bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparability and reliability of different techniques for the determination of phenolic compounds in virgin olive oil
Authors: Hrncirik Karel , Fritsche Sonja 
Published: August 2004

AbstractPhenolic compounds represent a unique and functional part of the polar fraction of virgin olive oils. Many different approaches for the analysis of these compounds have been published, which has led to ambiguous results that are difficult to compare. In order to explain the controversial data reported in the literature, extraction techniques (solid‐phase extraction, SPE, and liquid‐liquid extraction, LLE), methods of analysis (HPLC and colorimetric assay) and quantification methods have been re‐investigated with genuine olive oil phenols. The optimized LLE system led to high recovery of the nine major olive oil phenolics (93%) and, in addition, was at least as good as the SPE technique in view of costs, solvent and sample consumption, and analysis time. SPE was shown to be problematic because of the selectivity towards the individual phenolics, particularly the aglycone‐type ones. The proposed LLE/HPLC method was compared with the traditional colorimetric assay (Folin‐Ciocalteu method) by analyzing 23 samples of virgin olive oils. A strong correlation between both methods has been found, suggesting that the colorimetric assay is reasonably valid for a rough prediction of the total phenolic content. In the literature, the level of phenolics is expressed in several different units (reference compound equivalents in case of colorimetric measurements and ppm in HPLC measurements). As these units can differ in orders of magnitude, it is necessary to convert the data to a common base before comparing or combining them.
Analysis of genetic effects and heritabilities for linoleic and α‐linolenic acid content of Brassica napus L. across Chinese environments
Authors: Zhang Haizhen , Shi Chunhai , Wu Jianguo , Ren Yuling , Li Changtao , Zhang Dongqing , Zhang Yaofeng 
Published: August 2004

AbstractA genetic model for quantitative traits of seed in diploid plant was applied to analyze the main genetic effects and genotype × environment (GE) interaction effects for linoleic and α‐linolenic acid content of rapeseed (Brassica napus L.) by using two year experimental data with 8 parents and their F1 and F2. Results indicated that the performance of linoleic (C18:2) and α‐linolenic acid content (C18:3) of rapeseed were simultaneously controlled by diploid embryo nuclear genes, cytoplasmic genes and diploid maternal plant nuclear genes, and the GE interaction effects for these two seed quality traits were more important than the genetic main effects. The total narrow‐sense heritability was 69.5% and 41.8% for C18:2 and C18:3, respectively, and the GE interaction heritabilities were found to be larger than the general heritabilities for both quality traits. It was suggested by the predicted genetic effects that Huashuang 3 was better than other parents for improving offspring of C18:2 and Youcai 601, Zhongyou 821, Eyouchangjia and Zhong R‐888 for decreasing C18:3.
Degradation of the oxirane ring of epoxidized vegetable oils with solvated acetic acid using cation‐exchange resins
Authors: Campanella Alejandrina , Baltanás Miguel A. 
Published: August 2004

AbstractVegetable oil epoxides (oxiranes) are customarily manufactured using acetic acid (AA) as oxygen carrier and reactant source, in aqueous/organic media. Further attack of the oxirane ring by AA proceeds in this acid‐catalyzed process, lowering yield. We report a study of the degradation of the ring by water‐solvated AA, using Amberlite IR‐120 as heterogeneous catalyst. The ring opening with solvated AA was found to be first order with respect to the concentration of epoxide groups and second order with respect to the carboxylic acid, with an activation energy of 58.7 ± 0.42 kJ mol−1. This value is within the range found in liquid‐liquid systems (51.3–66.3 kJ mol−1). Yet, using IR‐120, the degradation increases identically either by adding more mass of catalyst or by reducing its particle diameter while keeping the total mass constant, as both situations lead to higher external (exposed) area of the acidic catalyst (i.e., free protons associated to the sulfonic group) on the outer surface of the ion exchange resin beads. These free protons, in turn, become available to catalyze the attack on the oxirane groups of the long‐chain fatty acids, which cannot enter (diffuse) into the gel phase of the resin. Despite the unavoidable presence of surface‐exposed protons, the degradation can be reduced by several orders of magnitude – for similar process conditions – by using this type of heterogeneous catalysts instead of mineral acids.
The prediction of fatty acid structure from selected ions in electron impact mass spectra of fatty acid methyl esters
Authors: Mjøs Svein A. 
Published: August 2004

