L-leucine Methyl Ester Research Articles

Synthesis and Oxidative Degradation of Leucine-Based Poly(diacylhydrazine).

Diacylhydrazine is thermally and chemically stable, and it remains inert to oxygen even at high temperatures. However, it is rapidly oxidized by sodium hypochlorite, leading to its decomposition into carboxylic acid and nitrogen gas. In the synthesis of a novel poly(diacylhydrazine) as an oxidatively degradable polymer, L-leucine methyl ester is acylated by terephthaloyl chloride. Subsequent hydrazination yields a bishydrazide monomer. The oxidative coupling polymerization of this monomer produces poly(diacylhydrazine). The molecular structures of the products are confirmed by an 1H NMR analysis. A polymodal molecular weight distribution and a large polydispersity index are observed by GPC in all cases. A 10% weight loss temperature is noted at 286 °C in air by TGA. The obtained polymer is not oxidized by oxygen. No glass transition is observed below the decomposition temperature. Upon the treatment of the poly(diacylhydrazine) with sodium hypochlorite solution, decomposition occurs rapidly, resulting in monomeric carboxylic acid and nitrogen gas. The L-leucine-based poly(diacylhydrazine) serves as a novel on-demand degradable polymer with high levels of thermal and chemical stability during usage.

Antiparasitic activity, DNA/BSA binding interaction, molecular docking and DFT studies of mesogenic l-leucine based Schiff base and its derivatize Cu(II) and Zn(II) complexes

A new copper(II) and zinc(II) complexes derived from smectogenic l-leucine methyl ester Schiff base ligand have been successfully synthesized and characterized by various techniques. The ligand is found to exhibit SmA mesophase but Cu(II) and Zn(II) complexes do not. The biological importances of the compounds are evaluated using photophysical techniques to comprehend the binding interaction with biomolecules viz., CT-DNA and BSA. The compounds were assessed for their in-vitro anti-parasitic efficacy against Leishmania donovani by MTT assay. Notably, all the compounds exhibited IC50 in the range of 31.29 to 57.01 (μM). Molecular docking was performed in order to establish the nature of binding ability of the compounds with CT-DNA. The computational studies indicate that the CuL2 has the maximum DNA interaction as revealed from libDock score. The Density Functional Theory (DFT) study was performed in order to ascertain the optimized geometry of the compounds using LanL2DZ and 6–31 G (d, p) basis set with meta-hybrid Truhlar's functional M06–2X.

Synthesis of hybrid compounds of 24-nor-lupane triterpene and amino acids via C-28 amide linkage

Betulinic acid derivatives exhibit different biological activity against diversified targets, such as anticarcinogenic activity in experimental animals, anti-HIV, antihyperglycemia, and anti-inflammatory in humans. In this work, we investigated the synthetic procedure of 24-nor-3-oxo-20(29)-lupen-28-oic acid (1) derivatives. Starting from compound 1 and L-leucine methyl ester, we proceeded with amidification, reduction, and hydrolysis under basic conditions. Finally, three hybrid compounds were successfully synthesised and elucidated with spectral means.

Differential production of interleukin‐6 and tumor necrosis factor‐α in primary rat astrocyte cultures using two distinct methods of microglia elimination

AbstractHepatic encephalopathy (HE) is a neurocognitive disorder due to acute or chronic liver failure as well as portosystemic bypass. Both neuroinflammation and oxidative stress have been strongly implicated in the pathogenesis of HE. An increasing body of evidence suggests that in the development of these mechanisms astrocytes may be involved. With regard of HE, this aspect of astrocytes is, however, neglected. While several studies focus on astrocytes related to the above‐mentioned pathological processes, the applied in vitro models are generated by diverse methods, which make the results difficult to compare with each other. In addition, these astrocyte cultures frequently contain microglia as well, complicating the interpretation of results. Therefore, we applied enriched primary rat astrocyte cultures generated by microglia elimination via shaking or the combination of cytosine β‐d‐arabinofuranoside hydrochloride (AraC) and l‐leucine methyl ester (LME). We examine whether some HE‐relevant pathological factors, such as ammonia, manganese (Mn), lipopolysaccharide (LPS), and H2O2 could elicit oxidative stress and cytokine production in astrocytes. Mn exposure increased the oxidative stress in astrocytes in a time‐dependent manner; furthermore, we could detect tumor necrosis factor (TNF)‐α production in both cultures at resting state. In addition, it was around 10‐fold higher in the cultures after shaking. LPS increased TNF‐α secretion in cultures after shaking, but not in cultures after AraC + LME treatment. In contrast, interleukin (IL)‐6 was detectable only in the AraC + LME‐treated cultures. In conclusion, we have demonstrated that HE‐relevant factors evoke oxidative stress and cytokine production, albeit depending on the elimination method used.

