The α‐Glycosidation of Partially Unprotected N‐Acetyl and N‐Glycolyl Sialyl Donors in the Absence of a Nitrile Solvent Effect

The synthesis of α‐sialosides is one of the most difficult reactions in carbohydrate chemistry and is considered to be both a thermodynamically and kinetically disfavored process. The use of acetonitrile as a solvent is an effective solution for the α‐selective glycosidation of N‐acetyl sialic acids. In this report, we report on the α‐glycosidation of partially unprotected N‐acetyl and N‐glycolyl donors in the absence of a nitrile solvent effect. The 9‐O‐benzyl‐N‐acetylthiosialoside underwent glycosidation in CH₂Cl₂ with a good α‐selectivity. On the other hand, the 4,7,8‐O‐triacetyl‐9‐O‐benzyl‐N‐acetylthiosialoside was converted to β‐sialoside as a major product under the same reaction conditions. The results indicate that the O‐acetyl protection of the sialyl donor was a major factor in reducing the α‐selectivity of sialylation. After tuning of the protecting groups of the hydroxy groups at the 4,7,8 position on the sialyl donor, we found that the 9‐O‐benzyl‐4‐O‐chloroacetyl‐N‐acetylthiosialoside underwent sialylation with excellent α‐selectivity in CH₂Cl₂. To demonstrate the utility of the method, straightforward synthesis of α(2,9) disialosides containing N‐acetyl and/or N‐glycolyl groups was achieved by using the two N‐acetyl and N‐glycolyl sialyl donors.     

Optimization of the dopant for the trace determination of polycyclic aromatic hydrocarbons by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry

The composition of the dopant for the analysis of polycyclic aromatic hydrocarbons (PAHs) by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry under reversed-phase conditions was optimized to enhance the ionization efficiency for PAHs. The most suitable dopant was a toluene/anisole mixture (99.5:0.5, v/v) and it could improve limit of detections (LODs) to 0.79-168 ng mL(-1) (signal-to-noise (S/N)=3) for 16 common PAHs. The LODs are 3.8-40 times lower than those obtained with toluene alone and are comparable to those obtained using gas chromatography/mass spectrometry.     

Protection of protein secondary structure by saccharides of different molecular weights during freeze-drying

The protective effects of saccharides with various molecular weights (glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltoheptaose, dextran 1060, dextran 4900, and dextran 10200) against lyophilization-induced structural perturbation of model proteins (BSA, ovalbumin) were studied. Fourier transform infrared (FT-IR) analysis of the proteins in initial solutions and freeze-dried solids indicated that maltose conferred the greatest protection against secondary structure change. The structure-stabilizing effect of maltooligosaccharides decreased in increasing the number of saccharide units. Larger molecules of dextran also showed a smaller structure-stabilizing effect. Increasing the effective saccharide molecular size by a borate-saccharide complexation reduced the protein structure-stabilizing effect of all of the saccharides except glucose. The results indicate that the larger saccharide molecules, and/or the complex formation with borate ion, reduce the free and accessible hydroxyl groups to interact with and stabilize the protein structure by a water-substitution mechanism.     

Formation of cyclic ethers via the palladium-catalyzed cycloaddition of activated olefins with allylic carbonates having a hydroxy group at the terminus of the carbon chain

The reaction of the activated olefins 1 with the allylic carbonate 2, having a hydroxy group at the terminus of the carbon chain, in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and dppe in THF at room temperature gave the corresponding cycloaddition products, tetrahydrofuran derivatives 5, in good to very high yields. The diastereoselectivities (trans/cis ratios) of the products were in the range of ca. 60-70/40-30. The reaction of 1 with the hydroxy allylic carbonate 3 in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and (o-tolyl)(3)P in THF at 50 degrees C afforded the corresponding cycloaddition products, tetrahydropyran derivatives 6, in good to high yields. The trans/cis ratios of the products were in the range of ca. 0-40/99-80. The reaction of 1a with the hydroxy allylic carbonate 4 needed higher reaction temperatures (approximately 100 degrees C) to give the cycloaddition product, the oxepane 7a, in 31% yield with low diastereoselectivity. Next, catalytic asymmetric syntheses of tetrahydrofuran and -pyran derivatives were carried out. With the Trost ligand 15, good to high ees were accomplished in the cycloaddition, although the diastereoselectivities were of low level. With the Hayashi ligand 16, good to high ees were also achieved in the cycloaddition. The absolute stereochemistries of the major enantiomers of 5l, 5m, and 6d were determined unambiguously by X-ray crystallographic analysis: trans-(2R,4R)-5l, cis-(2S,4R)-5l, 4R-5m, trans-(2S,4S)-6d, and cis-(2R,4S)-6d were major enantiomers. Based upon the absolute stereochemistries of the major enantiomers, the mechanism of catalytic asymmetric induction in the cycloaddition reaction is discussed.     

