bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory and Experiment in Concert: Templated Synthesis of Amide Rotaxanes, Catenanes, and Knots
Authors: Schalley Christoph A. , Reckien Werner , Peyerimhoff Sigrid , Baytekin Bilge , Vögtle Fritz 
Published: August 2004

AbstractThe synthesis of amide rotaxanes, amide catenanes, and trefoil amide knots is based on template effects mediated by hydrogen bonds. While a large body of experimental data is available, in‐depth theoretical studies of these template syntheses are virtually unavailable, although they would provide a more profound insight into the exact details of the hydrogen‐bonding patterns involved in the formation of these mechanically interlocked species. In this article we present a density functional study of the conformational properties of tetralactam macrocycles and the threading mechanism that produces the immediate precursor for rotaxane and catenane formation. Predictions of the geometries and relative energies made on the basis of semi‐empirical AM1 calculations are compared with these results in order to judge the reliability of the simpler approach. Since these calculations yield good agreement with the structural features, they have been used to extend the calculations in order to understand the mechanism of formation of a trefoil dodecaamide knot that has recently been synthesized. The inherent topological chirality of the knot is reflected in the intermediates generated during its formation; these involve helical loops. These loops parallel the rotaxane and catenane wheels with respect to the arrangement of the functional groups that mediate the template effect and may well serve as wheel analogues through which one of the precursor molecules can be threaded. This threading step finally results in the knotted structure. Good agreement between the results of the calculations presented here and experimental findings is achieved.
Synthesis and Biological Evaluation of a Lipid A Derivative That Contains an Aminogluconate Moiety
Authors: Santhanam Balaji , Wolfert Margreet A. , Moore James N. , Boons Geert‐Jan 
Published: August 2004

AbstractA highly convergent strategy for the synthesis of several derivatives of the lipid A of Rhizobium sin‐1 has been developed. The synthetic derivatives are 2‐aminogluconate 3 and 2‐aminogluconolactone 4, both of which lack C‐3 acylation. These derivatives were obtained by the preparation of disaccharides in which the two amino groups and the C‐3′ hydroxy group could be modified individually with acyl or β‐hydroxy fatty acyl groups. Detailed NMR spectroscopy and MS analysis of 3 and 4 revealed that, even under neutral conditions, the two compounds equilibrate. The synthetic compounds lack the proinflammatory effects of Escherichia coli lipopolysaccharide (LPS), as indicated by an absence of tumor necrosis factor production. Although 3 and 4 were able to antagonize E. coli LPS, they were significantly less potent than the synthetic compound 2, which is acylated at C‐3, and R. sin‐1 LPS; these results indicate that the β‐hydroxy fatty acyl group at C‐3 contributes to the antagonistic properties of R. sin‐1 LPS. Based on a comparison of the biological responses of the synthetic lipid A derivatives with those of the R. sin‐1 LPS and lipid A, the 3‐deoxy‐D‐manno‐octulosonic moieties appear to be important for the optimal antagonization of enteric LPS‐induced cytokine production.
Synthesis and Stereochemical Properties of Chiral Square Complexes of Iron(II)
Authors: Bark Thomas , von Zelewsky Alexander , Rappoport Dmitrij , Neuburger Markus , Schaffner Silvia , Lacour Jérôme , Jodry Jonathan 
Published: August 2004

AbstractThe hexadentate, and ditopic ligand 2,5‐bis([2,2′]bipyridin‐6‐yl)pyrazine yields a chiral, tetrameric, square‐shaped, self‐assembled species upon complexation with Fe2+ ions. The racemate of this complex was resolved with antimonyl tatrate as the chiral auxiliary. The purity of the enantiomer was determined by NMR spectroscopy, by using a chiral, diamagnetic shift reagent, and by circular dichroism (CD). The CD spectrum was also calculated by time‐dependent density functional theory, and the correlation that was found between CD spectrum and configuration was confirmed by X‐ray cristallography. When a “chiralised” version of the ligand was used instead, the corresponding iron complex was obtained in diastereomerically pure form.
Reactions of Hydrated Electrons (H2O)n− with Carbon Dioxide and Molecular Oxygen: Hydration of the CO2− and O2− Ions
Authors: Balaj O. Petru , Siu Chi‐Kit , Balteanu Iulia , Beyer Martin K. , Bondybey Vladimir E. 
Published: August 2004

