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  • Organic Chemistry  (4,651)
  • 1985-1989  (3,492)
  • 1920-1924  (1,159)
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  • 1
    Electronic Resource
    Electronic Resource
    Masthead (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680101
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  • 2
    Electronic Resource
    Electronic Resource
    Inverted Hyperconjugation in Symmetrical 1,4-DihalocubanesPart IV of ‘The Equivalent Bond Orbital Model Revisited’ (Part III: [1]), and Part 50 of ‘Small and Medium Rings’ (Part 49: [1]). (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 23-38 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The σ-orbital manifold of cubane 1, as suggested by its PE spectrum, is divided into two sets separated by a 3 eV gap extending from ∼ -10.5 eV to ∼ -13.5 eV. Halogen substituents with np AO basis energies falling into this gap (e.g. Cl or Br) will, therefore, hyperconjugate appreciably with both sets. Interaction with the lower-lying set will lead to the usual destabilization (‘normal’ hyperconjugation), whereas interaction with the set above will necessarily lead to a ‘stabilization’ (‘inverted’ hyperconjugation). As a result the lone-pair ionization energies of Cl or Br substituted cubanes (derived from PE spectra) are much larger than naively expected for an alkyl halide containing as much as 8 C-atoms. In particular no significant shift of the eg-1 lone-pair bands in the PE spectra of 1,4-dichloro- and 1,4-dibromocubane can be detected with respect to the first ionization energies of the free atoms Cl and Br, or of HCl and HBr.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680104
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  • 3
    Electronic Resource
    Electronic Resource
    Sesquiterpenoids of the Sponge Dysidea fragilis of the North-Brittany SeaPresented by F.P. as a part of a lecture at the University of Innsbruck on March 15th, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 39-48 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title sponge is shown to contain eight new sesquiterpenoids for which a common, unusual biogenetic origin is postulated. The compounds are shown to be: (-)-(1R*,4R*)-3-(3′-furyl)methyl-2-p-menthen-7-yl acetate ((-)-8b); two diols separated as the monoacetates (-)-(1S*,4R*)-3-(3′-furyl)methyl-l-hydroxy-2-p-menthen-7-yl acetate ((-)-13a) and the (-)-(1R*,4R*)-epimer (-)-13b, the two C(4)-epimeric 4-ethoxy-3-(1′(7′),2′-p-menthadien-3′-yl)methyl-2-buten-4-olides ((+)-14a and (-)-14b), (-)-3-(3′-furyl)methyl-7-nor-2-p-menthen-l-one ((-)-11), (-)-(3Z)-1-(3′-furyl)-4,8-dimethylnona-3, 7-dien-2-yl acetate ((-)-17), and (+)-3-(5′,7′-seco-2′(10′)-pinen-7′-yl)methylfuran ((+)-15).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680105
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  • 4
    Electronic Resource
    Electronic Resource
    Melanotropin Receptors I. Synthesis and Biological Activity of Nα-(5-Bromovaleryl)-Nα-deacetyl-α-melanotropinParts of this report have appeared as a thesis [1]. Nomenclature and abbreviations [2]. Additional abbreviations: MSH = melanophore stimulating hormone (melanotropin), DCC = N, N′-dicyclohexylcarbodiimide, DCU = N, N′-dicyclohexylurea, DMF = dimethylformamide, HOBt = 1-hydroxybenzotriazole, Boc = tert-butoxycarbonyl, OBut = tert-butoxy, Msoc = 2-(methylsulfonyl)ethoxycarbonyl, Np = 4-nitrophenyl, Z = benzyloxycarbonyl, TFA = trifluoroacetic acid. Chiral amino acids are in their L-configuration. Culture media see Experimental.Dedicated to Dr. Nitya Anand, Director of the Central Drug Research Institute, Lucknow, India, on the occasion of his 60th birthday (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1-11 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical synthesis and biological activities of a new α-melanotropin derivative are described. Nα-(5-Bromovaleryl)-Nα-deacetyl-α-melanotropin contains the 5-bromopentanoyl group as a chemical ‘handle’ in place of the acetyl group of the natural hormone. The synthesis involved a new protected intermediate which allowed the selective deprotection of either the Nα or Nα amino group. The title compound reacted with sodium thiosulfate to give Nα-deacetyl-Nα-(5-(sulfothio)valeryl)-α-melanotropin, a key intermediate for the preparation of tobaccomosaic virus/α-melanotropin disulfide conjugates. As a basis for the study of the conjugates, biological activities of the title compound on Cloudman S-91 mouse melanoma cell cultures (tyrosinase stimulation, binding, and cyclic AMP accumulation) were determined. They proved to be quite similar to the corresponding α-melanotropin activities. Differences in bindings may be explained by stronger hydrophobic interaction of the new derivative with the lipid phase of the target cell membranes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680102
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  • 5
    Electronic Resource
    Electronic Resource
    Bond Angles in Lactones and Lactams (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 76-82 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carbonyl group in lactones and, to a lesser extent, in lactams tends to show a C—C=O angle that is larger than the O—C=O or N—C=O angle, the difference increasing in magnitude as the ring size decreases. The observed trend provides information on ratios of force constants characterising the flexibility of the s-cis-ester group and may be interpreted in terms of incipient chemical reaction to -O—(CH2)n—C≡O+. Molecular orbital calculations (MINDO/3, MNDO, EH) for model compounds provide an electronic interpretation of this angle difference in terms of an anomeric interaction between the p-type lone pair on the carbonyl O-atom and the antibonding C-O or C-N orbital.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680110
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  • 6
    Electronic Resource
    Electronic Resource
    Cyclic Octa- and Decapeptides as Ionophores for Magnesium (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 110-118 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclic octa- and decapeptides have been prepared, and their ion selectivity in solvent polymeric membranes was studied. Cyclo(-LPro-DLeu-)5 behaves as an ionophore which selects Mg2+ over Ca2+ by a factor of 100. Cyclo(LPro-LLeu)5 induces selectivity in membranes for Mg2+ over Li+, Na+ and K+ by a factor of 400, 200 and 10, respectively, while selectivity of Mg2+ over Ca2+ is poor. Some evidence is presented which indicates that certain ionophores exhibit high selectivity for monovalent magnesium complexes.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680114
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  • 7
    Electronic Resource
    Electronic Resource
