Biofunctionalization on alkylated silicon substrate surfaces via "click" chemistry.

PubMed

Qin, Guoting; Santos, Catherine; Zhang, Wen; Li, Yan; Kumar, Amit; Erasquin, Uriel J; Liu, Kai; Muradov, Pavel; Trautner, Barbara Wells; Cai, Chengzhi

2010-11-24

Biofunctionalization of silicon substrates is important to the development of silicon-based biosensors and devices. Compared to conventional organosiloxane films on silicon oxide intermediate layers, organic monolayers directly bound to the nonoxidized silicon substrates via Si-C bonds enhance the sensitivity of detection and the stability against hydrolytic cleavage. Such monolayers presenting a high density of terminal alkynyl groups for bioconjugation via copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC, a "click" reaction) were reported. However, yields of the CuAAC reactions on these monolayer platforms were low. Also, the nonspecific adsorption of proteins on the resultant surfaces remained a major obstacle for many potential biological applications. Herein, we report a new type of "clickable" monolayers grown by selective, photoactivated surface hydrosilylation of α,ω-alkenynes, where the alkynyl terminal is protected with a trimethylgermanyl (TMG) group, on hydrogen-terminated silicon substrates. The TMG groups on the film are readily removed in aqueous solutions in the presence of Cu(I). Significantly, the degermanylation and the subsequent CuAAC reaction with various azides could be combined into a single step in good yields. Thus, oligo(ethylene glycol) (OEG) with an azido tag was attached to the TMG-alkyne surfaces, leading to OEG-terminated surfaces that reduced the nonspecific adsorption of protein (fibrinogen) by >98%. The CuAAC reaction could be performed in microarray format to generate arrays of mannose and biotin with varied densities on the protein-resistant OEG background. We also demonstrated that the monolayer platform could be functionalized with mannose for highly specific capturing of living targets (Escherichia coli expressing fimbriae) onto the silicon substrates.

Oxorhenium Complexes for Catalytic Hydrosilylation and Hydrolytic Hydrogen Production: A Multiweek Advanced Laboratory Experiment for Undergraduate Students

ERIC Educational Resources Information Center

Ison, A.; Ison, E. A.; Perry, C. M.

2017-01-01

An effective way of teaching undergraduates a full complement of research skills is through a multiweek advanced laboratory experiment. Here we outline a comprehensive set of experiments adapted from current primary literature focusing on organic and inorganic synthesis, catalysis, reactivity, and reaction kinetics. The catalyst,…

The Compatibility of Hepatocytes with Chemically Modified Porous Silicon with Reference to In Vitro Biosensors

PubMed Central

Alvarez, Sara D.; Derfus, Austin M.; Schwartz, Michael P.; Bhatia, Sangeeta N.; Sailor, Michael J.

2008-01-01

Porous Si is a nanostructured material that is of interest for molecular and cell-based biosensing, drug delivery, and tissue engineering applications. Surface chemistry is an important factor determining the stability of porous Si in aqueous media, its affinity for various biomolecular species, and its compatibility with tissues. In this study, the attachment and viability of a primary cell type to porous Si samples containing various surface chemistries is reported, and the ability of the porous Si films to retain their optical reflectivity properties relevant to molecular biosensing is assessed. Four chemical species grafted to the porous Si surface are studied: silicon oxide (via ozone oxidation), dodecyl (via hydrosilylation with dodecene), undecanoic acid (via hydrosilylation with undecylenic acid), and oligo(ethylene) glycol (via hydrosilylation with undecylenic acid followed by an oligo(ethylene) glycol coupling reaction). Fourier Transform Infrared (FTIR) spectroscopy and contact angle measurements are used to characterize the surface. Adhesion and short-term viability of primary rat hepatocytes on these surfaces, with and without pre-adsorption of collagen type I, are assessed using vital dyes (calcein-AM and ethidium homodimer I). Cell viability on undecanoic acid-terminated porous Si, oxide-terminated porous Si, and oxide-terminated flat (non-porous) Si are monitored by quantification of albumin production over the course of 8 days. The stability of porous Si thin films after 8 days in cell culture is probed by measuring the optical interferometric reflectance spectra. Results show that hepatocytes adhere better to surfaces coated with collagen, and that chemical modification does not exert a deleterious effect on primary rat hepatocytes. The hydrosilylation chemistry greatly improves the stability of porous Si in contact with cultured primary cells while allowing cell coverage levels comparable to standard culture preparations on tissue culture polystyrene. PMID:18845334

Thermal and UV Hydrosilylation of Alcohol-Based Bifunctional Alkynes on Si (111) surfaces: How surface radicals influence surface bond formation.

PubMed

Khung, Y L; Ngalim, S H; Scaccabarozi, A; Narducci, D

2015-06-12

Using two different hydrosilylation methods, low temperature thermal and UV initiation, silicon (111) hydrogenated surfaces were functionalized in presence of an OH-terminated alkyne, a CF3-terminated alkyne and a mixed equimolar ratio of the two alkynes. XPS studies revealed that in the absence of premeditated surface radical through low temperature hydrosilylation, the surface grafting proceeded to form a Si-O-C linkage via nucleophilic reaction through the OH group of the alkyne. This led to a small increase in surface roughness as well as an increase in hydrophobicity and this effect was attributed to the surficial etching of silicon to form nanosize pores (~1-3 nm) by residual water/oxygen as a result of changes to surface polarity from the grafting. Furthermore in the radical-free thermal environment, a mix in equimolar of these two short alkynes can achieve a high contact angle of ~102°, comparable to long alkyl chains grafting reported in literature although surface roughness was relatively mild (rms = ~1 nm). On the other hand, UV initiation on silicon totally reversed the chemical linkages to predominantly Si-C without further compromising the surface roughness, highlighting the importance of surface radicals determining the reactivity of the silicon surface to the selected alkynes.

Thermal and UV Hydrosilylation of Alcohol-Based Bifunctional Alkynes on Si (111) surfaces: How surface radicals influence surface bond formation

PubMed Central

Khung, Y. L.; Ngalim, S. H.; Scaccabarozi, A.; Narducci, D.

2015-01-01

Using two different hydrosilylation methods, low temperature thermal and UV initiation, silicon (111) hydrogenated surfaces were functionalized in presence of an OH-terminated alkyne, a CF3-terminated alkyne and a mixed equimolar ratio of the two alkynes. XPS studies revealed that in the absence of premeditated surface radical through low temperature hydrosilylation, the surface grafting proceeded to form a Si-O-C linkage via nucleophilic reaction through the OH group of the alkyne. This led to a small increase in surface roughness as well as an increase in hydrophobicity and this effect was attributed to the surficial etching of silicon to form nanosize pores (~1–3 nm) by residual water/oxygen as a result of changes to surface polarity from the grafting. Furthermore in the radical-free thermal environment, a mix in equimolar of these two short alkynes can achieve a high contact angle of ~102°, comparable to long alkyl chains grafting reported in literature although surface roughness was relatively mild (rms = ~1 nm). On the other hand, UV initiation on silicon totally reversed the chemical linkages to predominantly Si-C without further compromising the surface roughness, highlighting the importance of surface radicals determining the reactivity of the silicon surface to the selected alkynes. PMID:26067470

Hydrosilylated Porous Silicon Particles Function as an Intravitreal Drug Delivery System for Daunorubicin

PubMed Central

Hartmann, Kathrin I.; Nieto, Alejandra; Wu, Elizabeth C.; Freeman, William R.; Kim, Jae Suk; Chhablani, Jay; Sailor, Michael J.

2013-01-01

Abstract Purpose To evaluate in vivo ocular safety of an intravitreal hydrosilylated porous silicon (pSi) drug delivery system along with the payload of daunorubicin (DNR). Methods pSi microparticles were prepared from the electrochemical etching of highly doped, p-type Si wafers and an organic linker was attached to the Si-H terminated inner surface of the particles by thermal hydrosilylation of undecylenic acid. DNR was bound to the carboxy terminus of the linker as a drug-loading strategy. DNR release from hydrosilylated pSi particles was confirmed in the excised rabbit vitreous using liquid chromatography–electrospray ionization–multistage mass spectrometry. Both empty and DNR-loaded hydrosilylated pSi particles were injected into the rabbit vitreous and the degradation and safety were studied for 6 months. Results The mean pSi particle size was 30×46×15 μm with an average pore size of 15 nm. Drug loading was determined as 22 μg per 1 mg of pSi particles. An ex vivo drug release study showed that intact DNR was detected in the rabbit vitreous. An in vivo ocular toxicity study did not reveal clinical or pathological evidence of any toxicity during a 6-month observation. Hydrosilylated pSi particles, either empty or loaded with DNR, demonstrated a slow elimination kinetics from the rabbit vitreous without ocular toxicity. Conclusions Hydrosilylated pSi particles can host a large quantity of DNR by a covalent loading strategy and DNR can be slowly released into the vitreous without ocular toxicity, which would appear if an equivalent quantity of free drug was injected. PMID:23448595

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawano, Takahiro; Lin, Zekai; Boures, Dean

Mono(phosphine)–M (M–PR3; M = Rh and Ir) complexes selectively prepared by postsynthetic metalation of a porous triarylphosphine-based metal–organic framework (MOF) exhibited excellent activity in the hydrosilylation of ketones and alkenes, the hydrogenation of alkenes, and the C–H borylation of arenes. The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M–PR3 intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles.

First-row transition metal hydrogenation and hydrosilylation catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trovitch, Ryan J.; Mukhopadhyay, Tufan K.; Pal, Raja

Transition metal compounds, and specifically transition metal compounds having a tetradentate and/or pentadentate supporting ligand are described, together with methods for the preparation thereof and the use of such compounds as hydrogenation and/or hydrosilylation catalysts.

Enantioselective ProPhenol-catalyzed addition of 1,3-diynes to aldehydes to generate synthetically versatile building blocks and diyne natural products.

PubMed

Trost, Barry M; Chan, Vincent S; Yamamoto, Daisuke

2010-04-14

A highly enantioselective method for the catalytic addition of terminal 1,3-diynes to aldehydes was developed using our dinuclear zinc ProPhenol (1) system. Furthermore, triphenylphosphine oxide was found to interact synergistically with the catalyst to substantially enhance the chiral recognition. The generality of this catalytic transformation was demonstrated with aryl, alpha,beta-unsaturated and saturated aldehydes, of which the latter were previously limited in alkynyl zinc additions. The chiral diynol products are also versatile building blocks that can be readily elaborated; this was illustrated through highly selective trans-hydrosilylations, which enabled the synthesis of a beta-hydroxyketone and enyne. Additionally, the development of this method allowed for the rapid total syntheses of several biologically important diynol-containing natural products.

Highly versatile heteroditopic ligand scaffolds for accommodating group 8, 9 & 11 heterobimetallic complexes.

PubMed

Gatus, Mark R D; Bhadbhade, Mohan; Messerle, Barbara A

2017-10-24

Two highly versatile xanthene scaffolds containing pairs of heteroditopic ligands were found to be capable of accommodating a range of transition metal ions, including Au(i), Ir(i), Ir(iii), Rh(i), and Ru(ii) to generate an array of heterobimetallic complexes. The metal complexes were fully characterised and proved to be stable in the solid and solution state, with no observed metal-metal scrambling. Heterobimetallic complexes containing the Rh(i)/Ir(i) combinations were tested as catalysts for the two-step dihydroalkoxylation reaction of alkynediols and sequential hydroamination/hydrosilylation reaction of alkynamines.

Hydridosilylamido complexes of Ta and Mo isolobal with Berry's zirconocenes: syntheses, β-Si-H agostic interactions, catalytic hydrosilylation, and insight into mechanism.

PubMed

McLeod, Nicolas A; Kuzmina, Lyudmila G; Korobkov, Ilia; Howard, Judith A K; Nikonov, Georgii I

2016-02-14

The syntheses of novel Group 5 and Group 6 hydrosilylamido complexes of the type R(ArN[double bond, length as m-dash])M{N((t)Bu)SiMe2-H}X (M = Ta, R = Cp; M = Mo, R = ArN; X = Cl, H, OBn, Me) are described. The various substituents in the X position seem to play the key role in determining the extent of β-agostic interaction with the Si-H bond. The Mo agostic hydrido complex (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H is a pre-catalyst for the hydrosilylation of carbonyls. The stoichiometric reaction between benzaldehyde and (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H gives the benzoxy complex (ArN[double bond, length as m-dash])2Mo{N((t)Bu)SiMe2-H}(OBn), which showed a similar catalytic reactivity compared to the parent hydride. Mechanistic studies suggest that a non-hydride mechanism is operative.

Synthesis of polymer networks containing degradable polyacetal segments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goethals, E.J.; Trossaert, G.G.; Hartmann, P.J.

1993-12-31

In recent years, intensive research has been done in order to prepare different types of degradable polyacetal containing networks. In the present presentation four different routes for the production of polyacetal containing networks are described: (1) free radical copolymerization of {alpha},{omega}-(meth)acrylate terminated polyacetals (2) hydrosilylation reactions of {alpha},{omega}-allyl terminated poly-(1,3-dioxolane) with a multifunctional silane (3) modification of {alpha}{omega}-hydroxy terminated poly-(1,3-dioxepane) through reaction with 3-isocyanato propyl triethoxysilane and subsequent cross-linking under influence of H{sub 2}O and (4) synthesis of multifunctional hydroxy-terminated polyacetals, followed by cross-linking with di-isocyanates.

Chiral ligands derived from monoterpenes: application in the synthesis of optically pure secondary alcohols via asymmetric catalysis.

PubMed

El Alami, Mohammed Samir Ibn; El Amrani, Mohamed Amin; Agbossou-Niedercorn, Francine; Suisse, Isabelle; Mortreux, André

2015-01-19

The preparation of optically pure secondary alcohols in the presence of catalysts based on chiral ligands derived from monoterpenes, such as pinenes, limonenes and carenes, is reviewed. A wide variety of these ligands has been synthesized and used in several catalytic reactions, including hydrogen transfer, C-C bond formation via addition of organozinc compounds to aldehydes, hydrosilylation, and oxazaborolidine reduction, leading to high activities and enantioselectivities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

“Click” Immobilization on Alkylated Silicon Substrates: Model for the Study of Surface Bound Antimicrobial Peptides

PubMed Central

Li, Yan; Santos, Catherine M.; Kumar, Amit; Zhao, Meirong; Lopez, Analette I.; Qin, Guoting; McDermott, Alison M.

2011-01-01

We describe an effective approach for the covalent immobilization of antimicrobial peptides (AMPs) to bioinert substrates via CuI-catalyzed azide–alkyne cycloaddition (CuAAC). The bioinert substrates were prepared by surface hydrosilylation of oligo-(ethylene glycol) (OEG) terminated alkenes on hydrogen-terminated silicon surfaces. To render the OEG monolayers “clickable”, mixed monolayers were prepared using OEG-alkenes with and without a terminal alkyne protected by a trimethylgermanyl (TMG) group. The mixed monolayers were characterized by X-ray photoelectron spectroscopy (XPS), elliposometry and contact angle measurement. The TMG protecting group can be readily removed to yield a free terminal alkyne by catalytic amounts of CuI in an aqueous media. This step can then be combined with the subsequent CuAAC reaction. Thus, the immobilization of an azide modified AMP (N3-IG-25) was achieved in a one-pot de-protection/coupling reaction. Varying the ratio of the two alkenes in the deposition mixture allowed for control over the density of the alkynyl groups in the mixed monolayer, and subsequently the coverage of the AMPs on the monolayer. These samples allowed for study of the dependence of antimicrobial activities on the AMP density. The results show that a relative low coverage of AMPs (~1.6×1013 molecule per cm2) is sufficient to significantly suppress the viability of Pseudomonas aeruginosa, while the surface presenting the highest density of AMPs (~2.8×1013 molecule per cm2) is still cyto-compatible. The remarkable antibacterial activity is attributed to the long and flexible linker and the site-specific “click” immobilization, which may facilitate the covalently attached peptides to interact with and disrupt the bacterial membranes. PMID:21264959

Strongly hydrogen-bond acidic polymer and methods of making and using

DOEpatents

Grate, Jay W.; Kaganove, Steven N.

2000-01-01

The present invention is a sorbent polymer with the (AB)n sequence where the fluorinated interactive A segment is fluoroalkyl-substituted bisphenol and the oligosiloxane B segment is an oligodimethylsiloxane. More specifically, the fluoroalkyl-substituted bisphenol contains two allyl groups and the oligodimethylsiloxane has terminal Si--H groups. The sorbent polymer may be used as thin films on a variety of chemical sensors, or as a component of a thin film on a chemical sensor. Crosslinked sorbent polymers are processable into stable thin films on sensor devices. Sorbent polymers are also useful in sensor arrays, in surface acoustic wave sensors, and in cladding of optical fibers. Sensor arrays provide better selectivity than single sensors and permit identification and quantification of more than one species in a mixture. The sorbent polymer is synthesized by hydrosilylation polymerization which is achieved by catalyzed heating.

Thermodynamics of Enzyme-Catalyzed Reactions Database

National Institute of Standards and Technology Data Gateway

SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

Molybdenum compounds in organic synthesis

NASA Astrophysics Data System (ADS)

Khusnutdinov, R. I.; Oshnyakova, T. M.; Dzhemilev, U. M.

2017-02-01

The review presents the first analysis and systematic discussion of data published in the last 35-40 years on the use of molybdenum compounds and complexes in organic synthesis and catalysis of various ion coordination and radical reactions. Detailed account is given of the key trends in the use of molybdenum complexes as catalysts of alkene epoxidation and oxyketonation, oxidation of sulfur, nitrogen and phosphorus compounds, hydrosilylation of 1,3-dienes, ketones and aldehydes, hydrostannylation of acetylenes and hydrogermylation of norbornadienes. Considerable attention is paid to the description of new reactions and in situ generation of highly reactive hypohalites, ROX and HOX, induced by molybdenum complexes and the use of hypohalites in oxidative transformations. Data on the application of molybdenum complexes in well-known reactions are discussed, including Kharasch and Pauson-Khand reactions, allylic alkylation of C-nucleophiles, aminocarbonylation of halo derivatives and oligomerization of cyclic dienes, trienes, alkynes and 1,3-dienes. The last Section of the review considers 'unusual' organic reactions involving molybdenum compounds and complexes. The bibliography includes 257 references.

Carbene complexes of rhodium and iridium from tripodal N-heterocyclic carbene ligands: synthesis and catalytic properties.

PubMed

Mas-Marzá, Elena; Poyatos, Macarena; Sanaú, Mercedes; Peris, Eduardo

2004-03-22

Two tripodal trisimidazolium ligand precursors have been tested in the synthesis of new N-heterocyclic carbene rhodium and iridium complexes. [Tris(3-methylbenzimidazolium-1-yl)]methane sulfate gave products with coordination of the decomposed precursor. [1,1,1-Tris(3-butylimidazolium-1-yl)methyl]ethane trichloride (TIMEH(3)(Bu)) coordinated to the metal in a chelate and bridged-chelate form, depending on the reaction conditions. The crystal structures of two of the products are described. The compounds resulting from the coordination with TIME(Bu) were tested in the catalytic hydrosilylation of terminal alkynes.

Solution-processed photodetectors from colloidal silicon nano/micro particle composite.

PubMed

Tu, Chang-Ching; Tang, Liang; Huang, Jiangdong; Voutsas, Apostolos; Lin, Lih Y

2010-10-11

We demonstrate solution-processed photodetectors composed of heavy-metal-free Si nano/micro particle composite. The colloidal Si particles are synthesized by electrochemical etching of Si wafers, followed by ultra-sonication to pulverize the porous surface. With alkyl ligand surface passivation through hydrosilylation reaction, the particles can form a stable colloidal suspension which exhibits bright photoluminescence under ultraviolet excitation and a broadband extinction spectrum due to enhanced scattering from the micro-size particles. The efficiency of the thin film photodetectors has been substantially improved by preventing oxidation of the particles during the etching process.

Synthesis of novel chiral phosphinocyrhetrenyloxazoline ligands and their application in asymmetric catalysis.

PubMed

Bolm, Carsten; Xiao, Li; Kesselgruber, Martin

2003-01-07

Several novel planar chiral phosphinocyrhetrenyloxazolines have been synthesized, and their catalytic activities have been evaluated in a variety of asymmetric catalytic reactions. Preferable effects as compared to their ferrocenyl analogues have been observed in asymmetric allylic amination and asymmetric hydrosilylation, and up to 97% ee and 72% ee were reached, respectively. The Lewis basicity of the phosphorus on the ferrocene and the cyrhetrene, which contributes to their different behavior in catalysis, has been deduced by 31P NMR spectroscopy analysis, as indicated by 1J(77Se-31P) in the corresponding phosphine selenides.

Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels-Alder Reaction of Styrene-ynes.

PubMed

Mun, Hyeon Jin; Seong, Eun Young; Ahn, Kwang-Hyun; Kang, Eun Joo

2018-02-02

The intramolecular didehydro-Diels-Alder reaction of styrene-ynes was catalyzed by Fe(II) and Fe(III) to produce various naphthalene derivatives under microwave heating conditions. Mechanistic calculations found that the Fe(II) catalyst activates the styrenyl diene in an inverse-electron-demand Diels-Alder reaction, and the consecutive dehydrogenation reaction can be promoted by either Fe(II)-catalyzed direct dehydrogenation or an Fe(III)-catalyzed rearomatization/dehydrogenation pathway.

Synthesis of 1-methyleneindenes via palladium-catalyzed tandem reactions.

PubMed

Ye, Shengqing; Gao, Ke; Zhou, Haibo; Yang, Xiaodi; Wu, Jie

2009-09-28

Palladium-catalyzed tandem reactions of 2-alkenylphenyl-acetylenes with CuCl2 or CuBr2 afforded 3-chloro- or 3-bromo-1-methyleneindenes in good yields; these compounds could be further elaborated via palladium-catalyzed coupling reactions.

A highly efficient synthesis of the FGH ring of micrandilactone A. Application of thioureas as ligands in the Co-catalyzed Pauson-Khand reaction and Pd-catalyzed carbonylative annulation.

PubMed

Tang, Yefeng; Zhang, Yandong; Dai, Mingji; Luo, Tuoping; Deng, Lujiang; Chen, Jiahua; Yang, Zhen

2005-03-03

The functionalized FGH ring system of micrandilactone A was successfully constructed in high selectivity and good yields. The key reactions in our strategy are the Co-thiourea-catalyzed stereoselective, intramolecular Pauson-Khand reaction and Pd-thiourea-catalyzed stereoselective, intramolecular annulation. [structure: see text

Representing Rate Equations for Enzyme-Catalyzed Reactions

ERIC Educational Resources Information Center

Ault, Addison

2011-01-01

Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

Synthesis of water dispersible boron core silica shell (B@SiO2) nanoparticles

NASA Astrophysics Data System (ADS)

Walton, Nathan I.; Gao, Zhe; Eygeris, Yulia; Ghandehari, Hamidreza; Zharov, Ilya

2018-04-01

Water dispersible boron nanoparticles have great potential as materials for boron neutron capture therapy of cancer and magnetic resonance imaging, if they are prepared on a large scale with uniform size and shape and hydrophilic modifiable surface. We report the first method to prepare spherical, monodisperse, water dispersible boron core silica shell nanoparticles (B@SiO2 NPs) suitable for aforementioned biomedical applications. In this method, 40 nm elemental boron nanoparticles, easily prepared by mechanical milling and carrying 10-undecenoic acid surface ligands, are hydrosilylated using triethoxysilane, followed by base-catalyzed hydrolysis of tetraethoxysilane, which forms a 10-nm silica shell around the boron core. This simple two-step process converts irregularly shaped hydrophobic boron particles into the spherically shaped uniform nanoparticles. The B@SiO2 NPs are dispersible in water and the silica shell surface can be modified with primary amines that allow for the attachment of a fluorophore and, potentially, of targeting moieties. [Figure not available: see fulltext.

New Control Over Silicone Synthesis using SiH Chemistry: The Piers-Rubinsztajn Reaction.

PubMed

Brook, Michael A

2018-06-18

There is a strong imperative to synthesize polymers with highly controlled structures and narrow property ranges. Silicone polymers do not lend themselves to this paradigm because acids or bases lead to siloxane equilibration and loss of structure. By contrast, elegant levels of control are possible when using the Piers-Rubinsztajn reaction and analogues, in which the hydrophobic, strong Lewis acid B(C 6 F 5 ) 3 activates SiH groups, permitting the synthesis of precise siloxanes under mild conditions in high yield; siloxane decomposition processes are slow under these conditions. A broad range of oxygen nucleophiles including alkoxysilanes, silanols, phenols, and aryl alkyl ethers participate in the reaction to create elastomers, foams and green composites, for example, derived from lignin. In addition, the process permits the synthesis of monofunctional dendrons that can be assembled into larger entities including highly branched silicones and dendrimers either using the Piers-Rubinsztajn process alone, or in combination with hydrosilylation or other orthogonal reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

NASA Astrophysics Data System (ADS)

Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

2016-02-01

Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis.

PubMed

Liu, Yunyun; Wan, Jie-Ping

2011-10-21

Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized.

Bipyridine- and phenanthroline-based metal-organic frameworks for highly efficient and tandem catalytic organic transformations via directed C-H activation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manna, Kuntal; Zhang, Teng; Greene, Francis X.

2015-02-16

We report here the synthesis of a series of robust and porous bipyridyl- and phenanthryl-based metal–organic frameworks (MOFs) of UiO topology (BPV-MOF, mBPV-MOF, and mPT-MOF) and their postsynthetic metalation to afford highly active single-site solid catalysts. While BPV-MOF was constructed from only bipyridyl-functionalized dicarboxylate linker, both mBPV- and mPT-MOF were built with a mixture of bipyridyl- or phenanthryl-functionalized and unfunctionalized dicarboxylate linkers. The postsynthetic metalation of these MOFs with [Ir(COD)(OMe)] 2 provided Ir-functionalized MOFs (BPV-MOF-Ir, mBPV-MOF-Ir, and mPT-MOF-Ir), which are highly active catalysts for tandem hydrosilylation of aryl ketones and aldehydes followed by dehydrogenative ortho-silylation of benzylicsilyl ethers as wellmore » as C–H borylation of arenes using B₂pin₂. Both mBPV-MOF-Ir and mPT-MOF-Ir catalysts displayed superior activities compared to BPV-MOF-Ir due to the presence of larger open channels in the mixed-linker MOFs. Impressively, mBPV-MOF-Ir exhibited high TONs of up to 17000 for C–H borylation reactions and was recycled more than 15 times. The mPT-MOF-Ir system is also active in catalyzing tandem dehydrosilylation/dehydrogenative cyclization of N-methylbenzyl amines to azasilolanes in the absence of a hydrogen acceptor. Importantly, MOF-Ir catalysts are significantly more active (up to 95 times) and stable than their homogeneous counterparts for all three reactions, strongly supporting the beneficial effects of active site isolation within MOFs. This work illustrates the ability to increase MOF open channel sizes by using the mixed linker approach and shows the enormous potential of developing highly active and robust single-site solid catalysts based on MOFs containing nitrogen-donor ligands for important organic transformations.« less

Designer stabilizer for preparation of pristine graphene/polysiloxane films and networks

NASA Astrophysics Data System (ADS)

Parviz, Dorsa; Yu, Ziniu; Hedden, Ronald C.; Green, Micah J.

2014-09-01

A conductive polymer film containing pristine graphene was prepared by designing a polysiloxane-based stabilizer for graphene. The stabilizer was prepared by grafting 1-ethynylpyrene to the backbone of a poly(dimethylsiloxane)-co-(methylhydrosiloxane) (PDMS-PHMS) random copolymer by Pt-catalyzed hydrosilylation with a SiH-ethynyl ratio of 1.0 : 1.3. The resulting copolymer was able to stabilize pristine graphene in chloroform solution via π-π interactions between the pyrene groups and graphene sheets. TEM and SEM images show a homogeneous distribution of the graphene in cast films deposited from chloroform. The conductivity of a graphene/PDMS film prepared from copolymer with a 1.7 vol.% graphene loading was measured as 220 S m-1 after the removal of unbound polymer by a simple separation technique. With a SiH-ethynyl ratio of 1.7 : 1.0, the copolymer self-crosslinked at 110 °C in the presence of adventitious moisture, providing a straightforward route to incorporate graphene into silicone elastomers. The crosslinking process (with and without added graphene) was characterized by FT-IR spectroscopy and by swelling and extraction of the obtained networks. Again, unbound polymer removal increases the conductivity of the composite.A conductive polymer film containing pristine graphene was prepared by designing a polysiloxane-based stabilizer for graphene. The stabilizer was prepared by grafting 1-ethynylpyrene to the backbone of a poly(dimethylsiloxane)-co-(methylhydrosiloxane) (PDMS-PHMS) random copolymer by Pt-catalyzed hydrosilylation with a SiH-ethynyl ratio of 1.0 : 1.3. The resulting copolymer was able to stabilize pristine graphene in chloroform solution via π-π interactions between the pyrene groups and graphene sheets. TEM and SEM images show a homogeneous distribution of the graphene in cast films deposited from chloroform. The conductivity of a graphene/PDMS film prepared from copolymer with a 1.7 vol.% graphene loading was measured as 220 S m-1 after the removal of unbound polymer by a simple separation technique. With a SiH-ethynyl ratio of 1.7 : 1.0, the copolymer self-crosslinked at 110 °C in the presence of adventitious moisture, providing a straightforward route to incorporate graphene into silicone elastomers. The crosslinking process (with and without added graphene) was characterized by FT-IR spectroscopy and by swelling and extraction of the obtained networks. Again, unbound polymer removal increases the conductivity of the composite. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01431f

Resting State and Elementary Steps of the Coupling of Aryl Halides with Thiols Catalyzed by Alkylbisphosphine Complexes of Palladium

PubMed Central

Alvaro, Elsa

2010-01-01

Detailed mechanistic studies on the coupling of aryl halides with thiols catalyzed by palladium complexes of the alkylbisphosphine ligand CyPF-tBu (1-dicyclohexylphosphino-2-di-tert-butylphosphinoethylferrocene) are reported. The elementary steps that constitute the catalytic cycle, i.e. oxidative addition, transmetalation and reductive elimination, have been studied, and their relative rates are reported. Each of the steps of the catalytic process occurs at temperatures that are much lower than those required for the reactions catalyzed by a combination of palladium precursors and CyPF-tBu. To explain these differences in rates between the catalytic and stoichiometric reactions, studies were conducted to identify the resting state of the catalyst of the reactions catalyzed by a combination of Pd(OAc)2 and CyPF-tBu, a combination of Pd(dba)2 and CyPF-tBu, or the likely intermediate Pd(CyPF-tBu)(Ar)(Br). These show that the major palladium complex in each case lies off of the catalytic cycle. The resting state of the reactions catalyzed by Pd(OAc)2 and CyPF-tBu was the palladium bis-thiolate complex [Pd(CyPF-tBu)(SR)2] (R = alkyl or aryl). The resting state in reactions catalyzed by Pd2(dba)3 and CyPF-tBu was the binuclear complex [Pd(CyPF-tBu)]2(μ2, η2-dba) (9). The resting state of reactions of both aromatic and aliphatic thiols catalyzed by [Pd(CyPF-tBu)(p-tolyl)(Br)] (3a) was the hydridopalladium thiolate complex [Pd(CyPF-tBu)(H)(SR)] (R= alkyl and aryl). All these palladium species have been prepared independently, and the mechanisms by which they enter the catalytic cycle have been examined in detail. These features of the reaction catalyzed by palladium and CyPF-tBu have been compared with those of reactions catalyzed by the alkylbisphosphine DiPPF and Pd(OAc)2 or Pd(dba)2. Our data indicate that the resting states of these reactions are similar to each other and that our mechanistic conclusions about reactions catalyzed by palladium and CyPF-tBu can be extrapolated to reactions catalyzed by complexes of other electron-rich bisphosphines. PMID:19453106

Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation

PubMed Central

Serganov, Alexander; Keiper, Sonja; Malinina, Lucy; Tereshko, Valentina; Skripkin, Eugene; Höbartner, Claudia; Polonskaia, Anna; Phan, Anh Tuân; Wombacher, Richard; Micura, Ronald; Dauter, Zbigniew; Jäschke, Andres; Patel, Dinshaw J

2015-01-01

The majority of structural efforts addressing RNA’s catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with a reaction product. The RNA adopts a λ-shaped nested pseudoknot architecture whose preformed hydrophobic pocket is precisely complementary in shape to the reaction product. RNA folding and product binding are dictated by extensive stacking and hydrogen bonding, whereas stereoselection is governed by the shape of the catalytic pocket. Catalysis is apparently achieved by a combination of proximity, complementarity and electronic effects. We observe structural parallels in the independently evolved catalytic pocket architectures for ribozyme- and antibody-catalyzed Diels-Alder carbon-carbon bond-forming reactions. PMID:15723077

Organocatalytic Transfer Hydrogenation and Hydrosilylation Reactions.

PubMed

Herrera, Raquel P

2016-06-01

The reduction of different carbon-carbon or carbon-heteroatom double bonds is a powerful tool that generates in many cases new stereogenic centers. In the last decade, the organocatalytic version of these transformations has attracted more attention, and remarkable progress has been made in this way. Organocatalysts such as chiral Brønsted acids, thioureas, chiral secondary amines or Lewis bases have been successfully used for this purpose. In this context, this chapter will cover pioneering and seminal examples using Hantzsch dihydropyridines 1 and trichlorosilane 2 as reducing agents. More recent examples will be also cited in order to cover as much as possible the complete research in this field.

Practical Iron- and Cobalt-Catalyzed Cross-Coupling Reactions between N-Heterocyclic Halides and Aryl or Heteroaryl Magnesium Reagents.

PubMed

Kuzmina, Olesya M; Steib, Andreas K; Fernandez, Sarah; Boudot, Willy; Markiewicz, John T; Knochel, Paul

2015-05-26

The reaction scope of iron- and cobalt-catalyzed cross-coupling reactions in the presence of isoquinoline (quinoline) in the solvent mixture tBuOMe/THF has been further investigated. Various 2-halogenated pyridine, pyrimidine, and triazine derivatives were arylated under these mild conditions in excellent yields. The presence of isoquinoline allows us to perform Fe-catalyzed cross-coupling reactions between 6-chloroquinoline and aryl magnesium reagents. Furthermore, it was found that the use of 10% N,N-dimethylquinoline-8-amine increases the yields of some Co-catalyzed cross-coupling reactions with chloropyridines bearing electron-withdrawing substituents. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Existence of efficient divalent metal ion-catalyzed and inefficient divalent metal ion-independent channels in reactions catalyzed by a hammerhead ribozyme

PubMed Central

Zhou, Jing-Min; Zhou, De-Min; Takagi, Yasuomi; Kasai, Yasuhiro; Inoue, Atsushi; Baba, Tadashi; Taira, Kazunari

2002-01-01

The hammerhead ribozyme is generally accepted as a well characterized metalloenzyme. However, the precise nature of the interactions of the RNA with metal ions remains to be fully defined. Examination of metal ion-catalyzed hammerhead reactions at limited concentrations of metal ions is useful for evaluation of the role of metal ions, as demonstrated in this study. At concentrations of Mn2+ ions from 0.3 to 3 mM, addition of the ribozyme to the reaction mixture under single-turnover conditions enhances the reaction with the product reaching a fixed maximum level. Further addition of the ribozyme inhibits the reaction, demonstrating that a certain number of divalent metal ions is required for proper folding and also for catalysis. At extremely high concentrations, monovalent ions, such as Na+ ions, can also serve as cofactors in hammerhead ribozyme-catalyzed reactions. However, the catalytic efficiency of monovalent ions is extremely low and, thus, high concentrations are required. Furthermore, addition of monovalent ions to divalent metal ion-catalyzed hammerhead reactions inhibits the divalent metal ion-catalyzed reactions, suggesting that the more desirable divalent metal ion–ribozyme complexes are converted to less desirable monovalent metal ion–ribozyme complexes via removal of divalent metal ions, which serve as a structural support in the ribozyme complex. Even though two channels appear to exist, namely an efficient divalent metal ion-catalyzed channel and an inefficient monovalent metal ion-catalyzed channel, it is clear that, under physiological conditions, hammerhead ribozymes are metalloenzymes that act via the significantly more efficient divalent metal ion-dependent channel. Moreover, the observed kinetic data are consistent with Lilley’s and DeRose’s two-phase folding model that was based on ground state structure analyses. PMID:12034824

First Novozym 435 lipase-catalyzed Morita-Baylis-Hillman reaction in the presence of amides.

PubMed

Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

2016-03-01

The first Novozym 435 lipase-catalyzed Morita-Baylis-Hillman (MBH) reaction with amides as co-catalyst was realized. Results showed that neither Novozym 435 nor amide can independently catalyze the reaction. This co-catalytic system that used a catalytic amount of Novozym 435 with a corresponding amount of amide was established and optimized. The MBH reaction strongly depended on the structure of aldehyde substrate, amide co-catalyst, and reaction additives. The optimized reaction yield (43.4%) was achieved in the Novozym 435-catalyzed MBH reaction of 2, 4-dinitrobenzaldehyde and cyclohexenone with isonicotinamide as co-catalyst and β-cyclodextrin as additive only in 2 days. Although enantioselectivity of Novozym 435 was not found, the results were still significant because an MBH reaction using lipase as biocatalyst was realized for the first time. Copyright © 2015 Elsevier Inc. All rights reserved.

Nickel-Catalyzed Coupling of Alkenes, Aldehydes, and Silyl Triflates

PubMed Central

Ng, Sze-sze; Ho, Chun-Yu; Jamison, Timothy F.

2011-01-01

A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed. PMID:16939275

Reaction pathways and free energy profiles for cholinesterase-catalyzed hydrolysis of 6-monoacetylmorphine

PubMed Central

Qiao, Yan; Han, Keli; Zhan, Chang-Guo

2014-01-01

As the most active metabolite of heroin, 6-monoacetylmorphine (6-MAM) can penetrate into the brain for the rapid onset of heroin effects. The primary enzymes responsible for the metabolism of 6-MAM to the less potent morphine in humans are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The detailed reaction pathways for AChE- and BChE-catalyzed hydrolysis of 6-MAM to morphine have been explored, for the first time, in the present study by performing first-principles quantum mechanical/molecular mechanical free energy calculations. It has been demonstrated that the two enzymatic reaction processes follow the similar catalytic reaction mechanism, and the whole catalytic reaction pathway for each enzyme consists of four reaction steps. According to the calculated results, the second reaction step associated with the transition state TS2a/TS2b should be rate-determining for the AChE/BChE-catalyzed hydrolysis, and the free energy barrier calculated for the AChE-catalyzed hydrolysis (18.3 kcal/mol) is 2.5 kcal/mol lower than that for the BChE-catalyzed hydrolysis (20.8 kcal/mol). The free energy barriers calculated for the AChE- and BChE-catalyzed reactions are in good agreement with the experimentally derived activation free energies (17.5 and 20.7 kcal/mol for the AChE- and BChE-catalyzed reactions, respectively). Further structural analysis reveals that the aromatic residues Phe295 and Phe297 in the acyl pocket of AChE (corresponding to Leu286 and Val288 in BChE) contribute to the lower energy of TS2a relative to TS2b. The obtained structural and mechanistic insights could be valuable for use in future rational design of a novel therapeutic treatment of heroin abuse. PMID:24595354

Comparative investigation of two methods for Acetylcholinesterase enzyme immobilization on modified porous silicon

NASA Astrophysics Data System (ADS)

Khaldi, Khadidja; Sam, Sabrina; Lounas, Amel; Yaddaden, Chafiaa; Gabouze, Noure-Eddine

2017-11-01

In this work, Acetylcholinesterase enzyme (AChE) was immobilized on porous silicon (PSi) surface using two strategies. In the first method, acid chains were covalently grafted on the hydrogenated PSi by hydrosilylation reaction. The obtained acid-terminated surface was activated by a reaction with N-hydroxysuccinimide (NHS) in the presence of a peptide-coupling agent N-ethyl-N‧-(3-dimethylaminopropyl)-carbodiimide (EDC), and then reacted with the amino linker of the lysine residues AChE to anchor the enzyme by a covalent amide bond. In the second procedure, the PSi surface was first hydroxylated in piranha solution, followed by a silanization reaction with 3-aminopropyltriethoxysilane (APTES) to form amine-terminated surface. Finally, AChE was attached to the terminal amine groups by an aminolysis reaction with carboxylic acid groups of AChE in the presence of NHS/EDC mixture. Fourier transform infrared spectroscopy (FTIR) confirmed the efficiency of the surface modifications. The enzymatic activity of immobilized AChE was determined by means of a colorimetric test and was discussed according to the enzyme orientation on the surface which was revealed by contact angle measurements.

Copper-Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions: Simultaneous Generation and Trapping of Copper-Triazoles and -Ketenimines for the Synthesis of Triazolopyrimidines.

PubMed

Nallagangula, Madhu; Namitharan, Kayambu

2017-07-07

First simultaneous generation and utilization of both copper-triazole and -ketenimine intermediates in copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions is achieved for the one-pot synthesis of triazolopyrimidines via a novel copper-catalyzed multicomponent cascade of sulfonyl azides, alkynes, and azirines. Significantly, the reaction proceeds under very mild conditions in good yields.

Mechanistic diversity in the RuBisCO superfamily: RuBisCO from Rhodospirillum rubrum is not promiscuous for reactions catalyzed by RuBisCO-like proteins.

PubMed

Warlick, Benjamin P E; Imker, Heidi J; Sriram, Jaya; Tabita, F Robert; Gerlt, John A

2012-11-27

d-Ribulose 1,5-bisphosphate carboxylase/oxygenases (RuBisCOs) are promiscuous, catalyzing not only carboxylation and oxygenation of d-ribulose 1,5-bisphosphate but also other promiscuous, presumably nonphysiological, reactions initiated by abstraction of the 3-proton of d-ribulose 1,5-bisphosphate. Also, RuBisCO has homologues that do not catalyze carboxylation; these are designated RuBisCO-like proteins or RLPs. Members of the two families of RLPs catalyze reactions in the recycling of 5'-methylthioadenosine (MTA) generated by polyamine synthesis: (1) the 2,3-diketo-5-methylthiopentane 1-phosphate (DK-MTP 1-P) "enolase" reaction in the well-known "methionine salvage" pathway in Bacillus sp. and (2) the 5-methylthio-d-ribulose 1-phosphate (MTRu 1-P) 1,3-isomerase reaction in the recently discovered "MTA-isoprenoid shunt" that generates 1-deoxy-d-xylulose 5-phosphate for nonmevalonate isoprene synthesis in Rhodospirillum rubrum. We first studied the structure and reactivity of DK-MTP 1-P that was reported to decompose rapidly [Ashida, H., Saito, Y., Kojima, C., and Yokota, A. (2008) Biosci., Biotechnol., Biochem. 72, 959-967]. The 2-carbonyl group of DK-MTP 1-P is rapidly hydrated and can undergo enolization both nonenzymatically and enzymatically via the small amount of unhydrated material that is present. We then examined the ability of RuBisCO from R. rubrum to catalyze both of the RLP-catalyzed reactions. Contrary to a previous report [Ashida, H., Saito, Y., Kojima, C., Kobayashi, K., Ogasawara, N., and Yokota, A. (2003) Science 302, 286-290], we were unable to confirm that this RuBisCO catalyzes the DK-MTP 1-P "enolase" reaction either in vitro or in vivo. We also determined that this RuBisCO does not catalyze the MTRu 1-P 1,3-isomerase reaction in vitro. Thus, although RuBisCOs can be functionally promiscuous, RuBisCO from R. rubrum is not promiscuous for either of the known RLP-catalyzed reactions.

Bis(amino)cyclopropenylidene (BAC) catalyzed aza-benzoin reaction.

PubMed

Wilde, Myron M D; Gravel, Michel

2014-10-17

A bis(amino)cyclopropenylidene (BAC) catalyzed aza-benzoin reaction between aldehydes and phosphinoyl imines has been developed. The reaction is general with a wide range of aromatic aldehydes and aromatic imines. The reaction displays excellent chemoselectivity favoring aza-benzoin products over homobenzoin products.

A high-performance liquid chromatography-electronic circular dichroism online method for assessing the absolute enantiomeric excess and conversion ratio of asymmetric reactions

NASA Astrophysics Data System (ADS)

Zhang, Xiang; Wang, Mingchao; Li, Li; Yin, Dali

2017-03-01

Asymmetric reactions often need to be evaluated during the synthesis of chiral compounds. However, traditional evaluation methods require the isolation of the individual enantiomer, which is tedious and time-consuming. Thus, it is desirable to develop simple, practical online detection methods. We developed a method based on high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) that simultaneously analyzes the material conversion ratio and absolute optical purity of each enantiomer. In particular, only a reverse-phase C18 column instead of a chiral column is required in our method because the ECD measurement provides a g-factor that describes the ratio of each enantiomer in the mixtures. We used our method to analyze the asymmetric hydrosilylation of β-enamino esters, and we discussed the advantage, feasibility, and effectiveness of this new methodology.

Recent advances in copper-catalyzed asymmetric coupling reactions

PubMed Central

2015-01-01

Summary Copper-catalyzed (or -mediated) asymmetric coupling reactions have received significant attention over the past few years. Especially the coupling reactions of aryl or alkyl halides with nucleophiles became a very powerful tool for the formation of C–C, C–N, C–O and other carbon–heteroatom bonds as well as for the construction of heteroatom-containing ring systems. This review summarizes the recent progress in copper-catalyzed asymmetric coupling reactions for the formation of C–C and carbon–heteroatom bonds. PMID:26734106

A new route to methyl (R,E)-(-)-tetradeca-2,4,5-trienoate (pheromone of Acanthoscelides obtectus) utilizing a palladium-catalyzed asymmetric allene formation reaction.

PubMed

Ogasawara, Masamichi; Nagano, Takashi; Hayashi, Tamio

2005-07-08

[reaction: see text] A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(-)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes.

Diazo compounds and N-tosylhydrazones: novel cross-coupling partners in transition-metal-catalyzed reactions.

PubMed

Xiao, Qing; Zhang, Yan; Wang, Jianbo

2013-02-19

Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo compounds or N-tosylhydrazones show that these transformations also work with other transition metals, demonstrating the generality of the diazo compounds as new cross-coupling partners in transition-metal-catalyzed coupling reactions.

NHC-Catalyzed Asymmetric Benzoin Reaction in Water.

PubMed

Yan, Jun; Sun, Rong; Shi, Kuangxi; Li, Kai; Yang, Limin; Zhong, Guofu

2018-06-11

A chiral NHC-catalyzed benzoin condensation reaction in water was developed, thereby affording α-hydroxy ketones in good to high yields and high enantioselectivities. Water was proposed as a proton shuttle in the aqueous asymmetric condensation reaction.

Sequential Aldol Condensation – Transition Metal-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids

PubMed Central

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-01-01

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1′-spirobiindane-7,7′-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. PMID:21417359

Sequential aldol condensation-transition metal-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids.

PubMed

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-04-15

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. © 2011 American Chemical Society

Functional diversity of 2-oxoglutarate/Fe(II)-dependent dioxygenases in plant metabolism

PubMed Central

Farrow, Scott C.; Facchini, Peter J.

2014-01-01

Oxidative enzymes catalyze many different reactions in plant metabolism. Among this suite of enzymes are the 2-oxoglutarate/Fe(II)-dependent dioxygenases (2-ODDs). Cytochromes P450 (CYPs) as often considered the most versatile oxidative enzymes in nature, but the diversity and complexity of reactions catalyzed by 2-ODDs is superior to the CYPs. The list of oxidative reactions catalyzed by 2-ODDs includes hydroxylations, demethylations, desaturations, ring closure, ring cleavage, epimerization, rearrangement, halogenation, and demethylenation. Furthermore, recent work, including the discovery of 2-ODDs involved in epigenetic regulation, and others catalyzing several characteristic steps in specialized metabolic pathways, support the argument that 2-ODDs are among the most versatile and important oxidizing biological catalysts. In this review, we survey and summarize the pertinent literature with a focus on several key reactions catalyzed by 2-ODDs, and discuss the significance and impact of these enzymes in plant metabolism. PMID:25346740

Intravitreal properties of porous silicon photonic crystals

PubMed Central

Cheng, L; Anglin, E; Cunin, F; Kim, D; Sailor, M J; Falkenstein, I; Tammewar, A; Freeman, W R

2009-01-01

Aim To determine the suitability of porous silicon photonic crystals for intraocular drug-delivery. Methods A rugate structure was electrochemically etched into a highly doped p-type silicon substrate to create a porous silicon film that was subsequently removed and ultrasonically fractured into particles. To stabilise the particles in aqueous media, the silicon particles were modified by surface alkylation (using thermal hydrosilylation) or by thermal oxidation. Unmodified particles, hydrosilylated particles and oxidised particles were injected into rabbit vitreous. The stability and toxicity of each type of particle were studied by indirect ophthalmoscopy, biomicroscopy, tonometry, electroretinography (ERG) and histology. Results No toxicity was observed with any type of the particles during a period of >4 months. Surface alkylation led to dramatically increased intravitreal stability and slow degradation. The estimated vitreous half-life increased from 1 week (fresh particles) to 5 weeks (oxidised particles) and to 16 weeks (hydrosilylated particles). Conclusion The porous silicon photonic crystals showed good biocompatibility and may be used as an intraocular drug-delivery system. The intravitreal injectable porous silicon photonic crystals may be engineered to host a variety of therapeutics and achieve controlled drug release over long periods of time to treat chronic vitreoretinal diseases. PMID:18441177

Trypsin-catalyzed tandem reaction: one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones by in situ formed acetaldehyde.

PubMed

Xie, Zong-Bo; Wang, Na; Wu, Wan-Xia; Le, Zhang-Gao; Yu, Xiao-Qi

2014-01-20

A simple, mild, one-pot tandem method catalyzed by trypsin was developed for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones by the Biginelli reaction of urea, β-dicarbonyl compounds, and in situ-formed acetaldehyde. Trypsin was found to display dual promiscuous functions to catalyze transesterification and the Biginelli reaction in sequence. Copyright © 2013 Elsevier B.V. All rights reserved.

Copper-Catalyzed Tandem Reactions for Synthesis of Pyrazolo[5,1-a]isoquinolines with Heterocyclic Ketene Aminals as Ligands.

PubMed

Wen, Li-Rong; Jin, Xian-Jun; Niu, Xiao-Dong; Li, Ming

2015-01-02

A CuI-catalyzed tandem reaction of 5-(2-bromoaryl)-N-aryl-1H-pyrazol-3-amines with active acetonitrile derivatives to prepare pyrazolo[5,1-a]isoquinolines in good to excellent yields has been successfully developed under mild conditions with heterocyclic ketene aminals (HKAs) as new ligands. This is the first time HKAs have been used as ligands for copper-catalyzed coupling reactions.

Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

PubMed Central

Driver, Tom G.

2011-01-01

Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

Silica, Alumina and Clay Catalyzed Peptide Bond Formation: Enhanced Efficiency of Alumina Catalyst

NASA Astrophysics Data System (ADS)

Bujdák, Juraj; Rode, Bernd M.

1999-10-01

Catalytic efficiencies of clay (hectorite), silica and alumina were tested in peptide bond formation reactions of glycine (Gly), alanine (Ala), proline (Pro), valine (Val) and leucine (Leu). The reactions were performed as drying/wetting (hectorite) and temperature fluctuation (silica and alumina) experiments at 85 °C. The reactivity of amino acids decreased in order Gly > Ala > Pro ~ Val ~ Leu. The highest catalytic efficiency was observed for alumina, the only catalyst producing oligopeptides in all investigated reaction systems. The peptide bond formation on alumina is probably catalyzed by the same sites and via similar reaction mechanisms as some alumina-catalyzed dehydration reactions used in industrial chemistry.

Cu-catalyzed cross-coupling reactions of epoxides with organoboron compounds.

PubMed

Lu, Xiao-Yu; Yang, Chu-Ting; Liu, Jing-Hui; Zhang, Zheng-Qi; Lu, Xi; Lou, Xin; Xiao, Bin; Fu, Yao

2015-02-11

A copper-catalyzed cross-coupling reaction of epoxides with arylboronates is described. This reaction is not limited to aromatic epoxides, because aliphatic epoxides are also suitable substrates. In addition, N-sulfonyl aziridines can be successfully converted into the products. This reaction provides convenient access to β-phenethyl alcohols, which are valuable synthetic intermediates.

Pressure effects on enzyme-catalyzed quantum tunneling events arise from protein-specific structural and dynamic changes.

PubMed

Hay, Sam; Johannissen, Linus O; Hothi, Parvinder; Sutcliffe, Michael J; Scrutton, Nigel S

2012-06-13

The rate and kinetic isotope effect (KIE) on proton transfer during the aromatic amine dehydrogenase-catalyzed reaction with phenylethylamine shows complex pressure and temperature dependences. We are able to rationalize these effects within an environmentally coupled tunneling model based on constant pressure molecular dynamics (MD) simulations. As pressure appears to act anisotropically on the enzyme, perturbation of the reaction coordinate (donor-acceptor compression) is, in this case, marginal. Therefore, while we have previously demonstrated that pressure and temperature dependences can be used to infer H-tunneling and the involvement of promoting vibrations, these effects should not be used in the absence of atomistic insight, as they can vary greatly for different enzymes. We show that a pressure-dependent KIE is not a definitive hallmark of quantum mechanical H-tunneling during an enzyme-catalyzed reaction and that pressure-independent KIEs cannot be used to exclude tunneling contributions or a role for promoting vibrations in the enzyme-catalyzed reaction. We conclude that coupling of MD calculations with experimental rate and KIE studies is required to provide atomistic understanding of pressure effects in enzyme-catalyzed reactions.