AbstractThe gas‐phase reactions of hydrated electrons with carbon dioxide and molecular oxygen were studied by Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry. Both CO2 and O2 react efficiently with (H2O)n− because they possess low‐lying empty π* orbitals. The molecular CO2− and O2− anions are concurrently solvated and stabilized by the water ligands to form CO2−(H2O)n and O2−(H2O)n. Core exchange reactions are also observed, in which CO2−(H2O)n is transformed into O2−(H2O)n upon collision with O2. This is in agreement with the prediction based on density functional theory calculations that O2−(H2O)n clusters are thermodynamically favored with respect to CO2−(H2O)n. Electron detachment from the product species is only observed for CO2−(H2O)2, in agreement with the calculated electron affinities and solvation energies.
Phenylmalonate‐Containing Copper(II) Complexes: Synthesis, Crystal Structure and Magnetic Properties
Authors: Pasán Jorge , Sanchiz Joaquín , Ruiz‐Pérez Catalina , Lloret Francesc , Julve Miguel 
Published: August 2004

AbstractThree new copper(II) complexes of formula [Cu(2,2′‐bpy)(Phmal)(H2O)]·2H2O (1), [{Cu(2,2′‐bpym)(Phmal)}]n (2) and [{Cu(phen)(Phmal)}]n·3nH2O (3) (Phmal = phenylmalonate; 2,2′‐bpy = 2,2′‐bipyridine; 2,2′‐bpym = 2,2′‐bipyrimidine; phen = 1,10‐phenanthroline) have been prepared and their structures determined by X‐ray diffraction techniques. Complex 1 is mononuclear whereas 2 and 3 are uniform chain compounds. The copper atoms in 1−3 are distorted square‐pyramidal: two nitrogen atoms from the bidentate nitrogen heterocycle and two carboxylate oxygen atoms from the phenylmalonate ligand build the equatorial plane; the axial position is filled either by a water molecule (1) or a carboxylate oxygen atom from another phenylmalonate group (2 and 3). The values of the intrachain copper−copper separation through the phenylmalonate‐carboxylate bridge in the anti‐syn conformation are 4.6853(7) (2) and 5.014(3) Å (3). The phenyl ring of the Phmal ligand in 1 produces an unusual intramolecular π−π stacking interaction with the CuII−(aromatic 2,2′‐bpy) chelate ring. Intrachain edge‐to‐face phenyl−pyridyl and offset phen−phen‐type interactions occur in 2 and 3, respectively. Magnetic susceptibility measurements of 2 and 3 in the temperature range 1.9−290 K show the occurrence of weak intrachain ferromagnetic interactions between the copper(II) ions through the phenylmalonate‐carboxylate bridge [J = +0.10(1) (2) and +0.31(1) cm−1 (3)]. These values are compared with those reported for malonate‐containing copper(II) complexes with the same exchange pathway through the anti‐syn carboxylate bridge. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Characterization of Alkyllanthanum Biphenolate Complexes as Catalysts for Hydroamination/Cyclization and Hydrosilylation
Authors: Gribkov Denis V. , Hampel Frank , Hultzsch Kai C. 
Published: August 2004

