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1

Enantioselective synthesis of (-)-pentalenene.  

PubMed

A short, enantioselective synthesis of (-)-pentalenene is described. Catalytic enantioselective cyclopropenation with (R,R)-Rh2(OAc)(DPTI)3 was used to set the absolute stereochemistry, and an intramolecular Pauson-Khand reaction of the resulting cyclopropenyne was used to establish the quaternary center. PMID:18031057

Pallerla, Mahesh K; Fox, Joseph M

2007-11-22

2

Enantioselective total synthesis of (+)-dibromophakellstatin.  

PubMed

The first enantioselective total synthesis of (+)-phakellstatin and (+)-dibromophakellstatin was achieved. Key steps in the synthesis were a desymmetrization of the diketopiperazine (S,S)-cyclo (Pro, Pro) via a diastereoselective acylation, an intramolecular Mitsunobu reaction to introduce the C6 aminal, and a tandem Hofmann rearrangement/cyclization to simultaneously introduce the C10 quaternary aminal center and deliver the cyclic urea. The synthesis also demonstrates the unusual stability of pyrrolo aminals. Importantly, this strategy has the potential for producing phakellstatin derivatives, derived from (R,R)-cyclo (Pro, Pro), necessary for biological studies. A similar annulation protocol is also expected to be applicable to the synthesis of palau'amine. PMID:12785755

Poullennec, Karine G; Romo, Daniel

2003-05-28

3

Enantioselective Total Synthesis of (+)-Cassiol  

PubMed Central

An enantioselective total synthesis of (+)-cassiol is reported. The complex derived from Pd2(pmdba)3 and enantiopure t-BuPHOX ligand catalyzes enantioconvergent decarboxylative alkylation to generate the quaternary carbon stereocenter at an early stage. The overall synthetic strategy involves a convergent late-stage coupling of two fragments. The synthesis features a longest linear sequence of eight steps.

Petrova, Krastina V.; Mohr, Justin T.; Stoltz, Brian M.

2009-01-01

4

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

PubMed Central

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

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

2011-01-01

5

Enantioselective Total Synthesis of (+)-Lithospermic Acid  

PubMed Central

An enantioselective synthesis of (+)-lithospermic acid, a potent anti-HIV agent, has been accomplished in a convergent manner in 9 steps. The synthesis features an enantioselective intramolecular oxa-Michael addition catalyzed by a quinidine derivative, a hypervalent iodine-mediated rearrangement of chromanone to dihydrobenzofuran, an enantioselective ?-oxyamination, and an intermolecular C-H olefination.

Cheng, Xu; Zhou, Bing

2012-01-01

6

Enantioselective total synthesis of (+)-lithospermic acid.  

PubMed

An enantioselective synthesis of (+)-lithospermic acid, a potent anti-HIV agent, has been accomplished in a convergent manner in nine steps. The synthesis features an enantioselective intramolecular oxa-Michael addition catalyzed by a quinidine derivative, a hypervalent iodine-mediated rearrangement of chromanone to dihydrobenzofuran, an enantioselective ?-oxyamination, and an intermolecular C-H olefination. PMID:22978790

Ghosh, Arun K; Cheng, Xu; Zhou, Bing

2012-09-14

7

Enantioselective total synthesis of (-)-diversonol.  

PubMed

For the synthesis of (-)-diversonol (ent-1), an enantioselective domino-Wacker/carbonylation/methoxylation reaction and an enantioselective Wacker oxidation were used to give the chroman in high yield and 96% and 93% ee, respectively. Dihydroxylation at the vinyl moiety using the Sharpless procedure and a Wittig-Horner reaction followed by hydrogenation, benzylic oxidation, and an intramolecular acylation provided the tetrahydroxanthenone, from which ent-1 is accessible in a few steps. Furthermore, the synthesis of the diastereomeric diversonol rac-1,9a-epi-diversonol (rac-41) is also described. PMID:23417866

Tietze, Lutz F; Jackenkroll, Stefan; Raith, Christian; Spiegl, Dirk A; Reiner, Johannes R; Ochoa Campos, Maria Claudia

2013-02-18

8

Construction of 2-Substituted-3-Functionalized Benzofurans via Intramolecular Heck Coupling: Application to Enantioselective Total Synthesis of Daphnodorin B.  

PubMed

A novel approach was developed for the synthesis of 2-substituted-3-functionalized benzofurans, using an intramolecular Heck reaction which was further applied in the first enantioselective total synthesis of Daphnodorin B. PMID:24007373

Yuan, Hu; Bi, Kai-Jian; Li, Bo; Yue, Rong-Cai; Ye, Ji; Shen, Yun-Heng; Shan, Lei; Jin, Hui-Zi; Sun, Qing-Yan; Zhang, Wei-Dong

2013-09-05

9

Enantioselective total synthesis of (+)-reserpine.  

PubMed

A catalytic, enantioselective synthesis of (+)-reserpine is reported. The route features a highly diastereoselective, chiral catalyst-controlled formal aza-Diels-Alder reaction between a 6-methoxytryptamine-derived dihydro-?-carboline and an enantioenriched ?-substituted enone to form a key tetracyclic intermediate. This approach addresses the challenge of setting the C3 stereogenic center by using catalyst control. Elaboration of the tetracycle to (+)-reserpine includes an intramolecular aldol cyclization and a highly diastereoselective hydrogenation of a sterically hindered enoate. PMID:23331099

Rajapaksa, Naomi S; McGowan, Meredeth A; Rienzo, Matthew; Jacobsen, Eric N

2013-01-18

10

Enantioselective synthesis of levomilnacipran.  

PubMed

A novel approach for the asymmetric synthesis of the active (1S,2R)-enantiomer of the antidepressant milnacipran is reported. The two stereogenic centers borne by the cyclopropane ring were sequentially installed starting from phenylacetic acid. PMID:22767143

Alliot, Julien; Gravel, Edmond; Pillon, Florence; Buisson, David-Alexandre; Nicolas, Marc; Doris, Eric

2012-07-06

11

A Concise Enantioselective Synthesis of (-)-Ranirestat  

PubMed Central

A concise, enantioselective synthesis of the potent aldose reductase inhibitor ranirestat (1) is reported. The synthesis was accomplished employing inexpensive, commercially available starting materials. A palladium-catalyzed asymmetric allylic alkylation (Pd-AAA) of malonate 4 was utilized as a key transformation to construct the tetrasubstituted chiral center in the target.

Trost, Barry M.; Osipov, Maksim; Dong, Guangbin

2010-01-01

12

The first enantioselective synthesis of palinurin.  

PubMed

The first enantioselective synthesis of palinurin has been accomplished starting from commercially available furaldehyde and (R)-methyl-3-hydroxy-2-methylpropionate; the key steps of the synthesis include the use of a chiral pyrrolidine to create the chiral tetronic moiety, and Horner-Wadsworth-Emmons, Wittig and Wittig-Horner reactions to construct the alkene units. PMID:19587930

Pérez, Manuel; Pérez, Daniel I; Martínez, Ana; Castro, Ana; Gómez, Generosa; Fall, Yagamare

2009-05-05

13

Discovery and application of new bacterial strains for asymmetric synthesis of L-tert-butyl leucine in high enantioselectivity.  

PubMed

Discovery of new bacterial strains with fast identification in a miniaturized system was performed for the synthesis of optically active L-tert-butyl leucine. With tert-butyl leucine amide as nitrogen source, one bacterial strain with high conversion and high enantioselectivity was discovered among 120 isolated microorganisms from local soils and identified as Mycobacterium sp. JX009. Glucose and ammonium chloride were examined as the good carbon source and nitrogen source for the cells' growth separately. The cells grew better at 30 °C and at pH 7.5 with higher activity of 2,650 U/l in comparison with other conditions. Cells' stability was improved by immobilization on synthetic resin 0730 without pretreatment. Tert-butyl leucine amide (30 mM) was successfully hydrolyzed by immobilized cells and examined as the highest chemical concentration that cells could endure. After six reaction cycles, the immobilized cells retained 90% activity with production of L-tert-butyl leucine in 98% ee. The results firstly reported the application of new bacterial strain in the hydrolysis of tert-butyl leucine amide to produce optically active L-tert-butyl leucine in an efficient way with investigation in detail. PMID:21153891

Jin, Jian-Zhong; Chang, Dong-Liang; Zhang, Jie

2010-12-14

14

Studies on the Enantioselective Synthesis of Cymbalta?  

Microsoft Academic Search

The enantioselective synthesis of Cymbalta? is reported. Cymbalta? is a serotonin reuptake inhibitor intended for individuals with major depressive disorder (MDD), generalized anxiety disorder (GAD), and pain related to diabetic neuropathy. Cymbalta? is unique because it can provide protection from especially severe symptoms where other drugs cannot ( for instance Prozac?). Consequently, Cymbalta? is an excellent synthetic target. Our synthetic

Kenneth Feldman

2009-01-01

15

Expedient Enantioselective Synthesis of Cermizine D  

PubMed Central

An efficient enantioselective synthesis of cermizine D has been developed that exploits the use of a common intermediate to access over 85% of the carbon backbone. Key steps include an organocatalyzed heteroatom Michael addition, a diastereoselective alkylation with ?-iodomethyl phenyl sulfide, a conjugate addition to a vinyl sulfone species and a sulfone coupling / desulfurization sequence to join the two major subunits.

Veerasamy, Nagarathanam; Carlson, Erik C.; Carter, Rich G.

2012-01-01

16

Enantioselective Organocatalytic Hantzsch Synthesis of Polyhydroquinolines  

PubMed Central

The four component Hantzsch reaction provides access to pharmaceutically important dihydropyridines. To expand the utility of this method, we have developed a route under organocatalytic conditions with good yields and excellent ee's. Through catalyst screening, we found that a BINOL-phosphoric acid allowed enantioselective synthesis of six-membered heterocycles with a variety of substitution patterns.

Evans, Christopher G.; Gestwicki, Jason E.

2009-01-01

17

Enantioselective synthesis of 4-heterosubstituted cyclopentenones.  

PubMed

Racemic 4-hydroxycyclopentenone, readily derived from furfuryl alcohol, can be transformed via its O-Boc derivative to 4-acyloxy, 4-aryloxy-, 4-amino-, or 4-thio-substituted cyclopentenones with high enantioselectivity by palladium-catalyzed kinetic resolution via nucleophilic allylic substitutions. Applying this methodology, a short formal synthesis of ent-noraristeromycin was readily accomplished. PMID:23544701

Ulbrich, Kathrin; Kreitmeier, Peter; Vilaivan, Tirayut; Reiser, Oliver

2013-04-01

18

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

19

Creation of novel chiral synthons with enzymes: application to enantioselective synthesis of antibiotics.  

PubMed

Retrosynthesis was carried out to generate, from a target molecule, a symmetric diester in the prochiral or meso form. The symmetric diester was subjected to asymmetric hydrolysis with pig liver esterase to create the corresponding chiral half-ester. The chiral half-ester was converted into the target molecule by organic synthesis. Thus, various types of carbapenem antibiotics, negamycin, showdomycin, 6-azapseudouridine, cordycepin, aristeromycin, neplanocin A, and precursors of fortimicin were efficiently synthesized with the desired absolute configuration. The methods for asymmetric synthesis starting from substrates with sigma-symmetry have been extensively developed. PMID:3874758

Ohno, M

1985-01-01

20

Enantioselective synthesis of (+)-malbrancheamide B.  

PubMed

The asymmetric total synthesis of the chlorinated [2.2.2]-diazabicyclic indole alkaloid (+)-malbrancheamide B is reported. Key to the synthesis is a domino reaction sequence that employs an aldol condensation, alkene isomerization, and intramolecular Diels-Alder cycloaddition. Diastereofacial selection between the azadiene stereofaces is enforced with a chiral aminal auxiliary. A formal 7-step (longest linear route) synthesis of (±)-malbrancheamide B is also reported. PMID:23360221

Laws, Stephen W; Scheerer, Jonathan R

2013-02-08

21

Scalable, enantioselective taxane total synthesis  

PubMed Central

Taxanes are a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel) — a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which possesses a suitable functional handle to access more oxidised members of its family. This route enabled a gram-scale preparation of the ”parent” taxane, taxadiene, representing the largest quantity of this naturally occurring terpene ever isolated or prepared in pure form. The taxane family’s characteristic 6-8-6 tricyclic system containing a bridgehead alkene is forged via a vicinal difunctionalisation/Diels–Alder strategy. Asymmetry is introduced by means of an enantioselective conjugate addition that forms an all-carbon quaternary centre, from which all other stereocentres are fixed via substrate control. This study lays a critical foundation for a planned access to minimally oxidised taxane analogs and a scalable laboratory preparation of Taxol itself.

Mendoza, Abraham; Ishihara, Yoshihiro; Baran, Phil S.

2011-01-01

22

Enantioselective Total Synthesis of Pladienolide B: A Potent Spliceosome Inhibitor  

PubMed Central

An enantioselective and convergent total synthesis of pladienolide B (1) is described. Pladienolide B binds to the SF3b complex of a spliceosome and inhibits mRNA splicing activity. The synthesis features an epoxide opening reaction, an asymmetric reduction of a ?-keto ester, and a cross metathesis strategy for the side chain synthesis.

Anderson, David D.

2012-01-01

23

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D.  

PubMed

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction. PMID:16104734

Wilson, Rebecca M; Jen, Wendy S; Macmillan, David W C

2005-08-24

24

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

25

Enantioselective Synthesis of (+)-Isolysergol via Ring Closing Metathesis  

PubMed Central

The first enantioselective synthesis of (+)–isolysergol was completed in 12 steps from commercially available materials by a novel approach that features a late stage microwave-mediated, diastereomeric ring closing metathesis catalyzed by a chiral molybdenum catalyst to simultaneously form the D ring and set the stereocenter at C(8).

Deck, Jason A.; Martin, Stephen F.

2010-01-01

26

Enantioselective Total Synthesis of Spirofungins A and B  

PubMed Central

The enantioselective total synthesis of spirofungins A (1) and B (2) is reported in 14 steps over the longest linear sequence. Key steps include the use of thiazolidinethione mediated aldol reactions to assemble the major fragments and installation of the C1–C6 side chain using a cross metathesis reaction.

Crimmins, Michael T.; O'Bryan, Elizabeth A.

2010-01-01

27

Enantioselective total synthesis of (-)-blennolide?A.  

PubMed

Blennolide?A can be synthesized through an enantioselective domino-Wacker/carbonylation/methoxylation reaction of 7a with 96?% ee and an enantioselective Wacker oxidation of 7b with 89?% ee. Further transformations led to the ?,?-unsaturated ester (E)-17, which was subjected to a highly selective Michael addition, introducing a methyl group to give 18a. After a threefold oxidation and an intramolecular acylation, the tetrahydroxanthenone 4 was obtained, which could be transformed into (-)-blennolide?A (ent-1) in a few steps. PMID:23649592

Tietze, Lutz F; Ma, Ling; Reiner, Johannes R; Jackenkroll, Stefan; Heidemann, Sven

2013-05-03

28

Enantioselective Total Synthesis of (+)-Gliocladin C  

PubMed Central

The first total synthesis of gliocladin C, a fungal-derived marine alkaloid containing a rare trioxopiperazine fragment, is reported. This asymmetric synthesis establishes the absolute configuration of this structurally novel natural product.

Overman, Larry E.; Shin, Youseung

2008-01-01

29

Enantioselective synthesis of epi-(+)-Sch 642305: observation of an interesting diastereoselection during RCM  

Microsoft Academic Search

In an approach towards the enantioselective total synthesis of the novel bioactive natural product Sch 642305, an unusual diastereoselection during the key RCM reaction, resulted in the synthesis of the 11-epi-isomer of Sch 642305.

Goverdhan Mehta; Harish M. Shinde

2005-01-01

30

Enantioselective total synthesis of callipeltoside A: two approaches to the macrolactone fragment  

PubMed Central

The enantioselective total synthesis of callipeltoside A is described. Two syntheses of the macrolactone subunit are included: the first relies upon an Ireland–Claisen rearrangement to generate the trisubstituted olefin geometry and the second utilizes an enantioselective vinylogous aldol reaction for this purpose. Enantioselective syntheses of the sugar and chlorocyclopropane side chain fragments are also disclosed. The relative and absolute stereochemistry of this natural product was determined by fragment coupling with the two enantiomers of the side chain fragment.

Evans, David A.; Burch, Jason D.; Hu, Essa; Jaeschke, Georg

2012-01-01

31

Enantioselective total synthesis and confirmation of the absolute and relative stereochemistry of streptorubin B.  

PubMed

The enantioselective total synthesis of the pyrrolophane natural product streptorubin B is described. Key steps in the concise route include the application of a one-pot enantioselective aldol cyclization/Wittig reaction and an anionic oxy-Cope rearrangement to forge the crucial 10-membered ring. Comparisons between CD spectra of synthetic and natural samples of streptorubin B coupled with X-ray crystallography allowed for the determination of the absolute stereochemistry of this natural product for the first time. These studies also provided unambiguous proof of the relative configuration between the butyl side chain and the bispyrrole subunit. Additional studies revealed a novel atropstereoselective Paal-Knorr pyrrole condensation and provided fundamental experimental insight into the barrier for atropisomerization of the natural product. PMID:21166419

Hu, Dennis X; Clift, Michael D; Lazarski, Kiel E; Thomson, Regan J

2010-12-17

32

Enantioselective total synthesis of macrolide (+)-neopeltolide.  

PubMed

The asymmetric total synthesis of the anti-proliferative macrolide (+)-neopeltolide has been completed. The stereochemically defined trisubstituted tetrahydropyran ring was constructed via a catalytic hetero-Diels-Alder reaction creating two new chiral centers in a highly diastereoselective manner. The other key features of this synthesis included Brown's asymmetric allylation to install the requisite C-11 and C-13 stereocenters. The synthesis of the oxazole side chain consisted of a hydrozirconation of an alkynyl stannane to establish the Z stereochemistry, followed by a palladium catalyzed cross coupling to introduce the desired Z olefin in the oxazole side chain. PMID:24121457

Ghosh, Arun K; Shurrush, Khriesto A; Dawson, Zachary L

2013-10-11

33

Gold-catalyzed highly enantioselective synthesis of axially chiral allenes.  

PubMed

Axially chiral allenes are synthesized from chiral propargylamines catalyzed by KAuCl4 in high yields (up to 93% yield) and excellent enantioselectivities (up to 97% ee) in CH3CN at 40 degrees C. The reaction has been applied to the synthesis of novel allene-modified artemisinin derivatives with the delicate endoperoxide moieties remaining intact. A tentative mechanism regarding gold(I)-catalyzed intramolecular hydride transfer was proposed on the basis of deuterium-labeling experiments and ESI-MS analysis of the reaction mixture. PMID:18181641

Lo, Vanessa Kar-Yan; Wong, Man-Kin; Che, Chi-Ming

2008-01-09

34

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

PubMed Central

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

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

2011-01-01

35

Enamine/Carbene Cascade Catalysis in the Diastereo- and Enantioselective Synthesis of Functionalized Cyclopentanones  

PubMed Central

Herein we report an enantioselective synthesis of complex cyclopentanones using aliphatic aldehydes and activated enones. With the combination of a chiral secondary amine and a chiral triazolium catalyst, high diastereoselectivity and excellent enantioselectivity can be achieved. We present evidence of a clear cooperative effect when these two catalysts are present simultaneously in the system.

Ozboya, Kerem E.

2011-01-01

36

Enantioselective total synthesis of (+)-galbulin via organocatalytic domino Michael-Michael-aldol condensation.  

PubMed

A concise and practical enantioselective synthesis of (+)-galbulin has been achieved using organocatalytic domino Michael-Michael-aldol condensation and organocatalytic kinetic resolution as the key steps. PMID:22179766

Hong, Bor-Cherng; Hsu, Che-Sheng; Lee, Gene-Hsiang

2011-12-16

37

Enantioselective total synthesis of ?-lactonic marine natural products, (+)-tanikolide and (?)-malyngolide, via RCM reaction  

Microsoft Academic Search

Enantioselective total synthesis of ?-lactonic marine natural products, (+)-tanikolide and (?)-malyngolide isolated from Lyngbya majuscula, was achieved by using the Sharpless asymmetric epoxidation and a ring-closing metathesis, as key reactions.

Hirotake Mizutani; Masayuki Watanabe; Toshio Honda

2002-01-01

38

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

39

Asymmetric autocatalysis: crystallization-induced highly enantioselective synthesis of a conglomerating oxo-rhenium(V) complex  

Microsoft Academic Search

Experiments designed to elucidate the mechanistic foundation and origins of enantioselectivity in a symmetry breaking synthesis are described. The autocatalytic enantioselective preparation of the title complex cis-[ReOCl2(P?O)py] [py=pyridine; P?O=(OCMe2CMe2O)POCMe2CMe2O(1?)], either C or A handed, from optically inactive substrates can be controlled by catalytic quantities of the non-racemic conglomerating product. The synthesis can be accomplished due to enantioselective complex formation and

Witold K. Rybak

2008-01-01

40

Enantioselective synthesis of ?-/?-alkoxy-?-hydroxy-?-alkyl-substituted Weinreb amides via DKR-ATH: application to the synthesis of advanced intermediate of (-)-brevisamide.  

PubMed

A method of preparing stereodefined ?-/?-alkoxy-?-hydroxy-?-alkyl-substituted Weinreb amides containing two successive hydroxyl-alkyl stereocenters has been developed. Further, this strategy coupled with organo-catalyzed asymmetric epoxidation culminates in the synthesis of a critical intermediate of (-)-brevisamide and its diastereomers. PMID:23994971

Kumaraswamy, Gullapalli; Narayana Murthy, Akula; Narayanarao, Vykunthapu; Vemulapalli, Sahithya Phani Babu; Bharatam, Jagadeesh

2013-09-02

41

Synthesis of Poly(Ethylene Glycol)–Supported (R)-BINOL Derivatives and Their First Application in Enantioselective Mukaiyama Aldol Reactions  

Microsoft Academic Search

The Mukaiyama aldol reaction of 2-styryl-oxazole-4-carbaldehyde (1) as model substrate with S-ketene silyl acetal 2 catalyzed by poly(ethylene glycol)-supported binaphthyl-derived chiral titanium(IV) complexes afforded the corresponding aldol product in good to excellent yields and enantioselectivities up to 94% ee. The chemical yields and\\/or the enantioselectivities are enhanced by generating the active catalyst from Ti(OiPr)4, polymer-supported ligands (R)-6 or (R)-8, and

Reinhold Zimmer; Vjekoslav Dekaris; Markus Knauer; Luise Schefzig; Hans-Ulrich Reissig

2009-01-01

42

Enantioselective synthesis of atropisomeric benzamides through peptide-catalyzed bromination.  

PubMed

We report the enantioselective synthesis of atropisomeric benzamides employing catalytic electrophilic aromatic substitution reactions involving bromination. The catalyst is a simple tetrapeptide bearing a tertiary amine that may function as a Brønsted base. A series of tri- and dibrominations were accomplished for a range of compounds bearing differential substitution patterns. Tertiary benzamides represent appropriate substrates for the reaction since they exhibit sufficiently high barriers to racemization after ortho functionalization. Mechanism-driven experiments provided some insight into the basis for selectivity. Examination of the observed products at low conversion suggested that the initial catalytic bromination may be regioselective and stereochemistry-determining. A complex between the catalyst and substrate was observed by NMR spectroscopy, revealing a specific association. Finally, the products of these reactions may be subjected to regioselective metal-halogen exchange and trapping with I(2), setting the stage for utility. PMID:23410090

Barrett, Kimberly T; Miller, Scott J

2013-02-14

43

Enantioselective total synthesis of desbromoarborescidines A-C and the formal synthesis of (S)-deplancheine.  

PubMed

Starting from Boc-protected tryptamine and (S)-tetrahydro-5-oxo-2-furancarboxylic acid, facile enantioselective total synthesis of desbromoarborescidines A-C and the formal synthesis of (S)-deplancheine have been accomplished via a common intermediate (S)-indolo[2,3-a]quinolizine. Synthesis of enantiomerically pure (S)-acetoxyglutarimide, stereoselective reductive intramolecular cyclization, hydroxyl group-assisted in situ N-Boc-deprotection, selective deoxygenation of the xanthate ester, and lactam hydrolysis followed by an appropriate exchange of nitrogen regioselectivity in intramolecular cyclization were the decisive steps. PMID:23758537

Mondal, Pravat; Argade, Narshinha P

2013-06-25

44

Development of a Merged Conjugate Addition/Oxidative Coupling Sequence. Application to the Enantioselective Total Synthesis of Metacycloprodigiosin and Prodigiosin R1  

PubMed Central

A merged conjugate addition/oxidative coupling sequence that represents an efficient strategy for preparing structurally diverse pyrroles has been developed. Success of the method hinged upon the controlled oxidative coupling of unsymmetrical silyl bis-enol ether intermediates, formed by the 1,4-addition of a Grignard reagent with subsequent enolate trapping by a (chloro)silylenol ether. The process was applied to the first enantioselective syntheses of the biologically active pyrrolophane natural products, metacycloprodigiosin and prodigiosin R1.

Clift, Michael D.; Thomson, Regan J.

2009-01-01

45

Enantioselective Total Synthesis of (S)-Bisoranjidiol, an Axially Chiral Bisanthraquinone  

PubMed Central

The first enantioselective total synthesis of the bisanthraquinone (S)-bisoranjidiol and an unnatural regioisomer has been accomplished. Key features of the synthesis include the asymmetric oxidative biaryl coupling of a hindered 8-substituted 2-naphthol, selective para-quinone formation, and regioselective tandem Diels-Alder/aromatization reactions.

Podlesny, Erin E.; Kozlowski, Marisa C.

2012-01-01

46

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

Microsoft Academic Search

In biology-oriented synthesis the underlying scaffold classes of natural products selected in evolution are used to define biologically relevant starting points in chemical structure space for the synthesis of compound collections with focused structural diversity. Here we describe a highly enantioselective synthesis of natural-product-inspired 3,3'-pyrrolidinyl spirooxindoles-which contain an all-carbon quaternary centre and three tertiary stereocentres. This synthesis takes place by

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

2010-01-01

47

Phosphoramidite Gold(I)-Catalyzed Diastereo- and Enantioselective Synthesis of 3,4-Substituted Pyrrolidines  

PubMed Central

In this article the utility of phosphoramidite ligands in enantioselective AuI catalysis was explored in the development of highly diastereo- and enantioselective AuI-catalyzed cycloadditions of allenenes. A AuI-catalyzed synthesis of 3,4-disubstituted pyrrolidines and ?-lactams is described. This reaction proceeds through the enantioselective AuI-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (–)-isocynometrine.

Gonzalez, Ana Z.; Benitez, Diego; Tkatchouk, Ekaterina; Goddard, William A.; Toste, F. Dean

2011-01-01

48

Palladium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles via enantioselective C-H bond functionalization.  

PubMed

A Pd-catalyzed asymmetric synthesis of Si-stereogenic dibenzosiloles is developed through enantioselective C-H bond functionalization of prochiral 2-(arylsilyl)aryl triflates. High chemo- and enantioselectivities are achieved by employing a Josiphos-type ligand under mild conditions. PMID:22506681

Shintani, Ryo; Otomo, Haruka; Ota, Kensuke; Hayashi, Tamio

2012-04-19

49

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

ERIC Educational Resources Information Center

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

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

2010-01-01

50

Enantioselective synthesis of 5-epi-citreoviral using ruthenium-catalyzed asymmetric ring-closing metathesis.  

PubMed

Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in > or = 90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis. PMID:19785443

Funk, Timothy W

2009-11-01

51

Palladium(II)-Catalyzed Enantioselective Synthesis of ?-(Trifluoromethyl)arylmethylamines.  

PubMed

Trifluoromethylacetaldimines, generated in situ from the corresponding N,O-acetals, undergo 1,2-addition of arylboroxines under palladium(II) catalysis to generate a variety of ?-(trifluoromethyl)arylmethylamines with good to high enantioselectivity (up to 97% ee). The pyridine-oxazolidine (PyOX) class of ligands was found to be particularly suitable for this transformation, which proceeds without exclusion of ambient air and moisture. PMID:23883415

Johnson, Thomas; Lautens, Mark

2013-07-24

52

Enantioselective Total Synthesis of (+)-Largazole, a Potent Inhibitor of Histone Deacetylase  

PubMed Central

An enantioselective total synthesis of cytotoxic natural product, (+)-largazole (1) is described. It is a potent histone deacetylase inhibitor. Our synthesis is convergent and involves the assembly of thiazole 3-derived carboxylic acid with amino ester 4 followed by cycloamidation of the corresponding amino acid. The synthesis features an efficient cross metathesis, an enzymatic kinetic resolution of a ?-hydroxy ester, a selective removal of a Boc-protecting group, a HATU/HOAt-promoted cycloamidation reaction, and synthetic manipulations to a sensitive thioester functional group.

Ghosh, Arun K.; Kulkarni, Sarang

2010-01-01

53

Enantioselective Total Synthesis of Guanacastepene N Using an Uncommon 7-Endo Heck Cyclization as a Pivotal Step  

PubMed Central

A convergent, enantioselective total synthesis of (+)-guanacastepene N was developed that features a 7-endo Heck cyclization as the key step. In the course of this synthesis, short syntheses of the enantiomerically pure cyclopentenone and cyclohexene building blocks 5 and 6, which constitute A and C ring fragments of guanacastepene N, were developed. These fragments were linked by a challenging conjugate addition reaction that also generated the C11 quaternary carbon stereocenter. Regioselective 7-endo Heck cyclization gave rise to a tricyclic intermediate, which was elaborated to complete the first total synthesis of guanacastepene N and the second enantioselective total synthesis of a guanacastepene natural product.

Iimura, Shin; Paulini, Ralph; Zakarian, Armen

2013-01-01

54

An Enantioselective Synthesis of a Single Enantiomer of Prozac; Preparation of (S)-(+)Fluoxetine  

Microsoft Academic Search

An enantioselective synthesis of S-(+)-Fluoxetine is shown by utilizing the enzyme (R)-oxynitrilase to induce chirality, in high enantiomeric excess, in trans-cinnamaldehyde to form (R,E)-2-hydroxy-4-phenylbut-3-enenitrile. After converting the nitrile functionality to the ethyl ester thru a hydrolytic esterification, the hydroxy group is converted to the ethyl carbonate. Using a palladium(0) catalyst, the carbonate group is displaced and a 4-(trifluoromethyl)phenoxy group is

Derek Ross

2008-01-01

55

Catalytic Enantioselective Electrophilic Aminations of Acyclic ?-Alkyl ?-Carbonyl Nucleophilies  

PubMed Central

Highly enantioselective aminations of acyclic ?-alkyl ?-keto thioesters and trifluoroethyl ?-methyl ?-cyanoacetate (12) with as low as 0.05 mol % of a bifunctional cinchona alkaloid catalyst were established. This ability to afford highly enantioselectivity for the amination of ?-alkyl ?-carbonyl compounds renders the 6?-OH cinchona alkaloid-catalyzed amination applicable for the enantioselective synthesis of acyclic chiral compounds bearing N-substituted quaternary stereocenters. The synthetic application of this reaction is illustrated in a concise asymmetric synthesis of ?-methylserine, a key intermediate previously utilized in the total synthesis of a small molecule immunomodulator, conagenin.

Liu, Xiaofeng; Sun, Bingfeng

2009-01-01

56

Synthesis of cyclic peptide hemicryptophanes: enantioselective recognition of a chiral zwitterionic guest.  

PubMed

The synthesis of the first members of a new class of cyclic peptide-containing hemicryptophanes is described. Synthesis was achieved through attachment of veratryl groups to the l-tyrosine side chains of a cyclic hexapeptide, c(YG)3, followed by intramolecular cyclodehydration to generate the CTV unit. The diastereomeric P- and M-hemicryptophanes were generated in a 2?:?1 ratio and were separated by chromatography. The enantioselective binding properties of the hemicryptophanes were investigated by complexation with carnitine. Both isomers were found to have significant selectivity for binding (R)-carnitine. PMID:23942591

Cochrane, James R; Schmitt, Aline; Wille, Uta; Hutton, Craig A

2013-08-27

57

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

PubMed Central

Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered.

Bhanushali, Mayur; Zhao, Cong-Gui

2011-01-01

58

Pd(ii)-SDP-catalyzed enantioselective 5-exo-dig cyclization of ?-alkynoic acids: application to the synthesis of functionalized dihydofuran-2(3H)-ones containing a chiral quaternary carbon center.  

PubMed

The Pd(ii)-SDP-catalyzed first enantioselective intramolecular cyclization of ?,?-disubstituted ?-alkynoic acids is described. This 5-exo-dig cyclization afforded dihydrofuran-2(3H)-ones bearing a chiral quaternary carbon center in excellent yields with enantioselectivities up to 71%. A mechanism involving palladium(ii) species is proposed to rationalize the outcome of the reaction. PMID:23903490

Sridharan, Vellaisamy; Fan, Lulu; Takizawa, Shinobu; Suzuki, Takeyuki; Sasai, Hiroaki

2013-08-14

59

Highly enantioselective synthesis of a fluorescent amino acid  

Microsoft Academic Search

A high enantiomeric excess (>99.5%) synthesis of l-2-amino-3-(7-methoxy-4-coumaryl) propionic acid (l-Amp) is described. The two step synthesis route of this non-proteinogenic amino acid includes an oxazinone derivative as glycine enolate, which is alkylated with the fluorogenic group.

Péter Kele; Guodong Sui; Qun Huo; Roger M. Leblanc

2000-01-01

60

Enantioselective total synthesis of (+)-ibophyllidine via an asymmetric phosphine-catalyzed [3 + 2] annulation†  

PubMed Central

In this study we performed the total synthesis of the terpene indole alkaloid (+)-ibophyllidine through a pathway involving asymmetric phosphine catalysis, with our novel l-4-hydroxyproline–derived chiral phosphine mediating the key [3 + 2] annulation. Hydrogenation of the [3 + 2] adduct allowed the rapid formation of the stereochemically dense pyrrolidine ring of (+)-ibophyllidine in excellent yield with exceptionally high levels of both diastereo- and enantioselectivity. We constructed the remainder of the pentacyclic skeleton through an intramolecular alkylation and an intramolecular aza-Morita–Baylis–Hillman reaction.

Andrews, Ian P.

2012-01-01

61

Enantioselective synthesis of 1,2,4-triazolines catalyzed by a cinchona alkaloid-derived organocatalyst.  

PubMed

An enantioselective organocatalytic process for the one-step synthesis of poly-substituted 1,2,4-triazolines is reported. The heterocycle formation is believed to go through a step-wise mechanism of nucleophilic addition of an azlactone to an azodicarboxylate in the presence of an organic base catalyst, followed by a TMSCHN2 mediated heterocyclization. Both theoretical calculations and experimental evidence suggest the pre-organization of the transition state for the chirality determining step via a unique 7-membered intramolecular hydrogen bonding. PMID:24145477

Shao, Qian; Chen, Jiean; Tu, Meihua; Piotrowski, David W; Huang, Yong

2013-10-31

62

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; Vadalà, Alessandro; Zanoni, Giuseppe; Vidari, Giovanni

2004-12-10

63

Enantioselective Synthesis of (-)-Sclerophytin A by a Stereoconvergent Epoxide Hydrolysis  

PubMed Central

The cytotoxic natural product (-)-sclerophytin A was constructed in 13 steps from geranial. Highlights from the synthesis are a stereoselective Oshima-Utimoto reaction, a Shibata-Baba indium-promoted radical cyclization, and a novel stereoconvergent epoxide hydrolysis.

Wang, Bin; Ramirez, Armando P.; Slade, Justin J.; Morken, James P.

2010-01-01

64

Biocatalytic enantioselective synthesis of N-substituted aspartic acids by aspartate ammonia lyase.  

PubMed

The gene encoding aspartate ammonia lyase (aspB) from Bacillus sp. YM55-1 has been cloned and overexpressed, and the recombinant enzyme containing a C-terminal His(6) tag has been purified to homogeneity and subjected to kinetic characterization. Kinetic studies have shown that the His(6) tag does not affect AspB activity. The enzyme processes L-aspartic acid, but not D-aspartic acid, with a K(m) of approximately 15 mM and a k(cat) of approximately 40 s(-1). By using this recombinant enzyme in the reverse reaction, a set of four N-substituted aspartic acids were prepared by the Michael addition of hydroxylamine, hydrazine, methoxylamine, and methylamine to fumarate. Both hydroxylamine and hydrazine were found to be excellent substrates for AspB. The k(cat) values are comparable to those observed for the AspB-catalyzed addition of ammonia to fumarate ( approximately 90 s(-1)), whereas the K(m) values are only slightly higher. The products of the enzyme-catalyzed addition of hydrazine, methoxylamine, and methylamine to fumarate were isolated and characterized by NMR spectroscopy and HPLC analysis, which revealed that AspB catalyzes all the additions with excellent enantioselectivity (>97 % ee). Its broad nucleophile specificity and high catalytic activity make AspB an attractive enzyme for the enantioselective synthesis of N-substituted aspartic acids, which are interesting building blocks for peptide and pharmaceutical synthesis as well as for peptidomimetics. PMID:18844200

Weiner, Barbara; Poelarends, Gerrit J; Janssen, Dick B; Feringa, Ben L

2008-01-01

65

A general procedure for the enantioselective synthesis of the minor tobacco alkaloids nornicotine, anabasine, and anatabine.  

PubMed

The minor tobacco alkaloids nornicotine, anabasine, and anatabine from Nicotiana tobacum are known to possess nicotinic receptor agonist activity, although they are relatively less potent than S-(-)-nicotine, the principal tobacco alkaloid. Previous pharmacological investigations and structure-activity studies have been limited owing to the lack of availability of the optically pure forms of these minor alkaloids. We now report a 2-step synthetic procedure for the enantioselective synthesis of the optical isomers of nornicotine and anabasine, and a modified procedure for the synthesis of anatabine enantiomers. These procedures involve initial formation of the chiral ketimine resulting from the condensation of either 1R, 2R, 5R-(+)- or 1S, 2S, 5S-(-)-2-hydroxy-3-pinanone with 3-(aminomethyl)pyridine followed by enantioselective C-alkylation with an appropriate halogenoalkane or halogenoalkene species, N-deprotection, and base-catalyzed intramolecular ring closure, to form the appropriate, chirally pure minor tobacco alkaloid. Using this approach, the R-(+)- and S-(-)-enantiomers of the above minor tobacco alkaloids were obtained in good overall chemical yield and excellent enantomeric excess. PMID:16353951

Ayers, Joshua T; Xu, Rui; Dwoskin, Linda P; Crooks, Peter A

2005-10-31

66

Enantioselective total synthesis of otteliones A and B, novel and powerful antitumor agents from the freshwater plant Ottelia alismoides.  

PubMed

Otteliones A and B, isolated from the freshwater plant Ottelia alismoides, have attracted significant attention because of their potential as novel anticancer agents. In this review, four independent enantioselective total syntheses and one formal synthesis of these natural products are presented with particular focus on their methodology and strategy. PMID:23980432

Katoh, Tadashi

2013-07-01

67

Enantioselective total synthesis of (-)-minovincine in nine chemical steps: an approach to ketone activation in cascade catalysis.  

PubMed

Dressed to the nines: The first enantioselective total synthesis of (-)-minovincine has been accomplished in nine chemical steps and 13?% overall yield. A novel, one-step Diels-Alder/?-elimination/conjugate addition organocascade sequence allowed rapid access to the central tetracyclic core in an asymmetric manner. Boc=tert-butoxycarbonyl, LG=leaving group, PMB=para-methoxybenzyl. PMID:24000234

Laforteza, Brian N; Pickworth, Mark; Macmillan, David W C

2013-09-02

68

Modified chiral triazolium salts for enantioselective benzoin cyclization of enolizable keto-aldehydes: synthesis of (+)-sappanone B.  

PubMed

Asymmetric synthesis of (+)-sappanone B (1), a natural product with a 3-hydroxy chromanone structure, was achieved via enantioselective benzoin cyclization by using a modified Rovis catalyst and triethylamine. This catalyst enabled the successful benzoin cyclization of readily enolizable keto-aldehydes. PMID:17559218

Takikawa, Hiroshi; Suzuki, Keisuke

2007-06-09

69

Enantioselective formal synthesis of (-)-podophyllotoxin from (2S,3R)-3-arylaziridine-2-carboxylate.  

PubMed

Meyers' 4-aryl-1-tetralone-lactone and ent-Zhang's 2-diarylmethyl-4-oxobutanoate were synthesized in the formal synthesis of (-)-podophyllotoxin from (2S,3R)-3-arylaziridine-2-carboxylate, via 3,3-diarylpropanoate as a common intermediate, in an overall 42% yield through 10 steps and 31% yield through 6 steps, respectively. The key steps in the synthesis were regio- and diastereoselective ring opening with an aromatic nucleophile, samarium iodide promoted reductive C-N bond cleavage, and Stille coupling for introducing the vinyl functionality. The starting aziridine was enantioselectively prepared from 3,4,5-trimethoxybenzaldehyde by guanidinium ylide mediated asymmetric aziridination. All nitrogen components used in the reaction sequence are reusable as the starting guanidinium source. PMID:23496308

Takahashi, Masato; Suzuki, Noriyuki; Ishikawa, Tsutomu

2013-03-26

70

Stereoselective synthesis of 4-dehydroxydiversonol employing enantioselective palladium-catalysed domino reactions.  

PubMed

The stereoselective synthesis of 4-dehydroxydiversonol (4) employing enantioselective palladium-catalysed domino processes such as the domino Wacker-Heck and the domino Wacker-carbonylation reaction for the formation of the central chroman moiety is described. Thus, reaction of 8 with palladium(II) trifluoroacetate [Pd(OTFA)2] in the presence of carbon monoxide, methanol and the 2,2'- bis(oxazolin-2-yl)-1,1'-binaphthyl (BOXAX) ligand 17 led to 19 in 80% yield and 96% ee. Similarly, the chroman 7 was prepared using 8 and methyl acrylate (9) as starting material. Hydrogenation of the double bond, oxidation of the benzylic methylene group and intramolecular acylation of chromanone 6 provided the tetrahydroxanthenone core 5, from which the synthesis of 4 was completed. The relative configuration of 4 could be established by crystal structure analysis. PMID:18698572

Tietze, Lutz F; Spiegl, Dirk A; Stecker, Florian; Major, Julia; Raith, Christian; Grosse, Christian

2008-01-01

71

Highly regio-, diastereo- and enantioselective one-pot gold/chiral Brønsted acid-catalysed cascade synthesis of bioactive diversely substituted tetrahydroquinolines.  

PubMed

One-pot sequential asymmetric reactions of aminobenzaldehydes or aminophenones with alkynes catalysed by a gold(I)/Brønsted acid cooperative system are reported. This process provides a highly efficient method for the synthesis of optically active tetrahydroquinolines, with one or two chiral centres at different positions as well as highly divergent functional groups, in good to excellent yields and with high regio-, diastereo- and enantioselectivities. A preliminary study on the effect of stereochemistry on biological activity suggests a potential application of these optically active tetrahydroquinolines in drug discovery processes. PMID:22785458

Liu, Xin-Yuan; Xiao, Ya-Ping; Siu, Fung-Ming; Ni, Li-Chen; Chen, Yong; Wang, Lin; Che, Chi-Ming

2012-07-11

72

Catalytic highly enantioselective alkylation of aldehydes with deactivated grignard reagents and synthesis of bioactive intermediate secondary arylpropanols.  

