesis of phosphoramidate prodrugs.  

PubMed

An efficient protection protocol for the 6-exo-amino group of purine nucleosides with various chloroformates was developed utilizing N-methylimidazole (NMI). The reaction of an exo-N(6)-group of adenosine analogue 1 with alkyl/and aryl chloroformates under optimized conditions provided the N(6)-carbamoyl adenosines (2a-j) in good to excellent yields. The reaction of N(6)-Cbz-protected nucleosides (5a-c) with phenyl phosphoryl chloride (7) using t-BuMgCl followed by catalytic hydrogenation afforded the corresponding phosphoramidate pronucleotides (8a-c) in excellent yield. PMID:22554490

Cho, Jong Hyun; Coats, Steven J; Schinazi, Raymond F

2012-05-18

120

An Efficient Synthesis of Exo-N-carbamoyl Nucleosides: Application to the Synthesis of Phosphoramidate Prodrugs  

PubMed Central

An efficient protection protocol for the 6-exo-amino group of purine nucleosides with various chloroformates was developed utilizing N-methyl imidazole (NMI). The reaction of an exo-N6-group of adenosine analog 1 with alkyl/ and aryl chloroformates under optimized conditions provided the N6-carbamoyl adenosines (2a-j) in good to excellent yields. The reaction of N6-Cbz-protected nucleosides (5a-c) with phenyl phosphoryl chloride (7) using t-BuMgCl followed by catalytic hydrogenation afforded the corresponding phosphoramidate pronucleotides (8a-c) in excellent yield. PMID:22554490

Cho, Jong Hyun; Coats, Steven J.; Schinazi, Raymond F.

2012-01-01

121

Tandem ring-closing metathesis/transfer hydrogenation: practical chemoselective hydrogenation of alkenes.  

PubMed

An operationally simple chemoselective transfer hydrogenation of alkenes using ruthenium metathesis catalysts is presented. Of great practicality, the transfer hydrogenation reagents can be added directly to a metathesis reaction and effect hydrogenation of the product alkene in a single pot at ambient temperature without the need to seal the vessel to prevent hydrogen gas escape. The reduction is applicable to a range of alkenes and can be performed in the presence of aryl halides and benzyl groups, a notable weakness of Pd-catalyzed hydrogenations. Scope and mechanistic considerations are presented. PMID:25140991

Connolly, Timothy; Wang, Zhongyu; Walker, Michael A; McDonald, Ivar M; Peese, Kevin M

2014-09-01

122

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

123

Efficient multiview depth coding optimization based on allowable depth distortion in view synthesis.  

PubMed

Depth video is used as the geometrical information of 3D world scenes in 3D view synthesis. Due to the mismatch between the number of depth levels and disparity levels in the view synthesis, the relationship between depth distortion and rendering position error can be modeled as a many-to-one mapping function, in which different depth distortion values might be projected to the same geometrical distortion in the synthesized virtual view image. Based on this property, we present an allowable depth distortion (ADD) model for 3D depth map coding. Then, an ADD-based rate-distortion model is proposed for mode decision and motion/disparity estimation modules aiming at minimizing view synthesis distortion at a given bit rate constraint. In addition, an ADD-based depth bit reduction algorithm is proposed to further reduce the depth bit rate while maintaining the qualities of the synthesized images. Experimental results in intra depth coding show that the proposed overall algorithm achieves Bjontegaard delta peak signal-to-noise ratio gains of 1.58 and 2.68 dB on average for half and integer-pixel rendering precisions, respectively. In addition, the proposed algorithms are also highly efficient for inter depth coding when evaluated with different metrics. PMID:25216481

Zhang, Yun; Kwong, Sam; Hu, Sudeng; Kuo, Chung-Chieh Jay

2014-11-01

124

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

125

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

PubMed

We present the application of two-photon fluorescence (TPF) imaging to monitor intracellular hydrogen peroxide (H?O?) production in brain cells. For selective imaging of H?O? 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 H?O? and mitochondria peroxy yellow 1 detects mitochondrial H?O?. Two-photon absorption cross sections for these H?O? 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 H?O? and localized H?O? production in mitochondria. Endogenous cytoplasmic H?O? production is detected with TPF imaging in rat astrocytes modified with d-amino acid oxidase. The TPF H?O? imaging demonstrated that these chemoselective probes are powerful tools for the detection of intracellular H?O?. 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

2013-10-01

126

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

SciTech Connect

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

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

2010-02-19

127

A facile and chemoselective conjugate reduction using polymethylhydrosiloxane (PMHS) and catalytic B(C6F5)3.  

PubMed

A highly chemoselective conjugate reduction of electron-deficient Michael acceptors, including alpha,beta-unsaturated ketones, carboxylic esters, nitriles and nitro compounds with PMHS in the presence of catalytic B(C6F5)3 is described. PMID:16633555

Chandrasekhar, Srivari; Chandrashekar, Gudise; Reddy, Marepally Srinivasa; Srihari, Pabbaraja

2006-05-01

128

Carbonyl-inserted organo-hybrids of a Dawson-type phosphovanadotungstate: scope and chemoselective oxidation catalysis.  

PubMed

The Dawson-type polyoxometalate (POM) [P(2)V(3)W(15)O(62)](9-) is a prototype for inclusion of carbonyls of amides, ureas, carbamates, and thiocarbamates into polyoxometallic structures. The carbonyl-inserted POMs catalyze the oxidation of sulfides. Chemoselectivity depends primarily on the proton content of the POM, but it is also influenced by the organic substituent. PMID:22029255

Oble, Julie; Riflade, Benoît; Noël, Amandine; Malacria, Max; Thorimbert, Serge; Hasenknopf, Bernold; Lacôte, Emmanuel

2011-11-18

129

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

130

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

PubMed Central

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

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

2010-01-01

131

Highly enantioselective synthesis of tetrahydrocarbolines via iridium-catalyzed intramolecular Friedel-Crafts type allylic alkylation reactions.  

PubMed

A highly enantioselective synthesis of substituted tetrahydrocarbolines via Ir-catalyzed Friedel-Crafts type intramolecular asymmetric allylic alkylation of 2-indolyl allyl carbonates has been developed. This strategy features excellent chemoselectivity and enantioselectivity, mild reaction conditions, and an easily accessed chiral ligand. PMID:24215126

Xu, Qing-Long; Zhuo, Chun-Xiang; Dai, Li-Xin; You, Shu-Li

2013-12-01

132

Efficient Hybrid Grid Synthesis Method Based on Genetic Algorithm for Power/Ground Network Optimization with Dynamic Signal Consideration  

NASA Astrophysics Data System (ADS)

This paper proposes an efficient design algorithm for power/ground (P/G) network synthesis with dynamic signal consideration, which is mainly caused by Ldi/dt noise and Cdv/dt decoupling capacitance (DECAP) current in the distribution network. To deal with the nonlinear global optimization under synthesis constraints directly, the genetic algorithm (GA) is introduced. The proposed GA-based synthesis method can avoid the linear transformation loss and the restraint condition complexity in current SLP, SQP, ICG, and random-walk methods. In the proposed Hybrid Grid Synthesis algorithm, the dynamic signal is simulated in the gene disturbance process, and Trapezoidal Modified Euler (TME) method is introduced to realize the precise dynamic time step process. We also use a hybrid-SLP method to reduce the genetic execute time and increase the network synthesis efficiency. Experimental results on given power distribution network show the reduction on layout area and execution time compared with current P/G network synthesis methods.

Yang, Yun; Kimura, Shinji

133

Total synthesis of muricadienin, the putative key precursor in the solamin biosynthesis.  

PubMed

The first total synthesis of muricadienin, the unsaturated putative precursor in the biosynthesis of trans- and cis-solamin is described. Key steps in the synthesis are a chemoselective hydroboration, a Z-selective Wittig reaction, and a Fries rearrangement for introducing the terminal ?-substituted butenolide. Thus, muricadienin can be synthesized in 11 steps from commercially available starting materials in 42% overall yield. PMID:25380309

Adrian, Juliane; Stark, Christian B W

2014-11-21

134

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

135

Efficient synthesis of (R)-3-hydroxypentanenitrile in high enantiomeric excess by enzymatic reduction of 3-oxopentanenitrile.  

PubMed

(R)-3-Hydroxypentanenitrile (HPN) is an important intermediate in the synthesis of an immunosuppressive inosine 5?-monophosphate dehydrogenase inhibitor. An efficient enzymatic procedure for the synthesis of (R)-HPN with over 99 % enantiomeric excess using a novel acetoacetyl-CoA reductase (AdKR) from Achromobacter denitrificans was successfully established. Many microorganisms are known to reduce 3-oxopentannitrile (KPN) to (R)-HPN. An enzyme from A. denitrificans partially purified using ion exchange chromatography reduced KPN to (R)-HPN with high enantioselectivity. The AdKR gene was cloned and sequenced and found to comprise 738 bp and encode a polypeptide of 26,399 Da. The deduced amino acid sequence showed a high degree of similarity to those of other putative acetoacetyl-CoA reductases and putative 3-ketoacyl-ACP reductases. The AdKR gene was singly expressed and coexpressed together with a glucose dehydrogenase (GDH) as a coenzyme regenerator in Escherichia coli under the control of the lac promoter. (R)-HPN was synthesized with over 99 % e.e. using a cell-free extract of recombinant E. coli cells coexpressing AdKR and GDH. PMID:24658591

Kawano, Shigeru; Hasegawa, Junzo; Yasohara, Yoshihiko

2014-07-01

136

Efficient Synthesis of Fmoc-Protected Phosphinic Pseudodipeptides: Building Blocks for the Synthesis of Matrix Metalloproteinase Inhibitors  

E-print Network

for the Synthesis of Matrix Metalloproteinase Inhibitors Manishabrata Bhowmick,1 Ravinder R. Sappidi,1 Gregg B at biopolymers@wiley. com INTRODUCTION W e are interested in developing effective matrix metalloproteinase (MMP for the Synthesis of Matrix Metalloproteinase Inhibitors Additional Supporting Information may be found

Lepore, Salvatore D.

137

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

138

An Efficient, Modular Approach for the Synthesis of (+)-Strictifolione and a Related Natural Product  

PubMed Central

An efficient, library amenable, “pot economical” total synthesis of (+)-strictifolione and the related natural product, (6R)-6[(E,4R,6R)-4,6-dihydroxy-10-phenyl-1-decenyl]-5,6-dihydro-2H-2-pyrone are reported. This modular approach takes advantage of two consecutive phosphate tether-mediated, one-pot, sequential protocols, followed by a final cross metathesis to deliver both antifungal natural products in a three-pot process from the respective enantiomeric (R,R)- and (S,S)-trienes with minimal purification. A salient feature of this route is that additional protecting groups are not required as a result of the orthogonal protecting- and leaving-group properties innate to phosphate triesters. PMID:24294936

Jayasinghe, Susanthi; Venukadasula, Phanindra K. M.

2014-01-01

139

Design, synthesis and biological studies of efficient multivalent melanotropin ligands: tools towards melanoma diagnosis and treatment  

PubMed Central

In order to achieve early detection and specific cancer treatment we propose the use of multivalent interactions in which a series of binding events leads to increased affinity and consequently to selectivity. Using melanotropin (MSH) ligands, our aim is to target melanoma cells, which overexpress melanocortin receptors. In this study, we report the design and efficient synthesis of new trivalent ligands bearing MSH ligands. Evaluation of these multimers on a cell model engineered to overexpress melanocortin 4 receptors (MC4R) showed up to a 350-fold increase in binding compared to the monomer, resulting in a trivalent construct with nanomolar affinity starting from a micromolar affinity ligand. Cyclic adenosine monophosphate (cAMP) production was also investigated leading to more insights into the effects of multivalent compounds on transduction mechanisms. PMID:21928837

Brabez, Nabila; Lynch, Ronald M.; Xu, Liping; Gillies, Robert J.; Chassaing, Gerard; Lavielle, Solange; Hruby, Victor J.

2011-01-01

140

Concise and efficient synthesis of 3'-o-tetraphosphates of 2'-deoxyadenosine and 2'-deoxycytidine.  

PubMed

We describe concise and efficient synthesis of biologically very important 3'-O-tetraphosphates namely 2'-deoxyadenosine-3'-O-tetraphosphate (2'-d-3'-A4P) and 2'-deoxycytidine-3'-O-tetra-phosphate (2'-d-3'-C4P). N(6)-benzoyl-5'-O-levulinoyl-2'-deoxyadenosine was converted into N(6)-benzoyl-5'-O-levulinoyl-2'-deoxyadenosine-3'-O-tetraphosphate in 87% yield using a one-pot synthetic methodology. One-step concurrent deprotection of N(6)-benzoyl and 5'-O-levulinoyl groups using concentrated aqueous ammonia resulted 2'-d-3'-A4P in 74% yield. The same synthetic strategy was successfully employed to convert N(4)-benzoyl-5'-O-levulinoyl-2'-deoxycytidine into 2'-d-3'-C4P in 68% yield. PMID:25513862

Kore, Anilkumar R; Yang, Bo; Srinivasan, Balasubramanian; Senthilvelan, Annamalai

2015-01-01

141

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

PubMed Central

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

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

2014-01-01

142

Micelle-template synthesis of nitrogen-doped mesoporous graphene as an efficient metal-free electrocatalyst for hydrogen production.  

PubMed

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

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

2014-01-01

143

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

144

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

145

Contemporaneous dual catalysis: chemoselective cross-coupling of catalytic vanadium-allenoate and ?-allylpalladium intermediates.  

PubMed

This paper presents a detailed investigation of a dual catalytic system that combines a vanadium-catalyzed Meyer-Schuster rearrangement and a palladium-catalyzed allylic alkylation. The implementation of this novel reaction relies on matching the formation rates of vanadium-allenoate and ?-allylpalladium intermediates with their bimolecular coupling rate in order to minimize the undesired protonation or O-alkylation of the catalytically generated intermediates. Chemoselectivity in this dual catalytic process was successfully achieved by adjusting ligand structure and catalyst loading ratios of the vanadium and palladium catalysts. A great range of coupling partners for both the propargyl alcohol and allyl carbonate components are readily accommodated in this new transformation, which in turn provides a novel avenue to a variety of ?-allylated ?,?-unsaturated ketones, esters, and amides in moderate to excellent isolated yields. PMID:21714524

Trost, Barry M; Luan, Xinjun; Miller, Yan

2011-08-17

146

Chemoselective immobilization of proteins by microcontact printing and bio-orthogonal click reactions.  

PubMed

Herein, a combination of microcontact printing of functionalized alkanethiols and site-specific modification of proteins is utilized to chemoselectively immobilize proteins onto gold surfaces, either by oxime- or copper-catalyzed alkyne-azide click chemistry. Two molecules capable of click reactions were synthesized, an aminooxy-functionalized alkanethiol and an azide-functionalized alkanethiol, and self-assembled monolayer (SAM) formation on gold was confirmed by IR spectroscopy. The alkanethiols were then individually patterned onto gold surfaces by microcontact printing. Site-specifically modified proteins-horse heart myoglobin (HHMb) containing an N-terminal ?-oxoamide and a red fluorescent protein (mCherry-CVIA) with a C-terminal alkyne-were immobilized by incubation onto respective stamped functionalized alkanethiol patterns. Pattern formation was confirmed by fluorescence microscopy. PMID:24166802

Tolstyka, Zachary P; Richardson, Wade; Bat, Erhan; Stevens, Caitlin J; Parra, Dayanara P; Dozier, Jonathan K; Distefano, Mark D; Dunn, Bruce; Maynard, Heather D

2013-12-16

147

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr04390h

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

2013-12-01

148

Efficient synthesis of L-lactic acid from glycerol by metabolically engineered Escherichia coli  

PubMed Central

Background Due to its abundance and low-price, glycerol has become an attractive carbon source for the industrial production of value-added fuels and chemicals. This work reports the engineering of E. coli for the efficient conversion of glycerol into L-lactic acid (L-lactate). Results Escherichia coli strains have previously been metabolically engineered for the microaerobic production of D-lactic acid from glycerol in defined media by disrupting genes that minimize the synthesis of succinate, acetate, and ethanol, and also overexpressing the respiratory route of glycerol dissimilation (GlpK/GlpD). Here, further rounds of rationale design were performed on these strains for the homofermentative production of L-lactate, not normally produced in E. coli. Specifically, L-lactate production was enabled by: 1), replacing the native D-lactate specific dehydrogenase with Streptococcus bovis L-lactate dehydrogenase (L-LDH), 2) blocking the methylglyoxal bypass pathways to avoid the synthesis of a racemic mixture of D- and L-lactate and prevent the accumulation of toxic intermediate, methylglyoxal, and 3) the native aerobic L-lactate dehydrogenase was blocked to prevent the undesired utilization of L-lactate. The engineered strain produced 50 g/L of L-lactate from 56 g/L of crude glycerol at a yield 93% of the theoretical maximum and with high optical (99.9%) and chemical (97%) purity. Conclusions This study demonstrates the efficient conversion of glycerol to L-lactate, a microbial process that had not been reported in the literature prior to our work. The engineered biocatalysts produced L-lactate from crude glycerol in defined minimal salts medium at high chemical and optical purity. PMID:23347598

2013-01-01

149

130 Bull. Korean Chem. Soc. 2006, Vol. 27, No. 1 Notes Highly Efficient MCM-48-based Template Synthesis of  

E-print Network

solubility of nanoparticles, however, can impede facile recovery of the catalysts after reaction. Hyeon et al of other metals for efficient catalyses and facile catalyst recovery processes. Nanomaterials with smaller Synthesis of Osmium and Platinum 3-D Nanonetworks Chang Hoon Lee, Kwangyeol Lee,* Sukbok Chang, Joon T. Park

Kim, Bongsoo

150

On Water: A Practical and Efficient Synthesis of Benzoheterocycle Derivatives Catalyzed by Nanocrystalline Copper(II) Oxide  

Microsoft Academic Search

Recyclable CuO nanoparticles provide an efficient, economic, and novel method for the synthesis of quinoxaline, benzoxazine, and benzothiazine. This method provides a wide range of substrate applicability, avoids the use of organic solvents, and gives benzoheterocycles in satisfactory yields.

Sodeh Sadjadi; Rahim Hekmatshoar; Seyed Javad Ahmadi; Morteza Hosseinpour; Mohammad Outokesh

2010-01-01

151

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

EPA Science Inventory

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

152

Highly efficient one-pot three-component synthesis of naphthopyran derivatives in water catalyzed by hydroxyapatite  

EPA Science Inventory

An expeditious and efficient protocol for the synthesis of naphthopyrans has been developed that proceeds via one-pot three-component sequential reaction in water catalyzed by hydroxyapatite or sodium-modified-hydroxyapatite. The title compounds have been obtained in high yield a...

153

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

PubMed Central

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

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

2013-01-01

154

Efficient access to the core of the Strychnos, Aspidosperma and Iboga alkaloids. A short synthesis of norfluorocurarine.  

PubMed

An efficient anionic bicyclization of tryptamine-derived Zincke aldehydes forms the basis for a three-step route to the tetracyclic ABCE core of many Strychnos, Aspidosperma, and Iboga alkaloids. This powerful reaction is showcased in a five-step synthesis of the Strychnos alkaloid norfluorocurarine from tryptamine and pyridine. PMID:19236094

Martin, David B C; Vanderwal, Christopher D

2009-03-18

155

An Efficient One?Pot Synthesis of 3,4?Dihydropyrimidin?2?ones Catalyzed by Methanesulfonic Acid  

Microsoft Academic Search

An efficient synthesis of 3,4?dihydropyrimidin?2?ones (DHPMs) from the aldehydes, ??ketoesters, and urea in ethanol using methanesulfonic acid (CH3SO3H) as the catalyst is described. Compared with the classical Biginelli reaction conditions, this method has the advantage of excellent yields and short reaction time.

2004-01-01

156

The total synthesis of (-)-nitidasin.  

PubMed

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

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

2014-08-01

157

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

158

Novel reductive Friedel-Crafts alkylation of aromatics catalyzed by indium compounds: Chemoselective utilization of carbonyl moieties as alkylating reagents  

Microsoft Academic Search

Reductive Friedel-Crafts alkylation of aromatics with ketones or aldehydes was characteristically catalyzed by indium compounds in preference to general catalysts like AlCl3 and BF3, where hydrosilanes would play an important role both as a hydride donor and as a co-catalyst. Chemoselective utilization of ketone moieties as alkylating reagents took place even in the presence of halogen, ester or ether moieties

Takashi Miyai; Yoshiyuki Onishi; Akio Baba

1999-01-01

159

Chemoselective Chromium(II)-Catalyzed Cross-Coupling Reactions of Dichlorinated Heteroaromatics with Functionalized Aryl Grignard Reagents.  

PubMed

Chromium(II) chloride catalyzes the chemoselective cross-coupling reaction of dichloropyridines with a range of functionalized (hetero)aromatic Grignard reagents at room temperature. Functional groups, such as esters and acetals, are well tolerated in this transformation. Previously challenging substrates, quinolines and isoquinolines, participate in the selective Cr-catalyzed cross-coupling in cyclopentyl methyl ether (CPME) as the solvent. The effective purging of Cr salts is demonstrated by using various solid supports. PMID:25470669

Steib, Andreas K; Kuzmina, Olesya M; Fernandez, Sarah; Malhotra, Sushant; Knochel, Paul

2015-01-26

160

Highly efficient solid phase synthesis of large polypeptides by iterative ligations of  

E-print Network

,b Vincent Aucagne*b and Oleg Melnyk*a Up to now, the advantages of solid phase protein synthesis have been to give a 15 kDa polypeptide. Introduction Modern protein chemical synthesis is made possible for protein total synthesis.9 The ligation of two peptide segments potentially gives access to polypeptides

Paris-Sud XI, Université de

161

Simple and efficient synthesis of 2-[(18)F]fluoroethyl triflate for high yield (18)fluoroethylation.  

PubMed

The [(18)F]fluoroethyl moiety has been widely utilized in the synthesis of (18)F-labelled compounds. The aim of this work was the reliable synthesis of [(18)F]FEtOTf with a novel strategy to increase the reactivity of the commonly used [(18)F]FEB and [(18)F]FEtOTos. [(18)F]FEtOTf and the intermediate [(18)F]FEtOH were synthesized in high RCY (78% and 85%, respectively) and purified by SPE. The high potency of [(18)F]FEtOTf was shown by the efficient alkylation of the deactivated nucleophile aniline under mild conditions, as well as by the synthesis of [(18)F]FEC. PMID:25189703

Peters, Tanja; Vogg, Andreas; Oppel, Iris M; Schmaljohann, Jörn

2014-12-01

162

Development of an efficient procedure for indole ring synthesis from 2-ethynylaniline derivatives catalyzed by CuII salts and its application to natural product synthesis.  

PubMed

The development of efficient methods for the indole synthesis catalyzed by Cu(II) salts and its applications were investigated. Cu(OAc)(2) has been proved to be the best catalyst for the synthesis of various 1-p-tolylsulfonyl or 1-methylsulfonylindoles, which have both electron-withdrawing and electron-donating groups on the aromatic ring and C2 position of indoles. For the primary aniline derivatives, Cu(OCOCF(3))(2) showed good activities, while Cu(OAc)(2) was a good catalyst for the cyclization of secondary anilines. This methodology could be applied to the sequential cyclization reaction for the compounds which have the electrophilic part in the same molecule. By prior treatment with KH, the sequential cyclization was realized to provide the tricyclic ring systems, but it was limited to five- and six-membered rings for the second cyclization. Finally, formal and total synthesis of hippadine with the Cu(II)-promoted indole synthesis as the key step was accomplished. PMID:14961661

Hiroya, Kou; Itoh, Shin; Sakamoto, Takao

2004-02-20

163

An efficient protection of carbonyls and deprotection of acetals using decaborane  

Microsoft Academic Search

Carbonyls were efficiently converted to the corresponding dimethyl acetals at room temperature using trimethyl orthoformate and 1 mol% of decaborane under a nitrogen atmosphere. In turn, acetals were deprotected to the corresponding carbonyls using 1 mol% of decaborane in aqueous THF chemoselectively.

Seung Hwan Lee; Ji Hee Lee; Cheol Min Yoon

2002-01-01

164

Toward a protecting-group-free halogen-metal exchange reaction: practical, chemoselective metalation of functionalized aromatic halides using dianion-type zincate, tBu4ZnLi2.  

PubMed

A versatile preparation method for aromatic zincate compounds through a halogen-zinc exchange reaction using dilithium tetra-tert-butylzincate (tBu4ZnLi2) has been developed. This reagent permits efficient preparation of highly functionalized aromatic zincates, particularly, those with electrophilic functional groups, such as ester, amide, alcohol, and phenol. Halogen-zinc exchange reactions followed by electrophilic trapping (with allyl bromide or benzaldehyde) proved to be a powerful tool for C-C bond formation on functionalized aromatic rings. The functionalized aromatic zincate intermediate was also found to undergo copper- and palladium-catalyzed C-C bond-forming reactions with good yields and high chemoselectivity. PMID:16802798

Uchiyama, Masanobu; Furuyama, Taniyuki; Kobayashi, Minoru; Matsumoto, Yotaro; Tanaka, Kentaro

2006-07-01

165

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

PubMed

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

Avanzini, Federico; Marogna, Riccardo; Bank, Balázs

2012-01-01

166

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

167

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

168

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

PubMed

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

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

2006-04-01

169

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

NASA Astrophysics Data System (ADS)

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

Tang, Wei; Loo, Yueh-Lin

2009-03-01

170

An Efficient 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

171

INTERNATIONAL JOURNAL OF EMBEDDED SYSTEMS, VOL. X, NO. XX, JUNE 2004 1 Energy-Efficient Hardware/Software Co-Synthesis  

E-print Network

INTERNATIONAL JOURNAL OF EMBEDDED SYSTEMS, VOL. X, NO. XX, JUNE 2004 1 Energy-Efficient HardwareC. In order to develop applications on RSoCs for energy efficiency, we propose a three- step design process for application development, (b) a mathematical formulation of the energy-efficient synthesis problem for a class

Prasanna, Viktor K.

172

Efficient synthesis of ?- and ?-carbolines by sequential Pd-catalyzed site-selective C-C and twofold C-N coupling reactions.  

PubMed

Two concise and efficient approaches were developed for the synthesis of ?- and ?-carboline derivatives. The success of the synthesis relies on site-selective Suzuki-Miyaura reactions of 1-chloro-2-bromopyridine or 2,3-dibromopyridine with 2-bromophenylboronic acid and subsequent cyclization with amines which proceeds by twofold Pd-catalyzed C-N coupling reactions. PMID:25464277

Hung, Tran Quang; Dang, Tuan Thanh; Janke, Julia; Villinger, Alexander; Langer, Peter

2015-01-21

173

Multifunctional organoboron compounds for scalable natural product synthesis.  

PubMed

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). PMID:25230659

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

2014-09-18

174

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

175

Efficient sonochemical synthesis of alkyl 4-aryl-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylate derivatives.  

PubMed

A facile, efficient and environment-friendly protocol for the synthesis of 6-chloro-5-formyl-1,4-dihydropyridine derivatives has been developed by the convenient ultrasound-mediated reaction of 2(1H)pyridone derivatives with the Vilsmeier-Haack reagent. This method provides several advantages over current reaction methodologies including a simpler work-up procedure, shorter reaction times and higher yields. PMID:21840238

Ruiz, Enrique; Rodríguez, Hortensia; Coro, Julieta; Niebla, Vladimir; Rodríguez, Alfredo; Martínez-Alvarez, Roberto; de Armas, Hector Novoa; Suárez, Margarita; Martín, Nazario

2012-03-01

176

Efficient synthesis strategies by application of transition metal-catalyzed carbene/nitrene insertions into C-H bonds.  

PubMed

Transition metal-catalyzed insertion of carbenes and nitrenes into C-H bonds has become a powerful tool for the construction of C-C and C-N bonds in the synthesis of complex natural products. In this Highlight, a selection of syntheses are detailed involving the implementation of C-H insertion reactions leading to strategies marked by improved efficiency. PMID:24589531

Egger, Julian; Carreira, Erick M

2014-04-01

177

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

Microsoft Academic Search

In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were\\u000a directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl4·4H2O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show\\u000a that this method could bring excellent yields as high as 96%. THF was

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

2009-01-01

178

Efficient synthesis and in vitro antitubercular activity of 1,2,3-triazoles as inhibitors of Mycobacterium tuberculosis  

Microsoft Academic Search

Efficient and rapid synthesis of 1,2,3-triazole derivatives has been achieved via Huisgen’s 1,3-dipolar cycloaddition between alkyl\\/arylazides and diethyl\\/dimethyl acetylenedicarboxylate in excellent yields under solvent-free conditions. The environmentally friendly solvent-free protocol overcomes the limitations associated with the prevailing time-consuming solution phase protocols and affords the triazoles just in 1–3min. In vitro antitubercular activity of these triazoles was screened against Mycobacterium tuberculosis

Poovan Shanmugavelan; Sangaraiah Nagarajan; Murugan Sathishkumar; Alagusundaram Ponnuswamy; Perumal Yogeeswari; Dharmarajan Sriram

179

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

PubMed Central

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

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

2013-01-01

180

A simple and efficient synthesis of substituted 2,2'-bithiophene and 2,2':5',2?-terthiophene.  

