Stereochemistry of condensation and transaldimination of amino acids by pyridoxal

The stereochemistry of the products of condensation and transaldimination of L-α- and D-α- alanines with pyridoxal has been studied. Structure of intermediate amino alcohols, aminals, and of the final Schiff’s bases depends on their fragments location with respect to the pyridine ring plane. Basing on the collected data, we have proposed the reaction mechanism involving the in-plane attack of the carbonyl group, in contrast to commonly accepted out-of-plane attack.     

Effect of structure of the amino acids and amines on the rate and mechanism of their condensations with pyridoxal

Kinetics and mechanism of condensation of amino acids and amines of different structure and their derivatives with pyridoxal were studied. It was established that the amino acid with secondary amino group, proline, adds to pyridoxal with the formation of amino alcohol. α-Amino acids in the course of condensation with pyridoxal form amino alcohols which transform to Schiff bases. The latter compounds by elimination of the α-hydrogen atom or CO₂ from the amino acid fragment and the subsequent hydrolysis of the quinoid structure form the final products. β- And ɛ-amino acids react with pyridoxal to form Schiff bases which are stable to chemical transformations. The possibility was shown of their conversion to the quinoid structure. It was established that the guanidine structure of the molecule of L-arginine unlike its α-NH₂ group did not take part in the condensation with pyridoxal. The quantitative evaluation of the condensation rates of triptamine, Ltriptofane, and its methyl ester in the stage of dehydration of their amino alcohols was carried out.     

Kinetics and mechanism of oxidation of some basic amino acids with bromamine-T

Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO₄ has been worked out. Proton inventory studies in H₂O-D₂O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH₂. In alkaline media, the rate shows a first order dependence on [BAT]₀ and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.     

Reactions of pyridoxal with aromatic carboxylic acids in alcoholic medium

Russian Journal of General Chemistry - Reactions of pyridoxal with benzoic acid and its derivatives in alcoholic medium afforded alkoxyfuropyridinium salts with potential biological activity.     

Study on the interaction mechanism between aromatic amino acids and quercetin

In this paper, we selected quercetin and aromatic amino acids (tryptophan, tyrosine, phenylalanine) as the research objects to investigate the change rules in the reaction process. The thermodynamic functions (Ka, ΔG, and ΔS) of the interactions between quercetin and aromatic amino acids (tryptophan, tyrosine, phenylalanine) were measured by isothermal titration calorimetry. The values of binding constant (Ka) reached maximum at 25°C; the entropies and Gibbs free energies were both negative at different temperatures. The kinetic parameters of quercetin and amino acids in the interaction process was determined by microcalorimetry. The results inferred that the driving force of the reaction was hydrogen bond or van der Waals force.     

Mixed cobalt(III) complexes with aromatic amino acids and di­amines. III.

The title compound, [Co(C₉H₁₀NO₃)₂(C₂H₈N₂)]Cl·4H₂O, is one of six possible diastereomers of the (1,2‐di­amino­ethane)­bis(S‐tyrosinato)­cobalt(III) complex. The cobalt(III) ion has an octahedral coordination, with three five‐membered chelate rings which have deformed coordination angles and coordinated O atoms in trans positions. In comparison with the previously reported crystal structure of the Δ‐C₁‐cis(O) diastereomer [Miodragovi?et al. (2001). Enantiomer, 6 , 299–308], the compound presented in this paper has more planar five‐membered amino­carboxyl­ate rings. Complex cations, chloride anions and water mol­ecules of crystallization are linked together by a network of hydrogen bonds. The chloride anions lie approximately between two Co atoms and form hydrogen bonds with all coordinated NH₂ groups. In the crystal structure, there is a weak intermolecular π?π interaction between the phenyl rings.     

Orientation and mechanism of reactions of aromatic amines with sulfur monochloride

The reaction of m-substituted anilines with sulfur monochloride has been studied. It has been shown that cyclization with the formation of 1, 3, 2-benzothiazathiolium compounds takes place in the position para to the substituent. The introduction of methoxy groups into o-nitroanilines interferes with the displacement of the nitro group by the chlorine atom. A nucleophilic reaction mechanism has been proposed according to which the nitro group is displaced after the formation of the thiathioniaazine ring.     

Reaction of amines and amino acids with aqueous and nonaqueous acid-ninhydrin

Summary Under anhydrous conditions, ninhydrin in glacial acetic acid reacts with a number of amino acids, as well as amines and imino acids, to produce discernible colors. Hence, the reagent cannot be considered specific for imino acids under such circumstances. The effect of a small amount of water on the reaction was stressed, and some compounds were noted to produce one color (or none) when in aqueous solution, and another color when dry. Ninhydrin-reacted spots on paper chromatograms can be eluted into acid-ninhydrin, and the color produced may be useful in microanalytic identifications.

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Zusammenfassung In Abwesenheit von Wasser wirkt Ninhydrin in Eisessig auf eine Reihe von Aminosäuren sowie auf Amine und Iminosäuren unter Farbentwicklung ein, so daß das Reagens nicht als spezifisch für Iminosäuren angesehen werden kann. Selbst geringe Mengen Wasser beeinflussen die Reaktion, unterdrücken die Farbentwicklung oder ändern den Farbton. Mit Ninhydrin entwickelte Flecken in Papierchromatogrammen können mit Ninhydrin in Eisessig extrahiert werden und die erhaltenen Färbungen eignen sich für die Erkennung kleiner Stoffmengen.

