Protonation Equilibria of Some Selected α-Amino Acids in DMSO–Water Mixture and Their Cu(II)-Complexes

The protonation constants of some α-amino acids (glycine (Gly), l-alanine (Ala), l-valine (Val), l-serine (Ser), l-leucine (Leu) and l-isoleucine (Ile)) were studied in water and DMSO–water solution mixtures containing 30, 50 and 70 vol-% DMSO; in addition the complex formation equilibria of their copper(II) complexes were studied by potentiometric technique using a combined pH electrode system calibrated in concentration units of the hydrogen ion at 25 ± 0.1 °C under a nitrogen atmosphere, and at an ionic strength of 0.10 mol·dm^?3 NaNO₃. The protonation constants and the overall stability constants of copper(II) complexes were influenced by changes in solvent composition, and their variations are discussed in terms of solvent and structural properties.     

Volumetric Properties of l-Alanine and l-Serine in Aqueous N,N-Dimethylformamide Solutions at 298.15 K

The densities of l-alanine and l-serine in aqueous solutions of N,N-dimethylformamide (DMF) have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes $ (V_{\phi } ) $ ( V ? ) , standard partial molar volumes $ (V_{\phi }^{0} ) $ ( V ? 0 ) , standard partial molar volumes of transfer $ (\Updelta_{\text{tr}} V_{\phi }^{0} ) $ ( Δ tr V ? 0 ) and hydration numbers have been determined for the amino acids. The $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 values of l-serine are positive which suggest that hydrophilic–hydrophilic interactions between l-serine and DMF are predominant. The –CH₃ group of l-alanine has much more influence on the volumetric properties and the $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 have smaller negative values. The results have been interpreted in terms of the cosphere overlap model.     

Study of the interaction between ethanol and natural amino acids containing ionic side groups in water at T = 298.15 K

The enthalpies of solution of l-α-aspartic acid, l-α-glutamic acid, l-α-arginine, l-α-lysine, and l-α-histidine have been measured in aqueous ethanol solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of amino acids in water–ethanol solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer’s formalism. These values were interpreted in the terms of the ionic or no polar effect of the side chains of l-α-amino acids on their interactions with a molecule of ethanol in water.     

Effect of Cofactor Folate on the Growth of Corynebacterium glutamicum SYPS-062 and l-Serine Accumulation

The direct fermentative production of l-serine from sugar has attracted increasing attention. Corynebacterium glutamicum SYPS-062 can directly convert sugar to l-serine. In this study, the effects of exogenous and endogenous regulation of cofactor folate on C. glutamicum SYPS-062 growth and l-serine accumulation were investigated. For exogenous regulation, the inhibitor (sulfamethoxazole) or precursor (p-aminobenzoate) of folate biosynthesis was added to the medium, respectively. For endogenous regulation, the gene (pabAB) that encodes the key enzyme of folate biosynthesis was knocked out or overexpressed to obtain the recombinant C. glutamicum SYPS-062 ΔpabAB and SYPS-062(pJC-tac-pabAB), respectively. The results indicated that decreased levels of cofactor folate supported l-serine accumulation, whereas increased levels of cofactor folate aided in cell growth of C. glutamicum SYPS-062. Thus, this study not only elucidated the role of folate in C. glutamicum SYPS-062 growth and l-serine accumulation, but also provided a novel and convenient approach to regulate folate biosynthesis in C. glutamicum.     

Improved synthesis of rupintrivir

An improved synthesis of rupintrivir (AG7088) was accomplished using three amino acids (L-glutamic acid, D-4-fluorophenylalanine, and L-valine) as the building blocks. The key fragment ketomethylene dipeptide isostere was constructed with the valine derivative and phenylpropionic acid derivative, followed by coupling with a lactam derivative and an isoxazole acid chloride to provide AG7088 totally in eight steps.     

