Concise synthesis of two natural steroidal glycosides isolated from <Emphasis Type="Italic">Allium schoenoprasum</Emphasis>

Two natural steroidal glycosides, diosgenin 3-O-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-β-d-glucopyranoside (1) and laxogenin 3-O-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-β-d-glucopyranoside (2) with important cytotoxic activity against the HCT 116 and HT-29 human colon cancer cell lines have been efficiently synthesized via straightforward sequential glycosylation reaction with the combined use of N-phenyltrifluoroacetimidates and trichloroacetimidates donors at room temperature. All structures of the synthesized new compounds were identified by ¹H NMR, ¹³C NMR and HRMS spectra.     

Synthesis of N-glycyl-β-glycopyranosyl amines,derivatives of natural oligosaccharides — glucose analogs of Lex antigen

Treatment of the natural tri-, tetra-, and pentasaccharides, β-d-Galp-(1→4)-[α-l-Fucp-(1→3)]-d-Glcp, α-l-Fucp-(1→2)-β-d-Galp-(1→4)-[α-l-Fucp-(1→3)]-d-Glcp, and α-l-Fucp-(1→2)-[α-d-GalNAcp-(1→3)]-β-d-Galp-(1→4)-[α-l-Fucp-(1→3)]-d-Glcp, which are glucose analogs of Le^x, with ammonium carbamate in aqueous methanol gave the corresponding β-glycopyranosyl amines. After their N-acylation with N-Z-glycine N-hydroxysuccinimidyl ester (Z is benzyloxycarbonyl) with subsequent hydrogenolytic removal of Z-group, corresponding N-glycyl-β-glycopyranosyl amines were obtained in yields up to 70%.     

Thermodynamics of the Protonation of an Analogue of Glyphosate, <Emphasis Type="Italic">N</Emphasis>-(phosphonomethyl)-<Emphasis Type="SmallCaps">l</Emphasis>-proline,in Aqueous Solutions

N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, ³¹P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.     

Zur Biosynthese des Sinalbins, 2. Mitt.: Die Bildung von Sinalbin in Senfpflanzen verschiedenen Alters

1. 1.
   Young plants ofSinapis alba strongly catabolizel-tyrosine-2-¹⁴C. Therefore, in the course of the incorporation ofl-tyrosine-2-¹⁴C into sinalbin, a randomization of the activity within the molecule takes place. Older plants show a higher incorporation ofl-tyrosine-2-¹⁴C and less randomization of the activity in sinalbin.     
   
   

SYNTHESIS OF O-METHYLATED DISACCHARIDES RELATED TO EXCRETORY/ SECRETORY ANTIGENS OF TOXOCARA LARVAE[1]

The disaccharides 2-O-Me-α-L-Fucp-(1→2)-β-D-Galp-(1→OAllyl) 12, α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 15, and 2-O-Me-α-L-Fucp-(1→2)-4-O-Me-β-D-Galp-(1→OAllyl) 18 have been synthesized. Glycosylation reactions were performed using ethyl 1-thiofucopyranosides as glycosyl donors and N-iodosuccinimide-triflic acid as the activating agent. The O-methylated disaccharides correspond to highly immunogenic O-glycan antigens occurring at the surface of Toxocara canis and Toxocara cati larvae.     

Purification and Characterisation of a Thermostable β-Xylosidase from <Emphasis Type="Italic">Aspergillus niger</Emphasis> van Tieghem of Potential Application in Lignocellulosic Bioethanol Production

A locally isolated strain of Aspergillus niger van Tieghem was found to produce thermostable β-xylosidase activity. The enzyme was purified by cation and anion exchange and hydrophobic interaction chromatography. Maximum activity was observed at 70–75 °C and pH 4.5. The enzyme was found to be thermostable retaining 91 and 87% of its original activity after incubation for 72 h at 60 and 65 °C, respectively, with 52% residual activity detected after 18 h at 70 °C. Available data indicates that the purified β-xylosidase is more thermostable over industrially relevant prolonged periods at high temperature than those reported from other A. niger strains. Maximum activity was observed on p-nitrophenyl-β-d-xylopyranoside and the enzyme also hydrolysed p-nitrophenyl β-d-glucopyranoside and p-nitrophenyl α-l-arabinofuranoside. The purified enzyme acted synergistically with A. niger endo-1,4-β-xylanase in the hydrolysis of beechwood xylan at 65 °C. During hydrolysis of pretreated straw lignocellulose at 70 °C using a commercial lignocellulosic enzyme cocktail, inclusion of the purified enzyme resulted in a 19-fold increase in the amount of xylose produced after 6 h. The results observed indicate potential suitability for industrial application in the production of lignocellulosic bioethanol where thermostable β-xylosidase activity is of growing interest to maximise the enzymatic hydrolysis of lignocellulose.     

