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1.
J Biosci Bioeng ; 130(4): 437-442, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32616382

RESUMO

Fast enantiomeric separation of amino acids was studied by liquid chromatography/mass spectrometry (LC/MS) on a chiral crown ether stationary phase. A chiral crown ether bonded silica column (3 mm internal diameter (i.d.), 5 cm long) packed with 3 µm particles was employed instead of a 15 cm column packed with 5 µm particles used in our previous study. In addition, the extra-column variance, becoming more serious for smaller columns, was reduced by replacing 0.127 mm i.d. post-column tubes with shorter, smaller-diameter (0.0635 mm i.d.) tubes. The results demonstrated the benefits of using shorter columns packed with smaller particles and the reduction of the extra-column band broadening for fast enantiomeric separation. Finally, the enantiomeric separation of 18 pairs of proteinogenic amino acids was achieved within 2 min with a resolution (Rs) > 1.5 for each pair using an isocratic mobile phase of acetonitrile/water/trifluoroacetic acid (ACN/W/TFA) = 96/4/0.5, and a flow rate 1.2 mL/min at 30°C. This is the highest throughput method for simultaneous chiral separation of all proteinogenic amino acids except proline to date.


Assuntos
Aminoácidos/química , Aminoácidos/isolamento & purificação , Cromatografia Líquida/métodos , Éteres de Coroa/química , Espectrometria de Massas , Acetonitrilos/química , Aminas/química , Dióxido de Silício/química , Estereoisomerismo , Fatores de Tempo , Ácido Trifluoracético/química , Água/química
2.
J Chromatogr A ; 1618: 460851, 2020 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-32008826

RESUMO

Mixed-mode cation-exchange stationary phases are useful for the separation of mixtures containing hydrophobic, acidic, and basic molecules. To ensure that weak organic bases are protonated and carboxylic acids are neutral low pH mobile phases are required. Mixed-mode stationary phases that are stable at pH < 3 are needed. We synthesized a crosslinked structure along the surface of thiol functionalized silica gel particles using the thiol-yne click reaction. The alkyne, 1,7-octadiyne, was added to the 3-mercaptopropyl silica gel, then crosslinked using 1,6-hexanedithiol. Elemental analysis showed low octadiyne ligand surface coverage, but, stoichiometrically, three sulfurs were added to each octadiyne ligand during the crosslinking step, indicating that crosslinking occurred. The effect of the crosslinking on the stability was tested with a 50:50 (v/v) pH 0.50 5% TFA aqueous:acetonitrile mobile phase at 70 °C for six days, over 35,000 column volumes. The stationary phase showed good stability with the retention of triphenylene decreasing only 20% during that time. The Tanaka test showed that the phase has a methylene selectivity of 1.20 ± 0.04, a high shape selectivity of 2.71 ± 0.03, and a 3.98 ± 0.05 cation-exchange factor at pH 2.70. The phase has a selectivity factor for nitrobenzene and benzene of 1.41 ± 0.01, indicating the electron donating charge transfer characteristic of the phase. The mixed-mode characteristics of the phase were investigated using a mixture of the monoamine neurotransmitters norepinephrine, dopamine, and serotonin. Baseline resolution of the monoamines could be obtained using a simple 20 mM potassium phosphate (pH 2.70)/methanol mobile phase. Altering both the methanol content and the potassium ion concentration altered the retention of the monoamines indicating mixed-mode cation exchange characteristic of the crosslinked stationary phase.


Assuntos
Química Click/métodos , Compostos de Sulfidrila/química , Acetonitrilos/química , Benzeno/química , Cátions , Cromatografia por Troca Iônica , Intervalos de Confiança , Elétrons , Elementos , Concentração de Íons de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Neurotransmissores/análise , Nitrobenzenos/química , Ácido Trifluoracético/química , Água
3.
Int J Mol Sci ; 21(2)2020 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-31936463