Iron-catalyzed intermolecular cycloaddition of diazo surrogates with hexahydro-1,3,5-triazines.

PubMed

Liu, Pei; Zhu, Chenghao; Xu, Guangyang; Sun, Jiangtao

2017-09-26

We report here an unprecedented iron-catalyzed cycloaddition reaction of diazo surrogates with hexahydro-1,3,5-triazines, providing five-membered heterocycles in moderate to high yields under mild reaction conditions. This cycloaddition features C-N and C-C bond formation using a cheap iron catalyst. Importantly, different to our former report on a gold-catalyzed system, both donor/donor and donor/acceptor diazo substrates are tolerated in this iron-catalyzed protocol.

Copper(II)-Catalyzed Conversion of Aryl/Heteroaryl Boronic Acids, Boronates, and Trifluoroborates into the Corresponding Azides: Substrate Scope and Limitations.

PubMed

Grimes, Kimberly D; Gupte, Amol; Aldrich, Courtney C

2010-05-01

We report the copper(II)-catalyzed conversion of organoboron compounds into the corresponding azide derivatives. A systematic series of phenylboronic acid derivatives is evaluated to examine the importance of steric and electronic effects of the substituents on reaction yield as well as functional group compatibility. Heterocyclic substrates are also shown to participate in this mild reaction while compounds incorporating B-C(sp(3)) bonds are unreactive under the reaction conditions. The copper(II)-catalyzed boronic acid-azide coupling reaction is further extended to both boronate esters and potassium organotrifluoroborate salts. The method described herein complements existing procedures for the preparation of aryl azides from the respective amino, triazene, and halide derivatives and we expect that it will greatly facilitate copper- and ruthenium-catalyzed azide-alkyne cycloaddition reactions for the preparation of diversely functionalized 1-aryl- or 1-heteroaryl-1,2,3-triazoles derivatives.

Ligand-Controlled Regioselective Copper-Catalyzed Trifluoromethylation To Generate (Trifluoromethyl)allenes.

PubMed

Ambler, Brett R; Peddi, Santosh; Altman, Ryan A

2015-05-15

"Cu-CF3" species have been used historically for a broad spectrum of nucleophilic trifluoromethylation reactions. Although recent advancements have employed ligands to stabilize and harness the reactivity of this key organometallic intermediate, the ability of a ligand to differentiate a regiochemical outcome of a Cu-CF3-mediated or -catalyzed reaction has not been previously reported. Herein, we report the first example of a Cu-catalyzed trifluoromethylation reaction in which a ligand controls the regiochemical outcome. More specifically, we demonstrate the ability of bipyridyl-derived ligands to control the regioselectivity of the Cu-catalyzed nucleophilic trifluoromethylation reactions of propargyl electrophiles to generate (trifluoromethyl)allenes. This method provides a variety of di-, tri-, and tetrasubstituted (trifluoromethyl)allenes, which can be further modified to generate complex fluorinated substructures.

Thioureas as ligands in the pd-catalyzed intramolecular Pauson-Khand reaction.

PubMed

Tang, Yefeng; Deng, Lujiang; Zhang, Yangdong; Dong, Guangbin; Chen, Jiahua; Yang, Zhen

2005-04-14

[reaction: see text] The thiourea-Pd complex was established as a novel type of catalyst in the PKR of allylpropargylamine, and the demonstrated chemistry may prove to be valuable for developing thiuorea as a ligand for the Pd-catalyzed Pauson-Khand reaction.

Kinetics of the Reaction Between Alcohols and Isocyanates Catalyzed by Ferric Acetylacetonate

NASA Technical Reports Server (NTRS)

Schieler, Leroy

1961-01-01

The rate and temperature dependence of reaction for the ferric acetylacetonate catalyzed reaction between a-naphthyl, ortho-tolyl, and para-tolyl isocyanates and n-butyl alcohol are investigated. The effect of substituents on the reactivity of isocyanate and hydroxyl group are reported and for substituted isocyanates are correlated by means of the Hammett equation. Several metal chelates were studied and their catalytic activity was compared to that of ferric acetylacetonate. All rate data are interpreted in terms of a mechanism involving simultaneous second-order uncatalyzed and catalyzed reactions between alcohol and isocyanate.

Diastereo- and enantioselective iridium-catalyzed allylation of cyclic ketone enolates: synergetic effect of ligands and barium enolates.

PubMed

Chen, Wenyong; Chen, Ming; Hartwig, John F

2014-11-12

We report asymmetric allylic alkylation of barium enolates of cyclic ketones catalyzed by a metallacyclic iridium complex containing a phosphoramidite ligand derived from (R)-1-(2-naphthyl)ethylamine. The reaction products contain adjacent quaternary and tertiary stereocenters. This process demonstrates that unstabilized cyclic ketone enolates can undergo diastereo- and enantioselective Ir-catalyzed allylic substitution reactions with the proper choice of enolate countercation. The products of these reactions can be conveniently transformed to various useful polycarbocyclic structures.

Synthesis of isocoumarins through three-component couplings of arynes, terminal alkynes, and carbon dioxide catalyzed by an NHC-copper complex.

PubMed

Yoo, Woo-Jin; Nguyen, Thanh V Q; Kobayashi, Shū

2014-09-15

A copper-catalyzed multicomponent coupling reaction between in situ generated ortho-arynes, terminal alkynes, and carbon dioxide was developed to access isocoumarins in moderate to good yields. The key to this CO2-incorporating reaction was the use of a versatile N-heterocyclic carbene/copper complex that was able to catalyze multiple transformations within the three-component reaction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper-catalyzed domino reactions for the synthesis of cyclic compounds.

PubMed

Liao, Qian; Yang, Xianghua; Xi, Chanjuan

2014-09-19

Copper-catalyzed domino reactions are one of the most useful strategies for the construction of various cyclic compounds. In this Synopsis, we mainly focus on the latest advances in copper-catalyzed cross-coupling or addition-initiated domino reactions in the synthesis of cyclic compounds, including double alkenylation of N- or S-nucleophiles, alkenylation or alkynlation followed by cyclization of amides or amines, addition and cyclization of heteroallenes affording heterocycles, and coupling and cyclization of 1,3-dicarbonyl compounds toward heterocycles.

Diastereo- and enantioselective iridium-catalyzed allylation of cyclic ketone enolates: Synergetic effect of ligands and barium enolates

DOE PAGES

Chen, Wenyong; Chen, Ming; Hartwig, John F.

2014-10-22

Here, we report asymmetric allylic alkylation of barium enolates of cyclic ketones catalyzed by a metallacyclic iridium complex containing a phosphoramidite ligand derived from ( R)-1-(2-naphthyl)ethylamine. The reaction products contain adjacent quaternary and tertiary stereocenters. This process demonstrates that unstabilized cyclic ketone enolates can undergo diastereo- and enantioselective Ir-catalyzed allylic substitution reactions with the proper choice of enolate countercation. The products of these reactions can be conveniently transformed to various useful polycarbocyclic structures.

Quantum chemical studies of a model for peptide bond formation. 3. Role of magnesium cation in formation of amide and water from ammonia and glycine

NASA Technical Reports Server (NTRS)

Oie, T.; Loew, G. H.; Burt, S. K.; MacElroy, R. D.

1984-01-01

The SN2 reaction between glycine and ammonia molecules with magnesium cation Mg2+ as a catalyst has been studied as a model reaction for Mg(2+)-catalyzed peptide bond formation using the ab initio Hartree-Fock molecular orbital method. As in previous studies of the uncatalyzed and amine-catalyzed reactions between glycine and ammonia, two reaction mechanisms have been examined, i.e., a two-step and a concerted reaction. The stationary points of each reaction including intermediate and transition states have been identified and free energies calculated for all geometry-optimized reaction species to determine the thermodynamics and kinetics of each reaction. Substantial decreases in free energies of activation were found for both reaction mechanisms in the Mg(2+)-catalyzed amide bond formation compared with those in the uncatalyzed and amine-catalyzed amide bond formation. The catalytic effect of the Mg2+ cation is to stabilize both the transition states and intermediate, and it is attributed to the neutralization of the developing negative charge on the electrophile and formation of a conformationally flexible nonplanar five-membered chelate ring structure.

Copper-Catalyzed SN2'-Selective Allylic Substitution Reaction of gem-Diborylalkanes.

PubMed

Zhang, Zhen-Qi; Zhang, Ben; Lu, Xi; Liu, Jing-Hui; Lu, Xiao-Yu; Xiao, Bin; Fu, Yao

2016-03-04

A Cu/(NHC)-catalyzed SN2'-selective substitution reaction of allylic electrophiles with gem-diborylalkanes is reported. Different substituted gem-diborylalkanes and allylic electrophiles can be employed in this reaction, and various synthetic valuable functional groups can be tolerated. The asymmetric version of this reaction was initially researched with chiral N-heterocyclic carbene (NHC) ligands.

Copper-catalyzed oxidative Heck reactions between alkyltrifluoroborates and vinyl arenes.

PubMed

Liwosz, Timothy W; Chemler, Sherry R

2013-06-21

We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification, and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented.

Gold-Catalyzed Formal C-C Bond Insertion Reaction of 2-Aryl-2-diazoesters with 1,3-Diketones.

PubMed

Ren, Yuan-Yuan; Chen, Mo; Li, Ke; Zhu, Shou-Fei

2018-06-29

The transition-metal-catalyzed formal C-C bond insertion reaction of diazo compounds with monocarbonyl compounds is well established, but the related reaction of 1,3-diketones instead gives C-H bond insertion products. Herein, we report a protocol for a gold-catalyzed formal C-C bond insertion reaction of 2-aryl-2-diazoesters with 1,3-diketones, which provides efficient access to polycarbonyl compounds with an all-carbon quaternary center. The aryl ester moiety plays a crucial role in the unusual chemoselectivity, and the addition of a Brønsted acid to the reaction mixture improves the yield of the C-C bond insertion product. A reaction mechanism involving cyclopropanation of a gold carbenoid with an enolate and ring-opening of the resulting donor-acceptor-type cyclopropane intermediate is proposed. This mechanism differs from that of the traditional Lewis-acid-catalyzed C-C bond insertion reaction of diazo compounds with monocarbonyl compounds, which involves a rearrangement of a zwitterion intermediate as a key step. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermally induced hydrosilylation at deuterium-terminated silicon nanoparticles: an investigation of the radical chain propagation mechanism.

PubMed

Holm, Jason; Roberts, Jeffrey T

2009-06-16

Isotopic labeling techniques were employed to study alkene addition to hydrogen- and deuterium-terminated silicon nanoparticles. Deuterium-terminated silicon nanoparticle synthesis is described, as is the characterization of fresh deuterium-terminated particles by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in situ Fourier transform infrared spectroscopy (FTIR). Particles were refluxed in pure 1-dodecene and subsequently characterized by FTIR and nuclear magnetic resonance (NMR) spectroscopy. (1)H NMR results showed features consistent with dodecyl-terminated nanoparticles. Infrared absorption spectra of refluxed particles showed strong evidence of new C-D bond formation, which is consistent with a radical chain mechanism for alkene addition by hydrosilylation.

Metal-catalyzed Decarboxylative Fluoroalkylation Reactions.

PubMed

Ambler, Brett R; Yang, Ming-Hsiu; Altman, Ryan A

2016-12-01

Metal-catalyzed decarboxylative fluoroalkylation reactions enable the conversion of simple O-based substrates into biologically relevant fluorinated analogs. Herein, we present decarboxylative methods that facilitate the synthesis of trifluoromethyl- and difluoroketone-containing products. We highlight key mechanistic aspects that are critical for efficient catalysis, and that inspired our thinking while developing the reactions.

Computational Elucidation of Selectivities and Mechanisms Performed by Organometallic and Bioinorganic Catalysts

NASA Astrophysics Data System (ADS)

Grandner, Jessica Marie

Computational methods were used to determine the mechanisms and selectivities of organometallic-catalyzed reactions. The first half of the dissertation focuses on the study of metathesis catalysts in collaboration with the Grubbs group at CalTech. Chapter 1 describes the studies of the decomposition modes of several ruthenium-based metathesis catalysts. These studies were performed to better understand the decomposition of such catalysts in order to prevent decomposition (Chapter 1.2) or utilize decomposed catalysts for alternative reactions (Chapter 1.1). Chapter 2.1 describes the computational investigation of the origins of stereoretentive metathesis with ruthenium-based metathesis catalysts. These findings were then used to computationally design E-selective metathesis catalysts (Chapter 2.2). While the first half of the dissertation was centered around ruthenium catalysts, the second half of the dissertation pertains to iron-catalyzed reaction, in particular, iron-catalyzed reactions by P450 enzymes. The elements of Chapter 3 concentrate on the stereo- and chemo-selectivity of P450-catalyzed C-H hydroxylations. By combining multiple computational methods, the inherent activity of the iron-oxo catalyst and the influence of the active site on such reactions were illuminated. These discoveries allow for the engineering of new substrates and mutant enzymes for tailored C-H hydroxylation. While the mechanism of C-H hydroxylations catalyzed by P450 enzymes has been well studied, there are several P450-catalyzed transformations for which the mechanism is unknown. The components of Chapter 4 describe the use of computations to determine the mechanisms of complex, multi-step reactions catalyzed by P450s. The determination of these mechanisms elucidates how these enzymes react with various functional groups and substrate architectures and allows for a better understanding of how drug-like compounds may be broken down by human P450s.

Base catalyzed synthesis of bicyclo[3.2.1]octane scaffolds.

PubMed

Boehringer, Régis; Geoffroy, Philippe; Miesch, Michel

2015-07-07

The base-catalyzed reaction of achiral 1,3-cyclopentanediones tethered to activated olefins afforded in high yields bicyclo[3.2.1]octane-6,8-dione or bicyclo[3.2.1]octane-6-carboxylate derivatives bearing respectively three or five stereogenic centers. The course of the reaction is closely related to the reaction time and to the base involved in the reaction.

Gold-nanoparticle-catalyzed synthesis of propargylamines: the traditional A3-multicomponent reaction performed as a two-step flow process.

PubMed

Abahmane, Lahbib; Köhler, J Michael; Gross, G Alexander

2011-03-01

The alkyne, aldehyde, amine A(3)-coupling reaction, a traditional multicomponent reaction (MCR), has been investigated as a two-step flow process. The implicated aminoalkylation reaction of phenylacetylene with appropriate aldimine intermediates was catalyzed by gold nanoparticles impregnated on alumina. The aldimine formation was catalyzed by Montmorillonite K10 beforehand. The performance of the process has been investigated with respect to different reaction regimes. Usually, the A(3)-multicomponent reaction is performed as a "one-pot" process. Diversity-oriented syntheses using MCRs often have the shortcoming that only low selectivity and low yields are achieved. We have used a flow-chemistry approach to perform the A(3)-MCR in a sequential manner. In this way, the reaction performance was significantly enhanced in terms of shortened reaction time, and the desired propargylamines were obtained in high yields. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

1,1,1-tris(hydroxymethyl)ethane as a new, efficient, and versatile tripod ligand for copper-catalyzed cross-coupling reactions of aryl iodides with amides, thiols, and phenols.

PubMed

Chen, Yao-Jung; Chen, Hsin-Hung

2006-11-23

1,1,1-tris(hydroxymethyl)ethane was presented as a new, efficient, and versatile tridentate O-donor ligand suitable for the copper-catalyzed formation of C-N, C-S, and C-O bonds. This inexpensive and commercially available tripod ligand has been demonstrated to facilitate the copper-catalyzed cross-coupling reactions of aryl iodides with amides, thiols, and phenols to afford the corresponding desired products in good to excellent yields. [reaction: see text].

Formation of polycyclic lactones through a ruthenium-catalyzed ring-closing metathesis/hetero-Pauson-Khand reaction sequence.

PubMed

Finnegan, David F; Snapper, Marc L

2011-05-20

Processes that form multiple carbon-carbon bonds in one operation can generate molecular complexity quickly and therefore be used to shorten syntheses of desirable molecules. We selected the hetero-Pauson-Khand (HPK) cycloaddition and ring-closing metathesis (RCM) as two unique carbon-carbon bond-forming reactions that could be united in a tandem ruthenium-catalyzed process. In doing so, complex polycyclic products can be obtained in one reaction vessel from acyclic precursors using a single ruthenium additive that can catalyze sequentially two mechanistically distinct transformations.

N-heterocyclic carbene-catalyzed tandem aza-benzoin/Michael reactions: on site reversal of the reactivity of N-Boc imines.

PubMed

Wu, Ke-Jia; Li, Gong-Qiang; Li, Yi; Dai, Li-Xin; You, Shu-Li

2011-01-07

A tandem NHC-catalyzed aza-benzoin/Michael reaction has been developed as a method to efficiently produce dihydroindenones and pyrrolidinone-containing tricycles. The novel reaction pattern involves tert-butyl aryl(tosyl)methylcarbamates reacting as both electrophile and nucleophile on the same carbon.

Regioselective and enantiospecific rhodium-catalyzed allylic alkylation reactions using copper(I) enolates: synthesis of (-)-sugiresinol dimethyl ether.

PubMed

Evans, P Andrew; Leahy, David K

2003-07-30

The transition metal-catalyzed allylic alkylation represents a fundamentally important cross-coupling reaction for the construction of ternary carbon stereogenic centers. We have developed a regioselective and enantiospecific rhodium-catalyzed allylic alkylation of acyclic unsymmetrical allylic alcohol derivatives using copper(I) enolates to prepare beta-substituted ketones. This protocol represents a convenient asymmetric Claisen rearrangement surrogate in which alpha-substituted enolates permit the introduction of an additional stereogenic center. The synthetic utility of this transformation was highlighted in the construction of a trans-1,2-disubstituted cyclohexene and the total synthesis of (-)-sugiresinol dimethyl ether. Finally, we anticipate that copper(I) enolates may prove useful nucleophiles in related metal-catalyzed reactions.

A cis-prenyltransferase from Methanosarcina acetivorans catalyzes both head-to-tail and nonhead-to-tail prenyl condensation.

PubMed

Ogawa, Takuya; Emi, Koh-Ichi; Koga, Kazushi; Yoshimura, Tohru; Hemmi, Hisashi

2016-06-01

Cis-prenyltransferase usually consecutively catalyzes the head-to-tail condensation reactions of isopentenyl diphosphate to allylic prenyl diphosphate in the production of (E,Z-mixed) polyprenyl diphosphate, which is the precursor of glycosyl carrier lipids. Some recently discovered homologs of the enzyme, however, catalyze the nonhead-to-tail condensation reactions between allylic prenyl diphosphates. In this study, we characterize a cis-prenyltransferase homolog from a methanogenic archaeon, Methanosarcina acetivorans, to obtain information on the biosynthesis of the glycosyl carrier lipids within it. This enzyme catalyzes both head-to-tail and nonhead-to-tail condensation reactions. The kinetic analysis shows that the main reaction of the enzyme is consecutive head-to-tail prenyl condensation reactions yielding polyprenyl diphosphates, while the chain lengths of the major products seem shorter than expected for the precursor of glycosyl carrier lipids. On the other hand, a subsidiary reaction of the enzyme, i.e., nonhead-to-tail condensation between dimethylallyl diphosphate and farnesyl diphosphate, gives a novel diterpenoid compound, geranyllavandulyl diphosphate. © 2016 Federation of European Biochemical Societies.

Continuous In Vitro Evolution of a Ribozyme that Catalyzes Three Successive Nucleotidyl Addition Reactions

NASA Technical Reports Server (NTRS)

McGinness, Kathleen E.; Wright, Martin C.; Joyce, Gerald F.

2002-01-01

Variants of the class I ligase ribozyme, which catalyzes joining of the 3' end of a template bound oligonucleotide to its own 5' end, have been made to evolve in a continuous manner by a simple serial transfer procedure that can be carried out indefinitely. This process was expanded to allow the evolution of ribozymes that catalyze three successive nucleotidyl addition reactions, two template-directed mononucleotide additions followed by RNA ligation. During the development of this behavior, a population of ribozymes was maintained against an overall dilution of more than 10(exp 406). The resulting ribozymes were capable of catalyzing the three-step reaction pathway, with nucleotide addition occurring in either a 5' yieldig 3' or a 3' yielding 5' direction. This purely chemical system provides a functional model of a multi-step reaction pathway that is undergoing Darwinian evolution.

Attachment chemistry of aromatic compounds on a Silicon(100) surface

NASA Astrophysics Data System (ADS)

Henriksson, Anders; Nishiori, Daiki; Maeda, Hiroaki; Miyachi, Mariko; Yamanoi, Yoshinori; Nishihara, Hiroshi

2018-03-01

A mild method was developed for the chemical attachment of aromatic compounds directly onto a hydrogen-terminated Si(100) (H-Si(100)) surface. In the presence of palladium catalyst and base, 4-iodophenylferrocene and a π-conjugated iron complex were attached to H-Si(100) electrodes and hydrogen-terminated silicon nanowires (H-SiNWs), both of which have predominant dihydride species on their surfaces. The reactions were conducted in 1,4-dioxane at 100 °C and the immobilization of both 4-ferrocenylphenyl group and π-conjugated molecular wires were confirmed and quantified by XPS and electrochemical measurements. We reported densely packed monolayer whose surface coverage (Γ), estimated from the electrochemical measurements are in analogue to similar monolayers prepared via thermal or light induced hydrosilylation reactions with alkenes or alkynes. The increase in electrochemical response observed on nanostructured silicon surfaces corresponds well to the increase in surface area, those strongly indicating that this method may be applied for the functionalization of electrodes with a variety of surface topographies.

New strategy for surface functionalization of periodic mesoporous silica based on meso-HSiO1.5.

PubMed

Xie, Zhuoying; Bai, Ling; Huang, Suwen; Zhu, Cun; Zhao, Yuanjin; Gu, Zhong-Ze

2014-01-29

Organic functionalization of periodic mesoporous silicas (PMSs) offers a way to improve their excellent properties and wide applications owing to their structural superiority. In this study, a new strategy for organic functionalization of PMSs is demonstrated by hydrosilylation of the recently discovered "impossible" periodic mesoporous hydridosilica, meso-HSiO1.5. This method overcomes the disadvantages of present pathways for organic functionalization of PMSs with organosilica. Moreover, compared to the traditional functionalization on the surface of porous silicon by hydrosilylation, the template-synthesized meso-HSiO1.5 is more flexible to access functional-groups-loaded PMSs with adjustable microstructures. The new method and materials will have wider applications based on both the structure and surface superiorities.

Copper-catalyzed oxidative homo- and cross-coupling of Grignard reagents using diaziridinone.

PubMed

Zhu, Yingguang; Xiong, Tao; Han, Wenyong; Shi, Yian

2014-12-05

Transition-metal-catalyzed cross-coupling reactions are among the most powerful synthetic transformations. This paper describes an efficient copper-catalyzed homo- and cross-coupling of Grignard reagents with di-tert-butyldiaziridinone as oxidant under mild conditions, giving the coupling products in good to excellent yields. The reaction process has a broad substrate scope and is also effective for the C(sp)-C(sp(3)) coupling.

Theoretical studies on the Mo-catalyzed asymmetric intramolecular Pauson-Khand-type [2+2+1] cycloadditions of 3-allyloxy-1-propynylphosphonates.

PubMed

Meng, Qingxi; Li, Ming

2012-08-01

Density functional theory (DFT) was used to investigate the Mo-catalyzed intramolecular Pauson-Khand reaction of 3-allyloxy-1-propynylphosphonates. All intermediates and transition states were optimized completely at the B3LYP/6-31 G(d,p) level [LANL2DZ(f) for Mo]. In the Mo-catalyzed intramolecular Pauson-Khand reaction, the C–C oxidative cyclization reaction was the chirality-determining step, and the reductive elimination reaction was the rate-determining step. The carbonyl insertion reaction into the Mo–C(sp(3)) bondwas easier than into the Mo–C=C bond. And the dominant product predicted theoretically was of (S)-chirality, which agreed with experimental data. This reaction was solventd ependent, and toluene was the best among the three solvents toluene, CH3CN, and THF.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions.

PubMed

Ruiz-Castillo, Paula; Buchwald, Stephen L

2016-10-12

Pd-catalyzed cross-coupling reactions that form C-N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C-N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Applications of Palladium-Catalyzed C–N Cross-Coupling Reactions

PubMed Central

2016-01-01

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts. PMID:27689804

Studies on the oxidation reaction of tyrosine (Tyr) with H2O2 catalyzed by horseradish peroxidase (HRP) in alcohol-water medium by spectrofluorimetry and differential spectrophotometry.

PubMed

Tang, Bo; Wang, Yan; Liang, Huiling; Chen, Zhenzhen; He, Xiwen; Shen, Hanxi

2006-03-01

An oxidation reaction of tyrosine (Tyr) with H(2)O(2) catalyzed by horseradish peroxidase (HRP) was studied by spectrofluorimetry and differential spectrophotometry in the alcohol(methanol, ethanol, 1-propanol and isopropanol)-water mutual solubility system. Compared with the enzymatic-catalyzed reaction in the water medium, the fluorescence intensities of the product weakened, even extinguished. Because the addition of alcohols made the conformation of HRP change, the catalytic reaction shifted to the side of polymerization and the polymer (A(n)H(2), n>or=3) exhibited no fluorescence. The four alcohols cannot deactivate HRP. Moreover isopropanol activated HRP remarkably.

Kinetic Parameters for the Noncatalyzed and Enzyme-Catalyzed Mutarotation of Glucose Using a Blood Glucometer

ERIC Educational Resources Information Center

Hardee, John R.; Delgado, Bryan; Jones, Wray

2011-01-01

The kinetic parameters for the conversion of alpha-D-glucose to beta-D-glucose were measured using a blood glucometer. The reaction order, rate constant, and Arrhenius activation energy are reported for the noncatalyzed reaction and turnover number and Michaelis constant are reported for the reaction catalyzed by porcine kidney mutarotase. The…

The rhodium catalyzed three-component reaction of diazoacetates, titanium(IV) alkoxides and aldehydes.

PubMed

Lu, Chong-Dao; Liu, Hui; Chen, Zhi-Yong; Hu, Wen-Hao; Mi, Ai-Qiao

2005-05-28

The rhodium(II)-catalyzed three-component reaction of diazoacetates, titanium alkoxides and aldehydes is shown to give alpha-alkoxyl-beta-hydroxyl acid derivatives; the novel C-C bond formation reaction is proposed to occur through oxonium ylides derived from diazo compounds and titanium alkoxides, and followed by intermolecular trapping by aldehydes.

Construction of Benzene Rings by Copper-Catalyzed Cycloaddition Reactions of Oximes and Maleimides: An Access to Fused Phthalimides.

PubMed

Yang, Jie; Zhao, Bo; Xi, Yue; Sun, Si; Yang, Zhen; Ye, Ying; Jiang, Kun; Wei, Ye

2018-02-16

A useful Cu-catalyzed cycloaddition protocol for the construction of benzene rings has been achieved. The reactions, utilizing readily available oximes and maleimides as starting materials, proceed under mild reaction conditions to generate a series of structurally interesting fused-phthalimides that are difficult to be prepared by conventional methods.

Recent Development in Chemical Depolymerization of Lignin: A Review

DOE PAGES

Wang, Hai; Tucker, Melvin; Ji, Yun

2013-01-01

This article reviewed recent development of chemical depolymerization of lignins. There were five types of treatment discussed, including base-catalyzed, acid-catalyzed, metallic catalyzed, ionic liquids-assisted, and supercritical fluids-assisted lignin depolymerizations. The methods employed in this research were described, and the important results were marked. Generally, base-catalyzed and acid-catalyzed methods were straightforward, but the selectivity was low. The severe reaction conditions (high pressure, high temperature, and extreme pH) resulted in requirement of specially designed reactors, which led to high costs of facility and handling. Ionic liquids, and supercritical fluids-assisted lignin depolymerizations had high selectivity, but the high costs of ionic liquids recyclingmore » and supercritical fluid facility limited their applications on commercial scale biomass treatment. Metallic catalyzed depolymerization had great advantages because of its high selectivity to certain monomeric compounds and much milder reaction condition than base-catalyzed or acid-catalyzed depolymerizations. It would be a great contribution to lignin conversion if appropriate catalysts were synthesized.« less

Copper-Catalyzed Oxidative Reaction of β-Keto Sulfones with Alcohols via C-S Bond Cleavage: Reaction Development and Mechanism Study.

PubMed

Du, Bingnan; Wang, Wenmin; Wang, Yang; Qi, Zhenghang; Tian, Jiaqi; Zhou, Jie; Wang, Xiaochen; Han, Jianlin; Ma, Jing; Pan, Yi

2018-02-16

A Cu-catalyzed cascade oxidative radical process of β-keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β-keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C-S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four-coordinated Cu II intermediate, O-O bond homolysis induced C-S bond cleavage and Cu-catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C-S bond cleavage and transformations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Method for converting UF5 to UF4 in a molten fluoride salt

DOEpatents

Bennett, Melvin R.; Bamberger, Carlos E.; Kelmers, A. Donald

1977-01-01

The reduction of UF.sub.5 to UF.sub.4 in a molten fluoride salt by sparging with hydrogen is catalyzed by metallic platinum. The reaction is also catalyzed by platinum alloyed with gold reaction equipment.

Transesterification of oil mixtures catalyzed by microencapsulated cutinase in reversed micelles.

PubMed

Badenes, Sara M; Lemos, Francisco; Cabral, Joaquim M S

2010-03-01

Recombinant cutinase from Fusarium solani pisi was used to catalyze the transesterification reaction between a mixture of triglycerides (oils) and methanol in reversed micelles of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane for the purposes of producing biodiesel. The use of a bi-phase lipase-catalyzed system brings advantages in terms of catalyst re-use and the control of water activity in the medium and around the enzyme micro-environment. Small-scale batch studies were performed to study the influence of the initial enzyme and alcohol concentrations, and the substrates molar ratio. Conversions in excess of 75 were obtained with reaction times under 24 h, which makes this enzymatic process highly competitive when compared to similar lipase catalyzed reactions for biodiesel production using methanol.

Copper-Catalyzed Oxidative Homo- and Cross-Coupling of Grignard Reagents Using Diaziridinone

PubMed Central

2015-01-01

Transition-metal-catalyzed cross-coupling reactions are among the most powerful synthetic transformations. This paper describes an efficient copper-catalyzed homo- and cross-coupling of Grignard reagents with di-tert-butyldiaziridinone as oxidant under mild conditions, giving the coupling products in good to excellent yields. The reaction process has a broad substrate scope and is also effective for the C(sp)–C(sp3) coupling. PMID:25420218

Silylative Reductive Amination of α,β-Unsaturated Aldehydes: A Convenient Synthetic Route to β-Silylated Secondary Amines.

PubMed

Kim, Eunae; Park, Sehoon; Chang, Sukbok

2018-04-17

Described here is a reductive amination/hydrosilylation cascade of α,β-unsaturated aldehydes mediated by a Lewis acidic borane catalyst. The present reaction system provides an one-pot synthetic route towards β-silylated secondary amines that have not been accessible by other previous catalysis. Comparative 1 H NMR studies on the silylative reduction of enimines revealed that steric bulkiness of primary amine reactants strongly affects both catalytic efficiency and regioselectivity. This strategy was applicable to a broad range of substrates and amenable to one-pot gram-scale synthesis. Moreover, a diastereoselective introduction of the β-silyl group was also found to be feasible (d.r. up to 71:29). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Green Reductive Homocoupling of Bromobenzene

ERIC Educational Resources Information Center

Ballard, C. Eric

2011-01-01

Although transition-metal-catalyzed reactions are important in contemporary organic chemistry, relatively few resources for the second-year organic chemistry curriculum discuss the subject. The inquiry-based experiment described here, an iron-catalyzed preparation of biphenyl from bromobenzene, introduces this topic. The reaction uses an…

Synthesis of disulfides and diselenides by copper-catalyzed coupling reactions in water.

PubMed

Li, Zhengkai; Ke, Fang; Deng, Hang; Xu, Hualong; Xiang, Haifeng; Zhou, Xiangge

2013-05-14

A simple and efficient protocol for copper-catalyzed coupling reactions between aryl halides and elemental sulfur or selenium has been developed. A variety of disulfides and diselenides can be obtained in moderate to excellent yields up to 96%.

Chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reactions: importance of the fused ring in triazolium salts.

PubMed

Langdon, Steven M; Wilde, Myron M D; Thai, Karen; Gravel, Michel

2014-05-28

Morpholinone- and piperidinone-derived triazolium salts are shown to catalyze highly chemoselective cross-benzoin reactions between aliphatic and aromatic aldehydes. The reaction scope includes ortho-, meta-, and para-substituted benzaldehyde derivatives with a range of electron-donating and -withdrawing groups as well as branched and unbranched aliphatic aldehydes. Catalytic loadings as low as 5 mol % give excellent yields in these reactions (up to 99%).

Iron-catalyzed cross-coupling of imidoyl chlorides with Grignard reagents.

PubMed

Ottesen, Lars K; Ek, Fredrik; Olsson, Roger

2006-04-27

[reaction: see text] A general, high yielding rapid iron-catalyzed cross-coupling reaction between Grignard reagents and imidoyl chlorides is described. These reactions are typically completed within 5 min, resulting in high yields of 71-96% using 5% iron catalyst in a THF-NMP solvent mixture. Functionalized imidoyl chlorides (e.g., R = CO(2)Me) gave excellent yields (89%).

Copper-catalyzed tandem reactions of 1-(2-iodoary)-2-yn-1-ones with isocyanides for the synthesis of 4-oxo-indeno[1,2-b]pyrroles.

PubMed

Cai, Qian; Zhou, Fengtao; Xu, Tianfeng; Fu, Liangbing; Ding, Ke

2011-01-21

A novel copper-catalyzed tandem reaction of 1-(2-iodoaryl)-2-yn-1-ones with isocyanides is described. The reaction is through a formal [3 + 2] cycloaddition/coupling tandem process and leads to efficient formation of 4-oxo-indeno[1,2-b]pyrroles.

Copper-catalyzed cross-coupling reactions of epoxides with gem-diborylmethane: access to γ-hydroxyl boronic esters.

PubMed

Ebrahim-Alkhalil, Ahmed; Zhang, Zhen-Qi; Gong, Tian-Jun; Su, Wei; Lu, Xiao-Yu; Xiao, Bin; Fu, Yao

2016-04-07

Herein, we describe a novel copper-catalyzed epoxide opening reaction with gem-diborylmethane. Aliphatic, aromatic epoxides as well as aziridines are converted to the corresponding γ-pinacolboronate alcohols or amines in moderate to excellent yields. This new reaction provides beneficial applications for classic epoxide substrates as well as interesting gem-diborylalkane reagents.

All kinds of reactivity: recent breakthroughs in metal-catalyzed alkyne chemistry.

PubMed

Anaya de Parrodi, Cecilia; Walsh, Patrick J

2009-01-01

Alkynes of reactions: Recent breakthroughs in metal-catalyzed alkyne reactions, which expand the synthetic utility of alkynes, have been achieved. These approaches broaden the range of alkynes that are accessible by C--N and C--C bond-forming reactions and demonstrate that the use of bifunctional heterobimetallic catalysts can lead to new reactivity and excellent enantioselectivity (see scheme).

Study of the techniques feasible for food synthesis aboard a spacecraft

NASA Technical Reports Server (NTRS)

Weiss, A. H.

1972-01-01

Synthesis of sugars by Ca(OH)2 catalyzed formaldehyde condensation (the formose reaction) has produced branched carbohydrates that do not occur in nature. The kinetics and mechanisms of the homogeneously catalyzed autocatalytic condensation were studied and analogies between homogeneous and heterogeneous rate laws have been found. Aldol condensations proceed simultaneously with Cannizzaro and crossed-Cannizzaro reactions and Lobry de Bruyn-Van Eckenstein rearrangements. The separate steps as well as the interactions of this highly complex reaction system were elucidated. The system exhibits instabilities, competitive catalytic, mass action, and equilibrium phenomena, complexing, and parallel and consecutive reactions. Specific finding that have been made on the problem will be of interest for synthesizing sugars, both for sustained space flight and for large scale food manufacture. A contribution to methodology for studying complex catalyzed reactions and to understanding control of reaction selectivity was a broad goal of the project.

Desaturation reactions catalyzed by soluble methane monooxygenase.

PubMed

Jin, Y; Lipscomb, J D

2001-09-01

Soluble methane monooxygenase (MMO) is shown to be capable of catalyzing desaturation reactions in addition to the usual hydroxylation and epoxidation reactions. Dehydrogenated products are generated from MMO-catalyzed oxidation of certain substrates including ethylbenzene and cyclohexadienes. In the reaction of ethylbenzene, desaturation of ethyl C-H occurred along with the conventional hydroxvlations of ethyl and phenyl C-Hs. As a result, styrene is formed together with ethylphenols and phenylethanols. Similarly, when 1,3- and 1,4-cyclohexadienes were used as substrates, benzene was detected as a product in addition to the corresponding alcohols and epoxides. In all cases, reaction conditions were found to significantly affect the distribution among the different products. This new activity of MMO is postulated to be associated with the chemical properties of the substrates rather than fundamental changes in the nature of the oxygen and C-H activation chemistries. The formation of the desaturated products is rationalized by formation of a substrate cationic intermediate, possibly via a radical precursor. The cationic species is then proposed to partition between recombination (alcohol formation) and elimination (alkene production) pathways. This novel function of MMO indicates close mechanistic kinship between the hydroxylation and desaturation reactions catalyzed by the nonheme diiron clusters.

Rh-Catalyzed Annulations of N-Methoxybenzamides and Ketenimines: Sterically and Electronically Controlled Synthesis of Isoquinolinones and Isoindolinones.

PubMed

Zhou, Xiaorong; Zhang, Zhiyin; Zhao, Hongyang; Lu, Ping; Wang, Yanguang

2017-04-07

Rhodium-catalyzed C-H activation/annulation reactions of ketenimines with N-methoxybenzamides are reported. The outcome of reactions is dependent on the structure of ketenimines. The β-alkyl-substituted ketenimines furnish 3-iminoisoquinolin-1(2H)-ones in a formal [4 + 2] annulation manner, while the β-ester substituted ketenimines afford 3-aminoisoindolin-1-ones in a formal [4 + 1] annulation manner. The synthesized [4 + 2] products undergo an intramolecular Cu-catalyzed C-N coupling to be converted to benzo[4,5]imidazo[1,2-b]isoquinolin-11-ones, which can be directly prepared from ketenimines and N-methoxybenzamides by a one-pot Rh-catalyzed annulation/Cu-catalyzed C-N coupling sequence.

Expanding P450 catalytic reaction space through evolution and engineering

PubMed Central

McIntosh, John A.; Farwell, Christopher C.; Arnold, Frances H.

2014-01-01

Advances in protein and metabolic engineering have led to wider use of enzymes to synthesize important molecules. However, many desirable transformations are not catalyzed by any known enzyme, driving interest in understanding how new enzymes can be created. The cytochrome P450 enzyme family, whose members participate in xenobiotic metabolism and natural products biosynthesis, catalyzes an impressive range of difficult chemical reactions that continues to grow as new enzymes are characterized. Recent work has revealed that P450-derived enzymes can also catalyze useful reactions previously accessible only to synthetic chemistry. The evolution and engineering of these enzymes provides an excellent case study for how to genetically encode new chemistry and expand biology’s reaction space. PMID:24658056

Alkanes from Bioderived Furans by using Metal Triflates and Palladium-Catalyzed Hydrodeoxygenation of Cyclic Ethers.

PubMed

Song, Hai-Jie; Deng, Jin; Cui, Min-Shu; Li, Xing-Long; Liu, Xin-Xin; Zhu, Rui; Wu, Wei-Peng; Fu, Yao

2015-12-21

Using a metal triflate and Pd/C as catalysts, alkanes were prepared from bioderived furans in a one-pot hydrodeoxygenation (HDO) process. During the reaction, the metal triflate plays a crucial role in the ring-opening HDO of furan compounds. The entire reaction process has goes through two major phases: at low temperatures, saturation of the exocyclic double bond and furan ring are catalyzed by Pd/C; at high temperatures, the HDO of saturated furan compounds is catalyzed by the metal triflate. The reaction mechanism was verified by analyzing the changes of the intermediates during the reaction. In addition, different metal triflates, solvents, and catalyst recycling were also investigated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold(I)-catalyzed tandem cyclization approach to tetracyclic indolines.

PubMed

Liu, Yongxiang; Xu, Wenqing; Wang, Xiang

2010-04-02

Two highly stereoselective cationic gold(I)-catalyzed tandem cyclization reactions of alkynylindoles are described. These reactions demonstrated a novel and general strategy to rapidly construct highly functionalized polycyclic indolines. This approach was successfully employed for a formal synthesis of the akuammiline alkaloid minfiensine.

PALLADIUM-CATALYZED OXIDATION OF STYRENE AND ALKENES IN PRESENCE OF IONIC LIQUIDS (WACKER REACTION)

EPA Science Inventory

The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...

Catalytic total hydrodeoxygenation of biomass-derived polyfunctionalized substrates to alkanes.

PubMed

Nakagawa, Yoshinao; Liu, Sibao; Tamura, Masazumi; Tomishige, Keiichi

2015-04-13

The total hydrodeoxygenation of carbohydrate-derived molecules to alkanes, a key reaction in the production of biofuel, was reviewed from the aspect of catalysis. Noble metals (or Ni) and acid are the main components of the catalysts, and group 6 or 7 metals such as Re are sometimes added as modifiers of the noble metal. The main reaction route is acid-catalyzed dehydration plus metal-catalyzed hydrogenation, and in some systems metal-catalyzed direct CO dissociation is involved. The appropriate active metal, acid strength, and reaction conditions depend strongly on the reactivity of the substrate. Reactions that use Pt or Pd catalysts supported on Nb-based acids or relatively weak acids are suitable for furanic substrates. Carbohydrates themselves and sugar alcohols undergo CC dissociation easily. The systems that use metal-catalyzed direct CO dissociations can give a higher yield of the corresponding alkane from carbohydrates and sugar alcohols. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical Study of the Effects of Di-Muonic Molecules on Muon-Catalyzed Fusion

DTIC Science & Technology

2012-03-01

For example, synthetic zeolites could be used to separate molecular isotopes of hydrogen [12; 10] as could thermal diffusion and gas chromatography... thermal muon flux is large (see Chapter 8). Reactions which have the potential of increasing the muon-catalyzed fusion rate and reactions that could...the remainder of this document. Changes to the muon-catalyzed fusion cycle, that are expected to occur when the thermal muon flux is high, are

Intramolecular Benzoin Reaction Catalyzed by Benzaldehyde Lyase from Pseudomonas Fluorescens Biovar I.

PubMed

Hernández, Karel; Parella, Teodor; Petrillo, Giovanna; Usón, Isabel; Wandtke, Claudia M; Joglar, Jesús; Bujons, Jordi; Clapés, Pere

2017-05-02

Intramolecular benzoin reactions catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I (BAL) are reported. The structure of the substrates envisaged for this reaction consists of two benzaldehyde derivatives linked by an alkyl chain. The structural requirements needed to achieve the intramolecular carbon-carbon bond reaction catalyzed by BAL were established. Thus, a linker consisting of a linear alkyl chain of three carbon atoms connected through ether-type bonds to the 2 and 2' positions of two benzaldehyde moieties, which could be substituted with either Cl, Br, or OCH 3 at either the 3 and 3' or 5 and 5' positions, were suitable substrates for BAL. Reactions with 61-84 % yields of the intramolecular product and ee values between 64 and 98 %, were achieved. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solvent-dependent reactions for the synthesis of β-keto-benzo-δ-sultone scaffolds via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences.

PubMed

Ghandi, Mehdi; Bozcheloei, Abolfazl Hasani; Nazari, Seyed Hadi; Sadeghzadeh, Masoud

2011-12-16

We have developed a solvent-dependent method for the synthesis of novel benzo-δ-sultone scaffolds. A variety of benzylbenzo[e][1,2]oxathiin-4(3H)-one-2,2-dioxides were obtained in high yields in DMF using a one-pot, DBU-catalyzed condensation of 2-hydroxybenzaldehydes with a number of (E)-2-phenylethenesulfonyl chlorides. On the other hand, the initially prepared 2-formylphenyl-(E)-2-phenylethenesulfonate derivatives underwent DBU-catalyzed reactions to a series of 3-[methoxy(phenyl)methyl]benzo[e][1,2]oxathiine-2,2-dioxides in moderate to good yields in MeOH. These reactions presumably proceed via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences, respectively.

Rh(I)-catalyzed [(3 + 2) + 1] cycloaddition of 1-yne/ene-vinylcyclopropanes and CO: homologous Pauson-Khand reaction and total synthesis of (+/-)-alpha-agarofuran.

PubMed

Jiao, Lei; Lin, Mu; Zhuo, Lian-Gang; Yu, Zhi-Xiang

2010-06-04

A novel Rh(I)-catalyzed [(3 + 2) + 1] cycloaddition, which can be regarded as a homologous Pauson-Khand reaction, was developed to synthesize bicyclic cyclohexenones and cyclohexanones, enabling a new approach for synthesis of six-membered carbocycles ubiquitously found in natural products and pharmaceutics. The significance of the Rh-catalyzed [(3 + 2) + 1] cycloaddition has been demonstrated by the total synthesis of a furanoid sesquiterpene natural product, alpha-agarofuran, in which the bicyclic skeleton was constructed by the [(3 + 2) + 1] reaction of 1-yne-VCP and CO.

Water Oxidation by a Cytochrome P450: Mechanism and Function of the Reaction

PubMed Central

Prasad, Brinda; Mah, Derrick J.; Lewis, Andrew R.; Plettner, Erika

2013-01-01

P450cam (CYP101A1) is a bacterial monooxygenase that is known to catalyze the oxidation of camphor, the first committed step in camphor degradation, with simultaneous reduction of oxygen (O2). We report that P450cam catalysis is controlled by oxygen levels: at high O2 concentration, P450cam catalyzes the known oxidation reaction, whereas at low O2 concentration the enzyme catalyzes the reduction of camphor to borneol. We confirmed, using 17O and 2H NMR, that the hydrogen atom added to camphor comes from water, which is oxidized to hydrogen peroxide (H2O2). This is the first time a cytochrome P450 has been observed to catalyze oxidation of water to H2O2, a difficult reaction to catalyze due to its high barrier. The reduction of camphor and simultaneous oxidation of water are likely catalyzed by the iron-oxo intermediate of P450cam, and we present a plausible mechanism that accounts for the 1∶1 borneol:H2O2 stoichiometry we observed. This reaction has an adaptive value to bacteria that express this camphor catabolism pathway, which requires O2, for two reasons: 1) the borneol and H2O2 mixture generated is toxic to other bacteria and 2) borneol down-regulates the expression of P450cam and its electron transfer partners. Since the reaction described here only occurs under low O2 conditions, the down-regulation only occurs when O2 is scarce. PMID:23634216

Initiator and Photocatalyst-Free Visible Light Induced One-Pot Reaction: Concurrent RAFT Polymerization and CuAAC Click Reaction.

PubMed

Wang, Jie; Wang, Xinbo; Xue, Wentao; Chen, Gaojian; Zhang, Weidong; Zhu, Xiulin

2016-05-01

A new, visible light-catalyzed, one-pot and one-step reaction is successfully employed to design well-controlled side-chain functionalized polymers, by the combination of ambient temperature revisible addtion-fragmentation chain transfer (RAFT) polymerization and click chemistry. Polymerizations are well controlled in a living way under the irradiation of visible light-emitting diode (LED) light without photocatalyst and initiator, using the trithiocarbonate agent as iniferter (initiator-transfer agent-terminator) agent at ambient temperature. Fourier transfer infrared spectroscopy (FT-IR), NMR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) data confirm the successful one-pot reaction. Compared to the reported zero-valent metal-catalyzed one-pot reaction, the polymerization rate is much faster than that of the click reaction, and the visible light-catalyzed one-pot reaction can be freely and easily regulated by turning on and off the light. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-catalyzed domino C,N-coupling/carbonylation/Suzuki coupling reaction: an efficient synthesis of 2-aroyl-/heteroaroylindoles.

PubMed

Arthuis, Martin; Pontikis, Renée; Florent, Jean-Claude

2009-10-15

A convenient one-pot synthesis of 2-aroylindoles using a domino palladium-catalyzed C,N-coupling/carbonylation/C,C-coupling sequence is described. The reaction involved easily prepared 2-gem-dibromovinylanilines and boronic acids under carbon monoxide. Optimized reaction conditions allowed the construction of a wide variety of highly functionalized 2-aroyl-/heteroaroylindoles in satisfactory yields.

Room-temperature Pd-catalyzed C-H chlorination by weak coordination: one-pot synthesis of 2-chlorophenols with excellent regioselectivity.

PubMed

Sun, Xiuyun; Sun, Yonghui; Zhang, Chao; Rao, Yu

2014-02-07

A room-temperature Pd(II)-catalyzed regioselective chlorination reaction has been developed for a facile one-pot synthesis of a broad range of 2-chlorophenols. The reaction demonstrates an excellent regioselectivity and reactivity for C-H chlorination. This reaction represents one of the rare examples of mild C-H functionalization at ambient temperature.

Computationally designed and experimentally confirmed diastereoselective rhodium-catalyzed Pauson-Khand reaction at room temperature.

PubMed

Baik, Mu-Hyun; Mazumder, Shivnath; Ricci, Paolo; Sawyer, James R; Song, Ye-Geun; Wang, Huijun; Evans, P Andrew

2011-05-25

The computational analysis of the rhodium-catalyzed Pauson-Khand reaction indicates that the key transition state is highly charge-polarized, wherein different diastereoisomers have distinctively different charge polarization patterns. Experimental studies demonstrate that chloro-enynes provide the optimal σ-electron-withdrawing group to promote polarization and thereby reduce the activation barrier to provide a highly diastereoselective reaction at room temperature.

Aryl Ketone Synthesis via Tandem Orthoplatinated Triarylphosphite-Catalyzed Addition Reactions of Arylboronic Acids with Aldehydes Followed by Oxidation

PubMed Central

Liao, Yuan-Xi; Hu, Qiao-Sheng

2010-01-01

Tandem orthoplatinated triarylphosphite-catalyzed addition reactions of arylboronic acids with aldehydes followed by oxidation to yield aryl ketones is described. 3-Pentanone was identified as a suitable oxidant for the tandem aryl ketone formation reaction. By using microwave energy, aryl ketones were obtained in high yields with the catalyst loading as low as 0.01%. PMID:20849092

Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides

EPA Science Inventory

An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production.

Method to upgrade bio-oils to fuel and bio-crude

DOEpatents

Steele, Philip H; Pittman, Jr., Charles U; Ingram, Jr., Leonard L; Gajjela, Sanjeev; Zhang, Zhijun; Bhattacharya, Priyanka

2013-12-10

This invention relates to a method and device to produce esterified, olefinated/esterified, or thermochemolytic reacted bio-oils as fuels. The olefinated/esterified product may be utilized as a biocrude for input to a refinery, either alone or in combination with petroleum crude oils. The bio-oil esterification reaction is catalyzed by addition of alcohol and acid catalyst. The olefination/esterification reaction is catalyzed by addition of resin acid or other heterogeneous catalyst to catalyze olefins added to previously etherified bio-oil; the olefins and alcohol may also be simultaneously combined and catalyzed by addition of resin acid or other heterogeneous catalyst to produce the olefinated/esterified product.

RNA-Catalyzed RNA Ligation on an External RNA Template

NASA Technical Reports Server (NTRS)

McGinness, Kathleen E.; Joyce, Gerald F.

2002-01-01

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

Development of a Lewis Base Catalyzed Selenocyclization Reaction

ERIC Educational Resources Information Center

Collins, William

2009-01-01

The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

Pd-Catalyzed Cross-Coupling Reactions of Amides and Aryl Mesylates

PubMed Central

Dooleweerdt, Karin; Fors, Brett P.; Buchwald, Stephen L.

2010-01-01

A catalyst, based on a biarylphosphine ligand, for the Pd-catalyzed cross-coupling reactions of amides and aryl mesylates is described. This system allows an array of aryl and heteroaryl mesylates to be transformed into the corresponding N-arylamides in moderate to excellent yields. PMID:20420379

Enzyme Catalysis and the Gibbs Energy

ERIC Educational Resources Information Center

Ault, Addison

2009-01-01

Gibbs-energy profiles are often introduced during the first semester of organic chemistry, but are less often presented in connection with enzyme-catalyzed reactions. In this article I show how the Gibbs-energy profile corresponds to the characteristic kinetics of a simple enzyme-catalyzed reaction. (Contains 1 figure and 1 note.)