    Stereoselective Double Functionalization of Iron-Carbonyl Complexes of 5,6,7,8-Tetramethylidenebicyclo[2.2.2]oct-2-ene. Crystal Structure and Absolute Configuration of (-)-trans-μ-[(2S,5R,7S)-C,5,6,C-η:C,7,8,C-η-(6,7,8-trimethylidene-5-((Z)-2-oxopropylidene)-2-bicyclo[2.2.2]octyl acetate)]-bis(tricarbonyliron) (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 126-134 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Friedel-Crafts monoacylation of trans-η-[(1RS,2RS,4SR,5SR,6RS,7SR,8SR)-C,5,6,C-η:C,7,8,C-η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octyl acetate)]-bis(tricarbonyliron) ((±)-5) is highly stereoselective and yields trans-η-[(1RS,2RS,4RS,5SR,6RS,7RS,8SR)-C,6-η,oxo-σ:C,7,8,C-η-(6,7,8-trimethylidene-5-((Z)-2-oxopropylidene)-2-bicyclo[2.2.2]octyl acetate)]-bis(tricarbonyliron) ((±)-8) which equilibrates with the trans-η-[(1RS,2RS,4RS,5SR,6RS,7RS,8SR)-C,5,6,C-η:C,7,8,C-η-(6,7,8-trimethylidene-5-((Z)-2-oxopropylidene)-2-bicyclo[2.2.2]octyl acetate)]-bis(tricarbonyliron) ((±)-9) on heating. Optically pure (-)-9 has been prepared from the corresponding optically pure alcohol (+)-4. The structure and absolute configuration of (-)-9 was established by single-crystal X-ray diffraction.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680116
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  • 8
    Electronic Resource
    Electronic Resource
    Alkylierung in der 2-Stellung von (2S, 4R)- 4-Hydroxyprolin unter Retention (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 155-161 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation in the 2-Position of (2S, 4R)-4-Hydroxyproline with Retention of ConfigurationO-Acetyl-4-hydroxyproline (1b) is condensed with pivalaldehyde to give a single stereoisomer of the 2-(tert-butyl)-4-oxo-3-oxa-1-azabicyclo[3.3.0]oct-7-yl acetate (3). This is converted to the enolates 4 or 5, reactions of which with alkyl halides, aldehydes, and acetone (→6,9,10,11) are diastereoselective (lk-1,3-induction). Cleavage of the corresponding products furnishes the enantiomerically pure 2-deuterio-, 2-methyl-, 2-allyl-, and 2-benzyl-substituted 4-hydroxyprolines 2a-2d.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680119
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  • 9
    Electronic Resource
    Electronic Resource
    Über den sterischen Verlauf der Umsetzung von Enaminen aus offenkettigen Aldehyden und Ketonen mit Nitroolefinen zu 2,3-disubstituierten 4-NitroketonenTeilweise in einer Kurzmitteilung beschrieben [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 162-172 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Steric Course of the Reaction of Enamines Derived from Open-Chain Aldehydes and Ketones with Nitro-olefins Yielding 2,3-Disubstituted 4-NitroketonesThe relative configuration of the nitro-ketone 12 obtained by the title reaction has been proved by a Baeyer-Villiger degradation and subsequent reduction to the amino-alcohol (±)-(u)-20, the relative configuration of which is identical with a sample prepared from 2-methyl-3-hydroxybutyrate of known configuration (Scheme 1). The stereochemical course of the title reaction is thus as predicted by our topological rule. It is assumed that the other nitro-ketones 13-18 described here are also formed by (lk)-combination of the trigonal centers of the educts (diastereoselectivity 〉 90%, see Formulae and Fig. 1). It is not possible to reverse this relative topicity by employing (Z)- instead of (E)-components of the starting materials, due to the reversibility of the primary step of these Michael additions (Schemes 2 and 3, and Fig. 2).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680120
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  • 10
    Electronic Resource
    Electronic Resource
    Photochemical reactions. 142nd communication141st Communication: [1].. Photochemistry of a 6,7-epoxy-1,3-diene of the ionone series (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 207-211 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On singlet excitation (λ = 254 nm), the epoxydiene (E)-3 underwent (E)/(Z)-isomerization, electrocyclic ring closure of the diene side chain leading to the cyclobutenes 4A + B, and rearrangement to the cyclohexanones 5A + B. Compounds 5A + B were presumably formed in a series of processes including a 1,3-acyl shift of the homoconjugated ketone 8, arising from (Z)-3 by a 1,5-H-shift accompanied by cleavage of the C,O-bond of the oxirane.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680125
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  • 11
    Electronic Resource
    Electronic Resource
    Camphorsulfonamide-Shielded, Asymmetric 1,4-Additions and Enolate Alkylations; Synthesis of a Southern Corn Rootworm Pheromone. Preliminary CommunicationPresented in part at the Autumn Meeting of the Swiss Chemical Society, Berne, October 19, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 212-215 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using readily accessible 10-sulfonamido-isoborneols as regenerable, chiral auxiliaries, highly face-selective C-C-bond formations at Cα and Cβ of carboxylates could be conveniently achieved. Thus, conjugated additions of RCu to enoates (1→2) furnished, after saponification, β-substituted carboxylic acids 3 in 94-98% e.e. Similarly, propionates 12 yielded after deprotonation, enolate alkylation, and reductive ester cleavage the (R)-alcohols 15 in 78-98% e.e. The acid (+)-3e was converted to the pheromone (-)-11.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680126
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  • 12
    Electronic Resource
    Electronic Resource
    The crystal structure of racemic and meso-diastereoisomers of aqua[2,6-bis(3-carboxy-1,2-dimethyl-2-azapropyl)pyridine]-Co(III) · Hexafluorophosphate · Di- and monohydrate, respectively (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 185-191 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of the pentadentate ligand 2,6-bis(3-carboxy-1,2-dimethyl-2-azapropyl)pyridine yields a mixture of the racemic and meso-isomers which it was difficult to separate by column chromatography. When the cationic Co(III)-complex of this ligand was crystallized with hexafluorophosphate as anion, two distinct crystalline forms were produced. The complex of the racemic ligand, 1, has C2 symmetry and is a dihydrate; a = 8.999(8), b = 12.047(6), c = 20.65(1) Å, orthorhombic, space group Peen,Z = 4, R = 0.074 for 1439 observed reflections. The complex of the meso-ligand, 2, shows two independent molecules (2A and 2B) per asymmetric unit, both monohydrates with a resolved disordered H2O molecule in 2A; a = 10.109(4), b = 12.835(2), c = 16.651(3) Å, α = 89.5(1)°, β = 84.7(3)°, γ = 88.6(3)°, triclinic, space group P1, Z = 4, Rs = 0.054 for 4198 observed reflections. The coordination around the Co-atom is distorted octahedral in both complexes, with the coordinated H2O molecule trans to the pyridine N-atom. In the racemic form of the complex, 1, the pyridine ring is twisted about the Co-N(1) bond with respect to the plane defined by atoms Co, N(1), O(W1), N(2) and N(2P) by 17.2(2)°. In the meso-form of the complex, 2, the CH3 substituent C(8P) on atom C(4P), is now axial with respect to the 5-membered chelate ring. As a result of steric hinderance between atom O(1) and CH3(8P), the pyridine ring has been displaced from the best mean-plane formed by atoms Co, O(W1), N(2) and N(2P). The principal axis of the pyridine ring C(3)…N(1), makes an angle of 14.1(1)° (mean) with this plane. At the same time the pyridine ring is twisted about axis C(3)…N(1) with respect to this plane by 19.7(1)° (mean).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680123
