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1

Efficient, chemoselective synthesis of immunomicelles using single-domain antibodies with a C-terminal thioester  

PubMed Central

Background Classical bioconjugation strategies for generating antibody-functionalized nanoparticles are non-specific and typically result in heterogeneous compounds that can be compromised in activity. Expression systems based on self-cleavable intein domains allow the generation of recombinant proteins with a C-terminal thioester, providing a unique handle for site-specific conjugation using native chemical ligation (NCL). However, current methods to generate antibody fragments with C-terminal thioesters require cumbersome refolding procedures, effectively preventing application of NCL for antibody-mediated targeting and molecular imaging. Results Targeting to the periplasm of E. coli allowed efficient production of correctly-folded single-domain antibody (sdAb)-intein fusions proteins. On column purification and 2-mercapthoethanesulfonic acid (MESNA)-induced cleavage yielded single-domain antibodies with a reactive C-terminal MESNA thioester in good yields. These thioester-functionalized single-domain antibodies allowed synthesis of immunomicelles via native chemical ligation in a single step. Conclusion A novel procedure was developed to obtain soluble, well-folded single-domain antibodies with reactive C-terminal thioesters in good yields. These proteins are promising building blocks for the chemoselective functionalization via NCL of a broad range of nanoparticle scaffolds, including micelles, liposomes and dendrimers.

Reulen, Sanne WA; van Baal, Ingrid; Raats, Jos MH; Merkx, Maarten

2009-01-01

2

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.

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

2008-01-01

3

Chemoselective synthesis of ketones and ketimines by addition of organometallic reagents to secondary amides  

Microsoft Academic Search

The development of efficient and selective transformations is crucial in synthetic chemistry as it opens new possibilities in the total synthesis of complex molecules. Applying such reactions to the synthesis of ketones is of great importance, as this motif serves as a synthetic handle for the elaboration of numerous organic functionalities. In this context, we report a general and chemoselective

William S. Bechara; Guillaume Pelletier; André B. Charette

2012-01-01

4

Chemoselective synthesis of ketones and ketimines by addition of organometallic reagents to secondary amides  

NASA Astrophysics Data System (ADS)

The development of efficient and selective transformations is crucial in synthetic chemistry as it opens new possibilities in the total synthesis of complex molecules. Applying such reactions to the synthesis of ketones is of great importance, as this motif serves as a synthetic handle for the elaboration of numerous organic functionalities. In this context, we report a general and chemoselective method based on an activation/addition sequence on secondary amides allowing the controlled isolation of structurally diverse ketones and ketimines. The generation of a highly electrophilic imidoyl triflate intermediate was found to be pivotal in the observed exceptional functional group tolerance, allowing the facile addition of readily available Grignard and diorganozinc reagents to amides, and avoiding commonly observed over-addition or reduction side reactions. The methodology has been applied to the formal synthesis of analogues of the antineoplastic agent Bexarotene and to the rapid and efficient synthesis of unsymmetrical diketones in a one-pot procedure.

Bechara, William S.; Pelletier, Guillaume; Charette, André B.

2012-03-01

5

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

2013-07-16

6

Chemoselective Michael reactions on pyroglutamates. Expeditious synthesis of spiro-bis-?-lactams as ?-turn peptidomimetics  

Microsoft Academic Search

Starting from pyroglutamic acid, the synthesis of spiro-bis-?-lactams, using as key step a chemoselective Michael reaction of pyroglutamates is reported. Thus, the reaction of N-BOC-l-methyl pyroglutamate with LiHMDS gives the enolates at C4 which react with several Michael acceptors. On the other hand, N-benzyl-l-methyl pyroglutamate reacts under the same conditions, to give the ester enolate which reacts with Michael acceptors

Miguel F Brańa; Mar??a Garranzo; Beatriz de Pascual-Teresa; Javier Pérez-Castells; Mar??a Rosario Torres

2002-01-01

7

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.

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

2012-01-01

8

Highly Chemoselective Rauhut-Currier Reaction between Maleimides and Enones and Dual Phosphine-Mediated One-Pot Synthesis of Bicyclic and Polycyclic Skeletons.  

PubMed

A highly chemoselective phosphine-catalyzed Rauhut-Currier reaction between maleimides and enones has been realized under very mild conditions, affording the corresponding cross-coupling products in moderate to excellent yields. On the basis of this reaction, an efficient dual phosphine-mediated one-pot synthesis of bicyclic and polycyclic compounds containing a cyclopenta[c]pyrrole skeleton has been accordingly developed, which features a tandem sequence of intermolecular Rauhut-Currier reaction and intramolecular Wittig reaction. PMID:24087883

Zhou, Rong; Wang, Jianfang; Yu, Jia; He, Zhengjie

2013-10-14

9

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

PubMed

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

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

2003-03-21

10

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

PubMed

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

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

2013-02-21

11

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.

Smoot, James T.; Demchenko, Alexei V.

2009-01-01

12

How the arming participating moieties can broaden the scope of chemoselective oligosaccharide synthesis by allowing the inverse armed-disarmed approach.  

PubMed

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 the "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

2008-10-22

13

One-pot synthesis of heterocyclic compounds initiated by chemoselective addition to ?-acyl substituted unsaturated aldehydes with nucleophilic tin complexes  

Microsoft Academic Search

?-Acyl substituted unsaturated aldehydes 1 were revealed to be good precursors for the synthesis of various heterocyclic compounds by the combination with tin nucleophiles. Various 2-monosubstituted pyrroles were prepared in an one-pot procedure via the reductive amination of formyl groups of 1 by using Bu2SnIH–HMPA complex. One-pot synthesis of heterocycles was carried out initiated by chemoselective reduction of 1 with

Ikuya Shibata; Hirofumi Kato; Makoto Yasuda; Akio Baba

2007-01-01

14

Chemoselective ligation  

DOEpatents

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

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

2011-04-12

15

Chemoselective ligation  

DOEpatents

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

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

2011-05-10

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 Ruth (Berkeley, CA)

2010-11-23

17

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

18

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

19

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

20

Green chemoselective synthesis of thiazolo[3,2- a]pyridine derivatives and evaluation of their antioxidant and cytotoxic activities  

Microsoft Academic Search

The green chemoselective synthesis of thiazolo[3,2-a]pyridine derivatives was achieved in water via microwave-assisted three-component reactions of malononitrile, aromatic aldehydes and 2-mercaptoacetic acid with molar ratios of 2:1:1.5 and 2:2.2:1, respectively. These compounds were subject to the experiments of antioxidant activity and cytotoxicity to carcinoma HCT-116 cells and mice lymphocytes. Nearly all of the tested compounds possessed potent capacities for scavenging

Feng Shi; Chunmei Li; Ming Xia; Kangjie Miao; Yanxia Zhao; Shujiang Tu; Weifa Zheng; Ge Zhang; Ning Ma

2009-01-01

21

Comparison of the Armed/Disarmed Building Blocks of the D-Gluco and D-Glucosamino Series in the Context of Chemoselective Oligosaccharide Synthesis  

PubMed Central

A very elegant Fraser-Reid's armed-disarmed approach recently expanded to the building blocks of the superarmed and superdisarmed series shows very high utility in chemoselective oligosaccharide synthesis. Although a number of studies dedicated to the chemoselective activation of 2-amino-2-deoxysugars have emerged, little remains known how the reactivity of the armed/disarmed building blocks of the neutral sugars directly compare to that of their 2-aminosugar counterparts. A preliminary study of this comparative reactivity is presented.

Kamkhachorn, Teerada; Parameswar, Archana R.; Demchenko, Alexei V.

2010-01-01

22

Chemoselective synthesis of substituted pyrazoles through AgOTf-catalyzed cascade propargylic substitution-cyclization-aromatization.  

PubMed

A cascade AgOTf-catalyzed chemoselective approach to 3,5/1,3-disubstitued pyrazoles from propargylic alcohols and para-tolylsulfonohydrazide has been developed. Good chemoselectivity is observed depending on the different substituents in the alkyne moiety of the propargylic alcohols, generating two different kinds of products through different aromatization mechanisms. The pyrazolo[5,1-a]isoquinoline skeleton can also be effectively constructed by this method through a cascade bicyclization process. PMID:23188378

Xu, Su-Xia; Hao, Lu; Wang, Tao; Ding, Zong-Cang; Zhan, Zhuang-Ping

2012-11-27

23

Chemoselective alcoholysis/acetolysis of trans-ketals over cis-ketals and its application in the total synthesis of the cellular second messenger, D-myo-inositol-1,4,5-trisphosphate.  

PubMed

The involvement of natural phosphoinositols in various cellular signalling processes and the use of synthetic inositol derivatives in catalysis, supramolecular chemistry, natural product synthesis etc. gave momentum to myo-inositol chemistry. The presence of six secondary hydroxyl groups necessitates efficient protection-deprotection strategies for the synthesis of inositol derivatives. An important strategy for the initial protection of myo-inositol is the di-ketalization, which gives a mixture of three diketals, each having both cis-fused and trans-fused ketals. It is important to have methodologies either to selectively hydrolyze one of the two ketals or to convert one of the two acid labile ketals to an orthogonal base labile protecting group. By exploiting the difference in strain between trans-ketals and cis-ketals, we developed two operationally simple, high yielding methodologies for the chemoselective hydrolysis/acetolysis of trans-ketals (both isopropylidene and cyclohexylidene) of inositols, leaving the cis-ketal undisturbed, using cheap and easily preparable H2SO4-silica as the catalyst. Also, terminal ketal moieties of carbohydrates and acyclic polyols could be selectively hydrolyzed/acetolyzed leaving the internal ketals intact. The use of methanol as the solvent leads to chemoselective alcoholysis but the use of DCM and acetic anhydride leads to chemoselective acetolysis. Applying this methodology, a short synthesis of D-myo-inositol-1,4,5-trisphosphate has been achieved. PMID:23851711

Vidyasagar, Adiyala; Pathigoolla, Atchutarao; Sureshan, Kana M

2013-09-01

24

Comparison of the armed/disarmed building blocks of the D-gluco and D-glucosamino series in the context of chemoselective oligosaccharide synthesis.  

PubMed

A very elegant Fraser-Reid armed-disarmed approach recently expanded to the building blocks of the superarmed and superdisarmed series shows very high utility in chemoselective oligosaccharide synthesis. Although a number of studies dedicated to the chemoselective activation of 2-amino-2-deoxysugars have emerged, little remains known about how the reactivity of the armed/disarmed building blocks of the neutral sugars directly compares to that of their 2-aminosugar counterparts. A preliminary study of this comparative reactivity is presented. PMID:20527789

Kamkhachorn, Teerada; Parameswar, Archana R; Demchenko, Alexei V

2010-07-01

25

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

PubMed Central

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

Leboeuf, David; Huang, Jie; Gandon, Vincent

2012-01-01

26

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

PubMed Central

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

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

2010-01-01

27

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

PubMed

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

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

2013-02-21

28

Hafnium trifluoromethanesulfonate (hafnium triflate) as a highly efficient catalyst for chemoselective thioacetalization and transthioacetalization of carbonyl compounds.  

PubMed

A range of carbonyl compounds including aliphatic and aromatic aldehydes and ketones were converted to the corresponding thioacetals in high yields in the presence of a catalytic amount of hafnium trifluoromethanesulfonate (0.1 mol %, room temperature). The mild conditions tolerated various sensitive functional and protecting groups and were racemization-free when applied to alpha-aminoaldehydes. Transacetalization and chemoselective thioacetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones were also documented. PMID:18991383

Wu, Yan-Chao; Zhu, Jieping

2008-12-01

29

Chemoselective ligation in glycochemistry  

Microsoft Academic Search

This feature article describes chemoselective techniques for the assembly of neoglycopeptides and oligosaccharide mimics. Chemoselective ligation, allowing the use of aqueous environ- ments and non-protected substrates, provides rapid access to complex glycoconjugates. The role of these molecules in recognition, signal transduction pathways and other events of fundamental biomedical significance is an object of study in the emerging field of chemical

Francesco Peri; Francesco Nicotra

2004-01-01

30

Revisiting the armed-disarmed concept rationale: s-benzoxazolyl glycosides in chemoselective oligosaccharide synthesis.  

PubMed

[reaction: see text]. It has been discovered that 2-O-benzyl-3,4,6-tri-O-acyl SBox glycosides are significantly less reactive than even "disarmed" peracylated derivatives. This finding has been applied to the synthesis of various oligosaccharides, the monomeric units of which are connected via cis-cis, trans-cis, and cis-trans sequential glycosidic linkages. Two-stage activation of the armed (benzylated) donor over moderately (dis)armed (acylated) and, subsequently, over disarmed (2-O-benzyl-3,4-O-diacylated) acceptor has also proven to be feasible. PMID:16018624

Kamat, Medha N; Demchenko, Alexei V

2005-07-21

31

A new amino acid derivative with a masked side-chain aldehyde and its use in peptide synthesis and chemoselective ligation.  

PubMed

A new amino acid derivative with a diol side-chain, L-2-amino-4,5-dihydroxy-pentanoic acid (Adi), has been prepared from L-allylglycine by suitable protection, for use in peptide synthesis, as Fmoc-L-Adi(Trt)2. This building block enables the introduction of a side-chain aldehyde at any position in a given peptide sequence without use of specialized side-chain protection schemes. The aldehyde is revealed by mild oxidation with sodium periodate, circumventing the problematic release of reactive peptidic aldehydes in TFA solution. Peptides with aldehyde side-chains are useful for chemo-selective ligation, reacting selectively with oxyamines to yield oxime links, while all other peptide functions can be left unprotected. The utility of the new building block has been demonstrated by the synthesis of peptide dimers and a cyclo-peptide. PMID:11695649

Spetzler, J C; Hoeg-Jensen, T

2001-10-01

32

1,2Diol and Hydrazide Phosphoramidites for SolidPhase Synthesis and Chemoselective Ligation of 2?Modified Oligonucleotides  

Microsoft Academic Search

The preparation of two novel 2?-O-alkyl phosphoramidites bearing 1,2-diol and hydrazide functions for a chemoselective ligation is described. The former amidite was used to obtain 2?-modified oligodeoxyribonucleotides, which can be later oxidised by NaIO4 to generate 2?-aldehyde oligonucleotides. These were successfully conjugated to acceptor molecules. The latter amidite also showed good coupling yields, but the hydrazide function was demonstrated to

Eugeny M. Zubin; Dmitry A. Stetsenko; Tatiana S. Oretskaya; Michael J. Gait

2003-01-01

33

1,2-Diol and hydrazide phosphoramidites for solid-phase synthesis and chemoselective ligation of 2'-modified oligonucleotides.  

PubMed

The preparation of two novel 2'-O-alkyl phosphoramidites bearing 1,2-diol and hydrazide functions for a chemoselective ligation is described. The former amidite was used to obtain 2'-modified oligodeoxyribonucleotides, which can be later oxidised by NaIO4 to generate 2'-aldehyde oligonucleotides. These were successfully conjugated to acceptor molecules. The latter amidite also showed good coupling yields, but the hydrazide function was demonstrated to be labile under basic deprotection conditions. PMID:14565422

Zubin, Eugeny M; Stetsenko, Dmitry A; Oretskaya, Tatiana S; Gait, Michael J

34

Chemoselective Hydroxyl Group Transformation: An Elusive Target‡  

PubMed Central

The selective reaction of one functional group in the presence of others is not a trivial task. A noteworthy amount of research has been dedicated to the chemoselective reaction of the hydroxyl moiety. This group is prevalent in many biologically important molecules including natural products and proteins. However, targeting the hydroxyl group is difficult for many reasons including its relatively low nucleophilicity in comparison to other ubiquitous functional groups such as amines and thiols. Additionally, many of the developed chemoselective reactions cannot be used in the presence of water. Despite these complications, chemoselective transformation of the hydroxyl moiety has been utilized in the synthesis of complex natural product derivatives, the reaction of tyrosine residues in proteins, the isolation of natural products and is the mechanism of action of myriad drugs. Here, methods for selective targeting of this group, as well as applications of several devised methods, are described.

Trader, Darci J.; Carlson, Erin E.

2012-01-01

35

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of ?-amino-?-keto esters  

PubMed Central

Summary An efficient catalytic synthesis of ?-amino-?-keto esters has been newly developed. Cross-coupling of various aldehydes with ?-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to ?-amino-?-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the ?-amino-?-keto esters are formed under thermodynamic control.

Uno, Takuya; Kobayashi, Yusuke

2012-01-01

36

Efficient synthesis of an (aminooxy) acetylated-somatostatin derivative using (aminooxy)acetic acid as a 'carbonyl capture' reagent.  

PubMed

Owing to the high chemoselectivity between an aminooxy function and a carbonyl group, oxime ligation is one of the most preferred procedures for the preparation of peptide conjugates. However, the sensitivity of (aminooxy)acetylated peptides to ketones and aldehydes makes their synthesis and storage difficult. In our study, we established the efficient synthesis of an (aminooxy)acetylated-somatostatin derivative in the presence of free (aminooxy)acetic acid, which was used as a 'carbonyl capture' reagent in the final cleavage step. This (aminooxy)acetylated compound was further used for the chemoselective ligation (oxime bond formation) with daunorubicin and 4-fluorobenzaldehyde leading to the formation of conjugates with potential applications in targeted cancer chemotherapy and positron emission tomography. PMID:20812368

Mezö, Gábor; Szabó, Ildikó; Kertész, István; Hegedüs, Rózsa; Orbán, Erika; Leurs, Ulrike; Bösze, Szilvia; Halmos, Gábor; Manea, Marilena

2010-09-02

37

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

SciTech Connect

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

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

2002-12-02

38

Facile zeolite induced Fischer-indole synthesis: a new approach to bioactive natural product rutaecarpine  

Microsoft Academic Search

Starting from glutaric anhydride (5) we have demonstrated an elegant six-step practical synthesis of bioactive natural product rutaecarpine (1a) via o-amidoglutaranilic acid formation, esterification, chemoselective ester reduction, intramolecular dehydrative cyclizations, hydrazone formation and zeolite induced Fischer-indole synthesis with 53% overall yield. The conditions employed in the present synthesis are mild, efficient and general.

Santosh B Mhaske; Narshinha P Argade

2004-01-01

39

Highly chemoselective calcium-catalyzed propargylic deoxygenation.  

PubMed

A calcium-catalyzed direct reduction of propargylic alcohols and ethers has been accomplished by using triethylsilane as a nucleophilic hydride source. At room temperature a variety of secondary propargylic alcohols was deoxygenated to the corresponding hydrocarbons in excellent yields. Furthermore, for the first time, a catalytic deoxygenation of tertiary propargylic alcohols was generally applicable. The same protocol was suitable for an efficient reduction of secondary as well as tertiary propargylic methyl, benzyl and allyl ethers. Substrates containing an additional keto-, ester or secondary hydroxyl function were reduced with exceptional chemoselectivity at the propargylic position. PMID:22378484

Meyer, Vera J; Niggemann, Meike

2012-02-29

40

Chemoselective sp2-sp3 cross-couplings: iron-catalyzed alkyl transfer to dihaloaromatics.  

PubMed

The chemoselective functionalization of a range of dihaloaromatics with methyl, cyclopropyl, and higher alkyl Grignard reagents via iron-catalyzed cross-coupling is described. The site selectivity of C-X (X = halogen) activation is determined by factors such as the position of the halogen on the ring, the solvent, and the nucleophile. A one-pot protocol for the chemoselective synthesis of mixed dialkyl heterocycles is achieved solely employing iron catalysis. PMID:23829418

Malhotra, Sushant; Seng, Pamela S; Koenig, Stefan G; Deese, Alan J; Ford, Kevin A

2013-07-05

41

Micelles catalyzed chemoselective synthesis 'in water' and biological evaluation of oxygen containing hetero-1,4-naphthoquinones as potential antifungal agents.  

PubMed

Various oxygen containing 1,4-naphthoquinone derivatives have been synthesized chemoselectively by an economical, viable green methodology approach using water as solvent with or without surfactants such as Triton X-100, SDS, LD (laundry detergent), and TBAB, a phase transfer catalyst and evaluated for their in vitro antifungal and antibacterial activity. The antifungal profile of 3, 4a, 4b, and 6 indicated that compounds 3a, 3b, 4b, 6a, and 6c have potent antifungal activity compared to clinically prevalent antifungal drugs Fluconazole and Amphotericin-B against Sporothrix schenckii, Trichophyton mentagraphytes, and Candida parapsilosis and compound 3b has been found to be a lead antifungal agent for further study. PMID:21930375

Tandon, Vishnu K; Maurya, Hardesh K; Mishra, Nripendra N; Shukla, Praveen K

2011-08-31

42

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

43

Oligonucleotides containing 2?- O-[2-(2,3-dihydroxypropyl)amino-2-oxoethyl]uridine as suitable precursors of 2?-aldehyde oligonucleotides for chemoselective ligation  

Microsoft Academic Search

2?-O-[2-(2,3-Diacetoxypropyl)amino-2-oxoethyl]uridine 3?-phosphoramidite was prepared and used in solid-phase synthesis to obtain oligonucleotides containing a 1,2-diol group, which may then be converted into a 2?-aldehyde group. The oligonucleotides were conjugated efficiently to various molecules by chemoselective ligation that involves an addition–elimination reaction between the 2?-aldehyde group and a suitable nucleophile, such as a hydrazine, a O-alkylhydroxylamine or an 1,2-aminothiol. The method

Eugeny M. Zubin; Dmitry A. Stetsenko; Timofei S. Zatsepin; Michael J. Gait; Tatiana S. Oretskaya

2005-01-01

44

Oligonucleotides containing 2'-O-[2-(2,3-dihydroxypropyl)amino-2-oxoethyl]uridine as suitable precursors of 2'-aldehyde oligonucleotides for chemoselective ligation.  

PubMed

2'-O-[2-(2,3-Diacetoxypropyl)amino-2-oxoethyl]uridine 3'-phosphoramidite was prepared and used in solid-phase synthesis to obtain oligonucleotides containing a 1,2-diol group, which may then be converted into a 2'-aldehyde group. The oligonucleotides were conjugated efficiently to various molecules by chemoselective ligation that involves an addition-elimination reaction between the 2'-aldehyde group and a suitable nucleophile, such as a hydrazine, a O-alkylhydroxylamine or an 1,2-aminothiol. The method was applied successfully to the conjugation of peptides to oligonucleotides at the 2'-position. PMID:15993079

Zubin, Eugeny M; Stetsenko, Dmitry A; Zatsepin, Timofei S; Gait, Michael J; Oretskaya, Tatiana S

2005-08-15

45

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

46

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

47

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.

Goff, Randal D.; Thorson, Jon S.

2010-01-01

48

Atom-economical chemoselective synthesis of 1,4-diynes and polysubstituted furans/pyrroles from propargyl alcohols and terminal alkynes.  

PubMed

Under different conditions, the reaction of propargyl alcohols and terminal alkynes leads to the selective formation of 1,4-diynes and polysubstituted furans/pyrroles. Water is the only byproduct in the selective synthesis of 1,4-diynes and pyrroles, and the strategy for the furan synthesis is of 100% atom economy. PMID:21648402

Wang, Tao; Chen, Xin-liang; Chen, Li; Zhan, Zhuang-ping

2011-06-07

49

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

50

Chemoselective metal-free aerobic alcohol oxidation in lignin.  

PubMed

An efficient organocatalytic method for chemoselective aerobic oxidation of secondary benzylic alcohols within lignin model compounds has been identified. Extension to selective oxidation in natural lignins has also been demonstrated. The optimal catalyst system consists of 4-acetamido-TEMPO (5 mol %; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) in combination with HNO3 and HCl (10 mol % each). Preliminary studies highlight the prospect of combining this method with a subsequent oxidation step to achieve C-C bond cleavage. PMID:23570328

Rahimi, Alireza; Azarpira, Ali; Kim, Hoon; Ralph, John; Stahl, Shannon S

2013-04-19

51

Efficient supervisory synthesis of large systems  

Microsoft Academic Search

Due to the state-space explosion, many synthesis and verification problems for discrete event systems cannot be solved using traditional state-space traversal algorithms. This work presents efficient methods for reachability search based on symbolic computations using Binary Decision Diagrams. In addition, simple guidelines and quantities for separating hard and easy reachability problems are presented. Furthermore, the performance of the presented algorithms

Arash Vahidi; Martin Fabian; Bengt Lennartson

2006-01-01

52

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.

Coskun, Necdet; Erden, Ihsan

2011-01-01

53

Palladium-Catalyzed Chemoselective Decarboxylative Ortho Acylation of Benzoic Acids with ?-Oxocarboxylic Acids.  

PubMed

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

Miao, Jinmin; Ge, Haibo

2013-05-30

54

Chemoselective and Enantioselective Oxidation of Indoles Employing Aspartyl Peptide Catalysts  

PubMed Central

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

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

2011-01-01

55

Chemoselectivity Control: Gold(I)-Catalyzed Synthesis of 6,7-Dihydrobenzofuran-4(5H)-ones and Benzofurans from 1-(Alkynyl)-7-oxabicyclo[4.1.0]heptan-2-ones.  

PubMed

New and chemoselective gold(I)-catalyzed transformations of 1-(arylethynyl)-7-oxabicyclo[4.1.0]- heptan-2-ones were developed. Two completely different products-6,7-dihydrobenzofuran-4(5H)-ones and benzofurans-could be obtained from the same starting material. The selectivity is determined by the ligand of the gold catalyst: triphenylphosphine delivers 6,7-dihydrobenzofuran-4(5H)-ones, and 1,3-bis(diisopropylphenyl)imidazol-2-ylidene leads to benzofurans. Eleven examples of each case are provided. The mechanistic suggestions for the pathways to both product types are supported by isotope labeling experiments. PMID:23881797

Wang, Tao; Shi, Shuai; Vilhelmsen, Mie Hřjer; Zhang, Tuo; Rudolph, Matthias; Rominger, Frank; Hashmi, A Stephen K

2013-07-23

56

Efficient BDD Algorithms for FSM Synthesis and Verification  

Microsoft Academic Search

We describe a set of BDD based algorithms for efficient FSM synthesis and verification. We establish that the core compu- tation in both synthesis and verification is forming the image and pre-image of sets of states under the transition relatio n characterizing the design. To make these steps as efficient as possible, we address BDD variable ordering, use of parti-

Rajeev K. Ranjan; Adnan Aziz; Robert K. Brayton; Bernard Plessier; Carl Pixley

1995-01-01

57

P4VP-H2SO4 Catalyzed Chemoselective Protection of Aldehydes to Acylal along with Deprotection Reactions  

Microsoft Academic Search

Poly(4-vinylpyridine)-supported sulfuric acid is an excellent reusable heterogeneous catalyst for the chemoselective synthesis of 1,1-diacetates(acylal) from aldehydes in dichloromethane at room temperature within few minutes. The protection of salicyaldehyde generated anhydro-dimer as single product under similar reaction condition. The catalyst is equally applicable for the deprotection of acylal in acetonitrile. The catalyst was prepared by wet impregnation technique.

Papia Dutta; Parishmita Sarma; Ruli Borah

2012-01-01

58

Synthesis of a backbone hexasaccharide fragment of the pectic polysaccharide rhamnogalacturonan I.  

PubMed

Synthesis of the fully unprotected hexasaccharide backbone of the pectic polysaccharide rhamnogalacturonan I is described. The strategy relies on iterative coupling of a common pentenyl disaccharide glycosyl donor followed by a late-stage oxidation of the C-6 positions of the galactose residues. The disaccharide donor is prepared by an efficient chemoselective armed-disarmed coupling of a thiophenyl rhamnoside donor with a pentenyl galactoside acceptor bearing the strongly electron-withdrawing pentafluorobenzoyl ester (PFBz) protective group. PMID:23544444

Zakharova, Alexandra N; Madsen, Robert; Clausen, Mads H

2013-04-02

59

Chemoselective Protection of ?-Ketoacids by Direct Annulations with Oximes  

PubMed Central

Oximes and ?-ketoacids undergo an unexpectedly facile and chemoselective annulation to afford 2,5-dihydrooxazole 3-oxides. The resulting cyclic nitrones serve as chemically and configurationally stable masked ?-ketoacids that can be easily elaborated and manipulated. Deprotection is achieved by mild reduction with zinc metal and hydrolysis. This methodology allows for the protection, elaboration, and deprotection of enantiopure peptide derived ?-ketoacids, which are the key starting materials for the chemoselective ketoacid–hydroxylamine peptide ligation.

Flores, Melissa A.; Bode, Jeffrey W.

2010-01-01

60

Chemoselective probes for metabolite enrichment and profiling.  

PubMed

Chemical probes that target classes of proteins based on shared functional properties have emerged as powerful tools for proteomics. The metabolome rivals, if not surpasses, the proteome in terms of size and complexity, suggesting that efforts to profile metabolites would also benefit from targeted technologies. Here we apply the principle of chemoselective probes to the metabolome, creating a general strategy to tag, enrich and profile large classes of small molecules from biological systems. Key to success was incorporation of a protease-cleavage step to release captured metabolites in a format compatible with liquid chromatography-mass spectrometry (LC-MS) analysis. This technology, termed metabolite enrichment by tagging and proteolytic release (METPR), is applicable to small molecules of any physicochemical class, including polar, labile and low-mass (<100 Da) compounds. We applied METPR to profile changes in the thiol metabolome of human cancer cells treated with the antioxidant N-acetyl-L-cysteine. PMID:17417646

Carlson, Erin E; Cravatt, Benjamin F

2007-04-08

61

An Efficient Microscale Procedure for the Synthesis of Aspirin  

Microsoft Academic Search

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

Sangeeta Pandita; Samta Goyal

1998-01-01

62

Chemoselective amination of 5-bromo-2-chloro-3-fluoropyridine.  

PubMed

The chemoselective functionalization of 5-bromo-2-chloro-3-fluoropyridine (1c) is described. Catalytic amination conditions (Pd2dba3, Xantphos, base) afford exclusively the bromide substitution product (2) for both secondary amines and primary anilines. A reversal in chemoselectivity is observed under neat conditions in the absence of palladium catalysis, with substitution at the 2-chloro position preferred to generate 3. Last, selective substitution of the 3-fluoro group is achieved under SNAr conditions to afford the dihalo adduct (4). PMID:17447780

Stroup, Bryan W; Szklennik, Paul V; Forster, Cornelia J; Serrano-Wu, Michael H

2007-04-21

63

Efficient chemoenzymatic synthesis of sialyl Tn-antigen and derivatives†  

PubMed Central

An N-terminal and C-terminal truncated recombinant ?2–6-sialyltransferase cloned from Photobacterium sp. JH-ISH-224, Psp2,6ST(15–501)-His6, was shown to be an efficient catalyst for one-pot three-enzyme synthesis of sialyl Tn (STn) antigens and derivatives containing natural and non-natural sialic acid forms.

Ding, Li; Yu, Hai; Lau, Kam; Li, Yanhong; Muthana, Saddam; Wang, Junru; Chen, Xi

2011-01-01

64

DABCO Promoted an Efficient and Convenient Synthesis of Benzofurans  

Microsoft Academic Search

An efficient and convenient synthesis of benzofurans has been described from phenacyl halides and o-hydroxy benzaldehyde in the presence of DABCO. The procedure is applicable for a variety of phenacyl halides and provide a variety of benzofurans. DABCO act as a base and as well as nucleophile.

H. M. Meshram; B. Chennakesava Reddy; B. R. V. Prasad; P. Ramesh Goud; G. Santosh Kumar; R. Naveen Kumar

2012-01-01

65

DABCO-Promoted Efficient and Convenient Synthesis of Benzofurans  

Microsoft Academic Search

An efficient and convenient synthesis of benzofurans has been described from phenacyl halides and o-hydroxy benzaldehyde in the presence of DABCO. The procedure is applicable for a variety of phenacyl halides and provide a variety of benzofurans. DABCO act as a base and as well as nucleophile.

H. M. Meshram; B. Chennakesava Reddy; B. R. V. Prasad; P. Ramesh Goud; G. Santosh Kumar; R. Naveen Kumar

2012-01-01

66

Efficient one-pot synthesis of propargylamines using zinc dust  

Microsoft Academic Search

The one-pot synthesis of propargylamines is achieved efficiently via a three component coupling of various aldehydes, alkynes and amines using zinc dust under mild reaction conditions and in the absence of a co-catalyst. Zinc dust was recovered quantitatively by simple centrifugation and reused.

M. Lakshmi Kantam; V. Balasubrahmanyam; K. B. Shiva Kumar; G. T. Venkanna

2007-01-01

67

Overturning Established Chemoselectivities: Selective Reduction of Arenes over Malonates and Cyanoacetates by Photoactivated Organic Electron Donors  

PubMed Central

The prevalence of metal-based reducing reagents, including metals, metal complexes, and metal salts, has produced an empirical order of reactivity that governs our approach to chemical synthesis. However, this reactivity may be influenced by stabilization of transition states, intermediates, and products through substrate–metal bonding. This article reports that in the absence of such stabilizing interactions, established chemoselectivities can be overthrown. Thus, photoactivation of the recently developed neutral organic superelectron donor 5 selectively reduces alkyl-substituted benzene rings in the presence of activated esters and nitriles, in direct contrast to metal-based reductions, opening a new perspective on reactivity. The altered outcomes arising from the organic electron donors are attributed to selective interactions between the neutral organic donors and the arene rings of the substrates.

2013-01-01

68

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.

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

2010-01-01

69

Efficient chemical synthesis of human complement protein C3a.  

PubMed

We report the total chemical synthesis of human C3a by one-pot native chemical ligation of three unprotected peptide segments, followed by efficient in vitro folding that yielded the anaphylatoxin C3a in high yield and excellent purity. Synthetic C3a was fully active and its crystal structure at 2.1 Ĺ resolution showed 3 helices and a C-terminal turn motif. PMID:23407800

Ghassemian, Artin; Wang, Ching-I Anderson; Yau, Mei-Kwan; Reid, Robert C; Lewis, Richard J; Fairlie, David P; Alewood, Paul F; Durek, Thomas

2013-03-21

70

Efficient synthesis of nucleoside aryloxy phosphoramidate prodrugs utilizing benzyloxycarbonyl protection  

PubMed Central

An efficient method for the synthesis of nucleoside phosphoramidates prodrugs (6a–f) has been developed that employs a simple protection/deprotection sequence of the nucleoside with benzyloxycarbonyl (Cbz). The coupling reaction of Cbz-protected derivatives (5a–f) with phenyl-(ethoxy-L-alaninyl)-phosphorochloridate (7), followed by Cbz group removal by hydrogenolysis provided the phenyl phosphoramidate ProTides (6a–f) in excellent overall yields.