LEWIS ACID-CATALYZED REACTIONS IN PROTIC MEDIA - LANTHANIDE-CATALYZED REACTIONS OF INDOLES WITH ALDEHYDES OR KETONES. (R826123)

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

Two Palladium-Catalyzed Domino Reactions from One Set of Substrates/Reagents: Efficient Synthesis of Substituted Indenes and cis-Stilbenoid Hydrocarbons from the Same Internal Alkynes and Hindered Grignard Reagents

PubMed Central

Dong, Cheng-Guo; Yeung, Pik; Hu, Qiao-Sheng

2008-01-01

Two types of domino reactions from the same internal alkynes and hindered Grignard reagents based on carbopalladation, Pd-catalyzed cross-coupling reaction and C-H activation strategy are described. The realization of these domino reactions relied on the control of the use of the ligand and the reaction temperature. Our study provides an efficient access to useful polysubstituted indenes and cis-substituted stilbenes, and may offer new means to the development of tandem/domino reactions in a more efficient way. PMID:17217305

Kinetics of non-catalyzed hydrolysis of tannin in high temperature liquid water*

PubMed Central

Lu, Li-li; Lu, Xiu-yang; Ma, Nan

2008-01-01

High temperature liquid water (HTLW) has drawn increasing attention as an environmentally benign medium for organic chemical reactions, especially acid-/base-catalyzed reactions. Non-catalyzed hydrolyses of gallotannin and tara tannin in HTLW for the simultaneous preparation of gallic acid (GA) and pyrogallol (PY) are under investigation in our laboratory. In this study, the hydrolysis kinetics of gallotannin and tara tannin were determined. The reaction is indicated to be a typical consecutive first-order one in which GA has formed as a main intermediate and PY as the final product. Selective decomposition of tannin in HTLW was proved to be possible by adjusting reaction temperature and time. The present results provide an important basic data and reference for the green preparation of GA and PY. PMID:18500780

Co2(CO)8-catalyzed intramolecular hetero-Pauson-Khand reaction of alkynecarbodiimide: synthesis of (+/-)-physostigmine.

PubMed

Mukai, Chisato; Yoshida, Tatsunori; Sorimachi, Mao; Odani, Akira

2006-01-05

[reaction: see text] Herein we describe a novel Co(2)(CO)(8)-catalyzed intramolecular aza-Pauson-Khand-type reaction of alkynecarbodiimide derivatives affords pyrrolo[2,3-b]indol-2-one ring systems in reasonable yields. This is the first reported Co(2)(CO)(8) successfully applied in the hetero-Pauson-Khand reaction. Significantly, the transformation of one of our pyrrolo[2,3-b]indol-2-one derivatives into the indole alkaloid, (+/-)-physostigmine, was completed in a highly stereoselective manner.

A simple, multidimensional approach to high-throughput discovery of catalytic reactions.

PubMed

Robbins, Daniel W; Hartwig, John F

2011-09-09

Transition metal complexes catalyze many important reactions that are employed in medicine, materials science, and energy production. Although high-throughput methods for the discovery of catalysts that would mirror related approaches for the discovery of medicinally active compounds have been the focus of much attention, these methods have not been sufficiently general or accessible to typical synthetic laboratories to be adopted widely. We report a method to evaluate a broad range of catalysts for potential coupling reactions with the use of simple laboratory equipment. Specifically, we screen an array of catalysts and ligands with a diverse mixture of substrates and then use mass spectrometry to identify reaction products that, by design, exceed the mass of any single substrate. With this method, we discovered a copper-catalyzed alkyne hydroamination and two nickel-catalyzed hydroarylation reactions, each of which displays excellent functional-group tolerance.

Influence of hydroxylamine conformation on stereocontrol in Pd-catalyzed isoxazolidine-forming reactions.

PubMed

Lemen, Georgia S; Giampietro, Natalie C; Hay, Michael B; Wolfe, John P

2009-03-20

Palladium-catalyzed carboamination reactions between N-Boc-O-(but-3-enyl)hydroxylamine derivatives and aryl or alkenyl bromides afford cis-3,5- and trans-4,5-disubstituted isoxazolidines in good yield with up to >20:1 dr. The diastereoselectivity observed in the formation of cis-3,5-disubstituted isoxazolidines is superior to selectivities typically obtained in other transformations, such as 1,3-dipolar cycloaddition reactions, that provide these products. In addition, the stereocontrol in the C-N bond-forming Pd-catalyzed carboamination reactions of N-Boc-O-(but-3-enyl)hydroxylamines is significantly higher than that of related C-O bond-forming carboetherification reactions of N-benzyl-N-(but-3-enyl)hydroxylamine derivatives. This is likely due to a stereoelectronic preference for cyclization via transition states in which the Boc group is placed in a perpendicular orientation relative to the plane of the developing ring, which derives from the conformational equilibria of substituted hydroxylamines.

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols.

PubMed

Tait, Katrina; Horvath, Alysia; Blanchard, Nicolas; Tam, William

2017-01-01

The acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicylic alkene using alcohol nucleophiles were investigated. Although this acid-catalyzed ring-opening reaction did not cleave the cyclopropane unit as planned, this represent the first examples of ring-openings of cyclopropanated 3-aza-2-oxabicyclo[2.2.1]alkenes that lead to the cleavage of the C-O bond instead of the N-O bond. Different acid catalysts were tested and it was found that pyridinium toluenesulfonate in methanol gave the best yields in the ring-opening reactions. The scope of the reaction was successfully expanded to include primary, secondary, and tertiary alcohol nucleophiles. Through X-ray crystallography, the stereochemistry of the product was determined which confirmed an S N 2-like mechanism to form the ring-opened product.

Cu-catalyzed aerobic oxidative cyclizations of 3-N-hydroxyamino-1,2-propadienes with alcohols, thiols, and amines to form α-O-, S-, and N-substituted 4-methylquinoline derivatives.

PubMed

Sharma, Pankaj; Liu, Rai-Shung

2015-03-16

A one-pot, two-step synthesis of α-O-, S-, and N-substituted 4-methylquinoline derivatives through Cu-catalyzed aerobic oxidations of N-hydroxyaminoallenes with alcohols, thiols, and amines is described. This reaction sequence involves an initial oxidation of N-hydroxyaminoallenes with NuH (Nu = OH, OR, NHR, and SR) to form 3-substituted 2-en-1-ones, followed by Brønsted acid catalyzed intramolecular cyclizations of the resulting products. Our mechanistic analysis suggests that the reactions proceed through a radical-type mechanism rather than a typical nitrone-intermediate route. The utility of this new Cu-catalyzed reaction is shown by its applicability to the synthesis of several 2-amino-4-methylquinoline derivatives, which are known to be key precursors to several bioactive molecules. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A: The Progression of a Catalytic Immune Response. B: Molecular Recognition of Anions by Silica Bound Sapphyrin

DTIC Science & Technology

1994-08-01

Diels - Alder reactions (58-60), Claisen rearrangements (43-45), olefin isomerization (73), a O-elimination (74), an asymmetric ketone reduction (54...phosphorothioate hapten3 ........ 19 Figure 5. Carboxylic acid hydrolysis .................... 21 Figure 6. Reaction coordinates for antibody catalyzed ...and catalyze the reaction. Thus, it is important to design transition analogs that closely mimic the transition state in every possible chemical

Two palladium-catalyzed domino reactions from one set of substrates/reagents: efficient synthesis of substituted indenes and cis-stilbenoid hydrocarbons from the same internal alkynes and hindered Grignard reagents.

PubMed

Dong, Cheng-Guo; Yeung, Pik; Hu, Qiao-Sheng

2007-01-18

Two types of domino reactions from the same internal alkynes and hindered Grignard reagents based on carbopalladation, Pd-catalyzed cross-coupling reaction, and a C-H activation strategy are described. The realization of these domino reactions relied on the control of the use of the ligand and the reaction temperature. Our study provides efficient access to useful polysubstituted indenes and cis-substituted stilbenes and may offer a new means of development of tandem/domino reactions in a more efficient way. [reaction: see text].

OXALOACETATE DECARBOXYLATION AND OXALOACETATE-CARBON DIOXIDE EXCHANGE IN ACETOBACTER XYLINUM

PubMed Central

Benziman, Moshe; Heller, N.

1964-01-01

Benziman, Moshe (The Hebrew University of Jerusalem, Jerusalem, Israel), and N. Heller. Oxaloacetate decarboxylation and oxaloacetate-carbon dioxide exchange in Acetobacter xylinum. J. Bacteriol. 88:1678–1687. 1964.—Extracts of Acetobacter xylinum, prepared by sonic treatment, were shown to catalyze the decarboxylation of oxaloacetate (OAA) to pyruvate and CO2, and the exchange of C14-carbon dioxide into the β-carboxyl of OAA. Fractionation of the extracts with ammonium sulfate resulted in a 10-fold increase of the specific activity of the enzyme system catalyzing the CO2 exchange and OAA decarboxylation reactions. The purified preparation catalyzed the exchange of pyruvate-3-C14 into OAA. Similar pH curves with a pH optimum of 5.6 were obtained for the CO2 exchange and OAA decarboxylation reactions. Both reactions require the presence of Mn2+ or Mg2+ ions. OAA decarboxylation was more strongly inhibited than the exchange of CO2 by dialysis or metal-chelating agents. Avidin did not inhibit either reaction. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), guanosine triphosphate (GTP), guanosine diphosphate (GDP), pyrophosphate, or inorganic phosphate did not promote OAA decarboxylation and the CO2-exchange reaction catalyzed by the purified preparation. The purified preparation failed to catalyze the carboxylation of phosphoenolpyruvate in the presence of GDP, ADP, or inorganic phosphate, and that of pyruvate in the presence of ATP or GTP, even when supplemented with an OAA-trapping system. A scheme for OAA decarboxylation which could account for the observed exchange reactions and for the failure to obtain net fixation of CO2 is proposed. The relation between the exchange reaction and the synthesis of cellulose from pyruvate by A. xylinum is discussed. PMID:14240957

Applicability of PM3 to transphosphorylation reaction path: Toward designing a minimal ribozyme

NASA Technical Reports Server (NTRS)

Manchester, John I.; Shibata, Masayuki; Setlik, Robert F.; Ornstein, Rick L.; Rein, Robert

1993-01-01

A growing body of evidence shows that RNA can catalyze many of the reactions necessary both for replication of genetic material and the possible transition into the modern protein-based world. However, contemporary ribozymes are too large to have self-assembled from a prebiotic oligonucleotide pool. Still, it is likely that the major features of the earliest ribozymes have been preserved as molecular fossils in the catalytic RNA of today. Therefore, the search for a minimal ribozyme has been aimed at finding the necessary structural features of a modern ribozyme (Beaudry and Joyce, 1990). Both a three-dimensional model and quantum chemical calculations are required to quantitatively determine the effects of structural features of the ribozyme on the reaction it catalyzes. Using this model, quantum chemical calculations must be performed to determine quantitatively the effects of structural features on catalysis. Previous studies of the reaction path have been conducted at the ab initio level, but these methods are limited to small models due to enormous computational requirements. Semiempirical methods have been applied to large systems in the past; however, the accuracy of these methods depends largely on a simple model of the ribozyme-catalyzed reaction, or hydrolysis of phosphoric acid. We find that the results are qualitatively similar to ab initio results using large basis sets. Therefore, PM3 is suitable for studying the reaction path of the ribozyme-catalyzed reaction.

Spatial and temporal control of microwave triggered chemiluminescence: a protein detection platform.

PubMed

Previte, Michael J R; Aslan, Kadir; Geddes, Chris D

2007-09-15

We have combined the principles of microwave circuitry and antenna design and our recent work in microwave-triggered metal-enhanced chemiluminescence to now "trigger" chemically and enzyme-catalyzed chemiluminescent reactions with spatial and temporal control. With this technology platform, we achieve spatial and temporal control of enzyme and chemically catalyzed chemiluminescence reactions to achieve more than 500-fold increases in "on-demand" photon flux from chemically catalyzed chemiluminescent reactions. We also report a 6-fold increase in photon flux from HRP-catalyzed assays on disposable coverslips functionalized with HRP and placed proximal to the substrates modified with thin-film aluminum triangle disjointed "bow-tie" structures. In addition, we demonstrate the applicability of this technology to develop multiplexed or high-throughput chemiluminescent assays. We also demonstrate the clinical and biological relevance of this technology platform by affixing aluminum structures in proximity to HRP protein immobilized on nitrocellulose to improve the sensitivity for this model Western blot scheme by 50-fold. We believe analytical applications that rely on enzyme-catalyzed chemiluminescence, such as immunoassays, may greatly benefit from this new platform technology.

A new family of nucleophiles for photoinduced, copper-catalyzed cross-couplings via single-electron transfer: reactions of thiols with aryl halides under mild conditions (O °C).

PubMed

Uyeda, Christopher; Tan, Yichen; Fu, Gregory C; Peters, Jonas C

2013-06-26

Building on the known photophysical properties of well-defined copper-carbazolide complexes, we have recently described photoinduced, copper-catalyzed N-arylations and N-alkylations of carbazoles. Until now, there have been no examples of the use of other families of heteroatom nucleophiles in such photoinduced processes. Herein, we report a versatile photoinduced, copper-catalyzed method for coupling aryl thiols with aryl halides, wherein a single set of reaction conditions, using inexpensive CuI as a precatalyst without the need for an added ligand, is effective for a wide range of coupling partners. As far as we are aware, copper-catalyzed C-S cross-couplings at 0 °C have not previously been achieved, which renders our observation of efficient reaction of an unactivated aryl iodide at -40 °C especially striking. Mechanistic investigations are consistent with these photoinduced C-S cross-couplings following a SET/radical pathway for C-X bond cleavage (via a Cu(I)-thiolate), which contrasts with nonphotoinduced, copper-catalyzed processes wherein a concerted mechanism is believed to occur.

First application of an efficient and versatile ligand for copper-catalyzed cross-coupling reactions of vinyl halides with N-heterocycles and phenols.

PubMed

Kabir, M Shahjahan; Lorenz, Michael; Namjoshi, Ojas A; Cook, James M

2010-02-05

2-Pyridin-2-yl-1H-benzoimidazole L3 is presented as a new, efficient, and versatile bidentate N-donor ligand suitable for the copper-catalyzed formation of vinyl C-N and C-O bonds. This inexpensive and easily prepared ligand facilitates copper-catalyzed cross-coupling reactions of alkenyl bromides and iodides with N-heterocycles and phenols to afford the desired cross-coupled products in good to excellent yields with full retention of stereochemistry. This method is particularly noteworthy given its efficiency, that is, mild reaction conditions, low catalyst loading, simplicity, versatility, and exceptional level of functional group tolerance.

First Application of An Efficient and Versatile Ligand for Copper-Catalyzed Cross-Coupling Reactions of Vinyl Halides with N-Heterocycles and Phenols

PubMed Central

Kabir, M. Shahjahan; Lorenz, Michael; Namjoshi, Ojas A.; Cook, James M.

2010-01-01

2-Pyridin-2-yl-1H-benzoimidazole L3 is presented as a new, efficient, and versatile bidentate N-donor ligand suitable for the copper-catalyzed formation of vinyl C-N and C-O bonds. This inexpensive and easily prepared ligand facilitates copper-catalyzed cross-coupling reactions of alkenyl bromides and iodides with N-heterocycles and phenols to afford the desired cross-coupled products in good to excellent yields with full retention of stereochemistry. This method is particularly noteworthy given its efficiency i.e., mild reaction conditions, low catalyst loading, simplicity, versatility, and exceptional level of functional group tolerance. PMID:20039699

Pyrimidine Nucleosides with a Reactive (β-Chlorovinyl)sulfone or (β-Keto)sulfone Group at the C5 Position, Their Reactions with Nucleophiles and Electrophiles, and Their Polymerase-Catalyzed Incorporation into DNA

PubMed Central

2018-01-01

Transition-metal-catalyzed chlorosulfonylation of 5-ethynylpyrimidine nucleosides provided (E)-5-(β-chlorovinyl)sulfones A, which undergo nucleophilic substitution with amines or thiols affording B. The treatment of vinyl sulfones A with ammonia followed by acid-catalyzed hydrolysis of the intermediary β-sulfonylvinylamines gave 5-(β-keto)sulfones C. The latter reacts with electrophiles, yielding α-carbon-alkylated or -sulfanylated analogues D. The 5′-triphosphates of A and C were incorporated into double-stranded DNA, using open and one-nucleotide gap substrates, by human or Escherichia coli DNA-polymerase-catalyzed reactions. PMID:29732453

Enzymatic synthesis of chiral amino‐alcohols by coupling transketolase and transaminase‐catalyzed reactions in a cascading continuous‐flow microreactor system

PubMed Central

Gruber, Pia; Carvalho, Filipe; Marques, Marco P. C.; O'Sullivan, Brian; Subrizi, Fabiana; Dobrijevic, Dragana; Ward, John; Hailes, Helen C.; Fernandes, Pedro; Wohlgemuth, Roland; Baganz, Frank

2017-01-01

Abstract Rapid biocatalytic process development and intensification continues to be challenging with currently available methods. Chiral amino‐alcohols are of particular interest as they represent key industrial synthons for the production of complex molecules and optically pure pharmaceuticals. (2S,3R)‐2‐amino‐1,3,4‐butanetriol (ABT), a building block for the synthesis of protease inhibitors and detoxifying agents, can be synthesized from simple, non‐chiral starting materials, by coupling a transketolase‐ and a transaminase‐catalyzed reaction. However, until today, full conversion has not been shown and, typically, long reaction times are reported, making process modifications and improvement challenging. In this contribution, we present a novel microreactor‐based approach based on free enzymes, and we report for the first time full conversion of ABT in a coupled enzyme cascade for both batch and continuous‐flow systems. Using the compartmentalization of the reactions afforded by the microreactor cascade, we overcame inhibitory effects, increased the activity per unit volume, and optimized individual reaction conditions. The transketolase‐catalyzed reaction was completed in under 10 min with a volumetric activity of 3.25 U ml−1. Following optimization of the transaminase‐catalyzed reaction, a volumetric activity of 10.8 U ml−1 was attained which led to full conversion of the coupled reaction in 2 hr. The presented approach illustrates how continuous‐flow microreactors can be applied for the design and optimization of biocatalytic processes. PMID:28986983

Decoration of silicon nanostructures with copper particles for simultaneous selective capture and mass spectrometry detection of His-tagged model peptide.

PubMed

Coffinier, Yannick; Kurylo, Ievgen; Drobecq, Hervé; Szunerits, Sabine; Melnyk, Oleg; Zaitsev, Vladimir N; Boukherroub, Rabah

2014-10-21

We present in this work a simple and fast preparation method of a new affinity surface-assisted laser/desorption ionization mass spectrometry (SALDI-MS) substrate based on silicon nanostructures decorated with copper particles. The silicon nanostructures were fabricated by the metal-assisted chemical etching (MACE) method. Then, superhydrophilic areas surrounded by superhydrophobic regions were formed through hydrosilylation reaction of 1-octadecene, followed by local degradation of the octadecyl layer. After that, copper particles were deposited in the hydrophilic areas by using the electroless method. We have demonstrated that these surfaces were able to perform high selective capture of model His-tag peptide even in a complex mixture such as serum solution. Then, the captured peptide was detected by mass spectrometry at a femtomolar level without the need of organic matrix.

Cu-catalyzed C(sp³)-H bond activation reaction for direct preparation of cycloallyl esters from cycloalkanes and aromatic aldehydes.

PubMed

Zhao, Jincan; Fang, Hong; Han, Jianlin; Pan, Yi

2014-05-02

Cu-catalyzed dehydrogenation-olefination and esterification of C(sp(3))-H bonds of cycloalkanes with TBHP as an oxidant has been developed. The reaction involves four C-H bond activations and gives cycloallyl ester products directly from cycloalkanes and aromatic aldehydes.

Rhodium-catalyzed kinetic resolution of tertiary homoallyl alcohols via stereoselective carbon-carbon bond cleavage.

PubMed

Shintani, Ryo; Takatsu, Keishi; Hayashi, Tamio

2008-03-20

A nonenzymatic kinetic resolution of tertiary homoallyl alcohols has been developed through a rhodium-catalyzed retro-allylation reaction under simple conditions. Selectivity factors of up to 12 have been achieved by employing (R)-H8-binap as the ligand, and the reaction can be conducted on a preparative scale.

The effect of Mg/2+/ and Ca/2+/ on urea-catalyzed phosphorylation reactions

NASA Technical Reports Server (NTRS)

Handschuk, G. J.; Lohrmann, R.; Orgel, L. E.

1973-01-01

The effect of Mg(2+) and Ca(2+) on phosphorylation reactions catalyzed by urea is investigated, showing that Mg(2+) improves markedly the yield of products containing pyrophosphate bonds. Yields of up to 25% of uridine diphosphate can be obtained with struvite at temperatures as low as 65 C.

Pd-catalyzed one-pot synthesis of polysubstituted acrylamidines from isocyanides, diazo compounds, and imines.

PubMed

Yan, Xu; Liao, Jinxi; Lu, Yongzhi; Liu, Jinsong; Zeng, Youlin; Cai, Qian

2013-05-17

A novel and efficient Pd-catalyzed one-pot reaction of ethyl diazoacetate, isocyanides, and imines for the synthesis of acrylamidines was developed. The multicomponent reaction may have occurred through an unpredicted ring-opening process of the ketenimine-imine [2 + 2] intermediate to form the acrylamidine products.

A facile synthesis of pyrrolo[2,3-b]quinolines via a Rh(I)-catalyzed carbodiimide-Pauson-Khand-type reaction.

PubMed

Saito, Takao; Furukawa, Naoki; Otani, Takashi

2010-03-07

A new straightforward synthetic method for 2,3-dihydro-1H-pyrrolo[2,3-b]quinolin-2-ones via a [RhCl(CO)(2)](2)-dppp catalyzed Pauson-Khand-type reaction of N-[2-(2-alkyn-1-yl)phenyl]carbodiimides is reported.

Cu-catalyzed formal methylative and hydrogenative carboxylation of alkynes with carbon dioxide: efficient synthesis of α,β-unsaturated carboxylic acids.

PubMed

Takimoto, Masanori; Hou, Zhaomin

2013-08-19

The sequential hydroalumination or methylalumination of various alkynes catalyzed by different catalyst systems, such those based on Sc, Zr, and Ni complexes, and the subsequent carboxylation of the resulting alkenylaluminum species with CO2 catalyzed by an N-heterocyclic carbene (NHC)-copper catalyst have been examined in detail. The regio- and stereoselectivity of the overall reaction relied largely on the hydroalumination or methylalumination reactions, which significantly depended on the catalyst and alkyne substrates. The subsequent Cu-catalyzed carboxylation proceeded with retention of the stereoconfiguration of the alkenylaluminum species. All the reactions could be carried out in one-pot to afford efficiently a variety of α,β-unsaturated carboxylic acids with well-controlled configurations, which are difficult to construct by previously reported methods. This protocol could be practically useful and attractive because of its high regio- and stereoselectivity, simple one-pot reaction operation, and the use of CO2 as a starting material. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Elucidation of the Pathway to Astaxanthin in the Flowers of Adonis aestivalis[C][W

PubMed Central

Cunningham, Francis X.; Gantt, Elisabeth

2011-01-01

A few species in the genus Adonis are the only land plants known to produce the valuable red ketocarotenoid astaxanthin in abundance. Here, we ascertain the pathway that leads from the β-rings of β-carotene, a carotenoid ubiquitous in plants, to the 3-hydroxy-4-keto-β-rings of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4’-dione) in the blood-red flowers of Adonis aestivalis, an ornamental and medicinal plant commonly known as summer pheasant’s eye. Two gene products were found to catalyze three distinct reactions, with the first and third reactions of the pathway catalyzed by the same enzyme. The pathway commences with the activation of the number 4 carbon of a β-ring in a reaction catalyzed by a carotenoid β-ring 4-dehydrogenase (CBFD), continues with the further dehydrogenation of this carbon to yield a carbonyl in a reaction catalyzed by a carotenoid 4-hydroxy-β-ring 4-dehydrogenase, and concludes with the addition of an hydroxyl group at the number 3 carbon in a reaction catalyzed by the erstwhile CBFD enzyme. The A. aestivalis pathway is both portable and robust, functioning efficiently in a simple bacterial host. Our elucidation of the pathway to astaxanthin in A. aestivalis provides enabling technology for development of a biological production process and reveals the evolutionary origin of this unusual plant pathway, one unrelated to and distinctly different from those used by bacteria, green algae, and fungi to synthesize astaxanthin. PMID:21862704

Carbon Isotope Measurements of Experimentally-Derived Hydrothermal Mineral-Catalyzed Organic Products by Pyrolysis-Isotope Ratio Mass Spectrometry

NASA Technical Reports Server (NTRS)

Socki, Richard A.; Fu, Qi; Niles, Paul B.

2011-01-01

We report results of experiments to measure the C isotope composition of mineral catalyzed organic compounds derived from high temperature and high pressure synthesis. These experiments make use of an innovative pyrolysis technique designed to extract and measure C isotopes. To date, our experiments have focused on the pyrolysis and C isotope ratio measurements of low-molecular weight intermediary hydrocarbons (organic acids and alcohols) and serve as a proof of concept for making C and H isotope measurements on more complicated mixtures of solid-phase hydrocarbons and intermediary products produced during high temperature and high pressure synthesis on mineral-catalyzed surfaces. The impetus for this work stems from recently reported observations of methane detected within the Martian atmosphere [1-4], coupled with evidence showing extensive water-rock interaction during Martian history [5-7]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization reactions [8,9]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [10-12]. Further, recent experiments by Fu et al. [13] focus on examining detailed C isotope measurements of hydrocarbons produced by surface-catalyzed mineral reactions. Work described in this paper details the experimental techniques used to measure intermediary organic reaction products (alcohols and organic acids).

Wash Bottle Laboratory Exercises: Iodide-Catalyzed H[subscript 2]O[subscript 2] Decomposition Reaction Kinetics Using the Initial Rate Approach

ERIC Educational Resources Information Center

Barlag, Rebecca; Nyasulu, Frazier

2010-01-01

A wash bottle water displacement scheme is used to determine the kinetics of the iodide-catalyzed H[subscript 2]O[subscript 2] decomposition reaction. The reagents (total volume 5.00 mL) are added to a test tube that is placed in a wash bottle containing water. The mass of the water displaced in [approximately]60 s is measured. The reaction is…

Copper-Catalyzed γ-Selective and Stereospecific Allylic Cross-Coupling with Secondary Alkylboranes.

PubMed

Yasuda, Yuto; Nagao, Kazunori; Shido, Yoshinori; Mori, Seiji; Ohmiya, Hirohisa; Sawamura, Masaya

2015-06-26

The scope of the copper-catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete γ-E-selectivity and preferential 1,3-syn stereoselectivity. The reaction of γ-silicon-substituted allylic phosphates affords enantioenriched α-stereogenic allylsilanes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper(I)-Catalyzed Chemoselective Coupling of Cyclopropanols with Diazoesters: Ring-Opening C-C Bond Formations.

PubMed

Zhang, Hang; Wu, Guojiao; Yi, Heng; Sun, Tong; Wang, Bo; Zhang, Yan; Dong, Guangbin; Wang, Jianbo

2017-03-27

Reported herein is an exceptional chemoselective ring-opening/C(sp 3 )-C(sp 3 ) bond formation in the copper(I)-catalyzed reaction of cyclopropanols with diazo esters. The conventional O-H insertion product is essentially suppressed by judicious choice of reaction conditions. DFT calculations provide insights into the reaction mechanism and the rationale for this unusual chemoselectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rational approaches for engineering novel functionalities in carbon-carbon bond forming enzymes

PubMed Central

Baker, Perrin; Seah, Stephen Y. K.

2012-01-01

Enzymes that catalyze carbon-carbon bond formation can be exploited as biocatalyst for synthetic organic chemistry. However, natural enzymes frequently do not possess the required properties or specificities to catalyze industrially useful transformations. This mini-review describes recent work using knowledge-guided site-specific mutagenesis of key active site residues to alter substrate specificity, stereospecificity and reaction specificity of these enzymes. In addition, examples of de novo designed enzymes that catalyze C-C bond reactions not found in nature will be discussed. PMID:24688644

Chemoselective chromium(II)-catalyzed cross-coupling reactions of dichlorinated heteroaromatics with functionalized aryl grignard reagents.

PubMed

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

2015-01-26

Chromium(II) chloride catalyzes the chemoselective cross-coupling reaction of dichloropyridines with a range of functionalized (hetero)aromatic Grignard reagents at room temperature. Functional groups, such as esters and acetals, are well tolerated in this transformation. Previously challenging substrates, quinolines and isoquinolines, participate in the selective Cr-catalyzed cross-coupling in cyclopentyl methyl ether (CPME) as the solvent. The effective purging of Cr salts is demonstrated by using various solid supports. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct asymmetric aldol reaction of aryl ketones with aryl aldehydes catalyzed by chiral BINOL-derived zincate catalyst.

PubMed

Li, Hong; Da, Chao-Shan; Xiao, Yu-Hua; Li, Xiao; Su, Ya-Ning

2008-09-19

Direct asymmetric aldol reaction of aryl ketones with aryl aldehydes catalyzed by chiral metal complex is reported for the first time herein. Two novel semicrown chiral ligands 1a and 1b were synthesized from (S)- and (R)-BINOL, respectively, and then employed to catalyze the direct asymmetric aldol addition of aryl ketones to aryl aldehydes. Introduced with 2.0 equiv of diethylzinc, 1b had higher enantioselectivity than 1a. Up to 97% yield and up to 80% enantioselectivity were achieved.

Insights into the Competing Mechanisms and Origin of Enantioselectivity for N-Heterocyclic Carbene-Catalyzed Reaction of Aldehyde with Enamide

NASA Astrophysics Data System (ADS)

Qiao, Yan; Chen, Xinhuan; Wei, Donghui; Chang, Junbiao

2016-12-01

Hydroacylation reactions and aza-benzoin reactions have attracted considerable attention from experimental chemists. Recently, Wang et al. reported an interesting reaction of N-heterocyclic carbene (NHC)-catalyzed addition of aldehyde to enamide, in which both hydroacylation and aza-benzoin reactions may be involved. Thus, understanding the competing relationship between them is of great interest. Now, density functional theory (DFT) investigation was performed to elucidate this issue. Our results reveal that enamide can tautomerize to its imine isomer with the assistance of HCO3-. The addition of NHC to aldehydes formed Breslow intermediate, which can go through cross-coupling with enamide via hydroacylation reaction or its imine isomer via aza-benzoin reaction. The aza-benzoin reaction requires relatively lower free energy barrier than the hydroacylation reaction. The more polar characteristic of C=N group in the imine isomers, and the more advantageous stereoelectronic effect in the carbon-carbon bond forming transition states in aza-benzoin pathway were identified to determine that the imine isomer can react with the Breslow intermediate more easily. Furthermore, the origin of enantioselectivities for the reaction was explored and reasonably explained by structural analyses on key transition states. The work should provide valuable insights for rational design of switchable NHC-catalyzed hydroacylation and aza-benzoin reactions with high stereoselectivity.

Nature's Strategy for Catalyzing Diels-Alder Reaction.

PubMed

Oikawa, Hideaki

2016-04-21

The enzymes catalyzing a Diels-Alder-type reaction have been attractive targets for organic chemists for years. Recently, Zheng et al. (2016) reported the structure of a formal monofunctional Diels-Alderase PyrI4 complexed with the product and unveiled a detailed catalytic mechanism of a highly important enzyme. Copyright © 2016 Elsevier Ltd. All rights reserved.

Method for facilitating catalyzed oxidation reactions, device for facilitating catalyzed oxidation reactions

DOEpatents

Beuhler, Robert J [East Moriches, NY; White, Michael G [Blue Point, NY; Hrbek, Jan [Rocky Point, NY

2006-08-15

A catalytic process for the oxidation of organic. Oxygen is loaded into a metal foil by heating the foil while in contact with an oxygen-containing fluid. After cooling the oxygen-activated foil to room temperature, oxygen diffuses through the foil and oxidizes reactants exposed to the other side of the foil.

Palladium-catalyzed three-component reaction of N-tosyl hydrazones, isonitriles and amines leading to amidines.

PubMed

Dai, Qiang; Jiang, Yan; Yu, Jin-Tao; Cheng, Jiang

2015-12-04

A palladium-catalyzed three-component reaction between N-tosyl hydrazones, aryl isonitriles and amines was developed, leading to amidines in moderate to good yields. This procedure features the rapid construction of amidine frameworks with high diversity and complexity. Ketenimines serve as intermediates, which encounter nucleophilic attack by amines to produce amidines.

Copper-Catalyzed C(sp2)-S Coupling Reactions for the Synthesis of Aryl Dithiocarbamates with Thiuram Disulfide Reagents.

PubMed

Dong, Zhi-Bing; Liu, Xing; Bolm, Carsten

2017-11-03

An efficient protocol for the copper-catalyzed preparation of aryl dithiocarbamates from aryl iodides and inexpensive, environmentally benign tetraalkylthiuram disulfides was developed. The features of mild reaction conditions, high yields, and broad substrate scope render this new approach synthetically attractive for the preparation of potentially biologically active compounds.

Efficient Method for the Determination of the Activation Energy of the Iodide-Catalyzed Decomposition of Hydrogen Peroxide

ERIC Educational Resources Information Center

Sweeney, William; Lee, James; Abid, Nauman; DeMeo, Stephen

2014-01-01

An experiment is described that determines the activation energy (E[subscript a]) of the iodide-catalyzed decomposition reaction of hydrogen peroxide in a much more efficient manner than previously reported in the literature. Hydrogen peroxide, spontaneously or with a catalyst, decomposes to oxygen and water. Because the decomposition reaction is…

Vanadium-Catalyzed C(sp3)–H Fluorination Reactions†

PubMed Central

Xia, Ji-Bao; Ma, Yuyong; Chen, Chuo

2014-01-01

Vanadium(III) oxide catalyzes the direct fluorination of C(sp3)–H groups with Selectfluor. This reaction is operationally simple. The catalyst and the reaction byproduct can be removed easily by filtration. Using this method, a fluorine atom can be introduced to the tertiary position of 1,4-cineole and L-menthone selectively. PMID:24976971

Gold-catalyzed synthesis of benzil derivatives and α-keto imides via oxidation of alkynes.

PubMed

Xu, Cheng-Fu; Xu, Mei; Jia, Yi-Xia; Li, Chuan-Ying

2011-03-18

An efficient process based on the gold-catalyzed redox reaction has been developed to oxidize 1,2-diarylacetylene or ynamide to 1,2-diaryldiketone or α-keto imide respectively. This process can tolerate a variety of functional groups and affords 1,2-dicarbonyl compounds in excellent yields under mild reaction conditions.

Current Developments and Challenges in the Search for a Naturally Selected Diels-Alderase

PubMed Central

Kim, Hak Joong; Ruszczycky, Mark W.; Liu, Hung-wen

2012-01-01

Only a very few examples of enzymes known to catalyze pericyclic reactions have been reported, and presently no enzyme has been demonstrated unequivocally to catalyze a Diels-Alder reaction. Nevertheless, research into secondary metabolism has led to the discovery of numerous natural products exhibiting the structural hallmarks of [4+2] cycloadditions, prompting efforts to characterize the responsible enzymatic processes. These efforts have resulted in a growing collection of enzymes believed to catalyze pericyclic [4+2] cycloaddition reactions; however, in each case the complexity of the substrates and catalytic properties of these enzymes poses significant challenges in substantiating these hypotheses. Herein we consider the principles motivating these efforts and the enzymological systems currently under investigation. PMID:22260931

Synthesis of ketene N,N-acetals by copper-catalyzed double-amidation of 1,1-dibromo-1-alkenes.

PubMed

Coste, Alexis; Couty, François; Evano, Gwilherm

2009-10-01

An efficient procedure for the preparation of ketene N,N-acetals by copper-catalyzed double amidation of 1,1-dibromo-1-alkenes is reported. The reaction was found to be general, and ketene aminals could be obtained in good yields when potassium phosphate in toluene was used at 80 degrees C. The reaction was found to proceed through a regioselective monocoupling reaction followed by dehydrobromination and hydroamidation.

Copper-catalyzed decarboxylative trifluoromethylation of allylic bromodifluoroacetates.

PubMed

Ambler, Brett R; Altman, Ryan A

2013-11-01

The development of new synthetic fluorination reactions has important implications in medicinal, agricultural, and materials chemistries. Given the prevalence and accessibility of alcohols, methods to convert alcohols to trifluoromethanes are desirable. However, this transformation typically requires four-step processes, specialty chemicals, and/or stoichiometric metals to access the trifluoromethyl-containing product. A two-step copper-catalyzed decarboxylative protocol for converting allylic alcohols to trifluoromethanes is reported. Preliminary mechanistic studies distinguish this reaction from previously reported Cu-mediated reactions.

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Qinhua

2004-12-19

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I 2, ICl, PhSeCl, PhSCl and p-O 2NC 6H 4SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellentmore » yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution. A relatively efficient synthesis of cyclopropanes has been developed using palladium-catalyzed C-H activation chemistry, in which two new carbon-carbon bonds are formed in a single step. This method involves the palladium-catalyzed activation of relatively unreactive C-H bonds, and provides a very efficient way to synthesize cyclopropapyrrolo[1,2-a]indoles, analogues of the mitomycin antibiotics.« less

Pd-catalyzed versus uncatalyzed, PhI(OAc)2-mediated cyclization reactions of N6-([1,1'-biaryl]-2-yl)adenine nucleosides.

PubMed

Satishkumar, Sakilam; Poudapally, Suresh; Vuram, Prasanna K; Gurram, Venkateshwarlu; Pottabathini, Narender; Sebastian, Dellamol; Yang, Lijia; Pradhan, Padmanava; Lakshman, Mahesh K

2017-11-09

In this work we have assessed reactions of N 6 -([1,1'-biaryl]-2-yl)adenine nucleosides with Pd(OAc) 2 and PhI(OAc) 2 , via a Pd II /Pd IV redox cycle. The substrates are readily obtained by Pd/Xantphos-catalyzed reaction of adenine nucleosides with 2-bromo-1,1'-biaryls. In PhMe, the N 6 -biarylyl nucleosides gave C6-carbazolyl nucleoside analogues by C-N bond formation with the exocyclic N 6 nitrogen atom. In the solvent screening for the Pd-catalyzed reactions, an uncatalyzed process was found to be operational. It was observed that the carbazolyl products could also be obtained in the absence of a metal catalyst by reaction with PhI(OAc) 2 in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Thus, under Pd catalysis and in HFIP, reactions proceed to provide carbazolyl nucleoside analogues, with some differences. If reactions of N 6 -biarylyl nucleoside substrates were conducted in MeCN, formation of aryl benzimidazopurinyl nucleoside derivatives was observed in many cases by C-N bond formation with the N 1 ring nitrogen atom of the purine (carbazole and benzimidazole isomers are readily separated by chromatography). Whereas Pd II /Pd IV redox is responsible for carbazole formation under the metal-catalyzed conditions, in HFIP and MeCN radical cations and/or nitrenium ions can be intermediates. An extensive set of radical inhibition experiments was conducted and the data are presented.

Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

PubMed

Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

2014-12-01

The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of α,β-unsaturated ketones (Michael acceptor substrates) and α-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and α-keto acids, resulting in 2-hydroxy ketones.

Exerting control over the helical chirality in the main chain of sergeants-and-soldiers-type poly(quinoxaline-2,3-diyl)s by changing from random to block copolymerization protocols.

PubMed

Nagata, Yuuya; Nishikawa, Tsuyoshi; Suginome, Michinori

2015-04-01

Chiral random poly(quinoxaline-2,3-diyl) polymers of the sergeants-and-soldiers-type (sergeant units bearing (S)-3-octyloxymethyl groups) adopt an M- or P-helical conformation in the presence of achiral units bearing propoxymethyl or butoxy groups (soldier units), respectively. Unusual bidirectional induction of the helical sense can be observed for a copolymer with butoxy soldier units upon changing the mole fraction of the sergeant units. In the presence of 16-20% of sergeant units, the selective induction of a P-helix was observed, while the selective induction of an M-helix was observed for a mole fraction of sergeant units of more than 60%. This phenomenon could be successfully employed to control the helical chirality of copolymers by applying either random or block copolymerization protocols. Random or block copolymerization of sergeant and soldier monomers in a 18:82 ratio resulted in the formation of 250mers with almost absolute P- or M-helical conformation, respectively (>99% ee). Incorporation of a small amount of coordination sites into the random and block copolymers resulted in chiral macromolecular ligands, which allowed the enantioselective synthesis of both enantiomers in the Pd-catalyzed asymmetric hydrosilylation of β-methylstyrene.

Redox-neutral rhodium-catalyzed C-H functionalization of arylamine N-oxides with diazo compounds: primary C(sp(3))-H/C(sp(2))-H activation and oxygen-atom transfer.

PubMed

Zhou, Bing; Chen, Zhaoqiang; Yang, Yaxi; Ai, Wen; Tang, Huanyu; Wu, Yunxiang; Zhu, Weiliang; Li, Yuanchao

2015-10-05

An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nickel-catalyzed asymmetric α-arylation and heteroarylation of ketones with chloroarenes: effect of halide on selectivity, oxidation state, and room-temperature reactions.

PubMed

Ge, Shaozhong; Hartwig, John F

2011-10-19

We report the α-arylation of ketones with a range of aryl chlorides with enantioselectivities from 90 to 99% ee catalyzed by the combination of Ni(COD)(2) and (R)-BINAP and the coupling of ketones with a range of heteroaryl chlorides with enantioselectivities up to 99% ee catalyzed by Ni(COD)(2) and (R)-DIFLUORPHOS. The analogous reactions of bromoarenes occur with much lower enantioselectivities. Mechanistic studies showed that the difference in the rates of decomposition of the arylnickel(II) halide intermediates to {[(R)-BINAP]NiX}(2) likely accounts for the difference in the enantioselectivities of the reactions of bromoarenes and chloroarenes. This catalyst decomposition can be overcome by conducting the reactions with [(R)-BINAP]Ni(η(2)-NC-Ph) (4), which undergoes oxidative addition to haloarenes at room temperature.

Large-Scale First-Principles Molecular Dynamics Simulations with Electrostatic Embedding: Application to Acetylcholinesterase Catalysis

DOE PAGES

Fattebert, Jean-Luc; Lau, Edmond Y.; Bennion, Brian J.; ...

2015-10-22

Enzymes are complicated solvated systems that typically require many atoms to simulate their function with any degree of accuracy. We have recently developed numerical techniques for large scale First-Principles molecular dynamics simulations and applied them to study the enzymatic reaction catalyzed by acetylcholinesterase. We carried out Density functional theory calculations for a quantum mechanical (QM) sub- system consisting of 612 atoms with an O(N) complexity finite-difference approach. The QM sub-system is embedded inside an external potential field representing the electrostatic effect due to the environment. We obtained finite temperature sampling by First-Principles molecular dynamics for the acylation reaction of acetylcholinemore » catalyzed by acetylcholinesterase. Our calculations shows two energies barriers along the reaction coordinate for the enzyme catalyzed acylation of acetylcholine. In conclusion, the second barrier (8.5 kcal/mole) is rate-limiting for the acylation reaction and in good agreement with experiment.« less

Enzymatic synthesis of chiral amino-alcohols by coupling transketolase and transaminase-catalyzed reactions in a cascading continuous-flow microreactor system.

PubMed

Gruber, Pia; Carvalho, Filipe; Marques, Marco P C; O'Sullivan, Brian; Subrizi, Fabiana; Dobrijevic, Dragana; Ward, John; Hailes, Helen C; Fernandes, Pedro; Wohlgemuth, Roland; Baganz, Frank; Szita, Nicolas

2018-03-01

Rapid biocatalytic process development and intensification continues to be challenging with currently available methods. Chiral amino-alcohols are of particular interest as they represent key industrial synthons for the production of complex molecules and optically pure pharmaceuticals. (2S,3R)-2-amino-1,3,4-butanetriol (ABT), a building block for the synthesis of protease inhibitors and detoxifying agents, can be synthesized from simple, non-chiral starting materials, by coupling a transketolase- and a transaminase-catalyzed reaction. However, until today, full conversion has not been shown and, typically, long reaction times are reported, making process modifications and improvement challenging. In this contribution, we present a novel microreactor-based approach based on free enzymes, and we report for the first time full conversion of ABT in a coupled enzyme cascade for both batch and continuous-flow systems. Using the compartmentalization of the reactions afforded by the microreactor cascade, we overcame inhibitory effects, increased the activity per unit volume, and optimized individual reaction conditions. The transketolase-catalyzed reaction was completed in under 10 min with a volumetric activity of 3.25 U ml -1 . Following optimization of the transaminase-catalyzed reaction, a volumetric activity of 10.8 U ml -1 was attained which led to full conversion of the coupled reaction in 2 hr. The presented approach illustrates how continuous-flow microreactors can be applied for the design and optimization of biocatalytic processes. © 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Jun; Yang, Dali; Wen, Jianguo

A stable single-site Rh catalyst was formed inside individual channels of three-dimensional dendritic mesoporous silica nanospheres through aminosilane binding. The catalyst demonstrated an excellent activity, stability and recyclability in the reduction of 4-nitrophenol, high regioselectivity in the hydrosilylation of terminal alkyne.

Lipase-catalyzed transesterification of soybean oil and phytosterol in supercritical CO2.

PubMed

Hu, Lizhi; Llibin, Sun; Li, Jun; Qi, Liangjun; Zhang, Xu; Yu, Dianyu; Walid, Elfalleh; Jiang, Lianzhou

2015-12-01

The transesterification of phytosterol and soybean oil was performed using Novozym 435 in supercritical carbon dioxide (SC-CO2). The transesterification reaction was conducted in soybean oil containing 5-25% phytosterol at 55-95 °C and free-water solvent. The effects of temperature, reaction time, phytosterol concentration, lipase dosage and reaction pressure on the conversion rate of transesterification were investigated. The optimal reaction conditions were the reaction temperature (85 °C), reaction time (1 h), phytosterol concentration (5%), reaction pressure (8 Mpa) and lipase dosage (1%). The highest conversion rate of 92% could be achieved under the optimum conditions. Compared with the method of lipase-catalyzed transesterification of phytosterol and soybean oil at normal pressure, the transesterification in SC-CO2 reduced significantly the reaction temperature and reaction time.

Conversion of alkanes to linear alkylsilanes using an iridium-iron-catalysed tandem dehydrogenation-isomerization-hydrosilylation

NASA Astrophysics Data System (ADS)

Jia, Xiangqing; Huang, Zheng

2016-02-01

The conversion of inexpensive, saturated hydrocarbon feedstocks into value-added speciality chemicals using regiospecific, catalytic functionalization of alkanes is a major goal of organometallic chemistry. Linear alkylsilanes represent one such speciality chemical—they have a wide range of applications, including release coatings, silicone rubbers and moulding products. Direct, selective, functionalization of alkanes at primary C-H bonds is difficult and, to date, methods for catalytically converting alkanes into linear alkylsilanes are unknown. Here, we report a well-defined, dual-catalyst system for one-pot, two-step alkane silylations. The system comprises a pincer-ligated Ir catalyst for alkane dehydrogenation and an Fe catalyst that effects a subsequent tandem olefin isomerization-hydrosilylation. This method exhibits exclusive regioselectivity for the production of terminally functionalized alkylsilanes. This dual-catalyst strategy has also been applied to regioselective alkane borylations to form linear alkylboronate esters.

Method of making gold thiolate and photochemically functionalized microcantilevers

DOEpatents

Boiadjiev, Vassil I [Knoxville, TN; Brown, Gilbert M [Knoxville, TN; Pinnaduwage, Lal A [Knoxville, TN; Thundat, Thomas G [Knoxville, TN; Bonnesen, Peter V [Knoxville, TN; Goretzki, Gudrun [Nottingham, GB

2009-08-25

Highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage are taught. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species.

Mechanism and scope of the cyanide-catalyzed cross silyl benzoin reaction.

PubMed

Linghu, Xin; Bausch, Cory C; Johnson, Jeffrey S

2005-02-16

In this work, cross silyl benzoin addition reactions between acylsilanes (1) and aldehydes (2) catalyzed by metal cyanides are described. Unsymmetrical aryl-, heteroaryl-, and alkyl-substituted benzoin adducts can be generated in moderate to excellent yields with complete regiocontrol using potassium cyanide and a phase transfer catalyst. From a screen of transition metal cyanide complexes, lanthanum tricyanide was identified as an improved second-generation catalyst for the cross silyl benzoin reaction. A study of the influence of water on the KCN-catalyzed cross silyl benzoin addition revealed more practical reaction conditions using unpurified solvent under ambient conditions. A sequential silyl benzoin addition/cyanation/O-acylation reaction that resulted in two new C-C bonds was achieved in excellent yield. The mechanism of cross silyl benzoin addition is proposed in detail and is supported by crossover studies and a number of unambiguous experiments designed to ascertain the reversibility of key steps. No productive chemistry arises from cyanation of the more electrophilic aldehyde component. Formation of the carbon-carbon bond is shown to be the last irreversible step in the reaction.

Computational design of an enzyme catalyst for a stereoselective bimolecular Diels-Alder reaction

PubMed Central

Siegel, Justin B.; Zanghellini, Alexandre; Lovick, Helena M.; Kiss, Gert; Lambert, Abigail R.; St.Clair, Jennifer L.; Gallaher, Jasmine L.; Hilvert, Donald; Gelb, Michael H.; Stoddard, Barry L.; Houk, Kendall N.; Michael, Forrest E.; Baker, David

2011-01-01

The Diels-Alder reaction is a cornerstone in organic synthesis, forming two carbon-carbon bonds and up to four new stereogenic centers in one step. No naturally occurring enzymes have been shown to catalyze bimolecular Diels-Alder reactions. We describe the de novo computational design and experimental characterization of enzymes catalyzing a bimolecular Diels-Alder reaction with high stereoselectivity and substrate specificity. X-ray crystallography confirms that the structure matches the design for the most active of the enzymes, and binding site substitutions reprogram the substrate specificity. Designed stereoselective catalysts for carbon-carbon bond forming reactions should be broadly useful in synthetic chemistry. PMID:20647463

Computational design of an enzyme catalyst for a stereoselective bimolecular Diels-Alder reaction.

PubMed

Siegel, Justin B; Zanghellini, Alexandre; Lovick, Helena M; Kiss, Gert; Lambert, Abigail R; St Clair, Jennifer L; Gallaher, Jasmine L; Hilvert, Donald; Gelb, Michael H; Stoddard, Barry L; Houk, Kendall N; Michael, Forrest E; Baker, David

2010-07-16

The Diels-Alder reaction is a cornerstone in organic synthesis, forming two carbon-carbon bonds and up to four new stereogenic centers in one step. No naturally occurring enzymes have been shown to catalyze bimolecular Diels-Alder reactions. We describe the de novo computational design and experimental characterization of enzymes catalyzing a bimolecular Diels-Alder reaction with high stereoselectivity and substrate specificity. X-ray crystallography confirms that the structure matches the design for the most active of the enzymes, and binding site substitutions reprogram the substrate specificity. Designed stereoselective catalysts for carbon-carbon bond-forming reactions should be broadly useful in synthetic chemistry.

Palladium-catalyzed cyclization reactions of 2-vinylthiiranes with heterocumulenes. Regioselective and enantioselective formation of thiazolidine, oxathiolane, and dithiolane derivatives.

PubMed

Larksarp, C; Sellier, O; Alper, H

2001-05-18

The first palladium-catalyzed ring-expansion reaction of 2-vinylthiiranes with heterocumulenes to form sulfur-containing five-membered-ring heterocycles is described. This regioselective reaction requires 5 mol % of Pd(2)(dba)(3).CHCl(3) and 10 mol % of bidendate phosphine ligand (dppp, BINAP), at 50-80 degrees C, in THF. The reaction of 2-vinylthiiranes with carbodiimides, isocyanates, and ketenimines affords 1,3-thiazolidine derivatives, whereas the reaction with diphenylketene or isothiocyanates results in the formation of 1,3-oxathiolane or 1,3-dithiolane compounds in good to excellent isolated yields and in up to 78% ee.

Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?

NASA Technical Reports Server (NTRS)

Richardson, S. L.; Francisco, J. S.; Mebel, A. M.; Morokuma, K.

1997-01-01

The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

Direct asymmetric N-specific reaction of nitrosobenzene with aldehydes catalyzed by a chiral primary amine-based organocatalyst.

PubMed

Qin, Long; Li, Lei; Yi, Lei; Da, Chao-Shan; Zhou, Yi-Feng

2011-08-01

Nitroso compounds have two reactive nitrogen and oxygen atoms. It is interesting and important to perform a nitrogen or oxygen selective reaction with interesting substrates. These atom specific reactions are crucial to specifically synthesis of specific compounds. An enantioselective N-specific reaction of nitrosobenzene with unmodified aldehydes was successfully achieved catalyzed first by a variety of primary amine-based organocatalysts with higher yield and enantioselectivity. The bulkier substituted groups of the organocatalyst and two hydrogen bonds from the organocatalyst and the oxygen atom of nitrosobenzene make the reaction preferentially N-specific and predominantly afford R products. Copyright © 2011 Wiley-Liss, Inc.

Tandem Cu-catalyzed ketenimine formation and intramolecular nucleophile capture: Synthesis of 1,2-dihydro-2-iminoquinolines from 1-(o-acetamidophenyl)propargyl alcohols

PubMed Central

Kant, Ruchir

2014-01-01

Summary The copper-catalyzed ketenimine formation reaction of 1-(o-acetamidophenyl)propargyl alcohols with various sulfonyl azides is found to undergo a concomitant intramolecular nucleophile attack to generate 1,2-dihydro-2-iminoquinolines after aromatization (via elimination of acetyl and hydroxy groups) and tautomerization. The reaction produces 4-substituted and 3,4-unsubstituted title compounds in moderate to good yields under mild reaction conditions. PMID:24991276

Copper(II)-catalyzed oxidative [3+2] cycloaddition reactions of secondary amines with α-diazo compounds: a facile and efficient synthesis of 1,2,3-triazoles.

PubMed

Li, Yi-Jin; Li, Xue; Zhang, Shao-Xiao; Zhao, Yu-Long; Liu, Qun

2015-07-25

A novel copper-catalyzed [3+2] cycloaddition reaction of secondary amines with α-diazo compounds has been developed via a cross-dehydrogenative coupling process. The reaction involves a sequential aerobic oxidation/[3+2] cycloaddition/oxidative aromatization procedure and provides an efficient method for the construction of 1,2,3-triazoles in a single step in an atom-economic manner from readily available starting materials under very mild conditions.

