Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 2.046
Filtrar
1.
BMC Biotechnol ; 19(1): 49, 2019 07 18.
Artigo em Inglês | MEDLINE | ID: mdl-31319821

RESUMO

BACKGROUND: S-Phenyl-L-cysteine is regarded as having potential applicability as an antiretroviral/protease inhibitor for human immunodeficiency virus (HIV). In the present study, optically active S-phenyl-L-cysteine was prepared in a highly efficient manner from inexpensive bromobenzene using tryptophan synthase through a chemoenzymatic method. RESULTS: The chemoenzymatic method used a four-step reaction sequence. The process started with the reaction of magnesium and bromobenzene, followed by a Grignard reaction, and then hydrolysis and enzymatic synthesis using tryptophan synthase. Through this approach, S-phenyl-L-cysteine was chemoenzymatically synthesized using tryptophan synthase from thiophenol and L-serine as the starting material. CONCLUSIONS: High-purity, optically active S-phenyl-L-cysteine was efficiently and inexpensively obtained in a total yield of 81.3% (> 99.9% purity).


Assuntos
Química Orgânica/métodos , Cisteína/análogos & derivados , Compostos Organometálicos/metabolismo , Triptofano Sintase/metabolismo , Bromobenzenos/química , Bromobenzenos/metabolismo , Cisteína/química , Cisteína/metabolismo , Magnésio/química , Magnésio/metabolismo , Modelos Químicos , Estrutura Molecular , Compostos Organometálicos/química , Fenóis/química , Fenóis/metabolismo , Serina/química , Serina/metabolismo , Compostos de Sulfidrila/química , Compostos de Sulfidrila/metabolismo , Triptofano Sintase/química
2.
Molecules ; 24(13)2019 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-31269674

RESUMO

Composites of polyolefin matrices (HDPE and PP) were prepared by melt processing using two commercially available nano ZnO powders (Zinkoxyd aktiv and Zano 20). The mechanical and thermal properties, UV-Vis stability, and antibacterial activity of composites were studied. Tensile testing revealed that both nano ZnO types have no particular effect on the mechanical properties of HDPE composites, while some positive trends are observed for the PP-based composites, but only when Zano 20 was used as a nanofiller. Minimal changes in mechanical properties of composites are supported by an almost unaffected degree of crystallinity of polymer matrix. All polyolefin/ZnO composites exposed to artificial sunlight for 8-10 weeks show more pronounced color change than pure matrices. This effect is more evident for the HDPE than for the PP based composites. Color change also depends on the ZnO concentration and type; composites with Zano 20 show more intense color changes than those prepared with Zinkoxyd aktiv. Results of the antibacterial properties study show very high activity of polyolefin/ZnO composites against Staphylococcus aureus regardless of the ZnO surface modification, while antibacterial activity against Escherichia coli shows only the composites prepared with unmodified ZnO. This phenomenon is explained by different membrane structure of gram-positive (S. aureus) and gram-negative (E. coli) bacteria.


Assuntos
Química Orgânica/métodos , Polienos/química , Óxido de Zinco/química , Antibacterianos/farmacologia , Escherichia coli/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Nanopartículas/química , Nanopartículas/ultraestrutura , Silanos/química , Espectroscopia de Infravermelho com Transformada de Fourier , Staphylococcus aureus/efeitos dos fármacos , Ácidos Esteáricos/química , Propriedades de Superfície , Resistência à Tração , Difração de Raios X
3.
Molecules ; 24(9)2019 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-31075948

RESUMO

The preparation of 24-functionalized 12,22:26,32-terpyridines (4'-functionalized 3,2:6',3''-terpyridines) by the reaction of three 4-alkoxybenzaldehydes with 3-acetylpyridine and ammonia was investigated; under identical reaction conditions, two (R = nC4H9, C2H5) gave the expected products whereas a third (R = nC3H7) gave only a cyclohexanol derivative derived from the condensation of three molecules of 3-acetylpyridine with two of 4-(n-propoxy)benzaldehyde. A comprehensive survey of ''unexpected'' products from reactions of ArCOCH3 derivatives with aromatic aldehydes is presented. Three different types of alternative product are identified.


