bluuebunny/crossref_metadata_2025 huggingface dataset:
The Chiral Glycine Enolate Derivative from 1‐Benzoyl‐2‐(tert‐butyl)‐3‐methyl‐1,3‐imidazolidin‐4‐one is Alkylated in the 5‐Position with Relative Topicitylk. Preliminary Communication
Authors: Seebach Dieter , Miller David D. , Müller Stefan , Weber Theodor
Published: December 2004

An overall enantioselective substitution of the R‐group of an α‐hydroxy‐ or α‐amino acid1[RCH(XH)COOH] by another R‐group is possible through heterocycles2obtained from1with pivaladehyde (1 → 7). Therac‐ and the (S)‐(+)‐heterocycles8(title compounds of type5) are prepared from glycine andO‐benzyl‐(S)‐serine, respectively. Their enolates (cf.9, type6) are alkylated with iodomethane, iodobutane, 2‐iodopropane, benzyl bromide, and acetone to give thetrans‐disubstituted imidazolidinones10with ≥ 95% diastereoselectivity. The configuration of the products is established by chemical correlation with alanine, phenylalanine, and valine.
Deoxy‐nitrosugars. 11th Communication. Reactions of 1‐C‐nitroglycosyl halides and 1‐C‐nitroglycosyl sulfones with dialkyl‐phosphite anions: Nucleophilic attack vs. single‐electron transfer
Authors: Meuwly Roger , Vasella Andrea
Published: December 2004

Treatment of the chloro‐nitro‐ribofuranose 7 with KPO(OMe)2 gave the O‐amino phosphate 8 (5 %) and the nitrile 9 (62 %). Compound 9 was also obtained by the reaction of 8 with KPO(OMe)2, and its structure was established by X‐ray analysis. Treatment of the chloro‐nitro‐mannofuranose 10, the bromo‐nitro‐ribofuranose 14, or the bromo‐nitro‐mannofuranose 16, respectively, with the K or Na salt of HPO(OMe)2 lead also to O‐amino phosphates and nitriles. The (1‐C‐nitroglycosyl)phosphonate 22 was obtained (21 %) together with the nitrile 21 (51 %) from the chloro‐nitro‐mannofuranose 10 and KPO(OEt)2. The reaction of the 1‐C‐nitroglycosyl sulfone 25 (NO2‐group endo) with KPO(OEt)2 gave the (1‐C‐nitroglycosyl)phosphonate 22 (61%) and the nitrile 21 (11 %), whilst the anomeric sulfone 26 (NO2‐group exo) gave 22 (15 %) and 21 (58 %). In the presence of [18] crown‐6, a mixture of the anomers 25 and 26 gave the (1‐C‐nitroglycosyl)phosphonate 22 in 67 % yield together with 21 (13 %). These findings are rationalized as the result of a competition between a nucleophilic attack of the dialkyl‐phosphite anions on the NO2‐group leading ultimately to the nitrile 21 and a single‐electron transfer reaction leading to the (1‐C‐nitroglycosyl)phosphonate 22.
Diels‐Alder‐Reaktionen mit aktivierten 4‐Methyl‐1,3‐pentadienen
Authors: Kienzle Frank , Mergelsberg Ingrid , Stadlwieser Josef , Arnold Wolf
Published: December 2004

Diels‐Alder Reactions with Activated 4‐Methyl‐1,3‐pentadienes

Ethyl 4‐methyl‐1,3‐pentadienyl ether, trimethyl[(4‐methyl‐1,3‐pentadienyl)oxy]silane, and 1‐(4‐methyl‐1,3‐pentadienyl)pyrrolidine and the corresponding piperidine analogue have been used in Diels‐Alder reactions with acrylonitrile, ethyl acetylenedicarboxylate, maleic anhydride, and 2,6‐dimethyl‐p‐benzoquinone.
ESR‐Spectroscopic Investigation of Radical Cations, Radical Anions, and Radical Trianions of Didehydro[n]annulenes
Authors: Huber Walter
Published: December 2004

The didehydro[n]annulenes 1 (n = 14), 2 (n = 18), and 3 (n = 22) are oxidized to radical cations. Reduction of the title compounds leads to radical anions and, in the case of 2 and 3, to radical trianions. The hyperfine data of the paramagnetic derivatives are rationalized in terms of the occupation of n‐membered (n = 14, 18, 22) π‐perimeter MO's (HOMO, LUMO, NLUMO). The contact‐ion pairs of the radical anions show unexpectedly large alkali‐metal coupling constants.
Synthesis of Enantiomerically Pure Pheromones of South‐Pacific Brown Algae: Hormosirene and Dictyopterene A
Authors: Schotten Theo , Boland Wilhelm , Jaenicke Lothar
Published: December 2004

Hormosirene ((−)‐1; (1R,2R)‐1‐((1E,3Z)‐1,3‐hexadienyl)‐2‐vinylcyclopropane) is the specific sex attractant of several brown algae of the Australian shelf, while dictyopterene A ((+)‐2; (1R, 2R)‐1‐((1E)‐1‐hexenyl)‐2‐vinylcyclopropane) is found as a minor constituent of the pheromone bouquets. The asymmetric synthesis of the two hydrocarbons is performed by resolution of the amides (−)‐5 and (+)‐5a obtained from (−)‐(R)‐2‐phenylglycinol and racemic trans‐vinylcyclopropanecarboxylic acid (rac‐4) on silica gel. Both diastereoisomers are obtained optically pure. They are converted by stereoselective Wittig olefination into the title compounds. Compound (−)‐1 is the active mating pheromone of the reproductive system of the seaweed Xiphophora chondrophylla as established by biological‐activity assays.
Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Über die Natur der Isolierungsartefakte von F430, ein Beitrag zur Chemie von F430 und zur konformationellen Stereochemie der Ligandperipherie von hydroporphinoiden Nickel(II)‐Komplexen
Authors: Pfaltz Andreas , Livingston Douglas A. , Jaun Bernhard , Diekert Gabriele , Thauer Rudolf K. , Eschenmoser Albert
Published: December 2004

