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  • 1990-1994  (67)
  • 1985-1989  (43)
  • 1960-1964  (19)
  • 1800-1809
  • Alkaloids
  • Alkenes
  • Synthetic methods
  • 1
    Electronic Resource
    Electronic Resource
    Methyltransferase activity in Allanthm altissima cell suspension cultures (1994)
    Springer
    Plant cell reports 13 (1994), S. 277-281 
    Details
    ISSN: 1432-203X
    Keywords: Alkaloids ; Coumarins ; Methyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Enzymes for the methylation of 1hydroxycanthin-6-one and a series of coumarins have been isolated from Ailanthus altissima cell suspension cultures. The coumarin methyltransferases methylate aesculetin to scopoletin and isoscopoletin, but not scopoletin, to scoparone. Fraxetin was methylated to isofraxidine but not to fraxidine and only fraxidine was methylated to 6,7,8-trimethoxycoumarin. These enzymes were studied throughout the culture growth cycle with two cell lines: 1, which produced 1-methoxycanthin-6-one as the major alkaloid and 2, in which canthin-6-one was the major alkaloid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233319
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  • 2
    Electronic Resource
    Electronic Resource
    Dietary source for skin alkaloids of poison frogs (Dendrobatidae)? (1994)
    Springer
    Journal of chemical ecology 20 (1994), S. 943-955 
    Details
    ISSN: 1573-1561
    Keywords: Alkaloids ; indolizidines ; pyrrolizidines ; histrionicotoxins ; coccinellines ; dendrobatid frogs ; insects ; millipedes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A wide range of alkaloids, many of which are unknown elsewhere in nature, occur in skin of frogs. Major classes of such alkaloids in dendrobatid frogs are the batrachotoxins, pumiliotoxins, histrionicotoxins, gephyrotoxins, and decahydroquinolines. Such alkaloids are absent in skin of frogs (Dendrobates auratus) raised in Panama on wingless fruit flies in indoor terraria. Raised on leaf-litter arthropods that were collected in a mainland site, such terraria-raised frogs contain tricyclic alkaloids including the beetle alkaloid precoccinelline, 1,4-disubstituted quinolizidines, pyrrolizidine oximes, the millipede alkaloid nitropolyzonamine, a decahydroquinoline, a gephyrotoxin, and histrionicotoxins. The profiles of these alkaloids in the captive-raised frogs are closer to the mainland population ofDendrobates auratus at the leaf-litter site than to the parent population ofDendrobates auratus from a nearby island site. Extracts of a seven-month sampling of leaf-litter insects contained precoccinelline, pyrrolizidine oxime236 (major), and nitropolyzonamine (238). The results indicate a dietary origin for at least some “dendrobatid alkaloids,” in particular the pyrrolizidine oximes, the tricyclic coccinellines, and perhaps the histrionicotoxins and gephyrotoxins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02059589
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  • 3
    Electronic Resource
    Electronic Resource
    Comparison of the Nucleophilicities of Alkynes and Alkenes. Quantitative Determination of the Nucleophilicities of Alkynes toward Carbenium Ions (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 525-531 
    Details
    ISSN: 0009-2940
    Keywords: Alkynes ; Alkenes ; Nucleophilicity ; Carbenium ions ; Vinyl cations ; Kinetics ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Relative reactivities of alkenes and alkynes toward diarylmethyl cations have been determined by direct rate measurements and by competition experiments in dichloromethane. At -70°C alkynes are found to be one to two orders of magnitude less reactive than analogously substituted alkenes (e.g. phenylacetylene/styrene), but the reactivity difference reduces strongly as the temperature is raised. The stereochemistry of the vinyl chlorides produced by addition of benzhydryl chlorides to alkynes is characterized.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270311
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  • 4
    Electronic Resource
    Electronic Resource
    (1α,2α, 7α,8α,12α,17α,18α,19α)-Heptacyclo[17.3.1.18,12.05,23.06,18.07,17.016,24]-tetracosa-5(23),16(24)-dien, ein hyperstabiles Alken (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 219-221 
    Details
    ISSN: 0009-2940
    Keywords: Alkenes ; hyperstable ; Hydrogenation ; catalytic ; Hydrocarbons ; concave ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1α,6α,7α,8α,12α,17α,18α,19α)-Heptacyclo[17.3.1.18,12.05,23.06,18.07,17.016,24]tetracosa-5(23),16(24)-diene, a Hyperstable AlkeneHydrogenation of the cis-photodimer 1 of acenaphthylene yields the title compound 2, which, though still containing two double bonds, undergoes no further hydrogenation or reaction with bromine for steric reasons. The cyclobutane ring of 2 shows strong steric distortions as revealed by X-ray analysis as well as by force-field and semiempirical MO calculations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270131
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  • 5
    Electronic Resource
    Electronic Resource
    {Bis[bis(trimethylsilyl)methyl]stannio(II)}bis(η2-ethen)nickel(0) und verwandte Verbindungen, Teil II (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 489-500 
    Details
    ISSN: 0009-2940
    Keywords: Alkenes ; Nickel complexes ; Stannenes ; Metal-metal bonds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: {Bis[bis(trimethylsilyl)methyl]stannio(II)}bis(η2-ethene)nickel(0) and Related Compounds, Part IIThe coordinatively unsaturated (16e) (ethene)nickel(0) stannylene complex (C2H4)2Ni=Sn{CH(SiMe3)2}2 (1) reacts with 1,6-heptadiene with preservation of the Ni=Sn bond to yield quantitatively the 1,6-diene derivative (η2,η2-C7H12)Ni=Sn-{CH(SiMe3)2}2 (2). The alkene ligands of both 1 and 2 are readily displaceable. Compounds 1 and 2 react with butadiene at -50°C by a 4-e oxidation of the metal-metal pair Ni(0)/Sn(II) to Ni(II)/Sn(IV) and concomitant reduction of two butadiene molecules to butenediyl moieties to afford stereo-selectively the 16-e complex Ni-cis-{η3(Ni),η1(Sn)-anti-C3H4CH2}2Sn{CH(SiMe3)2}2 (3). Similarly, the reaction of 1 or 2 with isoprene yields regio- and stereoselectively the derivative Ni-cis-{η3(Ni,η1(Sn)-anti-C3(3-Me)H3CH2}2Sn{CH-(SiMe3)2}2 (4). These reactions imply the cleavage of one formal Ni—Sn bond and the formation of two new Sn—C bonds. Upon reaction of 3 with PMe3 the configuration of the allyl system changes and, again fully stereoselectively, the 18-e addition compound (Me3P)Ni-cis-{η3(Ni),η1(Sn)-syn-C3H4-CH2}2Sn{CH(SiMe3)2}2 (5) is formed. When 5 is treated with BPh3, the phosphane ligand is trapped and, kinetically controlled, Ni-cis-{η3(Ni),η1(Sn)-syn-C3H4CH2}2Sn{CH(SiMe3)2}2 (6) is obtained as a stereoisomer of 3. At 40°C 6 slowly rearranges into the thermodynamically stable stereoisomer Ni-trans-{η3(Ni),η1(Sn)-syn-C3H4CH2}2Sn{CH(SiMe3)2}2 (7). Mild protolysis of 3 with pyridine hydrochloride or hydrobromide affords region and stereoselectively (Me3Si)2CH}2(X)SnNi-(η3-1-MeC3H4)(NC5H5) (X = C1, 8a; Br, 8b). In the course of this protonation reaction one butadiene molecule is eliminated, accompanied by a 2-e reduction of the metal-metal pair Ni(II)/Sn(IV) to Ni(II)/Sn(II) and, at the expense of two Sn—C bonds, reformation of a Ni—Sn bond. All compounds are isolated in high yield and fully characterized by 1H-, 13C-, and 31P-NMR spectroscopy.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270307
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  • 6
    Electronic Resource
    Electronic Resource
    A preliminary study of food selection by the orangutan in relation to plant quality (1994)
    Springer
    Primates 35 (1994), S. 255-263 
    Details
    ISSN: 0032-8332
    Keywords: Orangutans ; Pongo pygmaeus ; Diet ; Protein ; Fiber ; Tannins ; Alkaloids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We observed the foraging behavior of orangutans in Central Indonesian Borneo during October, November, and December 1980, and analyzed food and nonfood items for water content, neutral detergent fiber, crude protein, available crude protein, and protein:fiber ratio and the presence of alkaloids and tannins. The diet of the orangutan during this season was unusual because it consisted predominantly of seeds and unripe, rather than ripe, fruits. Also, the major diet item, the seeds ofIrvingia malayana, had been ignored in previous years when it had fruited. In leaves, protein content was more closely associated with food choice than either neutral detergent fiber or the protein:fiber ratio. Flowers had the highest protein content and protein:fiber ratio of any food item. Tannins were found in most food items, but the presence of alkaloids was found in only one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02382723
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  • 7
    Electronic Resource
    Electronic Resource
    Partial Synthesis of Nitrogenous Brassinosteroid Analogues with 22,26-Epiminocholestane and Spirosolane Skeleton (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 1143-1147 
    Details
    ISSN: 0170-2041
    Keywords: Bassinosteroids ; Steroids ; Alkaloids ; Solasodine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting with the known (22S,25R)-16β-acetoxy-N-acetyl-22,26-epiminocholest-5-en-3β-ol (4), which has been prepared from the Solanum steroid alkaloid solasodine (3), we synthesized the nitrogenous brassinosteroid analogues (22S,25R)-2α,3α,16β-trihydroxy-22,26-epimino-5α-cholestan-6-one (11), (25R)-2α,22α-dihydroxy-5α,22αN-spirosolan-6-one (13), (22S,25R)-2α,3α,16β-trihydroxy-22,26-epimino-6,7-seco-5α-cholestano-6,7-lactone (15), and (25R)-2α-3α-dihydroxy-6,7-seco-5α,22αN-spirosolano-6,7-lactone (18) as well as some of their derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419941115
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  • 8
    Electronic Resource
    Electronic Resource
    Ein einfacher Zugang zu den tetracyclischen Vorläufern der Hetero- und Secoyohimbane, Strychnos- und Oxindolalkaloide (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 151-158 
    Details
    ISSN: 0170-2041
    Keywords: Indoles ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Simple Entry into the Series of Tetracyclic Hetero- and Secoyohimbanes, Strychnos and Oxindole AlkaloidsThe divinylogous urethane 4a reacts in diluted acetic acid to give the indolochinolizine 9 (yield 40%). The total amount grows up to 65%, if compound 14, prepared from 4a in nearly quantitative yield, is allowed to react with trifluoroacetic acid for a few minutes. Similarily, 4b and 4c give by treatment with SnCl2 and heat in an [4+2]-cycloaddition reaction the spiroindolines 17 and 18. Oxytryptamine reacts with 2 moles of 2 to give immediately the spirooxindole 21. This compound can be rearranged to give 23 (after treatment with acid, reduction and catalytic hydrogenation). 23 has the cis-configuration of rhyncophylline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940208
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  • 9
    Electronic Resource
    Electronic Resource
    Unusual reactivity of lithiated 2-alkylbenzotriazoles (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 7-12 
    Details
    ISSN: 0170-2041
    Keywords: Benzotriazoles, 2-alkyl ; Lithiation ; Alkenes ; Radicals ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of a 2-alkylbenzotriazole (BtCH2R) (2) with LDA at -78°C produces rapidly a mixture of a coupling product (BtCHR-CHRBt) (5) and a compound formed from four molecules of the starting material (BtCHR-CHR-CHR-CHRBt) (6). A mixture of 2-methylbenzotriazole and benzophenone, treated with LDA, gives adduct Ph2C(OH)CH2Bt (14) quantitatively whereas benzaldehyde does not react under these conditions. 2-Alkylbenzotriazoles (2) are alkylated at the α-carbon atom when their mixtures with alkyl halides are treated with LDA.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940103
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  • 10
    Electronic Resource
    Electronic Resource
    The Photochemical Synthesis of Fine Chemicals with SunlightDedicated to the memory of Klaus Gollnick (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 33 (1994), S. 2009-2023 
    Details
    ISSN: 0570-0833
    Keywords: Photochemistry ; Synthetic methods ; Fine chemicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199420091
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  • 11
    Electronic Resource
    Electronic Resource
    Induced responses in three alkaloid-containing plant species (1993)
    Springer
    Oecologia 95 (1993), S. 425-430 
    Details
    ISSN: 1432-1939
    Keywords: Senecio jacobaea ; Cynoglossum officinale ; Catharanthus roseus ; Alkaloids ; Induced responses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper we test three plant species for the inducibility of their alkaloid production. The plants were heavily damaged by cutting off 50% of their leaf surface using a pair of scissors. The cut-off leaf tips were used as controls for possible diurnal fluctuations. After 3, 6, 12, 24 and 48 h, respectively, the leaf bases of the damaged plants were harvested and the alkaloid concentration was measured. In Senecio jacobaea the pyrrolizidine alkaloid (Pa) concentration in damaged plants decreased within 6–12 h after damage. Within 24 h after damage the Pa concentration of Cynoglossum officinale doubled compared to control values. Indole alkaloid production in Catharanthus roseus was found not to be induced in this experiment. The responses are discussed in a functional context. We hypothesize that the nature of the response is not a feature of the type of secondary metabolite, but is related to whether the plants are damaged mainly by generalist or by specialist herbivores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320998
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  • 12
    Electronic Resource
    Electronic Resource
    Relationship of manganese with iron and zinc with respect to latex yield and composition in opium poppy (Papaver somniferum Linn) under two fertility conditions (1993)
    Springer
    Nutrient cycling in agroecosystems 34 (1993), S. 55-58 
    Details
    ISSN: 1573-0867
    Keywords: Alkaloids ; fertility ; iron ; manganese ; Papaver sominferum L. ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two different field experiments were conducted for two years during 1985–86 and 1986–87 to study the relationship of Mn (0, 15 and 30 kg ha−1) with Fe (0, 15 and 30 kg ha−1) and Zn (0, 10 and 20 kg ha−1) under two fertility (NPK) conditions on yield and quality of opium poppy. The main effect of these micronutrients with respect to latex yield was highest at 15 kg ha−1 of Mn or Fe and 10 kg ha−1 Zn. Increasing the level beyond that resulted in reduction in latex yield. Highest response was observed when 15 kg ha−1 Mn was applied with either 15 kg ha−1 Fe or 10 kg ha−1 Zn. Morphine, codeine, narcotine and thebaine content of the latex was highest with 15 kg Mn, 15 kg Fe or 10 kg ha−1 Zn or the combined application of 15 kg Mn with 15 kg Fe or 10 kg Zn ha−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00749960
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  • 13
    Electronic Resource
    Electronic Resource
    Capillary zone electrophoretic analysis of the main alkaloids fromEschscholtzia californica (1993)
    Springer
    Chromatographia 37 (1993), S. 579-583 
    Details
    ISSN: 1612-1112
    Keywords: Capillary zone electrophoresis ; Alkaloids ; Multi-wavelength detection ; Eschscholtzia californica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Capillary zone electrophoresis (CZE) with multi-wavelength detection has been used for the separation of the main alkaloids fromEschscholtzia californica. Optimum separation has been achieved with a fused silica capillary tube and a running electrolyte at pH 2.8 prepared from a 40 mM solution of citric acid and a 80 mM solution of Na2HPO4. The applied voltage was 20 kV and the capillary thermostating temperature was kept constant at 10°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274105
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  • 14
    Electronic Resource
    Electronic Resource
    Synthese von Manzamin C, Infractin und 6-Hydroxyinfractin (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 153-159 
    Details
    ISSN: 0170-2041