Platelet-rich plasma inhibits the apoptosis of highly adipogenic homogeneous preadipocytes in an in vitro culture system

Auto-transplantation of adipose tissue is commonly used for the treatment of tissue defects in plastic surgery. The survival of the transplanted adipose tissue is not always constant, and one of reasons is the accelerated apoptosis of the implanted preadipocytes. We have recently established highly homogeneous preadipocytes, named ccdPAs. The aim of the current study was to evaluate the regulation of the potency of platelet-rich plasma (PRP) on the apoptosis of ccdPAs in vitro. PRP stimulated the proliferation of the preadipocytes in a dose-dependent manner, and the stimulatory activity of 2% PRP was significantly higher than that of 2% FBS or 2% platelet-poor plasma (PPP). The presence of 2% PRP significantly inhibited serum starvation- or TNF-α/cycloheximide-induced apoptosis in comparison to 2% FBS or 2% PPP. DAPK1 and Bcl-2-interacting mediator of cell death (BIM) mRNAs were reduced in the preadipocytes cultured with 2% PRP in comparison to those cultured in 2% FBS. The gene expression levels were significantly higher in cells cultured without serum in comparison to cells cultured with 2% FBS, and the levels in the cells with 2% PRP were reduced to 5-10% of those in the cells without serum. These results indicated that ccdPAs exhibit anti- apoptotic activities, in addition to increased proliferation, when cultured in 2% PRP in comparison to the same concentration of FBS, and that this was accompanied with reduced levels of DAPK1 and BIM mRNA expression in in vitro culture. PRP may improve the outcome of transplantation of adipose tissue by enhancing the anti-apoptotic activities of the implanted preadipocytes.     

Mineral oil certified reference materials for the determination of polychlorinated biphenyls from the National Metrology Institute of Japan (NMIJ)

Four mineral oil certified reference materials (CRMs), NMIJ CRM 7902-a, CRM 7903-a, CRM 7904-a, and CRM 7905-a, have been issued by the National Metrology Institute of Japan, which is part of the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST), for the determination of polychlorinated biphenyls (PCBs). The raw materials for the CRMs were an insulation oil (CRM 7902-a and CRM 7903-a) and a fuel oil (CRM7904-a and CRM 7905-a). A solution of PCB3, PCB8, and technical PCB products, comprising four types of Kaneclor, was added to the oil matrices. The total PCB concentrations in the PCB-fortified oils (CRM 7902-a and CRM 7904-a) are approximately 6 mg kg⁻¹. In addition, the mineral oils which were not fortified with PCBs were also distributed as CRMs (CRM 7903-a and CRM 7905-a). Characterization of these CRMs was conducted by the NMIJ/AIST, where the mineral oils and the PCB solution were analyzed using multiple analytical methods such as dimethylsulfoxide extraction, normal-phase liquid chromatography, gel permeation chromatography, reversed-phase liquid chromatography, and chromatography using sulfoxide-bonded silica; and/or various capillary columns for gas chromatography, and two ionization modes for mass spectrometry. The target compounds in the mineral oils and those in the PCB solution were determined by one of the primary methods of measurement, isotope dilution–mass spectrometry (ID-MS). Certified values have been provided for 11 PCB congeners (PCB3, 8, 28, 52, 101, 118, 138, 153, 180, 194, and 206) in the CRMs. These CRMs have information values for PCB homologue concentrations determined by using a Japanese official method for determination of PCBs in wastes and densities determined with an oscillational density meter. Because oil samples having arbitrary PCB concentrations between respective property values of the PCB-fortified and nonfortified CRMs can be prepared by gravimetric mixing of the CRM pairs, these CRMs can be used for validation of PCB analyses using various instruments which have different sensitivities. Figure Preparation and certification processes of the mineral oil CRMs (example shown is polychlorinated biphenyls in insulation oil, high/low concentrations) Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Control of chemical reaction involving dissolved oxygen using magnetic field gradient

This study investigated the control of dissolved oxygen concentration using magnetic forces from gradient magnetic fields near a Nd–Fe–B permanent magnet. Maximum values of magnetic flux density and the product of the magnetic flux density and its gradient were 0.63 T and 44 T²/m, respectively. The magnet was placed under a Petri dish filled with 15 ml of 10% ammonia water. The Petri dish had a copper sheet in the center. Absorbance of tetraamminecopper(II) complex produced by the reaction in oxygen was measured using a spectrophotometer to observe oxygen concentration. Results showed that the magnetic field quantitatively enhanced tetraamminecopper(II) complex production. Moreover, remarkable enhancement of the copper complex production occurred in the magnetic field at less than 2 mm depth. The calculated magnetic force increase near the magnet surface supports this result. These results show that greater enhancement of the reaction rate occurs when the stronger magnetic force acts on oxygen molecules.     

Structural study of perovskite-type fine particles by synchrotron radiation powder diffraction

The crystal structures of BaTiO₃ and PbTiO₃ fine particles have been investigated by powder diffraction using synchrotron radiation high energy X-rays. It is revealed that a BaTiO₃ fine particle essentially consists of tetragonal and cubic structure components at 300 K, whereas a PbTiO₃ fine particle consists of a tetragonal structure. Adopting a structure model for the BaTiO₃ particle that a cubic shell covers a tetragonal core, the thickness of cubic BaTiO₃ shell is estimated at almost constant irrespective of particle sizes. Successive phase transitions are detected in 100 nm particles of BaTiO₃ near the phase-transition temperatures of a bulk crystal. The changes in diffraction profiles are small, but they are apparent for a most up-to-date powder diffractometry. This revised version was published online in August 2006 with corrections to the Cover Date.