AbstractThe homochiral, dimeric biphenolate alkyllanthanum complex [La{(R)‐Biphen}{CH(SiMe3)2}]2 can be prepared by facile alkane elimination starting from [La{CH(SiMe3)2}3] and enantiopure (R)‐3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethyl‐1,1′‐biphenyl‐2,2′‐diol [H2{(R)‐Biphen}]. Single‐crystal X‐ray diffraction revealed that the two La{(R)‐Biphen}{CH(SiMe3)2} fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. The biphenolate alkyl complex shows high catalytic activity for hydroamination/cyclization of aminoalkenes, similar to previously known lanthanocene catalysts, but only low enantioselectivity. Addition of THF to [La{(R)‐Biphen}{CH(SiMe3)2}]2 leads to a monomeric tris‐THF adduct [La{(R)‐Biphen}{CH(SiMe3)2}(THF)3] with higher catalytic activity than the THF‐free homochiral dimer in the cyclization of 2,2‐dimethylpent‐4‐enylamine, suggesting that the dimeric structure of the catalyst system prevails under catalytic conditions in the absence of THF. Addition of HN(SiHMe2)2 to [La{(R)‐Biphen}{CH(SiMe3)2}(THF)3] results in the formation of [La{(R)‐Biphen}{N(SiHMe2)2}(THF)3] which is in equilibrium with its homochiral dimer [La{(R)‐Biphen}{N(SiHMe2)2}(THF)]2 at elevated temperatures. The biphenolate alkyl complexes exhibit good catalytic activity and diastereoselectivity in the hydrosilylation of styrene. Hydrosilylation of 1‐hexene and norbornene also proceeds with high diastereoselectivity but rather low activity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Enzymatic synthesis of medium‐chain triacylglycerols by alcoholysis and interesterification of copra oil using a crude papain lipase preparation
Authors: Caro Yanis , Turon Fabrice , Villeneuve Pierre , Pina Michel , Graille Jean 
Published: August 2004

AbstractWe have examined the possibility of producing analogs of medium‐chain triglycerides (MCT) from copra oil, i.e. a triacylglycerol mixture with a high content of medium‐chain fatty acid moieties (C6–C10). A two‐step enzymatic process was used in which copra triacylglycerols were first split with papain lipase by alcoholysis with an alkyl alcohol and then subjected to interesterification with the alkyl esters recovered using papain lipase. Effects of temperature, water activity content, substrate ratio, biocatalyst amount, and alcohol chain length were also investigated. On the one hand, the sn‐3 stereoselectivity of the lipase in the alcoholysis of copra oil with butanol has permitted a direct enrichment of caproic, caprylic and capric moieties in the synthesized butyl esters. Thus, in the batch reactor, the reaction led to about 31% conversion of the oil after 24 h, and the content of C6–C10 acids in the synthesized esters increased from about 16% in the starting oil to almost 42%. A similar enzymatic alcoholysis in a packed‐bed column bioreactor gave 31% conversion of the oil after 120 min of reactor residence time. The reaction was also very selective because the C6–C10 fatty acyl groups represented about half of the newly formed butyl esters, whereas they accounted for only 16% of total fatty acids in the starting oil. On the other hand, the transesterification of the alkyl esters recovered (highly enriched in C6–C10 fatty acyl groups) with native copra oil directly led to an increase in the content of MCT in the oil, from 18 mol‐% at the beginning of the reaction to 61 mol‐% of MCT after a time period of 72 h in the batch reactor.
Temperature and concentration dependent effect of partial glycerides on milk fat crystallization
Authors: Foubert Imogen , Vanhoutte Bert , Dewettinck Koen 
Published: August 2004

