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  • General Chemistry  (7,644)
  • Cell & Developmental Biology  (2,961)
  • 1995-1999  (9,359)
  • 1945-1949  (1,246)
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  • 101
    ISSN: 1434-193X
    Keywords: Natural products ; Trilactide ; Lichen ; Macrocycles ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A structurally novel 24-membered C3-symmetrical macrolactone 2a, composed of three units of 3,7-dihydroxy-2,4-dimethyloctanoic acid, was isolated from the Indonesian lichen Usnea dasypoga Rohl.
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  • 102
    ISSN: 1434-193X
    Keywords: Sum of free valence numbers ; Benzo[g,h,i]perylenes ; [5]Helicenes ; Photocyclization ; HMO calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the new pentahelicenes 5, 11, 17, 21, and 28 with various substituents are described. In the case of 2,13-dicyano-[5]helicene (11) optical resolution was achieved by HPLC using a column packed with γ-cyclodextrin. However, the enantiomers racemized within a few hours. On the other hand, the enantiomers of 28 turned out to be stable after separation on triacetylcellulose using MPLC. The crystal structures of 11, 17, and 21 were solved and indicated the typical distortions which are expected for helicenes. The model of the sum of free valence numbers was applied in order to rationalize the reactivity pattern of the photochemical phenanthrene cyclization.
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  • 103
    ISSN: 1434-193X
    Keywords: Enzymes ; Kinetic resolution ; Sulfoxides ; Chiral resolution ; Hydrolyses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selected racemic trans-2-alkoxycarbonyl-3,6-dihydro-2H-thiopyran S-oxides 2a-h have been subjected to enzyme-assisted hydrolysis under conditions of kinetic resolution to give the corresponding acids and recovered esters with moderate to high enantiomeric purities (up to 95%). The enantioselectivity of the reaction was found to be strongly dependent on the structures of the substrates used.
    Additional Material: 3 Ill.
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  • 104
    ISSN: 1434-193X
    Keywords: Metallation ; Elimination reactions ; Cyclization ; Cyclodehydrogenation ; Polycyclic hydrocarbons ; Propellanes ; Strained olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the tribenzo[3.3.3]propellane ketone 1 (triptindan-9-one) with benzyllithium/TMEDA affords an efficient one-pot peri annulation of a dihydronaphthalene across two wings of the propellane framework. The key step of this surprising tandem reaction was determined to be a nucleophilic cyclization of (Z)-9-benzylidenetriptindane (4) with concomitant hydride elimination. The formation of the novel centrotetracyclo[5.5.5.6] framework bearing a distorted (E)-stilbene unit was confirmed by single-crystal X-ray structure analysis.
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  • 105
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Diacylglycerolphosphates ; Glycophosphoinositol anchors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The exploration of the molecular and structural basis for the sorting of GPI-anchored proteins is based on labeled partial structures of GPI′s which can be incorporated into the GPI anchor biosynthesis and cellular transport systems. To this end, from mannosyl donor 6 and the D-glucosaminyl-(1→6)-D-myo-inositol derivative 7 as acceptor, the pseudotrisaccharide 8 was prepared. Compound 8 was transformed into the GPI partial structures 5a,b which contain the pseudotrisaccharide ligated to two different phosphatidyl residues. Compounds 5a,b have Boc protection at the 2-amino group of the glucosamine residue (2b-position) and a free amino group at the 6b-position. The 6b-amino group was used for the ligation of the 3-(7-nitrobenzofurazan-4-yl)-aminopropanoyl group as a fluorescent label, the 5-azido-2-nitrobenzoyl and 4-azidophenylaminothiocarbonyl groups as photolabels, and the 4-azido-2-hydroxybenzoyl group as a radiolabel after the introduction of radioactive iodine by an electrophilic aromatic substitution. Thus, after acid-catalyzed removal of the protective groups, the unprotected target molecules 1-4 were obtained.
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  • 106
    ISSN: 1434-193X
    Keywords: Cyanines ; Dyes ; Chirality ; Hexahydroquinidine ; Hexahydroquinine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the 1′,2′,3′,4′,10,11-hexahydroquinines 3a-c (Schemes 1 and 3) and 1′,2′,3′,4′,10,11-hexahydroquinidine 6c (Scheme 2), we have synthesized the new chiral, symmetrical pentamethinium streptocyanine dyes 11a-c (Scheme 4) and 12c (Scheme 5). These products have a total of ten stereogenic centers in the two heterocyclic end groups, the absolute configurations of eight of which are known from the natural starting material, i.e. (-)-quinine 1a, (-)-10,11-dihydroquinine 2a, (+)-quinidine 4a, and (+)-10,11-dihydroquinidine 5a. The latter four compounds were hydrogenated at 70 bar and 70 °C in the presence of Raney nickel as catalyst to give the hexahydroquinine 3c and the hexahydroquinidine 6c, respectively. The hexahydroquinine 3c was separated into the corresponding diastereomers 3a and 3b by means of fractional crystallization of its salts with monochiral mandelic acid (Scheme 3).
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  • 107
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2929-2936 
    ISSN: 1434-193X
    Keywords: Local conformer populations ; syn-Pentane interactions ; Conformational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent patterns on 1,3,5…-polyoxygenated-2,4,6…-polymethylated alkane chains, which preferentially adopt a fully extended backbone conformation, have been identified. This is demonstrated by analysis of the vicinal H,H-coupling constants along the backbones of compounds 19, 23, and 24.
