Chiral methylbenzylammonium salts of aryldithiophosphonic acids containing glucofuranose,allofuranose, and galactopyranose diacetonide scaffolds

Abstract

New chiral methylbenzylammonium salts of aryldithiophosphonic acids containing glucofuranose, allofuranose, and galactopyranose diacetonide substituents were obtained using (S)-(–)-α-methylbenzylamine, (R)-(+)-α-methylbenzylamine, and (R,S)-(±)-α-methylbenzylamine. Salts obtained possess antimicrobial activity.     

Separation and determination of neuraminic acids in nanogram quantities by liquid chromatography — A comparative study with different amino phases

Summary Neuraminic acid derivatives were separated easily by liquid chromatography on amino phases and using acetonitrile/15 mM phosphate buffer, pH 5.2 as mobile phase. Detection at 200 nm allowed determination of substances in the nanomole range. All solvent systems were used isocratically at room temperature. The separation did not depend on ion-exchange but on a partition mechanism, the solutes being separated according to their polarity. Thus, it was possible to optimize the resolution by varying the stationary phase and the composition of the eluent.Part of this work has been presented at the 15th International Symposium on Chromatography, Nürnberg, October 1–5, 1984.     

Efficient Sialyltransferase Inhibitors Based on Transition-State Analogues of the Sialyl Donor

A 200- to 1000-fold higher affinity for sialyltransferase is shown by compounds 1 and 2 relative to the natural substrate. These inhibitors, which are derived from the transition state of S_N1-type sialyltransfer, contain a flat ring that is attached through a carbon atom with a phosphonate and a cytidine monophosphate group.     

味觉化学之酸味化学*

酸是五味之一。食物酸味的产生是由于其中所含的酸性化合物。不同的酸味食物,所含的酸性化合物结构有所不同。从酸味的产生原理出发,对常见酸味食物中所含酸性化合物的结构及性质进行了介绍。     

Chemistry and biochemistry of branched-chain sugars

Branched-chain sugars have recently been isolated in larger numbers from microorganisms and higher plants as glycoside components of antibiotics or phenolic compounds. They also occur in plants in cell wall polysaccharides. Sugars with methyl, hydroxymethyl,formyl, hydroxyethyl, and glycoloyl branches have so far been found in nature. Many new methods have been developed for the synthesis of these sugars. With one exception, the branched sugars known at present can be divided biogenetically into three groups. Sugars with methyl branches are formed by C₁ transfer, sugars with hydroxyethyl branches by C₂ transfer to a hexose chain, and sugars with hydroxymethyl or formyl branches by rearrangement of a hexose or pentose chain.     

Chemistry and Significance of the Carbohydrate Moieties of Human Serum Glycoproteins

The glycoproteins exercise important biological functions as transport proteins, inhibitors, enzymes, hormones, complement factors, and immunoglobulins. Their chemistry is characterized by a number of rules. Thus only asparagine, threonine, or serine can carry the oligosaccharide groups; for the N-acylglycosylamine linkage involving asparagine, the grouping Asn-X-Thr or Asn-X-Ser is always present in the peptide chain. However, practically no agreement is found in the molecular weights of the glycoproteins, their carbohydrate contents, and the relative contents of the-various sugars. The biological significance of the carbohydrate fraction has not yet been explained, but some idea of the part played by the easily removable neuraminic acid is being formed.     

Simultaneous determination of amino acids and carbohydrates in culture media of Clostridium thermocellum by valve-switching ion chromatography

An improved method for the simultaneous determination of 20 amino acids and 7 carbohydrates using one-valve switching after injection, ion chromatography, and integrated pulsed amperometric detection is proposed. The resolution of the amino acids and carbohydrates in the cation trap column was investigated. In addition, parameters including flow liquid type, flow rate, concentration, and valve-switch timing were optimized. The method is time-saving, effective, and accurate for the simultaneous separation of amino acids and carbohydrates, with a mean correlation coefficient of >0.99 and repeatability of 0.5–4.6% for eight replicates. The method was successfully applied in the analysis of amino acids and carbohydrates in aseptic media and in extracellular culture media of three phenotypes of Clostridium thermocellum.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids I. Separation of benzenecarboxylic acids with tartaric acid as eluent and with UV-photometric detection

