bluuebunny/crossref_metadata_2025_split huggingface dataset:
Über die Reaktion von tertiären Vinylcarbinolen mit Vinyläthern Eine neue Methode Zur Herstellung von γ,δ‐ungesättigten Aldehyden
Authors: Marbet R. , Saucy G. 
Published: December 2004

AbstractA novel acid catalysed reaction of vinyl ethers with tertiary vinyl carbinols giving γ, δ‐unsaturated aliphatic and alicyclic aldehydes in high yields is described. This new procedure for the utilization of the Claisen rearrangement reaction provides a convenient and efficient route to such aldehydes.
Komplexone XL. Die Protonierungskonstanten einiger Komplexone in verschiedenen wässerigen Salzmedien (NaClO4, (CH3)4NCl, KNO3)
Authors: Anderegg G. 
Published: December 2004

AbstractThe protonation constants of the anions of thirteen polyaminocarboxylic acids have been determined in solutions containing different inert salts: KNO3, NaClO4 and N(CH3)4Cl. The formation constants of the following species: H5EDTA+, H6EDTA2+, H5CDTA+ and H4NTA+ have been obtained from solubility measurements with ethylenediamine tetraacetic acid (H4EDTA), 1,2‐diaminocyclohexane tetraacetic acid (H4CDTA) and nitrilotriacetic acid (H3NTA) in acid solutions between pH = 3 and 0 at ionic strength 1M (NaClO4 + HClO4).
Zur Synthese. von D‐Glucopyrano‐(cis‐2′, 1′‐c)‐l,2,3,4‐tetrahydro‐isochinolinen
Authors: Wacker O. , Fritz H. 
Published: December 2004

AbstractBy a modified POMERANZ‐FRITSCH‐reaction substituted D‐glucopyrano‐1,2,3,4‐tetrahydro‐isoquinolines have been obtained in high yields from substituted N‐benzyl‐D‐glucosamines. The structure of the products has been confirmed by N.M.R. spectroscopy.
Die Pregnanderivate der Samen von Dregea abyssinica (HOCHST.) K. Schum. (Asclepiadaceae). I. Isolierungen Glykoside und Aglykone, 304. Mitteilung
Authors: Bhatnagar Ajay S. , Kaufmann H. , Stöcklin W. , Reichstein T. 
Published: December 2004

AbstractThe seeds of Dregea abyssinica (HOCHST.) K. Schum. are very rich in glycosides. These consist of a complicated mixture of ester glycosides, cardenolides are absent. All these glycosides are derived from only the two known pregnane derivatives drevogenin P and Drevogenin D. In the glycosides the latter are esterified with different acids (acetic, isovaleric, α‐hydroxyisovaleric and tiglic acid) and glycosidically linked to different 2‐deoxy‐sugars which in part carry 3‐O‐methyl‐6‐deoxy‐D‐allose and terminal D‐glucose. After mild acidic hydrolysis 5 crystalline sugars and 6 crystalline aglycones could be isolated. The sugars were identified as D‐cymarose, asclepobiose, pachybiose, drebyssobiose and «sugar T» (formerly found in Dregea volubilis). The following aglycones were obtained: drevogenin A, drevogenin B, and four new compounds called drebyssogenin F, G, J and K. The latter was a mixture of two components (K1 and K2). From the original mixture four genuine glycosides could be isolated (the drebyssosides 1, 2, 3 and 4). Of these the drebyssosides 1 and 3 were obtained crystalline, drebyssoside 2 in amorphous but pure form and drebyssoside 4 as a mixture of mainly two closely related components. The probable structures of the new substances (drebyssobiose, sugar T, the four drebyssogenins and the four drebyssosides) are reported in the following publication.
Abspaltung von Acyl‐Schutzgruppen bei alkaliempfindlichen Glucosiden. – Synthese von Podophyllotoxin‐β‐D‐glucosid. 20. Mitteilung über mitosehemmende Naturstoffe [1]
Authors: Kuhn M. , Von Wartburg A. 
Published: December 2004

