Isomerization and Antiacidolysis Properties of Molybdic Heteropoly Blues with Keggin Structure

For eight kinds of acidic potassium salts of hetcropoly blues which have not been reported in literature,the isomeri/.ation reaction in solution for these two-and four-electron hcteropoly blue solids were investigated by means of polarograms,cyclic voltammetry,31P NMR and X-ray diffraction methods.The heteropolynier of PMo12 and AsMo12 converte to their β-isomers during isomerization reaction which were found to have antiacidolysis property.     

Polycondensation of N-substituted borazoles with the bis-β, β′ -aminodiethyl ester of trimethylenediboric acid

Conclusions N-Triphenylborazole and B-methyl-N-triphenylborazole enter into a condensation reaction with the bis-, '-aminodiethyl ester of trimethylenediboric acid, forming polymers with reticular and linear structures, respectively.The authors would like to thank L. I. Zakharkin and A. I. Kovredov for providing the bis-, '-aminodiethyl ester of trimethylenediboric acid.     

Reaction of 2-aminopyridines with α, β-unsaturated acids

The reaction of 2-amino- and 2-amino-5-halopyridines with acrylic, methacrylic, and crotonic acids forms N-(2-pyridyl)- and N-(5-halo-2-pyridyl)--alanines and the betaines 2-amino-1-(2-carboxylatoethyl)pyridinium or 3,4-dihydropyrido[1,2-a]pyrimidin-2-ones, or their homologs.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 80–85, January, 1992.     

The reaction of carbohydrates and uronic acids with β-methylindole

Aldo- and ketu-hexoses produce with β-methylindole a pigment that is soluble with blue color in chloroform. The same applies to ω-hydroxymethylfurfural. Pentoses and uronic acids as well as furfural produce an olive color reaction, but no blue Soluble pigment. Methylpentoses and methylfurfural produce a red pigment, the chloroform extract of which is of raspberry color. The behavior of the heptoses is not characteristic. There is no possibility of differentiating between glucurone and galacturonic acid.     

The vibrational spectrum and the normal coordinate analysis of β-TiCl3

The vibrational spectrum of β-TiCl₃ is reported. The observed bands are assigned on the basis of the normal coordinate analysis by use of a valence force field. It was found that the A_2u mode is lower in frequency than that in α-TiCl₃ and one of the TiTi stretchings is 281 cm⁻¹, resulting in a TiTi stretching force constant of 81.6 N/m.     

Kinetic resolution in the directed hydrogenation of N-substituted α-(aminoalkyl) acrylates,precursors of optically active β-amino acids.

Of a variety of allylic substituents examined, NHCOCH₃ and NHCO₂Bu^t were particularly effective directing groups in homogeneous hydrogenation.     

Catalytic decarboxylative alkylation of β-keto acids with sulfonamides via the cleavage of carbon-nitrogen and carbon-carbon bonds

An efficient decarboxylative alkylation reaction of β-keto acids with N-benzylic or N-allylic sulfonamides has been developed, for the first time, through sequential cleavage of carbon-nitrogen and carbon-carbon bonds in the presence of 10 mol% of FeCl(3).     

Phe-Ala-based diazaspirocyclic lactam as nucleator of type II' β-turn

The synthesis of a novel Phe-Ala dipeptide mimic, built up on a diazaspirocyclic lactam core, is presented. This new scaffold was evaluated for conformational mimicry of reverse turn by combining molecular modeling, IR, NMR, and X-ray diffraction experiments. All these tools agree on the presence of a strong intramolecular hydrogen bond, thus demonstrating the ability of this spiro compound to act as a type II' β-turn inducer.     

pH-dependent complex formation of amino acids with β-cyclodextrin and quaternary ammonium β-cyclodextrin

Stability constants for the complexes of anionic, neutral (zwitterionic) and protonated forms of l- and d-enantiomers of eight amino acids with β-cyclodextrin and the positively charged quaternary ammonium β-cyclodextrin (QA-β-CD, DS?=?3.6?±?0.3) have been determined by spectrophotometric and pH-potentiometric methods. The highest stability constants have been obtained for the aromatic amino acids phenylalanine, tyrosine and tryptophan. Except the dianion of tyrosine and QA-β-CD, values for the anions in the range of 80–120 have been found, the stability constants for the zwitterionic forms are much smaller and complex formation is negligible with the protonated species. In the case of the other amino acids the differences are less pronounced. The results are interpreted in terms of hydrogen bonding, steric effects and electrostatic interactions between the amino acid moiety and the rims of the cyclodextrins, in addition to the inclusion of the side chain, and are supported by ¹H and ¹³C NMR investigations on the systems containing l-phenylalanine and l-tyrosine. The differences between the complex formation constants of the l- and d-enantiomers do not exceed the limits of experimental error in most cases.     