AbstractThe possibility of fatty acid identification from ions in the mass region of 50–110 amu in electron impact mass spectra has been studied by application of various multivariate techniques. The focus has mainly been on the prediction of the number of double bonds in methylene‐interrupted polyunsaturated fatty acids isolated from marine lipids.The number of double bonds in these fatty acids could be predicted with high accuracy, both by partial least squares regression on all ions in this region, and by multiple linear regressions on selected subsets of 5–6 ions. The subsets with optimal predictive power have been found, and the ability to distinguish between methylene interrupted polyunsaturated fatty acids and other fatty acids have also been evaluated.
Syntheses of 3‐C‐Methylceramides
Authors: Sawatzki Peter , Kolter Thomas 
Published: August 2004

AbstractWe report on the synthesis of a series of 3‐C‐methylceramide derivatives 2a,b, 12a,b, 13a,b, and 14a,b. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Electron‐Transfer‐Initiated Cascade Cyclizations of Terpenoid Polyalkenes in a Low‐Polarity Solvent: One‐Step Synthesis of Mono‐ and Polycylic Terpenoids with Various Functionalities
Authors: Ozser Mustafa E. , Icil Huriye , Makhynya Yevgeny , Demuth Martin 
Published: August 2004

AbstractA methodology for the one‐step synthesis of cyclic polyalkene terpenoids in a low‐polarity solvent (dichloromethane) by photoinduced electron transfer (PET) is described. For the efficiency of such processes in low‐polarity solvents, the use of the cationic electron acceptor N‐methylquinolinium hexafluorophosphate is vital. The first direct cyclizations of farnesol and geranylgeraniol to the corresponding all‐trans‐fused 6,6‐ and 6,6,6‐cyclic products are also reported. The mechanism of the termination of the cyclizations is also discussed, isotope‐labeling experiments having shown that it proceeds through reduction of the final radical to the corresponding anion, followed by protonation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
C−C Bond Formation at Ozonide Rings by Substitution of Chlorinated Ozonides
Authors: Griesbaum Karl , Quinkert Ralf‐Olaf , McCullough Kevin J. 
Published: August 2004

AbstractThe TiCl4‐mediated substitution of 3‐chloro‐3,5‐bis(chloromethyl)‐5‐methyl‐1,2,4‐trioxolane (1) with 1‐(trimethylsilyloxy)cyclopentene (4), 2‐methyl‐1‐(trimethylsilyloxy)propene (6) and allyltrimethylsilane (12) gave the corresponding 2‐oxocyclopentyl‐, 1,1‐dimethyl‐2‐oxo‐ethyl‐ and allyl‐substituted ozonides 5, 7 and 13, respectively. Substitution of 3,5‐dichloro‐3,5‐bis(chloromethyl)‐1,2,4‐trioxolane (2) with allyltrimethylsilane (12) gave the diallyl‐substituted ozonide 14. Ozonolysis of the allyl‐substituted ozonide 13 provided the corresponding diozonide 17, and ozonolysis of the diallyl‐substituted ozonide 14 provided the corresponding diozonide 18 and triozonide 19. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Brominated 4‐(Trifluoromethyl)pyrimidines: A Convenient Access to Versatile Intermediates
Authors: Ondi Levente , Lefebvre Olivier , Schlosser Manfred 
Published: August 2004