Diastereoselective Synthesis of Symmetrical and Unsymmetrical Tetrahydropyridines Catalyzed by Bi(III) Immobilized on Triazine Dendrimer Stabilized Magnetic Nanoparticles.

PubMed

Asadi, Beheshteh; Landarani-Isfahani, Amir; Mohammadpoor-Baltork, Iraj; Tangestaninejad, Shahram; Moghadam, Majid; Mirkhani, Valiollah; Amiri Rudbari, Hadi

2017-06-12

Unsymmetrical 1,2,5,6-tetrahydropyridine-3-carboxylates were obtained for the first time from a five-component Fe 3 O 4 @TDSN-Bi(III)-catalyzed reaction of aryl aldehydes, aryl amines, and ethyl acetoacetate. This magnetically separable catalyst enabled the selective incorporation of two different aryl amines or two different aryl aldehydes into the product, and provided excellent yields, short reaction times, mild reaction conditions, satisfactory catalyst recyclability, and low catalyst loading.

Nickel-Catalyzed Highly Regioselective Hydrocyanation of Terminal Alkynes with Zn(CN)2 Using Water as the Hydrogen Source.

PubMed

Zhang, Xingjie; Xie, Xin; Liu, Yuanhong

2018-06-08

The first efficient and general nickel-catalyzed hydrocyanation of terminal alkynes with Zn(CN) 2 in the presence of water has been developed. The reaction provides a regioselective protocol for the synthesis of functionalized vinyl nitriles with a range of structural diversity under mild reaction conditions while obviating use of the volatile and hazardous reagent of HCN. Deuterium-labeling experiments confirmed the role of water as the hydrogen source in this hydrocyanation reaction.

N-Triflylthiophosphoramide Catalyzed Enantioselective Mukaiyama Aldol Reaction of Aldehydes with Silyl Enol Ethers of Ketones

PubMed Central

Cheon, Cheol Hong; Yamamoto, Hisashi

2010-01-01

The first Brønsted acid catalyzed asymmetric Mukaiyama aldol reaction of aldehydes using silyl enol ethers of ketones as nucleophiles has been reported. A variety of aldehydes and silyl enol ethers of ketones afforded the aldol products in excellent yields and good to excellent enantioselectivities. Mechanistic studies revealed that the actual catalyst may be changed from the silylated Brønsted acid to Brønsted acid itself depending on the reaction temperature. PMID:20465277

N-triflylthiophosphoramide catalyzed enantioselective Mukaiyama aldol reaction of aldehydes with silyl enol ethers of ketones.

PubMed

Cheon, Cheol Hong; Yamamoto, Hisashi

2010-06-04

The first Brønsted acid catalyzed asymmetric Mukaiyama aldol reaction of aldehydes using silyl enol ethers of ketones as nucleophiles has been reported. A variety of aldehydes and silyl enol ethers of ketones afforded the aldol products in excellent yields and good to excellent enantioselectivities. Mechanistic studies revealed that the actual catalyst may be changed from the silylated Brønsted acid to the Brønsted acid itself depending on the reaction temperature.

Glycerol Dehydration to Acrolein Catalyzed by ZSM‐5 Zeolite in Supercritical Carbon Dioxide Medium

PubMed Central

Zou, Bin; Ren, Shoujie

2016-01-01

Abstract Supercritical carbon dioxide (SC‐CO2) has been used for the first time as a reaction medium for the dehydration of glycerol to acrolein catalyzed by a solid acid. Unprecedented catalyst stability over 528 hours of time‐on‐stream was achieved and the rate of coke deposition on the zeolite catalyst was the lowest among extensive previous studies, showing potential for industrial application. Coking pathways in SC‐CO2 were also elucidated for future development. The results have potential implications for other dehydration reactions catalyzed by solid acids. PMID:27796088

Nickel-based Enzyme Systems*

PubMed Central

Ragsdale, Stephen W.

2009-01-01

Of the eight known nickel enzymes, all but glyoxylase I catalyze the use and/or production of gases central to the global carbon, nitrogen, and oxygen cycles. Nickel appears to have been selected for its plasticity in coordination and redox chemistry and is able to cycle through three redox states (1+, 2+, 3+) and to catalyze reactions spanning ∼1.5 V. This minireview focuses on the catalytic mechanisms of nickel enzymes, with an emphasis on the role(s) of the metal center. The metal centers vary from mononuclear to complex metal clusters and catalyze simple hydrolytic to multistep redox reactions. PMID:19363030

Nitrous oxide-forming codenitrification catalyzed by cytochrome P450nor.

PubMed

Su, Fei; Takaya, Naoki; Shoun, Hirofumi

2004-02-01

Intact cells of the denitrifying fungus Fusarium oxysporum were previously shown to catalyze codenitrification to form a hybrid nitrous oxide (N2O) species from nitrite and other nitrogen compounds such as azide and ammonia. Here we show that cytochrome P450nor can catalyze the codenitrification reaction to form N2O from nitric oxide (NO) but not nitrite, and azide or ammonia. The results show that the direct substrate of the codenitrification by intact cells should not be nitrite but NO, which is formed from nitrite by the reaction of a dissimilatory nitrite reductase.

Application of meta- and para- phenylenediamine as enhanced oxime ligation catalysts for protein labeling, PEGylation, immobilization and release

PubMed Central

Mahmoodi, Mohammad M.; Rashidian, Mohammad; Zhang, Yi; Distefano, Mark D.

2015-01-01

Meta- and para- phenylenediamines have recently been shown to catalyze oxime and hydrazone ligation reactions at rates much faster than aniline, a commonly used catalyst. Here, it is demonstrated how these new catalysts can be used in a generally applicable procedure for fluorescent labeling, PEGylation, immobilization and release of aldehyde and ketone functionalized proteins. The chemical orthogonality of phenylenediamine-catalyzed oxime ligation versus copper catalyzed click reaction has also been harnessed for simultaneous dual labeling of bifunctional proteins containing both aldehyde and alkyne groups in high yield. PMID:25640893

Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions

DOEpatents

Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

2003-12-30

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

Catalytic Hydroamination of Alkynes and Norbornene with Neutral and Cationic Tantalum Imido Complexes

PubMed Central

Anderson, Laura L.; Arnold, John; Bergman, Robert G.

2005-01-01

Several tantalum imido complexes have been synthesized and shown to efficiently catalyze the hydroamination of internal and terminal alkynes. An unusual hydroamination/hydroarylation reaction of norbornene catalyzed by a highly electrophilic cationic tantalum imido complex is also reported. Factors affecting catalyst activity and selectivity are discussed along with mechanistic insights gained from stoichiometric reactions. PMID:15255680

Remarkable co-catalysis by copper(I) oxide in the palladium catalyzed cross-coupling of arylboronic acids with ethyl bromoacetate.

PubMed

Liu, Xing-xin; Deng, Min-zhi

2002-03-21

Copper(I) oxide can effectively co-catalyze the Suzuki type cross-coupling reactions of arylboronic acids with ethyl bromoacetate. As an alternative protocol for introducing the methylenecarboxy group into functionalized molecules, this reaction occurs in the absence of highly toxic thallium compounds or special ligands and should be convenient and practical.

Nerve Agent Sensing Biopolymer Wipe

DTIC Science & Technology

2003-04-01

3. Urease and BChE (at two concentrations) activity as function of pH. ..... 10 Figure 4. Reaction scheme Agentase nerve agent sensor...11 Figure 5. Signal development in Agentase’s Traffic Light Sensor Construct.......... 11 Figure 6. Effect of BChE/ urease ...between two competing enzyme reactions. BChE catalyzed butyrylcholine hydrolysis results in the production of acid (decreasing pH) while urease - catalyzed

γ-Alumina Nanoparticle Catalyzed Efficient Synthesis of Highly Substituted Imidazoles.

PubMed

Reddy, Bandapalli Palakshi; Vijayakumar, Vijayaparthasarathi; Arasu, Mariadhas Valan; Al-Dhabi, Naif Abdullah

2015-10-21

γ-Alumina nano particle catalyzed multi component reaction of benzil, arylaldehyde and aryl amines afforded the highly substituted 1,2,4,5-tetraaryl imidazoles with good to excellent yield in less reaction time under the sonication as well as the conventional methods. Convenient operational simplicity, mild conditions and the reusability of catalyst were the other advantages of this developed protocol.

H NMR studies of substrate hydrogen exchange reactions catalyzed by L-methionine gamma-lyase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esaki, N.; Nakayama, T.; Sawada, S.

Hydrogen exchange reactions of various L-amino acids catalyzed by L-methionine gamma-lyase (EC 4.4.1.11) have been studied. The enzyme catalyzes the rapid exchange of the alpha- and beta-hydrogens of L-methionine and S-methyl-L-cysteine with deuterium from the solvent. The rate of alpha-hydrogen exchange was about 40 times faster than that of the enzymatic elimination reaction of the sulfur-containing amino acids. The enzyme also catalyzes the exchange reaction of alpha- and beta-hydrogens of the straight-chain L-amino acids which are not susceptible to elimination. The exchange rates of the alpha-hydrogen and the total beta-hydrogens of L-alanine and L-alpha-aminobutyrate with deuterium followed first-order kinetics. Formore » L-norvaline, L-norleucine, S-methyl-L-cysteine, and L-methionine, the rate of alpha-hydrogen exchange followed first-order kinetics, but the rate of total beta-hydrogen exchange decreased due to a primary isotope effect at the alpha-position. L-Phenylalanine and L-tryptophan slowly underwent alpha-hydrogen exchange. The pro-R hydrogen of glycine was deuterated stereospecifically.« less

Structure–Function Studies of Hydrophobic Residues That Clamp a Basic Glutamate Side Chain during Catalysis by Triosephosphate Isomerase

PubMed Central

2016-01-01

Kinetic parameters are reported for the reactions of whole substrates (kcat/Km, M–1 s–1) (R)-glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) and for the substrate pieces [(kcat/Km)E·HPi/Kd, M–2 s–1] glycolaldehyde (GA) and phosphite dianion (HPi) catalyzed by the I172A/L232A mutant of triosephosphate isomerase from Trypanosoma brucei brucei (TbbTIM). A comparison with the corresponding parameters for wild-type, I172A, and L232A TbbTIM-catalyzed reactions shows that the effect of I172A and L232A mutations on ΔG⧧ for the wild-type TbbTIM-catalyzed reactions of the substrate pieces is nearly the same as the effect of the same mutations on TbbTIM previously mutated at the second side chain. This provides strong evidence that mutation of the first hydrophobic side chain does not affect the functioning of the second side chain in catalysis of the reactions of the substrate pieces. By contrast, the effects of I172A and L232A mutations on ΔG⧧ for wild-type TbbTIM-catalyzed reactions of the whole substrate are different from the effect of the same mutations on TbbTIM previously mutated at the second side chain. This is due to the change in the rate-determining step that determines the barrier to the isomerization reaction. X-ray crystal structures are reported for I172A, L232A, and I172A/L232A TIMs and for the complexes of these mutants to the intermediate analogue phosphoglycolate (PGA). The structures of the PGA complexes with wild-type and mutant enzymes are nearly superimposable, except that the space opened by replacement of the hydrophobic side chain is occupied by a water molecule that lies ∼3.5 Å from the basic side chain of Glu167. The new water at I172A mutant TbbTIM provides a simple rationalization for the increase in the activation barrier ΔG⧧ observed for mutant enzyme-catalyzed reactions of the whole substrate and substrate pieces. By contrast, the new water at the L232A mutant does not predict the decrease in ΔG⧧ observed for the mutant enzyme-catalyzed reactions of the substrate piece GA. PMID:27149328

Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

PubMed

Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

2016-05-17

Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in solving complex problems and proposing new detailed reaction mechanisms that rationalize the experimental findings. For each of the considered reactions, a consistent mechanism is presented, the experimentally observed selectivities are reproduced, and their sources are identified. Reproducing selectivities requires high accuracy in computing relative transition state energies. As demonstrated by the results summarized in this Account, this accuracy is possible with the use of the presented methodology, benefiting of course from a large extent of cancellation of systematic errors. It is argued that as the employed models become larger, the number of rotamers and isomers that have to be considered for every stationary point increases and a careful assessment of their energies is therefore necessary in order to ensure that the lowest energy conformation is located. This issue constitutes a bottleneck of the investigation in some cases and is particularly important when analyzing selectivities, since small energy differences need to be reproduced.

Mechanistic Comparison Between Pd-Catalyzed Ligand Directed C-H Chlorination and C-H Acetoxylation

PubMed Central

Stowers, Kara J.; Sanford, Melanie S.

2009-01-01

This communication describes detailed investigations of the mechanism of the Pd-catalyzed C-H chlorination and acetoxylation of 2-ortho-tolylpyridine. Under the conditions examined, both reactions proceed via rate limiting cyclopalladation. However, substrate and catalyst order as well as Hammett data indicate that the intimate mechanism of cyclopalladation differs significantly between PdCl2-catalyzed chlorination and Pd(OAc)2-catalyzed acetoxylation. PMID:19754074

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies

NASA Technical Reports Server (NTRS)

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

Mechanistic insights into iron catalyzed dehydrogenation of formic acid: β-hydride elimination vs. direct hydride transfer.

PubMed

Yang, Xinzheng

2013-09-07

Density functional theory calculations reveal a complete reaction mechanism with detailed energy profiles and transition state structures for the dehydrogenation of formic acid catalyzed by an iron complex, [P(CH2CH2PPh2)3FeH](+). In the cationic reaction pathway, a β-hydride elimination process is confirmed to be the rate-determining step in this catalytic reaction. A potential reaction pathway starting with a direct hydride transfer from HCOO(-) to Fe is found to be possible, but slightly less favorable than the catalytic cycle with a β-hydride elimination step.

Iron-catalyzed stereospecific activation of olefinic C-H bonds with Grignard reagent for synthesis of substituted olefins.

PubMed

Ilies, Laurean; Asako, Sobi; Nakamura, Eiichi

2011-05-25

The reaction of an aryl Grignard reagent with a cyclic or acyclic olefin possessing a directing group such as pyridine or imine results in the stereospecific substitution of the olefinic C-H bond syn to the directing group. The reaction takes place smoothly and without isomerization of the product olefin in the presence of a mild oxidant (1,2-dichloro-2-methylpropane) and an aromatic cosolvent. Several lines of evidence suggest that the reaction proceeds via iron-catalyzed olefinic C-H bond activation rather than an oxidative Mizoroki-Heck-type reaction.

Horseradish-Peroxidase-Catalyzed Tyrosine Click Reaction.

PubMed

Sato, Shinichi; Nakamura, Kosuke; Nakamura, Hiroyuki

2017-03-02

The efficiency of protein chemical modification on tyrosine residues with N-methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H 2 O 2 , oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N-methylluminol derivatives with a minimum amount of H 2 O 2 prevented the occurrence of oxidative side reactions under HRP-catalyzed conditions. As probes for HRP-catalyzed protein modification, N-methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β-nicotinamide adenine dinucleotide (NADH, H 2 O 2 -free conditions). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomically dispersed Au-(OH)x species bound on titania catalyze the low-temperature water-gas shift reaction.

PubMed

Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria

2013-03-13

We report a new method for stabilizing appreciable loadings (~1 wt %) of isolated gold atoms on titania and show that these catalyze the low-temperature water-gas shift reaction. The method combines a typical gold deposition/precipitation method with UV irradiation of the titania support suspended in ethanol. Dissociation of H2O on the thus-created Au-O-TiO(x) sites is facile. At higher gold loadings, nanoparticles are formed, but they were shown to add no further activity to the atomically bound gold on titania. Removal of this "excess" gold by sodium cyanide leaching leaves the activity intact and the atomically dispersed gold still bound on titania. The new materials may catalyze a number of other reactions that require oxidized active metal sites.

Rhodium-Catalyzed Acyloxy Migration of Propargylic Esters in Cycloadditions, Inspiration from Recent “Gold Rush”

PubMed Central

Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M.

2012-01-01

Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most π-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed. PMID:22895533

Insights into the Competing Mechanisms and Origin of Enantioselectivity for N-Heterocyclic Carbene-Catalyzed Reaction of Aldehyde with Enamide

PubMed Central

Qiao, Yan; Chen, Xinhuan; Wei, Donghui; Chang, Junbiao

2016-01-01

Hydroacylation reactions and aza-benzoin reactions have attracted considerable attention from experimental chemists. Recently, Wang et al. reported an interesting reaction of N-heterocyclic carbene (NHC)-catalyzed addition of aldehyde to enamide, in which both hydroacylation and aza-benzoin reactions may be involved. Thus, understanding the competing relationship between them is of great interest. Now, density functional theory (DFT) investigation was performed to elucidate this issue. Our results reveal that enamide can tautomerize to its imine isomer with the assistance of HCO3−. The addition of NHC to aldehydes formed Breslow intermediate, which can go through cross-coupling with enamide via hydroacylation reaction or its imine isomer via aza-benzoin reaction. The aza-benzoin reaction requires relatively lower free energy barrier than the hydroacylation reaction. The more polar characteristic of C=N group in the imine isomers, and the more advantageous stereoelectronic effect in the carbon-carbon bond forming transition states in aza-benzoin pathway were identified to determine that the imine isomer can react with the Breslow intermediate more easily. Furthermore, the origin of enantioselectivities for the reaction was explored and reasonably explained by structural analyses on key transition states. The work should provide valuable insights for rational design of switchable NHC-catalyzed hydroacylation and aza-benzoin reactions with high stereoselectivity. PMID:27905524

Micropatterned arrays of porous silicon: toward sensory biointerfaces.

PubMed

Flavel, Benjamin S; Sweetman, Martin J; Shearer, Cameron J; Shapter, Joseph G; Voelcker, Nicolas H

2011-07-01

We describe the fabrication of arrays of porous silicon spots by means of photolithography where a positive photoresist serves as a mask during the anodization process. In particular, photoluminescent arrays and porous silicon spots suitable for further chemical modification and the attachment of human cells were created. The produced arrays of porous silicon were chemically modified by means of a thermal hydrosilylation reaction that facilitated immobilization of the fluorescent dye lissamine, and alternatively, the cell adhesion peptide arginine-glycine-aspartic acid-serine. The latter modification enabled the selective attachment of human lens epithelial cells on the peptide functionalized regions of the patterns. This type of surface patterning, using etched porous silicon arrays functionalized with biological recognition elements, presents a new format of interfacing porous silicon with mammalian cells. Porous silicon arrays with photoluminescent properties produced by this patterning strategy also have potential applications as platforms for in situ monitoring of cell behavior.

Catalyzed Atomic Layer Deposition of Silicon Oxide at Ultralow Temperature Using Alkylamine.

PubMed

Mayangsari, Tirta R; Park, Jae-Min; Yusup, Luchana L; Gu, Jiyeon; Yoo, Jin-Hyuk; Kim, Heon-Do; Lee, Won-Jun

2018-06-12

We report the catalyzed atomic layer deposition (ALD) of silicon oxide using Si 2 Cl 6 , H 2 O, and various alkylamines. The density functional theory (DFT) calculations using the periodic slab model of the SiO 2 surface were performed for the selection of alternative Lewis base catalysts with high catalytic activities. During the first half-reaction, the catalysts with less steric hindrance such as pyridine would be more effective than bulky alkylamines despite lower nucleophilicity. On the other hand, during the second half-reaction, the catalysts with a high nucleophilicity such as triethylamine (Et 3 N) would be more efficient because the steric hindrance is less critical. The in situ process monitoring shows that the calculated atomic charge is a good indicator for expecting the catalyst activity in the ALD reaction. The use of Et 3 N in the second half-reaction was essential to improving the growth rate as well as the step coverage of the film because the Et 3 N-catalyzed process deposited a SiO 2 film with a step coverage of 98% that is better than 93% of the pyridine-catalyzed process. The adsorption of pyridine, ammonia (NH 3 ), or trimethylamine (Me 3 N) salts was more favorable than that of Et 3 N, n-Pr 3 N, or i Pr 3 N salts. Therefore, Et 3 N was expected to incorporate less amine salts in the film as compared to pyridine, and the compositional analyses confirmed that the concentrations of Cl and N by the Et 3 N-catalyzed process were significantly lower than those by the pyridine-catalyzed process.

The sugar model: catalysis by amines and amino acid products

NASA Technical Reports Server (NTRS)

Weber, A. L.

2001-01-01

Ammonia and amines (including amino acids) were shown to catalyze the formation of sugars from formaldehyde and glycolaldehyde, and the subsequent conversion of sugars to carbonylcontaining products under the conditions studied (pH 5.5 and 50 degrees C). Sterically unhindered primary amines were better catalysts than ammonia, secondary amines, and sterically hindered primary amines (i.e. alpha-aminoisobutyric acid). Reactions catalyzed by primary amines initially consumed formaldehyde and glycolaldehyde about 15-20 times faster than an uncatalyzed control reaction. The amine-catalyzed reactions yielded aldotriose (glyceraldehyde), ketotriose (dihydroxyacetone), aldotetroses (erythrose and threose), ketotetrose (erythrulose), pyruvaldehyde, acetaldehyde, glyoxal, pyruvate, glyoxylate, and several unindentified carbonyl products. The concentrations of the carbonyl products, except pyruvate and ketotetrose, initially increased and then declined during the reaction, indicating their ultimate conversion to other products (like larger sugars or pyruvate). The uncatalyzed control reaction yielded no pyruvate or glyoxylate, and only trace amounts of pyruvaldehyde, acetaldehyde and glyoxal. In the presence of 15 mM catalytic primary amine, such as alanine, the rates of triose and pyruvaldehyde of synthesis were about 15-times and 1200-times faster, respectively, than the uncatalyzed reaction. Since previous studies established that alanine is synthesized from glycolaldehyde and formaldehyde via pyruvaldehyde as its direct precursor, the demonstration that the alanine catalyzes the conversion of glycolaldehyde and formaldehyde to pyruvaldehyde indicates that this synthetic pathway is capable of autocatalysis. The relevance of this synthetic process, named the Sugar Model, to the origin of life is discussed.

Gold (I)-Catalyzed Diastereo- and Enantioselective 1,3-Dipolar Cycloaddition and Mannich Reactions of Azlactones

PubMed Central

Melhado, Asa D.; Amarante, Giovanni W.; Wang, Z. Jane; Luparia, Marco; Toste, F. Dean

2011-01-01

Azlactones participate in stereoselective reactions with electron-deficient alkenes and N-sulfonyl aldimines to give products of 1,3-dipolar cycloaddition and Mannich addition reactions respectively. Both of these reactions proceed with good to excellent diastereo- and enantioselectivity using a single class of gold-catalysts, namely C2-symmetric bis(phosphinegold(I) carboxylate)complexes. The development of the azlactone Mannich reaction to provide fully protected anti-α,β-diamino acid derivatives is described. 1,3-Dipolar cycloaddition reactions of several acyclic 1,2-disubstituted alkenes, and the chemistry of the resultant cycloadducts, are examined to probe the stereochemical course of this reaction. Reaction kinetics and tandem MS studies of both the cycloaddition and Mannich reactions are reported. These studies support a mechanism in which the gold complexes catalyze addition reactions through nucleophile activation rather than the more typical activation of the electrophilic reaction component. PMID:21341677

Stereospecific Nickel-Catalyzed Cross-Coupling Reactions of Alkyl Grignard Reagents and Identification of Selective Anti-Breast Cancer Agents**

PubMed Central

Osborne, Charlotte A.; Moore, Curtis E.; Morrissette, Naomi S.; Jarvo, Elizabeth R.

2014-01-01

β-Hydrogen-containing alkyl Grignard reagents were used in a stereospecific nickel-catalyzed cross-coupling reaction to form sp3–sp3 carbon–carbon bonds. Aryl Grignard reagents were also utilized to synthesize 1,1-diarylalkanes. Several compounds synthesized by this method exhibited selective inhibition of proliferation of MCF-7 breast cancer cells. PMID:24478275

Kinetics of Mn3+-oxalate formation and decay in reactions catalyzed by manganese peroxidase of Ceriporiopsis subvermispora

Treesearch

Ulises Urzua; Philip J. Kersten; Rafael Vicuna

1998-01-01

The kinetics of Mn3+- oxalate formation and decay were investigated in reactions catalyzed by manganese peroxidase (MnP) from the basiomycete Ceriporiopsis subvermispora in the absence of externally added hydrogen peroxide. A characteristic lag observed in the formation of this complex was shortened by glyoxylate or catalytic amounts of Mn3+ or hydrogen peroxide. MnP...

Selected soil enzyme activities in an oak-hickory forest following long-term prescribed burning

Treesearch

M. R. Bayan; F. Eivazi

1993-01-01

The biochemical reactions within the soil are mediated by soil flora and fauna, and are catalyzed by enzymes. Therefore, enzymes play a significant role in nutrient cycling. Enzymes are specific for the type of chemical reactions in which they participate. Arylsulfatase is the enzyme that catalyzes the hydrolysis of an arylsulfate anion by fission of the oxygen-sulfur...

Indole synthesis by palladium-catalyzed tandem allylic isomerization - furan Diels-Alder reaction.

PubMed

Xu, Jie; Wipf, Peter

2017-08-30

A Pd(0)-catalyzed elimination of an allylic acetate generates a π-allyl complex that is postulated to initiate a novel intramolecular Diels-Alder cycloaddition to a tethered furan (IMDAF). Under the reaction conditions, this convergent, microwave-accelerated cascade process provides substituted indoles in moderate to good yields after Pd-hydride elimination, aromatization by dehydration, and in situ N-Boc cleavage.

Mechanism and Catalytic Diversity of Rieske Non-Heme Iron-Dependent Oxygenases

PubMed Central

Barry, Sarah M.; Challis, Gregory L.

2013-01-01

Rieske non-heme iron-dependent oxygenases are important enzymes that catalyze a wide variety of reactions in the biodegradation of xenobiotics and the biosynthesis of bioactive natural products. In this perspective article, we summarize recent efforts to elucidate the catalytic mechanisms of Rieske oxygenases and highlight the diverse range of reactions now known to be catalyzed by such enzymes. PMID:24244885

Nickel-catalyzed synthesis of diarylamines via oxidatively induced C-N bond formation at room temperature.

PubMed

Ilies, Laurean; Matsubara, Tatsuaki; Nakamura, Eiichi

2012-11-02

A nickel-catalyzed oxidative coupling of zinc amides with organomagnesium compounds selectively produces diarylamines under mild reaction conditions, with tolerance for chloride, bromide, hydroxyl, ester, and ketone groups. A diamine is bis-monoarylated. A bromoaniline undergoes N-arylation followed by Kumada-Tamao-Corriu coupling in one pot. The reaction may proceed via oxidatively induced reductive elimination of a nickel species.

Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

PubMed Central

Edmunds, Michael; Raheem, Mohammed Abdul; Boutin, Rebecca; Tait, Katrina

2016-01-01

Summary Palladium-catalyzed ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl2(PPh3)2, ZnCl2, Et3N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing the steric bulk on the bridgehead carbon decreased the yield. These reactions were found to be highly regioselective, giving only one of the two possible regioisomers in all cases. A diverse collection of novel, highly substituted biphenyl derivatives were obtained. PMID:26977182

Palladium-catalyzed cyclocoupling of 2-halobiaryls with isocyanides via the cleavage of carbon-hydrogen bonds.

PubMed

Tobisu, Mamoru; Imoto, Shinya; Ito, Sana; Chatani, Naoto

2010-07-16

To demonstrate the utility of isocyanides in catalytic C-H bond functionalization reactions, a palladium-catalyzed cyclocoupling reaction of 2-halobiaryls with isocyanides was developed. The reaction afforded an array of fluorenone imine derivatives via the cleavage of a C-H bond at the 2'-position of 2-halobiaryls. The use of 2,6-disubstituted phenyl isocyanide was crucial for this catalytic cyclocoupling reaction to proceed. The reaction was applicable to heterocyclic and vinylic substrates, allowing the construction of a wide range of ring system. The large kinetic isotope effect observed (k(H)/k(D) = 5.3) indicates that C-H bond activation was the turnover-limiting step in this catalysis.

Unified mechanism of alkali and alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O

USGS Publications Warehouse

Chen, S.G.; Yang, R.T.

1997-01-01

From molecular orbital calculations, a unified mechanism is proposed for the gasification reactions of graphite by CO2 and H2O, both uncatalyzed and catalyzed by alkali and alkaline earth catalysts. In this mechanism, there are two types of oxygen intermediates that are bonded to the active edge carbon atoms: an in-plane semiquinone type, Cf(O), and an off-plane oxygen bonded to two saturated carbon atoms that are adjacent to the semiquinone species, C(O)Cf(O). The rate-limiting step is the decomposition of these intermediates by breaking the C-C bonds that are connected to Cf(O). A new rate equation is derived for the uncatalyzed reactions, and that for the catalyzed reactions is readily available from the proposed mechanism. The proposed mechanism can account for several unresolved experimental observations: TPD and TK (transient kinetics) desorption results of the catalyzed systems, the similar activation energies for the uncatalyzed and catalyzed reactions, and the relative activities of the alkali and alkaline earth elements. The net charge of the edge carbon active site is substantially changed by gaining electron density from the alkali or alkaline earth element (by forming C-O-M, where M stands for metal). The relative catalytic activities of these elements can be correlated with their abilities of donating electrons and changing the net charge of the edge carbon atom. As shown previously (Chen, S. G.; Yang, R. T. J. Catal. 1993, 141, 102), only clusters of the alkali compounds are active. This derives from the ability of the clusters to dissociate CO2 and H2O to form O atoms and the mobility of the dissociated O atoms facilitated by the clusters.

Synthesis of δ- and α-Carbolines via Nickel-Catalyzed [2 + 2 + 2] Cycloaddition of Functionalized Alkyne-Nitriles with Alkynes.

PubMed

Wang, Gaonan; You, Xu; Gan, Yi; Liu, Yuanhong

2017-01-06

A new method for the synthesis of δ- and α-carbolines through Ni-catalyzed [2 + 2 + 2] cycloaddition of ynamide-nitriles or alkyne-cyanamides with alkynes has been developed. The catalytic system of NiCl 2 (DME)/dppp/Zn with a low-cost Ni(II)-precursor was first utilized in Ni-catalyzed [2 + 2 + 2] cycloaddition reactions, and the in situ generated Lewis acid may play an important role for the successful transformation. Not only internal alkynes but also terminal alkynes undergo the desired cycloaddition reactions efficiently to furnish the carboline derivatives with wide diversity and functional group tolerance.

Glycerol Dehydration to Acrolein Catalyzed by ZSM-5 Zeolite in Supercritical Carbon Dioxide Medium.

PubMed

Zou, Bin; Ren, Shoujie; Ye, X Philip

2016-12-08

Supercritical carbon dioxide (SC-CO 2 ) has been used for the first time as a reaction medium for the dehydration of glycerol to acrolein catalyzed by a solid acid. Unprecedented catalyst stability over 528 hours of time-on-stream was achieved and the rate of coke deposition on the zeolite catalyst was the lowest among extensive previous studies, showing potential for industrial application. Coking pathways in SC-CO 2 were also elucidated for future development. The results have potential implications for other dehydration reactions catalyzed by solid acids. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Catalytic strategy for carbon−carbon bond scission by the cytochrome P450 OleT

PubMed Central

Grant, Job L.; Mitchell, Megan E.; Makris, Thomas Michael

2016-01-01

OleT is a cytochrome P450 that catalyzes the hydrogen peroxide-dependent metabolism of Cn chain-length fatty acids to synthesize Cn-1 1-alkenes. The decarboxylation reaction provides a route for the production of drop-in hydrocarbon fuels from a renewable and abundant natural resource. This transformation is highly unusual for a P450, which typically uses an Fe4+−oxo intermediate known as compound I for the insertion of oxygen into organic substrates. OleT, previously shown to form compound I, catalyzes a different reaction. A large substrate kinetic isotope effect (≥8) for OleT compound I decay confirms that, like monooxygenation, alkene formation is initiated by substrate C−H bond abstraction. Rather than finalizing the reaction through rapid oxygen rebound, alkene synthesis proceeds through the formation of a reaction cycle intermediate with kinetics, optical properties, and reactivity indicative of an Fe4+−OH species, compound II. The direct observation of this intermediate, normally fleeting in hydroxylases, provides a rationale for the carbon−carbon scission reaction catalyzed by OleT. PMID:27555591

An efficient synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and thiones catalyzed by a novel Brønsted acidic ionic liquid under solvent-free conditions.

PubMed

Zhang, Yonghong; Wang, Bin; Zhang, Xiaomei; Huang, Jianbin; Liu, Chenjiang

2015-02-26

We report here an efficient and green method for Biginelli condensation reaction of aldehydes, β-ketoesters and urea or thiourea catalyzed by Brønsted acidic ionic liquid [Btto][p-TSA] under solvent-free conditions. Compared to the classical Biginelli reaction conditions, the present method has the advantages of giving good yields, short reaction times, near room temperature conditions and the avoidance of the use of organic solvents and metal catalyst.

Non-Catalyzed Click Reactions of ADIBO Derivatives with 5-Methyluridine Azides and Conformational Study of the Resulting Triazoles

PubMed Central

Smyslova, Petra; Popa, Igor; Lyčka, Antonín; Tejral, Gracian; Hlavac, Jan

2015-01-01

Copper-free click reactions between a dibenzoazocine derivative and azides derived from 5-methyluridine were investigated. The non-catalyzed reaction yielded both regioisomers in an approximately equivalent ratio. The NMR spectra of each regioisomer revealed conformational isomery. The ratio of isomers was dependent on the type of regioisomer and the type of solvent. The synthesis of various analogs, a detailed NMR study and computational modeling provided evidence that the isomery was dependent on the interaction of the azocine and pyrimidine parts. PMID:26673606

Transition metal-catalyzed C-H activation reactions: diastereoselectivity and enantioselectivity.

PubMed

Giri, Ramesh; Shi, Bing-Feng; Engle, Keary M; Maugel, Nathan; Yu, Jin-Quan

2009-11-01

This critical review discusses historical and contemporary research in the field of transition metal-catalyzed carbon-hydrogen (C-H) bond activation through the lens of stereoselectivity. Research concerning both diastereoselectivity and enantioselectivity in C-H activation processes is examined, and the application of concepts in this area for the development of novel carbon-carbon and carbon-heteroatom bond-forming reactions is described. Throughout this review, an emphasis is placed on reactions that are (or may soon become) relevant in the realm of organic synthesis (221 references).

A new mild base-catalyzed Mannich reaction of hetero-arylamines in water: highly efficient stereoselective synthesis of beta-aminoketones under microwave heating.

PubMed

Hao, Wen-Juan; Jiang, Bo; Tu, Shu-Jiang; Cao, Xu-Dong; Wu, Shan-Shan; Yan, Shu; Zhang, Xiao-Hong; Han, Zheng-Guo; Shi, Feng

2009-04-07

A new mild base-catalyzed Mannich reaction of aromatic aldehydes with 1,2-diphenylethanone and hetero-arylamines including pyridin-2-amine and pyrimidin-2-amine is described. In this reaction, a series of new beta-aminoketones were stereoselectively synthesized in water by controlling the steric hindrance of the substrates under microwave heating. This method has the advantages of a short synthetic route, operational simplicity, increased safety for small-scale high-speed synthesis, and minimal environmental impact.

Rhodium-Catalyzed Insertion Reaction of PhP Group of Pentaphenylcyclopentaphosphine with Acyclic and Cyclic Disulfides.

PubMed

Arisawa, Mieko; Sawahata, Kyosuke; Yamada, Tomoki; Sarkar, Debayan; Yamaguchi, Masahiko

2018-02-16

Organophosphorus compounds with a phosphorus atom attached to a phenyl group and two organothio/organoseleno groups were synthesized using the rhodium-catalyzed insertion reaction of the PhP group of pentaphenylcyclopentaphosphine (PhP) 5 with acyclic disulfides and diselenides. The method was applied to the synthesis of heterocyclic compounds containing the S-P-S group by the reaction of (PhP) 5 and cyclic disulfides such as 1,2-dithietes, 1,2-dithiocane, 1,4,5-dithiopane, and 1,2-dithiolanes.

Alkylsilyl Peroxides as Alkylating Agents in the Copper-Catalyzed Selective Mono-N-Alkylation of Primary Amides and Arylamines.

PubMed

Sakamoto, Ryu; Sakurai, Shunya; Maruoka, Keiji

2017-07-06

The copper-catalyzed selective mono-N-alkylation of primary amides or arylamines using alkylsilyl peroxides as alkylating agents is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the alkylsilyl peroxides, as well as to the primary amides and arylamines. Mechanistic studies suggest that the present reaction should proceed through a free-radical process that includes alkyl radicals generated from the alkylsilyl peroxides. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transition-Metal-Catalyzed Laboratory-Scale Carbon–Carbon Bond-Forming Reactions of Ethylene

PubMed Central

Saini, Vaneet; Stokes, Benjamin J.; Sigman, Matthew S.

2014-01-01

Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transitionmetal–catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon–carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product. PMID:24105881

Solution-phase parallel synthesis of hexahydro-1H-isoindolone libraries via tactical combination of Cu-catalyzed three-component coupling and Diels-Alder reactions.

PubMed

Zhang, Lei; Lushington, Gerald H; Neuenswander, Benjamin; Hershberger, John C; Malinakova, Helena C

2008-01-01

Parallel solution-phase synthesis of combinatorial libraries of hexahydro-1 H-isoindolones exploiting a novel "tactical combination" of Cu-catalyzed three-component coupling and Diels-Alder reactions was accomplished. Three distinct libraries consisting of 24 members (library I), 60 members (library II), and 32 members (library III) were constructed. Variation of three substituents on the isoindolone scaffold in library I was exclusively achieved by the choice of the building blocks. In the syntheses of libraries II and III, sublibraries of isoindolone scaffolds were prepared initially in a one-pot/two-step process and were further diversified via Pd-catalyzed Suzuki cross-coupling reaction with boronic acids at two different diversification points. The Lipinski profiles and calculated ADME properties of the compounds are also reported.

Gold-catalyzed and N-iodosuccinimide-mediated cyclization of gamma-substituted allenamides.

PubMed

Hyland, Christopher J T; Hegedus, Louis S

2006-10-27

Chiral gamma-substituted allenamides have been shown to undergo efficient gold-catalyzed and N-iodosuccinimide-mediated cyclization to highly functionalized dihydrofurans. These reactions proceed rapidly and without loss of stereochemistry.

Glymes as benign co-solvents for CaO-catalyzed transesterification of soybean oil to biodiesel.

PubMed

Tang, Shaokun; Zhao, Hua; Song, Zhiyan; Olubajo, Olarongbe

2013-07-01

The base (such as CaO)-catalyzed heterogeneous preparation of biodiesel encounters a number of obstacles including the need for CaO pretreatment and the reactions being incomplete (typically 90-95% yields). In this study, a number of glymes were investigated as benign solvents for the CaO-catalyzed transesterification of soybean oil into biodiesel with a high substrate loading (typically soybean oil >50% v/v). The triglyceride-dissolving capability of glymes led to a much faster reaction rate (>98% conversions in 4h) than in methanol alone (typically 24h) and minimized the saponification reaction when catalyzed by anhydrous CaO or commercial lime without pre-activation. The use of glyme (e.g. P2) as co-solvent also activates commercial lime to become an effective catalyst without calcination pretreatment. The SEM images suggest a dissolution-agglomeration process of CaO surface in the presence of P2, which could remove the CaCO3 and Ca(OH)2 layer coated on the surface of lime. Copyright © 2013 Elsevier Ltd. All rights reserved.

An Efficient Process for Pd-Catalyzed C–N Cross-Coupling Reactions of Aryl Iodides: Insight Into Controlling Factors

PubMed Central

Fors, Brett P.; Davis, Nicole R.; Buchwald, Stephen L.

2009-01-01

An investigation into Pd-catalyzed C–N cross-coupling reactions of aryl iodides is described. NaI is shown to have a significant inhibitory effect on these processes. By switching to a solvent system in which the iodide byproduct was insoluble, reactions of aryl iodides were accomplished with the same efficiencies as aryl chlorides and bromides. Using catalyst systems based on certain biarylphosphine ligands, aryl iodides were successfully reacted with an array of primary and secondary amines in high yields. Lastly, reactions of heteroarylamines and heteroaryliodides were also conducted in high yields. PMID:19348431

Pd(OAc)(2)-catalyzed Domino reactions of 1-chloro-2-haloarenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes.

PubMed

Dong, Cheng-Guo; Hu, Qiao-Sheng

2006-10-26

The palladium-associated aryne generation strategy and Pd(OAc)(2)-catalyzed annulative Domino reactions of 1-chloro-2-halobenzenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes are described. The palladium-associated aryne generation strategy described here not only allows the high yield, one-step access to potentially useful substituted fluorenes from readily available 1-chloro-2-halobenzenes and 2-haloaryl tosylates, but may also lead to the development of other tandem reactions based on these readily available ortho leaving group bearing haloarenes. [reaction: see text

A Concise Synthesis of Presilphiperfolane Core through a Tandem TMTU-Co-Catalyzed Pauson-Khand Reaction and a 6π Electrocyclization Reaction (TMTU=Tetramethyl Thiourea).

PubMed

Zhang, Zichun; Li, Yuanhe; Zhao, Dandan; He, Yingdong; Gong, Jianxian; Yang, Zhen

2017-01-26

The synthesis of strained polycyclic systems from readily available precursors with a minimum number of steps and with regio- and stereochemical control constitutes an important synthetic challenge. Herein, we report a tandem reaction comprising Co-TMTU (tetramethyl thiourea)-catalyzed Pauson-Khand (PK) and 6π-electrocyclization reactions for the formation of the highly strained core of presilphiperfolanols. The developed chemistry has been applied to the total syntheses of 4-epi-presilphiperfolan-8-ol and 7-epi-presilphiperfolan-1-ol. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent advances in the chemistry of Rh carbenoids: multicomponent reactions of diazocarbonyl compounds

NASA Astrophysics Data System (ADS)

Medvedev, J. J.; Nikolaev, V. A.

2015-07-01

Multicomponent reactions of diazo compounds catalyzed by RhII complexes become a powerful tool for organic synthesis. They enable three- or four-step processes to be carried out as one-pot procedures (actually as one step) with high stereoselectivity to give complex organic molecules, including biologically active compounds. This review addresses recent results in the chemistry of Rh-catalyzed multicomponent reactions of diazocarbonyl compounds with the intermediate formation of N-, O- and C=O-ylides. The diastereo- and enantioselectivity of these reactions and the possibility of using various co-catalysts to increase the efficiency of the processes under consideration are discussed. The bibliography includes 120 references.

Evidence that a phosphorylated derivative of 5-oxoproline (5-OP) is an intermediate in the reaction catalyzed by 5-oxoprolinase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seddon, A.P.; Meister, A.

1986-05-01

5-oxo-L-proline + ATP + 2 H/sub 2/O ..-->.. L-Glutamate + ADP + P/sub i/ Pseudomonas putida 5-oxoprolinase consists of 2 protein components (A and B). A catalyzes 5-OP-dependent ATPase. B, which does not appear to interact with ATP or 5-OP, is required for catalysis of the complete reaction. Application of the isotope trapping method showed that 5-OP is converted stoichiometrically to an enzyme-bound form in a process requiring ATP and its cleavage. The overall reaction is not inhibited by high concentrations of borohydride. When the reaction catalyzed by A alone is carried out in the presence of 0.1-0.6 M KBH/submore » 4/ there is catalytic formation of proline. Studies with KB/sup 3/H/sub 4/ showed incorporation of /sup 3/H into proline. Proline formation is prevented by addition of B.« less

Benchmarking Quantum Mechanics/Molecular Mechanics (QM/MM) Methods on the Thymidylate Synthase-Catalyzed Hydride Transfer.

PubMed

Świderek, Katarzyna; Arafet, Kemel; Kohen, Amnon; Moliner, Vicent

2017-03-14

Given the ubiquity of hydride-transfer reactions in enzyme-catalyzed processes, identifying the appropriate computational method for evaluating such biological reactions is crucial to perform theoretical studies of these processes. In this paper, the hydride-transfer step catalyzed by thymidylate synthase (TSase) is studied by examining hybrid quantum mechanics/molecular mechanics (QM/MM) potentials via multiple semiempirical methods and the M06-2X hybrid density functional. Calculations of protium and tritium transfer in these reactions across a range of temperatures allowed calculation of the temperature dependence of kinetic isotope effects (KIE). Dynamics and quantum-tunneling effects are revealed to have little effect on the reaction rate, but are significant in determining the KIEs and their temperature dependence. A good agreement with experiments is found, especially when computed for RM1/MM simulations. The small temperature dependence of quantum tunneling corrections and the quasiclassical contribution term cancel each other, while the recrossing transmission coefficient seems to be temperature-independent over the interval of 5-40 °C.

Palladium-catalyzed C-H functionalization of acyldiazomethane and tandem cross-coupling reactions.

PubMed

Ye, Fei; Qu, Shuanglin; Zhou, Lei; Peng, Cheng; Wang, Chengpeng; Cheng, Jiajia; Hossain, Mohammad Lokman; Liu, Yizhou; Zhang, Yan; Wang, Zhi-Xiang; Wang, Jianbo

2015-04-08

Palladium-catalyzed C-H functionalization of acyldiazomethanes with aryl iodides has been developed. This reaction is featured by the retention of the diazo functionality in the transformation, thus constituting a novel method for the introduction of diazo functionality to organic molecules. Consistent with the experimental results, the density functional theory (DFT) calculation indicates that the formation of Pd-carbene species in the catalytic cycle through dinitrogen extrusion from the palladium ethyl diazoacetate (Pd-EDA) complex is less favorable. The reaction instead proceeds through Ag2CO3 assisted deprotonation and subsequently reductive elimination to afford the products with diazo functionality remained. This C-H functionalization transformation can be further combined with the recently evolved palladium-catalyzed cross-coupling reaction of diazo compounds with aryl iodides to develop a tandem coupling process for the synthesis of α,α-diaryl esters. DFT calculation supports the involvement of Pd-carbene as reactive intermediate in the catalytic cycle, which goes through facile carbene migratory insertion with a low energy barrier (3.8 kcal/mol).

Cobalt/rhodium heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and bisallenes to Pauson-Khand-type reaction products.

PubMed

Park, Ji Hoon; Kim, Eunha; Kim, Hyeong-Mook; Choi, Soo Young; Chung, Young Keun

2008-05-28

The first catalytic intra- and intermolecular [2+2+1] cocyclization reactions of allenes and carbon monoxide have been developed. In the Co(2)Rh(2) heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and carbon monoxide, the allenes formally serve both as an excellent alkene- and alkyne-like moiety within a Pauson-Khand-type process.

Convenient synthesis of benzothiazoles and benzimidazoles through Brønsted acid catalyzed cyclization of 2-amino thiophenols/anilines with β-diketones.

PubMed

Mayo, Muhammad Shareef; Yu, Xiaoqiang; Zhou, Xiaoyu; Feng, Xiujuan; Yamamoto, Yoshinori; Bao, Ming

2014-02-07

Brønsted acid catalyzed cyclization reactions of 2-amino thiophenols/anilines with β-diketones under oxidant-, metal-, and radiation-free conditions are described. Various 2-substituted benzothiazoles/benzimidazoles are obtained in satisfactory to excellent yields. Different groups such as methyl, chloro, nitro, and methoxy linked on benzene rings were tolerated under the optimized reaction conditions.

Development of A Concise Synthesis of (−)-Oseltamivir (Tamiflu®)

PubMed Central

Trost, Barry M.; Zhang, Ting

2011-01-01

We report a full account of our work towards the development of an eight-step synthesis of anti-influenza drug (−)-oseltamivir (Tamiflu®) from commercially available starting material. The final synthetic route proceeds with an overall yield of 30 %. Key transformations include a novel palladium-catalyzed asymmetric allylic alkylation reaction (Pd-AAA) as well as a rhodium-catalyzed chemo-, regio-, and stereoselective aziridination reaction. PMID:21365707

What Is Happening when the Blue Bottle Bleaches: An Investigation of the Methylene Blue-Catalyzed Air Oxidation of Glucose

ERIC Educational Resources Information Center

Anderson, Laurens; Wittkopp, Stacy M.; Painter, Christopher J.; Liegel, Jessica J.; Schreiner, Rodney; Bell, Jerry A.; Shakhashiri, Bassam Z.

2012-01-01

An investigation of the Blue Bottle Experiment, a well-known lecture demonstration reaction involving the dye-catalyzed air oxidation of a reducing sugar in alkaline solution, has delineated the sequence of reactions leading to the bleaching of the dye, the regeneration of color, and so forth. Enolization of the sugar is proposed as a key step in…

Copper(I)-catalyzed aryl bromides to form intermolecular and intramolecular carbon-oxygen bonds.

PubMed

Niu, Jiajia; Guo, Pengran; Kang, Juntao; Li, Zhigang; Xu, Jingwei; Hu, Shaojing

2009-07-17

A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K(3)PO(4) as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

Syntheses of the hexahydroindene cores of indanomycin and stawamycin by combinations of iridium-catalyzed asymmetric allylic alkylations and intramolecular Diels-Alder reactions.

PubMed

Gärtner, Martin; Satyanarayana, Gedu; Förster, Sebastian; Helmchen, Günter

2013-01-02

Short and concise syntheses of the hexahydroindene cores of the antibiotics indanomycin (X-14547 A) and stawamycin are presented. Key methods used are an asymmetric iridium-catalyzed allylic alkylation, a modified Julia olefination, a Suzuki-Miyaura coupling, and an intramolecular Diels-Alder reaction. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of aza-fused polycyclic quinolines through copper-catalyzed cascade reactions.

PubMed

Cai, Qian; Li, Zhengqiu; Wei, Jiajia; Fu, Liangbin; Ha, Chengyong; Pei, Duanqing; Ding, Ke

2010-04-02

A new and efficient method for the synthesis of aza-fused polycyclic quinolines (e.g., benzimidazo[1,2-a]quinolines) is described. This protocol includes an intermolecular condensation followed by a copper-catalyzed intramolecular C-N coupling reaction. The method is applied to a wide range of 2-iodo, 2-bromo, and 2-chloro aryl aldehyde substrates to yield the aza-fused polycyclic quinolines in good yields.

A beta-keto ester as a novel, efficient, and versatile ligand for copper(I)-catalyzed C-N, C-O, and C-S coupling reactions.

PubMed

Lv, Xin; Bao, Weiliang

2007-05-11

Employing ethyl 2-oxocyclohexanecarboxylate as a novel, efficient, and versatile ligand, the copper-catalyzed coupling reactions of various N/O/S nucleophilic reagents with aryl halides could be successfully carried out under mild conditions. A variety of products including N-arylamides, N-arylimidazoles, aryl ethers, and aryl thioethers were synthesized in good to excellent yields.

Use of Aryl Chlorides as Electrophiles in Pd-Catalyzed Alkene Difunctionalization Reactions

PubMed Central

Rosen, Brandon R.; Ney, Joshua E.; Wolfe, John P.

2010-01-01

The development of conditions that allow use of inexpensive aryl chlorides as electrophiles in Pd-catalyzed alkene carboamination and carboetherification reactions is described. A catalyst composed of Pd(OAc)2 and S-Phos minimizes N-arylation of the substrate and prevents formation of mixtures of regioisomeric products. A number of heterocycles, including pyrrolidines, isoxazolidines, tetrahydrofurans, and pyrazolidines, are efficiently generated with this method. PMID:20297834

"N"-Heterocyclic Carbene-Catalyzed Reaction of Chalcone and Cinnamaldehyde to Give 1,3,4-Triphenylcyclopentene Using Organocatalysis to Form a Homoenolate Equivalent

ERIC Educational Resources Information Center

Snider, Barry B.

2015-01-01

In this experiment, students carry out a modern organocatalytic reaction using IMes·HCl and NaOH to catalyze the formation of 1,3,4-triphenylcyclopentene from cinnamaldehyde and chalcone in water. Deprotonation of IMes·HCl with NaOH forms the "N"-heterocyclic carbene IMes that reacts with cinnamaldehyde to form a homoenolate equivalent…

Thermodynamics of Bioreactions.

PubMed

Held, Christoph; Sadowski, Gabriele

2016-06-07

Thermodynamic principles have been applied to enzyme-catalyzed reactions since the beginning of the 1930s in an attempt to understand metabolic pathways. Currently, thermodynamics is also applied to the design and analysis of biotechnological processes. The key thermodynamic quantity is the Gibbs energy of reaction, which must be negative for a reaction to occur spontaneously. However, the application of thermodynamic feasibility studies sometimes yields positive Gibbs energies of reaction even for reactions that are known to occur spontaneously, such as glycolysis. This article reviews the application of thermodynamics in enzyme-catalyzed reactions. It summarizes the basic thermodynamic relationships used for describing the Gibbs energy of reaction and also refers to the nonuniform application of these relationships in the literature. The review summarizes state-of-the-art approaches that describe the influence of temperature, pH, electrolytes, solvents, and concentrations of reacting agents on the Gibbs energy of reaction and, therefore, on the feasibility and yield of biological reactions.

Biodiesel Production from Citrillus colocynthis Oil Using Enzymatic Based Catalytic Reaction and Characterization Studies.