    Keywords: β-Carbolines ; Alkaloids ; Manzamine C ; Infractine derivatives ; (Z)-1-Aza-6-cycloundecene ; Pyrido[3,4-b]indoles ; Pictet-Spengler reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Manzamine C, Infractine and 6-HydroxyinfractineManzamine C (1), a β-carboline alkaloid with antitumor activity isolated from the marine sponge Haliclona sp. was synthesized. The dilithium derivative of 5-hexynoic acid (6) was alkylated with 7 to give after esterification the methyl 10-hydroxy-5-decynoate (8). The tosylate of 8 was converted into the azide 9 which could be selectively hydrogenated with Lindlar palladium catalyst to give the amino ester 10. Saponification of 10 and acylation with (Boc)2O yielded 11, which was converted with pentafluorophenol into 12. Removal of the Boc group in 12 gave an amino ester as intermediate, which cyclized immediately under high dilution conditions to give the lactam 13 in high yield. Reduction of 13 with LiAlH4 produced the macrocyclic amine 4. The β-carboline part of 1 was prepared by condensation of N-benzyltryptamine 14 with the formylacetic acid equivalent 15 to give 16. Dehydrogenation of 16 with Pd-on-carbon catalyst led to the orthoester 17, which could be converted into the methyl ester 5 in high overall yield. The 4-(dimethylamino)pyridine-catalyzed substitution of the methyl ester function in 5 by the amine 4 gave the amide 29. The analogous reaction of 5 with pyrrolidine or with azacyclotridecane yielded 30 and 31. Reduction of these three amides with LiAlH4 produced 1, 2 and 3. The spectroscopic properties of 1 were identical with those of natural manzamine C. - Condensation of 14 or N-benzyl-5-(benzyloxy)tryptamine (19) with aldehyde 18 yielded the products 20 and 21, which could be dehydrogenated to furnish 22 and 23. From these the methyl esters 24 and 25 with properties identical to those of the known β-carboline alkaloids infractine and 6-hydroxyinfractine could be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930128
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  • 15
    Electronic Resource
    Electronic Resource
    Solanum Alkaloids, 126. Degradation of Solasodine to 16β,22-Epoxy-23,24-dinorchol-5-ene-3β,22β-diol and Partial Synthesis of (23s)-23-Hydroxysolasodine (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 167-172 
    Details
    ISSN: 0170-2041
    Keywords: Solasodines ; Chol-5-ene-3β,22β-diol, 16β,22-epoxy-23,24-dinor- ; Solanum steroid alkaloids ; Steroids ; Alkaloids ; Ruschig reaction ; Grob fragmentation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (22R,23S,25R)-N-Chloro-22,26-epiminocholest-5-ene-3β,16β,23-triol (11) and its 3,16,23-O-triacetyl derivative 15 were prepared from solasodine (1). Treatment of 11 or 15 with sodium methanolate yielded the 22,23-secoaldehyde 16 as major product (Grob fragmentation) and (23S)-23-hydroxysolasodine (2) as minor product (Ruschig reaction). Hydrolysis of 16 with methanolic hydrochloric acid afforded 16β,22-epoxy-23,24-dinorchol-5-ene-3β,22β-diol (17) and its 22-O-methyl derivative 18, the 3-O-acetate 19 of which was oxidized to the known acetyldiosgenin lactone (20), thus confirming the structures of 16-19. Compound 2 was shown to be identical in every respect with a rare spirosolane alkaloid, recently isolated from some Solanum species. Photolysis of (22R,23S,25R)-3β,16β-diacetoxy-N-chloro-22,26-epiminocholest-5-en-23-ol (10) yielded also via 22,23-carbon-carbon cleavage (20S)-3β,16β-diacetoxypregn-5-ene-20-carbaldehyde (21) as major product, which was converted by treatment with methanolic hydrochloric acid into the compound 18.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930130
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  • 16
    Electronic Resource
    Electronic Resource
    Syntheses and Cardiovascular Activity of Stereoisomers and Derivatives of Eburnane Alkaloids (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 221-229 
    Details
    ISSN: 0170-2041
    Keywords: Eburnanes ; Alkaloids ; Cardiovascular effects ; Indolo[2,3-a]quinolizines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of all the possible isomers of the eburnameninevincamine type alkaloids 1b, 2a, 3a and derivatives 4, 8, 9, 10 is described. Structures were determined by 1H- and 13C-NMR spectroscopy including special techniques such as DR, DEPT, DNOE, and 2D-HSC. In contrast to the known cerebrovascular effects of cis-(3S,16S) compounds, trans-(3S,16R) derivatives show a significant peripheral vasodilator effect.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930140
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  • 17
    Electronic Resource
    Electronic Resource
    Novel Prenylated 2-Quinolinones from East Asian Zanthoxylum Species (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 355-358 
    Details
    ISSN: 0170-2041
    Keywords: Quinolines ; Alkaloids ; Pyrano-quinolines ; Schinifolines ; Flindersines ; Zanthoxylum spec. ; Terpenes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In addition to already known 2-quinolinones [flindersine (3), N-methylflindersine (4), 8-methoxyflindersine (5), zanthobungeanine (6), glycolone (1), O-methylglycosolone (2)], four novel derivatives have been isolated and identified by spectroscopic methods. The roots of Zanthoxylum schinifolium and Z. simulans contain the novel prenylated schinifoline (7) and N-methylschinifoline (8), whereas the leaves of Z. simulans predominantly form N-acetoxymethylflindersine (10). From the roots of Z. scandens zascanol epoxide (9) has been isolated whose prenyl side chain is characterized by an epoxide ring and a terminal hydroxy group.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930160
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  • 18
    Electronic Resource
    Electronic Resource
    Electroorganic Synthesis, 54. Enantioselective Cathodic Reduction of 4-Substituted Coumarins with Alkaloids as Catalysts, 1Dedicated to Professor Dr. Ulrich Schöllkopf on the occasion of his 65th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 601-607 
    Details
    ISSN: 0170-2041
    Keywords: Electrochemistry ; Coumarins, reduction of ; Enantioselective protonation ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical yield in the alkaloid-catalyzed enantioselective electroreduction of 4-methylcoumarin (1a) was increased from 17% to 47.4% by systematic variation of the electrolysis conditions. The results are explained by an induction mechanism in which the adsorbed protonated alkaloid acts as a chiral proton donor towards a prochiral carbanion derived from 1a. The preferred configuration of the product and the results obtained by variation of the alkaloid structure allow us to propose a model of the transition state. Furthermore, 4-phenylcoumarin (1b) and 4-(trifluoromethyl)coumarin (1c) were reduced with 13.2% and 8.4% ee, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930198
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  • 19
    Electronic Resource
    Electronic Resource
    Synthese des Azocino[4.3-b]indol-Grundgerüstes von Strychnos-Alkaloiden (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 705-710 
    Details
    ISSN: 0170-2041
    Keywords: Azocino[4.3-b]indole, 1,5-methano- ; Carbazoles ; Hexahydrocarbazoles ; Strychnos alkaloids ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of the Azocino[4.3-b]indole Core Structure of Strychnos AlkaloidsMichael addition of ethylmalonic dimethyl or diethyl ester with cyclohexenone and subsequent Fischer indole ring closure afford the (tetrahydrocarbazolyl)malonic esters 4a-c. Decarboxylation of 4a leads to the corresponding butyric acid methyl ester 5 which is oxidized by DDQ to the 4-oxo derivative 6a (byproduct: carbazole 7). Oximation of 6a to 8a and acylation of the oxime group to 8b, c as well as hydrogenation of this group yield 9a, b. Subsequent hydrogenation of the tetrahydrocarbazole ring by means of borane/pyridine yields the hexahydrocarbazole derivatives 10a and b. By cyclisation in boiling o-xylene (sodium hydride catalysis) 10a is converted into the tetracyclic 1,5-methanoazocino[4.3-b]indole derivative 11a with an alkaloid analogous ethyl side chain. The X-ray structural analysis of the corresponding phenylsulfonyl derivative 11b confirms constitution and stereochemistry. As a diastereoisomer of 11a the byproduct 11c could be isolated.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301115
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  • 20
    Electronic Resource
    Electronic Resource
    Natural Product Chemistry, 161. - Oxidation of (±)-Almeine with Aqueous Potassium Permanganate (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 921-922 
    Details
    ISSN: 0170-2041
    Keywords: Furo[3,2-c]quinolines ; (±)-Almeine ; Alkaloids ; Quinolines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (±)-almeine (3) with aqueous potassium permanganate affords the dihydrofuro[3,2-c]quinolin-4(2H)-ones 4 and 5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301145
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  • 21
    Electronic Resource
    Electronic Resource
    β-Carbolin-Alkaloide, IV. - Synthese von 1-Alkyl-β-carbolinen und Strukturrevision von Lycii-Alkaloid I (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 1335-1337 
    Details
    ISSN: 0170-2041
    Keywords: β-Carbolines ; 1-Ethyl-β-carboline ; Harman ; 9-Formylharman ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Carboline Alkaolids, IV. - Synthese of 1-Alkyl-β-carbolines and Structure Revision of Lycii Alkaloid IPalladium-catalyzed coupling reactions of 1-chloro-β-carboline (1) with triethylborane and trimethylaluminum give the alkaloids 1-ethyl-β-carboline (2) and harman (5). The intermediate 4 on treatment with ethyl formiate gives 9-formylharman (6). Comparison of the spectroscopic data shows, that lycii alkaloid I does not have the structure 6, but is identical with the alkaloid 1-acetyl-β-carboline (7).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301218
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  • 22
    Electronic Resource
    Electronic Resource
    Synthese der Theonelladine A, B, C, D und von Niphatesin A (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 161-165 
    Details
    ISSN: 0170-2041
    Keywords: Pyridines ; Alkaloids ; Theonelladines A-D ; Niphatesine A ; 4-(3-Pyridyl)-1-butin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of the Theonelladines A, B, C, D and of Niphatesine AThe pyridine alkaloids theonelladine A-D (1-4) and niphatesine (5) of marine origin have been synthesized starting either from 3-(4,4-dibromo-3-butenyl)pyridine (6) or from 3-pyridinecarbaldehyde. Reaction of 6 with two equivalents of BuLi gave the lithiated derivative of the alkyne 7, which could be alkylated with 1-bromo-10-(tetrahydro-2-pyranyloxy)decane (8) to yield the alkynol 9 after methanolysis. Selective hydrogenation of 9 with Lindlar palladium catalyst gave (Z)-14-(3-pyridyl)-11-tetradecan-1-ol (11). - Addition of the Grignard reagent of 12-(benzyloxy)-1-bromododecane (13) to 3-pyridinecarbaldehyde gave 17, which was first oxidized (Swern) to give 18 and then reduced (Wolff-Kishner) to give 14. Hydrogenolysis of the benzyl ether 14 yielded 15. The alcohol group in 9, 11, and 15 was converted into the tosyloxy group by reaction with tosyl chloride/pyridine. Subsequent reactions of the tosylates 10, 12, and 16 either with an excess of methylamine/ethanol or of ammonia/ethanol gave the pyridine alkaloids 1-5 in high yields as p-toluenesulfonates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930129
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  • 23
    Electronic Resource
    Electronic Resource
    Alkaloide aus Veratrum patulum, I. Isolierung und Strukturaufklärung neuer SteroidalkaloidglycosideHerrn Professor Dr. F. Zymalkowski zum 80. Geburtstag gewidmet. (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 281-285 
    Details
    ISSN: 0170-2041
    Keywords: Veratrum patulum ; Steroids ; Glycosides ; Liliaceae ; Alkaloids ; Carbohydrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkaloids from Veratrum patulum, I. - Isolation and Structure Elucidation of New Steroid Alkaloid GlycosidesHerrn Professor Dr. F. Zymalkowski zum 80. Geburtstag gewidmet.Beside the known veratrosine (1), two new steroid alkaloid glucosides, 23-O-β-D-glucopyranosyl-20-isoveratramine (2) and (22S,23R,25S)-23-O-β-D-glucopyranosyl-5,11,13-veratratrienine-3β,23-diol (3), were isolated from the roots of Veratrum patulum Loes. fil. (Liliaceae) and characterized by spectroscopic methods.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930148
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  • 24
    Electronic Resource
    Electronic Resource
    New Studies and a Reinvestigation on [4+2] Cycloadditions of (-)-Thebaine: Asymmetrical Diels-Alder Reactions with a Conformationally Fixed Chiral Diene (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 947-953 
    Details
    ISSN: 0170-2041
    Keywords: (-)-Thebaine ; 1,3-Cyclohexadiene, 1-methoxy- ; Diels-Alder Reactions ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some novel Diels-Alder reactions of the opium alkaloid (-)-thebaine (1) as an electron-rich diene and a reinvestigation of its reactions with cyclic and acyclic dienophiles are described. The π-facial selectivity has been studied on the basis of structural analyses of the cycloadducts. Some related results on [4 + 2] cycloaddition reactions of 1-methoxy-1,3-cyclohexadiene (11) are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301151
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  • 25
    Electronic Resource
    Electronic Resource
    Herstellung von 6,14-Ethenomorphinan-Derivaten (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 915-919 
    Details
    ISSN: 0170-2041
    Keywords: Buprenorphine ; Diprenorphine ; Rotamers, N-CHO ; Morphinane derivatives ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of 6,14-Ethenomorphinane DerivativesBuprenorphine (5j) and diprenorphine (5k) were synthesized from N-formyl-northebaine (1c) and N-benzyl-northebaine (1d) via new intermediates. N-cyclopropylmethyl-dihydronorthevinone 3d is a suitable compound for the synthesis of both 5j and 5k. We carried out detailed 1H- and 13C-NMR analysis of the new compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301144
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  • 26
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    Electronic Resource
    Synthesis of Enantiomerically Pure Tetrahydro-2-methylharman (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 137-140 
    Details
    ISSN: 0170-2041
    Keywords: Harman derivatives ; β-Carboline derivatives ; Pyrido[3,4-b]indole derivatives ; Alkaloids ; Arundo donax L. ; Pictet-Spengler reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-Tryptophan methyl ester reacts with acetaldehyde in a Pictet-Spengler condensation to give a 2.5:1 mixture of the stereoisomers (1S,3S)-2 and (1R,3S)-2. These were converted by ammonolysis into the corresponding amides (1S,3S)-3 or (1R,3S)-3. On methylation of (1S,3S)-3 or (1R,3S)-3 the corresponding 2-methylcarbolineamide (1S,3S)-4 or (1R,3S)-4 were obtained. Dehydration of (1S,3S)-4 or (1R,3S)-4 affords 2-methylcarbolinenitrile (1S,3S)-5 or (1R,3S)-5. After reduction with NaBH4 (1S,3S)-5 or (1R,3S)-5 was decyanated and the title compound (1S)-6 or (1R)-6 was obtained. With NOE experiments their stereochemistry were determined and their optical purities were confirmed by measurements using a chiral shift reagent.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930125
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  • 27
    Electronic Resource
    Electronic Resource
    Synthesis of enantiomerically pure indoloquinolizine derivatives (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 141-146 
    Details
    ISSN: 0170-2041
    Keywords: β-Carboline derivatives ; Pyrido[3,4-b]indole derivatives ; Indolo[2,3-a]quinolizine derivatives ; Alkaloids ; Pictet-Spengler reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-Tryptophan methyl ester reacts with 1,1,3,3-tetramethoxypropane to give methyl carbolinecarboxylate 2 as a 1:2 mixture of the (1R,3S) and (1S,3S) stereoisomers. Conversion to the corresponding amides (1R,3S)-3 and (1S,3S)-3 was accomplished by treatment of 2 with ammonia. Benzylation of (1R,3S)-3 or (1S,3S)-3 afforded the corresponding 2-benzylcarbolineamide (1R,3S)-4 or (1S,3S)-4. Dehydration of the amide group in (1R,3S)-4 or (1S,3S)-4 yielded the corresponding 2-benzylcarbolinenitrile (1R,3S)-5 or (1S,3S)-5, which was treated with NaBH4 to reductively remove the cyano group. Hydrogenation removed the benzyl-protectin group of 6 resulting in (1R)-7 or (1S)-7, which is then alkylated with methyl vinyl ketone to give the Michael adduct (1R)-8 or (1S)-8. Subsequent Aldol reaction and dehydration afforded the enantiomerically pure indoloquinolizine derivatives (12bR)-9 or (12bS)-9, which was shown to be enantiomerically pure by recording their 1H-NMR spectra in the presence of a chiral shift reagent.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930126
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  • 28
    Electronic Resource
    Electronic Resource