AbstractAn expedient route to all three monobrominated and all three dibrominated isomers of 4‐(trifluoromethyl)pyrimidine, and to several other halogenated pyrimidines, is described. Key steps are the electrophilic introduction of the halogen in the 5‐position of 2‐ or 4‐pyrimidinones, the bromodeoxygenation of pyrimidinones or thiopyrimidinones using phosphorus tribromide, and the partial debromination of dibromo‐4‐(trifluoromethyl)pyrimidines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Convenient, Benign and Scalable Synthesis of 2‐ and 4‐Substituted Benzylpiperidines
Authors: Ágai Béla , Proszenyák Ágnes , Tárkányi Gábor , Vida László , Faigl Ferenc 
Published: August 2004

AbstractA short, scalable and environmentally benign synthesis of 2‐ and 4‐substituted benzylpiperidines has been developed. The method is based on the temperature‐programmed consecutive deoxygenation and heteroaromatic ring saturation of aryl(pyridin‐2‐yl)‐ and aryl(pyridin‐4‐yl)methanols and aryl(pyridin‐4‐yl)methanones in the presence of Pd/C catalyst. The crucial roles of the temperature, the acidity and the substrate structure in the change of selectivity have been demonstrated by isolation of several substituted aryl(piperidine)methanols. The carbinols and ketones were prepared from commercially available pyridinecarbaldehydes or 4‐cyanopyridine and substituted bromobenzenes via organometallic intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Towards a Total Synthesis of Quinocarcin: Diastereoselective Synthesis of Functionalized Azepino[1,2‐b]isoquinolines
Authors: Koepler Oliver , Laschat Sabine , Baro Angelika , Fischer Peter , Miehlich Burkhard , Hotfilder Marc , le Viseur Christoph 
Published: August 2004

Abstract1,3‐Disubstituted tetrahydro‐oxazolo‐isoquinolinones 19a,b were obtained from phenylalanine in seven steps and 42% overall yield by Katritzky’s benzotriazole method. The tricyclic oxazolidinone 19a was further converted into amino alcohol 10 by employing a chemoselective reduction of the ester group with LiBH4/MeOH. Compound 10 and the corresponding 1‐unsubstituted tetrahydroisoquinoline alcohol 11 were converted into aldehydes 27 and 33, which cyclized in the presence of different Lewis acids to give the substituted azepino[1,2‐b]isoquinolines 34 and 35, respectively, which are key structural features of the alkaloid quinocarcin. The stereoselectivities of the Lewis‐acid‐catalyzed hetero‐ene reaction are highly dependent on the substitution pattern and the type of Lewis acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
N‐Tetrachlorophthaloyl (TCP) Protection for Solid‐Phase Peptide Synthesis
Authors: Cros Esther , Planas Marta , Barany George , Bardají Eduard 
Published: August 2004

AbstractThe N‐tetrachlorophthaloyl‐(TCP‐)amino protecting group has been evaluated for use in solid‐phase peptide synthesis. The TCP group was unaffected by exposure to either piperidine or N,N‐diisopropylethylamine (DIEA), which suggests compatibility with both Fmoc and Boc solid‐phase synthesis protocols. Quantitative TCP removal was achieved by treatment with hydrazine/DMF (3:17) at 35 °C for 30 min or with ethylenediamine/DMF (1:200) at 50 °C for 30 min. Several C‐terminal peptide amides were synthesized successfully by following protocols that use hydrazine/DMF (3:17) at 40 °C for 1 h for repetitive deprotection. Treatment of TCP‐amines with methylamine or with diamines did not give the corresponding amines (deprotected), but rather the appropriate N,N′‐disubstituted tetrachlorophthalamides, which corresponds to a single ring‐opening step. This observation was harnessed to prepare linear and macrocyclic peptide−arene hybrids based on the mild reaction of the parent TCP compound with 1,3‐diaminopropane/DMF (1:49) at 25 °C for 5 min. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Application of Furan as a Diene: Preparation of Condensed 1,3‐Oxazines by Retro‐Diels−Alder Reactions
Authors: Stájer Géza , Miklós Ferenc , Kanizsai Iván , Csende Ferenc , Sillanpää Reijo , Sohár Pál 
Published: August 2004