Specific features of the reaction of l-cysteine with pyridoxal and N-pyridoxylidene-β-alanine

The mechanisms of condensation of l-cysteine, l-methionine, and l-serine with pyridoxal and of transaldimination of N-pyridoxylidene-??-alanine with l-cysteine were studied by the kinetic method. Unlike methionine and serine, the condensation of cysteine with pyridoxal and transaldimination with Npyridoxylidene-??-alanine involves intermediate formation of stable product having a thiazolidine ring. Its structure was determined by elemental analysis, UV, and IR spectroscopy, and quantum-chemical calculations. The thiazolidine fragment in the pyridoxal condensation product with l-cysteine is turned through an angle of ??90° with respect to the pyridine ring plane due to mutual repulsion of the negatively charged oxygen atom in the ortho position of the pyridine ring and sulfur and nitrogen atoms in the thiazolidine ring.     

The yjjN of E. coli codes for an l-galactonate dehydrogenase and can be used for quantification of l-galactonate and l-gulonate

Escherichia coli is able to utilize l-galactonate as a sole carbon source. A metabolic pathway for l-galactonate catabolism is described in E. coli, and it is known to be interconnected with d-galacturonate metabolism. The corresponding gene encoding the first enzyme in the l-galactonate pathway, l-galactonate-5-dehydrogenase, was suggested to be yjjN. However, l-galactonate dehydrogenase activity was never demonstrated with the yjjN gene product. Here, we show that YjjN is indeed an l-galactonate dehydrogenase having activity also for l-gulonate. The K _m and k _cat for l-galactonate were 19.5?±?0.6 mM and 0.51?±?0.03 s^?1, respectively. In addition, YjjN was applied for a quantitative detection of the both of these substances in a coupled assay. The detection limits for l-galactonate and l-gulonate were 1.65 and 10 μM, respectively.     

Partial Molar Volumes of l-Serine and l-Threonine in Aqueous Ammonium Sulfate Solutions at (278.15, 288.15, 298.15, and 308.15) K

In this study, the partial molar volumes of l-serine and l-threonine in aqueous solutions of ammonium sulfate at (0.0, 0.1, 0.3, 0.7, and 1.0) mol·kg^?1 are reported between 278.15 and 308.15 K. Transfer volumes and hydration numbers were obtained, which are larger in l-serine than in l-threonine. Dehydration of the amino acids is observed, rising with the temperature and salt molality. The data suggest that interactions between ions and charged/hydrophilic groups are predominant, and by applying the McMillan and Mayer formalism, it was concluded that they are mainly pair wise. The combination of the data presented in this study with solubility and molecular dynamics data suggests a stronger interaction of the ammonium cation with the zwitterionic centers of the amino acids when compared to the interactions of those centers with the sulfate anion.     

Gas-phase basicities of serine and dipeptides of serine and glycine

The gas-phase basicities of serine and dipeptides containing amino acid residues of serine and glycine were determined by proton transfer reactions in a Fourier transform ion cyclotron resonance mass spectrometer. The gas-phase basicity (GB) of L-serine was found to be 205.9 kcal/mol, with addition of a hydroxymethyl group (?CH₂OH) increasing the basicity by 4.5 kcal/mol relative to the simplest amino acid glycine (GB = 201.4 kcal/mol). This is attributed to a combination of intramolecular hydrogen bonding, induction, and symmetry effects. For the dipeptides, addition of a hydroxymethyl group does not result in a large increase in basicity relative to the basicity of glycylglycine (GB = 208.0 kcal/mol). The gas-phase basicities determined for glycyl-l-serine, l-serylglycine, and l-sery-l-serine are 209.3,210.6, and 210.9 kcal/mol, respectively. In comparison to glycylglycine, addition of the hydroxymethyl group at the N terminus has a greater impact on basicity than its placement at the C terminus. These data suggest that the protonation site for these dipeptides is the N-terminal amino nitrogen.     