RESUMO

Age-related macular degeneration (AMD) is the primary cause of blindness in advanced countries. Repeated intravitreal delivery of anti-vascular endothelial growth factor (VEGF) agents has represented an important advancement for the therapy of wet AMD with significative results in terms of blindness prevention and partial vision restore. Nonetheless, some patients are not responsive or do not attain significant visual improvement, intravitreal injection may cause serious complications and important side effects have been reported for the prolonged block of VEGF-A. In order to evaluate new anti-angiogenic strategies, we focused our attention on VEGF receptor 1 (VEGFR1) developing a specific VEGFR-1 antagonist, a tetrameric tripeptide named inhibitor of VEGFR 1 (iVR1). We have evaluated its anti-angiogenic activity in the preclinical model of AMD, the laser-induced choroid neovascularization (CNV). iVR1 is able to potently inhibit CNV when delivered by intravitreal injection. Surprisingly, it is able to significantly reduce CNV also when delivered by gavage. Our data show that the specific block of VEGFR1 in vivo represents a valid alternative to the block of VEGF-A and that the inhibition of the pathological neovascularization at ocular level is also possible by systemic delivery of compounds not targeting VEGF-A.


Assuntos
Neovascularização de Coroide/tratamento farmacológico , Neovascularização de Coroide/patologia , Oligopeptídeos/administração & dosagem , Oligopeptídeos/uso terapêutico , Receptor 1 de Fatores de Crescimento do Endotélio Vascular/antagonistas & inibidores , Administração Oral , Animais , Injeções Intravítreas , Lasers , Camundongos Endogâmicos C57BL , Oligopeptídeos/química , Espectroscopia de Infravermelho com Transformada de Fourier , Ácido Trifluoracético/química , Receptor 1 de Fatores de Crescimento do Endotélio Vascular/metabolismo
4.
Eur J Med Chem ; 186: 111894, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31787361

RESUMO

Green chemistry is becoming the favored approach to preparing drug molecules in pharmaceutical industry. Herein, we developed a clean and efficient method to synthesize 3-benzoylquinoxalines via activated carbon promoted aerobic benzylic oxidation under "on-water" condition. Moreover, biological studies with this class of compounds reveal an antiproliferative profile. Further structure modifications are performed and the investigations exhibited that the most active 12a could inhibit the microtubule polymerization by binding to tubulin and thus induce multipolar mitosis, G2/M phase arrest, and apoptosis of cancer cells. In addition, molecular docking studies allow the rationalization of the pharmacodynamic properties observed. Our systematic studies provide not only guidance for applications of O2/AC/H2O system, but also a new scaffold targeting tubulin for antitumor agent discovery.


Assuntos
Antineoplásicos/farmacologia , Compostos de Benzil/química , Quinoxalinas/farmacologia , Tubulina (Proteína)/metabolismo , Antineoplásicos/síntese química , Antineoplásicos/química , Carbono/química , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Relação Dose-Resposta a Droga , Ensaios de Seleção de Medicamentos Antitumorais , Formiatos/química , Humanos , Modelos Moleculares , Estrutura Molecular , Oxirredução , Polimerização/efeitos dos fármacos , Quinoxalinas/síntese química , Quinoxalinas/química , Relação Estrutura-Atividade , Ácidos Sulfúricos/química , Ácido Trifluoracético/química
5.
J Chromatogr A ; 1612: 460687, 2020 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-31727354

RESUMO

Application of the superficially porous particles (SPPs) grafted with chiral selectors can substantially improve resolution in chromatographic techniques. In this work, we carried out a deeper study on supercritical fluid chromatography systems with 2.7 µm SPPs bonded with teicoplanin and vancomycin. Fast separations of the majority of enantiomers of phytoalexins, substituted tryptophans, and ketamine derivatives, as representatives of important biologically active and structurally diverse chiral compounds have been achieved. The chromatographic behavior of the structurally different analytes served to characterize these separation systems. The influence of separation conditions, namely mobile phase composition, i.e. type of co-solvent and additive on retention, enantioselective resolution and enantioselectivity was examined. The success rate of baseline and partial separations in individual groups of compounds differed with the chiral stationary phase and also with mobile phase composition. The best, baseline separations for the phytoalexins were achieved on the TeicoShell column using methanol as a co-solvent and trifluoroacetic acid as an additive if used. Mostly partial separations were achieved on the vancomycin-based column for all groups of analytes. Complementary separation behavior of these CSPs was confirmed for the majority of the chiral compounds examined in this work.


