Sample records for enantioselective synthesis application

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

    PubMed

    Corkey, Britton K; Heller, Stephen T; Wang, Yi-Ming; Toste, F Dean

    2013-07-01

    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. PMID:23772095

  2. Enantioselective total synthesis of (-)-laurenditerpenol.

    PubMed

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

    2012-09-01

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

  3. Enantioselective Total Synthesis of (+)-Lithospermic Acid

    PubMed Central

    Cheng, Xu; Zhou, Bing

    2012-01-01

    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. PMID:22978790

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

    PubMed Central

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

    2011-01-01

    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. PMID:21936576

  5. Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field

    NASA Astrophysics Data System (ADS)

    Xu, Yangyang; Yang, Guang; Xia, Hongyan; Zou, Gang; Zhang, Qijin; Gao, Jiangang

    2014-09-01

    Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine.

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

    PubMed

    Tamura, Keiji; Kumagai, Naoya; Shibasaki, Masakatsu

    2014-04-01

    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

  7. Enantioselective total synthesis of aspergillide C.

    PubMed

    Nagasawa, Tomohiro; Kuwahara, Shigefumi

    2009-02-01

    The first enantioselective total synthesis of aspergillide C, a cytotoxic 14-membered macrolide isolated from the marine-derived fungus Aspergillus ostianus, has been accomplished from a commercially available chiral glycidol derivative by a 12-step sequence involving an expeditious preparation of a cyclic acetal intermediate and a trans-selective Ferrier-type two-carbon homologation reaction. PMID:19128025

  8. Studies on the Enantioselective Synthesis of Cymbalta?

    Microsoft Academic Search

    Kenneth Feldman

    2009-01-01

    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

  9. A concise enantioselective synthesis of (+)-febrifugine

    Microsoft Academic Search

    Lourdusamy Emmanuvel; Dayanand A. Kamble; Arumugam Sudalai

    2009-01-01

    A short enantioselective synthesis of (+)-febrifugine, a potent antimalarial alkaloid, has been described based on the regioselective asymmetric dihydroxylation of a 1,4-dienic ester as the key step. The strategy also involves chemoselective [3,3]-sigmatropic rearrangement of 1,5-hexadiene-3-ol and intramolecular lactamization of azidolactone for the construction of piperidine core.

  10. Enantioselective synthesis of a dual orexin receptor antagonist.

    PubMed

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

    2012-07-01

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

  11. Concise enantioselective synthesis of diospongins A and B

    PubMed Central

    Stefan, Eric; Nalin, Ansel P.; Taylor, Richard E.

    2013-01-01

    Ether transfer methodology is capable of stereoselectively generating 1,3-diol mono- and diethers in good yield. Surprisingly, allylic and benzylic substrates provide none of the desired products when exposed to previously optimized conditions of iodine monochloride. Herein, second-generation activation conditions for ether transfer have been developed that circumvents undesired side reactions for these substrates. The application of this chemistry to the enantioselective synthesis of diospongins A and B has now been accomplished. PMID:24058215

  12. Concise enantioselective synthesis of diospongins A and B.

    PubMed

    Stefan, Eric; Nalin, Ansel P; Taylor, Richard E

    2013-09-01

    Ether transfer methodology is capable of stereoselectively generating 1,3-diol mono- and diethers in good yield. Surprisingly, allylic and benzylic substrates provide none of the desired products when exposed to previously optimized conditions of iodine monochloride. Herein, second-generation activation conditions for ether transfer have been developed that circumvents undesired side reactions for these substrates. The application of this chemistry to the enantioselective synthesis of diospongins A and B has now been accomplished. PMID:24058215

  13. Enantioselective synthesis of 12-amino alkylidenecyclopentenone prostaglandins.

    PubMed

    Roulland, Emmanuel; Monneret, Claude; Florent, Jean-Claude; Bennejean, Caroline; Renard, Pierre; Léonce, Stéphane

    2002-06-28

    An enantioselective synthesis of new 12-amino alkylidenecyclopentenone prostaglandins is reported. The key step of the synthesis involved a [3.3] sigmatropic rearrangement of an asymmetric allylic cyanate to elaborate an asymmetric 5-amino-1,6-diene which was further transformed into cyclopentenone by successive ring-closing metathesis reaction catalyzed by the Grubbs reagent and one-pot oxidation. A palladium-catalyzed cross-coupling reaction on a 5-iodo-1,5-diene allowed the synthesis of prostanoids with variable Rw side chains. These new compounds exhibit high cytotoxic activities. PMID:12076134

  14. Enantioselective formal total synthesis of (+)-aspergillide C.

    PubMed

    Panarese, Joseph D; Waters, Stephen P

    2009-11-01

    An enantioselective formal total synthesis of the cytotoxic macrolide (+)-aspergillide C has been accomplished from (S)-(-)-glyceraldehyde acetonide and the Danishefsky-Kitahara diene. Strategic transformations include a hetero Diels-Alder reaction, Ferrier-type addition, and palladium-catalyzed oxidative lactonization to set key stereocenters within the dihydropyran core, followed by fragment coupling via (E)-selective Julia-Kocienski olefination. PMID:19817392

  15. Catalytic enantioselective synthesis of quaternary carbon stereocentres

    NASA Astrophysics Data System (ADS)

    Quasdorf, Kyle W.; Overman, Larry E.

    2014-12-01

    Quaternary carbon stereocentres--carbon atoms to which four distinct carbon substituents are attached--are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

  16. Enantioselective Synthesis of ?-Arylamines via Chiral Phosphoric Acid-Catalyzed Asymmetric Reductive Amination.

    PubMed

    Kim, Kyung-Hee; Lee, Chun-Young; Cheon, Cheol-Hong

    2015-06-19

    A new method for the synthesis of chiral ?-aryl amines via chiral phosphoric acid-catalyzed enantioselective reductive amination of benzyl methyl ketone derivatives with Hantzsch ester was developed. Various chiral ?-aryl amines were obtained in high yields and with good to high enantioselectivities. This transformation is applicable to gram-scale reactions, and the catalyst loading can be reduced to 1 mol % without sacrificing any catalytic efficacy. Furthermore, the resulting ?-aryl amine was successfully converted into a tetrahydroisoquinoline compound without any loss of enantioselectivity. PMID:26000470

  17. Gold-catalyzed asymmetric allylic substitution of free alcohols: an enantioselective approach to chiral chromans with quaternary stereocenters for the synthesis of vitamin E and analogues.

    PubMed

    Uria, Uxue; Vila, Carlos; Lin, Ming-Yuan; Rueping, Magnus

    2014-10-20

    The enantioselective synthesis of ?- and ?-tocopherol (the most biologically active members of vitamin?E family) and analogues has been accomplished employing a new enantioselective gold catalyzed intramolecular allylic alkylation reaction followed by an olefin cross-metathesis as key steps. The methodology proved to be applicable to different olefins highlighting its potential for the synthesis of diverse libraries. PMID:25201099

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

    PubMed Central

    Yang, Hua; Carter, Rich G.

    2010-01-01

    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. PMID:20586477

  19. Catalytic enantioselective synthesis of 2-aryl-chromenes†

    PubMed Central

    Zeng, Bi-Shun; Yu, Xinyi; Siu, Paul W.

    2015-01-01

    An enantioselective Pd-catalyzed 6-endo-trig reaction for the synthesis of 2-aryl-chromenes has been developed. A systematic optimization of a TADDOL-derived ligand set resulted in the identification of a novel monodentate phosphoramidite–palladium catalyst that accesses 2-aryl-2H-chromenes with high yield and enantioselectivity under mild conditions. The products obtained from this method can be transformed into biologically active compounds through functionalization of the chromene alkene. PMID:25705366

  20. An enantioselective total synthesis of helioporins C and E.

    PubMed

    Lölsberg, Wibke; Werle, Susen; Neudörfl, Jörg-Martin; Schmalz, Hans-Günther

    2012-12-01

    A short and enantioselective total synthesis of helioporins C and E, which are bioactive marine diterpenes containing a serrulatane or amphilectane skeleton, was elaborated. The chirogenic step, i.e. a Cu(I)-catalyzed allylic alkylation of a cinnamyl chloride with methylmagnesium bromide, proceeded with virtually complete enantioselectivity (99% ee) in the presence of a chiral phosphine-phosphite ligand. The other stereocenters were diastereoselectively established through Me(2)AlCl-mediated cationic cyclization and Ir-catalyzed hydrogenation. PMID:23148527

  1. The enantioselective total synthesis of (+)-clusianone.

    PubMed

    Horeischi, Fiene; Guttroff, Claudia; Plietker, Bernd

    2015-02-11

    (+)-Clusianone, an exo-type B PPAP with reported anti-HIV and chemoprotective activities, was synthesized in eleven steps with 97% ee starting from acetylacetone. An enantioselective decarboxylative Tsuji-Trost-allylation and a Ru-catalyzed ring-closing metathesis-decarboxylative allylation were used to control both diastereo- and enantioselectivity. PMID:25563512

  2. Enantioselective total synthesis of spirofungins A and B.

    PubMed

    Crimmins, Michael T; O'Bryan, Elizabeth A

    2010-10-01

    The enantioselective total synthesis of spirofungins A (1) and B (2) is reported in 14 steps over the longest linear sequence. Key steps include the use of thiazolidinethione-mediated aldol reactions to assemble the major fragments and installation of the C1-C6 side chain using a cross metathesis reaction. PMID:20831229

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

    Microsoft Academic Search

    Nikhil Addleman

    2008-01-01

    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.

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

    PubMed Central

    Deck, Jason A.; Martin, Stephen F.

    2010-01-01

    The first enantioselective synthesis of (+)–isolysergol was completed in 12 steps from commercially available materials by a novel approach that features a late stage microwave-mediated, diastereomeric ring closing metathesis catalyzed by a chiral molybdenum catalyst to simultaneously form the D ring and set the stereocenter at C(8). PMID:20462232

  5. Design, synthesis, and application of a chiral sulfinamide phosphine catalyst for the enantioselective intramolecular rauhut-currier reaction.

    PubMed

    Su, Xiao; Zhou, Wei; Li, Yangyan; Zhang, Junliang

    2015-06-01

    A novel class of chiral sulfinamide phosphine catalysts (Xiao-Phos) are reported, which can be easily prepared from inexpensive commercially available starting materials. The Xiao-Phos catalysts showed good performance in enantioselective intramolecular Rauhut-Currier reactions, generating ?-methylene-?-butyrolactones in high yields with up to 99?% ee under mild conditions. Moreover, kinetic resolution and parallel kinetic resolution were also observed with the use of two different substituted racemic precursors. PMID:25907710

  6. Catalytic enantioselective 1,3-dipolar cycloadditions of azomethine ylides for biology-oriented synthesis.

    PubMed

    Narayan, Rishikesh; Potowski, Marco; Jia, Zhi-Jun; Antonchick, Andrey P; Waldmann, Herbert

    2014-04-15

    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. PMID:24730692

  7. Enantioselective formal total synthesis of the antitumor macrolide bryostatin 7.

    PubMed

    Manaviazar, Soraya; Frigerio, Mark; Bhatia, Gurpreet S; Hummersone, Marc G; Aliev, Abil E; Hale, Karl J

    2006-09-28

    A new enantioselective synthesis of Masamune's AB fragment (1) for bryostatin 7 is described. Key steps in the new route include a Meerwein-Ponndorf-Verley reduction to set the O(7) stereocenter and an alkylative union between the dithiane 6 and iodide 5 to construct the C(9)-C(10) bond. Because we have previously published a synthesis of Masamune's C-ring phenyl sulfone 2, our new route to 1 constitutes a formal total synthesis of bryostatin 7; it also corrects the previously reported spectral data for 1 in CDCl3. PMID:16986929

  8. Scalable enantioselective total synthesis of taxanes

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  9. Enantioselective synthesis of arylglycine derivatives by direct C-H oxidative cross-coupling.

    PubMed

    Wei, Xiao-Hong; Wang, Gang-Wei; Yang, Shang-Dong

    2015-01-18

    A new method for the synthesis of chiral ?-amino acid derivatives by enantioselective C-H arylation of N-aryl glycine esters with aryl boric acids in the presence of a chiral Pd(II)-catalyst has been developed. This work successfully integrates the direct C-H oxidation with asymmetric arylation and exhibits excellent enantioselectivity. PMID:25348347

  10. An Enantioselective Synthesis of CymbaltaTM

    Microsoft Academic Search

    Vincent van Rixel

    2010-01-01

    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

  11. Enantioselective total synthesis and assignment of the absolute configuration of (+)-laurokamurene B

    Microsoft Academic Search

    Adusumilli Srikrishna; Baire Beeraiah; R. Ramesh Babu

    2008-01-01

    The first enantioselective total synthesis of the rearranged aromatic sesquiterpene (+)-laurokamurene B, isolated from the Chinese red algae Laurencia okamurai Yamada, has been accomplished starting from (S)-campholenaldehyde, establishing the absolute configuration of laurokamurenes.

  12. Enantioselective total synthesis of (+)-lyngbyabellin m.

    PubMed

    Pirovani, Rodrigo V; Brito, Gilmar A; Barcelos, Rosimeire C; Pilli, Ronaldo A

    2015-01-01

    Lyngbyabellin M is a non-ribosomal peptide synthetase/polyketide synthase derived metabolite isolated from the cyanobacterium M. bouillonii displaying thiazole rings and a distinct chlorinated octanoic acid chain. Its absolute configuration was proposed based on the comparison of its spectroscopic data with those of other representatives of this family of marine natural products, as well as degradation and derivatization studies. Here the first total synthesis of (+)-lyngbyabellin M is described based on the coupling of three key intermediates: two chiral thiazole moieties and an anti hydroxycarboxylic acid prepared stereoselectively via a boron enolate mediated aldol reaction directed by Masamune's chiral auxiliary. PMID:26023838

  13. Enantioselective Total Synthesis of (+)-Lyngbyabellin M

    PubMed Central

    Pirovani, Rodrigo V.; Brito, Gilmar A.; Barcelos, Rosimeire C.; Pilli, Ronaldo A.

    2015-01-01

    Lyngbyabellin M is a non-ribosomal peptide synthetase/polyketide synthase derived metabolite isolated from the cyanobacterium M. bouillonii displaying thiazole rings and a distinct chlorinated octanoic acid chain. Its absolute configuration was proposed based on the comparison of its spectroscopic data with those of other representatives of this family of marine natural products, as well as degradation and derivatization studies. Here the first total synthesis of (+)-lyngbyabellin M is described based on the coupling of three key intermediates: two chiral thiazole moieties and an anti hydroxycarboxylic acid prepared stereoselectively via a boron enolate mediated aldol reaction directed by Masamune’s chiral auxiliary. PMID:26023838

  14. Enantioselective synthesis of (-)-dihydrocodeine and formal synthesis of (-)-thebaine, (-)-codeine, and (-)-morphine from a deprotonated ?-aminonitrile.

    PubMed

    Geffe, Mario; Opatz, Till

    2014-10-17

    The ?-benzylation of a deprotonated bicyclic ?-aminonitrile, followed by Noyori's asymmetric transfer hydrogenation combined with the Grewe cyclization onto a symmetrical A-ring precursor, are the key steps of a short and high-yielding enantioselective synthesis of the morphinan (-)-dihydrocodeine. This compound can be converted to (-)-thebaine in high yield by known transformations, while (-)-codeine and (-)-morphine are available from an advanced intermediate. PMID:25271381

  15. An Intramolecular Diels-Alder Approach to the Eunicelins: Enantioselective Total Synthesis of Ophirin B

    E-print Network

    An Intramolecular Diels-Alder Approach to the Eunicelins: Enantioselective Total Synthesis intramolecular Diels- Alder cycloaddition of tetraene 3. We report here the successful implementation ophirin B. Our strategy (Scheme 1) for the synthesis of the Diels-Alder substrate 3 was predicated on our

  16. Enantioselective Total Synthesis of (?)-Zampanolide, a Potent Microtubule-Stabilizing Agent

    PubMed Central

    Ghosh, Arun K.; Cheng, Xu

    2011-01-01

    An enantioselective total synthesis of zampanolide has been accomplished using a novel DDQ/Brønsted acid catalyzed cyclization as the key reaction. The synthesis features cross-metathesis to construct the tri-substituted olefin and a ring-closing metathesis to form the macrolactone. The final N-acyl aminal formation was stereoselectively accomplished by an organocatalytic reaction. PMID:21749032

  17. Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

    PubMed

    Wang, Dong-Ling; Liang, Zhi-Qin; Chen, Kun-Quan; Sun, De-Qun; Ye, Song

    2015-06-01

    The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of ?-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities. PMID:25933360

  18. Enantioselective synthesis of chiral heterocycles containing both chroman and pyrazolone derivatives catalysed by a chiral squaramide.

    PubMed

    Li, Jun-Hua; Du, Da-Ming

    2015-05-13

    An efficient chiral squaramide-catalysed enantioselective Michael addition of pyrazolin-5-ones to 3-nitro-2H-chromenes for the synthesis of chiral heterocyclic systems containing both chroman and pyrazolone derivatives has been developed. This reaction afforded the desired products in high to excellent yields (up to 98%) with high enantioselectivities (up to 96%) and excellent diastereoselectivities (up to 99?:?1) under very low catalyst loading (0.2 mol%). This catalytic asymmetric reaction provides an efficient route toward the synthesis of chiral heterocyclic systems containing both chroman and pyrazolone derivatives, which possess potential pharmaceutical activities. PMID:25882378

  19. Highly regio- and enantioselective synthesis of ?,?-unsaturated amido esters by catalytic hydrogenation of conjugated enamides.

    PubMed

    Gao, Min; Meng, Jing-jing; Lv, Hui; Zhang, Xumu

    2015-02-01

    An efficient and highly regio- and enantioselective catalytic asymmetric hydrogenation of ?,?-dienamido esters to ?,?-unsaturated amido esters has been achieved using Rh/TangPhos as the catalyst. A series of ?,?-unsaturated amido acids were furnished in excellent yields with up to 99% ee. This effective methodology was applied in the asymmetric synthesis of key intermediate of Ramipril, an ACE inhibitor. PMID:25511130

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

    ERIC Educational Resources Information Center

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

    2010-01-01

    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…

  1. Enantioselective Small Molecule Synthesis by Carbon Dioxide Fixation using a Dual Brønsted Acid/Base Organocatalyst.

    PubMed

    Vara, Brandon A; Struble, Thomas J; Wang, Weiwei; Dobish, Mark C; Johnston, Jeffrey N

    2015-06-17

    Carbon dioxide exhibits many of the qualities of an ideal reagent: it is nontoxic, plentiful, and inexpensive. Unlike other gaseous reagents, however, it has found limited use in enantioselective synthesis. Moreover, unprecedented is a tool that merges one of the simplest biological approaches to catalysis-Brønsted acid/base activation-with this abundant reagent. We describe a metal-free small molecule catalyst that achieves the three component reaction between a homoallylic alcohol, carbon dioxide, and an electrophilic source of iodine. Cyclic carbonates are formed enantioselectively. PMID:26039818

  2. Asymmetric synthesis of N-allylic indoles via regio- and enantioselective allylation of aryl hydrazines.

    PubMed

    Xu, Kun; Gilles, Thomas; Breit, Bernhard

    2015-01-01

    The asymmetric synthesis of N-allylic indoles is important for natural product synthesis and pharmaceutical research. The regio- and enantioselective N-allylation of indoles is a true challenge due to the favourable C3-allylation. We develop here a new strategy to the asymmetric synthesis of N-allylic indoles via rhodium-catalysed N-selective coupling of aryl hydrazines with allenes followed by Fischer indolization. The exclusive N-selectivities and good to excellent enantioselectivities are achieved applying a rhodium(I)/DTBM-Segphos or rhodium(I)/DTBM-Binap catalyst. This method permits the practical synthesis of valuable chiral N-allylated indoles, and avoids the N- or C-selectivity issue. PMID:26137886

  3. Asymmetric synthesis of N-allylic indoles via regio- and enantioselective allylation of aryl hydrazines

    PubMed Central

    Xu, Kun; Gilles, Thomas; Breit, Bernhard

    2015-01-01

    The asymmetric synthesis of N-allylic indoles is important for natural product synthesis and pharmaceutical research. The regio- and enantioselective N-allylation of indoles is a true challenge due to the favourable C3-allylation. We develop here a new strategy to the asymmetric synthesis of N-allylic indoles via rhodium-catalysed N-selective coupling of aryl hydrazines with allenes followed by Fischer indolization. The exclusive N-selectivities and good to excellent enantioselectivities are achieved applying a rhodium(I)/DTBM-Segphos or rhodium(I)/DTBM-Binap catalyst. This method permits the practical synthesis of valuable chiral N-allylated indoles, and avoids the N- or C-selectivity issue. PMID:26137886

  4. Organocatalytic Enantioselective Synthesis of Both Diastereomers of ?-Hydroxyphosphinates

    PubMed Central

    Samanta, Sampak; Perera, Sandun; Zhao, Cong-Gui

    2010-01-01

    Racemic ?-acylphosphinates and formylphosphinate hydrate were used directly as the substrates in a proline derivative-catalyzed cross aldol reaction with ketones. Because of the preexisting the phosphorus stereogenic center, a mixture of two diastereomers of the corresponding ?-hydroxyphosphinates were obtained in this reaction. Good to high enantioselectivities (up to 99% ee) were obtained simultaneously for both of these two diastereomers in good yields. Good diastereoselectivities were also obtained when the reaction generates an additional carbon stereogenic center. PMID:20085234

  5. Catalytic chemo-, regio-, and enantioselective bromochlorination of allylic alcohols.

    PubMed

    Hu, Dennis X; Seidl, Frederick J; Bucher, Cyril; Burns, Noah Z

    2015-03-25

    Herein we describe a highly chemo-, regio-, and enantioselective bromochlorination reaction of allylic alcohols, employing readily available halogen sources and a simple Schiff base as the chiral catalyst. The application of this interhalogenation reaction to a variety of substrates, the rapid enantioselective synthesis of a bromochlorinated natural product, and preliminary extension of this chemistry to dibromination and dichlorination are reported. PMID:25738419

  6. Improved synthesis and application of planar-chiral nucleophilic catalysts in asymmetric reactions and copper-catalyzed enantioselective N-H insertion reactions

    E-print Network

    Lee, Elaine C

    2007-01-01

    The development of an improved synthesis of nucleophilic planar-chiral catalysts is described in Chapter 1. This route is amenable to scale-up and preparative chiral HPLC is unnecessary to resolve the racemic catalysts. ...

  7. Enantioselective total syntheses of acylfulvene, irofulven, and the agelastatins

    E-print Network

    Siegel, Dustin S. (Dustin Scott), 1980-

    2010-01-01

    I. Enantioselective Total Synthesis of (-)-Acylfulvene, and (-)-Irofulven We report the enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven, which features metathesis reactions for the rapid assembly of ...

  8. Enantioselective hydrogenation of ?-aminomethylacrylates containing a free NH group for the synthesis of ?-amino acid derivatives

    PubMed Central

    Qiu, Liqin; Prashad, Mahavir; Hu, Bin; Prasad, Kapa; Repi?, Oljan; Blacklock, Thomas J.; Kwong, Fuk Yee; Kok, Stanton H. L.; Lee, Hang Wai; Chan, Albert S. C.

    2007-01-01

    We describe highly enantioselective synthesis of ?-amino acid derivatives (1a-c) using asymmetric hydrogenation of ?-aminomethylacrylates (2a-c), which contain a free basic NH group, as the key step. The ?-aminomethylacrylates (2a-c) were prepared using the Baylis–Hillman reaction of an appropriate aldehyde with methyl acrylate followed by acetylation of the resulting allylic alcohols (4a-b) and SN2?-type amination of the allylic acetates (3a-b). PMID:17942689

  9. A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines

    PubMed Central

    2013-01-01

    Summary A continuous-flow asymmetric organocatalytic photocyclization–transfer hydrogenation cascade reaction has been developed. The new protocol allows the synthesis of tetrahydroquinolines from readily available 2-aminochalcones using a combination of photochemistry and asymmetric Brønsted acid catalysis. The photocylization and subsequent reduction was performed with catalytic amount of chiral BINOL derived phosphoric acid diester and Hantzsch dihydropyridine as hydrogen source providing the desired products in good yields and with excellent enantioselectivities. PMID:24367413

  10. Enantioselective synthesis of 8-epi-xanthatin and biological evaluation of xanthanolides and their derivatives.

    PubMed

    Yokoe, Hiromasa; Noboru, Kentaro; Manabe, Yuki; Yoshida, Masahiro; Shibata, Hirofumi; Shishido, Kozo

    2012-01-01

    An enantioselective synthesis of 8-epi-xanthatin (9) has been accomplished starting from the bicyclic lactone 3, which has been used for the synthesis of other xanthanolides, sundiversifolide (4) and diversifolide (5), through a synthetic route without the use of a selenium species. Additionally we have evaluated antimicrobial activities of five natural xanthanolides and their derivatives. Although the synthetic xanthanolides did not show any activity against methicillin-resistant Staphylococcus aureus (MRSA), some of the synthetic intermediates did exhibit moderate antimicrobial activities. PMID:22850909

  11. Asymmetric Total Synthesis of (?)-Plicatic Acid via a Highly Enantioselective and Diastereoselective Nucleophilic Epoxidation of Acyclic Trisubstitued Olefins

    PubMed Central

    Sun, Bing-Feng; Hong, Ran; Kang, Yan-Biao; Deng, Li

    2009-01-01

    The first total synthesis of (?)-plicatic acid has been achieved by a concise and enantioselective route. In this synthesis, a conceptually new strategy featuring an asymmetric epoxidation-intramolecular epoxy-ring-opening Friedel-Crafts reaction sequence was developed for the stereoselective construction of the 2,7’-cyclolignane skeleton bearing contiguous quaternary-quaternary-tertiary stereocenters. The implementation of this strategy was enabled by the development of a modified protocol for the Seebach epoxidation with TADOOH, which affords an unprecedented, highly enantioselective and diastereoselective epoxidation with a range of ?-carbonyl-?-substituted acrylates 3. PMID:19601599

  12. Enantioselective Synthesis of Tertiary Propargylic Alcohols under N-Heterocyclic Carbene Catalysis.

    PubMed

    Sánchez-Díez, Eduardo; Fernández, Maitane; Uria, Uxue; Reyes, Efraim; Carrillo, Luisa; Vicario, Jose L

    2015-06-01

    A straightforward procedure to carry out the enantioselective benzoin reaction between aldehydes and ynones by employing a chiral N-heterocyclic carbene (NHC) as catalyst was developed. Under the optimized reaction conditions, these ynones undergo a clean and selective 1,2-addition with the catalytically generated Breslow intermediate, not observing any byproduct arising from competitive Stetter-type reactivity. This procedure allows the preparation of tertiary alkynyl carbinols as highly enantioenriched materials, which have the remarkable potential to be used as chiral building blocks in organic synthesis. PMID:25907587

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

    PubMed Central

    Andrews, Ian P.

    2012-01-01

    In this study we performed the total synthesis of the terpene indole alkaloid (+)-ibophyllidine through a pathway involving asymmetric phosphine catalysis, with our novel l-4-hydroxyproline–derived chiral phosphine mediating the key [3 + 2] annulation. Hydrogenation of the [3 + 2] adduct allowed the rapid formation of the stereochemically dense pyrrolidine ring of (+)-ibophyllidine in excellent yield with exceptionally high levels of both diastereo- and enantioselectivity. We constructed the remainder of the pentacyclic skeleton through an intramolecular alkylation and an intramolecular aza-Morita–Baylis–Hillman reaction. PMID:22798981

  14. Enantioselective Total Synthesis of (?)-Minovincine in Nine Chemical Steps: An Approach to Ketone Activation in Cascade Catalysis

    PubMed Central

    Laforteza, Brian N.; Pickworth, Mark

    2014-01-01

    More cycling–fewer steps The first enantioselective total synthesis of (?)-minovincine has been accomplished in nine chemical steps and 13% overall yield. A novel, one-step Diels–Alder/?-elimination/conjugate addition organocascade sequence allowed rapid access to the central tetracyclic core in an asymmetric manner. PMID:24000234

  15. Enantioselective synthesis of (-)-maoecrystal V by enantiodetermining C-H functionalization.

    PubMed

    Lu, Ping; Mailyan, Artur; Gu, Zhenhua; Guptill, David M; Wang, Hengbin; Davies, Huw M L; Zakarian, Armen

    2014-12-24

    The evolution of a program directed at the enantioselective total synthesis of maoecrystal V, a highly modified ent-kauranoid, is described. An early stage chiral auxiliary-directed asymmetric C-H functionalization for the construction of a key benzofuran intermediate enabled the first asymmetric synthesis of the natural enantiomer of maoecrystal V, confirming the assigned stereochemistry. A divergent course of the central intramolecular Diels-Alder reaction, which is dependent on the nature of the dienophile, initially led to the development of an unanticipated and previously unknown isomer of maoecrystal V, which we named maoecrystal ZG. In light of the reported selective and potent cytotoxic activity of maoecrystal V, the cytotoxic properties of maoecrystal ZG were also investigated. PMID:25409033

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

    PubMed Central

    Bhanushali, Mayur; Zhao, Cong-Gui

    2011-01-01

    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. PMID:21918584

  17. Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of C7-functionalized indoles.

    PubMed

    Shi, Feng; Zhang, Hong-Hao; Sun, Xiao-Xue; Liang, Jing; Fan, Tao; Tu, Shu-Jiang

    2015-02-16

    The first catalytic asymmetric cascade reaction of 7-vinylindoles has been established by the rational design of such substrates. Cascade reactions with isatin-derived 3-indolylmethanols in the presence of a chiral phosphoric acid derivative allow the diastereo- and enantioselective synthesis of C7-functionalized indoles as well as the construction of cyclopenta[b]indole and spirooxindole frameworks (all >95:5 d.r., 94->99?% ee). This approach not only addresses the great challenge of the catalytic asymmetric synthesis of C7-functionalized indoles, but also provides an efficient method for constructing biologically important cyclopenta[b]indole and spirooxindole scaffolds with excellent optical purity. Investigation of the reaction pathway and activation mode has suggested that this cascade reaction proceeds through a vinylogous Michael addition/Friedel-Crafts process, in which dual H-bonding activation of the two reactants plays a crucial role. PMID:25521722

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

    PubMed Central

    Roesner, Stefan; Aggarwal, Varinder K.

    2013-01-01

    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

  19. Studies Directed Toward the Enantioselective Synthesis of Cymbalta?

    Microsoft Academic Search

    Colin McKinlay

    2011-01-01

    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

  20. Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations

    E-print Network

    Colby Davie, Elizabeth A. (Elizabeth Anne)

    2005-01-01

    I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand ...

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

    In biology-oriented synthesis the underlying scaffold classes of natural products selected in evolution are used to define biologically relevant starting points in chemical structure space for the synthesis of compound collections with focused structural diversity. Here we describe a highly enantioselective synthesis of natural-product-inspired 3,3'-pyrrolidinyl spirooxindoles-which contain an all-carbon quaternary centre and three tertiary stereocentres. This synthesis takes place by means of an asymmetric Lewis acid-catalysed 1,3-dipolar cycloaddition of an azomethine ylide to a substituted 3-methylene-2-oxindole using 1-3 mol% of a chiral catalyst formed from a N,P-ferrocenyl ligand and CuPF6(CH3CN)4. Cellular evaluation has identified a molecule that arrests mitosis, induces multiple microtubule organizing centres and multipolar spindles, causes chromosome congression defects during mitosis and inhibits tubulin regrowth in cells. Our findings support the concept that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry will be a rich source of compounds with diverse bioactivity.

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

    PubMed

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

    2013-07-01

    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. PMID:24039305

  3. A Concise Enantioselective Synthesis and Cytotoxic Evaluation of the Anticancer Rotenoid Deguelin Enabled by a Tandem Knoevenagel/Conjugate Addition/Decarboxylation Sequence

    PubMed Central

    Farmer, Rebecca L.

    2013-01-01

    (?)-Deguelin is a rotenoid natural product that possesses significant potential as a chemopreventive and chemotherapeutic agent. While several racemic syntheses of deguelin have been reported, a formal evaluation of the anticancer activity of both the natural and unnatural enantiomers remains lacking. We describe herein the successful application of a flexible and selective thiourea-catalyzed cyclization strategy toward the enantioselective total synthesis of deguelin, which allows access to either stereoisomer for biological studies. The synthesis was completed in six steps (longest linear) with no protecting groups. The evaluation of both enantiomers of the natural product demonstrated potent inhibition of several cancer cell lines by these compounds, but interestingly showed that the unnatural (+)-deguelin preferentially inhibited the growth of MCF-7 breast cancer and HepG2 liver carcinoma cells when compared to the natural product. PMID:24101971

  4. Enantioselective Synthesis of Angularly Substituted 1-Azabicylic Rings: Coupled Dynamic Kinetic Epimerization and Chirality Transfer

    PubMed Central

    Aron, Zachary D.; Ito, Tatsuya; May, Tricia L.; Overman, Larry E.; Wang, Jocelyn

    2013-01-01

    A new strategy for enantioselective synthesis of azacyclic molecules in which dynamic kinetic equilibration of diastereomeric iminium ions precedes a stereochemistry-determining sigmatropic rearrangement is reported. The method is illustrated by the synthesis in high enantiomeric purity (generally 95–99% ee) of a variety of 1-azabicyclic molecules containing angular allyl or 3-substituted 2-propenyl side chains adjacent to nitrogen and up to three stereogenic centers. In these products, the size of the carbocyclic ring is varied widely (5–12 membered), however useful yields are obtained in forming 1-azabicyclic products containing only fused pyrrolidine and piperidine rings. Chi-rality transfer from substituents at carbons 1 and 2 of the 3-butenylamine fragment of the starting material is investigated, with methyl and phenyl substituents at the allylic position shown to provide exquisite stereocontrol (generally 98–99% chirality transfer). An attractive feature of the method is the ability to carry out the key transformation in the absence of solvent. Illustrated also is the high yielding conversion of four such products to a new family of bicyclic ?-amino acids of high enantiomeric purity. PMID:24090405

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    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.

  6. Enantioselective synthesis of schulzeines B and C via a beta-lactone-derived surrogate for bishomoserine aldehyde.

    PubMed

    Liu, Gang; Romo, Daniel

    2009-03-01

    Enantioselective syntheses of the glucosidase inhibitors schulzeines B and C were achieved by employing a Pictet-Spengler reaction of a beta-lactone-derived, masked bishomoserine aldehyde. Subsequent Corey-Link reaction unveiled an alpha-azido acid enabling cyclization to the delta-lactam fused tetrahydroisoquinoline. An efficient synthesis of the trisulfate-bearing side chain featured a Noyori hydrogenation and a Sharpless dihydroxylation. An unexpected reaction of a pendant amine during a Corey-Link process opens avenues for the synthesis of proline and related amino acid derivatives. PMID:19209875

  7. Enantioselective divergent synthesis of (-)-cis-?- and (-)-cis-?-irone by using Wilkinson's catalyst.

    PubMed

    Bugoni, Serena; Boccato, Debora; Porta, Alessio; Zanoni, Giuseppe; Vidari, Giovanni

    2015-01-01

    A simple, efficient synthesis is reported for (-)-cis-?- and (-)-cis-?-irone, two precious constituents of iris oils, in ?99?% diastereomeric and enantioselective ratios. The two routes diverge from a common intermediate prepared from (-)-epoxygeraniol. Of general interest in this approach is the installation of the enone moiety of irones through a NHC?Au(I) -catalyzed Meyer-Schuster-like rearrangement of a propargylic benzoate and the use of Wilkinson's catalyst for the stereoselective hydrogenation of a prostereogenic exocyclic double bond to secure the critical cis stereochemistry of the alkyl groups at C2 and C6 of the irones. The stereochemical aspects of this reaction are rationally supported by DFT calculation of the conformers of the substrates undergoing the hydrogenation and by a modeling study of the geometry of the rhodium ?(2) complexes involved in the diastereodifferentiation of the double bond faces. Thus, computational investigation of the ?(2) intermediates formed in the catalytic cycle of prostereogenic alkene hydrogenation by using Wilkinson's catalyst could be highly predictive of the stereochemistry of the products. PMID:25358720

  8. A lipid-coated lipase as an enantioselective ester synthesis catalyst in homogeneous organic solvents

    SciTech Connect

    Okahata, Yoshio; Fujimoto, Yoshitaka; Ijiro, Kuniharu [Tokyo Inst. of Technology, Yokohama (Japan)

    1995-04-07

    The authors studied the enantioselective preparation of esters using lipase as catalyst. The surface of the lipase was coated with lipids to assist in directing the formation of the ester by solubilizing the hydrophobic incipient tail of the ester.

  9. Asymmetric synthesis of amines by the catalytic enantioselective additions of hydrazoic acid to ketenes

    E-print Network

    Nakai, Takashi, S.M. Massachusetts Institute of Technology

    2007-01-01

    The development of a planar-chiral catalyst for the enantioselective additions of HN3 to hindered ketenes was investigated. It was demonstrated that a new planar-chiral catalyst (1.5) is an excellent catalyst for the ...

  10. Enantioselective nucleophile-catalyzed cycloadditions

    E-print Network

    Wilson, Jonathan E., Ph. D. Massachusetts Institute of Technology

    2007-01-01

    Chapter 1 describes the development of an asymmetric nucleophile-catalyzed [2+2] cycloaddition of ketenes with aldehydes. This is the first report of a catalytic enantioselective synthesis of trisubstituted [beta]-lactones. ...

  11. Divergent synthesis of chiral heterocycles via sequencing of enantioselective three-component reactions and one-pot subsequent cyclization reactions.

    PubMed

    Tang, Min; Xing, Dong; Huang, Haoxi; Hu, Wenhao

    2015-07-01

    A highly efficient sequencing of catalytic asymmetric three-component reactions of alcohols, diazo compounds and aldimines/aldehydes with one-pot subsequent cyclization reactions was reported. The development of a robust and versatile Rh(ii)/Zr(iv)-BINOL co-catalytic system not only gives high diastereo- and enantioselective controls of the three-component reaction, but also shows excellent functionality tolerances that allow a wide range of functionalities to be pre-installed in each component and readily undergo one-pot subsequent cyclization reactions, thus providing rapid and diversity-oriented synthesis (DOS) of different types of chiral nitrogen- and/or oxygen-containing polyfunctional heterocycles. PMID:25864421

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

    PubMed Central

    Page, Abigail

    2011-01-01

    Summary Diaryl ethers carrying carbamoyloxymethyl groups may be desymmetrised enantio- and diastereoselectively by the use of the sec-BuLi–(?)-sparteine complex in diethyl ether. Enantioselective deprotonation of one of the two benzylic positions leads to atropisomeric products with ca. 80:20 e.r.; an electrophilic quench typically provides functionalised atropisomeric diastereoisomers in up to 97:3 d.r. PMID:22043243

  13. Enantioselective Synthesis of Chromanones via a Peptidic Phosphane Catalyzed Rauhut-Currier Reaction.

    PubMed

    Scanes, Robert J H; Grossmann, Oleg; Grossmann, André; Spring, David R

    2015-05-15

    The enantioselective intramolecular Rauhut-Currier reaction has been developed using a bifunctional dipeptidic phosphane catalyst, providing a direct access to biologically active ?-methylene-?-valerolactones in high yields and enantiomeric excesses. The novel catalyst is accessible in only four steps from commercial sources and exhibits unusual binding selectivities for a small molecule, suggesting the possibility for long-range interactions between the catalyst and the substrate. PMID:25915565

  14. Chiral base-catalyzed enantioselective synthesis of 4-aryloxyazetidinones and 3,4-benzo-5-oxacephams.

    PubMed

    Kozio?, Anna; Furman, Bart?omiej; Frelek, Jadwiga; Wo?nica, Magdalena; Altieri, Elisa; Chmielewski, Marek

    2009-08-01

    Readily available 4-formyloxyazetidinone was enantioselectively transformed into 3,4-benzo-2-hydroxy-5-oxacephams and 4-phenyloxyazetidinones upon treatment with 0.1 equiv of the cinchona alkaloid in toluene via intermolecular nucleophilic trapping of N-acyliminium intermediate by the hydroxyl moiety of phenols or o-hydroxybenzaldehydes. Additionally, the absolute configuration of title compounds was established by CD spectroscopy. PMID:19572576

  15. Enantioselective synthesis of iclaprim enantiomers--a versatile approach to 2-substituted chiral chromenes.

    PubMed

    Tahtaoui, Chouaib; Demailly, Arnold; Guidemann, Carole; Joyeux, Cécile; Schneider, Peter

    2010-06-01

    Both enantiomers of the DHFR inhibitor iclaprim (R)-1 and (S)-1 were synthesized from the cyclopropyl homoallyl alcohols (R)-6 and (S)-6, respectively. As key steps these transformations include a Mitsunobu reaction and the formation of the diaminopyrimidine unit prior to a novel cyclization procedure to obtain the desired chromene heterocycle. The moderate enantioselectivity of the products (R)-1 and (S)-1 is related to the Mitsunobu reaction, which unfortunately did not proceed with complete inversion of configuration. PMID:20446707

  16. Synthesis of chiral triazine coupling reagents based on esters of N-alkylproline and their application in the enantioselective incorporation of D or L amino acid residue directly from racemic substrate.

    PubMed

    Kasperowicz-Frankowska, Katarzyna; Gzik, Anna; Dziemidkiewicz, Micha?; Kolesi?ska, Beata; Kami?ski, Zbigniew J

    2014-01-01

    Esters of N-methylproline and N-allylproline were prepared and used as component for synthesis of chiral triazine based coupling reagents. N-Triazinylammonium tetrafluoroborate obtained from methylester of L-N-methylproline, 2-chloro-4,6-dimethozxy-1,3,5-triazine and tetrafluoroboric acid in the coupling of rac-Z- A1a-OH with glycine methylester preferred formation of D-Z-AlaGly-OMe with L/D ratio 21/79. Coupling reagent prepared from D enantiomer of N-methylproline gave L-Z-AlaGly-OMe with L/D ratio 75/25. PMID:25745772

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

    Microsoft Academic Search

    A. A. Verstegen-Haaksma

    1994-01-01

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

  18. Organocatalytic Highly Enantioselective Substitution of 3-(1-Tosylalkyl)indoles with Oxindoles Enables the First Total Synthesis of (+)-Trigolutes?B.

    PubMed

    Huang, Jian-Zhou; Zhang, Chen-Long; Zhu, Yi-Fan; Li, Lu-Lu; Chen, Dian-Feng; Han, Zhi-Yong; Gong, Liu-Zhu

    2015-06-01

    A highly enantioselective organocatalytic substitution of 3-(1-tosylalkyl)indoles with oxindoles has been established by using chiral bifunctional organocatalysts, providing an efficient entry to multiply functionalized 3,3'-disubstituted oxindoles, and was exploited as the key step to enable the first asymmetric total synthesis of optically pure (+)-trigolutes?B to be accomplished in a concise manner, within seven steps with an 18?% overall yield. PMID:25916808

  19. Enantioselective Pictet-Spengler Reactions of Isatins for the Synthesis of Spiroindolones

    PubMed Central

    Badillo, Joseph J.; Silva-García, Abel; Shupe, Benjamin H.; Fettinger, James C.; Franz, Annaliese K.

