Note: This page contains sample records for the topic enantioselective synthesis application from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Bifunctional Iminophosphorane Organocatalysts for Enantioselective Synthesis: Application to the Ketimine Nitro-Mannich Reaction  

PubMed Central

The design, synthesis, and development of a new class of modular, strongly basic, and tunable bifunctional Brønsted base/H-bond-donor organocatalysts are reported. These catalysts incorporate a triaryliminophosphorane as the Brønsted basic moiety and are readily synthesized via a last step Staudinger reaction of a chiral organoazide and a triarylphosphine. Their application to the first general enantioselective organocatalytic nitro-Mannich reaction of nitromethane to unactivated ketone-derived imines allows the enantioselective construction of ?-nitroamines possessing a fully substituted carbon atom. The reaction is amenable to multigram scale-up, and the products are useful for the synthesis of enantiopure 1,2-diamine and ?-amino acid derivatives.

2013-01-01

2

Bifunctional iminophosphorane organocatalysts for enantioselective synthesis: application to the ketimine nitro-Mannich reaction.  

PubMed

The design, synthesis, and development of a new class of modular, strongly basic, and tunable bifunctional Brønsted base/H-bond-donor organocatalysts are reported. These catalysts incorporate a triaryliminophosphorane as the Brønsted basic moiety and are readily synthesized via a last step Staudinger reaction of a chiral organoazide and a triarylphosphine. Their application to the first general enantioselective organocatalytic nitro-Mannich reaction of nitromethane to unactivated ketone-derived imines allows the enantioselective construction of ?-nitroamines possessing a fully substituted carbon atom. The reaction is amenable to multigram scale-up, and the products are useful for the synthesis of enantiopure 1,2-diamine and ?-amino acid derivatives. PMID:24107070

Núñez, Marta G; Farley, Alistair J M; Dixon, Darren J

2013-11-01

3

Enantioselective cyclization of enamide-ynes and application to the synthesis of the kopsifoline core  

PubMed Central

We report the palladium-catalyzed enantioselective cyclization of 1,6-enamidynes to form spirocyclic ring systems. We applied this methodology to the concise synthesis of the skeletal core of the kopsifoline alkaloids.

Corkey, Britton K.; Heller, Stephen T.; Wang, Yi-Ming

2013-01-01

4

Enantioselective synthesis of xanthatin.  

PubMed

The enantioselective synthesis of cytostatic and antibiotic xanthatin (1?a) is reported. As a key intermediate, a bicyclic compound 2 was identified, which can be readily synthesized from methyl-2-furoic acid in diastereo- and enantiomerically pure form. Compound 2 can be functionalized regio- and stereoselectively at C-6 and C-7, allowing the facile introduction of the functionalities found in xanthatin, as well as the synthesis of derivatives thereof. Moreover, a robust strategy for the introduction of the exo-methylene group at C-3, commonly found in many sesquiterpenes, was developed that makes use of masking the alkene in the ?,?-unsaturated carbonyl system by O-pivaoyl, which is stable under acidic and mild basic conditions but eliminated upon treatment with strong bases. PMID:24823713

Bergmann, Andreas; Reiser, Oliver

2014-06-16

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

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

7

Enantioselective Total Synthesis of Aplyviolene  

PubMed Central

The enantioselective total synthesis of the rearranged spongian diterpene aplyviolene has been completed in 14 steps from the known hydroazulenone 8. The key junction of the hydrocarbon and oxygenated fragments to form the critical C8 quaternary carbon stereocenter and set the stage for elaborating the delicate bicyclic lactone functionality was accomplished in high yield and exquisite stereoselectivity by Michael addition of an enantioenriched hydroazulenone enolate to an enantiopure ?-bromocyclopentenone.

Overman, Larry E.; Schnermann, Martin J.

2011-01-01

8

Enantioselective total synthesis of borrelidin.  

PubMed

The first total synthesis of the natural product borrelidin is described. The propionate fragment of the molecule was concisely synthesized through catalytic enantioselective reductive aldol reactions, a catalytic Negishi coupling, and a catalytic directed hydrogenation. The propionate segment was then fused to the vinyl iodide fragment through a catalytic Sonogashira coupling. Subsequent catalytic hydrostannylation and catalytic cyanation allowed access to the target structure. PMID:12568588

Duffey, Matthew O; LeTiran, Arnaud; Morken, James P

2003-02-12

9

Enantioselective Total Synthesis of (+)-Reserpine  

PubMed Central

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.

Rajapaksa, Naomi S.; McGowan, Meredeth A.; Rienzo, Matthew

2013-01-01

10

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

2013-02-01

11

Enantioselective total synthesis of (-)-walsucochin B.  

PubMed

The first enantioselective total synthesis of the structurally unique nortriterpenoid (-)-walsucochin B has been accomplished through the cationic polyolefin cyclization initiated by chiral epoxide. The core framework and the stereocenters in the natural product were all constructed in this step. A site-selective, late-stage free-radical halogenation and Seyferth-Gilbert homologation was adopted to install the acetylene moiety to synthesize the phenylacetylene. The absolute configuration of walsucochin B was confirmed through enantioselective total synthesis. PMID:24670038

Xu, Shiyan; Gu, Jixiang; Li, Huilin; Ma, Donghui; Xie, Xingang; She, Xuegong

2014-04-01

12

An enantioselective synthesis of the key intermediate for triazole antifungal agents; application to the catalytic asymmetric synthesis of efinaconazole (Jublia).  

PubMed

A new synthetic route, the shortest reported to date, to access a key intermediate for the synthesis of various triazole antifungal agents was developed. The elusive tetrasubstituted stereogenic center that is essential in advanced triazole antifungal agents was constructed via the catalytic asymmetric cyanosilylation of a ketone. The subsequent transformations were performed in two one-pot operations, enhancing the overall synthetic efficiency toward the intermediate. This streamlined synthetic approach was successfully applied to efficient enantioselective syntheses of efinaconazole (Jublia) and ravuconazole. PMID:24635354

Tamura, Keiji; Kumagai, Naoya; Shibasaki, Masakatsu

2014-04-01

13

Enantioselective synthesis of endohedral metallofullerenes.  

PubMed

Endohedral metallofullerenes are promising materials in biomedical and material sciences. In particular, they are of interest as agents for magnetic resonance imaging (MRI), photovoltaic devices, and semimetallic components. The synthesis of chiral endofullerenes represents one step further in the potential use of these carbon allotropes; however, this step has not been addressed so far. In this regard, enantiopure endofullerenes are expected to open new avenues in fields in which chirality is a key issue. Here, the synthesis and characterization of the first chiral endohedral metallofullerenes, namely, chiral bis-adducts of La@C(72), are reported. Eight optically active isomers were obtained by enantioselective 1,3-dipolar cycloaddition of a N-metalated azomethine ylide onto a non-isolated-pentagon rule metallofullerene derivative, La@C(72)(C(6)H(3)Cl(2)), catalyzed by a copper chiral complex. The chiral bis-adducts of La@C(72), isolated by nonchiral HPLC, showed optical purities as high as 98% as revealed by the remarkable positive or negative Cotton effects observed in the circular dichroic spectra. PMID:21955273

Sawai, Koji; Takano, Yuta; Izquierdo, Marta; Filippone, Salvatore; Martín, Nazario; Slanina, Zdenek; Mizorogi, Naomi; Waelchli, Markus; Tsuchiya, Takahiro; Akasaka, Takeshi; Nagase, Shigeru

2011-11-01

14

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

15

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

16

Enantioselective Synthesis of an HCV NS5a Antagonist.  

PubMed

A concise, enantioselective synthesis of the HCV NS5a inhibitor MK-8742 (1) is reported. The features of the synthesis include a highly enantioselective transfer hydrogenation of an NH imine and a dynamic diastereoselective transformation. The synthesis of this complex target requires simple starting materials and nine linear steps for completion. PMID:24724971

Mangion, Ian K; Chen, Cheng-Yi; Li, Hongmei; Maligres, Peter; Chen, Yonggang; Christensen, Melodie; Cohen, Ryan; Jeon, Ingyu; Klapars, Artis; Krska, Shane; Nguyen, Hoa; Reamer, Robert A; Sherry, Benjamin D; Zavialov, Ilia

2014-05-01

17

Enantioselective Synthesis of the Strigolactone Mimic (+)-GR24.  

PubMed

A short and cost-effective synthesis of the important strigolactone analogue (+)-GR24 is described. Central to this new approach is the concise, enantioselective synthesis of the A-C ring system. PMID:24422520

Bromhead, Liam J; Visser, Johan; McErlean, Christopher S P

2014-02-01

18

Enantioselective synthesis of pactamycin, a complex antitumor antibiotic.  

PubMed

Medicinal application of many complex natural products is precluded by the impracticality of their chemical synthesis. Pactamycin, the most structurally intricate aminocyclopentitol antibiotic, displays potent antiproliferative properties across multiple phylogenetic domains, but it is highly cytotoxic. A limited number of analogs produced by genetic engineering technologies show reduced cytotoxicity against mammalian cells, renewing promise for therapeutic applications. For decades, an efficient synthesis of pactamycin amenable to analog derivatizations has eluded researchers. Here, we present a short asymmetric total synthesis of pactamycin. An enantioselective Mannich reaction and symmetry-breaking reduction sequence was designed to enable assembly of the entire carbon core skeleton in under five steps and control critical three-dimensional (stereochemical) functional group relationships. This modular route totals 15 steps and is immediately amenable for structural analog synthesis. PMID:23580525

Malinowski, Justin T; Sharpe, Robert J; Johnson, Jeffrey S

2013-04-12

19

Ureidopeptide-Based Brønsted Bases: Design, Synthesis and Application to the Catalytic Enantioselective Synthesis of ?-Amino Nitriles from (Arylsulfonyl)acetonitriles.  

PubMed

The addition of cyanoalkyl moieties to imines is a very attractive method for the preparation of ?-amino nitriles. We present a highly efficient organocatalytic methodology for the stereoselective synthesis of ?-amino nitriles, in which the key to success is the use of ureidopeptide-based Brønsted base catalysts in combination with (arylsulfonyl)acetonitriles as synthetic equivalents of the acetonitrile anion. The method gives access to a variety of ?-amino nitriles with good yields and excellent enantioselectivities, and broadens the stereoselective Mannich-type methodologies available for their synthesis. PMID:24737686

Diosdado, Saioa; López, Rosa; Palomo, Claudio

2014-05-19

20

A Nine-Step Enantioselective Total Synthesis of (+)-Minfiensine  

PubMed Central

An enantioselective total synthesis of the Strychnos alkaloid (+)-minfiensine has been accomplished. Prominent features of this synthesis include (i) a new enantioselective organocatalytic Diels–Alder/amine cyclization sequence to build the central tetracyclic pyrroloindoline framework in four steps from commercial materials and (ii) a 6-exo-dig radical cyclization to forge the final piperidinyl ring system. This total synthesis of (+)-minfiensine was completed in nine chemical steps and 21% overall yield.

Jones, Spencer B.; Simmons, Bryon; MacMillan, David W. C.

2009-01-01

21

Total Synthesis of (+)-Rishirilide B: Development and Application of General Processes for Enantioselective Oxidative Dearomatization of Resorcinol Derivatives  

PubMed Central

A concise synthesis of (+)-rishirilide B (2) is described. This is the first synthesis to be reported for the (+)-enantiomer of rishirilide B (2) as found in nature. The strategy accentuates the valuable combination of a method for o-quinone methide coupling with a method for enantioselective resorcinol dearomatization, which provides a densely functionalized chiral building block. The convergent synthesis illustrates several improvements and refinements to these methods and their supporting chemistries. Among these is the in situ generation of PhI[OTMS]OTf. Combination of this oxidant with phenol 31 constitutes the first example of a diastereoselective oxidative dearomatization of a resorcinol displaying a 2-alkyl substituent. In addition, the preparation of the cyclic sulfone 34 is reported. As a new dimethide precursor expressing a readily cleavable O-benzyl residue, sulfone 34 should prove useful in future endeavors. A protocol using the aluminum amide of dimethylhydrazine for opening and cleavage of a [1,4]-dioxan-2-one is also described. This procedure unmasks the hydroxy dione 36 by jettisoning the chiral directing group. Regioselective O-carbamylation of the 1,3-dione 36 enables the transformation of the remaining carbonyl into the ?-hydroxy carboxylic acid found in 2. The total synthesis of (+)-rishirilide B (2) requires 15 pots from benzaldehyde 17 and 13 pots from benzaldehyde 32. The final product emerges in yields of 12.5% and 20.3% from compounds 17 and 32, respectively. The longest linear sequence requires eight chromatographies. Important observations leading to the development of the principle asymmetric method are described within the context of the total synthesis.

Mejorado, Lupe H.

2008-01-01

22

Enantioselective total synthesis of hyperforin.  

PubMed

A modular, 18-step total synthesis of hyperforin is described. The natural product was quickly accessed using latent symmetry elements, whereby a group-selective, Lewis acid-catalyzed epoxide-opening cascade cyclization was used to furnish the bicyclo[3.3.1]nonane core and set two key quaternary stereocenters. PMID:23270309

Sparling, Brian A; Moebius, David C; Shair, Matthew D

2013-01-16

23

Enzyme assisted enantioselective synthesis of the alkaloid (+)-aloperine  

Microsoft Academic Search

The enantioselective synthesis of the lupinine alkaloid (+)-aloperine is described. The synthetic scheme presents three steps that are mediated by enzymes: kinetic resolution, oxidation of a primary alcohol to an aldehyde and oxidation of a secondary alcohol to a ketone.

Alessio Barilli; Francesca Belinghieri; Daniele Passarella; Giordano Lesma; Sergio Riva; Alessandra Silvani; Bruno Danieli

2004-01-01

24

Development of an Enantioselective Route towards the Lycopodium Alkaloids: Total Synthesis of Lycopodine  

PubMed Central

Synthesis of a C15-desmethyl tricycle core of lycopodine has been accomplished. Key steps in the synthetic sequence include organocatalytic, intramolecular Michael addition of a keto sulfone and a tandem 1,3-sulfonyl shift / Mannich cyclization to construct the tricyclic core ring system. Synthetic work towards this natural product family led to the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide – an organocatalyst which facilitiates enantioselective, intramolecular Michael additions. A detailed mechanistic discussion is provided for both the intramolecular Michael addition and the sulfone rearrangement. Finally, the application of these discoveries to the enantioselective total synthesis of alkaloid lycopodine is described.

Yang, Hua; Carter, Rich G.

2010-01-01

25

Enantioselective total synthesis of (+)-brazilin, (-)-brazilein and (+)-brazilide A.  

PubMed

An enantioselective strategy for the synthesis of (+)-brazilin, (-)-brazilein and (+)-brazilide A has been developed. A Lewis acid mediated lactonization established the novel fused bis-lactone core of brazilide A and finalized the first total synthesis of (+)-brazilide A. PMID:23657435

Wang, Xuequan; Zhang, Hongbin; Yang, Xiaodong; Zhao, Jingfeng; Pan, Chengxue

2013-06-14

26

Modular enantioselective synthesis of 8-aza-prostaglandin E1.  

PubMed

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-?-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based ?-amidalkylation protocol (dr = 6.8:1), with the chiral pre-?-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents. PMID:23957245

Wang, Xiao-Gang; Wang, Ai-E; Hao, Yi; Ruan, Yuan-Ping; Huang, Pei-Qiang

2013-09-20

27

Brønsted acid catalyzed enantioselective ?-amidoalkylation in the synthesis of isoindoloisoquinolines.  

PubMed

The Parham cyclization-intermolecular ?-amidoalkylation sequence results in the facile enantioselective synthesis of 12b-substituted isoindoloisoquinolines (ee up to 95%) using BINOL-derived Brønsted acids. ?-Amidoalkylation of indole occurs through the formation of a chiral conjugate base/bicyclic quaternary N-acyliminium ion pair. PMID:22356420

Aranzamendi, Eider; Sotomayor, Nuria; Lete, Esther

2012-03-16

28

An Enantioselective Synthesis of Cymbalta: Preparation of (+)-(S)-Duloxetine  

Microsoft Academic Search

Duloxitine is a serotonin-norepinephrine reuptake inhibitor used in the treatment of depression and anxiety. Duloxetine's chiral structure makes it an excellent target for using our novel enantioselective synthesis techniques. The proposed synthetic route establishes asymmetry by use of an enzyme and maintains chirality while adding functionality to the molecular backbone through palladium p-allyl substitution and ruthenium catalyzed cross metathesis.

Nikhil Addleman

2008-01-01

29

Catalytic Enantioselective 1,3-Dipolar Cycloadditions of Azomethine Ylides for Biology-Oriented Synthesis  

PubMed Central

Conspectus Cycloaddition reactions are among the most powerful methods for the synthesis of complex compounds. In particular, the development and application of the 1,3-dipolar cycloaddition, an important member of this reaction class, has grown immensely due to its powerful ability to efficiently build various five-membered heterocycles. Azomethine ylides are commonly used as dipoles for the synthesis of the pyrrolidine scaffold, which is an important motif in natural products, pharmaceuticals, and biological probes. The reaction between azomethine ylides and cyclic dipolarophiles allows access to polycyclic products with considerable complexity. The extensive application of the 1,3-dipolar cycloaddition is based on the fact that the desired products can be obtained with high yield in a regio- and stereocontrolled manner. The most attractive feature of the 1,3-dipolar cycloaddition of azomethine ylides is the possibility to generate pyrrolidines with multiple stereocenters in a single step. The development of enantioselective cycloadditions became a subject of intensive and impressive studies in recent years. Among many modes of stereoinduction, the application of chiral metal–ligand complexes has emerged as the most viable option for control of enantioselectivity. In chemical biology research based on the principle of biology-oriented synthesis (BIOS), compound collections are prepared inspired by natural product scaffolds. In BIOS, biological relevance is employed as the key criterion to generate hypotheses for the design and synthesis of focused compound libraries. In particular, the underlying scaffolds of natural product classes provide inspiration for BIOS because they define the areas of chemical space explored by nature, and therefore, they can be regarded as “privileged”. The scaffolds of natural products are frequently complex and rich in stereocenters, which necessitates the development of efficient enantioselective methodologies. This Account highlights examples, mostly from our work, of the application of 1,3-dipolar cycloaddition reactions of azomethine ylides for the catalytic enantioselective synthesis of complex products. We successfully applied the 1,3-dipolar cycloaddition in the synthesis of spiro-compounds such as spirooxindoles, for kinetic resolution of racemic compounds in the synthesis of an iridoid inspired compound collection and in the synthesis of a nitrogen-bridged bicyclic tropane scaffold by application of 1,3-fused azomethine ylides. Furthermore, we performed the synthesis of complex molecules with eight stereocenters using tandem cycloadditions. In a programmable sequential double cycloaddition, we demonstrated the synthesis of both enantiomers of complex products by simple changes in the order of addition of chemicals. Complex products were obtained using enantioselective higher order [6 + 3] cycloaddition of azomethine ylides with fulvenes followed by Diels–Alder reaction. The bioactivity of these compound collections is also discussed.

2014-01-01

30

Enantioselective Total Synthesis of (-) - Acetylaranotin, A Dihydrooxepine Epidithiodiketopiperazine  

PubMed Central

The first total synthesis of the dihydrooxepine-containing epidithiodiketopiperazine (ETP) (?)-acetylaranotin (1) is reported. The key steps of the synthesis include an enantioselective azomethine ylide (1, 3)-dipolar cycloaddition reaction to set the absolute and relative stereochemistry, a rhodium-catalyzed cycloisomerization/chloride elimination sequence to generate the dihydrooxepine moiety, and a stereoretentive diketopiperazine sulfenylation to install the epidisulfide. This synthesis provides access to (?)-1 in 18 steps from inexpensive, commercially available starting materials. We anticipate that the approach described herein will serve as a general strategy for the synthesis of additional members of the dihydrooxepine ETP family.

Codelli, Julian A.; Puchlopek, Angela L. A.; Reisman, Sarah E.

2011-01-01

31

Enhancement of enantioselectivity by THF in asymmetric mo-catalyzed olefin metathesis. Catalytic enantioselective synthesis of cyclic tertiary ethers and spirocycles.  

PubMed

Mo-catalyzed enantioselective rearrangement of achiral cyclopentenyl tertiary ethers to chiral cyclohexenyl tertiary ethers are reported. These olefin metathesis transformations proceed efficiently and with high levels of enantioselectivity. A noteworthy feature of these reactions is that added tetrahydrofuran exerts a remarkably positive influence on the enantioselectivity of the metathesis-based rearrangement. The first examples of catalytic asymmetric synthesis of spirocyclic structures by enantioselective olefin metathesis are also disclosed. PMID:12207534

Teng, Xin; Cefalo, Dustin R; Schrock, Richard R; Hoveyda, Amir H

2002-09-11

32

Imazethapyr enantioselectively affects chlorophyll synthesis and photosynthesis in Arabidopsis thaliana.  

PubMed

Imazethapyr (IM) is a chiral herbicide with reported enantioselective biological activities between its enantiomers. This report investigated the effect of enantioselectivity between R- and S-IM in Arabidopsis thaliana on chlorophyll synthesis and photosynthesis. The results suggest that R-IM inhibited the transcription of chlM to a greater extent than S-IM, which reduced chlorophyll synthesis. R-IM also showed a stronger inhibitory effect than S-IM on the transcription of photosynthesis-related genes, affecting linear electron transport and CO(2) fixation. IM stress enantioselectively induced transcriptional upregulation of the ndhH gene, a representative of the NDH complex. In contrast, the expression of pgr5 was downregulated, which demonstrated that IM stress enhanced adenosine 5'-triphosphate (ATP) synthesis by stimulating an NDH-dependent and not ferredoxin (FD)-independent route. This study suggested that R-IM has a greater toxic effect on photosynthesis than S-IM, affecting plant growth through chlorophyll synthesis. PMID:23343119

Qian, Haifeng; Han, Xiao; Zhang, Qiannan; Sun, Zhengqi; Sun, Liwei; Fu, Zhengwei

2013-02-13

33

A Nine-Step Enantioselective Total Synthesis of (-)-Vincorine  

PubMed Central

A concise and highly enantioselective total synthesis of the akuammiline alkaloid (?)-vincorine has been accomplished. A key element of the synthesis is a stereoselective organocatalytic Diels–Alder, iminium cyclization cascade sequence, which serves to construct the tetracyclic alkaloid core architecture in one step from simple achiral precursors. The challenging seven-membered, azepanyl ring system is installed by way of a single electron-mediated cyclization event initiated from an acyl telluride precursor. The total synthesis of (?)-vincorine is achieved in nine steps and 9% overall yield from commercially available starting materials.

Horning, Benjamin D.

2013-01-01

34

Perylenequinone Natural Products: Enantioselective Synthesis of the Oxidized Pentacyclic Core‡  

PubMed Central

An enantioselective approach to the perylenequinone core found in the mold perylenequinone natural products is outlined. Specifically, the first asymmetric syntheses of helical chiral perylenequinones absent any additional stereogenic centers are described. Key elements of the synthetic venture include a catalytic enantioselective biaryl coupling, a PIFA-induced naphthalene hydroxylation, and a palladium-mediated aromatic decarboxylation. Transfer of the binaphthalene axial stereochemistry to the perylenequinone helical stereochemistry proceeded with good fidelity. Furthermore, the resultant perylenequinones were shown to possess sufficient atropisomeric stability to be viable intermediates in the biogenesis of the perylenequinone natural products. This stability supports the use of the helical axis as a stereochemical relay in synthesis of the natural products containing additional stereochemical centers.

Mulrooney, Carol A.; Morgan, Barbara J.; Li, Xiaolin; Kozlowski, Marisa C.

2009-01-01

35

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

36

Enantioselective Synthesis of N1999A2  

PubMed Central

An enantioselective synthetic route to the enediyne antibiotic N1999A2 (1) is described, proceeding in 21 steps (0.4% yield, 77% average yield per step) from (R)-(+)-glycidol. The route involves the convergent assembly of three components: a (1-iodovinyl) stannane (2), a 1,5-hexadiyne-3,4-diol derivative (3), and a substituted naphthoic acid (4). Important transformations in the synthetic sequence include the palladium-catalyzed coupling of 2 and 3, an intramolecular oxidative cyclization of a terminal bis-acetylene, and a transannular anionic (bi)cyclization of a cyclic bromoenetriyne. The careful selection and manipulation of protective groups throughout the sequence proved to be critical to the development of the synthetic route, where all late-stage intermediates were unstable and could not be concentrated. In the final step of the sequence, three protective groups were removed in a single operation, providing synthetic N1999A2 (1) in 76% yield. Conditions were found that, for the first time, led to the precipitation of 1 as a solid.

Ji, Nan; O'Dowd, Hardwin; Rosen, Brad M.; Myers, Andrew G.

2008-01-01

37

Enantioselective Total Synthesis and Confirmation of the Absolute and Relative Stereochemistry of Streptorubin B  

PubMed Central

The enantioselective total synthesis of the pyrrolophane natural product streptorubin B is described. Key steps in the concise route include 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 sidechain and bis-pyrrole 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.

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

2010-01-01

38

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

2013-11-28

39

Asymmetric synthesis of trifluoromethylated amines via catalytic enantioselective isomerization of imines.  

PubMed

A new approach toward the asymmetric synthesis of optically active trifluoromethylated amines was enabled by an unprecedented, highly enantioselective catalytic isomerization of trifluoromethyl imines with a new chiral organic catalyst. Not only aryl but also alkyl trifluoromethylated amines could be obtained in high enantioselectivities. PMID:22906148

Wu, Yongwei; Deng, Li

2012-09-01

40

Total Synthesis of (S)-(+)-Tylophorine Via Enantioselective Intramolecular Alkene Carboamination  

PubMed Central

The enantioselective synthesis of (S)-(+)-tylophorine, a potent cancer cell growth inhibitor, has been accomplished in eight steps from commercially available 3,4-dimethoxybenzyl alcohol. A copper (II)-catalyzed enantioselective intramolecular alkene carboamination was employed as the key step to construct the chiral indolizidine ring.

Zeng, Wei; Chemler, Sherry R.

2009-01-01

41

Asymmetric synthesis of indolines by catalytic enantioselective reduction of 3H-indoles.  

PubMed

A highly enantioselective metal-free reduction of 3H-indoles has been developed. This Brønsted acid catalyzed transfer hydrogenation of indole derivatives with Hantzsch dihydropyridine as the hydrogen source constitutes an efficient method for the synthesis of various optically active indolines with high enantioselectivities. PMID:20857958

Rueping, Magnus; Brinkmann, Claus; Antonchick, Andrey P; Atodiresei, Iuliana

2010-10-15

42

An Enantioselective Synthesis of CymbaltaTM  

Microsoft Academic Search

Duloxetine or Cymbalta? is a potent antidepressant which targets neural serotonin channels, making it successful at treating patients with major depressive disorder, generalized anxiety disorder, diabetic neuropathy and fibromyalgia. Cymbalta? is an enantiopure molecule in which the (S)-enantiomer acts as the active antidepressant and the (R)-enantiomer has little biological activity. In the investigated alternative synthesis this enantiopurity is achieved in

Vincent van Rixel

2010-01-01

43

Highly enantioselective catalytic synthesis of neurite growth-promoting secoyohimbanes.  

PubMed

Natural products endowed with neuromodulatory activity and their underlying structural scaffolds may inspire the synthesis of novel neurotrophic compound classes. The spirocyclic secoyohimbane alkaloid rhynchophylline is the major component of the extracts of Uncaria species used in Chinese traditional medicine for treatment of disorders of the central nervous system. Based on the structure of rhynchophylline, a highly enantioselective and efficient organocatalyzed synthesis method was developed that gives access to the tetracyclic secoyohimbane scaffold, embodying a quaternary and three tertiary stereogenic centers in a one-pot multistep reaction sequence. Investigation of a collection of the secoyohimbanes in primary rat hippocampal neurons and embryonal stem cell-derived motor neurons led to discovery of compounds that promote neurite outgrowth and influence the complexity of neuronal network formation. PMID:23601639

Antonchick, Andrey P; López-Tosco, Sara; Parga, Juan; Sievers, Sonja; Schürmann, Markus; Preut, Hans; Höing, Susanne; Schöler, Hans R; Sterneckert, Jared; Rauh, Daniel; Waldmann, Herbert

2013-04-18

44

Enantioselective total synthesis of marine diterpenoid clavulactone.  

PubMed

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

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

2012-06-25

45

Synthesis of 1-[bis(trifluoromethyl)phosphine]-1'-oxazolinylferrocene ligands and their application in regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates  

PubMed Central

Summary A class of novel, easily accessible and air-stable 1-[bis(trifluoromethyl)phosphine]-1’-oxazolinylferrocene ligands has been synthesized from ferrocene. It became apparent that these ligands can be used in the regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates in a highly efficient manner. Excellent regio- and enantioselectivity could be obtained for a wide range of substrates.

Lai, Zeng-Wei; Yang, Rong-Fei; Ye, Ke-Yin

2014-01-01

46

Enantioselective Synthesis of Atropisomeric Benzamides through Peptide-Catalyzed Bromination  

PubMed Central

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 are 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 provide some insight into the basis for selectivity. Examination of the observed products at low conversion suggests that the initial catalytic bromination may be regioselective and stereochemistry-determining. A complex between catalyst and substrate is observed by NMR, revealing a specific association. Finally, products of these reactions may be subjected to regioselective metal-halogen exchange and trapping with I2, setting the stage for utility.

Barrett, Kimberly T.; Miller, Scott J.

2013-01-01

47

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A  

PubMed Central

Summary A concise enantioselective synthesis of the advanced intermediate 5 for the synthesis of pumiliotoxins (Gallagher’s intermediate) is described. The synthesis started from the regio- and trans-diastereoselective (dr = 98:2) reductive 3-butenylation of (R)-3-(tert-butyldimethylsilyloxy)glutarimide 14. After O-desilylation and Dess–Martin oxidation, the resulting keto-lactam 10 was subjected to a highly trans-stereoselective addition of the methylmagnesium iodide to give carbinol 11 as sole diastereomer. An efficient ring closure procedure consisting of ozonolysis and reductive dehydroxylation provided the indolizidine derivative 5, which completed the formal enantioselective total synthesis of pumiliotoxins 251D and 237A.

Zhang, Jie

2013-01-01

48

Enantioselective synthesis of (R)-bufuralol via dynamic kinetic resolution in the key step.  

PubMed

An enantioselective synthesis of (R)-bufuralol via a ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR) has been achieved. The synthesis starts from readily available 2-ethylphenol and provides (R)-bufuralol in high ee and a good overall yield of 31%. PMID:20524620

Johnston, Eric V; Bogár, Krisztián; Bäckvall, Jan-E

2010-07-01

49

Highly efficient and enantioselective biotransformations of racemic azetidine-2-carbonitriles and their synthetic applications.  

PubMed

Catalyzed by the Rhodococcus erythropolis AJ270 whole cell catalyst in neutral aqueous buffer at 30 degrees C, a number of racemic 1-benzylazetidine-2-carbonitriles, trans-1-benzyl-4-methylazetidine-2-carbonitrile, and 1-benzyl-2-methylazetidine-2-carbonitrile and their amide substrates underwent efficient and enantioselective biotransformations to afford the corresponding azetidine-2-carboxylic acids and their amide derivatives in excellent yields with ee up to >99.5%. The overall excellent enantioselectivity of the biocatalytic reactions stemmed from a combined effect of a very active but virtually nonenantioselective nitrile hydratase and a high R-enantioselective amidase involved in microbial whole cells. The synthetic applications have been demonstrated by the nucleophilic ring-opening reactions of azetidiniums of the resulting chiral azetidine-2-carbox amide derivatives for the preparation of alpha,gamma-diamino, alpha-phenoxy-gamma-amino, and alpha-cyano-gamma-amino carboxamides. The intramolecular CuI-catalyzed cross-coupling reaction for the synthesis of azetidine-fused 1,4-benzodiazepin-2-one derivative was also presented. PMID:19627128

Leng, Dong-Hui; Wang, De-Xiang; Pan, Jie; Huang, Zhi-Tang; Wang, Mei-Xiang

2009-08-21

50

Characteristics of a New Enantioselective Thermostable Dipeptidase from Brevibacillus borstelensis BCS-1 and Its Application to Synthesis of a d-Amino-Acid-Containing Dipeptide  

PubMed Central

A new thermostable dipeptidase gene was cloned from the thermophile Brevibacillus borstelensis BCS-1 by genetic complementation of the d-Glu auxotroph Escherichia coli WM335 on a plate containing d-Ala-d-Glu. Nucleotide sequence analysis revealed that the gene included an open reading frame coding for a 307-amino-acid sequence with an Mr of 35,000. The deduced amino acid sequence of the dipeptidase exhibited 52% similarity with the dipeptidase from Listeria monocytogenes. The enzyme was purified to homogeneity from recombinant E. coli WM335 harboring the dipeptidase gene from B. borstelensis BCS-1. Investigation of the enantioselectivity (E) to the P1 and P1? site of Ala-Ala revealed that the ratio of the specificity constant (kcat/Km) for l-enantioselectivity to the P1 site of Ala-Ala was 23.4 ± 2.2 [E = (kcat/Km)l,d/(kcat/Km)d,d], while the d-enantioselectivity to the P1? site of Ala-Ala was 16.4 ± 0.5 [E = (kcat/Km)l,d/(kcat/Km)l,l] at 55°C. The enzyme was stable up to 55°C, and the optimal pH and temperature were 8.5 and 65°C, respectively. The enzyme was able to hydrolyze l-Asp-d-Ala, l-Asp-d-AlaOMe, Z-d-Ala-d-AlaOBzl, and Z-l-Asp-d-AlaOBzl, yet it could not hydrolyze d-Ala-l-Asp, d-Ala-l-Ala, d-AlaNH2, and l-AlaNH2. The enzyme also exhibited ?-lactamase activity similar to that of a human renal dipeptidase. The dipeptidase successfully synthesized the precursor of the dipeptide sweetener Z-l-Asp-d-AlaOBzl.

Baek, Dae Heoun; Song, Jae Jun; Kwon, Seok-Joon; Park, Chung; Jung, Chang-Min; Sung, Moon-Hee

2004-01-01

51

Enantioselective Synthesis of the ABC Ring Motif of Norzoanthamine Based on Asymmetric Robinson Annulation Reactions  

PubMed Central

An enantioselective strategy for the synthesis of tetracyclic motif 5, representing the northern fragment of norzoanthamine, is presented. Key to the strategy is the use of two asymmetric Robinson annulation reactions that produce the tricyclic ABC ring system with excellent stereoselectivity. Further functionalization at the periphery of the C ring produces compound 5 containing six contiguous stereocenters of the natural product.

Nguyen, Thong X.; Dakanali, Marianna; Trzoss, Lynnie; Theodorakis, Emmanuel A.

2011-01-01

52

Pd-catalyzed enantioselective C-H iodination: asymmetric synthesis of chiral diarylmethylamines.  

PubMed

An enantioselective C-H iodination reaction using a mono-N-benzoyl-protected amino acid has been developed for the synthesis of chiral diarylmethylamines. The reaction uses iodine as the sole oxidant and proceeds at ambient temperature and under air. PMID:24151991

Chu, Ling; Wang, Xiao-Chen; Moore, Curtis E; Rheingold, Arnold L; Yu, Jin-Quan

2013-11-01

53

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

54

The enantioselective total synthesis of a beta-carboline alkaloid, (S)-(-)-dichotomine C.  

PubMed

The first enantioselective synthesis of a beta-carboline alkaloid, dichotomine C, possessing antiallergic effects, was achieved by constructing a beta-carboline framework based on the microwave-assisted thermal electrocyclic reaction of a 1-azahexatriene system, followed by the Sharpless asymmetric dihydroxylation. PMID:18239319

Omura, Kana; Choshi, Tominari; Watanabe, Shiroh; Satoh, Yuhsuke; Nobuhiro, Junko; Hibino, Satoshi

2008-02-01

55

Synthetic studies on borrelidin: enantioselective synthesis of the C1-C12 fragment.  

PubMed

[structure: see text] An efficient, enantioselective synthesis of the C1-C12 fragment 2 of borrelidin is presented. Construction of the "skipped" polymethylene chain of 2 was accomplished by iteration of Myers' alkylation, while formation of the C3 stereocenter was achieved by Roush's asymmetric allylboration methodology. PMID:12735735

Vong, Binh G; Abraham, Sunny; Xiang, Alan X; Theodorakis, Emmanuel A

2003-05-15

56

Oxazoline-based organocatalyst for enantioselective strecker reactions: a protocol for the synthesis of levamisole.  

PubMed

A chiral oxazoline-based organocatalyst has been found to efficiently catalyze asymmetric Strecker reactions of various aromatic and aliphatic N-benzhydrylimines with trimethylsilyl cyanide (TMSCN) as a cyanide source at -20?°C to give ?-aminonitriles in high yield (96?%) with excellent chiral induction (up to 98?%?ee). DFT calculations have been performed to rationalize the enantioselective formation of the product with the organocatalyst in these reactions. The organocatalyst has been characterized by single-crystal X-ray diffraction analysis, as well as by other analytical methods. This protocol has been extended to the synthesis of the pharmaceutically important drug molecule levamisole in high yield and with high enantioselectivity. PMID:24009109

Sadhukhan, Arghya; Sahu, Debashis; Ganguly, Bishwajit; Khan, Noor-ul H; Kureshy, Rukhsana I; Abdi, Sayed H R; Suresh, E; Bajaj, Hari C

2013-10-11

57

Organocatalyzed enantioselective synthesis of 6-amino-5-cyanodihydropyrano[2,3-c]pyrazoles  

PubMed Central

The first enantioselective synthesis of biologically active 6-amino-5-cyanodihydropyrano[2,3-c]pyrazoles has been achieved through a cinchona alkaloid-catalyzed tandem Michael addition and Thorpe-Ziegler type reaction between 2-pyrazolin-5-ones and benzylidenemalononitriles. The reaction may also be carried out in a three-component or a four-component fashion via the in situ formation of these two components from simple and readily available starting materials. The desired products were obtained in excellent yields with mediocre to excellent enantioselectivities (up to >99% ee).

Gogoi, Sanjib; Zhao, Cong-Gui

2009-01-01

58

Enantioselective synthesis of (s)- and (R)-tolterodine by asymmetric hydrogenation of a coumarin derivative obtained by a Heck reaction.  

PubMed

An efficient and short enantioselective synthesis of (S)- and (R)-tolterodine was performed by asymmetric hydrogenation of a coumarin intermediate, easily obtained by a Heck reaction from inexpensive and commercially available starting materials. PMID:17625882

Ulgheri, Fausta; Marchetti, Mauro; Piccolo, Oreste

2007-08-01

59

Enantioselective synthesis of helical polydiacetylenes in the visible light region.  

PubMed

Herein, we demonstrate for the first time that the enantio-selective polymerization of DA monomers could be realized upon irradiation with circularly polarized visible light (CPVL), which could effectively provide chiral order in the propagating step of a polymerization reaction. PMID:24448663

Yang, Guang; Han, Lu; Jiang, Hao; Zou, Gang; Zhang, Qijin; Zhang, Douguo; Wang, Pei; Ming, Hai

2014-03-01

60

Engineering an enantioselective amine oxidase for the synthesis of pharmaceutical building blocks and alkaloid natural products.  

PubMed

The development of cost-effective and sustainable catalytic methods for the production of enantiomerically pure chiral amines is a key challenge facing the pharmaceutical and fine chemical industries. This challenge is highlighted by the estimate that 40-45% of drug candidates contain a chiral amine, fueling a demand for broadly applicable synthetic methods that deliver target structures in high yield and enantiomeric excess. Herein we describe the development and application of a "toolbox" of monoamine oxidase variants from Aspergillus niger (MAO-N) which display remarkable substrate scope and tolerance for sterically demanding motifs, including a new variant, which exhibits high activity and enantioselectivity toward substrates containing the aminodiphenylmethane (benzhydrylamine) template. By combining rational structure-guided engineering with high-throughput screening, it has been possible to expand the substrate scope of MAO-N to accommodate amine substrates containing bulky aryl substituents. These engineered MAO-N biocatalysts have been applied in deracemization reactions for the efficient asymmetric synthesis of the generic active pharmaceutical ingredients Solifenacin and Levocetirizine as well as the natural products (R)-coniine, (R)-eleagnine, and (R)-leptaflorine. We also report a novel MAO-N mediated asymmetric oxidative Pictet-Spengler approach to the synthesis of (R)-harmicine. PMID:23808566

Ghislieri, Diego; Green, Anthony P; Pontini, Marta; Willies, Simon C; Rowles, Ian; Frank, Annika; Grogan, Gideon; Turner, Nicholas J

2013-07-24

61

Stereoselection in the prins-pinacol synthesis of 2,2-disubstituted 4-acyltetrahydrofurans. Enantioselective synthesis of (-)-citreoviral.  