A Study of Heteropoly Complexes of Rare Earths as Catalyst Promoter in the Synthesis of Ethyl Acetate

Ethyl acetate(EA) is a kind of important materials in chemistry industry. The synthesis of EA is catalyzed by the oil of vitriol (H2SO4) in the industry. The preparation method of EA from acetic acid and alcohol using the large quantity of H2SO4 has many shortages of environment pollution, equipment erosion and low yield 1. Recently heteropoly acids were used as catalysts 1,2. Because most of the heteropoly acids are in liquid state and need to have the solid supporting materials 3. …     

Reaction of aziridinecar☐ylic acids with thiols in aqueous solution. the formation of β-amino acid

Enantiomers of 3-methyl-2-aziridinecar☐ylic acids (1-d and 1-l) and 2-aziridinecar☐ylic acids (2-d and 2-l) reacted easily with thiophenol, cysteine and glutathione in aqueous solution or in sodium phosphate buffer solution at room temperature and gave predominantly β-amino acid derivatives with sulfur substituents at their α-position.From 1-d and thiophenol, (2S, 3R)-3-amino-2-phenylthiobutanoic acid (3-d) was produced predominantly. In order to confirm the structure, 3-d was converted to (3S, 4R)-3-phenylthio-4-methylazetidin-2-one (5) using the Ohno reaction. The configurations of 3-d and 6 were determined by X-ray diffraction and ¹³C NMR spectrum analysis, respectively. We concluded that the ring-opening reaction of unactivated aziridinecar☐yhc acids with thiols in aqueous solution occurred predominantly on C-2 of the aziridine ring with inversion of the configuration at this position. The reaction offers a good route for stereoselective synthesis of peptides or β-lactam derivatives.     

Environment- and sequence-dependence of helical type in membrane-spanning peptides composed of β3-amino acids

Transmembrane (TM) β-peptides comprised of acyclic β(3)-amino acids demonstrate equilibrium between 12- and 14-helical structures in an environment- and sequence-dependent manner. Circular dichroism (CD) spectra of TM β(3)-peptides may be described as linear combinations of the 12- and 14-helical CD spectra. The apparent malleability of β(3)-substituted acyclic β-peptides has practical implications for foldamer design, as it suggests that both the 14-helix and 12-helix might be reasonable platforms for molecular recognition.     

Spectrophotometric Study of the Interaction of β‐Cyclodextrin with Hydroxamic acids

Cyclodextrins have attracted considerable interest because of their ability to form stable inclusion complexes with a wide variety of inorganic and organic guest molecules. In the present communication, binding constant of β‐cyclodextrin and a series of substituted benzohydroxamic acids (X‐C₆H₄CON(OH)H), X=H, 4‐NO₂, 4‐Me 4‐OMe, and 2‐OH and N‐phenylbenzohydroxamic acid (C₆H₅CON(OH)C₆H₅) were determined at 27°C spectrophotometrically. In all the cases the formation of 1:1 host‐guest complex was established. The addition of β‐CD results in an increase in the absorbance intensity but does not cause a shift in λ_max. The values of binding constants are in good agreement with in those determined from kinetic and pH metric techniques.     

Enantiodifferentiation of aminophosphonic and aminophosphinic acids with α- and β-cyclodextrins

Cyclodextrins were used as chiral selectors for the ³¹P NMR determination of the enantiomeric excess of aminoalkanephosphonic and aminoalkanephosphinic acids. Most of these acids form inclusion complexes with α- and/or β-cyclodextrin and upon increasing the cyclodextrin to aminophosphonic acid molar ratio ³¹P NMR signals for (R)- and (S)-enantiomers separate. ROESY spectra allowed the determination of structures of the inclusion complexes.     

Recent topics in the syntheses of β-keto carboxylic acids and the derivatives

β-Keto carboxylic acids are key intermediates in organic syntheses, used for the development of fine chemicals, natural products, and various biologically relevant molecules. Their utilities stem from the structural features and facile bond formations, e.g., asymmetric reduction of carbonyl groups for the synthesis of β-hydroxy carboxylic acids and conjugated addition reactions through decarboxylative enolate nucleophiles, which utilize the amphiphilic reactivity of β-keto carboxylic acids. Despite their versatility and utilities, development of efficient and straightforward synthetic methods for β-keto carboxylic acids has not attracted considerable attention owing to their instability. As efficient synthetic strategies for β-keto carboxylic acids and their derivatives, reactions of α-diazoesters, acylation of malonate anions, cross-coupling reactions, and CO₂ insertion reactions are summarized in this review.     

The metal complexes of amino acids and their N-substituted derivatives—VI. The physical properties,i.r. spectra and normal coordinate analysis of bivalent metal complexes with dl-threonine

Complexes of five bivalent metals with dl-threonine have been prepared and characterized by means of i.r. absorption, powder diffuse reflection, and electronic spectra, X-ray diffraction and magnetic susceptibility. The complexes appear to be of three distinct types. The first type includes ML₂·nH₂O (M = Ni, Cu, Zn; L = dl-threoninato anion), in which the ligand chelates metal ions through the nitrogen atom and the oxygen atom of the carboxylato group. Three species of copper(II) complexes have been prepared. They seem to be two trans forms and one cis form. MnCl₂(HL)₄·H₂O is a second type in which the metal is coordinated through the oxygen atom of the carboxyl group and chloride ions, but is not coordinated through the nitrogen atom. 2CdCl₂·HL·HCl·2H₂O is a third type, in which the metal is coordinated through only chloride ions. In order to assign the observed frequencies of i.r. absorption spectra in detail, a normal coordinate analysis has been accomplished for the complexes of the first type as a 33-body problem. Copper(II) and zinc(II) complexes with l-threonine have been prepared for comparison.     

Iron-catalyzed hydroxylation of β-ketoesters with hydrogen peroxide as oxidant

The hydroxylation of β-ketoesters was studied using simple iron catalysts and 30 wt % hydrogen peroxide as the terminal oxidant. The highest activity and yield were achieved in the presence of iron(III) chloride. Cyclic β-ketoesters could be smoothly hydroxylated in 75-90% yield. For linear β-ketoester and β-ketoamide, the chloro-substituted products were obtained.