Factor F430 from Methanogenic Bacteria: On the Nature of the Isolation Artefacts of F430, a Contribution to the Chemistry of F430 and the Conformational Stereochemistry of the Ligand Periphery of Hydroporphinoid Nickel(II) Complexes

Factor F430 (1), a coenzyme from methanogenic bacteria, when heated in aqueous solution isomerizes to 12,13‐di‐epi‐F430 (5) via 13‐epi‐F430 (3). The equilibrium mixture of the three F430 isomers in aqueous phosphate buffer solution (pH 7, 100°) contains 88 % of 5, 8 % of 3, and 4 % of 1 (Scheme 1). The structural assignment for the F430 isomers rests on FAB‐MS‐, UV/VIS‐, 1H‐ and 13C‐NMR spectra of their pentamethyl esters. Chemical proof for the double epimerization at the two chiral centers of F430's ring C was provided by ozonolytic degradation of the di‐epimer to give a ring‐C‐derived succinimide derivative that was shown to be the enantiomer of the one previously obtained by ozonolysis of F430M (see Scheme 2). The two F430 ring‐C epimers 3 and 5 are the isolation artefacts described in the earlier F430 literature. F430 is susceptible to autoxidation in air and the product, that absorbs at 560 nm, was shown to be the 12,13‐didehydro derivative 8 of F430 by spectroscopic characterization of its pentamethyl ester 9. The dehydrogenation product 8 can be diastereoselectively reduced with Zn in AcOH to give natural F430 as the main product rather than the thermodynamically more stable F430‐di‐epimer (Scheme 3). In the double epimerization of F430, the two ring‐C side chains change from a trans‐quasi‐diaxial arrangement to the (locally) enantiomorphic position in which the same side chains are again in a trans‐quasi‐diaxial arrangement. This equilibrium paradox as well as the kinetic diastereoselectivity of the reduction of 12,13‐didehydro‐F430 (8) are rationalized to be consequences of the general phenomenon documented earlier (see the preceding paper) according to which hydroporphinoid Ni(II) complexes all show a characteristic conformational ruffling of their ligand system due to the tendency of the (small) Ni(II) ion to contract the size of the ligand's central coordination hole (see Fig. 5 and 6).
Photoisomerisierung und Relaxation symmetrischer Triazacarbocyanine in einem Alkoholgemisch
Authors: Balli Heinz , Eichenberger Thomas , Hellrung Bruno , Scheibli Peter
Published: December 2004

Photoisomerization and Relaxation of Symmetrical Triazacarbocyanine Dyes in an Alcoholic Mixture at Low Temperature

The partial photobleaching of a series of symmetrical triazacarbocyanine dyes with different heterocycles in EtOH/MeOH/i‐PrOH at low temperature (110 to 250 K) was investigated by UV/VIS spectra. Kinetic data of the dark reaction of photobleached compounds are given. The effect of electron‐donating or ‐accepting substituents, respectively, and of protonation of the photobleached compound on kinetic data and on UV/VIS spectra was studied. Products of photobleaching and mechanisms of the dark reaction are discussed.
Enantioselektive α‐Alkylierung von Asparagin‐ und Glutaminsäure über die Dilithium‐enolatocarboxylate von 2‐[3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]essigsäure und 3‐[3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]propionsäure
Authors: Aebi Johannes D. , Seebach Dieter
Published: December 2004

Overall Enantioselective α‐Alkylation of Aspartic and Glutamic Acid through Dilithium Enolatocarboxylates of 2‐ [3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]acetic and 3‐[3‐Benzoyl‐2‐(tert‐butyl)‐1‐methyl‐5‐oxoimidazolidin‐4‐yl]propionic Acid, respectively

The pure methyl esters10of the heterocyclic carboxylic acids specified in the title were prepared in several steps by known methods from aspartic and glutamic acid, with overall yields ofca.20%. The corresponding heterocyclic acids11were doubly deprotonated by LiNEt2/BuLi or LiN(i‐Pr)2/BuLi to give enolatocarboxylates (3). The latter were reacted with electrophiles (MeOD, Mel, C6H5CH2Br) to give the crystalline products14–21diastereoselectively. Hydrolysis of the imidazolidinone ring of three such products gave the corresponding α‐branched aspartic and glutamic acids22–24of known absolute configuration, thus establishing the stereochemical course of the overall enantioselective alkylations.
Photoactive Cryptands. Crystal Structure of the Sodium Cryptate of the Tris(phenanthroline) Macrobicyclic Ligand
Authors: Caron Aimery , Guilhelm Jean , Riche Claude , Pascard Claudine , Alpha Béatrice , Lehn Jean‐Marie , Rodriguez‐Ubis Juan‐Carlos
Published: December 2004

The crystal structure of the complex [phen · phen · phen] · NaBr · 2 CHCl3 of the macrobicyclic ligand 1 has been determined. The complex is of cryptate type, the Na+ cation being contained in the molecular cavity of 1 and coordinated to all eight N‐atoms. The ligand has a propeller shape and interconverts in solution between the two enantiomeric helical forms.
Photochemical reactions. 146th communication. Photochemistry of conjugated methano‐epoxydienes: Participation of the neighboring cyclopropane ring in product formation via carbonyl ylide and carbene intermediates
Authors: Bischofberger Norbert , Frei Bruno , Jeger Oskar
Published: December 2004

On singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano‐epoxydienes (E)‐6 and (E)‐7 undergo interconversion and yield the products 8–11. The main process is the cleavage of the oxirane ring to the vinyl carbene intermediate e which undergoes addition to the adjacent double bond furnishing the cyclopropene 8. The alternative carbene intermediate f is evidenced by the formation of the cyclobutene 10. For the fragmentation leading to 11, the carbene f as well as the dipolar species h are considered as possible intermediates. On triplet sensitization (acetone, λ > 280 nm), (E)‐7 shows behavior typical of epoxydienes, undergoing fission of the CO bond of the oxirane ring and isomerization to the compounds 13, 14 and (E/Z)‐15.
Uncinatone, a New Antifungal Hydroquinone Diterpenoid from Clerodendrum uncinatum SCHINZ
Authors: Dorsaz Anne‐Christine , Marston Andrew , Stoeckli‐Evans Helen , Msonthi Jerome D. , Hostettmann Kurt
Published: December 2004

A new hydroquinone diterpenoid was isolated from Clerodendrum uncinatum SCHINZ (Verbenaceae) by flash chromatography on silica gel. The structure was established as 7,11‐dihydroxy‐3,4,9,11b‐tetramethyl‐1,2,8,9,11b‐pentahydrophenanthro[3,2‐b]furan‐6(2H)‐one by spectroscopic methods and X‐ray analysis. The diterpene was strongly fungitoxic to spores of Cladosporium cucumerinum.
Über die Strukturaufklärung von (Hydroxy‐oxo‐cyclopentenyl)alkansäuren, den Aldolkondensationsprodukten von Dioxoencarbonsäuren aus Rinderleber
Authors: Schödel Rolf , Spiteller Gerhard
Published: December 2004

Structure Elucidation of (Hydroxy‐oxo‐cyclopentenyl)alkanoic Acids, the Aldol‐Condensation Products of Dioxoene Acids from Cattle Liver

During homogenization of cattle liver the highly instable dioxoene acids 13a, 13b, and 13c are formed. These acids cyclize in alkaline solution to yield pairs of stable (hydroxy‐oxo‐cyclopentenyl)alkanoic acids, which were isolated as methyl esters 4a/5a, 4b/5b, and 4c/5c. The structures of these compounds were deduced from an enriched 3‐mg mixture sample by microchemical reactions combined with a GC/MS analysis of the reaction products. Compound 13a was obtained as methyl ester by oxidation of the methyl ester of the corresponding F‐acid with NaOCl. It was not possible to isolate 13a in pure form due to its high sensitivity. Instead of the methyl ester of 13a, 4a and 5a were isolated, of which the structures were established.
Structure and Reactivity of Xanthocorrinoids. Part II. Influence of the c‐acetic‐acid chain on the course of the hydroxylation of the corrin chromophore by oxygen in the presence of ascorbic acid
Authors: Grüning Burghard , Holze Gerhard , Jenny Titus A. , Nesvadba Petr , Gossauer Albert , Ernst Ludger , Sheldrick William S.
Published: December 2004

The yield of the main product from the reaction of heptamethyl dicyanocobyrinate with O2 in the presence of ascorbic acid has been optimised by systematic variation of the reaction conditions, and the structure of the obtained ‘stable yellow corrinoid’ has been established by X‐ray analysis. From the relationship between the structures of analogous xanthocorrinoids obtained likewise from a series of dicyanocobyrinic‐acid derivatives, which has been prepared by systematic modifications of the c‐acetic‐acid chain, and the functionality of the substituent at C(7), a reaction mechanism is suggested.
Bestimmung des Chiralitätssinns der enantiomeren 2,6‐Adamantandiole
Authors: Gerlach Hans
Published: December 2004

Determination of the Chirality Sense of the Enantiomeric 2,6‐Adamantanediols

The enantiomers of 2,6‐adamantanediol (1) are resolved via the diastereoisomeric camphanoates. The (2R,6R)‐chirality sense for (−)‐1 and (2S,6S) for (+)‐1 was determined by chemical correlation with (−)‐(1R,5R)‐bicyclo[3.3.1]nonan‐2,6‐dion ((1R,5R)‐3) of known absolute configuration in the following way: alkylation of the bis(pyrrolidine enamine) of (−)‐(1R,5R)‐3 with CD2I2 and hydrolysis of the product gives the enantiomer 4 of (4,4‐D2)‐2,6‐adamantanedione. Reduction of 4 with LiAlH4 leads to one enantiomer (Scheme 2) of each of the three diols 5–7 of known absolute configuration. The three diols are themselves configurational isomers due to the presence of the CD2 group, but correspond otherwise entirely to the enantiomeric diols 1. Accordingly, they can also be separated by means of their diastereoisomeric camphanoates to give the diols 5/6 and 7. These samples are easily distinguished and identified by their characteristic 1H‐NMR spectra (cf. Fig. 2). This allows to identify the (2R,6R)‐ and (2S,6S)‐enantiomer of 1 on the basis of their behavior in the resolution experiment analogous to that of the diols 5/6 and 7, respectively. The diol (−)‐1 must have the (2R,6R)‐configuration because it forms, like the diols 5/6, with (−)‐camphanic acid the diastereoisomeric ester less soluble in benzene. The diol (+)‐1 has (2S,6S)‐configuration, because it forms, like 7, with (+)‐camphanic acid the diastereoisomeric ester less soluble in benzene. The bis(4‐methoxybenzoate) of (−)‐(2R,6R)‐1 shows chiroptical properties which are in accordance with Nakanishi's rule for two chromophores having coupled electric dipol transition moments arranged with a left‐handed torsion angle.
Synthese einiger 8‐substituierter 2‐Methyl‐1,2,3,4‐tetrahydroisochinoline
Authors: Rey Max , Vergnani Tiziana , Dreiding André S.
Published: December 2004