Energetics of lead(II), cadmium(II) and zinc(II) complexes with amino acids

The molar heat capacity and the standard (p ⁰ = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)₂; bis(dl-alaninate)lead(II), Pb(dl-ala)₂; bis(dl-valinate)lead(II), Pb(dl-val)₂; bis(dl-valinate)cadmium(II), Cd(dl-val)₂ and bis(dl-valinate)zinc(II), Zn(dl-val)₂, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies, M(II)–amino acid, \( \langle D_{\text{m}} \rangle \)(M–L), were derived and compared with analogous copper(II)–ligand and nickel(II)–ligand.θθ

M(II)–amino acid	\( \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \)(cr)/kJ mol?1
Bis(glycinate)lead(II), Pb(gly)2	?998.9 ± 1.9
Bis(dl-alaninate)lead(II), Pb(ala)2	?1048.7 ± 1.8
Bis(dl-valinate)lead(II), Pb(val)2	?1166.3 ± 2.5
Bis(dl-valinate)cadmium(II), Cd(val)2	?1243.7 ± 2.7
Bis(dl-valinate)zinc(II), Zn(val)2	?1306.1 ± 2.3

     

Measuring Positive Cooperativity Using the Direct ESI-MS Assay. Cholera Toxin B Subunit Homopentamer Binding to GM1 Pentasaccharide

Direct electrospray ionization mass spectrometry (ESI-MS) assay was used to investigate the stepwise binding of the GM1 pentasaccharide β-D-Galp-(1→3)-β-D-GalpNAc-(1→4)[α-D-Neu5Ac-(2→3)]-β-D-Galp-(1→4)-β-D-Glcp (GM1os) to the cholera toxin B subunit homopentamer (CTB₅) and to establish conclusively whether GM1os binding is cooperative. Apparent association constants were measured for the stepwise addition of one to five GM1os to CTB₅ at pH 6.9 and 22 °C. The intrinsic association constant, which was established from the apparent association constant for the addition of a single GM1os to CTB₅, was found to be (3.2 ± 0.2) × 10⁶ M^–1. This is in reasonable agreement with the reported value of (6.4 ± 0.3) × 10⁶ M^–1, which was measured at pH 7.4 and 25 °C using isothermal titration calorimetry (ITC). Analysis of the apparent association constants provides direct and unambiguous evidence that GM1os binding exhibits small positive cooperativity. Binding was found to be sensitive to the number of ligand-bound nearest neighbor subunits, with the affinities enhanced by a factor of 1.7 and 2.9 when binding occurs next to one or two ligand-bound subunits, respectively. These findings, which provide quantitative support for the binding model proposed by Homans and coworkers [14], highlight the unique strengths of the direct ESI-MS assay for measuring cooperative ligand binding.