    2011-01-01

    The condensation cyclization between isatins and 5-methoxy tryptamine catalyzed by chiral phosphoric acids provides spirooxindole tetrahydro-?-carboline products in excellent yields (up to 99%) and enantioselectivity (up to 98:2 er). A comparison of catalysts provides insight for the substrate scope and factors responsible for efficient catalytic activity and selectivity in the spirocyclization. Chiral phosphoric acids with different 3,3?-substitution on the binaphthyl system and opposite axial chirality afford the spiroindolone product with the same absolute configuration. PMID:22442499

  20. Design and enantioselective synthesis of Cashmeran odorants by using "enol catalysis".

    PubMed

    Felker, Irene; Pupo, Gabriele; Kraft, Philip; List, Benjamin

    2015-02-01

    Novel Cashmeran odorants were designed by molecular modeling. Their short syntheses involve a novel asymmetric Brønsted acid catalyzed Michael addition of unactivated ?-substituted ketones. This key transformation was realized by utilizing a new type of enol activation catalysis and affords different cyclic ketones bearing ?-quaternary stereocenters in good to excellent yields and with high enantioselectivity. Subsequent McMurry coupling and Saegusa-Ito oxidation furnished the enantiopure target odorants, one enantiomer of which indeed possesses the typical olfactory aspects of Cashmeran. PMID:25573140

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

    NASA Astrophysics Data System (ADS)

    Hanson, John

    2001-09-01

    Jacobsen's catalyst, N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, is a popular reagent for the enantioselective epoxidation of alkenes. This reagent is successfully prepared in three steps by beginning organic chemistry students. A mixture of 1,2-diaminocyclohexane isomers is purified and resolved by crystallization (and recrystallization) with L-tartaric acid; a diimine is formed between the resolved trans-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde to produce the Jacobsen ligand; and finally Jacobsen's catalyst is prepared from the ligand by treatment with manganese(II) acetate followed by oxidation with air. The students then use their Jacobsen catalyst to enantioselectively epoxidize one of the following alkenes: 1,2-dihydronaphthalene, styrene, or a-methylstyrene. After purifying their epoxides by flash chromatography, students determine the enantiopurity by GC using a chiral column. In this series of experiments students utilize a wide variety of laboratory techniques: running a reaction at reflux, aqueous workup with a separatory funnel, recrystallization, flash chromatography, TLC, polarimetry, IR and NMR spectroscopy, and chiral GC analysis. These labs also reinforce many important concepts related to chirality, stereochemistry, and optical activity.

  2. Enantioselective Protonation

    PubMed Central

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

    2010-01-01

    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. PMID:20428461

  3. Enantioselective Synthesis of Boron-Substituted Quaternary Carbon Stereogenic Centers through NHC–Catalyzed Conjugate Additions of (Pinacolato)boron Units to Enones**

    PubMed Central

    Radomkit, Suttipol

    2014-01-01

    The first examples of Lewis base-catalyzed enantioselective boryl conjugate additions (BCA) that generate boron-substituted quaternary carbon stereogenic centers are disclosed. Reactions are performed in the presence of 1.0–5.0 mol % of a readily available chiral accessible N-heterocyclic carbene (NHC) and commercially available bis(pinacolato)diboron; cyclic or linear ?,?-unsaturated ketones can be used and rigorous exclusion of air or moisture is not necessary. The desired products are obtained in 63–95% yield and 91:9 to >99:1 enantiomeric ratio (e.r.). The special utility of the NHC-catalyzed approach is demonstrated in the context of an enantioselective synthesis of natural product anti-fungal (?)-crassinervic acid. PMID:24615958

  4. Simple strategy for synthesis of optically active allylic alcohols and amines by using enantioselective organocatalysis

    PubMed Central

    Jiang, Hao; Holub, Nicole; Anker Jørgensen, Karl

    2010-01-01

    A simple organocatalytic one-pot protocol for the construction of optically active allylic alcohols and amines using readily available reactants and catalyst is presented. The described reaction is enabled by an enantioselective enone epoxidation/aziridination-Wharton-reaction sequence affording two highly privileged and synthetically important classes of compounds in an easy and benign way. The advantages of the described sequence include easy generation of stereogenic allylic centers, also including quaternary stereocenters, with excellent enantio- and diastereomeric-control and high product diversity. Furthermore, using monosubstituted enones as substrates, having moderate enantiomeric excess, the one-pot reaction sequence proceeds with an enantioenrichment of the products and high diastereoselectivity was achieved. PMID:20547884

  5. Enantioselective synthesis of chiral isotopomers of 1-alkanols by a ZACA-Cu-catalyzed cross-coupling protocol.

    PubMed

    Xu, Shiqing; Oda, Akimichi; Negishi, Ei-ichi

    2014-12-01

    Chiral compounds arising from the replacement of hydrogen atoms by deuterium are very important in organic chemistry and biochemistry. Some of these chiral compounds have a non-measurable specific rotation, owing to very small differences between the isotopomeric groups, and exhibit cryptochirality. This particular class of compounds is difficult to synthesize and characterize. Herein, we present a catalytic and highly enantioselective conversion of terminal alkenes to various ? and more remote chiral isotopomers of 1-alkanols, with ?99?% enantiomeric excess (ee), by the Zr-catalyzed asymmetric carboalumination of alkenes (ZACA) and Cu-catalyzed cross-coupling reactions. ZACA-in?situ iodinolysis of allyl alcohol and ZACA-in?situ oxidation of TBS-protected ?-alkene-1-ols protocols were applied to the synthesis of both (R)- and (S)-difunctional intermediates with 80-90?% ee. These intermediates were readily purified to provide enantiomerically pure (?99?% ee) compounds by lipase-catalyzed acetylation. These functionally rich intermediates serve as very useful synthons for the construction of various chiral isotopomers of 1-alkanols in excellent enantiomeric purity (?99?% ee) by introducing deuterium-labeled groups by Cu-catalyzed cross-coupling reactions without epimerization. PMID:25351794

  6. Organocatalytic enantioselective direct additions of aldehydes to 4-vinylpyridines and electron-deficient vinylarenes and their synthetic applications.

    PubMed

    Wang, Sinan; Li, Xiangmin; Liu, Hongwei; Xu, Li; Zhuang, Jinchen; Li, Jian; Li, Hao; Wang, Wei

    2015-02-18

    We describe a synergistic catalysis strategy for the asymmetric direct addition of simple aldehydes to 4-vinylpyridines. By means of independent activation of weakly electrophilic 4-vinylpyridines by the Brønsted acid CF3SO3H (TfOH) and aldehydes by chiral diphenylprolinol tert-butyldimethylsilyl (TBDMS) ether-catalyzed formation of nucleophilic enamines in a cooperative manner, the previously unattainable highly enantioselective addition process has been realized for the first time. Notably, the power of the addition process is fueled by its high efficiency in the production of synthetically valued chiral pyridines. (1)H NMR studies of the process suggested that the nucleophilic enamine formed in situ from the chiral amine catalyst and the aldehyde is directly added to the trimeric 4-vinylpyridinium-derived species as a highly active electrophile generated from the 4-vinylpyridine in the presence of TfOH. Moreover, inspired by the similar electronic natures of pyridine and nitrobenzene, we have achieved an unprecedented chiral diphenylprolinol TBDMS ether-promoted, highly enantioselective direct addition of aldehydes to 2-nitrostyrenes without the use of TfOH as a cocatalyst. In this approach, introducing a strong electron-withdrawing group such as NO2, CF3, SO2Me, etc. on the 2-nitrostyrene creates a highly electrophilic vinyl moiety, which enables the direct addition of the in situ-formed enamine derived from the chiral amine promoter and the aldehyde. This method significantly expands the scope of the enantioselective addition process. While the electron-withdrawing nitro group is essential for activation of the vinyl group, we have demonstrated that it can be readily transformed to diverse functionalities. Furthermore, as shown, a chiral pyridine adduct serves as a key building block in the synthesis of the potent fibrinogen receptor antagonist L-734,217. PMID:25629299

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

    E-print Network

    Shen, Xiaoqiang

    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)[subscript 2] and ...

  8. Enantioselective Synthesis of the C(1)–C(11) Fragment of Tedanolide C

    PubMed Central

    Geist, Julie G.; Barth, Roland

    2012-01-01

    A convergent synthesis of the protected C(1)–C(11) fragment 6 of the targeted enantiomer of tedanolide C is described. The key step of the synthesis is the Felkin-Ahn addition of vinyl iodide 7 to aldehyde 8 that proceeds in 80% yield with 4:1 diastereoselectivity. PMID:23249423

  9. Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis

    PubMed Central

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

    2009-01-01

    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. PMID:19011612

  10. Diastereo- and enantioselective synthesis of alpha,beta-disubstituted gamma-nitro methyl sulfonates.

    PubMed

    Enders, D; Berner, O M; Vignola, N; Bats, J W

    2001-12-01

    A novel asymmetric synthesis of highly enantioenriched homotaurine precursors has been developed via diastereo-selective Michael addition of lithiated enantiopure sulfonates to nitroalkenes by using 1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose as chiral auxiliary. PMID:12240033

  11. An Enantioselective Synthesis of CymbaltaTM Colin McKinlay and Vincent van Rixel

    Microsoft Academic Search

    Colin McKinlay; Vincent van Rixel

    2010-01-01

    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

  12. Enantioselective synthesis of 4-substituted phenylalanines by cross-coupling reactions

    Microsoft Academic Search

    Fariborz Firooznia; Candido Gude; Kenneth Chan; Nicholas Marcopulos; Yoshitaka Satoh

    1999-01-01

    The enantiomerically enriched BOC-protected (4-pinacolylborono)phenylalanine methyl ester (8) is produced via enzymatic resolution of the racemic material, or direct synthesis from the corresponding iodide (or triflate), and undergoes Suzuki-Miyaura coupling reactions with aromatic halides and triflates in the presence of catalytic amounts of PdCl2(dppf) to produce enantiomerically enriched 4-substituted phenylalanine derivatives.

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

    PubMed Central

    Wilson, Matthew R.; Taylor, Richard E.

    2012-01-01

    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. PMID:22720980

  14. A novel, efficient, diastereo- and enantioselective Mukaiyama aldol-based synthesis of a vinyl cyclopentanone core derivative of viridenomycin.

    PubMed

    Batsanov, Andrei S; Knowles, Jonathan P; Lightfoot, Andrew P; Maw, Graham; Thirsk, Carl E; Twiddle, Steven J R; Whiting, Andrew

    2007-12-20

    A strategy has been developed for a rapid seven-step construction of a chiral, nonracemic vinyl cyclopentanone building block as part of a synthetic approach to viridenomycin, using a diastereo- and enantioselective Mukaiyama aldol and intramolecular Knoevenagel condensation as key steps. PMID:18020354

  15. Synthesis of 2,3,4-Trisubstituted Thiochromanes using an Organocatalytic Enantioselective Tandem Michael–Henry Reaction

    PubMed Central

    Dodda, Rajasekhar; Goldman, Joshua J.; Mandal, Tanmay; Broker, Grant A.; Tiekink, Edward R. T.

    2009-01-01

    Enantioenriched 2,3,4-trisubstituted thiochromanes have been synthesized by using a cupreine-catalyzed tandem Michael addition–Henry reaction between 2-mercaptobenzaldehydes and ?-nitrostyrenes. Good diastereoselectivities and enantioselectivities were obtained for the title compounds, which may be further improved through a single recrystallization (up to 98% de and> 99% ee). PMID:19829750

  16. Efficient Asymmetric Synthesis of 1-Cyano-tetrahydroisoquinolines from Lipase Dual Activity and Opposite Enantioselectivities in ?-Aminonitrile Resolution

    PubMed Central

    Sakulsombat, Morakot; Vongvilai, Pornrapee; Ramström, Olof

    2014-01-01

    Dual promiscuous racemization/amidation activities of lipases leading to efficient dynamic kinetic resolution protocols of racemic ?-aminonitrile compounds are described. ?-Amidonitrile products of high enantiomeric purity could be formed in high yields. Several lipases from different sources were shown to exhibit the dual catalytic activities, where opposite enantioselectivities could be recorded for certain substrates. PMID:25055970

  17. Stereoconvergent arylations and alkenylations of unactivated alkyl electrophiles: catalytic enantioselective synthesis of secondary sulfonamides and sulfones.

    PubMed

    Choi, Junwon; Martín-Gago, Pablo; Fu, Gregory C

    2014-08-27

    The development of efficient methods for the generation of enantioenriched sulfonamides and sulfones is an important objective for fields such as organic synthesis and medicinal chemistry; however, there have been relatively few reports of direct catalytic asymmetric approaches to controlling the stereochemistry of the sulfur-bearing carbon of such targets. In this report, we describe nickel-catalyzed stereoconvergent Negishi arylations and alkenylations of racemic ?-bromosulfonamides and -sulfones that furnish the desired cross-coupling product in very good ee and yield for an array of reaction partners. Mechanistic studies are consistent with the generation of a radical intermediate that has a sufficient lifetime to diffuse out of the solvent cage and to cyclize onto a pendant olefin. PMID:25127186

  18. Exploring Nitrilase Sequence Space for Enantioselective Catalysis

    Microsoft Academic Search

    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

    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

  19. Enantioselective synthesis of alkyne-substituted quaternary carbon stereogenic centers through NHC-Cu-catalyzed allylic substitution reactions with (i-Bu)2(alkynyl)aluminum reagents.

    PubMed

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

    2011-04-01

    A catalytic enantioselective method for the formation of alkyne-substituted all-carbon quaternary stereogenic centers is reported. Additions of alkynylaluminums to alkyl-, aryl-, carboxylic ester-, or silyl-substituted allylic phosphates are promoted by 1.0-5.0 mol % loadings of NHC-Cu complexes derived from air-stable and commercially available CuCl(2)·2H(2)O. The requisite Al-based reagents are prepared through treatment of the corresponding aryl-, heteroaryl-, alkyl-, or alkenyl-substituted terminal alkynes with diisobutylaluminum hydride in the presence of 5.0 mol % Et(3)N at ambient temperature. The desired 1,4-enynes are obtained in up to 98% yield and >99:1 enantiomeric ratio. Selected Au-catalyzed cyclizations involving the alkyne unit of the enantiomerically enriched products are presented as a demonstration of the method's utility in chemical synthesis. PMID:21384918

  20. Highly enantioselective synthesis of 1,3-mercapto alcohols from ?,?-unsaturated ketones: asymmetric bifunctional group exchange reaction

    Microsoft Academic Search

    Hiroaki Shiraki; Kiyoharu Nishide; Manabu Node

    2000-01-01

    Optically active 1,3-mercapto alcohols were synthesized from ?,?-unsaturated ketones using a chiral reagent B and dimethylaluminum chloride in two steps. The transformation involved a tandem Michael addition–MPV reduction and a base-catalyzed elimination. The two newly created chiral carbons in trans-chalcone derivatives were enantioselectively controlled to a high degree. Using the above transformation, an asymmetric bifunctional group exchange reaction between the

  1. Cloning and Characterization of a Novel Esterase from Rhodococcus sp. for Highly Enantioselective Synthesis of a Chiral Cilastatin Precursor.

    PubMed

    Zhang, Yan; Pan, Jiang; Luan, Zheng-Jiao; Xu, Guo-Chao; Park, Sunghoon; Xu, Jian-He

    2014-12-01

    A novel nonheme chloroperoxidase (RhEst1), with promiscuous esterase activity for enantioselective hydrolysis of ethyl (S)-2,2-dimethylcyclopropanecarboxylate, was identified from a shotgun library of Rhodococcus sp. strain ECU1013. RhEst1 was overexpressed in Escherichia coli BL21(DE3), purified to homogeneity, and functionally characterized. Fingerprinting analysis revealed that RhEst1 prefers para-nitrophenyl (pNP) esters of short-chain acyl groups. pNP esters with a cyclic acyl moiety, especially that with a cyclobutanyl group, were also substrates for RhEst1. The Km values for methyl 2,2-dimethylcyclopropanecarboxylate (DmCpCm) and ethyl 2,2-dimethylcyclopropane carboxylate (DmCpCe) were 0.25 and 0.43 mM, respectively. RhEst1 could serve as an efficient hydrolase for the bioproduction of optically pure (S)-2,2-dimethyl cyclopropane carboxylic acid (DmCpCa), which is an important chiral building block for cilastatin. As much as 0.5 M DmCpCe was enantioselectively hydrolyzed into (S)-DmCpCa, with a molar yield of 47.8% and an enantiomeric excess (ee) of 97.5%, indicating an extremely high enantioselectivity (E = 240) of this novel and unique biocatalyst for green manufacturing of highly valuable chiral chemicals. PMID:25239898

  2. Cloning and Characterization of a Novel Esterase from Rhodococcus sp. for Highly Enantioselective Synthesis of a Chiral Cilastatin Precursor

    PubMed Central

    Zhang, Yan; Pan, Jiang; Luan, Zheng-Jiao; Park, Sunghoon

    2014-01-01

    A novel nonheme chloroperoxidase (RhEst1), with promiscuous esterase activity for enantioselective hydrolysis of ethyl (S)-2,2-dimethylcyclopropanecarboxylate, was identified from a shotgun library of Rhodococcus sp. strain ECU1013. RhEst1 was overexpressed in Escherichia coli BL21(DE3), purified to homogeneity, and functionally characterized. Fingerprinting analysis revealed that RhEst1 prefers para-nitrophenyl (pNP) esters of short-chain acyl groups. pNP esters with a cyclic acyl moiety, especially that with a cyclobutanyl group, were also substrates for RhEst1. The Km values for methyl 2,2-dimethylcyclopropanecarboxylate (DmCpCm) and ethyl 2,2-dimethylcyclopropane carboxylate (DmCpCe) were 0.25 and 0.43 mM, respectively. RhEst1 could serve as an efficient hydrolase for the bioproduction of optically pure (S)-2,2-dimethyl cyclopropane carboxylic acid (DmCpCa), which is an important chiral building block for cilastatin. As much as 0.5 M DmCpCe was enantioselectively hydrolyzed into (S)-DmCpCa, with a molar yield of 47.8% and an enantiomeric excess (ee) of 97.5%, indicating an extremely high enantioselectivity (E = 240) of this novel and unique biocatalyst for green manufacturing of highly valuable chiral chemicals. PMID:25239898

  3. Enantioselective synthesis of (E)-delta-stannyl homoallylic alcohols via aldehyde allylboration using alpha-stannylallylboranes generated by allene hydroboration followed by a highly diastereoselective 1,3-boratropic shift.

    PubMed

    Chen, Ming; Ess, Daniel H; Roush, William R

    2010-06-16

    A highly enantioselective synthesis of (E)-delta-stannyl homoallylic alcohols 4 via aldehyde allylboration reactions of the double-chiral allylborane reagent 2a is reported. Allylborane 2a was generated from the hydroboration of commercially available allenylstannane 1 with ((d)Ipc)(2)BH at -40 to -20 degrees C followed by a kinetically controlled and highly diastereoselective 1,3-boratropic shift in intermediate 3a. PMID:20496899

  4. Isoindolinones as Michael Donors under Phase Transfer Catalysis: Enantioselective Synthesis of Phthalimidines Containing a Tetrasubstituted Carbon Stereocenter.

    PubMed

    Scorzelli, Francesco; Di Mola, Antonia; Palombi, Laura; Massa, Antonio

    2015-01-01

    Readily available chiral ammonium salts derived from cinchona alkaloids have proven to be effective phase transfer catalysts in the asymmetric Michael reaction of 3-substituted isoindolinones. This protocol provides a convenient method for the construction of valuable asymmetric 3,3-disubstituted isoindolinones in high yields and  moderate to good enantioselectivity. Diastereoselectivity was also investigated in the construction of contiguous tertiary and quaternary stereocenters. The use of acrolein as Michael acceptor led to an interesting tricyclic derivative, a pyrroloisoindolinone analogue, via a tandem conjugated addition/cyclization reaction. PMID:25985353

  5. Catalytic asymmetric difunctionalization of stable tertiary enamides with salicylaldehydes: highly efficient, enantioselective, and diastereoselective synthesis of diverse 4-chromanol derivatives.

    PubMed

    He, Ling; Zhao, Liang; Wang, De-Xian; Wang, Mei-Xiang

    2014-11-21

    Catalyzed by a chiral BINOL-Ti(OiPr)4 complex, various stable tertiary enamides reacted with salicylaldehydes to afford diverse cis,trans-configured 4-chromanols that contain three continuous stereogenic centers in good yields with excellent diastereoselectivity and enantioselectivity. The reaction proceeded through the addition of enamide to aldehyde followed by the intramolecular interception of the resulting iminium by the hydroxy group. Oxidation of the resulting 4-chromanols yielded almost quantitatively chroman-4-one derivatives which underwent diastereospecific reduction with NaBH4 to produce cis,cis-configured 4-chromanols. PMID:25358127

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

    PubMed Central

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

    2014-01-01

    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

  7. Palladacyclic imidazoline-naphthalene complexes: synthesis and catalytic performance in Pd(II)-catalyzed enantioselective reactions of allylic trichloroacetimidates.

    PubMed

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

    2012-02-17

    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 R(1) and R(2) 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 S(N)2' 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. PMID:22288535

  8. Enantioselective HPLC determination of oxiracetam enantiomers and application to a pharmacokinetic study in beagle dogs.

    PubMed

    Zhang, Qiuyang; Yang, Wei; Zhang, Qing; Yang, Yue; Li, Junxiu; Lu, Yang; Zheng, Yi; He, Jiake; Zhao, Di; Chen, Xijing

    2015-07-01

    An enantioselective high-performance liquid chromatography method was developed and validated for the determination of oxiracetam enantiomers, a cognition and memory enhancer, in beagle dog plasma. The plasma samples were prepared by methanol extraction from 200?L plasma, and then the baseline resolution was achieved on a Chiralpak ID column (250mm×4.6mm, 5?m) with mobile phase of hexane-ethanol-trifluoroacetic acid (78:22:0.1, v/v/v) at flow rate of 1.0mL/min. The column elute was monitored using ultraviolet detection at 214nm. The method was linear over concentration range 0.50-100?g/mL for both enantiomers. The relative standard deviation values for intra- and inter-day precision were 0.78-13.61 and 0.74-8.92% for (R)- and (S)-oxiracetam, respectively. The relative error values of accuracy ranged from -4.74 to 10.48% for (R)-oxiracetam and from -0.19 to 11.48% for (S)-oxiracetam. The method was successfully applied to a pharmacokinetic study of individual enantiomer and racemic oxiracetam in beagle dogs after oral administration. The disposition of the two enantiomers was not stereoselective and chiral inversion was not observed in beagle dogs. The pharmacokinetic profiles of (S)-oxiracetam were similar with racemic oxiracetam in beagle dogs. PMID:25978861

  9. Total synthesis and study of myrmicarin alkaloids

    E-print Network

    Ondrus, Alison Evelynn, 1981-

    2009-01-01

    I. Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids An enantioselective gram-scale synthesis of a key dihydroindolizine intermediate for the preparation of myrmicarin alkaloids is described. Key transformations ...

  10. 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

    Fuentes, José A; Phillips, Scott D; Clarke, Matthew L

    2012-01-01

    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. PMID:23216944

  11. 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

    2012-01-01

    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. PMID:23216944

  12. Nanostructures for Energy Application: Synthesis, Characterization and Advanced Applications

    E-print Network

    Vardi, Amichay

    , shape, and composition. The synthesis of 1-dimensional nanostructures is conducted by gas- and solution and composition Control of nanostructures Synthesis of nanowires and other structures using gas phase techniquesNanostructures for Energy Application: Synthesis, Characterization and Advanced Applications

  13. Enantioselective synthesis of d-?-amino amides from aliphatic aldehydes† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00064e Click here for additional data file. Click here for additional data file.

    PubMed Central

    Schwieter, Kenneth E.

    2015-01-01

    Peptides consisting of d-amino amides are highly represented among both biologically active natural products and non-natural small molecules used in therapeutic development. Chemical synthesis of d-amino amides most often involves approaches based on enzymatic resolution or fractional recrystallization of their diastereomeric amino acid salt precursors, techniques that produce an equal amount of the l-amino acid. Enantioselective synthesis, however, promises selective and general access to a specific ?-amino amide, and may enable efficient peptide synthesis regardless of the availability of the corresponding ?-amino acid. This report describes the use of a cinchona alkaloid-catalyzed aza-Henry reaction using bromonitromethane, and the integration of its product with umpolung amide synthesis. The result is a straightforward 3-step protocol beginning from aliphatic aldehydes that provides homologated peptides bearing an aliphatic side chain at the resulting d-?-amino amide. PMID:25838883

  14. 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

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

    2012-01-01

    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. PMID:22272931

  15. Stereoselective synthesis of multisubstituted alkenes via ring opening reactions of cyclopropenes. Enantioselective copper catalysed asymmetric reduction of alkenylheteroarenes. 

    E-print Network

    Wang, Yi

    2010-01-01

    A catalytic organometallic addition-ring opening sequence of cyclopropenes that enables the efficient and highly stereoselective synthesis of multisubstituted alkenes has been developed. A possible mechanism of organoaluminium ...

  16. Enantioselective Nucleophile-Catalyzed Synthesis of Tertiary Alkyl Fluorides via the ?-Fluorination of Ketenes: Synthetic and Mechanistic Studies

    E-print Network

    Lee, Sarah Yunmi

    The catalytic asymmetric synthesis of alkyl fluorides, particularly ?-fluorocarbonyl compounds, has been the focus of substantial effort in recent years. While significant progress has been described in the formation of ...

  17. Regio- and enantioselective synthesis of N-substituted pyrazoles by rhodium-catalyzed asymmetric addition to allenes.

    PubMed

    Haydl, Alexander M; Xu, Kun; Breit, Bernhard

    2015-06-01

    The rhodium-catalyzed asymmetric N-selective coupling of pyrazole derivatives with terminal allenes gives access to enantioenriched secondary and tertiary allylic pyrazoles, which can be employed for the synthesis of medicinally important targets. The reaction tolerates a large variety of functional groups and labelling experiments gave insights into the reaction mechanism. This new methodology was further applied in a highly efficient synthesis of JAK?1/2 inhibitor (R)-ruxolitinib. PMID:25926026

  18. The derivation of a chiral substituent code for secondary alcohols and its application to the prediction of enantioselectivity.

    PubMed

    Suo, Jing-Jie; Zhang, Qing-You; Li, Jing-Ya; Zhou, Yan-Mei; Xu, Lu

    2013-06-01

    A chiral substituent code was proposed based on the features of secondary alcohols, in which a chiral center is attached to two substituents in addition to OH and H substituents. The new chirality code, which was generated by predefining positional information of four substituents attached to stereocenter, was applied to two datasets composed of secondary alcohols as the enantioselective products of asymmetric reactions. In the first dataset, the chemical reaction was catalyzed by a biocatalyst, lipase from Candida rugosa. The catalyst for the second dataset was (-)-diisopinocampheylchloroborane. The structure-enantioselectivity relationship models were constructed using random forests with the chiral substituent code as the input. The resulting models were assessed both in terms of single enantiomers and pairs of enantiomers. Satisfactory results were obtained for both datasets. Although the chiral substituent code was specifically developed for secondary alcohols, it can easily be extended to represent chiral compounds possessing a specific chiral center bonded to two variable substituents. PMID:23666031

  19. Regiocontrol by remote substituents. An enantioselective total synthesis of frenolicin B via a highly regioselective Diels-Alder reaction

    SciTech Connect

    Kraus, G.A.; Li, J. (Iowa State Univ., Ames (United States)); Gordon, M.S.; Jensen, J.H. (Ames Lab. US-DOE, IA (United States))

    1993-06-30

    The quinone subunit is contained in a broad range of biologically important natural products such as frenolicin B, which is a member of the pyranonaphthoquinone family. The diverse biological activity of quinones has led to the development of several new synthetic methods for quinones. Among the pathways featuring a cycloaddition reaction, one of the most general methods for the regiospecific synthesis of substituted quinones was pioneered by H.J. Rapoport and others. This method involves the Diels-Alder reaction of a substituted quinone. As part of a program to evaluate the directing effects of functional groups not directly attached to the atoms undergoing Diels-Alder cycloaddition, we now report that remote substituents on a dienophile can confer excellent regioselectivity in Diels-Alder reactions. This work has led to an extremely direct synthesis of the pyranonaphthoquinone framework and to the first synthesis of frenolicin B (1). 19 refs., 1 fig.

  20. Enantioselective Radical Justin Potnick

    E-print Network

    Johnson, Jeff S.

    Enantioselective Radical Reactions Justin Potnick March 12, 2004 #12;Outline · Introduction to Radical Reactions · Atom Transfers · Reductive Alkylations · Fragmentations · Tandem Addition-Trapping Reactions · Oxidations · Summary #12;Introduction · Typical radical reactions go through 3 steps 1

  1. DOI: 10.1002/chem.200900776 Enantioselective Total Synthesis of Brevetoxin A: Unified Strategy for the B,

    E-print Network

    in a stereoselective Horner­Wittig reaction precedented in the previous synthesis by Nicolaou and co- workers (Scheme 1).[4,5] The Horner­Wittig coupling part- ners 2 and 3 would be obtained from advanced fragments 4 and 5, respectively

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

    Microsoft Academic Search

    Takashi Ooi; Minoru Kameda; Hidenori Tannai; Keiji Maruoka

    2000-01-01

    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.

  3. Nine-Step Enantioselective Total Synthesis of (-)-Vincorine Benjamin D. Horning and David W. C. MacMillan*

    E-print Network

    MacMillan, David W. C.

    alkaloid (-)-vincorine has been accomplished. A key element of the synthesis is a stereoselective alkaloid core architecture in one step from simple achiral precursors. The challenging seven-mem- bered yield from commercially available starting materials. The Vinca alkaloid natural products have

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

    PubMed Central

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

    2011-01-01

    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. PMID:22088096

  5. Formal chemoselective synthesis of leucascandrolide A.

    PubMed

    Ferrié, Laurent; Reymond, Sébastien; Capdevielle, Patrice; Cossy, Janine

    2007-06-21

    A chemoselective synthesis of the macrocyclic core of leucascandrolide A has been achieved, utilizing highly enantioselective allylmetalations, an enantioselective Noyori reduction of a propargylic ketone and olefin metatheses as the key steps. PMID:17536809

  6. Enantioselective synthesis of ?-hydroxy carboxylic acids: direct conversion of ?-oxocarboxylic acids to enantiomerically enriched ?-hydroxy carboxylic acids via neighboring group control

    Microsoft Academic Search

    Zhe Wang; Chunlin Zhao; Michael E. Pierce; Joseph M. Fortunak

    1999-01-01

    ?-Oxocarboxylic acids can be reduced to the corresponding ?-hydroxy carboxylic acids employing DIP-Cl™ as a reducing agent. The ?-carboxylic substituent exerts a remarkable neighboring group effect on the reduction. The reaction presumably proceeds in an intramolecular fashion through a `rigid' bicyclic transition state assembly, which produces enantioselectivities approaching 99%.

  7. Enantioselective alkynylation of benzo[e][1,2,3]-oxathiazine 2,2-dioxides catalysed by (R)-VAPOL-Zn complexes: synthesis of chiral propargylic cyclic sulfamidates.

    PubMed

    De Munck, Lode; Monleón, Alicia; Vila, Carlos; Muñoz, M Carmen; Pedro, José R

    2015-07-01

    (R)-VAPOL-Zn(ii) complexes catalysed the enantioselective addition of terminal alkynes to cyclic benzoxathiazine 2,2-dioxides, providing the corresponding chiral propargylic sulfamidates with high yields (up to 93%) and good enantiomeric excesses (up to 87%). PMID:26081255

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

    SciTech Connect

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

    1994-12-01

    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.

  9. COMBUSTION SYNTHESIS OF ADVANCED MATERIALS: PRINCIPLESAND APPLICATIONS

    E-print Network

    Mukasyan, Alexander

    COMBUSTION SYNTHESIS OF ADVANCED MATERIALS: PRINCIPLESAND APPLICATIONS Arvind Varma, Alexander S. Gasless Combustion SynthesisFrom Elements B. Combustion Synthesis in Gas-Solid Systems C. Products of Thermite-vpe SHS D. Commercial Aspects IV. Theoretical Considerations A. Combustion Wave Propagation Theory

  10. Enantioselective separation of mirtazapine and its metabolites by capillary electrophoresis with acetonitrile field-amplified sample stacking and its application.

    PubMed

    Wen, Jun; Zhang, Wen-Ting; Cao, Wei-Qun; Li, Ji; Gao, Fang-Yuan; Yang, Nan; Fan, Guo-Rong

    2014-01-01

    A simple, rapid and sensitive chiral capillary zone electrophoresis coupled with acetonitrile-field-amplified sample stacking method was developed that allows the simultaneous enantioselective separation of the mirtazapine, N-demethylmirtazapine, 8-hydroxymirtazapine and mirtazapine-N-oxide. The separation was achieved on an uncoated 40.2 cm×75 ?M fused silica capillary with an applied voltage of 16 kV. The electrophoretic analyses were carried out in 6.25 mM borate-25 mM phosphate solution at pH 2.8 containing 5.5 mg/mL carboxymethyl-?-cyclodextrin. The detection wavelength was 200 nm. Under these optimized conditions, satisfactory chiral separations of four pair enantiomers were achieved in less than 7 min in vitro. After one step clean-up liquid-liquid extraction using 96-well format, sample was introduced capillary zone electrophoresis with acetonitrile-field-amplified sample stacking to enhance the sensitivity of enantiomers. The method was validated with respect to specificity, linearity, lower limit of quantitation, accuracy, precision, extraction recovery and stability. The lower limit of quantification was 0.5 ng/mL with linear response over the 0.5-50 ng/mL concentration range for each mirtazapine, N-demethylmirtazapine and 8-hydroxymirtazapine enantiomer. The developed and validated method has been successfully applied to the enantioselective pharmacokinetic studies in 12 healthy volunteers after oral administration of rac- mirtazapine. PMID:24747648

  11. Carbon Nanosheets: Synthesis and Application.

    PubMed

    Fan, Huailin; Shen, Wenzhong

    2015-06-22

    Carbon nanosheets (CNSs) with tunable sizes, morphologies, and pore structures have been synthesized through several chemical routes. Graphitized CNSs have been synthesized through exfoliation, chemical vapor deposition, or high-temperature carbonization. Porous CNSs have been synthesized by using various methods, including pyrolysis, self-assembly, or a solvothermal method in connection with carbonization. These CNSs have successfully been used as detectors for metal ions, as cathodes for field electron emissions, as electrodes for supercapacitors and fuel cells, and as supports for photocatalytic and catalytic oxygen reduction. Therefore, the synthesis and application of CNSs are receiving increasing levels of interest, particularly as application benefits, in the context of future energy/chemical industry, are becoming recognized. This review provides a summary of the most recent and important progress in the production of CNSs and highlights their application in environmental and energy-related fields. PMID:26036331

  12. Rhodium-catalyzed 1,4-addition of lithium 2-furyltriolborates to unsaturated ketones and esters for enantioselective synthesis of ?-oxo-carboxylic acids by oxidation of the furyl ring with ozone.

    PubMed

    Yu, Xiao-Qiang; Shirai, Tomohiko; Yamamoto, Yasunori; Miyaura, Norio

    2011-03-01

    Rhodium-catalyzed 1,4-addition of lithium 5-methyl-2-furyltriolborate ([ArB(OCH(2))(3)CCH(3)]Li, Ar = 5-methyl-2-furyl) to unsaturated ketones to give ?-furyl ketones was followed by ozonolysis of the furyl ring for enantioselective synthesis of ?-oxo-carboxylic acids. [Rh(nbd)(2)]BF(4) (nbd = 2,5-norbornadiene) chelated with 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap) or 2,3-bis(diphenylphosphino)butane (chiraphos) gave high yields and high selectivities in a range of 91-99%?ee at 30?°C in a basic dioxane/water solution. The corresponding reaction of unsaturated esters, such as methyl crotonate, had strong resistance under analogous conditions, but the 1,4-adduct was obtained in 70% yield and with 94%?ee when more electron-deficient phenyl crotonate was used as the substrate. PMID:21344669

  13. Asymmetric Catalysis Special Feature Part II: Development of an efficient, scalable, aldolase-catalyzed process for enantioselective synthesis of statin intermediates

    Microsoft Academic Search

    William A. Greenberg; Alexander Varvak; Sarah R. Hanson; Kelvin Wong; Hongjun Huang; Pei Chen; Mark J. Burk

    2004-01-01

    A process is reported for efficient, enantioselective production of key intermediates for the common chiral side chain of statin-type cholesterol-lowering drugs such as Lipitor (atorvastatin) and Crestor (rosuvastatin). The process features a one-pot tandem aldol reaction catalyzed by a deoxyribose-5-phosphate aldolase (DERA) to form a 6-carbon intermediate with installation of two stereogenic centers from 2-carbon starting materials. An improvement of

  14. Enantioselective [4 + 2] cycloadditions of iminoacetonitriles : application to the total synthesis of (-)-quinolizidine 2071

    E-print Network

    Fontaine, Shaun D. (Shaun David)

    2011-01-01

    Iminoacetonitriles participate as reactive dienophiles in intramolecular Diels-Alder cycloadditions affording quinolizidines and indolizidines. The resulting a-amino nitrile cycloadducts are versatile intermediates that ...

  15. Enantioselective Total Syntheses of (?)-Palau’amine, (?)- Axinellamines, and (?)-Massadines

    PubMed Central

    Seiple, Ian B.; Su, Shun; Young, Ian S.; Nakamura, Akifumi; Yamaguchi, Junichiro; Jørgensen, Lars; Rodriguez, Rodrigo A.; O’Malley, Daniel P.; Gaich, Tanja; Köck, Matthias; Baran, Phil S.

    2011-01-01

    Dimeric pyrrole-imidazole alkaloids represent a rich and topologically unique class of marine natural products. This full account will follow the progression of efforts that culminated in the enantioselective total syntheses of the most structurally ornate members of this family: the axinellamines, the massadines, and palau’amine. A bio-inspired approach capitalizing on the pseudo-symmetry of the members of this class is recounted, delivering a deschloro derivative of the natural product core. Next, the enantioselective synthesis of the chlorocyclopentane core featuring a scalable, catalytic, enantioselective Diels–Alder reaction of a 1-siloxydiene is outlined in detail. Finally, the successful divergent conversion of this core to each of the aforementioned natural products, and the ensuing methodological developments are described. PMID:21861522

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

    PubMed Central

    Grillet, Francois; Brummond, Kay M.

    2013-01-01

    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

  17. Enantioselective fluorescent sensors: a tale of BINOL.

    PubMed

    Pu, Lin

    2012-02-21

    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

  18. Enantioselective Hydroformylation of Aniline Derivatives

    PubMed Central

    Joe, Candice L.; Tan, Kian L.

    2011-01-01

    We have developed a ligand that reversibly binds to aniline substrates allowing for the control of regioselectivity and enantioselectivity in hydroformylation. In this paper we address how the electronics of the aniline ring affect both binding of the substrate to the ligand and the enantioselectivity in this reaction. PMID:21842847

  19. Lipase-catalyzed enantioselective esterification of (S)-naproxen hydroxyalkyl ester in organic media.

    PubMed

    Chang, Chun-Sheng; Hsu, Chin-Shuo; Shang, Chun-Sheng

    2003-03-01

    A lipase-catalyzed, enantioselective esterification process in organic solvents was developed for the synthesis of (S)-naproxen hydroxyalkyl ester. With the selection of lipase (Candida rugosa lipase) and reaction medium (isooctane and cyclohexane), a high enantiomeric ratio of > 100 for the enzyme was obtained. 1,4-Butanediol was the best acyl acceptor. The carbon chain length of the alcohol had a major effect on the enzyme activity and enantioselectivity of lipase-catalyzed esterification. PMID:12882564

  20. Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation

    PubMed Central

    Liu, Yiyang; Liniger, Marc; McFadden, Ryan M; Roizen, Jenny L; Malette, Jacquie; Reeves, Corey M; Behenna, Douglas C; Seto, Masaki; Kim, Jimin; Mohr, Justin T; Virgil, Scott C

    2014-01-01

    Summary Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of “classic” natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge. PMID:25383121

  1. Enantioselective separation and phytotoxicity on rice seedlings of paclobutrazol.

    PubMed

    Zhang, Anping; Xie, Xuemei; Liu, Weiping

    2011-04-27

    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

  2. Catalytic Enantioselective Total Syntheses of Bakkenolides I, J and S: Application of a Carbene-Catalyzed Desymmetrization

    PubMed Central

    Phillips, Eric M.; Roberts, John M.; Scheidt, Karl A.

    2010-01-01

    A general strategy for the catalytic asymmetric syntheses of the bakkenolides is reported. The key bond-forming step involves an N-heterocyclic carbene catalyzed desymmetrization of a 1,3-diketone to form three new bonds in one step with excellent enantio– and diastereoselectivity. This intramolecular reaction allows direct access to the hydrindane core of the bakkenolides family and enables a facile synthesis of these natural products. PMID:20469924

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

    PubMed Central

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

    2010-01-01

    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. PMID:20698695

  4. Enantioselective Construction of Cyclic Quaternary Centers: (-)-Mesembrine

    E-print Network

    Taber, Douglass

    Enantioselective Construction of Cyclic Quaternary Centers: (-)-Mesembrine Douglass F. Taber, (-)-mesembrine 1. Amide 2 should be a useful chiron for the enantioselective construction of cyclic quaternary of mesembrine2,3 and its analogues is the enantioselective construction of the chiral quaternary center.4 We

  5. 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

    E-print Network

    Yu, Miao

    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, ...

  6. Synthesis Techniques, Properties, and Applications of Nanodiamonds

    Microsoft Academic Search

    Boris I. Kharisov; Oxana V. Kharissova; Leonardo Chávez-Guerrero

    2010-01-01

    Synthesis methods (ion and laser bombarding, CVD, hydrothermal, ultrasonic, electrochemical, and detonation techniques) for obtaining various forms of nanodiamonds (NDs) are generalized. Structure, physical and chemical properties, functionalization of NDs and composites on its basis are discussed, as well as their applications in medicine, electrochemistry, materials chemistry and technology.

  7. Voice synthesis application based on syllable concatenation

    Microsoft Academic Search

    O. Buza; G. I. Toderean; J. Domokos; A. Z. Bodo

    2008-01-01

    This article presents a voice synthesis application based on syllable concatenation. The system is dedicated for Romanian language, so it was need to work on special rules to decompose Romanian text into syllables. Also for preserving initial prosody of text, accentuation of syllables inside word had to be determined. Then we have recorded a vocal database with the most frequent

  8. New entries in Lewis acid-Lewis base bifunctional asymmetric catalyst: catalytic enantioselective Reissert reaction of pyridine derivatives.

    PubMed

    Ichikawa, Eiko; Suzuki, Masato; Yabu, Kazuo; Albert, Matthias; Kanai, Motomu; Shibasaki, Masakatsu

    2004-09-29

    The first catalytic enantioselective Reissert reaction of pyridine derivatives that affords products with excellent regio- and enantioselectivity is described. The key for success is the development of new Lewis acid-Lewis base bifunctional asymmetric catalysts containing an aluminum as a Lewis acid and sulfoxides or phosphine sulfides as a Lewis base. These reactions are useful for the synthesis of a variety of chiral piperidine subunits, and catalytic enantioselective formal synthesis of CP-293,019, a selective D4 receptor antagonist, was achieved. Preliminary mechanistic studies indicated that both sulfoxides and phosphine sulfides can activate TMSCN as a Lewis base. In addition, the sulfoxides with appropriate stereochemistry might stabilize a highly enantioselective bimetallic complex (a presumed active catalyst) through internal coordination to aluminum. PMID:15382912

  9. Novel chiral hydrogen bond donor catalysts based on a 4,5-diaminoxanthene scaffold: application to enantioselective conjugate addition of 1,3-dicarbonyl compounds to nitroalkenes

    Microsoft Academic Search

    Tetsuhiro Nemoto; Kazumichi Obuchi; Shinji Tamura; Takashi Fukuyama; Yasumasa Hamada

    2011-01-01

    Novel chiral hydrogen bond donor catalysts based on a 4,5-diamino-9,9?-dimethylxanthene skeleton were designed and synthesized. Among the phenylurea-amide hybrid molecules prepared from various natural\\/unnatural chiral amino acids, the phenylalanine-derived catalyst, and the proline-derived catalyst were successfully applied to enantioselective conjugate addition of 1,3-dicarbonyl compounds to nitroalkenes. Using 2-acetylcyclopentanone and 2-methoxycarbonylcyclopentanone as prochiral nucleophiles, asymmetric conjugate addition to ?-aryl nitroalkenes proceeded

  10. MICROWAVE TECHNOLOGY CHEMICAL SYNTHESIS APPLICATIONS

    EPA Science Inventory

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

  11. Enantioselective synthesis of (+)-petromyroxol, enabled by rhodium-catalyzed denitrogenation and rearrangement of a 1-sulfonyl-1,2,3-triazole.

    PubMed

    Boyer, Alistair

    2015-05-01

    Petromyroxol is a nonracemic mixture of enantiomeric oxylipids isolated from water conditioned with larval sea lamprey. The (+)-antipode exhibits interesting biological properties, but only 1 mg was isolated from >100?000 L of water. Recently, transition-metal-catalyzed denitrogenation of 1-sulfonyl-1,2,3-triazoles has emerged as a powerful strategy for the synthesis of value-added products, including efficient diastereocontrolled construction of tetrahydrofurans. This methodology enabled the rapid development of the first synthesis of (+)-petromyroxol in 9 steps and 20% overall yield from a readily accessible starting material. PMID:25891197

  12. Synthesis, Properties, and Applications Of Boron Nitride

    NASA Technical Reports Server (NTRS)

    Pouch, John J.; Alterovitz, Samuel A.

