Regioselective Monoacetylation of Methyl Pyranosides of Pentoses and 6‐Deoxyhexoses by Acetic Anhydride in the Presence of MoCl5

Convenient regioselective syntheses of 3‐acetates of methyl pyranosides of α‐L‐rhamnose, α‐ and β‐L‐arabinose, α‐D‐fucose, α‐D‐lyxose, and β‐D‐ribose with good yields have been attained using MoCl₅ as catalyst. Methyl β‐L‐rhamnopyranoside under this conditions gave 2‐acetate.     

Synthesis,characterization and crystal structures of two binary acid complexes based on L-glutamate and L-aspartate

Two amino acid complexes, [Cd(L-glu)(H₂O)] _n ?·?nH₂O (1) and [Co(L-asp)(phen)(N₃)]?·?2H₂O (2) (L-glu?=?L-glutamate, L-asp?=?L-aspartate, phen?=?1,10-phenanthroline), have been synthesized and characterized by elemental analyses, IR spectra and TG-DSC analysis. Single crystal X-ray structure analyses revealed that each L-glutamate acts as a pentadentate ligand binding to three octahedral Cd(II) atoms through the amino group and two carboxyl groups to form a neutral helical network. Complex 2 is a mononuclear compound in which Co(III) is octahedrally coordinated by tridentate L-aspartate, monodentate azide and chelating phen ligand. Thermal stability and fluorescence of 1 have been investigated. The complex shows strong blue fluorescence in the solid state.     

Formation of 1-D ladder- and 2-D sheet-like networks due to stereospecific π–π stacking and hydrogen bonding between enantiomeric sulfur-bridged dinuclear complexes of penicillaminates

Reaction of trans(N)-[Co(D-pen)₂]^? (pen = penicillaminate) or trans(N)-[Co(L-pen)₂]^? with [MCl₂(L)] {M = Pd or Pt, L = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)} in the presence of tetrafluoroborate stereoselectively gave an optically active S-bridged dinuclear complex, [M(L){Co(D-pen)₂}]BF₄ · 2H₂O or [M(L){Co(L-pen)₂}]BF₄ · 2H₂O. The mixture of equimolar amounts of these enantiomers in H₂O crystallizes as [M(L){Co(D-pen)₂}]_0.5[M(L){Co(L-pen)₂}]_0.5BF₄ · 4H₂O (DLbpyM · 4H₂O, DLphenM-A · 4H₂O), in which the enantiomeric complex cations are included by the ratio of 1 : 1. In crystals of DLbpyM · 4H₂O and DLphenM-A · 4H₂O, [M(L){Co(D-pen)₂}]⁺ and [M(L){Co(L-pen)₂}]⁺ interact stereospecifically with each other through π-conjugated systems to form dimeric structures. Other racemic crystals with the same chemical compositions as DLphenM-A · 4H₂O, DLphenM-B · 4H₂O, were obtained from equimolar amounts of [M(phen){Co(D-pen)₂}]⁺ and [M(phen){Co(L-pen)₂}]⁺ in aqueous acetonitrile solution. In the crystals of DLphenM-B · 4H₂O, [M(phen){Co(D-pen)₂}]⁺ and [M(phen){Co(L-pen)₂}]⁺ are arranged alternately while overlapping phen planes, and the π electronic systems of phen interact with each other. Although stereospecific hydrogen bonds between the coordinated ?NH₂ and ?COO^? groups are formed in both DLphenM-A · 4H₂O and DLphenM-B · 4H₂O, their bonding modes differ noticeably from each other. As a result, DLphenM-A · 4H₂O builds up 1-D ladder-like networks due to the stereospecific π–π stackings and hydrogen bondings between enantiomers, while 2-D sheet-like networks are established for DLphenM-B · 4H₂O.     