Synthesis of Some 8‐Substituted 2‐Methyl‐1,2,3,4‐tetrahydroisoquinolines

A general route to 8‐substituted tetrahydroisoquinolines is exemplified by the preparation of the 2‐methyl‐1,2,3,4‐tetrahydroisoquinolin‐8‐ol (11), the ‐8‐carbaldehyde oxime (12) and the ‐8‐carbonitrile (13). It involves the conversion of isoquinoline (1) by partially modified Steps 1, 2, 3, and 5 (see the Scheme) into the 5‐bromo‐8‐nitro derivative 5, reduction of the latter to the 8‐amino derivative 8 and replacement of the NH2‐group with an appropriate substituent by a Sandmeyer‐like reaction. The selective reductions of the N‐containing ring in 6 (Steps 5, 6, and 8) and of the NO2‐group in 5 (Steps 4 and 7) were also studied.
A Unified Interpretation of Kinetic Data on the Acid‐Induced Cleavage and of Product‐Analysis Data on Spontaneous Cleavage of the Mono‐ol Cation μ‐Hydroxo‐bis[pentaamminecobalt(III)] ([(NH3)5CoOHCo(NH3)5]5+)
Authors: Rotzinger François P. , Marty Werner
Published: December 2004

Recent work on the spontaneous (= acid‐independent) cleavage of the mono‐ol cation, i.e.

in Cl−/ClO and NO/ClO mixed‐electrolyte media has established (by analysis of anion‐competition experiments) the existence of reactive ion pairs of the mono‐ol cation with Cl− and NO. Their existence must be allowed for in the analysis of the rate data for the acid‐induced cleavage (pH 0–1) of the mono‐ol cation in these mixed‐electrolyte media. Thus, previous data for acidic Cl−/ClO media have been re‐interpreted in this work, and new data for NO/ClO media have been analyzed in the same sense. This analysis removes an apparent discrepancy in the orders of magnitude of ion aggregate stability constants between the mono‐ol and similar binuclear cations.
Gas‐Phase Basicities of Furan Compounds. The Role of Alkyl Substitution on Proton Affinity and on the Site of Protonation
Authors: Houriet Raymond , Rolli Eric , Bouchoux Guy , Hoppilliard Yannick
Published: December 2004

The gas‐phase protonation of alkyl‐substituted furan compounds is investigated in equilibrium proton‐transfer reactions conducted in an ion cyclotron resonance (ICR) spectrometer. From the effects of substituents on the stability of protonated species, it is concluded that protonation of the majority of these systems occurs specifically on the C(α)‐atom to form carbenium ions. Parallel MO calculations performed on different structures of the products reinforce the experimental conclusions and provide energy values for the less stable structures. The solution reactivity of these compounds towards electrophilic agents and NMR spectra of protonated species obtained in strong acidic media have been investigated.
Enantioselective Syntheses and Absolute Configurations of Viridiene and Aucantene, Two Constitutents of Algae Pheromone Bouquets
Authors: Boland Wilhelm , Niedermeyer Uwe , Jaenicke Lothar , Görisch Helmut
Published: December 2004

Viridiene ((+)‐6; (+)‐(3R,4S)‐3‐((1Z)‐1,3‐butadienyl)‐4‐vinylcyclopentene) and aucantene ((+)‐18; (+)‐(4R,5R)‐4‐((1E)‐1‐propenyl)‐5‐vinylcyclohexene) are constituents of the pheromone bouquets of several brown algae species. Key synthons to the title compounds are optically active γ‐lactones with known or experimentally determined absolute configurations. Horse liver alcohol dehydrogenase, which catalyses the oxidation of meso‐ and racemic non‐meso diols to chiral lactones, and pig‐liver esterase, which catalyzes the saponification of meso‐diesters to chiral half‐esters, were utilized for the asymmetric synthesis of such precursors. The racemic non‐meso diol rac‐1 is converted to the two stereoisomeric γ‐lactones (+)‐2 and (+)‐3 which are readily separated. meso‐Diol 12 is oxidized to the chiral γ‐lactone (−)‐11. Its enantiomer (+)‐11 is obtained by enantioselective saponification of the meso‐diester 9 with pig‐liver esterase. Appropriately designed syntheses lead from these chiral intermediates to both enantiomers (+)‐ and (−)‐6 of viridiene and (+)‐ and (−)‐18 of aucantene. In addition, kinetically controlled reduction of the racemic aldehydes rac‐5a and rac‐15 with horse liver alcohol dehydrogenase offers a convenient alternative to the enantioselective preparation of the enantiomers of the two hydrocarbons 6 and 18. Chromatography of 6 on triacetylated cellulose as a stationary chiral phase confirms the enantiospecificity of the synthetic routes designed.
Face Selectivity of the Diels‐Alder Additions of Sulfur‐Substituted Dienes and Tetraenes Grafted onto 7‐Oxabicyclo[2.2.1]heptanes
Authors: Tornare Jean‐Marc , Vogel Pierre , Pinkerton A. Alan , Schwarzenbach Dieter
Published: December 2004