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  • 108
    ISSN: 1434-193X
    Keywords: Nonlinear effects ; Asymmetric catalysis ; Ruthenium complexes ; Atropisomeric phosphanes ; Hydrogenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strong positive nonlinear effect (asymmetric amplification) was found to take place during asymmetric hydrogenations using chiral atropisomeric diphosphane-ruthenium catalysts. As an example, at atmospheric pressure the use of 50% ee BINAP to prepare [(binap)Ru(Br)2] give rise to a hydrogenated product with 91% ee. The influence of temperature and hydrogen pressure on this effect are presented. These nonlinear effects can be explained on the basis of a hydrogenation mechanism in which diastereomeric dimers as pre-catalytic species are present.
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  • 109
    ISSN: 1434-193X
    Keywords: Sonogashira-Linstrumelle cross-coupling ; Stille cross-coupling ; Protected enynals ; Transacetalisation ; Pent-2-en-4-yn-1-al ; Deca-2,8-diene-4,6-diyne-1,10-dial ; Dienediynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (3E)-5,5-Diethoxypent-3-en-1-yne was stereospecifically prepared by Sonogashira-Linstrumelle cross-coupling between (E)-3-iodoacrolein diethylacetal and (trimethylsilyl)acetylene. The (Z) isomer was obtained by Stille cross-coupling between the corresponding (Z)-vinyltin and 1-bromo-2-(trimethylsilyl)acetylene. In the case of the (E) isomer, transacetalisation occurred without isomerization affording a large variety of (E)-enynals protected as acetals. It has also been shown to be possible to obtain the corresponding (E,E)-dienediyne through sp-sp homocoupling under appropriate experimental conditions.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2965-2967 
    ISSN: 1434-193X
    Keywords: Amino alcohol ; Asymmetric synthesis ; Cell signaling ; Dihydroxylations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cytoxazone [(4R,5R)-(-)-5-hydroxymethyl-4-(4-methoxyphenyl)-2-oxazolidinone, 1], a new immunosuppressant, was synthesized by starting from p-methoxycinnamyl alcohol (2) employing the Sharpless asymmetric dihydroxylation as the key reaction in 26% overall yield (7 steps).
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  • 111
    ISSN: 1434-193X
    Keywords: Vinyl triflones ; Vinyl nonaflones ; Knoevenagel reaction ; Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ethyl 3-aryl-2-(perfluoroalkanesulfonyl)propenoates were prepared by the Knoevenagel reaction from various aldehydes and ethyl (trifluoromethanesulfonyl)acetate or ethyl (nonafluorobutanesulfonyl)acetate. These deactivated olefins were used in Diels-Alder cycloaddition reactions with cyclopentadiene. The reactions occurred at room temperature to give [4+2] cycloadducts as racemates. The endo stereochemistry of the carboxylic ester and aryl groups was unambiguously assigned by NOE experiments and X-ray analysis.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99164_s.pdf or from the author.
    Additional Material: 2 Ill.
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  • 112
    ISSN: 1434-193X
    Keywords: Arenediazonium salts ; Potassium organotrifluoroborates ; Cross-coupling ; Palladium ; Biaryls ; Styrenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of various potassium organotrifluoroborates bearing either aryl, alkenyl, or alkynyl substituents is described. These stable salts are shown to be very efficient partners in palladium-catalysed cross-coupling reactions with arenediazonium salts, affording biaryl and styrene derivatives in high yields.
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  • 113
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Heterocycles ; Electrostatic interactions ; Glycosylation ; Glycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pairs of novel stereoisomeric, cyclic glycosyl donors exhibit different behaviors in glycosylation processes. In the pair of α-gluco (1) and β-manno (2), the former exhibits reversability with its glycoside product whereas the latter does not. In the α-gluco (3) and β-manno (4) set, the former undergoes glycosyl transfer via an isolable intermediate whereas the latter does not. The differing anomeric effects exerted in the ground states are proposed as the force which explains the differences in behavior.
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  • 114
    ISSN: 1434-193X
    Keywords: Electrochemistry ; Carbon dioxide fixation ; Cyclizations ; Nickel ; Dihydrobenzofuran ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical reduction of a series of 2-haloaryl ethers containing allyl and propargyl groups under CO2 allows the synthesis of benzofuranacetic acid derivatives. This novel intramolecular cyclization-carboxylation reaction is carried out in single-compartment cells and is catalyzed by [Ni(cyclam)Br2].
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  • 115
    ISSN: 1434-193X
    Keywords: Hydroformylation ; Amination ; Rhodium ; Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from diallyl ethers, -silanes, or -amines various di- or triamines with potential biological activity are obtainable in one step by RhI-catalysed hydroaminomethylation of the alkene moieties in the presence of synthesis gas.