Abstract(Di‐exo‐3‐amino‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐yl)methanol (3) was treated with oxo carboxylic acids [p‐toluoylpropionic acid, cis‐ or trans‐(p‐toluoyl)cyclohexanecarboxylic acid, ‐benzoic acid or methanobenzocyclooctenecarboxylic acid] to furnish the oxanorbornene‐fused pyrrolo[1,3]oxazine 4, the isoindolo[1,3]oxazines 5 and 6, and the methanobenzocyclooctenepyrrolo[1,3]oxazine 10, together with the retro‐Diels−Alder products pyrrolooxazinone 7, oxazinoisoindolones 8 and 9, and oxazinopyrrolobenzocyclooctene 11. On reflux in chlorobenzene, furan was released from the oxanorbornene heterocycles 5 and 10 to give the retro‐Diels−Alder products. The structures of the new compounds were established by NMR spectroscopy and also (for 6 and 9) by single‐crystal X‐ray structure determination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Lithium Bromide, an Inexpensive and Efficient Catalyst for Opening of Epoxide Rings by Amines at Room Temperature under Solvent‐Free Condition
Authors: Chakraborti Asit K. , Rudrawar Santosh , Kondaskar Atul 
Published: August 2004

AbstractLithium bromide has been found to be an inexpensive and efficient catalyst for the opening of epoxide rings by amines, and this provides an environmentally friendly method for the synthesis of β‐amino alcohols. Aromatic and aliphatic amines react with cycloalkene oxides to exclusively form trans‐2‐(aryl/alkylamino)cycloalkanols in high yields. A 98−100% selectivity in favour of nucleophilic attack at the benzylic carbon atom of styrene oxide is observed with aromatic amines. However, aliphatic amines exhibit a marginal preference for the reaction at the terminal carbon atom of the epoxide ring in styrene oxide. Non‐styrenoidal, unsymmetrical alkene oxides undergo selective nucleophilic attack at the sterically less hindered carbon atom by aniline. The chelation effect of the Li+ ion enables selective opening of the epoxide ring in 3‐phenoxypropylene oxide in the presence of styrene oxide. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Enantiomeric separation of neutral hydrophobic dihydrofuroflavones by cyclodextrin‐modified micellar capillary electrophoresis
Authors: Lantz Andrew W. , Rozhkov Roman V. , Larock Richard C. , Armstrong Daniel W. 
Published: August 2004

AbstractThe enantiomeric separations of several very hydrophobic dihydrofuroflavones were performed and optimized using cyclodextrin‐modified micellar capillary electrophoresis. Overall, the greatest enantiomeric peak‐to‐peak separations for the greatest number of flavones were obtained with hydroxypropyl‐γ‐cyclodextrin. The effects of cyclodextrin and sodium dodecyl sulfate concentration and pH were examined in order to optimize the separation conditions. The ratio of surfactant‐to‐cyclodextrin concentration affected the chiral discrimination of the system significantly, with increases in the derivatized cyclodextrin concentration generally enhancing resolution. Higher efficiencies were obtained with lower concentrations of surfactant and cyclodextrin, although enantioseparation optimization often required higher concentrations to be used. A highly acidic pH was necessary to effectively suppress the electroosmotic flow when operating in the reversed polarity mode. Experiments utilizing the normal polarity mode and higher pH produced no separations.
Enantioselectivity of structurally modified poly(sodium undecenoyl‐L‐leucinate) by insertionof Triton X‐102 surfactant molecules
Authors: Tarus Jepkoech , Jernigan Thomasas , Morris Kevin , Warner Isiah M. 
Published: August 2004

