Vibrational analysis of l-alanine and deuterated analogs

Raman spectra of the polycrystalline l-alanine analogs CH₃CH(NH⁺₃)COO^?, CH₃CH(ND⁺₃)-COO^?, CD₃CD(NH⁺₃)COO^?, and CD₃CD(ND⁺₃)COO^? have been obtained. A normal coordinate analysis is carried out based on the experimental frequencies of the four isotopic analogs and a 34 parameter valence-type force field defined in terms of local symmetry coordinates. The final refinement, in which five stretching force constants are constrained to fixed values obtained from bond length data, results in an average error of 7 cm^?1 (0.9%) for the observed frequencies of the four isotopically substituted molecules. Band assignments are given in terms of the potential energy distribution for local symmetry coordinates. For non-deuterated l-alanine, the vibrations above 1420 cm^?1 and below 950 cm^?1 may be described as localized group vibrations. By contrast, the eight modes in the middle frequency range, viz. the three skeletal stretching, the COO^? symmetric stretching, one NH⁺₃ rocking, the symmetric CH₃ deformation, and the two methyne CH deformation vibrations, are very strongly coupled to one another. Some decoupling appears to take place in the perdeutero molecule, and all but five modes can be described as localized group vibrations.     

Bound coefactor/dual enzyme electrode system for l-alanine

A dual enzyme-bound coenzyme electrode system for quantifying l-alanine is described. Commercially available dextran-bound NAD was incorporated into an l-alanine dehydrogenase (E.C. 1.4.1.1)/l-lactate dehydrogenase (E.C. 1.1.1.27) enzyme system and held at the surface of a potentiometric ammonia gas sensor. Using this system, l-alanine calibration curves with a slope of 45 mV/decade and 10^?5 M detection limit were obtained with a sensor lifetime of at least 10 days. This system is potentially useful for the clinical determination of l-alanine in serum.     

The first chemical conversion of l-proline to l-glutamic acid

The ruthenium tetroxide oxidation of N-acyl-l-proline esters gave the corresponding l-pyroglutamic acid derivatives in good yields with no appreciable racemization, which led to the first chemical conversion of l-proline to l-glutamic acid.     

Synthesis and proposed conformations of l-prolyl-l-leucyl-β-alanine alkylamides

The synthesis of H-Pro-Leu-β-Ala-NH₂, H-Pro-Leu-β-Ala-NHCH₃ and H-Pro-Leu-β-Ala-N(CH₃)₂ is described. On the basis of IR and ¹H NMR spectral data, a 7-membered ring including the NH of β-alanine with the CO of proline should be assigned for the H-Pro-Leu-β-Ala-N(CH₃)₂. Consequently, the plausible conformations for H-Pro-Leu-β-Ala-NH₂ and H-Pro-Leu-β-Ala-NHCH₃ derive from the formation of an 11-membered ring, between the trans amide proton and the CO of Pro, or from the formation of an 8-membered ring, between this carboxamide proton and the CO of Leu, plus the aforementioned 7-membered ring.     

Synthesis of l-aminohomohistidine (l-Ahh)

A short synthesis of l-aminohomohistidine (l-Ahh), which starts from readily available δ-hydroxy-l-lysine is described. The embedding of the basic guanidino moiety in the aromatic imidazole lowers the basicity of the side chain to a pK_a of 8.3. It is proposed that l-Ahh may be employed as an arginine-mimetic in medicinal chemistry.     

Molecular recognition of l-leucyl-l-alanine: enantioselective inclusion of alkyl methyl sulfoxides

A simple aliphatic dipeptide, l-leucyl-l-alanine (Leu-Ala), includes several alkyl methyl sulfoxides enantioselectively to form inclusion crystals. From single-crystal X-ray analyses of three inclusion compounds of dimethyl sulfoxide (DMSO), isobutyl methyl sulfoxide, and benzyl methyl sulfoxide, it was elucidated that Leu-Ala molecules self-assemble to form layer structures and the sulfoxides are included via hydrogen bonding in a cavity between these layers. The inclusion cavity has methyl group and isobutyl group at its each side, and the guest sulfoxide is placed in such a manner that its methyl group faces toward the methyl of the Leu-Ala cavity. When the alkyl group of the sulfoxide is comparably large, it is located in the residual space of the cavity to attain effective crystal packing. Thus, the sulfoxides having a comparably large group such as isobutyl, butyl, and benzyl are included with a high (R)-enantioselectivity in Leu-Ala crystals.     