Magnetic hybrid imprinted polymers with three-templates modified by DESs for the rapid purification of monosaccharide from seaweed

Fe₃O₄@hybrid-molecular-imprinted polymers (Fe₃O₄@HMIPs) with three monosaccharide templates (D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose), and hybrid materials were modified by deep eutectic solvents (DESs). The materials obtained were combined with solid-phase extraction (SPE) to purify of D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose from seaweed, and the SPE procedure was optimized further. Compared to Fe₃O₄@HMIPs, DESs-Fe₃O₄@HMIPs were developed to achieve stronger recognition and higher recoveries of D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose from seaweed. The optimal practical recoveries of the three monosaccharides, D-(+)-galactose, L-(?)-fucose, and D-(+)-mannose, purified by DESs-4-Fe₃O₄@HMIPs from seaweed were 90.12, 92.82, and 91.94%, respectively. When acetone was used as the washing solution, the actual amounts extracted were 6.87, 4.17, and 5.29?mg?·?g^?1, respectively.     

Synthesis of Analogues of (1 → 6)‐Branched (1 → 3)‐Glucohexaose

Abstract

β‐D‐Galp‐(1 → 3)‐[β‐D‐Galp‐(1 → 6)‐]α‐D‐Glcp‐(1 → 3)‐β‐D‐Glcp‐(1 → 3)‐[α‐D‐Manp‐(1 → 6)‐]D‐Glcp 16 and β‐D‐Galp‐(1 → 3)‐[β‐D‐Glcp‐(1 → 6)‐]α‐D‐Glcp‐(1 → 3)‐β‐D‐Glcp‐(1 → 3)‐[α‐D‐Manp‐(1 → 6)‐]D‐Glcp 18 were synthesized as the analogues of the immunomodulator β‐D‐Glcp‐(1 → 3)‐[β‐D‐Glcp‐(1 → 6)‐]α‐D‐Glcp‐(1 → 3)‐β‐D‐Glcp‐(1 → 3)‐[β‐D‐Glcp‐(1 → 6)‐]D‐Glcp through coupling of trisaccharide donors 8 and 13 with trisaccharide acceptor 14 followed by deprotection, respectively.     

Synthesis of metal-organic frameworks from the system metal/L-glutamic acid/TEA/H2O

Three metal-organic frameworks (MOFs) with similar zeolite-like 3-D structures, Zn(L-Glu)(H₂O) · H₂O, Cu(L-Glu)(H₂O) · H₂O, and Co(L-Glu)(H₂O) · H₂O, have been obtained from metal/L-glutamic acid/TEA/H₂O systems, whereby the weak base triethylamine (TEA), rather than the more typically used NaOH or Na₂CO₃, has been used to adjust the pH of the solution. A systematic and detailed exploration of the synthesis conditions has revealed that not all transition metals may be coordinated to L-glutamic acid and that the range of conditions under which the three MOFs remained stable was different. The metal/L-glutamic acid/TEA/H₂O system offers an effective means of obtaining MOFs.     

Enantioselective,Potentiometric Membrane Electrodes Based on Cyclodextrins for the Assay of L‐ and D‐2‐Hydroxyglutaric Acid

Abstract

Enantioselective, potentiometric membrane electrodes (EPMEs) based on immobilization of β‐, γ‐cyclodextrin (CD) or 2‐hydroxy‐3‐trimethylammoniopropyl‐β‐cyclodextrin (as chloride salt) (β‐CD‐derivative) in carbon paste have been designed. The β‐CD and β‐CD‐derivative‐based electrodes were applied in the 10^?8–10^?6 and 10^?7–10^?5 mol/L concentration ranges for the determination of L‐2‐hydroxyglutaric acid (L‐2‐HGA), whereas γ‐CD‐based electrode was applied for the determination of D‐2‐hydroxyglutaric acid (D‐2‐HGA) in the concentration range 10^?6–10^?4 mol/L. The β‐CD‐based EPME showed the lowest detection limit (1×10^?9 mol/L). The enantioselectivity and selectivity of the proposed electrodes for the assay of L‐2‐HGA and D‐2‐HGA, respectively, were determined over D‐2‐HGA/L‐2‐HGA, creatine, and creatinine. The proposed EPMEs can be applied for the enantioanalysis of 2‐hydroxyglutaric acid in urine samples.     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

