Synthetic Studies Toward Gangliosides and Their Analogs: Synthesis of Appropriately Protected Core Oligosaccharides as Construction Blocks

Abstract

2-(Trimethylsilyl)ethyl 2, 3, 6, 2′-tetra-O-acetyl-3′-O-benzyl-6′-O-benzyloxymethyl-β-d-lactoside (9) was synthesized starting from acetobromolactose (1) via 2-(trimethylsilyl)ethyl β-d-lactoside (3). Compound 9 was converted to the trisaccharide derivative 17 after coupling with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-α-d-galacto-pyranosyl bromide (11). Coupling of 17 with acetobromogalactose (19) gave the tetrasaccharide 20.     

Synthesis and photochemical properties of solar energy storage-exchange polymers containing pendant norbornadiene moieties

New photoresponsive polymers 1–4 containing pendant norbornadiene (NBD) moieties with N,N-disubstituted amide groups were synthesized with 97, 98, 92, and 94% conversions by the substitution reaction of poly (p-chloromethyl) styrene] with potassium salts of 3piperidyloxo-2,5-NBD-2-carboxylic acid, 3-(NN-dipropylcarbamoyl) -2,5-NBD-2-carboxylic acid, 3-(N-methyl-N-phenylcarbamoyl)-2,5-NBD-2-carboxylic acid, and 3-(N,N-dipheylcarbmoyl)-2,5-NBD-2-carboxylic acid, respectively, using tetrabutylammonium bromide as a phase transfer catalyst for all. Polymers 1–4 with N,N-disubstituted amide groups on the NBD moieties were sensitized by adding appropriate photosensitizers such as Michler's ketone and 4- (N,N-dimethylamino) benzophenone in the film state, although the reactivities of the polymers without photosensitizer were lower than that of our previously reported polymer 5 containing pendant 3- (N-phenylcarbamoyl) -2,5-NBD-2-carboxylate moiety. It was also found that the photo-irradiated retaining polymers 1–4 containing the corresponding QC moieties can be stored about 80–86 kJ/mol of their thermal energy. © 1994 John Wiley & Sons, Inc.     

Colloidal titration of aqueous zirconium solutions with poly(vinyl sulfate) by potentiometric endpoint detection using a toluidine blue selective electrode.

Zirconium oxy-salts were hydrolyzed to form positively charged polymer or cluster species in acidic solutions. The zirconium hydrolyzed polymer was found to react with a negatively charged polyelectrolyte, such as poly(vinyl sulfate), and to form a stoichiometric polyion complex. Thus, colloidal titration with poly(vinyl sulfate) was applied to measure the zirconium concentration in an acidic solution by using a Toluidine Blue selective plasticized poly(vinyl chloride) membrane electrode as a potentiometric end-point detecting device. The determination could be performed with 1% of the relative standard deviation. The colloidal titration stoichiometry at pH < or = 2 was one mol of zirconium per equivalent mol of poly(vinyl sulfate).     

Synthetic Studies on Sialoglycoconjugates 59: Total Synthesis of Tumor-Associated Ganglioside,Sialyl Le

Abstract

The first total synthesis of tumor-associated glycolipid antigen, sialyl Le^a, is described. Methylsulfenyl bromide-silver triflate-promoted coupling of 2-(trimethylsilyl)ethyl O-(2-acetamido-6-O-benzyl-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 (2) 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 (3) afforded the pentasaccharide 4a and 5a in good yields. Glycosylation of 4a with methyl 2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside (6) by use of N-iodosuccinimide (NIS) — trifluoromethanesulfonic acid (TfOH) as a promoter, gave the desired hexasaccharide 7. Compound 7 was converted into the α-trichloroacetimidate 10, via reductive removal of 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-octadecene-1, 3-diol (11), gave the β-glycoside 12. Finally, 12 was transformed, via selective reduction of the azide group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 15 in good yield.     

New polymers with mesogens in the side chain and kinked aromatic structures in the main chain from the polyaddition of bis(epoxide)s and di(ester)s

Nine polymers with kinked aromatic structures in the main chain and biphenylene‐type mesogenic groups in the side chain were synthesized by the polyaddition of bis(epoxide)s and thio‐ and O‐esters. Tetrabutylphosphonium chloride and tetraphenylphosphonium chloride effectively catalyzed the polymerization. The thermal behavior of the polymers was measured by DSC and polarizing optical microscopy. The effect of annealing time on the degree of crystallization was investigated by DSC analysis. Polymers containing 100% of the kinked aromatic groups and 1,3‐propylene glycol in the main chain were amorphous. However, when half of the main‐chain aromatic moieties were composed of kinked groups and the other half of the aromatics were linear rodlike groups, the polymers were crystalline. The incorporation of kinked groups into the main chain of side‐chain liquid‐crystalline polymers suppressed the formation of liquid crystallinity. The polymer with mesogenic aromatic structures in both the main chain and the side chain was capable of forming a liquid‐crystalline phase. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 988–998, 2000     