PubMed

[reaction: see text] The condensation of allylic diols with unsymmetrical ketones proceeds with high stereoselection to form 2,2-disubstituted 4-acyltetrahydrofurans when the alpha-substituents of the ketone differ substantially in size. A Prins-pinacol condensation of this type is the central strategic step in an enantioselective synthesis of (-)-citreoviral. PMID:10814287

Hanaki, N; Link, J T; MacMillan, D W; Overman, L E; Trankle, W G; Wurster, J A

2000-01-27

62

Enantioselective total synthesis of (+)-largazole, a potent inhibitor of histone deacetylase.  

PubMed

An enantioselective total synthesis of the 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 beta-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. PMID:18662003

Ghosh, Arun K; Kulkarni, Sarang

2008-09-01

63

An enantioselective synthesis of 2-aryl cycloalkanones by Sc-catalyzed carbon insertion.  

PubMed

Current methods for asymmetric ?-arylation require blocking groups to prevent reaction at the ?'-carbon, basic conditions that promote racemization, or multistep synthesis. This work records the first catalytic enantioselective examples of the diazoalkane-carbonyl homologation reaction. Medium ring 2-aryl ketones are prepared in one step in up to 98:2 er and 99% yield from the unsubstituted lower homologue by Sc-catalyzed aryldiazomethyl insertion with simple bis- and tris(oxazoline) ligands. PMID:21401070

Rendina, Victor L; Moebius, David C; Kingsbury, Jason S

2011-04-15

64

Catalytic enantioselective synthesis of P-stereogenic compounds.  

PubMed

Catalytic enantioselective strategies have become synthetically useful to access P-stereogenic phosphines. To date, enantioselective desymmetrisations and dynamic kinetic resolutions dominate the field. Desymmetrisation strategies do not necessarily require the formation of a P-carbon or P-heteroatom bond. This approach has been validated with variable levels of success using organocatalysed asymmetric deprotonation (chiral diamine) or methylation (phase transfer catalysis), enzyme-mediated esterification, rhodium catalysed [2+2+2] cycloadditions and more recently molybdenum-based ring closing metathesis. The dynamic kinetic resolution of racemic P-templates relying on a P-C bond-forming event has been the object of extensive investigations, which have culminated with the arylation and alkylation (benzylation) of equilibrating diastereomeric palladium, platinum or ruthenium phosphido complexes. Although all these routes allow access to a myriad of highly interesting P-stereogenic compounds, the level of enantiocontrol is substrate- and reactant-dependent. Pleasingly, ee's up to 98% were obtained on selected systems. PMID:20835471

Harvey, James Stephen; Gouverneur, Véronique

2010-10-28

65

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

66

Enantioselective synthesis of allylboronates and allylic alcohols by copper-catalyzed 1,6-boration.  

PubMed

Chiral secondary allylboronates are obtained in high enantioselectivities and 1,6:1,4 ratios by the copper-catalyzed 1,6-boration of electron-deficient dienes with bis(pinacolato)diboron (B2(pin)2). The reactions proceed efficiently using catalyst loadings as low as 0.0049?mol?%. The allylboronates may be oxidized to the allylic alcohols, and can be used in stereoselective aldehyde allylborations. This process was applied to a concise synthesis of atorvastatin, in which the key 1,6-boration was performed using only a 0.02?mol?% catalyst loading. PMID:24623638

Luo, Yunfei; Roy, Iain D; Madec, Amaël G E; Lam, Hon Wai

2014-04-14

67

Facile and highly enantioselective synthesis of (+)- and (-)-fluvastatin and their analogues.  

PubMed

A highly enantioselective synthesis of (+)- and (-)-fluvastatin and their analogues has been facilitated by the reaction of an aldehyde with diketene in the presence of Ti(O-i-Pr)4 and a chiral Schiff base ligand. Either enantiomer of the Schiff base could be employed to obtain (+)- or (-)-fluvastatin. Diastereoselective reductions of the resultant keto moiety of ?-hydroxy ketoesters provided the syn-1,3-diol esters (91% ee), which were subsequently recrystallized and saponified to afford (+)- and (-)-fluvastatin in >99.9% ee. PMID:20939538

Zacharia, James T; Tanaka, Takanori; Hayashi, Masahiko

2010-11-19

68

Enantioselective synthesis of H-phosphinic acids bearing natural amino acid residues.  

PubMed

The first systematic study on the asymmetric synthesis of H-phosphinic acids bearing natural protein amino acid residues was reported on the basis of the asymmetric addition of ethyl diethoxymethylphosphinate to N-tert-butanesulfinyl imines. Good yields and moderate to high enantioselectivities were obtained. Reliable methods were developed for the elucidation of the stereochemistry of these phosphinic acids and derivatives thereof. The transformation of the side chains of these analogues was studied. Methods for the conversion of the ?-aminophosphinates to oligopetides were reported. PMID:23772951

Yao, Qiuli; Yuan, Chengye

2013-07-19

69

Enantioselective total synthesis of altohyrtin C (spongistatin 2)  

Microsoft Academic Search

The first total synthesis of a spongipyran macrolide, altohyrtin C, is described. The convergent synthesis strategy relies on a regioselective macrolactonization, a stereoselective Wittig coupling of the two major synthetic fragments, a complex anti aldol reaction to join the C1–C15 and C16–C28 spiroketal regions, and an anomeric sulfone acylation to join the C29–C37 and C38–C43 pyran regions. The incorporation of

David A. Evans; B. Wesley Trotter; Paul J. Coleman; Bernard Côté; Luiz Carlos Dias; Hemaka A. Rajapakse; Andrew N. Tyler

1999-01-01

70

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

71

Enantioselective synthesis of isotopically labeled homocitric acid lactone.  

PubMed

A concise synthesis of homocitric acid lactone was developed to accommodate systematic placement of carbon isotopes (specifically (13)C) for detailed studies of this cofactor. This new route uses a chiral allylic alcohol, available in multigram quantities from enzymatic resolution, as a starting material, which transposes asymmetry through an Ireland-Claisen rearrangement. PMID:24180620

Moore, Jared T; Hanhan, Nadine V; Mahoney, Maximillian E; Cramer, Stephen P; Shaw, Jared T

2013-11-15

72

A concise enantioselective synthesis of the guaiane sesquiterpene (-)-oxyphyllol  

PubMed Central

Summary (?)-Oxyphyllol was prepared in only 4 steps from an epoxy enone that already served as an intermediate for the total synthesis of the anticancer guaiane (?)-englerin A. A regio- and diastereoselective Co(II)-catalyzed hydration of the olefin and a transannular epoxide opening were used as the key reactions.

Zahel, Martin

2013-01-01

73

Synthetic studies on (+)-biotin, part 15: A chiral squaramide-mediated enantioselective alcoholysis approach toward the total synthesis of (+)-biotin.  

PubMed

An efficient stereocontrolled total synthesis of (+)-biotin (1) has been achieved via the intermediacy of Roche's lactone 5 starting from cis-1,3-dibenzyl-2-imidazole-4,5-dicarboxylic acid (2). The bifunctional cinchona alkaloid-derived squaramide-promoted enantioselective alcoholysis was utilizing as a tool for the construction of two contiguous stereocenters of C-3a and C-6a in biotin molecular with excellent enantioselectivity. In addition, the 4-carboxybutyl side chain was assembled by first using C4+C1 approach via a novel tricyclic thiophanium salt intermediate. PMID:21467680

Chen, Xu-Xiang; Xiong, Fei; Fu, Han; Liu, Zhi-Qian; Chen, Fen-Er

2011-01-01

74

Practical enantioselective synthesis of beta-substituted-beta-amino esters.  

PubMed

[reaction: see text] A practical, large-scale synthesis of a beta-amino ester 1 was developed. A chiral imine derived from (S)-phenylglycinol and 3-trimethylsilylpropanal was coupled with the Reformatsky reagent 3 with high diastereoselectivity (de > 98%) to give (SS)-4a as the major isomer. The amino alcohol residue of the coupling product 4 was oxidatively cleaved with sodium periodate in the presence of methylamine. An unusual selective oxidative cleavage of the (SS)-isomer was observed and the imine 6 was obtained with ee > 99% while the (RS)-4b isomer was not cleaved. Reaction with p-toluenesulfonic acid monohydrate allowed for the hydrolysis of the imine and the isolation of the amine as its salt. The title compound 1 was then obtained by transesterification, desilylation, and hydrochloride salt formation in a one-pot process. The method was successfully applied toward the synthesis of a wide variety of beta-amino esters. PMID:15989317

Awasthi, Alok K; Boys, Mark L; Cain-Janicki, Kimberly J; Colson, Pierre-Jean; Doubleday, Wendel W; Duran, Joseph E; Farid, Payman N

2005-07-01

75

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

2013-04-01

76

Enantioselective synthesis of (R)-tolterodine using lithiation/borylation-protodeboronation methodology.  

PubMed

The synthesis of the pharmaceutical (R)-tolterodine is reported using lithiation/borylation-protodeboronation of a homoallyl carbamate as the key step. This step was tested with two permutations: an electron-neutral aryl Li-carbamate reacting with an electron-rich boronic ester and an electron-rich aryl Li-carbamate reacting with an electron-neutral boronic ester. It was found that the latter arrangement was considerably better than the former. Further improvements were achieved using magnesium bromide in methanol leading to a process that gave high yield and high enantioselectivity in the lithiation/borylation reaction. The key step was used in an efficient synthesis of (R)-tolterodine in a total of eight steps in a 30% overall yield and 90% ee. PMID:23750041

Roesner, Stefan; Aggarwal, Varinder K

2012-11-01

77

Enantioselective synthesis of (R)-tolterodine using lithiation/borylation-protodeboronation methodology  

PubMed Central

The synthesis of the pharmaceutical (R)-tolterodine is reported using lithiation/borylation–protodeboronation of a homoallyl carbamate as the key step. This step was tested with two permutations: an electron-neutral aryl Li-carbamate reacting with an electron-rich boronic ester and an electron-rich aryl Li-carbamate reacting with an electron-neutral boronic ester. It was found that the latter arrangement was considerably better than the former. Further improvements were achieved using magnesium bromide in methanol leading to a process that gave high yield and high enantioselectivity in the lithiation/borylation reaction. The key step was used in an efficient synthesis of (R)-tolterodine in a total of eight steps in a 30% overall yield and 90% ee.

Roesner, Stefan; Aggarwal, Varinder K.

2013-01-01

78

Studies Directed Toward the Enantioselective Synthesis of Cymbalta?  

Microsoft Academic Search

Progress on the synthesis of duloxetine, marketed as Cymbalta?, will be presented. Cymbalta?, a potent antidepressant, targets neural serotonin-norepinephrine channels, successfully treating patients with major depressive disorder, generalized anxiety disorder, diabetic neuropathy, and fibromyalgia. The (S)-enantiomer of duloxetine acts as a serotonin reuptake inhibitor while the (R)-enantiomer exhibits little biological activity. Consequently, we have developed an enantiosynthetic strategy for the

Colin McKinlay

2011-01-01

79

Enantioselective Synthesis of anti- and syn-homopropargyl alcohols via Chiral Br?nsted Acid Catalyzed asymmetric Allenylboration reactions  

PubMed Central

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 triple asymmetric 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.

Chen, Ming; Roush, William R.

2012-01-01

80

Highly enantioselective [4+2] annulation via organocatalytic Mannich-reductive cyclization: one-pot synthesis of functionalized piperidines.  

PubMed

A new method for one-pot synthesis of 2,3-substituted piperidine from N-PMP aldimine and aqueous glutaraldehyde via formal [4+2] cycloaddition is reported. This reaction involves organocatalytic direct Mannich reaction-reductive cyclization with high yields (up to 90%) and excellent enantioselectivities (up to >99%). The practicability of this method is also shown at a gram scale as well as through the synthesis of functionalized (-)-anabasine. PMID:23689916

Kumar, Indresh; Ramaraju, Panduga; Mir, Nisar A; Singh, Deepika; Gupta, Vivek K; Rajnikant

2013-06-25

81

A greener enantioselective synthesis of the antiviral agent North-methanocarbathymidine (N-MCT) from 2-deoxy-d-ribose  

PubMed Central

An enantioselective synthesis of suitably protected (1R,2S,4S,5S)-4-amino-1-(hydroxymethyl)bicyclo[3.1.0]hexan-2-ol, a key starting material for the synthesis of conformationally locked carbocyclic nucleosides, including the antiviral active North-methanocarba thymidine, is reported. Starting from 2-deoxyribose the target Boc-protected amine was prepared in 33% overall yield under condition that are ecologically friendlier than previous methods.

Ludek, Olaf R.; Marquez, Victor E.

2009-01-01

82

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

2013-10-14

83

Application of a chiral metal-organic framework in enantioselective separation.  

PubMed

A modular approach for the synthesis of highly ordered porous and chiral auxiliary (Evans auxiliary) decorated metal-organic frameworks is developed. Our synthesis strategy, which uses known porous structures as model materials for incorporation of chirality via linker modification, can provide access to a wide range of porous materials suitable for enantioselective separation and catalysis. Chiral analogues of UMCM-1 have been synthesized and investigated for the enantioseparation of chiral compounds in the liquid phase and first promising results are reported. PMID:21960280

Padmanaban, Mohan; Müller, Philipp; Lieder, Christian; Gedrich, Kristina; Grünker, Ronny; Bon, Volodymyr; Senkovska, Irena; Baumgärtner, Sandra; Opelt, Sabine; Paasch, Silvia; Brunner, Eike; Glorius, Frank; Klemm, Elias; Kaskel, Stefan

2011-11-28

84

Mukaiyama-Michael reactions with acrolein and methacrolein: a catalytic enantioselective synthesis of the C17-C28 fragment of pectenotoxins.  

PubMed

Enantioselective iminium-catalyzed reactions with acrolein and methacrolein are rare. A catalytic enantioselective Mukaiyama-Michael reaction that readily accepts acrolein or methacrolein as substrates, affording the products in good yields and 91-97% ee, is presented. As an application of the methodology, an enantioselective route to the key C17-C28 segment of the pectenotoxin using the Mukaiyama-Michael reaction as the key step is described. PMID:22296172

Kemppainen, Eeva K; Sahoo, Gokarneswar; Valkonen, Arto; Pihko, Petri M

2012-02-17

85

Enantioselective iridium-catalyzed allylic arylation.  

PubMed

We describe herein the development of the first iridium-catalyzed allylic substitution using arylzinc nucleophiles. High enantioselectivities were obtained from the reactions, which used commercially available Grignard reagents as the starting materials. This methodology was also shown to be compatible with halogen/metal exchange reactions. Its synthetic potential is demonstrated by its application towards the formal synthesis of (+)-sertraline. PMID:19072966

Polet, Damien; Rathgeb, Xavier; Falciola, Caroline A; Langlois, Jean-Baptiste; El Hajjaji, Samir; Alexakis, Alexandre

2009-01-01

86

Direct, Enantioselective Synthesis of Pyrroloindolines and Indolines From Simple Indole Derivatives  

PubMed Central

The (R)-BINOL•SnCl4-catalyzed formal (3 + 2) cycloaddition between 3-substituted indoles and benzyl 2-trifluoroacetamidoacrylate is a direct, enantioselective method to prepare pyrroloindolines from simple starting materials. However, under the originally disclosed conditions, the pyrroloindolines are formed as mixtures of diastereomers, typically in the range of 3:1 to 5:1 favoring the exo-product. The poor diastereoselectivity detracts from the synthetic utility of the reaction. We report here that use of methyl 2-trifluoroacetamidoacrylate in conjunction with (R)-3,3'-dichloro-BINOL•SnCl4 provides the corresponding pyrroloindolines with improved diastereoselectivity (typically ?10:1). Guided by mechanistic studies, a one-flask synthesis of enantioenriched indolines by in situ reduction of a persistent iminium ion is also described.

Ni, Jane; Wang, Haoxuan; Reisman, Sarah E.

2013-01-01

87

Enantioselective synthesis of ?-methyl carboxylic acids from readily available starting materials via chemoenzymatic dynamic kinetic resolution.  

PubMed

An enantioselective method for the synthesis of ?-methyl carboxylic acids starting from trans-cinnamaldehyde, a readily available and inexpensive compound, has been developed. Allylic alcohol 1 was obtained via a standard Grignard addition to trans-cinnamaldehyde. Dynamic kinetic resolution was applied to allylic alcohol 1 utilizing a ruthenium catalyst and either an (R)-selective lipase or an (S)-selective protease to provide the corresponding allylic esters in high yield and high ee. A copper-catalyzed allylic substitution was then applied to provide the corresponding alkenes with inversion of stereochemistry. Subsequent C-C double bond cleavage afforded pharmaceutically important ?-methyl substituted carboxylic acids in high ee and overall yields of up to 76%. PMID:20857917

Thalén, Lisa K; Sumic, Anna; Bogár, Krisztián; Norinder, Jakob; Persson, Andreas K Å; Bäckvall, Jan-E

2010-10-15

88

Asymmetric phosphorylation through catalytic P(III) phosphoramidite transfer: Enantioselective synthesis of d-myo-inositol-6-phosphate  

PubMed Central

Despite the ubiquitous use of phosphoramidite chemistry in the synthesis of biophosphates, catalytic asymmetric phosphoramidite transfer remains largely unexplored for phosphate ester synthesis. We have discovered that a tetrazole-functionalized peptide, in the presence of 10-? molecular sieves, functions as an enantioselective catalyst for phosphite transfer. This chemistry in turn has been used as the key step in a streamlined synthesis of myo-inositol-6-phosphate. Mechanistic insights implicate phosphate as a directing group for a highly selective kinetic resolution of a protected inositol monophosphate. This work represents a distinct and efficient method for the selective catalytic phosphorylation of natural products.

Jordan, Peter A.; Kayser-Bricker, Katherine J.; Miller, Scott J.

2010-01-01

89

Catalytic asymmetric amination of N-nonsubstituted ?-alkoxycarbonyl amides: concise enantioselective synthesis of mycestericin F and G.  

PubMed

In an attempt to explore the synthetic utility of a ternary asymmetric catalyst comprising La(NO(3))(3)·6H(2)O, amide-based ligand (R)-L1, and D-valine tert-butyl ester H-D-Val-OtBu, we investigated a catalytic, asymmetric amination of functionalized N-nonsubstituted ?-alkoxycarbonyl amides using di-tert-butyl azodicarboxylate as an electrophilic aminating reagent. A highly functionalized, cyclic N-nonsubstituted ?-alkoxycarbonyl amide delivered the desired amination product in up to 96% enantiometric excess, with the requisite functionalities of the polar heads of sphingosines with the appropriate stereochemical arrangement. The rapid asymmetric assembly of these functional groups allowed a concise enantioselective synthetic route to sphingosines to be established with a broad flexibility towards derivative synthesis. These studies have culminated in an efficient catalytic enantioselective total synthesis of immunosuppressive fungal metabolites mycestericin?F (3a) and G (3b). PMID:21274942

Berhal, Farouk; Takechi, Sho; Kumagai, Naoya; Shibasaki, Masakatsu

2011-02-01

90

Rhodium-catalyzed sequential allylic amination and olefin hydroacylation reactions: enantioselective synthesis of seven-membered nitrogen heterocycles.  

PubMed

Dynamic kinetic asymmetric amination of branched allylic acetimidates has been applied to the synthesis of 2-alkyl-dihydrobenzoazepin-5-ones. These seven-membered-ring aza ketones are prepared in good yield with high enantiomeric excess by rhodium-catalyzed allylic substitution with 2-amino aryl aldehydes followed by intramolecular olefin hydroacylation of the resulting alkenals. This two-step procedure is amenable to varied functionality and proves useful for the enantioselective preparation of these ring systems. PMID:24591294

Arnold, Jeffrey S; Mwenda, Edward T; Nguyen, Hien M

2014-04-01

91

Development of ProPhenol ligands for the diastereo- and enantioselective synthesis of ?-hydroxy-?-amino esters.  

PubMed

A zinc-ProPhenol-catalyzed direct asymmetric aldol reaction between glycine Schiff bases and aldehydes is reported. The design and synthesis of new ProPhenol ligands bearing 2,5-trans-disubstituted pyrrolidines was essential for the success of this process. The transformation operates at room temperature and affords syn ?-hydroxy-?-amino esters in high yields with good to excellent levels of diastereo- and enantioselectivity. PMID:24502188

Trost, Barry M; Miege, Frédéric

2014-02-26

92

Enantioselective synthesis of C2-functionalized, N-protected morpholines and orthogonally N,N?-protected piperazines via organocatalysis  

PubMed Central

In this Letter, we describe a novel three-step, one-pot procedure for the enantioselective synthesis of N-benzyl protected morpholines and orthogonally N,N?-protected piperazines with chiral alkyl groups installed at the C2 position of each heterocyclic core via organocatalysis. This methodology allows for the rapid preparation of functionalized morpholines and piperazines that are not readily accessible through any other chemistry in good to excellent % ee (55–98% ee).

O'Reilly, Matthew C.; Lindsley, Craig W.

2012-01-01

93

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

94

Catalytic, enantioselective synthesis of 1,2-anti-diols by asymmetric ring-opening/cross-metathesis.  

PubMed

An enantioselective method for the synthesis of 1,2-anti-diols has been developed. A cyclometalated chiral-at-ruthenium complex catalyzes the asymmetric ring-opening/cross-metathesis of dioxygenated cyclobutenes, thus resulting in functionally rich synthetic building blocks. Syntheses of the insect pheromone (+)-endo-brevicomin and monosaccharide ribose demonstrate the synthetic utility of the 1,2-anti-diol fragments generated in the title reaction. PMID:24554613

Hartung, John; Grubbs, Robert H

2014-04-01

95

Enantioselective synthesis of 4-substituted 4,5-dihydro-1H-[1,5]benzodiazepin-2(3H)-ones by the Lewis base-catalyzed hydrosilylation.  

PubMed

Enantioselective synthesis of 4-substituted 4,5-dihydro-1H-[1,5]benzodiazepin-2(3H)-ones has been accomplished through chiral Lewis base-catalyzed hydrosilylation. The corresponding products were obtained in excellent yields (up to 99%) and enantioselectivities (up to 98%). The absolute configuration of product 3n has been determined as S by X-ray crystallographic analysis. PMID:21958202

Chen, Xing; Zheng, Yongsheng; Shu, Chang; Yuan, Weicheng; Liu, Bo; Zhang, Xiaomei

2011-11-01

96

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

97

Enantioselective total synthesis of briarellins E and F: the first total syntheses of briarellin diterpenes.  

PubMed

Enantioselective total syntheses of briarellin E (4) and briarellin F (5) have been achieved starting with (S)-(+)-carvone and (S)-(-)-glycidol. These total syntheses are the first of briarellin diterpenes. The central step in these syntheses is acid-promoted condensation of cyclohexadienyl diol 15 and (Z)-alpha,beta-unsaturated aldehyde 16 to form, with complete stereocontrol, the hexahydroisobenzofuran core and six stereocenters of these coral metabolites. These syntheses also feature stereospecific photolytic deformylation of beta,gamma-unsaturated aldehyde 17 to remove the extraneous carbon introduced in the Prins-pinacol step, chemo- and stereoselective hydroxyl-directed epoxidation of dienyl alcohol 18 to incorporate the C3 oxygen stereocenter, regio- and stereoselective rearrangement of epoxy ester 19 to install the C4 oxygen substituent, efficient dehydrative cyclization of a 1,6-diol intermediate to form the oxepane ring, and diastereoselective Nozaki-Hiyama-Kishi cyclization of vinyl iodide aldehyde 25 to forge the oxacyclononane ring and the C6 hydroxyl stereocenter. These total syntheses establish the absolute configurations of 4 and 5, define a concise strategy for the total synthesis of briarellin diterpenes, and provide additional illustrations of the uncommon utility of pinacol-terminated cationic cyclizations for stereocontrolled synthesis of complex oxacyclic natural products. PMID:12769572

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

2003-06-01

98

Enantioselective synthesis of tatanans A-C and reinvestigation of their glucokinase-activating properties  

NASA Astrophysics Data System (ADS)

The tatanans are members of a novel class of complex sesquilignan natural products recently isolated from the rhizomes of Acorus tatarinowii Schott plants. Tatanans A, B and C have previously been reported to have potent glucokinase-activating properties that exceed the in vitro activity of known synthetic antidiabetic agents. Here, using a series of sequential [3,3]-sigmatropic rearrangements, we report the total synthesis of tatanan A in 13 steps and 13% overall yield. We also complete a concise enantioselective total synthesis of more complex, atropisomeric tatanans B and C via a distinct convergent strategy based on a palladium-catalysed diastereotopic aromatic group differentiation (12 steps, 4% and 8% overall yield, respectively). A plausible biosynthetic relationship between acyclic tatanan A and spirocyclic tatanans B and C is proposed and probed experimentally. With sufficient quantities of the natural products in hand, we undertake a detailed functional characterization of the biological activities of tatanans A-C. Contrary to previous reports, our assays utilizing pure recombinant human enzyme demonstrate that tatanans do not function as allosteric activators of glucokinase.

Xiao, Qing; Jackson, Jeffrey J.; Basak, Ashok; Bowler, Joseph M.; Miller, Brian G.; Zakarian, Armen

2013-05-01

99

Enantioselective Synthesis of Tryptophan Derivatives by a Tandem Friedel - Crafts Conjugate Addition/Asymmetric Protonation Reaction  

PubMed Central

The tandem Friedel–Crafts conjugate addition/asymmetric protonation reaction between 2-substituted indoles and methyl 2-acetamidoacrylate is reported. The reaction is catalyzed by (R)-3,3?-dibromo-BINOL in the presence of stoichiometric SnCl4, and is the first example of a tandem conjugate addition/asymmetric protonation reaction using a BINOL•SnCl4 complex as the catalyst. A range of indoles furnished synthetic tryptophan derivatives in good yields and high levels of enantioselectivity, even on preparative scale. The convergent nature of this transformation should lend itself to the preparation of unnatural tryptophan derivatives for use in a broad array of synthetic and biological applications.

Kieffer, Madeleine E.; Repka, Lindsay M.; Reisman, Sarah E.

2012-01-01

100

Synthesis of (-)-paroxetine via enantioselective phase-transfer catalytic monoalkylation of malonamide ester.  

PubMed

A new enantioselective synthetic method of (-)-paroxetine is reported. (-)-Paroxetine could be obtained in 15 steps (95% ee and 9.1% overall yield) from N,N-bis(p-methoxyphenyl)malonamide tert-butyl ester via the enantioselective phase-transfer catalytic alkylation and the diastereoselective Michael addition as the key steps. PMID:20499863

Kim, Mi-Hyun; Park, Yohan; Jeong, Byeong-Seon; Park, Hyeung-Geun; Jew, Sang-Sup

2010-06-18

101

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

102

Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon  

PubMed Central

The chiral, nucleophilic catalyst TADMAP (1) has been prepared from 3-lithio-4-dimethylamino-pyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient, and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity.

Shaw, Scott A.; Aleman, Pedro; Christy, Justin; Kampf, Jeff W.; Va, Porino

2008-01-01

103

Enantioselective palladium-catalyzed total synthesis of vitamin e by employing a domino Wacker-Heck reaction.  

PubMed

An enantioselective total synthesis of vitamin E in which a novel palladium-catalyzed domino reaction was employed as the key step is described. This reaction allows the formation of the chiral chroman framework and the concurrent introduction of part of the side chain of vitamin E. The sequence comprises an enantioselective Wacker cyclization and a subsequent Heck reaction. Accordingly, reaction of alkenylphenol 12 with methyl vinyl ketone (13) in the presence of catalytic amounts of Pd(OTFA)(2) (TFA = trifluoroacetate), the enantiopure ligand (S,S)-Bn-BOXAX (8 b; Bn = benzyl, BOXAX = 2,2'-bis(oxazolyl)-1,1'-binaphthyl, and p-benzoquinone (9) as an oxidant gives access to chiral chroman 10 with an enantioselectivity of 97 % ee in 84 % yield. Chroman 10 is then converted into 24 by an aldol condensation reaction with (3R)-3,7-dimethyloctanal (11). Subsequent 1,2-addition of methyllithium, elimination of water, and hydrogenation yields vitamin E. PMID:17001611

Tietze, Lutz F; Stecker, Florian; Zinngrebe, Julia; Sommer, Konrad M

2006-11-24

104

N-heterocyclic carbene-catalyzed highly enantioselective synthesis of substituted dihydropyranopyrazolones.  

PubMed

Highly optically pure multisubstituted dihydropyrano[2,3-c]pyrazol-6-(1H)-ones were synthesized via the N-heterocyclic carbene-catalyzed enantioselective [4 + 2] annulation of ?-chloroaldehydes and pyrazolone-derived oxodienes. PMID:23959516

Zhang, Han-Ming; Lv, Hui; Ye, Song

2013-10-01

105

Combination of stereospecific dihydroxylation and enzyme catalyzed enantioselective resolution for synthesis of enantiopure vicinal diols  

Microsoft Academic Search

By employing a combination of stereospecific osmium catalyzed dihydroxylation of selected alkenes, and enantioselective lipase catalyzed kinetic resolution, nine alkenes were converted into nine enantiopure vicinal diols and nine enantiopure hydroxy butanoates.

Anders Riise Moen; Kjersti Ruud; Thorleif Anthonsen

2008-01-01

106

A process in need is a process indeed: scalable enantioselective synthesis of chiral compounds for the pharmaceutical industry.  

PubMed

This report deals with enantioselective synthesis of viracept 1 (nelfinavir mesylate, AG 1343), a potent HIV protease inhibitor, and 3-hydroxytetradecanoic acid 3, a component of lipid A comprising lipopolysaccharide embedded in the cell surface of Gram-negative bacteria, from both strategic and practical perspectives. As regards the synthesis of 1, the synthetic approaches to its central intermediate 2 possessing the common structural motif of 1,4-differentially substituted-2-amino-3-hydroxylbutane are mainly discussed with emphasis on the molecular symmetry that has helped streamline the synthetic strategy. In the discussion of the synthetic strategies to access a single enantiomer of 3, the chiral methodologies that have been applied so far are assessed for industrial viability; the synthetic alternatives explored include resolution via diastereomeric salt formation, lipase-catalyzed kinetic resolution, asymmetric synthesis, and chiral pool approaches. PMID:12532286

Ikunaka, Masaya

2003-01-20

107

Organocatalytic enantioselective cascade Michael-Michael-Wittig reactions of phosphorus ylides: one-pot synthesis of the all-cis trisubstituted cyclohexenecarboxylates via the [1 + 2 + 3] annulation.  

PubMed

The stereoselective synthesis of all-cis 5-nitro-4,6-diphenylcyclohex-1-enecarboxylic ester has been achieved by an organocatalytic asymmetric Michael-Michael-Wittig cascade reaction of phosphorus ylides, nitroolefins, and alpha,beta-unsaturated aldehydes with excellent enantioselectivities (up to >99% ee). PMID:19852490

Hong, Bor-Cherng; Jan, Rei-Hau; Tsai, Chih-Wei; Nimje, Roshan Y; Liao, Ju-Hsiou; Lee, Gene-Hsiang

2009-11-19

108

Asymmetric decarboxylative 1,4-addition of malonic Acid half thioesters to vinyl sulfones: highly enantioselective synthesis of 3-monofluoromethyl-3-arylpropanoic esters.  

PubMed

An asymmetric decarboxylative 1,4-addition of malonic acid half thioesters (MAHTs) to 2-aryl-substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97?% ee). In view of tuning pKa values, a quinine-based benzyl-substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3-monofluorinated analogues of 3-methyl indanone and (+)-turmerone has been accomplished from decarboxylative 1,4-addition adducts with satisfactory results. PMID:24591040

Qiao, Baokun; Liu, Qian; Liu, Hongjun; Yan, Lin; Jiang, Zhiyong

2014-05-01

109

Copper(II)-catalyzed enantioselective hydrosilylation of halo-substituted alkyl aryl and heteroaryl ketones: asymmetric synthesis of (R)-fluoxetine and (S)-duloxetine.  

PubMed

A set of reaction conditions has been established to facilitate the non-precious copper-catalyzed enantioselective hydrosilylation of a number of structurally diverse ?-, ?- or ?-halo-substituted alkyl aryl ketones and ?-, ?- or ?-halo-substituted alkyl heteroaryl ketones under air to afford a broad spectrum of halo alcohols in high yields and good to excellent enantioselectivities (up to 99% ee). The developed procedure has been successfully applied to the asymmetric synthesis of antidepressant drugs (R)-fluoxetine and (S)-duloxetine, which highlighted its synthetic utility. PMID:24382650

Zhou, Ji-Ning; Fang, Qiang; Hu, Yi-Hu; Yang, Li-Yao; Wu, Fei-Fei; Xie, Lin-Jie; Wu, Jing; Li, Shijun

2014-02-14

110

Enantioselective total synthesis of (-)-lansai?b and (+)-nocardioazines?a and B.  

PubMed

The concise total syntheses of the bis(pyrroloindolines) (-)-lansai?B and (+)- nocardioazines?A and B are reported. The key pyrroloindoline building blocks are rapidly prepared by enantioselective formal [3+2] cycloaddition reactions. The macrocycle of (+)-nocardioazine?A is constructed by an unusual intramolecular diketopiperazine formation. PMID:24777757

Wang, Haoxuan; Reisman, Sarah E

2014-06-10

111

Bioinspired total synthesis of katsumadain A by organocatalytic enantioselective 1,4-conjugate addition  

PubMed Central

Summary Katsumadain A, a naturally occurring in?uenza virus neuraminidase (NA) inhibitor, was synthesized by using a bioinspired, organocatalytic enantioselective 1,4-conjugate addition of styryl-2-pyranone with cinnamaldehyde, followed by a tandem Horner–Wadsworth–Emmons/oxa Michael addition.

Wang, Yongguang; Bao, Ruiyang; Huang, Shengdian

2013-01-01

112

Bioinspired total synthesis of katsumadain A by organocatalytic enantioselective 1,4-conjugate addition.  

PubMed

Katsumadain A, a naturally occurring in?uenza virus neuraminidase (NA) inhibitor, was synthesized by using a bioinspired, organocatalytic enantioselective 1,4-conjugate addition of styryl-2-pyranone with cinnamaldehyde, followed by a tandem Horner-Wadsworth-Emmons/oxa Michael addition. PMID:23946860

Wang, Yongguang; Bao, Ruiyang; Huang, Shengdian; Tang, Yefeng

2013-01-01

113

Bifunctional N-Heterocyclic Carbene-Catalyzed Highly Enantioselective Synthesis of Spirocyclic Oxindolo-?-lactams.  

PubMed

The N-heterocyclic carbene-catalyzed Staudinger reaction of ketenes with isatin-derived ketimines was investigated. The bifunctional NHCs with a free hydroxyl group were demonstrated as efficient catalysts for the reaction, giving the corresponding spirocyclic oxindolo-?-lactams in high yields with excellent diastereo- and enantioselectivities. PMID:24856000

Zhang, Han-Ming; Gao, Zhong-Hua; Ye, Song

2014-06-01

114

Enantioselective synthesis of tert-butyl tert-butanethiosulfinate catalyzed by cyclohexanone monooxygenase.  

PubMed

Cyclohexanone monooxygenase from Acinetobacter calcoaceticus catalyzes the asymmetric oxidation of tert-butyl disulfide to enantiomerically pure (R)-tert-butyl tert-butanethiosulfinate. Lower enantioselectivities and conversions were observed in the oxidation of i-propyl, n-butyl, p-tolyl tert-butyl disulfides and alkylthiophosphonates. PMID:11135413

Colonna, S; Gaggero, N; Carrea, G; Pasta, P; Alphand, V; Furstoss, R

2001-01-01

115

Desymmetrization of diolefinic diols by enantioselective amino-thiocarbamate-catalyzed bromoetherification: synthesis of chiral spirocycles.  

PubMed

A facile, efficient, and highly diastereo- and enantioselective bromoetherification of diolefinic diols has been developed using an amino-thiocarbamate catalyst. Further manipulations of the bromoether products enabled entry into a new class of spirocycles which are distinctively lacking in the literature. PMID:24706539

Tay, Daniel Weiliang; Leung, Gulice Y C; Yeung, Ying-Yeung

2014-05-12

116

Phosphoric Acid catalyzed diastereo- and enantioselective synthesis of substituted 1,3-diaminotetralins.  

PubMed

The reaction of anilines and phenylacetaldehydes in the presence of chiral phosphoric acid afforded optically active 1,2-trans, 2,3-cis 1,3-diaminotetralins in high yields with excellent diastereo- and enantioselectivities. The trans/cis product was readily isomerized to a trans/trans stereoisomer with no significant loss of enantiomeric purity. PMID:24762190

Dagousset, Guillaume; Erb, William; Zhu, Jieping; Masson, Géraldine

2014-05-01

117

Enantioselective synthesis of both enantiomers of vicinal norbornanediamines through the Leuckart reaction of 2-norbornanones  

Microsoft Academic Search

The reaction of 2-norbornanones bearing an amine derivative in the bridgehead position with formamide and formic acid yields enantiomerically pure 1,2-norbornane diamides. These compounds are excellent precursors of chiral vicinal diamines, which have been increasingly used due to their numerous applications in medicinal chemistry and asymmetric synthesis. The rigid structure of the norbornane framework allows the study of conformational equilibrium

Antonio Garc??a Mart??nez; Enrique Teso Vilar; Amelia Garc??a Fraile; Paloma Mart??nez-Ruiz

2001-01-01

118

A Multicomponent Ni-, Zr-, and Cu-Catalyzed Strategy for Enantioselective Synthesis of Alkenyl-Substituted Quaternary Carbons**  

PubMed Central

The availability of enantiomerically enriched carbonyl-containing compounds is essential to the synthesis of biologically active molecules. Since catalytic enantioselective conjugate addition (ECA) reactions directly generate the latter valuable class of molecules, the design and development of such protocols represents a compelling objective in modern chemistry. Herein, we disclose the first solution to the problem of ECA of alkenyl groups to acyclic trisubstituted enones, an advance achieved by adopting an easily modifiable and fully catalytic approach. The requisite alkenylaluminum reagents are synthesized with exceptional site- and/or stereoselectivity by a Ni-catalyzed hydroalumination process, and the necessary enones are prepared through a site- and stereoselective zirconocene-catalyzed carboalumination/acylation reaction. The all-catalytic procedure is complete within four hours, furnishing the desired products in up to 77% overall yield and 99:1 enantiomeric ratio.

McGrath, Kevin P.

2014-01-01

119

Enantioselective Synthesis of ?-(3-Hydroxypyrazol-1-yl)ketones Using An Organocatalyzed Michael Addition Reaction  

PubMed Central

?-(3-Hydroxypyrazol-1-yl)ketones have been prepared in high yields and excellent enantioselectivities (94–98% ee) via a Michael addition reaction between 2-pyrazolin-5-ones and aliphatic acyclic ?,?-unsaturated ketones using 9-epi-9-amino-9-deoxyquinine as the catalyst. These results account for the first example of an aza-Michael addition of the ambident 2-pyrazolin-5-one anion to a Michael acceptor.

Gogoi, Sanjib; Zhao, Cong-Gui; Ding, Derong

2009-01-01

120

Co-catalyzed reductive cyclization of azido and cyano substituted ?,?-unsaturated esters with NaBH 4: enantioselective synthesis of ( R)-baclofen and ( R)-rolipram  

Microsoft Academic Search

Sodium borohydride in combination with a catalytic amount of CoCl2 has been found to be an excellent catalytic system in reductive cyclizations of suitably substituted azido and cyano groups of ?,?-unsaturated esters to afford ? and ?-lactams in high yields. The process has been demonstrated for the enantioselective synthesis of (R)-baclofen, (R)-rolipram, and (R)-4-fluorophenylpiperidinone, a key intermediate for (?)-paroxetine.

Abhimanyu S. Paraskar; Arumugam Sudalai

2006-01-01

121

Enantioselective synthesis of ?-heteroarylpyrrolidines by copper-catalyzed 1,3-dipolar cycloaddition of ?-silylimines.  

PubMed

?-Heteroarylpyrrolidines have been efficiently prepared via 1,3-dipolar cycloaddition between silylimines and activated olefins. In the presence of Cu(CH3CN)4PF6/Walphos as catalytic system, high levels of enantioselectivity (up to ?99% ee) and diastereoselectivity were achieved (major formation of C-2/C-4 trans-substituted pyrrolidines). The reaction is compatible with a broad variety of dipolarophiles including maleimides, maleates, fumarates, nitroalkenes, and vinylsulfones. The resulting cycloadducts can be transformed into bioactive pyrrolidine derivatives. PMID:24697804

Pascual-Escudero, Ana; González-Esguevillas, María; Padilla, Silvia; Adrio, Javier; Carretero, Juan C

2014-04-18

122

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

123

Improved cyclopropanation activity of histidine-ligated cytochrome?p450 enables the enantioselective formal synthesis of levomilnacipran.  

PubMed

Engineering enzymes capable of modes of activation unprecedented in nature will increase the range of industrially important molecules that can be synthesized through biocatalysis. However, low activity for a new function is often a limitation in adopting enzymes for preparative-scale synthesis, reaction with demanding substrates, or when a natural substrate is also present. By mutating the proximal ligand and other key active-site residues of the cytochrome?P450 enzyme from Bacillus megaterium (P450-BM3), a highly active His-ligated variant of P450-BM3 that can be employed for the enantioselective synthesis of the levomilnacipran core was engineered. This enzyme, BM3-Hstar, catalyzes the cyclopropanation of N,N-diethyl-2-phenylacrylamide with an estimated initial rate of over 1000 turnovers per minute and can be used under aerobic conditions. Cyclopropanation activity is highly dependent on the electronic properties of the P450 proximal ligand, which can be used to tune this non-natural enzyme activity. PMID:24802161

Wang, Z Jane; Renata, Hans; Peck, Nicole E; Farwell, Christopher C; Coelho, Pedro S; Arnold, Frances H

2014-06-23

124

Highly Enantioselective Catalytic Dynamic Resolution of N-Boc-2-lithiopiperidine: Synthesis of (R)-(+)-N-Boc-Pipecolic Acid, (S)-(-)-Coniine, (S)-(+)-Pelletierine, (+)-?-Conhydrine, (S)-(-)-Ropivacaine, and Formal Synthesis of (-)-Lasubine II and (+)-Cermizine C  

PubMed Central

The catalytic dynamic resolution (CDR) of rac-2-lithio-N-Boc-piperidine using chiral ligand 8 or its diastereomer 9, in the presence of TMEDA has led to the highly enantioselective syntheses of either enantiomer of 2-substituted piperidines using a wide range of electrophiles. The CDR has been applied to the synthesis of R- or S-pipecolic acid derivatives, (+)-?-conhydrine, (S)-(+)-pelletierine, (S)-(?)-ropivacaine, and formal synthesis of (?)-lasubine II and (+)-cermizine C.

Beng, Timothy K.; Gawley, Robert E.

2010-01-01

125

Enantioselective synthesis of tacrine–huperzine A hybrids. Preparative chiral MPLC separation of their racemic mixtures and absolute configuration assignments by X-ray diffraction analysis  

Microsoft Academic Search

A new synthesis of racemic 7-substituted bicyclo[3.3.1]non-6-en-3-ones, rac-4, whose key-step involves the reaction of a vinyl triflate, rac-7, with an organometallic reagent, has been developed. This procedure has been applied to the enantioselective synthesis of (+)- and (?)-7-ethylbicyclo[3.3.1]non-6-en-3-one, (+)- and (?)-4b, from which both enantiomers of the cholinesterase inhibitor, tacrine–huperzine A hybrid, 9b, have been obtained. Rac-9b and its related

Pelayo Camps; Joan Contreras; Jordi Morral; Diego Muñoz-Torrero; Xavier Solans

1998-01-01

126

Enantioselective organocatalytic oxa-Michael addition of oximes to ?-CF3-?-disubstituted nitroalkenes: efficient synthesis of ?-amino-?-trifluoromethyl alcohols.  

PubMed

An enantioselective oxa-Michael addition of oximes to ?-CF3-?-disubstituted nitroalkenes catalyzed by a chiral bifunctional cinchona alkaloid-based thiourea has been developed. A variety of trifluoromethylated oxime ethers possessing a tetrasubstituted carbon stereocenter were obtained in good yields with high enantioselectivities. PMID:24407351

Liu, Feng-Lei; Chen, Jia-Rong; Feng, Bin; Hu, Xiao-Qiang; Ye, Li-Hua; Lu, Liang-Qiu; Xiao, Wen-Jing

2014-02-21

127

Synthesis and enantioselective rearrangement of (Z)-4-triphenylmethoxy-2,3-epoxybutan-1-ol enantiomers.  

PubMed

Efficient enzyme catalyzed kinetic resolutions of a synthetically useful chiral building block, (Z)-4-triphenylmethoxy-2,3-epoxybutan-1-ol, are reported. The highest selectivities were achieved by Lipozyme TL IM and Amano Lipase PS enzymes in the presence of vinyl acetate. Enantiomeric enrichment of the optically active acetate isomer was accomplished by selective crystallization of the racemic part of the enantiomeric mixture. Enzyme catalyzed hydrolysis of the acetate also provided an optically pure epoxybutanol derivative. O-Benzylation of (+)-(Z)-1-hydroxy-4-triphenylmethoxy-2,3-epoxybutane followed by super base promoted diastereo- and enantio-selective rearrangement resulted in (+)-(2R,3R,1'R)-3-[1-hydroxy-2-(triphenylmethoxy)ethyl]-2-phenyloxetane in >98% ee and de. Configurations of the new optically active products were determined by chemical correlation. PMID:17192839

Faigl, Ferenc; Thurner, Angelika; Farkas, Ferenc; Battancs, Melinda; Poppe, László

2007-03-01

128

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

129

Enantioselective, protecting group-free synthesis of 1S-ethyl-4-substituted quinolizidines.  

PubMed

A practical enantioselective protecting group-free four-step route to the key quinolizidinone 6 from phenylglycinol-derived bicyclic lactam 1 is reported. The Grignard addition reaction to 6 takes place stereoselectively to give 1-ethyl-4-substituted quinolizidines 4-epi-207I and 7-9. Following a similar synthetic sequence, 9a-epi-6 is also accessed. However, the addition of Grignard reagents to 9a-epi-6 proceeds in a non-stereoselective manner. In order to gain insight into the different stereochemical outcome in the two series, theoretical calculations on the iminium salts A and B have been performed. The study concludes that the addition of the hydride, which is the step that determines the configuration of the final products, occurs in a stereoelectronic controlled manner. The theoretical study is in agreement with the experimental results. PMID:22837110

Amat, Mercedes; Semak, Vladislav; Escolano, Carmen; Molins, Elies; Bosch, Joan

2012-09-14

130

Chiral Brønsted acids in enantioselective carbonyl activations--activation modes and applications.  

PubMed

Chiral phosphoric acids and derivatives have attracted considerable attention as a powerful tool in asymmetric catalysis. Various enantioselective reactions have been developed by using these efficient Brønsted acid organocatalysts. Although initially the activation was restricted to reactive Brønsted basic substrates, recent reports are demonstrating the versatility of phosphoric acid catalysts in the activation of carbonyl compounds in a stereochemically controlled fashion. This tutorial review gives an overview of enantioselective Brønsted acid catalyzed transformations with the main focus on carbonyl activation. Different activation modes, key features of the catalysts and the applied substrates are presented and discussed with the goal to elucidate the origin of stereoselectivity in these Brønsted acid catalyzed transformations. PMID:21614342

Rueping, Magnus; Kuenkel, Alexander; Atodiresei, Iuliana

2011-09-01

131

Kinetic investigation of a solvent-free, chemoenzymatic reaction sequence towards enantioselective synthesis of a ?-amino acid ester.  

PubMed

A solvent-free, chemoenzymatic reaction sequence for the enantioselective synthesis of ?-amino acid esters has been kinetically and thermodynamically characterized. The coupled sequence comprises a thermal aza-Michael addition of cheap starting materials and a lipase catalyzed aminolysis for the kinetic resolution of the racemic ester. Excellent ee values of >99% were obtained for the ?-amino acid ester at 60% conversion. Kinetic constants for the aza-Michael addition were obtained by straightforward numerical integration of second-order rate equations and nonlinear fitting of the progress curves. A different strategy had to be devised for the biocatalytic reaction. Initially, a simplified Michaelis-Menten model including product inhibition was developed for the reaction running in THF as an organic solvent. Activity based parameters were used instead of concentrations in order to facilitate the transfer of the kinetic model to the solvent-free system. Observed solvent effects not accounted for by the use of thermodynamic activities were incorporated into the kinetic model. Enzyme deactivation was observed to depend on the ratio of the applied substrates and also included in the kinetic model. The developed simple model is in very good agreement with the experimental data and allows the simulation and optimization of the solvent-free process. PMID:22275046

Strompen, Simon; Weiss, Markus; Ingram, Thomas; Smirnova, Irina; Gröger, Harald; Hilterhaus, Lutz; Liese, Andreas

2012-06-01

132

Simple organic molecules as catalysts for enantioselective synthesis of amines and alcohols.  

PubMed

The discovery of catalysts that can be used to synthesize complex organic compounds by enantioselective transformations is central to advances in the life sciences; for this reason, many chemists aim to discover catalysts that allow for preparation of chiral molecules as predominantly one mirror-image isomer. The ideal catalyst should not contain precious elements and should bring reactions to completion in a few hours through operationally simple procedures. Here we introduce a set of small organic molecules that can catalyse reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which might serve as intermediates in the preparation of biologically active molecules. A distinguishing feature of this catalyst class is the presence of a 'key' proton embedded within their structure. Catalysts are derived from the abundant amino acid valine and are prepared in large quantities in four steps with inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mole per cent catalyst in less than six hours at room temperature to generate products in more than 85 per cent yield and ?97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents are expected to render this advance important for future progress in syntheses of amines and alcohols, which are useful in chemistry, biology and medicine. PMID:23407537

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

2013-02-14

133

Enantioselective synthesis of natural trinorsesquiterpene tetralones by chemo-enzymatic approaches.  

PubMed

The enantioselective syntheses of both the enantiomeric forms of the four natural tetralones 1a-d are here described. The aforementioned trinorsesquiterpenes were prepared starting either from substituted (S)-3-arylbutanols 5a-c or from substituted (S)-2-arylpropanols 7a-c. The latter chiral building blocks were in turn obtained through two different kinds of enzymatic transformations consisting of the baker's yeast mediated reduction of substituted (E)-3-aryl-but-2-enals 4a-c and the lipase-mediated resolution of racemic 2-arylpropanols 7a-c, respectively. Further key steps of the presented syntheses were C1 and C2 homologation procedures as well as the ring closure of the substituted 4-aryl-pentanoic acids 3a-c. By these means the target compounds were obtained in good yields and with very high stereoisomeric purity. In addition, the trinorsesquiterpene schiffnerone-B was synthesized for the first time and its absolute configuration was unambiguously assigned. PMID:23980412

Serra, Stefano

2013-07-01

134

Asymmetric cycloaddition of ?,?-unsaturated ?-ketoesters with electron-rich alkenes catalyzed by a chiral Er(OTf)3/N,N'-dioxide complex: highly enantioselective synthesis of 3,4-dihydro-2H-pyrans.  

PubMed

The asymmetric inverse-electron-demand hetero-Diels-Alder (HDA) reactions of ?,?-unsaturated ?-ketoesters with electron-rich alkenes were investigated, with an N,N'-dioxide/erbium(III) complex employed as the catalyst. Quantitative conversion of the ?,?-unsaturated ?-ketoesters and excellent enantioselectivities (up to >99% ee) and diastereoselectivities (up to >99:1 d.r.) were observed for a broad range of substrates by using a 0.5-0.05 mol% catalyst loading under mild reaction conditions. The reaction could be scaled up to the gram scale with the same results. In addition, this was the first application of Er(OTf)(3) to the asymmetric inverse-electron-demand HDA reaction and it behaved as an efficient catalyst. Moreover, the synthetic utility of this methodology was demonstrated with the synthesis of key intermediates of some natural products. PMID:21647990

Zhu, Yin; Xie, Mingsheng; Dong, Shunxi; Zhao, Xiaohu; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming

2011-07-11

135

Cinchona alkaloid derivative-catalyzed enantioselective synthesis via a Mannich-type reaction and antifungal activity of ?-amino esters bearing benzoheterocycle moieties.  

PubMed

An efficient synthesis of highly functionalized chiral ?-amino ester derivatives containing benzothiophene and benzothiazole moieties is developed by a Mannich-type reaction using a cinchona alkaloid-derived thiourea catalyst. The desired products were obtained in good yields and high enantioselectivities (~86% yield, >99% ee) using to the optimized reaction conditions. The synthesized compounds were characterized by 1H-NMR, 13C-NMR, IR, and HREI-MS analyses. The bioassays identified that compound 5dr has excellent antifungal activity, with a 60.53% inhibition rate against F. oxysporum, higher than that of the commercial agricultural fungicide hymexazol, whose inhibition rate was 56.12%. PMID:24694652

Xiao, Han; Wu, Fang; Shi, Li; Chen, Zhiwei; Su, Shihu; Tang, Chenghao; Wang, Hongtao; Li, Zhining; Li, Meichuan; Shi, Qingcai

2014-01-01

136

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

2011-08-19

137

Application of aminoacylase I to the enantioselective resolution of ?-amino acid esters and amides  

Microsoft Academic Search

Aminoacylase I from Aspergillus melleus, a readily available and inexpensive enzyme mainly used in the industrial production of enantiopure l-amino acids from their N-acetyl derivatives, is shown to hydrolyze the esters and amides of natural and non-natural amino acids with high enantioselectivity (for the ester hydrolysis, E is up to 76, in case of amides E >300). The reaction rates

Maxim I Youshko; Luuk M van Langen; Roger A Sheldon; Vytas K Švedas

2004-01-01

138

First enantioselective total synthesis of (+)-(R)-Pinnatolide using an asymmetric domino allylation reaction.  

PubMed

An efficient total synthesis of (+)-(R)-Pinnatolide is described. As a key step an asymmetric multicomponent domino allylation reaction of methyl levulinate is used to form the quaternary stereogenic center in a highly selective way. PMID:22853329

Tietze, Lutz F; Wolfram, Thomas; Holstein, Julian J; Dittrich, Birger

2012-08-17

139

Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis  

PubMed Central

Discovery of efficient catalysts is one of the most compelling objectives of modern chemistry. Chiral catalysts are in particularly high demand, as they facilitate synthesis of enantiomerically enriched small molecules that are critical to developments in medicine, biology and materials science1. Especially noteworthy are catalysts that promote—with otherwise inaccessible efficiency and selectivity levels—reactions demonstrated to be of great utility in chemical synthesis. Here we report a class of chiral catalysts that initiate alkene metathesis1 with very high efficiency and enantioselectivity. Such attributes arise from structural fluxionality of the chiral catalysts and the central role that enhanced electronic factors have in the catalytic cycle. The new catalysts have a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are prepared stereoselectively by a ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands scarcely used in enantioselective catalysis2,3. We demonstrate the application of the new catalysts in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, through an alkene metathesis reaction that cannot be promoted by any of the previously reported chiral catalysts.

Malcolmson, Steven J.; Meek, Simon J.; Sattely, Elizabeth S.; Schrock, Richard R.; Hoveyda, Amir H.

2009-01-01

140

Enantioselective synthesis of (10S)- and (10R)-methyl-anandamides  

PubMed Central

For the development of novel endocannabinoid templates with potential resistance to hydrolytic and oxidative metabolism, we are targeting the bis-allylic carbons of the arachidonoyl skeleton. Toward this end, we recently disclosed the synthesis and preliminary biological data for the (13S)-methyl-anandamide. We report now the total synthesis of the (10S)- and (10R)-methyl-counterparts. Our synthetic approach is stereospecific, efficient, and provides the analogs without the need for resolution. Peptide coupling, P-2 nickel partial hydrogenation, and cis-selective Wittig olefination are the key steps.

Nikas, Spyros P.; D'Souza, Marsha; Makriyannis, Alexandros

2013-01-01

141

Toward general access to the aspidosperma-type terpenoid indole alkaloids: synthesis of the key 3,3-disubstituted piperidones through enantioselective intramolecular heck-type reaction of chloroformamides.  

PubMed

An enantioselective intramolecular Heck-type reaction of chloroformamides has been developed for the synthesis of 3,3-disubstituted piperidones. The desired piperidone was formed in the presence of a palladium catalyst, an optically active phosphoramidite ligand, K3PO4 and Ag3PO4. The obtained piperidone was converted to epieburnamonine. PMID:18981607

Yasui, Yoshizumi; Takeda, Hiroshi; Takemoto, Yoshiji

2008-11-01

142

Enantioselective and protecting group-free synthesis of 1-deoxythionojirimycin, 1-deoxythiomannojirimycin, and 1-deoxythiotalonojirimycin.  

PubMed

1-Deoxythioglyconojirimycins were synthesized by using a protecting group-free strategy, starting from readily available carbohydrates, in good overall yield. Use of benzyltriethylammonium tetrathiomolybdate, [BnEt(3)N](2)MoS(4), as a sulfur transfer reagent and borohydride exchange resin (BER) reduction of a lactone enabled the efficient synthesis of the title compounds. PMID:20815372

Gunasundari, Thanikachalam; Chandrasekaran, Srinivasan

2010-10-01

143

An Enantioselective Synthesis of CymbaltaTM Colin McKinlay and Vincent van Rixel  

Microsoft Academic Search

A complete synthesis of Duloxetine, marketed as Cymbalta?, is achieved using an enantiomerically conserved route. Cymbalta? is a potent antidepressant which targets neural serotonin channels, making it successful at treating patients with major depressive disorder, generalized anxiety disorder, diabetic neuropathy, and fibromyalgia. However, Cymbalta? is a chiral molecule, in which the (S) enantiomer acts as the serotonin reuptake inhibitor, while

Colin McKinlay; Vincent van Rixel

2010-01-01

144

Cloning, overexpression, and characterization of a high enantioselective nitrilase from Sphingomonas wittichii RW1 for asymmetric synthesis of (R)-phenylglycine.  

PubMed

In this study, a high (R)-enantioselective nitrilase gene from Sphingomonas wittichii RW1 was cloned and overexpressed in Escherichia coli BL21 (DE3). The recombinant nitrilase was purified to homogeneity with a molecular weight of 40 kDa. The pH and temperature optima were shown to be pH 8.0 and 40 °C, respectively. The purified nitrilase was most active toward succinonitrile, approximately 30-fold higher than that for phenylglycinonitrile. Using the E. coli BL21/ReSWRW1 whole cells as biocatalysts, the kinetic resolution for asymmetric synthesis of (R)-phenylglycine was investigated at pH 6.0. A yield of 46 % was obtained with 95 % enantiomeric excess (ee), which made it a promising biocatalyst for synthesis of (R)-phenylglycine. PMID:24664232

Qiu, Jian; Su, Er-Zheng; Wang, Hua-Lei; Cai, Wen-Wen; Wang, Wei; Wei, Dong-Zhi

2014-05-01

145

Towards an Enantioselective Synthesis of (-)-Zampanolide: Preparation of the C9-C20 Region  

PubMed Central

Progress towards the synthesis of the microtubule-stabilizing agent, (?)-zampanolide, is reported. Construction of the 2,6-cis-tetrahydropyran ring was accomplished utilizing ether transfer methodology in conjunction with an intramolecular radical cyclization reaction. Efficient installation of the C16-C20 side chain relied on a one-pot cross-metathesis/olefination sequence, Sharpless epoxidation, and selective reduction of a vinyl epoxide.

Wilson, Matthew R.; Taylor, Richard E.

2012-01-01

146

Synthesis of enantiomerically pure glycidol via a fully enantioselective lipase-catalyzed resolution  

Microsoft Academic Search

The efficient enzymatic synthesis of enantiopure 2,3-epoxypropanol (glycidol) has been achieved. The racemic glycidyl butyrate was successfully resolved by enzymatic hydrolysis using a strategy that combines different immobilization protocols and different experimental reaction conditions. A new enzyme (25kDa lipase)—which is a lipase-like enzyme purified from the pancreatic porcine lipase (PPL) extract—immobilized on DEAE–Sepharose was selected as the optimal biocatalyst. The

Jose M. Palomo; Rosa L. Segura; Cesar Mateo; Marco Terreni; José M. Guisan; Roberto Fernández-Lafuente

2005-01-01

147

Organocatalyzed cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes: enantioselective synthesis of cyclopropanes bearing a chiral quaternary center.  

PubMed

An enantioselective cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes with bromomalonate has been successfully developed through a domino Michael/alpha-alkylation strategy. The method allows the efficient formation of cyclopropanes bearing a quaternary carbon stereocenter at the alpha-position of the aldehydes by using iminium/enamine catalysis and gives a nice extension on the organocatalytic cyclopropanation of bromomalonate and alpha,beta-unsaturated aldehydes previously reported by other groups. Very good yields (up to 81%) and enantioselectivities (up to 97% ee) have been obtained. The optically active cyclopropane derivatives are of high synthetic interest as useful targets for further elaboration into more complex structures. PMID:20512823

Terrasson, Vincent; van der Lee, Arie; de Figueiredo, Renata Marcia; Campagne, Jean Marc

2010-07-12

148

Copper-catalyzed enantioselective allylic substitution with alkylboranes.  

PubMed

The first catalytic enantioselective allylic substitution reaction with alkylboron compounds has been achieved. The reaction between alkyl-9-BBN reagents and primary allylic chlorides proceeded with excellent ?-selectivities and high enantioselectivities under catalysis of a Cu(I)-DTBM-SEGPHOS system. The protocol produces terminal alkenes with an allylic stereogenic center branched with functionalized sp(3)-alkyl groups. The reaction with a ?-silicon-substituted allyl chloride affords an efficient strategy for the enantioselective synthesis of functionalized ?-stereogenic chiral allylsilanes. PMID:23106350

Shido, Yoshinori; Yoshida, Mika; Tanabe, Masahito; Ohmiya, Hirohisa; Sawamura, Masaya

2012-11-14

149

Enantioselective synthesis of the fragrance trans-magnolione under asymmetric phase transfer catalysis  

Microsoft Academic Search

The stereoselective synthesis of the fragrance trans-magnolione (1) through conjugate Michael addition of alkyl acetoacetates to 2-pentyl-2-cyclopentenone (2) under solid\\/liquid phase transfer catalysis (PTC) is reported. Under optimized conditions, the 1,4-addition of tert-butyl acetoacetate to enone 2 catalyzed by N-9-anthracenylmethylquininium chloride (4) affords, after hydrolysis and decarboxylation, trans-(2S,3S)-1 with 85\\/15 d.r. and 74% ee. The use of the pseudo-enantiomeric catalyst

Stefano Superchi; Mariangela Nardiello; Maria Irene Donnoli; Patrizia Scafato; Rita Menicagli; Carlo Rosini

2005-01-01

150

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

151

Organocatalytic cascade sulfa-Michael/aldol reaction of ?,?-disubstituted enones: enantioselective synthesis of tetrahydrothiophenes with a trifluoromethylated quaternary center.  

PubMed

A bifunctional squaramide-catalyzed sulfa-Michael/aldol cascade reaction initiated by sulfa-Michael addition of mercaptoacetaldehyde to ?-aryl-?-trifluoromethylated enones is successfully developed. The functionalized tetrahydrothiophenes with three continuous stereocenters including a trifluoromethylated quaternary carbon are readily obtained with moderate to good yields and high enantioselectivities. PMID:24079617

Su, Yu; Ling, Jun-Bing; Zhang, Shuang; Xu, Peng-Fei

2013-11-01

152

Pd(II)-Catalyzed Enantioselective C-H Activation/C-O Bond Formation: Synthesis of Chiral Benzofuranones  

PubMed Central

Pd(II)-catalyzed enantioselective C–H activation of phenylacetic acids followed by an intramolecular C–O bond formation afforded chiral benzofuranones. This reaction provides the first example of enantioselecctive C–H functionalizations through Pd(II)/Pd(IV) redox catalysis.

Cheng, Xiu-Fen; Li, Yan; Su, Yi-Ming; Yin, Feng; Wang, Jian-Yong; Sheng, Jie; Vora, Harit U.; Wang, Xi-Sheng; Yu, Jin-Quan

2013-01-01

153

Enantioselective synthesis of ?-nitro-?-ketosulfones via a quinine-squaramide catalyzed conjugate addition of ?-nitrosulfones to enones.  

PubMed

Conjugate addition of ?-nitrosulfones to vinyl ketones in the presence of 0.2 mol% of a quinine-squaramide organocatalyst afforded ?-nitro-?-ketosulfones possessing a tetrasubstituted chiral center in excellent yield and enantioselectivity in most cases. This strategy also offers a facile and convenient entry into ?-sulfonylhydroxamates that are one carbon homologs of potent enzyme inhibitors. PMID:24098891

Bera, Kalisankar; Namboothiri, Irishi N N

2013-11-21

154

Highly enantioselective synthesis of ?-azido-?-hydroxy methyl ketones catalyzed by a cooperative proline-guanidinium salt system.  

PubMed

The combined activity of (S)-proline and an achiral tetraphenylborate TBD-derived guanidinium salt permits the aldol reaction between azidoacetone and aromatic, or heteroaromatic aldehydes. The ?-azido-?-hydroxy methyl ketones obtained as products can be isolated in good yield, with high diastereo- and enantioselectivity. PMID:24468918

Martínez-Castañeda, Ángel; K?dziora, Kinga; Lavandera, Iván; Rodríguez-Solla, Humberto; Concellón, Carmen; del Amo, Vicente

2014-03-11

155

Highly enantioselective epoxidation catalyzed by cinchona thioureas: synthesis of functionalized terminal epoxides bearing a quaternary stereogenic center.  

PubMed

A brilliant debut! Cinchona thioureas have been reported for the first time as catalysts in the area of asymmetric oxidations. They efficiently promote an unprecedented highly enantioselective epoxidation of deactivated 1,1-disubstituted alkenes to terminal epoxides containing a quaternary stereogenic center (see scheme). PMID:22511471

Russo, Alessio; Galdi, Gerardina; Croce, Gianluca; Lattanzi, Alessandra

2012-05-14

156

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

157

Enantioselective synthesis of spiroacetals via silver(I)-promoted alkylation of hemiacetals: total synthesis of cephalosporolides E and F.  

PubMed

A silver(I)-promoted intramolecular hemiacetal alkylation has been developed that converts readily available keto-chlorodiols into functionalized spiroacetals containing 5,5-, 5,6-, and 5,7-membered ring systems. The efficiency of this process is demonstrated in a concise total synthesis of the fungal metabolites cephalosporolides E and F. PMID:23145960

Chang, Stanley; Britton, Robert

2012-12-01

158

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

2013-01-18

159

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

160

Palladium-catalyzed asymmetric amination of allenyl phosphates: enantioselective synthesis of allenes with an additional unsaturated unit.  

PubMed

A highly enantioselective Pd-catalyzed amination of allenyl phosphates generating 2,3-allenyl amines with central chirality has been developed. Under the optimized conditions, chiral 2,3-allenyl amines with or without (an) additional C-C double or triple bond(s) have been prepared at 0?°C with up to 90% yield and 94%?ee by identifying (R)-3,4,5-(MeO)3-MeOBIPHEP as the ligand. PMID:24799033

Li, Qiankun; Fu, Chunling; Ma, Shengming

2014-06-16

161

Enantioselective analysis of triazole fungicide myclobutanil in cucumber and soil under different application modes by chiral liquid chromatography/tandem mass spectrometry.  

PubMed

A sensitive and enantioselective method was developed and validated for the determination of myclobutanil enantiomers by chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a Chiralcel OD-RH column, with ACN-water (70/30, v/v) as the mobile phase under isocratic conditions at 0.5 mL/min flow rate. The matrix effect, linearity, precision, accuracy, and stability were evaluated. The proposed method then was successfully applied to the study of enantioselective degradation of rac-myclobutanil in cucumber and soil under different application modes. The results showed that the preferential degradation of (+)-myclobutanil resulted in an enrichment of the (-)-myclobutanil residue in plant and soil. Moreover, in cucumber, the stereoselective intensity of myclobutanil under root douche treatment was stronger than that under foliar spraying treatment, whereas in soil, the intensity was exactly opposite. The probable reasons underlying these enantioselective effects were also discussed. This study highlighted the importance of examining the fate of both enantiomers in the greenhouse system for the correct use of chiral pesticides. PMID:22288843

Dong, Fengshou; Cheng, Li; Liu, Xingang; Xu, Jun; Li, Jing; Li, Yuanbo; Kong, Zhiqiang; Jian, Qiu; Zheng, Yongquan

2012-02-29

162

Application of capillary electrophoresis to study the enantioselective transformation of five chiral pesticides in aerobic soil slurries.  

PubMed

The enantiomers of five chiral pesticides of environmental interest, metalaxyl, imazaquin, fonofos (dyfonate), ruelene (cruformate), and dichlorprop, were separated analytically using capillary electrophoresis (CE) with cyclodextrin chiral selectors. For metalaxyl, imazaquin, and fonofos, aqueous slurries of soil samples from two sites in Georgia and one in Ohio were spiked with the racemate of each pesticide at 50-60 mg/L of aqueous phase of the slurry, and CE analyses were performed at various time intervals to determine enantiomer fractions (EF). Metalaxyl underwent enantioselective transformation; in one soil, the half-life of the target active R-(+)-enantiomer was 17 days while that for the S-(-)-enantiomer was 69 days. Transformation occurred more slowly in the other two soils but was still selective for the R-(+)-enantiomer. Imazaquin and fonofos exhibited nonselective enantiomer loss over their 3 months of incubation time; this could have been due to abiotic or nonselective microbial reactions. Ruelene and dichlorprop were transformed selectively in a variety of soils in a previously reported study (7) that showed the influence of environmental changes on the transformation of chiral pollutants in soils; analytical methods used in that study are reported here to further illustrate the application of CE. CE is shown to be a simple, efficient, and inexpensive way to follow the transformation of chiral pesticides in laboratory microcosms where concentrations can be made high enough (25-50 mg/L initial racemate concentration) for detection of residual parent enantiomers during most of the process. PMID:16076090

Jarman, Jessica L; Jones, W Jack; Howell, Lorrie A; Garrison, A Wayne

2005-08-10

163

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

164

Straightforward methodology for the enantioselective synthesis of benzo[a]- and indolo[2,3-a]quinolizidines.  

PubMed

An enantioselective two-step route to substituted benzo[a]- and indolo[2,3-a]quinolizidines has been developed. It consists of (i) a stereoselective cyclocondensation of a racemic or prochiral delta-oxo(di)ester with either (S)-(3,4-dimethoxyphenyl)alaninol or (S)-tryptophanol in a process involving a dynamic kinetic resolution and/or the differentiation of enantiotopic or diastereotopic ester groups, and (ii) a subsequent stereocontrolled cyclization on the aromatic ring taking advantage of the masked N-acyl iminium ion present in the resulting oxazolopiperidone lactams. PMID:17547461

Amat, Mercedes; Santos, Maria M M; Bassas, Oriol; Llor, Núria; Escolano, Carmen; Gómez-Esqué, Arantxa; Molins, Elies; Allin, Steven M; McKee, Vickie; Bosch, Joan

2007-07-01

165

A General and Enantioselective Approach to Pentoses: A Rapid Synthesis of PSI-6130, the Nucleoside Core of Sofosbuvir.  

PubMed

An efficient route towards biologically relevant pentose derivatives is described. The de novo synthetic strategy features an enantioselective ?-oxidation reaction enabled by a chiral amine in conjunction with copper(II) catalysis. A subsequent Mukaiyama aldol coupling allows for the incorporation of a wide array of modular two-carbon fragments. Lactone intermediates accessed via this route provide a useful platform for elaboration, as demonstrated by the preparation of a variety of C-nucleosides and fluorinated pentoses. Finally, this work has facilitated expedient syntheses of pharmaceutically active compounds currently in clinical use. PMID:24670208

Peifer, Manuel; Berger, Raphaëlle; Shurtleff, Valerie W; Conrad, Jay C; Macmillan, David W C

2014-04-23

166

Palladacyclic Imidazoline-Naphthalene Complexes: Synthesis and Catalytic Performance in Pd(II)-Catalyzed Enantioselective Reactions of Allylic Trichloroacetimidates  

PubMed Central

A new family of air- and moisture-stable enantiopure C,N-palladacycles (PIN-acac complexes) were prepared in good overall yield in three steps from 2-iodo-1-naphthoic acid and enantiopure ?-amino alcohols. Three of these PIN complexes were characterized by single-crystal X-ray analysis. As anticipated, the naphthalene and imidazoline rings of PIN-acac complexes 18a and 18b were canted significantly from planarity and projected the imidazoline substituents R1 and R2 on opposite faces of the palladium square plane. Fifteen PIN complexes were evaluated as catalysts for the rearrangement of prochiral (E)-allylic trichloroacetimidate 19 (eq 2) and the SN2? allylic substitution of acetic acid with prochiral (Z)-allylic trichloroacetimidate 23. Although these complexes were kinetically poor catalysts for the Overman rearrangement, they were good catalysts for the allylic substitution reaction, providing branched allylic esters in high yield. However, enantioselectivities were low to moderate and significantly less than that realized with palladacyclic complexes of the COP family. Computational studies support an anti-acetoxypalladation/syn-deoxypalladation mechanism analogous to that observed with COP catalysts. The computational study further suggests that optimizing steric influence in the vicinity of the carbon ligand of a chiral C,N-palladacycle, rather than near the nitrogen heterocycle, is the direction to pursue in future development of improved enantioselective catalysts of this motif.

Cannon, Jeffrey S.; Frederich, James H.; Overman, Larry E.

2012-01-01

167

Highly enantioselective synthesis of ?-, ?-, and ?-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling.  

PubMed

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (?99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (?99% ee) and catalytic synthesis of various ?- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)-Cu- or Pd-catalyzed cross-coupling. ZACA-in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ?-alkene-1-ols produced both (R)- and (S)-?,?-dioxyfunctional intermediates (3) in 80-88% ee, which were readily purified to the ?99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These ?,?-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-Ichi

2014-06-10

168

Discovery, application and protein engineering of Baeyer-Villiger monooxygenases for organic synthesis.  

PubMed

Baeyer-Villiger monooxygenases (BVMOs) are useful enzymes for organic synthesis as they enable the direct and highly regio- and stereoselective oxidation of ketones to esters or lactones simply with molecular oxygen. This contribution covers novel concepts such as searching in protein sequence databases using distinct motifs to discover new Baeyer-Villiger monooxygenases as well as high-throughput assays to facilitate protein engineering in order to improve BVMOs with respect to substrate range, enantioselectivity, thermostability and other properties. Recent examples for the application of BVMOs in synthetic organic synthesis illustrate the broad potential of these biocatalysts. Furthermore, methods to facilitate the more efficient use of BVMOs in organic synthesis by applying e.g. improved cofactor regeneration, substrate feed and in situ product removal or immobilization are covered in this perspective. PMID:22733152

Balke, Kathleen; Kadow, Maria; Mallin, Hendrik; Sass, Stefan; Bornscheuer, Uwe T

2012-08-21

169

Cinchona alkaloid squaramide catalyzed enantioselective hydrazination/cyclization cascade reaction of ?-isocyanoacetates and azodicarboxylates: synthesis of optically active 1,2,4-triazolines.  

PubMed

An efficient enantioselective hydrazination/cyclization cascade reaction of ?-substituted isocyanoacetates to azodicarboxylates catalyzed by Cinchona alkaloid derived squaramide catalysts has been investigated, affording the optically active 1,2,4-triazolines in excellent yields (up to 99%) and good to excellent enantioselectivities (up to 97% ee) under mild conditions. PMID:23984761

Zhao, Mei-Xin; Bi, Hong-Lei; Zhou, Hao; Yang, Hui; Shi, Min

2013-09-20

170

Highly enantioselective synthesis of chiral 7-ring O- and N-heterocycles by a one-pot nitro-Michael-cyclization tandem reaction.  

PubMed

A concise enantioselective approach to synthesise medium-sized 7-ring O- and N-heterocycles has been developed. The synthetic strategy relies on an organocatalytic nitro-Michael-nitrile oxide cycloaddition tandem reaction, leading to the corresponding chiral benzoxe- and benzazepine derivatives containing an additional fused dihydroisoxazoline ring in good yields and excellent enantioselectivities (up to 97% ee). PMID:24190160

Rohlmann, Renate; Daniliuc, Constantin-Gabriel; Mancheño, Olga García

2013-12-25

171

Enantioselective tandem reaction of chromone-derived Morita-Baylis-Hillman carbonates with benzylamines catalyzed by a trifunctional organocatalyst: the synthesis of chiral 3-aminomethylene-flavanones.  

PubMed

An enantioselective tandem reaction of chromones-derived MBH carbonates (1) with benzylamines (2) catalyzed by a trifunctional organocatalyst, cinchonidine-amide-thiourea, has been developed in moderate to good yields (50-87%) and enantioselectivities (up to 89% ee). PMID:23532090

Zhong, Neng-jun; Liu, Li; Wang, Dong; Chen, Yong-Jun

2013-05-01

172

Direct amino acid-catalyzed cascade biomimetic reductive alkylations: application to the asymmetric synthesis of Hajos-Parrish ketone analogues.  

PubMed

A direct amino acid-catalyzed chemo- and enantioselective process for the double cascade synthesis of highly substituted 2-alkyl-cyclopentane-1,3-diones, 2-alkyl-3-methoxy-cyclopent-2-enones and Hajos-Parrish (H-P) ketone analogs is presented via reductive alkylation chemistry. For the first time, we have developed a single-step alkylation of cyclopentane-1,3-dione with aldehydes/ketones and a Hantzsch ester through an organocatalytic reductive alkylation strategy. A direct combination of amino acid-catalyzed cascade olefination-hydrogenation and cascade Robinson annulations of cyclopentane-1,3-dione, aldehydes/ketones, a Hantzsch ester and methyl vinyl ketone furnished the highly functionalized H-P ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products have shown direct applications in pharmaceutical chemistry. PMID:18972048

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2008-11-21

173

Synthesis of alpha-stereogenic amides and ketones by enantioselective conjugate addition of 1,4-dicarbonyl but-2-enes.  

PubMed

In the conjugate addition reaction of a alpha,beta-unsaturated compound, the new stereogenic center is created in the beta-position. In contrast, conjugate addition to 1,4-dicarbonyl but-2-enes will generate an alpha-stereogenic center with respect to one of the carbonyl groups, which informally, can be considered as an inversion of normal reactivity patterns or Umpolung. In this paper, we demonstrate that chiral bicyclic guanidine can catalyze the addition of 1,3-dicarbonyl compounds to 1,4-dicarbonyl but-2-enes [(E)-4-oxo-4-arylbutenamides and (E)-4-oxo-4-arylbutenones] with high regioselectivity and enantioselectivity (ee values up to 97%). PMID:19301341

Jiang, Zhiyong; Yang, Yuanyong; Pan, Yuanhang; Zhao, Yujun; Liu, Hongjun; Tan, Choon-Hong

2009-01-01

174

New phosphine-diamine and phosphine-amino-alcohol tridentate ligands for ruthenium catalysed enantioselective hydrogenation of ketones and a concise lactone synthesis enabled by asymmetric reduction of cyano-ketones  

PubMed Central

Enantioselective hydrogenation of ketones is a key reaction in organic chemistry. In the past, we have attempted to deal with some unsolved challenges in this arena by introducing chiral tridentate phosphine-diamine/Ru catalysts. New catalysts and new applications are presented here, including the synthesis of phosphine-amino-alcohol P,N,OH ligands derived from (R,S)-1-amino-2-indanol, (S,S)-1-amino-2-indanol and a new chiral P,N,N ligand derived from (R,R)-1,2-diphenylethylenediamine. Ruthenium pre-catalysts of type [RuCl2(L)(DMSO)] were isolated and then examined in the hydrogenation of ketones. While the new P,N,OH ligand based catalysts are poor, the new P,N,N system gives up to 98% e.e. on substrates that do not react at all with most catalysts. A preliminary attempt at realising a new delta lactone synthesis by organocatalytic Michael addition between acetophenone and acrylonitrile, followed by asymmetric hydrogenation of the nitrile functionalised ketone is challenging in part due to the Michael addition chemistry, but also since Noyori pressure hydrogenation catalysts gave massively reduced reactivity relative to their performance for other acetophenone derivatives. The Ru phosphine-diamine system allowed quantitative conversion and around 50% e.e. The product can be converted into a delta lactone by treatment with KOH with complete retention of enantiomeric excess. This approach potentially offers access to this class of chiral molecules in three steps from the extremely cheap building blocks acrylonitrile and methyl-ketones; we encourage researchers to improve on our efforts in this potentially useful but currently flawed process.

