Homochiral rigid γ-amino acid glycosides from aucubin

Two homochiral glucosylated hydroxy γ-amino acids 7 and 11 were synthesized by chiral pool synthesis in eight steps from the natural iridoid aucubin.     

Physico-chemical characterization of γ-amino n-butyric acid nanoparticles

This work deals with the preparation and characterization of high-purity nanoparticles of γ-amino n-butyric acid (GABA) in order to enhance the efficiency of this drug. A sublimation procedure at low pressure was applied to GABA after improving the experimental parameters of this physical transformation. The elaboration of the molecule is solvent-free. The process does not change the chemical formula of the compound but modifies its physico-chemical characteristics. In this work, we present the experimental parameters for preparing monoclinic GABA nanoparticles. Their identification and physico-chemical properties were determined with a large number of investigations: Powder X-ray diffraction (PXRD), density and purity measurements, differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), calorimetric measurements (ΔH(dissolution) and C(p)), thermally stimulated current (TSC), and electrochemical impedance.     

Asymmetric syntheses of α-methyl γ-amino acid derivatives

This project was undertaken to demonstrate the potential of asymmetric hydrogenations mediated by the chiral, carbene-oxazoline analogue of Crabtree's catalyst "cat" in asymmetric hydrogenations of allylic amine derivatives of amino acids. Peripheral features of the substrates (protecting groups, functional groups related by redox processes, and alkene geometries) were varied to optimize the stereochemical vectors exerted by the substrate and align them with the catalyst vector. N-Acetyl-protected, O-TBDPS-protected allylic substrates 9a-e emerged as the best for this reaction; syn-products were formed from the E-alkenes, while the Z-isomers gave anti-target materials, both with high diastereoselectivities. This study featured asymmetric catalysis to elaborate optically active substrates into more stereochemically complex chirons; we suggest that the approach used, optimization of stereocontrol by varying peripheral aspects of the substrate, tends to be easier than de novo catalyst design for each substrate type. In other words, optimization of the substrate vector is likely to be more facile than enhancement of the catalyst vector via ligand modifications.     

Low-temperature heat capacity and thermodynamic parameters of γ-aminobutyric acid

Thermodynamic properties of γ-aminobutyric acid were studied in the temperature interval from 5.7 to 300 K using a vacuum adiabatic calorimeter. The curve C _p (T) in the mentioned temperature interval is S-shaped without any anomalies. Based on the smoothed values of heat capacity, the calorimetric entropy $ S_{m}^{0} (T) - S_{m}^{0} (0) $ and the difference in the enthalpies $ H_{m}^{0} (T) - H_{m}^{0} (0) $ were calculated and tabulated. At the standard temperature 298.15 K, these values are equal to 158.1 ± 0.3 J K^?1 mol^?1 and 23020 ± 50 J mol^?1, respectively. At temperatures from 5 to 10 K, the function C _p (T) was found to obey the Debye law C = AT ³. Contrary to what has been supposed previously, the empirical Parks–Huffman rule for estimating entropy in the homologous series was shown to be not valid for the series glycine–β-alanine–γ-aminobutyric acid.     

Stereodivergent synthesis of cyclic γ-aminobutyric acid – GABA analogues

A novel synthetic route towards two series of enantiomerically pure cyclic analogues of 2,3-cis- and 2,3-trans-γ-aminobutyric acid (GABA) was developed. The route is based on the elongation and stereodivergent manipulation of a readily accessible enantiomerically pure γ-substituted α-aminolactone. The five-step route towards the 2,3-cis-substituted GABA analogues was achieved via straightforward carbon chain extension of the lactone using a non-classical Wittig reaction followed by chemoselective reduction and a protecting group switch. The five-step route towards the 2,3-trans-substituted GABA analogues employed elongation of the same aminolactone using a Horner-Wadsworth-Emmons reaction and highly stereoselective intramolecular oxa-Michael addition as the key synthetic manipulations. Altogether this chemistry has allowed the stereodivergent preparation of a novel class of GABA analogues in two diastereomeric series.     