Exploiting thermodynamic data to optimize the enantioseparation of underivatized amino acids in ligand exchange capillary electrophoresis

Stereoselective amino acid analysis has increasingly moved into the scope of interest of the scientific community. In this work, we report a study on the chiral separation of underivatized d,l-His by ligand exchange capillary electrophoresis (LECE), utilizing accurate ex ante calculations. This has been obtained by the addition to the background electrolytes (BGE) of NaClO₄ which renders the separations “all in solution processes”, allowing to accurately calculate in advance the concentrations of the species present in solution and to optimize the system performances. To this aim, the formation of ternary complexes of Cu²⁺ ion and l-lysine (l-Lys) or l-ornithine (l-Orn) with l- and d-histidine (His), and histamine (Hm) have been studied by potentiometry and calorimetry at 25 °C and with 0.1 mol dm^?3 (KNO₃) in aqueous solution. The ternary species [Cu(L)(l-His)H]⁺ and [Cu(L)(d-His)H]⁺ (where L?=?l-Lys or l-Orn) show a slight but still detectable stereoselectivity, and the determination of ΔH° and ΔS° values allowed the understanding of the factors which determine this phenomenon. The stereoselectivity showed by the protonated ternary species has been exploited to chirally separate d,l-His in LECE, by using the binary complexes of copper(II) with l-Lys or l-Orn as background electrolytes added with the appropriate amounts of NaClO₄.

Sensitive chemiluminescence method for the determination of glutathione, l-cysteine and 6-mercaptopurine

Glutathione (GSH), l-cysteine (l-Cys) and 6-mercaptopurine (6-MP) inhibit the CL reaction of luminol–H₂O₂ catalyzed by gold colloids. In order to explore this, GSH, l-Cys and 6-MP were injected into the chemiluminescence system of luminol and H₂O₂ catalyzed by gold colloids. The results showed that gold colloids interact with GSH, l-Cys and 6-MP and decrease the CL emission. Based on this phenomenon, a simple, sensitive and convenient flow injection CL method was developed for the determination of GSH, l-Cys and 6-MP. This method provides a novel, and effective CL assay for GSH, l-Cys and 6-MP that has been applied to the determination of GSH in human serum.     

Cis-Cycloprolylprolin-Anion-ein konfigurationsstabiles Carbanion

The racemisation ofcyclo-(l-Pro?l-Pro) (2) with metal amides in liq. ammonia was examined. The K-kation causes more extensive racemisation than Na-kation, which in turn is more effective than Li⁺. This, the racemisation of2 int-butyl alcohol with K⁺C₆H₅O^? and the data gained from corresponding deuterated medium show that the racemisation of2 proceeds in two steps: in the first, the less stabletrans-cyclo-(l-Pro?d-Pro) (3) is formed, followed by the rapid conversion of3 to a mixture ofcyclo-(l-Pro?l-Pro) andcyclo-(d-Pro?d-Pro) in the second step.     

In vitro and in silico inhibition of angiotensin-converting enzyme by carbohydrates and cyclitols

Fifteen carbohydrates (d-mannose, d-glucose, d-galactose, methyl-α-d-glucose, l-rhamnose, d-xylose, d-fructose, d-arabinose, dulcitol, mannitol, β-maltose, α-lactose, melibiose, sucrose, and raffinose) and four cyclitols [l-(+)-bornesitol, myo-inositol, per-O-acetyl-1-l-(+)-bornesitol, and quinic acid] were assayed for in vitro ACE inhibition. Of these molecules, per-O-Acetyl-1-l-(+)-bornesitol, quinic acid, methyl-α-d-glucose, d-rhamnose, raffinose, and the disaccharides were determined to be either inactive or weak ACE inhibitors, whereas l-(+)-bornesitol, d-galactose, d-glucose, and myo-inositol exhibited significant ACE inhibition. Molecular docking studies were performed to investigate interactions between active compounds and human ACE (Protein Data Bank, PDB 1O83). The results of various calculations showed that all active sugars bind to the same enzyme region, which is a tunnel directed towards the active site. With the exception of myo-inositol (K _i = 13.95 μM, IC₅₀ = 449.2 μM), the active compounds presented similar K _i and IC₅₀ values. d-Galactose (K _i = 19.6 μM, IC₅₀ = 35.7 μM) and l-(+)-bornesitol (K _i = 25.3 μM, IC₅₀ = 41.4 μM) were the most active compounds, followed by d-glucose (K _i = 32.9 μM, IC₅₀ = 85.7 μM). Our docking calculations are in agreement with the experimental data and show a new binding region for sugar-like molecules, which may be explored for the development of new ACE inhibitors.     