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  • 13
    Electronic Resource
    Electronic Resource
    Halochrome Molekeln. 6. Mitteilung. Spektrophotometrische Untersuchungen zum acidobasischen Verhalten substituierter 6,6-Diphenyl-6H-chromeno[4,3-b]indolizine und ihrer Aza-analogen (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 64-71 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Halochromic Molecules. Spectrophotometric Investigation of the Acidobasic Behaviour of Substituted 6,6-Diphenyl-6H-chromeno[4, 3-b]indolizines and their Aza-analoguesSubstituted 6,6-diphenyl-6H-chromeno[4,3-b]indolizines form ring-opened, intensely coloured (diphenyl)-indolizinylcarbenium salts with acid. UV/VIS spectra of the coloured salts are discussed on the basis of VEPPPCI calculations. The ∊pH* curves in buffered MeOH/H2O solutions and the pK* values are determined. The title compounds undergo very complex protonation equilibria.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680108
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  • 14
    Electronic Resource
    Electronic Resource
    Dimerisation of caffeine (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 72-75 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Displacements of 1H-NMR chemical shifs for caffeine in D2O solution as a function of concentration conform to the behaviour expected for pure dimer formation according to the equilibrium 2(caffeine)⇄(caffeine)2 with a statistical probability of at least 95%. Confidence limits reported earlier for the dimerisation constant of caffeine represent the real statistical dispersion in the experimental data and do not reflect a systematic error such as tetramer formation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680109
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  • 15
    Electronic Resource
    Electronic Resource
    The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part IVPart III: [1].. Hydride-ion abstraction in 1,2-exo-trimethylenenorbornane (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 104-109 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the AlBr3-catalyzed adamantane rearrangement in CS2 of 1,2-exo-trimethylenenorbornane (1) to 2-endo,6-endo-trimethylenenorbornane (3), hydride-ion abstraction occurs at C(6) from the exo-side. The kH/kD value for competition between 1 and 5 (Dexo-C(6)) was 1.58 ± 0.05, whereas no kinetic isotope effect was operative for competition between unlabeled 1 and 4 (Dendo-C(5)) and between 1 and 6 (Dendo-C(6)).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680113
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  • 16
    Electronic Resource
    Electronic Resource
    Syntheses of Racemic Diaminosugar Derivatives Starting from 1,2-Dihydropyridines and from Nitrosobenzene (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 95-103 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic diaminosugars were easily obtained by a regio- and stereoselective three-step synthetis. In the first step, regiospecific hetero-Diels-Alder cycloadditions between 1,2-dihydropyridines 1a and 10 and nitrosobenzene led to the bicyclic compounds 2a and 11, respectively, cis-Glycol formation starting from these latter adducts, followed by hydrogenolysis of the N—O bond and by exhaustive acetylation of the OH-groups, led to the diaminolyxose 5, the diaminomannose 14 and the diaminoallose 15. When starting from benzyl 1,2-dihydropyridine-1-carboxylate (1b) and using the same reaction sequence, the racemic piperidine derivative 8 was obtained.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680112
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  • 17
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen. 231. Mitteilung230. Mitteilung s. [1].. Bafilomycin-A1-21-O-(α-L-rhamnopyranosid): Strukturaufklärung durch chemische Verknüpfung mit Bafilomycin A1 und Leucanicidin (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 83-94 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isolation of Bafilomycin-A1-21-O-(α-L-rhamnopyranoside). Structural Determination by Chemical Correlation with Bafilomycin A1 and LeucanicidinFrom cultures of an actinomycete strain, the known antifungal and insecticidal antibiotic leucanicidin (1) and a hitherto unknown antifungal antibiotic, bafilomycin-A1-21-O-(α-L-rhamnopyranoside) (2), were isolated. The latter is spectroscopically closely related to 1 and bafilomycin A1 (3) and gave degradation products identical with compounds obtained by analogous degradation of 1 and 3.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680111
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  • 18
    Electronic Resource
    Electronic Resource
    Steric Effects on Reaction Rates. VI. Application of a New MM2 Force-Field for Carbenium Ions to Solvolysis Rates of Secondary p-Toluenesulfonates (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 119-125 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An empirical force-field for carbenium ions has been incorporated in Allinger's MM2 programme. Structural parameters of secondary carbenium ions calculated by this method are compared with those obtained with Schleyer's BIGSTRN calculations. The strain changes occurring upon solvolysis of secondary p-toluenesulfonates are evaluated by means of this force-field and correlated with the rate constants for solvolysis. The equation for correlation of acetolysis, relative to cyclohexyl p-toluenesulfonate, of 28 kc substrates is ΔGrel+ = 0.67 ΔEst - 0.20 (r = 0.958).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680115
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  • 19
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    Electronic Resource
    Herstellung enantiomerenreiner cis- oder trans-konfigurierter 2-(tert-Butyl)-3-methylimidazolidin-4-one aus den Aminosäuren (S)-Alanin, (S)-Phenylalanin, (R)-Phenylglycin, (S)-Methionin und (S)-Valin (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 135-143 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of the Enantiomerically Pure cis- and trans-Configurated 2-(tert-Butyl)-3-methylimidazolidin-4-ones from the Amino Acids (S)-Alanine, (S)-Phenylalanine, (R)-Phenylglycine, (S)-Methionine, and (S)-ValineIn contrast to α-hydroxy and α-mercapto carboxylic acids, simple α-amino acids do not form acetal-type derivatives (2, X = NH) with pivalaldehyde. For the generation of amino-acid-derived chiral, nonracemic enolates (cf. 3), and hence, for the α-alkylation of amino acids without racemization and without an external chiral auxiliary, the imidazolidinones 12-14 were prepared diastereoselectively. To this end, the methyl or ethyl esters of amino-acid hydrochlorides were first converted to N-methylamides of amino acids which in turn were condensed with pivalaldehyde to give (neopentylidenamino)amides (11). These Schiff bases could be cyclized either to trans-or to cis-imidazolidinones (12, 14 and 13, respectively), which were obtained in enantiomerically pure form after recrystallization. The enantiomeric purities were confirmed by HPLC with chiral stationary phases or by 1H-NMR spectroscopy in the presence of chiral shift reagents. The configurations (cis, trans) were assigned by NOE measurements on 300- or 360-MHz 1H-NMR spectrometers.