Assuntos
Cromatografia com Fluido Supercrítico/métodos , Teicoplanina/química , Vancomicina/química , Alcaloides/química , Ligação de Hidrogênio , Ketamina/química , Porosidade , Sesquiterpenos/química , Solventes/química , Estereoisomerismo , Ácido Trifluoracético/química
6.
Environ Sci Pollut Res Int ; 27(1): 983-991, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31820231

RESUMO

Trifluoroacetic acid (TFA) is a ubiquitous and extremely stable contaminant in the ambient environment and may be discharged during fluorochemical production processes. However, the impacts of fluorochemical production on surrounding areas have seldom been evaluated. We focused on Jinan, the capital of Shandong Province, China, and measured TFA levels in water, soil, and air samples. Our results showed that the average TFA concentrations in flowing water bodies were lower than those in landscape water bodies. The average TFA concentrations in soils were significantly higher than the background concentration. As for atmospheric TFA levels, the mean concentrations in the gas phase were higher than those in the particle phase, and average daytime levels were slightly higher than nighttime levels. In addition, the quotient method was used to assess the ecological risk of TFA in water in Jinan. The ratio of pollutant environmental concentration to predicted no-effect concentration (PEC/PNEC) for TFA was greater than 1, indicating that TFA does potentially damage the aquatic ecosystem of Jinan. Our findings suggest that TFA pollution around fluoride production plants is a serious problem and that actions are required to avoid exacerbating the local ecological and environmental risks of TFA.


Assuntos
Ácido Trifluoracético/análise , China , Ecossistema , Monitoramento Ambiental/métodos , Solo , Ácido Trifluoracético/química , Poluentes Químicos da Água/análise
7.
Chemistry ; 26(2): 379-383, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31609031

RESUMO

Peptide alcohols are clinically important compounds that are underexplored in structure-activity relationship (SAR) studies in drug discovery. One reason for this underutilization is that current syntheses are laborious and time consuming. Herein, we describe the preparation and utility of Rink, Ramage, and Sieber-chloride resins, which enables the use of a general, easy and practical method for the attachment of fluorenylmethoxycarbonyl (Fmoc)-amino alcohols to a solid support, in the synthesis of peptide alcohols. This method is the first straightforward Fmoc/tBu synthesis of peptide alcohols starting from a pre-loaded resin. The synthesized peptide alcohols can be detached from the linkers through conventional methods. Treatment with trifluoroacetic acid (TFA) (95 %) and scavengers such as triisopropylsilane and water for 2 h is sufficient to obtain a fully deprotected peptide alcohol, while treatment with 20 % hexafluoroisopropanol in dichloromethane renders a fully protected peptide alcohol that can be further modified at the C-terminus. As examples, the new resins were used in straightforward, relatively rapid syntheses of the peptide alcohols octreotide, alamethicin, and a segment of trichogin GA IV, as well as the first synthesis of stapled peptide alcohols.


Assuntos
Amino Álcoois/química , Peptídeos/química , Peptídeos/síntese química , Fenilalanina/análogos & derivados , Fenilalanina/química , Poliestirenos/química , Ácido Trifluoracético/química
8.
J Pept Sci ; 26(3): e3236, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31856422

RESUMO

There are many examples of bioactive, disulfide-rich peptides and proteins whose biological activity relies on proper disulfide connectivity. Regioselective disulfide bond formation is a strategy for the synthesis of these bioactive peptides, but many of these methods suffer from a lack of orthogonality between pairs of protected cysteine (Cys) residues, efficiency, and high yields. Here, we show the utilization of 2,2'-dipyridyl diselenide (PySeSePy) as a chemical tool for the removal of Cys-protecting groups and regioselective formation of disulfide bonds in peptides. We found that peptides containing either Cys(Mob) or Cys(Acm) groups treated with PySeSePy in trifluoroacetic acid (TFA) (with or without triisopropylsilane (TIS) were converted to Cys-S-SePy adducts at 37 °C and various incubation times. This novel Cys-S-SePy adduct is able to be chemoselectively reduced by five-fold excess ascorbate at pH 4.5, a condition that should spare already installed peptide disulfide bonds from reduction. This chemoselective reduction by ascorbate will undoubtedly find utility in numerous biotechnological applications. We applied our new chemistry to the iodine-free synthesis of the human intestinal hormone guanylin, which contains two disulfide bonds. While we originally envisioned using ascorbate to chemoselectively reduce one of the formed Cys-S-SePy adducts to catalyze disulfide bond formation, we found that when pairs of Cys(Acm) residues were treated with PySeSePy in TFA, the second disulfide bond formed spontaneously. Spontaneous formation of the second disulfide is most likely driven by the formation of the thermodynamically favored diselenide (PySeSePy) from the two Cys-S-SePy adducts. Thus, we have developed a one-pot method for concomitant deprotection and disulfide bond formation of Cys(Acm) pairs in the presence of an existing disulfide bond.


