bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deoxy‐nitrosugars 15th communication Synthesis of N‐acetylneuraminic acid and N‐acetyl‐4‐epineuraminic Acid
Authors: Baumberger Franz , Vasella Andrea 
Published: December 2004

AbstractA synthesis of N‐acetylneuraminic acid (1) and of N‐acetyl‐4‐epineuraminic acid (2, R = H) from 2‐acetamido‐4,6‐O‐benzylidene‐1,2‐dideoxy‐1‐nitro‐D‐mannopyranose (3) and 2‐acetamido‐1,2‐dideoxy‐4,6‐O‐isopropylidene‐1‐nitro‐D‐mannopyranose (4), respectively, is described. Michael addition of 3 and 4 to tert‐butyl 2‐(bromomethyl)prop‐2‐enoate (5) and subsequent hydrolytic removal of the NO2 group gave the 4‐nonulosonate tautomers 6/7 and 8/9, respectively (Scheme). Stereoselective reduction of 6/7 and 8/9 with NaBH4/AcOH in dioxane/H2O yielded 12/13 (94:6) and 14/15 (92:8), respectively. Reduction of 6/7 and 8/9 in the absence of AcOH or in EtOH gave 12/13 (15:85) and 14/15 (15:85), respectively. Ozonolysis of 12 and 13 followed by hydrolysis gave tert‐butyl neuraminate 22 and tert‐butyl 4‐epineuraminate 24, respectively. Ozonolysis of 14/15, separation of the products 20 and 21, and hydrolytic removal of the isopropylidene groups gave 22 and 24, respectively. The tert‐butyl ester 22 was saponified to give 1, which was further characterized as the methyl ester 23. Saponification of 24 gave the crude 4‐epimer of 1, which was converted into the stable Na salt 2 and also into the methyl ester 25.
Diels‐AlderRegioselectivity Controlled by Remote Substituents. The Cycloadditions of 1‐(Dimethoxymethyl)‐2,3‐dimethylidene‐ and ‐2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptanes
Authors: Métral Jean‐Lue , Lauterwein JüRgen , Vogel Pierre 
Published: December 2004

AbstractThe syntheses of 2,3‐dimethylidene‐ and 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptanes substituted in position C(1) are reported. The 1‐dimethoxymethyl group in derivatives2and6controls the regioselectivity of theLewis‐acid‐catalyzedDiels‐Alderadditions with methyl vinyl ketone and butynone. For the EtAlCl2‐catalyzed addition of methyl vinyl ketone to6, the regioselectivity can be reversed by a small solvent modification. The tetraene2is a versatile reagent for regioselective ‘tandem’ cycloadditions.
Eine neue Synthese von (±)‐Dihydrorecifeiolid
Authors: Milenkov Branimir , Hesse Manfred 
Published: December 2004

A New Synthesis of (±)‐DihydrorecifeiolideEthyl 1‐(2′‐formylethyl)‐2‐oxocyclooctane‐1‐carboxylate (2) prepared by Michael reaction of ethyl 2‐oxocyclooctane‐1‐carboxylate (1) was regioselectively methylated at the aldehyde group with (CH3)2Ti[OCH(CH3)2]2 to give 3 (Scheme 1). The alcohol 3 was treated with Bu4NF to give the deethoxycarbonylated product 4 which by distillation gave the bicyclic enol ether 5. Oxidation (m‐chloroperbenzoic acid) of 5 and reduction of the resulting oxolacton 6 yielded the title compound (±)‐dihydrorecifeiolide (7) in an overall yield of nearly 50 %. Methylation of the aldehyde 2 with MeLi gave the ring‐enlarged lacton 9 in poor yield (13 %). The deethoxycarbonylation reaction 3 → 4 was studied in more detail (Scheme 3).
Stoffwechselprodukte von Mikroorganismen. 236. Mitteilung. Schwefelhaltige Ansa‐Verbindungen des Naphthomycin‐Typus
Authors: Meyer Michael , Keller‐Schierlein Walter , Megahed Salva , Zähner Hans , Segre Annalaura 
Published: December 2004

Metabolites of Microorganisms. Sulfur‐Containing Ansa Compounds of the Naphthomycin TypeFrom a strain of Streptomyces (Tü 2357) in addition to naphthomycin A, 4 new yellow pigments were isolated and their structures determined by spectroscopic comparison with naphthomycin A. Whereas the naphthomycins D and E are simple derivatives of naphthomycin A, having OH and H, respectively, instead of Cl, the naphthomycins F and G contain an N‐acetylcysteine residue linked to the aromatic moiety by a thioether group. Degradations with O3 yielded identical products from the naphthomycins A, D, F, and G, showing coincident configurations in parts of the molecules. Naphthomycin F shows some biological activity against gram‐positive bacteria and fungi, although much weaker than naphthomycin A. The naphthomycins D, E, and G are inactive against microorganisms.
Intramolecular Hydrogen Bonds of the CO…︁HO Type as Studied by 17O‐NMR
Authors: Jaecard Guy , Lauterwein Jürgen 
Published: December 2004

AbstractThe 17O‐NMR spectra of 1,4‐naphthoquinone and 5‐hydroxy‐1,4‐naphthoquinone (juglone) have been recorded in CDCl3 solution at 40°. In juglone the 17O resonance of the carbonyl peri to the OH group was displaced by 70 ppm to low frequency relative to the resonance in the para‐position. It is shown that this chemical shift arises mainly from intramolecular H‐bonding, the substituent and steric effects being one order of magnitude smaller. Large carbonyl 17O chemical shifts between −34 and −100 ppm were also observed in a series of aromatic aldehydes and ketones where intramolecular H‐bonds of the CO…︁HO type are formed. The H‐bond‐induced carbonyl 17O chemical shifts were linearly correlated with both the 17O and 1H chemical shifts of the OH groups. They represent a most sensitive measure of the strength of intramolecular H‐bonds. The 17O resonances of the OH groups were directed to high frequency on H‐bonding. Analysis of the 17O chemical shifts in 2,2′‐dihydroxy‐benzophenone showed clearly that the two OH groups build H‐bonds simultaneously to the single carbonyl group. The 17O linewidths decreased strongly on H‐bonding; the linewidth of the H‐bonded carbonyl O‐atom in juglone, for example, was reduced by 25% with respect to that of the free carbonyl O‐atom. The carbonyl O‐atom quadrupole coupling constants in juglone, evaluated from the combined use of 13C and 17O relaxation times, were 9.5 and 11.0 MHz, respectively. No correlation was observed between the H‐bond‐induced 17O chemical shifts and the variations in 17O quadrupole coupling constants.
Isolation and Characterisation of (5R, 6S,5′R,8′R)‐ and (5R,6S,5′R,8′S)‐Luteochrome from Brazilian Sweet Potatoes (Ipomoea batatas LAM.)
Authors: de Almeida Ligia Bicudo , De Vuono Camargo Penteado Marilene , Simpson Kenneth L. , Britton George , Acemoglu Murat , Eugster Conrad Hans 
Published: December 2004

AbstractLuteochrome isolated from the tubers of a white‐fleshed variety of sweet potato (Ipomoea batatas LAM.) has been shown by HPLC, 1H‐NMR and CD spectra to consist of a mixture of (5R,6S,5′R,8′R)‐ and (5R,6S,5′R,8′S)‐ 5,6:5′,8′‐diepoxy‐5,6,5′,8′‐tetrahydro‐β,β‐carotene (1 and 2, resp.). Therefore, its precursor is (5R,6S,5′R,6′S)‐5,6:5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene (4). This is the first identification of luteochrome as a naturally occurring carotenoid and, at the same time, gives the first clue to the as yet unknown chirality of the widespread β,β‐carotene diepoxide. These facts demonstrate that the enzymic epoxidation of the β‐end group occurs from the α‐side, irrespective of the presence of OH groups on the ring.
Cycloaddition of Carbodiimides and Triphenylketen‐imine to Allenic Acids. Preliminary Communication
Authors: Trifonov Latchezar S. , Orahovats Alexander S. 
Published: December 2004

AbstractAllenic acids are found to add to dicyclohexylcarbodiimide affording, in the presence of secondary amines, the 1,3‐oxazine‐4‐ones. 5. Under neutral conditions, they add to diaryl‐ or aryl(cyclohexyl)carbodiimides and triphenylketen‐imine to give the corresponding tricyclo[5.2.2.01,5]undecatriene‐3‐ones 7–9 and 12.
Synthese von Betenamin und von Betalain‐Modellsubstanzen
Authors: Parikh Indu , Hilpert Hans , Hermann Kurt , Dreiding Andrè S. 
Published: December 2004

Synthesis of Betenamine and of Betalaine Model SubstancesFor comparisons of color, spectroscopic properties, pKa values, and stabilities, a number of model substances containing the 1,7‐diazaheptamethinium chromophore 8 of the yellow and red betalaine plant pigments were prepared by the thermal or photolytic ring opening of simple pyridine derivatives (such as 2 and 14‐16), followed by the introduction of amines. Among the novel compounds prepared were betenamine perchlorate (5), the ‘naked’ ring system of the beet‐pigment betanine (C) as well as two 1,7‐diazaheptamethinium salts 25 and 27 with terminal amono acids. The synthesis of 5 started with 4‐(2‐aminoethyl)pyridine (1) and proceeded via 2, ring opening with indoline to 4, saponification, and intramolecular amine replacement (Scheme 1). The syntheses of 25 and 27 involved only one step, namely ring opening of γ‐picoline using (S)‐cyclodopa (24) and (S)‐proline (26), respectively (Scheme 3).
Membrane structure and biologic activity of adrenocorticotropin (ACTH) and melanotropin (MSH) peptides. Estimation of structural parameters including the influence of the helix dipole moment
Authors: Schwyzer Robert 
Published: December 2004

AbstractEstimation of preferred conformation, orientation, and accumulation of adrenocorticotropin (1–24)‐peptide at an aqueous‐hydrophobic interface produced a model that agreed with that developed from experimental observations with lipid membranes. Thus, the N‐terminal message segment (residues 1–11) was incorporated into the hydrophobic phase as an α‐helical, perpendicularly oriented domain with an apparent dissociation constant of ca. 5 · 10−5 M. The C‐terminal address segment (residues 12‐24) remained in the aqueous phase as a random‐coil domain. Three parameters proved sufficient to define the model: the Gibbs free energy of hydrophobic association, the molecular amphiphilic moment, and the molecular electric dipole moment. For estimating interactions with biologic membranes (that carry a net negative charge), the Boltzmann distribution of charged peptides was also considered. The estimations were extended to adrenocorticotropin (1‐10)‐peptide and α‐melanotropin. In the first case, the prediction agreed with the earlier observations, in the second, it awaits its experimental proof. The estimated membrane structures were compared with available biologic data. As for opioid peptides, it appears that the amphiphilic moment is an important new parameter for determining quantitative structure‐activity relationships (QSAR) in receptor selection and biologic potency.
Synthese und Struktur zweier Gold‐Komplexe des Triphenylphosphonium‐[bis(diphenylphosphino)methylids]
Authors: Schmidbaur Hubert , Graf Wilhelm , Müller Gerhard 
Published: December 2004

Synthesis and Structure of Two Gold Complexes of Triphenylphosnium [Bis(diphenylphosphino)methylide]Triphenylphosphonium [bis(diphenylphosphino)methylide] (1) reacts with 1 or 2 equiv. of (CO)AuCl in a solvent to give mono‐ or binuclear Au(I) complexes 2 or 3, respectively. The Au‐atoms are bound exclusively to P‐atoms, and the ylidic C‐atom remins an uncoordinated link between the three P‐atoms. Contrary to findings with the free ligand 1, 31P‐NMR spectra of 3 are in agreement with free PC bond rotation in solution. 197Au‐Mössbauer data for both complexes indicate the presence of Au(I) centers in a very similar environment. X‐Ray structure analysis shows that the basic geometry of the free ligand is essentially retained in the complexes. Apart from the different degree of complexation, the structures of 2 and 3 differ only slightly in the conformation of the phenyl rings.
Nucleotides. Part XXV. Chemical synthesis of the hexaribonucleotide C‐A‐A‐C‐C‐A
Authors: Lchiba Misuzu , Charubala Ramamurthy , Varma Rajendra S. , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe chemical synthesis of the ribo‐hexamer C‐A‐A‐C‐C‐A has been achieved by two different routes applying the phosphotriester approach and using the (p‐nitrophenyl)ethyl group for phosphate protection. The 2′‐hydroxy groups as well as the terminal 2′,3′‐diol function have been blocked by the (tert‐butyl) dimethylsilyl group as permanent protection throughout all the synthetic steps with great success. Final deblocking of all protective groups could be performed with 80% yield to give the hexamer 23. The various protected intermediates have been characterized by elemental analysis and UV spectra.
Membrane Structure of Substance P. III. Secondary Structure of Substance P in 2,2,2‐Trifluoroethanol, Methanol, and on Flat Lipid Membranes Studied by Infrared Spectroscopy
Authors: Erne Daniel , Rolka Krzysztof , Schwyzer Robert 
Published: December 2004

AbstractIR data of the neuropeptide substance P (1) and its synthetic segments des‐(Arg1‐Gln6)‐substance P (6), des‐(Arg1‐Pro4)‐substance P (4), des‐(Arg1‐Lys3)‐substance P (3), and des‐Arg1‐substance P (2) indicate predominant β‐structures in the solid state and α‐helical structures in CF3CH2OH (amide I band shape analysis). In MeOH, the spectra of 1 suggest a partly helical structure. On membranes prepared from 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine, a C‐terminal α‐helix consisting of 8 or 9 peptide bonds appears to be induced (IR attenuated total reflection studies). Its perpendicular orientation on the membrane is suggested by the dichroic ratios of the amide‐I and ‐II bands. This study is consistent with our CD experiments and lends support to the membrane structure of 1 predicted from the estimated amphiphilic moment, hydrophobic‐association constant, and helix length.
Metal complexes of macrocyclic ligands. Part XXIV. Binuclear complexes with tetraazamacrocycle‐N,N′,N″,N‴‐tetraacetic acids
Authors: Riesen Andreas , Zehnder Margareta , Kaden Thomas A. 
Published: December 2004

AbstractThe three ligands H4dota, H4teta, and H4heta give binuclear complexes with Cu2+ and Ni2+, the spectral properties of which have been studied. The structures of Cu2(dota)·5H2O and Cu2(teta)·6H2O have been established by X‐ray diffraction analysis.
Ionization Energies of 1‐R‐2,2‐dimesitylethenols, 1,2‐Dimesityl‐2‐phenylethenol, and Some of their Keto Tautomers
Authors: Lecoultre Jacques , Heilbronner Edgar , Biali Silvio E. , Rappoport Zvi 
Published: December 2004

AbstractThe He(Iα) PE spectra of the two pairs of 1(Ph)‐3 and 2–4 have been recorded and assigned by comparison with spectra of related molecules, or by using simple MO arguments. This analysis shows that the PE spectra are in agreement with the assumption that the twist angles observed in the crystalline state are more or less conserved in the gas phase. The observed first adiabatic ionization energies I allow the calculation of the molar reaction enthalpy ΔrH which accompanies the enolization of the radical cations of the title compounds. It is found that ΔrH ≈︁ –−70 kJ mol−1 is roughly the same for both keto/enol pairs, in qualitative and quantitative agreement with expectation. These results complement and correct ionization energies determined previously by mass spectrometric methods and conclusions based on them.
Charge Dispersal in the Quinuclidine Radical Cation and in the Quinuclidinium Ion, as Revealed by PE and ICR Spectroscopy
Authors: Heilbronner Edgar , Honegger Evi , Lecoultre Jacques , Grob Cyril A. , Houriet Raymond , Rolli Eric 
Published: December 2004

AbstractThe n ionization energies I and the gas‐phase basicities GB of CH3‐, Cl‐, or CN‐substituted quinuclidines have been measured by PE and ICR spectroscopy. The dependence of the shifts ΔI and ΔGB (relative to the values of the parent molecule) allow conclusions about the charge dispersal accompanying the n ionization or the protonation of quinuclidine in the gas phase. The agreement with the results of a minimal basis set ab initio calculation is excellent. Comparison of the solution pKa values with either I or GB reveals that 2‐substituted quinuclidines exhibit sizeable solvent‐induced proximity effects, i.e. that the corresponding quinuclidinium ions are more acidic in solution than expected on the basis of the gas‐phase basicities. This agrees with earlier results concerning 2‐substituted pyridines.
3‐Hydroxyglutarate and β,γ‐Epoxy Esters as Substrates for Pig Liver Esterase (PLE) and α‐Chymotrypsin
Authors: Mohr Peter , Rösslein Lukas , Tamm Christoph 
Published: December 2004

AbstractThe pH dependence of the α‐chymotrypsin‐catalyzed hydrolysis of dimethyl 3‐hydroxyglutarate (3) has been studied. The e.e. was determined by HPLC analysis of diastereoisomeric camphanoic‐acid derivatives. Kinetic resolution of the β,α‐epoxy esters 10 and 24 by pig liver esterase has been shown to provide an alternative access to chiral β‐hydroxy esters and acids of high optical purity. By this latter method, the unnatural enantiomer of γ‐amino‐β‐hydroxybutyric acid (GABOB) has been synthesized. Finally, dimethyl meso‐3,4‐epoxyadipate (19) was hydrolyzed by pig liver esterase with almost 100% selectivity.
Herstellung und Charakterisierung in Membranen von Ionophoren mit Selektivität fü Natrium‐Ionen
Authors: Bongardt Frank , Vögtle Fritz , Wegmann Dorothée , Ammann Daniel , Maruizumi Takuya , Simon Wilhelm 
Published: December 2004

Preparation of Neutral Sodium‐Selective Ionophores and their Characterization in Membrane ElectrodesDifferent ionopbores based on N,N′‐dibenzyl‐N,N′‐diphenyl‐1,2‐phenylenedioxydiacetamide (1) have been prepared by substitution of the aromatic ring carrying the ether O‐atoms. Substituents of widely different electronegativity (CH3, CH3O, CHO, CN NO2, Br) do not relevantly influence the ion selectivity.
Aza‐2‐dienes‐1,3. Partie 5. Préparation de N‐aminoimidazoles, 3H‐pyrroles, triazolo[1,2,4][1,5‐a]pyrazines et imidazo[1,2‐a]pyrazines
Authors: Legroux Didier , Schoeni Jean‐Paul , Pont Christiane , Fleury Jean‐Pierre 
Published: December 2004

2‐Aza‐1,3‐dienes. Access to N‐Aminoimidazoles, 3H‐Pyrroles, [1,2,4]Triazolo[1,5‐a]pyrazines, or Imidazo[1,2‐a]pyrazinesNucleophilic attack of 5‐(dialkylamino)‐2‐aza‐1,3‐diene‐1,1‐dicarbonitriles (or their 1‐methoxycarbonyl analogous) by hydrazines or hydrazdes gives substituted N‐aminoimidazoles, [1,2,4]triazolo‐[1,5‐a]pyrazines, or α‐dihydrazino derivatives. With α‐amino esters (or analogous), imidazo[1,2‐a]pyrazines are produced. Addtion of cyanide anions occurs also with formation of substituted 3H‐pyrroles. Structures and rationalisation of this nucleophilic attack are discussed.
Electrochemical Investigation of Potassium Heptacyanorhenate(III) in Aqueous Solution
Authors: Marty Werner , Renaud Philippe , Gampp Harald 
Published: December 2004

AbstractThe electrochemistry of potassium heptacyanorhenate(III) in aqueous solution was studied by cyclic and by rotating disk voltammetry at planar microelectrodes. The results are consistent with a single, reversible electron transfer: Re(CN)3−7 + e⇄Re(CN)4−7 with E′0 = 643 mV vs. NHE. A single protonation equilibrium is observed: Re(CN)4−7 + H+⇄ Re(CN)7H3− with pK = 1.31 determined from combined voltammetric and pH data. The Re–CN bond appears to be kinetically inert, and none of the cyano complexes in other oxidation states of Re claimed in the literature was found in the potential range − 2 V to + 1 V.
Asymmetric Diels‐Alder Reactions of Cyclopentadiene with N‐Crotonoyl‐ and N‐Acryloyl‐4,4‐Dimethyl‐1,3‐Oxazolidin‐2‐one, Mediated by Chiral Lewis Acids
Authors: Chapuis Christian , Jurczak Janusz 
Published: December 2004

AbstractOne‐pot Diels‐Alder reactions of cyclopentadiene with 3‐crotonoyl‐ (2) and 3‐acryloyl‐4,4‐dimethyl‐1,3‐oxazolidin‐2‐one (3), Mediated by chiral Lewis acids, are described. AlCl3, EtAlCl2, Et2AlCl, TiCl4, ZrCl4, SnCl4, SiCl4, and BBr3, modified with derivatives of D‐mannitol, L‐tartaric acid, and (R)‐binaphthol, were applied as chiral promotors. The reaction with dienophile 2, carried out in CH2Cl2 at −78° with high yield, was characterized by excellent π‐face selectivity. In case of the reaction with dienophile 3, the efficiency of the chirality transfer was much lower.
Synthesis of the (+)‐Enantiomer of Taonianone, a Furanoid Diterpene from Brown Algae
Authors: Huckestein Martina , Kreiser Wolfgang , Rüschenbaum Volker 
Published: December 2004

AbstractThe constitution and absolute configuration of the furanoditerpene taonianone (1) has been established by synthesis starting from (–)‐carveol (2).
Molluscicidal Saponins from Swartzia madagascariensis DESVAUX
Authors: Borel Christian , Hostettmann Kurt 
Published: December 2004

AbstractThe phytochemical investigation of the dried fruits of Swartzia madagascariensis (Leguminosae) afforded the five triterpenoid saponins 1–5. They were shown to be glucuronides of oleanolic acid and of gypsogenin by chemical and spectral means (FAB‐MS, 13C‐NMR, GC/MS). One of the isolated compounds, identified as 3‐O‐[O‐α‐L‐rhamnopyranosyl‐(1→3)‐(β‐D‐glucopyranosyluronic acid)]oleanolic acid, was responsible for the high molluscicidal activity of Swartzia madagascariensis fruits against the schistosomiasis‐transmitting snails Biomphalaria glabrata and Bulinus globosus.
Catalysis of Friedel‐Crafts Alkylation by a Montmorillonite Doped with Transition‐Metal Cations
Authors: Laszlo Pierre , Mathy Arthur 
Published: December 2004

AbstractCatalysts are obtained by exchange of the interstitial cations in the K10 montmorillonite. They are applied to Friedel‐Crafts alkylations with halides, alcohols, and olefins. They are quite effective even with unactivated hydrocarbons. Isomer distribution depends little on the catalyst used. Thermodynamic equilibration does not take place, the reactions appear to be kinetically controlled. Efficiency of the catalysts bears no apparent relation to that of the corresponding Lewis acids under homogeneous conditions, and it depends on the nature of the alkylating agent. Zr(IV) and Ti(IV), in general, give the best results.
Fe(II)‐Induced Fragmentation Reaction of γ‐Hydroperoxy‐α,β‐enones. Part 1. Synthesis of 13(14→8)‐abeo‐Steroids
Authors: Canonica† Luigi , Danieli Bruno , Lesma Giordano , Palmisano Giovanni , Mugnoli Angelo 
Published: December 2004

AbstractSome steroidal analogues embodying the hitherto unknown 13(14→8)‐abeo skeleton have been synthesized by Fe(II)‐induced rearrangement (tandem β‐fission/reductive alkylation) of 14α‐hydroperoxy‐7‐en‐6‐ones. The configurational assignment was made by thorough analysis of NMR spectra; the structure of one of the products was unambiguously assessed by X‐ray single‐crystal analysis.