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  • Articles: DFG German National Licenses  (38)
  • 1995-1999  (34)
  • 1960-1964  (4)
  • 1890-1899
  • Alkaloids
  • 1
    Electronic Resource
    Electronic Resource
    Further Alkaloids Common to Ants and Frogs: Decahydroquinolines and a Quinolizidine (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 1179-1193 
    Details
    ISSN: 1573-1561
    Keywords: Alkaloids ; mass spectrometry ; infrared spectroscopy ; amphibians ; ants ; decahydroquinolines ; quinolizidines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Three alkaloids—two minor decahydroquinolines (DHQs) and a major quinolizidine—were detected in an extract of a Brazilian myrmicine ant (Solenopsis (Diplorhoptrum) sp. picea group). One DHQ (3) was identical to a known frog-skin alkaloid, cis-195A (cis-5-methyl-2-propyldecahydroquinoline), while the second DHQ, an isomer of 3, designated 195J, was assigned a tentative cis-2-methyl-5-propyldecahydroquinoline structure (2) based on mass and infrared spectra. The third alkaloid proved identical to the frog-skin alkaloid 195C, for which a structure had not been previously proposed. Mass and infrared spectral analysis, including chemical ionization tandem mass spectrometry, indicated a 4-methyl-6-propylquinolizidine structure (1) for 195C. The four possible diastereomers were synthesized and the (6Z,10E)-4-methyl-6-propylquinolizidine diastereomer (1b) was identical to the natural alkaloid. Skin extracts of a population of a Madagascan mantelline frog contained, among other alkaloids, minor amounts of the same alkaloid triad 1–3 with 1 again predominating. The common occurrence of alkaloids 1–3 in both ant and frog supports the hypothesis that ants are a likely dietary source for sequestered frog-skin alkaloids and brings to six, the alkaloid classes common to ant and frog.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020898229304
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  • 2
    Electronic Resource
    Electronic Resource
    A Unified Synthetic Strategy for the Indolopyridine Alkaloid Group (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 373-378 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Cross-coupling ; N-Heterocycles ; Palladium ; Synthesis design ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Thermal or acetyl chloride induced cyclization of bromoenamide 10 affords the pentacyclic derivative 12 with high yield and regioselectivity. From this common synthetic intermediate, palladium-catalyzed reactions allow the total synthesis of indolopyridine alkaloids 1-6.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98332_s.pdf or from the author.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Syntheses of Batzelline A, Batzeline B, Isobatzelline A, and Isobatzelline B (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1173-1183 
    Details
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Pyrroloquinoline ; Total synthesis ; Heterocycles ; Alkaloids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characterized by the presence of a methylthio substituent at C-2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Iodocyclisation of 1,4-Dihydropyridines; Synthesis and Reactivity of 1-Iodoindolo[2,3-a]quinolizidines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2997-3003 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Cyclizations ; Iodine ; Nitrogen heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of iodine (or related species) to β-acyl-N-alkyl-1,4-dihydropyridines 1, which possess an N-substituent with an appropriate nucleophile moiety, leads to the corresponding 3-iododihydropyridinium ions, which undergo an internal nucleophilic attack to give, regio- and stereoselectively, the iodobi(poly)heterocyclic ring systems 2a-f in good yields. Reactivity studies on the iodoindoloquinolizidines 2e,f lead to the pentacyclic cyclopropane systems 4a,b, azides 5 and 6, norderivative 9 and, by a base-induced elimination, dihydropyridine 10, a precursor of the zwitterionic alkaloids flavopereirine and 6,7-dihydroflavopereirine.