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  • 116
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1921-1924 
    ISSN: 1434-193X
    Keywords: Cyclizations ; Electrocyclic reactions ; Solvent effects ; Salt effect ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constants of the electrocyclic ring closure of (1Z,3Z,5E)-1,2,6-triphenylhexa-1,3,5-triene (1) and of the ring opening of dimethyl 3,4-dimethyl-1,2-diphenylcyclobutene-cis-3,4-dicarboxylate (3) were determined in 15 and 16 solvents, respectively. The ring closure of 1 shows, in spite of theoretical predictions, neither solvent nor salt effects. For the ring opening of 3, small solvent and salt effects were found, suggesting the possibility of observing small acceleration due to specific solute-solvent or salt interactions.
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  • 117
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1925-1933 
    ISSN: 1434-193X
    Keywords: γ-Lycorane ; Radicals ; Cyclizations ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-γ-Lycorane has been synthesized in ten steps from piperonylic alcohol. Two radical reactions were used successively to build the D and B rings. A formal synthesis of (+)-γ-lycorane was achieved via an optically active unsaturated aldehyde intermediate.
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  • 118
    ISSN: 1434-193X
    Keywords: Diazo compounds ; Carbenes ; Carbenoids ; Silicon ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolysis of (ethoxy)silyl-, (propyloxy)silyl-, and (isopro-pyloxy)silyl-substituted diazoacetates 1a-c leads to tetrahydro-1,2-oxasiloles 2a-c by intramolecular C-H insertion of a carbene intermediate. Photochemical or catalytic decomposition of (allyloxysilyl)diazoacetates 3a-e results in intramolecular cyclopropanation which provides 3-oxa-2-silabicyclo[3.1.0]hexane systems 5a-e. In contrast, the thermal reaction of 3b-d gives rise to 2,5-dihydro-1,2-oxasiloles 4b-d, which are likely to be formed on a pyrazoline rather than a carbene route. For (3-butenyloxysilyl)diazoacetate 3f, all modes of decomposition generate the 3-oxa-2-silabicyclo[4.1.0]heptane system 7. Fluoride-induced cleavage of the bicyclic systems 5b-d provides trans-2-hydroxyalkyl-1-cyclopropanecarboxylates 9 diastereospecifically.
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  • 119
    ISSN: 1434-193X
    Keywords: Hydroxamic acids ; Acylnitroso ; Oxidation ; Ene reactions ; Allylic amidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A one-pot allylic amidation procedure, which employs the ene reaction of acylnitroso compounds 2 with electron-rich olefins 3a,b, is presented; the acylnitroso enophile is generated in situ by oxidation of hydroxamic acids 1 with iodosobenzene diacetate. The resulting N-allylhydroxamic acids 4 (ene products) are quantitatively acetylated for ease of handling; as an example, the reduction of the acetylated derivative 5b by samarium diiodide was carried out to afford the N-allyl amide 6b in quantitative yields.
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  • 120
    ISSN: 1434-193X
    Keywords: McMurry reaction ; C-C coupling ; Low-valent titanium ; Reductive “trimerization” ; Semiempirical calculations ; Overcrowding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive “trimerization” was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1° and 58.0° between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated Cs transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (-sc,-sc) conformation in solution.
    Additional Material: 3 Ill.
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  • 121
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1991-2005 
    ISSN: 1434-193X
    Keywords: Molecular recognition ; Cavitands ; Encapsulation ; Self-assembly ; Hydrogen bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The review describes the synthesis of deep open-ended cavities, based on calixarene and resorcinarene modules, and the host-guest properties that arise from their unique structures.
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  • 122
    ISSN: 1434-193X
    Keywords: Hydroxy ketones ; Lactones ; Fruticolide ; Fruticolone ; α-Epoxy ketones ; β-Diketones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some neoclerodane (2-4) and labdane (5 and 6) diterpene ketones having a β- or γ-hydroxy function, an α-epoxy group, or an α-olefinic double bond have been irradiated at λ = 313 nm in dry solvents (benzene or methanol). Fruticolone (2) yielded the naturally occurring 5,6-seco-neoclerodan-6,1α-olide derivative fruticolide (1), while hispanolone (5) gave the δ-lactone 8, both transformations involving a Norrish type I photoreaction. The α,β-unsaturated ketone derivative 4 was transformed into 7 by a stereoselective intramolecular [2+2] cycloaddition reaction involving its furanic 13(16)-double bond. Finally, the α-epoxy ketone 6 was rearranged to the 10(9→8)abeo-labda-7,9-dione derivative 10. Apart from the interest in these reactions for synthetic purposes, the photochemical transformation of fruticolone (2) into fruticolide (1) suggests that the latter might originate from the former as an artefact during the extraction and isolation procedure, rather than from any biogenetic pathway.
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  • 123
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2695-2703 
    ISSN: 1434-193X
    Keywords: Annulation ; Multi-state switch ; Photochromism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This Microreview highlights the chemistry of the metacyclophanediene-dihydropyrene system, which is a reversible photochromic π switch. Although most studies have been carried out on systems with a single dihydropyrene, recently multiple dihydropyrenes have been fused to conjugated spacers to give multi-state switches.
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  • 124
    ISSN: 1434-193X
    Keywords: Aminations ; Azides ; Cyclizations ; Nitrogen heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azidoformates derived from chiral enol ethers, when irradiated, give 3,6-dioxazocan-2-one derivatives 7 by a highly diastereoselective intramolecular cycloaddition. The hydrolysis of 7 gives a single derivative of 2-aminocyclohexanone.