PubMed

Nehdi, Imededdine Arbi; Sbihi, Hassen Mohamed; Blidi, Lahssen El; Rashid, Umer; Tan, Chin Ping; Al-Resayes, Saud Ibrahim

2018-01-01

Biodiesel is a green fuel consisting of long chain fatty acid monoalkyl esters, which can be blended with diesel or used alone which is usually produced from vegetable oils/fats by either lipasecatalyzed transesterification. In this investigation, an enzyme (Novozym 435) catalyzed process was optimized to prepare methyl esters from crude Citrullus colocynthis oil (CCO) by transesterification of CCO with methanol. However, as per our knowledge, lipase-catalyzed transesterification have not been used for biodiesel production from Citrullus colocynthis. The purpose of this work was to transesterify the CCO in the presence of Candida antarctica lipase as catalyst and methanol. Additionally, the physicochemical parameters/fuel properties of the Citrullus colocynthis methyl ester (CCME) were assessed and compared. Lipase-catalyzed reactions were carried out in three necked flask (50 mL) attached with reflux condenser and thermometer, immersed in oil bath at constant stirring speed (400 rpm). The reaction mixture was consisted of CCO and varying the calculated amount of methanol, tert-butyl alcohol, and Novozym 435. The experimental parameters reaction time, methanol/oil molar ratio, reaction temperature, tert-butanol content, Novozym 435 content and water content were optimized for the transesterification reaction. The CCME yield was measured using gas chromatograph. The fuel properties of the produced CCME were determined as per American Society for Testing and Materials (ASTM) and European (EN) biodiesel standard methods. In this study, an enzymatic catalyst was employed to synthesize the CCME from CCO via transesterification. Several variables affecting the CCME yield were optimized as lipase quantity (4%), water content (0.5%), methanol/oil molar ratio (5:1), reaction temperature (43 °C), reaction medium composition (80% tertbutanol/ oil), and reaction time (3.7 h). A CCME yield of 97.8% was achieved using enzyme catalyzed transesterification of CCO under optimal conditions. The significant biodiesel fuel properties of CCME, i.e. cloud point (0.70 °C); cetane number (49.07); kinematic viscosity (2.27 mm2/s); flash point (143 °C); sulfur content (2 ppm) density (880 kg/m3) and acid value (0.076 mg KOH/g) were appraised. CCME also exhibited long-term storage stability (4.80 h) and all the biodiesel fuel properties were within the range of standards (ASTM D6751 and EN 14214). The lipase-catalyzed transesterification produced better conversion than the base-catalyzed reaction. The fuel properties of CCME were within the limits of the ASTM D6751 and EN14214 standards. Furthermore, CCME showed good oxidative stability and a long shelf life due its high natural antioxidant content. CCME showed better fuel properties and long-term storage stability due to which it can be used as a potential alternative fuel. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Catalysis of Photochemical Reactions.

ERIC Educational Resources Information Center

Albini, A.

1986-01-01

Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

Copper-catalyzed aerobic spirocyclization of biaryl-N-H-imines via 1,4-aminooxygenation of benzene rings.

PubMed

Tnay, Ya Lin; Chen, Cheng; Chua, Yi Yuan; Zhang, Line; Chiba, Shunsuke

2012-07-06

A synthetic method of azaspirocyclohexadienones has been developed through copper-catalyzed aerobic spirocyclization of biaryl-N-H-imines prepared by the reaction of biarylcarbonitriles and Grignard reagents.

Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klobukowski, Erik

2011-01-01

This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallicmore » complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly compared using the same reaction system and conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and morpholinones and related analogues such as quinoxalinones and benzoxazin-2-ones.« less

Electrophilic assistance to the cleavage of an RNA model phopshodiester via specific and general base-catalyzed mechanisms.

PubMed

Corona-Martínez, David Octavio; Gomez-Tagle, Paola; Yatsimirsky, Anatoly K

2012-10-19

Kinetics of transesterification of the RNA model substrate 2-hydroxypropyl 4-nitrophenyl phosphate promoted by Mg(2+) and Ca(2+), the most common biological metals acting as cofactors for nuclease enzymes and ribozymes, as well as by Co(NH(3))(6)(3+), Co(en)(3)(3+), Li(+), and Na(+) cations, often employed as mechanistic probes, was studied in 80% v/v (50 mol %) aqueous DMSO, a medium that allows one to discriminate easily specific base (OH(-)-catalyzed) and general base (buffer-catalyzed) reaction paths. All cations assist the specific base reaction, but only Mg(2+) and Na(+) assist the general base reaction. For Mg(2+)-assisted reactions, the solvent deuterium isotope effects are 1.23 and 0.25 for general base and specific base mechanisms, respectively. Rate constants for Mg(2+)-assisted general base reactions measured with different bases fit the Brønsted correlation with a slope of 0.38, significantly lower than the slope for the unassisted general base reaction (0.77). Transition state binding constants for catalysts in the specific base reaction (K(‡)(OH)) both in aqueous DMSO and pure water correlate with their binding constants to 4-nitrophenyl phosphate dianion (K(NPP)) used as a minimalist transition state model. It was found that K(‡)(OH) ≈ K(NPP) for "protic" catalysts (Co(NH(3))(6)(3+), Co(en)(3)(3+), guanidinium), but K(‡)(OH) ≫ K(NPP) for Mg(2+) and Ca(2+) acting as Lewis acids. It appears from results of this study that Mg(2+) is unique in its ability to assist efficiently the general base-catalyzed transesterification often occurring in active sites of nuclease enzymes and ribozymes.

Ballistic Motion of Enzymes that Catalyze Highly Exothermic Reactions

NASA Astrophysics Data System (ADS)

Tsekouras, Konstantinos; Pressé, Steve

Recently we proposed that the experimentally observed enhanced diffusion of enzymes catalyzing highly exothermic reactions is a consequence of their mechanism for dissipating reaction energy. More specifically, we proposed that reaction energy spreads out from the reaction site in the form of an acoustic wave which causes the enzyme to asymmetrically deform into the solvent. The solvent reaction propels the enzyme. However, it has been noted that in water, high viscosity should reduce enzyme momentum to zero within a few ps, so any diffusion increase should not be observable. Here we provide a model explaining how small volumetric expansions of biomolecules inside water may cause fluid compression that in turn creates regions of low fluid density around the biomolecule. We then investigate the dynamics of the biomolecule in the presence of these perturbations.

Free energy landscape for glucose condensation reactions.

PubMed

Liu, Dajiang; Nimlos, Mark R; Johnson, David K; Himmel, Michael E; Qian, Xianghong

2010-12-16

Ab initio molecular dynamics and metadynamics simulations were used to determine the free energy surfaces (FES) for the acid catalyzed β-D-glucose condensation reaction. Protonation of C1-OH on the β-D-glucose, breakage of the C1-O1 bond, and the formation of C1 carbocation is the rate-limiting step. The effects of solvent on the reaction were investigated by determining the FES both in the absence and presence of solvent water. It was found that water played a critical role in these reactions. The reaction barrier for the proton-catalyzed glucose condensation reaction is solvent induced because of proton's high affinity for water. During these simulations, β-D-glucose conversion to α-d-glucose process via the C1 carbocation was also observed. The associated free energy change and activation barrier for this reaction were determined.

Mechanism of intermolecular hydroacylation of vinylsilanes catalyzed by a rhodium(I) olefin complex: a DFT study.

PubMed

Meng, Qingxi; Shen, Wei; Li, Ming

2012-03-01

Density functional theory (DFT) was used to investigate the Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with benzaldehyde. All intermediates and transition states were optimized completely at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Rh). Calculations indicated that Rh(I)-catalyzed intermolecular hydroacylation is exergonic, and the total free energy released is -110 kJ mol(-1). Rh(I)-catalyzed intermolecular hydroacylation mainly involves the active catalyst CA2, rhodium-alkene-benzaldehyde complex M1, rhodium-alkene-hydrogen-acyl complex M2, rhodium-alkyl-acyl complex M3, rhodium-alkyl-carbonyl-phenyl complex M4, rhodium-acyl-phenyl complex M5, and rhodium-ketone complex M6. The reaction pathway CA2 + R2 → M1b → T1b → M2b → T2b1 → M3b1 → T4b → M4b → T5b → M5b → T6b → M6b → P2 is the most favorable among all reaction channels of Rh(I)-catalyzed intermolecular hydroacylation. The reductive elimination reaction is the rate-determining step for this pathway, and the dominant product predicted theoretically is the linear ketone, which is consistent with Brookhart's experiments. Solvation has a significant effect, and it greatly decreases the free energies of all species. The use of the ligand Cp' (Cp' = C(5)Me(4)CF(3)) decreased the free energies in general, and in this case the rate-determining step was again the reductive elimination reaction.

Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction†

PubMed Central

Sciacca, Beniamino; Alvarez, Sara D.; Geobaldo, Francesco; Sailor, Michael J.

2011-01-01

The high stability of Salonen’s thermally carbonized porous silicon (TCPSi) has attracted attention for environmental and biochemical sensing applications, where corrosion-induced zero point drift of porous silicon-based sensor elements has historically been a significant problem. Prepared by the high temperature reaction of porous silicon with acetylene gas, the stability of this silicon carbide-like material also poses a challenge—many sensor applications require a functionalized surface, and the low reactivity of TCPSi has limited the ability to chemically modify its surface. This work presents a simple reaction to modify the surface of TCPSi with an alkyl carboxylate. The method involves radical coupling of a dicarboxylic acid (sebacic acid) to the TCPSi surface using a benzoyl peroxide initiator. The grafted carboxylic acid species provides a route for bioconjugate chemical modification, demonstrated in this work by coupling propylamine to the surface carboxylic acid group through the intermediacy of pentafluorophenol and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC). The stability of the carbonized porous Si surface, both before and after chemical modification, is tested in phosphate buffered saline solution and found to be superior to either hydrosilylated (with undecylenic acid) or thermally oxidized porous Si surfaces. PMID:20967329

Features of the hydrosilylation of polyfunctional methylvinyl- and methylhydrosiloxanes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kopylov, V.M.; Kovyazine, T.G.; Buslaeva, T.M.

1987-11-10

A study of the reactivity of polyfunctional methylvinyl- and methylhydrosiloxanes in the presence of platinum catalysts has shown that the reactivity of the Si-CH=CH/sub 2/ groups is unchanged, but that of the Si-H groups decreases as the extent of reaction of the functional groups increases. Examination of the influence of the type of catalysts, comprising H/sub 2/PtCl/sub 6/ x 6H/sub 2/O and tetraorganoammonium platinum salts, on the reactions of polyfunctional methylvinyl- and methylhydrosiloxanes has shown that the catalytic activity of the salts is lower than that of H/sub 2/PtCl/sub 6/ x 6H/sub 2/O, and varies over a wide range withmore » changes in the organic radical in the tetraorganoammonium cation, the oxidation state of the platinum, and the nature of the acido ligand. In the presence of these tetraorganoammonium platinum salts, addition of silicon hydrides to methylvinylcycloxiloxanes takes place predominantly in the ..beta..-position. The PMR spectra of the addition products were obtained on Bruker WM-90 and WM-250 instruments, operating frequencies 90 and 250 MHz, in CCl/sub 4/ and CDCl/sub 3/, cyclohexane being used as internal standard.« less

Synthesis of Quaternary Carbon Stereogenic Centers through Enantioselective Cu-Catalyzed Allylic Substitutions with Vinylaluminum Reagents

PubMed Central

Gao, Fang; McGrath, Kevin P.; Lee, Yunmi; Hoveyda, Amir H.

2010-01-01

Catalytic enantioselective allylic substitution (EAS) reactions, which involve the use of alkyl- or aryl-substituted vinylaluminum reagents and afford 1,4-dienes containing a quaternary carbon stereogenic center at their C-3 site, are disclosed. The C–C bond forming transformations are promoted by 0.5–2.5 mol % of sulfonate bearing chiral bidentate N-heterocyclic carbene (NHC) complexes, furnishing the desired products efficiently (66–97% yield of isolated products) and in high site- (>98% SN2′) and enantioselectivity [up to 99:1 enantiomer ratio (er)]. To the best of our knowledge, the present report puts forward the first cases of allylic substitution reactions that result in the generation of all-carbon quaternary stereogenic centers through the addition of a vinyl unit. The aryl- and vinyl-substituted vinylaluminum reagents, which cannot be prepared in high efficiency through direct reaction with diisobutylaluminum hydride, are accessed through a recently introduced Ni-catalyzed reaction of the corresponding terminal alkynes with the same inexpensive metal-hydride agent. Sequential Ni-catalyzed hydrometallations and Cu-catalyzed C–C bond forming reactions allow for efficient and selective synthesis of a range of enantiomerically enriched EAS products, which cannot cannot be accessed by previously disclosed strategies (due to inefficient vinylmetal synthesis or low reactivity and/or selectivity with Si-substituted derivatives). The utility of the protocols developed is demonstrated through a concise enantioselective synthesis of natural product bakuchiol. PMID:20860365

Spontaneous, Metal-Catalyzed, and Enzyme-Catalyzed Decarboxylation of Oxalosuccinic Acid.

DTIC Science & Technology

1980-01-01

acid, 2,4- dinitrophenylhydrazine was added. This yielded a hydrazone which, after two recrystallizations, melted at 2200C. A sample of the a...accurately determined to be 24,500 at a wavelength of 352 nm (46). 34 2,4- Dinitrophenylhydrazine . Obtained from the Eastman Kodak Chemicals Division...reaction with 2,4- dinitrophenylhydrazine (57). The reaction mixture was sampled hourly during the daytime for a period of three days. The concentration of a

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

PubMed

Uno, Takuya; Kobayashi, Yusuke; Takemoto, Yoshiji

2012-01-01

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

Rhodium(III)-catalyzed three-component reaction of imines, alkynes, and aldehydes through C-H activation.

PubMed

Huang, Ji-Rong; Song, Qiang; Zhu, Yu-Qin; Qin, Liu; Qian, Zhi-Yong; Dong, Lin

2014-12-15

An efficient rhodium(III)-catalyzed tandem three-component reaction of imines, alkynes and aldehydes through CH activation has been developed. High stereo- and regioselectivity, as well as good yields were obtained in most cases. The simple and atom-economical approach offers a broad scope of substrates, providing polycyclic skeletons with potential biological properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium(II)-catalyzed enantioselective synthesis of troponoids.

PubMed

Murarka, Sandip; Jia, Zhi-Jun; Merten, Christian; Daniliuc, Constantin-G; Antonchick, Andrey P; Waldmann, Herbert

2015-06-22

We report a rhodium(II)-catalyzed highly enantioselective 1,3-dipolar cycloaddition reaction between the carbonyl moiety of tropone and carbonyl ylides to afford troponoids in good to high yields with excellent enantioselectivity. We demonstrate that α-diazoketone-derived carbonyl ylides, in contrast to carbonyl ylides derived from diazodiketoesters, undergo [6+3] cycloaddition reactions with tropone to yield the corresponding bridged heterocycles with excellent stereoselectivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds: large accelerating effects of bases and ligands.

PubMed

Itooka, Ryoh; Iguchi, Yuki; Miyaura, Norio

2003-07-25

The effects of ligands and bases in the rhodium(I)-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds were reinvestigated to carry out the reaction under mild conditions. Rhodium(I) complexes possessing a 1,5-cyclooctadiene (cod) and a hydroxo ligand such as [RhOH(cod)](2) exhibited excellent catalyst activities compared to those of the corresponding rhodium-acac or -chloro complexes and their phosphine derivatives. The reaction was further accelerated in the presence of KOH, thus allowing the 1,4-addition even at 0 degrees C. A cationic rhodium(I)-(R)-binap complex, [Rh(R-binap)(nbd)]BF(4), catalyzed the reaction at 25-50 degrees C in the presence of Et(3)N with high enantioselectivities of up to 99% ee for alpha,beta-unsaturated ketones, 92% for aldehydes, 94% for esters, and 92% for amides.

Atomistic insight into the catalytic mechanism of glycosyltransferases by combined quantum mechanics/molecular mechanics (QM/MM) methods.

PubMed

Tvaroška, Igor

2015-02-11

Glycosyltransferases catalyze the formation of glycosidic bonds by assisting the transfer of a sugar residue from donors to specific acceptor molecules. Although structural and kinetic data have provided insight into mechanistic strategies employed by these enzymes, molecular modeling studies are essential for the understanding of glycosyltransferase catalyzed reactions at the atomistic level. For such modeling, combined quantum mechanics/molecular mechanics (QM/MM) methods have emerged as crucial. These methods allow the modeling of enzymatic reactions by using quantum mechanical methods for the calculation of the electronic structure of the active site models and treating the remaining enzyme environment by faster molecular mechanics methods. Herein, the application of QM/MM methods to glycosyltransferase catalyzed reactions is reviewed, and the insight from modeling of glycosyl transfer into the mechanisms and transition states structures of both inverting and retaining glycosyltransferases are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imker,H.; Fedorov, A.; Fedorov, E.

D-Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant enzyme, is the paradigm member of the recently recognized mechanistically diverse RuBisCO superfamily. The RuBisCO reaction is initiated by abstraction of the proton from C3 of the D-ribulose 1,5-bisphosphate substrate by a carbamate oxygen of carboxylated Lys 201 (spinach enzyme). Heterofunctional homologues of RuBisCO found in species of Bacilli catalyze the tautomerization ('enolization') of 2,3-diketo-5-methylthiopentane 1-phosphate (DK-MTP 1-P) in the methionine salvage pathway in which 5-methylthio-D-ribose (MTR) derived from 5'-methylthioadenosine is converted to methionine [Ashida, H., Saito, Y., Kojima, C., Kobayashi, K., Ogasawara, N., and Yokota, A. (2003) A functional link between RuBisCO-likemore » protein of Bacillus and photosynthetic RuBisCO, Science 302, 286-290]. The reaction catalyzed by this 'enolase' is accomplished by abstraction of a proton from C1 of the DK-MTP 1-P substrate to form the tautomerized product, a conjugated enol. Because the RuBisCO- and 'enolase'-catalyzed reactions differ in the regiochemistry of proton abstraction but are expected to share stabilization of an enolate anion intermediate by coordination to an active site Mg{sup 2+}, we sought to establish structure-function relationships for the 'enolase' reaction so that the structural basis for the functional diversity could be established. We determined the stereochemical course of the reaction catalyzed by the 'enolases' from Bacillus subtilis and Geobacillus kaustophilus. Using stereospecifically deuterated samples of an alternate substrate derived from D-ribose (5-OH group instead of the 5-methylthio group in MTR) as well as of the natural DK-MTP 1-P substrate, we determined that the 'enolase'-catalyzed reaction involves abstraction of the 1-proS proton. We also determined the structure of the activated 'enolase' from G. kaustophilus (carboxylated on Lys 173) liganded with Mg{sup 2+} and 2,3-diketohexane 1-phosphate, a stable alternate substrate. The stereospecificity of proton abstraction restricts the location of the general base to the N-terminal {alpha}+ {beta} domain instead of the C-terminal ({beta}/{alpha}){sub 8}-barrel domain that contains the carboxylated Lys 173. Lys 98 in the N-terminal domain, conserved in all 'enolases', is positioned to abstract the 1-proS proton. Consistent with this proposed function, the K98A mutant of the G. kaustophilus 'enolase' is unable to catalyze the 'enolase' reaction. Thus, we conclude that this functionally divergent member of the RuBisCO superfamily uses the same structural strategy as RuBisCO for stabilizing the enolate anion intermediate, i.e., coordination to an essential Mg{sup 2+}, but the proton abstraction is catalyzed by a different general base.« less

Rhodium-Catalyzed Dehydrogenative Borylation of Cyclic Alkenes

PubMed Central

Kondoh, Azusa; Jamison, Timothy F.

2010-01-01

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki-Miyaura cross-coupling applications are also presented. PMID:20107646

Iron- and cobalt-catalyzed arylation of azetidines, pyrrolidines, and piperidines with Grignard reagents.

PubMed

Barré, Baptiste; Gonnard, Laurine; Campagne, Rémy; Reymond, Sébastien; Marin, Julien; Ciapetti, Paola; Brellier, Marie; Guérinot, Amandine; Cossy, Janine

2014-12-05

Iron- and cobalt-catalyzed cross-couplings between iodo-azetidines, -pyrrolidines, -piperidines, and Grignard reagents are disclosed. The reaction is efficient, cheap, chemoselective and tolerates a large variety of (hetero)aryl Grignard reagents.

A Mechanistic Investigation of the Gold(III)-Catalyzed Hydrofurylation of C-C Multiple Bonds.

PubMed

Hossein Bagi, Amin; Khaledi, Yousef; Ghari, Hossein; Arndt, Sebastian; Hashmi, A Stephen K; Yates, Brian F; Ariafard, Alireza

2016-11-09

The gold-catalyzed direct functionalization of aromatic C-H bonds has attracted interest for constructing organic compounds which have application in pharmaceuticals, agrochemicals, and other important fields. In the literature, two major mechanisms have been proposed for these catalytic reactions: inner-sphere syn-addition and outer-sphere anti-addition (Friedel-Crafts-type mechanism). In this article, the AuCl 3 -catalyzed hydrofurylation of allenyl ketone, vinyl ketone, ketone, and alcohol substrates is investigated with the aid of density functional theory calculations, and it is found that the corresponding functionalizations are best rationalized in terms of a novel mechanism called "concerted electrophilic ipso-substitution" (CEIS) in which the gold(III)-furyl σ-bond produced by furan auration acts as a nucleophile and attacks the protonated substrate via an outer-sphere mechanism. This unprecedented mechanism needs to be considered as an alternative plausible pathway for gold(III)-catalyzed arene functionalization reactions in future studies.

DNA-Catalyzed Amide Hydrolysis.

PubMed

Zhou, Cong; Avins, Joshua L; Klauser, Paul C; Brandsen, Benjamin M; Lee, Yujeong; Silverman, Scott K

2016-02-24

DNA catalysts (deoxyribozymes) for a variety of reactions have been identified by in vitro selection. However, for certain reactions this identification has not been achieved. One important example is DNA-catalyzed amide hydrolysis, for which a previous selection experiment instead led to DNA-catalyzed DNA phosphodiester hydrolysis. Subsequent efforts in which the selection strategy deliberately avoided phosphodiester hydrolysis led to DNA-catalyzed ester and aromatic amide hydrolysis, but aliphatic amide hydrolysis has been elusive. In the present study, we show that including modified nucleotides that bear protein-like functional groups (any one of primary amino, carboxyl, or primary hydroxyl) enables identification of amide-hydrolyzing deoxyribozymes. In one case, the same deoxyribozyme sequence without the modifications still retains substantial catalytic activity. Overall, these findings establish the utility of introducing protein-like functional groups into deoxyribozymes for identifying new catalytic function. The results also suggest the longer-term feasibility of deoxyribozymes as artificial proteases.

Expanding the Enzyme Universe: Accessing Non-Natural Reactions by Mechanism-Guided Directed Evolution

PubMed Central

Renata, Hans; Wang, Z. Jane

2015-01-01

High selectivities and exquisite control over reaction outcomes entice chemists to use biocatalysts in organic synthesis. However, many useful reactions are not accessible because they are not in nature’s known repertoire. We will use this review to outline an evolutionary approach to engineering enzymes to catalyze reactions not found in nature. We begin with examples of how nature has discovered new catalytic functions and how such evolutionary progressions have been recapitulated in the laboratory starting from extant enzymes. We then examine non-native enzyme activities that have been discovered and exploited for chemical synthesis, emphasizing reactions that do not have natural counterparts. The new functions have mechanistic parallels to the native reaction mechanisms that often manifest as catalytic promiscuity and the ability to convert from one function to the other with minimal mutation. We present examples of how non-natural activities have been improved by directed evolution, mimicking the process used by nature to create new catalysts. Examples of new enzyme functions include epoxide opening reactions with non-natural nucleophiles catalyzed by a laboratory-evolved halohydrin dehalogenase, cyclopropanation and other carbene transfer reactions catalyzed by cytochrome P450 variants, and non-natural modes of cyclization by a modified terpene synthase. Lastly, we describe discoveries of non-native catalytic functions that may provide future opportunities for expanding the enzyme universe. PMID:25649694

Copper-catalyzed one-pot synthesis of 1,2,4-triazoles from nitriles and hydroxylamine.

PubMed

Xu, Hao; Ma, Shuang; Xu, Yuanqing; Bian, Longxiang; Ding, Tao; Fang, Xiaomin; Zhang, Wenkai; Ren, Yanrong

2015-02-06

A simple and efficient copper-catalyzed one-pot synthesis of substituted 1,2,4-triazoles through reactions of two nitriles with hydroxylamine has been developed. The protocol uses simple and readily available nitriles and hydroxylamine hydrochloride as the starting materials and inexpensive Cu(OAc)2 as the catalyst, and the corresponding 1,2,4-triazole derivatives are obtained in moderate to good yields. The reactions include sequential intermolecular addition of hydroxylamine to one nitrile to provide amidoxime, copper-catalyzed treatment of the amidoxime with another nitrile, and intramolecular dehydration/cyclization. This finding provides a new and useful strategy for synthesis of 1,2,4-triazole derivatives.

On the stereochemical course of palladium-catalyzed cross-coupling of allylic silanolate salts with aromatic bromides.

PubMed

Denmark, Scott E; Werner, Nathan S

2010-03-17

The stereochemical course of palladium-catalyzed cross-coupling reactions of an enantioenriched, alpha-substituted, allylic silanolate salt with aromatic bromides has been investigated. The allylic silanolate salt was prepared in high geometrical (Z/E, 94:6) and high enantiomeric (94:6 er) purity by a copper-catalyzed S(N)2' reaction of a resolved allylic carbamate. Eight different aromatic bromides underwent cross-coupling with excellent constitutional site-selectivity and excellent stereospecificity. Stereochemical correlation established that the transmetalation event proceeds through a syn S(E)' mechanism which is interpreted in terms of an intramolecular delivery of the arylpalladium electrophile through a key intermediate that contains a discrete Si-O-Pd linkage.

Copper-catalyzed C(sp3)-OH cleavage with concomitant C-C coupling: synthesis of 3-substituted isoindolinones.

PubMed

Rao, H Surya Prakash; Rao, A Veera Bhadra

2015-02-06

Copper(II) trifluoromethanesulfonate (Cu(OTf)2) efficiently catalyzes the C-C coupling of 3-hydoxyisoindolinones with a variety of aryl-, heteroaryl-, and alkenylboronic acids to furnish C(3) aryl-, heteroaryl-, and alkenyl-substituted isoindolinones. The coupling reactions work smoothly in 1,2-dicholoroethane (DCE) reflux, to effect both inter- and intramolecular versions. This is the first report on C(sp(3))-OH cleavage with concomitant C-C coupling. The photolabile 2-nitrobenzyl protecting group is most appropriate for promotion of the coupling reaction and for deprotection. The tetracyclic ring motif of the alkaloid neuvamine was prepared by applying the newly developed copper-catalyzed C-C coupling.

Nanocrystal assembly for tandem catalysis

DOEpatents

Yang, Peidong; Somorjai, Gabor; Yamada, Yusuke; Tsung, Chia-Kuang; Huang, Wenyu

2014-10-14

The present invention provides a nanocrystal tandem catalyst comprising at least two metal-metal oxide interfaces for the catalysis of sequential reactions. One embodiment utilizes a nanocrystal bilayer structure formed by assembling sub-10 nm platinum and cerium oxide nanocube monolayers on a silica substrate. The two distinct metal-metal oxide interfaces, CeO.sub.2--Pt and Pt--SiO.sub.2, can be used to catalyze two distinct sequential reactions. The CeO.sub.2--Pt interface catalyzed methanol decomposition to produce CO and H.sub.2, which were then subsequently used for ethylene hydroformylation catalyzed by the nearby Pt--SiO.sub.2 interface. Consequently, propanal was selectively produced on this nanocrystal bilayer tandem catalyst.

Nickel-Catalyzed, Carbonyl-Ene-Type Reactions: Selective for Alpha Olefins and More Efficient with Electron-Rich Aldehydes

PubMed Central

Ho, Chun-Yu; Ng, Sze-Sze; Jamison, Timothy F.

2011-01-01

Described are several classes of unusual or unprecedented carbonyl-ene-type reactions, including those between alpha olefins and aromatic aldehydes. Catalyzed by nickel, these processes complement existing Lewis acid-catalyzed methods in several respects. Not only are monosubstituted alkenes, aromatic aldehydes, and tert-alkyl aldehydes effective substrates, but monosubstituted olefins also react faster than those that are more substituted, and large or electron-rich aldehydes are more effective than small or electron-poor ones. Conceptually, in the presence of a nickel-phosphine catalyst, the combination of off-the-shelf alkenes, silyl triflates, and triethylamine functions as a replacement for an allylmetal reagent. PMID:16620106

The selective activation of a C-F bond with an auxiliary strong Lewis acid: a method to change the activation preference of C-F and C-H bonds.

PubMed

Wang, Lin; Sun, Hongjian; Li, Xiaoyan; Fuhr, Olaf; Fenske, Dieter

2016-11-15

The selective activation of the C-F bonds in substituted (2,6-difluorophenyl)phenylimines (2,6-F 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-n'-R-C 6 H 4 (n' = 2, R = H (1); n' = 2, R = Me (2); n' = 4, R = tBu (3))) by Fe(PMe 3 ) 4 with an auxiliary strong Lewis acid (LiBr, LiI, or ZnCl 2 ) was explored. As a result, iron(ii) halides ((H 5 C 6 -(C[double bond, length as m-dash]NH)-2-FH 3 C 6 )FeX(PMe 3 ) 3 (X = Br (8); Cl (9)) and (n-RH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-FH 3 C 6 )FeX(PMe 3 ) 3 (n = 2, R = Me, X = Br (11); n = 4, R = tBu, X = I (12))) were obtained. Under similar reaction conditions, using LiBF 4 instead of LiBr or ZnCl 2 , the reaction of (2,6-difluorophenyl)phenylimine with Fe(PMe 3 ) 4 afforded an ionic complex [(2,6-F 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-H 4 C 6 )Fe(PMe 3 ) 4 ](BF 4 ) (10) via the activation of a C-H bond. The method of C-F bond activation with an auxiliary strong Lewis acid is appropriate for monofluoroarylmethanimines. Without the Lewis acid, iron(ii) hydrides ((2-RH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-FH 3 C 6 )FeH(PMe 3 ) 3 (R = H (13); Me (14))) were generated from the reactions of Fe(PMe 3 ) 4 with the monofluoroarylmethanimines (2-FH 4 C 6 -(C[double bond, length as m-dash]NH)-2'-RC 6 H 4 (R = H (4); Me (5))); however, in the presence of ZnCl 2 or LiBr, iron(ii) halides ((2-RH 4 C 6 -(C[double bond, length as m-dash]NH)-H 4 C 6 )FeX(PMe 3 ) 3 (R = H, X = Cl (15); R = Me, X = Br (16))) could be obtained through the activation of a C-F bond. Furthermore, a C-F bond activation with good regioselectivity in (pentafluorophenyl)arylmethanimines (F 5 C 6 -(C[double bond, length as m-dash]NH)-2,6-Y 2 C 6 H 3 (Y = F (6); H (7))) could be realized in the presence of ZnCl 2 to produce iron(ii) chlorides ((2,6-Y 2 H 3 C 6 -(C[double bond, length as m-dash]NH)-F 4 C 6 )FeCl(PMe 3 ) 3 (Y = F (17); H (18))). This series of iron(ii) halides could be used to catalyze the hydrosilylation reaction of aldehydes. Due to the stability of iron(ii) halides to high temperature, the reaction mixture was allowed to be heated to 100 °C and the reaction could finish within 0.5 h.

Mechanistic Study of Nickel-Catalyzed Ynal Reductive Cyclizations Through Kinetic Analysis

PubMed Central

Baxter, Ryan D.; Montgomery, John

2011-01-01

The mechanism of nickel-catalyzed, silane-mediated reductive cyclization of ynals has been evaluated. The cyclizations are first-order in [Ni] and [ynal] and zeroth-order in [silane]. These results, in combination with the lack of rapid silane consumption upon reaction initiation are inconsistent with mechanisms involving reaction initiation by oxidative addition of Ni(0) to the silane. Silane consumption occurs only when both the alkyne and aldehyde and are present. Mechanisms involving rate-determining oxidative cyclization to a metallacycle followed by rapid reaction with the silane are consistent with the data obtained. PMID:21438642

Mechanistic Study of the Oxidative Coupling of Styrene with 2-Phenylpyridine Derivatives Catalyzed by Cationic Rhodium( III) via C–H Activation

PubMed Central

Brasse, Mikaël; Cámpora, Juan; Ellman, Jonathan A.; Bergman, Robert G.

2013-01-01

The Rh(III) catalyzed oxidative coupling of alkenes with arenes provides a greener alternative to the classical Heck reaction for the synthesis of arene-functionalized alkenes. The present mechanistic study gives insights for the rational development of this key transformation. The catalyst resting states and the rate law of the reaction have been identified. The reaction rate is solely dependent on catalyst and alkene concentrations and the rate determining step is the migratory insertion of alkene into a Rh–C(aryl) bond. PMID:23590843

Synthesis of (E)-2-Styrylchromones and Flavones by Base-Catalyzed Cyclodehydration of the Appropriate β-Diketones Using Water as Solvent.

PubMed

Pinto, Joana; Silva, Vera L M; Silva, Ana M G; Silva, Artur M S

2015-06-22

A low cost, safe, clean and environmentally benign base-catalyzed cyclodehydration of appropriate β-diketones affording (E)-2-styrylchromones and flavones in good yields is disclosed. Water was used as solvent and the reactions were heated using classical and microwave heating methods, under open and closed vessel conditions. β-Diketones having electron-donating and withdrawing substituents were used to evaluate the reaction scope. The reaction products were isolated in high purity by simple filtration and recrystallization from ethanol, when using 800 mg of the starting diketone under classical reflux heating conditions.

Reactivity and Selectivity in Hydrovinylation of Strained Alkenes

PubMed Central

Liu, Wang; RajanBabu, T. V.

2010-01-01

Scope of Ni(II)-catalyzed hydrovinylation has been extended to strained alkenes such as heterobicyclic- [2.2.1]heptanes and cylobutenes. Reactions involving the heterobicyclic compounds are rare examples for this class of compounds where the metal-catalyzed C-C bond-forming reactions proceed without a concomitant ring-opening process. While the enantioselectivity in these systems remains modest, hydrovinylation of endo-5,6--bis-benzyloxymethylbicyclo[2.2.1]hept-2-ene gives excellent yield (>90%) of the product with one of the highest enantioselectivities (95–99 %ee) reported for a C-C bondforming reaction of norbornenes. PMID:20964350

Palladium-Catalyzed Dehydrogenative Coupling: An Efficient Synthetic Strategy for the Construction of the Quinoline Core

PubMed Central

Carral-Menoyo, Asier; Ortiz-de-Elguea, Verónica; Martinez-Nunes, Mikel; Sotomayor, Nuria; Lete, Esther

2017-01-01

Palladium-catalyzed dehydrogenative coupling is an efficient synthetic strategy for the construction of quinoline scaffolds, a privileged structure and prevalent motif in many natural and biologically active products, in particular in marine alkaloids. Thus, quinolines and 1,2-dihydroquinolines can be selectively obtained in moderate-to-good yields via intramolecular C–H alkenylation reactions, by choosing the reaction conditions. This methodology provides a direct method for the construction of this type of quinoline through an efficient and atom economical procedure, and constitutes significant advance over the existing procedures that require preactivated reaction partners. PMID:28867803

A General, Efficient and Functional-Group-Tolerant Catalyst System for the Palladium-Catalyzed Thioetherification of Aryl Bromides and Iodides

PubMed Central

Fernández-Rodríguez, Manuel A.; Hartwig, John F.

2010-01-01

The cross-coupling reaction of aryl bromides and iodides with aliphatic and aromatic thiols catalyzed by palladium complexes of the bisphosphine ligand CyPF-tBu (1) is reported. Reactions occur in excellent yields, broad scope, high tolerance of functional groups and with turnover numbers that exceed those of previous catalysts by two or three orders of magnitude. These couplings of bromo- and iodoarenes are more efficient than the corresponding reactions of chloroarenes and could be conducted with less catalyst loading and/or milder reaction conditions. Consequently, limitations regarding scope and functional group tolerance previously reported in the coupling of aryl chlorides are now overcome. PMID:19154131

Catalysis of concerted reactions by antibodies: the Claisen rearrangement.

PubMed Central

Hilvert, D; Carpenter, S H; Nared, K D; Auditor, M T

1988-01-01

Monoclonal antibodies were prepared against a transition state analog inhibitor of chorismate mutase (EC 5.4.99.5). One of the antibodies catalyzes the rearrangement of chorismate to prephenate with rate accelerations of more than 2 orders of magnitude compared to the uncatalyzed reaction. Saturation kinetics were observed, and at 25 degrees C the values of kcat and Km were 1.2 X 10(-3) s-1 and 5.1 X 10(-5) M respectively. The transition state analog was shown to be a competitive inhibitor of the reaction with Ki equal to 0.6 microM. These results demonstrate the feasibility of using rationally designed immunogens to generate antibodies that catalyze concerted reactions. PMID:3393525

Rh(II)-catalyzed Reactions of Diazoesters with Organozinc Reagents

PubMed Central

Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M.

2015-01-01

Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethylacetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed. PMID:26241081

Rh(II)-Catalyzed Reactions of Diazoesters with Organozinc Reagents.

PubMed

Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M

2015-08-21

Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethyl acetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed.

Novozyme 435-catalyzed asymmetric acylation of (R, S)-3-n- butylphthalide in hexane.

PubMed

He, Laping; Li, Cuiqin; Gao, Bing

2009-01-01

The asymmetric acylation of (R, S)-3-n-butylphthalide could be efficiently catalyzed by Novozyme 435. The effect of various reaction parameters such as water activity, temperature, molar ratio of acetic anhydride to (R, S)-3-n-butylphthalide, and reaction time on the asymmetric acylation were studied. The optimums of the reaction parameters were water activity 0.62, temperature 30 degrees C, molar ratio of acetic anhydride to (R, S)-3-n-butylphthalide 8:1, and reaction time 48 h, respectively. Under the optimum conditions, enantiopure 3-n-butylphthalide with an optical purity of 95.7% enantiomeric excess and 49.1% yield could be obtained. Furthermore, the enantiomeric excess of product was over 98%.

Recent advances in sortase-catalyzed ligation methodology.

PubMed

Antos, John M; Truttmann, Matthias C; Ploegh, Hidde L

2016-06-01

The transpeptidation reaction catalyzed by bacterial sortases continues to see increasing use in the construction of novel protein derivatives. In addition to growth in the number of applications that rely on sortase, this field has also seen methodology improvements that enhance reaction performance and scope. In this opinion, we present an overview of key developments in the practice and implementation of sortase-based strategies, including applications relevant to structural biology. Topics include the use of engineered sortases to increase reaction rates, the use of redesigned acyl donors and acceptors to mitigate reaction reversibility, and strategies for expanding the range of substrates that are compatible with a sortase-based approach. Copyright © 2016 Elsevier Ltd. All rights reserved.

Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step.

PubMed

Jayakumar, Jayachandran; Cheng, Chien-Hong

2016-01-26

A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Decarbonylative Cross-Couplings: Nickel Catalyzed Functional Group Interconversion Strategies for the Construction of Complex Organic Molecules.

PubMed

Guo, Lin; Rueping, Magnus

2018-05-15

The utilization of carboxylic acid esters as electrophiles in metal-catalyzed cross-coupling reactions is increasingly popular, as environmentally friendly and readily available ester derivatives can be powerful alternatives to the commonly used organohalides. However, key challenges associated with the use of these chemicals remain to be addressed, including the stability of ester substrates and the high energy barrier associated with their oxidative addition to low-valent metal species. Due to recent developments in nickel catalysis that make it easier to perform oxidative additions, chemists have become interested in applying less reactive electrophiles as coupling counterparts in nickel-catalyzed transformations. Hence, our group and others have independently investigated various ester group substitutions and functionalizations enabled by nickel catalysis. Such methods are of great interest as they enable the exchange of ester groups, which can be used as directing groups in metal-catalyzed C-H functionalizations prior to their replacement. Here, we summarize our recent efforts toward the development of nickel-catalyzed decarbonylative cross-coupling reactions of carboxylic esters. Achievements accomplished by other groups in this area are also included. To this day, a number of new transformations have been successfully developed, including decarbonylative arylations, alkylations, cyanations, silylations, borylations, aminations, thioetherifications, stannylations, and hydrogenolysis reactions. These transformations proceed via a nickel-catalyzed decarbonylative pathway and have shown a high degree of reactivity and chemoselectivity, as well as several other unique advantages in terms of substrate availability, due to the use of esters as coupling partners. Although the mechanisms of these reactions have not yet been fully understood, chemists have already provided some important insights. For example, Yamamoto explored the stoichiometric nickel-mediated decarbonylation process of esters and proposed a reaction mechanism involving a C(acyl)-O bond cleavage and a CO extrusion. Key nickel intermediates were isolated and characterized by Shi and co-workers, supporting the assumption of a nickel/ N-heterocyclic carbene-promoted C(acyl)-O bond activation and functionalization. Our combined experimental and computational study of a ligand-controlled chemoselective nickel-catalyzed cross-coupling of aromatic esters with alkylboron reagents provided further insight into the reaction mechanism. We demonstrated that nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step, resulting in decarbonylative alkylations, while nickel complexes with monodentate phosphorus ligands promote the activation of the C(acyl)-O bond, leading to the production of ketone products. Although more detailed mechanistic investigations need to be undertaken, the successful development of decarbonylative cross-coupling reactions can serve as a solid foundation for future studies. We believe that this type of decarbonylative cross-coupling reactions will be of significant value, in particularly in combination with the retrosynthetic analysis and synthesis of natural products and biologically active molecules. Thus, the presented ester substitution methods will pave the way for successful applications in the construction of complex frameworks by late-stage modification and functionalization of carboxylic acid derivatives.

Beyond Iron: Iridium-Containing P450 Enzymes for Selective Cyclopropanations of Structurally Diverse Alkenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Key, Hanna M.; Dydio, Paweł; Liu, Zhennan

Enzymes catalyze organic transformations with exquisite levels of selectivity, including chemoselectivity, stereoselectivity, and substrate selectivity, but the types of reactions catalyzed by enzymes are more limited than those of chemical catalysts. Thus, the convergence of chemical catalysis and biocatalysis can enable enzymatic systems to catalyze abiological reactions with high selectivity. Recently, we disclosed artificial enzymes constructed from the apo form of heme proteins and iridium porphyrins that catalyze the insertion of carbenes into a C-H bond. Here, we postulated that the same type of Ir(Me)-PIX enzymes could catalyze the cyclopropanation of a broad range of alkenes with control of multiplemore » modes of selectivity. Here, we report the evolution of artificial enzymes that are highly active and highly stereoselective for the addition of carbenes to a wide range of alkenes. These enzymes catalyze the cyclopropanation of terminal and internal, activated and unactivated, electron-rich and electron-deficient, conjugated and nonconjugated alkenes. In particular, Ir(Me)-PIX enzymes derived from CYP119 catalyze highly enantio- and diastereoselective cyclopropanations of styrene with ±98% ee, > 70:1 dr, > 75% yield, and ~10,000 turnovers (TON), as well as 1,2-disubstituted styrenes with up to 99% ee, 35:1 dr, and 54% yield. Moreover, Ir(Me)-PIX enzymes catalyze cyclopropanation of internal, unactivated alkenes with up to 99% stereoselectivity, 76% yield, and 1300 TON. They also catalyze cyclopropanation of natural products with diastereoselectivities that are complementary to those attained with standard transition metal catalysts. Finally, Ir(Me)-PIX P450 variants react with substrate selectivity that is reminiscent of natural enzymes; they react preferentially with less reactive internal alkenes in the presence of more reactive terminal alkenes. Altogether, the studies reveal the suitability of Ir-containing P450s to combine the broad reactivity and substrate scope of transition metal catalysts with the exquisite selectivity of enzymes, generating catalysts that enable reactions to occur with levels and modes of activity and selectivity previously unattainable with natural enzymes or transition metal complexes alone.« less

Beyond Iron: Iridium-Containing P450 Enzymes for Selective Cyclopropanations of Structurally Diverse Alkenes

DOE PAGES

Key, Hanna M.; Dydio, Paweł; Liu, Zhennan; ...

2017-04-01

Enzymes catalyze organic transformations with exquisite levels of selectivity, including chemoselectivity, stereoselectivity, and substrate selectivity, but the types of reactions catalyzed by enzymes are more limited than those of chemical catalysts. Thus, the convergence of chemical catalysis and biocatalysis can enable enzymatic systems to catalyze abiological reactions with high selectivity. Recently, we disclosed artificial enzymes constructed from the apo form of heme proteins and iridium porphyrins that catalyze the insertion of carbenes into a C-H bond. Here, we postulated that the same type of Ir(Me)-PIX enzymes could catalyze the cyclopropanation of a broad range of alkenes with control of multiplemore » modes of selectivity. Here, we report the evolution of artificial enzymes that are highly active and highly stereoselective for the addition of carbenes to a wide range of alkenes. These enzymes catalyze the cyclopropanation of terminal and internal, activated and unactivated, electron-rich and electron-deficient, conjugated and nonconjugated alkenes. In particular, Ir(Me)-PIX enzymes derived from CYP119 catalyze highly enantio- and diastereoselective cyclopropanations of styrene with ±98% ee, > 70:1 dr, > 75% yield, and ~10,000 turnovers (TON), as well as 1,2-disubstituted styrenes with up to 99% ee, 35:1 dr, and 54% yield. Moreover, Ir(Me)-PIX enzymes catalyze cyclopropanation of internal, unactivated alkenes with up to 99% stereoselectivity, 76% yield, and 1300 TON. They also catalyze cyclopropanation of natural products with diastereoselectivities that are complementary to those attained with standard transition metal catalysts. Finally, Ir(Me)-PIX P450 variants react with substrate selectivity that is reminiscent of natural enzymes; they react preferentially with less reactive internal alkenes in the presence of more reactive terminal alkenes. Altogether, the studies reveal the suitability of Ir-containing P450s to combine the broad reactivity and substrate scope of transition metal catalysts with the exquisite selectivity of enzymes, generating catalysts that enable reactions to occur with levels and modes of activity and selectivity previously unattainable with natural enzymes or transition metal complexes alone.« less

Theoretical investigation for the reaction of NO 2 with CO catalyzed by Sc +

NASA Astrophysics Data System (ADS)

Wang, Yong-Cheng; Zhang, Jian-Hui; Geng, Zhi-Yuan; Chen, Dong-Ping; Liu, Ze-Yu; Yang, Xiao-Yan

2007-09-01

The mechanism of the reaction NO(2A)+CO(1∑+)→NO(2∏)+CO(1∑g+) catalyzed by Sc + has been investigated by means of UB3LYP/6-311+G(2d) level. Our calculated results strongly indicate that both the reactions NO 2( 2A 1) + Sc +(X 3D) → NO( 2∏) + ScO +(X 1∑ +) and ScO(X1∑+)+CO(1∑+)→Sc(XD)+CO(1∑g+) are spin-forbidden reactions. The crossing points (CPs) that are involved and the possible spin inversion processes are discussed using the intrinsic reaction coordinate (IRC) approach. On the basis of Hammond postulate, they are typical 'two-state reactivity' (TSR) reactions. And the O-atom affinities (OA) testified that the argumentation is thermodynamically allowed.

Kinetic investigation of catalytic disproportionation of superoxide ions in the non-aqueous electrolyte used in Li–air batteries

DOE PAGES

Wang, Qiang; Zheng, Dong; McKinnon, Meaghan E.; ...

2014-10-28

Superoxide reacts with carbonate solvents in Li–air batteries. Tris(pentafluorophenyl)borane is found to catalyze a more rapid superoxide (O 2 -) disproportionation reaction than the reaction between superoxide and propylene carbonate (PC). With this catalysis, the negative impact of the reaction between the electrolyte and O 2 -produced by the O 2 reduction can be minimized. A simple kinetic study using ESR spectroscopy was reported to determine reaction orders and rate constants for the reaction between PC and superoxide, and the disproportionation of superoxide catalyzed by Tris(pentafluorophenyl)borane and Li ions. As a result, the reactions are found to be first ordermore » and the rate constants are 0.033 s -1 M -1, 0.020 s -1 M -1and 0.67 s -1M -1 for reactions with PC, Li ion and Tris(pentafluorophenyl)borane, respectively.« less

Palladium-Catalyzed Arylation of Fluoroalkylamines

PubMed Central

Brusoe, Andrew T.; Hartwig, John F.

2015-01-01

We report the synthesis of fluorinated anilines by palladium-catalyzed coupling of fluoroalkylamines with aryl bromides and aryl chlorides. The products of these reactions are valuable because anilines typically require the presence of an electron-withdrawing substituent on nitrogen to suppress aerobic or metabolic oxidation, and the fluoroalkyl groups have steric properties and polarity distinct from those of more common electron-withdrawing amide and sulfonamide units. The fluoroalkylaniline products are unstable under typical conditions for C–N coupling reactions (heat and strong base). However, the reactions conducted with the weaker base KOPh, which has rarely been used in cross-coupling to form C–N bonds, occurred in high yield in the presence of a catalyst derived from commercially available AdBippyPhos and [Pd(allyl)Cl]2. Under these conditions, the reactions occur with low catalyst loadings (<0.50 mol % for most substrates) and tolerate the presence of various functional groups that react with the strong bases that are typically used in Pd-catalyzed C–N cross-coupling reactions of aryl halides. The resting state of the catalyst is the phenoxide complex, (BippyPhosPd(Ar)OPh); due to the electron-withdrawing property of the fluoroalkyl substituent, the turnover-limiting step of the reaction is reductive elimination to form the C–N bond. PMID:26065341

Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, Including Unactivated Tertiary Halides, to Generate Carbon–Boron Bonds

PubMed Central

Dudnik, Alexander S.

2012-01-01

Through the use of a catalyst formed in situ from NiBr2•diglyme and a pybox ligand (both of which are commercially available), we have achieved our first examples of coupling reactions of unactivated tertiary alkyl electrophiles, as well as our first success with nickel-catalyzed couplings that generate bonds other than C–C bonds. Specifically, we have determined that this catalyst accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates, a family of compounds with substantial (and expanding) utility, under mild conditions; indeed, the umpolung borylation of a tertiary alkyl bromide can be achieved at a temperature as low as −10 °C. The method exhibits good functional-group compatibility and is regiospecific, both of which can be issues with traditional approaches to the synthesis of alkylboronates. In contrast to seemingly related nickel-catalyzed C–C bond-forming processes, tertiary halides are more reactive than secondary or primary halides in this nickel-catalyzed C–B bond-forming reaction; this divergence is particularly noteworthy in view of the likelihood that both transformations follow an inner-sphere electron-transfer pathway for oxidative addition. PMID:22668072

Piper-betle-shaped nano-S-catalyzed synthesis of 1-amidoalkyl-2-naphthols under solvent-free reaction condition: a greener "nanoparticle-catalyzed organic synthesis enhancement" approach.

PubMed

Das, Vijay K; Borah, Madhurjya; Thakur, Ashim J

2013-04-05

Nano-S prepared by an annealing process showed excellent catalytic activity for the synthesis of 1-amidoalkyl-2-naphthols under solvent-free reaction condition at 50 °C. The catalyst could be reused up to the fifth cycle without loss in its action. The green-ness of the present protocol was also measured using green metrics drawing its superiority.

Selective Formation of Secondary Amides via the Copper-Catalyzed Cross-Coupling of Alkylboronic Acids with Primary Amides

PubMed Central

Rossi, Steven A.; Shimkin, Kirk W.; Xu, Qun; Mori-Quiroz, Luis M.; Watson, Donald A.

2014-01-01

For the first time, a general catalytic procedure for the cross coupling of primary amides and alkylboronic acids is demonstrated. The key to the success of this reaction was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the mono-alkylation of amides. PMID:23611591

Stereospecific nickel-catalyzed cross-coupling reactions of alkyl Grignard reagents and identification of selective anti-breast-cancer agents.

PubMed

Yonova, Ivelina M; Johnson, A George; Osborne, Charlotte A; Moore, Curtis E; Morrissette, Naomi S; Jarvo, Elizabeth R

2014-02-24

Alkyl Grignard reagents that contain β-hydrogen atoms were used in a stereospecific nickel-catalyzed cross-coupling reaction to form C(sp(3))-C(sp(3)) bonds. Aryl Grignard reagents were also utilized to synthesize 1,1-diarylalkanes. Several compounds synthesized by this method exhibited selective inhibition of proliferation of MCF-7 breast cancer cells. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Step into an eco-Compatible Future: Iron- and Cobalt-catalyzed Borrowing Hydrogen Transformation.

PubMed

Quintard, Adrien; Rodriguez, Jean

2016-01-08

Living on borrowed hydrogen: Recent developments in iron- and cobalt-catalyzed borrowing hydrogen have shown that economically reliable catalysts can be used in this type of waste-free reactions. By using well-defined inexpensive catalysts, known reactions can now be run efficiently without the necessary use of noble metals; however, in addition new types of reactivity can also be discovered. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dual palladium- and proline-catalyzed allylic alkylation of enolizable ketones and aldehydes with allylic alcohols.

PubMed

Usui, Ippei; Schmidt, Stefan; Breit, Bernhard

2009-03-19

The dual Pd/proline-catalyzed alpha-allylation reaction of a variety of enolizable ketones and aldehydes with allylic alcohols is described. In this reaction, the choice of a large-bite angle ligand Xantphos and proline as the organocatalyst was essential for generation of the crucial pi-allyl Pd intermediate from allylic alcohol, followed by nucleophilic attack of the enamine formed in situ from the corresponding enolizable carbonyl substrate and proline.