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Lewis Acid Assisted Vinylogous Mannich and Mukaiyama Aldol Reactions: A Route to Densely Hydroxylated Indolizidine Alkaloid Analogues (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1395-1400 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Vinylogous Mannich reaction ; Vinylogous Mukaiyama aldol reaction ; Glycosylation inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The hydroxymethyl-substituted indolizidines 6 and 7, representative members of a ring-B-expanded alexine-australine subclass, are readily accessible by starting with furan-based silyloxydiene 12 and hydroxymethyl hemiaminal 11, through a synthesis sequence involving a scantily exploited vinylogous version of the Mannich reaction. The key iminium electrophilic acceptor 11 is, in turn, available through a vinylogous intermolecular Mukaiyama aldolization process between pyrrole-based silyloxydiene 8 and (S)-glyceraldehyde 9.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    A General Approach to Indolizidine Alkaloids From 1-Benzyloxy-5-(p-toluenesulfonamido)-3-alken-2-ols: Synthesis of (+)-Monomorine I (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3277-3280 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Asymmetric synthesis ; Palladium ; Amino alcohols ; Natural products ; Monomorine I ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A versatile method for the preparation of indolizidine alkaloids from 1-benzyloxy-5-(p-toluenesulfonamido)-3-alken-2-ols as stereodefined key intermediates has been developed. The utility of this approach was demonstrated by the synthesis of (+)-monomorine I.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    An Efficient Synthesis of 5-(or 6-)Arylbenzoindolizidine and -quinolizidine Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2345-2352 
    Details
    ISSN: 1434-193X
    Keywords: Horner reaction ; Enamides ; Reductions ; Cyclizations ; Alkaloids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new methodology for the synthesis of (hetero)arylated benzoindolizidine and benzoquinolizidine derivatives through sequential reduction of pyrrolidine- and piperidine-based aromatic enamides, and ultimate cyclization, is reported.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Plakinamines C and D and Three Other New Steroidal Alkaloids from the Sponge Corticium sp. (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 697-701 
    Details
    ISSN: 1434-193X
    Keywords: Corticium sp. ; Steroids ; Alkaloids ; Secondary metabolites ; Cytotoxic activity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Five new steroidal alkaloids, plakinamines C (1) and D (2), and the related compounds 3-5 have been isolated from the Vanuatu sponge Corticium sp. Their structures have been elucidated by a detailed spectroscopic analysis, including 2D-HMBC and ROESY correlation experiments. The new compounds show significant in vitro cytotoxicity against human bronchopulmonary non-small-cell lung carcinoma cells (NSCLC-N6) with IC50 values of 〈 3.3-5.7 μg/mL. When tested against T leukemia virus type one (HTLV-I), compounds 1, 4 and 5 were found to exhibit slight anti-HIV activity.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis Mediated by Ring-Closing Metathesis - Applications in the Synthesis of Azasugars and Alkaloids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 959-968 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Alkaloids ; Castanospermine ; Metathesis ; Azasugars ; Manzamine A ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the ring-closing metathesis (RCM) reaction to the construction of a wide variety of nitrogen-containing ring systems is described. The examples include pyrrolizidine, indolizidine, and quinolizidine derivatives related to azasugars. A formal total synthesis of castanospermine (5) is presented. The utilisation of two RCM steps in the synthetic sequence leading to the multicyclic ABCDE nucleus 7 of the complex alkaloid manzamine A (6) is discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    A Stereoselective Synthesis of Nonracemic (+)-Desoxoprosophylline by a Tandem Wittig [2+3]-Cycloaddition Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1407-1414 
    Details
    ISSN: 1434-193X
    Keywords: L-Ascorbic acid ; (+)-Desoxoprosophylline ; Lactones ; Alkaloids ; Domino reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -L-Ascorbic acid serves as chiral starting material for the synthesis of (+)-desoxoprosophylline. The synthetic pathway includes the formation of an O-protected 5-azido-2,3-dideoxysugar which is subjected to a tandem Wittig [2+3]-cycloaddition reaction, leading to the heterocyclic core unit of (+)-prosophylline. Stereoselective hydrogenation and chain elongation yields the desired alkaloid.