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

2011-01-01

71

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

PubMed

The simplicity, efficiency and generality of the transition-metal-catalysed Suzuki-Miyaura cross-coupling reaction has led to its application in the preparation of a wide variety of organic compounds. Cross-coupling of alkylboron derivatives, however, remains a major challenge, in particular with regard to stereochemical control. Here, we describe the preparation and reaction of highly optically enriched 1,1-diboron compounds. A catalytic asymmetric conjugate borylation of ?-boronylacrylates provided geminal diboronate products that feature two distinct boronyl units, in 99% enantiomeric excess. Chemoselective cross-coupling of one-boronyl unit, a trifluoroborate salt, occurred stereospecifically via inversion of its configuration to generate enantioenriched benzylic or allylic boronates. The difficult transmetallation in the Suzuki-Miyaura catalytic reaction cycle is believed to be facilitated by a stabilization effect from the second boronyl unit, and internal coordination by the oxygen of the proximal carboxyester. We also explored subsequent functionalization of the second boronyl unit. PMID:22024887

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

2011-09-25

72

Energy efficiency in nanoscale synthesis using nanosecond plasmas.  

PubMed

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

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

2013-02-05

73

Alginate esters via chemoselective carboxyl group modification.  

PubMed

Alginates are (1?4) linked linear copolysaccharides composed of ?-d-mannuronic acid (M) and its C-5 epimer, ?-l-guluronic acid (G). Several strategies for synthesis of carboxyl modified alginate derivatives exist in the literature. Most of these however employ aqueous chemistries, such as carbodiimide coupling reactions. Based on our recently discovered method for homogeneous dissolution of tetrabutylammonium (TBA)-alginate, we now describe use of tetrabutylammonium fluoride (TBAF)-based two component solvent systems as media for synthesis of carboxyl-modified alginate esters. Partially and fully esterified benzyl, butyl, ethyl, and methyl alginates were synthesized via reaction with the corresponding alkyl halides. The newly synthesized derivatives were soluble in polar aprotic solvents without the addition of TBAF. Saponification was performed to demonstrate that alkylation was completely regioselective for carboxylate groups in preference to hydroxyl groups to form esters. We demonstrate the utility of these alginate esters to enhance aqueous solubility of the flavonoid naringenin by formation of solid dispersions. PMID:24053805

Pawar, Siddhesh N; Edgar, Kevin J

2013-08-13

74

In vivo imaging of hydrogen peroxide production in a murine tumor model with a chemoselective bioluminescent reporter.  

PubMed

Living organisms produce hydrogen peroxide (H(2)O(2)) to kill invading pathogens and for cellular signaling, but aberrant generation of this reactive oxygen species is a hallmark of oxidative stress and inflammation in aging, injury, and disease. The effects of H(2)O(2) on the overall health of living animals remain elusive, in part owing to a dearth of methods for studying this transient small molecule in vivo. Here we report the design, synthesis, and in vivo applications of Peroxy Caged Luciferin-1 (PCL-1), a chemoselective bioluminescent probe for the real-time detection of H(2)O(2) within living animals. PCL-1 is a boronic acid-caged firefly luciferin molecule that selectively reacts with H(2)O(2) to release firefly luciferin, which triggers a bioluminescent response in the presence of firefly luciferase. The high sensitivity and selectivity of PCL-1 for H(2)O(2), combined with the favorable properties of bioluminescence for in vivo imaging, afford a unique technology for real-time detection of basal levels of H(2)O(2) generated in healthy, living mice. Moreover, we demonstrate the efficacy of PCL-1 for monitoring physiological fluctuations in H(2)O(2) levels by directly imaging elevations in H(2)O(2) within testosterone-stimulated tumor xenografts in vivo. The ability to chemoselectively monitor H(2)O(2) fluxes in real time in living animals offers opportunities to dissect H(2)O(2)'s disparate contributions to health, aging, and disease. PMID:21115844

Van de Bittner, Genevieve C; Dubikovskaya, Elena A; Bertozzi, Carolyn R; Chang, Christopher J

2010-11-29

75

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

PubMed

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

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

2013-04-15

76

Efficient Synthesis of Gold Nanoparticles Using Ion Irradiation in Gas--Liquid Interfacial Plasmas  

NASA Astrophysics Data System (ADS)

The efficient synthesis of gold nanoparticles using plasma irradiation in gas--liquid interfacial discharges is carried out. The availability of plasma ion irradiation to an ionic liquid on nanoparticle synthesis was revealed by direct comparison with an electron shower system. It was found that the ion irradiation generated hydrogen radicals in the ionic liquid, which were effective for the synthesis of gold nanoparticles.

Baba, Kazuhiko; Kaneko, Toshiro; Hatakeyama, Rikizo

2009-03-01

77

Enantioselective synthesis of a dual orexin receptor antagonist.  

PubMed

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

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

2012-06-22

78

Diverging chemoselective reactions of separable amide rotational isomers.  

PubMed

Diverging chemoselective reactions of a pair of amide rotamers have been observed by separating the rotamers and then reacting them individually. Reduction of (Z)-N-allyl-2-(phenylselanyl)-N-(2,4,6-tri-tert-butylphenyl)acetamide with tributyltin hydride at room temperature provides only the product of 5-exo cyclization, 4-methyl-1-(2,4,6-tri-tert-butylphenyl)pyrrolidin-2-one. In contrast, reduction of the corresponding (E) amide rotational isomer under identical conditions provides only the reduced product, (E)-N-allyl-N-(2,4,6-tri-tert-butylphenyl)acetamide. Such diverging reactions of rotamers may be common in transformations involving reactive intermediates (carbenes, radicals, organometallic intermediates) that have low barriers to onward reactions relative to amide rotation. PMID:20038129

Li, Xiben; Curran, Dennis P

2010-02-01

79

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

Microsoft Academic Search

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

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

2005-01-01

80

Novel and Efficient One-Pot Synthesis of (Aminophenyl)carbamic Acid Esters  

Microsoft Academic Search

A novel and efficient protocol is developed for the synthesis of various (aminophenyl)carbamic acid esters from the reduction and condensation of nitrophenyl isocyanate derivatives. The reaction takes place in various hydroxy derivatives such as alcohols or phenols under a hydrogen atmosphere using Raney nickel as catalyst. Products are obtained by a convenient one–pot synthesis with excellent yields and short reaction

Antonio Garofalo; Laurence Goossens; Perrine Six; Nicolas Lebegue; Patrick Depreux

2011-01-01

81

A simple and efficient enantioselective synthesis of piperidine alkaloids dihydropinidine and isosolenopsins A, B and C  

Microsoft Academic Search

A diastereospecific intramolecular Mannich-type reaction, involving enantiopure amine 4 and achiral aldehydes, is employed as the key step of an efficient total enantioselective synthesis of five piperidine alkaloids.

Stéphane Ciblat; Pascale Besse; Vassiliki Papastergiou; Henri Veschambre; Jean-Louis Canet; Yves Troin

2000-01-01

82

Efficient synthesis of tetrasubstituted thiophenes by reaction of benzoyl isothiocyanates, ethyl bromopyruvate and enaminones  

Microsoft Academic Search

An efficient synthesis of ethyl 2-(4-acetyl-5-benzoylamino-3-methyl-2-thienyl)-2-oxoacetates is described via reaction between benzoyl isothiocyanates and ethyl bromopyruvate in the presence of enaminones.

Issa Yavari; Zinatossadat Hossaini; Maryam Sabbaghan

2008-01-01

83

Effective chemoselective deprotection of 3,4-dimethoxybenzyl ( 3,4DMB) ethers in the presence of benzyl and p-methoxybenzyl (PMB) ethers by phenyliodine(III) bis(trifluoroacetate) (PIFA)  

Microsoft Academic Search

In this Letter, a selective deprotection of the alcohol protecting 3,4-dimethoxybenzyl (3,4DMB) group is described. The hypervalent iodine(III) reagent phenyliodine bis(trifluoroacetate) (PIFA) is found to be an efficient reagent for the chemoselective deprotection of 3,4DMB ethers in the presence of benzyl, p-methoxybenzyl, methoxymethyl, tert-butyldimethylsilyl, and tert-butyldiphenylsilyl ethers under mild conditions. This is the first example of the selective deprotection of

Kazuhiro Watanabe; Tadashi Katoh

2011-01-01

84

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

Microsoft Academic Search

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

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

85

Stereocontrolled access to orthogonally protected anti,anti-4-aminopiperidine-3,5-diols through chemoselective reduction of enantiopure beta-lactam cyanohydrins.  

PubMed

The cyanosilylation of enantiopure 4-oxoazetidine-2-carbaldehydes with tert-butyldimethylsilyl cyanide was promoted by either molecular sieves or catalytic amount of sodium carbonate to give O-silylated beta-lactam cyanohydrins with good yield and diastereoselectivity. In contrast, Lewis acids did not effectively promote the cyanosilylation under different experimental conditions, and instead hydrocyanation took place affording the corresponding free cyanohydrins in variable yield and selectivity. Starting from beta-lactam cyanohydrin hybrids, two concise, complementary stereocontrolled routes to optically pure orthogonally protected anti,anti-4-amino-3,5-piperidine diols were achieved. Key features of the first approach include chemoselective reductive opening of the beta-lactam ring with LiBH4 to a 3-amino-5-hydroxy pentanenitrile followed by reductive cyclization of a conveniently functionalized cyanomesylate derivative with NaBH4/NiCl2. The second approach involves LiAlH4 reduction of protected anti,anti-4-amino-3,5-dihydroxypiperidin-2-ones, which were easily obtained by chemoselective reduction of the cyano group in the beta-lactam cyanohydrin hybrids with NaBH4/NiCl2 and subsequent intramolecular rearrangement of the resulting amino beta-lactams. Both routes make use of an oxidative N-dearylation with diacetoxyiodobenzene of a 4-methoxyphenylamino group as a common synthetic step. Specifically, the utility of this novel reaction sequence has been demonstrated by the synthesis of fully orthogonally protected sialidase inhibitors. PMID:17867703

Alcaide, Benito; Almendros, Pedro; Cabrero, Gema; Ruiz, M Pilar

2007-09-15

86

Synthesis of 2-substituted indoles and indolines via Suzuki-Miyaura coupling/5-endo-trig cyclization strategies.  

PubMed

New strategies for the synthesis of 2-substituted indoles and indolines using acyclic, imide-derived enol phosphates, which were readily prepared from o-haloanilides, have been developed based on Suzuki-Miyaura coupling-cyclization sequences. A highly chemoselective cross-coupling of imide-derived enol phosphates with boron nucleophiles under Suzuki-Miyaura conditions allowed for the efficient preparation of various N-(o-halophenyl)enecarbamates that served as useful precursors for subsequent 5-endo-trig Heck or 5-endo-trig aryl radical cyclizations to furnish 2-substituted indoles or indolines, respectively. Furthermore, a one-pot Suzuki-Miyaura coupling-cyclization cascade starting from enol phosphates has been developed, which was successfully applied to the efficient synthesis of an indol-2-yl-1H-quinolin-2-one KDR inhibitor. PMID:19007181

Fuwa, Haruhiko; Sasaki, Makoto

2009-01-01

87

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

Microsoft Academic Search

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

David R. Barstow; Elaine Kant

1976-01-01

88

[Development of efficient methods for synthesis of nitrogen-containing compounds using carbamates, acylhydrazines, and ammonia].  

PubMed

For the efficient synthesis of divergent nitrogen-containing compounds of pharmaceutical and agricultural importance, the development of efficient, complementary, and new synthetic methodologies is essential. One of the key subjects is how to introduce nitrogen atoms in to organic molecules. This review summaries our recent efforts on this issue, focusing on the use of carbamates, acylhydrazines, and ammonia as nitrogen sources. PMID:17139157

Sugiura, Masaharu

2006-12-01

89

Methyl mercapturate synthesis: an efficient, convenient and simple method.  

PubMed

A safe and simple method for methyl S-arylmercapturate synthesis is described. Thirteen such compounds, to be used afterwards in metabolism studies, have been obtained with yields ranging from 71 to 99.6%. These compounds were obtained using a sulfa-Michael addition and synthesized by adding the corresponding thiophenols to a mixture composed of methyl 2-acetamidoacrylate (MAA), potassium carbonate and a phase transfer catalyst, Aliquat 336. MAA, the initial synthon, was itself isolated in quasi quantitative yield following a fully described synthesis. PMID:18830162

Cossec, Benoît; Cosnier, Frédéric; Burgart, Manuella

2008-10-01

90

Efficient Synthesis of Olmesartan Medoxomil, an Antihypertensive Drug  

Microsoft Academic Search

This document describes a simple and robust process for the synthesis of olmesartan medoxomil. This tailored process allows us to synthesize olmesartan medoxomil on a large scale with 50% overall yield. Also, our process has excellent control of the impurity profile in all the stages.

Karrothu Srihari Babu; Mallepalli Srinivasa Reddy; Amirisetty Ravindranath Tagore; Gade Srinivas Reddy; Sony Sebastian; Mudunuru Satish Varma; Gandu Venkateswarlu; Apurba Bhattacharya; Padi Pratap Reddy; Ramasamy Vijaya Anand

2008-01-01

91

A Subsystem Synthesis Method for Efficient Vehicle Multibody Dynamics  

Microsoft Academic Search

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

Sung-Soo Kim

2002-01-01

92

Efficient ytterbium triflate catalyzed microwave-assisted synthesis of 3-acylacrylic acid building blocks.  

PubMed

The derivatives of 4-(hetero)aryl-4-oxobut-2-enoic acid are useful as building blocks in the synthesis of biologically active compounds. An efficient general protocol for the synthesis of these building blocks was developed. This method combines microwave assistance and ytterbium triflate catalyst and allows the fast preparation of the target acids starting from different (hetero)aromatic ketones and glyoxylic acid monohydrate giving pure products in 52-75% isolated yields. PMID:18715040

Tolstoluzhsky, Nikita V; Gorobets, Nikolay Yu; Kolos, Nadezhda N; Desenko, Sergey M

2008-08-21

93

An Efficient Binary Solvent Mixture for Monoacylglycerol Synthesis by Enzymatic Glycerolysis  

Microsoft Academic Search

The present study was aimed at selecting an efficient binary solvent mixture for monoacylglycerol (MAG) synthesis by enzymatic\\u000a glycerolysis of soybean oil. Solvent combinations of tert-butanol\\/isopropanol (v\\/v) at different ratios were studied. Of the investigated cases, tert-butanol:isopropanol at ratio 80:20 was the most suitable organic medium. The optimum conditions for MAG synthesis under the\\u000a selected mixture were: water 10 wt% based

Nanjing Zhong; Lin Li; Xuebing Xu; Lingzhi Cheong; Bing Li; Songqing Hu; Xihong Zhao

2009-01-01

94

Chemoselective Selenium Dioxide Oxidation of 1,4Adducts Derived from Substituted Arylidene Acetophenones  

Microsoft Academic Search

The chemoselective reactions of selenium dioxide with differently substituted adducts generated by 1,4-addition on benzylidene acetophenone are described. This reaction has been shown to be dependent on the nature of the substituent present, leading to different products by ?-oxidation\\/?-oxidation followed by dehydrogenation\\/dehydrogenation, enolization, and cyclization.

Sivaperuman Saravanan; Santhanagopalan Purushothaman; Irudayaraj Bernadette Amali; Shanmugam Muthusubramanian

2009-01-01

95

Facile and chemoselective rhodium-catalysed intramolecular hydroacylation of ?,?-disubstituted 4-alkylidenecyclopropanals.  

PubMed

Mild intramolecular hydroacylation of ?,?-disubstituted 4-alkylidenecyclopropanals has been developed, avoiding decarbonylation and affording cycloheptenones in good yields. The reaction is chemoselective in favour of the alkylidenecyclopropane moiety when potential alkene or alkyne acceptors are tethered to the substrate. PMID:21897921

Crépin, Damien; Tugny, Coralie; Murray, James H; Aďssa, Christophe

2011-09-06

96

Gold(I)-phosphine catalyst for the highly chemoselective dehydrogenative silylation of alcohols.  

PubMed

[reaction: see text] A gold(I) complex of Xantphos AuCl(xantphos) catalyzes the dehydrogenative silylation of alcohols with high chemoselectivity and solvent tolerance. It is selective for the silylation of hydroxyl groups in the presence of alkenes, alkynes, alkyl halides (RCl, RBr), ketones, aldehydes, conjugated enones, esters, and carbamates. PMID:15987190

Ito, Hajime; Takagi, Katsuhiro; Miyahara, Takahiro; Sawamura, Masaya

2005-07-01

97

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

Microsoft Academic Search

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

Wang Bo; Yang Li Ming; Suo Ji Shuan

2003-01-01

98

An Efficient Synthesis of 2-Nitropyrrole-3,4-dicarboxamide  

Microsoft Academic Search

The synthesis of N-1-substituted 2-nitropyrrole-3,4-dicarboxamides (4–5, 7–9) was accomplished from diethyl 2-nitropyrrole-3,4-dicarboxylate (2). 2-nitro-pyrrole-3,4-dicarboxamide (1) was prepared by deprotection of 2-nitro-1-[2-(2-pyridyl)ethyl]pyrrole-3,4-dicarboxamide (9). Compound 9 was obtained by two different methods.

Michael T. Migawa; Leroy B. Townsend

1999-01-01

99

Efficient multiview depth video coding using depth synthesis prediction  

NASA Astrophysics Data System (ADS)

The view synthesis prediction (VSP) method utilizes interview correlations between views by generating an additional reference frame in the multiview video coding. This paper describes a multiview depth video coding scheme that incorporates depth view synthesis and additional prediction modes. In the proposed scheme, we exploit the reconstructed neighboring depth frame to generate an additional reference depth image for the current viewpoint to be coded using the depth image-based-rendering technique. In order to generate high-quality reference depth images, we used pre-processing on depth, depth image warping, and two types of hole filling methods depending on the number of available reference views. After synthesizing the additional depth image, we encode the depth video using the proposed additional prediction modes named VSP modes; those additional modes refer to the synthesized depth image. In particular, the VSP_SKIP mode refers to the co-located block of the synthesized frame without the coding motion vectors and residual data, which gives most of the coding gains. Experimental results demonstrate that the proposed depth view synthesis method provides high-quality depth images for the current view and the proposed VSP modes provide high coding gains, especially on the anchor frames.

Lee, Cheon; Choi, Byeongho; Ho, Yo-Sung

2011-07-01

100

Assimilation efficiencies of chemical contaminants in aquatic invertebrates: A synthesis  

SciTech Connect

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

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

1999-09-01

101

Efficient enantiomeric synthesis of pyrrolidine and piperidine alkaloids from tobacco.  

PubMed

An enantiomeric synthesis of six piperidine and pyrrolidine alkaloids, (S)-nornicotine 1, (S)-nicotine 2, (S)-anatabine 3, (S)-N-methylanatabine 4, (S)-anabasine 5, and (S)-N-methylanabasine 6, known as natural products in tobacco, was established from a common chiral homoallylic (S)-3-(1-azido-but-3-enyl)-pyridine 15. An intramolecular hydroboration-cycloalkylation of the homoallylic azide intermediate 15 served as the key step in the pyrrolidine ring formation. A ring closing metathesis reaction (RCM) of a diethylenic amine intermediate (S)-allyl-(1-pyridin-3-yl-but-3-enyl)-carbamic acid benzyl ester 20 served as the key step in the piperidine ring formation. From the commercially available 3-pyridinecarboxaldehyde 13, a short and convenient enantiomeric synthesis of tobacco alkaloids is described: (S)-nornicotine 1 (5 steps, with an overall yield of 70%), (S)-nicotine 2 (6 steps, 65%), (S)-anatabine 3 (8 steps, 30%), (S)-N-methylanatabine 4 (8 steps, 25%), (S)-anabasine 5 (8 steps, 35%), and (S)-N-methylanabasine 6 (8 steps, 25%). PMID:11559179

Felpin, F X; Girard, S; Vo-Thanh, G; Robins, R J; Villiéras, J; Lebreton, J

2001-09-21

102

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

PubMed Central

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

2011-01-01

103

Recent progress in the improvement of the coupling efficiency of "difficult sequences" in peptide synthesis.  

PubMed

Even though chemistry is now in place that potentially allows high coupling efficiencies to be attained, successful coupling is usually a challenge when so-called "difficult sequences" is encountered in peptide synthesis. Some factors that affect the coupling efficiency have been discussed and related methods to overcome those obstacles have been introduced in present review. All suggestions proposed here are valuable and also feasible to improve the coupling completeness in both liquid-phase or solid-phase PMID:17518036

Han, Xiang; Wang, De-xin

2007-02-01

104

Efficient Synthesis of Quantum Logic Circuits by Rotation-based Quantum Operators and Unitary Functional Bi-decomposition  

Microsoft Academic Search

1. Abstract Quantum information processing technology is in its pioneering stage and no efficient method for synthesizing quantum circuits has been introduced so far. This paper introduces an efficient analysis and synthesis framework for quantum logic circuits. The proposed synthesis algorithm and flow can generate a quantum circuit using the most basic quantum operators, i.e., the rotation and controlled-rotation primitives.

Afshin Abdollahi; Massoud Pedram

105

Efficient synthesis of aligned nitrogen-doped carbon nanotubes in a fluidized-bed reactor  

Microsoft Academic Search

Vertically aligned nitrogen-doped carbon nanotubes (NCNTs) with uniform size distribution, large aspect ratio, good orientation, and high purity were employed as novel platforms to understand the dopant-induced perturbations and found widely applications in catalysis, electrochemistry, energy conversion and storages. However, the efficient way to synthesis CNTs with ordered alignment in large scale is still a challenge. We reported NCNTs were

Jia-Qi Huang; Meng-Qiang Zhao; Qiang Zhang; Jing-Qi Nie; Li-De Yao; Dang Sheng Su; Fei Wei

2012-01-01

106

Simple, Efficient, and Green Method for Synthesis of Trisubstituted Electrophilic Alkenes Using Lipase as a Biocatalyst  

Microsoft Academic Search

A simple and efficient Knoevenagel condensation method for the synthesis of trisubstituted electrophilic alkenes was developed using lipase as a biocatalyst. Knoevenagel condensation was performed using the conventional method and using lipases (Aspergillus oryzae or Rhizopus oryzae) as biocatalysts, and reaction time, reaction temperature, yield, and recyclability were compared. Using a lipase as a biocatalyst eliminated the need for bases

Bhushan Nanasaheb Borse; Sanjeev Ramchandra Shukla; Yogesh Ashok Sonawane

2012-01-01

107

A simple and efficient synthesis of 2,3-diarylnaphthofurans using sequential hydroarylation/Heck oxyarylation.  

PubMed

An efficient and simple strategy has been developed for the synthesis of 2,3-diarylnaphthofurans using sequential hydroarylation of naphthols and alkynes in the presence of In(OTf)3 under microwave irradiation followed by one-pot Heck-oxyarylation of generated 1-substituted-?-hydroxy styrenes. PMID:23586966

Rao, V Kameshwara; Shelke, Ganesh M; Tiwari, Rakesh; Parang, Keykavous; Kumar, Anil

2013-04-15

108

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

PubMed Central

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

Lei, Xiaoguang; Danishefsky, Samuel J.

2011-01-01

109

Highly efficient synthesis of 2,5-disubstituted pyrazines from (Z)-?-haloenol acetates.  

PubMed

A highly efficient synthesis of a wide range of 2,5-disubstituted pyrazines from (Z)-?-haloenol acetates is described. The reactions are conducted under convenient conditions and provide products with excellent regioselectivity in moderate to excellent yields with a broad substrate scope, including a variety of aromatic and aliphatic haloenol acetates. PMID:23999970

Chen, Zhengwang; Ye, Dongnai; Xu, Guohai; Ye, Min; Liu, Liangxian

2013-09-02

110

An efficient synthesis of aldohexose-derived piperidine nitrones: precursors of piperidine iminosugars.  

PubMed

D-glucopyranose-derived and L-idopyranose-derived piperidine nitrones were synthesized in good overall yields through six-step reaction sequence starting from readily available 2,3,4,6-tetra-O-benzyl-D-glucopyranose. The method is efficient and could be general for the synthesis of aldohexose-derived piperidine nitrones which are precursors of piperidine iminosugars. PMID:23698053

Zhao, Hui; Zhao, Wen-Bo; Zhu, Jian-She; Jia, Yue-Mei; Yu, Chu-Yi

2013-05-21

111

Expedient synthesis of 4- O-methylhonokiol via Suzuki–Miyaura cross-coupling  

Microsoft Academic Search

Concise and practical synthesis of 4-O-methylhonokiol was achieved in 34% overall yield. The key features of our synthesis include chemoselective ortho-mono bromination of phenol as well as biaryl formation via Suzuki–Miyaura cross-coupling, in which bromophenol was reacted with potassium aryltrifluoroborate using Pd(OAc)2 and RuPhos under microwave conditions.

Jae-Hwan Kwak; Young Ae Cho; Jae-Yong Jang; Seung-Yong Seo; Heesoon Lee; Jin Tae Hong; Sang-Bae Han; Kiho Lee; Young-Shin Kwak; Jae-Kyung Jung

2011-01-01

112

Efficient Synthesis of the Tetracyclic Aminoquinone Moiety of Marmycin A  

PubMed Central

An efficient four-step route to the tetracyclic aminoquinone moiety of marmycin A that proceeds in 41% overall yield from 5-nitronaphthoquinone and 5-methyl-1-vinylcyclohexene will facilitate preparation of marmycin A analogues for biological evaluation. The Diels-Alder reaction gave exclusively the desired adduct that is favored by steric considerations rather than the regioisomeric adduct that is favored by electronic considerations.

Maugel, Nathan; Snider, Barry B.

2009-01-01

113

Isomerizing ethenolysis as an efficient strategy for styrene synthesis.  

PubMed

A shrinking chain: A bimetallic system consisting of [{Pd(?-Br)(tBu3P)}2] and a ruthenium metathesis catalyst has been found to efficiently promote the cross-metathesis between substituted alkenes and ethylene, while continuously migrating the double bond along the alkenyl chain (see scheme). When alkenylarenes, such as the natural products eugenol, safrol, or estragol, were treated with this catalyst under an ethylene atmosphere, they were cleanly converted into the corresponding styrenes and propylene gas. PMID:23776109

Baader, Sabrina; Ohlmann, Dominik M; Gooßen, Lukas J

2013-06-17

114

Efficient synthesis of building blocks for branched rhamnogalacturonan I fragments.  

PubMed

Starting from allyl 2-O-acetyl-3-O-benzyl-?-l-rhamnopyranoside (3), allyl (2,3,4,6-tetra-O-benzoyl-?-d-galactopyranosyl)-(1?4)-2-O-acetyl-3-O-benzyl-?-l-rhamnopyranoside (5) was synthesized under Helferich conditions. Module 5 was converted to 2,3,4,6-tetra-O-benzoyl-?-d-galactopyranosyl-(1?4)-2-O-acetyl-3-O-benzyl-?-l-rhamnopyranosyl bromide (8) which was then coupled with methyl (allyl 2,3-di-O-benzyl-?-d-galactopyranosid)uronate (11) to provide methyl (2,3,4,6-tetra-O-benzoyl-?-d-galactopyranosyl)-(1?4)-(2-O-acetyl-3-O-benzyl-?-l-rhamnopyranosyl)-(1?4)-(allyl 2,3-di-O-benzyl-?-d-galactopyranosid)uronate (14). Alternatively, module 5 was transformed into allyl 2,3,4,6-tetra-O-benzoyl-?-d-galactopyranosyl-(1?4)-3-O-benzyl-?-l-rhamnopyranoside (9) suitable as an acceptor for the glycosylation with methyl 4-O-acetyl-2,3-di-O-benzyl-?/?-d-galactopyranosyluronate N-phenyl trifluoroacetimidate (13) to yield allyl (methyl 4-O-acetyl-2,3-di-O-benzyl-?-d-galactopyranosyluronate)-(1?2)-[2,3,4,6-tetra-O-benzoyl-?-d-galactopyranosyl]-(1?4)-3-O-benzyl-?-l-rhamnopyranoside (15). Both trisaccharides modules are suitable for the synthesis of branched pectin fragments. PMID:23896158

Pogosyan, Amayak; Gottwald, Andreas; Michalik, Dirk; Endress, Hans-Ulrich; Vogel, Christian

2013-06-28

115

Efficient synthesis of cis- and trans-3,4-dihydroxy-3,4-dihydromollugin.  

PubMed

An efficient synthesis of naturally occurring compounds isolated from Pentas longiflora, cis-3,4-dihydroxy-3,4-dihydromollugin 2, and trans-3,4-dihydroxy-3,4-dihydromollugin 3 is described. The O-protected mollugins were dihydroxylated using OsO4 to achieve the corresponding cis-dihydroxy derivatives in excellent yield. The synthesis of trans-3,4-dihydroxy-3,4-dihydromollugin was achieved using Oxone in good yield. A mechanism for the formation of cis-3,4-dihydroxymollugin acetonide from the reaction of mollugin with Oxone is proposed. PMID:18412388

Mudiganti, Naga Venkata Sastry; Claessens, Sven; Habonimana, Pascal; De Kimpe, Norbert

2008-04-16

116

Highly efficient procedure for the synthesis of fructone fragrance using a novel carbon based acid.  

PubMed

The novel carbon based acid has been synthesized via one-step hydrothermal carbonization of furaldehyde and hydroxyethylsulfonic acid. A highly efficient procedure for the synthesis of fructone has been developed using the novel carbon based acid. The results showed that the catalyst possessed high activity for the reaction, giving a yield of over 95%. The advantages of high activity, stability, reusability and low cost for a simple synthesis procedure and wide applicability to various diols and beta-keto esters make this novel carbon based acid one of the best choices for the reaction. PMID:20714302

Hu, Baowei; Li, Chunqing; Zhao, Sheng-Xian; Rong, Lin-Mei; Lv, Shao-Qin; Liang, Xuezheng; Qi, Chenze

2010-08-05

117

Switching the chemoselectivity in the amination of 4-chloroquinazolines with aminopyrazoles.  

PubMed

The chemoselectivity in the amination of 4-chloroquinazolines with 3-amino-1H-pyrazoles was studied. Under the conditions of Pd(2)(dba)(3)/Xantphos/Na(2)CO(3), 4-chloroquinazolines underwent selective amination with the cyclic secondary amino group of 3-amino-1H-pyrazoles, whereas 4-chloroquinazolines were exclusively aminated with the primary amino group of 3-amino-1H-pyrazoles via S(N)Ar substitution in the presence of HCl. PMID:20043642

Shen, Zhenlu; Hong, Yiming; He, Xiaofei; Mo, Weimin; Hu, Baoxiang; Sun, Nan; Hu, Xinquan

2010-02-01

118

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

2013-09-13

119

Kinetic analysis of inhibition of glucoamylase and active site mutants via chemoselective oxime immobilization of acarbose on SPR chip surfaces.  

PubMed

We here report a quantitative study on the binding kinetics of inhibition of the enzyme glucoamylase and how individual active site amino acid mutations influence kinetics. To address this challenge, we have developed a fast and efficient method for anchoring native acarbose to gold chip surfaces for surface plasmon resonance studies employing wild type glucoamylase and active site mutants, Y175F, E180Q, and R54L, as analytes. The key method was the chemoselective and protecting group-free oxime functionalization of the pseudo-tetrasaccharide-based inhibitor acarbose. By using this technique we have shown that at pH 7.0 the association and dissociation rate constants for the acarbose-glucoamylase interaction are 10(4)M(-1)s(-1) and 10(3)s(-1), respectively, and that the conformational change to a tight enzyme-inhibitor complex affects the dissociation rate constant by a factor of 10(2)s(-1). Additionally, the acarbose-presenting SPR surfaces could be used as a glucoamylase sensor that allowed rapid, label-free affinity screening of small carbohydrate-based inhibitors in solution, which is otherwise difficult with immobilized enzymes or other proteins. PMID:23680647

Sauer, Jřrgen; Abou Hachem, Maher; Svensson, Birte; Jensen, Knud J; Thygesen, Mikkel B

2013-04-20

120

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.

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

2012-01-01

121

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

122

Efficient synthesis of functional isoprenoids from acetoacetate through metabolic pathway-engineered Escherichia coli  

Microsoft Academic Search

We show here an efficient synthesis system of isoprenoids from acetoacetate as the main substrate. We expressed in Escherichia coli a Streptomyces mevalonate pathway gene cluster starting from HMG-CoA synthase and including isopentenyl diphosphate isomerase (idi) type 2 gene and the yeast idi type 1 and rat acetoacetate-CoA ligase (Aacl) genes. When the ?-humulene synthase (ZSS1) gene of shampoo ginger

Hisashi Harada; Fengnian Yu; Sho Okamoto; Tomohisa Kuzuyama; Ryutaro Utsumi; Norihiko Misawa

2009-01-01

123

Efficient Synthesis of Silver Telluride Using Solid-State Microwave Technique  

NASA Astrophysics Data System (ADS)

In this paper, we report an efficient preparation of silver telluride by rapid solid-state microwave heating. Single phase products have been obtained within as little as 30 min of irradiation time. The rate of the synthesis is significantly increased as compared to the solid state reaction method in a conventional furnace. The quality of the as-prepared samples are attested by structural, compositional and magnetoresistance characterizations.

Ran, Guangxu; Shi, Yunfeng; Zhu, Hanming; Sun, Peng; Yue, Song

2013-06-01

124

Copper Perchlorate Hexahydrate: An Efficient Catalyst for the Green Synthesis of Polyhydroquinolines under Ultrasonication  

PubMed Central

Copper perchlorate hexahydrate as an efficient catalyst was used for the synthesis of polyhydroquinolines by four-component condensation reaction of aldehyde, ethyl acetoacetate, dimedone, and ammonium acetate in excellent yields and short reaction times at room temperature under ultrasound irradiation. This novel synthetic method is especially favoured because it provides a synergy between copper perchlorate hexahydrate and ultrasound irradiation which offers the advantages of high yields, short reaction times, simplicity, and easy workup compared to the conventional methods reported in the literature.

Puri, Saurabh; Kaur, Balbir; Parmar, Anupama; Kumar, Harish

2011-01-01

125

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

126

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

127

Click Reaction: Highly Efficient Synthesis of 2,3-Dihydroquinazolin-4(1H)-ones  

Microsoft Academic Search

In this work, condensation reaction of 2-aminobenzamide with various alkyl, aryl, and alicyclic aldehydes or ketones to 2,3-dihydroquinazolin-4(1H)-one derivatives in the presence of a catalytic amount of ammonium chloride in ethanol at room temperature is described. This reaction can be classified as a click chemical synthesis because of its high yields, short reaction times, and green and efficient reaction medium.