Influence of Sulfolane on ESI-MS Measurements of Protein–Ligand Affinities

The results of an investigation into the influence of sulfolane, a commonly used supercharging agent, on electrospray ionization mass spectrometry (ESI-MS) measurements of protein–ligand affinities are described. Binding measurements carried out on four protein–carbohydrate complexes, lysozyme with β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-d-GlcNAc, a single chain variable fragment and α-d-Gal-(1→2)-[α-d-Abe-(1→3)]-α-d-Man-OCH₃, cholera toxin B subunit homopentamer with β-d-Gal-(1→3)-β-d-GalNAc-(1→4)[α-d-Neu5Ac-(2→3)]-β-d-Gal-(1→4)-β-d-Glc, and a fragment of galectin 3 and α-l-Fuc-(1→2)-β-d-Gal-(1→3)-β-d-GlcNAc-(1→3)-β-d-Gal-(1→4)-β-d-Glc, revealed that sulfolane generally reduces the apparent (as measured by ESI-MS) protein–ligand affinities. To establish the origin of this effect, a detailed study was undertaken using the lysozyme–tetrasaccharide interaction as a model system. Measurements carried out using isothermal titration calorimetry (ITC), circular dichroism, and nuclear magnetic resonance spectroscopies reveal that sulfolane reduces the binding affinity in solution but does not cause any significant change in the higher order structure of lysozyme or to the intermolecular interactions. These observations confirm that changes to the structure of lysozyme in bulk solution are not responsible for the supercharging effect induced by sulfolane. Moreover, the agreement between the ESI-MS and ITC-derived affinities indicates that there is no dissociation of the complex during ESI or in the gas phase (i.e., in-source dissociation). This finding suggests that supercharging of lysozyme by sulfolane is not related to protein unfolding during the ESI process. Binding measurements performed using liquid sample desorption ESI-MS revealed that protein supercharging with sulfolane can be achieved without a reduction in affinity.

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Graphical Abstract ?

     

Thermodynamic Properties of <Emphasis Type="SmallCaps">l</Emphasis>-Aspartates of Alkali and Alkali-Earth Metals in Aqueous Solutions at 298.15 and 310.15 K and Specific Cation Effects on Biomolecule Solvation

Vapor pressure osmometry was applied to the systems calcium l-aspartate ((S)-aminobutanedioic acid calcium salt)?+?water for varying molalities of Ca–l-Asp (m_Ca–l-Asp?=?0.01–1.02 mol·kg^?1) and guanidinium hydrochloride (methanamidine hydrochloride)?+?sodium L–aspartate ((S)–aminobutanedioic acid sodium salt)?+?water, varying the molalities of GndmCl and Na–l-Asp (m_Na–l-Asp?=?0.1, 0.25, 0.4, 0.57 mol·kg^?1 and m_GndmCl?=?0.1–1.1 mol·kg^?1) at T?=?298.15 K and 310.15 K. From vapor pressure osmometry, activities of water, and the corresponding osmotic coefficients of the mixtures Ca–l-Asp?+?water and Na–l-Asp?+?GndmCl?+?water have been calculated, both being directly related to the chemical potentials of the different species and therefore to their Gibbs energy. Mean molal ion activity coefficients were obtained from experimental data fits with the Pitzer equations and the corresponding dual and triple interaction parameters were derived for the Ca–l-Asp?+?water binary system. β⁽²⁾ Pitzer parameters different from zero are required for Ca–l-Asp in water to reproduce the osmotic coefficient decrease with increasing concentration. Mean Spherical Approximation parameters accounting for Coulomb and short range interactions that describe the calcium and magnesium aspartates and glutamates are given. The decrease in the chemical potential of the aspartates corresponds to the Hofmeister series: NaAsp?>?Mg(Asp)₂?>?CaAsp. A strong interaction between amino acid and salt due to specific dispersion interactions in amino acid salt systems containing guanidinium based salt has been revealed that is in agreement with MD and half-empirical quantum-chemical calculations.     

Cobalt and manganese complexes with redox-active ligands in polymerization of acrylonitrile and methyl methacrylate

The influence of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinonato]cobalt(ii) and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzosemiquinonato]-[4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate]manganese(iii) on polymerization of methyl methacrylate and acrylonitrile in the presence of azobisisobutyronitrile (as a traditional radical initiator) and alkyl halides (used for initiation of controlled atom transfer radical polymerization process) was studied. The effect of the nature of the activating agents (amines) and the temperature conditions on the overall polymerization rate of the indicated monomers, as well as molecular weight characteristics of the synthesized polymers, were analyzed. The optimal conditions for the synthesis of polyacrylonitrile and poly(methyl methacrylate) with a relatively narrow molecular weight distribution were selected.     

