bluuebunny/crossref_metadata_2025 huggingface dataset:
π‐Bond Configurations, Conformations, and Dynamic Behaviour of Benzo[c]octalene and Dibenzo[c,j]octalene
Authors: Oth Jean F. M. , Müllen Klaus , Schmickler Hans , Engels Hans‐Wilhelm , Vogel Emanuel
Published: December 2004

The π‐bond configurations, the conformations, and the dynamic behaviour of dibenzo [c,j]octalene (2) and of benzo [c]octalene (3) have been investigated by 13C‐NMR. spectroscopy at different temperatures. Dibenzooctalene was found to present π‐bond fixation in the octalene unit as in 2b; with this π‐bond fixation the molecule is not planar and takes two different conformations which are rapidly interconverted by inversion of one cyclooctatetraene ring. Monobenzooctalene (3) also presents π‐bond fixation in the octalene unit but exists as two valence isomers, 3b and 3c. Isomer 3c dominates the dynamic equilibrium. With this π‐bond configuration, the molecule is chiral but undergoes several isodynamic processes, namely inversion of the cyclooctatriene and/or of the cyclooctatetraene ring. The valence isomer 3b can have two different conformations which are rapidly interconverted by inversion of one cyclooctatetraene ring. The interconversion 3c ⇌ 3b implies the occurrence of a π‐bond shift process; this process affects the 13C‐NMR. lineshape above 50°.
Nucleoside und Nucleotide. Teil 14. Synthese des Octanucleosidheptaphosphats d(G‐A‐T‐T‐T‐T‐G‐A)
Authors: Bühlmayer Peter , Graf Georg , Waldmeier Felix , Tamm Christoph
Published: December 2004

Nucleosides and Nucleotides. Part 14. Synthesis of the Octanucleosideheptaphosphate d(G‐A‐T‐T‐T‐T‐G‐A)

The synthesis of the oligonucleotide d(G‐A‐T‐T‐T‐T‐G‐A) by the diester method is described. The condensations were performed using dinucleotide blocks carrying suitable protecting groups. The intermediary products were d(G‐A), d(G‐A‐T‐T) and d(G‐A‐T‐T‐T‐T). These intermediates and the final product were characterized by UV. spectroscopy, high pressure liquid chromatography (HPLC.) and enzymatic degradation. The cleavage products were separated and analyzed by paper chromatography or HPLC. with an anion exchange column. They yielded the corresponding nucleosides and nucleotides in the correct ratios.
Nucleoside und Nucleotide. Teil 16. Verhalten von 1‐(2′‐Desoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyrimidinon‐5′‐triphosphat, 1‐(2′‐Desoxy‐β‐D‐ribofuranosyl)‐2(1 H)pyridinon‐5′‐triphosphat und 4‐Amino‐1‐(2′‐Desoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyridinon‐5′‐triphosphat gegenüber DNA‐Polymerase
Authors: Wachtl Michael , Kohler Peter , Tamm Christoph
Published: December 2004

Nucleosides and Nucleotides. Part 16. The Behaviour of 1‐(2′‐Deoxy‐β‐D‐ribofuranosyl)‐2(1H)‐pyrimidinone‐5′‐triphosphate, 1‐(2′‐Deoxy‐β‐D‐ribofuranosyl‐2(1H))‐pyridinone‐5′‐triphosphate and 4‐Amino‐1‐(2′‐desoxy‐β‐D‐ribofuranosyl)‐2(1H)‐pyridinone‐5′‐triphosphate towards DNA Polymerase

The behaviour of nucleotide base analogs in the DNA synthesis in vitro was studied. The investigated nucleoside‐5′‐triphosphates 1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyrimidinone‐5′‐triphosphate (pppMd), 1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyridinone‐5′‐triphosphate (pppIId) and 4‐amino‐1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyridinone‐5′‐triphosphate (pppZd) can be considered to be analogs of 2′‐deoxy‐cytidine‐5′‐triphosphate. However, their ability to undergo base pairing to the complementary guanine is decreased. When pppMd, pppIId or pppZd are substituted for pppCd in the enzymatic synthesis of DNA by DNA polymerase no incorporation of these analogs is observed. They exhibit only a weak inhibition of the DNA synthesis. The mode of the inhibition is uncompetitive which shows that these nucleotide analogs cannot serve as substrates for the DNA polymerase.
Über Pterinchemie 76. Mitteilung [1] Eine einfache Synthese von Leucovorin
Authors: Khalifa Esam , Ganguly Abhoy N. , Bieri Jost H. , Viscontini Max
Published: December 2004

A Convenient Synthesis of Leucovorin

The synthesis of leucovorin, a 5‐formyl‐(6R or S)‐5,6,7,8‐tetrahydropteroyl‐L‐glutamic acid (II) is described. The L‐folic acid was first reduced to (6R, S)‐tetrahy‐dro‐L‐folic acid (I); formylation with methyl‐formate in DMSO gave directly leucovorin (as a diastereomeric mixture) in good yields. To demonstrate, that the formylation occurred regiospecifically at N (5) and not at N (10), N (10)‐nitroso‐(6 R, S)‐tetrahydro‐L‐folic acid was formylated under the same conditions. Reductive elimination of the N (10)‐nitrosogroup gave the identical leucovorin as in the previous case. The synthetic leucovorin was biologically as active as the natural product with Streptococcus faecalis ATCC 8043 and Pediococcus cerevisiae ATCC 8081.
3‐Azawurtzitan und 3(4 → 5)abeo‐3‐Azawurtzitan
Authors: Klaus Rolf Otto , Ganter Camille
Published: December 2004

3‐Azawurtzitane and 3(4 → 5)abeo‐3‐Azawurtzitane

3‐Azawurtzitane (14) and 3(4 → 5)abeo‐3‐azawurtzitane (15) as well as derivatives thereof are described. The known tricyclic unsaturated ketone 1 was transformed to the properly functionalized endo‐amines 3, 5 and 12. Entry to the azawurtzitane system and its corresponding abeo‐compounds was achieved by three different cyclization procedures: aminomercuration with mercuric acetate in water (3 → 14, 5 → 16), olefin amination with mercuric acetate in dimethyl sulfoxide (3 → 18, 5 → 20 + 21) and intramolecular attack at an epoxide (12 → 24 + 25). Molecular rearrangements of 3‐azawurtzitanes to 3(4 → 5)abeo‐3‐azawurtzitanes and vice versa are described involving neighbouring group participation of the N (3) atom.
Synthesen und chemische Eigenschaften neuer «Donor‐Akzeptor»‐stabilisierter Molekülsysteme mit zentraler Bicyclo [4.4.1]undeca‐l (10), 3,6,8‐tetraen‐2,5‐diyliden‐Gruppe
Authors: Neidlein Richard , Zeiner Hartmut
Published: December 2004