Assuntos
Química Orgânica/métodos , Piridinas/síntese química , Ciclização , Isomerismo , Ligantes , Espectroscopia de Prótons por Ressonância Magnética , Piridinas/química
4.
Nat Commun ; 10(1): 2169, 2019 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-31092815

RESUMO

Previous studies have shown that aqueous solutions of designer surfactants enable a wide variety of valuable transformations in synthetic organic chemistry. Since reactions take place within the inner hydrophobic cores of these tailor-made nanoreactors, and products made therein are in dynamic exchange between micelles through the water, opportunities exist to use enzymes to effect secondary processes. Herein we report that ketone-containing products, formed via initial transition metal-catalyzed reactions based on Pd, Cu, Rh, Fe and Au, can be followed in the same pot by enzymatic reductions mediated by alcohol dehydrogenases. Most noteworthy is the finding that nanomicelles present in the water appear to function not only as a medium for both chemo- and bio-catalysis, but as a reservoir for substrates, products, and catalysts, decreasing noncompetitive enzyme inhibition.


Assuntos
Química Orgânica/métodos , Enzimas/química , Metais/química , Elementos de Transição/química , Catálise , Micelas , Estrutura Molecular , Tensoativos/química , Água/química
5.
Spectrochim Acta A Mol Biomol Spectrosc ; 213: 301-308, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30708287

RESUMO

A facile and straightforward microwave-assisted method was used to prepare polyamine-functionalized carbon dots (CDs) from a precursor comprising renewable xylan and branched polyethyleneimine (BPEI). The as-prepared BPEI-CDs were monodispersed sphere particles with an average diameter of about 8.62 nm, and exhibited excellent fluorescent property and high stability, as well as excitation-independent emission behavior. Furthermore, it is attractive that the BPEI-CDs can be used as novel fluorescent probes for detecting tannic acid (TA) sensitively and selectively. At the optimum condition, the TA detection system was established in water solution and ethanol solution with a dynamic range from 0.1 to 5 µM, and their detection limit of 36.8 nM and 44.9 nM were also determined, respectively. Most importantly, the BPEI-CDs-based sensors can be successfully applied to detect TA in real lake water and white wine samples, suggesting the low-cost and excellent BPEI-CDs are potential suitable for TA detection in practical application.


Assuntos
Carbono/química , Química Orgânica/métodos , Micro-Ondas , Poliaminas/química , Pontos Quânticos/química , Taninos/análise , Xilanos/química , Fluorescência , Concentração de Íons de Hidrogênio , Lagos/química , Tamanho da Partícula , Polietilenoimina/química , Pontos Quânticos/ultraestrutura , Espectrofotometria Ultravioleta , Taninos/química , Água/química
6.
Molecules ; 23(12)2018 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-30572693

RESUMO

Lignans comprise a family of secondary metabolites existing widely in plants and also in human food sources. As important components, these compounds play remarkable roles in plants' ecological functions as protection against herbivores and microorganisms. Meanwhile, foods rich in lignans have revealed potential to decrease of risk of cancers. To date, a number of promising bioactivities have been found for lignan natural products and their unnatural analogues, including antibacterial, antiviral, antitumor, antiplatelet, phosphodiesterase inhibition, 5-lipoxygenase inhibition, HIV reverse transcription inhibition, cytotoxic activities, antioxidant activities, immunosuppressive activities and antiasthmatic activities. Therefore, the synthesis of this family and also their analogues have attracted widespread interest from the synthetic organic chemistry community. Herein, we outline advances in the synthesis of lignan natural products in the last decade.