A new triterpenoid glycoside from the leaves and stems of Duranta repens

A new triterpenoid glycoside (1) was isolated from the methanol extract of the leaves and stems of Duranta repens L. (Verbenaceae) along with 14 known compounds consisting of eight triterpenoids, four iridoids, one phenylethanoid glycoside and one flavonoid. The chemical structure of 1 was determined to be bayogenin 3-O-[β-D-glucopyranoside]-28-O-[α-L-rhamnopyranosyl-(1→5)-O-β-D-apiofuranosyl-(1→4)-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl] ester, based on spectroscopic data. In addition, the inhibitory effects of the isolates on lipoxygenase activity were examined. Among them, acteoside and apigenin resulted in 94 ± 3.6% and 82 ± 4.7% inhibition, respectively, at 0.5 mM.     

Enantioselective Recognition of Proline Enantiomers Using Sulfhydryl-modified Self-assembled Gold Electrodes

Penicillamine, cysteine, and N-isobutyryl-cysteine enantiomers self-assembled gold electrodes were used for the enantioselective recognition of proline in the presence of copper(II). High stereoselectivity for proline was obtained for the D-form of the sulfhydryl compounds, particularly on the D-penicillamine-modified gold electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were used to confirm the chiral discrimination of proline enantiomers on the D-penicillamine modified gold electrode in the presence of copper(II). The largest electrochemical response was obtained for D-proline for the recognition of its enantiomers, whereas small responses were obtained for the L- and D-forms of phenylalanine, tyrosine, serine, and glutamic acid. The influences of incubation time and pH for chiral ligand exchange were evaluated. This study complements and enhances applications for the recognition of amino acid enantiomers based on ligand exchange by electrochemical analysis.     

Complex formation of curium(III) with amino acids of different functionalities: L-threonine and O -phospho-L-threonine

The speciation of curium(III) with L-threonine and O-phospho-L-threonine was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3?×?10^?7?M). Curium species of the type M_pH_qL_r were identified in the L-threonine- and O-phospho-L-threonine system. These complexes are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined (a) for L-threonine: log?β₁₀₁?=?6.72?±?0.07, log?β₁₀₂?=?10.22?±?0.09, and log?β_1–22?=?(7.22?±?0.19) at ionic strength I?=?0.5?M and (b) for O-phospho-L-threonine: log?β₁₂₁?=?18.03?±?0.13 and log?β₁₁₁?=?14.17?±?0.09 at ionic strength I?=?0.154?M. Possible structures of the identified curium species are discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.     

Conformational Analysis of Thiosugars: Theoretical NMR Chemical Shifts and 3 J H,H Coupling Constants of 5‐Thio‐Pyranose Monosaccharides

The conformational space of D and L, deoxy and nondeoxy, 5‐thio‐pyranoses with biological properties as enzymatic inhibitors was explored using MM and B3LYP/6–31+G* methods in gas phase and solution. The preferred ring conformation for α and β anomers of 5‐thio‐L‐fucopyranose was the ¹C₄ form (about 99%), and for 5‐thio‐D‐glucopyranose and 5‐thio‐D‐mannopyranose, the ⁴C₁ one. The experimental conformational order (⁴C₁>¹C₄>²S_S) for L‐ido derivatives was reproduced only considering the solvent, though for 3‐O‐methyl‐5‐thio‐α‐L‐idopyranose, the inclusion of methyl in C₃ changed the ²S_S form to the B_1,4 one.     