    1993-01-01

    Report describes synthesis, properties, and applications of boron nitride. Especially in thin-film form. Boron nitride films useful as masks in x-ray lithography; as layers for passivation of high-speed microelectronic circuits; insulating films; hard, wear-resistant, protective films for optical components; lubricants; and radiation detectors. Present status of single-crystal growth of boron nitride indicates promising candidate for use in high-temperature semiconductor electronics.

  13. Tetrazolium compounds: synthesis and applications in medicine.

    PubMed

    Wei, Cheng-Xi; Bian, Ming; Gong, Guo-Hua

    2015-01-01

    Tetrazoles represent a class of five-membered heterocyclic compounds with polynitrogen electron-rich planar structural features. This special structure makes tetrazole derivatives useful drugs, explosives, and other functional materials with a wide range of applications in many fields of medicine, agriculture, material science, etc. Based on our research works on azoles and other references in recent years, this review covers reported work on the synthesis and biological activities of tetrazole derivatives. PMID:25826789

  14. Catalytic Enantioselective Synthesis of N,C(?) ,C(?) -Trisubstituted ?-Amino Acid Derivatives Using 1H-Imidazol-4(5H)-ones as Key Templates.

    PubMed

    Etxabe, Julen; Izquierdo, Joseba; Landa, Aitor; Oiarbide, Mikel; Palomo, Claudio

    2015-06-01

    1H-Imidazol-4(5H)-ones are introduced as novel nucleophilic ?-amino acid equivalents in asymmetric synthesis. These compounds not only allow highly efficient construction of tetrasubstituted stereogenic centers, but unlike hitherto known templates, provide direct access to N-substituted (alkyl, allyl, aryl) ?-amino acid derivatives. PMID:25907987

  15. Substituted Ureas. Methods of Synthesis and Applications

    NASA Astrophysics Data System (ADS)

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

    1985-03-01

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

  16. Amphiphilic conetworks: Definition, synthesis, applications

    Microsoft Academic Search

    Gabor Erdodi; Joseph P. Kennedy

    2006-01-01

    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

  17. Dendrimers: synthesis, applications, and properties

    PubMed Central

    2014-01-01

    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

  18. DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications

    E-print Network

    Weiss, Sharon

    DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications Jenifer L. Lawrie for improving the sensitivity of label-free optical biosensors based on in-situ synthesis of DNA probes within was utilized as the sensor structure. Synthesis of DNA probe, as well as sensing of target DNA, was verified

  19. Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application

    E-print Network

    Amrhein, Valentin

    Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application.................................................................................................................20 1.10.1. Administration of antioxidant enzymes................................................................................20 1.10. 2. Administration of enzyme mimics

  20. Unexpected endo selectivity of conjugate nucleophilic addition to an arene-Cr(CO)3 complex: enantioselective synthesis of the diterpene 11-epi-helioporin B.

    PubMed

    Dehmel, F; Schmalz, H G

    2001-11-01

    [reaction: see text]. Starting from a nonracemic planar-chiral arene tricarbonyl chromium complex, an epimer of the bioactive marine diterpene helioporin B was synthesized in a highly stereoselective fashion. The stereostructure of the product (11-epi-helioporin B) corresponds to that of other serrulatane-type natural products. In a key step of the synthesis, 2-lithioacetonitrile undergoes conjugate nucleophilic addition to an unsaturated complex. Remarkably, this addition occurs in an endo mode, i.e., from the complexed face of the pi-ligand. PMID:11678713

  1. Efficient enantioselective synthesis of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol by Leifsonia xyli CCTCC M 2010241 using isopropanol as co-substrate.

    PubMed

    Ouyang, Qi; Wang, Pu; Huang, Jin; Cai, Jinbo; He, Junyao

    2013-03-01

    (R)-[3,5-Bis(trifluoromethyl)phenyl] ethanol is a key chiral intermediate for the synthesis of aprepitant. In this paper, an efficient synthetic process for (R)-[3,5- bis(trifluoromethyl)phenyl] ethanol was developed via the asymmetric reduction of 3,5-bis(trifluoromethyl) acetophenone, catalyzed by Leifsonia xyli CCTCC M 2010241 cells using isopropanol as the co-substrate for cofactor recycling. Firstly, the substrate and product solubility and cell membrane permeability of biocatalysts were evaluated with different co-substrate additions into the reaction system, in which isopropanol manifested as the best hydrogen donor of coupled NADH regeneration during the bioreduction of 3,5-bis(trifluoromethyl) acetophenone. Subsequently, the optimization of parameters for the bioreduction were undertaken to improve the effectiveness of the process. The determined efficient reaction system contained 200 mM of 3,5-bis(trifluoromethyl) acetophenone, 20% (v/v) of isopropanol, and 300 g/l of wet cells. The bioreduction was executed at 30°C and 200 rpm for 30 h, and 91.8% of product yield with 99.9% of enantiometric excess (e.e.) was obtained. The established bioreduction reaction system could tolerate higher substrate concentrations of 3,5- bis(trifluoromethyl) acetophenone, and afforded a satisfactory yield and excellent product e.e. for the desired (R)-chiral alcohol, thus providing an alternative to the chemical synthesis of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol. PMID:23462007

  2. ?-Hydroxyamide-based ligands and their use in the enantioselective borane reduction of prochiral ketones.

    PubMed

    Azizoglu, Murat; Erdogan, Asli; Arslan, Nevin; Turgut, Yilmaz

    2014-01-01

    Hydroxyamide-based ligands have occupied a considerable place in asymmetric synthesis. Here we report the synthesis of seven ?-hydroxyamide-based ligands from the reaction of 2-hydroxynicotinic acid with chiral amino alcohols and test their effect on the enantioselective reduction of aromatic prochiral ketones with borane in tetrahydofuran (THF). They produce the corresponding secondary alcohols with up to 76% enantiomeric excess (ee) and good to excellent yields (86-99%). PMID:24203254

  3. Synthesis, Characterization and Application of Water-soluble Gold and Silver Nanoclusters

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh

    The term `nanotechnology' has emerged as a buzzword since the last few decades. It has found widespread applications across disciplines, from medicine to energy. The synthesis of gold and silver nanoclusters has found much excitement, due to their novel material properties. Seminal work by various groups, including ours, has shown that the size of these clusters can be controlled with atomic precision. This control gives access to tuning the optical and electronic properties. The majority of nanoclusters reported thus far are not water soluble, which limit their applications in biology that requires water-solubility. Going from organic to aqueous phase is by no means a simple task, as it is associated with many challenges. Their stability in the presence of oxygen, difficulty in characterization, and separation of pure nanoclusters are some of the major bottlenecks associated with the synthesis of water-soluble gold nanoclusters. Water-soluble gold nanoclusters hold great potential in biological labeling, bio-catalysis and nano-bioconjugates. To overcome this problem, a new ligand with structural rigidity is needed. After considering various possibilities, we chose Captopril as a candidate ligand. In my thesis research, the synthesis of Au25 nanocluster capped with captopril has been reported. Captopril-protected Au25 nanocluster showed significantly higher thermal stability and enhanced chiroptical properties than the Glutathione-capped cluster, which confirms our initial rationale, that the ligand is critical in protecting the nanocluster. The optical absorption properties of these Au25 nanoclusters are studied and compared to the plasmonic nanoparticles. The high thermal stability and solubility of Au25 cluster capped with Captopril motivated us to explore this ligand for the synthesis of other gold clusters. Captopril is a chiral molecule with two chiral centers. The chiral ligand can induce chirality to the overall cluster, even if the core is achiral. Therefore, to obtain Au38 clusters as an enantiomer, the ligand employed should be chiral. The enantioselective synthesis of Au 38 capped with different chiral ligands has been reported and their chiroptical properties have been compared. The synthesis of a series of water-soluble Au nanoclusters has motivated us to study the effect of capping ligands and the core-size on their steady-state and time-resolved fluorescence properties, since the photoluminescence properties are particularly important for bioimaging and biomedical applications of nanoclusters. To gain fundamental insights into the origin of luminescence in nanoclusters, the effect of temperature on the fluorescence properties of these clusters has also been studied. The different sized nanoclusters ranging from a few dozen atoms to hundreds of atoms form a bridge between discrete atoms and the plasmonic nanocrystals; the latter involves essentially collective electron excitation-a phenomenon well explained by classical physics as opposed to quantum physics. The central question is: at what size does this transition from quantum behavior to classical behavior occur? To unravel this, we have successfully synthesized a series of silver nanoclusters. The precise formula assignment and their structural determination are still ongoing. We have successfully demonstrated the application of these water-soluble Au nanoclusters in photodynamic therapy for the treatment of cancer. We have successfully demonstrated that Au nanocluster system can produce singlet oxygen without the presence of any organic photosensitizers. In a collaborative project with Dr. Peteanu's group, the quenching efficiency of organic dyes by these water soluble nanoclusters is studied in different systems. Overall, this thesis outlines the successful synthesis of a family of water-soluble nanoclusters, their optical, chiroptical and fluorescence properties, as well as some applications of these nanoclusters.

  4. Enantioselective Synthesis of Allylboronates Bearing a Tertiary or Quaternary B-Substituted Stereogenic Carbon by NHC–Cu-Catalyzed Substitution Reactions

    PubMed Central

    Guzman-Martinez, Aikomari; Hoveyda, Amir H.

    2010-01-01

    Allylic substitutions that afford ?-substituted allylboronates bearing B-substituted tertiary or quaternary carbon stereogenic centers are presented. C–B bond forming reactions, catalyzed by chiral bidentate Cu–NHC complexes, are performed in the presence of commercially available bis(pinacolato)diboron. Transformations proceed in high yield (up to >98%), site selectivity (>98% SN2?) and in up to >99:1 enantiomer ratio (er). Trans as well as cis disubstituted alkenes can be used; alkyl- (linear as well as branched) and aryl-substituted trisubstituted allylic carbonates serve as effective substrates. Allylboronates that bear a quaternary carbon center are air-stable and can be easily purified by silica gel chromatography; in contrast, secondary allylboronates cannot be purified in the same manner and are significantly less stable. Oxidation of the enantiomerically enriched products furnishes secondary or tertiary allylic alcohols, valuable small molecules that cannot be easily obtained in high enantiomeric purity by alternative synthesis or kinetic resolution approaches. PMID:20681681

  5. Enantioselective Copper-Catalyzed Carboetherification of Unactivated Alkenes**

    PubMed Central

    Bovino, Michael T.; Liwosz, Timothy W.; Kendel, Nicole E.; Miller, Yan; Tyminska, Nina

    2014-01-01

    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 is reported a highly efficient copper-catalyzed cyclization of ?-unsaturated pentenols that terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, 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

  6. Enantioselective recognition at mesoporous chiral metal surfaces

    PubMed Central

    Wattanakit, Chularat; Côme, Yémima Bon Saint; Lapeyre, Veronique; Bopp, Philippe A.; Heim, Matthias; Yadnum, Sudarat; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

    2014-01-01

    Chirality is widespread in natural systems, and artificial reproduction of chiral recognition is a major scientific challenge, especially owing to various potential applications ranging from catalysis to sensing and separation science. In this context, molecular imprinting is a well-known approach for generating materials with enantioselective properties, and it has been successfully employed using polymers. However, it is particularly difficult to synthesize chiral metal matrices by this method. Here we report the fabrication of a chirally imprinted mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and chiral template molecules. The porous platinum retains a chiral character after removal of the template molecules. A matrix obtained in this way exhibits a large active surface area due to its mesoporosity, and also shows a significant discrimination between two enantiomers, when they are probed using such materials as electrodes. PMID:24548992

  7. 1-Phosphanorbornadienes in Enantioselective Catalysis

    Microsoft Academic Search

    Frederic Robin; Stephane Lelièvre; Louis Ricard

    2002-01-01

    Recent developments in the chemisty of 1-phosphanorbornadienes are reviewed. Due to their bicyclic structure with a non-racemisable phosphorus atom at the bridgehead, they are ideally suited to enantioselective catalysis as transition metal complexes. Amongst this family, two enantiopure species play a special role, i.e., the so-called BIPNOR, a 2,2'-bis-1,1'-phosphanorbornadienyl ( 1 ), and a 2-formyl-1-phosphanorbornadiene ( 2 ). BIPNOR displays

  8. Enantioselective Conjugate Allylation of Cyclic Enones

    PubMed Central

    Taber, Douglass F.; Gerstenhaber, David A.; Berry, James F.

    2011-01-01

    Enantioselective organocatalytic 1,2-allylation of a cyclic enone followed by anionic oxy-Cope rearrangement delivered the ketone as a mixture of diastereomers. This appears to be a general method for the net enantioselective conjugate allylation of cyclic enones. PMID:21830779

  9. Nanocrystalline Zeolites: Synthesis, Mechanism, and Applications

    NASA Astrophysics Data System (ADS)

    Severance, Michael Andrew

    Nanocrystalline zeolite particles are becoming an important material in many technical applications (e.g. zeolite membranes). Synthetic methods that minimize the zeolite crystal diameter, while providing a narrow particle size distribution, are of primary importance in these technical applications. However, there are several limitations to currently existing synthetic routes aimed at producing nanozeolites and zeolite membrane devices. For example, zeolite growth in these contexts typically requires days to weeks at high temperature to crystallize. Despite excellent performance of zeolite membranes in several separation applications, the long synthesis times required undermine any practical application of these technologies. This work focuses on chemical manipulation of zeolite nucleation processes in sol gel systems in effort to address such limitations. The primary findings indicate that careful control of the nucleation stage of a clear zeolite synthesis (optically transparent sol gel) allow the formation of zeolite Y nanocrystals less than 50 nm in diameter with a polydispersity index less than 0.2. Furthermore, chemical perturbations made during the nucleation stage of zeolite Y hydrogel synthesis is shown to accelerate crystal growth by a factor of 3-4, depending on the specific sol gel chemistry. These findings are applied to the nanocrystal seeding and rapid hydrothermal growth of zeolite Y membranes on inexpensive polymeric supports. A novel synthetic method is developed to this end. Also, the chemical and physical properties of monodisperse nanocrystalline zeolite Y synthesized herein are explored by electrochemical impedance spectroscopy. It is found that the particle interface plays an important role in the ionic conductivity of nanocrystalline zeolites in contrast to their larger zeolite counterparts in analogy to other ceramic and metal oxide ion conductors. Finally, the possibility to produce novel organic and inorganic composite systems through zeolite host-guest chemistry is explored. A nanozeolite-silver nanoparticle host-guest system is synthesized and a mechanism describing its evolution is developed. Also, the photochemistry of a colloidal nanozeolite-organic dye host-guest system is explored with ultrafast transient UV-Vis absorption spectroscopy. This allows some of the fastest chemical events to be probed within the host-guest system.

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

    E-print Network

    Movassaghi, Mohammad

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

  11. Studies toward the total synthesis of glycinoeclepin A

    E-print Network

    Thongsornkleeb, Charnsak

    2006-01-01

    Studies directed toward the synthesis of the A-ring portion of glycinoeclepin A are described. The enantioselective synthesis of key diketone intermediate 128 in four steps from 2,2-dimethyl-1,3-cyclohexanedione (5) has ...

  12. Synthesis, characterization and application of electrode materials

    SciTech Connect

    He, L.

    1995-07-07

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

  13. Synthesis of novel C2-symmetric chiral bis(oxazoline) ligands and their application in the enantioselective addition of diethylzinc

    E-print Network

    Wang, Jianbo

    and Molecular Engineering of Ministry of Education, Peking University, Beijing 100871, PR China Received 6 Biology, College of Chemistry and Molecular Engineering, Key Laboratory of Bioorganic Chemistry by the following procedure: (1) hydrolysis in methanol solution of NaOH; (2) acyl chloride formation with thionyl

  14. Catalytic Asymmetric Synthesis of Enantioenriched Heterocycles Bearing a C?CF3 Stereogenic Center.

    PubMed

    Huang, Yi-Yong; Yang, Xing; Chen, Zhuo; Verpoort, Francis; Shibata, Norio

    2015-06-01

    Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost-effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo- and organometal-catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles. PMID:25736019

  15. Application of global sensitivity equations in multidisciplinary aircraft synthesis

    Microsoft Academic Search

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

    1990-01-01

    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

  16. High density peptide microarrays. In situ synthesis and applications

    Microsoft Academic Search

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

    2004-01-01

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

  17. Applications of Ultrasound to the Synthesis of Nanostructured Materials

    E-print Network

    Suslick, Kenneth S.

    Applications of Ultrasound to the Synthesis of Nanostructured Materials By Jin Ho Bang and Kenneth of ultrasound for materials synthesis has been extensively examined over many years, and is now positioned successful ultrasound-assisted synthetic methods (sonochemistry and ultrasonic spray pyrolysis

  18. Combinatorial evolution of site- and enantioselective catalysts for polyene epoxidation

    NASA Astrophysics Data System (ADS)

    Lichtor, Phillip A.; Miller, Scott J.

    2012-12-01

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

  19. Highly enantioselective and anti-diastereoselective catalytic intermolecular glyoxylate-ene reactions: effect of the geometrical isomers of alkenes.

    PubMed

    Zhang, Xiang; Wang, Min; Ding, Ran; Xu, Yun-He; Loh, Teck-Peng

    2015-06-01

    An efficient method for the synthesis of homoallylic alcohols with high enantioselectivities and anti-diastereoselectivities via an In(III)-catalyzed intermolecular glyoxylate-ene reaction has been developed. The geometrical isomers of alkenes were shown to have different reactivities. Only the isomers of the alkenes having a proton ?-cis to the substituent reacted in this catalytic system. PMID:25965690

  20. Hyperbranched polyphosphates: synthesis, functionalization and biomedical applications.

    PubMed

    Liu, Jinyao; Huang, Wei; Pang, Yan; Yan, Deyue

    2015-06-01

    Hyperbranched polyphosphates (HBPPs) are newly emerged polymeric biomaterials with repeating phosphate bonds in a highly branched framework over the past 5 years. Due to the integration of the advantages of both hyperbranched polymers and polyphosphates, HBPPs are versatile in chemical structure, flexible in physicochemical properties, water soluble, biocompatible and biodegradable in biological features. On the basis of their excellent water solubility, biocompatibility, biodegradability and potential functionalization as well as their simple preparation in one-pot synthesis, HBPPs have fascinating biomedical applications, especially for drug delivery. In this tutorial review, the recent advances of HBPPs are summarized. HBPPs with different topological structures and various functionalities were synthesized via adjusting the side group of cyclic phosphate monomers, which have shown promising biomedical applications, for example, using as a macromolecular anticancer agent and constructing advanced drug delivery systems, including site-specific delivery systems, self-delivery systems, and stimuli-responsive delivery systems. Such progress may promote the further development of interdisciplinary research between polymer chemistry, material science and biomedicine. PMID:26008957

  1. ENANTIOSELECTIVITY IN THE BIODEGRADATION OF PCB ATROPISOMERS

    EPA Science Inventory

    Microcosms inoculated with sediment from two locations in a contaminated reservoir, Lake Hartwell, SC, USA, degraded certain PCB atropisomers enantioselectively while other atropisomers were degraded in racemic proportions. The microcosms were spiked with either 234-236 PCB (PCB...

  2. Scalable enantioselective total synthesis of taxanes

    Microsoft Academic Search

    Abraham Mendoza; Yoshihiro Ishihara; Phil S. Baran

    2011-01-01

    Taxanes form a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel), a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which has a suitable functional handle with which to access more oxidized members of its family. This

  3. Enantioselective Organocatalytic ?-Fluorination of Cyclic Ketones

    PubMed Central

    Kwiatkowski, Piotr; Beeson, Teresa D.; Conrad, Jay C.

    2011-01-01

    The first highly enantioselective ?-fluorination of ketones using organocatalysis has been accomplished. The long-standing problem of enantioselective ketone ?-fluorination via enamine activation has been overcome via high-throughput evaluation of a new library of amine catalysts. The optimal system, a primary amine functionalized Cinchona alkaloid, allows the direct and asymmetric ?-fluorination of a variety of carbo- and heterocyclic substrates. Furthermore, this protocol also provides diastereo-, regio- and chemoselective catalyst control in fluorinations involving complex carbonyl systems. PMID:21247133

  4. Activation of pig liver esterase in organic media with organic polymers: application to the enantioselective acylation of racemic functionalized secondary alcohols.

    PubMed

    Gais, H J; Jungen, M; Jadhav, V

    2001-05-18

    Pig liver esterase (PLE) shows practically no activity in acylation of alcohols with vinylic esters in organic solvents. However, addition of methoxypoly(ethylene glycol) (MPEG), bovine serum albumin (BSA), TentaGelAmino resin (TGA), or aminomethyl polystyrene (AMPS) confers activity to PLE in acylation of alcohols with vinyl propionate in organic solvents of low water content. Polymer-activated PLE showed high enantioselectivities (E > 100) in the acylation of racemic 1-alkoxy-, 1-ethylsulfanyl-, and 1-fluoro-3-aryl-2-propanols as well as racemic 1-phenoxy-2-propanol and racemic 1-methoxy-2-phenoxy-2-propanol. The synthetic utility of polymer-activated PLE has been demonstrated by the gram-scale resolution of 1-methoxy-3-phenyl-2-propanol, 1-ethylsulfanyl-3-phenyl-2-propanol, 1-methoxy-3-p-methoxyphenyl-2-propanol, 1-fluoro-3-phenyl-2-propanol, and 1-methoxy-3-phenoxy-2-propanol. In PLE-catalyzed acylation of alcohols with vinyl propionate, acetaldehyde and propionic acids, both being detrimental to the enzyme, are formed as byproducts. In addition, the water content of the system, which is critical for the activity of pig liver esterase, is lowered because of a competing enzymatic hydrolysis of the acyl donor. The polymers TGA, BSA, and AMPS not only scavenge the aldehyde and the acid through imine formation and neutralization, respectively, but replenish at least in part also the water consumed in the competing hydrolysis of the acyl donor. A recovery of PLE together with the polymer was achieved without major loss of activity through their immobilization on a water-saturated polyaramide membrane, which occurs spontaneously in organic solvents. PMID:11348121

  5. Organocatalytic enantioselective tandem aldol-cyclization reaction of ?-isothiocyanato imides and activated carbonyl compounds

    PubMed Central

    Guang, Jie; Zhao, Cong-Gui

    2011-01-01

    The organocatalytic enantioselective tandem aldol-cyclization reactions of ?-isothiocyanato imides and activated carbonyl compounds, such as isatins, an ?-ketolactone and a 1,2-dione, have been studied with cinchona alkaloid-derived thiourea-catalysts. This methodology provided an easy way to access enantiomerically enriched spirobicyclic thiocarbamates with high yields and good to excellent stereoselectivity, which have been demonstrated to be useful precursors for the synthesis of biologically active molecules. PMID:21921975

  6. Enantioselective intramolecular aldehyde ?-alkylation with simple olefins: direct access to homo-ene products.

    PubMed

    Comito, Robert J; Finelli, Fernanda G; MacMillan, David W C

    2013-06-26

    A highly selective method for the synthesis of asymmetrically substituted carbocycles and heterocycles from unactivated aldehyde-olefin precursors has been achieved via enantioselective SOMO-catalysis. Addition of a catalytically generated enamine radical cation across a pendent olefin serves to establish a general asymmetric strategy toward the production of a wide range of formyl-substituted rings with alkene transposition. Conceptually, this novel mechanism allows direct access to "homo-ene"-type products. PMID:23745728

  7. Hyperbranched polymers: advances from synthesis to applications.

    PubMed

    Zheng, Yaochen; Li, Sipei; Weng, Zhulin; Gao, Chao

    2015-06-01

    Hyperbranched polymers (HPs) are highly branched three-dimensional (3D) macromolecules. Their globular and dendritic architectures endow them with unique structures and properties such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility. HPs can be facilely synthesized via a one-pot polymerization of traditional small molecular monomers or emerging macromonomers. The great development in synthetic strategies, from click polymerization (i.e., copper-catalyzed azide-alkyne cycloaddition, metal-free azide-alkyne cycloaddition, strain-promoted azide-alkyne cycloaddition, thiol-ene/yne addition, Diels-Alder cycloaddition, Menschutkin reaction, and aza-Michael addition) to recently reported multicomponent reactions, gives rise to diverse HPs with desirable functional/hetero-functional groups and topologies such as segmented or sequential ones. Benefiting from tailorable structures and correspondingly special properties, the achieved HPs have been widely applied in various fields such as light-emitting materials, nanoscience and technology, supramolecular chemistry, biomaterials, hybrid materials and composites, coatings, adhesives, and modifiers. In this review, we mainly focus on the progress in the structural control, synthesis, functionalization, and potential applications of both conventional and segmented HPs reported over the last decade. PMID:25902871

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

    PubMed

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

    2013-08-01

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

  9. Synthesis and applications of metal oxide nanowires

    NASA Astrophysics Data System (ADS)

    Tien, Li-Chia

    The one-dimensional nanostructured materials have attracted much attention because of their superior properties from the deducing size in the nanometer range. Among them, metal oxide materials provide a wide diversity and functionality in both theoretical study and applications. This work focused on the synthesis of metal oxide nanowires, and further investigated possible applications of nanostructured metal oxide materials. High quality ZnO nanowires have been synthesized by catalyst-assisted molecular beam epitaxy. The control of initial Au or Ag film thickness and subsequent annealing conditions is shown to provide an effective method for controlling the size and density of nucleation sites for catalyst-driven growth of ZnO nanowires. For gas sensing applications, it is found that the sensitivity for detecting hydrogen is greatly enhanced by sputter-depositing metal catalysts (Pt and Pt) on surface. The sensors are shown to detect ppm hydrogen at room temperature using <0.4 mW of power when using multiple nanowires. A comparison study of the hydrogen-sensing characteristics of ZnO thin films with different thickness and ZnO nanowires was studied. The Pt-coated single nanowires show a current response by approximately a factor of 3 larger at room temperature. Both types of sensors are shown to be capable of the detection of ppm hydrogen at room temperature with nW power levels, but the nanowires show different recovery characteristics, consistent with the expected higher surface coverage of adsorbed hydrogen. The feasibility of a number of metal oxide nanowires has been synthesized by a high-pressure assisted pulsed laser deposition. The high density well-aligned metal oxide nanowires can be directly grown on substrate without metal catalysts. The results suggest the possibility of growing complex metal oxide nanostructures, including tailored heterostructures and aligned heterojunction arrays with PLD technique. The growth of epitaxial SnO2 on c-sapphire using pulsed laser deposition is examined. X-ray diffraction analysis shows that the films are highly a-axis oriented SnO2 with the rutile structure. The effects of Ga doping on SnO2 films were studied. The Hall data showed p-type behavior occurs only at specific growth condition, but converted back to n-type and degraded as time proceeds.

  10. Spherical harmonic analysis and synthesis for global multiresolution applications

    Microsoft Academic Search

    J. A. R. Blais; D. A. Provins

    2001-01-01

    On the Earth and in its neighborhood, spherical harmonic analysis and synthesis are standard mathematical procedures for scalar, vector and tensor fields. However, with the advent of multiresolution applications, additional considerations about convolu- tion filtering with decimation and dilation are required. As global applications often imply discrete observations on regular grids, computational challenges arise and conflicting claims about spherical harmonic

  11. Review on oxides of antimony nanoparticles: synthesis, properties, and applications

    Microsoft Academic Search

    Hui Shun Chin; Kuan Yew Cheong; Khairunisak Abdul Razak

    2010-01-01

    In this article, synthesis methods, properties, and applications of antimony oxide nanoparticles are reviewed. Oxides of antimony\\u000a exist in three phases, namely antimony trioxide, antimony tetroxide, and antimony pentoxide. Physical and optical properties\\u000a of these nanoparticles are reviewed and compared with their bulk forms. According to literature works, a total of eight synthesis\\u000a methods have been used to produce these

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

    PubMed

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

    2013-02-01

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

  13. Cellulose Nanocrystals as Chiral Inducers: Enantioselective Catalysis and Transmission Electron Microscopy 3D Characterization.

    PubMed

    Kaushik, Madhu; Basu, Kaustuv; Benoit, Charles; Cirtiu, Ciprian M; Vali, Hojatollah; Moores, Audrey

    2015-05-20

    Cellulose nanocrystals (CNCs), derived from cellulose, provide us with an opportunity to devise more sustainable solutions to current technological challenges. Enantioselective catalysis, especially heterogeneous, is the preferred method for the synthesis of pure chiral molecules in the fine chemical industries. Cellulose has been long sought as a chiral inducer in enantioselective catalysis. We report herein an unprecedentedly high enantiomeric excess (ee) for Pd patches deposited onto CNCs used as catalysts for the hydrogenation of prochiral ketones in water at room temperature and 4 bar H2. Our system, where CNCs acted as support and sole chiral source, achieved an ee of 65% with 100% conversions. Cryo-electron microscopy, high-resolution transmission electron microscopy, and tomography were used for the first time to study the 3D structure of a metal functionalized CNC hybrid. It established the presence of sub-nanometer-thick Pd patches at the surface of CNCs and provided insight into the chiral induction mechanism. PMID:25915443

  14. New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels-Alder

    E-print Network

    MacMillan, David W. C.

    New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels transformations. In this context, we document the first highly enantioselective organocatalytic Diels this hypothesis we investigated the capacity of chiral amines to enantioselectively catalyze the Diels

  15. Synthesis of Cartesian Stiffness for Robotic Applications

    Microsoft Academic Search

    Namik Ciblak; Harvey Lipkin

    1999-01-01

    A new, systematic approach to the synthesis of Cartesian sti®ness by springs is presented using screw (spatial vector) algebra. The space of solutions is fully characterized for all sti®nesses realizable by springs. The main result shows that a rank r sti®ness can al- ways be synthesized by r springs. Further, it can also be synthesized by an arbitrarily large number

  16. One-dimensional boron nanostructures: Prediction, synthesis, characterizations, and applications

    E-print Network

    Gao, Hongjun

    One-dimensional boron nanostructures: Prediction, synthesis, characterizations, and applications January 2010, Accepted 24th March 2010 DOI: 10.1039/c0nr00051e One-dimensional (1D) boron nanostructures nanomaterials. In this article, we review the current progress that has been made on 1D boron nanostructures

  17. The Chemistry of Nanomaterials: Synthesis, Properties and Applications, 2 Volumes

    Microsoft Academic Search

    C. N. R. Rao; Achim Müller; Anthony K. Cheetham

    2004-01-01

    With this handbook the distinguished team of editors has combined the expertise of leading nanomaterials scientists to provide the latest overview of this field. The authors cover the whole spectrum of nanomaterials, ranging from theory, synthesis, properties, characterization to application, including such new developments as: quantum dots, nanoparticles, nanoporous materials, as well as nanowires, nanotubes and nanostructural polymers nanocatalysis, nanolithography,

  18. Synthesis and photovoltaic application of coper (I) sulfide nanocrystals

    SciTech Connect

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

    2008-06-24

    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.

  19. Spherical harmonic analysis and synthesis for global multiresolution applications

    Microsoft Academic Search

    J. A. R. Blais; D. A. Provins

    2002-01-01

    .  ?On the Earth and in its neighborhood, spherical harmonic analysis and synthesis are standard mathematical procedures for\\u000a scalar, vector and tensor fields. However, with the advent of multiresolution applications, additional considerations about\\u000a convolution filtering with decimation and dilation are required. As global applications often imply discrete observations\\u000a on regular grids, computational challenges arise and conflicting claims about spherical harmonic transforms

  20. Titanium-Catalyzed Enantioselective Additions of

    E-print Network

    Walsh, Patrick J.

    Titanium-Catalyzed Enantioselective Additions of Alkyl Groups to Aldehydes: Mechanistic Studies by zinc- or titanium- based catalysts. While the mechanism of the zinc/amino alcohol catalysts has received significant attention, the titanium-based catalysts have been less studied. This Account

  1. Enantioselective Transaminations by Dendrimeric Enzyme Mimics

    PubMed Central

    Wei, Sujun; Kenesky, Craig

    2007-01-01

    PAMAM dendrimers have been constructed with a pyridoxamine core, and chiral capping amino groups. Transamination to form phenylalanine and alanine from their related ketoacids produced enantioselectivities induced by the formally remote chiral caps, supporting computer models that indicate folding of the dendrimer chains back into the core region. PMID:18596840

  2. Enantioselective organocatalytic epoxidation using hypervalent iodine reagents

    E-print Network

    MacMillan, David W. C.

    Enantioselective organocatalytic epoxidation using hypervalent iodine reagents Sandra Lee and David Abstract--A rare example of a hypervalent iodine reagent participating in a 1,4-heteroconjugate addition in the asymmetric epoxidation of electron-deficient olefins. 15 N NMR studies were conducted to elucidate

  3. Aerosol synthesis and application of folded graphene-based materials

    NASA Astrophysics Data System (ADS)

    Chen, Yantao; Wang, Zhongying; Qiu, Yang

    2015-12-01

    Graphene oxide colloid has been widely used in the synthesis of various graphene-based materials. Graphene oxide sheets, with a low bending rigidity, can be folded when assembled in aqueous phase. A simple but industrial scalable way, aerosol processing, can be used to fabricate folded graphene-based materials. These folded materials can carry various cargo materials and be used in different applications such as time-controlled drug release, medical imaging enhancement, catalyst support and energy related areas. The aerosol synthesis of folded graphene-based materials can also be easily extended to fabricate hybrid nanomaterials without any complicated chemistries.

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

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-01

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

  5. Semiconductor nanowhiskers: Synthesis, properties, and applications

    SciTech Connect

    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

    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.

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

    PubMed

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

    2014-09-01

    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

  7. Nanoparticles: synthesis and applications in life science and environmental technology

    NASA Astrophysics Data System (ADS)

    Luong Nguyen, Hoang; Nguyen, Hoang Nam; Hai Nguyen, Hoang; Quynh Luu, Manh; Hieu Nguyen, Minh

    2015-03-01

    This work focuses on the synthesis, functionalization, and application of gold and silver nanoparticles, magnetic nanoparticles Fe3O4, combination of 4-ATP-coated silver nanoparticles and Fe3O4 nanoparticles. The synthesis methods such as chemical reduction, seeding, coprecipitation,and inverse microemulsion will be outlined. Silica- and amino-coated nanoparticles are suitable for several applications in biomedicine and the environment. The applications of the prepared nanoparticles for early detection of breast cancer cells, basal cell carcinoma, antibacterial test, arsenic removal from water, Herpes DNA separation, CD4+ cell separation and isolation of DNA of Hepatitis virus type B (HBV) and Epstein–Barr virus (EBV) are discussed. Finally, some promising perspectives will be pointed out. Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

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

    Microsoft Academic Search

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

    1991-01-01

    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

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

    Microsoft Academic Search

    Werner Geurts; F. Catthoor; H. De Man

    1991-01-01

    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

  10. Zirconium-catalyzed desymmetrization of aminodialkenes and aminodialkynes through enantioselective hydroamination.

    PubMed

    Manna, Kuntal; Eedugurala, Naresh; Sadow, Aaron D

    2015-01-14

    The catalytic addition of alkenes and amines (hydroamination) typically provides ?- or ?-amino stereocenters directly through C-N or C-H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C-N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the ?-amino stereocenter generated by C-N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H2NR vs D2NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselective processes in aminodialkene cyclization and the peripheral stereocenter in aminodialkyne desymmetrization/cyclization. PMID:25560913

  11. Synthesis of boron nitride nanotubes and their applications

    PubMed Central

    Kalay, Saban; Yilmaz, Zehra; Sen, Ozlem; Emanet, Melis; Kazanc, Emine

    2015-01-01

    Summary Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed. PMID:25671154

  12. Biologically Relevant Glycopeptides: Synthesis and Applications

    NASA Astrophysics Data System (ADS)

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

    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.

  13. A general enantioselective route to the chamigrene natural product family

    PubMed Central

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

    2010-01-01

    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. PMID:20798895

  14. Microwave-Assisted Synthesis of II-VI Semiconductor Micro- and Nanoparticles towards Sensor Applications 

    E-print Network

    Majithia, Ravish

    2013-01-15

    Engineering particles at the nanoscale demands a high degree of control over process parameters during synthesis. For nanocrystal synthesis, solution-based techniques typically include application of external convective heat. This process often...

  15. Conducting Polymer Nanostructures: Template Synthesis and Applications in Energy Storage

    PubMed Central

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

    2010-01-01

    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. PMID:20717527

  16. Green synthesis of water soluble semiconductor nanocrystals and their applications

    Microsoft Academic Search

    Ying Wang

    2006-01-01

    II-VI semiconductor nanomaterials, e.g. CdSe and CdTe, have attracted great attention over the past decades due to their fascinating optical and electrical properties. The research presented here focuses on aqueous semiconductor nanomaterials. The work can be generally divided into three parts: synthesis, property study and application. The synthetic work is devoted to develop new methods to prepare shape- and structure-controlled

  17. The application of micro reactors for organic synthesis.

    PubMed

    Watts, Paul; Haswell, Stephen J

    2005-03-01

    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

  18. Waveform synthesis for imaging and ranging applications

    DOEpatents

    Doerry, Armin W.; Dudley, Peter A.; Dubert, Dale F.; Tise, Bertice L.

    2004-12-07

    Frequency dependent corrections are provided for quadrature imbalance and Local Oscillator (LO) feed-through. An operational procedure filters imbalance and LO feed-through effects without prior calibration or equalization. Waveform generation can be adjusted/corrected in a synthetic aperture radar system (SAR), where a rolling phase shift is applied to the SAR's QDWS signal where it is demodulated in a receiver; unwanted energies, such as LO feed-through and/or imbalance energy, are separated from a desired signal in Doppler; the separated energy is filtered from the receiver leaving the desired signal; and the separated energy in the receiver is measured to determine the degree of imbalance that is represented by it. Calibration methods can also be implemented into synthesis. The degree of LO feed-through and imbalance can be used to determine calibration values that can then be provided as compensation for frequency dependent errors in components, such as the QDWS and SSB mixer, affecting quadrature signal quality.

  19. Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications

    SciTech Connect

    Peter C. Kong; Alex W. Kawczak

    2008-09-01

    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.

  20. Diastereoselective and enantioselective conjugate addition reactions utilizing ?,?-unsaturated amides and lactams

    PubMed Central

    2015-01-01

    Summary The conjugate addition reaction has been a useful tool in the formation of carbon–carbon bonds. The utility of this reaction has been demonstrated in the synthesis of many natural products, materials, and pharmacological agents. In the last three decades, there has been a significant increase in the development of asymmetric variants of this reaction. Unfortunately, conjugate addition reactions using ?,?-unsaturated amides and lactams remain underdeveloped due to their inherently low reactivity. This review highlights the work that has been done on both diastereoselective and enantioselective conjugate addition reactions utilizing ?,?-unsaturated amides and lactams. PMID:25977728

  1. Nanoceria as Antioxidant: Synthesis and Biomedical Applications

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The therapeutic application of nanomaterials has been a focus of numerous studies in the past decade. Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by the reactive oxygen intermediates (ROI). The radical-scavenging rol...

  2. Vancomycin Molecular Interactions: Antibiotic and Enantioselective Mechanisms

    NASA Astrophysics Data System (ADS)

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

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

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

    PubMed

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

    2013-03-01

    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

  4. Plasma assisted synthesis of WS2 for gas sensing applications

    NASA Astrophysics Data System (ADS)

    O'Brien, Maria; Lee, Kangho; Morrish, Rachel; Berner, Nina C.; McEvoy, Niall; Wolden, Colin A.; Duesberg, Georg S.

    2014-11-01

    We report the plasma assisted synthesis of WS2 thin films and demonstrate their suitability for sensing applications. This was achieved by using a H2S plasma to sulphurise WO3 films at temperatures as low as 500 °C. This is a significant step towards semiconductor compatible growth of transition metal dichalcogenide (TMD) thin films without the need for highly elevated temperatures. We found that the electrical transport in thin films is highly sensitive to the presence of NH3. A sensitivity of 1.4 ppm NH3 in nitrogen at room temperature has been achieved, demonstrating the potential of 2D TMD films for sensing applications.

  5. Enantioselective ?-Protonation by a Cooperative Catalysis Strategy

    PubMed Central

    Wang, Michael H.; Cohen, Daniel T.; Schwamb, C. Benjamin; Mishra, Rama K.; Scheidt, Karl A.

    2015-01-01

    An enantioselective N-heterocyclic carbene (NHC)-catalyzed ?-protonation through the orchestration of three distinct organocatalysts has been developed. This cooperative catalyst system enhances both yield and selectivity, compared to only the NHC-catalyzed process. This new method allows for the efficient conversion of a large scope of aryl-oxobutenoates to highly enantioenriched succinate derivatives and demonstrates the benefits of combining different activation modes in organocatalysis. PMID:25929160

  6. Photo-organocatalytic Enantioselective Perfluoroalkylation of ?-Ketoesters

    PubMed Central

    2015-01-01

    The visible-light-driven, phase-transfer-catalyzed, enantioselective perfluoroalkylation and trifluoromethylation of cyclic ?-ketoesters is described. The photo-organocatalytic process, which occurs at ambient temperature and under visible light illumination, is triggered by the photochemical activity of in situ-generated electron donor–acceptor complexes, arising from the association of chiral enolates and perfluoroalkyl iodides. Preliminary mechanistic studies are reported. PMID:25901659

  7. Electrospun metallic nanowires: Synthesis, characterization, and applications

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

  8. Norbornene based polybetaines: Synthesis and biological applications

    NASA Astrophysics Data System (ADS)

    Colak, Semra

    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.

  9. Nitroderivatives of catechol: from synthesis to application.

    PubMed

    Gavazov, Kiril B

    2012-03-01

    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

  10. Enantioselective Biotransformation of Chiral PCBs in Whole Poplar Plants

    PubMed Central

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

    2011-01-01

    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. PMID:21329345

  11. Lewis Base Catalyzed, Enantioselective, Intramolecular Sulfenoamination of Olefins

    PubMed Central

    2015-01-01

    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

  12. Asymmetric hydrogenation of ethyl pyruvate: Diffusion effects on enantioselectivity

    SciTech Connect

    Sun, Yongkui; Wang, Jian; LeBlond, C. [Merck & Co., Inc., Rahway, NJ (United States)] [and others] [Merck & Co., Inc., Rahway, NJ (United States); and others

    1996-07-01

    Enantioselectivity in the hydrogenation of ethyl pyruvate over cinchona-alkaloid-modified Pt has been studied. Kinetic studies indicated different mechanisms in different reaction regimes. Solution hydrogen concentration strongly corrrelated with reaction rates and enantioselectivity. 28 refs., 5 figs., 2 tabs.

  13. Organocatalytic enantioselective peroxidation of ketimines derived from isatins.

    PubMed

    Nakamura, Shuichi; Takahashi, Shun

    2015-06-01

    The first catalytic enantioselective addition of hydroperoxides to ketimines derived from isatins has been developed. Excellent yields and enantioselectivities were observed for the reaction of various ketimines with peroxides using a cinchona alkaloid sulfonamide catalyst. Both enantiomers of products could be obtained by using pseudoenantiomeric chiral catalysts. The obtained product can be converted to optically active ?-amino hydroperoxide. PMID:25965522

  14. A convenient new route to piperidines, pyrrolizidines, indolizidines, and quinolizidines by cyclization of acetylenic sulfones with beta and gamma-chloroamines. Enantioselective total synthesis of indolizidines (-)-167B, (-)-209D, (-)-209B, and (-)-207A.