    Additional Material: 1 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    New Piperidine Alkaloids from Two Ladybird Beetles of the Genus Calvia (Coccinellidae) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1749-1755 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Piperidines ; Alkaloids ; Coccinellidae ; Calvia14-guttata ; Calviaguttata ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkaloids of two coccinellid beetles, Calvia14-guttata and C.10-guttata have been studied. The major alkaloid of these two species is the new piperidinic cis-lactone 1a, for which the name calvine has been coined. The corresponding trans-lactone 1b (2-epicalvine) is also present as a minor constituent (±10%) in both species. We report here the structure determination and the total synthesis of these compounds. Kept in methanolic solution, these lactones undergo epimerisation as well as opening of the lactone ring leading to a complex mixture of nine main components.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    A sponge/dinoflagellate association in the haplosclerid sponge Haliclona sp.: cellular origin of cytotoxic alkaloids by Percoll density gradient fractionation (1998)
    Springer
    Cell & tissue research 293 (1998), S. 365-373 
    Details
    ISSN: 1432-0878
    Keywords: Key words Sponges ; Alkaloids ; Nematocysts ; Percoll density gradient fractionation ; Secondary metabolites ; Dinoflagellates ; Symbiodinium microadriaticum ; Sponge ; Haliclona sp. (Porifera)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Light-microscopic and electron-microscopic studies of the tropical marine sponge Haliclona sp. (Order: Haplosclerida; Family: Haliclonidae) from Heron Island, Great Barrier Reef, have revealed that this sponge is characterized by the presence of dinoflagellates and by nematocysts. The dinoflagellates are 7–10 μm in size, intracellular, and contain a pyrenoid with a single stalk, whereas the single chloroplast is branched, curved, and lacks grana. Mitochondria are present, and the nucleus is oval and has distinct chromosomal structure. The dinoflagellates are morphologically similar to Symbiodinium microadriaticum, the common intracellular symbiont of corals, although more detailed biochemical and molecular studies are required to provide a precise taxonomic assignment. The major sponge cell types found in Haliclona sp. are spongocytes, choanocytes, and archaeocytes; groups of dinoflagellates are enclosed within large vacuoles in the archaeocytes. The occurrence of dinoflagellates in marine sponges has previously been thought to be restricted to a small group of sponges including the excavating hadromerid sponges; the dinoflagellates in these sponges are usually referred to as symbionts. The role of the dinoflagellates present in Haliclona sp. as a genuine symbiotic partner requires experimental investigation. The sponge grows on coral substrates, from which it may acquire the nematocysts, and shows features, such as mucus production, which are typical of some excavating sponges. The cytotoxic alkaloids, haliclonacyclamines A and B, associated with Haliclona sp. are shown by Percoll density gradient fractionation to be localized within the sponge cells rather than the dinoflagellates. The ability to synthesize bioactive compounds such as the haliclonacyclamines may help Haliclona sp. to preserve its remarkable ecological niche.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410051128
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  • 13
    Electronic Resource
    Electronic Resource
    Modes of Action of Allelochemical Alkaloids: Interaction with Neuroreceptors, DNA, and Other Molecular Targets (1998)
    Springer
    Journal of chemical ecology 24 (1998), S. 1881-1937 
    Details
    ISSN: 1573-1561
    Keywords: Alkaloids ; molecular targets ; neuroreceptors ; DNA intercalation ; DNA polymerase ; reverse transcriptase ; protein biosynthesis ; membrane stability ; nicotine receptor ; muscarinic receptor ; serotonin receptor ; adrenergic receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Several alkaloids are toxic to insects and vertebrates and, in addition, can inhibit the growth of bacteria and plant seedlings. In vitro assays were established to elucidate their modes of action and to understand their allelochemical properties. Basic molecular targets studied, present in all cells, included DNA intercalation, protein biosynthesis, and membrane stability. The degree of DNA intercalation was positively correlated with inhibition of DNA polymerase I, reverse transcriptase, and translation at the molecular level and with toxicity against insects and vertebrates at an organismic level. Inhibition of protein biosynthesis was positively correlated with animal toxicity. Molecular targets studied, present only in animals, included neuroreceptors (alpha1, alpha2, serotonin, muscarinic, and nicotinic acetylcholine receptors) and enzymes related to acetylcholine (acetylcholine esterase and choline acetyltransferase). The degree of binding of alkaloids to adrenergic, serotonin, and muscarinic acetylcholine receptors was positively correlated in G-protein-coupled receptors. Receptor binding and toxicity was correlated in insects. The biochemical properties of alkaloids are discussed. It is postulated that their structures were shaped in a process termed “evolutionary molecular modeling” to interact with a single and, more often, with several molecular targets at the same time. Many alkaloids are compounds with a broad activity spectrum that apparently have evolved as “multipurpose” defense compounds. The evolution of allelochemicals affecting more than one target could be a strategy to counteract adaptations by specialists and to help fight off different groups of enemies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022315802264
