Synthesis of a new 2‐amino‐glycan,poly‐(1→6)‐α‐D‐mannosamine,by ring‐opening polymerization of 1,6‐anhydro‐mannosamine derivatives

A stereoregular 2‐amino‐glycan composed of a mannosamine residue was prepared by ring‐opening polymerization of anhydro sugars. Two different monomers, 1,6‐anhydro‐2‐azido‐mannose derivative ( 3 ) and 1,6‐anhydro‐2‐(N, N‐dibenzylamino)‐mannose derivative ( 6 ), were synthesized and polymerized. Although 3 gave merely oligomers, 6 was promptly polymerized into high polymers of the number‐average molecular weight (M_n) of 2.3 × 10⁴ to 2.9 × 10⁴ with 1,6‐α stereoregularity. The differences of polymerizability of 3 and 6 from those of the corresponding glucose homologs were discussed. It was found that an N‐benzyl group is exceedingly suitable for protecting an amino group in the polymerization of anhydro sugars of a mannosamine type. The simultaneous removal of O‐ and N‐benzyl groups of the resulting polymers was achieved by using sodium in liquid ammonia to produce the first 2‐amino‐glycan, poly‐(1→6)‐α‐D ‐mannosamine, having high molecular weight through ring‐opening polymerization of anhydro sugars.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

An improved method for the measurement of the isotope ratio of ethanol in various samples, including alcoholic and non-alcoholic beverages

The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages.     

Chemical modification of neodymium high cis-1,4 polybutadiene with styreneoxide

The polymerization of 1,3-butadiene (BD) was carried out in the presence of a catalyst composed of neodymium 2-ethylhexanoate, triisobutyl aluminum, diisobutyl aluminum hydride (DIBAH), ethylaluminum sesquichloride and acetylacetone. The molecular weight of the BR could be controlled with DIBAH. The reactive polymer was then chemically modified with styreneoxide (STO). The STO content of BR increased with the decrease in the molecular weight of the BR. This polymer was modified by the STO at the chain terminal end. The physical properties of the vulcanizates with the modified BR were measured. The abrasion resistance and the tensile strength were found to be improved.     

Extensive oxygen exchange between carbon dioxide and magnesium oxide surface

Temperature-programmed desorption study of C¹⁸O₂ adsorbed on MgO has revealed that the desorbed carbon dioxide is composed exclusively of C¹⁶O₂, indicating that the adsorbed CO₂ species roll over the MgO surface.     

Synthesis of Oligosaccharide‐Branched Ribofuranan by Ring‐Opening Polymerization of a New Anhydroribo Trisaccharide Monomer

A new anhydroribotrisaccharide monomer, A2B3LR ( 1 ), was synthesized and ROP was carried out to elucidate the polymerizability and to obtain oligosaccharide‐branched polysaccharides with defined structures. The new trisaccharide monomer was found to be polymerized readily with BF₃ · OEt₂ as a catalyst at ?40 °C to give a lactose‐branched polymer. Copolymerization with ADBR gave the corresponding copolymers in good yields. After removal of protective benzyl groups, D ‐lactose‐branched ribofuranans with free hydroxyl groups were obtained in good yields. The structure of polymers was analyzed by ¹H, ¹³C, and two‐dimensional NMR measurements, suggesting that D ‐lactose‐branched ribofuranans had (1 → 5)‐α stereoregularity.

     

Computational assignment of the EC numbers for genomic-scale analysis of enzymatic reactions