Ionic liquids derived from α-amino acid ester salts as potent green corrosion inhibitors for mild steel in 1M HCl

In 1 M HCl solution, three selected amino acid ester salt based ionic liquids ([AAE][Sac] ILs), namely L-Phenyl Alanine methyl ester saccharinate ([PheME][Sac]), L-Leucine methyl ester saccharinate ([LeuME][Sac]), and L-Alanine methyl ester saccharinate ([AlaME][Sac]) under static conditions were examined as potent green corrosion inhibitors for mild steel by means of electrochemical measurements, weight loss, FT-IR spectroscopy, contact angle measurement, UV–vis spectroscopy, SEM/EDAX study, quantum chemical calculations and Monte Carlo (MC) simulation studies. 1H NMR, and FTIR spectroscopy has confirmed the structure of obtained ILs. The investigations were done in the temperature range of 303–353 K. [AAE][Sac] ILs are assessed as an efficient steel corrosion inhibitors in 1 M HCl up to 333 K but have less inhibiting properties above 333 K i.e., 343 and 353 K. Among the [AAE][Sac] ILs analysed, [PheME][Sac] showed the greatest inhibition efficiency and obey the order as: [PheME][Sac] > [LeuME][Sac] > [AlaME][Sac]. Polarization measurements showed all the [AAE][Sac] ILs tested to be mixed-type inhibitors. The adsorption of the examined [AAE][Sac] ILs obeyed the Langmuir adsorption isotherm perfectly. The theoretical descriptors provided by quantum chemical calculations and advanced MC simulation also reinforced the experimental conclusions adequately.

Novel skin permeation enhancers based on amino acid ester ionic liquid: Design and permeation mechanism

This study developed novel ionic liquids (ILs) based on amino acids. We first screened 15 methyl amino acid ester hydrochlorides ([AAC1]Cl) for their skin permeation enhancements using 5-Fluorouracil (5-Fu) and Hydrocortisone (HC) as model drugs. Glycine methyl ester hydrochloride ([GlyC1]Cl), L-proline methyl ester hydrochloride ([L-ProC1]Cl), and L-leucine methyl ester hydrochloride ([L-LeuC1]Cl) were selected, and their ester sites were modified with different carbon chains (C8 and C12). The resulting ILs showed improved permeation to the two drugs. TEWL and CLSM assays revealed the moderation effects of the modified ILs on skin barrier function, whereas L-proline dodecyl ester hydrochloride ([ProC12]Cl) and L-leucine dodecyl ester hydrochloride ([L-LeuC12]Cl) exhibited the strongest activities. Permeation mechanisms were further investigated by ATR-FTIR, solid-NMR, SEM, and TEM analyses. The results suggested that [L-ProC12]Cl and [L-LeuC12]Cl combined the advantages of amino acid esters and IL solvent and could interact with the intercellular lipid domain by the multi-functions of lipid fluidization and lipid extraction, which were observed in a dosage- and time-dependent manner. Additionally, pathological examination suggested that the amino acid ester-based ILs (AAE-ILs) had good biocompatibility. In conclusion, this study has generated novel chemical penetration enhancers (CPEs) based on AAE-ILs and may be potentially utilized in drug transdermal delivery systems (TDDSs).