Conductometric and fluorescence probe investigations of molecular interactions between dodecyltrimethylammonium bromide and dipeptides

The effect of five dipeptides (glycylglycine, glycyl-l-valine, glycyl-l-leucine, glycyl-l-glutamine, and l-alanyl-l-glutamine) on the micellar properties of catonic surfactant dodecyltrimethylammonium bromide (DTAB) has been investigated by electrical conductivity and fluorescence spectroscopy. From the conductivity data, the critical micellar concentration (c _cmc), counterion binding constant (β), and thermodynamic parameters of micellization (ΔG _m ^o , ΔH _m ^o and ΔS _m ^o ) have been calculated. The effect of dipeptides on the micellar properties of DTAB depends upon their nature and concentration as well as on temperature and has been used to study the interactions present in the micellar systems. Enthalpy–entropy compensation effect has also been observed. The pyrene fluorescence spectra were used as an index for the estimation of micropolarity of micellar produced by the interaction of DTAB with dipeptides and the aggregation behavior of DTAB. Comparison on the interactions between different types of surfactants and dipeptide showed that the order of the strength for these interactions is TX-100?相似文献   

Application of Hydrazino Dinitrophenyl-Amino Acids as Chiral Derivatizing Reagents for Liquid Chromatographic Enantioresolution of Carbonyl Compounds

A new series of chiral derivatizing reagents (CDRs) consisting of five hydrazino dinitrophenyl (HDNP)-amino acids (CDR 1?C5) was prepared by a two-step synthesis procedure starting from 1,5-difluoro-2,4-dinitrobenzene (DFDNB). In the first step, five fluoro-dinitrophenyl (FDNP)-reagents, namely FDNP-l-Leu, FDNP-l-Val, FDNP-l-Phe, FDNP-l-Ala and FDNP-d-Phg were synthesized by substituting one of the fluorine atoms in DFDNB moiety with amino acids l-Leu, l-Val, l-Phe, l-Ala and d-Phg, respectively. In the following step, the remaining fluorine atom of the FDNP reagents was substituted with hydrazine hydrate to obtain five HDNP reagents (i.e. CDR 1?C5; HDNP-l-Leu, HDNP-l-Val, HDNP-l-Phe, HDNP-l-Ala and HDNP-d-Phg). These five CDRs were used for synthesis of diastereomers of six racemic carbonyl compounds which were resolved by high-performance liquid chromatography using C18 column and gradient eluting mixture of acetonitrile or methanol with triethylammonium phosphate buffer with UV detection at 348 nm. Microwave irradiation was used for synthesis of both the CDRs and the diastereomers. The newly synthesized CDRs were observed to be superior in comparison to their counterparts having amino acid amides as chiral auxiliaries in terms of cost effectiveness and providing better resolution of diastereomers. The method was validated for limit of detection, linearity, accuracy and precision.     

Comparison of ordered mesoporous materials sorption properties towards amino acids

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.     

Enhancing Production of l-Serine by Increasing the glyA Gene Expression in Methylobacterium sp. MB200

Microbial fermentation using methylotrophic bacteria is one of the most promising methods for l-serine production. Here we describe the metabolic engineering of a Methylobacterium strain to increase the production of l-serine. The glyA gene, encoding serine hydroxymethyltransferase (SHMT), was isolated from the genomic DNA of Methylobacterium sp. MB200, using a DNA fragment encoding Methylobacterium extorquens AM1 SHMT as a probe, and inserted into the vector pLAFR3. The resulting construct was transformed into Methylobacterium sp. MB200 using triparental mating. The genetic-engineered strain, designated as Methylobacterium sp. MB202, was shown to produce 11.4?±?0.6 mg/ml serine in resting cell reactions from 30 mg/ml wet cells, 20 mg/ml glycine, and 70 mg/ml methanol in 2 days, representing a 4.4-fold increase from that of the wild strain. The results demonstrated the potential for improving l-serine production by manipulating the glyA in bacteria and should facilitate the production of l-serine using Methylobacterium sp. strains.     