2012-01-01

175

Enantioselective Synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine and their Racemization-free Incorporation into Oligopeptides via Solid-phase Synthesis  

PubMed Central

An efficient method for the enantioselective synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine (tfT) on multi-gram scales was developed. Absolute configurations of the two stereoisomers were ascertained by X-ray crystallography. Racemization-free coupling conditions for the incorporation of tfT into oligopeptides were then explored. For solution-phase synthesis, tfT racemization was not an issue under conventional coupling conditions. For solid-phase synthesis, the following conditions were identified to achieve racemization-free synthesis: if tfT (3.0 eq.) was not the first amino acid to be linked to the resin (1.0 eq.), the condition is: 2.7 eq. DIC/3.0 eq. HOBt as the coupling reagent at 0 °C for 20 h; if tfT (3.0 eq.) was the first amino acid to be linked to the resin (1.0 eq.), then 1.0 eq. of CuCl2 needs to be added to the coupling reagent.

Xiao, Nu; Jiang, Zhong-Xing; Yu, Y. Bruce

2010-01-01

176

Detonation-synthesis nanodiamonds: synthesis, structure, properties and applications  

Microsoft Academic Search

The review outlines the theoretical foundations and industrial implementations of modern detonation synthesis of nanodiamonds and chemical purification of the nanodiamonds thus obtained. The structure, key properties and promising fields of application of detonation-synthesis nanodiamonds are considered.

Valerii Yu Dolmatov

2007-01-01

177

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

178

N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition of ketenes and 3-aroylcoumarins: highly enantioselective synthesis of dihydrocoumarin-fused dihydropyranones.  

PubMed

The N-heterocyclic carbene-catalyzed [4 + 2] cyclization of ketenes and 3-aroylcoumarins has been developed to give the corresponding dihydrocoumarin-fused multisubstituted dihydropyranones in high yield with good diastereoselectivity and high enantioselectivity. PMID:23117299

Jian, Teng-Yue; Chen, Xiang-Yu; Sun, Li-Hui; Ye, Song

2013-01-01

179

Organocatalytic enantioselective one-pot four-component ugi-type multicomponent reaction for the synthesis of epoxy-tetrahydropyrrolo[3,4-b]pyridin-5-ones.  

PubMed

Enantioselective multicomponent reaction: in the presence of a catalytic amount of chiral BINOL-derived phosphoric acid (TRIP), the reaction of an ?-isocyanoacetate 1, an aldehyde 2, and an aniline 3, followed by addition of a toluene solution of ?,?-unsaturated acyl chloride 4 afforded the oxa-bridged tricycle 5 in excellent yield, diastereoselectivity, and enantioselectivity. Six chemical bonds, five stereogenic centers, and three cycles were formed in this one-pot four-component reaction. PMID:22930594

Su, Yingpeng; Bouma, Marinus J; Alcaraz, Lilian; Stocks, Mike; Furber, Mark; Masson, Géraldine; Zhu, Jieping

2012-10-01

180

Chiral phosphorus-based 1,3-dipoles: a modular approach to enantioselective 1,3-dipolar cycloaddition and polycyclic 2-pyrroline synthesis.  

PubMed

The design of a new class of chiral 1,3-dipoles for enantioselective cycloaddition reactions is reported. These phosphorus-based dipoles are easily formed (from imines, acid chlorides, and chiral phosphites), rigidly chiral, and undergo intramolecular alkene cycloaddition with high enantioselectivity. Overall, this provides a straightforward and modular approach to synthesize chiral 2-pyrrolines and pyrrolidines in up to 99% ee. PMID:24502319

Morin, Marie S T; Arndtsen, Bruce A

2014-02-21

181

Enantioselective total syntheses of several bioactive natural products based on the development of practical asymmetric catalysis.  

PubMed

I present herewith enantioselective total syntheses of several bioactive natural products, such as (-)-strychnine, (+)-decursin, (-)-cryptocaryolone diacetate, (-)-fluoxetine, and aeruginosin 298-A, based on practical asymmetric catalyses (Michael reaction, epoxidation, and phase-transfer reaction) that I developed with co-workers in Prof. Shibasaki's group over the past 5 years. In the first part of this review, I discuss the great improvement of catalyst efficiency in an ALB-catalyzed asymmetric Michael reaction of malonate and application to the pre-manufacturing scale (greater than kilogram scale) and enantioselective total synthesis of (-)-strychnine with the development of novel domino cyclization. To broaden the substrate generality of the Michael reaction, we developed a highly stable, storable, and reusable La-O-linked-BINOL complex. Further extension of the reaction using beta-keto ester as a Michael donor was achieved with the development of a La-NR-linked-BINOL complex, thereby improving indole alkaloid syntheses. In the second section, I discuss enantioselective total synthesis of (+)-decursin using catalytic asymmetric epoxidation. To achieve the synthesis, we developed a new La-BINOL-Ph(3)As = O (1:1:1) complex catalyst system, which has much higher reactivity and broader substrate generality than the previously developed catalyst systems. This allowed us to achieve catalytic asymmetric epoxidation of alpha,beta-unsaturated carboxylic acid derivatives with high enantioselectivity and broad substrate generality for the first time by changing the lanthanide metal and reaction conditions. Among them, catalytic asymmetric epoxidation of alpha,beta-unsaturated morpholinyl amides is quite useful in terms of synthetic utility of the corresponding alpha,beta-epoxy morpholinyl amides. Highly catalyst-controlled enantio- or diastereoselective epoxidation of the alpha,beta-unsaturated morpholinyl amides, coupled with diastereoselective reduction of beta-hydroxy ketones, enabled the synthesis of all possible stereoisomers of 1,3-polyol arrays with successful enantioselective total synthesis of several 1,3-polyol natural products, such as (-)-cryptocaryolone diacetate. In addition, the development of a new regioselective epoxide-opening reaction of alpha,beta-epoxy amides to the corresponding alpha- and beta-hydroxy amides enhanced the usefulness of the present epoxidation and was applied to the enantioselective total synthesis of (-)-fluoxetine. In the final section, I report the development of a new asymmetric two-center organocatalyst (TaDiAS) and its application to the enantioselective synthesis of aeruginosin 298-A and its analogues. Because of the remarkable structural diversity of TaDiAS, a practical asymmetric phase-transfer reaction with broad substrate generality was achieved. As a result, we succeeded in developing a highly versatile synthetic method for aeruginosin 298-A and its analogues. Inhibitory activity studies of the compounds against the serine protease trypsin provided preliminary information about their structure-activity relations. PMID:15340187

Ohshima, Takashi

2004-09-01

182

Facile synthesis of l-Dopa tert-butyl ester by catalytic enantioselective phase-transfer alkylation  

Microsoft Academic Search

Facile asymmetric synthesis of l-Dopa and related amino acid esters has been achieved by phase-transfer catalysis of the rationally designed C2-symmetric chiral quaternary ammonium salts 1. The ‘scale-up’ experiment performed with 5.00 g of tert-butyl glycinate-benzophenone Schiff base (2) represents the practical aspect of our approach.

Takashi Ooi; Minoru Kameda; Hidenori Tannai; Keiji Maruoka

2000-01-01

183

Crosslinked aggregates of Rhizopus oryzae lipase as industrial biocatalysts: preparation, optimization, characterization, and application for enantioselective resolution reactions.  

PubMed

Lipase from Rhizopus oryzae (ROL) was immobilized as crosslinked enzyme aggregate (CLEA) via precipitation with ammonium sulfate and simultaneous crosslinking with glutaraldehyde. The optimum conditions of the immobilization process were determined. Lipase CLEAs showed a twofold increase in activity when Tween 80-pretreated lipase was used for CLEA preparation. CLEAs were shown to have several advantages compared to free lipase. CLEAs were more stable at 50°C and 60°C as well as for a wide range of pH. After incubation at 50°C, CLEA showed 74% of initial activity whereas free enzyme was totally inactivated. Reduction of Schiff bases has been performed for the first time in the CLEA preparation process significantly improving the chemically modified CLEAs' reusability, thus providing an enzyme with high potential for recycling even under aqueous reaction conditions where enzyme leakage is, in general, one of the major problems. The CLEA retained 91% activity after 10 cycles in aqueous medium. The immobilized enzyme was used for kinetic resolution reactions. Results showed that immobilization had an enhancing effect on the conversion (c) as well as on the enantiomeric ratio (E). ROL CLEA displayed five times higher enantioselectivity for the hydrolysis of (R,S)-1-phenylethyl acetate and likewise 1.5 times higher enantioselectivity for the transesterification of racemic (R-S)-1-phenylethanol with vinylacetate. PMID:22685034

Kartal, Funda; Kilinc, Ali

2012-07-01

184

The Development of the Enantioselective Addition of Ethyl Diazoacetate to Aldehydes: Asymmetric Synthesis of 1,2-Diols  

PubMed Central

A novel synthetic strategy towards the asymmetric synthesis of vicinal diols bearing a tertiary center is presented. The method encompasses the dinuclear Mg-catalyzed asymmetric addition of ethyl diazoacetate into several aldehydes, oxidation of the diazo functionality, and diastereoselective alkyl transfer of various organometallics into the resulting chiral ?-hydroxy-?-ketoesters to afford a diverse range of 1,2-diols in high yield, diastereoselectivity, and chirality transfer.

Trost, Barry M.; Malhotra, Sushant; Koschker, Philipp; Ellerbrock, Pascal

2011-01-01

185

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

186

Enantioselective synthesis of 6-[fluorine-18]-fluro-l-dopa from no-carrier-added fluorine-18-fluoride  

SciTech Connect

A trimethylammonium veratraldehyde triflate was synthesized and used as a precursor for the asymmetric synthesis of 6-[{sup 18}F]fluoro-L-dopa. Its nucleophilic fluorination with {sup 18} F-fluoride produced by the {sup 18}O(p,n) {sup 18}F nuclear reaction on enriched {sup 18}O-water led to the corresponding no-carrier-added [{sup 18}F]fluoroveratraldehyde (45 {plus_minus} 5% EOB). Diiodosilane was used to prepare the corresponding [{sup 18}F] fluorobenzyl iodide (36.5 {plus_minus} 5.3% EOB). Alkylation of (S)-1-tert-boc-2-tert-butyl-3-methyl-4-imidazolidinone with this electrophilic agent, hydrolysis and purification by preparative high-pressure liquid chromatography made 6-[{sup 18}F]fluoro-L-dopa ready for human injection, in a 23% {plus_minus} 6% decay-corrected radiochemical yield. The enantiomeric purity and the specific activity were above 96% and 1 Cl/{mu}mole respectively. Through this procedure, starting from 250 mCi of {sup 18}F-fluoride, multimillicurie amounts (32 {plus_minus} 8.5 mCi) of no-carrier-added 6-[{sup 18}F]fluoro-L-dopa are now available at the end of synthesis (90 min) with a good radiochemical purity (more than 98%). 28 refs., 3 figs., 1 tab.

Lemaire, C.; Damhaut, P.; Plenvaux, A. [Liege Univ. (Belgium)] [and others

1994-12-01

187

Chiral functionalization of graphene oxide by optically active helical-substituted polyacetylene chains and its application in enantioselective crystallization.  

PubMed

This article reports an original, versatile strategy to chirally functionalize graphene oxide (GO) with optically active helical-substituted polyacetylene. GO was first converted into alkynyl-GO containing polymerizable -C?C moieties, which took part in the polymerization of another chiral acetylenic monomer, yielding the expected GO hybrid covalently grafted with chiral helical polyacetylene chains. Transmission electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyses verified the successful attachment of substituted polyacetylene chains on GO by covalent chemical bonding. Moreover, circular dichroism effects and UV-vis absorption demonstrated that the GO hybrid possessed fascinating optical activity. It also largely improved the dispersibility of GO in tetrahydrofuran. The GO-derived hybrid was further used as a chiral inducer toward enantioselective crystallization of alanine enantiomers. l-Alanine was preferably induced to crystallize, forming rodlike crystals. PMID:24902050

Li, Weifei; Liang, Junya; Yang, Wantai; Deng, Jianping

2014-06-25

188

Enantioselective Approach to Quinolizidines: Total Synthesis of Cermizine D and Formal Syntheses of Senepodine G & Cermizine C  

PubMed Central

The formal total syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselecetive, 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 has 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.

Veerasamy, Nagarathanam; Carlson, Erik C.; Collett, Nathan D.; Saha, Mrinmoy

2013-01-01

189

Enantioselective syntheses of ( R)-3-phenyl GABA, ( R)-baclofen and 4-arylpyrrolidin-2-ones  

Microsoft Academic Search

Enantioselective synthesis of (R)-4-amino-3-phenylbutyric acid and (R)-baclofen has been achieved through a diastereoselective conjugate addition of cyanide to enantiomericaly pure 2-(2-arylethenyl)oxazolines, followed by chemoselective reduction into cyclic amidines.

Nicole Langlois; Nathalie Dahuron; Hai-Shan Wang

1996-01-01

190

Apparent and true enantioselectivity in enantioseparations.  

PubMed

The separation factor of two compounds in chromatography is the ratio of their equilibrium constants or retention factors. This parameter is universally employed to investigate their resolution and to optimize the experimental conditions of their analysis. In enantioseparations, the situation is more complex because there is a mixed retention mechanism. The retention factor is the sum of two contributions, one enantioselective, the other nonselective. Although both contribute to retention, the latter being identical for the two enantiomers and does not contribute to their separation. We show how these two contributions can be measured and how it becomes necessary to distinguish between the apparent, alpha(app), and the true, alpha(true), separation factors. The existence of nonselective sites is responsible for alpha(app) being less than alpha(true). Depending on the difference between these two factors, the more effective approach to improve a separation is either to increase the enantioselectivity or to reduce the nonselective interactions. Practical applications to separations of different beta-blockers on cellobiohydrolase are discussed. The apparent enantioselectivity of alprenolol is larger and increases faster with increasing pH than that of the more hydrophobic propranolol, in spite of the importance of hydrophobic interactions in the enantioselective mechanism. These two unexpected properties are discussed and explained. PMID:10861955

Götmar, G; Fornstedt, T; Guiochon, G

2000-07-01

191

Enantioselective ?-hydroxylation of ?-ketoamides.  

PubMed

The first enantioselective ?-hydroxylation reaction of ?-substituted ?-ketoamides has been developed by using the commercially available hydroquinine/TBHP system. The tertiary alcohols are obtained in good to high yield and up to 83% ee, which can be improved by a single crystallization. PMID:23292494

De Fusco, Claudia; Meninno, Sara; Tedesco, Consiglia; Lattanzi, Alessandra

2013-02-14

192

Asymmetric biomimetic oxidations of phenols: the mechanism of the diastereo- and enantioselective synthesis of dehydrodiconiferyl ferulate (DDF) and dehydrodiconiferyl alcohol (DDA)  

Microsoft Academic Search

Stereoselective bimolecular radical coupling of enantiopure phenylpropenoidic phenols are described, starting from enantiopure amidic derivatives of ferulic acid. The latter were prepared from ferulic acid by reaction with (S)-alanine or Oppolzer camphor sultam. The oxidation step was performed both enzymatically (HRP\\/H2O2) and chemically (Ag2O). The observed enantioselectivity in the oxidation step encompasses the range 65–84% and is consistent with the

Marco Orlandi; Bruno Rindone; Giorgio Molteni; Petteri Rummakko; Gösta Brunow

2001-01-01

193

Asymmetric ?-amination of 4-substituted pyrazolones catalyzed by a chiral Gd(OTf)3/N,N'-dioxide complex: highly enantioselective synthesis of 4-amino-5-pyrazolone derivatives.  

PubMed

The asymmetric ?-amination of 4-substituted pyrazolones with azodicarboxylates was investigated for the first time, employing an N,N'-dioxide gadolinium(III) complex as the catalyst. The novel transformations exhibited high yield, and 4-amino-5-pyrazolone derivatives bearing a chiral quaternary center were obtained in excellent yields (up to 99%) and enantioselectivities (90%-97% ee) for a broad scope of 5-pyrazolones by using 1 mol % or only 0.05 mol % of catalyst. PMID:21214254

Yang, Zhigang; Wang, Zhen; Bai, Sha; Liu, Xiaohua; Lin, Lili; Feng, Xiaoming

2011-02-18

194

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

2013-01-01

195

Catalytic Enantioselective Silylation of N-Sulfonylimines: Asymmetric Synthesis of ?-Amino Acids from CO2 via Stereospecific Carboxylation of ?-Amino Silanes.  

PubMed

A catalytic enantioselective silylation of N-tert-butylsulfonylimines using a Cu-secondary diamine complex was demonstrated. The resulting optically active ?-amino silanes could be carboxylated under a CO2 atmosphere (1 atm) to afford the corresponding ?-amino acids in a stereoretentive manner. This two-step sequence provides a new synthetic protocol for optically active ?-amino acids from gaseous CO2 and imines in the presence of a catalytic amount of a chiral source. PMID:24834796

Mita, Tsuyoshi; Sugawara, Masumi; Saito, Keisuke; Sato, Yoshihiro

2014-06-01

196

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

197

Enantioselective imine reduction catalyzed by imine reductases and artificial metalloenzymes.  

PubMed

Adding value to organic synthesis. Novel imine reductases enable the enantioselective reduction of imines to afford optically active amines. Likewise, novel bioinspired artificial metalloenzymes can perform the same reaction as well. Emerging proof-of-concepts are herein discussed. PMID:24695640

Gamenara, Daniela; Domínguez de María, Pablo

2014-05-21

198

Synthesis and electrochemical applications of gold nanoparticles  

Microsoft Academic Search

This review covers recent advances in synthesis and electrochemical applications of gold nanoparticles (AuNPs). Described approaches include the synthesis of AuNPs via designing and choosing new protecting ligands; and applications in electrochemistry of AuNPs including AuNPs-based bioelectrochemical sensors, such as direct electrochemistry of redox-proteins, genosensors and immunosensors, and AuNPs as enhancing platform for electrocatalysis and electrochemical sensors.

Shaojun Guo; Erkang Wang

2007-01-01

199

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

200

Enantioselective Pd-Catalyzed Allylation of Acyclic ?-Fluorinated Ketones.  

PubMed

Significant synthetic challenges remain for the asymmetric synthesis of tertiary ?-fluoro ketones, which are potentially useful molecules for the development of drugs, agrochemicals, and functional materials. Herein, we describe the development of a method for the catalytic enantioselective synthesis of tertiary ?-fluoro ketones via the Tsuji-Trost reaction of racemic acyclic ?-fluorinated ketones. Enantioenriched acyclic ?-cabonyl tertiary fluorides can be produced with the aid of a palladium/phosphinooxazoline catalyst. PMID:24915625

Wang, Wengui; Shen, Haiming; Wan, Xiao-Long; Chen, Qing-Yun; Guo, Yong

2014-07-01

201

Catalytic, enantioselective vinylogous Michael reactions.  

PubMed

Recent progress in the field of catalytic, enantioselective vinylogous Michael reactions of latent dienolates is described which furnish optically highly enriched chiral 1,7-dioxo compounds of great utility in one synthetic operation. Emphasis is given to new catalysis modes which realise this challenging transformation with high regio- as well as enantioselectivity. PMID:24760480

Schneider, Christoph; Abels, Falko

2014-06-14

202

Enantioselective fluorescent sensors: a tale of BINOL.  

PubMed

The development of automated, high-throughput organic synthesis and screening techniques has created an urgent demand for methods that rapidly determine the enantiomeric composition of chiral compounds. Enantioselective fluorescent sensors offer the potential for real-time, high-sensitivity techniques for determining enantiomeric data in high-throughput chiral assays. In this Account, we describe a range of fluorescent sensors derived from 1,1'-bi-2-naphthol (BINOL), a readily available biaryl compound with axial chirality. We show that BINOL can be used to construct structurally diverse, chiral fluorescent sensors to carry out highly enantioselective, sensitive recognition of chiral amino alcohols, ?-hydroxycarboxylic acids, and amino acid derivatives. For example, we prepared an (S)-BINOL derivative whose 3,3'-positions are attached to two chiral amino alcohol units, each having two phenyl substituents. This compound shows a fluorescence enhancement of 950-fold in the presence of (S)-mandelic acid but very little change in the presence of (R)-mandelic acid. It also allows the enantiomers of this ?-hydroxycarboxylic acid to be visually discriminated by an enantioselective precipitation process. A structurally similar (S)-BINOL-amino alcohol molecule, but with three rather than two phenyl substitutents in each of the two amino alcohol units, was found to exhibit generally enantioselective fluorescence responses toward structurally diverse ?-hydroxycarboxylic acids. We further prepared a pseudoenantiomeric analogue of this compound from (R)-H(8)BINOL, which has the opposite chiral configuration at both the biaryl center as well as the pendant amino alcohols. These two compounds have opposite enantioselectivity in the recognition of a chiral substrate, with distinctly different fluorescence emission wavelengths. By mixing them together, we developed a pseudoenantiomeric sensor pair to facilitate chiral assays. Using this pseudoenantiomeric sensor pair allows both the concentration and the enantiomeric composition of a substrate to be determined in a single fluorescence measurement. We synthesized another compound by ligating a terpyridine unit to BINOL and found that coordination of a Cu(II) ion to the terpyridine unit almost completely quenched its fluorescence. Displacement of the Cu(2+) ion from this complex by chiral amino alcohols leads to enantioselective fluorescence enhancement. This BINOL-terpyridine-Cu(II) complex also exhibits enantioselective gel collapsing in the presence of chiral amino alcohols, providing a new visual chiral discrimination method. When a series of light-absorbing conjugated units are attached to the BINOL structure, the resulting multiarmed dendritic molecules show greatly amplified fluorescence responses. Thus, the light harvesting effect of dendrimers can be used to greatly increase the sensitivity of the fluorescent sensors. The progress described here demonstrates that highly enantioselective and sensitive fluorescent sensors can be obtained through a systematic investigation of the structure-property relation between the sensors and the substrates. These sensors show great potential for the development of rapid assays of chiral organic compounds. PMID:21834528

Pu, Lin

2012-02-21

203

Asymmetric allylation of ?-ketoester-derived N-benzoylhydrazones promoted by chiral sulfoxides/N-oxides Lewis bases: highly enantioselective synthesis of quaternary ?-substituted ?-allyl-?-amino acids.  

PubMed

Chiral sulfoxides/N-oxides (R)-1 and (R,R)-2 are effective chiral promoters in the enantioselective allylation of ?-keto ester N-benzoylhydrazone derivatives 3a-g to generate the corresponding N-benzoylhydrazine derivatives 4a-g, with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a-b were subsequently treated with SmI2, and the resulting amino esters 5a-b with LiOH to obtain quaternary ?-substituted ?-allyl ?-amino acids 6a-b, whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data. PMID:23846830

Reyes-Rangel, Gloria; Bandala, Yamir; García-Flores, Fred; Juaristi, Eusebio

2013-09-01

204

Enantioselective Synthesis of 5,7-Bicyclic Ring Systems from Axially Chiral Allenes Using a Rh(I)-Catalyzed Cyclocarbonylation Reaction  

PubMed Central

A transfer of chirality in an intramolecular Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta[c]azepinones and dihydrocyclopenta[c]oxepinones enantioselectively (22 – 99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done.

Grillet, Francois; Brummond, Kay M.

2013-01-01

205

Enantioselective synthesis of 5,7-bicyclic ring systems from axially chiral allenes using a Rh(I)-catalyzed cyclocarbonylation reaction.  

PubMed

A transfer of chirality in an intramolecular Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta[c]azepinones and dihydrocyclopenta[c]oxepinones enantioselectively (22-99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done. PMID:23485149

Grillet, Francois; Brummond, Kay M

2013-04-19

206

Lithium binaphtholate-catalyzed enantioselective enyne addition to ketones: access to enynylated tertiary alcohols.  

PubMed

A new catalytic enantioselective enyne addition to ketones has been developed. In the presence of chiral lithium binaphtholate, the addition reaction proceeded smoothly to produce a series of enynylated tertiary alcohols in up to 96% yield and 94% enantiomeric excess. Convenient transformation of the adduct via Pauson-Khand cycloaddition reaction afforded the bicyclic product without detectable loss of enantioselectivity. Furthermore, catalytic asymmetric enyne addition to trifluoromethylketone was applied in the synthesis of the Efavirenz analogue. PMID:24849808

Cai, Hua; Nie, Jing; Zheng, Yan; Ma, Jun-An

2014-06-20

207

Organocatalytic sequential one-pot double cascade asymmetric synthesis of Wieland-Miescher ketone analogues from a Knoevenagel/hydrogenation/Robinson annulation sequence: scope and applications of organocatalytic biomimetic reductions.  

PubMed

A practical and novel organocatalytic chemo- and enantioselective process for the cascade synthesis of highly substituted 2-alkyl-cyclohexane-1,3-diones and Wieland-Miescher (W-M) ketone analogs is presented via reductive alkylation as a key step. First time, we developed the one-step alkylation of dimedone and 1,3-cyclohexanedione with aldehydes and Hantzsch ester through an organocatalytic reductive alkylation strategy. Direct combination of l-proline-catalyzed cascade Knoevenagel/hydrogenation and cascade Robinson annulation of CH acids (dimedone and 1,3-cyclohexanedione), aldehydes, Hantzsch ester, and methyl vinyl ketone furnished the highly functionalized W-M ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products show a direct application in pharmaceutical chemistry. PMID:17552564

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2007-07-01

208

Highly enantioselective oxidative couplings of 2-naphthols catalyzed by chiral bimetallic oxovanadium complexes with either oxygen or air as oxidant.  

PubMed

The chiral bimetallic oxovanadium complexes have been designed for the enantioselective oxidative coupling of 2-naphthols bearing various substituents at C6 and/or C7. The chirality transferring from the amino acid to the axis of the biphenyl in oxovanadium complexes 2 was found to occur with the use of UV and CD spectra and DFT calculation. The homo-coupling reaction with oxygen as the oxidant was promoted by 5 mol % of an oxovanadium complex derived from L-isoleucine and achiral biphenol to afford binaphthols in nearly quantitative yields with high enantioselectivities of up to 98% ee. An oxovanadium complex derived from L-isoleucine and H8-binaphthol is highly efficient at catalyzing the air-oxidized coupling of 2-naphthols with excellent enantioselectivities of up to 97% ee. 51V NMR study shows that the oxovanadium complexes have two vanadium(V) species. Kinetic studies, the cross-coupling reaction, and HRMS spectral studies on the reaction have been carried out and illustrate that two vanadium(V) species are both involved in catalysis and that the coupling reaction undergoes a radical-radical mechanism in an intramolecular manner. Quantum mechanical calculations rationalize the importance of the cooperative effects of the axial chirality matching S-amino acids on the stereocontrol of the oxidative coupling reaction. The application of the transformation in the preparation of chiral ligands and conjugated polymers confirms the importance of the current process in organic synthesis. PMID:17956093

Guo, Qi-Xiang; Wu, Zhi-Jun; Luo, Zhi-Bin; Liu, Quan-Zhong; Ye, Jian-Liang; Luo, Shi-Wei; Cun, Lin-Feng; Gong, Liu-Zhu

2007-11-14

209

Chiral amide directed assembly of a diastereo- and enantiopure supramolecular host and its application to enantioselective catalysis of neutral substrates.  

PubMed

The synthesis of a novel supramolecular tetrahedral assembly of K12Ga4L6 stoichiometry is reported. The newly designed chiral ligand exhibits high diastereoselective control during cluster formation, leading exclusively to a single diastereomer of the desired host. This new assembly also exhibits high stability toward oxidation or a low pH environment and is a more robust and efficient catalyst for asymmetric organic transformations of neutral substrates. PMID:24283463

Zhao, Chen; Sun, Qing-Fu; Hart-Cooper, William M; DiPasquale, Antonio G; Toste, F Dean; Bergman, Robert G; Raymond, Kenneth N

2013-12-18

210

A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (-)-cephalimysin A  

PubMed Central

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(?)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A.

Lathrop, Stephen P.

2013-01-01

211

Enantioselective separation and phytotoxicity on rice seedlings of paclobutrazol.  

PubMed

The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(-)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(-)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(-)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance. PMID:21395310

Zhang, Anping; Xie, Xuemei; Liu, Weiping

2011-04-27

212

Organocatalytic cascade reactions: diversity-oriented synthesis for the construction of hydroisoquinoline scaffolds.  

PubMed

The organocatalytic enantioselective synthesis of highly functionalized hydroisoquinolines by trienamine-mediated [4+2]-cycloaddition/nucleophilic ring-closing reaction cascade sequence of cyanoacrylamides with 2,4-dienals is presented. The corresponding cycloadducts are formed in high yields and excellent stereoselectivities. Moreover, a series of transformations demonstrate the synthetic application of the obtained hydroisoquinolines. PMID:24769648

Gómez, Clarisa Villegas; Cruz, David Cruz; Mose, Rasmus; Jørgensen, Karl Anker

2014-06-01

213

Synthesis of chiral N-phosphoryl aziridines through enantioselective aziridination of alkenes with phosphoryl azide via Co(II)-based metalloradical catalysis  

PubMed Central

Summary The Co(II) complex of a new D 2-symmetric chiral porphyrin 3,5-DiMes-QingPhyrin, [Co(P6)], can catalyze asymmetric aziridination of alkenes with bis(2,2,2-trichloroethyl)phosphoryl azide (TcepN3) as a nitrene source. This new Co(II)-based metalloradical aziridination is suitable for different aromatic olefins, producing the corresponding N-phosphorylaziridines in good to excellent yields (up to 99%) with moderate to high enantioselectivities (up to 85% ee). In addition to mild reaction conditions and generation of N2 as the only byproduct, this new metalloradical catalytic system is highlighted with a practical protocol that operates under neutral and non-oxidative conditions.

Tao, Jingran; Jin, Li-Mei

2014-01-01

214

Applications of Bartoli indole synthesis.  

PubMed

In 1989, the reaction of vinyl magnesium halides with ortho-substituted nitroarenes leading to indoles was discovered. This reaction is now frequently reported as the "Bartoli reaction" or the "Bartoli indole synthesis" (BIS). It has rapidly become the shortest and most flexible route to 7-substituted indoles, because the classical indole syntheses generally fail in their preparation. The flexibility of the Bartoli reaction is great as it can be extended to heteroaromatic nitro derivatives and can be run on solid support. This review will focus on the use of the Bartoli indole synthesis as the key step in preparations of complex indoles, which appeared in the literature in the last few years. PMID:24718836

Bartoli, Giuseppe; Dalpozzo, Renato; Nardi, Monica

2014-06-01

215

?,?-Unsaturated acyl cyanides as new bis-electrophiles for enantioselective organocatalyzed formal [3+3]spiroannulation.  

PubMed

?,?-Unsaturated acyl cyanides are key bis-electrophile substrates for successful domino enantioselective organocatalyzed Michael-intramolecular acylation domino sequences. This new reactivity has been applied to the synthesis of enantioenriched azaspiro[4,5]decanone ring systems by a formal [3+3]spiroannulation, constituting a rare example of synthesis of glutarimides in an optically active form. PMID:24307550

Goudedranche, Sébastien; Bugaut, Xavier; Constantieux, Thierry; Bonne, Damien; Rodriguez, Jean

2014-01-01

216

SYNTHESIS, CHARACTERIZATON, AND APPLICATION OF CARBON NANOTUBES  

Microsoft Academic Search

Carbon nanotubes (CNTs) have attracted increasing attention because of their unique structural, mechanical, and electronic properties. Surface chemistry modifications are also useful and critical to manipulate the adsorptive properties of CNTs and develop their potential of environmental application. Therefore, the main objectives of this study were to investigate the optimal synthesis methods or characteristics identification of multiwall CNTs (MWCNTs) and

Ruey-Bing Li; Frank Lee; Li-Cheng Lou; Su-Wei Chiu

217

Synthesis, characterization, and application of carbon cubes  

Microsoft Academic Search

Carbon nanotubes (CNTs) have attracted increasing attention because of their unique structural, mechanical, and electronic properties. Surface chemistry modifications are also useful and critical to manipulate the adsorptive properties of CNTs and develop their potential of environmental application. Therefore, the main objectives of this study were to investigate the optimal synthesis methods or characteristics identification of multiwall CNTs (MWCNTs) and

K.-S. Lin; Ruey-Bing Li; Frank Lee; Li-Cheng Lou; Su-Wei Chiu

2007-01-01

218

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

219

APPLICATIONS OF CAPILLARY ELECTROPHORESIS TO THE STUDY OF CHIRAL ENVIRONMENTAL POLLUTANTS: ENANTIOMER SEPARATION AND MEASUREMENTS OF ENANTIOSELECTIVITY  

EPA Science Inventory

CE is rarely used for routine environmental analysis of organic pollutants -- certainly not to the extent of gas chromatography or high pressure liquid chromatography. There are advantages to CE, however, that belie this lack of application. For example, CE is preferred over GC f...

220

Synthesis, characterisation and application of inherently conducting polymer nanoparticles  

Microsoft Academic Search

Synthesis of inherently conducting polymers (ICPs) nanoparticles is an option to improve the processability and conductivity of ICPs. In this thesis, the synthesis and application of ICPs nanoparticles has been demonstrated. Various polymerisation methods, such as emulsion polymerisation, use of steric stabiliser and synthesis in ionic liquid (IL) media, have been used to synthesise polymer nanoparticles. These synthesis methods render

Orawan Ngamna

2006-01-01

221

Characterization, crystallization and preliminary X-ray diffraction analysis of an (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767: enantioselectivity for potential industrial applications.  

PubMed

The structures and reaction mechanisms of enantioselective hydrolases, which can be used in industrial applications such as biotransformations, are largely unknown. Here, the X-ray crystallographic study of a novel (S)-specific esterase (pfEstA) from Pseudomonas fluorescens KCTC 1767, which can be used in the production of (S)-ketoprofen, is described. Multiple sequence alignments with other hydrolases revealed that pfEstA contains a conserved Ser67 within the S-X-X-K motif as well as a highly conserved Tyr156. Recombinant protein containing an N-terminal His tag was expressed in Escherichia coli, purified to homogeneity and characterized using SDS-PAGE, MALDI-TOF MS and enantioselective analysis. pfEstA was crystallized using a solution consisting of 1?M sodium citrate, 0.1?M CHES pH 9.5, and X-ray diffraction data were collected to a resolution of 1.9?Å with an Rmerge of 7.9%. The crystals of pfEstA belonged to space group P2(1)2(1)2(1), with unit-cell parameters a=65.31, b=82.13, c=100.41?Å, ?=?=?=90°. PMID:23143253

Kim, Seulgi; Ngo, Tri Duc; Kim, Kyeong Kyu; Kim, T Doohun

2012-11-01

222

Guggullipid derivatives: synthesis and applications.  

PubMed

Two guggullipid derivatives, Z-guggulsulfate [4,17(20)-pregnadiene-3-one-16beta-sulfate] sodium salt and Z-guggullaurate [4,17(20)-pregnadiene-3-one-16beta-laurate], have been synthesized and evaluated for liposomal drug delivery system. Its precursor, Z-guggulsterol [4,17(20)-pregnadiene-3-one-16beta-ol], is also synthesized in gram scale starting from guggulsterone using the novel combination of known reactions in fewer steps and with higher yield than previously reported synthesis. These new synthetic guggullipid derivatives were also used in the preparation of liposomes. This new class of lipid molecules will be a useful tool in the development of nanosomal or liposomal drug delivery system. PMID:20188717

Ahmad, Moghis U; Ali, Shoukath M; Ahmad, Ateeq; Sheikh, Saifuddin; Ahmad, Imran

2010-05-01

223

Enantioselective Synthesis of Axially Chiral Biaryls by the Pd-Catalyzed Suzuki-Miyaura Reaction: Substrate Scope and Quantum Mechanical Investigations  

PubMed Central

We report efficient syntheses of axially chiral biaryl amides in yields ranging from 80–92%, and with enantioselectivity in the range 88–94% ee employing an asymmetric Suzuki-Miyaura process with Pd(OAc)2 and KenPhos as ligand. These studies demonstrate that electron-rich and electron-deficient o-halobenzamides can be efficiently coupled with 2-methyl-1-naphthylboronic acid and 2-ethoxy-1-naphthylboronic acid. The yields and selectivities of the reactions are independent of the nature of halogen substituent on the benzamide coupling partner. Our investigations demonstrate that axially chiral heterocyclic and biphenyl compounds can also be synthesized with this methodology. We also report computational studies used to determine the origin of stereoselectivity during the selectivity-determining reductive elimination step of the related coupling of tolyl boronic acid with naphthylphosphonate bromide that was reported in a previous publication (J. Am. Chem. Soc. 2000, 122, 12051–12052). These studies indicate that the stereoselectivity arises from a combination of weak -(C)H•••O interactions as well as steric interactions between the tolyl and naphthylphosphonate addends in the transition state for C-C coupling.

Shen, Xiaoqiang; Jones, Gavin O.; Watson, Donald A.; Bhayana, Brijesh; Buchwald, Stephen L.

2010-01-01

224

Substrate scope and synthetic applications of the enantioselective reduction of ?-alkyl-?-arylenones mediated by Old Yellow Enzymes.  

PubMed

The ene-reductases mediated bioreduction of a selection of open-chain ?-alkyl-?-aryl enones afforded the corresponding saturated ?-chiral ketones in high yield and optical purity in several cases. The stereo-electronic requirements of the reaction have been investigated, considering the nature and location of substituents on the aromatic ring as well as the steric hindrance at the ?-position and adjacent to the carbonyl functionality. The general considerations drawn allow us to guide the design of ?,?-unsaturated ketones to be employed as substrates of ene-reductases in future preparative applications. An interesting case of orthogonality between enzyme-based and substrate-based stereocontrol within the highly homologous ene-reductases from Saccharomyces species (OYE1-3) has been reported and rationalized with the help of computational docking studies. Furthermore, to demonstrate the synthetic versatility of the reaction, the key chiral precursors of biologically active compounds such as (2'R)-stenusines and (S)-iopanoic acid were obtained. The very robust protocol allowed us to run the reactions on preparative scale in quantitative yields, with a simple work-up and no chromatographic purification steps. PMID:23532545

Brenna, Elisabetta; Cosi, Sara Lucia; Ferrandi, Erica Elisa; Gatti, Francesco G; Monti, Daniela; Parmeggiani, Fabio; Sacchetti, Alessandro

2013-05-14

225

Exploring Nitrilase Sequence Space for Enantioselective Catalysis†  

PubMed Central

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 specificity shortcomings, their utility has been largely unrealized. In this study, 137 unique nitrilases, discovered from screening of >600 biotope-specific environmental DNA (eDNA) libraries, were characterized. Using culture-independent means, phylogenetically diverse genomes were captured from entire biotopes, and their genes were expressed heterologously in a common cloning host. Nitrilase genes were targeted in a selection-based expression assay of clonal populations numbering 106 to 1010 members per eDNA library. A phylogenetic analysis of the novel sequences discovered revealed the presence of at least five major sequence clades within the nitrilase subfamily. Using three nitrile substrates targeted for their potential in chiral pharmaceutical synthesis, the enzymes were characterized for substrate specificity and stereospecificity. A number of important correlations were found between sequence clades and the selective properties of these nitrilases. These enzymes, discovered using a high-throughput, culture-independent method, provide a catalytic toolbox for enantiospecific synthesis of a variety of carboxylic acid derivatives, as well as an intriguing library for evolutionary and structural analyses.

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

2004-01-01

226

Bidentate urea-based chiral selectors for enantioselective high performance liquid chromatography: synthesis and evaluation of "Crab-like" stationary phases.  

