Two-dimensional mapping by high-performance liquid chromatography of pyridylamino oligosaccharides from various glycosphingolipids.

A method to map sugars two-dimensionally for the analysis of the structures of oligosaccharides from glycosphingolipids is described. Nine neutral and ten acidic oligosaccharides were obtained from glycosphingolipids by endoglycoceramidase digestion and labelled with 2-aminopyridine. The pyridylamino oligosaccharides were clearly separated by high-performance liquid chromatography on commercially available C18-silica and amide-silica column. All compounds tested were mapped without any overlapping. The separation of the pyridylamino oligosaccharides on the C18-silica column depended on the numbers and positions of sialic acid and N-acetylhexosamine residues; on the amide-silica column, the separation depended on the total number of sugar residues.     

Template-directed excimer formation via specific non-covalent interactions between pyrene guanidinium derivatives and nucleic acids

Structurally distinct guanidinium derivatives were evaluated for their ability to interact non-covalently with various nucleic acid sequences. Among the evaluated derivatives, 4-[(pyrene-1-ylmethyl)amino]butyl] guanidinium (pbg) was found to demonstrate strong excimer emission upon nucleic acid addition and high levels of discrimination between ds- and ss-DNA. The intensity of excimer emission proved to be dependent on the length of the linker probe as well as the oligonucleotide length and sequence. In particular, G-quadruplex prone structures were found to induce the highest excimer emissions among all nucleic acids tested.     

Thermosensitive poly(methyl methacrylate) emulsion prepared in the presence of poly(vinyl alcohol) with a cloud point as a protective colloid

An emulsion of poly(methyl methacrylate) (PMMA) was prepared using poly(vinyl alcohol) (PVA) of low degree of hydrolysis with a cloud point as a protective colloid. The behaviour of an aqueous solution of PVA with 80% degree of hydrolysis was first investigated in terms of the Huggins constant in viscometry. MMA was polymerized using the PVA at 20 °C, where no abnormality in the aqueous PVA was observed. The change in transmittance of the emulsion observed with a UV–vis photometer revealed that in the case of UV light of wavelength 370 nm, the transmittance decreased markedly at around 30 °C with an increase in temperature, and then increased with a decrease in temperature. The thermosensitive property resulted from PVA with a low degree of hydrolysis with a cloud point, at a higher temperature of which the PVA loses solubility in water owing to weakening of the hydrogen bond between PVA molecules and water.     

Mass spectrometric analysis of low molecular mass polyesters by laser desorption/ionization on porous silicon

A low molecular mass polyester was analyzed by desorption/ionization on porous silicon (DIOS) mass spectrometry. The results were compared with those of matrix-assisted laser desorption ionization (MALDI) mass spectrometry using matrixes of alpha-cyano-4-hydroxycinnamic acid (CHCA) and 10,15,20-tetrakis(pentafluorophenyl)porphyrin (F20TPP). The CHCA matrix was not suitable for characterization of low molecular mass components of the polyester because the matrix-related ions interfered with the component ions. On the other hand, the F20TPP matrix showed no interference because no matrix-related ions appeared below m/z 822. However, the solvent selection for determining optimal conditions of sample preparation was limited, because F20TPP does not dissolve readily in any of the available organic solvents. In the DIOS spectra, the polymer ions were observed at high sensitivity without a contaminating ion. No matrix is needed for DIOS spectra of low molecular mass polyesters, facilitating sample preparation and selectivity of a precursor ion in post-source decay measurements.     

Studies on the mechanism for stereoisomerization of 1-zirconacyclopent-3-yne compounds

The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η⁵-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d₆ solution were observed using ¹H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (k_H/k_D = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η⁴-π,π-coordination mode is proposed.     

Direct Enantioselective Three‐Component Synthesis of Optically Active Propargylamines in Water

An enantioselective three‐component reaction of aldehydes, amines, and alkynes in water by using a bis(imidazoline)–Cu^I catalysts having a hydrophobic substituent and sodium dodecyl sulfate as a surfactant was developed. The reaction was applied to a broad range of aldehydes and alkynes to give optically active propargylamines with excellent yields (up to 99 %) and enantiomeric excesses (up to 99 % ee).     

Synthesis of Urea‐Tethered Disaccharides in Water

A new method for the synthesis of urea‐linked disaccharides in aqueous media has been developed. The key feature of our approach is two strained Steyermark‐type gluco‐ and galactopyranosyl oxazolidinones. Each oxazolidinone is attached to a pyranose ring in a di‐equatorial trans‐annulation framework. Reaction of these oxazolidinones with 4‐aminohexopyranose in water proceeded smoothly to afford the urea‐tethered cellobiose and lactose analogues. The galactose‐type oxazolidinone proved to be more reactive than the glucose‐type, which is explained by the presence of an axial hydroxy group at C4 in the former.