Syntheses and Chemical Properties of New ‘Donor‐Acceptor’‐stahilized Molecular Systems with a Central Bicyclo[4.4.1] undeca‐l(10).3,6,8‐tetraene‐2,5‐diylidenc Group

The synthesis of X‐methyl‐2‐(5‐oxobicyclo[4.4.1]undeca‐l)10(,3,6,8‐tetraen‐2‐yliden)‐l,3‐benzodithiol (4) is described starting with the keto‐enol mixture 2 and 5‐methyl‐1,3‐benzodithiolium perchlorate. Under rearomatization of the central frame protonation of 4 yields the salt 4c. The reaction of 4 with dicyanoketene gives the ‘push‐pull‐substituted’ 5, and with 9‐carbonylfluorene the fulvalene derivative 7, which can be protonated by CF3CO2H at C(9″) to the salt 8. The reaction of 2‐methylthio‐l,3‐dithiolium jodide 9 with the keto‐enol mixture 2 yields 10, which, on protonation at the carbonyl group by CF3CO2H, gives the salt 11 under rearomatization. The spectral data of the new compounds 4, 4c, 5, 7, 8, 10 and 11 are reported and discussed.
The Synthesis of Dibenzyl trans‐{7‐oxo‐3‐phenyl‐6‐phenylacetamido‐1‐azabicyclo [3.2.0]heptane}‐2,2‐dicarboxylate (Carbapenam)
Authors: Hakimelahi Gholam Hosein , Ugolini Antonio , Just George
Published: December 2004

The synthesis of the title compound is described.
132. The Synthesis of Highly Strained Monocyclic and Bicyclic β‐Lactams (Δ1‐Carbapenem)
Authors: Hakimelahi Gholam Hosein
Published: December 2004

The synthesis of some β‐lactams and one Δ1‐carbapenem is described. The electronic activation of monocyclic β‐lactams of type 1 is not sufficient to generate a bioactive compound.
Stoffwechselprodukte von Mikroorganismen 215. Mitteilung Röntgenstrukturanalyse von Di‐O‐acetyl‐aspochalasin C
Authors: Neupert‐Laves Katartna , Dobler Max
Published: December 2004

The X‐ray crystal structure analysis of the 17,18‐di‐O‐acetyl derivative of the antibiotic aspochalasin C (monoclinic, a = 26.377, b = 10.840, c = 11.937 Å, β = 102.08°, space group C 2) confirms the constitution elucidated by spectroscopic methods and chemical degradation, and establishes the relative configuration.
Stoffwechselprodukte von Mikroorganismen 217. Mitteilung Röntgenstrukturanalyse von O‐Acetyldihydrostreptazolin
Authors: Karrer Andreas , Dobler Max
Published: December 2004

The X‐ray crystal structure analysis of the O‐acetyl dihydro derivative of the antibiotic streptazolin (orthorhombic, a = 8.628, b = 9.814, c = 14.932 Å, space group P212121) established the constitution of the latter as 1.
Sigmatropic Rearrangements Accompanying the Addition of Dichlorocarbene to Norbornadiene
Authors: Jefford Charles W. , Bernardinelli Gérald , Rossier Jean‐Claude , Zuber Jacques A.
Published: December 2004

A new product arising from the reaction of dichlorocarbene with norbornadiene, 6endo‐(2,2‐dichlorovinyl)‐cis‐bicyclo[3.1.0]hex‐2‐ene, is described. It does not arise from the normal exo‐l,2‐adduct, but possibly originates by sigmatropic rearrangement of an initially formed zwitterionic intermediate.
Der [M+11]+‐Pik in den Massenspektren von Diaminen 38. Mitteilung über massenspektrometrische Untersuchungen
Authors: Kühne Hardy , Hesse Manfred
Published: December 2004

The [M+ U]+‐Peak in the Mass Spectra of Diamines

The mass spectra of di‐ and polyamines containing a 1,2‐ethandiamine or a 1,3‐propandiamine unit are quite often characterized by [M+ 1l]+‐peaks. It is demonstrated that these peaks correspond to a fragment‐ion formed by loss of H. from a formaldehyde‐condensation product (e. g. 15) or by loss of CH3. from a acetaldehyde‐condensation product (e. g. 16) with the diamine. The aldehydes are usually impurities in solvents (especially methanol) used by chromatography, synthesis etc. of the diamines.
Übergangsmetall‐katalysierte Additionsreaktionen von 3‐Phenyl‐2H‐azirinen und Acetylencarbonsäureestern
Authors: Inada Akira , Hefmgartner Heinz
Published: December 2004

Transition Metal Catalyzed Addition Reactions of 3‐Phenyl‐2H‐azirines and Alkyl Acetylene Carboxylates

In the presence of molybdenum hexacarbonyl, the 3‐phenyl‐2H‐azirines 1 and 7 react with alkyl acetylene carboxylates 2 via the cleavage of the C, N‐double bond to give 2H‐pyrroles 5 or pyrrole 9 (Table), whose structures were deduced from the spectra data, in particular 13C‐NMR. data. The 2H‐pyrrole 5a was also obtained by treatment of a mixture of 1 and 2a with tungsten hexachloride. A tentative mechanism for the formation of the 2H‐pyrroles is formulated.
Kreuzkonjugierte Cyanine und Merocyanine aus Salzen 1‐substituierter 2,3‐Dimethylchinoxaline. 2. Mitteilung Über die oxydative Umwandlung der Farbbasen
Authors: Schelz Dieter
Published: December 2004

Crossconjugated Cyanines and Meroeyanines, Obtained from Salts of 1‐Substituted 2,3‐Dimethylquinoxslines. 2nd Communication. On the Syntheses of Dehydro‐Forms

Products 3 of the readily oxidized 1 and 2 are found to be sensitive to solvolysis, especially when X and R are electron‐withdrawing substituents. In some cases, the salts 3 could be identified as the oxidation products of the salts 9. The oxidation of 9p (X = 5,6‐benzo, R=CH3) by an alkaline solution of K3Fe(CN)6 leading to the quinoxalinone 10p is compared with the voltammetric oxidation of 81 (X = H, R=4‐C1C6H4) and related to Viehe's [15] c, d‐stabilized radicals. 1H‐NMR.‐spectra of the salts 3 are discussed with regard to the (E/Z)‐isomers,
Iridoide aus Verbascum nigrum L. 182. Mitteilung über organische Naturstoffe
Authors: Seifert Karlheinz , Schöpp Emanuel , Hesse Manfred , Johne Siegfried
Published: December 2004

Iridoids from Verbascum nigrum L.