Assuntos
Produtos Biológicos/síntese química , Química Orgânica/métodos , Lignanas/síntese química
7.
Biointerphases ; 13(6): 06E407, 2018 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-30408965

RESUMO

Traditional strategies for the functionalization of materials displaying hydroxyl groups either require active esterification reagents or involve the nucleophilic attack of the hydroxyl group toward electrophilic groups. The former tends to hydrolyze in aqueous solutions while the latter occurs under harsh conditions. Herein, the authors reported a new method for the functionalization of hydroxyl groups on the surface via catalytic oxa-Michael addition with vinyl sulfones. Using hydroxyl group terminated self-assembled monolayers as a model surface, a series of organocatalysts were screened and triphenylphosphine stood out for the best catalytic activity. The catalytic reaction on the surface was characterized by x-ray photoelectron spectroscopy. The information of reaction kinetics was obtained using static water contact angle measurements. Once conjugated with ligands onto the functionalized surfaces, the multivalence binding of proteins was investigated by quartz crystal microbalance experiments. By varying the reaction conditions, e.g., catalyst types and reaction times, ligands can be anchored with a controllable density, which would be helpful to establish the relationships between ligand density and bioactivity.


Assuntos
Química Orgânica/métodos , Hidróxidos/metabolismo , Compostos Organofosforados/metabolismo , Sulfonas/metabolismo , Propriedades de Superfície , Cinética , Espectroscopia Fotoeletrônica , Ligação Proteica , Proteínas/metabolismo , Técnicas de Microbalança de Cristal de Quartzo
8.
J Oleo Sci ; 67(11): 1435-1442, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30404964

RESUMO

Δ5-Olefinic acids have been characterized in gymnosperm plants and have been reported to have several biological health benefits. Δ5-Olefinic acids from pine nut oil were effectively concentrated by repeated lipase-catalyzed esterification. The pine nut oil contained three major Δ5-olefinic acids, namely taxoleic acid (C18:2 Δ5,9), pinolenic acid (C18:3 Δ5,9,12), and sciadonic acid (C20:3 Δ5,11,14). The fatty acids present in pine nut oil were selectively esterified with ethanol using Lipozyme RM IM from Rhizomucor miehei as a biocatalyst. The Δ5-olefinic acids were concentrated in the unesterified fatty acid fraction. The optimum molar ratio of the substrates (fatty acid:ethanol), temperature, the enzyme loading, and the reaction time were 1:7, 25°C, 5% of total substrate weight, and 6 h, respectively. There was no significant effect in the concentration of Δ5-olefinic acids when water was added in the reaction mixture. The same protocol and optimum conditions were employed for two times repeated lipase-catalyzed esterifications. In first lipase-catalyzed esterification, the Δ5-olefinic acids content in the pine nut oil increased from 17 mol% to 51 mol% with a yield of 40 mol%. In a second lipase-catalyzed esterification, with the Δ5-olefinic acids-concentrated fatty acids obtained from the first reaction as the substrate, the Δ5-olefinic acids content increased to 86 mol% with a yield of 15 mol%. Finally, a maximum Δ5-olefinic acids content of ca. 96 mol% with a yield of 6 mol% was obtained via a third lipase-catalyzed esterification.


Assuntos
Alcenos/isolamento & purificação , Química Orgânica/métodos , Lipase , Nozes/química , Pinus/química , Óleos Vegetais/química , Ácidos Araquidônicos/isolamento & purificação , Biocatálise , Esterificação , Etanol , Ácidos Linolênicos/isolamento & purificação , Rhizomucor , Temperatura Ambiente
10.
Yakugaku Zasshi ; 138(11): 1335-1344, 2018.
Artigo em Japonês | MEDLINE | ID: mdl-30381641

RESUMO

Marine natural products and biologically active compounds often contain cyclic ether units. Thus, regio- and stereoselective construction of these structures has long been a topic of interest in organic synthesis. This review summarizes new synthetic approaches to polycyclic ether natural products utilizing the features of chemical elements.


