Inter- and intramolecular glycosylation of exo-glycals promoted by metallic Lewis acids

exo-Glycosyl carbonates were employed for inter- and intramolecular glycosylation reactions. A number of metallic Lewis Acids and solvents were examined to enhance the reactivity. The optimum conditions were found to be the use of AlCl3 in 1-nitropropane. The method was demonstrated to be useful for the intermolecular glycosyl transfer of several nucleophiles, including simple alcohols, sugars, and amino acid derivatives; however, intramolecular glycosylations were not successful.     

4-phenylylboronic acid: A new type of enhancer for the horseradish peroxidase catalysed chemiluminescent oxidation of luminol

4-Phenylylboronic acid enhances the light emission from the horseradish peroxidase catalysed oxidation of luminol by hydrogen peroxide. Optimization studies showed that the greatest enhancement was obtained using micromolar concentrations of the new enhancer. The largest degree of enhancement was found with the basic isoenzyme of horseradish peroxidase (Type VIA), and lesser degrees of enhancement were obtained with Type VII and Type IX horseradish peroxidase. The enhancer was also effective in the peroxidase catalysed oxidation of isoluminol by peroxide.     

Aerobic biotransformation of 4-fluorocinnamic acid to 4-fluorobenzoic acid

The biotransformation of 4-fluorocinnamic acid (FCA) using non-acclimated industrial activated sludge was investigated. FCA is a common intermediate in organic synthesis, and it is often present in aqueous waste streams. Hence, the biotransformation reactions this compound undergoes when exposed to activated sludge micro-organisms should be understood before waste streams are sent to biological wastewater treatment plants (WWTPs). FCA biotransformation was monitored using a wide range of analytical techniques. These techniques were used to monitor not only FCA disappearance, but also the formation of degradation products, in order to propose the metabolic pathway. FCA was biotransformed to 4-fluorobenzoic acid via the formation of 4-fluoroacetophenone. The removal of FCA up to 200 mg L^-1 followed first order kinetics. The half-lives for removal of FCA from the test solutions supplied with 200 mg L^-1, 100 mg L^-1, and 50 mg L^-1 were 53, 18, and 5 hours respectively.     

Preparative production of colominic acid oligomers via a facile microwave hydrolysis

The hydrolysis of colominic acid via microwave irradiation was studied for the production of short-chain oligomers with a degree of polymerization (DP) of 1-5. This method was compared to the traditional acid hydrolytic method for the production of preparative quantities of short colominic acid oligomers. The oligomers were purified by size exclusion chromatography and characterized by ¹H NMR. Optimal conditions for producing the dimer were found to be 12 min at 10% power in a 1000-Watt domestic microwave. This method is advantageous over the traditional technique in that the hydrolysis can be completed in just a few minutes, rather than in a few hours, it is reproducible, and yields large quantities of the desirable short chain oligomers of colominic acid.     

Process intensification of immobilized lipase catalysis by microwave irradiation in the synthesis of 4-chloro-2-methylphenoxyacetic acid (MCPA) esters

4-Chloro-2-methylphenoxyacetic acid (MCPA) is a selective systemic herbicide which is absorbed by leaves and roots. MCPA esters are preferred due to their low water solubility and environmental friendliness. Esterification of MCPA with n-butanol was investigated as a model reaction using immobilized enzymes under the influence of microwave irradiation. Different immobilized enzymes such as Novozym 435, Lipozyme TL IM, Lipozyme RM IM and Lipase AYS Amano were studied under microwave irradiation amongst which Novozym 435 (immobilized Candida antarctica lipase B) was the best catalyst. Effects of various parameters were systematically studied on rates and conversion. Under microwave irradiation, the initial rates were observed to increase up to 2-fold. Under optimized conditions of 0.1 mmol MCPA and 0.3 mmol n-butanol in 15 mL 1,4-dioxane as solvent, Novozym 435 showed a conversion of 83% at 60 °C in 6 h. Based on initial rate and progress curve data, the reaction was shown to follow the Ping Pong bi–bi mechanism with inhibition by MCPA and n-butanol. Esterification of MCPA was also studied with different alcohols such as isopropyl alcohol, n-pentanol, n-hexanol, benzyl alcohol and 2-ethyl-1-hexanol.     

Peroxidase catalysed oxidative decarboxylation of vanillic acid to methoxy-p-hydroquinone

Horseradish peroxidase catalysed the oxidative decarboxylation of vanillic acid to methoxy-p-hydroquinone and subsequent oxidation of the hydroquinone to methoxy-p-benzoquinone. Peroxidase also catalysed the oxidation of vanillyl alcohol to vanillin and vanillic acid; however, neither vanillyl alcohol nor vanillin appeared to give rise to methoxyhydroquinone directly. Correspondingly, peroxidase catalysed the oxidative decarboxylation of syringic acid to 2,6-dimethoxy-p-hydroquinone and subsequent oxidation of the hydroquinone to 2,6-dimethoxy-p-benzoquinone.     