Two new iridoid glycosides, nigroside 1 (  6‐O‐(3‐O‐einnamoyl‐α‐L‐rhamno‐pyranosyl)aucubin (2), and nigroside 2 (6‐O‐(2‐O‐cinnamoyl‐α‐L‐rhamnopy‐ranosyl)aucubin (3), and the known compound laterioside (1) have been isolated from extracts of the stems of Verbascum nigrum L., and their structures established primarily on the basis of NMR. spectroscopy. Harpagoside (4), a known iridoid glucoside, was also isolated from the roots of this plant.
Synthesis of 1,2‐cis‐Configurated Glycosylphosphonates
Authors: Meuwly Roger , Vasella Andrea
Published: December 2004

A synthesis of 1,2‐cis‐configurated, non‐isosteric phosphonate analogues of aldose‐1‐phosphates is described. Treatment of 1‐O‐acyl‐glycoses 1, 7, 13, and 19 with trialkyl phosphite in the presence of trimethylsilyl trifluoromethanesulfonate gave the 1,2‐cis‐configurated glycosylphosphonates 2, 4, 8, 10, 14, 16, 20, and 22 as the major anomers and the 1,2‐trans‐configurated glycosylphosphonates 3, 5, 9, 11, 15, 17, 21, and 23 as the minor anomers. The 1,2‐cis‐configurated phosphonates 4, 10, 16, and 22 were deprotected to give the (β‐D‐glucopyranosyl)phosphonate 6, the (β‐D‐mannopyranosyl)phosphonate 12, the (β‐D‐ribofuranosyl)phosphonate 18, and the (β‐D‐arabinofuranosyl)phosphonate 24, respectively, in high yields. The preferred formation of 1,2‐cis‐configurated phosphonates is explained by postulating an equilibrium between the anomeric phosphonium‐salt intermediates (such as 25 and 26) and a stabilization of the cis‐configurated salts through formation of a pentacoordinated species (such as 28).
Optisch aktive Lycopin‐epoxide und Lycopin‐glycole: Synthesen und chiroptische Eigenschaften
Authors: Meier Heidi , Uebelhart Peter , Eugster Conrad Hans
Published: December 2004

Optically Active Lycopene Epoxides and Lycopene Glycols: Synthesis and Chiroptical Properties

We present extensive spectral and chiroptical data on the pure and crystalline lycopene diepoxides 1–3 and glycols 4–9. A first synthetic approach to 1–9 with (+)‐malic acid as starting material afforded 30 as a complex mixture of isomers (Scheme 1). Pure stereoisomers 1–9 were obtained using the enantiomerically pure epoxygeraniol 31 as starting material (Scheme 2). Differentiation of the (5Z)‐from the (all‐E)‐isomers by 1H‐NMR and UV/VIS alone is very difficult.
Ein neues Esteriridoidglycosid aus Sambucus ebulus L. (Caprifoliaceae). 1. Mitteilung über die inhaltsstoffe der Zwergholunderwurzel
Authors: Gross Gian‐Andrea , Sticher Otto , Anklin Clemens
Published: December 2004

A Novel Ester Iridoid Glucoside from Sambucus ebulus L. (Caprifoliaceae)

A novel ester iridoid glucoside, ebuloside (1,), which shows structure elements of the rare 7‐Dehydrologanin derivatives combined with those of the Valerianaceae iridoids, was isolated from the roots of Sambucus ebulus L. Its structure was determined by MS, NMR, and CD spectroscopy as 7‐oxo‐8‐deoxyvalerosidatum.
Photosolvolysis of 2‐Allylated Anilines to 2‐Indanols
Authors: Scholl Bernhard , Jolidon Synèse , Hansen Hans‐Jürgen
Published: December 2004

It is shown that 2‐allylated anilines (cf. Schemes 2–4, 7, and 8) on irradiation in protic solvents such as H2O. MeOH, and EtOH in the presence of H2SO4 undergo a novel photosolvolysis reaction to yield specifically trans‐2‐hydroxy‐ and trans‐2‐alkoxy‐1‐methylindanes. Intermediates are presumably tricyclo[4.3.0.01,8]nona‐2,4‐dienes formed in an intramolecular [2s + 2s] cycloaddition reaction (cf. Scheme 7). On the other hand, N,N,N‐trimethyl‐2‐(1′‐methylallyl)anilinium salts 18 (Scheme 6) and 2‐(3′‐butenyl)‐N,N‐dimethylaniline (17) lose on irradiation in MeOH or H2SO4/MeOH the ammonium group reductively to yield (1‐methylallyl)benzene (19) and 1‐methylindane (20), respectively.
Crystal Structure of Tricarbonyl‐[2,3‐η:O‐σ‐(7,7‐dimethoxy‐5,6‐dimethylidenebicyclo[2.2.1]hept‐2‐ene)]iron
Authors: Barbay Yvan , Ioset Jacques , Roulet Raymond , Chapuis Gervais
Published: December 2004

The product of the reaction of [Fe(benzalacetone)(CO)3] with 7,7‐dimethoxy‐5,6‐dimethylidenebicyclo[2.2.1] hept‐2‐ene is tricarbonyl‐[2,3‐η:O‐σ‐(7,7‐dimethoxy‐5,6‐dimethylidenebicyclo [2.2.1]hept‐2‐ene)]iron. Crystals are monoclinic, space group P21/c with a = 6.612(2), b = 11.610(4), c = 18.604(6) Å, and β = 95.91(2)°. The coordination at the metal atom is trigonal bipyramidal. The equatorial sites are occupied by 2 CO's and by the midpoint of the endocyclic double bond of the organic ligand. The axial sites are occupied by one CO group and the O‐atom of one MeO group of the C(OMe)2 bridge. It is an uncommon example of a d8 metal carbonyl complex bearing an O‐bonded ligand.
Synthesis and Crystal Structure of meso‐Δ,Λ‐μ‐Peroxo‐μ‐hydroxobis[bis(ethylenediamine)rhodium(III)]trifluoromethane Sulfonate
Authors: Springborg Johan , Zehnder Margareta
Published: December 2004

The reaction of the meso‐diol, Δ,Λ‐[(en)2Rh(OH)2Rh(en)2]4+, with aqueous H2O2 and 1 equiv. of NaOH at 90° forms the μ‐peroxo‐μ‐hydroxo‐bridged species Δ,Λ‐[(en)2Rh(O2,OH)Rh(en)2]3+ in a yield of ca. 50%. The compound was crystallized as perchlorate and trifluoromethanesulfonate salts. The structure of the latter salt was determined by single‐crystal X‐ray diffraction. The crystals are triclinic with space group P1 and lattice constants a = 11.895(5), b = 12.491(4), c = 13.053(5) Å, α = 103.98(3), β = 92.59(3), γ = 119.52(6)°. The distances of the metal centres to the bridging peroxo ligand are 1.999(8) and 1.983(6) Å. The OO distance in the peroxo group is 1.521(14) Å, and the dihedral angle of the RhOORh unit deviates 65° from planarity. The peroxo complex reacts reversibly with acid, and spectrophotometric studies suggest that the reaction involves protonation of the peroxo bridge, with pKa = 2.70(2) at 25° in 1M NaClO4.
New Saponins and a Prosapogenin from Polygala chamaebuxus L
Authors: Hamburger Matthias , Hostettmann Kurt
Published: December 2004