    PubMed

    Back, T G; Nakajima, K

    2000-07-28

    The methyl esters of (L)-phenylalanine and (L)-methionine underwent conjugate additions via their free amino groups to 1-(p-toluenesulfonyl)hexyne, followed by intramolecular acylation of the corresponding enamide anions and tautomerization to afford 2-benzyl-5-n-butyl-3-hydroxy-4-(p-toluenesulfonyl)pyrrole and 5-n-butyl-3-hydroxy-2-(2-methylthioethyl)-4-(p-toluenesulfonyl)pyr role, respectively. The conjugate additions of a series of acyclic and cyclic secondary beta- and gamma-chloroamines to acetylenic sulfones proceeded similarly under mild conditions. The resulting adducts were deprotonated with LDA in THF at -78 degrees C, and the resulting sulfone-stabilized carbanions underwent intramolecular alkylation to afford cyclic enamine sulfones. Thus, acyclic gamma-chloroalkyl-benzylamines afforded the corresponding 2- or 2,6-disubstituted piperidines, while 2-(chloromethyl)pyrrolidines, 2-(2-chloroethyl)pyrrolidines, 2-(chloromethyl)piperidines, and 2-(2-chloroethyl)piperidines produced the corresponding 3-substituted pyrrolizidines, 5- or 3-substituted indolizidines, and 4-substituted quinolizidines, respectively. 8-Methyl-5-substituted indolizidines were also prepared from the appropriate methyl-substituted chloroamine precursor. Enantioselective syntheses were achieved by employing chiral chloroamines derived from amino acids or other enantiopure precursors. Further transformations of several of the products provided concise syntheses of four dendrobatid alkaloids. Thus, reduction of (8aS)-5-n-propyl-6-(p-toluenesulfonyl)-delta5,6-indolizidine with sodium cyanoborohydride in trifluoroacetic acid, followed by reductive desulfonylation, afforded (-)-indolizidine 167B. The corresponding 5-n-hexyl derivative similarly produced (-)-indolizidine 209D, while (-)-(8R, 8aS)-8-methyl-5-n-pentyl-6-(p-toluenesulfonyl)-delta5,6-indo lizidine furnished (-)-indolizidine 209B. Finally, the similar reduction and debenzylation of (-)-(8R,8aS)-5-(2-benzyloxyethyl)-8-methyl-6-(p-toluenesulfo nyl)-delta5,6-indolizidine produced the corresponding 5-hydroxyethyl indolizidine. This was subjected to chlorination of the alcohol group with thionyl chloride and substitution with a higher order allyl cuprate reagent to afford (-)-indolizidine 207A. PMID:10959857

  15. Engineering and Applications of fungal laccases for organic synthesis.

    PubMed

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

    2008-01-01

    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. PMID:19019256

  16. Engineering and Applications of fungal laccases for organic synthesis

    PubMed Central

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

    2008-01-01

    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. PMID:19019256

  17. Recent Research Progress in the Synthesis of Polyphosphazene Elastomers and Their Applications

    Microsoft Academic Search

    Abid Muhammad Amin; Li Wang; Jianjun Wang; Haojie Yu; Jingmin Gao; Chao Li; Jia Huo; Wael A. Amer; Guangqing Yan; Liang Ma

    2010-01-01

    Polyphosphazenes elastomers have major utilization as fire resistant materials, gas kits, O-rings, electrical insulation, oil-resistant hoses, foam, ceramics, especially helicopter, air craft, aerospace, military and navy hardware applications. Tremendous achievements have been obtained for the synthesis and applications of polyphosphazenes. In this review, we highlighted the types, synthesis, characterization and applications of polyphosphazenes elastomers.

  18. Doped Carbon Nanotubes: Synthesis, Characterization and Applications

    Microsoft Academic Search

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

    \\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-,

  19. Chiral separation by enantioselective liquid-liquid extraction.

    PubMed

    Schuur, Boelo; Verkuijl, Bastiaan J V; Minnaard, Adriaan J; de Vries, Johannes G; Heeres, Hero J; Feringa, Ben L

    2011-01-01

    The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid-liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid-liquid extraction including host-guest chemistry, extraction and phase transfer mechanisms, and multistage liquid-liquid extraction processing. Then the literature on enantioselective liquid-liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants. PMID:21107491

  20. Application of global sensitivity equations in multidisciplinary aircraft synthesis

    SciTech Connect

    Hajela, P.; Bloebaum, C.L.; Sobieszczanski-sobieski, J. (Florida Univ., Gainesville (USA) NASA, Hampton, VA (USA))

    1990-12-01

    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. 10 refs.

  1. Application of global sensitivity equations in multidisciplinary aircraft synthesis

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  2. Homochiral porous metal-organic coordination polymers: synthesis, structure and functional properties

    NASA Astrophysics Data System (ADS)

    Yutkin, M. P.; Dybtsev, D. N.; Fedin, Vladimir P.

    2011-11-01

    The review concerns the state of the art in and prospects for the development of chemistry of a new class of porous compounds, homochiral metal-organic coordination polymers. Main approaches to the synthesis and structure determination of such systems by X-ray diffraction analysis, as well as stability of metal-organic frameworks and supramolecular chemistry of host-guest inclusion compounds are considered. Prospects for practical application of these compounds first of all for enantioselective resolution and catalysis are discussed. The bibliography includes 175 references. Dedicated to Academician O M Nefedov on the occasion of his 80th birthday.

  3. Boron Nitride Nanotube: Synthesis and Applications

    NASA Technical Reports Server (NTRS)

    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

    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.

  4. Biomedical Nanocrystal Agents: Design, Synthesis, and Applications

    NASA Astrophysics Data System (ADS)

    Cho, Minjung

    In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2 ) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T 1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2˜22 nm) and iron based magnetic nanocrystals (4 ˜33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3˜4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.

  5. Gold Nanocages: Synthesis, Properties, and Applications

    PubMed Central

    SKRABALAK, SARA E.; CHEN, JINGYI; SUN, YUGANG; LU, XIANMAO; AU, LESLIE; COBLEY, LAIRE M.; XIA, YOUNAN

    2008-01-01

    Conspectus Noble-metal nanocages represent a novel class of nanostructures with hollow interiors and porous walls. They are prepared using the remarkably simple galvanic replacement reaction between solutions containing metal precursor salts and Ag nanostructures prepared by polyol reduction. The electrochemical potential difference between the two species drives the reaction, with the reduced metal depositing on the surface of the Ag nanostructure. In our most studied example involving HAuCl4 as the metal precursor, the resultant Au epitaxially deposits on the surface of the Ag nanocubes, adopting their cubic structure. Concurrent with this deposition, the interior Ag is oxidized and removed, together with alloying and dealloying, to produce hollow and eventually porous structures that we commonly refer to as Au nanocages. This approach has proven versatile, with a wide range of morphologies – including nanorings, prism-shaped nanoboxes, nanotubes, and multiple-walled nanoshells or nanotubes – being produced by changing the shape of the initial Ag template. Besides Au-based structures, Pt- and Pd-containing hollow nanostructures have been prepared by switching the metal salt precursors to Na2PtCl4 or Na2PdCl4, respectively. Additionally, we have found it easy to tune both the composition and localized surface plasmon resonance (LSPR) of the metal nanocages by simply changing the amount of metal precursor added to the suspension of Ag nanocubes. In this way, we are developing these structures for biomedical and catalytic applications. As the Au nanocages are predicted by discrete dipole approximations (DDA) to have large absorption cross-sections and their LSPR can be tuned into the near-infrared where the attenuation of light by blood and soft tissue is greatly reduced, they are attractive for biomedical applications in which the selective absorption of light at great depths is desirable. For example, we have explored their use as contrast enhancement agents for both optical coherence tomography (OCT) and photoacoustic tomography (PAT), with improvements being observed in each case. As the Au nanocages have large absorption cross-sections, they are also effective photothermal transducers, which when targeted to cancer cells could provide a therapeutic effect by selectively killing them by hyperthermia. Our in vitro work illustrates the feasibility of this technique as a less invasive form of cancer treatment. PMID:18570442

  6. Chapter 1Catalytic, Enantioselective Construction of Pyrroloindolines 1 Recent Developments in the Catalytic, Enantioselective Construction of

    E-print Network

    Winfree, Erik

    Developments in the Catalytic, Enantioselective Construction of Pyrroloindolines Bearing All-Carbon Quaternary pyrroloindoline natural products bear C3a all-carbon quaternary stereocenters and the synthetic challenge inherent and coworkers identified a bifunctional tertiary amine thiourea (15) that catalyzes the conjugate addition of 3

  7. Preparation of Optically Active Tertiary Alcohols by Enzymatic Methods. Application to the Synthesis of Drugs and Natural Products.

    PubMed

    Chen, Same-Ting; Fang, Jim-Min

    1997-06-27

    By the catalysis of AK or porcine pancreas lipases, 3-iodo-2-phenyl-1,2-propanediol, 1-(hydroxymethyl)-1-phenyloxirane, 2-(iodomethyl)-4-phenyl-3-butyne-1,2-diol, 2-(iodomethyl)-4-(trimethylsilyl)-3-butyne-1,2-diol, and 5,5-dimethyl-2-(iodomethyl)-3-hexyne-1,2-diol were resolved in very high enantioselectivities (E >/= 153). The obtained enantiomerically pure or optically enriched compounds, containing an iodo atom, an oxirane moiety, or an alkynyl group, are versatile building blocks for the synthesis of chiral azido diols, sulfanyl diols, cyano diols, the side chain of a vitamin D(3) metabolite, the omega-chain of a prostaglandin analog, and an aggregation pheromone (1S,5R)-(-)-frontalin. Models based on the consideration of the importance of size, distance, and electron effect are proposed to interpret the observed stereospecificity in the enzymatic reactions. Thus, the lipase-catalyzed reactions of 1,1-disubstituted 1,2-diols occurred efficiently at the primary hydroxyl groups while the enantioselectivity was controlled by the tertiary carbinyl centers. PMID:11671758

  8. Enantioselective analysis of melagatran via an LSPR biosensor integrated with a microfluidic chip.

    PubMed

    Guo, Longhua; Yin, Yuechun; Huang, Rong; Qiu, Bin; Lin, Zhenyu; Yang, Huang-Hao; Li, Jianrong; Chen, Guonan

    2012-10-21

    The impact of chiral compounds on pharmacological and biological processes is well known. With the increasing need for enantiomerically pure compounds, effective strategies for enantioseparation and chiral discrimination are in great demand. Herein we report a simple but efficient approach for the enantioselective determination of chiral compounds based on a localized surface plasmon resonance (LSPR) biosensor integrated with a microfluidic chip. A glass microfluidic chip with an effective volume of ~0.75 ?L was fabricated for this application. Gold nanorods (AuNRs) with an aspect ratio of ~2.6 were self-assembled onto the surface of the inner wall of the chip to serve as LSPR transducers, which would translate the analyte binding events into quantitative concentration information. Human ?-thrombin was immobilized onto the AuNR surface for enantioselective sensing of the enantiomers of melagatran. The proposed sensor was found to be highly selective for RS-melagatran, while the binding of its enantiomer, SR-melagatran, to the sensor was inactive. Under optimal conditions, the limit of detection of this sensor for RS-melagatran was found to be 0.9 nM, whereas the presence of 10,000-fold amounts of SR-melagatran did not interfere with the detection. To the best of our knowledge, this is the first demonstration of an LSPR-based enantioselective biosensor. PMID:22836379

  9. Enantioselective, continuous (R)- and (S)-2-butanol synthesis: achieving high space-time yields with recombinant E. coli cells in a micro-aqueous, solvent-free reaction system.

    PubMed

    Erdmann, Vanessa; Mackfeld, Ursula; Rother, Dörte; Jakoblinnert, Andre

    2014-12-10

    The stereoselective production of (R)- or (S)-2-butanol is highly challenging. A potent synthesis strategy is the biocatalytic asymmetric reduction of 2-butanone applying alcohol dehydrogenases. However, due to a time-dependent racemisation process, high stereoselectivity is only obtained at incomplete conversion after short reaction times. Here, we present a solution to this problem: by using a continuous process, high biocatalytic selectivity can be achieved while racemisation is suppressed successfully. Furthermore, high conversion was achieved by applying recombinant, lyophilised E. coli cells hosting Lactobacillus brevis alcohol dehydrogenase in a micro-aqueous solvent-free continuous reaction system. The optimisation of residence time (?) and 2-butanone concentration boosted both conversion (>99%) and enantiomeric excess (ee) of (R)-2-butanol (>96%). When a residence time of only ?=3.1 min was applied, productivity was extraordinary with a space-time yield of 2278±29g/(L×d), thus exceeding the highest values reported to date by a factor of more than eight. The use of E. coli cells overexpressing an ADH of complementary stereoselectivity yielded a synthesis strategy for (S)-2-butanol with an excellent ee (>98%). Although conversion was only moderate (up to 46%), excellent space-time yields of up to 461g/(L×d) were achieved. The investigated concept represents a synthesis strategy that can also be applied to other biocatalytic processes where racemisation poses a challenge. PMID:25036751

  10. Application-layer Connector Synthesis Paola Inverardi, Romina Spalazzese, and Massimo Tivoli

    E-print Network

    Paris-Sud XI, Université de

    Application-layer Connector Synthesis Paola Inverardi, Romina Spalazzese, and Massimo Tivoli interoperability via con- nector synthesis. We consider application-layer connectors by referring to two conceptually distinct notions of connector: coordinator and medi- ator. The former is used when the NSs

  11. Enantioselective degradation kinetics of metalaxyl in rabbits

    Microsoft Academic Search

    Jing Qiu; QiuXia Wang; Ping Wang; GuiFang Jia; JunLing Li; ZhiQiang Zhou

    2005-01-01

    Metalaxyl [methyl-N-(2?-methoxyacetyl)-N-(2,6-dimethylphenyl)-d,l- alaninate] is a potent phenylamide fungicide. The (?)-(R)-isomer accounts for most of the fungicidal activity. A possible stereo and\\/or enantioselective kinetics of metalaxyl in rabbits was investigated by intravenous injection. The concentrations of (?)-(R)- and (+)-(S)-metalaxyl in plasma, liver, and kidney tissue were determined by HPLC with a cellulose–Tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase and gas chromatography-mass spectroscopy. After intravenous

  12. Enantioselective esterification of racemic naproxen by lipases in organic solvent.

    PubMed

    Tsai, S W; Wei, H J

    1994-04-01

    Enantioselective esterification of naproxen, 2-(6-methoxy-2-naphthyl) propionic acid, was attempted by lipases in nearly anhydrous isooctane. The nature of the alcohol affects the reactivity and enantioselectivity of the lipase from Candida cylindracea. Alcohols containing a trimethylsilyl group are highly reactive and enantioselective to the S-isomer of the acid. An optimal temperature around 65 degrees C and an enzyme concentration less than 7 mg ml-1 were proposed to resolve the racemate, with trimethylsilyl methanol as nucleophile, from a consideration of the enantiomeric ratio, the ester formation, and the resistance of mass transfer for the substrate. PMID:7764635

  13. Upconversion Nanoparticles: Synthesis, Surface Modification, and Biological Applications

    PubMed Central

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

    2011-01-01

    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. PMID:21419877

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  15. Catalytic, Enantioselective Bifunctional Inverse Electron Demand Hetero-Diels-Alder Reactions of Ketene Enolates and o-Benzoquinone

    E-print Network

    Lectka, Thomas

    Catalytic, Enantioselective Bifunctional Inverse Electron Demand Hetero-Diels-Alder Reactions@jhu.edu Catalytic, enantioselective Diels-Alder reactions ([4 + 2] cycloadditions) constitute a vital part

  16. Total syntheses of ?-lactone containing natural products: I. total synthesis of belactosin C II. synthetic studies toward spongiolactone

    E-print Network

    Cho, Sung Wook

    2009-05-15

    The recently isolated bacterial metabolites, belactosins A-C from a fermentation broth of Streptomyces sp. UCK14, uniquely contain a ?-lactone dipeptide motif and exhibit anticancer activities. The enantioselective synthesis of (-)-belactosin C...

  17. [Development of boomerang-type intramolecular cascade reactions and application to natural product synthesis].

    PubMed

    Takasu, K

    2001-12-01

    Intramolecular cascade reaction has received much attention as a powerful methodology to construct a polycyclic framework in organic synthesis. We have been developing "boomerang-type cascade reaction" to construct a variety of polycyclic skeletons efficiently. In the above reactions, a nucleophilic function of substrates changes the character into an electrophile after the initial reaction, and the electrophilic group acts as a nucleophile in the second reaction. That is, the reaction center stepwise moves from one functional group back to the same one via other functional groups. The stream of the electron concerning the cascade reaction is like a locus of boomerang. We show here three different boomerang-type reactions via ionic species or free radicals. 1) Diastereoselective Michael-aldol reaction based on the chiral auxiliary method and enantioselective Michael-aldol reaction by the use of external chiral sources. 2) Short and efficient total syntheses of longifolane sesquiterpenes utilizing intramolecular double Michael addition as a key step. 3) Development of boomerang-type radical cascade reaction of halopolyenes to construct terpenoid skeletons and its regioselectivity. PMID:11766403

  18. Enantioselective construction of remote quaternary stereocentres

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  19. Novel ZnS nanostructures: Synthesis, growth mechanism, and applications

    NASA Astrophysics Data System (ADS)

    Moore, Daniel F.

    Motivated by a desire to understand the basic concepts of one-dimensional nanostructure growth, the research described in this thesis aims at understanding the basic mechanisms controlling the synthesis and formation of a specific group of II-VI semiconducting nanostructures. In particular, this thesis examines one-dimensional nanostructures (such as nanobelts and nanowires) and different morphologies of ZnS that result from the interesting properties that the materials have at the nanoscale. In order to understand how to tune these properties in the nanostructure, it is necessary to have an understanding of the growth mechanism that dictates the morphology, structure, and rate of growth of the nanomaterial. It is necessary to understand what impact changes to the macroscopic setup in the experiment have on the nanoscopic scale of the nanomaterials. Having a larger understanding and exerting more precise control over the growth of nanomaterials will allow a higher level of selectivity, more control over dimensionality and the type of morphology, easier manipulation, and the simpler incorporation of these structures into a nanotechnological device. The main focus of the research was on CdSe and ZnS, with the bulk of the research being conducted on ZnS nanostructures. These materials were chosen for their potential for extensive research, their possible applications in optoelectronics, their potential to form the wurtzite crystal structure, and the potential generalization of results to other nanomaterials. The framework for the research is given first. Then a description of the experimental setup and a model for the growth of nanostructures is discussed. A brief overview of the synthesis of CdSe nanostructures is given and then a detailed analysis of the synthesis of specific ZnS one-dimensional morphologies is presented.

  20. Highly Enantioselective Catalytic Phenylation of Ketones with a

    E-print Network

    Walsh, Patrick J.

    Highly Enantioselective Catalytic Phenylation of Ketones with a Constrained Geometry Titanium, 2003 ABSTRACT The catalytic asymmetric addition of phenyl groups from diphenylzinc to ketones us to report our independent investigations that define the scope of the phenyl addition to ketones

  1. Enantioselective Copper-Catalyzed Reductive Coupling of Alkenylazaarenes with Ketones 

    E-print Network

    Saxena, Aakarsh; Choi, Bonnie; Hon, Lam Wai

    2012-05-23

    Catalytic enantioselective methods for the preparation of chiral azaarene-containing compounds are of high value. By combining the utility of copper hydride catalysis with the ability of C?N-containing azaarenes to activate adjacent alkenes toward...

  2. Chemoselective and Enantioselective Oxidation of Indoles Employing Aspartyl Peptide Catalysts

    E-print Network

    Movassaghi, Mohammad

    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 ...

  3. Organocatalytic enantioselective ?-hydroxymethylation of aldehydes: mechanistic aspects and optimization.

    PubMed

    Boeckman, Robert K; Biegasiewicz, Kyle F; Tusch, Douglas J; Miller, John R

    2015-04-17

    Further studies of the direct enantioselective ?-hydroxymethylation of aldehydes employing the ?,?-diarylprolinol trimethylsilyl ether class of organocatalysts are described. This process has proven efficient for access to ?-hydroxycarboxylic acids and ?-hydroxy-?,?-unsaturated esters from aldehydes in generally good yields, excellent enantioselectivity, and compatibility with a broad range of functional groups in the aldehyde. The goal of these studies was to identify the critical reaction variables that influence the yield and enantioselectivity of the ?-hydroxymethylation process such as catalyst structure, pH of the medium, purity of the reactants and reagents particularly with respect to the presence of acidic impurities, and the nature of the buffer, along with the standard variables including solvent, time, temperature and mixing efficiency. The previously identified intermediate lactol has been further characterized and its reactivity examined. These studies have led to identification of the most critical variables translating directly into improved substrate scope, reproducibility, enantioselectivity, and yields. PMID:25793648

  4. (S)-2Amino3-(2,5-dimethylphenyl)-1,1-diphenyl-1-propanol: Synthesis and Application in Enantioselective Reduction of Prochiral Ketones

    Microsoft Academic Search

    Ya-Wen Zhang; Zong-Xuan Shen; De-Ben Gu; Wei-Yi Chen; Zheng-Hao Fei; Qing-Fei Dai

    1996-01-01

    The title chiral amino alcohol 6 was prepared from (s)-3-(2,5-dimethylphenyl)-alanine methyl ester hydrochloride by its reaction with phenyl magnesium bromide. In the presence of 2 mol% of 6, the borane reduction of prochiral ketones gave optically active secondary alcohols in high yields with the ee's ranged from 40.5 to 100%.

  5. Synthesis and applications of {sup 13}C glycerol

    SciTech Connect

    Stocking, E.; Khalsa, O.; Martinez, R.A.; Silks, L.A. III [Los Alamos National Laboratory, NM (United States)

    1994-12-01

    Due in part to the use of labeled glycerol for the {sup 13}C enrichment of biomolecules, we are currently developing new synthetic routes to various isotopomers of glycerol. Judging from our experience, traditional methods of glycerol synthesis are not easily adapted for isotopic enrichment and/or have poor overall yields (12 to 15%). Furthermore, the use of glycerol for enrichment can be prohibitively expensive and its availability is limited by the level of demand. We are presently developing a short de novo synthesis of glycerol from carbon dioxide ({approximately}53% overall yield for four steps) and are examining the feasibility of synthesizing site-specific {sup 13}C-labeled glycerol and dihydroxyacetone (DHA) from labeled methanol and carbon dioxide. One application of {sup 13}C glycerol we have examined is enzymatic conversion of glycerol to glyceraldehyde-3-monophosphate or dihydroxyacetone monophosphate (DHAP) with yields ranging from 25 to 50% (as determined by NMR spectroscopy). We are also pursuing the chemical conversion of {sup 13}C-labeled DHA to DHAP. We are especially interested in {sup 13}C-labeled DHAP because we are investigating its use as a chemo-enzymatic precursor for both labeled 2-deoxyribose and 2-deoxyribonucleic acids.

  6. Asymmetric, stereocontrolled total synthesis of paraherquamide A.

    PubMed

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

    2003-10-01

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

  7. Adaptation of a Small-Molecule Hydrogen-Bond Donor Catalyst to an Enantioselective Hetero-Diels–Alder Reaction Hypothesized for Brevianamide Biosynthesis

    PubMed Central

    2015-01-01

    Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels–Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis. PMID:25697748

  8. Adaptation of a small-molecule hydrogen-bond donor catalyst to an enantioselective hetero-Diels-Alder reaction hypothesized for brevianamide biosynthesis.

    PubMed

    Sprague, Daniel J; Nugent, Benjamin M; Yoder, Ryan A; Vara, Brandon A; Johnston, Jeffrey N

    2015-02-20

    Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels-Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis. PMID:25697748

  9. 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

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

    2014-06-01

    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

  10. Colloidal nanocrystals: on the way from synthesis to applications

    NASA Astrophysics Data System (ADS)

    Gaponik, N.; Eychmüller, A.

    2007-08-01

    The synthesis of strongly luminescing semiconductor nanocrystals reported is based on a wet-chemical approach. The use of aqueous solutions and the avoiding of dangerous and unstable precursors make this synthetic approach to be easily up-scaleable. The reaction yields are approaching gram amounts of the dried product and are limited solely by the laboratory facilities and thus may be further increased by using industrial equipments. The nanocrystals obtained by this route are strongly luminescing and suitable for various assembling procedures allowing the creation of core-shell spherical and thin-film composites, that are promising for photonic and optoelectronic applications. New assembly procedures allowing template-based formations of different types of metal-dielectric and porous metal nanostructures are presented.

  11. Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma.

    PubMed

    Verma, Jyoti; Lal, Sumit; Van Noorden, Cornelis J F

    2014-01-01

    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. PMID:24959075

  12. Framed carbon nanostructures: synthesis and applications in functional SPM tips.

    PubMed

    Mukhin, I S; Fadeev, I V; Zhukov, M V; Dubrovskii, V G; Golubok, A O

    2015-01-01

    We present a synthesis method to fabricate framed carbon-based nanostructures having highly anisotropic shapes, in particular, the nanofork and nanoscalpel structures which are obtained systematically under optimized growth conditions. A theoretical model is developed to explain the formation of such nanostructures on Si cantilevers and W etched wires exposed to a focused electron beam. We then demonstrate the potentials of these nanostructures as functional tips for scanning probe microscopy. Owing to their anisotropic shapes, such tips can be very useful for nanolithography, nanosurgery of biological objects, and precise manipulation with surface particles. Overall, our method provides a simple and robust way to produce functional scanning probe microscopy tips with variable shapes and enhanced capabilities for different applications compared to standard cantilevers. PMID:25461592

  13. Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma

    PubMed Central

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

    2014-01-01

    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. PMID:24959075

  14. Diastereoselective synthesis of fused lactone-pyrrolidinones; application to a formal synthesis of (-)-salinosporamide A.

    PubMed

    Logan, Angus W J; Sprague, Simon J; Foster, Robert W; Marx, Léo B; Garzya, Vincenzo; Hallside, Michal S; Thompson, Amber L; Burton, Jonathan W

    2014-08-15

    A mild, diastereoselective synthesis of fused lactone-pyrrolidinones using an oxidative radical cyclization is reported. The methodology is demonstrated in a formal synthesis of (-)-salinosporamide A. PMID:25068416

  15. Rhodium/phospholane-phosphite catalysts give unusually high regioselectivity in the enantioselective hydroformylation of vinyl arenes.

    PubMed

    Noonan, Gary M; Cobley, Christopher J; Mahoney, Thomas; Clarke, Matthew L

    2014-02-11

    Using the phospholane-phosphite ligand, BOBPHOS, almost perfect regioselectivities and high enantioselectivities (up to 92% ee) are observed in Rh catalysed enantioselective hydroformylation of vinyl arenes. This can be achieved under solvent-free conditions. PMID:24362887

  16. Discovery of an Escherichia coli Esterase with High Activity and Enantioselectivity toward 1,2-O-Isopropylideneglycerol Esters?†

    PubMed Central

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

    2011-01-01

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

  17. Structure, Synthesis, and Applications of TiO2 Nanobelts.

    PubMed

    Zhao, Zhenhuan; Tian, Jian; Sang, Yuanhua; Cabot, Andreu; Liu, Hong

    2015-04-01

    TiO2 semiconductor nanobelts have unique structural and functional properties, which lead to great potential in many fields, including photovoltaics, photocatalysis, energy storage, gas sensors, biosensors, and even biomaterials. A review of synthetic methods, properties, surface modification, and applications of TiO2 nanobelts is presented here. The structural features and basic properties of TiO2 nanobelts are systematically discussed, with the many applications of TiO2 nanobelts in the fields of photocatalysis, solar cells, gas sensors, biosensors, and lithium-ion batteries then introduced. Research efforts that aim to overcome the intrinsic drawbacks of TiO2 nanobelts are also highlighted. These efforts are focused on the rational design and modification of TiO2 nanobelts by doping with heteroatoms and/or forming surface heterostructures, to improve their desirable properties. Subsequently, the various types of surface heterostructures obtained by coupling TiO2 nanobelts with metal and metal oxide nanoparticles, chalcogenides, and conducting polymers are described. Further, the charge separation and electron transfer at the interfaces of these heterostructures are also discussed. These properties are related to improved sensitivity and selectivity for specific gases and biomolecules, as well as enhanced UV and visible light photocatalytic properties. The progress in developments of near-infrared-active photocatalysts based on TiO2 nanobelts is also highlighted. Finally, an outline of important directions of future research into the synthesis, modification, and applications of this unique material is given. PMID:25800706

  18. Solution synthesis, optical properties, and bioimaging applications of silicon nanocrystals.

    PubMed

    McVey, Benjamin F P; Tilley, Richard D

    2014-10-21

    Understanding and unlocking the potential of semiconductor nanocrystals (NCs) is important for future applications ranging from biomedical imaging contrast agents to the next generation of solar cells and LEDs. Silicon NCs (Si NCs) have key advantages compared with other semiconductor NCs due to silicon's high natural abundance, low toxicity and strong biocompatibility, and unique size, and surface dependent optical properties. In this Account, we review and discuss the synthesis, surface modification, purification, optical properties, and applications of Si NCs. The synthetic methods used to make Si NCs have improved considerably in the last 5-10 years; highly monodisperse Si NCs can now be produced on the near gram scale. Scaled-up syntheses have allowed scientists to drive further toward the commercial utilization of Si NCs. The synthesis of doped Si NCs, through addition of a simple elemental precursor to a reaction mixture or by the production of a single source precursor, has shown great promise. Doped Si NCs have demonstrated unique or enhanced properties compared with pure Si NCs, for example, magnetism due to the presence of magnetic metals like Fe and Mn. Surface reactions have reached a new level of sophistication where organic (epoxidation and diol formation) and click (thiol based) chemical reactions can be carried out on attached surface molecules. This has led to a wide range of biocompatible functional groups as well as a degree of emission tuneability. The purification of Si NCs has been improved through the use of size separation columns and size selective precipitation. These purification approaches have yielded highly monodisperse and pure Si NCs previously unachieved. This has allowed scientists to study the size and surface dependent properties and toxicity and enabled the use of Si NCs in biomedical applications. The optical properties of Si NCs are complex. Using a combination of characterization techniques, researchers have explored the relation between the optical properties and the size, surface functionalization, and preparation method. This work has led to a greater fundamental understanding of the unique optical properties of Si NCs. Si NCs are being studied for a wide range of important applications, including LEDS with tunable electroluminescence ranging from NIR to yellow, the encapsulation of Si NCs within micelles terminated with proteins to allow targeted in vivo imaging of cells, Si NC-polymer hybrid solar cells, and the use of Si NCs in battery anodes with high theoretical capacity and good charge retention. PMID:25252604

  19. APPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH

    E-print Network

    Luther, Douglas S.

    APPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH AND PRODUCTION. Stroup Tom Humphreys #12;ABSTRACT The rate of nucleic acid synthesis was used as a measure of growth grown under controlled conditions. These studies demonstrated that accurate rates of nucleic acid

  20. Application of -Synthesis based H-Control for Adaptive Optics in Laser Material Processing

    E-print Network

    Knobloch,Jürgen

    Application of µ-Synthesis based H-Control for Adaptive Optics in Laser Material Processing Steffen Mauch1 and Johann Reger1 Abstract-- An adaptive optics system is used for the con- trolled attenuation-- adaptive optics, robust control, H-control, material processing, µ-synthesis I. INTRODUCTION As the costs

  1. Application of the plane wave synthesis technique based on the least square method in antenna measurements

    Microsoft Academic Search

    Yu Ding; Yang Lin; Fu De-min; Liu Qi-zhong

    2009-01-01

    A novel plane wave synthesis technique based on the least square method is presented and its application in antenna measurements is studied by the method of computer simulation. With the linear array made up of the infinitely long current filament as the theoretical model of plane wave synthesis, and with the uniform linear array made up of half-wavelength dipole elements

  2. Texture Synthesis from Non-Fronto-Parallel Textures and Related Applications

    E-print Network

    Dyer, Charles R.

    Texture Synthesis from Non-Fronto-Parallel Textures and Related Applications CS 790 Project Report Saurabh Goyal saurabh@cs.wisc.edu Advisor: Prof. Chuck Dyer 1 Introduction Previous work on texture synthesis has only addressed fronto-parallel tex- tures, i.e., when a camera is parallel to a planar texture

  3. Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis

    E-print Network

    Pedram, Massoud

    Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis Revision of TCAD synthesis which relies on alphabetic tree construction is presented. Alphabetic trees are trees which any internal edge crossing. First, a mechanism for generating all alphabetic trees on a given number

  4. A one-pot combination of amine and heterocyclic carbene catalysis: direct asymmetric synthesis of ?-hydroxy and ?-malonate esters from ?,?-unsaturated aldehydes

    Microsoft Academic Search

    Gui-Ling Zhao; Armando Córdova

    2007-01-01

    The one-pot combination of amine and heterocyclic carbene catalysis (AHCC) enabled the synthesis of ?-hydroxy, ?-malonate and ?-amino esters from ?,?-unsaturated aldehydes with high enantioselectivity (91–97% ee).

  5. Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towards

    E-print Network

    Paris-Sud XI, Université de

    1 Understanding water effect on Candida antarctica lipase B activity and enantioselectivity towardsW) on Candida antarctica lipase B (CALB) activity and enantioselectivity towards secondary alcohols was assessed that water has many effects on Candida antarctica lipase B (CALB) catalyzed enantioselective reactions

  6. Enantioselective pharmacokinetics of ibuprofen and involved mechanisms.

    PubMed

    Hao, Haiping; Wang, Guangji; Sun, Jianguo

    2005-01-01

    Although dexibuprofen (S-ibuprofen) was marketed in Austria and Switzerland, the racemate at various formulations is still extensively used worldwide, and there are no indications that the racemate will be replaced by the single enantiomer. Thus, elucidation of the characteristics and involved mechanisms of the chiral pharmacokinetics of racemic ibuprofen is of special importance for the understanding of the pharmacological and toxicological consequences, and for prediction of the clinically potential drug interactions and influence of the pathological states. Stereoselective pharmacokinetics and metabolism are common features for chiral nonsteroidal antiinflammatory drugs (NSAIDs) and especially for 2-arylpropionic acid derivatives characterized with a chiral center adjacent to the carboxyl group. Although the enantioselective pharmacokinetic characteristics of different NSAIDs should be treated case by case, they share similar mechanisms underlying the protein binding, metabolism and chiral inversion. Ibuprofen was the most extensively researched drug in terms of chiral characteristics and mechanisms. Therefore, elucidation of the mechanisms derived from research on ibuprofen may provide better understanding and prediction of other chiral drugs. This article attempts to elucidate the chiral pharmacokinetics and involved mechanisms of ibuprofen in comparison with other NSAIDs based on recent developments. Topics on history of ibuprofen, enantioselective analysis method, absorption, protein binding, conventional metabolism, metabolic chiral inversion, gene polymorphism, and biochemical developments were included. It is worth mentioning that some underlying biochemical mechanisms, especially for the metabolic chiral inversion and ethnic differences still remain to be seen. Further research is required to develop human-resourced researching model and to provide more evidence concerning the site of inversion, species variation, CYP450 gene polymorphisms, and biochemical mechanisms. PMID:15747501

  7. Enantioselective disposition of clenbuterol in rats.

    PubMed

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

    2014-05-01

    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. PMID:24323748

  8. Triply Hydrogen-Bond-Directed Enantioselective Assembly of Pyrrolobenzo-1,4-diazine Skeletons with Quaternary Stereocenters.

    PubMed

    Shen, Xiaoming; Wang, Yongtao; Wu, Tiandi; Mao, Zhenjun; Lin, Xufeng

    2015-06-15

    Highly efficient synthesis of optically enriched pyrrolobenzo-1,4-diazines bearing quaternary stereocenters has been realized through the chiral Brønsted acid-catalyzed Pictet-Spengler reaction of 2-(1H-pyrrol-1-yl)anilines and ?-ketoamides in good to excellent yields and enantioselectivities. Computational studies suggest an unprecedented phenomenon whereby the chiral phosphoric acid catalyst employs attractive arene C?H???N hydrogen bonding to activate the substrate and induce chirality through a triple hydrogen-bonding interaction. PMID:25965054

  9. Triaziflam and Diaminotriazine derivatives affect enantioselectively multiple herbicide target sites.

    PubMed

    Grossmann, K; Tresch, S; Plath, P

    2001-01-01

    Enantiomers of triaziflam and structurally related diaminotriazines were synthesized and their herbicidal mode of action was investigated. The compounds caused light and dark-dependent effects in multiple test systems including heterotrophic cleaver and photoautotrophic algal cell suspensions, the Hill reaction of isolated thylakoids and germinating cress seeds. Dose-response experiments revealed that the (S)-enantiomers of the compounds preferentially inhibited photosystem II electron transport (PET) and algae growth with efficacies similar to that of the herbicide atrazine. In contrast, the (R)-enantiomers of the diaminotriazines were up to 100 times more potent inhibitors of growth in cleaver cell suspensions and cress seedlings in the dark than the (S)-enantiomers. The most active compound, the (R)-enantiomer of triaziflam, inhibited shoot and root elongation of cress and maize seedlings at concentrations below 1 microM. The meristematic root tips swelled into a club shape which is typical for the action of mitotic disrupter herbicides and cellulose biosynthesis inhibitors. Microscopic examination using histochemical techniques revealed that triaziflam (R)-enantiomer blocks cell division in maize root tips 4 h after treatment. The chromosomes proceeded to a condensed state of prometaphase but were unable to progress further in the mitotic cycle. Disruption of mitosis was accompanied by a loss of spindle and phragmoplast micotubule arrays. Concomitantly, cortical microtubules decreased which could lead to isodiametric cell growth and consequently to root swelling. In addition, a decline in cellulose deposition in cell walls was found 24 h after treatment. Compared to the (R)-form, triaziflam (S)-enantiomer was clearly less active. The results suggest that triaziflam and related diaminotriazines affect enantioselectively multiple sites of action which include PET inhibitory activity, mitotic disruption by inhibiting microtubule formation and inhibition of cellulose synthesis. PMID:11531090

  10. Green synthesis and applications of Au-Ag bimetallic nanoparticles.

    PubMed

    Meena Kumari, M; Jacob, John; Philip, Daizy

    2015-02-25

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenolapplication. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field. PMID:25218228

  11. Green synthesis and applications of Au-Ag bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Meena Kumari, M.; Jacob, John; Philip, Daizy

    2015-02-01

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol < k2-nitrophenol < k3-nitrophenol. Thermal conductivity is measured as a function of volume fraction and it is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

  12. Qualitative Analysis of Distributed Physical Systems with Applications to Control Synthesis \\Lambda

    E-print Network

    Bailey-Kellogg, Chris

    Qualitative Analysis of Distributed Physical Systems with Applications to Control Synthesis \\Lambda­ ature distribution, air flow, and acoustic waves, are described as continuous, distributed parameter fields. Analyzing and controlling these physical processes and systems are common tasks in many

  13. A new method of synthesis of fluorescently labelled oligonucleotides and their application in DNA sequencing.

    PubMed Central

    Markiewicz, W T; Gröger, G; Rösch, R; Zebrowska, A; Markiewicz, M; Klotz, M; Hinz, M; Godzina, P; Seliger, H

    1997-01-01

    A new approach to the chemical synthesis of oligodeoxynucleotides bearing reporter functional groups at base residues of 3'-end nucleosides is reported. Applications of the 3'-end fluorescently labelled primers for automated DNA sequencing are shown. PMID:9278489

  14. Stop-flow lithography for complex particle synthesis and application in directed assembly

    E-print Network

    Panda, Priyadarshi

    2012-01-01

    The synthesis of complex microparticles is an important objective. These particles can find use in a number of applications ranging from tissue engineering to ceramics and assembly. Tuned assembly of anisotropic particles ...

  15. Enantioselective Recognition in Solution: The Case of Countercurrent Chromatography

    NASA Astrophysics Data System (ADS)

    Rubio, Núria; Minguillón, Cristina

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

  16. Synthesis, characterization and biosensing application of photon upconverting nanoparticles

    NASA Astrophysics Data System (ADS)

    Kumar, Manoj; Zhang, Peng

    2009-02-01

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

  17. Sustainable synthesis, characterization, and applications of metal oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Tiano, Amanda Lyn

    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.

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

    PubMed

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

    2014-02-18

    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

  19. SYSTEMATIC EXPLOITATION OF DATA PARALLELISM IN HARDWARE SYNTHESIS OF DSP APPLICATIONS1

    E-print Network

    Bhattacharyya, Shuvra S.

    SYSTEMATIC EXPLOITATION OF DATA PARALLELISM IN HARDWARE SYNTHESIS OF DSP APPLICATIONS1 Mainak Sen signal, image, and video processing (DSP) applications. In particular, we con- sider the systematic a dedicated hardware implementation. Data parallelism occurs com- monly in DSP applications, and provides

  20. Asymmetric Synthesis of Functionalized Dihydro- and Tetrahydropyrans via an Organocatalytic Domino Michael–Hemiacetalization Reaction

    PubMed Central

    Urbanietz, Gregor; Atodiresei, Iuliana; Enders, Dieter

    2014-01-01

    Starting from ?-hydroxymethyl nitroalkenes and various 1,3-dicarbonyl compounds, a one-pot organocatalyzed diastereo- and enantioselective synthesis of polyfunctionalized dihydro- and tetrahydropyran derivatives via a domino Michael-hemiacetalization sequence is reported. The title compounds bearing a variety of functional groups can be synthesized in this way in good yields (59–91%) and with moderate to excellent diastereoselectivities (26–98% de) and enantioselectivities (71–99% ee). PMID:25284900

  1. Silver nanoparticles: synthesis, properties, toxicology, applications and perspectives

    NASA Astrophysics Data System (ADS)

    Tran, Quang Huy; Quy Nguyen, Van; Le, Anh-Tuan

    2013-09-01

    In recent years the outbreak of re-emerging and emerging infectious diseases has been a significant burden on global economies and public health. The growth of population and urbanization along with poor water supply and environmental hygiene are the main reasons for the increase in outbreak of infectious pathogens. Transmission of infectious pathogens to the community has caused outbreaks of diseases such as influenza (A/H5N1), diarrhea (Escherichia coli), cholera (Vibrio cholera), etc throughout the world. The comprehensive treatments of environments containing infectious pathogens using advanced disinfectant nanomaterials have been proposed for prevention of the outbreaks. Among these nanomaterials, silver nanoparticles (Ag-NPs) with unique properties of high antimicrobial activity have attracted much interest from scientists and technologists to develop nanosilver-based disinfectant products. This article aims to review the synthesis routes and antimicrobial effects of Ag-NPs against various pathogens including bacteria, fungi and virus. Toxicology considerations of Ag-NPs to humans and ecology are discussed in detail. Some current applications of Ag-NPs in water-, air- and surface- disinfection are described. Finally, future prospects of Ag-NPs for treatment and prevention of currently emerging infections are discussed.

  2. Synthesis of Boron Nitride Nanotubes for Engineering Applications

    NASA Technical Reports Server (NTRS)

    Hurst, Janet; Hull, David; Gorican, Dan

    2005-01-01

    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.

  3. Dendrimers in layer-by-layer assemblies: synthesis and applications.

    PubMed

    Sato, Katsuhiko; Anzai, Jun-ichi

    2013-01-01

    We review the synthesis of dendrimer-containing layer-by-layer (LbL) assemblies and their applications, including biosensing, controlled drug release, and bio-imaging. Dendrimers can be built into LbL films and microcapsules by alternating deposition of dendrimers and counter polymers on the surface of flat substrates and colloidal microparticles through electrostatic bonding, hydrogen bonding, covalent bonding, and biological affinity. Dendrimer-containing LbL assemblies have been used to construct biosensors, in which electron transfer mediators and metal nanoparticles are often coupled with dendrimers. Enzymes have been successfully immobilized on the surface of electrochemical and optical transducers by forming enzyme/dendrimer LbL multilayers. In this way, high-performance enzyme sensors are fabricated. In addition, dendrimer LbL films and microcapsules are useful for constructing drug delivery systems because dendrimers bind drugs to form inclusion complexes or the dendrimer surface is covalently modified with drugs. Magnetic resonance imaging of cancer cells by iron oxide nanoparticles coated with dendrimer LbL film is also discussed. PMID:23867653

  4. Aerosol Route Synthesis and Applications of Doped Nanostructured Materials

    Microsoft Academic Search

    Manoranjan Sahu

    2011-01-01

    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.

  5. General approach for preparing epidithiodioxopiperazines from trioxopiperazine precursors: enantioselective total syntheses of (+)- and (-)-gliocladine C, (+)-leptosin D, (+)-T988C, (+)-bionectin A, and (+)-gliocladin A.