PubMed

Because of the high reactivity of Grignard reagents, a direct, highly enantioselective Grignard reaction with aldehydes has rarely been disclosed. In this report, Grignard reagents were introduced with bis[2-(N,N'-dimethylamino)ethyl] ether (BDMAEE) to effectively deactivate their reactivity; thus, a highly enantioselective alkylation of aldehydes with Grignard reagents resulted from catalysis by (S)-BINOL-Ti(O(i)Pr)(2). It is thought that BDMAEE chelates the in situ generated salts MgBr(2) from a Schlenk equilibrium of RMgBr and Mg(O(i)Pr)Br from transmetalation of RMgBr with Ti(O(i)Pr)(4). The Mg salts can actively promote the undesired background reaction to give the racemate. The chelation definitely inhibits the catalytic activity of the Mg salts, suppresses the unwanted background reaction, and enables the highly enantioselective addition catalyzed by (S)-BINOL-Ti(O(i)Pr)(2). Consequently, the Mg salt byproducts were not removed, less Ti(O(i)Pr)(4) than RMgBr was used, and extremely low temperature was avoided in this catalytic asymmetric reaction in comparison with the research disclosed before. Various alkyl Grignard reagents were investigated in the asymmetric addition, and (i)BuMgBr resulted in the highest enantioselectivity, >99%. Furthermore, important intermediate secondary arylpropanols for chiral drug synthesis were effectively synthesized with high enantioselectivity, up to 97%, in one step. PMID:20836546

Liu, Yi; Da, Chao-Shan; Yu, Sheng-Li; Yin, Xiao-Gang; Wang, Jun-Rui; Fan, Xin-Yuan; Li, Wei-Ping; Wang, Rui

2010-10-15

73

Enantioselective synthesis of 3-hydroxy oxindoles by ytterbium-catalysed decarboxylative addition of ?-ketoacids to isatins.  

PubMed

A ytterbium(iii)-indapybox catalysed enantioselective decarboxylative addition reaction of ?-ketoacids to isatins is described. The biologically important 3-hydroxy oxindoles were obtained in high yields and excellent enantioselectivities. PMID:23979548

Duan, Zhiqiang; Han, Jianlin; Qian, Ping; Zhang, Zirui; Wang, Yi; Pan, Yi

2013-08-27

74

Enantioselective Synthesis of (+)-Chamaecypanone C, a Novel Microtubule Inhibitor**  

PubMed Central

A number of bicyclo[2.2.2]octenone-containing natural products have been isolated from the heartwood of Chamaecyparis obtusa var. formosana (Figure 1) including the Diels-Alder adducts[1] obtunone (1),[2] chamaecypanone C (2),[3] and the [4+2] dimer (+)-3.[2],[4] Compound (+)-2 was shown to exhibit potent cytotoxicity against several human cancer cells including human oral epidermoid carcinoma (KB) (IC50 = 190 nM).[3] The biosynthesis of 2 was proposed[3] to occur via endo [4+2] cycloaddition between 1-hydroxymentha-3,5-dien-2-one 4 (Figure 2) and 1,3-bis-arylcyclopenta-1,3-diene 5, followed by oxidation to an enone in accord with literature reports of cyclopentadienes as biosynthetic precursors to natural products.[1b] An alternative possibility involving the corresponding cyclopentadienone 6 as dienophile may also be considered in light of known biosyntheses involving reactive cyclopentadienones.[5] Herein, we report a concise synthesis of both enantiomers of chamaecypanone C involving a retro-DA/DA cascade of dimer 3, obtained utilizing copper-mediated asymmetric oxidative dearomatization,[6] as well as biological studies documenting that the cytotoxic action of (+)-2 involves mitotic arrest as a consequence of its binding in the colchicine site of tubulin.

Dong, Suwei; Hamel, Ernest; Bai, Ruoli; Covell, David G.; Beutler, John A.; Porco, John A.

2009-01-01

75

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

PubMed

In biology-oriented synthesis the underlying scaffold classes of natural products selected in evolution are used to define biologically relevant starting points in chemical structure space for the synthesis of compound collections with focused structural diversity. Here we describe a highly enantioselective synthesis of natural-product-inspired 3,3'-pyrrolidinyl spirooxindoles--which contain an all-carbon quaternary centre and three tertiary stereocentres. This synthesis takes place by means of an asymmetric Lewis acid-catalysed 1,3-dipolar cycloaddition of an azomethine ylide to a substituted 3-methylene-2-oxindole using 1-3 mol% of a chiral catalyst formed from a N,P-ferrocenyl ligand and CuPF(6)(CH(3)CN)(4). Cellular evaluation has identified a molecule that arrests mitosis, induces multiple microtubule organizing centres and multipolar spindles, causes chromosome congression defects during mitosis and inhibits tubulin regrowth in cells. Our findings support the concept that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry will be a rich source of compounds with diverse bioactivity. PMID:20729892

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

2010-07-11

76

Enantioselective total synthesis of eurylene, 14-deacetyl eurylene, and their 11-epimers: the relation between ionophoric nature and cytotoxicity.  

PubMed

[structure: see text] Enantioselective synthesis of eurylene, 14-deacetyl eurylene, and their 11-epimers was achieved. The characteristic structural feature of these compounds is two tetrahydrofuran (THF) rings substituted in different stereochemistry. The synthetic approach involves nonstereoselective THF ring formation to afford both segments from a common precursor. We also investigated their ionophoric nature and cytotoxicity. The complexation of these compounds with K(+) might be related to their cytotoxic activity. PMID:15012075

Hioki, Hideaki; Yoshio, Suzuyo; Motosue, Masatoshi; Oshita, Yuka; Nakamura, Yukari; Mishima, Daisaku; Fukuyama, Yoshiyasu; Kodama, Mitsuaki; Ueda, Keisuke; Katsu, Takashi

2004-03-18

77

The enantioselective intramolecular aminative functionalization of unactivated alkenes, dienes, allenes and alkynes for the synthesis of chiral nitrogen heterocycles  

PubMed Central

The enantioselective intramolecular aminative functionalization of unactivated alkenes and related ?-systems is a straight-forward and atom economical strategy for the synthesis of chiral nitrogen heterocycles. These reactions can be categorized as oxidatively neutral, such as alkene hydroamination, or as oxidative reactions, such as alkene difunctionalization, e.g. aminooxygenation and carboamination. This perspective reviews the current work in the field and explores mechanistic trends that are common among the different catalysts and reaction types.

Chemler, Sherry R.

2010-01-01

78

Organocatalyzed enantioselective synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylates  

PubMed Central

The organocatalyzed enantioselective synthesis of biologically active 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylate derivatives was achieved using bifunctional cinchona alkaloids as the catalysts. Using quinine thiourea as the catalyst, the tandem Michael addition-cyclization reaction between 1,3-cyclohexanediones and alkylidenecyanoacetate derivatives gives the desired products in high yields (up to 92%) and good ee values (up to 82%).

Ramireddy, Naresh; Abbaraju, Santhi; Zhao, Cong-Gui

2011-01-01

79

Enantioselective synthesis of ( R)- and ( S)-2-methyl-4-octanol, the male-produced aggregation pheromone of Curculionidae species  

Microsoft Academic Search

This work describes an enantioselective synthesis of (R)- and (S)-2-methyl-4-octanol, a compound that has been identified as the aggregation pheromone of some sugarcane weevils. (S)-2-Methyl-4-octanol was efficiently prepared in five steps and 20% overall yield, and its (R)-enantiomer, in six steps and 14% overall yield, both from commercial isovaleryl chloride. The key step of our synthetic route is the asymmetric

Patricia T. Baraldi; Paulo H. G. Zarbin; Paulo C. Vieira; Arlene G. Corrêa

2002-01-01

80

Diastereo- and Enantioselective Copper-Catalyzed Intramolecular Carboamination of Alkenes for the Synthesis of Hexahydro-1H-benz[f]indoles  

PubMed Central

A new method for the enantioselective synthesis of hexahydro-1H-benz[f]indoles is described. This copper-catalyzed enantioselective intramolecular alkene carboamination process can install vicinal tertiary and quaternary carbon stereocenters with high levels of diastereo- and enantioselectivity. The C-C bond-forming component of the reaction constitutes a C-H functionalization and no electronic activation of the aryl ring that undergoes addition is required. A known 5-HT1A receptor antagonist was synthesized efficiently using this method.

Miao, Lei; Haque, Imranul; Manzoni, Maria R.; Tham, Weng Siong; Chemler, Sherry R.

2010-01-01

81

Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More  

PubMed Central

Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations.

Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

2012-01-01

82

Enantioselective synthesis of planar chiral ferrocenes via palladium-catalyzed annulation with diarylethynes  

PubMed Central

Summary When Boc-L-Val-OH was used as a ligand for the enantioselective Pd(II)-catalyzed annulation of N,N-substituted aminomethyl ferrocene derivatives with diarylethynes, ferrocenes with planar chirality could be achieved with excellent enantioselectivity (up to 99% ee).

Shi, Yan-Chao; Yang, Rong-Fei; Gao, De-Wei

2013-01-01

83

Enantioselective synthesis of chiral 5-carbamoyl-3-pyridyl alcohols by asymmetric autocatalytic reaction  

Microsoft Academic Search

A catalytic amount of a chiral zinc alkoxide of 5-carbamoyl-3-pyridyl alkyl alcohol catalyzes an enantioselective alkylation of 5-carbamoylpyridine-3-carbaldehyde by diisopropylzinc to afford itself in up to 86% e.e. with the same configuration as the catalyst. Enantioselectivity is dependent on the structure of substituents on the nitrogen atom of the amide.

Takanori Shibata; Hiroshi Morioka; Shigehisa Tanji; Tadakatsu Hayase; Yasutaka Kodaka; Kenso Soai

1996-01-01

84

Enantioselective synthesis of planar chiral ferrocenes via palladium-catalyzed annulation with diarylethynes.  

PubMed

When Boc-L-Val-OH was used as a ligand for the enantioselective Pd(II)-catalyzed annulation of N,N-substituted aminomethyl ferrocene derivatives with diarylethynes, ferrocenes with planar chirality could be achieved with excellent enantioselectivity (up to 99% ee). PMID:24062858

Shi, Yan-Chao; Yang, Rong-Fei; Gao, De-Wei; You, Shu-Li

2013-09-18

85

Enantioselective synthesis of anti- and syn-homopropargyl alcohols via chiral Brønsted acid catalyzed asymmetric allenylboration reactions.  

PubMed

Chiral Brønsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in highly diastereoselective syntheses of a variety of anti, anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R

2012-06-25

86

Enantioselective synthesis of 3,3'-dihydropyrryl-spirooxindoles via an organocatalytic three-component reaction.  

PubMed

An organocatalytic three-component reaction of isatins, malononitrile and isocyanoacetates provided 3,3'-dihydropyrryl-spirooxindoles in excellent yields and enantioselectivities. The products could be readily converted to valuable 3,3'-pyrrolidinyl-spirooxindoles. PMID:22684421

Wei, Wen-Tao; Chen, Chun-Xia; Lu, Rui-Jiong; Wang, Jin-Jia; Zhang, Xue-Jing; Yan, Ming

2012-06-11

87

Enantioselective synthesis induced by tetrathia-[7]-helicenes in conjunction with asymmetric autocatalysis  

Microsoft Academic Search

Highly enantioenriched 5-pyrimidyl alkanol was formed using tetrathia-[7]-helicenes as a chiral initiator in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, in conjunction with asymmetric autocatalysis.

Tsuneomi Kawasaki; Kenta Suzuki; Emanuela Licandro; Alberto Bossi; Stefano Maiorana; Kenso Soai

2006-01-01

88

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

89

Enantioselective organocatalytic one-pot amination/aza-Michael/aldol condensation reaction sequence: synthesis of 3-pyrrolines with a quaternary stereocenter.  

PubMed

Primary amine-catalyzed direct conversion of ?,?-disubstituted aldehydes into 3-pyrrolines with a quaternary stereocenter is reported. The one-pot enantioselective sequence is based on a ?-amination, an aza-Michael addition of hydrazine, an aldol condensation dehydratation and proceeds with good yields and excellent levels of enantioselectivity. Synthetically attractive applications including the formation of aziridinopyrrolidine or epoxypyrrolidine derivatives with good yields and selectivities are also described. PMID:22927036

Desmarchelier, Alaric; Coeffard, Vincent; Moreau, Xavier; Greck, Christine

2012-08-27

90

An improved asymmetric total synthesis of (+)-biotin via the enantioselective desymmetrization of a meso-cyclic anhydride mediated by cinchona alkaloid-based sulfonamide  

Microsoft Academic Search

The highly enantioselective total synthesis of (+)-biotin 1 via the Hoffmann–Roche lactone–thiolactone strategy has been achieved starting from cis-1,3-dibenzyl-2-imidazolidone-4,5-dicarboxylic acid 2 with an overall yield of 35%. Two contiguous stereogenic centers at C-3a and C-6a were established through a rapid cinchona alkaloid-based sulfonamide-mediated enantioselective alcoholysis of meso-cyclic anhydride 3 to afford (4S,5R)-cinnamyl hemiester 4h, the direct precursor to (3aS,6aR)-lactone 5

Fei Xiong; Xu-Xiang Chen; Fen-Er Chen

2010-01-01

91

Catalytic, Enantioselective Synthesis of Stilbene cis-Diamines: A Concise Preparation of (-)-Nutlin-3, a Potent p53/MDM2 Inhibitor  

PubMed Central

The first highly diastereo- and enantioselective additions of aryl nitromethane pronucleophiles to aryl aldimines are described. Identification of an electron rich chiral Bis(Amidine) catalyst for this aza-Henry variant was key to this development, leading ultimately to differentially protected cis-stilbene diamines in two steps. This method then became the lynchpin for an enantioselective synthesis of (–)-Nutlin-3 (Hoffmann-LaRoche), a potent cis-imidazoline small molecule inhibitor of p53-MDM2 used extensively as a probe of cell biology and currently in drug development.

Davis, Tyler A.

2012-01-01

92

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines  

PubMed Central

Summary Enantioselective organocatalysis has become a field of central importance within asymmetric chemical synthesis and appears to be efficient approach toward the construction of complex chiral molecules from simple achiral materials in one-pot transformations under mild conditions with high stereocontrol. This review addresses the most significant synthetic methods reported on chiral-amine-catalyzed tandem Michael conjugate addition of heteroatom-centered nucleophiles to ?,?-unsaturated compounds followed by cyclization reactions for the enantioselective construction of functionalized chiral chromenes, thiochromenes and 1,2-dihydroquinolines in optically enriched forms found in a myriad of bioactive natural products and synthetic compounds.

Bhanja, Chittaranjan; Jena, Satyaban; Nayak, Sabita

2012-01-01

93

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers  

PubMed Central

Summary Diaryl ethers carrying carbamoyloxymethyl groups may be desymmetrised enantio- and diastereoselectively by the use of the sec-BuLi–(?)-sparteine complex in diethyl ether. Enantioselective deprotonation of one of the two benzylic positions leads to atropisomeric products with ca. 80:20 e.r.; an electrophilic quench typically provides functionalised atropisomeric diastereoisomers in up to 97:3 d.r.

Page, Abigail

2011-01-01

94

Enantioselective synthesis of 3,3-disubstituted oxindoles through Pd-catalyzed cyanoamidation.  

PubMed

The first enantioselective cyanoamidation of olefins provides quick access to a variety of 3,3-disubstituted oxindoles. The combination of Pd(dba)2, an optically active phosphoramidite, and N, N-dimethylpropylene urea (DMPU) in decalin were found to be the best conditions. PMID:18582078

Yasui, Yoshizumi; Kamisaki, Haruhi; Takemoto, Yoshiji

2008-06-27

95

Enantioselective radical reactions. Evaluation of nitrogen protecting groups in the synthesis of ?2-amino acids  

PubMed Central

We have investigated the effect of nitrogen protecting groups in radical addition trapping experiments leading to ?2-amino acids. Of the three N-protecting groups examined, the phthalimido group was optimal with respect to both yields and enantioselectivity. Additionally, radical additions to more complex acrylates were also investigated, which provided access to functionalized ?2-amino acids in modest selectivity.

Sibi, Mukund P.; Patil, Kalyani

2006-01-01

96

Catalytic and stoichiometric approaches to the desymmetrisation of centrosymmetric piperazines by enantioselective acylation: a total synthesis of dragmacidin A.  

PubMed

The enantioselective desymmetrisation of centrosymmetric piperazines was investigated using both catalytic and stoichiometric asymmetric acylation approaches. The catalytic approach involved the desymmetrisation of 2,5-trans-dimethylpiperazine under the control of chiral DMAP analogues. With one equivalent of piperazine, relative to the acylating agent, low yields of products were obtained in up to 70% ee. It was shown that an inevitable 'proof reading' effect was occurring which increased the enantiomeric excess of the desymmetrised product through its kinetic resolution. The desymmetrisation of centrosymmetric piperazines with chiral acylating agents [(1R,2R)-N-formyl-1,2-bis(pentafluoro-benzenesulfonamido)cyclohexane and (1R,2R)-N-acetyl-1,2-bis(trifluoromethanesulfonamido)-cyclohexane] was also studied. The yield and enantioselectivity of the process was highly dependent on the solvent used and the substitution of the piperazine. However, in some cases, good yields of enantiomerically enriched products could be obtained (up to 87% based on the limiting chiral reagent) in good enantiomeric excesses (up to 84% ee). The approach was exploited in the total synthesis of Dragmacidin A. PMID:17312969

Anstiss, Mark; Nelson, Adam

2006-11-21

97

S-(+)-carvone as starting material in the enantioselective synthesis of natural products  

Microsoft Academic Search

In this thesis the applicability of S-(+)-carvone as chiral starting material in the synthesis of biologically active compounds is examined. S-(+)-carvone is the major compound of caraway essential oil. The essential oil content of caraway seed may vary from 2-7% and it contains about 50-60% of S-(+)-carvoneS-(+)-carvone exhibits a number of interesting biological activities, eg., antifungal, insecticidal and plant growth

A. A. Verstegen-Haaksma

1994-01-01

98

Versatile construction of functionalized tropane ring systems based on lactam activation: enantioselective synthesis of (+)-pervilleine B.  

PubMed

The halo-assisted intramolecular addition of silyl enol ethers with in situ activated lactams yielded (hydroxylated) 1-halo-8-azabicyclo[3,2,1]octane and 1-halo-9-azabicyclo[3,3,1]nonane ring systems, which provided an easy enantioselective access to 6?-silyloxytropane-3-one, 3?,6?-dihydroxytropane, and pervilleine B. The absolute configuration of the natural (-)-pervilleine B was determined to be 1R,3R,5S,6R. PMID:23824038

Huang, Su-Yu; Chang, Zong; Tuo, Shi-Chuan; Gao, Long-Hui; Wang, Ai-E; Huang, Pei-Qiang

2013-08-14

99

Enantioselective electrodes: synthesis and use of polypyrroles prepared from chiral pyrrole derivatives  

Microsoft Academic Search

Polypyrroles substituted by chiral side chains have been electrochemically deposited on platinum from acetonitrile solutions in the presence of lithium perchlorate, tetraemyhammonium perchlorate, tetrabutylammonium perchlorate, tetraethylammonium tetrafluoroborate and tetramethylammonium hexafluorophosphate. The electrodes exhibited a good redox reversibility, long-term stability and were stable over a wide potential range (?3.0 to + 1.2 V versus Ag\\/0.01 M AgNO3). The enantioselective recognition properties

Susanne Pleus; Marion Schwientek

1998-01-01

100

Verdazyls: synthesis, properties, application  

NASA Astrophysics Data System (ADS)

Synthesis, structure, properties and reactivity of stable heterocyclic radicals, verdazyls, are considered. Special attention is focused on metal verdazyl complexes. Major areas of application of such radicals are discussed. The bibliography includes 164 references.

Lipunova, G. N.; Fedorchenko, T. G.; Chupakhin, O. N.

2013-08-01

101

Asymmetric synthesis of cyclic hydroxy ketones derived from enol ethers via sharpless asymmetric dihydroxylation. A study in the correlation of the enol ether chain length and enantioselectivity.  

PubMed

The Sharpless asymmetric dihydroxylation reaction of enol ethers derived from their corresponding cyclic ketones, gave alpha-hydroxyketones with high enantioselectivity. The enantiomeric excess was found to be proportional to the length of the unbranched enol ether chain with a maximum ee for the pentyl enol ether. An efficient synthesis of alpha-hydroxy chromanone in >90% ee was demonstrated using this method. PMID:14535787

Marcune, Benjamin F; Karady, Sandor; Reider, Paul J; Miller, Ross A; Biba, Mirlinda; DiMichele, Lisa; Reamer, Robert A

2003-10-17

102

Enantioselective synthesis of phyllanthurinolactone, a leaf-closing substance of Phyllanthus urinaria L., and its analogs toward the development of molecular probes  

Microsoft Academic Search

We report enantioselective synthesis of phyllanthurinolactone (1), a leaf-closing substance of Phyllanthus urinaria L., and its analogs with sugars other than d-glucose. Structure–activity relationship study using them revealed that the structure of the sugar moiety did not affect their bioactivity at all. This result is very important for the development of molecular probes based on the structure of 1.

Yoshifumi Urakawa; Takanori Sugimoto; Hirotaka Sato; Minoru Ueda

2004-01-01

103

An easily removable stereo-dictating group for enantioselective synthesis of propargylic amines.  

PubMed

We report herein a CuBr-catalyzed three-component coupling of 2-methylbut-3-yn-2-ol, aldehydes and pyrrolidine or 1,2,3,4-tetrahydroisoquinoline leading to the corresponding chiral propargylamines in excellent enantiomeric excess (91 to >99% ee) and high yields (79-95% yield). The dimethylcarbinol unit in 2-methylbut-3-yn-2-ol, which may be easily removed at the later stage to regenerate a terminal alkyne unit for further elaboration, plays a very important role in ensuring high enantioselectivity. This protocol provides easy and very general access to different terminal and non-terminal tertiary propargylic amines. PMID:24051867

Fan, Wu; Ma, Shengming

2013-10-01

104

Enantioselective synthesis of 3,4-dihydropyran derivatives via organocatalytic Michael reaction of ?,?-unsaturated enones.  

PubMed

A simple chiral diamine catalyst (1a) was successfully applied in the asymmetric Michael reaction between cyclic dimedone and ?,?-unsaturated ketones. Both acyclic enones with aryl or alkyl ?-substituents and cyclic enones were tolerated well in the reaction. The desired adducts were obtained in high yields (up to 98%) with excellent enantioselectivities (up to 97% ee). The additives were found to increase the reactivity dramatically. The biologically active 2,4-disubstituted polyhydroquinoline scaffold was conveniently prepared through an ammoniation from the generated 3,4-dihydropyran product. PMID:22432769

Liu, Yangbin; Liu, Xiaohua; Wang, Min; He, Peng; Lin, Lili; Feng, Xiaoming

2012-03-29

105

Copper-dipyridylphosphine-catalyzed hydrosilylation: enantioselective synthesis of aryl- and heteroaryl cycloalkyl alcohols.  

PubMed

The non-precious metal copper-catalyzed enantioselective hydrosilylation of a vast array of aryl cycloalkyl ketones with different ring sizes was studied systematically for the first time (up to 99% enantiomeric excess). The results demonstrated that the steric size of cycloalkyl groups has a significant influence on the reaction outcomes. The first stereoselective formation of a selection of cyclohexyl heteroaryl alcohols of up to 97% enantiopurity was realized as well. Dramatic temperature effects on both the enantiopurity and the absolute configuration of the alcohol products were observed in the reduction of some cyclohexyl pyridyl ketones. PMID:23247695

Qi, Shan-Bin; Li, Min; Li, Shijun; Zhou, Ji-Ning; Wu, Jun-Wen; Yu, Feng; Zhang, Xi-Chang; Chan, Albert S C; Wu, Jing

2012-12-18

106

Synthesis and Use of Jacobsen's Catalyst: Enantioselective Epoxidation in the Introductory Organic Laboratory  

Microsoft Academic Search

Jacobsen's catalyst, N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, is a popular reagent for the enantioselective epoxidation of alkenes. This reagent is successfully prepared in three steps by beginning organic chemistry students. A mixture of 1,2-diaminocyclohexane isomers is purified and resolved by crystallization (and recrystallization) with L-tartaric acid; a diimine is formed between the resolved trans-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde to produce the Jacobsen ligand; and finally

John Hanson

2001-01-01

107

Asymmetric synthesis of chiral diols by the catalytic enantioselective dialkylation of tere-, iso-, and phthalaldehydes and by a catalytic enantioselective autoinductive reaction  

Microsoft Academic Search

Optically pure aromatic diols were synthesized by the highly enantioselective dialkylation of aromatic dialdehydes with dialkylzincs in the presence of a catalytic amount of chiral aminoalcohol 1 or chiral thiophosphoramide alcohol 2 with Ti(O-i-Pr)4. The chiral titanium(IV) alkoxide of 4b, a diisopropylated product of isophthalaldehyde, catalyzed the addition of diisopropylzinc to isophthalaldehyde to gave a chiral zinc alkoxide of 4b

Kenso Soai; Yukikazu Inoue; Tomohide Takahashi; Takanori Shibata

1996-01-01

108

Enantioselective Protonation  

PubMed Central

Enantioselective protonation is a common process in biosynthetic sequences. The decarboxylase and esterase enzymes that effect this valuable transformation are able to control both the steric environment around the proton acceptor (typically an enolate) and the proton donor (typically a thiol). Recently, several chemical methods to achieve enantioselective protonation have been developed by exploiting various means of enantiocontrol in different mechanisms. These laboratory transformations have proven useful for the preparation of a number of valuable organic compounds.

Mohr, Justin T.; Hong, Allen Y.; Stoltz, Brian M.

2010-01-01

109

Palladium(II)-Catalyzed Enantioselective Synthesis of 2-Vinyl Oxygen Heterocycles  

PubMed Central

2-Vinylchromanes (1), 2-vinyl-1,4-benzodioxanes (2), and 2,3-dihydro-2-vinyl-2H-1,4-benzoxazines (3) can be prepared in high yields (90–98%) and excellent enantiomeric purities (87–98% ee) by [COP-OAc]2-catalyzed cyclization of phenolic (E)-allylic trichloroacetimidate precursors. Deuterium-labeling and computational experiments are consistent with these cyclization reactions taking place by an anti-oxypalladation/syn-deoxypalladation mechanism. 2-Vinylchromanes can be prepared also in good yields and high enantiomeric purities from analogous (E)-allylic acetate precursors, which constitutes the first report that acetate is a competent leaving group in COP-catalyzed enantioselective SN2? substitution reactions.

Cannon, Jeffrey S.; Olson, Angela C.; Overman, Larry E.; Solomon, Nicole S.

2012-01-01

110

Enantioselective synthesis of diversely substituted quaternary 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones.  

PubMed

Benzodiazepines are privileged scaffolds in medicinal chemistry, but enantiopure examples containing quaternary stereogenic centers are extremely rare. We demonstrate that installation of the di(p-anisyl)methyl (DAM) group at N1 of 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones derived from enantiopure proteinogenic amino acids allows retentive replacement of the C3-proton via a deprotonation/trapping protocol. A wide variety of carbon and nitrogen electrophiles function well in this reaction, providing the corresponding quaternary benzodiazepines with excellent enantioselectivity. Deprotonation/trapping experiments on a pair of diastereomeric 1,4-benzodiazepine-2,5-diones provide evidence for a key role of conformational chirality in these enantioselective reactions. Acidic removal of the DAM group is fast and high-yielding and can be performed selectively in the presence of a N-Boc indole. Thus the synthesis of quaternary benzodiazepines with diverse N1 functionality can now be accomplished. PMID:17117873

Carlier, Paul R; Zhao, Hongwu; MacQuarrie-Hunter, Stephanie L; DeGuzman, Joseph C; Hsu, Danny C

2006-11-29

111

Catalytic, enantioselective, vinylogous aldol reactions.  

PubMed

In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed. PMID:15940727

Denmark, Scott E; Heemstra, John R; Beutner, Gregory L

2005-07-25

112

Enantioselective synthesis of 2,2-disubstituted terminal epoxides via catalytic asymmetric Corey-Chaykovsky epoxidation of ketones.  

PubMed

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li(3)-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%-91% ee) and yield ( > 99%-88%) from a broad range of methyl ketones with 1-5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%-67% ee). PMID:22314382

Sone, Toshihiko; Yamaguchi, Akitake; Matsunaga, Shigeki; Shibasaki, Masakatsu

2012-02-07

113

Simple Organic Molecules as Catalysts for Enantioselective Synthesis of Amines and Alcohols  

PubMed Central

The discovery of new catalysts that can generate complex organic compounds via enantioselective transformations is central to advances in the life sciences;i for this reason, many chemists try to discover catalysts that can be used to produce chiral molecules with a strong preference for one mirror image isomer.ii The ideal catalyst should be devoid of precious elementsiii and should bring reactions to completion in a few hours using operationally simple procedures. In this manuscript, we introduce a set of small organic molecules that can catalyze reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which can be used to synthesize more complex, biologically active molecules. A distinguishing feature of this new catalyst class is the presence of a 'key' proton embedded within their structure. The catalyst is derived from the abundant amino acid valine and was prepared in large quantities in four steps using inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mol % catalyst in less than six hours at room temperature to generate products in >85% yield and ?97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents render this advance vital to future progress in chemistry, biology and medicine.

Silverio, Daniel L.; Torker, Sebastian; Pilyugina, Tatiana; Vieira, Erika M.; Snapper, Marc L.; Haeffner, Fredrik; Hoveyda, Amir H.

2012-01-01

114

Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.  

PubMed

An efficient catalytic asymmetric synthesis of chiral ?-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid. PMID:21268603

Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

2011-01-26

115

Organocatalyzed Michael-Henry reactions: enantioselective synthesis of cyclopentanecarbaldehydes via the dienamine organocatalysis of a succinaldehyde surrogate.  

PubMed

Asymmetric formal [3+2] cycloadditions of 4-hydroxybut-2-enal, a succinaldehyde surrogate, and nitroalkenes with an organocatalyst provided cyclopentanecarbaldehydes containing four consecutive stereogenic centers with excellent enantioselectivities. PMID:22714728

Hong, Bor-Cherng; Chen, Po-Yuan; Kotame, Prakash; Lu, Pei-Ying; Lee, Gene-Hsiang; Liao, Ju-Hsiou

2012-06-20

116

Enantioselective synthesis of the C10-C20 fragment of fusicoccin A.  

PubMed

A synthesis of the fully protected C-ring fragment of the tricyclic diterpene fusicoccin A is reported. The desired cyclopentenyl halides 5a,b are obtained in a total of nine steps. Key transformations of the synthesis sequence are a nonconventional Cr-catalyzed allylic oxidation of a protected intermediate cylcopentenone, a diastereoselective addition of a propenyl Grignard/CeCl(3) reagent to the unmasked cyclopentenone, and an asymmetric hydroboration of the isopropenyl substituent. The protected and suitably functionalized C-ring fragment paves the way to explore further the total synthesis of fusicoccin A. PMID:21755994

Richter, Anja; Hedberg, Christian; Waldmann, Herbert

2011-07-28

117

Establishing the absolute configuration of the asbestinins: enantioselective total synthesis of 11-acetoxy-4-deoxyasbestinin D.  

PubMed

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C-14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this subclass of the C-2-C-11-cyclized cembranoid natural products. PMID:16332064

Crimmins, Michael T; Ellis, J Michael

2005-12-14

118

Establishing the Absolute Configuration of the Asbestinins: Enantioselective Total Synthesis of 11-Acetoxy-4-deoxyasbestinin D  

PubMed Central

A highly stereoselective synthesis of 11-acetoxy-4-deoxyasbestinin D (1) has been completed in 26 linear steps. The synthesis hinges on a selective glycolate aldol addition to establish the C-2 stereocenter, a ring-closing metathesis reaction to complete the oxonene, and an intramolecular Diels-Alder cycloaddition to establish the relative configuration at C-1, C-10, and C14. This initial total synthesis of an asbestinin also serves to confirm the absolute configuration of this sub-class of the C2-C11-cyclized cembranoid natural products.

Crimmins, Michael T.; Ellis, J. Michael

2008-01-01

119

An enantioselective synthesis of carbafuranose sugars based on a linchpin carbacyclisation approach  

Microsoft Academic Search

Enantiopure carbafuranose derivatives were synthesised via a linchpin carbacyclisation process starting from 1,4-bisepoxides. Both 2-deoxy and 2-deoxy-6-hydroxycarbafuranose derivatives were obtained, which were converted to suitably protected precursors for carbanucleoside synthesis.

Leo M. H. Leung; Mark E. Light; Vicky Gibson; Bruno Linclau

2009-01-01

120

Efficient and enantioselective total syntheses of heliannuols A and K  

Microsoft Academic Search

The second-generation enantioselective synthesis of heliannuol A and the first enantioselective total synthesis of heliannuol K (via two routes) have both been accomplished efficiently; (heliannuol A, nine steps and 25% yield; heliannuol K, seven steps and 47% yield). Highlights of our synthetic strategy include a substrate-controlled chirality transfer in the Lewis acid mediated Claisen rearrangement of the allyl aryl ether

Makoto Kanematsu; Kana Soga; Yuki Manabe; Sachie Morimoto; Masahiro Yoshida; Kozo Shishido

2011-01-01

121

Enantioselective synthesis and enantiomeric amplification of amino acids under prebiotic conditions.  

PubMed

A plausible origin of biomolecular homochirality is advanced, where alpha-methyl amino acids found on meteorites transfer their chirality in the synthesis of normal amino acids. This asymmetry can be amplified to nearly homochiral levels, thus providing the necessary prerequisite for life to start on this planet and elsewhere in the universe. PMID:18491865

Levine, Mindy; Kenesky, Craig Scott; Mazori, Daniel; Breslow, Ronald

2008-05-21

122

A catalytic multicomponent coupling reaction for the enantioselective synthesis of spiroacetals.  

PubMed

The first multicomponent catalytic asymmetric synthesis of spiroacetals has been described. Hybrid molecules comprising a spiroacetal scaffold (a natural-product inspired scaffold) and an ?-amino acid motif (a privileged fragment) are easily available through a gold phosphate-catalysed one-pot three component coupling reaction of alkynols, anilines and glyoxylic acid. PMID:23435368

Cala, Lara; Mendoza, Abraham; Fañanás, Francisco J; Rodríguez, Félix

2013-04-01

123

Atroposelective Heck macrocyclization: enantioselective synthesis of bis(bibenzylic) natural products.  

PubMed

The Heck protocol was applied for the first time to the atroposelective synthesis of macrocyclic natural products. As ring closure to bis(bibenzyls) of the isoplagiochin type leads to a configurationally stable biaryl axis in the molecule, cyclization could be conducted atroposelectively in the presence of a chiral BINAP ligand. PMID:22917271

Groh, Matthias; Meidlinger, Daniel; Bringmann, Gerhard; Speicher, Andreas

2012-08-23

124

First enantioselective total synthesis and structure determination of the anthrapyran metabolite gamma-indomycinone.  

PubMed

The first total synthesis of (R)-gamma-indomycinone has been achieved which allowed the determination of the configuration of the stereogenic center of natural gamma-indomycinone as (S). The approach stands out for its generality and efficiency. [reaction: see text] PMID:17134294

Tietze, Lutz F; Singidi, Ramakrishna Reddy; Gericke, Kersten M

2006-12-01

125

Enantioselective Synthesis of Ceralure B 1, Ethyl cis-5-Iodo- trans-2-methylcyclohexane-1-carboxylate  

Microsoft Academic Search

Ethyl (1R, 2R, 5R)-5-iodo-2-methylcyclohexane-1-carboxylate is a potent attractant for the Mediterranean fruit fly. This compound was stereoselectively synthesized on a multigram scale in nine steps in 15% yield. Key steps of the synthesis involved an asymmetric Diels–Alder reaction, iodolactonization, stereoselective reduction of the carbonyl, and inversion of configuration with iodide.

Andre S. Raw; Eric B. Jang

2000-01-01

126

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

PubMed

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

Olsson, Susanne; Lennartson, Anders; Håkansson, Mikael

2013-07-23

127

Highly enantioselective synthesis of 1,2,3-substituted cyclopropanes by using ?-Iodo- and ?-chloromethylzinc carbenoids.  

PubMed

Herein, we report the enantio- and diastereoselective formation of trans-iodo- and trans-chlorocyclopropanes from ?-iodo- and ?-chlorozinc carbenoids by using a dioxaborolane-derived chiral ligand. The synthetically useful iodocyclopropane building blocks were derivatized by an electrophilic trapping of the corresponding cyclopropyl lithium species or a Negishi coupling to give access to a variety of enantioenriched 1,2,3-substituted cyclopropanes. The synthetic utility of this method was demonstrated by the formal synthesis of an HIV-1 protease inhibitor. In addition, the related stereoselective bromocyclopropanation was also investigated. New insights about the relative electrophilicity of haloiodomethylzinc carbenoids are also presented. PMID:23012181

Beaulieu, Louis-Philippe B; Zimmer, Lucie E; Gagnon, Alexandre; Charette, André B

2012-09-25

128

Enantioselective synthesis of (+)-obolactone based on a symmetry-breaking Wacker monooxidation of a diene.  

PubMed

A concise synthesis of the dihydro-?-pyrone/dihydro-?-pyrone natural product (+)-obolactone (13) is disclosed. The dienediol acetonide 23 (?97% ee) was obtained from 1,5-dichloropentane-2,4-dione in four steps. A Wacker monooxidation of 23 furnished the monoketone 24 in 64% yield. The OH group of the ensuing dihydro-?-pyrone 31 was esterified under Mitsunobu conditions with cinnamic acid (? 80% inversion and 20% retention of configuration). A ring-closing metathesis formed the dihydro-?-pyrone moiety of the target in the terminating step. PMID:23451721

Walleser, Patrick; Brückner, Reinhard

2013-03-01

129

Chiral fluorinated ?-sulfonyl carbanions: enantioselective synthesis and electrophilic capture, racemization dynamics, and structure.  

PubMed

Enantiomerically pure triflones R(1) CH(R(2) )SO2 CF3 have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF3 Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF3 SSCF3 . The deprotonation of RCH(Me)SO2 CF3 (R=CH2 Ph, iHex) with nBuLi with the formation of salts [RC(Me)?SO2 CF3 ]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO2 CF3 group of (S)-MeOCH2 C(Me)(CH2 Ph)SO2 CF3 (95?%?ee) by an ethyl group through the reaction with AlEt3 gave alkane MeOCH2 C(Me)(CH2 Ph)Et of 96?%?ee. Racemization of salts [R(1) C(R(2) )SO2 CF3 ]Li follows first-order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a C? ?S bond rotation as the rate-determining step. Lithium ?-(S)-trifluoromethyl- and ?-(S)-nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding ?-(S)-tert-butylsulfonyl carbanion salts. Whereas [PhCH2 C(Me)SO2 tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half-life of racemization at -105?°C of 2.4?h, that of [PhCH2 C(Me)SO2 CF3 ]Li at -78?°C is 30?d. DNMR spectroscopy of amides (PhCH2 )2 NSO2 CF3 and (PhCH2 )N(Ph)SO2 CF3 gave N?S rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH2 C(Ph)SO2 R]M (M=Li, K, NBu4 ; R=CF3 , tBu) shows for both salts a confinement of the negative charge mainly to the C? atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH2 C(Ph)SO2 CF3 ]Li?L}2 (L=2?THF, tetramethylethylenediamine (TMEDA)) and [PhCH2 C(Ph)SO2 CF3 ]NBu4 have the typical chiral C? ?S conformation of ?-sulfonyl carbanions, planar C? atoms, and short C? ?S bonds. Ab initio calculations of [MeC(Ph)SO2 tBu](-) and [MeC(Ph)SO2 CF3 ](-) showed for the fluorinated carbanion stronger nC ??*?S?CF?3 and nO ??*?S?CF?3 interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R(1) C(R(2) )SO2 R](-) (R=tBu, CF3 ) the nC ??*S?R interaction is much stronger for R=CF3 . Ab initio calculations gave for [MeC(Ph)SO2 tBu]Li?2?Me2 O an O,Li,C? contact ion pair (CIP) and for [MeC(Ph)SO2 CF3 ]Li?2?Me2 O an O,Li,O CIP. According to cryoscopy, [PhCH2 C(Ph)SO2 CF3 ]Li, [iHexC(Me)SO2 CF3 ]Li, and [PhCH2 C(Ph)SO2 CF3 ]NBu4 predominantly form monomers in tetrahydrofuran (THF) at -108?°C. The NMR spectroscopic data of salts [R(1) (R(2) )SO2 R(3) ]Li (R(3) =tBu, CF3 ) indicate that the dominating monomeric CIPs are devoid of C? ?Li bonds. PMID:23401229

Hellmann, Gunther; Hack, Achim; Thiemermann, Eric; Luche, Olaf; Raabe, Gerhard; Gais, Hans-Joachim

2013-02-10

130

Total Synthesis of the Strychnos Alkaloid (+)-Minfiensine: Tandem Enantioselective Intramolecular Heck-Iminium Ion Cyclization  

PubMed Central

A 1,2,3,4-tetrahydro-9a,4a-(iminoethano)-9H-carbazole (4) is a central structural feature of the Strychnos alkaloid minfiensine (1) and akuammiline alkaloids such as vincorine (5) and echitamine (6). A cascade catalytic asymmetric Heck-iminium cyclization was developed that rapidly provides 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazoles in high enantiomeric purity. Two sequences were developed for advancing 3,4-dihydro-9a,4a-(iminoethano)-9H-carbazole 27 to (+)-minfiensine. In our first-generation approach, a reductive Heck cyclization was employed to form the fifth ring of (+)-minfiensine. In a second more concise total synthesis, an intramolecular palladium-catalyzed ketone enolate vinyl iodide coupling was employed to construct the final ring of (+)-minfiensine. This second-generation total synthesis of enantiopure (+)-minfiensine was accomplished in 6.5% overall yield and 15 steps from 1,2-cyclohexanedione and anisidine 13. A distinctive feature of this sequence is the use of palladium-catalyzed reactions to form all carbon–carbon bonds in the transformation of these simple precursors to (+)-minfiensine.

Dounay, Amy B.; Humphreys, Philip G.; Overman, Larry E.; Wrobleski, Aaron D.

2010-01-01

131

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

NASA Astrophysics Data System (ADS)

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

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

2000-04-01

132

A practical enantioselective fluorescent sensor for mandelic acid.  

PubMed

A novel optically active bisbinaphthyl fluorescent sensor, (S,S)- or (R,R)-1, is designed for the recognition of chiral alpha-hydroxycarboxylic acids. A convenient method has been developed to synthesize this compound. It is observed that (S)-mandelic acid enhances the fluorescence intensity of the (S,S)-sensor significantly more than (R)-mandelic acid does. The enantioselective fluorescent response is confirmed with the observation of a mirror image relationship for the interaction of (S,S)- and (R,R)-sensors with mandelic acid. The enantioselectivity in fluorescence response [(I(S) - I(0))/(I(R) - I(0)) = 2.49] is quite high, which makes the sensor useful for practical application. The fluorescence intensity change of the sensor is found to be linearly related to the enantiomeric composition of mandelic acid. This sensor is potentially useful for the combinatorial search of chiral catalysts for the asymmetric synthesis of alpha-hydroxycarboxylic acids. PMID:11878942

Lin, Jing; Hu, Qiao-Sheng; Xu, Ming-Hua; Pu, Lin

2002-03-13

133

Enantioselective synthesis of chiral sulfones by Ir-catalyzed asymmetric hydrogenation: a facile approach to the preparation of chiral allylic and homoallylic compounds.  