PubMed

A simple and efficient approach is developed for the synthesis of substituted 2,2'-bithiophene- and 2,2':5',2?-terthiophene-5-carboxylic acids and esters which is based on thiophene ring closure in the Fiesselmann reaction. Using this method, derivatives containing a long alkyl chain with or without an end functional group or an aryl substituent can be conveniently prepared. PMID:24624889

Kostyuchenko, Anastasia S; Averkov, Alexey M; Fisyuk, Alexander S

2014-04-01

181

Solvent-Free Green and Efficient One-Pot Synthesis of Dihydropyrano[3,2-c]chromene Derivatives  

PubMed Central

A rapid, clean, and highly efficient method for synthesis of dihydropyrano[3,2-c]chromene derivatives by one-pot, three-component condensation of aromatic aldehydes, malononitrile, and 4-hydroxycoumarin using DABCO as catalyst in solvent-free neat conditions is described. The present method has the advantages of mild reaction conditions, short reaction times, easy isolation of products, and excellent yields. PMID:24282643

Jain, Shubha; Rajguru, Deepika; Keshwal, Balwant S.; Acharya, Aman D.

2013-01-01

182

Sequence and structure-specific elements of HERG mRNA determine channel synthesis and trafficking efficiency  

PubMed Central

Human ether-á-gogo-related gene (HERG) encodes a potassium channel that is highly susceptible to deleterious mutations resulting in susceptibility to fatal cardiac arrhythmias. Most mutations adversely affect HERG channel assembly and trafficking. Why the channel is so vulnerable to missense mutations is not well understood. Since nothing is known of how mRNA structural elements factor in channel processing, we synthesized a codon-modified HERG cDNA (HERG-CM) where the codons were synonymously changed to reduce GC content, secondary structure, and rare codon usage. HERG-CM produced typical IKr-like currents; however, channel synthesis and processing were markedly different. Translation efficiency was reduced for HERG-CM, as determined by heterologous expression, in vitro translation, and polysomal profiling. Trafficking efficiency to the cell surface was greatly enhanced, as assayed by immunofluorescence, subcellular fractionation, and surface labeling. Chimeras of HERG-NT/CM indicated that trafficking efficiency was largely dependent on 5? sequences, while translation efficiency involved multiple areas. These results suggest that HERG translation and trafficking rates are independently governed by noncoding information in various regions of the mRNA molecule. Noncoding information embedded within the mRNA may play a role in the pathogenesis of hereditary arrhythmia syndromes and could provide an avenue for targeted therapeutics.—Sroubek, J., Krishnan, Y., McDonald, T V. Sequence- and structure-specific elements of HERG mRNA determine channel synthesis and trafficking efficiency. PMID:23608144

Sroubek, Jakub; Krishnan, Yamini; McDonald, Thomas V.

2013-01-01

183

Regio- and Chemoselective Covalent Immobilization of Proteins through Unnatural Amino Acids  

PubMed Central

A general approach was developed for the regio- and chemoselective covalent immobilization of soluble proteins on glass surfaces through an unnatural amino acid created by posttranslationally modifying the cysteine residue in a CaaX recognition motif with functional groups suitable for “click” chemistry or a Staudinger ligation. Farnesyl diphosphate analogs bearing ?-azide or ?-alkyne moieties were attached to the cysteine residue in Cys-Val-Ile-Ala motifs at the C-termini of engineered versions of green fluorescent protein (GFP) and glutathione S-transferase (GST) by protein farnesyltransferase. The derivatized proteins were attached to glass slides bearing linkers containing azide (“click” chemistry) or phosphine (Staudinger ligation) groups. “Click” immobilized proteins were detected by fluorescently labeled antibodies and remained attached to the slide through two cycles of stripping under stringent conditions at 80 °C. GFP immobilized by a Staudinger ligation was detected by directly imagining the GFP fluorophore over a period of 6 days. These methods for covalent immobilization of proteins should be generally applicable. CaaX recognition motifs can easily be appended to the C-terminus of a cloned protein by a simple modification of the corresponding gene, and virtually any soluble protein or peptide bearing a CaaX motif is a substrate for protein farnesyltransferase. PMID:16848430

Gauchet, Cécile; Labadie, Guillermo R.; Poulter, C. Dale

2008-01-01

184

A Unique Chemoenzymatic Synthesis of r-Galactosyl Epitope Derivatives Containing Free Amino Groups: Efficient Separation  

E-print Network

A Unique Chemoenzymatic Synthesis of r-Galactosyl Epitope Derivatives Containing Free Amino Groups-(1f3)- -Gal-(1f4)- -Glc-N3 (15). Compounds 2 and 15 are derivatives of natural R-Gal epitopes. Both of the cell surface antigenic determinants (epitopes).2 The chemical synthesis of oligosaccharides containing

Chen, Xi

185

HELP (high efficiency liquid phase) new oligonucleotide synthesis on soluble polymeric support.  

PubMed Central

A simple, rapid and high-yielding method for the synthesis of oligonucleotides by the phosphotriesters approach is described. The use of polyethylene glycol (PEG) as soluble polymeric support preserves some convenient features of the solid-phase synthesis with new interesting advantages. Short oligonucleotides in hundred milligrams scale can be obtained from few grams of functionalized PEG. PMID:2356115

Bonora, G M; Scremin, C L; Colonna, F P; Garbesi, A

1990-01-01

186

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

187

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

188

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

189

African green monkey kidney Vero cells require de novo protein synthesis for efficient herpes simplex virus 1-dependent apoptosis.  

PubMed

During HSV-1 infection, IE gene expression triggers apoptosis, but subsequent synthesis of infected cell proteins blocks apoptotic death from ensuing. This "HSV-1-dependent" apoptosis was identified in HEp-2/HeLa cells infected with wild-type HSV-1 in the presence of an inhibitor of protein synthesis or a virus lacking ICP27 {HSV-1(vBSDelta27)}. Unlike HEp-2/HeLa cells, vBSDelta27-infected Vero cells fail to exhibit dramatic apoptotic morphologies at times prior to 24 hpi. Here, we examined the basis of these different apoptotic responses to HSV-1. We found that infected Vero cells take substantially longer than HEp-2/HeLa cells to display membrane blebbing, chromatin condensation, DNA laddering, and PARP cleavage. Vero, but not HEp-2/HeLa, cells required de novo protein synthesis to exhibit efficient HSV-1-dependent apoptosis, which included changes in mitochondrial membrane potential, and these factors were produced prior to 3 hpi. Vero cells infected with recombinant viruses devoid of the ICP27 and ICP4 proteins alone or both the ICP27 and ICP22 proteins were apoptotic. These results indicate a requirement for cellular or other viral protein synthesis in Vero cells and provide insight into cell type differences in HSV-1-dependent apoptosis. PMID:15892968

Nguyen, Marie L; Kraft, Rachel M; Blaho, John A

2005-06-01

190

Synthesis of conjugated polyenes via sequential condensation of sulfonylphosphonates and aldehydes.  

PubMed

Selective metalation of sulfonylphosphonates results in sufficiently stable carbanions that undergo chemoselective Julia-Kocienski condensation with various aldehydes to provide (E)-allylic phosphonates in good yields and selectivities. The subsequent Horner-Wadsworth-Emmons condensation with aldehydes is used to synthesize various unsymmetrical trans-dienes, trienes, and tetraenes. This methodology is utilized for the concise synthesis of a naturally occurring fluorescent probe for membrane properties, ?-parinaric acid. PMID:22292860

Cichowicz, Nathan R; Nagorny, Pavel

2012-02-17

191

Recent advances in the chemoselective reduction of functional groups mediated by samarium(II) iodide: a single electron transfer approach.  

PubMed

Recently, samarium(II) iodide reductants have emerged as powerful single electron donors for the highly chemoselective reduction of common functional groups. Complete control of the product formation can be achieved on the basis of a judicious choice of a Sm(II) complex/proton donor couple, even in the presence of extremely sensitive functionalities (iodides, aldehydes). In most cases, the reductions are governed by thermodynamic control of the first electron transfer, which opens up new prospects for unprecedented transformations via radical intermediates under mild regio-, chemo- and diastereoselective conditions that are fully orthogonal to hydrogenation or metal-hydride mediated processes. PMID:24013846

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

2013-12-01

192

Protease-catalyzed peptide synthesis using inverse substrates: the influence of reaction conditions on the trypsin acyl transfer efficiency.  

PubMed

Benzyloxycarbonyl-L-alanine p-guanidinophenyl ester behaves as a trypsin "inverse substrate," i.e., a cationic center is included in the leaving group instead of being in the acyl moiety. Using this substrate as an acyl donor, trypsin catalyzes the synthesis of peptide bonds that cannot be split by this enzyme. An optimal acyl transfer efficiency was achieved between pH 8 and 9 at 30 degrees C.The addition of as much as 50% cosolvent was shown to be of minor influence on the acyl transfer efficiency, whereas the reaction velocity decreases by more than one order of magnitude. The efficiency of H-Leu-NH(2) and H-Val-NH(2) in deacylation is almost the same for "inverse" and normal type substrates. PMID:18600704

Schellenberger, V; Jakubke, H D; Zapevalova, N P; Mitin, Y V

1991-06-01

193

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

194

Very efficient template/primer-independent DNA synthesis by thermophilic DNA polymerase in the presence of a thermophilic restriction endonuclease.  

PubMed

We have found that, in the presence of a thermophilic restriction endonuclease, thermophilic DNA polymerase efficiently synthesizes and amplifies DNA in the absence of any added template and primer nucleic acid under isothermal conditions. More than 10 microg of DNA can be synthesized by 1 unit of DNA polymerase in 1 h, and the reaction proceeds until available dNTPs are consumed. We used mostly the Tsp509I restriction endonuclease (recognition sequence: decreasing AATT), the TspRI restriction endonuclease (recognition sequence: NNCA(G/C)TGNN decreasing), and Vent (exo(-)) and Vent DNA polymerase. The synthesized double-stranded DNA has a highly repetitive palindromic sequence, e.g. (AAAAATTTTT)(n) and (ATACACTGTATATACAGTGTAT)(n). In every repeating unit, there are one or two recognition sites for the restriction enzyme. Our data show that the high efficiency of the restriction-endonuclease-DNA-polymerase (RE-pol) DNA synthesis results from an efficient exponential amplification involving digestion-elongation cycles: a longer DNA with numerous recognition sites for the restriction enzyme is digested to short fragments, and the short fragments are used as seeds for elongation to synthesize longer DNA. A possible role of RE-pol DNA synthesis in the evolutionary development of genetic materials is briefly discussed. PMID:15491153

Liang, Xingguo; Jensen, Kari; Frank-Kamenetskii, Maxim D

2004-10-26

195

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

196

Tailor Made Synthesis of T-Shaped and ?-STACKED Dimers in the Gas Phase: Concept for Efficient Drug Design and Material Synthesis  

NASA Astrophysics Data System (ADS)

Non-covalent interactions play a key role in governing the specific functional structures of biomolecules as well as materials. Thus molecular level understanding of these intermolecular interactions can help in efficient drug design and material synthesis. It has been found from X-ray crystallography that pure hydrocarbon solids (i.e. benzene, hexaflurobenzene) have mostly slanted T-shaped (herringbone) packing arrangement whereas mixed solid hydrocarbon crystals (i.e. solid formed from mixtures of benzene and hexafluorobenzene) exhibit preferentially parallel displaced (PD) ?-stacked arrangement. Gas phase spectroscopy of the dimeric complexes of the building blocks of solid pure benzene and mixed benzene-hexafluorobenzene adducts exhibit similar structural motifs observed in the corresponding crystal strcutures. In this talk, I will discuss about the jet-cooled dimeric complexes of indole with hexafluorobenzene and p-xylene in the gas phase using Resonant two photon ionzation and IR-UV double resonance spectroscopy combined with quantum chemistry calculations. In stead of studying benzene...p-xylene and benzene...hexafluorobenzene dimers, we have studied corresponding indole complexes because N-H group is much more sensitive IR probe compared to C-H group. We have observed that indole...hexafluorobenzene dimer has parallel displaced (PD) ?-stacked structure whereas indole...p-xylene has slanted T-shaped structure. We have shown here selective switching of dimeric structure from T-shaped to ?-stacked by changing the substituent from electron donating (-CH3) to electron withdrawing group (fluorine) in one of the complexing partners. Thus, our results demonstrate that efficient engineering of the non-covalent interactions can lead to efficient drug design and material synthesis.

Kumar, Sumit; Das, Aloke

2013-06-01

197

Efficient [Formula: see text]-catalyzed synthesis of novel and diverse 2,3-dihydroquinazolin-4(1[Formula: see text])-ones.  

PubMed

An efficient one-pot synthesis of various 2,3-dihydroquinazolin-[Formula: see text]-one derivatives was accomplished using [Formula: see text]-catalyzed multi-component reactions between isatoic anhydride, ketones, and amines. The method has several significant advantages; mild reaction conditions, easy handling, and efficiency of catalyst. PMID:25403260

Zhu, Xiaoyan; Kang, So Rang; Xia, Likai; Lee, Jihye; Basavegowda, Nagaraj; Lee, Yong Rok

2015-02-01

198

Deep eutectic solvents and glycerol: a simple, environmentally benign and efficient catalyst\\/reaction media for synthesis of N-aryl phthalimide derivatives  

Microsoft Academic Search

Deep eutectic solvents (DES) and glycerol have been successfully employed as efficient catalysts\\/reaction media in the synthesis of N-aryl phthalimide derivatives from phthalic anhydride and primary aromatic amines. The DES prepared from choline chloride and malonic acid proved to be an efficient catalyst whereas glycerol and the DES of choline chloride and urea played a dual role of catalyst and

Hyacintha Rennet Lobo; Balvant Shyam Singh; Ganapati Subray Shankarling

2012-01-01

199

Gold nanoparticles supported on titanium dioxide: an efficient catalyst for highly selective synthesis of benzoxazoles and benzimidazoles.  

PubMed

A highly efficient and selective reaction for the synthesis of 2-substituted benzoxazoles and benzimidazoles catalyzed by Au/TiO2 has been developed via two hydrogen-transfer processes. This reaction has a good tolerance to air and water, a wide substrate scope, and represents a new avenue for practical C-N and C-O bond formation. More importantly, no additional additives, oxidants and reductants are required for the reaction and the catalyst can be recovered and reused readily. PMID:24776805

Tang, Lin; Guo, Xuefeng; Yang, Yu; Zha, Zhenggen; Wang, Zhiyong

2014-06-11

200

Highly enantioselective and efficient synthesis of flavanones including pinostrobin through the rhodium-catalyzed asymmetric 1,4-addition.  

PubMed

An efficient synthesis of bioactive chiral flavanones (1) was achieved through the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to chromone. The reaction in toluene proceeded smoothly at room temperature in the presence of 0.5% Rh catalyst with electron-poor chiral diphosphine MeO-F(12)-BIPHEP. In this reaction, the 1,2-addition to (S)-1 frequently occurred to yield (2S,4R)-2,4-diaryl-4-chromanol as a byproduct, which could be reduced by changing the reaction solvent to CH(2)Cl(2) to deactivate the Rh catalyst (3% required). PMID:21413690

Korenaga, Toshinobu; Hayashi, Keigo; Akaki, Yusuke; Maenishi, Ryota; Sakai, Takashi

2011-04-15

201

Efficient synthesis of glycopeptide-?-thioesters with a high-mannose type oligosaccharide by means of tert-Boc-solid phase peptide synthesis.  

PubMed

High-mannose type oligosaccharides consist of nine mannose and two N-acetylglucosamine residues (Man(9)GlcNAc(2):M9) and play an important role in protein folding processes in the endoplasmic reticulum. A highly efficient preparation method of this asparaginyl-M9-oligosaccharide from hen egg yolk was established by a two-step proteolysis with commercially available proteases and subsequent purification using high performance liquid chromatography (HPLC). To avoid the hydrolysis of the desired M9-oligosaccharide during the proteolysis steps, several commercially available proteases were screened for their contamination with mannosidases. The ?-amino group of the resultant H(2)N-Asn-(M9-oligosaccharide)-OH was protected with 9-fluorenylmethyloxycarbonyl (Fmoc) group for convenient separation by HPLC. The structure of Fmoc-Asn-(M9-oligosaccharide)-OH thus obtained was confirmed by ESI-MS spectrometry and several NMR experiments. Using this Fmoc-Asn-(M9-oligosaccharide)-OH, the synthesis of the M9-glycopeptide-?-thioester was demonstrated by means of tert-Boc-solid phase peptide synthesis. These tert-Boc conditions afforded the M9-glycopeptide-?-thioester in moderate yield. PMID:23149340

Makimura, Yutaka; Kiuchi, Tatsuto; Izumi, Masayuki; Dedola, Simone; Ito, Yukishige; Kajihara, Yasuhiro

2012-12-15

202

An Efficient Convergent Synthesis of 1?,25-Dihydroxy-3-epi-vitamin D2.  

PubMed

The first synthesis of 1?,25-dihydroxy-3-epi-vitamin D2 is described. Key steps of the synthesis entail the construction of the triene unit by a Pd-catalyzed ring closure of an enol-triflate (A-ring fragment) followed by a Suzuki-Miyaura coupling with a boronate (upper fragment), and the installation of the methyl group at C-24 by an SN2'-syn displacement of an allylic carbamate. This article is part of a Special Issue entitled 'SI:17th Vitamin D Workshop'. PMID:25460301

Sigüeiro, Rita; Otero, R; González-Berdullas, Patricia; Maestro, Miguel; Mouriño, Antonio

2014-10-16

203

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

204

Efficient synthesis of oligosaccharyl 1,2-O-orthoesters from n-pentenyl glycosides and application to the pentaarabinofuranoside of the mycobacterial cell surface.  

PubMed

Complex oligosaccharide syntheses employ the use of more than one glycosyl donor and hence, methods for the interconversion of glycosyl donors are highly valuable for the overall synthesis plan. Herein, n-pentenyl glycosides are efficiently converted to glycosyl 1,2-O-orthoesters in the presence of both acid and base sensitive functional groups. The identified protocol was found to be suitable for the synthesis of trisaccharyl and tetrasaccharyl 1,2-O-orthoester as well. Furthermore, an iterative synthesis of pentaarabinofuranoside present on the Mycobacterium tuberculosis cell surface was accomplished using this method. PMID:25360691

Thadke, Shivaji A; Hotha, Srinivas

2014-12-28

205

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

2015-01-01

206

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

PubMed Central

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

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

2014-01-01

207

Recent Advances in Efficient and Selective Synthesis of Di-, Tri-, and Tetrasubstituted  

E-print Network

, No. 11 Published on the Web 09/11/2008 www.pubs.acs.org/acr 10.1021/ar800038e CCC: $40.75 © 2008 to the synthesis of acyclic alkenes, there are close to ten dif- ferent, basic structural types just

Charette, André

208

Chemoselectivity in Chemical Biology: Acyl Transfer Reactions with Sulfur and Selenium  

PubMed Central

CONSPECTUS A critical source of insight into biological function is derived from the chemist’s ability to create new covalent bonds between molecules, whether they are endogenous or exogenous to a biological system. A daunting impediment to selective bond formation, however, is the myriad of reactive functionalities present in biological milieu. The high reactivity of the most abundant molecule in biology—water—makes the challenges all the more difficult. We have met these challenges by exploiting the reactivity of sulfur and selenium in acyl transfer reactions. The reactivity of both sulfur and selenium is high compared to that of their chalcogen congener, oxygen. In this Account, we highlight recent developments in this arena, emphasizing contributions from our laboratory. One focus of our research is furthering the chemistry of native chemical ligation (NCL) and expressed protein ligation (EPL), two related processes that enable the synthesis and semisynthesis of proteins. These techniques exploit the lower pKa of thiols and selenols relative to alcohols. Although a deprotonated hydroxyl group in the side chain of a serine residue is exceedingly rare in a biological context, the pKa value of the thiol in cysteine (8.5) and of the selenol in selenocysteine (5.7) often render these side chains anionic under physiological conditions. NCL and EPL take advantage of the high nucleophilicity of the thiolate as well as its utility as a leaving group, and we have expanded the scope of these methods to include selenocysteine. Although the genetic code limits the components of natural proteins to 20 or so ?-amino acids, NCL and EPL enable the semisynthetic incorporation of a limitless variety of nonnatural modules into proteins. These modules are enabling chemical biologists to interrogate protein structure and function with unprecedented precision. We are also pursuing the further development of the traceless Staudinger ligation, through which a phosphinothioester and azide form an amide. We first reported this chemical ligation method, which leaves no residual atoms in the product, in 2000. Our progress in effecting the reaction in water, without an organic co-solvent, was an important step in the expansion of its utility. Moreover, we have developed the traceless Staudinger reaction as a means for immobilizing proteins on a solid support, providing a general method of fabricating microarrays that display proteins in a uniform orientation. Along with NCL and EPL, the traceless Staudinger ligation has made proteins more readily accessible targets for chemical synthesis and semisynthesis. The underlying acyl transfer reactions with sulfur and selenium provide an efficient means to synthesize, remodel, and immobilize proteins, and they have enabled us to interrogate biological systems. PMID:21639109

McGrath, Nicholas A.; Raines, Ronald T.

2011-01-01

209

Metal-Free Synthesis of ortho-CHO Diaryl Ethers by a Three-Component Sequential Coupling.  

PubMed

A practical, metal-free, and highly chemoselective approach was developed for the synthesis of ortho-CHO diaryl ethers by a three-component sequential coupling of arynes, N,N-dimethylformamide (DMF), and diaryliodonium salts. Diverse functional groups including halo, nitryl, and bulky substituents and heteroaromatics are well tolerated. Mechanistically, isotopic tracer experiments reveal that the diaryliodonium salt serves as an electrophile to trap the transient intermediates generated from the [2 + 2] cyclization of an aryne and DMF. PMID:25473728

Liu, Fangliang; Yang, Huameng; Hu, Xinquan; Jiang, Gaoxi

2014-12-19

210

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

PubMed

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

Candish, Lisa; Lupton, David W

2011-12-01

211

Chemoselective methoxycarbonylation of terminal alkynes catalyzed by Pd(II)-TROPP complexes.  

PubMed

The mono-phosphanes 5-(diphenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP(Ph)) and 5-((2-methoxy)phenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP((2-MeOPh))) have been employed to coordinate PdCl(2), yielding [PdCl(2)(TROPP(Ph))] (1a) and [PdCl(2)(TROPP((2-MeOPh)))] (1b), respectively. The corresponding tosylate (OTs) complexes [Pd(OTs)(2)(TROPP(Ph))] (2a) and [Pd(OTs)(2)(TROPP((2-MeOPh)))] (2b) have been successfully applied in the p-benzoquinone (BQ)-assisted methoxycarbonylation of terminal alkynes to give chemoselectively the corresponding alkynylcarboxylic acid methyl ester with high TOF (up to 980 h(-1)). Unlike 2a/b, the Pd(II)-(tosylate)-diphosphane complexes [Pd(OTs)(H(2)O)(dppp)](OTs) 2c (dppp = 1,3-bis-di(phenylphosphanyl)propane and [Pd(H(2)O)(2)(MeO-dppp)](OTs)(2) 2d (MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane) preferentially catalyzed a double alkyne insertion. The "in situ" spectroscopic observation of the Pd-methoxycarbonyl compound [Pd(COOMe)(TROPP(Ph))](OTs) (3a) in conjunction with the evidence of the fast beta-hydride elimination reaction of TROPP-based Pd-catalysts in the dimerization reaction of ethene are indicative for a strongly electrophilic metal centre. The X-ray crystal structures of 1a x 0.5 C(2)H(4)Cl(2) and of the neutral and cationic Pd-alkyl complexes [Pd(Me)(Cl)(TROPP(Ph)) (7a x 0.5 CH(2)Cl(2)) and [Pd(CH(2)CH(2)COMe)(TROPP(Ph))](PF(6)) (10a x 0.5 C(6)H(6)), respectively, confirm unambiguously the bidentate coordination mode of TROPP-ligands to Pd(II), that persists even in the presence of CO pressure. PMID:20532337

Bettucci, Lorenzo; Bianchini, Claudio; Oberhauser, Werner; Vogt, Matthias; Grützmacher, Hansjörg

2010-07-28

212

Highly efficient automated synthesis of [(11)C]choline for multi dose utilization.  

PubMed

[(11)C]Choline has been under investigation as a PET ligand for imaging tumor tissue, especially prostate cancer. An improved, automated synthesis of the tracer now was established. [(11)C] Choline was produced by labeling 2-(dimethylamino)-ethanol (DMAE) with [(11)C]CH(3)I in a Tefzel tube at room temperature without solvent. The product was purified using a cation exchange cartridge. Reaction conditions were optimized with respect to synthesis time and amount of DMAE, resulting in radiochemical yields higher than 80% using 60 microl of DMAE in 20 min, radiochemical purity was >99% and residual DMAE was below 10 ppm. After (11)C-production of 1h at 50 microA [(11)C]choline activities of 30.0+/-5.6 GBq (n = 29) were obtained in sterile solution ready for intravenous administration. PMID:15110347

Reischl, G; Bieg, C; Schmiedl, O; Solbach, C; Machulla, H-J

2004-06-01

213

Efficient Synthesis and Evaluation of Quorum Sensing Modulators Using Small Molecule Macroarrays  

PubMed Central

A method for the synthesis of small molecule macroarrays of N-acylated L-homoserine lactones (AHLs) is reported. A focused library of AHLs was constructed, and the macroarray platform was found to be compatible with both solution and agar-overlay assays using quorum-sensing (QS) reporter strains. Several QS antagonists were discovered and serve to showcase the macroarray as a straightforward technique for QS research. PMID:19743816

Praneenararat, Thanit; Geske, Grant D.; Blackwell, Helen E.

2011-01-01

214

An efficient synthesis of (+/-)-grandisol featuring 1,5-enyne metathesis.  

PubMed

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

2010-01-01

215

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

216

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

217

Three-component coupling reactions of silylglyoxylates, alkynes, and aldehydes: a chemoselective one-step glycolate aldol construction.  

PubMed

A single-pot three-component coupling reaction of silylglyoxylates (1), terminal alkynes, and aldehydes in the presence of ZnI2 and Et3N is presented. The products of the reaction, densely functionalized silyl-protected glycolate aldols (2), can be converted to the corresponding acetonides (3) in a one-pot deprotection/ketalization sequence. A variety of terminal alkynes and aldehydes can be successfully employed to give a range of highly functionalized, fully protected 1,2-diols in good yields and moderate diastereoselectivities. Mechanistic experiments suggest that the zinc acetylide reacts with the silylgyloxylate (1) in a chemoselective manner. Using an unoptimized (+)-N-methylephedrine and Zn(OTf)2 system, silyl-deprotected adduct 2 was formed in 64% ee and 89:11 dr. PMID:15853312

Nicewicz, David A; Johnson, Jeffrey S

2005-05-01

218

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

219

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

SciTech Connect

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

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

1999-06-01

220

Highly efficient methyl ketone synthesis with photoactivated acetone and olefins assisted by Mg(II)-exchanged zeolite Y.  

PubMed

We previously found that photoirradiation of an acetone/water mixture containing olefins affords the corresponding methyl ketones highly efficiently and selectively via a water-assisted C-C coupling between the acetonyl radical and olefins (Org. Lett. 2008, 10, 3117-3120). The reaction proceeds at room temperature without any additives and has a potential to be a powerful method for methyl ketone synthesis. Here we report that an addition of Mg(2+)-exchanged zeolite Y (MgY) to the above photoreaction system accelerates the methyl ketone formation, while maintaining high selectivity. Ab initio molecular orbital calculation reveals that the accelerated methyl ketone formation is due to the electrostatic interaction between Mg(2+) and excited-state acetone. This leads to a charge polarization of the carbonyl moiety of excited-state acetone and accelerates the hydrogen abstraction from ground-state acetone (acetonyl radical formation). This promotes efficient addition of the acetonyl radical to olefins, resulting in methyl ketone formation enhancement. Adsorption experiments reveal that accumulation of olefins inside the zeolite pore also affects efficient radical addition to olefins. The present process successfully produces various methyl ketones with very high yield, and the MgY recovered can be reused for further reaction without loss of activity. PMID:20143861

Tsukamoto, Daijiro; Shiraishi, Yasuhiro; Hirai, Takayuki

2010-03-01

221

Efficient transcription of the Epstein-Barr virus immediate-early BZLF1 and BRLF1 genes requires protein synthesis.  