    PubMed

    DeLorbe, John E; Horne, David; Jove, Richard; Mennen, Steven M; Nam, Sangkil; Zhang, Fang-Li; Overman, Larry E

    2013-03-13

    A common strategy for preparing tryptophan-derived epidithiodioxopiperazine (ETP) natural products containing a hydroxyl substituent adjacent to a quaternary carbon stereocenter is reported. This strategy is exemplified by enantioselective total syntheses of four heptacyclic ETP natural products--gliocladine C (6), leptosin D (7), T988C (8), and bionectin A (9)--starting with the di-(tert-butoxycarbonyl) derivative 17 of the trioxopiperazine natural product gliocladin C, which is readily available by enantioselective chemical synthesis. In addition, total syntheses of the enantiomer of gliocladine C (ent-6) and gliocladin A (11), the di(methylthio) congener of bionectin A, are reported. These syntheses illustrate a synthetic strategy wherein diversity in the dioxopiperazine unit of ETP natural products is introduced at a late stage in a synthetic sequence. In vitro cytotoxicity of compounds in this series against invasive human prostrate (DU145) and melanoma (A2058) cancer cell lines is described and compared to that of chaetocin A (4). PMID:23452236

  6. Rh2(S-PTTL)3TPA—A Mixed Ligand Dirhodium(II) Catalyst for Enantioselective Reactions of ?-Alkyl-?-Diazoesters

    PubMed Central

    Boruta, David T.; Dmitrenko, Olga; Yap, Glenn P. A.

    2012-01-01

    Herein we report the synthesis of the mixed ligand paddlewheel complex dirhodium(II) tris[N-phthaloyl-(S)-tert-leucinate] triphenylacetate, Rh2(S-PTTL)3TPA, the structure of which bears similarity to the chiral crown complex Rh2(S-PTTL)4. Rh2(S-PTTL)3TPA engages substrate classes (aliphatic alkynes, silylacetylenes, ?-olefins) that are especially challenging in intermolecular reactions of ?-alkyl-?-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh2(S-PTTL)4. Mixing ligands on paddlewheel complexes offers a versatile handle for diversifying catalyst structure and reactivity. The results described herein illustrate how mixed ligand catalysts can create new opportunities for the optimization of catalytic asymmetric processes. PMID:23125912

  7. Asymmetric one-pot synthesis of 1,3-oxazolidines and 1,3-oxazinanes via hemiaminal intermediates.

    PubMed

    Nimmagadda, Sri Krishna; Zhang, Zuhui; Antilla, Jon C

    2014-08-15

    A highly efficient method for the enantioselective one-pot synthesis of 1,3-oxazolidines and 1,3-oxazinanes has been reported. The reaction proceeds via the formation of hemiaminal intermediates obtained by the enantioselective addition of respective alcohols to imines catalyzed by a chiral magnesium phosphate catalyst, followed by intramolecular cyclization under mildly basic conditions. A wide range of substrates have been converted to the respective chiral heterocyclic products in high yields and with excellent enantioselectivities using this one-pot procedure. PMID:25075467

  8. Total synthesis of (+)-madangamine D.

    PubMed

    Ballette, Roberto; Pérez, Maria; Proto, Stefano; Amat, Mercedes; Bosch, Joan

    2014-06-10

    Madangamines are a group of bioactive marine sponge alkaloids, embodying an unprecedented diazapentacyclic skeletal type. The enantioselective total synthesis of madangamine?D has been accomplished, and represents the first total synthesis of an alkaloid of the madangamine group. It involves the stereoselective construction of the diazatricyclic ABC core using a phenylglycinol-derived lactam as the starting enantiomeric scaffold and the subsequent assembly of the peripheral macrocyclic rings. The synthesis provides, for the first time, a pure sample of madangamine?D and confirms the absolute configuration of this alkaloid family. PMID:24798407

  9. PDMS based microfluidic chips and their application in material synthesis

    NASA Astrophysics Data System (ADS)

    Gong, Xiuqing

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

  10. Synthesis, characterization and applications of a perdeuterated amphipol.

    PubMed

    Giusti, Fabrice; Rieger, Jutta; Catoire, Laurent J; Qian, Shuo; Calabrese, Antonio N; Watkinson, Thomas G; Casiraghi, Marina; Radford, Sheena E; Ashcroft, Alison E; Popot, Jean-Luc

    2014-10-01

    Amphipols are short amphipathic polymers that can substitute for detergents at the hydrophobic surface of membrane proteins (MPs), keeping them soluble in the absence of detergents while stabilizing them. The most widely used amphipol, known as A8-35, is comprised of a polyacrylic acid (PAA) main chain grafted with octylamine and isopropylamine. Among its many applications, A8-35 has proven particularly useful for solution-state NMR studies of MPs, for which it can be desirable to eliminate signals originating from the protons of the surfactant. In the present work, we describe the synthesis and properties of perdeuterated A8-35 (perDAPol). Perdeuterated PAA was obtained by radical polymerization of deuterated acrylic acid. It was subsequently grafted with deuterated amines, yielding perDAPol. The number-average molar mass of hydrogenated and perDAPol, ~4 and ~5 kDa, respectively, was deduced from that of their PAA precursors, determined by size exclusion chromatography in tetrahydrofuran following permethylation. Electrospray ionization-ion mobility spectrometry-mass spectrometry measurements show the molar mass and distribution of the two APols to be very similar. Upon neutron scattering, the contrast match point of perDAPol is found to be ~120% D2O. In (1)H-(1)H nuclear overhauser effect NMR spectra, its contribution is reduced to ~6% of that of hydrogenated A8-35, making it suitable for extended uses in NMR spectroscopy. PerDAPol ought to also be of use for inelastic neutron scattering studies of the dynamics of APol-trapped MPs, as well as small-angle neutron scattering and analytical ultracentrifugation. PMID:24652511

  11. Perspective view of GSC: How to realize the industrial application of artificial photo synthesis?

    NASA Astrophysics Data System (ADS)

    Setoyama, T.

    2013-12-01

    Artificial photo synthesis is one of the dream reactions, which can contribute to the industrial application from a view point of green sustainable chemistry. Considering the hardness of subjects to obtain the enough performance on artificial photo synthesis and the difference between the current infrastructure and required ones, which can fit to this application, we have to solve these subjects one by one from a strategic view point. Diversification of chemical resource and compatibility of process technologies will be the keys for industrial application.

  12. Synthesis and Characterization of Polymer Nanocomposites for Energy Applications

    E-print Network

    Park, Wonchang

    2011-10-21

    -polymer nanocomposites were prepared to confirm the thermal conductivity enhancement. The procedures of synthesis for CNTs and graphite-polymer nanocomposites for TIM are described below. Filler such as CNTs and graphite and surfactants such as SDS (sodium lauryl...

  13. Beta-methylcysteines: synthesis and application in native chemical ligation 

    E-print Network

    Lai, Zhi

    2000-01-01

    Native chemical ligation has emerged as a powerful method in peptide synthesis. In this method, an initial transthioesterification step involves a chemoselective reaction that occurs between a peptide fragment containing ...

  14. Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)

    DOEpatents

    Samsel, E.G.

    1992-10-20

    A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-[alpha]-benzoylamino-4boronocinnamic acid, asymmetrically hydrogenating the z-[alpha]-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA. 3 figs.

  15. Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)

    DOEpatents

    Samsel, Edward G. (Baton Rouge, LA)

    1992-01-01

    A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-.alpha.-benzoylamino-4-boronocinnamic acid, asymmetrically hydrogenating the z-.alpha.-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA.

  16. Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)

    Microsoft Academic Search

    Samsel

    1992-01-01

    A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to

  17. Enantioselective synthesis of L-(-)-4-boronophenylalanine (L-BPA)

    SciTech Connect

    Samsel, E.G.

    1991-12-31

    4-Boronophenylalanine (BPA) is being investigated for boron neutron capture therapy of metastatic melanomas and other tumors. It is believed that the pure enantiomer L-BPA is more biologically active than the D,L racemate. This patent discloses a method of making substantially pure L-BPA. The method comprises the steps of reacting 4-bromobenzaldehyde with ethylene glycol, reacting the resulting acetal with Mg to produce a Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, which is then reacted with diethanol amine, condensing the resulting ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide, asymmetrically hydrogengating the product in the presence of Rh chelate to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying this in an organic medium to produce L-BPA.

  18. Enantioselective synthesis of L-(-)-4-boronophenylalanine (L-BPA)

    Microsoft Academic Search

    Samsel

    1991-01-01

    4-Boronophenylalanine (BPA) is being investigated for boron neutron capture therapy of metastatic melanomas and other tumors. It is believed that the pure enantiomer L-BPA is more biologically active than the D,L racemate. This patent discloses a method of making substantially pure L-BPA. The method comprises the steps of reacting 4-bromobenzaldehyde with ethylene glycol, reacting the resulting acetal with Mg to

  19. A concise enantioselective synthesis of antimalarial febrifugine alkaloids.

    PubMed

    Ooi, H; Urushibara, A; Esumi, T; Iwabuchi, Y; Hatakeyama, S

    2001-03-22

    Reaction of (S)-2-(tert-butyldiphenylsilyloxy)-5-(mesyloxy)pentanal with hydroxylamine in allyl alcohol brought about simultaneous 1,3-dipolar cycloaddition of the resulting nitrone to allyl alcohol to give three diastereoisomeric adducts, from which (+)-febrifugine and (+)-isofebrifugine, potent antimalarial alkaloids, were synthesized. PMID:11263924

  20. One-Dimensional Metal Oxide Nanotubes, Nanowires, Nanoribbons, and Nanorods: Synthesis, Characterizations, Properties and Applications

    Microsoft Academic Search

    Yu Li; Xiao-Yu Yang; Yi Feng; Zhong-Yong Yuan; Bao-Lian Su

    2012-01-01

    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

  1. ARMA Synthesis of Fading Channels-an Application to the Generation of Dynamic MIMO

    E-print Network

    Blostein, Steven D.

    ARMA Synthesis of Fading Channels-an Application to the Generation of Dynamic MIMO Channels Hani fashion are extremely valuable. Previously, the application of autoregres- sive moving average (ARMA. This paper presents a numerically stable and ac- curate method to synthesize ARMA rational approximations

  2. Combinatorial synthesis of solid state electronic materials for renewable energy applications

    Microsoft Academic Search

    Q. Wang; John Perkins; Howard M Branz; Jeff Alleman; Chris Duncan; David Ginley

    2002-01-01

    We report on the development of new combinatorial capabilities for both the synthesis of new solid state opto-electronic materials and optimization of existing materials for renewable energy applications especially photovoltaic devices. Some of the important materials for these renewable energy applications include semiconductors (such as for absorber layers), transparent conductors, energy storage materials and more. In this paper, we focus

  3. Synthesis and applications of one-dimensional nano-structured polyaniline: An overview

    Microsoft Academic Search

    Donghua Zhang; Yangyong Wang

    2006-01-01

    This paper summarizes and reviews the various synthesizing approaches of one-dimensional nano-structured polyaniline (PANI) and several potential applications of the nanomaterial. The synthesizing approaches can be generally categorized into template synthesis and non-template synthesis according to whether template(s), hard (physical template) or soft (chemical template), is (are) used or not. However, though the various approaches established, preparation of one-dimensional nano-structured

  4. Synthetic studies on the icetexones: enantioselective formal syntheses of icetexone and epi-icetexone

    PubMed Central

    de Jesus Cortez, Felipe; Lapointe, David; Hamlin, Amy M.; Simmons, Eric M.; Sarpong, Richmond

    2013-01-01

    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. PMID:24249921

  5. Synthetic studies on the icetexones: enantioselective formal syntheses of icetexone and epi-icetexone.

    PubMed

    de Jesus Cortez, Felipe; Lapointe, David; Hamlin, Amy M; Simmons, Eric M; Sarpong, Richmond

    2013-07-01

    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. PMID:24249921

  6. Biomimetic total synthesis of (±)-doitunggarcinone A and (+)-garcibracteatone.

    PubMed

    Pepper, Henry P; Tulip, Stephen J; Nakano, Yuji; George, Jonathan H

    2014-03-21

    A full account of our oxidative radical cyclization approach to the synthesis of garcibracteatone and doitunggarcinone A is presented. This includes the first enantioselective synthesis of garcibracteatone, which allowed the absolute configuration of the natural compound to be determined. The first synthesis of doitunggarcinone A is also described, which confirms our reassignment of the relative configuration of this molecule. Novel syntheses of monoterpene fragments used to construct the target molecules are also reported. PMID:24575789

  7. Nonlinear Robust Control Synthesis Methods for Spacecraft Applications

    NASA Astrophysics Data System (ADS)

    LeBel, Stefan

    This thesis focuses on practical methods for constructing robust nonlinear control systems. In general, the development of such control systems is characterized by the solution to one or more Hamilton-Jacobi partial differential equations (HJE). However, no general analytical solution has yet been obtained to solve this optimization problem. Solutions have thus far only been obtained under certain conditions. Therefore, the first significant contribution of this thesis is a method for obtaining analytical expressions for approximate solutions to a common form of HJE (under certain assumptions regarding the class of nonlinear systems used). Additionally, modern state space controller synthesis techniques typically result in state estimators of equal or greater dimension than the plant model. However, it is often desirable, or even necessary, to approximate these controllers by models of lower state dimension. Presently, methods for developing nonlinear state balancing transformations are not very well understood. Therefore, the second significant contribution of this thesis is a proper algorithm for the application of state balancing techniques to nonlinear control systems and the subsequent reduction of the number of control states. The method to be developed for state balancing is based on the above framework for constructing analytical solutions to the HJE. In this thesis we will make use of three existing robust nonlinear control methods from the literature. These three methods have the advantage that they can all be constructed from solutions to a single form of HJE. Thus, by developing a method for obtaining analytical expressions for the solution to a single form of HJE, we are able to develop explicit polynomial solutions for each of these three control methods. Due to the difficulties associated with quantifying robustness and performance properties for nonlinear systems, the effectiveness of the three control methods considered shall be demonstrated via numerical simulations. The particular applications of interest to us here are space systems. First, we will consider the attitude control of a single spacecraft. Second, we examine the problem of formation flying control for a pair of spacecraft. The third and final problem we consider is the control of a nonlinear mass-spring chain.

  8. Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step

    PubMed Central

    Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

    2012-01-01

    Summary The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed. PMID:23019438

  9. Palladium-Catalyzed Asymmetric Alkylation in the Synthesis of Cyclopentanoid and Cycloheptanoid Core Structures Bearing All-

    E-print Network

    Stoltz, Brian M.

    , iodoethane, acrylonitrile, methyl vinyl ketone, and acrolein were distilled prior to use. Purified water for the Synthesis of Ligands L3 and L4 SI 8 Procedures for Synthesis of Enantioenriched Vinylogous Esters 7 SI 10 using Enantioselective Decarboxylative Alkylation Reactions Synthetic Studies on Vinylogous Esters 8/7a

  10. Catalytic, Enantioselective, Intramolecular Carbosulfenylation of Olefins. Preparative and Stereochemical Aspects

    PubMed Central

    Denmark, Scott E.; Jaunet, Alex

    2014-01-01

    The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a co-catalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50–92%) and high enantioselectivities (71:29 – 97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with mono-activated arene nucleophiles. PMID:24328051

  11. Catalytic enantioselective intramolecular aza-diels-alder reactions.

    PubMed

    Min, Chang; Lin, Chih-Tsung; Seidel, Daniel

    2015-05-26

    A readily available chiral Brønsted acid was identified as an efficient catalyst for intramolecular Povarov reactions. Polycyclic amines containing three contiguous stereogenic centers were obtained with excellent stereocontrol in a single step from secondary anilines and aldehydes possessing a pendent dienophile. These transformations constitute the first examples of catalytic enantioselective intramolecular aza-Diels-Alder reactions. PMID:25867945

  12. Directed Evolution of Enantioselective Enzymes NO2 P. aeruginosa

    E-print Network

    Stoltz, Brian M.

    by Mullis in 1994. Random mutations are induced over the entire gene. Established by varying parameters (e230Ile mutant Random mutagenesis using E. coli mutator strain Quick E No improvement 175 colonies Site-412. Reviews on directed evolution of enantioselective enzymes: 1 2 3 4 51 2 3 4 5 2 2 Gene (DNA) Mutagenesis

  13. Catalytic enantioselective direct Michael additions of ketones to alkylidene malonates

    Microsoft Academic Search

    Juan M Betancort; Kandasamy Sakthivel; Rajeswari Thayumanavan; Carlos F Barbas

    2001-01-01

    Enantioselective direct Michael additions of ketones using (S)-1-(2-pyrrolidinylmethyl)-pyrrolidine as a catalyst are described. Michael adducts with up to 91% e.e. were obtained by the reaction of alkylidene malonates with simple unactivated ketones under mild reaction conditions.

  14. A Hybrid Phosphorus Ligand for Highly Enantioselective Asymmetric Hydroformylation

    E-print Network

    Zhang, Xumu

    A Hybrid Phosphorus Ligand for Highly Enantioselective Asymmetric Hydroformylation Yongjun Yan phosphorus ligand has been prepared starting from chiral NOBIN (2-amino-2- hydroxy-1,1-binaphthyl). Excellent phosphorus ligands bearing two different phosphorus groups are effective in asymmetric hydroformylation.2a

  15. The Enantioselective Addition of Alkyne Nucleophiles to Carbonyl Groups

    PubMed Central

    Trost, Barry M.; Weiss, Andrew H.

    2013-01-01

    Over the past decade, large strides have been achieved in the invention of methods for the direct enantioselective addition of alkynes and metal alkynylide nucleophiles into prochiral aldehydes, ketones, and imines. This review highlights and compares the available methods for these transformations. PMID:24353484

  16. Whole cells in enantioselective reduction of benzyl acetoacetate

    PubMed Central

    Ribeiro, Joyce Benzaquem; Ramos, Aline de Souza; Lopes, Raquel de Oliveira; da Silva, Gabriela Veloso Vieira; de Souza, Rodrigo Octavio Mendonça Alves

    2014-01-01

    The ?-ketoester benzyl acetoacetate was enantioselectively reduced to benzyl (S)-3-hydroxybutanoate by seven microorganism species. The best result using free cells was obtained with the yeast Hansenula sp., which furnished 97% ee and 85% of conversion within 24 h. After immobilization in calcium alginate spheres, K.marxianus showed to be more stable after 2 cycles of reaction. PMID:25477927

  17. Supporting Information for Petrova, Mohr, and Stoltz: Enantioselective Total Synthesis of (+)-Cassiol SI 1 Enantioselective Total Synthesis of (+)-Cassiol

    E-print Network

    Stoltz, Brian M.

    solutions are saturated aqueous sodium chloride solutions. Liquids and solutions were transferred via 4(82% yield) Vinylogous Thioester 4.4 To a solution of diketone SI1 (5.00 g, 39.82 mmol, 1.00 equiv) in CH3CN (44 mL) was added Et3N (6.2 mL, 44.40 mmol, 1.12 equiv), and the solution was allowed to stir

  18. Improved enantioselectivity of thermostable esterase from Archaeoglobus fulgidus toward (S)-ketoprofen ethyl ester by directed evolution and characterization of mutant esterases.

    PubMed

    Kim, Jinyeong; Kim, Seungbum; Yoon, Sangyoung; Hong, Eunsoo; Ryu, Yeonwoo

    2015-08-01

    Thermostable esterases have potential applications in various biotechnology industries because of their resistance to high temperature and organic solvents. In a previous study, we isolated an esterase from Archaeoglobus fulgidus DSM 4304 (Est-AF), which showed high thermostability but low enantioselectivity toward (S)-ketoprofen ethyl ester. (R)-ketoprofenor (S)-ketoprofenis produced by esterase hydrolysis of the ester bond of (R,S)-ketoprofen ethyl ester and (S)-ketoprofen has better pharmaceutical activity and lower side effects than (R)-ketoprofen. Therefore, we have generated mutants of Est-AF that retained high thermostability whilst improving enantioselectivity. A library of Est-AF mutants was created by error-prone polymerase chain reaction, and mutants with improved enantioselectivity were isolated by site-saturation mutagenesis. The regions of Est-AF containing amino acid mutations were analyzed by homology modeling of its three-dimensional structure, and structure-based explanations for the changes in enantioselectivity are proposed. Finally, we isolated two mutants showing improved enantioselectivity over Est-AF (ee%?=?-16.2?±?0.2 and E?=?0.7?±?0.0): V138G (ee%?=?35.9?±?1.0 and E?=?3.0?±?0.1) and V138G/L200R (ee%?=?89.2?±?0.2 and E?=?19.5?±?0.5). We also investigated various characteristics of these mutants and found that the mutants showed similar thermostability and resistance to additives or organic solvents to Est-AF, without a significant trade-off between activity and stability. PMID:25661815

  19. Composite membrane of bacterially-derived cellulose and molecularly imprinted polymer for use as a transdermal enantioselective controlled-release system of racemic propranolol.

    PubMed

    Bodhibukkana, Chatchada; Srichana, Teerapol; Kaewnopparat, Sanae; Tangthong, Naruedom; Bouking, Pisit; Martin, Gary P; Suedee, Roongnapa

    2006-06-12

    A composite membrane for transdermal delivery of S-propranolol enantiomer was developed based on the controlled pore functionalization of bacterial cellulose membranes using a molecularly imprinted polymer (MIP) layer synthesis. The reactive pore-filling of an asymmetric porous cellulose membrane with a MIP thin-layer was effected using a silanized coupler as an additional anchor for the MIP. MIP thin-layers with specific binding sites for S-propranolol were synthesized by copolymerization of methacrylic acid with a cross-linker, ethylene glycol dimethacrylate in the presence of S-propranolol as the template molecule and the latter was subsequently extracted. Selective transport of S-propranolol through the MIP composite membrane was obtained, although this was determined mostly by the parent cellulose membrane with some ancillary contributory effect from the MIP layer. In addition, an enantioselectivity in the transport of propranolol prodrug enantiomers was found, suggesting that the shape and functional groups orientation, which are similar to that of the print molecule were essential for enantiomeric recognition of the MIP composite membrane. The enantioselectivity of S-MIP membranes was also shown when the release of propranolol enantiomers was studied in vitro using rat skin, with racemic propranolol contained in the donor compartment. The composite membrane of bacterially-derived cellulose and molecularly imprinted polymer may have great potential for use as a transdermal enantioselective controlled-release system for racemic propranolol. PMID:16713005

  20. Fluorescent Carbon Nanoparticle: Synthesis, Characterization and Bio-imaging Application

    Microsoft Academic Search

    S. C. Ray; Arindam Saha; Nikhil R. Jana; Rupa Sarkar

    2009-01-01

    Fluorescent carbon nanoparticle (CNP) having 2-6 nm in size with quantum yield of about ~3% were synthesized via nitric acid oxidation of carbon soot and this approach can be used for milligram scale synthesis of these water soluble particles. These CNPs are nano-crystalline with predominantly graphitic structure and shows green fluorescence under UV exposure. While nitric acid oxidation induces nitrogen

  1. Modular Distribution and Application to Discrete Controller Synthesis

    E-print Network

    Fradet, Pascal

    -directed projection operation. This operation allows then the safe recombination of the result of the synthesis interaction with their environment, are intrinsically critical. The failure of such systems can involve the complementary of this abstraction, whose recombination with the transformed abstraction is safe and preserves

  2. Microwave-Assisted Synthesis ? Catalytic Applications in Aqueous Media

    EPA Science Inventory

    The development of sustainable methods directed towards the synthesis of molecules is due to the heightened awareness and recognition of alternative eco-friendly and economical protocols that have minimum impact on environment. Among others, microwave (MW)-assisted methodology ha...

  3. Direct digital RF synthesis and modulation for MSAT mobile applications

    NASA Technical Reports Server (NTRS)

    Crozier, Stewart; Datta, Ravi; Sydor, John

    1993-01-01

    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.

  4. Size-Dependent Enantioselective Adsorption of Racemic Molecules through Homochiral Metal-Organic Frameworks Embedding Helicity.

    PubMed

    Xu, Zhong-Xuan; Fu, Hong-Ru; Wu, Xin; Kang, Yao; Zhang, Jian

    2015-07-01

    Homochiral metal-organic frameworks (HMOFs) are efficient materials for enantioselective adsorption. However, the combination of size selectivity and enantioselectivity is still a major challenge in the field of HMOFs. Herein, two enantiomorphic HMOFs built from predesigned proline-derived ligands are presented. Both of them show multiple homochiral features: they contain four different helical chains and three types of helical channels. Due to the size effect of the helical channels, each HMOF can enantioselectively adsorb methyl lactate with high ee. The results reveal a new approach toward size-dependent enantioselective separation of racemic compounds by using HMOFs built from inexpensive proline derivatives. PMID:26041141

  5. An organocatalytic Mannich/denitration reaction for the asymmetric synthesis of 3-ethylacetate-substitued 3-amino-2-oxindoles: formal synthesis of AG-041R.

    PubMed

    Zhao, Kun; Shu, Tao; Jia, Jiaqi; Raabe, Gerhard; Enders, Dieter

    2015-03-01

    The highly enantioselective organocatalytic addition of ethyl nitroacetate to isatin-derived N-Boc ketimines (Boc = tert-butoxycarbonyl), followed by the removal of the nitro group, is described. The scalable reaction sequence leads to the title compounds as important intermediates of pyrroloindoline alkaloids and related drugs in excellent yields and enantioselectivities. The synthesis of the hexahydrofurano[2,3-b]indole skeleton, the spirocarbamate oxindole unit, and the formal synthesis of AG-041R have been carried out to demonstrate the synthetic utility of this protocol. PMID:25630891

  6. Total Synthesis of (+)-18-epi-Latrunculol A

    PubMed Central

    Williams, Brett D.

    2013-01-01

    An enantioselective total synthesis of the cytotoxic latrunculin congener (+)-18-epi-latrunculol A has been achieved. Key steps in the synthetic route include an acid-mediated enone cyclization / equilibration sequence, a Carreira alkynylation, and a late-stage Mitsunobu macrolactonization to construct the macrolide skeleton. PMID:23972216

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

    PubMed Central

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

    2006-01-01

    A method of wet chemical synthesis suitable for high throughput and combinatorial applications has been developed for the synthesis of porous resistive thick-film gas sensors. This method is based on the robot-controlled application of unstable metal oxide suspensions on an array of 64 inter-digital electrodes positioned on an Al2O3 substrate. SnO2, WO3, ZrO2, TiO2, CeO2, In2O3 and Bi2O3 were chosen as base oxides, and were optimised by doping or mixed oxide formation. The parallel synthesis of mixed oxide sensors is illustrated by representative examples. The electrical characteristics and the sensor performance of the films were measured by high-throughput impedance spectroscopy while supplying various test gases (H2, CO, NO, NO2, propene). Data collection, data mining techniques applied and the best potential sensor materials discovered are presented.

  8. A genomic search approach to identify carbonyl reductases in Gluconobacter oxydans for enantioselective reduction of ketones.

    PubMed

    Chen, Rong; Liu, Xu; Lin, Jinping; Wei, Dongzhi

    2014-01-01

    The versatile carbonyl reductases from Gluconobacter oxydans in the enantioselective reduction of ketones to the corresponding alcohols were exploited by genome search approach. All purified enzymes showed activities toward the tested ketoesters with different activities. In the reduction of 4-phenyl-2-butanone with in situ NAD(P)H regeneration system, (S)-alcohol was obtained with an e.e. of up to 100% catalyzed by Gox0644. Under the same experimental condition, all enzymes catalyzed ethyl 4-chloroacetoacetate to give chiral products with an excellent e.e. of up to 99%, except Gox0644. Gox2036 had a strict requirement for NADH as the cofactor and showed excellent enantiospecificity in the synthesis of ethyl (R)-4-chloro-3-hydroxybutanoate. For the reduction of ethyl 2-oxo-4-phenylbutyrate, excellent e.e. (>99%) and high conversion (93.1%) were obtained by Gox0525, whereas the other enzymes showed relatively lower e.e. and conversions. Among them, Gox2036 and Gox0525 showed potentials in the synthesis of chiral alcohols as useful biocatalysts. PMID:25130736

  9. Nature versus nurture in two highly enantioselective esterases from Bacillus cereus and Thermoanaerobacter tengcongensis.

    PubMed

    Grosse, Stephan; Bergeron, Hélène; Imura, Akihiro; Boyd, Jason; Wang, Shaozhao; Kubota, Kazuo; Miyadera, Akihiko; Sulea, Traian; Lau, Peter C K

    2010-01-01

    There is an increasing need for the use of biocatalysis to obtain enantiopure compounds as chiral building blocks for drug synthesis such as antibiotics. The principal findings of this study are: (i) the complete sequenced genomes of Bacillus cereus ATCC 14579 and Thermoanaerobacter tengcongensis MB4 contain a hitherto undescribed enantioselective and alkaliphilic esterase (BcEST and TtEST respectively) that is specific for the production of (R)-2-benzyloxy-propionic acid ethyl ester, a key intermediate in the synthesis of levofloxacin, a potent antibiotic; and (ii) directed evolution targeted for increased thermostability of BcEST produced two improved variants, but in either case the 3-5 °C increase in the apparent melting temperature (T(m)) of the mutants over the native BcEST that has a T(m) of 50 °C was outperformed by TtEST, a naturally occurring homologue with a T(m) of 65 °C. Protein modelling of BcEST mapped the S148C and K272R mutations at protein surface and the I88T and Q110L mutations at more buried locations. This work expands the repertoire of characterized members of the ?/?-fold hydrolase superfamily. Further, it shows that genome mining is an economical option for new biocatalyst discovery and we provide a rare example of a naturally occurring thermostable biocatalyst that outperforms experimentally evolved homologues that carry out the same hydrolysis. PMID:21255307

  10. Structural basis for high substrate-binding affinity and enantioselectivity of 3-quinuclidinone reductase AtQR.

    PubMed

    Hou, Feng; Miyakawa, Takuya; Kataoka, Michihiko; Takeshita, Daijiro; Kumashiro, Shoko; Uzura, Atsuko; Urano, Nobuyuki; Nagata, Koji; Shimizu, Sakayu; Tanokura, Masaru

    2014-04-18

    (R)-3-Quinuclidinol, a useful compound for the synthesis of various pharmaceuticals, can be enantioselectively produced from 3-quinuclidinone by 3-quinuclidinone reductase. Recently, a novel NADH-dependent 3-quinuclidionone reductase (AtQR) was isolated from Agrobacterium tumefaciens, and showed much higher substrate-binding affinity (>100 fold) than the reported 3-quinuclidionone reductase (RrQR) from Rhodotorula rubra. Here, we report the crystal structure of AtQR at 1.72 Å. Three NADH-bound protomers and one NADH-free protomer form a tetrameric structure in an asymmetric unit of crystals. NADH not only acts as a proton donor, but also contributes to the stability of the ?7 helix. This helix is a unique and functionally significant part of AtQR and is related to form a deep catalytic cavity. AtQR has all three catalytic residues of the short-chain dehydrogenases/reductases family and the hydrophobic wall for the enantioselective reduction of 3-quinuclidinone as well as RrQR. An additional residue on the ?7 helix, Glu197, exists near the active site of AtQR. This acidic residue is considered to form a direct interaction with the amine part of 3-quinuclidinone, which contributes to substrate orientation and enhancement of substrate-binding affinity. Mutational analyses also support that Glu197 is an indispensable residue for the activity. PMID:24642255

  11. Substrate range and enantioselectivity of epoxidation reactions mediated by the ethene-oxidising Mycobacterium strain NBB4.

    PubMed

    Cheung, Samantha; McCarl, Victoria; Holmes, Andrew J; Coleman, Nicholas V; Rutledge, Peter J

    2013-02-01

    Mycobacterium strain NBB4 is an ethene-oxidising micro-organism isolated from estuarine sediments. In pursuit of new systems for biocatalytic epoxidation, we report the capacity of strain NBB4 to convert a diverse range of alkene substrates to epoxides. A colorimetric assay based on 4-(4-nitrobenzyl)pyridine) has been developed to allow the rapid characterisation and quantification of biocatalytic epoxide synthesis. Using this assay, we have demonstrated that ethene-grown NBB4 cells epoxidise a wide range of alkenes, including terminal (propene, 1-butene, 1-hexene, 1-octene and 1-decene), cyclic (cyclopentene, cyclohexene), aromatic (styrene, indene) and functionalised substrates (allyl alcohol, dihydropyran and isoprene). Apparent specific activities have been determined and range from 2.5 to 12.0 nmol min(-1) per milligram of cell protein. The enantioselectivity of epoxidation by Mycobacterium strain NBB4 has been established using styrene as a test substrate; (R)-styrene oxide is produced in enantiomeric excesses greater than 95%. Thus, the ethene monooxygenase of Mycobacterium NBB4 has a broad substrate range and promising enantioselectivity, confirming its potential as a biocatalyst for alkene epoxidation. PMID:22410742

  12. Anisotropic Hexagonal Boron Nitride Nanomaterials - Synthesis and Applications

    SciTech Connect

    Han,W.Q.

    2008-08-01

    Boron nitride (BN) is a synthetic binary compound located between III and V group elements in the Periodic Table. However, its properties, in terms of polymorphism and mechanical characteristics, are rather close to those of carbon compared with other III-V compounds, such as gallium nitride. BN crystallizes into a layered or a tetrahedrally linked structure, like those of graphite and diamond, respectively, depending on the conditions of its preparation, especially the pressure applied. Such correspondence between BN and carbon readily can be understood from their isoelectronic structures [1, 2]. On the other hand, in contrast to graphite, layered BN is transparent and is an insulator. This material has attracted great interest because, similar to carbon, it exists in various polymorphic forms exhibiting very different properties; however, these forms do not correspond strictly to those of carbon. Crystallographically, BN is classified into four polymorphic forms: Hexagonal BN (h-BN) (Figure 1(b)); rhombohedral BN (r-BN); cubic BN (c-BN); and wurtzite BN (w-BN). BN does not occur in nature. In 1842, Balmain [3] obtained BN as a reaction product between molten boric oxide and potassium cyanide under atmospheric pressure. Thereafter, many methods for its synthesis were reported. h-BN and r-BN are formed under ambient pressure. c-BN is synthesized from h-BN under high pressure at high temperature while w-BN is prepared from h-BN under high pressure at room temperature [1]. Each BN layer consists of stacks of hexagonal plate-like units of boron and nitrogen atoms linked by SP{sup 2} hybridized orbits and held together mainly by Van der Waals force (Fig 1(b)). The hexagonal polymorph has two-layered repeating units: AA'AA'... that differ from those in graphite: ABAB... (Figure 1(a)). Within the layers of h-BN there is coincidence between the same phases of the hexagons, although the boron atoms and nitrogen atoms are alternatively located along the c-axis. The rhombohedral system consists of three-layered units: ABCABC..., whose honeycomb layers are arranged in a shifted phase, like as those of graphite. Reflecting its weak interlayer bond, the h-BN can be cleaved easily along its layers, and hence, is widely used as a lubricant material. The material is stable up to a high temperature of 2300 C before decomposition sets in [2] does not fuse a nitrogen atmosphere of 1 atm, and thus, is applicable as a refractory material. Besides having such properties, similar to those of graphite, the material is transparent, and acts as a good electric insulator, especially at high temperatures (10{sup 6} {Omega}m at 1000 C) [1]. c-BN and w-BN are tetrahedrally linked BN. The former has a cubic sphalerite-type structure, and the latter has a hexagonal wurtzite-type structure. c-BN is the second hardest known material (the hardest is diamond), the so-called white diamond. It is used mainly for grinding and cutting industrial ferrous materials because it does not react with molten iron, nickel, and related alloys at high temperatures whereas diamond does [1]. It displays the second highest thermal conductivity (6-9 W/cm.deg) after diamond. This chapter focuses principally upon information about h-BN nanomaterials, mainly BN nanotubes (BNNTs), porous BN, mono- and few-layer-BN sheets. There are good reviews book chapters about c-BN in [1, 4-6].

  13. Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects

    NASA Astrophysics Data System (ADS)

    Prabhu, Sukumaran; Poulose, Eldho K.

    2012-10-01

    Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative. The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles. The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

  14. Stiffness coupling application to modal synthesis program, users guide

    NASA Technical Reports Server (NTRS)

    Kuhar, E. J.

    1976-01-01

    A FORTRAN IV computer program used to perform modal synthesis of structures by stiffness coupling, using the dynamic transformation method is described. The program was named SCAMP (Stiffness Coupling Approach Modal-Synthesis Program). The program begins with the entry of a substructure's physical mode shapes and eigenvalues or a substructure's mass and stiffness matrix. If the mass and stiffness matrices are entered, the eigen problem for the individual substructure is solved. Provisions are included for a maximum of 20 substructures which are coupled by stiffness matrix springs. Each substructure has a number degrees of freedom (DOF), except that for DOF greater than 100; vector sets having maximum row and column size of 100 were generated prior to entering SCAMP. The substructures are then coupled together via coupling springs, and the dynamic transformation is used to reduce the size of the eigen problem.

  15. Self-propagating high-temperature synthesis of MnZn-ferrites for inductor applications

    NASA Astrophysics Data System (ADS)

    Agrafiotis, C. C.; Zaspalis, V. T.

    2004-12-01

    The self-propagating high-temperature synthesis (SHS) route is evaluated for the synthesis of MnZn-ferrite powders that are subsequently processed towards the manufacturing of high initial magnetic permeability polycrystalline specimens for inductor applications. The conditions for the synthesis of particular phases by SHS reactions between iron metal and oxide powders were optimized and the effects of the synthesis parameters on ignition and propagation characteristics were studied. By "fine-tuning" the synthesis parameters, products of a wide spectrum of phases from single-phase, pure and well crystallized (Mn xZn y)Fe 2+?O 4 to the oxide of the divalent metals (Mn x'Zn y'Fe 1-x'-y')O could be controllably synthesized. Advantages of the synthesis route are demonstrated by tests on properties of merit on final products: combustion powder products were subsequently pressed to torroids, sintered and characterized with respect to their magnetic properties, in comparison to conventionally synthesized samples of the same composition. When sintered under appropriate schedules of oxygen partial pressure profile to avoid phase oxidation at 600 °C, SHS powders could be processed to high permeability MnZn-ferrites. At equal average particle sizes SHS powders exhibit higher reactivity and grain growth compared to conventionally synthesized powders. This advantage can be utilized in the manufacturing of high permeability MnZn-ferrites with shorter firing schedules and thus all associated advantages in terms of productivity, production costs or zinc evaporation loss.

  16. The application of green chemistry methods in organophosphorus synthesis

    NASA Astrophysics Data System (ADS)

    Odinets, Irina L.; Matveeva, E. V.

    2012-03-01

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

  17. A fluorous phosphate protecting group with applications to carbohydrate synthesis.

    PubMed

    Liu, Lin; Pohl, Nicola L B

    2011-04-01

    The first fluorous protecting group for phosphate is reported. This group can be used as a facile tag for purification and be removed under mild reducing conditions using zinc and ammonium formate. Synthesis of a disaccharide from Leishmania using this fluorous protecting group demonstrated the group's stability to the acidic conditions necessary for glycosylation as well as its orthogonality to several other common protecting groups. PMID:21384825

  18. Fluorescent Carbon Nanoparticles: Synthesis, Characterization, and Bioimaging Application

    Microsoft Academic Search

    S. C. Ray; Arindam Saha; Nikhil R. Jana; Rupa Sarkar

    2009-01-01

    Fluorescent carbon nanoparticle (CNP) having 2-6 nm in size with quantum\\u000ayield of about ~3% were synthesized via nitric acid oxidation of carbon soot\\u000aand this approach can be used for milligram scale synthesis of these water\\u000asoluble particles. These CNPs are nano-crystalline with predominantly graphitic\\u000astructure and shows green fluorescence under UV exposure. While nitric acid\\u000aoxidation induces nitrogen

  19. Plasma synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications

    Microsoft Academic Search

    Uwe Kortshagen; Lorenzo Mangolini; Ameya Bapat

    Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous\\u000a synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal\\u000a plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration;\\u000a particles can be electrostatically confined in a reactor

  20. Plasma synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications

    Microsoft Academic Search

    Uwe Kortshagen; Lorenzo Mangolini; Ameya Bapat

    2007-01-01

    Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous\\u000a synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal\\u000a plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration;\\u000a particles can be electrostatically confined in a reactor

  1. Synthesis and application studies of novel coumarin derivatives

    Microsoft Academic Search

    Peter Kele

    2002-01-01

    Current dissertation explores the possible uses of newly synthesized 4- and 7-substituted coumarin derivatives. In the initial phase of this work, the synthesis and surface properties of an amphiphilic coumarin derivative is discussed, along with its spectroscopic features as building-blocks of a monolayer at the air-water interface. Such amphiphilic fluorophores can be used for fluorescent probes in investigation of molecular

  2. Synthesis and characterization of polyphosphazenes as polymer electrolytes for secondary lithium battery applications

    Microsoft Academic Search

    David L. Olmeijer

    1998-01-01

    This thesis describes the synthesis and characterization of polyphosphazenes as polymer electrolytes for secondary lithium battery applications. The polyphosphazenes that were synthesized include (a) species with linear and branched oligo(oxyethylene) side groups, (b) examples which incorporate crown ethers of various sizes, and (c) polymers which include sulfone or sulfoxide functional groups. Additional work involved the investigation of the factors that

  3. Global scheduling with code-motions for high-level synthesis applications

    Microsoft Academic Search

    Minjoong Rim; Yaw Fann; Rajiv Jain

    1995-01-01

    In this paper, we present a global scheduling technique for synthesis applications. The algorithm accepts a specification containing conditional branches and while-loop constructs and schedules it for a given set of resources. The algorithm performs several types of code motions across different basic blocks and trades off cost with performance. Several real-life examples taken from Numerical Recipes in C are

  4. Synthesis and processing of CdS/ZnS multilayer films for solar cell application

    E-print Network

    Chow, Lee

    Synthesis and processing of CdS/ZnS multilayer films for solar cell application Isaiah O. Oladeji chemical bath deposited CdS/ZnS multilayers through low-temperature chemical and thermal-activated diffusion. The secondary ion mass spectrometry depth profiles indicate that Cd diffuses into ZnS film more

  5. REVIEW doi:10.1038/nature10381 Synthesis, assembly and applications of

    E-print Network

    Rogers, John A.

    REVIEW doi:10.1038/nature10381 Synthesis, assembly and applications of semiconductor nanomembranes J. A. Rogers1 , M. G. Lagally2 & R. G. Nuzzo3 Research in electronic nanomaterials, historically electronics. S emiconductor nanomembranes (NMs) are monocrystalline structures with thick- nesses of less than

  6. Synthesis, Properties, and Applications of Low-Dimensional Carbon-Related Nanomaterials

    Microsoft Academic Search

    Ali Mostofizadeh; Yanwei Li; Bo Song; Yudong Huang

    2011-01-01

    In recent years, many theoretical and experimental studies have been carried out to develop one of the most interesting aspects of the science and nanotechnology which is called carbon-related nanomaterials. The goal of this paper is to provide a review of some of the most exciting and important developments in the synthesis, properties, and applications of low-dimensional carbon nanomaterials. Carbon

  7. Cycle-based Decomposition of Markov Chains with Applications to Low Power Synthesis and Sequence

    E-print Network

    Pedram, Massoud

    1 Cycle-based Decomposition of Markov Chains with Applications to Low Power Synthesis and Sequence sequence and then selecting a subset of these cycles to construct the compacted sequence. 1 1 Copyright (c is based on the fact that a Markov process can be decomposed into a collection of directed cycles

  8. Automatic Synthesis of High-Performance Codes for Quantum Chemistry Applications

    E-print Network

    Baumgartner, Gerald

    Automatic Synthesis of High-Performance Codes for Quantum Chemistry Applications£ Gerald State University clam@cis.ohio-state.edu Marcel Nooijen Department of Chemistry Princeton University-performance parallel programs for a class of computations encountered in quantum chem- istry and physics

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

    PubMed Central

    Beng, Timothy K.; Gawley, Robert E.

    2012-01-01

    The diastereoselective synthesis of trans-2,6-disubstituted piperidines has been rendered enantioselective by incorporating a catalytic dynamic resolution into the first alkylation step. The method has been applied to the synthesis of (?)-epidihydropinidine and (+)-trans-lupetidine PMID:22408286

  10. Engineering Homochiral Metal-Organic Frameworks by Spatially Separating 1D Chiral Metal-Peptide Ladders: Tuning the Pore Size for Enantioselective Adsorption.