PubMed

A highly efficient and enantioselective Ir-catalyzed hydrogenation of unsaturated sulfones was developed. Chiral cyclic and acyclic sulfones were produced in excellent enantioselectivities (up to 98% ee). Coupled with the Ramberg-Bäcklund rearrangement, this reaction offers a novel route to chiral allylic and homoallylic compounds in excellent enantioselectivities (up to 97% ee) and high yields (up to 94%). PMID:22835144

Zhou, Taigang; Peters, Byron; Maldonado, Matías F; Govender, Thavendran; Andersson, Pher G

2012-08-07

134

Exploring Nitrilase Sequence Space for Enantioselective Catalysis  

Microsoft Academic Search

Nitrilases are important in the biosphere as participants in synthesis and degradation pathways for naturally occurring, as well as xenobiotically derived, nitriles. Because of their inherent enantioselectivity, nitrilases are also attractive as mild, selective catalysts for setting chiral centers in fine chemical synthesis. Unfortunately, <20 nitrilases have been reported in the scientific and patent literature, and because of stability or

Dan E. Robertson; Jennifer A. Chaplin; Grace DeSantis; Mircea Podar; Mark Madden; Ellen Chi; Toby Richardson; Aileen Milan; Mark Miller; David P. Weiner; Kelvin Wong; Jeff McQuaid; Bob Farwell; Lori A. Preston; Xuqiu Tan; Marjory A. Snead; Martin Keller; Eric Mathur; Patricia L. Kretz; Mark J. Burk; Jay M. Short

2004-01-01

135

Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: enantioselectivity and enzyme-substrate docking studies.  

PubMed

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form alcohol. The homology models and docking models with ECOB and NADPH elucidated their substrate specificities and enantioselectivities. A glucose dehydrogenase-coupling reaction was used as NADPH recycling system to perform continuously the reduction reaction. Recombinant E. coli cell co-expressing YDL124W and Bacillus subtilis glucose dehydrogenase produced (S)-ECHB exclusively. PMID:20601218

Jung, Jihye; Park, Hyun Joo; Uhm, Ki-Nam; Kim, Dooil; Kim, Hyung-Kwoun

2010-06-20

136

Enantioselective Synthesis of Alkyne-Substituted Quaternary Carbon Stereogenic Centers through NHC-Cu-Catalyzed Allylic Substitution Reactions with (i-Bu)2(Alkynyl)aluminum Reagents  

PubMed Central

A catalytic enantioselective method for formation of alkyne-substituted all-carbon quaternary carbon stereogenic centers is reported. Additions of alkynylaluminums to alkyl-, aryl-, carboxylic ester-, or silyl-substituted allylic phosphates are promoted by 1.0–5.0 mol % of NHC–Cu complexes derived from air stable and commercially available CuCl2•2H2O. The requisite Al-based reagents are prepared through treatment of the corresponding aryl-, heteroaryl-, alkyl-, or alkenyl-substituted terminal alkynes with di-iso-butylaluminum hydride in the presence of 5.0 mol % Et3N at ambient temperature. The desired 1,4-enynes are obtained in up to >98% yield and >99:1 enantiomeric ratio. Selected Au-catalyzed cyclizations involving the alkyne unit of the enantiomerically enriched products are presented as a demonstration of the method’s utility in chemical synthesis.

Dabrowski, Jennifer A.; Gao, Fang; Hoveyda, Amir H.

2011-01-01

137

Using heteroaryl-lithium reagents as hydroxycarbonyl anion equivalents in conjugate addition reactions with (S,S)-(+)-pseudoephedrine as chiral auxiliary; enantioselective synthesis of 3-substituted pyrrolidines.  

PubMed

We have developed an efficient protocol for carrying out the stereocontrolled formal conjugate addition of hydroxycarbonyl anion equivalents to ?,?-unsaturated carboxylic acid derivatives using (S,S)-(+)-pseudoephedrine as chiral auxiliary, making use of the synthetic equivalence between the heteroaryl moieties and the carboxylate group. This protocol has been applied as key step in the enantioselective synthesis of 3-substituted pyrrolidines in which, after removing the chiral auxiliary, the heteroaryl moiety is converted into a carboxylate group followed by reduction and double nucleophilic displacement. Alternatively, the access to the same type of heterocyclic scaffold but with opposite absolute configuration has also been accomplished by making use of the regio- and diastereoselective conjugate addition of organolithium reagents to ?,?,?,?-unsaturated amides derived from the same chiral auxiliary followed by chiral auxiliary removal, ozonolysis, and reductive amination/intramolecular nucleophilic displacement sequence. PMID:23260037

Alonso, Beatriz; Ocejo, Marta; Carrillo, Luisa; Vicario, Jose L; Reyes, Efraim; Uria, Uxue

2013-01-04

138

Molecular Bases of Enantioselectivity of Haloalkane Dehalogenase DbjA  

NASA Astrophysics Data System (ADS)

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

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

139

Second-Generation DBFOX Ligands for the Synthesis of ?-Substituted ?-Amino Acids via Enantioselective Radical Conjugate Additions  

PubMed Central

A set of second-generation DBFOX ligands possessing extended aryl or benzyl-type groups was synthesized. The requisite amino alcohols were either commercially available (DBFOX/Bn) or constructed via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/t-BuPh, DBFOX/Pip) or phase-transfer-catalyzed asymmetric alkylation (DBFOX/MeNap). Complexes of the ligands with Mg(NTf2)2 were evaluated as promoters of enantioselective radical conjugate additions to ?,?-unsaturated ?-nitro amides and esters. Reactions employing the DBFOX/Nap ligand exhibited improved enantioselectivity relative to previously published additions mediated by DBFOX/Ph. However, the relatively modest increase in diastereomeric ratio suggests that our substrate–Lewis acid binding model, which was formulated based on results from DBFOX/Ph-promoted radical conjugate additions, is in need of revision.

Banerjee, Biplab; Capps, Steven G.; Kang, Junghoon; Robinson, Joshua W.; Castle, Steven L.

2009-01-01

140

Enantioselective synthesis of bicylco[3.2.1]octan-8-ones using a tandem Michael-Henry reaction.  

PubMed

Bicyclo[3.2.1]octan-8-ones have been prepared from a tandem Michael-Henry reaction between cyclohexane-1,2-diones and nitroalkenes using a quinine-derived thiourea as the catalyst. Although four stereogenic centers were created during the reaction, only two diastereomers were obtained in good diastereoselectivity and high enantioselectivity (92-99% ee). When 3-methylcyclohexane-1,2-dione (R(1) = Me) was used as the substrate, only the regioisomeric product of the corresponding thermodynamic enolate was obtained. PMID:20532185

Ding, Derong; Zhao, Cong-Gui; Guo, Qunsheng; Arman, Hadi

2010-06-19

141

Enantioselective synthesis of bicylco[3.2.1]octan-8-ones using a tandem Michael-Henry reaction  

PubMed Central

Bicyclo[3.2.1]octan-8-ones have been prepared from a tandem Michael-Henry reaction between cyclohexane-1,2-diones and nitroalkenes using a quinine-derived thiourea as the catalyst. Although four stereogenic centers were created during the reaction, only two diastereomers were obtained in good diastereoselectivity and high enantioselectivity (92-99% ee). When 3-methylcyclohexane-1,2-dione (R1 = Me) was used as the substrate, only the regioisomeric product of the corresponding thermodynamic enolate was obtained.

Ding, Derong; Zhao, Cong-Gui; Guo, Qunsheng; Arman, Hadi

2010-01-01

142

Expression of a lipase on the cell-surface of Escherichia coli using the OmpW anchoring motif and its application to enantioselective reactions.  

PubMed

Microbial-surface display is the expression of proteins or peptides on the surface of cells by fusing an appropriate protein as an anchoring motif. Here, the outer membrane protein W (OmpW) was selected as a fusion partner for functional expression of Pseudomonas fluorescence SIK W1 lipase (TliA) on the cell-surface of Escherichia coli. Localization of the truncated OmpW-TliA fusion protein on the cell-surface was confirmed by immunoblotting and functional assay of lipase activity. Enantioselective hydrolysis of rac-phenylethyl butanoate by the displayed lipase resulted in optically active (R)-phenyl ethanol with 96 % enantiomeric excess and 44 % of conversion in 5 days. Thus, a small outer membrane protein OmpW, is a useful anchoring motif for displaying an active enzyme of ~50 kDa on the cell-surface and the surface-displayed lipase can be employed as an enantioselective biocatalyst in organic synthesis. PMID:23881313

Lee, Hyuk; Park, Si Jae; Han, Mee-Jung; Eom, Gyeong Tae; Choi, Min-Jung; Kim, Seong Ho; Oh, Young Hoon; Song, Bong Keun; Lee, Seung Hwan

2013-07-24

143

Asymmetric diboration of terminal alkenes with a rhodium catalyst and subsequent oxidation: enantioselective synthesis of optically active 1,2-diols.  

PubMed

Pin it down: A highly enantioselective diboration of terminal alkenes with chiral 1 and bis(pinacolato)diboron (B2 pin2 ) was realized. Subsequent oxidation of the diboron adducts with sodium peroxoborate readily gave the corresponding optically active 1,2-diols in high yields and high enantioselectivities. PMID:24000239

Toribatake, Kenji; Nishiyama, Hisao

2013-09-02

144

Asymmetric catalytic [4 + 1] annulations catalyzed by quinidine: enantioselective synthesis of multi-functionalized isoxazoline N-oxides.  

PubMed

A highly regio-, chemo-, diastereo- and enantioselective organocatalytic [4 + 1] annulation of 2-halo-1,3-dicarbonyl compounds with Morita-Baylis-Hillman adducts catalyzed by commercially available, low cost quinidine for the preparation of synthetically unique and medicinally multi-functionalized isoxazoline N-oxides with three stereogenic centers including adjacent quaternary and tertiary stereocenters has been developed. Notably, the unexpected product ethyl 2-((tert-butyldimethylsilyl)oxy)-2-(5,5-diacetyl-3-((methylsulfonyl)oxy)-4-phenylisoxazolidin-3-yl)acetate (8) bearing a quaternary stereocenter and two tertiary stereocenters was obtained from the undocumented 5,5-diacetyl-3-(2-ethoxy-1-hydroxy-2-oxoethyl)-4-phenyl-4,5-dihydroisoxazole 2-oxide (4ba). PMID:23001215

Guo, Zhi-Wei; Xie, Jian-Wu; Chen, Ce; Zhu, Wei-Dong

2012-09-24

145

Development of Tartaric Acid Derived Chiral Guanidines and Their Application to Catalytic Enantioselective ?-Hydroxylation of ?-Dicarbonyl Compounds.  

PubMed

A novel library of chiral guanidines featuring a tartaric acid skeleton was developed from diethyl l-tartrate. These guanidines are easily accessed with tunable steric and electronic properties. The utilities of the guanidines were highlighted by their ability to catalyze the ?-hydroxylation of ?-ketoesters and ?-diketones with remarkable efficiency and excellent enantioselectivity. PMID:23758045

Zou, Liwei; Wang, Baomin; Mu, Hongfang; Zhang, Huanrui; Song, Yuming; Qu, Jingping

2013-06-11

146

Enantioselective, potentiometric membrane electrodes based on cyclodextrins: application for the determination of R-baclofen in its pharmaceutical formulation.  

PubMed

Two enantioselective, potentiometric membrane electrodes based on alpha- and gamma-cyclodextrins were proposed for the assay of R-baclofen. The slopes of the electrodes were 59.50 and 51.00 mV/pR-baclofen for alpha- and gamma-cyclodextrin-based electrodes, respectively. The detection limits of the proposed electrodes were 7 x 10(-9)mol l(-1) for alpha-cyclodextrin-based electrode and 1.44 x 10(-10)mol l(-1) for gamma-cyclodextrin-based electrode. The enantioselectivity was determined over S-baclofen. The proposed electrodes can be employed for the assay of R-baclofen raw materials and its pharmaceutical formulation, Norton-Baclofen tablets. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper. PMID:18970679

Stefan van Staden, Raluca-Ioana; Rat'ko, Alexander A

2006-01-19

147

Development of ruthenium catalysts for the enantioselective synthesis of P-stereogenic phosphines via nucleophilic phosphido intermediates.  

PubMed

This work details the development of ruthenium(II) catalysts for the enantioselective alkylation of chiral racemic secondary phosphines. The reactions proceed through the intermediacy of nucleophilic phosphido species, which have low barriers to pyramidal inversion; this allows for a dynamic kinetic asymmetric alkylation. The initially discovered [((R)-iPr-PHOX)(2)Ru(H)][BPh(4)] (6) catalyst was found to be effective in the reaction with benzylic chlorides; moreover, the alkylation displayed an unusual temperature dependence. However, the limited scope of alkylation of 6 motivated further studies which led to the development of two complementary chiral mixed ligand Ru(II) catalysts of type [L(1)L(2)Ru(H)](+). These catalysts were derived from a combination of one chiral and one achiral ligand, where a synergistic interaction of the two ligands creates an effective asymmetric environment around the ruthenium center. The (R)-MeO-BiPHEP/dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) catalyst (10) was found to be effective for the asymmetric alkylation of benzylic chlorides, while the (R)-DIFLUORPHOS/dmpe catalyst (11) was optimal for the nucleophilic substitution of less activated alkyl bromides; the scope of the respective catalysts was also explored. PMID:19338305

Chan, Vincent S; Chiu, Melanie; Bergman, Robert G; Toste, F Dean

2009-04-29

148

Enol Ethers as Substrates for Efficient Z- and Enantioselective Ring-Opening/Cross-Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes. Utility in Chemical Synthesis and Mechanistic Attributes  

PubMed Central

The first examples of catalytic enantioselective ring-opening/cross-metathesis (EROCM) reactions that involve enol ethers are reported. Specifically, we demonstrate that catalytic EROCM of several oxa- and azabicycles, cyclobutenes and a cyclopropene with an alkyl- or aryl-substituted enol ether proceed readily in the presence of a stereogenic-at-Mo monopyrrolide-monoaryloxide. In some instances, as little as 0.15 mol % of the catalytically active alkylidene is sufficient to promote complete conversion within 10 minutes. The desired products are formed in up to 90% yield and >99:1 enantiomeric ratio (er) with the disubstituted enol ether generated in >90% Z selectivity. The enol ether of the enantiomerically enriched products can be easily differentiated from the terminal alkene through a number of functionalization procedures that lead to the formation of useful intermediates for chemical synthesis (e.g., efficient acid hydrolysis to afford the enantiomerically enriched carboxaldehyde). In certain cases, enantioselectivity is strongly dependent on enol ether concentration: larger equivalents of the cross partner leads to the formation of products of high enantiomeric purity (versus near racemic products with one equivalent). The length of reaction time can be critical to product enantiomeric purity; high enantioselectivity in reactions that proceed to >98% conversion in as brief a reaction time as 30 seconds can be nearly entirely eroded within 30 minutes. Mechanistic rationale that accounts for the above characteristics of the catalytic process is provided.

Yu, Miao; Ibrahem, Ismail; Hasegawa, Masayuki; Schrock, Richard R.; Hoveyda, Amir H.

2012-01-01

149

Enantioselective Construction of All-Carbon Quaternary Centers by Branch-Selective Pd-Catalyzed Allyl-Allyl Cross Coupling  

PubMed Central

The Pd-catalyzed cross coupling of racemic tertiary allylic carbonates and allyl boronates is described. This reaction generates all-carbon quaternary centers in a highly regioselective and enantioselective fashion. The outcome of these reactions is consistent with a process that proceeds by way of 3,3’-reductive elimination of bis(?1-allyl)palladium intermediates. Strategies for distinguishing the product alkenes and application to the synthesis of cuparenone are also described.

Zhang, Ping; Le, Hai; Kyne, Robert E.; Morken, James P.

2011-01-01

150

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

PubMed Central

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

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

2012-01-01

151

Application of a C2-Symmetric Copper Carbenoid in the Enantioselective Hydrosilylation of Dialkyl and Aryl Alkyl Ketones  

PubMed Central

We report excellent reactivity and enantioselectivity of a C2-symmetric copper-bound N-heterocyclic carbene (NHC) in the hydrosilylation of a variety of structurally diverse ketones. This catalyst exhibits extraordinary enantioselctivity in the reduction of such challenging substrates as 2-butanone and 3-hexanone. Even at low catalyst loading (2.0 mol%) the reactions occur in under an hour at room temperature and often do not require purification beyond catalyst and solvent removal. The scope of this transformation was investigated in the reduction of ten aryl-alkyl and alkyl-alkyl ketones.

Albright, Abigail; Gawley, Robert E.

2011-01-01

152

An enantioselective approach to furanoeremophilanes: (+)-9-oxoeuryopsin.  

PubMed

An enantioselective total synthesis of the furanoeremophilane sesquiterpene (+)-9-oxoeuryopsin 1 is reported. The synthesis involves as a key step a copper(II) triflate catalyzed tandem asymmetric conjugate addition of AlMe3 to 2-methyl-2-cyclohexen-1-one with the Feringa (S,R,R)-phosphoramidite binaphthol ligand, followed by aldol condensation of the resulting aluminum enolate with 4-methyl-3-furaldehyde 4. This tandem transformation has not been previously reported with a 2-substituted-2-cyclohexen-1-one. Conventional functional group manipulations completed the synthesis. PMID:23647365

Silva, Ana L; Toscano, Rubén A; Maldonado, Luis A

2013-05-20

153

Enantioselective entry into benzoxabicyclo[2.2.1]heptyl systems via enzymatic desymmetrization: Toward chiral building blocks for lignan synthesis  

Microsoft Academic Search

The meso diacetate, 9, available in seven steps from piperonal, is efficiently desymmetrized with preferential cleavage of the R-arm-acetate under catalysis by porcine pancreatic lipase in 10% DMSO-phosphate buffer, pH 8. The resulting monoacetate 12, a potentially useful chiral building block for the synthesis of derivatives of the Podophyllum lignans, is obtained in good chemical yield (66–83%) and in high

David B. Berkowitz; Jun-Ho Maeng

1996-01-01

154

Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(I) catalyst†  

PubMed Central

A racemic Au(I)-catalyzed three-component reaction has been developed to prepare cyclic carbamimidates from imines, terminal alkynes, and sulfonylisocyanates. This reaction exploits the carbophilic ?-acidity of gold catalysts to first activate an alkyne toward deprotonation and secondly, to activate the internal alkyne generated toward intramolecular O-cyclization. Unlike similar previously reported multicomponent gold-catalyzed reactions, the stereocenter generated during the alkynylation is preserved in the product. This trait was exploited by developing an enantioselective variant, using an unusual trans-1-diphenylphosphino-2-arylsulfamidocyclohexane ligand. Moderate to excellent levels of enantioselectivity were obtained using a variety of N-arylbenzylidene anilines (41–95% ee, 18 examples).

Campbell, Matthew J.

2012-01-01

155

Enantioselective sensing by luminescence.  

PubMed

Enantiomeric analysis is one of the crucial points for the sensor technology, due to the increasing importance that enantiomerically pure compounds and drugs have in pharmaceutic and agrochemical applications. Enantiomeric luminescent sensors give different responses by interaction or reaction with chiral molecules, allowing one to assess their optical purity by spectroscopic measurements. Moreover, chemosensors have been developed to perform enantiomeric analysis of both luminescent and non-luminescent organic compounds. In the present chapter we focus on the recent advances in the sensing of chiral molecules by luminescent sensory systems, with the aim of outlining different mechanisms: fluorescence quenching by metal complexes, photoinduced electron transfer (PET) quenching, fluorescence enhancement by PET inhibition, analyte induced sensor conformational changes, modulation of excimer and exciplex formation, and aggregation induced emission enhancement (AIEE). Recent advances in the use of more elaborate techniques such as anisotropy measurements, gated detection, circularly polarized luminescence (CPL) and perspectives in the field are also discussed. Emphasis is given to the methods which have provided high enantioselectivity and which are amenable to fast screening procedures. PMID:21516438

Accetta, Alessandro; Corradini, Roberto; Marchelli, Rosangela

2011-01-01

156

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

157

Asymmetric syntheses and transformations--tools for chirality multiplication in drug synthesis.  

PubMed

A review of currently used methods for the synthesis and resolution of enantiomers of drugs and their precursors is presented. For the synthesis part the methods of diastereoselective as well as enantioselective synthesis are discussed, with particular consideration given to enantioselective catalysis with either metal complexes or biocatalysts. Desymmetrization processes are also included as methods to access enantiomerically pure compounds. Racemate resolution still remains an important method to obtain pure enantiomers and methods involving kinetic resolution in enzymatic or chemical systems, and particularly in connection with racemization (dynamic kinetic resolution) are on the rise in fine chemical industry, when applicable. PMID:17357583

Gawro?ski, Jacek

158

Enantioselective approach to quinolizidines: total synthesis of cermizine D and formal syntheses of senepodine G and cermizine C.  

PubMed

The formal syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselective, intramolecular amide Michael addition process. The total synthesis of cermizine D has been achieved through use of an organocatalyzed, heteroatom Michael addition to access a common intermediate. Additional key steps of this sequence include a matched, diastereoselective alkylation with an iodomethylphenyl sulfide and sulfone-aldehyde coupling/reductive desulfurization sequence to combine the major subunits. The utility of a Hartwig-style C-N coupling has been explored on functionally dense coupling partners. Diastereoselective conjugate additions to ?,?-unsaturated sulfones have been investigated, which provided the key sulfone intermediate in just six steps from commercially available starting materials. The formal syntheses of senepodine G and cermizine C have been accomplished through an intramolecular cyclization process of a N-Boc-protected piperidine sulfone. PMID:23627426

Veerasamy, Nagarathanam; Carlson, Erik C; Collett, Nathan D; Saha, Mrinmoy; Carter, Rich G

2013-04-29

159

Enantioselective construction of all-carbon quaternary centers by branch-selective Pd-catalyzed allyl-allyl cross-coupling.  

PubMed

The Pd-catalyzed cross-coupling of racemic tertiary allylic carbonates and allylboronates is described. This reaction generates all-carbon quaternary centers in a highly regioselective and enantioselective fashion. The outcome of these reactions is consistent with a process that proceeds by way of 3,3'-reductive elimination of bis(?(1)-allyl)palladium intermediates. Strategies for distinguishing the product alkenes and application to the synthesis of (+)-?-cuparenone are also described. PMID:21648464

Zhang, Ping; Le, Hai; Kyne, Robert E; Morken, James P

2011-06-07

160

Asymmetric synthesis of ?-adrenergic blockers through multistep one-pot transformations involving in situ chiral organocatalyst formation.  

PubMed

Two birds one stone: A new atom-economical one-pot approach to enantioselective chiral drug synthesis, involving in situ multistep organocatalyst formation and the application of the reaction for multistep sequential synthesis of ?-adrenergic blockers is disclosed (see scheme). PMID:22113987

Wei, Shengwei; Messerer, Regina; Tsogoeva, Svetlana B

2011-11-23

161

Asymmetric Palladium-Catalyzed Carboamination Reactions for the Synthesis of Enantiomerically Enriched 2-(Arylmethyl)- and 2-(Alkenylmethyl) pyrrolidines  

PubMed Central

The enantioselective synthesis of 2-(arylmethyl)- and 2-(alkenylmethyl)pyrrolidine derivatives via Pd-catalyzed alkene carboamination reactions is described. These transformations generate enantiomerically enriched products with up to 94% ee from readily available alkenyl or aryl bromides and N-boc-pent-4-enylamines. The application of this method to a concise asymmetric synthesis of (?)-tylophorine is also discussed.

Mai, Duy N.; Wolfe, John P.

2010-01-01

162

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

Microsoft Academic Search

The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles

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

2011-01-01

163

Enantioselective synthesis of derivatives and structure-activity relationship study in the development of NA255 as a novel host-targeting anti-HCV agent.  

PubMed

Hepatitis C virus (HCV) infection represents a serious health-care problem. Previously we reported the identification of NA255 from our natural products library using a HCV sub-genomic replicon cell culture system. Herein, we report how the absolute stereochemistry of NA255 was determined and an enantioselective synthetic method for NA255 derivatives was developed. The structure-activity relationship of the NA255 derivatives and rat pharmacokinetic profiles of the representative compounds are disclosed. PMID:23164713

Kawasaki, Ken-ichi; Masubuchi, Miyako; Hayase, Tadakatsu; Komiyama, Susumu; Watanabe, Fumio; Fukuda, Hiroshi; Murata, Takeshi; Matsubara, Yasuaki; Koyama, Kouhei; Shindoh, Hidetoshi; Sakamoto, Hiroshi; Okamato, Kohichi; Ohta, Atsunori; Katsume, Asao; Aoki, Masahiro; Aoki, Yuko; Shimma, Nobuo; Sudoh, Masayuki; Tsukuda, Takuo

2012-10-30

164

Enantioselective synthesis of heteroaromatic epoxyketones under phase-transfer catalysis using d-glucose- and d-mannose-based crown ethers  

Microsoft Academic Search

Heteroaromatic epoxyketones have been synthesized in an asymmetric Darzens condensation of 2-chloroacetylfuran or 2- and 3-chloroacetylthiophene with aromatic aldehydes and in the enantioselective epoxidation of ?,?-enones with an N-methylpyrrole unit, in both cases in the presence of d-glucose- 1 or d-mannose-based 2 crown ethers as phase transfer catalysts. The use of d-glucose-based 1 lariat ether as the catalyst gave the

Zsolt Rapi; Tamás Szabó; György Keglevich; Áron Szöll?sy; László Drahos; Péter Bakó

2011-01-01

165

Asymmetric synthesis of tetrabenazine and dihydrotetrabenazine.  

PubMed

The enantioselective synthesis of (+)-tetrabenazine (TBZ) and (+)-dihydrotetrabenazine (DTBZ), agents of significant interest for therapeutic and molecular imaging applications, has been completed in 21% (TBZ) and 16% (DTBZ) overall yield and in >97% ee from the starting dihydroisoquinoline. The synthesis utilizes Sodeoka's palladium-catalyzed asymmetric malonate addition to set the initial stereocenter followed by a number of diastereoselective transformations to incorporate the remaining asymmetric centers. PMID:19374381

Rishel, Michael J; Amarasinghe, Kande K D; Dinn, Sean R; Johnson, Bruce F

2009-05-15

166

A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

|A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in…

Bennett, George D.

2006-01-01

167

A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

Bennett, George D.

2006-01-01

168

Enzymatic enantioselective C-C-bond formation in microreactors  

Microsoft Academic Search

We have demonstrated that multiple crude enzyme lysates containing a hydroxynitrile lyase can be used for the enantioselective synthesis of cyanohydrins from aldehydes in microchannels. Using a microreactor setup, two important parameters were efficiently screened consuming only minute amounts of reagents. More impor- tantly, results from the continuous flow reaction were fully consistent with results obtained from larger batchwise processes

K. Koch; R. J. F. van den Berg; P. J. Nieuwland; R. Wijtmans; H. E. Schoemaker; J. C. M. van Hest; F. P. J. T. Rutjes

2008-01-01

169

Formation of highly substituted tetrahydropyranones: application to the total synthesis of cyanolide A.  

PubMed

A new tetrahydropyranone synthesis has been developed that leads to cis-2,6-disubstituted 3,3-dimethyltetrahydropyran-4-one rings by condensation of an aldehyde and a hydroxy silyl enol ether. The reaction works with a variety of aldehydes to produce the tetrahydropyranone products in moderate to high yields. This new method was applied to the enantioselective synthesis of cyanolide A and its aglycone. PMID:23962271

Tay, Gidget C; Gesinski, Michael R; Rychnovsky, Scott D

2013-08-20

170

Enantioselective Michael addition of 1,3-dicarbonyl compounds to a nitroalkene catalyzed by chiral squaramides - a key step in the synthesis of pregabalin.  

PubMed

Asymmetric organocatalytic 1,4-additions provide access to a large number of biologically relevant compounds. Chiral squaramides efficiently catalyse enantioselective Michael addition of 1,3-dicarbonyl compounds to aliphatic nitroalkenes. The resulting ?-nitro carboxylic derivatives were obtained in high yields and in high enantiomeric purities. Quantum chemical calculations helped us to devise a transition state model, which explains the observed stereochemical course of the addition. The best results were obtained with Meldrum's acid as a donor, with which enantiomeric purity of the Michael adduct was 97?:?3 e.r. Using this methodology pregabalin was synthesized in three steps in overall 52% yield. PMID:24108386

Baran, Rastislav; Veverková, Eva; Skvorcová, Andrea; Sebesta, Radovan

2013-10-10

171

A highly enantioselective catalyst for asymmetric hydroformylation of [2.2.1]-bicyclic olefins  

Microsoft Academic Search

Rh(CO)2(acac)\\/TangPhos was found to be a highly enantioselective catalyst for asymmetric hydroformylation of norbornylene under mild conditions. Application of the protocol to the desymmetrization of other [2.2.1]-bicyclic olefins gave moderate to excellent enantioselectivity (55–92% ee).

Jinkun Huang; Emilio Bunel; Alan Allgeier; Jason Tedrow; Thomas Storz; J. Preston; Tiffany Correll; Deana Manley; Troy Soukup; Randy Jensen; Rashid Syed; George Moniz; Robert Larsen; Michael Martinelli; Paul J. Reider

2005-01-01

172

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

173

Bimetallic enantioselective approach to axially chiral allenes.  

PubMed

An efficient bimetallic Zn(II)/Cu(I)-mediated asymmetric synthesis of simple axially chiral allenes from terminal alkynes and aldehydes was realized by taking advantage of the chiral amine (S)-?,?-diphenylprolinol 3. This one-pot procedure is compatible with broad scopes of both terminal alkynes and aldehydes, providing axially chiral allenes in practical yields with an excellent enantioselectivity. Control experiments revealed that CuBr is responsible for the efficient formation of propargylic amine while the combination of CuBr and ZnBr2 plays crucial roles in the amine-to-allene transformation. PMID:23607897

Lü, Ruizhi; Ye, Juntao; Cao, Tao; Chen, Bo; Fan, Wu; Lin, Weilong; Liu, Jinxian; Luo, Hongwen; Miao, Bukeyan; Ni, Shengjun; Tang, Xinjun; Wang, Nan; Wang, Yuli; Xie, Xi; Yu, Qiong; Yuan, Weiming; Zhang, Wanli; Zhu, Can; Ma, Shengming

2013-04-22

174

Enantioselective Hydroformylation of Aniline Derivatives  

PubMed Central

We have developed a ligand that reversibly binds to aniline substrates allowing for the control of regioselectivity and enantioselectivity in hydroformylation. In this paper we address how the electronics of the aniline ring affect both binding of the substrate to the ligand and the enantioselectivity in this reaction.

Joe, Candice L.; Tan, Kian L.

2011-01-01

175

Development of new methods in organic synthesis and their applications to the synthesis of biologically interesting natural products.  

PubMed

2,6-Dimethyl-9-Aryl-9-phosphabicyclo[3.3.1]nonanes (9-PBN and 9-NapBN) and the chiral diaminophosphine oxides (DIAPHOXs) derived from aspartic acid have been introduced as useful ligands and preligands, respectively, for transition metal-catalyzed asymmetric synthesis. anti-Selective asymmetric hydrogenation of ?-amino-?-ketoesters using Ru-, Rh-, Ir-, and Ni-catalysts through dynamic kinetic resolution have been developed for the first time, producing efficiently important anti ?-hydroxy-?-amino acids. The total synthesis of several biologically active natural products was achieved by use of the transition metal-catalyzed reaction using DIAPHOX, anti-selective asymmetric hydrogenation, and reactions developed by us. Synthesis of tangutorine, an antitumor indole alkaloid, has been enantioselectively achieved for the first time. Enantioselective synthesis of a martinelline chiral core was accomplished using the asymmetric tandem Michael-Aldol reaction as a key step developed by us. This synthesis represents the formal total synthesis of martinelline and martinellic acid. Papuamide B was synthesized through the elucidation of unknown stereostructures by using the anti-selective asymmetric hydrogenation and reactions developed by us. PMID:22223369

Hamada, Yasumasa

2012-01-01

176

Synthesis, characterization and applications of magnetite nanoparticles  

Microsoft Academic Search

In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic

Vikram Kumar Kanmukhla

2007-01-01

177

Enantioselective Gas Chromatographic Separation of Racemic N-alkylated Barbiturates: Application of C11-Chirasil-Dex as Chiral Stationary Phase in GC  

PubMed Central

Chirasil-?-Dex containing an undecamethylene spacer (C11-Chirasil-Dex) was synthesized and used as chiral stationary phase (CSP) in enantioselective gas chromatography (GC). The versatility of the new stationary phase in the simultaneous enantiomeric separation of a set of N-alkylated barbiturates is demonstrated.

Ghanem, Ashraf

2007-01-01

178

Peptide dendrimers: applications and synthesis  

Microsoft Academic Search

Peptide dendrimers are radial or wedge-like branched macromolecules consisting of a peptidyl branching core and\\/or covalently attached surface functional units. The multimeric nature of these constructs, the unambiguous composition and ease of production make this type of dendrimer well suited to various biotechnological and biochemical applications. Applications include use as biomedical diagnostic reagents, protein mimetics, anticancer and antiviral agents, vaccines

Kristen Sadler; James P. Tam

2002-01-01

179

Enantioselectivity in the phytotoxicity of herbicide imazethapyr.  

PubMed

Chiral compounds usually behave enantioselectively in phyto-biochemical processes. With the increasing application of chiral herbicides, their enantioselective phytotoxicity to plants merits further study, and little information is available in this area. The purpose of this study was to examine the enantioselective phytotoxicity of the herbicide imazethapyr (IM) on the roots of maize (Zea mays L.) seedlings. Enantiomers of IM were separated by HPLC, and their absolute configurations were confirmed as S-(+)-IM and R-(-)-IM by the octant rule. Plant growth measurements and morphological, microscopic, and ultrastructural observations were conducted after treatment with individual IM enantiomers and the racemate. Observations of root morphology showed that the root diameter significantly increased, whereas the root volume, surface area, and number of root tips decreased significantly. IM enantiomers selectively damaged root hair growth and significantly reduced the sloughing of border cells from the tips. IM also had adverse effects on cell organelles, such as statocytes, mitochondria, dictyosomes, and endoplasmic reticulum in maize roots. Moreover, cell membranes and cell walls were thicker than usual after IM treatment. All of the results showed the same trend that the R-(-)-IM affected the root growth of maize seedlings more severely than the S-(+)-IM. The inhibition abilities of (+/-)-IM was between S-(+)- and R-(-)-IM. The behavior of the active enantiomer, instead of just the racemate, may have more relevance to the herbicidal effects and ecological safety of IM. Therefore, enantiomeric differences should be considered when evaluating the bioavailability of the herbicide IM. PMID:19199589

Zhou, Qingyan; Xu, Chao; Zhang, Yongsong; Liu, Weiping

2009-02-25

180

MICROWAVE TECHNOLOGY CHEMICAL SYNTHESIS APPLICATIONS  

EPA Science Inventory

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

181

Ethylene glycol: properties, synthesis, and applications.  

PubMed

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

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

2012-04-10

182

BIOINSPIRED CATALYSTS: SYNTHESIS, CHARACTERISATION AND SOME APPLICATIONS  

Microsoft Academic Search

Our recent work concerning the synthesis, characterisation and some applications of bioinspired electron-transfer catalysts is reviewed in this contribution. The catalysts were various mono- or heterobimetallic complexes having either Cu(II) or Cu(II) and Zn(II) as central ions and amino acids, their derivatives or various N- containing organic molecules as ligands. Emphasis was based upon the solid support immobilised versions of

István Pálinkó

183

Merocyanine dyes: synthesis, structure, properties and applications  

NASA Astrophysics Data System (ADS)

Key approaches to the synthesis of merocyanine dyes are summarised. The dependence of the dye properties on their chemical structure, the solvent nature and the aggregation type is analysed. The main methods of studying the electronic structure of merocyanines are considered. Attention is focused on polyene-polymethine electron transitions. The applications of merocyanines in modern research, including the design of new materials and technologies (non-linear optics, photovoltaics, holography, etc.) are presented.

Kulinich, A. V.; Ishchenko, Aleksandr A.

2009-02-01

184

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

Microsoft Academic Search

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

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

2005-01-01

185

Substituted Ureas. Methods of Synthesis and Applications  

NASA Astrophysics Data System (ADS)

Systematic data on the method of synthesis of ureas by the interaction of compounds containing the amino-group with organic isocyanates, of amines and alkyl halides with alkali metal cyanates, and of primary and secondary amines with phosgene, carbon dioxide, urea, or nitrourea and by the carbonylation of amines are presented. The reactions involving the alkylation of urea and its interaction with various compounds containing functional groups are considered. The advantages and disadvantages of various methods are noted. The principal and practical applications of substituted ureas, including their applications as additives to organic materials, are discussed. The bibliography includes 314 references.

Vishnyakova, T. P.; Golubeva, I. A.; Glebova, E. V.

1985-03-01

186

Nanoceria as Antioxidant: Synthesis and Biomedical Applications  

PubMed Central

The therapeutic application of nanomaterials has been a focus of numerous studies in the past decade. Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by the reactive oxygen intermediates (ROI). The radical-scavenging role of ceria nanoparticles (nanoceria) have been established, as well as the autocatalytic ability of nanoceria to regenerate under various environmental conditions. The synthesis of nanoceria in biocompatible media has also been reported along with cell viability in order to determine the potential use of nanoceria in biomedical applications.

Karakoti, A.S.; Monteiro-Riviere, N.A.; Aggarwal, R.; Davis, J.P.; Narayan, R.J.; Self, W.T.; McGinnis, J.; Seal, S.

2009-01-01

187

C3-symmetric trisimidazoline-catalyzed enantioselective bromolactonization of internal alkenoic acids.  

PubMed

A method for conducting enantioselective bromolactonization reactions of trisubstituted alkenoic acids, using the C(3)-symmetric trisimidazoline 1 and 1,3-dibromo-5,5-dimethyl hydantoin as a bromine source, has been developed. The process generates chiral ?-lactones that contain a quaternary carbon. The results of studies probing geometrically different olefins show that (Z)-olefins rather than (E)-olefins are favorable substrates for the process. The method is not only applicable to acyclic olefin reactants but can also be employed to transform cyclic trisubstituted olefins into chiral spirocyclic lactones. Finally, the synthetic utility of the newly developed process is demonstrated by its application to a concise synthesis of tanikolide, an antifungal marine natural product. PMID:22623128

Murai, Kenichi; Nakamura, Akira; Matsushita, Tomoyo; Shimura, Masato; Fujioka, Hiromichi

2012-05-23

188

Germanium nanocrystals: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

The aim of this work was to demonstrate a simple synthesis route of Ge nanostructures (nanoparticles and nanowires), to characterize the physical and optical properties of Ge nanocrystal, and to demonstrate their biological and optoelectronics applications. The appropriate organometallic Ge 2+ precursors for the synthesis of Ge nanocrystals were identified. These precursors were used to develop a simple route that produced high quality Ge nanocrystals in high yield under mild conditions without using potentially contaminating catalysts and forming byproducts. The particle size was varied from 1 to 10 nm, depending on the reaction parameters. The relatively low-temperature, low-pressure nanocrystal synthesis condition allowed the use of organic solvents and surfactants. We also demonstrated morphological control over Ge nanocrystals via Ge2+ precursor reactivity modification. During synthesis, the surfactants passivate the nanocrystal surface and minimize surface oxidation. This synthesis method allowed optical characterization of Ge nanocrystals decoupled from contamination and oxidation. When excited with photons, Ge nanoparticles exhibit quantum confinement effect in both infrared and ultraviolet regions, as well as optical nonlinearity by the presence of two-photon absorption. These free-standing Ge nanocrystals could be further become integral elements in various optoelectronic devices. Herein, the production of water-soluble Ge nanoparticles was demonstrated as a proof of the effectiveness of our synthesis method. Addition of secondary layer surfactants such as cationic cetyltrimethylammonium bromide (CTAB) or functionalized polyethylene glycol (PEG), transforms the Ge nanoparticles to become water-soluble. The biocompatible, functionalized, water-soluble Ge nanoparticles were bound to extracellular receptors and also incorporated into the cells as a proof-of-concept demonstration for potential biomarker applications. In expectation of forming a 3-D superlattice of Ge nanocrystals within a SiO2 matrix, the real-time monitoring of ordered mesoporous SiO 2 structure formation via evaporation induced self assembly was also conducted to understand the structural ordering inside the silica matrix. The mesoporous film was then used for in situ and real-time study of profile evolution during plasma etching using attenuated total reflection Fourier transform infrared spectroscopy. We envision that the patterned 3-D superlattice of Ge nanocrystals will lead to advanced materials applications, such as coherent phonon generator and high-sensitivity biosensor.

Gerung, Henry

189

Monodentate non-C(2)-symmetric chiral N-heterocyclic carbene complexes for enantioselective synthesis. Cu-catalyzed conjugate additions of aryl- and alkenylsilylfluorides to cyclic enones.  

PubMed

A new class of enantioselective conjugate addition (ECA) reactions that involve aryl- or alkenylsilyl fluoride reagents and are catalyzed by chiral non-C(2)-symmetric Cu-based N-heterocyclic carbene (NHC) complexes are disclosed. Transformations have been designed based on the principle that a catalytically active chiral NHC-Cu-aryl or NHC-Cu-alkenyl complex can be accessed from reaction of a Cu-halide precursor with in situ-generated aryl- or alkenyltetrafluorosilicate. Reactions proceed in the presence of 1.5 equiv of the aryl- or alkenylsilane reagents and 1.5 equiv of tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF). Desired products are isolated in 63-97% yield and 73.5:26.5-98.5:1.5 enantiomeric ratio (47%-97% ee). A major focus of the present studies is the design, evaluation, and development of new chiral imidazolinium salts and their derived NHC-Cu complexes as catalysts that promote reactions of various carbosilanes to a range of electrophilic substrates. Toward this end, nearly 20 new chiral monodentate imidazolinium salts, most of which are non-C(2)-symmetric, have been prepared and fully characterized and their ability to serve as catalysts in the ECA reactions has been investigated. PMID:19445467

Lee, Kang-sang; Hoveyda, Amir H

2009-06-19

190

Synthesis, characterization and applications of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

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

Kanmukhla, Vikram Kumar

191

Microwave effect on catalytic enantioselective Claisen rearrangement.  

PubMed

Catalytic enantioselective Claisen rearrangement was drastically enhanced under microwave irradiation conditions without any loss of the enantioselectivity. Based on Arrhenius plots it was revealed that enantioselectivity decreased as the internal reaction temperature increased. Therefore, this reaction acceleration would NOT be caused by only a simple thermal effect. PMID:23928823

Nushiro, Kazuya; Kikuchi, Satoshi; Yamada, Tohru

2013-08-22

192

Synthesis, characterization and applications of different nanostructures  

NASA Astrophysics Data System (ADS)

There has been a growing interest in the field of nanoscience for the last several decades including the use in optical, electrical, biological and medicinal applications. This thesis focuses on the synthesis of different nanoparticles for their potential uses in drug delivery and antimicrobial agents as well as porous alumina membranes as surface enhanced Raman scattering or SERS substrates. The synthesis of nanocomposites (NCs) composed of silica and poly(4-vinyl pyridine) (P4VP) in a basic ethanol solution is presented in chapter 2. The composition of the NCs appears to be homogenous after synthesis and is greatly affected by heat and pH changes. When the NCs are heated, a core-shell nanostructure is produced with silica forming a shell around a P4VP core. At lower pHs, the NCs form a silica core with a P4VP shell while at higher pHs the silica is etched away causing the NC to decompose. A novel synthesis method of growing stable copper oxide nanoparticles with poly(acrylic acid) (PAA) is presented in chapter 3. Insoluble copper (I) oxide is dissolved with ammonium hydroxide and reduced using sodium borohydride to form metallic copper nanoparticles that oxidize overtime to form copper oxide nanoparticles stable in an aqueous environment. In addition to copper oxide nanoparticles, copper (I) iodide and copper (II) sulfide particles were also synthesized in the presence of PAA. In chapter 4, alumina membranes with 100nm and 200nm pores were coated with silver and used as SERS substrates to detect small molecules. The alumina membranes are coated with silver by reducing silver (I) oxide with ethanol. The thickness of the silver layer depends primarily on the length of time the substrate comes into contact with the Ag2O in solution with longer exposure times producing thicker films. Raman scattering of 10-100nM adenine concentrations were collected.

