Glycoconjugates of amino acids. Preparation throughN-alkylation of amino acids withN-chloroacetyl-β-glycopyranosylamines

Monoalkylation of amino acids of different structural types withN-chloroacetyl-glycosylamines was shown to be applicable for the preparation of glycoconjugates containing β-d-galactose,N-acetyl-β-d-glucosamine, β-d-mannose, and lactose residues. The glycoconjugates were synthesized from amino acids with secondary (sarcosine,l-proline) or primary (l-2- and 4-aminobutyric acids,l-tryptophan) amino groups as well as from various amino dicarboxylic acids (N-methyl-dl-aspartic,dl-aspartic,l-glutamic, anddl-2-aminoadipic acids). The derivatives obtained may be of interest for glycotargeting of physiologically active compounds of this series. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1377–1380, July, 1999.     

Microbial production of natural poly amino acid

Three kinds of poly amino acids, poly-γ-glutamic acid, poly(ε-L-lysine) and multi-L-arginyl-poly (L-aspartic acid) can be synthesized by enzymatic process independently from ribosomal protein biosynthesis pathways in microorganism. These biosynthesized polymers have attracted more and more attentions because of their unique properties and various applications. In this review, the current knowledge on the biosynthesis, biodegradations and applications of these three poly amino acids are summarized.     

Catalytic α-allylation of unprotected amino acid esters

Catalytic α-allylation of unprotected amino acid esters to produce α-quaternary α-allyl amino acid esters is reported. Catalytic loadings of picolinaldehyde and Ni(II) salts induce preferential reactivity at the enolizable α-carbon of amino acid esters over the free nitrogen with electrophilic palladium π-allyl complexes. Fourteen examples are given. Additionally, the use of chiral ligands to access enantioenriched α-quaternary amino acid esters from racemic precursors is demonstrated by the enantioselective synthesis of α-allyl phenylalanine methyl ester from racemic phenylalanine methyl ester.     

Preparation and characterization of amino or carboxyl-functionalized ionic liquids

New functionalized ionic liquids,1-carboxylmethyl-3-methylimimidazolium hexafluorophosphate or fluoborate and 1-ami- noethyl-3-methylimimidazolium hexafluorophosphate or fluoborate have been synthesized and investigated.The obtained amino or carboxyl-functionalized ionic liquids were all characterized by FT-IR,~1H NMR and MS(ESI)and their properties such as freezing point,viscosity,solubility,specific gravity,surface tension,and interracial tension were also determined.     

Mass spectrometric study of amino acid–triethylborane chelates

Abstract  Synthesis of chelates from selected l-amino acids and triethylborane, and the mass spectra of the chelates, are described. Conditions for forming dimers between the chelates and the sodium ion are discussed, and structures are proposed for the dimers. Graphical abstract        

Enantioselective synthesis of stimulus-responsive amino acid via asymmetric α-amination of aldehyde

Development of a methodology to control the function of peptides and proteins is an indispensable task in the field of chemical biology and drug delivery. Recently, we reported synthesis of racemic stimulus-responsive amino acids and their application for controlling peptidyl function. In this study, we report enantioselective synthesis of a key intermediate of stimulus-responsive amino acids via asymmetric α-amination reaction of an aldehyde. The obtained chiral intermediate was converted to an Fmoc protected UV-responsive amino acid with (S)-configuration, and it was successfully incorporated into a model peptide by Fmoc solid phase peptide synthesis.     

Reactions of organometallics with oximes. Synthesis of α-N-hydroxy amino acids

Reaction of organolithium reagents with glyoxylate and pyruvate derived oximes provides a direct route for the synthesis of unusual α-N-hydroxy amino acids.     

A reappraisal of the Ni-[(Benzylprolyl)amino]benzophenone complex in the synthesis of α,α-disubstituted amino acid derivatives

α,α-Disubstituted alkenyl amino acid derivatives (e.g. Fmoc-S₅-OH) are valuable monomers in the construction of stapled peptide derivatives. Synthetic access to these is possible using the Ni-[(Benzylprolyl)amino]benzophenone (BPB) complex as a chiral auxiliary. We discuss a reappraisal of the use of this, and demonstrate that epimerisation of the proline α-centre occurs during formation of the complex, leading to erosion in the enantiomeric excess of the final product. Modified conditions have been developed, providing the target compounds in high enantiomeric excess.     

Reaction of amino acid derivatives with C_(60)

Ammo acid derivatives react with C60 at 110-120℃to form adduct compounds.The products were isolated by column chromatography and were identified by FD-MS,UV-Vis,FT-IR and 13C NMR spectroscopies.     

Thermodynamics of protonation of amino acid carboxylate groups from 50 to 125°C

Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C _p ^° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C _p ^° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C _p ^° values which approach those associated with charge reduction reactions. As the temperature increases, C _p ^° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.     