Assuntos
Produtos Biológicos/síntese química , Elementos , Éteres Cíclicos/síntese química , Biologia Marinha , Toxinas Marinhas/síntese química , Oxocinas/síntese química , Animais , Produtos Biológicos/química , Catálise , Química Orgânica/métodos , Éteres Cíclicos/química , Ouro , Interações Hidrofóbicas e Hidrofílicas , Toxinas Marinhas/química , Camundongos , Conformação Molecular , Fenômenos de Química Orgânica , Oxocinas/química , Rênio/química , Estereoisomerismo
11.
Yakugaku Zasshi ; 138(11): 1353-1361, 2018.
Artigo em Japonês | MEDLINE | ID: mdl-30381643

RESUMO

Heterogeneous metal catalysts constitute a very important tool for the synthesis of functional materials and fine chemicals owing to their high efficiency, robustness, and facile recyclability. Biaryls are privileged structural motifs in many natural products, chiral ligands, and catalysts. The oxidative biaryl coupling reaction is one of the most promising methods for biaryl synthesis in terms of atom and step economies. However, although oxidative biaryl coupling of naphthols has been studied thoroughly, the coupling of aryl amines providing biaryl amines like 2,2'-diamino-1,1'-binaphthyl (BINAM) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) derivatives remains elusive. Recently, we have found that aryl amines are efficiently dimerized with the use of a heterogeneous Rh/C catalyst under acidic conditions. This heterogeneously catalyzed method can be adapted to the highly selective cross-coupling reaction of aryl amines and the intramolecular biaryl coupling reaction. Furthermore, we developed an aerobic direct C-H oxidation of polycyclic aromatics catalyzed by a recyclable heterogeneous rhodium catalyst. These methodologies are advantageous compared with the existing reactions owing to the mild aerobic conditions employed and the facile recyclability of the heterogeneous catalysts used.


Assuntos
Antracenos/química , Química Orgânica/métodos , Naftalenos/química , Naftalenos/síntese química , Naftóis/química , Naftóis/síntese química , Aminas/química , Catálise , Estrutura Molecular , Fenômenos de Química Orgânica , Oxirredução , Ródio/química
12.
J Vis Exp ; (141)2018 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-30474625

RESUMO

A recently developed pressurized hot water extraction (PHWE) method which utilizes an unmodified household espresso machine to facilitate natural products research has also found applications as an effective teaching tool. Specifically, this technique has been used to introduce second- and third-year undergraduates to aspects of natural products chemistry in the laboratory. In this report, two experiments are presented: the PHWE of eugenol and acetyleugenol from cloves and the PHWE of seselin and (+)-epoxysuberosin from the endemic Australian plant species Correa reflexa. By employing PHWE in these experiments, the crude clove extract, enriched in eugenol and acetyleugenol, was obtained in 4-9% w/w from cloves by second-year undergraduates and seselin and (+)-epoxysuberosin were isolated in yields of up to 1.1% w/w and 0.9% w/w from C. reflexa by third-year students. The former exercise was developed as a replacement for the traditional steam distillation experiment providing an introduction to extraction and separation techniques, while the latter activity featured guided-inquiry teaching methods in an effort to simulate natural products bioprospecting. This primarily derives from the rapid nature of this PHWE technique relative to traditional extraction methods that are often incompatible with the time constraints associated with undergraduate laboratory experiments. This rapid and practical PHWE method can be used to efficiently isolate various classes of organic molecules from a range of plant species. The complementary nature of this technique relative to more traditional methods has also been demonstrated previously.


Assuntos
Produtos Biológicos/química , Química Orgânica/métodos , Temperatura Alta/uso terapêutico , Laboratórios/normas , Água/química , Produtos Biológicos/análise , Óleos Voláteis
13.
Biol Pharm Bull ; 41(10): 1502-1507, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30270318

RESUMO

An organic chemistry approach to the mechanistic elucidation of iron acquisition in graminaceous plants is introduced here. To elucidate this detailed mechanism using phytosiderophores, the efficient synthesis of 2'-deoxymugineic acid (DMA), a phytosiderophore of rice, was established. The synthetic DMA was confirmed to have similar iron transport activity to that of natural mugineic acid (MA). It was also revealed that the addition of synthetic DMA, along with iron, to a rice hydroponic solution enabled the rice to grow well even under an alkaline condition, and DMA clearly showed its high potential as a fertilizer to improve food production. On the other hand, the 2'-hydroxy group of MA was confirmed to serve as a point of introduction for labeling, allowing the synthesis of various mugineic acid derivatives as molecular probes. The incorporation of fluorescent mugineic acid into cells allowed them to be clearly observed by fluorescence confocal analysis, and this provided the first direct experimental evidence of transporter-mediated internalization of mugineic acid into cells.