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    α-Alkylation of Amino Acids without Racemization. Preparation of Either (S)- or (R)-α-Methyldopa from (S)-Alanine (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 144-154 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure cis- and trans-5-alkyl-1-benzoyl-2-(tert-butyl)-3-methylimidazolidin-4-ones (1, 2, 11, 15, 16) and trans-2-(tert-butyl)-3-methyl-5-phenylimidazolidin-4-one (20), readily available from (S)-alanine, (S)-valine, (S)-methionine, and (R)-phenylglycine are deprotonated to chiral enolates (cf. 3, 4, 12, 21). Diastereoselective alkylation of these enolates to 5,5-dialkyl- or 5-alkyl-5-arylimidazolidinones (5, 6, 9, 10, 13a-d, 17, 18, 22) and hydrolysis give α-alkyl-α-amino acids such as (R)- and (S)-α-methyldopa (7 and 8a, resp.), (S)-α-methylvaline (14), and (R)-α-methyl-methionine (19). The configuration of the products is proved by chemical correlation and by NOE 1H-NMR measurements (see 23, 24). In the overall process, a simple, enantiomerically pure α-amino acid can be α-alkylated with retention or with inversion of configuration through pivaladehyde acetal derivatives. Since no chiral auxiliary is required, the process is coined ‘self-reproduction of a center of chirality’. The method is compared with other α-alkylations of amino acids occurring without racemization. The importance of enantiomerically pure, α-branched α-amino acids as synthetic intermediates and for the preparation of biologically active compounds is discussed.
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    Nucleophilic 1,2-Shifts of Alkoxycarbonyl and Carboxylate Groups in the Benzilic-Acid Type Rearrangement of α,β-Dioxobutyric EstersReductones and Tricarbonyl Compounds, Part 31. Part 30: [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 173-180 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: tert-Butyl α,β-dioxobutyrate (hydrate; 1d) undergoes, at medium or high pH, the benzilic-acid rearrangement with exclusive 1,2-shift of the COO(t-Bu) group; the same is true for the corresponding isopropyl ester 1c and ethyl ester 1b at high pH, whereas at lower pH, the overall picture of these reactions is complicated by concurrent hydrolysis of the ester, followed by a 1,2-shift of the COO- group. Consequently, the shift of these electron-attracting groups cannot be considered to be systematically disfavoured (compared, e.g., with alkyl-group shifts). Kinetic measurements of the rearrangement show for both esters (as well as for the analogous ethyl ester 1b, and also for ethyl 3-cyclopropyl-α,β-dioxopropionate (4)) a characteristic rate profile: at relatively low pH, k is proportional to [HO-], approaching saturation with increasing [HO-] (interpreted as complete transformation of the substrate into the hydrate monoanion), which is followed at higher pH by another rate increase with k proportional to [HO-] (probably due to the reaction of the hydrate dianion). The similarity of k values for 1b-d shows that in the shift of COOR steric hindrance caused by R is negligible.
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    Photochemical reactions. 141st communication.140th Communication: [1]. Photochemistry of α,β-unsaturated δ,∊-epoxyketones of the ionone series (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 192-206 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On n,π*- as well as on π,π*-excitation, the 4,5-epoxy-α-ionones (E)-1, (E)-2, and (E)-3 undergo (E)/(Z)-isomerization and subsequent γ-H-abstraction leading to the corresponding 4-hydroxy-β-ionones (E/Z)-9, (E/Z)-13, and (E/Z)-17 as primary photoproducts. On photolysis of (E)-3, as an additional primary photoproduct, the β,γ-unsaturated σ,∊-epoxy ketone 18 was obtained. The other isolated compounds, namely the 2H-pyrans 10A + B and 14A + B as well as the retro γ-ionones 11 and 15A + B, represent known types of products, which are derived from the 4-hydroxy-β-ionones (E/Z)-9 and (E/Z)-13, respectively.
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    The Structures of Some Products from the Photodegradation of the Pluramycin Antibiotics Hedamycin and Kidamycin (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 391-402 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photolability of the antitumor antibiotic hedamycin (1) was investigated by irradiation in different solvents in the presence or in the absence of oxygen. The products formed were separated chromatographically and their structures determined by NMR spectroscopy. Photolysis of 1 in the presence of oxygen gave only one isolable product, photohedamycin A (3), where ring E of hedamycin had been transformed into an enol ether. The reaction in the absence of oxygen yielded the photohedamycins B, C, and D (5, 6, and 7, respectively). In these compounds, one of the epoxides of hedamycin had been opened reductively, and in photohedamycin D (7) the substituent at C(8) - originally ring E of hedamycin - was now acyclic. In addition to these compounds, the photolyses yielded a large number of unstable minor products, which could not be isolated.
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    Synthesis of 1,2-Dihydropyridines, 2,3-Dihydro-4(1H)-pyridinone, and 1,2,3,4-Tetrahydropyridines via N-Acyl N,O-Hemiacetal FormationPresented at the Swiss Chemical Society meeting in Bern, October 19th, 1982. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 403-414 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New procedures are described for the synthesis of α,β-ethylenic and acetylenic aldehydes from 2-butene- and 2-butyne-1,4-diol, respectively (see Scheme 1). These are applied to the preparation of a particular δ-acetylamino-α,β-ethylenic aldehyde ((E)-5) as well as of its acetylenic analogue 15. On heating in the presence of a silyl enol ether, the former undergoes a complete dehydrative cyclization affording the N-acetyl-1,2-dihydropyridine 19. The addition of HCl to aldehyde (E)-5 results in the production of the 4-chloro-1,2,3,4-tetrahydropyridine 22 which is hydrolyzed to the corresponding alcohol 23 on silica gel. Similarly, the addition of HCl or HBr to the δ-acetyl-amino-α,β-acetylenic aldehyde 15 leads to the previously unknown 4-halo-1,2-dihydropyridines 26; these are easily hydrolyzed to the 2,3-dihydro-4(1H)-pyridinone 27. The ring-forming process involves a N-acyl N,O-hemiacetal as intermediate which is eventually dehydrated.