AbstractTwo diglycerides (distearin and diolein) and two monoglycerides (monostearin and monoolein) were added to milk fat in a concentration of 0.5% and 1%. The isothermal crystallization behavior was evaluated at 22 °C, 23.5 °C, 25 °C and 26.5 °C by DSC and pNMR. The crystallization kinetic was quantified by means of two models. It was noticed that the effect of the minor components on the crystallization behavior depends on temperature and concentration. The type of esterified fatty acids and the polar head of the amphiphilic molecule determine to what extent partial glycerides influence the nucleation and crystal growth of triglycerides. Moreover the degree of insolubility of partial glycerides in the melt determines which effect (on growth or on nucleation) predominates. Stearic acid based partial glycerides enhance nucleation at low temperatures, while at higher temperatures an interaction with the crystal growth predominates. Oleic acid based partial glycerides have an effect on the nucleation process while no interaction with the crystal growth was observed.
Progress in the analysis of Stratum corneum ceramides
Authors: Raith Klaus , Farwanah Hany , Wartewig Siegfried , Neubert Reinhard H. H. 
Published: August 2004

AbstractThe stratum corneum with its unique structure of corneocytes and intercellular lipid lamellae enables a protection of human and other mammalian skin against transepidermal water loss and harmful substances from the environment. Among these lipids, ceramides play a key role. Several skin disorders such as psoriasis, atopic dermatitis and others show a disturbed barrier function, which can be linked in part to a changed ceramide pattern. Research in dermatology and cosmetic industry requires the use of analytical methods to characterize ceramides. However, the amazing variability of ceramide structures found in stratum corneum makes their analysis a challenge. This is to our knowledge the first review that deals with ceramide analysis. It is focused on stratum corneum ceramides which show much more complexity than intracellular ceramides known to be signal transducers. After a short summary of lipid extraction methods, we discuss the following set of methods: thin‐layer chromatography, gas chromatography, HPLC, LC/MS, mass spectrometry, NMR spectroscopy, vibrational spectroscopy, and X‐ray diffraction. It will be lined out which information about structure, concentration or physical state is available by means of each particular method. Although the focus is clearly on stratum corneum ceramides, some methods of general skin lipid analysis and structure analysis of sphingolipids are also discussed when appropriate.
Synthesis of fatty acid esters from acid oils using lipase B from Candida antarctica
Authors: Tüter Melek , Aksoy H. Ayşe , Gılbaz E. Elif , Kurşun Emel 
Published: August 2004

AbstractEsterification of corn and sunflower acid oils with straight‐ and branched‐chain alcohols were conducted using lipase B from Candida antarctica (Novozym 435) in n‐hexane. Sunflower acid oil consisted of 55.6% free fatty acids and 24.7% triacylglycerols, while the free fatty acids and triacylglycerols contents of corn acid oil were 75.3% and 8.6%, respectively. After 1.5 h of methanolysis of sunflower acid oil, the highest fatty acid methyl ester content (63.6%) was obtained at 40 °C and the total fatty acid/methanol molar ratio was 1/1, using 15% enzyme based on acid oil weight. The conversion of both acid oils with straight‐ and branched‐chain alcohols was not significantly affected by the chain length of the alcohols. However, the lowest fatty acid methyl ester content (50%) was obtained in the reaction of corn acid oil with methanol. Sunflower acid oil was converted to fatty acid esters using primer alcohols such as n‐propanol, i‐ and n‐butanol, n‐amylalcohols, n‐octanol, and a mixture of amylalcohol isomers, resulting in a fatty acid ester content of about 70% at 40 °C.
C‐Phosphorylated N‐(Trichloroethylidene)sulfonamides: A New Type of Highly Electrophilic Imines
Authors: Rassukana Yuliya V. , Onys’ko Petro P. , Davydova Kateryna O. , Sinitsa Anatolii D. 
Published: August 2004

AbstractA convenient preparative approach to previously unknown, highly electrophilic C‐phosphorylated N‐arylsulfonylimines 1, based on fairly readily accessible α‐phosphorylated sulfonamides 5, has been developed. Compounds 1 react with trialkyl phosphites or ethyl diphenylphosphinite in the aza‐Perkow reaction scheme to give C,N‐diphosphorylated N‐dichlorovinylsulfonamides 8. On treatment with O‐ and S‐nucleophilic agents (alcohols, thiols, thiophenols), 1 forms addition products 12 and 15, the functionalized derivatives of α‐aminophosphonic acids, while interaction between 1 and mercaptoacetic acid proceeds with intramolecular cyclization of the intermediate adduct to produce the novel 2‐phosphorylated thiazolidinones 17. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Radical Polymerization of Various 2‐Cyclopropylacrylates
Authors: Meijere Armin de , Bagutski Viktor , Zeuner Frank , Fischer Urs Karl , Rheinberger Volker , Moszner Norbert 
Published: August 2004