Perylene-Cy3 FRET System to Analyze Photoactive DNA Structures

We report a new Förster resonance energy transfer (FRET) system for structural analyses of DNA duplexes using perylene and Cy3 as donor and acceptor, respectively, linked at the termini of a DNA duplex via D-threoninol. Experimentally obtained FRET efficiencies were in good agreement with theoretical values calculated based on canonical B-form DNA. Due to the relatively long Förster radius, this system can be used to analyze large DNA structures, and duplexes containing photo-reactive molecules can be analyzed since perylene can be excited with visible light. The system was used to analyze a DNA duplex containing stilbene, demonstrating that in the region of the stilbene cluster the duplex adopts a ladder-like structure rather than helical one. Upon photodimerization between stilbene residues, FRET efficiencies indicated the reaction does not disturb DNA duplex. This FRET system will be useful for analysis of photoreactions of nucleobases as well as a wide range of nucleic acid structures.     

Neutron scattering and electrophoresis of dodecyldimethylamine oxide micelles

Small-angle neutron scattering (SANS) measurements were carried out at 25 °C on dodecyldimethylamine oxide solutions under different conditions. In media with no added salt, the micelle aggregation number remained nearly constant (70–78) over the range of the degree of ionization, α_M, between 0 and 0.73 in contrast with the sharp critical micelle concentration increase in a narrow range of α_M from 0.35 to 0.40. This characteristic α_M dependence that deviates markedly from the prediction of the regular solution approach is thus shown to take place without a considerable change with respect to micelle size and shape. The surface electric potential employed to calculate the intermicellar repulsion under the Debye–Hückel approximation was found to be much lower than the actual surface potential determined from hydrogen ion titration. This inconsistency was solved by introducing a rescaled particle size for the hard-sphere interaction part. The surface potential from SANS was rather similar to the zeta potential determined by electrophoretic light scattering. In the range of NaCl concentrations higher than about 0.2 M, micelle growth was observed for both the hemihydrochloride (1:1 complex) and the cationic species and the growth into a cylindrical shape was confirmed. Received: 3 March 1999 Accepted in revised form: 22 April 1999     

Quantitative analysis of dissociation of LDH by high pressure native PAGE

ABSTRACT

High pressure native polyacrylamide gel electrophoresis has been designed to visualize the dissociation/association process of protein complexes. This paper reports this methodology in more quantitative way by inspecting pressure dissociation of pig heart lactate dehydrogenase, a tetrameric protein, which was extensively investigated in spectroscopic methods. We observed the change of electrophoresis pattern with pressure up to 150?MPa. By optimizing the buffer system and careful image analysis of the stained gels, we quantified all the dissociates in the process of pressurization. We discussed the characteristics of our methodology by comparing the result with the previously reported.     

A linear stability analysis on the onset of thermal convection of a fluid with strongly temperature-dependent viscosity in a spherical shell

A linear stability analysis was performed in order to study the onset of thermal convection in the presence of a strong viscosity variation, with a special emphasis on the condition for the stagnant-lid (ST) convection where a convection takes place only in a sublayer beneath a highly viscous lid of cold fluid. We consider the temporal evolution (growth or decay) of an infinitesimal perturbation superimposed to a Boussinesq fluid with an infinite Prandtl number which is in a static (motionless) and conductive state in a basally heated planar layer or spherical shell. The viscosity of the fluid is assumed to be exponentially dependent on temperature. The linearized equations for conservations of mass, momentum, and internal (thermal) energy are numerically solved for the critical Rayleigh number, Ra _c , as well as the radial profiles of eigenfunctions for infinitesimal perturbations. The above calculations are repeatedly carried out by systematically varying (i) the magnitude of the temperature dependence of viscosity, E, and (ii) the ratio of the inner and outer radii of the spherical shell, γ. A careful analysis of the vertical structure of incipient flows demonstrated that the dominance of the ST convection can be quantitatively identified by the vertical profile of Δ _h (a measure of conversion between horizontal and vertical flows), regardless of the model geometries. We also found that, in the spherical shell relevant to the Earth’s mantle (γ = 0.55), the transition into ST convection takes place at the viscosity contrast across the layer ${r_\eta\simeq10^4}$ . Taken together with the fact that the threshold value of r _η falls in the range of r _η for a so-called sluggish-lid convection, our finding suggests that the ST-mode of convection with horizontally elongated convection cells is likely to arise in the Earth’s mantle solely from the temperature-dependent viscosity.