    The Biosynthesis of the Cularine Alkaloids (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 557-563 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Benzylisoquinoline ; Biosynthesis ; Cularine ; Crassifoline ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study the cularine biosynthesis, L-[β-13C]tyrosine (L-18), [α-13C]tyramine (20), L-[3′-18O]DOPA (L-19) and [α-13C, 3′-18O]dopamine (21) were synthesized and fed to Corydalis claviculata and Sarcocapnos crassifolia plants, which are rich sources of cularine-type alkaloids. (S)-Crassifoline [(S)-15, an established cularine (1) precursor] and cularine-type alkaloids subsequently isolated, showed upon L-[β-13C]tyrosine feeding approximately equal labeling (1:0.8) of the isoquinoline and benzyl moiety, whereas the other precursors were solely incorporated into the isoquinoline half, indicating that three of the four oxygen functions present in cularine-type alkaloids are derived from simple, early precursors. The fourth oxygen atom appears to be introduced later into a trioxygenated alkaloidal intermediate. [α-13C, 3-18O]Dopamine was incorporated into the upper half of the 7,8-oxygenated (S)-crassifoline [(S)-15] molecule, without loss of 18O-label. This fact excludes an isomerization mechanism of 6,7-oxygenated isoquinolines through a dehydroxylation/hydroxylation step. Furthermore, these findings proved to be correct by separate feeding experiments with a novel 3′,7,8-trihydroxylated (S)-tetrahydrobenzylisoquinoline [(S)-10] and its 3′,6,7-trihydroxylated isomer, (S)-norcoclaurine [(S)-9], the common precursor of benzylisoquinoline alkaloids in nature. The first alkaloid was exclusively biotransformed into (S)-crassifoline [(S)-15] and cularine-type alkaloids, whereas (S)-norcoclaurine [(S)-9] was only metabolized to its well established metabolite, (S)-reticuline [(S)-16], but not to cularine-type alkaloids. Feeding experiments with (S)- and (R)-[1-13C]norjuziphine [(S)-11, (R)-11], (RS)-[N-13C]juziphine [(RS)-13], (RS)-[N-13C]3′-hydroxyjuziphine [(RS)-14] and (RS)-[N-13C]crassifoline [(RS)-15] confirmed a new pathway to (S)-crassifoline and the (S)-configurated cularine-type alkaloids 1-5, and showed in addition that there must be at least one enzyme in the pathway which is (S)-stereospecific.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199319930191
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  • 29
    Electronic Resource
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    Synthesis of 2,3-Dihydro-7-hydroxymethyl-1H-pyrrolizin-1-one, the Alkaloid LoroquineDedicated to Prof. Liang Xiao-tian, President of the Chinese Chemical Society, Beijing, P. R. China, on the occasion of his 70th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 711-713 
    Details
    ISSN: 0170-2041
    Keywords: Pheromones ; Pyrrolizidine alkaloids ; Pyrrolizines ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound 4 is synthesized in 8 steps by cyclization of N-tosylglycinate 5 with vinyl ketone 6. After elimination of water and sulfinic acid the pyrrolecarboxylate 9 is obtained which, on N-alkylation with ethyl acrylate, Dieckmann cyclization, saponification and decarboxylation, yields methylloroquine 12. The reaction with chlorotrimethylsilane/sulfuric acid in acetic anhydride and subsequent saponification give loroquine (4) in 2.1% overall yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301116
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  • 30
    Electronic Resource
    Electronic Resource
    β-Carbolin-Alkaloide, II Tributyl(1-ethoxyvinyl)stannan als C2-Baustein für die Synthese von β-Carbolin-Alkaloiden (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 837-839 
    Details
    ISSN: 0170-2041
    Keywords: β-Carbolines ; Alkaloids ; Annomontine ; Nitramarine ; Stannanes ; Tin compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Carboline Alkaloids, II. - Tributyl(1-ethoxyvinyl)stannane as a C2-Building Block in the Syntheses of β-Carboline Alkaloids1-Acetyl-β-carboline (4) is prepared by palladium-catalyzed coupling of 1-chloro-β-carboline (1) with tributyl(1-ethoxyvinyl)stannane (3) and subsequent hydrolysis with aqueous acid. Reduction of 4 with NaBH4 gives the alkaloid 5. Nitramarine (7) and annomontine (9) are prepared from 4 by one-pot conversions of the acetyl group to a quinoline or an aminopyrimidine ring, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301132
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  • 31
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    Carbohydrates as Chiral Auxiliaries in Stereoselective Synthesis. New Synthetic Methods (90) (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 336-358 
    Details
    ISSN: 0570-0833
    Keywords: Carbohydrates ; Chiral auxiliaries ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbohydrates are inexpensive natural products in which numerous functional groups and stereogenic centers are combined in one molecule. By directed regio-and stereoselective formation of derivatives they can be converted into efficient chiral auxiliaries for controlling asymmetric syntheses. Stereoelectronic effects and pre-orientation of the reactive and shielding groups through formation of complexes can often be used for effective diastereofacial differentiation. In aldol reactions and alkylations on carbohydrate ester enolates intramolecular complexation promotes simultaneous elimination with formation of ketene. The steric, stereoelectronic, and coordinating properties of carbohydrate templates can also be used selectively to attain high levels of asymmetric induction in processes such as Diels-Alder reactions, hetero-Diels-Alder reactions, [2 + 2] cycloadditions, cyclopropanations, and Michael additions. It was possible with bicyclic, strongly stereodifferentiating carbohydrate auxiliaries to achieve a diastereoselective synthesis of carboxylic acid derivatives branched in the β position by a new 1,4-addition of alkylaluminum halides to α,β-unsaturated N-acylurethanes, in which methylaluminum halides and higher alkyl- or arylaluminum compounds behave mechanistically in a strikingly different manners. As complex ligands in chiral reagents and promoters, carbohydrates allow highly stereoselective reductions and aldol reactions that lead, amongst others, to chiral alcohols and β-hydroxy-α-amino acids in excellent enantiomeric excesses. Glycosylamines offer the possibility of versatile stereoselective applications: in the presence of Lewis acids the corresponding aldimines permit high-yielding syntheses of enantiomerically pure α-amino acids by Strecker and Ugi reactions, controlled by steric and stereoelectronic effects and by complex formation. They can be used with equal efficiency for asymmetric syntheses of chiral homoallylamines and for asymmetric Mannich syntheses of β-amino acids and chiral heterocycles, for example alkaloids.
    Additional Material: 15 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199303361
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  • 32
    Electronic Resource
    Electronic Resource
    Chemistry of and with Highly Reactive Metals (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 164-189 
    Details
    ISSN: 0570-0833
    Keywords: Metals ; Reactivity ; Activation ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Today, the synthetic chemist has a large repertoire of metal activation methods at his disposal. After a first breakthrough was made at the beginning of the seventies with the introduction of the Rieke metals, a series of further, in part more efficient methods were describes, based on which not only classical metal-induced reactions could be substantially improved but also completely new reactions could be discovered. In this article the individual activation methods are discussed and compared as far as is possible using the currently available data. Especially noteworthy are the metal-graphite combinations because of their unsurpassed reactivity and concomitant easy preparation and manipulation. As shown by numerous applications of these reagents on polyfunctional substrates, particularly natural products, high reactivity of the metal and excellent selectivity are by no means precluded. Besides the purely preparative aspects also insights gained so far into the general principles and limits of metal activation are outlined, and attempts at determining the morphology of highly dispersed systems are reported.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199301641
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  • 33
    Electronic Resource
    Electronic Resource
    Syntheses of Polycyclic Natural Products Employing the Intramolecular Double Michael Reaction (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 1010-1022 
    Details
    ISSN: 0570-0833
    Keywords: Natural products ; Polycycles ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.
    Additional Material: 28 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199310101
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  • 34
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    Electronic Resource
    The influence of nutritional and genetic factors on larval performance of the cinnabar moth, Tyria jacobaeae (1992)
    Springer
    Entomologia experimentalis et applicata 62 (1992), S. 29-36 
    Details
    ISSN: 1570-7458
    Keywords: Alkaloids ; cinnabar moth ; insect genetics ; larval performance ; Lepidoptera ; nutritional ecology ; nitrogen ; sugar ; Tyria jacobaeae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a laboratory experiment using full-sibs, 60% of the variation in pupal weight of the monophage Tyria jacobaeae L. (Lepidoptera, Arctiidae) could be explained by variation in the nitrogen concentration of the food plant, Senecio jacobaea L. and only 4% by variation in sugar concentration. Larval weight and growth rates of young and old larvae were also positively correlated with nitrogen and sugar concentration. Developmental time was negatively correlated with nitrogen concentration. In a second experiment full-sib families differed significantly in larval weight at day 7, mortality, growth rate and developmental time. Pupal weight did not differ significantly among families, but was positively correlated with nitrogen concentration of Senecio. Larval performance was not significantly influenced by concentrations of sugars or alkaloids. We conclude that larval performance of Tyria during most of the larval period is mainly determined by genetic factors, but pupal weights are primarily determined by nitrogen concentration of the food plant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185638
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  • 35
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    Determination of alkaloids by differential pulse polarography. III Corydalis alkaloids (1992)
    Weinheim : Wiley-Blackwell
    Electroanalysis 4 (1992), S. 737-740 
    Details
    ISSN: 1040-0397
    Keywords: Alkaloids ; pulse polarography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Corydalis alkaloids have been investigated by differential pulse polarography as part of our continuing study of alkaloids. In this study, the alkaloidal content of Corydalis solida (L.) subsp. solida was determined. The results were compared by their structure and reduction mechanism. Quantitative analysis illustrates that Corydalis alkaloids can be determined down to sub-ppm level using differential pulse polarography in Britton-Robinson buffer pH 10. The amount of the various alkaloids in Corydalis solida (L.) subsp. solida have been shown. It was concluded that the reduction process at the dropping mercury electrode was catalytic in nature.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140040712
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    Polycyclic Aromatic Alkaloids, 8. The Structure of Neocalliactine Acetate  -  Proof by Total Synthesis (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1205-1207 
    Details
    ISSN: 0170-2041
    Keywords: Calliactine ; Neocalliactine acetate ; Alkaloids ; Calliactis parasitica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pentacyclic compound 1 is prepared in six steps by starting from 5,8-quinolinedione (7). Its spectral data are in accordance with those of neocalliactine acetate, a derivative or the marine alkaloid calliactine. This represents the first definite confirmation of the structure of neocalliactine acetate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201199
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  • 37
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    β-Carbolin-Alkaloide, I. Synthese von 1-Aryl- und 1-Alkenyl-β-carbolinen durch Palladium-katalysierte Kupplungsreaktionen (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1315-1319 
    Details
    ISSN: 0170-2041
    Keywords: β-Carbolines ; Komaroine ; Perlolyrine ; Pavettine ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Carboline Alkaloids, I.  -  Syntheses of 1-Aryl- and 1-Alkenyl-β-carbolines by Palladium-Catalyzed Coupling Reactions1-Chloro-β-carboline (6) is prepared in three steps starting from tryptamine (3). Palladium-catalyzed coupling reactions of 6 with aryl boronic acids offer an easy access to the alkaloids komaroine (11) and perlolyrine (15). Pavettine (16) is prepared by coupling of 6 with tributylvinylstannane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201216
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    Eine kurze, effektive Synthese von rac-Deplanchein (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1321-1323 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Deplancheine ; Indoles ; β-Carbolines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Short and Effective Synthesis of rac-DeplancheineTryptamine and dimethyl methoxyallylidenemalonate (1) react to give the divinylogous urethane 2, which yields by reaction with acroleine under acid catalysis the β-carboline 3a. Reductive decarboxylation gives the target compound deplancheine (4a) in excellent overall yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201217
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  • 39
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    Solanum Alkaloids, 124. Preparation of N-Hydroxyspirosolane Alkaloids (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1091-1093 
    Details
    ISSN: 0170-2041
    Keywords: Solasodines ; Tomatidines ; Alkaloids ; Solanum steroid alkaloids ; Spirosolanes ; Steroids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N-Hydroxyspirosolane alkaloids N-hydroxysolasodine (1) and N-hydroxytomatidine (10) as well as the N-hydroxy-22,26-epiminocholestene 7 have been prepared by oxidation of the respective amines 2, 11, and 5 with hydrogen peroxide in the presence of selenium dioxide.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201179
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    The Enchanting Alkaloids of YuzurihaThis review article grew out of a series of lectures presented in Germany in July 1990, as the Merck-Schuchardt Lectureship. The full details of our work on the total synthesis of Daphniphyllum alkaloids are reported in a series of articles recently published in the Journal of Organic Chemistry: see ref. [1]. (1992)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 31 (1992), S. 665-681 
    Details
    ISSN: 0570-0833
    Keywords: Alkaloids ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oriental plant Yuzuriha (Daphniphyllum macropodum) elaborates a fascinating family of polycyclic, squalene-derived alkaloids that provide a test for state-of-the-art methods of organic synthesis. The intriguing structures of these natural products have inspired us to design and explore two rather different approaches for their laboratory synthesis. This article recounts and contrasts these two different syntheses. The first approach was based on a method of synthetic design that emphasizes efficient construction of the polycyclic skeleton of the molecule (Corey's “network analysis”). A strategic bond was identified and the synthesis planned around the late formation of this bond. The synthesis that was designed by this approach proceeded smoothly until the point where it was necessary to remove functional groups that had been incorporated solely for the purpose of forming the strategic bond. Although the problems were eventually overcome, the resulting synthesis was too long and did not control the configuration of one of the stereocenters. The second approach was based on a possible biosynthesis of one of the alkaloids and provided surprisingly easy access to the simpler members of the family. The success of this synthesis led to a concrete proposal about the biosynthesis of the alkaloids and to the discovery of the astonishing transformation depicted in Scheme 27. In this marvelous reaction, an acyclic squalene derivative is converted by successive treatment with ordinary commodity chemicals into a pentacyclic alkaloid. The transformation involves the formation of four carbon-carbon bonds, two carbon-nitrogen bonds, and one carbon-hydrogen bond!