PubMed Central

The Epstein-Barr virus BRLF1 and BZLF1 genes appear to be the first viral genes transcribed upon induction of the Epstein-Barr virus lytic cycle. Both gene products activate transcription of other viral genes, thereby initiating the lytic cascade. Among the viral antigens expressed upon induction of the lytic cycle, the product of the BZLF1 gene is unique in its ability to disrupt viral latency; thus, expression of this gene is both necessary and sufficient for triggering the viral lytic cascade. Moreover, transcription initiation from both the BRLF1 and BZLF1 promoters can be activated by the BZLF1 gene product. The latter results suggest a two-step model for induction of the viral lytic cycle in which the initial signal leads to low-level transcription of the BZLF1 gene, followed by upregulation of transcription by the BZLF1 gene product. In this report we demonstrate that efficient transcription from the BRLF1 and BZLF1 promoters after anti-immunoglobulin induction of the lytic cycle, in a synchronous induction system, is dependent on de novo protein synthesis. These data support the two-step induction model in which synthesis of BZLF1 protein is required to activate expression of the BRLF1 and BZLF1 genes. Images PMID:1658397

Flemington, E K; Goldfeld, A E; Speck, S H

1991-01-01

222

Synthesis route to supported gold nanoparticle layered double hydroxides as efficient catalysts in the electrooxidation of methanol.  

PubMed

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells. PMID:23025480

Ballarin, Barbara; Mignani, Adriana; Scavetta, Erika; Giorgetti, Marco; Tonelli, Domenica; Boanini, Elisa; Mousty, Christine; Prevot, Vanessa

2012-10-23

223

An efficient synthesis of nanocrystalline MFI zeolite using different silica sources: A green approach  

SciTech Connect

Nanocrystalline MFI zeolite was synthesized with a very broad range of silica to alumina ratios using an autoclave for periods of 7 h at 473 K under autogeneous pressure without seeding gel, promoter, organic solvent or sulfuric acid. The procedure has been successfully employed for the synthesis of MFI samples using fumed silica, colloidal silica, aerosil and tetraethylorthosilicate as silica sources. The synthesized samples were characterized by different techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy. Their average crystallite size ranges from about 26 to 55 nm and they exhibit high crystallinity.

Kalita, Banani [Department of Chemistry, Gauhati University, Guwahati 781014, Assam (India); Talukdar, Anup K. [Department of Chemistry, Gauhati University, Guwahati 781014, Assam (India)], E-mail: anup_t@sify.com

2009-02-04

224

An efficient and expeditious synthesis of di- and monosubstituted 2-aminoimidazoles.  

PubMed

A microwave-assisted protocol was developed for the construction of di- and monosubstituted 2-aminoimidazoles. The two-step reaction involves the synthesis of N-(1H-imidazol-2-yl)acetamides from readily available alpha-haloketones and N-acetylguanidine, followed by deacetylation. Significant rate enhancement was observed for both steps of the protocol, and the overall reaction time was shortened to 20 min compared to 48 h of the conventional procedures. A representative set of di- and monosubstituted 2-aminoimidazoles was prepared using commercially available parallel reactors. PMID:18159933

Soh, Chai Hoon; Chui, Wai Keung; Lam, Yulin

2008-01-01

225

A novel and efficient samarium iodide-mediated synthesis of neoflavonoids (4-arycloumarins)  

SciTech Connect

Bioactive 4-arylcoumarins (4-aryl-2H-1-benzopyran-2-ones) have been recently isolated from the plants belonging to the families like Leguminosae, Guttiferae, and Compositae, some of which are still used as the traditional folk medicine. Despite many methods reported so far, there appears to be of limited success or of no success in some cases (II{sub b-g}) and, therefore, a simpler and more reliable one remains to be highly desired. Thus, a new and sterling protocol is now presented for the synthesis of neoflavonoids, which involves the intramolecular Reformatsky-type reaction via a one electron transfer process with samarium diiodide as a key step.

Nagasawa, Kazuo; Ryohke, Hirosi; Ohnishi, Makoto; Ito, Keiichi [Hokkaido College of Pharmacy, Otaru (Japan)

1995-12-31

226

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

227

Efficient and stereocontrolled synthesis of 1,2,4-trioxolanes useful for ferrous iron-dependent drug delivery.  

PubMed

Ferrous iron-promoted reduction of a hindered peroxide bond underlies the antimalarial action of the 1,2,4-trioxane artemisinin and the 1,2,4-trioxolane arterolane. In appropriately designed systems, a 1,2,4-trioxolane ring can serve as a trigger to realize ferrous iron-dependent and parasite-selective drug delivery, both in vitro and in vivo. A stereocontrolled, expeditious (three steps), and efficient (67-71% overall yield) synthesis of 1,2,4-trioxolanes possessing the requisite 3? substitution pattern that enables ferrous iron-dependent drug delivery is reported. The key synthetic step involves a diastereoselective Griesbaum co-ozonolysis reaction to afford primarily products with a trans relationship between the 3? substituent and the peroxide bridge, as confirmed by X-ray structural analysis of a 3?-substituted 4-nitrobenzoate analogue. PMID:25331549

Fontaine, Shaun D; DiPasquale, Antonio G; Renslo, Adam R

2014-11-01

228

Organocatalyzed solvent free an efficient novel synthesis of 2,4,5-trisubstituted imidazoles for ?-glucosidase inhibition to treat diabetes.  

PubMed

A new and efficient solvent free synthesis of 2,4,5-trisubstituted imidazoles (3a-3j) was achieved by N-acetyl glycine (NAG) catalyzed three components condensation of aldehydes, benzil and ammonium acetate. Our synthetic methodology accommodated a range of various substituted alkyl and aryl aldehydes. Evaluation of ?-glucosidase inhibitory activity of these imidazole derivatives revealed that most of them presented good ?-glucosidase inhibition at low micro-molar concentrations. Among the synthesized compounds, compound 3c, bearing the ortho-hydroxy phenyl substituent at position 2 displayed the highest inhibitory activity with an IC50 value 74.32±0.59?M. In silico molecular docking for all compounds and computational studies of the most active compound 3c were also performed. PMID:25462626

Yar, Muhammad; Bajda, Marek; Shahzad, Sohail; Ullah, Nisar; Gilani, Mazhar Amjad; Ashraf, Muhammad; Rauf, Abdul; Shaukat, Ayesha

2015-02-01

229

Towards the assembly of heparin and heparan sulfate oligosaccharide libraries: efficient synthesis of uronic acid and disaccharide building blocks.  

PubMed

The monosaccharide moieties found in heparin (HP) and heparan sulfate (HS), glucosamine and two kinds of uronic acids, glucuronic and iduronic acids, were efficiently synthesized by use of glucosamine hydrochloride and glucurono-6,3-lactone as starting compounds. In the synthesis of the disaccharide building block, the key issues of preparation of uronic acids (glucuronic acid and iduronic acid moieties) were achieved in 12 steps and 15 steps, respectively, without cumbersome C-6 oxidation. The resulting monosaccharide moieties were utilized to the syntheses of HP/HS disaccharide building blocks possessing glucosamine-glucuronic acid (GlcN-GlcA) or iduronic acid (GlcN-IdoA) sequences. The disaccharide building blocks were also suitable for further modification such as glycosylation, selective deprotection, and sulfation. PMID:20473366

Saito, Akihiro; Wakao, Masahiro; Deguchi, Hiroshi; Mawatari, Aya; Sobel, Michael; Suda, Yasuo

2010-05-29

230

Cross-metathesis reactions as an efficient tool in the synthesis of fluorinated cyclic beta-amino acids.  

PubMed

The synthesis of enantiomerically pure, cyclic, gamma,gamma-difluorinated beta-amino acids with various ring sizes has been carried out with a cross-metathesis (CM) reaction being one of the key steps, followed by a Dieckmann-type condensation to bring about the cyclization. Subsequent catalytic hydrogenation under microwave irradiation with (-)-8-phenylmenthol as a chiral auxiliary led to the successful chemo- and diastereoselective chemical reduction of the resulting cyclic beta-enamino esters. The efficiency and scope of the CM reaction with different types of fluorinated imidoyl chlorides and unsaturated esters has also been studied in order to determine the optimal reaction conditions with regard to selectivity and reactivity. PMID:19348493

Fustero, Santos; Sánchez-Roselló, María; Aceña, José Luis; Fernández, Begoña; Asensio, Amparo; Sanz-Cervera, Juan F; del Pozo, Carlos

2009-05-01

231

Facile and efficient synthesis of quinoline-4-carboxylic acids under microwave irradiation  

Microsoft Academic Search

A facile and efficient method for the preparation of 2-non-substituted quinoline-4-carboxylic acids is described via the Pfitzinger reaction of isatins with sodium pyruvate following consequent decarboxylation under microwave irradiation.

Hui Zhu; Ri Fang Yang; Liu Hong Yun; Jin Li

2010-01-01

232

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

233

Efficient pyridinylmethyl functionalization: synthesis of 10, 10-Bis[(2-fluoro-4-pyridinyl)methyl]-9(10H)-anthracenone (DMP 543), an acetylcholine release enhancing agent.  

PubMed

2-Fluoro-4-methylpyridine (3) is efficiently functionalized by chlorination, hydrolysis and methanesulfonylation into the novel alkylating agent 7. This mesylate is used for the bisalkylation of anthrone under carefully defined conditions to prepare the cognition enhancer drug candidate 1. This process proceeds in up to 37% overall yield and is adaptable for large scale synthesis. PMID:11073571

Pesti, J A; Huhn, G F; Yin, J; Xing, Y; Fortunak, J M; Earl, R A

2000-11-17

234

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

235

A highly efficient asymmetric synthesis of quaternary stereocenter-containing indolizidine and quinolizidine alkaloids using aldehydes, nitroalkenes, and unactivated cyclic ketimines.  

PubMed

A highly efficient approach for the construction of indolizidines and quinolizidines bearing a bridged quaternary stereocenter has been established in a one-pot fashion using aldehydes, nitroalkenes, and cyclic ketimines with excellent enantioselectivities and in high yields. Moreover, this method could be applied to the synthesis of indolizidines in the gram scale. PMID:25379636

Tan, Yu; Chen, Yong-Jian; Lin, Hua; Luan, Han-Lin; Sun, Xing-Wen; Yang, Xiao-Di; Lin, Guo-Qiang

2014-12-28

236

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

Microsoft Academic Search

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

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

2004-01-01

237

A Facile and Efficient Synthesis of 2,2?Bis(3?\\/2??indolyl)ethylamines and Three Bisindolic Natural Products  

Microsoft Academic Search

A simple and efficient synthesis of bis(indolyl)ethylamines and three bisindolic natural products, viz. hallucinogenic 6, genotoxic 7 and the alkanoic acid 8 has been developed by the reaction of indoles with appropriate carbonyl compounds on montmorillonite K10 clay.

Manas Chakrabarty; Nandita Ghosh; Ramkrishna Basak; Yoshihiro Harigaya

2004-01-01

238

A simple, efficient and green procedure for the synthesis of bis-indolyl methanes in 1,1,1,3,3,3-hexafluoro-2-propanol  

Microsoft Academic Search

A simple, inexpensive, environmentally friendly and efficient route for the synthesis of bis-indolyl methanes derivatives by the reaction of indole or N-methyl indole with aldehydes using hexafluoroisopropanol as a solvent is described. The solvent (HFIP) can be readily separated from reaction products and recovered in excellent purity for direct reuse.

Samad Khaksar; Saeed Mohammadzadeh Talesh

239

KF/Clinoptilolite: an efficient promoter for the synthesis of thioethers.  

PubMed

Potassium fluoride impregnated on natural zeolite as a new solid base system effectively catalyzes the coupling of thiophenols with electron-deficient fluoro-, chloro- and bromo-arenes in DMSO. This versatile and efficient solid base has been demonstrated to afford the corresponding desired products in good to excellent yields. This procedure provides a convenient, efficient and practical method for the preparation of diaryl thioethers. PMID:23360209

Salmanpour, Sadegh; Khalilzadeh, Mohammad A; Hosseini, Abolfazl

2013-06-01

240

Selective synthesis of ?,?-dideuterio alcohols by the reduction of carboxylic acids using SmI2 and D2O as deuterium source under SET conditions.  

PubMed

The first general method for the chemoselective synthesis of ?,?-dideuterio alcohols directly from feedstock carboxylic acids under single electron transfer conditions using SmI2 is reported. This reaction proceeds after the activation of Sm(II) with a Lewis base, results in excellent levels of deuterium incorporation across a wide range of substrates, and represents an attractive alternative to processes mediated by pyrophoric alkali metal deuterides. PMID:25247236

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

2014-10-01

241

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

242

Automated synthesis of reliable and efficient systems through game theory: a case study  

E-print Network

Reactive computer systems bear inherent complexity due to continuous interactions with their environment. While this environment often proves to be uncontrollable, we still want to ensure that critical computer systems will not fail, no matter what they face. Examples are legion: railway traffic, power plants, plane navigation systems, etc. Formal verification of a system may ensure that it satisfies a given specification, but only applies to an already existing model of a system. In this work, we address the problem of synthesis: starting from a specification of the desired behavior, we show how to build a suitable system controller that will enforce this specification. In particular, we discuss recent developments of that approach for systems that must ensure Boolean behaviors (e.g., reachability, liveness) along with quantitative requirements over their execution (e.g., never drop out of fuel, ensure a suitable mean response time). We notably illustrate a powerful, practically useable algorithm for the aut...

Randour, Mickael

2012-01-01

243

Gene cloning and molecular characterization of the Talaromyces thermophilus lipase catalyzed efficient hydrolysis and synthesis of esters.  

PubMed

A genomic bank from Talaromyces thermophilus fungus was constructed and screened using a previously isolated fragment lipase gene as probe. From several clones isolated, the nucleotide sequence of the lipase gene (TTL gene) was completed and sequenced. The TTL coding gene consists of an open reading frame (ORF) of 1083bp encoding a protein of 269 Aa with an estimated molecular mass of 30kDa. The TTL belongs to the same gene family as Thermomyces lanuginosus lipase (TLL, Lipolase®), a well known lipase with multiple applications. The promoter sequence of the TTL gene showed the conservation of known consensus sequences PacC, CreA, Hap2-3-4 and the existence of a particular sequence like the binding sites of Oleate Response Element (ORE) and Fatty acids Responsis Element (FARE) which are similar to that already found to be specific of lipolytic genes in Candida and Fusarium, respectively. Northern blot analysis showed that the TTL expression was much higher on wheat bran than on olive oil as sole carbon source. Compared to the Lipolase®, this enzyme was found to be more efficient for the hydrolysis and the synthesis of esters; and its synthetic efficiency even reached 91.6% from Waste Cooking Oil triglycerides. PMID:22178764

Romdhane, Ines Belhaj-Ben; Frikha, Fakher; Maalej-Achouri, Inès; Gargouri, Ali; Belghith, Hafedh

2012-02-15

244

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

SciTech Connect

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

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

2014-05-21

245

Efficient synthesis of trisaccharide saponins and their tumor cell killing effects through oncotic necrosis  

Microsoft Academic Search

To investigate the relationship of cytotoxicity and saponins with varied aglycones, based on the structure of indioside E 1, a natural derived anti-tumor active ingredient from Chinese medicinal plant Solanum indicum L., five novel saponins 2–6 bearing the same trisaccharide moiety together with 1 were efficiently synthesized via a transglycosylation strategy. MTT assay revealed the killing effects to tumor cells

Jian Gao; Xia Li; Guofeng Gu; Bin Sun; Min Cui; Mei Ji; Hong-Xiang Lou

2011-01-01

246

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

E-print Network

in either FPGA or ASIC represents a trade-off between programmability and design efficiency. In this work implementations can achieve about 60X power reduction on average and run 3.5X faster over corresponding FPGA, coprocessors, A/D and D/A converters, and memory. Given the specifications of an application, the coprocessor

Bhunia, Swarup

247

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

E-print Network

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. Li-ion batteries, functioning as a key component of energy-storage, have been heralded

Cao, Guozhong

248

Efficient utilization of crude glycerol as fermentation substrate in the synthesis of poly(3-hydroxybutyrate) biopolymers  

Technology Transfer Automated Retrieval System (TEKTRAN)

One refined and 2 crude glycerol samples were utilized to produce poly(3-hydroxybutyrate) (PHB) by Pseudomonas oleovorans NRRL B-14682. Fermentation conditions were determined to efficiently utilize glycerol while maintaining PHB yields. A batch culture protocol including 1% glycerol and an aerati...

249

Efficient and convenient synthesis of pyrrolo[1,2-a]quinazoline derivatives with the aid of tin(II) chloride.  

PubMed

An efficient, convenient, one-pot synthesis of 2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazolin-5(1H)-one and 2,3,3a,4-tetrahydropyrrolo[1,2-a]quinazoline-1,5-dione was accomplished in good yields via the novel reductive cyclization of 2-nitrobenzamides with haloketones or keto acids mediated by SnCl(2).2H(2)O system. A variety of substrates can participate in the process with good yields, making this methodology suitable for library synthesis in drug discovery efforts. PMID:20545357

Wang, Manman; Dou, Guolan; Shi, Daqing

2010-07-12

250

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

251

Modified B-spline interpolators and filters: synthesis and efficient implementation  

Microsoft Academic Search

Interpolation techniques are widely used in many applications of signal processing. This paper is devoted to synthesizing and efficiently implementing a class of generalized spline-interpolators. A new parametric class of generalized B-splines is introduced. It contains as special cases B-splines and alternative B-splines. In the most general case, the proposed spline functions can be represented as a linear combination of

Karen Egiazarian; Tapio Saramaki; Hegine Chugurian; J. Astola

1996-01-01

252

An efficient synthesis of 2-benzoxepines from Morita-Baylis-Hillman adducts using heterogeneous recyclable catalysts.  

PubMed

2-Benzoxepines have efficiently been synthesized from Morita-Baylis-Hillman adducts, alkyl 3-aryl-3-hydroxy-2-methylenepropanoates by treatment with HCHO catalyzed by silica supported perchloric acid (HClO4.SiO2) or Amberlyst-15 in CH2Cl2 under reflux for a short period of time (1.5-2.5 h). The catalyst can be recovered and recycled. The antibacterial properties of the new 2-benzoxepines were studied but no activity was found. PMID:16508203

Das, Biswanath; Majhi, Anjoy; Banerjee, Joydeep; Chowdhury, Nikhil; Holla, Harish; Harakishore, Kankipati; Murty, Upadhayula Suryanarayana

2006-03-01

253

Efficient Synthesis of a 72-kDa Mitochondrial Polypeptide Using the Yeast Ty Expression System  

Microsoft Academic Search

Using the Ty system from yeast we report the efficient expression of a heterologous eukaryotic gene encoding a 72 kDa mitochondrial polypeptide. The pFM2IIBglII expression vector was initially modified for this purpose by inserting the factor Xaprotease cleavage site. TheTyAgene, which encodes the structural component of the yeast virus-like particles (VLPs), and the eukaryoticyst1 gene, encoding a 72 kDa mitochondrial

Stefanie Pöggeler; Christian Schwerk; Ute Kämper; Ulrich Kück

1996-01-01

254

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

PubMed

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

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

2015-02-01

255

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

PubMed

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

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

2015-05-01

256

Polyvinyl alcohol: an efficient fuel for synthesis of superparamagnetic LSMO nanoparticles for biomedical application.  

PubMed

La(0.7)Sr(0.3)MnO(3) (LSMO) nanoparticles have been prepared using glycine and polyvinyl alcohol (PVA) as fuels. Their crystal structure, particle morphology and compositions are characterized using X-ray diffraction, transmission electron microscopy, field-emission electron microscopy and energy dispersive analysis of X-ray. They show a pseudo-cubic perovskite structure. The spherical particle sizes of 30 and 20 nm have been obtained from samples prepared by glycine and PVA respectively. The field cooled (FC) and zero field cooled (ZFC) magnetizations have been recorded from 5 to 375 K at 500 Oe and superparamagnetic blocking temperatures (T(B)) of 75 and 30 K are obtained from samples prepared by glycine and PVA respectively. Particle size distribution is observed from dynamic light scattering measurements. Dispersion stability of the particles in water is studied by measuring the Zeta potential with varying the pH of the medium from 1 to 12. Under induction heating experiments, a hyperthermia temperature (42-43 °C) is achieved by both the samples (3-6 mg mL(-1)) at magnetic fields of 167-335 Oe and at a frequency of 267 kHz. The bio-compatibility of the LSMO nanoparticles is studied on the L929 and HeLa cell lines by MTT assay for up to 48 h. The present work reveals the importance of synthesis technique and fuel choice on structural, morphological, magnetic, hyperthermia and biocompatible properties of LSMO and predicts the suitability for biomedical applications. PMID:22277953

Thorat, N D; Shinde, K P; Pawar, S H; Barick, K C; Betty, C A; Ningthoujam, R S

2012-03-14

257

Efficient synthesis of sulfonic, phosphoric, and phosphinic esters employing alkylating polymer-bound reagents.  

PubMed

The efficient esterification of various sulfonic acids and sulfonates using polymer-bound triazenes based on the triazene T2 linker is described. Esterification of enantiopure alpha-substituted sodium sulfonates was performed in the presence of an alkylating resin without racemization. Racemization is a serious drawback in the esterification route via sulfonyl chlorides because of intermediate sulfene formation. To demonstrate the versatility of this protocol, phosphoric and phosphinic acids have been converted into the corresponding esters as well. All products were obtained in good yield and excellent purities without any further purification steps. PMID:12625703

Vignola, Nicola; Dahmen, Stefan; Enders, Dieter; Bräse, Stefan

2003-01-01

258

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

PubMed

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

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

2014-01-01

259

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

PubMed

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

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

2014-11-01

260

Efficient synthesis of kinsenoside and goodyeroside a by a chemo-enzymatic approach.  

PubMed

Kinsenoside (1) and goodyeroside A (2), two naturally occurring stereoisomers with diverse biological activities, have been synthesized efficiently by a chemo-enzymatic approach with a total yield of 12.7%. The aglycones, (R)- and (S)-3-hydroxy-?-butyrolactone, were prepared from D- and L-malic acid by a four-step chemical approach with a yield of 75%, respectively. These butyrolactones were then successfully glycosidated using ?-D-glucosidase as a catalyst in a homogeneous organic-water system. Under the optimized enzymatic conditions, the yields of kinsenoside and goodyeroside A in the enzymatic steps both reached 16.8%. PMID:25340300

Zhang, Yang; Xia, Yihong; Lai, Yongji; Tang, Fang; Luo, Zengwei; Xue, Yongbo; Yao, Guangmin; Zhang, Yonghui; Zhang, Jinwen

2014-01-01

261

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

PubMed Central

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

2011-01-01

262

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

263

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

PubMed

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

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

2011-01-01

264

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.

265

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

266

An Efficient Synthesis of ?-Hydroxy-?,?-unsaturated Aldehydic Esters of 2-Lysophosphatidylcholine  

PubMed Central

The diverse biological activities of ?-hydroxyalkenal phospholipids and their involvement in disease are the subject of intense study. Phospholipid aldehydes, such as the 4-hydroxy-7-oxohept-5-enoic acid ester of 2-lyso-phosphatidylcholine (HOHA-PC), the 5-hydroxy-8-oxo-6-octenoic acid ester of 2-lyso-PC (HOOA-PC), and the 9-hydroxy-12-oxododec-10-enoic acid ester of 2-lyso-PC (HODA-PC), are generated by oxidative cleavage of polyunsaturated fatty acyl phospholipids. To facilitate investigations of their chemistry and biology, we now report efficient total syntheses of HOOA, HODA, and HOHA phospholipids. Because the target ?-hydroxyalkenals readily decompose through oxidation of the aldehyde group to a carboxylic acid or through cyclization to furans, these syntheses generate the sensitive functional array of the target phospholipids under mild conditions from acetal derivatives that are suitable for long-term storage. PMID:21123073

Choi, Jaewoo; Laird, James M.; Salomon, Robert G.

2010-01-01

267

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

268

One-pot synthesis of dihydropyrimidones using silica-supported heteropoly acid as an efficient and reusable catalyst: Improved protocol conditions for the Biginelli reaction  

Microsoft Academic Search

An efficient synthesis of 3,4-dihydropyrimidinones or thiones (DHPMs) is described, using silica-supported heteropoly acid H3PW12O40\\/SiO2 (PW\\/SiO2) for the first time as the catalyst from an aldehyde, ?-keto ester and urea or thiourea in acetonitrile. Compared to the classical Biginelli reaction conditions, this method consistently has the advantage of excellent yields, mild reaction conditions, ease of workup, survival of different functional

Ezzat Rafiee; Fomaida Shahbazi

2006-01-01

269

An efficient Biginelli one-pot synthesis of new benzoxazole-substituted dihydropyrimidinones and thiones catalysed by trifluoro acetic acid under solvent-free conditions  

Microsoft Academic Search

An efficient synthesis of benzoxazole-substituted 3,4-dihydropyrimidinones (DHPMs) using trifluoro acetic acid as the catalyst for the first time from an aldehyde, ?-keto ester and benzoxazole-substituted urea\\/thiourea under solvent-free conditions is described. Compared to the classical Biginelli reaction conditions, this new method consistently has the advantage of excellent yields (80–91%) and short reaction time (40–130min) at reflux temperature.

D. Shobha; M. Adharvana Chari; K. H. Ahn

2009-01-01

270

One-pot synthesis of 2,4,5-trisubstituted imidazoles using [BPy]H2PO4, an efficient and recyclable catalyst.  

PubMed

[BPy]H(2)PO(4) was easily prepared and used as an efficient and recyclable catalyst for the one-pot synthesis of 2,4,5-trisubstituted imidazoles under solvent-free conditions in good to excellent yields. Solvent-free conditions, simple experimental and workup procedures, and the use of a nontoxic, recyclable catalyst of an environmentally benign nature are remarkable features of the procedure. PMID:23302106

Zhang, Yuliang; Zhou, Zhongqiang

2013-01-01

271

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

Microsoft Academic Search

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

Kairat Madin; Tatsuya Sawasaki; Tomio Ogasawara; Yaeta Endo

2000-01-01

272

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

273

Efficient synthesis of 2-aminoindane-2-carboxylic acid via dialkylation of nucleophilic glycine equivalent.  

PubMed

An efficient, easy to scale-up method for preparing 2-aminoindane-2-carboxylic acid via two-step alkylation of a Ni(II)-complex of glycine Schiff base with 2-[N-(alpha-picolyl)amino]benzophenone (PAAP) (2b) with o-dibromoxylylene (3) is reported. The first step, monoalkylation of 2b with 3, conducted under phase-transfer conditions, gave the corresponding complex 6 in excellent chemical yield (97.2%). Without any purification the intermediate 6 was cyclized under homogeneous conditions (DMF, NaO-t-Bu) to give the product 7 in high chemical yield (93.1%). Decomposition of prepared 7 afforded the target amino acid 2-aminoindane-2-carboxylic acid (1) in 97.9% yield, along with recovery of ligand 8, which was converted back to the starting glycine complex 2b. Operationally convenient experimental procedures, mild reaction conditions, as well as high chemical and volume yields render the method practical for preparing amino acid 1 and its analogues. PMID:12790614

Ellis, Trevor K; Hochla, Veronica M; Soloshonok, Vadim A

2003-06-13

274

Efficient three-component one-pot synthesis of fully substituted pyridin-2(1H)-ones via tandem Knoevenagel condensation-ring-opening of cyclopropane-intramolecular cyclization.  

PubMed

An efficient synthesis of fully substituted pyridin-2(1H)-ones was developed via three-component one-pot reactions of readily available 1-acetyl-1-carbamoyl cyclopropanes, malononitrile and cyclic secondary amines. PMID:19521633

Liang, Fushun; Cheng, Xin; Liu, Jing; Liu, Qun

2009-06-28

275

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

ERIC Educational Resources Information Center

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

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

2004-01-01

276

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

PubMed Central

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

Bouillon, Isabelle; Krch?ák, Viktor

2008-01-01

277

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

PubMed Central

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

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

2013-01-01

278

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

PubMed

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

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

2014-11-01

279

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

PubMed Central

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

Pan, Guojun; Williams, Robert M.