Stereoselective synthesis of 2‐methylidene‐3‐[(Z)‐(2‐nitrophenylsulfenyl)methylidene]‐7‐oxabicyclo[2.2.1]‐heptane (16), 1,4‐epoxy‐1,2,3,4‐tetrahydro‐5,8‐dimethoxy‐2‐methylidene‐3‐[(Z)‐(2‐nitrophenylsulfenyl)methylidene]anthracene (18), and 1,4‐epoxy‐1,2,3,4‐tetrahydro‐5,8‐dimethyoxy‐2‐methylidene‐3‐[(Z)‐(phenylsulfenyl)‐methylidene]anthracene (19) are presented. The Diels‐Alder additions of these S‐substituted dienes and those of 2,5‐dimethylidene‐3,6‐bis{[(Z)‐(2‐nitrophenyl)sulfenyl]methylidene}‐7‐oxabicyclo[2.2.1]heptane (17) have been found to be face selective and ‘ortho’ regiospecific. The face selectivity depends on the nature of the dienophile. It is exo‐face selective with bulky dienophiles such as ethylene‐tetracarbonitrile (TCNE) and 2‐nitro‐1‐butene and endo‐face selective with methyl vinyl ketone, methyl acrylate, and 3‐butyn‐2‐one. In the presence of a Lewis acid, the face selectivity of the Diels‐Alder reaction can be reversed. The addition of the first equivalent of a dienophile to tetraene 17 is at least 100 times faster than the addition of the second equivalent of the same dienophile to the corresponding mono‐adduct. The X‐ray structure of the crystalline bis‐adduct 43, a 7‐oxabicyclo[2.2.1]hepta‐2,5‐diene system annellated to two cyclohexene rings, resulting from the successive additions of methyl acrylate and methyl vinyl ketone to tetraene 17 is presented. Only one of the two endocyclic double bonds of the 7‐oxabicyclo[2.2.1]hepta‐2,5‐diene deviates from planarity, the substituents bending towards the endo face by 5.7°.
Aldonhydroximo‐lactones. Preparation and Determination of Configuration
Authors: Beer Dieter , Vasella Andrea
Published: December 2004

The syntheses of the unprotected, (Z)‐configurated hexon‐ and pentonhydroximo‐lactones 2a–12a by oxidation of D‐glucose, cellobiose, D‐galactose, D‐mannose, 2‐acetamido‐2‐deoxy‐D‐glucose, D‐ribose, and D‐arabinose oxime with MnO2, Hg(OAc)2, or O2 in the presence of Cu2Cl2/pyridine are described. An (E/Z)‐pair of protected hydroximo‐lactones 14 and 15 was obtained by oxidation of the diisopropylidene‐D‐mannose oxime 13 with MnO2. In CH2Cl2 solution, the minor (E)‐isomer 15 was slowly transformed into the major (Z)‐isomer 14. The structure assignments for 2a–12a are based upon IR and NMR data, the Beckmann rearrangement of 1 and 14, and the X‐ray structure analysis of 7a and 47. From the selectively deprotected hydroximo‐lactones 2c, 8c, and 9c, the urethanes 2d, 2f, 8d, and 9d were prepared. (E/Z)‐mixtures of the amino phosphates 27/28, 29/30, and 31/32 were obtained from the bromonitroso ethers 16, 19, and 17 and NaPO(OEt)2. The configuration of the bromonitroso ethers 18 and 19 were assigned on the basis of their CD spectra and of their correlation with the corresponding bromonitro ethers 24 and 25. Factors influencing the configuration of the hydroximo‐lactones are briefly discussed.
The Synthesis and Protonation of 1,1‐Di(1‐pyrrolyl)alkenes
Authors: Schärer Jean‐Claude , Etienne Robert , Burger Ulrich
Published: December 2004

It is shown that lithiation of di(1‐pyrrolyl)methane (3) can be directed either towards the C(α) ring positions or to the central CH2 group, depending upon the solvent and the complexing agents chosen. Di(1‐pyrrolyl)‐methyllithium (6), resulting from CH2 deprotonation, is intercepted by aldehydes and converted to the title alkenes in a few straightforward steps. Protonation of 1,1‐di(1‐pyrrolyl)ethylene (10) is found to occur under kinetic control at the terminal olefinic position. In HBF4. Me2O the resulting 5‐azionafulvene‐type ion 14 can be observed by low‐temperature NMR spectroscopy. In FSO3H, however, protonation is directed under thermodynamic control to both pyrrole rings. The resulting symmetrical dication 13 persists even at room temperature.
Structure and Stereochemistry of New Sesquiterpene Esters from Echinacea purpurea (L.) MOENCH. (Preliminary communication)
Authors: Bauer Rudolf F. X. , Khan Ikhlas A. , Lotter Hermann , Wagner Hildebert , Wray Victor
Published: December 2004

The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities.
Synthesis of xanthone O‐glycosides. Part III. Synthesis of 1‐ and 8‐O‐β‐D‐glycosides of 5‐O‐methyl‐ and de‐O‐methylbellidifolin
Authors: Vermes Barbara , Seligmann Otto , Wagner Hildebert
Published: December 2004

The unambiguous synthesis of three naturally occurring and biologically active xanthone 1‐O and 8‐O‐β‐D‐glucosides of 5‐O‐methyl‐ and de‐O‐methylbellidifolin (2–4) was accomplished. The protected xanthone aglycones having only a single reactive OH group were prepared by selective benzylation, methylation, and debenzoylation reactions. An unexpected stability of the 1‐MeO group towards demethylation was observed.
Die toxischen und sedierend wirkenden Bufadienolide von Kalanchoedaigremontiana HAMETet PERR
Authors: Wagner Hildebert , Lotter Hermann , Fischer Manfred
Published: December 2004

The Toxic and Sedative Bufadienolides of Kalanchoe daigremontiana HAMET et PERR.

