Heats of combustion for L-α-amino acids

The heats of combustion for series of L-α-amino acids of different composition were analyzed using an additivity scheme. Group contributions were calculated, and these data were used to calculate the heats of combustion for 50 L-α-amino acids.     

Chemical transformations of the condensation products of pyridoxal with L-α-alanine and D-α-alanine

The kinetics and mechanism of the reactions of pyridoxal with L- and D-α-alanine were studied. Under comparable conditions, the condensation of L- and D-α-alanines with pyridoxal includes three kinetically different steps. The first fast step is addition of the amino acid to pyridoxal with formation of the corresponding amino alcohol, the second (slower) step is dehydration of the amino alcohol to give Schiff base, and the third (very slow) step is elimination of α-hydrogen atom from the L-α-amino acid fragment or decarboxylation of the D-α-amino acid fragment, followed by isomerization of the Schiff base to quinoid structure whose subsequent hydrolysis yields pyridoxamine and pyruvic acid or acetaldehyde, respectively. A scheme was proposed for chemical transformations of the pyridoxal condensation products with L- and D-α-alanines.     

The thermochemistry of solution of L-α-alanyl-L-α-alanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of L-α-alanyl-L-α-alanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x ₂ ranging from 0 to 0.4 mole fractions. The standard enthalpy of peptide solution Δ_sol H ^o and transfer Δ_tr H ^o from water into a mixed solvent were calculated. The effect of the structure and properties of peptides and mixture composition on the enthalpy characteristics is discussed. The enthalpy coefficients of pair interactions h _xy between L-α-alanyl-L-α-alanine and alcohol molecules were calculated; these coefficients were positive and increased in the series ethanol, n-propanol, isopropanol. The analysis performed allowed the differences in the thermodynamic characteristics of solution of L-α-alanyl-L-α-alanine and DL-α-alanyl-DL-α-alanine in water-alcohol mixtures to be determined.     

Synthesis and Properties of L-α-aming-γ-nitroguanidinobutyric acid

We wish to report the synthesis of L-α-amino-γ-nitroguanidinobutyric acid, a hitherto unkonwn amino acid derivative. This derivative can be the base for preparing peptides (for instance hormonse) contairing Lα-amono-γ-guanidinobutyric acid, the lower homologue of L-arginine. The higher homologue, L-homoarginine, has already been built in peptides through its nitroderivative, as was the case with angiotensin IIanalogues¹and Har-Bradykinin².     

The enthalpies of solution of L-α-alanyl-L-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (T = 298.15 K) of L-α-alanyl-L-α-alanine in aqueous-organic solvents (acetonitrile, 1,4-dioxane, acetone, formamide, N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, and N,N-dimethylsulfoxide) were measured at organic component concentrations x ₂ = 0–0.3 mole fractions. The standard enthalpies of solution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of the peptide from water into mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics is considered. The enthalpy pair interaction coefficients h _xy between L-α-alanyl-L-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft four-parameter equation was used to reveal correlation between the h _xy values and the properties of organic solvents.     

Kinetic and mechanism of reactions of L-α-Glutamic acid and L-Glutamine with pyridoxal

The kinetics and mechanisms of condensation of pyridoxal with L-α-glutamic acid and L-glutamine were studied by UV spectroscopy and polarimetry. L-α-Glutamic acid reacts with pyridoxal to form a Schiff base whose subsequent hydrolysis gives rise to pyridoxamine and α-ketoglutaric acid. The reaction of Lglutamine with pyridoxal involves the Γ-NH₂ group and affords a Schiff base whose subsequent hydrolysis gives rise to pyridoxamine and L-α-glutamic acid.     

Thermodynamics of interaction of L-α-phenylalanine with urea and dimethylformamide in aqueous solution

The thermal effects of solution of L-phenylalanine in aqueous solutions of urea and dimethylformamide (DMF) at 25°C were determined. The solubility of L-phenylalanine in water and aqueous DMF solutions was measured. The standard enthalpies, free energies, and entropies of solution of the amino acid in aqueous solutions of amides were calculated. The parameters of pair and ternary amino acid-amide interactions were determined within the framework of the McMillan-Mayer theory. The amino acid-amide pair interaction is accompanied by a decrease in the Gibbs free energy, controlled by the entropy term with DMF and by the enthalpy term with urea. The interaction of L-phenylalanine with two amide molecules is repulsive, which in the case of DMF leads to an increase in the standard free energies of solution of the amino acid at the amide mole fraction X ₂ > 0.05.     

Response of D-, L- and DL-α-alanines to ionizing radiations

There is no statistically significant difference in the response of the enantiomers and the racemate of -alanine to -radiation (⁶⁰Co) and accelerated electrons (10 MeV). The response was measured by the yield of ammonia, one of the separated final products of solid alanine radiolysis and the concentration of free radical CH₃·CH·COO^–, the intermediate product of radiolysis. Some of the properties of the racemate may affect the precision of measurements. The_DL-alanine shows different crystal structure, morphology of crystals, specific density and bulk density than the enantiomers. The response of_L and_DL alanines built into composites may be different because of different reactivity of the enantiomer and the racemate with components during the processing and irradiation.     

L-α-Aminoadipic Acid from L-Glutamic Acid

A convenient procedure for the preparation of L-α-aminoadipic acid from L-glutamic acid is described.     

L-α氨基酸消旋化作用的探讨

Ｌ－α氨基酸消旋化作用的探讨方百盈冯大炎（安徽师范大学化学系，芜湖，２４１０００）关键词Ｌ－α－氨基酸消旋化负碳离子作为人体必需的８种氨基酸及２种半必需氨基酸往往易在食品加工过程中发生变化，并导致营养值下降［１］。虽原因有多种，但构型的转变，旋光度下...     