Pre-staining paper chromatography method for quantification of γ-aminobutyric acid

The routine method of paper chromatography includes five steps: spotting, separating, drying, spraying/immersing and color development. In this paper, a pre-staining paper chromatography which only consisted of spotting, separating and color development was developed for quantitative analysis of γ-aminobutyric acid. Compared to the routine paper chromatography, the improved method is clean, rapid, inexpensive and reproducible. The effects of ninhydrin concentration, color temperature, color time and Cu²⁺ concentration on the color yield in the ninhydrin reaction were optimized. And then the pre-staining paper chromatography coupled with vis spectrophotometry was applied to γ-aminobutyric acid quantification. The results indicated that the limit of detection was 0.05 mg mL⁻¹ and the linear range was from 0.5 to 20.0 mg mL⁻¹. Furthermore, an excellent correlation coefficient was observed with an R² = 0.998. The method is accurate (RSD < 2.64%), and has good recoveries (102.7–103.9%). The validation of the modified technique was verified by a HPLC method.     

Asymmetric synthesis of 2-alkyl-substituted 2-hydroxyglutaric acid γ-lactones

3-Alkyl-1,2-cyclopentanediones 1 are transformed into 2-alkyl-2-hydroxyglutaric acid γ-lactones 3 in up to 83% isolated yields and up to 96% ee, affording a simple access to many bioactive compounds, including diacylglycerol lactones (DAG-lactones).     

Radiolytic gas formation under γ-irradiation of oxalic acid solutions

Radiolytic gas formation under -irradiation (10⁴–10⁶ Gy) of 10^–2–10^–4 M aqueous solutions of oxalic acid at 25–60°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1836–1839.Original Russian Text Copyright © 2004 by Popova, Voronin, Byvsheva.     

Theoretical studies on the inactivation mechanism of γ-aminobutyric acid aminotransferase

The inactivation mechanism of γ-aminobutyric acid aminotransferase (GABA-AT) in the presence of γ-vinyl-aminobutyric acid, an anti-epilepsy drug, has been studied by means of theoretical calculations. Density functional theory methods have been applied to compare the three experimentally proposed inactivation mechanisms (Silverman et al., J. Biol. Chem., 2004, 279, 363). All the calculations were performed at the B3LYP/6-31+G(d,p) level of theory. Single point solvent calculations were carried out in water, by means of an integral equation formalism-polarizable continuum model (IEFPCM) at the B3LYP/6-31+G(d,p) level of theory. The present calculations provide an insight into the mechanistic preferences of the inactivation reaction of GABA-AT. The results also allow us to elucidate the key factors behind the mechanistic preferences. The computations also confirm the importance of explicit water molecules around the reacting center in the proton transfer steps.     

Synthesis and characterization of γ-alumina nanospheres templated by lauric acid

A novel route for the synthesis of alumina nanospheres was reported by a surfactant-governed approach in the presence of lauric acid.The products were characterized using X-ray diffraction (XRD),scanning electron microscope (SEM) and N2 adsorption-desorption techniques.The results show that the produced alumina nanospheres possess uniform nanosphere sizes ranging from 80 120 nm,and high surface area of 550 m2/g.It suggests that the synthesized alumina nanospheres are formed through self-assembly of surfactant/alumina species complex in 1-propanol system.     

Vibrational spectroscopic study on polymorphism of erucic acid and palmitoleic acid: γ1→α1 and γ→α reversible solid state phase transitions

The infrared and Raman spectra of four polymorphic phases (α, α1, γ and γ1) of erucic acid (cis-13-docosenoic acid) and those of two polymorphic phases (α and γ) of palmitoleic acid (cis-9-hexadecenoic acid) were investigated. The γ and γ1 phases of erucic acid were analyzed on the basis of crystal structures determined by us. There were large spectral differences between γ and γ1 phases, which could be ascribed to the differences in the conformation of cis-olefin groups and the subcell structure. Two types of reversible solid state phase transitions (γ→α and γ1→α1 transitions) were followed by the infrared and Raman spectra. It was concluded that the mechanism of the γ→α phase transition of erucic and palmitoleic acids is essentially the same as that of oleic acid previously reported by us [J. Phys. Chem. 90, 6371 (1986)], i.e. this phase transition is of order-disorder type accompanied by a conformational disordering at the methyl-terminal chain. Spectral changes on the γ1→α1 transition suggested that a similar structural change took place during this transition but there were large structural differences between α and α1.     

