The synthesis ofN-acetyl-β-l-fucosamine-1-phosphate and uridine 5′-diphospho-N-acetyl-β-l-fucosamine

Uridine 5′-(2-acetamido-2,6-dideoxy-β-l-galactopyranosyl) diphosphate (uridine 5′-diphospho-N-acetyl-β-l-fucosamine) was synthesized. The key intermediate, 3,4-di-O-acetyl-2-azido-2,6-dideoxy-β-l-galactopyranosyl dibenzyl phosphate, was prepared by a previously unknown reaction of cesium dibenzyl phosphate with the corresponding α-glycosyl nitrate and was then converted into theN-acetylated glycosyl phosphate and nucleoside diphosphate sugarsvia 3,4-di-O-acetyl-2-amino-2,6-dideoxy-β-l-galactopyranosyl phosphate using mildN-acetylation andO-deacetylation as the last synthetic steps. Published inIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 1919–1923, November, 2000.     

Cyclodextrins with heterocyclic substitution as GC stationary phases

Summary Two new cyclodextrin (CD) derivatives, heptakis{2,6-di-O-pentyl-3-O-[3′-(2″-chloro-4″,5″-dioxylmethene)-phenyl-5′-iso-oxazolylmethyl]}-β-CD (CD I) and heptakis{2,6-di-O-methyl-3-O-[3′-(2″-chloro)-phenyl-5′-iso-oxazolylmethyl]}-β-CD (CD II) were synthesized and coated on fused-silica capillary columns. Their chromatographic characteristics, including column efficiency, polarity, selectivity and phase transition were studied and compared with similar β-CD stationary phases. It was found that the heterocycle group has a significant effect on the selectivity of the CD stationary phases. Both stationary phases can be successfully used to separate many di- and trisubstituted benzene positional isomers and show stronger separation ability in separating low-polarity benzene positional isomers than other β-CD stationary phases.     

Novel purification method of commercial o- and m-xylenes by shape selective adsorption on HZSM-5

Liquid-phase competitive adsorption of three xylene isomers on ZSM-5 zeolites was studied. HZSM-5 zeolites exhibited an extremely high para-selectivity, this para-selectivity decreased with increasing adsorption temperatures. The introduction of Na⁺ enhanced the para-selectivity. It is apparent that such a high para-selectivity is caused solely by thermodynamic shape selectivity. The complete removal of impurities with small molecular dimensions, such as p-xylene and benzene, from commercial o- and m- xylenes could be attained by the repetition of the shape-selective adsorption on HZSM-5 zeolites.     

Diene condensation on zeolites, II. Influence of the zeolite structure and the nature of substituting cation on the reaction of alloocimene with α-methacrolein

The interaction of alloocimene with α-methacrolein on β-zeolite with various substituent cations (Fe, Ni, Zn, Cu and La) as well as on ZSM-5, erionite and mordenite has been studied at room temperature in dichloromethane. Substituent cations in β-zeolite as well as the silica/alumina ratio and alkali metal content in the zeolite structure were found to affect the formation of ocinal diastereomers. Therefore, we assume that a complex of active sites participates in the diene condensation: Alkali metals present in the zeolite suppress the (3+2)-cycloaddition reaction.     

Synthesis and structural modification of <Emphasis Type="Italic">tert</Emphasis>-butyl ester of 7α-chloro-2-(N,N-dimethylaminomethylene)-3-methyl-1,1-dioxoceph-3-em-4-carboxylic acid