Snyder, Whitney Elaine

193

Synthesis of complex fluorides for optical applications  

NASA Astrophysics Data System (ADS)

Large single crystals of alkali metal fluorides are desirable for many reasons. Fluoride laser crystals have a wide transmission range and on account of their low phonon energies, many efficient laser emissions have been obtained from 285 nm to 4.34 microm.1,2 Inorganic fluoride single crystals feature large bandgaps, very wide optical transmittance ranges from vacuum-ultraviolet (VUV) to mid-IR wavelength regions, lower refractive indices than those of oxides, and typically lower phonon energies (which drastically reduce multiphonon relaxation rates of rare earth ions).3 The main goal of this work was to investigate the hydrothermal synthesis of alkali metal fluorides. Melt techniques have been used thoroughly to research a variety of fluoride systems and showed many phases that were inaccessible due to incongruent melting or phase stability. The existence of these phases was shown but never characterized or grown as a crystalline material. Solution growth in supercritical water was an ideal way to attempt the synthesis of novel compounds and phases. New synthetic routes to known phases and compounds also arose as a part of this work. Optically clear colorless crystals of K2BeF4 were synthesized up to 2 mm in size, and showed no phase transitions up to 1029 K, which suggests paraelectricitys at room temperature, contradicting previous reports.4 Attempts to incorporate a rare earth ion into the fluoroberyllate lattice proved unsuccessful however reactions between beryllium fluoride and lanthanide fluorides could be exploited as a synthetic route to single crystal rare earth fluorides. Hydrothermal reactions with KF produced crystals of three different phases: hexagonal KY2F7, trigonal KYF4 and orthorhombic K2YF5. All were optically clear, colorless crystals, with the K2YF5 crystals growing the largest. This compound is beneficial due to its application as a radiation dosimeter and laser host. 5,6 Optical quality colorless crystals of RbY2F7 and CsY2F7 up to 4 mm in size were produced, and many spectroscopically active rare earth elements were doped into both hosts. A novel synthetic pathway to the hexagonal beta-RbGd3F 10, was discovered which led to the novel compound, beta-RbHo 3F10. The hydrothermal synthesis of hexafluoroelpasolites and lanthanide sesquioxides is also investigated. The hydrothermal synthesis described in this work has furthered the study of complex fluorides for optical applications. Novel synthetic pathways were discovered to known optical materials. Novel materials were also discovered. 1Takashima, M. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 176. 2Fouassier, C. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 316. 3Capper, P. In Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials, John Wiley and Sons: Great Britain, 2005. 4Solans, X.; Gonzalez-Silgo, C.; Calvet, T.; Ruiz-Perez, C.; Martinez-Sarrion, M. L.; Mestres, L. Phys. Rev. B 1998, 57(9), 5122-5125. 5Azorin-Nieto, J.; Khaidukov, N.M.; Sanchez-Rodriguez, A.; Azorin-Vega, J.C. Nuclear Instruments and Methods in Physics Research, 2007, B263, 36-40. 6Wang, D.; Min, Y.; Xia, S.; Makhov, V.N.; Khaidukov, N.M.; J.C. Krupa, J.C. Journal of Alloys and Compounds, 2003, 361, 294-298.

Stepleton, Seth Eugene

194

Electroconductive hydrogels: synthesis, characterization and biomedical applications.  

PubMed

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

Guiseppi-Elie, Anthony

2010-01-08

195

Two approaches toward the formal total synthesis of oseltamivir phosphate (Tamiflu): catalytic enantioselective three-component reaction strategy and L-glutamic acid strategy.  

PubMed

Two independent formal total syntheses of oseltamivir phosphate were successfully achieved: the first utilized a copper-catalyzed asymmetric three-component reaction strategy, and the second utilized L-glutamic acid ?-ester as a chiral source to install the correct stereochemistry. Both strategies used Dieckmann condensation to construct a six-membered ring core, after which manipulation of the functional groups and protecting groups accessed Corey's intermediate for the synthesis of oseltamivir phosphate. While the first synthesis was accomplished via four purification steps in 25.7% overall yield, albeit with moderate optical purity (76% ee), the second strategy achieved the synthesis via six purification steps in 19.8% overall yield with perfect enantiocontrol. PMID:23517385

Alagiri, Kaliyamoorthy; Furutachi, Makoto; Yamatsugu, Kenzo; Kumagai, Naoya; Watanabe, Takumi; Shibasaki, Masakatsu

2013-03-21

196

Synthesis, characterization and application of electrode materials  

SciTech Connect

It has been known that significant advances in electrochemistry really depend on improvements in the sensitivity, selectivity, convenience, and/or economy of working electrodes, especially through the development of new working electrode materials. The advancement of solid state chemistry and materials science makes it possible to provide the materials which may be required as satisfactory electrode materials. The combination of solid state techniques with electrochemistry expands the applications of solid state materials and leads to the improvement of electrocatalysis. The study of Ru-Ti{sub 4}O{sub 7} and Pt-Ti{sub 4}O{sub 7} microelectrode arrays as introduced in paper 1 and paper 4, respectively, focuses on their synthesis and characterization. The synthesis is described by high temperature techniques for Ru or Pt microelectrode arrays within a conductive Ti{sub 4}O{sub 7} ceramic matrix. The characterization is based on the data obtained by x-ray diffractometry, scanning electron microscopy, voltammetry and amperometry. These microelectrode arrays show significant enhancement in current densities in comparison to solid Ru and Pt electrodes. Electrocatalysis at pyrochlore oxide Bi{sub 2}Ru{sub 2}O{sub 7.3} and Bi{sub 2}Ir{sub 2}O{sub 7} electrodes are described in paper 2 and paper 3, respectively. Details are reported for the synthesis and characterization of composite Bi{sub 2}Ru{sub 2}O{sub 7.3} electrodes. Voltammetric data are examined for evidence that oxidation can occur with transfer of oxygen to the oxidation products in the potential region corresponding to anodic discharge of H{sub 2}O with simultaneous evolution of O{sub 2}. Paper 3 includes electrocatalytic activities of composite Bi{sub 2}Ir{sub 2}O{sub 7} disk electrodes for the oxidation of I{sup -} and the reduction of IO{sub 3}{sup -}.

He, L.

1995-07-07

197

Highly enantioselective synthesis of chiral secondary amines by gold(I)/chiral Brønsted acid catalyzed tandem intermolecular hydroamination and transfer hydrogenation reactions.  

PubMed

A method for the synthesis of enantiomerically enriched secondary amines with excellent ee values through the tandem intermolecular hydroamination/transfer hydrogenation of alkynes using a "gold(I) complex-chiral Brønsted acid" protocol is developed. The catalysis works for a wide variety of aryl, alkenyl, and aliphatic alkynes as well as anilines with different electronic properties. PMID:19678678

Liu, Xin-Yuan; Che, Chi-Ming

2009-09-17

198

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

199

Tetracalcium phosphate: Synthesis, properties and biomedical applications.  

PubMed

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

Moseke, C; Gbureck, U

2010-05-21

200

Nanostructured metal foams: synthesis and applications  

SciTech Connect

Fabrication of monolithic metallic nanoporous materials is difficult using conventional methodology. Here they report a relatively simple method of synthesizing monolithic, ultralow density, nanostructured metal foams utilizing self-propagating combustion synthesis of novel metal complexes containing high nitrogen energetic ligands. Nanostructured metal foams are formed in a post flame-front dynamic assembly with densities as low as 0.011 g/cc and surface areas as high as 270 m{sup 2}/g. They have produced metal foams via this method of titanium, iron, cobalt, nickel, zirconium, copper, palladium, silver, hafnium, platinum and gold. Microstructural features vary as a function of composition and process parameters. Applications for the metal foams are discussed including hydrogen absorption in palladium foams. A model for the sorption kinetics of hydrogen in the foams is presented.

Luther, Erik P [Los Alamos National Laboratory; Tappan, Bryce [Los Alamos National Laboratory; Mueller, Alex [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Volz, Heather [Los Alamos National Laboratory; Cardenas, Andreas [Los Alamos National Laboratory; Papin, Pallas [Los Alamos National Laboratory; Veauthier, Jackie [Los Alamos National Laboratory; Stan, Marius [Los Alamos National Laboratory

2009-01-01

201

Cyclopalladated complexes in enantioselective catalysis  

NASA Astrophysics Data System (ADS)

The results of the use of optically active palladacycles in enantioselective catalysis of [3,3]-sigmatropic rearrangements, aldol condensation, the Michael reaction and cross-coupling are analyzed. Reactions with allylic substrates or reagents and some other transformations are considered.

Dunina, Valeria V.; Gorunova, Olga N.; Zykov, P. A.; Kochetkov, Konstantin A.

2011-01-01

202

Catalytic enantioselective synthesis of 18F-fluorinated alpha-amino acids under phase-transfer conditions using (S)-NOBIN.  

PubMed

We describe a new method for the asymmetric synthesis of [(18)F]fluorinated aromatic alpha-amino acids (FAA) under phase transfer conditions using achiral glycine derivative NiPBPGly and (S)-NOBIN as a novel substrate/catalyst pair. The key alkylation step proceeds under mild conditions. Substituted [(18)F]fluorobenzylbromides were prepared using nucleophilic [(18)F]fluoride and were used as alkylation agents. Two important FAA, 2-[(18)F]fluoro-L-tyrosine (2-FTYR) and 6-[(18)F]fluoro-L-3,4-dihydroxyphenylalanine (6-FDOPA), were synthesized with an ee of 92 and 96%, respectively. The total synthesis time was 110-120 min and radiochemical yields (d.c.) were 25+/-6% for 2-FTYR and 16+/-5% for 6-FDOPA. PMID:15219278

Krasikova, R N; Zaitsev, V V; Ametamey, S M; Kuznetsova, O F; Fedorova, O S; Mosevich, I K; Belokon, Y N; Vyskocil, S; Shatik, S V; Nader, M; Schubiger, P A

2004-07-01

203

Enantioselective Synthesis of the C1-C6 and C7-C23 Fragments of the Proposed Structure of Iriomoteolide 1a  

PubMed Central

Synthesis of the C1-C6 and C7-C23 fragments of the proposed structure of iriomoteolide 1a has been accomplished. Key steps include a cross metathesis to form the C15-C16 E olefin and a chelation controlled Grignard addition to form the tertiary alcohol at C14. Notably, 7 of the 9 stereocenters of the proposed structure have been set using various aldol reactions employing metallo enolates of thiazolidinethiones.

Crimmins, Michael T.; Dechert, Anne-Marie R.

2012-01-01

204

Asymmetric synthesis of ( S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: Enantioselectivity and enzyme–substrate docking studies  

Microsoft Academic Search

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form

Jihye Jung; Hyun Joo Park; Ki-Nam Uhm; Dooil Kim; Hyung-Kwoun Kim

2010-01-01

205

A Unified Strategy for Enantioselective Total Synthesis of Cladiellin and Briarellin Diterpenes: Total Synthesis of Briarellins E and F, and the Putative Structure of Alcyonin and Revision of Its Structure Assignment  

PubMed Central

Enantioselective total syntheses of briarellin E (12) and briarellin F (13), as well as the structure originally proposed for the cladiellin diterpene alcyonin (10), have been realized. Comparison of the spectral data for synthetic 10, natural alcyonin, cladiellisin (33), and cladiellaperoxide (34), as well as chemical transformations of 10 and natural alcyonin, suggest that the structure of this coral metabolite is allylic peroxide 11. The unified approach detailed herein can be used to access both C4-deoxygenated and C4-oxygenated cladiellins and briarellins. The central step in these syntheses is acid-promoted condensation of (Z)-?,?-unsaturated aldehydes 17 with cyclohexadienyl diols 18, to form intermediates 16 incorporating the hexahydroisobenzofuran core and five stereocenters of these marine diterpenes (Scheme 1).

Corminboeuf, Olivier; Overman, Larry E.; Pennington, Lewis D.

2009-01-01

206

Catalytic enantioselective carbon insertion into the ?-vinyl C-H bond of cyclic enones.  

PubMed

Chiral oxazaborolidinium ion-catalyzed Csp(2)-H functionalization of enones using diazoacetate has been developed. Various ?-substituted cyclic enones were synthesized in high yield (up to 99%) with high to excellent enantioselectivity (up to 99% ee). The synthetic utility of this reaction was demonstrated by the formal synthesis of (+)-epijuvabione. PMID:23634956

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

2013-05-06

207

Catalytic enantioselective allyl-allyl cross-coupling with a borylated allylboronate.  

PubMed

Catalytic enantioselective allyl-allyl cross-coupling of a borylated allylboronate reagent gives versatile borylated chiral 1,5-hexadienes. These compounds may be manipulated in a number of useful ways to give functionalized chiral building blocks for asymmetric synthesis. PMID:23510460

Le, Hai; Kyne, Robert E; Brozek, Laura A; Morken, James P

2013-03-19

208

Organocatalyzed enantioselective desymmetrization of diols in the preparation of chiral building blocks.  

PubMed

Desymmetrization of diols is a powerful tool to the synthesis of chiral building blocks. Among the different approaches to perform discrimination between both enantiotopic hydroxyl groups, the organocatalytic approach has gained importance in the last years. A diverse range of organocatalysts has been used to efficiently promote this enantioselective transformation and this Minireview examines the different contributions in this field. PMID:23033139

Díaz-de-Villegas, María D; Gálvez, José A; Badorrey, Ramón; López-Ram-de-Víu, M Pilar

2012-10-02

209

Block Copolymers: Synthesis and Applications in Nanotechnology  

NASA Astrophysics Data System (ADS)

This study is focused on the synthesis and study of (block) copolymers using reversible deactivation radical polymerizations (RDRPs), including atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. In particular, two primary areas of study are undertaken: (1) a proof-of-concept application of lithographic block copolymers, and (2) the mechanistic study of the deposition of titania into block copolymer templates for the production of well-ordered titania nanostructures. Block copolymers have the ability to undergo microphase separation, with an average size of each microphase ranging from tens to hundreds of nanometers. As such, block copolymers have been widely considered for nanotechnological applications over the past two decades. The development of materials for various nanotechnologies has become an increasingly studied area as improvements in many applications, such as those found in the semiconductor and photovoltaic industries are constantly being sought. Significant growth in developments of new synthetic methods ( i.e. RDRPs) has allowed the production of block copolymers with molecular (and sometimes atomic) definition. In turn, this has greatly expanded the use of block copolymers in nanotechnology. Herein, we describe the synthesis of statistical and block copolymers of 193 nm photolithography methacrylate and acrylate resist monomers with norbornyl and adamantyl moieties using RAFT polymerization.. For these resist (block) copolymers, the phase separation behaviors were examined by atomic force microscopy (AFM). End groups were removed from the polymers to avoid complications during the photolithography since RAFT end groups absorb visible light. Poly(glycidyl methacrylate-block-polystyrene) (PGMA-b-PS) was synthesize by ATRP and demonstrated that this block copolymer acts as both a lithographic UV (365 nm) photoresist and a self-assembly material. The PGMA segments can undergo cationic ring-opening crosslinking and can act as a negative-tone photoresist. The PGMA-b-PS thin films were also studied for phase separation with ˜25 nm patterns using transmission electron microscopy (TEM). Poly(styrene-block-4-vinyl pyridine) (PS-b-P4VP) block copolymer thin films are shown to form perpendicular cylinder phase separated structures, and these may be used to template the formation of ordered titania nanostructures with sub-50 nm diameters on either silicon or indium tin oxide (ITO) substrates. A study of the mechanism of TiO2 formation within the P4VP cylinder phase was developed and tested. It was found that the titania nanostructure morphology is affected by pH and deposition temperatures, and successful deposition required the cross-linking of the P4VP phase in order to obtain individual nanostructures.

Lou, Qin

210

Epoxide hydrolase-catalyzed enantioselective synthesis of chiral 1,2-diols via desymmetrization of meso-epoxides. lzhao@diversa.com.  

PubMed

The discovery, from nature, of a diverse set of microbial epoxide hydrolases is reported. The utility of a library of epoxide hydrolases in the synthesis of chiral 1,2-diols via desymmetrization of a wide range of meso-epoxides, including cyclic as well as acyclic alkyl- and aryl-substituted substrates, is demonstrated. The chiral (R,R)-diols were furnished with high ee's and yields. The discovery of the first microbial epoxide hydrolases providing access to complementary (S,S)-diols is also described. PMID:15355089

Zhao, Lishan; Han, Bin; Huang, Zilin; Miller, Mark; Huang, Hongjun; Malashock, Dan S; Zhu, Zuolin; Milan, Aileen; Robertson, Dan E; Weiner, David P; Burk, Mark J

2004-09-15

211

High density peptide microarrays. In situ synthesis and applications  

Microsoft Academic Search

The technologies enabling the creation of large scale, miniaturized peptide or protein microarrays are emerging. The focuses of this review are the synthesis and applications of peptide and peptidomimetic microarrays, especially the light directed parallel synthesis of individually addressable high density peptide microarrays using a novel photogenerated reagent chemistry and digital photolithography (Gao et al., 1998, J. Am. Chem. Soc.

Xiaolian Gao; Jean Philippe Pellois; Younghwa Na; Younkee Kim; Erdogan Gulari; Xiaochuan Zhou

2004-01-01

212

Enantioselective aza-Michael addition of imides by using an integrated strategy involving the synthesis of a family of multifunctional catalysts, usage of multiple catalysis, and rational design of experiment.  

PubMed

A challenging asymmetric reaction (aza-Michael addition of imides to enones) has been optimized through an integrated approach involving the synthesis of a family of organocatalysts, multiple catalysis (usage of additives), and finally with rational exploration of the chemical space by the application of the experiment design. PMID:23765568

Silvi, Mattia; Renzi, Polyssena; Rosato, Deborah; Margarita, Cristiana; Vecchioni, Alessio; Bordacchini, Ivan; Morra, Diego; Nicolosi, Alessandro; Cari, Riccardo; Sciubba, Fabio; Scarpino Schietroma, Daniele M; Bella, Marco

2013-06-13

213

Suzuki-Miyaura approach to JNJ-26076713, an orally active tetrahydroquinoline-containing alphaVbeta3/alphaVbeta5 integrin antagonist. enantioselective synthesis and stereochemical studies.  

PubMed

An improved scale-up synthesis was required for the alpha(V)beta(3)/alpha(V)beta(5) integrin antagonist 1, which had demonstrated oral efficacy in eye disease models of angiogenesis and vascular permeability. A stereodefined, quinoline-substituted, unsaturated ester was conveniently prepared by a Suzuki-Miyaura coupling to facilitate exploration of multiple methods of asymmetric reduction. The catalytic chiral hydrogenation of the corresponding unsaturated acid (Z-5b) with a ruthenium-based metal precursor and the (R)-XylPhanePhos ligand proved particularly efficient and economical. The resulting (3S)-quinoline-containing intermediate was reduced to an equal mixture of tetrahydroquinoline diastereomers. The undesired diastereomer could be recycled to the desired one by an oxidation/reduction protocol. The absolute stereochemistry of 1 was established as 3S,3'S by a combination of X-ray diffraction and chemical means. PMID:18278942

Kinney, William A; Teleha, Christopher A; Thompson, Andrew S; Newport, Maria; Hansen, Ryan; Ballentine, Scott; Ghosh, Shyamali; Mahan, Andrew; Grasa, Gabriela; Zanotti-Gerosa, Antonio; Dingenen, Jules; Schubert, Carsten; Zhou, Yong; Leo, Gregory C; McComsey, David F; Santulli, Rosemary J; Maryanoff, Bruce E

2008-02-16

214

(+)-Fluorenylethylchloroformate (FLEC)--improved synthesis for application in chiral analysis and peptidomimetic synthesis.  

PubMed

An efficient synthesis of the enantiomers of fluorenylethylchloroformate (FLEC) has been achieved that allows the routine application of the reagent for the resolution of chiral amines including unusual amino acids. The utility of the fluorenylethoxycarbonyl (Feoc) group as a chiral Fmoc equivalent, for combined resolution and protection of amino acids, in solid phase peptide synthesis is also shown. PMID:23483118

Camerino, Michelle A; Chalmers, David K; Thompson, Philip E

2013-04-28

215

Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams  

PubMed Central

The enantioselective synthesis of Nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines including the total synthesis of natural products and medicinal chemistry. In this manuscript, we describe the highly enantioselective palladium-catalyzed decarboxylative allylic alkylation of readily available lactams to form 3,3,-disubstituted pyrrolidinones, piperidinones, caprolactams, and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envision that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

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

2011-01-01

216

Synthesis and Applications of Titanium Oxide Nanotubes  

NASA Astrophysics Data System (ADS)

Titanium oxide nanotube (TiO2 nanotube, TNT) is synthesized by the low-temperature solution chemical method via the self-organization to form unique open-end nanotubular morphology with typically 8-10 and 5-7 nm in outer and inner diameters, respectively. Because of the mutual and synergy combination of its low-dimensional nanostructure and physical-chemical characteristics of TiO2 semiconductor, properties enhancements and novel functionalization are expected in the TiO2 nanotube. In this chapter, synthesis, nanostructures, formation mechanism, various physicochemical characteristics, and prospects of future application for the TiO2 nanotube are described in detail. In such an oxide material, property control and enhancement is possible by tuning appropriate chemical compositions, crystal structures, and composite structures. Therefore, special emphasis is also placed to introduce modification of the nanotubes by doping and/or nanocompositing to meet the requirements as for the environmental friendly and energy creation systems and various functional devices.

Sekino, Tohru

217

Enantioselective Cycloadditions of Azomethine Ylides  

Microsoft Academic Search

The asymmetric 1,3-DCR of azomethine ylides, which is generated from the corresponding imino ester\\u000a and alkenes, is one of the most fascinating transformations because the configuration of the four new stereogenic\\u000a centers of the finally obtained proline can be absolutely established in only one step with total atom economy.\\u000a Since 2002, the catalyzed enantioselective 1,3-DCRs have been performed using chiral

Carmen Nájera; José Sansano

218

Cyberinstruments via Physical Modeling Synthesis: Compositional Applications  

Microsoft Academic Search

This paper details compositional approaches in music for cyberinstruments by means of physical modeling synthesis. Although the focus is on compositions written with the models simulated by the digital waveguides, modal synthesis and mass-spring-damper algorithms, music written with other modeling techniques is also reviewed.

Juraj Kojs; Stefania Serafin; Chris Chafe

2007-01-01

219

Evaluation of Chiral ?-Cyanoesters as General Fluorescent Substrates for Screening Enantioselective Esterases  

PubMed Central

Esterases play a crucial role in industrial chemical synthesis, maintaining normal physiological metabolism and detoxifying exogenous ester-containing toxicants. To meet the rapidly increasing industrial need for all kinds of esterases, especially enantioselective esterases used to generate highly pure chiral compounds, general substrates are necessary for rapid screening, monitoring, purification, and characterization. In this study, general fluorescent substrates including phenolic derivatives and ?-cyanoesters were evaluated for sensitivity in detecting esterases in buffer systems. Results with two different esterases and different incubation times suggested that the ?-cyanoesters examined were significantly more sensitive at detecting esterases than the corresponding tested phenolic derivatives. More importantly, ?-cyanoesters, containing a secondary alcohol, possess at least one chiral center; thus, they are tools to screen for enantioselective hydrolysis. Results indicated that the enantioselectivity of esterases toward general ?-cyanoesters strongly depended on the esterase and the substrate, but the majority of esterases examined preferred S-isomers to their corresponding R-enantiomers. Most appealing was the very high enantioselectivity displayed in cytosolic esterases of the house fly. The potential utility of such esterases is discussed. In addition, the use of ?-cyanoesters as chiral fluorescent substrates was demonstrated for monitoring in enantioselective esterases.

HUANG, HUAZHANG; NISHI, KOSUKE; GEE, SHIRLEY J.; HAMMOCK, BRUCE D.

2006-01-01

220

Enantioselective Transesterification Catalysis by Nanosized Serine Protease Subtilisin Carlsberg Particles in Tetrahydrofuran  

PubMed Central

Enzyme catalysis in organic solvents is a powerful tool for stereo-selective synthesis but the enantioselectivity is still hard to predict. To overcome this obstacle, we employed a nanoparticulate formulation of subtilisin Carlsberg (SC) and designed a series of 14 structurally related racemic alcohols. They were employed in the model transesterification reaction with vinyl butyrate and the enantioselectivities were determined. In general, short alcohol side chains led to low enantioselectivties, while larger and bulky side chains caused better discrimination of the enantiomers by the enzyme. With several bulky substrates high enantioselectivities with E>100 were obtained. Computational modeling highlighted that key to high enantioselectivity is the discrimination of the R and S substrates by the sole hydrophobic binding pocket based on their size and bulkiness. While bulky S enantiomer side chains could be accommodated within the binding pocket, bulky R enantiomer side chains could not. However, when also the S enantiomer side chain becomes too large and does not fit into the binding pocket anymore, enantioselectivity accordingly drops.

Castillo, Betzaida; Delgado, Yamixa; Barletta, Gabriel; Griebenow, Kai

2010-01-01

221

Enantioselective Transesterification Catalysis by Nanosized Serine Protease Subtilisin Carlsberg Particles in Tetrahydrofuran.  

PubMed

Enzyme catalysis in organic solvents is a powerful tool for stereo-selective synthesis but the enantioselectivity is still hard to predict. To overcome this obstacle, we employed a nanoparticulate formulation of subtilisin Carlsberg (SC) and designed a series of 14 structurally related racemic alcohols. They were employed in the model transesterification reaction with vinyl butyrate and the enantioselectivities were determined. In general, short alcohol side chains led to low enantioselectivties, while larger and bulky side chains caused better discrimination of the enantiomers by the enzyme. With several bulky substrates high enantioselectivities with E>100 were obtained. Computational modeling highlighted that key to high enantioselectivity is the discrimination of the R and S substrates by the sole hydrophobic binding pocket based on their size and bulkiness. While bulky S enantiomer side chains could be accommodated within the binding pocket, bulky R enantiomer side chains could not. However, when also the S enantiomer side chain becomes too large and does not fit into the binding pocket anymore, enantioselectivity accordingly drops. PMID:20661313

Castillo, Betzaida; Delgado, Yamixa; Barletta, Gabriel; Griebenow, Kai

2010-03-20

222

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides  

PubMed Central

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

2013-01-01

223

New pathways for organic synthesis. Practical applications of transition metals  

Microsoft Academic Search

This book contains a considerable number of transition-metal-based procedures that have genuine applications in synthesis, and which are arranged according to the nature of the organic product or synthetic transformation being carried out. The objective is to provide those engaged in the preparation of pharmaceuticals, natural products, herbicides, dyestuffs, and other organic chemicals with a practical guide to the application

H. M. Colquhoun; J. Holton; D. J. Thompson; M. V. Twigg

1984-01-01

224

Cell-free protein synthesis: applications come of age.  

PubMed

Cell-free protein synthesis has emerged as a powerful technology platform to help satisfy the growing demand for simple and efficient protein production. While used for decades as a foundational research tool for understanding transcription and translation, recent advances have made possible cost-effective microscale to manufacturing scale synthesis of complex proteins. Protein yields exceed grams protein produced per liter reaction volume, batch reactions last for multiple hours, costs have been reduced orders of magnitude, and reaction scale has reached the 100-liter milestone. These advances have inspired new applications in the synthesis of protein libraries for functional genomics and structural biology, the production of personalized medicines, and the expression of virus-like particles, among others. In the coming years, cell-free protein synthesis promises new industrial processes where short protein production timelines are crucial as well as innovative approaches to a wide range of applications. PMID:22008973

Carlson, Erik D; Gan, Rui; Hodgman, C Eric; Jewett, Michael C

2011-10-08

225

Synthesis and Biological Applications of Heterocyclic and Organofluorine Compounds  

Microsoft Academic Search

Heterocyclic and organofluorine compounds play a crucial role in human life, since they have exceptional biological activities. The traditional methods for their synthesis usually do not comply contemporary safety and environmental regulations. The goal of this work was to design new, safer and environmentally benign methods for synthesis of heterocyclic and organofluorine compounds for biological applications.\\u000aInitially work was focused

Dmitry A. Borkin

2011-01-01

226

Enantioselective Sensing by Luminescence  

Microsoft Academic Search

\\u000a \\u000a Abstract  Enantiomeric analysis is one of the crucial points for the sensor technology, due to the increasing importance that enantiomerically\\u000a pure compounds and drugs have in pharmaceutic and agrochemical applications. Enantiomeric luminescent sensors give different\\u000a responses by interaction or reaction with chiral molecules, allowing one to assess their optical purity by spectroscopic measurements.\\u000a Moreover, chemosensors have been developed to perform enantiomeric

Alessandro Accetta; Roberto Corradini; Rosangela Marchelli

227

Synthesis and medical applications of oligosaccharides  

Microsoft Academic Search

Our understanding of the different glycoconjugates present on cells, proteins and entire organisms is lagging far behind advances in genomics and proteomics. Carbohydrate sequencing and the synthesis of defined oligosaccharides are two key technologies that have contributed to progress in glycomics research. Synthetic tools and high-throughput experiments such as carbohydrate arrays are beginning to affect biological research. These techniques are

Daniel B. Werz; Peter H. Seeberger

2007-01-01

228

Drug Development of the Antimalarial Agent Artemisinin: Total Synthesis, Analog Synthesis, and Structure-Activity Relationship Studies.  

National Technical Information Service (NTIS)

The enantioselective total synthesis of (+)-artemisinin has been optimized and carried out at multigram scale. An alternate approach to the total synthesis afforded racemic 6, 9-desmethylartemisinin 79 and a related analog 80. A synthetic intermediate fro...

M. A. Avery

1990-01-01

229

New pathways for organic synthesis. Practical applications of transition metals  

SciTech Connect

This book contains a considerable number of transition-metal-based procedures that have genuine applications in synthesis, and which are arranged according to the nature of the organic product or synthetic transformation being carried out. The objective is to provide those engaged in the preparation of pharmaceuticals, natural products, herbicides, dyestuffs, and other organic chemicals with a practical guide to the application of transition metals in organic synthesis. Topics considered include the formation of carbon-carbon bonds, the formation of carbocyclic compounds, the formation of heterocyclic compounds, the isomerization of alkenes, the direct introduction and removal of carbonyl groups, reduction, oxidation, and preparing and handling transition metal catalysts.

Colquhoun, H.M.; Holton, J.; Thompson, D.J.; Twigg, M.V.

1984-01-01

230

Design and synthesis of mixed oxides nanoparticles for biofuel applications  

SciTech Connect

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

Chen, Senniang

2010-05-15

231

Combinatorial evolution of site- and enantioselective catalysts for polyene epoxidation  

NASA Astrophysics Data System (ADS)

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

Lichtor, Phillip A.; Miller, Scott J.

2012-12-01

232

Application of heterogeneous catalysts prepared by mechanochemical synthesis.  

PubMed

Mechanochemical synthesis has the potential to provide more sustainable preparative routes to catalysts than the current multistep solvent-based routes. In this review, the mechanochemical synthesis of catalysts is discussed, with emphasis placed on catalysts for environmental, energy and chemical synthesis applications. This includes the formation of mixed-metal oxides as well as the process of dispersing metals onto solid supports. In most cases the process involves no solvent. Encouragingly, there are several examples where the process is advantageous compared with the more normal solvent-based methods. This can be because of process cost or simplicity, or, notably, where it provides more active/selective catalysts than those made by conventional wet chemical methods. The need for greater, and more systematic, exploration of this currently unconventional approach to catalyst synthesis is highlighted. PMID:23752744

Ralphs, Kathryn; Hardacre, Christopher; James, Stuart L

2013-06-11

233

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

PubMed

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

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

2013-05-13

234

Organocatalytic Enantioselective Synthesis of ?-Hydroxy Phosphonates  

PubMed Central

Tertiary ?-hydroxy phosphonates have been synthesized in good yields and high enantiomeric purity (up to 99% ee) through a novel L-proline-catalyzed cross aldol reaction of ?-keto phosphonates and ketones.

Samanta, Sampak; Zhao, Cong-Gui

2008-01-01

235

Enantioselective synthesis of helicenequinones and -bisquinones.  

PubMed

A convergent approach based on Diels-Alder reactions between polycyclic dienes and benzoquinones has emerged as a powerful tool for the construction of helicenequinones and bisquinones. Chemical resolution and asymmetric Diels-Alder reactions with sulfinyl quinones provide direct access to enantiopure derivatives. Biaryl or ferrocenyl dienes can be resolved leading to helicenequinones having additional axial or planar chirality. PMID:23242103

Urbano, Antonio; Carreño, M Carmen

2012-12-17

236

Synthesis of the Advance in and Application of Fractal Characteristics of Traffic Flow, Summary Report.  

National Technical Information Service (NTIS)

The project provides a synthesis of existing applications of fractal theory in various fields, as well as its potential applications in traffic management. The specific information gathered and summarized in the report includes: (1) a synthesis of fractal...

A. Gan

2013-01-01

237

Synthesis of the Advance in and Application of Fractal Characteristics of Traffic Flow.  

National Technical Information Service (NTIS)

The project provides a synthesis of existing applications of fractal theory in various fields, as well as its potential applications in traffic management. The specific information gathered and summarized in the report includes: (1) a synthesis of fractal...

A. Gan H. Li K. Haleem P. Alluri T. Li

2013-01-01

238

Enantioselective conjugate addition of ketones to nitroalkenes catalyzed by pyrrolidine-sulfamides.  

PubMed

A series of chiral pyrrolidine-sulfamides were prepared and examined as the catalysts for conjugate addition of ketones to nitroalkenes. Benzoic acid was identified as the most efficient additives for the transformation. Excellent enantioselectivities, diastereoselectivities, and yields were achieved for the reaction of cyclohexanone with ?-aryl nitroethylenes under solvent free conditions. ?-Isopropyl nitroethylene is also applicable and the product could be obtained with excellent enantioselectivity after extended reaction time. A comparison of the catalytic behaviors of pyrrolidine-sulfamide organocatalysts with different side chains demonstrates that the enantioselectivity is mainly controlled by the chiral pyrrolidine unit and the additional chiral center at the side chain exerts neglectable effects. The H-bonding interaction between the sulfamide and the nitro group is proposed to be crucial for the activation of the nitroalkene and the constitution of well-organized transition state. PMID:22278831

Wang, Jinjia; Lao, Jinhua; Du, Quansheng; Nie, Shaozhen; Hu, Zhipeng; Yan, Ming

2012-01-25

239

Synthesis and photovoltaic application of coper (I) sulfide nanocrystals  

SciTech Connect

We present the rational synthesis of colloidal copper(I) sulfide nanocrystals and demonstrate their application as an active light absorbing component in combination with CdS nanorods to make a solution-processed solar cell with 1.6percent power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period.

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

2008-06-24

240

Synthesis and Electronic Applications of Oxide-Metal Eutectic Composites.  

National Technical Information Service (NTIS)

A review is given of important developments in the synthesis of oxide-metal eutectic composites and the composite application in the continuing development of field emitters. Known metal oxide-metal binary and ternary eutectic systems are listed. The synt...

J. D. Holder J. K. Cochran D. N. Hill A. T. Chapman G. W. Clark

1980-01-01

241

Trace driven logic synthesis—application to power minimization  

Microsoft Academic Search

A trace driven methodology for logic synthesis and optimization is proposed. Given a logic description of a digital circuit C and an expected trace of input vectors T an implementation of C that optimizes a cost function under application of T is derived. This approach is effective in capturing and utilizing the correlations that exist between input signals on an

Luca P. Carloni; Patrick C. McGeer; Alexander Saldanha; Alberto L. Sangiovanni-Vincentelli

1997-01-01

242

Trace driven logic synthesis-application to power minimization  

Microsoft Academic Search

A trace driven methodology for logic synthesis and optimization is proposed. Given a logic description of a digital circuit C and an expected trace of input vectors T, an implementation of C that optimizes a cost function under application of T is derived. This approach is effective in capturing and utilizing the correlations that exist between input signals on an

Luca P. Carlonit; Patrick C. McGeer; Alexander Saldanhat; Alberto L. Sangiovanni-Vincentelli

1997-01-01

243

Synthesis, assembly, and applications of single-walled carbon nanotube  

Microsoft Academic Search

This dissertation presents the synthesis and assembly of aligned carbon nanotubes, and their applications in both nano-electronics such as transistor and integrated circuits and macro-electronics in energy conversion devices as transparent conducting electrodes. Also, the high performance chemical sensor using metal oxide nanowire has been demonstrated. Chapter 1 presents a brief introduction of carbon nanotube, followed by discussion of a

Koungmin Ryu

2009-01-01

244

Semiconductor nanowhiskers: Synthesis, properties, and applications  

SciTech Connect

Recent results of studying the semiconductor's whisker nanocrystals are reviewed. Physical grounds of growing whisker nanocrystals using the mechanism vapor-liquid-crystal are given and the main epitaxial technologies of synthesis of whisker nanocrystals are described. Thermodynamic and kinetic factors controlling the morphological properties, composition, and crystal structure of whisker nanocrystals are considered in detail. The main theoretical models of the growth and structure of whisker nanocrystals are described. The data on physical properties of whisker nanocrystals and possibilities of their use in nanophotonics, nanoelectronics, and nanobiotechnology are presented.

Dubrovskii, V. G., E-mail: dubrovskii@mail.ioffe.ru; Cirlin, G. E., E-mail: Cirlin@beam.ioffe.ru; Ustinov, V. M., E-mail: Vmust@beam.ioffe.ru [Russian Academy of Sciences, St. Petersburg Physics and Technology Center for Research and Education (Russian Federation)

2009-12-15

245

Lipase-catalyzed enantioselective ring opening of unactivated alicyclic-fused beta-lactams in an organic solvent.  

PubMed

[reaction: see text] A highly efficient and very simple method was developed for the synthesis of enantiopure beta-amino acids (e.g. cispentacin) and beta-lactams through the enzyme-catalyzed enantioselective ring opening of unactivated alicyclic beta-lactams in organic media. High enantioselectivity (E > 200) was observed when the Lipolase (lipase B from Candida antarctica)-catalyzed reactions were performed with H(2)O (1 equiv) in diisopropyl ether at 60 degrees C. The resolved products, obtained in good chemical yield (36-47%), could be easily separated. PMID:12688721

Forró, Eniko; Fülöp, Ferenc

2003-04-17

246

Lipase-catalyzed chemo- and enantioselective acetylation of 2-alkyl/aryl-3-hydroxypropiophenones.  

PubMed

The chemo- and enantioselective capabilities of porcine pancreatic lipase (PPL) in tetrahydrofuran, and Candida rugosa lipase (CRL) in diisopropyl ether have been investigated for the acetylation of racemic 2-alkyl/aryl-3-hydroxypropiophenones, which are important precursors in the synthesis of biologically active chromanones and isoflavanones. A highly chemoselective acetylation of primary hydroxy group in preference to phenolic hydroxy group leading to the formation of enantiomerically enriched monoacetates has been observed. PMID:11557352

Kumar, R; Azim, A; Kumar, V; Sharma, S K; Prasad, A K; Howarth, O W; Olsen, C E; Jain, S C; Parmar, V S

2001-10-01

247

Synthesis and applications of 2-aminopyrimidine derivatives as key intermediates in chemical synthesis of biomolecules  

NASA Astrophysics Data System (ADS)

Published data on the main approaches to the formation of the heterocyclic 2-aminopyrimidine system, which is one of important pharmacophores responsible for the biological properties of its derivatives, are described systematically. Main chemical transformations of functionalized 2-aminopyrimidines and their application in the synthesis of modern pharmaceuticals are considered.

Koroleva, Elena V.; Gusak, K. N.; Ignatovich, Zh V.

2010-10-01

248

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

PubMed Central

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

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

2012-01-01

249

Scope and mechanistic analysis of the enantioselective synthesis of allenes by rhodium-catalyzed tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor carbenoids and propargylic alcohols.  

PubMed

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

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

2012-09-11

250

Chiral Sulfinamide/Achiral Sulfonic Acid Co-Catalyzed Enantioselective Protonation of Enol Silanes  

PubMed Central

The application of chiral sulfinamides and achiral sulfonic acids as a co-catalyst system for enantioselective protonation reactions is described. Structurally simple, easily accessible sulfinamides were found to induce moderate-to-high ee's in the formation of 2-aryl-substituted cycloalkanones from the corresponding trimethylsilyl enol ethers.

Beck, Elizabeth M.; Hyde, Alan M.

2011-01-01

251

Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications.  

PubMed

Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals. PMID:22382898

Fu, Huiying; Tsang, Sai-Wing

2012-03-01

252

?-Tricalcium phosphate: synthesis, properties and biomedical applications.  

PubMed

Nowadays, ?-tricalcium phosphate (?-TCP, ?-Ca(3)(PO(4))(2)) is receiving growing attention as a raw material for several injectable hydraulic bone cements, biodegradable bioceramics and composites for bone repair. In the phase equilibrium diagram of the CaO-P(2)O(5) system, three polymorphs corresponding to the composition Ca(3)(PO(4))(2) are recognized: ?-TCP, ?-TCP and ?'-TCP. ?-TCP is formed by heating the low-temperature polymorph ?-TCP or by thermal crystallization of amorphous precursors with the proper composition above the transformation temperature. The ?-TCP phase may be retained at room temperature in a metastable state, and its range of stability is strongly influenced by ionic substitutions. It is as biocompatible as ?-TCP, but more soluble, and hydrolyses rapidly to calcium-deficient hydroxyapatite, which makes ?-TCP a useful component for preparing self-setting osteotransductive bone cements and biodegradable bioceramics and composites for bone repairing. The literature published on the synthesis and properties of ?-TCP is sometimes contradictory, and therefore this article focuses on reviewing and critically discussing the synthetic methods and physicochemical and biological properties of ?-TCP-based biomaterials (excluding ?-TCP-based bone cements). PMID:21712105

Carrodeguas, R G; De Aza, S

2011-10-01

253

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

Microsoft Academic Search

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

Werner Geurts; F. Catthoor; H. De Man

1991-01-01

254

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

Microsoft Academic Search

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

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

1991-01-01

255

Magnetic Nanotubes: Synthesis, Properties, and Applications  

Microsoft Academic Search

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

Yixing Ye; Baoyou Geng

2012-01-01

256

Carbon nanotubes: Synthesis, characterization, and applications  

Microsoft Academic Search

Carbon nanotubes (CNTs) possess exceptional material properties, making them desirable for use in a variety of applications. In this work, CNTs were grown using two distinct catalytic chemical vapor deposition (CVD) procedures, floating catalyst CVD and thermal CVD, which differed in the method of catalyst introduction. Reaction conditions were optimized to synthesize nanotubes with desired characteristics, and the effects of

Christian Peter Deck

2009-01-01

257

Conducting Polymer Nanostructures: Template Synthesis and Applications in Energy Storage  

PubMed Central

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

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

2010-01-01

258

Magnetic nanocomposites with mesoporous structures: synthesis and applications.  

PubMed

Magnetic nanocomposites with well-defined mesoporous structures, shapes, and tailored properties are of immense scientific and technological interest. This review article is devoted to the progress in the synthesis and applications of magnetic mesoporous materials. The first part briefly reviews various general methods developed for producing magnetic nanoparticles (NPs). The second presents and categorizes the synthesis of magnetic nanocomposites with mesoporous structures. These nanocomposites are broadly categorized into four types: monodisperse magnetic nanocrystals embedded in mesoporous nanospheres, microspheres encapsulating magnetic cores into perpendicularly aligned mesoporous shells, ordered mesoporous materials loaded with magnetic NPs inside the porous channels or cages, and rattle-type magnetic nanocomposites. The third section reviews the potential applications of the magnetic nanocomposites with mesoporous structures in the areas of heath care, catalysis, and environmental separation. The final section offers a summary and future perspectives on the state-of-the art in this area. PMID:21246712

Liu, Jian; Qiao, Shi Zhang; Hu, Qiu Hong; Lu, Gao Qing Max

2011-01-19

259

[Biochemical characterization and substrate profile of a highly enantioselective carbonyl reductase from Pichia pastoris].  

PubMed

Carbonyl reductases catalyze carbonyl compounds to chiral alcohols that are important building blocks in fine chemical industry. To study carbonyl reductase from Pichia pastoris GS115 (ppcr), we discovered a new gene (ppcr) encoding an NADPH-dependent carbonyl reductase by genomic data mining. It was amplified by PCR from the genomic DNA, and expressed in Escherichia coli BL21 (DE3). The recombinant protein was purified to homogeneity. The optimum temperature was 37 degrees C and the optimum pH of PPCR was 6.0. PPCR was stable below 45 degrees C. The Km and k(cat) value of the enzyme for ethyl 3-methyl-2-oxobutanoate were 9.48 mmol/L and 0.12 s, respectively. The enzyme had broad substrate specificity and high enantioselectivity. It catalyzed the reduction of aldehydes, a-ketoesters, beta-ketoesters and aryl ketones to give the corresponding alcohols with >97% ee with only a few exceptions, showing its application potential in the synthesis of chiral alcohols. PMID:23697162

Tian, Laiqiang; Liu, Weidong; Chen, Xi; Feng, Jinhui; Yang, Hongjiang; Wu, Qiaqing; Zhu, Dunming; Ma, Yanhe

2013-02-01

260

Synthesis, properties, and applications of iron nanoparticles.  

SciTech Connect

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earths crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Irons reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of irons potential, and work in this field appears to be blossoming.

Huber, Dale L.

2005-01-01

261

Synthesis, properties, and applications of iron nanoparticles.  

PubMed

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth's crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron's reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron's potential, and work in this field appears to be blossoming. PMID:17193474

Huber, Dale L

2005-05-01

262

Carbon Nanofibers: Catalytic Synthesis and Applications  

Microsoft Academic Search

Carbon nanofibers (diameter range, 3–100 nm; length range, 0.1–1000 µm) have been known for a long time as a nuisance that often emerges during catalytic conversion of carbon-containing gases. The recent outburst of interest in these graphitic materials originates from their potential for unique applications as well as their chemical similarity to fullerenes and carbon nanotubes. In this review, we

KRIJN P. DE JONG; JOHN W. GEUS

2000-01-01

263

System Synthesis of Synchronous Multimedia Applications  

Microsoft Academic Search

Modern system design is being increasingly driven by applications such as multimedia and wireless sensing and communications, which all have intrinsic quality of service (QoS) requirements, such as throughput, error-rate, and resolution. One of the most crucial QoS guarantees that the system has to provide is the timing constraints among the interacting media (synchronization) and within each media (latency). We

Gang Qu; Malena R. Mesarina; Miodrag Potkonjak

1999-01-01

264

Synthesis and applications of electrically conducting polymer nanocomposites  

Microsoft Academic Search

This research focuses on the synthesis and applications of electrically conducting polymer nanocomposites through molecular self-assembly. Two different classes of polymers, polyaniline (PANI) and polyacetylenes have been synthesized by biomimetic catalysis and spontaneous polymerization method. For gas barrier materials, commercially available polymers, poly(allylamine hydrochloride) (PAH) and poly (acrylic acid) (PAA), have also been used and thermally cross-linked. The morphological, optical

Bon-Cheol Ku

2005-01-01

265

Synthesis and applications of quantum dots and magnetic quantum dots  

Microsoft Academic Search

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and Zn1-xCdxSe alloyed QDs derived are tunable in fluorescence emissions between 360 nm and 700 nm. They show high quantum yields (QYs) of up to 50%, with narrow bandwidths of 19-55 nm. The synthesis of glutathione-capped

Jackie Y. Ying; Yuangang Zheng; S. Tamil Selvan

2008-01-01

266

Shape-controlled synthesis and catalytic application of ceria nanomaterials.  

PubMed

Because of their excellent properties and extensive applications, ceria nanomaterials have attracted much attention in recent years. This perspective provides a comprehensive review of current research activities that focus on the shape-controlled synthesis methods of ceria nanostructures. We elaborate on the synthesis strategies in the following four sections: (i) oriented growth directed by the crystallographic structure of cerium-based materials; (ii) oriented growth directed by the use of an appropriate capping reagent; (iii) growth confined or dictated by various templates; (iv) other potential methods for generating CeO(2) nanomaterials. In this perspective, we also discuss the catalytic applications of ceria nanostructures. They are often used as active components or supports in many catalytic reactions and their catalytic activities show morphology dependence. We review the morphology dependence of their catalytic performances in carbon monoxide oxidation, water-gas shift, nitric oxide reduction, and reforming reactions. At the end of this review, we give a personal perspective on the probable challenges and developments of the controllable synthesis of CeO(2) nanomaterials and their catalytic applications. PMID:23027607

Zhang, Dengsong; Du, Xianjun; Shi, Liyi; Gao, Ruihua

2012-12-28

267

Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications  

SciTech Connect

The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic and mechanical properties from those of the bulk material. Nanoparticles synthesis can be grouped into 3 broad approaches. The first one is wet phase synthesis (sol-gel processing), the second is mechanical attrition, and the third is gas-phase synthesis (aerosol). The properties of the final product may differ significantly depending on the fabrication route. Currently, there are no economical large-scale production processes for nanoparticles. This hinders the widespread applications of nanomaterials in products. The Idaho National Laboratory (INL) is engaging in research and development of advanced modular hybrid plasma reactors for low cost production of nanoparticles that is predicted to accelerate application research and enable the formation of technology innovation alliances that will result in the commercial production of nanocomposites for alternative energy production devices such as fuel cells, photovoltaics and electrochemical double layer capacitors.

Peter C. Kong; Alex W. Kawczak

2008-09-01

268

Enantioselective esterification of ibuprofen under microwave irradiation.  

PubMed

Enantioselective esterification of ibuprofen has been successfully carried out in an organic solvent catalyzed by recombinant APE 1547 (a thermophilic esterase from the archaeon Aeropyrum pernix K1). Here we used microwave irradiation (MW) as the mode of heating to improve the enzyme performance. Under the optimum conditions, the enzyme activity of APE 1547 was 4.16 ?mol/mg/h and the enantioselectivity (E value) was 52.9. Compared with conventional heating, the enzyme activity and the enantioselectivity were increased about 21.9-fold and 1.4-fold, respectively. The results also indicated that APE 1547 can maintain 95% of its activity even after being used five times, suggesting that the enzyme is stable under low power MW conditions. PMID:23669631

Yang, Zecheng; Niu, Xuedun; Fang, Xuedong; Chen, Ge; Zhang, Hong; Yue, Hong; Wang, Lei; Zhao, Dantong; Wang, Zhi

2013-05-13

269

Synthesis and applications of silver nanoparticles  

NASA Astrophysics Data System (ADS)

Due to their unique properties, silver nanoparticles are used in a wide range of applications, like electronics, optics, catalysis, biology, etc. The preferred route for their preparation has been, and still is, the reduction of silver salts in solutions. While dedicated reducing agents, solvents, and dispersants are typically used in this approach, in some cases, the same additive (ex: polyols) may play multiple roles. Such dual-function additives are particularly interesting alternatives as they offer the possibility of replacing the undesirable reductants often used in conventional precipitation methods. In the current research, an environmentally friendly route to prepare stable concentrated aqueous dispersions of silver nanoparticles is investigated experimentally. It was found that Arabic gum, a well known stabilizing agent, can also rapidly and completely reduce Ag 2O to metallic silver in alkaline solutions (pH >12.0) and elevated temperature (65 °C). The average size of the silver nanoparticles could be tailored from 13 to 30 nm by varying the experimental conditions. To prepare stable metal colloids by chemical precipitation methods requires in most cases a high concentration of polymeric dispersants. Consequently, the particles are embedded in the organic matrix, which can not be removed without affecting the properties of the particles and/or the dispersion stability. This can have a negative effect in many applications. In this work, an enzymatic hydrolysis method for isolating the silver particles from dispersions containing high concentrations of polymer was identified. In addition, a chemical hydrolysis method yielding dispersed silver nanoparticles with low content of residual polymer for printable electronics applications is investigated. The low sintering temperature of silver nanoparticles and high electrical conductivity make them very attractive for the fabrication of conductive patterns especially for flexible electronic applications. In the final section of this thesis, the silver nanoparticles are deposited using inkjet printing technology with a Dimatix printer DMP -2831. Silver nanoparticles of 13 nm, 80 nm, and mixtures of the two sizes were used to evaluate the effect of particle size and size distribution on the electrical properties of sintered films. The silver layers deposited with a 'drop-on-demand' inkjet printer were heated at temperatures ranging from 125°C to 200°C. The small particles formed less resistive films at 125°C, while the larger ones provided better electrical conductivity above 150°C. The inks containing mixed small and large particles yielded the most conductive silver films over the entire investigated temperature range. A mechanism explaining these results is proposed based on the evolution of film microstructure with temperature.

Balantrapu, Krishna Chaitanya

270

Doped Carbon Nanotubes: Synthesis, Characterization and Applications  

Microsoft Academic Search

\\u000a Various applications of carbon nanotubes require their chemical modification in\\u000a order to tune\\/control their physicochemical properties. One way for achieving this\\u000a control is by carrying out doping processes through which atoms and molecules\\u000a interact (covalently or noncovalently) with the nanotube surfaces. The aim of this\\u000a chapter is to emphasize the importance of different types of doping in carbon\\u000a nanotubes (single-,

Mauricio Terrones; Antonio G. Souza Filho; Apparao M. Rao

271

Gold Nanocages: From Synthesis to Theranostic Applications  

PubMed Central

CONSPECTUS Gold nanostructures have garnered considerable attention in recent years for their potential to enhance both the diagnosis and treatment of cancer through their advantageous chemical and physical properties. The key feature of Au nanostructures for enabling this diverse array of biomedical applications is their attractive optical properties, i.e. the scattering and absorption of light at resonant wavelengths due to the excitation of plasmon oscillations. This phenomenon is commonly known as localized surface plasmon resonance (LSPR) and is the source of the ruby red color of conventional Au colloids. The resonant wavelength is highly dependent on the size, shape, and geometry of the nanostructures, providing a set of knobs to maneuver the optical properties as needed. For in vivo applications, especially when optical excitation or transduction is involved, the LSPR peaks of the Au nanostructures have to be tuned to the transparent window of soft tissues in the near-infrared (NIR) region (from 700–900 nm) in order to maximize the penetration depth. One class of nanostructures with tunable LSPR peaks in the NIR region is Au nanocages. These versatile nanostructures are characterized by hollow interiors, ultrathin and porous walls, and can be prepared in relatively large quantities using a remarkably simple procedure based on the galvanic replacement between Ag nanocubes and aqueous chloroauric acid. The LSPR peaks of Au nanocages can be readily and precisely tuned to any wavelength in the NIR region by controlling their size and/or wall thickness. Other significant features of Au nanocages that make them particularly intriguing materials for biomedical applications include their compact sizes, large absorption cross sections (almost five orders of magnitude greater than those of conventional organic dyes), bio-inertness, as well as a robust and straightforward procedure for surface modification based on the Au-thiolate chemistry. In this article, we present some of the most recent advances in the use of Au nanocages for a broad range of theranostic applications, including their use: i) as tracers for tracking by multi-photon luminescence; ii) as contrast agents for photoacoustic (PA) and mutimodal (PA/fluorescence) imaging; iii) as photothermal agents for the selective destruction of cancerous or diseased tissue; and iv) as drug delivery vehicles for controlled and localized release in response to external stimuli such as NIR radiation or high-intensity focused ultrasound (HIFU).

XIA, YOUNAN; LI, WEIYANG; COBLEY, CLAIRE M.; CHEN, JINGYI; XIA, XIAOHU; ZHANG, QIANG; YANG, MIAOXIN; CHO, EUN CHUL; BROWN, PAIGE K.

2011-01-01

272

Gold nanocages: from synthesis to theranostic applications.  

PubMed

Gold nanostructures have garnered considerable attention in recent years for their potential to facilitate both the diagnosis and treatment of cancer through their advantageous chemical and physical properties. The key feature of Au nanostructures for enabling this diverse array of biomedical applications is their attractive optical properties, specifically the scattering and absorption of light at resonant wavelengths due to the excitation of plasmon oscillations. This phenomenon is commonly known as localized surface plasmon resonance (LSPR) and is the source of the ruby red color of conventional Au colloids. The resonant wavelength depends on the size, shape, and geometry of the nanostructures, providing a set of knobs to manipulate the optical properties as needed. For in vivo applications, especially when optical excitation or transduction is involved, the LSPR peaks of the Au nanostructures have to be tuned to the transparent window of soft tissues in the near-infrared (NIR) region (from 700 to 900 nm) to maximize the penetration depth. Gold nanocages represent one class of nanostructures with tunable LSPR peaks in the NIR region. These versatile nanostructures, characterized by hollow interiors and ultrathin, porous walls, can be prepared in relatively large quantities using a remarkably simple procedure based on the galvanic replacement between Ag nanocubes and aqueous chloroauric acid. The LSPR peaks of Au nanocages can be readily and precisely tuned to any wavelength in the NIR region by controlling their size, wall thickness, or both. Other significant features of Au nanocages that make them particularly intriguing materials for biomedical applications include their compact sizes, large absorption cross sections (almost five orders of magnitude greater than those of conventional organic dyes), and their bio-inertness, as well as a robust and straightforward procedure for surface modification based on Au-thiolate chemistry. In this Account, we present some of the most recent advances in the use of Au nanocages for a broad range of theranostic applications. First, we describe their use as tracers for tracking by multiphoton luminescence. Gold nanocages can also serve as contrast agents for photoacoustic (PA) and mutimodal (PA/fluorescence) imaging. In addition, these nanostructures can be used as photothermal agents for the selective destruction of cancerous or diseased tissue. Finally, Au nanocages can serve as drug delivery vehicles for controlled and localized release in response to external stimuli such as NIR radiation or high-intensity focused ultrasound (HIFU). PMID:21528889

Xia, Younan; Li, Weiyang; Cobley, Claire M; Chen, Jingyi; Xia, Xiaohu; Zhang, Qiang; Yang, Miaoxin; Cho, Eun Chul; Brown, Paige K

2011-04-29

273

Synthesis, characterisation and applications of coiled carbon nanotubes.  

PubMed

Coiled carbon nanotubes are helical carbon structures formed when heptagonal and pentagonal rings are inserted into the hexagonal backbone of a 'straight' nanotube. Coiled carbon nanotubes have been reported with both regular and irregular helical structures. In this work the structure, growth mechanism(s), synthesis, properties and potential applications of coiled carbon nanotubes are reviewed. Published data suggests that coiled carbon nanotube synthesis occurs due to nonuniform extrusion of carbon from a catalyst surface. To date, coiled carbon nanotubes have been synthesised using catalyst modification techniques including: (i) the addition of S or P containing compounds during synthesis; (ii) the use of binary or ternary metal catalysts; (iii) the use of microwaves to create a local temperature gradient around individual catalyst particles and; (iv) the use of pH control during catalyst preparation. In most instances coiled carbon nanotubes are produced as a by-product; high yield and/or large-scale synthesis of coiled carbon nanotubes remains problematic. The qualitative analysis of coiled carbon nanotubes is currently hindered by the absence of specific characterisation data in the literature, e.g., oxidation profiles measured by thermogravimetric analysis and Raman spectra of pure coiled carbon nanotube samples. PMID:20355423

Hanus, Monica J; Harris, Andrew T

2010-04-01

274

Conjugated microporous polymers: design, synthesis and application.  

PubMed

Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine ?-conjugated skeletons with permanent nanopores, in sharp contrast to other porous materials that are not ?-conjugated and with conventional conjugated polymers that are nonporous. As an emerging material platform, CMPs offer a high flexibility for the molecular design of conjugated skeletons and nanopores. Various chemical reactions, building blocks and synthetic methods have been developed and a broad variety of CMPs with different structures and specific properties have been synthesized, driving the rapid growth of the field. CMPs are unique in that they allow the complementary utilization of ?-conjugated skeletons and nanopores for functional exploration; they have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas adsorption, heterogeneous catalysis, light emitting, light harvesting and electrical energy storage. This review describes the molecular design principles of CMPs, advancements in synthetic and structural studies and the frontiers of functional exploration and potential applications. PMID:23846024

Xu, Yanhong; Jin, Shangbin; Xu, Hong; Nagai, Atsushi; Jiang, Donglin

2013-09-23

275

Enantioselective degradation of the chiral fungicides metalaxyl and furalaxyl by Brevibacillus brevis.  

PubMed

For almost four decades, the chiral fungicides metalaxyl and furalaxyl have been in use in plant protection on a global scale. Both substances are distributed as racemic mixtures, yet the desirable interference in nucleic acid synthesis of harmful fungi only occurs by the (-)-R-enantiomer. As enantioselective degradation in Scheyern (Germany) and Yaoundé (Cameroon) soils has been documented, the influence of 50 isolated microorganisms on the R/S ratio was investigated. A high-pressure liquid chromatography method with a chiral column to separate enantiomers of metalaxyl and furalaxyl, and subsequent detection by tandem mass spectrometry, was employed. Only one of these microorganisms, a strain of Brevibacillus brevis, showed an enantioselective degradation pattern in liquid culture; the respective (-)-R-enantiomers were preferably degraded. Moreover, (-)-R-furalaxyl was degraded faster in cultures supplemented simultaneously with both fungicides of the same concentration. PMID:23716265

Sulimma, Lutz; Bullach, Anke; Kusari, Souvik; Lamshöft, Marc; Zühlke, Sebastian; Spiteller, Michael

2013-06-01

276

A century of thioxanthones: through synthesis and biological applications.  

PubMed

The interest in the synthesis and applications of thioxanthones, dibenzo-gamma-thiopyrones, started in the beginning of the 20th century. Thioxanthones are traditionally synthesized via benzophenone, diarylthioether or diarylthioester intermediates. In recent years, more efficient and cleaner synthetic methodologies are being applied to obtain thioxanthone derivatives, especially for photochemical applications. Considering biological activities, the first thioxanthone introduced in therapy in 1945 was Miracil D, as an antischistosomal agent. Since then, the variety of studies of biological/ pharmacological activities of thioxanthones led to the discovery of new agents and to the disclosure of their mechanisms of action. Moreover, the ability to sensitize cancer cells suggested new and promising applications in chemotherapy. New antitumor derivatives are being developed by molecular modifications such as isosterism (aza-thioxanthones and aminoethylthioxanthones) or hybridation (psorospermine and acronycin analogues). The last generation of antitumor thioxanthones rendered a derivative, SR271425, with an excellent preclinical antitumor efficacy. The last decade has been excited in the research of thioxanthones with important achievements in both synthesis and biochemical applications, especially in order to dissociate the antitumor activity from the toxicity of drug candidates. Recently, thioxanthones emerged as dual inhibitors of P-glycoprotein and tumor cell growth. It is expected that in the following years new analogues with the thioxanthone scaffold emerge in the field of anticancer therapy, with enhanced antitumor activity and without serious side effects. PMID:23521678

Paiva, A M; Pinto, M M; Sousa, E

2013-01-01

277

Synthesis and catalytic applications of combined zeolitic/mesoporous materials  

PubMed Central

Summary In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials.

Vernimmen, Jarian; Cool, Pegie

2011-01-01

278

Bismuth-based oxide semiconductors: Mild synthesis and practical applications  

NASA Astrophysics Data System (ADS)

In this dissertation study, bismuth based oxide semiconductors were prepared using 'mild' synthesis techniques---electrodeposition and solution combustion synthesis. Potential environmental remediation and solar energy applications of the prepared oxides were evaluated. Bismuth vanadate (BiVO4) was prepared by electrodeposition and solution combustion synthesis. A two step electrosynthesis strategy was developed and demonstrated for the first time. In the first step, a Bi film was first electrodeposited on a Pt substrate from an acidic BiCl3 medium. Then, this film was anodically stripped in a medium containing hydrolyzed vanadium precursor, to generate Bi3+, and subsequent BiVO4 formation by in situ precipitation. The photoelectrochemical data were consistent with the in situ formation of n-type semiconductor films. In the solution combustion synthesis procedure, BiVO4 powders were prepared using bismuth nitrate pentahydrate as the bismuth precursor and either vanadium chloride or vanadium oxysulfate as the vanadium precursor. Urea, glycine, or citric acid was used as the fuel. The effect of the vanadium precursor on the photocatalytic activity of combustion synthesized BiVO 4 was evaluated in this study. Methyl orange was used as a probe to test the photocatalytic attributes of the combustion synthesized (CS) samples, and benchmarked against a commercial bismuth vanadate sample. The CS samples showed superior activity to the commercial benchmark sample, and samples derived from vanadium chloride were superior to vanadium oxysulfate counterparts. The photoelectrochemical properties of the various CS samples were also studied and these samples were shown to be useful both for environmental photocatalytic remediation and water photooxidation applications. Silver bismuth tungstate (AgBiW2O8) nanoparticles were prepared for the first time by solution combustion synthesis by using silver nitrate, bismuth nitrate, sodium tungstate as precursors for Ag, Bi, and W respectively and urea as the fuel. The photocatalytic activity of these nanoparticles was superior to a sample prepared by solid-state synthesis. The combustion-synthesized particles were subsequently modified with Pt catalyst islands using a photodeposition technique and then used for the photo-generation of syngas (CO + H2). Formic acid was used in these experiments for in situ generation of CO2 and its subsequent reduction to CO. In the absence of Pt modification, H2 was not obtained. These results were compared with those obtained with acetic acid in place of formic acid, and finally the mechanistic pathways for syngas and methane photogeneration are presented.

Timmaji, Hari Krishna

279

Synergistic effects on enantioselectivity of zwitterionic chiral stationary phases for separations of chiral acids, bases, and amino acids by HPLC.  

PubMed

In an attempt to overcome the limited applicability scope of earlier proposed Cinchona alkaloid-based chiral weak anion exchangers (WAX) and recently reported aminosulfonic acid-based chiral strong cation exchangers (SCX), which are conceptionally restricted to oppositely charged solutes, their individual chiral selector (SO) subunits have been fused in a combinatorial synthesis approach into single, now zwitterionic, chiral SO motifs. The corresponding zwitterionic ion-exchange-type chiral stationary phases (CSPs) in fact combined the applicability spectra of the parent chiral ion exchangers allowing for enantioseparations of chiral acids and amine-type solutes in liquid chromatography using polar organic mode with largely rivaling separation factors as compared to the parent WAX and SCX CSPs. Furthermore, the application spectrum could be remarkably expanded to various zwitterionic analytes such as alpha- and beta-amino acids and peptides. A set of structurally related yet different CSPs consisting of either a quinine or quinidine alkaloid moiety as anion-exchange subunit and various chiral or achiral amino acids as cation-exchange subunits enabled us to derive structure-enantioselectivity relationships, which clearly provided strong unequivocal evidence for synergistic effects of the two oppositely charged ion-exchange subunits being involved in molecular recognition of zwitterionic analytes by zwitterionic SOs driven by double ionic coordination. PMID:18855417

Hoffmann, Christian V; Pell, Reinhard; Lämmerhofer, Michael; Lindner, Wolfgang

2008-10-15

280

Synthesis, Characterization and Application Of PbS Quantum Dots  

SciTech Connect

Lead Chalcogenides (PbS, PbSe, PbTe) quantum dots (QDs) are ideal for fundamental studies of strongly quantum confined systems with possible technological applications. Tunable electronic transitions at near--infrared wavelengths can be obtained with these QDs. Applications of lead chalcogenides encompass quite a good number of important field viz. the fields of telecommunications, medical electronics, optoelectronics etc. Very recently, it has been proposed that 'memristor'(Memory resistor) can be realized in nanoscale systems with coupled ionic and electronic transports. The hystersis characteristics of 'memristor' are observed in many nanoscale electronic devices including semiconductor quantum dot devices. This paper reports synthesis of PbS QDs by chemical route. The fabricated samples are characterized by UV-Vis, XRD, SEM, TEM, EDS, etc. Observed characteristics confirm nano formation. I-V characteristics of the sample are studied for investigating their applications as 'memristor'.

Sarma, Sweety; Datta, Pranayee [Department of Electronics Science, Gauhati University, Gnwahait-781014, Assam (India); Barua, Kishore Kr. [Department of Physics, Central University, Tezpur-784028, Assam (India); Karmakar, Sanjib [Department of Instrumentation and USIC, Gauhati University, Guwahati-781014, Assam (India)

2009-06-29

281

CATALYTIC DYNAMIC RESOLUTION APPLIED TO THE SYNTHESIS OF 2,6-DISUBSTITUTED PIPERIDINES: PREPARATION OF (+)-LUPETIDINE AND (-)-EPIDIHYDROPINIDINE‡  

PubMed Central

The diastereoselective synthesis of trans-2,6-disubstituted piperidines has been rendered enantioselective by incorporating a catalytic dynamic resolution into the first alkylation step. The method has been applied to the synthesis of (?)-epidihydropinidine and (+)-trans-lupetidine

Beng, Timothy K.; Gawley, Robert E.

2012-01-01

282

Perfluorophenyl Azides: New Applications in Surface Functionalization and Nanomaterial Synthesis  

PubMed Central

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

Liu, Li-Hong; Yan, Mingdi

2010-01-01

283

Perfluorophenyl azides: new applications in surface functionalization and nanomaterial synthesis.  

PubMed

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

Liu, Li-Hong; Yan, Mingdi

2010-08-06

284

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

Microsoft Academic Search

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

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

2008-01-01

285

Pro-antibiotic Substrates for the Identification of Enantioselective Hydrolases  

Microsoft Academic Search

A new growth-based screening method for the identification of enantioselective hydrolases, such as lipases and esterases, using pro-antibiotic substrates was devised. An enantioselective hydrolase could be identified by measuring growth rates of cells in liquid media containing (R)- or (S)-2–phenylbutyric chloramphenicol esters. This method can be applied to the screening of novel enantioselective microbes and to the high-throughput screening for

Bum-Yeol Hwang; Jong-Min Oh; Juhan Kim; Byung-Gee Kim

2006-01-01

286

Enantioselective Analysis in instruments onboard ROSETTA/PHILAE and ExoMars  

NASA Astrophysics Data System (ADS)

It has been suggested a number of times in the past, to look for chirality as a biomarker. So far, for lack of appropriate instrumentation, space missions have never included enantioselective analysis. The distinction between enantiomers is of crucial importance to the question of the origin of the very first (pre)biotic molecules. If molecules detected in situ on another celestial body were found to exhibit a chiral bias, this would mean that at least partial asymmetric synthesis could take place abiotically. If this chiral bias should be found to be near 100For the currently flying ESA mission ROSETTA an enantioselective instrument was built, to try for the first time to detect and separate chiral molecules in situ. This instrument is COSAC, the Cometary Sampling and Acquisition Experiment, an enantioselective GCMS device[1,2], which is included in the lander PHLIAE that will eventually in 2014 land on the nucleus of comet 67P/Churyumov-Gerasimenko. A similar but even more powerful type of enantioselective GC-MS is in preparation for ESA's ExoMars mission. This instrument is part of MOMA, the Mars Organic Molecules Analyser. It has the objective of identifying and quantifying chiral organic molecules in surface and subsurface samples of Mars. Currently ExoMars is scheduled for 2018. The newly developed enantioselective technique utilized by both COSAC and MOMA will be described, including sample acquisition, derivatization, and separation in space-resistant chiral stationary capillary columns with time-of-flight mass spectrometric detection. Results of enantioselective analyses of representative test samples with special emphasis on amino acids[3], the building blocks of protein polymers, will be presented and we will discuss potential results of space missions Rosetta and ExoMars. [1] Thiemann W.H.-P., Meierhenrich U.: ESA Mission ROSETTA Will Probe for Chirality of Cometary Amino Acids. Origins of Life and Evolution of Biospheres 31 (2001), 199-210. [2] Goesmann F., Rosenbauer H., Roll R., Szopa C., Raulin F., Sternberg R., Israel G., Meier-henrich U., Thiemann W., Muñoz Caro G.M.: COSAC, The cometary sampling and composi-n tion experiment on Philae. Space Science Reviews 128 (2007), 257-280. [3] Meierhenrich U.J.: Amino Acids and the Asymmetry of Life -Caught in the Act of Forma-tion. Springer, Heidelberg Berlin New York (2008).

Hendrik Bredehöft, Jan; Thiemann, Wolfram; Meierhenrich, Uwe; Goesmann, Fred

287

Synthesis and characterization of zinc oxide nanostructures for piezoelectric applications  

NASA Astrophysics Data System (ADS)

Union between top-down and bottom-up assembly is inevitable when scaling down physical, chemical, and biological sensors and probes. Current sensor/probe-based technologies are firmly founded on top-down manufacturing, with limitations in cost of production, manufacturing methods, and material constraints. As an alternative to such limitations, contemporary synthesis techniques for one-dimensional nanostructures have been combined with established methods of micro-fabrication for the development of novel tools and techniques for nanotechnology. More specifically, this dissertation is a systematic study of the synthesis and characterization of ZnO nanostructures for piezoelectric applications. Within this study the following goals have been achieved: (1) rational design and control of a diversity of novel ZnO nanostructures, (2) improved understanding of polar-surface-dominated (PSD) phenomena among Wurtzite crystal structures, (3) confirmation of Tasker's Rule via the synthesis, characterization, and modeling of polar-surface-dominated nanostructures, (4) measurement of the surface-charge density for real polar surfaces of ZnO, (5) confirmation of the electrostatic polar-charge model used to describe polar-surface-dominated phenomena, (6) dispersion of ZnO nanobelts onto the selective layers of surface acoustic wave (SAW) devices for gas sensing applications, (7) manipulation of ZnO nanostructures using an atomic force microscope (AFM) for the development of piezoelectric devices, (8) fabrication of bulk acoustic resonator (BAR) and film bulk acoustic resonator (FBAR) devices based on the integrity of individual ZnO belts, (9) electrical characterization of a ZnO belt BAR device, (10) prediction and confirmation of the electrical response from a BAR device using a one-dimensional Krimholt-Leedom-Matthaei (KLM) model, and (11) development of a finite element model (FEM) to accurately predict the electrical response from ZnO belt BAR and FBAR devices in 3D.

Hughes, William L.

288

Synthesis, properties and applications of nanoscale nitrides, borides and carbides.  

PubMed

Nanoscale nitrides, borides and carbides are a fascinating type of materials, which have aroused tremendous and continuous research interest for decades owing to their special mechanical, electrical, optical, photoelectronic, catalytic properties and widespread uses. In this feature article, recent developments and breakthroughs in the synthesis, properties and applications of nanometre scale nitrides (BN, Si(3)N(4), GaN, noble nitrides), borides (LnB(6), LnB(2), Fe(3)BO(5), LiMBO(3)) and carbides (carbon, SiC, TiC, NbC, WC) were briefly reviewed in sequence of their different dimensions (1D, 2D and 3D). In particular, our latest advances in the "autoclave route" fabrication of nanoscale nitrides, borides, and carbides were highlighted. The challenges, issues and perspectives of the synthetic methodologies and potential applications concerning the above-mentioned materials were also briefly discussed. PMID:22782140

Xu, Liqiang; Li, Shouli; Zhang, Yuxu; Zhai, Yanjun

2012-07-10

289

Synthesis, properties and applications of nanoscale nitrides, borides and carbides  

NASA Astrophysics Data System (ADS)

Nanoscale nitrides, borides and carbides are a fascinating type of materials, which have aroused tremendous and continuous research interest for decades owing to their special mechanical, electrical, optical, photoelectronic, catalytic properties and widespread uses. In this feature article, recent developments and breakthroughs in the synthesis, properties and applications of nanometre scale nitrides (BN, Si3N4, GaN, noble nitrides), borides (LnB6, LnB2, Fe3BO5, LiMBO3) and carbides (carbon, SiC, TiC, NbC, WC) were briefly reviewed in sequence of their different dimensions (1D, 2D and 3D). In particular, our latest advances in the ``autoclave route'' fabrication of nanoscale nitrides, borides, and carbides were highlighted. The challenges, issues and perspectives of the synthetic methodologies and potential applications concerning the above-mentioned materials were also briefly discussed.

Xu, Liqiang; Li, Shouli; Zhang, Yuxu; Zhai, Yanjun

2012-07-01

290

A general enantioselective route to the chamigrene natural product family  

PubMed Central

Described in this report is an enantioselective route toward the chamigrene natural product family. The key disconnections in our synthetic approach include sequential enantioselective decarboxylative allylation and ring-closing olefin metathesis to form the all-carbon quaternary stereocenter and spirocyclic core present in all members of this class of compounds. The generality of this strategy is demonstrated by the first total syntheses of elatol and the proposed structure of laurencenone B, as well as the first enantioselective total syntheses of laurencenone C and ?-chamigrene. A brief exploration of the substrate scope of the enantioselective decarboxylative allylation/ring-closing metathesis sequence with fully substituted vinyl chlorides is also presented.

White, David E.; Stewart, Ian C.; Seashore-Ludlow, Brinton A.; Grubbs, Robert H.; Stoltz, Brian M.

2010-01-01

291

Diffractive Optic Synthesis and Analysis of Light Fields and Recent Applications  

Microsoft Academic Search

The synthesis and analysis of light fields having specific properties are the main issues in diffractive optics. Light field synthesis technology with diffractive optical elements can provide actual solutions for various applications that require extraordinary optical functions. Also, the rigorous analysis of a light field is an essential element for the design and application of micro- or nanoscale diffractive optical

Hwi Kim; Kyongsik Choi; Byoungho Lee

2006-01-01

292

Enantioselective conjugate addition of donor-acceptor hydrazones to ?,?-unsaturated aldehydes through formal diaza-ene reaction: access to 1,4-dicarbonyl compounds.  

PubMed

Donor-acceptor monosubstituted hydrazones participate as suitable reagents able to undergo an enantioselective formal diaza-ene reaction with ?,?-unsaturated aldehydes under chiral secondary amine catalysis. This constitutes a new approach for the enantioselective conjugate addition of hydrazones to enals under metal-free conditions and leads to the formation of ?-hydrazono carboxylic acids after oxidation/[1,3]-H shift. The methodology is also useful for the synthesis of enantioenriched ?-substituted ?-keto-1,5-diesters by using the hydrazone moiety as a masked carbonyl group. PMID:22780683

Fernández, Maitane; Uria, Uxue; Vicario, Jose L; Reyes, Efraím; Carrillo, Luisa

2012-07-16

293

Synthesis and application of chiral triazine condensing reagents prepared from esters of amino acids.  

PubMed

Treatment of cyanuric chloride with chiral amines or esters of chiral amino acids gave chiral 2,4-dichloro-6-alkylamino-1,3,5-triazines (2-5) in 49-69% yield, which were found useful as coupling reagents. Enantioselective activation and enantioselective aminolysis in the presence of 2-5 was observed. PMID:11995981

Kami?ski, Z J; Zajac, K J; Jastrzabek, K

2001-01-01

294

Synthesis and Applications of Non-spherical Dimer Colloids  

NASA Astrophysics Data System (ADS)

Colloids are promising building blocks in material synthesis because of their controllability of size and surface properties. The synthesis of chemically and/or geometrically anisotropic colloidal particles has received attentions with the expectation of building blocks for complex structures. However, the synthesis of anisotropic colloidal particles is by far more difficult than the synthesis of spherical colloidal particles. Lack of monodispersity and productivity of many anisotropic particles often limits their applications as a building block for complex structures. Thus, it is highly desirable to develop methods which can produce a large amount of monodisperse non-spherical particles with controllable asymmetric surface properties. This dissertation details the work for developing such a method. The major result of this dissertation is a synthetic method to produce monodisperse non-spherical colloids with anisotropic surface property in a large quantity. The anisotropic colloid, which we call it as Dimer particle, has two fused lobes like a dumbbell and each lobe's size can be independently controlled. We present a novel method to synthesize sub-micron size Dimer particles. This method can produce a large amount of submicron-sized Dimer particles with good monodispersity and well-controlled shape. Submicron-sized Dimer particles have been highly desired since they can be used as a building block for self assembly using Brownian motion, colloidal surfactant for Pickering emulsion, and photonic materials. To fully take advantage of the anisotropy of the particles, we develop a facile method to tailor the surface property of each lobe independently by asymmetrically coating the particles with gold nanoparticles. This method doesn't need the arrangement of particles onto any type of interfaces. Asymmetric coating of gold nanoparticles can be carried out simply by mixing Dimer particles with gold nanoparticles. The formation mechanism of the submicron-sized Dimer particles is explained with evidences. Finally, we illustrate that Dimer particles show rich phase behavior under electric fields and explain the behavior by considering various interactions involved in the system. Our investigation shows that electric field can effectively control the orientation and assembled structure of Dimer particles. In conclusion, these asymmetrically functionalized Dimer particles are promising building blocks to generate suprastructures that will be useful in photonic, electronic and diagnostic applications.

Yoon, Kisun

295

Continuous-flow enantioselective ?-aminoxylation of aldehydes catalyzed by a polystyrene-immobilized hydroxyproline  

PubMed Central

Summary The application of polystyrene-immobilized proline-based catalysts in packed-bed reactors for the continuous-flow, direct, enantioselective ?-aminoxylation of aldehydes is described. The system allows the easy preparation of a series of ?-aminoxy alcohols (after a reductive workup) with excellent optical purity and with an effective catalyst loading of ca. 2.5% (four-fold reduction compared to the batch process) working at residence times of ca. 5 min.

Cambeiro, Xacobe C; Martin-Rapun, Rafael; Miranda, Pedro O; Sayalero, Sonia; Alza, Esther; Llanes, Patricia

2011-01-01

296

Catalytic enantioselective halolactonization of enynes and alkenes.  

PubMed

New organocatalysts have been developed for the enantioselective halolactonization of (Z)-1,3-enynes and 1,1-disubstituted alkenes. In the case of 1,3-enynes, the carboxylate nucleophile and halogen electrophile were added to the conjugated ?-system from the same face. Up to 99% ee was achieved for the 1,4-syn-bromolactonization of conjugated (Z)-1,3-enynes. Based on the results from the enyne halolactonization, a second generation of catalysts was designed for simple olefins. Up to 91% ee was observed for chlorolactonization of 1,1-disubstituted alkenes. The catalysts developed for the enantioselective halolactonization of both enynes and alkenes are composed of a cinchona alkaloid skeleton tethered to a urea group. PMID:22549978

Zhang, Wei; Liu, Na; Schienebeck, Casi M; Decloux, Kyle; Zheng, Suqing; Werness, Jenny B; Tang, Weiping

2012-04-30

297

Vancomycin Molecular Interactions: Antibiotic and Enantioselective Mechanisms  

NASA Astrophysics Data System (ADS)

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

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

298

Inter- and intramolecular enantioselective carbolithiation reactions  

PubMed Central

Summary In this review we summarize recent developments in inter- and intramolecular enantioselective carbolithiation reactions carried out in the presence of a chiral ligand for lithium, such as (?)-sparteine, to promote facial selection on a C=C bond. This is an attractive approach for the construction of new carbon–carbon bonds in an asymmetric fashion, with the possibility of introducing further functionalization on the molecule by trapping the reactive organolithium intermediates with electrophiles.

Gomez-SanJuan, Asier; Sotomayor, Nuria

2013-01-01

299

Applications of ultrasound to the synthesis of nanostructured materials.  

PubMed

Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of approximately 5000 K, pressures of approximately 1000 bar, heating and cooling rates of >10(10) K s(-1); these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis. PMID:20401929

Bang, Jin Ho; Suslick, Kenneth S

2010-03-12

300

Carbon nanotubes and tungsten oxide nanorods: Synthesis and applications  

NASA Astrophysics Data System (ADS)

Synthesis and applications of two types of one-dimensional nanomaterials, carbon nanotubes (CNTs) and tungsten oxide nanorods, are investigated in this dissertation. Multi-walled CNTs have been successfully synthesized using two types of chemical vapor deposition (CVD) methods: microwave plasma enhanced CVD and atmospheric pressure thermal CVD. CNTs and their synthesis processes are characterized with various analysis techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical emission spectroscopy. Ultra-thin and high quality multi-walled CNTs are discovered in CNT films produced by MPCVD, which exhibit good field emission performance that is found to be dependent on the synthesis conditions, like the growth time and CH4/H2 flow ratio. CNTs grown by thermal CVD have similar field emission performance. Based on silicon surface micromachining techniques and thermal CVD method, a self-aligned method has been developed to fabricate CNT based gated field emitter arrays (FEAs) which demonstrate low turn-on voltage and good emission current. Tungsten oxide nanorods have been synthesized on various tungsten substrates via thermal annealing in argon at atmospheric pressure. Nanorod growth mechanism is proposed based on thermal oxidation of tungsten in gas ambient with a very low partial pressure of oxygen as well as the self-catalytic effect on tungsten surface. The lattice structure and composition of the tungsten oxide nanorods are observed and analyzed using high resolution TEM, selected area electron diffraction (SAD), and energy dispersive X-ray spectroscopy (EDXS). The analysis results reveal that the lattice structure of the tungsten oxide nanorods is closest to that of the monoclinic WO3 crystal. Tungsten oxide nanorods have been successfully grown on tungsten tips for use in scanning tunneling microscope (STM) as probes which readily produce atomic resolution images on sample surface. Nanorod based FEAs are also successfully fabricated using similar techniques as those for fabricating CNTs based FEAs. Low turn-on voltage and low gate current are achieved.

Xiao, Bing

301

Enantioselective ring opening of epoxides by fluoride anion promoted by a cooperative dual-catalyst system.  

PubMed

An enantioselective method for the synthesis of beta-fluoroalcohols by catalytic nucleophilic fluorination of epoxides is described. Mild reaction conditions and high selectivity are made possible by the use of benzoyl fluoride as a soluble, latent source of fluoride anion. A chiral amine and chiral Lewis acid serve as cooperative catalysts for desymmetrizations of five- through eight-membered cyclic epoxides, affording products in up to 95% ee. The cocatalytic protocol is also effective for kinetic resolutions of racemic terminal epoxides, which proceed with k(rel) values as high as 300. PMID:20163118

Kalow, Julia A; Doyle, Abigail G

2010-03-17

302

Enantioselective Syntheses of FR901464 and Spliceostatin A: Potent Inhibitors of Spliceosome.  

PubMed

Enantioselective syntheses of FR901464 and spliceostatin A, potent spliceosome inhibitors, are described. The synthesis of FR901464 has been accomplished in a convergent manner in 10 linear steps (20 total steps). The A-tetrahydropyran ring was constructed from (R)-isopropylidene glyceraldehyde. The functionalized tetrahydropyran B-ring was synthesized utilizing a Corey-Bakshi-Shibata reduction, an Achmatowicz reaction, and a stereoselective Michael addition as the key steps. Coupling of A- and B-ring fragments was accomplished via cross-metathesis. PMID:24050251

Ghosh, Arun K; Chen, Zhi-Hua

2013-09-19

303

Late-Stage Diversification of Chiral N-Heterocyclic-Carbene Precatalysts for Enantioselective Homoenolate Additions  

PubMed Central

A library of chiral triazolium salts has been prepared by late-state diversification of a triazolium amine salt. By utilizing a primary amine as a functional handle, a single triazolium salt can be transformed into a variety of chiral N-heterocyclic carbene precatalysts. This approach makes the preparation of chiral N-heterocyclic carbenes possible by a single-step modification of a triazolium salt, rather than the usual need for multistep organic synthesis and challenging heterocycle formation for each member of a catalyst library. We have screened these catalysts for control of diastereo- and enantioselectivity in a ?-lactam-forming reaction between ?,?-unsaturated aldehydes and cyclic ketimines.

