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1.
J Org Chem ; 81(16): 7155-60, 2016 08 19.
Artigo em Inglês | MEDLINE | ID: mdl-27276418

RESUMO

Despite the number of methods available for dehalogenation and carbon-carbon bond formation using aryl halides, strategies that provide chemoselectivity for systems bearing multiple carbon-halogen bonds are still needed. Herein, we report the ability to tune the reduction potential of metal-free phenothiazine-based photoredox catalysts and demonstrate the application of these catalysts for chemoselective carbon-halogen bond activation to achieve C-C cross-coupling reactions as well as reductive dehalogenations. This procedure works both for conjugated polyhalides as well as unconjugated substrates. We further illustrate the usefulness of this protocol by intramolecular cyclization of a pyrrole substrate, an advanced building block for a family of natural products known to exhibit biological activity.


Assuntos
Carbono/química , Radicais Livres/química , Hidrocarbonetos Halogenados/química , Catálise , Halogenação , Processos Fotoquímicos
2.
J Am Chem Soc ; 136(45): 16096-101, 2014 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-25360628

RESUMO

Overcoming the challenge of metal contamination in traditional ATRP systems, a metal-free ATRP process, mediated by light and catalyzed by an organic-based photoredox catalyst, is reported. Polymerization of vinyl monomers are efficiently activated and deactivated with light leading to excellent control over the molecular weight, polydispersity, and chain ends of the resulting polymers. Significantly, block copolymer formation was facile and could be combined with other controlled radical processes leading to structural and synthetic versatility. We believe that these new organic-based photoredox catalysts will enable new applications for controlled radical polymerizations and also be of further value in both small molecule and polymer chemistry.

3.
J Am Chem Soc ; 135(38): 14106-9, 2013 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-24025201

RESUMO

A modular and general method based on a photomediated ATRA reaction for the spatially controlled functionalization of surfaces with visible light is reported. The ability to control reactivity with light intensity combined with the orthogonality of ATRA chemistry allows well-defined chemically differentiated monolayers and complex nonlinear chemical concentration gradients to be easily prepared. Use of light to mediate these reactions permits spatial regulation and the generation of unique, multifunctional chemical gradients.

4.
Nat Chem Biol ; 6(6): 449-56, 2010 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20418879

RESUMO

Cycles of depalmitoylation and repalmitoylation critically control the steady-state localization and function of various peripheral membrane proteins, such as Ras proto-oncogene products. Interference with acylation using small molecules is a strategy to modulate cellular localization--and thereby unregulated signaling--caused by palmitoylated Ras proteins. We present the knowledge-based development and characterization of a potent inhibitor of acyl protein thioesterase 1 (APT1), a bona fide depalmitoylating enzyme that is, so far, poorly characterized in cells. The inhibitor, palmostatin B, perturbs the cellular acylation cycle at the level of depalmitoylation and thereby causes a loss of the precise steady-state localization of palmitoylated Ras. As a consequence, palmostatin B induces partial phenotypic reversion in oncogenic HRasG12V-transformed fibroblasts. We identify APT1 as one of the thioesterases in the acylation cycle and show that this protein is a cellular target of the inhibitor.


Assuntos
Inibidores Enzimáticos/farmacologia , Propiolactona/análogos & derivados , Tioléster Hidrolases/antagonistas & inibidores , Tioléster Hidrolases/química , Proteínas ras/fisiologia , Animais , Linhagem Celular , Cães , Regulação para Baixo , Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/química , Humanos , Rim/efeitos dos fármacos , Rim/fisiologia , Ligantes , Lipase/química , Lipase/metabolismo , Lipoilação/efeitos dos fármacos , Modelos Moleculares , Propiolactona/síntese química , Propiolactona/química , Propiolactona/farmacologia , Conformação Proteica , Proto-Oncogene Mas , Transdução de Sinais , Estômago/enzimologia , Tioléster Hidrolases/genética , Proteínas ras/efeitos dos fármacos , Proteínas ras/metabolismo
5.
J Am Chem Soc ; 131(44): 16042-4, 2009 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-19835375

RESUMO

The ring-opening polymerization of a mixture of enantiomerically pure but different monomers using an yttrium complex as initiator proceeds readily at room temperature to give the corresponding highly alternating polyester.