Lipase-catalyzed synthesis of fattythioic acids from palm oil.

PubMed

Al-Mulla, Emad A Jaffar

2011-01-01

The present work focuses on the synthesis of fattythioic acids (FTAs) by a one-step lipase catalyzed reaction of palm oil with carbonothioic S,S-acid using Lipozyme. The product was characterized using Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance ((1)H NMR) technique and elemental analysis. The effects of various reaction parameters such as reaction time, temperature, amount of enzyme, molar ratio of substrates, and various organic solvents of the reaction system were investigated. The optimum conditions to produce FTAs were respectively, incubation time, 20 h, temperature, 40°C, amount of enzyme, 0.05 g and molar ratio of carbonothioic S,S-acid to palm oil, 5.0:1.0. Hexane was the best solvent for this reaction. The conversion of the products at optimum conditions was around 91%.

Mechanistic Study on Cu(II)-Catalyzed Oxidative Cross-Coupling Reaction between Arenes and Boronic Acids under Aerobic Conditions.

PubMed

Zhang, Qian; Liu, Yang; Wang, Ting; Zhang, Xinhao; Long, Chao; Wu, Yun-Dong; Wang, Mei-Xiang

2018-04-25

Substantial attention has been given to modern organocopper chemistry in recent years since copper salts are naturally abundant, cheap, and less toxic in comparison to precious metals. Copper salts also exhibit versatility in catalyzing and mediating carbon-carbon and carbon-heteroatom bond forming reactions. Despite the wide applications of copper salts in catalysis, reaction mechanisms have remained elusive. Using azacalix[1]arene[3]pyridine, an arene-embedded macrocycle, and its isolated and structurally well-defined ArCu(II) and ArCu(III) compounds as molecular tools, we now report an in-depth experimental and computational study on the mechanism of a Cu(II)-catalyzed oxidative cross-coupling reaction between arenes and boronic acids with air as the oxidant. Stoichiometric reaction of organocopper compounds with p-tolylboronic acid validated arylcopper(II) rather than arylcopper(III) as a reactive organometallic intermediate. XPS, EPR, 1 H NMR, HRMS, and UV-vis spectroscopic evidence along with the isolation and quantification of all products and copper speciation, combined with computational analysis of the electronic structure and energetics of the transient intermediates, suggested a reaction sequence involving electrophilic metalation of arene by Cu(II), transmetalation of arylboronate to ArCu(II), the redox reaction between the resulting ArCu(II)Ar' and ArCu(II) to form respectively ArCu(III)Ar' and ArCu(I), and finally reductive elimination of ArCu(III)Ar'. Under aerobic catalytic conditions, all Cu(I) ions released from reductive elimination of ArCu(III)Ar' and from protolysis of ArCu(I) were oxidized by oxygen to regenerate Cu(II) species that enters into the next catalytic cycle. The unraveled reactivity of arylcopper(II) compounds and the catalytic cycle would enrich our knowledge of modern organocopper chemistry and provide useful information in the design of copper-catalyzed reactions.

Catalytic "active-metal" template synthesis of [2]rotaxanes, [3]rotaxanes, and molecular shuttles, and some observations on the mechanism of the cu(i)-catalyzed azide-alkyne 1,3-cycloaddition.

PubMed

Aucagne, Vincent; Berna, José; Crowley, James D; Goldup, Stephen M; Hänni, Kevin D; Leigh, David A; Lusby, Paul J; Ronaldson, Vicki E; Slawin, Alexandra M Z; Viterisi, Aurélien; Walker, D Barney

2007-10-03

A synthetic approach to rotaxane architectures is described in which metal atoms catalyze covalent bond formation while simultaneously acting as the template for the assembly of the mechanically interlocked structure. This "active-metal" template strategy is exemplified using the Huisgen-Meldal-Fokin Cu(I)-catalyzed 1,3-cycloaddition of azides with terminal alkynes (the CuAAC "click" reaction). Coordination of Cu(I) to an endotopic pyridine-containing macrocycle allows the alkyne and azide to bind to metal atoms in such a way that the metal-mediated bond-forming reaction takes place through the cavity of the macrocycle--or macrocycles--forming a rotaxane. A variety of mono- and bidentate macrocyclic ligands are demonstrated to form [2]rotaxanes in this way, and by adding pyridine, the metal can turn over during the reaction, giving a catalytic active-metal template assembly process. Both the stoichiometric and catalytic versions of the reaction were also used to synthesize more complex two-station molecular shuttles. The dynamics of the translocation of the macrocycle by ligand exchange in these two-station shuttles could be controlled by coordination to different metal ions (rapid shuttling is observed with Cu(I), slow shuttling with Pd(II)). Under active-metal template reaction conditions that feature a high macrocycle:copper ratio, [3]rotaxanes (two macrocycles on a thread containing a single triazole ring) are also produced during the reaction. The latter observation shows that under these conditions the mechanism of the Cu(I)-catalyzed terminal alkyne-azide cycloaddition involves a reactive intermediate that features at least two metal ions.

Energy-converting [NiFe] hydrogenases from archaea and extremophiles: ancestors of complex I.

PubMed

Hedderich, Reiner

2004-02-01

[NiFe] hydrogenases are well-characterized enzymes that have a key function in the H2 metabolism of various microorganisms. In the recent years a subfamily of [NiFe] hydrogenases with unique properties has been identified. The members of this family form multisubunit membrane-bound enzyme complexes composed of at least four hydrophilic and two integral membrane proteins. These six conserved subunits, which built the core of these hydrogenases, have closely related counterparts in energy-conserving NADH:quinone oxidoreductases (complex I). However, the reaction catalyzed by these hydrogenases differs significantly from the reaction catalyzed by complex I. For some of these hydrogenases the physiological role is to catalyze the reduction of H+ with electrons derived from reduced ferredoxins or poly-ferredoxins. This exergonic reaction is coupled to energy conservation by means of electron-transport phosphorylation. Other members of this hydrogenase family mainly function to provide the cell with reduced ferredoxin with H2 as electron donor in a reaction driven by reverse electron transport. As complex I these hydrogenases function as ion pumps and have therefore been designated as energy-converting [NiFe] hydrogenases.

Mild copper-catalyzed vinylation reactions of azoles and phenols with vinyl bromides.

PubMed

Taillefer, Marc; Ouali, Armelle; Renard, Brice; Spindler, Jean-Francis

2006-07-05

An efficient and straightforward copper-catalyzed method allowing vinylation of N- or O-nucleophiles with di- or trisubstituted vinyl bromides is reported. The procedure is applicable to a broad range of substrates since N-vinylation of mono-, di-, and triazoles as well as O-vinylation of phenol derivatives can be performed with catalytic amounts of copper iodide and inexpensive nitrogen ligands 3 or 8. In the case of more hindered vinyl bromides, the use of the original bidentate chelator 8 was shown to be more efficient to promote the coupling reactions than our key tetradentate ligand 3. The corresponding N-(1-alkenyl)azoles and alkenyl aryl ethers are obtained in high yields and selectivities under very mild temperature conditions (35-110 degrees C for N-vinylation reactions and 50-80 degrees C for O-vinylation reactions). Moreover, to our knowledge, this method is the first example of a copper-catalyzed vinylation of various azoles. Finally, this protocol, practical on a laboratory scale and easily adaptable to an industrial scale, is very competitive compared to the existing methods that allow the synthesis of such compounds.

Combined cross-linked enzyme aggregates of horseradish peroxidase and glucose oxidase for catalyzing cascade chemical reactions.

PubMed

Nguyen, Le Truc; Yang, Kun-Lin

2017-05-01

Cascade reactions involved unstable intermediates are often encountered in biological systems. In this study, we developed combined cross-linked enzyme aggregates (combi-CLEA) to catalyze a cascade reaction which involves unstable hydrogen peroxide as an intermediate. The combi-CLEA contains two enzymes̶ glucose oxidase (GOx) and horseradish peroxidase (HRP) which are cross-linked together as solid aggregates. The first enzyme GOx catalyzes the oxidation of glucose and produces hydrogen peroxide, which is used by the second enzyme HRP to oxidize 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The apparent reaction rate of the cascade reaction reaches 10.5±0.5μM/min when the enzyme ratio is 150:1 (GOx:HRP). Interestingly, even in the presence of catalase, an enzyme that quickly decomposes hydrogen peroxide, the reaction rate only decreases by 18.7% to 8.3±0.3μM/min. This result suggests that the intermediate hydrogen peroxide is not decomposed by catalase due to a short diffusion distance between GOx and HRP in the combi-CLEA. Scanning electron microscopy images suggest that combi-CLEA particles are hollow spheres and have an average diameter around 250nm. Because of their size, combi-CLEA particles can be entrapped inside a nylon membrane for detecting glucose by using the cascade reaction. Copyright © 2017 Elsevier Inc. All rights reserved.

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review.

PubMed

He, Jie; Yang, Xiaofang; Men, Bin; Wang, Dongsheng

2016-01-01

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals (OH) from reactions between recyclable solid catalysts and H2O2 at acidic or even circumneutral pH. Hence, it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology. Due to the complex reaction system, the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating, and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies. Iron-based materials usually possess high catalytic activity, low cost, negligible toxicity and easy recovery, and are a superior type of heterogeneous Fenton catalysts. Therefore, this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials. OH, hydroperoxyl radicals/superoxide anions (HO2/O2(-)) and high-valent iron are the three main types of reactive oxygen species (ROS), with different oxidation reactivity and selectivity. Based on the mechanisms of ROS generation, the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron, the heterogeneous catalysis mechanism, and the heterogeneous reaction-induced homogeneous mechanism. Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed. Finally, related future research directions are also suggested. Copyright © 2015. Published by Elsevier B.V.

Antibody-catalyzed benzoin oxidation as a mechanistic probe for nucleophilic catalysis by an active site lysine.

PubMed

Sklute, Genia; Oizerowich, Rachel; Shulman, Hagit; Keinan, Ehud

2004-05-03

Aldolase antibody 24H6, which was obtained by reactive immunization against a 1,3-diketone hapten, is shown to catalyze additional reactions, including H/D exchange and oxidation reactions. Comparison of the H/D exchange reaction at the alpha-position of a wide range of aldehydes and ketones by 24H6 and by other aldolase antibodies, such as 38C2, pointed at the significantly larger size of the 24H6 active site. This property allowed for the catalysis of the oxidation of substituted benzoins to benzils by potassium ferricyanide. This reaction was used as a mechanistic probe to learn about the initial steps of the 24H6-catalyzed aldol condensation reaction. The Hammett correlation (rho=4.7) of log(k(cat)) versus the substituent constant, sigma, revealed that the reaction involves rapid formation of a Schiff base intermediate from the ketone and an active site lysine residue. The rate-limiting step in this oxidation reaction is the conversion of the Schiff base to an enamine intermediate. In addition, linear correlation (rho=3.13) was found between log(K(M)) and sigma, indicating that electronic rather than steric factors are dominant in the antibody-substrate binding phenomenon and confirming that the reversible formation of a Schiff base intermediate comprises part of the substrate-binding mechanism.

Modulating the DNA polymerase β reaction equilibrium to dissect the reverse reaction

PubMed Central

Shock, David D.; Freudenthal, Bret D.; Beard, William A.; Wilson, Samuel H.

2017-01-01

DNA polymerases catalyze efficient and high fidelity DNA synthesis. While this reaction favors nucleotide incorporation, polymerases also catalyze a reverse reaction, pyrophosphorolysis, removing the DNA primer terminus and generating deoxynucleoside triphosphates. Since pyrophosphorolysis can influence polymerase fidelity and sensitivity to chain-terminating nucleosides, we analyzed pyrophosphorolysis with human DNA polymerase β and found the reaction to be inefficient. The lack of a thio-elemental effect indicated that it was limited by a non-chemical step. Utilizing a pyrophosphate analog, where the bridging oxygen is replaced with an imido-group (PNP), increased the rate of the reverse reaction and displayed a large thio-elemental effect indicating that chemistry was now rate determining. Time-lapse crystallography with PNP captured structures consistent with a chemical equilibrium that favored the reverse reaction. These results highlight the importance of the bridging atom between the β- and γ-phosphates of the incoming nucleotide in reaction chemistry, enzyme conformational changes, and overall reaction equilibrium. PMID:28759020

Photon Energy Threshold in Direct Photocatalysis with Metal Nanoparticles: Key Evidence from the Action Spectrum of the Reaction.

PubMed

Sarina, Sarina; Jaatinen, Esa; Xiao, Qi; Huang, Yi Ming; Christopher, Philip; Zhao, Jin Cai; Zhu, Huai Yong

2017-06-01

By investigating the action spectra (the relationship between the irradiation wavelength and apparent quantum efficiency of reactions under constant irradiance) of a number of reactions catalyzed by nanoparticles including plasmonic metals, nonplasmonic metals, and their alloys at near-ambient temperatures, we found that a photon energy threshold exists in each photocatalytic reaction; only photons with sufficient energy (e.g., higher than the energy level of the lowest unoccupied molecular orbitals) can initiate the reactions. This energy alignment (and the photon energy threshold) is determined by various factors, including the wavelength and intensity of irradiation, molecule structure, reaction temperature, and so forth. Hence, distinct action spectra were observed in the same type of reaction catalyzed by the same catalyst due to a different substituent group, a slightly changed reaction temperature. These results indicate that photon-electron excitations, instead of the photothermal effect, play a dominant role in direct photocatalysis of metal nanoparticles for many reactions.

Advances in copper-catalyzed C-C coupling reactions and related domino reactions based on active methylene compounds.

PubMed

Liu, Yunyun; Wan, Jie-Ping

2012-06-01

Active methylene compounds are a major class of reaction partners for C-C bond formation with sp(2) C-X (X = halide) fragments. As one of the most-classical versions of the Ullmann-type coupling reaction, activated-methylene-based C-C coupling reactions have been efficiently employed in a large number of syntheses. Although this type of reaction has long relied on noble-metal catalysis, the renaissance of copper catalysis at the end of last century has led to dramatic developments in Ullmann C-C coupling reactions. Owing to its low cost, abundance, as well as excellent catalytic activity, the exceptional atom economy of copper catalysis is gaining widespread attention in various organic synthesis. This review summarizes the advances in copper-catalyzed intermolecular and intramolecular C-C coupling reactions that use activated methylene species as well as in tandem reactions that are initiated by this transformation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic Insight Facilitates Discovery of a Mild and Efficient Copper-Catalyzed Dehydration of Primary Amides to Nitriles Using Hydrosilanes.

PubMed

Liu, Richard Y; Bae, Minwoo; Buchwald, Stephen L

2018-02-07

Metal-catalyzed silylative dehydration of primary amides is an economical approach to the synthesis of nitriles. We report a copper-hydride(CuH)-catalyzed process that avoids a typically challenging 1,2-siloxane elimination step, thereby dramatically increasing the rate of the overall transformation relative to alternative metal-catalyzed systems. This new reaction proceeds at ambient temperature, tolerates a variety of metal-, acid-, or base-sensitive functional groups, and can be performed using a simple ligand, inexpensive siloxanes, and low catalyst loading.

Copper-Catalyzed Oxidative Dehydrogenative Carboxylation of Unactivated Alkanes to Allylic Esters via Alkenes

PubMed Central

2015-01-01

We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV–vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C–H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C–H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper–carboxylate, copper–amidate, and copper–imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)–amidate > Cu(II)–imidate > Cu(II)–benzoate. Consistent with this trend, Cu(II)–amidates and Cu(II)–benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products. PMID:25389772

Iron-Catalyzed C-O Bond Activation: Opportunity for Sustainable Catalysis.

PubMed

Bisz, Elwira; Szostak, Michal

2017-10-23

Oxygen-based electrophiles have emerged as some of the most valuable cross-coupling partners in organic synthesis due to several major strategic and environmental benefits, such as abundance and potential to avoid toxic halide waste. In this context, iron-catalyzed C-O activation/cross-coupling holds particular promise to achieve sustainable catalytic protocols due to its natural abundance, inherent low toxicity, and excellent economic and ecological profile. Recently, tremendous progress has been achieved in the development of new methods for functional-group-tolerant iron-catalyzed cross-coupling reactions by selective C-O cleavage. These methods establish highly attractive alternatives to traditional cross-coupling reactions by using halides as electrophilic partners. In particular, new easily accessible oxygen-based electrophiles have emerged as substrates in iron-catalyzed cross-coupling reactions, which significantly broaden the scope of this catalysis platform. New mechanistic manifolds involving iron catalysis have been established; thus opening up vistas for the development of a wide range of unprecedented reactions. The synthetic potential of this sustainable mode of reactivity has been highlighted by the development of new strategies in the construction of complex motifs, including in target synthesis. The most recent advances in sustainable iron-catalyzed cross-coupling of C-O-based electrophiles are reviewed, with a focus on both mechanistic aspects and synthetic utility. It should be noted that this catalytic manifold provides access to motifs that are often not easily available by other methods, such as the assembly of stereodefined dienes or C(sp 2 )-C(sp 3 ) cross-couplings, thus emphasizing the synthetic importance of this mode of reactivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Octahedral molecular sieve sorbents and catalysts

DOEpatents

Li, Liyu [Richland, WA; King, David L [Richland, WA

2010-04-20

Octahedral molecular sieve sorbents and catalysts are disclosed, including silver hollandite and cryptomelane. These materials can be used, for example, to catalyze the oxidation of CO.sub.x (e.g., CO), NO.sub.x (e.g., NO), hydrocarbons (e.g., C.sub.3H.sub.6) and/or sulfur-containing compounds. The disclosed materials also may be used to catalyze other reactions, such as the reduction of NO.sub.2. In some cases, the disclosed materials are capable of sorbing certain products from the reactions they catalyze. Silver hollandite, in particular, can be used to remove a substantial portion of certain sulfur-containing compounds from a gas or liquid by catalysis and/or sorption. The gas or liquid can be, for example, natural gas or a liquid hydrocarbon.

Computational enzyme design: transitioning from catalytic proteins to enzymes.

PubMed

Mak, Wai Shun; Siegel, Justin B

2014-08-01

The widespread interest in enzymes stem from their ability to catalyze chemical reactions under mild and ecologically friendly conditions with unparalleled catalytic proficiencies. While thousands of naturally occurring enzymes have been identified and characterized, there are still numerous important applications for which there are no biological catalysts capable of performing the desired chemical transformation. In order to engineer enzymes for which there is no natural starting point, efforts using a combination of quantum chemistry and force-field based protein molecular modeling have led to the design of novel proteins capable of catalyzing chemical reactions not catalyzed by naturally occurring enzymes. Here we discuss the current status and potential avenues to pursue as the field of computational enzyme design moves forward. Published by Elsevier Ltd.

Gold-Catalyzed Enantio- and Diastereoselective Syntheses of Left Fragments of Azadirachtin/Meliacarpin-Type Limonoids.

PubMed

Shi, Hang; Tan, Ceheng; Zhang, Weibin; Zhang, Zichun; Long, Rong; Gong, Jianxian; Luo, Tuoping; Yang, Zhen

2016-02-05

Meliacarpin-type limonoids are an important class of organic insecticides. Their syntheses are challenging due to their chemical complexity. Here, we report the highly enantio- and diastereoselective synthesis of the left fragments of azadirachtin I and 1-cinnamoylmelianolone, being two important family members of meliacarpin-type limonoids, via pairwise palladium- and gold-catalyzed cascade reactions. Gold-catalyzed reactions of 1,7-diynes were performed as model studies, and the efficient construction of tetracyclic late-stage intermediates was achieved on the basis of this key transformation. Our unique route gave both of the left fragments in 23 steps from the commercially available chiral starting material (-)-carvone. This study significantly advances research on the synthesis of the meliacarpin-type limonoids.

A New Synthetic Route to N-Benzyl Carboxamides through the Reverse Reaction of N-Substituted Formamide Deformylase

PubMed Central

Hashimoto, Yoshiteru; Sakashita, Toshihide; Fukatsu, Hiroshi; Sato, Hiroyoshi

2014-01-01

Previously, we isolated a new enzyme, N-substituted formamide deformylase, that catalyzes the hydrolysis of N-substituted formamide to the corresponding amine and formate (H. Fukatsu, Y. Hashimoto, M. Goda, H. Higashibata, and M. Kobayashi, Proc. Natl. Acad. Sci. U. S. A. 101:13726–13731, 2004, doi:10.1073/pnas.0405082101). Here, we discovered that this enzyme catalyzed the reverse reaction, synthesizing N-benzylformamide (NBFA) from benzylamine and formate. The reverse reaction proceeded only in the presence of high substrate concentrations. The effects of pH and inhibitors on the reverse reaction were almost the same as those on the forward reaction, suggesting that the forward and reverse reactions are both catalyzed at the same catalytic site. Bisubstrate kinetic analysis using formate and benzylamine and dead-end inhibition studies using a benzylamine analogue, aniline, revealed that the reverse reaction of this enzyme proceeds via an ordered two-substrate, two-product (bi-bi) mechanism in which formate binds first to the enzyme active site, followed by benzylamine binding and the subsequent release of NBFA. To our knowledge, this is the first report of the reverse reaction of an amine-forming deformylase. Surprisingly, analysis of the substrate specificity for acids demonstrated that not only formate, but also acetate and propionate (namely, acids with numbers of carbon atoms ranging from C1 to C3), were active as acid substrates for the reverse reaction. Through this reaction, N-substituted carboxamides, such as NBFA, N-benzylacetamide, and N-benzylpropionamide, were synthesized from benzylamine and the corresponding acid substrates. PMID:24123742

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

PubMed Central

Pipic, Alma; Zeller, Matthias; Tsetsakos, Panagiota

2013-01-01

Summary The tin(IV)-catalyzed reaction of β-nitrostyrene with (E)-3-methyl-1,3-pentadiene in toluene afforded two major nitronic ester cycloadducts in 27% and 29% yield that arise from the reaction at the less substituted diene double bond. Also present were four cycloadducts from the reaction at the higher substituted diene double bond, two of which were the formal cycloadducts of (Z)-3-methyl-1,3-pentadiene. A Friedel–Crafts alkylation product from the reaction of the diene, β-nitrostyrene, and toluene was also obtained in 10% yield. The tin(IV)-catalyzed reaction of β-nitrostyrene with (Z)-3-methyl-1,3-pentadiene in dichloromethane afforded four nitronic ester cycloadducts all derived from the reaction at the higher substituted double bond. One cycloadduct was isolated in 45% yield and two others are formal adducts of the E-isomer of the diene. The product formation in these reactions is consistent with a stepwise mechanism involving a zwitterionic intermediate. The initially isolated nitronic ester cycloadducts underwent tin(IV)-catalyzed interconversion, presumably via zwitterion intermediates. Cycloadducts derived from the reaction at the less substituted double bond of (E)-3-methyl-1,3-pentadiene underwent a [3,3]-sigmatropic rearrangement on heating to afford 4-nitrocyclohexenes. Cycloadducts derived from the reaction at the higher substituted diene double bond of either diene failed to undergo a thermal rearrangement. Rates and success of the rearrangement are consistent with a concerted mechanism possessing a dipolar transition state. An initial assessment of substituent effects on the rearrangement process is presented. PMID:24204426

Insights into the carboxyltransferase reaction of pyruvate carboxylase from the structures of bound product and intermediate analogues

PubMed Central

Lietzan, Adam D.; St. Maurice, Martin

2014-01-01

Pyruvate carboxylase (PC) is a biotin-dependent enzyme that catalyzes the MgATP- and bicarbonate-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in central metabolism. The carboxyltransferase (CT) domain of PC catalyzes the transfer of a carboxyl group from carboxybiotin to the accepting substrate, pyruvate. It has been hypothesized that the reactive enolpyruvate intermediate is stabilized through a bidentate interaction with the metal ion in the CT domain active site. Whereas bidentate ligands are commonly observed in enzymes catalyzing reactions proceeding through an enolpyruvate intermediate, no bidentate interaction has yet been observed in the CT domain of PC. Here, we report three X-ray crystal structures of the Rhizobium etli PC CT domain with the bound inhibitors oxalate, 3-hydroxypyruvate, and 3-bromopyruvate. Oxalate, a stereoelectronic mimic of the enolpyruvate intermediate, does not interact directly with the metal ion. Instead, oxalate is buried in a pocket formed by several positively charged amino acid residues and the metal ion. Furthermore, both 3-hydroxypyruvate and 3-bromopyruvate, analogs of the reaction product oxaloacetate, bind in an identical manner to oxalate suggesting that the substrate maintains its orientation in the active site throughout catalysis. Together, these structures indicate that the substrates, products and intermediates in the PC-catalyzed reaction are not oriented in the active site as previously assumed. The absence of a bidentate interaction with the active site metal appears to be a unique mechanistic feature among the small group of biotin-dependent enzymes that act on α-keto acid substrates. PMID:24157795

Butanolysis: Comparison of potassium hydroxide and potassium tert-butoxide as catalyst for biodiesel preparing from rapeseed oil.

PubMed

Musil, Martin; Skopal, Frantisek; Hájek, Martin; Vavra, Ales

2018-07-15

Biodiesel is a mixture of esters of fatty acids (most often palmitic, stearic and oleic) and lower alcohols (in our work butanol) produced by transesterification. It is a renewable source of energy, prepared from triacylglycerides, which are contained in vegetable oils and animal fats. This work focuses on alkaline catalyzed transesterification of rapeseed oil with butanol and comparison of two catalysts (potassium hydroxide and potassium tert-butoxide). In industry is usually transesterification of rapeseed oil carried out like reaction catalyzed by potassium hydroxide. Potassium hydroxide have high content of K 2 CO 3 , KHCO 3 and water. Moreover water is formed by neutralization of potassium hydroxide with free fatty acids contained in oil. In cause of tert-butoxide catalyzed reaction, it is not possible because tert-butoxide have not a OH - aniont, which is needed for water forming. The influence of various conditions (addition of water, temperature of separation, intensity of stirring and type of catalyst) on butanolysis process was studied for both catalysts. For both catalysts dependence of conversions on time were plotted. When tert-butoxide was used, satisfactory phase separation was not achieved. The only way was separation of hot crude reaction mixture without adding water. Ester formed by this method had high content of free glycerol and soaps, but reached higher conversion. The best results were obtained with KOH and subsequent separation of cold crude reaction mixture with the addition of water and slow stirring. The difference between reactions catalyzed by potassium hydroxide and potassium tert-butoxide was described. Copyright © 2018 Elsevier Ltd. All rights reserved.

Mild Aromatic Palladium-Catalyzed Protodecarboxylation: Kinetic Assessment of the Decarboxylative Palladation and the Protodepalladation Steps

PubMed Central

Dickstein, Joshua S.; Curto, John M.; Gutierrez, Osvaldo; Mulrooney, Carol A.; Kozlowski, Marisa C.

2013-01-01

Mechanism studies of a mild palladium catalyzed decarboxylation of aromatic carboxylic acids are described. In particular, reaction orders and activation parameters for the two stages of the transformation were determined. These studies guided development of a catalytic system capable of turnover. Further evidence reinforces that the second stage, protonation of the aryl palladium intermediate, is the rate-determining step of the reaction. The first step, decarboxylative palladation is proposed to occur through an intramolecular electrophilic palladation pathway, which is supported by computational and mechansim studies. In contrast to the reverse reaction (C-H insertion), the data support an electrophilic aromatic substitution mechanism involving a stepwise intramolecular protonation sequence for the protodepalladation portion of the reaction. PMID:23590518

Titanocene(III)-Catalyzed Three-Component Reaction of Secondary Amides, Aldehydes, and Electrophilic Alkenes.

PubMed

Zheng, Xiao; He, Jiang; Li, Heng-Hui; Wang, Ao; Dai, Xi-Jie; Wang, Ai-E; Huang, Pei-Qiang

2015-11-09

An umpolung Mannich-type reaction of secondary amides, aliphatic aldehydes, and electrophilic alkenes has been disclosed. This reaction features the one-pot formation of C-N and C-C bonds by a titanocene-catalyzed radical coupling of the condensation products, from secondary amides and aldehydes, with electrophilic alkenes. N-substituted γ-amido-acid derivatives and γ-amido ketones can be efficiently prepared by the current method. Extension to the reaction between ketoamides and electrophilic alkenes allows rapid assembly of piperidine skeletons with α-amino quaternary carbon centers. Its synthetic utility has been demonstrated by a facile construction of the tricyclic core of marine alkaloids such as cylindricine C and polycitorol A. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed SN2'-Cyclization of Ambivalent (Bromoalkadienyl)malonates: Preparation of Medium- to Large-Membered Endocyclic Allenes.

PubMed

Ichio, Hiroaki; Murakami, Hidetoshi; Chen, Yen-Chou; Takahashi, Tamotsu; Ogasawara, Masamichi

2017-07-21

A palladium-catalyzed reaction for preparing various endocyclic allenes was developed. The substrates for the reaction were readily available ω-(pronucleophile-tethered)-3-bromo-1,3-alkadienes, and a palladium-catalyst facilitated their unimolecular S N 2'-cyclization in the presence of potassium tert-butoxide to give the corresponding 9- to 16-membered endocyclic allenes in fair yields of up to 67% together with the dimeric 16- to 32-membered endocyclic bis-allenes and other oligomeric/polymeric intermolecular reaction products. For higher yields of the monomeric endocyclic allenes, the reaction needed to be conducted under high-dilution conditions. Using a chiral palladium catalyst, axially chiral endocyclic allenes were obtained in up to 70% ee.

Supercritical CO2 as a reaction medium for synthesis of capsaicin analogues by lipase-catalyzed transacylation of capsaicin.

PubMed

Kobata, Kenji; Kobayashi, Mamiko; Kinpara, Sachiyo; Watanabe, Tatsuo

2003-09-01

Capsaicin analogues having different acyl moiety were synthesized by lipase-catalyzed transacylation of capsaicin with a corresponding acyl donor in supercritical CO2 as a reaction medium. Transacylation with methyl tetradecanoate using Novozym 435 as a catalyst gave vanillyl tetradecanamide in a 54% yield at 80 degrees C and 19 MPa over 72 h. Vanillyl (Z)-9-octadecenamide, olvanil, was synthesized from triolein in a 21% yield over 7 d.

Asymmetric synthesis of 2-aryl-2,3-dihydro-4-quinolones by rhodium-catalyzed 1,4-addition of arylzinc reagents in the presence of chlorotrimethylsilane.

PubMed

Shintani, Ryo; Yamagami, Takafumi; Kimura, Takahiro; Hayashi, Tamio

2005-11-10

[reaction: see text] The first catalytic asymmetric synthesis of 2-aryl-2,3-dihydro-4-quinolones has been developed by way of a rhodium-catalyzed 1,4-addition of arylzinc reagents to 4-quinolones. These 1,4-adducts can be obtained with high enantioselectivity by the use of (R)-binap as a ligand, and high yields are realized by conducting the reactions in the presence of chlorotrimethylsilane.

Highly Selective Coupling of Alkenes and Aldehydes Catalyzed by NHC–Ni–P(OPh)3: Synergy Between a Strong σ-Donor and a Strong π-Acceptor**

PubMed Central

Ho, Chun-Yu; Jamison, Timothy F.

2011-01-01

Both a strong electron donor (IPr) and a strong electron acceptor (P(OPh)3) are necessary for a highly selective, nickel-catalyzed coupling reaction between alkenes, aldehydes, and silyltriflates. Without the phosphite, catalysis is not observed and several side reactions are observed. The phosphite appears to suppress the formation of these byproducts and rescue the catalytic cycle by accelerating reductive elimination from an (IPr–Ni–H)(OTf) complex. PMID:17154217

Construction of Pyrrolo[1,2-a]indoles via Cobalt(III)-Catalyzed Enaminylation of 1-(Pyrimidin-2-yl)-1H-indoles with Ketenimines and Subsequent Base-Promoted Cyclization.

PubMed

Zhou, Xiaorong; Fan, Zili; Zhang, Zhiyin; Lu, Ping; Wang, Yanguang

2016-09-16

A cobalt(III)-catalyzed cross-coupling reaction of 1-(pyrimidin-2-yl)-1H-indoles with ketenimines is reported. The reaction provided 2-enaminylated indole derivatives in moderate to excellent yields with a broad substrate scope. The prepared 2-enaminylated indoles could be conveniently converted into pyrrolo[1,2-a]indoles, which are an important class of compounds in medicinal chemistry.

Sonochemical enzyme-catalyzed regioselective acylation of flavonoid glycosides.

PubMed

Ziaullah; Rupasinghe, H P Vasantha

2016-04-01

This work compares a highly efficient and alternative method of sonication-assisted lipase catalyzed acylation of quercetin-3-O-glucoside and phloretin-2'-glucoside, using Candida antarctica lipase B (Novozyme 435(®)), with a range of fatty acids. In this study, sonication-assisted irradiation coupled with stirring has been found to be more efficient and economical than conventional reaction conditions. Sonication-assisted acylation accelerated the reactions and reduced the time required by 4-5 folds. Copyright © 2016 Elsevier Inc. All rights reserved.

General Synthesis of Alkenyl Sulfides by Palladium-Catalyzed Thioetherification of Alkenyl Halides and Tosylates.

PubMed

Velasco, Noelia; Virumbrales, Cintia; Sanz, Roberto; Suárez-Pantiga, Samuel; Fernández-Rodríguez, Manuel A

2018-05-08

The cross-coupling reaction of alkenyl bromides with thiols catalyzed by palladium complexes derived from inexpensive dppf ligand is reported. These reactions occur under low catalyst loading and in high yields and display wide scope, including the coupling of bulky thiols and trisubstituted bromoolefins, and functional group tolerance. In addition, the thioetherification of less reactive chloroalkenes and, for the first time, alkenyl tosylates was accomplished using a catalyst generated from CyPF tBu alkylbisphosphine ligand.

Ligand- and base-free copper(II)-catalyzed C-N bond formation: cross-coupling reactions of organoboron compounds with aliphatic amines and anilines.

PubMed

Quach, Tan D; Batey, Robert A

2003-11-13

[reaction: see text] A ligandless and base-free Cu-catalyzed protocol for the cross-coupling of arylboronic acids and potassium aryltrifluoroborate salts with primary and secondary aliphatic amines and anilines is described. The process utilizes catalytic copper(II) acetate monohydrate and 4 A molecular sieves in dichloromethane at slightly elevated temperatures under an atmosphere of oxygen. A broad range of functional groups are tolerated on both of the cross-coupling partners.

Vinyl azides derived from allenes: thermolysis leading to multisubstituted 1,4-pyrazines and Mn(III)-catalyzed photochemical reaction leading to pyrroles.

PubMed

Sajna, K V; Kumara Swamy, K C

2012-10-05

Thermolysis of phosphorus-based vinyl azides under solvent- and catalyst-free conditions furnished a new route for 1,4-pyrazines. A simple one-pot, Mn(III)-catalyzed photochemical route has been developed for multisubstituted pyrroles starting from allenes and 1,3-dicarbonyls via in situ-generated vinyl azides. The utility of new phosphorus-based pyrroles is also demonstrated in the Horner reaction. The structures of key products are unequivocally confirmed by X-ray crystallography.

Synthesis of phenanthridinones from N-methoxybenzamides and arenes by multiple palladium-catalyzed C-H activation steps at room temperature.

PubMed

Karthikeyan, Jaganathan; Cheng, Chien-Hong

2011-10-10

Many steps make light work: substituted phenanthridinones can be obtained with high regioselectivity and in very good yields by palladium-catalyzed cyclization reactions of N-methoxybenzamides with arenes. The reaction proceeds through multiple oxidative C-H activation and C-C/C-N formation steps in one pot at room temperature, and thus provides a simple method for generating bioactive phenanthridinones. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Total synthesis of (+)-achalensolide based on the rh(i)-catalyzed allenic Pauson-Khand-type reaction.

PubMed

Hirose, Toshiyuki; Miyakoshi, Naoki; Mukai, Chisato

2008-02-01

The first total synthesis of (+)-achalensolide was achieved from a commercially available d-(-)-isoascorbic acid. The known epoxide, derived from d-(-)-isoascorbic acid, was converted into the allenyne, the Rh(I)-catalyzed Pauson-Khand-type reaction of which directly provided the bicyclo[5.3.0]decane system, a core framework of the title natural product. The construction of the gamma-lactone moiety and some chemical modifications resulted in the completion of the total synthesis of (+)-achalensolide.

Rh(III)-Catalyzed C-H Activation of Benzoylacetonitriles and Tandem Cyclization with Diazo Compounds to Substituted Benzo[ de]chromenes.

PubMed

Fang, Feifei; Zhang, Chunmei; Zhou, Chaofan; Li, Yazhou; Zhou, Yu; Liu, Hong

2018-04-06

Rh (III)-catalyzed C-H activation of benzoylacetonitriles in coupling with diazo compounds was developed to synthesize diversified substituted benzo[ de]chromenes via a formal (4 + 2) cycloaddition with a diazo compound and subsequent tandem (4 + 2) cycloaddition with another diazo compound. Intriguingly, synthesis of substituted benzo[ de]chromenes and their decarboxylation products could be realized by controlling the reaction conditions. These reactions have a broad range of substrates, moderate to good yields, and high regioselectivity.

Synthesis of Imidazopyridines via Copper-Catalyzed, Formal Aza-[3 + 2] Cycloaddition Reaction of Pyridine Derivatives with α-Diazo Oxime Ethers.

PubMed

Park, Sangjune; Kim, Hyunseok; Son, Jeong-Yu; Um, Kyusik; Lee, Sooho; Baek, Yonghyeon; Seo, Boram; Lee, Phil Ho

2017-10-06

The Cu-catalyzed, formal aza-[3 + 2] cycloaddition reaction of pyridine derivatives with α-diazo oxime ethers in trifluoroethanol was used to synthesize imidazopyridines via the release of molecular nitrogen and elimination of alcohol. These methods enabled modular synthesis of a wide range of N-heterobicyclic compounds such as imidazopyridazines, imidazopyrimidines, and imidazopyrazines with an α-imino Cu-carbenoid generated from the α-diazo oxime ethers and copper.

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

PubMed

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

2015-06-08

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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dinuclear Zinc-Prophenol-Catalyzed Enantioselective α-Hydroxyacetate Aldol Reaction with Activated Ester Equivalents

PubMed Central

Trost, Barry M.; Michaelis, David J.; Truica, Mihai I.

2013-01-01

An enantioselective α-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc Prophenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting α,β-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Isotope Effects and Mechanism of the Asymmetric BOROX Brønsted Acid Catalyzed Aziridination Reaction

PubMed Central

Vetticatt, Mathew J.; Desai, Aman A.; Wulff, William D.

2013-01-01

The mechanism of the chiral VANOL-BOROX Brønsted acid catalyzed aziridination reaction of imines and ethyldiazoacetate has been studied using a combination of experimental kinetic isotope effects and theoretical calculations. A stepwise mechanism where reversible formation of a diazonium ion intermediate precedes rate-limiting ring-closure to form the cis-aziridine is implicated. A revised model for the origin of enantio- and diastereoselectivity is proposed based on relative energies of the ring closing transition structures. PMID:23687986

Heterogeneous atmospheric chemistry

NASA Technical Reports Server (NTRS)

Schryer, D. R.

1982-01-01

The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.

6-Azabicyclo[3.2.1]octanes Via Copper-Catalyzed Enantioselective Alkene Carboamination

PubMed Central

Casavant, Barbara J.; Hosseini, Azade S.

2014-01-01

Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)2 or related catalysts in the presence of MnO2 as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities. Two new stereocenters are formed in the reaction, and the C-C bond-forming arene addition is a net C-H functionalization. PMID:25484848

Pd(OAc)2-Catalyzed Domino Reactions of 1-Chloro-2-Haloarenes and 2-Haloaryl Tosylates with Hindered Grignard Reagents via Palladium Associated Arynes

PubMed Central

Dong, Cheng-Guo; Hu, Qiao-Sheng

2008-01-01

The palladium associated aryne generation strategy and Pd(OAc)2-catalyzed annulative Domino reactions of 1-chloro-2-halobenzenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium associated arynes are described. The palladium associated aryne generation strategy described here not only allows the high yield, one-step access to potentially useful substituted fluorenes from readily available 1-chloro-2-halobenzenes and 2-haloaryl tosylates, but may also lead to the development of other tandem reactions based on these readily available o-leaving group bearing haloarenes PMID:17048842

Phosphine-catalyzed cycloadditions of allenic ketones: new substrates for nucleophilic catalysis.

PubMed

Wallace, Debra J; Sidda, Rachel L; Reamer, Robert A

2007-02-02

A range of phosphine-catalyzed cycloaddition reactions of allenic ketones have been studied, extending the scope of these processes from the more widely used 2,3-butadienoates to allow access to a number of synthetically useful products. Reaction of allenyl methyl ketone 4 with exo-enones afforded spirocyclic compounds in good regioselectivity and promising enantioselectivity via a [2 + 3] cycloaddtion. Aromatic allenyl ketones undergo a phosphine-promoted dimerization to afford functionalized pyrans, leading to a formal [2 + 4] Diels-Alder product, but did not react in the [2 + 3] cycloaddition. The results from other reactions that had found utility with 2,3-butadienoates are also reported.

Indium-catalyzed direct chlorination of alcohols using chlorodimethylsilane-benzil as a selective and mild system.

PubMed

Yasuda, Makoto; Yamasaki, Satoshi; Onishi, Yoshiyuki; Baba, Akio

2004-06-16

The InCl3-catalyzed reaction of alcohols with chlorodimethylsilane (HSiMe2Cl) in the presence of benzil gave the corresponding organic chlorides under mild conditions. Benzil significantly changes the reaction course because the reducing product through dehydroxyhydration was obtained in the absence of benzil. The secondary or tertiary alcohols were effectively chlorinated. The substrates bearing acid-sensitive functional groups were also applied to this system. The highly selective chlorination of the tertiary site was observed in the competitive reaction between tertiary and primary alcohols. The highly coordinated hydrosilane generated from benzil and HSiMe2Cl is an important intermediate.

Rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction.

PubMed

Kwong, Fuk Yee; Li, Yue Ming; Lam, Wai Har; Qiu, Liqin; Lee, Hang Wai; Yeung, Chi Hung; Chan, Kin Shing; Chan, Albert S C

2005-06-20

An interesting rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions. Various enynes were transformed to the corresponding bicyclic cyclopentenones in good yield and enantiomeric excess (up to 95 % ee). A study of the electronic effects of the enyne substrates revealed a correlation between the electronic properties of the substrates and the ee value obtained in the product of the Pauson-Khand-type reaction. A linear free-energy relationship was observed from a Hammett study.

19F NMR ligand perturbation studies on 6,7-bis(trifluoromethyl)-8-ribityllumazine-7-hydrates and the lumazine synthase complex of Bacillus subtilis. Site-directed mutagenesis changes the mechanism and the stereoselectivity of the catalyzed haloform-type reaction.

PubMed

Scheuring, J; Kugelbrey, K; Weinkauf, S; Cushman, M; Bacher, A; Fischer, M

2001-06-01

The riboflavin synthase/lumazine synthase complex of Bacillus subtilis catalyzes the last two steps in riboflavin biosynthesis. The protein comprises a capsid of 60 beta subunits with lumazine synthase activity and a core of three alpha subunits with riboflavin synthase activity. The beta subunits catalyze the formation of 6,7-dimethyl-8-ribityllumazine (3) from 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione (1) and 3,4-dihydroxy-2-butanone 4-phosphate (2). Complexes of recombinant lumazine synthase (beta(60) capsids) with 6-trifluoromethyl-7-oxo-8-ribityllumazine (10) as well as 7S- or 7R-6,7-bistrifluoromethyl-8-ribityllumazine hydrate (11) were studied by (19)F NMR spectroscopy. Despite the large molecular weight of approximately 960 kDa of the protein, spectra with separated signals of free and bound ligand could be obtained. An unusually large shift difference of 8 ppm was observed between the 7-trifluoromethyl signals of free and bound ligand for epimer B of 11 and the enzyme. The signal is sensitive to the replacement of amino acid residues F22 and H88. Lumazine synthase catalyzes the elimination of the 7-trifluoromethyl group of R-diastereomer epimer A in a haloform-like reaction. The elimination reaction is also catalyzed by F22 mutants. The H88R mutant displays an opposite stereoselectivity for epimer B and a greatly enhanced reaction rate. From a model of the epimers in the active site of the protein, the main function of the side chain of F22 seems to be to keep the substrate ring in the correct position. H88 is in a position suited to act as proton acceptor in both the physiological as well as the haloform reaction. A different mechanism of the haloform-reaction is proposed in the case of the H88R mutant, initiated by hydrogen bonding of the 7-trifluorormethyl group and the guanidinium group of the arginine residue.

Computational Study of a Model System of Enzyme-Mediated [4+2] Cycloaddition Reaction

PubMed Central

2015-01-01

A possible mechanistic pathway related to an enzyme-catalyzed [4+2] cycloaddition reac-tion was studied by theoretical calculations at density functional (B3LYP, O3LYP, M062X) and semiempirical levels (PM6-DH2, PM6) performed on a model system. The calculations were carried out for the key [4+2] cycloaddition step considering enzyme-catalyzed biosynthesis of Spinosyn A in a model reaction, where a reliable example of a biological Diels-Alder reaction was reported experimentally. In the present study it was demonstrated that the [4+2] cycloaddition reaction may benefit from moving along the energetically balanced reaction coordinate, which enabled the catalytic rate enhancement of the [4+2] cycloaddition pathway involving a single transition state. Modeling of such a system with coordination of three amino acids indicated a reliable decrease of activation energy by ~18.0 kcal/mol as compared to a non-catalytic transformation. PMID:25853669

Pop-it beads to introduce catalysis of reaction rate and substrate depletion effects.

PubMed

Gehret, Austin U

2017-03-04

A kinesthetic classroom activity was designed to help students understand enzyme activity and catalysis of reaction rate. Students served the role of enzymes by manipulating Pop-It Beads as the catalytic event. This activity illuminates the relationship between reaction rate and reaction progress by allowing students to experience first-hand the effect of substrate depletion on catalyzed reaction rate. Preliminary findings based on survey results and exam performance suggest the activity could prove beneficial to students in the targeted learning outcomes. Unique to previous kinesthetic approaches that model Michaelis-Menten kinetics, this activity models the effects of substrate depletion on catalyzed reaction rate. Therefore, it could prove beneficial for conveying the reasoning behind the initial rate simplification used in Michaelis-Menten kinetics. © 2016 by The International Union of Biochemistry and Molecular Biology, 45(2):179-183, 2017. © 2016 The International Union of Biochemistry and Molecular Biology.

Metal centers in the anaerobic microbial metabolism of CO and CO2.

PubMed

Bender, Güneş; Pierce, Elizabeth; Hill, Jeffrey A; Darty, Joseph E; Ragsdale, Stephen W

2011-08-01

Carbon dioxide and carbon monoxide are important components of the carbon cycle. Major research efforts are underway to develop better technologies to utilize the abundant greenhouse gas, CO(2), for harnessing 'green' energy and producing biofuels. One strategy is to convert CO(2) into CO, which has been valued for many years as a synthetic feedstock for major industrial processes. Living organisms are masters of CO(2) and CO chemistry and, here, we review the elegant ways that metalloenzymes catalyze reactions involving these simple compounds. After describing the chemical and physical properties of CO and CO(2), we shift focus to the enzymes and the metal clusters in their active sites that catalyze transformations of these two molecules. We cover how the metal centers on CO dehydrogenase catalyze the interconversion of CO and CO(2) and how pyruvate oxidoreductase, which contains thiamin pyrophosphate and multiple Fe(4)S(4) clusters, catalyzes the addition and elimination of CO(2) during intermediary metabolism. We also describe how the nickel center at the active site of acetyl-CoA synthase utilizes CO to generate the central metabolite, acetyl-CoA, as part of the Wood-Ljungdahl pathway, and how CO is channelled from the CO dehydrogenase to the acetyl-CoA synthase active site. We cover how the corrinoid iron-sulfur protein interacts with acetyl-CoA synthase. This protein uses vitamin B(12) and a Fe(4)S(4) cluster to catalyze a key methyltransferase reaction involving an organometallic methyl-Co(3+) intermediate. Studies of CO and CO(2) enzymology are of practical significance, and offer fundamental insights into important biochemical reactions involving metallocenters that act as nucleophiles to form organometallic intermediates and catalyze C-C and C-S bond formations.

Metal centers in the anaerobic microbial metabolism of CO and CO2

PubMed Central

Bender, Güneş; Pierce, Elizabeth; Hill, Jeffrey A.; Darty, Joseph E.

2014-01-01

Carbon dioxide and carbon monoxide are important components of the carbon cycle. Major research efforts are underway to develop better technologies to utilize the abundant greenhouse gas, CO2, for harnessing ‘green’ energy and producing biofuels. One strategy is to convert CO2 into CO, which has been valued for many years as a synthetic feedstock for major industrial processes. Living organisms are masters of CO2 and CO chemistry and, here, we review the elegant ways that metalloenzymes catalyze reactions involving these simple compounds. After describing the chemical and physical properties of CO and CO2, we shift focus to the enzymes and the metal clusters in their active sites that catalyze transformations of these two molecules. We cover how the metal centers on CO dehydrogenase catalyze the interconversion of CO and CO2 and how pyruvate oxidoreductase, which contains thiamin pyrophosphate and multiple Fe4S4 clusters, catalyzes the addition and elimination of CO2 during intermediary metabolism. We also describe how the nickel center at the active site of acetyl-CoA synthase utilizes CO to generate the central metabolite, acetyl-CoA, as part of the Wood-Ljungdahl pathway, and how CO is channelled from the CO dehydrogenase to the acetyl-CoA synthase active site. We cover how the corrinoid iron–sulfur protein interacts with acetyl-CoA synthase. This protein uses vitamin B12 and a Fe4S4 cluster to catalyze a key methyltransferase reaction involving an organometallic methyl-Co3+ intermediate. Studies of CO and CO2 enzymology are of practical significance, and offer fundamental insights into important biochemical reactions involving metallocenters that act as nucleophiles to form organometallic intermediates and catalyze C–C and C–S bond formations. PMID:21647480

Greener Pathways to Organics and Nanomaterials: Sustainable Applications of Nano-Catalysts(South Korea)

EPA Science Inventory

Sustainable chemical synthetic activity involving alternate energy input, and greener reaction medium in aqueous or solvent-free conditions will be summarized for heterocyclic compounds, coupling reactions, and a variety of name reactions; these reactions are catalyzed by basic w...

Steric and Electronic Effects of Bidentate Phosphine Ligands on Ruthenium(II)-Catalyzed Hydrogenation of Carbon Dioxide.

PubMed

Zhang, Pan; Ni, Shao-Fei; Dang, Li

2016-09-20

The reactivity difference between the hydrogenation of CO2 catalyzed by various ruthenium bidentate phosphine complexes was explored by DFT. In addition to the ligand dmpe (Me2 PCH2 CH2 PMe2 ), which was studied experimentally previously, a more bulky diphosphine ligand, dmpp (Me2 PCH2 CH2 CH2 PMe2 ), together with a more electron-withdrawing diphosphine ligand, PN(Me) P (Me2 PCH2 N(Me) CH2 PMe2 ), have been studied theoretically to analyze the steric and electronic effects on these catalyzed reactions. Results show that all of the most favorable pathways for the hydrogenation of CO2 catalyzed by bidentate phosphine ruthenium dihydride complexes undergo three major steps: cis-trans isomerization of ruthenium dihydride complex, CO2 insertion into the Ru-H bond, and H2 insertion into the ruthenium formate ion. Of these steps, CO2 insertion into the Ru-H bond has the lowest barrier compared with the other two steps in each preferred pathway. For the hydrogenation of CO2 catalyzed by ruthenium complexes of dmpe and dmpp, cis-trans isomerization of ruthenium dihydride complex has a similar barrier to that of H2 insertion into the ruthenium formate ion. However, in the reaction catalyzed by the PN(Me) PRu complex, cis-trans isomerization of the ruthenium dihydride complex has a lower barrier than H2 insertion into the ruthenium formate ion. These results suggest that the steric effect caused by the change of the outer sphere of the diphosphine ligand on the reaction is not clear, although the electronic effect is significant to cis-trans isomerization and H2 insertion. This finding refreshes understanding of the mechanism and provides necessary insights for ligand design in transition-metal-catalyzed CO2 transformation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ruthenium-catalyzed regioselective allylic amination of 2,3,3-trifluoroallylic carbonates.

PubMed

Isobe, Shin-Ichi; Terasaki, Shou; Hanakawa, Taisyun; Mizuno, Shota; Kawatsura, Motoi

2017-04-05

We demonstrated the ruthenium-catalyzed allylic amination of 2,3,3-trifluoroallylic carbonates with several types of amines. The reactions proceeded with several types of amines, and succeeded in obtaining polyfluorinated terminal alkenes possessing branched allylic amines as a single regioisomer.

BASE-CATALYZED DESTRUCTION OF PCBS-NEW DONORS, NEW TRANSFER AGENTS/CATALYSTS

EPA Science Inventory

The use of hydrogen transfer agents and catalysts to improve the base-catalyzed decomposition of polychlorinated biphenyls (PCBs) was investigated. The reaction proceeded only in the presence of base, but the rate of PCB disappearance increased with increasing amount of hydrogen ...

Transglutaminase catalyzed cross-linking of sodium caseinate improves oxidative stability of flaxseed oil emulsion.