AbstractThe synthesis of podophyllotoxin‐β‐D‐glucoside (III), an antimitotic lignan compound isolated from Podophyllum species, is reported. Reaction of podophyllotoxin (I) with tetra‐O‐acetyl‐α‐D‐glucopyranosyl bromide in acetonitrile in the presence of Hg(CN)2 yields tetra‐O‐acetyl‐podophyllotoxin‐α‐D‐glucoside (II), which is converted into podophyllotoxin‐β‐D‐glucoside (III) by ZnCl2‐catalysed methanolysis. This transesterification is an advantageous method for the preparation of glycosides, sensitive to base and acid, from their corresponding acetyl derivatives. Scope and conditions of the reaction are discussed.
Photochemische Reaktionen. 44. Mitteilung [1]. Zur Photochemie von gesättigten β‐Ketosulfiden
Authors: Ganter C. , Moser J.‐F. 
Published: December 2004

AbstractUltraviolet irradiation of the saturated β‐ketosulfides 6 and 7 (direct n → π* excitation) in benzene and methanol solutions resulted mainly in the selective α‐cleavage of the bond between CO and Cα‐S, producing ketenes by the well known hydrogen transfer as secondary reactions. Depending upon the availability of internal and/or external nucleophiles, the compounds 8, 9, 10 and 11 were formed as major products. The high yields in some of these light‐induced transformations open an attractive synthetic approach to new heterocompounds.
Stereochemie der Umwandlung von Dihydrothebain in Thebain Synthese von markierten Thebainen
Authors: Eppenberger U. , Warren M. E. , Rapoport H. 
Published: December 2004

AbstractThe complete stereochemistry of the Δ6‐dihydrothebaine → 7‐bromodihydrocodeinone dimethyl ketal → codeinone dimethyl ketal → thebaine sequence of transformations has been elucidated by NMR studies of the isotopically labeled compounds prepared using diimide‐d2, methyl hypobromite‐[14C], and methyl hypobromite‐d3. Final elimination of methanol from codeinone dimethyl ketal proceeds in a stereospecific manner: cis under acid catalysis with POC13, and trans under alkaline catalysis with EtO−. As a result of these reactions, variously isotopically labeled thebaines can be prepared.
Elektronen‐Donator‐Acceptor‐Komplexe bei Polypeptiden II. Problemstellung und orientierende Versuche mit Acceptoren des neuen Phtalimid‐ Typs
Authors: Carrión J. P. , Deranleau D. A. , Donzel B. , Esko K. , Moser P. , Schwyzer R. 
Published: December 2004

AbstractPhthalimides, 4‐nitrophthalimides, and tetrachlorophthalimides (exemplified by methyl Nα‐phthalyl‐glycinate, 4‐nitrophthalimide, ethyl Nα‐(4‐nitrophthalyl)‐glycinate, and methyl Nα‐tetrachlorophthalyl‐glycinate) give colored molecular complexes with Nα‐benzyloxycarbonyl‐ar‐pentamethyl‐phenylalanine, Nα‐acetyl‐p‐dimethylamino‐phenylalanine, and Nα‐acetyl‐tryptophane, as well as with the simpler compounds hexamethylbenzene, N, N‐dimethylaniline, N, N‐dimethyl‐p‐toluidine, and indole, in various organic solvents.The association constants are small, and vary between 0.4 and 1.2 l/mol as measured spectroscopically. Enthalpies of complex formation lie between (−) 0.5 and (−) 2.5 kcal/mole. They are within the range assumed for VAN DER WAALS interactions between hydrophobic side‐chains of amino‐acids. This is essential if one would want to use such complexes as intra‐ or intermolecular conformational probes in synthetic polypeptides.The broad absorption maxima of the complexes lie between 350 and 490 nm, extinction coefficients are in the range reported for charge transfer complexes, 500 to 2000. Assignment of the long wavelength absorption to a charge transfer transition seems quite justified by the calculated values of energy coefficients (HMO‐method) for the new class of phthalimide acceptors and the donors, as well as by the applicability of the BRIEGLEB relationship between h νmax, ionisation energy, electron affinity, and distance between the planes of donor and acceptor in the complex between ethyl Nα‐(4‐nitrophthalyl)‐glycinate and hexamethylbenzene. On the basis of absorption maxima, the relative acceptor strengths are: 4‐ nitrophthalimide > tetrachlorophthalimide > phthalimide.Phthalyl, nitrophthalyl, and tetrachlorophthalyl derivatives of tryptophane, pentamethylphenylalanine, and p‐dimethylamino‐phenylalanine are colored compounds and behave like intramolecular charge transfer complexes.The syntheses of all required compounds are described. N‐Ethoxycarbonyl derivatives of 4‐nitrophthalimide and of tetrachlorophthalimide are used to prepare 4‐nitrophthalyl and tetrachlorophthalyl derivatives of amino‐acids.
Photochemische Reaktionen 45. Mitteilung. α‐Sulfonyloxyketone: Sterische Voraussetzungen für die photolytische RSO3‐Elimination – Nachweis von kationischen Produkten Vorläufige Mitteilung
Authors: Iwasaki S. , Schaffner K. 
Published: December 2004