Two glycosides 2 and 3 of the formerly undescribed triterpene 3β,23,27,29‐tetrahydroxyolean‐12‐en‐28‐oic acid (4) have been isolated from the aerial parts of Polygala chamaebuxus L. In addition, a prosapogenin, obtained by basic hydrolysis of a mixture of bidesmosidic saponins, has been identified as tenuifolin (1). The structures have been established by spectroscopic (IR, 1H‐and 13‐C‐NMR, DCI‐ and FAB‐MS) and chemical methods (acid, basic, and enzymatic hydrolysis, acetylation, bromination).
Synthesis of (5R,8S,10R)‐6‐(Allyloxy)‐ and (5R,8S,10R)‐6‐(Propyloxy)ergolines from the 6‐Methyl Precursors
Authors: Nordmann René , Gull Peter
Published: December 2004

Novel (5R,8S,10R)‐6‐(allyloxy)‐ and (5R,8S,10R)‐6‐(propyloxy)ergolines have been synthesized by use of a Meisenheimer [2,3]‐sigmatropic rearrangement of a (5R,8S,10R)‐6‐allyl‐ergoline N6‐oxide as key step.
Isolement et identification de deux glucosyl‐lutéolines mono‐C‐substituées et de la diglucosyl‐6,8‐lutéoline di‐C‐substituée dans les tiges feuillées de Passiflora incarnata L
Authors: Congora C. , Proliac A. , Raynaud J.
Published: December 2004

Isolation and Identification of two Mono‐C‐glucosyl‐luteolins and of the Di‐C‐substituted 6,8‐Diglucosyl‐luteolin from the Leavy Stalks of Passiflora incarnata L.

The present work on Passiflora incarnata presents the isolation and the structural identification of C‐glycosylluteolins, i.e. of orientin (1), homoorientin (2) and lucenin 2 (3). The latter compound is new for this plant.
Interactions between Oxygen Lone‐Pair Orbitals and Double‐Bond π‐Orbitals in β,γ‐Unsaturated, Bicyclic Ketones; a PE‐Spectroscopic Investigation
Authors: Carrupt Pierre‐Alain , Gabioud Raphy , Rubello Albino , Vogel Pierre , Honegger Evi , Heiloronner Edgar
Published: December 2004

The HE(Iα) photoelectron (PE) spectra of 2,3,5,6‐tetramethylidene‐2‐bicyclo[2.2.1]heptanone (12), 5,6‐dimethylidene‐2‐bicyclo[2.2.1]heptanone (14), 5,6‐dimethylidene‐2‐bicyclo[2.2.2]octanone (16), and 5,6,7,8‐tetramethylidene‐2‐bicyclo[2.2.2]octanone (17) have been recorded, Comparison with the PE data of other β,γ‐unsaturated ketones and parent alkenes, and with the result of ab initio STO‐3G calculations, confirm the existence of significant interactions between the oxygen lone‐pair orbital no and the double‐bond π orbital(s). It is argued that the major contributions to the basis energy shifts and to the cross term between the no and π orbitals are due to a ‘through‐bond’ mechanism.
The Radical Anions of 1,2‐diphenylcyclohexene and Structurally Related Compounds. Conformational ESR and ENDOR studies
Authors: Gerson Fabian , Martin Williiam B.
Published: December 2004

ESR, ENDOR, and TRIPLE resonance studies have been performed on the radical anions of 1,2‐diphenylcyclohex‐1‐ene (4), 1,2‐di(perdeuteriophenyl)cyclohex‐1‐ene ((D10)4) the trans‐configurated 3,4‐diphenyl‐8‐oxabicyclo[4.3.0]non‐3‐ene (5) and its 2,2,5,5‐tetradeuterio derivative (D4)5, and 2,3‐diphenyl‐8,9,10‐trinorborn‐2‐ene (6). The spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} exhibit strong temperature dependence along with a specific broadening of ESR hyperfine lines and proton ENDOR signals. The coupling constant, which bears the main responsibility for these features, is that of the β‐protons in the quasi‐equatorial positions of the cyclohexene ring, and the experimental findings are readily rationlized in terms of relatively modest conformational changes without invoking the inversion of the half‐chair form. The hyperfine data for the β‐protons in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} closely resemble the corresponding low‐temperature values for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document}, However, the ‘unusual’ features observed for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} are absent in the ESR and ENDOR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document}, because the half‐chair conformation of the cyclohexene ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} is deprived of its flexibility. Although the boat form of this ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} is also rigid, the spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} are temperature‐dependent, due to an interconversion between two propeller‐like conformations of the phenyl groups. The pertinent barrier is 30 ± 5 kJ·mol−1. An analogous interconversion presumably takes place in \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} as well, but, unlike \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document}, it is not amenable to experimental study.
Diasterio‐ und enantioselektive Reduktion von β‐Ketoestern mit Cyclopentanon‐, Cyclohexanon‐, Piperidon‐ und Tetralon‐Struktur durch nicht fermentierende Bäcker‐Hefe
Authors: Seebach Dieter , Roggo Silvio , Maetzke Thomas , Braunschweiger Hans , Cercus Jacques , Krieger Manfred
Published: December 2004

Diastereo‐ and Enantioselective Reduction of beta;‐Keto Esters Derived from Cyclopentanone, Cyclohexanone, Piperidone and Tetralone by ‘Non‐fermenting’ Baker's Yeast

Under ‘non‐fermenting’ conditions, i.e. in tap water, in the absence of nutrients baker's yeast (25–380 g/g of substrate, aerobic) reduces β‐keto esters such as those mentioned in the title with better selectivity than under the normally employed ‘fermenting’ conditions (sugar and nutrients, CO2 development). With the β‐ keto esters containing the tetralone substructure, large amount of yeast are required (250–380 g/g); the substrate disappears in the biomass, and the desired reduction product can be extracted after reaction times of up to a week at 30°. The configuration of most products(16–24) is established. Generally, the (R)‐β‐keto ester is reduced faster than the (S)‐enantiomer (the two esters are in equilibrium under the reactio conditions), and the hydride transfer takes place preferentially from the diastereotopic Re‐face. The β‐hydroxy esters thus available are useful starting materials for syntheses of enantiomerically pure compounds (EPC).
Nonafulvalen: Synthese durch oxidative Kupplung von Cyclononatetraenid und Valenzisomerisierung
Authors: Escher André , Neuenschwander Markus , Engel Peter
Published: December 2004

Nonafulvalene: Synthesis by Oxidative Coupling of Cyclononatetraenide and Valence Isomerisation