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199206653
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    Monitoring exposure to simple epoxides and alkenes through gas chromatographic determination of hemoglobin adducts (1991)
    Springer
    International archives of occupational and environmental health 63 (1991), S. 27-31 
    Details
    ISSN: 1432-1246
    Keywords: Hemoglobin adducts ; Exposure control ; Gas chromatography ; Epoxides ; Alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A method for monitoring exposure to ethylene oxide (EO) and propylene oxide (PO) and their corresponding alkenes through the analysis of adducts to N-terminal valine in hemoglobin (Hb) using gas chromatography (GC) and electron-capture detection has been developed. The method is a further development of the so-called N-alkyl Edman method, which has thus far been carried out using gas chromatography-mass spectrometry (GC/MS). The correlation between GC and GC/MS determinations of adduct levels in human samples was found to be good. The newly developed GC method enables the determination of adducts to Hb from EO and PO down to levels of about 100 pmol/g globin. This adduct level corresponds to the expected increment from ethene in inhaled tobacco smoke in a smoker of about 10 cigarettes/day or from an average exposure to about 50 Wpb EO or 1 Wpm PO during working hours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406194
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    Venom alkaloids in Monomorium “rothsteini” Forel repel other ants: is this the secret to success by Monomorium in Australian ant communities? (1991)
    Springer
    Oecologia 88 (1991), S. 157-160 
    Details
    ISSN: 1432-1939
    Keywords: Alkaloids ; Ant communities ; Interference competition ; Monomorium ; Venom
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Species of the cosmopolitan ant genus Monomorium are small, slow-moving and non-aggressive ants that are extremely successful members of diverse Australian ant communities. Unlike other abundant taxa, they have no obvious specializations enabling them to co-exist with the highly aggressive species of Iridomyrmex that dominate these communities. Here we report results which suggest that Monomorium species owe their success to the topical application of venom alkaloids which repel other ants. The venom alkaloids (trans-2-ethyl-5-undecylpyrrolidine and trans-2-ethyl-5-tridecylpyrrolidine) of Monomorium “rothsteini” were identified and synthesized, and the repellency to other ants of the synthetic alkaloids were tested using bioassays involving the attraction to honey baits of three native species of Iridomyrmex, three tropical “tramp” species, and M. “rothsteini” itself. Repellency to all other ant species was total or nearly so, but only partial to M. “rothsteini”. Defensive alkaloids produced from a variety of glands are found in other ant genera, and may be a potent yet poorly appreciated force in interference competition between ant species and thereby the structure of ant communities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320805
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    Inactivation modifiers of Na+ currents and the gating of rat brain Na+ channels in planar lipid membranes (1991)
    Springer
    Pflügers Archiv 419 (1991), S. 514-521 
    Details
    ISSN: 1432-2013
    Keywords: Na+ channels ; Inactivation ; Membrane currents ; Gating trypsin ; Chloramine-T ; Alkaloids ; Membrane conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rat brain Na+ channels whose inactivation process had been removed either by batrachotoxin (BTX) or veratridine (VT) were reconstituted into planar lipid membranes. The voltage dependence of the open probability (P o) of the channel, of the opening and closing rate constants, and the conductance and relative permeability for Na+ and K+ were studied in voltage-clamp conditions in the presence of agents known to modify the inactivation of Na+ currents. In relation to alkaloids (BTX, VT, and aconitine), it was found that once a Na+ channel was modified by BTX or VT, the addition of another alkaloid did not change further the gating and permeation properties of the channel over a period of about 1 h. Once the inactivation process of the channels is removed by BTX, the addition of a proteolytic enzyme (trypsin) or an halogenated compound (chloramine-T, CT) induced profound and specific modifications on the opening and closing events of Na+ channels: (1) the voltage dependence of the channel P o shifted to more hyperpolarized potentials; (2) this voltage shift can be explained by equal hyperpolarizing voltage shifts of the opening and closing rate constants of the channel; (3) although the gating properties of the channel were modified by these compounds, the permeation properties of the channel, as evaluated by the conductance and the selectivity to Na+ and K+ ions, were unaltered; (4) trypsin and CT were active only in the intracellular side of the channel and were irreversible within the time course of the experiments, suggesting covalent modifications of the channel. Inactivation modifiers also affected the gating of toxin-activated single Na+ channels. This alteration is compatible with a simple increase in the intracellular potential as seen by the voltage sensor of the channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370798
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    Inheritance of morphological and chemical characters in interspecific hybrids between Papaver bracteatum and Papaver pseudo-orientale (1991)
    Springer
    Theoretical and applied genetics 81 (1991), S. 537-540 
    Details
    ISSN: 1432-2242
    Keywords: Papaver bracteatum ; P. pseudo-orientale ; Interspecific hybrids ; Alkaloids ; Thebaine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The alkaloid profiles and morphological traits of the capsules of Papaver bracteatum, P. pseudo-orientale, and their hybrids were studied. Dominance of the hexaploid parent P. pseudo-orientale was observed for various characters. A genetic model assuming allelic additive effects and polysomic inheritance was elaborated for the control of isothebaine content in the capsules. The distribution of thebaine content in the segregating generations, F2 and BCF1 was evidence of the transfer of genes from the diploid parent P. bracteatum in the gametes of the interspecific hybrid and their expression in its progenies. These findings indicate the potential use of inter-specific hybrids between the Oxytona species in the breeding of cultivars for industrial or ornamental purposes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00219446
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    Estimating product yields of carbon-containing products from the atmospheric photooxidation of ambient air alkenes (1991)
    Springer
    Journal of atmospheric chemistry 13 (1991), S. 131-154 
    Details
    ISSN: 1573-0662
    Keywords: Alkenes ; tropospheric chemistry ; product yields ; sources ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The yields of products have been calculated for the reactions of hydroxyl radicals and ozone with 19 of the two-through-six carbon anthropogenic alkenes. Based on their rate of reaction, mechanisms of reactions and the ambient air distribution for these alkenes their seasonal ambient air yields have been estimated. Aldehydes predominate as products irrespective of season, with smaller yields of several ketones. Other minor products include carboxylic acids, carbon monoxide, carbon dioxide, and alkenes. About a two-fold increase is estimated in the yields of ‘hot’ biradicals and their products from summer to winter. One sensitivity analysis was made by recomputing yields at a different OH radical to O3 concentration than assumed most likely in the calculations discussed above. In addition, the sensitivity of product yields to an estimated range of seasonally averaged sunset-to-sunrise NO3 radical concentrations was calculated. The effects of free radical reactions are discussed, but these are believed to make a relatively minor contribution within the NO x -rich atmospheres that contain anthropogenic alkenes. The uncertainties in product yields associated with the range of NO3 radical concentrations assumed present is relatively small for aldehydes, as is the decrease in yield of the one carbon ‘hot’ biradical. Larger uncertainties occur for ketones. Significant decreases in yields occur for larger ‘hot’ biradicals, especially the branched-chain ‘hot’ radicals in the presence of NO3 radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115970
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  • 46
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    Ozonolysen von α-Oxo-alkenen: Zur Existenz von α-Oxo-ozoniden (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 947-956 
    Details
    ISSN: 0009-2940
    Keywords: Ozonolysis ; Alkenes ; α-Oxo- ; 1,2,4-Trioxolanes ; acyl- ; 3,3′-Bi-1,2,4-trioxolanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ozonolyses of α-Oxo-alkenes: On the Existence of α-Oxo-ozonidesOzonolyses of nine acyclic (1a-i) and of two cyclic (14, 29) α-Oxo-alkenes on polyethylene or in pentane afforded in eight cases (1d-i, 14, 29) isolable α-Oxo-ozonides. α-Diozonides (9) are obtained from five of the acyclic α-Oxo-alkenes (1a, b, d, g, h). All isolated ozonides are labile; the 2,4-dinitrophenylhydrazones of the α-Oxo-ozonides, however, are very stable. Decomposition of the α-Oxo-ozonides affords not only the hitherto known fragments, but non-peroxidic isomers (8) of the ozonides, too.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240440
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  • 47
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    {Bis[bis(trimethylsilyl)methyl]stannio(II)}bis(η2-ethen)nickel(O) und verwandte Verbindungen, Teil I (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1321-1325 
    Details
    ISSN: 0009-2940
    Keywords: Alkenes ; Nickel complexes ; Stannenes ; Metal-metal bonds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: {Bis[bis(trimethylsilyl)methyl]stannio(II)}bis(η2-ethene)nickel(O) and Related Compounds, Part IThe reaction of Ni(C2H4)3 and bis{bis(trimethylsilyl)methyl}-stannene affords the crystalline, coordinatively unsaturated complex (C2H4)2Ni = Sn{CH(SiMe3)2}2 (1). The NMR spectra of 1 show for the tin moiety a temperature-dependent solvate complex formation (thf) and for the nickel moiety a hindered rotation of the ethene ligands at low temperature. X-ray structure analysis indicates Sn - Ni multiple-bond character. Upon addition of donor molecules to 1 the addition compounds (C2H4)2Ni - Sn{CH(SiMe3)2}2(donor) [donor = NH3: 2a; pyridine: 2b; (Me2N)3PO: 2c] are obtained. According to the low-temperature NMR spectra the complexes are asymmetric in their ground state. Similar to the formation of the adducts 2a - c, the title compound 1 reacts with LiHAliBu3 as a source of LiH in ether/tmeda to form the hydride adduct [Li(tmeda)2]+ [(C2H4)2Ni - Sn{CH(SiMe3)2}2}2(H)]ominus; (2d). Displacement of the ethene ligands in 1 by CO yields with conservation of the Ni - Sn bond the complex (CO)3Ni= Sn{CH(SiMe3)2}2 (3). From this complex the donor adducts (CO)3Ni - Sn{CH(SiMe3)2}2(donor) [donor = NH3: 4a; pyridine: 4b; (Me2N)3PO: 4c] are prepared. For the donor-ligand carbonyl complexes the ground state has been shown to be asymmetric by low-temperature NMR spectra.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240603
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    Acetogenic isoquinoline alkaloids, XXI. An atropisomer-differentiating reaction for the chemical analysis of axial chirality and its computational investigation: Proof of the stereostructure of dioncophylline ADedicated to Professor Dr. Dr. h. c. mult. Siegfried Hünig on the occasion of his 70th birthday. (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 803-809 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Axial chirality, determination of ; Calculations, AM1, MM2, MMX ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chemical method for the unambiguous elucidation of axial chirality in naphthylisoquinoline alkaloids such as dioncophylline A (1a) is described. It involves synthetic connection of the stereogenic axis to be investigated with the stereocenters present in the same molecule. The resulting macrocyclic ansa compound 7c is formed in high yield, yet exclusively for only one of the two atropodiastereomers (4c), the other isomer (4b) does not cyclize at all. This cyclization behavior fully confirms the stereostructure 1a of dioncophylline A, as postulated by us earlier. For an interpretation of the striking atropisomer specificity of this ring closure reaction, computer-assisted theoretical investigations on the molecular geometries and thus thermodynamical properties of both of the imaginable cyclization products 7b/c have been performed by using force-field (MM2, MMX) and semiempirical methods (AM1). The optimized structures show the obtained macrocycle 7c to be a nonstrained, stable compound, whereas the other possible product 7b (which definitely is not formed) should be severely distorted.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101137
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    Synthese von 6-Methoxy-2,5-dimethyl-2H-isoindol-4,7-dion, einem Alkaloid aus Reniera-Arten (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 973-973 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Isoindole derivative ; 1,3-Dipolar cycloaddition ; Reniera species ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 6-Methoxy-2,5-dimethyl-2H-isoindole-4,7-dione, an Alkaloid from Reniera Species6-Methoxy-2,5-dimethyl-2H-isoindole-4,7-dione (4) can easily be obtained in high yields in a one-pot synthesis by heating sarcosine (2) and paraformaldehyde in the presence of 3-methoxy-2-methyl-1,4-benzoquinone (1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101168
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    Application of two-dimensional shift correlated NMR techniques to the structure determination of an unusual marine alkaloid, isosaraine-2 (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 327-332 
    Details
    ISSN: 0749-1581
    Keywords: Saraines ; 2D COSY NMR ; 2D 1H-13C COSY NMR ; Alkaloids ; Sponge ; Reniera sarai ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extensive application of two-dimensional proton-proton and proton-carbon shift correlated spectroscopy allowed the structural elucidation of isosaraine-2, a minor component of an unique family of alkaloids from the sponge Reniera sarai.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290408
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    The Logic of Chemical Synthesis: Multistep Synthesis of Complex Carbogenic Molecules (Nobel Lecture)Copyright © The Nobel Foundation, 1991. We thank the Nobel Foundation, Stockholm, for permission to print this lecture. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 455-465 
    Details
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Retro reactions ; Computer chemistry ; Nobel lecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199104553
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  • 52
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    Synthetic and stereochemical studies on phthalideisoquinoline hemiacetals (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 287-289 
    Details
    ISSN: 0170-2041
    Keywords: Isoquinoline alkaloids ; Egenine ; Corytensine ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two new phthalideisoquinoline hemiacetals rac-egenine (3) and rac-corytensine (4) are prepared by stereoselective DIBAL reduction of rac-bicuculline (1) and rac-adlumidine (2), respectively. The identity of egenine (3) with decumbensine as well as of corytensine (4) with epi-α-decumbensine and humosine A is postulated. The configuration around the anomeric center in natural (+)-egenine (3), (+)-corytensine (4) and (-)-narcotine hemiacetal (7) is deduced as (7′S), (7′R) and (7′R), respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199119910148
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    Enantioselective Addition of Organometallic Reagents to Carbonyl Compounds: Chirality Transfer, Multiplication, and AmplificationParts of this review were presented by R. N. during his Merck-Schuchardt lecture series in the Federal Republic of Germany in May 1989. Ar represents aryl substituents in this article. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 49-69 
