bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation d'images photolytiques sur les macrocristaux d'halogénure de plomb
Authors: Reber J. F. , Fernandez‐Garcia J. G. , Steiger R. , Boissonnas Ch. G. 
Published: December 2004

AbstractThe preparation and some properties of large lead halide crystals are described. The photolysis of these crystals was followed by chemical etching (photosolubilization), showing that the rate of solubilization decreases if the crystal is exposed in the presence of oxygen.
Synthesen mit Nitrilen. 34. Mitteilung. Phenylhydrazone des Dicyanmethylenindandions: Photolyse von 2‐Dicyanmethylen‐1,3‐indandion‐monophenylhydrazon in Methylenchlorid
Authors: Braun A. M. , Loeliger H. , Junek H. 
Published: December 2004

AbstractPhotolysis of 2‐dicyanomethylene‐1, 3‐indandione‐monophenylhydrazone 1 during several days yielded 3‐(N‐chlorimino)‐5‐oxo‐2‐phenyl‐2.3‐dihydro‐5H‐indeno[1.2‐c]pyridazine‐4‐carbonitrile 2. Isomerization to 3‐imino‐5‐oxo‐2‐phenyl‐2.3‐dihydro‐5H‐indeno[1.2‐c]pyridazine‐4‐carbonitrile 4 was also observed. Radical formation from the first triplet state leads to chlorine abstraction from the solvent and to formation of 2. The same reaction occurs from the first triplet state of 4.
Synthese von racemischen, isomeren Desoxo‐4, 14‐didemethyl‐cassain‐Derivaten. 4. Mitteilung über Cassain‐Analoga
Authors: Hauth H. , Stauffacher D. 
Published: December 2004

AbstractFor the synthesis of demethyl analogues of Erythrophleum alkaloids, the tricyclic ketone 14 (trans‐anti‐trans) was prepared. The Horner reaction on 14 led to a mixture of cis/trans compounds, which could be separated into the homogeneous racemic isomers 21 and 22. These compounds were transformed into the corresponding 2‐dimethylamino‐ethyl esters of their 3‐dehydro and 3‐O‐carbamoyl derivatives.
Synthèses dans la série des bis‐indéno‐anthracènes, III. Le dioxo‐15,16‐dihydro‐15, 16‐bis‐indéno[1.2‐a;2′.1′‐c]anthracène et le tétraoxo‐5,10,15,16‐tétrahydro‐5,10,15,16‐bis‐indéno[1.2‐a; 2′.1′‐c]anthracène
Authors: Chardonnens Louis , Schorderet François 
Published: December 2004

AbstractThe title compounds, a dioxo (XVIII) and a tetraoxoderivative (VI) of a new diindenoanthracene, are synthesized in several steps (overall yield 35 and 26%, respectively) starting from 2,3‐dimethyl‐1,4‐diphenyl‐butadiene‐1,3 (VIII). The corresponding hydrocarbon could not be obtained by reduction.
Thermische Cyclodehydratisierung von Salicylalkoholen; eine einfache Synthese von 4‐substituierten 2H‐Chromenen
Authors: Hug R. , Hansen H.‐J. , Schmid H. 
Published: December 2004

AbstractHeating of 1‐(o‐hydroxyaryl)‐2‐propen‐1‐ols (9–13; see scheme 1) in diglyme solution at 147° leads to a 1,4‐elimination of water to yield ω‐vinyl‐o‐quinomethides (b; see scheme 2) as intermediates which cyclise rapidly to form 2H‐chromenes (17–21). 1‐(o‐Hydroxyphenyl)‐5‐hexen‐1‐ol (14) on heating at 147° is transformed into o‐(1,5‐hexadienyl)‐phenol (23). This phenol rearranges at higher temperature (270°) in N,N‐diethylaniline to yield a mixture of 2,4‐propanochromane (25) and cis‐ and trans‐3,4‐propanochromane (cis‐ and trans‐26). The kinetically controlled ratio of these compounds is 2,8:1:2,9. The formation of 25 and 26 can be explained by an intramolecular Diels‐Alder reaction (see scheme 3).
The Epimerization of Trimethylsilyl Ethers During Their Gas Chromatographic Analysis
Authors: Kagan Jacques , Harrison David A. 
Published: December 2004

AbstractWe are grateful to the donors of the Petroleum Research Fund, administered by the American Chemical Society, to the National Science Foundation and to the Research Board of the University of Illinois for support of this research, to Dr. B. Willhalm for useful comments and to the Department of Organic Chemistry, University of Geneva, for its hospitality (1971/72).
Die photolyse von Anthranilen in saurer Lösung; Vergleich mit der photochemischen und thermischen Zersetzung entsprechender 2‐Azido‐acylbenzole in saurer Lösung. Vorläufige Mitteilung
Authors: Doppler Th. , Hansen H.‐J. , Schmid H. 
Published: December 2004

AbstractAnthranils 1a, b, 4 und 5 yield on irradiation in cone. sulfuric acid 2‐amino‐5 hydroxy‐acylbenzenes 2a, b, 6 and 7 which are isolated mainly as their acetates. Small amounts of 2‐amino‐3‐hydroxy‐acylbenzenes 3a and 3b are formed as by‐products (cf. tables 1 and 2). Simila results were obtained when the corresponding 2‐azido‐acylbenzenes were decomposed thermally i cone. sulfuric acid (cf. tables 1 and 2). 3,5‐Dimethylanthranil (8) forms, on irradiation in sulfuric acid and subsequent acetylation, 2‐acetamino‐5‐acetoxy‐6‐methylacetophenone (6) and 2‐acetamino‐5‐acetoxymethyl‐acetophenone (10). The same compounds were obtained from the thermaldecomposition of 2‐azido‐5‐methyl‐acetophenone (19) in sulfuric acid.
Structure and spectra of murexide and of alkali purpurates: Crystal structure of lithium purpurate dihydrate
Authors: Bürgi H. B. , Djurić S. , Dobler M. , Dunitz J. D. 
Published: December 2004

AbstractCrystals of lithium purpurate dihydrate are triclinic, a = 6.715, b = 6.822, c = 14.038 Å, α = 96.85, β = 100.94, γ = 67.41°, space group P1, Z = 2. From the results of a detailed three‐dimensional analysis the lithium ion is found to be bonded to three atoms (two oxygen plus central nitrogen) of one purpurate anion, and also to an oxygen atom of a second purpurate anion and to a water molecule to complete a roughly square‐pyramidal 5‐coordination. The purpurate anion is markedly nonplanar, the two six‐membered rings being twisted by 22° around the central CN bonds. A molecular mechanics calculation, based on reasonable interatomic potential functions, reproduces the observed geometry of the lithium complex and indicates that with larger cations the degree of out‐of‐plane twisting should increase. The observed dependence of the characteristic long‐wave absorption of purpurate complexes on ionic radius is explained qualitatively on the basis of simple HMO‐theory.
Substituierte 9‐Oxabicyclo[4.2.1]‐ und 9‐Oxabicyclo[3.3.1]nonane IV. endo, endo‐2,5‐Dihydroxy‐9‐oxabicyclo[4.2.1]nonan, endo, endo‐, endo, exo‐ und exo, exo‐2,6‐Dihydroxy sowie endo, exo‐2,7‐Dihydroxy‐9‐oxabicyclo[3.3.1]nonan; Darstellung und Umwandlungsprodukte
Authors: Duthaler R. O. , Wicker K. , Ackermann P. , Ganter C. 
Published: December 2004

AbstractThe synthesis of the following compounds and reaction products thereof are described: endo, endo‐2,5‐dihydroxy‐9‐oxabicyclo[4.2.1]nonane (3–5), epimeric 2,6‐dihydroxy‐9‐oxabicyclo[3.3.1]nonanes (endo, endo: 6–8, exo, exo: 29–32, and endo, exo: 43–45), and endo, exo 2,7‐dihydroxy‐9‐oxabicyclo[3.3.1]nonane (46–50).
Die thermische Umlagerung von 2‐(Buta‐1′,3′‐dienyl)‐phenolen in 2‐Alkyl‐2H‐chromene; Beispiele für aromatische [1,7a]‐ und [1,5s]sigmatropische Wasserstoffverschiebungen
Authors: Hug R. , Hansen H.‐J. , Schmid H. 
Published: December 2004

Abstract2‐(1′‐cis,3′‐cis‐)‐ and 2‐(1′‐cis,3′‐trans‐Penta‐1′,3′‐dienyl)‐phenol (cis, cis‐4 and cis, trans‐4, cf. scheme 1) rearrange thermally at 85–110° via [1,7 a] hydrogen shifts to yield the o‐quinomethide 2 (R  CH3) which rapidly cyclises to give 2‐ethyl‐2H‐chromene (7). The trans formation of cis, cis‐ and cis, trans‐4 into 7 is accompanied by a thermal cis, trans isomerisation of the 3′ double bond in 4. The isomerisation indicates that [1,7 a] hydrogen shifts in 2 compete with the electrocyclic ring closure of 2. The isomeric phenols, trans, trans‐ and trans, cis‐4, are stable at 85–110° but at 190° rearrange also to form 7. This rearrangement is induced by a thermal cis, trans isomerisation of the 1′ double bond which occurs via [1, 5s] hydrogen shifts. Deuterium labelling experiments show that the chromene 7 is in equilibrium with the o‐quinomethide 2 (R  CH3), at 210°. Thus, when 2‐benzyl‐2H‐chromene (9) or 2‐(1′‐trans,3′‐trans,‐4′‐phenyl‐buta1′,3′‐dienyl)‐phenol (trans, trans‐6) is heated in diglyme solution at >200°, an equilibrium mixture of both compounds (∼ 55% 9 and 45% 6) is obtained.
Struktur und photochemische Reaktivität: Photohydrolyse von Trifluormethylsubstituierten Phenolen und Naphtholen
Authors: Seiler P. , Wirz J. 
Published: December 2004

AbstractIrradiation of trifluoromethylphenols (three isomers) and ‐naphthols (eight isomers) in water solution yields the corresponding hydroxybenzoic and naphthoic acids, respectively. The reaction mechanism has been investigated by means of flash photolysis and quenching experiments. It is proposed that the photohydrolysis is initiated in the lowest excited singlet state by a heterolytic CF bond cleavage. The observed photochemical and thermal reaction rates as well as the shifts of the lowest electronic transitions upon CF3‐substitution compare well with predictions from semiempirical π‐electron calculations (PPP SCF CI). A rationale for the correlation between excited state charge densities and photochemical reactivity is given. pK values for the ground state and first excited singlet state are reported.
Pinacol‐Pinacolone Rearrangement of 1, 2‐Di‐(p‐methoxyphenyl)‐ethane‐1, 2‐diol and Bis‐(4‐methoxyphenyl)‐acetaldehyde in Acid Media
Authors: Tadros Wadie , Sakla Alfy Badie , Awad Sami Bassili , Helmy Abdul‐Aziz Amine 
Published: December 2004

Abstract1, 2‐Di‐(p‐methoxyphenyl)‐ethane‐1, 2‐diol gave in acid media bis‐(4‐methoxy‐phenyl)‐acetaldehyde, 4‐4′‐dimethoxy‐deoxybenzoin, and 1, 2‐di‐(p‐methoxyphenyl)‐ethylene oxide; their respective yields being influenced by at least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period.Bis‐(4‐methoxyphenyl)‐acetaldehyde rearranged to the deoxybenzoin in boiling sulfuric (50%) or phosphoric (75%) acids (w/w), and to two isomeric 1, 2‐diacetoxy‐1, 2‐di‐(p‐methoxyphenyl) ethanes when it was heated with acetic anhydride.The mechanisms of these reactions are discussed.
Utlisation d'ylides du phosphore en chimie des sucres. XIII. Synthèse de dérivés des hydroxyméthyl‐3‐D‐glucose et‐D‐galactose et de composés voisins
Authors: Tronchet J. M. J. , Bourgeois J. M. 
Published: December 2004

AbstractThe treatment of the 1, 2:5, 6‐di‐O‐isopropylidene‐α‐D‐ribo‐ and xylo‐hexofuranos‐3‐uloses with cyanomethylenetriphenylphosphorane led in each case, and in almost quantitative yields, to a pair of geometrical isomers of C‐cyanomethylenic sugars having respectively the ribo and the xylo configurations. Permanganate oxidation of these branched‐chain unsaturated sugars afforded the corresponding gem‐hydroxyformyl compounds bearing the formyl group on the more hindered face of the molecule. The formyl group of these sugars is easily derivatized to an oximino or reduced to a hydroxymethyl. The configuration at the new asymmetric carbon has been established by comparison with known compounds or by synthesis of a C(3) epimer by the classical route involving a Grignard reagent.
Recherches dans la série des cyclitols XLIII. Sur des éthylène‐cétals de cétoses dérivés du cyclopentane
Authors: Cocu F. G. , Posternak Th. 
Published: December 2004

AbstractThe synthesis of a series of keto derivatives of cyclopentane is described. The configurations of these derivatives have been determined by chemical methods and verified by IR. and NMR. spectroscopy. The preferred conformation of the cyclopentane part of the molecule has been established by the study of intramolecular hydrogen bonds and the values of the coupling constants JHCOH and JH, H.
Synthese von Tricyclo[4.4.1.13, 8]dodecan‐4, 9‐dion und Tricyclo[4.4.1.13, 8]dodeca‐4, 9‐dien
Authors: Gerlach H. 
Published: December 2004

AbstractTreatment of 2, 6‐bis‐aminomethyladamantane‐2, 6‐diol (II) with nitrous acid gives tricyclo[4.4.1.13, 8]dodecane‐4, 9‐dione (III), which is converted into the tricyclo[4.4.1.13, 8]dodeca‐4, 9‐diene (V) by reduction to the corresponding diols (IV, R = H) and pyrolysis of their O‐4‐methylphenyl thiocarbonate O‐esters. II is accessible from 2, 6‐adamantanedione by reaction with diethyl aluminium cyanide and subsequent reduction with lithiumaluminium hydride. The physical properties of the new compounds including 13C NMR. spectra of III, V and tricyclo‐[4.4.1.13, 8]dodecane are given.
Antibiotic X‐5108. III. Structure of the chromophore. Preliminary communication
Authors: Maehr Hubert , Blount John F. , Leach Michael , Stempel Arthur , Büchi George 
Published: December 2004

AbstractAntibioticum X‐5108 wurde in den 4‐Brombenzyläther übergeführt, der, durch oxydative Spaltung mit Perjodat, eine Carbonsäure (5 a) lieferte, deren UV.‐Spektra im langwelligen Bereich denen des Antibioticums ähnlich sind. Der Chromophor des Antibioticums ist somit mit der Carbonsäure 5a verwandt, die als 8‐[4‐(4‐Brombenzyloxy)‐1, 2‐dihydro‐1‐methy1‐ 2‐oxo‐3‐pyridyl]‐7‐methyl‐8‐oxo‐2(trans), 4(trans), 6 (trans)‐octatriensäure identifiziert wurde.
Photochromism of O‐Analogs of Thiathiophthenes
Authors: Calzaferri Gion , Gleiter Rolf , Knauer Karl‐Heinz , Rommel Erika , Schmidt Erika , Behringer Hans 
Published: December 2004

AbstractIrradiation of O‐analogs of thiathiophthenes yield a photoproduct which reverts thermally to the starting material. Kinetic measurements for this thermal reaction yield Ea values in the range of 10–15 kcal/mol and Δ S* values between −16 and −41 eu. Based on NMR. and IR. results the structure of the photoproduct is established. The electronic spectra of the starting material and of the photoproduct are discussed. The experimental results are compared with MO‐calculations.
Nucleoside und nucleotide. Teil 4. Festphasensynthese von Oligonucleotiden an einem unlöslichen, makroporösen Träger
Authors: Glaser Remo , Séquin Urs , Tamm Christoph 
Published: December 2004

AbstractInsoluble, macroreticular, highly cross‐linked polystyrene with projecting mono‐methoxytrityl chloride groups 4 was prepared and condensed with thymidine (TD) as well as with 1‐(2′‐deoxy‐ß‐D‐ribofuranosyl)‐2(1H)‐pyridone (IId) to give the polymers 5 and 6 respectively, containing approximately 465 μmoles resp. 650 μmoles of bound nucleoside per gram of polymer. A standard procedure for removal of the products from the support is described. Condensation of the polymer‐bound nucleosides 5 and 6, respectively, with 3′‐O‐acetyl‐thymidine‐5′‐phosphate (7) in the presence of mesitylenesulfonyl chloride (MS) and subsequent removal from the polymer yielded the dinucleoside phosphates Td‐Td (9) and IId‐Td (11) respectively.Condensation of the polymer 8 with 3′‐O‐acetyl‐thymidine‐5′‐phosphate (7) in the presence of MS and cleavage of the polymer linkage gave the trithymidine diphosphate (Td‐Td‐Td) (13). Phosphorylation of the polymer‐bound nucleosides 5 and 6 with ß‐cyanoethyl phosphate in presence of MS took place in 3′‐position. Similarly the polymer‐bound dinucleoside phosphates 8 and 10 gave 16 and 17 respectively.
Dielectric Shielding of Ionic Charges in Aqueous Solutions of Different Ionic Strength
Authors: Fabbrizzi Luigi , Paoletti Piero , Zobrist Markus C. , Schwarzenbach Gerold 
Published: December 2004

AbstractThe thermodynamic functions of the proton transfer H2tn2++tn → 2 Htn+ (tn = 1,3‐diaminopropane) have been determined in aqueous solutions containing different amounts of KCl (0.05 ⩽ μ ⩽ 3.01). The free energy (−ΔG) of the process decreases, whereas the enthalpy (‐ΔH) increases with μ. There is reason to believe that the reaction is entirely controlled by the Coulomb forces between the two protonic charges. The electrostatic energy involved can be described in terms of a model incorporating an effective dielectric constant εe, such that δεe/δμ and δ2εe/δμδT are both positive. The polarisation of pure water is produced by orientation of hydrogen‐bonded dipole molecules H2O, whereas the electrolyte solution is polarised in addition by dislocation of the ions K+ and Cl−. Our results demonstrate that the former type of polarisation is much more temperature dependent than the latter.
Synthese und thermisches Verhalten von 6,8‐Dimethylentricyclo[3.2.1.02,7]oct‐3‐enen; [3s 3s]‐sigmatropische Umlagerungen von 6‐Allenyl‐ und 6‐Propargly‐1‐ Methylen‐cyclohexa‐2,4‐dienen in aromatische Kohlenwasserstoffe als Beispiele für konzertierte Semibenzol → Benzol‐Umlagerungen
Authors: Gilgen Paul , Zsindely Janos , Schmid Hans 
Published: December 2004

AbstractThe tricyclic dimethylene hydrocarbons 5, 6, 7, 8 and d2‐5, (Scheme 2), which are prepared by Wittig‐reaction from the corresponding ketones, are rearranged, by heating, to 4‐aryl‐but‐1‐yne derivatives via the unstable 6‐allenyl‐1‐methylene‐cyclohexa‐2, 4‐diene intermediates (e.g. Scheme 14). Using the deuterium‐labelled compound d2‐5, it was shown that the allenyl moiety, formed by a retro‐Diels‐Alder reaction (cycloreversion) of the tricyclic dimethylene compound, migrates with complete inversion in the final o‐semibenzene‐benzene rearrangement (Schemes 11 and 14). Reaction of 6‐propargyl‐cyclohexa‐2, 4‐dien‐1‐ones with triphenylphosphonium methylide gives 6‐propargyl‐1‐methylene‐cyclohexa‐2 4‐dienes, which immediately undergo a [3s, 3s]‐rearrangement to form 4‐aryl‐buta‐1, 2‐dienes (Scheme 9). In contrast, the rearrangement of the corresponding 4‐propargyl‐1‐methylene‐cyclohexa‐2, 5‐ dienes proceeds by a radical mechanism (Schemes 10 and 13).
A New Method for the Detection of Racemization during Peptide Synthesis: Stereoselective hydrolysis of diastereomeric peptides by leucine aminopeptidase
Authors: Bonsshard Hans Rudolf , Schechter Israel , Berger Arieh 
Published: December 2004

AbstractA suitably protected dipeptide of configuration L‐D, e.g. Z‐L‐Ala‐D‐Ala is coupled with an all L alanine peptide, e.g. L‐Ala‐L‐Ala‐ONbAbbreviations according to the IUPAC‐IUB rules, ‘Symbols for Amino‐Acid Derivatives and Peptides, Recommendations (1971)’'. see e.g. J. biol. Chemistry 247, 977 (1972). In particular the following abbreviations have been used: Z = benzyloxycarbonyl‐, ‐ONb = p‐nitrobenzyloxy‐, ‐ONSu = succinimido‐oxy‐. Additional abbreviations are LAP = leucine aminopeptidase, DCCI = N,N′‐dicyclohexylcarbodiimide, DMF = dimethylformamide.
. The blocking groups are removed and the free peptide hydrolyzed by leucine amino peptidase (E.C. 3.4.1.1). This enzyme shows absolute L‐specificity for the penultimate peptide bond from the amino end and therefore cleaves only the all L peptide formed through racemization. The amount of free alanine determined by amino acid analysis gives a multiple of the degree of racemization. The sensitivity of the test allows 0.1% of (L‐Ala)4 to be detected in the synthesis of L‐Ala‐D‐Ala‐L‐Ala‐LAla. Coupling of Z‐L‐Ala‐D‐Ala and Z‐L‐Ala‐D‐Phe with di‐ and trialanine peptides has been studied using DCCI and DCCI + 1‐hydroxybenzotriazole as coupling reagents. The degree of racemization was around 80% for the coupling by DCCI in DMF but was reduced to 0.2–0.4% in the presence of 2 equivalents of 1‐hydroxybenzotriazole. Coupling using the succinimide esters Z‐L‐Ala‐D‐Ala‐ONSu and Z‐L‐Ala‐D‐Phe‐ONSu resulted in 0.8 to 10% racemization, depending on the solvent and base used.
Contribution à la phytochimie du genre Gentiana. II. Etude des cyclitols dans les feuilles de Gentiana lutea L.
Authors: Bellmann Günter , Jacot‐Guillarmod André 
Published: December 2004

AbstractL‐(+)‐bornesitol has been isolated from the leaves of G. lutea L. in the proportion of 1,6% by weight of dried material. Meso‐inositol has also been detected by chromatography. Distribution of L‐(+)‐bornesitol and its taxonomic interest are discussed.
Die phloroglucide von neun dryopteris‐arten aus kenya sowie der d. oligodonta (desv.) pic.‐serm. und d. “dilatata” von den canarischen inseln
Authors: Widén C.‐J. , Faden R. B. , Lounasmaa M. , Vida G. , Euw J. V. , Reichstein T. 
Published: December 2004

AbstractAmong the eight species of the fern genus Dryopteris which have been recorded from Kenya (East Africa), the group of D. inacqualis, D. pentheri and D. schimperana is regarded as critical. There is no agreement among experts as to whether D. inaequalis s. str. is restricted to South Africa and whether it should be separated specifically from D. pentheriChemical and, as far as possible, cytological investigations of available material showed that the following taxa of Dryopteris occur in Kenya (ploidy in brackets) : 1. D. athamantica (2 × );2. D. callolepis (4 × ); 3. D. inaequalis (4 × ); 4. D. kilenzensis (2 × ); 5. D. manniana (4 × ); 6. D. pentheri (2 × ); 7. D. schimperana (2 × ); 8. D. sp. RBF‐71/885 (TR‐330.5) (4 × ); 9. D. squamiseta(ploidy not determined). The nomenclature of the four critical taxa, 3, 6, 7 and 8 is provisional. For comparison, two taxa from the Canary Islands, 10. D. ‘dilatata’ (4 × ) and 11. D. oligodonta (2 × ) were also investigated.Among the nine taxa from Kcnya, two (4 and 9) did not contain any phloroglucides. Dryopteris kilomensis must be regarded as one of the few representatives of the genus Dryopteris which lacks such compounds. On the other hand, the negative result for 9 is in agreement with the fact that this species has recently been transferred to a new genus Nothopevanema.The following three new compounds havc been isolated: Trisaspidinol (8), from D. inaequalis; Pentherin‐I (not quitc pure) and Pentherin‐I1 (hypothetical partial formula 25), from D. pentheri. Pentherin‐I is also present in D. sp. RBF‐71/885. Chemical and cytological results are compatiblc with the hypothesis that the latter is an allotetraploid derived from the diploids 6 and 7. The chemical patterns of 6, 7 and 8 show similarities to that of D. manniana, which in turn also shows similarities to the European D. filix‐mas. Dryopteris ‘dilatata’ from the Canary Islands is chemically different from Europcan D. dilatata s. str. in lacking para‐aspidin, while D. oligodonta gave results rather different from D. inaequalis or other East African species, and also from known European taxa.
Synthese von 3‐Oxacholestanen
Authors: Sandmeier Rudolf , Tamm Christoph 
Published: December 2004

AbstractSuccessive treatment of 5α‐cholestan‐3‐one (1) with O2 under basic conditions and then NaBH4 led to 5α‐3‐oxa‐cholestan‐2‐one (5). Analogous reactions with 5β‐cholestan‐3‐one (6) yielded 5α‐4‐oxa‐cholestan‐3‐one (7) and 5 ξ‐3‐oxa‐cholestan‐4‐one (8). 4‐Cholesten‐2‐one (10), which was prepared starting from 4‐cholesten‐3‐one, was isomerized by methanolic KOH to give a mixture of 5α‐cholest‐3‐en‐2‐one (11) and 5β‐cholest‐3‐en‐2‐one (12). 5β‐Cholestane‐2,3‐dione (17) was synthesized from 4β‐bromo‐5β‐cholestan‐3‐one (13). Ozonolysis of the dione 17 and subsequent NaBH4 reduction of the oxidation product gave both 5β‐2‐oxa‐cholestan‐3‐one (18) and 5β‐3‐oxa‐cholestan‐2‐one (19).
Electron‐Nuclear Double Resonance Study of Flavodoxin from Peptostreptococcus Elsdenii
Authors: Fritz J. , Müller F. , Mayhew S. G. 
Published: December 2004

AbstractThe proton electron‐nuclear double resonance (ENDOR) of the semiquinone of Peptostreptococcus elsdenii flavodoxin has been studied at – 155°. Studies with flavodoxin derivatives in which the natural coenzyme has been replaced by C(8)CD3,C(9)D, C(6,9)D2, and iso‐FMN2 have made it possible to unequivocally assign the ENDOR lines to C(8)CH3 and C(6)H.
Ansamycine, eine neuartige Klasse von mikrobiellen Stoffwechselprodukten
Authors: Prelog Vladimir , Oppolzer Wolfgang 
Published: December 2004

AbstractIsolation, structure elucidation, and biological properties of a novel class of microbial metabolites, ansamycins, are reviewed as background for the following papers. Structural similarities and differences of ansamycins (rifamycins, tolypomycin, streptovaricins, and geldanamycin) relevant to the common steps in their biogenesis are discussed.
Zuordnung des 13C‐NMR.‐Spektrums von Rifamycin‐S Aufgrund der selektiven Protonen‐Entkopplung
Authors: Fuhrer Hermann 
Published: December 2004

Abstract13C‐NMR. spectra of rifamycin‐S and some of its derivatives have been measured. A unambigous assignment of the signals, due to the hydrogen bearing 13C atoms, was possible with heteronuclear double resonance experiments. On the other hand the resonances of the quarternary 13C atoms could be ascribed only tentatively. 13C‐NMR. spectroscopy gives a more complete picture of the rifamycins, especially about the naphthoquinone chromophore, than previously obtained by 1H‐NMR.