2014-01-01

280

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

281

Chemoselective Immobilization of Peptides on Abiotic and Cell Surfaces at Controlled Densities  

PubMed Central

We report herein a new and enabling approach for decorating both living and abiotic surfaces with the extracellular matrix IKVAV peptide in a site-specific manner using strain promoted azide-alkyne cycloaddition. A cyclooctyne derivatized IKVAV peptide was synthesized and immobilized on the surface of pancreatic islets through strain-promoted azide-alkyne cycloaddition with cell surface azides generated by electrostatic adsorption of cytocompatible poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) copolymer bearing azido groups (PP-N3). Both “one-pot” and sequential addition of PP-N3 and a cyclooctyne derivatized IKVAV peptide conjugate enabled efficient modification of pancreatic islet surface in less than 60 min. The ability to bind peptides at controlled surface densities was demonstrated in a quantitative manner using microarrays. Additionally, the technique is remarkably rapid and highly efficient, opening new avenues for molecular engineering of cellular interfaces and protein and peptide microarrays. PMID:20450194

Krishnamurthy, Venkata R.; Wilson, John T.; Cui, Wanxing; Song, XueZheng; Yi, Lasanajak; Cummings, Richard D.; Chaikof, Elliot L.

2010-01-01

282

Stimuli-responsive hydrogel hollow capsules by material efficient and robust cross-linking-precipitation synthesis revisited.  

PubMed

Monodisperse stimuli-responsive hydrogel capsules were synthesized in the 100-nm-diameter to 10-?m-diameter range from poly(4-vinylpyridine) (P4VP) and poly(ethyleneimine) (PEI) through a simple, efficient two-step cross-linking-precipitation template method under conditions of a good solvent. In this method, the core-shell particles were obtained by the deposition (heterocoagulation mechanism) of the cross-linked P4VP, PEI, or their mixtures on the surfaces of the template colloidal silica particles in nitromethane (for PEI) or a nitromethane-acetone mixture (for P4VP and P4VP-PEI mixtures) in the presence of cross-linker 1,4-diiodobutane. The cross-linked polymeric shell swollen in a good solvent stabilized the core-shell colloids. This mechanism provided the conditions for the synthesis of core-shell colloids in a submicrometer range of dimensions with an easily adjusted shell thickness (wall of the capsules) ranging from a few to hundreds of nanometers. The chemical composition of the shell was tuned by varying the ratio of co-cross-linked shell-forming polymers (P4VP and PEI). In the second step, the hollow capsules were obtained by etching the silica core in HF solutions. In this step, the colloidal stability of the hollow capsules was provided by ionized P4VP and PEI cross-linked shells. The hollow capsules demonstrate that the pH- and ionic-strength-triggered swelling and shrinking result in size-selective uptake and release properties. Cross-linked via quaternized functional groups, P4VP capsules undergo swelling and shrinking transitions at a physiologically relevant pH of around 6. The 200-nm-diameter hollow capsule with 25-nm-thick walls demonstrated a factor of 2 greater capacity to accommodate cargo molecules than the core-shell particles of the same dimensions because of an internal compartment and a combination of radial and a circumferential swelling modes in the capsules. PMID:22053870

Motornov, Mikhail; Royter, Halyna; Lupitskyy, Robert; Roiter, Yuri; Minko, Sergiy

2011-12-20

283

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

284

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

285

Efficient one-step synthesis of pyrrolo[3,4-c]quinoline-1,3-dione derivatives by organocatalytic cascade reactions of isatins and ?-ketoamides.  

PubMed

We describe an efficient one-step synthesis of pyrrolo[3,4-c]quinolinedione derivatives using ethylenediamine diacetate (EDDA)-catalyzed cascade reactions of isatins and ?-ketoamides. It is the first direct conversion of isatins to pyrrolo[3,4-c]quinolinedione derivatives via C-N bond cleavage and isatin ring expansion. Furthermore, this reaction provides a one-step synthetic route for the production of biologically interesting complex molecules that are generally prepared using multi-step reactions. PMID:23824233

Xia, Likai; Lee, Yong Rok

2013-08-28

286

An efficient solvent-free synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromenes using silica-immobilized L-proline.  

PubMed

An efficient synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates was carried out under solvent-free conditions in an oven or microwave oven via the Knoevenagel condensation of salicylaldehydes with ethyl trifluoroacetoacetate followed by intramolecular cyclization in the presence of silica-immobilized L-proline. The structures of the title compounds were characterized by IR, ¹H-NMR, ¹³C-NMR, HRMS and X-ray single crystal diffraction. The improved method described herein is economical, easily-operated and environmentally friendly. Furthermore, the catalyst can be recovered conveniently and reused without obvious loss of activity. PMID:24077175

Xu, Cuilian; Yang, Guoyu; Wang, Caixia; Fan, Sufang; Xie, Lixia; Gao, Ya

2013-01-01

287

Microwave-assisted synthesis: A fast and efficient route to produce LaMO{sub 3} (M = Al, Cr, Mn, Fe, Co) perovskite materials  

SciTech Connect

Research highlights: {yields} Lanthanum perovskites can be prepared by microwave irradiation in a domestic set-up. {yields} Microwave-assisted synthesis yields well crystallized and pure materials, sometimes nanosized. {yields} Rietveld analysis has been performed to refine the structures. {yields} Magnetic and electric measurements are similar to those previously reported. {yields} Microwave-assisted synthesis is a fast and efficient method for the synthesis of lanthanum perovskites. -- Abstract: A series of lanthanum perovskites, LaMO{sub 3} (M = Al, Cr, Mn, Fe, Co), having important technological applications, have been successfully prepared by a very fast, inexpensive, reproducible, environment-friendly method: the microwave irradiation of the corresponding mixtures of nitrates. Worth to note, the microwave source is a domestic microwave oven. In some cases the reaction takes place in a single step, while sometimes further annealings are necessary. For doped materials the method has to be combined with others such as sol-gel. Usually, nanopowders are produced which yield high density pellets after sintering. Rietveld analysis, oxygen stoichiometry, microstructure and magnetic measurements are presented.

Prado-Gonjal, J.; Arevalo-Lopez, A.M. [Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid (Spain)] [Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Moran, E., E-mail: emoran@quim.ucm.es [Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid (Spain)

2011-02-15

288

Efficient biocatalyst for large-scale synthesis of cephalosporins, obtained by combining immobilization and site-directed mutagenesis of penicillin acylase.  

PubMed

We describe the rational design of a new efficient biocatalyst and the development of a sustainable green process for the synthesis of cephalosporins bearing a NH? group on the acyl side chain. The new biocatalyst was developed starting from the WT penicillin acylase (PA) from Escherichia coli by combining enzyme mutagenesis, in position ?146 and ?24 (?F24A/?F146Y), and immobilization on an appropriate modified industrial support, glyoxyl Eupergit C250L. The obtained derivative was used in the kinetically controlled synthesis of cephalexin, cefprozil and cefaclor and compared to the WT-PA and an already described mutant, PA-?F24A, with improved properties. The new biocatalyst posses a very high ratio between the rates of the synthesis and two undesired hydrolyses (acylating ester and the amidic product). In particular, a very low amidase activity was observed with PA-?F24A/?F146Y and, consequently, the hydrolysis of the produced antibiotic was avoided during the process. Taking advantage of this property, higher conversions in the synthesis of cephalexin (99% versus 76%), cefaclor (99% versus 65%) and cefprozil (99% versus 60%) were obtained compared to the WT enzyme. Furthermore, the new mutant also show a higher synthetic activity compared to PA-?F24A immobilized on the same support, allowing the maximum yields to be achieved in very short reaction times. The production of cephalexin with the immobilized ?F24A/?F146Y acylase has been developed on a pre-industrial scale (30 l). After 20 cycles, the average yield was 93%. The biocatalyst showed good stability properties and no significant decrease in performance. PMID:22228258

Cecchini, Davide A; Pavesi, Roberto; Sanna, Sara; Daly, Simona; Xaiz, Roberto; Pregnolato, Massimo; Terreni, Marco

2012-09-01

289

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

PubMed Central

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

2014-01-01

290

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

PubMed

Peptide synthesis on cellulose using SPOT technology allows the parallel synthesis of large numbers of addressable peptides in small amounts. In addition, the cost per peptide is less than 1% of peptides synthesized conventionally on resin. The SPOT method follows standard fluorenyl-methoxy-carbonyl chemistry on conventional cellulose sheets, and can utilize more than 600 different building blocks. The procedure involves three phases: preparation of the cellulose membrane, stepwise coupling of the amino acids and cleavage of the side-chain protection groups. If necessary, peptides can be cleaved from the membrane for assays performed using soluble peptides. These features make this method an excellent tool for screening large numbers of peptides for many different purposes. Potential applications range from simple binding assays, to more sophisticated enzyme assays and studies with living microbes or cells. The time required to complete the protocol depends on the number and length of the peptides. For example, 400 9-mer peptides can be synthesized within 6 days. PMID:17545971

Hilpert, Kai; Winkler, Dirk F H; Hancock, Robert E W

2007-01-01

291

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

PubMed Central

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

Chaudhury, Aritra; Maity, Sajal K

2014-01-01

292

Efficient disruption of a polyketide synthase gene ( pks1 ) required for melanin synthesis through Agrobacterium -mediated transformation of Glarea lozoyensis  

Microsoft Academic Search

Glarea lozoyensis produces pneumocandin B0, a potent inhibitor of fungal glucan synthesis. This industrially important filamentous fungus is slow-growing, is very darkly pigmented, and has not been easy to manipulate genetically. Using a PCR strategy to survey the G. lozoyensis genome for polyketide synthase (PKS) genes, we have identified pks1, a gene that consists of five exons interrupted by four

A. Zhang; P. Lu; A. M. Dahl-Roshak; P. S. Paress; S. Kennedy; J. S. Tkacz; Z. An

2003-01-01

293

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

294

A fast and efficient one-pot microwave assisted synthesis of variously di-substituted 1,2,4-oxadiazoles.  

PubMed

A one-pot two-step microwave assisted synthesis of variously disubstituted 1,2,4-oxadiazoles from carboxylic acids and amidoximes is reported. This methodology is characterized by short reaction times, is versatile, robust and high-yielding and allows for the preparation of heterocycles with a stereocenter with 100% enantiomeric purity. PMID:21938295

Porcheddu, Andrea; Cadoni, Roberta; De Luca, Lidia

2011-11-01

295

A highly tunable stereoselective dimerization of methyl ketone: efficient synthesis of E- and Z-1,4-enediones.  

PubMed

A new method for the tunable synthesis of 1,4-enedione directly from aromatic methyl ketone is described. This tandem reaction enables the construction of symmetric and unsymmetric 1,4-enediones with complete E-selectivity. Moreover, the resulting E-1,4-enedione could be transformed into a Z-isomer by irradiation with 23 W of white light. PMID:23590409

Xu, Kun; Fang, Yang; Yan, Zicong; Zha, Zhenggen; Wang, Zhiyong

2013-05-01

296

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

PubMed Central

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

2013-01-01

297

CTAB-assisted synthesis of monoclinic BiVO4 photocatalyst and its highly efficient degradation of organic dye under visible-light irradiation.  

PubMed

A highly efficient monoclinic BiVO(4) photocatalyst (C-BVO) was synthesized by an aqueous method with the assistance of cetyltrimethylammonium bromide (CTAB). The structure, morphology and photophysical properties of the C-BVO were characterized by XRD, FE-SEM and diffuse reflectance spectroscopy, respectively. The photocatalytic efficiencies were evaluated by the degradation of rhodamine B (RhB) under visible-light irradiation, revealing that the degradation rate over the C-BVO was much higher than that over the reference BiVO(4) prepared by aqueous method and over the one prepared by solid-state reaction. The efficiency of de-ethylation and that of the cleavage of conjugated chromophore structure were investigated, respectively. The chemical oxygen demand (COD) values of the RhB were measured after the photocatalytic degradation over the C-BVO and demonstrated a 53% decrease in COD. The effects of CTAB on the synthesis of C-BVO were investigated, which revealed that CTAB not only changed the reaction process via the formation of BiOBr as an intermediate, but also facilitated the transition from BiOBr to BiVO(4). Comparison experiments were carried out and showed that the existence of impurity level makes significant contribution to the high photocatalytic efficiency of the C-BVO. PMID:19733435

Yin, Wenzong; Wang, Wenzhong; Zhou, Lin; Sun, Songmei; Zhang, Ling

2010-01-15

298

Lewis base mediated efficient synthesis and solvation-like host-guest chemistry of covalent organic framework-1.  

PubMed

N-Lewis base mediated room temperature synthesis of covalent organic frameworks (COFs) starting from a solution of building blocks instead of partially soluble building blocks was developed. This protocol shifts COF synthetic chemistry from sealed tubes to open beakers. Non-conventional inclusion compounds of COF-1 were obtained by vapor phase infiltration of ferrocene and azobenzene, and solvation like effects were established. PMID:23208512

Kalidindi, Suresh Babu; Wiktor, Christian; Ramakrishnan, Ayyappan; Weßing, Jana; Schneemann, Andreas; Van Tendeloo, Gustaaf; Fischer, Roland A

2013-01-18

299

Aminative umpolung of aldehydes to ?-amino anion equivalents for Pd-catalyzed allylation: an efficient synthesis of homoallylic amines.  

PubMed

An attractive strategy for generation of ?-amino anions from aldehydes with applications in synthesis of homoallylic amines is described. Aromatic aldehydes can be converted to ?-amino anion equivalents via amination with 2,2-diphenylglycine and subsequent decarboxylation. The in situ generated ?-imino anions are highly reactive for Pd-catalyzed allylation, forming the corresponding homoallylic amines in high yields with excellent regioselectivity. PMID:24437506

Ding, Lei; Chen, Jing; Hu, Yifan; Xu, Juan; Gong, Xing; Xu, Dongfang; Zhao, Baoguo; Li, Hexing

2014-02-01

300

Highly Chemoselective Reduction of Amides (Primary, Secondary, Tertiary) to Alcohols using SmI2/Amine/H2O under Mild Conditions  

PubMed Central

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 nX ? ?*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

2014-01-01

301

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

302

Replication of M13 single-stranded viral DNA bearing single site-specific adducts by escherichia coli cell extracts: differential efficiency of translesion DNA synthesis for SOS-dependent and SOS-independent lesions.  

PubMed

In order to characterize mutagenic translesion DNA synthesis in UVM-induced Escherichia coli, we have developed a high-resolution DNA replication system based on E. coli cell extracts and M13 genomic DNA templates bearing mutagenic lesions. The assay is based on the conversion of M13 viral single-stranded DNA (ssDNA) bearing a single site-specific DNA lesion to the double-stranded replicative form (RF) DNA, and permits one to quantitatively measure the efficiency of translesion synthesis. Our data indicate that DNA replication is most strongly inhibited by an abasic site, a classic SOS-dependent noninstructive lesion. In contrast, the efficiency of translesion synthesis across SOS-independent lesions such as O6-methylguanine and DNA uracil is around 90%, very close to the values obtained for control DNA templates. The efficiency of translesion synthesis across 3,N4-ethenocytosine and 1, N6-ethenoadenine is around 20%, a value that is similar to the in vivo efficiency deduced from the effect of the lesions on the survival of transfected M13 ssDNA. Neither DNA polymerase I nor polymerase II appears to be required for the observed translesion DNA synthesis because essentially similar results are obtained with extracts from polA- or polB-defective cells. The close parallels in the efficiency of translesion DNA synthesis in vitro and in vivo for the five site-specific lesions included in this study suggest that the assay may be suitable for modeling mutagenesis in an accessible in vitro environment. PMID:9235993

Wang, G; Rahman, M S; Humayun, M Z

1997-08-01

303

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

304

Amphiphilic core-shell nanocarriers based on hyperbranched poly(ester amide)-star-PCL: synthesis, characterization, and potential as efficient phase transfer agent.  

PubMed

Amphiphilic biodegradable star-shaped polymer was conveniently prepared by the Sn(Oct)2-catalyzed ring opening polymerization of epsilon-caprolactone (CL) with hyperbranched poly(ester amide) (PEA) as a macroinitiator. Various monomer/initiator ratios were employed to vary the length of the PCL arms. (1)H NMR and FTIR characterizations showed the successful synthesis of star polymer with high initiation efficiency. SEC analysis using triple detectors, RI, light scattering, and viscosity confirmed the controlled manner of polymerization and the star architecture. Because of the hydrophilic PEA core and hydrophobic PCL shell, the obtained star polymers displayed inverted unimolecular micellar structure confirmed by dynamic light scattering. Three water soluble dyes, congo red, methyl orange, and bromophenol blue, were used to investigate the host-guest behavior of the micelles. It proved that the core-shell unimolecular reverse micelles were able to transport polar dyes from water to the organic phase with a high efficiency of up to 22.6 dyes per polymer, indicating a great potential of the micelles as drug carriers. The influence of arm length and core size on the load efficiency of the nanocarrier was also evaluated. PMID:18698818

Lin, Ying; Liu, Xiaohui; Dong, Zhongmin; Li, Baixiang; Chen, Xuesi; Li, Yue-Sheng

2008-10-01

305

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

2014-12-01

306

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

307

Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction.  

PubMed

Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu-M, M[double bond, length as m-dash]Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process. PMID:25628256

Kumar Barman, Barun; Kar Nanda, Karuna

2015-02-17

308

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

PubMed Central

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

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

2014-01-01

309

An innovative approach for efficient and reusable catalization for synthesis of α, β-unsaturated compounds using polymer - NPs composites as catalyst  

NASA Astrophysics Data System (ADS)

Catalyst plays an important role in many of synthesis and chemical reactions, like ?,?-unsaturated products cannot be synthesized without presence of suitable catalyst, but for efficient catalization of reactions catalyst must have high surface area as well as they must be easily removed after termination of reaction without leaving an impurity in final product. To achieve both of these conditions an innovative approach is used. Here Polycarbonate (PC)-ZnO NPs composites membranes have been successfully fabricated by solution casting technique in where ZnO NPs (45nm) acts as a catalyst with increased surface area, while as these catalyst are embedded in PC matrix that can be easily removed after termination of reaction. Membranes were characterized via different techniques like SEM, FTIR etc. Activity of this nanocomposite based catalytic system for the stereoselective synthesis of ?, ?-unsaturated compounds is tested and found increased in yield of compounds with increase in concentration of ZnO nanoparticle content upto 5%. Above this at high ZnO loadings (9%) slight agglomeration of NPs occurred which hindered the catalytic effect of Nano composite.

Pimpliskar, Prashant; Bagra, Bhawna; Kumar, Gautam Aashish; Khandelwal, Saurabh; Agrawal, Narendra Kumar

2014-04-01

310

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

PubMed Central

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

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

2012-01-01

311

Efficient synthesis of novel glutamate homologues and investigation of their affinity and selectivity profile at ionotropic glutamate receptors.  

PubMed

A convenient synthesis of four new enantiomerically pure acidic amino acids is reported and their affinity at ionotropic glutamate receptors was determined. The new compounds are higher homologues of glutamic acid in which the molecular complexity has been increased by introducing an aromatic/heteroaromatic ring, that is a phenyl or a thiophene ring, that could give additional electronic interactions with the receptors. The results of the present investigation indicate that the insertion of an aromatic/heteroaromatic ring into the amino acid skeleton of glutamate higher homologues is well tolerated and this modification could be exploited to generate a new class of NMDA antagonists. PMID:24630559

Pinto, Andrea; Tamborini, Lucia; Mastronardi, Federica; Ettari, Roberta; Romano, Diego; Nielsen, Birgitte; De Micheli, Carlo; Conti, Paola

2014-04-15

312

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

313

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

314

[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

315

Phosphomolybdic and phosphotungstic acids as efficient catalysts for the synthesis of bridged 1,2,4,5-tetraoxanes from ?-diketones and hydrogen peroxide.  

PubMed

Phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) efficiently catalyze the addition of H2O2 to ?-diketones to form bridged 1,2,4,5-tetraoxanes. These reactions are not accompanied by the formation of monocyclic peroxides containing hydroxy and hydroperoxide groups or polymeric peroxides. The use of these catalysts made it possible to obtain bridged tetraoxanes from easily oxidizable benzoylacetone derivatives and ?-unsubstituted ?-diketones. The syntheses are scaled up to ten grams. The resulting peroxides can be easily isolated from the reaction mixture by column chromatography. The yield of tetraoxanes depends on the structure of ?-diketone and varies from 12 to 83%. NMR monitoring of two bridged 1,2,4,5-tetraoxanes synthesis was carried out. PMID:23446630

Terent'ev, Alexander O; Yaremenko, Ivan A; Vil', Vera A; Moiseev, Igor K; Kon'kov, Sergey A; Dembitsky, Valery M; Levitsky, Dmitri O; Nikishin, Gennady I

2013-04-28

316

One pot efficient diversity oriented synthesis of polyfunctional styryl thiazolopyrimidines and their bio-evaluation as antimalarial and anti-HIV agents.  

PubMed

An efficient one pot synthesis of a series of pluripotent (E)-1-(3-methyl-5-aryl-7-styryl-5H-thiazolo[3,2-a]pyrimidin-6-yl)-3-arylprop-2-en-1-ones is reported. It involves reaction of 5-acetyl-6-methyl-4-aryl-dihydropyrimidine-2-thiones, propargyl bromide and aromatic aldehydes in presence of ethanolic KOH. The newly synthesized compounds were evaluated for antimalarial activity against Plasmodium falciparum and as HIV-RT inhibitors. Most of the compound displayed potent antimalarial activity with IC(50)<2 ?g/mL. Compounds 6, 11 and 20 showed better activity against P. falciparum K1 strains in comparison to standard drug chloroquine. Compounds 6, 11, and 16 exhibited 73.44, 66.92, and 70.81% HIV-RT inhibition at 100 ?g/mL. PMID:22871486

Fatima, Seerat; Sharma, Anindra; Saxena, Reshu; Tripathi, Rajkamal; Shukla, Sanjeev K; Pandey, Swaroop Kumar; Tripathi, Renu; Tripathi, Rama P

2012-09-01

317

Highly efficient methyl ketone synthesis by water-assisted C-C coupling between olefins and photoactivated acetone.  

PubMed

Photoirradiation of an acetone/water mixture containing olefins affords the corresponding methyl ketones highly efficiently via a water-assisted C-C coupling between acetonyl radical and olefins. PMID:18572950

Shiraishi, Yasuhiro; Tsukamoto, Daijiro; Hirai, Takayuki

2008-07-17

318

Efficient and Scalable Synthesis of 4-Carboxy-Pennsylvania Green Methyl Ester: A Hydrophobic Building Block for Fluorescent Molecular Probes  

PubMed Central

Fluorinated fluorophores are valuable tools for studies of biological systems. However, amine-reactive single-isomer derivatives of these compounds are often very expensive. To provide an inexpensive alternative, we report a practical synthesis of 4-carboxy-Pennsylvania Green methyl ester. Derivatives of this hydrophobic fluorinated fluorophore, a hybrid of the dyes Oregon Green and Tokyo Green, are often cell permeable, enabling labeling of intracellular targets and components. Moreover, the low pKa of Pennsylvania Green (4.8) confers bright fluorescence in acidic cellular compartments such as endosomes, enhancing its utility for chemical biology investigations. To improve access to the key intermediate 2,7-difluoro-3,6-dihydroxyxanthen-9-one, we subjected bis-(2,4,5-trifluorophenyl)methanone to iterative nucleophilic aromatic substitution by hydroxide on scales of > 40 g. This intermediate was used to prepare over 15 grams of pure 4-carboxy-Pennsylvania Green methyl ester in 28% overall yield without requiring chromatography. This compound can be converted into the amine reactive N-hydroxysuccinimidyl ester in essentially quantitative yield for the synthesis of a wide variety of fluorescent molecular probes. PMID:24914246

Woydziak, Zachary R.; Fu, Liqiang

2013-01-01

319

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

PubMed Central

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

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

2014-01-01

320

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

321

Melamine trisulfonic acid: A new, efficient and recyclable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1 H)-ones\\/thiones in the absence of solvent  

Microsoft Academic Search

Melamine trisulfonic acid (MTSA) can be used as an efficient and recyclable catalyst for the promotion of the synthesis of 3,4-dihydropyrimidin-2(1H)-ones\\/thiones (DHPMs) in the absence of solvent. All reactions were performed at 80°C in good to high yields.

Farhad Shirini; Mohammad Ali Zolfigol; Jalal Albadi

2011-01-01

322

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

Microsoft Academic Search

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

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

2010-01-01

323

Fe(ClO 4 ) 3 · 6H 2 O: a mild and efficient catalyst for one-pot three component synthesis of ? -acetamido carbonyl compounds under solvent-free conditions  

Microsoft Academic Search

A one-pot multi-component reaction for the synthesis of ?-acetamido carbonyl compounds is reported. The reaction uses a variety of aldehydes, acetophenone derivatives or methyl acetoacetate,\\u000a acetonitrile, and acetyl chloride in the presence of ferric perchlorate, a mild, efficient and inexpensive catalyst effective\\u000a under solvent free conditions.

Majid M. Heravi; Farahnaz K. Behbahani; Mansoureh Daraie; Hossein A. Oskooie

2009-01-01

324

Novel pyridinium-based tags: synthesis and characterization for highly efficient analysis of thiol-containing peptides by mass spectrometry.  

PubMed

In this study, a novel type of pyridinium-based tags, 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-4-methylpyridinium bromide (IMP) and 1-[3-[(2-iodo-1-oxoethyl)amino]propyl]-4-propylpyridinium bromide (IPP), were designed, synthesized, and applied to the derivatization of thiol-containing peptides. With model peptides as the sample, the labeling efficiency and the stability of the peptide derivatives were investigated. The results indicate that nearly 100% derivatization yield was achieved with the developed tags and the peptide derivatives were stable at room temperature for at least one week. Furthermore, improved ionization efficiency and increased charge states were achieved via both matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MS) and electrospray ionization (ESI) MS, of which IPP exhibited the more obvious improvement of ionization efficiency. Further analysis of tryptic digests of bovine serum albumin (BSA) and ?-transferrin, showed that increased identification efficiency of the thiol-containing peptides was achieved by combination with IMP or IPP derivatization. For example, the identification efficiency of the thiol-containing peptides of ?-transferrin increased more than 42% upon combination with the IMP or IPP derivatives. We anticipate the novel tags are promising for highly efficient thiol-containing peptide identification in proteome research, especially for low concentrations. PMID:25422830

Qiao, Xiaoqiang; Yang, Yanjun; Liu, Shijia; Chen, Shiheng; Wang, Xin; Li, Guangyue; Yan, Hongyuan; Yang, Xun

2014-12-15

325

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

PubMed

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

Licht, S

2011-12-15

326

Combining the petasis 3-component reaction with multiple modes of cyclization: a build/couple/pair strategy for the synthesis of densely functionalized small molecules.  

PubMed

A build/couple/pair strategy for the synthesis of complex and densely functionalized small molecules is presented. The strategy relies on synthetically tractable building blocks (build), that is, diversely substituted hydrazides, ?-hydroxy aldehydes, and boronic acids, which undergo Petasis 3-component reactions (couple) to afford densely functionalized anti-hydrazido alcohols. The resulting scaffolds can subsequently be converted via chemoselective cyclization reactions (pair), including intramolecular Diels-Alder or Ru-alkylidene catalyzed ring-closing metathesis, into sets of structurally diverse heterocycles in good yields in only 3-4 steps. PMID:25469710

Flagstad, Thomas; Hansen, Mette R; Le Quement, Sebastian T; Givskov, Michael; Nielsen, Thomas E

2015-01-12

327

Stereoselective Synthesis of Highly Functionalized Indanes and Dibenzocycloheptadienes through Complex Radical Cascade Reactions.  

PubMed

Two highly stereoselective radical-mediated syntheses of densely functionalized indanes and dibenzocycloheptadienes from ortho-vinyl- and ortho-vinylaryl-substituted N-(arylsulfonyl)-acrylamides, respectively, are presented here. The chemoselective addition of in?situ generated radicals (X(.) ) onto the styrene moieties triggers an unprecedented reaction cascade, resulting in the formation of one new C?X bond and two new C?C bonds, a formal 1,4-aryl migration, and the extrusion of SO2 to generate an amidyl radical intermediate. This intermediate, upon H?abstraction, leads to the observed 5- and 7-membered ring carbocyclic products, respectively, in a highly efficient manner. PMID:25597296

Kong, Wangqing; Fuentes, Noelia; García-Domínguez, Andres; Merino, Estíbaliz; Nevado, Cristina

2015-02-16

328

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

329

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

330

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

PubMed

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

Rafiee, Ezzat; Rahpeima, Nasibeh; Eavani, Sara

2014-01-01

331

Efficient solid-phase synthesis of a library of imidazo[1,2-a]pyridine-8-carboxamides.  