Zheng, Pinguan; Gondo, Chenaimwoyo A.

2011-01-01

304

Semi-synthesis of labeled proteins for spectroscopic applications.  

PubMed

Since the introduction of SPPS by Merrifield in the 60s, peptide chemists have considered the possibility of preparing large proteins. The introduction of native chemical ligation in the 90s and then of expressed protein ligation have opened the way to the preparation of synthetic proteins without size limitations. This review focuses on semi-synthetic strategies useful to prepare proteins decorated with spectroscopic probes, like fluorescent labels and stable isotopes, and their biophysical applications. We show that expressed protein ligation, combining the advantages of organic chemistry with the easy and size limitless recombinant protein expression, is an excellent strategy for the chemical synthesis of labeled proteins, enabling a single protein to be functionalized at one or even more distinct positions with different probes. PMID:23282535

De Rosa, Lucia; Russomanno, Anna; Romanelli, Alessandra; D'Andrea, Luca Domenico

2013-01-02

305

Group IV nanoparticles: synthesis, properties, and biological applications.  

PubMed

In this review, the emerging roles of group IV nanoparticles including silicon, diamond, silicon carbide, and germanium are summarized and discussed from the perspective of biologists, engineers, and medical practitioners. The synthesis, properties, and biological applications of these new nanomaterials have attracted great interest in the past few years. They have gradually evolved into promising biomaterials due to their innate biocompatibility; toxic ions are not released when they are used in vitro or in vivo, and their wide fluorescence spectral regions span the near-infrared, visible, and near-ultraviolet ranges. Additionally, they generally have good resistance against photobleaching and have lifetimes on the order of nanoseconds to microseconds, which are suitable for bioimaging. Some of the materials possess unique mechanical, chemical, or physical properties, such as ultrachemical and thermal stability, high hardness, high photostability, and no blinking. Recent data have revealed the superiority of these nanoparticles in biological imaging and drug delivery. PMID:20730824

Fan, Jiyang; Chu, Paul K

2010-10-01

306

THE ENANTIOSELECTIVITY OF CHIRAL PESTICIDES PRESENTS A GREEN CHEMISTRY OPPORTUNITY  

EPA Science Inventory

This presentation will include a summary of the use and environmental occurrence of modern chiral pesticides with data on their enantioselective fate and effects. Information on enantioselectivity will facilitate a science-based approach toward fostering the production and use o...

307

Tin-Free Enantioselective Radical Reactions Using Silanes  

PubMed Central

Readily available hexyl silane is an excellent choice as a H-atom donor and a chain carrier in Lewis acid mediated enantioselective radical reactions. Conjugate radical additions to ?,?-unsaturated imides at room temperature proceed in good yields and excellent enantioselectivities.

Sibi, Mukund P.; Yang, Yong-Hua; Lee, Sunggi

2009-01-01

308

Total synthesis of the tricyclic marine alkaloids (-)-lepadiformine, (+)-cylindricine c, and (-)-fasicularin via a common intermediate formed by formic acid-induced intramolecular conjugate azaspirocyclization.  

PubMed

A very short and efficient enantioselective total synthesis of the tricyclic marine alkaloids (-)-lepadiformine (3), (+)-cylindricine C (1c), and (-)-fasicularin (4) has been developed utilizing the formyloxy 1-azaspiro[4.5]decane 5 as a common intermediate. The key strategic element for the synthesis was the formic acid-induced intramolecular conjugate azaspirocyclization, which proved to be a highly efficient and stereoselective way to rapid construction of the 1-azaspirocyclic substructure of these natural products in a single operation. Thus, the common intermediate 5, synthesized in two steps with 70% overall yield starting from the known (S)-N-Boc-2-pyrrolidinone 7 via the conjugate spirocyclization using an acyclic ketoamide 6, was utilized for the concise and stereoselective total synthesis of (-)-lepadiformine (3), which was accomplished in seven steps with 45% overall yield from 5 (31% yield from 7). The developed strategy based on the conjugate spirocyclization was also applied to the stereoselective total synthesis of (+)-cylindricine C (1c), which was achieved in 10 steps from 5 in 18% overall yield (12% yield from 7). Further application of this approach using 5 led to the synthesis of (-)-fasicularin (4), wherein an extremely efficient method for the introduction of the thiocyanato group via an aziridinium intermediate at the last step was developed. Thus, the highly efficient first enantioselective total synthesis of (-)-fasicularin was accomplished in nine steps with an overall yield of 41% from 5 (28% yield from 7). PMID:15686380

Abe, Hideki; Aoyagi, Sakae; Kibayashi, Chihiro

2005-02-01

309

Synthesis, charaterization and application of metal and semiconductor nanowires  

NASA Astrophysics Data System (ADS)

Nanostructured materials such as nanowires have attracted significant attention in the past two decades. Both metallic and semiconducting nanowires have been demonstrated as important building blocks for numerous electronic and optoelectronic device applications. In this thesis, we have demonstrated a scalable route for synthesizing vertically aligned semiconducting nanowires using nanosphere lithography (NSL) technique in combination with selected area metal organic chemical vapor deposition (SA- MOCVD). Comparable optical properties were observed between the nanowires produced by NSL patterning technique and nanowires produced by using more expensive and slow electron beam lithography. We have also used capacitance-voltage measurement technique to determine the doping level in these nanowire arrays. In metallic nanowires, we have demonstrated fabrication of high performance transparent conductive electrodes by using Ag nanowires and proposed a technique to synthesis thin Ag nanowires which can have applications in various optoelectronic devices. This dissertation describes the above-mentioned aspects in detail and accordingly consists of seven chapters. Following an overview and an introduction of fundamental knowledge of nanolithography and transparent conductive electrodes in Chapter 1, Chapter 2 discusses the scalable nanosphere lithography patterning and selected area growth of vertically aligned GaAs nanowire arrays, a route towards optimized optical absorption and reflection. Chapter 3 discusses the continued work on GaAs nanowire array and employs the use of capacitance-voltage measurement technique to determine the doping level of these nanowires which is important for using these nanowires for fabrication of any electronic devices. Chapter 4 deals with an important issue of replacement of traditional ITO as a transparent conductive electrode (TCE) for optoelectronic devices. There is a need for replacement of ITO due to several drawback associated with ITO as will be discussed in detail in the chapter. We demonstrate the viability of silver nanowire based random network film as a potential replacement. We achieve remarkable performance in terms of sheet resistance and transparency which rivals that of ITO, supporting a very strong case for Ag nanowire film. We combine traditional spray coating technique with novel Ag nanowires to fabricate high performance TCE. In chapter 5, we further improve the performance of the TCE produced by Ag nanowires by using a dry transfer technique demonstrating a performance comparable to ITO and much better than other potential candidates that can be used as TCE. In chapter 6 we addressed an important issue associated with using Ag nanowires as a future candidate for TCE by proposing a technique to synthesis thin Ag nanowires which can find application in optoelectronic device. Finally in chapter 7, we conclude by discussing the future directions and work that needs to be done in order to carry forward the advance made in this thesis.

Madaria, Anuj Rahul

310

Defect-related luminescent materials: synthesis, emission properties and applications.  

PubMed

Luminescent materials have found a wide variety of applications, including information displays, lighting, X-ray intensification and scintillation, and so on. Therefore, much effort has been devoted to exploring novel luminescent materials so far. In the past decade, defect-related luminescent materials have inspired intensive research efforts in their own right. This kind of luminescent material can be basically classified into silica-based materials, phosphate systems, metal oxides, BCNO phosphors, and carbon-based materials. These materials combine several favourable attributes of traditional commercially available phosphors, which are stable, efficient, and less toxic, being free of the burdens of intrinsic toxicity or elemental scarcity and the need for stringent, intricate, tedious, costly, or inefficient preparation steps. Defect-related luminescent materials can be produced inexpensively and on a large scale by many approaches, such as sol-gel process, hydro(solvo)thermal reaction, hydrolysis methods, and electrochemical methods. This review article highlights the recent advances in the chemical synthesis and luminescent properties of the defect-related materials, together with their control and tuning, and emission mechanisms (solid state physics). We also speculate on their future and discuss potential developments for their applications in lighting and biomedical fields. PMID:23019577

Zhang, Cuimiao; Lin, Jun

2012-12-01

311

Controlled synthesis and biomolecular probe application of gold nanoparticles.  

PubMed

In addition to their optical properties, the ability of gold nanoparticles (Au NPs) to generate table immobilization of biomolecules, whilst retaining their bioactivities is a major advantage to apply them as biosensors. Optical biosensors using Au NPs are simple, fast and reliable and, recently, they have been moving from laboratory study to the point of practical use. The optical properties of Au NPs strongly depend on their size, shape, degree of aggregation and the functional groups on their surface. Rapid advances in the field of nanotechnology offer us a great opportunity to develop the controllable synthesis and modification of Au NPs as well as to study on their properties and applications. The size-controlled growth of Au NPs requires the isotropic growth on the surface of Au nuclei whereas anisotropic growth will induce the formation of Au NPs of varying shape. Functionalized Au NPs provide sensitive and selective biosensors for the detection of many targets, including metal ions, small organic compounds, protein, DNA, RNA and cell based on their optical, electrical or electrochemical signals. In this review, we will discuss the size- and shape-controlled growth and functionalization of Au NPs to obtain Au nanoprobes. The basis of the optical detection of Au nanoprobes and their applications in nucleic acid, protein detection and cell imaging are also introduced. PMID:20952201

Nguyen, Dung The; Kim, Dong-Joo; Kim, Kyo-Seon

2010-10-01

312

Diffractive Optic Synthesis and Analysis of Light Fields and Recent Applications  

NASA Astrophysics Data System (ADS)

The synthesis and analysis of light fields having specific properties are the main issues in diffractive optics. Light field synthesis technology with diffractive optical elements can provide actual solutions for various applications that require extraordinary optical functions. Also, the rigorous analysis of a light field is an essential element for the design and application of micro- or nanoscale diffractive optical elements. In this paper we review the theoretical aspects of the diffractive optic synthesis and analysis of light fields, and present some recent applications of diffractive optical elements for information, nano-, and biotechnologies.

Kim, Hwi; Choi, Kyongsik; Lee, Byoungho

2006-08-01

313

Synthesis and Characterization of Photosensitive Polyimides for Optical Applications  

NASA Astrophysics Data System (ADS)

The objective of this research was to prepare photosensitive polyimides for optical applications. The work was begun with the synthesis of a series of poly(amic esters) containing cinnamyl groups. However, these systems required high imidization temperatures where they darkened considerably. Two new photosensitive end-capping agents, i.e., 6-(4-aminophenoxy)hexyl methacrylate, and di(2-(methacryloyloxy)ethyl) 5-aminoisophthalate, for polyimides were also prepared. These agents were used along with 2,2^' -bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2^'-bis(trifluoromethyl) -4,4^' -diaminobiphenyl (PFMB) to prepare a series of methacrylate end-capped imide oligomers. However, the oligomers required long exposures to UV-radiation to affect cure. To improve their photosensitivity, multifunctional additives and photoinitiators were used. A difunctional end-capped oligomer that contained trimethylolpropane triacrylate (TMPTA) and trimethylbenzoyldiphenyl phosphine oxide (TMDPO) was highly photosensitive and displayed good photo-patterning properties. The third approach involved the synthesis of a diamine monomer in which methacrylate moieties were attached to the 2- and 2^ '-positions of biphenyl structures. The monomer, i.e., 2,2^'-dimethacryloyloxy -4,4^'-diaminobiphenyl (DMB), was polymerized with commercially available dianhydrides such as 6FDA and 4,4^' -oxydiphthalic anhydride (ODPA). The polyimides obtained were optically transparent and soluble in common organic solvents such as acetone and chloroform. The polymers were highly photosensitive and displayed good photo-patterning properties. The polymers, which afforded high-resolution patterns, did not develop color or shrink during UV-exposure and thermal curing.

Kim, Kye-Hyun

314

A Concise Asymmetric Total Synthesis of (+)-Brevisamide  

PubMed Central

A new protecting-group-free synthesis of the marine monocyclic ether (+)-brevisamide is reported. The enantioselective synthesis utilizes a key asymmetric Henry reaction and an Achmatowicz rearrangement for the formation of the tetrahydropyran ring. A penultimate Stille cross-coupling allows for an efficient installation of the conjugated (E,E)-diene side chain ultimately delivering (+)-brevisamide.

Herrmann, Aaron T.; Martinez, Steven R.; Zakarian, Armen

2012-01-01

315

Synthesis and Application of Inorganic Nanoparticles as Lubricant Components – a Review  

Microsoft Academic Search

Recent achievements in chemistry and technology of nanosized inorganic particles provide possibility of synthesis in various metal oxides, chalcogenides, and so on. Surface modification of nanoparticles in some cases provides formation of their stable dispersions in liquid hydrocarbons. State of art in the field of inorganic nanoparticles’ synthesis and their application in tribology is discussed. Special attention is paid to

V. N. Bakunin; A. Yu. Suslov; G. N. Kuzmina; O. P. Parenago; A. V. Topchiev

2004-01-01

316

An efficient Amano PS-catalyzed chemo-, regio- and enantioselective hydrolysis of (±)-2,3-di- O-acetyl-2- C-methyl- d-erythrono-1,4-lactone: a facile preparation of bioactive natural products (?)-saccharinic acid lactone and potassium (2 R,3 R)-2,3,4-trihydroxy-2-methylbutanoate  

Microsoft Academic Search

Saccharinic acid lactone (?)-1a is a suitable building block for the synthesis of many bioactive natural products. Amano PS-induced chemo-, regio- and enantioselective hydrolysis of diacetyl lactone (±)-3 has been carried out to obtain (?)-1a in 46% yield with 99% ee and diacetyl lactone (+)-3 in 49% yield with 99% ee. The Amano PS-catalyzed enantioselective acylation of (±)-1a with vinyl

Sanjib Gogoi; Narshinha P. Argade

2006-01-01

317

Synthesis, characterization and biosensing application of photon upconverting nanoparticles  

NASA Astrophysics Data System (ADS)

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

Kumar, Manoj; Zhang, Peng

2009-02-01

318

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

PubMed Central

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

Trost, Barry M.; Silverman, Steven M.

2012-01-01

319

Synthesis and Applications of Inorganic/Organic-Polymer Nanocomposites  

NASA Astrophysics Data System (ADS)

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

Goyal, Anubha

320

Chemical Synthesis and Biological Applications of Nucleic Acids to Nitrogen Fixation.  

National Technical Information Service (NTIS)

The purpose of this research is the development of new and improved methods for the chemical synthesis of oligodeoxyribonucleotides and their application to gene transfer studies involving biological nitrogen fixation. The use of the pivaloyl group for th...

1978-01-01

321

Development of a Double Allylboration Reagent Targeting 1,5-syn-(E)-Diols: Application to the Synthesis of the C(23)-C(40) Fragment of Tetrafibricin  

PubMed Central

Interest in the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin prompted us to develop a new method for the synthesis of 1,5-syn-(E)-diols. Toward this end, the kinetically controlled hydroboration of allenes 6, 33, ent-39, 42 and 45 with the Soderquist borane 25R were studied. Tetrabutylammonium allenyltrifluoroborate 45 gave superior results and was utilized in a double allylboration sequence with two different aldehydes to provide the targeted 1,5-syn-(E)-diols in generally high yields (72–98%), and with high enantioselectivity (>95% e.e.), diastereoselectivity (d.r. >20:1), and (E)/(Z) selectivity (>20:1). This new method was applied to the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin.

Nuhant, Philippe; Kister, Jeremy; Lira, Ricardo; Sorg, Achim; Roush, William R.

2011-01-01

322

Nucleophilic addition of methyllithium to chiral oxime ethers: asymmetric preparation of 1-(aryl)ethylamines and application to a synthesis of calcimimetics (+)NPS R-568 and its thio analogue  

Microsoft Academic Search

Chiral (E)-arylaldehyde oxime ethers, prepared using (R)-1-phenyl-1,2-ethanediol as a chiral auxiliary, undergo nucleophilic addition with methyllithium to give diastereomerically enriched O-alkyl hydroxylamines which, after reductive N?O bond cleavage, lead to the corresponding (R)-1-(aryl)ethylamines. This methodology has been applied to the enantioselective synthesis of a new type of arylalkylamine calcimimetics (R)-(+)-NPS R-568 and its thio analogue.

Naoki Yamazaki; Masakazu Atobe; Chihiro Kibayashi

2001-01-01

323

Enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones.  

PubMed

Two approaches have been developed for the enantioselective Reformatsky reaction of ethyl iododifluoroacetate with ketones to form a quaternary carbon centre using (1R,2S)-1-phenyl-2-(1-pyrrolidinyl)-1-propanol as the chiral ligand. Good yields and high enantioselectivities (80-91% ee) were achieved with a range of alkyl aryl ketones in a convenient one-pot protocol using ethyl iododifluoroacetate and diethylzinc to form the difluorinated Reformatsky reagent homogeneously. In the traditional two-step Reformatsky reaction using the preformed Reformatsky reagent generated from ethyl iododifluoroacetate and zinc dust, good yields and good enantioselectivities (75-84% ee) were also obtained. PMID:22421710

Fornalczyk, Michal; Singh, Kuldip; Stuart, Alison M

2012-03-15

324

Surfactantless synthesis of silver nanoplates and their application in SERS.  

SciTech Connect

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

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

2007-11-01

325

Synthesis and applications of quantum dots and magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and Zn1-xCdxSe alloyed QDs derived are tunable in fluorescence emissions between 360 nm and 700 nm. They show high quantum yields (QYs) of up to 50%, with narrow bandwidths of 19-55 nm. The synthesis of glutathione-capped QDs is simple and cost-effective compared to the conventional organometallic approaches. It can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions. We have also demonstrated the fabrication of magnetic quantum dots (MQDs) through a seed-mediated approach. The formation and assembly of these bifunctional nanocomposites have been elucidated by high-resolution transmission electron microscopy (HRTEM). The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components in this hybrid system. We have created biocompatible silica-coated MQDs that effectively target the cell membranes.

Ying, Jackie Y.; Zheng, Yuangang; Selvan, S. Tamil

2008-03-01

326

Synthesis and Applications of Functionalized Nanoporous Materials for Specific Adsorption  

SciTech Connect

Surface chemistry is one of the most important properties of mesoporous materis for many applications. There are several approaches to functionalize mesoporous materials in order to tailor the surface chemistry: one step synthesis by co-condensation, direct silanation of partially hydroxylated surface, controlled hydrolysis and condensation, and silanation using supercritical fluid as the reaction medium. Varying the amount chemically and physically adsorbed water can systematically tailor the quality and the population density of functional groups. Furthermore, using supercritical fluid as the reaction medium, organic molecules can be effectively delivered and attached to the internal surfaces of pores less than 1 nm in diameter. The ability to construct high quality functional monolayers allows rational design of molecular recognition and binding sites in mesoporous materials, and has led to the development of very efficient adsorbing materials. One approach to form a host structure that matches the size and shape of the target species is to take advantage of the coordinate chemistry between the functional molecules and metal ions. Highly selective bindings of the target species have been observed against competing species of similar sizes and shapes. More sophisticated surface sites can be constructed for the recognition of complicated molecules and species using large pore mesoporous materials.

Liu, Jun (BATTELLE (PACIFIC NW LAB)); Fryxell, Glen E. (BATTELLE (PACIFIC NW LAB)); Mattigod, Shas V. (BATTELLE (PACIFIC NW LAB)); Zemanian, Thomas S. (BATTELLE (PACIFIC NW LAB)); Shin, Yongsoon (BATTELLE (PACIFIC NW LAB)); Wang, L. Q. (PNNL)

2000-01-01

327

Noble-metal nanocrystals with concave surfaces: synthesis and applications.  

PubMed

Metal nanocrystals with concave surfaces are interesting for a wide variety of applications that are related to catalysis, plasmonics, and surface-enhanced spectroscopy. This interest arises from their high-index facets, surface cavities, and sharp corners/edges. Two major challenges are associated with this novel class of nanocrystals: 1)?how to generate a concave surface with negative curvature, which is not favored by thermodynamics owing to its higher energy than the convex counterpart; and 2)?how to stabilize the morphology of a nanocrystal with concave structures on the surface. Recently, a number of different procedures have been developed for the synthesis of noble-metal nanocrystals with concave surfaces. This Review provides a brief account of these developments, with the aim of offering new insights into the growth mechanisms. We focus on methods based on two general strategies: 1)?site-specific dissolution through etching and galvanic replacement; and 2)?directionally controlled overgrowth by facet-selective capping, kinetic control, and template-directed epitaxy. Their enhanced catalytic and electrocatalytic properties are also described. PMID:22639064

Zhang, Hui; Jin, Mingshang; Xia, Younan

2012-05-25

328

Synthesis and properties of unagglomerated nanocomposite particles for nanomedical applications  

NASA Astrophysics Data System (ADS)

Methods have been developed to prepare stable, unagglomerated active-medical-agent nanoparticles in a range of sizes, based on reverse-micelle microemulsion techniques. The process used to prepare monodisperse, spherical nanocomposite particles is based on methods originally outlined in detail by Adair et al. and Li et al. The "Molecular Dot" (MD) nanoparticles incorporate a variety of medically-active substances, such as organic fluorophores and therapeutic drugs, internally distributed in silica, titania, calcium phosphate, or calcium phospho-silicate matrices. The synthesis techniques have also been modified to produce nanoparticles containing combinations of fluorophores and medicinal agents, in order to monitor drug release and location. The specific biomedical application for the nanocomposite particles dictates the selection of core and shell-matrix materials. For example, the protective shell-matrices of the silica and titania MDs shield the active-medical agents from damage due to changes in pH, temperature, and other environmental effects. Conversely, the calcium phosphate and calcium phospho-silicate shell-matrix nanoparticles can potentially be engineered to dissolve in physiological environments. The method used to remove residual precursor materials while maintaining a well-dispersed assembly of nanoparticles is critical to the use of nanocolloids in medical applications. The dispersion approach is based on protection-dispersion theory tailored to accommodate the high surface areas and reactivity of sub-50 nm particles in aqueous or water/ethanol mixtures. Dispersion of the nanocomposite particles is further enhanced with the use of size-exclusion high performance liquid chromatography (HPLC) to simultaneously wash and disperse the nanocomposite particle suspensions. The state of dispersion of the nanosuspensions is evaluated using the average agglomeration number (AAN) approach in conjunction with other characterization techniques. The formulation of a non-aggregating colloid to deliver active-medical agents has the potential to revolutionize controlled, targeted, systemic delivery for a variety of drug and genetic therapies. The active-medical agent nanoparticles may be applied to a range of biomedical applications, including bioimaging, drug delivery, gene therapy, and combinations thereof. The fluorescent Molecular Dot nanoparticles have been utilized in applications such as in vitro cell labeling, as well as chemical and biological targeting. In addition, the Molecular Dots are a promising alternative to current bioimaging technologies, as the fluorescent emissions from the nanoparticulates do not exhibit blinking/intermittent qualities. (Abstract shortened by UMI.)

Rouse, Sarah M.

329

Synthesis and characterization of advanced nanomaterials for energy applications  

NASA Astrophysics Data System (ADS)

Energy is essential for life. It is thus important to continue understanding how to reduce energy consumption, and increase energy generation. The use of nanoscale materials (nanomaterials) are expected to reduce resources and energy needed in fabricating electrical and electronic devices and help in reducing energy consumption. For example, boron nitride nanotubes (BNNTs) which have uniform band structures, are expected to find application in nanoscale electronic and optoelectronic devices. These devices will have smaller dimension, cost fewer resources and less energy to fabricate, and consume less energy due to minimum electron scattering in their ideally defect-free tubular structures. On the other hand, nanomaterials are also expected to improve the performance of thermoelectric devices that can convert heat into energy. In this thesis, we first investigated low-temperature synthesis of BNNTs (Chapter 1). Effects of substrate temperatures, bias voltages, and catalysts are discussed and a selective-phase growth model is proposed. During the course of this investigation, we discovered Si nanotubes (SiNTs) by catalytic plasma treatment (Chapter 2). The detailed growth parameters and characterizations are presented and a modified growth model is discussed. In addition, electronic properties are measured by AFM. Since Si has exceptional thermoelectric properties, the newly discovered SiNTs are prospects for related applications. We have thus evaluated the potential conversion efficiency and production cost of various nanostructured thermoelectric materials (Chapter 3 and 4). Based on state-of-the-art dish-stirling systems, we evaluate the feasibility of replacing stirling engines by thermoelectric modules. Finally, we have decided to investigate the properties of boron-nanocarbon ensembles (Chapter 5 and 6) as prospective thermoelectric materials. Detailed characterizations includes SEM, HRTEM, Raman, XRD are presented. Seebeck coefficient and electrical conductivity are both measured with various temperatures. Induction quenching confirms that boron-doping help improve power factor of nanocarbon ensembles.

Xie, Ming

330

Synthesis and Characterization of Dyes with Solar Energy Applications  

NASA Astrophysics Data System (ADS)

The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis.

Brennan, Bradley J.

331

Different enantioselective degradation of pyraclofos in soils.  

PubMed

This study investigated the enantioselective degradation behavior of pyraclofos in three soils (NC, HZ, and ZZ) under native and sterilized conditions. The absolute configuration of pyraclofos enantiomers has been determined by the combination of experimental and calculated electronic circular dichroism spectra. S-(+)- and R-(-)-Pyraclofos were separated and determined on a cellulose tri-(4-chloro-3-methylphenylcarbamate) (Lux Cellulose-4) chiral column by reversed-phase high-performance liquid chromatography-tandem mass spectrometry. Pyraclofos enantiomers were configurationally stable in three soils and no interconversion was observed during the incubation of enantiopure S-(+)- or R-(-)-pyraclofos under native conditions. The enantioselective degradation behavior of chiral pyraclofos was dramatically different in three soils under native conditions, with half-lives (t(1/2)) of pyraclofos in NC, HZ, and ZZ soils of 2.6, 13.4, and 7.8 days for S-(+)-pyraclofos and 9.2, 9.3, and 8.2 days for R-(-)-pyraclofos. Compared to the half-lives (t(1/2)) of rac-pyraclofos of 21.5, 55.9, and 14.4 days in sterilized NC, HZ and ZZ soils, the degradation velocity was greatly improved in native soils, indicating that degradation was greatly attributed to microbially mediated processes in agricultural cultivating soils. PMID:22494269

Xu, Yuxin; Zhang, Hu; Zhuang, Shulin; Yu, Man; Xiao, Hua; Qian, Mingrong

2012-04-24

332

An Asymmetric Synthesis of Prozac  

Microsoft Academic Search

A total enantioselective synthesis of the SSRI (-)-Fluoxetine (Prozac?) is presented. Selective Serotonin Reuptake Inhibitors (SSRIs) work to prevent the reabsorption of serotonin, thus increasing the extracellular concentration of this important neurotransmitter. Low concentrations of serotonin are responsible for a variety of mental disorders, including depression, anxiety, and personality disorders. While Prozac is sold as a racemic drug, it has

Anders Eliasen

2010-01-01

333

Synthesis and applications of electrically conducting polymer nanocomposites  

NASA Astrophysics Data System (ADS)

This research focuses on the synthesis and applications of electrically conducting polymer nanocomposites through molecular self-assembly. Two different classes of polymers, polyaniline (PANI) and polyacetylenes have been synthesized by biomimetic catalysis and spontaneous polymerization method. For gas barrier materials, commercially available polymers, poly(allylamine hydrochloride) (PAH) and poly (acrylic acid) (PAA), have also been used and thermally cross-linked. The morphological, optical and electrical properties of amphiphilic polyacetylenes have been studied. Furthermore, barrier properties, permselectivity, pervaporation properties of polyacetylenes/aluminosilicate nanocomposites have been investigated. For processability and electrical properties of carbon nanotube and conducting polymers, substituted ionic polyacetylenes (SIPA) have been covalently incorporated onto single-walled carbon nanotubes (SWNT) using the "grafting-from" technique. In the first study, a nanocomposite film catalyst has been prepared by electrostatic layer-by-layer (ELBL) self-assembly of a polyelectrolyte and a biomimetic catalyst for synthesis of polyaniline. Poly(dimethyl diallylammonium chloride) (PDAC) and hematin have been used as polycation and counter anions, respectively. The absorption spectra by UV-vis-NIR spectroscopy showed that conductive form polyaniline was formed not only as a coating on the surface of the ELBL composites but was also formed in solution. Furthermore, it was found that the reaction rate was affected by pH and concentration of hematin in the multilayers. The feasibility of controlled desorption of hematin molecules from the LBL assembly was explored and demonstrated by changing the pH and hematin concentration. The polymerization rate of aniline in solution was enhanced with decreasing pH of the solutions due to increased desorption of hematin nanoparticles from the multilayers. These ELBL hematin assemblies demonstrated both a way to functionalize surfaces with conductive polyaniline and a potential method of reusability of the catalyst for improved cost effectiveness. For fabrication of multifunctional nanocomposite membranes, (P2EPy-R/Saponite) n on NafionRTM substrate was demonstrated by electrostatic layer-by layer assembly technique. (Abstract shortened by UMI.)

Ku, Bon-Cheol

334

Patterns in Organometallic Chemistry with Application in Organic Synthesis.  

ERIC Educational Resources Information Center

|Of interest in this discussion of organometallic complexes are stoichiometric or catalytic reagents for organic synthesis in the complex transformations observed during synthesis for transition metal organometallic complexes. Detailed are general reaction types from which the chemistry or many transition metal organometallic complexes can be…

Schwartz, Jeffrey; Labinger, Jay A.

1980-01-01

335

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

PubMed

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

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

2013-06-25

336

Catalytic enantioselective conjugate allylation of unsaturated methylidene ketones.  

PubMed

The use of unsaturated methylidene ketones in catalytic conjugate allylations allows a significant expansion in substrate scope and, with appropriate chiral ligands, occurs in a highly enantioselective fashion. PMID:21288009

Brozek, Laura A; Sieber, Joshua D; Morken, James P

2011-02-02

337

Catalytic Enantioselective Conjugate Allylation of Unsaturated Methylidene Ketones  

PubMed Central

The use of unsaturated methylidene ketones in catalytic conjugate allylations allows for a significant expansion in substrate scope and, with appropriate chiral ligands, occurs in a highly enantioselective fashion.

Brozek, Laura A.; Sieber, Joshua D.; Morken, James P.

2011-01-01

338

Elucidating absolute configuration of unsaturated alcohols via enantioselective acylation reactions.  

PubMed

Enantioselective nucleophilic acylation catalysis provides a simple method of determining absolute configuration for unsaturated alcohols. Extension of this technique to natural products and synthetic compounds, as well as current limitations of this approach, are also described. PMID:23619624

LeGay, Christina M; Boudreau, Colton G; Derksen, Darren J

2013-04-25

339

BIOACCUMULATION AND ENANTIOSELECTIVE BIOTRANSFORMATION OF FIPRONIL AND SELECTED CONAZOLE FUNGICIDES  

EPA Science Inventory

In this research, dietary accumulation and enantioselective biotransformation were determined for rainbow trout (Oncorhynchus mykiss) exposed separately to the phenylpyrazole insecticide fipronil and to a series of selected conazole fungicides. Bioaccumulation of each pesticide ...

340

Enantioselective hydrogenation of ethyl acetoacetate on asymmetric Raney Ni catalysts  

SciTech Connect

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

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

1987-09-10

341

Ni(II)-Bis[(R,R)-N,N'-dibenzylcyclohexane-1,2-diamine]Br2 catalyzed enantioselective Michael additions of 1,3-dicarbonyl compounds to conjugated nitroalkenes.  

PubMed

A highly enantioselective Michael addition of 1,3-dicarbonyl compounds to nitroalkenes has been developed that employs a newly developed Ni(II)-(bis)diamine based catalyst. The reaction scope includes substituted and unsubstituted malonates, beta-ketoesters, and nitroalkenes bearing aromatic and aliphatic residues. Ease of synthesis of this complex is noteworthy. PMID:16011333

Evans, David A; Seidel, Daniel

2005-07-20

342

PDMS based microfluidic chips and their application in material synthesis  

NASA Astrophysics Data System (ADS)

Microfluidics is a highly interdisciplinary science which is to deal with the behavior, control and manipulation of fluids that are constrained to sub-milimeter scale. It incorporates the knowledge and technique intersecting physics, chemistry, mechanics, nanoscience and biotechnology, with practical applications to the design of systems in which small volumes of fluids will be used. In this thesis, we started our research from GER fluid synthesis which then is applied to designing different functions of microfluidic devices, valve, pump, and mixer. We built a way to correlate mechanical signal with electric signal by soft matter. The mechanical devices based GER fluid had good operating stability and mechanical performance. We studied how to improve the performance of GER fluid by increasing the yield stress while avoiding the sendimentation of nanoparticles in GER suspension. The meaning of this work is to enhance the stability and mechanical strength of GER fluid when it is applyed to the microfluidc channels. We tried different oils and studied the particle size for the GER effect. The largest yield stress which amounts to 300 kPa is achievable compared to previous GER fluid with 100 kPa. Microfluidic reactor, directing the flow of microliter volumes along microscale channels, offers the advantages of precise control of reagent loading, fast mixing and an enhanced reaction rate, cessation of the reaction at specific stages, and more. Basically, there are two microfluidic flow regimes, continuous flow and segmented flow (suspended droplets, channel-spanning slug, and wall-wetting films). Both flow regimes offer chemical reaction applications, e.g., continuous flow formation of polymer nanospheres and inorganic nanoparticles, size- and shape-control synthesis by segmented flow, and precipitate-forming reactions in droplets, wherein the segmented flow has gained more popularity in that area. The compartmentalization of segmented flow offers advantages to chemical reactions. Here, we report the microfluidic fabrication of magnetically responsive microsphere, macroporous polymer microspheres and hollow titania microspheres. To prepare magnetically responsive microsphere, we introduced magnetic particles into liquid shell and drug into liquid core. After cross-linking reaction of the shell, we studied the magnetic contraction and extention behavior which induced the drug release efficiency. To prepare porous polymer, the H 2O2 solution was encapsulated in polymer precursor, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H 2O2 decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H2O2-decomposition/polymer precursor polymerization reaction. To prepare hollow titanium gel microspheres, water droplets were first formed by the flow focusing geometry in microfluidic chip and used as a soft template. Then hydrolysis and gelation of titanium alkoxide on the droplet's surface were induced in following serpentine channels, controlled by interface water diffusion. The water diffusion process can be controlled by the amount of the "dewetting" reagent butanol, by which the surface morphology of the titania microspheres can be tuned.

Gong, Xiuqing

343

Marketing: Exploring Applications for Educational Dissemination. Literature Synthesis.  

National Technical Information Service (NTIS)

This synthesis of information about marketing and information dissemination of education-related products is divided into three parts: an overview of major writings, specific marketing strategies, and resources for further study. The first part opens with...

L. Reed

1978-01-01

344

Synthesis and Applications of new Polymer Bound Catalysts.  

National Technical Information Service (NTIS)

Catalysis plays an important role in our world. From drug synthesis to polymer production, the use of catalysts allows society to improve the quality of life. Two important classes of catalysts are based on anions, and phosphoramides. Anionic catalysts pl...

B. M. Fetterly

2005-01-01

345

Applications of NMR spectroscopy to the Study of Zeolite Synthesis.  

National Technical Information Service (NTIS)

NMR spectroscopy is a powerful technique for identifying the structure and concentration of silicate and aluminosilicate anions in gels and solution used for zeolite synthesis. A review is presented of the types of species that have been observed and the ...

A. T. Bell

1989-01-01

346

Recent Applications of Alkene Metathesis in Fine Chemical Synthesis  

Microsoft Academic Search

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies\\u000a used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction\\u000a of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions\\u000a serve, inter alia, as key steps in the synthesis of

Dario Bicchielli; Yannick Borguet; Lionel Delaude; Albert Demonceau; Ileana Dragutan; Valerian Dragutan; Christo Jossifov; Radostina Kalinova; François Nicks; Xavier Sauvage

2010-01-01

347

Synthesis of peptide-oligonucleotide conjugates: application to basic peptides.  

PubMed

Efficient methods of synthesis of peptide-oligonucleotide conjugates are badly needed for studies of uptake into cells in culture. We describe improvements to the procedures involved in "native ligation" conjugation in solution to extend the method to basic peptides. Further, we describe progress in development of a total solid-phase synthesis approach that makes use of a L-homoserine linker as the key reagent for growing of oligonucleotide and peptide chains on a single solid support. PMID:12836310

Stetsenko, D A; Williams, D; Gait, M J

2001-01-01

348

Temperature measurements in arc-discharge synthesis of nanomaterials dedicated for medical applications  

NASA Astrophysics Data System (ADS)

The article presents the plasma synthesis method of carbon nanotubes using an electric arc discharge. In this method different carbon nanotubes are produced as a cathode deposit growth or are deposed on various substrates such as silicon, metals and other materials. The examples of applications of carbon nanotubes in medical applications were presented. Conditions required for the synthesis of carbon nanotubes and process parameters were mentioned. Applications of carbon nanotubes for cancer treatment were discussed. The method of temperature measurement of the arc was described. Contribution to the Topical Issue "13th International Symposium on High Pressure Low Temperature Plasma Chemistry (Hakone XIII)", Edited by Nicolas Gherardi, Henryca Danuta Stryczewska and Yvan Ségui.

Raniszewski, Grzegorz

2013-02-01

349

Asymmetric catalytic alkynylation of acetaldehyde and its application to the synthesis of (+)-tetrahydropyrenophorol  

PubMed Central

By controlling the kinetics of alkynylation over aldolisation (by slowing adding the acceptor), the challenging asymmetric catalytic alkynylation of acetaldehyde has been realized. This protocol yields the corresponding attractive synthons in good to excellent enantiocontrol and shows broad tolerance and applicability. This was highlighted by its application to the synthesis of several natural products such as the rapid construction of the macrocyclic diolide (+)-tetrahydropyrenophorol.

Trost, Barry. M.; Quintard, Adrien

2012-01-01

350

Ceramic transactions: Synthesis and application of lanthanide-doped materials. Volume 67  

SciTech Connect

This document contains reports from the proceedings of the Synthesis and APplications of Lanthanide-Doped ceramics, Crystals, and Glasses Symposium. Topics include the role of lanthanides in optical materials; emissive materials and active waveguides; phosphors and scintillators; and optical and magneto-optical applications. Individual projects have been processed separately for the United States Department of Energy databases.

Potter, B.G. Jr.; Bruce, A.J. [eds.

1996-12-31

351

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

PubMed

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

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

352

Stereoselective Synthesis of Highly Functionalized Cyclopropanes. Application to the Asymmetric Synthesis of (1S,2S)-2,3-Methanoamino Acids.  

PubMed

One-pot palladium(0)-catalyzed alkylation and S(N)(') cyclization of 1,4-dichlorobut-2-ene 1 by the anion of alpha-substituted carbonitriles 2a-d can provide highly functionalized cyclopropanes (E)-4a-d, diastereoselectivity, (de 88-100%). Several attempts to achieve the asymmetric synthesis of the 1-amino-2-ethenylcyclopropanecarbonitrile (E)-9, by means of this new procedure, i.e., using chiral palladium ligands, chiral aminoacetonitriles (-)- and (+)-12 (from 1-hydroxypinanone) or chiral allyl chlorides (4S)-20b-d and (4R)-20e (from (2S) ethyl lactate) have pointed up the reversibility of the palladium-catalyzed cyclization step, responsible for the low enantioselectivity observed (ee 88%) and provided the enantiomerically enriched 1-amino-2-propenylcyclopropanecarbonitrile (E)-22 (ee > 83%) suitable precursor of (1S,2S)-2,3-methanoamino acids. PMID:11674544

Dorizon, Philippe; Su, Guifa; Ludvig, Gitte; Nikitina, Lilyia; Paugam, Renée; Ollivier, Jean; Salaün, Jacques

1999-06-25

353

Discovery of an Escherichia coli esterase with high activity and enantioselectivity toward 1,2-O-isopropylideneglycerol esters.  

PubMed

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

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

2011-07-15

354

Synthesis, characterization, and processing of organic polymers for nonlinear optical applications  

NASA Astrophysics Data System (ADS)

Polyimides possess interesting nonlinear optical properties. The overall goal of our effort is to develop the requisite synthesis and processing techniques to produce polyimides with high (Chi) (3) and low absorptive losses. The target value for many applications is (Chi) (3)/(alpha) equals 10-7 esu-cm. The synthesis and characterization of both the linear and nonlinear optical properties of these materials and the requirements for their utilization in optical bistability is reported.

Druy, Mark A.; Glatkowski, Paul J.; He, Guang S.; Casstevens, Martin K.; Burzynski, Ryszard

1992-04-01

355

n-Type conjugated polymers: advances in synthesis, photophysics, charge transport, and device applications  

Microsoft Academic Search

Our recent studies in the synthesis, photophysics, charge transport, and optoelectronic and electronic device applications of n-type conjugated polymers and oligomers will be presented. Recent synthesis of organic-solvent soluble polyquinolines has facilitated studies of their solution and solid photophysics and fabrication of more efficient light-emitting diodes. For example, large improvements in external efficiencies (2.5 2300 cd\\/m2), and ambient air stability

Samson A. Jenekhe

2002-01-01

356

Ceramic conductors for electrochemical cell applications: new perspectives in materials and synthesis  

Microsoft Academic Search

A great number of compounds with electronic and ionic conductivity and new synthesis routes are being explored for electrochemical applications. In this work, selected examples are described. (a) CaO–TiO2–Fe2O3 materials prepared by combustion synthesis are low cost products with interesting mixed conduction, the electrical behavior of which indicates the existence of a transition, where the grain interior electrical contribution is

J. R Jurado; E Chinarro; M. T Colomer

2000-01-01

357

Synthesis and characterization of ZnO nanowires for nanosensor applications  

Microsoft Academic Search

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650°C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy

O. Lupan; G. A. Emelchenko; V. V. Ursaki; G. Chai; A. N. Redkin; A. N. Gruzintsev; I. M. Tiginyanu; L. Chow; L. K. Ono; B. Roldan Cuenya; H. Heinrich; E. E. Yakimov

2010-01-01

358

Highly Stereoselective Synthesis of 2,6-cis-Substituted Tetrahydropyrans Using a One-Pot Sequential Catalysis.  

PubMed

A catalytic highly diastereo- and enantioselective synthesis of 2,6-cis-substituted tetrahydropyrans was realized using a one-pot sequential catalysis involving Henry and oxa-Michael reactions. The nitroaldol products obtained in a highly enantioselective copper(II)-catalyzed Henry reaction between nitromethane and 7-oxo-hept-5-enals were subsequently treated with a catalytic amount of camphorsulfonic acid (CSA) to give the desired tetrahydropyran derivatives in excellent yields, diastereoselectivities (dr >99:1), and enantioselectivities (ee = 98-99%). The reaction can also be used for the high stereoselective synthesis of a cis-2,6-disubstituted morpholine. PMID:23758096

Dai, Qipu; Rana, Nirmal K; Zhao, John Cong-Gui

2013-06-11

359

A highly enantioselective phosphabicyclooctane catalyst for the kinetic resolution of benzylic alcohols.  