Assuntos
2,2'-Dipiridil/análogos & derivados , Cisteína/química , Dissulfetos/análise , Compostos Organosselênicos/química , 2,2'-Dipiridil/química , Ácido Ascórbico/química , Hormônios Gastrointestinais/química , Humanos , Estrutura Molecular , Peptídeos Natriuréticos/química , Peptídeos/química , Ácido Trifluoracético/química
9.
J Chromatogr A ; 1604: 460494, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31488292

RESUMO

The objective of this study is to understand the behavior of a peptide in a medium containing supercritical carbon dioxide mixed with an alcohol (methanol) and acidic or basic additives in uncommonly high concentrations. Chirobiotic TAG is a chromatographic column made of silica bonded with a macrocyclic peptide, teicoplanin aglycone. With this stationary phase, two additives (trifluoroacetic acid and isopropylamine) were tested under extreme concentration conditions to observe the behavior of this peptide. Indeed, concentrations exceeding 1 M in the methanol co-solvent (>0.1 M overall concentration in the CO2-methanol mixture) were used whereas usual additive concentrations employed in supercritical fluid chromatography (SFC) rarely exceed 50 mM in the co-solvent. One purpose was to modify the apparent pH of the fluid, which is normally slightly acidic (around 5) and consequently possibly changing the ionization state of the peptide. Firstly, the effect of acidic and basic additives on the polarity and the apparent pH were evaluated with the help of color indicators. This served to assess the ionization state of the peptide under the selected operating conditions. Secondly, 54 achiral and 24 chiral molecules were injected in the chromatographic column at different levels of additives. The achiral species served at establishing retention models based on linear solvation energy relationships (LSER), while the chiral species were examined for their enantioresolution. From the LSER equations and observation of chromatograms, it appeared that specific interactions between the peptide-based stationary phase and the analytes evolved when increasing the concentration of additives, particularly hydrogen bonds and ionic interactions. A bare silica stationary phase (Acquity BEH) served as reference to deconvolute the contributions of silica support and bonded peptide. This study, with these extreme conditions of mobile phase, could be useful to understand the behavior of such peptides in SFC mobile phases and also improve the knowledge of the effects of additives in SFC, which should be helpful in the future prospect of analyzing large biomolecules in SFC.


Assuntos
Cromatografia com Fluido Supercrítico/métodos , Teicoplanina/análogos & derivados , Compostos Azabicíclicos/química , Ligação de Hidrogênio , Concentração de Íons de Hidrogênio , Íons , Metanol/química , Piperazinas/química , Solventes/química , Estereoisomerismo , Teicoplanina/química , Teicoplanina/isolamento & purificação , Ácido Trifluoracético/química
10.
Eur J Med Chem ; 182: 111645, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31494472

RESUMO

As our research focus on anticancer drugs, two series of novel derivatives of Flexicaulin A (FA), an ent-kaurene diterpene, condensation with amino acid trifluoroacetate were synthesized, and their anti-proliferative activity against four human cancer cell lines (TE-1, MCF-7, A549 and MGC-803) were evaluated. Compared with FA, the anticancer activity and solubility of most derivatives were significantly improved. Among them, compound 6d had the best activity, and its IC50 value against Esophageal cancer cells (TE-1) was up to 0.75 µM. Subsequent cellular mechanism studies showed that compound 6d could inhibit the proliferation of cancer cells, the formation of cell colonies, and increase the level of ROS on TE-1 cells. In addition, 6d could up-regulate the expressions of SAPK/JNK pathway-associated proteins (p-ASK1, p-MKK4 and p-JNK) and pro-apoptotic proteins (Bak, Bad and Noxa), remarkably increase the ratio of Bax to Bcl-2 and activate Cleaved Caspase-3/9/PARP. These results indicate that compound 6d induces apoptosis through the ROS/JNK/Bcl-2 pathway and holds promising potential as an anti-proliferative agent.