PubMed

A rational approach for the design and preparation of two new "Crab-like" totally synthetic, brush-type chiral stationary phases is presented. Enantiopure diamines, namely 1,2-diaminocyclohexane and 1,2-diphenyl-1,2-ethylene-diamine were treated with 3-(triethoxysilyl)propyl isocyanate, to yield reactive ureido selectors that were eventually attached to unmodified silica particles through a stable, bidentate tether, through a facile two-step one-pot procedure. A full chemical characterization of the new materials has been obtained through solid-state NMR (both (29)Si and (13)C CPMAS) spectroscopy. Columns packed with the two Crab-like chiral stationary phases allow for different mechanisms of separation: normal phase liquid chromatography, reversed phase liquid chromatography and polar organic mode and show a high stability at basic pH values. In particular, the Crab-like column containing the 1,2-diphenyl-1,2-ethylene-diamine selector proved a promising candidate for the resolution of a wide range of racemates (including benzodiazepines, N-derivatized amino acids, and free carboxylic acids) both in normal phase and polar organic mode. An Hmin of 9.57 at a ?sf of 0.80mm/s (corresponding to 0.8mL/min) was obtained through van Deemter analysis, based on toluene, for the Crab-like column with the 1,2-diphenyl-1,2-ethylene-diamine selector (250mm×4.6mm I.D.), with a calculated reduced height equivalent to a theoretical plate (h) of only 1.91. Finally, comparative studies were performed with a polymeric commercially available P-CAP-DP column in order to evaluate enantioselectivity and resolution of the Crab-like columns. PMID:23726086

Kotoni, Dorina; Villani, Claudio; Bell, David S; Capitani, Donatella; Campiglia, Pietro; Gasparrini, Francesco

2013-07-01

227

Amphiphilic conetworks: Definition, synthesis, applications  

Microsoft Academic Search

The emerging field of amphiphilic conetworks (APCNs) is critically reviewed. A definition of APCNs is proposed and discussed in depth. The field of APCN science, born in 1988, is delineated and differentiated from similar constructs (e.g. interpenetrating networks, grafted networks). Among the justifications for sustained scientific\\/technological interest in APCNs are hosts of high-technology applications, some in commercial use and some

Gabor Erdodi; Joseph P. Kennedy

2006-01-01

228

Enantioselective Total Synthesis of (+)-Gliocladine C. A Convergent Construction of Cyclotryptamine-Fused Polyoxopiperazines and a General Approach for Preparing Epidithiodioxopiperazines from Trioxopiperazine Precursors  

PubMed Central

A concise second-generation total synthesis of the fungal-derived alkaloid (+)-gliocladin C (11), in ten steps and 11% overall yield from isatin, is reported. In addition, the ETP natural product (+)-gliocladine C (6) is prepared in six steps and 29% yield from the di-(tert-butoxycarbonyl) precursor of 11. The total synthesis of (+)-gliocladine C (6) constitutes the first total synthesis of an ETP natural product containing a hydroxyl substituent adjacent to a quaternary carbon stereocenter in the pyrrolidine ring.

DeLorbe, John E.; Jabri, Salman Y.; Mennen, Steven M.; Overman, Larry E.; Zhang, Fang-Li

2011-01-01

229

Synthesis and Applications of Imogolite Nanotubes  

NASA Astrophysics Data System (ADS)

Imogolite is a naturally occurring nanotube aluminum silicate. It is classified as a clay mineral, with tube dimensions of about 2 nm in outside diameter, 1 nm in inside diameter, and lengths ranging from tens of nanometers to several micrometers. Imogolite is remarkable not only for its nanoscale fibrous microstructure and its high surface area but also in its ability to adsorb water. So it can be expected to find a wide range of applications. In this chapter, synthesis method for imogolite and applications for anti-dewing materials and heat exchange material in adsorption-type heat pump systems are described.

Suzuki, Masaya; Inukai, Keiichi

230

Dendrimers: synthesis, applications, and properties.  

PubMed

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications. PMID:24994950

Abbasi, Elham; Aval, Sedigheh Fekri; Akbarzadeh, Abolfazl; Milani, Morteza; Nasrabadi, Hamid Tayefi; Joo, Sang Woo; Hanifehpour, Younes; Nejati-Koshki, Kazem; Pashaei-Asl, Roghiyeh

2014-01-01

231

Dendrimers: synthesis, applications, and properties  

PubMed Central

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications.

2014-01-01

232

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

233

Highly enantioselective organocatalytic Biginelli reaction.  

PubMed

A series of binol- and H8-binol-based phosphoric acids have for the first time been evaluated for their ability to catalyze Biginelli reactions of aldehydes, thiourea or urea, and beta-keto esters. A new chiral phosphoric acid, derived from 3,3'-diphenyl-H8-binol, exhibited superior catalytic activity and enantioselectivity compared to its structural analogues, affording high enantioselectivities ranging from 85 to 97% ee with a wide scope of substrates. A metal-free preparation of optically active monastrol was achieved on the basis of the current process. PMID:17105279

Chen, Xiao-Hua; Xu, Xiao-Ying; Liu, Hua; Cun, Lin-Feng; Gong, Liu-Zhu

2006-11-22

234

Development of (Trimethylsilyl)ethyl Ester Protected Enolates and Applications in Palladium-Catalyzed Enantioselective Allylic Alkylation: Intermolecular Cross-Coupling of Functionalized Electrophiles.  

PubMed

The development of (trimethylsilyl)ethyl ester protected enolates is reported. The application of this class of compounds in palladium-catalyzed asymmetric allylic alkylation is explored, yielding a variety of ?-quaternary six- and seven-membered ketones and lactams. Independent coupling partner synthesis engenders enhanced allyl substrate scope relative to traditional ?-ketoester substrates; highly functionalized ?-quaternary ketones generated by the union of (trimethylsilyl)ethyl ?-ketoesters and sensitive allylic alkylation coupling partners serve to demonstrate the utility of this method for complex fragment coupling. PMID:24724872

Reeves, Corey M; Behenna, Douglas C; Stoltz, Brian M

2014-05-01

235

Continuous flow, highly enantioselective Michael additions catalyzed by a PS-supported squaramide.  

PubMed

A polystyrene (PS) supported bifunctional squaramide organocatalyst promotes fast Michael addition of 2-hydroxy-1,4-naphthoquinone to nitroalkenes with very high enantioselectivities at low catalyst loadings. The polystyrene supported catalyst can be recycled up to 10 times without any decrease in enantioselectivity (average 96% ee) and adapted to continuous flow operation (24 h). A single flow experiment involving six different nitroalkenes in a sequential manner highlights the applicability of this methodology for rapid access to chemical diversity. PMID:23837657

Kasaplar, Pinar; Rodríguez-Escrich, Carles; Pericàs, Miquel A

2013-07-19

236

Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and ?,?-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives  

PubMed Central

Summary The catalytic synthesis of nitrogen-containing heterocycles is of great importance to medicinal and synthetic chemists, and also a challenge for modern chemical methodology. In this paper, we report the synthesis of pyrazolidine derivatives through a domino aza-Michael/hemiacetal sequence with chiral or achiral secondary amines as organocatalysts. Thus, a series of achiral pyrazolidine derivatives were obtained with good yields (up to 90%) and high diastereoselectivities (>20:1) with pyrrolidine as an organocatalyst, and enantioenriched pyrazolidines are also achieved with good results (up to 86% yield, >10/1 regioselectivity, >20:1 dr, 99% ee) in the presence of (S)-diphenylprolinol trimethylsilyl ether catalyst.

Geng, Zhi-Cong; Chen, Jian; Li, Ning; Huang, Xiao-Fei; Zhang, Yong

2012-01-01

237

Enantioselective Total Syntheses of (-)-Taiwaniaquinone H and (-)-Taiwaniaquinol B by Iridium-Catalyzed Borylation and Palladium-Catalyzed Asymmetric ?-Arylation  

PubMed Central

We report a concise, enantioselective total synthesis of (?)-taiwaniaquinone H and the first enantioselective total synthesis of (?)-taiwaniaquinol B by a route that includes enantioselective, palladium-catalyzed ?-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C–H borylation. This asymmetric ?-arylation creates the benzylic, quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic, quaternary, stereogenic centers, even those lacking a carbonyl group in the ?-position, by asymmetric ?-arylation.

Liao, Xuebin; Stanley, Levi M.; Hartwig, John F.

2011-01-01

238

Highly Regio- and Enantioselective Synthesis of Polysubstituted 2H-Pyrroles via Pd-Catalyzed Intermolecular Asymmetric Allylic Dearomatization of Pyrroles.  

PubMed

A highly efficient synthesis of chiral polysubstituted 2H-pyrrole derivatives via a Pd-catalyzed intermolecular asymmetric allylic dearomatization reaction of pyrroles is presented. With the commercially available palladium precursor and chiral ligand, the polysubstituted 2H-pyrrole products containing a chiral quaternary carbon center were obtained with up to 97% ee and >95/5 regioselectivity. PMID:24758260

Zhuo, Chun-Xiang; Zhou, Yong; You, Shu-Li

2014-05-01

239

Total synthesis of (+)-angelmarin.  

PubMed

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

Magolan, Jakob; Coster, Mark J

2009-07-17

240

Synthesis and applications of monolithic HPLC columns  

NASA Astrophysics Data System (ADS)

Silica and carbon monolithic columns were synthesized and modified for liquid chromatography applications. Column configurations and cladding techniques were investigated in detail. Three novel approaches have been developed for the synthesis of bimodal porous rods. Out of these three methods, gel-casting was adopted for the synthesis of silica monoliths with ordered mesopores and uniform macropores; the use of colloidal templates and dual phase separation has been successfully implemented for the synthesis of carbon monoliths with well-controlled meso- and macro- porosities. The formation of mesopores in carbon materials has been further studied in the microphase separation of block copolymers. Electrochemical modification of carbon monoliths was discovered to be an efficient method for converting covalently bonded functionalities to carbon monoliths. N,N'-diethylaminobenzene has been attached to carbon surface for the separation of proteins and protein digests. The performances of carbon-based monolithic columns were studied intensely through frontal analysis and Van Deemter plot. Temperature and pressure effects were also investigated in carbon-based columns. The density of bonding on the modified carbon monoliths was characterized by thermogravimetric analysis.

Liang, Chengdu

241

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

242

Gold(I)-Catalyzed Enantioselective [4+2]-Cycloaddition of Allene-Dienes  

PubMed Central

An enantioselective gold(I)-catalyzed intramolecular [4+2]-cycloaddition of allenes and dienes is reported. The reactions allows for the asymmetric synthesis of trans-hexahydroindenes and pyrrolidine products using C3-symmetric phosphitegold(I) and ortho-arylphosphoramiditegold(I) complexes as catalysts, respectively.

Gonzalez, Ana Z.; Toste, F. Dean

2009-01-01

243

Pd-catalyzed highly regio-, diastereo-, and enantioselective allylic alkylation of ?-fluorophosphonates.  

PubMed

Highly efficient Pd-catalyzed asymmetric allylic alkylation reaction of ethyl-2-fluoro-2-(diethoxyphosphoryl)acetate with monosubstituted allylic substrates has been developed, affording corresponding ?-fluorophosphonates with two chiral centers in high regio-, diastereo- and enantio-selectivities. The usefulness of the products in organic synthesis has been demonstrated. PMID:24831029

Huang, Ying; Zhang, Qing-Song; Fang, Ping; Chen, Tie-Gen; Zhu, Jun; Hou, Xue-Long

2014-05-29

244

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

245

Highly Z-selective and enantioselective ring-opening/cross-metathesis catalyzed by a resolved stereogenic-at-Ru complex.  

PubMed

The synthesis of a ruthenium complex that catalyzes Z-selective (up to 98% Z) asymmetric ring-opening/cross-metathesis with high enantioselectivity (up to 95% ee) is reported. The synthesis of the catalyst features the resolution of a chelating N-heterocyclic carbene complex by ligand substitution with a chiral carboxylate. PMID:23822901

Hartung, John; Grubbs, Robert H

2013-07-17

246

Dynamic kinetic asymmetric ring-opening/reductive amination sequence of racemic nitroepoxides with chiral amines: enantioselective synthesis of chiral vicinal diamines.  

PubMed

We report a highly diastereoselective synthesis of vicinal diamines by the treatment of nitroepoxides with primary amines and then a reducing agent. When using a chiral primary amine, racemic nitroepoxides are transformed into chiral diamines as a single enantiomers (>95:5 er) through a dynamic kinetic asymmetric transformation (DYKAT). The overall process is a one-pot procedure combining the exposure of nitroepoxides to chiral amines to afford diastereomeric mixtures of aminoimines and subsequent stereoselective imine reduction. PMID:23641667

Agut, Juan; Vidal, Andreu; Rodríguez, Santiago; González, Florenci V

2013-06-01

247

Enantioselective synthesis of 2-substitued-tetrahydroisoquinolin-1-yl glycine derivatives via oxidative cross-dehydrogenative coupling of tertiary amines and chiral nickel(II) glycinate.  

PubMed

The asymmetric synthesis of 2-substituted-tetrahydroisoquinolin-1-yl glycines was achieved by an oxidative cross-dehydrogenative coupling (CDC) reaction. This method for activation of the ?-C-H bonds of amines with chiral nickel(II) glycinate using o-chloranil as the sole oxidant afforded highly diastereoselective coupling adducts. The decomposition of coupling adducts readily afforded 2-substituted-tetrahydroisoquinolin-1-yl glycine derivatives. PMID:24111642

Zhou, Shengbin; Wang, Jiang; Lin, Daizong; Zhao, Fei; Liu, Hong

2013-11-15

248

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

249

Enantioselective liquid chromatographic-electrospray mass spectrometric assay of beta-adrenergic blockers: application to a pharmacokinetic study of sotalol in human plasma.  

PubMed

An enantioselective high performance liquid chromatographic-electrospray ionization mass spectrometric (HPLC-ESI-MS) method for the direct determination of several beta-adrenergic blockers was developed and validated. The method is based on the direct separation of the enantiomers of drugs on a laboratory-made chiral stationary phase (CSP) containing covalently bonded teicoplanin (TE) as chiral selector. Detection of the effluent was performed by electrospray ionization mass spectrometry, run in the selected-ion recording (SIR) mode. The method was applied to the pharmacokinetic monitoring of sotalol (STL) in the plasma of five young healthy volunteers, dosed with racemic drug. The limits of quantitation (LOQ) reached 4 ng/ml for both sotalol enantiomers. Such a method, fully validated, offers a novel, fast and very efficient tool for the direct determination of sotalol enantiomers in human plasma, and can be generally applied to the beta-adrenergic blockers stereoselective pharmacokinetics. PMID:14552815

Badaloni, Elena; D'Acquarica, Ilaria; Gasparrini, Francesco; Lalli, Silvana; Misiti, Domenico; Pazzucconi, Franco; Sirtori, Cesare R

2003-10-25

250

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

251

Squaramide-catalyzed enantioselective Michael addition of masked acyl cyanides to substituted enones.  

PubMed

Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective Michael addition to substituted enones. The reactions are catalyzed by chiral squaramides and afford adducts in high yields (90-99%) and with excellent enantioselectivities (85-98%). The addition products are unmasked to produce dicyanohydrins that, upon treatment with a variety of nucleophiles, provide ?-keto acids, esters, and amides. The use of this umpolung synthon has enabled, in enantiomerically enriched form, the first total synthesis of the prenylated phenol (+)-fornicin C. PMID:24090310

Yang, Kin S; Nibbs, Antoinette E; Türkmen, Yunus E; Rawal, Viresh H

2013-10-30

252

Experimental evidence for the all-up reactive conformation of chiral rhodium(II) carboxylate catalysts: enantioselective synthesis of cis-cyclopropane alpha-amino acids.  

PubMed

Useful empirical insights onto the enantioinduction process of chiral Rh(II)-carboxylate catalysts are described in the first catalytic asymmetric cyclopropanation of alkenes with alpha-nitro diazoacetophenones. X-ray, solution NMR, and reactivity studies made on these complexes suggest that the level of asymmetric induction strongly depends on their active symmetry, which in turn relies on the nature of the chiral ligands' substituents. The catalyst's 'All Up' reactive conformation resulted in being necessary to obtain good stereoselectivity, and the resulting products are shown to be key intermediates in a concise synthesis of highly enantioenriched cis-cyclopropane alpha-amino acids. PMID:19860407

Lindsay, Vincent N G; Lin, Wei; Charette, André B

2009-11-18

253

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

NASA Astrophysics Data System (ADS)

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 in biologically active alkaloids and pharmaceutical agents, we envisage 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 used 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.

2012-02-01

254

Consecutive iridium catalyzed C-C and C-H bond forming hydrogenations for the diastereo- and enantioselective synthesis of syn-3-fluoro-1-alcohols: C-H (2-fluoro)allylation of primary alcohols†  

PubMed Central

Commercially available (2-fluoro)allyl chloride serves as an efficient allyl donor in highly enantioselective iridium catalyzed carbonyl (2-fluoro)allylations from the alcohol or aldehyde oxidation level via transfer hydrogenation. Diastereoselective Crabtree hydrogenation of the resulting homoallylic alcohols provides syn-3-fluoro-1-alcohols.

Hassan, Abbas; Montgomery, T. Patrick

2012-01-01

255

Consecutive iridium catalyzed C-C and C-H bond forming hydrogenations for the diastereo- and enantioselective synthesis of syn-3-fluoro-1-alcohols: C-H (2-fluoro)allylation of primary alcohols.  

PubMed

Commercially available (2-fluoro)allyl chloride serves as an efficient allyl donor in highly enantioselective iridium catalyzed carbonyl (2-fluoro)allylations from the alcohol or aldehyde oxidation level via transfer hydrogenation. Diastereoselective Crabtree hydrogenation of the resulting homoallylic alcohols provides syn-3-fluoro-1-alcohols. PMID:22473044

Hassan, Abbas; Montgomery, T Patrick; Krische, Michael J

2012-05-16

256

Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric Aminocatalysis  

PubMed Central

The concept of combining heterogeneous transition metal and amine catalysis for enantioselective cascade reactions has not yet been realized. This is of great advantage since it would allow for the recycling of expensive and non-environmentally friendly transition metals. We disclose that the use of a heterogeneous Pd-catalyst in combination with a simple chiral amine co-catalyst allows for highly enantioselective cascade transformations. The preparative power of this process has been demonstrated in the context of asymmetric cascade Michael/carbocyclization transformations that delivers cyclopentenes bearing an all carbon quaternary stereocenters in high yields with up to 30:1?dr and 99% ee. Moreover, a variety of highly enantioselective cascade hetero-Michael/carbocyclizations were developed for the one-pot synthesis of valuable dihydrofurans and pyrrolidines (up to 98% ee) by using bench-stable heterogeneous Pd and chiral amines as co-catalysts.

Deiana, Luca; Afewerki, Samson; Palo-Nieto, Carlos; Verho, Oscar; Johnston, Eric V.; Cordova, Armando

2012-01-01

257

Enantioselective copper-catalyzed carboetherification of unactivated alkenes.  

PubMed

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of ?-unsaturated pentenols which terminates in C?C bond formation, a net alkene carboetherification. Both intra- and intermolecular C?C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step. PMID:24798697

Bovino, Michael T; Liwosz, Timothy W; Kendel, Nicole E; Miller, Yan; Tyminska, Nina; Zurek, Eva; Chemler, Sherry R

2014-06-16

258

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

259

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

2010-10-01

260

Tertiary Aminourea-Catalyzed Enantioselective Iodolactonization  

PubMed Central

Binding the anion: A highly enantioselective iodolactonization of 5-hexenoic acids has been achieved using a tertiary aminourea-catalyst. The use of catalytic iodine in this process is critical to enhancing both the reactivity and enantioselectivity of the stoichiometric I+source.The mechanism is proposed to involve binding of an iodonium imidate intermediate by the H-bond donor catalyst.

Veitch, Gemma E.

2010-01-01

261

Application and comparison of immobilized and coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases for the enantioselective separation of beta-blockers enantiomers by liquid chromatography.  

PubMed

A direct liquid chromatographic enantioselective separation of a set of beta-blocker enantiomers on the new immobilized and conventional coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) was studied using methanol as mobile phase and ethanolamine as an organic modifier (100:0.1, v/v). The separation, retention and elution order of the enantiomers on both columns under the same conditions were compared. The effect of the immobilization of the amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted when compared to the coated phase (Chiralpak AD) which possesses a higher resolving power than the immobilized one (Chiralpak IA). A few racemates, which were not or poorly resolved on the immobilized Chiralpak IA were most efficiently resolved on the coated Chiralpak AD. However, the immobilized phase withstand solvents like dichloromethane when used as an eluent or as a dissolving agent for the analyte. The versatility of the immobilized Chiralpak IA in monitoring reactions performed in dichloromethane using direct analysis techniques without further purification, workup or removal of dichloromethane was studied on a representative example consisting of the lipase-catalyzed irreversible transesterification of a beta-blocker using either vinyl-acetate or isopropenyl acetate as acyl donor in dichloromethane as organic solvent. PMID:18970363

Ghanem, Ashraf; Hoenen, Hubert; Aboul-Enein, Hassan Y

2006-01-15

262

Enantioselective determination of triazole fungice tetraconazole by chiral high-performance liquid chromatography and its application to pharmacokinetic study in cucumber, muskmelon, and soils.  

PubMed

A simple chiral high-performance liquid chromatography method with diode array detector was developed and validated for stereoselective determination of tetraconazole enantiomers in cucumber, muskmelon, and soils. Good separation was achieved at 20°C using cellulose tris-(4-methylbenzoate) as chiral stationary phase, a mixture of n-hexane and ethanol (90:10) as mobile phase at a flow rate of 0.8 ml/min. The assay method was linear over a range of concentrations (0.5-50 ?g/ml) and the mean recoveries in all samples were more than 85% for the two enantiomers. The limits of detection for both enantiomers in plant and soil samples were 0.06 and 0.12 ?g/g, respectively. Then, the proposed method was successfully applied to the study of enantioselective degradation of rac-tetraconazole in cucumber, muskmelon, and soils. The results showed that the degradation of two enantiomers of tetraconazole followed first-order kinetics and significantly stereoselective behavior was observed in cucumber, muskmelon, and Beijing soil. The preferential absorption and degradation of (-)-S-tetraconzole resulted in an enrichment of the (+)-R-tetraconazole residue in plant samples, whereas the (+)-R-tetraconazole showed a faster degradation in Beijing soil and the stereoselectivity might be caused by microorganisms. No stereoselective degradation was observed in Heilongjiang soil. PMID:22278951

Li, Jing; Dong, Fengshou; Xu, Jun; Liu, Xingang; Li, Yuanbo; Shan, Weili; Zheng, Yongquan

2012-04-01

263

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

264

Synthesis, Characterization and Catalytic Applications of Organized Mesoporous Aluminas  

Microsoft Academic Search

The synthesis of organized mesoporous aluminas has opened a very interesting area for application of this type of materials, particularly as catalysts or catalyst supports. This review focuses on the individual synthesis routes to produce organized mesoporous aluminas with large surface areas and narrow pore size distributions, and on the evaluation of their textural, chemical and thermal properties and outlines

Nad?žda Žilková; Ji?í ?ejka

2008-01-01

265

(+)-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

266

Enantioselective Synthesis of (Z)-2-Methyl-1,5-anti- and (E)-2-Methyl-1,5-anti-Pentenediols Via an Allene Hydroboration-Double Allylboration Reaction Sequence  

PubMed Central

Kinetic controlled hydroboration of allenylboronate 5 followed by double allylboration with resulting allylborane (Z)-7 gave (Z)-2-methyl-1,5-anti-pentenediols 6 in good yield and high enantioselectivity in the presence of 10% BF3•OEt2 as the catalyst in the second allylboration step. Under thermodynamically controlled isomerization conditions, (Z)-7 can readily isomerize to (E)-7. Double allylboration of representative aldehydes with allylborane (E)-7 gave (E)-2-methyl-1,5-anti-pentenediols 4 in good yield and high enantioselectivity without requiring use of the BF3•OEt2 catalyst. Thus, 2-methyl-1,5-anti-pentenediols with either olefin geometry can be synthesized from the same allenylboronate precursor 5. Furthermore, 1,5-pentenediols 4 and 6 can be easily converted to 1,3,5-triols with excellent diastereoselectivity in one step.

Chen, Ming; Roush, William R.

2013-01-01

267

Highly l and d enantioselective variants of horseradish peroxidase discovered by an ultrahigh-throughput selection method  

PubMed Central

A highly efficient selection method for enhanced enzyme enantioselectivity based on yeast surface display and fluorescence-activated cell sorting (FACS) is developed and validated. Its application to horseradish peroxidase has resulted in enzyme variants up to 2 orders of magnitude selective toward either substrate enantiomer at will. These marked improvements in enantioselectivity are demonstrated for the surface-bound and soluble enzymes and rationalized by computational docking studies.

Antipov, Eugene; Cho, Art E.; Wittrup, K. Dane; Klibanov, Alexander M.

2008-01-01

268

Synthesis and characterization of advanced materials for Navy applications  

NASA Technical Reports Server (NTRS)

The synthesis of ceramics and ceramic coatings through the sol-gel process has extensive application with the United States Navy and a broad range of potential commercial applications as well. This paper surveys seven specific applications for which the Navy is investigating these advanced materials. For each area, the synthetic process is described and the characteristics of the materials are discussed.

Covino, J.; Lee, I.

1994-01-01

269

Nitroxides: applications in synthesis and in polymer chemistry.  

PubMed

This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures. PMID:21538729

Tebben, Ludger; Studer, Armido

2011-05-23

270

Organocatalytic enantioselective hydrophosphonylation of aldehydes.  

PubMed

We report our results concerning the first squaramide-catalysed hydrophosphonylation of aldehydes. In all cases, the reactions proceeded smoothly and cleanly under mild reaction conditions rendering final ?-hydroxy phosphonates in very good yields and high enantioselectivities. It is one of the few organocatalytic examples of this reaction using aldehydes. It is the first time that diphenylphosphite (1e) has been successfully employed in a chiral Pudovik reaction with aldehydes, in contrast to the dialkylphosphites used in previously published procedures, extending the generality of this asymmetric methodology. PMID:24413980

Alegre-Requena, Juan V; Marqués-López, Eugenia; Sanz Miguel, Pablo J; Herrera, Raquel P

2014-02-28

271

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

272

Enthalpic and entropic contributions to lipase enantioselectivity  

Microsoft Academic Search

The enantioselective properties of lipases in the kinetic resolution of chiral substrates are conveniently expressed as the enantiomeric ratio, E. It has been stated that E is related to the difference of the Gibbs free energy of activation of the enantioselective reaction steps by RTlnE=???G#=T??S#???H#. From the temperature dependence of E we estimated the enthalpic, ??H#, and entropic, ??S#, contributions.

P. L. Antoine Overbeeke; S. Christian Orrenius; Jaap A Jongejan; Johannis A Duine

1998-01-01

273

Arbitrary waveform synthesis for communication applications  

NASA Astrophysics Data System (ADS)

For optical wireless laser transmissions we take advantage of a specific comblike structure of the spectrum of mode-locked laser ultrashort pulse trains and present a pulse-shaping technique for arbitrary waveform synthesis. The shaped pulses are free of space-time coupling effects and high-order spatial modes. As examples, we provide simulation results for the synthesis of waveforms that are of particular interest for optical communications, namely, square-root-raised cosines and Meyer wavelets.

Hamzeh, B.; Jivkova, S.; Kavehrad, Mohsen

2005-10-01

274

System synthesis for multiprocessor embedded applications  

Microsoft Academic Search

This paper presents the system synthesis techniques available in S3E2S, a CAD environment for the specification, simulation, and synthesis of embedded electronic systems that can be modeled as a combination of analog parts, digital hardware, and software. S3E2S is based on a distributed, object-oriented system model, where objects are initially modeled by their abstract behavior and may be later refined

Luigi Carro; Márcio Eduardo Kreutz; Flávio Rech Wagner; Márcio Oyamada

2000-01-01

275

Cell-Free Protein Synthesis: Applications Come of Age  

PubMed Central

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.

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

2014-01-01

276

Catalytic Enantioselective Formation of Chiral Bridged Dienes Which Are Themselves Ligands for Enantioselective Catalysis  

PubMed Central

This paper reports a method for highly enantioselective Diels-Alder reaction with an acetylene equivalent to produce chiral bridged dienes. These dienes, by coordination to Rh(I), can serve as catalysts for the enantioselective addition of vinyl or aryl groups to ?,?-unsaturated ketones.

Brown, M. Kevin; Corey, E. J.

2009-01-01

277

Solution synthesis of metal oxides for electrochemical energy storage applications  

NASA Astrophysics Data System (ADS)

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.

Xia, Xinhui; Zhang, Yongqi; Chao, Dongliang; Guan, Cao; Zhang, Yijun; Li, Lu; Ge, Xiang; Bacho, Ignacio Mínguez; Tu, Jiangping; Fan, Hong Jin

2014-04-01

278

Solution synthesis of metal oxides for electrochemical energy storage applications.  

PubMed

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices. PMID:24696018

Xia, Xinhui; Zhang, Yongqi; Chao, Dongliang; Guan, Cao; Zhang, Yijun; Li, Lu; Ge, Xiang; Bacho, Ignacio Mínguez; Tu, Jiangping; Fan, Hong Jin

2014-05-21

279

Synthesis, Nanoprocessing, and Yarn Application of Carbon Nanotubes  

Microsoft Academic Search

The synthesis of brush-like carbon nanotubes (CNTs), the nanoprocessing, and the application to twisted yarns for CNTs are reviewed. The large-scale synthesis has been established, where 170-mum-height brush-like CNTs are grown on a 6-in. Si wafer every three minutes. 7-mm-long brush-like CNTs have also been achieved by activating Fe catalysts using H2 and H2O. It has been observed that the

Yoshikazu Nakayama

2008-01-01

280

Supramolecular dendritic polymers: from synthesis to applications.  

PubMed

Conspectus Supramolecular dendritic polymers (SDPs), which perfectly combine the advantages of dendritic polymers with those of supramolecular polymers, are a novel class of non-covalently bonded, highly branched macromolecules with three-dimensional globular topology. Because of their dynamic/reversible nature, unique topological structure, and exceptional physical/chemical properties (e.g., low viscosity, high solubility, and a large number of functional terminal groups), SDPs have attracted increasing attention in recent years in both academic and industrial fields. In particular, the reversibility of non-covalent interactions endows SDPs with the ability to undergo dynamic switching of structure, morphology, and function in response to various external stimuli, such as pH, temperature, light, stress, and redox agents, which further provides a flexible and robust platform for designing and developing smart supramolecular polymeric materials and functional supramolecular devices. The existing SDPs can be systematically classified into the following six major types according to their topological features: supramolecular dendrimers, supramolecular dendronized polymers, supramolecular hyperbranched polymers, supramolecular linear-dendritic block copolymers, supramolecular dendritic-dendritic block copolymers, and supramolecular dendritic multiarm copolymers. These different types of SDPs possess distinct morphologies, unique architectures, and specific functions. Benefiting from their versatile topological structures as well as stimuli-responsive properties, SDPs have displayed not only unique characteristics or advantages in supramolecular self-assembly behaviors (e.g., controllable morphologies, specific performance, and facile functionalization) but also great potential to be promising candidates in various fields. In this Account, we summarize the recent progress in the synthesis, functionalization, and self-assembly of SDPs as well as their potential applications in a wide range of fields. A variety of synthetic methods using non-covalent interactions have been established to prepare different types of SDPs based on varied mono- or multifunctionalized building blocks (e.g., monomer, dendron, dendrimer, and hyperbranched polymer) with homo- or heterocomplementary units. In addition, SDPs can be further endowed with excellent functionalities by employing different modification approaches involving terminal, focal-point, and backbone modification. Similar to conventional dendritic polymers, SDPs can self-assemble into diverse supramolecular structures such as micelles, vesicles, fibers, nanorings, tubes, and many hierarchical structures. Finally, we highlight some typical examples of recent applications of SDP-based systems in biomedical fields (e.g., controlled drug/gene/protein delivery, bioimaging, and biomimetic chemistry), nanotechnology (e.g., nanoreactors, catalysis, and molecular imprinting), and functional materials. The current research on SDPs is still at the very early stage, and much more work needs to be done. We anticipate that future studies of SDPs will focus on developing multifunctional, hierarchical supramolecular materials toward their practical applications by utilization of cooperative non-covalent interactions. PMID:24779892

Dong, Ruijiao; Zhou, Yongfeng; Zhu, Xinyuan

2014-07-15

281

The organocatalytic three-step total synthesis of (+)-frondosin B†  

PubMed Central

The frondosins are a family of marine sesquiterpenes isolated from the sponge Dysidea frondosa that exhibit biological activities ranging from anti-inflammatory properties to potential application in anticancer and HIV therapy. Herein, a concise enantioselective total synthesis of (+)-frondosin B is described which requires a total of three chemical steps. The enantioselective conjugate addition of a benzofuran-derived boronic acid to crotonaldehyde in the presence of an imidazolidinone organocatalyst builds the critical stereogenic center of frondosin B in the first operation, while the remaining two ring systems of this natural product are installed in the two subsequent steps. A combination of X-ray crystallographic data, deuterium labeling, and chemical correlation studies provides further evidence as to the correct absolute stereochemical assignment of (+)-frondosin B.

Reiter, Maud; Torssell, Staffan; Lee, Sandra; MacMillan, David W. C.

2012-01-01

282

Gold nanoparticles: various methods of synthesis and antibacterial applications.  

PubMed

Colloidal gold is very attractive for several applications in biotechnology because of its unique physical and chemical properties. Many different synthesis methods have been developed to generate gold nanoparticles (AuNPs). Here, we will introduce these methods and discuss the differences between fabrication techniques. We will also discuss ecofriendly synthesis methods being developed to efficiently generate AuNPs without the use of toxic substrates. Finally, we will discuss the medical applications for AuNPs by highlighting the potential use of intact or functionalized AuNPs in combating bacterial infections. PMID:24896353

Shah, Monic; Badwaik, Vivek; Kherde, Yogesh; Waghwani, Hitesh Kumar; Modi, Tulsi; Aguilar, Zoraida; Rodgers, Hannah; Hamilton, William; Marutharaj, Tamilselvi; Webb, Cathleen; Lawrenz, Matthew B; Dakshinamurthy, Rajalingam

2014-01-01

283

77 FR 8324 - Applications for the Environment: Real-Time Information Synthesis (AERIS) User Needs Workshop...  

Federal Register 2010, 2011, 2012, 2013

...Applications for the Environment: Real-Time Information Synthesis (AERIS) User Needs Workshop; Notice of Public Meeting AGENCY...Applications for the Environment: Real- Time Information Synthesis (AERIS) Program and solicit user needs for its...

2012-02-14

284

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

285

On the application of the curve curvature in path synthesis  

Microsoft Academic Search

This paper presents an analysis of the applicability of the curve curvature in optimal synthesis of mechanisms. The concept of utilizing the normalized Fourier coefficients of the curvature as a curve description is known, but so far it was not applied to curves for which the continuity of the first or second derivatives cannot be assumed. An additional discussion aims

Jacek Bu?kiewicz; Roman Starosta; Tomasz Walczak

2009-01-01

286

Synthesis of 2-substituted-5-halo-2,3-dihydro-4(H)-pyrimidin-4-ones and their derivatization utilizing the Sonogashira coupling reaction in the enantioselective synthesis of alpha-substituted beta-amino acids.  

PubMed

A convenient, one-pot procedure for the synthesis of 1-benzoyl-2(S)-substituted-5-iodo-2,3-dihydro-4(H)-pyrimidin-4-ones by tandem decarboxylation/beta-iodination of the corresponding 6-carboxy-perhydropyrimidin-4-ones was developed. In addition, several 1-benzoyl-2(S)-substituted-5-bromo-2,3-dihydro-4(H)-pyrimidin-4-ones were readily prepared by bromination of 1-benzoyl-2(S)-substituted-2,3-dihydro-4(H)-pyrimidin-4-ones. Subsequently, Sonogashira coupling of the halogenated heterocyclic enones with various terminal alkynes produced 1-benzoyl-2(S)-isopropyl-5-alkynyl-2,3-dihydro-4(H)-pyrimidin-4-ones in good yields. Hydrogenation of the unsaturated C-C moieties in the Sonogashira products followed by acid hydrolysis afforded highly enantioenriched alpha-substituted beta-amino acids. PMID:17523668

Díaz-Sánchez, Blanca R; Iglesias-Arteaga, Martín A; Melgar-Fernández, Roberto; Juaristi, Eusebio

2007-06-22

287

Group IV clathrates: synthesis, optoelectonic properties, and photovoltaic applications  

NASA Astrophysics Data System (ADS)

Group IV clathrates are a unique class of guest/framework type compounds that are considered potential candidates for a wide range of applications (superconductors to semiconductors). To date, most of the research on group IV clathrates has focused heavily on thermoelectric applications. Recently, these materials have attracted attention as a result of their direct, wide band gaps for possible use in photovoltaic applications. Additionally, framework alloying has been shown to result in tunable band gaps. In this review, we discuss the current work and future opportunities concerning the synthesis and optical characterization of group IV clathrates for optoelectronics applications.

Krishna, Lakshmi; Martinez, Aaron D.; Baranowski, Lauryn L.; Brawand, Nicholas P.; Koh, Carolyn A.; Stevanovi?, Vladan; Lusk, Mark T.; Toberer, Eric S.; Tamboli, Adele C.

2014-03-01

288

Enantioselective degradation of warfarin in soils.  

PubMed

Environmental enantioselectivity information is important to fate assessment of chiral contaminants. Warfarin, a rodenticide and prescription medicine, is a chiral chemical but used in racemic form. Little is known about its enantioselective behavior in the environment. In this study, enantioselective degradation of warfarin in a turfgrass and a groundcover soils was examined in aerobic and ambient temperature conditions. An enantioselective analytical method was established using a novel triproline chiral stationary phase in high performance liquid chromatography. Unusual peak profile patterns, i.e., first peak (S(-)) broadening/second peak (R(+)) compression with hexane (0.1%TFA)/2-propanol (92/8, v/v) mobile phase, and first peak compression/second peak broadening with the (96/4, v/v) mobile phase, were observed in enantioseparation. This unique tunable peak property was leveraged in evaluating warfarin enantioselective degradation in two types of soil. Warfarin was extracted in high recovery from soil using methylene chloride after an aqueous phase basic-acidic conversion. No apparent degradation of warfarin was observed in the sterile turfgrass and groundcover soils during the 28 days incubation, while it showed quick degradation (half-life <7 days) in the nonsterile soils after a short lag period, suggesting warfarin degradation in the soils was mainly caused by micro-organisms. Limited enantioselectivity was found in the both soils, which was the R(+) enantiomer was preferentially degraded. The half-lives in turfgrass soil were 5.06 ± 0.13 and 5.97 ± 0.05 days, for the R(+) and the S(-) enantiomer, respectively. The corresponding values for the groundcover soil were 4.15 ± 0.11 and 4.47 ± 0.08 days. PMID:22012790

Lao, Wenjian; Gan, Jay

2012-01-01

289

Enantioselective cyclopropanation of indoles: construction of all-carbon quaternary stereocenters.  

PubMed

The first enantioselective copper-catalyzed cyclopropanation of N-acyl indoles is described. Using carbohydrate-based bis(oxazoline) ligands (glucoBox), the products were obtained in up to 72% ee. Cyclopropanation of N-Boc 3-methyl indole yielded a product with an all-carbon quaternary stereocenter, which is a valuable building block for the synthesis of indole alkaloids: Deprotection and rearrangement gave a tricyclic hemiaminal ester in 96% ee, which was subsequently employed as a key intermediate for the synthesis of (-)-desoxyeseroline. PMID:23009104

Özüduru, Gülsüm; Schubach, Thea; Boysen, Mike M K

2012-10-01

290

Naphthodithiophenediimide (NDTI): synthesis, structure, and applications.  

PubMed

A straightforward synthesis of ?,?-unsubstituted and ?-halogenated naphtho[2,3-b:6,7-b']dithiophenediimides (NDTIs) is described. Electrochemical and optical studies of N,N-dioctyl-NDTI demonstrate that the compound has a low-lying LUMO energy level (4.0 eV below the vacuum level) and a small HOMO-LUMO gap (~2.1 eV). With its interesting electronic and optical properties, in addition to its planar structure, NDTI is a promising building block for the development of novel ?-functional materials. In fact, it afforded n-channel, p-channel, and ambipolar materials, depending on the molecular modification. PMID:23879366

Fukutomi, Yuta; Nakano, Masahiro; Hu, Jian-Yong; Osaka, Itaru; Takimiya, Kazuo

2013-08-01

291

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

292

Asymmetric synthesis of cis-2,5-disubstituted pyrrolidine, the core scaffold of ?3-AR agonists.  

PubMed

A practical, enantioselective synthesis of cis-2,5-disubstituted pyrrolidine is described. Application of an enzymatic DKR reduction of a keto ester, which is easily accessed through a novel intramolecular N?C benzoyl migration, yields syn-1,2-amino alcohol in >99% ee and >99:1 dr. Subsequent hydrogenation of cyclic imine affords the cis-pyrrolidine in high diastereoselectivity. By integrating biotechnology into organic synthesis and isolating only three intermediates over 11 steps, the core scaffold of ?3-AR agonists is synthesized in 38% overall yield. PMID:23451898

Xu, Feng; Chung, John Y L; Moore, Jeffery C; Liu, Zhuqing; Yoshikawa, Naoki; Hoerrner, R Scott; Lee, Jaemoon; Royzen, Maksim; Cleator, Ed; Gibson, Andrew G; Dunn, Robert; Maloney, Kevin M; Alam, Mahbub; Goodyear, Adrian; Lynch, Joseph; Yasuda, Nobuyashi; Devine, Paul N

2013-03-15

293

Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia  

PubMed Central

Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

Pouy, Mark J.; Stanley, Levi M.; Hartwig, John F.