The reaction of tert-butyl 7α-chloro-and 7-β-chloro-7α-isopropoxy-3-methyl-1,1-dioxoceph-3-em-4-carboxylates with the Vilsmeier reagent was carried out with introduction of N,N-dimethylaminomethylene group at position 2 in the E-and Z-isomeric forms. Prolonged treatment of tert-butyl 7α-chloro-3-methyl-2-(N,N-dimethylaminomethylene)-1,1-dioxoceph-3-em-4-carboxylate with hydroxylamine hydrochloride in acetonitrile at 40–50°C gave tert-butyl 10(S)-chloro-6-methyl-5-oxa-1,1,9-trioxo-1-thia-4,8-diazatricyclo[7,2,0,0^2,6]undecane-7(R)-carboxylate which isomerized into 1-tertbutoxycarbonylmethyl-3α-chloro-4-(5-methylisoxazole-4-sulfonyl)azetidin-2-one. In the case of tertbutyl 7β-chloro-7α-isopropoxy-3-methyl-2-(N,N-dimethylaminomethylen)-1,1-dioxoceph-3-em-4-carboxylate the analogous reaction gave tert-butyl 10β-chloro-(2S,6S,7S,10R,11R)-10α-isopropoxy-6-methyl-5-oxa-1,1,9-trioxo-1-thia-4,8-diazatricyclo[7,2,0,0^2,6]undecane-7(R)-carboxylate, the struc-ture of which was determined by 2D-NOESY two-dimensional spectroscopy. The compounds synthesized showed weak or no cytotoxic activity with respect to monolayers of cancer cells in vitro.     

Reaction of several resveratrol glycoside derivatives with hypochlorites in various media

The reactions of pterostilbenoside (trans-3,5-dimethoxystilben-4′-O-β-D-glucoside) and Ar–O–Tr derivatives of resveratroloside (3,5-dihydroxystilben-4′-O-β-D-glucoside) and pinostilbenoside (3-methoxy-5-hydroxystilben-4′-O-β-D-glucoside) with NaOCl and t-BuOCl in the presence of the stable nitroxyl radical TEMPO were studied in various media. It was found that the principal product of pterostilbenoside transformation was its 2,6-dichloroderivative, a part of which was oxidized to form 2,6-dichloropterostilbene glucuronide. Trityl ethers of resveratroloside and pinostilbenoside reacted with the hypochlorites to form mixtures of products.     

Beta-amyloid toxicity increases with hydrophobicity in the presence of metal ions

Abstract  

Alzheimer’s disease is a multifactorial neurodegenerative disorder characterized by the pathological brain deposition of neurofibrillary tangles and senile plaques. The latter consist mainly of insoluble β-amyloid (Aβ) fibril deposition. Aβ aggregation and deposition can be increased by several factors, including metal ions. In this study we investigated the role played by metal ions in affecting Aβ oligomerization in the presence and in the absence of its hydrophobic fragment Aβ_17–28. This was done not as a physiological investigation, but as a paradigmatic study to confirm the key role of Aβ superficial hydrophobicity as a relevant aggravating factor that contributes to the toxicity of Aβ and Aβ–metal complexes. The structural conformations of Aβ–metal complexes were monitored through fluorescence and turbidity measurements as well as transmission electron microscopy. Results reported herein indicate that various metals differentially influence Aβ conformation, with aluminum being the only metal ion for which we are able to determine a dramatic enhancement of peptide oligomer formation with a consequent toxic effect. This scenario was further enhanced by the presence of Aβ_17–28, which resulted in a marked toxicity in a neuroblastoma cell culture as a consequence of the enhancement of the hydrophobicity of the amyloid and amyloid–metal complexes.     

Study on the Inclusion Compounds of Eugenol with α-, β-, γ- and Heptakis (2,6-di-O-methyl)-β-cyclodextrins

Several host–guest inclusion compounds of eugenol as a guest molecule and cyclodextrins (α-,β-,γ-CD) and heptakis (2,6-di-O-methyl)-β-cyclodextrin (DMβ-CD) as hosts were investigated in the solid state and in aqueous solution. The one-to-one solid inclusion compounds of eugenol and β-CD or γ-CD were prepared, but those of eugenol with α- or DMβ-CD were not obtained under the same condition. However, the UV-visible absorption spectroscopy data indicated that the liquid guest could form a 1:1 inclusion compound with all four hosts respectively in aqueous solution. The two solid inclusion compounds were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The association constants (K), calculated from the modified Benesi–Hidebrand equation, of eugenol with α-, β-, γ- and DMβ-CD is 4.95 × 10⁴, 3.96 × 10⁵, 1.47 × 10⁵ and 9.33 × 10⁴ mol⁻¹ dm³, respectively.     