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    Rh-Catalyzed Oxidation of Anthracenes with tert-Butyl Hydroperoxide. Kinetic Aspects (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 450-455 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polar effects of substituents on reactivity in oxidation of 2-substituted anthracenes with tert-butyl hydroperoxide (TBHP)/Rh(PPh3)3Cl have been investigated and compared with those obtained with TBHP/VO(acac)2 and chromic acid. The anthracene reactivities obtained from competition experiments are correlated with Hammett's σp-constants. The P-values are -2.60 for chromic acid and 0.72 for TBHP/VO(acac)2. A poor correlation with p = -0.17 (r = 0.756) was obtained for TBHP/Rh (PPh3)3Cl. It is concluded that the Rh-catalyzed reaction does not consist in electrophilic oxygen transfer to the anthracene.
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    Synthese von 3,3-Dimethylperhydro-1,4-diazepin-2,5,7-trionen aus 3-Dimethylamino-2,2-dimethyl-2H-azirin und Malonsäuremonoamiden (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 465-474 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Synthesis of 3,3-Dimethylperhydro-1,4-diazepin-2,5,7-triones from 3-Dimethylamino-2,2-dimethyl-2H-azirine and Malonic Acid MonoamidesReaction of the aminoazirine 1 and malonic acid monoamides 5 in CH3CN yielded triamides of type 6 (Scheme 2), which were transformed to the corresponding phenylthioates 9 by treatment of a solution of 6 and thiophenol in CH3CN with HCl (Scheme 4). Cyclization of 9 to give the 1,4-diazepin-2,5,7-trione of type 10 was achieved with NaH in toluene at about 90°. It has been shown that 2-oxazolin-5-ones are intermediates in the selective cleavage of the therminal amide function of 6 (Scheme 3).
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    Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. I. Polyazapolyoxa macrotricycle cylindrique et monocycle constitutif (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 456-464 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution. I. A Polyazapolyoxa Cylindrical Macrotricycle and its Monocyclic SubunitpH-metry and UV spectrophotometry were used to study the complexing properties of the cylindrical macrotricycle, 1,7,13,19-tetraaza-4,16-dioxa-10,22,27,32-tetraoxatricyclo[17.5.5.5]tetratriacontane (1) and of its constitutive monocyclic subunit, 1,7-diaza-4,10-dioxacyclododecane (2) with some transition and heavy metal cations (Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Ag+), in aqueous medium 0.1M Et4NClO4, at 25°. The protonation constants of the ligands as well as the nature and the stabilities of the complexes formed in the pH-regions studied were determined. The tricycle 1 only formed dinuclear M2L complexes with Cu2+, Zn2+, and Ag+, accompanied in the latter case by a protonated mononuclear MLH species, and with Cu2+ and Zn2+ at high pH-values by dinuclear hydroxo complexes. Only mononuclear complexes were evidenced with the other cations, ML being accompanied either by protonated or hydroxy mononuclear species. The mononuclear complexes of 1, when they existed, were more stable than the corresponding complexes of 2, except for cobalt which formed complexes of comparable stability with both ligands. In the other cases (Cd2+, Pb2+, Ag+), the stability differences between the complexes of 1 and 2 increased with the size of the cation.
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    Planarisierung von tetrakoordiniertem Kohlenstoffatom. Synthese des überbrückten all-cis-[5.5.5.5]Fenestrans 13-Oxapentacyclo[5.5.2.11.7.04,15.010,15] pentadecan-14-onVorläufige Mitteilung: [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 493-507 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Planarisation of Tetracoordinate Carbon Atom, Synthesis of the Brigded all-cis-[5.5.5.5]Fenestrane 13-Oxapentacyclo[5.5.2.11,7.04,15.010,15]pentadecan-14-oneThe synthesis of the ketolactone 23 from (Z,Z)-1,5-cyclooctadiene is reported. Transannular carben insertion, achieved via photolysis of the deprotonated (2,4,6-trisisopropylphenylsulfonyl)hydrazone of 23 gives the bridged all-cis-[5.5.5.5]fenestrane 3.
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    Water Exchange on Hexaaquavanadium(III): a Variable-Temperature and Variable-Pressure 17O-NMR Study at 1.4 and 4.7 TeslaPart 24 of the series ‘High-Pressure NMR Kinetics’. Part 23: [1].These results are part of the Ph. D. thesis of A. H., University of Lausanne, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 508-521 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water exchange on hexaaquavanadium (III) has been studied as a function of temperature (255 to 413 K) and pressure (up to 250 MPa, at several temperatures) by 17O-NMR spectroscopy at 8.13 and 27.11 MHz. The samples contained V3+ (0.30-1.53 m), H+ (0.19-2.25 m) and 17O-enriched (10-20%) H2O. The trifluoromethanesulfonate was used as counter-ion, and, contrary to the previously used chloride or bromide, CF3SO3- is shown to be non-coordinating. The following exchange parameters were obtained: kex298 = (5.0 ± 0.3) · 102 s-1, ΔH* = (49.4 ± 0.8) kJ mol-1, ΔS* = -(28 ± 2) JK-1 mol-1, ΔV* = -(8.9 ± 0.4) cm3 mol-1 and Δβ* = -(1.1 ± 0.3) · 10-2 cm3 mol-1 MPa-1. They are in accord with an associative interchange mechanism, Ia. These results for H2O exchange are discussed together with the available data for complex formation reactions on hexaaquavanadium(III). A semi-quantitative analysis of the bound H2O linewidth led to an estimation of the proportions of the different contributions to the relaxation mechanism in the coordinated site: the dipole-dipole interaction hardly contributes to the relaxation (less than 7%); the quadrupolar relaxation, and the scalar coupling mechanism are nearly equally efficient at low temperature (∼ 273 K), but the latter becomes more important at higher temperature (75-85% contribution at 360 K).
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    Spontane Öffnung des Pyrimidinringes in Pyrrolo[2,3-d]pyrimidinen nach intramolekularer Acylierung (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 534-544 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spontaneous Opening of the Pyrimidine Ring of Pyrrolo[2,3-d]pyrimidines after Intramolecular AcylationPhase-transfer alkylation of 4-methoxy-2-methylthio-7H-pyrrolo[2,3-d]pyrimidine (2) with ethyl 3-bromopropionate leads regioselectively to the ester 3a. After displacement of its methylthio group and saponification of the ester function, the acid 3e is obtained which can be transferred to the functionalized deazahypoxanthine 3f by either treatment with dry HBr/glacial AcOH or by nucleophilic displacement of the 4-methoxide. Reaction of 3f with a H2O-soluble carbodiimide results in an intramolecular acylation at N(1) by the activated ester; the intermediate 4 undergoes spontaneous hydroxylation and subsequent opening of the pyrimidine ring under formation of the pyrrolo[1,2-a]pyrimidine derivative 6. Its structure was proved by X-ray analysis. Subsequent deformylation of 6 in alkaline medium leads to the compound 7 in almost quantitative yield.