Following a general strategy (Scheme 2) for the synthesis of fulvalenes by oxidative coupling of Hückel anions, the synthesis of nonafulvalene (1), has been realised (Scheme 3). The most tricky step is a twofold deprotonation of bi(cyclononatetraenydl) 3 with K(t‐BuO) to give 4; it is only possible after equilibration 3⇄3a; otherwise, deprotonation of one cyclononatetraene unit of 3 followed by oxidative coupling with AgBF4 gives quater(cyclononatetraenyl) 12 as an isomeric mixture. The reaction of 3 with Kgives potassium cct‐cyclononatetraenide 11 (M = K; Scheme 5) and not the dianion 4 as reported in the literature. Nonafulvalene (1)is extremely reactive due to its very easy valence isomerisation to geve an isomeric mixture of tetrahydro‐dibenzopentafulvalenes 13 (Scheme 4). The structure of crystalline isomer (E‐anti)‐13 has been proved by X‐ray analysis.
Solubilization of Peptides in Non‐polar Organic Solvents by the Addition of Inorganic Salts: Facts and Implications
Authors: Seebach Dieter , Thaler Adrian , Beck Albert K.
Published: December 2004

The solubility of open‐chain peptide derivatives (12 examples) in non‐polar, ether‐type organic solvents may be greatly increased by addition of salts (LiCl, LiBr, LiI, LiBF4, LiClO4, NaI, MgBr2 CaBr2, ZnCl2) or of titanates (Ti(OEt)4, Ti(OCHMe2)4). Examples are reported (Tables 2–6) in which this solubilizing effect leads to peptide concentrations more than one‐hundred‐fold those in the absence of salt (cf, BocAlaGlyGlyGlyOH in THF from 2g·1−1 to ≥ 300 g·1−1 with 6 equiv. of LiCl), 1H‐NMR Spectra of one of these solutions are reported (Fig. 1). There are no indications for epimerizations of stereogenic centres on the peptide backbone. Possible applications of these solutions in peptide chemistry are discussed.
Catechol‐O‐methyltransferase‐Inhibiting Pyrocatechol Derivatives: Synthesis and Structure‐Activity Studies
Authors: Borgulya Janos , Bruderer Hans , Bernauer Karl , Zürcher Gerhard , Prada Mosé Da
Published: December 2004

3‐Nitro‐ and 3‐cyanopyrocatechols bearing electron‐withdrawing substituents at C(5) have been found to inhibit the enzyme catechol‐O‐methyltransferase. Structure‐activity studies are discussed on the basis of the pharmocological data of 50 compounds (cf, Chapt. 4, Tables 1–7). Some 3‐nitro‐5‐aroylpyrocatechols (Type A2, Table 1) fulfil the requirements for a clinical candidate, being orally active, specific, reversible, and relatively short‐acting. The chemical work involved is illustrated by describing a choice of exemplary syntheses, dealing with compounds 9, 11, 14, 18, 22, 24, 25, 35, 41, and 42 (Chapt. 5, Schemes 1–10).
Photochemical Synthesis of Cyclic 2‐(2,2‐Dimethylpropylidene)‐1,3‐dicarbonyl Compounds
Authors: Hobel Klaus , Margaretha Paul
Published: December 2004

Photolysis (λ = 254 nm) of 4‐(t‐Bu)‐substituted [b]‐fused bi‐ and tricyclic pyrandiones 5 affords title compounds 4 in good yields as well as small amounts of spiroalkanediones 8. The alkyl‐substitution pattern at C(4) of the pyran ring in 5 determines the relative amount of α vs. β‐cleavage products obtained from the primarily formed acyl‐vinyloxy biradical.
The Carbonyl Group as Homoconjugated Electron‐Releasing Substituent. Regioselective electrophilic additions at bicyclo[2.2.1]hept‐5‐en‐2‐one, bicyclo[2.2.2]oct‐5‐en‐2‐one, and derivatives
Authors: Carrupt Pierre‐Alain , Vogel Pierre
Published: December 2004

In CHCl3, CH3CN, or AcOH, benzeneselenenyl chloride (PhSeCl), bromide (PhSeBr), and acetate (PhSeOAc), 2‐nitrobenzenesulfenyl chloride (NO2C6H4SCl), and 2,4‐dinitrobenzenesulfenyl chloride ((NO2)2C6H3SCl) added to bicyclo[2.2.1]hept‐5‐en‐2‐one (5) in an. anti fashion with complete stereo‐ and regioselectivity, giving adducts 20–24 in which the chloride, bromide, or acetoxy substituent (X) occupies the endo position at C(6) and the Se‐ or S‐substituent (E) the exo position at C(5), The addition 5+ (NO2)2C6H3SCl→24 was accompanied by the formation of (1RS, 2RS)‐2‐(2,4‐dinitrophenylthio)cyclopent‐3‐ene‐l‐acetic acid (25). The latter was the major product in AcOH containing LiClO4. The additions of PhSeCl and PhSeBr to bicyclo[2.2.2]oct‐5‐en‐2‐one (6) were less stereoselective (proportion of exo vs. endo mode of electrophilic attack was ca. 3:1) but highly regioselective gazing adducts 27/28 and 29/30, respectively, the regioselectivity being the same as that of the electrophilic additions of 5. The reaction of PhSeCl with a 4:1 mixture of 2‐exo‐chloro‐ and 2‐endo‐chlorobicyclo[2.2.1]hept‐5‐ene‐2‐carbonitriles (12) was slower than addition 5+ PhSeCl; it gave adducts 31/32 (4:1) in which the PhSe moiety occupies the exo position at C(6) and the Cl atom the endo position at C(5). The addition of PhSeCl to 2‐chlorobicyclo[2.2.1]oct‐5‐ene‐2‐carbonitriles (13) was very slow and gave adducts with the same regioselectivity as 12 + PhSeCl, but opposite with that of reactions of the corresponding enones 5 and 6. PhSeX (X = Cl, Br, OAc) added to 2‐cyanobicyclo[2.2.1]hept‐5‐en‐2‐yl acetates (14) with the same regioselectivity as 12 + PhSeCl. The additions of PhSeCl, PhSeBr, NO2C6H4SCl, and (NO2)2C6H3SCl to 2‐(bicyclo[2.2.1]hept‐5‐en‐2‐ylidene)propanedinitrile (49) were not regioselective, showing that a dicyanomethylidene function is not like a carbonyl function when homoconjugated with a π system. The results are in agreement with predictions based on MO calculations suggesting that a carbonyl group homoconjugated with an electron‐deficient centre can behave as an electron‐donating, remote substituent because of favourable n(CO)↔σC(1), C(2)↔p(C(6) hyperconjugative interaction.
Enantioselective Synthesis: Steric and electronic effects of the substrates upon stereoselectivity in the gold(I)‐catalyzed aldol reaction with chiral ferrocenylamine ligands, preliminary communication
Authors: Togni Antonio , Pastor Stephen D.
Published: December 2004