A sensitive method for 4-hydroxybutyric acid in urine using gas chromatography-mass spectrometry

4-Hydroxybutyric acid (4HB) was analyzed by gas chromatography-mass spectrometry. Under acidified conditions, 4HB is difficult to detect due to lactonization. Using a urine sample containing 0.01 mg creatinine, we performed trimethylsilyl derivatization without extraction, only adding dimethylsuccinic acid as an internal standard and 10 microl of 0.1 N NaOH methanol solution with adequate evaporation. Urine 4HB levels in a patient with 4-hydroxybutyric aciduria was determined to be 1258 mmol/mol Cr (control, 0.28-2.81 mmol/mol Cr) in this method. Direct derivatization of samples without extraction showed good reproducibility and linearity. Only a small sample of urine was required. Alkalinization by NaOH prevented not only lactonization of 4HB, but also loss of the compounds during evaporation.     

Microwave assisted synthesis of naphthopyrans catalysed by silica supported fluoroboric acid as a new class of non purine xanthine oxidase inhibitors

A series of naphthopyrans was synthesized employing silica supported fluoroboric acid under solvent free conditions in a microwave reactor. The catalytic influence of HBF₄–SiO₂ was investigated in detail to optimize the reaction conditions. The synthesised compounds were evaluated for in vitro xanthine oxidase inhibitory activity for the first time. Structure–activity relationship analyses have also been presented. Among the synthesised compounds, NP-17, NP-19, NP-20, NP-23, NP-24, NP-25 and NP-26 were the active inhibitors with an IC₅₀ ranging from 4 to 17 μM. Compound NP-19 with a thiophenyl ring at position 1 emerged as the most potent xanthine oxidase inhibitor (IC₅₀ = 4 μM) in comparison to allopurinol (IC₅₀ = 11.10 μM) and febuxostat (IC₅₀ = 0.025 μM). The basis of significant inhibition of xanthine oxidase by NP-19 was rationalized by its molecular docking at MTE binding site of xanthine oxidase.     

Application and limitations of the methyl imidate protection strategy of N-acetylglucosamine for glycosylations at O-4: synthesis of Lewis A and Lewis X trisaccharide analogues

We describe here the synthesis of the allyl Le^a trisaccharide antigen as well as that of an analogue of the Le^x trisaccharide antigen, in which the galactose residue has been replaced by a glucose unit. Although successful fucosylations at O-4 of N-acetylglucosamine acceptors have been reported using perbenzylated thioethyl fucosyl donors under MeOTf activation, such conditions led in our case to the conversion of our acceptor to the corresponding alkyl imidates. Indeed, in this synthesis of the Le^a analogue, we demonstrate that the temporary protection of the N-acetyl group as a methyl imidate is advantageous to fucosylate at O-4. In contrast, we report here that glucosylation at O-4 of an N-acetylglucosamine monosaccharide acceptor using the α-trichloroacetimidate of peracetylated glucopyranose as a donor proceeded in better yields under activation with excess BF₃·OEt₂ than that of the corresponding methyl imidate. Therefore, we conclude that activation of thioglycoside donors by MeOTf to glycosylate at O-4 of a glucosamine acceptor is best accomplished following the temporary protection of the N-acetyl group as a methyl imidate, especially when the donors are highly reactive and prone to degradation. In contrast, if donor and acceptor can withstand multiple equivalents of BF₃·OEt₂, glycosylations at O-4 of a glucosamine acceptor with a trichloroacetimidate donor does not benefit from the temporary protection of the N-acetyl group as a methyl imidate.     

A proteomic approach to the identification of early molecular targets changed by L-ascorbic acid in NB4 human leukemia cells

The pro-oxidant effect of L-ascorbic acid (LAA) is toxic to leukemia cells. LAA induces the oxidation of glutathione to its oxidized form (GSSG) and this is followed by a concentration-dependent H(2)O(2) accumulation, which occurs in parallel to the induction of apoptosis. To identify early protein targets of LAA in leukemia cells, we used a differential proteomics approach in NB4 human leukemia cells treated with 0.5 mM of LAA for 30 min. This exposure was determined to efficiently block cellular proliferation and to activate oxidative stress-inducible apoptosis. We identified nine proteins that sensitively reacted to LAA treatment by using two-dimensional (2-D) gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight-MS. A subunit of protein-disulfide isomerase (a thiol/disulfide exchange catalyst) and immunoglobulin-heavy-chain binding protein (BiP, identical to Hsp70 chaperone) showed quantitative expression profile differences. A myeloid leukemia associated antigen protein (a tropomyosin isoform) showed changes in pI as a result of phosphorylation. Our studies demonstrate for the first time that the addition of LAA to cells results in an immediate change in the intracellular thiol/disulfide condition and that this includes an increase in the GSH oxidation with changes in the superfamily of thiol/disulfide exchange catalysts. These results suggest that LAA oxidizes intracellular reduced glutathione and modulates disulfide bond formation in proteins.     