Optimization of the Synthesis of 2,6–Dinitro-4-trifluoromethylphenyl Ether Substituted Cyclodextrin Bonded Chiral Stationary Phases

The comparisons of five different chiral stationary phases (CSPs) based on 2,6-dinitro-4-trifluoromethylphenyl (DNP-TFM) ether substituted β-cyclodextrin are presented. The five CSPs differ from each other in the linkage/spacer chemistry, or on the position of the substituents on β-cyclodextrin, or in the sequence of the synthetic procedure. The results show that there are two optimum combinations: (1) DNP-TFM randomly substituted on the β-cyclodextrin as the chiral selector along with a carbamate linkage chain bonding it to the silica support; and (2) β-cyclodextrin derivatized by DNP-TFM substituents only on the C-2 and C-3 positions of the cyclodextrin with an ether linkage chain anchoring it to the silica gel. These two combinations show complementary separations for some enantiomers. The spacer chain effect is much more pronounced for the CSP based on the β-cyclodextrin derivatives with DNP-TFM substituents only on C-2 and C-3 positions than its randomly substituted counterpart. The sequence of derivatizing the cyclodextrin and attaching it to silica gel also affects its selectivity and efficiency. The β-cyclodextrin should be derivatized before it is linked to the silica gel.     

Surface chemical modification of zeolites and their catalytic performance for naphthalene alkylation

Acid-catalyzed naphthalene alkylation products, such as 2,6-dialkylnaphthalenes (2,6-DAN), are industrially important compounds used to make monomers for advanced polymer materials [1]. Zeolite molecular sieves can be extensively used in many catalytic applications, specifically in naphthalene alkylations due to their high activity and stability as well as their high selectivity. The initial studies have mainly focused on gas phase alkylation of naphthalene with methanol, and only obtained th…     

Insect pheromones and their analogues XLII. Synthesis of 2,6-dimethyloct-1-yl formate — A mimic of the aggregation pheromone of flour beetles

2-6-Dimethyloctan-1-ol, the formate of which is a mimic of the aggregation pheromone of the flour beetlesTribolium confusum andT. castaneum, has been synthesized by the hydroboration of 2,6-diemthyloct-1-ene, obtained from β-methylvaleric acid. Institute of Organic Chemistry, Urals Branch, Russian Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 571–573, September–October, 1992.     

Correlation between the chromatographic poperties of silica phenyl packing materials and the retention behaviour of methylated β-cyclodextrins

Summary The chromatographic properties of five columns packed with phenyl-bonded phases were characterized by an approach based on Tanaka's method for column to column comparisons in order to develop an LC analysis of partially methylated β-cyclodextrins. The retention behaviour of β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin was examined in order to evaluate the different interactions between phenyl stationary phase and this family of compound. Chromatograms show that the residual silanol activity of the packing materials plays a beneficial role in the partially methylated β-cyclodextrins separation process. It is concluded that knowledge of the interactions involved allows one to make a reasoned choice of the stationary phase in order to obtain the best possible analysis of three different commercial samples of partially methylated β-cyclodextrins.     

Oxidative dehydrogenation of isobutane to isobutylene over supported transition metal oxide catalysts

Para-selectivity of ZSM-5 zeolites with similar bulk Si/Al ratio, but different particle size and surface Al concentration has been investigated in toluene disproportionation. Results showed that enhancedpara-selectivity is a consequence not only of the particle size but also of the external surface aluminium concentration in the particles.     

Relationship of textural properties and catalytic behavior in polycrystalline ZSM-5 zeolites

Polycrystalline ZSM-5 zeolites were studied in the cracking ofn-pentane and the isomerization ofm-xylene. It was found that slow deactivation rates and lowp-selectivity are related to large external surface areas determined by the t-plot method.     