The application of zirconium-modified silica gels (Zr–Silicas) as stationary phases for ion-exclusion chromatography with UV-photometric detection (IEC–PD) for mono-, di-, tri- and tetrabenzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, salicylic and benzoic acids) and phenol was carried out using tartaric acid as the eluent. Zr–Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. The effect of the amount of zirconium adsorbed on silica gel on chromatographic behavior of these benzenecarboxylic acids and phenol was investigated. As a result, Zr–Silica adsorbed on 20 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in the IEC–PD for the simultaneous separation of these benzenecarboxylic acids and phenol. Excellent simultaneous separation and highly sensitive UV detection at 254 nm for these benzenecarboxylic acids and phenol were achieved in 20 min by the IEC–PD using the Zr–Silica column (250×4.6 mm I.D.) and a 10 mM tartaric acid at pH 2.5 as eluent.     

Synthesis and characterization of chiral iron carbonyl complexes from imine ligands with carbohydrates and amino acids as substituents

Imine ligands derived from 6-amino-6-desoxy-1,2,3-O-trimethyl--d-glucopyranose or from various amino acid esters react with Fe₂(CO)₉ to give chiral iron carbonyl complexes. Derivatives produced from benzaldehyde react via a C–H activation reaction in ortho-position with respect to the exocyclic imine substituent followed by an intramolecular hydrogen transfer reaction of the activated hydrogen towards the former imine carbon atom. The molecular structure of the diiron hexacarbonyl complexes of benzylideneamino-l-phenylalanine ethyl ester and benzylideneamino-l-methionine methyl ester were characterized by means of X-ray structure determinations. Imines produced from cinnamaldehyde upon reaction with Fe₂(CO)₉ produce mononuclear iron tricarbonyl complexes with the imine ligand being coordinated in a η⁴-fashion.     

Chemistry and biology of glycosaminoglycans in blood coagulation

Glycosaminoglycans (GAGs) are widely distributed in animal tissues where they are usually associated with proteins. Six types are commonly recognized: heparin (Hep), heparan sulfate (HS), dermatan sulfate (DS), chondroitin sulfate (Ch-S), keratan sulfate (KS) and hyaluronic acid (Hyal). They are structurally related with a carbohydrate backbone consisting of alternating hexuronic acid (L-iduronic acid and/or D-glucuronic acid) or galactose units and hexosamine (D-glucosamine or D-galactosamine) residues. All GAGs, except Hyal, show sulfate groups along their chains. Certain sulfate glycoaminoglycans have the ability to interfere with blood coagulation, as demonstrated by the extensive clinical use of Hep as an anticoagulant agent. HS and DS show a good anticoagulant activity, although weaker than that of Hep. In contrast, Ch-S has a low ability to inhibit plasma serine proteases, and KS and Hyal are devoid of any effect on coagulation cascade. The interaction between blood coagulation serine proteases and GAGs can be found to have two principle mechanisms: the specific “lock and key” binding and the nonspecific cooperative electrostatic association. This different ability of GAGs to interact with coagulation cascade proteins depends on the molecular weight, the ratio of iduronic/glucoronic acid and the sulfation degree. Many attempts have been made to improve or induce anticoagulant activity of natural GAGs-by chemical modification. Increasing sulfation degree of DS and Ch-S is followed by their biological activity increasing. Hyal, which is devoid of any anticoagulant effect, acquires a good ability to inactivate plasma serine proteases, i.e. thrombin and Factor Xa, when it is sulfated. This ability increases by increasing the number of sulfate groups per disaccharide unit, although the mechanism of action is different from that of Hep, but seems to be independent of its molecular weight.     