Preparation and application of mesoporous core-shell nanosilica using leucine derivative as template in effective drug delivery

Core-shell structured mesoporous silica nanoparticles have been firstly synthesized with the new template from L-leucine methyl ester hydrochloride (H-Leu-OMe·HCl). LMSNs were characterized by transmission electron microscopy (TEM), nitrogen adsorption/desorption, and small-angle X-ray diffraction (SAXRD), demonstrating a well-ordered mesostructure. After loading doxorubicin hydrochloride (Dox) into pores, considerable loading capacity of 30.5% and favorable cumulative release amount were obtained. MTT assay suggested that Dox-loaded LMSNs demonstrated great promise to anti-tumor. The use of MSNs with the synthesized template, as a drug delivery carrier, will extend the pharmaceutical applications of silica materials.

Synthesis and biological evaluation of amino acid derivatives containing chrysin that induce apoptosis

A series of chrysin amino acid derivatives were synthesized to evaluate for their antiproliferative activities against several cancer cell lines. Among the compounds tested, N-(2-((5-hydroxy-4-oxo-2-phenyl-4H-chromen-7-yl)oxy)octanoyl)-L-leucine methyl ester(5d) presented a good anti-proliferative activity in MDA-MB-231 and MCF-7 cells. Flow cytometry analysis showed that 5d induced apoptosis and prolonged cell cycle progression in MDA-MB-231 and MCF-7 cells. Western blot analysis showed that 5d significantly inhibited Akt phosphorylation (Ser473) in MDA-MB-231 and MCF-7 cells. In addition, 5d treatment markedly downregulated Bcl-2 and upregulated Bax in a dose-dependent manner. In vitro caspase activation assay showed that 5d induced apoptosis of MDA-MB-231 cells by enhancing caspase 3/7 activity. The regulatory effect of 5d on apoptosis of MDA-MB-231 and MCF-7 cells may be induced by mitochondrial apoptosis pathway. This study is of great significance for designing and developing more effective chrysin amino acid derivatives.

A possible role of microglia-derived nitric oxide by lipopolysaccharide in activation of astroglial pentose-phosphate pathway via the Keap1/Nrf2 system

BackgroundToll-like receptor 4 (TLR4) plays a pivotal role in the pathophysiology of stroke-induced inflammation. Both astroglia and microglia express TLR4, and endogenous ligands produced in the ischemic brain induce inflammatory responses. Reactive oxygen species (ROS), nitric oxide (NO), and inflammatory cytokines produced by TLR4 activation play harmful roles in neuronal damage after stroke. Although astroglia exhibit pro-inflammatory responses upon TLR4 stimulation by lipopolysaccharide (LPS), they may also play cytoprotective roles via the activation of the pentose phosphate pathway (PPP), reducing oxidative stress by glutathione peroxidase. We investigated the mechanisms by which astroglia reduce oxidative stress via the activation of PPP, using TLR4 stimulation and hypoxia in concert with microglia.MethodsIn vitro experiments were performed using cells prepared from Sprague–Dawley rats. Coexisting microglia in the astroglial culture were chemically eliminated using l-leucine methyl ester (LME). Cells were exposed to LPS (0.01 μg/mL) or hypoxia (1 % O2) for 12–15 h. PPP activity was measured using [1-14C]glucose and [6-14C]glucose. ROS and NO production were measured using 2′,7′-dichlorodihydrofluorescein diacetate and diaminofluorescein-FM diacetate, respectively. The involvement of nuclear factor-erythroid-2-related factor 2 (Nrf2), a cardinal transcriptional factor under stress conditions that regulates glucose 6-phosphate dehydrogenase, the rate-limiting enzyme of PPP, was evaluated using immunohistochemistry.ResultsCultured astroglia exposed to LPS elicited 20 % increases in PPP flux, and these actions of astroglia appeared to involve Nrf2. However, the chemical depletion of coexisting microglia eliminated both increases in PPP and astroglial nuclear translocation of Nrf2. LPS induced ROS and NO production in the astroglial culture containing microglia but not in the microglia-depleted astroglial culture. LPS enhanced astroglial ROS production after glutathione depletion. U0126, an upstream inhibitor of mitogen-activated protein kinase, eliminated LPS-induced NO production, whereas ROS production was unaffected. U0126 also eliminated LPS-induced PPP activation in astroglial–microglial culture, indicating that microglia-derived NO mediated astroglial PPP activation. Hypoxia induced astroglial PPP activation independent of the microglia–NO pathway. Elimination of ROS and NO production by sulforaphane, a natural Nrf2 activator, confirmed the astroglial protective mechanism.ConclusionsAstroglia in concert with microglia may play a cytoprotective role for countering oxidative stress in stroke.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0564-0) contains supplementary material, which is available to authorized users.