Assuntos
Aminoácidos/farmacologia , Antineoplásicos/farmacologia , Diterpenos de Caurano/farmacologia , Ácido Trifluoracético/farmacologia , Aminoácidos/química , Antineoplásicos/síntese química , Antineoplásicos/química , Apoptose/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Diterpenos de Caurano/química , Relação Dose-Resposta a Droga , Ensaios de Seleção de Medicamentos Antitumorais , Humanos , Estrutura Molecular , Espécies Reativas de Oxigênio/análise , Espécies Reativas de Oxigênio/metabolismo , Relação Estrutura-Atividade , Ácido Trifluoracético/química , Células Tumorais Cultivadas
11.
J Pharm Biomed Anal ; 174: 495-499, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31234040

RESUMO

The study of glycoproteins is a rapidly growing field, which is not surprising considering that approximately 70% of human proteins are glycosylated and that numerous biological functions are associated to the glycosylation. In this work, our interest focused on the heterodimeric human Chorionic Gonadotropin (hCG) glycoprotein that is the specific hormone of the human pregnancy, consisting of an α and a ß subunit, so-called hCGα and hCGß, respectively. This protein possesses a very high structural heterogeneity, essentially due to the presence of 8 glycosylation sites, but also other types of post-translational modifications. In this study, for the first time, the potential of hydrophilic interaction liquid chromatography (HILIC) was investigated to separate the intact hCG isoforms. Three different HILIC stationary phases were tested using an hCG-based drug as standard, a recombinant hCG. For each stationary phase, the effect of the initial mobile phase composition based on ACN/H2O mixture, the slope of the gradient, the content and nature of the acidic additive (formic acid and trifluoroacetic acid (TFA)), and the addition of a volatile salt (ammonium formate) on the retention and the resolution were studied. The best HILIC separation was obtained with the amide column and a mobile phase composed of water/ACN containing 0.1% of TFA. The repeatability in terms of retention times and peak areas was then assessed. Finally, the method was applied to the analysis of a second hCG-based drug obtained from urine of pregnant women. Both drugs gave chromatograms with more than 10 peaks. However, they were significantly different, which demonstrated the potential of HILIC method for hCG isoform fingerprinting.


Assuntos
Gonadotropina Coriônica/química , Cromatografia Líquida/métodos , Gonadotropina Coriônica/urina , Feminino , Formiatos/química , Glicoproteínas/química , Glicosilação , Humanos , Interações Hidrofóbicas e Hidrofílicas , Gravidez , Isoformas de Proteínas/química , Multimerização Proteica , Proteínas Recombinantes , Espectrofotometria Ultravioleta , Ácido Trifluoracético/química
12.
J Chromatogr A ; 1598: 92-100, 2019 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-30961963