Enantioselectivity in the gold(I)‐catalyzed aldol reaction with chiral ferrocenylamine ligands is strongly dependent upon both the steric and electronic effects of the substrates. In the reaction of pyridine‐2‐, 3‐, and 4‐carbaldehydes with ethyl 2‐isocyanoacetate, surprisingly and significantly different enantioselectivities were observed in the formation of the cis‐ and trans‐dihydro‐oxazoles that must be due to electronic rather than steric effects. The first example of double stereodifferentiation in the gold(l)‐catalyzed aldol reaction is reported.
2′, 3′‐Dideoxy‐3′‐fluorotubercidin and Related Dideoxyribonucleosides:. Synthesis via a 2′‐deoxy‐3′‐oxoribofuranoside intermediate and conformation studies
Authors: Rosemeyer Helmut , Seela Frank
Published: December 2004

An efficient synthesis of the unknown 2′‐deoxy‐D‐threo‐tubercidin (1b) and 2′, 3′‐dideoxy‐3′‐fluorotubercidin (2) as well as of the related nucleosides 9a, b and 10b is described. Reaction of 4‐chloro‐7‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine (5) with (tert‐butyl)diphenylsilyl chloride yielded 6 which gave the 3′‐keto nucleoside 7 upon oxidation at C(3′). Stereoselective NaBH4 reduction (→8) followed by deprotection with Bu4NF(→9a)and nucleophilic displacement at C(6) afforded 1b as well as 7‐deaza‐2′‐deoxy‐D‐threo‐inosine (9b). Mesylation of 4‐chloro‐7‐{2‐deoxy‐5‐O‐[(tert‐butyl)diphenylsilyl]‐β‐D‐threo‐pentofuranosyl}‐7H‐pyrrolo[2,3‐d]‐pyrimidine (8), treatment with Bu4NF (→12a) and 4‐halogene displacement gave 2′, 3′‐didehydro‐2′, 3′‐dideoxy‐tubercidin (3) as well as 2′, 3′‐didehydro‐2′, 3′‐dideoxy‐7‐deazainosne (12c). On the other hand, 2′, 3′‐dideoxy‐3′‐fluorotubercidin (2) resulted from 8 by treatment with diethylamino sulfurtrifluoride (→10a), subsequent 5′‐de‐protection with Bu4NF (→10b), and Cl/NH2 displacement. 1H‐NOE difference spectroscopy in combination with force‐field calculations on the sugar‐modified tubercidin derivatives 1b, 2, and 3 revealed a transition of the sugar puckering from the 3′T2′ conformation for 1b via a planar furanose ring for 3 to the usual 2′T3′ conformation for 2.
Structural Aspects of the Enantioselectivity of Tartrates with α‐Amino‐alcohol Salts. Part II. Crystal structures of (1R, 2S)‐norephedrine hydrochloride and (1R, 2R)‐ norpseudoephedrine hydrochloride
Authors: Egli Martin , Dobler Max
Published: December 2004

Enantioselective host‐guest complexes between α‐amino‐alcohol salts and chiral tartrates can not be crystallised up to now. To study structural aspects of their enantioselectivity, crystal structures of the components were determined. Norephedrine was used as a reference guest α‐amino‐alcohol. (1R, 2S)‐Norephedrine hydrochloride (monoclinic, space group P21 Z = 4, a = 8.455, b = 10.331, c = 12.570 Å, β = 107.45°) and (1R, 2R)‐norpseudoephedrine hydrochloride (monoclinic, space group P21 Z = 2, a = 5.493, b = 8.052, c = 11.986 Å, β = 104.62°) both adopt M‐synclinal conformations with respect to the ammonium and hydroxy groups. Rather short intramolecular N…︁O distances indicate interaction between ammonium and hydroxy groups.
Synthesis and Metal‐Binding Properties of Polybipyridine Ligands Derived from Acyclic and Macrocyclic Polyamines
Authors: Ziessel Raymond , Lehn Jean‐Marie
Published: December 2004

Synthetic procedures have been developed for the preparation of ligands bearing two to six pendent, unsubstituted or substituted 2, 2′‐bipyridine groups attached to acyclic (tripode, tetrapode) and macrocyclic (triazanonade‐cane, cyclam, hexacyclen, bis(bipyrido)hexaazamacrocycle) polyamines. Ligands 1‐5 have been obtained in high yield by condensation of 6‐(bromomethyl)‐2, 2′‐bipyridine (9b) with the corresponding amines in the presence of NaOH, H2O, and MeOH. Ligands 6‐8 have been prepared in good yield by condensation of 9b or the di‐ or tetrasubstituted mono (bromomethyl) bipyridine 10b or 11b, respectively, with the corresponding amines in the presence of Na2CO3 and MeCN. Ligand 1 forms hemi‐cage complexes with RuII, FeI, CrII, and CrIII cations and trinuclear complexes with [RuCl2(bpy)2] and [ReCl(CO)5]. Tetrapode 2 and hexapode 4 gave tetranuclear and dinuclear complexes, respectively, by reaction with Fe11 salts. These complexes possess a variety of interesting physical and chemical properties.
Eine weitere, diesmal erfolgreiche Suche nach 3′‐Epilutein in Pflanzen
Authors: Märki‐Fischer Edith , Eugster Conrad Hans
Published: December 2004

A Further, Now Successful Search for 3′‐Epilutein in Plants

The 3′‐epilutein, an extremely rare carotenoid, found till now in only one plant, was detected in anthers of flowers of several roses and in those of peonies.
Transport Properties of Anion‐Selective Membranes Based on Cobyrinates and Metalloporphyrin Complexes as Ionophores
Authors: Huser Mario , Morf Werner E. , Fluri Karl , Seiler Kurt , Schulthess Peter , Simon Wilhelm
Published: December 2004

Zero‐current counter‐transport studies as well as electrodialytic transport experiments on solvent polymeric membranes doped with ionophores for anions have been carried out and were compared with potentiometric measurements on the same membranes. A theoretical description of the observed phenomena corroborates that lipophilic complexes of Co(III) (e. g. aquacyano[heptakis(2‐phenylethyl)]Co(III) cobyrinate perchlorate) and Mn(III) (e. g. lipophilic Mn(III)porphyrin complexes) act as positively charged carriers for anions, whereas a lipophilic Ru(II)porphyrin complex has to be described as an electrically neutral carrier for anions.
2,4‐Disubstituted Pyrrolo[2,3‐d]pyrimidine α‐D‐ and β‐D‐Ribofuranosides Related to 7‐Deazaguanosine
Authors: Seela Frank , Soulimane Tewfik , Mersmann Kann , Jürgens Thomas
Published: December 2004