Hemicucurbiturils as receptors in extraction and transport of some amino acids

The molecular recognition properties of hemicucurbit[6]uril (HemiCB[6]) and hemicucurbit[12]uril (HemiCB[12]) towards a series of amino acid native and methyl esters (L-phenylalanine, L-leucine, L-valine, L-cysteine, L-tryptophan, L-isoleucine, L-phenylalanine methyl ester hydrochloride (L-PheOMe), L-tyrosine methyl ester hydrochloride (L-TyrOMe), L-valine methyl ester hydrochloride (L-ValOMe), L-leucine methyl ester hydrochloride (L-LeuOMe), L-serine methyl ester hydrochloride (L-SerOMe) and L-cysteine methyl ester hydrochloride (L-CysOMe) were investigated. In this respect, by means of liquid–liquid extraction, a series of amino acid native and methyl esters were extracted from an aqueous phase (pH = 5.5) into a chloroform phase as ion pairs in the presence of tropaeolin 00 as counterion. Based on results obtained in extraction experiments, the active transport assisted by pH gradient of amino acids as ion pairs through chloroform liquid membrane employing HemiCB[6] as carrier was performed. Both receptors used in experiments exhibited extractability towards amino acids under study. From the results obtained, one can observed the good affinity of both receptors, hemiCB[6, 12], towards hydrophobic amino acids (L-PheOMe, L-LeuOMe and L-ValOMe)). It was emphasised that the structure of hemicucurbiturils and amino acids together with the anion nature, and pH have influenced the experimental results.

Selective Depletion of Microglia from Cerebellar Granule Cell Cultures Using L-leucine Methyl Ester.

Microglia, the resident immunocompetent cells of the CNS, play multifaceted roles in modulating and controlling neuronal function, as well as mediating innate immunity. Primary rodent cell culture models have greatly advanced our understanding of neuronal-glial interactions, but only recently have methods to specifically eliminate microglia from mixed cultures been utilized. One such technique - described here - is the use of L-leucine methyl ester, a lysomotropic agent that is internalized by macrophages and microglia, wherein it causes lysosomal disruption and subsequent apoptosis(13,14). Experiments using L-leucine methyl ester have the power to identify the contribution of microglia to the surrounding cellular environment under diverse culture conditions. Using a protocol optimized in our laboratory, we describe how to eliminate microglia from P5 rodent cerebellar granule cell culture. This approach allows one to assess the relative impact of microglia on experimental data, as well as determine whether microglia are playing a neuroprotective or neurotoxic role in culture models of neurological conditions, such as stroke, Alzheimer's or Parkinson's disease.

High specific activity tritium labelling of biologically active small peptides and a related analogue

Small peptides are often endowed with useful biological activity and two of these are l-leucyl-l-leucine methyl ester (1) and glycyl-l-glutamine (2). To advance research in this important area, they were tritiated at high specific activity. [3H] l-Leucyl-l-leucine methyl ester (5) was prepared by the reaction of [3H] l-leucine methyl ester (4) with BOC-Leu-OSu. [3H] Glycyl-l-glutamine (7) was synthesized by the reaction of [3H] l-glutamine with BOC-Gly-OSu. Biosynthesized from l-lysine and l-methionine, related small molecule l-propionylcarnitine taurinamide (3) was also tritiated, employing [3H] taurine (10) and l-propionylcarnitine acid chloride (9).

Chiral discrimination by ionic liquids: impact of ionic solutes.