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    Molluscicidal Saponins from Talinum tenuissimum DINTERPart 3 of the series ‘Phytochemistry of African Medicinal Plants’. For part 2, see [1].Dedicated to Prof. K. Nakanishi on the occasion of his 60th birthday (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 555-558 
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    Keywords: Chemistry ; Organic Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Two new saponins, β-D-glucopyranosyl 3-O[O-βD-xylopyranosyl-(1→3)-O-(β-D-glucopyranosyluronic acid)]oleanolate (1) and 3-O-[O-β-D-xylopyranosyl-(1→3)-O-(β-D-glucopyranosyluronic acid)]oleanolic acid (2), have been isolated from the tubers of Talinum tenuissimum. The structures have been established mainly by 13C-NMR and FAB-MS. The monodesmosidic saponin 2 exhibits very strong molluscicidal activity against the schistosomiasis-transmitting snail Biomphalaria glabrata.
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    Variable-Temperature and Variable-Pressure 17O-NMR Study of Water Exchange of Hexaaquaaluminium(III)Part 25 of the series ‘High-Pressure NMR Kinetics’. Part 24: [1].These results are part of the Ph. D. thesis of D. H.-C., University of Lausanne, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 545-554 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transverse relaxation rate of H2O in Al(H2O)63+ has been measured as a function of temperature (255 to 417 K) and pressure (up to 220 MPa) using the 17O-NMR line-broadening technique, in the presence of Mn(II) as a relaxation agent. At high temperatures the relaxation rate is governed by chemical exchange with bulk H2O, whereas at low temperatures quadrupolar relaxation is prevailing. Low-temperature fast-injection 17O-NMR was used to extend the accessible kinetic domain. The samples studied contained Al3+ (0.5 m), Mn2+ (0.2-0.5 m), H+ (0.2-3.1 m) and 17O-enriched (20-40%) H2O. Non-coordinating perchlorate was used as counter ion. The following H2O exchange parameters were obtained: kex298 = (1.29 ± 0.04) s-1, ΔH* = (84.7 ± 0.3) kJ mol-1, ΔS* = +(41.6 ± 0.9) J K-1 mol-1, and ΔVex* = +(5.7 ± 0.2) cm3 mol-1, indicating a dissociative interchange, Id, mechanism. These results of H2O exchange on Al(H2O)63+ are discussed together with the available complex-formation rate data and permit also the assignment of Id mechanisms to these latter reactions.
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    Esters of 1-O-Demethylthiocolchicines: Formation of Isomers in Chloroform Solution (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 571-580 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: 1-O-Acetyl-1-O-demethylcolchicine, and acylated 1-O,2-O-didemethylthiocolchicines, in contrast to 2-O-acetyl-, 2-O,3-O-diacetyl- and 3-O-acetyl analogs, showed after standing in CHCl3 solution significant changes in optical rotation, a duplication of 1H-NMR signals, and the formation of new isomers on TLC. Solid-state X-ray diffraction of O-acetylated colchinoids and thio analogs, showed out of planar arrangements of the aromatic substituents, but the analysis could not help to explain the structures of the newly formed isomers in CHCl3 solution.
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    Facile Synthesis of 2′-Deoxyribofuranosides of Allopurinol and 4-Amino-1H-pyrazolo[3,4-d]pyrimidine via Phase-Transfer Glycosylation (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 563-570 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phase-transfer glycosylation of 4-methoxy-1H-pyrazolo[3,4-d]pyrimidine with the 2-deoxyribofuranosyl chloride 9 formed the N(1)-β-nucleoside 10a as main product (39%). As by-products the α-D-anomer 11a (7%) and the N(2)-isomer 12a (18%) were isolated. Assignment of these isomers was made on the basis of their 1H- and 13C-NMR spectra. Removal of the sugar-protecting groups yielded the 4-methoxy-nucleosides 10b, 11b, and 12b, respectively. Nucleophilic displacement of the 4-MeO-group gave the 2-deoxyribofuranosides 1-4 of allopurinol and 4-amino-1H-pyrazolo[3,4-d]pyrimidine.
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    Liquid Crystals with Large Negative Dielectric Anisotropy. Part V (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 606-609 
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid crystals with negative Δ∊ can be obtained by incorporating a cyano group in the terminal alkyl substituent or in an ethylene bridge between the cyclic units of the rigid core. The clearing points of such compounds are higher than those of the corresponding derivatives where the cyano group is laterally attached to a phenyl moiety. In compounds where both cyclic units of the rigid core are cyclohexyl, this type of substitution leads to an optimal contribution to ∊⊥ in contrast to the cyanophenyl derivatives.
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    Propellanes. Part LXXVIII. Preparation of Several Triaza[3.3.3]propellanes and an Oxadiaza[3.3.3]propellanePart LXXVII: [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 610-613 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,7,10-Tribenzyl-3,7,10-triaza[3.3.3]propellane (4a), 3,7-dibenzyl-10-phenyl-3,7,10-triaza[3.3.3]propellane (4c), 3,7-dibenzyl-10-(p-tolyl)-3,7,10-triaza[3.3.3]propellane (4b), and 3-oxa-7,10-diaza[3.3.3]propellane (6) have been prepared.
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    Synthesis of the Glycopeptide Partial Sequence A80-A84 of Human Fibroblast Interferon (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 618-622 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The glycopentapeptide H-(GlcNAcβ1-)Asn-Glu-Thr-Ile-Val-OH (10) representing the partial sequence A80-A84 of human fibroblast interferon was synthesized using the newly developed allyl-ester protection of carboxy functions. The allyl esters, which are stable to acids and to bases, can be cleaved under very mild, neutral conditions using tris(triphenylphosphine)rhodium(I) chloride or tetrakis(triphenylphosphine)palladium(0) as a catalyst. This synthetic method opens up a preparative route to glycopeptide model structures of glycoproteins of high biological interest.
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  • 38
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    Polar effects. Part 12. Inductivity and carbon participation in the solvolysis of 4-substituted 2-adamantyl arenesulfonates (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 651-660 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constants (log k) for the solvolysis of 4e-substituted 2e- and 2a-adamantyl p-nitrobenzenesulfonates 14 and 15, respectively, in 80% EtOH correlate linearly with the respective inductive substituent constants σIq. Therefore, relative rates are controlled by the I effect of the substituents at C(4). The derived reaction constants, or inductivities, ρI of -0.80 and -0.64 for the series 14 and 15, respectively, are far smaller than those previously determined for 6-substituted 2-norbornyl and 2-bicyclo[2.2.2]octyl sulfonates, in which the partial structure containing the substituent and the leaving group is the same. The ratio of the retained and inverted adamantanols obtained upon hydrolysis of the series 14 falls from 2.85 for R = CH3 to ca. 1 for R = CN, i.e. as the substituent at C(4) becomes more electron-attracting. In the 2a-series 15 this ratio is uniformly higher. These findings confirm that the 2-adamantyl cation is weakly bridged and that through-space induction in carbocations involves graded bridging of the cationic center by neighboring C-atoms.