AbstractThe effectiveness of Triton X‐102 (TX‐102), as a structural modifier of the polymeric surfactant sodium undecanoyl‐L‐leucinate (L‐SUL) was investigated for enhanced enantiomeric recognition of various chiral compounds in micellar electrokinetic chromatography (MEKC). Increasing concentrations of TX‐102 were separately added into the micellar solutions of L‐SUL and then polymerized to form poly‐L‐SUL. The resulting polymers were purified by use of 3500 molecular‐weight‐cutoff (MWCO) dialysis membranes. Fluorescence and pulsed field gradient‐nuclear magnetic resonance (PFG‐NMR) techniques were used to elucidate the structural effects of TX‐102 on poly‐L‐SUL. Evaluation of data from fluorescence measurements suggested an increase in polarity with increasing concentration of TX‐102. However, the polarity decreased at higher concentrations of TX‐102. Evaluation of data from PFG‐NMR suggested an increase in hydrodynamic radius upon increasing the concentration of TX‐102. The racemates of coumarinic and phenythiohydantoin amino acid derivatives, and pindolol were used as test analytes in MEKC. A notable increase in resolution and capacity factors of the test analytes was observed when the modified poly‐L‐SUL was used in MEKC measurements. Examination of the data obtained from fluorescence, PFG‐NMR, and MEKC suggests a strong correlation between the polarity and the hydrodynamic radii of TX‐102 modified micelles and the enantiomeric resolution of the test analytes.
Single‐isomer sulfated α‐cyclodextrins for capillary electrophoresis: Hexakis(2,3‐di‐O‐methyl‐6‐O‐sulfo)‐α‐cyclodextrin, synthesis, analytical characterization, and initial screening tests
Authors: Li Shulan , Vigh Gyula 
Published: August 2004

AbstractThe third, concluding member of the family of single‐isomer, fully sulfated α‐cyclodextrins, the sodium salt of hexakis(2,3‐di‐O‐methyl‐6‐O‐sulfo)‐α‐cyclodextrin (HxDMS), has been synthesized on the kilogram scale, completing the nine‐member array of the single‐isomer, 6‐O‐sulfo CDs now available. HxDMS was tested for the capillary electrophoretic (CE) resolution of the enantiomers of nonelectrolyte, weak acid and weak base analytes contained in our CD screening kit. HxDMS complexed differently with many of the analytes tested than either its larger‐ring analogs, heptakis(2,3‐di‐O‐methyl‐6‐O‐sulfo)‐β‐CD (HDMS) and octakis(2,3‐di‐O‐methyl‐6‐O‐sulfo)‐γ‐CD (ODMS) or its same‐ring, but differently substituted analogs, hexakis(6‐O‐sulfo)‐α‐CD (HxS) and hexakis(2,3‐di‐O‐acetyl‐6‐O‐sulfo)‐α‐CD (HxDAS). For all analytes, the effective mobilities and separation selectivities as a function of the background electrolyte concentration of HxDMS followed the trends that were found for the other single‐isomer, 6‐O‐sulfo CDs.
Chiral separation of N‐imidazole derivatives, aromatase inhibitors, by cyclodextrin‐capillary zone electrophoresis. Mechanism of enantioselective recognition
Authors: Foulon Catherine , Danel Cécile , Vaccher Marie‐Pierre , Bonte Jean‐Paul , Vaccher Claude , Goossens Jean‐François 
Published: August 2004

AbstractBaseline separation of ten new, substituted [1‐(imidazo‐1‐yl)‐1‐phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives with one chiral center was achieved using cyclodextrin‐capillary zone electrophoresis (CD‐CZE). A method for the enantiomeric resolution of these compounds was developed using neutral CDs (native α‐, β‐, γ‐CDs or α‐, β‐, γ‐hydroxypropyl (HP)‐CDs) as chiral selectors. Operational parameters including the nature and concentration of the chiral selectors, pH, ionic strength, organic modifiers, temperature, and applied voltage were investigated. The use of neutral CDs provides enantiomeric resolution by inclusion of compounds in the CD cavity. The HP‐α‐CD and HP‐β‐CD were found to be the most effective complexing agents and allowed efficient enantiomeric resolutions. Optimal separation of N‐imidazole derivatives was obtained using 50 mM phosphate buffer at pH 2.5 containing either HP‐α‐CD or HP‐β‐CD (7.5–12.5 mM) at 25°C, with an applied field of 0.50 kV·cm−1 giving resolution factors Rs superior to 1.70 with migration times of the second enantiomer less than 13 min. The same enantiomer migration order observed for all molecules can be related to a close interaction mechanism with CDs. The influence of structural features of the solutes on Rs and tm was studied. The lipophilic character (log kw) of the solutes and the apparent and averaged association constants of inclusion complexes for four compounds with the six different CDs led us to rationalize the enantioseparation mechanisms. The conclusions were corroborated with reversed‐phase high‐performance liquid chromatography (HPLC) on chiral stationary phases (CSPs) based on CDs.
Determination of the chiral and achiral related substances of methotrexate by cyclodextrin‐modified micellar electrokinetic chromatography
Authors: Gotti Roberto , El‐Hady Deia Abd , Andrisano Vincenza , Bertucci Carlo , El‐Maali Nagwa Abo , Cavrini Vanni 
Published: August 2004