From the toxic Crassulacee Kalanchoe daigremontiana five biosynthetically related bufadienolides have been isolated and structurally elucidated by X‐ray and 1H‐ and 13C‐NMR spectroscopy. The compounds were identified as bersaldegenin 1,3,5‐orthoacetate (2), bersaldegenin 1‐acetate (4), bersaldegenin 3‐acetate (3), 1β,3β,5,11α,14‐pentahydroxy‐12,19‐dioxo‐5β,14β‐bufa‐20,22‐dienolide 1,3,5‐orthoacetate ( = daigremontianin; 1), and 3β‐acetoxy‐1β,5,14‐trihydroxy‐5β,14β‐bufa‐20,22‐dienolide ( = daigredorigenin‐3‐acetate, 5). According to the pharmacological investigations, the two orthoacetates 1 and 2 comprise the positive inotropic, sedative, and toxic activity of the plant.
Enantioselective Synthesis of D‐erythro‐Sphingosine and of Ceramide
Authors: Julina Radomir , Herzig Thomas , Bernet Bruno , Vasella Andrea
Published: December 2004

The enynol 2 was transformed into D‐erythro‐sphingosine 11 (7 steps, 46%) and into ceramide 1 (8 steps, 41% overall yield). The key steps were the mono‐epoxidation of the enynol 5 (Ti(t‐BuO)4, (−)‐D‐diethyl tartrate, t‐BuOOH) to 6 (86%, ≥ 98% ee), the regioselective intramolecular opening of the oxirane 6 via the benzylurethane 7, and the reductive tranformation of the acetylene 9 into the oxazolidinone 10 (Li, EtNH2, 88%).
Herstellung von disubstituierten Maleinsäure‐anhydriden mit Hilfe von reaktiven 2‐Oxo‐3H‐imidazo[1,2‐a]pyridinium‐Verbindungen
Authors: Baumann Marcus E. , Bosshard Hans , Breitenstein Werner , Rist Günter
Published: December 2004

Preparation of Disubstituted Maleic Anhydrides from Reactive 2‐Oxo‐3H‐imidazo[1,2‐a]pyridinium Compounds

A new useful method for the preparation of disubstituted maleic anhydrides, most of them bearing additional functional groups in the side chain, is described. The key step of the synthesis consists of the addition of 2‐oxo‐3H‐imidazo[1,2‐a]pyridinium compounds to a variety of different Michael acceptors.
Single‐Centre Model for the Active Site of α‐Chymotrypsin
Authors: Vorherr Thomas , Altmann Karl‐Heinz , Mutter Manfred
Published: December 2004

The polymer‐bound heptapeptide H‐Glu‐His‐Pro‐Gly‐Ser‐Gly‐PEGM was designed as a ‘single‐centre model’ for the active site of α‐chymotrypsin. The peptide was synthesized according to the general principles of the liquid‐phase method for peptide synthesis, and its conformational properties were investigated by CD and IR spectroscopy in solution and in the solid state. In harmony with empirical prediction codes, experimental and theoretical conformational considerations, the peptide adopts a β‐turn conformation stabilized by H‐bonds involving the side chains of Glu, His, and Ser. The development of a H‐bonded system similar to the active site of α‐chymotrypsin leads to implications with respect to a possible catalytic activity of the model peptide.
1,4‐Dithiafulvene aus der Umsetzung von 4,4‐disubstituierten 1,3‐Thiazol‐5(4H)‐thionen mit Acetylenderivaten
Authors: Jenny Christjohannes , Heimgartner Heinz
Published: December 2004

1,4‐Dithiafulvenes, Products of the Reaction of 4,4‐Disubstituted 1,3‐Thiazol‐5(4H)‐thiones and Acetylenic Compounds

On heating in toluene, 4,4‐disubstituted 1,3‐thiazol‐5(4H)‐thiones 1 and acetylenecarboxylates or acetylenecarbonitriles 2 undergo a cyclosubstitution reaction to yield 2‐methylidene‐1,3‐dithiol derivatives 3 (1,4‐dithiafulvenes) and a nitrile. Further heating of 3a and 3b in the presence of excess 2a leads to the isomeric 2,3‐dihydrothiophene‐2‐thiones 4a and 4b, respectively. The benzodithiafulvene 14 has been formed in a similar reaction from 1a and in situ generate benzyne.
Photochemical reactions. 147th Communication. Further investigation of the photochemistry of 5,6‐epoxy‐5,6‐dihydro‐β‐ionone: Product formation via a carbonyl‐ylide intermediate
Authors: O'Sullivan Anthony , Frei Bruno , Jeger Oskar
Published: December 2004

On π,π*‐excitation of the epoxyenone (E)‐1 (λ = 254 nm, MeCN), in addition to the previously isolated compounds 2–9, the new products 10–12, derived from the ylide intermediate c were isolated. Further evidence for the ylide c was obtained by the rapid racemization of the optically active epoxyenone (−)‐(E)‐1.
Cacospongione A, cacospongienone A, and cacospongienone B, new C21 difuran terpenoids from the marine sponge Cacospongiascalaris SCHMIDT of the Côte d' Azur
Authors: Guella Graziano , Amade Philippe , Pietra Francesco
Published: December 2004