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  • 14
    Electronic Resource
    Electronic Resource
    Cyclization of 3-Aminoacrylates - Total Synthesis of Pumiliotoxin C and Related Stereoisomeric Compounds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2641-2646 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Total synthesis/Pumiliotoxin ; PTX-C ; PTX isomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the synthesis of pumiliotoxin C (1a) and related stereoisomeric compounds 1c-1f. Starting from (+)- or (-)-3-methylcyclohexanone (6a,b), the oxo esters 7a and 7b were prepared. Condensation with (+)- or (-)-3-aminohexanol (8a,b) gave the stereoisomeric 3-aminoacrylates 9a, 9b and 9c. The hydroxy group of the amino-acrylates was transformed into bromide using the tosylate method. Cyclization of the bromides led to unsaturated quinoline ring systems. Finally, decarboxylation and catalytic hydrogenation gave the different cis- and trans-fused stereoisomeric alkaloids of the pumiliotoxin C type. The structures were verified by X-ray analysis.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    2-(Het)aryl-Substituted 7-Azabicyclo[2.2.1]heptane Systems (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1997-2001 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Acetylcholine receptor ; Palladium ; C-C coupling ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epibatidine (1) is a recently discovered trace alkaloid found in the skin of a Latin-American poisonous frog. Its remarkably high analgetic activity is accompanied by high toxicity. Therefore, in order to tune its biological activity, a convergent and efficient synthetic pathway was sought to synthesize epibatidine derivatives with different (het)aryl substituents. The hydro(het)arylation of the key intermediate 7-azabicycloheptene (10) represents such an approach. The synthesis of 10 by a Diels-Alder reaction of an N-activated pyrrole (7) with ethynyl p-tolyl sulfone (6) and subsequent steps has been optimized. The crucial last step, the reductive cleavage of the vinyl sulfone 9, has been replaced by a high-yield fluoride-induced degradation of the β-silylated sulfone 12 to give 10. A number of structurally different racemic epibatidine analogs (16b-e) can be prepared by palladium-catalyzed hydro(het)arylation of 10 with iodo(het)arenes 15b-e in good yields.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    An Expeditious Synthesis of the Dendrobatid Indolizidine Alkaloid 167B (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 865-870 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Enaminones ; Indolizidines ; Sulfide contraction ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the racemic title alkaloid 1 has been accomplished in eight steps and 7.2% overall yield from pyrrolidine-2-thione (5) and ethyl hex-2-enoate (6). Key steps include a ring closure that takes advantage of the nucleophilicity of a vinylogous urethane 8, and stereoselective reduction of the C=C double bond of a bicyclic vinylogous amide 12.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Synthesis of 5-epi-Isofagomine via Asymmetric Chelate-Enolate Claisen Rearrangement (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1155-1159 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Alkaloids ; Chelates ; Rearrangements ; Glycosidases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyhydroxylated piperidines are an interesting class of glycosidase inhibitors. Chelate enolate Claisen rearrangement of N-protected chiral amino acid esters gives rise to γ,δ-unsaturated amino acids, which can be converted to this type of alkaloids. The potential glycosidase inhibitor 5-epi-isofagomine (5) was synthesized by this approach in a highly stereoselective fashion.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Stereoselective Total Synthesis of Enantiomerically Pure 1-Trifluoromethyl Tetrahydroisoquinoline Alkaloids (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 435-440 
    Details
    ISSN: 1434-193X
    Keywords: β-Iminosulfoxides ; Quaternary stereocentre ; Pictet-Spengler reaction ; Alkaloids ; Fluorine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure 1-trifluoromethyl-tetrahydroisoquinoline alkaloid analogues, in which C-1 is a quaternary stereogenic centre, have been synthesized by stereoselective intramolecular Pictet-Spengler reaction of the N-arylethyl γ-trifluoro-β-iminosulfoxide (R)-3, and subsequent elaborations of the sulfinyl auxiliary. The absolute stereochemistry of the stereogenic centre was determined by X-ray diffraction on the α-phenylpropionic ester (1R,2′S)-10.
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  • 19
    Electronic Resource
    Electronic Resource
    Effect of acetylsalicylic acid on secondary metabolism ofCatharanthus roseus tumor suspension cultures (1997)
    Springer
    Plant cell reports 16 (1997), S. 287-290 
    Details
    ISSN: 1432-203X