AbstractA cyclodextrin‐modified micellar electrokinetic chromatographic (CD‐MEKC) method for the determination of the most important potential impurities of methotrexate (MTX): 2,4‐diamino‐6‐(hydroxymethyl)pteridine, aminopterine hydrate, 4‐[N‐(2‐amino‐4‐hydroxy‐6‐pteridinylmethyl)‐N‐methylamino] benzoic acid, 4‐[N‐(2,4‐diamino‐6‐pteridinylmethyl)‐N‐methylamino] benzoic acid, and the distomer D‐MTX is presented. The MEKC separation of these compounds was optimized by applying a step‐by‐step approach. The addition of β‐CD to a conventional MEKC system, based on sodium dodecyl sulfate (SDS) as surfactant, showed to be essential for the enantioresolution of racemic MTX as well as for the separation of the achiral impurities. To achieve high‐resolution factor between the peaks adjacent to the main component (L‐MTX), as required in the analysis of related impurities, the separation conditions were stressed; in particular, the addition of methanol to the CD‐MEKC system resulted in a very effective choice. Under the optimized final conditions (100 mM SDS and 45 mM β‐CD in a mixture of 50 mM borate buffer, pH 9.30‐methanol (75:25 v/v)), the method was validated showing a general adequate accuracy (93–106% recovery) in the determination of L‐MTX related substances at the impurity level of 0.12% w/w with a relative standard deviation (RSD)% lower than 8% (n = 4). The method was successfully applied to the analysis of pharmaceuticals (tablets and injections) which showed to contain the distomer D‐MTX as major impurity and aminopterine hydrate as a further related substance in the commercial tablets.
Enantioseparations by capillary electro‐chromatography: Differences exhibited by normal‐ and reversed‐phase versions of polysaccharide stationary phases
Authors: Mangelings Debby , Maftouh Mohamed , Massart D. Luc , Vander Heyden Yvan 
Published: August 2004

AbstractThe influence of using normal‐phase and reversed‐phase versions of four commercial polysaccharide stationary phases on chiral separations was investigated with capillary electrochromatography (CEC). Both versions of the stationary phases, Chiralcel OD, OJ, and Chiralpak AD, AS were tested for the separation of two basic, two acidic, a bifunctional, and a neutral compound. Different background electrolytes were used, two at low pH for the acid, bifunctional and neutral substances, and three at high pH for the basic, bifunctional and neutral ones. This setup allowed evaluating differences between both stationary‐phase versions and between mobile‐phase compositions on a chiral separation. Duplicate CEC columns of each stationary phase were in‐house prepared and tested, giving information about the intercolumn reproducibility. In general, reversed‐phase versions of the current commercial polysaccharide stationary phases are found to be best for reversed‐phase CEC, even though at high pH no significant differences were seen between both versions. Most differences were observed at low pH. For acidic compounds, it was seen that an ammonium formate electrolyte performed best, which is also an excellent electrolyte if coupling with mass spectrometry is desired. For basic, bifunctional and neutral compounds, no significant differences between the three tested electrolytes were observed at high pH. Here, a phosphate buffer is preferred as electrolyte because of its buffering capacities. However, if coupling to mass spectrometry is wanted, the more volatile ammonium bicarbonate electrolyte can be used as an alternative.