Direct titrimetric microdetermination of uranium(VI) and l-asparagine

Uranium and l-asparagine have been quantitatively determined in micro amounts by direct titrations. Uranium has been titrated against, l-asparagine in solution using Congo red solution as indicator. l-Asparagine has been directly titrated against uranyl nitrate using gallocyanine or Congo red as indicator. A complex is formed, in the reaction between uranyl nitrate and l-asparagine, in the ratio of 1:2. Maximum error for uranium and l-asparagine is 0.8 and 1.6%, respectively. Interference by certain metal ions has also been observed in the case of uranium.     

Phase behavior of biodegradable amphiphilic poly(l,l-lactide)-b-poly(ethylene glycol)-b-poly(l,l-lactide)

This study describes the miscibility phase behavior in two series of biodegradable triblock copolymers, poly(l-lactide)-block-poly(ethylene glycol)-block-poly(l-lactide) (PLLA-PEG-PLLA), prepared from two di-hydroxy-terminated PEG prepolymers (M_n = 4000 or 600 g mol⁻¹) with different lengths of poly(l-lactide) segments (polymerization degree, DP = 1.2-145.6). The prepared block copolymers presented wide range of molecular weights (800-25,000 g mol⁻¹) and compositions (16-80 wt.% of PEG). The copolymer multiphases coexistance and interaction were evaluated by DSC and TGA. The copolymers presented a dual stage thermal degradation and decreased thermal stability compared to PEG homopolymers. In addition, DSC analyses allowed the observation of multiphase separation; the melting temperature, T_m, of PLLA and PEG phases depended on the relative segment lengths and the only observed glass transition temperature (T_g) in copolymers indicated miscibility in the amorphous phase.     

Dications of l-histidine and l-ornithine in layers of copper(II) and cobalt(II) dipicolinato anions

Cobalt(II) and copper(II) dipicolinato complexes having l-histidine and l-ornithine dications are synthesized in water and are characterized by various spectroscopic techniques. X-ray studies reveal that the l-histidine dications are strongly hydrogen bonded and intercalated in the layered structures of dipicolinato complex anions with repeated unit in 1:1 ratio. Whereas l-ornithine dications form hydrogen bonded repeated units of cations and anions in 2:2 ratio. The cations are held in the layered structures formed by the association of the amino acid cations and metal dipicolinato anions supported by water through strong hydrogen-bond interactions. The complexes thus formed are optically active and exhibit specific rotation in the range of +4 to +12°.     

14N quadrupole coupling in thermochromic N-5-chlorosalicylideneaniline

The temperature dependence on the proton—¹⁴N double resonance spectra demonstrates that thermochromism in solid N-5-chlorosalicylideneaniline is accompanied by intramolecular proton transfer and an enol—keto transformation.     

Development of a disposable miniature l-lysine sensor

A hybrid l-lysine sensor consisting of an immobilized l-lysine decarboxylase and a miniature bacterial CO₂ sensor was fabricated using semiconductor techniques. The bacteria was immobilized in a calcium alginate gel in a miniature oxygen electrode cell together with the electrolyte. The enzyme was immobilized in a bovine serum albumin matrix on a gas-permeable membrane. The cell was formed on a silicon substrate by anisotropic etching and had a two-gold-electrode configuration. The response time of the l-lysine sensor was 1–3 min. The optimum pH was 6.0 and the optimum temperature was 33°C. The response to l-lysine concentration was linear from 25 to 400 μM. Reproducible responses were obtained by adding more than 1 μM pyridoxal-5′-phosphate. The sensor had excellent selectivity for l-lysine and a stable response for more than 25 repetitive operations.     

