Oxidation of Fursemide by Diperiodatocuprate(III) in Aqueous Alkaline Medium—a Kinetic Study

Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III) in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant] and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive form of the oxidant was inferred to be [Cu(H₃IO₆)₂]⁻. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E _a,ΔH ^#,ΔS ^# and ΔG ^# were determined to be 51 kJ⋅mol⁻¹,48.5 kJ⋅mol⁻¹,−63.5 J⋅K⁻¹⋅mol⁻¹ and 67 kJ⋅mol⁻¹, respectively. The value of log ₁₀ A was calculated to be 6.8.     

Effect of Temperature on The Solubility of α-Amino Acids and α,ω-Amino Acids in Water

The aqueous solubilities of glycine, dl-α-alanine (2-aminopropanoic acid), dl-α-aminobutyric acid (2-aminobutanoic acid), dl-α-norvaline (2-aminopentanoic acid), dl-α-norleucine (2-aminohexanoic acid), β-alanine (3-aminopropanoic acid), γ-aminobutyric acid (4-aminobutanoic acid), 5-aminovaleric acid (5-aminopentanoic acid), and 6-aminocaproic acid (6-aminohexanoic acid) were determined from 293.15 to 323.15 K at intervals of 5.00 K using the gravimetric method. The temperature dependence of the solubility of α-amino acids and α,ω-amino acids in water is well described by the van’t Hoff equation. Linear van’t Hoff plots were used to determine the differential enthalpy of solution. The results obtained are compared with reported values in literature and are discussed in terms of the position of the ionic groups in the hydrocarbon chain.     

Use of Diphenyliodonium Bromide in the Synthesis of Some N-Phenyl α-Amino Acids

The N-phenyl methyl esters 4 of glycine, alanine, valine, leucine, isoleucine, phenylalanine, methionine, proline, serine, threonine, tyrosine, aspartic acid, and glutamic acid have been synthesized in good to excellent yields using diphenyliodonium bromide, AgNO₃, and a catalytic amount of CuBr starting from the relevant amino acid ester. The chiral integrity of the amino acids 5 was maintained during these reactions, which were confirmed by the synthesis of dipeptide for each N-phenyl amino acid. The structures of the new compounds were confirmed by the analysis of their IR, ¹H, and ¹³C NMR spectra in addition to CHN microanalysis or high-resolution mass spectrometry for the new N-phenyl amino acids 5 and the esters 4.     

Recognition of α-Amino Acid from β- and γ-Amino Acid by N -Phosphorylation

The reactivity of N -phosphoryl f -alanine differs from N -phosphoryl g -alanine and N -phosphoryl n -amino butyric acid enormously. N -phospho- f -alanine could self-activate to yield N -phosphopeptides either in aqueous or nonaqueous media, but not g - or n -amino acid analogues. The mechanism of the reaction is discussed.     

Enzymatic Resolution of α-Amino Phosphonous Acids -A Kinetic Comparison with Other α-Amino Acids Using 19F and 31P NMR Analysis

Abstract

We have previously reported (1,) the synthesis of a range of α-aminophosphonous acids and found them to be mimics of the naturally occurring amino acids. They inhibit the protein synthesis of E.Coli B (2) and other synthetases (3). We have now found that such compounds can be conveniently resolved via their N-acyl derivatives by enzymatic methods. Using penicillin-G-amidase from E.Coli (EC 3.5.1.11) the R-enantiomer is cleanly hydrolysed leaving the S-enantiomer intact.     

Kinetics and Mechanism of Oxidation of Lactic Acid by Dihydroxyditelluratoargentate（Ⅲ）in Alkaline Medium

The kinetics of the oxidation of lactic acid(Lac) by dihydroxyditelluratoargentate(Ⅲ）[abbreviated as DDA of Ag(Ⅲ）]anions was studied in an aqueous alkaline medium by conventional spectrophotometry in a temperature range of 25-40℃.The order of the redox reaction of lactic acid and DDA was found to be first-order.The rates increased with the increase in [OH^-]and decreased with the increase in [tellurate].No free radical was detected.In the view of this the dihydroxymonotelluratoargentate(Ⅲ）species(DMA) is assumed to be the active species.A plausible mechanism involving a two-electron transfer is proposed,and the rate equation derived from the mechanism can be used to explain all the experimenttal results.The activation parameters(25℃）and the rate constants of the rate-determining step along with the preequilibrium constants at different temperatures were evaluated.     

Equilibrium Studies of Binary and Ternary Complexes Involving Tricine and Some Selected α-Amino Acids

Summary. The formation equilibria for the binary complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Mn^II, Pb^II, Th^IV, UO₂^II, and Ce^III with tricine and for the ternary complexes involving some -amino acids (glycine, -alanine, proline, serine, asparagine, and aspartic acid) were investigated using pH-metric technique. The formation of binary and ternary complexes was inferred from the pH-metric titration curves. It was deduced that tricine acts as a primary ligand in the ternary complexes involving the monocarboxylic amino acids (glycine, -alanine, proline, serine, and asparagine), whereas it behaves as a secondary ligand in the ternary systems containing the dicarboxylic aspartic acid. The ternary complex formation was found to take place in a stepwise manner. The stability constants of the complexes formed in aqueous solutions were determined potentiometrically under the experimental conditions (t=25°C, I=0.1moldm^–3 NaNO₃). The order of stability of the ternary complexes in terms of the nature of the amino acids is investigated and discussed. The values of log K for the ternary complexes have been evaluated and discussed. Evaluation of the effects of ionic strength and temperature of the medium on the stability of the ternary system M^II-tricine--alanine (M^II=Co^II, Ni^II, and Cu^II) has been studied. The thermodynamic parameters were calculated and discussed.     