Nucleobase‐anion glycosylation (KOH, tris[2‐(2‐methoxyethoxy)ethyl]amine (TDA‐1), MeCN) of the pyrrolo[2,3‐d]pyrimidines 4a–d with 5‐O‐[(1,1‐dimethylethyl)dimethylsilyl]‐2,3‐O‐(1‐methylethylidene)‐α‐D‐ribo‐furanosyl chloride (5) gave the protected β‐D‐nucleosides 6a–d stereoselectively (Scheme 1). Contrary, the β‐D‐halogenose 8 yielded the corresponding α‐D‐nucleosides (9a and 9b) apart from minor amounts of the β‐D‐anomers. The deprotected nucleosides 10a and 11a were converted into 4‐substituted 2‐aminopyrrolo[2,3‐d]‐pyrimidine β‐D‐ribofuranosides 1. 10c, 12, 14, and 16 and into their α‐D‐anomers, respectively (Scheme 2). From the reaction of 4b with 5, the glycosylation product 7 was isolated, containing two nucleobase moieties.
Reaktionen von 5H‐1,2λ5‐Azaphospholen mit Arylazocarbonitrilen sowie Acetylendicarbonsäure‐estern
Authors: Rieda Walter , Fulde Maria , Bats Jan W.
Published: December 2004

Reactions of 5H,2λ5‐Azaphospholes with Arylazocarbonitriles and Dialkyl Acetylenedicarboxylates

Azaphospholes 1a–c react with activated arylazocarbonitriles to 1,5,2λ5‐diazaphosphorines 2a–c and 3a–c. The reaction of 1a–c with diethyl or dimethyl acetylenedicarboxyiates yields 7H‐1,4λ5‐azaphosphepines 4a–c. The structures of 2b, 3a, and 4a are established by an X‐ray diffraction analysis.
Anion Selectivity of Tetravalent Tin Compounds in Membranes Studied by 119Sn‐, 13C‐ and 1H‐NMR
Authors: Pham Hung‐Viet , Pretsch Ernö , Fluri Karl , Bezegh Andras , Simon Wilhelm
Published: December 2004

The fundamental molecular aspects of trialkyltin compounds of the type R3SnY have been investigated in view of their applicability as ion‐selective components in solvent polymeric membranes. The interaction between these compounds and anions has been studied using 119Sn‐ and 13C‐NMR. Neutral tetracoordinated trialkyltin compounds form a negatively charged pentacoordinated complex upon interaction with Cl‐ions in homogeneous organic phases as well as in membranes in contact with aqueous solutions. Although in a homogeneous phase, the electronegative substituent Y determines the complex‐formation constant, it has no influence on the potentiometric anion selectivity in liquid membranes containing trialkyltin carriers R3SnY with different Y. The observed selectivity pattern is not given by the magnitude of the stability constants in a homogeneous phase but is dictated by the prevailing association‐dissociation process leading to tetracoordinated compounds which change in constitution due to varying sample composition, The results obtained from equilibrium studies of tetravalent mono tin compounds with anions in both homogeneous phase and in two‐phase systems confirm the earlier hypothesis that trialkyltin compounds incorporated in solvent polymeric membranes act as electrically neutral carriers for anions.
Neue Synthese von (−)‐(R)‐Cembren A, Synthese von (+)‐(R)‐Cembrenen und (+)‐(S)‐Cembren
Authors: Farkas Imre , Pfander Hanspeter
Published: December 2004

Novel Synthesis of (−)‐(R)‐Cembrene A, Synthesis of (+)‐(R)‐Cembrenene and (+)‐(S)‐Cembrene

A novel synthesis of (−)‐(R)‐cembrene A ((−)‐3) was developed using the Sharpless epoxidation for the introduction of the chiral center. Furthermore, the synthesis of (+)‐(R)‐cembrenene ((+)‐4) showed that this cembranoid must have the (R)‐configuration and not, as previously reported, the (S)‐configuration. Selective hydrogenation of (+)‐4 afforded (+)‐(S)‐cenibrene ((+)‐5).
1‐(2′‐Deoxy‐β‐D‐xylofuranosyl)thymine Building Blocks for Solid‐Phase Synthesis and Properties of Oligo(2′‐Deoxyxylonucleotides)
Authors: Rosemeyer Helmut , Seela Frank
Published: December 2004

1‐(2′‐Deoxy‐β‐D‐threo‐pentofuranosyl)thymine (= 1‐(2′‐deoxy‐β‐D‐xylofuranosyl)thymine; xTd; 2) was converted into its phosphonate 3b as well as its 2‐cyanoethyl phosphoramidite 3c. Both compounds were used for solid‐phase synthesis of d[(xT)12‐T] (5), representing the first DNA fragment build up from 3′–5′‐linked 2′‐deoxy‐‐β‐D‐xylonucleosides. Moreover, xTd was introduced into the innermost part of the self‐complementary dodecamer d(G‐T‐A‐G‐A‐A‐xT‐xT‐C‐T‐A‐C)2 (9). The CD spectrum of d[(xT)12–T] (5) exhibits reversed Cotton effects compared to d(T12) (6; see Fig. 1), implying a left‐handed single strand. With d(A12) (7) it could be hybridized to form a propably Left‐handed double strand d(A12) · d[(xT)12–T] (7·5) which was confirmed by melting experiments in combination with temperature‐dependent CD spectroscopy. While 5 was hydrolyzed by snake‐venom phosphodiesterase, it was resistant towards calf‐spleen phosphodiesterase. The modified, self‐complementary duplex 9 was hydrolyzed completely by snake‐venom phosphodiesterase, at a twelvefold slower rate compared to unmodified 8; calf‐spleen phosphodiesterase hydrolyzed 9 only partially.
Versatile Stereoselective Synthesis of Completely Protected Trifunctional α‐Methylated α‐Amino Acids Starting from Alanine
Authors: Altmann Eva , Nebel Kurt , Mutter Manfred
Published: December 2004

A new route to completely protected α‐methylated α‐amino acids starting from alanine is described (see Scheme). These derivatives, which are obtained via base‐catalyzed opening of the oxazolidinones (2S,4R)‐ and (2R,4S)‐2, can be directly employed in peptide synthesis. The synthesis of both enantiomers of Z‐protected α‐methylaspartic acid β‐(tert‐butyl)ester (O4‐(tert‐butyl) hydrogen 2‐methylaspartates (R) or (S)‐4a), α‐methyl‐glutamic acid γ‐(tert‐butyl) ester (O5‐(tert‐butyl) hydrogen 2‐methylglutamate (R)‐ or (S)‐4b), and of Nε‐bis‐Boc‐protected α‐methyllysine (N6,N6‐bis[(tert‐butyloxy)carbonyl]‐2‐methyllysine (R)‐ or (S)‐4c) is described in full detail.
Synthesis of 1H,2,3‐Triazoles from 2‐Substituted Cyclododecanones and Phenyl Azide
Authors: Ognyanov Vassil I. , Hesse Manfred
Published: December 2004