2009-01-01

294

Enantioselective inhibition of dichlorprop on catalase.  

PubMed

The enantioselectivity interaction of 2,4-dichlorprop (DCPP) and catalase were studied, and it was further evaluated with the presence of humus. Both of rac-DCPP and R-DCPP can inhibit the activity of catalase with the concentrations of 0.05-80 mg L(-1), the inhibitory type of rac-DCPP was uncompetitive, and of R-DCPP was complex. The presence of humic acid has changed the inhibitory ability of DCPP on catalase, the inhibition of rac-DCPP disappeared and the inhibition type of R-DCPP mainly became uncompetitive. These results suggest that inhibition of chiral DCPP on catalase is enantioselective. PMID:22961377

Ma, Yun; Jiang, Jihong; Xu, Chao; Lu, Xianting

2012-11-01

295

Synthesis and Characterization of Polymers for Fuel Cells Application  

NASA Technical Reports Server (NTRS)

The goal of this summer research is to prepare Polymer Exchange Membranes (PEM s) for fuel cell application. Several high temperature polymers such as polybenzimidazoles and polyether ketones were known to possess good high temperature stability and had been investigated by post-sulfonation to yield sulfonated polymers. The research project will involve two approaches: 1. Synthesis of polybenzimidazoles and then react with alkyl sultonse to attach an aliphatic sulfonic groups. 2. Synthesis of monomers containing sulfonic acid units either on a aromatic ring or on an aliphatic chain and then polymerize the monomers to form high molecular weight sulfonate polymers.

Tytko, Stephen F.

2003-01-01

296

Fluorescent sensors for the enantioselective recognition of mandelic acid: signal amplification by dendritic branching.  

PubMed

Novel chiral bisbinaphthyl compounds have been synthesized for the enantioselective fluorescent recognition of mandelic acid. By introducing dendritic branches to the chiral receptor unit, the fluorescence signals of the receptors are significantly amplified because of the light-harvesting effect of the dendritic structure. This has greatly increased the sensitivity of the sensors in the fluorescent recognition. Study of the three generation sensors demonstrates that the generation zero sensor is the best choice for the recognition of mandelic acid because of its greatly increased fluorescence signal over the core and its high enantioselectivity. This sensor is potentially useful for the high throughput screening of chiral catalysts for the asymmetric synthesis of alpha-hydroxycarboxylic acids. PMID:12440923

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

2002-11-27

297

Nanosilver particles in medical applications: synthesis, performance, and toxicity.  

PubMed

Nanosilver particles (NSPs), are among the most attractive nanomaterials, and have been widely used in a range of biomedical applications, including diagnosis, treatment, drug delivery, medical device coating, and for personal health care. With the increasing application of NSPs in medical contexts, it is becoming necessary for a better understanding of the mechanisms of NSPs' biological interactions and their potential toxicity. In this review, we first introduce the synthesis routes of NSPs, including physical, chemical, and biological or green synthesis. Then the unique physiochemical properties of NSPs, such as antibacterial, antifungal, antiviral, and anti-inflammatory activity, are discussed in detail. Further, some recent applications of NSPs in prevention, diagnosis, and treatment in medical fields are described. Finally, potential toxicology considerations of NSPs, both in vitro and in vivo, are also addressed. PMID:24876773

Ge, Liangpeng; Li, Qingtao; Wang, Meng; Ouyang, Jun; Li, Xiaojian; Xing, Malcolm M Q

2014-01-01

298

Nanosilver particles in medical applications: synthesis, performance, and toxicity  

PubMed Central

Nanosilver particles (NSPs), are among the most attractive nanomaterials, and have been widely used in a range of biomedical applications, including diagnosis, treatment, drug delivery, medical device coating, and for personal health care. With the increasing application of NSPs in medical contexts, it is becoming necessary for a better understanding of the mechanisms of NSPs’ biological interactions and their potential toxicity. In this review, we first introduce the synthesis routes of NSPs, including physical, chemical, and biological or green synthesis. Then the unique physiochemical properties of NSPs, such as antibacterial, antifungal, antiviral, and anti-inflammatory activity, are discussed in detail. Further, some recent applications of NSPs in prevention, diagnosis, and treatment in medical fields are described. Finally, potential toxicology considerations of NSPs, both in vitro and in vivo, are also addressed.

Ge, Liangpeng; Li, Qingtao; Wang, Meng; Ouyang, Jun; Li, Xiaojian; Xing, Malcolm MQ

2014-01-01

299

Biologically Relevant Glycopeptides: Synthesis and Applications  

NASA Astrophysics Data System (ADS)

Over the past two decades interest in glycopeptides and glycoproteins has intensified, due in part to the development of new and efficient methods for the synthesis of these compounds. This includes a number of chemical and enzymatic techniques for incorporating glycosylation onto the peptide backbone as well as the introduction of powerful peptide ligation methods for the construction of glycoproteins. This review discusses these methods with a special emphasis on biologically relevant glycopeptides and glycoproteins. This includes the development of a number of antigens which hold promise as potential vaccines for HIV, cancer, or a host of other clinically important diseases. In addition the development of new antibiotics aimed at overcoming the problem of resistance will be discussed. Finally, chemical and enzymatic methods for the construction of glycopeptide mimetics will be described.

Bennett, Clay S.; Payne, Richard J.; Koeller, Kathryn M.; Wong, Chi-Huey

300

Synthesis of hydroxyapatite nanotubes for biomedical applications.  

PubMed

Single phase, stoichiometrically pure, hollow nanotubes of hydroxyapatite have been synthesized and single-particle analysis has been performed to successfully prove the sole formation of Ca10(PO4)6(OH)2 phase. The facile synthesis involves a sol-gel process under neutral conditions in the presence of a sacrifical anodic alumina template. The structures formed are hollow nanotubes that have been characterized by XRD, SEM, TEM, SAED, EELS, EDS and BET measurements. The diameter of the resulting tubes is in the range of 140-350 nm, length is on the order of a few microns and the wall thickness of the tubes was found to be ca. 30 nm. Moreover these tubes had a large BET surface area of 115 m(2)/g and were found to be biocompatible. They displayed inertness in the presence of NIH 3T3 mouse fibroblast cells as dictated by an MTT assay. PMID:23623122

Chandanshive, Balasaheb B; Rai, Priyanka; Rossi, Andre L; Ersen, Ovidiu; Khushalani, Deepa

2013-07-01

301

Enantioselective transesterification of glycidol catalysed by a novel lipase expressed from Bacillus subtilis.  

PubMed

A novel plasmid (pBSR2) was constructed by incorporating a strong lipase promoter and a terminator into the original pBD64. The lipase gene from Bacillus subtilis strain IFFI10210 was cloned into the plasmid pBSR2 and transformed into B. subtilis A.S.1.1655 to obtain an overexpression strain. The recombinant lipase [BSL2 (B. subtilis lipase 2)] has been expressed from the novel constructed strain and used in kinetic resolution of glycidol through enantioselective transesterification. The effects of reaction conditions on the activity as well as enantioselectivity were investigated. BSL2 showed a satisfying enantioselectivity (E>30) under the optimum conditions [acyl donor: vinyl butyrate; the mole ratio of vinyl butyrate to glycidol was 3:1; organic medium: 1,2-dichloroethane with water activity (a(w))=0.33; temperature 40 degrees C]. The remaining (R)-glycidol with a high enantiomeric purity [ee (enantiomeric excess) >99%] could be obtained when the conversion was approx. 60%. The results clearly show a good potential for industrial application of BSL2 in the resolution of glycidol through enantioselective transesterification. PMID:20397973

Wang, Lei; Tai, Jian-Dong; Wang, Ren; Xun, Er-Na; Wei, Xiao-Fei; Wang, Lei; Wang, Zhi

2010-05-01

302

The Construction of All-Carbon Quaternary Stereocenters by Use of Pd-Catalyzed Asymmetric Allylic Alkylation Reactions in Total Synthesis  

PubMed Central

All-carbon quaternary stereocenters have posed significant challenges in the synthesis of complex natural products. These important structural motifs have inspired the development of broadly applicable palladium-catalyzed asymmetric allylic alkylation reactions of unstabilized non-biased enolates for the synthesis of enantioenriched ?-quaternary products. This microreview outlines key considerations in the application of palladium-catalyzed asymmetric allylic alkylation reactions and presents recent total syntheses of complex natural products that have employed these powerful transformations for the direct, catalytic, enantioselective construction of all-carbon quaternary stereocenters.

Hong, Allen Y.

2014-01-01

303

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

304

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

305

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

2008-11-15

306

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

307

Synthesis of fluorosurfactants for emulsion-based biological applications.  

PubMed

Microemulsion represents an attractive platform for fundamental and applied biomedical research because the emulsified droplets can serve as millions of compartmentalized micrometer-sized reactors amenable to high-throughput screening or online monitoring. However, establishing stable emulsions with surfactants that are compatible with biological applications remains a significant challenge. Motivated by the lack of commercially available surfactants suitable for microemulsion-based biological assays, this study describes the facile synthesis of a biocompatible fluorosurfactant with nonionic tris(hydroxymethyl)methyl (Tris) polar head groups. We have further demonstrated compatibility of the developed surfactant with diverse emulsion-based applications, including DNA polymeric nanoparticle synthesis, enzymatic activity assay, and bacterial or mammalian cell culture, in the setup of both double- and multiphases of emulsions. PMID:24646088

Chiu, Ya-Ling; Chan, Hon Fai; Phua, Kyle K L; Zhang, Ying; Juul, Sissel; Knudsen, Birgitta R; Ho, Yi-Ping; Leong, Kam W

2014-04-22

308

Large-scale de novo DNA synthesis: technologies and applications.  

PubMed

For over 60 years, the synthetic production of new DNA sequences has helped researchers understand and engineer biology. Here we summarize methods and caveats for the de novo synthesis of DNA, with particular emphasis on recent technologies that allow for large-scale and low-cost production. In addition, we discuss emerging applications enabled by large-scale de novo DNA constructs, as well as the challenges and opportunities that lie ahead. PMID:24781323

Kosuri, Sriram; Church, George M

2014-05-01

309

Synthesis and application of a T-2 toxin imprinted polymer  

Microsoft Academic Search

The synthesis of a T-2 toxin imprinted polymer and its application in food analysis are reported for the first time. A molecularly imprinted polymer (MIP) for the selective recognition of T-2 toxin (T-2) was synthesized by bulk polymerization. Methacrylamide and ethyleneglycol dimethacrylate were applied as functional monomer and cross-linker, respectively. Molecularly imprinted solid-phase extraction (MISPE) procedures were optimized for further

David De Smet; Sofie Monbaliu; Peter Dubruel; Carlos Van Peteghem; Etienne Schacht; Sarah De Saeger

2010-01-01

310

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

311

The application of micro reactors for organic synthesis.  

PubMed

This tutorial review describes how micro reactors are being applied to synthetic chemistry covering a wide range of applications, from the preparation of nanograms of material for drug discovery and screening to the multi-tonne production of fine chemicals. This article explores how miniaturisation may revolutionise chemical synthesis and demonstrates that products are generated in higher yield and purity compared to the equivalent bulk reactions, in much shorter periods of time. PMID:15726160

Watts, Paul; Haswell, Stephen J

2005-03-01

312

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

313

Construction of spiro-fused 2-oxindole/?-methylene- ?-butyrolactone systems with extremely high enantioselectivity via indium-catalyzed amide allylation of N-methyl isatin.  

PubMed

A remarkably effective method allowing an extremely high enantioselective synthesis of the spiro-fused 2-oxindole/?-methylene-?-butyrolactones is described. The key strategy lies in the use of indium-catalyzed asymmetric amide allylation of N-methyl isatin with functionalized allylstannanes, which can lead to the antineoplastic spirocyclic lactones in almost enantiopure forms. PMID:24224753

Murata, Yusuke; Takahashi, Masaki; Yagishita, Fumitoshi; Sakamoto, Masami; Sengoku, Tetsuya; Yoda, Hidemi

2013-12-20

314

Electrospun metallic nanowires: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

Metals are known to have unique thermal, mechanical, electrical, and catalytic properties. On the other hand, metallic nanowires are promising materials for variety of applications such as transparent conductive film for photovoltaic devices, electrodes for batteries, as well as nano-reinforcement for composite materials. Whereas varieties of methods have been explored to synthesize metal nanowires with different characteristics, electrospinning has also been found to be successful for that purpose. Even though electrospinning of polymeric nanofibers is a well-established field, there are several challenges that need to be overcome to use the electrospinning technique for the fabrication of metallic nanowires. These challenges are mainly related to the multi-steps fabrication process and its relation to the structure evolution of the nanowires. In addition to reviewing the literature, this article identifies promising avenues for further research in this area with particular emphasis on the applications that nonwoven metal wires confined in a nano-scale can open.

Khalil, Abdullah; Singh Lalia, Boor; Hashaikeh, Raed; Khraisheh, Marwan

2013-11-01

315

Norbornene based polybetaines: Synthesis and biological applications  

NASA Astrophysics Data System (ADS)

Polymeric betaines gain considerable attention for their interesting solution properties, but even more so, for their favorable bio- and haemocompatible properties. When incorporated into materials or used as surface coatings, some of these zwitterionic polymers strongly resist protein absorption due to their hygroscopic nature, making betaines promising candidates for medical diagnostics, drug delivery, and tissue engineering applications. This dissertation introduces novel norbornene-based polybetaines as foundational materials for biological applications, including non-fouling coatings and antimicrobial macromolecules. Sulfo- and carboxybetaines, composed of backbones that do not contain hydrolyzable units under physiological conditions, as well as new polymers that carry a dual functionality at the repeat unit level, coupling a zwitterionic functionality with an alkyl moiety varied to adjust the amphiphilicity of the overall system, are introduced. How structural changes, backbone chemistry, hydrophilicity/amphiphilicity, and coating surface roughness impact their non-fouling properties is investigated.

Colak, Semra

316

Enantioselective toxicities of chiral ionic liquids 1-alkyl-3-methylimidazolium lactate to aquatic algae.  

PubMed

With the wide application of chiral ionic liquids (CILs) as green solvents, their threats to the aquatic environment cannot be ignored. Thus, risk assessment and the prospective design of inherently safe CILs have become more urgent. However, whether enantioselectivity is a feature of the aquatic toxicity of CILs is poorly understood. Herein, we describe the first investigation into the ecotoxicities of CILs toward green algae Scenedesmus obliquus and Euglena gracilis. A series of methylimidazolium lactic ionic liquids, which cation parts with different alkyl chains and anion part is enantiomers of lactate, are used as representative CILs. The results of S. obliquus showed that the EC50 value of l-(+)-1-ethyl-3-methylimidazolium lactate (l-(+)-EMIM L) was more than 5000?M, while the EC50 value of d-(-)-1-ethyl-3-methylimidazolium lactate (d-(-)-EMIM L) was 2255.21?M. Such a distinct difference indicates the enantioselective toxicity of CILs to algae. This enantioselectivity initially persisted with increasing carbon chain length, but no longer exhibited when with greater carbon chain lengths, due to changes in the toxicity weightings of the cation parts. Further research showed that the enantioselective effects of CILs resulted from the differences in the production of reactive oxygen species, the damage to cell membrane integrity and cell wall after exposure to CILs. Results from this study showed that monitoring for the racemate CILs will give an inadequate or misleading environmental risk assessment. Thus, we should improve our ability to predict their effects in natural environments. In the meantime, non-selective use of CILs will do harm to aquatic organisms. Therefore, to minimize their potential for environmental impact, the enantioselective toxicities of CILs with short alkyl chains should be taken into consideration. PMID:24880783

Chen, Hui; Zou, Yuqin; Zhang, Lijuan; Wen, Yuezhong; Liu, Weiping

2014-09-01

317

Nitroderivatives of catechol: from synthesis to application.  

PubMed

Nitroderivatives of catechol (NDCs) are reviewed with special emphasis on their complexes and applications. Binary, ternary and quaternary NDC complexes with more than 40 elements (aluminum, arsenic, boron, beryllium, calcium, cobalt, copper, iron, gallium, germanium, magnesium, manganese, molybdenum, niobium, rare earth elements, silicon, tin, strontium, technetium, thallium, titanium, uranium, vanadium, tungsten, zinc and zirconium) are discussed and the key characteristics of the developed analytical procedures - tabulated. The bibliography includes 206 references. PMID:24061167

Gavazov, Kiril B

2012-03-01

318

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

319

[Progress in synthesis technologies and application of aviation biofuels].  

PubMed

Development of aviation biofuels has attracted great attention worldwide because that the shortage of fossil resources has become more and more serious. In the present paper, the development background, synthesis technologies, current application status and existing problems of aviation biofuels were reviewed. Several preparation routes of aviation biofuels were described, including Fischer-Tropsch process, catalytic hydrogenation and catalytic cracking of bio-oil. The status of flight tests and commercial operation were also introduced. Finally the problems for development and application of aviation biofuels were stated, and some accommodation were proposed. PMID:23789270

Sun, Xiaoying; Liu, Xiang; Zhao, Xuebing; Yang, Ming; Liu, Dehua

2013-03-01

320

Total Synthesis of Herboxidiene/GEX 1A  

PubMed Central

A convergent enantioselective synthesis of herboxidiene/GEX 1A (1) is described, which features a double stereodifferentiating crotylation, [4+2]-annulation and a silicon-based sp2-sp2 cross-coupling to assemble the conjugated diene.

Zhang, Yun; Panek, James S.

2011-01-01

321

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

322

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

323

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

324

Directed evolution of an enantioselective epoxide hydrolase: uncovering the source of enantioselectivity at each evolutionary stage.  

PubMed

Directed evolution of enzymes as enantioselective catalysts in organic chemistry is an alternative to traditional asymmetric catalysis using chiral transition-metal complexes or organocatalysts, the different approaches often being complementary. Moreover, directed evolution studies allow us to learn more about how enzymes perform mechanistically. The present study concerns a previously evolved highly enantioselective mutant of the epoxide hydrolase from Aspergillus niger in the hydrolytic kinetic resolution of racemic glycidyl phenyl ether. Kinetic data, molecular dynamics calculations, molecular modeling, inhibition experiments, and X-ray structural work for the wild-type (WT) enzyme and the best mutant reveal the basis of the large increase in enantioselectivity (E = 4.6 versus E = 115). The overall structures of the WT and the mutant are essentially identical, but dramatic differences are observed in the active site as revealed by the X-ray structures. All of the experimental and computational results support a model in which productive positioning of the preferred (S)-glycidyl phenyl ether, but not the (R)-enantiomer, forms the basis of enhanced enantioselectivity. Predictions regarding substrate scope and enantioselectivity of the best mutant are shown to be possible. PMID:19469578

Reetz, Manfred T; Bocola, Marco; Wang, Li-Wen; Sanchis, Joaquin; Cronin, Annette; Arand, Michael; Zou, Jinyu; Archelas, Alain; Bottalla, Anne-Lise; Naworyta, Agata; Mowbray, Sherry L

2009-06-01

325

Boron Nitride Nanotube: Synthesis and Applications  

NASA Technical Reports Server (NTRS)

Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800 C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha I.; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

2014-01-01

326

Boron nitride nanotube: synthesis and applications  

NASA Astrophysics Data System (ADS)

Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA/JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800°C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

2014-04-01

327

Engineering and Applications of fungal laccases for organic synthesis  

PubMed Central

Laccases are multi-copper containing oxidases (EC 1.10.3.2), widely distributed in fungi, higher plants and bacteria. Laccase catalyses the oxidation of phenols, polyphenols and anilines by one-electron abstraction, with the concomitant reduction of oxygen to water in a four-electron transfer process. In the presence of small redox mediators, laccase offers a broader repertory of oxidations including non-phenolic substrates. Hence, fungal laccases are considered as ideal green catalysts of great biotechnological impact due to their few requirements (they only require air, and they produce water as the only by-product) and their broad substrate specificity, including direct bioelectrocatalysis. Thus, laccases and/or laccase-mediator systems find potential applications in bioremediation, paper pulp bleaching, finishing of textiles, bio-fuel cells and more. Significantly, laccases can be used in organic synthesis, as they can perform exquisite transformations ranging from the oxidation of functional groups to the heteromolecular coupling for production of new antibiotics derivatives, or the catalysis of key steps in the synthesis of complex natural products. In this review, the application of fungal laccases and their engineering by rational design and directed evolution for organic synthesis purposes are discussed.

Kunamneni, Adinarayana; Camarero, Susana; Garcia-Burgos, Carlos; Plou, Francisco J; Ballesteros, Antonio; Alcalde, Miguel

2008-01-01

328

Graphene and Graphene-Based Nanocomposites:. Synthesis and Supercapacitor Applications  

NASA Astrophysics Data System (ADS)

Graphene, a single-atomic-thick sheet, consists of sp2-bonded carbon atoms in hexagonal lattice and possesses excellent physical and chemical properties such as high surface area, conductivity, mechanical strength and lightweight. The two-dimensional geometry of graphene nanosheets is ideal for many applications especially in electrochemical energy storage. However, the large-scale production of graphene materials is still a bottleneck limiting the development of advanced energy storage devices. The production of graphene oxide is one of the most critical restrictions in term of synthesis of graphene by wet chemical methods. We have demonstrated the synthesis of high quality graphene oxide by simple chemical reactions with less exo-therm involved without emission of toxic gases, which is more favorable than conventional methods for commercialized synthesis of graphene materials (Figure 1.). Meanwhile, pseudo-capacitive materials such as Co3O4 and MnSn(OH)6 coupled with graphene nanosheets were synthesized by soft chemical methods in order to utilize both advantages from electrical double layer and pseudo-mechanisms. Their electrochemical properties were evaluated and the potential applications used as high performance electrodes for capacitive energy storage were discussed as well.

Wang, Gongkai; Liu, Changsheng; Sun, Xiang; Lu, Fengyuan; Sun, Hongtao; Lian, Jie

2012-08-01

329

Modification of the enantioselectivity of two homologous thermophilic carboxylesterases from Alicyclobacillus acidocaldarius and Archaeoglobus fulgidus by random mutagenesis and screening  

Microsoft Academic Search

The esterase genes est2 from Alicyclobacillus acidocaldarius and AF1716 from Archaeoglobus fulgidus were subjected to error-prone PCR in an effort to increase the low enantioselectivity of the corresponding enzymes EST2 and AFEST, respectively. The model substrate (RS)-p-nitrophenyl-2-chloropropionate was chosen to produce (S)-2-chloropropionic acid, an important intermediate in the synthesis of some optically pure compounds, such as the herbicide mecoprop. In

Giuseppe Manco; Giacomo Carrea; Elena Giosuè; Gianluca Ottolina; Giovanna Adamo; Mosè Rossi

2002-01-01

330

Enantioselective domino reaction of CO2, amines and allyl chlorides under iridium catalysis: formation of allyl carbamates.  

PubMed

The enantioselective domino reaction between CO2 (1 atm), amines and linear allyl chlorides in the presence of an iridium complex, DABCO and toluene at 15 °C was realized, which gave branched allyl carbamates in acceptable to high yields with up to excellent regioselectivity (99/1) and 94% ee. This is the first example of the synthesis of chiral allyl carbamates through catalytic domino reactions using CO2. PMID:24652315

Zhang, Min; Zhao, Xiaoming; Zheng, Shengcai

2014-05-01

331

Enantioselective resolution of methyl 2-chloromandelate by Candida antarctica lipase A in a solvent-free transesterification reaction  

Microsoft Academic Search

Enantiomerically pure 2-chloromandelic acid esters are important chiral building blocks for synthesis of a wide range of pharmaceutical products, such as an anti-thrombotic agent, (S)-clopidogrel. An efficient and novel process for resolution of methyl 2-chloromandelate was developed by using a lipase-mediated transesterification. Among 11 hydrolytic enzymes examined, Candida antarctica lipase A (CAL-A) showed the highest enantioselectivity and reaction rate toward

Ki-Nam Uhm; Sang-Joon Lee; Hyung-kwoun Kim; Han-Young Kang; Younghoon Lee

2007-01-01

332

A Catalytic, Asymmetric Formal Synthesis of (+)-Hamigeran B  

PubMed Central

A concise asymmetric, formal synthesis of (+)-hamigeran B is reported. A Pd-catalyzed, decarboxylative allylic alkylation, employing a trifluoromethylated derivative of t-BuPHOX, is utilized as the enantioselective step to form the critical quaternary carbon center in excellent yield and enantioselectivity. The product is converted in three steps to a late-stage intermediate previously used in the synthesis of hamigeran B.

Mukherjee, Herschel; McDougal, Nolan T.; Virgil, Scott C.

2011-01-01

333

One-dimensional zinc oxide nanomaterials synthesis and photovoltaic applications  

NASA Astrophysics Data System (ADS)

As humanly engineered materials systems approach the atomic scale, top-down manufacturing approaches breakdown and following nature's example, bottom-up or self-assembly methods have the potential to emerge as the dominant paradigm. Synthesis of one-dimensional nanomaterials takes advantage of such self-assembly manufacturing techniques, but until now most efforts have relied on high temperature vapor phase schemes which are limited in scalability and compatibility with organic materials. The solution-phase approach is an attractive low temperature alternative to overcome these shortcomings. To this end, this thesis is a study of the rationale solution-phase synthesis of ZnO nanowires and applications in photovoltaics. The following thesis goals have been achieved: rationale synthesis of a single ZnO nanowire on a polymer substrate without seeding, design of a wafer-scale technique to control ZnO nanowire array density using layer-by-layer polymers, determination of optimal nanowire field emitter density to maximize the field enhancement factor, design of bridged nanowires across metal electrodes to order to circumvent post-synthesis manipulation steps, electrical characterization of bridged nanowires, rationale solution-phase synthesis of long ZnO nanowires on optical fibers, fabrication of ZnO nanowire dye-sensitized solar cells on optical fibers, electrical and optical characterization of solar cell devices, comparison studies of 2-D versus 3-D nanowire dye-sensitized solar cell devices, and achievement of 6-fold solar cell power conversion efficiency enhancement using a 3-D approach. The thesis results have implications in nanomanufacturing scale-up and next generation photovoltaics.

Weintraub, Benjamin A.

334

Application of global sensitivity equations in multidisciplinary aircraft synthesis  

NASA Technical Reports Server (NTRS)

The present paper investigates the applicability of the Global Sensitivity Equation (GSE) method in the multidisciplinary synthesis of aeronautical vehicles. The GSE method provides an efficient approach for representing a large coupled system by smaller subsystems and accounts for the subsystem interactions by means of first-order behavior sensitivities. This approach was applied in an aircraft synthesis problem with performance constraints stemming from the disciplines of structures, aerodynamics, and flight mechanics. Approximation methods were considered in an attempt to reduce problem dimensionality and to improve the efficiency of the optimization process. The influence of efficient constraint representations, the choice of design variables, and design variable scaling on the conditioning of the system matrix was also investigated.

Hajela, P.; Bloebaum, C. L.; Sobieszczanski-Sobieski, Jaroslaw

1990-01-01

335

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

336

Hollow-structured mesoporous materials: chemical synthesis, functionalization and applications.  

PubMed

Hollow-structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft-templating and hard-templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented. PMID:24687906

Li, Yongsheng; Shi, Jianlin

2014-05-28

337

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

338

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

339

Lipase-catalyzed highly enantioselective kinetic resolution of boron-containing chiral alcohols.  

PubMed

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained. PMID:19552446

Andrade, Leandro H; Barcellos, Thiago

2009-07-16

340

Functional Metal Oxide Nanostructures: Their Synthesis, Characterization, and Energy Applications  

NASA Astrophysics Data System (ADS)

This research focuses on studying metal oxides (MnO 2, Co3O4, MgO, Y2O3) for various applications including water oxidation and photocatalytic oxidation, developing different synthesis methodologies, and presenting detailed characterization studies of these metal oxides. This research consists of three major parts. The first part is studying novel applications and developing a synthesis method for manganese oxide nanomaterials. Manganese oxide materials were studied for renewable energy applications by using them as catalysts for water oxidation reactions. In this study, various crystallographic forms of manganese oxides (amorphous, 2D layered, 1D 2 x 2 tunnel structures) were evaluated for water oxidation catalysis. Amorphous manganese oxides (AMO) were found to be catalytically active for chemical and photochemical water oxidation compared to cryptomelane type tunnel manganese oxides (2 x 2 tunnels; OMS2) or layered birnessite (OL-1) materials. Detailed characterization was done to establish a correlation between the properties of the manganese oxide materials and their catalytic activities in water oxidation. The gas phase photocatalytic oxidation of 2-propanol under visible light was studied using manganese oxide 2 x 2 tunnel structures (OMS-2) as catalysts (Chapter 3). The reaction is 100% selective to acetone. As suggested by the photocatalytic and characterization data, important factors for the design of active OMS-2 photocatalysts are synthesis methodology, morphology, mixed valency and the release of oxygen from the OMS-2 structure. Manganese oxide octahedral molecular sieves (2 x 2 tunnels; OMS-2) with self-assembled dense or hollow sphere morphologies were fabricated via a room temperature ultrasonic atomization assisted synthesis (Chapter 4). The properties and catalytic activities of these newly developed materials were compared with that of OMS-2 synthesized by conventional reflux route. These materials exhibit exceptionally high catalytic activities in oxidation reactions and adsorption of heavy metal. Spontaneous formation of OMS-2 nanospheres was possible by tuning reaction parameters in the ultrasonic atomization process. In the second part, a microwave-hydrothermal route has been developed for the synthesis of 1D cobalt compounds (Chapter 5). These compounds are transformed to spinel type Co3O4 nanorods. The effects of solvents, cobalt sources, and microwave radiation time in the formation of 1D cobalt oxide nanostructures were studied in detail. These materials are catalytically active for CO oxidation and styrene oxidation reactions. Magnesia-yttria nanocomposites with controlled nanoscale grain sizes and homogenous microstructures are useful as IR transparent materials. A simple cost-effective sucrose based sol-gel route was devised for making MgO-Y 2O3 nanocomposites. Grain growth in these nanocomposites was systematically evaluated using transmission electron microscopy studies.

Iyer, Aparna

341

Gold(I)-catalyzed enantioselective cycloaddition reactions  

PubMed Central

Summary In recent years there have been extraordinary developments of gold(I)-catalyzed enantioselective processes. This includes progress in the area of cycloaddition reactions, which are of particular interest due to their potential for the rapid construction of optically active cyclic products. In this article we will summarize some of the most remarkable examples, emphasizing reaction mechanisms and key intermediates involved in the processes.

2013-01-01

342

Metal-organic framework membranes: from synthesis to separation application.  

PubMed

Metal-organic framework (MOF) materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers, exhibit regular crystalline lattices with relatively well-defined pore structures and interesting properties. As a new class of porous solid materials, MOFs are attractive for a variety of industrial applications including separation membranes - a rapidly developing research area. Many reports have discussed the synthesis and applications of MOFs and MOF thin films, but relatively few have addressed MOF membranes. This critical review provides an overview of the diverse MOF membranes that have been prepared, beginning with a brief introduction to the current techniques for the fabrication of MOF membranes. Gas and liquid separation applications with different MOF membranes are also included (175 references). PMID:24967810

Qiu, Shilun; Xue, Ming; Zhu, Guangshan

2014-07-21

343

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

2013-10-01

344

Bismuth hexagons: facile mass synthesis, stability and applications.  

PubMed

A unique direct electrodeposition technique involving very high current densities, high voltages and high electrolyte concentrations is applied for highly selective mass synthesis of stable, isolable, surfactant-free, single-crystalline Bi hexagons on a Cu wire at room temperature. A formation mechanism of the hexagons is proposed. The morphology, phase purity, and crystallinity of the material are well characterized by FESEM, AFM, TEM, SAED, EDX, XRD, and Raman spectroscopy. The thermal stability of the material under intense electron beam and intense laser light irradiation is studied. The chemical stability of elemental Bi in nitric acid shows different dissolution rates for different morphologies. This effect enables a second way for the selective fabrication of Bi hexagons. Bi hexagons can be oxidized exclusively to ?-Bi(2)O(3) hexagons. The Bi hexagons are found to be promising for thermoelectric applications. They are also catalytically active, inducing the reduction of 4-nitrophenol to 4-aminophenol. This electrodeposition methodology has also been demonstrated to be applicable for synthesis of bismuth-based bimetallic hybrid composites for advanced applications. PMID:22508562

Som, Tirtha; Simo, Anne; Fenger, Robert; Troppenz, Gerald V; Bansen, Roman; Pfänder, Norbert; Emmerling, Franziska; Rappich, Jörg; Boeck, Torsten; Rademann, Klaus

2012-06-01

345

Controlled synthesis of porous platinum nanostructures for catalytic applications.  

PubMed

Porous platinum, that has outstanding catalytic and electrical properties and superior resistant characteristics to corrosion, has been widely applied in chemical, petrochemical, pharmaceutical, electronic, and automotive industries. As the catalytic activity and selectivity depend on the size, shape and structure of nanomaterials, the strategies for controlling these factors of platinum nanomaterials to get excellent catalytic properties are discussed. Here, recent advances in the design and preparation of various porous platinum nanostructures are reviewed, including wet-chemical synthesis, electro-deposition, galvanic replacement reaction and de-alloying technology. The applications of various platinum nanostructures are also discussed, especially in fuel cells. PMID:24749422

Cao, Yanqin; Zhang, Junwei; Yang, Yong; Huang, Zhengren; Long, Nguyen Viet; Nogami, Masayuki

2014-02-01

346

Enantioselective Biotransformation of Chiral PCBs in Whole Poplar Plants  

PubMed Central

Chiral PCBs have been used as molecular probes of biological metabolic processes due to their special physical, chemical and biological properties. Many animal studies showed the enantioselective biotransformation of chiral PCBs, but it is unclear whether plants can enantioselectively biotransform chiral PCBs. In order to explore the enantioselectivity of chiral PCBs in whole plants, poplars (Populus deltoides × nigra, DN34), a model plant with complete genomic sequence, were hydroponically exposed to 2,2?,3,5?,6-pentachlorobiphenyl (PCB95) and 2,2?,3,3?,6,6?-hexachlorobiphenyl (PCB136) for 20 days. PCB95 and PCB136 were shown to be absorbed, taken-up and translocated in whole poplars, and they were detected in various tissues of whole poplars. However, the enantioselectivity of poplar for PCB95 and PCB136 proved to be quite different. The first eluting enantiomer of PCB95 was enantioselectively removed in whole poplar, especially in the middle and bottom xylem. It was likely enantioselectively metabolized inside poplar tissues, in contrast to racemic mixtures of PCB95 remaining in hydroponic solutions in contact with plant roots of whole and dead poplars. Unlike PCB95, PCB136 remained nearly racemic in most parts of whole poplars after 20 days exposure. These results suggest that PCB136 is more difficult to be enantioslectively biotransformed than PCB95 in whole poplars. This is the first evidence of enantioselectivity of chiral PCBs in whole plants, and suggests that poplars can enantioselectively biotransform at least one chiral PCB.

Zhai, Guangshu; Hu, Dingfei; Lehmler, Hans-Joachim; Schnoor, Jerald L.

2011-01-01

347

Squaramide-catalyzed enantioselective Michael addition of malononitrile to chalcones.  

PubMed

A highly enantioselective Michael addition of malononitrile to chalcones catalyzed by a chiral quinine-derived squaramide catalyst has been developed. This organocatalytic reaction at a very low catalyst loading (0.5 mol%) led to chiral ?-cyano carbonyl compounds in good yields with high enantioselectivities (up to 96% ee) under mild reaction conditions. PMID:22071519

Yang, Wen; Jia, Yang; Du, Da-Ming

2012-01-14

348

The First Catalytic Enantioselective Nozaki-Hiyama Reaction.  

PubMed

The Nozaki-Hiyama reaction can be performed in an enantioselective catalytic way! The catalytic system utilizes 10 mol % of an inexpensive chiral [Cr(salen)] complex. The [Cr(salen)]/Mn/Me(3)SiCl system effectively promotes the enantioselective addition of allyl chloride to aliphatic and aromatic aldehydes at room temperature (65-89 % ee, 40-60 % yield). PMID:10602193

Bandini; Cozzi; Melchiorre; Umani-Ronchi

1999-11-15

349

Chiral Brønsted acid catalyzed enantioselective intermolecular allylic aminations.  

PubMed

This paper describes an enantioselective intermolecular allylic amination catalyzed by a chiral Brønsted acid via a possible chiral contact ion pair intermediate. A variety of symmetrical or unsymmetrical allylic alcohols can be smoothly aminated to afford the desired products in moderate to high yields with good enantioselectivities and/or regioselectivities. PMID:24872122

Zhuang, Minyang; Du, Haifeng

2014-06-11

350

Lewis base catalyzed, enantioselective, intramolecular sulfenoamination of olefins.  

PubMed

A method for the enantioselective, intramolecular sulfenoamination of various olefins has been developed using a chiral BINAM-based selenophosphoramide, Lewis base catalyst. Terminal and trans disubstituted alkenes afforded pyrrolidines, piperidines, and azepanes in high yields and high enantiomeric ratios via enantioselective formation and subsequent stereospecific capture of the thiiranium intermediate with the pendant tosyl-protected amine. PMID:24926794

Denmark, Scott E; Chi, Hyung Min

2014-06-25

351

Breaking news on the enantioselective intermolecular Heck reaction.  

PubMed

Glowing results with less phosphorus: Tremendous progress has been made recently in asymmetric intermolecular Heck chemistry. Previously unprecedented enantioselective Heck-Matsuda reactions have been accomplished, and mixed phosphine/phosphine oxides have been shown to be superior ligands in enantioselective Mizoroki-Heck reactions. All of this was achieved with chiral ligands containing few or even no phosphorus donors (see scheme). PMID:24481834

Oestreich, Martin

2014-02-24

352

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

353

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.

354

Upconversion Nanoparticles: Synthesis, Surface Modification, and Biological Applications  

PubMed Central

New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a non-linear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photo-bleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this review, we discuss the recent progress in the synthesis and surface modification of rare earth doped UCNPs with a specific focus on their biological applications.

Wang, Meng; Abbineni, Gopal; Clevenger, April; Mao, Chuanbin; Xu, Shukun

2011-01-01

355

Luminescent metal nanoclusters: controlled synthesis and functional applications  

NASA Astrophysics Data System (ADS)

Luminescent metal nanoclusters that consist of only several, to tens of, metal atoms and which possess sizes comparable to the Fermi wavelength of electrons have recently attracted significant attention. This new class of luminescent materials not only provides the missing link between atomic and nanoparticle behaviors in metals but also they present abundant novel information for the development of new applicable material systems to meet urgent needs in many areas (such as ultrasensitive sensors for heavy metals, bioimaging, as well as information technology) mainly because of their attractive characteristics, including ultra-small size, good dispersibility, excellent biocompatibility and photostability. In this review, we summarize recent advances in the controlled synthesis and application of luminescent metal nanoclusters, with a particular emphasis on Pt, Mo, Bi and alloy clusters. We also speculate on their future and discuss potential developments for their use in sensors, bioimaging and energy harvesting and conversion.

Sun, Hong-Tao; Sakka, Yoshio

2014-02-01

356

Nanocrystals-Related Synthesis, Assembly, and Energy Applications  

SciTech Connect

During the past decades, nanocrystals have attracted broad attention due to their unique shape- and size-dependent physical and chemical properties that differ drastically from their bulk counterparts. Hitherto, much effort has been dedicated to achieving rational controlling over the morphology, assembly, and related energy applications of the nanomaterials. Therefore, the ability to manipulate the morphology, size, and size distribution of inorganic nanomaterials is still an important goal in modern materials physics and chemistry. Especially, the world s demand for energy supply is causing a dramatic escalation of social and political unrest. Likewise, the environmental impact of the global climate change due to the combustion of fossil fuel is becoming increasingly alarming. These problems compel us to search for effective routes to build devices that can supply sustainable energy, with not only high efficiency but also environmental friendship. One of ways to relieve the energy crisis is to exploit devices based on renewable energy sources, such as solar energy and water power. Aiming at this exploration, the primary stage requires the design of appropriate strategies for the synthesis of high-quality nanocrystals with respect to size uniformity and superior electrochemical performances. As a consequence, we organize the current special issue for Journal of Nanomaterials to provide the authors with a platform and readers with the latest achievements of nanocrystals-related synthesis, assembly, and energy applications.