    Details
    ISSN: 0570-0833
    Keywords: Chirality transfer ; Carbonyl compounds ; Addition ; Enantioselectivity ; Synthetic methods ; Alcohols ; Reaction mechanisms ; Catalysis ; Alkylation ; Organometallic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic addition of organometallic reagents to carbonyl substrates constitutes one of the most fundamental operations in organic synthesis. Modification of the organometallic compounds by chiral, nonracemic auxiliaries offers a general opportunity to create optically active alcohols, and the catalytic version in particular provides maximum synthetic efficiency. The use of organozinc chemistry, unlike conventional organolithium or -magnesium chemistry, has realized an ideal catalytic enantioselective alkylation of aldehydes leading to a diverse array of secondary alcohols of high optical purity. A combination of dialkylzinc compounds and certain sterically constrained β-dialkylamino alcohols, such as (-)-3-exo-dimethylaminoiso- borneol [(-)-DAIB], as chiral inducers affords the best result (up to 99% ee). The alkyl transfer reaction occurs via a dinuclear Zn complex containing a chiral amino alkoxide, an aldehyde ligand, and three alkyl groups. The chiral multiplication method exhibits enormous chiral amplification: a high level of enantioselection (up to 98%) is attainable by use of DAIB in 14% ee. This unusual nonlinear effect is a result of a marked difference in chemical properties of the diastereomeric (homochiral and heterochiral) dinuclear complexes formed from the dialkylzinc and the DAIB auxiliary. This phenomenon may be the beginning of a new generation of enantioselective organic reactions.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199100491
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    3-Amino-2H-Azirines. Synthons for α,α-Disubstituted α-Amino Acids in Heterocycle and Peptide Synthesis [New Analytical Methods (43)] (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 238-264 
    Details
    ISSN: 0570-0833
    Keywords: 3-Amino-2H-azirines ; Azirines ; Amino acids ; Peptides ; Heterocycles ; Synthetic methods ; 2-Aminoisobutyric acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recent upswing in peptide chemistry has been accompanied by an increasing interest in nonproteinogenic amino acids. These include the α,α-disubstituted glycines, the best known of which is Aib (2-aminoisobutyric acid, 2-methylalanine). These α-amino acids occur in natural oligopeptides such as the peptaibols, a class of membrane-active ionophores that has been isolated from fungal cultures. The twofold substitution at the α-C atom of the amino acids severely restricts the conformational freedom of the peptides and causes particular secondary structures to be favored; thus, α, α-disubstituted α-amino acids induce the formation of β turns or helices. 3-Amino-2H-azirines are ideal synthons for the construction of oligopeptides, cyclic peptides and depsipeptides (peptolides) containing such α,α-disubstituted α-amino acids. The presence of the ring strain in these molecules means that they can be used in peptide coupling without the need for additional activating reagents. Using 3-amino-2H-azirines a large array of heterocycles containing α, α-disubstituted α-amino acids as structural elements within their skeleton can be synthesized. The driving force in these reactions is the release of the strain on the three-membered ring, which usually takes place in a ring-expansion reaction. The mechanistic elucidation of these reactions, which can be quite complex, contains some surprises.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199102381
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    The Isocyanide-Cyanide Rearrangement; Mechanism and Preparative ApplicationsBesides this IUPAC name, the rearrangement is often referred to as the isonitrile-nitrile rearrangement in the literature. Nomenclature example: acetonitrile ≡ methyl cyanide ≡ ethanenitrile.Dedicated to Professor Horst Prinzbach on the occasion of his 60th birthday. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 893-901 
    Details
    ISSN: 0570-0833
    Keywords: Rearrangement ; Synthetic methods ; Cyanides ; Isocyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Until recently the isocyanide-cyanide rearrangement was of interest almost solely as an example of a unimolecular gas-phase reaction, and kinetic studies had been carried out in only a few simple cases. Kinetic measurements in solution were made possible only by the discovery and suppression of a parallel free-radical chain process which leads to the same products. The rate of the isomerization is almost independent of the structure of the starting material and of the substituents present. An exception is provided by extreme steric hindrance in three dimensions which, as in tris-α-substituted triptycyl isocyanides, leads to a considerable increase in the activation energy. The results can be interpreted in terms of a purely sigmatropic mechanism, as predicted by ab initio calculations. The preparative application of this rearrangement reaction requires the suppression of side reactions and can best be carried out by flash pyrolysis; yields are then almost quantitative. Allyl isocyanides react without allyl isomerization, optically active isocyanides with complete retention of configuration. New, economically interesting syntheses for the known nonsteroidal anti-inflammatory drugs ibuprofen and (S)-naproxene are described. The application of the useful synthetic building blocks, the optically active β-acyloxy cyanides, which are formed from optically active α-amino acids, will be demonstrated.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199108933
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    Chemistry and Biology of the Enediyne Anticancer Antibiotics (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 1387-1416 
    Details
    ISSN: 0570-0833
    Keywords: Calicheamicins ; Synthetic methods ; Antitumor agents ; Antibiotics ; Enediynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, biologically active substances from nature often provide excitement, stimulation, challenges, and opportunities for the scientific and medical communities. Experience and wisdom dictate investigation of their chemistry and pursuit of their chemical synthesis for more often than not, the rewards for both chemistry and medicine are great. The enediyne anticancer antibiotics are a rapidly emerging class of such compounds derived from bacterial sources. Combining unprecedented and highly unusual molecular architecture, phenomenal biological activities and fascinating modes of action, these DNA cleaving compounds burst onto the scene in the latter half of the 1980s when their structures became known, and they rapidly moved to center stage. Today the enediyne family includes the neocarzinostatin chromophore, the calicheamicins, the esperamicins, and the dynemicins, and soon the number of family members is certain to increase. These molecules elicited extensive research activities in chemical, biological, and biomedical circles and inspired the design of a number of novel molecular assemblies to probe and mimic their chemical and biological actions. A new body of synthetic technology and several novel synthetic strategies have already been devised to address the challenges posed by these molecules, and several new DNA cleaving agents have been designed and synthesized. This article summarizes the chemistry and biology of the enediynes and discusses mechanistic, synthetic, molecular design, and DNA cleavage aspects associated with the field.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199113873
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    New Approaches to the Use of Amino Acids as Chiral Building Blocks in Organic Synthesis [New Synthetic Methods (85)]Dedicated to Professor Karl Heinz Büchel on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 1531-1546 
    Details
    ISSN: 0570-0833
    Keywords: Amino acids ; Asymmetric synthesis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Amino acids protected at nitrogen in quite different ways can be transformed without racemization into the corresponding α-amino aldehydes. Provided one chooses the right protecting groups (e.g., two benzyl residues on nitrogen) it is possible for the first time to carry out Grignard-like, aldol, and Me3SiCN additions, and hetero-Diels-Alder reactions with a high degree of nonchelation control. If the reactions of classical carbanions turn out to be nonselective, transmetalation, for example into organotitanium reagents, constitutes an important tool in controlling stereoselectivity. Diastereoselectivity can be reversed by specific variation of the protecting group and reagent. “Protecting-group tuning”, “metal tuning”, and “ligand tuning” are very useful in reactions of α-amino aldimines as well. The α-amino aldehydes can also be converted by Wittig reactions into electron-poor γ-amino olefins, which in turn undergo stereoselective cuprate, Michael, and cycloadditions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199115313
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  • 58
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    Microbial degradation of the morphine alkaloids: identification of morphinone as an intermediate in the metabolism of morphine by Pseudomonas putida M10 (1990)
    Springer
    Archives of microbiology 154 (1990), S. 465-470 
    Details
    ISSN: 1432-072X
    Keywords: Pseudomnas putida ; Morphine ; Codeine ; Codeinone ; Morphinone ; Alkaloids ; Morphine dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A strain of Pseudomonas putida was isolated by selective enrichment with morphine that was capable of utilising morphine as a primary source of carbon and energy for growth. Experiments with whole cells showed that both morphine and codeine, but not thebaine, could be utilised. A novel NADP-dependent dehydrogenase, morphine dehydrogenase, was purified from crude cell extracts and was shown to be capable of oxidising morphine and codeine to morphinone and codeinone, respectively. This NADP-dependent morphine dehydrogenase was not observed in any other species of pseudomonads examined and was quite distinct from the β-hydroxysteroid dehydrogenase found in Pseudomonas testosteroni, which had previously been shown to have activity against morphine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245229
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    Folgereaktionen von Sulfenen aus Sulfonylchloriden und tertiären Aminen, 2. Bildung von Episulfonen, Sulfonylsulfen  -  Amin-S,N-Addukten und Chlorsulfinen aus primären Sulfonylchloriden und tertiären Aminen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1989-1998 
    Details
    ISSN: 0009-2940
    Keywords: Episulfones ; Thiirane 1,1-dioxides ; Alkenes ; Sulfines ; Sulfonylsulfene-amine S,N-adducts ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Secondary Reactions of Sulfenes from Sulfonyl Chlorides and Tertiary Amines, 2.  -  Formation of Episulfones, Sulfonylsulfene  -  Amine S.N-Adducts. and Chlorosulfines from Primary Sulfonyl Chlorides and Tertiary AminesThe reaction of primary sulfonyl chlorides 1b-m with the tertiary amine bases quinuclidine, DABCO, Me3N, Et3N, Bu3N, EtiPr2N, and 1,2,2,6,6-pentamethylpiperidine is studied in acetonitrile solution between - 40 and 80°C. The 2,3-dialkylthiirane 1,1-dioxides 4 (trans/cis 〉 1) and the alkenes 5 [(E)/(Z) 〉 1] are obtained in high yields with Et3N at - 40°C. The stereochemistry is influenced by the amine base B in the ring closure reaction and partially by epimerization of the episulfones 4. Hindered bases favor the cis, β-branched sulfonyl chlorides the trans isomer. Competing formation of the sulfonylsulfene-amine S,N-adducts 7 is only observed with quinuclidine, DABCO, and Me3N, which are also the most active amines in the epimerization of the cis-2,3-diarylthiirane 1,1-dioxides 4. Methanesulfonyl chloride (1a) yields the mesylsulfene-amine S,N-adducts 7a with Me3N and Et3N in MeCN, but thiirane 1,1-dioxide (4a) with EtiPr2N in MeCN or with Et3N in Et2O. Formation of chlorosulfines 10 is favored by higher temperature (T 〉 20°C), hindered amine bases and β-branched sulfonyl chlorides. Isolation of 10g and 10h in high yields shows that tert-alkylchlorosulfines are rather stable sulfines.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19901231010
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    Fate of plant-derived secondary metabolites in three moth species (Syntomis mogadorensis, Syntomeida epilais, andCreatonotos transiens) (1990)
    Springer
    Journal of comparative physiology 160 (1990), S. 389-400 
    Details
    ISSN: 1432-136X
    Keywords: Lepidoptera ; Herbivores ; Resorption ; Cardenolides ; Alkaloids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Larvae of three moth species were compared with respect to strategies used to cope with secondary metabolites (allelochemicals) present in their diet.Syntomeida epilais is monophagous and accepted only oleander (which contains cardenolides, CG). CG were detected as stored products in the larvae and also in the faeces and exuviae. Pure CG (digoxin and gitoxin) which do not occur in oleander fed on oleander leaves were sequestered as the oleander CG.Syntomis mogadorensis is polyphagous: given a choice larvae avoided plants with a high load of allelochemicals. Upon shortage of preferred plants they ate a wide variety of plants which contain alkaloids, terpenes, or phenolics. Of these allelochemicals, alkaloids and CG were mainly recovered in the faeces and only minute fractions in the larvae.Creatonotos transiens larvae behaved similarly toSyntomis in terms of polyphagy and non-resorption. However, the larvae took up and stored pyrrolizidine alkaloids (PA) such as heliotrine selectively.Creatonotos is thus polyphagous (a generalist) but also a PA-specialist which exploits PA as defensive agents, as a morphogen for the male pheromone gland, and as a precursor for the male pheromone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01075670
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    Highly Reactive Intermediates from the Cocondensation Reactions of Iron, Cobalt and Nickel Vapor with ArenesReactive π-Complexes of Electron-rich Transition Metals, Part 10. - Part 9: D. Hu, H. Schäufele, H. Pritzkow and U. Zenneck, Angew. Chem. 101 (1989) 929; Angew. Chem. Int. Ed. Engl. 28 (1989) 900. (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 126-137 
    Details
    ISSN: 0570-0833
    Keywords: Arene ligands ; Intermediates ; Cocondensation ; Sandwich complexes ; Synthetic methods ; Iron ; Metal atoms ; Cobalt ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 1969, P. L. Timms reported the first preparative cocondensation reactions of metal vapors with organic and inorganic substrates. The use of this technique in preparative chemistry soon spread rapidly, but in recent years there has been less activity in this sector. If metal atom reactions are not utilized primarily for the formation of new products, but for the synthesis of highly reactive intermediates, a new synthetic strategy may be developed. Our aims are reaction sequences which, based on an effective cocondensation reaction, lead gradually and selectively to new substance classes. This principle can be illustrated by the example of the cocondensation products of arenes and iron, cobalt, or nickel vapor, which decompose between -70 and -50°C. The classes of products accessible by this method extend from clusters, through π-complexes, organophosphorus and organoboron cage compounds to pure organic cycloaddition products.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199001261
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    Natural product chemistry, 140. Synthesis of some new acridones (1990)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 1047-1049 
    Details
    ISSN: 0170-2041
    Keywords: Acridones ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl 6-amino-2,3-dimethoxybenzoate (6) which was obtained from 6-formyl-2,3-dimethoxybenzoic acid (1), was treated with phloroglucinol to give two new acridone alkaloids, 1,3,8-trihydroxy-7-methoxy-9-acridone (7) and 1,3-dihydroxy-7,8-dimethoxy-9-acridone (8). Methylation of 7 and 8 gave another four new acridone alkaloids, 1,8-dihydroxy-3,7-dimethoxy-9-acridone (9), 1,8-dihydroxy-3,7-dimethoxy-10-methyl-9-acridone (10), 1-hydroxy-3,7,8-trimethoxy-10-methyl-9-acridone (11) and 1,3,7,8-tetramethoxy-10-methyl-9-acridone (12).