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  • 125
    ISSN: 1434-193X
    Keywords: Sucrose ; Acetalation ; Etherification ; Carbohydrate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of unprotected sucrose with tert-butyl chloromethyl ketone in dimethylformamide was investigated as a model for the study of the relative reactivity of the various hydroxy groups of sucrose. Besides the monoethers arising from the substitution of the chlorine atom by 2-OH and 1′-OH of sucrose, the major product is a tert-butyl hydroxymethyl 5-membered ring acetal involving 2-OH and 3-OH. The formation of this product illustrates the preeminent reactivity of 2-OH towards the carbonyl group of the α-chloromethyl ketone, leading to an intermediate hemiacetalic anion, which can enter by intramolecular acetal formation through an intermediate epoxide.
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  • 126
    ISSN: 1434-193X
    Keywords: Antibiotics ; Thiangazoles ; Polythiazolines ; Oxazoles ; Structure-activity relationships ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The partial synthesis of 54 derivatives of thiangazole A (1a), a new polythiazoline antibiotic from Polyangium spec. (myxobacteria), is described. Derivatives with chemical modification of the carboxamide group in the oxazole region were prepared either by N-alkylation to amides 5-14 or by methanolysis to ester 15, and its transformation products 16, 19, 20. Oxidation of the C-5 methyl group of 1a with molecular oxygen led to the hydroxymethyl derivative 21, and two by-products lacking the C-5 methyl group (22), or the entire oxazole ring (23). Key intermediate for analogues with modifications in the styryl region is the aldehyde 27, obtained by direct cleavage of the C-21/C-22 double bond. 27 was transformed into the oximes 37-42 and by Wittig reaction to (21Z)-thiangazole (43) and analogues 44-46 with proton and alkyl residues replacing phenyl. 21,22-Didehydrothiangazole (50) was synthesized in a multi-step reaction from 27 via the 20-alkinyl intermediate 49. The insecticidal activities and inhibition of the respiratory chain (complex I) by the thiangazole analogues were determined and compared with the natural product.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99007_s.pdf or from the author.
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  • 127
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Enzyme catalysis ; Epoxide hydrolase ; Transketolase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Deoxy-D-fructose 6-phosphate is synthesised from nonnatural sources in four steps, including two enzymatic reactions. (3S)-1,1-Diethoxy-3,4-epoxybutane is first obtained by epoxide hydrolase-catalysed resolution. Opening of this epoxide by inorganic phosphate leads to 2-deoxy-D-erythrose 4-phosphate. In the last step, transketolase transfers a hydroxyacetyl group from L-erythrulose onto this aldehyde, controlling the second asymmetric center.
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  • 128
    ISSN: 1434-193X
    Keywords: Amino acids ; Enzyme catalysis ; Glutamate ; Oxoglutarate ; Aminotransferase ; Aminotransferase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation of dimethyl 2,2-dimethoxyglutarate followed by enzymatic resolution afforded (4S)- and (4R)-4-methyl-2-oxoglutaric acid in an enantiomerically pure form. The activity of glutamic oxalacetic transaminase towards these compounds has been measured. Their enzymatic transamination provides an efficient synthesis of (4S)- and (4R)-4-methyl-L-glutamic acids which are very useful for characterisation of glutamate receptors in the central nervous system.
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  • 129
    ISSN: 1434-193X
    Keywords: Enyne pyrolysis ; 13C,D labelling ; Alkenylidene carbenes ; 1,2-Styryl migration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal conversion of [4-13C,4-D]- (1) and [4-13C]-1-phenyl-1-buten-3-yne (7) has been studied in a quartz tubular reactor at 650 °C (1, in the presence of N2 and N2/toluene, respectively) and at 600 and 620 °C (mixture of 1 and 7, in N2 only) at a reaction time of approximately 0.3 s. The liquid pyrolyzates were analyzed spectroscopically. By means of a special calculation method reported recently, the naphthalene isotopomers formed by reaction pathways other than those proceeding via cinnamylidene carbenes were arithmetically eliminated and the reaction events proceeding via carbene intermediates were mechanistically analyzed. The result of this analysis undoubtedly suggests a complex reaction in which the rates of the partial reactions may be placed in the following order: 1,2-D(H) 〉〉 1,2-styryl 〉 1,6-C,H.
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  • 130
    ISSN: 1434-193X
    Keywords: Natural products ; Diterpenes ; Ingenol ; Antitumor agents ; Isosters ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic protocols for the manipulation of the polyhydroxylated southern region of ingenol (1a) were developed, and a series of isosteres of the anticancer compound ingenol 3,20-dibenzoate (1b) was prepared. The biological evaluation of these compounds showed that cytotoxicity was relatively tolerant to changes at C-20, while PKC activation was markedly affected by these modifications. These data suggest that chemical manipulation can effectively dissect cytotoxicity and tumour-promoting activity (or potential) of ingenoids, affording more optimal candidates for development, like 20-deoxy-20-fluoroingenol 3,20-dibenzoate (5b). In mild acidic medium, an unexpected vinylogous retro-pinacol rearrangement of ingenol to a tigliane derivative was observed.