PubMed

A versatile method for the solid-phase synthesis of imidazo[1,2-a]pyridine-based derivatives, imidazo[1,2-a]pyridine-8-carboxamides, has been developed. They were obtained by treatment of the amino group of the polymer-bound 2-aminonicotinate with different alpha-haloketones, followed by halogenation at the 3-position of the polymer-bound imidazo[1,2-a]pyridine. The derived polymer-bound imidazo[1,2-a]pyridines 5, 6, and 7 were finally cleaved from the solid-support with an excess of primary or secondary amines. The final crude products were purified from excess amines by solid-supported liquid-liquid extraction (SLE). PMID:17319727

Kamal, Ahmed; Devaiah, V; Reddy, K Laxma; Rajendar; Shetti, Rajesh V C R N C; Shankaraiah, N

2007-01-01

332

Ultrasonic-assisted preparation of nano eggshell powder: a novel catalyst in green and high efficient synthesis of 2-aminochromenes.  

PubMed

The nano eggshell powder (NESP) has been prepared by ultrasound irradiation and used as a novel and biodegradable catalyst with high catalytic activity and reusability in green synthesis of 2-aminochromenes via condensation of ?- or ?-phathol, malononitrile and aromatic aldehydes at 120 °C under solvent-free conditions. The reaction proceeds to completion within 10-35 min in 91-98% yield. Nano eggshell catalyst was characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and X-ray fluorescence, thermal gravimetric, surface area and elemental analyses. In addition, the catalytic activity and chemical structure of nano-sized eggshell were compared with pure CaCO3. PMID:23684545

Mosaddegh, Elaheh

2013-11-01

333

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

334

Hydrothermal synthesis of a crystalline rutile TiO2 nanorod based network for efficient dye-sensitized solar cells.  

PubMed

One-dimensional (1D) TiO2 nanostructures are desirable as photoanodes in dye-sensitized solar cells (DSSCs) due to their superior electron-transport capability. However, making use of the DSSC performance of 1D rutile TiO2 photoanodes remains challenging, mainly due to the small surface area and consequently low dye loading. Herein, a new type of photoanode with a three-dimensional (3D) rutile-nanorod-based network structure directly grown on fluorine-doped tin oxide (FTO) substrates was developed by using a facile two-step hydrothermal process. The resultant photoanode possesses oriented rutile nanorod arrays for fast electron transport as the bottom layer and radially packed rutile head-caps with an improved large surface area for efficient dye adsorption. The diffuse reflectance spectra showed that with the radially packed top layer, the light-harvesting efficiency was increased due to an enhanced light-scattering effect. A combination of electrochemical impedance spectroscopy (EIS), dark current, and open-circuit voltage decay (OCVD) analyses confirmed that the electron-recombiantion rate was reduced on formation of the nanorod-based 3D network for fast electron transport. As a resut, a light-to-electricity conversion efficiency of 6.31% was achieved with this photoanode in DSSCs, which is comparable to the best DSSC efficiencies that have been reported to date for 1D rutile TiO2 . PMID:23939704

Yu, Hua; Pan, Jian; Bai, Yang; Zong, Xu; Li, Xinyong; Wang, Lianzhou

2013-09-27

335

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

EPA Science Inventory

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

336

Trifluoroethanol as a Metal-Free, Homogeneous and Recyclable Medium for the Efficient One-pot Synthesis of Dihydropyrimidones  

Microsoft Academic Search

Trifluoroethanol is found to be an efficient and recyclable medium in promoting one-pot, three-component condensation reactions of ?-ketoesters, aldehydes and urea (or thiourea) to afford the corresponding dihydropyrimidones in high yields. This protocol does not require the use of an acid or base catalyst.

S. V. Rashmi Raghava; M. N. Kumara; K. Mantelingu; K. S. Rangappa

2011-01-01

337

Trifluoroethanol as a Metal-Free, Homogeneous, and Recyclable Medium for the Efficient One-Pot Synthesis of Dihydropyrimidones  

Microsoft Academic Search

Trifluoroethanol is an efficient and recyclable medium in promoting one-pot, three-component condensation reactions of ?-ketoesters, aldehydes, and urea (or thiourea) to afford the corresponding dihydropyrimidones in good yields. This protocol does not require the use of an acid or base catalyst.

S. V. Rashmi; N. C. Sandhya; B. Raghava; M. N. Kumara; K. Mantelingu; K. S. Rangappa

2012-01-01

338

Efficient synthesis of 1,4-disubstituted 1,2,3-triazoles in ionic liquid\\/water system  

Microsoft Academic Search

A copper(I) catalyst in a mixture of the ionic liquid [bmim][BF4] and water, can effect three-component reaction of halides, sodium azide and alkynes to form 1,4-disubstituted 1,2,3-triazoles in good to high yields. The method is efficient and environmentally friendly.

Ya-Bin Zhao; Ze-Yi Yan; Yong-Min Liang

2006-01-01

339

Efficient thermal- and photocatalyst of Pd nanoparticles on TiO? achieved by an oxygen vacancies promoted synthesis strategy.  

PubMed

Pd nanoparticles supported on defective TiO2 with oxygen vacancies (TiO2-OV) have been prepared by an oxygen vacancies mediated reduction strategy. The resulting Pd-TiO2-OV catalyst with uniform Pd nanoparticles deposition demonstrates a remarkably thermocatalytic activity toward rapid, efficient reduction of nitroaromatics in water. The reaction proceeds efficiently using HCOONH4 as a hydrogen source under ambient conditions. The controlled experiments show that the (•)CO2(-) radicals produced by dehydrogenation of HCOONH4 are the main active species for the selective nitro reduction. Moreover, defective TiO2 nanostructures deposited with Pd nanoparticles, featuring excellent visible-light absorption via the creation of oxygen vacancies, can take advantage of the solar and thermal energy to drive catalytic reduction reactions more efficiently at room temperature. During this process, the oxygen vacancies and Pd nanoparticles play synergetic roles in the photoreduction of nitro compounds. Our work would be beneficial for implementation of a novel defect-mediated catalytic system in which solar light energy can be coupled with thermal energy to drive an energy efficient catalytic process. PMID:24392776

Pan, Xiaoyang; Xu, Yi-Jun

2014-02-12

340

Protein synthesis and degradation gene SNPs related to feed intake, feed efficiency, growth, and ultrasound carcass traits in Nellore cattle.  

PubMed

We looked for possible associations of SNPs in genes related to protein turnover, with growth, feed efficiency and carcass traits in feedlot Nellore cattle. Purebred Nellore bulls and steers (N = 290; 378 ± 42 kg body weight, 23 months ± 42 days old) were evaluated for daily feed intake, body weight gain (BWG), gross feed efficiency, feed conversion ratio, partial efficiency of growth, residual feed intake (RFI), ultrasound backfat, rump fat, and ribeye area. Genotypes were obtained for SNPs in the growth hormone receptor (GHR-1 and GHR-2); calpain (CAPN4751); calpastatin (UoGCAST); ubiquitin-conjugating enzyme 2I (UBE2I-1 and UBE2I-2); R3H domain containing 1 (R3HDM1-1, -2, -3, and -4), ring finger protein 19 (RNF19); proteasome 26S subunit, non-ATPase, 13 (PSMD13); ribosomal protein, large, P2 (RPLP2); and isoleucine-tRNA synthetase 2, mitochondrial (IARS2) genes. Allelic substitution, additive and dominant effects were tested and molecular breeding values were computed. CAPN4751, GHR-1 and -2, IARS2, R3HDM1-4, and UoGCAST were found to be normally segregating polymorphisms. Additive and dominance effects were observed on BWG, feed efficiency and carcass traits, although dominant effects predominated. Significant allelic substitution effects were observed for CAPN4751, GHR-1 and -2, and UoGCAST on BWG, gross feed efficiency, RFI, and carcass traits, under single- or multiple-marker analyses. Correlations between molecular breeding values and phenotypes were low, excepted for RFI, based on allelic substitution estimates obtained by stepwise linear regression. We conclude that SNPs in genes related to protein turnover are related to economically important traits in Nellore cattle. PMID:24065648

Gomes, R C; Silva, S L; Carvalho, M E; Rezende, F M; Pinto, L F B; Santana, M H A; Stella, T R; Meirelles, F V; Rossi Júnior, P; Leme, P R; Ferraz, J B S

2013-01-01

341

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

342

Efficient synthesis of D-branched-chain amino acids and their labeled compounds with stable isotopes using D-amino acid dehydrogenase.  

PubMed

D-Branched-chain amino acids (D-BCAAs) such as D-leucine, D-isoleucine, and D-valine are known to be peptide antibiotic intermediates and to exhibit a variety of bioactivities. Consequently, much effort is going into achieving simple stereospecific synthesis of D-BCAAs, especially analogs labeled with stable isotopes. Up to now, however, no effective method has been reported. Here, we report the establishment of an efficient system for enantioselective synthesis of D-BCAAs and production of D-BCAAs labeled with stable isotopes. This system is based on two thermostable enzymes: D-amino acid dehydrogenase, catalyzing NADPH-dependent enantioselective amination of 2-oxo acids to produce the corresponding D-amino acids, and glucose dehydrogenase, catalyzing NADPH regeneration from NADP(+) and D-glucose. After incubation with the enzymes for 2 h at 65°C and pH 10.5, 2-oxo-4-methylvaleric acid was converted to D-leucine with an excellent yield (>99 %) and optical purity (>99 %). Using this system, we produced five different D-BCAAs labeled with stable isotopes: D-[1-(13)C,(15)N]leucine, D-[1-(13)C]leucine, D-[(15)N]leucine, D-[(15)N]isoleucine, and D-[(15)N]valine. The structure of each labeled D-amino acid was confirmed using time-of-flight mass spectrometry and nuclear magnetic resonance analysis. These analyses confirmed that the developed system was highly useful for production of D-BCAAs labeled with stable isotopes, making this the first reported enzymatic production of D-BCAAs labeled with stable isotopes. Our findings facilitate tracer studies investigating D-BCAAs and their derivatives. PMID:23661083

Akita, Hironaga; Suzuki, Hirokazu; Doi, Katsumi; Ohshima, Toshihisa

2014-02-01

343

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

344

Polyphosphazenes as tunable and recyclable supports to immobilize alcohol dehydrogenases and lipases: synthesis, catalytic activity, and recycling efficiency.  

PubMed

The polyphosphazene {NP[O(2)C(12)H(7.5)(NH(2))(0.5)]}(n), prepared by reacting {NP[O(2)C(12)H(7.5)(NO(2))(0.5)]} with the Lalancette's reagent, was used for attaching enzymes such as alcohol dehydrogenase (ADH-A) and lipase (CAL-B). The resulting new biocatalysts exhibited great potential as tunable supports for enzymatic reactions in both aqueous and organic media. The material with immobilized ADH-A was as efficient as the commercial enzyme to perform stereoselective bioreductions of ketones in aqueous solutions and could be used for the reduction of various aliphatic and aromatic ketones up to 60 degrees C and recycled several times without significant loss of activity even after three months of storage. The biocatalyst obtained with CAL-B was more efficient than the free enzyme for kinetic resolutions in organic solvents and exhibited a moderately good capability of reutilization. PMID:20359182

Cuetos, Aníbal; Valenzuela, María L; Lavandera, Iván; Gotor, Vicente; Carriedo, Gabino A

2010-05-10

345

Efficient oxygen reduction electrocatalyst based on edge-nitrogen-rich graphene nanoplatelets: toward a large-scale synthesis.  

PubMed

The large-scale synthesis of nitrogen doped graphene (N-graphene) with high oxygen reduction reaction (ORR) performance has received a lot of attention recently. In this work, we have developed a facile and economical procedure for mass production of edge-nitrogen-rich graphene nanoplatelets (ENR-GNPs) by a combined process of ball milling of graphite powder (GP) in the presence of melamine and subsequent heat treatment. It is found that the ball milling process can not only crack and exfoliate pristine GP into edge-expanded nanoplatelets but also mechanically activate GP to generate appropriate locations for N-doping. Analysis results indicate that the doped N atoms mainly locate on the edge of the graphitic matrix, which contains ca. 3.1 at.% nitrogen content and can be well-dispersed in aqueous to form multilayer nanoplatelets. The as-prepared ENR-GNPs electrocatalyst exhibits highly electrocatalytic activity for ORR due to the synergetic effects of edge-N-doping and nanosized platelets. Besides, the stability and methanol tolerance of ENR-GNPs are superior to that of the commercial Pt/C catalyst, which makes the nanoplatelets a promising candidate for fuel cell cathode catalysts. The present approach opens up the possibility for simple and mass production of N-graphene based electrocatalysts in practice. PMID:24598249

Fu, Xiaogang; Jin, Jutao; Liu, Yanru; Wei, Zhiyang; Pan, Fuping; Zhang, Junyan

2014-03-26

346

Synthesis of highly efficient antibacterial agent Ag doped ZnO nanorods: Structural, Raman and optical properties  

SciTech Connect

Here, synthesis, structural, morphological, Raman, optical properties and antibacterial activity of undoped and Ag doped ZnO nanorods by chemical co-precipitation technique have been reported. Structural analysis has revealed that Ag doping cannot deteriorate the structure of ZnO and wurtzite phase is maintained. Lattice constants are found to be decreased with the Ag doping. Fourier transform infrared and Raman spectroscopy also confirm the X-ray diffraction results. Scanning electron microscopy results have demonstrated the formation of ZnO nanorods with average diameter and length of 96?nm and 700?nm, respectively. Raman spectroscopy results suggest that the Ag doping enhances the number of defects in ZnO crystal. It has been found from optical study that Ag doping results in positional shift of band edge absorption peak. This is attributed to the successful incorporation of Ag dopant into ZnO host matrix. The antibacterial activity of prepared nanorods has been determined by two different methods and compared to that of undoped ZnO nanorods. Ag doped ZnO nanorods exhibit excellent antibacterial activity as compared to that of undoped ZnO nanorods. This excellent antibacterial activity may be attributed to the presence of oxygen vacancies and Zn{sup 2+} interstitial defects. Our preliminary findings suggest that Ag doped ZnO nanorods can be used externally to control the spreading of infections related with tested bacterial strains.

Jan, Tariq; Iqbal, Javed, E-mail: javed.saggu@iiu.edu.pk [Laboratory of Nanoscience and Technology, Department of Physics, International Islamic University Islamabad (Pakistan); Ismail, Muhammad [Institute of Biomedical and Genetic Engineering (IBGE), Islamabad (Pakistan); Mahmood, Arshad [Nano Devices Labs, National Institute of Lasers and Optronics, Islamabad (Pakistan)

2014-04-21

347

Spot arrays on modified glass surfaces for efficient SPOT synthesis and on-chip bioassay of peptides.  

PubMed

To make SPOT synthesis of peptides and their assays on glass surfaces more convenient, a simple method for making spot arrays on a slide glass was designed through patterning with a photoresist and perfluorination followed by amination with various silane compounds and polymers. With these spot-arrayed glass surfaces, we could measure the coupling completion of each Fmoc amino acid on the glass surface by direct fluorescence analysis after fluorescence-labeling the amino groups on the surface of each spot. Then we synthesized several types of decapeptides and HPQ-pentapeptides on the spot-arrayed glasses and identified the optimal surface condition for stepwise peptide coupling and on-chip bioassay. After optimizing the surface conditions, we synthesized a model library of biotin-Gly-Ala-P(1)-Gly (P(1): one of 19 amino acids) and successfully replicated the well-known alpha-chymotrypsin subsite specificities through Cy5-streptavidin binding to the remaining biotin on the surface after the enzymatic digestion. PMID:17694567

Kim, Do-Hyun; Shin, Dong-Sik; Lee, Yoon-Sik

2007-10-01

348

Iodine-catalyzed Friedel–Crafts alkylation of electron-rich arenes with aldehydes: efficient synthesis of triarylmethanes and diarylalkanes  

Microsoft Academic Search

Iodine is shown to be an efficient catalyst for the Friedel–Crafts alkylation of arenes with a wide variety of aldehydes in toluene under ‘open-flask’ and mild conditions. In the presence of 10mol% of iodine, the reaction of arenes with aromatic aldehydes gives the corresponding triarylmethane derivatives (TRAMs), regioselectively, in good to excellent yields. On the other hand, a series of

Jaray Jaratjaroonphong; Supaporn Sathalalai; Prapapan Techasauvapak; Vichai Reutrakul

2009-01-01

349

Efficient one-pot synthesis and loading of self-assembled amphiphilic chitosan nanoparticles for low-leaching wood preservation  

Microsoft Academic Search

A simple, one-step and one-pot method was used to synthesize amphiphilic self-assembling chitosan-g-PMMA nanoparticles (?100nm diameter by SEM, but ?150–200nm in water by DLS), containing ?25–28wt.% (?82–93% capture efficiency) of the fungicide tebuconazole. The matrix composition was selected to be environmentally low impact, while the nanoparticle preparation conditions were designed to ensure the nanoparticles were sufficiently small to be able

Xiaochu Ding; Dana L. Richter; Laurent M. Matuana; P. A. Heiden

2011-01-01

350

Synthesis and evaluation of diethylethylamine-chitosan for gene delivery: composition effects on the in vitro transfection efficiency.  

PubMed

Chitosan has been indicated as a safe and promising polycation vector for gene delivery. However its low transfection efficiency has been a challenging obstacle for its application. To address this limitation, we synthesized chitosan derivatives which had increasing amounts of diethylethylamine groups (DEAE) attached to the chitosan main chain. The plasmid DNA VR1412 (pDNA), encoding the ß-galactosidase (ß-gal) reporter gene was used to prepare nanoparticles with the chitosan derivatives, and the transfection studies were performed with HeLa cells. By means of dynamic light scattering and zeta potential measurements, it was shown that diethylethylamine-chitosan derivatives (DEAE(x)-CH) were able to condense DNA into small particles having a surface charge depending on the polymer/DNA ratio (N/P ratio). Nanoparticles prepared with derivatives containing 15 and 25% of DEAE groups (DEAE(15)-CH and DEAE(25)-CH) exhibited transfection efficiencies ten times higher than that observed with deacetylated chitosan (CH). For derivatives with higher degrees of substitution (DS), transfection efficiency decreased. The most effective carriers showed low cytotoxicity and good transfection activities at low charge ratios (N/P). Vectors with low DS were easily degraded in the presence of lysozyme at physiological conditions in vitro and the nontoxicity displayed by these vectors opens up new opportunities in the design of DEAE-chitosan-based nanoparticles for gene delivery. PMID:23306549

de Paula Pansani Oliveira, Franciele; Dalla Picola, Isadora Pfeifer; Shi, Qin; Barbosa, Hellen Franciane Gonçalves; Tiera, Vera Aparecida de Oliveira; Fernandes, Júlio Cesar; Tiera, Marcio José

2013-02-01

351

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

352

Effect of post-synthesis acid activation of TiO2 nanofilms on the photocatalytic efficiency under visible light  

NASA Astrophysics Data System (ADS)

Nanosized TiO2 films were deposited by spray pyrolysis and thermally treated at 400oC. Then the films were dipped in 1M aqueous solution of HCl. The activated samples were divided into two parts - one part was dried (A) and another was annealed (AT) in air. The photocatalytic degradation of Reactive Black (RB5) textile dye under visible light was tested. The following instrumental methods: X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied for the phase and surface characterization of obtained samples. According to Raman and XRD analyses all films are anatase. The XRD showed that activated films are better crystallized than non activated TiO2 film. The presence of chlorine at 200.3 eV was registered for acid activated samples by X-Ray photoelectron spectroscopy. The acidic activated films exhibited higher rate of dye photodegradation than that of the reference TiO2 sample. The photocatalytic efficiency decreases in the order A > AT> non activated TiO2 films. The degradation rate constant for acid activated films is two times higher than those of the reference film. The hydroxyl content in TiO2 acidic activated films is greater than that of the non- activated films, which results in significant increase in the photocatalytic activity. In addition, the presence of chlorine may also lead to enhancement in efficiency.

Stambolova, I.; Blaskov, V.; Shipochka, M.; Eliyas, A.; Vassilev, S.

2014-12-01

353

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

354

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

355

New tetracyclic tacrine analogs containing pyrano[2,3-c]pyrazole: Efficient synthesis, biological assessment and docking simulation study.  

PubMed

A new series of tacrine-based acetylcholinesterase (AChE) inhibitors 7a-l were designed by replacing the benzene ring of tacrine with aryl-dihydropyrano[2,3-c]pyrazole. The poly-functionalized hybrid molecules 7a-l were efficiently synthesized through multi-component reaction and subsequent Friedländer reaction between the obtained pyrano[2,3-c]pyrazoles and cyclohexanone. Most of target compounds showed potent and selective anti-AChE activity at sub-micromolar range. The most potent compound 7h bearing a 3,4-dimethoxyphenyl group was more active than reference drug tacrine. The representative compound 7h could significantly protect neurons against oxidative stress as potent as quercetin at low concentrations. The docking study of compound 7h with AChE enzyme revealed that the (R)-enantiomer binds preferably to CAS while the (S)-enantiomer prone to be a PAS binder. PMID:25462245

Khoobi, Mehdi; Ghanoni, Farzaneh; Nadri, Hamid; Moradi, Alireza; Pirali Hamedani, Morteza; Homayouni Moghadam, Farshad; Emami, Saeed; Vosooghi, Mohsen; Zadmard, Reza; Foroumadi, Alireza; Shafiee, Abbas

2015-01-01

356

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

357

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

358

Synthesis and in vitro transfection efficiency of spermine-based cationic lipids with different central core structures and lipophilic tails.  

PubMed

Twelve spermine-based cationic lipids with four different central core structures (di(oxyethyl)amino, di(oxyethyl)amino carboxy, 3-amino-1,2-dioxypropyl and 2-amino-1,3-dioxypropyl) and three hydrophobic tails (lauric acid, myristic acid and palmitic acid) were synthesized. The liposomes containing lipids and DOPE showed moderate to good in vitro DNA delivery into HeLa cells. GFP expression experiments revealed that liposomes composed of lipids with 3-amino-1,2-dioxypropyl as a central core structure exhibited highest transfection efficiency under serum-free condition. Whereas, lipid with 2-amino-1,3-dioxypropyl core structure showed highest transfection under 10% serum condition. Moreover, the liposomes and lipoplexes composted of these cationic lipids exhibited low cytotoxicity. PMID:25556091

Niyomtham, Nattisa; Apiratikul, Nuttapon; Suksen, Kanoknetr; Opanasopit, Praneet; Yingyongnarongkul, Boon-Ek

2015-02-01

359

SiO2/H2SO4: An Efficient Catalytic System for Solvent-free 1, 5-benzodiazepines Synthesis  

PubMed Central

Background 1, 5-Benzodiazepines have been investigated extensively by organic chemists due to their medicinal and pharmacological properties. These compounds are synthesized by condensation of o-phenylenediamines with carbonyl compounds in the presence of acid catalysts. Objectives During our studies on the application of silica resin with acid functional moieties, we found that SiO2/H2SO4 mixture is a simple and efficient catalyst for this method under microwave irradiation. Materials and Methods The reaction was carried out simply by grinding SiO2/H2SO4 mixture with o-phenylenediamine, and ketone in the mortar; then the mixture was poured out into a sealed flask. Subsequently, it was irradiated in a microwave oven. Results In this method a series of cyclic and acyclic ketones underwent above conversion to form corresponding 1, 5-benzodiazepines. Conclusions In conclusion, this method is a simple, rapid, and high yielding reaction (78–95%). PMID:24624156

Shushizadeh, Mohammad Reza; Dalband, Narges

2012-01-01

360

Efficient synthesis of 3H,3'H-spiro[benzofuran-2,1'-isobenzofuran]-3,3'-dione as novel skeletons specifically for influenza virus type B inhibition.  

PubMed

An efficient and novel two step synthetic procedure to prepare various substituted 3H,3'H-spiro[benzofuran-2,1'-isobenzofuran]-3,3'-diones A, was established from very simple and easily available starting materials. The developed method is a robust and general approach for the synthesis of these structures. The prepared compounds were tested against influenza virus type A viz., A/Taiwan/1/86 (H1N1), A/Hong Kong/8/68 (H3N2) and type B viz., B/Panama/45/90, B/Taiwan/2/62, B/Lee/40, B/Brisbane/60/2008. Among 31 compounds tested, some of them showed good activity (selective index values >10) against these influenza viruses preferentially for type B. The most active compound 3b showed activity in 3.0-16.1 ?M range with a selectivity index value between 30 and 166 against these type B viruses, in which it was comparable to the antiviral agent favipiravir. Also, 3b is found to be inactive against other enveloped viruses (viz., HIV and HSV) showing its specificity for influenza viruses. PMID:23419738

Malpani, Yashwardhan; Achary, Raghavendra; Kim, So Yeon; Jeong, Hee Chun; Kim, Pilho; Han, Soo Bong; Kim, Meehyein; Lee, Chong-Kyo; Kim, Jae Nyoung; Jung, Young-Sik

2013-04-01

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

N-Substituted benzoxazolyl ureas and thioureas in Biginelli reaction promoted by trifluoromethane sulfonic acid: An efficient and convenient synthesis of substituted benzoxazolyl 3,4-dihydropyrimidine (1 H)-(thio)-ones  

Microsoft Academic Search

An efficient synthesis of 3,4-dihydropyrimidine 2 (1H)-ones and thiones (3,4-DHPMs) core was prepared by one-pot three-component Biginelli condensation and which was catalyzed by trifluoromethane sulfonic acid. The classical Bignelli reaction has been extended by the use of N-substituted benzoxazolyl semicarbazides and thiosemicarbazides and this method has the advantage of excellent yields and short reaction times.

M. Saranga Pani; M. Arjun; D. Sridhar; K. Srinivas; T. Raviprasad

2009-01-01

363

Xanthan Sulfuric Acid: An Efficient Bio-Supported and Recyclable Solid Acid Catalyst for the Synthesis of 4,4-(Arylmethylene)bis(1 h-Pyrazol-5-ols)  

Microsoft Academic Search

A simple and efficient method has been developed for the synthesis of 4,4-(arylmethylene)bis(1H-pyrazol-5-ols) by the condensation reaction between substituted aldehydes, and 1-phenyl-3-methylpyrazol-5-one in the presence of Xanthan sulfuric acid (XSA) as a solid acid catalyst. This method is simple, cost effective, requires short reaction times, yields are excellent with high purity and the catalyst could be easily recycled.

B. Suresh Kuarm; B. Rajitha

2012-01-01

364

Total synthesis of (+)-angelmarin.  

PubMed

An efficient 8-step enantioselective total synthesis of (+)-angelmarin, starting from commercially available umbelliferone, has been achieved. Key reactions include olefin cross-metathesis and a Shi epoxidation-cyclization sequence. PMID:19459593

Magolan, Jakob; Coster, Mark J

2009-07-17

365

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

2014-12-01

366

Synthesis of CdS/ZnO/graphene composite with high-efficiency photoelectrochemical activities under solar radiation  

NASA Astrophysics Data System (ADS)

A novel ternary CdS/ZnO/graphene composite has been successfully prepared by loading ZnO and CdS nanoparticles in graphene nanosheets via a facile one-step hydrothermal method. The microstructures and properties have been examined by X-ray diffraction (XRD), scanning electron microscopy with an energy dispersive spectroscope (EDS), transmission electron microscopy, Raman and UV-vis diffuse reflectance spectra (DRS). The characterization results reveal that the crystalline of the composite is very well, the graphene sheets were tightly coated with ZnO and CdS nanoparticles, and the light-harvesting was effectively strengthened. Taking photoelectrochemical test, the ternary CdS/ZnO/graphene composite exhibits enhanced photocatalytic activity compared with its foundation matrix binary composites and pure ZnO and CdS. The improved photocatalytic performance can be attributed to the enhanced light absorption, the extremely efficient charge separation, as well as superior durability of the ternary composite. It is proposed that graphene-based composites by coupling graphene to suitable, multiple semiconductors can not only greatly improve the capacity for photocatalytic, but also expand the exploration and utilization of graphene-based nanocomposites for energy conversion.