    Keywords: Catharanthus roseus ; Acetylsalicylic acid ; Aspirin ; Alkaloids ; suspension cultures ; tumor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Addition of various concentrations (0.5–20 mM) of acetylsalicylic acid (ASA) to tumor lines ofCatharanthus roseus cultivatedin vitro and requiring corn starch as carbon source, produced remarkable effects on secondary metabolite production. An increase of 505% total alkaloids per culture (cells plus liquid medium), 1587% total phenolics (liquid medium), 612% total furanocoumarins (liquid medium) and 1476% total anthocyanins (liquid medium) was detected. 1 mM ASA in combination with other elicitors, such as homogenates ofAspergillus fumigatus or trans-cinnamic acid, did not further increase the metabolite content substantially. The results suggest that ASA could act as a new biotic elicitor of metabolite production inC. roseus cell suspension culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01088282
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  • 20
    Electronic Resource
    Electronic Resource
    Synthese und Konformation von Hexahydro-isochino[1,2-b][3]benzazepinen (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 447-457 
    Details
    ISSN: 0947-3440
    Keywords: Isoquino[1,2-b][3]benzazepines ; Iso-C-homoberbines ; Conformation analysis ; Bischler-Napieralski reaction ; Methyl ∊-hydroxycarboxylates ; Heterocycles ; Alkaloids ; Drug research ; Medicinal chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Conformation of Hexahydro-isoquino[1.2.-b][3]benzazepinesThe synthesis of the six hexahydro-isoquino[1,2-b][3]benzazepines 13a-f is described; their conformation is investigated by NMR spectroscopic methods, X-ray analysis and dehydrogenation with mercury(II) acetate.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970225
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  • 21
    Electronic Resource
    Electronic Resource
    Enantiospecific Synthesis of 2,5-Disubstituted Piperidine Derivatives: Synthesis of (+)-Pseudoconhydrine (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1267-1272 
    Details
    ISSN: 0947-3440
    Keywords: Alkaloids ; Enantiospecific synthesis ; Chiral building blocks ; 2,5-Disubstituted piperidines ; (+)-Pseudoconhydrine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel methodology for the synthesis of any one of the four stereoisomers of a 2,5-disubstituted piperidine in optically pure form is described, starting from readily available chiral building blocks 10 and 11 (or their antipodes). The utility of this approach is demonstrated in the total synthesis of (+)-pseudoconhydrine hydrochloride, the structure of which was confirmed by X-ray analysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970633
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  • 22
    Electronic Resource
    Electronic Resource
    Dihydrocolchicine 8,12-Endoperoxide: A Novel Starting Material for Convenient Syntheses of the Allocolchicinoids N-Acetylcolchinol O-Methyl Ether and Androbiphenyline (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2275-2279 
    Details
    ISSN: 0947-3440
    Keywords: Semisynthetic colchicine analogues ; Endoperoxide transformations ; Colchicine-allocolchicine rearrangement ; Axial chirality ; Biaryls ; Alkaloids ; Colchicum autumnale ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically pure dihydrocolchicine-8,12-endoperoxide 2 is used as the starting material for the synthesis of some bioactive allocolchicinoids. Depending on the reaction conditions and reagents employed, different modifications of the C ring of colchicine (1) are achieved. Triphenylphosphane deoxygenation of 2 leads to the well known N-acetylcolchinol O-methyl ether (NCME, 6, 40% yield from 1). Treatment of the endoperoxide 2 with CH3OH/CH2Cl2/silica gel provides the plant alkaloid androbiphenyline (11) in a yield of 60% from 1. Triethylamine-catalysed transformation of 2 yields (-)-colchicine-8,12-dione (12) (17% yield), together with a mixture of interconverting tetracyclic hemiketals 8a and 8b. For the formation of the allo colchicinoids 6 and 11 plausible reaction pathways are suggested. In contrast to what is found in the literature, the assignment of the absolute configuration of natural (-)-colchicine (1), and the allo-congeners 6 and 11, should be (M,7S) or (aR,7S) instead of (aS,7S).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971115
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    Electronic Resource
    Biotransformation of Ergot Alkaloids by Haloperoxidase from Streptomyces aureofaciens: Stereoselective Acetoxylation and Propionoxylation (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2379-2383 
    Details
    ISSN: 0947-3440
    Keywords: Alkaloids ; Enzyme catalysis ; Oxidases ; Peroxides ; Acylations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Agroclavine (1) was oxidized, by haloperoxidase from Streptomyces aureofaciens, to 2,3-dihydro-6,8-dimethyl-3β-acetoxy-8-ergolen-2-one (2) in the presence of sodium acetate and bromine ions. Acetate was incorporated into the above product during oxidation. In a propionate buffer, incorporation of propionate into the product was observed, yielding 2,3-dihydro-6,8-dimethyl-3β-propionoxy-8-ergolen-2-one (4). The biotransformation proceeded faster in the propionate buffer, affording also the higher oxidation product (4aS),(10bS)-7-amino-3,4,4a,5,6,10b-hexahydro-2,4-dimethyl-6-oxobenzo[f]quinoline (3).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971129