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  • 131
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Lutzomyia longipalpis ; Pheromones ; Sandfly ; Terpenoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both germacrene-B (2) and 9-methylgermacrene-B [(±)-1] were synthesized by employing cyclization reactions [8 → 9 and (±)-20 → (±)-21] as the key steps. The latter [(±)-1] was shown to be the racemate of the male-produced sex pheromone of the sandfly Lutzomyia longipalpis from Lapinha, Brazil.
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  • 132
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Lipases ; Microdiprion pallipes ; Pheromones ; Pine sawfly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1S,2S,6S,10R)- and (1S,2R,6R,10R)-1,2,6,10-tetramethyldodecyl propanoate (1 and 2), the components of the pheromone of Microdiprion pallipes, were synthesized from two chiral and nonracemic building blocks, (R)-3-tert-butoxycarbonyl-2-methylpropanoic acid (D) and (2R,6S)-7-acetoxy-2,6-dimethyl-1-heptanol (G), by employing lipase-catalyzed kinetic resolution in a later step.
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  • 133
    ISSN: 1434-193X
    Keywords: Ecology ; Lactones ; Mass Spectrometry ; Orobanchol ; Natural Products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of orobanchol, a new seed germination stimulant for clover broomrape (Orobanche minor), was proposed as 5a (tentative absolute configuration) on the basis of GC-MS comparison of the natural product with several synthetic compounds [(±)-4a-(±)-4h, (±)-5a and (±)-5b]. All of the synthetic compounds showed significant seed germination activities for Orobanche minor and witchweed (Striga asiatica).
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  • 134
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    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2231-2234 
    ISSN: 1434-193X
    Keywords: Palladium ; Allyl complexes ; Phenolic nucleophiles ; Chromene ; C-C couplings ; Flavonoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of 2-phenyl-2H-chromene (3-flavene) and cinnamaldehyde aryloxy-hemiacetal, involving nucleophilic substitution by phenols of the π-allyl palladium complex formed from the acylal of cinnamaldehyde in the presence of catalytic amounts of palladium(0) (10 mol-%), are presented. Alternatively, the corresponding alcohol acetates furnish 1,3-diarylpropenes and cinnamyl aryl ethers. Our results demonstrate the potent C-nucleophilicity of phloroglucinol in Tsuji-Trost reactions in flavonoid synthesis, and again illustrate the already well established O-nucleophilicity of phenols.
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  • 135
    ISSN: 1434-193X
    Keywords: 14,20-Bis-epi Inhoffen-Lythgoe diol ; Hajos-Wiechert ketone, enantiomeric purity ; Acyclic diastereoselective alkylation ; Alkylations ; Hydroborations ; Epimerisation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 14,20-Bis-epi-1α,25-dihydroxy-19-norvitamin D3 and side chain analogues thereof have been synthesised via the 14,20-bis-epi-Inhoffen-Lythgoe diol 9. The synthesis of this precursor was performed via degradation of vitamin D2 and by total synthesis starting from Hajos-Wiechert ketone 24.
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  • 136
    ISSN: 1434-193X
    Keywords: Hexameric structure ; Hydrogen bonds ; Hydroxyresorc[4]arenes ; Self-assembly ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report herein the observation of a hexameric structure of a hydroxyresorc[4]arene in the solid state, enclosing a large interior space. This artificial molecular container is stabilized only by hydrogen bonds. The tendency to form aggregates in solution is demonstrated mainly by means of ESI-MS methods.
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  • 137
    ISSN: 1434-193X
    Keywords: Calixarenes ; Monofunctionalization ; p-Epoxypropylcalix[4]arene ; p-(2-Oxoethyl)calix[4]arene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four new tri-tert-butylcalix[4]arenes bearing an epoxy or a carbaldehyde function at the upper rim have been prepared by a multi-step synthetic pathway involving initial selective allylation of tris-(O-benzoyl)-tri-tert-butylcalix[4]arene, followed by either m-CPBA oxidation or ozonolysis of the allyl group. The benzoylated epoxycalixarene was obtained as single crystals, analysis of which confirmed the formation of the epoxide group and the partial-cone conformation of the macrocyclic structure.
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  • 138
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A sulfahydantoin (3-oxo-1,2,5-thiadiazolidine 1,1-dioxides) motif is used as a new type of peptidic constraint to lock two consecutive amide nitrogens by a sulfonyl bridge. The 5-membered heterocyclic motif was prepared starting from proteogenic and synthetic amino acids and chlorosulfonyl isocyanate. Constrained dipeptides were obtained under alkaline conditions (methoxide or tert-butoxide) by cyclization of symmetric and dissymmetric sulfamides. The absolute configuration of the chiral centers for the derivative L-Phe-D-Ala, a congener of the series, was established by X-ray diffraction crystallographic analysis. In addition, the chemo-, regio-, and stereoselectivities of the reactions were studied. In the acylated derivatives, the sulfahydantoin constraint induces a unique backbone conformation with coplanarity of two consecutive peptide bonds.
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  • 139
    ISSN: 1434-193X
    Keywords: Organocerium reagents ; Phosphane oxides ; Phosphonates ; Electrophiles ; Synthetic methods ; Electrophilic Additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of organocerium reagents 2a-g to phosphinoyl chloride 1a or chlorophosphates 1b leads to the synthesis of phosphane oxides 3aa-ag and phosphonates 3bb, be in good to high yield. The reaction can be extended to cerium enolates 4 (of ketones) and 6 (of nitriles) except when a benzyl group bound to the carbonyl moiety should be metallated. The latter reaction is the first reported synthesis of β-oxophosphane oxides by a simple reaction between enolates and a phosphorus(V) halide.