Assuntos
Ácido Azetidinocarboxílico/análogos & derivados , Hordeum/metabolismo , Ferro/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Compostos Organometálicos/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Ácido Azetidinocarboxílico/metabolismo , Química Orgânica/métodos , Fertilizantes , Hordeum/crescimento & desenvolvimento , Compostos de Ferro/metabolismo , Oryza/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Sideróforos/metabolismo , Coloração e Rotulagem
14.
Molecules ; 23(9)2018 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-30200476

RESUMO

The development and optimization of synthetic methods leading to functionalized biologically active compounds is described. Two alternative pathways based on Heck-type reactions, employing iodobenzene or phenylboronic acid, were elaborated for the arylation of eugenol and estragole. Cinnamyl alcohol was efficiently transformed to saturated arylated aldehydes in reaction with iodobenzene using the tandem arylation/isomerization sequential process. The arylation of cinnamyl alcohol with phenylboronic acid mainly gave unsaturated alcohol, while the yield of saturated aldehyde was much lower. Catalytic reactions were carried out using simple, phosphine-free palladium precursors and water as a cosolvent, following green chemistry rules as much as possible.


Assuntos
Química Orgânica/métodos , Paládio/química , Fosfinas/química , Anisóis/química , Ácidos Borônicos/química , Catálise , Eugenol/química , Iodobenzenos/química , Monoterpenos/química , Propanóis/química
15.
Molecules ; 23(9)2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-30208621

RESUMO

Organocatalysis has emerged as a powerful synthetic tool in organic chemistry in the last few decades. Among various classes of organocatalysis, chiral diol-based scaffolds, such as BINOLs, VANOLs, and tartaric acid derivatives, have been widely used to induce enantioselectivity due to the ability of the hydroxyls to coordinate with the Lewis acidic sites of reagents or substrates and create a chiral environment for the transformation. In this review, we will discuss the applications of these diol-based catalysts in different types of reactions, including the scopes of reactions and the modes of catalyst activation. In general, the axially chiral aryl diol BINOL and VANOL derivatives serve as the most competent catalyst for most examples, but examples of exclusive success using other scaffolds, herein, suggests that they should not be overlooked. Lastly, the examples, to date, are mainly from tartrate and biaryl diol catalysts, suggesting that innovation may be available from new diol scaffolds.


Assuntos
Química Orgânica/métodos , Naftalenos/química , Tartaratos/química , Catálise , Ácidos de Lewis , Estrutura Molecular , Naftóis/química , Estereoisomerismo
16.
Molecules ; 23(9)2018 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-30181479

RESUMO

A one-pot fluorination and organocatalytic Robinson annulation sequence has been developed for asymmetric synthesis of 6-fluoroyclohex-2-en-1-ones and 4,6-difluorocyclohex-2-en-1-ones. The reactions promoted by cinchona alkaloid amine afforded products bearing two or three stereocenters in good to excellent yields with up to 99% ee and 20:1 dr.