Studies on the endogenous L-selectin ligands: systematic and highly efficient total synthetic routes to lactamized-sialyl 6-O-sulfo Lewis X and other novel gangliosides containing lactamized neuraminic acid

Systematic syntheses of lactamized neuraminic acid-containing gangliosides GM4, sulfated sialylparagloboside, and sulfated/nonsulfated sialyl Lewis X are described. The highly efficient, one-step lactamization of neuraminic acid was accomplished by treatment of the N-deacetylated sialic acid (neuraminic acid)-containing gangliosides with HBTU and HOBt in DMF at 65 degrees C. Both the lactamized neuraminic acid residue and the sulfate group at O-6 of the GlcNAc residue were found to be involved in the antigenic determinant defined by G159 monoclonal antibody, while the fucose residue may not be critical for the recognition by G159 mAb.     

Binding of a 2-pyridyl moiety to a B/Sn bidentate Lewis acid

Reaction of the bidentate Lewis acid 1,2-Fc(SnMe₂Cl)(B(Me)Cl) (1, Fc = 1,2-ferrocenylene) with 2-trimethylstannylpyridine gave a complex (2), in which the 2-pyridyl group forms a bridge between the Lewis acidic tin and boron centers. The structure of 2 was confirmed by multinuclear and two-dimensional NMR, single crystal X-ray diffraction, and elemental analysis. The crystal structure shows that the pyridyl moiety is positioned endo relative to the substituted Cp ring and UV-Vis spectroscopy revealed an enhancement of the ferrocene-centered dd transition in comparison to related complexes with pyridine as a terminal ligand.     

A novel Aspergillus oryzae esterase that hydrolyzes 4-hydroxybenzoic acid esters

In this study we report the biochemical characterization of a hypothetical protein from Aspergillus oryzae exhibiting sequence identity with feruloyl esterase and tannase from the genus Aspergillus. The purified recombinant protein showed a hydrolytic activity toward the ethyl, propyl, or butyl esters of 4-hydroxybenzoic acid, but did not show feruloyl esterase or tannase activity. Finally, the enzyme decreased the antimicrobial activity of parabens against A. oryzae via hydrolysis of the ester bond present in butyl 4-hydroxybenzoic acid.     

Salt-assisted acid hydrolysis of chitosan to oligomers under microwave irradiation

The effect of inorganic salts such as sodium chloride on the hydrolysis of chitosan in a microwave field was investigated. While it is known that microwave heating is a convenient way to obtain a wide range of products of different molecular weights only by changing the reaction time and/or the radiation power, the addition of some inorganic salts was shown to effectively accelerate the degradation of chitosan under microwave irradiation. The molecular weight of the degraded chitosan obtained by microwave irradiation was considerably lower than that obtained by traditional heating. Moreover, the molecular weight of degraded chitosan obtained by microwave irradiation assisted under the conditions of added salt was considerably lower than that obtained by microwave irradiation without added salt. Furthermore, the effect of ionic strength of the added salts was not linked with the change of molecular weight. FTIR spectral analyses demonstrated that a significantly shorter time was required to obtain a satisfactory molecular weight by the microwave irradiation-assisted inorganic salt method than by microwave irradiation without inorganic salts and conventional technology.     

New bulky chiral Lewis acid catalyst: 3,3'-di(2-mesitylethynyl)binaphthol-titanium(IV) complex

A new chiral Lewis acid catalyst 9 was prepared in situ from a 1:2 molar mixture of (R)-3,3'-di(2-mesitylethynyl)binaphthol (6) and titanium(IV) isopropoxide at ambient temperature. The 3- and 3'-substituents on 6 were effective for preventing undesired aggregation between Ti(IV) complexes and increasing the enantioselectivity (up to 82% ee) in the Diels-Alder reaction of methacrolein with cyclopentadiene.     

Conformational studies of Lewis X and Lewis A trisaccharides using NMR residual dipolar couplings.

The conformations of the histo-blood group carbohydrate antigens Lewis X (Le(x)) and Lewis A (Le(a)) were studied by NMR measurements of one-bond C-H residual dipolar couplings in partially oriented liquid crystal solutions. A strategy for rapid calculation of the difference between theoretical and experimental dipolar couplings of a large number of model structures generated by computer simulations was developed, resulting in an accurate model structure for the compounds. Monte Carlo simulations were used to generate models for the trisaccharides, and orientations of each model were sought that could reproduce the experimental residual dipolar coupling values. For both, Le(a) and Le(x), single low energy models giving excellent agreement with experiment were found, implying a compact rigidly folded conformation for both trisaccharides. The new approach was also applied to the pentasaccharides lacto-N-fucopentaose 2 (LNF-2) and lacto-N-fucopentaose 3 (LNF-3) proving its consistency and robustness. For describing the conformation of tightly folded oligosaccharides, a definition for characterization of ring planes in pyranoside chairs is proposed and applied to the analysis of the relation between the fucose and galactose residues in the epitopes, revealing the structural similarity between them.     