PubMed

A new class of chiral phosphines belonging to the P-aryl-2-phosphabicyclo[3.3.0]octane family (PBO) has been prepared by enantioselective synthesis starting from lactate esters and 2,2-dimethylcyclopentanone enolate 5. A selective enolate alkylation method has been developed for preparation of 9 and 10 using a chelating ester substituent in the triflate alkylating agent 11. Subsequent conversion to the PBO catalysts 2 and 39 relies on a diastereoselective cyclization from the cyclic sulfate 17 and LiPHAr to afford the more hindered endo-aryl phosphines. These phosphines function as efficient catalysts for the kinetic resolutions of aryl alkyl carbinols by benzoylation (16, 21, 22) or iso-butyroylation in the case of the less hindered aryl alkyl carbinol substrates. With o-substituted aryl alkyl carbinols, the enantioselectivities exceed 100, and s = 380 +/- 10 has been demonstrated in the case of methyl mesityl carbinol. The PBO-catalyzed acylations probably involve a P-acylphosphonium carboxylate intermediate and a tightly ion paired transition state. PMID:12670239

Vedejs, Edwin; Daugulis, Olafs

2003-04-01

360

Mechanistic analysis and optimization of the copper-catalyzed enantioselective intramolecular alkene aminooxygenation.  

PubMed

The catalytic asymmetric aminooxygenation of alkenes provides an efficient and straightforward approach to prepare chiral vicinal amino alcohols. We have reported a copper(II)-catalyzed enantioselective intramolecular alkene aminooxygenation, using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as the oxygen source, which results in the synthesis of chiral indolines and pyrrolidines. Herein we disclose that kinetics studies indicate the reaction is first order both in substrate and the [Cu(R,R)-Ph-bis(oxazoline)]OTf(2) catalyst and zero order in TEMPO. Furthermore, kinetic isotope effect studies support that the cis-aminocupration step, the addition of N-Cu across the alkene, is the rate-limiting step. Subsequent formation of a carbon radical intermediate and direct carbon radical trapping with TEMPO is the indicated mechanism for the C-O bond formation as suggested by a deuterium labeling experiment. A ligand screen revealed that C(4)-phenyl substitution on the bis(oxazoline) is optimal for high asymmetric induction. The size of the substrate's N-sulfonyl group also influences the enantioselectivity of the reaction. The preparative-scale catalytic aminooxygenation reaction (gram scale) was demonstrated, and an unexpected dependence on reaction temperature was uncovered on the larger scale reaction. PMID:23244027

Paderes, Monissa C; Keister, Jerome B; Chemler, Sherry R

2012-12-28

361

Concise synthesis of anti-HIV-1 active (+)-inophyllum B and (+)-calanolide A by application of (-)-quinine-catalyzed intramolecular oxo-Michael addition.  

PubMed

(-)-Quinine-catalyzed intramolecular oxo-Michael addition (IMA) of 7-hydroxy-5-methoxy-8-tigloylcoumarins was developed for the enantioselective construction of 2,3-dimethyl-4-chromanone systems in the context of the asymmetric synthesis of anti-HIV-1 active Calophyllum coumarins. Combination of the IMA and MgI(2)-assisted demethylation of the 5-methoxy group along with isomerization of the formed chromanone systems as key steps successfully led to the concise synthesis of (+)-inophyllum B and (+)-calanolide A, possible candidates for AIDS drugs. Further examination of the asymmetric IMA with cinchona alkaloids lacking a methoxy group on the quinoline skeleton suggested the influence of the methoxy substituent on stereoselectivity at the stereogenic centers of the chromanone systems. PMID:15074925

Sekino, Etsuko; Kumamoto, Takuya; Tanaka, Tomohiro; Ikeda, Tomoko; Ishikawa, Tsutomu

2004-04-16

362

Synthesis and applications of bioinspired inorganic nanostructured materials  

NASA Astrophysics Data System (ADS)

Although the study of biominerals may be traced back many centuries, it is only recently that biological principles have been applied to synthetic systems in processes termed "biomimetic" and "bioinspired" to yield materials syntheses that are otherwise not possible and may also reduce the expenditure of energy and/or eliminate toxic byproducts. Many investigators have taken inspiration from interesting and unusual minerals formed by organisms, in a process termed biomineralisation, to tailor the nanostructure of inorganic materials not necessarily found biogenically. However, the fields of nanoparticle synthesis and biomineralisation remain largely separate, and this thesis is an attempt to apply new studies on biomineralisation to nanomaterials science. Principally among the proteins that influence biomineralisation is a group comprised largely of negatively charged aspartic acid residues present in serum. This study is an investigation determining the ability of these serum proteins and other anolagous biomolecules to stabilise biologically relevant amorphous minerals and influence the formation of a variety of materials at the nanoscale. Three different materials were chosen to demonstrate this effect; gold was templated into nanosized single crystals by the action of bioorganic molecules, and the utility of these nanoparticles as a biosensor was explored. The influence of bioorganic molecules on the phase selection and crystal size restriction of titanium dioxide, an important semiconductor with many applications, was explored. The use of bioorganically derived nanoparticles of titanium dioxide was then demonstrated as a highly efficient photocatalyst. Finally, calcium carbonate, a prevalent biomineral was shown to form highly ordered structures over a variety of length scales and different crystalline polymorphs under the influence of a templating protein. In addition, an alternative route to producing calcium phosphate nanoparticle dispersions by mechanical filtration was explored and use as a transfection vector was optimised in two cell lines. Several significant achievements are presented: (i) the assessment of the relative ability of serum, serum derived proteins and their analogues to stabilize the amorphous state, (ii) the formation of single crystalline gold templated by an antibody, (iii) the formation of highly photocatalytically active nanoparticulate anatase by a phosphorylated cyclic esther, (iv) the formation of conical structures at the air liquid interface by the templating ability of a protein and (v) the optimisation of calcium phosphate nanoparticle mediated transfection in two cell lines by mechanical filtration.

Bassett, David C.

363

Chemically functionalized gold nanoparticles: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

This thesis focuses on the development and application of gold nanoparticle based detection systems and biomimetic structures. Each class of modified nanoparticle has properties that are defined by its chemical moieties that interface with solution and the gold nanoparticle core. In Chapter 2, a comparison of the biomolecular composition and binding properties of various preparations of antibody oligonucleotide gold nanoparticle conjugates is presented. These constructs differed significantly in terms of their structure and binding properties. Chapter 3 reports the use of electroless gold deposition as a light scattering signal enhancer in a multiplexed, microarray-based scanometric immunoassay using the gold nanoparticle probes evaluated in Chapter 2. The use of gold development results in greater signal enhancement than the typical silver development, and multiple rounds of metal development were found to increase the resulting signal compared to one development. Chapter 4 describes an amplified scanometric detection method for human telomerase activity. Gold nanoparticles functionalized with specific oligonucleotide sequences can efficiently capture telomerase enzymes and subsequently be elongated. Both the elongated and unmodified oligonucleotide sequences are simultaneously measured. At low telomerase concentrations, elongated strands cannot be detected, but the unmodified sequences, which come from the same probe particles, can be detected because their concentration is higher, providing a novel form of amplification. Chapter 5 reports the development of a novel colorimetric nitrite and nitrate ion assay based upon gold nanoparticle probes functionalized with Griess reaction reagents. This assay takes advantage of the distance-dependent plasmonic properties of the gold nanoparticles and the ability of nitrite ion to facilitate the cross coupling of novel nanoparticle probes. The assay works on the concept of a kinetic end point and can be triggered at the EPA limit for this ion in drinking water. Finally, Chapter 6 describes the synthesis of high density lipoprotein biomimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL and bind free cholesterol with a Kd of 4 nM.

Daniel, Weston Lewis

364

Enantioselective Recognition in Solution: The Case of Countercurrent Chromatography  

NASA Astrophysics Data System (ADS)

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

Rubio, Núria; Minguillón, Cristina

365

Asymmetric, stereocontrolled total synthesis of paraherquamide A.  

PubMed

The first total synthesis of paraherquamide A, a potent anthelmintic agent isolated from various Penicillium sp. with promising activity against drug-resistant intestinal parasites, is reported. Key steps in this asymmetric, stereocontrolled total synthesis include a new enantioselective synthesis of alpha-alkylated-beta-hydroxyproline derivatives to access the substituted proline nucleus and a highly diastereoselective intramolecular S(N)2' cyclization to generate the core bicyclo[2.2.2]diazaoctane ring system. PMID:14519003

Williams, Robert M; Cao, Jianhua; Tsujishima, Hidekazu; Cox, Rhona J

2003-10-01

366

Enhanced enantioselectivity of chiral hydrogenation catalysts after immobilisation in thin films of ionic liquid  

Microsoft Academic Search

Chiral organometallic complexes were immobilized in silica supported thin films of ionic liquid. The heterogenized catalysts were tested in the hydrogenation of acetophenone, which was chosen as test reaction for the enantioselective reduction of prochiral ketones. High enantioselectivities (up to 74% ee) were achieved in supported ionic liquids using a catalyst\\/substrate pair, which showed no enantioselectivity in methanol. This is

Kam Loon Fow; Stephan Jaenicke; Thomas E. Müller; Carsten Sievers

2008-01-01

367

Total synthesis of (-)-teucvidin.  

PubMed

A concise enantioselective synthesis of (-)-teucvidin has been achieved. Our synthetic strategy involved the diastereoselective Michael/Conia-ene cascade cyclization reaction for rapid establishment of the cis-decalin skeleton with three new stereogenic centers in one pot (72%, single diastereomer), the epoxidation/dealkoxycarbonylation protocol for construction of the fused furanone moiety, and the O-allylation/Claisen rearrangement protocol for construction of the all-carbon quaternary center at C9 of the clerodane skeleton. PMID:22594711

Liu, Xiaozu; Lee, Chi-Sing

2012-05-17

368

Marketing: Exploring Applications for Educational Dissemination. Literature Synthesis.  

ERIC Educational Resources Information Center

|This synthesis of information about marketing and information dissemination of education-related products is divided into three parts: an overview of major writings, specific marketing strategies, and resources for further study. The first part opens with a definition of marketing as it relates to education. A review of the literature provides…

Reed, Linda

369

Triaxial Burke-Schumann Flames with Applications to Flame Synthesis  

Microsoft Academic Search

The problem of a flame generated by three coaxial flows is solved by extending the Burke-Schumann methodology to include a third stream. The solution is particularly relevant to flame synthesis wherein multiple tubes are often employed either to introduce inert as a diffusion barrier or to introduce more than two reactants. The general problem is solved where the inner and

B. H. CHAO; R. L. AXELBAUM

2000-01-01

370

Design, synthesis, and evaluation of materials for microelectronics applications  

Microsoft Academic Search

The advancement of the microelectronics industry is heavily dependent on the design, synthesis, and integration of new materials. Non-chemically amplified photoresists (NCAR) consist of a base resin and photoactive additive which inhibits the dissolution of the this resin. The robustness of NCARs has made them well suited to the unique material requirements of the photomask making industry for many years.

William Hoy Heath

2006-01-01

371

New asymmetrical per-substituted cyclodextrins (2- O-methyl-3- O-ethyl- and 2- O-ethyl-3- O-methyl-6- O- t-butyldimethylsilyl-?-derivatives) as chiral selectors for enantioselective gas chromatography in the flavour and fragrance field  

Microsoft Academic Search

Asymmetrically substituted 6I-VII-O-t-butyldimethylsilyl(TBDMS)-3I-VII-O-ethyl-2I-VII-O-methyl-?-cyclodextrin (MeEt-CD) and 6I-VII-O-TBDMS-2I-VII-O-ethyl-3I-VII-O-methyl-?-cyclodextrin (EtMe-CD) were synthesised to evaluate the role of the substitution pattern in positions 2 and 3 on the enantioselectivity, in particular in view of their application to routine analysis in fast enantioselective gas chromatography (Es-GC). The chromatographic properties and enantioselectivities of the new derivatives were tested by separating the enantiomers of a series of

Carlo Bicchi; Cecilia Cagliero; Erica Liberto; Barbara Sgorbini; Katia Martina; Giancarlo Cravotto; Patrizia Rubiolo

2010-01-01

372

Wet Chemical Synthesis and Screening of Thick Porous Oxide Films for Resistive Gas Sensing Applications  

Microsoft Academic Search

A method of wet chemical synthesis suitable for high throughput and combinatorial applications has been developed for the synthesis of porous resistive thick- film gas sensors. This method is based on the robot-controlled application of unstable metal oxide suspensions on an array of 64 inter-digital electrodes positioned on an Al2O3 substrate. SnO2, WO3, ZrO2, TiO2, CeO2, In2O3 and Bi2O3 were

Gerald Frenzer; Andreas Frantzen; Daniel Sanders; Ulrich Simon; Wilhelm F. Maier

2006-01-01

373

Synthesis and applications of biomedical and pharmaceutical polymers via click chemistry methodologies.  

PubMed

In this review, the synthesis and application of biomedical and pharmaceutical polymers synthesized via the copper(I)-catalyzed alkyne-azide cycloaddition, the thiol-ene reaction, or a combination of both click reactions are discussed. Since the introduction of both "click" methods, numerous articles have disclosed new approaches for the synthesis of polymers with different architectures, e.g., block and graft copolymers, dendrimers, and hydrogels, for pharmaceutical and biomedical applications. By describing selected examples, an overview is given of the possibilities and limitations that these two "click" methods may offer. PMID:19606898

van Dijk, Maarten; Rijkers, Dirk T S; Liskamp, Rob M J; van Nostrum, Cornelus F; Hennink, Wim E

2009-11-01

374

Synthesis, functionalisation and characterisation of mesoporous materials and sol–gel glasses for applications in catalysis, adsorption and photonics  

Microsoft Academic Search

In this review, synthesis and functionalisation approaches for ordered mesoporous materials and sol–gel glasses are described. Catalytic and adsorption applications are emphasised for the ordered mesoporous materials, while optical applications are the focus for sol–gel glasses.

Gisle Øye; Wilhelm R. Glomm; Torbjørn Vrålstad; Sondre Volden; Heléne Magnusson; Michael Stöcker; Johan Sjöblom

2006-01-01

375

Enantioselectivity in Candida antarctica lipase B: A molecular dynamics study  

PubMed Central

A major problem in predicting the enantioselectivity of an enzyme toward substrate molecules is that even high selectivity toward one substrate enantiomer over the other corresponds to a very small difference in free energy. However, total free energies in enzyme-substrate systems are very large and fluctuate significantly because of general protein motion. Candida antarctica lipase B (CALB), a serine hydrolase, displays enantioselectivity toward secondary alcohols. Here, we present a modeling study where the aim has been to develop a molecular dynamics-based methodology for the prediction of enantioselectivity in CALB. The substrates modeled (seven in total) were 3-methyl-2-butanol with various aliphatic carboxylic acids and also 2-butanol, as well as 3,3-dimethyl-2-butanol with octanoic acid. The tetrahedral reaction intermediate was used as a model of the transition state. Investigative analyses were performed on ensembles of nonminimized structures and focused on the potential energies of a number of subsets within the modeled systems to determine which specific regions are important for the prediction of enantioselectivity. One category of subset was based on atoms that make up the core structural elements of the transition state. We considered that a more favorable energetic conformation of such a subset should relate to a greater likelihood for catalysis to occur, thus reflecting higher selectivity. The results of this study conveyed that the use of this type of subset was viable for the analysis of structural ensembles and yielded good predictions of enantioselectivity.

Raza, Sami; Fransson, Linda; Hult, Karl

2001-01-01

376

Enantioselective separations using chiral supported liquid crystalline membranes.  

PubMed

Porous and nonporous supported liquid crystalline membranes were produced by impregnating porous cellulose nitrate supports with cholesteric liquid crystal (LC) materials consisting of 4-cyano-4'-pentylbiphenyl (5CB) mixed with a cholesterol-based dopant (cholesteryl oleyl carbonate [COC], cholesteryl nonanoate [CN], or cholesteryl chloride [CC]). The membranes exhibit selectivity for R-phenylglycine and R-1-phenylethanol because of increased interactions between the S enantiomers and the left-handed cholesteric phase. The selectivity of both phenylglycine and 1-phenylethanol in 5CB/CN membranes decreases with effective pore diameter while the permeabilities increase, as expected. Phenylglycine, which is insoluble in the LC phase, exhibits no transport in the nonporous (completely filled) membranes; however, 1-phenylethanol, which is soluble in the LC phase, exhibits transport but negligible enantioselectivity. The enantioselectivity for 1-phenylethanol was higher (1.20 in 5CB/COC and 5CB/CN membranes) and the permeability was lower in the cholesteric phase than in the isotropic phase. Enantioselectivity was also higher in the 5CB/COC cholesteric phase than in the nematic phase of undoped 5CB (1.03). Enantioselectivity in the cholesteric phase of 5CB doped with CC (1.1), a dopant lacking hydrogen bonding groups, was lower than in the 5CB/COC phases. Finally, enantioselectivity increases with the dopant concentration up to a plateau value at approximately 17 mol%. PMID:22581655

Han, Sangil; Rabie, Feras; Marand, Eva; Martin, Stephen M

2012-05-12

377

Interspecies differences in the enantioselectivity of epoxide hydrolases in Cryptococcus laurentii (Kufferath) C.E. Skinner and Cryptococcus podzolicus (Bab'jeva & Reshetova) Golubev.  

PubMed

Isolates representing Cryptococcus laurentii and Cryptococcus podzolicus, originating from soil of a heathland indigenous to South Africa, were screened for the presence of enantioselective epoxide hydrolases for 2,2-disubstituted epoxides. Epoxide hydrolase activity for the 2,2-disubstituted epoxide (+/-)-2-methyl-2-pentyl oxirane was found to be abundantly present in all isolates. The stereochemistry of the products formed by the epoxide hydrolase enzymes from isolates belonging to the two species (11 isolates representing C. laurentii and 23 isolates representing C. podzolicus) was investigated. The enantiopreferences of the epoxide hydrolases for 2,2-disubstituted epoxides of these two species were found to be opposite. All strains of C. laurentii preferentially hydrolysed the (S)-epoxides while all C. podzolicus isolates preferentially hydrolysed the (R)-epoxides of (+/-)-2,2-disubstituted epoxides. These findings indicate that the stereochemistry of the products formed from 2,2-disubstituted epoxides by the epoxide hydrolase enzymes of these yeasts should be evaluated as additional taxonomic criterion within the genus Cryptococcus. Also, the selectivity of some epoxide hydrolases originating from isolates of C. podzolicus was high enough to be considered for application in biotransformations for the synthesis of enantiopure epoxides and vicinal diols. PMID:15709362

Botes, Adriana L; Lotter, Jeanette; Rhode, Owen H J; Botha, Alfred

2005-01-01

378

Directed hydrogenation of acyclic homoallylic alcohols: enantioselective syntheses of (+)- and (-)-laurenditerpenol.  

PubMed

Laurenditerpenol is the first marine natural product shown to inhibit hypoxia-inducible factor 1 (HIF-1) activation. Preclinical studies support that the inhibition of HIF-1 is one of the molecular targets for antitumor drug discovery. The synthetically challenging molecular architecture of laurenditerpenol, its absolute stereostructure, and the biological activity of several diastereoisomers were accomplished by our group in 2007 by diastereoselective synthesis. Herein, we report enantioselective syntheses of both enantiomers of laurenditerpenol involving sequential Michael addition and remote homoallylic hydroxyl group-directed asymmetric hydrogenation at ambient temperature and pressure as key reaction steps. The current approach is elegant and overall more efficient than the ones previously reported in the literature. PMID:23985032

Chittiboyina, Amar G; Peddikotla, Prabhakar; Avery, Mitchell A; Khan, Ikhlas A

2013-09-11

379

The application of green chemistry methods in organophosphorus synthesis  

NASA Astrophysics Data System (ADS)

Data concerning the synthesis of organophosphorus compounds in ionic liquids, in water and under solvent-free conditions are considered and summarized. It is shown that this strategy, which complies with the definition of green chemistry, has advantages in terms of the rate of the process and the yields of target products as compared with syntheses in common organic solvents. The Wittig, Horner-Wadsworth-Emmons, Kabachnik-Fields, Arbuzov and Michaelis reactions are considered as examples. The bibliography includes 178 references.

Odinets, Irina L.; Matveeva, E. V.

2012-03-01

380

A fluorous phosphate protecting group with applications to carbohydrate synthesis.  

PubMed

The first fluorous protecting group for phosphate is reported. This group can be used as a facile tag for purification and be removed under mild reducing conditions using zinc and ammonium formate. Synthesis of a disaccharide from Leishmania using this fluorous protecting group demonstrated the group's stability to the acidic conditions necessary for glycosylation as well as its orthogonality to several other common protecting groups. PMID:21384825

Liu, Lin; Pohl, Nicola L B

2011-03-08

381

Synthesis, Characterization, and Applications of Hemifluorinated Dibranched Amphiphiles  

PubMed Central

Here we describe the synthesis, the physicochemical and preliminary pharmaceutical assessment of a novel class of hemifluorinated dibranched derivatives (M1diHxFy). These novel compounds have the remarkable ability of completely stopping the Ostwald ripening commonly associated with nanoemulsions. The developed synthesis is modular and it allows easy incremental structural variations in the fluorophilic (fluorous chains)-, lipophilic (alkyl spacer head)- and hydrophilic (polar head) domains. Furthermore, the synthesis can be easily scaled-up and highly pure compounds can be readily obtained through silica gel and fluoro-silica gel column chromatography, without any need to use HPLC or other time-consuming techniques. Surface properties like micelle formation, critical aggregation concentration (CAC) and emulsion stability studies demonstrated the different behavior of dibranched hemifluorinated surfactant (M1diHxFy) with respect to that of single chain semifluorinated analogues (MzFy). Remarkably, the new polymer M1diH3F8 drastically slowed the ripening of nanoemulsions of the commonly used fluorinated anesthetic sevoflurane over a period of more than one year. During this time, the nanodroplet size did not increase to more than 400 nm. This result is very promising for inducing and maintaining general anesthesia through intravenous delivery of volatile anesthetics, eliminating the need for the use of large and costly vaporizers in the operating room.

Parlato, Maria Cristina; Jee, Jun-Pil; Teshite, Motti; Mecozzi, Sandro

2011-01-01

382

Synthesis, characterization, and applications of hemifluorinated dibranched amphiphiles.  

PubMed

Here we describe the synthesis and the physicochemical and preliminary pharmaceutical assessment of a novel class of hemifluorinated dibranched derivatives: M(1)diH(x)F(y). These compounds have the remarkable ability to completely stop the Ostwald ripening commonly associated with nanoemulsions. The developed synthesis is modular and allows easy incremental structural variations in the fluorophilic (fluorous chains), lipophilic (alkyl spacer head), and hydrophilic (polar head) domains. Furthermore, the synthesis can be easily scaled up and highly pure compounds can be readily obtained through silica gel and fluoro-silica gel column chromatography, without any need to use HPLC or other time-consuming techniques. Surface properties such as micelle formation, critical aggregation concentration (CAC), and emulsion stability studies demonstrated the different behavior of the dibranched hemifluorinated surfactant M(1)diH(x)F(y) with respect to that of single-chain semifluorinated analogues M(z)F(y). Remarkably, the new polymer M(1)diH(3)F(8) drastically slowed the ripening of nanoemulsions of the commonly used fluorinated anesthetic sevoflurane over a period of more than 1 year. During this time, the nanodroplet size did not increase to more than 400 nm. This result is very promising for inducing and maintaining general anesthesia through intravenous delivery of volatile anesthetics, eliminating the need for the use of large and costly vaporizers in the operating room. PMID:21736353

Parlato, Maria Cristina; Jee, Jun-Pil; Teshite, Motti; Mecozzi, Sandro

2011-07-21

383

Enantioselective cyclizations of silyloxyenynes catalyzed by cationic metal phosphine complexes.  

PubMed

The discovery of complementary methods for enantioselective transition metal-catalyzed cyclization with silyloxyenynes has been accomplished using chiral phosphine ligands. Under palladium catalysis, 1,6-silyloxyenynes bearing a terminal alkyne led to the desired five-membered ring with high enantioselectivities (up to 91% ee). As for reactions under cationic gold catalysis, 1,6- and 1,5-silyloxyenynes bearing an internal alkyne furnished the chiral cyclopentane derivatives with excellent enantiomeric excess (up to 94% ee). Modification of the substrate by incorporating an ?,?-unsaturation led to the discovery of a tandem cyclization. Remarkably, using silyloxy-1,3-dien-7-ynes under gold catalysis conditions provided the bicyclic derivatives with excellent diastereo- and enantioselectivities (up to >20:1 dr and 99% ee). PMID:22296571

Brazeau, Jean-François; Zhang, Suyan; Colomer, Ignacio; Corkey, Britton K; Toste, F Dean

2012-01-31

384

Synthesis of C1-symmetric chiral secondary diamines and their applications in the asymmetric copper(II)-catalyzed Henry (nitroaldol) reactions.  

PubMed

A small library of C(1)-symmetric chiral diamines (L1-L9) was constructed via condensing exo-(-)-bornylamine or (+)-(1S,2S,5R)-menthylamine with various Cbz-protected amino acids. Among them, ligand L1/CuCl(2)·2H(2)O complex (2.5 mol %) shows outstanding catalytic efficiency for Henry reaction between a variety of aldehydes and nitroalkanes to afford the expected products in high yields (up to 98%) with excellent enantioselectivities (up to 99%) and moderate to good diastereoselectivities (up to 90:10). This process is air- and moisture tolerant and has been applied to the synthesis of (S)-2-amino-1-(3,4-dimethoxyphenyl)ethanol (9), a key intermediate for (S)-epinephrine and (S)-norepinephrine. On the basis of HRMS and X-ray diffraction analysis of the L1/CuCl(2) complex, a transition-state model was proposed to explain the origin of asymmetric induction. The low catalyst loading, excellent yields and enantioselectivities, inexpensive copper salt, and mild reaction conditions make our catalytic system to be practically useful. PMID:21190323

Zhou, Yirong; Dong, Junfang; Zhang, Fanglin; Gong, Yuefa

2010-12-29

385

Application-driven architecture synthesis of on-chip Multiprocessor systems  

Microsoft Academic Search

The exploitation of the rapid growing field of Multiprocessor on chip requires efficient design methodologies and tools. Besides the extraction of task level parallelism, architecture synthesis is of growing importance, in particular for programmable hardware devices, which allow for the reuse of the hardware across applications. Using programmable devices to implement on-chip multiprocessor systems, the architecture of the computing and

Christophe Bobda; Philipp Mahr; Benjamin Andres; Harold Ishebabi

2010-01-01

386

Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials  

Microsoft Academic Search

This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is

Sutthira Sutthasupa; Masashi Shiotsuki; Fumio Sanda

2010-01-01

387

Synthesis and Surface Modification of Poly (dimethylsiloxane) - Gold Nanocomposite Films for Biosensing Applications  

Microsoft Academic Search

Gold - poly(dimethylsiloxane) (Au - PDMS) nanocomposite freestanding films were prepared and used to study the binding of Human Serum Albumin (HSA) to polyclonal anti-HSA. A new method of synthesis was developed for sensing application when most of the gold nanoparticles have to be localized in the surface layer. The localized surface plasmon resonance band in gold nanoparticles is used

Pooja Devi; Alaa Yahya Mahmoud; Simona Badilescu; Muthukumaran Packirisamy; P. Jeevanandam; Vo-Van Truong

2010-01-01

388

On an Application of Dynamic Programming to the Synthesis of Logical Systems  

Microsoft Academic Search

In this paper we wish to initiate the study of the application of dynamic programming to the domain of problems arising in the synthesis of logical systems.In a number of fields one encounters the problem of converting a system in one state into another state in a most efficient fashion—in mathematical economics, in the theory of control processes, in network

Richard Bellman; John H. Holland; Robert Kalaba

1959-01-01

389

Magnetic nanoparticles and concentrated magnetic nanofluids: Synthesis, properties and some applications  

Microsoft Academic Search

This paper reviews some recent results concerning chemical synthesis of magnetic nanoparticles and preparation of various types of magnetic nanofluids. Structural properties and behaviour in external magnetic field of magnetic nanofluids will be emphasized with relation to their use in leakage-free rotating seals and in biomedical applications.

Ladislau Vékás; Doina Bica; Mikhail V. Avdeev

2007-01-01

390

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two ? position(s) of a carbonyl group) with high diastereo- and enantioselectivities. PMID:23828817

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-07-04

391

Enantioselective Properties of Nucleic Acid Aptamer Molecular Recognition Elements  

NASA Astrophysics Data System (ADS)

Target-specific chiral selectors, which are characterized by a predictable elution order depending on the target enantiomer employed for the selection of the chiral selector, have recently received much attention in the enantioselective analysis field. In this context, bioaffinity-based molecular recognition tools such as nucleic acid aptamers have notably demonstrated very attractive features for the chiral discrimination of active molecules. In this chapter, the enantioselective properties of aptamer chiral selectors and the major factors that control and modulate the liquid chromatography and capillary electrophoresis enantiomer separation are addressed.

Peyrin, Eric

392

Aminopyridine-benzoxanthene enantioselective receptor for sulfonylamino acids.  

PubMed

Combination of a cis-tetrahydrobenzoxanthene skeleton with a benzoxazole and an amidopyridine provides an enantioselective receptor for sulfonylamino acids with chiral recognitions of up to 18. The structure of the complex between receptor 1 and the leucine triflate is known by X-ray analysis. The receptor racemic mixture can be suitably resolved through crystalization in the presence of leucine triflate as guest. Receptor 1 can be used for the enantioselective extraction of sulfonylamino acids from aqueous solutions of their salts. PMID:15040746

Oliva, Ana I; Simón, Luis; Muñiz, Francisco M; Sanz, Francisca; Morán, Joaquín R

2004-04-01

393

Synthesis of pipelined memory access controllers for streamed data applications on FPGA-based computing engines  

Microsoft Academic Search

Commercially available behavioral synthesis tools do not adequately support FPGA vendor-specific external memory interfaces making it extremely difficult to exploit pipelined memory access modes as well as application specific memory operations scheduling critical for high-performance solutions. This lack of support substantially increases the complexity and the burden on designers in the mapping of applications to FPGA-based computing engines. In this

Pedro C. Diniz

2001-01-01

394

Synthesis of Complex Plasmonic Nanostructures for Applications in Surface-Enhanced Raman Spectroscopy and Biomedicine  

Microsoft Academic Search

This research centers around techniques to engineer the properties of noble-metal nanostructures for applications in surface-enhanced Raman spectroscopy (SERS) and biomedicine. Many of these potential applications are made possible by the strong localized surface plasmon resonance (LSPR) of noble-metal nanostructures, which is heavily influenced by the particle's morphology. The first part of this work focuses on the solution-phase synthesis of

Claire Cobley

2010-01-01

395

Application of Chemoenzymatic Hydrolysis in the Synthesis of 2-Monoacylglycerols  

PubMed Central

The selective biocatalyzed synthesis of 2-monoacylglycerols (2-MAGs) through the use of commercially available immobilized Candida antarctica (Novozym435) and Rhizomucor miehei is explored. Reactions at room temperature result in the formation of a 2-MAG and a corresponding ethyl ester of the fatty acid with immobilized Candida antarctica within 2h with yields ranging from 36%–83%. Similar reaction conditions with immobilized Rhizomucor miehei yielded exclusively the 2-MAG after 24h with yields ranging from 37% to 88%. Yields vary on the acyl group at the sn-2 position and choice of enzyme involved.

Whitten, Kyle M.; Makriyannis, Alexandros; Vadivel, Subramanian K.

2012-01-01

396

Application of Chemoenzymatic Hydrolysis in the Synthesis of 2-Monoacylglycerols.  

PubMed

The selective biocatalyzed synthesis of 2-monoacylglycerols (2-MAGs) through the use of commercially available immobilized Candida antarctica (Novozym435) and Rhizomucor miehei is explored. Reactions at room temperature result in the formation of a 2-MAG and a corresponding ethyl ester of the fatty acid with immobilized Candida antarctica within 2h with yields ranging from 36%-83%. Similar reaction conditions with immobilized Rhizomucor miehei yielded exclusively the 2-MAG after 24h with yields ranging from 37% to 88%. Yields vary on the acyl group at the sn-2 position and choice of enzyme involved. PMID:22822273

Whitten, Kyle M; Makriyannis, Alexandros; Vadivel, Subramanian K

2012-05-01

397

Group 4 ketimide complexes: Synthesis, reactivity and catalytic applications  

Microsoft Academic Search

The synthesis and reactivity of Group 4 ketimide complexes, comprising bent-metallocene, half-sandwich and cyclopentadienyl-free compounds is described. Neutral compounds of general formulas Cp2?M(NCR1R2)X and Cp2?M(NCR1R2)2 have been prepared by transmetallation reactions of metal halide derivatives with appropriate lithium, tin or silicon ketimide derivatives and by acid–base reactions between ketimines and anionic ligands attached to the metals. Ti(III) and cationic M(IV)

M. J. Ferreira; A. M. Martins

2006-01-01

398

An N-Heterocyclic Carbene/Lewis Acid Strategy for the Stereoselective Synthesis of Spirooxindole Lactones  

PubMed Central

A cooperative catalysis approach for the enantioselective formal [3+2] addition of ?,?-unsaturated aldehydes to isatins has been developed. The N-heterocyclic carbene (NHC)-catalyzed homoenolate annulations of ?-aryl enals require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation provides efficient access to the 3-hydroxy indole skeleton and has been applied to the first eantioselective total synthesis of maremycin B.

Dugal-Tessier, Julien; O'Bryan, Elizabeth A.; Schroeder, Thomas B. H.; Cohen, Daniel T.

2012-01-01

399

Synthesis and characterization of semiconductor nanomaterials for thermoelectric applications  

NASA Astrophysics Data System (ADS)

In this dissertation, I explore simple chemical means to produce various nanomaterials. In Chapter 2, the synthesis of size-tuned bismuth telluride nanoparticles is discussed. The solution phase synthesis of bismuth telluride nanoparticles has been accomplished in the presence of a library of thiols as the capping ligand. These crystalline nanostructures range in size from ˜20 to ˜100nm with a relatively narrow size dispersity. Size and shape of the resulting nanostructures has been investigated as a function of chain length of the thiol and temperature. An investigation into the thermoelectric properties of the nanostructures shows promising electrical conductivity, thermopower, and thermal conductivity for undoped bismuth telluride. In Chapter 3, a soluble precursor for antimony telluride is described. This precursor was used to fabricate semiconductor nanowires of varying diameter and thin films through simple templating methods. Electrical conductivity and thermoelectric power measurements of these films are only slightly lower than for antimony telluride films fabricated by vacuum deposition. In Chapter 4, the polytetrafluoroethylene (PTFE)/metal nanocomposites are discussed. Palladium and nickel PTFE nanocomposites were made by impregnation of the polymer with metal acetates. Annealing and jet blowing of these materials form PTFE nanofiber/metal nanoparticle composites.

Dirmyer, Matthew R.

400

Synthesis, properties, and applications of magnetic iron oxide nanoparticles  

Microsoft Academic Search

Magnetic nanoparticles exhibit many interesting properties that can be exploited in a variety of applications such as catalysis and in biomedicine. This review discusses the properties, applications, and syntheses of three magnetic iron oxides – hematite, magnetite, and maghemite – and outlines methods of preparation that allow control over the size, morphology, surface treatment and magnetic properties of their nanoparticles.

Amyn S. Teja; Pei-Yoong Koh

2009-01-01

401

Occurrence, synthesis and medical application of bacterial polyhydroxyalkanoate  

Microsoft Academic Search

Polyhydroxyalkanoates (PHAs) comprise a large class of polyesters that are synthesized by many bacteria as an intracellular carbon and energy compound. Analysis of isolated PHAs reveal interesting properties such as biodegradability and biocompatibility. Research was focused only recently on the application of PHA in implants, scaffolds in tissue engineering, or as drug carriers. Such applications require that PHA be produced

Manfred Zinn; Bernard Witholt; Thomas Egli

2001-01-01

402

AUTOMATION FOR THE SYNTHESIS AND APPLICATION OF PET RADIOPHARMACEUTICALS  

Microsoft Academic Search

The development of automated systems supporting the production and application of PET radiopharmaceuticals has been an important focus of researchers since the first successes of using carbon-11 (Comar et al., 1979) and fluorine-18 (Reivich et al., 1979) labeled compounds to visualize functional activity of the human brain. These initial successes of imaging the human brain soon led to applications in

Alexoff

2001-01-01

403

Facile synthesis and application of a carbon foam with large mesopores.  

PubMed

By combining elements of hard- and soft-templating, a facile synthesis method for carbon foams with large mesopores has been demonstrated. A commercial Pluronic surfactant was used as the structure-directing agent as well as the carbon precursor. No micelle swelling agent or post treatment is necessary to enlarge mesopores. As such this method requires fewer synthesis steps and is highly scalable. The as-synthesized meso-carbons showed potential applications in the fields of carbon oxide capture and lithium-sulfur batteries. PMID:24121594

Fu, Liling; Qi, Genggeng; Sahore, Ritu; Sougrat, Rachid; Disalvo, Francis J; Giannelis, Emmanuel P

2013-10-23

404

Substrate Specificity and Enantioselectivity of 4-Hydroxyacetophenone Monooxygenase  

PubMed Central

The 4-hydroxyacetophenone monooxygenase (HAPMO) from Pseudomonas fluorescens ACB catalyzes NADPH- and oxygen-dependent Baeyer-Villiger oxidation of 4-hydroxyacetophenone to the corresponding acetate ester. Using the purified enzyme from recombinant Escherichia coli, we found that a broad range of carbonylic compounds that are structurally more or less similar to 4-hydroxyacetophenone are also substrates for this flavin-containing monooxygenase. On the other hand, several carbonyl compounds that are substrates for other Baeyer-Villiger monooxygenases (BVMOs) are not converted by HAPMO. In addition to performing Baeyer-Villiger reactions with aromatic ketones and aldehydes, the enzyme was also able to catalyze sulfoxidation reactions by using aromatic sulfides. Furthermore, several heterocyclic and aliphatic carbonyl compounds were also readily converted by this BVMO. To probe the enantioselectivity of HAPMO, the conversion of bicyclohept-2-en-6-one and two aryl alkyl sulfides was studied. The monooxygenase preferably converted (1R,5S)-bicyclohept-2-en-6-one, with an enantiomeric ratio (E) of 20, thus enabling kinetic resolution to obtain the (1S,5R) enantiomer. Complete conversion of both enantiomers resulted in the accumulation of two regioisomeric lactones with moderate enantiomeric excess (ee) for the two lactones obtained [77% ee for (1S,5R)-2 and 34% ee for (1R,5S)-3]. Using methyl 4-tolyl sulfide and methylphenyl sulfide, we found that HAPMO is efficient and highly selective in the asymmetric formation of the corresponding (S)-sulfoxides (ee >?99%). The biocatalytic properties of HAPMO described here show the potential of this enzyme for biotechnological applications.

Kamerbeek, Nanne M.; Olsthoorn, Arjen J. J.; Fraaije, Marco W.; Janssen, Dick B.

2003-01-01

405

Substrate specificity and enantioselectivity of 4-hydroxyacetophenone monooxygenase.  

PubMed

The 4-hydroxyacetophenone monooxygenase (HAPMO) from Pseudomonas fluorescens ACB catalyzes NADPH- and oxygen-dependent Baeyer-Villiger oxidation of 4-hydroxyacetophenone to the corresponding acetate ester. Using the purified enzyme from recombinant Escherichia coli, we found that a broad range of carbonylic compounds that are structurally more or less similar to 4-hydroxyacetophenone are also substrates for this flavin-containing monooxygenase. On the other hand, several carbonyl compounds that are substrates for other Baeyer-Villiger monooxygenases (BVMOs) are not converted by HAPMO. In addition to performing Baeyer-Villiger reactions with aromatic ketones and aldehydes, the enzyme was also able to catalyze sulfoxidation reactions by using aromatic sulfides. Furthermore, several heterocyclic and aliphatic carbonyl compounds were also readily converted by this BVMO. To probe the enantioselectivity of HAPMO, the conversion of bicyclohept-2-en-6-one and two aryl alkyl sulfides was studied. The monooxygenase preferably converted (1R,5S)-bicyclohept-2-en-6-one, with an enantiomeric ratio (E) of 20, thus enabling kinetic resolution to obtain the (1S,5R) enantiomer. Complete conversion of both enantiomers resulted in the accumulation of two regioisomeric lactones with moderate enantiomeric excess (ee) for the two lactones obtained [77% ee for (1S,5R)-2 and 34% ee for (1R,5S)-3]. Using methyl 4-tolyl sulfide and methylphenyl sulfide, we found that HAPMO is efficient and highly selective in the asymmetric formation of the corresponding (S)-sulfoxides (ee > 99%). The biocatalytic properties of HAPMO described here show the potential of this enzyme for biotechnological applications. PMID:12514023

Kamerbeek, Nanne M; Olsthoorn, Arjen J J; Fraaije, Marco W; Janssen, Dick B

2003-01-01

406

Natural compounds in the synthesis of chiral organophosphorous ligands  

NASA Astrophysics Data System (ADS)

Methods for the synthesis of chiral organophosphorus compounds based on natural optically active compounds (hydroxy acids, amino acids and their derivatives, mono- and disaccharides, mono- and diterpenoids, steroids) are discussed. Particular attention is given to the synthesis of bisphosphines and bisphosphinites. These compounds serve as ligands for transition metal complexes, which catalyse asymmetric hydrogenation. Data on the enantioselectivity of hydrogenation of unsaturated precursors of amino acids and unsaturated prochiral acids as well as on information on the enantioselectivity of hydrosilylation of ketones are surveyed.

Tolstikov, Alexander G.; Khlebnikova, Tatiana B.; Tolstikova, Olga V.; Tolstikov, Genrikh A.

2003-09-01

407

Handedness Enantioselection of Carbon Nanotubes using Helical Assemblies of Flavin Mononucleotide  

PubMed Central

In order to truly unlock advanced applications of single-walled carbon nanotubes (SWNTs), one needs to separate them according to both chirality and handedness. Here we show that the chiral d-ribityl phosphate chain of flavin mononucleotide (FMN) induces a right-handed helix that enriches the left-handed SWNTs for all suspended (n,m) species. Such enantioselectivity stems from the sp3-hybridization of the N atom anchoring the sugar moiety to the flavin ring. This produces two FMN conformations (syn and anti) analogous to DNA. Electrostatic interactions between the neighboring uracil moiety and the 2?-OH group of the side chain provide greater stability to the anti-FMN conformation that leads to a right-handed FMN helix. The right-handed twist that the FMN helix imposes to the underlying nanotube similar to “Indian burn”, causes diameter dilation of only the left-handed SWNTs, whose improved intermolecular interactions with the overlaying FMN helix, impart enantioselection.

Ju, Sang-Yong; Abanulo, Darlington C.; Badalucco, Christopher A.; Gascon, Jose A.; Papadimitrakopoulos, Fotios

2012-01-01

408

Enantioselective toxicity and bioaccumulation of fipronil in fathead minnows (Pimephales promelas) following water and sediment exposures.  