AbstractUpon irradiation in the n→* transition, the 2, 5‐cis tosyloxyketone 9 reacted readily to give the cyclohexenone 11 in benzene solution, and a 4:1 mixture of products 11 and 12 in dioxane solution, while the 2, 5‐ trans isomer 10 remained almost photostable under comparative conditions. Prolonged irradiation of 10 afforded only small amount of products 11 and 12 in an approximate 1:1 ratio. It is concluded that for the photolytic elimination of the tosyloxy group a non‐eclipsed conformation of the CO and the CαO bonds, as already present in the ground state of compound 9, is required. When 9 was irradiated in aqueous dioxane solution, the β‐hydroxy‐ketone 13 was formed in addition to 11. Similarly, the photochemical conversion of the aliphatic tosyloxyketone 5 to the unsaturated ketone 6 was largely suppressed in aqueous dioxane, and the hydroxyketone 15 was formed instead. These results are evidence for the intervention of cationic intermediates in the pathways leading to the rearranged products 11 and 15, and hence point to a heterolytic mode of photocleavage.
Beiträge zur Chemie der Si‐N‐Bindung, XVII [1]. 2,2,4,4,6,6‐Hexamethyl‐1‐oxa‐3,5‐diaza‐cyclohexasilan
Authors: Fink Walter 
Published: December 2004

Abstract2.2.4.4.6.6‐Hexamethyl‐1‐oxa‐3.5‐diaza‐cyclohexasilane was obtained by the controlled hydrolysis of hexamethylcyclotrisilazane and by the co‐ammonolysis of dimethyl‐dichlorsilane and 1.3‐dichloro‐tetramethyldisiloxane.
Organische Phorsphorverbindungen XXXV. Die α‐Aminoalkylierung von elementarem weissem Phosphor und von Biphosphinen. Darstellung und Reaktionen von dialkylaminomethyl‐substituierten tertiären Phosphinoxiden [1]
Authors: Maier Ludwig 
Published: December 2004

AbstractFurther examples of the α‐aminoalkylation of white phosphorus and of a biphosphine are reported. The reaction is described using C‐methyl piperidines, methylamine, ethylamine or propylamine as the amine component, and formaldehyde or benzaldehyde as the carbonyl component. The reaction mechanism has been clarified. Furthermore the direct synthesis of the diethylamine salt of phosphorous acid is reported. In addition, some physical and chemical properties of tris (dialkylamino‐methyl)‐phosphine oxides are given and their coordination compounds with nickel halides are described.
Die Kristallstruktur von Ag3Co(CN)6
Authors: Ludi A. , Güdel H. U. 
Published: December 2004

AbstractThe crystal structure of the hexagonal Ag3Co(CN)6 (a = 7.03 Å, c = 7.13 Å, Z = 1) has been determined by X‐ray powder methods. The structure factor calculations based on the space group D lead to a reliability index R of 0.062, the R̃‐value from F2‐sums of systematically coinciding reflections being 0.064. The cobalt atoms are located in the position 1 a (0,0,0), the silver atoms in 3g (1/2,0,1/2;0,1/2,1/2;1/2,1/2,1/2). The carbon and nitrogen atoms occupy the position 6k. The interatomic distance are: Co‐C = 1.89 Å, C‐N = 1.14 Å, Ag‐N = 2.06 Å. The angle C‐N‐Ag is 157.3º.
Die Acidität von Silanolgruppen. Vorläufige Mitteillung
Authors: Schindler P. , Kamber H. R. 
Published: December 2004