PubMed

Ma, Hairan; Forssell, Pirkko; Kylli, Petri; Lampi, Anna-Maija; Buchert, Johanna; Boer, Harry; Partanen, Riitta

2012-06-20

Sodium caseinate was modified by transglutaminase catalyzed cross-linking reaction prior to the emulsification process in order to study the effect of cross-linking on the oxidative stability of protein stabilized emulsions. The extent of the cross-linking catalyzed by different dosages of transglutaminase was investigated by following the ammonia production during the reaction and using SDS-PAGE gel. O/W emulsions prepared with the cross-linked and non-cross-linked sodium caseinates were stored for 30 days under the same conditions. Peroxide value measurement, oxygen consumption measurement, and headspace gas chromatography analysis were used to study the oxidative stability of the emulsions. The emulsion made of the cross-linked sodium caseinate showed an improved oxidative stability with reduced formation of fatty acid hydroperoxides and volatiles and a longer period of low rate oxygen consumption. The improving effect of transglutaminase catalyzed cross-linking could be most likely attributed to the enhanced physical stability of the interfacial protein layer against competitive adsorption by oil oxidation products.

Lewis super-acid catalyzed cyclizations: a new route to fragrance compounds.

PubMed

Coulombel, Lydie; Grau, Fanny; Weïwer, Michel; Favier, Isabelle; Chaminade, Xavier; Heumann, Andreas; Bayón, J Carles; Aguirre, Pedro A; Duñach, Elisabet

2008-06-01

This review deals with the application of Lewis super acids such as Al(III), In(III), and Sn(IV) triflates and triflimidates as catalysts in the synthesis of fragrance materials. Novel catalytic reactions involving C-C and C-heteroatom bond-forming reactions, as well as cycloisomerization processes are presented. In particular, Sn(IV) and Al(III) triflates were employed as catalysts in the selective cyclization of unsaturated alcohols to cyclic ethers, as well as in the cyclization of unsaturated carboxylic acids to lactones. The addition of thiols and thioacids to non-activated olefins, both in intra- and intermolecular versions, was efficiently catalyzed by In(III) derivatives. Sn(IV) Triflimidates catalyzed the cycloisomerization of highly substituted 1,6-dienes to gem-dimethyl-substituted cyclohexanes bearing an isopropylidene substituent. The hydroformylation of these unsaturated substrates, catalyzed by a Rh(I) complex with a bulky phosphite ligand, selectively afforded the corresponding linear aldehydes. The olfactory evaluation of selected heterocycles, carbocycles, and aldehydes synthesized is also discussed.

Protein complexes formed during the incision reaction catalyzed by the Escherichia coli UvrABC endonuclease.

PubMed Central

Yeung, A T; Mattes, W B; Grossman, L

1986-01-01

An examination has been made into the nature of the nucleoprotein complexes formed during the incision reaction catalyzed by the Escherichia coli UvrABC endonuclease when acting on a pyrimidine dimer-containing fd RF-I DNA species. The complexes of proteins and DNA form in unique stages. The first stage of binding involves an ATP-stimulated interaction of the UvrA protein with duplex DNA containing pyrimidine dimer sites. The UvrB protein significantly stabilizes the UvrA-pyrimidine dimer containing DNA complex which, in turn, provides a foundation for the binding of UvrC to activate the UvrABC endonuclease. The binding of one molecule of UvrC to each UvrAB-damaged DNA complex is needed to catalyze incision in the vicinity of pyrimidine dimer sites. The UvrABC-DNA complex persists after the incision event suggesting that the lack of UvrABC turnover may be linked to other activities in the excision-repair pathway beyond the initial incision reaction. PMID:3960727

Biodiesel production from Nannochloropsis gaditana lipids through transesterification catalyzed by Rhizopus oryzae lipase.

PubMed

Navarro López, Elvira; Robles Medina, Alfonso; González Moreno, Pedro Antonio; Esteban Cerdán, Luis; Martín Valverde, Lorena; Molina Grima, Emilio

2016-03-01

Biodiesel (fatty acid methyl esters, FAMEs) was produced from saponifiable lipids (SLs) extracted from wet Nannochloropsis gaditana biomass using methanolysis catalyzed by Rhizopus oryzae intracellular lipase. SLs were firstly extracted with ethanol to obtain 31 wt% pure SLs. But this low SL purity also gave a low biodiesel conversion (58%). This conversion increased up to 80% using SLs purified by crystallization in acetone (95 wt% purity). Polar lipids play an important role in decreasing the reaction velocity - using SLs extracted with hexane, which have lower polar lipid content (37.4% versus 49.0% using ethanol), we obtained higher reaction velocities and less FAME conversion decrease when the same lipase batch was reused. 83% of SLs were transformed to biodiesel using a 70 wt% lipase/SL ratio, 11:1 methanol/SL molar ratio, 10 mL t-butanol/g SLs after 72 h. The FAME conversion decreased to 71% after catalyzing three reactions with the same lipase batch. Copyright © 2015 Elsevier Ltd. All rights reserved.

Chemical models and their mechanistic implications for the transformation of 6-cyanouridine 5'-monophosphate catalyzed by orotidine 5'-monophosphate decarboxylase.

PubMed

Chien, Tun-Cheng; Jen, Cheng-Hung; Wu, Yuen-Jen; Liao, Chen-Chieh

2008-01-01

Orotidine 5'-monophosphate decarboxylase (ODCase) catalyzes an unprecedented transformation of 6- cyanouridine 5'-monophosphate (6-CN-UMP) into barbiturate nucleoside 5'-monophosphate (6-hydroxyuridine 5'-monophosphate, BMP). The reactions of 6- cyano-1,3-dimethyluracil toward various nucleophilic conditions have been studied as chemical models in order to understand the possible mechanism for the ODCase-catalyzed transformation of 6-CN-UMP.

Intramolecular π-π Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase.

PubMed

Blomeyer, Sebastian; Linnemannstöns, Marvin; Nissen, Jan Hendrick; Paulus, Jannik; Neumann, Beate; Stammler, Hans-Georg; Mitzel, Norbert W

2017-10-16

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH 2 ) 3 and (CH 2 ) 2 SiMe 2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C 6 H 5 (CH 2 ) 3 C 6 F 5 , in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of Iron Doped Silicon Nanoparticles as Bimodal Imaging Agents

PubMed Central

Singh, Mani P.; Atkins, Tonya M.; Muthuswamy, Elayaraja; Kamali, Saeed; Tu, Chuqiao; Louie, Angelique Y.; Kauzlarich, Susan M.

2012-01-01

We demonstrate the synthesis of water-soluble allylamine terminated Fe doped Si (SixFe) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single source iron containing precursor, Na4Si4 with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH4Br to produce hydrogen terminated SixFe nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy (TEM) indicates that the average particle diameter is ~3.0±1.0 nm. The Si5Fe nanoparticles show strong photoluminescence quantum yield in water (~ 10 %) with significant T2 contrast (r2/r1value of 4.31). Electron paramagnetic resonance (EPR) and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity. PMID:22616623

Development of iron-doped silicon nanoparticles as bimodal imaging agents.

PubMed

Singh, Mani P; Atkins, Tonya M; Muthuswamy, Elayaraja; Kamali, Saeed; Tu, Chuqiao; Louie, Angelique Y; Kauzlarich, Susan M

2012-06-26

We demonstrate the synthesis of water-soluble allylamine-terminated Fe-doped Si (Si(xFe)) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single-source iron-containing precursor, Na(4)Si(4) with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH(4)Br to produce hydrogen-terminated Si(xFe) nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy indicates that the average particle diameter is ∼3.0 ± 1.0 nm. The Si(5Fe) nanoparticles show strong photoluminescence quantum yield in water (∼10%) with significant T(2) contrast (r(2)/r(1) value of 4.31). Electron paramagnetic resonance and Mössbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity.

Methylene-bridged bis(benzimidazolium) salt as a highly efficient catalyst for the benzoin reaction in aqueous media.

PubMed

Iwamoto, Ken-ichi; Kimura, Hitomi; Oike, Masaaki; Sato, Masayuki

2008-03-07

Benzoin reactions are catalyzed effectively by a methylene-bridged bis(benzimidazolium) salt to yield alpha-hydroxy ketones, and the reactions proceed in water as the aqueous medium under mild conditions.

The Copper-nicotinamide complex: sustainable applications in coupling and cycloaddition reactions

EPA Science Inventory

Crystalline copper (II)-nicotinamide complex, synthesized via simple mixing of copper chloride and nicotinamide solution at room temperature, catalyzes the C-S, C-N bond forming and cycloaddition reactions under a variety of sustainable reaction conditions.

In Vivo Studies in Rhodospirillum rubrum Indicate That Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (Rubisco) Catalyzes Two Obligatorily Required and Physiologically Significant Reactions for Distinct Carbon and Sulfur Metabolic Pathways*♦

PubMed Central

Dey, Swati; North, Justin A.; Sriram, Jaya; Evans, Bradley S.; Tabita, F. Robert

2015-01-01

All organisms possess fundamental metabolic pathways to ensure that needed carbon and sulfur compounds are provided to the cell in the proper chemical form and oxidation state. For most organisms capable of using CO2 as sole source of carbon, ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) catalyzes primary carbon dioxide assimilation. In addition, sulfur salvage pathways are necessary to ensure that key sulfur-containing compounds are both available and, where necessary, detoxified in the cell. Using knock-out mutations and metabolomics in the bacterium Rhodospirillum rubrum, we show here that Rubisco concurrently catalyzes key and essential reactions for seemingly unrelated but physiologically essential central carbon and sulfur salvage metabolic pathways of the cell. In this study, complementation and mutagenesis studies indicated that representatives of all known extant functional Rubisco forms found in nature are capable of simultaneously catalyzing reactions required for both CO2-dependent growth as well as growth using 5-methylthioadenosine as sole sulfur source under anaerobic photosynthetic conditions. Moreover, specific inactivation of the CO2 fixation reaction did not affect the ability of Rubisco to support anaerobic 5-methylthioadenosine metabolism, suggesting that the active site of Rubisco has evolved to ensure that this enzyme maintains both key functions. Thus, despite the coevolution of both functions, the active site of this protein may be differentially modified to affect only one of its key functions. PMID:26511314

Novel syn intramolecular pathway in base-catalyzed 1,2-elimination reactions of beta-acetoxy esters.

PubMed

Mohrig, Jerry R; Carlson, Hans K; Coughlin, Jane M; Hofmeister, Gretchen E; McMartin, Lea A; Rowley, Elizabeth G; Trimmer, Elizabeth E; Wild, Andrew J; Schultz, Steve C

2007-02-02

As part of a comprehensive investigation of electronic effects on the stereochemistry of base-catalyzed 1,2-elimination reactions, we observed a new syn intramolecular pathway in the elimination of acetic acid from beta-acetoxy esters and thioesters. 1H and 2H NMR investigation of reactions using stereospecifically labeled tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanoate (1) and its (2R*,3S*) diastereomer (2) shows that 23 +/- 2% syn elimination occurs. The elimination reactions were catalyzed with KOH or (CH3)4NOH in ethanol/water under rigorously non-ion-pairing conditions. By contrast, the more sterically hindered beta-trimethylacetoxy ester produces only 6 +/- 1% syn elimination. These data strongly support an intramolecular (Ei) syn path for elimination of acetic acid, most likely through the oxyanion produced by nucleophilic attack at the carbonyl carbon of the beta-acetoxy group. The analogous thioesters, S-tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanethioate (3) and its (2R*,3S*) diastereomer (4), showed 18 +/- 2% syn elimination, whereas the beta-trimethylacetoxy substrate gave 5 +/- 1% syn elimination. The more acidic thioester substrates do not produce an increased amount of syn stereoselectivity even though their elimination reactions are at the E1cb interface.

An Experiment to Illustrate the Hazards of Exothermic Reaction Scale-Up

ERIC Educational Resources Information Center

Clark, William; Lei, Melinda; Kirichenko, Erika; Dickerson, Kellie; Prytko, Robert

2017-01-01

Exothermic reactions can present safety hazards and there is a recognized need for reaction safety education at the undergraduate level. We present an experiment that illustrates the pitfall of direct scale-up of an exothermic reaction that can lead to thermal runaway. The iodide-catalyzed hydrogen peroxide decomposition reaction yields…

Cabbage Patch Chemistry.

ERIC Educational Resources Information Center

Journal of Chemical Education, 2000

2000-01-01

This activity takes students through the process of fermentation. Requires an entire month for the full reaction to take place. The reaction, catalyzed by bacterial enzymes, produces lactic acid from glucose. (SAH)

Sequential Dy(OTf)3 -Catalyzed Solvent-Free Per-O-Acetylation and Regioselective Anomeric De-O-Acetylation of Carbohydrates.

PubMed

Yan, Yi-Ling; Guo, Jiun-Rung; Liang, Chien-Fu

2017-09-19

Dysprosium(III) trifluoromethanesulfonate-catalyzed per-O-acetylation and regioselective anomeric de-O-acetylation of carbohydrates can be tuned by adjusting the reaction medium. In this study, the per-O-acetylation of unprotected sugars by using a near-stoichiometric amount of acetic anhydride under solvent-free conditions resulted in the exclusive formation of acetylated saccharides as anomeric mixtures, whereas anomeric de-O-acetylation in methanol resulted in a moderate-to-excellent yield. Reactions with various unprotected monosaccharides or disaccharides followed by a semi-one-pot sequential conversion into the corresponding acetylated glycosyl hemiacetal also resulted in high yields. Furthermore, the obtained hemiacetals could be successfully transformed into trichloroimidates after Dy(OTf) 3 -catalyzed glycosylation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen-bonded intermediates and transition states during spontaneous and acid-catalyzed hydrolysis of the carcinogen (+)-anti-BPDE.

PubMed

Palenik, Mark C; Rodriguez, Jorge H

2014-07-07

Understanding mechanisms of (+)-anti-BPDE detoxification is crucial for combating its mutagenic and potent carcinogenic action. However, energetic-structural correlations of reaction intermediates and transition states during detoxification via hydrolysis are poorly understood. To gain mechanistic insight we have computationally characterized intermediate and transition species associated with spontaneous and general-acid catalyzed hydrolysis of (+)-anti-BPDE. We studied the role of cacodylic acid as a proton donor in the rate limiting step. The computed activation energy (ΔG‡) is in agreement with the experimental value for hydrolysis in a sodium cacodylate buffer. Both types of, spontaneous and acid catalyzed, BPDE hydrolysis can proceed through low-entropy hydrogen bonded intermediates prior to formation of transition states whose energies determine reaction activation barriers and rates.

Biocatalytic synthesis of maltodextrin-based acrylates from starch and α-cyclodextrin.

PubMed

Kloosterman, Wouter M J; Spoelstra-van Dijk, Gerda; Loos, Katja

2014-09-01

Novel 2-(β-maltooligooxy)-ethyl (meth)acrylate monomers are successfully synthesized by CGTase from Bacillus macerans catalyzed coupling of 2-(β-glucosyloxy)-ethyl acrylate and methacrylate with α-cyclodextrin or starch. HPLC-UV analysis shows that the CGTase catalyzed reaction yields 2-(β-maltooligooxy)-ethyl acrylates with 1 to 15 glucopyranosyl units. (1) H NMR spectroscopy reveals that the β-linkage in the acceptor molecule is preserved during the CGTase catalyzed coupling reaction, whereas the newly introduced glucose units are attached by α-(1,4)-glycosidic linkages. The synthesized 2-(β-maltooligooxy)-ethyl acrylate monomers are successfully polymerized by aqueous free radical polymerization to yield the comb-shaped glycopolymer poly(2-(β-maltooligooxy)-ethyl acrylate). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stereochemical analysis of the elimination reaction catalyzed by D-amino-acid oxidase.

PubMed

Cheung, Y F; Walsh, C

1976-06-01

The stereochemistry of the intramolecular proton transfer catalyzed by the flavoenzyme, D-amino-acid oxidase, during the elimination reaction of beta-chloro-alpha-amino acid substrates (Walsh et al. (1973), J. Biol. Chem. 248, 1964) has been established. Both D-erythro- and D-threo-2-amino-3-chloro(2-3H) butyrate have been shown to yield (3R)-2-keto (3-3H)-2- butyrate predominantly. Tritium kinetic isotope effects on the rate of the reaction (4.7 for the D-erythro, and 3.8 for the D-threo compound) and percentages of intramolecular triton transfer (7.2% for the D-erythro- and 2.6% for the D-threo compound) have been measured. Their implications on the mechanism of this unusual elimination reaction are discussed.

Theoretical investigation on the chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reactions.

PubMed

Liu, Tao; Han, Shu-Min; Han, Ling-Li; Wang, Lu; Cui, Xiang-Yang; Du, Chong-Yang; Bi, Siwei

2015-03-28

A density functional theory study was performed to understand the detailed mechanisms of the cross-benzoin reactions catalyzed by N-heterocyclic carbene (NHC) species. Our theoretical study predicted that the first H-transfer operates with water in solution as a mediator, and the second H-transfer undergoes a concerted mechanism rather than a stepwise one. In addition, the chemoselectivity of the reactions studied in this work has been explored. P1 was obtained as a major product mainly due to the more stable intermediate formed by reaction of NHC with reactant R1. Different steric effects resulting from the fused six-membered ring in transition state TS7 and the fused five-membered ring in transition state TS13 are the origin leading to the chemoselectivity.

Stereospecific nickel-catalyzed cross-coupling reactions of alkyl ethers: enantioselective synthesis of diarylethanes.

PubMed

Taylor, Buck L H; Swift, Elizabeth C; Waetzig, Joshua D; Jarvo, Elizabeth R

2011-01-26

Secondary benzylic ethers undergo stereospecific substitution reactions with Grignard reagents in the presence of nickel catalysts. Reactions proceed with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols.

Divergent pathways in the reaction of Fischer carbenes and palladium.

PubMed

López-Alberca, María P; Mancheño, María J; Fernandez, Israel; Gómez-Gallego, Mar; Sierra, Miguel A; Torres, Rosario

2007-04-26

[reaction: see text] The Pd-catalyzed reaction of beta-arylaminochromium(0) carbene complexes produces by transmetalation the first isolated and X-ray structurally characterized bis-Pd(II) carbene complex, as well as other alternative reaction pathways, such as the oxidative addition-transmetalation sequence, not seen before in this chemistry.

Comparison of the active-site design of molybdenum oxo-transfer enzymes by quantum mechanical calculations.

PubMed

Li, Jilai; Ryde, Ulf

2014-11-17

There are three families of mononuclear molybdenum enzymes that catalyze oxygen atom transfer (OAT) reactions, named after a typical example from each family, viz., dimethyl sulfoxide reductase (DMSOR), sulfite oxidase (SO), and xanthine oxidase (XO). These families differ in the construction of their active sites, with two molybdopterin groups in the DMSOR family, two oxy groups in the SO family, and a sulfido group in the XO family. We have employed density functional theory calculations on cluster models of the active sites to understand the selection of molybdenum ligands in the three enzyme families. Our calculations show that the DMSOR active site has a much stronger oxidative power than the other two sites, owing to the extra molybdopterin ligand. However, the active sites do not seem to have been constructed to make the OAT reaction as exergonic as possible, but instead to keep the reaction free energy close to zero (to avoid excessive loss of energy), thereby making the reoxidation (SO and XO) or rereduction of the active sites (DMSOR) after the OAT reaction facile. We also show that active-site models of the three enzyme families can all catalyze the reduction of DMSO and that the DMSOR model does not give the lowest activation barrier. Likewise, all three models can catalyze the oxidation of sulfite, provided that the Coulombic repulsion between the substrate and the enzyme model can be overcome, but for this harder reaction, the SO model gives the lowest activation barrier, although the differences are not large. However, only the XO model can catalyze the oxidation of xanthine, owing to its sulfido ligand.

A Price To Pay for Relaxed Substrate Specificity: A Comparative Kinetic Analysis of the Class II Lanthipeptide Synthetases ProcM and HalM2

PubMed Central

2015-01-01

Lanthipeptides are a class of ribosomally synthesized and posttranslationally modified peptide natural products (RiPPs) that typically harbor multiple intramolecular thioether linkages. For class II lanthipeptides, these cross-links are installed in a multistep reaction pathway by a single enzyme (LanM). The multifunctional nature of LanMs and the manipulability of their genetically encoded peptide substrates (LanAs) make LanM/LanA systems promising targets for the engineering of new antibacterial compounds. Here, we report the development of a semiquantitative mass spectrometry-based assay for kinetic characterization of LanM-catalyzed reactions. The assay was used to conduct a comparative kinetic analysis of two LanM enzymes (HalM2 and ProcM) that exhibit drastically different substrate selectivity. Numerical simulation of the kinetic data was used to develop models for the multistep HalM2- and ProcM-catalyzed reactions. These models illustrate that HalM2 and ProcM have markedly different catalytic efficiencies for the various reactions they catalyze. HalM2, which is responsible for the biosynthesis of a single compound (the Halβ subunit of the lantibiotic haloduracin), catalyzes reactions with higher catalytic efficiency than ProcM, which modifies 29 different ProcA precursor peptides during prochlorosin biosynthesis. In particular, the rates of thioether ring formation are drastically reduced in ProcM, likely because this enzyme is charged with installing a variety of lanthipeptide ring architectures in its prochlorosin products. Thus, ProcM appears to pay a kinetic price for its relaxed substrate specificity. In addition, our kinetic models suggest that conformational sampling of the LanM/LanA Michaelis complex could play an important role in the kinetics of LanA maturation. PMID:25409537

Direct characterization of cotton fabrics treated with di-epoxide by nuclear magnetic resonance.

PubMed

Xiao, Min; Chéry, Joronia; Keresztes, Ivan; Zax, David B; Frey, Margaret W

2017-10-15

A non-acid-based, di-functional epoxide, neopentyl glycol diglycidyl ether (NPGDGE), was used to modify cotton fabrics. Direct characterization of the modified cotton was conducted by Nuclear Magnetic Resonance (NMR) without grinding the fabric into a fine powder. NaOH and MgBr 2 were compared in catalyzing the reaction between the epoxide groups of NPGDGE and the hydroxyl groups of cellulose. Possible reaction routes were discussed. Scanning electron microscopy (SEM) images showed that while the MgBr 2 -catalyzed reaction resulted in self-polymerization of NPGDGE, the NaOH-catalyzed reaction did not. Fourier transform infrared spectroscopy (FTIR) showed that at high NaOH concentration cellulose restructures from allomorph I to II. NMR studies verified the incorporation of NPGDGE into cotton fabrics with a clear NMR signal, and confirmed that at higher NaOH concentration the efficiency of grafting of NPGDGE was increased. This demonstrates that use of solid state NMR directly on woven fabric samples can simultaneously characterize chemical modification and crystalline polymorph of cotton. No loss of tensile strength was observed for cotton fabrics modified with NPGDGE. Copyright © 2017 Elsevier Ltd. All rights reserved.

Copper-Catalyzed Chan-Lam Cyclopropylation of Phenols and Azaheterocycles.

PubMed

Derosa, Joseph; O'Duill, Miriam L; Holcomb, Matthew; Boulous, Mark N; Patman, Ryan L; Wang, Fen; Tran-Dubé, Michelle; McAlpine, Indrawan; Engle, Keary M

2018-04-06

Small molecules containing cyclopropane-heteroatom linkages are commonly needed in medicinal chemistry campaigns yet are problematic to prepare using existing methods. To address this issue, a scalable Chan-Lam cyclopropylation reaction using potassium cyclopropyl trifluoroborate has been developed. With phenol nucleophiles, the reaction effects O-cyclopropylation, whereas with 2-pyridones, 2-hydroxybenzimidazoles, and 2-aminopyridines the reaction brings about N-cyclopropylation. The transformation is catalyzed by Cu(OAc) 2 and 1,10-phenanthroline and employs 1 atm of O 2 as the terminal oxidant. This method is operationally convenient to perform and provides a simple, strategic disconnection toward the synthesis of cyclopropyl aryl ethers and cyclopropyl amine derivatives bearing an array of functional groups.

Rhodium(i)-catalyzed asymmetric [4 + 2] cycloaddition reactions of 2-alkylenecyclobutanols with cyclic enones through C–C bond cleavage: efficient access to trans-bicyclic compounds† †Electronic supplementary information (ESI) available. CCDC 1575240. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc04784c

PubMed Central

Zheng, Xinxin; Guo, Rui

2018-01-01

We report a rhodium-catalyzed asymmetric formal intermolecular [4 + 2] cycloaddition reaction of 2-alkylenecyclobutanols with α,β-unsaturated cyclic ketones leading to synthetically useful trans-bicyclic molecules. Three consecutive stereogenic centers are formed in a highly enantio- and diastereoselective manner. Stepwise C–C bond cleavage and annulation are likely involved in the reaction pathway. Here, iPr-Duphos is the viable chiral ligand that promotes excellent enantio-control. PMID:29675233

Biocatalytic Synthesis of Poly(δ-Valerolactone) Using a Thermophilic Esterase from Archaeoglobus fulgidus as Catalyst

PubMed Central

Cao, Hong; Han, Haobo; Li, Guangquan; Yang, Jiebing; Zhang, Lingfei; Yang, Yan; Fang, Xuedong; Li, Quanshun

2012-01-01

The ring-opening polymerization of δ-valerolactone catalyzed by a thermophilic esterase from the archaeon Archaeoglobus fulgidus was successfully conducted in organic solvents. The effects of enzyme concentration, temperature, reaction time and reaction medium on monomer conversion and product molecular weight were systematically evaluated. Through the optimization of reaction conditions, poly(δ-valerolactone) was produced in 97% monomer conversion, with a number-average molecular weight of 2225 g/mol, in toluene at 70 °C for 72 h. This paper has produced a new biocatalyst for the synthesis of poly(δ-valerolactone), and also deeper insight has been gained into the mechanism of thermophilic esterase-catalyzed ring-opening polymerization. PMID:23202895

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

Gold-Catalyzed Formal [4+1]/[4+3] Cycloadditions of Diazo Esters with Triazines.

PubMed

Zhu, Chenghao; Xu, Guangyang; Sun, Jiangtao

2016-09-19

Reported herein is the unprecedented gold-catalyzed formal [4+1]/[4+3] cycloadditions of diazo esters with hexahydro-1,3,4-triazines, thus providing five- and seven-membered heterocycles in moderate to high yields under mild reaction conditions. These reactions feature the use of a gold complex to accomplish the diverse annulations and the first example of the involvement of a gold metallo-enolcarbene in a cycloaddition. It is also the first utilization of stable triazines as formal dipolar adducts in the carbene-involved cycloadditions. Mechanistic investigations reveal that the triazines reacted directly, rather than as formaldimine precursors, in the reaction process. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrasound mediated, iodine catalyzed green synthesis of novel 2-amino-3-cyano-4H-pyran derivatives.

PubMed

Tabassum, Sumaiya; Govindaraju, Santhosh; Khan, Riyaz-ur-Rahaman; Pasha, Mohamed Afzal

2015-05-01

An efficient synthesis of a novel series of twelve substituted 2-amino-3-cyano-4H-pyran derivatives was achieved by a one-pot three-component cyclocondensation reaction of heteroaryl aldehydes, malononitrile and active methylene compounds catalyzed by iodine in aqueous medium under ultrasound irradiation. In comparison with conventional methods, our protocol is convenient and offers several advantages, such as shorter reaction time, higher yields, milder conditions and environmental friendliness. We have herein successfully demonstrated the synergistic outcome of multi-component reaction (MCR) and sonication to offer a facile route for the design of these derivatives. Copyright © 2014 Elsevier B.V. All rights reserved.

Nucleophilic substitution at centers other than carbon: reaction at the chlorine of N-chloroacetanilides with triethylamine as the nucleophile

DOE Office of Scientific and Technical Information (OSTI.GOV)

Underwood, G.R.; Dietze, P.E.

1984-12-28

The reaction between triethylamine (TEA) and a series of para-substituted N-chloroacetanilides has been studied in aqueous solution buffered to pHs between 1 and 5. The exclusive product derived from the aromatic moiety is the corresponding acetanilide. The reaction occurs via two parallel pseudo-second-order paths, one acid catalyzed (the Orton-like mechanism), the other uncatalyzed. The uncatalyzed reaction is accelerated by the presence of electron-withdrawing substituents on the aromatic ring and can best be represented as nucleophilic displacement at chlorine. It therefore appears to be the prototype of a convenient class of reactions for the study of displacement reactions at chlorine. Themore » rho value for this reaction is 3.87, indicating substantial negative charge buildup in the aromatic ring during of the transition state. The acid-catalyzed reaction is more complex, presumable involving a protonation equilibrium for the N-chloroacetanilide prior to the rate-determining step similar to that in the Orton reaction. 15 references, 2 figures, 3 tables.« less

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

EPA Science Inventory

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

Beta-D-xylosidase from Selenomonas ruminantium: thermodynamics of enzyme-catalyzed and noncatalyzed reactions

USDA-ARS?s Scientific Manuscript database

Beta-D-xylosidase/alpha-L-arabinofuranosidase from Selenomonas ruminantium (SXA) is the most active enzyme known for catalyzing hydrolysis of 1,4-beta-D-xylooligosaccharides to D-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-beta-D-xylopyranoside (4NPX), 4-nitrophenyl-alpha-L-arabi...

Synthesis of Nitriles via Palladium-Catalyzed Water Shuffling from Amides to Acetonitrile

PubMed Central

Zhang, Wandi; Haskins, Christopher W.; Yang, Yang; Dai, Mingji

2014-01-01

Palladium-catalyzed synthesis of nitriles from amides has been described. Two similar, but complementary reaction conditions have been identified to convert various amides including α,β,γ,δ-unsaturated amides, cinnamides, aromatic amides and alkyl amides to the corresponding nitriles in good to excellent yield. PMID:25316145

Synthesis of nitriles via palladium-catalyzed water shuffling from amides to acetonitrile.

PubMed

Zhang, Wandi; Haskins, Christopher W; Yang, Yang; Dai, Mingji

2014-12-07

Palladium-catalyzed synthesis of nitriles from amides has been described. Two similar, but complementary reaction conditions have been identified to convert various amides including α,β,γ,δ-unsaturated amides, cinnamides, aromatic amides and alkyl amides to the corresponding nitriles in good to excellent yield.

Syntheses of calix[4]pyrroles by amberlyst-15 catalyzed cyclocondensations of pyrrole with selected ketones.

PubMed

Chauhan, Shive Murat Singh; Garg, Bhaskar; Bisht, Tanuja

2007-11-09

A facile and efficient protocol is reported for the synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles in moderate to excellent yields by reaction of dialkyl or cycloalkyl ketones with pyrrole catalyzed by reusable Amberlyst(TM)-15 under eco-friendly conditions.

Cross-coupling of alkenyl/aryl carboxylates with Grignard reagent via Fe-catalyzed C-O bond activation.

PubMed

Li, Bi-Jie; Xu, Li; Wu, Zhen-Hua; Guan, Bing-Tao; Sun, Chang-Liang; Wang, Bi-Qin; Shi, Zhang-Jie

2009-10-21

Iron-catalyzed cross-coupling of alkenyl/aryl carboxylates with primary alkyl Grignard reagent was described. This reaction brought a new family of electrophiles to iron catalysis. The combination of an inexpensive carboxylate electrophile and an iron catalyst would generate ample advantages.

Mild rhodium(iii)-catalyzed intramolecular annulation of benzamides with allylic alcohols to access azepinone derivatives.

PubMed

Peneau, Augustin; Tricart, Quentin; Guillou, Catherine; Chabaud, Laurent

2018-05-23

Azepinone derivatives are important frameworks of several natural products and bioactive compounds. They are synthetized using a Rh(iii)-catalyzed intramolecular annulation of benzamide-tethered allylic alcohols. The reaction requires mild conditions at room temperature and affords diversely substituted azepinones bearing a quaternary carbon.

Intermolecular rhodium-catalyzed [2 + 2 + 2] carbocyclization reactions of 1,6-enynes with symmetrical and unsymmetrical alkynes†

PubMed Central

Andrew Evans, P.; Sawyer, James R.; Lai, Kwong Wah; Huffman, John C.

2006-01-01

The crossed intermolecular rhodium-catalyzed [2 + 2 + 2] carbocyclization of carbon and heteroatom tethered 1,6-enynes can be accomplished with symmetrical and unsymmetrical alkynes, to afford the corresponding bicyclohexadienes in an efficient and highly selective manner. PMID:16075089

Pd-Catalyzed Carbonylative Conjugate Addition of Dialkylzinc Reagents to Unsaturated Carbonyls

PubMed Central

Custar, Daniel W.; Le, Hai; Morken, James P.

2010-01-01

The Pd-catalyzed addition of organozinc reagents to unsaturated carbonyls in the presence of carbon monoxide provides 1,4-diketones in good yield. The reaction was studied with a number of substituted cyclic and acyclic ketones as well as α,β-unsaturated aldehydes. PMID:20687574

Imidazole catalyzes chlorination by unreactive primary chloramines

PubMed Central

Roemeling, Margo D.; Williams, Jared; Beckman, Joseph S.; Hurst, James K.

2015-01-01

Hypochlorous acid and simple chloramines (RNHCl) are stable biologically-derived chlorinating agents. In general, the chlorination potential of HOCl is much greater than that of RNHCl, allowing it to oxidize or chlorinate a much wider variety of reaction partners. However, in this study we demonstrate by kinetic analysis that the reactivity of RNHCl can be dramatically promoted by imidazole and histidyl model compounds via intermediary formation of the corresponding imidazole chloramines. Two biologically relevant reactions were investigated—loss of imidazole-catalyzed chlorinating capacity and phenolic ring chlorination using fluorescein and the tyrosine analog, 4-hydroxyphenylacetic acid (HPA). HOCl reacted stoichiometrically with imidazole, N-acetylhistidine (NAH), or imidazoleacetic acid to generate the corresponding imidazole chloramines which subsequently decomposed. Chloramine (NH2Cl) also underwent a markedly accelerated loss in chlorinating capacity when NAH was present, although in this case NAHCl did not accumulate, indicating that the catalytic intermediate must be highly reactive. Mixing HOCl with 1-methylimidazole (MeIm) led to very rapid loss in chlorinating capacity via formation of a highly reactive chlorinium ion (MeImCl+) intermediate; this behavior suggests that the reactive forms of the analogous imidazole chloramines are their conjugate acids, e.g., the imidazolechlorinium ion (HImCl+). HOCl-generated imidazole chloramine (ImCl) reacted rapidly with fluorescein in a specific acid-catalyzed second order reaction to give 3′-monochloro and 3′,5′-dichloro products. Equilibrium constants for the transchlorination reactions: HOCl + HIm = H2O + ImCl and NH2Cl + HIm = NH3 + ImCl were estimated from the dependence of the rate constants upon [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl+; consistent with this interpretation, MeIm markedly catalyzed fluorescein chlorination by HOCl. Time-dependent imidazole-catalyzed HPA chlorination by NH2Cl was also demonstrated by product analyses. Quantitative assessment of the data suggests that physiological levels of histidyl groups will react with primary chloramines to generate a flux of imidazole chloramine sufficient to catalyze biological chlorination via HImCl+, particularly in environments that generate high concentrations of HOCl such as the neutrophil phagosome. PMID:25660996

Evolution of Enzymatic Activities in the Enolase Superfamily: D-Tartrate Dehydratase from Bradyrhizobium japonicum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yew,W.; Fedorov, A.; Fedorov, E.

2006-01-01

We focus on the assignment of function to and elucidation of structure-function relationships for a member of the mechanistically diverse enolase superfamily encoded by the Bradyrhizobium japonicum genome (bll6730; GI:27381841). As suggested by sequence alignments, the active site contains the same functional groups found in the active site of mandelate racemase (MR) that catalyzes a 1,1-proton transfer reaction: two acid/base catalysts, Lys 184 at the end of the second {beta}-strand, and a His 322-Asp 292 dyad at the ends of the seventh and sixth -strands, respectively, as well as ligands for an essential Mg{sup 2+}, Asp 213, Glu 239, andmore » Glu 265 at the ends of the third, fourth, and fifth {beta}-strands, respectively. We screened a library of 46 acid sugars and discovered that only D-tartrate is dehydrated, yielding oxaloacetate as product. The kinetic constants (k{sub cat} = 7.3 s{sup -1}; k{sub cat}/K{sub M} = 8.5 x 10{sup 4} M{sup -1} s{sup -1}) are consistent with assignment of the D-tartrate dehydratase (TarD) function. The kinetic phenotypes of mutants as well as the structures of liganded complexes are consistent with a mechanism in which Lys 184 initiates the reaction by abstraction of the {alpha}-proton to generate a Mg{sup 2+}-stabilized enediolate intermediate, and the vinylogous -elimination of the 3-OH group is general acid-catalyzed by the His 322, accomplishing the anti-elimination of water. The replacement of the leaving group by solvent-derived hydrogen is stereorandom, suggesting that the enol tautomer of oxaloacetate is the product; this expectation was confirmed by its observation by {sup 1}H NMR spectroscopy. Thus, the TarD-catalyzed reaction is a 'simple' extension of the two-step reaction catalyzed by MR: base-catalyzed proton abstraction to generate a Mg{sup 2+}-stabilized enediolate intermediate followed by acid-catalyzed decomposition of that intermediate to yield the product.« less

Mild Palladium Catalyzed ortho C-H Bond Functionalizations of Aniline Derivatives.

PubMed

Tischler, Ms Orsolya; Tóth, Mr Balázs; Novák, Zoltán

2017-02-01

This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho-directed C-H activation of aniline derivatives from the first attempts to up-to-date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cu-catalyzed esterification reaction via aerobic oxygenation and C-C bond cleavage: an approach to α-ketoesters.

PubMed

Zhang, Chun; Feng, Peng; Jiao, Ning

2013-10-09

The Cu-catalyzed novel aerobic oxidative esterification reaction of 1,3-diones for the synthesis of α-ketoesters has been developed. This method combines C-C σ-bond cleavage, dioxygen activation and oxidative C-H bond functionalization, as well as provides a practical, neutral, and mild synthetic approach to α-ketoesters which are important units in many biologically active compounds and useful precursors in a variety of functional group transformations. A plausible radical process is proposed on the basis of mechanistic studies.

Rapid Construction of Complex 2-Pyrrolines through Lewis Acid-Catalyzed, Sequential Three-Component Reactions via in Situ-Generated 1-Azaallyl Cations.

PubMed

Schlegel, Marcel; Schneider, Christoph

2018-05-09

The first Sc(OTf) 3 -catalyzed dehydration of 2-hydroxy oxime ethers to generate benzylic stabilized 1-azaallyl cations, which are captured by 1,3-carbonyls, is described. A subsequent addition of primary amines in a sequential three-component reaction affords highly substituted and densely functionalized tetrahydroindeno[2,1- b]pyrroles as single diastereomers with up to quantitative yield. Thus, three new σ-bonds and two vicinal quaternary stereogenic centers are generated in a one-pot operation.

Copper(II)-catalyzed hydroxylation of aryl halides using glycolic acid as a ligand.

PubMed

Xiao, Yan; Xu, Yongnan; Cheon, Hwan-Sung; Chae, Junghyun

2013-06-07

Copper(II)-catalyzed hydroxylation of aryl halides has been developed to afford functionalized phenols. The protocol utilizes the reagent combination of Cu(OH)2, glycolic acid, and NaOH in aqueous DMSO, all of which are cheap, readily available, and easily removable after the reaction. A broad range of aryl iodides and activated aryl bromides were transformed into the corresponding phenols in excellent yields. Moreover, it has been shown that C-O(alkyl)-coupled product, instead of phenol, can be predominantly formed under similar reaction conditions.

Iron(II)-catalyzed intermolecular amino-oxygenation of olefins through the N-O bond cleavage of functionalized hydroxylamines.

PubMed

Lu, Deng-Fu; Zhu, Cheng-Liang; Jia, Zhen-Xin; Xu, Hao

2014-09-24

An iron-catalyzed diastereoselective intermolecular olefin amino-oxygenation reaction is reported, which proceeds via an iron-nitrenoid generated by the N-O bond cleavage of a functionalized hydroxylamine. In this reaction, a bench-stable hydroxylamine derivative is used as the amination reagent and oxidant. This method tolerates a range of synthetically valuable substrates that have been all incompatible with existing amino-oxygenation methods. It can also provide amino alcohol derivatives with regio- and stereochemical arrays complementary to known amino-oxygenation methods.

Triphenylphosphine as Ligand for Room Temperature Ni(0)-Catalyzed Cross-Coupling Reactions of Aryl Chlorides with Arylboronic Acids

PubMed Central

Tang, Zhen-Yu; Hu, Qiao-Sheng

2008-01-01

Room temperature Ni(0)-catalyzed cross-coupling reactions of deactivated aryl chlorides with arylboronic acids with inexpensive triphenylphosphine (PPh3) as a supporting ligand have been accomplished in good to excellent yields. Air-stable Ni(PPh3)2Cl2 has also been established as catalyst precursor and highly active nickel catalysts were obtained when the reduction of Ni(PPh3)2Cl2 with n-BuLi was carried out in presence of an aryl chloride. PMID:16497011

Computational Studies on the Pt(II)-Catalyzed Cycloisomerization of 1,6-dienes into Bicyclopropanes: A Mechanistic Quandary Evaluated by DFT

PubMed Central

Bell, Franziska; Holland, Jason; Green, Jennifer C.; Gagné, Michel R.

2009-01-01

The mechanism of the (bis(phosphanylethyl)phosphane)Pt2+ catalyzed cyclo-isomerization reaction of 7-methyl-octa-1,6-diene to form 1-isopropylbicyclo[3.1.0]hexane was studied using computational methods. The cyclopropanation step was found to be the turnover-limiting step. The overall reaction proceeds via both a 5-exo and a 6-endo route. W conformations were shown to facilitate cyclopropanation, but do not have any influence on the rate of the 1,2-hydride shifts. PMID:20161262

Diversity-oriented asymmetric catalysis (DOAC): stereochemically divergent synthesis of thiochromanes using an imidazoline-aminophenol-nickel-catalyzed Michael/Henry reaction.

PubMed

Arai, Takayoshi; Yamamoto, Yushi

2014-03-21

The (S,S)-diphenylethylenediamine-derived imidazoline-aminophenol-Ni complex catalyzed tandem asymmetric Michael/Henry reaction of 2-mercaptobenzaldehydes with β-nitrostyrenes to give the corresponding (2S,3R,4R)-2-aryl-3-nitrothiochroman-4-ols in up to 99% diastereoselectivity with 95% ee was demonstrated in diversity-oriented asymmetric catalysis. Reduction of the nitro group of the chiral thiochromanes gave a new series of (2S,3R,4R)-3-amino-2-arylthiochroman-4-ols with retention of the strereoselectivity.

Gold-catalyzed sequential annulations towards 3,4-fused bi/tri-cyclic furans involving a [3+2+2]-cycloaddition.

PubMed

Liu, Suna; Yang, Pu; Peng, Shiyong; Zhu, Chenghao; Cao, Shengyu; Li, Jian; Sun, Jiangtao

2017-01-17

A gold-catalyzed sequential annulation reaction to prepare 3,4-fused bicyclic furan compounds has been realized by employing 2-(1-alkynyl)-2-alken-1-ones and 1,3,5-triazines as the starting materials under mild reaction conditions. This protocol features multiple bond formation in a single operation with the incorporation of two nitrogen and two carbon atoms into the final products. A mechanistic investigation reveals that the sequential annulations involved an unprecedented stepwise [3+2+2]-cycloaddition.

Copper-Catalyzed, Directing Group-Assisted Fluorination of Arene and Heteroarene C-H Bonds

PubMed Central

Truong, Thanh; Klimovica, Kristine; Daugulis, Olafs

2013-01-01

We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of β-sp2 C-H bonds of benzoic acid derivatives and γ-sp2 C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs CuI catalyst, AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids. PMID:23758609

A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines.

PubMed

Unhale, Rajshekhar A; Sadhu, Milon M; Ray, Sumit K; Biswas, Rayhan G; Singh, Vinod K

2018-04-03

A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-hydroxyisoindolinones has been demonstrated in this communication. A variety of isoindolinone-based α-amino diazo esters bearing a quaternary stereogenic center were afforded in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). Furthermore, the synthetic utility of the products has been depicted by the hydrogenation of the diazo moiety of adducts.

Iridium-Catalyzed Asymmetric Hydrogenation of Ketones with Accessible and Modular Ferrocene-Based Amino-phosphine Acid (f-Ampha) Ligands.

PubMed

Yu, Jianfei; Long, Jiao; Yang, Yuhong; Wu, Weilong; Xue, Peng; Chung, Lung Wa; Dong, Xiu-Qin; Zhang, Xumu

2017-02-03

A series of tridentate ferrocene-based amino-phosphine acid (f-Ampha) ligands have been successfully developed. The f-Ampha ligands are extremely air stable and exhibited excellent performance in the Ir-catalyzed asymmetric hydrogenation of ketones (full conversions, up to >99% ee, and 500 000 TON). DFT calculations were performed to elucidate the reaction mechanism and the importance of the -COOH group. Control experiments also revealed that the -COOH group played a key role in this reaction.

Base-catalyzed efficient tandem [3 + 3] and [3 + 2 + 1] annulation-aerobic oxidative benzannulations.

PubMed

Diallo, Aboubacar; Zhao, Yu-Long; Wang, He; Li, Sha-Sha; Ren, Chuan-Qing; Liu, Qun

2012-11-16

An efficient synthesis of substituted benzenes via a base-catalyzed [3 + 3] aerobic oxidative aromatization of α,β-unsaturated carbonyl compounds with dimethyl glutaconate was reported. All the reactions were carried out under mild, metal-free conditions to afford the products in high to excellent yields with molecular oxygen as the sole oxidant and water as the sole byproduct. Furthermore, a more convenient tandem [3 + 2 + 1] aerobic oxidative aromatization reaction was developed through the in situ generation of the α,β-unsaturated carbonyl compounds from aldehydes and ketones.

Noble metal catalyzed aqueous phase hydrogenation and hydrodeoxygenation of lignin-derived pyrolysis oil and related model compounds.

PubMed

Mu, Wei; Ben, Haoxi; Du, Xiaotang; Zhang, Xiaodan; Hu, Fan; Liu, Wei; Ragauskas, Arthur J; Deng, Yulin

2014-12-01

Aqueous phase hydrodeoxygenation of lignin pyrolysis oil and related model compounds were investigated using four noble metals supported on activated carbon. The hydrodeoxygenation of guaiacol has three major reaction pathways and the demethylation reaction, mainly catalyzed by Pd, Pt and Rh, produces catechol as the products. The presence of catechol and guaiacol in the reaction is responsible for the coke formation and the catalysts deactivation. As expected, there was a significant decrease in the specific surface area of Pd, Pt and Rh catalysts during the catalytic reaction because of the coke deposition. In contrast, no catechol was produced from guaiacol when Ru was used so a completely hydrogenation was accomplished. The lignin pyrolysis oil upgrading with Pt and Ru catalysts further validated the reaction mechanism deduced from model compounds. Fully hydrogenated bio-oil was produced with Ru catalyst. Copyright © 2014 Elsevier Ltd. All rights reserved.

Investigation to biodiesel production by the two-step homogeneous base-catalyzed transesterification.

PubMed

Ye, Jianchu; Tu, Song; Sha, Yong

2010-10-01

For the two-step transesterification biodiesel production made from the sunflower oil, based on the kinetics model of the homogeneous base-catalyzed transesterification and the liquid-liquid phase equilibrium of the transesterification product, the total methanol/oil mole ratio, the total reaction time, and the split ratios of methanol and reaction time between the two reactors in the stage of the two-step reaction are determined quantitatively. In consideration of the transesterification intermediate product, both the traditional distillation separation process and the improved separation process of the two-step reaction product are investigated in detail by means of the rigorous process simulation. In comparison with the traditional distillation process, the improved separation process of the two-step reaction product has distinct advantage in the energy duty and equipment requirement due to replacement of the costly methanol-biodiesel distillation column. Copyright 2010 Elsevier Ltd. All rights reserved.

Removal of emerging pollutants by Ru/TiO2-catalyzed permanganate oxidation.

PubMed

Zhang, Jing; Sun, Bo; Xiong, Xinmei; Gao, Naiyun; Song, Weihua; Du, Erdeng; Guan, Xiaohong; Zhou, Gongming

2014-10-15

TiO2 supported ruthenium nanoparticles, Ru/TiO2 (0.94‰ as Ru), was synthesized to catalyze permanganate oxidation for degrading emerging pollutants (EPs) with diverse organic moieties. The presence of 1.0 g L(-1) Ru/TiO2 increased the second order reaction rate constants of bisphenol A, diclofenac, acetaminophen, sulfamethoxazole, benzotriazole, carbamazepine, butylparaben, diclofenac, ciprofloxacin and aniline at mg L(-1) level (5.0 μM) by permanganate oxidation at pH 7.0 by 0.3-119 times. The second order reaction rate constants of EPs with permanganate or Ru/TiO2-catalyzed permanganate oxidation obtained at EPs concentration of mg L(-1) level (5.0 μM) underestimated those obtained at EPs concentration of μg L(-1) level (0.050 μM). Ru/TiO2-catalyzed permanganate could decompose a mixture of nine EPs at μg L(-1) level efficiently and the second order rate constant for each EP was not decreased due to the competition of other EPs. The toxicity tests revealed that Ru/TiO2-catalyzed permanganate oxidation was effective not only for elimination of EPs but also for detoxification. The removal rates of sulfamethoxazole by Ru/TiO2-catalyzed permanganate oxidation in ten successive cycles remained almost constant in ultrapure water and slightly decreased in Songhua river water since the sixth run, indicating the satisfactory stability of Ru/TiO2. Ru/TiO2-catalyzed permanganate oxidation was selective and could remove selected EPs spiked in real waters more efficiently than chlorination. Therefore, Ru/TiO2-catalyzed permanganate oxidation is promising for removing EPs with electron-rich moieties. Copyright © 2014 Elsevier Ltd. All rights reserved.

Complex Cure Kinetics of the Tertiary Amine activated Reaction in DGEBA Epoxy Hardened with Diethanolamine

NASA Astrophysics Data System (ADS)

Ancipink, Windy; McCoy, John; Clarkson, Caitlyn; Kropka, Jamie; Celina, Mathias; Giron, Nicholas; Hailesilassie, Lebelo; Fredj, Narjes

The curing of a diglycidyl ether of bisphenol-A (DGEBA) epoxy with diethanolamine (DEA) involves a well understood fast amine-epoxide reaction followed by a more complicated slower hydroxyl-epoxide reaction. The time scale of these two reactions are well separated and can be studied independently from one another. The initial amine-epoxide reaction results in a tertiary amine adduct which is a product of the direct reaction of a secondary amine from the DEA reacting with a single DGEBA epoxide. The second hydroxyl-epoxide reaction results in a highly crosslinked glassy epoxy resin. The deviation in the mechanisms between high and low temperatures are discerned through the use of differential scanning calorimetry (DSC), infrared spectroscopy (IR), and isothermal microcalorimetry (IMC) data. Observations of reaction rates at temperatures ranging from 30° C to 110° C have led to the determination that the hydroxyl-epoxide reaction is temperature sensitive. The hydroxyl-epoxide reaction occurs through two different mechanisms: at low temperatures, the reaction is catalyzed by the tertiary amine adduct; at higher temperatures, the reaction does not appear to be catalyzed. Sandia National Laboratories, Albuquerque, NM.

Oxidative trifluoromethylation and trifluoromethylthiolation reactions using (trifluoromethyl)trimethylsilane as a nucleophilic CF3 source.

PubMed

Chu, Lingling; Qing, Feng-Ling

2014-05-20

The trifluoromethyl group is widely prevalent in many pharmaceuticals and agrochemicals because its incorporation into drug candidates could enhance chemical and metabolic stability, improve lipophilicity and bioavailability, and increase the protein bind affinity. Consequently, extensive attention has been devoted toward the development of efficient and versatile methods for introducing the CF3 group into various organic molecules. Direct trifluoromethylation reaction has become one of the most efficient and important approaches for constructing carbon-CF3 bonds. Traditionally, the nucleophilic trifluoromethylation reaction involves an electrophile and the CF3 anion, while the electrophilic trifluoromethylation reaction involves a nucleophile and the CF3 cation. In 2010, we proposed the concept of oxidative trifluoromethylation: the reaction of nucleophilic substrates and nucleophilic trifluoromethylation reagents in the presence of oxidants. In this Account, we describe our recent studies of oxidative trifluoromethylation reactions of various nucleophiles with CF3SiMe3 in the presence of oxidants. We have focused most of our efforts on constructing carbon-CF3 bonds via direct trifluoromethylation of various C-H bonds. We have demonstrated copper-mediated or -catalyzed or metal-free oxidative C-H trifluoromethylation of terminal alkynes, tertiary amines, arenes and heteroarenes, and terminal alkenes. Besides various C-H bonds, aryl boronic acids proved to be viable nucleophilic coupling partners for copper-mediated or -catalyzed cross-coupling reactions with CF3SiMe3. To further expand the reaction scope, we also applied H-phosphonates to the oxidative trifluoromethylation system to construct P-CF3 bonds. Most recently, we developed silver-catalyzed hydrotrifluoromethylation of unactivated olefins. These studies explore boronic acids, C-H bonds, and P-H bonds as novel nucleophiles in transition-metal-mediated or -catalyzed cross-coupling reactions with CF3SiMe3, opening new viewpoints for future trifluoromethylation reactions. Furthermore, we also achieved the oxidative trifluoromethylthiolation reactions of aryl boronic acids and terminal alkynes to construct carbon-SCF3 bonds by using CF3SiMe3 and elemental sulfur as the nucleophilic trifluoromethylthiolating reagent. These oxidative trifluoromethylation and trifluoromethylthiolation reactions tolerate a wide range of functional groups, affording a diverse array of CF3- and CF3S-containing compounds with high efficiencies, and provide elegant and complementary alternatives to classical trifluoromethylation and trifluoromethylthiolation reactions. Because of the importance of the CF3 and SCF3 moieties in pharmaceuticals and agrochemicals, these reactions would have potential applications in the life science fields.