The sponge Cacospongia scalaris (family Thorectidae), collected at the Cap de Nice (Cǒte d'Azur), is shown to contain a series of truncated, linear C21 difuran terpenoids comprising the known sponge products furospongin‐1 ((+)‐1), furospongin‐2 (2), and dihydrofurospongin‐2 ((−)‐(E)‐3), besides the new products cacospongione A ((−)‐4), cacospongienone A ((−)‐(Z)‐6), and cacospongienone B ((−)‐(E)‐6), whose absolute configurations have been assigned by chemical correlations with (+)‐1. Possibly, one of the two cacospongienones is an artifact, as these two terpenoids interconvert on standing. This is the first finding of linear C21 difuran terpenoids, which are typical of the Spongiidae, in a member of the family Thorectidae.
Preparation via Diastereoselective Hydrogenation, Absolute Conformation and Configuration of Exogeneous Anabolic Zeranol ((3S, 7R)‐3,4,5,6,7,8,9,10,11,12‐Decahydro‐7,14,16‐trihydroxy‐3‐methy‐1H‐2‐benzoxacyclotetradecin‐1‐one)
Authors: Snatzke Günther , Angeli Cristina , Decorte Enio , Moimas Flavio , Kojié‐Prodié Biserka , Ruz̆ić‐Toroš Z̆iva , S̆unjić Vitomir
Published: December 2004

Hydrogenation of the ketone group in di‐O‐benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼40%, d. e. at −60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature‐dependent CD spectra of its acetyl congeners 18 and 19. X‐Ray structure analysis of 7‐O‐acetylderivative (13) of 11 revealed the (R)‐configuration at C(7). Two crystallographically independent H2O molecules are involved in the H‐bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)‐]C(161)‐C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)‐C(12) bond (torsional angle [C(11)‐]C(12)‐C(121)[C(161)] is −93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic‐acid lactone) derivatives from the 6‐membered lactone derivative 20, studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and n→π* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.
Conformational Analysis of Endoperoxides Grafted onto Bicyclo[2.2.n]alkanes as a Test of the Rigidity of the Bicyclic Skeleton. Photo‐oxidation of [2.2.2] Hericene and 2,3,5,6‐Tetramethylidenebicyclo[2.2.n]alkanes
Authors: Birbaum Jean‐Luc , Vogel Pierre
Published: December 2004

The photo‐oxidation of [2.2.2]hericene (6) gave successively the endoperoxides 11 (9,10,11,12‐tetramethylidene‐4,5‐dioxatricyclo[6.2.2.02,7]dodec‐2(7)‐ene), the bis‐endoperoxide 16 (15,16‐dimethylidene‐4,5,11,12‐tetraoxatetracyclo[6.6.2.02,7.o9,14]hexadeca‐2(7),9(14)‐diene), and the tris‐endoperoxide 19 (4,5,11,12,17,18‐hexaoxapentacyclo[6.6.6.02,7.09,14.015,20]icosa‐2(7),9(14),15(20)‐triene). The endoperoxides 11, 16, and 19 were formed in the presence or in the absence of a dye sensitizer. The sensitized photo‐oxidations of 2,3,5,6‐tetramethylidenebicyclo[2.2.2]octane (4), 5,6,7,8‐tetramethylidenebicyclo[2.2.2]oct‐2‐ene (5), 2,3,5,6‐tetramethylidenebicyclo[2.2.1]‐heptane (7), and 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptane (8) gave successively the corresponding mono‐endoperoxides 9, 10, 12, and 13 and the bis‐endoperoxides 14, 15, 17, and 18, respectively. Low‐temperature NMR spectra of the bis‐endoperoxides 14 and 16 indicated that their C2 and Cs conformers have the same stability. Similarly, there was no difference in the enthalpy of the D3 and C2 conformers of the tris‐endoperoxide 19. The following reactivity sequence was observed for the sensitized photo‐oxidations of 6–8 and 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (23): 6 + 1O2→11 > 7 + 1O2→12>8 + 1O2→13>23 + 1O2→24, a trend parallel with that reported for the ethylenetetracarbonitrile (TCNE) cycloadditions to the same polyenes. The rate‐constant ratios k1/k2 and k2/k3 for the three successive photo‐oxidations of [2.2.2]hericene (6) did not differ significantly from unity, in contrast with the Diels‐Alder additions of 6. Similarly, the rate‐constant ratios k1/k2 for the two successive photo‐oxidations of tetraenes 7 and 8 were significantly smaller than those reported for the successive TCNE cycloadditions to 7 to 8. The endoperoxide formations are not sensitive to the change in the exothermicity of the reactions but they are sensitive to the electronic properties (IP's) of the polyenes.
Aza‐2‐diènes‐1,3 3. Nouvelles voies d'accès à des amino‐2‐pyrazines substituées
Authors: Lang Mare , Schoeni Jean‐Paul , Pont Christiane , Fleury Jean‐Pierre
Published: December 2004

2‐Aza‐1,3‐dienes. A New Approach to Substituted 2‐Aminopyrazines

Treatment of enamines by tosylated isonitrosomalono derivatives gives access to 5‐dialkylamino‐1, 1‐dicyano 2‐aza‐1,3‐dienes (or 1‐methoxycarbonyl analogous) which are precursors of various regiospecific 5,6‐substituted 2‐amino‐3‐cyano (or methoxycarbonyl) pyrazines. Some examples of utilisation of these intermediates for synthesis of lumazines, pteridines, and other bicyclic skeletons are described.
Approaches to Synthetic Vaccines Design of Epitope‐Containing Amphiphilic Peptides Matching the Antigenic Structure in the Native Protein
Authors: Mutter Manfred , Altmann Karl‐Heinz , Müller Klaus , Vuilleumier StéPhane , Vorherr Thomas
Published: December 2004