Han, Weijia; Ren, Long; Qi, Xiang; Liu, Yundan; Wei, Xiaolin; Huang, Zongyu; Zhong, Jianxin

2014-04-01

367

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

368

Fast and Highly Chemoselective Alkynylation of Thiols with Hypervalent Iodine Reagents Enabled through a Low Energy Barrier Concerted Mechanism  

PubMed Central

Among all functional groups, alkynes occupy a privileged position in synthetic and medicinal chemistry, chemical biology, and materials science. Thioalkynes, in particular, are highly useful, as they combine the enhanced reactivity of the triple bond with a sulfur atom frequently encountered in bioactive compounds and materials. Nevertheless, general methods to access these compounds are lacking. In this article, we describe the mechanism and full scope of the alkynylation of thiols using ethynyl benziodoxolone (EBX) hypervalent iodine reagents. Computations led to the discovery of a new, three-atom concerted transition state with a very low energy barrier, which rationalizes the high reaction rate. On the basis of this result, the scope of the reaction was extended to the synthesis of aryl- and alkyl-substituted alkynes containing a broad range of functional groups. New sulfur nucleophiles such as thioglycosides, thioacids, and sodium hydrogen sulfide were also alkynylated successfully to lead to the most general and practical method yet reported for the synthesis of thioalkynes. PMID:25365776

2014-01-01

369

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

370

?-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

371

Total Synthesis of Laulimalide: Synthesis of the Northern and Southern Fragments  

PubMed Central

The first stage of the development of a synthetic route for the total synthesis of laulimalide (1) is described. Our retrosynthetic analysis envisioned a novel macrocyclization route to the natural product using a Ru-catalyzed alkene-alkyne coupling. This would be preceded by an esterification of the C19 hydroxyl group, joining together two equally sized synthons, the northern fragment 7 and the southern fragment 8. Our first generation approach to the northern fragment entailed a key sequential Ru-Pd coupling sequence to assemble the dihydropyran. The key reactions proceeded smoothly, however, the inability to effect a key olefin migration led to the development of an alternative route based on an asymmetric dinuclear Zn-catalyzed aldol reaction of a hydroxyl acylpyrrole. This key reaction led to the desired diol adduct 66 with excellent syn:anti selectivity (10:1), and allowed for the successful completion of the northern fragment 7. The key step for the synthesis of the southern fragment was a chemoselective Rh-catalyzed cycloisomerization reaction to form the dihydropyran ring from a diyne precursor. This reaction proved to be selective for the formation of a six-membered ring, over a seven. The use of an electron-deficient bidentate phosphine allowed for the reaction to proceed with a reduced catalyst loading. PMID:22307837

Seganish, W. Michael; Chung, Cheol K.; Amans, Dominique

2012-01-01

372

Interactions at the Dimer Interface Influence the Relative Efficiencies for Purine Nucleotide Synthesis and Pyrophosphorolysis in a Phosphoribosyltransferase  

SciTech Connect

Enzymes that salvage 6-oxopurines, including hypoxanthine phosphoribosyltransferases (HPRTs), are potential targets for drugs in the treatment of diseases caused by protozoan parasites. For this reason, a number of high-resolution X-ray crystal structures of the HPRTs from protozoa have been reported. Although these structures did not reveal why HPRTs need to form dimers for catalysis, they revealed the existence of potentially relevant interactions involving residues in a loop of amino acid residues adjacent to the dimer interface, but the contributions of these interactions to catalysis remained poorly understood. The loop, referred to as active-site loop I, contains an unusual non-proline cis-peptide and is composed of residues that are structurally analogous with Leu67, Lys68, and Gly69 in the human HPRT. Functional analyses of site-directed mutations (K68D, K68E, K68N, K68P, and K68R) in the HPRT from Trypanosoma cruzi, etiologic agent of Chagas disease, show that the side-chain at position 68 can differentially influence the K{sub m} values for all four substrates as well as the k{sub cat} values for both IMP formation and pyrophosphorolysis. Also, the results for the K68P mutant are inconsistent with a cis-trans peptide isomerization-assisted catalytic mechanism. These data, together with the results of structural studies of the K68R mutant, reveal that the side-chain of residue 68 does not participate directly in reaction chemistry, but it strongly influences the relative efficiencies for IMP formation and pyrophosphorolysis, and the prevalence of lysine at position 68 in the HPRT of the majority of eukaryotes is consistent with there being a biological role for nucleotide pyrophosphorolysis.

Canyuk, Bhutorn; Medrano, Francisco J.; Wenck, MaryAnne; Focia, Pamela J.; Eakin, Ann E.; Craig III, Sydney P. (UNC); (Connecticut)

2010-03-05

373

Synthesis and characterization of novel pyrene-dendronized porphyrins exhibiting efficient fluorescence resonance energy transfer: optical and photophysical properties.  

PubMed

A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core. PMID:22738369

Zaragoza-Galán, Gerardo; Fowler, Michael A; Duhamel, Jean; Rein, Regis; Solladié, Nathalie; Rivera, Ernesto

2012-07-31

374

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

375

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

376

Large-scale and highly efficient synthesis of micro- and nano-fibers with controlled fiber morphology by centrifugal jet spinning for tissue regeneration  

NASA Astrophysics Data System (ADS)

PLLA fibrous tissue scaffolds with controlled fiber nanoscale surface roughness are fabricated with a novel centrifugal jet spinning process. The centrifugal jet spinning technique is a highly efficient synthesis method for micron- to nano-sized fibers with a production rate up to 0.5 g min-1. During the centrifugal jet spinning process, a polymer solution jet is stretched by the centrifugal force of a rotating chamber. By engineering the rheological properties of the polymer solution, solvent evaporation rate and centrifugal force that are applied on the solution jet, polyvinylpyrrolidone (PVP) and poly(l-lactic acid) (PLLA) composite fibers with various diameters are fabricated. Viscosity measurements of polymer solutions allowed us to determine critical polymer chain entanglement limits that allow the generation of continuous fiber as opposed to beads or beaded fibers. Above a critical concentration at which polymer chains are partially or fully entangled, lower polymer concentrations and higher centrifugal forces resulted in thinner fibers. Etching of PVP from the PLLA-PVP composite fibers doped with increasing PVP concentrations yielded PLLA fibers with increasing nano-scale surface roughness and porosity, which increased the fiber hydrophilicity dramatically. Scanning electron micrographs of the etched composite fibers suggest that PVP and PLLA were co-contiguously phase separated within the composite fibers during spinning and nano-scale roughness features were created after the partial etching of PVP. To study the tissue regeneration efficacy of the engineered PLLA fiber matrix, human dermal fibroblasts are used to simulate partial skin graft. Fibers with increased PLLA surface roughness and porosity demonstrated a trend towards higher cell attachment and proliferation.PLLA fibrous tissue scaffolds with controlled fiber nanoscale surface roughness are fabricated with a novel centrifugal jet spinning process. The centrifugal jet spinning technique is a highly efficient synthesis method for micron- to nano-sized fibers with a production rate up to 0.5 g min-1. During the centrifugal jet spinning process, a polymer solution jet is stretched by the centrifugal force of a rotating chamber. By engineering the rheological properties of the polymer solution, solvent evaporation rate and centrifugal force that are applied on the solution jet, polyvinylpyrrolidone (PVP) and poly(l-lactic acid) (PLLA) composite fibers with various diameters are fabricated. Viscosity measurements of polymer solutions allowed us to determine critical polymer chain entanglement limits that allow the generation of continuous fiber as opposed to beads or beaded fibers. Above a critical concentration at which polymer chains are partially or fully entangled, lower polymer concentrations and higher centrifugal forces resulted in thinner fibers. Etching of PVP from the PLLA-PVP composite fibers doped with increasing PVP concentrations yielded PLLA fibers with increasing nano-scale surface roughness and porosity, which increased the fiber hydrophilicity dramatically. Scanning electron micrographs of the etched composite fibers suggest that PVP and PLLA were co-contiguously phase separated within the composite fibers during spinning and nano-scale roughness features were created after the partial etching of PVP. To study the tissue regeneration efficacy of the engineered PLLA fiber matrix, human dermal fibroblasts are used to simulate partial skin graft. Fibers with increased PLLA surface roughness and porosity demonstrated a trend towards higher cell attachment and proliferation. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr33423f

Ren, Liyun; Pandit, Vaibhav; Elkin, Joshua; Denman, Tyler; Cooper, James A.; Kotha, Shiva P.

2013-02-01

377

Synthesis of Cruentaren A  

PubMed Central

Cruentaren A, an antifungal benzolactone produced by the myxobacterium Byssovorax cruenta, is highly cytotoxic against various human cancer cell lines and a highly selective inhibitor of mitochondrial F-ATPase. A convergent and efficient synthesis of cruentaren A is reported, based upon a diastereoselective alkylation, a series of stereoselective aldol reactions utilizing Myers’ pseudoephedrine propionamide, an acyl bromide–mediated esterification and a ring-closing metathesis (RCM) as the key steps. The RCM reaction was applied for the first time towards the total synthesis of cruentaren A, which led to a convergent and efficient synthesis of the natural product. PMID:23205851

Kusuma, Bhaskar Reddy; Brandt, Gary E. L.

2012-01-01

378

Designed synthesis of well-defined Pd@Pt core-shell nanoparticles with controlled shell thickness as efficient oxygen reduction electrocatalysts.  

PubMed

Improving the electrocatalytic activity and durability of Pt-based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well-defined Pd@Pt core-shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4-1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as-synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well-defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single-cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low-cost and high-efficient applications of PEMFCs. PMID:23613263

Choi, Ran; Choi, Sang-Il; Choi, Chang Hyuck; Nam, Ki Min; Woo, Seong Ihl; Park, Joon T; Han, Sang Woo

2013-06-17

379

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

380

Structure of the Human Angiotensin II Type 1 (AT1) Receptor Bound to Angiotensin II from Multiple Chemoselective Photoprobe Contacts Reveals a Unique Peptide Binding Mode*  

PubMed Central

Breakthroughs in G protein-coupled receptor structure determination based on crystallography have been mainly obtained from receptors occupied in their transmembrane domain core by low molecular weight ligands, and we have only recently begun to elucidate how the extracellular surface of G protein-coupled receptors (GPCRs) allows for the binding of larger peptide molecules. In the present study, we used a unique chemoselective photoaffinity labeling strategy, the methionine proximity assay, to directly identify at physiological conditions a total of 38 discrete ligand/receptor contact residues that form the extracellular peptide-binding site of an activated GPCR, the angiotensin II type 1 receptor. This experimental data set was used in homology modeling to guide the positioning of the angiotensin II (AngII) peptide within several GPCR crystal structure templates. We found that the CXC chemokine receptor type 4 accommodated the results better than the other templates evaluated; ligand/receptor contact residues were spatially grouped into defined interaction clusters with AngII. In the resulting receptor structure, a ?-hairpin fold in extracellular loop 2 in conjunction with two extracellular disulfide bridges appeared to open and shape the entrance of the ligand-binding site. The bound AngII adopted a somewhat vertical binding mode, allowing concomitant contacts across the extracellular surface and deep within the transmembrane domain core of the receptor. We propose that such a dualistic nature of GPCR interaction could be well suited for diffusible linear peptide ligands and a common feature of other peptidergic class A GPCRs. PMID:23386604

Fillion, Dany; Cabana, Jérôme; Guillemette, Gaétan; Leduc, Richard; Lavigne, Pierre; Escher, Emanuel

2013-01-01

381

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

382

Parallel synthesis and screening of peptide conjugates.  

PubMed

Peptide conjugates represent an emerging class of therapeutics. However, in contrast to that of small molecules and peptides, the discovery and optimization of peptide conjugates is low in throughput, resource intensive, time-consuming, and based on educated decisions rather than screening. A strategy for the parallel synthesis and screening of peptide conjugates is presented that (1) reduces variability in the conjugation steps; (2) provides a new method to rapidly and quantitatively measure conversion in crude conjugation mixtures; (3) introduces a purification step using an immobilized chemical scavenger that does not rely on protein-specific binding; and (4) is supported by robust analytical methods to characterize the large number of end products. Copper-free click chemistry is used as the chemoselective ligation method for conjugation and purification. The productivity in the generation and screening of peptide conjugates is significantly improved by applying this strategy as is demonstrated by the optimization of the anti-Angiopoietin-2 (Ang2) CovX-body, CVX-060, a peptide-antibody scaffold conjugate that has advanced in clinical trials for oncology indications. PMID:24824568

Dirksen, Anouk; Madsen, Mark; Dello Iacono, Giuseppe; Matin, Marla J; Bacica, Michael; Stankovi?, Nebojša; Callans, Sherri; Bhat, Abhijit

2014-06-18

383

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

384

Ammonia synthesis  

Microsoft Academic Search

In a process for producing ammonia in a synthesis loop in which fresh synthesis gas containing hydrogen, nitrogen and, lesser amounts of argon and methane is combined with a hydrogen enriched recycle gas to provide combined synthesis gas, the combined synthesis is introduced to and reacted over ammonia synthesis catalyst under synthesis conditions to provide converted gas containing ammonia, hydrogen,

B. G. Mandelik; J. R. Cassata; P. J. S. Katy; C. P. Van Dijk

1986-01-01

385

An Efficient One-Pot Green Protocol for the Synthesis of 5-Unsubstituted 3,4-Dihydropyrimidin-2(1H)-Ones Using Recyclable Amberlyst 15 DRY as a Heterogeneous Catalyst via Three-Component Biginelli-Like Reaction  

PubMed Central

An environmentally benign green protocol for the synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones using Amberlyst 15 DRY as a recyclable catalyst has been developed. The use of resinous, nontoxic, thermally stable, and inexpensive Amberlyst 15 DRY, as a recyclable heterogeneous catalyst, makes the process simple with negligible chemical waste. Among the various solid acid catalysts Amberlyst 15 DRY was found to be the most efficient catalyst with regard to reaction time, yield, and ease of work-up procedure. PMID:24052845

Jetti, Srinivasa Rao; Verma, Divya; Jain, Shubha

2012-01-01

386

An Efficient One-Pot Green Protocol for the Synthesis of 5-Unsubstituted 3,4-Dihydropyrimidin-2(1H)-Ones Using Recyclable Amberlyst 15 DRY as a Heterogeneous Catalyst via Three-Component Biginelli-Like Reaction.  

PubMed

An environmentally benign green protocol for the synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones using Amberlyst 15 DRY as a recyclable catalyst has been developed. The use of resinous, nontoxic, thermally stable, and inexpensive Amberlyst 15 DRY, as a recyclable heterogeneous catalyst, makes the process simple with negligible chemical waste. Among the various solid acid catalysts Amberlyst 15 DRY was found to be the most efficient catalyst with regard to reaction time, yield, and ease of work-up procedure. PMID:24052845

Jetti, Srinivasa Rao; Verma, Divya; Jain, Shubha

2012-01-01

387

Xanthan Sulfuric Acid: A New and Efficient Bio-Supported Solid Acid Catalyst for the Synthesis of 3,4-Dihydropyrimidin-2(1H)-Ones  

Microsoft Academic Search

Xanthan sulfuric acid (XSA) is employed as a recyclable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones. These syntheses were performed via a one-pot three-component condensation of aldehydes, amines, and urea\\/thiourea under Solvent-free conditions.

B. Suresh Kuarm; J. Venu Madhav; S. Vijaya Laxmi; B. Rajitha

2011-01-01

388

Efficient and Convenient Synthesis of 1,8-Dioxodecahydroacridine Derivatives Using Cu-Doped ZnO Nanocrystalline Powder as a Catalyst under Solvent-Free Conditions  

PubMed Central

A simple and convenient one-step method for synthesis of acridines and their derivatives from condensation of aromatic aldehydes, cyclic diketones, and aryl amines using Cu-doped ZnO nanocrystalline powder as a catalyst is reported. The present protocol provides several advantages such as good yields, short reaction time, easy workup, and simplicity in operation. PMID:24294130

Alinezhad, Heshmatollah; Mohseni Tavakkoli, Sahar

2013-01-01

389

Enantioselective Synthesis of Apoptolidin Sugars  

E-print Network

Enantioselective Synthesis of Apoptolidin Sugars Michael T. Crimmins* and Alan Long Venable synthesis of the C9 and C27 sugar subunits (2) and (3), respectively, of the potent antitumor agent of the aldol adducts efficiently provided the three sugar units. A -selective glycosidation completed

390

N-halosuccinimide/AgNO3-efficient reagent systems for one-step synthesis of 2-haloglycals from glycals: application in the synthesis of 2C-branched sugars via Heck coupling reactions.  

PubMed

An expedient one-step synthesis of 2-iodoglycals and 2-bromoglycals from glycals using NIS/AgNO3 and NBS/AgNO3 as reagent systems has been developed. The utility of these 2-haloglycals has been demonstrated by converting them into 2C-branched glycals via the Heck coupling reaction. Ferrier reaction of tri-O-acetyl-2-iodoglycals followed by Heck coupling reaction with methyl acrylate leads to 2C-branched O-glycosides. PMID:24499471

Dharuman, Suresh; Vankar, Yashwant D

2014-02-21

391

Vanillin Synthesis from 4-Hydroxybenzaldehyde  

ERIC Educational Resources Information Center

A regioselective, safe and efficient method for the synthesis of vanillin from 4-hydroxybenzaldehyde is being described. The vanillin derived from the process is cheap and can be used as a flavor or in the paper industry.

Taber, Douglass F.; Patel, Shweta; Hambleton, Travis M.; Winkel, Emma E.

2007-01-01

392

Convenient and Efficient Synthesis of a Lanthanide3+-Coordinated, Diethylene Triamine Pentaacetic Acid Labeled Biopolymer as an Assay for the Cholecystokinin B Receptor  

PubMed Central

To develop an assay for the cholecystokinin B receptor with an Eu3+-labeled cholecystokinin peptide via a diethylene triamine pentaacetic acid chelating linker, a commercial dianhydride diethylene triamine pentaacetic acid precursor was directly attached to the N-terminus of cholecystokinin peptides by a solid-phase synthesis method with a satisfactory yield and purity after reverse-phase high-performance liquid chromatography separation. Lanthanide was then coordinated to the peptide via a diethylene triamine pentaacetic acid bifunctional agent. This method is a useful approach to the large-scale synthesis of lanthanide3+-coordinated, diethylene triamine pentaacetic acid labeled biopolymers. This research provides not only a simple and convenient method for the preparation of lanthanide-based peptide ligand libraries but also possible lanthanide-based high-throughput screening of peptide receptors with a timeresolved fluorescence assay system. Five biopolymers were synthesized and characterized with high-resolution electrospray ionization in this study. PMID:19562042

Gao, F.; Handl, H.; Vagner, J.; Hruby, V.; Gillies, R.

2009-01-01

393

Efficient synthesis of supercoiled M13 DNA molecule containing a site specifically placed psoralen adduct and its use as a substrate for DNA replication  

SciTech Connect

The authors report a simple method for the in vitro synthesis of large quantities of site specifically modified DNA. The protocol involves extension of an oligonucleotide primer annealed to M13 single-stranded DNA using part of the T4 DNA polymerase holoenzyme. The resulting nicked double-stranded circles are ligated and supercoiled in the same tube, producing good yields of form I DNA. When the oligonucleotide primer is chemically modified, the resultant product contains a site-specific lesion. In this study, they report the synthesis of an M13 mp19 form I DNA which contains a psoralen monoadduct or cross-link at the KpnI site. They demonstrate the utility of these modified substrates by assessing the ability of the bacteriophage T4 DNA replication complex to bypass the damage and show that the psoralen monoadduct poses a severe block to the holoenzyme when attached to the template strand.

Kodadek, T.; Gamper, H.

1988-05-03

394

Efficient two-step sequence for the synthesis of 2,5-disubstituted furan derivatives from functionalized nitroalkanes: successive Amberlyst A21- and Amberlyst 15-catalyzed processes.  

PubMed

The nitroaldol reaction of ketal-functionalized nitroalkanes with alpha-oxoaldehydes, promoted by Amberlyst A21, followed by acidic treatment (Amberlyst 15) of the obtained nitroalkanol, leads to the formation of 2,5-disubstituted furans in good yields. The procedure was successfully applied to the total synthesis of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)-indazole (YC-1), an important pharmaceutical target. PMID:20657907

Palmieri, Alessandro; Gabrielli, Serena; Ballini, Roberto

2010-09-01

395

An efficient tandem approach for the synthesis of functionalized 2-pyridone-3-carboxylic acids using three-component reaction in aqueous media.  

PubMed

Novel analogs of 2-pyridone-3-carboxylic acids 4a-l have been prepared by the three-component reaction of 3-formyl chromone, Meldrum's acid, and primary amines in the presence of a catalytic amount of diammonium hydrogen phosphate in water. Good-to-high yields, easy work-up, and an environmentally friendly profile are the advantages of this method for the synthesis of 2-pyridone-3-carboxylic acid derivatives. PMID:24792225

Mehrparvar, Saber; Balalaie, Saeed; Rabbanizadeh, Mahnaz; Ghabraie, Elmira; Rominger, Frank

2014-08-01

396

Aerobic iron-based cross-dehydrogenative coupling enables efficient diversity-oriented synthesis of coumestrol-based selective estrogen receptor modulators.  

PubMed

An iron-based cross-dehydrogenative coupling (CDC) approach was applied for the diversity-oriented synthesis of coumestrol-based selective estrogen receptor modulators (SERMs), representing the first application of CDC chemistry in natural product synthesis. The first stage of the two-step synthesis of coumestrol involved a modified aerobic oxidative cross-coupling between ethyl 2-(2,4-dimethoxybenzoyl)acetate and 3-methoxyphenol, with FeCl3 (10 mol%) as the catalyst. The benzofuran coupling product was then subjected to sequential deprotection and lactonization steps, affording the natural product in 59% overall yield. Based on this new methodology other coumestrol analogues were prepared, and their effects on the proliferation of the estrogen receptor (ER)-dependent MCF-7 and of the ER-independent MDA-MB-231 breast cancer cells were tested. As a result, new types of estrogen receptor ligands having an acetamide group instead of the 9-hydroxyl group of coumestrol were discovered. Both 9-acetamido-coumestrol and 8-acetamidocoumestrol were found more active than the natural product against estrogen-dependent MCF-7 breast cancer cells, with IC50 values of 30 and 9 nM, respectively. PMID:23946113

Kshirsagar, Umesh A; Parnes, Regev; Goldshtein, Hagit; Ofir, Rivka; Zarivach, Raz; Pappo, Doron

2013-09-27

397

Large-scale synthesis of TiO2 microspheres with hierarchical nanostructure for highly efficient photodriven reduction of CO2 to CH4.  

PubMed

In this study, a simple and reproducible synthesis strategy was employed to fabricate TiO2 microspheres with hierarchical nanostructure. The microspheres are macroscopic in the bulk particle size (several hundreds to more than 1000 ?m), but they are actually composed of P25 nanoparticles as the building units. Although it is simple in the assembly of P25 nanoparticles, the structure of the as-prepared TiO2 microspheres becomes unique because a hierarchical porosity composed of macropores, larger mesopores (ca. 12.4 nm), and smaller mesopores (ca. 2.3 nm) has been developed. The interconnected macropores and larger mesopores can be utilized as fast paths for mass transport. In addition, this hierarchical nanostructure may also contribute to some extent to the enhanced photocatalytic activity due to increased multilight reflection/scattering. Compared with the state-of-the-art photocatalyst, commercial Degussa P25 TiO2, the as-prepared TiO2 microsphere catalyst has demonstrated significant enhancement in photodriven conversion of CO2 into the end product CH4. Further enhancement in photodriven conversion of CO2 into CH4 can be easily achieved by the incorporation of metals such as Pt. The preliminary experiments with Pt loading reveal that there is still much potential for considerable improvement in TiO2 microsphere based photocatalysts. Most interestingly and significantly, the synthesis strategy is simple and large quantity of TiO2 microspheres (i.e., several hundred grams) can be easily prepared at one time in the lab, which makes large-scale industrial synthesis of TiO2 microspheres feasible and less expensive. PMID:25140917

Fang, Baizeng; Bonakdarpour, Arman; Reilly, Kevin; Xing, Yalan; Taghipour, Fariborz; Wilkinson, David P

2014-09-10

398

Efficient synthesis of 2,3-disubstituted-2,3-dihydroquinazolin-4(1H)-ones catalyzed by dodecylbenzenesulfonic acid in aqueous media under ultrasound irradiation.  

PubMed

Synthesis of 2,3-disubstituted-2,3-dihydroquinazolin-4(1H)-one derivatives catalyzed by dodecylbenzenesulfonic acid was carried out in 80-92% yields at 40-42°C within 1-2h in aqueous media via one-pot three-component condensation of isatoic anhydride, aromatic aldehyde and amine under ultrasound irradiation. Convenient work-up procedures, mild reaction conditions, avoiding the use of organic solvents, and friendly to environment are the salient features of this protocol. PMID:25224856

Chen, Bao-Hua; Li, Ji-Tai; Chen, Guo-Feng

2015-03-01

399

Three Component Reaction: An Efficient Synthesis and Reactions of 3,4-Dihydropyrimidin-2(1H)-Ones and Thiones Using New Natural Catalyst.  

PubMed

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

400

Yttria-Zirconia–Based Lewis Acid Catalysis of the Biginelli Reaction: An Efficient One-Pot Synthesis of 3,4-Dihydropyrimidin-2-(1H)-ones  

Microsoft Academic Search

Yttria-zirconia–based Lewis acid efficiently catalyzes the three-component cyclocondensation reaction of aldehyde, ?-keto ester, and urea or thiourea in refluxing acetonitrile to produce the corresponding dihydropyrimidones in high yields.

S. Ramalingam; Pradeep Kumar

2009-01-01

401

An efficient synthesis of 3-OBn-6?,14-epoxy-bridged opiates from naltrexone and identification of a related dual MOR inverse agonist/KOR agonist.  

PubMed

In an effort to better understand the conformational preferences that inform the biological activity of naltrexone and related naltrexol derivatives, a new synthesis of the restricted analog 3-OBn-6?,14-epoxymorphinan 4 is described. 4 was synthesized starting from naltrexone in 50% overall yield, proceeding through the OBn-6?-triflate intermediate 8. Key steps to the synthesis include benzylation (96% yield), reduction (90% yield, ?:?:3:2), followed by a one-pot triflation/displacement sequence (96% yield) to yield the desired bridged epoxy derivative 4. X-ray crystallographic analysis of intermediate 3-OBn-6?-naltrexol 7a supports population of the key boat conformation required for the epoxy ring closure. We also report that the 6?-mesylate 10-a high affinity opioid receptor ligand, the epimeric derivative of 11, and an analog of 12-functions as an inverse agonist at the mu opioid receptor using herkinorin pre-conditioned cells and an agonist at the kappa opioid receptor when evaluated in independent in vitro [(35)S]-GTP-?-S assays. PMID:22771010

Martin, David J; FitzMorris, Paul E; Li, Bo; Ayestas, Mario; Sally, Ellicott J; Dersch, Christina M; Rothman, Richard B; Deveau, Amy M

2012-11-15

402

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

403

A novel sodium iodide and ammonium molybdate co-catalytic system for the efficient synthesis of 2-benzimidazoles using hydrogen peroxide under ultrasound irradiation.  

PubMed

The reaction of aldehydes and o-phenylenediamine for the preparation of 2-benzimidazoles has been studied using hydrogen peroxide as an oxidant under ultrasound irradiation at room temperature in this paper. The combination of substoichiometric sodium iodide and ammonium molybdate as co-catalysts, together with using small amounts of hydrogen peroxide, makes this transformation very efficient and attractive under ultrasound. Thus, a mild, green and efficient method is established to carry out this reaction in high yield. PMID:24074960

Bai, Guo-Yi; Lan, Xing-Wang; Chen, Guo-Feng; Liu, Xiao-Fang; Li, Tian-Yu; Shi, Ling-Juan

2014-03-01

404

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

405

One-pot green synthesis of Prussian blue nanocubes decorated reduced graphene oxide using mushroom extract for efficient 4-nitrophenol reduction.  

PubMed

One-pot green approach to the synthesis of Prussian blue nanocubes/reduced graphene oxide (PBNCs/RGO) nanocomposite had been attempted. It was based on the extract of mushroom with K3[Fe(CN)6] and graphene oxide (GO) as precursors, where the reduction of GO and the deposition of PBNCs occurred simultaneously. The obtained nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and electrochemical techniques. With the introduction of ?-cyclodextrin (?-CD), the ?-CD/PBNCs/RGO system showed linear behavior in the range from 0.01 to 700?M for 4-nitrophenol with a low detection limit of 2.34nM (S/N=3). PMID:25467506

Chen, Ruixue; Zhang, Qiuping; Gu, Yue; Tang, Liu; Li, Cong; Zhang, Zhiquan

2015-01-01

406

Synthesis and pharmacokinetics of valopicitabine (NM283), an efficient prodrug of the potent anti-HCV agent 2'-C-methylcytidine.  