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/jlac.1990199001189
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    Reactions of hydridotrihalostannato complexes of platinum {trans-[PtH(SnX3)(PR3)2]} with alkenes (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 4 (1990), S. 111-117 
    Details
    ISSN: 0268-2605
    Keywords: Alkenes ; Pt—H insertion ; platinum hydrides ; alkyl complexes ; phosphine complexes ; 31P NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An interaction of trans-[PtH(SnX3)L2] (I, L = PPh3, PMePh2, PEt3; PBu3; X = Cl, Br) with ethylene, propene and 2-methylpropene has been studied by means of 31P and 1H NMR spectroscopy. The reactions of platinum hydrides I with ethylene are rapid and reversible at -90°C, giving cis-[PtR(SnX3)L2] (II, R = C2H5). The reaction of propene with I (L = PPh3, PMePh2) gives II, R = C3H7. 13C and 1H NMR spectra prove the n-propyl structure for II, L = PMePh2, X = Cl. Complexes II irreversibly isomerize into trans-[PtR(SnX3)L2] between -50° and 0°C. The equilibrium constants and rates are estimated for the reactions of I with alkenes. They decrease as a function of L (PMePh2 〉 PPh3 〉 PBu3 〉 PEt3) and X (Br 〉 Cl). The reactivities of alkenes decrease with increase of steric hindrances at the double bond.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590040205
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  • 64
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    The Directed Synthesis of Biaryl Compounds: Modern Concepts and Strategies (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 977-991 
    Details
    ISSN: 0570-0833
    Keywords: Biaryls ; Arenes ; Synthetic methods ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and utilization of specific biaryl systems, particularly those which suffer hindered rotation, is a demanding goal not only in the synthesis of natural products and Pharmaceuticals, but also for example in the discovery of new reagents for asymmetric synthesis. This article will attempt to provide a topical review of modern, efficient processes for the specific preparation of biaryls. This appears to be of particular urgency, since, under the pressure of continually increasing demand, a wealth of new or modified synthetic approaches to the ever more important biaryl systems has been realized in recent years. The high standard which has been reached in this field is impressively demonstrated by regio- and stereoselective syntheses of important biaryl natural products such as steganone, ancistrocladine, ancistrocladisine, and dioncophylline A. Besides the utilization of asymmetric induction in the actual coupling step, the thermodynamically or kinetically controlled torsion of biaryl axes belongs to the most important concepts discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199009771
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    Stereocontrolled Construction of Complex Cyclic Ketones via Oxy-Cope Rearrangement (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 609-626 
    Details
    ISSN: 0570-0833
    Keywords: Oxy-Cope rearrangement ; Ring expansion ; Cope rearrangement ; Diastereoselectivity ; Rearrangement ; Ketones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Convergency is a highly serviceable aspect of organic synthesis, particularly when its application is accompanied by high levels of chirality transfer and regiocontrol. A reaction that is notably well suited to these objectives is the oxy-Cope rearrangement. In addition, the benefits that can accrue from suitable condensation of β γ-unsaturated ketones with a vinyl organometallic and subsequent [3,3] sigmatropic shift are substantive enhancement in structural complexity and the ability to generate a myriad of polycyclic frameworks. Another profitable feature is the complementary regeneration of the carbonyl group in a new structural context. In view of the pivotal role played by the carbonyl functionality in synthetic transformations, reacquisition of such a reaction site translates into heightened chemical versatility. The trajectories followed by vinyl organometallics as they engage in 1,2 addition to ketones are gradually being understood. Proper diastereoselective control of this bond-making process, when coupled with full awareness of the chair or boat topography adopted during the ensuing oxy-Cope electronic reorganization, provides for exciting new strategy-level dimensions not often available in other contexts. The use of this two-step sequence as a prelude to a third chemical event clearly serves to expand the possibilities for molecular construction still more. While a considerable amount of the work to date has focused on the preparation of rather elaborate carbocyclic molecules, principally with a view to gaining access to complex natural products, the possibilities for heterocyclic synthesis are currently being accorded increased attention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199006091
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    Organic Synthesis - Where now? (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1320-1367 
    Details
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Future of chemistry ; Chemistry today ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review article is an attempt to sketch the important developments in organic synthesis during the past 25 years, and to project them into the future. - The primary motivations that once induced chemists to undertake natural product syntheses no longer exist. Instead of target structures themselves, molecular function and activity now occupy center stage. Thus, inhibitors with an affinity for all the important natural enzymes and receptors have moved to the fore as potential synthetic targets. - New synthetic methods are most likely to be encountered in the fields of biological and organometallic chemistry. Enzymes, whole organisms, and cell cultures for enan-tioselective synthesis of specific substances have already been incorporated into the synthetic arsenals of both research laboratories and industry. In addition, designing appropriate analogues to transition states and intermediates should soon make it possible, with the aid of the mammalian immune system and gene technology, to prepare catalytically active monoclonal antibodies for almost any reaction; perhaps, more important, such processes will increasingly come to be applied on an industrial scale.-The discovery of truly new reactions is likely to be limited to the realm of transition-metal organic chemistry, which will almost certainly provide us with additional “miracle reagents” in the years to come. As regards main group elements (“organoelemental chemistry”), we can surely anticipate further stepwise improvements in experimental procedures and the broader application of special techniques, leading to undreamed of efficiency and selectivity with respect to known procedures. The primary center of attention for all synthetic methods will continue to shift toward catalytic and enantioselective variants; indeed, it will not be long before such modifications will be available with every standard reaction for converting achiral educts into chiral products. Analysis, spectroscopy, structure determination, theory, and electronic data processing have all become indispensable in organic synthesis. Only with the aid of these “tools” will the methods of organic chemistry permit selective syntheses of ever larger and more complex systems on both the molecular and supramolecular levels. - Examples have been introduced throughout this discourse to illustrate its many themes, and a very comprehensive bibliography should help the interested reader become more familiar with important keywords and authors.[The list of references is also available upon request in the form of a Microsoft Word© file on diskette.] - This article will have served its intended purpose if it changes the minds of some of those who claim organic chemistry is a mature science, and if it causes students to discover the vitality and forcefulness with which organic synthesis is meeting new challenges and attempting to fulfill old dreams.Er zeigt uns so in seinem wissenschaftlichen Leben, daß die Chemie nicht von einer Theorie, nicht von einer Methode aus zu erschöpfen ist, und daß Erkenntnis und Nutzen in ihr untrennbar verwoben sind.“He showed us through his scientific life that chemistry cannot be exploited fully with the aid of a single theory or a single methodology, and that it is a field in which knowledge and application are inextricably linked.” G. Bugge: Das Buch der großen Chemiker, Vol. 2, 4th reprint, Verlag Chemie, Weinheim 1974.R. Koch, writing about Louis Pasteur
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/anie.199013201
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    CC Bond Formation by Addition of Carbenium Ions to Alkenes: Kinetics and MechanismDedicated to Professor Rolf Huisgen on the occasion of his 70th birthday (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 29 (1990), S. 1371-1384 
    Details
    ISSN: 0570-0833
    Keywords: Kinetics ; Addition ; Alkenes ; Reaction mechanisms ; Carbocations ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of carbenium ions to CC double bonds, a key step in many syntheses in organic and macromolecular chemistry, is analyzed using the Lewis acid promoted reactions of alkyl chlorides with alkenes as an example. Stereochemical and kinetic experiments suggest that the transition state is slightly bridged and product-like. Rearrangements of the carbenium ions that result from the electrophilic attack can be minimized by adding salts with nucleophilic counter ions. The thermodynamics of the addition reactions are analyzed, and the conditions necessary in order to observe the back reaction (i.e. the Grob fragmentation) are discussed. Multiparameter equations that predict rate constants are derived from kinetic studies on the reactivities of carbenium ions and alkenes. Reactivity-selectivity relationships over a reactivity range that covers eight orders of magnitude show that the structure of the transition state is only changed by variation of substituents in the immediate vicinity of the reaction center.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199013713
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    Synthese der Hydroxypiperidinalkaloide (±)-Cassin, (±)-Spectalin, (±)-Spicigerin-methylester, der (±)-Azimsäure und (±)-Carpamsäure (1989)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 255-261 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Piperidine alkaloids ; 3-Pyridinols; 2,6-dlialkylated ; Bromine-lithium exchange and alkylation, regiospecific ; Hydrogenation of 3-pyridinols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Syntheses of the Piperidine Alkaloids (±)-Cassine, (±)-Spectaline, (±)-Spicigerine Methyl Ester and of (±)-Azimic Acid and (±)-Carpamic AcidThe piperidine alkaloids (±)-cassine (1), (±)-spectaline (2), (±)-spicigerine methyl ester (3), (±)-azimic acid (4), and (±)-carpamic acid (5) have been synthesized stereoselectively in the following way: In the SEM ether 7 of 2,6-dibromo-3-pyridinol (6) the bromine atom in position 2 can be regiospecifically exchanged with nBuLi to give 8. Reaction of 8 with methyl iodide gave the key compound 9 exclusively. In the presence of Kumada′s NidpppCl2 catalyst in ether solution 9 reacts with the Grignard reagents from the bromides 14-18 to give the products 19-23. Methanolysis of the products gave the substituted 3-pyridinol derivatives 24-28. Subsequent acetalisation led to 29, 30 and hydrolysis to 31, 32. Hydrogenation of 28-32 with Rh on alumina catalyst and 90 bar pressure gave exclusively the (±) products 33, 34, 3, 4, and 5 with (2r,3c,6c) configuration. Hydrolysis of the ethylene acetal group in 33 and 34 gave (±)-1 and (±)-2.
    Notes: Die Piperidinalkaloide (±)-Cassin (1), (±)-Spectalin (2), (±)-Spicigerin-methylester (3) sowie (±)-Azimsäure (4) und (±)-Carpamsäure (5) werden stereoselektiv synthetisiert: Im SEM-Ether 7 des 2,6-Dibromo-3-pyridinols (6) erfolgt bei der Reaktion mit nBuLi ein regiospezifischer Austausch des Bromatoms in Position 2. Die entstandene Li-Verbindung 8 läßt sich mit Methyliodid zur Schlüsselverbindung 9 methylieren. Diese reagiert in Gegenwart von Kumadas NidpppCl2-Katalysator in Ether mit den Grignard-Reagenzien aus den Bromiden 14-18 zu den 6-substituierten Pyridinen 19-23. Methanolyse und Hydrolyse liefern die 3-Pyridinol-Derivate 24-28 und durch nachfolgende Acetalisierung 29, 30 sowie durch Hydrolyse 31, 32. Die Hydrierung von 28-32 mit Rh auf Alox-Katalysator unter 90 bar Druck ergibt ausschließlich die (±)-Produkte 33, 34, 3, 4 und 5 mit (2r,3c,6c)-Konfiguration. Hydrolyse der Ethylenacetalgruppe in 33 und 34 ergibt (±)-1 und (±)-2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198919890148
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    Heteroyohimban-Analoga aus 3-Acetyl-7,12-dihydro-2-methyl-6H-indolo-[2,3-a]chinolozinium-chlorid (1989)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 443-447 
    Details
    ISSN: 0170-2041
    Keywords: Alkaloids ; Heteroyohimbane analogues ; Indolo[2,3-a]quinolizines ; Stilbazoles ; Aldol condensation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Heteroyohimbane Analogues from 3-Acetyl-7,12-dihydro-2-methyl-6H-indolo[2,3-a]quinolizinium Chloride1)The methyl side chain of 3-Acetyl-7,12-dihydro-2-methyl-6H-indolo[2,3-a] quinolizinium chloride (1a) and its acetal 1b, prepared from tryptamine hydrochloride and acetoacetaldehyde dimethylacetal, are treated with carbonyl compounds. Starting from 1b, benzaldehyde and furfural yield the stilbazoles 4a-d, after hydrogenation of ring C the tetrahydropyridines 5a-c. With hydrate-forming carbonyl compounds like chloral, diethyl mesoxalate, and ninhydrin, water is not eliminated (6-8, 10, 12) and, starting from 1a, the acetyl side chain participates in forming the heteroyohimbane-like ring E (9, 11, 13).