Efficient Microbial Conversion of l-Tyrosine to l-DOPA by Brevundimonas sp. SGJ

l-DOPA (3,4-dihydroxyphenyl-l-alanine), the most widely used drug for the treatment of Parkinson??s disease, was produced in buffer using biomass of Brevundimonas sp. SGJ. The effects of enhancers, such as carrageenan, diatomaceous earth, and activated charcoal, on the l-DOPA production were evaluated to obtain the maximum yield. The optimal process conditions found were pH?8, 2?g?l^?1 cell mass, 2?g?l^?1 l-tyrosine, 0.04?g?l^?1 CuSO₄, 0.02?g?l^?1 l-ascorbic acid, 0.5?g?l^?1 carrageenan, and 40?°C temperature. In addition, repeated use of cells resulted in the highest yield of 3.81?g?l^?1 (95.2%) of l-DOPA with utilization of 4?g?l^?1 l-tyrosine, and the highest tyrosinase activity (9,201?U?mg^?1) was observed at 18?h of incubation. Furthermore, the produced l-DOPA was confirmed by high-performance thin-layer chromatography, high-performance liquid chromatography, and gas chromatography?Cmass spectroscopy. Kinetic studies showed significant values of Y _p/s, Q _s, and q _s after optimization of the process. Thus, Brevundimonas sp. SGJ could be an eventual new source for large-scale production of l-DOPA.     

Enhancing l-Isoleucine Production by thrABC Overexpression Combined with alaT Deletion in Corynebacterium glutamicum

l-isoleucine is synthesized from 2-ketobutyrate and pyruvate in Corynebacterium glutamicum, and the supplies of these two precursors are important for l-isoleucine synthesis. C. glutamicum YILWΔalaT with alaT gene deletion (encoding alanine aminotransferase, a principal enzyme for l-alanine synthesis) was constructed to increase intracellular pyruvate availability, and the thrABC genes from Escherichia coli (encoding bifunctional aspartate kinase I-homoserine dehydrogenase I, homoserine kinase, and threonine synthetase) were overexpressed in C. glutamicum YILW and YILWΔalaT to increase the supply of intracellular 2-ketobutyrate. In the fed-batch fermentation, YILWpXMJ19thrABC, YILWΔalaT, and YILWΔalaTpXMJ19thrABC exhibited 5.3, 17.6, and 8.4 % higher l-isoleucine production than the original strain, respectively. Both YILWpXMJ19thrABC and YILWΔalaT excreted lower concentrations of l-lysine, l-alanine, and l-valine. YILWΔalaTpXMJ19thrABC exhibited a cumulative reduction of these by-products excretion, which indicated that thrABC overexpression combined with alaT deletion resulted in the metabolic flux redistribution from 2-ketobutyrate and pyruvate to l-isoleucine synthesis, and decreased the fluxes to by-products synthesis accordingly.     

RP-LC Resolution of (R,S)-Atenolol via Diastereomerization with Marfey’s Reagent and Its Structural Variants Under Conventional and Microwave Heating

(R,S)-Atenolol was derivatized with Marfey’s reagent, (MR; 1-fluoro-2,4-dinitrophenyl-5-l-alanine amide or FDNP-l-Ala-NH₂) and its four structural variants (FDNP-l-Phe-NH₂, FDNP-l-Val-NH₂, FDNP-l-Leu-NH₂ and FDNP-l-Pro-NH₂). MR reacts quantitatively with 1° and 2° amino groups and atenolol has a secondary amino group. The derivatization reactions were carried out under conventional and microwave heating and compared. The resulting diastereomers were separated on RP-TLC and on a C18 column with detection at 340 nm. (R)-Isomer eluted before (S). The conditions of derivatization and chromatographic separation were optimized. The method was validated for linearity, repeatability, limits of detection and limit of quantification.