Chiral ionic liquids hold promise in many asymmetric applications. This study explores the impact of ionic solutes on the chiral discrimination of five amino acid methyl ester-based ionic liquids, including L- and D-alanine methyl ester, L-proline methyl ester, L-leucine methyl ester, and L-valine methyl ester cations combined with bis(trifluoromethanesulfonimide) anion. Circularly polarized luminescence spectroscopy was used to study the chiral discrimination by measuring the racemization equilibrium of a dissymmetric europium complex, Eu(dpa)3(3-) (where dpa = 2,6-pyridinedicarboxylate). The chiral discrimination measured was dependent on the concentration of Eu(dpa)3(3-) and this concentration-dependence was different in each of the ionic liquids. Ionic liquids with L-leucine methyl ester and L-valine methyl ester even switched enantiomeric preference based on the solute concentration. Changing the cation of the Eu(dpa)3(3-) salt from tetrabutylammonium to tetramethylammonium ion also affected the chiral discrimination demonstrated by the ionic liquids.

Synthesis and biological activities of some new (Nα-dinicotinoyl)-bis-L-leucyl linear and macrocyclic peptides.

A series of linear and macrocyclic peptides 3–12 were synthesized using 3,5-pyridinedicarboxylic acid (1) as starting material and screened for their antimicrobial, anti-inflammatory and anticancer activities. Bis-ester 3 was prepared from 1 and l-leucine methyl ester. Hydrazinolysis and hydrolysis of dipeptide methyl ester 3 with hydrazine hydrate or 1 N sodium hydroxide afforded compounds 4 and 5, respectively. Cyclization of the dipeptide 5 with l-lysine methyl ester afforded cyclic pentapeptide ester 6. Compounds 7–9 were synthesized by reacting hydrazide 4 with phthalic anhydride, 1,8-naphthalene anhydride or acetophenone derivatives. Treatment of acid hydrazide 4 with aromatic aldehydes or tetraacid dianhydrides afforded the corresponding bis-dipeptide hydrazones 10a–e and macrocyclic peptides 11 and 12, respectively. The structures of newly synthesized compounds were confirmed by IR, 1H-NMR, MS spectral data and elemental analysis. The detailed synthesis, spectroscopic data, biological and pharmacological activities of the synthesized compounds was reported.

Crystal structures and magnetic properties of a set of dihalo-bridged oxalamidato copper(II) dimers.

A set of four copper(ii) complexes, and (X = Cl, Br; = N-(l-leucine methyl ester)-N'-((2-pyridin-2-yl)methyl)oxalamide and = N-benzyl-N'-((2-pyridin-2-yl)methyl)oxalamide), have been synthesized and characterized by X-ray structural analysis, electron paramagnetic resonance (EPR) spectroscopy on single crystals and by SQUID magnetization measurements. X-ray diffraction studies show one-dimensional hydrogen bonded networks of dimeric copper(ii)-complexes bridged by two halide ions and with the two metal centers 3.44-3.69 Å apart. The geometry at each copper(ii) atom is ideal or near ideal square pyramidal. EPR and SQUID studies indicate that all complexes exhibit weak antiferromagnetic interactions between the Cu(ii) paramagnetic centers, with exchange parameter |J| ∼ 1 cm(-1). Magneto-structural comparisons among similar dihalo-bridged Cu(ii) dinuclear complexes are also provided, and a possible correlation has been established.

Interactions of some protonated α-amino acid methyl esters with hexaethyl p-tert-butylcalix[6]arene hexaacetate in nitrobenzene saturated with water

The exchange extraction constants corresponding to the general equilibrium C+(aq) + 1·Cs+(nb) ⇔ 1·C+ (nb) + Cs+(aq) occurring in the two-phase water–nitrobenzene system (C+ = protonated α-amino acid methyl ester, 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated on the basis of extraction experiments and γ-activity measurements. Further, the stability constants of the 1·C+ cationic complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated l-tryptophan methyl ester < protonated l-phenylalanine methyl ester < protonated l-leucine methyl ester < protonated l-methionine methyl ester < protonated l-valine methyl ester.

Complexation of some protonated α-amino acid methyl esters with benzo-18-crown-6 in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C+(aq)+1·Na+(nb)⇔⟺1·C+ (nb)+Na+ (aq) taking place in the two-phase water–nitrobenzene system (C+=protonated α-amino acid methyl ester, 1=benzo-18-crown-6; aq=aqueous phase, nb=nitrobenzene phase) were evaluated. Furthermore, the stability constants of the 1·C+ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated l-tryptophan methyl ester<protonated l-phenylalanine methyl ester<protonated l-leucine methyl ester, protonated l-methionine methyl ester<protonated l-valine methyl ester.