    Notes: In dem aus Tryptamin-hydrochlorid und Acetylacetaldehyd-dimethylacetal gebildeten 3-Acetyl-7,12-dihydro-2-methyl-6H-indolo[2,3-a]chinolizinium-chlorid (1a) und seinem Acetal 1b wird die Methyl-Seitenkette durch Umsetzung mit Carbonyl-Verbindungen kondensiert. Benzaldehyd und Furfural führen ausgehend von 1b zu den Stilbazolen 4a-d, nach Hydrierung von Ring C zu den Tetrahydropyridinen 5a-c. Mit Hydrat-bildenden Carbonyl-Verbindungen wie Chloral, Mesoxalsäure-diethylester und Ninhydrin bleibt die Wasser-Abspaltung aus (6-8, 10, 12), und es kommt ausgehend von 1a unter Beteiligung der Acetyl-Seitenkette zur Schließung des Heteroyohimban-ähnlichen Ringes E (9, 11, 13).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198919890178
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  • 70
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    Intramolecular, Stoichiometric (Li, Mg, Zn) and Catalytic (Ni, Pd, Pt) Metallo-Ene Reactions in Organic Synthesis [New Synthetic Methods (75)]Dedicated to Professor Elias J. Corey on the occasion of his 60th birthday (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 38-52 
    Details
    ISSN: 0570-0833
    Keywords: Metallo-ene reaction ; Ene reaction ; Synthetic methods ; Catalysis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C—O→C—;Pd-→ C—C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon-carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198900381
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  • 71
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    Gene Synthesis [New Synthetic Methods (77)]Dedicated to Professor Hansgeorg Gareis on the occasion of his 60th birthday (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 716-734 
    Details
    ISSN: 0570-0833
    Keywords: Gene technology ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligonucleotide synthesis, until a few years ago the rather exotic preserve of a few experts, has become an integral part of the arsenal of molecular-biological techniques. The last decade, in particular, has seen unbelievably rapid development in this area. DNA synthesis has been automated and can now produce genes greater than 1000 base pairs in length. Tailor-made synthetic genes also permit the synthesis of altered or even novel proteins (de novo protein design) by gene-technological methods. Together with modern methods of gene isolation, sequencing, and expression, gene synthesis has played a major part in the enormous advances achieved in gene technology.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198907161
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  • 72
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    Cyclizations via Palladium-Catalyzed Allylic Alkylations [New Synthetic Methods (79)] (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 1173-1192 
    Details
    ISSN: 0570-0833
    Keywords: Cyclization ; Allylic alkylation ; Alkylation ; Synthetic methods ; Palladium ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The history of ring systems in organic chemistry parallels their synthetic accessibility. Transition-metal-catalyzed cyclizations offer a new opportunity to create carbo- and heterocyclic compounds with great facility. Among these methods, allylic alkylations catalyzed by palladium have proven unusually productive because of the extraordinary chemo-, regio-, and diastereoselectivity and the continuing possibility for the development of enantioselectivity. The rules for ring closure differ from those for non-transition-metal-catalyzed reactions. A major benefit is the ability to generate medium (eight-, nine-, ten-, and eleven-membered) and large rings in preference to normal (five-, six- and seven-membered) rings. With the appropriate substrate, efficient macrocyclizations are possible under conditions of normal concentrations. A second major benefit derives from the complementary stereochemistry of the metalcatalyzed substitution (net retention of configuration) compared to non-metal-catalyzed reactions (inversion of configuration). Further, the requirement for the substrate to conform to the transition-metal template may impose a stereochemical preference in the intermediate that ultimately translates into the thermodynamically less stable organic product regardless of the stereochemistry of the starting material. While more work has focused on carbocyclic synthesis, the possibilities for heterocyclic synthesis are just beginning to be tapped. In addition to forming heterocycles by C—C bond formation, use of a heteroatom as a nucleophile has already proven effective for oxygen and nitrogen, with other nucleophiles awaiting investigation. New dimensions for cyclization via allylic alkylation arise by generating the requisite π-allylpalladium intermediates by methods other than palladium(0)-initiated allylic ionizations. In addition, metals other than palladium will clearly expand the possibilities, but as yet remain untapped.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198911731
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  • 73
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    General Aspects and Optimization of Enantioselective Biocatalysis in Organic Solvents: The Use of Lipases [New Synthetic Methods (76)] (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 695-707 
    Details
    ISSN: 0570-0833
    Keywords: Enantioselectivity ; Lipases ; Synthetic methods ; Enzyme catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective biocatalysis in nonaqueous media is becoming increasingly important in preparative synthetic chemistry. This article discusses (1) the general catalytic properties of enzymes in nonaqueous environments, (2) the basic principles that govern lipase-catalyzed enantioselective esterification and transesterification reactions in organic media for the preparation of optically active acids and alcohols, (3) the determination of kinetic and thermodynamic parameters, and (4) the quantitative analysis of published data.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198906951
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  • 74
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    The Stereoselectivity of Intermolecular Free Radical Reactions [New Synthetic Methods (78)]Dedicated to Professor Christoph Rüchardt on the occasion of his 60th birthday (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 969-980 
    Details
    ISSN: 0570-0833
    Keywords: Stereoselectivity ; Reaction mechanisms ; Synthetic methods ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regio- and chemoselectivities of free radical reactions are often high and largely predictable; systematic studies have now shown that the stereoselectivity of free radical reactions can also be directed. Examples involving five- and six-membered cyclic radicals will be used to show how steric and stereoelectronic effects influence the diastereoselectivity of reactions of cyclic radicals with olefins. The temperature, the solvent, and the nature of the radical scavenger used also play a role, so that, if the correct reaction conditions are used, the stereoselectivity of reactions for cyclic reactants can be very high. Lower stereoselectivities are often observed for reactions between acyclic radicals and acyclic alkenes. However, preliminary experiments have indicated that under certain conditions such systems can also react in a stereoselective manner.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198909693
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  • 75
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    Natural product chemistry. Part 116. Synthesis of daurine and folidine: Two 2(1H)-quinolinone alkaloids fromHaplophyllum species (1988)
    Springer
    Monatshefte für Chemie 119 (1988), S. 1169-1178 
    Details
    ISSN: 1434-4475
    Keywords: Alkaloids ; Daurine ; Folidine ; Haplophyllum ; 2(1H)-Quinolinones ; Rutaceae ; Total synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Strukturen der kürzlich aufgefundenen 2(1H)-Chinolinon-Alkaloide Daurin und Folidin konnten durch Totalsynthese bestätigt werden.
    Notes: Abstract Structures of the recently isolated 2(1H)-quinolinone alkaloids, daurine and folidine have been confirmed by total synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809269
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  • 76
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    Influence of structure of alkenes on their retention on different stationary phases (1988)
    Springer
    Chromatographia 25 (1988), S. 655-658 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Structure-retention relationships ; Connectivity indices, topological indices ; Alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention indices of different alkenes are correlated with connectivity and topological parameters. The appropriate statistically valid relations hips are derived and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327667
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  • 77
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    Reduction and Hydrogenation with the System Hydrocarbon/Carbon [New Synthetic Methods (70)]Dedicated to Professor Helmut Dörfel on the occasion of his 60th birthday (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 679-682 
    Details
    ISSN: 0570-0833
    Keywords: Reduction ; Hydrogenation ; Hydrocarbons ; Carbon ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the synthesis of organic compounds, reduction is an indispensible reaction type which is also widely used on an industrial scale. In industrial processes hydrogen is usually used as reducing agent, since strong reducing agents like alkali metals and hydrides can only be used to a limited extent for safety and economic reasons. Very economical reducing agents that are convenient to handle and have high potential application are hydrocarbons in presence of carbon. Hydrocarbon/carbon systems can be readily used instead of molecular hydrogen and expensive metal catalysts for the hydrogenation of compounds containing, for example, CC-, CO-, or NO-double bonds. Furthermore, these systems can be used for carrying out reductions which hitherto required strong reducing agents such as zinc, tin, alkali metals and hydrides. Especially suitable as economic sources of hydrogen are refinery products such as vacuum gas oil, fuel oil S or vacuum residue oil. Hydrocarbons are dehydrogenated to unsaturated systems and finally to carbon.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198806791
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  • 78
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    Cyclobutanones and Cyclobutenones in Nature and in Synthesis [New Synthetic Methods(71)]Dedicated to Professor Vladimir Prelog (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 797-827 
    Details
    ISSN: 0570-0833
    Keywords: Cyclobutanes ; Cyclobutenes ; Synthetic methods ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical reactivity of cyclobutanones and cyclobutenones is considerably different from that of cyclic ketones with larger rings; this is due to their ring strain of ca. 25 kcal/mol. Detailed knowledge regarding the influence of this ring strain on regio-, chemo- and stereoselective transformations of four-membered ring ketones is of particular importance. While several reactions, such as the Baeyer-Villiger reaction, the Beckmann and Favorskii rearrangements and cine-substitution often proceed in a manner specific to four-membered rings, other reactions such as the facile ring-opening by nucleophiles, the rearrangement to tropolones, the thermal [2+2]-cycloreversion, the isomerization to vinylketenes and the photochemical formation of oxacarbenes are rather specific to cyclobutanones and cyclobutenones. The remarkable selectivity and the excellent yields of such transformations, which are favored or caused by ring strain as the inherent driving force, offer the synthetic chemist fascinating possibilities for the development of new strategies for the synthesis of natural products and biologically active compounds.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198807971
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  • 79
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    Transition Metals in the Synthesis and Functionalization of Indoles [New Synthesis Methods (72)] (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1113-1126 
    Details
    ISSN: 0570-0833
    Keywords: Indoles ; Synthetic methods ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of transition-metal complexes as reagents for the synthesis of complex organic compounds has been under development for at least several decades, and many extraordinary organic transformations of profound potential have been realized. However, adoption of this chemistry by the practicing synthetic organic chemist has been inordinately slow, and only now are transition-metal reagents beginning to achieve their rightful place in the arsenal of organic synthesis. Several factors contributed to the initial reluctance of synthetic organic chemists to use organometallic reagents. Lacking education and experience in the ways of elements having d electrons, synthetic chemists viewed organometallic processes as something mysterious and unpredictable, and not to be discussed in polite society. Organometallic chemists did not help matters by advertising their latest advances as useful synthetic methodology, but restricting their studies to very simple organic systems lacking any serious functionality (e.g., the “methyl, ethyl, butyl, futile” syndrome). Happily, things have changed. Organometallic chemists have turned their attention to more complex systems, and more recently trained organic chemists have benefited from exposure to the application of transition metals. This combination has set the stage for major advances in the use of transition metals in the synthesis of complex organic compounds. This review deals with one aspect of this area, the use of transition metals in the synthesis of indoles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198811133
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  • 80
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    Zeolites: Catalysts for Organic SynthesesDedicated to Professor Helmut Dörfel on the occasion of his 60th birthday (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 226-246 
    Details
    ISSN: 0570-0833
    Keywords: Zeolites ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198802261
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  • 81
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    Ketenimine Complexes from Carbene Complexes and Isocyanides: Versatile Building Blocks for Carbocycles and N-Heterocycles [New Synthetic Methods (74)]Dedicated to Professor Ernst Otto Fischer on the occasion of his 70th birthday (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1456-1467 
    Details
    ISSN: 0570-0833
    Keywords: Ketenimines ; Carbene ligands ; Isocyanides ; Carbocycles ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ketenimine complexes are readily available in great variety by reaction of isocyanides with carbene complexes. They have proven to be useful building blocks in new synthetic approaches to carbocyclic and N-heterocyclic four-, five-, and six-membered rings. The reactions involve new metal-induced bond formation patterns of the ketenimine ligands, which can be influenced across a wide range by varying the following five parameters: the metal, the ligands, and the three substituents on the N=C=C unit.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198814561
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    Phosphaalkynes - Syntheses, Reactions, Coordination Behavior [New Synthetic Methods (73)]Phosphorus Compounds with Unusual Coordination, Part 30. Part 29: [119]. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1484-1508 
    Details
    ISSN: 0570-0833
    Keywords: Phosphaalkynes ; Synthetic methods ; Phosphorus-carbon compounds ; Multiple bonds ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198814841
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  • 83
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    Microbial and Enzymatic Processes for the Production of Biologically and Chemically Useful Compounds [New Synthetic Methods (69)] (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 622-642 
    Details
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Enzyme catalysis ; Fermentation ; Biotechnology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In recent years, the most significant development in the field of synthetic organic chemistry has been the application of biological systems to chemical reactions. Reactions catalyzed by enzymes and enzyme systems display far greater specificities than more conventional organic reactions. Biological and/or enzymatic syntheses and transformations, that is, “microbial transformations,” have great potential. Some of these reactions have already been shown to have useful applications in the fields of synthetic organic chemistry and biotechnology. This article reviews the current status of the rapidly developing field of microbial transformation, the methodology, available technological procedures, and fields of application being described especially in relation to conventional organic synthesis methods.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198806221
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  • 84
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    Some adaptations in the method of the ‘Pharmacopoeia Helvetica Editio Sixta’ for the determination of total alkaloids in Strychnos seeds (1987)
    Springer
    Pharmacy world & science 9 (1987), S. 324-325 
    Details
    ISSN: 1573-739X
    Keywords: Alkaloids ; Extraction ; Pharmacopoeias ; Strychnos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01956513
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  • 85
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    Totally Synthetic Routes to the Higher Monosaccharides (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 15-23 
    Details
    ISSN: 0570-0833
    Keywords: Monosaccharides ; Synthetic methods ; Carbohydrates ; Heptoses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evolution of a strategy to synthesize the title compounds is described. Three principal developments allowed realization of this goal: (1) the attainment of high margins of diastereofacial selectivity and regioselectivity in the construction of pyranoid systems via the Lewis acid-catalyzed cyclocondensation reaction of activated dienes and aldehydes; (2) the exploitation of stereoselective reactions for functionalization of the pyranoid matrix; and (3) the discovery of stereoselective reactions for extending the chiral biases of pyranoid systems to newly emerging stereogenic centers on side chains. The coordination of these components in the synthesis of target systems of high biological interest is described.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198700151
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    Directed Homogeneous Hydrogenation [New Synthetic Methods (65)] (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 190-203 
    Details
    ISSN: 0570-0833
    Keywords: Homogeneous hydrogenation ; Hydrogenation ; Synthetic methods ; Catalysis ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198701901