    PubMed

    Stylianou, Kyriakos C; Gómez, Laura; Imaz, Inhar; Verdugo-Escamilla, Cristóbal; Ribas, Xavi; Maspoch, Daniel

    2015-07-01

    The reaction of the chiral dipeptide glycyl-L(S)-glutamate with Co(II) ions produces chiral ladders that can be used as rigid 1D building units. Spatial separation of these building units with linkers of different lengths allows the engineering of homochiral porous MOFs with enhanced pore sizes, pore volumes, and surface areas. This strategy enables the synthesis of a family of isoreticular MOFs, in which the pore size dictates the enantioselective adsorption of chiral molecules (in terms of their size and enantiomeric excess). PMID:26033709

  11. Frontispiece: Engineering Homochiral Metal-Organic Frameworks by Spatially Separating 1D Chiral Metal-Peptide Ladders: Tuning the Pore Size for Enantioselective Adsorption.

    PubMed

    Stylianou, Kyriakos C; Gómez, Laura; Imaz, Inhar; Verdugo-Escamilla, Cristóbal; Ribas, Xavi; Maspoch, Daniel

    2015-07-01

    Porous Materials The reaction of the chiral dipeptide glycyl-L(S)-glutamate with Co(II) ions produces chiral ladders that can be used as rigid 1D building units. Spatial separation of these building units with linkers of different lengths allows the engineering of homochiral porous MOFs with enhanced pore sizes, pore volumes, and surface areas. This strategy enables the synthesis of a family of isoreticular MOFs, in which the pore size dictates the enantioselective adsorption of chiral molecules. For more details, see the Communication by D. Maspoch et?al. on page?9964?ff. PMID:26118729

  12. Silyl imine electrophiles in enantioselective catalysis: a Rosetta Stone for peptide homologation, enabling diverse N-protected aryl glycines from aldehydes in three steps.

    PubMed

    Makley, Dawn M; Johnston, Jeffrey N

    2014-06-01

    We report that N-(trimethylsilyl)imines serve in the Bis(AMidine)-catalyzed addition of bromonitromethane with a high degree of enantioselection. This allows for the production of a range of protected ?-bromo nitroalkane donors (including Fmoc) for use in Umpolung Amide Synthesis (UmAS). Hence, peptide homologation with nonnatural aryl glycine amino acids is achieved in three steps from aromatic aldehydes, which are plentiful and inexpensive. Epimerization during the homologation step is circumvented by avoiding an ?-amino acid intermediate. PMID:24828455

  13. Synthesis, Properties, and Environmental Applications of Nanoscale Iron-Based Materials: A Review

    Microsoft Academic Search

    Ling Li; Maohong Fan; Robert C. Brown; J. Van Leeuwen; Jianji Wang; Wenhua Wang; Yonghui Song; Panyue Zhang

    2006-01-01

    Due to their special properties, people have been increasingly interested in studying applications of nanoscale metal materials in environmental engineering. Literature about the current research on the synthesis, properties, and environmental applications of nanoscale iron-based materials is reviewed and summarized in this article. Different physical and chemical methods used for synthesizing nano-iron-based particles with desired size, structure, and surface properties

  14. Synthesis of pipelined memory access controllers for streamed data applications on FPGA-based computing engines

    Microsoft Academic Search

    Pedro C. Diniz

    2001-01-01

    Commercially available behavioral synthesis tools do not adequately support FPGA vendor-specific external memory interfaces making it extremely difficult to exploit pipelined memory access modes as well as application specific memory operations scheduling critical for high-performance solutions. This lack of support substantially increases the complexity and the burden on designers in the mapping of applications to FPGA-based computing engines. In this

  15. Synthesis of chiral polymorph A-enriched zeolite Beta with an extremely concentrated fluoride route.

    PubMed

    Tong, Mingquan; Zhang, Daliang; Fan, Weibin; Xu, Jun; Zhu, Liangkui; Guo, Wen; Yan, Wenfu; Yu, Jihong; Qiu, Shilun; Wang, Jianguo; Deng, Feng; Xu, Ruren

    2015-01-01

    Chiral zeolitic materials with intrinsically chiral frameworks are highly desired because they can combine both shape selectivity and enantioselectivity. In the field of zeolite, the synthesis of chiral polymorph A of zeolite Beta or chiral polymorph A-enriched zeolite Beta is one of the biggest challenges. We demonstrate here a generalized extremely concentrated fluoride route for the synthesis of chiral polymorph A-enriched zeolite Beta in the presence of five achiral organic structure-directing agents. The polymorph A-enriched Ti-Beta shows a higher enantioselectivity for the asymmetric epoxidation of alkenes than the normal Ti-Beta. PMID:26096214

  16. Synthesis of chiral polymorph A-enriched zeolite Beta with an extremely concentrated fluoride route

    PubMed Central

    Tong, Mingquan; Zhang, Daliang; Fan, Weibin; Xu, Jun; Zhu, Liangkui; Guo, Wen; Yan, Wenfu; Yu, Jihong; Qiu, Shilun; Wang, Jianguo; Deng, Feng; Xu, Ruren

    2015-01-01

    Chiral zeolitic materials with intrinsically chiral frameworks are highly desired because they can combine both shape selectivity and enantioselectivity. In the field of zeolite, the synthesis of chiral polymorph A of zeolite Beta or chiral polymorph A-enriched zeolite Beta is one of the biggest challenges. We demonstrate here a generalized extremely concentrated fluoride route for the synthesis of chiral polymorph A-enriched zeolite Beta in the presence of five achiral organic structure-directing agents. The polymorph A-enriched Ti-Beta shows a higher enantioselectivity for the asymmetric epoxidation of alkenes than the normal Ti-Beta. PMID:26096214

  17. Guide to Enantioselective Dirhodium(II)-Catalyzed Cyclopropanation with Aryldiazoacetates.

    PubMed

    Chepiga, Kathryn M; Qin, Changming; Alford, Joshua S; Chennamadhavuni, Spandan; Gregg, Timothy M; Olson, Jeremy P; Davies, Huw M L

    2013-07-01

    Catalytic enantioselective methods for the generation of cyclopropanes has been of longstanding pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh2(R-DOSP)4 is generaally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh2(R-BNP)4 plays a complementary role to Rh2(R-DOSP)4 and Rh2(S-PTAD)4 in catalyzing highly enantioselective cyclopropanation of 3- methoxy-substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation. PMID:24273349

  18. Proposed study to determine potential flight applications and human factors design guidelines of voice recognition/synthesis systems

    NASA Technical Reports Server (NTRS)

    Bergeron, H. P.

    1983-01-01

    An effort to evaluate the human factors aspects and potential of voice recognition/synthesis techniques and the application of present and near-future (5 years) voice recognition/synthesis systems as a pilot/aircraft cockpit interface capability in an operational environment is discussed. The analysis will emphasize applications for single pilot instrument flight rules operations but will also include applications for other categories of aircraft with various levels of complexity.

  19. Metal ion mediated imprinting for electrochemical enantioselective sensing of L-histidine at trace level.

    PubMed

    Prasad, Bhim Bali; Kumar, Deepak; Madhuri, Rashmi; Tiwari, Mahavir Prasad

    2011-10-15

    Enantioselective trace level sensing of l-histidine (limit of detection, 1.980 ngm L(-1), S/N=3) was feasible with the use of a typical, reproducible, and rugged complex imprinted polymer-based pencil graphite electrode, in aqueous samples. In the present instance, the Cu(2+) ion-mediated imprinting of l-histidine in an molecularly imprinted polymer motif actually helped upbringing electrocatalytic activity to respond an enhanced differential pulse anodic stripping voltammetric oxidation peak of l-histidine, without any cross-reactivity and false-positive, in real samples. The proposed sensor could be considered suitable for the practical applications in biomarking histedinemia, a disease associated with L-histidine metabolic disorders, in clinical settings. PMID:21802278

  20. Hydrogels formed by enantioselective self-assembly of histidine-derived amphiphiles with tartaric acid.

    PubMed

    Zhang, Fanjun; Xu, Zhenghu; Dong, Shuli; Feng, Lei; Song, Aixin; Tung, Chen-Ho; Hao, Jingcheng

    2014-07-21

    Two chiral enantiomers of histidine-derived amphiphilic gelators, (4R,6S)-UIPCA and (4S,6R)-UIPCA, were synthesized through Pictet-Spengler reaction and their gelation behaviors with different organic acids were investigated. Interestingly, the chiral enantiomers of UIPCA showed smart enantioselectivity for gelating tartaric acid enantiomers to form hydrogels with excellent mechanical strength. The TEM and SEM images demonstrated that the hydrogels were composed of networks by physical entanglement of nanofibers with high aspect ratios. The formation of nanofibers was considered to be driven by the interplay of hydrogen bonding, electrostatic attraction, and hydrophobic interaction, which was supported by XRD and FT-IR spectra. The hydrogels exhibited sensitive response to a series of external stimuli, such as temperature, metal ions, and host-guest interactions, to realize the reversible gel-sol transition. The property of the gelation was elaborated and the gelators were expected to find their applications in chiral discrimination. PMID:24865976

  1. Optimizing database-backed applications with query synthesis

    E-print Network

    Cheung, Alvin K.

    Object-relational mapping libraries are a popular way for applications to interact with databases because they provide transparent access to the database using the same language as the application. Unfortunately, using ...

  2. Pd-Catalyzed Enantioselective Allyl-Allyl Cross Coupling

    PubMed Central

    Zhang, Ping; Brozek, Laura A.; Morken, James P.

    2010-01-01

    The Pd-catalyzed cross coupling of terminal allylic carbonates and allylB(pin) is described. The regioselectivity of this reaction is sensitive to the bite angle of the ligand with small bite angle ligands favoring the branched substitution product. This mode of regioselection is consistent with a reaction that operates by a 3,3? reductive elimination reaction. In the presence of appropriate chiral ligands, this reaction is rendered enantioselective and applies to both aromatic and aliphatic allylic carbonates. PMID:20681700

  3. De novo asymmetric synthesis of cladospolide B-D: structural reassignment of cladospolide D via the synthesis of its enantiomer.

    PubMed

    Xing, Yalan; O'Doherty, George A

    2009-03-01

    The enantioselective synthesis of cladospolide B, C, and (ent)-cladospolide D has been achieved in 11-15 steps from 1-nonyne. The route relies upon an alkyne zipper reaction to relay an ynone and dienoate functional groups across a nine carbon fragment, which enables a highly enantioselective Noyori ynone reduction and a diastereo- and regioselective Sharpless dihydroxylation of a dienoate. In addition to being a flexible approach to three members of the cladospolide natural products, this route for the first time correctly established the structure for cladospolide D. PMID:19193044

  4. A Nucleophilic Strategy for Enantioselective Intermolecular ?-Amination: Access to Enantioenriched ?-Arylamino Ketones.

    PubMed

    Miles, Dillon H; Guasch, Joan; Toste, F Dean

    2015-06-24

    The enantioselective addition of anilines to azoalkenes was accomplished through the use of a chiral phosphoric acid catalyst. The resulting ?-arylamino hydrazones were obtained in good yields and excellent enantioselectivities and provide access to enantioenriched ?-arylamino ketones. A serendipitous kinetic resolution of racemic ?-arylamino hydrazones is also described. PMID:26066512

  5. NHC-Catalyzed/Titanium(IV);#8722;Mediated Highly Diastereo- and Enantioselective Dimerization of Enals

    SciTech Connect

    Cohen, Daniel T.; Cardinal-David, Benoit; Roberts, John M.; Sarjeant, Amy A.; Scheidt, Karl A. (NWU)

    2012-05-09

    An NHC-catalyzed, diastereo- and enantioselective dimerization of enals has been developed. The use of Ti(Oi-Pr){sub 4} is a key element for the reactivity and selectivity of this process. The cyclopentenes are obtained with high levels of diastereo- and enantioselectivity and their synthetic utility is demonstrated by functionalization of the product alkene.

  6. Concise Total Syntheses of Palominol, Dolabellatrienone, -Araneosene, and Isoedunol via an Enantioselective Diels-Alder Macrobicyclization

    E-print Network

    Snyder, Scott A.

    an Enantioselective Diels-Alder Macrobicyclization Scott A. Snyder and E. J. Corey* Department of Chemistry-mail: corey@chemistry.harvard.edu Although 75 years of study have proven that the Diels-Alder reaction is one of coaxing an achiral precursor to undergo an enantioselective Type I Diels-Alder-based macrobi- cyclization

  7. The First General Enantioselective Catalytic Diels-Alder Reaction with Simple r, -Unsaturated Ketones

    E-print Network

    MacMillan, David W. C.

    The First General Enantioselective Catalytic Diels-Alder Reaction with Simple r, -Unsaturated, the Diels-Alder reaction has remained arguably the most powerful organic transformation in chemical, we document the first enantioselective catalytic Diels-Alder reaction with simple ketone dienophiles

  8. Organocatalytic enantioselective formal arylation of azlactones using quinones as the aromatic partner.

    PubMed

    Li, Guofeng; Sun, Wangsheng; Li, Jingyi; Jia, Fengjing; Hong, Liang; Wang, Rui

    2015-06-30

    A new method for the catalytic enantioselective formal arylation of azlactones using quinones as the aromatic partner was developed for the first time. Under mild conditions, the domino Michael/aromatization/cyclization reaction worked well to afford the corresponding products in moderate to high yields with excellent enantioselectivities, some of which have promising cytotoxicity against cancer cells and antibacterial activities. PMID:26083993

  9. Catalytic enantioselective 1,2-diboration of 1,3-dienes: versatile reagents for stereoselective allylation.

    PubMed

    Kliman, Laura T; Mlynarski, Scott N; Ferris, Grace E; Morken, James P

    2012-01-01

    More with boron: The development of catalytic enantioselective 1,2-diboration of 1,3-dienes enables a new strategy for enantioselective carbonyl allylation reactions (see scheme). These reactions occur with outstanding levels of stereoselection and can be applied to both monosubstituted and 1,1-disubstituted dienes. The carbonyl allylation reactions provide enantiomerically enriched functionalized homoallylic alcohol products. PMID:22135105

  10. A metalorganic framework material that functions as an enantioselective catalyst for olefin epoxidation{

    E-print Network

    The notion is that MOF-based catalysts may be able to replicate some of the key features of zeolitic with purely zeolitic catalysts is enantioselectivity. Herein, we report that a microporous MOF containingA metal­organic framework material that functions as an enantioselective catalyst for olefin

  11. Palladium(II)/Brønsted Acid-Catalyzed Enantioselective Oxidative Carbocyclization–Borylation of Enallenes**

    PubMed Central

    Jiang, Tuo; Bartholomeyzik, Teresa; Mazuela, Javier; Willersinn, Jochen; Bäckvall, Jan-E

    2015-01-01

    An enantioselective oxidative carbocyclization–borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol-type chiral phosphoric acids were superior co-catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess. PMID:25808996

  12. Nano-engineered materials based on fullerenes: synthesis and biomedical applications

    NASA Astrophysics Data System (ADS)

    Fierascu, Radu Claudiu; Dumitriu, Irina; Ion, Rodica Mariana; Neagu, Monica; Constantin, Carolina; Stavaru, Crina

    2010-11-01

    The nanoengineering of various materials for biomedical application has became in the last decade one of the most important research areas, due to the continuous struggle to find new and more efficient instruments for the therapy of cancer and other diseases. Attempts to obtain functionalized derivatives of fullerene seek the synthesis of watersoluble materials, in order to investigate their effects in physiological conditions. International studies on the biological properties of fullerenes and their derivatives, are now targeted towards anti-tumor effects, pharmacology and their involvement in oxidative stress. Their toxicity, demonstrated both in vitro and in vivo is important for characterization and selection of applications. Phototoxicity of some molecules of fullerenes has been identified as future therapeutic tool. The present paper describes the synthesis, characterization and some biomedical applications of some nanomaterials based on fullerenes.

  13. Hydrothermal synthesis of ceramic nanomaterials for functional applications

    NASA Astrophysics Data System (ADS)

    Piticescu, Roxana M.; Piticescu, R. R.; Taloi, D.; Badilita, V.

    2003-02-01

    Yttria-doped zirconia, lead zirconate titanate (PZT) and barium titanate were successfully obtained using hydrothermal procedures. Based on these results mathematical models describing the correlation between the nanopowders' characteristics and the main synthesis parameters are proposed. Powders from the systems (Y2O3)0.1 (ZrO2)0.9 and (Y2O3)0.04 (ZrO2)0.96 obtained from soluble Zr(IV) peroxide precursors show that cubic/tetragonal phases have been formed by controlled crystallization from the solution. With increasing temperature and hydrothermal treatment temperature the mean crystallite sizes increase from a minimum of 5 nm to a maximum of 22 nm. The activation energy shows a diffusion-controlled process. Barium titanate powders with controlled stoichiometry could also be hydrothermally synthesized in the temperature range 110- 175°C. Synthesis of PZT powders with controlled stoichiometry and mean crystallite sizes from 4 to 43 nm is finally presented. Dense yttria-partial stabilized zirconia with high ionic conductivity and PZT with a good stability of electric-physical parameters for use in the design of materials with improved sensorial characteristics was obtained after sintering the nanopowders.

  14. Triaxial Burke-Schumann Flames with Applications to Flame Synthesis

    NASA Technical Reports Server (NTRS)

    Chao, B. H.; Axelbaum, R. L.; Gokoglu, Suleyman (Technical Monitor)

    2000-01-01

    The problem of a flame generated by three coaxial flows is solved by extending the Burke-Schumann methodology to include a third stream. The solution is particularly relevant to flame synthesis wherein multiple tubes are often employed either to introduce inert as a diffusion barrier or to introduce more than two reactants. The general problem is solved where the inner and outer tubes contain reactants and the middle tube contains either an inert or a third reactant. Relevant examples are considered and the results show that the triaxial Burke-Schumann flame can be substantially more complicated than the traditional Burke-Schumann flame. When the middle flow is inert the flame temperature is no longer constant but increases axially, reaching a maximum at the flame centerline. At the exit the flame does not sit on the tube exit but instead resides between the inner and outer tubes, resulting in an effective barrier for particle build-up on the burner rim. For the case of a third reactant in the middle flow, synthesis chemistry where the inner reaction is endothermic and the outer reaction is exothermic is considered. In addition to showing the flame temperature and flame shape, the results identify conditions wherein reaction is not possible due to insufficient heat transfer from the outer flame to support the inner flame reaction.

  15. An application of j? transformation and discrete oscillation index Md in dynamic synthesis of control system for undersea robot

    Microsoft Academic Search

    Li Junpeng; Xu Fengan

    1991-01-01

    The paper proposes the conversion from z-domain to discrete frequency j? domain, the basic concept of discrete oscillation index Md, the dynamic synthesis of second order astatic digital following systems and the application of Md in dynamic synthesis of heading control for an undersea robot

  16. Catalytic asymmetric synthesis of sterically hindered tertiary ?-aryl ketones.

    PubMed

    Doran, Robert; Guiry, Patrick J

    2014-10-01

    The catalytic asymmetric synthesis of a series of tertiary ?-aryl cyclopentanones and cyclohexanones has been accomplished via a Pd-catalyzed decarboxylative protonation of the corresponding ?-aryl-?-keto allyl esters. Enantioselectivities of up to 92% ee and 74% ee were achieved for cyclopentanone and cyclohexanone substrates, respectively. The route described gives access to these important structural motifs in moderate to high levels of enantioselectivity. In particular, this is only the second direct approach for the preparation of tertiary ?-aryl cyclopentanones. The synthetic approach allows for simple modification of the aryl group. Significantly, substrates containing sterically hindered aryl groups gave the highest levels of enantioselectivity, and these aryl groups were readily installed by a Pb-mediated arylation of a ?-keto allyl ester. PMID:25233274

  17. Synthesis of an application-specific soft multiprocessor system

    Microsoft Academic Search

    Jason Cong; Guoling Han; Wei Jiang

    2007-01-01

    The application-specific multiprocessor System-on-a-Chip is a promising design alternative because of its high degree of flexibility, short development time, and potentially high performance attributed to application-specific optimizations. However, designing an optimal application-specific multiprocessor system is still challenging because there are a number of important metrics, such as throughput, latency, and resource usage, that need to be explored and optimized. This

  18. Synthesis of Application Specific Instructions for Embedded DSP Software

    Microsoft Academic Search

    Hoon Choi; Jong-sun Kim; Chi-won Yoon; In-cheol Park; Seung Ho Hwang; Chong-min Kyung

    1999-01-01

    Application specific instructions play an important role in reducing the required code size and increasing perform- ance. This paper describes a new approach to generate application specific instructions for DSP applications. The proposed approach is based on a modified subset-sum problem, and can support multi-cycle complex instructions as well as single cycle instructions, while the previous state-of-the-art approaches can generate

  19. The enantioselective construction of tetracyclic diterpene skeletons with Friedel-Crafts alkylation and palladium-catalyzed cycloalkenylation reactions.

    PubMed

    Burke, Sarah J; Malachowski, William P; Mehta, Sharan K; Appenteng, Roselyn

    2015-03-01

    Due to the profound extent to which natural products inspire medicinal chemists in drug discovery, there is demand for innovative syntheses of these often complex materials. This article describes the synthesis of tricarbocyclic natural product architectures through an extension of the enantioselective Birch-Cope sequence with intramolecular Friedel-Crafts alkylation reactions. Additionally, palladium-catalyzed enol silane cycloalkenylation of the tricarbocyclic structures afforded the challenging bicyclo[3.2.1]octane C/D ring system found in the gibberellins and the ent-kauranes, two natural products with diverse medicinal value. In the case of the ent-kaurane derivative, an unprecedented alkene rearrangement converted four alkene isomers to one final product. PMID:25598198

  20. Synthesis of anisotropic silver nanoparticles using novel strain, Bacillus flexus and its biomedical application.

    PubMed

    Priyadarshini, S; Gopinath, V; Meera Priyadharsshini, N; MubarakAli, D; Velusamy, P

    2013-02-01

    Synthesis of metallic nanoparticles has attracted by bacterial based production and alternative to physical and chemical approaches. The present work was focused to nominate a bacterial strain for synthesis of potential silver nanoparticles. The target was achieved by screening of 127 isolates from silver mining wastes. A strain designated S-27 found to be a potential candidate for rapid synthesis of silver nanoparticles among tested microorganisms. It was subjected to molecular characterization by 16S rDNA sequence analysis. It was found that S-27 belonging to Bacillus flexus. Synthesis of silver nanoparticles was achieved by addition of culture supernatants with aqueous silver nitrate solution, immediately it turns to brown colour solution showed a peak at 420 nm corresponding to the plasmon absorbance of silver nanoparticles by UV-vis spectroscopy. Various instrumentation techniques, such as AFM, FESEM, XRD and FTIR, were adopted to characterize the synthesized nanoparticles. Anisotropic nanoparticles, such as spherical and triangular shaped nanoparticles, have been synthesized and sizes were found to be 12 and 65 nm, respectively. It was stable in aqueous solution in five months period of storage at room temperature in the dark. Synthesized nanoparticles showed efficacy on antibacterial property against clinically isolated multi-drug resistant (MDR) microorganisms. It is suggested that biogenic synthesis of nanoparticles have wide-application in medicine and physical chemistry and it can produce with eco-friendly, easy downstream processing and rapid scale-up processing. PMID:23018021

  1. Synthesis and size classification of metal oxide nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Atsumi, Takashi; Jeyadevan, Balachandran; Sato, Yoshinori; Tamura, Kazuchika; Aiba, Setsuya; Tohji, Kazuyuki

    2004-12-01

    Magnetic nanoparticles are considered for biomedical applications, such as the medium in magnetic resonance imaging, hyperthermia, drug delivery, and for the purification or classification of DNA or virus. The performance of magnetic nanoparticles in biomedical application such as hyperthermia depends very much on the magnetic properties, size and size distribution. We briefly described the basic idea behind their use in drug delivery, magnetic separation and hyperthermia and discussed the prerequisite properties magnetic particles for biomedical applications. Finally reported the synthesis and classification scheme to prepare magnetite (Fe3O4) nanoparticles with narrow size distribution for magnetic fluid hyperthermia.

  2. Synthesis of new porphyrinoids for biomedical and materials applications

    NASA Astrophysics Data System (ADS)

    Stewart, Fraser

    The facile synthesis of three non-hydrolysable thioglycosylated porphyrinoids is reported. Starting from meso perfluorophenylporphyrin (TPPF20), the non-hydrolysable thioglycosylated porphyrin (PGlc4), chlorin (CGlc4), isobacteriochlorin (IGlc4), and bacteriochlorin (BGlc4) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. With reduction of one or two pyrrole double bonds, there is a red shift in the lowest energy absorption band and a significant increase in intensity. The fluorescence of these porphyrinoids is in the order PGlc4 = BGlc4 < CGlc4 < IGlc4 and there is a corresponding decrease in the amount of triplet formed. Fluorescence micrographs of cells after treatment with these four porphyrinoids indicate they are taken up. The CGlc4 and IGlc4 may be dual function agents that can detect cancer by luminescence, and treat cancer by photodynamic therapy (PDT). Porphyrins appended with four rigid hydrogen bonding motifs on the meso positions were synthesized and self-assembled into a cofacial cage with four complementary bis- (decyl)melamine units in dry solvents, these hydrogen-bonded cages were analysed by diffusion-ordered spectroscopy (DOSY) in solution. The hydrocarbon chains on the melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates. A water soluble zinc (II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluoro-phthalocyaninato zinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups by thio-sugars. The photophysical properties and cancer cell uptake studies of this nonhydrolyzable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically and photochemically stable, and can potentially be used as a photosensitizer in photodynamic therapy. A porphyrin bearing pyridyl groups at the meso positions was synthesized using 2,6-diacetamido-4-formylpyridine. A new method has been developed for the synthesis of the precursor aldehyde that avoid much of the problems associated with the earlier synthesis. With this porphyrin it is possible to build hetero-complementary rigid, multi-porphyrin supramolecular arrays via hydrogen bonds. For example, when using naphthalenediimide (NDI) units a checkerboard pattern is expected to be formed using this porphyrin as a donor and NDI as an acceptor where triple hydrogen bond is formed between the diimide and pyridyl units. Energy transfer can be studied through this hydrogen bonded supramolecular assembly. The synthesis of a triply bridged diporphyrin appended with six thioglucose units is reported. The electronic spectrum of this triply bridged porphyrin has enhanced intensity at low-energy wavelengths that reaches the near infrared region. The goal of this project is to create tumor targeting dyes that can be activated with red wavelengths of light that penetrate deeper into tissues. This new compound is amphiphilic in nature, chemically and photochemically stable, expected to have unusual photophysical and electrochemical properties, and can potentially be used as a photosensitizer in photodynamic therapy.

  3. One-Pot Synthesis of 3,4-Diaryl-Substituted 2(5H)-Furanone and Its Commercial Application

    Microsoft Academic Search

    Anil Argade; Jigar Desai; Pravin Thombare; Kiran Shah; Sanjay Gite; Vijay Prajapati; Bipin Pandey; Mukul Jain; Pankaj Patel; Rajesh Bahekar

    2012-01-01

    One-pot synthesis of 3,4-diaryl substituted 2(5H)-furanones was established and its commercial application has been demonstrated by accomplishing total synthesis of rofecoxib, under mild reaction conditions, with good yields and purity.

  4. Transition-Metal Catalyzed Synthesis of Aspergillide B: An Alkyne Addition Strategy

    PubMed Central

    Bartlett, Mark J.

    2012-01-01

    A catalytic enantioselective formal total synthesis of aspergillide B is reported. This linchpin synthesis was enabled by the development of new conditions for Zn-ProPhenol catalyzed asymmetric alkyne addition. This reaction was used in conjunction with ruthenium-catalyzed trans-hydrosilylation to affect the rapid construction of a late-stage synthetic intermediate of aspergillide B to complete a formal synthesis of aspergillide B in a highly efficient manner. PMID:22356535

  5. Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis

    PubMed Central

    Frings, Marcus; Thomé, Isabelle

    2012-01-01

    Summary For the first time, chiral sulfoximine derivatives have been applied as asymmetric organocatalysts. In combination with a thiourea-type backbone the sulfonimidoyl moiety leads to organocatalysts showing good reactivity in the catalytic desymmetrization of a cyclic meso-anhydride and moderate enantioselectivity in the catalytic asymmetric Biginelli reaction. Straightforward synthetic routes provide the newly designed thiourea-sulfoximine catalysts in high overall yields without affecting the stereohomogeneity of the sulfur-containing core fragment. PMID:23019479

  6. Synthesis and Functionalization of Carbon and Boron Nitride Nanomaterials and Their Applications

    NASA Astrophysics Data System (ADS)

    Erickson, Kristopher John

    Carbon and boron-nitride based nanomaterials possess many exciting properties making them suitable for numerous applications spanning from electronics to advanced composites. However, these materials when synthesized often differ significantly from the idealized crystals usually considered theoretically. A thorough understanding of the structure of the materials as synthesized and how the resultant materials can be utilized for specific application purposes is required such that these applications can be effectively realized. To this end, the synthesis and characterization of carbon and boron-nitride based nanomaterials is undertaken with specific application purposes in mind. As a potential scalable synthetic route for graphene, graphene oxide (GO) and reduced graphene oxide are synthesized and characterized using atomic resolution electron microscopy. This elucidates their underlying structures revealing that the reduced form of GO does not resemble pristine graphene. The long-standing debate over the structure of GO is successfully ended with this study given the direct observation of the atomic structure of this material. To develop advanced composite materials, the functionalization of carbon and boron nitride nanotubes is undertaken. The characterization of their functionalization and incorporation within composite materials, specifically within a Kevlar polymer matrix, is presented to allow for the development of composites with significantly enhanced mechanical properties. Given a significant body of theoretical work paired with a single previous synthetic success, the synthesis of boron nitride nanoribbons is outlined. The first scalable synthesis of boron nitride nanoribbons is demonstrated resulting in long, consistent width, narrow, few-layer boron nitride nanoribbons which could be ideal for addressing these theoretical considerations. To establish a method for the synthesis of thin hexagonal-boron nitride (h-BN), the design of a specialized CVD system is described. The material resulting from this system is analyzed with methods including atomic resolution electron microscopy with the results informing future approaches for the synthesis of h-BN. Finally, high surface area boron nitride materials should be promising for hydrogen storage applications, especially if templated with a microporous scaffold. To this end, the first synthesis of a high surface area, microporous boron-nitride material is accomplished and the resultant surface areas of these materials are reported.

  7. Asymmetric total synthesis of mycoleptodiscin?a.

    PubMed

    Zhou, Shupeng; Chen, Hao; Luo, Yijie; Zhang, Wenhao; Li, Ang

    2015-06-01

    The first total synthesis of mycoleptodiscin?A, a structurally unusual indolosesquiterpenoid possessing an ortho-benzoquinone motif, has been accomplished. A sulfone alkylation coupled two readily available fragments to give an aryl triene intermediate. The tetracyclic core of the molecule was assembled through a highly enantioselective iridium-catalyzed polyene cyclization. The benzylic homologation was achieved by a cationic cyanation. The indole motif was constructed via a copper-mediated intramolecular C?N bond formation at a late stage. PMID:25907827

  8. Stereoselective synthesis of unsaturated ?-amino acids.

    PubMed

    Fanelli, Roberto; Jeanne-Julien, Louis; René, Adeline; Martinez, Jean; Cavelier, Florine

    2015-06-01

    Stereoselective synthesis of unsaturated ?-amino acids was performed by asymmetric alkylation. Two methods were investigated and their enantiomeric excess measured and compared. The first route consisted of an enantioselective approach induced by the Corey-Lygo catalyst under chiral phase transfer conditions while the second one involved the hydroxypinanone chiral auxiliary, both implicating Schiff bases as substrate. In all cases, the use of a prochiral Schiff base gave higher enantiomeric excess and yield in the final desired amino acid. PMID:25715756

  9. SYNTHESIS, APPLICATIONS, AND CHARACTERIZATION OF GUERBET COMPOUNDS AND THEIR DERIVATIVES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Guerbet reaction and Guerbet compounds, particularly Guerbet alcohols, have been known for more than a century. Guerbet compounds are used in commercial applications such as lubricants, plasticizers, cosmetics, etc., due to their interesting properties. This article provides basic information ...

  10. Synthesis and Characterization of Mesoporous Semiconductors and Their Energy Applications

    E-print Network

    Kang, Chris Byung-hwa

    2013-01-01

    formation mechanism of mesoporous silicon. ” Materials Science and Engineering,Formation Mechanism of Mesoporous Silicon. Materials Science and Engineering:Formation and application of porous silicon. ” Materials Science and Engineering

  11. Synthesis and applications of electron deficient conjugated polymers

    E-print Network

    Kim, Youngmi, Ph. D

    2005-01-01

    Chapter 1. In this introductory chapter, we present the general properties of conjugated polymers for sensory and electronic applications, with a special emphasis placed on electron-deficient materials. Chapter 2. In this ...

  12. Design and synthesis of nanocrystal heterostructures for optoelectronic applications

    E-print Network

    Halpert, Jonathan E

    2008-01-01

    Colloidal semiconductor nanocrystals can be used for a variety of optoelectronic applications including light emitting devices (LEDs) and photovoltaics. Their narrow emission spectra make them excellent fluorophors for use ...

  13. Synthesis and Characterization of Polymer Nanocomposites for Energy Applications 

    E-print Network

    Park, Wonchang

    2011-10-21

    Polymer nanocomposites are used in a variety of applications due to their good mechanical properties. Specifically, better performance of lithium ion batteries and thermal interface material can be obtained by using conductive materials and polymer...

  14. Distribution, industrial applications, and enzymatic synthesis of D-amino acids.

    PubMed

    Gao, Xiuzhen; Ma, Qinyuan; Zhu, Hailiang

    2015-04-01

    D-Amino acids exist widely in microbes, plants, animals, and food and can be applied in pharmaceutical, food, and cosmetics. Because of their widespread applications in industry, D-amino acids have recently received more and more attention. Enzymes including D-hydantoinase, N-acyl-D-amino acid amidohydrolase, D-amino acid amidase, D-aminopeptidase, D-peptidase, L-amino acid oxidase, D-amino acid aminotransferase, and D-amino acid dehydrogenase can be used for D-amino acids synthesis by kinetic resolution or asymmetric amination. In this review, the distribution, industrial applications, and enzymatic synthesis methods are summarized. And, among all the current enzymatic methods, D-amino acid dehydrogenase method not only produces D-amino acid by a one-step reaction but also takes environment and atom economics into consideration; therefore, it is deserved to be paid more attention. PMID:25758960

  15. Highly enantioselective Cu(I)-Tol-BINAP-catalyzed asymmetric conjugate addition of Grignard reagents to ?,?-unsaturated esters.

    PubMed

    Wang, Shun-Yi; Loh, Teck-Peng

    2010-12-14

    The copper-catalyzed conjugate addition (CA) of organometallic reagents to ?,?-unsaturated carbonyl compounds is one of the most versatile synthetic methods for the construction of C-C bonds. Interestingly, the application of Grignard reagents, which are among the most widely used of organometallic compounds, in asymmetric conjugate addition (CA) reactions has received less attention. Therefore, our group and others have been exploring better catalytic systems to effect the asymmetric 1,4-conjugate addition of Grignard reagents to ?,?-unsaturated esters. It is only in the past decade that significant breakthroughs have been made in this field. In our studies, we found that CuI-Tol-BINAP could catalyze the asymmetric conjugate addition (CA) reactions of Grignard reagents, including the addition of MeMgBr to ?,?-unsaturated esters to afford the ?-methylated esters in good yields with excellent regio- and enantioselectivities. Both enantiomers of the products could be obtained by either using the enantiomers of the chiral Tol-BINAP or by using the geometrical isomer of the starting material. This method is also suitable for other Michael acceptors. In this article, we describe the development of the asymmetric Cu(I)-Tol-BINAP catalyzed 1,4-conjugate addition of Grignard reagents to ?,?-unsaturated esters and applications of this chemistry. This method provides a convenient method to synthesize ?-alkyl esters with high enantioselectivity or diastereoselectivity using CuI and the inexpensive chiral ligand, Tol-BINAP. PMID:21038042

  16. Synthesis and application of new polymer bound catalysts

    SciTech Connect

    Fetterly, Brandon Michael

    2005-08-01

    Nitric acid has been shown to be a weak acid in acetonitrile. It is conceivable that a nitrate salt of a weakly Lewis acidic cation could furnish a ''naked'' nitrate anion as a basic catalyst in a variety of reactions in non-aqueous solvents. Such a nitrate salt could also be bound to a polymeric support via the cation, thereby allowing for reclamation and recycling of the nitrate ion. This subject is dealt with in Chapter 2, wherein my contributions consisted of performing all the reactions with the polymer supported catalyst and carrying out the experiments necessary to shed light on the reaction mechanisms. Chapter 3 contains a description of the structure and catalytic properties of an azidoproazaphosphatrane. This compound is an air-stable versatile catalyst that has proven useful not only homogeneously, but also when bound to a solid support. The synthesis of a polymer bound proazaphosphatrane containing a trivalent phosphorus is presented in Chapter 4. Such a compound has been sought after by our group for a number of years. Not only does the synthesis I have accomplished for it allow for easier separation of proazaphosphatrane catalysts from reaction mixtures, but recycling of the base is made much simpler. Proazaphosphatranes are useful homogeneous catalysts that activate atoms in other reagents, thus enhancing their reactivity. The next chapters deal with two such reactions with aldehydes and ketones, namely silylcyanations with trialkylsilylcyanides (Chapters 5 and 6) and reductions with poly(methylhydrosiloxane), in Chapter 7. In Chapter 5, Zhigang Wang performed the initial optimization and scoping of the reaction, while repetitions of the scoping experiments for reproducibility, determination of diastereomeric ratios, and experiments aimed at elucidating aspects of the mechanism were performed by me. The proazaphosphatrane coordinates to the silicon atom in both cases, thereby allowing the aforementioned reactions to proceed under much milder conditions. Proazaphosphatranes are also effective Broensted-Lowry bases. This is illustrated in Chapter 8 wherein a wide variety of conjugate addition reactions are catalyzed by proazaphosphatranes. In that chapter, repetitions of the nitroalkane addition reactions for reproducibility, improved spectral data for the products and comparisons of literature yields of all reactions were performed by the author.

  17. Recent Research on One-Dimensional Silicon-Based Semiconductor Nanomaterials: Synthesis, Structures, Properties and Applications

    Microsoft Academic Search

    Zhenyu Zhang; Rujia Zou; Li Yu; Junqing Hu

    2011-01-01

    The field of silicon nanowires (SiNWs) and silicon-based 1D nanostructured heterostructures represent one of the most important research subjects within the nanomaterials family. A series of synthesis approaches of SiNWs and silicon-based 1D nanostructured heterostructures have been developed, and have garnered the greatest attention in the past decades for a variety of applications. This article provides an overview on recent

  18. Catalytic C-H Activation and Functionalization: Some Applications in Organic Synthesis

    E-print Network

    Stoltz, Brian M.

    which then attacks the C-H bond - Metal compex activates some other reactants (e.g. O2 or H2O2) to form, 189, 33 Fe2+ + H2O2 Fe3+ HO- HO+ + HO + RH R + H2O R Fe3+ + R+ + Fe2+ - If reaction is carriedCatalytic C-H Activation and Functionalization: Some Applications in Organic Synthesis Yeeman

  19. Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers

    Microsoft Academic Search

    Alessio Becheri; Maximilian Dürr; Pierandrea Lo Nostro; Piero Baglioni

    2008-01-01

    We report the synthesis and characterization of nanosized zinc oxide particles and their application on cotton and wool fabrics\\u000a for UV shielding. The nanoparticles were produced in different conditions of temperature (90 or 150 °C) and reacting medium\\u000a (water or 1,2-ethanediol). A high temperature was necessary to obtain small monodispersed particles. Fourier transformed infrared\\u000a spectroscopy (FTIR), transmission electron microscopy (TEM), and

  20. Synthesis of optical-coherence function and its applications in distributed and multiplexed optical sensing

    Microsoft Academic Search

    Kazuo Hotate; Zuyuan He

    2006-01-01

    We have proposed and demonstrated in recent years a unique technique to synthesize the optical-coherence function by manipulating the frequency and the phase of lightwave. Based upon this technique, the synthesis of optical coherence function (SOCF), various distributed photonic sensing and optical-information-processing applications have been developed. In this paper, the principle of SOCF is summarized. A series of functional optical-sensing

  1. Synthesis of novel fullerene-functionalized polysulfones for optical limiting applications

    Microsoft Academic Search

    Annamaria Celli; Paola Marchese; Micaela Vannini; Corrado Berti; Ilaria Fortunati; Raffaella Signorini; Renato Bozio

    2011-01-01

    High-performance materials in the optical field, with special reference to optical limiting applications, can be obtained by combining nonlinear optical (NLO) active molecules with high optical quality hosts. An interesting method is the synthesis of fullerene–polymer systems. In this paper novel fullerene–polysulfone samples were obtained by direct fullerenation between a commercial sample of polysulfone and fullerene, using electrophilic aromatic substitution

  2. Application of N-methylpyrrolidin-2-one hydrotribromide in organic synthesis

    NASA Astrophysics Data System (ADS)

    Jain, S. L.; Sain, B.

    2010-10-01

    The review describes the broad applicability of a modern reagent, N-methylpyrrolidin-2-one hydrotribromide (MPHT), in organic synthesis. The methods for its preparation and use in the bromination reactions of different classes of organic compounds (alkenes, alcohols, ketones, etc.), in the oxidation and epoxide ring-opening reactions, in conversions of alkenes to aziridines are considered. Special attention is given to the environmentally friendly character of MPHT.

  3. Immobilization of lipases on hydrophobilized zirconia nanoparticles: highly enantioselective and reusable biocatalysts.

    PubMed

    Chen, Yi Zhao; Yang, Cai Ting; Ching, Chi Bun; Xu, Rong

    2008-08-19

    Our study has demonstrated for the first time that zirconia nanoparticles modified by a simple carboxylic surfactant of a very long alkyl chain can significantly enhance the activity of the immobilized lipases for asymmetric synthesis in organic media. Zirconia nanoparticles of ca. 20 nm diameter were grafted with carboxylic surfactant modifiers from Tween 85 and erucic acid. The surface of nanoparticles was successfully changed from hydrophilic to hydrophobic. Lipases from Candida rugosa and Pseudomonas cepacia were immobilized on the modified zirconia nanoparticles by adsorption in aqueous solution. The immobilized lipases were used for the resolution of ( R, S)-ibuprofen and ( R, S)-1-phenylethanol through esterification and acylation, respectively, in isooctane organic solvent. When immobilized on erucic acid-modified zirconia, both lipases gave significantly higher activity and enantioselectivity compared with those from their corresponding crude lipase powders. The nanohybrid biocatalysts are stable and can be reused for eight cycles without loss in activity and selectivity. The interaction between the hydrophobic surface of zirconia support and lipases probably induces the conformational rearrangement of lipases into an active, stable form. PMID:18656972

  4. Mesoporous nano/micro noble metal particles: synthesis and applications

    NASA Astrophysics Data System (ADS)

    Yang, Shengchun; Luo, Xiao

    2014-04-01

    The morphology, size and composition often govern the physical and chemical properties of noble metal units with a size in the nano or micro scale. Thus, the controlled growth of noble metal crystals would help to tailor their unique properties and this would be followed by their practical application. Mesoporous nano/micro noble metal units are types of nanostructured material that have fascinating properties that can generate great potential for various applications. This review presents a general view on the growth mechanisms of porous noble metal units and is focused on recent progresses in their synthetic approaches. Then, their potential applications in the field of drug delivery, cell imaging and SERS substrates, as well as fuel cell catalysts are overviewed.

  5. Enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile for production of (R)-(-)-mandelic acid by a newly isolated mutant strain.