Synthesis of 3,6‐Branched β‐d‐Glucose Oligosaccharides

A glucohexasaccharide, β‐d‐Glcp‐(1 → 3)‐[β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp‐(1 → 6)]‐β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp was synthesized as its 4‐methoxyphenyl glycoside via 2 + 2 + 2 strategy with benzylidenated glucose mono‐ and disaccharides as the key intermediates.     

Effect of L‐Aspartate Concentration on the Response of the Amperometric L‐Glutamate Sensor for the Measurement of L‐Glutamate and Aspartate Aminotransferase Activity in Serum

Abstract

L‐glutamate oxidase was immobilized in a photo‐cross‐linkable polymer membrane on a palladium strip electrode for the amperometric measurement of aspartate aminotransferas eactivity. The sample, serum for example, was injected into a buffered L‐aspartate and α‐ketoglutarate solution. L‐aspartate is the essential substrate and can transfer to L‐glutamate via the aspartate aminotransferase catalyzing reaction. Aspartate aminotransferase activity can be measured by determining the increasing rate of L‐glutamate. Under the optimal condition, the current increasing rate was proportional to the aspartate aminotransferase activity of the sample in the range of 8–200 U/L. The data are in good correlation (R²= 0.998) with data from a commercial aspartate aminotransferase assay kit. Good reproducibility (relative standard deviation=3.03%, n=8) was obtained from a sample with 50 U/L aspartate aminotransferase activity. The sensor is expectable to be applied in a clinical point‐of‐care diagnosis.     

Primary Amine‐Initiated Polymerizations of α–Amino Acid N‐Thiocarbonic Acid Anhydrosulfide

The N‐thiocarbonic acid anhydrosulfides NTAs of D,L‐leucine, D,L‐phenylalanine and sarcosine were polymerized in dioxane by addition of n‐hexylamine as initiator. Despite variation of the monomer‐initiator ratio (M/I) only low yields of oligopeptides were obtained from D,L‐Leu‐ and D,L‐Phe‐NTA. Both yields and molecular weights were almost twice as high for polymerizations of Sar‐NTA. MALDI‐TOF mass spectra confirmed that the isolated oligo‐and polypeptides possess the expected structure with one reactive amino end group. Therefore, it is surprising that the polymerizations stopped at low conversions. Two hypotheses explaining this phenomenon are discussed.     

Supramolecular Complex of 2-Hydroxypropyl-β-cyclodextrin with d- and l-tryptophan

Cyclodextrins are known by their properties of molecular recognition. In the present work, it was established, by using high-performance liquid chromatography, that complexes between 2-hydroxypropyl-β-cyclodextrin (HPCD) and d- and l-tryptophan are readily formed in solution. Association constants of (2 ± 1) × 10 and of (9 ± 2) × 10^? 1 for d and l-isomers, respectively, were calculated from UV electronic spectroscopy experiments. Solid state complexes were characterized by Fourier-transform infrared spectroscopy, which showed that the subtracted/deconvoluted spectra present wavenumber changes of the NH₃ ⁺ asymmetric angular deformation and of the COO^?  asymmetric stretching.     

Interaction of L-3,4-dihydroxyphenylalanin (L-DOPA) as a coordinating ligand with a series of metal ions; reaction of L-DOPA

L-DOPA is an important neurotransmitter that is found in the brain and as a hormone in the circulatory system. We report in this article the similarities and differences in behaviour of this important neurotransmitter as a chelating agent among some divalent and trivalent metal ions using potentiometric titration in aqueous solutions at 25.0?±?1.0°C. The careful and detailed potentiometric titrations of L-DOPA with Al³⁺, Cr³⁺, Fe³⁺, Cu²⁺, and Zn²⁺ are discussed and compared. UV-Vis-spectroscopy is utilized for both the free L-DOPA and for the Fe³⁺/L-DOPA system. The characteristic peak due to the π?→?π* transition of the free L-DOPA at ～280?nm (ε_280?nm?=?1927?±?65?M^?1?cm^?1 between pH values of 2.0 to 3.0) disappeared when the iron solution was added to the L-DOPA sample in the same pH range. For the Fe³⁺/L-DOPA system we have observed a new peak at 470?nm with ε₄₇₀?=?800?±?50?M^?1?cm^?1. These comparison studies of the similarities and differences among these di- and tri-valent metal ions shed light on these systems in aqueous solutions. The appropriate metal simulation and speciation diagrams were constructed using the model that fit the titration data points.     