Zou, Bo [Jilin University, Changchun; Yu, Williams [Worcester Polytechnic Institute; Seo, Jaetae [Hampton University; Zhu, Ting [Philips Lumileds Lighting Company; Hu, Michael Z. [ORNL

2012-01-01

357

Aerosol Route Synthesis and Applications of Doped Nanostructured Materials  

NASA Astrophysics Data System (ADS)

Nanotechnology presents an attractive opportunity to address various challenges in air and water purification, energy, and other environment issues. Thus, the development of new nanoscale materials in low-cost scalable synthesis processes is important. Furthermore, the ability to independently manipulate the material properties as well as characterize the material at different steps along the synthesis route will aide in product optimization. In addition, to ensure safe and sustainable development of nanotechnology applications, potential impacts need to be evaluated. In this study, nanomaterial synthesis in a single-step gas phase reactor to continuously produce doped metal oxides was demonstrated. Copper-doped TiO2 nanomaterial properties (composition, size, and crystal phase) were independently controlled based on nanoparticle formation and growth mechanisms dictated by process control parameters. Copper dopant found to significantly affect TiO2 properties such as particle size, crystal phase, stability in the suspension, and absorption spectrum (shift from UV to visible light absorption). The in-situ charge distribution characterization of the synthesized nanomaterials was carried out by integrating a tandem differential mobility analyzer (TDMA) set up with the flame reactor synthesis system. Both singly- and doubly- charged nanoparticles were measured, with the charged fractions dependent on particle mobility and dopant concentration. A theoretical calculation was conducted to evaluate the relative importance of the two charging mechanisms, diffusion and thermo-ionization, in the flame. Nanoparticle exposure characterization was conducted during synthesis as a function of operating condition, product recovery and handling technique, and during maintenance of the reactors. Strategies were then indentified to minimize the exposure risk. The nanoparticle exposure potential varied depending on the operating conditions such as precursor feed rate, working conditions of the fume hood, ventilation system, and distance from the reactors. Nanoparticle exposure varied during product recovery and handling depending on the quantity of nanomaterial handled. Most nanomaterial applications require nanomaterials to be in solution. Thus, the role of nanomaterial physio-chemical properties (size, crystal phase, dopant types and concentrations) on dispersion properties was investigated based on hydrodynamic size and surface charge. Dopant type and concentration were found to significantly affect iso-electric point (IEP)-shifting the IEP to a high or lower pH value compared to pristine TiO2 based on the oxidation state of the dopant. The microbial inactivation effectiveness of as-synthesized nanomaterials was investigated under different light irradiation conditions. Microbial inactivation was found to strongly depend on the light irradiation condition as well as on material properties such chemical composition, crystal phase, and particle size. The potential interaction mechanisms of copper-doped TiO2 nanomaterial with microbes were also explored. The studies conducted as part of this dissertation addressed issues in nanomaterial synthesis, characterization and their potential environmental applications.

Sahu, Manoranjan

358

The enantioselective organocatalytic 1,4-addition of electron-rich benzenes to alpha,beta-unsaturated aldehydes.  

PubMed

The first enantioselective organocatalytic alkylation of electron-rich benzene rings with alpha,beta-unsaturated aldehydes has been accomplished. The use of iminium catalysis has provided a new strategy for the enantioselective construction of benzylic stereogenicity, an important chiral synthon for natural product and medicinal agent synthesis. The (2S,5S)-5-benzyl-2-tert-butylimidazolidinone amine catalyst has been found to mediate the conjugate addition of a wide variety of substituted and unsubstituted anilines to unsaturated aldehydes. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. While catalyst quantities of 10 mol % were generally employed in this study, successful alkylations conducted with catalyst loadings as low as 1 mol % are described. PMID:12095321

Paras, Nick A; MacMillan, David W C

2002-07-10

359

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

360

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

361

A highly fluorescent metallosalalen-based chiral cage for enantioselective recognition and sensing.  

PubMed

A highly fluorescent coordination cage [Zn8 L4 I8 ] has been constructed by treating enantiopure pyridyl-functionalized metallosalalen units (L) with zinc(II) iodide and characterized by a variety of techniques including microanalysis, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, and single-crystal and powder X-ray diffraction. Strong intermolecular ?-?, CH????, and CH???I interactions direct packing of the cage molecules to generate a 3D polycage network interconnected by pentahedral cages formed by adjacent pentamers. The cage has an amphiphilic helical cavity decorated with chiral NH functionalities capable of interactions with guest species such as saccharides. The fluorescence of the cage was greatly enhanced by five enantiomeric saccharides in solution, with enantioselectivity factors of 2.480-4.943, and by five enantiomeric amines in the solid state, with enantioselective fluorescence enhancement ratios of 1.30-3.60. This remarkable chiral sensing of both saccharides and amines with impressive enantioselectivity may result from the steric confinement of the cavity as well as its conformational rigidity. It holds great promise for the development of novel chiral cage materials for sensing applications. PMID:24710843

Dong, Jinqiao; Zhou, Yanfang; Zhang, Fangwei; Cui, Yong

2014-05-19

362

An enantioselective strategy for the total synthesis of (S)-tylophorine via catalytic asymmetric allylation and a one-pot DMAP-promoted isocyanate formation/Lewis acid catalyzed cyclization sequence.  

PubMed

A new asymmetric total synthesis of a phenanthroindolizidine alkaloid (S)-tylophorine is reported, which features a catalytic asymmetric allylation of aldehydes and an unexpected one-pot DMAP promoted isocyanate formation and Lewis acid catalyzed intramolecular cyclization reaction. In addition, White's direct C-H oxidation catalyst system converting monosubstituted olefins to linear allylic acetates was also employed for late-stage transformation. PMID:24756131

Su, Bo; Zhang, Hui; Deng, Meng; Wang, Qingmin

2014-06-14

363

Selective access to both diastereoisomers in an enantioselective intramolecular Michael reaction by using a single chiral organocatalyst and application in the formal total synthesis of (-)-epibatidine.  

PubMed

Two in one: Both diastereoisomers of 4-nitro-3-substituted cyclohexanones are accessed selectively by an intramolecular Michael reaction using a single chiral aminocatalyst (see scheme). Mechanistic studies show that the reaction is selective for the cis-diastereoisomer and that the trans-diastereoisomer arises over time. DFT calculations suggest that the cis-selectivity is due to a favorable electrostatic interaction between the iminium ion and the nucleophile. PMID:22907652

Jensen, Kim L; Weise, Christian F; Dickmeiss, Gustav; Morana, Fabio; Davis, Rebecca L; Jørgensen, Karl Anker

2012-09-17

364

Organocatalytic enantioselective construction of multi-functionalized spiro oxindole dienes.  

PubMed

A diastereo- and enantio-selective domino Michael-cyclization-tautomerization reaction of isatylidene malononitriles with ?,?-dicyanoalkenes catalyzed by a cinchona alkaloid-derived bifunctional thiourea catalyst has been developed. A series of multi-functionalized spiro oxindole diene derivatives have been obtained in good to excellent yields (up to 97%) with good to excellent enantioselectivities (up to 96%) as well as good diastereoselectivities (up to 7.9?:?1). In addition, an anomalous temperature effect on the enantioselectivity has also been studied for this transformation. PMID:24840651

Huang, Xiao-Fei; Zhang, Ya-Fei; Qi, Zheng-Hang; Li, Nai-Kai; Geng, Zhi-Cong; Li, Kun; Wang, Xing-Wang

2014-07-01

365

Promiscuous enantioselective (-)-?-lactamase activity in the Pseudomonas fluorescens esterase I.  

PubMed

A promiscuous but very enantioselective (-)-?-lactamase activity in the kinetic resolution of the Vince lactam (2-azabicyclo[2.2.1]hept-5-en-3-one) was detected in the Pseudomonas fluorescens esterase I (PFEI). The lactamase activity was increased 200-fold by the introduction of a point mutation and resulted as enantioselective as the Microbacterium sp. enzyme used industrially in this resolution. The structural and mechanistic determinants for the catalytic promiscuity and enantioselectivity were identified by molecular modeling, setting a ground stone to engineer further amidase-related activities from this esterase. PMID:22359066

Torres, Leticia L; Schliessmann, Anna; Schmidt, Marlen; Silva-Martin, Noella; Hermoso, Juan A; Berenguer, José; Bornscheuer, Uwe T; Hidalgo, Aurelio

2012-05-01

366

Facile synthesis and biosensing application of hybrid zinc nanoparticles.  

PubMed

Hybrid zinc nanoparticles were synthesized by adding thioglycolic acid (TGA) into a ZnO-particle synthesis procedure. Compared to the ZnO particles prepared without TGA, the hybrid nanoparticles are markedly different in their morphology, chemical composition, and growth kinetics. Moreover, they display colloidal stability and appropriate surface properties for bioconjugation. To demonstrate their biosensing application, the hybrid nanoparticles were conjugated and applied as biolabels or signal transducers in a sandwich immunoassay for mouse IgG. The immunoassay fluorescence signal was obtained by releasing zinc ions from these nanoparticle labels and further incubating the released zinc ions with zinc-sensitive fluorescence indicator Fluozin-3. The immunoassay presents a dynamic detection range from 10 pM to 1 nM. PMID:22905498

Cowles, Chad; Chen, Benjamin; Zhu, Xiaoshan

2012-06-01

367

A new membrane probing steroidal spin label: synthesis and applications.  

PubMed

The applicability of a new steroidal spin label, 3-oxo-androstan-17 beta-yl-(2",2",6",6"-tetramethyl-N-oxyl) piperidyl butan-1',4'-dioate, in studying the phase transition properties of model membrane L-alpha-dipalmitoyl phosphatidyl choline (DPPC) in the presence and absence of drugs has been explored. Its synthesis and characterization has been described herein. Besides, the localization of this spin label in lipid liposomes has been studied using electron spin resonance (ESR), differential scanning calorimetry (DSC) and 1H and 31P NMR spectroscopic techniques. The label has also been used to study the permeability of epinephrine into membrane. The results show that the spin label has a good potential as a spin probe in the study of biomembranes. PMID:10983412

Katoch, R; Trivedi, G K; Phadke, R S

2000-02-01

368

Oligothiophene semiconductors: synthesis, characterization, and applications for organic devices.  

PubMed

Oligothiophenes provide a highly controlled and adaptable platform to explore various synthetic, morphologic, and electronic relationships in organic semiconductor systems. These short-chain systems serve as models for establishing valuable structure-property relationships to their polymer analogs. In contrast to their polymer counterparts, oligothiophenes afford high-purity and well-defined materials that can be easily modified with a variety of functional groups. Recent work by a number of research groups has revealed functionalized oligothiophenes to be the up-and-coming generation of advanced materials for organic electronic devices. In this review, we discuss the synthesis and characterization of linear oligothiophenes with a focus on applications in organic field effect transistors and organic photovoltaics. We will highlight key structural parameters, such as crystal packing, intermolecular interactions, polymorphism, and energy levels, which in turn define the device performance. PMID:24641239

Zhang, Lei; Colella, Nicholas S; Cherniawski, Benjamin P; Mannsfeld, Stefan C B; Briseno, Alejandro L

2014-04-23

369

Design, synthesis, and application of stimulus-sensing biohybrid hydrogels.  

PubMed

A key feature of any living system is the ability to sense and react to the environmental stimuli. The biochemical characterization of the underlying biological sensors combined with advances in polymer chemistry has enabled the development of stimulus-sensitive biohybrid materials that translate most diverse chemical and biological input into a precise change in material properties. In this review article, we first describe synthesis strategies of how biological and chemical polymers can functionally be interconnected. We then provide a comprehensive overview of how the different properties of biological sensor molecules such as competitive target binding and allosteric modulation can be harnessed to develop responsive materials with applications in tissue engineering and drug delivery. PMID:23982955

Hotz, Natascha; Wilcke, Louisa; Weber, Wilfried

2013-10-01

370

Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma  

PubMed Central

Glioblastoma multiforme (GBM) is the most common and most aggressive malignant primary brain tumor in humans. Current GBM treatment includes surgery, radiation therapy, and chemotherapy, sometimes supplemented with novel therapies. Despite recent advances, survival of GBM patients remains poor. Major challenges in GBM treatment are drug delivery across the blood–brain barrier, restriction of damage to healthy brain tissues, and limitation of resistance to therapies. This article reviews recent advances in the application of magnetic nanoparticles (MNPs), gold nanorods (GNRs), and carbon nanotubes (CNTs) for hyperthermia ablation of GBM. First, the article introduces GBM, its current treatment, and hyperthermia as a potential modality for the management of GBM. Second, it introduces MNPs, GNRs, and CNTs as inorganic agents to induce hyperthermia in GBM. Third, it discusses different methodologies for synthesis of each inorganic agent. Finally, it reviews in vitro and in vivo studies in which MNPs, GNRs, and CNTs have been applied for hyperthermia ablation and drug delivery in GBM.

Verma, Jyoti; Lal, Sumit; Van Noorden, Cornelis JF

2014-01-01

371

Hollow magnetic nanoparticles: synthesis and applications in biomedicine.  

PubMed

Magnetic hollow particles (MHP) are widely used in biomedicine field due to their biocompatibility, low-toxicity, low-density and the large fraction void space in the MHP, which have been successfully used to encapsulate and control drugs release, and magnetic resonance imaging (MRI). This review focuses on all kinds of MHP preparation method, compares the advantages and disadvantages in the process of synthesis, and introduces especially the special formation mechanisms such as the Kirkendall effect and Ostwald ripening. Both the compatible interior space and good magnetism of magnetic hollow structures enable them promising and unique candidates as biomedicine vehicles. Particularly, the progress of MHP widely used in the biomedical engineering applications containing drug delivery and magnetic resonance imaging are described. The main problems and the directions in the future researches are pointed out. PMID:22849051

He, Quanguo; Wu, Zhaohui; Huang, Chunyan

2012-04-01

372

Graphene Oxide: Synthesis, Characterization, Electronic Structure, and Applications  

NASA Astrophysics Data System (ADS)

While graphite oxide was first identified in 1855 [1, 2], the recent discovery of stable graphene sheets has led to renewed interest in the chemical structure and potential applications of graphene oxide sheets. These structures have several physical properties that could aid in the large scale development of a graphene electronics industry. Depending on the degree of oxidization, graphene oxide layers can be either semiconducting or insulating and provide an important complement to metallic graphene layers. In addition, the electronic and optical properties of these films can be controlled by the selective removal or addition of oxygen. For example, selective oxidationof graphene sheets could lead to electronic circuit fabrication on the scale of a single atomic layer. Graphene oxide is also dispersible in water and other solvents and this provides a facile route for graphene deposition on a wide range of substrates for macroelectronics applications. Although graphite oxide has been known for roughly 150 years, key questions remain in regards to its chemical structure, electronic properties, and fabrication. Answering these issues has taken on special urgency with the development of graphene electronics. In this chapter, we will provide an overview of the field with special focus on synthesis, characterization, and first principles analysis of bonding and electronic structures. Finally, we will also address some of the most promising applications for graphene oxide in electronics and other industries.

Stewart, Derek A.; Mkhoyan, K. Andre

373

Enantioselective construction of remote quaternary stereocentres.  

PubMed

Small molecules that contain all-carbon quaternary stereocentres-carbon atoms bonded to four distinct carbon substituents-are found in many secondary metabolites and some pharmaceutical agents. The construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for synthesizing quaternary stereocentres that are remote from other functional groups are underdeveloped. Here we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. This method provides direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ?-aryl carbonyl compounds, because the unsaturation of the alkene is relayed to the alcohol, resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocentres along the alkyl chain, which links the alkene and the alcohol, in which the stereocentre is preserved. The method described allows access to diverse molecular building blocks containing an enantiomerically enriched quaternary centre. PMID:24717439

Mei, Tian-Sheng; Patel, Harshkumar H; Sigman, Matthew S

2014-04-17

374

Enantioselective construction of remote quaternary stereocentres  

NASA Astrophysics Data System (ADS)

Small molecules that contain all-carbon quaternary stereocentres--carbon atoms bonded to four distinct carbon substituents--are found in many secondary metabolites and some pharmaceutical agents. The construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for synthesizing quaternary stereocentres that are remote from other functional groups are underdeveloped. Here we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. This method provides direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ?-aryl carbonyl compounds, because the unsaturation of the alkene is relayed to the alcohol, resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocentres along the alkyl chain, which links the alkene and the alcohol, in which the stereocentre is preserved. The method described allows access to diverse molecular building blocks containing an enantiomerically enriched quaternary centre.

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-04-01

375

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules.  

PubMed

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules. PMID:25001884

Ben-Moshe, Assaf; Wolf, Sharon Grayer; Sadan, Maya Bar; Houben, Lothar; Fan, Zhiyuan; Govorov, Alexander O; Markovich, Gil

2014-01-01

376

Total Synthesis of (+)-Lepadin F  

PubMed Central

An enantioselective total synthesis of (+)-lepadin F is described. The synthetic sequence features an intermolecular aza-[3 + 3] annulation, homologation of a vinylogous amide via Eschenmoser’s episulfide contraction, and a highly stereoselective hydrogenation essential for achieving the 1,3-anti relative stereochemistry at C2 and C8a.

Li, Gang; Hsung, Richard P.; Slafer, Brian W.; Sagamanova, Irina K.

2009-01-01

377

Total synthesis of (+)-kopsihainanine A.  

PubMed

Total synthesis of (+)-kopsihainanine A was accomplished on the basis of (i) Stoltz's enantioselective decarboxylative asymmetric allylation and (ii) the proposed biogenetic pathway from the related alkaloid, kopsihainanine B. In addition, HPLC analysis of the synthetic (+)-kopsihainanine A confirmed its ee to be 99% with [?] = 25.35. PMID:24756124

Mizutani, Masaya; Yasuda, Shigeo; Mukai, Chisato

2014-06-01

378

Enantioselective effects of herbicide imazapyr on Arabidopsis thaliana.  

PubMed

The enantioselective toxicity of chiral herbicides in the environment is of increasing concern. To investigate the enantioselective effects of the chiral herbicide imazapyr on target organisms, we exposed Arabidopsis thaliana to imazapyr enantiomers and racemate. The results show that imazapyr was enantioselectively toxic to A. thaliana. The total chlorophyll content in A. thaliana was affected more by (+)-imazapyr than (±)-imazapyr and (-)-imazapyr. Concentrations of proline and malondialdehyde reflected a toxic effect in the order of (+)-imazapyr > (±)-imazapyr > (-)-imazapyr at every concentration. Acetolactate synthase (ALS) activity was inhibited more by (+)-imazapyr than (±)-imazapyr or (-)-imazapyr. At 100 mg L(-1) of imazapyr, ALS activity was 78%, 43%, and 19% with (-)-, (±)-, and (+)-imazapyr, respectively. The results suggest the significant enantioselective toxicity of imazapyr in A. thaliana for greater toxicity with (+)-imazapyr than (±)-imazapyr and (-)-imazapyr, which suggests that (+)-imazapyr has more herbicidal effect. PMID:25035913

Hsiao, Yu-Ling; Wang, Yei-Shung; Yen, Jui-Hung

2014-09-01

379

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 ...

380

A genetic selection system for evolving enantioselectivity of enzymes.  

PubMed

As an alternative to screening in the directed evolution of enantioselective enzymes, a selection system has been implemented for a lipase-catalyzed hydrolytic kinetic resolution of a chiral ester. PMID:18997932

Reetz, Manfred T; Höbenreich, Horst; Soni, Pankaj; Fernández, Layla

2008-11-21

381

Synthesis of internally functionalized silica nanoparticles for theranostic applications  

NASA Astrophysics Data System (ADS)

This thesis addresses the synthesis and characterization of novel inorganic silica nanoparticle hybrids. It focuses in large part on their potential applications in the medical field. Silica acts as a useful carrier for a variety of compounds and this thesis silica will demonstrate its use as a carrier for boron or gadolinium. Boron-10 and gadolinium-157 have been suggested for the radiological treatment of tumor cells through the process called neutron capture therapy (NCT). Gadolinium is also commonly used as a Magnetic Resonance Imaging (MRI) contrast agent. Particles that carry it have potential theranostic applications of both imaging and treating tumors. Chapter 1 presents a background on synthetic strategies and usages of silica nanoparticles, and NCT theory. Chapter 2 describes a procedure to create mesoporous metal chelating silica nanoparticles, mDTTA. This is achieved via a co-condensation of tetraethoxysilane (TEOS) and 3-trimethoxysilyl-propyl diethylenetriamine (SiDETA) followed by a post-synthesis modification step with bromoacetic acid (BrAA). These particles have a large surface area and well-defined pores of ~2 nm. The mDTTA nanoparticles were used to chelate the copper(II), cobalt(II) and gadolinium(III). The chelating of gadolinium is the most interesting since it can be used as a MRI contrast agent and a neutron capture therapeutic. The synthetic procedure developed also allows for the attachment of a fluorophore that gives the gadolinium chelating mDTTA nanoparticles a dual imaging modality. Chapter 3 presents the synthetic method used to produce two classes of large surface area organically modified silica (ORMOSIL) nanoparticles. Condensating the organosilane vinyltrimethoxysilane in a micellar solution results in nanoparticles that are either surface rough (raspberry-like) or mesoporous nanoparticles, which prior to this thesis has not been demonstrated in ORMOSIL chemistry. Furthermore, the vinyl functionalities are modified, using hydroboration, to make the nanoparticles into water-dispersible boron carriers that also have potential boron neutron capture therapy (BNCT) applications. Lastly, Chapter 4 provides a general description of NCT, specifically that involving boron-10 and gadolinium-157. It further describes the synthetic methodology used in producing fatty acid coated boron nanoparticles (BNPs). The BNPs are encapsulated with silica to add a hydrophilic shell so that they can potentially be used in biological systems as BNCT agents. The silica shell is also modified with a fluorophore, dansyl chloride, so that the particle hybrid could be imaged during cell studies.

Walton, Nathan Isaac

382

Catalytic enantioselective epoxidation of tertiary allylic and homoallylic alcohols.  

PubMed

An efficient and versatile method for the enantioselective epoxidation of both tertiary allylic and homoallylic alcohols catalyzed by Hf(IV)-bishydroxamic acid (BHA) complexes is described. Asymmetric epoxidation, kinetic resolution, and desymmetrization have been developed, demonstrating the flexible nature of the Hf(IV)-BHA system. This is the first report in which these substrates were obtained with enantioselectivities of up to 99%. PMID:23406082

Olivares-Romero, José Luis; Li, Zhi; Yamamoto, Hisashi

2013-03-01

383

Salen promoted enantioselective Nazarov cyclizations of activated and unactivated dienones.  

PubMed

A novel class of chiral 5,5'-di(2,4,6-trialkyl)aryl salen-metal complexes have been developed and shown to catalyze highly enantioselective Nazarov cyclization reactions, giving rise to cyclopentenoids in 90:10-98:2 er. Significantly, the catalysts also promote, for the first time, highly enantioselective Nazarov reactions of "unactivated" dienones, producing hydrindenone products having in place three contiguous chiral centers. PMID:23506509

Hutson, Gerri E; Türkmen, Yunus E; Rawal, Viresh H

2013-04-01

384

Photopolymerizable and injectable polyurethanes for biomedical applications: synthesis and biocompatibility.  

PubMed

Two types of photopolymerizable and injectable polyurethane acrylates (PUAs), based on poly(propylene glycol) or poly(caprolactone diol) and hydroxyethyl methacrylate, were synthesized and characterized in order to obtain information regarding their use as an injectable material for biomedical applications. Structural characteristics of the biomaterials, including the degree of phase separation, were evaluated by Fourier transform infrared spectroscopy. The viscosities of the obtained biomaterials make them suitable for injection, molding and photopolymerization using visible light, as demonstrated by the injection test. The cured polymers had mechanical properties comparable to those of certain soft tissues, such as skin. An in vitro cell-polyurethane cytotoxicity study was carried out with mesenchymal stem cells from rat tibias and femurs. The proliferation/viability of the cells in the presence of the synthesized material was assessed by the MTT assay, collagen synthesis analysis and the expression of alkaline phosphatase. The results that were obtained through the in vitro tests indicated that PUAs are cytocompatible. The in vivo experiments were correlated with the in vitro tests and showed low levels of toxicity for the obtained biomaterials. Histology cross-sections showed that the biomaterials induced no significant inflammatory reaction. Our study demonstrates the potential for using synthesized photocurable polyurethanes in biomedical applications. Furthermore, the obtained injectable polymer systems employ minimally invasive procedures and can be molded in situ before photopolymerization with visible light. PMID:20193783

Pereira, Ildeu H L; Ayres, Eliane; Patrício, Patrícia S; Góes, Alfredo M; Gomide, Viviane S; Junior, Eduardo P; Oréfice, Rodrigo L

2010-08-01

385

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

2011-04-01

386

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

387

Sustainable synthesis, characterization, and applications of metal oxide nanostructures  

NASA Astrophysics Data System (ADS)

Nanomaterials have attracted significant research focus due to their advantageous and unique properties (i.e. electronic, magnetic, optical, and mechanical) as compared with the bulk. Metal oxide nanostructures are of particular interest, as they are very robust and display high chemical and thermal stability, while offering a diverse array of fascinating properties. By reliably controlling the size, morphology, composition, and crystallinity of these nanostructures, their properties can be tuned for a specific purpose. These advantageous tailorable properties render them as ideal candidates for many applications such as catalysis, sensing, electronics, optoelectronics, energy storage, and even medicine. Driven by their increased popularity and potential applications, efforts to synthesize nanomaterials have moved toward environmentally-friendly methodologies, such as wet-chemical, molten-salt, hydrothermal, and sol-gel methods. We will discuss the green synthesis of strontium ruthenate (SrRuO 3), the yttrium manganese oxides (YMnO3 and YMn2O 5), and the magnetic spinel ferrites (MFe2O4 where 'M' is Mg, Fe, Co, Ni, Cu, and Zn) and our ability to reliably tune their properties for various applications. The effects of the molten salt parameters on the resulting particle size and morphology were explored for SrRuO 3 and the yttrium manganese oxides. For example, rapid cooling rates and the use of surfactants allowed us to produced faceted octahedra of SrRuO 3, which resulted in a 4-fold enhancement of their activity towards methanol oxidation with respect to smooth rounded particles. Similarly, using the hydrothermal method, we generated ferrite nanoparticles of different compositions and sizes. We investigated their potential as contrast agents for magnetic resonance imaging (MRI) and as photocatalysts, and observed significant differences as a function of both size and composition. Similarly, we will also examine surface and structural effects upon the electronic properties of V2O 3 nanowires.

Tiano, Amanda Lyn

388

Synthesis, Characterization and Biosensing Application of Photon Upconverting Nanoparticles.  

PubMed

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 NaYF(4):Yb(3+), Er(3+) 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. PMID:21191468

Kumar, Manoj; Zhang, Peng

2009-02-16

389

Colloidal-sized metal-organic frameworks: synthesis and applications.  

PubMed

Colloidal metal-organic frameworks (CMOFs), nanoporous colloidal-sized crystals that are uniform in both size and polyhedral shape, are crystals composed of metal ions and organic bridging ligands, which can be used as building blocks for self-assembly in organic and aqueous liquids. They stand in contrast to conventional metal-organic frameworks (MOFs), which scientists normally study in the form of bulk crystalline powders. However, powder MOFs generally have random crystal size and shape and therefore do not possess either a definite mutual arrangement with adjacent particles or uniformity. CMOFs do have this quality, which can be important in vital uptake and release kinetics. In this Account, we present the diverse methods of synthesis, pore chemistry control, surface modification, and assembly techniques of CMOFs. In addition, we survey recent achievements and future applications in this emerging field. There is potential for a paradigm shift, away from using just bulk crystalline powders, towards using particles whose size and shape are regulated. The concept of colloidal MOFs takes into account that nanoporous MOFs, conventionally prepared in the form of bulk crystalline powders with random crystal size, shape, and orientation, may also form colloidal-sized objects with uniform size and morphology. Furthermore, the traditional MOF functions that depend on porosity present additional control over those MOF functions that depend on pore interactions. They also can enable controlled spatial arrangements between neighboring particles. To begin, we discuss progress regarding synthesis of MOF nano- and microcrystals whose crystal size and shape are well regulated. Next, we review the methods to modify the surfaces with dye molecules and polymers. Dyes are useful when seeking to observe nonluminescent CMOFs in situ by optical microscopy, while polymers are useful to tune their interparticle interactions. Third, we discuss criteria to assess the stability of CMOFs for various applications. In another section of this Account, we give examples of supracrystal assembly in liquid, on substrates, at interfaces, and under external electric fields. We end this Account with discussion of possible future developments, both conceptual and technological. PMID:24328052

Sindoro, Melinda; Yanai, Nobuhiro; Jee, Ah-Young; Granick, Steve

2014-02-18

390

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

391

Synthesis, Characterization, and Application of Gold Nanoparticles in Green Nanochemistry Dye-Sensitized Solar Cells.  

National Technical Information Service (NTIS)

Gold (Au) nanoparticles (NPs) have a wide range of scientific applications due to their innate ability to efficiently bind with organic and bio molecules in conjunction with possessing excellent optical properties. In this experiment, Au NPs were synthesi...

H. E. Cramer M. H. Griep S. P. Karna

2012-01-01

392

A New Synthesis of Vinylene Sulfones. Application to the Monomethyl Derivative.  

National Technical Information Service (NTIS)

A new method for the synthesis of vinylene sulfones and its successful application to an aliphatic example, the monomethyl derivative, is reported. The results show that the recent suggestion that the relative stabilities of substituted vinylene sulfones ...

L. A. Carpino R. H. Rynbrandt

1966-01-01

393

Enantioselective ?-Amination of 1,3-Dicarbonyl Compounds Using Squaramide Derivatives as Hydrogen Bonding Catalysts  

PubMed Central

Catalytic enantioselective ?-hydrazination of 1,3-dicarbonyl compounds with azodicarboxylates was investigated in the presence of our newly developed hydrogen bonding catalyst, squaramide 3j. High yields and high enantioselectivities were achieved with low catalyst loading under mild conditions.

Konishi, Hideyuki; Lam, Tin Yiu; Malerich, Jeremiah P.; Rawal, Viresh H.

2010-01-01

394

Enantioselective cascade formal reductive insertion of allylic alcohols into the c(o)-C bond of 1,3-diketones: ready access to synthetically valuable 3-alkylpentanol units.  

PubMed

An unprecedented cascade reaction combining dual iron-amine-catalyzed enantioselective functionalization of allylic alcohols and chemoselective acyl transfer is presented. It allows, from diketones and allylic alcohols, preparation of efficiently functionalized ?-chiral alcohols in up to 96% yield and 96:4 er. The interest of this redox-, atom-, and step-economomical approach was further demonstrated in the short synthesis of several key fragments of biologically active natural products or odorant molecules. PMID:24849709

Roudier, Mylène; Constantieux, Thierry; Quintard, Adrien; Rodriguez, Jean

2014-06-01

395

Review on the progress in synthesis and application of magnetic carbon nanocomposites  

Microsoft Academic Search

This review focuses on the synthesis and application of nanostructured composites containing magnetic nanostructures and carbon-based materials. Great progress in fabrication of magnetic carbon nanocomposites has been made by developing methods including filling process, template-based synthesis, chemical vapor deposition, hydrothermal\\/solvothermal method, pyrolysis procedure, sol-gel process, detonation induced reaction, self-assembly method, etc. The applications of magnetic carbon nanocomposites expanded to a

Maiyong Zhu; Guowang Diao

2011-01-01

396

Enantioselective disposition of clenbuterol in rats.  

PubMed

Clenbuterol is a long-acting ?2-adrenoceptor agonist and bronchodilator that is used for the treatment of asthma, but the desired activities reside almost exclusively in the (-)-R-enantiomer. This study examined enantioselectivity in the disposition of clenbuterol following administration of clenbuterol racemate to rats. Concentrations of clenbuterol enantiomers in plasma, urine and bile were determined by LC-MS/MS assay with a Chirobiotic T column. This method was confirmed to show high sensitivity, specificity and precision, and clenbuterol enantiomers in 0.1?ml volumes of plasma were precisely quantified at concentrations as low as 0.25?ng/ml. The pharmacokinetic profiles of clenbuterol enantiomers following intravenous and intraduodenal administration of clenbuterol racemate (2?mg/kg) in rats were significantly different. The distribution volume of (-)-R-clenbuterol (9.17?l/kg) was significantly higher than that of (+)-S-clenbuterol (4.14?l/kg). The total body clearance of (-)-R-clenbuterol (13.5?ml/min/kg) was significantly higher than that of the (+)-S-enantiomer (11.5?ml/min/kg). An in situ absorption study in jejunal loops showed no difference in the residual amount between the (-)-R- and (+)-S-enantiomers. Urinary clearance was the same for the two enantiomers, but biliary excretion of (-)-R-clenbuterol was higher than that of the (+)-S-enantiomer. The fractions of free (non-protein-bound) (-)-R- and (+)-S-clenbuterol in rat plasma were 48.8% and 33.1%, respectively. These results indicated that there are differences in the distribution and excretion of the clenbuterol enantiomers, and these may be predominantly due to enantioselective protein binding. Copyright © 2013 John Wiley & Sons, Ltd. PMID:24323748

Hirosawa, Iori; Ishikawa, Mai; Ogino, Mio; Ito, Hiroshi; Hirao, Takuya; Yamada, Harumi; Asahi, Mariko; Kotaki, Hajime; Sai, Yoshimichi; Miyamoto, Ken-Ichi

2014-05-01

397

Perfluopolyether (PFPE) (poly)diacyl peroxides: synthesis and applications  

Microsoft Academic Search

This paper deals with the synthesis of perfluoropolyether (PFPE) (poly)diacyl peroxides with mean EWs ranging from 500 to 4000geq.?1 via H2O2 and base from the corresponding PFPE diacyl halides, their decomposition (thermal and hydrolytic) and the synthesis of the corresponding di-halides by the reaction with elemental halides. A great advantage of this novel synthesis over other synthetic approaches is the

Ivan Wlassics; Vito Tortelli; Marco Sala; Donato Montrone

2003-01-01

398

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation  

PubMed Central

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)]OTf2 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.

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

2013-01-01

399

Synthesis and application of hepatitis E virus peptides to diagnosis.  

PubMed

Based on computer analysis of hydrophobicity and prediction of secondary structures for the full-length putative proteins encoded by open reading frame-1 (ORF-1), ORF-2 and ORF-3 of hepatitis E virus (HEV), we selected antigenic regions with hydrophilicity, beta-turn, and beta-sheet, and synthesized 7 peptides of possible epitope-containing regions of the polypeptide encoded by all 3 ORFs of HEV genomic RNA by Merrifield's method of solid-phase synthesis. The synthetic peptides were screened and identified by solid-phase enzyme-linked immunosorbent assay (ELISA). Three of the peptides (EH174 from ORF-1, EH286 from ORF-2 and EH362 from ORF-3) showed antigenic activity and possible application for the development of anti-HEV test kits (the peptide-based ELISA). The laboratory experiments and clinical trials showed that the kits, using a set of 3 synthetic HEV peptides as coating antigens, were of high specificity and exhibited good reproducibility. The small-scale seroepidemiological survey indicated high seroprevalence (14.3%) of anti-HEV in Tibetan populations. Additionally, the results also demonstrated good agreement with clinical findings, suggesting that the test kits will be of major use for immunodiagnosis and seroepidemiological surveys of HEV infection. PMID:8576309

Qi, Z; Cui, D; Pan, W; Yu, C; Song, Y; Cui, H; Arima, T

1995-09-01

400

Synthesis of Boron Nitride Nanotubes for Engineering Applications  

NASA Technical Reports Server (NTRS)

Boron Nitride nanotubes (BNNT) are of interest to the scientific and technical communities for many of the same reasons that carbon nanotubes (CNT) have attracted large amounts of attention. Both materials have potentially unique and significant properties which may have important structural and electronic applications in the future. However of even more interest than their similarities may be the differences between carbon and boron nanotubes. Whilt boron nitride nanotubes possess a very high modulus similaar to CNT, they are also more chemically and thermally inert. Additionally BNNT possess more uniform electronic properties, having a uniform band gap of approximately 5.5 eV while CNT vary from semi-conductin to conductor behavior. Boron Nitride nanotubes have been synthesized by a variety of methods such as chemical vapor deposition, arc discharge and reactive milling. Consistently producing a reliable product has proven difficult. Progress in synthesis of 1-2 gram sized batches of Boron Nitride nanotubes will be discussed as well as potential uses for this unique material.

Hurst, Janet; Hull, David; Gorican, Dan

2005-01-01

401

Synthesis, characterizations, and applications of carbon nanotubes and silicon nanowires  

NASA Astrophysics Data System (ADS)

Carbon nanotubes (CNTs) have received great attention because of their unique structure and promising applications in microelectronic devices such as field electron emitters. Silicon nanowires (SiNWs) are also very popular because Si is a well established electronic material. This thesis will present my effort on synthesis, characterizations, and applications of CNTs and SiNWs by thermal chemical vapor deposition (CVD) method. For CNTs growth, block copolymer micelles were used as a template to create large area arrays of metal nanoclusters as catalysts for patterned arrays, and Fe/Al/Fe sandwich film on single crystal magnesium oxide (MgO) substrate was used as the catalyst for growth of long length aligned CNTs by CVD. The factors that affect the structure and length of CNTs have been investigated. CNTs were also grown on etched Si substrate by PECVD method. Continuous dropwise condensation was achieved on a biomimetic two-tier texture with short CNTs deposited on micromachined pillars. Superhydrophobic condensation model was studied. For SiNWs growth, hydrogen gold tetrachloride was uniformly mixed into the salt and decomposed into gold nanoparticles at the growth temperature and acted as the catalyst particles to start the growth of Si nanowires. The as-grown Si nanowires are about 70--90 nm in diameter and up to 200 micrometers long. The salt was completely removed by water rinse after growth. Field emission of aligned CNTs grown on Si substrates and SiNWs on Si substrates and carbon clothes has been studied. A post growth annealing procedure has been found to drastically improve the field emission performance of these CNTs and SiNWs.

Xiong, Guangyong

402

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

403

A computational study of enantioselective adsorption in a homochiral metal–organic framework  

Microsoft Academic Search

The potential application of a homochiral metal–organic framework (MOF) made from cadmium corners and BINOL-type linkers for enantioselective separations of chiral hydrocarbons was investigated using grand canonical Monte Carlo simulations. Adsorption of racemic mixtures of (R,S)-1,3-dimethyl-1,2-propadiene, (R,S)-1,2-dimethylcyclobutane and (R,S)-1,2-dimethylcyclopropane was simulated. The results show that an enantiomeric excess (ee) of over 50% can be achieved for 1,3-dimethyl-1,2-propadiene, while more moderate

Xiaoying Bao; Linda J. Broadbelt; Randall Q. Snurr

2009-01-01

404

Enantioselectivity of a recombinant esterase from Pseudomonas fluorescens towards alcohols and carboxylic acids  

Microsoft Academic Search

A recombinant esterase from Pseudomonas fluorescens (PFE) was produced from E. coli cultures and the enantioselectivity towards a series of racemic substrates was investigated. PFE exhibited high rate and enantioselectivity in the acylation of ?-phenyl ethanol with vinyl acetate in toluene (E>100) and the hydrolysis of the corresponding acetate in phosphate buffer (E=58). In sharp contrast, extremely low enantioselectivity (E

Niels Krebsfänger; Kerstin Schierholz; Uwe T Bornscheuer

1998-01-01

405

DNA Synthesis, Assembly and Applications in Synthetic Biology  

PubMed Central

The past couple of years saw exciting new developments in microchip-based gene synthesis technologies. Such technologies hold the potential for significantly increasing the throughput and decreasing the cost of gene synthesis. Together with more efficient enzymatic error correction and genome assembly methods, these new technologies are pushing the field of synthetic biology to a higher level.

Ma, Siying; Tang, Nicholas; Tian, Jingdong

2012-01-01

406

Enantioselective syntheses of ?-amino-?-hydroxy acids, [ 15 N]- L-allo threonine and [ 15N]-L-threonine  

Microsoft Academic Search

The enantioselective synthesis of [15N]-L-allothreonine from ethyl (S)-lactatevia methyl (S)-3-methoxymethoxy-2-oxobutanoate15 is described. The stereogenic centre at C-2 was established by a one-pot, dual enzyme catalysed hydrolysis of the ester (by a lipase) and reductive amination of the ketone of 15 (with leucine dehydrogenase) to give, after deprotection, [15N]-(2S,3S)-2-amino-3-hydroxybutanoic acid as a single diastereomer in 93% yield. [15N]-L-Threonine was prepared by

Andrew Sutherland; Christine L. Willis

1997-01-01

407

Functional Group Tolerant Nickel-Catalyzed Cross-Coupling Reaction for Enantioselective Construction of 30 Methyl-Bearing Stereocenters  

PubMed Central

The first Negishi nickel-catalyzed stereospecific cross-coupling reaction of secondary benzylic esters is reported. A series of traceless directing groups are evaluated for ability to promote cross-coupling with dimethylzinc. Esters with a chelating thioether derived from commercially-available 2-(methylthio)acetic acid are most effective. The products are formed in high yield and with excellent stereospecificity. A variety of functional groups are tolerated in the reaction including alkenes, alkynes, esters, amines, imides, and O-, S-, and N-heterocycles. The utility of this transformation is highlighted in the enantioselective synthesis of a retinoic acid receptor (RAR) agonist and a fatty acid amide hydrolase (FAAH) inhibitor.