Assuntos
Poliésteres/síntese química , Ítrio , Catálise , Polímeros/síntese química , Estereoisomerismo
6.
Tetrahedron ; 64(29): 6973-6978, 2008 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-19606203

RESUMO

Efficient and mild reaction conditions were developed for the catalytic carbonylation of fluorinated epoxides to their corresponding ß-lactones. Six new lactones with fluorinated side chains were prepared in high isolated yields. These lactones were polymerized to form a series of new poly(ß-hydroxyalkanoate)s with fluorinated side chains, and their properties were examined with respect to their hydrocarbon analogs. Finally, copolymerizations were performed with fluorinated lactones and ß-butyrolactone, which resulted in tapered copolymers rather than the expected random copolymers.

8.
Org Lett ; 9(26): 5581-3, 2007 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-18027958

RESUMO

Substituted 3-hydroxy-delta-lactones (3HLs) are valuable intermediates in the synthesis of pharmaceuticals and other biologically active natural products. Herein we report the first example of the catalytic carbonylation of substituted homoglycidols to 3HLs using HCo(CO)4. Upon optimization of the catalyst and reaction conditions, a functionally diverse set of 3HLs was prepared. Mechanistic insight was gained by observation of the carbonylation reaction using in situ IR spectroscopy, and we propose a mechanism that is consistent with previously studied epoxide carbonylation systems.


Assuntos
Compostos de Epóxi/química , Cetonas/química , Lactonas/química , Espectrofotometria Infravermelho
9.
ACS Cent Sci ; 3(6): 654-661, 2017 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-28691078

RESUMO

A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red-green-blue arrays to yield white emission.

10.
Org Lett ; 8(17): 3709-12, 2006 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-16898798

RESUMO

[reaction: see text] A readily prepared bimetallic catalyst is capable of effecting epoxide carbonylation to produce beta-lactones at substantially lower CO pressures than previously reported catalyst systems. A functionally diverse array of beta-lactones is produced in excellent yields at CO pressures as low as 1 atm. This procedure allows for epoxide carbonylation on a multigram scale without the requirement of specialized, high-pressure equipment.


Assuntos
Compostos de Epóxi/química , Cetonas/síntese química , Lactonas/síntese química , Catálise , Cromo/química , Cristalografia por Raios X , Cetonas/química , Lactonas/química , Conformação Molecular , Estrutura Molecular , Compostos Organometálicos/química , Estereoisomerismo
11.
ACS Macro Lett ; 3(6): 580-584, 2014 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-35590731

RESUMO

The controlled radical polymerization of a variety of acrylate monomers is reported using an Ir-catalyzed visible light mediated process leading to well-defined homo-, random, and block copolymers. The polymerizations could be efficiently activated and deactivated using light while maintaining a linear increase in molecular weight with conversion and first order kinetics. The robust nature of the fac-[Ir(ppy)3] catalyst allows carboxylic acids to be directly introduced at the chain ends through functional initiators or along the backbone of random copolymers (controlled process up to 50 mol % acrylic acid incorporation). In contrast to traditional ATRP procedures, low polydispersity block copolymers, poly(acrylate)-b-(acrylate), poly(methacrylate)-b-(acrylate), and poly(acrylate)-b-(methacrylate), could be prepared with no monomer sequence requirements. These results illustrate the increasing generality and utility of light mediated Ir-catalyzed polymerization as a platform for polymer synthesis.

13.
Chem Commun (Camb) ; (38): 5704-6, 2009 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-19774242

RESUMO

4-Substituted oxazolines, which are readily synthesized from naturally occurring alpha-amino acids, are converted efficiently and stereospecifically to beta-amidoaldehydes in the presence of synthesis gas and catalytic dicobalt octacarbonyl.


Assuntos
Aldeídos/química , Oxazóis/química , Catálise , Cobalto/química , Gases/química , Conformação Molecular , Estereoisomerismo
14.
Vet Clin Pathol ; 25(1): 10-13, 1996.
Artigo em Inglês | MEDLINE | ID: mdl-12660981

RESUMO

Canine serum was used to compare seven chemistry analytes on two tabletop clinical dry chemistry analyzers, Boehringer's Reflotron and Kodak's Ektachem. Results were compared to those obtained on a wet chemistry reference analyzer, Roche Diagnostic's Cobas Mira. Analytes measured were urea nitrogen (BUN), creatinine, glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), cholesterol and bilirubin. Nine to 12 canine sera with values in the low, normal, and high range were evaluated. The correlations were acceptable for all comparisons with correlation coefficients greater than 0.98 for all analytes. Regression analysis resulted in significant differences for both tabletop analyzers when compared to the reference analyzer for cholesterol and bilirubin, and for glucose and AST on the Kodak Ektachem. Differences appeared to result from proportional systematic error occurring at high analyte concentrations.

15.
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