Role of Lewis A and Lewis B blood group antigens in Helicobacter pylori infection

BACKGROUND AND AIMS: We investigated the prevalence of Helicobacter pylori infection in a large group of women to determine whether there was an association of current infection status with Lewis blood group antigen A and B phenotype. METHODS: Between November 2000 and November 2001, mothers were recruited after delivery of their offspring at the Department of Gynecology and Obstetrics at the University of Ulm, Ulm, Germany. The H. pylori infection status of the women was determined by 13C urea breath test. Their Lewis A and Lewis B phenotype was determined using standard laboratory techniques. RESULTS: In total, 22.2% of the 712 women included in the study (mean age 30.7 years) had a current H. pylori infection. The prevalence of infection varied from 15.5% in women of German nationality to 75.0% in women of Turkish nationality (p < .001). Most women (68.1%) had a Le(a-b+) phenotype. The prevalence of H. pylori infection in women with Le(a-b+) phenotypes was lower than in other women (p = .02). In multivariate analysis, the odds ratio (OR) for a current H. pylori infection given Le(a-b+) was 0.56 [95% confidence interval (CI) 0.33-0.95] compared to women with Le(a-b-). CONCLUSION: Le(a-b+) blood group phenotype in combination with secretor status may hinder colonization of H. pylori in the population studied.     

Vanillic acid, a metabolite of 4-hydroxy-3-methoxyphenylglycol and 4-hydroxy-3-methoxymandelic acid in man

Abstract: 4-Hydroxy-3-methoxyphenylglycol (HMPG) labelled with ¹⁴C was used to study the metabolic fate of HMPG in six healthy volunteers. Besides conjugation and oxidation to 4-hydroxy-3-methoxymandelic acid (HMMA, VMA) a minor portion, 8.4 ± 1.1% (mean ± SEM) was excreted as ¹⁴C-labelled vantllic acid (VA). To study if VA was formed from HMPG or HMMA (VMA), deuterium-labelled HMPG ([²H₃]HMPG) and HMMA ([²H₆]HMMA) were simultaneously injected intravenously to seven healthy volunteers. The recovery of [²H₃]VA from [²H₃]HMPG was 8.3 ± 2.1% and the recovery of [²H₆]VA from [²H₆]HMMA was 9.0 ± 2.1%. The ²H-labelled VAs were probably formed by a decar boxylation reaction, in the case of HMPG after previous oxidation to HMMA.     

Susceptibility of urea and uric acid levels to neurohormone influence in the freshwater pulmonate,lymnaea acuminata

Effects of pooled ganglionic extract on the urea and uric acid levels from blood, hepatopancreas, mantle and kidney of the pulmonate L. acuminata have been analysed. Blood urea and mantle uric acid were significantly (P<0.005 and P<0.05 respectively) increased following injection with pleuroparietalpedal-visceral (PPPV Complex) ganglia homogenate within 2 hrs. On the contrary hepatopancreas urea and kidney uric acid levels were significantly (P<0.00) lowered. Cerebral ganglia homogenate and boiled extract of PPPV complex did not provoke any significant change in urea and uric acid levels. It is advocated that (a) neurohormone(s) which is (are) heat-labile and originate from the PPPV complex, influence(s) the nitrogen end-products in these snails.     

Fatty acid composition,antioxidant and antibacterial properties of the microwave aqueous extract of three varieties of Labisia pumila Benth

Background

The present study was conducted in order to evaluate the fatty acid profile, anti-oxidant and anti-bacterial activities from the microwave aqueous extract of the leaves of three different varieties of Labisia pumila Benth.

Results

The chemical analysis of the extract showed that fatty acids (palmitic, palmitoleic, stearic, oleic, linoleic and α-linolenic) acid as the main components in three varieties of L. pumila leaves. Furthermore, the obtained results of the anti-oxidant revealed that L. pumila var. alata contained higher anti-oxidative activities compared to var. pumila and var. lanceolata. However, these values were lower than the tested anti-oxidant standards. On the other hand, the aqueous leaf extracts in all three varieties of L. pumila were also found to inhibit a variable degree of antibacterial activities against eight bacteria (four Gram-positive and four Gram-negative bacteria).

Conclusions

In this study, it was observed the leaves of three varieties of L. pumila exhibited variable patterns of fatty acids and the microwave aqueous extraction possess anti-oxidant and anti-bacterial activities.