AbstractFourteen new alkyl 2‐cyclopropylacrylates 1a−n with various substituents R1−R5 were synthesized from readily available precursors by applying standard transformations such as cyanohydrin formation from an aldehyde, alcoholysis to an α‐hydroxycarboxylic ester, oxidation and Wittig methylenation of an α‐oxocarboxylic ester. Overall yields ranged from 33 to 54%. A new method for the hydrolysis of dimethyl cyclopropanedicarboxylates to the corresponding half‐esters was developed. The α‐oxocarboxylates 7g−n were prepared by dirhodium tetraacetate catalyzed cyclopropanation of alkenes 8g−n with methyl or ethyl diazopyruvate in 32−58% yield. The monomers 1a−n were characterized by 1H, 13C NMR spectroscopy, mass spectrometry and elemental analysis. The radical homopolymerizations of 1a−n were carried out with 2,2′‐azabisisobutyronitrile (AIBN) as initiator in chlorobenzene at 65 °C. The highest polymer yields were obtained in the polymerizations of 1f and 1h or 1k and 1l, i.e. from monomers with an annelated five‐ or six‐membered ring. In the case of 1h and 1k, both the polymer yields (99 and 98%, respectively) and the glass transition temperatures (Tg) of 57 and 93 °C were significantly higher than those observed for the polymer from 1,1‐bis(ethoxycarbonyl)‐2‐vinylcyclopropane (DECVCP), which was used as a benchmark for the monomer reactivities in the radical polymerizations of all the vinylcyclopropane derivatives 1a−n. The bicyclic monomers 1h and 1k also demonstrated drastically improved reactivities in the radical copolymerization with methyl methacrylate when compared to DECVCP. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
A Straightforward Synthesis of 1‐Adamantylmethyl Glycosides, and Their Binding to Cyclodextrins
Authors: Charbonnier Florence , Penadés Soledad 
Published: August 2004

AbstractA single‐step synthesis of 1‐adamantylmethyl α‐ and β‐glycosides starting from commercially available peracetylated monosaccharides is reported. The α‐ and β‐glucopyranosides 1a and 1b bind to β‐cyclodextrin with association constants in the order of 105 M−1, as determined by 1H NMR spectroscopy. The carbohydrate moiety contributes to the binding depending on the pyranose stereochemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Development of a Continuous‐Flow System for Catalysis with Palladium(0) Particles
Authors: Solodenko Wladimir , Wen Hongliang , Leue Stefanie , Stuhlmann Friedrich , Sourkouni‐Argirusi Georgia , Jas Gerhard , Schönfeld Hagen , Kunz Ulrich , Kirschning Andreas 
Published: August 2004

AbstractHeterogeneous catalysis for organic synthesis under continuous‐flow conditions becomes possible by a new reactor‐based approach. Continuous‐flow reactors with a monolithic glass/polymer composite interior are loaded with palladium particles by ion exchange followed by reduction. When incorporated into a continuous‐flow setup (PASSflow) this reactor allows the transfer‐hydrogenation of alkenes, alkynes, nitro‐substituted aromatic compounds and benzyl ethers in the flow‐through mode. In addition, the activity of the catalysts is well suited to achieve Suzuki, Sonogashira and Heck cross‐coupling reactions in the absence of phosphanes or any other ligands, resulting in a greatly simplified purification. As an extension to this concept a bifunctional support was prepared inside the reactor consisting of Pd particles and an ion‐exchange group (hydroxide form). In the Suzuki− Miyaura reaction the reactor serves as a base for immobilisation and activation of the boronic acid as boronate and as a catalyst for promoting the C−C coupling reaction under continuous‐flow conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Palladium‐Catalysed Amination of Electron‐Deficient or Relatively Electron‐Rich Benzo[b]thienyl Bromides − Preliminary Studies of Antimicrobial Activity and SARs
Authors: Queiroz Maria‐João R. P. , Begouin Agathe , Ferreira Isabel C. F. R. , Kirsch Gilbert , Calhelha Ricardo C. , Barbosa Sandra , Estevinho Letícia M. 
Published: August 2004