Chiroptical Study of Chiral Discrimination by Amino Acid Based Ionic Liquids

The chiral discrimination ability of amino acid based chiral ionic liquids is studied using chiroptical luminescence techniques. A racemic mixture of dissymmetric europium tris(2,6-pyridinedicarboxylate) complexes are dissolved in five chiral ionic liquids, including l- and d-alanine methyl ester bis(trifluoromethanesulfonimide), l-leucine methyl ester bis(trifluoromethanesulfonimide), l-proline methyl ester bis(trifluoromethanesulfonimide), and tetrabutylammonium l-alanate. Circularly polarized luminescence spectra are measured for the samples over the 283-323 K temperature range. Analysis of the spectroscopic results shows that the amino acid methyl ester chiral ionic liquids show discrimination with a preference (handedness) that corresponds to the stereoisomer (l- vs d-). Most of the chiral ionic liquids show enthalpically dominated discrimination, but l-leucine methyl ester bis(trifluoromethanesulfonimide) shows entropically dominated chiral discrimination.

Saturated long-chain fatty acids activate inflammatory signaling in astrocytes.

This study describes the effects of long-chain fatty acids on inflammatory signaling in cultured astrocytes. Data show that the saturated fatty acid palmitic acid, as well as lauric acid and stearic acid, trigger the release of TNFα and IL-6 from astrocytes. Unsaturated fatty acids were unable to induce cytokine release from cultured astrocytes. Furthermore, the effects of palmitic acid on cytokine release require Toll-like receptor 4 rather than CD36 or Toll-like receptor 2, and do not depend on palmitic acid metabolism to palmitoyl-CoA. Inhibitor studies revealed that pharmacologic inhibition of p38 or p42/44 MAPK pathways prevents the pro-inflammatory effects of palmitic acid, whereas JNK and PI3K inhibition does not affect cytokine release. Depletion of microglia from primary astrocyte cultures using the lysosomotropic agent l-leucine methyl ester revealed that the ability of palmitic acid to trigger cytokine release is not dependent on the presence of microglia. Finally, data show that the essential ω-3 fatty acid docosahexaenoic acid acts in a dose-dependent manner to prevent the actions of palmitic acid on inflammatory signaling in astrocytes. Collectively, these data demonstrate the ability of saturated fatty acids to induce astrocyte inflammation in vitro. These data thus raise the possibility that high levels of circulating saturated fatty acids could cause reactive gliosis and brain inflammation in vivo, and could potentially participate in the reported adverse neurologic consequences of obesity and metabolic syndrome.

Different EDC/NHS Activation Mechanisms between PAA and PMAA Brushes and the Following Amidation Reactions

Infrared spectroscopy was applied to investigate the well-known EDC/NHS (N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide/N-hydroxysuccinimide) activation details of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) brushes grafted on porous silicon. Succinimidyl ester (NHS-ester) is generally believed to be the dominant intermediate product, conveniently used to immobilize biomolecules containing free primary amino groups via amide linkage. To our surprise, the infrared spectral details revealed that the EDC/NHS activation of PMAA generated anhydride (estimated at around 76% yield and 70% composition), but not NHS-ester (around 5% yield and 11% composition) under the well-documented reaction conditions, as the predominant intermediate product. In contrast, EDC/NHS activation of PAA still follows the general rule, i.e., the expected NHS-ester is the dominant intermediate product (around 45% yield and 57% composition), anhydride the side product (40% yield and 28% composition), under the optimum reaction conditions. The following amidation on PAA-based NHS-esters with a model amine-containing compound, L-leucine methyl ester, generated approximately 70% amides and 30% carboxylates. In contrast, amidation of PAA- or PMAA-based anhydrides with L-leucine methyl ester only produced less than 30% amides but more than 70% carboxylates. The above reaction yields and percentage compositions were estimated by fitting the carbonyl stretching region with 5 possible species, NHS-ester, anhydride, N-acylurea, unreacted acid, unhydrolyzed tert-butyl ester, and using the Beer-Lambert law. The different surface chemistry mechanisms will bring significant effects on the performance of surface chemistry-derived devices such as biochips, biosensors, and biomaterials.