By reaction with phenyl azide, 2‐cyano‐ and 2‐(ethoxycarbonyl)‐substituted cyclododecanones are converted into 5‐amino‐ and 5‐hydroxy‐1H‐1,2,3‐triazoles, respectively. The possible reaction mechanism is discussed.
Regioselektive 1,3‐dipolare Cycloadditionen von Thiocarbonyl‐yliden mit 1,3‐Thiazol‐5(4H)‐thionen
Authors: Mlostoń Grzegorz , Linden Anthony , Heimgartner Heinz
Published: December 2004

Regioselective 1,3‐Dipolar Cycloadditions of Thiocarbonyl Ylides with 1,3‐Thiazole‐5(4H)‐thiones

The thiocarbonyl ylides 13 and 1,3‐thiazol‐5(4H)‐thiones 1 undergo a smooth reaction to yield spirocyclic 1,3‐dithiolanes 14–16 (Schemes 4–6). The 1,3‐dipolar cycloadditions occur in a regioselective manner, but the orientation of the thiobcnzophenone‐S‐methylide (13b) differs from that of the cycloalkane thione‐S‐methylides 13a and 13c. Whereas the 1,3‐cycloadduct with 13b is formed in accordance with frontier‐orbital considerations, the inverse orientation in the reactions with 13a and 13c most likely is the result of steric hindrance in the transition state. The thiocarbonyl ylides have been prepared in situ from the corresponding 2,5‐dihydro‐1,3,4‐thiadiazoles 12. The more stable aliphatic precursors 12a and 12c undergo decomposition at 50°, the unstable 12b at −30°.
Asymmetric Catalysis by Vitamin B12. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol
Authors: Bonhôte Pierre , Scheffold Rolf
Published: December 2004

The isomerization of 1,2‐epcxycyclopentane (1) to enantiomerically enriched (R)‐cyclopent‐2‐enol (2) in protic solvents is catalyzed by cob(I)alamin. The enantiomeric excess (e.e.) of (R)‐2 is usually ca. 60%; it is only slightly dependent on the temperature, but increases with decreasing dielectric constant ε of the solvent. Standard kinetic methods show the reaction to be first order in vitamin B12 and zero order in 1. The rate constant increases exponentially with increasing ε of the solvent. An Arrhenius plot at ε = 40 gives activation parameters ΔH≠ = 78 ± 4 kJ·mol−1 and ΔS≠ = −49 ± 1 J·mol−1·K−1. The isomerization 1 → 2 proceeds in two steps (Schemes 2 and 7): (i) The epoxide ring is first opened by the proton‐assisted fast and irreversible nucleophilic attack of the chiral CoI catalyst to form diastereoisomeric (1R,2R)‐ and (1S,2S)‐(2‐hydroxycyclo‐pentyl)cob(III)alamins 6 in a ratio of ca. 4:1 which are the dominant species in the steady state; (ii) The intermediates 6 then decompose in the rate‐limiting step to form 2 and recycled catalyst. Experiments with specifically 2H‐labeled 1 showed the hydro‐cobalt elimination 6 → 2 to be non‐stereoselective. It proceeds via reversible CoC bond homolysis to a free 2‐hydroxycyclopentyl radical from which stereoelectronically controlled H‐abstraction by Co11 takes place.
C‐Glykoside der N‐Acetylneuraminsäure. Synthese und Untersuchung ihrer Wirkung auf die Vibrio cholerae Sialidase
Authors: Wallimann Kurt , Vasella Andrea
Published: December 2004

C‐Glycosides of N‐Acetylneuraminic Acid

The synthesis of the C‐glycosides 8, 15, and 9 of N‐acetylneuraminic acid is described. Hydroxymethylation of the Li‐ester enolate, derived from 5, yielded the protected C‐glycosides 7 and 10 (46%; 3:1), which were deprotected to yield 8 (54%) and 15 (51%; Scheme 2). The mesylate 16 was obtained from 7 (73%) and transformed via the azide 17 (75%) into the acid 18 (66%) and the amino acid 9 (Scheme 3). The configuration at C(2) of 17 was proved by transforming 17 into the bicyclic lactam 19. Both 8 and 15 are very weak inhibitors of Vibrio cholerae sialidase; 9 appears to stimulate this enzyme.
Trialkyltin Compounds as Neutral Carriers for Anions in PVC Liquid Membranes and Complex Formation with Oxoanions
Authors: Fluri Karl , Koudelka Juraj , Simon Wilhelm
Published: December 2004

Under the influence of an electric field, trialkyltin compounds of the type R3SnX behave as electrically neutral carriers for anions in poly(vinyl chloride) liquid membranes. The interaction of tinorganic compounds with oxoanions was studied in organic phase by means of119Sn‐NMR‐monitored titrations. In the case of tributyltin chloride, no appreciable amount of complex was formed with hydrogensulfate, whereas dihydrogenphosphate gave rise to a new species. Dioctyltin dichloride and dioctyltin dioctyltin diacetate formed a 1:2 (salt/ligand) complex with hydrogenphosphate.
Efficient Synthesis of Enantiomerically Pure α‐Ionone from (R)‐ and (S)‐α‐Damascone
Authors: Fehr Charles , Guntern Olivier
Published: December 2004

(R)‐ and (S)‐α‐ionone ((R)‐ and (S)‐1, resp.) were prepared from (R)‐ and (S)‐α‐damascone ((R)‐ and (S)‐3, resp.) without racemization in 48% yield employing a new enone transposition. The described transposition is complementary to existing methods whose application is often prohibited by the structural requirements of the substrate. The now easily accessible α‐ionones of desired absolute configuration are useful as chiral building blocks for terpenoid synthesis.
1,7‐Dideaza‐2′‐deoxyadenosine: Building blocks for solid‐phase synthesis and secondary structure of base‐modified oligodeoxyribonucleotides
Authors: Seela Frank , Wenzel Thomas
Published: December 2004

The 1,7‐dideaza‐2′‐deoxyadenosine (c1c7Ad; 1) was converted into building blocks 3a,b for solid‐phase oligodeoxyribonucleotide synthesis. Testing various N‐protecting groups – benzoyl, phenoxyacetyl, [(fluoren‐9‐yl)methoxy]carbonyl, and (dimethylamino)methylidene – only the latter two were found to be suitable (1 → 4b, d). Ensuing 4,4′‐dimethoxytritylation of 4d and phosphitylation afforded the 3′‐phosphonate 3a or the 3′‐[(2‐cyanoethyl)diisopropylphosphoramidite] 3b. Self‐complementary oligonucleotides with alternating dA or c1c7Ad and dT residues (7 and 8) as well as palindromic oligomers such as d(C‐G‐C‐G‐c1c7 A‐c1c7 A‐T‐T‐C‐G‐C‐G) (10) and d(G‐T‐A‐G‐c1c7 A‐c1c7 A‐T‐T‐C‐T‐A‐C) (12) were synthesized. Duplex stability was decreased because 1 cannot form Watson‐Crick or Hoogsteen base pairs if incorporated into oligonucleotides. On the other hand, the structural modifications in 10 and 12 forced these palindromic oligomers to form hairpin structures.