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  • 24
    Electronic Resource
    Electronic Resource
    Chemistry of Opium Alkaloids, XLIIIPart XLII. M. de Grauw, E. F. Muller, R. H. Woudenberg, L. Maat, Recl. Trav. Chim. Pays-Bas 1996, 115, 58. - A PM3 Computational Approach to the Selectivity in the Diels-Alder Reactions of Thebaine and Analogues with Methyl Propenoate (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 13-19 
    Details
    ISSN: 0947-3440
    Keywords: 6-Demethoxythebaine ; Ethenoisomorphinans ; Ethenomorphinans ; Calculations, semiempirical ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometrically fully-optimized transition structures are calculated for the Diels-Alder adducts of methyl propenoate and the 3-demethoxy derivatives of the dienes thebaine, 6-demethoxythebaine, 5β-methylthebaine, and 5β-methyl-6-demethoxythebaine using the semiempirical PM3 method. The number of calculated forms is limited according to a search of the conformational space of methyl propenoate and of the dienes. The lengths of the incipient bonds in the transition structures vary from 2.0 to 2.4 Å, but the average value of the lengths of these two bonds in the same structure is much more constant: 2.18 ± 0.02 Å. The effects of the methoxycarbonyl group and of the 6-methoxy group on the lengths of the incipient bonds are in agreement with the relative magnitudes of the frontier orbital coefficients. Comparison of the energetic data with experimental results shows that the prediction of the stereo- and regioselectivities from the Gibbs energy of activation differences is good as far as it concerns the main products. The absence of minor products and the formation of the remarkably large amount of 8β-ethoxycarbonyl-6β,14β-ethenomorphinan from 5β-methyl-6-demethoxythebaine does not follow from the calculations.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970105
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  • 25
    Electronic Resource
    Electronic Resource
    Solanum Alkaloids, 139 - Photolysis of N-Chlorospirosolanes (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1589-1592 
    Details
    ISSN: 0947-3440
    Keywords: Photolysis ; N-Chlorospirosolanes, photolysis of ; 23-Chloro- and 23,23-dichlorospirosolanes ; Steroids ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: UV irradiation of N-chlorosoladulcidine (2) in trifluoroacetic acid, followed by separation and hydrolysis of the obtained 3-O-trifluoroacetates affords (23R)-23-chlorosoladulcidine (5) and 23,23-dichlorosoladulcidine (7). Similar treatment of N-chlorotomatidine (9) affords 23,23-dichloro-22-isotomatidine (12).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970741
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  • 26
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    Synthesis of rac-Midpacamide and the spiro-Cyclization of Its Precursor (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1525-1528 
    Details
    ISSN: 0947-3440
    Keywords: Alkaloids ; Biomimetic synthesis ; spiro-Cyclization ; Marine sponges ; Natural products ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkylidene hydantoin 8 was synthesized as an analogue of the marine natural product oroidin (1) by employing a Horner-Wadsworth-Emmons reaction. Treatment of 8 with bromine in acetic acid induced a biomimetic spiro-cyclization forming the ACD ring system of dibromophakellin (2) in one step. rac-Midpacamide (10) was obtained from the same precursor through a chemoselective, ruthenium-catalyzed hydrogenation leaving the brominated pyrrole moiety intact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970731
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  • 27
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    Electronic Resource
    Capillary electrophoresis of natural products (1997)
    Weinheim : Wiley-Blackwell
    Electrophoresis 18 (1997), S. 2438-2452 
    Details
    ISSN: 0173-0835
    Keywords: Natural products ; Capillary electrophoresis ; Micellar electrokinetic capillary chromatography ; Chinese herbal preparations ; Alkaloids ; Toxins ; Illicit drugs ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Capillary electrophoresis (CE) and micellar electrokinetic chromatography were used for the separation of widely different compounds from natural materials including antibiotics, humic substances, flavonoids, isoflavonoids, illicit drugs, coumarins, alkaloids, steroids, Chinese herbal preparations, nicotine, caffeine, amphetamines, toxins such as aflatoxins B1, B2, G1, G2, mycotoxins, heptapeptide aflatoxins and others, ephedrine compounds, mineral elements, and natural compounds in biological samples. A discussion of sample extraction and clean-up and the advantages of using CE is also presented.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150181234
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  • 28
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    Electronic Resource
    The Configuration of (+)-8-Ethylnorlobelol-I; a Correction of the Literature (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2083-2086 
    Details
    ISSN: 0947-3440