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Résumé En milieu anhydre, la ninhydrine dans l'acide acétique glacial réagit avec un certain nombre d'amino-acides ainsi qu'avec les amines et les iminoacides en donnant des colorations discernables. Dans ces circonstances, on ne peut donc pas considérer le réactif comme spécifique des imino-acides. On a fait ressortir l'influence de l'eau en petite quantité sur la réaction et l'on a remarqué que certains composés donnaient une coloration (ou pas) en milieu aqueux et une autre à sec. Sur les chromatogrammes sur papier on peut éluer en ninhydrine-acide, les taches qui ont réagi avec la ninhydrine et l'on peut utiliser pour les identifications micro-analytiques la coloration qui apparaît.

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Supported by Grant GM 11 690 from the U. S. Public Health Service.     

Adamantylation of nitro-substituted aromatic amines in protic acids

Adamantylation of mono-and dinitro-substituted aromatic amines in sulfuric and phosphoric acids and in a mixture of phosphoric and acetic acids gives mainly the corresponding N-adamantyl derivatives. The results of kinetic measurements showed reversible character of the process.     

Convenient preparations of azo-dye labeled amino acids and amines

N-(4-Arylazobenzoyl)-1H-benzotriazoles 3 react with amino acids 4 and amines 6 to give azo-dye labeled amino acids (5a-m) and amines (7a-n) in high yields (74-100%) with retention of chirality.     

Kinetics of heat-induced transformation of copper complexes with amino acids

We have studied the effect of substituent R on the rate and mechanism of thermal decomposition of copper(II) complexes with L-α-amino acids anions H₂NCH(R)COO^?. The homolytic decomposition rate increases in the series of CuL₂ complexes with alanine, glycine, valine, isoleucine, leucine, phenylalanine, and serine. Intramolecular redox formation of ^·+CuGly cation-radical upon reduction of Cu(II) to Cu(I) and oxidation of H₂NCH₂COO^? into H₂NCH₂COO^· carboxylamine radical is the primary stage of heat-induced decomposition.     

Modeling of the mechanism for the acidolysis of epichlorohydrin by aliphatic and aromatic carboxylic acids catalyzed by amines

A model was constructed for the mechanism of the reaction of aliphatic and aromatic carboxylic acids with epichlorohydrin catalyzed by tertiary amines. A mechanism for the catalysis of the transfer of the anion of the nucleophilic reagent by an ion pair was proposed taking account of the kinetic data and selected chemical and mathematical models.     

Regioselective copper-catalyzed amination of bromobenzoic acids using aliphatic and aromatic amines

A chemo- and regioselective copper-catalyzed cross-coupling procedure for amination of 2-bromobenzoic acids is described. The method eliminates the need for acid protection and produces N-aryl and N-alkyl anthranilic acid derivatives in up to 99% yield. N-(1-Pyrene)anthranilic acid has been employed in metal ion-selective fluorosensing. Titration experiments showed that this pyrene-derived amino acid forms an equimolar complex with Hg(II) in water resulting in selective fluorescence quenching even in the presence of other metal ions such as Zn(II) and Cd(II).     

Umpolung reactivity of difluoroenol silyl ethers with amines and amino alcohols. application to the synthesis of enantiopure alpha-difluoromethyl amines and amino acids

Difluoroenol silyl ethers, produced in situ from acylsilanes and CF3TMS, react as electrophiles with amines to give difluoroimines, via the corresponding hemiaminal adduct, as evidenced by 19F NMR spectroscopy. Reaction with (R)-phenylglycinol led to 2-difluoromethyloxazolidines. After separation of the diastereomers, reduction with LAH and Strecker-type synthesis gave enantiopure alpha-difluoromethylamines and alpha-difluoromethyl-alpha-amino acids, respectively.     

Mechanisms of reactions of flavin mononucleotide triplet with aromatic amino acids

Chemical reactions between the photoexcited triplet state of flavin mononucleotide and the aromatic amino acids, N-acetyl tryptophan (TrpH), N-acetyl tyrosine (TyrOH), and N-acetyl histidine (HisH) in aqueous solution have been studied in the pH range 2-12. Across the whole pH range, the principal mechanism of reaction of both TrpH and TyrOH is shown to be electron transfer. For HisH, the mechanism and rate of the reaction depend on the protonation state of the reactants. In acidic conditions (pH < 4), reaction does not occur. At 4 < pH < 11, the reaction proceeds via hydrogen atom abstraction with a rate constant varying from 3.0 x 10(6) to 2.5 x 10(8) M(-1) s(-1). In extremely basic solution (pH > 12) the mechanism switches to electron transfer.     

Interaction of supramolecular centers of silica surface with aromatic amino acids

Surface grafting of β-cyclodextrin onto aminopropylsilica has been carried out under mild conditions using 1,1'-carbonyldiimidazole as an activator. The obtained β-cyclodextrin-silica has been characterized by means of chemical and IR spectral analysis. Adsorption of para-aminobenzoic and para-aminosalicylic acids onto the surface of hydroxylated silica, aminopropylsilica, and silica with chemically attached β-cyclodextrin moieties has been studied in relation to duration of contact, equilibrium concentration, and solution pH. Chemical immobilization of β-cyclodextrin onto silica surface improves adsorption parameters for aromatic amino acids. The well-known mathematical models for the kinetic and equilibrium adsorption processes have been used, and the main adsorption parameters have been calculated. Kinetic curves of aromatic amino acids adsorption correspond to the model of pseudo-second order reaction. The major contribution to the equilibrium adsorption of para-aminobenzoic and para-aminosalicylic acids onto β-cyclodextrin-containing silica is due to the formation of surface inclusion complexes between grafted oligosaccharide molecules and aromatic amino acids.