Comparison of metallic electrodes for constant-potential amperometric detection of carbohydrates,amino acids and related compounds in flow systems

Constant-potential amperometric detection of carbohydrates, amino acids, and other aliphatic organic compounds is possible by means of their oxidation in alkaline solution at a variety of metal/metal oxide electrodes including Pt, Au, Cu, Ni, Ag and Co. The experimental conditions required for optimum detection and the analytical performance obtainable vary widely for different electrode materials and analytes. In this work, the cyclic voltammetric behavior exhibited by selected analytes (glucose, glycine, lactic acid, ethylamine and ethanol) at each of these electrodes was used to determine the optimum potentials suitable for flow detection so that the capabilities of the different metal electrodes could be evaluated and systematically compared. In general, the Cu electrode was found to provide superior detection capabilities in terms of its range of response, detection limits and especially stability. Despite the fact that Pt and Au are typically used only with a pulsed applied potential, both can provide long-lived constant-potential detection of carbohydrates and other analytes at low concentrations if the potentials ere carefully chosen and the electrodes are allowed to undergo an initial stabilization period.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids II. Separation of aliphatic carboxylic acids with pyromellitic acid as eluent and with suppressed conductimetric detection

The application of zirconium-modified silica gels (Zr-Silica) as stationary phases for ion-exclusion chromatography with conductimetric detection (IEC–CD) for C₁–C₈ aliphatic carboxylic acids (formic, acetic, propionic, butyric, valeric, caproic, heptanoic and caprylic acids) was carried out using pyromellitic acid as the eluent. Zr-Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. An ASRS-Ultra anion self-regenerating suppressor in the K⁺ form was used for the enhancement of conductimetric detector response of these aliphatic carboxylic acids. A Zr-Silica adsorbed on 10 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in IEC–CD for the separation of these aliphatic carboxylic acids. Excellently simultaneous separation and highly sensitive detection for these aliphatic carboxylic acids were achieved in 25 min by IEC–CD with the Zr-Silica column (250×4.6 mm I.D.) and a 0.2 mM pyromellitic acid containing 0.15% heptanol as the eluent.     

An expeditious hydroxyamidation of carboxylic acids

Capitalizing on in situ activation with the cyclic phosphonic anhydride PPAA (1), the conversion of carboxylic acids into hydroxamic acids has been reduced to an experimentally simple one-pot operation that addresses the issue of polyacylation without resorting to a large excess of hydroxylamine or to protection. Scope and selectivity were satisfactory with a wide range of substrates, including α,β-unsaturated acids and hydroxyacids.     

Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate-Mediated Biological Recognition

Useful strategies for the design of molecules to mimic carbohydrates have been developed over the past few years. Mimics of the target may contain new functional groups, a new scaffold, or both (in the schematic representation the natural ligand is shown on the left and the modified version on the right). Many examples of successful carbohydrate mimetics that interfere with sugar–protein and sugar–nucleic acid interactions are known.     

Enhancement of conductometric detection of weak acids in ion chromatography

Anions of weak acids can represent a problem when determined via chemically suppressed ion chromatography as the acids can be weakly ionised, giving low conductivity and hence low sensitivity. Previous work showed that converting some weak acids back to their sodium salts, using a second micromembrane suppressor, greatly enhanced conductivity and thus sensitivity. This paper will discuss further work in optimising the conversion for boric acid by using sodium salts of EDTA and the mechanisms involved.     

Dynamic control and indirect absorption detection for high-speed capillary electrophoretic separation of organic acids

Dynamic control and indirect absorption detection have been combined for the separation of eight small aliphatic organic acids in less than 4 min. Electroosmotic flow (EOF) coefficients in 5 mM 8-hydroxyquinoline-5-sulfonic acid (8-HQSA) (pH 3.00) and 3 mM 1,2,4,5-benzenetetracarboxylic acid (BTA) solutions are 4.35 and 1.65·10⁻⁴ cm²/V s, respectively. In the BTA system, relatively large amounts of sodium ions adsorbed into the capillary wall are the most probable reason for the small EOF, in turn causing problems for the separation of all acids. In contrast to BTA, 8-HQSA could be used for the separation of all eight organic acids. Limits of detection of analytes are at the level of several tens of μM at pH 3.00 in the 8-HQSA system. This new technique provides several features such as high speed, reasonable resolution and sensitivity, and ease of operation.