PubMed

In our search for new therapeutic agents against chronic hepatitis C, a ribonucleoside analogue, 2'-C-methylcytidine, was discovered to be a potent and selective inhibitor in cell culture of a number of RNA viruses, including the pestivirus bovine viral diarrhea virus, a surrogate model for hepatitis C virus (HCV), and three flaviviruses, namely, yellow fever virus, West Nile virus, and dengue-2 virus. However, pharmacokinetic studies revealed that 2'-C-methylcytidine suffers from a low oral bioavailability. To overcome this limitation, we have synthesized the 3'-O-l-valinyl ester derivative (dihydrochloride form, valopicitabine, NM283) of 2'-C-methylcytidine. We detail herein for the first time the chemical synthesis and physicochemical characteristics of this anti-HCV prodrug candidate, as well as a comparative study of its pharmacokinetic parameters with those of its parent nucleoside analogue, 2'-C-methylcytidine. PMID:17064080

Pierra, Claire; Amador, Agnès; Benzaria, Samira; Cretton-Scott, Erika; D'Amours, Marc; Mao, John; Mathieu, Steven; Moussa, Adel; Bridges, Edward G; Standring, David N; Sommadossi, Jean-Pierre; Storer, Richard; Gosselin, Gilles

2006-11-01

407

Efficient one-pot synthesis of hierarchical flower-like ?-Fe2O3 hollow spheres with excellent adsorption performance for water treatment  

NASA Astrophysics Data System (ADS)

A simple one-step method has been developed for the controllable synthesis of hierarchical flower-like ?-Fe2O3 hollow spheres in a glycerol-ethanol system. It is found that the volume ratio of glycerol/ethanol and reaction time have a significant effect on the morphology of the products. The growth process of ?-Fe2O3 hollow spheres has been investigated and a possible mechanism is proposed. The ?-Fe2O3 hollow spheres have a high surface area of 98 m2 g-1 and a total pore volume of 0.32 cm3 g-1, which exhibit outstanding water treatment performance with high removal capacities toward organic dyes and heavy metal ions. The as-obtained products may have potential applications in water treatment and other related micro- or nanoscale devices.

Zhu, Daozheng; Zhang, Jian; Song, Jiming; Wang, Haisheng; Yu, Zheng; Shen, Yuhua; Xie, Anjian

2013-11-01

408

Efficient construction of pyrano[3,2-a]carbazoles: application to a biomimetic total synthesis of cyclized monoterpenoid pyrano[3,2-a]carbazole alkaloids.  

PubMed

We have developed a highly efficient route to 2-hydroxy-3-methylcarbazole (1) via a palladium-catalyzed construction of the carbazole skeleton. Using 1 as relay compound, different methods for annulations of pyran rings by reaction with terpenoid building blocks have been tested. The Lewis acid promoted reaction of 1 with prenal (21) opened up an efficient route to girinimbine (3) and the corresponding reaction with citral (25) afforded mahanimbine (5). Oxidation of compounds 3 and 5 provided murrayacine (4) and murrayacinine (6). Following the biogenetic proposal, mahanimbine (5) has been exploited for efficient biomimetic syntheses of the cyclized monoterpenoid pyrano[3,2-a]carbazole alkaloids cyclomahanimbine (7), mahanimbidine (8) and bicyclomahanimbine (9). The interconversions of 5, 7, 8 and 9 are described and mechanistic implications are discussed. Structural assignments are unambiguously verified by X-ray crystal structure determinations. Moreover, cyclomahanimbine (7) was transformed into murrayazolinine (10) and exozoline (11). PMID:24030919

Hesse, Ronny; Gruner, Konstanze K; Kataeva, Olga; Schmidt, Arndt W; Knölker, Hans-Joachim

2013-10-11

409

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

410

One-pot synthesis of nitrogen and sulfur co-doped graphene as efficient metal-free electrocatalysts for the oxygen reduction reaction.  

PubMed

Novel N, S co-doped graphene (NSG) was prepared by annealing graphene oxide with thiourea as the single N and S precursor. The NSG electrodes, as efficient metal-free electrocatalysts, show a direct four-electron reaction pathway, high onset potential, high current density and high stability for the oxygen reduction reaction. PMID:24687131

Wang, Xin; Wang, Jie; Wang, Deli; Dou, Shuo; Ma, Zhaoling; Wu, Jianghong; Tao, Li; Shen, Anli; Ouyang, Canbin; Liu, Qiuhong; Wang, Shuangyin

2014-05-14

411

Synthesis of aminoacylated N6,N6-dimethyladenosine solid support for efficient access to hydrolysis-resistant 3?-charged tRNA mimics  

PubMed Central

RNA-amino acid and RNA-peptide conjugates that mimic charged tRNA 3?-ends are valuable substrates for structural and functional investigations of ribosomal complexes. To obtain such conjugates, most synthetic approaches that are found in the literature make use of puromycin. This well available aminonucleoside antibiotic contains a dimethylamino group at the nucleobase and a methylated tyrosine that is connected via an amide linkage to the ribose moiety. To increase structural diversity, we present the synthesis of a N6,N6-dimethylated 3?-azido-3?-deoxyadenosine precursor that can be coupled to any amino acid. Further derivatization results in the solid support that is eligible for the preparation of stable 3?-aminoacyl- or 3?-peptidyl-tRNA termini with an amide instead of the natural ester linkage. The present work expands our previously established route that delivered a broad range of peptidyl-tRNA mimics to the corresponding counterparts with N6,N6-dimethylation pattern of the terminal adenosine (A76). This aspect is of significance to modulate the binding preferences of the mimics for ribosomal A- versus P-site. PMID:25457127

Neuner, Sandro; Micura, Ronald

2014-01-01

412

Supported heteropoly acids offering strong option for efficient and cleaner processing for the synthesis of imidazole derivatives under solvent-free condition.  

PubMed

A series of 12-phosphotungstic acid (PWA) supported on various porous carriers, such as silica, alumina, titania, clay, and carbon were prepared, and their catalytic performance evaluated in the synthesis of imidazoles in solvent-free condition. It was found that PWA supported on silica (PWA/SiO(2)) showed higher activity compared to other catalysts. The observed behavior has more or less correlated with the acidic characteristic found through the potentiometrically titrated acidic sites and proton availability. The catalyst was characterized by FTIR, XRD, TGA/DSC, BET, and SEM. The presence of the Keggin structure can be followed by the above techniques, eliminating any doubt about the collapse of the supported anion. It can be observed that the process tolerates both electron donating and electron withdrawing substituents on the aldehyde with both benzil and benzoin. The general applicability of the method is demonstrated by using both benzylic and aromatic amines. The yields obtained were excellent without forming any side products such as trisubstituted imidazoles, which are normally produced in the presence of strong acids. The protocol developed using PWA/SiO(2) is superior in terms of process simplicity, reusable catalyst, high yields, short reaction time, and preclusion of toxic solvent. PMID:20101458

Rafiee, Ezzat; Mahdavi, Houri; Joshaghani, Mohammad

2011-02-01

413

An efficient chiral moderator prepared from inexpensive (+)-3-carene: synthesis of the HIV-1 non-nucleoside reverse transcriptase inhibitor DPC 963.  

PubMed

The beta-amino alcohol 4 beta-morpholinocaran-3 alpha-ol is prepared by addition of morpholine to alpha-3,4-epoxycarane utilizing anhydrous magnesium bromide as Lewis acid promoter. The enantiopure amino alcohol is uniquely effective as a chiral moderator for the addition of lithium cyclopropylacetylide to an unprotected N-acylketimine. This reaction provides an efficient route to the second generation NNRTI drug candidate DPC 963. PMID:11009360

Kauffman, G S; Harris, G D; Dorow, R L; Stone, B R; Parsons, R L; Pesti, J A; Magnus, N A; Fortunak, J M; Confalone, P N; Nugent, W A

2000-10-01

414

Phototandem Catalysis: Efficient Synthesis of 3-Ester-3-hydroxy-2-oxindoles by a Visible Light-Induced Cyclization of Diazoamides through an Aerobic Oxidation Sequence.  

PubMed

An unprecedented phototandem catalysis based on a single iridium photocatalyst has been successfully developed. This powerful strategy consists of two mechanistically distinct catalytic cycles, namely, photocatalytic energy transfer (ET) and single electron transfer (SET). The novel protocol allows a rapid and efficient construction of biologically and synthetically important 3-ester-3-hydroxy-2-oxindole derivatives from readily available diazoamides through a cyclization/aerobic oxidation sequence under very mild conditions. PMID:25294598

Xia, Xu-Dong; Ren, Yan-Liang; Chen, Jia-Rong; Yu, Xing-Long; Lu, Liang-Qiu; Zou, You-Quan; Wan, Jian; Xiao, Wen-Jing

2015-01-01

415

Synthesis of FeCo nanocrystals encapsulated in nitrogen-doped graphene layers for use as highly efficient catalysts for reduction reactions.  

PubMed

A facile strategy to fabricate FeCo nanocrystals with nitrogen-doped graphene shells has been designed, which involves one-step thermal decomposition of Prussian blue analogue (PBA) Fe3[Co(CN)6]2 spheres. The as-prepared product can be used as a non-precious-metal catalyst with a highly efficient catalytic activity and a magnetically separable capability in the reduction of 4-nitrophenol. PMID:25429694

Hu, Lin; Zhang, Ruirui; Wei, Lingzhi; Zhang, Fapei; Chen, Qianwang

2015-01-14

416

Stereoselective introduction of two chiral centers by a single diketoreductase: an efficient biocatalytic route for the synthesis of statin side chains.  

PubMed

Statins, including atorvastatin (Lipitor), are the top-selling drugs in the world. The biocatalytic production of chiral side chains of statin drugs is of great interest to academia and industry. Stereoselective double reduction of a beta,delta-diketo ester catalyzed by a diketoreductase offers a simple and efficient route for the preparation of statin side chains. Comparison of different cofactor regeneration systems resulted in an easy and cost-effective process for this enzymatic reduction. PMID:19916068

Wu, Xuri; Wang, Lili; Wang, Shuzhen; Chen, Yijun

2010-06-01

417

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

418

One-step synthesis of highly efficient three-dimensional Cd1-xZnxS photocatalysts for visible light photocatalytic water splitting.  

PubMed

Visible light accounts for about 43% of the solar spectrum, and developing highly efficient visible-light-driven photocatalyst is of special significance. In this work, highly efficient three-dimensional (3D) Cd1-xZnxS photocatalysts for hydrogen generation under the irradiation of visible light were synthesized via one-step solvothermal pathway. Scanning electron microscope, X-ray diffractometer, Raman spectrometer, and X-ray photoelectron spectrometer were utilized to characterize the morphology, crystal structure, vibrational states, and surface composition of the obtained 3D Cd1-xZnxS. UV-Vis spectra indicated that the as-synthesized Cd1-xZnxS had appropriate bandgap and position of the conduction band that is beneficial for visible light absorption and photo-generated electron-hole pair separation. Moreover, the 3D structure offers a larger surface area thus supplying more surface reaction sites and better charge transport environment, and therefore, the efficiency of water splitting was improved further. PMID:23883429

Xiong, Zuzhou; Zheng, Maojun; Zhu, Changqing; Zhang, Bin; Ma, Li; Shen, Wenzhong

2013-01-01

419

Synthesis, optical and electrochemical properties of the A-?-D-?-A porphyrin and its application as an electron donor in efficient solution processed bulk heterojunction solar cells.  

PubMed

A conjugated acceptor-donor-acceptor (A-?-D-?-A) with the Zn-porphyrin core and the di-cyanovinyl substituted thiophene (A) connected at meso positions denoted as was designed and synthesized. The optical and electrochemical properties of were investigated. This new porphyrin exhibits a broad and intense absorption in the visible and near infrared regions. Bulk-heterojunction (BHJ) solution processed organic solar cells based on this porphyrin, as electron donor material, and PC71BM ([6,6]-phenyl C71 butyric acid methyl ester), as electron acceptor material, were fabricated using THF and a pyridine-THF solvent exhibiting a power conversion efficiency of 3.65% and 5.24%, respectively. The difference in efficiencies is due to the enhancement of the short circuit current Jsc and FF of the solar cell, which is ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and a better balanced charge transport in the device processed with the pyridine-THF solvent. PMID:25408154

Vijay Kumar, Challuri; Cabau, Lydia; Koukaras, Emmanuel N; Sharma, Ganesh D; Palomares, Emilio

2014-11-27

420

One-step synthesis of highly efficient three-dimensional Cd1-xZnxS photocatalysts for visible light photocatalytic water splitting  

PubMed Central

Visible light accounts for about 43% of the solar spectrum, and developing highly efficient visible-light-driven photocatalyst is of special significance. In this work, highly efficient three-dimensional (3D) Cd1?xZnxS photocatalysts for hydrogen generation under the irradiation of visible light were synthesized via one-step solvothermal pathway. Scanning electron microscope, X-ray diffractometer, Raman spectrometer, and X-ray photoelectron spectrometer were utilized to characterize the morphology, crystal structure, vibrational states, and surface composition of the obtained 3D Cd1?xZnxS. UV-Vis spectra indicated that the as-synthesized Cd1?xZnxS had appropriate bandgap and position of the conduction band that is beneficial for visible light absorption and photo-generated electron-hole pair separation. Moreover, the 3D structure offers a larger surface area thus supplying more surface reaction sites and better charge transport environment, and therefore, the efficiency of water splitting was improved further. PMID:23883429

2013-01-01

421

Synthesis, optical and electrochemical properties of the A-?-D-?-A porphyrin and its application as an electron donor in efficient solution processed bulk heterojunction solar cells  

NASA Astrophysics Data System (ADS)

A conjugated acceptor-donor-acceptor (A-?-D-?-A) with the Zn-porphyrin core and the di-cyanovinyl substituted thiophene (A) connected at meso positions denoted as VC62 was designed and synthesized. The optical and electrochemical properties of VC62 were investigated. This new porphyrin exhibits a broad and intense absorption in the visible and near infrared regions. Bulk-heterojunction (BHJ) solution processed organic solar cells based on this porphyrin, as electron donor material, and PC71BM ([6,6]-phenyl C71 butyric acid methyl ester), as electron acceptor material, were fabricated using THF and a pyridine-THF solvent exhibiting a power conversion efficiency of 3.65% and 5.24%, respectively. The difference in efficiencies is due to the enhancement of the short circuit current Jsc and FF of the solar cell, which is ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and a better balanced charge transport in the device processed with the pyridine-THF solvent.

Vijay Kumar, Challuri; Cabau, Lydia; Koukaras, Emmanuel N.; Sharma, Ganesh D.; Palomares, Emilio

2014-11-01

422

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

423

Magnetic Cross-Linked Enzyme Aggregates (mCLEAs) of Candida antarctica Lipase: An Efficient and Stable Biocatalyst for Biodiesel Synthesis  

PubMed Central

Enzyme-catalyzed production of biodiesel is the object of extensive research due to the global shortage of fossil fuels and increased environmental concerns. Herein we report the preparation and main characteristics of a novel biocatalyst consisting of Cross-Linked Enzyme Aggregates (CLEAs) of Candida antarctica lipase B (CALB) which are covalently bound to magnetic nanoparticles, and tackle its use for the synthesis of biodiesel from non-edible vegetable and waste frying oils. For this purpose, insolubilized CALB was covalently cross-linked to magnetic nanoparticles of magnetite which the surface was functionalized with –NH2 groups. The resulting biocatalyst combines the relevant catalytic properties of CLEAs (as great stability and feasibility for their reutilization) and the magnetic character, and thus the final product (mCLEAs) are superparamagnetic particles of a robust catalyst which is more stable than the free enzyme, easily recoverable from the reaction medium and reusable for new catalytic cycles. We have studied the main properties of this biocatalyst and we have assessed its utility to catalyze transesterification reactions to obtain biodiesel from non-edible vegetable oils including unrefined soybean, jatropha and cameline, as well as waste frying oil. Using 1% mCLEAs (w/w of oil) conversions near 80% were routinely obtained at 30°C after 24 h of reaction, this value rising to 92% after 72 h. Moreover, the magnetic biocatalyst can be easily recovered from the reaction mixture and reused for at least ten consecutive cycles of 24 h without apparent loss of activity. The obtained results suggest that mCLEAs prepared from CALB can become a powerful biocatalyst for application at industrial scale with better performance than those currently available. PMID:25551445

Cruz-Izquierdo, Álvaro; Picó, Enrique A.; López, Carmen; Serra, Juan L.; Llama, María J.

2014-01-01

424

Facile synthesis of organic-inorganic layered nanojunctions of g-C3N4/(BiO)2CO3 as efficient visible light photocatalyst.  

PubMed

Novel g-C3N4/(BiO)2CO3 organic-inorganic nanojunctioned photocatalysts were synthesized by in situ depositing (BiO)2CO3 nanoflakes onto the surface of g-C3N4 nanosheets through a one-pot efficient capture of atmospheric CO2 method at room temperature. The as-synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (DRS), N2 adsorption-desorption analysis and electron spin resonance (ESR). The photocatalytic activity of as-synthesized samples was evaluated by degrading Rhodamine B (RhB) and phenol in aqueous solution under visible-light irradiation. The g-C3N4/(BiO)2CO3 nanojunctions showed much higher visible-light photocatalytic activity than those of pure g-C3N4 and (BiO)2CO3 for the degradation of RhB and phenol. The enhanced photocatalytic activity can be mainly ascribed to the well-matched band structures, dye photosensitization and efficient crystal facets coupling interaction between g-C3N4 {002} and (BiO)2CO3 {002}. The ?O2(-) radicals were identified as the main active species. Furthermore, the pure (BiO)2CO3 with highly exposed {002} crystal facets also exhibited excellent visible-light photoactivity for the degradation of RhB, which can be originated from the indirect dye photosensitization. The present work could provide a new strategy for the efficient utilization of atmospheric CO2 in green synthetic chemistry. PMID:24975506

Zhang, Wendong; Sun, Yanjuan; Dong, Fan; Zhang, Wei; Duan, Shuo; Zhang, Qin

2014-08-21

425

The Efficient Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones and Their Sulfur Derivatives with H2SO4 Immobilized on Activated Charcoal  

Microsoft Academic Search

Various 3,4-dihydropyrimidin-2-(1H)-ones (DHPMs) and their sulfur derivatives were efficiently synthesized by a one-pot cyclocondensation reaction of aromatic and aliphatic aldehydes, ?-dicarbonyl compounds and urea (or thiourea) in the presence of sulfuric acid immobilized on activated charcoal (133% w\\/w). The reactions were carried out in refluxing n-hexane-acetonitrile (2.5:0.5 mL) within 5–150 min to give 3,4-dihydropyrimidinones (or thiones) in high to excellent

Karim Akbari Dilmaghani; Behzad Zeynizadeh; Hadi Parasajam

2012-01-01

426

Fine-tuning Interaction between Aminoacyl-tRNA Synthetase and tRNA for Efficient Synthesis of Proteins Containing Unnatural Amino Acids.  

PubMed

By using a directed evolution approach, we have identified aminoacyl-tRNA synthetase variants with significantly enhanced activity for the incorporation of unnatural amino acids into proteins in response to the amber nonsense codon in bacteria. We demonstrated that the optimization of anticodon recognition of tRNA by aminoacyl-tRNA synthetase led to improved incorporation efficiency that is unnatural amino acid-specific. The findings will facilitate the creation of an optimized system for the genetic incorporation of unnatural amino acids in bacteria. PMID:24847685

Wang, Nanxi; Ju, Tong; Niu, Wei; Guo, Jiantao

2014-05-23

427

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

428

Highly efficient click labeling using 2-[18F]fluoroethyl azide and synthesis of an 18F N-hydroxysuccinimide ester as conjugation agent  

PubMed Central

Introduction Click labeling using 2-[18F]fluoroethyl azide has been proven to be promising methods of radiolabeling small molecules and peptides, some of which are undergoing clinical evaluations. However, the previously reported method afforded low yield, poor purities and under desirable reproducibility. Methods A vacuum distillation method was used to isolate 2-[18F]fluoroethyl azide, and the solvent effect of acetonitrile (ACN) and dimethylformamide (DMF) on the click labeling using Cu(I) from copper sulfate/sodium ascorbate was studied. The labeling conditions were optimized to radiosynthesize a hydroxysuccinimide ester (NHS). Results 2-[18F]fluoroethyl azide was isolated by the vacuum distillation method with > 80% yield within 10 min in a “pure” and click-ready form. It was found that the amount of DMF was critical for maintaining high levels of Cu(I) from copper sulfate/sodium ascorbate in order to rapidly complete the click labeling reaction. The addition of bathophenanthrolinedisulfonic acid disodium salt (BPDS) to the mixture of copper sulfate/sodium ascorbate also greatly improved the click labeling efficiency. Through exploiting these optimizations, a base-labile N-hydroxysuccinimide (NHS) ester was rapidly radiosynthesized in 90% isolated yield with good chemical and radiochemical purities. Conclusions We have developed a general method to click-label small molecules efficiently using [18F]2 for research and clinical use. This NHS ester can be used for conjugation chemistry to label antibodies, peptides and small molecules as PET tracers. PMID:22770647

Zhou, Dong; Chu, Wenhua; Dence, Carmen S.; Mach, Robert H.; Welch, Michael J.

2012-01-01

429

Synthesis of FeCo nanocrystals encapsulated in nitrogen-doped graphene layers for use as highly efficient catalysts for reduction reactions  

NASA Astrophysics Data System (ADS)

A facile strategy to fabricate FeCo nanocrystals with nitrogen-doped graphene shells has been designed, which involves one-step thermal decomposition of Prussian blue analogue (PBA) Fe3[Co(CN)6]2 spheres. The as-prepared product can be used as a non-precious-metal catalyst with a highly efficient catalytic activity and a magnetically separable capability in the reduction of 4-nitrophenol.A facile strategy to fabricate FeCo nanocrystals with nitrogen-doped graphene shells has been designed, which involves one-step thermal decomposition of Prussian blue analogue (PBA) Fe3[Co(CN)6]2 spheres. The as-prepared product can be used as a non-precious-metal catalyst with a highly efficient catalytic activity and a magnetically separable capability in the reduction of 4-nitrophenol. Electronic supplementary information (ESI) available: Experimental details and characterization; Fig. S1-S15. See DOI: 10.1039/c4nr05570e

Hu, Lin; Zhang, Ruirui; Wei, Lingzhi; Zhang, Fapei; Chen, Qianwang

2014-12-01

430

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

431

A facile and green method for synthesis of reduced graphene oxide/Ag hybrids as efficient surface enhanced Raman scattering platforms.  

PubMed

Reduced graphene oxide/Ag nanoparticles hybrids (rGO/AgNPs) were fabricated via a green and facile hydrothermal method. The as-synthesized materials were characterized in detail using various spectroscopic and microscopic techniques. Under a suitable dosage of silver ions, well-dispersed AgNPs on the reduced graphene oxide sheets were obtained. The surface plasmon resonance properties of AgNPs on graphene show that there is an interaction between AgNPs and graphene. Trace detection of organic dyes is studied based on rGO/AgNPs hybrids as efficient surface enhanced Raman scattering platforms. It has been found that the suitable experiment parameter is crucial to trace detection of organic dyes molecules. This work is of importance in the practical application in device-design based on the SERS effect of noble metal/reduced oxide graphene (or oxide graphene) hybrids. PMID:25262484

Huang, Qingli; Wang, Jiaming; Wei, Wenxian; Yan, Qiuxiang; Wu, Changle; Zhu, Xiashi

2015-02-11

432

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

433

A versatile cyclic 2,2'-azobenzenophane with a functional handle and its polymers: efficient synthesis and effect of topological structure on chiroptical properties.  

PubMed

Two novel cyclic azobenzenophanes (SC, RC) with functional handles have been synthesized efficiently by a Glaser coupling reaction. Through a Suzuki coupling reaction, alternating ring/linear polymers with rigid (conjugated)/flexible (unconjugated) bridges were obtained from the resultant cyclic azobenzenophanes. The optical activities of linear, cyclic, and macromolecular binaphethyl-azobenzene derivatives were investigated by UV/Vis and circular dichroism (CD) spectra and the time-dependent (TD)-DFT method. Experimental results and theoretical analyses indicated that the cyclic configurations exhibited better chiroptical features than the others, and the reverse conformation and difference of dextro-/levo-rotation of azobenzenophanes were detected by comparing linear and cyclic structures, which provides an opportunity for the optical-rotation-controlled "smart" materials systems in future. PMID:25510346

Lu, Jinjie; Xia, Aiyou; Zhou, Nianchen; Zhang, Wei; Zhang, Zhengbiao; Pan, Xiangqiang; Yang, Yonggang; Wang, Yong; Zhu, Xiulin

2015-02-01

434

One-pot synthesis of nitrogen and sulfur co-doped onion-like mesoporous carbon vesicle as an efficient metal-free catalyst for oxygen reduction reaction in alkaline solution  

NASA Astrophysics Data System (ADS)

Nitrogen and sulfur co-doped onion-like mesoporous carbon vesicle (NS-MCV) with multilayer lamellar structure is synthesized as a metal-free catalyst through a convenient and economical procedure. The synthesized materials are systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrate that N and S atoms can be successfully doped into the framework of MCV with little impact on the morphology and structure. The NS-MCV manifests a remarkably high electrocatalytic activity as a metal-free electrocatalyst for the oxygen reduction reaction (ORR) with mainly a four-electron transfer pathway. Moreover, in contrast to the commercially available Pt/C catalyst, the NS-MCV shows much better long-term stability and tolerance toward methanol crossover in an alkaline medium. Such excellent performances can be mainly attributed to the synergistic effect arising from the addition of N and S heteroatom, optimized S content and high surface area. The NS-MCV with a simple synthesis method may further exploited as potentially efficient and inexpensive metal-free ORR catalyst materials.

Han, Ce; Bo, Xiangjie; Zhang, Yufan; Li, Mian; Guo, Liping

2014-12-01

435

An efficient and user-friendly method for the synthesis of hexagonal-phase NaYF4:Yb, Er/Tm nanocrystals with controllable shape and upconversion fluorescence  

NASA Astrophysics Data System (ADS)

Hexagonal-phase NaYF4:Yb, Er/Tm nanocrystals are the best IR-to-visible upconverting materials to date, but user-friendly methods for making pure hexagonal-phase NaYF4:Yb, Er/Tm nanocrystals with upconversion fluorescence are still lacking. Most of the methods reported so far require excess fluoride reactants in a high-temperature reaction which are very unfriendly to users and raise safety concerns. In this work, an efficient and user-friendly method was developed for the synthesis of uniform hexagonal-phase NaYF4:Yb, Er/Tm nanocrystals with upconversion fluorescence, by forming small solid-state crystal nuclei and further growth and ripening of the nuclei. NaYF4:Yb, Er/Tm nanoplates, nanospheres and nanoellipses were also selectively produced by varying the concentration of the surfactant. All the nanocrystals showed strong upconversion fluorescence, and fluorescence from the nanoplates was observed even when the laser power density was reduced to about 50 mW cm-2. These nanocrystals have great potential for use in biology and medicine as fluorescent labels or imaging probes.

Li, Zhengquan; Zhang, Yong

2008-08-01

436

The Environment of "Mycobacterium avium subsp. hominissuis" Microaggregates Induces Synthesis of Small Proteins Associated with Efficient Infection of Respiratory Epithelial Cells.  