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  • 140
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    Liebigs Annalen 1999 (1999), S. 2315-2321 
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Transfer hydrogenations ; Ruthenium ; Coordination chemistry ; Nitrogen heterocycles ; Synthetic methods ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral 1,2,3,4-tetrahydroisoquinoline intermediates in the Rice and Beyerman routes to morphine, (+)-(R)-1-(3-hydroxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (6) and (+)-(R)-1-(3,5-dibenzyloxy-4-methoxybenzyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline (5), were prepared in high ee by ruthenium-catalyzed asymmetric transfer hydrogenation of the corresponding imine precursors (Noyori method). The yield of the key raw material in the Beyerman route, 3,5-dibenzyloxy-4-methoxyphenylacetic acid (1), starting from gallic acid methyl ester (7) was improved by a factor of 5 over previously described syntheses. Key steps in the new procedure are the selective formation of methyl 3,5-dihydroxy-4-methoxybenzoate (9) via the 3,5-diacetate and an improved benzylation of the hydroxyl groups in 9.
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  • 141
    ISSN: 1434-193X
    Keywords: Phthalocyanines ; Conjugation ; UV/Vis spectroscopy ; Nonlinear optics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following our studies on styryl phthalocyanines with extended conjugation, we report here the synthesis and characterization of new push-pull unsymmetrically substituted styryl phthalocyanines 2-6. They have been prepared for studying the influence of the position and electronic character of the substituents and the role of the central metal atom on their optical properties.
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  • 142
    ISSN: 1434-193X
    Keywords: Trypanosoma Brucei ; Nucleosides ; Oligonucleotides ; Glycosylation ; Modified nucleobase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the recently discovered modified DNA base 5-(β-D-glucopyranosyloxymethyl)-2′-deoxyuridine (β-dJ, 1) is described. TMSOTf mediated β-glucosylation of 5-hydroxymethyl-2′-deoxyuridine (5-HMdU) derivative 10 (obtained in 20% from 2′-deoxyuridine) with trichloroacetimidate 12 gave dimer 13 in 47% yield. On the other hand, condensation of 12with N3-POM-protected derivative 20, readily available from thymidine in 48%, afforded the fully protected nucleoside 22 in 96% yield. The latter compound was converted into phosphoramidite 3 which was applied in the automated solid phase synthesis of several biological interesting β-dJ containing DNA fragments.
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  • 143
    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.
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  • 144
    ISSN: 1434-193X
    Keywords: Prooligonucleotides ; Solid-phase synthesis ; Phosphoramidite chemistry ; H-Phosphonate chemistry ; Nucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of mixed SATE-phosphotriester and phosphodiester prooligonucleotides using both phosphoramidite and H-phosphonate chemistries is described. The key step is the selective oxidation of phosphite triester and H-phosphonate linkages to yield thiono- or oxo-triester SATE and thiono- or oxo-diester linkages. This approach allows the synthesis of any desired mixed prooligos bearing either tBu- or Me-SATE enzymolabile protecting groups.
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  • 145
    ISSN: 1434-193X
    Keywords: Aliphatic sulfine ; Organolithium, thiophilic addition of ; Carbanions ; Protonation ; Stereoselectivity ; Sulfur ; Lithium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Protonation of α-sulfinyl carbanions 3, resulting from the selective thiophilic addition of organolithium compounds to aliphatic sulfines 2, provided dithioacetal oxides 4 (63-94% yield). The diastereomeric ratio ranged from 52:48 up to 100:0 with sterically hindered substituents. Thus, (1S*,SS*)-2,2-dimethyl-1-methylsulfanyl-1-methylsulfinylpropane (4ca) was obtained as a single isomer. The origin of the stereoselectivity is rationalized in terms of a thermodynamic equilibrium between the two diastereomers of α-sulfinyl carbanions 3, at which protonation occurs under kinetic control and with retention of configuration with the assistance of the lithium cation. Moreover, the stereochemistry could be totally reversed by converting the lithiated anion intermediate into an aluminium “ate” complex. Thus, (1R*,SS*)-2,2-dimethyl-1-methylsulfanyl-1-methylsulfinylpropane (4ca) was selectively obtained by this method (dr = 0:100).
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  • 146
    ISSN: 1434-193X
    Keywords: Ambruticin ; Asymmetric synthesis ; Pyranose ; Carbohydrates ; C-Glycosylation ; Alkylations ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new methodology has been applied to synthesize an isomer of the west part of (+)-ambruticin based on an efficient asymmetric de novo access to the A unit and sequential stereospecific reactions catalyzed by Pd0 for the construction of the B unit.
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  • 147
    ISSN: 1434-193X
    Keywords: Acetylene ; Ethylene ; Carbocations ; Vinyl cation ; Ethyl cation ; Basicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protonation of acetylene and ethylene (yielding the vinyl and ethyl cation, respectively) was investigated computationally by ab initio calculations [B3LYP/6-31G(d,p)], in the gas phase and in water, as modeled by the IPCM and SCIPCM continuum methods. The structures and NBO atomic charges were thus determined for the neutral bases and their protonated forms, while the comparison of gas-phase and aqueous basicities afforded the hydration energies of the protonated bases. It was found that the aqueous protonation of acetylene is more endothermic than that of ethylene by 5 kcal/mol, owing to the lower intrinsic basicity of the former (by 7.4 kcal/mol), which is only partly compensated for by the more exothermic hydration (by 3.8 kcal/mol) of the vinyl cation.
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  • 148
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    Liebigs Annalen 1999 (1999), S. 2909-2914 
    ISSN: 1434-193X
    Keywords: Methyl methacrylate ; 13C label ; Mass spectrometry ; 1H NMR ; 13C NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic scheme has been developed to prepare methyl methacrylate specifically 13C-labelled at all different positions and in any combination of positions, from simple, commercially available starting materials. According to this scheme methyl (1-13C)- and methyl (2-13C)methacrylate (1a and 1b) have been prepared with high label incorporation (99%).
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  • 149
    ISSN: 1434-193X
    Keywords: Conformational analysis ; Conformational isomerism ; Isotopic labeling ; 2,4-Disubstituted pentanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4-Disubstituted pentanes are molecules which adopt essentially only two conformations. Substituents have been varied in order to find those which lead to a strong preference of the conformer equilibrium. Studying 2-substituted 4-methylpentanes 3 and 4-benzyloxypentanes 12, it has been shown that substituent effects on the conformer equilibria are not additive, as would be expected on the grounds of steric effects alone. Rather, interactions between polar groups reinforce the bias of the conformer equilibria. When applied to 2,4-disubstituted pentanes, substituents such as chloro or phthalimido shift the conformer equilibrium to the side of the gg conformer with preferences exceeding 90%.
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  • 150
    ISSN: 1434-193X
    Keywords: Amino acids ; α-Amino acid phenylhydrazides ; Heterocycles ; Cyclization reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L-tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality.
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  • 151
    ISSN: 1434-193X
    Keywords: Marine fungi ; Tyrosine kinase ; Natural products ; Macrodiolides ; Polyketides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sponge-derived fungi Ulocladium botrytis and Asteromyces cruciatus, and the algal-derived fungus Varicosporina ramulosa, were isolated and extracts from cultures investigated for their metabolite production. Investigations of the extract of the culture of U. botrytis guided by bioassay yielded the new tyrosine kinase (p56lck) inhibitor ulocladol (1) together with 1-hydroxy-6-methyl-8-(hydroxymethyl)xanthone (3), which showed antifungal activity. The extract of the culture medium of A. cruciatus yielded the new metabolite (+)-2,4-dimethyl-4,5-dihydrofuran-3-carbaldehyde (4) together with the known compounds (3S,5R)-dimethyldihydrofuran-2-one (5) and tri-O-acetyl glycerol. From V. ramulosa the five macrodiolides grahamimycin A1 (6), colletoketol (7), (6R,11R,12R,14R)-colletodiol (8), 9,10-dihydro-(6R,11S,12S,14R)-colletodiol (9) and 9,10-dihydro-(6R,11R,12R,14R)-colletodiol (10) together with ergosterol were obtained, 9 and 10 being new fungal metabolites.
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  • 152
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    Liebigs Annalen 1999 (1999), S. 2991-2995 
    ISSN: 1434-193X
    Keywords: Polyketide ; Macrocyclic lactone ; Stereoselective carbonyl olefination ; Marine natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The C1-C16-segment of lasonolide A has been prepared stereoselectively in high chemical and optical yield starting from 2α-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (rac -1).
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  • 153
    ISSN: 1434-193X
    Keywords: β-Turn mimetic ; Conformational analysis ; Synthesis design ; Tetrahydrofuran ; THF amino acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N- and C-protected derivatives of 2,5-disubstituted trans- and cis-THF amino acids 6 and 7 were prepared in enantiomerically pure form from L-alanine. Felkin-Anh-controlled reduction of the ketone 9 was achieved with a 85:15 diastereoselectivity. Epoxidation of 10 and subsequent intramolecular epoxide opening gave the trans- and cis-THF alcohols 11 and 12, which were further transformed into the corresponding N- and C-protected 2,5-disubstituted trans- and cis-THF amino acids. Conformational studies show that the cis-THF diamide 34 is a β-turn mimetic in the solid state and in CDCl3 solution.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99165_s.pdf or from the author.
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  • 154
    ISSN: 1434-193X
    Keywords: Natural product ; Ellagitannins ; Gluconic acid derivatives ; Atropisomerism ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The opening of the D-glucono-δ-lactone ring of the ellagitannin derivative 8, which contains a hexabenzyloxydiphenoyl moiety, to the corresponding gluconic acid derivative 9 under mild acidic conditions was investigated. This transformation was found to occur quantitatively upon treatment of the D-glucono-δ-lactone derivative 8 with silica gel.
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  • 155
    ISSN: 1434-193X
    Keywords: Aminophosphane ; Chirality ; Chromium complexes/ Diastereoselective reactions ; P ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral α-aminophosphane (α-P-C-N) ligands have been prepared by reversible addition of Ph2PH to tricarbonylchromium benzaldimine complexes (CO)3Cr[η6-o-C6H4(Y)(CH=NR)] (with Y, R = CH3, CH3 or CH2COOCH3; CH3O, CH3 or p-CH3OC6H4; Cl, C6H5), with complete diastereoselectivity. These complexes are stabilized in solution by electron-withdrawing group(s) on the imine.