Asymmetric Reduction of Acetophenone with Borane Catalyzed by Chiral Oxazaborolidinones Derived from L-α-Amino Acids

Some chiral oxazaborolidinones were prepared from L-α-amino acids reacting with borane and used as a new type of catalysts for asymmetric reduction of acetophenone with borane to afford R-(+)-1-phenyl ethanol with 23–76%ee in high yield.     

α-Amino 1,3-dithioketal mediated asymmetric synthesis of piperidines (L-733,060) and tetrahydrofuran glycines

Sulfinimine-derived α-amino 1,3-dithianes and α-amino carbonyl chiral building blocks, are utilized in asymmetric syntheses of (+)-(tetrahydrofuran-2-yl)glycine and the 2,3-disubstituted piperidine (+)-L-733,060.     

FAB MS of Permethylated L-β-Aspartamido-Carbohydrates

ＦＡＢＭＳｏｆＰｅｒｍｅｔｈｙｌａｔｅｄＬ┐β┐Ａｓｐａｒｔａｍｉｄｏ┐ＣａｒｂｏｈｙｄｒａｔｅｓＷＡＮＧＴｓｏｎｇ－ｈｕｉ＊（ＤｅｐａｒｔｍｅｎｔｏｆＩｎｓｔｒｕｍｅｎｔａｌＡｎａｌｙｓｉｓ，ＩｎｓｔｉｔｕｔｅｏｆＦｏｒｅｎｓｉｃＳｃｉｅｎｃｅ，Ｂ...     

逆流色谱法手性分离D,L-α-苯甘氨酸

以(D)-(+)-樟脑-10-磺酸作为手性选择剂,运用逆流色谱技术对苯甘氨酸对映异构体进行手性分离。以正己烷-乙酸乙酯-甲醇-水(1+5+1+5)溶液作为两相溶剂系统,手性选择剂在上相中的浓度为258mmol·L-1,可在2h内一次性实现10mg苯甘氨酸的手性分离,分离效果通过手性液相色谱获得验证。     

Molar heat capacities and volumes of transfer of cytosine,thymine, caffeine and 1,3-diethylthymine to aqueous solutions of glycyl-glycine and L-α-alanyl-L-α-alanine at 25°C

Densities and specific heat capacities of ternary aqueous systems containing dipeptides (glycyl-glycine or L--alanyl-L--alanine) and nucleic acid bases (cytosine or thymine) or their alkyl derivatives (1,3-diethylthymine or caffeine) were determined at 25°C by flow calorimetry and flow densimetry. The partial molar volumes and heat capacities of transfer at infinite dilution of the different nucleic acid bases from water to water+dipeptide solutions were obtained therefrom. Except for the case of the transfer of cytosine to aqueous glycyl-glycine solutions where a small positive dependence of the transfer quantities was observed with the dipeptide concentration, the values of the heat capacities of transfer were in general low, positive or negative, depending on the compensation of hydrophobic-hydrophilic interactions between the dipeptide and the base. The volumes of transfer of most of the bases are very small, within the limit of the experimental error.     

Sorption Catalytic Determination of Copper(II) and L-α-alanine on Mg-, Al-Layered Double Hydroxides

Mg-, Al and Mg-, Cu-, Al-layered double hydroxides well-known synthetic hydrotalcite-like sorbents, were used for the first time as carriers for indicators in the sorption catalytic determination of copper(II) and L-α-alanine. Mg-, Al and Mg-, Cu-, Al-layered double hydroxides were synthesized by coprecipitation and characterized using infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The adsorption of 0.50?mg?L^?1 copper(II) solution by Mg-, Al-layered double hydroxides followed a pseudo-second-order model with an equilibrium sorption capacity of 24.2?×?10^?3?mg?g^?1 (3.8?×?10^?4?mmol g^?1) and a reaction rate constant of 4.2?g mg^?1?min^?1. Mg-, Al-layered double hydroxide tablets were prepared and used for sorption concentration and subsequent sensitive and selective sorption catalytic determination of 5.5?×?10^?3 to 1.0?mg?L^?1 copper(II) at the sorbent phase. The method was used for the analysis of natural water. A method was developed for the determination of α-alanine in Mg-, Cu-, Al-layered double hydroxide tablets with a limit of detection of 4.0?×?10^?3 mol?L^?1. In addition, thin layers of Mg-, Cu-, Al-layered double hydroxide were used to separate α-alanine and determine α-amino acids by thin-layer chromatography.     

α-Thioureidoalkylation of urea heteroanalogs

α-Thioureidoalkylation of urea heteroanalogs such as thiosemicarbazide, amino-guanidine, sulfamide, and sulfonamides with 4,5-dihydroxyimidazolidine-2-thiones has been studied. Previously unknown 4,5-bis[thiosemicarbazido(guanidinoamino)]imidazolidine-2-thiones, 5,7-dialkylperhydroimidazo[4,5- e][1,2,4]triazine-3,6-dithiones, 4,6-diethyl-5(3H)-thioxotetrahydro-1 H-imidazo[4,5- c][1,2,5]thiadiazole 2,2-dioxide, and 1,3-dialkyl-4-[guanidinoimino(arylsulfonylimino)]imidazolidine-2-thiones have been synthesized.     

Hydrazones ofα-pyrazolidinylacetoacetic ester

The p-nitrophenylhydrazones and acetylhydrazones of trans--(1-acetyl-2-phenyl-3-methyl-5-pyrazolidinyl)-acetoacetic ester have been obtained in the form of a mixture of diastereomeric pairs of syn-isomers. Individual diastereomeric pairs that have been isolated do not undergo any tautomeric conversions in nonpolar solvents. Heterocyclization of these hydrazones is difficult.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 311–320, March, 1998.