PubMed

Fipronil is a widely used, broad-spectrum pesticide that is applied as an equal mixture of two enantiomers. As regulations on older pesticides become more stringent, production and application of fipronil is expected to grow, leading to increased inputs into aquatic environments and complex exposures to biota. To better understand the potential exposures introduced by fipronil contamination, we conducted subchronic toxicity tests with larval fathead minnows (Pimephales promelas) and waterborne fipronil and its enantiomers and exposed juvenile fathead minnows to fipronil-spiked sediment. Enantioselective toxicity was observed in fish after the 7-d subchronic exposure, with increased toxicity of the racemate and (+) enantiomer observed compared with the (-) enantiomer. Curiously, toxicities of the racemate and (+) enantiomer were not significantly different, even though the racemate contains 50% of the (+) enantiomer and 50% of the less toxic (-) enantiomer. During the sediment exposure, racemic fipronil in sediment was transformed primarily to fipronil sulfide, while exposed fish rapidly accumulated fipronil and/or fipronil sulfide and transformed the majority to fipronil sulfone. Using the results of the sediment-exposure experiment, the authors explored a mechanism that may contribute to the interesting trends in enantioselective toxicity observed during the waterborne exposures. In tandem, the aquatic toxicity experiment and the spiked sediment exposure demonstrate the potentially complex behavior of fipronil in sediment and fish. PMID:23109279

Baird, Suzanne; Garrison, Arthur; Jones, Jack; Avants, Jimmy; Bringolf, Robert; Black, Marsha

2012-11-21

409

Application of metal alkoxides in the synthesis of oxides  

Microsoft Academic Search

Powders and thin films of the following simple and complex oxides have been obtained from metal alkoxides: MTiO3 (M= Mg, Ca-Ba), MM1\\/3B2\\/3O3 (M= Sr, Ba, M' = Mg-Zn; B= Nb, Ta); MNbO3(M= Li, Na); ZrTiO4; PbTiO3; PZT, PLZT-materials; M2BO4 (M= Li, Na; B= Mo, W), Bi2BO6(B= Mo, W); LixWO3, WO3, MoO3, Bi2O3-WO3(solid solutions), YFeO3, Y3Fe5O12; YBa2Cu3O7-; Bi2Sr2CaCu2Ox; Bi2Sr2Ca2Cu3Ox. For synthesis

M. I. Yanovskaya; E. P. Turevskaya; V. G. Kessler; I. E. Obvintseva; N Ya Turova

1992-01-01

410

Applications of acceptorless dehydrogenation and related transformations in chemical synthesis.  

PubMed

Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis. PMID:23869021

Gunanathan, Chidambaram; Milstein, David

2013-07-19

411

Synthesis of asymmetric biphenyl derivatives for optoelectronic applications  

NASA Astrophysics Data System (ADS)

We report the synthesis and optical properties of a series of ten organic compounds with biphenyl as the backbone and asymmetrically modified by triphenylamines, carbazoles and tetraphenylsilanes (BP 1-10). BP 1-10 were synthesized mainly by Ullmann coupling reaction and Suzuki cross-coupling reaction and characterized by EA, NMR, MS, UV-Vis, DSC, TGA, fluorescence spectra and cyclic voltammetry. They exhibit reversible electrochemical behavior with low oxidation potentials and emit intense pure-blue light with high fluorescence quantum yields (up to 80%). BP 1 was fabricated into multi-layered light-emitting diodes as blue-emitting, host and hole transport materials. Based on the performance of BP 1 and the similarity in chemical structure to those compounds reported in literature, these compounds are expected to be good and versatile hole transport, host and blue emitting materials.

Zhu, Cai-Cai; Guo, Kun-Ping; Liu, Wang-Bo; He, Yan-Bo; Li, Zhi-Mei; Gao, Xi-Cun; Deng, Feng-Jie; Wei, Bin

2013-10-01

412

Synthesis and electrochromic application of surfactants tailored WO3 nanostructures  

NASA Astrophysics Data System (ADS)

As WO3 is excellent material for electrochromic displays more investigation is needed to find the good and low cost method for preparation of WO3 nanostructures with uniform morphology and narrow distributions using a surfactant mediated method. In this study, the synthesis of WO3 nanostructures was accomplished using various surfactants such as polyethylene glycol, sodium chloride and sodium dodecyl sulfate and sodium tungstate and diethyl sulfate as the inorganic precursors. All samples were characterized for their opto-structural and morphological studies by UV-Vis spectrophotometer, X-ray diffractometer and scanning electron microscopy techniques. The electrochromic performance of these samples was studied in LiClO4/PC as electrolyte for Li+ insertion/extraction. The use of surfactants has been employed to enhance the uniformity of WO3 samples.

Kharade, Rohini R.; Patil, S. P.; Mane, R. M.; Patil, P. S.; Bhosale, P. N.

2011-11-01

413

Synthesis of new porphyrinoids for biomedical and materials applications  

NASA Astrophysics Data System (ADS)

The facile synthesis of three non-hydrolysable thioglycosylated porphyrinoids is reported. Starting from meso perfluorophenylporphyrin (TPPF20), the non-hydrolysable thioglycosylated porphyrin (PGlc4), chlorin (CGlc4), isobacteriochlorin (IGlc4), and bacteriochlorin (BGlc4) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. With reduction of one or two pyrrole double bonds, there is a red shift in the lowest energy absorption band and a significant increase in intensity. The fluorescence of these porphyrinoids is in the order PGlc4 = BGlc4 < CGlc4 < IGlc4 and there is a corresponding decrease in the amount of triplet formed. Fluorescence micrographs of cells after treatment with these four porphyrinoids indicate they are taken up. The CGlc4 and IGlc4 may be dual function agents that can detect cancer by luminescence, and treat cancer by photodynamic therapy (PDT). Porphyrins appended with four rigid hydrogen bonding motifs on the meso positions were synthesized and self-assembled into a cofacial cage with four complementary bis- (decyl)melamine units in dry solvents, these hydrogen-bonded cages were analysed by diffusion-ordered spectroscopy (DOSY) in solution. The hydrocarbon chains on the melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates. A water soluble zinc (II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluoro-phthalocyaninato zinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups by thio-sugars. The photophysical properties and cancer cell uptake studies of this nonhydrolyzable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically and photochemically stable, and can potentially be used as a photosensitizer in photodynamic therapy. A porphyrin bearing pyridyl groups at the meso positions was synthesized using 2,6-diacetamido-4-formylpyridine. A new method has been developed for the synthesis of the precursor aldehyde that avoid much of the problems associated with the earlier synthesis. With this porphyrin it is possible to build hetero-complementary rigid, multi-porphyrin supramolecular arrays via hydrogen bonds. For example, when using naphthalenediimide (NDI) units a checkerboard pattern is expected to be formed using this porphyrin as a donor and NDI as an acceptor where triple hydrogen bond is formed between the diimide and pyridyl units. Energy transfer can be studied through this hydrogen bonded supramolecular assembly. The synthesis of a triply bridged diporphyrin appended with six thioglucose units is reported. The electronic spectrum of this triply bridged porphyrin has enhanced intensity at low-energy wavelengths that reaches the near infrared region. The goal of this project is to create tumor targeting dyes that can be activated with red wavelengths of light that penetrate deeper into tissues. This new compound is amphiphilic in nature, chemically and photochemically stable, expected to have unusual photophysical and electrochemical properties, and can potentially be used as a photosensitizer in photodynamic therapy.

Stewart, Fraser

414

Backbone modification of nucleic acids: synthesis, structure and therapeutic applications.  

PubMed

Nucleic acids have been extensively modified by replacing the phosphodiester group or the whole sugar phosphodiester with alternative anionic, neutral and cationic structures. Several of these modified oligonucleotides exhibit improved properties including enhanced recognition and binding to RNA, duplex DNA and proteins. This has resulted in the development of new and more potent antisense and antigene agents, as well as aptamers. Furthermore, backbone modified oligonucleotides have also been used in the development of several alternative strategies, which rely on altogether different mechanisms of action and show significant promise for therapeutic intervention. In this review the latest advances in the synthesis and evaluation of the most promising backbone modified oligos will be discussed, with a view to their future as novel pharmaceuticals. PMID:11472234

Micklefield, J

2001-08-01

415

SYNTHESIS, APPLICATIONS, AND CHARACTERIZATION OF GUERBET COMPOUNDS AND THEIR DERIVATIVES  

Technology Transfer Automated Retrieval System (TEKTRAN)

The Guerbet reaction and Guerbet compounds, particularly Guerbet alcohols, have been known for more than a century. Guerbet compounds are used in commercial applications such as lubricants, plasticizers, cosmetics, etc., due to their interesting properties. This article provides basic information ...

416

Automation for the synthesis and application of pet radiopharmaceuticals..  

National Technical Information Service (NTIS)

The development of automated systems supporting the production and application of PET radiopharmaceuticals has been an important focus of researchers since the first successes of using carbon-11 (Comar et al., 1979) and fluorine-18 (Reivich et al., 1979) ...

L. Alexoff

2001-01-01

417

High-throughput screening of activity and enantioselectivity of esterases  

Microsoft Academic Search

A procedure for the high-throughput screening of esterases is described. This includes enzyme expression in microtiter plates and the measurement of activity and enantioselectivity (E) of the esterase variants using acetates of secondary alcohols as model substrates. Acetic acid released is converted in an enzyme cascade leading to the stoichiometric formation of NADH, which is quantified in a spectrophotometer. The

Dominique Böttcher; Uwe T Bornscheuer

2006-01-01

418

Enantioselective chemo- and bio-catalysis in ionic liquids  

Microsoft Academic Search

Recent developments in the enantioselective chemo- and bio- catalysis in ionic liquids are reviewed. In many cases, the use of ionic liquids provides many advantages over reactions in conventional organic solvents in terms of activity, enantiose- lectivity, stability and the reusability of the solvent-catalyst systems.

Choong Eui Song

2004-01-01

419

An enantioselective organocatalytic approach to both enantiomers of lasubine II.  

PubMed

A concise stereoselective route providing access to both enantiomers of the bioactive quinolizidine alkaloid lasubine II has been developed. The enantioselectivity was introduced by taking advantage of a proline-catalyzed asymmetric Mannich reaction. Next, the bicyclic system was constructed via a diastereoselective Mannich cyclization and subsequent ring-closing metathesis as the key steps. PMID:19284717

Verkade, Jorge M M; van der Pijl, Ferdi; Willems, Marian M J H P; Quaedflieg, Peter J L M; van Delft, Floris L; Rutjes, Floris P J T

2009-04-17

420

Pyrones to Pyrans: Enantioselective Radical Additions to Acyloxy Pyrones  

PubMed Central

This manuscript describes a highly site, diastereo-, and enantioselective intermolecular radical addition/hydrogen atom transfer to hydroxypyrones pyromeconic and kojic acids. The methodology can be extended to the formation of chiral quaternary centers. The products obtained are densely functionalized pyran moieties. The products contain structural features amenable for the introduction of additional substituents.

Sibi, Mukund P.; Zimmerman, Jake

2008-01-01

421

Iminonitroso ene reactions: experimental studies on reactivity, regioselectivity and enantioselectivity  

PubMed Central

Ene reactions of iminonitroso agents with olefins were investigated in both solution and solid phase. Reactions afforded allyl hydroxylamine products in up to 99% yield and with high regioselectivity. A Cu(I)-mediated enantioselective nitroso ene reaction gave an ene product with up to 40% ee.

Yang, Baiyuan; Miller, Marvin J.

2009-01-01

422

Anionic synthesis of block copolymers for photonics applications  

NASA Astrophysics Data System (ADS)

Anionic synthesis of well-defined polystyrene-block-polyvinylpyridine copolymers required the use of special conditions including lithium chloride and 1,1-diphenylethylene as additives, low temperature of reaction (-78°C), highly diluted monomer at -78°C and efficient stirring (Morton-type, creased reactor). Low molecular weight polystyrene-block-poly(2-vinylpyridine) copolymers (Mn = 6000 g/mol) were synthesized with average-molecular weights in agreement with the theoretically calculated Mns and narrow Mw/Mns (?1.1). Polystyrene-block-polyvinylpyridine copolymers were selected for the fabrication of uniformly dispersed metal oxide nanoparticles (cobalt and iron oxides) due to the coordinating ligand character of the vinylpyridine units. The incorporation of the inorganic salts (1 mol-eq of inorg. salt per mol of vinylpyridine units) was 57 wt% when polystyrene- block-poly(2-vinylpyridine-co-4-vinylpyridine) (M n = 59,000 g/mol, Mw/Mn = 1.09, fv PVP = 0.19) was used and 18 wt% when polystyrene-block-poly(2-vinylpyridine) (Mn = 39,000 g/mol, Mw/Mn = 1.07, f v PVP = 0.14) was used. The end-capping reaction of polymeric chain-ends with 1,1-diphenylethylene (DPE) was studied using 2D NMR spectroscopic and MALDI-TOF mass spectrometric analyses. Oligomerization of DPE was observed using a 15-fold excess of DPE in the end-capping of poly(butadienyl)lithium (Mn = 2,200 g/mol, Mw/Mn = 1.06) but not in the case of poly(styryl)lithium (Mn = 2,000 g/mol, Mw/Mn = 1.02). Although oligomerization of DPE has been previously reported in the synthesis of 1,1-diphenylhexyllithium (6-11% oligomer with 5.4-fold excess of DPE), there are no studies showing the presence of DPE oligomer in the end-capping reaction of polymeric living carbanions. Additionally, the synthesis of poly(para-phenylene) has been studied using different precursor polymers [poly(1,3-cyclohexadienes) (Mn = 1,600 and 3,100 g/mol, Mw/Mn = 1.1 and 1.03) and poly(2-phenyl-1,3-cyclohexadiene) (Mn = 10,000 g/mol, Mw/Mn = 1.27) homopolymers] and dehydrogenating agents [2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil)] (4 mol-eq of benzoquinone per mol of cyclohexadiene unit). The results indicate that the efficiency of the dehydrogenation reaction was limited by precipitation of the polymer in the case of poly(1,3-cyclohexadiene). The advantage of using poly(2-phenyl-1,3-cyclohexadiene) lies in the formation of a soluble poly(2-phenyl-para-phenylene) with thermal stability and mechanical properties similar to those of the insoluble poly( para-phenylene) (TGAres [1000°C] = 40.2%).

Garces Cortes, Camila

423

Synthesis of Enantiomerically Pure Anthracyclinones  

NASA Astrophysics Data System (ADS)

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

Achmatowicz, Osman; Szechner, Barbara

424

A new asymmetric synthesis of 2,6- cis-disubstituted 4-methylenepiperidines: total synthesis of (+)-alkaloid 241D and (+)-isosolenopsin A  

Microsoft Academic Search

A highly diastereoselective synthesis of 2,6-cis-disubstituted-4-methylenepiperidines based on a Mannich type intramolecular cyclization of an allylsilane on an iminium ion is described. The synthetic potential of this methodology is demonstrated by the enantioselective synthesis of two natural piperidine alkaloids: (+)-alkaloid 241D and (+)-isosolenopsin A.

Jérémy Monfray; Yvonne Gelas-Mialhe; Jean-Claude Gramain; Roland Remuson

2005-01-01

425

UV-emitting phosphors: synthesis, photoluminescence and applications  

NASA Astrophysics Data System (ADS)

UV-emitting phosphors find uses in various applications, such as photocopying, phototherapy, sun tanning, etc. The phosphor requirements for these applications vary. Simple methods for preparing different UV-emitting phosphors are described. Novel syntheses for some borates (SrB4O7:Eu, CeMgB5O10:Gd, GdBO3:Pr, LaB3O6:Ce,Bi, LaB3O6:Gd,Bi, LaB3O6:Ce, Ba2B5O9Cl:Eu), a silicate (Ba2SiO5:Pb), phosphates (Sr2-xMgxP2O7:Eu) and a sulphate (CaSO4:Eu) are reported. Photoluminescence spectra of the phosphors so prepared are presented and discussed in the context of applications like phototherapy and photocopying lamps, photoluminescent liquid crystal displays, radiophotoluminescence, etc.

Thakare, D. S.; Omanwar, S. K.; Muthal, P. L.; Dhopte, S. M.; Kondawar, V. K.; Moharil, S. V.

2004-02-01

426

Biogenic synthesis of nanostructured iron compounds: applications and perspectives.  

PubMed

'Green nanotechnology' has attracted increasing attention in recent years because of the possibility to reduce and/or eliminate toxic substances. Indeed, biogenic syntheses of nanomaterials, such as nanoparticles (NPs), are considered economic and valuable alternatives for the production of metallic NPs for diverse applications. Recent studies have revealed that the development of eco-friendly technologies in material science is under extensive investigation in the field of nanobiotechnology. Considering this scenario, this review highlights the recent advances in the biogenic syntheses of metallic iron, iron sulphides and iron oxide NPs for a wide range of applications. Moreover, this review also discusses the medical, environmental and technological applications of biogenically synthesised NPs, and the challenges to be faced to optimise the eco-friendly production of these important nanomaterials. PMID:24028807

Seabra, Amedea B; Haddad, Paula; Duran, Nelson

2013-09-01

427

Synthesis and application of new polymer bound catalysts  

SciTech Connect

Nitric acid has been shown to be a weak acid in acetonitrile. It is conceivable that a nitrate salt of a weakly Lewis acidic cation could furnish a ''naked'' nitrate anion as a basic catalyst in a variety of reactions in non-aqueous solvents. Such a nitrate salt could also be bound to a polymeric support via the cation, thereby allowing for reclamation and recycling of the nitrate ion. This subject is dealt with in Chapter 2, wherein my contributions consisted of performing all the reactions with the polymer supported catalyst and carrying out the experiments necessary to shed light on the reaction mechanisms. Chapter 3 contains a description of the structure and catalytic properties of an azidoproazaphosphatrane. This compound is an air-stable versatile catalyst that has proven useful not only homogeneously, but also when bound to a solid support. The synthesis of a polymer bound proazaphosphatrane containing a trivalent phosphorus is presented in Chapter 4. Such a compound has been sought after by our group for a number of years. Not only does the synthesis I have accomplished for it allow for easier separation of proazaphosphatrane catalysts from reaction mixtures, but recycling of the base is made much simpler. Proazaphosphatranes are useful homogeneous catalysts that activate atoms in other reagents, thus enhancing their reactivity. The next chapters deal with two such reactions with aldehydes and ketones, namely silylcyanations with trialkylsilylcyanides (Chapters 5 and 6) and reductions with poly(methylhydrosiloxane), in Chapter 7. In Chapter 5, Zhigang Wang performed the initial optimization and scoping of the reaction, while repetitions of the scoping experiments for reproducibility, determination of diastereomeric ratios, and experiments aimed at elucidating aspects of the mechanism were performed by me. The proazaphosphatrane coordinates to the silicon atom in both cases, thereby allowing the aforementioned reactions to proceed under much milder conditions. Proazaphosphatranes are also effective Broensted-Lowry bases. This is illustrated in Chapter 8 wherein a wide variety of conjugate addition reactions are catalyzed by proazaphosphatranes. In that chapter, repetitions of the nitroalkane addition reactions for reproducibility, improved spectral data for the products and comparisons of literature yields of all reactions were performed by the author.

Fetterly, Brandon Michael

2005-08-01

428

Multiwalled carbon nanotube CVD synthesis, modification, and composite applications  

NASA Astrophysics Data System (ADS)

Well-aligned carbon multiwall nanotube (MWNT) arrays have been continuously synthesized by a floating catalytic chemical vapor deposition (CVD) method involving the pyrolysis of xylene-ferrocene mixtures. The CVD parameters have been studied to selectively synthesize nanotubes with required dimensions. A mixed tip-root growth model has been proposed for the floating catalytic CVD synthesis. Coarsening of the catalyst particle at the root end promoted MWNT wall coarsening (addition of new concentric graphene shells), while the smaller catalyst particle at the tip contributed to MWNT elongation. A two-step process in which ferrocene was fed for only five minutes to nucleate the DTs was developed to understand if a continuous supply of catalyst was necessary for continued growth. The results show that the ferrocene was only necessary for initial nucleation. To simplify the CVD process further, another two-step synthesis method was developed in which the ferrocene was pre-decomposed so that the nanotube nucleation could be isolated from the growth, enabling quantification of growth mechanisms and kinetics. Mass spectra and hydrocarbon analyses of the CVD reactor tail gas were performed to understand the pyrolysis chemistry. Well-aligned N-doped and Ru-doped MWNT arrays have been produced by pyrolysis of pyridine ferrocene mixtures and xylene-ferrocene-ruthenocene mixtures, respectively. Various material characterization techniques were used to measure the dopant distributions and correlate the catalyst phase with the novel nanotube structures. High-temperature annealing has been shown to be a viable means to remove both the catalyst particles and certain microstructural defects within the CVD-derived DTs. The phase transformation of catalyst during annealing has also been studied. Homogeneous distribution of MWNTs in polystyrene matrices was achieved by an ultrasonic assisted solution-evaporation method. Addition of only 1 wt % DTs to polystyrene increased the polymer mechanical properties significantly. In-situ transmission electron microscopy (TEM) straining studies of MWNT-polystyrene composites revealed that the flexible nanotubes bridge the wakes of propagating matrix cracks regardless of their orientation. The in-situ studies also provide direct evidence of single MWNTs rupturing in a sword-in-sheath mechanism in the tensile direction. Shear fracture was also observed in tubes that were nearly parallel to the propagating cracks.

Qian, Dali

429

Carbon nanotube based hybrid nanostructures: Synthesis and applications  

NASA Astrophysics Data System (ADS)

Hybrid nanostructures are fascinating materials for their promising applications in future nanoelectronics, electrical interconnects and energy storage devices. Practical ways of connecting individual carbon nanotubes to metal contacts for their use as interconnects and in electronic devices have been challenging. In this thesis, carbon nanotube based hybrids that combine the best properties of carbon nanotubes and metal nanowires have been fabricated. The electrical properties and Raman spectra of the hybrid nanowires are also studied. This thesis will focus on our recent results in the development of carbon nanotube hybrids for various applications. Various hybrid structures of multiwalled carbon nanotubes and metal nanowires can be fabricated using a combination of electrodeposition and chemical vapor deposition techniques. Controlled fabrication of multi-segmented structures will be studied. Several novel applications of these structures, for example, as electrodes in ultra-high power supercapacitors, multi-functional smart materials are also studied. The thesis will also highlight the development of carbon nanotube hybrids based smart materials. Hybrid nanowires with hydrophobic carbon nanotube tails and hydrophilic metal nanowire heads, allows for the assembly of spheres in solution. The design and manipulation of these carbon nanotube hybrids based smart structures for various novel applications will be discussed. Such new class of carbon nanotube hybrids surfactants are likely to lead as new tools in various fields such as microfluidics or water purification. In addition, we will also look at other variations of hybrid nanostructures fabricated from our method.

Ou, Fung Suong

430

One-dimensional conducting polymer nanocomposites: Synthesis, properties and applications  

Microsoft Academic Search

Intrinsically conducting polymers have been studied extensively due to their intriguing electronic and redox properties and numerous potential applications in many fields since their discovery in 1970s. To improve and extend their functions, the fabrication of multi-functionalized conducting polymer nanocomposites has attracted a great deal of attention because of the emergence of nanotechnology. This article presents an overview of the

Xiaofeng Lu; Wanjin Zhang; Ce Wang; Ten-Chin Wen; Yen Wei

2011-01-01

431

Synthesis, properties and applications of bio-based materials  

Microsoft Academic Search

Bio-based feedstock have become very significant as they offer a value proposition in terms of carbon balance and also in terms of endowing biodegradability where needed. Thus a lot of attention is being given to the modification such feedstock for different applications. Soybean oil is one such feedstock. The oil is a triglyceride ester composed of different fatty acids, which

Madhusudhan Srinivasan

2010-01-01

432

Application of Fuzzy Logic to Approximate Reasoning Using Linguistic Synthesis  

Microsoft Academic Search

This paper describes an application of fuzzy logic in designing controllers for industrial plants. A fuzzy logic is used to synthesize linguistic control protocol of a skilled operator. The method has been applied to pilot scale plants as well as in practical situations. The merits of this method and its usefulness to control engineering are discussed. An avenue for further

E. H. Mamdani

1977-01-01

433

Biodegradable injectable polyurethanes: Synthesis and evaluation for orthopaedic applications  

Microsoft Academic Search

Biodegradable polyurethanes offer advantages in the design of injectable or preformed scaffolds for tissue engineering and other medical implant applications. We have developed two-part injectable prepolymer systems (prepolymer A and B) consisting of lactic acid and glycolic acid based polyester star polyols, pentaerythritol (PE) and ethyl lysine diisocyanate (ELDI). This study reports on the formulation and properties of a series

Raju Adhikari; Pathiraja A. Gunatillake; Ian Griffiths; Lisa Tatai; Malsha Wickramaratna; Shadi Houshyar; Tim Moore; Roshan T. M. Mayadunne; John Field; Margaret McGee; Tania Carbone

2008-01-01

434

Nanostructured calcium phosphates for biomedical applications: novel synthesis and characterization  

Microsoft Academic Search

Materials play a key role in several biomedical applications, and it is imperative that both the materials and biological aspects are clearly understood for attaining a successful biological outcome. This paper illustrates our approach to implement calcium phosphates as gene delivery agents. Calcium phosphates (CaP) belong to the family of biocompatible apatites and there are several CaP phases, the most

Prashant N. Kumta; Charles Sfeir; Dong-Hyun Lee; Dana Olton; Daiwon Choi

2005-01-01

435

Silyl Ketene Imines: Highly Versatile Nucleophiles for Catalytic, Asymmetric Synthesis  

PubMed Central

This Minireview provides an overview on the development of silyl ketene imines and their recent applications in catalytic, enantioselective reactions. The unique structure of the ketene imine allows a diverse range of reactivity patterns and provides solutions to existing challenges in the enantioselective construction of quaternary stereogenic carbon centers and cross-benzoin adducts. A variety of reactions for which silyl ketene imines have been applied are presented with an overall goal of inspiring new uses for these underutilized nucleophiles.

Denmark, Scott E.; Wilson, Tyler W.

2012-01-01

436

Enantioselective liquid-liquid extractions of underivatized general amino acids with a chiral ketone extractant.  

PubMed

The chiral ketone (S)-3 shows high kinetic enantioselectivities toward the L form for general underivatized amino acids with hydrophobic side chains and a high thermodynamic enantioselectivity toward the D form for cysteine with its -SH polar side chain when used as an extractant in enantioselective liquid-liquid extractions in the presence of Aliquat 336. Consecutive extractions by imine formation and hydrolysis increase the enantiopurity of the amino acid, as both of these reactions are L-form-selective. PMID:23317343

Huang, Haofei; Nandhakumar, Raju; Choi, Misun; Su, Zhishan; Kim, Kwan Mook

2013-02-05

437

A new approach to enantioselective cyanation of imines with Et 2AlCN  

Microsoft Academic Search

An enantioselective Strecker-type reaction of imines with Et2AlCN in the presence of chiral additives has been examined. The enantioselectivity varied depending on the substituents of the imino group as well as the chiral additives used. Thus, ?-aminonitriles were obtained in good yields with good enantioselectivities in the reaction of N-benzylidenebenzhydrylamine with Et2AlCN and BINOL. The reaction with excess BINOL gave

Shuichi Nakamura; Naoki Sato; Masashige Sugimoto; Takeshi Toru

2004-01-01

438

Synthesis and application of mesoporous and macroporous particles  

NASA Astrophysics Data System (ADS)

Phosphine and amine functionalized mesoporous silica materials were metallated with Rh(CO)2(i-Pr2NH)Cl or Rh2 (CO)4Cl2, respectively to yield catalysts containing the Rh(PPh2R)2(CO)Cl or Rh(CO)2(NH2 R)Cl, where R is a propyl chain bonded to the silica surface, reactive centers. In order to ascertain the effect of pore size on rates of hydroformylation catalysis both 35 A and 45 A pore size materials were used. Using the hydroformylation of octene as a reference reaction, the phosphine based, 45 A catalysts were 1.5 to 1.3 times faster than the amine based, 45 A catalysts, and the 45 A materials were 2.6 to 2.1 times faster than the 35 A materials. The ability of the surface bound phosphine catalysts to affect hydroformylation was strongly influenced by the steric constraints of the substrate. Terminal alkenes were readily hydroformylated and norbornene was slowly hydroformylated, but pinene, trans-cyclododecene, cyclohexene and cholesterol were completely unaffected. Hollow porous microspheres can be created for use as electrolyte storage within the active material of the battery electrode. Synthesis of porous hollow glass microspheres (HGMs) has been accomplished by pyrolyzing a mixture of cobalt, titanium, and colloidal silica. The porous HGMs are generated by spray flame pyrolysis of a solution of cobalt, titanium, and silica into a 7000 tube furnace. A phase separation condenses the cobalt to the center of the sphere where it can be etched as well as titanium. Other etching techniques include using HF to etch commercial hollow glass microspheres, and sodium diffusion.

Newell, J. David

439

Synthesis and characterization of nickel hydroxide powders for battery application  

SciTech Connect

The primary objective of this research was to investigate the synthesis and characterization of Ni(OH){sub 2} powders by homogeneous precipitation. Previous research of the same method showed conflicting results and complete characterization of the particle morphology was not carried out. This study has produced precipitates having a composition of 2Ni(OH){sub 2}{center_dot}Ni(HCO{sub 3}){sub 1.85}(NO{sub 3}){sub 0.15}. The XRD patterns showed peaks commonly observed for {alpha}-Ni(OH){sub 2}. The precipitates produced from low and high cation concentration solutions showed that the mean particle size and specific surface area increased with aging time. The high specific surface area measured suggested that the particle growth occurred through the aggregation of nanosized crystallites. The TEM micrographs confirmed that the particles were actually aggregates of thin films or sheets that were crumpled and intertwined together. This work also investigated the effect of dispersant on the particle morphology. The addition of dispersants did not alter the density of the particles implying that the dispersants were not incorporated into the solid phase. A general decrease in mean particle size at each aging time was observed resulting in an increase in specific surface area. The use of dispersants provided steric hindrance for the particles in the solution to aggregate, thus smaller particles were observed. Cyclic voltammetric tests were carried out to see if the high surface area Ni(OH){sub 2} produced in this work had superior performance characteristics compared to the commercial powders currently available. Indeed, the study showed that the homogeneously precipitated Ni(OH){sub 2} had higher coulombic efficiency and degree of reversibility than the commercial powders. The efficiency values of all the homogeneously precipitated powders were approximately 90%. The same efficiency values observed were probably due to the same specific surface areas of the powders after aging in KOH solution.

Widjaja, A.

1997-10-08

440

Application of chiral critical clusters to assymetric synthesis  

DOEpatents

Disclosed is a composition, a method of making and a method of using critical clusters for asymmetric synthesis using substantially optically-pure chiral solvent molecules in a supercritical fluid. The solvent molecules are capable of forming a multipoint hydrogen bonded solvate as they encage at least one solute molecule. The encaged solute molecule is capable of reacting to form an optically active chiral center. In another aspect, there is disclosed a method of directing the position of bonding between a solute molecule and a ligand involving encaging the solute molecule and the ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution in the solute molecule. In yet another aspect, disclosed is a method of making pharmaceutical compounds involving encaging a solute molecule, which is capable of forming a chiral center, and a ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution of the solute molecule. The solute molecule and ligand are then reacted whereby the ligand bonds to the solute molecule forming a chiral center. Also disclosed is a method for racemic resolution using critical clusters involving encaging racemic mixtures of solute molecules with substantially optically-pure chiral solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to form critical clusters. The solvent molecules are capable of multipoint hydrogen bonding with the solute molecules. The encaged solute molecules are then nonenzymatically reacted to enhance the optical purity of the solute molecules.

Ferrieri, Richard A. (Patchogue, NY)

2002-01-01

441

Total Synthesis of (-)-Tirandamycin C  

PubMed Central

Tirandamycin C is a newly isolated member of the tetramic acid family natural products. We described herein the first enantioselective synthesis of natural (?)-tirandamycin C, the postulated biosynthetic precursor of other members of this family. The highly stereoselective (>15:1) mismatched double asymmetric ?-stannylcrotylboration reaction of aldehyde 8 with crotylborane reagent (R)-E-9 was utilized to access the key anti, anti-stereotriad 18.

Chen, Ming; Roush, William R.

2011-01-01

442

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications.  

PubMed

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing ?-cyclodextrin (?-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe3S4) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. ?-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8?mM(-1)s(-1) which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs. PMID:24141204

Feng, Mei; Lu, Yang; Yang, Yuan; Zhang, Meng; Xu, Yun-Jun; Gao, Huai-Ling; Dong, Liang; Xu, Wei-Ping; Yu, Shu-Hong

2013-10-21

443

Aligned carbon nanotubes: from controlled synthesis to electronic applications.  

PubMed

Single-wall carbon nanotubes (SWNTs) possess superior geometrical, electronic, chemical, thermal, and mechanical properties and are very attractive for applications in electronic devices and circuits. To make this a reality, the nanotube orientation, density, diameter, electronic property, and even chirality should be well controlled. This Feature article focuses on recent achievements researchers have made on the controlled growth of horizontally aligned SWNTs and SWNT arrays on substrates and their electronic applications. Principles and strategies to control the morphology, structure, and properties of SWNTs are reviewed in detail. Furthermore, electrical properties of field-effect transistors fabricated on both individual SWNTs and aligned SWNT arrays are discussed. State-of-the-art electronic devices and circuits based on aligned SWNTs and SWNT arrays are also highlighted. PMID:23969970

Liu, Bilu; Wang, Chuan; Liu, Jia; Che, Yuchi; Zhou, Chongwu

2013-09-26

444

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications  

PubMed Central

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing ?-cyclodextrin (?-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe3S4) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. ?-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8?mM?1s?1 which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs.

Feng, Mei; Lu, Yang; Yang, Yuan; Zhang, Meng; Xu, Yun-Jun; Gao, Huai-Ling; Dong, Liang; Xu, Wei-Ping; Yu, Shu-Hong

2013-01-01

445

Aligned carbon nanotubes: from controlled synthesis to electronic applications  

NASA Astrophysics Data System (ADS)

Single-wall carbon nanotubes (SWNTs) possess superior geometrical, electronic, chemical, thermal, and mechanical properties and are very attractive for applications in electronic devices and circuits. To make this a reality, the nanotube orientation, density, diameter, electronic property, and even chirality should be well controlled. This Feature article focuses on recent achievements researchers have made on the controlled growth of horizontally aligned SWNTs and SWNT arrays on substrates and their electronic applications. Principles and strategies to control the morphology, structure, and properties of SWNTs are reviewed in detail. Furthermore, electrical properties of field-effect transistors fabricated on both individual SWNTs and aligned SWNT arrays are discussed. State-of-the-art electronic devices and circuits based on aligned SWNTs and SWNT arrays are also highlighted.

Liu, Bilu; Wang, Chuan; Liu, Jia; Che, Yuchi; Zhou, Chongwu

2013-09-01

446

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications  

NASA Astrophysics Data System (ADS)

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing ?-cyclodextrin (?-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe3S4) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. ?-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8 mM-1s-1 which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs.

Feng, Mei; Lu, Yang; Yang, Yuan; Zhang, Meng; Xu, Yun-Jun; Gao, Huai-Ling; Dong, Liang; Xu, Wei-Ping; Yu, Shu-Hong

2013-10-01

447

Continuous supercritical hydrothermal synthesis: lithium secondary ion battery applications  

Microsoft Academic Search

Nanosized lithium iron phosphate (LiFePO4) and transition metal oxide (MO, where M is Cu, Ni, Mn, Co, and Fe) particles are synthesized continuously in supercritical\\u000a water at 25–30 MPa and 400°C under various conditions for active material application in lithium secondary ion batteries.\\u000a The properties of the nanoparticles, including crystallinity, particle size, surface area, and electrochemical performance,\\u000a are characterized in detail.

Seung-Ah Hong; Agung Nugroho; Su Jin Kim; Jaehoon Kim; Kyung Yoon Chung; Byung-Won Cho; Jeong Won Kang

2011-01-01

448

Synthesis, Structural Analysis, and Applications of Titanium Oxide Nanotubes  

Microsoft Academic Search

\\u000a An explanation of the new synthesizing method for mono-dispersed titanium oxide nanotubes (TNT) is provided. By using the\\u000a latest transmission electron microscopy method, the electric structure, crystal structure, and morphology of the TNT were\\u000a analyzed. As a practical application, we studied the properties of TNT as the light electrodes of dye-sensitized solar cells\\u000a and photo-catalysts in visible light. For DSC,

Tsuguo Koyanagi

2010-01-01

449

Synthesis of metal polymer nanocomposite for optical applications  

Microsoft Academic Search

Thin films of Ag-PET nanocomposite were synthesized by a novel route of atom beam co-sputtering. The nanocomposites were characterized by UV-visible and IR absorption spectroscopy, Rutherford backscattering spectroscopy and transmission electron microscopy. The absorption spectra exhibit features suitable for applications as (i) absorber extending from the visible region to about 2400 nm in the infrared region and (ii) bandpass filter

D. K. Avasthi; Y. K. Mishra; D. Kabiraj; N. P. Lalla; J. C. Pivin

2007-01-01

450

Synthesis of metal–polymer nanocomposite for optical applications  

Microsoft Academic Search

Thin films of Ag–PET nanocomposite were synthesized by a novel route of atom beam co-sputtering. The nanocomposites were characterized by UV–visible and IR absorption spectroscopy, Rutherford backscattering spectroscopy and transmission electron microscopy. The absorption spectra exhibit features suitable for applications as (i)absorber extending from the visible region to about 2400nm in the infrared region and (ii)bandpass filter at 320nm, useful

D K Avasthi; Y K Mishra; D Kabiraj; N P Lalla; J C Pivin

2007-01-01

451

Synthesis, characterization and application of magnetic-zirconia nanocomposites  

Microsoft Academic Search

In the present study, a magnetic-zirconia nanocomposite was successfully synthesized by a single-step co-precipitation method. The as-prepared nanocomposite was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and nitrogen sorption measurements. The ultimate material was found to be Fe3O4–ZrO2 nanoparticles with average diameter of 80nm, high surface area up to 166m2\\/g, and strong magnetic property. The application

Qing-Zhong Guo; Bo Mei; Shu-Xiang Zhou; Zhi-Guo Shi; Yu-Qi Feng; Jiang-Yu Wu; Guo-Ping Yan; Liang Li

2009-01-01

452

Synthesis of Cr 3C 2 coatings for tribological applications  

Microsoft Academic Search

PVD coatings such as TiN and CrN have been successfully applied to metal forming industries for their advanced wear resistance. Metal pick-up and sticking problems in certain deep drawing and plastic injection molding processes, however, demand more sophisticated tribological thin films. In this study, we evaluated chromium carbide coatings synthesized by PVD processes for potential applications in forming and molding

Da-Yung Wang; Ko-Wei Weng; Chi-Lung Chang; Wei-Yu Ho

1999-01-01

453

Synthesis and applications of one-dimensional semiconductors  

Microsoft Academic Search

Nanoscale inorganic materials such as quantum dots (0-dimensional) and one-dimensional (1D) structures, such as nanowires, nanobelts and nanotubes, have gained tremendous attention within the last decade. Among the huge variety of 1D nanostructures, semiconducting nanowires have gained particular interest due to their potential applications in optoelectronic and electronic devices. Despite the huge efforts to control and understand the growth mechanisms

Sven Barth; Francisco Hernandez-Ramirez; Justin D. Holmes; Albert Romano-Rodriguez

2010-01-01

454

Controlled synthesis of high quality carbon nanotubes and their applications in transparent conductive films  

Microsoft Academic Search

Carbon nanotubes (CNTs) have exceptional electrical, mechanical and electronic properties which make them attractive for numerous applications. Catalytic chemical vapor deposition (cCVD) is one of the most promising methods for large-scale production of high-quality CNTs at a relatively low cost. Synthesis conditions such as catalyst composition, reaction temperature, hydrocarbon type and flow rate, have an enormous influence on the morphological

Enkeleda Dervishi

2009-01-01

455

Synthesis of Iron-Iron Oxide Core Shell Nanoclusters for Environmental Applications  

Microsoft Academic Search

Nanoscale iron particles have gained much attention recently for their potential application in the remediation of a wide variety of common environmental contaminants. Fe0 iron nanoparticles are difficult to synthesize by conventional methods. Here we report room-temperature synthesis of iron-iron oxide core-shell nanoclusters using a new type of source. Oxide shells act as passivation layers preventing further oxidation of the

Antony Jiji; You Qiang; Baer R; David E. McCready; Engelhard H

2004-01-01

456

Recent advances in synthesis, physical properties and applications of conducting polymer nanotubes and nanofibers  

Microsoft Academic Search

This article summarizes and reviews the various preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis approaches include hard physical template method, soft chemical template method, electrospinning, and lithography techniques. Particularly, the electronic transport (e.g., electrical conductivity, current–voltage (I–V) characteristics, magnetoresistance, and nanocontact resistance) and mechanical properties of

Yun-Ze Long; Meng-Meng Li; Changzhi Gu; Meixiang Wan; Jean-Luc Duvail; Zongwen Liu; Zhiyong Fan

2011-01-01

457

A review on polysiloxane-immobilized ligand systems: Synthesis, characterization and applications  

Microsoft Academic Search

The immobilized silica gel ligand systems made by modification of silica surfaces have been briefly summarized. Short background was described based on the synthesis methods and their applications. In this review more attention towards the functionalized polysiloxane xerogels and their postmodification has been given. Polysiloxane-immobilized ligand systems bearing organofunctionalized ligand groups of general formula P–(CH2)3–X (where P represents a three-dimensional

Issa M. El-Nahhal; Nizam M. El-Ashgar

2007-01-01

458

TOPICAL REVIEW: Synthesis and applications of magnetic nanoparticles for biorecognition and point of care medical diagnostics  

Microsoft Academic Search

Functionalized magnetic nanoparticles are important components in biorecognition and medical diagnostics. Here, we present a review of our contribution to this interdisciplinary research field. We start by describing a simple one-step process for the synthesis of highly uniform ferrite nanoparticles (d = 20-200 nm) and their functionalization with amino acids via carboxyl groups. For real-world applications, we used admicellar polymerization

Adarsh Sandhu; Hiroshi Handa; Masanori Abe

2010-01-01

459

One-dimensional CdS nanostructures: synthesis, properties, and applications  

NASA Astrophysics Data System (ADS)

One-dimensional (1D) semiconductor nanostructures are of prime interest due to their potential in investigating the size and dimensionality dependence of the materials' physical properties and constructing nanoscale electronic and optoelectronic devices. Cadmium sulfide (CdS) is an important semiconductor compound of the ii-vi group, and its synthesis and properties have been of growing interest owing to prominent applications in several fields. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, novel properties and unique applications of 1D CdS nanostructures in nanotechnology. It begins with the rational design and synthesis of 1D CdS nanostructures, and then highlights a range of unique properties and applications (e.g. photoluminescence, cathodoluminescence, electrochemiluminescence, photocatalysis, lasers, waveguides, modulators, solar cells, field-effect transistors, photodetectors, field-emitters, and nanogenerators) associated with them. Finally, the review is concluded with the author outlook of the perspectives with respect to future research on 1D CdS nanostructures.

Zhai, Tianyou; Fang, Xiaosheng; Li, Liang; Bando, Yoshio; Golberg, Dmitri

2010-02-01

460

Colorimetric enantioselective recognition of chiral secondary alcohols via hydrogen bonding to a chiral metallocene containing chemosensor.  

PubMed

An operationally simple colorimetric method for enantioselective detection of chiral secondary alcohols via hydrogen bonding interactions using a chiral ferrocene derivative is reported. PMID:23814789

Xu, Su-Ying; Hu, Bin; Flower, Stephen E; Jiang, Yun-Bao; Fossey, John S; Deng, Wei-Ping; James, Tony D

2013-09-28

461

Total synthesis of (+)-clavilactone a and (-)-clavilactone B by ring-opening/ring-closing metathesis.  

PubMed

The enantioselective total synthesis of natural enantiomers of clavilactones A and B has been achieved. A key feature of the synthesis is the use of a ring-opening/ring-closing metathesis, which allows the one-pot transformation of a strained cyclobutenecarboxylate into a ?-butenolide. PMID:24147799

Takao, Ken-Ichi; Nanamiya, Ryuki; Fukushima, Yuuki; Namba, Ayumi; Yoshida, Keisuke; Tadano, Kin-Ichi