Assuntos
Química Orgânica/métodos , Cicloexanonas/química , Cicloexanonas/síntese química , Halogenação , Catálise , Espectroscopia de Prótons por Ressonância Magnética
17.
J Oleo Sci ; 67(8): 1005-1014, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30068826

RESUMO

This study aims to investigate the production of ethylene and diethyl ether from ethanol via catalytic dehydration using Si- and Al-based catalysts with Pd modification. First, six catalysts including H-beta zeolite (HBZ), mixed phases of γ-χ-Al2O3 (M-Al) and γ-Al2O3 (G-Al) with and without Pd modification (0.5 wt%) were prepared. The catalytic dehydration of vaporized ethanol at temperature ranging from 200 to 400°C was performed over the catalysts. For ethylene production, the most promising catalyst is HBZ (giving ethylene yield of ca. 99% at 400°C), whereas Pd modification has no significant effect on ethylene production. Considering the production of diethyl ether, it is produced at lower temperature (ca. 250°C) than that of ethylene. The most active catalyst to produce diethyl ether is HBZ with Pd modification (giving diethyl ether yield of ca. 48% at 250°C). Thus, increased diethyl ether yield can be achieved with Pd modification at low temperature for the HBZ catalyst. Other catalysts such as M-Al and G-Al can also produce significant amounts of ethylene. To elucidate the effect of Pd modification on these catalysts, different characterization techniques such as nitrogen physisorption (BET and BJH methods), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and ammonia temperature-programmed desorption were performed and further discussed in more detail.


Assuntos
Compostos de Alumínio/química , Etanol/química , Éter/síntese química , Etilenos/síntese química , Paládio/química , Compostos de Silício/química , Catálise , Química Orgânica/métodos , Dessecação , Temperatura Ambiente , Volatilização
18.
Molecules ; 23(8)2018 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-30087293

RESUMO

The concepts of sustainable development, bioeconomy, and circular economy are being increasingly applied for the synthesis of molecules of industrial interest. Among these molecules, hydroxymethylfurfural as a platform molecule is the subject of various research approaches to improve its synthesis and productivity, and extend its potential uses. Accordingly, this review paper aims essentially at outlining recent breakthroughs obtained in the field of hydroxymethylfurfural production from sugars and polysaccharide feedstocks under microwave-assisted technology. The review discusses advances obtained via microwave activation in major production pathways recently explored, split into the following categories: (i) use of various homogeneous catalysts like mineral or organic acids, metal salts, or ionic liquids; (ii) feedstock dehydration making use of various solid acid catalysts; and (iii) non-catalytic routes.


Assuntos
Celulose/química , Química Orgânica/métodos , Furaldeído/análogos & derivados , Micro-Ondas , Catálise , Furaldeído/síntese química , Hidrólise
19.
Methods Mol Biol ; 1804: 293-310, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29926415

RESUMO

Various methods for the chemical synthesis of gangliosides have been investigated to date and numerous natural gangliosides and their structural analogues have been synthesized during the past three decades. Key technologies in the synthesis of gangliosides include α-selective sialylation and introduction of the ceramide moiety into the oligosaccharide chain. This chapter introduces two major strategies for ganglioside synthesis-the most commonly used strategy and the recently developed glucosylceramide cassette approach. Synthetic procedures for selected reactions are also presented.


Assuntos
Química Orgânica/métodos , Gangliosídeos/síntese química , Animais , Galactose/metabolismo , Gangliosídeos/química , Glucosilceramidas/metabolismo , Mamíferos , Conformação Molecular , Ácido N-Acetilneuramínico/metabolismo
20.
Nat Commun ; 9(1): 1972, 2018 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-29773787

RESUMO

Transition-metal-catalyzed diazo activation is a classical way to generate metal carbene, which are valuable intermediates in synthetic organic chemistry. An alternative iodine-catalyzed diazo activation is disclosed herein under either photo-initiated or thermal-initiated conditions, which represents an approach to enable carbene radical reactivity. This metal-free diazo activation strategy were successfully applied into olefin cyclopropanation and epoxidation, and applying this method to pyrrole synthesis under thermal-initiated conditions further demonstrates the unique reactivity using this method over typical metal-catalyzed conditions.


Assuntos
Alcenos/química , Química Orgânica/métodos , Iodo/química , Metano/análogos & derivados , Pirróis/síntese química , Catálise , Luz , Metano/química , Temperatura Ambiente
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA