bluuebunny/crossref_metadata_2025_split huggingface dataset:
[2 + 2]‐Cycloadditions to Strained Bridgehead Olefins. II. Diphenylketene
Authors: Becker Konrad B. , Hohermuth Martin K. , Rihs Grety 
Published: December 2004

AbstractThe strained bridgehead olefins bicyclo [3.3.1]non‐1‐ene (1), bicyclo [4.2.1 ]non‐1(8)‐ene (2), and bicyclo [4.2.1]non‐1‐ene (3), and the comparable monocyclic (E)‐1‐methylcyclooctene (4) react with diphenylketene (6) to give a single cycloadduct 7, 8, 9 and 10, respectively, in which the diphenyl‐substituted C‐atom is bound to the bridgehead. The structure of the cyclobutanone 8 has been determined by X‐ray analysis of a twin crystal obtained by crystallization with spontaneous enrichment of enantiomers.
Visible Light Induced Generation of Hydrogen from H2S in CdS‐Dispersions, Hole Transfer Catalysis by RuO2
Authors: Borgarello Enrico , Kalyanasundaram Kuppuswamy , Grätzel Michael , Pelizzetti Ezio 
Published: December 2004

AbstractIllumination of US‐dispersions by visible light in solutions containing H2S or sulfide ions leads to efficient generation of hydrogen and sulfur. Very small quantities of RuO2 deposited on the CdS‐particles improve markedly the quantum yield of H2‐formation for which the optimum value obtained so far is ϕ = 0.35 ± 0.1. The effect of RuO2 is attributed to catalysis of hole transfer from the valence band of CdS to H2S or sulfide in solution.
Heterocyclische und carbocyclische 12‐π‐ and 14‐π‐Molekülsysteme, 47. Mitteilung. Herstellung von 7, 9‐Dimethyl‐4, 5‐dihydro‐3 H‐benz [cd]‐ azulen‐3‐on and 7,9‐Dimethyl‐3H‐benz [cd]azulen‐3‐on. Eine einfache Synthese eines Azulenopseudophenalenons
Authors: Neidlein Richard , Kramer Walter 
Published: December 2004

Heterocyclic and Carbocyclic 12‐π‐and 14‐π‐Systems, 47th Commnunication1. Synthesis of 7,9‐Dimethyl‐4,5‐dihydro‐3H‐benz[cd]azualene‐3‐one and 7,9‐Dimethyl‐3H‐benz[cd]azulene‐3‐one. A Simple Synthesis of Azulenopseudophenalenons4, 6, 8‐Trimethylazulene (3) reacts after metalation with lithiumdiisopropyl‐amide in ether with bromoacetic acid to the 6, 8‐dimethylaltulene‐4‐propionic acid (4), which undergoes cyclization to the 7, 9‐dimethyl‐4, 5‐dihydro‐3H‐benz [cd]‐azulene‐3‐one (5) in the presence of p‐toluenesulfonic acid; oxidation of 5 with 2, 3‐dichloro‐5, 6‐dicyanobenzoquinone yields 7, 9‐dimethyl‐3H‐benz [cd]azulene‐3‐‐one (1b). Alkylation of 1b with triethyloxonium tetrafluoroborate in CH2C12 gives the 3‐ethoxy [cd]benzazulenium tetrafluoroborate (6).
d5‐Reactions of Doubly Deprotonated γ,δ‐Unsaturated Carbonyl Derivatives with Electrophiles. A Novel Approach to the Synthesis of Tetrahydrofuran and Tetrahydropyran Derivatives
Authors: Seebach Dieter , Pohmakotr Manat , Schregenberger Christian , Weidmann Beat , Mali Raghao S. , Pohmakotr Srisuke 
Published: December 2004

AbstractThe dienone‐dianion derivatives 1 react with all types of electrophiles tested (alkyl halide, silyl chloride, ester, ketone, aldehyde, epoxide) to give β, γ‐unsaturated carbonyl compounds of type A (see Formulae 2–6, 13, 14 and Tables 1–5). The α‐ and β‐hydroxyalkylation products obtained from 1a–1d can be converted to tetra‐hydrofuran and tetrahydropyran derivatives 7 and 16, respectively (Tables 1 and 2), those from the sulfur analogues 1e and 1f to ketene thioacetals 9 and to dienone derivatives 10 and 12. The t‐butyl and α‐hydroxy‐ketones are cleaved to give nitriles, amides, carboxylic acids and esters (Formulae 16‐25). The reagents 1 allow to synthesize products with distant functional groups in one step (cf. 1,8‐diketones 14 and Formulae 26–30); they correspond to the d5‐synthons 31–33; in Table 6, they are compared with other d5‐reagents.
Über die Depolymerisierung von Poly‐(R)‐3‐hydroxy‐buttersäureester (PHB)
Authors: Seebach Dieter , Züger Max 
Published: December 2004

On the Depolymerization of Poly‐(R)‐3‐hydroxy‐butanoate (PHB)From cell‐free PHB or from dried cells of Alcaligenes eutrophus H 16, which had been grown in an aqueous fructose solution, enantiomerically pure methyl, ethyl, butyl or β‐methoxyethyl (R)‐3‐hydroxy‐butanoates are obtained in yields ranging from 75–90% (0.1 to 70 g scale). The depolymerization is achieved by heating the PHB‐containing materials to temperatures of 80–160° in the corresponding alcohol with or without the cosolvent dichloroethane in the presence of either sulfuric acid or tetraethoxytitanium catalyst. Since (S)‐3‐hydroxy‐butanoates are also readily obtained (by yeast reduction of aceto‐acetates), starting materials derived from 3‐hydroxy‐butyric acid now belong to the especially useful group of synthetic building blocks which are available in both enantiomeric forms.
Linear‐Reactor‐IR.‐Matrix and Microwave Spectroscopy of the System O3/NO2/(Z)‐2‐Butene
Authors: Dommen Joseph , Forster Martin , Ruprecht Heidi , Bauder Alfred , Günthard Hans‐Heinrich 
Published: December 2004

AbstractInvestigation of the formation of complex reaction products in the gas‐phase system O3/NO2/(Z)‐2‐butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas‐phase ozonolysis of (Z)‐2‐butene, the following products were identified; N2O5, HNO3, HNO4, CH3NO2, CH3ONO, CH3COONO2 and CH3COO2NO2 (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N2O5, HNO3. CH3COONO, CH3COONO2 required for reference purposes are presented. It is shown that PAN‐formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NOx‐containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.
The ESR. Spectrum of the Radical Anion of 1,1,2,2,9,9,10,10‐Octafluoro [2.2]paracyclophane
Authors: Gerson Fabian , Ohya‐Nishiguchi Hiroaki , Plattner Georges 
Published: December 2004

AbstractThe radical anion of 1,1,2.2,9,9,10, 10‐octafluoro[2.2]paracyclophane (1) has been generated by electrolytic reduction of 1 in 1,2‐dimethoxyethane (tetrabutylammonium perchlorate as the supporting salt). The hyperfine coupling constants of the eight 19F‐nuclei and the eight protons, af = 3.35 and aH ≈ 0.10 mT, are qualitatively reproduced by INDO. calculations. According to these calculations, the singly occupied orbital of 1⊖ can be represented by an Ag‐combination of two ‘symmetric’ benzene LUMO's, with a substantial transfer of spin population into the 2s‐AO's of the F‐atoms. Line‐width alternation in the ESR. spectrum of 1⊖ indicates an ion pairing of the radical anion with its counter‐ion Bu4N⊖. The energy barrier to the migration of the cation between two equivalent sites at the radical anion is determined as 14±2 kJ/mol.
Transition metal complexes with bidentate ligands spanning trans‐positions. XII. The preparation and properties of complexes trans‐[MX2 (1)] and trans‐[PtHCl (1)] (M = Ni, Pd and Pt; X = Cl and NCS; 1 = ditertiary phosphine)
Authors: Kapoor Pramesh N. , Pregosin Paul S. , Venanzi Luigi M. 
Published: December 2004

AbstractComplexes [MX2(1)] (M = Ni, Pd and Pt; X=Cl and NCS; 1 = 2,11‐bis(dialkyl‐[or diaryl]phosphinomethyl)benzo[c]phenanthrene; alkyl = cyclohexyl t‐butyl; aryl = m‐tolyl, p‐anisyl and m‐CF3 C6H4) have been synthesized.An NMR. study of the t‐butyl complexes provides evidence for a “fan‐like” motion of the benzo[c]phenanthrene moiety over the plane of the complex.
Stereoselektive Totalsynthese von natürlichem Phytol und Phytolderivaten und deren Verwendung zur Herstellung von natürlichem Vitamin K1
Authors: Schmid Max , Gerber Fernand , Hirth Georges 
Published: December 2004

Steroselective Total Synthesis of Natural Phytol and Derivatives thereof; Use of these Compounds in the Synthesis of Natural Vitamin K1The Li2CuCl4‐catalyzed couplings of the easily accessible bifunctional C5 allylic acetates (E)‐18a and (E)‐18b with racemic hexahydrofarnesylmagnesium bromide ((3 RS/RS, 7 RS/SR)‐19a) proceed with high chemo‐ and stereoselectivity (≥98% (E)‐retention) to give the (2E, 7 RS/RS, 11 RS/SR)‐phytol derivatives 1a and 1b, respectively, in yields of 72–80% (Scheme 5). The same couplings performed with optically active hexahydrofarnesylmagnesium bromide (3 R, 7 R)‐19a yielded the (E)‐phytol derivatives of the natural series (7 R, 11R)‐1a and (7 R, 11 R)‐1b. Acid‐catalyzed hydrolysis of(2 E, 7 R, 11 R)‐1b gave natural phytol((2 E, 7 R, 11 R)‐1c) Friedel‐Crafts alkylation of ‘menadiol monobenzoate’ 11b with (2 E, 7 R, 11 R)‐1a or (2 E, 7 R, 11 R)‐1b gave the dihydrovitamine K1 derivative (2 E/Z, 7′ R, 11′R)‐12b ((E/Z)≈︁ 9:l). Conversion of configurationally pure (2 E, 7′ R, 11′ R)‐12b (yield 73%; obtained after chromatographic removal of the (Z)‐isomer) into natural vitamine K1 ((2 E,7′ R, 11′ R)‐2) was achieved in the usual way by saponification and oxidation with air.Some further investigations of the coupling reactions of bifunctional C5 allylic synthons with hexahydrofarnesylmagnesium bromide (3 RS/RS, 7 RS/SR)‐19a showed the outcome of these reactions to be critically dependent on the nature of the leaving group, the double‐bond geometry and the nature and concentration of the catalyst. Thus, the Li2CuCl4‐catalyzed couplings of (3 RS/RS,7 RS/SR)‐19a with the allylic halides 29a and 29c as well as with p‐toluenesulfonate 29b yielded besides the phytol derivatives 1a and 1b ‐ also the SN2′‐type products 30a and 30b (Scheme 8, Table 2); the same result was found for the coupling with the cis‐configurated allylic acetates (Z)‐18a and (Z)‐18b (Table 3). A similar loss of chemo selectivity as well as the loss of stereoselectivity in the coupling reactions of 19 with the bifunctional (E)‐olefins of type 18 was observed when the Li2CuCl4‐catalyst concentration was increased from 0.2 to 25 mol‐% or upon substitution of Li2CuCl4 by copper (I) chloride or iodide (Table 4).
Heterodiamantane und strukturell verwandte Verbindungen. IV. Pentacyclische Diäther der C12‐Reihe: 5,14‐Dioxapentaccology[7.5.0.02,6.03,13.04,10]terradecan,4,14‐Dioxapentacyclo[7.4.1.02,8.03n,11.05,10]tetradecan,3,11‐Dioxapentacyclo[8.3.1.02,8.04,13.07,12]tetradecan und 3,10‐Dioxapentacyclo[7.3.1.1.4,12.02,7.06,11]tetradecan (3,10‐Dioxadiamantan)
Authors: Ammann Willi , Pfund Holland A. , Ganter Camille 
Published: December 2004

Heterodiamantanes and Structurally Related Compounds. Part IV. The Pentacyclic C12‐Diethers 5, 14‐Dioxapentacyclo[7.5.0.02,6.03,13.04,10]tetradecane, 4,14‐Dioxapentacyclo[7.4.1.02,8.03,11.05,10]tetradecane, 3,11‐Dioxapentacyclo[8.31.02,8.04,13.07,12]tetradecane, and 3,10‐Dioxapentacyclo[7.3.1.14,12.02,7.06,11]tetradecane (3,10‐Dioxadiamantane)In connection with the studies on heterodiamantanes and structurally related compounds the four novel pentacyclic diethers 6–9 were prepared starting from the cyclopentadienone dimer 12, All five compounds have as common features a central carbocyclic 6‐membered ring with four axial alkyl substituents and two oxygen functions in 1,4‐positions. The required twelfth C‐ atom was introduced by dichlorocarbene addition to 11 (the rnonocarbene adduct of 12) (→ 10, Scheme 2). The two three‐membered rings in 10 had to be opened step wise. Controlled thermolysis of 10 yielded the chloride 13 and the acetate 14, respectively, from which the alcohols 16, 17 and 20 as well as the acetates 22 and 23 were obtained by reduction (Scheme 2). The remaining second ring was opened again thermally either to tricyclic compounds as 22 → 25 + 26, 23 → 27 + 28 or under simultaneous ether formation to tetra‐cyclic compounds as 16 → 29 + 30, 17 → 32 + 33, 20 → 34 + 35 (Scheme 3). The two compounds 29 and 30 were also obtained from 37, the dichlorocarbene adduct of the tricyclic C11‐ether 36 (Scheme 4). These tri‐ and tetracyclic compounds 25–30 and 32–35 were suitable intermediates for the syntheses of all four pentacyclic diethers 6–9.Diether 6 was prepared from 25, 26, 29 as well as 30 via 38 (Scheme 5), and from 29 by the route depicted in Scheme 6. By a procedure analogous to the latter one, diether 7 was obtained from 30 (Scheme 6). Diether 8 was the result of transformations starting from either 27, 28, 32 or 33 (Scheme 7). The synthesis of diether 9 (3,10‐dioxadiamantane), the thermodynamically most stable of the four diethers 6–9, was achieved in three different ways : ring closure starting from the highly substituted tricyclic compounds 25 and 26 (Scheme 9), skeletal rearrangement of the group‐A
The Novel Adamantane Isomer 2,5‐Trimethylenenorbornane (Tricycio‐[5.3.0.3,9]decane, 4‐Homotwistbrendane)
Authors: Känel Hans‐Ruedi , Capraro Hans‐Georg , Ganter Camille 
Published: December 2004

AbstractA synthesis of the novel C10H16 hydrocarbon 2,5‐trimethylenenorbornane (tricyclo[5.3.0.03,9]decane, 1), one of the 19 members of the ‘adamantaneland’, and its Lewis‐acid‐catalyzed rearrangement is described.
2‐Pyridylhydrazone als Carbonylderivate zur Steuerung der Fragmentierung in der Massenspektrometrie
Authors: Vetter Walter , Meister Walter 
Published: December 2004

2‐Pyridylhydrazones as Carbonyl Derivatives to induce Fragmentation in Mass SpectrometryIt was found that the 2‐pyridylhydrazone is a derivative of the carbonyl group, which is able to induce fragmentation of an alicyclic skeleton with an efficiency comparable to that of the tertiary amino group and the ethylene acetal group.
The Crystal structure of 2‐Diisopropylamino‐3,7‐dehydrotropone
Authors: Grieb Rita , Gray Robert W. , Dreiding André S. 
Published: December 2004

AbstractDie erste Röntgenstrukturanalyse eines 3,7‐Dehydrotropon (1)‐Derivates, nämlich von 2‐Diisopropylammo‐3,7‐dehydrotropon (4) zeigt das Ringsystem in 4 als planaren Bicyclus mit nahezu C2V‐Symmetrie. Dementsprechend enthalten Dehydrotropone formell zwei trans‐konfigurierte Doppelbindungen in einem 7‐gliedrigen Ring; auch das O‐Atom und das N‐Atom mit seinen Ligandatomen liegen in derselben Ebene wie die Ringatome. Die Bindung zwischen den beiden C‐Atomen, welche die Heteroatome tragen, (C(1) and C(2)), ist wesentlich langer (1,56 Å) als die anderen Bindungen im Ringsystem (1,37‐1,46 Å). Dies impliziert eine ‘push‐pull’‐π‐Elektronen‐Delokalisierung, in der auch das O‐und das N‐Atom involviert sind, und macht eine ‘aromatische’ Ring‐Delokalisierung weniger wahr‐scheinlich. Im Gegensatz zu 2‐(t‐Butyl)‐3,7‐dehydrotropon (3) existiert das 2‐Diiso‐propylamino‐3,7‐dehydrotropon (4) im Kristall als Monomeres, was dem stabili‐sierenden Einfluss der ‘push‐pull’‐Delokausierung zugeschrieben werden kann.
Diastereoselektive Synthese von β‐Methyl‐homoallylalkoholen durchlk‐Addition von (2‐Butenyl)triphenoxytitan an Aldehyde
Authors: Widler Leo , Seebaeh Dieter 
Published: December 2004

Diastereoselective Synthesis of β‐Methyl‐homoallylic Alcohols bylk‐Addition of (2‐Butenyl)triphenoxytitanium to Aldehydes(2‐Butenyl)triphenoxytitanium, prepared insitufrom (2‐butenyl)magnesium halogenide and chlorotriphenoxytitanium in tetrahydrofuran solution, adds to aldehydes withlike(Re,Re/Si,SiRe*,Re*) relative topicity in diastereoselectivities of 80–99%.
Über Pterinchemie 80. Mitteilung Die Herstellung von (6RS)Tetra‐ und (6RS)Pentaacetyl‐5,6,7,8‐tetrahydro‐L‐bioplerinen
Authors: Ganguly Subhendu Narayaa , Viscontini Max 
Published: December 2004

Preparation of (6RS)Tetra‐ and (6RS)‐Pentaacetyl‐5,6,7,8‐tetrahydro‐L‐biopterinesBoiling of (6RS) l′‐O,2′‐O,2‐N‐triacetyl‐5,6,7,8‐tetrahydro‐L‐biopterine in acetic anhydride as described in [2], leads to a mixture of the diastereoisomeric (6R)‐ and (65)‐l′‐O,2′‐O,2‐N‐,5,8‐pentaacetyl‐5,6,7,8‐L,‐biopterines. One of the diastereoisomers can be obtained as pure crystals. It corresponds to the pentaacetate of the natural (6R)‐ or (6S).,5,6,7,8‐tetrahydro‐L‐biopterine. For the preparation of the earlier described (6RS)‐ and (6S)‐tetraacetyl‐tetrahydro‐L‐biopterines [2] improved conditions are reported.
Totalsynthese von Nojirimycin
Authors: Vasella Andrea , Voeffray Robert 
Published: December 2004

Total synthesis of NojirimycinAddition of the nitrone 3 (from 8 and 9) to furane, followed by oxidation with OsO4 and then isopropylidenation gave the fully functionalized glycoside 12 (40% from 8) via the glycal 10 and the hemiacetal 11. Since the glycoside cleavage of 12, leading to 13 after benzyloxycarbonylation proceeded in a mediocre yield, and since the acetolysis of 12 giving 14 (69%) was not practical, compound 12 was transformed into the hydroxy ester 17 by sequential hydrogenolysis, hydrolysis and benzyloxycarbonylation (69% overall). The hydroxy ester 17 was lactonized to give 18 (87%). Reduction of 18 first with LiBH4 (97%) and then with H2/Pd gave the key compound 20 which was transformed into nojirimycin (1) and into 1‐deoxy‐nojirimycin (2) using prior art. The overall yield of 1 was 19.5%.
Stereospezifische Synthese einer neuen Morphin‐Teilstruktur
Authors: Haefliger Walter , Klöppner Edgar 
Published: December 2004

We describe here a synthesis of the morphine partial structures 28 and 36, and of their enantiomers, which uses 7‐methoxy‐benzofurancarboxylic acid as starting material. A key intermediate in this scheme is compound 15, which is converted, via 1,2‐ketone shift, into 22. This latter is stereospecifically reduced to the alcohol 24 and converted to the amide 25. The diastereomer of 25 is afforded by stereospecific introduction of a ethoxycarbonyl group in 15 to yield the β‐ketoester 31, followed by Curtius degradation of the acid 32 to the acylamine 34.An efficient method for removal of the methoxy group in methoxy‐dihydro‐benzofurans is presented (Scheme 9), as is the functionalization of the N‐atom in 27 with concurrent complex formation between the free hydroxy group and boric‐acid. The aromatization of the furan ring (Scheme 10) with DDQ gave the expected benzofuran derivative 30.
Preparation and Conformational Properties of Benzylpenicilloyl‐oligo‐L‐lysine Conjugates
Authors: Rolli Hanspeter , Lüscher Immanuel F. , Schneider Conrad H. , Toniolo Claudio , Bonora Gian Maria 
Published: December 2004

AbstractSelected oligo‐L‐lysine carriers and a poly‐L‐lysine were penicilloylated with benzylpenicillin. The resulting conjugates 2–6 were studied by IR. absorption in the solid state and circular dichroism measurements in solution. The IR. data demonstrate the lack of β‐structure formation even in medium‐sized peptides where such structures might be expected on the basis of previous studies on differently substituted oligo‐L‐lysines. Considerable proportions of right‐handed α ‐helical conformation are exhibited by the icosa‐L‐lysine and poly‐L‐lysine conjugates 5 and 6 in water and 2,2,2‐trifluoroethanol. Difficulties in obtaining fully penicilloylated conjugates are not related to the extent of α‐helical conformation in aqueous solution.
Molecular Quantum Beat Spectroscopy in External Fields as a Sensitive Probe of Excited State Properties
Authors: Lendi Karl 
Published: December 2004

AbstractThe new phenomenon of the external field dependence of quantum beats in polyatomic molecules is studied on a model which offers analytical formulas for a series expansion to lowest order in the field. A comparison with recent experiments on the magnetic field effect in biacetyl suggests that, in addition to the level shift the triplet deactivation is also strongly field‐dependent. New experiments are proposed.
A Note on Intramolecular Photochemical Cycloaddition of N‐substituted Dimethacrylimides
Authors: Alder Alex , Bühler Niklaus , Bellus Daniel 
Published: December 2004

AbstractThe intramolecular photochemical [2+ 2]‐cycloaddition of N‐substituted dimethacrylimides 1a and 1c, respectively, proceeds under conditions of direct irradiation (λ = 254 nm) as well as triplet photosensitization highly regioselectively yielding predominantly the «cross» bonding (head‐to‐tail) cycloadducts 3a and 3c, respectively, with a 3‐azabicyclo [3.1.1]heptane ring system.
2, 3‐Alkadiensäureester als Dienophile; Anwendung bei der Synthese von (+)‐(R)‐Lasiodiplodin
Authors: Fink Margot , Gaier Hans , Gerlacho Hans 
Published: December 2004

2,3‐Alkadienoates as Dienophiles, Application in the Synthesis of (+)‐(R)‐LasiodiplodinMethyl 2, 3‐alkadienoates 2 are shown to react at 80° with l, 1‐dimethoxy‐3trimethylsilyloxy‐l, 3‐butadiene (1) to give the adducts 3 in good yields. Rearrangement of 3, catalyzed by p‐toluenesulfonic acid or by sodium methoxide, affords the 6‐substituted methyl 4‐hydroxy‐2‐methoxybenzoates 4 (R  H, CH3, C6H5). An analogous reaction sequence starting with (‐)‐(11 R)‐dodeca‐2, 3‐dien‐11‐olide ((‐)‐6) and 1 leads, via the adduct (R)‐7, to (+)‐(R)‐lasiodiplodin ((+)−8) with properties identical to those of the natural product. The allene lactone (‐)‐6 was prepared by an intramolecular Wittig condensation of (R)−5, produced from (–)‐(R)‐9‐hydroxydecanoic acid.
Abkömmlinge der 3‐Chinolincarbonsäure mit Sauerstoffsubstitution in Stellung 4, 5 and 8: Synthese, Reaktionen, NMR.‐Studien
Authors: Link Helmut , Bernauer Karl , Englert Gerhard 
Published: December 2004

Derivatives of 3‐Quinolinecarboxylic Acid with Oxygen Substitution in Positions 4, 5 and 8: Synthesis, Reactions, NMR. StudiesStarting from either 1, 4‐dibenzyloxybenzene (7) or 2, 5‐dimethoxyaniline (16), synthetic routes have been developed to benzenoid and quinoid derivatives of 4‐oxo‐1, 4‐dihydro‐3‐quinolinecarboxylic acid with O‐bearing substituents in the positions 5 and 8 (compounds 12‐15, 19, 20, 23, and 24). With the 1‐ethyl‐4, 5, 8 trioxo acid 14 as a dienophile, a series of linear tricyclic diene adducts (29‐32) has been prepared, the structures of which were further modified by aromatization, reduction or dehydrogenation (compounds 33‐40). A series of benzenoid and quinoid compounds with an additional substituent in position 6 or 7 (Table 1) has been derived mainly from the quinone 14, primarily by addition of nucleophiles and eventually subsequent steps, and by aromatic electrophilic substitution of the 1‐ethyl‐5, 8‐dimethoxy acid 23. The substitution pattern of some of these compounds has been elucidated by detailed 13C‐NMR. studies (Table 2) and/or nuclear Overhauser‐effect studies (Table 3). Correlations, based essentially on chemical arguments, allowed to define the structures of most of the residual new compounds (Table 4).
Stoffwechselprodukte von Mikroorganismen. 218. Mitteilung. Versuche zur Strukturaufklärung von Niphimycin, 1. Teil. Reinigung und Charakterisierung der Niphimycine Iα und Iβ sowie Abbau mit Salpetersäure
Authors: Bassi Luciano , Joos Beda , Gassmann Peter , Kaiser Hans‐Peter , Leuenberger Heinz , Keller‐Schierlein Walter 
Published: December 2004

On the Structure Elucidation of Niphimycin, Part I. Purification and Characterization of the Niphimycins Iα and Ib̃; Degradation by Nitric AcidFrom a sample of niphimycin the pure components, niphimycin Iα and Ib̃, were isolated by column chromatography and droplet counter‐current chromatography. They were characterized by UV., IR., 1H‐NMR. (300 MHz) and 13C‐NMR. spectra. A vigorous degradation of niphimycin with nitric acid, followed by esterification with diazomethane, gave a complex mixture, from which many components could be isolated and identified. Several of the degradation products were synthesized, one of them (dimethyl 2,4‐dimethyladipate) in a stereospecific manner, establishing the configuration of two of the centers of chirality of niphimycin.Niphithricin was identified with copiamycin and yielded with nitric acid a degradation mixture very similar to that from niphimycin. The structures of the degradation products are in good agreement with a macrolide‐type structure of niphimycin and copiamycin.Further work for structure elucidation of niphimycin and copiamycin is in progress.