Thermo-sensitive random poly(L-alanine-co-L-lactic acid) with no cytotoxicity by the structure-controlled synthesis for a nano-drug carrier

A random poly(L-alanine-co-L-lactic acid) (PAL) with excellent thermo-sensitivity and no cytotoxicity was synthesized by the structure-controlled polycondensation from natural L-alanine and L-lactic acid. Only those PALs in which the contents of L-alanine structural unit are rigidly controlled in the smaller range of 53–65% show a reversible lower critical solution temperature of 35–60°C. The change of secondary structure in poly(L-alanine) segments by the introduction of L-lactic acid structural unit plays a decisive role in regulating the thermo-sensitivity of PAL. The viability of HeLa cells exposed to PAL reaches up to 91–116% after incubation of 24 and 72?h, indicating no cytotoxicity. Furthermore, PAL can easily form curcumin-loaded nano-carriers through its thermo-sensitivity and self-assembly. The curcumin-loaded PAL nano-particles are observed to clearly internalize into the cells by confocal laser-scanning microscopy, and thus can be used as a potential nano-drug-carrier.     

A new acylated flavonoid tetraglycoside with anti-inflammatory activity from Tipuana tipu leaves

A new acylated kaempferol glycoside, kaempferol 3-O-α-l-rhamnopyranosyl-(1 → 6)-O-[β-d-glucopyranosyl-(1 → 2)-4-O-acetyl-α-l-rhamnopyranosyl-(1 → 2)]-β-d-galactopyranoside, has been isolated from the leaves of Tipuana tipu (Benth.) Lillo growing in Egypt, along with three known flavonol glycosides, kaempferol 3-O-rutinoside, quercetin 3-O-rutinoside (rutin) and kaempferol 3-O-[α-l-rhamnopyranosyl-(1 → 6)]-[α-l-rhamnopyranosyl-(1 → 2]-β-d-glucopyranoside. Structure elucidation was achieved through different spectroscopic methods. Structure relationship with anti-inflammatory activity using carrageenin-induced rat paw oedema model is discussed.     

1–D Framework l-arginine zinc(II) units bridged by oxalate: synthesis,structure, properties,and theoretical studies

We synthesized a l-arginine containing Zn²⁺ complex and oxalate ions. {[Zn₂(l-Arg)₂(ox)₂]·8H₂O}_n (1) (l-Arg =l-arginine, ox = oxalate) crystallize in the monoclinic space group P2₁ with a = 8.979(2), b = 9.840(2) (Å), c = 18.509(3) (Å), β = 95.58(3) (Å), V = 1627.6(6) ų, and Z = 2. The zinc centers are six-coordinate via one l-arginine zwitterion and two bridging oxalates. The binuclear [Zn₂(l-Arg)₂(ox)₂] units are linked via oxalate and form 1-D “stair-like” linear chains. The complex was characterized using FT-IR, FT-Raman, UV–vis spectroscopy, and thermal analysis techniques, as well as DFT methods. Electronic bands above 31,000 cm^?1 originate in ^1,3A_u (n→π*) transitions within oxalate ions. Theoretical studies were performed for the model compound {[Zn(l-Arg)(Hox)₂]·4H₂O} using the fragment of the crystallographic structure of 1. The interaction energy (ΔE) values for l-arginine and two oxalate ions are comparable at -145 kcal mol^?1. Natural bond orbital (NBO) analysis of the electronic structure and bonding is also discussed.