The EC (Enzyme Commission) numbers represent a hierarchical classification of enzymatic reactions, but they are also commonly utilized as identifiers of enzymes or enzyme genes in the analysis of complete genomes. This duality of the EC numbers makes it possible to link the genomic repertoire of enzyme genes to the chemical repertoire of metabolic pathways, the process called metabolic reconstruction. Unfortunately, there are numerous reactions known to be present in various pathways, but they will never get EC numbers because the EC number assignment requires published articles on full characterization of enzymes. Here we report a computerized method to automatically assign the EC numbers up to the sub-subclasses, i.e., without the fourth serial number for substrate specificity, given pairs of substrates and products. The method is based on a new classification scheme of enzymatic reactions, named the RC (reaction classification) number. Each reaction in the current dataset of the EC numbers is first decomposed into reactant pairs. Each pair is then structurally aligned to identify the reaction center, the matched region, and the difference region. The RC number represents the conversion patterns of atom types in these three regions. We examined the correspondence between computationally assigned RC numbers and manually assigned EC numbers by the jackknife cross-validation test and found that the EC sub-subclasses could be assigned with the accuracy of about 90%. Furthermore, we examined the correlation with genomic information as represented by the KEGG ortholog clusters (OC) and confirmed that the RC numbers are correlated not only with elementary reaction mechanisms but also with protein families.     

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)-Ir(0) bond

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.     

Field survey of Glycyrrhiza plants in Central Asia (3). Chemical characterization of G. glabra collected in Uzbekistan

The chemical characteristics of Glycyrrhiza glabra L. were investigated at a habitat in Uzbekistan. HPLC analysis of the underground parts indicated that glycyrrhizin contents varied from 3.3 to 6.1% of dry weight, and that glabridin, a species-specific flavonoid for G. glabra, was detected in all underground samples (0.08-0.35% of dry weight). HPLC analysis of the leaves indicated that G. glabra plants collected in the present study could be divided into two types, RT-type and IQ-type, according to their major flavonol glycosides, rutin or isoquercitrin, respectively.     

Tishchenko Reaction Over Solid Base Catalysts

Catalytic behavior of solid bases for mixed Tishchenko reaction in which an equimolar mixture of two different aldehydes is allowed to react was investigated employing the combinations of benzaldehyde and pivalaldehyde, pivalaldehyde and cyclopropanecarbaldehyde, and cyclopropanecarbaldehyde and benzaldehyde. The reactions were performed at 353K for 4h in vacuo without solvent using 5mmol of each aldehyde and 100mg of solid base catalyst. For all the combinations, the catalytic activity of alkaline earth oxides increased in the order of BaOMgO2O₃, ZrO₂, ZnO, -alumina, hydrotalcite, KF/alumina, and KOH/alumina produced either no amount or very small amounts of cross-esterification and self-esterification products. Quantum chemical calculations carried out at the PM3-MO level for the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations indicated that the selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH₂O^-, ^tBuCH₂O^-, and C₃H₅CH₂O^-) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having more positively charged and sterically less hindered carbonyl carbon atom with the active species having less hindered oxygen atom proceeds faster.We also attempted the application of solid base catalysts to the challenging Tishchenko reaction of furfural, and excellent results were obtained with CaO and SrO. For instance, when furfural (10mmol) was treated with SrO (100mg) without solvent at 353K for 6h in vacuo, almost quantitative conversion to the corresponding ester was accomplished. Furthermore, application of SrO to the Tishchenko reaction of 3-furaldehyde was carried out successfully. The catalytic systems were also successfully applicable to the intramolecular Tishchenko reaction (lactonization) of o-phthalaldehyde to phthalide. For example, treatment of o-phthalaldehyde (1mmol) with CaO (50mg) in benzene (1mL) solvent at 313K under N₂ produced phthalide quantitatively in a short time of 15min. We finally refer to the perspective of application of solid base catalysts to Tishchenko reaction.     

Biotransformation of a C-glycosylflavone, abrusin 2''-O-beta-D-apioside, by human intestinal bacteria

After anaerobic incubation of abrusin 2'-O-beta-D-apioside (1) with a human fecal suspension, five metabolites were isolated and identified as abrusin (2), 1-(2',6'-dihydroxy-3',4'-dimethoxyphenyl)-3-(4'-hydroxyphenyl)propan-1- one (5), 5,6-dimethoxybenzene-1,3-diol (6), 3-(4'-hydroxyphenyl)propionic acid (7) and 3-phenylpropionic acid (8). However, methyl ether derivatives of abrusin (4'-O-methylabrusin and 4'-O-, 5-O-dimethylabrusin) resisted degradation under the same conditions.