Organometallic chiral Schiff base for enantio-selective fluorescent recognition of methionine

Herein, the synthesis and characterization of a novel chiral Schiff bases derived from ferrocene, coded as 3, have been reported. The sensing behavior of the synthesized compound has been examined towards the enantiomers of some amino acids (methionine, alanine, serine, histidine, and threonine) by spectrofluorimetric method. The fluorescence response of compound 3 showed noticeable enhancement upon addition of d-methionine compared to l-methionine and kept nearly linear correlation with the concentration of d-methionine. The value of enantiomeric fluorescence difference ratio (ef) has been determined to be 1.54 when d - and l- methionine amount is 100 times more than compound 3. The results showed that the compound 3 can be used as a sensor for enantio-selective recognition of d-methionine.     

Tyrosine alkyl esters as prodrug: the structure and intermolecular interactions of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine methyl ester compared to <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine and its ethyl and <Emphasis Type="Italic">n</Emphasis>-butyl esters

l-Tyrosine alkyl esters are used as prodrugs for l-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of l-tyrosine methyl ester has been determined and compared to published structures of l-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P2₁2₁2₁, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å³ with Z′ = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of l-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because l-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine.     

Study on the Interaction of Nicotinic Acid with <Emphasis Type="SmallCaps">l</Emphasis>-Phenylalanine in Buffer Solution by Heat Capacity Measurements at Various Temperatures

The interaction between nicotinic acid (NA) and l-phenylalanine (Phe) was studied in aqueous phosphate buffer solutions (pH = 7.35) by differential scanning calorimetry. Heat capacities of nicotinic acid–buffer, l-phenylalanine–buffer, and nicotinic acid–l-phenylalanine–buffer mixtures were determined at (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K using the microdifferential scanning calorimeter SCAL-1 (Pushchino, Russia). The apparent molar heat capacities, ^? C _p , of nicotinic acid in buffer solution and in buffer 0.0216 mol·kg^?1 amino acid solutions were evaluated. The concentration of NA was varied from (0.0106–0.0701) mol·kg^?1. The interaction of NA with Phe is accompanied by complex formation. The partial molar heat capacities of transfer of nicotinic acid from buffer to buffer amino acid solutions are positive. The results are discussed in terms of various interactions operating in this system.     

Enhancing the Production of <Emphasis Type="SmallCaps">d</Emphasis>-Mannitol by an Artificial Mutant of <Emphasis Type="Italic">Penicillium</Emphasis> sp. T2-M10

d-Mannitol belongs to a linear polyol with six-carbon and has indispensable usage in medicine and industry. In order to obtain more efficient d-mannitol producer, this study has screened out a stable mutant Penicillium sp. T2-M10 that was isolated from the initial d-mannitol-produced strain Penicillium sp.T2-8 via UV irradiation as well as nitrosoguanidine (NTG) induction. The mutant had a considerable enhancement in yield of d-mannitol based on optimizing fermentation. The production condition was optimized as the PDB medium with 24 g/L glucose for 9 days. The results showed that the production of d-mannitol from the mutant strain T2-M10 increased 125% in contrast with the parental strain. Meanwhile, the fact that d-mannitol is the main product in the mutant simplified the process of purification. Our finding revealed the potential value of the mutant strain Penicillium sp. T2-M10 to be a d-mannitol-producing strain.     

Effect of Amino Acids and Sodium Chloride on <Emphasis Type="SmallCaps">d</Emphasis>-Sorbitol in Aqueous Solutions at Different Temperatures: Volumetric and Acoustic Approach

Apparent molar volumes and apparent molar compressibilities for d-sorbitol in (0.05, 0.1, 0.2 and 0.3) mol·kg^?1 aqueous solutions of l-alanine, l-cysteine and l-histidine and NaCl have been determined from measurements of solution density at T?=?(288.15, 298.15, 308.15 and 318.15) K and sound velocity at T?=?298.15 K, as a function of the concentration of the sugar alcohol. The data were used to obtain the limiting apparent molar volumes, limiting apparent molar compressibilities and the corresponding transfer parameters. Limiting apparent molar expansibilities and their second order derivatives and volume interaction coefficients were also estimated. These parameters are discussed in terms of d-sorbitol and co-solute (amino acid or sodium chloride) interactions in aqueous solutions.     