Direct synthesis of α-thio aromatic acids from aromatic amino acids

Modified amino acids are useful synthetic components in both chemistry and biology. Here we describe a simple, scalable two-step procedure to generate α-thio aromatic acids from aromatic amino acids with yields of up to 96%. Diazotization and α-lactone mediated bromination efficiently form the α-bromo acid with retention of configuration. Thiol substitution with mild reagents such as sodium hydrosulfide or sodium trithiocarbonate provides the inverted, free α-thio acid. The mildly acidic soft nucleophile can then be utilized in many synthetic applications.     

Sensitive analysis of amino acids in injection liquor by reversed-phase HPLC

A convenient derivatization method of amino acids with l-fluoro-2,4-dimtrobenzene as reaction reagent and a separation system were described. The derivative amino acids were separated on a specific chemically bonded phase column with a simple linear gradient elution consisting of aqueous buffer and methanol. The eluate was detected by common ultraviolet absorption detector at 360 nm. The detection limits of amino acids were as low as 10 picomole. This method has been successfully applied to assay amino acid injection liquor used in hospital. It has good repro-ducibility and precision. The procedures avoid the requirements of particular derivative equipment and analyzer employed in conventional amino acid analysis.     

Synthesis and properties of a sterically unencumbered δ-silanediol amino acid

An amino acid carrying a 1-(4-dihydroxymethylsilyl)butyl side chain has been prepared in enantiomerically pure form as a potential inhibitor of the enzyme arginase, a pharmaceutical target. As a water-soluble silanediol, this compound was anticipated to be entropically stabilized against polymerization and siloxane formation. At 50 mM in D(2)O, the degree of oligomerization was found to be pH dependent, with diastereomeric mixtures formed on condensation. Above pH 11 the silane is largely monomeric.     

Asymmetric synthesis of α-aryl amino acids; aryne-mediated diastereoselective arylation

An aryne-mediated α-arylation reaction of Scho?llkopf's bis-lactim ether is described. Arynes were generated via an ortho-lithiation approach, affording syn-arylated products in up to 94:6 dr with moderate to good yields and excellent regioselectivities. Hydrolysis provided a variety of substituted arylglycines containing a range of functional groups without racemization.     

Fast quantification of amino acids by microchip electrophoresis–mass spectrometry

A fast microchip electrophoresis–nano-electrospray ionization-mass spectrometric method (MCE-nanoESI-MS) was developed for analysis of amino acids in biological samples. A glass/poly(dimethylsiloxane) hybrid microchip with a monolithic nanoESI emitter was used in the platform. The proposed MCE-nanoESI-MS analytical method showed high separation efficiency for amino acids. Baseline separation of an amino acid mixture containing Lys, Arg, Val, Tyr, and Glu was completed within 120 s with theoretical plate numbers of >7,500. The method was applied to study cellular release of excitatory amino acids (i.e., aspartic acid (Asp) and glutamic acid (Glu)) under chemical stimulations. Linear calibration curves were obtained for both Asp and Glu in a concentration range from 1.00 to 150.0 μM. Limits of detection were found to be 0.37 μM for Asp and 0.33 μM for Glu (S/N?=?3). Assay repeatability (relative standard deviation, n?=?6) was 4.2 and 4.5 %, for Asp and Glu at 5.0 μM, respectively. In the study of cellular release, PC-12 nerve cells were incubated with alcohol at various concentrations for 1 h. Both extra- and intracellular levels of Asp and Glu were measured by the proposed method. The results clearly indicated that ethanol promoted the release of both Asp and Glu from the cells.     

Efficient chemoenzymatic synthesis of enantiomerically pure β-heterocyclic amino acid derivatives

Enantiomerically pure (S)-pyrazolyl alanine and its derivatives are nonproteinogenic amino acids with antidiabetic activity. A short and effective enantioselective synthesis of these compounds is described, using a kinetic resolution by an acylase from Aspergillus sp.     

Synthesis and characterization of N-3-phenyl-2-propenoyl amino acids

Three N-3-phenyl-2-propenoyl amino acids were synthesized through interaction between 3-phenyl-2-propenoyl chloride and amino acids in alkaline with a high Yield . Structure of the products were identified by elemental analysis,IR and NMR spectroscopy. The reaction is described as: CH CHCOOH + SOCl2 CH CHCOCl CH CHCOCl + R CH COOH NaOH CH CHCONH CH COOH NH2 RSynthesis and characterization of N-3-phenyl-2-propenoyl amino acids…     

Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented.     

Aminopyridines as amino components in the catalytic synthesis of α-aminophosphonates

6h-Aminophosphonates containing alicyclic, aromatic, and heterocyclic fragments were obtained in high yields by the Kabachnick—Fields reaction of the corresponding carbonyl compounds with 2-, 3- and 4-aminopyridines and diethyl phosphite using tetra- tert-butyl- phthalocyanine aluminum chloride as the catalyst. 2-, 3-, 4-Aminopyridines were found to vary in their reactivity with ketones and diethyl phosphite in the catalytic three-component one-pot process.