    Keywords: Cycloaddition, 1,3-dipolar ; Piperidine ; Alkaloids ; Lobelia ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The piperidine alkaloid (+)-8-ethylnorlobelo-I is assigned the revised 2S,8,S absolute configuration as depicted in 7. LiAl(O-tBu)3H reduction of the ketone rac-5 proceeded with a high stereoselectivity to give, after hydrolysis of the carbamate function, the syn amino alcohol rac-6. Inversion of the C-8 configuration of ent-6 yielded (-)-8-ethylnorlobelol-I ent-7. A short nitrone-alkene-based synthesis of rac-7 has been developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961220
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  • 29
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    Synthesis of New Nepenthone DerivativesMorphine alkaloids, 135. For part 134 see: J. Marton, Z. Szabó, I. Csorvássy, Cs. Simon, S. Hosztafi, S. Makleit, Tetrahedron 1996, 52, 2449-2464. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1653-1656 
    Details
    ISSN: 0947-3440
    Keywords: Alkaloids ; Morphinans ; Dihydronepenthone ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogenation of nepenthone (3a) leads to a mixture of dihydronepenthone (3c) and the secondary alcohol (20S)-4b. The enantiomeric secondary alcohol (20S)-4b is prepared from the 7α-formyl-6,14-ethenomorphinan derivative 3b by reaction with phenylmagnesium bromide to afford a mixture of the diastereoisomeric alcohols 4a. Hydrogenation of 4a leads to (20S)-4b and (20R)-4b, which are separated by fractional crystallization. The conformations of (20S)-4b and (20R)-4b are determined by NOE difference experiments.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961025
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  • 30
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    Natural products and enzymes from plant cell cultures (1995)
    Springer
    Plant cell, tissue and organ culture 43 (1995), S. 97-109 
    Details
    ISSN: 1573-5044
    Keywords: Alkaloids ; enzymes ; natural products ; plant cell cultures ; Rauwolfia serpentina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plants represent an unlimited source of natural products. Many of the recently detected phytochemicals exhibit remarkable bioactivities, ranging from anticancer activity, phosphodiesterase inhibition to cytotoxicity against HIV-infected cells. Cultivated plant cells produce at their unorganized, dedifferentiated stage secondary metabolites, but in very different amounts in so far as new compounds are concerned. In fact, more than 140 novel natural products are presently known from plant cell cultures, which also include new metabolites formed by biotransformation. The biotransformation capacity of suspended cells is described and recent high yielding transformations, like the formation of arbutin by hydroquinone-transformation withRauwolfia cells are discussed. As an example of alkaloid production by cell suspensions, the pattern of monoterpenoid indole alkaloids of the Indian medicinal plantRauwolfia serpentina Benth. is described and the so far 30 identified compounds are divided into eight groups which are biosynthetically closely related. Some of the key biosynthetic reactions leading to theRauwolfia alkaloids are discussed and an overview of the enzymes involved in the formation of the alkaloid ajmaline and proteins catalyzing side reactions of the ajmaline pathway are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00052163
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  • 31
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    New alkaloids from ants: Identification and synthesis of (3R,5S,9R)-3-butyl-5-(1-oxopropyl)indolizidine and (3R,5R,9R)-3-butyl-5-(1-oxopropyl)indolizidine, constituents of the poison gland secretion in Myrmicaria eumenoides (hymenoptera, formicidae)Dedicated to Professor Dr. K. Mori on the occasion of his 60th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 965-977 
    Details
    ISSN: 0947-3440
    Keywords: Ants ; Alkaloids ; Myrmicaria eumenoides ; 3-Butyl-5-(1-oxopropyl)indolizidine, (3R,5S,9R)-,(3R,5R,9R)- ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (3R,5S,9R) and (3R,5R,9R) stereoisomers of 3-butyl-5-(1-oxopropyl)indolizidine (9) were identified as major constituents of the poison gland secretion of the African ant, Myrmicaria eumenoides. Racemates of the four diastereomers of 9 were synthesized via the corresponding ethyl 5-(5-butylpyrrolidin-2-yl)pentanoates (6). Enantiomerically pure samples of the (3R)-stereoisomers of 9 were obtained by starting from (2R)-2,3-O-isopropylideneglyceric aldehyde (21) and 6-methylpyridine-2-carboxaldehyde (20). In addition, the enantiomeric separation by chiral gas chromatography and unambiguous structure assignment of the target compounds are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199506138
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  • 32
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    Synthesis of vinca alkaloids and related compounds, 73.Part 72: L. Szabó, Gy. Kalaus, Cs. Szántay, ACH-Models in Gem. 1994, 131, 541. Synthesis and ring transformations of deethylaspidospermane derivatives. Synthesis of (±)-20-deethyl-3-oxotabersonine (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1245-1251 
    Details
    ISSN: 0947-3440
    Keywords: Deethylvincadifformine ; Deethyltabersonine ; Deethyl-3-oxotabersonine ; Deethylapovincamine ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the key compound 14 with methyl 4-formyl-butanoate (9) or with 5-benzoyloxypentanal (13) gave the D-seco-aspidospermane derivatives 17 and 18, respectively. Compound 17 was indirectly and 18 was directly converted to (±)-20-deethylvincadifformine (7) and (±)-20-deethyl-20-epivincadifformine (8). Epimerization occurred in both cases. The thioxo compound 23 was used for the synthesis of (±)-20-deethyltabersonine (28) and (±)-20-deethyl-3-oxotabersonine (27). Oxidative ring transformation of the (±)-20-deethylvincadifformine (7) gave (±)-16-deethylapovincamine (29).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507165