Ahmad Shaabani; Ali Maleki; Hamid Mofakham

2008-01-01

128

Synthesis of Imidazo[2,1-b]-1,3,4-thiadiazoles in DABCO as an Efficient and Recyclable Catalyst  

Microsoft Academic Search

An efficient and general method has been described for the synthesis of imidazo[2,1-b]-1,3,4-thiadiazole by the reaction of 2-aminothiadiazoles with phenacyl bromides in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO). The method is suitable for the synthesis of functionalized imidazothiadiazoles.

Kamleshwar Tiwari; Pankaj Kumar Verma; Shyam Babu Singh; Jagdamba Singh

2012-01-01

129

Synthesis of Imidazo [2,1-b]-1,3,4-thiadiazoles in DABCO as an Efficient and Recyclable Catalyst  

Microsoft Academic Search

An efficient and general method has been described for the synthesis of imidazo[2,1-b]-1,3,4-thiadiazole by the reaction of 2-aminothiadiazoles with phenacyl bromides in the presence of DABCO. The method is suitable for the synthesis of functionalised imidazothiadiazoles.

Kamleshwar Tiwari; Pankaj Kumar Verma; Shyam Babu Singh; Jagdamba Singh

2012-01-01

130

AN EFFICIENT SYNTHESIS OF 1,4-OXAZEPINES FROM ?-FORMYL ENAMIDE USING I2-NaHCO3 SYSTEM  

Microsoft Academic Search

A new and efficient method for synthesis of 1,4-oxazepine has been developed utilizing I2-NaHCO3 promoted intramolecular cyclisation of N-progargyl-?-hydroxylmethyl enamide. The method is mild and simple.

Moanochet Longchar; Apurba Chetia; Shahadat Ahmed; Romesh C. Boruah; Jagir S. Sandhu

2001-01-01

131

Efficient synthesis of enantiomeric ethyl lactate by Candida antarctica lipase B (CALB)-displaying yeasts.  

PubMed

The whole-cell biocatalyst displaying Candida antarctica lipase B (CALB) on the yeast cell surface with alpha-agglutinin as the anchor protein was easy to handle and possessed high stability. The lyophilized CALB-displaying yeasts showed their original hydrolytic activity and were applied to an ester synthesis using ethanol and L: -lactic acid as substrates. In water-saturated heptane, CALB-displaying yeasts catalyzed ethyl lactate synthesis. The synthesis efficiency increased depending on temperature and reached approximately 74% at 50 degrees C. The amount of L: -ethyl lactate increased gradually. L: -Ethyl lactate synthesis stopped at 200 h and restarted after adding of L: -lactic acid at 253 h. It indicated that CALB-displaying yeasts retained their synthetic activity under such reaction conditions. In addition, CALB-displaying yeasts were able to recognize L: -lactic acid and D: -lactic acid as substrates. L: -Ethyl lactate was prepared from L: -lactic acid and D: -ethyl lactate was prepared from D: -lactic acid using the same CALB-displaying whole-cell biocatalyst. These findings suggest that CALB-displaying yeasts can supply the enantiomeric lactic esters for preparation of useful and improved biopolymers of lactic acid. PMID:19288094

Inaba, Chiaki; Maekawa, Kenjiro; Morisaka, Hironobu; Kuroda, Kouichi; Ueda, Mitsuyoshi

2009-03-14

132

Microfluidic approach for highly efficient synthesis of heparin-based bioconjugates for drug delivery.  

PubMed

This paper demonstrates the highly efficient synthesis of amphiphilic heparin-folic acid-retinoic acid (HFR) bioconjugates with a high drug coupling ratio by a microfluidic approach. The microfluidic synthesis enabled the conjugation of 17 molecules of retinoic acid to each heparin chain with 21 possible groups for attachment after reacting for several minutes. In contrast, about 11 molecules of the drug were covalently conjugated to one heparin chain after 4 days in the bulk reaction. The microfluidic based-HFR bioconjugates readily self-assembled in aqueous media to form uniform nanoparticles, while the product from the bulk reaction formed non-uniform nanoparticles with broad size distribution. The HFR nanoparticles with high drug content effectively delivered the drug to folate receptor-positive cancer cells with superior cellular uptake and selective cytotoxicity in vitro compared to HFR nanoparticles synthesized in bulk reaction. With the ability to achieve high drug content in heparin carrier within a short reaction time, the microfluidic technique offers new alternatives for the efficient synthesis of polymer-based conjugates for drug delivery. PMID:22134726

Tran, Thanh Huyen; Nguyen, Chi Thanh; Kim, Dong-Pyo; Lee, Yong-Kyu; Huh, Kang Moo

2011-12-02

133

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.

2013-01-01

134

Method for the efficient synthesis of highly-substituted oxetan- and azetidin-, dihydrofuran- and pyrrolidin-3-ones and its application to the synthesis of (±)-pseudodeflectusin.  

PubMed

Highly substituted four- and five-membered heterocycles were prepared starting with O,P- and N,P-acetals by using a one-pot method involving base induced cyclization and a Horner-Wadsworth-Emmons (HWE) olefination reaction. Divergent synthesis of various heterocycles was achieved by using this method and transformations of the alkenyl group in the products of these processes were exemplified. Finally, a short and efficient synthesis of (±)-pseudodeflectusin based on the new methodology was achieved. PMID:22931431

Maegawa, Tomohiro; Otake, Kazuki; Hirosawa, Keiichi; Goto, Akihiro; Fujioka, Hiromichi

2012-08-29

135

Enhancement of the reduction efficiency of soluble starch for platinum nanoparticles synthesis.  

PubMed

In this work, the efficiency of soluble starch as a reducing and a stabilizing agent in the synthesis of platinum nanoparticles under acidic-alkaline treatment is systematically studied. The degraded intermediates with reducing potential (i.e., small molecules containing aldehyde and ?-hydroxy ketone moieties) are concomitantly generated when the alkaline concentration is greater than 0.025 M. The in situ generated species could completely reduce platinum ions (20 mM) and sufficiently stabilize the obtained platinum nanoparticles (5 mM) of uniform particle size (2-4 nm). The reduction is efficient and rapid as a complete conversion is achieved within 5 min. In a stronger alkaline condition, the platinum nanoparticles tend to aggregate and form a bigger domain because extensive degradation generates small starch fragments with less stabilization efficiency. This observation suggests that starch is a promising green material which could be chemically treated and transformed to a powerful reducing agent and stabilizer for the synthesis of metal nanoparticles. PMID:22682312

Tongsakul, Duangta; Wongravee, Kanet; Thammacharoen, Chuchaat; Ekgasit, Sanong

2012-04-23

136

High efficiency 3D video coding using new tools based on view synthesis.  

PubMed

We propose a new coding technology for 3D video represented by multiple views and the respective depth maps. The proposed technology is demonstrated as an extension of the recently developed high efficiency video coding (HEVC). One base views are compressed into a standard bitstream (like in HEVC). The remaining views and the depth maps are compressed using new coding tools that mostly rely on view synthesis. In the decoder, those views and the depth maps are derived via synthesis in the 3D space from the decoded baseview and from data corresponding to small disoccluded regions. The shapes and locations of those disoccluded regions can be derived by the decoder without any side information transmitted. To achieve high compression efficiency, we propose several new tools such as depth-based motion prediction, joint high frequency layer coding, consistent depth representation, and nonlinear depth representation. The experiments show high compression efficiency of the proposed technology. The bitrate needed for transmission of two side views with depth maps is mostly less than 50% than that of the bitrate for a single-view video. PMID:23771335

Dománski, Marek; Stankiewicz, Olgierd; Wegner, Krzysztof; Kurc, Maciej; Konieczny, Jacek; Siast, Jakub; Stankowski, Jakub; Ratajczak, Robert; Grajek, Tomasz

2013-06-12

137

Chemical methods for peptide-oligonucleotide conjugate synthesis.  

PubMed

Methods of peptide-oligonucleotide conjugate synthesis are presented that may be useful in the study of cell targeting and delivery of oligonucleotides and their analogs. The first method involves total stepwise solid-phase synthesis on a single support. The second involves preparation of oligonucleotides containing 2'-aldehydes and subsequent chemoselective ligation with functionalized peptides to form hydrazine, oxime, or thiazolidine linkages. PMID:15333905

Stetsenko, Dmitry A; Gait, Michael J

2005-01-01

138

ZnO Catalyzed Efficient Synthesis of Some New 2-Substituted-4,6-diarylpyrimidines  

PubMed Central

A simple and efficient protocol is developed for the synthesis of 2-substituted-4,6-diarylpyrimidines from one-pot three-component reaction of 4?-hydroxy-3?,5?-dinitro substituted chalcones, S-benzylthiouronium chloride (SBT), and heterocyclic secondary amines (morpholine/pyrrolidine/piperidine) in the presence of 15 mol% of ZnO as a heterogeneous catalyst. The present methodology offers several advantages such as being a simple procedure as well as providing excellent yields, and short reaction time. The catalyst is inexpensive, stable, and can be easily recycled and reused for several cycles with consistent activity.

Ameta, K. L.; Kumar, Biresh; Rathore, Nitu S.

2012-01-01

139

Efficient synthesis of quantum gates on a three-spin system with triangle topology  

NASA Astrophysics Data System (ADS)

Experiments in coherent nuclear and electron magnetic resonance and optical spectroscopy correspond to control of quantum-mechanical ensembles, guiding them from initial states to target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and decoherence, and to optimize the sensitivity of the experiments. Here, we give an efficient synthesis of a class of unitary transformations on a three coupled spin-(1)/(2) system with equal Ising coupling strengths. We show a significant time saving compared with conventional methods.

Yuan, Haidong; Khaneja, Navin

2011-12-01

140

Efficient synthesis of quantum gates on a three-spin system with triangle topology  

SciTech Connect

Experiments in coherent nuclear and electron magnetic resonance and optical spectroscopy correspond to control of quantum-mechanical ensembles, guiding them from initial states to target states by unitary transformations. The control inputs (pulse sequences) that accomplish these unitary transformations should take as little time as possible so as to minimize the effects of relaxation and decoherence, and to optimize the sensitivity of the experiments. Here, we give an efficient synthesis of a class of unitary transformations on a three coupled spin-(1/2) system with equal Ising coupling strengths. We show a significant time saving compared with conventional methods.

Yuan, Haidong; Khaneja, Navin [School of Engineering and Applied Science, Harvard University, 33 Oxford Street, Cambridge, Massachusetts 02138 (United States)

2011-12-15

141

ZnO Catalyzed Efficient Synthesis of Some New 2-Substituted-4,6-diarylpyrimidines.  

PubMed

A simple and efficient protocol is developed for the synthesis of 2-substituted-4,6-diarylpyrimidines from one-pot three-component reaction of 4'-hydroxy-3',5'-dinitro substituted chalcones, S-benzylthiouronium chloride (SBT), and heterocyclic secondary amines (morpholine/pyrrolidine/piperidine) in the presence of 15 mol% of ZnO as a heterogeneous catalyst. The present methodology offers several advantages such as being a simple procedure as well as providing excellent yields, and short reaction time. The catalyst is inexpensive, stable, and can be easily recycled and reused for several cycles with consistent activity. PMID:24052838

Ameta, K L; Kumar, Biresh; Rathore, Nitu S

2012-10-15

142

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.

2011-01-01

143

A simple and efficient highly enantioselective synthesis of alpha-ionone and alpha-damascone.  

PubMed

An efficient highly enantioselective (ee > or =99%) synthesis of alpha-ionone and alpha-damascone is described. Both enantiomers of title compounds were synthesized through two straightforward pathways diverging from enantiopure (R)- or (S)-alpha-cyclogeraniol. These versatile building blocks were obtained by regioselective ZrCl(4)-promoted biomimetic cyclization of (6S)- or (6R)-(Z)-6,7-epoxygeraniol, respectively, followed by deoxygenation of the so formed secondary alcohol. The chiral information was encoded by a highly regioselecive Sharpless asymmetric dihydroxylation of inexpensive geranyl acetate. PMID:15575784

Bovolenta, Marcella; Castronovo, Francesca; Vadalŕ, Alessandro; Zanoni, Giuseppe; Vidari, Giovanni

2004-12-10

144

Synthesis of lactones using substituted benzoic anhydride as a coupling reagent  

Microsoft Academic Search

This protocol describes a procedure for the synthesis of a 29-membered macrolactone. The facile mixed-anhydride method is very effective for the preparation of carboxylic esters and lactones using substituted benzoic anhydrides by the promotion of Lewis acid or basic catalysts under mild reaction conditions. Owing to the reaction rapidly proceeding to produce the monomeric compounds with high chemoselectivity, the protocol

Hiroki Fukui; Akane Sasaki; Isamu Shiina

2007-01-01

145

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, Natŕlia; Wilson, Ian A.; Kelly, Jeffery W. (Scripps)

2010-02-19

146

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

PubMed

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

2013-10-01

147

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

PubMed

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

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

2013-05-09

148

Chemoselective cross-linking and functionalization of alginate via Staudinger ligation  

PubMed Central

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

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

2010-01-01

149

Synthesis of Ordered Mesoporous Silica for Energy-efficient Adsorption Systems  

NASA Astrophysics Data System (ADS)

Energy-efficient adsorption systems, such as adsorption heat pump, desiccant cooling, humidity control system, and so on, are expected as a energy exchange process because they are able to utilize low temperature exhaust heat. As an adsorbent for such systems, materials with large adsorption capacity in the pressure range of practical operation are preferable. To enable the design and synthesis of materials with large heat storage capacity, the pore structure of adsorbents should be optimized for each systems. In this paper, we synthesized ordered mesoporous silica (MPS) with an arrow pore size distribution of around 2nm by a solvent evaporation method and evaluated their water adsorption properties. The adsorption isotherms for MPSs showed steep increase at a relative humidity corresponding to their pore size. Since MPSs have a large adsorption capacity than conventional materials in the relative humidity region of practical operation, they are expected for new adsorbents for energy-efficient adsorption systems.

Endo, Akira; Komori, Kou; Inagi, Yuki; Fujisaki, Satoko; Yamamoto, Takuji

150

Total synthesis of lodopyridone.  

PubMed

A convergent total synthesis of the structurally unprecedented alkaloid lodopyridone was achieved using a cross-coupling of an iodopyridone fragment with a quinolinethiazolylstannane. Key features of the syntheses of the pentasubstituted 4-pyridone were a regioselective bromination of a 4-pyridone derived from kojic acid, a subsequent Cu-mediated introduction of the thioether, and a directed lithiation/iodination step. A chemoselective Negishi cross-coupling of a dibromothiazole and a quinolinylzinc reagent was used to assemble the chloroquinolinethiazol moiety. PMID:22909023

Burckhardt, Tobias; Harms, Klaus; Koert, Ulrich

2012-08-21

151

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

2011-10-26

152

Chemoselective transfer hydrogenation of ?,?-unsaturated ketones catalyzed by pincer-Pd complexes using alcohol as a hydrogen source.  

PubMed

A pincer-Pd complex was utilized in the chemoselective transfer hydrogenation of ?,?-unsaturated ketones using n-BuOH as a hydrogen source and solvent. Good to excellent yields were obtained for various substrates even with reducible groups. Based on deuterium-labeling experiments, the reaction mechanism is proposed to occur via a pincer-Pd-hydride intermediate. PMID:23802845

Ding, Boqiang; Zhang, Zhenfeng; Liu, Yangang; Sugiya, Masashi; Imamoto, Tsuneo; Zhang, Wanbin

2013-06-26

153

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

PubMed Central

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

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

2003-01-01

154

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.

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

2010-01-01

155

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

PubMed

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

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

2013-08-01

156

Diversity-Oriented Synthesis of 2,4,6-Trisubstituted Piperidines via Type II Anion Relay Chemistry (ARC)  

PubMed Central

An effective, general protocol for the Diversity-Oriented Synthesis (DOS) of 2,4,6-trisubstituted piperidine congeners has been designed and validated. The successful strategy entails a modular approach to all possible stereoisomers of the selected piperidine scaffold, exploiting Type II Anion Relay Chemistry (ARC), followed in turn by intramolecular SN2 cyclization, chemoselective removal of the dithiane moieties and carbonyl reductions.

Smith, Amos B.; Han, Heeoon; Kim, Won-Suk

2011-01-01

157

Green and efficient synthesis of sulfonamides catalyzed by nano-Ru/Fe(3)O(4).  

PubMed

The environmentally benign synthesis of carbon-nitrogen bonds continues to be an active and challenging field of chemical research. Here, a novel, environmentally benign method for the direct coupling of sulfonamides and alcohols is described. Despite the importance of sulfonamide derivatives as intermediates in drug synthesis, till now such transformations are rarely known. For the first time a domino dehydrogenation-condensation-hydrogenation sequence of alcohols and sulfonamides has been realized in the presence of a nanostructured catalyst. The magnetic property of the catalyst system allows for convenient isolation of the product and efficient recycling of the catalyst. A variety of coupling reactions of benzylic alcohols and sulfonamides including various heterocycles were successfully realized, often with >80% isolated yield. Advantageously, only one equivalent of the primary alcohol is consumed in the process. Mechanistic investigations of the competitive reactions of benzyl alcohol and d(7)-benzyl alcohol with p-toluenesulfonamide revealed a kinetic isotope effect (k(H)/k(D)) of 2.86 (+/-0.109) for the dehydrogenation of benzyl alcohol and 0.74 (+/-0.021) for the hydrogenation of N-benzylidene-p-toluenesulfonamide intermediate, which suggests dehydrogenation of the alcohol to be the rate determining step. PMID:19191701

Shi, Feng; Tse, Man Kin; Zhou, Shaolin; Pohl, Marga-Martina; Radnik, Jörg; Hübner, Sandra; Jähnisch, Klaus; Brückner, Angelika; Beller, Matthias

2009-02-11

158

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

159

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

PubMed Central

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

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

2012-01-01

160

Efficient synthesis and antioxidant evaluation of 2-aryl-3-(pyrimidin-2-yl)-thiazolidinones.  

PubMed

In the present study, we reported the efficient synthesis of 11 3-(pyrimidin-2-yl)-thiazolidinones in good yields using molecular sieve as the desiccant agent. In addition, we have evaluated the antioxidant capacity of the synthesized compounds by the 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH•) and the 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS(+•) ) radicals scavenging assay. Six compounds showed antioxidant activity towards DPPH• (EC50 between 16.13 and 49.94 µg/mL) and also demonstrated excellent activity regarding ABTS(+•) (TEAC: 10.32-53.52). These results showed that compounds 3-(pyrimidin-2-yl)-thiazolidinones may be easily synthesized by a less expensive procedure and could be a good starting point to the development of new antioxidant compounds. PMID:23798366

Campos Júnior, José C; Gouvęa, Daniela P; Ribeiro, Camila da S; Dutra, Filipe S P; Stefanello, Francieli M; Pereira, Claudio M P; Cunico, Wilson; Siqueira, Geonir M

2013-06-24

161

Chemoselective Tryptophan Labeling with Rhodium Carbenoids at Mild pH  

PubMed Central

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

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

2009-01-01

162

Efficient synthesis of 2-deoxy- l- erythro-pentose (2-deoxy- l-ribose) from l-arabinose  

Microsoft Academic Search

An efficient and practical route for the large-scale synthesis of 2-deoxy-l-erythro-pentose (2-deoxy-l-ribose) starting from l-arabinose was developed using Barton-type free-radical deoxygenation reaction as a key step. The radical precursor, a phenoxythiocarbonyl ester, was prepared in situ, and the most efficient deoxygenation was achieved by slow addition of tributyltin hydride to the reaction mixture.

Youhoon Chong; Chung K Chu

2002-01-01

163

A Simple, Efficient and Green Method for Synthesis of Trisubstituted Electrophilic Alkenes Using Lipase as a Biocatalyst  

Microsoft Academic Search

A simple and efficient Knoevenagel condensation method for the synthesis of trisubstituted electrophilic alkenes was developed using Lipase as a biocatalyst. Knoevenagel condensation was performed using either the conventional method, with an lipases viz., Aspergillus Oryzae or with a Rhizopus Oryzae as a biocatalyst and reaction time, reaction temperature, yield and recyclability were compared among the three methods. The reaction

Bhushan Nanasaheb Borse; Sanjeev Ramchandra Shukla; Yogesh Ashok Sonawane

2011-01-01

164

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

PubMed

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

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

2013-02-21

165

Lithium bromide as an efficient, green, and inexpensive catalyst for the synthesis of quinoxaline derivatives at room temperature  

Microsoft Academic Search

An efficient, simple, and green procedure for the synthesis of quinoxaline derivatives is described. The condensation of 1,2-diamines with 1,2-diketones using lithium bromide (LiBr) in H2O\\/EtOH as a green reaction media at room temperature affords the title compounds in high to excellent yields and in short reaction times.

Alireza Hasaninejad; Abdolkarim Zare; Mohammad Reza Mohammadizadeh; Mohsen Shekouhy

2010-01-01

166

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...

167

Efficient synthesis of hydroxyl isoindolones by a pd-mediated c?h activation/annulation reaction.  

PubMed

Radical reaction: A convenient synthesis of hydroxyl isoindolones by a Pd-catalyzed C?H activation/annulation reaction with near "click chemistry" efficiency is presented (see scheme; TBHP=tert-butyl hydrogen peroxide). This methodology features short reaction times (10-30?min), high atom economy, wide substrate scope (22 examples), and good reaction yields (up to 93?%). PMID:23843382

Yu, Qingzhen; Zhang, Nana; Huang, Jianhui; Lu, Shaonan; Zhu, Yi; Yu, Xiaoxiao; Zhao, Kang

2013-07-10

168

Efficient synthesis of p-quinols using catalytic hypervalent iodine oxidation of 4-arylphenols with 4-iodophenoxyacetic acid and oxone.  

PubMed

Efficient synthesis of p-quinols (2) using catalytic hypervalent iodine oxidation of 4-arylphenols (1) with 4-iodophenoxyacetic acid (3) and Oxone was developed. Reaction of 1 with a catalytic amount of 3 in the presence of Oxone as a co-oxidant in tetrahydrofuran or 1,4-dioxane-water gave the corresponding 2 in excellent yields. PMID:19483353

Yakura, Takayuki; Omoto, Masanori

2009-06-01

169

Efficient and Novel Synthesis of Benzoxazole Derivatives in the Presence of Zinc Dust Under Solvent-Free Conditions  

Microsoft Academic Search

A mild and efficient method has been developed for the synthesis of 2-cyclic amine-substituted benzoxazole derivatives using zinc dust under microwave irradiation in the absence of solvent is described. A comparative study was performed under conventional and microwave heating conditions. Zinc dust can be reused several times after reactivation. The significant feature of this method is the isolation of the

M. S. R. Murty; Kesur R. Ram; Rayudu Venkateswara Rao; J. S. Yadav

2010-01-01

170

Evaluation of an automated double-synthesis module: efficiency and reliability of subsequent radiosyntheses of FHBG and FLT.  

PubMed

We optimized the synthesis methods for 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) and 9-(4-[(18)F]fluoro-3-[hydroxymethyl]butyl)guanine) ([(18)F]FHBG) and automated them on an Explora General Nucleophilic double-synthesis module. Furthermore, the synthesis efficiency and reliability and the formation of cross-contaminations of the products when preparing two consecutive batches were evaluated. Whereas the preinstalled FLT synthesis conditions required substantial modification in reaction and neutralization conditions to achieve radiochemical yields of up to 60% within 70±10 min including high-performance liquid chromatography purification, the synthesis of FHBG had to be implemented to the module to obtain competitive radiochemical yields of up to 40% in an overall synthesis time of 60±10 min. The radiochemical purities obtained were ?99% and ?96% for the synthesis of [(18)F]FLT and [(18)F]FHBG, respectively. No significant changes in yield or purity could be observed between both batch productions. We found that the yields and purities also did not change when performing FLT after FHBG syntheses and vice versa. Hence, we developed a synthesis setup that offers the opportunity to perform two subsequent syntheses of either [(18)F]FLT, [(18)F]FHBG or [(18)F]FLT after [(18)F]FHBG without decrease in radiochemical yields and purities. Also, no cross-contaminations were observed, which can be attributed to the use of separate product delivery tubes, purification columns and an automated intermediate cleaning program. These results open up the possibility of producing consecutively either two equal (18)F-fluorinated tracers or two different ones in high yields on the same synthesis module. PMID:22172393

Niedermoser, Sabrina; Pape, Manuela; Gildehaus, Franz Josef; Wängler, Carmen; Hartenbach, Markus; Schirrmacher, Ralf; Bartenstein, Peter; Wängler, Björn

2011-12-14

171

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

NASA Astrophysics Data System (ADS)

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

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

1998-01-01

172

DNA or RNA oligonucleotide 2'-hydrazides for chemoselective click-type ligation with carbonyl compounds.  

PubMed

An efficient method for the synthesis of DNA or RNA oligonucleotide 2'-hydrazides is described. Fully deprotected oligonucleotides containing a hydrazide group at the 2'-position of a uridine residue were obtained by a novel two-step procedure: periodate cleavage of an oligonucleotide with 1,2-diol group followed by conversion of the aldehyde to hydrazide with an extended linker arm using a homobifunctional reagent succinic dihydrazide and NaBH(3)CN. The resulting oligonucleotide 2'-hydrazides were efficiently conjugated by a click-type reaction at acidic pH to aliphatic or aromatic aldehydes with or without NaBH(3)CN reduction to afford novel 2'-conjugates. PMID:21888548

Khomyakova, Elena A; Zubin, Eugeny M; Smirnov, Igor P; Pozmogova, Galina E; Stetsenko, Dmitry A; Oretskaya, Tatiana S

173

Efficient Microwave-Assisted Synthesis of Human Islet Amyloid Polypeptide Designed to Facilitate the Specific Incorporation of Labeled Amino Acids  

PubMed Central

A cost-efficient, time-reducing solid-phase synthesis of the amyloidogenic, 37 residue islet amyloid polypeptide (IAPP) is developed using two pseudoprolines (highlighted blue in sequence) in combination with microwave technology. A yield twice that obtained with conventional syntheses is realized. The utility of this protocol is demonstrated by the synthesis of a 13C18O-labeled Ser-20 IAPP variant, a prohibitively expensive and chemically challenging site to label via other protocols. TEM analysis shows the peptide forms normal amyloid.

Marek, Peter; Woys, Ann Marie; Sutton, Kelvin; Zanni, Martin T.; Raleigh, Daniel P.

2011-01-01

174

Total synthesis of vineomycin b2.  

PubMed

The first total synthesis of vineomycin B2 (1) has been accomplished. The aglycon segment, a vineomycinone B2 derivative, and the glycon segment, an ?-l-acurosyl-l-rhodinose derivative, were prepared via C-glycosylation using an unprotected sugar and powerful chemoselective O-glycosylation using a 2,3-unsaturated sugar, respectively, as the key steps. Furthermore, effective and simultaneous introduction of the two glycon moieties to the aglycon part by concentration-controlled glycosylation led to the total synthesis of 1. PMID:24074200

Kusumi, Shunichi; Tomono, Satoshi; Okuzawa, Shunsuke; Kaneko, Erika; Ueda, Takashi; Sasaki, Kaname; Takahashi, Daisuke; Toshima, Kazunobu

2013-10-11

175

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

176

Synthesis of core-shell Y2O3 nanoparticles for enhanced luminescence efficiency  

NASA Astrophysics Data System (ADS)

In this works, rare earth ion doped core and core-shell Y2O3 phosphors have been extensively studied for many applications due to the high stability and emission range and intensity. The core-shell Y2O3: (RE= Eu, Dy, Tb) nanoparticles are synthesized using a two-step process in which 100-150 nm Y2O3 core particles are synthesized using a molten salt synthesis and the shell is deposited using a sol-gel process The core-shell architecture was designed for enhanced luminescence efficiency with long emission lifetimes. Specifically, a multi-shell architecture was necessary to spatially separate Dy3+, Eu3+ and Tb3+ within the phosphor to circumvent the energy transfer to the surface quenching sites. First, the crystallinity of Y2O3nanophosphors was characterized using X-ray analysis. RE-doped Y2O3 core nanoparticles have a good compositional homogeneity. We have also recorded emission spectra and measured fluorescence lifetime. After coating passive shell layer, emission spectra and measured emission lifetimes were compared with those form Y2O3 nanophosphor core system and the effectiveness of these core-shell phosphors were successfully assessed.

Choi, Ju H.; Hyun, Jae Y.; Kim, Ki H.; Kim, Jae P.

2013-09-01

177

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

PubMed

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

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

2010-07-01

178

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

179

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

PubMed Central

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

2013-01-01

180

Tandem reactions for streamlining synthesis: enantio- and diastereoselective one-pot generation of functionalized epoxy alcohols.  

PubMed

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

Hussain, Mahmud M; Walsh, Patrick J

2008-08-01

181

Efficient synthesis of heat exchanger networks combining heuristic approaches with a genetic algorithm  

NASA Astrophysics Data System (ADS)

In this work an innovative method for heat exchanger network (HEN) synthesis is introduced and examined. It combines a genetic algorithm (GA) with a heuristic based optimization procedure. The novel algorithm removes appearing heat load loops from the HEN structures when profitable, throughout the evolution. Two examples were examined with the new HEN synthesis method and for both better results were obtained. Thus, a positive effect of heuristic based optimization methods on the HEN synthesis with GA could be located.

Brandt, Christopher; Fieg, Georg; Luo, Xing

2011-08-01

182

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

2011-07-21

183

A convenient, eco-friendly, and efficient method for synthesis of bis(3-indolyl)methanes “on-water”  

Microsoft Academic Search

A convenient, eco-friendly, and efficient method for synthesis of bis(3-indolyl)methanes by the reaction of indoles with various aromatic aldehydes “on-water” has been developed. The attractive features of this method are that in cases of aldehydes which are easily oxidized to acids, no external catalyst is necessary while in other cases a trace amount (ca. 5 mol%) of commercially available and

Asok K. Mallik; Rammohan Pal; Chayan Guha; Haimanti Mallik

2011-01-01

184

An Efficient Total Synthesis of a Potent Anti-Inflammatory Agent, Benzocamphorin F, and Its Anti-Inflammatory Activity  

PubMed Central

A naturally occurring enynyl-benzenoid, benzocamphorin F (1), from the edible fungus Taiwanofungus camphoratus (Antrodia camphorata) was characterized by comprehensive spectral analysis. It displays anti-inflammatory bioactivity and is valuable for further biological studies. The present study is the first total synthesis of benzocamphorin F and the developed strategy described is a more efficient procedure that allowe the large-scale production of benzocamphorin F for further research of the biological activity both in vitro and in vivo.

Liao, Yu-Ren; Kuo, Ping-Chung; Liang, Jun-Weil; Shen, Yuh-Chiang; Wu, Tian-Shung

2012-01-01

185

DABCO?Catalyzed Efficient Synthesis of Naphthopyran Derivatives via One?Pot Three?Component Condensation Reaction at Room Temperature  

Microsoft Academic Search

Diazabicyclo[2.2.2]octane (DABCO) has been used as a mild and efficient catalyst for synthesis of 2?amino?3?cyano naphthopyran derivatives via a one?pot three?component reaction of aromatic aldehydes, naphthols, and malononitrile at room temperature. The short reaction times, easy workup, good to excellent yields, and mild reaction conditions make this domino Knoevenagel–Michael reaction both practical and attractive.

Saeed Balalaie; Sorour Ramezanpour; Morteza Bararjanian; Jürgen H. Gross

2008-01-01

186

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.

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

2013-01-01

187

Cellulose Sulfuric Acid: Novel and Efficient Biodegradable and Recyclable Acid Catalyst for the Solid-State Synthesis of Thiadiazolo Benzimidazoles  

Microsoft Academic Search

An efficient method for the synthesis of 2-substituted benzimidazoles has been developed. In this method, benzo[c][1,2,5]thiadiazole-4,5-diamine was condensed with different aldehydes in the presence of cellulose sulfuric acid under solvent-free conditions by simple physical grinding of reactants using a mortar and pestle at room temperature. The methodology is mild, high-yielding, and green, and the catalyst could be easily recycled.

B. Suresh Kuarm; J. Venu Madhav; B. Rajitha; Y. Thirupathi Reddy; P. Narsimha Reddy; Peter A. Crooks

2011-01-01

188

An efficient synthesis of benzodiazepinyl phosphonates as clostripain inhibitors via FeCl3 catalyzed four-component reaction.  

PubMed

A novel one-pot route for the synthesis of benzodiazepinyl phosphonates (BDPs) has been achieved. FeCl(3) efficiently catalyzed four-component condensation of diamines, acetone and phosphites in the presence of molecular sieves to furnish BDPs as novel chemical entities with good yield. The synthesized BDPs have shown significant protease inhibition activity against clostripain, a disease model for gas gangrene, suggesting that these novel chemical entities could be further explored as cysteine protease inhibitors. PMID:21584307

Bhattacharya, Asish K; Rana, Kalpeshkumar C; Raut, Dnyaneshwar S; Mhaindarkar, Vaibhav P; Khan, Mohamad I

2011-05-16

189

Efficient asymmetric synthesis of P-chiral phosphine oxides via properly designed and activated benzoxazaphosphinine-2-oxide agents.  

PubMed

A general, efficient, and highly diastereoselective method for the synthesis of structurally and sterically diverse P-chiral phosphine oxides was developed. The method relies on sequential nucleophilic substitution on the versatile chiral phosphinyl transfer agent 1,3,2-benzoxazaphosphinine-2-oxide, which features enhanced and differentiated P-N and P-O bond reactivity toward nucleophiles. The reactivities of both bonds are fine-tuned to allow cleavage to occur even with sterically hindered nucleophiles under mild conditions. PMID:23369026

Han, Zhengxu S; Goyal, Navneet; Herbage, Melissa A; Sieber, Joshua D; Qu, Bo; Xu, Yibo; Li, Zhibin; Reeves, Jonathan T; Desrosiers, Jean-Nicolas; Ma, Shengli; Grinberg, Nelu; Lee, Heewon; Mangunuru, Hari P R; Zhang, Yongda; Krishnamurthy, Dhileep; Lu, Bruce Z; Song, Jinhua J; Wang, Guijun; Senanayake, Chris H

2013-02-06

190

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

PubMed Central

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

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

2012-01-01

191

Divergent and convergent synthesis of polymannosylated dibranched antigenic peptide of the immunodominant epitope MBP(83-99).  

