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  • Organic Chemistry  (68,935)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 233-239 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentafluorophenyluronium salts and related coupling reagents for the solid-phase synthesis of peptides and glycopeptides have been developed and employed in the synthesis of a glycopeptide sequence from the cell adhesion molecule E-CAD 1.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly Reactive Trialkylsilylation Reagents Derived from Bis(trifluoromethanesulfonyl)imide - Silylation of Functional Groups, Alkines and Reactive AromaticsThe synthesis of trialylsilyl-bis(trifluormethane-sulfonyl)imides 3 is described. Compounds 3 with bulky trialkylsilyl groups 3a,b only exist in the silatautomeric form 3a′, b′ under usual conditions, 3c in the N-trimethylsilyl structure. Despite of the bulky silyl substituents in 3a′, b′ their reactivity is higher than of trimethylsilyltriflate. Alcohols, carbonyl compounds, nitroalkanes and carboxylic acid esters are silylated in good yields, especially by the more reactive triisopropylsilyl derivative 3b′ in presence of tertiary amines. tert.-Butyl carboxylates and benzylcarboxylates are cleaved. Monosubstituted alkines and electron-rich (hetero) aromatics are carbosilylated in presence of N-ethyl-diisopropylamine.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 544-550 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amphiphilic and Mesogenic Carbohydrates. 10. Change of the Type of the Mesophase by Variation of the Acyl Chain of Amphiphilic Tetradecyl (N-acylamino)-2-deoxy-1-thio-β-D-glucopyranosidesThe homologous amphiphilic tetradecyl-2-(N-alkanoylamino)-2-deoxy-1-thio-β-D-glucopyranosides 5a-f were synthesized from the 2-(N-alkanoylamino)-2-deoxy-D-glucopyranoses 1a-f via the glucosyl chlorides 2a-f, the glucosyl isothiuronium chlorides 3a-f, and the acetylated thioglucosides 4a-f. On heating the amphiphiles 5a-f form different types of liquid crystalline phases in dependence of the length of the acyl chain, i.e. 5a and 5b form smectic phases, 5d-f form columnar mesophases. Polarisation microscopy, DSC-measurements and contact preparations were used to characterise the liquid crystaline phases.
    Additional Material: 3 Ill.
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  • 6
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cis or trans-glycidic esters 1 or 7 give ring transformations with hydrazines affording optically active 4-hydroxypyrazolidin-3-ones 3 and 4 or 6 or 9 and 10, respectively, in different regioselectivities. 4-Hydroxypyrazolidin-3-ones 3 and 9 can serve as precursors for enantiomerically pure β-amino-α-hydroxycarboxylic acid amides 5 and 11 by hydrogenation in the presence of Raney-Ni.
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 90-93 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998) 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of new 3,1′-bridged 2-[2′-(4″-dialkylaminophenyl)ethenyl]-4,6-diarylpyrylium perchlorates (3), 2-[2′-(4″-dialkylaminophenyl)ethenyl]-7-diethylamino-1-benzopyrylium perchlorates 5-8, 2-[4′-(4″-dialkylaminophenyl)butadien-1′,3″-yl]-, and 2-[2′-(7″-diethylaminocoumar-3″-yl)ethenyl]-7-diethylamino-1-benzopyrylium perchlorates 10-12 were synthesized and characterized by means of elemental analysis, m.p., Vis/NIR, and 1H NMR spectra. Semiempirical MO calculations were performed to elucidate the essential features of the chromophores. The size of the bridging ring strongly affects the geometry of the chromophores which, in turn, determines the extent of charge transfer of the longest wavelength electronic transition. Increasing deviation from planarity causes the polymethine-like chromophore to become more polyene-like.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 256-263 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and stereochemical characteristics of pyrrolidino-, isoquinolino- and indolo-enaminones 2-11 are reported. The inhibition of cyclooxygenase was determined in a bovine thrombocyte intact cell assay and that of 5-lipoxygenase using intact bovine polymorphonuclear leucocytes. Except compound 2c′ which is a well-balanced dual inhibitor of both enzymes, all other enaminone derivatives are weak inhibitors of both cyclooxygenase and 5-lipoxygenase. Structure-activity relationships of the enaminones in relation to known anti-inflammatory drugs are discussed.