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    Synthesis of Glycopeptides, Partial Structures of Biological Recognition Components [New Synthetic Methods (67)]An expanded version of a lecture delivered on October 24, 1985, at the Max-Bergmann Conference in Bozen.Dedicated to Professor Leopold Horner on the occasion of his 75th birthday (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 294-308 
    Details
    ISSN: 0570-0833
    Keywords: Glycopeptides ; Molecular recognition ; Molecular recognition ; Synthetic methods ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycopeptides are partial structures of the connecting regions of glycoproteins and, like these, always contain glycosidic bonds between the carbohydrate and peptide parts. Glycoproteins are not only widely distributed but are also decisive factors in post-translational biological selectivity, especially in biological recognition. Targeted syntheses of glycopeptides require stereoselective formation of the glycosidic bonds between the carbohydrate and the peptide parts and protective group methods that enable selective deblocking of only one functional group in these polyfunctional molecules. These heavy demands have been met by the well-established use of benzylic protective groups, which can be removed by hydrogenolysis, combined with the use of base-labile 2-phosphonioethoxycarbonyl (Peoc) or 9-fluorenylmethoxycarbonyl (Fmoc) protective groups or of bromoethyl esters, which can be removed under neutral conditions. The acidolysis of tert-butyloxycarbonyl (Boc) groups and of tert-butyl esters has also been successfully used, although, under acidic conditions, anomerization or rupture of the glycosidic bonds may occur, especially when nucleophiles are present. The stable, two-stage 2-(pyridyl)ethoxycarbonyl (Pyoc) protective groups allow a more reliable synthesis of complex glycopeptides since they can be removed, after modifications, under mild conditions. Particularly suitable for the synthesis of sensitive glycopeptides are the stable allyl protective groups. They can be removed from the complex glycopeptides in a highly selective and effective manner by means of noble-metal catalysts under practically neutral conditions. These methods have been employed to synthesize glycopeptides corresponding to partial structures of interesting glycoproteins. Deprotected glyopeptides representing tumor-associated antigen structures can be coupled to bovine serum albumin, which serves as a biological carrier molecule, without the necessity of using an artificial coupling component (spacer).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198702941
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  • 88
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    Stereoselective Aldol Reactions with α-Unsubstituted Chiral EnolatesDedicated to Professor George Büchi on the occasion of his 65th birthday (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 24-37 
    Details
    ISSN: 0570-0833
    Keywords: Stereoselective aldol reactions ; Aldol reaction ; Chiral enolates ; Enolates ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aldol reaction is among the most important methods of forming carbon-carbon bonds. The addition of an enolate to an aldehyde leads to the formation of at least one chiral center. In the case of α-substituted enolates it has to a large extent been possible to control the product stereochemistry, while the aldol reaction of α-unsubstituted chiral enolates was for many years a “problem child” for synthetic chemists because of its insufficient stereoselectivity. Progress in this area has only been made in the last few years using either new chiral auxiliaries or alternatives to the aldol reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198700241
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  • 89
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    New Reductive Transformations of Unsaturated Cyclic Hydrocarbons [New Synthetic Methods (66)] (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 204-217 
    Details
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Reduction ; Carbanions ; Cycloannelation ; Cycloalkenes ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The successive reduction of fully conjugated cyclic hydrocarbons leads to singly and multiply charged ions with unusual bonding. The charge distribution in these ions can be determined spectroscopically, and the information so obtained is then used in kinetically controlled trapping reactions for the regioselective introduction of electrophilic groups. When non-benzenoid substrates are used, syntheses become possible which can either not be carried out or can only be carried out with great difficulty in other ways. Examples of new preparative applications are cycloannelation and bridging reactions as well as polymerization reactions. The ion pair structure of the intermediate and the type of electrophile used are of paramount importance in controlling the mechanism of these reductive transformations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198702041
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  • 90
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    Stereoselective Syntheses of Building Blocks with Three Consecutive Stereogenic Centers: Important Precursors of Polyketide Natural Products [New Synthetic Methods (68)] (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 489-503 
    Details
    ISSN: 0570-0833
    Keywords: Natural products ; Synthetic methods ; Polyketides ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sequences of directly adjacent stereogenic centers were first discovered for the monosaccharides, which therefore constituted the first focus of interest in Stereoselective synthesis. The structures of many polyketide-derived natural products that have been elucidated in recent years often exhibit longer sequences of stereogenic centers in which hydroxy-substituted secondary carbon atoms alternate with tertiary carbon atoms. This finding inspired the development of methods allowing the specific construction of first two and then - more importantly-three neighboring stereogenic centers. The diverse methodologies that have thereby emerged reveal common principles and stress the variety of approaches possible in stereoselective synthesis.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198704893
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  • 91
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    Lespedeza phenolics andPenstemon alkaloids: Effects on digestion efficiencies and growth of voles (1986)
    Springer
    Journal of chemical ecology 12 (1986), S. 713-728 
    Details
    ISSN: 1573-1561
    Keywords: Alkaloids ; phenolics ; feeding trials ; digestibility ; growth ; Lespedeza cuneata ; Penstemon digitalis ; Microtus pennsylvanicus ; Microtus ochrogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Lespedeza cuneata contains high levels of phenolics and is a common food plant of the meadow vole (Microtus pennsylvanicus);Penstemon digitalis contains substantial quantities of alkaloids and is a common food plant of meadow voles and prairie voles (M. ochrogaster). We investigated the palatability of these plants and the effects of their secondary compounds on the digestion efficiencies and growth of both species of voles. Voles ate very little of either plant when alternative food was present. Phenolics and alkaloids were extracted from the plants, incorporated into separate artificial diets, and fed to weanling voles for three weeks.Lespedeza phenolics reduced the growth of meadow voles but not prairie voles throughout the feeding trial. These compounds disrupted digestion, reducing protein digestibility by more than half.Penstemon alkaloids lowered only the initial growth rates of prairie voles and had no significant effect on meadow voles. Prairie voles tended to increase food consumption rates on bothLespedeza andPenstemon diets. This response offset some of the decrease in digested protein intake in the first case, and offset the increased metabolic cost of processing the diet in the latter case. Our results indicate that althoughLespedeza phenolics andPenstemon alkaloids do influence consumption and digestibility of artificial diets, they do not greatly reduce the performance (i.e., growth or survival) of voles when consumed at levels generally observed for wild voles. However, these compounds probably do place an upper limit on the amount of freshLespedeza andPenstemon that can be consumed and contribute to the generalist feeding strategy of voles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01012104
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  • 92
    Electronic Resource
    Electronic Resource
    On-line gas chromatographic analysis of light Fischer-Tropsch synthesis products (1986)
    Springer
    Chromatographia 21 (1986), S. 265-268 
    Details
    ISSN: 1612-1112
    Keywords: Capillary gas chromatography ; Alumina PLOT columns ; C1−C7 hydrocarbons ; Alkenes ; Fischer-Tropsch products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple gas chromatographic system has been developed for the rapid on-line analysis of light Fischer-Tropsch products. This involves a single chromatography fitted with two columns, a porous-layer open-tubular column coated with KCl deactivated alumina and a packed Porapak-Q column. The capillary column separates the 16 most common C1−C4 hydrocarbons and permits a reasonable analysis of the hydrocarbons in the C5−C7 range. The packed column is used for the separation of methane, carbon monoxide, carbon dioxide, water and methanol. Retention characteristics for the analysis on the capillary column are presented. The total analysis cycle is 30 minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02311879
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  • 93
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    Oxidation of propene and 1-butene byMethylococcus capsulatus andMethylosinus trichosporium (1986)
    Springer
    Journal of industrial microbiology and biotechnology 1 (1986), S. 119-127 
    Details
    ISSN: 1476-5535
    Keywords: Olefins ; Alkenes ; Epoxidation ; Biotransformation ; Methylococcus capsulatus ; Methylosinus trichosporium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Methane-grown cells ofMethylococcus capsulatus andMethylosinus trichosporium readily oxidized propene and various isomers of butene to their respective epoxides. When examined in a proton NMR spectrum using tris([3-trifluoromethylhydroxymethylene]-d-camphorato), europium III derivative as an optically active chemical shift reagent, the products propylene oxide and 1,2-epoxybutane were found to contain equal amounts of both isomers. Methane-grown cells of both bacteria had considerable levels of reducing equivalents to catalyze the epoxidation of gaseous olefins. Cells depleted of reductants catalyzed the oxidation in the presence of low levels of methanol or formaldehyde with a stoichiometry of about 2:1. The rates of epoxidation of propene and 1-butene in a continuous reactor were 2–3-times that of a batch-wise reaction; the epoxidation activity, however, was lost within 3 h. The inactivation was attributed to the reactivity of the accumulated epoxides in the reactor. Propene and 1-butene oxidation by both bacteria were drastically inhibited by the respective products. Thus, the major problem in the application of microorganisms for production of epoxides from gaseous olefins is the rapid separation of the reactive products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01569320
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  • 94
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    Gas chromatographic retention indices for alkenes on OV-101 and squalane capillary columns (1986)
    Springer
    Chromatographia 21 (1986), S. 149-151 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention indices ; Comparison of data ; Alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic retention indices for 47 C5 to C8 alkenes on OV-101 dimethylsilicone at 50 and 70 °C were determined within a standard deviation of 0.3i.u. Data obtained on OV-101 are compared with those measured on squalane. The comparison of the retention index and dl/dT values from both columns is presented as linear regression equations with correlation coefficients greater than 0.98.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02311743
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  • 95
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    New constituents of Zanthoxylum tessmannii(Engl.) Ayafor root (1986)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 412-414 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary columns ; Zanthoxylum tessmannii (Engl.) Ayafor ; Amides ; Terpene hydrocarbons ; Alkaloids ; Medicinal plant ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240090712
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  • 96
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    13C NMR and lanthanide-induced shifts in epoxides of Terpenes and related compounds (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 718-722 
    Details
    ISSN: 0749-1581
    Keywords: Epoxidation induced ; 13C NMR shifts ; Lanthanide induced shifts ; Epoxides ; Alkanes ; Alkenes ; Terpenes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on literature data, and new measurements with both simple and complicated skeletons, it is shown that epoxidation-induced shifts (EIS) usually vary by only 〈4ppm if compared with the corresponding olefins, but by 〈9 ppm if compared with the saturated analogues. Shift differences between stereoisomers (E/Z or trans/cis) are consistent and, again, similar in epoxides and olefins. Larger variations are observed only for cyclic systems in which flexibility and conformational coupling can lead to significant conformational differences between the epoxide and olefin. Yb(fod)3-induced LIS values are regular if normalized by setting the LIS for the α-carbon atoms to 100%; these and the EIS values can be used to confirm or correct13C signal assignments.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240818
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  • 97
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    185-nm Photochemistry of Olefins, Strained Hydrocarbons, and Azoalkanes in SolutionDedicated to Professor Dietrich Schulte-Frohlinde on the occasion of his 60th birthday (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 661-672 
    Details
    ISSN: 0570-0833
    Keywords: Photochemistry ; Azoalkanes ; Strained molecules ; Alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibility to excite directly at 185 nm chromophores that absorb in the vacuum-UV has stimulated increased activity during the last decade in this field of photochemistry. Whereas photochemical reactions at λ〈200 nm have been thoroughly investigated in the gas phase, only recently have intensive studies on the 185-nm photochemistry of organic compounds in solution provided new insights. Despite the high excitation energies, selective photoreactions are promoted in the short-lived singlet excited states (Rydberg photochemistry). In contrast to conventional photochemistry (λ 〉 220 nm), 185-nm irradiation preferentially results in intramolecular rearrangement, fragmentation, and isomerization reactions. Intermolecular radical couplings and abstractions as well as dimerizations (π, π*-excitation) compete minimally. Besides the straightforward denitrogenation of photoresistant (“reluctant”) azoalkanes, important applications of the short-wavelength photolysis are also found in technology (photolithography) and medicine (193-nm laser). Broadening the scope of the synthetic potential of the 185-nm photochemistry, which so far has been limited to direct cis/trans isomerizations, presents a challenge for the chemist.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198606613
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  • 98
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    New Methods for the Synthesis of Glycosides and Oligosaccharides - Are There Alternatives to the Koenigs-Knorr Method? [New Synthetic Methods (56)]Dedicated to Professor Rudolf Gompper on the occasion of his 60th birthday (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 212-235 
    Details
    ISSN: 0570-0833
    Keywords: Glycosides ; Oligosaccharides ; Koenigs-Knorr method ; Synthetic methods ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycoproteins, glycolipids, and glycophospholipids (glycoconjugates) are components of membranes. The oligosaccharide residue is responsible for intercellular recognition and interaction; it acts as a receptor for proteins, hormones, and viruses and governs immune reactions. These significant activities have stimulated interest in oligosaccharides and glycoconjugates. With their help it should be possible to clarify the molecular basis of these phenomena and to derive new principles of physiological activity. Major advances in the synthesis of oligosaccharides have been made by the use of the Koenigs-Knorr method, in which glycosyl halides in the presence of heavy-metal salts are employed to transfer the glycosyl group to nucleophiles. The disadvantages of this procedure have led to an intensive search for new methods. Such methods will be discussed in this article. Emphasis is placed on glycoside and saccharide formation by 1-O-alkylation, on the trichloroacetimidate method, and on activation through the formation of glycosylsulfonium salts and glycosyl fluorides.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198602121
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  • 99
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    Organic Synthesis at High Temperatures. Gas-Phase Flow Thermolysis [New Synthetic Methods (57)]Part of the Habilitationsschrift, M. Karpf, Universität Zürich 1984. (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 414-430 
    Details
    ISSN: 0570-0833
    Keywords: Gas-phase flow thermolysis ; Thermolysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preference for carrying out synthetic organic reactions at the lowest possible temperature is due to the expectation that the selectivity often increases with decreasing temperature, as is confirmed by many examples and also theoretically justified. Selectivity, however, is not the only problem at high temperatures; further factors include the frequently limited thermal stability of the functional groups and structural elements not directly involved in the transformation. In spite of these limitations, the advantages of high temperatures and the greatly improved knowledge of the mechanisms of dynamic gas-phase processes accumulated in recent years can be exploited in directed organic synthesis. In this review the synthetic potential of gas-phase flow thermolysis will be described from the viewpoint of the synthetic chemist with the aid of typical examples of application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198604141
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  • 100
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    The Palladium-Catalyzed Cross-Coupling Reactions of Organotin Reagents with Organic Electrophiles [New Synthetic Methods (58)] (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 508-524 
    Details
    ISSN: 0570-0833
    Keywords: Cross-coupling ; Organotin compounds ; Electrophilicity ; Palladium ; Catalysis ; C-C coupling ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross-coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon-carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198605081
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