Plant tissue-based membrane biosensor for l-ascorbic acid

Coupling of a slice of the mesocarp of squash (Cucurbita pepo) or cucumber (Cucumis sativus) to a Clark-type oxygen electrode allows 0.02–0.57 mmol l^?1l-ascorbic acid to be determined amperometrically. The method is based on monitoring the decrease in the curretn of oxygen at an applied potential of ?650 mV vs. Ag/AgCl; oxygen is consumed in the analyte oxidation catalyzed by ascorbate oxidase in the plant tissue. One tissue slice serves for 50–80 measurements at 30°C and pH 6. Spare slices can be stored for at least a year in aqueous 50% glycerol without substantial loss of enzyme activity. The biosensor is highly selective towards ascorbic acid with a response time of 70–90 s, the relative standard deviation being about 3%. Satisfactory results were obtained in the analysis of some fruit juices and vitamin tablets.     

14N ENDOR study of Cu(II)-doped triglycine sulfate crystals (TGS)

¹⁴N ENDOR investigations of the bis(glycinato)-Cu(II) complex substituted into single crystals of ferroelectric triglycine sulfate (TGS) reveal the full tensors of the magnetic dipole as well as the electric quadrupole couplings. The two nitrogen nuclei of the copper complex are magnetically non-equivalent and consequently the point symmetry of the Cu(gly)₂ complex in the ferroelectric TGS is C₁. The nuclear quadrupole couplings are analysed using the Townes-Dailey approach and sp³ hybridization to obtain the electronic population at the nitrogen. The results are compared with the findings from the treatment of the magnetic nitrogen hyperfine coupling.     

Enzymatic determination of l-lysine by flow-injection techniques

An enzymatic assay that is highly selective for l-lysine, based on flow-injection techniques combined with spectrophotometric detection, is presented. l-Lysine-α-oxidase (E.C. 1.4.3.14) from Trichoderma viride and horseradish peroxidase were used in a coupled enzyme assay. Peroxide produced in the first reaction was converted by peroxidase with phenol and 4-aminoantipyrine to a quinoneimine dye detectable at 500 nm. An analytical enzyme reactor filled with coimmobilized enzymes was incorporated in the flow-injection system. The assay has a measuring frequency of 30 samples h^?1 and a response time of less than 2 min. To adapt the assay to high concentrations of l-Lysine and to minimize interferences, the injected sample volume was reduced to 2 μ-l, resulting in a linearity range of 1–16 mM l-lysine with a sensitivity of 6–7 mV 1 mmol^?1, a limit of detection (3σ) of 1 mM and a reproducibility of 0.5% (repetitive injection of a 10 mM l-lysine sample). The enzyme cartridge is stable for several months and thousands of measurements.     

Electrospun poly(l-lactide)-grafted hydroxyapatite/poly(l-lactide) nanocomposite fibers

Composite fibers composed of poly(l-lactide)-grafted hydroxyapatite (PLA-g-HAP) nanoparticles and polylactide (PLA) matrix were prepared by electro-spinning. Environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM) were employed to investigate the morphology of the composite fibers and the distribution of PLA-g-HAP nanoparticles in the fibers, respectively. At a low content (∼4 wt%) of PLA-g-HAP, the nanoparticles dispersed uniformly in the fibers and the composite fibrous mats exhibited higher strength properties, compared with the pristine PLA fiber mats and the simple hydroxyapatite/PLA blend fiber mats. But when the content of PLA-g-HAP further increased, the nanoparticles began to aggregate, which resulted in the deterioration of the mechanical properties of the composite fiber mats. The degradation behaviors of the composite fiber mats were closely related to the content of PLA-g-HAP. At a low PLA-g-HAP content, degradation may be delayed due to the reduction of autocatalytic degradation of PLA. When PLA-g-HAP content was high, degradation rate increased because of the enhanced wettability of the composite fibers and the escape of the nanoparticles from fiber surfaces during incubation.     

