摘要:

The Witting reaction of (carbethoxymethylene)triphenylphosphorane with perbenzylated sugar δ-lactones and their 2-acetamido-2-deoxy derivatives is described. It is shown that this olefination occurred readily with thegalactoandglucoderivatives, leading stereoselectively toZ-C-glycosylidenes in good yields. However, the same reaction with the perbenzylated 2-deoxy-D-arabino-hexono-1,5-lactone and the mannonolactones worked poorly. Reduction over Pd/C followed by acetylation of the obtainedC-glycosylidenes led stereoselectively to peracetylated β-C-glycosides and amino β-C-glycosides. The olefin function could also be reduced selectively by Raney nickel or NiCl2/NaBH4, affording the perbenzylatedC-glycosides and amino β-C-glycosides. Other transformation of the enol ether function is also reported.

ISSN:0732-8303    

DOI:10.1080/07328309908544013

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Five multivalent β-D-GalNAc-(1→4)-β-D-Gal oligomers were selected and synthesized as probes for investigating the adhesin-receptor interactions ofP. aeruginosapili with multivalent receptors. They were synthesized by the amide coupling reactions of 8-(N-2-aminoethyl)carboxamidooctyl 4-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-β-D-galactopyranoside (7) with EDTA dianhydride, EDTA, Kemp's triacid and adipic acid with EDC, DIC and DCC combined with HOBt as coupling reagents and by the reaction of per-O-acetylated 7 with 1,3,5-benzenetricarbonyl trichloride followed by de-O-acetylation. These resulting multivalent compounds contain flexible C9spacer arms as linkers attached to either flexible hydrophilic moieties or rigid hydrophobic cores.

ISSN:0732-8303    

DOI:10.1080/07328309908544014

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We examined the effect as donors of three aryl β-D-galactosides (i.e. p-nitrophenyl β-D-galactopyranoside,o-nitrophenyl β-D-galactopyranoside and phenyl β-D-galacto-pyranoside) on the regioselectivity and the yield of the synthesis ofN-acetyllactosamine obtained from the transglycosylation reaction catalyzed by a crude preparation of β-D-galactosidase fromBacillus circulansat 25 °C, 37 °C and 55 °C, respectively. Usingp-nitrophenyl β-D-galactopyranoside the reaction results were fully regiospecific at all the temperatures considered: the maximum molar yield (74%) was obtained at an incubation temperature of 55 °C. Usingo-nitrophenyl β-D-galactopyranoside as the donor the reaction was still highly regioselective and the maximum molar yield (50%) was achieved at an incubation temperature also of 55 °C. Using phenyl β-D-galactopyranoside transglycolytic products appear only at an incubation temperature of 55 °C but at very low molar yield (about 14%) and lower regioselectivity.

ISSN:0732-8303    

DOI:10.1080/07328309908544015

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

1H and13C NMR spectra of four fucosyllactoses were analyzed and interresidual NOEs were detected in solution. Several interresidual NOE cross peaks between non-direct-bonding pyranoses were obtained in common with trisaccharides including fucose. Three-dimensional (3D) structures of the four saccharides were simulated with DADAS90 software using distance constraints estimated by NOE intensity. Results suggest approximate C2 rotating symmetry in the 3D 3,2'-difucosyllactose structure.

ISSN:0732-8303    

DOI:10.1080/07328309908544016

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Methyl 2-deoxy-D-glucofuranoside has been conveniently prepared starting from 3-O-benzyl-1,2-O-isopropylidene-α-D-glucofuranose, involving the first described deoxygenation at the 2-position.

ISSN:0732-8303    

DOI:10.1080/07328309908544017

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Lipopolysaccharide (LPS) ofHafnia alvei23 has an acid-labile O-specific polysaccharide (OPS) with a pentasaccharide-phosphate repeating unit containing D-Glc1P, D-GlcNAc, L-Fuc, 6-deoxy-D-talose (D-6dTal), 4-acetamido-4,6-dideoxy-D-glucose (D-Qui4NAc), and anO-acetyl group. A partially degraded OPS was obtained by hydrolysis of LPS with 0.25 M sodium acetate in aqueous 0.5% acetic acid. Fractionation of LPS on Sephadex G-200 in DOC buffer allowed isolation of long-chain LPS species which, together with OPS, were studied by methylation analysis, chemical degradations (O-deacetylation, dephosphorylation with 48% hydrofluoric acid, Smith degradation), and1H and13C NMR spectroscopy, including 2D COSY, TOCSY, NOESY, and H-detected1H,13C heteronuclear single-quantum coherence (HSQC) experiments. The following structure of the repeating unit of OPS was established:

ISSN:0732-8303    

DOI:10.1080/07328309908544018

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spontaneous removal of monocarboxylic (formic, acetic, propionic or butyric) acids accompanying dehydration of the corresponding chitosan salts was observed from X-ray fiber diffraction diagrams obtained during the storage of these salts for a given period of time. The first three salts were prepared by immersing a tendon chitosan (a hydrated crystal) in an aqueous solution of respective monocarboxylic acid and 2-propanol. The salts showed similar fiber patterns not only to one another but also to the “Eight-fold” polymorph of the original chitosan, indicating that they are Type II salts, hydrated crystals, where the backbone chitosan molecule takes up an eight-fold helical conformation. The temperature required for the salt formation depended on the hydrophobicity of the acid, e.g., the chitosan formic acid salt could be prepared at room temperature, whereas, formation of the propionic acid salt was carried out at 4 °C. All the acids spontaneously evaporated accompanied by dehydration during storage of the salts, resulting in formation of anhydrous crystalline chitosan. Removal of the monocarboxylic acids was accelerated by increasing the hydrophobicity of the acid: at 100% relative humidity approximately 3 months for the formic, 1 month for the acetic and 3 weeks for the propionic acid salts. In the case of butyric acid the anhydrous polymorph of chitosan was obtained immediately after the reaction, suggesting that the water removing action of this acid was too fast to detect a Type II salt by the present X-ray method. The anhydrous crystals of chitosan were irreversibly prepared by annealing a hydrated crystal in water at a high temperature, such as 240 °C, leading to a little loss of orientation and to thermal decomposition of the sample specimen to some extent. But it was found that, through Type II salts of monocarboxylic acids, the hydrated crystals of chitosan can be dehydrated even at room temperature without any loss of orientation and decomposition of the chitosan specimen.

ISSN:0732-8303    

DOI:10.1080/07328309908544019

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The non-Newtonian behavior and dynamic viscoelasticity of rice starch (Nihonbare; amylose content, 15.8%) solutions were measured with a rheogoniometer. A gelatinization of Nihonbare starch occurred above 3.0% after heating at 100 °C for 30 min. The Nihonbare starch showed shear-thinning behavior at a concentration of 2.0%, but plastic behavior above 3.0% at 25 °C. The viscosity of Nihonbare starch at a concentration of 2.0% solution decreased gradually with increase in temperature from 10 to 55 °C, then it stayed at a constant value with further increase in the temperature. However, for 4.0% solution, rapid decrease in the viscosity was observed after the temperature reached 25 °C up to 50 °C, then it stayed at a constant value. The dynamic modulus of Nihonbare starch stayed at a constant value during increase in the temperature at 4%. The tan δ of the starch showed low values, 0.28, at low temperature range and stayed at a constant up to 30 °C, then it increased a little with increasing temperature. A little decrease of dynamic modulus of Nihonbare starch was observed at low temperature range upon addition of urea (4.0 M). The dynamic modulus, however, decreased rapidly when the temperature reached 50 °C, which was estimated to be a transition temperature. The dynamic modulus also decreased rapidly in 0.10 M NaOH solution above 50 °C. A possible mode of intermolecular hydrogen bonding between amylose and amylopectin molecules of Nihonbare starch is proposed. The short chains (A and B1) of the amylopectin molecules may take part in the intermolecular association in aqueous solution.

ISSN:0732-8303    

DOI:10.1080/07328309908544020

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Graft copolymerization reactions onto some polysaccarides were carried out using acryloylcyanoacetohydrazide (ACAH) as chelating monomer. Different grafting variables onto chitin were studied, namely time, temperature, concentrations of monomer and initiator. Grafting by the prementioned chelating monomer was also carried out on chitosan and bagasse raw materials for different periods. The grafting parameters obtained were compared with those values of PACAH-grafted chitin and polyacrylonitrile-grafted polysaccharides. FTIR-spectra of the grafted polysaccharides were also studied to evidence the grafting. The PACAH- and PAN-grafted carbohydrates with the same range as molecular substitution (M.S. 0.8- 1.2) were compared their ability to chelate some metal ions, namely Cu (II), Mn(II), Fe(III) and Cr(III). The adsorption ability of metals onto the grafted polysaccharides was also compared with that obtained from previously examined modified polysaccharides, under nearly the same adsorption conditions.

ISSN:0732-8303    

DOI:10.1080/07328309908544021

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Polysialoglycoconjugates, such as polysialylated ganglio-series gangliosides and N-CAM (neural cell adhesion molecule), are of interest because of their important physiological functions in association with neural cell development, differentiation, neuron network formation, and so on.2-4Chemical synthesis of these glycoconjugates provides an effective method to elucidate their biological significance in nature at the molecular level, providing not only genuine original glycoconjugates but also their derivatives and analogs designed for biological investigation. We have established5an efficient method to construct dimeric and trimeric sialoglycosides by using the lactonated sialic acid derivatives as building blocks, and succeeded in the systematic synthesis of various polysialogangliosides such as GD3, GQ1b, GQlbα and, very recently, GT3.6In this paper, as a part of our continuous synthetic approach directed toward the polysialoglycoconjugates, we report the first synthesis of α-linked tetrameric sialoglycosides coupled with a galactose and lactose residue.

ISSN:0732-8303    

DOI:10.1080/07328309908544022

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor