bluuebunny/crossref_metadata_2025_split huggingface dataset:
Die Addition von Fluorcarbenen an Norbornadien: Eine Homo‐1,4‐addition
Authors: Jefford Charles W. , Kabengele Ntanda , Kovacs Josef , Burger Ulrich 
Published: December 2004

AbstractIt has been found that difluorocarbene undergoes extensive addition to the endo‐face of norbornadiene, yeilding the cheletropic adduct, 4.4‐difluorotetracyclo[3.3.0.02,8.03,6]‐octane. Similar behaviour has been observed for fluorochlorocarbene. Possible mechanisms to rationalize this novel behaviour of carbenes are discussed.
Haschisch‐Inhaltsstoffe. 7. Mitteilung. Synthese von (−)‐11‐Hydroxy‐Δ8‐6a, 10a‐trans‐Tetrahydrocannabinol
Authors: Petrzilka Theodor , Demuth Martin 
Published: December 2004

AbstractWhen (−)‐Δ8‐6a, 10a‐trans‐THC (THC = Tetrahydrocannabinol), in the form of its diacetate, was irradiated in the presence of oxygen and a sensitizer, followed by reduction with NaBH4, three allylic alcohols were formed: (−)‐8α‐and (−)‐8β‐hydroxy‐Δ9,11‐THC (proportion 3:1) and (−)‐9α‐hydroxy‐Δ7,8‐THC. Acetylation of the epimeric 8‐hydroxy‐compounds with Ac2O/pyridine gave the corresponding diacetates.When (−)‐Δ8‐6a, 10a‐trans‐THC, in the form of its tetrahydropyranyl derivative, was heated with m‐chloroperbenzoic acid, the two epimeric 8,9‐epoxides were formed in equal amounts. These compounds, on treatment with butyllithium, afforded (−)‐8α‐ and (−)‐8β‐hydroxy‐Δ9,11‐ 6a, 10a‐trans‐THC‐tetrahydropyranylether. After removing the protecting group and treatment with Ac2O/pyridine the same diacetates, as formed by photooxygenation of (−)‐Δ8‐THC‐acetate, were obtained as a 1:1‐mixture.On heating these epimeric diacetates to 290° they underwent allylic rearrangement to (−)‐11‐acetoxy‐Δ8‐THC‐acetate. From this (−)‐11‐hydroxy‐Δ8‐6a, 10a‐trans‐THC was obtained by treatment with LiAlH4.
Stereoselective Effects in Reactions of Metal Complexes III. Asymmetric hydrogenation of 5, 7, 7, 12, 14, 14‐hexamethyl‐1, 4, 8, 11‐tetraazacyclotetradeca‐4, 11‐diene‐nickel (II)
Authors: Wermeille Maurice , Sledziewska Ewa , Bernauer Klaus 
Published: December 2004

AbstractThe catalytic hydrogenation in acidic solution (pH ∼ 2) of the title compoundIn order to represent this and the related compounds by meaningful abbreviations, we shall adopt the numerotation system proposed in the literature [8] [12]. The complete abbreviation of the title compound is [Ni(5, 7, 7, 12, 14, 14‐Me6‐[14]‐4, 11‐diene‐1, 4, 8, 11‐N4)]2+. As in the present work the 14‐membered ring system with six methyl groups remains unchanged, we shall use [Ni(4, 11‐dieneN4)]2+ and [Ni(4, 11‐aneN4)]2+ and [Ni(4, 11‐aneN4)]2+ for the complex with the unsaturated and saturated ligand, respectively.
[Ni(4, 11‐dieneN4)]2+ (I) has been studied. The reaction yields only C‐meso‐ 5, 7, 7, 12, 14, 14‐hexa‐methyl‐1, 4, 8, 11‐tetraaza‐cyclotetradecane‐nickel (II) (C‐meso‐[Ni(4, 11‐aneN4)]2+), when meso‐[Ni(4, 11‐dieneN4)]2+ is the starting material. Rac‐[Ni(4, 11‐dieneN4)]2+ yields the unstable α‐C‐rac‐[Ni(4, 11‐aneN4)]2+. When optically active [Ni(4, 11‐dieneN4)]2+ is reduced, optically active α‐[Ni(4, 11‐aneN4)]2+ is obtained, which in neutral or basic solution shows mutarotation due to conversion into optically active β‐[Ni(4, 11‐aneN4)]2+ no racemization is observed. Reaction with cyanide ions yields the optically active free tetramine ligand.The reaction mechanism of this asymmetric synthesis is discussed.
Edman‐Abbau als analytische methode in der ‘Solid phase’‐Peptidsynthese. Vorläufige Mitteilung
Authors: Fankhauser Peter , Fries Peter , Stahala Peter , Brenner Max 
Published: December 2004

AbstractThe systematic analysis of solid phase peptide synthesis by Edman degradation becomes possible by the development of a technique (high pressure liquid chromatography) for the determination of phenylthiohydantoins in trace amounts. By its qualitative beside the quantitative results the degradation method offers the possibility to follow formation and propagation of failure sequences over more than one synthetic cycle. Scope and limitations of the method are discussed.
Über Pterinchemie. 48. Mitteilung. Zur Herstellung und analytischen Charakterisierung reiner, hydrierter Pterine
Authors: Weber Rudolf , Frick Willi , Viscontini Max 
Published: December 2004

AbstractZur Abklärung von stereochemischen und rückoxydativen Problemen an vier verschiedenen methylsubstituierten 5,6,7,8‐Tetrahydropterinen wurden diese durch Umkristallisation gereinigt und die Reinheit der kristallinen Substanzen durch DC. in basischem Milieu unter Stickstoff, GC., NMR. und MS. festgestellt. Die reinen Substanzen wurden silyliert und wiesen je nach Reaktionsbedingungen verschiedene Silylierungsgrade auf. Die erhaltenen Derivate wurden durch kombinierte GC./MS. getrennt und identifiziert. Der Ort der Silylierung im hydrierten Pyrazinring wird vorwiegend von sterischen Faktoren bestimmt und erweist sich als unabhängig von der Basizität der reaktiven Zentren. Das Gemisch von vier Tetrahydro‐ und zwei Dihydropterinen konnte durch hochauflösende Glaskapillarchromatographie getrennt werden.
Formation and Properties of Losod, a New Sodium Zeolite
Authors: Sieber Werner , Meier Walter M. 
Published: December 2004

AbstractLosod, a new type of crystalline hydrated sodium aluminosilicate, Na12Al12Si12O48 · q H2O, has been prepared from reaction mixtures containing bulky quaternary alkylammonium ions, particularly azonia‐spiro[4.4]nonane, besides sodium ions. Losod crystallizes from batches with a low sodium content (Na/Al ≤ 1 and Si/Al ≈︁ 1). The quaternary ammonium hydroxide primarily serves as a source of hydroxide ions and is not incorporated into the zeolite crystals. These bulky bases provide a useful means for controlling the alkalinity of the system independently of the concentration of the necessary cations built into the zeolite.The crystals of Losod are hexagonal (a = 12.91 and c = 10.54 Å) and the proposed framework structure shows a polytypic relationship to sodalite and cancrinite. Losod has reversible sorption and ion exchange properties typical of a small‐pore zeolite and in essential agreement with the proposed structure.
Substituent Increments for the 1H‐NMR. Chemical Shifts of the 18‐ and 19‐Methyl Protons of Steroids. Part I: 9β, 10α(Retro)‐Steroids
Authors: Englert Gerhard , Arnold Wolf , Els Hans , Fürst Andor , Meier Arthur , Meister Walter 
Published: December 2004

AbstractThis paper reports 261 substituent increments for the 1HNMR. chemical shifts (solvent: CDCl3) of the 18‐ and 19‐methyl protons of 9β, 10α(retro)‐steroids relative to 5β,9β,10α,‐androstane. The increments were calculated by a least‐squares procedure from 1334 spectra of 759 different steroids.
Carotinoid‐Glycoside. 1. Mitteilung. Partialsynthese und Charakterisierung von Zeaxanthin Mono‐ und Diglucosid
Authors: Pfander Hanspeter , Hodler Martin 
Published: December 2004

AbstractPeracetyliertes Zeaxanthin Mono‐ und Diglucosid sowie die entsprechenden freien Glucoside wurden partialsynthetisiert und mit Hilfe von UV./VIS.‐, IR.‐, Massen‐ und NMR.‐Spektren identifiziert. Mit den kristallinen freien Glucosiden wurden anschliessend Beständigkeitsversuche durchgeführt.Die Partialsynthese erfolgte aus α‐Acetobromglucose und Zeaxanthin (3,3′‐Dihydroxy‐β,β‐carotin) nach der Methode von Koenigs & Knorr. Die freien Glucoside wurden durch Verseifen der peracetylierten Verbindungen in methanolischem Kaliumhydroxid erhalten.Die kristallinen freien Glucoside liessen sich in Mengen von ungefähr 100 ppm (Monoglucosid) und 800 ppm (Diglucosid) in Wasser lösen. Die wässerigen Lösungen erwiesen sich als sehr beständig gegen Lichteinwirkung und Kontakt mit Luftsauerstoff. Das Diglucosid erwies sich sowohl gegenüber der sauren (pH 3) als auch gegenüber der basischen (pH 9) Hydrolyse als beständig.
Über Pterinchemie. 49. Mitteilung. Eine neue Synthese von 5‐Formyl‐6, 7‐dimethyl‐5,6,7,8‐tetrahydropterin und 5,6,7‐Trimethyl‐5,6,7,8‐tetrahydropterin
Authors: Bieri Jost H. , Viscontini Max 
Published: December 2004

AbstractStarting with 5‐formyl‐6,7‐dimethyl‐5,6,7,8‐tetrahydropterine (II), a new synthesis of 5,6,7‐trimethyl‐5,6,7,8‐tetrahydropterine (III) is described. Thereby the chemical behaviour of the 5‐formyl group in II is investigated, in order to enable the unequivocal differentiation between formylation at position 5 and at position 10 in folic and tetrahydrofolic acid derivatives. 13C‐NMR. spectra of II and III are discussed.
Spezifisch π→π*‐induzierte Reaktionen von γ‐Dimethoxymethylcyclohexen‐2‐onen: 1,3‐Umlagerung und Wasserstoffabstraktion durch das α‐Kohlenstoffatom
Authors: Gloor Jean , Schaffner Kurt 
Published: December 2004

AbstractWhen α,β‐unsaturated γ‐dimethoxymethyl cyclohexenones are excited to the S2(π,π*) state, certain unimolecular reactions can be observed to compete with S2 → S1 internal conversion. These reactions do not occur from the S1(n,π*) or the lowest T(π,π* and n,π*) states. They comprise the radical elimination of the formylacetal substituent (cf. 8, 9 → 32 + 33), γ → α formylacetal migration (cf. 6 → 27, 8 → 30, 9 → 34, 12 → 37), and a cyclization process involving the transfer of a methoxyl hydrogen to the α carbon and ring closure at the β position (cf. 6 → 28, 8 → 31, 12 → 38, 20 → 40 + 41).The quantum yield of the ring closure 20a → 40a + 41a is 0.016 at ≤ 0.05M concentration. It is independent of the excitation wavelength within the π→π* absorption band (238–254 nm), but Φ (40a + 41a) decreases at higher concentrations. According to the experimental data the reactive species of these specifically π→π*‐induced transformations is placed energetically higher than the S1(n,π*) state, and it is either identical with the thermally equilibrated S2(n,π*) state, or reached via this latter state.The linear dienone 14 undergoes a similar π→π*‐induced cyclization (→ 42) whereas the benzohomologue 26 proved unreactive, and the dienone 22 at both n → π and π→π* excitation only gives rise to rearrangements generally characteristic of cross‐conjugated cyclohexadienones.
Structure of a Tricyclic Photoproduct C15H24O3 by X‐Ray Analysis
Authors: Bernardinelli Gérald , Gerdil Raymond 
Published: December 2004

AbstractThe crystal structure of the photoproduct 1 (C15H24O3; monoclinic, a = 7.682, b = 14.448, c = 12.925 Å, β = 108.4°; space group P21/c, Z = 4) has been determined by X‐ray analysis. The structure was solved by direct methods and the positions of all hydrogen atoms were obtained from a difference synthesis. The final R factor is 0.049. The polycyclic skeleton of 1 consists of a trans‐decalone ring system axially fused to an oxolane ring in a conformation intermediate between the envelope and twist form. Strong intramolecular non‐bonded interactions are observed among the substituent atoms.
Synthesis and Structure of Tris (2′‐[2‐phenyl‐1,3‐dioxolano])‐chromium(III)
Authors: Daly John J. , Sanz Francisco , Sneeden Raymond P. A. , Zeiss Harold H. 
Published: December 2004

AbstractTris(2′‐[2‐phenyl‐1,3‐dioxolano])chromium(III) 3 has been synthesised and has been shown to have the cis (or fac) configuration 3a by X‐ray analysis: the CrC bond length is 2.037 (10) Å.
Automerisierung von 1,3,5,5‐Tetramethylcyclohexa‐1,3‐dien. Vorläufige Mitteilung
Authors: Baumann Bruno C. , Dreiding André S. 
Published: December 2004

Abstract1,3,5,5‐Tetramethylcyclohexa‐1,3‐diene, specifically deuterated in all positions except the gem.‐dimethyl groups (11), was synthesized and found to undergo a rearrangement in the gas phase at 560°, which leads to a statistical distribution of the 6 hydrogen atoms to all 16 positions. This shows that the title compound (2) automerizes under these conditions and that the reaction proceeds via a series of ring openings (to 5) followed by degenerate [1,7]‐H‐shifts and rig closures (back to 2) rather than via [1,5]‐CH3‐shifts. It is suggested that the previously studied rearrangement of 5,5‐dimethylcyclohexa‐1,3‐diene (1) to 1,5‐dimethylcyclohexa‐1,3‐diene (3) takes its course by the same reaction pathway.
Vinca alkaloids XXXIV. Preparation of des‐Na‐methyl‐vindoline by microbiological conversion of vindoline, a major alkaloid from Vinca roseaL
Authors: Neuss Norbert , Fukuda D. S. , Brannon D. R. , Huckstep L. L. 
Published: December 2004

AbstractThe conversion of vindoline (II) using S. albogriseolus led to the isolation of several compounds including des‐Na‐methyl vindoline (III) in 8–10% yield.
Carotinoid‐Glykoside 2. Mitteilung Untersuchungen zur Carotinoid‐Zusammensetzung im Safran
Authors: Pfander Hanspeter , Wittwer Fritz 
Published: December 2004

AbstractIn der vorliegenden Arbeit wurde der Äthanolextrakt (70proz.) von Safran naturalis untersucht und die drei Hauptprodukte isoliert. Die kristallisierten Verbindungen wurden in natürlich vorkommender und in peracetylierter Form mit Hilfe von UV./VIS.‐, IR.‐, NMR.‐ und Massen‐Spektren charakterisiert. Der Zuckernachweis in den drei verseiften Komponenten erfolgte mittels Papier‐, Dünnschicht‐ und Gas‐Chromatographie. Bei den drei Verbindungen handelt es sich um Crocin = Crocetin‐di‐(β‐D‐gentiobiosyl)‐ester (I), Crocetin‐(β‐D‐gentiobiosyl)‐(β‐D‐glucosyl)‐ester (II) und Crocetin‐di‐(β‐D‐glucosyl)‐ester (III). Die Vergleichsspektren der partialsynthetisierten, peracetylierten Derivate Crocetin‐di‐(2,3,4,8,9,10,12‐hepta‐O‐acetyl‐β‐D‐gentiobiosyl)‐ester (IV) und Crocetin‐di‐(2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucosyl)‐ester (VI) bestätigen die Strukturen der gefundenen Verbindungen.
MO‐Calculation of the Optical Activity of Oligopeptides. II. Open‐chain conformations. Comparison with some cyclic systems
Authors: Iseli Max , Geiger Rudolf , Wagnière Georges 
Published: December 2004

AbstractUsing the Frozen Core (FC) MO procedure described in a previous communication, we have computed the long‐wavelength chiroptic properties of oligopeptides in the parallel‐chain (PC) pleated sheet conformation, in the poly (L‐proline) I and poly (L‐proline) II conformations. The main features of the computed results are: (a) In the PC pleated sheet conformation the π–π* transition with the highest positive rotatory strength appears at shorter wavelength than the π–π* transition with highest negative rotatory strength and is polarized mainly perpendicularly to the chain axis. There is an analogy between the computed PC pleated sheet spectrum and that calculated for a cyclohexapeptide of low symmetry, in a conformation which is probably stabilized by intra‐annular hydrogen bonds. (b) In the polyproline I conformation the computed π–π* transition with highest positive rotatory strength is also the longest‐wavelength π–π* transition and is polarized mainly along the helix axis. There is an analogy between this spectrum and that calculated for cyclo(tri‐L‐proline) of symmetry C3. (c) The poly‐proline II CD. spectrum may be qualitatively reproduced only by invoking very strong n – π interaction. The local n –π mixing parameter Λ must take on values ⪖3 eV, which is of the order of a nearest‐neighbor core resonance integral between atomic 2p orbitals of same spatial orientation. The question concerning the structural reasons for this situation is raised. As far as comparisons with experimental data are possible, qualitative agreement is obtained.
Fermentation of Fragrances: Biotransformation of β‐Ionone by Lasiodiplodia theobromae
Authors: Krasnobajew Victor , Helmlinger Daniel 
Published: December 2004

AbstractPre‐grown mycelia of Lasiodiplodia theobromae ATCC 28570 transform β‐ionone (1) into a large variety of metabolites, by mainly degrading the side‐chain of the β‐ionone molecule by a C2‐unity. The enzyme system responsible for this degradation is proposed to be an oxygenase, which gives rise to the formation of the main product β‐cyclo‐homogeraniol (8) in analogy to a Baeyer‐ Villiger oxidation. Further enzymic actions of Lasiodiplodia such as hydrogenations and hydroxylations lead to an accumulation of several not yet described β‐ionone metabolites.
Synthése totale d'α‐disaccharidyles de tridésoxy‐2,5,6‐streptamine apparentés aux aminosides à partir du maltose et du lactose
Authors: Rolland Nicole , Vass Georges , Cleophax Jeanine , Sepulchre Anne‐Marie , Gero Stephan D. , Cier André 
Published: December 2004

Total synthesis of α‐disaccharidyl‐2,5,6‐trideoxy‐streptamines related to aminoglycoside antibiotics derived from maltose and lactoseThe synthesis of the hitherto unknown 4‐O‐substituted α‐linked pseudo‐tri‐saccharides 1,2 and 3 is described. The key intermediates required in the reaction sequence are the glycals 12, 13 and 14, prepared from maltose, lactose and the chiral ditosyloxy‐cyclohexanol 15, readily accessible from quinic acid. The pivotal step in the reaction's scheme ‐ a stereospecific α‐glycosylution procedure ‐, is an acid‐catalyzed addition of the alcohol 15 to the glycals 12, 13 and 14 leading to the corresponding 2,3‐unsaturated trisaccharides. The latter compounds were transformed to the target α‐glycosides of 2,5,6‐trideoxystreptamine 1, 2 and 3 which were devoid of significant antibacterial activity. These results indicate that the presence of an ether linkage at the position 4′ is probably critical for antibacterial activity.
Makrocyclische Benzolactone durch Ringerweiterung von 2‐Nitrocycloalkanonen
Authors: Stach Hans , Hesse Manfred 
Published: December 2004

Macrocyclic Benzolactones by Ring Enlargement of 2‐NitrocycloalkanonesReaction of 2‐nitroalkanones with 1,4‐benzoquinone in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐en gave (hydroxybenzo)nitrolactones of general formula 6 (Scheme 1). The transformation involves a Michael reaction, aromatization, and ring enlargement via a five‐membered intermediate. The (hydroxybenzo)nitrolactones were converted to the already known (acetoxybenzo)oxolactones 15–17. The characteristic mass spectral behavior of the ring‐enlarged products is discussed.
Analytic and preparative resolution of recemic γ‐ and δ‐lactones by chromatography on cellulose triacetate. Relationship between elution order and absolute configuration
Authors: Francotte Eric , Lohmann Dieter 
Published: December 2004

AbstractEnantiomers of various chiral five‐ and six‐membered‐ring lactones, Which are important classes of compounds (flavour and Pheromone components, key intermediates in the synthesis of biologically active substances) have been separated chromatographically on the chiral phase cellulose triacetate, crystallographic form I (CTAI). For different series of five‐membered‐ring lactones, relationships have been found between the elution order of the enantiomers and their absolute configuration. Preparative resolutions of γ‐Phenyl‐γ‐butyrolactone (1) and of the Pheromone component 5b have been carried out to demonstrate the applicability of the method to g‐scale separations.
Chemie von a‐Aminonitrilen. Aldomerisierung von Glycolaldehyd‐phosphat zu racemischen Hexose‐2,4,6‐triphosphaten und (in Gegenwart von Formaldehyd) racemischen Pentose‐2,4‐diphosphaten: rac‐Allose‐2,4,6‐triphosphat und rac‐Ribose‐2,4‐diphosphat sind die Reaktionshauptprodukte
Authors: Müller Daniel , Pitsch Stefan , Kittaka Atsushi , Wagner Ernst , Wintner Claude E. , Eschenmoser Albert , Ohlofjgewidmet Güntner 
Published: December 2004

Chemistry of α‐Aminonitriles. Aldomerisation of Glycolaldehyde Phosphate to rac‐Hexose 2,4,6‐Triphosphates and (in Presence of Formaldehyde) rac‐Pentose 2,4‐Diphosphates: rac‐Allose 2,4,6‐Triphosphate and rac‐Ribose 2,4‐Diphosphate Are the Main Reaction ProductsGlyclaldehyde phosphate aldomerizes in aqueous NaOH solution to a product mixture containing the racemates of the two diastereoisomeric tetrose 2,4‐diphosphates and eight hexose 2,4,6‐triphosphates. At room temperature in the absence of air and after 7 days, a solution 0.08Min glycolaldehyde phosphate (=formylmethyl dihydrogenphosphate)and 2M in NaOH gives products, in up to 80% yield, with a tetrose/hexose derivative ratio of ca 1:10 and with rac‐allose, 2,4,6‐triphosphate comprising up to 50% of the mixture of sugar phosphates. When the reaction is run under the same conditions but in the presence of 0.5 mol‐equiv. of formaldehyde, sugar phosphates are formed in up to 45% yield, with pentose 2,4‐diphosphates now predominating over hexose triphosphates by a ration f 3:1 rac‐Ribose 2,4‐diphosphate is found to be the major component, the ratios am ribose, arabinose, lyxose, and xylose 2,4‐diphosphates being 52:14:23:11 in a representative experiment. The pentose diphosphates are constitutionally stable under the reaction conditions (observed for 23 weeks), but the diastereoisomeric ratios slowly change with time (tc 22:34:30:14 after 23 weeks), showing that ribose 2,4‐diphosphate is not the thermodynamically favored diastereoisomer. The observed product distributions in both the pentose and the hexose series (after 1 week) reveal an aldolization mode that is preferentially erythro in the product‐determining step (the reaction of glycolaldehyde phosphate as its enolate with glycerinaldehyde 2‐phosphate and tetrose 2,4‐diphosphate, respectively). An attempt is made to rationalize both this fact and the kinetic predominance of ribose 2,4‐diphosphate in the pentose series and allose 2,4,6‐triphosphate in the hexose series. Their configuration along the C‐chain can be interpreted as corresponding to a minimum number of 1‐5 repulsions in the packing of phosphate and OH substituents and minimal steric interaction between substituents at the reaction centers in the transition state of the product‐determining step. The aldomerization of glycolaldehyde phosphate in the presence of formaldehyde is a variant of the formose reaction, It avoids the formation of complex formose product mixtures, largely as a consequence of the fact that aldoses which are phosphorylated at the C(2)
Reinvestigation of the Conformation of Cyclosporin A in Chloroform
Authors: Kessler Horst , Köck Matthias , Wein Thomas , Gehrke Matthias 
Published: December 2004

AbstractNew investigations of cyclosporin A in CDCl3 have been performed to obtain additional and more accurate distance restraints than utilized in our previous studies of cyclosporin A. Build‐up rates at 600 MHz using 6 different mixing times at low temperatures (252.5 K) were determined and transformed into distances using the two‐spin approximation. With the new distance restraints in the MD simulations using the GROMOS package, we can unambiguously conclude the presence of a βII′‐turn. The new structure resembles the X‐ray structure more than the structure previously determined, especially regarding the orientation of the MeBmt side chain. In the new structure and in the solid state, the side chain is folded over the backbone (although there are substantial differences in the χ1 torsion), in contrast to the old structure, where the side chain is extended away from the backbone.
A Novel, Degraded Polyketidic Lactone, Leptosphaerolide, and Its Likely Diketone Precursor, Leptosphaerodione. Isolation from Cultures of the Marine Ascomycete Leptosphaeria oraemaris (LINDER)
Authors: Guerriero Antonio , D'Ambrosio Michele , Cuomo Vincenzo , Pietra Francesco 
Published: December 2004

AbstractAcetone extraction of cultures of the marine ascomycete Leptosphaeria oraemaris (LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide ( = (+)‐7‐[(1E)‐l,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐3‐methoxybenzo[1,2‐b:5,4‐c′]dipyran‐2(9H)‐one; (4+)‐8) besides the o‐dihydroquinone 3‐[(1E)‐1,3‐dimethylpent‐1‐euyl]‐8,10‐dihydroxy‐7‐methoxy‐8‐(2‐oxopropyl)‐1H‐naphtho[2,3‐c]pyran‐9(8H)‐one (1) as a 10:9 mixture of epimers. retro‐Aldol reaction of 1 gave leptosphaerodione ( = (−)‐3‐[(1E)‐1,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐7‐methoxy‐1H‐naphtho[2,3‐c]pyran‐8,9(8H)‐dione; (−)‐6) which was also present in small amounts in the extracts and which gave 1 on reaction with acetone. It is thus likely that 1 is an artefact of the extraction by acetone. Biogenetically (+)‐8 might derive from (−)‐6 via an unusual oxidation with loss of CO2.