New polyhydroxysteroids and steroid glycosides from the far east starfishCeramaster patagonicus

Two new polyhydroxysteroids and five new glycosides were isolated from the starfishCeramaster patagonicus and their structures were elucidated: 5α-cholestane-3β,6α,15β,16β,26-pentol, (22E)-5α-cholest-22-ene-3β,6α,8,15α,24-pentol, (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,4β, 6α,8,15β,16β,28-heptol (ceramasteroside C₁), (22E)-28-O-[O-(2,4-di-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β, 6α,8,15β,16β,28-hexol (ceramasteroside C₂), (22E)-28-O-[O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,6α,8,15β,16β 28-hexol (eramasteroside C₃), (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-methyl-5α-cholest-22-ene-3β,4β,6α,8, 15β, 26-hexol (ceramasteroside C₄), and (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-xylopyranosyl]-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (ceramasteroside C₅)). Three known polyhydroxysteroids (24-methylene-5α-cholestane-3β,6α,8,15β,16β,26-hexol, 5α-cholestane-3β,6α,8,15β,16β,26-hexol, and 5α-cholestane-3β,6β,15α,16β,26-pentol) were also isolated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 190–195, January, 1997.     

Cyclodextrins-Kaempferol Inclusion Complexes: Spectroscopic and Reactivity Studies

The slightly water-soluble flavonoid kaempferol (KAE) and its inclusion complexes with β-cyclodextrin (βCD), hydroxypropyl-β-cyclodextrin (HPβCD) or heptakis-2,6-O-dimethyl-β-cyclodextrin (DMβCD) were investigated. The stoichiometric ratios and association constants describing the extent of the formation of the complexes have been determined. Binding constants, estimated from fluorescence studies at different temperatures, were analyzed so as to gain information about the mechanisms involved in the association processes. The thermodynamic data for the inclusion of KAE in DMβCD and HPβCD indicated that it is mainly enthalpy-driven whereas for βCD it is an entropy-driven process. Complex formation was monitored by two-dimensional ROESY experiments through the detection of intramolecular dipolar interaction. ROESY experiments provided data indicating that the B-ring of kaempferol is immersed in the apolar cavity with the A- and C-ring protruding from the wider rim for the three cyclodextrins studied. The antioxidant studies of KAE and CDs complexes showed an increment in its antioxidant activity. The complexes behave as better antioxidants than kaempferol alone.     

Experimental design methodologies to optimize the CE separation of epinephrine enantiomers

Summary A capillary electrophoretic method using a chiral selector was optimized by experimental design for the enantioresolution of epinephrine enantiomers. Two β-cyclodextrins derivatives, namely heptakis-2,6-di-O-methyl-β-cyclodextrin and carboxy-methyl-β-cyclodextrin, respectively neutral and charged, were used as chiral selectors employing an uncoated capillary. By using a statistical experimental design in which all factors are varied at the same time, it was possible to optimize the method with regard to the resolution between peaks and the two migration times. A fractional factorial design and a central composite design were used. A compromise between conflicting goals, such as maximization of resolution and minimization of analysis time, was found by means of a desirability function D. Balancing these goals against each other, the most acceptable solution to the problem was found and the optimized method gave a fast separation with complete resolution between the adrenaline enantiomers. The response surfaces obtained confirmed the robustness of the method.     

Synthesis and characterization of benzyl β-cyclodextrins used as GC stationary phases

Summary Heptakis(2,6-di-O-benzyl)-β-CD(I), heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD(II), heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD(III) and heptakis(2,6-di-O-benzyl-3-O-acetyl)-β-CD(IV) derivatives were synthesized and identified. Their thermal stabilities were tested using PyGC. These CD derivatives are stable up to 300°C and suitable for use as gas chromatographic stationary phases. The fused silica capillary columns coated with heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD and heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD showed excellent chromatographic properties in separating positional isomers.     

Vinyltetrazoles: I. Synthesis of NH-unsubstituted 5-vinyltetrazole

The NH-unsubstituted 5-vinyltetrazole was obtained in 55% yield by exhaustive methylation of 5-(β-dimethylaminoethyl)tetrazole with dimethyl sulfate at the terminal dimethylamino group with the subsequent elimination of a proton from the α-CH₂ group and Hofmann β-cleavage of the intermediate 5-(β-trimethylammoniumethyl)tetrazolide methyl sulfate. The microwave irradiation was shown to reduce 5-fold the time of the synthesis of the initial substrate, 5-(β-dimethylaminoethyl)tetrazole.