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  • 156
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    Liebigs Annalen 1999 (1999), S. 3099-3103 
    ISSN: 1434-193X
    Keywords: Antibiotics ; Biomimetic-type synthesis ; Polyketides ; Quinones ; Aldol reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trioxo ester 15 was prepared by attachment of two vicinal C-4 and C-6 ketide side chains on the anthraquinone core (6b). Mild base treatment of 15 initiated successive aldol condensations to produce the benzo[a]naphthacenequinone 16 regioselectively in one operation. Deprotection of 16 afforded the antibiotic G-2A (1) and decarboxylation of 1 lead to G-2N (2).
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  • 157
    ISSN: 1434-193X
    Keywords: Heterocycles ; Thiazoles ; Pyrido[3,4-c]thiazoles ; Triflates ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 2-substituted 5-acetyl-4-thiazolyl triflates 2are useful building blocks for the preparation of functionalised thiazoles by means of palladium-catalysed cross-coupling reactions with organometallic reagents and alkoxycarbonylation and deoxygenation reactions. The combination of palladium-catalysed coupling of 2 together with 1-alkynes/6-endo-dig annulation reactions in the presence of ammonia leads to functionalised pyrido[3,4-c]thiazoles in satisfactory yields. The utilisation of uncatalysed displacement reactions of the triflate group represents a very simple method for the synthesis of 4-N-,4-O-, and 4-S-substituted thiazoles.
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  • 158
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    Liebigs Annalen 1999 (1999), S. 3131-3133 
    ISSN: 1434-193X
    Keywords: Amino acids ; DCG-IV ; Drug research ; m-Glu receptors ; Stereocontrol ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Feist′s acid (5) was used in enantiomerically pure form as starting material for the synthesis of (2S,2′R,3′R)-2-(2′,3′-dicarboxylcyclopropyl)-glycine (DCG-IV) (2). This conformationally restricted analog of L-glutamic acid (L-Glu) 1 is a potent group II mGlu receptor agonist.
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  • 159
    ISSN: 1434-193X
    Keywords: Glycosyl iodides ; Triphenylphosphane-iodine complex ; Carbohydrates ; Glycosides ; Polymer bound reagents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-D-Glycosyl iodides are stereoselectively obtained by iodine replacement of the free anomeric hydroxyl group of fully protected sugars treated with a polymer bound triarylphosphane-iodine complex and imidazole. High yields and mild conditions, compatible with all the common protecting groups used in carbohydrate chemistry, characterize the conversion.
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  • 160
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    Weinheim : Wiley-Blackwell
    ISSN: 1434-1948
    Keywords: Zinc ; Aldehyde ligands ; Weakly coordinating anions ; Structural chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinc salts of low or zero water content were obtained from the hexahydrates of zinc nitrate, zinc perchlorate, and zinc tetrafluoroborate by dehydration with triethoxymethane or by solvation with acetonitrile or nitromethane. The compounds incorporated aldehydes as ligands when treated with an excess of the aromatic aldehydes benzaldehyde, mesitylaldehyde, 2-chlorobenzaldehyde, and 4-fluorobenzaldehyde. Eighteen zinc-aldehyde complexes were isolated and identified by crystal structure determinations. All contain octahedral zinc to which 2, 3, 4, 5, or 6 aldehyde ligands are bound. Water, ethanol, and acetonitrile molecules act as coligands. Of the anions employed, BF4- and SbCl6- were found to be only noncoordinating and NO3- only coordinating, whereas complexes with one or two perchlorate ligands were obtained in addition to perchlorate salts.
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  • 161
    ISSN: 1434-1948
    Keywords: Sandwich complexes ; Iron ; Tin ; NMR spectroscopy ; Mössbauer spectroscopy ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1,1′-bis(chlorostannyl)-substituted ferrocenes Fe(C5H4-SnMe2Cl)2 (2), Fe(C5H4-SnMeCl2)2 (3) and Fe(C5H4-SnCl3)2 (4) were prepared, starting from 1,1′-bis(trimethylstannyl)ferrocene (1). Treatment of the chlorides with Li[AlH4] afforded the 1,1′-bis(hydridostannyl)-subsituted ferrocenes Fe(C5H4-SnMe2H)2 (5), Fe(C5H4-SnMeH2)2 (6) and Fe(C5H4-SnH3)2 (7), respectively. All complexes 1-7 were studied by 1H-, 13C-, and 119Sn-NMR spectroscopy with 1D and 2D techniques. The compounds 1-4 were investigated by temperature-dependent 119Sn- and 57Fe-Mössbauer spectroscopy. The electrochemistry of 1-5 gave evidence of reversible one-electron oxidation processes. The molecular structure of 1,1′-bis(trichlorostannyl)ferrocene (4) was determined by X-ray structural analysis, and there was no indication of intra- or intermolecular Sn···Cl···Sn interactions. This direct structural information proved to be consistent with both the Mössbauer and the solution NMR spectroscopic data.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 162
    ISSN: 1434-1948
    Keywords: P Ligands ; N Ligands ; Copper ; Zinc ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000