Wisniewska, Hanna M.; Swift, Elizabeth C.; Jarvo, Elizabeth R.

2013-01-01

408

Nanomanufacturing of silica nanowires: Synthesis, characterization and applications  

NASA Astrophysics Data System (ADS)

In this research, selective and bottom-up manufacturing of silica nanowires on silicon (Si) and its applications has been investigated. Localized synthesis of these nanowires on Si was achieved by metal thin film catalysis and metal ion implantation based seeding approach. The growth mechanism of the nanowires followed a vapor-liquid-solid (VLS) mechanism. Mass manufacturing aspects such as growth rate, re-usability of the substrate and experimental growth model were also investigated. Further, silica nanowires were explored as surface enhanced Raman (SER) substrate and immunoassay templates towards optical and electrochemical detection of cancer biomarkers respectively. Investigating their use in photonic applications, optically active silica nanowires were synthesized by erbium implantation after nanowire growth and implantation of erbium as a metal catalyst in Si to seed the nanowires. Ion implantation of Pd in Si and subsequent annealing in Ar at 1100 0 C for 60 mins in an open tube furnace resulted in silica nanowires of diameters ranging from 15 to 90 nm. Similarly, Pt was sputtered on to Si and further annealed to obtain silica nanowires of diameters ranging from 50 to 500 nm. Transmission electron microscopy studies revealed the amorphous nature of the wires. In addition, nano-sized Pd catalyst was found along the body of the nanowires seeded by Pd implantation into Si. After functionalization of the wires with 3 - AminoPropylTriMethoxySilane (APTMS), the Pd decorated silica nanowires served as an SER substrate exhibiting a sensitivity of 10 7 towards the detection of interleukin-10 (IL-10, a cancer biomarker) with higher spatial resolution. Voltammetric detection of IL-10 involved silica nanowires synthesized by Pd thin film catalysis on Si as an immunoassay template. Using the electrochemical scheme, the presence of IL-10 was detected down to 1fg/mL in ideal pure solution and 1 pg/mL in clinically relevant samples. Time resolved photoluminescence (PL) results from the Er doped silica nanowires indicate a sharp emission around 1.54 microm representative of the I13/2 to I15/2 transition in Erbium. Also, a five-fold increase in the PL intensity and 30% augment in luminescence life time have been observed in nanowires when compared to fused silica sample prepared under similar conditions. The experimental results indicate the potential of silica nanowires in a wide variety of applications such as the development of orthogonal biosensors, fabrication of metallic nanowires, and environmental sensing probes.

Sekhar, Praveen Kumar

409

Synthesis of orthogonally protected azahistidine: application to the synthesis of a GHK analogue.  

PubMed

The synthesis of various orthogonally protected azahistidine derivatives are obtained via 1,3-dipolar cycloaddition reactions. The newly obtained amino-acids can be selectively deprotected either at the side chain or at the N-terminus of the amino acid and should thus allow the use of these derivatives in (solid phase) peptide synthesis. PMID:19219577

Roux, Stéphane; Ligeti, Melinda; Buisson, David-Alexandre; Rousseau, Bernard; Cintrat, Jean-Christophe

2010-01-01

410

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

2012-06-01

411

Asymmetric synthesis of fortucine and reassignment of its absolute configuration.  

PubMed

A convergent and enantioselective synthesis of fortucine was achieved from the starting materials tyrosine methyl ester and 3-hydroxy-4-methoxybenzaldehyde. The synthesis is based on two key steps mediated by a hypervalent iodine reagent. This work has enabled us to reassign the absolute configuration of the natural product reported in the literature. PMID:24782396

Beaulieu, Marc-André; Ottenwaelder, Xavier; Canesi, Sylvain

2014-06-16

412

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

2012-07-01

413

Synthesis, characterization and potential applications of iron-platinum nanoparticles  

NASA Astrophysics Data System (ADS)

Monodisperse FePt nanoparticles with controlled size and geometry have drawn great attention in the last decade for fundamental scientific studies and for their potential applications in advanced materials and devices such as ultra-high-density magnetic recording media, exchange-coupled nanocomposite magnets, biomedicines and nanodevices. This dissertation focuses on the synthesis and characterization of FePt nanoparticles and their use in potential applications. The FePt nanoparticles of different size (2 to 16 nm) and shape (spherical, cubic, rod) were synthesized by a chemical solution method. The size and shape of these particles were controlled by adjusting reaction parameters. The as-synthesized FePt nanoparticles have chemically disordered fcc structure and are superparamagnetic at room temperature. Upon heat treatment the nanoparticles were transformed into ordered L10 structure, and high coercivity up to 27 kOe was achieved. Magnetic properties of annealed FePt nanoparticles including magnetization and coercivity were strongly dependent on particle size, shape, composition and annealing temperature. FePt/Fe3O4 bimagnetic nanoparticles with two different morphologies, core/shell and heterodimer, were prepared by coating or attaching Fe3O4 on surface of FePt nanoparticles. The size of FePt and Fe3O4 was tuned very finely to obtain most effective exchange coupling. The heterodimer nanoparticles resulted in relatively poor magnetic properties compared to the core/shell nanoparticles due to insufficient exchange coupling. By optimizing the dimensions of the FePt and Fe3O 4 in core/shell bimagnetic nanoparticles, energy products up to 17.8 MGOe were achieved. FePt/Fe3O4 core/shell and FePt+Fe3O 4 mixed nanoparticles with similar magnetic properties were compacted under 2.0 GPa at 400°C, 500°C and 600°C. A density up to 84% of the full density was achieved. After annealing at 650°C in forming gas, the FePt/Fe3O4 compacted samples were converted into L10 FePt/Fe3Pt magnetic nanocomposite. The nanoscale morphology was retained before and after annealing for bulk samples made from both core/shell and mixed nanoparticles. After annealing, the highest energy product in the bulk samples was 18.1 MGOe based on the theoretical density. The core/shell nanoparticle compacted samples had more effective exchange coupling than the mixed nanoparticle compacted samples. FePt/Au core/shell nanoparticles were successfully synthesized where Au shell was coated by reduction of gold acetate on surface of FePt nanoparticles. The FePt/Au core/shell nanoparticles show ferromagnetism after annealing at optimum temperature without any significant sintering. Also, FePtAu nanoparticles were prepared by doping Au into FePt nanoparticles during the synthesis. By tuning right stoichiometry of the FexPtyAu100-x-y nanoparticles, the phase transition temperature from fcc to L1 0 was reduced by more than 200°C. After annealing at 500°C, the highest coercivity of 18 kOe was obtained from the Fe51Pt 36Au13 nanoparticles compared to 2 kOe from Fe51Pt 49 nanoparticles without any sacrifice in saturation magnetization.

Nandwana, Vikas

414

Synthesis of 1-substituted tetrahydroisoquinolines by lithiation and electrophilic quenching guided by in situ IR and NMR spectroscopy and application to the synthesis of salsolidine, carnegine and laudanosine.  

PubMed

The lithiation of N-tert-butoxycarbonyl (N-Boc)-1,2,3,4-tetrahydroisoquinoline was optimized by in situ IR (ReactIR) spectroscopy. Optimum conditions were found by using n-butyllithium in THF at -50?°C for less than 5?min. The intermediate organolithium was quenched with electrophiles to give 1-substituted 1,2,3,4-tetrahydroisoquinolines. Monitoring the lithiation by IR or NMR spectroscopy showed that one rotamer reacts quickly and the barrier to rotation of the Boc group was determined by variable-temperature NMR spectroscopy and found to be about 60.8?kJ?mol(-1), equating to a half-life for rotation of approximately 30?s at -50?°C. The use of (-)-sparteine as a ligand led to low levels of enantioselectivity after electrophilic quenching and the "poor man's Hoffmann test" indicated that the organolithium was configurationally unstable. The chemistry was applied to N-Boc-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline and led to the efficient synthesis of the racemic alkaloids salsolidine, carnegine, norlaudanosine and laudanosine. PMID:23677770

Li, Xiabing; Leonori, Daniele; Sheikh, Nadeem S; Coldham, Iain

2013-06-10

415

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

416

Highly efficient, enantioselective syntheses of (S)-(+)- and (R)-(-)-dapoxetine starting with 3-phenyl-1-propanol.  

PubMed

A highly efficient, enantioselective sequence has been developed for the synthesis of (S)- and (R)-dapoxetine. The pathways involve the intermediacy of the 6-membered-ring sulfamate esters 4, which were generated by Du Bois asymmetric C-H amination reactions of the prochiral sulfamate 3, catalyzed by the chiral dirhodium(II) complexes. During the course of our research, the absolute configuration of the enantiomer of 4-pheny[1,2,3]oxathiazinane 2,2-dioxide (4r), prepared by the Du Bois asymmetric C-H amination reaction of 3 and the Rh(2)(S-nap)(4) catalyst, is determined to be R and not S as was originally reported. PMID:19957926

Kang, Soyeong; Lee, Hyeon-Kyu

2010-01-01

417

Highly enantioselective reduction of beta,beta-disubstituted aromatic nitroalkenes catalyzed by Clostridium sporogenes.  

PubMed

This is the first report of the use of Clostridium sporogenes extracts for enantioselective reduction of CC double bonds of beta,beta-disubstituted (1) and alpha,beta-disubstituted nitroalkenes (3). Crude enzyme preparations reduced aryl derivatives 1a-e and 1h, in 35-86% yield with > or =97% ee. Reduction of (E)- and (Z)-isomers of 1c gave the same enantiomer of 2c (> or =99% ee). In contrast, alpha,beta-disubstituted nitroalkene 3a was a poor substrate, yielding (S)- 4a in low yield (10-20%), and the ee (30-70% ee) depended on NADH concentration. An efficient synthesis of a library of nitroalkenes 1 is described. PMID:18452336

Fryszkowska, Anna; Fisher, Karl; Gardiner, John M; Stephens, Gill M

2008-06-01

418

Multifocus synthesis and its application to 3D image capturing  

NASA Astrophysics Data System (ADS)

A new technique for the high-resolution image synthesis called multifocus synthesis is presented. As an important extension, the 3-D real-world image capture is discussed. In the approach, the object image is taken at a number of focal distances by a single camera placed at a fixed position. Each of these images are then converted into the multiresolution using the optimized QMF. The resultant volume of coefficients are then analyzed and 3-D distance information is computed.

Yamaguchi, Hirohisa

1993-10-01

419

Synthesis and characterization of iron based nanoparticles for novel applications  

NASA Astrophysics Data System (ADS)

The work in this thesis has been focused on the fabrication and characterization of iron based nanoparticles with controlled size and morphology with the aim: (i) to investigate their properties for potential applications in MICR toners and biomedical field and (ii) to study finite size effects on the magnetic properties of the nanoparticles. For the biomedical applications, core/shell structured iron/iron-oxide and hollow shell nanoparticles were synthesized by thermal decomposition of iron organometallic compounds [Fe(CO)5] at high temperature. Core/shell structured iron/iron-oxide nanoparticles have been prepared in the presence of oleic acid and oleylamine. Particle size and composition was controlled by varying the reaction parameters during synthesis. The as-made particles are hydrophobic and not dispersible in water. Water dispersibility was achieved by ligand exchange a with double hydrophilic diblock copolymer. Relaxometery measurements of the transverse relaxation time T2 of the nanoparticles solution at 3 Tesla confirm that the core/shell nanoparticles are an excellent MRI contrast agent using T2 weighted imaging sequences. In comparison to conventionally used iron oxide nanoparticles, iron/iron-oxide core/shell nanoparticles offer four times stronger T2 shortening effect at comparable core size due to their higher magnetization. The magnetic properties were studied as a function of particle size, composition and morphology. Hollow nanostructures are composed of randomly oriented grains arranged together to make a shell layer and make an interesting class of materials. The hollow morphology can be used as an extra degree of freedom to control the magnetic properties. Owing to their hollow morphology, they can be used for the targeted drug delivery applications by filling the drug inside their cavity. For the magnetic toners applications, particles were synthesized by chemically reducing iron salt using sodium borohydride and then coated with polyethylene glycol. Parameters such as the reactant concentrations and their flow rate were varied to study the effect of particle size, structure and crystallinity on the magnetic nanoparticles. Many different hydrophilic surfactants and polymers electrolytes were investigated for the particles' stability in water. PSSNa was found to be the best coating agent among all the other investigated polymer and surfactants for particles stability in water. Particles have an average size of 50 nm and magnetization above 150 emu/g. It is anticipated that owing to their high saturation magnetization and magneto crystalline anisotropy, the incorporations of PSSNa coated nanoparticles into the MICR toner can reduce the pigment loading and hence optimize the toner quality. The magnetic properties were studied as a function of particle size, composition and morphology. The saturation magnetization and coercivity was found to be strongly dependent on the particle size and morphology. The estimated effective anisotropy of the particles was found to be much higher than their bulk values because of their morphology and finite size effects. Core/shell particles below an average size of 12 nm display superparamagnetism and exchange bias phenomenon. The hollow morphology can be used as an extra degree of freedom to control magnetic properties. The enormously large number of pinned spins at the inner and outer surface and at the interface between the grain boundaries in hollow nanoparticles, gives rise to a very large value of effective anisotropy in these nanoparticles and measured hyteresis loops are minor loops. The surface spin disorder contribution to magnetic behavior is strongly influenced by the cooling field magnitude.

Khurshid, Hafsa

420

One-Dimensional Metal Oxide Nanotubes, Nanowires, Nanoribbons, and Nanorods: Synthesis, Characterizations, Properties and Applications  

Microsoft Academic Search

One dimensional nanomaterials have attracted much attention from academia and industry. A large series of devices have been created on the basis of 1D nanomaterials. Their applications have changed and will continuously change our daily life. In this paper, we will present a comprehensive review on the synthesis, structure characterization, properties and actual and future potential applications of one dimensional

Yu Li; Xiao-Yu Yang; Yi Feng; Zhong-Yong Yuan; Bao-Lian Su

2012-01-01

421

Molecular mechanism of enantioselective proton transfer to carbon in catalytic antibody 14D9  

PubMed Central

Catalytic antibody 14D9 catalyzes the enantioselective protonation of prochiral enol ethers with high enantioselectivity (>99% ee) and a practical turnover (kcat = 0.4 s-1), allowing for preparative scale applications. This antibody represents one of the rare examples of catalytic antibodies promoting acid-catalyzed processes. Antibody 14D9 was cloned and expressed as a chimeric Fab fragment in Escherichia coli. Crystal structures of Fab 14D9 as apo form and of its close analog 19C9 in complex with the transition state analog were determined at 2.8-Å resolution. A series of site-directed mutagenesis experiments was carried out to probe the role of individual active-site amino acids. Proton transfer to carbon is catalyzed by a hydrogen bond network formed by the side chains of AspH101 and TyrL36 with a water molecule serving as a relay. The intermediate oxocarbonium ion formed during the protonation step is trapped by the same water molecule, resulting in an overall syn-addition of water to the enol ether's double bond. The enantioselectivity is caused by steric crowding at the active site, mainly because of the side chain of PheH84. The 20-fold lower activity of 19C9 compared with 14D9 was traced down to residue ThrL46, which forms a nonproductive hydrogen bond with the catalytic residue AspH101, which competes with the critical AspH101—TyrL36 hydrogen bond and therefore reduces catalytic efficiency. The catalytic activity of 19C9 was restored to that of 14D9 by using either site-directed mutagenesis (ThrL46Ala) or chain shuffling.

Zheng, Lei; Baumann, Ulrich; Reymond, Jean-Louis

2004-01-01

422

Controlled Synthesis of Monolayer Graphene Toward Transparent Flexible Conductive Film Application  

Microsoft Academic Search

We demonstrate the synthesis of monolayer graphene using thermal chemical vapor deposition and successive transfer onto arbitrary\\u000a substrates toward transparent flexible conductive film application. We used electron-beam-deposited Ni thin film as a synthetic\\u000a catalyst and introduced a gas mixture consisting of methane and hydrogen. To optimize the synthesis condition, we investigated\\u000a the effects of synthetic temperature and cooling rate in

Byeong-Joo Lee; Han-Young Yu; Goo-Hwan Jeong

2010-01-01

423

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

424

Synthesis of nano-structured materials by laser-ablation and their application to sensors  

Microsoft Academic Search

We describe the synthesis of nano-structured materials of ZnO and Pd by laser ablation and their applications to sensors. The synthesis of ZnO nano-wires was performed by nano-particle assisted deposition (NPAD) where nano-crystals were grown with nano-particles generated by laser-ablating a ZnO sintered target in an Ar background gas. The synthesized ZnO nano-wires were characterized with a scanning electron microscopy

T. Okada; J. Suehiro

2007-01-01

425

Enantioselective Iodolactonization of Disubstituted Olefinic Acids Using a Bifunctional Catalyst  

PubMed Central

The enantioselective iodolactonizations of a series of diversely-substituted olefinic carboxylic acids are promoted by a BINOL-derived, bifunctional catalyst. Reactions involving 5-alkyl- and 5-aryl-4(Z)-pentenoic acids and 6-alkyl- and 6-aryl-5(Z)-hexenoic acids provide the corresponding ?- and ?-lactones having stereogenic C–I bonds in excellent yields and >97:3 er. Significantly, this represents the first organocatalyst that promotes both bromo- and iodolactonization with high enantioselectivities. The potential of this catalyst to induce kinetic resolutions of racemic unsaturated acids is also demonstrated.

Fang, Chao; Paull, Daniel H.; Hethcox, J. Caleb; Shugrue, Christopher R.; Martin, Stephen F.

2012-01-01

426

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.

427

Synthesis of novel carbon materials and their applications  

NASA Astrophysics Data System (ADS)

The synthesis of novel forms of carbon, diamond thin-films, fullerenes, and nanotubes, can be accomplished using well established chemical vapor deposition (CVD) processes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are valuable tools for examining the morphological variations associated with changes in the growth environment, while micro-Raman, Uv-vis, and infra-red spectroscopy provide insight into the purity of the products and the nature of the carbon-carbon bonds. Here, by selective application of these techniques, evidence is presented for fullerene formation, in conjunction with diamond nucleation, during hot-filament CVD. The plate-like deposition of diamond is also observed on graphite substrates subjected to intense hydrogen bombardment. These results may have implications in understanding both diamond and fullerene nucleation processes and in developing strategies aimed toward improving the quality of CVD diamond films. One of the greatest challenges facing the micro-electronics industry is the characterization of surface features on devices with structures smaller than 100 mn. This type of characterization will be critical in fabrication and quality control for the next generation of electronic devices. The currently used silicon probes, with a roughly pyramidal tip structure are adequate for resolving structures of about 130--150 mn. Carbon nanotubes have a demonstrated potential for resolving structures one to two orders of magnitude smaller and, because of their relative straight and smooth walls, with greater lateral resolution. Carbon nanotubes also deform elastically under loads much smaller than those generated by atomic force microscopes operating in a "tapping" mode, thus having a built-in safety factor which protects both the tip and the imaged surface from inadvertent tip "crashes". It is shown that by selectively tailoring the growth environment during carbon fiber and nanotube deposition, using a catalyst-mediated process, that it is possible to produce hollow multi-walled nanotubes with diameters of less than 20 nm extending from a macroscopic (>1mum diameter) carbon fiber. Nanotubes fabricated in this way are easily handled using conventional micro-manipulation techniques and might be more easily employed as mechanical, electrical, and chemical nanoprobes.

Kleckley, Stephen H.

428

Synthesis, electronic properties and applications of oxide nanowires  

NASA Astrophysics Data System (ADS)

Two types of oxide nanowires were synthesized and systematically studied. Single-crystalline Indium oxide nanowires were synthesized using a laser ablation method and characterized using various techniques to confirm their composition and single crystalline structures. Precise control over the nanowire diameter down to 10 nm was achieved by using mono-dispersed gold clusters as the catalytic nanoparticles. These nanowires were further exploited to work as field effect transistors with on/off ratios as high as 2 x 104. Photodetectors were also demonstrated based on these nanowire transistors for ultraviolet light. We have further demonstrated multilevel molecular memories based on nanowires functionalized with a self-assembled monolayer of redox active molecular wires, where the bit was represented by the charge stored in the redox molecules and the nanowire conductance was used as the readout. In addition, the ultra high surface-to-volume ratios of nanowires enabled us to explore using In 2O3 nanowires as chemical and bio sensors. Upon exposure to a small amount of NO2 or NH3, the nanowire transistors showed a decrease in conductance up to six or five orders of magnitude, in addition to substantial shifts in the threshold gate voltage. Our devices exhibited significantly improved chemical sensing performance compared to existing solid-state sensors in many aspects, including the sensitivity, the selectivity, the response time and the lowest detectable concentrations. We also applied In2O3 nanowires as protein and DNA sensors and demonstrated great promise for the selective detection of desired biomolecules for health care and biomedical research. We have carried out extensive studies on the synthesis and electronic properties of transition metal oxide nanowires based on La0.67Ca 0.33MnO3 (LCMO) and La0.67Sr0.33MnO 3 (LSMO). Key to our success is the growth of vertically aligned single-crystalline MgO nanowires, which worked as excellent templates for epitaxial deposition of the desired transition metal oxides and led to high-quality core-shell nanowires. Transport studies on LCMO and LSMO nanowires have revealed the remarkable persistence of metal-insulator transition and magnetoresistance down to nanometer scale. Our work paves the way for novel applications based on these fascinating materials.

Li, Chao

429

Stereoselective synthesis of both enantiomers of rugulactone.  

PubMed

The stereoselective total synthesis of both enantiomers of rugulactone 1 has been completed by applying enantioselective allyl additions as key steps. Two different strategies based on highly stable and enantiomerically pure ?-substituted allylboronic esters 2 and 3 were performed starting from boronic ester 4. PMID:21434691

Böse, Dietrich; Fernández, Enrique; Pietruszka, Jörg

2011-05-01

430

Engineered enzymes for improved organic synthesis  

Microsoft Academic Search

Recent developments to modify enzymes for use in organic synthesis have targeted several areas. These include altering the reaction mechanism of the enzyme to catalyse new reactions, switching substrate specificity, expanding substrate specificity, and improving substrate specificity, such as enantioselectivity in kinetic resolutions. Such modifications can be achieved either by rational redesign, which requires knowledge of the enzyme structure, or

Karl Hult; Per Berglund

2003-01-01

431

SYNTHESIS AND APPLICATION OF 4-(COUMARIN3-YL)-THIOPHENES  

Microsoft Academic Search

A facile synthesis of 4-(coumarin-3-yl)thiophenes (6a-6j) was achieved by the condensation of ethyl 2-acetamido-3, 5-dicarbethoxythiophene-4 acetate (4) with selected o-hydroxyaldehydes (5a-5j) in the presence of piperidine. The key intermediate, ethyl 2-acetamido-3, 5-dicarbethoxythiophene-4-acetate (4) was synthesized by cyclocondensation of diethyl acetonedicarboxylate (1), sulfur and ethyl cyanoacetate (2) by a Gewald synthesis followed by acetylation. 4-(Coumarin-3-yl)thiophenes (6a-6j) were applied on polyester fibers

Ram W. Sabnis; Ghadir J. Kazemi; Dinesh W. Rangnekar

1992-01-01

432

Asymmetric Synthesis of Spiropyrazolones through Phosphine-Catalyzed [4+1] Annulation.  

PubMed

An enantioselective synthesis of spiropyrazolones from allenoate-derived MBH acetates and pyrazolones through a phosphine-mediated [4+1] annulation process has been developed. Spiropyrazolones were readily prepared in good chemical yields and good to high enantioselectivities. This is the first asymmetric example in which ?-substituted allenoates were utilized as a C4 synthon for phosphine-catalyzed [4+1] annulation. PMID:24737675

Han, Xiaoyu; Yao, Weijun; Wang, Tianli; Tan, Yong Ren; Yan, Ziyu; Kwiatkowski, Jacek; Lu, Yixin

2014-05-26

433

Design, synthesis, and characterization of new materials for thermoelectric applications  

NASA Astrophysics Data System (ADS)

Currently, the best known material for thermoelectric refrigeration at room temperature is and alloy of Bi2Te3 and Sb 2Te3. This material has been the basis for room temperature thermoelectric cooling for over 40 years, but its low cooling efficiency (?10% of Carnot Efficiency) has limited its adaptation to small-market specialty applications. Since Bi2Te3 and its alloys have been studied so extensively, it is doubtful that large improvements in efficiency can be made by further modifications of Bi2Te3 (ie. by changing doping or processing of the material). Therefore, this dissertation deals with the discovery and exploration of completely new systems of compounds. The most important parameter for characterizing the efficiency of a thermoelectric material is the dimensionless quantity ZT, where ZT = S2T/rhokappa. Here, S is the thermopower, T is the temperature, kappa is the thermal conductivity, and rho is the electrical resistivity. These variables are not independent of each other, and usually if one of the values is altered by changing composition or doping, the others change as well. Understanding these parameters in depth leads us to several guidelines for searching for better thermoelectric materials and these are discussed in the dissertation. The concept of obtaining highly symmetric crystal structures and also its relation to increasing the value of ZT is discussed. The synthesis of several new quaternary compounds by starting with highly symmetric tetrahedral anion building blocks is presented. While some of these compounds did in fact have high symmetry structures, none were suitable for further studies because they all had large bandgaps. Further systems we explored include heavy metal telluride compounds and compounds that have multiple ordered anions. These systems were chosen based on the concept of minimizing thermal conductivity. A brief chapter on skutterudite materials explores a few new compounds discovered in this highly researched area. The skutterudites are potentially good thermoelectric materials at temperatures above room temperature, however, the compounds discovered were metals and unsuitable for thermoelectric applications. Perhaps the most promising area of research in thermoelectrics presented in this dissertation involves the use of thallium as an alkali metal-like cation. It is shown here that thallium chalcogenides form a wide variety of structures that in many ways mimic the chemistry of alkali metal chalcogenides, yet often form different structures. We present 18 new compounds in that chapter, one of which (Tl1-xSn3+2 xBi7-xSe 14) has an estimated ZT of 0.2--0.3 at room temperature. Since this is not an optimized value, the value of ZT may be able to be increased considerably by carefully adjusting the carrier density. Finally, we present a chapter on measuring the various important thermoelectric parameters (S, rho, and kappa). The construction of a new apparatus for such measurements is presented, along with a new method for measuring kappa, which is much more rapid than steady-state methods.

Reynolds, Thomas Kent

434

Enantioselective synthesis and antimicrobial activities of tetrahydro-?-carboline diketopiperazines.  

PubMed

A series of single isomers tetrahydro-?-carboline diketopiperazines were stereoselectively synthesized starting from l-tryptophan methyl ester hydrochloride and six aldehydes through a four-step reaction including Pictet-Spengler reaction, crystallization-induced asymmetric transformations (CIAT), Schotten-Baumann reaction, and intramolecular ester amidation. The chemical structures were characterized by nuclear magnetic resonance (NMR) and elemental analysis, among which two compounds were determined by x-ray single crystal diffraction. Moreover, antimicrobial activities of all the compounds were also tested. PMID:23861205

Ma, Yangmin; Wu, Hao; Zhang, Jin; Li, Yanchao

2013-10-01

435

Highly enantioselective synthesis of isoxazoline N-oxides.  

PubMed

The reaction of cinchonidine (cinchonine)-derived ammonium salts with nitroolefins in the presence of Cs2CO3 to afford optically active isoxazoline N-oxides with excellent ee and high de values has been developed. PMID:18478708

Zhu, Chun-Yin; Deng, Xian-Ming; Sun, Xiu-Li; Zheng, Jun-Cheng; Tang, Yong

2008-02-14

436

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

437

Direct digital RF synthesis and modulation for MSAT mobile applications  

NASA Technical Reports Server (NTRS)

A practical method of performing direct digital RF synthesis using the Hilbert transform single sideband (SSB) technique is described. It is also shown that amplitude and phase modulation can be achieved directly at L-band with frequency stability and spurii performance exceeding stringent MSAT system requirements.

Crozier, Stewart; Datta, Ravi; Sydor, John

1993-01-01

438

Enantioselective determination of cetirizine in human urine by HPLC.  

PubMed

In order to study the simultaneous determination of (+)- and (-)-cetirizine in human urine we have developed a chiral separation method by HPLC. A chiral stationary phase of alpha1-acidglycoprotein, the AGP-CSP, was used to separate the enantiomers. The pH of the phosphate buffer, as well as the content of the organic modifier in the mobile phase, markedly affected the chromatographic separation of (+)- and (-)-cetirizine. A mobile phase of 10 mmol/l phosphate buffer (pH 7.0)-acetonitrile (95: 5, v/v) was used for the urine assays. Ultraviolet absorption was monitored at 230 nm and roxatidine was employed as the internal standard for quantification. (+)-Cetirizine, (-)-cetirizine and the internal standard were eluted at retention times of 12, 16, and 32 mins, respectively. The detection limit for cetirizine enantiomers was 400 ng/ml of urine. A pharmacokinetic study was conducted with the help of 5 healthy female volunteers who were administered with a single oral dose of racemic cetirizine (20 mg). The peak area ratios provided by the cetirizine enantiomers were linear (r>0.997) over a concentration range of 2.5-200 microg/ml. The peak of the excreted cetirizine enantiomers appeared in the urine sample during the period of 1-2 hrs following the administration of the oral dose. The excreted level of (+)-cetirizine was slightly higher than (-)-cetirizine but the difference was not statistically significant. However, this method appears to have applications for enantioselective pharmacokinetic studies of racemic drugs. PMID:10836747

Choi, S O; Lee, S H; Kong, H S; Kim, E J; Choo, H Y

2000-04-01

439

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

440

Synthetic studies on the icetexones: enantioselective formal syntheses of icetexone and epi-icetexone  

PubMed Central

Two strategies for the synthesis of the icetexane diterpenoids icetexone and epi-icetexone that rely on Ga(III)-catalyzed cycloisomerization of alkynyl indene substrates to yield fused [6-7-6] tricycles have been explored. In the first approach, access to a tricycle bearing a gem-dimethyl group paved the way for explorations of C–H functionalization of one of the methyl groups in close proximity to a hydroxyl-directing group. This approach was ultimately unsuccessful and led only to ring cleaved products. In the second approach, an alkynyl indene substrate bearing a cyano substituent was utilized, which was effective in providing a functional handle to access the icetexone subclass of diterpenoids. A key epoxide opening/diazene rearrangement sequence was utilized to complete a formal synthesis of icetexone and epi-icetexone, which is discussed in detail. Furthermore, the cyano-containing substrate has been prepared in enantioenriched form using a Rh-catalyzed conjugate addition reaction, which now provides a route to the enantioselective synthesis of these natural products.

de Jesus Cortez, Felipe; Lapointe, David; Hamlin, Amy M.; Simmons, Eric M.; Sarpong, Richmond

2013-01-01

441

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

442

A highly enantioselective approach towards 2-substituted 3-bromopyrrolidines.  

PubMed

A facile and highly enantioselective approach towards 2-substituted 3-bromopyrrolidines has been developed. The process involves an amino-thiocarbamate catalyzed bromoaminocyclization of 1,2-disubstituted olefinic amides. The pyrrolidine products could readily be converted into other useful building blocks including a dihydropyrrole and a 2-substituted pyrrolidine. PMID:22437158

Chen, Jie; Zhou, Ling; Yeung, Ying-Yeung

2012-05-21

443

Enantioselective toxic effects and biodegradation of benalaxyl in Scenedesmus obliquus.  

PubMed

Enantioselectivity in ecotoxicity and biodegradation of chiral pesticide benalaxyl to freshwater algae Scenedesmus obliquus was studied. The 96 h-EC(50) values of rac-, R-(-)-, S-(+)-benalaxyl were 2.893, 3.867, and 8.441 mg L(-1), respectively. Therefore, the acute toxicities of benalaxyl enantiomers were enantioselective. In addition, the pigments chlorophyll a and chlorophyll b, antioxidant enzyme activities catalase (CAT) and superoxide dismutase (SOD) as well as lipid peroxide malondialdehyde (MDA) were determined to evaluate the different toxic effects. Chlorophyll a was induced by S-(+)-benalaxyl but inhibited by R-(-)-benalaxyl at 1 mg L(-1). Chlorophyll b were both induced at 1 mg L(-1), but S-(+)-form was fourfold higher than R-(-)-form. S-(+)-benalaxyl inhibited more CAT activities at 3 mg L(-1) and 5 mg L(-1), induced less SOD activity and MDA content at 5 mg L(-1) than R-(-)-benalaxyl. Based on these data, enantioselectivity occurred in anti-oxidative stress when S. obliquus response to benalaxyl. In the biodegradation experiment, the half-lives of S-(+)-benalaxyl and R-(-)-benalaxyl were 4.07 d and 5.04 d, respectively, resulting in relative enrichment of the R-(-)-form. These results showed that toxic effects and biodegradation of benalaxyl in S. obliquus were enantioselective, and such enantiomeric differences must be taken into consideration in pesticide risk. PMID:22169712

Huang, Ledan; Lu, Dahai; Diao, Jinling; Zhou, Zhiqiang

2012-03-01

444

Loop grafting of Bacillus subtilis lipase A: inversion of enantioselectivity.  

PubMed

Lipases are successfully applied in enantioselective biocatalysis. Most lipases contain a lid domain controlling access to the active site, but Bacillus subtilis Lipase A (LipA) is a notable exception: its active site is solvent exposed. To improve the enantioselectivity of LipA in the kinetic resolution of 1,2-O-isopropylidene-sn-glycerol (IPG) esters, we replaced a loop near the active-site entrance by longer loops originating from Fusarium solani cutinase and Penicillium purpurogenum acetylxylan esterase, thereby aiming to increase the interaction surface for the substrate. The resulting loop hybrids showed enantioselectivities inverted toward the desired enantiomer of IPG. The acetylxylan esterase-derived variant showed an inversion in enantiomeric excess (ee) from -12.9% to +6.0%, whereas the cutinase-derived variant was improved to an ee of +26.5%. The enantioselectivity of the cutinase-derived variant was further improved by directed evolution to an ee of +57.4%. PMID:18721749

Boersma, Ykelien L; Pijning, Tjaard; Bosma, Margriet S; van der Sloot, Almer M; Godinho, Luís F; Dröge, Melloney J; Winter, Remko T; van Pouderoyen, Gertie; Dijkstra, Bauke W; Quax, Wim J

2008-08-25

445

Pyrones to pyrans: enantioselective radical additions to acyloxy pyrones.  

PubMed

This paper describes a highly site-, diastereo-, and enantioselective intermolecular radical addition/hydrogen atom transfer to hydroxypyrone 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. PMID:17031933

Sibi, Mukund P; Zimmerman, Jake

2006-10-18

446

Control of enantioselectivity with flexible biaryl axes: terpene-based alkylzinc catalysts in enantioselective dialkylzinc additions.  

PubMed

New enantiopure pyridyl alcohols are efficiently accessible through few synthetic steps from commercially available terpenes, that is, (+)-fenchone, (-)-menthone and (-)-verbenone as well as 2,6-diphenylpyridine. These chelating pyridyl alcohols exhibit flexible pyridyl-phenylene axes, which give rise to P and M conformers. Alkylzincation of the hydroxy groups eliminates equilibria of the conformers and generates alkylzinc complexes with adjusted biaryl axes, as it is demonstrated by NMR studies. These alkylzinc catalysts perform well in the addition of dimethylzinc or diethylzinc to benzaldehyde with yields up to 99% and ee's up to 95%. The adjusted pyridylphenylene conformations in the ligands now control enantioselectivities of the catalysts, which were also analysed by computations at the DFT level. PMID:20927784

Leven, Matthias; Schlörer, Nils E; Neudörfl, Jörg M; Goldfuss, Bernd

2010-12-01

447

Enantioselective stable isotope analysis (ESIA) of polar Herbicides  

NASA Astrophysics Data System (ADS)

The complexity of aquatic systems makes it challenging to assess the environmental fate of chiral micropolutants. As an example, chiral herbicides are frequently detected in the environment (Buser and Muller, 1998); however, hydrological data is needed to determine their degradability from concentration measurements. Otherwise declining concentrations cannot unequivocally be attributed to degradation, but could also be caused by dilution effects. In contrast, isotope ratios or enantiomeric ratios are elegant alternatives that are independent of dilution and can even deliver insights into reaction mechanisms. To combine the advantages of both approaches we developed an enatioselective stable isotope analysis (ESIA) method to investigate the fate of the chiral herbicides 4-CPP ((RS)-2-(4-chlorophenoxy)-propionic acid), mecoprop (2-(4-Chloro-2-methylphenoxy)-propionic acid) and dichlorprop (2-(2,4-Dichlorophenoxy)-propionic acid). After testing the applicable concentration range of the method, enantioselective isotope fractionation was investigated by microbial degradation using dichlorprop as a model compound. The method uses enantioselective gas-chromatography (GC) to separate enantiomers. Subsequently samples are combusted online to CO2 and carbon isotope ratios are determined for each enantiomer by isotope-ratio-mass-spectrometry (IRMS). Because the analytes contain a polar carboxyl-group, samples were derivatised prior to GC-IRMS analysis with methanolic BF3 solution. Precise carbon isotope analysis (2? ?0.5‰) was achieved with a high sensitivity of ? 7 ng C that is needed on column for one analysis. Microbial degradation of the model compound dichlorprop was conducted with Delftia acidovorans MC1 and pronounced enantiomer fractionation, but no isotope fractionation was detected. The absence of isotope fractionation can be explained by two scenarios: either the degrading enzyme has no isotopic preference, or another step in the reaction without an isotopic preference was rate determining. Our findings are in contrast to previously reported results for the degradation of ?-hexachlorocyclohexane (Badea et al., 2012), where isotope fractionation, but no enantiomeric fractionation was observed. Hence the two lines of evidence seem to be independent of each other. Enhanced insight maybe provided when both effects appear simultaneously, as shown downstream of a landfill site under anaerobic conditions for the chiral herbicide 4-CPP (Milosevic et al., 2013). Buser HR, Muller MD (1998): Occurrence and transformation reactions of chiral and achiral phenoxyalkanoic acid herbicides in lakes and rivers in Switzerland. Environmental Science & Technology 32 (5):626-633. Badea S-L, Vogt C, Gehre M, Fischer A, Danet A-F, Richnow H-H (2011): Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of alpha-hexachlorocyclohexane in the environment. Rapid Communications in Mass Spectrometry 25 (10):1363-1372. Milosevic N, Qiu S, Elsner M, Einsiedl F, Maier MP, Bensch HKV, Albrechtsen HJ, Bjerg PL (2013): Combined isotope and enantiomer analysis to assess the fate of phenoxy acids in a eterogeneous geologic setting at an old landfill. Water Research 47 (2): 637-649.

Maier, Michael; Qiu, Shiran; Elsner, Martin

2013-04-01

448

Enantioselective diamination with novel chiral hypervalent iodine catalysts.  

PubMed

Vicinal diamines constitute one the most important functional motif in organic chemistry because of its wide occurrence in a variety of biological and pharmaceutical molecules. We report an efficient metal-free, highly stereoselective intramolecular diamination using a novel chiral hypervalent iodine reagent together with its application as an efficient catalyst for the synthesis of diamines. PMID:25042733

Mizar, Pushpak; Laverny, Aragorn; El-Sherbini, Mohammad; Farid, Umar; Brown, Michael; Malmedy, Florence; Wirth, Thomas

2014-08-01

449

Nanoporous Silica Matrices and Their Application in Synthesis of Nanostructures  

NASA Astrophysics Data System (ADS)

The effect of the presence of I-4 Me-Ph ionene in the supramolecular template (cetyltrimethylammonium bromide) on formation of porous structure of silicas was studied. We also studied the peculiarities of template synthesis of mesoporous silicas inside of large pores of silica gel. Mesoporous silicas with chemically modified surface were applied in synthesis of metallic nanostructures. Porous silicas with grafted layer of hydridepolysiloxane were used for in situ p