RESUMO

A strategy for determining a suitable solvent gradient in silico in preparative peptide separations is presented. The strategy utilizes a machine-learning-based method, called ELUDE, for peptide retention time predictions based on the amino acid sequences of the peptides. A suitable gradient is calculated according to linear solvent strength theory by predicting the retention times of the peptides being purified at three different gradient slopes. The advantage of this strategy is that fewer experiments are needed to develop a purification method, making it useful for labs conducting many separations but with limited resources for method development. The preparative separation of met-enkephalin and leu-enkephalin was used as model solutes on two stationary phases: XBridge C18 and CSH C18. The ELUDE algorithm contains a support vector regression and is pre-trained, meaning that only 10-50 peptides are needed to calibrate a model for a certain stationary phase and gradient. The calibration is done once and the model can then be used for new peptides similar in size to those in the calibration set. We found that the accuracy of the retention time predictions is good enough to usefully estimate a suitable gradient and that it was possible to compare the selectivity on different stationary phases in silico. The absolute relative errors in retention time for the predicted gradients were 4.2% and 3.7% for met-enkephalin and leu-enkephalin, respectively, on the XBridge C18 column and 2.0% and 2.8% on the CSH C18 column. The predicted retention times were also used as initial values for adsorption isotherm parameter determination, facilitating the numerical calculation of overloaded elution profiles. Changing the trifluoroacetic acid (TFA) concentration from 0.05% to 0.15% in the eluent did not seriously affect the error in the retention time predictions for the XBridge C18 column, an increase of 1.0 min (in retention factor, 1.3). For the CSH C18 column the error was, on average, 2.6 times larger. This indicates that the model needs to be recalibrated when changing the TFA concentration for the CSH column. Studying possible scale-up complications from UHPLC to HPLC such as pressure, viscous heating (i.e., temperature gradients), and stationary-phase properties (e.g., packing heterogeneity and surface chemistry) revealed that all these factors were minor to negligible. The pressure effect had the largest effect on the retention, but increased retention by only 3%. In the presented case, method development can therefore proceed using UHPLC and then be robustly transferred to HPLC.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia de Fase Reversa , Aprendizado de Máquina , Peptídeos/isolamento & purificação , Adsorção , Peptídeos/química , Solventes/química , Temperatura , Tempo , Ácido Trifluoracético/química
13.
Methods Mol Biol ; 1943: 1-25, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30838606

RESUMO

Sequence-defined cationic lipo-oligomers containing unsaturated fatty acids are potent nucleic acid carriers that are produced by solid-phase supported synthesis. However, the trifluoroacetic acid (TFA)-mediated removal of acid-labile protecting groups and cleavage from the resin can be accompanied by side products caused by an addition of TFA to the double bonds of unsaturated fatty acids. These TFA adducts are converted into hydroxylated derivatives under aqueous conditions. Here we describe an optimized cleavage protocol (precooling cleavage solution to 4 °C, 20 min cleavage at 22 °C), which minimizes TFA adduct formation, retains the unsaturated hydrocarbon chain character, and ensures high yields of the synthesis.


Assuntos
Ácidos Graxos Insaturados/química , Nanopartículas/química , RNA Interferente Pequeno/genética , Transfecção/métodos , Sequência de Aminoácidos , Aminoácidos/química , Animais , Cátions/química , Linhagem Celular Tumoral , Terapia Genética/métodos , Humanos , Camundongos , Estrutura Molecular , Polimerização , Interferência de RNA , Temperatura , Ácido Trifluoracético/química
14.
Org Lett ; 21(7): 2459-2463, 2019 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-30869905

RESUMO

A handle for the protection of the C-terminus of peptides after cleaving with low concentration of trifluoroacetic acid (2-4%) is reported. The handle prevents polymerization reactions in the convergent condensation of peptidic fragments. Moreover, it is traceless, being removed during the final deprotection step of the peptide synthesis. This cheap and convenient handle is easily attached to the solid support, causing no disturbance to peptide elongation and thus proving to be useful in the convergent synthesis of long peptides.


Assuntos
Fragmentos de Peptídeos/síntese química , Peptídeos/síntese química , Ácido Trifluoracético/química , Sequência de Aminoácidos , Liraglutida , Fragmentos de Peptídeos/química , Peptídeos/química
15.
Molecules ; 24(5)2019 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-30857232

RESUMO

Bisindolyl alkaloids represent a large family of natural and synthetic products that display various biological activities. Among the bisindole compounds, 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles have received little attention. Only two methods have been developed for the construction of the 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindole scaffold thus far, including the classical Fischer indole synthesis conducted by reacting indole-fused cycloheptanone and hydrazines, and the condensation reaction to build the seven-membered ring. Here, we report for the first time a new route to synthesize 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles through intramolecular oxidative coupling of 1,3-di(1H-indol-3-yl)propanes in the presence of PIFA, DDQ and TMSCl with moderate to excellent yields.