    PubMed

    Xue, Ya-Ping; Xu, Sai-Zhen; Liu, Zhi-Qiang; Zheng, Yu-Guo; Shen, Yin-Chu

    2011-02-01

    (R)-(-)-Mandelic acid (R-MA) is an important intermediate with broad uses. Recently, R-MA production using nitrilase has been gaining more and more attention due to its higher productivity and enantioselectivity. In this work, a new bacterium WT10, which exhibited favorable nitrilase activity and excellent enantioselectivity for production of R-MA by enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile, was isolated and identified as a strain of Alcaligenes faecalis. In order to improve its nitrilase activity for industrial application, the wild-type strain WT10 was further subjected to mutagenesis using a combined LiCl-ultraviolet irradiation and low energy N(+) ion beams implantation technique. A valuable mutant strain A. faecalis ZJUTB10 was obtained. The nitrilase specific activity of the mutant strain was greatly improved up to 350.8 U g(-1), in comparison with wild-type strain WT10 of 53.09 U g(-1). The reaction conditions for R-MA production by mutant strain A. faecalis ZJUTB10 were also optimized. Nitrilase activity in mutant strain showed a broad pH optimum at pH 7.7-8.5. The optimal temperature was 35°C. The highest production rate reached 9.3 mmol h(-1) g(-1). The results showed that mutant strain A. faecalis ZJUTB10 was a new candidate for efficient R-MA production from (R,S)-mandelonitrile and could potentially be used in industrial production. PMID:20640871

  6. Enantioselective ?-Arylation of Ketones with Aryl Triflates Catalyzed by Difluorphos Complexes of Palladium and Nickel

    PubMed Central

    Liao, Xuebin; Weng, Zhiqiang; Hartwig, John F.

    2008-01-01

    The asymmetric ?-arylation of ketones with aryl triflates is described, and the use of this electrophile with nickel and palladium catalysts containing a segphos derivative increases substantially the scope of highly enantioselective arylations of ketone enolates. The combination of aryl triflates as reactant, difluorphos as ligand, palladium catalysts for reactions of electron-neutral to (or) electron-rich aryl triflates, and nickel catalysts for reactions of electron-poor aryl triflates led to a series of ?-arylations of tetralone, indanone, cyclopentanone, and cyclohexanone derivatives with electron-rich and electron poor aryl electrophiles. Enantioselectivities ranged from 70–98% with ten examples over 90%. Systematic studies on these ?-arylations have revealed a number of factors that affect enantioselectivity. Ligands containing biaryl backbones with small dihedral angles generate catalysts that react with higher enantioselectivity than related ligands with larger dihedral angles. In addition, faster rates for reactions of aryl triflates vs those for reactions of aryl bromides allow the ?-arylations of aryl triflates to be conducted at lower temperatures, and this lower temperature improves enantioselectivity. Finally, studies that compare the enantioselectivities of catalytic reactions to those of stoichiometric reactions of isolated [(segphos)Pd(Ar)(Br)], [(segphos)Pd(Ar)(I)] and [(segphos)Ni(C6H4-4-CN)Br] suggest that catalyst decomposition affects enantioselectivity. PMID:18076166

  7. Substitution of Val72 residue alters the enantioselectivity and activity of Penicillium expansum lipase.

    PubMed

    Tang, Lianghua; Su, Min; Zhu, Ling; Chi, Liying; Zhang, Junling; Zhou, Qiong

    2013-01-01

    Error-prone PCR was used to create more active or enantioselective variants of Penicillium expansum lipase (PEL). A variant with a valine to glycine substitution at residue 72 in the lid structure exhibited higher activity and enantioselectivity than those of wild-type PEL. Site-directed saturation mutagenesis was used to explore the sequence-function relationship and the substitution of Val72 of P. expansum lipase changed both catalytic activity and enantioselectivity greatly. The variant V72A, displayed a highest enantioselectivity enhanced to about twofold for the resolution of (R, S)-naproxen (E value increased from 104 to 200.7 for wild-type PEL and V72A variant, respectively). In comparison to PEL, the variant V72A showed a remarkable increase in specific activity towards p-nitrophenyl palmitate (11- and 4-fold increase at 25 and 35 °C, respectively) whereas it had a decreased thermostability. The results suggest that the enantioselective variant V72A could be used for the production of pharmaceutical drugs such as enantiomerically pure (S)-naproxen and the residue Val 72 of P. expansum lipase plays a significant role in the enantioselectivity and activity of this enantioselective lipase. PMID:22972595

  8. Microfluidic synthesis of multifunctional Janus particles for biomedical applications

    E-print Network

    development of micro/ nanostructure fabrication through wet- chemistry based techniques which carefully, have shed light on the limitations of conventional micro/ nanostructures. For these complex appli. However, to achieve many of these applications, high-throughput, low-cost techniques are needed

  9. Nanostructured calcium phosphates for biomedical applications: novel synthesis and characterization

    Microsoft Academic Search

    Prashant N. Kumta; Charles Sfeir; Dong-Hyun Lee; Dana Olton; Daiwon Choi

    2005-01-01

    Materials play a key role in several biomedical applications, and it is imperative that both the materials and biological aspects are clearly understood for attaining a successful biological outcome. This paper illustrates our approach to implement calcium phosphates as gene delivery agents. Calcium phosphates (CaP) belong to the family of biocompatible apatites and there are several CaP phases, the most

  10. Anisotropic nanomaterials: Synthesis, optical and magnetic properties, and applications

    Microsoft Academic Search

    Matthew John Banholzer

    2010-01-01

    As nanoscience and nanotechnology mature, anisotropic metal nanostructures are emerging in a variety of contexts as valuable class of nanostructures due to their distinctive attributes. With unique properties ranging from optical to magnetic and beyond, these structures are useful in many new applications. Chapter two discusses the nanodisk code: a linear array of metal disk pairs that serve as surface-enhanced

  11. System Synthesis for Multiprocessor Embedded Applications Luigi Carro*

    E-print Network

    Wagner, Flávio Rech

    are a major trend in the system industry, and their design is currently performed using a mix of different is targeted to a multiprocessor platform. Each processor, either a custom-designed one or an off and application characteristics. The paper illustrates the architecture selection process with concrete examples

  12. Functionalized Silicone Nanospheres: Synthesis, Transition Metal Immobilization, and Catalytic Applications

    SciTech Connect

    Bradley, Christopher A.; Yuhas, Benjamin D.; McMurdo, Meredith J.; Tilley, T. D.

    2008-12-11

    Silicone nanospheres containing a variety of functional groups (pyridines, phosphines, thiols, amines, etc.) have been prepared by emulsion copolymerization of methyltrimethoxysilane, MeSi(OMe)3, and the functionalized monomer of interest, RSi(OMe)3. This procedure provides a reproducible synthesis of spherical particles in the 12-28 nm size regime as determined by transmission electronSilicone nanospheres containing a variety of functional groups (pyridines, phosphines, thiols, amines, etc.) have been prepared by emulsion copolymerization of methyltrimethoxysilane, MeSi(OMe)?, and the functionalized monomer of interest, RSi(OMe)?. This procedure provides a reproducible synthesis of spherical particles in the 12-28 nm size regime as determined by transmission electron microscopy (TEM). The presence of the functional groups is supported by a combination of spectroscopic methods including DRUV-vis, DRIFTS, and NMR spectroscopy. Comonomer dispersity within the nanospheres was probed using elemental mapping techniques, and these support a homogeneous distribution of functional groups within the particles. Palladium(0) immobilization on phosphine-substituted nanospheres also results in a random distribution of the transition metal throughout the particles. Nanospheres containing multiple acid/base functionalities were also prepared, and these demonstrate functional group cooperativity based on enhanced conversions in the base-catalyzed Henry reaction, relative to nanosphere catalysts containing only basic groups. The diversity of functional groups that may be incorporated into the spheres suggests that these materials hold considerable promise as ligand supports and catalysts.Graphene nanoribbons (GNRs) have been suggested as a promising material for its use as nanoelectromechanical reasonators for highly sensitive force, mass, and charge detection. Therefore the accurate determination of the size-dependent elastic properties of GNRs is desirable for the design of graphene-based nanoelectromechanical devices. In this study we determine the size-dependent Young’s modulus and carbon-carbon binding energy in a homologous series of GNRs, C4n2+6n+2H6n+4 (n=2–12), with the use of all electron first principles computations. An unexpected linearity between the binding energy and Young’s modulus is observed, making possible the prediction of the size-dependent Young’s modulus of GNRs through a single point energy calculation of the GNR ground state. A quantitative-structure-property relationship is derived, which correlates Young’s modulus to the total energy and the number of carbon atoms within the ribbon. In the limit of extended graphene sheets we determine the value of Young’s modulus to be 1.09 TPa, in excellent agreement with experimental estimates derived for graphite and suspended grapheme sheets. microscopy (TEM). The presence of the functional groups is supported by a combination of spectroscopic methods including DRUV-vis, DRIFTS, and NMR spectroscopy. Comonomer dispersity within the nanospheres was probed using elemental mapping techniques, and these support a homogeneous distribution of functional groups within the particles. Palladium(0) immobilization on phosphine-substituted nanospheres also results in a random distribution of the transition metal throughout the particles. Nanospheres containing multiple acid/base functionalities were also prepared, and these demonstrate functional group cooperativity based on enhanced conversions in the base-catalyzed Henry reaction, relative to nanosphere catalysts containing only basic groups. The diversity of functional groups that may be incorporated into the spheres suggests that these materials hold considerable promise as ligand supports and catalysts.

  13. Synthesis and application of mesoporous and macroporous particles

    NASA Astrophysics Data System (ADS)

    Newell, J. David

    Phosphine and amine functionalized mesoporous silica materials were metallated with Rh(CO)2(i-Pr2NH)Cl or Rh2 (CO)4Cl2, respectively to yield catalysts containing the Rh(PPh2R)2(CO)Cl or Rh(CO)2(NH2 R)Cl, where R is a propyl chain bonded to the silica surface, reactive centers. In order to ascertain the effect of pore size on rates of hydroformylation catalysis both 35 A and 45 A pore size materials were used. Using the hydroformylation of octene as a reference reaction, the phosphine based, 45 A catalysts were 1.5 to 1.3 times faster than the amine based, 45 A catalysts, and the 45 A materials were 2.6 to 2.1 times faster than the 35 A materials. The ability of the surface bound phosphine catalysts to affect hydroformylation was strongly influenced by the steric constraints of the substrate. Terminal alkenes were readily hydroformylated and norbornene was slowly hydroformylated, but pinene, trans-cyclododecene, cyclohexene and cholesterol were completely unaffected. Hollow porous microspheres can be created for use as electrolyte storage within the active material of the battery electrode. Synthesis of porous hollow glass microspheres (HGMs) has been accomplished by pyrolyzing a mixture of cobalt, titanium, and colloidal silica. The porous HGMs are generated by spray flame pyrolysis of a solution of cobalt, titanium, and silica into a 7000 tube furnace. A phase separation condenses the cobalt to the center of the sphere where it can be etched as well as titanium. Other etching techniques include using HF to etch commercial hollow glass microspheres, and sodium diffusion.

  14. Synthesis and characterization of nickel hydroxide powders for battery application

    SciTech Connect

    Widjaja, A.

    1997-10-08

    The primary objective of this research was to investigate the synthesis and characterization of Ni(OH){sub 2} powders by homogeneous precipitation. Previous research of the same method showed conflicting results and complete characterization of the particle morphology was not carried out. This study has produced precipitates having a composition of 2Ni(OH){sub 2}{center_dot}Ni(HCO{sub 3}){sub 1.85}(NO{sub 3}){sub 0.15}. The XRD patterns showed peaks commonly observed for {alpha}-Ni(OH){sub 2}. The precipitates produced from low and high cation concentration solutions showed that the mean particle size and specific surface area increased with aging time. The high specific surface area measured suggested that the particle growth occurred through the aggregation of nanosized crystallites. The TEM micrographs confirmed that the particles were actually aggregates of thin films or sheets that were crumpled and intertwined together. This work also investigated the effect of dispersant on the particle morphology. The addition of dispersants did not alter the density of the particles implying that the dispersants were not incorporated into the solid phase. A general decrease in mean particle size at each aging time was observed resulting in an increase in specific surface area. The use of dispersants provided steric hindrance for the particles in the solution to aggregate, thus smaller particles were observed. Cyclic voltammetric tests were carried out to see if the high surface area Ni(OH){sub 2} produced in this work had superior performance characteristics compared to the commercial powders currently available. Indeed, the study showed that the homogeneously precipitated Ni(OH){sub 2} had higher coulombic efficiency and degree of reversibility than the commercial powders. The efficiency values of all the homogeneously precipitated powders were approximately 90%. The same efficiency values observed were probably due to the same specific surface areas of the powders after aging in KOH solution.

  15. Synthesis and Applications of Ionic Liquids Derived from Natural Sugars

    NASA Astrophysics Data System (ADS)

    Chiappe, Cinzia; Marra, Alberto; Mele, Andrea

    Aiming to develop environmentally compatible chemical syntheses, the replacement of traditional organic solvents with ionic liquids (ILs) has attracted considerable attention. ILs are special molten salts with melting points below 100°C that are typically constituted of organic cations (imidazolium, pyridinium, sulfonium, phosphonium, etc.) and inorganic anions. Due to their ionic nature, they are endowed with high chemical and thermal stability, good solvent properties, and non-measurable vapor pressure. Although the recovery of unaltered ILs and recycling partly compensate their rather high cost, it is important to develop new synthetic approaches to less expensive and environmentally sustainable ILs based on renewable raw materials. In fact, most of these alternative solvents are still prepared starting from fossil feedstocks. Until now, only a limited number of ILs have been prepared from renewable sources. Surprisingly, the most available and inexpensive raw material, i.e., carbohydrates, has been hardly exploited in the synthesis of ILs. In 2003 imidazolium-based ILs were prepared from d-fructose and used as solvents in Mizoroki-Heck and Diels-Alder reactions. Later on, the first chiral ILs derived from sugars were prepared from methyl d-glucopyranoside. In the same year, a family of new chiral ILs, obtained from commercial isosorbide (dianhydro-d-glucitol), was described. A closely related approach was followed by other researchers to synthesize mono- and bis-ammonium ILs from isomannide (dianhydro-d-mannitol). Finally, a few ILs bearing a pentofuranose unit as the chiral moiety were prepared using sugar phosphates as glycosyl donors and 1-methylimidazole as the acceptor.

  16. Application of chiral critical clusters to assymetric synthesis

    DOEpatents

    Ferrieri, Richard A. (Patchogue, NY)

    2002-01-01

    Disclosed is a composition, a method of making and a method of using critical clusters for asymmetric synthesis using substantially optically-pure chiral solvent molecules in a supercritical fluid. The solvent molecules are capable of forming a multipoint hydrogen bonded solvate as they encage at least one solute molecule. The encaged solute molecule is capable of reacting to form an optically active chiral center. In another aspect, there is disclosed a method of directing the position of bonding between a solute molecule and a ligand involving encaging the solute molecule and the ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution in the solute molecule. In yet another aspect, disclosed is a method of making pharmaceutical compounds involving encaging a solute molecule, which is capable of forming a chiral center, and a ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution of the solute molecule. The solute molecule and ligand are then reacted whereby the ligand bonds to the solute molecule forming a chiral center. Also disclosed is a method for racemic resolution using critical clusters involving encaging racemic mixtures of solute molecules with substantially optically-pure chiral solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to form critical clusters. The solvent molecules are capable of multipoint hydrogen bonding with the solute molecules. The encaged solute molecules are then nonenzymatically reacted to enhance the optical purity of the solute molecules.

  17. Remote Enantioselection Transmitted by an Achiral Peptide Nucleic Acid Backbone

    NASA Technical Reports Server (NTRS)

    Kozlov, Igor A.; Orgel, Leslie E.; Nielsen, Peter E.

    2000-01-01

    short homochiral segment of DNA into a PNA helix could have guaranteed that the next short segment of DNA to be incorporated would have the same handedness as the first. Once two segments of the same handedness were present, the probability that a third segment would have the same handedness would increase, and so on. Evolution could then slowly dilute out the PNA part. This scenario would ultimately allow the formation of a chiral oligonucleotide by processes that are largely resistant to enantiomeric crossinhibition. It is important to note that the ligation of homochiral dinucleotides on a nucleic acid template would probably be at least as enantiospecific as the reaction that we have studied. The disadvantage of using chiral monomers as components of a replicating system arises from the difficulty of generating a first long homochiral template from a racemic mixture of monomers, although results of experiments designed to overcome this difficulty by employing homochiral tetramers have been reported.l l The probability of obtaining a homochiral n-mer from achiral substrates is approximately 1P-I if the nontemplate-directed extension of the primer is not enantioselective. Hence, it would be very hard to get started with a homochiral 40-mer, for example. No such difficulty exists in a scenario that originates with an achiral genetic material and in which the incorporation of very few chiral monomers in this achiral background gradually progresses towards homochirality. It seems possible that some PNA sequences could act as catalysts, analogous to ribozymes, even though PNA lacks clear metal binding sites. Although such catalysts could not be enantioselective, the incorporation of as few as two chiral nucleotides could then impose chiral specificity on the system. Furthermore, such patch chimeras could help to bridge the gap in catalytic potential between PNA and RNA, while guaranteeing enantioselectivity.

  18. Combined model- and rule-based controller synthesis with application to helicopter flight

    NASA Astrophysics Data System (ADS)

    Jiang, Tian-Yue

    This thesis deals with synthesis of combined (nonlinear) model-based and (fuzzy logic) rule-based controllers, along with their applications to helicopter flight control problem. The synthesis involves superimposing two control techniques in order to meet both stability and performance objectives. One is model-based control technique, which is based on inversion of an approximate model of the real system. The other is rule-based control technique that adaptively cancels the inversion errors caused by the approximate model inversion. There are two major aspects of the research effort in this thesis. The first is the development of the adaptive rule-based (fuzzy logic) controllers. The linguistic rule weights and defuzzification output weights in the controllers are adapted for ultimate boundedness of the tracking errors. Numerical results from a helicopter flight control problem indicate improvement and demonstrate effectiveness of the control technique. The second aspect of this research work is the extension of the synthesis to account for control limits. In this thesis, a control saturation related rule-bank in conjunction with the adaptive fuzzy logic controller is designed to trade-off system performance for closed-loop stability when the tendency towards control amplitude and/or rate saturation is detected. Simulation results from both a fixed-wing aircraft trajectory control problem and a helicopter flight control problem show the effectiveness of the synthesis method and the resulting controller in avoiding control saturations.

  19. Recent advances in noble metal based composite nanocatalysts: colloidal synthesis, properties, and catalytic applications

    NASA Astrophysics Data System (ADS)

    Xu, Yong; Chen, Lei; Wang, Xuchun; Yao, Weitang; Zhang, Qiao

    2015-06-01

    This Review article provides a report on progress in the synthesis, properties and catalytic applications of noble metal based composite nanomaterials. We begin with a brief discussion on the categories of various composite materials. We then present some important colloidal synthetic approaches to the composite nanostructures; here, major attention has been paid to bimetallic nanoparticles. We also introduce some important physiochemical properties that are beneficial from composite nanomaterials. Finally, we highlight the catalytic applications of such composite nanoparticles and conclude with remarks on prospective future directions.

  20. Recent advances in noble metal based composite nanocatalysts: colloidal synthesis, properties, and catalytic applications.

    PubMed

    Xu, Yong; Chen, Lei; Wang, Xuchun; Yao, Weitang; Zhang, Qiao

    2015-06-28

    This Review article provides a report on progress in the synthesis, properties and catalytic applications of noble metal based composite nanomaterials. We begin with a brief discussion on the categories of various composite materials. We then present some important colloidal synthetic approaches to the composite nanostructures; here, major attention has been paid to bimetallic nanoparticles. We also introduce some important physiochemical properties that are beneficial from composite nanomaterials. Finally, we highlight the catalytic applications of such composite nanoparticles and conclude with remarks on prospective future directions. PMID:26036784

  1. Carbon nanotubes: properties, synthesis, purification, and medical applications

    PubMed Central

    2014-01-01

    Current discoveries of different forms of carbon nanostructures have motivated research on their applications in various fields. They hold promise for applications in medicine, gene, and drug delivery areas. Many different production methods for carbon nanotubes (CNTs) have been introduced; functionalization, filling, doping, and chemical modification have been achieved, and characterization, separation, and manipulation of individual CNTs are now possible. Parameters such as structure, surface area, surface charge, size distribution, surface chemistry, and agglomeration state as well as purity of the samples have considerable impact on the reactivity of carbon nanotubes. Otherwise, the strength and flexibility of carbon nanotubes make them of potential use in controlling other nanoscale structures, which suggests they will have a significant role in nanotechnology engineering. PMID:25170330

  2. Synthesis of Graphene and Its Applications: A Review

    Microsoft Academic Search

    Wonbong Choi; Indranil Lahiri; Raghunandan Seelaboyina; Yong Soo Kang

    2010-01-01

    Graphene, one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbed appreciable attention due to its exceptional electronic and optoelectronic properties. The reported properties and applications of this two-dimensional form of carbon structure have opened up new opportunities for the future devices and systems. Although graphene is known as one of the best electronic materials,

  3. Synthesis and application of dipeptides; current status and perspectives

    Microsoft Academic Search

    Makoto Yagasaki; Shin-ichi Hashimoto

    2008-01-01

    The functions and applications of l-?-dipeptides (dipeptides) have been poorly studied compared with proteins or amino acids. Only a few dipeptides, such as\\u000a aspartame (l-aspartyl-l-phenylalanine methyl ester) and l-alanyl-l-glutamine (Ala-Gln), are commercially used. This can be attributed to the lack of an efficient process for dipeptide production\\u000a though various chemical or chemoenzymatic method have been reported. Recently, however, novel methods

  4. Recent advances in carbon nanodots: synthesis, properties and biomedical applications

    NASA Astrophysics Data System (ADS)

    Miao, Peng; Han, Kun; Tang, Yuguo; Wang, Bidou; Lin, Tao; Cheng, Wenbo

    2015-01-01

    Herein, a mini review is presented concerning the most recent research progress of carbon nanodots, which have emerged as one of the most attractive photoluminescent materials. Different synthetic methodologies to achieve advanced functions and better photoluminescence performances are summarized, which are mainly divided into two classes: top-down and bottom-up. The inspiring properties, including photoluminescence emission, chemiluminescence, electrochemical luminescence, peroxidase-like activity and toxicity, are discussed. Moreover, the biomedical applications in biosensing, bioimaging and drug delivery are reviewed.

  5. Design, synthesis, and characterization of new materials for thermoelectric applications

    Microsoft Academic Search

    Thomas Kent Reynolds

    2003-01-01

    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

  6. Polymers containing phosphorus groups and polyethers: from synthesis to application

    PubMed Central

    2012-01-01

    Background Phosphorus-containing high performance polymers have aroused wide interest, mainly due to good mechanical properties and their excellent fire resistance. The flexibility of synthetic polyphosphoesters allows the development of polymers in order to obtain solid polymer electrolytes for rechargeable lithium batteries based on solid films with superior fire resistance. Results Novel linear Phosphonate-PEG polymers were synthesized by solution polycondensation of 4-chlorophenyldichlorophosphonate as a linking agent and poly(ethylene glycol)s with different molecular weights in the presence of triethylamine or 1-methylimidazole as acid scavenger. The yields were between 54% and 88% and inherent viscosity between 0.18-0.48 dl/g. Molar masses, Mn were about 26300 g/mol for polyphosphonates with PEG 2000 and 4600 g/mol for polyphosphonates with PEG 200. The LOI values for these polymers and membranes are in the range of 26–29. The membranes based on polyphosphonate with PEG 200 and 2000 showed conductivity between 6 × 10-8 S.cm-1 and 6 × 10-7 S.cm-1 at room temperature and total ionic transference number between 0.87- 0.96. The evolution of conductivity vs. temperature is linear. Conclusions 1-methylimidazole was found to be better HCl scavenger than triethylamine, and allowed higher yields and more eco-friendly synthesis of the Phosphonate-PEG polymers for SPE. These polymers and membranes based on these polymers showed good LOI values and indicate an improvement of the safety of lithium batteries. The membranes present conductivities around 6 × 10-7 S.cm-1at room temperature and total ionic transference number is higher for membranes based on polymers with high EG unit content. Best results yield 88%, inherent viscosities 0.48 dl/g and Mn 26000 were obtained with 1-methylimidazole and PEG 2000. These membranes based on these polymers showed good LOI values (in the range 26-29%) and indicate an improvement of the safety of lithium batteries. PMID:23134834

  7. Synthesis, morphologies and applications of polyoxometalate-containing diblock copolymers

    NASA Astrophysics Data System (ADS)

    Chakraborty, Sanjiban

    Block copolymers by virtue of their ability to self assemble and microphase-separation due to the contrast in chemical and physical properties of the covalently linked blocks constitute the essential building blocks towards various nano or micro sized architectures. Polyoxometalates (POM), on the other hand, being an interesting class of metal-oxygen nanometer-sized anionic clusters, are regarded highly due to their excellent electron accepting capability. Combining POM clusters with diblock copolymers can lead to a fascinating class of hybrid materials where the POM cluster not only affect the self-assembly process of various diblock copolymers but also brings its unique electronic properties into the hybrid system. Herein we report the detailed synthesis and characterizations of two hybrid coil-coil diblock copolymers along with two hybrid rod-coil diblock copolymers through polymerization-hybridization approach. The coil-coil diblocks were synthesized via atom transfer radial polymerization (ATRP) of styryl-type monomers and 4-vinylpyridine in sequence. For rod-coil diblock copolymers, the coil block was synthesized through ATRP, followed by the conversion of the terminal bromide to an azide. Ethynyl terminated poly (p-phenylenevinylene) (PPV) and poly (3-hexylthiophene) (P3HT) were prepared separately as the rod blocks. The rod block and the coil block were connected through click chemistry to yield rod-coil diblock copolymers. After removing the phthalimide protecting groups to regenerate aryl amines, POM clusters were finally linked to the coil block of all diblock copolymers to yield the targeted hybrid diblock copolymers. The covalent cluster attachment was confirmed by UV-Vis spectroscopy, FTIR and cyclovoltammetry measurements. The structures, solution and film optical properties, self-assembled morphologies and solar cell performances of these hybrids have been studied. It has been found that solar cell devices based on hybrid P3HT exhibited rather poor performances. Fluorescence dynamic studies indicate that the photoinduced electron transfer process from the rod block to pendant POMs is quite inefficient which may account for the poor device performance. Though the self-assembly process of these hybrid diblock copolymers and the preliminary morphologies has been demonstrated, detailed and systematic study of morphological control requires further extensive research.

  8. Biomolecule mediating synthesis of inorganic nanoparticles and their applications

    NASA Astrophysics Data System (ADS)

    Wei, Zengyan

    Project 1. The conventional phage display technique focuses on screening peptide sequences that can bind on target substrates, however the selected peptides are not necessary to nucleate and mediate the growth of the target inorganic crystals, and in many cases they only show moderate affinity to the targets. Here we report a novel phage display approach that can directly screen peptides catalytically growing inorganic nanoparticles in aqueous solution at room temperature. In this study, the phage library is incubated with zinc precursor at room temperature. Among random peptide sequences displayed on phages, those phages that can grow zinc oxide (ZnO) nanoparticles are selected with centrifugation. After several rounds of selection, the peptide sequences displayed on the phage viruses are analyzed by DNA sequencing. Our screening protocol provide a simple and convenient route for the discovery of catalytic peptides that can grow inorganic nanoparticles at room temperature. This novel screening protocol can extend the method on finding a wide range of new catalysts. Project 2. Genetically engineered collagen peptides are assembled into freestanding films when quantum dots (QDs) are co-assembled as joints between collagen domains. These peptide-based films show excellent mechanical properties with Young's modulus of 20 GPa, much larger than most of the multi-composite polymer films and previously reported freestanding nanoparticle-assembled sheets, and it is even close to that reported for the bone tissue in nature. These films show little permanent deformation under small indentation while the mechanical hysteresis becomes remarkable when the load approaches near and beyond the rupture point, which is also characteristic of the bone tissue. Project 3. The shape-controlled synthesis of nanoparticles have been established in single-phase solutions by controlling growth directions of crystalline facets on seed nanocrystals kinetically; however, it is difficult to rationally predict and design nanoparticle shapes. Here we introduce a methodology to fabricate nanoparticles in smaller sizes by evolving shapes thermodynamically. This strategy enables a more rational approach to fabricate shaped nanoparticles by etching specific positions of atoms on facets of seed nanocrystals in reverse micelle reactors where the surface energy gradient induces desorption of atoms on specific locations on the seed surfaces. From seeds of 12 nm palladium nanocubes, the shape is evolved to concave nanocubes and finally hollow nanocages in the size 10 nm by etching the center of {200} facets. The high surface area-to-volume ratio and the exposure of a large number of palladium atoms on ledge and kink sites of hollow nanocages are advantageous to enhance catalytic activity and recyclability.

  9. New chiral phosphinephosphinite ligands: Application to stereoselective synthesis of a key intermediate of 1{beta}-methyl carbapenems by Rh(I)-catalyzed asymmetric hydroformylation

    SciTech Connect

    Saito, Takao; Yoshida, Akifumi; Matsumura, Kazuhiko [Takasago International Corp., Kanagawa (Japan)] [and others

    1995-12-31

    Transition metal catalyzed asymmetric hydroformylation is an attractive and highly useful homologation process for organic synthesis. Recently, the authors reported that the Rh(I) complexes of phosphinephosphite BINAPHOS are highly efficient catalysts for enantioselective hydroformylation of a variety of olefins. This time, the authors have designed and synthesized new chiral phosphinephosphinite ligands having binaphthyl backbone, (R)-2-diarylphosphino-2{prime}-diarylphosphinoxy-1,1{prime}-binaphthy1 (hereafter abbreviated (R)-BIPNITE). The Rh(I) complexes of these ligands are effective catalysts for the asymmetric hydroformylation of 4-vinylazetidin-2-one to give the corresponding oxo-aldehyde 3{beta} as the major product in very high diastereoselectivities and in good regioselectivities. Interestingly, modifications of the aryl substituents in phosphine and phosphinite moieties afforded higher selectivities. Aldehyde 3{beta} was easily oxidized with NaClO{sub 2} to 4, a key intermediate of 1{beta}-methyl carbapenems. Thus, the present method provides a new practical route to a versatile key intermediate for the synthesis of carbapenem antibiotics.

  10. trans-Directing ability of the amide group: enabling the enantiocontrol in the synthesis of 1,1-dicarboxy cyclopropanes. Reaction development, scope, and synthetic applications.

    PubMed

    Marcoux, David; Goudreau, Sébastien R; Charette, André B

    2009-12-01

    In this article, we describe our efforts toward the enantioselective formation of 1,1-cyclopropane diesters via the metal-catalyzed cyclopropanation of olefins. The strategies envisioned to achieve such a goal are discussed as well as the results that led us to the discovery of the powerful trans-directing ability of the amide group in Rh(II)-catalyzed cyclopropanation reactions. We show how this feature enables a solution for the stereoselective synthesis of 1,1-dicarboxy cyclopropane derivatives. The scope and limitations are discussed as well as the demonstration that these newly formed cyclopropanes display reactivity similar to that of 1,1-cyclopropane diesters. Conversely, 1,1-cyclopropane diesters could be accessed in two steps from commercially available alkenes. The potential utility of this methodology is illustrated by several functional group transformations and its use in the expedient stereoselective formal synthesis of (S)-(+)-curcumene, (S)-(+)-nuciferal, (S)-(+)-nuciferol, (+)-erogorgiaene, (+/-)-xanthorrhizol, and (+/-)-2-hydroxycalamenene. PMID:19894700

  11. Catalytic, Asymmetric Indolizidinone Aza-Quaternary Stereocenter Synthesis: Expedient Synthesis of the Cylindricine Alkaloids Core

    PubMed Central

    Dalton, Derek M.; Rovis, Tomislav

    2013-01-01

    The Rh(I)•CKphos catalyzed [2+2+2] cycloaddition of 1,1-disubstituted alkenyl isocyanates and alkyl alkynes selectively forms previously inaccessible vinylogous amide indolizidinone cycloadducts, establishing an azaquaternery stereocenter with excellent enantioselectivies (up to 98% ee). This advance enables a seven step catalytic, asymmetric synthesis of the tricyclic core of the cylindricine alkaloids with excellent control of product-, regio- and enantioselectivity. PMID:23631448

  12. Enantioselective determination of acaricide etoxazole in orange pulp, peel, and whole orange by chiral liquid chromatography with tandem mass spectrometry.

    PubMed

    Yao, Zhoulin; Li, Zuguang; Zhuang, Shulin; Li, Xiaoge; Xu, Mingfei; Lin, Mei; Wang, Qiang; Zhang, Hu

    2015-02-01

    An efficient enantioselective method for the determination of etoxazole in orange pulp, peel, and whole orange was developed using liquid chromatography with tandem mass spectrometry. The enantioseparation was performed on a Chiralpak AD-3R column at 30ºC using acetonitrile with 0.1% formic acid solution (80:20, v/v) as the mobile phase in less than 5 min. Quantification was achieved using matrix-matched standard calibration curves. The overall mean recoveries for two enantiomers from orange pulp and whole orange were 91.0-99.6% and the orange peel was 92.6-103.1%, with relative standard deviations of 0.8-5.4% intraday and 2.0-4.8% interday at 1, 10, and 100 ?g/kg levels, and 1.3-5.2% intraday and 3.5-4.3% interday at 5, 50, and 500 ?g/kg levels, respectively. The limits of quantification for all enantiomers in three matrices did not exceed 5 ?g/kg. Moreover, the absolute configuration of etoxazole enantiomers had been determined by the combination of experimental and predicted electronic circular dichroism spectra, and the first eluted enantiomer was confirmed as (S)-etoxazole on a Chiralpak AD-3R column while (R)-etoxazole was first on three cellulose chiral columns. The application of the proposed method to real sample analysis suggests its potential use in enantioselective determination of etoxazole enantiomers in citrus. PMID:25581871

  13. New materials graphyne, graphdiyne, graphone, and graphane: review of properties, synthesis, and application in nanotechnology.

    PubMed

    Peng, Qing; Dearden, Albert K; Crean, Jared; Han, Liang; Liu, Sheng; Wen, Xiaodong; De, Suvranu

    2014-01-01

    Plenty of new two-dimensional materials including graphyne, graphdiyne, graphone, and graphane have been proposed and unveiled after the discovery of the "wonder material" graphene. Graphyne and graphdiyne are two-dimensional carbon allotropes of graphene with honeycomb structures. Graphone and graphane are hydrogenated derivatives of graphene. The advanced and unique properties of these new materials make them highly promising for applications in next generation nanoelectronics. Here, we briefly review their properties, including structural, mechanical, physical, and chemical properties, as well as their synthesis and applications in nanotechnology. Graphyne is better than graphene in directional electronic properties and charge carriers. With a band gap and magnetism, graphone and graphane show important applications in nanoelectronics and spintronics. Because these materials are close to graphene and will play important roles in carbon-based electronic devices, they deserve further, careful, and thorough studies for nanotechnology applications. PMID:24808721

  14. Synthesis of nanostructured materials in inverse miniemulsions and their applications

    NASA Astrophysics Data System (ADS)

    Cao, Zhihai; Ziener, Ulrich

    2013-10-01

    Polymeric nanogels, inorganic nanoparticles, and organic-inorganic hybrid nanoparticles can be prepared via the inverse miniemulsion technique. Hydrophilic functional cargos, such as proteins, DNA, and macromolecular fluoresceins, may be conveniently encapsulated in these nanostructured materials. In this review, the progress of inverse miniemulsions since 2000 is summarized on the basis of the types of reactions carried out in inverse miniemulsions, including conventional free radical polymerization, controlled/living radical polymerization, polycondensation, polyaddition, anionic polymerization, catalytic oxidation reaction, sol-gel process, and precipitation reaction of inorganic precursors. In addition, the applications of the nanostructured materials synthesized in inverse miniemulsions are also reviewed.

  15. Synthesis of nanostructured materials in inverse miniemulsions and their applications.

    PubMed

    Cao, Zhihai; Ziener, Ulrich

    2013-11-01

    Polymeric nanogels, inorganic nanoparticles, and organic-inorganic hybrid nanoparticles can be prepared via the inverse miniemulsion technique. Hydrophilic functional cargos, such as proteins, DNA, and macromolecular fluoresceins, may be conveniently encapsulated in these nanostructured materials. In this review, the progress of inverse miniemulsions since 2000 is summarized on the basis of the types of reactions carried out in inverse miniemulsions, including conventional free radical polymerization, controlled/living radical polymerization, polycondensation, polyaddition, anionic polymerization, catalytic oxidation reaction, sol-gel process, and precipitation reaction of inorganic precursors. In addition, the applications of the nanostructured materials synthesized in inverse miniemulsions are also reviewed. PMID:24056795

  16. Recent developments of polymer liquid crystals - Synthesis, properties and applications

    NASA Astrophysics Data System (ADS)

    Noel, C.

    Recent developments of polymer liquid crystals (PLCs) are reviewed. Both lyotropic (polymer solutions) and thermotropic (polymer melts) types of polymer liquid crystals are considered. The general properties of mesophases formed by such polymers are surveyed and some chemical structures capable of producing mesophases are classified in relation to their ability to form lyotropic and thermotropic systems. The synthetic routes, the effects of polymer structure on physical properties, and applications of the major class of lyotropic systems (polyamides) and of a range of potentially important thermotropic polymers are discussed.

  17. The first total synthesis of (?)-mitragynine, an analgesic indole alkaloid in mitragyna speciosa

    Microsoft Academic Search

    Hiromitsu Takayama; Moriyoshi Maeda; Satoshi Ohbayashi; Mariko Kitajima; Shin-ichiro Sakai; Norio Aimi

    1995-01-01

    Starting from an optically pure alcohol, (R)-(3), which was prepared by enzymatic hydrolysis of the racemic acetate (2) or enantioselective reduction of the ketone derivative (4), the chiral total synthesis of mitragynine (1), a major corynanthe-type indole alkaloid having an analgesic effect in Mitragyna speciosa, was accomplished.

  18. Radiation synthesis of superabsorbent CMC based hydrogels for agriculture applications

    NASA Astrophysics Data System (ADS)

    Raafat, Amany I.; Eid, Mona; El-Arnaouty, Magda B.

    2012-07-01

    A series of superabsorbent hydrogel based on carboxymethylcellulose (CMC) and polyvinylpyrrolidone (PVP) crosslinked with gamma irradiation have been proposed for agriculture application. The effect of preparation conditions such as feed solution composition and absorbed irradiation dose on the gelation and swelling degree was evaluated. The structure and the morphology of the superabsorbent CMC/PVP hydrogel were characterized using Fourier transform infrared spectroscopy technique (FTIR), and scanning electron microscope (SEM). Effect of ionic strength and cationic and anionic kinds on the swelling behavior of the obtained hydrogel was investigated. Urea as an agrochemical model was loaded onto the obtained hydrogel to provide nitrogen (N) nutrients. The water retention capability and the urea release behavior of the CMC/PVP hydrogels were investigated. It was found that, the obtained CMC/PVP hydrogels have good swelling degree that greatly affected by its composition and absorbed dose. The swelling was also extremely sensitive to the ionic strength and cationic kind. Owing to its considerable slow urea release, good water retention capacity, being economical, and environment-friendly, it might be useful for its application in agriculture field.

  19. AUTOMATION FOR THE SYNTHESIS AND APPLICATION OF PET RADIOPHARMACEUTICALS.

    SciTech Connect

    Alexoff, D.L.

    2001-09-21

    The development of automated systems supporting the production and application of PET radiopharmaceuticals has been an important focus of researchers since the first successes of using carbon-11 (Comar et al., 1979) and fluorine-18 (Reivich et al., 1979) labeled compounds to visualize functional activity of the human brain. These initial successes of imaging the human brain soon led to applications in the human heart (Schelbert et al., 1980), and quickly radiochemists began to see the importance of automation to support PET studies in humans (Lambrecht, 1982; Langstrom et al., 1983). Driven by the necessity of controlling processes emanating high fluxes of 511 KeV photons, and by the tedium of repetitive syntheses for carrying out these human PET investigations, academic and government scientists have designed, developed and tested many useful and novel automated systems in the past twenty years. These systems, originally designed primarily by radiochemists, not only carry out effectively the tasks they were designed for, but also demonstrate significant engineering innovation in the field of laboratory automation.

  20. Facile synthesis of SiO2 nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Scano, A.; Pilloni, M.; Cabras, V.; Vazquez-Vazquez, C.; Ennas, G.

    2014-10-01

    Silica nanoparticles (SiO2 NPs) for biomedical applications have been prepared by using a facile modified Stöber-synthesis. Potassium borohydride (KBH4) has been introduced in the synthesis procedure in order to control NP size. Several samples have been prepared varying tetraethylorthosilicate (TEOS) concentration, and using different process conditions (temperature, reaction time and atmosphere). In order to study the influence of the process conditions on the NP size, morphology and properties, several characterization techniques were used. Size and morphology of the as-prepared SiO2 NPs have been studied by using Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS) techniques. Structural characterization was carried out by X-ray powder diffraction. To investigate the SiO2 NP fluorescence emission properties the fluorescence spectroscopy was also used.

  1. Combustion synthesis and engineering of nanoparticles for electronic, structural and superconductor applications

    SciTech Connect

    Stangle, G.C.; Amarakoon, V.R.W.; Schulze, W.A.

    1993-05-28

    Fully dense, nanocrystalline ceramic articles were prepared by the new nanofabrication process. The process consists of two steps: synthesis of ceramic nanoparticles and fabrication of dense, nanocrystalline ceramic parts. The synthesis step produced 10-nanometer-diameter crystallites, and is capable of being scaled up to kilogram/hour production rates. The fabrication step produced dense parts at significantly reduced sintering temperatures and times -- representing a factor of 10--100 reduction in process energy requirements. The process was demonstrated by producing ultrafine-grained yttria-stabilized ZrO[sub 2], an important material with a variety of energy-related applications (solid electrolytes, oxygen sensors, electrode materials, thermal barrier coatings, etc.). Results from this period clearly illustrate the capabilities of this energy-efficient and directly commercializable process for producing dense, nanocrystalline, multicomponent oxide ceramics.

  2. Design, synthesis, conformational analysis and application of indolizidin-2-one dipeptide mimics.

    PubMed

    Khashper, Arkady; Lubell, William D

    2014-07-28

    Growth in the field of peptide mimicry over the past few decades has resulted in the synthesis of many new compounds and the investigation of novel pharmacological agents. Azabicyclo[X.Y.0]alkanone amino acids are among the attractive classes of constrained mimics, because they can create rigid peptide structures for probing the conformation and roles of natural motifs in recognition events important for biological activity. Herein, we review the last ten years of the synthesis, conformational analysis and activity of analogs of the azabicyclo[4.3.0]alkan-2-one amino acid subclass, so-called indolizidin-2-one amino acids, with particular attention on their employment as inputs for biological applications. PMID:24899358

  3. Synthesis, properties and applications of bio-based materials

    NASA Astrophysics Data System (ADS)

    Srinivasan, Madhusudhan

    Bio-based feedstock have become very significant as they offer a value proposition in terms of carbon balance and also in terms of endowing biodegradability where needed. Thus a lot of attention is being given to the modification such feedstock for different applications. Soybean oil is one such feedstock. The oil is a triglyceride ester composed of different fatty acids, which are common to other plant oils. Thus soybean oil serves as a platform for plant oils, as modifications of this oil, can in theory be extended to cover other plant oils. Methyl oleate was used as a model fatty acid ester, to synthesize hydroxyesters with ethylene glycol via a two stage oxidative cleavage of the double bonds. Ozone was chosen as the oxidant due to its many advantages. The first stage involved oxidation of the double bond to aldehydes, ozonides and acetals, which were subsequently converted to hydroxyesters (hydroxy values of 220 - 270) in near quantitative yield by treatment with Oxone. This method could be extended to soybean oil to make "polyols" which could find applications in resin syntheses. Silylation was employed as another platform to functionalize soybean oil and fatty acid methyl esters with a reactive silane (vinyltrimethoxy silane). This simple modification produced materials that are cured by atmospheric moisture and are useful as coatings. The silylation was controlled by varying the grafting time, cure temperature and the concentration of the silane. Products with gel content as high as 90% could be achieved. The coating exhibited good adhesion to metal, glass, concrete and paper. Steel panels coated with these coatings exhibited good stability against corrosion in high humidity conditions and moderate stability against a salt spray. The silylation was also successfully utilized to improve the tensile strength of the blend of biodegradable polyester, poly (butylene adipate-co-terephthalate) with talc. A reactive extrusion process was employed to graft vinyl silanes on the polyester in short reaction times of 5 minutes. This improved the compatibility with the talc filler. This biodegradable polyester product was characterized by high tensile strength and moderate elongation. The modification method is simple is applicable to a variety of aliphatic biodegradable polyesters. Finally a rapid polymerization of 1, 4-dioxan-2-one in very short times was accomplished with titanium alkoxides as initiators. At low [monomer]/ [initiator] ratios (100:1), nearly all the alkoxide groups initiated polymerization. High conversions up to 90% were achieved even at high ratios (2400:1). The activation energy for polymerization for titanium tetraisopropoxide is the lowest reported (33.5 kJ/mol) for this monomer system.