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    Peptide conformations. Part 31Part 30: [1a].. The conformation of cyclosporin a in the crystal and in solution (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 682-704 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The all-light-atom X-ray crystal-structure analysis of cyclosporin A (1), a cyclic undecapeptide containing seven N-methylated amino acids, reveals a conformation very similar to that of the previously analysed iodo derivative which is characterised by a twisted β-pleated sheet involving the residues Me-Val-11, MeBmt-1, Abu-2, Sar-3, MeLeu-4, Val-5, MeLeu-6, and Ala-7. The β-bend at Sar-MeLeu-4 is of type II′, and the loop of the residual amino acids involves a cis-peptide bond between MeLeu-9 and MeLeu-10. The NH proton of D-Ala-8 closes a yi-bend with a H-bond to the MeLeu-6 CO group. The crystal was grown from acetone. A closely similar backbone conformation in apolar solvents such as CDCl3 or C6D6 has been derived from the interpretation of the NMR spectral parameters (homo- and heteronuclear NOE effects, coupling constants, chemical-shift values of the C-, H-, and N-atoms). A minor variation in the backbone conformation between crystal and solution is observed in the region of D-Ala-8, where in solution a 3-center H-bond is established between the NH of D-Ala-8 und the carbonyl O-atoms of both MeLeu-6 (yi-turn) and D-Ala-8 (C5-bend). A recently proposed technique to identify intramolecular H-bond via heteronuclear NOE from NH proton to carbonyl C-atoms is critically analysed. The main difference between crystal and solution conformations lies in the orientation of the side chains of the unusual amino acid MeBmt (χ1 = +60° in solution, -168° in the crystal) and of MeLeu-10 (X1 = -60° in solution, +60° in the crystal). The differences in crystal and solution are caused by the break of the intermolecular H-bond of the OH group of MeBmt on dissolution of the crystal. The bifurcated H-bond of D-Ala-8 twists the backbone in this region. Molecular modeling demonstrates that this is the origin of the change in the side chain conformation of MeLeu-10. The intramolecular flexibility in the crystal indicated by the thermal parameters obtained from the X-ray refinement, and in solution by an analysis of spin-lattice relaxation times in the NMR experiments, indicate a fairly rigid backbone and fixed conformations for all the side chains except for that of Abu-2 and the distal atoms of MeBmt.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19850680319
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    The Crystal Structure of trans-2,2′-AzoquinoxalineDedicated to Prof. Dr. Silvio Fallab on the occasion of his 60th birthday (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 581-583 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the title compound obtained from 2(1H)-quinoxalinone oxime by the template effect of Co(II) and Ni(II) ion has been determined by three dimensional X-ray analysis.
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  • 41
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    Photochemische Synthesen potentiell hypoglykämisch wirkender 3-Oxazoline (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 584-591 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemical Syntheses of 3-Oxazolines which Possibly Exhibit Hypoglycemic ActivityReactions of photochemically generated benzonitrile methylides 2 with carbonyl compounds 3 yielded 3-oxazolines of the types 5 and 6 (Scheme 1). Photooxidation of 5-[p-(dimethylamino)phenyl]-2,2-dimethyl-4-phenyl-3-oxazoline (5a) gave 4′-(2,2-dimethyl-4-phenyl-3-oxazolin-5-yl)-N-methylformanilide (6r) which could be transformed to 2,2-dimethyl-5-[p-(methylamino)phenyl]-4-phenyl-3-oxazoline (6s) by photodecarbonylation. Thirty 3-oxazolines of types 5 and 6 have been synthesized and tested by oral and/or intraperitoneal administration to starved rats and obese-hyperglycemic mice.
    Additional Material: 5 Tab.
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    Photochemische und chemische Synthesen biologisch aktiver 3-Oxazoline (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 600-605 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemical and Chemical Syntheses of Biologically Active 3-OxazolinesUsing the photoreaction of 2H-azirines with carbonyl compounds, the 2,2-dimethyl-3-oxazolines 5a, 5b, and 6a have been obtained which bear a mono- or dichlorophenyl substituent at C(4) of the five-membered heterocycle and pyridyl at C(5). These compounds exhibit interesting activities against phytopathogenic fungi. Because 6a had been selected for field testing, its photochemical preparation was supplemented by a chemical synthesis. However, the overall performance of 6a in the field was inferior to some of the recently introduced agricultural fungicides of the ergosterol biosynthesis inhibitor type. Although 16 additional 3-oxazolines with varied substituents have been prepared, the fungicidal activity found with 6a could not be improved.
    Additional Material: 2 Tab.
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    Synthese und Reaktionen des 5-[p-(Dimethylamino)phenyl]-2,2-dimethyl-4-phenyl-3-oxazolins (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 592-599 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Reactions of 5-[p-(Dimethylamino)phenyl]-2,2-dimethyl-4-phenyl-3-oxazolineThe title compound 8 has been synthesized in a one-pot reaction of 4′-(dimethylamino)benzoin (4) with 2-propanone and NH3. The preparation of the intermediate 4 from 3 is the first example of an acid-catalyzed transformation of the stable benzoin 3 into the corresponding less stable benzoin 4. Structures and yields of various by-products occurring under different reaction conditions during the synthesis of 8 from 4 are given. The O-atom of the 3-oxazoline ring in 8 could be replaced by S from P2S5 yielding the 3-thiazoline 14. Separation of the enantiomers of the racemate 8 could only be performed by transforming them into the trimethylanilinium salts 8b and 8c of (-)- and (+)-10-camphorsulfonic acid, respectively. Solid NaOAc in boiling toluene caused the precipitation of the 10-camphorsulfonic acids from the quaternary ammonium salts as sodium salts and the removing of the third methyl group from the quaternary ammonium salts as AcOMe to give the enantiomers (-)-(5S)-8 and (+)-(5R)-8. Their absolute configurations are deduced from an X-ray analysis of 8b.
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    Propellanes. Part LXXX. Baeyer-Villiger Oxidation of [4.3.3]Propellane-8,11-dionePart LXXIX: [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 614-617 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of the title compound with m-chloroperbenzoic acid affords a keto-lactone, two bis-lactones and a bis-spirolactone, in varying amounts depending upon the reaction conditions. The structures were established by means of X-ray diffraction, 1H- and 13C-NMR spectroscopy.
