Glycopolymers from Synthetic Fragments (Amides of α-d-Galacturonic Acid with Amino Acids) of Proteus O-Antigens

Abstract

Galacturonamides of amino acids (alanine, lysine, serine, and threonine), constituents of Proteus O-specific polysaccharides, have been synthesised. O-tert-Butyl and N^?-tert-butyloxycarbonyl protected amino acid tert-butyl esters were condensed with the 2-azidoethyl α-glycoside of d-galacturonic acid, prepared by Fischer glycosidation. Reduction of the azido group followed by N-acryloylation and deprotection gave the target monomers. By copolymerisation with acryl-amide, these were converted into glycopolymers potentially useful for defining epitopes in Proteus O-antigens.     

NMR Studies of a New Binding Mode of the Amino Acid Esters by Porphyrinatozinc(Ⅱ)

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Synthesis of β–Amino Acid Derivatives

In recent years, β-amino acids and their derivatives have attracted considerable attention due to their occurrence in biologically active natural products, such as dolastatins, cyclohexylnorstatine and Taxol. β–Amino acids also find application in the synthesis of β–lactams, piperidines, indolizidines. Moreover, the peptides consisting of β–amino acids, the so-called β–peptides, have been extensively studied recently. Consequently, considerable efforts have been directed to the synthe…     

The Regulation Effect of Phosphoryl Group on Amino Acid Side Chain

The amino acids' side chains act as the relay device to modulate the chemical reactivity of the N-phosphoryl amino acids. The N-dialkyl phosphoryl cysteine is stable, but the N-dialkyl phosphoryl serine or threoine was converted into many kinds of products at 40℃. The N-dialkyl phosphoryl gltamic acid is a stable compound, while the N-dislkyl phosphoryl aspartic acid was transferred into the peptides, esters and the phosphoryl ester-exchanged products under mild conditions. The N-dialkyl phosphoryl histidine has the similar reactivity through the co-participation of the side chain, carboxyl and phosphoryl groups. A hexacoordinate phosphorus was proposed to account for this differentiation and promotion effect.     

Glycine Imine—The Elusive α-Imino Acid Intermediate in the Reductive Amination of Glyoxylic Acid

Simple unhindered aldimines tend to hydrolyze or oligomerize and are therefore spectroscopically not well characterized. Herein we report the formation and spectroscopic characterization of the simplest imino acid, namely glycine imine, by cryogenic matrix isolation IR and UV/Vis spectroscopy. Glycine imine forms after UV irradiation of 2-azidoacetic acid by N₂ extrusion in anti-(E,E)- and anti-(Z,Z)-conformation that can be photochemically interconverted. In matrix isolation pyrolysis experiments with 2-azidoacetic acid, glycine imine cannot be trapped as it further decarboxylates to aminomethylene. In aqueous solution glycine imine is hydrolyzed to hydroxy glycine and hydrated glyoxylic acid. At higher concentrations or in the presence of Fe^IISO₄ as a reducing agent glycine imine undergoes self-reduction by oxidative decarboxylation chemistry. Glycine imine may be seen as one of the key reaction intermediates connecting prebiotic amino acid and sugar formation chemistry.     

The Synthesis of Amino Acid Methyl Ester 5′-Phosphoamidates of Protected Uridine

In this article, we used the Atherton–Todd reaction to synthesize amino acid methyl ester 5′-phosphoamidates of uridine as prodrugs. Their structures were confirmed by ¹H NMR, ³¹P NMR, ¹³C NMR, IR, and mass spectrometry.

Supplemental materials are available for this article. Go to the publisher′s online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

The Role of the Alcohol and Carboxylic Acid in Directed Ruthenium-Catalyzed C(sp(3) )H α-Alkylation of Cyclic Amines

A general directed Ru-catalyzed C(sp(3) )?H α-alkylation protocol for piperidines (less-reactive substrates than the corresponding five-membered cyclic amines) has been developed. The use of a hindered alcohol (2,4-dimethyl-3-pentanol) as the solvent and catalyst activator, and a catalytic amount of trans-1,2-cyclohexanedicarboxylic acid is necessary to achieve a high conversion to product. This protocol was used to effectively synthesize a number of 2-hexyl- and 2,6-dihexyl piperidines, as well as the alkaloid (±)-solenopsin?A. Kinetic studies have revealed that the carboxylic acid additive has a significant effect on catalyst initiation, catalyst longevity, and reverses the reaction selectivity compared with the acid-free reaction (promotes alkylation versus competing alkene reduction).     

Amino Acid Sequence of an Excitatory Insect-selective Toxin (BmK IT) From Venom of the Scorpion Buthus martensi Karsch

The insect-selective neurotoxin(BmK IT) of scorpion Buthus martensi Karsch was first reduced and S-alkylated, and then digested by TPCK-trypsin and Staphylococcus aureus V-8 Protease. The enzymatic peptides were purified on TLC-plastic sheet and submitted to determine their amino acid compositions and sequences. The sequence of the 70 amino acid residues of BmK IT was established with reference to the primary structure of AaH IT, another excitatory insect-selective toxin from the venom of North African scorpion Androctonus australis Hector. About 75% of the homologous sequence was found in the molecules of BmK IT and AaH IT. It is obvious that the results contribute toward better understanding of the molecular structure characteristics, structure/activity relationship of scorpion insect-selective toxins, and they can serve as the molecular basis for utilizing the toxins as a tool to clarify molecular mechanism involved in channel gating, and to infer the possibility of developing them as new selective b     