A general procedure for the design of synthetic vaccines with the retained conformational features of protein antigenic determinants is described. This new concept emerges from detailed studies on the relationship between primary sequence and secondary structure formation of synthetic peptides and takes advantage of the amphiphilic nature of epitope‐containing peptide segments in the native protein to accomplish structural modifications. These segments, for example amphiphilic helices or β‐sheets, are stabilized by the insertion of secondary structure‐inducing amino‐acid residues on the hydrophobic part of the peptide without affecting the spatial arrangement of functional residues on the hydrophilic side. The availability of amphiphilic peptides with tailor‐made conformational properties, e.g. helices, β‐sheets, and, moreover, assemblies of these blocks to structures of higher order (‘folding units’), allows the presentation and stabilization of continuous as well as discontinuous epitopes by this approach. This strategy is exemplified for the case of two discontinuous epitopes taken from lysozyme, which are matched to host molecules with adequate conformational features by the help of computer‐assisted molecular modelling. The implications of this new concept for the design of synthetic vaccines are discussed with special emphasis to the important role of peptide synthesis and chemical structure modification.
Aza‐2‐diènes‐1,3 4. Préparation et propriétés d'alkyl‐1‐pyrazone‐imines et de leurs isomères
Authors: Lang Marc , Lacroix Alain , Pont Christiane , Fleury Jean‐Pierre
Published: December 2004

2‐Aza‐1,3‐dienes. Synthesis and Properties of 1‐Alkylpyrazone‐imines and their Tautomers

Treatment of 5‐dialkylamino‐1,1‐dicyano‐2‐aza‐1,3‐dienes (or their 1‐methoxycarbonyl analogoues) with primary amines gives substituted 1‐alkyl‐3‐cyano‐(or methoxycarbonyl‐)pyrazoneimines. Tautomeric behaviour, nucleophilic addition to imino function and spectroscopic data of these isomers are examined.
Desoxy‐nitrozucker. 13. Mitteilung. Herstellung ungeschützter und partiell geschützter 1‐Desoxy‐1‐nitro‐D‐aldosen sowie Röntgenstrukturanalysen einiger ihrer Vertreter
Authors: Beer Dieter , Bieri Jost H. , Macher Ingolf , Prewo Roland , Vasella Andrea
Published: December 2004

Preparation of Unprotected and Partially Protected 1‐Deoxy‐1‐nitro‐D‐aldoses and Some Representative X‐Ray Structure Analyses

The unprotected and partially protected 1‐deoxy‐1‐nitro derivatives of α‐and β‐D‐glucopyranose (see 15 and 14), β‐D‐mannopyranose (see 16), N‐acetyl‐β‐D‐glucosamine (see 17), β‐D‐galactofuranose (see 19), β‐D‐ribofuranose (see 20), α‐D‐arabinofuranose (see 21), 4,6‐O‐benzylidene‐β‐D‐glucose (see 40), N‐acetyl‐4,6‐O‐benzylidene‐β‐D‐glucosamine (see 41), and 4,6‐O‐benzylidene‐β‐D‐galactose (see 42) were prepared by ozonolysis of the corresponding nitrones which were obtained from the acid‐catalyzed reaction of p‐nitrobenzaldehyde with the hydroxylamine 4, the unprotected oximes 3 and 5–9 and the 4,6‐O‐benzylidene oximes 35–37, respectively (Schemes 1–3). The gluco‐ and manno‐nitrones 10 and 12 were isolated, and their ring size and their anomeric and (E/Z) configurations were determined by NMR spectroscopy and by their transformation into their corresponding nitro derivatives. The structure of the deoxynitroaldoses were determined by NMR spectroscopy, polarimetry, and, in the case of 14, 16, and 17, by formation of the 4,6‐O‐benzylidene (14→40) or 4,6‐O‐isopropylidene (16→43, 17→23) derivatives (Scheme 3). Acetylation of the nitroglucopyranose 14, the 2‐acetamido‐nitroglucopyranose 17, and the nitrogalactofuranose 19 gave the crystalline peracetylated nitroaldoses 22, 24, and 45, respectively (Scheme 4, Figs. 1 and 3); acetylation of the nitromannopyranose 16 gave the nitro‐arabino‐glycal 44 (Scheme 4). The structure of the peracetylated nitroglucopyranose 22, the nitroglucosamine 25, the nitrogalactofuranose 45, and the nitroribofuranose 20 were confirmed by X‐ray analysis (Figs. 1 4). In all cases, including the β‐D‐glucopyranose derivative 22, considerably shortening of the (endocyclic) C(1)‐O bond was observed. Base‐catalyzed anomerization of the β‐D‐configurated nitroglucopyranose 14, the nitromannopyranose 16, the benzylidene acetal 40 of nitroglucose, and the 2,3,4,6‐tetraacetylated glucosamine derivative 24 gave the corresponding nitro‐α‐D‐aldoses 15, 26, 47, and 25, respectively (Scheme 4).
Deoxy‐nitrosugars 15th communication Synthesis of N‐acetylneuraminic acid and N‐acetyl‐4‐epineuraminic Acid
Authors: Baumberger Franz , Vasella Andrea
Published: December 2004

A 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

The 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 (±)‐Dihydrorecifeiolide

Ethyl 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 Type

From 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

The 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

Luteochrome 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

Allenic 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 Substances

For 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).