  4. Marine bromopyrrole alkaloids: synthesis and diverse medicinal applications.

    PubMed

    Rane, Rajesh; Sahu, Niteshkumar; Shah, Chetan; Karpoormath, Rajshekhar

    2014-01-01

    Marine organisms have been found to be a very rich source of bioactive molecules. Among marine organisms, sponges have been proven to be excellent producers of secondary metabolites. More than 5,300 compounds have been isolated from sponges with around 200 new molecules reported each year. Bromopyrrole alkaloids constitute a family of exclusively marine alkaloids and represent a fascinating example of the large variety of compounds formed by marine sponges which exhibit different biological activities such as antifeedent, anti-biofilm, anticancer, antiinflammatory, antimicrobial, immunomodulatory, analgesic, antiserotonergic, antiangiogenic, antihistaminic, chitinase inhibitor and actimyosin ATPase activator. More than 140 derivatives with different structures and biological activities, have been isolated from more than 20 different sponges. Most of these alkaloids share a key building block, pyrrole-imidazole with oroidin being their underlying structural motif. In this review detailed account of isolation and medicinal application of marine bromopyrrole alkaloids and their synthetic derivatives are discussed. PMID:24359195

  5. Pushing the limits of aminocatalysis: enantioselective transformations of ?-branched ?-ketocarbonyls and vinyl ketones by chiral primary amines.

    PubMed

    Zhang, Long; Fu, Niankai; Luo, Sanzhong

    2015-04-21

    Enantioselective ?-functionalizations of carbonyl compounds are fundamental transformations for the asymmetric synthesis of organic compounds. One of the more recent developments along this line is in aminocatalysis, which leads to the direct ?-functionalization of simple aldehydes and ketones. However, most of the advances have been achieved with linear aldehydes and ketones as substrates. Effective aminocatalysis with ?-branched carbonyls, particularly ?-branched ketones, has remained elusive. The primary difficulty arises from the space-demanding ?-substituent, which impedes iminium/enamine formation. In 2005, synthetic organic chemists revived catalysis using primary amines, which brought new attention to these challenges, because of the conformational flexibility of primary amines. On the basis of early biomimetic studies by Hine, in 2007 we developed the bioinspired chiral primary amine catalysts featuring primary-tertiary diamines. This type of catalyst involves enamine/iminium catalysis, and we could apply this chemistry to all of the major types of ketones and aldehydes. In this Account, we present research from our laboratory that significantly expands aminocatalysis to include ?-branched ketones such as ?-ketocarbonyls and ?-substituted vinyl ketones. Our primary amine catalysis methodology, when used alone or in conjunction with metal catalysts, provides convenient access to both enantiopure ?-tertiary and quaternary ketones, structures that are not available via other approaches. Our mechanistic studies showed that acidic additives play the critical role in facilitating catalytic turnover, most likely by shuttling protons during the enamine/iminium tautomerizations. These additives are also critical to induce the desired stereochemistry via ammonium N-H hydrogen bonding. Proton transfer by shuttling is also stereoselective, resulting in enantioselective enamine protonation as observed in the reactions of ?-substituted vinyl ketones. In addition, we have carried out density functional theory studies that help to delineate the origins of the stereoselectivity in these reactions. PMID:25831453

  6. An Intramolecular Diels-Alder Approach to the Eunicellins: Enantioselective Total Syntheses of Ophirin B and

    E-print Network

    An Intramolecular Diels-Alder Approach to the Eunicellins: Enantioselective Total Syntheses to the oxonene rings, and highly diastereoselective intramolecular Diels-Alder reactions resulted control element for stereo- selective intramolecular Diels-Alder reaction to construct the University

  7. How a Single-Point Mutation in Horseradish Peroxidase Markedly Enhances Enantioselectivity

    E-print Network

    Antipov, Eugene

    The effect of all possible mutations at position 178 on the enantioselectivity of yeast surface-bound horseradish peroxidase (HRP) toward chiral phenols has been investigated. In contrast to their wild-type predecessor, ...

  8. Residue Val237 is critical for the enantioselectivity of Penicillium expansum lipase.

    PubMed

    Tang, Lianghua; Su, Min; Chi, Liying; Zhang, Junling; Zhang, Huihui; Zhu, Ling

    2014-03-01

    The shape of the hydrophobic tunnel leading to the active site of Penicillium expansum lipase (PEL) was redesigned by single-point mutations, in order to better understand enzyme enantioselectivity towards naproxen. A variant with a valine-to-glycine substitution at residue 237 exhibited almost no enantioselectivity (E = 1.1) compared with that (E = 104) of wild-type PEL. The function of the residue, Val237, in the hydrophobic tunnel was further analyzed by site-directed mutagenesis. For each of these variants a significant decrease of enantioselectivity (E < 7) was observed compared with that of wild-type enzyme. Further docking result showed that Val237 plays the most important role in stabilizing the correct orientation of (R)-naproxen. Overall, these results indicate that the residue Val237 is the key amino acid residue maintaining the enantioselectivity of the lipase. PMID:24338160

  9. Catalytic Enantioselective Conia-Ene Reaction Britton K. Corkey and F. Dean Toste*

    E-print Network

    Toste, Dean

    for the stereoselective construction of all carbon quaternary centers.1 Recently, significant progress has been made conditions,12 addition of an amine base completely inhibited our enantioselective Conia-ene re- action (entry

  10. Enantioselective Functionalization of Radical Intermediates in Redox Catalysis: Copper-Catalyzed Asymmetric Oxytrifluoromethylation of Alkenes

    E-print Network

    Zhu, Rong

    Something radical: An efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system. Mechanistic studies are consistent with a metal-catalyzed redox radical addition mechanism ...

  11. BIOACCUMULATION AND ENANTIOSELECTIVE BIOTRANSFORMATION OF FIPRONIL BY RAINBOW TROUT (ONCORHYNCHUS MYKISS)

    EPA Science Inventory

    Dietary accumulation and enantioselective biotransformation was determined for rainbow trout (Oncorhynchus mykiss) exposed to fipronil, a widely used chiral pesticide. Measurement of the fish carcass tissue (whole fish minus GI tract and liver) showed a rapid accumulation of fip...

  12. Cobalt-catalyzed enantioselective hydroboration of 1,1-disubstituted aryl alkenes.

    PubMed

    Zhang, Lei; Zuo, Ziqing; Wan, Xiaolong; Huang, Zheng

    2014-11-01

    We report the synthesis of cobalt complexes of novel iminopyridine-oxazoline (IPO) ligands and their application to the asymmetric hydroboration of 1,1-disubstituted aryl alkenes. The new catalysts afforded ?-alkyl-?-pinacolatoboranes with exclusive regioselectivity in high yields with up to 99.5% ee. Furthermore, we have applied this method to an efficient synthesis of naproxen. PMID:25325782

  13. Semibullvalene and Diazasemibullvalene: Recent Advances in the Synthesis, Reaction Chemistry, and Synthetic Applications.

    PubMed

    Zhang, Shaoguang; Zhang, Wen-Xiong; Xi, Zhenfeng

    2015-07-21

    Semibullvalene (SBV) and its aza analogue 2,6-diazasemibullvalene (NSBV) are theoretically interesting and experimentally challenging organic molecules because of four unique features: highly strained ring systems, intramolecular skeletal rearrangement, extremely rapid degenerate (aza-)Cope rearrangement, and the predicted existence of neutral homoaromatic delocalized structures. SBV has received much attention in the past 50 years. In contrast, after NSBV was predicted in 1971 and the first in situ synthesis was realized in 1982, no progress on NSBV chemistry was made until our results in 2012. We have been interested in the reaction chemistry of 1,4-dilithio-1,3-butadienes (dilithio reagents for short), especially for their applications in the synthesis of SBV and NSBV, because (i) the cyclodimerization of dilithio reagents could provide the potential eight-carbon skeleton of SBV from four-carbon butadiene units and (ii) the insertion reaction of dilithio reagents with C?N bonds of two nitriles could provide a 6C + 2N skeleton that might be a good precursor for the synthesis of NSBV. Therefore, we initiated a journey into the synthesis and reaction chemistry of SBV and NSBV starting from dilithio reagents that has been ongoing since 2006. In this Account, we outline mainly our recent achievements in the synthesis, structural characterization, reaction chemistry, synthetic application, and theoretical/computational analysis of NSBV. Two efficient strategies for the synthesis of NSBV from dilithio reagents and nitriles via oxidant-induced C-N bond formation are described. Structural investigations of NSBV, including X-ray crystal structure analysis, determination of the activation barrier for the aza-Cope rearrangement, and theoretical analysis, show that the localized structure of NSBV is the predominant form and that the homoaromatic delocalized structure exists as a minor component in the equilibrium. We also discuss the reaction chemistry and synthetic applications of NSBV. Several novel reaction patterns have been explored, including thermolysis, C-N bond insertion, rearrangement-cycloaddition, oxidation, and nucleophilic ring-opening reactions. Diverse and interesting N-containing polycyclic skeletons can be constructed, such as nickelaazetidine, 1,5-diazatriquinacenes, and triazabrexadienes, which are not available by other means. Our results show that NSBV not only features a rapid aza-Cope rearrangement with a low activation barrier but also acts as unique synthetic reagent that is significantly different from aziridine. The strained rigid ring systems as a whole can be involved in the reactions. Our achievements highlight two significant advances: (i) the well-established efficient synthesis and isolation of NSBV has greatly accelerated the development of NSBV chemistry, and (ii) the previously unattainable molecules have become "normal" and routine starting materials for the synthesis of otherwise unavailable but interesting structures. We expect that our pursuits will inspire and help direct future chemical and physical research on NSBV. PMID:26061608

  14. Ferrocene-peptido conjugates: from synthesis to sensory applications.

    PubMed

    Marti?, Sanela; Labib, Mahmoud; Shipman, Patrick O; Kraatz, Heinz-Bernhard

    2011-07-28

    The field of chemical and biological sensing is increasingly dependent on the availability of new functional materials that enhance the ability of the system to respond to chemical interactions. Organometallic bioconjugates derived from amino acids, peptides, proteins, peptide nucleic acids, and dendrimers have had a profound effect in this area and have endowed modern sensory systems with a superior performance. Owing to their fairly high stability, solubility in various solvents, and excellent redox properties, ferrocene and ferrocenyl conjugates have emerged as one of the most important classes of materials that enable direct observation of molecular interactions and as electron mediators. The low potential, reversible redox behavior of the ferrocene/ferrocenium couple is a unique property that finds widespread application in the design of sensory platforms. Currently, there is significant drive to exploit new organometallic systems, in which the presence of ferrocene acting as a redox center is critical and allows the design of highly sensitive electrochemical sensors for the sensing and recognition of a vast array of analytes. PMID:21483964

  15. Synthesis, functionalization and bioimaging applications of highly fluorescent carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Chandra, Sourov; Das, Pradip; Bag, Sourav; Laha, Dipranjan; Pramanik, Panchanan

    2011-04-01

    Highly fluorescent crystalline carbon nanoparticles (CNPs) have been synthesized by one step microwave irradiation of sucrose with phosphoric acid at 100 W for 3 min 40 s. This method is very simple, rapid and economical and hence can be used for large scale applications. The average particle sizes are 3 to 10 nm and they emit bright green fluorescence under the irradiation of UV-light. Therefore, the particles can be used as a unique material for bioimaging as well as drug delivery. To further increase the fluorescence property of the synthetic carbon nanoparticles we simply functionalized them by using different organic dyes, such as fluorescein, rhodamine B and ?-naphthylamine the maximum fluorescence intensity was observed for the particles functionalized with fluorescein. It is very interesting to note that all of those compounds show maximum fluorescence intensity at 225 nm excitation wavelength and for any excitation wavelength the peak positions are exactly same the position as that of CNPs itself, which is completely different from the individual precursors (dyes). All of the above compounds, including CNPs, have also been successfully introduced into the erythrocyte enriched fraction of healthy human blood cells with minimum cytotoxicity.

  16. Catalytic performance of a highly enantioselective ( R)-ester hydrolase from a new isolate Acinetobacter sp. CGMCC 0789

    Microsoft Academic Search

    Jing-Hua Qian; Jian-He Xu

    2004-01-01

    A highly enantioselective (R)-ester hydrolase was partially purified from a newly isolated bacterium, Acinetobacter sp. CGMCC 0789, whose resting cells exhibited a highly enantioselective activity toward the acetate of (4R)-hydroxy-3-methyl-2-(2-propynyl)- cyclopent-2-enone (R-HMPC). The optimum pH and temperature of the partially purified enzyme were 8.0 and 60°C, respectively. The enantioselectivity of the crude enzyme was increased by 1.2-fold from 16 to

  17. Bis(oxazoline)-based coordination polymers: a recoverable system for enantioselective Henry reactions.

    PubMed

    Angulo, Beatriz; García, José I; Herrerías, Clara I; Mayoral, José A; Miñana, Ana C

    2012-07-01

    An efficient release-capture strategy for the recovery and reuse of enantioselective catalysts in the Henry reaction is described. This strategy is based on the precipitation of an insoluble coordination polymer at the end of each reaction, allowing easy separation from products. The coordination polymer is formed through aggregation of Cu(II) ions with ditopic bisoxazoline-based chiral ligands. Up to 11 catalytic cycles have been conducted keeping good yields and enantioselectivities. PMID:22667829

  18. Enantioselective iridium-catalyzed allylic substitutions with hydroxamic acid derivatives as N-nucleophiles.

    PubMed

    Gärtner, Martin; Jäkel, Mascha; Achatz, Manuel; Sonnenschein, Christoph; Tverskoy, Olena; Helmchen, Günter

    2011-06-01

    Enantioselective Ir-catalyzed allylic aminations with hydroxamic acid derivatives are described. Catalysts were prepared in situ from [Ir(cod)Cl](2) or [Ir(dbcot)Cl](2), a phosphoramidite and base. In addition, pure (?-allyl)Ir complexes containing cod or dbcot as auxiliary ligands were used. Very high degrees of regio- and enantioselectivity were achieved. The reaction products were transformed into piperidine derivatives suited as precursors for aza-sugars. PMID:21534551

  19. Gadolinium-Catalyzed Regio- and Enantioselective Aminolysis of Aromatic trans-2,3-Epoxy Sulfonamides.

    PubMed

    Wang, Chuan; Yamamoto, Hisashi

    2015-07-20

    The first enantioselective aminolysis of aromatic trans-2,3-epoxy sulfonamides has been accomplished, which was efficiently catalyzed by a Gd-N,N'-dioxide complex. Under the directing effect of the sulfonamide moiety the ring-opening reaction proceeded selectively at the C-3 position in a highly enantioselective manner furnishing various Ts- and SES-protected 3-amino-3-phenylpropan-2-olamines as products. PMID:26058560

  20. Mn-based nanostructured building blocks: Synthesis, characterization and applications

    NASA Astrophysics Data System (ADS)

    Beltran Huarac, Juan

    The quest for smaller functional elements of devices has stimulated increased interest in charge-transfer phenomena at the nanoscale. Mn-based nanostructured building blocks are particularly appealing given that the excited states of high-spin Mn2+ ions induce unusual d-d energy transfer processes, which is critical for better understanding the performance of electronic and spintronic devices. These nanostructures also exhibit unique properties superior to those of common Fe- and Co-based nanomaterials, including: excellent structural flexibility, enhanced electrochemical energy storage, effective ion-exchange dynamics, more comprehensive transport mechanisms, strong quantum yield, and they act as effective luminescent centers for more efficient visible light emitters. Moreover, Mn-based nanostructures (MBNs) are crucial for the design and assembly of inexpensive nanodevices in diluted magnetic semiconductors (DMS), optoelectronics, magneto-optics, and field-effect transistors, owing to the great abundance and low-cost of Mn. Nonetheless, the paucity of original methods and techniques to fabricate new multifunctional MBNs that fulfill industrial demands limits the sustainable development of innovative technology in materials sciences. In order to meet this critical need, in this thesis we develop and implement novel methods and techniques to fabricate zero- and one-dimensional highly-crystalline new-generation MBNs conducive to the generation of new technology, and provide alternative and feasible miniaturization strategies to control and devise at nanometric precision their size, shape, structure and composition. Herein, we also establish the experimental conditions to grow Mn-based nanowires (NWs), nanotubes (NTs), nanoribbons (NRs), nanosaws (NSs), nanoparticles (NPs) and nanocomposites (NCs) via chemical/physical deposition and co-precipitation chemical routes, and determine the pertinent arrangements to our experimental schemes in order to extend our bottom-up approaches towards the fabrication of different types of functional MBNs. Likewise, strategic procedures that advance the facile integration of these self-assembled nanostructures with carbon-based and magnetic/optical materials, chalcogenides, oxides, and ferroics are widely analyzed and discussed. Furthermore, we present the attractive peculiarities of three versatile MBN systems (bridging the gap between their advantageous properties and the lack of methods for their fabrication): single-crystal saw-like MnS NRs, and single-crystal MnS NWs conformally coated with carbon; doped rare-earth manganite NCs, and carbon NTs conformally coated with doped rare-earth manganite; and ZnS:Mn NPs, and Fe3O4/ZnS:Mn NCs. Concerning the applicative significance, the main features of these three systems obtained by our method are suitable to advance direct applications in nanotechnology. In this regard, this work represents a step ahead in the following areas: i) alternative anode materials to enhance the capacity and cycling performance of low-drain, long-life, low-cost, high-energy density light-weight and safer lithium-ion batteries; ii) promising luminescent materials to improve the optoelectronic performance of visible light emitters; iii) new elements for field-effect transistors that outperform the transport properties of conventional carbon-based channels; iv) bifunctional materials exhibiting optical response sensitive to external magnetic fields vital for DMS; v) novel types of nanocantilevers useful for nanosensors and nanotweezers; vi) unique multiferroics materials that exhibit magnetoelectric coupling at room temperature for spintronics; vii) potential core-shell materials showing stress-free and protective carbon shells for shock-resistance semiconductors; and viii) high-quality ceramics useful as starting materials to deposit films by pulsed laser deposition, sputtering and thermal evaporation techniques.

  1. Shape matters: synthesis and biomedical applications of high aspect ratio magnetic nanomaterials

    NASA Astrophysics Data System (ADS)

    Fratila, Raluca M.; Rivera-Fernández, Sara; de La Fuente, Jesús M.

    2015-04-01

    High aspect ratio magnetic nanomaterials possess anisotropic properties that make them attractive for biological applications. Their elongated shape enables multivalent interactions with receptors through the introduction of multiple targeting units on their surface, thus enhancing cell internalization. Moreover, due to their magnetic anisotropy, high aspect ratio nanomaterials can outperform their spherical analogues as contrast agents for magnetic resonance imaging (MRI) applications. In this review, we first describe the two main synthetic routes for the preparation of anisotropic magnetic nanomaterials: (i) direct synthesis (in which the anisotropic growth is directed by tuning the reaction conditions or by using templates) and (ii) assembly methods (in which the high aspect ratio is achieved by assembly from individual building blocks). We then provide an overview of the biomedical applications of anisotropic magnetic nanomaterials: magnetic separation and detection, targeted delivery and magnetic resonance imaging.

  2. Core-Shell Composite Nanoparticles: Synthesis, Characterization, and Applications

    NASA Astrophysics Data System (ADS)

    Sanyal, Sriya

    Nanoparticles are ubiquitous in various fields due to their unique properties not seen in similar bulk materials. Among them, core-shell composite nanoparticles are an important class of materials which are attractive for their applications in catalysis, sensing, electromagnetic shielding, drug delivery, and environmental remediation. This dissertation focuses on the study of core-shell type of nanoparticles where a polymer serves as the core and inorganic nanoparticles are the shell. This is an interesting class of supramolecular building blocks and can "exhibit unusual, possibly unique, properties which cannot be obtained simply by co-mixing polymer and inorganic particles". The one-step Pickering emulsion polymerization method was successfully developed and applied to synthesize polystyrene-silica core-shell composite particles. Possible mechanisms of the Pickering emulsion polymerization were also explored. The silica nanoparticles were thermodynamically favorable to self-assemble at liquid-liquid interfaces at the initial stage of polymerization and remained at the interface to finally form the shells of the composite particles. More importantly, Pickering emulsion polymerization was employed to synthesize polystyrene/poly(N-isopropylacrylamide) (PNIPAAm)-silica core-shell nanoparticles with N-isopropylacrylamide incorporated into the core as a co-monomer. The composite nanoparticles were temperature sensitive and could be up-taken by human prostate cancer cells and demonstrated effectiveness in drug delivery and cancer therapy. Similarly, by incorporating poly-2-(N,N)-dimethylamino)ethyl methacrylate (PDMA) into the core, pH sensitive core-shell composite nanoparticles were synthesized and applied as effective carriers to release a rheological modifier upon a pH change. Finally, the research focuses on facile approaches to engineer the transition of the temperature-sensitive particles and develop composite core-shell nanoparticles with a metallic shell.

  3. Noble metal aerogels-synthesis, characterization, and application as electrocatalysts.

    PubMed

    Liu, Wei; Herrmann, Anne-Kristin; Bigall, Nadja C; Rodriguez, Paramaconi; Wen, Dan; Oezaslan, Mehtap; Schmidt, Thomas J; Gaponik, Nikolai; Eychmüller, Alexander

    2015-02-17

    CONSPECTUS: Metallic and catalytically active materials with high surface area and large porosity are a long-desired goal in both industry and academia. In this Account, we summarize the strategies for making a variety of self-supported noble metal aerogels consisting of extended metal backbone nanonetworks. We discuss their outstanding physical and chemical properties, including their three-dimensional network structure, the simple control over their composition, their large specific surface area, and their hierarchical porosity. Additionally, we show some initial results on their excellent performance as electrocatalysts combining both high catalytic activity and high durability for fuel cell reactions such as ethanol oxidation and the oxygen reduction reaction (ORR). Finally, we give some hints on the future challenges in the research area of metal aerogels. We believe that metal aerogels are a new, promising class of electrocatalysts for polymer electrolyte fuel cells (PEFCs) and will also open great opportunities for other electrochemical energy systems, catalysis, and sensors. The commercialization of PEFCs encounters three critical obstacles, viz., high cost, insufficient activity, and inadequate long-term durability. Besides others, the sluggish kinetics of the ORR and alcohol oxidation and insufficient catalyst stability are important reasons for these obstacles. Various approaches have been taken to overcome these obstacles, e.g., by controlling the catalyst particle size in an optimized range, forming multimetallic catalysts, controlling the surface compositions, shaping the catalysts into nanocrystals, and designing supportless catalysts with extended surfaces such as nanostructured thin films, nanotubes, and porous nanostructures. These efforts have produced plenty of excellent electrocatalysts, but the development of multisynergetic functional catalysts exhibiting low cost, high activity, and high durability still faces great challenges. In this Account, we demonstrate that the sol-gel process represents a powerful "bottom-up" strategy for creating nanostructured materials that tackles the problems mentioned above. Aerogels are unique solid materials with ultralow densities, large open pores, and ultimately high inner surface areas. They magnify the specific properties of nanomaterials to the macroscale via self-assembly, which endow them with superior properties. Despite numerous investigations of metal oxide aerogels, the investigation of metal aerogels is in the early stage. Recently, aerogels including Fe, Co, Ni, Sn, and Cu have been obtained by nanosmelting of hybrid polymer-metal oxide aerogels. We report here exclusively on mono-, bi- and multimetallic noble metal aerogels consisting of Ag, Au, Pt, and Pd and their application as electrocatalysts. PMID:25611348

  4. Synthesis, characterization and application of zinc oxide nanomaterials

    NASA Astrophysics Data System (ADS)

    Mai, Wenjie

    2009-08-01

    In this thesis, high temperature vapor deposition method has been extensively used to synthesize nanomaterials. One of the as-synthesized nanostructures is superlattice-structured nanohelix, which is made of two types of alternating and periodically distributed long crystal strips. The manipulation of the nanohelix showed super-elasticity and special fracture mechanism, suggesting possible applications in micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS). The other widely studied nanomaterial is vertically aligned ZnO nanowire array, which is epitaxially grown on GaN and SiC substrates. Several manipulation methods such as e-beam lithography (EBL), dielectrophoresis, and in situ direct manipulation, have been developed, so that the mechanical and electrical properties of a single nanowire can be characterized, which provide essential references for fabricating bridged nanowire based MEMS/NEMS devices. Specifically, an improved atomic force microscope (AFM) based method has been developed to accurately measure the elastic modulus of bridged ZnO nanowires. Bridged nanostructure is an extremely important configuration in planar MEMS/NEMS devices and this new approach provides insights to the importance of boundary conditions. Novel physical and statistical models have been firstly developed to obtain better estimate of elastic modulus. For electrical properties of bridged nanowires, it is found that the direct contact of ZnO nanowire and Au electrodes displays a back-to-back Schottky behavior. Self-assembled monolayer (SAM) can improve the mechanical contact and tune the work function of metal electrode to a small extend, thus increase the contact area and lower the barrier height, in turn increase the conductance. These devices with Schottky contacts show much better UV sensing performance than the ones with Ohmic contacts. Barrier height change is believed to play an important role in a lot of sensors. A thermionic emission-diffusion model is deduced to successfully explain the current change in a strain sensor. This thesis clearly exhibits the unique properties of ZnO nanomaterials and provides deeper understanding to methodologies as well as the phenomena. With further exploration, ZnO nanomaterials should be able to better understood and utilized, and come close to the next step of commercialization.

  5. Enantioselectivity in tebuconazole and myclobutanil non-target toxicity and degradation in soils.

    PubMed

    Li, Yuanbo; Dong, Fengshou; Liu, Xingang; Xu, Jun; Han, Yongtao; Zheng, Yongquan

    2015-03-01

    Tebuconazole and myclobutanil are two widely used triazole fungicides, both comprising two enantiomers with different fungicidal activity. However, their non-target toxicity and environmental behavior with respect to enantioselectivity have received limited attention. In the present study, tebuconazole and myclobutanil enantiomers were isolated and used to evaluate the occurrence of enantioselectivity in their acute toxicity to three non-target organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Significant differences were found: R-(-)-tebuconazole was about 1.4-5.9 times more toxic than S-(+)-tebuconazole; rac-myclobutanil was about 1.3-6.1 and 1.4-7.3 more toxic than (-)-myclobutanil and (+)-myclobutanil, respectively. Enantioselectivity was further investigated in terms of fungicide degradation in seven soil samples, which were selected to cover a broad range of soil properties. In aerobic or anaerobic soils, the S-(+)-tebuconazole degraded faster than R-(-)-tebuconazole, and the enantioselectivity showed a correlation with soil organic carbon content. (+)-Myclobutanil was preferentially degraded than (-)-myclobutanil in aerobic soils, whereas both enantiomers degraded at similar rates in anaerobic soils. Apparent correlations of enantioselectivity with soil pH and soil texture were observed for myclobutanil under aerobic conditions. In addition, both fungicides were configurationally stable in soils, i.e., no enantiomerization was found. Enantioselectivity may be a common phenomenon in both aquatic toxicity and biodegradation of chiral triazole fungicides, and this should be considered when assessing ecotoxicological risks of these compounds in the environment. PMID:25475972

  6. Synthesis of acid-labile diplasmenyl lipids for drug and gene delivery applications.

    PubMed

    Boomer, J A; Thompson, D H

    1999-06-01

    The low pH environments characteristic of endosomal compartments and ischemic tissues provide an intrinsic pathway for triggering site-specific contents release from appropriately designed delivery vehicles. Accordingly, research in this group has focused on the design, synthesis and application of novel acid-sensitive lipids that will undergo facile lamellar (L alpha) to hexagonal (HII) phase transitions within these acidic sites. Previously, it has been demonstrated that plasmenylcholine-type lipids have excellent acid hydrolysis and contents release kinetics (Gerasimov et al., Biochim. Biophys. Acta. 1324 (1997) 200-214; Rui et al., J. Am. Chem. Soc. 120 (1998) 11213-11218). This paper describes the synthesis of three new acid sensitive lipids, based on a chiral 1,2-di-O-(1Z',9Z'-octadecadienyl)-sn-glycerol (6) platform, displaying phosphocholine (7), poly(ethyleneoxide) (8), and O-carbamoyl-N-diethylen-etriamine (10) headgroups. Intermediate 6 was obtained in 28% overall yield via a six step synthesis from (S)-(+)-2,2-dimethyl-1,2-dioxolane-4-methanol. Subsequent conversion to the final products was acheived in moderate (7 and 10) to excellent yields (8). PMID:10390837

  7. Image Based Hair Segmentation Algorithm for the Application of Automatic Facial Caricature Synthesis

    PubMed Central

    Peng, Zhenyun; Zhang, Yaohui

    2014-01-01

    Hair is a salient feature in human face region and are one of the important cues for face analysis. Accurate detection and presentation of hair region is one of the key components for automatic synthesis of human facial caricature. In this paper, an automatic hair detection algorithm for the application of automatic synthesis of facial caricature based on a single image is proposed. Firstly, hair regions in training images are labeled manually and then the hair position prior distributions and hair color likelihood distribution function are estimated from these labels efficiently. Secondly, the energy function of the test image is constructed according to the estimated prior distributions of hair location and hair color likelihood. This energy function is further optimized according to graph cuts technique and initial hair region is obtained. Finally, K-means algorithm and image postprocessing techniques are applied to the initial hair region so that the final hair region can be segmented precisely. Experimental results show that the average processing time for each image is about 280?ms and the average hair region detection accuracy is above 90%. The proposed algorithm is applied to a facial caricature synthesis system. Experiments proved that with our proposed hair segmentation algorithm the facial caricatures are vivid and satisfying. PMID:24592182

  8. Formal Synthesis of (+)-Brefeldin A: Application of a Zinc-mediated Ring Expansion Reaction

    PubMed Central

    Lin, Weimin; Zercher, Charles K.

    2008-01-01

    An efficient formal synthesis of (+)-brefeldin A was accomplished through a synthetic approach that relied upon three keys steps. The five-membered ring was generated in a stereocontrolled fashion through application of a tandem conjugate addition-intramolecular cyclization method developed by Toru. Ring-closing metathesis provided access to a twelve-membered ?-keto lactone, which was ring-expanded to the ?,?-unsaturated-?-keto lactone through a zinc carbenoid-mediated reaction. Conversion of this lactone to (+)-brefeldin A has been reported previously. PMID:17497923

  9. Facile Synthesis of Chevrel Phase Nanocubes and their Applications for Multivalent Energy Storage

    SciTech Connect

    Cheng, Yingwen; Parent, Lucas R.; Shao, Yuyan; Wang, Chong M.; Sprenkle, Vincent L.; Li, Guosheng; Liu, Jun

    2014-08-14

    The Chevrel phases (CPs, MxMo6T8, M=metal, T=S or Se) are capable of rapid and reversible intercalation of multivalent ions and are the most practical cathode materials for rechargeable magnesium batteries. For the first time, we report a facile method for synthesizing Mo6S8 nanoparticles and demonstrate that these nanoparticles have significantly better Mg2+ intercalation kinetics compared with microparticles. The results described in this work could inspire the synthesis of nanoscale CPs, which could substantially impact their application.

  10. Enantioselective Copper-Catalyzed Construction of Aryl Pyrroloindolines via an Arylation-Cyclization Cascade

    E-print Network

    MacMillan, David W. C.

    amphibians, plants, and marine algae.1 An important structural subclass, the C(3)-aryl pyrroloindoline unit applicable to natural product and medicinal agent synthesis. Our design plan is outlined in Scheme 1. We

  11. Microwave-assisted synthesis of II-VI semiconductor micro-and nanoparticles towards sensor applications

    NASA Astrophysics Data System (ADS)

    Majithia, Ravish Yogesh

    Engineering particles at the nanoscale demands a high degree of control over process parameters during synthesis. For nanocrystal synthesis, solution-based techniques typically include application of external convective heat. This process often leads to slow heating and allows decomposition of reagents or products over time. Microwave-assisted heating provides faster, localized heating at the molecular level with near instantaneous control over reaction parameters. In this work, microwave-assisted heating has been applied for the synthesis of II-VI semiconductor nanocrystals namely, ZnO nanopods and CdX (X = Se, Te) quantum dots (QDs). Based on factors such as size, surface functionality and charge, optical properties of such nanomaterials can be tuned for application as sensors. ZnO is a direct bandgap semiconductor (3.37 eV) with a large exciton binding energy (60 meV) leading to photoluminescence (PL) at room temperature. A microwave-assisted hydrothermal approach allows the use of sub-5 nm ZnO zero-dimensional nanoparticles as seeds for generation of multi-legged quasi one-dimensional nanopods via heterogeneous nucleation. ZnO nanopods, having individual leg diameters of 13-15 nm and growing along the [0001] direction, can be synthesized in as little as 20 minutes. ZnO nanopods exhibit a broad defect-related PL spanning the visible range with a peak at ~615 nm. Optical sensing based on changes in intensity of the defect PL in response to external environment (e.g., humidity) is demonstrated in this work. Microwave-assisted synthesis was also used for organometallic synthesis of CdX(ZnS) (X = Se, Te) core(shell) QDs. Optical emission of these QDs can be altered based on their size and can be tailored to specific wavelengths. Further, QDs were incorporated in Enhanced Green-Fluorescent Protein -- Ultrabithorax (EGFP-Ubx) fusion protein for the generation of macroscale composite protein fibers via hierarchal self-assembly. Variations in EGFP- Ubx?QD composite fiber surface morphology and internal QD distribution were studied with respect to (i) time of QD addition (i.e., pre or post protein self-assembly) and (ii) QD surface charge---negatively charged QDs with dihydrolipoic acid functionalization and positively charged QDs with polyethyleneimine coating. Elucidating design motifs and understanding factors that impact the protein-nanoparticle interaction enables manipulation of the structure and mechanical properties of composite materials.

  12. Total synthesis of (+)-lysergic acid.

    PubMed

    Liu, Qiang; Zhang, Yu-An; Xu, Ping; Jia, Yanxing

    2013-11-01

    We report the enantioselective total synthesis of (+)-lysergic acid using two different strategies, which featured three metal-catalyzed reactions for the construction of the BCD three rings, involving Pd-catalyzed indole synthesis for the construction of the B ring, a ring-closing metathesis reaction for the formation of the D ring, and an intramolecular Heck reaction to forge the C ring. In synthetic strategy I, the synthesis was achieved in 20 steps following the ring construction sequence of BDC. In synthetic strategy II, the synthetic route was shortened to only 12 steps by following the ring construction sequence of DBC and using a 4-chlorotryptophan derivative for the intramolecular Heck reaction. Moreover, we also discussed an unsuccessful synthetic strategy. PMID:24111583

  13. One-pot organocatalytic domino Michael/alpha-alkylation reactions: direct catalytic enantioselective cyclopropanation and cyclopentanation reactions.

    PubMed

    Ibrahem, Ismail; Zhao, Gui-Ling; Rios, Ramon; Vesely, Jan; Sundén, Henrik; Dziedzic, Pawel; Córdova, Armando

    2008-01-01

    The development of one-pot organocatalytic domino Michael/alpha-alkylation reactions between bromomalonates or bromoacetoacetate esters and alpha,beta-unsaturated aldehydes is presented. The chiral-amine-catalyzed reactions with bromomalonates as substrates give access to the corresponding 2-formylcyclopropane derivatives in high yields with excellent diastereoselectivity and up to 99 % ee. The catalytic domino Michael/alpha-alkylation reactions between 4-bromo-acetoacetate and enals provide a route for the synthesis of functionalized cyclopentanones in good to high yields with 93-99 % ee. The products from the organocatalytic reactions were also reduced with high diastereoselectivity to the corresponding cyclopropanols and cyclopentanols, respectively. Moreover, one-pot combinations of amine and heterocyclic carbene catalysis (AHCC) enabled the highly enantioselective synthesis of beta-malonate esters (91-97 % ee) from the reaction between bromomalonates and enals. The tandem catalysis included the catalytic domino reaction followed by catalytic in situ chemoselective ring-opening of the 2-formylcyclopropane intermediates. PMID:18618876

  14. Enantioselective recognition of phenylalanine by a chiral amphiphilic macrocycle at the air-water interface: a copper-mediated mechanism.

    PubMed

    Shahgaldian, Patrick; Pieles, Uwe; Hegner, Martin

    2005-07-01

    The synthesis of a new chiral amphiphilic calix[4]resorcinarene, tetrakis(N-methylprolyl)tetraundecylcalix[4]resorcinarene (L-RA-Pro), bearing four L-prolyl moieties at the macrocyclic upper rim and four undecyl chains at the lower rim is described. This synthesis has been carried out via a Mannich-type reaction of L-proline and formaldehyde. It has been shown by means of Langmuir balance technique that L-RA-Pro self-assemble as well-defined monomolecular layers at the air-water interface. The effect of various cations on the stability of these monolayers has been studied. The experiments reveal that while there is a slight stabilization effect of K+, Cd2+, Co2+, Mg2+, and Ni2+, there is a high decrease in the collapse pressure in the presence of Cu(II) cation, showing that monolayers of L-RA-Pro, formed at the air-water interface, have a certain selectivity for copper(II) ions with regard to other cations tested. This supramolecular complex exhibits enantioselective recognition properties vs phenylalanine; the mechanism of this interaction is discussed. PMID:15982059

  15. Gold(I)/chiral Brønsted acid catalyzed enantioselective hydroamination-hydroarylation of alkynes: the effect of a remote hydroxyl group on the reactivity and enantioselectivity.

    PubMed

    Shinde, Valmik S; Mane, Manoj V; Vanka, Kumar; Mallick, Arijit; Patil, Nitin T

    2015-01-12

    The catalytic enantioselective hydroamination-hydroarylation of alkynes under the catalysis of (R3P)AuMe/(S)-3,3'-bis(2,4,6-triisopropylphenyl)-1,1'-binaphthyl-2,2'-diyl hydrogenphosphate ((S)-TRIP) is reported. The alkyne was reacted with a range of pyrrole-based aromatic amines to give pyrrole-embedded aza-heterocyclic scaffolds bearing a quaternary carbon center. The presence of a hydroxyl group in the alkyne tether turned out to be very crucial for obtaining products in high yields and enantioselectivities. The mechanism of enantioinduction was established by carefully performing experimental and computational studies. PMID:25421270

  16. Photomechanical actuation of ligand geometry in enantioselective catalysis.

    PubMed

    Kean, Zachary S; Akbulatov, Sergey; Tian, Yancong; Widenhoefer, Ross A; Boulatov, Roman; Craig, Stephen L

    2014-12-22

    A catalyst that couples a photoswitch to the biaryl backbone of a chiral bis(phosphine) ligand, thus allowing photochemical manipulation of ligand geometry without perturbing the electronic structure is reported. The changes in catalyst activity and selectivity upon switching can be attributed to intramolecular mechanical forces, thus laying the foundation for a new class of catalysts whose selectivity can be varied smoothly and in situ over a useful range by controlling molecular stress experienced by the catalyst during turnover. Forces on the order of 100?pN are generated, thus leading to measurable changes in the enantioselectivities of asymmetric Heck arylations and Trost allylic alkylations. The differential coupling between applied force and competing stereochemical pathways is quantified and found to be more efficient for the Heck arylations. PMID:25359436

  17. Intrinsic enantioselectivity of natural polynucleotides modulated by copper ions.

    PubMed

    Fu, Yan; Chen, Xiongfei; Zhang, Jinli; Li, Wei

    2015-04-01

    Natural polynucleotides including Micrococcus lysodeikticus and calf thymus DNA exhibit enantioselective recognition to S-ofloxacin regulated by Cu(2+). This is the first report that ofloxacin and Cu(2+) have cooperative effects on the local distortions of polynucleotides. At the [Cu(2+)]/[base] ratio of 0.1, S-ofloxacin is more liable to induce the locally distorted structures of polynucleotides, of which the association constant of S-ofloxacin toward DNA-Cu(II) is three times higher than that of the R-enantiomer. The apparent increase of adsorption capability and cooperativity, as well as the change of adsorption mechanism were detected in the adsorption of ofloxacin enantiomers on polynucleotides upon Cu(II)-coordination. This study not only discloses the effect of the chiral drug on the structural transition of long double-stranded DNA, but provides fundamental data to develop a novel enantioseparation method based on natural polynucleotides. PMID:25665144

  18. Solution Synthesis and Processing of PZT Materials for Neutron Generator Applications

    SciTech Connect

    Anderson, M.A.; Ewsuk, K.G.; Montoya, T.V.; Moore, R.H.; Sipola, D.L.; Tuttle, B.A.; Voigt, J.A.

    1998-12-01

    A new solution synthesis route has been developed for the preparation of lead-based ferroelectric materials (patent filed). The process produces controlled stoichiometry precursor powders by non-aqueous precipitation. For a given ferroelectric material to be prepared, a metal acetate/alkoxide solution containing constituent metal species in the appropriate ratio is mixed with an oxalic acid/n-propanol precipitant solution. An oxalate coprecipitate is instantly fonned upon mixing that quantitatively removes the metals from solution. Most of the process development was focused on the synthesis and processing of niobium-substituted lead zirconate titanate with a Zr-to-Ti ratio of 95:5 (PNZT 95/5) that has an application in neutron generator power supplies. The process was scaled to produce 1.6 kg of the PNZT 95/5 powder using either a sen-ii-batch or a continuous precipitation scheme. Several of the PNZT 95/5 powder lots were processed into ceramic slug form. The slugs in turn were processed into components and characterized. The physical properties and electrical performance (including explosive functional testing of the components met the requirements set for the neutron generator application. Also, it has been demonstrated that the process is highly reproducible with respect to the properties of the powders it produces and the properties of the ceramics prepared from its powders. The work described in this report was funded by Sandia's Laboratory Directed Research and Development Program.

  19. Composite Sensor Particles for Tuned SERS Sensing: Microfluidic Synthesis, Properties and Applications.

    PubMed

    Visaveliya, Nikunjkumar; Lenke, Steffen; Köhler, J Michael

    2015-05-27

    Surface-enhanced Raman scattering (SERS) is a promising platform for particle-based sensor signaling, and droplet-based microfluidic systems are particularly advantageous for control of the size and composition of micro- and nanoparticles. For controlled sensing application, a high homogeneity of the sensor particles is a key requirement, and the particles with functional properties demand for the preparation in a minimum number of synthesis steps. Frequently used coflow and flow focusing arrangements, however, produce the microparticles of only larger size. To address such concern for downscaling of particle size, which is crucial for strong sensing outcome, we have used a peculiar micro cross-flow arrangement here for generating the polymer microparticles of broad size range between 30 and 600 ?m along with in situ embedded silver nanoparticles. Embedded silver acts as nuclei for additional silver enforcement via silver-catalyzed silver deposition in order to realize the composite microparticles for SERS sensing. The homogeneous size and spatial distribution of silver nanoparticles inside the matrix and enforcement over the surface together with controlled pore size provides a high and homogeneous loading of polymer composite sensor. Moreover, different parameters such as analytes concentration and particles size have been studied here for SERS sensing application of biochemical molecules (amino acids and vitamins). Overall, the platform for size-tuned droplets generation, synthesis of composite microparticles, mechanism for synchronized photopolymerization-photoreduction, tuned silver enforcement, and the impacts of different analytes on differently composed microparticles are systematically investigated in this paper. PMID:25939496

  20. Graphene hybrids: synthesis strategies and applications in sensors and sensitized solar cells

    PubMed Central

    Badhulika, Sushmee; Terse-Thakoor, Trupti; Villarreal, Claudia; Mulchandani, Ashok

    2015-01-01

    Graphene exhibits unique 2-D structural, chemical, and electronic properties that lead to its many potential applications. In order to expand the scope of its usage, graphene hybrids which combine the synergetic properties of graphene along with metals/metal oxides and other nanostructured materials have been synthesized and are a widely emerging field of research. This review presents an overview of the recent progress made in the field of graphene hybrid architectures with a focus on the synthesis of graphene-carbon nanotube (G-CNT), graphene-semiconductor nanomaterial (G-SNM), and graphene-metal nanomaterial (G-MNM) hybrids. It attempts to identify the bottlenecks involved and outlines future directions for development and comprehensively summarizes their applications in the field of sensing and sensitized solar cells. PMID:26176007