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  • 33
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    A new synthetic route to the azocino[4,3-b]indole core structure (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1561-1562 
    Details
    ISSN: 0947-3440
    Keywords: Carbazoles ; Azocino[4,3-b]indole ; Alkaloids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 2 with 2-methoxyethylamine in the presence of ZnCl2 afforded imine 3, which was reduced with NaBH4 to amine 4 without isolation. After deprotection of the carbonyl function by treatment with benzeneseleninic anhydride, ketone 5 was converted to compound 6 with 2-oxobutyric acid and dicyclohexylcarbodiimide. The isodasycarpidone derivative 7, formed by aldol reaction of 6, represents a tetracyclic substructure of strychnos-type alkaloids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199508214
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  • 34
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    Synthesis and stereostructure of some spiro[morphinan-6,2′(3′H)-[1,3,4]oxa(thia)diazolines] (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1393-1395 
    Details
    ISSN: 0947-3440
    Keywords: Alkaloids ; Morphinans ; Oxadiazolines ; Thiadiazolines ; (Thio)Semicarbazones, acetylation of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of dihydrocodeinone (thio)semicarbazones 1a-d with Ac2O/ZnCl2 afforded (6S)-spiro[morphinan-6,2′(3′H)-[1,3,4]oxadiazolines] (2a, b) and (6R)-spiro[morphinan-6,2′-(3′H)-[1,3,4]thiadiazolines] (3a, b), respectively. The structure of the products including the configuration of the spiro carbons was determined by 1H- and 13C-NMR measurements.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507188
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  • 35
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    Oxidative Condensation of Quaternary Phenolic BasesBased on lectures delivered at the International Symposium on Organic Chemistry held by the Societé Chimique de Belgique in Brussels, June 15th, 1962, the XIXth IUPAC Congress in London, July 11th, 1963, a Gordon Research Conference in New Hampton, August 2nd, 1963, and at several American universities and research institutes.Dedicated to Prof Dr. H. Brockmann on the occasion of his 60th birthday (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 192-200 
    Details
    ISSN: 0570-0833
    Keywords: Phenolic bases ; Alkaloids ; Condensation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Provided they contain quaternary nitrogen, simple phenolic bases can undergo oxidative condensation under conditions similar to those of biogenesis to form alkaloids of the isoquinoline series with good yields. By means of such oxidative condensations, more than sixty alkaloids of various structural types have become more easily obtainable. Of the numerous possible condensations of the intermediate mesomeric radicals only those which lead to naturally occurring alkaloids give good yields and few by-products. The results suggest that oxidative condensations of quaternary bases are also involved in the biosynthesis of alkaloids in the plant cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196401921
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    The Biosynthesis of Alkaloids IIPart I of this review appeared in Angew. Chem. Internet. Edit. 2, 341 (1963). (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 441-458 
    Details
    ISSN: 0570-0833
    Keywords: Biosynthesis ; Alkaloids ; 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.196304411
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  • 37
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    The Biogenesis of Ergot AlkaloidsDedicated to Professor Hans von Euler on the occasion of his 90th birthday (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 243-247 
    Details
    ISSN: 0570-0833
    Keywords: Ergot alkaloids ; Alkaloids ; Biosynthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article the biogenesis of the ergoline ring in lysergic acid derivatives and the clavines is discussed. T·yptophan and mevalonic acid are the precursors. The N-methyl group is supplied by formate or methionine. Concepts and results dealing with the manner in which the compounds are formed are discussed. Finally, the known biogenetic relationships among the ergot alkaloids are discussed in connection with their biogenesis.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196302431
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  • 38
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    The Biosynthesis of Alkaloids IPart II of this review will appear in a subsequent issue of this journal.Dedicated to Professor Dr. Adolf Butenandt on the occasion of his 60th birthday (1963)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 341-357 
    Details
    ISSN: 0570-0833
    Keywords: Biosynthesis ; Alkaloids ; 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.196303411
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