PubMed

"Mycobacterium avium subsp. hominissuis" is an opportunistic environmental pathogen that causes respiratory illness in immunocompromised patients, such as those with cystic fibrosis as well as other chronic respiratory diseases. Currently, there is no efficient approach to prevent or treat M. avium subsp. hominissuis infection in the lungs. During initial colonization of the airways, M. avium subsp. hominissuis forms microaggregates composed of 3 to 20 bacteria on human respiratory epithelial cells, which provides an environment for phenotypic changes leading to efficient mucosal invasion in vitro and in vivo. DNA microarray analysis was employed to identify genes associated with the microaggregate phenotype. The gene encoding microaggregate-binding protein 1 (MBP-1) (MAV_3013) is highly expressed during microaggregate formation. When expressed in noninvasive Mycobacterium smegmatis, MBP-1 increased the ability of the bacteria to bind to HEp-2 epithelial cells. Using anti-MBP-1 immune serum, microaggregate binding to HEp-2 cells was significantly reduced. By far-Western blotting, and verified by coimmunoprecipitation, we observed that MBP-1 interacts with the host cytoskeletal protein vimentin. As visualized by confocal microscopy, microaggregates, as well as MBP-1, induced vimentin polymerization at the site of bacterium-host cell contact. Binding of microaggregates to HEp-2 cells was inhibited by treatment with an antivimentin antibody, suggesting that MBP-1 expression is important for M. avium subsp. hominissuis adherence to the host cell. MBP-1 immune serum significantly inhibited M. avium subsp. hominissuis infection throughout the respiratory tracts of mice. This study characterizes a pathogenic mechanism utilized by M. avium subsp. hominissuis to bind and invade the host respiratory epithelium, suggesting new potential targets for the development of antivirulence therapy. PMID:25422262

Babrak, Lmar; Danelishvili, Lia; Rose, Sasha J; Kornberg, Tiffany; Bermudez, Luiz E

2015-02-01

437

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

438

Energetic analysis of ammonia synthesis unit  

Microsoft Academic Search

In order to identify possible reserves in the ammonia synthesis, an exergetic analysis was made of the stages of nitrogen-hydrogen compression, ammonia synthesis and separation at an operating plant. The analysis showed that the unit has a relatively low degree of thermodynamic completeness: the target exergetic efficiency of the stages studied is 0.26. The margins for improvement are not great.

G. A. Britina; I. L. Leites; S. A. Mikhailova; M. B. Aizenbud

1977-01-01

439

Synthesis of Psymberin Analogs  

PubMed Central

In this communication we describe an efficient synthesis of ‘psympederin’, a hybrid between the novel antitumor natural product psymberin and the blister beetle toxin pederin. Evaluation of antiproliferative activity reveals that the dihydroisocoumarin fragment is important for psymberin toxicity and the cyclic pederate fragment is important for pederin/mycalamide toxicity. Based on preliminary results described herein, we speculate that, despite their structural resemblance, psymberin and pederin/mycalamide induce toxicity through different mechanisms. PMID:17217271

Jiang, Xin; Williams, Noelle; De Brabander, Jef K.

2008-01-01

440

The reaction of primary aromatic amines with alkylene carbonates for the selective synthesis of bis-N-(2-hydroxy)alkylanilines: the catalytic effect of phosphonium-based ionic liquids.  

PubMed

At T? 140 °C, different primary aromatic amines (pX-C(6)H(4)NH(2); X = H, OCH(3), CH(3), Cl) react with both ethylene- and propylene-carbonates to yield a chemoselective N-alkylation process: bis-N-(2-hydroxyalkyl)anilines [pX-C(6)H(4)N(CH(2)CH(R)OH)(2); R = H, CH(3)] are the major products and the competitive formation of carbamates is substantially ruled out. At 140 °C, under solventless conditions, the model reaction of aniline with ethylene carbonate goes to completion by simply mixing stoichiometric amounts of the reagents. However, a class of phosphonium ionic liquids (PILs) such as tetraalkylphosphonium halides and tosylates turn out to be active organocatalysts for both aniline and other primary aromatic amines. A kinetic analysis monitored by (13)C NMR spectroscopy, shows that bromide exchanged PILs are the most efficient systems, able to impart a more than 8-fold acceleration to the reaction. The reactions of propylene carbonate take place at a higher temperature than those of ethylene carbonate, and only in the presence of PIL catalysts. A mechanism based on the Lewis acidity of tetraalkylphosphonium cations and the nucleophilicity of halide anions has been proposed to account for both the reaction chemoselectivity and the function of the catalysts. PMID:20844790

Selva, Maurizio; Fabris, Massimo; Lucchini, Vittorio; Perosa, Alvise; Noè, Marco

2010-11-21

441

Rational design of hyperbranched 3D heteroarrays of SrS/CdS: synthesis, characterization and evaluation of photocatalytic properties for efficient hydrogen generation and organic dye degradation  

NASA Astrophysics Data System (ADS)

Hyperbranched 3D SrS/CdS nanostructures were synthesized using a one pot hydrothermal method. Transmission Electron Microscopy (TEM) and Field Emission-Scanning Electron Microscopy (FE-SEM) analysis showed the formation of flower-like structure and the crystalline phase was confirmed by powder X-ray diffraction. The prepared 3D SrS/CdS exhibited improved photocatalytic activity for water splitting leading to H2 generation (AQY 10%) and nearly complete degradation of methyl orange (MO) dye. The dye degradation followed first order kinetics and the apparent reaction rate constant (kapp) was 0.136 min-1. The present 3D SrS/CdS structure promise to be efficient photocatalysts due to (i) the facile intersystem charge transfer resulting from their band alignment (ii) enhanced specific surface area and (iii) crystallinity.Hyperbranched 3D SrS/CdS nanostructures were synthesized using a one pot hydrothermal method. Transmission Electron Microscopy (TEM) and Field Emission-Scanning Electron Microscopy (FE-SEM) analysis showed the formation of flower-like structure and the crystalline phase was confirmed by powder X-ray diffraction. The prepared 3D SrS/CdS exhibited improved photocatalytic activity for water splitting leading to H2 generation (AQY 10%) and nearly complete degradation of methyl orange (MO) dye. The dye degradation followed first order kinetics and the apparent reaction rate constant (kapp) was 0.136 min-1. The present 3D SrS/CdS structure promise to be efficient photocatalysts due to (i) the facile intersystem charge transfer resulting from their band alignment (ii) enhanced specific surface area and (iii) crystallinity. Electronic supplementary information (ESI) available: Schematic experimental setup for photocatalytic hydrogen generation, TEM of CdS NWs and SrS NPs, FESEM images of 3D SrS/CdS, Low resolution TEM images for 3D SrS/CdS, EDX and SAED, SEM of SrS/CdS at different ratios, progress of hydrogen production at different time interval, different UV-Vis absorption spectra of MO. See DOI: 10.1039/c2nr30666b

Khan, Ziyauddin; Chetia, Tridip Ranjan; Qureshi, Mohammad

2012-05-01

442

One-pot Synthesis of CdS Nanocrystals Hybridized with Single-Layer Transition-Metal Dichalcogenide Nanosheets for Efficient Photocatalytic Hydrogen Evolution.  

PubMed

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition-metal dichalcogenides (TMDs) showed outstanding performance as co-catalysts for the hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for the HER still remains challenge. Here, a facile one-pot wet-chemical method is developed to prepare MS2 -CdS (M=W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4-10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2 -CdS nanohybrids possess a large number of edge sites in the MS2 layers, which are active sites for the HER. The photocatalytic performances of WS2 -CdS and MoS2 -CdS nanohybrids towards the HER under visible light irradiation (>420 nm) are about 16 and 12 times that of pure CdS, respectively. Importantly, the MS2 -CdS nanohybrids showed enhanced stability after a long-time test (16 h), and 70?% of catalytic activity still remained. PMID:25470356

Chen, Junze; Wu, Xue-Jun; Yin, Lisha; Li, Bing; Hong, Xun; Fan, Zhanxi; Chen, Bo; Xue, Can; Zhang, Hua

2014-12-01

443

Facile method for synthesis of TiO{sub 2} film and its application in high efficiency dye sensitized-solar cell (DSSC)  

SciTech Connect

Dye-sensitized solar cells (DSSC) is a device which converts a solar energy to electrical energy. Different with semiconductor thin film based solar cell, DSSC utilize the sensitized-dye to absorb the photon and semiconductor such as titanium dioxide (TiO{sub 2}) and zinc oxide (ZnO) as a working electrode photoanode. In this report, the preparation of TiO{sub 2} film using a facile method of spray deposition and its application in DSSC have been presented. TiO{sub 2} photoanode was synthesized by growing the droplet of titanium tetraisopropoxide diluted in acid solution on the substrate of conductive glass flourine-doped tin oxide (FTO) with variation of precursor volume. DSSC was assemblied by sandwiching both of photoanode electrode and platinum counter electrode subsequently filling the area between these electrodes with triodine/iodine electrolite solution as redox pairs. The characterization of the as prepared DSSC using solar simulator (AM 1.5G, 100 mW/cm{sup 2}) and I-V source meter Keithley 2400 showed that the performance of DSSC was affected by the precursor volume.. The overall conversion efficiency of DSSC using the optimum TiO{sub 2} film was about 1.97% with the open circuit voltage (V{sub oc}) of 0.73 V, short circuit current density (J{sub sc}) of 4.61 mA and fill factor (FF) of 0.58.

Widiyandari, Hendri, E-mail: h.widiyandari@undip.ac.id; Gunawan, S. K.V.; Suseno, Jatmiko Endro [Department of Physics, Diponegoro University, Jl. Prof. H. Soedarto SH, Semarang, Central Java 50275 (Indonesia); Purwanto, Agus [Department of Chemical Engineering, Sebelas Maret University, Jl. Ir. Sutami No. 36 A, Surakarta (Indonesia); Diharjo, Kuncoro [Department of Mechanical Engineering, Sebelas Maret University, Jl. Ir. Sutami No. 36 A, Surakarta (Indonesia)

2014-02-24

444

Design, synthesis and biological evaluation of 6-(nitroimidazole-1H-alkyloxyl)-4-anilinoquinazolines as efficient EGFR inhibitors exerting cytotoxic effects both under normoxia and hypoxia.  

PubMed

A series of novel 6-(nitroimidazole-1H-alkyloxyl)-4-anilinoquinazoline derivatives (15a-15r) were designed, synthesized and evaluated as efficient EGFR inhibitors through introduction of hypoxia activated nitroimidazole moiety into the quinazoline scaffold of EGFR inhibitors. The majority of these newly synthesized compounds exhibited comparable EGFR inhibitory activities to gefitinib and moderate to excellent anti-proliferative activities against HT-29 cells under normoxia and hypoxia. The most promising compound 15c displayed the IC50 value of 0.47 nM against EGFR kinase and excellent cytotoxic effect against HT-29 cells under normoxia and hypoxia with the IC50 values of 2.21 ?M and 1.62 ?M, respectively. The mimic reductive activation study revealed that compound 15c exerted reductive activation properties under hypoxia, which were consistent with the in vitro metabolic study, wherein 15c was easily reductive activated under hypoxia and much more stable under normoxia. All these results suggested that 15c was a potential cancer therapeutic agent both under normoxia and hypoxia and was worth of further development. PMID:25462282

Cheng, Weiyan; Zhu, Shijun; Ma, Xiaodong; Qiu, Ni; Peng, Peng; Sheng, Rong; Hu, Yongzhou

2015-01-01

445

Variable dimension automatic synthesis programs (VASP)  

NASA Technical Reports Server (NTRS)

Variable dimension FORTRAN 4 version of the Automatic Synthesis Program (ASP) compensates for limitations within the program itself. Improvements are versatile programming language, convenient input/output format, new subprograms, variable dimensioning, and efficient storage.

White, J. S.; Lee, H. Q.

1972-01-01

446

"Click" synthesis of nona-PEG-branched triazole dendrimers and stabilization of gold nanoparticles that efficiently catalyze p-nitrophenol reduction.  

PubMed

Two new water-soluble 1,2,3-triazole-containing nona-PEG-branched dendrimers are obtained with nine intradendritic 1,2,3-triazoles (trz). Addition of HAuCl4 in water to these dendrimers quantitatively leads to the intradendritic formation of AuCl3(trz) moieties subsequent to complete Cl(-) substitution by trz on Au(III), whereas the analogous complexation reaction of AuCl3 with a linear PEG trz ligand forms only an equilibrium between trz-coordinated Au(III) and Au(III) that is not coordinated to trz. Reduction of the dendrimer-Au(III) complexes to Au(0) by NaBH4 then leads to stabilization of gold nanoparticles (AuNPs) in water. The sizes of the AuNPs stabilized by the dendritic macromolecules are further controlled between 1.8 and 12 nm upon selecting the stoichiometry of Au(III) addition per dendritic trz followed by NaBH4 reduction. With a 1:1 Au/trz stoichiometry, the AuNP size depends on the length of the PEG tether of the dendrimer; small dendrimer-encapsulated AuNPs are formed with PEG2000, whereas large AuNPs are formed with PEG550. With Au/trz stoichiometries larger than unity, Au(III) is reduced outside the macromolecule, resulting in the formation of large interdendritically stabilized AuNPs. The formation of very small and only mildly stabilized AuNPs by neutral hydrophilic triazole ligands offers an opportunity for very efficient p-nitrophenol reduction by NaBH4 in water at the AuNP surface. PMID:24910892

Li, Na; Echeverría, María; Moya, Sergio; Ruiz, Jaime; Astruc, Didier

2014-07-01

447

The use of N-urethane-protected N-carboxyanhydrides (UNCAs) in amino acid and peptide synthesis.  

PubMed

N-Urethane-protected N-carboxyanhydrides (UNCAs) are very reactive amino acid derivatives. They have been successfully used in peptide synthesis, in both solution and solid phase. We have demonstrated that UNCAs are interesting starting materials for the synthesis of various amino acid derivatives. Chemoselective reduction of UNCAs with sodium borohydride led the corresponding N-protected beta amino alcohols. Reaction of UNCAs with Meldrum's acid, followed by cyclisation, yielded enantiomerically pure tetramic acid derivatives. Diastereoselective reduction of tetramic acid derivatives produced [4S,5S)-N-alkoxycarbonyl-4-hydroxy-5-alkylpyrrolidin-2-ones derived from amino acids, which after hydrolysis yielded statine and statine analogues. Tetramic acid derivatives could also be obtained by reaction of UNCAs with benzyl ethyl malonate in the presence of sodium hydride to yield gamma-N-benzyloxycarbonylamino-beta-oxodicarboxyl esters followed by hydrogenolytic deprotection and decarboxylation. UNCAs also reacted with phosphoranes to produce the ketophosphorane in excellent yields. Subsequent oxidation with oxone or with [bis(acetoxy)-iodo]-benzene produced vicinal tricarbonyl derivatives. These reactions usually proceeded smoothly and with high yields. PMID:9222989

Fehrentz, J A; Genu-Dellac, C; Amblard, M; Winternitz, F; Loffet, A; Martinez, J

1995-01-01

448

Efficient and versatile catalysis of N-alkylation of heterocyclic amines with alcohols and one-pot synthesis of 2-aryl substituted benzazoles with newly designed ruthenium(II) complexes of PNS thiosemicarbazones.  

PubMed

Ruthenium(II) carbonyl complexes with phosphine-functionalized PNS type thiosemicarbazone ligands [RuCl(CO)(EPh3)(L)] (1-6) (E = P or As, L = 2-(2-(diphenylphosphino)benzylidene) thiosemicarbazone (PNS-H), 2-(2-(diphenylphosphino)benzylidene)-N-methylthiosemicarbazone (PNS-Me), 2-(2-(diphenylphosphino)benzylidene)-N-phenylthiosemicarbazone (PNS-Ph)) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, (1)H, (13)C, (31)P-NMR) as well as ESI mass spectrometry. The molecular structures of complexes 1, 2 and 6 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that all the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate PNS fashion. All the ruthenium complexes (1-6) were tested as catalyst for N-alkylation of heteroaromatic amines with alcohols. Notably, complex 2 was found to be a very efficient and versatile catalyst towards N-alkylation of a wide range of heterocyclic amines with alcohols. Complex 2 can also catalyze the direct amination of 2-nitropyridine with benzyl alcohol to the corresponding secondary amine. Furthermore, a preliminary examination of performance for N,N-dialkylation of diamine showed promising results, giving good conversion and high selectivity. In addition, N-alkylation of ortho-substituted anilines (-NH2, -OH and -SH) led to the one-pot synthesis of 2-aryl substituted benzimidazoles, benzoxazoles and benzothiazoles, also revealing the catalytic activity of complex 2. PMID:24705796

Ramachandran, Rangasamy; Prakash, Govindan; Selvamurugan, Sellappan; Viswanathamurthi, Periasamy; Malecki, Jan Grzegorz; Ramkumar, Venkatachalam

2014-06-01

449

Discovery of 1-(?-amino substituted-?-alanyl)-N,N-dimethylindoline-2-carboxamides as novel nonpeptide antagonists of nociceptin/orphanin FQ receptor: efficient design, synthesis, and structure-activity relationship studies.  

PubMed

Since the discovery of endogenous nociceptin/orphanin FQ (N/OFQ) peptide and N/OFQ peptide (NOP) receptor [or opioid-receptor-like-1 (ORL1) receptor], the structures, distribution, and pharmacology have been reported in detail. N/OFQ and NOP receptor are located in the corticolimbic regions that are involved in the integration of the emotional activity, and located in the spinal cord, the peripheral nervous systems or other peripheral tissues that are related to pain as well as urinary signal transmissions, with a pattern distinct from that of classical opioid peptides and their receptors in rodents or primates. Furthermore, N/OFQ-NOP receptor system plays an important role in the regulation of various human physiologies such as depression effect, hyperphasia effect, and blood pressure effect. In this study, the structure-activity relationship of novel NOP receptor antagonist for various 1-(?-amino substituted-?-alanyl)-N,N-dimethylindoline-2-carboxamides was investigated in vitro to elucidate structural requisites to identify and develop potent and selective NOP receptor antagonists, which resulted in the discovery of 1-{3-[4-(substituted phenyl)piperidin-1-yl]propanoyl}-N,N-dimethylindoline-2-carboxamide analogues that display potent and selective human NOP (hNOP) receptor binding affinity and potent hNOP receptor antagonist activity. The efficient design, synthesis, and structure-activity relationship studies for potent and selective novel NOP receptor antagonists and significant findings in vitro, that include insights for binding and functional mechanisms via receptor-ligand interactions, are reported herein. PMID:22898529

Hayashi, Shigeo; Ohashi, Katsuyo; Nakata, Eriko; Emoto, Chie

2012-09-01

450

The synthesis of gemcitabine.  

PubMed

Gemcitabine is a fluorinated nucleoside currently administered against a number of cancers. It consists of a cytosine base and a 2-deoxy-2,2-difluororibose sugar. The synthetic challenges associated with the introduction of the fluorine atoms, as well as with nucleobase introduction of 2,2-difluorinated sugars, combined with the requirement to have an efficient process suitable for large scale synthesis, have spurred significant activity towards the synthesis of gemcitabine exploring a wide variety of synthetic approaches. In addition, many methods have been developed for selective crystallisation of diastereomeric (including anomeric) mixtures. In that regard, the 2-deoxy-2,2-difluororibose sugar is one of the most investigated fluorinated carbohydrates in terms of its synthesis. The versatility of synthetic methods employed is illustrative of the current state of the art of fluorination methodology for the synthesis of CF2-containing carbohydrates, and involves the use of fluorinated building blocks, as well as nucleophilic and electrophilic fluorination of sugar precursors. PMID:24636495

Brown, Kylie; Dixey, Michael; Weymouth-Wilson, Alex; Linclau, Bruno

2014-03-31

451

Beta-enamino esters in heterocyclic synthesis: synthesis of pyrazolone and pyridinone derivatives.  

PubMed

An efficient and convenient synthesis of pyrrolidinones and pyridinones utilizing enamino esters as starting material has been described. The structures of the compounds obtained were confirmed by spectral and elemental analyses. PMID:20657446

Salaheldin, Abdellatif Mohamed; Abdullah Al-Sheikh, Mariam

2010-06-01

452

Recent advances in microwave initiated synthesis of nanocarbon materials.  

PubMed

This Feature Article focuses on the recent advances in synthesis of nanostructured carbon materials using microwave irradiation as the heating source. Although the microwave approach to chemical synthesis is relatively mature in organic synthesis, it is still in the early stage for nanomaterials synthesis, especially nanocarbons. Due to the energy efficient nature of microwave heating, there is a great opportunity to apply microwave irradiation to nanocarbon production, which normally requires high temperature, high vacuum or inert gas protections. Using microwave irradiation will give a green feature to the nanocarbon synthesis, since it offers high efficiency heating and fast carbonization. With our recent discovery, multi-walled carbon nanotubes can be synthesized through the microwave process even in air. Background about nanocarbons and microwave chemistry are introduced, the application of microwaves in synthesis of different types of nanocarbons is discussed and finally, the perspectives in the future research directions of microwave assisted nanocarbon synthesis are deliberated as well. PMID:22179691

Zhang, Xinyu; Liu, Zhen

2012-02-01

453

A total-synthesis framework for the construction of high-order colloidal hybrid nanoparticles  

NASA Astrophysics Data System (ADS)

Colloidal hybrid nanoparticles contain multiple nanoscale domains fused together by solid-state interfaces. They represent an emerging class of multifunctional lab-on-a-particle architectures that underpin future advances in solar energy conversion, fuel-cell catalysis, medical imaging and therapy, and electronics. The complexity of these ‘artificial molecules’ is limited ultimately by the lack of a mechanism-driven design framework. Here, we show that known chemical reactions can be applied in a predictable and stepwise manner to build complex hybrid nanoparticle architectures that include M-Pt-Fe3O4 (M = Au, Ag, Ni, Pd) heterotrimers, MxS-Au-Pt-Fe3O4 (M = Pb, Cu) heterotetramers and higher-order oligomers based on the heterotrimeric Au-Pt-Fe3O4 building block. This synthetic framework conceptually mimics the total-synthesis approach used by chemists to construct complex organic molecules. The reaction toolkit applies solid-state nanoparticle analogues of chemoselective reactions, regiospecificity, coupling reactions and molecular substituent effects to the construction of exceptionally complex hybrid nanoparticle oligomers.

Buck, Matthew R.; Bondi, James F.; Schaak, Raymond E.

2012-01-01

454

An Efficient Synthesis of Bis-indolylindane-1,3-diones, Indan-1,3-diones, and Indene-1,3(2H)-denies Using [Hbim]BF4 Ionic Medium  

PubMed Central

We prepared a brand new molecule in one step for the synthesis of bis-indolylindane-1,3-dione and indan-1,3-diones from the reaction of ninhydrin and 3 substituted/unsubstituted indoles using [Hbim]BF4 ionic liquid in excellent yields. The method was also used for the synthesis of novel indene-1,3(2H)-denies derivatives. PMID:24455297

Poor Heravi, Mohammad Reza

2013-01-01

455

HIGH EFFICIENCY DESULFURIZATION OF SYNTHESIS GAS  

SciTech Connect

Mixed metal oxides containing CeO{sub 2} and ZrO{sub 2} are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv of less H{sub 2}S. The research is justified by recent results in this laboratory that showed that reduced CeO{sub 2}, designated CeO{sub n} (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO{sub 2} has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO{sub 2}, and should have similar beneficial effects on CeO{sub 2} desulfurization sorbents. An electrochemical method for synthesizing CeO{sub 2}-ZrO{sub 2} has been developed and the products have been characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO{sub 2} have been prepared. XRD showed the product to be a solid solution at low ZrO{sub 2} contents with a separate ZrO{sub 2} phase emerging at higher ZrO{sub 2} levels. Phase separation did not occur when the solid solutions were heat treated at 700 C. A flow reactor system constructed of quartz and teflon has been constructed, and a gas chromatograph equipped with a pulsed flame photometric detector (PFPD) suitable for measuring sub-ppmv levels of H{sub 2}S has been purchased with LSU matching funds. Preliminary desulfurization tests using commercial CeO{sub 2} and CeO{sub 2}-ZrO{sub 2} in highly reducing gas compositions has confirmed that CeO{sub 2}-ZrO{sub 2} is more effective than CeO{sub 2} in removing H{sub 2}S. At 700 C the product H{sub 2}S concentration using CeO{sub 2}-ZrO{sub 2} sorbent was near the 0.1 ppmv PFPD detection limit during the prebreakthrough period.

Anirban Mukherjee; Kwang-Bok Yi; Elizabeth J. Podlaha; Douglas P. Harrison

2001-11-01

456

The development of new synthetic strategies and methodologies for complex alkaloid total synthesis : a concise synthesis of (+)-chimonanthine, (+)-WIN 64821, (-)-ditryptophenaline and related alkaloids  

E-print Network

I. The Development of a General Strategy Towards Dimeric Hexahydropyrroloindole Alkaloids. A Concise Total Synthesis of (+)-Chimonanthine, (+)-Folicanthine and (-)Calycanthine. An efficient and convergent strategy for the ...

Schmidt, Michael Anthony, 1980-

2008-01-01

457

Mechanism of SmI2/Amine/H2O-Promoted Chemoselective Reductions of Carboxylic Acid Derivatives (Esters, Acids, and Amides) to Alcohols.  

PubMed

Samarium(II) iodide-water-amine reagents have emerged as some of the most powerful reagents (E° = -2.8 V) for the reduction of unactivated carboxylic acid derivatives to primary alcohols under single electron transfer conditions, a transformation that had been considered to lie outside the scope of the classic SmI2 reductant for more than 30 years. In this article, we present a detailed mechanistic investigation of the reduction of unactivated esters, carboxylic acids, and amides using SmI2-water-amine reagents, in which we compare the reactivity of three functional groups. The mechanism has been studied using the following: (i) kinetic, (ii) reactivity, (iii) radical clock, and (iv) isotopic labeling experiments. The kinetic data indicate that for the three functional groups all reaction components (SmI2, amine, water) are involved in the rate equation and that the rate of electron transfer is facilitated by base assisted deprotonation of water. Notably, the mechanistic details presented herein indicate that complexation between SmI2, water, and amines can result in a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to a variety of carboxylic acid derivatives. These observations will have important implications for the design and optimization of new processes involving Sm(II)-reduction of ketyl radicals. PMID:25232891

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

2014-12-19

458

An efficient method for the synthesis of phenacyl ester-protected dipeptides using neutral alumina-supported sodium carbonate 'Na2 CO3 /n-Al2 O3 '.  

PubMed

In the synthesis of dipeptides (Boc-AA(1)-AA(2)-OPac: AA(1) and AA(2) represent amino acids) protected by phenacyl (Pac) ester, amines and solid bases as the base for the conversion of the trifluoroacetic acid (TFA) salt of the amino component (TFA·H-AA(2)-OPac) into the corresponding free amino component (H-AA(2)-OPac) were examined. The synthesis of a dipeptide (Boc-Ala-Gly-OPac) using amines for the conversion afforded an unsatisfactory yield with by-products. On the other hand, the use of neutral alumina-supported Na(2) CO(3) (Na(2)CO(3) /n-Al(2)O(3)) as a solid base for the conversion provided the dipeptide in a quantitative yield without by-products. The application of Na(2)CO(3) /n-Al2 O3 to the synthesis of some dipeptides protected by Pac ester gave the desired peptides in excellent yields. PMID:23982992

Hashimoto, Chikao; Sugimoto, Kazuhiro; Takahashi, Youhei; Kodomari, Mitsuo

2013-10-01

459

Synthesis and Characterization of Oligodeoxyribonucleotides Modified with 2?-Amino-?-L-LNA Adenine Monomers: High-affinity Targeting of Single-Stranded DNA  

PubMed Central

Development of conformationally restricted nucleotide building blocks continues to attract considerable interest due to their successful use within antisense, antigene and other gene-targeting strategies. Locked nucleic acid (LNA) and its diastereomer ?-L-LNA are two interesting examples hereof. Oligonucleotides modified with these units display greatly increased affinity toward nucleic acid targets, improved binding specificity and enhanced enzymatic stability relative to unmodified strands. Here, we present the synthesis and biophysical characterization of oligodeoxyribonucleotides (ONs) modified with 2?-amino-?-L-LNA adenine monomers W–Z. The synthesis of target phosphoramidites 1–4 initiates from pentafuranose 5, which upon Vorbrüggen glycosylation, O2?-deacylation, O2?-activation and C2?-azide introduction yields nucleoside 8. A one-pot tandem Staudinger/intramolecular nucleophilic substitution converts 8 into 2?-amino-?-L-LNA adenine intermediate 9, which after a series of non-trivial protecting group manipulations affords key intermediate 15. Subsequent chemoselective N2?-functionalization and O3?-phosphitylation gives targets 1–4 in ~1–3% overall yield over eleven steps from 5. ONs modified with pyrene-functionalized 2?-amino-?-L-LNA adenine monomers X-Z display greatly increased affinity toward DNA targets (?Tm/modification up to +14 °C). Results from absorption and fluorescence spectroscopy suggest that the duplex stabilization is a result of pyrene intercalation. These characteristics render N2?-pyrene-functionalized 2?-amino-?-L-LNA of considerable interest for DNA-targeting applications. PMID:24304240

Andersen, Nicolai K.; Anderson, Brooke A.; Wengel, Jesper

2014-01-01

460

Supplemental ammonia synthesis  

Microsoft Academic Search

In a process for producing ammonia in a