Elucidating the structure of surface acid sites on γ-Al2O3

Differential pair distribution function analysis was applied to resolve, with crystallographic detail, the structure of catalytic sites on the surface of nanoscale γ-Al(2)O(3). The structure was determined for a basic probe molecule, monomethylamine (MMA), bound at the minority Lewis acid sites. These active sites were found to be five-coordinate, forming distorted octahedra upon MMA binding. This approach could be applied to study the interaction of molecules at surfaces in dye-sensitized solar cells, nanoparticles, sensors, materials for waste remediation, and catalysts.     

Esterification of acetic acid with n-Butanol using vanadium oxides supported on γ-alumina

Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N₂ adsorption, EDX analysis and NH₃-TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V₂O₅ (10V-Al₂O₃ sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH₃ increased in the following order: Al₂O₃ < 5V-Al₂O₃ (5 wt % V₂O₅/Al₂O₃) < 10V-Al₂O₃. In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V₂O₅–Al₂O₃ catalyst was observed.     

The role of oxidizing radicals in neptunium speciation in γ-irradiated nitric acid

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ^?OH, ^?NO₃ and ^?NO₂. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Regioselective lipase-catalysed γ-monoamidation of d-glutamic acid diesters: effect of the N-protecting group

N-Blocked-d-glutamic acid diethylesters are γ-regioselectively amidated in a reaction catalysed by Candida antarctica lipase B, carried out in an anhydrous organic solvent. The ratio of γ:α-monoamides, as a measure of regioselectivity, depends on the N-protecting group present in the substrate. In the examples reported in this work, we have found that γ:α ranges from about four (N-group=Cbz) to 35 (N-group=isobutyryl). No diamides were detected.     

Preparation and antibacterial activity of aromatic derivatives of β-aminopropionic and γ-aminobutyric acid

Ten aromatic derivatives of β-aminopropionic acid and γ-aminobutyric acid were prepared.Their compositions and structures were identified by elemental analysis,IR,and 1H NMR.They have been examined for their antibacterial action against Staphylococcua aurens and Escherichia coli.These compounds showed higher activity than the aromatic derivatives of ct-amino acid which were reported previously.The general conclusion to be drawn is that the distance between amino and carboxylic group in these molecules could affect their antibacterial activity.Furthermore,those compounds with p-methyl substituent in phenyl ring exhibit higher activity than the others,and all the compounds exhibit higher activity against Escherichia coli and against Staphylococcua aureus.     

Highly enantioselective γ-amination of α,β-unsaturated acyl chlorides with azodicarboxylates: efficient synthesis of chiral γ-amino acid derivatives

The cinchona alkaloid-catalyzed γ-amination of α,β-unsaturated acyl chlorides with azodicarboxylates to give the corresponding dihydropyridazinones in good yields with high enantioselectivities has been developed. Reductive ring opening of the dihydropyridazinones afforded series of cyclic and acyclic γ-amino acid derivatives in good yields with high enantiopurity.     

Rhodium-catalyzed asymmetric addition of arylboronic acids to γ-phthalimido-substituted-α,β-unsaturated carboxylic acid esters: an approach to γ-amino acids

Efficient Rh-catalyzed asymmetric 1,4-addition of arylboronic acids to ethyl-γ-phthalimidocrotonate by using bis-sulfoxide ligand affords γ-aminobutyric acid (GABA) derivatives with high enantioselectivities (90-96% ee) under mild conditions. Optically pure (S)-Baclofen and (S)-Rolipram have been prepared successfully through this synthetic route.     

A multicoincidence study of fragmentation dynamics in collision of γ-aminobutyric acid with low-energy ions

Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3?a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH(2)CH(2)(+), HCNH(+), CH(2)CH(2)(+), and COOH(+) fragments. State-of-the-art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential-energy surface. For example, the weak contribution at [M-18](+), where M is the mass of the parent ion, can be interpreted as resulting from H(2)O loss that follows molecular folding of the long carbon chain of the amino acid.