N-Phospho-α-Amino Acids and Co-Evolution of Nucleic Acid and Protein

N-phospho-α -amino acids obtainable from aqueous condition were different from their corresponding β -analogues intrinsically. As the self-reproduction unites, N-phospho-α -amino acids were capable to produce non-random oligopeptides. As the phosphoryl donor, they were able to phosphorylate the nucleosides much faster than the deoxynucleosides.     

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.     

Stereoselective and Asymmetric-Selective Polymerization of α-Amino Acid N-Carboxyanhydride

The enantiomer selectivity in the propagation reaction of NCA was investigated by using suitable model reactions. Contrary to the assumption usually made, the enantiomer selectivity in the nucleophilic addition of chiral amines to NCA depended strongly on the structure of amine or NCA and the solvent. In the polymerization by an activated-NCA mechanism, the addition of activated NCA to NCA was found for the first time to be enantiomer-selective. In addition to this, the chiral penultimate unit was found to participate in the enantiomer selection. Structures of the transition states leading to the different types of enantiomer selection were proposed.     

HPLC Determination of α-Amino Acids in Phytoplanktonic Marine Cells

Abstract

A procedure for the quantitative determination of 17 amino acids in a marine matrix using HPLC is reported. Pre-column derivatization with o-phthalaldehyde, separation on C₁₈-bonded silica with phosphate buffer (pH 7.2)-acetonitrile as eluent and fluorescence detection have been used. The good variation coefficient (average 2% with working curves in real matrix) and the low detection limit (1-5 fmoles) make the procedure suitable for the determination of total or free amino acids in matrix cultures.     

Ring-Closing Metathesis in the Synthesis of Cyclic α-Amino Acids

The review summarizes recent advances in the synthesis of cyclic -amino acids via intramolecular ring-closing metathesis of dienes and enynes.     

Enantioselective Hydrolysis of α-Amino Acid Ester by Chiral Metallomicelles

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Micellar Catalysis on Pentavalent Vanadium Ion Oxidation of D-Sorbitol in Aqueous Acid Media: A Kinetic Study

Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the concentrations of D-sorbitol, vanadium(V), H⁺ and HSO₄⁻. These observations remain unaltered in the presence of externally added surfactants. The effects of the cationic surfactant (i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to different extents. SDS and TX-100 can be used as catalysts in the production of D-glucose from D-sorbitol.     

A New and Efficient Synthesis of α-Amino Cycloalkyl-Phosphonic Acids via Electrophilic Azidation of Cycloalkylphosphonates

α-Amino cyclobutyl-, cyclopentyl-and cyclohexylphosphonic acids (13) were efficiently prepared from the related unsubstituted cycloalkylphosphonates (5), in three steps including electrophilic azidation of the corresponding lithiated carbanions, catalytic hydrogenation of the intermediate α-azido cycloalkyl-phosphonates (10) and acidic hydrolysis of the resulting α-amino cycloalkyl-phosphonates (12).     

Direct Synthesis of α-Amino Acid Derivatives by Hydrative Amination of Alkynes

α-Amino acid derivatives are key components of the molecules of life. The synthesis of α-amino carbonyl/carboxyl compounds is a contemporary challenge in organic synthesis. Herein, we report a practical method for the preparation of α-amino acid derivatives via direct hydrative amination of activated alkynes under mild conditions, relying on sulfinamides as the nitrogen source. Computational studies suggest that the reaction is enabled by a new type of sulfonium [2,3]-sigmatropic rearrangement.     

Exploring Helical Folding in Oligomers of Cyclopentane-Based ϵ-Amino Acids: A Computational Study

The conformational preferences of oligopeptides of an ϵ-amino acid (2-((1R,3S)-3-(aminomethyl)cyclopentyl)acetic acid, Amc₅a) with a cyclopentane substituent in the C^β−C^γ−C^δ sequence of the backbone were investigated using DFT methods in chloroform and water. The most preferred conformation of Amc₅a oligomers (dimer to hexamer) was the H₁₆ helical structure both in chloroform and water. Four residues were found to be sufficient to induce a substantial H₁₆ helix population in solution. The Amc₅a hexamer adopted a stable left-handed (M)-2.3₁₆ helical conformation with a rise of 4.8 Å per turn. The hexamer of Ampa (an analogue of Amc₅a with replacing cyclopentane by pyrrolidine) adopted the right-handed mixed (P)-2.9_18/16 helical conformation in chloroform and the (M)-2.4₁₆ helical conformation in water. Therefore, hexamers of ϵ-amino acid residues exhibited different preferences of helical structures depending on the substituents in peptide backbone and the solvent polarity as well as the chain length.     

Oxidation of Two α-Hydroxy Acids by Vanadium(V)

The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.     

Oxidation of Two α-Hydroxy Acids by Vanadium(V)

Summary. The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.Received April 8, 2003; accepted May 10, 2003 Published online September 18, 2003