AbstractSeveral diarylamines in the benzo[b]thiophene series were prepared in good to high yields by palladium‐catalysed amination of ethyl 3‐bromobenzo[b]thiophene‐2‐carboxylate with anilines and 5‐aminoindole in the presence of Pd(OAc)2, BINAP and Cs2CO3 in toluene. The presence of the ester group at the 2‐position of the benzo[b]thiophene moiety increases the yields and lowers the heating times relative to the reactions performed with 3‐bromobenzo[b]thiophene. When aminopyridines were used instead of anilines, the ligand and the solvent need to be changed to XANTHPHOS and dioxane in the amination reaction. With 2‐aminopyridine a one‐pot C−N coupling and intramolecular cyclization involving the nitrogen atom of the pyridine ring occurred, with loss of ethanol, giving an interesting fluorescent tetracyclic heteroaromatic compound. The antimicrobial activity, the minimal inhibitory concentrations (MICs) and the structure‐activity relationships (SARs) were evaluated. A selectivity with low MICs was observed against Bacillus Cereus, and good results were also obtained against Candida albicans. The acids obtained by hydrolysis of the ester group, as non‐proteinogenic α,β‐unsaturated β‐amino acids, can be incorporated into peptide chains to induce conformational constraints. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Amino Carba Sugars and Conformationally Restricted Polyhydroxy γ‐Amino Acids from (−)‐Quinic Acid
Authors: Carballido Montserrat , Castedo Luis , González‐Bello Concepción 
Published: August 2004

AbstractEfficient syntheses of two novel positional stereoisomers of valiolamine, a potent glycosidase inhibitor, and two polyhydroxy γ‐amino acids are reported. The syntheses involve regio‐ and stereoselective azidolysis of epoxides by trimethylsilyl azide with BF3·OEt2 as Lewis acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Radioiodination of Some 9‐Aminoacridine Derivatives
Authors: Ghirmai Senait , Mume Eskender , Henssen Cecile , Ghaneolhusseini Hadi , Lundqvist Hans , Tolmachev Vladimir , Sjöberg Stefan , Orlova Anna 
Published: August 2004

AbstractDerivatives of 9‐aminoacridine, namely N‐[ψ‐(acridin‐9‐ylamino)alkyl]‐3‐(trimethylstannyl)benzamides (1), where the alkyl group is propyl (1a) and octyl (1b), and 2‐(acridin‐9‐ylamino)‐3‐(4‐hydroxyphenyl)propionic acid (2), have been synthesized with the aim to use them as precursors in the syntheses of radiolabeled DNA intercalators for biological experiments. It was observed that compounds 1a and 1b can exist in two isomeric forms at room temperature. Radioiodination of the two benzamides 1a and 1b was carried out with the Auger‐emitting nuclide 125I by exchange of the trimethylstannyl group. The optimal conditions for radioiodination of the octyl derivative 1b were established and the labeling yield was found to be as high as 92%, according to TLC analysis in model experiments. Purification of the radioiodinated products gave radiochemical yields of 56% for the propyl and 74% for the octyl compound. The amino acid 2 was directly labeled with 125I at the ortho position to the hydroxyl group by taking advantage of the activated ring. The experiment afforded a very high labeling yield (92%). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)