AbstractThe intrinsic acidity constant Kint. of surface silanol groups has been determined by coulometric titration of silicagel at 25° in solutions of the constant ionic strength 0,1M consisting primarily of sodium perchlorate. The experimental data are consistent with
Katalysierte Dehalogenierungen mit Natriumborhydrid
Authors: Egli Robert A. 
Published: December 2004

AbstractSodium tetrahydroborate has a poor reduction capacity for the elimination of aromatic halogens. The addition of metal catalysts (in particular Pd, Co, Ni, Cu) accelerates this reaction to such an extent that even the rather stable aromatic chlorine can be exchanged by hydrogen at room temperature. An activity order of catalysts (the best is palladium on charcoal), a reactivity comparison of iodine, bromine and chlorine, and the influence of ortho, meta or para position in halogenobenzoic acids in relation to halogenobenzenes and to several other halogen compounds are given. Two preparative examples are described.
Essais de réactions dissymétriques sur quartz optiquement actif
Authors: Amariglio Annie , Amariglio Henri , Duval Xavier 
Published: December 2004

AbstractI. Three catalytical reactions are investigated (hydrogenation of methylethylketone, dehydrogenation and dehydration of 2‐butanol) the catalyst being optically active quartz, either pure or metal covered. Emphasis is laid upon the most appropriate experimental conditions, generally neglected heretofore, when stereospecificity may be expected in a catalytic heterogeneous reaction. Numerous attempts under carefully controlled conditions have always led to negative results. Apparent optical rotations sometimes observed are shown to result from an extraneous effect due to minute quartz particles carried away with the reaction products.II. Attempts to separate at room temperature various racemic modifications (2‐butanol, cobalt or chromium complexes, ammonium tartrate) by liquid‐solid chromatography on optically active quartz have always led to negative results. The resolution of (±)‐2‐butanol at dry ice temperature was also unsuccessful.III. The failure to observe any asymmetric effect in catalysis as well as in adsorption on optically active quartz prompts to a critical analysis of previous work where small but positive effects have been claimed. It is shown that most of the small rotatory powers observed are within the limit of error of the measurements and that a number of results are inconsistent or unlike. These may have been vitiated by an extraneous effect which has been recognised and had been overlooked previously (dichroism or double refraction due to minute quartz particles suspended in the observed liquid).
Linear Korrelation der 13C‐Kernresonanzfrequenzen mit den LCAO‐MO‐π‐Elektronendichten in substituierten Benzonitrilen
Authors: Wehrli F. W. , Simon W. , de Haan J. W. , Keulemans A. I. M. , Exner O. 
Published: December 2004

AbstractThe 13C NMR. spectra of seventeen m‐ and p‐ subsituted benzonitriles were examined and partially anlayzed. The C‐1 carbon shieldings can be expressed in terms of a linear correlation with the LCAO‐MO‐π‐electron density at C‐1. No such correlation was found for the cyanocarbon, whose electron density shows only slight varriations for the different substitutents. This fact is consistent with the relatively small range of the chemical shifts at this center.
Niederdruck‐Oligomerisation von Mono‐Olefinen mit löslichen Nickel/Aluminium‐Bimetallkatalysatoren, Teil IV. Reaktionskinetische Untesuchungen über die Codimerisation von Áthylen und Propen
Authors: Onsager Olav‐Torgeir , Wang Hagbarth , Blindheim Ulf 
Published: December 2004