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  • 45
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    Synthese substituierter Cyclononatetraene42. Mitt. über Fulvene, Fulvalene. 41. Mitt.: [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 623-634 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Substituted CyclononatetraenesIn the course of an exploration of possible synthetic pathways to nonafulvenes, a series of 1-substituted cyclononatetraenes (CNT) 4b-1 have been prepared in yields of about 60%. Their structures follow from spectroscopic data as well as from the quantitative valence isomerisation to 1-endo-substituted cis-3a, 7a-dihydroindenes 8. Both all-cis-CNT- 1 and cis,cis,cis,trans-CNT- 2 have been used as nucleophiles. Whereas 2 is normally more nucleophilic than 1, the yield of cyclononatetraenes 4 prepared with 2 may be reduced due to by-products such as 9 and 10.
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  • 46
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    Peptide conformations. Part 30Part 29: [1]. Assignment of the 1H-, 13C-, and 15N-NMR spectra of cyclosporin A in CDCl3 and C6D6 by a combination of homo- and heteronuclear two-dimensional techniques (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 661-681 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H-, 13C-, and 15N-NMR spectra of the immunosuppressive cyclic undecapeptide cyclosporin A (1) have been analyzed at 300 MHz in CDCl3, C6D6, and mixtures of these solvents. A combination of different homo- and heteronuclear two-dimensional NMR techniques enable complete assignment of all H-, C- and 4 N-signals. Recognition of the proton spin systems has been achieved via 1H,1H-COSY and double-quantum-1H-NMR spectroscopy. NOESY spectra yield some sequence assignments, but two techniques using coupling across amide bonds have been applied to get independent assignments of all amino acids in the sequence: (i) An 1H,1H-COSY spectrum optimized for small coupling constants enables the detection of long-range couplings from N-methyl groups to both α-protons attached to that amide bond. (ii) An 1H, 13C-COSY spectrum optimized for C,H-long-range couplings (J = 5 to 10 Hz) to the eleven CO groups again yields coupling to both α-protons attached to that amide bond. Additionally these two experiments yield the assignment of N-methyl protons and carbonyl C-atoms. Normal and relayed 1H,13C-COSY in both solvents have been applied to assign all C-atoms via their directly attached and remote protons. An 1H,13C-COLOC spectrum at 500 MHz in CDCl3, which uses H,C-long-range couplings confirms the assignment of all proton spin systems as well as the C-signals of each individual amino acid. Ambiguities in the assignment of the C(δ)'s of MeLeu have thus been removed. An 1H,15N-COSY spectrum enables the assignment of the 4 NH N-atoms.
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    Photochemical reactions. 143rd communication142nd Communication: [1].. Photochemistry of 5,6-epoxy-1,3-dienes in the ionone series. Influence of a hydroxy group in the 7-position (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 635-650 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and photolyses of the epoxydiene (E)-5 are described. On triplet excitation (λ 〉 280 nm, acetone), (E)-5 undergoes initial cleavage of the C(5)—O bond leading to the intermediate c. Presumably an H-shift (c → e) followed by the fragmentation of the 1,4-diradical e leads (via the enol 37) to the diketones (E)-6 and (Z)-12. Alternatively cleavage of the C(6)—C(7) bond of c furnishes the diradical intermediate d which reacts by recombination leading to (E)-13A + B, 16, and 17A + B, or by an H-shift to the enol intermediate 38. The latter undergoes an aldol-type reaction to (E/Z)-14A + B and (E/Z)-15A + B, as well as a photochemical [2 + 2]-cycloaddition to 18. On singlet excitation (λ = 254 nm, MeCN), (E)-5 undergoes photocleavage to the carbene intermediates f and g. The vinyl carbene f reacts with the adjacent double bond furnishing the cyclopropene 22 as the main product. From the carbene intermediate g, compounds 23, 24, and 25 arise by carbene insertion into the neighboring C—C or C—H bond. Furthermore, the diastereomer of the starting material, the epoxydiene (E)-20, is formed via the ylide intermediate h.
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    The Structure of Pyroergotamine (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 724-733 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structure of pyroergotamine has been determined by single-crystal X-ray diffraction analysis to be the pyruvoyldiketopiperazine 1. The diketopiperazine ring exists in a folded or boat conformation, with a dihedral angle of 40° between the two almost planar peptide units. The R-group of the phenylalanine residue occupies a quasi-axial position of the diketopiperazine ring, while that of the proline residue is in a quasi-equatorial position. Puzzling spectroscopic and chemical properties of the compound can be rationalised in terms of crowding within the molecule.
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    URL: http://dx.doi.org/10.1002/hlca.19850680322
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    The Electronic Structure of Dopamine. An ab initio Electrostatic Potential Study of the Catechol Moiety (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 715-723 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electronic properties of dopamine were studied by the ab initio STO-3G MO method. The molecular electrostatic potential (MEP) around the aromatic ring and the catechol group remains practically the same in 3,4-dihydroxytoluene (a model compound) and in neutral dopamine examined in its two extended conformations, namely that found in the crystal (side-chain and aromatic ring almost perpendicular) and the one corresponding to 2-amino-6,7-dihydroxytetralin (6,7-ADTN) (side-chain and aromatic ring almost coplanar). In protonated dopamine and in dopamine hydrochloride, the electrostatic potential of the catechol moiety is overshadowed by the positive charge, but the main features remain discernible. The catechol moiety was examined in its two coplanar conformations containing a ‘flip-flop H-bond’. The electrostatic potential around the catechol moiety is quite complex, with alternating positive and negative maxima. At increasing distances above and away from the catechol moiety, only two peripheral maxima, one negative and one positive, remain perceptible. The ‘flip-flop’ mechanism results in an approximate interchange of these two potential maxima, a fact which tends to level out the structural differences between the α- and β-rotamer of dopamine. Based on these results and on the structure of rigid agonists, some pharmacophoric features of dopamine agonists are proposed.
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    URL: http://dx.doi.org/10.1002/hlca.19850680321
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    Synthese und Hydrolyse von 4-substituierten p-Nitrobenzolsulfonsäure (2-adamantyl)estern (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 760-769 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Hydrolysis of 4-Substituted 2-Adamantyl p-NitrobenzenesulfonatesSeveral 4e -substituted 2e- and 2a-adamantyl p-nitrobenzensulfonates have been prepared by new routes. Their hydrolysis products are described.
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    URL: http://dx.doi.org/10.1002/hlca.19850680326
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