Assuntos
Indóis/química , Iodo/química , Indicadores e Reagentes/química , Iodetos/química , Iodobenzenos/química , Estrutura Molecular , Ácido Trifluoracético/química
16.
ACS Comb Sci ; 21(3): 154-157, 2019 03 11.
Artigo em Inglês | MEDLINE | ID: mdl-30640439

RESUMO

The synthesis of different diketomorpholines via N-acyl-3,4-dihydro-2 H-1,4-oxazine-3-carboxylic acids is reported in this article. The key intermediates were prepared using a convenient solid-phase synthesis starting from polymer-supported Ser( tBu)-OH. After subsequent sulfonylation with 4-nitrobenzenesulfonyl chloride (4-Nos-Cl), alkylation with an α-bromoketone, cleavage of the 4-Nos group and acylation with an α-halocarboxylic acids, acid-mediated cleavage from the resin yielded dihydrooxazine-3-carboxylic acids in high crude purities. Depending on the reaction conditions, exposure to base resulted in cyclization to either oxazino[3,4- c][1,4]oxazine-diones or 3-methylidenemorpholine-2,5-diones. Further reaction with triethylsilane-trifluoroacetic acid (TES/TFA) led to olefin reduction, in the case of oxazino[3,4- c][1,4]oxazine-dione with full control of the newly formed stereocenter.


Assuntos
Morfolinas/síntese química , Polímeros/química , Técnicas de Síntese em Fase Sólida/métodos , Acilação , Alquilação , Ácidos Carboxílicos/química , Ciclização , Estrutura Molecular , Nitrobenzenos/química , Oxazinas/química , Silanos/química , Estereoisomerismo , Ácido Trifluoracético/química
17.
Biomacromolecules ; 19(11): 4396-4410, 2018 11 12.
Artigo em Inglês | MEDLINE | ID: mdl-30281286

RESUMO

The conformational analysis of spider dragline silks is difficult because of the amorphous character of the silks. In this article, the fractions of several conformations were determined for three 47-mer peptides, (Glu)4(Ala)6GlyGly12Ala13Gly14GlnGlyGlyTyrGlyGlyLeuGlySerGlnGly25Ala26Gly27-ArgGlyGlyLeuGlyGlyGlnGly35Ala36Gly37(Ala)6(Glu)4, with three underlined 13C-labeled blocks using a 13C CP/MAS NMR method. The conformations of the 13C-labeled sites change significantly depending on the location of the labeled blocks when treated with trifluoroacetic acid, low pH, and freeze-drying. The conformations of Ala36 and Gly37 residues are strongly influenced by the specific conformation of the (Ala)6 sequence at the C-terminal side, but those of other residues, Ala13 and Gly14, and Ala 26 and Gly27, are basically not influenced by the conformations of (Ala)6. Through hydration of the ß-sheet peptide, sharp peaks with random coil could be observed depending on the position of the residue, and this result could be interpreted via the change in the Ramachandran map obtained from the molecular dynamics simulation.


Assuntos
Fibroínas/química , Proteínas de Insetos/química , Espectroscopia de Ressonância Magnética/métodos , Fragmentos de Peptídeos/química , Seda/química , Aranhas/química , Ácido Trifluoracético/química , Animais , Isótopos de Carbono , Liofilização , Concentração de Íons de Hidrogênio , Conformação Molecular , Simulação de Dinâmica Molecular
18.
J Pept Sci ; 24(11): e3130, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30353614

RESUMO

Triisopropylsilane (TIS), a hindered hydrosilane, has long been utilized as a cation scavenger for the removal of amino acid protecting groups during peptide synthesis. However, its ability to actively remove S-protecting groups by serving as a reductant has largely been mischaracterized by the peptide community. Here, we provide strong evidence that TIS can act as a reducing agent to facilitate the removal of acetamidomethyl (Acm), 4-methoxybenzyl (Mob), and tert-butyl (But ) protecting groups from cysteine (Cys) residues in the presence of trifluoroacetic acid (TFA) at 37 °C. The lability of the Cys protecting groups in TFA/TIS (98/2) in this study are in the order: Cys(Mob) > Cys(Acm) > Cys(But ), with Cys(Mob) being especially labile. Unexpectedly, we found that TIS promoted disulfide formation in addition to aiding in the removal of the protecting group. Our results raise the possibility of using TIS in orthogonal deprotection strategies of Cys-protecting groups following peptide synthesis as TIS can be viewed as a potential deprotection agent instead of merely a scavenger in deprotection cocktails based on our results. We also tested other common scavengers under these reaction conditions and found that thioanisole and triethylsilane were similarly effective as TIS in enhancing deprotection and catalyzing disulfide formation. Our findings reported herein show that careful consideration should be given to the type of scavenger used when it is desirable to preserve the Cys-protecting group. Additional consideration should be given to the concentration of scavenger, temperature of the reaction, and reaction time.