AbstractThe kinetics of the condimerization of ethylene and propene in organic solvents under the influence of a homogeneous catalyst containing π‐tetramethylcyclobutadiene‐nickeldichloride and a prereacted mixture of ethylaluminiumdichloride and tri‐n‐butylphosphine are reported. The primary reaction products are: 1‐pentene, 2‐pentene (cis/trans), 2‐methyl‐1‐butene and 3‐methyl‐1‐butene.The effect of other phosphines was also studied. The activity as well as the selectivity of the catalyst are strongly dependent upon the amount and the LEWIS base strength of the phosphine present.The results are in accordance with a coordinative mechanism on nickel.
Cyclisations par l'intermédiaire de fonctions phénylthioet phénoxy‐carbamyle. I. Diphényl‐1,2‐alcoyl‐5‐dioxo‐3,6‐hexahydro‐triazines‐1,2,4
Authors: Baudet P. , Calin M. 
Published: December 2004

AbstractThe N‐(p‐nitrophenoxy‐carbonyl) and N‐(phenylthio‐carbonyl) derivatives of α‐amino‐acyl‐hydrazides cyclize in presence of diazomethane, yielding hexahydro‐1, 2, 4‐triazines with simultaneous formation of p‐nitro‐anisole or thio‐anisole respectively. The molecules with a phenoxycarbonyl function such as N‐(phenoxycarbonyl)‐glycyl‐(N, N′‐diphenylhydrazide) give the corresponding ring products and anisole only in solvents with high dielectric constant (e.g. nitromethane). The phenylthio‐carbonyl derivatives give the same ring products in presence of lead acetate by the intervention of HO−. The p‐nitrophenoxycarbonyl derivatives give rise to the same cyclisations in the presence of pyridine by the intermediate of carbamyle‐pyridinium ion acting as electrophile.These different types of intramolecular reactions are illustrated by the formation of 1, 2‐diphenyl‐5‐alcoyl‐3, 6‐dioxo‐1, 2, 4‐hexahydro‐triazines.
Preparation of Protected β2‐ and β3‐Homocysteine, β2‐ and β3‐Homohistidine, and β2‐Homoserine for Solid‐Phase Syntheses
Authors: Lelais Gérald , Micuch Peter , Josien‐Lefebvre Delphine , Rossi Francesco , Seebach Dieter 
Published: December 2004

AbstractThe Ser, Cys, and His side chains play decisive roles in the syntheses, structures, and functions of proteins and enzymes. For our structural and biomedical investigations of β‐peptides consisting of amino acids with proteinogenic side chains, we needed to have reliable preparative access to the title compounds. The two β3‐homoamino acid derivatives were obtained by Arndt–Eistert methodology from Boc‐His(Ts)‐OH and Fmoc‐Cys(PMB)‐OH (Schemes 2–4), with the side‐chain functional groups' reactivities requiring special precautions. The β2‐homoamino acids were prepared with the help of the chiral oxazolidinone auxiliary DIOZ by diastereoselective aldol additions of suitable Ti‐enolates to formaldehyde (generated in situ from trioxane) and subsequent functional‐group manipulations. These include OH→OtBu etherification (for β2hSer; Schemes 5 and 6), OH→STrt replacement (for β2hCys; Scheme 7), and CH2OH→CH2N3→CH2NH2 transformations (for β2hHis; Schemes 9–11). Including protection/deprotection/re‐protection reactions, it takes up to ten steps to obtain the enantiomerically pure target compounds from commercial precursors. Unsuccessful approaches, pitfalls, and optimization procedures are also discussed. The final products and the intermediate compounds are fully characterized by retention times (tR), melting points, optical rotations, HPLC on chiral columns, IR, 1H‐ and 13C‐NMR spectroscopy, mass spectrometry, elemental analyses, and (in some cases) by X‐ray crystal‐structure analysis.
Rainfall‐runoff modelling using artificial neural networks: comparison of network types
Authors: Senthil Kumar A. R. , Sudheer K. P. , Jain S. K. , Agarwal P. K. 
Published: December 2004