PubMed

Multiple antigenic peptide (MAP) systems are dendrimeric structures bearing multiple copies of identical or different peptide epitopes, and they have been demonstrated to show enhanced immunogenicity. Herein, we report the direct (divergent) and indirect (convergent) synthesis, using contemporary synthetic approaches, of a di-branched antigenic peptide (di-BAP) containing the immunodominant epitope MBP(83-99), which is implicated in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). The direct synthesis (di-BAP 1) was performed using microwave irradiation. The indirect synthesis (di-BAP 2) was carried out performing an efficient chemoselective coupling reaction through the formation of a thioether bond. Both di-BAPs were conjugated to polysaccharide mannan since mannosylation is a promising technique to achieve modulation in immune response. The conjugation was achieved through free amino groups of both di-BAPs via the formation of Schiff bases. The mannan-conjugated di-BAPs were further evaluated in vivo in a prophylactic vaccination protocol, prior to EAE induction in Lewis rats. PMID:23993671

Friligou, Irene; Rizzolo, Fabio; Nuti, Francesca; Tselios, Theodore; Evangelidou, Maria; Emmanouil, Mary; Karamita, Maria; Matsoukas, John; Chelli, Mario; Rovero, Paolo; Papini, Anna Maria

2013-08-13

192

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

PubMed Central

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

Hoover, Jessica M.; Stahl, Shannon S.

2011-01-01

193

Efficient synthesis of fluorophosphonylated alkyles by ring-opening reaction of cyclic sulfates.  

PubMed

Ring-opening reactions of functionalized 1,2-cyclic sulfates and oxetanes with the phosphonodifluoromethyl carbanion are reported. This approach allows an easy access to fluorinated beta-hydroxyphosphonates that are building blocks in the synthesis of acyclic nucleosides. Synthesis of precursors of nucleoside phosphorylase inhibitors from these alcohols is described. PMID:18666773

Diab, Sonia Amel; Sene, Aboubacary; Pfund, Emmanuel; Lequeux, Thierry

2008-07-31

194

Automated analysis and computationally efficient synthesis of acoustic guitar strings and body  

Microsoft Academic Search

Synthesis of stringed instrument sounds that match an acoustic prototype requires models for the string oscillation and the instrument body. Cost-effective digital filters that implement physical models of oscillating strings have been extensively studied; the current challenge is in the inexpensive replication of the spectral changes induced by the body of a physical instrument. Currently reported synthesis efforts suggest that

Kevin Bradley; Mu-Huo Cheng; Virginia L. Stonick

1995-01-01

195

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.

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

1990-01-01

196

Efficient handling of operating range and manufacturing linevariations in analog cell synthesis  

Microsoft Academic Search

We describe a synthesis system that takes operating range constraints and inter and intracircuit parametric manufacturing variations into account while designing a sized and biased analog circuit. Previous approaches to computer-aided design for analog circuit synthesis have concentrated on nominal analog circuit design, and subsequent optimization of these circuits for statistical fluctuations and operating point ranges. Our approach simultaneously synthesizes

Tamal Mukherjee; L. Richard Carley; Rob A. Rutenbar

2000-01-01

197

Highly efficient, four-component one-pot synthesis of tetrasubstituted imidazoles using Keggin-type heteropolyacids as green and reusable catalysts  

Microsoft Academic Search

An efficient and improved procedure for the synthesis of tetrasubstituted imidazoles is developed by Keggin-type heteropolyacid (HPA) catalyzed four-component one-pot coupling protocol in refluxing ethanol.

Majid M. Heravi; Fatemeh Derikvand; Fatemeh F. Bamoharram

2007-01-01

198

Requirements at the 3? End of the Sindbis Virus Genome for Efficient Synthesis of Minus-Strand RNA  

PubMed Central

The 3?-untranslated region of the Sindbis virus genome is 0.3 kb in length with a 19-nucleotide conserved sequence element (3? CSE) immediately preceding the 3?-poly(A) tail. The 3? CSE and poly(A) tail have been assumed to constitute the core promoter for minus-strand RNA synthesis during genome replication; however, their involvement in this process has not been formally demonstrated. Utilizing both in vitro and in vivo analyses, we have examined the role of these elements in the initiation of minus-strand RNA synthesis. The major findings of this study with regard to efficient minus-strand RNA synthesis are the following: (i) the wild-type 3? CSE and the poly(A) tail are required, (ii) the poly(A) tail must be a minimum of 11 to 12 residues in length and immediately follow the 3? CSE, (iii) deletion or substitution of the 3? 13 nucleotides of the 3? CSE severely inhibits minus-strand RNA synthesis, (iv) templates possessing non-wild-type 3? sequences previously demonstrated to support virus replication do not program efficient RNA synthesis, and (v) insertion of uridylate residues between the poly(A) tail and a non-wild-type 3? sequence can restore promoter function to a limited extent. This study shows that the optimal structure of the 3? component of the minus-strand promoter is the wild-type 3? CSE followed a poly(A) tail of at least 11 residues. Our findings also show that insertion of nontemplated bases can restore function to an inactive promoter.

Hardy, Richard W.; Rice, Charles M.

2005-01-01

199

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

PubMed

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

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

2001-02-23

200

Mild Rh(III)-catalyzed C-H activation and annulation with alkyne MIDA boronates: short, efficient synthesis of heterocyclic boronic acid derivatives.  

PubMed

Taking advantage of Rh(III)-catalyzed C-H activation reactions, we have developed a mild, short, and efficient method for the synthesis of bench-stable 3-isoquinolone MIDA boronates. The reaction is practical and scalable. The product formed has been applied in the Suzuki-Miyaura reaction with high efficiency. This strategy has also been successfully expanded to the synthesis of MIDA boronate functionalized heterocycles such as isoquinoline, pyrrole, and indole. PMID:23146122

Wang, Honggen; Grohmann, Christoph; Nimphius, Corinna; Glorius, Frank

2012-11-20

201

Efficient synthesis of biindenylidene derivatives via a domino-Heck-type double cyclization of diaryldienynes.  

PubMed

[reaction: see text] Synthesis of aromatic ring substituted (E)-1,1'-biindenylidene derivatives was achieved by a domino-Heck type double cyclization of (Z,Z)-1,6-diaryl-1,5-hexadien-3-ynes. PMID:12967287

Abdur Rahman, S M; Sonoda, Motohiro; Itahashi, Kayo; Tobe, Yoshito

2003-09-18

202

Synthesis of Abeta[1-42] and its derivatives with improved efficiency.  

PubMed

It has been proved that the principal component of senile plaques is aggregates of beta-amyloid peptide (Abeta) in cases of one of the most common forms of age-related neurodegenerative disorders, Alzheimer's disease (AD). Although the synthetic methods for the synthesis of Abeta peptides have been developed since their first syntheses, Abeta[1-42] is still problematic to prepare. The highly hydrophobic composition of Abeta[1-42] results in aggregation between resin-bound peptide chains or intrachain aggregation which leads to a decrease in the rates of deprotection and repetitive incomplete coupling reactions during 9-flurenylmethoxycarbonyl (Fmoc) synthesis. In order to avoid aggregation and/or disrupt internal aggregation during stepwise Fmoc solid phase synthesis and to improve the quality of crude products, several attempts have been made. Since highly pure Abeta peptides in large quantities are used in biological experiments, we wanted to develop a method for a rational synthesis of human Abeta[1-42] with high purity and adequate yield. This paper reports a convenient methodology with a novel solvent system for the synthesis of Abeta[1-42], its N-terminally truncated derivatives Abeta[4-42] and Abeta[5-42], and Abeta[1-42] labeled with 7-amino-4-methyl-3-coumarinylacetic acid (AMCA) at the N-terminus using Fmoc strategy. The use of 10% anisole in Dimethylformamide/Dichloromethane (DMF/DCM) can substantially improve the purity and yield of crude Abeta[1-42] and has been shown to be an optimal coupling condition for the synthesis of Abeta[1-42]. Anisole is a cheap and simple aid in the synthesis of 'difficult sequences' where other solvents are less successful in the prevention of aggregation during the synthesis. PMID:17103463

Zarándi, Márta; Soós, Katalin; Fülöp, Lívia; Bozsó, Zsolt; Datki, Zsolt; Tóth, Gábor K; Penke, Botond

2007-02-01

203

A green and efficient protocol for the synthesis of quinoxaline, benzoxazole and benzimidazole derivatives using heteropolyanion-based ionic liquids: as a recyclable solid catalyst.  

PubMed

In this paper, we introduce two nonconventional ionic liquid compounds which are composed of propane sulfonate functionalized organic cations and heteropolyanions as green solid acid catalysts for the highly efficient and green synthesis of 2,3-disubstitutedquinoxaline derivatives. These ionic liquids are in the solid state at room temperature and the synthesis is carried out via the one-pot condensation reaction of various o-phenylenediamine with 1,2-diketone derivatives. Benzoxazole and benzimidazole derivatives were also synthesized by these novel catalysts via the one-pot condensation from reaction orthoester with o-aminophenol (synthesis of benzoxazole derivatives) and ophenylenediamine (synthesis of benzimidazole derivatives). All experiments successfully resulted in the desired products. The described novel synthesis method has several advantages of safety, mild condition, high yields, short reaction times, simplicity and easy workup compared to the traditional method of synthesis. PMID:23547570

Vahdat, Seyed Mohammad; Baghery, Saeed

2013-09-01

204

Efficient in vitro synthesis of biologically active RNA and RNA hybridization probes from plasmids containing a bacteriophage SP6 promoter.  

PubMed Central

A simple and efficient method for synthesizing pure single stranded RNAs of virtually any structure is described. This in vitro transcription system is based on the unusually specific RNA synthesis by bacteriophage SP6 RNA polymerase which initiates transcription exclusively at an SP6 promoter. We have constructed convenient cloning vectors that contain an SP6 promoter immediately upstream from a polylinker sequence. Using these SP6 vectors, optimal conditions have been established for in vitro RNA synthesis. The advantages and uses of SP6 derived RNAs as probes for nucleic acid blot and solution hybridizations are demonstrated. We show that single stranded RNA probes of a high specific activity are easy to prepare and can significantly increase the sensitivity of nucleic acid hybridization methods. Furthermore, the SP6 transcription system can be used to prepare RNA substrates for studies on RNA processing (1,5,9) and translation (see accompanying paper). Images

Melton, D A; Krieg, P A; Rebagliati, M R; Maniatis, T; Zinn, K; Green, M R

1984-01-01

205

Accelerated chemical synthesis of peptides and small proteins  

PubMed Central

The chemical synthesis of peptides and small proteins is a powerful complementary strategy to recombinant protein overexpression and is widely used in structural biology, immunology, protein engineering, and biomedical research. Despite considerable improvements in the fidelity of peptide chain assembly, side-chain protection, and postsynthesis analysis, a limiting factor in accessing polypeptides containing greater than 50 residues remains the time taken for chain assembly. The ultimate goal of this work is to establish highly efficient chemical procedures that achieve chain-assembly rates of approximately 10–15 residues per hour, thus underpinning the rapid chemical synthesis of long polypeptides and proteins, including cytokines, growth factors, protein domains, and small enzymes. Here we report Boc chemistry that employs O-(7-azabenzotriazol-1-yl)-N,N,N?,N?-tetramethyluronium hexafluorophosphate (HATU)/dimethyl sulfoxide in situ neutralization as the coupling agent and incorporates a protected amino acid residue every 5 min to produce peptides of good quality. This rapid coupling chemistry was successfully demonstrated by synthesizing several small to medium peptides, including the “difficult” C-terminal sequence of HIV-1 proteinase (residues 81–99); fragment 65–74 of the acyl carrier protein; conotoxin PnIA(A10L), a potent neuronal nicotinic receptor antagonist; and the pro-inflammatory chemotactic protein CP10, an 88-residue protein, by means of native chemical ligation. The benefits of this approach include enhanced ability to identify and characterize “difficult couplings,” rapid access to peptides for biological and structure–activity studies, and accelerated synthesis of tailored large peptide segments (<50 residues) for use in chemoselective ligation methods.

Miranda, Les P.; Alewood, Paul F.

1999-01-01

206

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

PubMed Central

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

2010-01-01

207

A rapid and efficient ultrasound-assisted synthesis of 5,5-diphenylhydantoins and 5,5-diphenyl-2-thiohydantoins.  

PubMed

To obtain a rapid, efficient and mild synthesis of 5,5-diphenylhydantoin and 5,5-diphenyl-2-thiohydantoin derivatives, ultrasonic irradiation has been applied to the reaction mixtures containing substituted benzils and urea or thiourea derivatives catalyzed by KOH in DMSO/H(2)O, which allowed us to achieve products at room temperature in a good yield and short time without any side product. This convenient procedure will allow a further increase of the diversity within the hydantoin family. PMID:20920873

Arani, Naimeh Moshtael; Safari, Javad

2010-09-09

208

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

PubMed

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 1-3 min. In vitro antitubercular activity of these triazoles was screened against Mycobacterium tuberculosis H(37)Rv strain. Four of the compounds showed MIC in the range of 1.56-3.13 ?g/mL proving their potential activity. PMID:22061642

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

2011-10-19

209

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

2011-03-17

210

Silacarboxylic acids as efficient carbon monoxide releasing molecules: synthesis and application in palladium-catalyzed carbonylation reactions.  

PubMed

Silacarboxylic acids have been demonstrated to be easy to handle, air-stable carbon monoxide precursors. Different silacarboxylic acids were synthesized from the corresponding chlorosilanes and carbon dioxide, and their decarbonylation, upon treatment with an array of activators, was evaluated. The release of CO from crystalline MePh(2)SiCO(2)H proved to be highly efficient, and it was successfully applied in a selection of palladium-catalyzed carbonylative couplings using near-stoichiometric quantities of carbon monoxide precursor. Finally, the synthesis of MePh(2)Si(13)CO(2)H and its application in carbonyl labeling of two bioactive compounds was demonstrated. PMID:22014278

Friis, Stig D; Taaning, Rolf H; Lindhardt, Anders T; Skrydstrup, Troels

2011-10-24

211

Chemoselective Oxidative C(CO)?C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen.  

PubMed

Aldehyde Termination: A novel copper-catalyzed transformation from methyl ketones into aldehydes has been accomplished. This method is applicable to a wide range of aromatic and aliphatic methyl ketones and chemoselectively produces aldehydes, accompanied by the release of hydrogen (H2 ) and carbon dioxide (CO2 ) as by-products. PMID:24000196

Zhang, Lin; Bi, Xihe; Guan, Xiaoxue; Li, Xingqi; Liu, Qun; Barry, Badru-Deen; Liao, Peiqiu

2013-09-02

212

Assembly of synthetic peptide vaccines by chemoselective ligation of epitopes: influence of different chemical linkages and epitope orientations on biological activity  

Microsoft Academic Search

In this paper, we describe the assembly of synthetic peptide vaccines composed of a T helper cell epitope and a B cell epitope that were synthesized separately and then attached using three different chemoselective ligation methods: oxime bond formation, thioether bond formation and disulfide bond formation. The resulting vaccines were tested in animals to investigate their efficacy. We found that

Weiguang Zeng; Souravi Ghosh; Mary Macris; Joanne Pagnon; David C Jackson

2001-01-01

213

Highly efficient synthesis of endomorphin-2 under thermodynamic control catalyzed by organic solvent stable proteases with in situ product removal.  

PubMed

An efficient enzymatic synthesis of endomorphin-2 (EM-2) was achieved using organic solvent stable proteases in nonaqeous media, based on thermodynamic control and an in situ product removal methodology. The high stability of biocatalysts in organic solvents enabled the aleatoric modulation of the nonaqueous reaction media to shift thermodynamic equilibrium toward synthesis. Peptide Boc-Phe-Phe-NH2 was synthesized with a high yield of 96% by the solvent stable protease WQ9-2 in monophase medium with an economical molar ratio of the substrate of 1:1. The tetrapeptide Boc-Tyr-Pro-Phe-Phe-NH2 was synthesized with a yield of 88% by another organic solvent tolerant protease PT121 from Boc-Tyr-Pro-OH and Phe-Phe-NH2 in an organic-aqueous biphasic system. The reaction-separation coupling in both enzymatic processes provides "driving forces" for the synthetic reactions and gives a high yield and high productivity without purification of the intermediate, thereby making the synthesis more amenable to scale-up. PMID:23305895

Xu, Jiaxing; Sun, Honglin; He, Xuejun; Bai, Zhongzhong; He, Bingfang

2012-12-19

214

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

215

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

PubMed

Mass production of soluble graphene still remains a challenge, although several methodologies have been proposed. Here we report a rapid and efficient method for the synthesis of soluble graphene nanosheets (GNSs) with long-term dispersion stability in both aqueous and common organic solvents. Within only 12 min at 95 °C, exfoliated graphite oxide in ammonia solution (pH 10) was reduced to soluble GNSs using N-methyl-p-aminophenol sulfate (metol) as a reducing agent without external stabilizers. The prepared GNSs were characterized by different techniques and a comparison of metol and hydrazine hydrate as reducing agents was made. The results indicated that, with the advantages of being rapid, efficient, inexpensive and relatively environmentally friendly, the reduction of graphite oxide into soluble GNSs by metol is a promising substitute for hydrazine hydrate in the mass production of soluble GNSs. PMID:23128046

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

2012-11-06

216

Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst.  

PubMed

In this paper, a stable and highly efficient plasmonic photocatalyst, Ag@AgCl, with cube-like morphology, has been successfully prepared via a simple hydrothermal method. Using methylene dichloride as chlorine source in the synthesis can efficiently control the morphology of Ag@AgCl, due to the low release rate of chloride ions. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra were used to characterize the obtained product. The photocatalytic activity of the obtained product was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation, and it was found, interestingly, that Ag@AgCl exhibits high visible light photocatalytic activity and good stability. PMID:21611675

Han, Lei; Wang, Ping; Zhu, Chengzhou; Zhai, Yueming; Dong, Shaojun

2011-05-25

217

An efficient synthesis of gougerotin and related analogues using solid- and solution-phase methodology.  

PubMed

The first solid-phase synthesis of the natural product gougerotin has been accomplished. The synthetic route is versatile and allows for diversification at position C-4 of the heterocycle, C-6' of the sugar ring, and both residues of the peptidic moiety at N-4' in a parallel fashion. [structure: see text] PMID:16048309

Migawa, Michael T; Risen, Lisa M; Griffey, Richard H; Swayze, Eric E

2005-08-01

218

Efficient synthesis of methylene exo-glycals: another use of glycosylthiomethyl chlorides.  

PubMed

A new approach to the synthesis of methylene exo-glycals is described. Oxidation of glycosylthiolmethyl chloride (GTM-Cl) with mCPBA afforded the corresponding glycosylchloromethyl sulfone in almost quantitative yield, which underwent KOtBu-induced Ramberg-Bäcklund rearrangement to furnish the desired methylene exo-glycal in excellent yield. PMID:17326686

Zhu, Xiangming; Jin, Ying; Wickham, John

2007-02-28

219

Rapid and efficient synthesis of symmetrical alkyl disulfides under phase transfer conditions  

Microsoft Academic Search

A one-pot, rapid and general method for the synthesis of symmetrical disulfides based on reaction of sulfur with sodium sulfide in the presence of didecyldimethylammonium bromide (DDAB) as a phase transfer catalyst is reported. Reaction with a variety of alkyl halides, at room temperature, afforded the disulfides in good to excellent isolated yields in a short time.

Sachin U. Sonavane; Mandan Chidambaram; Joseph Almog; Yoel Sasson

2007-01-01

220

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

2012-05-23

221

Enhancing solid phase synthesis by a noncovalent protection strategy-efficient coupling of rhodamine to resin-bound peptide nucleic acids  

Microsoft Academic Search

Resins for solid-phase synthesis can affect coupling efficiencies by interacting with reactants. We have observed that polyethylene glycol-polystyrene (PEG-PS) solid support absorbs added activated fluorophores, preventing efficient labeling of peptide nucleic acids (PNAs). We now report that addition of an inexpensive unactivated fluorophore blocks the resin and allows efficient labeling. This protection strategy may have general benefits for peptide and

Lynn D. Mayfield; David R. Corey

1999-01-01

222

A highly efficient and direct approach for synthesis of enantiopure beta-amino alcohols by reductive cross-coupling of chiral N-tert-butanesulfinyl imines with aldehydes.  

PubMed

A highly efficient and practical approach for the synthesis of optically pure beta-amino alcohols by the SmI2-induced reductive cross-coupling of chiral N-tert-butanesulfinyl imines with aldehydes was developed. This method allows the preparation of a broad range of chiral beta-amino alcohols, including functionalized ones under mild conditions. It provides a straightforward access to enantiopure beta-amino alcohols that are widely applicable in asymmetric synthesis. PMID:16117531

Zhong, Yu-Wu; Dong, Yi-Zhou; Fang, Kai; Izumi, Kenji; Xu, Ming-Hua; Lin, Guo-Qiang

2005-08-31

223

An efficient and scalable one-pot double Michael addition-Dieckmann condensation for the synthesis of 4,4-disubstituted cyclohexane beta-keto esters.  

PubMed

A simple, scalable, and efficient one-pot methodology for the synthesis of 4,4-disubstituted cyclohexane beta-keto esters from benzylic nitriles or esters and methyl acrylate promoted by potassium tert-butoxide is described. The process relies on a tandem double Michael addition-Dieckmann condensation reaction, which results in the formation of three discrete carbon-carbon bonds in a single pot, including a quaternary center. The method allows for the convenient and rapid synthesis of a variety of 4-aryl-4-cyano-2-carbomethoxycyclohexanone and 4-aryl-2,4-biscarbomethoxycyclohexanone building blocks for use in natural products synthesis and medicinal chemistry. PMID:17696402

DeGraffenreid, Michael R; Bennett, Sarah; Caille, Sebastien; Gonzalez-Lopez de Turiso, Felix; Hungate, Randall W; Julian, Lisa D; Kaizerman, Jacob A; McMinn, Dustin L; Rew, Yosup; Sun, Daqing; Yan, Xuelei; Powers, Jay P

2007-08-14

224

Efficient synthesis of exo-olefinated deoxoartemisinin derivatives by Ramberg-Bäcklund rearrangement.  

PubMed

10-exo-Bromoalkylidene- and benzylidenedeoxoartemisinins were synthesized from corresponding 10-alkanesulfonyldihydroartemisinin and 10-phenylmethanesulfonyldihydroartemisinin using a highly efficient, mild, and simple Ramberg-Bäcklund rearrangement. PMID:14750835

Oh, Sangtae; Jeong, In Howa; Lee, Seokjoon

2004-02-01

225

Green synthesis of polysaccharide/gold nanoparticle nanocomposite: an efficient ammonia sensor.  

PubMed

A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using guar gum (GG) as a reducing agent is reported. The nanoparticles obtained are characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on these results, a potential mechanism for this method of AuNPs synthesis is discussed. GG/AuNPs nanocomposite (GG/AuNPs NC) was exploited for optical sensor for detection of aqueous ammonia based on surface plasmon resonance (SPR). It was found to have good reproducibility, response times of ?10 s and excellent sensitivity with a detection limit of 1ppb (parts-per-billion). This system allows the rapid production of an ultra-low-cost GG/AuNPs NC-based aqueous ammonia sensor. PMID:23544533

Pandey, Sadanand; Goswami, Gopal K; Nanda, Karuna K

2013-01-16

226

Copper-catalyzed trifluoromethyl thiolation-mild and efficient synthesis of trifluoromethyl thioethers.  

PubMed

Mild-mannered sulfur: A general method for the synthesis of vinyl trifluoromethyl thioethers starting from readily available di-, tri-, and tetrasubstituted vinyl iodides was developed. A wide variety of substrates were applied in the reaction with CuSCF3 to give the corresponding products in high yields, within short reaction times, with retention of the initial E/Z isomer ratio. In addition, a copper-catalyzed trifluoromethyl thioether protocol has been also developed. PMID:24108595

Rueping, Magnus; Tolstoluzhsky, Nikita; Nikolaienko, Pavlo

2013-09-17

227

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

228

Structure and protein separation efficiency of poly(N-isopropylacrylamide) gels: Effect of synthesis conditions  

Microsoft Academic Search

Crosslinked poly(N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslink- ing copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition

Nilhan Kayaman; Dilek Kazan; Altan Erarslan; UZ OKAY; Bahattin M. Baysal

1998-01-01

229

Efficient Synthesis of Simvastatin by Use of Whole-Cell Biocatalysis  

Microsoft Academic Search

Simvastatin is a semisynthetic derivative of the fungal polyketide lovastatin and is an important drug for lowering cholesterol levels in adults. We have developed a one-step, whole-cell biocatalytic process for the synthesis of simvastatin from monacolin J. By using an Escherichia coli strain overexpressing the previously discovered acyltransferase LovD (X. Xie, K. Watanabe, W. A. Wojcicki, C. C. Wang, and

Xinkai Xie; Yi Tang

2007-01-01

230

Synthesis of Memory-Efficient Real-Time Controllers for Safety Objectives (Full Version)  

Microsoft Academic Search

We study synthesis of controllers for real-time systems, where the objective\\u000ais to stay in a given safe set. The problem is solved by obtaining winning\\u000astrategies in concurrent two-player \\\\emph{timed automaton games} with safety\\u000aobjectives. To prevent a player from winning by blocking time, we restrict each\\u000aplayer to strategies that ensure that the player cannot be responsible for

Krishnendu Chatterjee; Vinayak S. Prabhu

2011-01-01

231

Synthesis of the Apelsvoll Cropping System Experiment in Norway – Nutrient Balances, Use Efficiencies and Leaching  

Microsoft Academic Search

In this overview, a synthesis of the first 10 years of the Apelsvoll cropping system experiment, located in southeast Norway,\\u000a is given. All major flows of N, P and K in six different cropping systems, each covering 0.18 ha of separately tile-drained\\u000a plots, were either measured or estimated. The effects of the cropping system on the soil nutrient pools (total-N,

Audun Korsaeth; Ragnar Eltun

232

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

PubMed

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

Warad, Ismail

2010-06-30

233

Efficient construction of therapeutics, bioconjugates, biomaterials and bioactive surfaces using azide-alkyne "click" chemistry.  

PubMed

The concept of "click" chemistry, introduced by Sharpless and coworkers a couple of years ago, promotes the use of efficient, selective and versatile chemical reactions in synthetic chemistry. For instance, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is regarded as a prime example of "click" chemistry. This reaction is regioselective, chemoselective and moreover can be performed in aqueous medium at room or physiological temperature. Thus, CuAAC became lately a very popular ligation tool in biological and medical sciences. Several hundred of articles exploring the synthetic possibilities of CuAAC in biosciences have been published within the last four years. The aim of the present review is to give an overall--non exhaustive--picture of this emerging field of research. The advantages and versatility of CuAAC in scientific disciplines as diverse as drug discovery, biochemistry, bioconjugates synthesis, drug-delivery, gene therapy, bioseparation or diagnostics are presented and discussed in detail. PMID:18406491

Lutz, Jean-François; Zarafshani, Zoya

2008-03-04

234

Efficient \\  

Microsoft Academic Search

In 1999, Poupard and Stern proposed on the fly signature scheme (PS-scheme), which aims at minimizing the on-line computa- tional work for a signer. In this paper, we propose more efficient on the fly signature schemes by improving the PS-scheme. In PS-scheme, the size of secret-key is fixed by modulus n, so that this feature leads to some drawbacks in

Takeshi Okamoto; Mitsuru Tada; Atsuko Miyaji

2001-01-01

235

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

PubMed

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

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

2010-10-12

236

The total synthesis of (-)-7-deoxyloganin via N-heterocyclic carbene catalyzed rearrangement of ?,?-unsaturated enol esters.  

PubMed

The diastereoselective N-heterocyclic carbene (NHC) catalyzed rearrangement of ?,?-unsaturated enol ester (S)-2b has been used to assemble dihydropyranone (S)-3b, a material embodying the bicyclic core of the iridoid family of natural products. Elaboration of this intermediate, by chemoselective reduction followed by stereoselective ?-glycosylation, has allowed the total synthesis of (-)-7-deoxyloganin (1) to be achieved in four subsequent steps. PMID:20873828

Candish, Lisa; Lupton, David W

2010-11-01

237

RCM macrocyclization made practical: an efficient synthesis of HCV protease inhibitor BILN 2061.  

PubMed

We report here that dramatic improvement of the key RCM reaction in the synthesis of HCV protease inhibitor BILN2061 can be achieved by N-substitution of the diene substrate with an electron-withdrawing group. Mechanistic studies using 1H NMR spectroscopy showed an unprecedented switch of the initiation sites and the correlation between such switch and the results of RCM, from the unmodified to the modified substrates. We also provided theoretical evidence that such modification may also increase the thermodynamic preference of the macrocyclic product over the diene substrate. PMID:18293994

Shu, Chutian; Zeng, Xingzhong; Hao, Ming-Hong; Wei, Xudong; Yee, Nathan K; Busacca, Carl A; Han, Zhengxu; Farina, Vittorio; Senanayake, Chris H

2008-02-23

238

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

239

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

PubMed

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

Ahmadi, Ali; Saidi, Kazem; Khabazzadeh, Hojattollah

2009-02-14

240

Asymmetric organocatalytic double-conjugate addition of malononitrile to dienones: efficient synthesis of optically active cyclohexanones.  

PubMed

9-Amino-9-deoxyepiquinine efficiently catalyzed the double-conjugate addition of malononitrile to dienones. A number of 1,1,2,6-tetrasubstituted cyclohexanones were prepared in good yields, diastereoselectivities, and excellent enantioselectivities. PMID:21188969

Li, Xue-ming; Wang, Bo; Zhang, Jun-min; Yan, Ming

2010-12-28

241

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

242

In Vitro Screening of Feed Resources for Efficiency of Microbial Protein Synthesis  

Microsoft Academic Search

\\u000a Recent advances in ration balancing include manipulation of feed to increase the quantity and quality of protein and energy\\u000a delivered to the small intestine. Proportionally high conversion of feed degraded in the rumen into microbial mass, i.e. a\\u000a high efficiency of microbial mass production, will lead to efficient utilization of feed nitrogen and carbon. Selection of\\u000a fibrous feeds based on

Harinder P. S. Makkar

243

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

PubMed Central

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

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

2010-01-01

244

Efficient synthesis of 16 aromatic Morita-Baylis-Hillman adducts: Biological evaluation on Leishmania amazonensis and Leishmania chagasi.  

PubMed

Sixteen aromatic Morita-Baylis-Hillman adducts (MBHA) 1-16 were efficiently synthesized in a one step Morita-Baylis-Hillman reaction (MBHR) involving commercial aldehydes with methyl acrylate or acrylonitrile (81-100% yields) without the formation of side products on DABCO catalysis and at low temperature (0°C). The toxicities of these compounds were assessed against promastigote form of Leishmania amazonensis and Leishmania chagasi. The low synthetic cost of these MBHA, green synthetic protocols, easy one-step synthesis from commercially available and cheap reagents as well as the very good antileishmanial activity obtained for 14 and 16 (IC?? values of 6.88?gmL?ą and 11.06?gmL?ą respectively on L. amazonensis; 9.58?gmL?ą and 14.34?gmL?ą respectively on L. chagasi) indicates that these MBHA can be a novel and promising class of anti-parasitic compounds. PMID:20855101

Junior, Cláudio G L; de Assis, Priscila A C; Silva, Fábio P L; Sousa, Suervy C O; de Andrade, Natália G; Barbosa, Ticiano P; Nerís, Patrícia L N; Segundo, Luiz V G; Anjos, Italo C; Carvalho, Gabriel A U; Rocha, Gerd B; Oliveira, Márcia R; Vasconcellos, Mário L A A

2010-09-19

245

From highly efficient impurity-free CNT synthesis to DWNT forests, CNT solids, and super-capacitors  

NASA Astrophysics Data System (ADS)

We demonstrate an extremely efficient chemical vapour deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by controlling the ambient of the CVD furnace, a growth mode we call "Super Growth" [1]. The enhanced catalytic activity of super growth results in massive growth of super-dense and vertically-aligned single-walled nanotubes forests with heights up to 2.5 millimeters. In addition, these SWNT forests were easily separated from the catalysts, producing the most pure SWNT material (over 99.98%) ever made, through an all-dry process without any purification. Moreover, patterned highly organized intrinsic single-walled nanotube structures were successfully fabricated. Super Growth simultaneously addresses many critical problems such as scalability, purity, and cost, and opens up innumerable opportunities ranging from fundamental research to real applications.

Hata, Kenji

2007-03-01

246

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

PubMed

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

Safari, Javad; Zarnegar, Zohre

2012-10-17

247

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

Microsoft Academic Search

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

Yuying Du; Fuli Tian; Wenzhi Zhao

2006-01-01

248

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

SciTech Connect

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

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

2011-01-01

249

Efficient synthesis of single gold nanoparticle hybrid amphiphilic triblock copolymers and their controlled self-assembly.  

PubMed

We report on a robust approach to the size-selective and template-free synthesis of asymmetrically functionalized ultrasmall (<4 nm) gold nanoparticles (AuNPs) stably anchored with a single amphiphilic triblock copolymer chain per NP. Directed NP self-assembly in aqueous solution can be facilely accomplished to afford organic/inorganic hybrid micelles, vesicles, rods, and large compound micelles by taking advantage of the rich microphase separation behavior of the as-synthesized AuNP hybrid amphiphilic triblock copolymers, PEO-AuNP-PS, which act as the polymer-metal-polymer analogue of conventional amphiphilic triblock copolymers. Factors affecting the size-selective fabrication and self-assembly characteristics and the time-dependent morphological evolution of NP assemblies were thoroughly explored. PMID:22524544

Hu, Jinming; Wu, Tao; Zhang, Guoying; Liu, Shiyong

2012-04-30

250

Search for highly efficient, stereoselective, and practical synthesis of complex organic compounds of medicinal importance as exemplified by the synthesis of the c21?c37 fragment of amphotericin?b.  

PubMed

Highly stereoselective: A highly efficient, stereoselective and practical synthesis of the C21?C37 fragment of amphotericin?B was realized in 25?% overall yield in eight longest linear steps from commercially available ethyl (S)-3-hydroxybutyrate by using Fráter-Seebach alkylation, Brown crotylboration, Negishi coupling, Heck reaction, and Horner-Wadsworth-Emmons (HWE) olefination as key steps. PMID:24038187

Wang, Guangwei; Xu, Shiqing; Hu, Qian; Zeng, Fanxing; Negishi, Ei-Ichi

2013-09-03

251

An efficient asymmetric synthesis of the potent beta-blocker ICI-118,551 allows the determination of enantiomer dependency on biological activity.  

PubMed

A highly efficient, practical and flexible two-step asymmetric synthesis of the beta(2)-selective beta-blocker ICI 118,551 is reported, allowing an unambiguous determination of the dependency of biological activity with optical activity, revealing the S,S-enantiomer to be the most potent. PMID:20431838

Baker, James R; Hothersall, J Daniel; Fitzmaurice, Richard J; Tucknott, Matthew; Vinter, Andy; Tinker, Andrew; Caddick, Stephen

2010-04-30

252

Zirconium Tetrakis(dodecyl Sulfate) [Zr(DS)4] as an Efficient Lewis Acid–Surfactant Combined Catalyst for the Synthesis of Quinoxaline Derivatives in Aqueous Media  

Microsoft Academic Search

Zirconium tetrakis(dodecyl sulfate) [Zr(DS)4] efficiently catalyzes the synthesis of quinoxaline derivatives via the condensation of 1,2-diamines with 1,2-diketones in H2O as a green media at room temperature. Using this method, the title compounds are produced in good to excellent yields and relatively short reaction times.

Alireza Hasaninejad; Abdolkarim Zare; Mohammad Ali Zolfigol; Mohsen Shekouhy

2009-01-01

253

Efficient synthesis of indenes by FeCl 3·6H 2O-catalyzed intramolecular Friedel–Crafts reaction of aryl-substituted allylic alcohols  

Microsoft Academic Search

An efficient procedure for the synthesis of substituted indenes through the FeCl3·6H2O-catalyzed intramolecular Friedel–Crafts cyclization of aryl-substituted allylic alcohols has been developed. This method features the easily available starting materials, cheap catalyst, simple manipulation, and mild conditions.

Jialiang Wang; Lixin Zhang; Yufeng Jing; Wen Huang; Xigeng Zhou

2009-01-01

254

DABCO as a mild and efficient catalytic system for the synthesis of highly substituted imidazoles via multi-component condensation strategy  

Microsoft Academic Search

A simple and efficient protocol for the synthesis of highly substituted imidazoles is developed through the condensation of 1,2-dicarbonyl compound, aldehyde, and ammonium acetate or amine via multi-component condensation strategy. The present method gives good to excellent yields of substituted imidazoles.

S. Narayana Murthy; B. Madhav; Y. V. D. Nageswar

2010-01-01

255

High efficiency synthesis of F-18 fluoromethyl ethers: an attractive alternative for C-11 methyl groups in positron emission tomography radiopharmaceuticals.  

PubMed

A rapid and efficient method for the synthesis of O-fluoromethyl aliphatic and aromatic ethers is presented. This method is so mild that it can be used for the preparation of positron emission tomography (PET) radiopharmaceuticals bearing O-[(18)F]fluoromethyl groups. PMID:23930998

Park, Chansoo; Lee, Byoung Se; Chi, Dae Yoon

2013-08-09

256

Nano-sized copper as an efficient catalyst for one pot three component synthesis of thiazolidine-2,4-dione derivatives  

Microsoft Academic Search

A simple, efficient, stereoselective, one pot three component condensation reaction between thiazolidine-2,4-dione, aldehyde and amine derivatives using monodispersed, recyclable and inexpensive Cu-nanoparticles for the synthesis of thiazolidine-2,4-dione derivatives in excellent yields and high purity has been described here for the first time.

Ajeet Kumar; Prashant Singh; Amit Saxena; Arnab De; Ramesh Chandra; Subho Mozumdar

2008-01-01

257

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

Microsoft Academic Search

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

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

2008-01-01

258

An efficient electrochemical synthesis of diamino-o-benzoquinone: mechanistic and kinetic evaluation of the reaction of azide ion with o-benzoquinone.  

PubMed

An efficient method for the synthesis of diamino-o-benzoquinone based on the Michael reaction of electrochemically generated o-benzoquinone with azide ion is described, as well as an estimation of the homogeneous rate constant (k(obs)) of the reaction of o-benzoquinone with azide ion by the digital-simulation method. PMID:17180233

Nematollahi, Davood; Afkhami, Abbas; Tammari, Esmail; Shariatmanesh, Tahere; Hesari, Mahdi; Shojaeifard, Maryam

2006-10-25

259

An efficient synthesis of the fully elaborated isoindolinone unit of muironolide A.  

PubMed

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

Xiao, Qing; Young, Kyle; Zakarian, Armen

2013-06-13

260

An efficient synthesis of the benzhydrylpiperazine delta opioid agonist (+)BW373U86  

Microsoft Academic Search

A diastereoselective version of Katritzky's method for tertiary amine formation provides an efficient route to the highly selective, non-peptidal, delta opioid agonist (+)-4-[(?R)-?-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl]-N,N-diethylbenzamide [(+)-BW373U86], 1.

Michael J. Bishop; Robert W. McNutt

1995-01-01

261

An efficient modeling and synthesis procedure of asynchronous sequential logic circuits  

Microsoft Academic Search

A model and procedure are developed for synthesizing asynchronous sequential logic circuits (ASLCs). This model represents the functional behavior with a more compact form and the procedure can synthesize them more efficiently than the traditional one. With the identification of edge inputs from the design specification, a set of equations can be generated which describes the functional behavior of the

Jun-Woo Kang; Chin-Long Wey; P. D. Fisher

1992-01-01

262

Efficient and versatile synthesis of star polymers in water and their use as emulsifiers.  

PubMed

Core cross-linked star polymers of low polydispersity were efficiently prepared in high yield by RAFT-mediated emulsion and dispersion polymerizations in water at high solid content. These star polymers were demonstrated to be effective emulsifiers, and the emulsion was successfully used as template to fabricate polymer particles. PMID:22037974

Qiu, Qian; Liu, Guangyao; An, Zesheng

2011-10-31

263

An efficient approach to the synthesis of novel pyrene-fused azaacenes.  

PubMed

An efficient synthetic approach for functionalization of both the active sites (1,3-) and the K-region (4,5,9,10-) of pyrene was accomplished by bromination and oxidation with considerable yield. These novel pyrene-fused azaacenes were thoroughly investigated by X-ray diffraction studies, electrochemistry, and DFT calculations. PMID:23822170

Feng, Xing; Iwanaga, Fumitaka; Hu, Jian-Yong; Tomiyasu, Hirotsugu; Nakano, Masahiro; Redshaw, Carl; Elsegood, Mark R J; Yamato, Takehiko

2013-07-03

264

Efficient coupling and solid-phase synthesis of steroidal ketone derivative using polymer-bound glycerol  

Microsoft Academic Search

High-yield coupling of steroidal hindered ketones onto polymer-bound glycerol by an efficient acetal exchange reaction is reported under mild conditions. A solid-phase model sequence of five steps is thereafter achieved to synthesize a steroidal ketone derivative having two levels of diversity in good yield and purity.

René Maltais; Marie Bérubé; Olivier Marion; Richard Labrecque; Donald Poirier

2000-01-01

265

Highly efficient synthesis of phenols by copper-catalyzed hydroxylation of aryl iodides, bromides, and chlorides.  

PubMed

8-Hydroxyquinolin-N-oxide was found to be a very efficient ligand for the copper-catalyzed hydroxylation of aryl iodides, aryl bromides, or aryl chlorides under mild reaction conditions. This methodology provides a direct transformation of aryl halides to phenols and to alkyl aryl ethers. The inexpensive catalytic system showed great functional group tolerance and excellent selectivity. PMID:21786767

Yang, Kai; Li, Zheng; Wang, Zhaoyang; Yao, Zhiyi; Jiang, Sheng

2011-07-25

266

Synthesis and Preliminary Demulsification Efficiency Evaluation of New Demulsifiers Based on Fatty Oils  

Microsoft Academic Search

Three raw fatty oils were used as precursors for demulsifiers. The hydrolyzed form of each oil was adducted with maleic anhydride then modified by esterification with polyethylene glycols or ethyleneoxide-propyleneoxide block copolymers. The demulsfication efficiency, coalescence rate, some surface active, thermodynamic properties, and partition coefficient of a selected demulsifier were investigated. The best demulsifier shows 100% demulsification after 19 minutes

Rasha A. El-Ghazawy; Ahmed M. Al-Sabagh; Nadia G. Kandile; Mahmoud R. Noor El-Din

2010-01-01

267

Farm productivity and efficiency in the CEE applicant countries: a synthesis of results  

Microsoft Academic Search

This article draws together results from farm efficiency studies in six Central and East European countries that are part of the EU enlargement process. The main questions addressed concern whether there is a clear superiority of one organisational type, namely, family farms, over corporate structures (production co-operatives and various types of farming companies) and the nature of the relationship between

Matthew Gorton; Sophia Davidova

2004-01-01

268

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

PubMed

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

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

2013-08-30

269

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

PubMed

We report chemical-vapor-deposition (CVD) synthesis of high-density lead sulfide (PbS) nanowire arrays and nano pine trees directly on Ti thin films, and the fabrication of photovoltaic devices based upon the PbS nanowires. The as-grown nanowire arrays are largely vertically aligned to the substrates and are uniformly distributed over a relatively large area. Field effect transistors incorporating single PbS nanowires show p-type conduction and high mobilities. These catalytic metal thin films also serve as photocarrier collection electrodes and greatly facilitate device integration. For the first time, we have fabricated Schottky junction photovoltaic devices incorporating PbS nanowires, which demonstrate the capability of converting near-infrared light to electricity. The PbS nanowire devices are stable in air and their external quantum efficiency shows no significant decrease over a period of 3 months in air. We have also compared the photocurrent direction and quantum efficiencies of photovoltaic devices made with different metal electrodes, and the results are explained by band bending at the Schottky junction. Our research shows that PbS nanowires are promising building blocks for collecting near-infrared solar energy. PMID:22699324

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

2012-06-15

270

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

271

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, Inčs; Gargouri, Ali; Belghith, Hafedh

2011-12-09

272

Synthesis of ZnO/CdSe hierarchical heterostructure with improved visible photocatalytic efficiency  

NASA Astrophysics Data System (ADS)

ZnO/CdSe hierarchical heterostructure was prepared using pompon-like ZnO as substrate materials, and hexagonal CdSe nanoparticles were dispersed on the ZnO plates. The hybrid ZnO/CdSe samples were intensively investigated by XRD, SEM, TEM, HRTEM, PL and UV-vis absorption spectrum. The photocatalytic experiments confirm that ZnO/CdSe heterostructure exhibits improved photocatalytic efficiency compared to pure ZnO under visible light irradiation. CdSe nanoparticles are believed to serve as photosensitizers to extend the absorption spectrum to visible light region. In addition, the incorporation of CdSe can suppress the recombination of photogenerated electron-hole pairs, which contributes to the enhancement of photocatalytic efficiency.

Wu, Yao; Xu, Fang; Guo, Defu; Gao, Zhiyong; Wu, Dapeng; Jiang, Kai

2013-06-01

273

Evidence synthesis as the key to more coherent and efficient research  

Microsoft Academic Search

BACKGROUND: Systematic review and meta-analysis currently underpin much of evidence-based medicine. Such methodologies bring order to previous research, but future research planning remains relatively incoherent and inefficient. METHODS: To outline a framework for evaluation of health interventions, aimed at increasing coherence and efficiency through i) making better use of information contained within the existing evidence-base when designing future studies; and

Alexander J Sutton; Nicola J Cooper; David R Jones

2009-01-01

274

A highly efficient "metalloligand" strategy for the synthesis of ternary Ln-Ru-W hybrids.  

PubMed

A series of novel ternary Ln-Ru-W hybrids constructed by metalloligands ([Ru(II)(bpy)2(4,4'-dcbpy)](PF6)2, m-H2LRu) and high-nuclear lanthanide clusters have been successfully synthesized using an efficient "metalloligand" strategy for the first time. Slow magnetic relaxation has been observed within the Dy-based hybrid. PMID:23900431

Wang, Lei; Yang, Weiting; Yi, Fei-Yan; Wang, Hao; Xie, Zhigang; Tang, Jinkui; Sun, Zhong-Ming

2013-07-30

275

Efficient synthesis of pure monotosylated beta-cyclodextrin and its dimers.  

PubMed

6-O-Monotosyl-?-cyclodextrin (mono-Ts-?CD) is one of the most important intermediates in the production of substituted ?CD. So far, performing the monotosylation reaction and, in particular, the purification steps was challenging, relied on toxic solvents, and resulted in long and expensive procedures at, importantly, low yields. Here, the reaction of cyclodextrin with p-toluenesulfonyl chloride in aqueous environment is described to obtain a highly pure mono-Ts-?CD, for which a single-step purification with a cation exchange resin was applied. With this synthetic route and purification, yields could be increased from typically <10-15% to 35%, and organic solvents could be avoided. As characterized by FTIR, mass spectrometry, elemental analysis, and NMR, mono-Ts-?CD was obtained with a molar purity of >98mol%. From mono-Ts-?CD, ?-cyclodextrin dimers linked by ethylenediamine (bis-Et-?CD) were successfully prepared (yield 93%, purity 96mol%) in a one-step approach using an anion exchange resin to trap leaving groups that typically interfere in the reaction. This synthesis procedure with a direct collection of side-products may be a general strategy applicable for nucleophilic substitution of tosylated cyclodextrins. PMID:24060538

Tripodo, Giuseppe; Wischke, Christian; Neffe, Axel T; Lendlein, Andreas

2013-08-25

276

Radioiodinated phenoxyacetic acid derivatives as potential brain imaging agents. I. Efficient synthesis via trimethylsilyl intermediates.  

PubMed

The usefulness of radioiodination via demetallation of aryltrimethylsilanes was demonstrated. The radioiodination reaction was found to be very rapid and the regiospecific incorporation of radioiodine could be carried out with high radiochemical yields and high radiospecific activity. 125I-Labeled dimethylaminoethyl iodophenoxyacetate derivatives (5a--e), dimethylaminoethyl iodophenoxyacetamide derivatives (7a--c), iodophenoxyethyl ethylenediamine derivatives (9,14) and an iodophenoxyethylpiperazine derivative (18) were efficiently synthesized from the corresponding aryltrimethylsilyl intermediates (4a--e, 6a--c, 8, 13, 17) by this method. PMID:2605676

Ohmomo, Y; Okuyama, S; Magata, Y; Ueno, Y; Tanaka, C; Yokoyama, A

1989-09-01

277

Designed synthesis of uniformly sized iron oxide nanoparticles for efficient magnetic resonance imaging contrast agents.  

PubMed

Various magnetic nanoparticles have been extensively investigated as novel magnetic resonance imaging (MRI) contrast agents owing to their unique characteristics, including efficient contrast effects, biocompatibility, and versatile surface functionalization capability. Nanoparticles with high relaxivity are very desirable because they would increase the accuracy of MRI. Recent progress in nanotechnology enables fine control of the size, crystal structure, and surface properties of iron oxide nanoparticles. In this tutorial review, we discuss how MRI contrast effects can be improved by controlling the size, composition, doping, assembly, and surface properties of iron-oxide-based nanoparticles. PMID:22138852

Lee, Nohyun; Hyeon, Taeghwan

2011-12-02

278

Synthesis and transfection efficiency of cationic oligopeptide lipids: role of linker.  

PubMed

In the design of new cationic lipids for gene transfection, the chemistry of linkers is widely investigated from the viewpoint of biodegradation and less from their contribution to the biophysical properties. We synthesized two dodecyl lipids with glutamide as the backbone and two lysines to provide the cationic headgroup. Lipid 1 differs from Lipid 2 by the presence of an amide linkage instead of an ester linkage that characterizes Lipid 2. The transfection efficiency of lipoplexes with cholesterol as colipid was found to be very high with Lipid 1 on Chinese Hamster Ovary (CHO) and HepG2 cell lines, whereas Lipid 2 has shown partial transfection efficiency on HepG2 cells. Lipid 1 was found to be stable in the presence of serum when tested in HepG2 and CHO cells albeit with lower activity. Fluorescence-based dye-binding and agarose gel-based assays indicated that Lipid 1 binds to DNA more efficiently than Lipid 2 at charge ratios of >1:1. The uptake of oligonucleotides with Lipid 1 was higher than Lipid 2 as revealed by confocal microscopy. Transmission electron microscopy (TEM) images reveal distinct formation of liposomes and lipoplexes with Lipid 1 but fragmented and unordered structures with Lipid 2. Fusion of Lipids 1 and 2 with anionic vesicles, with composition similar to plasma membrane, suggests that fusion of Lipid 2 was very rapid and unlike a fusion event, whereas the fusion kinetics of Lipid 1 vesicles was more defined. Differential scanning calorimetry (DSC) revealed a high T(m) for Lipid 1 (65.4 °C) while Lipid 2 had a T(m) of 23.5 °C. Surface area-pressure isotherms of Lipid 1 was less compressible compared to Lipid 2. However, microviscosity measured using 1,6-diphenyl-1,3,5-hexatriene (DPH) revealed identical values for vesicles made with either of the lipids. The presence of amide linker apparently resulted in stable vesicle formation, higher melting temperature, and low compressibility, while retaining the membrane fluid properties suggesting that the intermolecular hydrogen bonds of Lipid 1 yielded stable lipoplexes of high transfection efficiency. PMID:21985175

Gopal, Vijaya; Xavier, Jennifer; Kamal, Md Zahid; Govindarajan, Srinath; Takafuji, Makoto; Soga, Shuta; Ueno, Takayuki; Ihara, Hirotaka; Rao, Nalam M

2011-10-26

279

Fast synthesis and size control of gibbsite nanoplatelets, their pseudomorphic dehydroxylation, and efficient dye adsorption.  

PubMed

In this paper, a simple and fast (4 days) procedure to synthesize colloidal gibbsite nanoplatelets (NPTs) from a single aluminum alkoxide (aluminum sec-butoxide) as precursor is presented. The introduction of a preheating step accelerated the precursor's hydrolysis/peptization and considerably shortened the overall reaction time while the acid concentration affected the uniformity of the platelets shape. This procedure was successfully exploited to rapidly produce gibbsite platelets of controllable sizes by combination with the seeded growth method. The use of a single alkoxide precursor induced high growth rates and allowed a fast control of the platelets size over a wide range (nano- to microscale after only three growth steps). No signs for size limitation were observed. The dehydroxylation sequence of the as-synthesized NPTs was systematically investigated. Thermally stable chi-alumina NPTs, pseudomorphs of the parent gibbsite platelets, with a micro/mesoporous structure and high specific surface area, were obtained. The synthesized gibbsite NPTs can efficiently adsorb Methyl Orange dye in wastewater treatment with removal efficiency up to 94.8%. PMID:24001258

Louaer, Seifeddine; Wang, Yao; Guo, Lin

2013-09-18

280

Synthesis, structure, and highly efficient copper-catalyzed aziridination with a tetraaza-bispidine ligand.  

PubMed

The distorted trigonal-bipyramidal Cu(II) complex [Cu(L(1))(NCCH(3))](2+) of the novel tetradentate bispidine-derived ligand L(1) with four tertiary amine donors (L(1)=1,5-diphenyl-3-methyl-7-(1,4,6-trimethyl-1,4-diazacycloheptane-6-yl)diazabicyclo[3.3.1]nonane-9-one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper-bispidine complexes and the novel L(1)-based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture. PMID:19746459

Comba, Peter; Haaf, Christina; Lienke, Achim; Muruganantham, Amsaveni; Wadepohl, Hubert

2009-10-19

281

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

PubMed

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

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

2013-09-25

282

Highly Efficient Synthesis of Heterocyclic and Alicyclic ?(2) -Amino Acid Derivatives by Catalytic Asymmetric Hydrogenation.  

PubMed

A valuable class of new heterocyclic and alicyclic prochiral ?-aminomethylacrylates has been conveniently synthesized through a three-step transformation involving a Baylis-Hillman reaction, O-acetylation, and a subsequent allylic amination. The corresponding novel ?(2) -amino acid derivatives were prepared with excellent enantioselectivities and high yields by catalytic asymmetric hydrogenation using the catalyst rhodium(Et-Duphos) (Et-Duphos=2',5',2'',5''-tetraethyl-1,2-bis(phospholanyl)benzene)) under mild reaction conditions (up to 99?% ee and S/C=1000). The influence of the substrate on the enantioselectivity and reactivity is investigated, and the most suitable substrate configuration for the highly efficient enantioselective hydrogenation of ?-substituted ?-aminomethylacrylates under the Rh-Duphos system is reported. The current protocol provides a very practical, facile, and scalable method for the preparation of heterocyclic and alicyclic ?(2) -amino acids and their derivatives. PMID:23776190

Li, Lanning; Chen, Bin; Ke, Yuanyuan; Li, Qing; Zhuang, Yue; Duan, Kun; Huang, Yichun; Pang, Jiyan; Qiu, Liqin

2013-06-17

283

"In-gel" purified ditags direct synthesis of highly efficient SAGE Libraries  

PubMed Central

Background SAGE (serial analysis of gene expression) is a recently developed technique for systematic analysis of eukaryotic transcriptomes. The most critical step in the SAGE method is large scale amplification of ditags which are then are concatemerized for the construction of representative SAGE libraries. Here, we report a protocol for purifying these ditags via an 'in situ' PAGE purification method. This generates ditags free of linker contaminations, making library construction simpler and more efficient. Results Ditags used to generate SAGE libraries were demarcated 'in situ' on preparative polyacrylamide gels using XC and BPB dyes, which precisely straddle the ditag band when a 16% PAGE gel (19:1 acrylamide:bis, 5% cross linker) is used to resolve the DNA bands. Here, the ditag DNA was directly excised from gel without visualization via EtBr or fluorescent dye staining, resulting in highly purified ditag DNA free of contaminating linkers. These ditags could be rapidly self ligated even at 4°C to generate concatemers in a controlled manner, which in turn enabled us to generate highly efficient SAGE libraries. This reduced the labor and time necessary, as well as the cost. Conclusions This approach greatly simplified the ditag purification procedure for constructing SAGE libraries. Since the traditional post-run staining with EtBr or fluorescent dyes routinely results in cross contamination of a DNA band of interest by other DNA in the gel, the dry gel DNA excision method described here may also be amenable to other molecular biology techniques in which DNA purity is critically important.

Mathupala, Saroj P; Sloan, Andrew E

2002-01-01

284

Efficient Formation of Luminescent Lanthanide(III) Complexes by Solid-Phase Synthesis and On-Resin Screening.  

PubMed

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

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

2013-08-15

285

Highly efficient synthesis of low polydispersity core cross-linked star polymers by Ru-catalyzed living radical polymerization.  

PubMed

The efficient formation of low polydispersity core cross-linked star (CCS) polymers via controlled/living radical polymerization (LRP) and the arm-first approach was found to be dependent on the mediating catalyst system. The Ru catalyst, Ru(Ind)Cl(PPh?)? Cat. 1, and tertiary amine co-catalyst were used to synthesize highly living poly(methyl methacrylate) (PMMA) macroinitiators, which were then linked together with ethylene glycol dimethacrylate (EGDMA) to form PMMA(arm)PEGDMA(core) CCS polymers. The quantitative and near-quantitative synthesis of CCS polymers were observed for low to moderate molecular weight macroinitiators (M(n) = ?8 and 20?kDa), respectively. Lower conversions were observed for high-molecular weight macroinitiators (M(n) ?? ?60?kDa). Overall, an improvement of between 10 and 20% was observed when comparing the Cat. 1 system to a conventional Cu-catalyzed system. This significant improvement in macroinitiator-to-star conversion is explained in the context of catalyst system selection and CCS polymer formation. PMID:21433199

Goh, Tor Kit; Yamashita, Satoshi; Satoh, Kotaro; Blencowe, Anton; Kamigaito, Masami; Qiao, Greg G

2011-01-07

286

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

PubMed

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

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

2013-08-07

287

Highly efficient synthesis of chiral alcohols with a novel NADH-dependent reductase from Streptomyces coelicolor.  

PubMed

An NADH-dependent reductase (ScCR) from Streptomyces coelicolor was discovered by genome mining for carbonyl reductases. ScCR was overexpressed in Escherichia coli BL21, purified to homogeneity and its catalytic properties were studied. This enzyme catalyzed the asymmetric reduction of a broad range of prochiral ketones including aryl ketones, ?- and ?-ketoesters, with high activity and excellent enantioselectivity (>99% ee) towards ?-ketoesters. Among them, ethyl 4-chloro-3-oxobutanoate (COBE) was efficiently converted to ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), an important pharmaceutical intermediate, in water/toluene biphasic system. As much as 600 g/L (3.6M) of COBE was asymmetrically reduced within 22 h using 2-propanol as a co-substrate for NADH regeneration, resulting in a yield of 93%, an enantioselectivity of >99% ee, and a total turnover number (TTN) of 12,100. These results indicate the potential of ScCR for the industrial production of valuable chiral alcohols. PMID:21570826

Wang, Li-Juan; Li, Chun-Xiu; Ni, Yan; Zhang, Jie; Liu, Xiang; Xu, Jian-He

2011-04-28

288

Synthesis of graphene-ZnO-Au nanocomposites for efficient photocatalytic reduction of nitrobenzene.  

PubMed

A simple hydrothermal method of preparing highly photocatalytic graphene-ZnO-Au nanocomposites (G-ZnO-Au NCs) has been developed. Zinc acetate and graphene oxide are reduced by catechin to form graphene-zinc oxide nanospheres (G-ZnO NSs; average diameter of (45.3 ± 3.7) nm) in the presence of ethylenediamine (EDA) as a stabilizing agent and gold nanorods (Au NRs) at 300 °C for 2 h. Then Au NRs are deposited onto as-formed G-ZnO NSs to form G-ZnO-Au NCs. Upon ultraviolet light activation, G-ZnO-Au NCs (4 mg mL(-1)) in methanol generates electron-hole pairs. Methanol (hydroxyl group) assists in trapping holes, enabling photogenerated electrons to catalyze reduction of nitrobenzene (NB) to aniline with a yield of 97.8% during a reaction course of 140 min. The efficiency of G-ZnO-Au NCs is 3.5- and 4.5-fold higher than those provided by commercial TiO2 and ZnO NSs, respectively. Surface assisted laser desorption/ionization mass spectrometry has been for the first time applied to detect the intermediates (nitrosobenzene and phenylhydroxylamine) and major product (aniline) of NB through photoelectrocatalytic or photocatalytic reactions. The result reveals that the reduction of NB to aniline is through nitrosobenzene to phenylhydroxylamine in the photoelectrocatalytic reaction, while via nitrosobenzene directly in the photocatalytic reaction. G-ZnO-Au NC photocatalyst holds great potential in removal of organic pollutants like NB and in the production of aniline. PMID:23701390

Roy, Prathik; Periasamy, Arun Prakash; Liang, Chi-Te; Chang, Huan-Tsung

2013-06-04

289

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

290

Support-controlled chemoselective olefin-imine addition photocatalyzed by cadmium sulfide on a zinc sulfide carrier.  

PubMed

The semiconductor catalyzed photoaddition of cyclopentene or cyclohexene to various novel electron-poor imines of type p-XC(6)H(4)(CN)C[double bond, length as m-dash]N(COPh) (X = H, F, Cl, Br, Me, MeO) was investigated as a function of the nature of the cadmium sulfide photocatalyst. Irradiation (lambda>/= 350 nm) of silica supported cadmium sulfide surprisingly did not afford the expected olefin-imine adducts but an imine hydrocyanation product via an unprecedented dark reaction. However, when silica was replaced by zinc sulfide as the support for cadmium sulfide, the expected homoallylic N-benzoyl-alpha-amino cyanides were isolated in yields of 65-84%. Thus, chemoselectivity is introduced through replacing an insulating by a semiconducting support, a hitherto unknown effect in semiconductor photocatalysis. From the sign of the time resolved photovoltage it is found that the mixed metal sulfide interface CdS/ZnS increases the lifetime of photogenerated electron-hole pairs by about one order of magnitude as compared to the SiO(2)/CdS system. The reaction rate increases with increasing imine sigma-Hammett constants and decreasing stability of intermediate benzyl radicals. PMID:17277839

Gärtner, Marc; Ballmann, Joachim; Damm, Cornelia; Heinemann, Frank W; Kisch, Horst

2006-12-19

291

Efficient assessment of modified nucleoside stability under conditions of automated oligonucleotide synthesis: characterization of the oxidation and oxidative desulfurization of 2-thiouridine.  

PubMed

In order to efficiently assess the chemical stability of modified nucleosides to the reagents and conditions of automated oligonucleotide synthesis, we designed, developed and tested a scheme in which the modified nucleoside, directly attached to a solid support, is exposed to the cyclic chemistry of the instrument. Stability of 2-thiouridine against different oxidizers was investigated. Tertbutyl hydroperoxide (1 M) in anhydrous acetonitrile was a more effective oxidizer for the incorporation of 2-thiouridine into oligonucleotide chains than the same oxidizer in methylene chloride. Carbon tetrachloride/water in the presence of a basic catalyst was superior in maintaining the thiocarbonyl function, but its utility for RNA synthesis has yet to be fully tested, whereas 2-phenylsulfonyloxaziridine was a very efficient reagent for oxidative desulfurization of 2-thiouridine. PMID:11720000

Sochacka, E

292

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

PubMed Central

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

Babiss, L E; Ginsberg, H S

1984-01-01

293

Precise synthesis of polymers containing functional end groups by living ring-opening metathesis polymerization (ROMP): Efficient tools for synthesis of block\\/graft copolymers  

Microsoft Academic Search

This article summarizes recent examples for precise synthesis of (co)polymers containing functional end groups prepared by living ring-opening metathesis polymerization (ROMP) using molybdenum, ruthenium complex catalysts. In particular, this article reviews recent examples for synthesis of amphiphilic block\\/graft copolymers by adopting transition metal-catalyzed living ROMP technique. Unique characteristics of the living ROMP initiated by the molybdenum alkylidene complexes (so-called Schrock

Kotohiro Nomura; Mohamed Mehawed Abdellatif

2010-01-01

294

Enantioselective allylation of imines catalyzed by newly developed (-)-?-pinene-based ?-allylpalladium catalyst: an efficient synthesis of (R)-?-propylpiperonylamine and (R)-pipecolic acid.  

PubMed

A newly developed ?-allylpalladium with a (-)-?-pinene framework and an isobutyl side chain catalyzed the enantioselective allylation of imines in good yields and enantioselectivities (20 examples, up to 98% ee). An efficient enantioselective synthesis of the (R)-?-propyl piperonylamine part of DMP 777, a human leukocyte elastase inhibitor and (R)-pipecolic acid have been achieved as a useful application of this methodology. PMID:22910971

Fernandes, Rodney A; Nallasivam, Jothi L

2012-10-14

295

An efficient mixed-ligand Pd catalytic system to promote C-N coupling for the synthesis of N-arylaminotriazole nucleosides.  

PubMed

Make it unique! A mixed-ligand system of Pd/Synphos/Xantphos promotes effective C-N coupling in the synthesis of various N-arylaminotriazole and N-arylaminopurine nucleoside analogues. This catalytic system is strikingly powerful and efficient, allowing for unparalleled substrate scope and high product yields as well as promotion of C-Cl bond activation for C-N coupling (see scheme). PMID:22266830

Fan, Yuting; Xia, Yi; Tang, Jingjie; Ziarelli, Fabio; Qu, Fanqi; Rocchi, Palma; Iovanna, Juan L; Peng, Ling

2012-01-20

296

Highly Efficient Synthesis of (R)-3-Quinuclidinol in a Space-Time Yield of 916 g L(-1) d(-1) Using a New Bacterial Reductase ArQR.  

PubMed

A new keto reductase (ArQR), identified from Agrobacterium radiobacter ECU2556, can efficiently reduce 3-quinuclidinone in excellent enantioselectivity and high space-time yield for the synthesis of (R)-3-quinuclidinol, a chiral building block of many antimuscarinic agents. This is the first time that a high yield of (R)-3-quinuclidinol up to 916 g L(-1) d(-1) using a bioreduction approach is reported. PMID:24050153

Zhang, Wen-Xia; Xu, Guo-Chao; Huang, Lei; Pan, Jiang; Yu, Hui-Lei; Xu, Jian-He

2013-09-19

297

An efficient one-pot organocatalyzed synthesis of spiro[chroman-3,6'- furo[2,3-d]pyrimidine]-tetraones.  

PubMed

An efficient synthesis of new spiro[chroman-3,6'-furo[2,3-d]pyrimidine]- tetraones by an organocatalyzed three-component condensation reaction of aldehydes, barbituric acids and 3-bromo-4-hydroxy-2H-chromen-2-one in refluxing acetic acid in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is reported. We are hopeful that the products will lead to a wider range pharmacological and physiological activity. PMID:23363063

Ahadi, Somayeh; Mirzaei, Peiman; Bazgir, Ayoob

2013-07-01

298

A novel and efficient one step synthesis of 2-amino-5-cyano-6-hydroxy-4-aryl pyrimidines and their anti-bacterial activity.  

PubMed

The first simple and efficient approach towards one step synthesis of 2-amino-5-cyano-6-hydroxy-4-aryl pyrimidines has been developed by three component condensation of aromatic aldehydes, ethyl cyanoacetate and guanidine hydrochloride in alkaline ethanol. The synthesized compounds evaluated for their anti-bacterial activity against gram-positive and gram-negative bacteria. The some of the compounds showed excellent zone of inhibition against tested bacteria. PMID:19036478

Deshmukh, M B; Salunkhe, S M; Patil, D R; Anbhule, P V

2008-10-26

299

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

300

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

Microsoft Academic Search

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

Yuliang Zhang; Zhongqiang Zhou

2012-01-01

301

Efficient synthesis of stable phosphonate ylides and ?phosphonate esters: reaction between activated acetylenes and triphenylphosphite in the presence of sulfonamide and heterocyclic NH-acids.  

PubMed

An efficient synthesis of stable phosphonate ylides and phosphonate esters is described via a ?one-pot reaction between activated acetylenes and triphenylphosphite in the presence of sulfonamides and heterocyclic ?NH-acids. Single X-ray diffraction analysis and NMR studies were used in characterizing the ylides and phosphonate ester products. Dynamic NMR studies performed on a phosphonate ylide allowed the calculation of the free energy barrier for the inter-conversion between the geometrical isomers (E) and (Z). PMID:20673221

Charati, Faramarz Rostami; Maghsoodlou, Malek Taher; Habibi-Khorassani, Sayyed Mostafa; Hazeri, Nourallah; Ebrahimi, Ali; Hossaini, Zinatossadat; Ebrahimi, Pouneh; Maleki, Nariman; Adhamdoust, Sayyed Reza; Farahani, Fatemeh Vasheghani; Marandi, Ghasem; Sobolev, Alexandre; Makha, Mohamed

2011-01-01

302

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

Microsoft Academic Search

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

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

2008-01-01

303

Efficient synthesis of ribonucleotide reductase inhibitors 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3AP) and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (3AMP) via palladium mediated cross-coupling reactions  

Microsoft Academic Search

An efficient synthesis of potent ribonucleotide reductases inhibitors 3-amino-pyridine-2-carboxaldehyde thiosemicarbazone (3-AP) and 3-amino-4-methyl-pyridine-2-carboxaldehyde thiosemicarbazone (3-AMP) is described. The synthesis of 3-AP and 3-AMP was achieved in 4 and 5 steps, with overall yields of 61% and 39%, respectively. The synthesis featured a convergent approach utilizing a Stille coupling strategy to prepare vinylpyridine derivatives. A more economic way to synthesize vinylpyridine

Jun Li; Shu-Hui Chen; Xiuyan Li; Chuansheng Niu; Terrence W Doyle

1998-01-01

304

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

Microsoft Academic Search

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

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

2007-01-01

305

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

306

Timely Synthesis of the Adenovirus Type 5 E1B 55-Kilodalton Protein Is Required for Efficient Genome Replication in Normal Human Cells  

PubMed Central

Previous studies have indicated that the adenovirus type 5 E1B 55-kDa protein facilitates viral DNA synthesis in normal human foreskin fibroblasts (HFFs) but not in primary epithelial cells. To investigate this apparent difference further, viral DNA accumulation was examined in primary human fibroblasts and epithelial cells infected by the mutant AdEasyE1?2347, which carries the Hr6 frameshift mutation that prevents production of the E1B 55-kDa protein, in an E1-containing derivative of AdEasy. Impaired viral DNA synthesis was observed in normal HFFs but not in normal human bronchial epithelial cells infected by this mutant. However, acceleration of progression through the early phase, which is significantly slower in HFFs than in epithelial cells, eliminated the dependence of efficient viral DNA synthesis in HFFs on the E1B 55-kDa protein. These observations suggest that timely synthesis of the E1B 55-kDa protein protects normal cells against a host defense that inhibits adenoviral genome replication. One such defense is mediated by the Mre11-Rad50-Nbs1 complex. Nevertheless, examination of the localization of Mre11 and viral proteins by immunofluorescence suggested that this complex is inactivated similarly in AdEasyE1?2347 mutant-infected and AdEasyE1-infected HFFs.

Chahal, Jasdave S.

2012-01-01

307

General and efficient synthesis of 2-alkylcarbapenems: synthesis of dethiacarba analogs of Clinically Useful carbapenems via palladium-catalyzed cross-coupling reaction  

Microsoft Academic Search

Palladium-catalyzed cross-coupling reaction of carbapenem-2-yl triflate with alkylborane gave 2-alkylcarbapenem in good yield. The usefulness of this reaction was demonstrated by the synthesis of highly functionalized 2-alkylcarbapenems, dethiacarba analogs of imipenem, panipenem, biapenem, meropenem, and S-4661.

Yukitoshi Narukawa; Koichi Nishi; Hiroshi Onoue

1997-01-01

308

Novel, fast and efficient one-pot sonochemical synthesis of 2-aryl-1,3,4-oxadiazoles.  

PubMed

Ultrasound promoted synthesis of 2-aryl-1,3,4-oxadiazoles at ambient temperature is reported. The remarkable features of the new procedure are shorter reaction time, excellent yields, cleaner reaction profile and simple experimental and workup procedure. PMID:23845411

Rouhani, Morteza; Ramazani, Ali; Joo, Sang Woo

2013-06-20

309

KSF: an efficient catalyst for the regioselective synthesis of 1,5-diaryl pyrazoles using Baylis–Hillman adducts  

Microsoft Academic Search

A facile and convenient protocol was developed for the regioselective synthesis of 1,5-diarylpyrazoles using Baylis–Hillman\\u000a adducts over KSF catalyst in high yields (70–90%) and low reaction times.

Mohammad Nikpassand; Manouchehr Mamaghani; Khalil Tabatabaeian; Maryam Kupaei Abiazi

2009-01-01

310

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.

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

2010-01-01

311

Efficient routes to carbon-silicon bond formation for the synthesis of silicon-containing peptides and azasilaheterocycles.  

PubMed

Silasubstitution, where silicon is substituted for carbon at specific sites of the substrate, has become a growing practice in medicinal chemistry. Introducing silicon into bioactive compounds provides slight physical and electronic alterations to the parent compound, which in certain instances could make the substrate a more viable candidate for a drug target. One application is in the field of protease inhibition. Various silane diol isosteres can act as potent inhibitors of aspartic and metalloproteases because of their ability to mimic the high-energy tetrahedral intermediate in peptide bond hydrolysis. In particular, since 1998, the Sieburth group has prepared a number of functionalized peptide silane diol isosteres. In a seminal study, they demonstrated that these molecules can bind to the active site of the enzymes. Inspired by these results, we initiated a study to develop a concise and straightforward route to access highly functionalized silicon diol based peptidomimetic analogs, which we describe in this Account. The synthesis of such analogs is challenging because the dipeptide mimics require the formation of two carbon-silicon bonds as well as two chiral carbon centers. Our first strategy was to assemble the two C-Si bonds from diphenylsilane through an initial regioselective hydrosilylation step of a terminal alkene, followed by lithiation of the formed alkyldiphenylsilane by a simple lithium metal reduction. Subsequent diastereoselective addition of this silyllithium species to a tert-butylsulfinimine provided a rapid method to assemble the dipeptide mimic with stereochemical control at the new chiral carbon center adjacent to the silicon. This strategy worked with a wide range of functional groups. However, there were some limitations with the more elaborate targets. In particular, we needed to exchange the phenyl groups of the diphenylsilane with aryl groups that were more labile under acidic conditions in order to introduce Si-O bonds in the end product. We demonstrated that a variety of Ar(2)SiH(2) compounds with methyl substituents on the aromatic core could effectively undergo hydrosilylation and reductive lithiation with a soluble reducing agent, lithium naphthalenide. The electron-rich aromatic groups were more acid labile and, depending on the conditions, could produce either the silane diol or the silanol. In an alternative strategy, we used a highly regioselective Rh-catalyzed sequential double hydrosilylation to form the two C-Si bonds with a single catalyst. This approach is a more efficient, atom economical way to synthesize a wider range of highly functionalized organosilanes with the added possibility of extending this method into an asymmetric protocol. By this method, various functional groups that were not previously tolerated in the lithiation protocol, including OBn, OAc, furyl, and thiophenes, could now be incorporated. Hydrosilylation of a terminal olefin and a peptide functionalized with an enamide at the C-terminus achieved the desired silane in high yields in a one pot reaction without compromising the stereochemical integrity of the peptide. As an extension of this work, we used these methods to efficiently generate a variety of chiral azasilaheterocycles, including silapiperidines and silaindolizidines. PMID:23214467

Min, Geanna K; Hernández, Dácil; Skrydstrup, Troels

2012-12-06

312

Titanocene(III)-Catalyzed 6-exo Versus 7-endo Cyclizations of Epoxypolyprenes: Efficient Control and Synthesis of Versatile Terpenic Building Blocks.  

PubMed

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

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

2013-09-17

313

Combined directed ortho and remote metalation-Suzuki cross-coupling strategies. Efficient synthesis of heteroaryl-fused benzopyranones from biaryl O-carbamates.  

PubMed

A concise synthesis of heteroaryl dibenzopyranones 9a,b, 10a,b, 11a-c, and 12a-c has been achieved by the LDA-induced migration of heterobiaryl O-carbamates 18, 21, 25, and 30 which, in turn, were prepared in good yield using a combined directed ortho lithiation (DoM)-transition-metal-catalyzed Suzuki cross-coupling strategy. An efficient and general route to a wide variety of heterocycles including coumestans 19a,c and the previously unknown isothiocoumestan ring system 22b has been thereby achieved. PMID:19441801

James, Clint A; Coelho, Antonio Luiz; Gevaert, Matt; Forgione, Pat; Snieckus, Victor

2009-06-01

314

Stereoselective and efficient synthesis of (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-ol.  

PubMed

[reaction: see text] Two short and efficient synthesis routes have been developed for bis-THF-alcohol 2, a key building block of the investigational HIV protease inhibitor TMC114 (1). Using S-2,3-O-isopropylideneglyceraldehyde (4) as the source of chirality, both routes are based on a diastereoselective Michael addition of nitromethane to give predominantly the syn congeners 6 followed by a Nef oxidation and cyclization to afford lactone acetals 8, which are reduced and cyclized to give 2. PMID:16354099

Quaedflieg, Peter J L M; Kesteleyn, Bart R R; Wigerinck, Piet B T P; Goyvaerts, Nicolaas M F; Vijn, Robert Jan; Liebregts, Constantinus S M; Kooistra, Jaap H M H; Cusan, Claudia

2005-12-22

315

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

2013-09-26

316

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

317

Efficient and large-scale synthesis of few-layered graphene using an arc-discharge method and conductivity studies of the resulting films  

Microsoft Academic Search

An arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale\\u000a synthesis of few-layered graphene. The resulting samples of few-layered graphene, well-dispersed in organic solvents such\\u000a as N,N-dimethylformamide (DMF) and 1,2-dichlorobenzene (o-DCB), were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, atomic force\\u000a microscopy (AFM), and thermal gravimetric analysis (TGA).

Yingpeng Wu; Bin Wang; Yanfeng Ma; Yi Huang; Na Li; Fan Zhang; Yongsheng Chen

2010-01-01

318

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.

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

2013-01-01

319

NHC-mediated cross-coupling of sugar-derived cyclic nitrones with enals: general and efficient synthesis of polyhydroxylated pyrrolizidines and indolizidines.  

PubMed

A general and efficient method for the synthesis of polyhydroxylated pyrrolizidines and indolizidines has been developed based on the NHC-catalyzed cross-coupling of sugar-derived cyclic nitrones with enals, which afforded the key intermediates, ?-hydroxyl amino esters, in good to excellent yields. Thus, a variety of polyhydroxylated pyrrolizidines and indolizidines have been synthesized and assayed against various glycosidases, which showed that aryl or alkyl substituents at C-7 of pyrrolizidines or at C-8 of indolizidines reduced the potency of the glycosidase inhibition of these bicyclic iminosugars. PMID:23749268

Xu, Wen-Yuan; Iwaki, Ren; Jia, Yue-Mei; Zhang, Wei; Kato, Atsushi; Yu, Chu-Yi

2013-06-07

320

An efficient method for solution-phase parallel synthesis of 2-quinoxalinol salen Schiff-base ligands.  

PubMed

A solution-phase parallel method for the synthesis of 2-quinoxalinol salen ligands was designed and optimized. The synthesis begins with commercially available 1,5-difluoro-2, 4-dinitrobenzene (DFDNB) and employs a sequence of five straightforward and high-yielding reaction steps. Simple laboratory techniques with low sensitivity to water or air for solution-phase parallel reactions were coupled with convenient workup and purification procedures to give high-purity and yield a small ligand library of 20 compounds. The final step, a Schiff-base condensation of an aldehyde with the diaminoquinoxaline results in a new category of ligands for metal coordination or of potential bioactivity, based on the skeleton 2,2'-(1E,1'E)-(quinoxaline-6,7-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)diphenol. The approach described here is easily adaptable for parallel synthesis of a larger library. PMID:17497932

Wu, Xianghong; Gorden, Anne E V

2007-05-12

321

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

PubMed

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

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

2011-12-16

322

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

PubMed Central

We report a novel approach to the synthesis of GlcNAcstatins—members of an emerging family of potent and selective inhibitors of peptidyl O-GlcNAc hydrolase build upon tetrahydroimidazo[1,2-a]pyridine scaffold. Making use of a streamlined synthetic sequence featuring de novo synthesis of imidazoles from glyoxal, ammonia and aldehydes, a properly functionalised linear GlcNAcstatin precursor has been efficiently prepared starting from methyl 3,4-O-(2?,3?-dimethoxybutane-2?,3?-diyl)-?-d-mannopyranoside. Subsequent ring closure of the linear precursor in an intramolecular SN2 process furnished the key fused d-mannose-imidazole GlcNAcstatin precursor in excellent yield. Finally, a sequence of transformations of this key intermediate granted expeditious access to a variety of the target compounds bearing a C(2)-phenethyl group and a range of N(8) acyl substituents. The versatility of the new approach stems from an appropriate choice of a set of acid labile permanent protecting groups on the monosaccharide starting material. Application was demonstrated by the synthesis of GlcNAcstatins containing polyunsaturated and thiol-containing amido substituents.

Borodkin, Vladimir S.; van Aalten, Daan M.F.

2010-01-01

323

Total Synthesis of Bryostatin 7 via C-C Bond Forming Hydrogenation: Merged Redox-Construction Events for Synthetic Efficiency  

PubMed Central

The marine macrolide bryostatin 7 is prepared in 20 steps (longest linear sequence) and 36 total steps. A total of 5 C-C bonds are formed using hydrogenative methods. The present approach represents the most concise synthesis of any bryostatin reported, to date, setting the stage for practical syntheses of simplified functional analogues.

Lu, Yu; Woo, Sang Kook; Krische, Michael J.

2011-01-01

324

Copper-Catalyzed Regioselective Intramolecular Oxidative ?-Functionalization of Tertiary Amines: An Efficient Synthesis of Dihydro-1,3-Oxazines.  

PubMed

Traffic control: The hydroxy functional group directs the ?-functionalization of tertiary amines, synthesizing 1,3-oxazines by C?O bond formation. Reaction occurs with both benzylic and non-benzylic amines. In the case of naphthoxazine synthesis, 100?% diastereoselectivity was observed. A tentative two-pathway mechanism is proposed for the reaction. PMID:23893574

Deb, Mohit L; Dey, Suvendu S; Bento, Isabel; Barros, M Teresa; Maycock, Christopher D

2013-07-24

325

Cascade electrophilic iodocyclization: efficient preparation of 4-iodomethyl substituted tetrahydro-?-carbolines and formal synthesis of oxopropaline G.  

PubMed

4-Iodomethyl substituted tetrahydro-?-carbolines, the core structure of numerous natural products and bioactive molecules, are readily prepared via I2-promoted cascade electrophilic cyclization. The reactivity differences of olefins and alkynes ensure that the reaction proceeds smoothly. This methodology was successfully applied to the formal synthesis of oxopropaline G. PMID:23826674

Song, Hongjian; Liu, Yongxian; Wang, Qingmin

2013-06-19

326

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

327

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

328

A simple and efficient approach to 1,3-polyols: application to the synthesis of cryptocarya diacetate.  

PubMed

A highly enantio- and stereoselective synthetic strategy for both syn- and anti-1,3-polyols has been developed. The sequence involves iterative Jacobsen's hydrolytic kinetic resolution (HKR), diastereoselective iodine-induced electrophilic cyclization, and ring-closing metathesis (RCM). This protocol has subsequently been utilized for the synthesis of cryptocarya diacetate, a natural product with broad range of biological activity. PMID:16308881

Kumar, Pradeep; Gupta, Priti; Naidu, S Vasudeva

2006-02-01

329

A new and efficient method for the synthesis of 3,4-disubstituted pyrrolidine-2,5-diones.  

PubMed

A newly found reaction for the synthesis of 3,4-disubstituted 1-hydroxy-pyrrolidine-2,5-diones from 3-substituted coumarins and nitromethane has been elaborated. The reaction involved a simple and convenient experimental procedure. The applicability of the rearrangement reaction is determined. PMID:22547316

Ilieva, Eleonora D; Petkova, Nevena I; Nikolova, Rositca D

2012-04-30

330

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

PubMed

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

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

2013-08-16

331

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

2012-01-08

332

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

2009-08-22

333

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

PubMed Central

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

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

2012-01-01

334

Inhibition of protein synthesis by an efficiently expressed mutation in the yeast 5.8S ribosomal RNA.  

PubMed Central

Recent studies on the inhibition of protein synthesis by specific anti 5.8S rRNA oligonucleotides strongly suggested that this RNA plays an important role in eukaryotic ribosome function. To evaluate this possibility further, a ribosomal DNA transcription unit from Schizosaccharomyces pombe was cloned into yeast shuttle vectors with copy numbers ranging from 2 to approximately 90 per cell; to allow direct detection of expressed RNA and to disrupt the function of the 5.8S rRNA molecule, a five base insertion was made in a universally conserved GAAC sequence. The altered mobility of the mutant RNA was readily detected by gel electrophoresis and analyses indicated that mutant RNA transcription reflected the ratio of plasmid to endogenous rDNA. The highest copy number plasmid resulted in about 40-50% mutant RNA. This mutant RNA was readily integrated into the ribosome structure resulting in an in vivo ribosome population which was also about 40-50% mutant; the rates of growth and protein synthesis were equally reduced by approximately 40%. A comparable level of inhibition in protein synthesis was demonstrated in vitro and polyribosomal profiles revealed a consistent increase in size. Subsequent RNA analyses indicated a normal distribution of mutant RNA in both monoribosomes and polyribosomes, but elevated tRNA levels in mutant polyribosomes. Additional mutations in alternate GAAC sequences revealed similar but cumulative effects on both protein synthesis and polyribosome profiles. Taken together, these results suggest little or no effect on initiation but provide in vivo evidence of a functional role for the 5.8S rRNA in protein elongation. Images

Abou Elela, S; Good, L; Melekhovets, Y F; Nazar, R N

1994-01-01

335

Efficient synthesis of dimethyl carbonate via transesterification of ethylene carbonate with methanol over binary zinc-yttrium oxides  

Microsoft Academic Search

The binary zinc–yttrium oxides were prepared by co-precipitation method, characterized and tested in the synthesis of DMC via transesterification of ethylene carbonate with methanol. The catalytic results showed that the catalyst with Zn\\/Y molar ratio of 3 and calcined at 400°C exhibited superior catalytic activity, corresponding to TOF of 236mmol\\/gcath. Appropriate content of yttrium in the catalyst enhanced the catalytic

Liguo Wang; Ying Wang; Shimin Liu; Liujin Lu; Xiangyuan Ma; Youquan Deng

2011-01-01

336

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

Microsoft Academic Search

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

Marc Ostermeier; Richard Goddard; Christian Limberg; Stefan Hecht

2007-01-01

337

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

Microsoft Academic Search

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

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

2007-01-01

338

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

Microsoft Academic Search

We report chemical-vapor-deposition (CVD) synthesis of high-density lead sulfide (PbS) nanowire arrays and nano pine trees directly on Ti thin films, and the fabrication of photovoltaic devices based upon the PbS nanowires. The as-grown nanowire arrays are largely vertically aligned to the substrates and are uniformly distributed over a relatively large area. Field effect transistors incorporating single PbS nanowires show

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

2012-01-01

339

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

340

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

PubMed

Silicon nanoparticles can be considered a green material, especially when prepared via a microwave-assisted method without the use of highly reactive reducing agents or hydrofluoric acid. A simple solution synthesis of hydrogen-terminated Si- and Mn-doped Si nanoparticles via microwave-assisted synthesis is demonstrated. The reaction of the Zintl salt, Na(4)Si(4), or Mn-doped Na(4)Si(4), Na(4)Si(4(Mn)), with ammonium bromide, NH(4)Br, produces small dispersible nanoparticles along with larger particles that precipitate. Allylamine and 1-amino-10-undecene were reacted with the hydrogen-terminated Si nanoparticles to provide water solubility and stability. A one-pot, single-reaction process and a one-pot, two-step reaction process were investigated. Details of the microwave-assisted process are provided, with the optimal synthesis being the one-pot, two-step reaction procedure and a total time of about 15 min. The nanoparticles were characterized by transmission electron microscopy (TEM), x-ray diffraction, and fluorescence spectroscopies. The microwave-assisted method reliably produces a narrow size distribution of Si nanoparticles in solution. PMID:22743660

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

2012-06-28

341

Efficient and accurate high-degree spherical harmonic synthesis of gravity field functionals at the Earth's surface using the gradient approach  

NASA Astrophysics Data System (ADS)

Spherical harmonic synthesis (SHS) of gravity field functionals at the Earth's surface requires the use of heights. The present study investigates the gradient approach as an efficient yet accurate strategy to incorporate height information in SHS at densely spaced multiple points. Taylor series expansions of commonly used functionals quasigeoid heights, gravity disturbances and vertical deflections are formulated, and expressions of their radial derivatives are presented to arbitrary order. Numerical tests show that first-order gradients, as introduced by Rapp (J Geod 71(5):282-289, 1997) for degree 360 models, produce cm- to dm-level RMS approximation errors over rugged terrain when applied with EGM2008 to degree 2190. Instead, higher-order Taylor expansions are recommended that are capable of reducing approximation errors to insignificance for practical applications. Because the height information is separated from the actual synthesis, the gradient approach can be applied along with existing highly efficient SHS routines to compute surface functionals at arbitrarily dense grid points. This confers considerable computational savings (above or well above one order of magnitude) over conventional point-by-point SHS. As an application example, an ultra-high resolution model of surface gravity functionals (EurAlpGM2011) is constructed over the entire European Alps that incorporates height information in the SHS at 12,000,000 surface points. Based on EGM2008 and residual topography data, quasigeoid heights, gravity disturbances and vertical deflections are estimated at ~200m resolution. As a conclusion, the gradient approach is efficient and accurate for high-degree SHS at multiple points at the Earth's surface.

Hirt, Christian

2012-09-01

342

Iron-catalyzed bromination of aryl azides by N-bromosuccinimide: Efficient method for the synthesis of brominated aryl azides  

Microsoft Academic Search

An efficient and mild protocol for bromination of aryl azides with N-bromosuccinimide (NBS) under FeCl3 catalysis in 1,2-dichloroethane was developed. It is proved to be an efficient method for obtaining brominated aryl azides.

Hui Jin; Zhen Dong Huang; Chun Xiang Kuang; Xiao Kun Wang

2011-01-01

343

O-acyl isopeptide method: efficient synthesis of isopeptide segment and application to racemization-free segment condensation.  

PubMed

We report the establishment of the O-acyl isopeptide method-based racemization-free segment condensation reaction toward future chemical protein synthesis. Peptide segments containing C-terminal O-acyl Ser/Thr residues were successfully synthesized by use of a lower nucleophilic base cocktail for Fmoc removal, and then coupled to an amino group of a peptide-resin without side reactions or epimerization. We also succeeded in performing the segment condensation in a sequential manner and in solution phase conditions as well. PMID:19582299

Yoshiya, Taku; Kawashima, Hiroyuki; Sohma, Youhei; Kimura, Tooru; Kiso, Yoshiaki

2009-05-18

344

Efficient synthesis of multicyclic spirooxindoles via a cascade Michael/Michael/oxa-Michael reaction of curcumins and isatylidene malononitriles.  

PubMed

A cascade Michael/Michael/oxa-Michael reaction between curcumins and isatylidene malononitriles has been developed. Multicyclic spirooxindoles were prepared in excellent yields and diastereoselectivities. DMAP was found to catalyze this transformation efficiently under mild reaction conditions. PMID:22231456

Yin, Xiao-Gang; Liu, Xin-Yun; Hu, Zhi-Peng; Yan, Ming

2012-01-09

345

Highly efficient synthesis and characterization of the GPR30-selective agonist G-1 and related tetrahydroquinoline analogs  

PubMed Central

The GPR30 agonist probe G-1 and structural analogs were efficiently synthesized using multicomponent or stepwise Sc(III)-catalyzed aza-Diels Alder cyclization. Optimization of solvent and reaction temperature provided enhanced endo-diastereoselectivity.

Burai, Ritwik; Ramesh, Chinnasamy; Shorty, Marvin; Curpan, Ramona; Bologa, Cristian; Sklar, Larry A.; Oprea, Tudor; Prossnitz, Eric R.

2010-01-01

346

Concise and efficient synthesis of 2-acetamido-2-deoxy-beta-D-hexopyranosides of diverse aminosugars from 2-acetamido-2-deoxy-beta-D-glucose.  

PubMed

The furanose acetonide derivative 1 is readily prepared from 2-acetamido-2-deoxy-D-glucose on a large scale without the need for chromatography. Mesylation of 1 provides an efficient, concise, synthetic route to rare 2-acetamido-2-deoxy-beta-D-hexopyranosides (2 and 3) via the corresponding methyl 2-acetamido-2-deoxy-3-O-methanesulfonyl-beta-D-glucopyranoside and subsequent inversion of configuration by direct displacement or formation of a 3,4-epoxide. Opening of this epoxide by azide provided a direct route to methyl 2-acetamido-4-amino-2,4,6-trideoxy-beta-D-gulopyranoside 4. Benzylation of 1 followed by ring expansion to the glucopyranoside, deoxygenation at C-6, and subsequent displacement of a C-4 triflate permitted the synthesis of methyl 2-acetamido-4-amino-2,4,6-trideoxy-beta-D-galactopyranoside 5. Methyl 2-acetamido-2-deoxy-beta-D-glucopyranoside available from 1 in quantitative yield was readily converted to methyl 2-acetamido-2-deoxy-beta-D-galactopyranoside 6 (>60%) by inversion of configuration at C-4. Introduction of a lactyl substituent at C-3 of oxazoline 1 also provides a facile synthesis of the biologically important muramic acid beta-glycoside 7. An interesting reaction to convert 2-acetamido-2-deoxyhexopyranosides to the corresponding 2-deoxy-2-tetrazole is also reported. PMID:19132941

Cai, Ye; Ling, Chang-Chun; Bundle, David R

2009-01-16

347

Efficient synthesis of diverse heterobifunctionalized clickable oligo(ethylene glycol) linkers: potential applications in bioconjugation and targeted drug delivery.  

PubMed

Herein we describe the sequential synthesis of a variety of azide-alkyne click chemistry-compatible heterobifunctional oligo(ethylene glycol) (OEG) linkers for bioconjugation chemistry applications. Synthesis of these bioorthogonal linkers was accomplished through desymmetrization of OEGs by conversion of one of the hydroxyl groups to either an alkyne or azido functionality. The remaining distal hydroxyl group on the OEGs was activated by either a 4-nitrophenyl carbonate or a mesylate (-OMs) group. The -OMs functional group served as a useful precursor to form a variety of heterobifunctionalized OEG linkers containing different highly reactive end groups, e.g., iodo, -NH(2), -SH and maleimido, that were orthogonal to the alkyne or azido functional group. Also, the alkyne- and azide-terminated OEGs are useful for generating larger discrete poly(ethylene glycol) (PEG) linkers (e.g., PEG(16) and PEG(24)) by employing a Cu(I)-catalyzed 1,3-dipolar cycloaddition click reaction. The utility of these clickable heterobifunctional OEGs in bioconjugation chemistry was demonstrated by attachment of the integrin (?(v)?(3)) receptor targeting peptide, cyclo-(Arg-Gly-Asp-D-Phe-Lys) (cRGfKD) and to the fluorescent probe sulfo-rhodamine B. The synthetic methodology presented herein is suitable for the large scale production of several novel heterobifunctionalized OEGs from readily available and inexpensive starting materials. PMID:23296079

Goswami, Lalit N; Houston, Zachary H; Sarma, Saurav J; Jalisatgi, Satish S; Hawthorne, M Frederick

2013-02-21

348

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

PubMed

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

Otvös, Sándor B; Georgiádes, Adám; Mándity, István M; Kiss, Lóránd; Fülöp, Ferenc

2013-07-29

349

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.

Otvos, Sandor B; Georgiades, Adam; Mandity, Istvan M; Kiss, Lorand

2013-01-01

350

A mild and efficient method for the synthesis of a new class of furo[3,2-c]chromenes in aqueous media.  

PubMed

An efficient synthesis of 2-hydroxy-3-[2-oxo-2-phenylethylidene]-2-phenyl-2, 3-dihydro-4 H-furo[3, 2-c]chromene-4(2H)-one is described. This involves the reaction between dibenzoylacetylene and 4-hydroxycoumarine in the presence of NaH (10 mol %) in nearly quantitative yield. Treatment of this heterocyclic system with trimethyl chlorosilane in CHCl(3) leads quantitatively to 4-oxo-3-[2-oxo-2-phenylethylidene]-2-phenyl-3H, 4H-furo[3,2-c]chromene-1-ium chloride. Direct addition of nucleophiles, such as alcohols, amines or trialkyl phosphites to this salt in water as the solvent produces functionalized 2-phenyl-4H-furo[3,2-c] chromen derivatives in excellent yields. PMID:20737213

Khalilzadeh, Mohammad A; Hossaini, Zinatossadat; Charati, Faramarz Rostami; Hallajian, Sara; Rajabi, Mehdi

2010-08-25

351

Oxyma: an efficient additive for peptide synthesis to replace the benzotriazole-based HOBt and HOAt with a lower risk of explosion.  

PubMed

Oxyma [ethyl 2-cyano-2-(hydroxyimino)acetate] has been tested as an additive for use in the carbodiimide approach for formation of peptide bonds. Its performance in relation to those of HOBt and HOAt, which have recently been reported to exhibit explosive properties, is reported. Oxyma displayed a remarkable capacity to inhibit racemization, together with impressive coupling efficiency in both automated and manual synthesis, superior to those of HOBt and at least comparable to those of HOAt, and surpassing the latter coupling agent in the more demanding peptide models. Stability assays showed that there was no risk of capping the resin under standard coupling conditions. Finally, calorimetry assays (DSC and ARC) showed decomposition profiles for benzotriazole-based additives that were consistent with their reported explosivities and suggested a lower risk of explosion in the case of Oxyma. PMID:19575348

Subirós-Funosas, Ramon; Prohens, Rafel; Barbas, Rafael; El-Faham, Ayman; Albericio, Fernando

2009-09-21

352

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

PubMed

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

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

2013-06-14

353

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

PubMed

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

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

2012-08-21

354

Efficient synthesis of individual single-walled carbon nanotube by water-based catalyst with poly(vinylpyrrolidone).  

PubMed

Individual single-walled carbon nanotubes (SWCNTs) were synthesized on the patterned water-soluble catalyst by thermal chemical vapor deposition. The individual SWCNTs were obtained by introducing polyvinylpyrrolidone (PVP) as a dispersant. The number of SWCNTs between two electrodes were approximately 1-2 with an average diameter of about 1.7 nm and a yield of forming electrodes of nearly 70%. The PVP played an important role in dispersing catalysts and suppressing the active sites to limit the number of SWCNTs during synthesis, which is a critical condition for fabrication of field effect transistors (FETs). The measured I-V characteristics of the over layer-deposited electrodes revealed a clear gating effect in large portion, in good agreement with Raman observations in several excitation energies. The patterning procedure, catalyst preparation, and growth condition for fabrication of the SWCNT-FET were further discussed. PMID:18468078

Jeong, Seung Yol; Jeon, Sang Hyun; Han, Gang Hee; An, Kay Hyeok; Bae, Dong Jae; Lim, Seuong Chu; Hwang, Ha Ryong; Han, Chang Soo; Yun, Minhee; Lee, Young Hee

2008-01-01

355

Design, synthesis, and evaluation of carnosine derivatives as selective and efficient sequestering agents of cytotoxic reactive carbonyl species.  

PubMed

Carnosine aryl derivatives as sequestering agents of RCS: Reactive carbonyl species (RCS) are cytotoxic mediators representing a novel drug target, as they are presumed to play a pathogenic role in several diseases. Carnosine is a selective RCS-sequestering agent, but is rapidly hydrolyzed by serum carnosinase. Herein we describe the in silico design, synthesis, and evaluation of a set of carnosine aryl derivatives.Reactive carbonyl species (RCS) are important cytotoxic mediators generated by lipid oxidation of polyunsaturated fatty acids (PUFAs) and represent a novel drug target, as they are presumed to play a pathogenic role in several diseases. L-Carnosine (L-CAR, beta-alanyl-L-histidine) is a specific detoxifying agent of RCS, but is rapidly hydrolyzed in human serum by carnosinase, a specific dipeptidase. Herein we describe the in silico design, synthesis, and biological evaluation of carnosine derivatives that are resistant to carnosinase and that have increased quenching efficacy. Stability against carnosinase-mediated turnover was achieved by isomerization of the histidine residue, leading to D-carnosine (D-CAR, beta-alanyl-D-histidine), which maintains the same quenching activity of L-carnosine. A molecular modeling approach was then used to design derivatives characterized by an increased quenching efficacy. The most promising candidates were synthesized, and their stability and quenching activity were evaluated. This study describes a set of aryl derivatives that are characterized by high stability in human plasma and a quenching activity toward 4-hydroxy-trans-2-nonenal (HNE), chosen as a model of RCS, up to threefold greater than D-carnosine. PMID:19301317

Vistoli, Giulio; Orioli, Marica; Pedretti, Alessandro; Regazzoni, Luca; Canevotti, Renato; Negrisoli, Gianpaolo; Carini, Marina; Aldini, Giancarlo

2009-06-01

356

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.

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

2013-01-01

357

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

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

2013-09-02

358

KF\\/Al2O3 as a Highly Efficient, Green, Heterogeneous, and Reusable Catalytic System for the Solvent-Free Synthesis of Carboacyclic Nucleosides via Michael Addition Reaction  

Microsoft Academic Search

KF\\/Al2O3 acts as an efficient catalytic system for the synthesis of carboacyclic nucleosides via Michael addition of pyrimidine and purine nucleobases to ?,?-unsaturated esters under solvent-free and microwave conditions. Using this method, the title compounds are produced in good to excellent yields and short reaction times.

Abdolkarim Zare; Alireza Hasaninejad; Mohammad Hassan Beyzavi; Ahmad Reza Moosavi Zare; Ali Khalafi-Nezhad; Fatemeh Asadi; Leila Baramaki; Sedigheh Jomhori-Angali; Rokhsareh Ghaleh-Golabi

2008-01-01

359

N,N-Dichloro poly(styrene-co-divinyl benzene) sulfonamide polymeric beads: an efficient and recyclable reagent for the synthesis of dialkyl chlorophosphates from dialkylphosphites at room temperature  

Microsoft Academic Search

An efficient and operationally simple method is developed for the synthesis of dialkyl chlorophosphates from dialkylphosphites using a new chlorine bearing reagent, N,N-dichloro poly(styrene-co-divinyl benzene) sulfonamide in the form of polymeric beads. The reagent afforded dialkyl chlorophosphates at room temperature, and is recyclable.

Hemendra K. Gupta; Avik Mazumder; Prabhat Garg; Pranav K. Gutch; Devendra K. Dubey

2008-01-01

360

Efficient Synthesis of 12Aryl8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Derivatives Catalyzed by p-Dodecylbenzenesulfonic Acid in Aqueous Media Under Ultrasound Irradiation  

Microsoft Academic Search

An efficient synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives via the three-component condensation of aromatic aldehyde, 2-naphthol, and 5,5-dimethyl-1,3-cyclohexanedione was carried out in 76–93% yields at 40–42 °C using p-dodecylbenzenesulfonic acid as catalyst in aqueous media under ultrasound irradiation.

Ji-Tai Li; Yan-Wei Li; Ya-Li Song

2012-01-01

361

Calcium fluoride: an efficient and reusable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1 H)-ones and their corresponding 2(1 H)thione: an improved high yielding protocol for the Biginelli reaction  

Microsoft Academic Search

A simple and effective synthesis of 3,4-dihydropyrimidinone derivatives from aldehydes, 1,3-dicarbonyl compounds, and urea\\/thiourea in ethanol by using calcium fluoride as catalyst has been described. Compared with classical Biginelli reaction conditions, this new method has the advantage of excellent yields and shorter reaction times. Also, the catalyst can be reused without any reduction in efficiency.

S. Chitra; K. Pandiarajan

2009-01-01

362

Efficient method for the synthesis of 2-(3-arylbenzo[ f]quinolin-2-yl)ethanol derivatives through an unusual ring-opening of THF-involved reaction  

Microsoft Academic Search

An efficient synthesis of 2-(3-arylbenzo[f]quinolin-2-yl)ethanol derivatives by an unusual THF-involved reaction of aromatic aldehyde and naphthalen-2-amine promoted by iodine has been demonstrated with good yields. The ring-opening of THF reaction is proposed in the possible mechanism.

Xiang-Shan Wang; Jie Zhou; Ke Yang; Yu-Ling Li

2011-01-01

363

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

2013-08-12

364

Very Efficient Template\\/Primer-Independent DNA Synthesis by Thermophilic DNA Polymerase in the Presence of a Thermophilic Restriction Endonuclease  

Microsoft Academic Search

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 Ěg of DNA can be synthesized by 1 unit of DNA polymerase in 1 h, and the reaction proceeds until available dNTPs are

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

2004-01-01

365

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 ...

366

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

2013-08-12

367

An efficient, simple and expedition synthesis of 1-amidoalkyl-2-naphthols as ‘drug like’ molecules for biological screening  

Microsoft Academic Search

An efficient and direct protocol for the preparation of amidoalkyl naphthols employing a multi-component, one-pot condensation reaction of ?-naphthol, aromatic aldehydes and acetamide in the presence of ferric hydrogensulfate under solvent, solvent-free and microwave conditions is described. The thermal solvent-free and microwave green procedures offer advantages such as shorter reaction times, simple work-up, excellent yield, recovery and reusability of catalyst.

Hamid Reza Shaterian; Hossein Yarahmadi; Majid Ghashang

2008-01-01

368

P-TSA catalyzed facile and efficient synthesis of polyhydroquinoline derivatives through hantzsch multi-component condensation.  

PubMed

A facile and efficient synthetic route to polyhydroquinolines has been developed via four-component condensation reactions of aldehydes, dimedone, ethyl acetoacetate and ammonium acetate in the presence of p-toluenesulfonic acid (p-TSA) catalyst in ethanol at ambient temperature through Hantzsch reaction. Simple work-up procedure, environmentally friendly, inexpensive and non-toxic catalyst, shorter reaction times along with excellent product yields are the significant features of this practical method. PMID:18591819

Cherkupally, Sanjeeva Reddy; Mekala, Raghu

2008-07-01

369

Efficient and eco-friendly process for the synthesis of N-substituted 4-methylene-2-oxazolidinones in ionic liquids  

Microsoft Academic Search

The carbonylation of amines with propargylic alcohol using CO2 as carbonyl source to yield N-substituted 4-methylene-2-oxazolidinones could efficiently proceed in ionic liquids, and various 4-methylene oxazolidinones with high yields could be obtained under relatively mild conditions. This result showed that ionic liquid might be an effective catalyst and reaction medium for the activation of CO2, which also offered a new

Qinghua Zhang; Feng Shi; Yanlong Gu; Jing Yang; Youquan Deng

2005-01-01

370

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

PubMed Central

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

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

2008-01-01

371

Highly efficient synthesis and antitumor activity of monosaccharide saponins mimicking components of Chinese folk medicine Cordyceps sinensis.  

PubMed

Ergosterol 3-O-?-D-glucopyranoside (1a) and ergosterol 3-O-?-D-galactopyranoside (1b) were highly efficiently synthesized and evaluated for their inhibitory activities against two tumor cell lines. The structures of these compounds were extensively confirmed by (1)H, (13)C NMR, IR, and HRMS. Compounds 1a and 1b exhibited interesting cytotoxic profiles. The antitumor activity of compound 1a was higher than that of 1b. PMID:22428587

Zhu, Zhen-Yuan; Yao, Qiang; Liu, Yang; Si, Chuan-Ling; Chen, Jing; Liu, Nian; Lian, Hong-Yu; Ding, Li-Na; Zhang, Yong-Min

2012-03-20

372

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

NASA Astrophysics Data System (ADS)

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 (DEAEx-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 (DEAE15-CH and DEAE25-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.

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

2013-02-01

373

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

2013-01-11

374

Synthesis and efficient hepatocyte targeting of galactosylated chitosan as a gene carrier in vitro and in vivo.  

PubMed

While chitosan (CS) has been researched widely as a non-viral vector, its usefulness has been limited by its low cell specificity and transfection efficiency. Therefore, we successfully synthesized galactosylated chitosan (GC) and complexed it with an enhanced green fluorescent protein plasmid (pIRES-EGFP) for transfection into cultured H22 cells (murine hepatic cancer cell line) using various GC/EGFP (N/P) charge ratios. Maximal gene transfection rates detected by flow cytometry occurred at an N/P ratio 5:1. Compared with those of lipofectin/EGFP and naked pIRES-EGFP, GC/EGFP complexes show a very efficient cell-selective transfection to hepatocytes. The MTT assay detected relatively low cytotoxicity in cells transfected with GC. A recombinant plasmid granulocyte-macrophage colony-stimulating factor (GM-SCF) and interleukin (IL) 21 (pIRES/GM-CSF-IL21) was successfully constructed and GC/GM-CSF-IL21 nanoparticles (average diameter, 82.1 nm) were administered via the tail vein of mice with liver metastasis of colon cancer model, for 5 consecutive days. The GC/GM-CSF-IL21 nanoparticles exhibited hepatocyte and passive tumor specificity, increased therapeutic efficacy compared to control groups, promoted leukocytes to aggregate in tumor tissues, and activated the cytotoxicity of natural killer (NK) cells and cytolytic T lymphocyte (CTL). Our results indicate that GC can be used in gene therapy to improve transfection efficiency and can be used as an immunological stimulant in vivo. PMID:21656667

Cheng, Mingrong; Li, Qing; Wan, Tao; Hong, Xiaowu; Chen, Houxiang; He, Bing; Cheng, Zhijian; Xu, Hongzhi; Ye, Tao; Zha, Bingbing; Wu, Jingbo; Zhou, Runjiao

2011-06-07

375

Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments.  

PubMed

InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure. PMID:21194707

Byun, Ho-June; Lee, Ju Chul; Yang, Heesun

2010-12-13

376

The economies of synthesis  

PubMed Central

In this tutorial review the economies of synthesis are analysed from both detailed and macroscopic perspectives, using case-studies from complex molecule synthesis. Atom, step, and redox economy are more than philosophical constructs, but rather guidelines, which enable the synthetic chemist to design and execute an efficient synthesis. Students entering the field of synthesis might find this tutorial helpful for understanding the subtle differences between these economic principles and also see real-world situations where such principles are put into practice.

Newhouse, Timothy

2010-01-01

377

Highly efficient synthesis of exopolysaccharides by Lactobacillus curvatus DPPMA10 during growth in hydrolyzed wheat flour agar.  

PubMed

The aim of this study was to optimize the production of exopolysaccharides (EPS) by sourdough Lactobacillus curvatus DPPMA10 for industrial application. The effects of pH, temperature, planktonic or attached cells and of some food matrices as substrates were studied. Wheat flour hydrolysate (WFH), reconstituted skimmed milk (RSM) and whey milk were supplemented with fresh yeast extract, mineral salts, and/or molasses. Non-controlled pH, starting from 5.6 to 3.5, was the optimal condition for L. curvatus DPPMA10. Temperature of 30 degrees C was also found to be optimal. Solid surfaces (agar culture media) stimulated attached bacteria to synthesize EPS (> or = of two-fold, P<0.05) with respect to planktonic cells (broth media). The highest production of EPS (ca. 46-50 g/kg of wet medium) was found during growth as attached cells in WFH agar supplemented with glucose, sucrose or molasses, mineral salts and fresh yeast extract at 30 degrees C for 48 h. As shown by high-performance liquid chromatography analysis, glucose was the only hydrolysis end-product for EPS synthesized during 48 h of incubation. The EPS synthesized by L. curvatus DPPMA10 improved the quality of bread and was utilized as carbon course by intestinal strains of lactobacilli and bifidobacteria. The synthesis of EPS by L. curvatus DPPMA10 under the conditions of this study may open new perspectives for their industrial applications. PMID:20398955

Minervini, F; De Angelis, M; Surico, R F; Di Cagno, R; Gänzle, M; Gobbetti, M

2010-03-19

378

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

PubMed

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

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

2012-12-02

379

Efficient synthesis of hydroxystyrenes via biocatalytic decarboxylation/deacetylation of substituted cinnamic acids by newly isolated Pantoea agglomerans strains.  

PubMed

BACKGROUND: Decarboxylation of substituted cinnamic acids is a predominantly followed pathway for obtaining hydroxystyrenes-one of the most extensively explored bioactive compounds in the food and flavor industry (e.g. FEMA GRAS approved 4-vinylguaiacol). For this, mild and green strategies providing good yields with high product selectivity are needed. RESULTS: Two newly isolated bacterial strains, i.e. Pantoea agglomerans KJLPB4 and P. agglomerans KJPB2, are reported for mild and effective decarboxylation of substituted cinnamic acids into corresponding hydroxystyrenes. Key operational parameters for the process, such as incubation temperature, incubation time, substrate concentration and effect of co-solvent, were optimized using ferulic acid as a model substrate. With strain KJLPB4, 1.51 g L(-1) 4-vinyl guaiacol (98% yield) was selectively obtained from 2 g L(-1) ferulic acid at 28 °C after 48 h incubation. However, KJPB2 provided vanillic acid in 85% yield after 72 h following the oxidative decarboxylation pathway. In addition, KJLPB4 was effectively exploited for the deacetylation of acetylated ?-phenylcinnamic acids, providing corresponding compounds in 65-95% yields. CONCLUSION: Two newly isolated microbial strains are reported for the mild and selective decarboxylation of substituted cinnamic acids into hydroxystyrenes. Preparative-scale synthesis of vinyl guaiacol and utilization of renewable feedstock (ferulic acid extracted from maize bran) have been demonstrated to enhance the practical utility of the process. Copyright © 2011 Society of Chemical Industry. PMID:21919002

Sharma, Upendra K; Sharma, Nandini; Salwan, Richa; Kumar, Rakesh; Kasana, Ramesh C; Sinha, Arun K

2011-09-14

380

Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel extract.  

PubMed

In the present study, the biosynthesis of rutile TiO(2) nanoparticles (TiO(2) NPs) was achieved by a novel, biodegradable and convenient procedure using fruit peel Annona squamosa aqueous extract. This is the first report on the new, simple, rapid, eco-friendly and cheaper methods for the synthesis of rutile TiO(2) NPs at lower temperature using agricultural waste. Rutile TiO(2) NPs were characterized by UV, XRD, SEM, TEM and EDS studies. The UV-Vis spectrophotometer results were promising and showed a rapid production of TiO(2) NPs with a surface plasmon resonance occurring at 284 nm. The formation of the TiO(2) NPs as observed from the XRD spectrum is confirmed to be TiO(2) particles in the rutile form as evidenced by the peaks at 2?=27.42°, 36.10°, 41.30° and 54.33° when compared with the literature. The TEM images showed polydisperse nanoparticles with spherical shapes and size 23±2 nm ranges. PMID:22983203

Roopan, Selvaraj Mohana; Bharathi, A; Prabhakarn, A; Rahuman, A Abdul; Velayutham, K; Rajakumar, G; Padmaja, R D; Lekshmi, Mohan; Madhumitha, G

2012-08-27

381

An efficient rhythmic component expression and weighting synthesis strategy for classifying motor imagery EEG in a brain computer interface  

NASA Astrophysics Data System (ADS)

The recognition of mental states during motor imagery tasks is crucial for EEG-based brain computer interface research. We have developed a new algorithm by means of frequency decomposition and weighting synthesis strategy for recognizing imagined right- and left-hand movements. A frequency range from 5 to 25 Hz was divided into 20 band bins for each trial, and the corresponding envelopes of filtered EEG signals for each trial were extracted as a measure of instantaneous power at each frequency band. The dimensionality of the feature space was reduced from 200 (corresponding to 2 s) to 3 by down-sampling of envelopes of the feature signals, and subsequently applying principal component analysis. The linear discriminate analysis algorithm was then used to classify the features, due to its generalization capability. Each frequency band bin was weighted by a function determined according to the classification accuracy during the training process. The present classification algorithm was applied to a dataset of nine human subjects, and achieved a success rate of classification of 90% in training and 77% in testing. The present promising results suggest that the present classification algorithm can be used in initiating a general-purpose mental state recognition based on motor imagery tasks.

Wang, Tao; He, Bin

2004-03-01

382

Poly(N,N?-dibromo-N-ethyl-benzene-1,3-disulfonamide) and N,N,N?,N?- Tetrabromobenzene-1,3-disulfonamide as Highly Efficient Catalysts, and (AC2O\\/SIO2) as a Heterogeneous System for the Acetylation of Alcohols, Amines, and Thiols Under Microwave Irradiation  

Microsoft Academic Search

Poly-(N,N?-dibromo-N-ethyl-benzene-1,3-disulfonamide) (PBBS) and N,N,N?,N?-tetrabromobenzene-1,3-disulfonamide (TBBDA) are good activators and catalytic reagents for the acetylation of alcohols, amines, and thiols. The presented method has the advantages of mild conditions, chemoselectivity, and good to high yields, and uses noncorrosive, inexpensive, recyclable, and environmentally friendly catalysts. We have also demonstrated that combining SiO2 with microwave energy provides an efficient, fast, convenient, and easy

Hojat Veisi; Ramin Ghorbani-Vaghei; Hosna Eskandari; Saba Hemmati; Ardashir Rezaei; Somaye Hajinazari; Mohammad Raoof Heidari Far; Azam Entezari

2011-01-01

383

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

2013-05-10

384

Efficient synthesis of octyl-?-d-galactopyranoside by Bacillus spore-displayed ?-galactosidase using an amphiphilic 1,2-dimethoxyethane co-solvent.  

PubMed

For enzymatic synthesis of octyl-?-d-galactopyranoside (octyl-gal) from lactose and n-octanol, Escherichia coli ?-galactosidase (?-Gal) was expressed and displayed on the surfaces of Bacillus subtilis spores. The spore-displayed ?-Gal was found to be stable when an amphiphilic 1,2-dimethoxyethane (DME) was used as a co-solvent; the transgalactosylation efficiency and octyl-gal conversion were optimal at 50% (v/v) DME. In addition, the product was maximally obtained from 100mM lactose in a phosphate buffer/n-octanol/DME (25/25/50, v/v) mixture. By increasing the agitation speed and the amount of spores displaying ?-Gal, a yield of 33.7 mM octyl-gal was obtained over 24h in a batch mode, which is much higher than in other octyl-gal bioconversion processes, such as those involving lipid-coating, reverse micelles, or whole cells. On the other hand, intermittent addition of spore-displayed ?-Gal and/or lactose in the reaction medium had no effect on the octyl-gal yield. The synthesized octyl-gal was hydrolyzed by the spore-displayed ?-Gal, and a high concentration of octyl-gal competitively inhibited the enzymes (K(i) value of 10.8mM). In summary, we demonstrate that octyl-gal synthesis by spore-displayed ?-Gal in non-aqueous medium can be significantly improved with the use of DME as a co-solvent. PMID:22112905

Bae, Jungdon; Choi, Eun Hwa; Pan, Jae-Gu

2010-11-13

385

Facile and Selective Synthesis of Oligothiophene-Based Sensitizer Isomers: An Approach toward Efficient Dye-Sensitized Solar Cells.  

PubMed

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

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

2013-09-09

386

Design and synthesis of a novel anchoring ligand for highly efficient thin film dye-sensitized solar cells.  

PubMed

A novel ligand, 5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid) (BTC), and its Ru(II) complex (BTC-1) in which the anchoring group is attached to the thiophene units were developed. Using a low-volatility electrolyte and 3.3 mum mesoporous TiO2 films BTC-1 achieved a solar-to-electricity conversion efficiency of 6.1%, compared to 4.8% for N719 under the same experimental conditions. PMID:19921011

Mishra, Amaresh; Pootrakulchote, Nuttapol; Fischer, Markus K R; Klein, Cedric; Nazeeruddin, Md K; Zakeeruddin, Shaik M; Bäuerle, Peter; Grätzel, Michael

2009-10-29

387

Q-sized CdS: Synthesis, characterization, and efficiency of photoinitiation of polymerization of several vinylic monomers  

SciTech Connect

The effect of temperature, stirring, excess cadmium, solvent viscosity, and dielectric strength on Q-sized CdS semiconductors in nonaqueous solvents is examined. Q-sized semiconductors have higher photopolymerization quantum yields than bulk sized CdS, ZnO, and TiO{sub 2} and need hole scavenging by the solvent to occur. There is also a correlation between monomer reactivity toward polymerization and its Alfrey and Price Q and e values. There is also a correlation between semiconductor photoinitiation efficiency and conduction band electron reduction potential. Based on this, anionic initiation followed by free radical propogation has been proposed. 42 refs., 6 figs., 7 tabs.

Hoffman, A.J.; Mills, G.; Yee, H.; Hoffmann, M.R. [California Inst. of Technology, Pasadena, CA (United States)

1992-06-25

388

Asymmetric synthesis of a selective endothelin A receptor antagonist.  

PubMed

An asymmetric synthesis of a selective endothelin A receptor antagonist 1b is described. Asymmetric conjugate addition of aryllithium derived from 18 to the chiral oxazoline 17 followed by hydrolysis afforded 15 in 96% ee via purification as (S)-(-)-1-phenylethylamine salt. Pd(OAc)(2)/dppf (1,1'-bis(diphenylphosphino)ferrocene) catalyzed carbonylation followed by chemoselective addition of aryllithium derived from 23 which gave ketone 24. Diastereoselective reduction of the ketone with catecholborane followed by concomitant activation of the resulting alcohol and cyclization gave the late intermediate 26. Introduction of amino moiety on the pyridine ring by imidoyl rearrangement followed by deprotection and purification by crystallization furnished the enantiomerically pure target molecule 1b in 8% overall yield from 16. PMID:12192138

Kato, Yoshiaki; Niiyama, Kenji; Jona, Hideki; Okada, Shigemitsu; Akao, Atsushi; Hiraga, Shouichi; Tsuchiya, Yoshimi; Tomimoto, Koji; Mase, Toshiaki

2002-08-01

389

Efficient alkyl ether synthesis via palladium-catalyzed, picolinamide-directed alkoxylation of unactivated C(sp3)-H and C(sp2)-H bonds at remote positions.  

PubMed

We report the efficient synthesis of alkyl ethers by the functionalization of unactivated sp(3)- and sp(2)-hybridized C-H bonds. In the Pd(OAc)(2)-catalyzed, PhI(OAc)(2)-mediated reaction system, picolinamide-protected amine substrates undergo facile alkoxylation at the ? or ? positions with a range of alcohols, including t-BuOH, to give alkoxylated products. This method features a relatively broad substrate scope for amines and alcohols, inexpensive reagents, and convenient operating conditions. This method highlights the emerging value of unactivated C-H bonds, particularly the C(sp(3))-H bond of methyl groups, as functional groups in organic synthesis. PMID:22486219

Zhang, Shu-Yu; He, Gang; Zhao, Yingsheng; Wright, Kiwan; Nack, William A; Chen, Gong

2012-04-19

390

Chemical synthesis of circular proteins.  

PubMed

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

Tam, James P; Wong, Clarence T T

2012-06-14

391

Chemical Synthesis of Circular Proteins*  

PubMed Central

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

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

2012-01-01

392

Synthesis and characterization of the efficient visible-light-induced photocatalyst AgBr and its photodegradation activity  

NASA Astrophysics Data System (ADS)

AgBr photocatalysts were prepared with the 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) reactable ionic liquid at different temperatures by one-step hydrothermal method, in which the ionic liquid acted as a precursor and a template to control the size of AgBr crystal. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), the Brunauer-Emmett-Teller (BET) surface area and diffuse reflectance spectroscopy (DRS). Methyl orange (MO) dye was chosen as a model pollutant to investigate the photocatalytic activity and the stability of the samples under visible light irradiation. The results indicated that the AgBr photocatalysts showed high efficiency in the degradation of MO under visible light irradiation. The kinetic property of the reaction followed the first-order reaction model. During the photocatalytic degradation reaction, AgBr was transformed to the Ag0/AgBr composite. However, the photocatalytic efficiency was still high and the photocatalytic activity was stable. The possible photocatalytic mechanism of the photocatalysts was also eventually proposed.

Liu, Ling; Xu, Hui; Li, Huaming; Xu, Yuanguo; Xia, Jiexiang; Yin, Sheng

2012-04-01

393

Highly efficient diglycolamide-based task-specific ionic liquids: synthesis, unusual extraction behaviour, irradiation, and fluorescence studies.  

PubMed

Two new diglycolamide-based task-specific ionic liquids (DGA-TSILs) were evaluated for the extraction of actinides and lanthanides from acidic feed solutions. These DGA-TSILs were capable of exceptionally high extraction of trivalent actinide ions, such as Am(3+), and even higher extraction of the lanthanide ion, Eu(3+) (about 5-10 fold). Dilution of the DGA-TSILs in an ionic liquid, C(4)mim(+)·NTf(2)(-), afforded reasonably high extraction ability, faster mass transfer, and more efficient stripping of the metal ion. The nature of the extracted species was studied by slope analysis, which showed that the extracted species contained one NO(3)(-) anion, along with the participation of two DGA-TSIL molecules. Time-resolved laser fluorescence spectroscopy (TRLFS) analysis showed a strong complexation with no inner-sphere water molecule in the Eu(III)-DGA-TSIL complexes in the presence and absence of C(4)mim(+)·NTf(2)(-) as the diluent. The very high radiolytic stability of DGA-TSIL 6 makes it one of the most-efficient solvent systems for the extraction of actinides under acidic feed conditions. PMID:23319409

Mohapatra, Prasanta K; Sengupta, Arijit; Iqbal, Mudassir; Huskens, Jurriaan; Verboom, Willem

2013-01-14

394

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

PubMed

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

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

2000-12-01

395

The efficient synthesis of a molybdenum carbide catalyst via H2-thermal treatment of a Mo(VI)-hexamethylenetetramine complex.  

PubMed

An efficient method for preparation of Mo(2)C catalyst is described, where Mo(2)C is obtained by the heat treatment of a single solid precursor containing (NH(4))(6)Mo(7)O(24) and hexamethylenetetramine (HMT) at 923 K in H(2) flow without conventional prolonged carbonization. The catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area measurement, and transmission electron microscopy (TEM). Furthermore, these catalysts are evaluated in the dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction, and proved to be superior to those prepared by a temperature-programmed reduction (TPRe) method. The better catalytic performance is ascribed to higher dispersion of Mo(2)C on the support and a lower surface polymeric carbon content. This hydrogen thermal treatment (HTT) method provided a new strategy for the preparation of a highly active molybdenum carbide catalyst. PMID:21157590

Wang, Zhi-Qiang; Zhang, Zhong-Biao; Zhang, Ming-Hui

2010-12-14

396

Facile and effective synthesis of hierarchical TiO2 spheres for efficient dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) crystalline anatase TiO2 hierarchical spheres were successfully derived from Ti foils via a fast, template-free, low-temperature hydrothermal route followed by a calcination post-treatment. These dandelion-like TiO2 spheres are composed of numerous ultrathin nanoribbons, which were subsequently split into fragile nanoflakes as a result of the decomposition of Ti-complex intermediates to TiO2 and H2O at high temperature. The dye-sensitized solar cells (DSSCs) employing such hierarchically structured TiO2 spheres as the photoanodes exhibited a light-to-electricity conversion efficiency of 8.50%, yielding a 28% enhancement in comparison with that (6.64%) of P25-based DSSCs, which mainly benefited from the enhanced capacity of dye loading in combination with effective light scattering and trapping from hierarchical architecture.Three-dimensional (3D) crystalline anatase TiO2 hierarchical spheres were successfully derived from Ti foils via a fast, template-free, low-temperature hydrothermal route followed by a calcination post-treatment. These dandelion-like TiO2 spheres are composed of numerous ultrathin nanoribbons, which were subsequently split into fragile nanoflakes as a result of the decomposition of Ti-complex intermediates to TiO2 and H2O at high temperature. The dye-sensitized solar cells (DSSCs) employing such hierarchically structured TiO2 spheres as the photoanodes exhibited a light-to-electricity conversion efficiency of 8.50%, yielding a 28% enhancement in comparison with that (6.64%) of P25-based DSSCs, which mainly benefited from the enhanced capacity of dye loading in combination with effective light scattering and trapping from hierarchical architecture. Electronic supplementary information (ESI) available: FESEM images of samples prepared in other control experiments and a cross-sectional view of the three films. See DOI: 10.1039/c3nr01604h

Ye, Meidan; Chen, Chang; Lv, Miaoqiang; Zheng, Dajiang; Guo, Wenxi; Lin, Changjian

2013-06-01

397

Synthesis of Ag/ZnO nanostructures by different methods and investigation of their photocatalytic efficiency for 4-nitrophenol degradation  

NASA Astrophysics Data System (ADS)

In this paper, Ag/ZnO photocatalysts with different Ag loadings were prepared by photo reduction, chemical reduction and polyacrylamide-gel methods. The Ag/ZnO photocatalysts were characterized by XRD, SEM, TEM, EDS and DRUV-vis methods. The results of the photocatalytic degradation of 4-NP in aqueous suspensions showed that silver ions doping greatly improved the photocatalytic efficiency of ZnO nanocrystallites. The enhancement of photocatalytic activity is due to the fact that the modification of ZnO with an appropriate amount of Ag can increase the separation efficiency of photogenerated electrons and holes in ZnO, and the improvement of photo stability of ZnO is attributed to a considerable decrease of the surface defect sites of ZnO after the Ag loading. The chemisorptions of molecular oxygen and the chemisorption of atomic oxygen on Ag in the Ag/ZnO photocatalysts were observed. It was found that the metallic Ag in the Ag/ZnO photocatalysts does play a new role of O2 chemisorption sites except for electron acceptor, by which chemisorbed molecular oxygen reacts with photogenerated electrons to form active oxygen species, and thus facilitates the trapping of photogenerated electrons and further improves the photocatalytic activity of the Ag/ZnO photocatalysts. Also the method of preparation is regarded as important factors for determining photocatalysis. The best photocatalytic performance was exhibited for Ag/ZnO prepared by polyacrylamide gel method in comparison with chemical reduction and photo reduction method and the optimum Ag content was approximately 0.5%.

Divband, B.; Khatamian, M.; Eslamian, G. R. Kazemi; Darbandi, M.

2013-11-01

398

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

PubMed Central

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

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

2008-01-01

399

O-Aryl ?,?-d-ribofuranosides: synthesis & highly efficient biocatalytic separation of anomers and evaluation of their Src kinase inhibitory activity.  

PubMed

A series of peracetylated O-aryl ?,?-d-ribofuranosides have been synthesized and an efficient biocatalytic methodology has been developed for the separation of their anomers which was otherwise almost impossible by column chromatographic or other techniques. The incubation of 2,3,5-tri-O-acetyl-1-O-aryl-?,?-d-ribofuranoside with Lipozyme® TL IM immobilized on silica led to the selective deacetylation of only one acetoxy group, viz the C-5'-O-acetoxy group of the ?-anomer over the other acetoxy groups derived from the two secondary hydroxyl groups present in the molecule and also over three acetoxy groups (derived from one primary and two secondary hydroxyls of the ?-anomer). This methodology led to the easy synthesis of both, ?- and ?-anomers of O-aryl d-ribofuranosides. All the arylribofuranosides were screened for inhibition of Src kinase. 1-O-(3-Methoxyphenyl)-?-d-ribofuranoside exhibited the highest activity for inhibition of Src kinase (IC(50)=95.0?M). PMID:23098606

Sharma, Raman K; Singh, Sukhdev; Tiwari, Rakesh; Mandal, Deendayal; Olsen, Carl E; Parmar, Virinder S; Parang, Keykavous; Prasad, Ashok K

2012-10-04

400

Efficient Electrochemical Synthesis, Antimicrobial and Antiinflammatory Activity of 2-amino-5-substituted- 1,3,4-oxadiazole Derivatives  

PubMed Central

An efficient electrochemical method for the preparation of 2-amino-5-substituted-1,3,4-oxadiazoles (4a-k) at platinum anode through the electrooxidation of semicarbazone (3a-k) at controlled potential electrolysis has been reported in the present study. The electrolysis was carried out in the acetic acid solvent and lithium perchlorate was used as supporting electrolyte. The products were characterized by IR,1H-NMR,13C-NMR, mass spectra and elemental analysis. The synthesized compounds were screened for their in vitro growth inhibiting activity against different strains of bacteria viz., Klebsilla penumoniae, Escherichia coli, Bassilus subtilis and Streptococcus aureus and antifungal activity against Aspergillus niger and Crysosporium pannical and results have been compared with the standard antibacterial streptomycin and antifungal griseofulvin. Compounds exhibits significant antibacterial activity and antifungal activity. Compounds 4a and g exhibited equal while 4c, d, i and j slightly less antibacterial activity than standard streptomycin. Compounds 4a and g exhibited equal while 4b, c, d, f and i displayed slightly less antifungal activity than standard griseofulvins.

Kumar, S.; Srivastava, D. P.

2010-01-01

401

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

PubMed

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

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

2013-01-16

402

Ph 2S 2–CaH 2 in N-methyl-2-pyrrolidone as an efficient protocol for chemoselective cleavage of aryl alkyl ethers  

Microsoft Academic Search

CaH2 was been found, for the first time, as a mild reducing agent to generate thiophenolate anion from Ph2S2 in N-methyl-2-pyrrolidone (NMP) for deprotection of aryl alkyl ethers. Excellent chemoselctivity was observed for substrates having chloro and nitro groups without displacement of the chlorine atom and the nitro group. Selective ether cleavage took place in the presence of ?,?-unsaturated carbonyl

Navnath S. Gavande; Sonia Kundu; Naresh S. Badgujar; Gurmeet Kaur; Asit K. Chakraborti

2006-01-01

403

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

404

A simple and efficient enantioselective route to 2,6-disubstituted piperidines: synthesis of (2 R,6 S)-isosolenopsin A and (2 S,6 R)-isosolenopsin  

Microsoft Academic Search

The enantioselective synthesis of 2,6-cis-disubstituted piperidine alkaloids, (2R,6S)-isosolenopsin A 2 and (2S,6R)-isosolenopsin 5 from fire ant venom is described. Starting from the dodecanal and decanal, the synthesis presents two key steps. The first step involves Keck allylation to afford the chiral homoallylalcohol with the required stereochemistry and the second key step consists of Grubbs olefin cross metathesis. The synthesis was

R. Sateesh Chandra Kumar; Eppakayala Sreedhar; G. Venkateswar Reddy; K. Suresh Babu; J. Madhusudana Rao

2009-01-01

405

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

2013-09-23

406

Solid phase synthesis of peptide-selenoesters.  

PubMed

The synthesis of proteins by native chemical ligation greatly enhances the application of chemistry to complex molecules such as proteins. The essential building blocks for this approach traditionally have been peptide-thioester segments that are linked chemoselectively in consecutive reactions. By using peptide selenoesters instead of thioesters, the ligation rate can be significantly accelerated permitting couplings at difficult sites and potentially enabling new ligation strategies. To facilitate the routine synthesis of selenoester peptides, a general and straightforward procedure has been developed that generates a suitably functionalized resin from which the desired selenoester peptide can be readily synthesized. This simple approach utilizes readily available and cheap chemical agents and enables production of peptide selenoesters of excellent quality in short time and with high recovery. In addition, the stability of peptide selenoesters was examined under different native chemical ligation conditions and compared to thioesters. Selenoesters are slightly more reactive and more susceptible to hydrolysis and aminolysis than thioesters but sufficiently stable under mildly acidic conditions (pH 6.5). Under these conditions, rapid selenoester-mediated ligation is kinetically favoured. PMID:23608106

Ghassemian, Artin; Vila-Farrés, Xavier; Alewood, Paul F; Durek, Thomas

2013-04-06

407

Use of the vinyl group as an efficient protecting group for azole N- atoms: Synthesis of polyfunctionalized imidazoles and thieno[2,3- d] ? [3,2- d]imidazole  

Microsoft Academic Search

2,4,5-Tribromo-1-vinylimidazole was prepared from 2,4,5-tribromoimidazole and 1,2-dibromoethane and its Br-atoms were replaced regioselectively in the order 2 ? 5 ? 4 via Br ? MgBr and other exchange reactions. Efficient removal of the vinyl groups from the resulting polyfunctionalized imidazoles was achieved with ozone or potassium permanganate. An extension of this methodology has allowed the first synthesis of thieno[2,3-d] ?

David J. Hartley; Brian Iddon

1997-01-01

408

Silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO): A highly efficient, reusable and new heterogeneous catalyst for the synthesis of 4 H-benzo[ b]pyran derivatives  

Microsoft Academic Search

The reaction of 3-chloropropyl silica with diazabicyclo[2.2.2]octane in dry acetone affords silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO) as a new basic catalyst. The catalyst is used for the efficient synthesis of 4H-benzo[b]pyran derivatives via one-pot three-component reaction of cyclic ketones\\/1,3-diketones with aromatic aldehydes and alkylmalonates.

Alireza Hasaninejad; Mohsen Shekouhy; Nooshin Golzar; Abdolkarim Zare; Mohammad Mahdi Doroodmand

2011-01-01

409

Efficient Synthesis of 12-aryl -8,9,10,12-tetrahydrobenzo[A]xanthen-11-one Derivatives Catalyzed by p-dodecylbenzenesulfonic Acid in Aqueous Media Under Ultrasound Irradiation  

Microsoft Academic Search

An efficient synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives via the three-component condensation of aromatic aldehyde, 2-naphthol and 5,5-dimethyl-1,3-cyclohexanedione was carried out in 76-93% yields at 40-42 °C using p-dodecylbenzenesulfonic acid (DBSA) as catalyst in aqueous media under ultrasound irradiation.

Ji-Tai Li; Yan-Wei Li; Ya-Li Song

2012-01-01

410

Convenient synthesis of non-conjugated alkynyl ketones from keto aldehydes by a chemoselective one-pot nonaflation—base catalyzed elimination sequence  

Microsoft Academic Search

Keto aldehydes were selectively converted to non-conjugated alkynyl ketones possessing an unsubstituted alkyne terminus using one-pot nonaflation—base catalyzed elimination reaction sequences. Consecutive one-pot nonaflation of keto aldehydes with perfluorobutane-1-sulfonyl fluoride and elimination of the nonaflyl group using the P1 phosphazene base resulted in the formation of a terminal CC triple bond with the keto group remaining intact. Careful optimization of

Ekaterina V. Boltukhina; Andrey E. Sheshenev; Ilya M. Lyapkalo

2011-01-01

411

A new synthesis of enaminoketones  

Microsoft Academic Search

A new and efficient synthesis of enaminoketones is described. E,Z ?-chloroacroleine derivatives react with secondary amines to produce enaminoketones. The reaction was essentially studied with ?-trifluoromethylacroleines.

Romuald Bartnik; Abdelkader Bensadat; Dariusz Cal; Zofia Cebulska; André Laurent; Eliane Laurent; Caroline Rizzon

1996-01-01

412

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

413

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

PubMed Central

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

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

2010-01-01

414

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

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

2013-02-05

415

EFFICIENT CHEMICAL SYNTHESIS USING MICROWAVES  

EPA Science Inventory

Synthetic organic transformations performed under non-traditional conditions are becoming popular primarily to circumvent the growing environmental concerns. A solvent-free approach that involves microwave (MW) exposure of neat reactants catalyzed by the surfaces of less-expensiv...

416

Novel galactosyl donor with 2-naphthylmethyl (NAP) as the non participating group at C-2 position: Efficient synthesis of ?-galactosyl ceramide  

PubMed Central

Predominant ?-linked products can be generated in glycosylation involving galactosyl trichloroacetimidate donors with 2-naphthylmethyl (NAP) as the non participating group at C-2 position. The above donor was successfully utilized for the synthesis of ?-galactosyl ceramide.

Khaja, Sirajud D.; Kumar, Vipin; Ahmad, Misbah; Xue, Jun; Matta, Khushi L.

2010-01-01

417

Cobalt-catalyzed oxidative [3 + 2] cycloaddition reactions: an efficient synthesis of pyrrolo- and imidazo-[2,1-a]isoquinolines.  

PubMed

A cobalt-catalyzed oxidative [3 + 2] cycloaddition cascades of dihydroisoquinoline esters with nitroolefins or N-sulfuryl aldimines were developed at room temperature. A multi-component reaction for the synthesis of 5,6-dihydroimidazo[2,1-a]isoquinolines were also realized under almost identical conditions. This method is particularly suitable for the synthesis of tricyclic nitrogen heterocycles due to its simple manipulation, wide scope of the reaction substrates and excellent regioselectivity. PMID:23995231

Feng, Chengtao; Su, Ji-Hu; Yan, Yizhe; Guo, Fengfeng; Wang, Zhiyong

2013-08-30

418

Synthesis of ?-Keto-Imides via Oxidation of Ynamides  

PubMed Central

A de novo preparation of ?-keto-imides via ynamide oxidation is described. With a number of alkyne oxidation conditions screened, a highly efficient RuO2-NaIO4 mediated oxidation and a DMDO oxidation have been identified to tolerate a wide range of ynamide types. In addition to accessing a wide variety of ?-keto-imides, the RuO2-NaIO4 protocol provides a novel entry to the vicinal tricarbonyl motif via oxidation of push-pull ynamides, and imido acylsilanes from silyl-substituted ynamides. Chemoselective oxidation of ynamides containing olefins can be achieved using DMDO, while the RuO2-NaIO4 protocol is not effective. These studies provide further support for the synthetic utility of ynamides.

Al-Rashid, Ziyad F.; Johnson, Whitney L.; Hsung, Richard P.; Wei, Yonggang; Yao, Pei-Yuan; Liu, Renhei; Zhao, Kang

2009-01-01

419

Influence of the porous structure of a promoted Zn/Cr catalyst on efficiency and selectivity of the synthesis of methanol and higher alcohols from CO and H/sub 2/  

SciTech Connect

This paper studies the influence of the porous structure of a promoted Zn/Cr catalyst on selectivity, efficiency, and thermal stability for the synthesis of methanol and higher alcohols from CO and H/sub 2/, at a pressure of 24.5 MPa in the range 300-420 C. It is shown that a variation of volume and size of the macropores in the catalyst samples changes the selectivity of the entire process. The sample with the highest selectivity towards higher alcohols also shows increased thermal stability. An increase of the CO/sub 2/ concentration in the synthesis gas leads to a decreased selectivity towards higher alcohols; an increase of the CO partial pressure enhances the selectivity to higher alcohols, although accompanied by a reduction of the overall CO conversion to useful products and by increased formation of methane and CO/sub 2/.

Lunev, N.K.; Artyukh, Y.N.; Leonov, V.E.; Ryzhak, I.A.; Yakubovich, M.N.

1986-01-01

420

Organocatalytic synthesis of carbohydrates.  

PubMed

The key role of carbohydrates in biological processes and their visible existence in our everyday life have stimulated the interest of leading research groups on the smart and simple synthesis of common and rare sugar molecules. Now, more than 120 years after Fischer's first synthesis of (D)-glucose (1890), we are witnessing important development in this field of total synthesis. Using modern methods of direct activation of carbonyl compounds chemists can prepare sugars in an elegant and efficient way similar to that of Nature. This tutorial review presents recent impressive progress in the area of de novo synthesis of carbohydrates by using organocatalytic direct aldol reaction as a key step. PMID:21796310

Mlynarski, Jacek; Gut, Bartosz

2011-07-28

421

Synthesis of cruentaren A.  

PubMed

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 toward 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; Blagg, Brian S J

2012-12-03

422

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.

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

2012-01-01

423

A green, efficient and recyclable Fe+3@K10 catalyst for the synthesis of bioactive pyrazolo[3,4-b]pyridin-6(7H)-ones under "on water" conditions  

NASA Astrophysics Data System (ADS)

An efficient regioselective one-pot three-component synthesis of 4-aryl-3-methyl-4,5-dihydro-1H-pyrazolo[3,4-b]pyridin-6(7H)-ones and their bis-derivatives (Table 3 and Fig. 2) catalyzed by Fe+3-K10 montmorillonite (Fe+3@K10) under the Sharpless conditions ("On water" contdiions) is described. This rapid method produced the products in short reaction times (10-15 min) and excellent yields (87-95%). The antibacterial activity of the synthesized products was examined. Some products showed promising activities.

Mamaghani, Manouchehr; Shirini, Farhad; Mahmoodi, Nosrat O.; Azimi-Roshan, Abbas; Hashemlou, Hussein

2013-11-01

424

Efficient large-scale synthesis of BILN 2061, a potent HCV protease inhibitor, by a convergent approach based on ring-closing metathesis.  

PubMed

A multistep scalable synthesis of the clinically important hepatitis C virus (HCV) protease inhibitor BILN 2061 (1) is described. The synthesis is highly convergent and consists of two amide bond formations, one etherification, and one ring-closing metathesis (RCM) step, using readily available building blocks 2-5. The optimization of each step is described at length. The main focus of the paper is the study of the RCM step and the description of the main problems faced when scaling up to pilot scale this highly powerful but very challenging synthetic operation. Eventually, the RCM reaction was smoothly scaled up to produce >400 kg of cyclized product. PMID:16958506

Yee, Nathan K; Farina, Vittorio; Houpis, Ioannis N; Haddad, Nizar; Frutos, Rogelio P; Gallou, Fabrice; Wang, Xiao-Jun; Wei, Xudong; Simpson, Robert D; Feng, Xuwu; Fuchs, Victor; Xu, Yibo; Tan, Jonathan; Zhang, Li; Xu, Jinghua; Smith-Keenan, Lana L; Vitous, Jana; Ridges, Michael D; Spinelli, Earl M; Johnson, Michael; Donsbach, Kai; Nicola, Thomas; Brenner, Michael; Winter, Eric; Kreye, Paul; Samstag, Wendelin

2006-09-15

425

Efficient synthesis of benzo[1,2-b:6,5-b']dithiophene-4,5-dione (BDTD) and its chemical transformations into precursors for ?-conjugated materials.  

PubMed

A straightforward synthesis of the fused-aromatic dione benzo[1,2-b:6,5-b']dithiophene-4,5-dione (BDTD) has been developed. This fused-aromatic dione was subjected to various chemical transformations to generate diverse molecules with potential use in ?-conjugated materials for organic electronics. PMID:23214445

Arroyave, Frank A; Richard, Coralie A; Reynolds, John R

2012-12-05

426

The effect of grain species, processing and time of feeding on the efficiency of feed utilization and microbial protein synthesis in sheep  

Microsoft Academic Search

This study investigated the effect of cereal grain species (sorghum, wheat, oats and barley), extent of processing (cracked barley, finely ground barley, and wet whole barley) and time of feeding (barley grain mixed with ryegrass hay or fed 2 h before hay was fed), on whole tract dry matter digestibility (WTDMD), and microbial protein synthesis (MPS), as a supplement to ryegrass

A. Horadagoda; W. J. Fulkerson; I. Barchia; R. C. Dobos; K. S. Nandra

2008-01-01

427

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

Microsoft Academic Search

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

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

2001-01-01

428

Efficient synthesis of new (R)-2-amino-1-butanol derived ureas, thioureas and acylthioureas and in vitro evaluation of their antimycobacterial activity.  

PubMed

The synthesis of 22 structurally diverse urea, thiourea and acylthiourea derivatives containing the (R)-2-amino-1-butanol motif has been performed. The evaluation of their in vitro activity against Mycobacterium tuberculosis (H37Rv and strain 43) showed promising results in the case of the acylthiourea derivatives (MIC range 0.36-7.46 ?M for H37Rv strain). PMID:23524112

Dobrikov, Georgi M; Valcheva, Violeta; Nikolova, Yana; Ugrinova, Iva; Pasheva, Evdokia; Dimitrov, Vladimir

2013-03-05

429

Novel galactosyl donor with 2-naphthylmethyl (NAP) as the non participating group at C-2 position: Efficient synthesis of alpha-galactosyl ceramide.  

PubMed

Predominant alpha-linked products can be generated in glycosylation involving galactosyl trichloroacetimidate donors with 2-naphthylmethyl (NAP) as the non participating group at C-2 position. The above donor was successfully utilized for the synthesis of alpha-galactosyl ceramide. PMID:20730042

Khaja, Sirajud D; Kumar, Vipin; Ahmad, Misbah; Xue, Jun; Matta, Khushi L

2010-08-18

430

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

PubMed

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

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

2000-09-01

431

Synthesis of new benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates with efficient DNA-binding affinity and potent cytotoxicity.  

PubMed

The synthesis of new benzimidazole linked pyrrolobenzodiazepine conjugates is described. Some of these conjugates show significant DNA-binding affinity and, a representative compound 4c shows promising in vitro cytotoxicity against a number of human cancer cell lines. PMID:18378445

Kamal, Ahmed; Kumar, P Praveen; Sreekanth, K; Seshadri, B N; Ramulu, P

2008-03-16

432

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

Microsoft Academic Search

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

Surya K. De

2008-01-01

433

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

Microsoft Academic Search

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

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

2005-01-01

434

An Efficient One-Pot Synthesis of Benzo[4,5]imidazo[1,2-a]quinoxalines via Copper-Catalyzed Process.  

PubMed

A copper-catalyzed one-pot process for the construction of benzo[4,5]imidazo[1,2-a]quinoxalines under air is described. Aryl chlorides, aryl bromides, and aryl iodides can be applied to the synthesis of these compounds. PMID:24147823

Huang, Aiping; Chen, Yimu; Zhou, Yige; Guo, Wei; Wu, Xiaodong; Ma, Chen

2013-10-22

435

Monosaccharides as Scaffolds for the Synthesis of Novel Compounds  

NASA Astrophysics Data System (ADS)

This chapter focuses on monosaccharides and scaffolds their derivatives as scaffolds for the synthesis of primarily bioactive compounds. Such carbohydrate derivatives have been designed to modulate mainly protein-protein and peptide-protein interactions although modulators of carbohydrate-protein and carbohydrate-nucleic acid interactions have also been of interest. The multiple hydroxyl groups that are present on saccharides have made pyranose, furanose and iminosugars ideal templates or scaffolds to which recognition or pharmacophoric groups can be grafted to generate novel compounds for medicinal chemistry. The synthesis of compounds for evaluations require strategies for regioselective reactions of saccharide hydroxyl groups and use of orthogonally stable protecting groups. Syntheses have been carried out on the solid phase and in solution. Also the use of uronic acids, amino sugars and sugar amino acids has facilitated the synthesis of peptidomimetics and prospecting libraries as they enable, through presence of amino or carboxylic acid groups, chemoselective approaches to be employed in solution and on solid phase. Sugar amino acids are readily incorporated, as peptide isosteres, to generate sugar-peptide hybrids or for the synthesis of novel carbopeptoids . The synthesis of new cyclic compounds, derived in part from saccharides, and their application as scaffolds is an emerging area and recent examples include spirocyclic compounds, benzodiazepine-saccharide hybrids and macrolide-saccharide hybrids. Potent bioactive saccharide derivatives have been identified that include enzyme inhibitors , somatostatin receptor ligands, integrin ligands, anti-viral compounds, shiga toxin inhibitors and cell growth inhibitors. Some saccharide derivatives have demonstrated improved cellular permeability when compared with peptides and are in clinical trials.

Murphy, Paul V.; Velasco-Torrijos, Trinidad

436

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.

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

2009-01-01

437

Introduction of poly(4-vinylpyridinium) perchlorate as a new, efficient, and versatile solid acid catalyst for one-pot synthesis of substituted coumarins under ultrasonic irradiation.  

PubMed

Poly(4-vinylpyridinium) perchlorate, is a supported, recyclable, eco-benign catalyst for synthesis of substituted coumarins via Pechmann reaction using ultrasound irradiation at room temperature and neat condition in high yields with short reaction times. The catalyst was studied by FT-IR, X-ray diffraction, scanning electron microscope, thermo-gravimetric and energy dispersion X-ray analyses. All the products were extensively characterized by (1)H NMR, FT-IR, MS and melting point analyses. This methodology offers momentous improvements over various options for the synthesis of coumarins with regard to yield of products, simplicity in operation and green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused and recovered for several times without loss of activity. PMID:22922036

Khaligh, Nader Ghaffari; Shirini, Farhad

2012-08-02

438

Combinatorial Solid-Phase Synthesis of 4,6-Diaryl and 4-Aryl, 6-Alkyl-1,3,5-triazines and Their Application to Efficient Biofuel Production.  

PubMed

Herein we report the solid-phase synthesis of a combinatorial aryl, alkyl-triazine library and its application to biofuel production. The combination of Grignard reactions and solid supported Suzuki coupling reactions afforded unique 120 triazine compounds with high purities and minimum purification steps. Through an unbiased phenotypic screening for improved biofuel generation in oleaginous yeast, we found one diaryl triazine derivative (E4) which increased the biolipid production up to 86%. PMID:22681245

Kim, Jaoon Y H; Lee, Jae Wook; Lee, Woo Sirl; Ha, Hyung-Ho; Vendrell, Marc; Bork, Jacqueline T; Lee, Youngsook; Chang, Young-Tae

2012-06-12

439

The effects of organic solvents on the efficiency and regioselectivity of N-acetyl-lactosamine synthesis, using the ?-galactosidase from Bacillus circulans in hydro-organic media.  

PubMed

The enzymatic synthesis of N-acetyl-lactosamine (LacNAc) by the transgalactosylation of N-acetyl-D-glucosamine (GlcNAc), catalyzed by the ?-galactosidase from Bacillus circulans (Bc?Gal), was studied in hydro-organic media, starting from o-nitrophenyl-?-D-galactopyranoside (oNPG) as a galactosyl donor. Thermal stability and synthesis activity of Bc?Gal were shown to depend on the organic solvent polarity, characterized by its Log P value. Bc?Gal was thus most stable in 10% (v/v) t-BuOH, an organic solvent found to have a stabilizing and/or weakly denaturing property, which was confirmed for high t-BuOH concentrations. In the same manner, the optimal synthesis yield increased as the Log P value of the organic solvent increased. The best results were obtained for reactions carried out in 10% (v/v) pyridine or 2-methyl-2-butanol, which gave 47% GlcNAc transgalactosylation yield based on starting oNPG, of which 23% (11 mM; 4.3 g/L) consisted in LacNAc synthesis. Furthermore, it was also established that both the GlcNAc transgalactosylation yield and the enzyme regioselectivity depended on the percentage of organic solvent used, the optimal percentage varying from 10 to 40% (v/v), depending on the solvent. This phenomenon was found to correlate mainly with the thermodynamic activity of water (a(w)) in the aqueous organic solvent mixture, which was found to be optimal when close to 0.96, whatever the organic solvent used. Finally, this study highlighted the fact that the regioselectivity of Bc?Gal for 1-4 linkage formation could be advantageously managed by controlling the a(w) parameter. PMID:20568279

Bridiau, Nicolas; Issaoui, Neyssčne; Maugard, Thierry

440

Scalable, efficient process for the synthesis of ( R)-3,5-bistrifluoromethylphenyl ethanol via catalytic asymmetric transfer hydrogenation and isolation as a DABCO inclusion complex  

Microsoft Academic Search

(R)-3,5-Bistrifluoromethylphenyl ethanol 2, a key building block in the synthesis of aprepitant, has been synthesized from ketone 5 via catalytic asymmetric transfer hydrogenation using a simplified catalyst generation procedure. The process uses (1S,2R)-cis-1-aminoindan-2-ol 10 and dichloro(p-cymene)Ru(II)dimer 9 as the chiral ligand and metal source for the reduction. While the reduction provides 2 in 90–92% ee, an isolation of 2 as

Karl B. Hansen; Jennifer R. Chilenski; Richard Desmond; Paul N. Devine; Edward J. J. Grabowski; Richard Heid; Michele Kubryk; David J. Mathre; Richard Varsolona

2003-01-01

441

Three Component Reaction: An Efficient Synthesis and Reactions of 3,4-Dihydropyrimidin-2(1H)-Ones and Thiones Using New Natural Catalyst  

PubMed Central

Synthesis of 3,4-dihydropyrimidin-2(1H)-one and 3,4-dihydropyrimidin-2(1H)-thione derivatives from aldehydes, 1,3-dicarbonyl derivatives and urea or thiourea using granite and quartz as new, natural and reusable catalysts. Some of the 3,4-dihydropyrimidin-2(1H)-thione derivatives were used to prepare new heterocyclic compounds. The antimicrobial activity of selected examples of the synthesized compounds was tested and showed moderate activity.

Elmaghraby, A. M.; Mousa, I. A.; Harb, A. A.; Mahgoub, M. Y.

2013-01-01

442

A novel total synthesis of kinsenoside and goodyeroside A relying on the efficient reaction of the chiral 2(5H)-furanones.  

PubMed

A new total synthesis of the bioactive compounds, kinsenoside and goodyeroside A, has been accomplished from readily available starting materials. The chiral 2(5H)-furanone and its enantiomer were employed as the key chiral intermediates to construct the chiral glycosides and with the appropriate stereochemistry. The spectral data of the target compounds and their acetylated derivatives and are identical with those of the natural and corresponding acetylated products. PMID:16176903

Zhang, Xiang; Huang, Hai-Hong; Chen, Qing-Hun

2005-10-01

443

A novel total synthesis of kinsenoside and goodyeroside A relying on the efficient reaction of the chiral 2(5H)-furanones  

Microsoft Academic Search

A new total synthesis of the bioactive compounds, kinsenoside (1) and goodyeroside A (2), has been accomplished from readily available starting materials. The chiral 2(5H)-furanone 5a and its enantiomer 5b were employed as the key chiral intermediates to construct the chiral glycosides 8a and 8b with the appropriate stereochemistry. The spectral data of the target compounds and their acetylated derivatives

Xiang Zhang; Hai-hong Huang; Qing-hun Chen

2005-01-01

444

At the same hepatic amino acid load, portal infusion of amino acids is more efficient than peripheral infusion in stimulating liver protein synthesis in the dog  

PubMed Central

Background Hepatic glucose uptake is enhanced by portal delivery of glucose which creates a negative arterio-portal substrate gradient. Hepatic amino acid (AA) utilization may be regulated by the same phenomenon, but this has not been proven. Objective We aimed to assess hepatic AA balance and protein synthesis with or without a negative arterio-portal AA gradient. Design Somatostatin was infused IV, and insulin and glucagon were replaced intraportally at 4- and 3-fold basal rates, respectively, in 3 groups (n=9 each) of conscious dogs with catheters for hepatic balance measurement. Arterial glucose concentrations were clamped at 9 mM. An AA mixture was infused IV to maintain basal concentrations (EuAA), intraportally to mimic the post-meal AA increase (PoAA), or IV (PeAA) to match the hepatic AA load in PoAA. Protein synthesis was assessed with a primed, continuous [14C]leucine infusion. Results Net hepatic glucose uptake in PoAA was ?50% of that in EuAA and PeAA (P<0.05). The hepatic intracellular leucine concentration was 2- to 2.5-fold greater in PoAA and PeAA than EuAA (P<0.05); net hepatic leucine uptake and 14C leucine utilization were ?2-fold greater (P<0.05) and albumin synthesis was 30% greater (P<0.05) in PoAA than EuAA and PeAA, Phosphorylation of ribosomal protein S6 (downstream of the mammalian target of Rapamycin complex 1 [mTORC1]) was significantly increased in PoAA, but not PeAA, vs EuAA. Conclusions Portal, but not peripheral, AA delivery significantly enhanced hepatic protein synthesis under conditions where AA, glucose, insulin and glucagon did not differ at the liver, an effect apparently mediated by mTORC1 signalling.

Dardevet, Dominique; Kimball, Scot R; Jefferson, Leonard S; Cherrington, Alan D; Remond, Didier; DiCostanzo, Catherine A; Moore, Mary Courtney

2009-01-01

445

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

2013-08-14

446

Total Synthesis of Vinigrol  

PubMed Central

The longstanding challenge posed by the complex diterpene vinigrol has been answered for the first time. The notorious difficulty in synthesizing vinigrol stems from its unprecedented decahydro-1,5-butanonaphthalene ring system, eight contiguous stereocenters, and highly congested functionality. This communication delineates a stereocontrolled 23-step route to vinigrol that is scalable (>5 grams prepared of a late stage intermediate), minimally reliant on protecting group chemistry, and facilitated by a number of unique and chemoselective transformations.

Maimone, Thomas J.; Shi, Jun; Ashida, Shinji; Baran, Phil S.

2009-01-01

447

Total Synthesis of (-)-Brevisin: A Concise Synthesis of a New Marine Polycyclic Ether  

PubMed Central

The first and highly efficient total synthesis of (–)-brevisin has been achieved. The title compound was synthesized in only 29 steps (longest linear sequence) from commercially available starting materials. The synthesis provided over 70 mg of marine polycyclic ether compound.

Kuranaga, Takefumi; Ohtani, Naohito; Tsutsumi, Ryosuke; Baden, Daniel G.; Wright, Jeffrey L. C.; Satake, Masayuki; Tachibana, Kazuo

2011-01-01

448

A versatile method for the preparation of conjugates of peptides with DNA\\/PNA\\/analog by employing chemo-selective click reaction in water  

Microsoft Academic Search

The specific 1,3 dipolar Huisgen cycloaddition reaction known as 'click-reaction' between azide and alkyne groups is employed for the synthesis of peptide-oligonucleotide conjugates. The peptide nucleic acids (PNA)\\/DNA and peptides may be appended either by azide or alkyne groups. The cycloaddition reaction between the azide and alkyne appended substrates allows the synthesis of the desired conjugates in high purity and

Khirud Gogoi; Meenakshi V. Mane; Sunita S. Kunte; Vaijayanti A. Kumar

2007-01-01

449

Pd-aminoclay nanocomposite as an efficient recyclable catalyst for hydrogenation and Suzuki cross coupling reactions.  

PubMed

A highly water dispersible Pd-aminoclay nanocomposite is found to be effective catalytic system for the hydrogenation of alpha,beta-unsaturated carbonyl compounds and Suzuki coupling reactions in aqueous media. The catalytic hydrogenation of alpha,beta-unsaturated carbonyl compounds proceeds at room temperature to afford the corresponding products in excellent yields with high chemoselectivity. The cross coupling of aryl bromides and iodides with aryl boronic acids proceeds efficiently under aqueous conditions at 90 degrees C to afford the corresponding biaryls in excellent yields with high selectivity. The Suzuki reaction proceeds smoothly even in the absence of external base due to the basic nature of the catalyst support. The catalyst could be easily recovered and recycled three times without a significant loss of activity in hydrogenation and Suzuki cross coupling reactions. PMID:22755012

Kumar, A Sravanth; Datta, K K R; Rao, T Srinivasa; Raghavan, K V; Eswaramoorthy, M; Reddy, B V Subba

2012-03-01

450

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

2013-08-18

451

Highly efficient one-pot synthesis of 1-substituted-1,2,3,4-tetrahydropyrazino[1,2- a]indoles  

Microsoft Academic Search

A practical and general one-pot synthesis of 1-substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles is described. The approach uses 2-(3-methyl-1H-indol-1-yl) ethylamine, benzotriazole and aldehydes in the presence of catalytic amount of acid catalysts (AlCl3, ZnCl2, ZnBr2, p-TsOH, CH3SO3H) and proceeds in high yields via iminium cation intramolecular cyclization. The mechanism of the observed intramolecular cyclization reaction has been investigated theoretically by means of PM3 semiempirical method

Rakesh K. Tiwari; Jaspal Singh; Devender Singh; Akhilesh K. Verma; Ramesh Chandra

2005-01-01

452

An Atom-Economic and Selective Ruthenium-Catalyzed Redox Isomerization of Propargylic Alcohols. An Efficient Strategy for the Synthesis of Leukotrienes  

PubMed Central

Catalytic ruthenium complexes in conjunction with an indium cocatalyst and Bronsted acid isomerize primary and secondary propargylic alcohols in good yields to provide trans enals and enones exclusively. Readily available indenylbis(triphenylphosphine)ruthenium chloride in the presence of indium triflate and camphorsulfonic acid give the best turnover numbers and reactivity with the broadest range of substrates. Deuterium labeling experiments suggest that the process occurs through propargylic hydride migration followed by protic cleavage of the resultant vinylruthenium intermediate. Application of this method to the synthesis of leukotriene B4 demonstrates its utility and extraordinary selectivity.

Trost, Barry M.; Livingston, Robert C.

2008-01-01

453

Silphox [POCl3?n(SiO2)n] as a New, Efficient, and Heterogeneous Reagent for the Synthesis of Benzimidazole Derivatives Under Microwave Irradiation  

Microsoft Academic Search

Silphox [POCl3-n(SiO2)n] efficiently catalyzes the condensation of benzene-1,2-diamine with mono and dicarboxylic acids under microwave irradiation to afford benzimidazole derivatives in high yields and short reaction times.

Alireza Hasaninejad; Khodabakhsh Niknam; Abdolkarim Zare; Ehsan Farsimadan; Mohsen Shekouhy

2008-01-01

454

X-Ray and Ultraviolet Luminescence of Li3Ta1- xNbxO4 Prepared by Flux Synthesis and Characterization of a New High Efficiency X-Ray Phosphor  

NASA Astrophysics Data System (ADS)

The phase development and luminescence properties, under both X-ray and ultraviolet excitation, of the lithium orthotantalate-lithium orthoniobate system, Li3Ta1-xNbxO4 for x=0 to 1, were examined. Using a flux synthesis technique, it was found that the levels of Nb-doping in monoclinic Li3TaO4 and of Ta-doping in cubic Li3NbO4 are higher than previously reported. Under 30 kVp molybdenum X-ray excitation, Li3Ta1-xNb4O4 is an efficient blue-emitting phosphor with broadband emission, peaking in the range of 390 to 435 nm. For x=0 to 0.1, the overall luminescence efficiency is comparable to, or better than, a commercial calcium tungstate, CaWO4, Hi-Plus material. The composition Li3Ta0.995Nb0.005O4 demonstrates an overall luminescence efficiency that makes this phosphor 45% brighter than CaWO4 Hi-Plus, thereby making it a potentially attractive candidate for use in medical diagnostic imaging systems. Under ultraviolet excitation, broadband blue emission is also observed. For all the Li3Ta1-xNbxO4 (x>0) solid solutions, the emission peak maximums agree well with those seen under X-ray excitation and are the result of Nb5+ emission.

Miao, C. R.; Torardi, C. C.

1999-06-01

455

Synthesis, Spectroscopic and Thermal Characterization of Copper(II) and Iron(III) Complexes of Folic Acid and Their Absorption Efficiency in the Blood  

PubMed Central

The absorption efficiency of any drug in blood is of prime importance. Compounds having the general formula: Kn[M(FO)2(H2O)2] · xH2O, where (M = Cu(II) or Fe(III), n = 2 or 1, FO = folate anion, x = 2 or 3 with respect), were prepared, and their absorption efficiency in rodent's blood was determined. The obtained compounds were characterized by elemental analysis, infrared as well as thermogravimetric analysis and polarization of light. The results suggest that the two folate complexes were formed in 1 : 2 molar ratio (metal : folic acid) which acted as a bidentate ligand through both carboxylic groups. Polarization of light proved that the folate complexes have symmetric geometry. Biological application proved that Cu(II) and Fe(III) complexes were absorbed more efficiently in rodent blood than folic acid itself.

Hamed, E.; Attia, M. S.; Bassiouny, K.

2009-01-01

456

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

2013-09-12

457

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

458

Synthesis and characterization of novel push-pull thiophene and thienylpyrrole derivatives functionalized with indanonedicyanovinyl acceptor moiety as efficient NLO-chromophores  

NASA Astrophysics Data System (ADS)

The synthesis and characterization of new chromophores with second-order nonlinearities containing thienylpyrrole 1a, 2a-b, bithiophene 3 and arylthiophene 4 as ?-conjugated bridges and indanonedicyanovinyl acceptor group are reported. The effect of placing the acceptor group at thiophene or pyrrole rings on the optoelectronic properties was also evaluated for thienylpyrrole derivatives 1a and 2a-b. The linear optical properties (absorption and emission) for all compounds were evaluated in dioxane solutions. In addition, the hyperpolarizabilities ? of chromophores 1-4 were measured using hyper-Rayleigh scattering in dioxane solutions and thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that chromophores 1-4 are endowed with both excellent optical nonlinearities and high thermal stability making them interesting candidates for nonlinear optical (NLO) applications.

Batista, Rosa M. F.; Costa, Susana P. G.; Belsley, Michael; Raposo, M. Manuela M.

2011-05-01

459

Facile synthesis of 1,3,7-trihydroxyxanthone and its regioselective coupling reactions with prenal: simple and efficient access to osajaxanthone and nigrolineaxanthone F.  

PubMed

A facile five-step synthesis of naturally occurring 1,3,7-trihydroxyxanthone has been described starting from 1,3,5-trimethoxybenzene via NBS-induced nuclear bromination, lithiation followed by an in situ benzoylation with methyl 2,5-dibenzyloxybenzoate, selective deprotection of the two benzyl groups, base-catalyzed intramolecular cyclization, and demethylations pathway with 62% overall yield. The regioselective coupling reactions of 1,3,7-trihydroxyxanthone with prenal in the presence of calcium hydroxide at room temperature and under thermal conditions at 140-150 degrees C have been demonstrated to exclusively obtain the natural products osajaxanthone in 75% yield and nigrolineaxanthone F in 98% yield, respectively. PMID:16776532

Mondal, Mukulesh; Puranik, Vedavati G; Argade, Narshinha P

2006-06-23

460

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

461

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

Microsoft Academic Search

OBJECTIVE: To distinguish between the effects of reduced oxidative capacity and reduced metabolic efficiency on skeletal muscle bioenergetics during exercise in patients with congestive heart failure. DESIGN AND PATIENTS: Patients were studied by 31P magnetic resonance spectroscopy during aerobic exercise and recovery, and results compared with controls. RESULTS: In flexor digitorum superficialis muscle (26 patients) there was a 30% decrease

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

1996-01-01

462

Effect of the thickness and porosity of carbon-black gas-diffusion air electrodes on the efficiency of hydrogen peroxide synthesis from atmospheric oxygen  

Microsoft Academic Search

Effect of the porosity and thickness of hydrophobized gas-diffusion air electrodes composed of A 437-E acetylene black or\\u000a its mixture with P 702 and P 701 furnace blacks on the efficiency of electroreduction of atmospheric oxygen to H2O2 in 0.5 M NaOH was studied.

G. V. Kornienko; N. V. Chaenko; I. S. Vasil’eva; G. A. Kolyagin; V. L. Kornienko

2010-01-01

463

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

PubMed

Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (?70 s) for the reduction of 4-nitrophenol. PMID:23546439

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

2013-04-02

464

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

Microsoft Academic Search

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

Varsha Brahmkhatri; Anjali Patel

2012-01-01

465

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

Microsoft Academic Search

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

Varsha Brahmkhatri; Anjali Patel

2011-01-01

466

Tetrabutylammonium tetra ( tert-butyl alcohol) coordinated fluoride-an efficient reagent for the synthesis of fluorine derivatives of phosphorus(V) compounds  

Microsoft Academic Search

Direct conversion of phosphorus(V) chlorides to the corresponding phosphorus(V) fluorides was achieved using a solid reagent, tetrabutylammonium tetra (tert-butyl alcohol) coordinated fluoride. The phosphorus(V) fluorides were directly synthesized and efficiently isolated in very good yields.

Hemendra K. Gupta; Deepak Pardasani; Avik Mazumder; Ajay Kumar Purohit; Devendra K. Dubey

2009-01-01