Assuntos
Cisteína/química , Peptídeos/síntese química , Silanos/química , Dissulfetos/química , Oxirredução , Peptídeos/química , Ácido Trifluoracético/química
19.
Sensors (Basel) ; 18(10)2018 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-30322092

RESUMO

Quinoxaline-based novel acid-responsive probe Q1 was designed on the basis of a conjugated donor-acceptor (D-A) subunit. Q1 shows colorimetric and fluorometric changes through protonation and deprotonation in dichloromethane. With the addition of the trifluoroacetic acid (TFA), UV-vis absorption spectral changes in peak intensity of Q1 was observed. Moreover, the appearance of a new peaks at 284 nm 434 nm in absorption spectra with the addition of TFA indicating protonation of quinoxaline nitrogen and form Q1.H⁺ and Q1.2H⁺. The emission spectra display appearance of new emission peak at 515 nm. The optical property variations were supported by time resolved fluorescence studies. The energy band gap was calculated by employing cyclic voltammetry and density functional calculations. Upon addition of triethylamine (TEA) the fluorescence emission spectral changes of Q1 are found to be reversible. Q1 shows color changes from blue to green in basic and acidic medium, respectively. The paper strip test was developed for making Q1 a colorimetric and fluorometric indicator.


Assuntos
Colorimetria/métodos , Quinoxalinas/química , Espectrometria de Fluorescência/métodos , Espectrofotometria Ultravioleta/métodos , Cor , Colorimetria/instrumentação , Eletroquímica/métodos , Etilaminas/química , Corantes Fluorescentes/química , Concentração de Íons de Hidrogênio , Nitrilos/química , Prótons , Quinoxalinas/síntese química , Fitas Reagentes/química , Espectrometria de Fluorescência/instrumentação , Ácido Trifluoracético/química
20.
J Chromatogr A ; 1578: 35-44, 2018 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-30340763

RESUMO

The separation mechanism of amino acid enantiomers using a chiral crown ether-bonded stationary phase, CROWNPAK CR-I(+), and acetonitrile (ACN)-rich mobile phases (MPs) was studied. The retention factors of proteinogenic l-amino acids (except proline) formed U-shaped plots against the ACN content in the MP with a sharp increase at a high ACN content, while d-amino acids showed much smaller increases or monotonous decreases in retention within the same range. The use of an acidic, highly organic MP with trifluoroacetic acid (TFA) provided a high enantioselectivity with a short separation time from the contribution of the increased binding of the ammonium group of the analytes to the crown ether functionality of the stationary phase and electrostatic repulsion counteracting the hydrophilic partition mechanism. Optimizing the sample diluent and MP alleviated the peak distortion caused by a moving water band that accompanied the hydrophilic interaction liquid chromatography-like elution conditions. The liquid chromatography/time-of-flight mass spectrometry method with the optimized MP - ACN/ethanol/water/TFA = 80/15/5/0.5 (v/v/v/v) - enabled the determination of eighteen pairs of proteinogenic amino acid enantiomers within 10 min. The conditions also provided the following advantages: (i) fast and highly reproducible separations under isocratic conditions, (ii) high sensitivity and low backpressure using the MP with a high organic content, and (iii) highly reliable peak identification by combining two columns (CR-I(+) and CR-I(-)), reversing the elution orders of the enantiomers.


Assuntos
Aminoácidos/isolamento & purificação , Técnicas de Química Analítica/métodos , Cromatografia Líquida , Éteres de Coroa/química , Espectrometria de Massas , Acetonitrilos/química , Aminoácidos/química , Interações Hidrofóbicas e Hidrofílicas , Estereoisomerismo , Ácido Trifluoracético/química , Água/química
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