Fast synthesis of uronamides by non-catalyzed opening of glucopyranurono-6,1-lactone with amines, amino acids, and aminosugars

A series of glucuronamides have been easily prepared by reaction of glucopyranurono-6,1-lactone with a wide variety of amines. Primary and secondary amines gave the corresponding amides in short times, high yields. Diamines led to diuronamide compounds, whereas glucuronic acid conjugates were obtained with amino acids. The reaction with aminosugars afforded disaccharide analogues. In all products, the anomeric position is free for further conversion.     

Hantzsch-type three-component approach to a new family of carbon-linked glycosyl amino acids. Synthesis of C-glycosylmethyl pyridylalanines

C-Glycosylmethyl pyridylalanines reported in this paper constitute a novel family of glycosyl amino acids that contain a pyridine ring linking the carbohydrate and amino acid residues. These amino acids may serve to prepare nonnatural glycopeptides displaying firmly bound carbohydrate fragments through a rigid and highly stable tether. A viable route to these new hybrid molecules has been opened via thermally induced Hantzsch-type cyclocondensation using an aldehyde-ketoester-enamino ester system. To one of these reagents was attached a C-glycosyl residue, while to another was bound an amino acid fragment. In a one-pot optimized methodology, the dihydropyridine was not isolated while its purification was carried out by removal of unreacted material and side products using polymer-supported scavengers. Then the dihydropyridine (mixture of diastereoisomers) was oxidized by a polymer-bound oxidant to give the target pyridine bearing the two bioactive residues. In this way a range of eight compounds (58-68% yield) was prepared in which the elements of diversity were (i) the gluco and galacto configurations of the pyranose ring, (ii) the alpha- and beta-configurations at the anomeric center, and (iii) the positions of the carbohydrate and amino acid sectors in the pyridine ring. The orthogonal functional group protection in these amino acids allowed their easy incorporation into oligopeptides via sequential amino and carboxylic group coupling.     

A versatile strategy for the synthesis of N-linked glycoamino acids from glycals

A versatile route for the synthesis of N-linked glycoamino acids from readily available glycals is reported. A variety of glycals possessing different carbohydrate templates (mono-, di- and trisaccharide glycals) were shown to undergo a novel iodine catalyzed stereoselective diamination reaction with chloramine-T. Taking advantage of the difference in the reactivity between the anomeric and C2 sulfonamido groups of these diamines 7, 13, 15, 17 and 19, they could be protected differentially at the C2 and anomeric nitrogen atoms. Thus, chemoselective acetylation of these diamines installed the C2 acetamido group, an essential functionality that plays a crucial role in inducing a beta-turn in N-linked glycoproteins. Subsequent protection of the anomeric nitrogens of 20a,b,e as their Alloc (allyloxycarbonyl) derivatives followed by SmI(2) mediated facile didetosylation afforded 24a-c. Deprotection of the Alloc group of 24a and 24c and coupling of the liberated free amine with a variety of protected amino acids provided N-linked glycoamino acids 25 and 27 in high yields. An illustrative synthesis of an N-linked glycopeptide 29 is also reported.     

Silicon amino acids

The existence and gas phase stability of silicon analogues of three natural amino acids (i.e., silicon glycine, silicon alanine, and silicon valine) belonging to the novel class of compounds termed silicon amino acids (SiAA) are investigated theoretically on the basis of ab initio QCISD/aug‐cc‐pVTZ and MP2/aug‐cc‐pVTZ calculations. All molecules studied (in their gas phase canonical forms) are structurally comparable to their proteinogenic counterparts (i.e., glycine, l ‐alanine, and l ‐valine) and capable of forming several structural isomers as such. These higher energy isomers are characterized by small relative energies (not exceeding 4 kcal mol⁻¹). The simulated IR spectra of the Si‐Gly, Si‐Ala, and Si‐Val global minima are also presented and discussed.     

Excitatory amino acids

Recent developments in the understanding of the molecular function of memory and other CNS-mediated processes have arisen from the multidisciplinary interplay of excitatory amino acid synthesis and medicinal chemistry, X-ray crystallographic structural protein analysis, molecular biology, pharmacology and physiology. This review seeks to place recent synthetic developments of EAA analogues in the wider pharmacological setting, illustrating the need for and importance of these compounds.     

Sulfenic acids in the carbohydrate field. Synthesis of transient glycosulfenic acids and their addition to unsaturated acceptors

A new method is described for building up anomeric glycosyl sulfoxides, via the formation of transient glycosulfenic acids and their addition to unsaturated acceptors. Thermolysis of alpha- and beta-3-[(2,3,4,6-tetra-O-acetyl-D-glucopyranosyl)sulfinyl]propanenitriles affords 1-glucosulfenic acids, which are reacted in situ with common substituted alkynes. The obtained (R(S),E)-2-[(2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl)sulfinyl]-2-butendioates are involved as enantiopure sulfinyl dienophiles in Diels-Alder reactions with 2,3-dimethyl-1,3-butadiene to evaluate the role that the sugar moiety plays in the steric control of the cycloaddition. This chemistry provides a direct synthetic strategy for the stereocontrolled connection between thioglycon and aglycon moieties, thus offering the basis for an easy elaboration of new molecules incorporating thiosugar residues.     

Characterization of positional and anomeric isomers of methyl 2-O- and 3-O-sulfo-D-glucopyranosiduronic acids and methyl 2-O- and 3-O-sulfo-D-glucopyranosides by secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) of anomeric pairs of methyl 2-O- and 3-O-sulfo-D -glucopyranosiduronic acids and methyl 2-O- and 3-O-sulfo-D -glucopyranosides show the deprotonated molecule in the negative-ion mode and ammoniated and sodiated molecules in the positive-ion mode. The four isomers were distinguished from each other by linked scanning at constant B/E in negative- and positive-ion SIMS, which gave information characteristic of the position of the sulfate group and even the configuration of the anomeric methoxy group. The main fragmentation processes correspond to the loss of methanol and the elimination of SO₃.     