Polyacrylic acid polymer brushes as substrates for the incorporation of anthraquinone derivatives. Unprecedented application of decorated polymer brushes on organocatalysis

NASA Astrophysics Data System (ADS)

Ruiz-Muelle, Ana Belén; Contreras-Cáceres, Rafael; Oña-Burgos, Pascual; Rodríguez-Dieguez, Antonio; López-Romero, Juan Manuel; Fernández, Ignacio

2018-01-01

The synthesis of amino-terminated anthraquinone derivatives and their incorporation onto polymer brushes for the fabrication of silicon-based nanometric functional coatings are described for the first time. The general process involves the covalent grafting of anthraquinone 1 onto two different polymer-brushes by amidation reactions. They are composed by amino- and carboxy-terminated poly(acrylic acid) chains (PAA-NH2- and PAA-COOH, respectively) tethered by one end to an underlying silicon oxide (SiO2) substrate in a polymer brush configuration. A third substrate is fabricated by UV induced hydrosilylation reaction using undecenoic acid as adsorbate on hydrogen-terminated Si(111) surfaces. One- and two-dimensional nuclear magnetic resonance (NMR), FT-IR, MS and X-ray diffraction (XRD) were used to characterize anthraquinone 1. Ellipsometric and X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the polymer brushes on the silicon wafers, and atomic force microscopy (AFM) was used to study its surface morphology. The covalent linkage between anthraquinone and polymer brushes was proven by XPS and confocal fluorescence microscopy. The resulting surfaces were assayed in the heterogenous organocatalytic transformation of (1H)-indole into 3-benzyl indole with moderate yields but with high recyclability.

Greener routes to organics and nanomaterials: Sustainable applications of nano-catalysts (JA)

EPA Science Inventory

Sustainable synthetic activity involving alternate energy input and greener reaction medium in aqueous or under solvent-free conditions is summarized. This includes the synthesis of heterocyclic compounds, coupling reactions, and a variety of reactions catalyzed by basic water o...

21 CFR 173.395 - Trifluoromethane sulfonic acid.

Code of Federal Regulations, 2014 CFR

2014-04-01

... reaction mixture to catalyze the directed esterification. (c) The esterification reaction is quenched with... by washing batches of the product three times with an aqueous solution of 0.5 percent sodium...

New function of aldoxime dehydratase: Redox catalysis and the formation of an expected product

PubMed Central

Kumano, Takuto; Tsujimura, Seiya; Kobayashi, Michihiko

2017-01-01

In general, hemoproteins are capable of catalyzing redox reactions. Aldoxime dehydratase (OxdA), which is a unique heme-containing enzyme, catalyzes the dehydration of aldoximes to the corresponding nitriles. Its reaction is a rare example of heme directly activating an organic substrate, unlike the utilization of H2O2 or O2 as a mediator of catalysis by other heme-containing enzymes. While it is unknown whether OxdA catalyzes redox reactions or not, we here for the first time detected catalase activity (which is one of the redox activities) of wild-type OxdA, OxdA(WT). Furthermore, we constructed a His320 → Asp mutant of OxdA [OxdA(H320D)], and found it exhibits catalase activity. Determination of the kinetic parameters of OxdA(WT) and OxdA(H320D) revealed that their Km values for H2O2 were similar to each other, but the kcat value of OxdA(H320D) was 30 times higher than that of OxdA(WT). Next, we examined another redox activity and found it was the peroxidase activity of OxdAs. While both OxdA(WT) and OxdA(H320D) showed the activity, the activity of OxdA(H320D) was dozens of times higher than that of OxdA(WT). These findings demonstrated that the H320D mutation enhances the peroxidase activity of OxdA. OxdAs (WT and H320D) were found to catalyze another redox reaction, a peroxygenase reaction. During this reaction of OxdA(H320D) with 1-methoxynaphthalene as a substrate, surprisingly, the reaction mixture changed to a color different from that with OxdA(WT), which was due to the known product, Russig’s blue. We purified and identified the new product as 1-methoxy-2-naphthalenol, which has never been reported as a product of the peroxygenase reaction, to the best of our knowledge. These findings indicated that the H320D mutation not only enhanced redox activities, but also significantly altered the hydroxylation site of the substrate. PMID:28410434

New function of aldoxime dehydratase: Redox catalysis and the formation of an unexpected product.

PubMed

Yamada, Masatoshi; Hashimoto, Yoshiteru; Kumano, Takuto; Tsujimura, Seiya; Kobayashi, Michihiko

2017-01-01

In general, hemoproteins are capable of catalyzing redox reactions. Aldoxime dehydratase (OxdA), which is a unique heme-containing enzyme, catalyzes the dehydration of aldoximes to the corresponding nitriles. Its reaction is a rare example of heme directly activating an organic substrate, unlike the utilization of H2O2 or O2 as a mediator of catalysis by other heme-containing enzymes. While it is unknown whether OxdA catalyzes redox reactions or not, we here for the first time detected catalase activity (which is one of the redox activities) of wild-type OxdA, OxdA(WT). Furthermore, we constructed a His320 → Asp mutant of OxdA [OxdA(H320D)], and found it exhibits catalase activity. Determination of the kinetic parameters of OxdA(WT) and OxdA(H320D) revealed that their Km values for H2O2 were similar to each other, but the kcat value of OxdA(H320D) was 30 times higher than that of OxdA(WT). Next, we examined another redox activity and found it was the peroxidase activity of OxdAs. While both OxdA(WT) and OxdA(H320D) showed the activity, the activity of OxdA(H320D) was dozens of times higher than that of OxdA(WT). These findings demonstrated that the H320D mutation enhances the peroxidase activity of OxdA. OxdAs (WT and H320D) were found to catalyze another redox reaction, a peroxygenase reaction. During this reaction of OxdA(H320D) with 1-methoxynaphthalene as a substrate, surprisingly, the reaction mixture changed to a color different from that with OxdA(WT), which was due to the known product, Russig's blue. We purified and identified the new product as 1-methoxy-2-naphthalenol, which has never been reported as a product of the peroxygenase reaction, to the best of our knowledge. These findings indicated that the H320D mutation not only enhanced redox activities, but also significantly altered the hydroxylation site of the substrate.

Semisupervised Gaussian Process for Automated Enzyme Search.

PubMed

Mellor, Joseph; Grigoras, Ioana; Carbonell, Pablo; Faulon, Jean-Loup

2016-06-17

Synthetic biology is today harnessing the design of novel and greener biosynthesis routes for the production of added-value chemicals and natural products. The design of novel pathways often requires a detailed selection of enzyme sequences to import into the chassis at each of the reaction steps. To address such design requirements in an automated way, we present here a tool for exploring the space of enzymatic reactions. Given a reaction and an enzyme the tool provides a probability estimate that the enzyme catalyzes the reaction. Our tool first considers the similarity of a reaction to known biochemical reactions with respect to signatures around their reaction centers. Signatures are defined based on chemical transformation rules by using extended connectivity fingerprint descriptors. A semisupervised Gaussian process model associated with the similar known reactions then provides the probability estimate. The Gaussian process model uses information about both the reaction and the enzyme in providing the estimate. These estimates were validated experimentally by the application of the Gaussian process model to a newly identified metabolite in Escherichia coli in order to search for the enzymes catalyzing its associated reactions. Furthermore, we show with several pathway design examples how such ability to assign probability estimates to enzymatic reactions provides the potential to assist in bioengineering applications, providing experimental validation to our proposed approach. To the best of our knowledge, the proposed approach is the first application of Gaussian processes dealing with biological sequences and chemicals, the use of a semisupervised Gaussian process framework is also novel in the context of machine learning applied to bioinformatics. However, the ability of an enzyme to catalyze a reaction depends on the affinity between the substrates of the reaction and the enzyme. This affinity is generally quantified by the Michaelis constant KM. Therefore, we also demonstrate using Gaussian process regression to predict KM given a substrate-enzyme pair.

A Pre-Steady State Kinetic Analysis of the αY60W mutant of trans-3-Chloroacrylic Acid Dehalogenase: Implications for the Mechanism of the Wild-type Enzyme†

PubMed Central

Huddleston, Jamison P.; Schroeder, Gottfried K.; Johnson, Kenneth A.; Whitman, Christian P.

2012-01-01

The bacterial degradation of the nematicide 1,3-dichloropropene, an isomeric mixture, requires the action of trans- and cis-3-chloracrylic acid dehalogenase (CaaD and cis-CaaD, respectively). Both enzymes are tautomerase superfamily members and share a core catalytic mechanism for the hydrolytic dehalogenation of the respective isomer of 3-haloacrylate. The observation that cis-CaaD requires two additional residues raises the question of how CaaD carries out a comparable reaction with fewer catalytic residues. As part of an effort to determine the basis for the apparently simpler CaaD-catalyzed reaction, the kinetic mechanism was determined by stopped-flow and chemical quench techniques using a fluorescent mutant form of the enzyme, αY60W-CaaD, and trans-3-bromoacrylate as the substrate. The data from these experiments as well as bromide inhibition studies are best accommodated by a six-step model that provides individual rate constants for substrate binding, chemistry, and a proposed conformational change occurring after chemistry followed by release of malonate semialdehyde and bromide. The conformational change and product release rates are comparable and together they limit the rate of turnover. The kinetic analysis and modeling studies validate the αY60W-CaaD mutant as an accurate reporter of active site events during the course of the enzyme-catalyzed reaction. The kinetic mechanism for the αY60W-CaaD-catalyzed reaction is comparable to that obtained for the cis-CaaD-catalyzed reaction. The kinetic model and the validated αY60W-CaaD mutant set the stage for an analysis of active site mutants to explore the contributions of individual catalytic residues and the basis for the simplicity of the reaction. PMID:23110338

Flavin-N5 Covalent Intermediate in a Nonredox Dehalogenation Reaction Catalyzed by an Atypical Flavoenzyme.

PubMed

Dai, Yumin; Kizjakina, Karina; Campbell, Ashley C; Korasick, David A; Tanner, John J; Sobrado, Pablo

2018-01-04

The flavin-dependent enzyme 2-haloacrylate hydratase (2-HAH) catalyzes the conversion of 2-chloroacrylate, a major component in the manufacture of acrylic polymers, to pyruvate. The enzyme was expressed in Escherichia coli, purified, and characterized. 2-HAH was shown to be monomeric in solution and contained a non-covalent, yet tightly bound, flavin adenine dinucleotide (FAD). Although the catalyzed reaction was redox-neutral, 2-HAH was active only in the reduced state. A covalent flavin-substrate intermediate, consistent with the flavin-acrylate iminium ion, was trapped with cyanoborohydride and characterized by mass spectrometry. Small-angle X-ray scattering was consistent with 2-HAH belonging to the succinate dehydrogenase/fumarate reductase family of flavoproteins. These studies establish 2-HAH as a novel noncanonical flavoenzyme. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Copper-catalyzed trifluoromethylthiolation of aryl halides with diverse directing groups.

PubMed

Xu, Jiabin; Mu, Xin; Chen, Pinhong; Ye, Jinxing; Liu, Guosheng

2014-08-01

The expansion of cross-coupling components in Cu-catalyzed C-X bond forming reactions have received much attention recently. A novel Cu-catalyzed trifluoromethylthiolation of aryl bromides and iodides with the assistance of versatile directing groups such as pyridyl, methyl ester, amide, imine and oxime was reported. CuBr was used as the catalyst, and 1,10-phenanthroline as the ligand. By changing the solvent from acetonitrile to DMF, the coupling process could even take place at room temperature.

Regio-selectivity of the Oxidative C-S Bond Formation in Ergothioneine and Ovothiol Biosyntheses

PubMed Central

Song, Heng; Leninger, Maureen; Lee, Norman

2014-01-01

Ergothioneine (5) and ovothiol (8) are two novel thiol-containing natural products. Their C-S bonds are formed by oxidative coupling reactions catalyzed by EgtB and OvoA enzymes, respectively. In this work, it was discovered that besides catalyzing the oxidative coupling between histidine and cysteine (1 → 6 conversion), OvoA can also catalyze a direct oxidative coupling between hercynine (2) and cysteine (2 → 4 conversion), which can shorten the ergothioneine biosynthetic pathway by two steps. PMID:24016264

The Catalytic Asymmetric Intramolecular Stetter Reaction

PubMed Central

de Alaniz, Javier Read; Rovis, Tomislav

2010-01-01

This account chronicles our efforts at the development of a catalytic asymmetric Stetter reaction using chiral triazolium salts as small molecule organic catalysts. Advances in the mechanistically related azolium-catalyzed asymmetric benzoin reaction are discussed, particularly as they apply to catalyst design. A chronological treatise of reaction discovery, catalyst optimization and reactivity extension follows. PMID:20585467

Parameters governing ruthenium sawhorse-based decarboxylation of oleic acid

USDA-ARS?s Scientific Manuscript database

Ruthenium-catalyzed decarboxylation of 9-cisoctadecenoic is a path to produce biobased olefins. Here, a mechanistic study of this reaction was undertaken utilizing a closed reaction system and a pressure reactor. The proposed mechanism of an isomerization followed by a decarboxylation reaction was c...

Soil oxidoreductases and FDA hydrolysis

USDA-ARS?s Scientific Manuscript database

The oxidoreductases (E.C. 1.) comprise the largest enzyme group and consist of enzymes that catalyze reactions between two compounds, one of which is oxidized (the donor) while reducing the other (the acceptor) (Dixon and Webb, 1979). In common with all redox reactions, the reaction mechanism involv...

Mixed quantum-classical simulation of the hydride transfer reaction catalyzed by dihydrofolate reductase based on a mapped system-harmonic bath model

NASA Astrophysics Data System (ADS)

Xu, Yang; Song, Kai; Shi, Qiang

2018-03-01

The hydride transfer reaction catalyzed by dihydrofolate reductase is studied using a recently developed mixed quantum-classical method to investigate the nuclear quantum effects on the reaction. Molecular dynamics simulation is first performed based on a two-state empirical valence bond potential to map the atomistic model to an effective double-well potential coupled to a harmonic bath. In the mixed quantum-classical simulation, the hydride degree of freedom is quantized, and the effective harmonic oscillator modes are treated classically. It is shown that the hydride transfer reaction rate using the mapped effective double-well/harmonic-bath model is dominated by the contribution from the ground vibrational state. Further comparison with the adiabatic reaction rate constant based on the Kramers theory confirms that the reaction is primarily vibrationally adiabatic, which agrees well with the high transmission coefficients found in previous theoretical studies. The calculated kinetic isotope effect is also consistent with the experimental and recent theoretical results.

In Vivo Studies in Rhodospirillum rubrum Indicate That Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (Rubisco) Catalyzes Two Obligatorily Required and Physiologically Significant Reactions for Distinct Carbon and Sulfur Metabolic Pathways.

PubMed

Dey, Swati; North, Justin A; Sriram, Jaya; Evans, Bradley S; Tabita, F Robert

2015-12-25

All organisms possess fundamental metabolic pathways to ensure that needed carbon and sulfur compounds are provided to the cell in the proper chemical form and oxidation state. For most organisms capable of using CO2 as sole source of carbon, ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) catalyzes primary carbon dioxide assimilation. In addition, sulfur salvage pathways are necessary to ensure that key sulfur-containing compounds are both available and, where necessary, detoxified in the cell. Using knock-out mutations and metabolomics in the bacterium Rhodospirillum rubrum, we show here that Rubisco concurrently catalyzes key and essential reactions for seemingly unrelated but physiologically essential central carbon and sulfur salvage metabolic pathways of the cell. In this study, complementation and mutagenesis studies indicated that representatives of all known extant functional Rubisco forms found in nature are capable of simultaneously catalyzing reactions required for both CO2-dependent growth as well as growth using 5-methylthioadenosine as sole sulfur source under anaerobic photosynthetic conditions. Moreover, specific inactivation of the CO2 fixation reaction did not affect the ability of Rubisco to support anaerobic 5-methylthioadenosine metabolism, suggesting that the active site of Rubisco has evolved to ensure that this enzyme maintains both key functions. Thus, despite the coevolution of both functions, the active site of this protein may be differentially modified to affect only one of its key functions. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

In Situ Synthesis of Lipid Membranes

NASA Astrophysics Data System (ADS)

Devaraj, N. K.

2017-07-01

We have a strong interest in applying covalent coupling reactions to the formation and modification of lipid membranes. We have utilized chemoselective reactions, such as copper-catalyzed triazole formation or the native chemical ligation.

Engineering entropy-driven reactions and networks catalyzed by DNA.

PubMed

Zhang, David Yu; Turberfield, Andrew J; Yurke, Bernard; Winfree, Erik

2007-11-16

Artificial biochemical circuits are likely to play as large a role in biological engineering as electrical circuits have played in the engineering of electromechanical devices. Toward that end, nucleic acids provide a designable substrate for the regulation of biochemical reactions. However, it has been difficult to incorporate signal amplification components. We introduce a design strategy that allows a specified input oligonucleotide to catalyze the release of a specified output oligonucleotide, which in turn can serve as a catalyst for other reactions. This reaction, which is driven forward by the configurational entropy of the released molecule, provides an amplifying circuit element that is simple, fast, modular, composable, and robust. We have constructed and characterized several circuits that amplify nucleic acid signals, including a feedforward cascade with quadratic kinetics and a positive feedback circuit with exponential growth kinetics.

A General Synthetic Route to Polycyclic Aromatic Dicarboximides by Palladium-Catalyzed Annulation Reaction.

PubMed

Shoyama, Kazutaka; Mahl, Magnus; Seifert, Sabine; Würthner, Frank

2018-03-20

Here we report a general method for the synthesis of polycyclic aromatic dicarboximides (PADIs) by palladium-catalyzed annulation of naphthalene dicarboximide to different types of aromatic substrates. Reaction conditions were optimized by systematic variation of ligand, solvent, and additive. It was shown that solvent has a decisive effect on the yield of the reaction products, and thus 1-chloronaphthalene as solvent afforded the highest yield. By applying the optimized reaction conditions, a broad series of planar carbo- and heterocycle containing PADIs were synthesized in up to 97% yield. Moreover, this approach could be applied to curved aromatic scaffold to achieve the respective bowl-shaped PADI. Two-fold annulation was accomplished by employing arene diboronic esters, affording polycyclic aromatic bis(dicarboximides). The optical and electrochemical properties of this broad series of PADIs were explored as well.

α-Unsubstituted Pyrroles by NHC-Catalyzed Three-Component Coupling: Direct Synthesis of a Versatile Atorvastatin Derivative.

PubMed

Fleige, Mirco; Glorius, Frank

2017-08-10

A practical one-pot cascade reaction protocol provides direct access to valuable 1,2,4-trisubstituted pyrroles. The process involves an N-heterocyclic carbene (NHC)-catalyzed Stetter-type hydroformylation using glycolaldehyde dimer as a novel C1 building-block, followed by a Paal-Knorr condensation with primary amines. The reaction makes use of simple and commercially available starting-materials and catalyst, an important feature regarding applicability and utility. Low catalyst loading under mild reaction conditions afforded a variety of 1,2,4-substituted pyrroles in a transition-metal-free reaction with high step economy and good yields. This methodology is applied in the synthesis of a versatile Atorvastatin precursor, in which a variety of modifications at the pyrrole core structure are possible. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Copper Catalyzed Alkyne Activation as an Entry to Multicomponent Syntheses of Heterocycles

NASA Astrophysics Data System (ADS)

Müller, Thomas J. J.

Alkynones and chalcones are of paramount importance in heterocyclic chemistry as three-carbon building blocks. In a very efficient manner, they can be easily generated by palladium-copper catalyzed reactions: ynones are formed from acid chlorides and terminal alkynes, and chalcones are synthesized in the sense of a coupling-isomerization (CI) sequence from (hetero)aryl halides and propargyl alcohols. Mild reaction conditions now open entries to sequential and consecutive transformations to heterocycles, such as furans, 3-halo furans, pyrroles, pyrazoles, substituted and annelated pyridines, annelated thiopyranones, pyridimines, meridianins, benzoheteroazepines and tetrahydro-β-carbolines, by consecutive coupling-cyclocondensation or CI-cyclocondensation sequences, as new diversity oriented routes to heterocycles. Domino reactions based upon the coupling-isomerization reaction (CIR) have been probed in the synthesis of antiparasital 2-substituted quinoline derivatives and highly luminescent spiro-benzofuranones and spiro-indolones.

Organic reactions catalyzed by methylrhenium trioxide: Reactions of ethyl diazoacetate and organic azides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Z.; Espenson, J.H.

1996-10-16

Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) catalyzes several classes of reactions of ethyl diazoacetate, EDA. It is the first high valent oxo complex for carbene transfer. Under mild conditions and in the absence of other substrates, EDA was converted to a 9:1 mixture of diethyl maleate and diethyl fumarate. In the presence of alcohols, {alpha}-alkoxy ethyl acetates were obtained in good yield. The yields dropped for the larger and more branched alcohols, the balance of material being diethyl maleate and fumarate. An electron-donating group in the para position of phenols favors the formation of {alpha}-phenoxy ethyl acetates. The usemore » of EDA to form {alpha}-thio ethyl acetates and N-substituted glycine ethyl esters, on the other hand, is hardly affected by the size or structure of the parent thiol or amine, with all of these reactions proceeding in high yield. MTO-catalyzed cycloaddition reactions occur between EDA and aromatic imines, olefins, and carbonyl compounds. Three-membered ring products are formed: aziridines, cyclopropanes, and epoxides, respectively. The reactions favor the formation of trans products, and provide a convenient route for the preparation of aziridines. Intermediate carbenoid and nitrenoid species have been proposed. In the presence of an oxygen source such as an epoxide, ethyl diazoacetate and azibenzil are converted to an oxalic acid monoethyl ester and to benzil; at the same time the epoxide was converted to an olefin. 75 refs., 1 fig., 7 tabs.« less

Biochemical identification of residues that discriminate between 3,4-dihydroxyphenylalanine decarboxylase and 3,4-dihydroxyphenylacetaldehyde synthase-mediated reactions.

PubMed

Liang, Jing; Han, Qian; Ding, Haizhen; Li, Jianyong

2017-12-01

In available insect genomes, there are several L-3,4-dihydroxyphenylalanine (L-dopa) decarboxylase (DDC)-like or aromatic amino acid decarboxylase (AAAD) sequences. This contrasts to those of mammals whose genomes contain only one DDC. Our previous experiments established that two DDC-like proteins from Drosophila actually mediate a complicated decarboxylation-oxidative deamination process of dopa in the presence of oxygen, leading to the formation of 3,4-dihydroxyphenylacetaldehyde (DHPA), CO 2 , NH 3, and H 2 O 2 . This contrasts to the typical DDC-catalyzed reaction, which produces CO 2 and dopamine. These DDC-like proteins were arbitrarily named DHPA synthases based on their critical role in insect soft cuticle formation. Establishment of reactions catalyzed by these AAAD-like proteins solved a puzzle that perplexed researchers for years, but to tell a true DHPA synthase from a DDC in the insect AAAD family remains problematic due to high sequence similarity. In this study, we performed extensive structural and biochemical comparisons between DHPA synthase and DDC. These comparisons identified several target residues potentially dictating DDC-catalyzed and DHPA synthase-catalyzed reactions, respectively. Comparison of DHPA synthase homology models with crystal structures of typical DDC proteins, particularly residues in the active sites, provided further insights for the roles these identified target residues play. Subsequent site-directed mutagenesis of the tentative target residues and activity evaluations of their corresponding mutants determined that active site His192 and Asn192 are essential signature residues for DDC- and DHPA synthase-catalyzed reactions, respectively. Oxygen is required in DHPA synthase-mediated process and this oxidizing agent is reduced to H 2 O 2 in the process. Biochemical assessment established that H 2 O 2 , formed in DHPA synthase-mediated process, can be reused as oxidizing agent and this active oxygen species is reduced to H 2 O; thereby avoiding oxidative stress by H 2 O 2 . Results of our structural and functional analyses provide a reasonable explanation of mechanisms involved in DHPA synthase-mediated reactions. Based on the key active site residue Asn192, identified in Drosophila DHPA synthase, we were able to distinguish all available insect DHPA synthases from DDC sequences primarily. Copyright © 2017. Published by Elsevier Ltd.

Oxygen isotope effects of enzyme-catalyzed organophosphorus hydrolysis reactions: implications for interpretation of dissolved PO4 δ18O values in natural waters

NASA Astrophysics Data System (ADS)

Liang, Y.; Blake, R. E.

2002-12-01

The geochemical cycling of P in Earth surface environments is controlled largely by biota. It has been recently demonstrated that intracellular cycling of P in microbial cultures and biological turnover of P in natural waters leads to temperature-dependent O isotope equilibrium between dissolved inorganic PO4 (Pi) and ambient water, and that the δ18O of Pi can be a useful tracer of biological reactions and P cycling in aquatic systems/sediments. Oxygen isotope exchange between Pi and water during biological turnover of P is catalyzed by enzymes at low-temperature. Phosphoenzymes play a crucial role in the intracellular functions of all living organisms and also have important extracellular functions in aquatic ecosystems such as regeneration of Pi from organophosphorus compounds (e.g., phosphoesters). Laboratory experiments indicate that extracellular enzyme reactions may result in incomplete Pi turnover and non-equilibrium Pi-water O isotope exchange. Determination of the O isotope effects of phosphoenzyme-catalyzed reactions is fundamental to the understanding of mechanisms of PO4-water O isotope exchange, pathways of biogeochemical P cycling, and interpretation of PO4 δ18O values from natural systems. Here we report on the O isotope fractionation between enzymatically-released Pi and water, in cell-free abiotic systems. Alkaline phosphatase (Apase) is a non-specific phosphohydrolase commonly found in fresh and marine coastal waters that catalyzes the hydrolysis of Pi from phosphomonoesters. We examined the O isotope effects of Apase derived from both microbial and eukaryotic sources and acting on different phosphomonoester substrates (e.g., α-D-Glucose 1-Phosphate, β-Glycerophosphate, AMP) in 18O-labeled waters. Oxygen isotope ratios of Pi released by Apase indicate that only 1 of the 4 O atoms in PO4 is incorporated from water with little or no apparent O isotopic fractionation at the site of incorporation. This observation is consistent with phosphomonoester structure and the Apase active site configuration and reaction mechanism. 5'-nucleotidase is another important phosphoenzyme identified in marine ecosystems. The O isotope effects of 5'-nucleotidase- catalyzed reactions will also be presented and implications of these results for interpretation of PO4 δ18O values in natural systems will be discussed.

GREEN CATALYZED OXIDATION OF HYDROCARBONS IN ALTERNATIVE SOLVENT SYSTEMS GENERATED BY PARIS II DECHEMA; GREEN SOLVENTS FOR CATALYSIS - ENVIRONMENTALLY BENIGN REACTION MEDIA

EPA Science Inventory

Green catalyzed oxidation of hydrocarbons in alternative solvent systems generated by PARIS II
Thomas M. Becker, Michael A. Gonzalez, Paul F. Harten; Sustainable Technology Division, Office of Research and Development; United States Environmental Protection Agency, 26 West Mar...

Rhodium-catalyzed synthesis of silafluorene derivatives via cleavage of silicon-hydrogen and carbon-hydrogen bonds.

PubMed

Ureshino, Tomonari; Yoshida, Takuya; Kuninobu, Yoichiro; Takai, Kazuhiko

2010-10-20

The rhodium-catalyzed synthesis of silafluorenes from biphenylhydrosilanes is described. This highly efficient reaction proceeds via both Si-H and C-H bond activation, producing only H(2) as a side product. Using this method, a ladder-type bis-silicon-bridged p-terphenyl could also be synthesized.

Clostridium acidurici electron-bifurcating formate dehydrogenase.

PubMed

Wang, Shuning; Huang, Haiyan; Kahnt, Jörg; Thauer, Rudolf K

2013-10-01

Cell extracts of uric acid-grown Clostridium acidurici catalyzed the coupled reduction of NAD(+) and ferredoxin with formate at a specific activity of 1.3 U/mg. The enzyme complex catalyzing the electron-bifurcating reaction was purified 130-fold and found to be composed of four subunits encoded by the gene cluster hylCBA-fdhF2.

Microorganisms detected by enzyme-catalyzed reaction

NASA Technical Reports Server (NTRS)

Vango, S. P.; Weetall, H. H.; Weliky, N.

1966-01-01

Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

Pd-catalyzed allylic alkylation of dienyl carbonates with nitromethane with high C-5 regioselectivity.

PubMed

Yang, Xiao-Fei; Li, Xiao-Hui; Ding, Chang-Hua; Xu, Chao-Fan; Dai, Li-Xin; Hou, Xue-Long

2014-01-14

A highly regioselective palladium-catalyzed allylic alkylation of dienyl esters with nitromethane has been developed, providing selective access to the C-5 attacked products. The structures of the ligands as well as the steric effect of the substrates are important factors in determining the regiochemical outcome of the reaction.

Cu-catalyzed Suzuki-Miyaura reactions of primary and secondary benzyl halides with arylboronates.

PubMed

Sun, Yan-Yan; Yi, Jun; Lu, Xi; Zhang, Zhen-Qi; Xiao, Bin; Fu, Yao

2014-09-28

A copper-catalyzed Suzuki-Miyaura coupling of benzyl halides with arylboronates is described. Varieties of primary benzyl halides as well as more challenging secondary benzyl halides with β hydrogens or steric hindrance could be successfully converted into the corresponding products. Thus it provides access to diarylmethanes, diarylethanes and triarylmethanes.

Acid-catalyzed dehydrogenation of amine-boranes

DOEpatents

Stephens, Frances Helen; Baker, Ralph Thomas

2010-01-12

A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R.sup.1R.sup.2B--NR.sup.3R.sup.4].sub.n product. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources.

Iron-catalyzed cross-coupling of N-heterocyclic chlorides and bromides with arylmagnesium reagents.

PubMed

Kuzmina, Olesya M; Steib, Andreas K; Flubacher, Dietmar; Knochel, Paul

2012-09-21

A simple, practical iron salt catalyzed procedure allows fast cross-couplings of N-heterocyclic chlorides and bromides with various electron-rich and -poor arylmagnesium reagents. A solvent mixture of THF and tBuOMe is found to be essential for achieving high yields mainly by avoiding homocoupling side reactions.

Stepwise oxygenations of toluene and 4-nitrotoluene by a fungal peroxygenase

Treesearch

Matthias Kinne; Christian Zeisig; Rene Ullrich; Gernot Kayser; Kenneth E. Hammel; Martin Hofrichter

2010-01-01

Fungal peroxygenases have recently been shown to catalyze remarkable oxidation reactions. The present study addresses the mechanism of benzylic oxygenations catalyzed by the extracellular peroxygenase of the argic basidiomycete Agrocybe aegerita. The peroxygenase oxidized toluene and 4-nitrotoluene via the corresponding alcohols and aldehydes to give benzoic acids. The...

Kinetic profiling of prolinate-catalyzed α-amination of aldehydes.

PubMed

Hein, Jason E; Armstrong, Alan; Blackmond, Donna G

2011-08-19

Deconvolution of the role of off-cycle species from the desired catalytic cycle leads to an optimized protocol for the prolinate-catalyzed amination of aldehydes. The scope of complex reaction networks will be greatly broadened by understanding ancillary rate processes that influence the productive catalytic pathway. © 2011 American Chemical Society

Copper-catalyzed α-amination of aliphatic aldehydes.

PubMed

Tian, Jie-Sheng; Loh, Teck-Peng

2011-05-21

A highly efficient copper-catalyzed α-amination of aliphatic aldehydes for the synthesis of α-amino acetals using secondary amines with readily removable protecting groups as a nitrogen source was developed. This reaction can be operated under very mild conditions, affording the desired products in moderate to good yields. © The Royal Society of Chemistry 2011

Pd-Catalyzed C-H activation/oxidative cyclization of acetanilide with norbornene: concise access to functionalized indolines.

PubMed

Gao, Yang; Huang, Yubing; Wu, Wanqing; Huang, Kefan; Jiang, Huanfeng

2014-08-07

An efficient Pd-catalyzed oxidative cyclization reaction for the synthesis of functionalized indolines by direct C-H activation of acetanilide has been developed. The norbornylpalladium species formed via direct ortho C-H activation of acetanilides is supposed to be a key intermediate in this transformation.

Structural Analysis of Substrate, Reaction Intermediate, and Product Binding in Haemophilus influenzae Biotin Carboxylase

PubMed Central

Broussard, Tyler C.; Pakhomova, Svetlana; Neau, David B.; Bonnot, Ross; Waldrop, Grover L.

2015-01-01

Acetyl-CoA carboxylase catalyzes the first and regulated step in fatty acid synthesis. In most Gram-negative and Gram-positive bacteria, the enzyme is composed of three proteins: biotin carboxylase, a biotin carboxyl carrier protein (BCCP), and carboxyltransferase. The reaction mechanism involves two half-reactions with biotin carboxylase catalyzing the ATP-dependent carboxylation of biotin-BCCP in the first reaction. In the second reaction, carboxyltransferase catalyzes the transfer of the carboxyl group from biotin-BCCP to acetyl-CoA to form malonyl-CoA. In this report, high-resolution crystal structures of biotin carboxylase from Haemophilus influenzae were determined with bicarbonate, the ATP analogue AMPPCP; the carboxyphosphate intermediate analogues, phosphonoacetamide and phosphonoformate; the products ADP and phosphate; and the carboxybiotin analogue N1′-methoxycarbonyl biotin methyl ester. The structures have a common theme in that bicarbonate, phosphate, and the methyl ester of the carboxyl group of N1′-methoxycarbonyl biotin methyl ester all bound in the same pocket in the active site of biotin carboxylase and as such utilize the same set of amino acids for binding. This finding suggests a catalytic mechanism for biotin carboxylase in which the binding pocket that binds tetrahedral phosphate also accommodates and stabilizes a tetrahedral dianionic transition state resulting from direct transfer of CO2 from the carboxyphosphate intermediate to biotin. PMID:26020841

Structure and Function of the Unusual Tungsten Enzymes Acetylene Hydratase and Class II Benzoyl-Coenzyme A Reductase.

PubMed

Boll, Matthias; Einsle, Oliver; Ermler, Ulrich; Kroneck, Peter M H; Ullmann, G Matthias

2016-01-01

In biology, tungsten (W) is exclusively found in microbial enzymes bound to a bis-pyranopterin cofactor (bis-WPT). Previously known W enzymes catalyze redox oxo/hydroxyl transfer reactions by directly coordinating their substrates or products to the metal. They comprise the W-containing formate/formylmethanofuran dehydrogenases belonging to the dimethyl sulfoxide reductase (DMSOR) family and the aldehyde:ferredoxin oxidoreductase (AOR) families, which form a separate enzyme family within the Mo/W enzymes. In the last decade, initial insights into the structure and function of two unprecedented W enzymes were obtained: the acetaldehyde forming acetylene hydratase (ACH) belongs to the DMSOR and the class II benzoyl-coenzyme A (CoA) reductase (BCR) to the AOR family. The latter catalyzes the reductive dearomatization of benzoyl-CoA to a cyclic diene. Both are key enzymes in the degradation of acetylene (ACH) or aromatic compounds (BCR) in strictly anaerobic bacteria. They are unusual in either catalyzing a nonredox reaction (ACH) or a redox reaction without coordinating the substrate or product to the metal (BCR). In organic chemical synthesis, analogous reactions require totally nonphysiological conditions depending on Hg2+ (acetylene hydration) or alkali metals (benzene ring reduction). The structural insights obtained pave the way for biological or biomimetic approaches to basic reactions in organic chemistry. © 2016 S. Karger AG, Basel.

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 β 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 ω-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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large enhancement of oscillating chemiluminescence with [Ru(bpy)3 ](2+) -catalyzed Belousov-Zhabotinsky reaction in the presence of tri-n-propylamine.

PubMed

Lan, Xiaolan; Zheng, Baozhan; Zhao, Yan; Yuan, Hongyan; Du, Juan; Xiao, Dan

2013-01-01

Oscillating chemiluminescence enhanced by the addition of tri-n-propylamine (TPrA) to the typical Belousov-Zhabotinsky (BZ) reaction system catalyzed by ruthenium(II)tris(2.2'-bipyridine)(Ru(bpy)3 (2+) ) was investigated using a luminometry method. The [Ru(bpy)3 ](2+) /TPrA system was first used as the catalyst for a BZ oscillator in a closed system, which exhibited a shorter induction period, higher amplitude and much more stable chemiluminescence (CL) oscillation. The effects of various concentrations of TPrA, oxygen and nitrogen flow rate on the oscillating behavior of this system were examined. In addition, the CL intensity of the [Ru(bpy)3 ](2+) /TPrA-BZ system was found to be inhibited by phenol, thus providing a way for use of the BZ system in the determination of phenolic compounds. Moreover, the possible mechanism of the oscillating CL reaction catalyzed by [Ru(bpy)3 ](2+) /TPrA and the inhibition effects of oxygen and phenol on this oscillating CL system were considered. Copyright © 2012 John Wiley & Sons, Ltd.

New reactions and products resulting from alternative interactions between the P450 enzyme and redox partners.

PubMed

Zhang, Wei; Liu, Yi; Yan, Jinyong; Cao, Shaona; Bai, Fali; Yang, Ying; Huang, Shaohua; Yao, Lishan; Anzai, Yojiro; Kato, Fumio; Podust, Larissa M; Sherman, David H; Li, Shengying

2014-03-05

Cytochrome P450 enzymes are capable of catalyzing a great variety of synthetically useful reactions such as selective C-H functionalization. Surrogate redox partners are widely used for reconstitution of P450 activity based on the assumption that the choice of these auxiliary proteins or their mode of action does not affect the type and selectivity of reactions catalyzed by P450s. Herein, we present an exceptional example to challenge this postulate. MycG, a multifunctional biosynthetic P450 monooxygenase responsible for hydroxylation and epoxidation of 16-membered ring macrolide mycinamicins, is shown to catalyze the unnatural N-demethylation(s) of a range of mycinamicin substrates when partnered with the free Rhodococcus reductase domain RhFRED or the engineered Rhodococcus-spinach hybrid reductase RhFRED-Fdx. By contrast, MycG fused with the RhFRED or RhFRED-Fdx reductase domain mediates only physiological oxidations. This finding highlights the larger potential role of variant redox partner protein-protein interactions in modulating the catalytic activity of P450 enzymes.

Palladium-Catalyzed Anti-Markovnikov Oxidation of Allylic Amides to Protected β-Amino Aldehydes.

PubMed

Dong, Jia Jia; Harvey, Emma C; Fañanás-Mastral, Martín; Browne, Wesley R; Feringa, Ben L

2014-12-10

A general method for the preparation of N-protected β-amino aldehydes from allylic amines or linear allylic alcohols is described. Here the Pd(II)-catalyzed oxidation of N-protected allylic amines with benzoquinone is achieved in tBuOH under ambient conditions with excellent selectivity toward the anti-Markovnikov aldehyde products and full retention of configuration at the allylic carbon. The method shows a wide substrate scope and is tolerant of a range of protecting groups. Furthermore, β-amino aldehydes can be obtained directly from protected allylic alcohols via palladium-catalyzed autotandem reactions, and the application of this method to the synthesis of β-peptide aldehydes is described. From a mechanistic perspective, we demonstrate that tBuOH acts as a nucleophile in the reaction and that the initially formed tert-butyl ether undergoes spontaneous loss of isobutene to yield the aldehyde product. Furthermore, tBuOH can be used stoichiometrically, thereby broadening the solvent scope of the reaction. Primary and secondary alcohols do not undergo elimination, allowing the isolation of acetals, which subsequently can be hydrolyzed to their corresponding aldehyde products.

Study of silicone-based materials for the packaging of optoelectronic devices

NASA Astrophysics Data System (ADS)

Lin, Yeong-Her

The first part of this work is to evaluate the main materials used for the packaging of high power light-emitting diodes (LEDs), i.e., the die attach materials, the encapsulant materials, and high color rendering index(CRI) sol-gel composite materials. All of these materials had been discussed the performance, reliability, and issues in high power LED packages. High power white LEDs are created either from blue or near-ultraviolet chips encapsulated with a yellow phosphor, or from red-green-blue LED light mixing systems. The phosphor excited by blue LED chip was mostly used in experiment of this dissertation. The die attach materials contains filler particles possessing a maximum particle size less than 1.5 mum in diameter blended with epoxy polymer matrix. Such compositions enable thin bond line thickness, which decreases thermal resistance that exists between thermal interface materials and the corresponding mating surfaces. The thermal conductivity of nano silver die attach materials is relatively low, the thermal resistance from the junction to board is just 1.6 KW-1 in the bond line thickness of 5.3 mum, which is much lower than the thermal resistance using conventional die attach materials. The silicone die attach adhesive made in the lab cures through the free radical reaction of epoxy-functional organopolysiloxane and through the hydrosilylation reaction between alkenyl-functional organopolysiloxane and silicone-boned hydrogen-functional organopolysiloxane. By the combination of the free radical reaction and the hydrosilylation reaction, the low-molecular-weight silicone oil will not be out-migrated and not contaminate wire bondability to the LED chip and lead frame. Hence, the silicone die attach adhesive made in the lab can pass all reliability tests, such as operating life test JEDEC 85°C/85RH and room temperature operating life test. For LED encapsulating materials, most of commercial silicone encapsulants still suffer thermal/radiation induced degradations, and thus cause reliability issues and shorten the lifetime. A new high performance silicone has been developed and its performance has been compared with other commercial silicone products in the packaging of high power white LEDs. The high performance silicone also has better results than commercial high refractive index silicone and optical grade epoxy under JEDEC reliability standard for moisture sensitivity test. In synthesis of red dye-doped particles by sol-gel method, it is a novel method to get high color rendering index (CRI) LEDs. These red dye-doped particles, with average diameter of 5 mum, can be mixed with liquid encapsulants to form a uniform distribution in polymer matrix. The red dye-doped particles can be excited by phosphor-emitted yellow light instead of blue light from LED chip. Therefore, warm white LEDs with high CRI can be gotten at high lumen efficiency. The second part of this work is silicone elastomer for biomedical applications, especially in making urological implantable devices. A cross-linked, heat curable, addition-reaction silicone material is prepared. The material may be molded or formed into one or more medical devices. One such medical device could be a catheter used in urological applications. The material is a long term indwelling material that resists encrustation like a metal stent, but is more comfortable because it is silicone-based. The material can be made relatively cheaply compared to metal stents. Furthermore, the material is biocompatible with bladder epithelial cells.

Preventing Corrosion by Controlling Cathodic Reaction Kinetics

DTIC Science & Technology

2016-03-25

electrochemical reaction rates of processes that drive corrosion, e.g. the oxygen reduction reaction (ORR). To this end, we have used reactive...elements on the kinetics of oxygen reduction reaction catalyzed on titanium oxide in order to develop new approaches for controlling galvanic corrosion... consumption of anions in reactions with metal cations can deplete the electrolyte. However, in the atmospheric electrolyte, the electrolyte

Mechanistic insights into the dehalogenation reaction of fluoroacetate/fluoroacetic acid

NASA Astrophysics Data System (ADS)

Miranda-Rojas, Sebastián; Toro-Labbé, Alejandro

2015-05-01

Fluoroacetate is a toxic compound whose environmental accumulation may represent an important contamination problem, its elimination is therefore a challenging issue. Fluoroacetate dehalogenase catalyzes its degradation through a two step process initiated by an SN2 reaction in which the aspartate residue performs a nucleophilic attack on the carbon bonded to the fluorine; the second step is hydrolysis that releases the product as glycolate. In this paper, we present a study based on density functional theory calculations of the SN2 initiation reaction modeled through the interaction between the substrate and the propionate anion as the nucleophile. Results are analyzed within the framework of the reaction force and using the reaction electronic flux to identify and characterize the electronic activity that drives the reaction. Our results reveal that the selective protonation of the substrate catalyzes the reaction by decreasing the resistance of the structural and electronic reorganization needed to reach the transition state. Finally, the reaction energy is modulated by the degree of stabilization of the fluoride anion formed after the SN2 reaction. In this way, a site-induced partial protonation acts as a chemical switch in a key process that determines the output of the reaction.

Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with Alpha-Alpha Domain Architecture that Catalyzes a Unique Cyclization-Fragmentation Reaction Sequence

PubMed Central

Harris, Golda G.; Lombardi, Patrick M.; Pemberton, Travis A.; Matsui, Tsutomu; Weiss, Thomas M.; Cole, Kathryn E.; Köksal, Mustafa; Murphy, Frank V.; Vedula, L. Sangeetha; Chou, Wayne K.W.; Cane, David E.; Christianson, David W.

2015-01-01

Geosmin synthase from Streptomyces coelicolor (ScGS) catalyzes an unusual, metal-dependent terpenoid cyclization and fragmentation reaction sequence. Two distinct active sites are required for catalysis: the N-terminal domain catalyzes the ionization and cyclization of farnesyl diphosphate to form germacradienol and inorganic pyrophosphate (PPi), and the C-terminal domain catalyzes the protonation, cyclization, and fragmentation of germacradienol to form geosmin and acetone through a retro-Prins reaction. A unique αα domain architecture is predicted for ScGS based on amino acid sequence: each domain contains the metal-binding motifs typical of a class I terpenoid cyclase, and each domain requires Mg2+ for catalysis. Here, we report the X-ray crystal structure of the unliganded N-terminal domain of ScGS and the structure of its complex with 3 Mg2+ ions and alendronate. These structures highlight conformational changes required for active site closure and catalysis. Although neither full-length ScGS nor constructs of the C-terminal domain could be crystallized, homology models of the C-terminal domain were constructed based on ~36% sequence identity with the N-terminal domain. Small-angle X-ray scattering experiments yield low resolution molecular envelopes into which the N-terminal domain crystal structure and the C-terminal domain homology model were fit, suggesting possible αα domain architectures as frameworks for bifunctional catalysis. PMID:26598179

Site-specific recombination in the cyanobacterium Anabaena sp. strain PCC 7120 catalyzed by the integrase of coliphage HK022.

PubMed

Melnikov, Olga; Zaritsky, Arieh; Zarka, Aliza; Boussiba, Sammy; Malchin, Natalia; Yagil, Ezra; Kolot, Mikhail

2009-07-01

The integrase (Int) of the lambda-like coliphage HK022 catalyzes the site-specific integration and excision of the phage DNA into and from the chromosome of its host, Escherichia coli. Int recognizes two different pairs of recombining sites attP x attB and attL x attR for integration and excision, respectively. This system was adapted to the cyanobacterium Anabaena sp. strain PCC 7120 as a potential tool for site-specific gene manipulations in the cyanobacterium. Two plasmids were consecutively cointroduced by conjugation into Anabaena cells, one plasmid that expresses HK022 Int recombinase and the other plasmid that carries the excision substrate P(glnA)-attL-T1/T2-attR-lacZ, where T1/T2 are the strong transcription terminators of rrnB, to prevent expression of the lacZ reporter under the constitutive promoter P(glnA). The Int-catalyzed site-specific recombination reaction was monitored by the expression of lacZ emanating as a result of T1/T2 excision. Int catalyzed the site-specific excision reaction in Anabaena cells when its substrate was located either on the plasmid or on the chromosome with no need to supply an accessory protein, such as integration host factor and excisionase (Xis), which are indispensable for this reaction in its host, E. coli.

Intramolecular Hydroamination of Unbiased and Functionalized Primary Aminoalkenes Catalyzed by a Rhodium Aminophosphine Complex

PubMed Central

Julian, Lisa D.; Hartwig, John F.

2010-01-01

We report a rhodium catalyst that exhibits high reactivity for the hydroamination of primary aminoalkenes that are unbiased toward cyclization and that possess functional groups that would not be tolerated in hydroaminations catalyzed by more electrophilic systems. This catalyst contains an unusual diaminophosphine ligand that binds to rhodium in a κ3-P,O,P mode. The reactions catalyzed by this complex typically proceed at mild temperatures (room temperature to 70 °C), occur with primary aminoalkenes lacking substituents on the alkyl chain that bias the system toward cyclization, occur with primary aminoalkenes containing chloride, ester, ether, enolizable ketone, nitrile, and unprotected alcohol functionality, and occur with primary aminoalkenes containing internal olefins. Mechanistic data imply that these reactions occur with a turnover-limiting step that is different from that of reactions catalyzed by late transition metal complexes of Pd, Pt, and Ir. This change in the turnover-limiting step and resulting high activity of the catalyst stem from favorable relative rates for protonolysis of the M-C bond to release the hydroamination product vs reversion of the aminoalkyl intermediate to regenerate the acyclic precursor. Probes for the origin of the reactivity of the rhodium complex of L1 imply that the aminophosphine groups lead to these favorable rates by effects beyond steric demands and simple electron donation to the metal center. PMID:20839807

Turning Cucurbit[8]uril into a Supramolecular Nanoreactor for Asymmetric Catalysis

PubMed Central

Zheng, Lifei; Sonzini, Silvia; Ambarwati, Masyitha; Rosta, Edina

2015-01-01

Abstract Chiral macromolecules have been widely used as synthetic pockets to mimic natural enzymes and promote asymmetric reactions. An achiral host, cucurbit[8]uril (CB[8]), was used for an asymmetric Lewis acid catalyzed Diels–Alder reaction. We achieved a remarkable increase in enantioselectivity and a large rate acceleration in the presence of the nanoreactor by using an amino acid as the chiral source. Mechanistic and computational studies revealed that both the amino acid–Cu2+ complex and the dienophile substrate are included inside the macrocyclic host cavity, suggesting that contiguity and conformational constraints are fundamental to the catalytic process and rate enhancement. These results pave the way towards new studies on asymmetric reactions catalyzed in confined achiral cavities. PMID:27478269

Turning Cucurbit[8]uril into a Supramolecular Nanoreactor for Asymmetric Catalysis

PubMed Central

Zheng, Lifei; Sonzini, Silvia; Ambarwati, Masyitha; Rosta, Edina; Scherman, Oren A; Herrmann, Andreas

2015-01-01

Chiral macromolecules have been widely used as synthetic pockets to mimic natural enzymes and promote asymmetric reactions. An achiral host, cucurbit[8]uril (CB[8]), was used for an asymmetric Lewis acid catalyzed Diels–Alder reaction. We achieved a remarkable increase in enantioselectivity and a large rate acceleration in the presence of the nanoreactor by using an amino acid as the chiral source. Mechanistic and computational studies revealed that both the amino acid–Cu2+ complex and the dienophile substrate are included inside the macrocyclic host cavity, suggesting that contiguity and conformational constraints are fundamental to the catalytic process and rate enhancement. These results pave the way towards new studies on asymmetric reactions catalyzed in confined achiral cavities. PMID:26383272

Macrocyclic bis-thioureas catalyze stereospecific glycosylation reactions.

PubMed

Park, Yongho; Harper, Kaid C; Kuhl, Nadine; Kwan, Eugene E; Liu, Richard Y; Jacobsen, Eric N

2017-01-13

Carbohydrates are involved in nearly all aspects of biochemistry, but their complex chemical structures present long-standing practical challenges to their synthesis. In particular, stereochemical outcomes in glycosylation reactions are highly dependent on the steric and electronic properties of coupling partners; thus, carbohydrate synthesis is not easily predictable. Here we report the discovery of a macrocyclic bis-thiourea derivative that catalyzes stereospecific invertive substitution pathways of glycosyl chlorides. The utility of the catalyst is demonstrated in the synthesis of trans-1,2-, cis-1,2-, and 2-deoxy-β-glycosides. Mechanistic studies are consistent with a cooperative mechanism in which an electrophile and a nucleophile are simultaneously activated to effect a stereospecific substitution reaction. Copyright © 2017, American Association for the Advancement of Science.

Real-time monitoring of disintegration activity of catalytic core domain of HIV-1 integrase using molecular beacon.

PubMed

Zhang, Da-wei; Zhao, Ming-ming; He, Hong-qiu; Guo, Shun-xing

2013-09-15

HIV-1 integrase, an essential enzyme for retroviral replication, is a validated target for anti-HIV therapy development. The catalytic core domain of integrase (IN-CCD) is capable of catalyzing disintegration reaction. In this work, a hairpin-shaped disintegration substrate was designed and validated by enzyme-linked immunosorbent assay; a molecular beacon-based assay was developed for disintegration reaction of IN-CCD. Results showed that the disintegration substrate could be recognized and catalyzed by IN-CCD, and the disintegration reaction can be monitored according to the increase of fluorescent signal. The assay can be applied to real-time detection of disintegration with advantages of simplicity, high sensitivity, and excellent specificity. Copyright © 2013 Elsevier Inc. All rights reserved.

Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

NASA Technical Reports Server (NTRS)

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

A Forty Year Odyssey in Metallo-Organic Chemistry.

PubMed

Nicholas, Kenneth M

2015-07-17

In this invited Perspective, I provide a personal account highlighting several of my group's research contributions in metallo-organic chemistry over the past 40 years. Our early work focused primarily in stoichiometric structure/reactivity of transition metal-organic compounds and their use in organic synthesis. More recent efforts have centered on the discovery and development of new metal-catalyzed organic reactions via reactive metal-organic intermediates. The major research findings that are described here include (1) propargyl-cobalt complexes as electrophilic agents for C-C and C-Nu coupling; (2) the activation of carbon dioxide by metal complexes; (3) metal-promoted C-H nitrogenation reactions; (4) oxo-metal catalyzed deoxygenation reactions; and (5) catalyst discovery via dynamic templating with substrate- and transition-state analogues.