The Synthesis of Some Novel N-[α-(Isoflavone-7-O-) Acetyl]Amino Acid Derivatives

IsoflavonoidsarebiologicallyimportantnaturalproductsoccurringmainlyinspeciesoftheLeguminosaefamilyandhaveshownawidespectrumofbiologicalactivitiesincludingestrogenic,anticancer,insecticidal,pisciadalandantifungalproperty'.Theseisoflavonoidphytoestrogensarerichinsomeplantdietsuchassoybean'.Animalexperimentshadshownthatsoybeandietinhibitradiation-andchemical-inducedtumorofthemammary',skin',andlivers.AstudyconductedbyBarnesetal.6suggestedthatsoybeanisoflavonesmayberesponsiblefortheanticarcinogeni…     

Synthesis of Cyclopropenone-Containing Amino Acid Mimic. Addition of Cyclopropenyl Cerium Reagent to α-Amino Aldehydes

A novel amino acid mimic, 2-(2-amino-1-hydroxyalkyl)-cyclopropenone, has been prepared via chelation controlled addition of a cyclopropenyl cerium reagent to an α-amino aldehyde.     

First Example of Intramolecular C-H Insertion Reaction in an Amino Acid Derived α-Diazoketone

Rh-Catalyzed intramolecular C-H insertion reaction of L-leucine derived α-diazoketone is described.     

Complex Formation Reactions of (2,2′-dipyridylamine)copper(II) with Various Biologically Relevant Ligands. The Kinetics of Hydrolysis of Amino Acid Esters

Binary and ternary copper(II) complexes involving 2,2′-dipyridylamine (DPA) and various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. The ternary complexes of copper(II) with DPA and DNA are formed in a stepwise process, whereby binding of copper(II) to DPA is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(DPA)²⁺. The concentration distribution of the complexes in solution was evaluated. [Cu(DPA)(CBDCA)], [Cu(DPA)(malonate)] and [Cu(DPA)(oxalate)] were isolated and characterized by elemental analysis, i.r. and magnetic measurements. Spectroscopic studies of [Cu(DPA)(malonate)] revealed that the complex exhibits square planner coordination with copper(II). The hydrolysis of glycine methyl ester (MeGly) is catalyzed by the Cu(DPA)²⁺ complex. The reaction has been studied by a pH-state technique over the pH range 5.8–6.8 at 25 °C and I=0.1 mol dm⁻¹. The kinetic data fits assuming that the hydrolysis proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carboxylic group, is followed by the rate-determining attack by the OH⁻ ion. The second step involves equilibrium formation of the hydroxo-complex, Cu(DPA)(MeGly)(OH), followed by intramolecular attack.     

A Green Synthesis of Diisopropyl Phosphoryl Amino Acid

In this paper,we report that diisopropyl phosphoryl amino acid be prepared with reasonable yields under solvent-free condition by adding amino acid to the mixture of diisopropyl phosphite and N-chlorodiisopropylamine.     

Crystal-state conformation of homo-oligomers of α-aminoisobutyric acid: Molecular and crystal structure of pBrBz-(Aib)6-OMe

A synthetic, terminally blocked homohexapeptide from-aminoisobutyric acid has been examined by single-crystal X-ray diffraction and the structure refined toR = 0.047. The compound is folded into almost two turns of a 3₁₀-helix, stabilized by four consecutive intramolecular N—H·O=C H-bonds. An asymmetric covalent geometry for the-aminoisobutyric acid residues, known to be responsible for the onset of the 3₁₀-helix in homopeptides from this C^,-dialkylated-aminoacid on the basis of a theoretrical conformational analysis, has been experimentally found also in this structure.     

Amino acid-catalyzed asymmetric α-amination of carbonyls

Electrophilic amination of ketones and aldehydes in the presence of dibenzylazodicarboxylate in dichloromethane, using l-azetidine carboxylic acid as a catalyst, is described. Yields and ee are discussed in comparison with the corresponding l-proline-catalyzed reaction.     

Diastereoselective α—Alkylation of β—Amino Esters：Preparation of Novel α—Substituted β—Amino Esers from α—Amino Acids

Enantiomerically pure α-substituted β-amino esters were prepared from natural L-α-amino acids through Arndt-Eistert homologation and diastereoselective α-alkylation.     

Complexes of Zn(II) and Сu(II) with the Amino Derivatives of Deoxycholic Acid: Syntheses,Structures, and Properties

Russian Journal of Coordination Chemistry - Complexes [Zn(L)Cl2] (I), Cu(L)Cl2 ? H2O (II), Zn(L1)Cl2 ? 0.5H2O (III), and Cu(L1)Cl2 ? 0.5H2O (IV) (where L and L1 are the...     

Lewis Acid Catalyzed α-Functionalization of Ketals for the Regioselective Synthesis of α-Carbamoyl Ketals

Treatment of 1 with DEAD in the presence of BF(3)·OEt(2) gave 2 (R = H), which was N-alkylated to give 2 (R = CH(2)CO(2)Et), and insitu eliminated (E1cb) to give α-carbamoyl ketals.     

The Synthesis of Cyclic Amino Acids

Several cyclic amino acids (1-4) were synthesized from glycine. Isocyanate ester was prepared as the key intermediate and reacted with dibromoalkanes to afford the target compounds.