AbstractGrowing interest in the use of artificial neural networks (ANNs) in rainfall‐runoff modelling has suggested certain issues that are still not addressed properly. One such concern is the use of network type, as theoretical studies on a multi‐layer perceptron (MLP) with a sigmoid transfer function enlightens certain limitations for its use. Alternatively, there is a strong belief in the general ANN user community that a radial basis function (RBF) network performs better than an MLP, as the former bases its nonlinearities on the training data set. This argument is not yet substantiated by applications in hydrology. This paper presents a comprehensive evaluation of the performance of MLP‐ and RBF‐type neural network models developed for rainfall‐runoff modelling of two Indian river basins. The performance of both the MLP and RBF network models were comprehensively evaluated in terms of their generalization properties, predicted hydrograph characteristics, and predictive uncertainty. The results of the study indicate that the choice of the network type certainly has an impact on the model prediction accuracy. The study suggests that both the networks have merits and limitations. For instance, the MLP requires a long trial‐and‐error procedure to fix the optimal number of hidden nodes, whereas for an RBF the structure of the network can be fixed using an appropriate training algorithm. However, a judgment on which is superior is not clearly possible from this study. Copyright © 2004 John Wiley & Sons, Ltd.
Development of a multipoint model for sulfur in proteins: A new parametrization scheme to reproduce high‐levelab initiointeraction energies
Authors: Wennmohs F. , Schindler M. 
Published: December 2004

AbstractTo properly represent weak hydrogen bonds to sulfur in biological systems, a new multipoint model of atomic sulfur for the amino acid methionine is introduced. This is of particular importance for the description of ligand‐protein interactions. The parametrization is performed by fitting the nonbonding parameters of dimethyl sulfide to high levelab initiointeraction energy surfaces of the dimethyl sulfide‐methanol system and incorporating them in the GROMACS force field. Two examples demonstrate the performance of the new model, the molecular dynamics simulations of the hRAR receptor and of α‐lytic protease. In hRAR the origin of the discrimination between the R‐ and S‐enantiomers of the synthetic ligand BMS 184394 is explained, and in the simulation of the α‐lytic protease it is shown that no artificial long range disorders are introduced by the new parametrization. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 283–293, 2005
Sonographic umbilical vessel morphometry and perinatal outcome of fetuses with a lean umbilical cord
Authors: Ghezzi Fabio , Raio Luigi , Günter Duwe Daniela , Cromi Antonella , Karousou Evgenia , Dürig Peter 
Published: December 2004

AbstractPurposeThis study was undertaken to assess whether changes in umbilical cord vessel morphometry are associated with an increased risk of adverse perinatal outcome among fetuses with a lean umbilical cord on sonography.Patients and MethodsA total of 160 fetuses with a sonographically lean umbilical cord (cross‐sectional area below the 10th percentile for gestational age) after 20 weeks of gestation were enrolled. The cross‐sectional areas of the umbilical cord and its vessels were measured. Outcome variables investigated were perinatal death, admission to the neonatal intensive care unit, intrauterine growth restriction, and 5‐minute Apgar score.ResultsThe proportions of perinatal death (1/96 versus 6/64, p < 0.05) and admission to the neonatal intensive care unit (17/96 versus 22/64, p < 0.05) was significantly higher among fetuses with an umbilical vein area below or equal to the 10th percentile for gestational age than among those with an umbilical vein area greater than the 10th percentile. No differences were found in the proportions of perinatal death, neonatal intensive care unit admission, 5‐minute Apgar score < 7, and intrauterine growth restriction when fetuses with umbilical vein areas below or equal to the 10th, the 5th, and the 2.5th percentiles for gestational age were compared. No difference was found in the umbilical artery area and Wharton's jelly area among the groups.ConclusionAmong fetuses with a sonographically lean umbilical cord, a significant relationship exists between an umbilical vein area below or equal to the 10th percentile and an adverse neonatal outcome. © 2004 Wiley Periodicals, Inc. J Clin Ultrasound 33:18–23, 2005
The right thing? Leaders speak out on corporate ethics
Authors: Hernez‐Broome Gina , Steed Judith , Lundberg Sue 
Published: December 2004

AbstractThe recent rash of corporate scandals has turned the spotlight on the issue of ethics among senior leaders. These executives are receiving increased scrutiny from the public and the government, but how do they themselves feel about the state of ethics in their own and other organizations? CCL asked them.