Purification of Two Novel Sugar Acid-binding Lectins from <Emphasis Type="Italic">Haplomitrium Mnioides</Emphasis> (bryophyte,Plantae) and their Preliminary Characterization

Two novel sugar acid-binding lectins were purified from Haplomitrium mnioides (Lindb.) Schust. using a procedure consisting of ammonium sulfate precipitation, G-50 gel filtration, hydroxyapatite chromatography, and HW-50 gel filtration. We reported their partial physicochemical properties: molecular weight, affinity for carbohydrates and organic acids, pH stability, and dependence of their hemagglutination activity on metal ions. We also determined their N-terminal amino acid sequences. H. mnioides lectins (HMLs) were monomers (one with a molecular weight of approximately 27 kDa, and the other with a molecular weight of approximately 105 kDa) under both nonreducing and reducing conditions. They were named HML27 and HML105, respectively. Both HMLs had an affinity for N-acetylneuraminic acid, d-glucuronic acid, d-glucaric acid, bovine submaxillary mucin, heparin, and organic acids, such as citrate, 2-oxoglutaric acid, and d-2-hydroxyglutarate. Furthermore, HML27 had an affinity for α-d-galacturonic acid, d-malate, l-malate, and pyruvate, while HML105 had an affinity for d-gluconic acid. HML27 and HML105 are novel plant lectins: they have an affinity for sugar acids and organic acids and specifically recognize the carboxyl group, and there is no homology between their N-terminal amino acid sequences and those of the previously described lectins and agglutinins.     

Thermal and redox dual responsive poly(<Emphasis Type="SmallCaps">L</Emphasis>-glutamate) with oligo(ethylene glycol) side-chains

A series of poly(L-glutamate)s grafted with oligo(ethylene glycol) (OEG) side-chains through the thioether linkages (PALG _n -g-EG _x , x = 2, 3 and 4) were prepared by ring-opening polymerization (ROP) of γ-allyl-L-glutamate N-carboxyanhydride (ALG-NCA) and thiol-ene photoaddition. The chemical structures and physical properties were characterized by ¹H-NMR, Fourier transform infrared (FTIR), circular dichroism (CD), etc. The PALG _n -g-EG _x samples with x = 3 and 4 displayed lower critical solution temperature (LCST) in water due to the presence of OEG units. The clouding point (CP) of polypeptides can be finely tuned by changing the side chain structures, molecular weights and sample concentrations. In addition, the thioether linkages in the side chains offer additional redox-responsive properties. The influence of both OEG units and thioether linkages on the LCST behavior was systematically investigated. This work provides an efficient way to prepare multi-stimuli responsive materials with highly tunable properties.     

Functional diversity of rhamnogalacturonans I

Rhamnogalacturonans I represent a group of plant cell wall polysaccharides having the most complex organization and variable structure. These polymers, combined in one group due to the presence of a backbone composed of alternating [→4)-α-d-GalpA-(1→2)-α-l-Rhap(1→] dimers, can occur in the cell wall both as parts of a pectin complex and by themselves. Types of rhamnogalacturonans I are unique not only for each plant but also for different tissues of the same plants and, in some cases, for different stages of development of the same tissue. Perception of the causes and consequences of this diversity is a sophisticated problem of plant glycobiology. The review summarizes the available information on the correlation of structure, physicochemical properties, and functions of rhamnogalacturonans I.     

Thermodynamics of a third-generation poly(phenylene-pyridyl) dendron decorated with dodecyl groups in the range of <Emphasis Type="Italic">T</Emphasis> → 0 to 480 K

The heat capacity of a glassy third-generation poly(phenylene-pyridyl) dendron decorated with dodecyl groups is studied for the first time via high-precision adiabatic vacuum and differential scanning calorimetry in the temperature range of 6 to 520 K. The standard thermodynamic functions (molar heat capacity C_p^°, enthalpy H°(T), entropy S°(T), and Gibbs energy G°(T)-H°(0)) in the range of T → 0 to 480 K, and the entropy of formation at 298.15 K, are calculated on the basis of the obtained data. The thermodynamic properties of the dendron and the corresponding third-generation poly(phenylene-pyridyl) dendrimer studied earlier are compared.