Synthetic Studies on Sialoglycoconjugates 22: Total Synthesis of Tumor-Associated Ganglioside,Sialyl Lewis X1

ABSTRACT

The first total synthesis of tumor-associated glycolipid antigen, sialyl Lewis X is described. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (1) with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fuco-pyranoside (4) gave the α-glycoside (5), which was converted by reductive ring-opening of the benzylidene acetal into the glycosyl acceptor (6). Dimethyl(methylthio)sulfonium triflate-promoted coupling of 6 with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-galactopyranoside (7) afforded the desired hexasaccharide 8 in good yield. Compound 8 was converted into the α-trichloroacetimidate 11, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octa-decene-1,3-diol (12), gave the β-glycoside 13. Finally, 13 was transformed, via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title compound 16.     

Syntheses of Novel Nonreducing-Sugar Subunit Analogs of Lipid a Carrying 2-Acyloxytetradecanoyl and 2-Hydroxyacyl Groups of Different Carbon Chain Length

Abstract

To investigate the biological influence of the 2-(acyloxy)tetradecanoyl and 2-hydroxyacyl groups in the nonreducing-sugar subunit analogs of lipid A, a novel series of 3-(O-[(2RS)-2-acyloxytetradecanoyl]-2-deoxy-2-[(2RS)-2-hydroxytetradecanamido]-4-O-phosphono-d-glucoses (10a-d), 3-O-[(2RS)-2-acyloxytetradecanoyl]-2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-4-O-phosphono-d-glucoses (19a-d), and 2-deoxy-2-[(2RS)-2-hydroxyacyl]amino-4-O-phosphono-3-O-[(3R)-3-tetradecanoyloxytetradecanoyl]-d-glucoses (23e-h) were systematically synthesized.     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Proper composition for superconductivity in Pb(Ba, Sr)2(Y, Ca)Cu3O7

Superconductivity and composition analysis of PbBaSr(Y, Ca)Cu₃O_y with fixed ratio of Sr/Ba = 1 were studied. Synthesis condition and superconductivity of Pb(Ba, Sr)₂(Y, Ca)Cu₃O_y with various ratio of Sr/Ba and Ca/Y were also studied. It was found that T_c increased with increasing Ca concentration, and that Sr-rich specimens allowed to contain more Ca. PbBa_0.8Sr_1.2Y_0.6Ca_0.4Cu₃O₇ showed superconductivity with zero-resistance temperature of 42 K, which was higher than PbBaSrY_0.7Ca_0.3Cu₃O₇ with maximum Ca content for Sr/Ba = 1. Decrease in averaged ionic radii of Ba and Sr in Sr-rich compositions would be favorable for the contraction of Cu-O bonds by hole-doping via Ca substitution for Y.     

Synthesis of the glycan moiety of ganglioside HPG-7 with an unusual trimer of sialic acid as the inner sugar residue

The glycan moiety of ganglioside HPG-7, isolated from the sea cucumber (Holothuria pervicax), was synthesized for the first time. The characteristic substructure, a trisialic acid sequence embedded in the glycan, was deliberately constructed by utilizing suitably differentiated sialyl units for various synthetic purposes. Finally, a pentasaccharide was successfully delivered as the hexyl glycoside.     

Mode coupling and radiation loss of clad-type optical waveguides due to the index inhomogeneities of the core material

Closed form approximate expressions are derived for the mode-coupling, radiation loss and losses of each guided mode in multimode clad-type dielectric slab waveguides due to the index inhomogeneities of the core material. The analysis considers the inhomogeneities of the core-index in the axial and transverse directions and includes correlation lengths of any magnitude. It allows us to conclude that there will be considerable mode-dependency for the mode-coupling and radiation loss if the axial and/or transverse correlation lengths are of the order of or greater than the wavelength. It is also found that the mode-coupling and radiation loss peak at some value of the axial correlation length, and the radiation loss can be reduced by increasing the refractive-index difference of the core and cladding materials. Finally, it is shown that if the correlation lengths are shorter than, or of the order of the wavelength, the losses of each guided mode will mainly be due to the radiation process. But, in the case where the axial correlation length is much greater than the wavelength, the scattering into other guided modes is the dominant mechanism.     

Topological structure of the inter-band phase difference soliton in two-band superconductivity

Two-component superconductivity based on the two-band superconductor has a functional topology such as an inter-band phase difference soliton (i-soliton) to realize topological electronics (topolonics). Many gauge field theories are applied to investigate the topology of two-band superconductivity. To ease experimental and electronics applications, these theories should be refined. Weinberg–Salam theory and SU(2) (two-dimensional special unitary symmetry) gauge field theory are proper starting points. An effective extra force field because of the crystal structure and inter-band Josephson interaction, rather than spontaneous symmetry breaking, simplifies the conventional gauge field theory.     

A new type of amino amide organocatalyzed enantioselective crossed aldol reaction of ketones with aromatic aldehydes

A new type of amino amide organocatalysts was designed and synthesized from commercially available amino acids in easy steps. Their catalytic activities were examined in enantioselective crossed aldol reaction of various acyclic and cyclic ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn:anti?=?1:99, up to 97% ee).     

Interaction of wheat germ agglutinin with an N-acetylglucosamine-carrying telomer brush accumulated on a colloidal gold monolayer

A disulfide-carrying telomer with many pendent N-acetylglucosamine (GlcNAc) residues (Cys-PMHGlcNAc) was obtained by photo-polymerization of 1-(6'-methacryloylaminohexyl)-2-N-acetoamido-2-deoxy d-glucopyranoside) (MHGlcNAc) using a benzyl N,N-diethyldithiocarbamoyl (BDC) derivative that shows abilities of initiation, transfer, and termination (iniferter). The disulfide-carrying telomer was accumulated on a monolayer of colloidal Au on a glass substrate, and the interaction of wheat germ agglutinin (WGA) with GlcNAc residue at the polymer brush-solution interface was examined by using the localized surface plasmon resonance (LSPR) technique. For comparison, an amphiphile carrying many pendent GlcNAc residues was also prepared with MHGlcNAc and a lipophilic radical initiator and was incorporated in a phospholipid liposome to examine interaction of the GlcNAc residue with WGA on the liposome surface using turbidity measurements. Both the colloidal gold optical device and the liposome showed a concentration-dependent specific binding of WGA, and the GlcNAc-carrying liposome had a detection limit of 100 nM for WGA, whereas that of the colloidal gold device was 10nM. The sugar-carrying telomer-coated device examined here is not only useful as a simple biosensor chip but is also expected to expand our knowledge of bio-related phenomena at the liquid-telomer brush interfaces on a colloidal Au.