Synthesis of l,l-puromycin

l,l-Puromycin, a diastereomer of the natural peptidyl nucleoside antibiotic puromycin, has been synthesized from l-xylose in 13 steps.     

Intermolecular/interionic interactions in l-isoleucine-, l-proline-, and l-glutamine-aqueous electrolyte systems

Speed of sound and density values for ternary systems (amino acid + salt + water): l-isoleucine/l-proline/l-glutamine in aqueous solutions of 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ have been measured for several concentrations of amino acids at different temperatures (303.15, 308.15, 313.15, 318.15, and 323.15 K). Using speed of sound and density data, the thermodynamic parameters such as isentropic compressibility (κ_s), change in isentropic compressibility (Δκ_s) and relative change (Δκ_s/κ₀) in isentropic compressibility have been computed. The isentropic compressibility values decrease with increase in the amino acid concentration as well as with temperature. The decrease in κ_s values with increase in concentration of l-isoleucine/l-proline/l-glutamine in 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ has been ascribed to an increase in the number of incompressible zwitterions in solutions, and the formation of ‘zwitterions-ions’ and ‘zwitterions-water dipole’ entities in solutions. The decrease in κ_s values with increase in temperature has been attributed to the corresponding decrease of κ_relax (a relaxational part of compressibility), which is dominant over the corresponding increase of κ_∞ (an instantaneous part of compressibility). The trends of variation of Δκ_s and Δκ_s/κ₀ with variations in solute concentration and temperature have also been discussed in terms of solute-solute and solute-solvent intermolecular/interionic interactions operative in the systems.     

Studies towards the synthesis of ertugliflozin from l-Arabinose

A new method for the diastereoselective synthesis of enantiomerically pure ertugliflozin was developed. The crucial step involves an aldol condensation between 1-(4-chloro-3-(4-ethoxybenzyl)phenyl)ethanone and (4R,5R)-5-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyl-5-((trityloxy)methyl)-1,3-dioxolane-4-carbaldehyde, which was prepared from known 2-C-trityloxymethyl-2,3-O-isopropylidene-l-erythrose (easily accessible in three steps from l-arabinose) by standard reduction/oxidation and protection/deprotection manipulations. Dihydroxylation of the aldol condensation product and further global deprotection led to the formation of the target molecule.     

Deuterium isotope effect in l(+)-glutamic acid hydrochloride

A study of the effects of deuterium substitution in l(+)-glutamic acid hydrochloride is described. Solid state vibrational spectra depicting band shifts resulting from deuterium indicate that interatomic bond distances remain virtually unchanged. The cell volume expands only 0.05% upon deuteration, while the macroscopic linear and nonlinear polarizabilities are unaffected. The optical nonlinearity is therefore ascribed to the electronic nature of the hydrogen bonds.     

Control of impurities in l-aspartic acid and l-alanine by high-performance liquid chromatography coupled with a corona charged aerosol detector

In this study a reversed phase ion-pair high-performance liquid chromatography (HPLC) method using charged aerosol detection (CAD) was developed and fully validated for the pharmaceutical quality control of l-aspartic acid (Asp). With a slight modification, the method also allows the evaluation of related substances in l-alanine (Ala). The method enables simultaneous control of related amino acids and of possibly occurring organic acids contaminants. A minimum limit of quantification of 0.03% could be achieved for all occurring related substances. Moreover, the detector sensitivity of the CAD was compared with an evaporative light scattering detector (ELSD). Depending on the analyte the CAD was found to be 3.6–42 times more sensitive than the ELSD. The HPLC method was applied to the purity testing of 8 samples of pharmaceutical grade and reagent grade Asp and of 12 samples of Ala supplied by various manufacturers. Both substances were found to be of high purity (greater than 99.8% for Asp and greater than 99.9% for Ala). Malic acid and Ala were the major impurities in Asp. Asp and glutamic acid (Glu) were the only detectable impurities in Ala.