Fatty acids and amino acids of entomopathogenic fungus <Emphasis Type="Italic">Conidiobolus coronatus</Emphasis> grow on minimal and rich media

Entomopathogenic fungi are referred to as potential candidates as insect pest control agents. The objective of the study was to identify fatty acids and amino acids from Conidiobolus coronatus cultured on two different media. Each medium was extracted with ethyl acetate and its mixtures with isopropanol, acetonitrile and methanol. Analyses of fatty acids and amino acids of entomopathogenic fungus C. coronatus were performed by means of gas chromatography coupled with mass spectrometry. The analysis showed that the fungus C. coronatus produces the following groups of compounds: fatty acids and amino acids; α- and β-glucopyranose were also identified. The identified fatty acids included 12–20, 22 and 24 carbon atoms per chain. The highest content of fatty acids was detected in a mycelium sample cultured in a liquid minimal medium extracted with ethyl acetate. The lowest content of these organic compounds was identified in mycelium cultured in a liquid nutrient-rich medium extracted with ethyl acetate–methanol mixture. Fatty acids were found to account for 62.0 mass % to 94.4 mass % of all organic compounds in the analyzed mycelia. C18:1 acids were detected in the highest amounts when ethyl acetate was used as the extracting agent. The identified amino acids accounted for 4 mass % to 21 mass % of all organic compounds. Upon extraction of C. coronatus mycelium samples with the ethyl acetate—methanol mixture, two anomeric forms of glucose were also identified. An analysis of the studied material confirmed, that the entomopathogenic fungus C. coronatus is a very rich source of organic compounds, which might encourage its further research so as to identify an even larger number of compounds being produced by this species.     

Methylthiohydantoin amino acids: chromatographic separation and comparison to phenylthiohydantoin amino acids

Most phenylthiohydantoin (PTH) amino acids and most methylthiohydantoin (MTH) amino acids may be separated from one another by thin-layer chromatography (TLC) using the same sequential development technique with the same two solvents. Similarly, a single solvent system may be used in high-performance liquid chromatography (HPLC) to separate most PTH-amino acids and most MTH-amino acids. When both TLC and HPLC separations are performed on a sample, all MTH-and PTH-amino acids can be uniquely identified. Since many solid-phase protein sequencing techniques generate both MTH-and PTH-amino acids, these analytical systems simplify identification of the amino acid derivatives. Although the chromatographic properties of MTH-and PTH-amino acids are similar, they are not identical (contrary to a previous report).     

Helix-forming carbohydrate amino acids

[reaction: see text] The solution-phase conformational properties of tetrameric and octameric chains of C-glycosyl alpha-d-lyxofuranose configured tetrahydrofuran amino acids (where the C-2 and C-5 substituents on the tetrahydrofuran ring are trans to each other) were examined using NMR and IR and CD in organic solvents. Studies by NMR and IR demonstrated that in chloroform solution, the tetramer 7 does not adopt a hydrogen-bonded conformation whereas the octamer 10 populates a well-defined helical secondary structure stabilized by 16-membered (i, i - 3) interresidue hydrogen bonds, similar to a pi-helix. Circular dichroism studies in trifluoroethanol are consistent with this conformation for the octamer 10, and also indicate that the tetramer 7 adopts a rigid conformation not stabilized by hydrogen bonds.     

Thermal stability of amino acids

Thermal decomposition of L-α-amino acids RCH₂(NH₂)COOH where R = Me₂CH, Me₂CHCH₂, MeEtCH, and C₆H₅CH₂ was studied at temperatures below the melting points of their crystals. From the effective rate constants of the first order reactions energy parameters in the Arrhenius equation were calculated. Correlations between the reaction rate constants k _R and the inductive constants σ* of substituents R and also between the rate constants of the reactions and the dipole moments of amino acids was established. Value of ρ* parameter +8.8 in the Taft equation indicates the heterolytic mechanism of transformation of the amino acids. Chromato-mass spectrometric analysis of decomposition products shows that condensation, decarboxylation, and deamination of the amino acids take place.     

Electrochemical detection of amino acids

Conclusion A method for the separation and the quantification of amino acids by high performance liquid chromatography and electrochemical detection using an isocratic mobile phase is possible and satisfactory.

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Elektrochemischer Nachweis von Aminosäuren

     

Triolsulphonate derivatives of amino acids

The synthesis and chemical properties of a series of amino acid derivatives containing the thiolsulphonate functionality are described.     

有机化学中的异头效应

1955年Edward 首次发现吡喃糖C(1)位的电负性强的取代基处于a键上, 随后被Lemieux和Chü定义为异头效应. 它是有机化学中最重要的立体电子效应之一, 通常存在于有Lp-X-A-Y结构单元的分子中, 其中X是带有孤对电子的电负性强的元素, A是一般元素, Y 也是电负性强的元素, Lp是X的孤对电子, 其轨道与A—Y键反平行. 异头效应对分子的结构和反应活性有重要影响. 综述了各类化合物中存在的异头效应、广义异头效应、反异头效应及在有机化学中的应用.     

Desulfolanylation of N-sulfolanyl amino acids

N-Sulfolanyl amino acids are cleaved at the C-N bond in ammonium hydroxide and aqueous solutions of amines to give the corresponding aminosulfolanes and amino acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1341, October, 1973.