    Additional Material: 1 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998) 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 315-322 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper-catalyzed alkoxycarbonylcarbene transfer from methyl or tert-butyl diazoacetate to acyclic enaminoesters 6a,b and enaminocarboxanilide 13 yields vicinal push-pullsubstituted cyclopropanes 7a,b,8, and 14. In contact with dry silica gel, the latter compounds undergo facile ring-opening leading to enaminoesters 9, 10, and 15. Treatment with aqueous acid transforms 9 and 10 into 2-acylsuccinates 11 and 12, and 15 into pyrrolinone 16. Methoxycarbonylcarbene transfer to enaminoketones 1a-c does not yield isolable cyclopropanes, but after hydrolytic work-up α-acyl-γ-ketoesters 2a-c are obtained.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iminium Salts in Quantitative Gas/Solid and Solid/Solid ReactionsIminium salts that are highly susceptible to hydrolysis are quantitatively prepared and reacted in the solid state without solvents or liquid phases. Atomic force microscopy AFM helps in elucidating the mechanism of these still unusual gas-solid and solid-solid syntheses by recording surface topographies of reacting crystals of L-histidine (10) and triphenylverdazyl (15). Various imines add gaseous HCl or HBr to form stable iminium halides (1, 3, 4, 5, 11) even if frozen liquids of very weak heterocyclic bases are treated at low temperatures. Another way for quantitative yields of iminium salt hydrates (6) starts with solid primary ammonium halides and gaseous acetone. o-Phenylenediamines (7) give quantitatively 1,5-benzodiazepines (9) by solid state cyclization of bis-iminium salt intermediates (8). Crystalline nitroxyls (12) and triphenylverdazyl (15) undergo stoichiometric one-electron transfer with gaseous NO2 or XeF2 to give nitrosonium (14) and azonium salts (17). The solid state chlorination of tetramethylthiuramdisulfide (18) or dimethylthiocarbamoylchloride (20) yields phosgene dimethyliminiumchloride (Viehe salt 21) in quantitative yield. Solid Viehe salt is quantitatively treated with gaseous Cl2 to give the trichloride 19 and solid SbCl5 or PCl5 to produce the hexachloroantimoniates (22), -phosphates (23). Solid brenzcatechol (24), mercaptobenzimidazole (27), p-nitroaniline (30), N-methylbenzothiazolone-2-hydrazone (34) and acetophenone (41) are treated with 21 to give the corresponding chloroiminium salts (25, 28, 31, 35, 43). p-Toluenesulfonamide (37) and 22 give the chloroiminium salt 38. These quantitative solid-solid reactions are most easily run in ball mills with cooling device. The “waste-free” techniques achieve exclusion of moisture in an elegant way. The preparative use of the versatile products with nucleophiles is indicated. The three-step solid-state mechanisms are discussed.
    Additional Material: 4 Ill.
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  • 14
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By the reaction of N-acylthioureas 7 with 1,3-dichloroacetone 9 2-dialkylamino-5-chloroacetyl-thiazoles 11 are available. These compounds react with thioureas or arylthioamides under heterocyclisation to give bis-(2-dialkylamino-5-thiazolyl)-ketones 13, 2-aryl-4-(2-dialkylamino-5-thiazolyl)-thiazoles 14, or 2-dialkylamino-4-(2-dialkylamino-5-thiazolyl)-thiazoles 15, resp., from which the last-mentioned compound exhibit a high reactivity towards several electrophilic reagents. Thus, deeply colored cyanovinyl, arylazo, and arylmethine substituted bisthiazole dyes 17, 18, and 19, resp., have been formed.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 393-407 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterobimetallic Complexes Containing 2-(Dimethylaminomethyl)ferrocenyl LigandsThe chemistry of heterobimetallic complexes containing the 2-(dimethylaminomethyl)ferrocenyl ligand is reviewed, including main group element, transition metal, and f-element derivatives. An overview on synthetic methods and molecular structures is given.
    Additional Material: 23 Ill.
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  • 16
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1-Substituted 3-hydroxy-1H-pyrazoles 1 react with chloroform, NaOH, and aceton resp. butan-2-one O-regiospecifically to yield 2-methyl-2-[(1H-pyrazol-3-yl)oxy]-propanoic resp. -butanoic acids 14 via a dichlorocarbene (12)-dichlorooxirane (9) pathway. Chlorides 17 of 14 easily cyclize to N-acylpyrazolium salts 18/19, which quantitatively afford esters 22-26 and amides 27-29 of 14. Enantiomers of the butanoic acid 14th, obtained via their diastereomeric cholesterol esters, differ in their stimulus to peroxisome proliferation. At 140 °C pyrazolium salts 18 undergo thermolysis to bicyclic β-oxa-γ-lactams 30-32. 3-Carboxyisoalkylamino-pyrazoles similarly give 1H-β-aza-γ-lactams 34. Reactions of 14 with surplus SOCl2 result in 6-chloro- 37 resp. 7-chloro-β-oxa-γ-lactams 38 via chlorosulfinylation and extrusion of SO, and in 4,4-bispyrazolyl-sulfoxide 39. A mild introduction of additional O-functions into pyrazoles affording 4,5-dihydro-3-hydroxy-5-oxo-1H-pyrazoles 52-57 is presented. Biological effects of the new pyrazoles are protection against shock and ADP-induced thromboembolism, reduction of serum lipids and improvement of blood flow.
    Additional Material: 4 Tab.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 309-314 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclization reactions of 2-vinylaniline derivatives, proceeding via anils, amides, imidic acid esters, ureas, thioureas, carbodiimides, formamidine ylids, sulfonamides or ketenes, leading to quinoline or indole derivatives, are described. In a short introduction interesting results from the literature, excluding our results, are presented. In the centre of this progress report our results on acid catalyzed reactions of 2-vinylanilines with aldehydes and ketones are discussed in a more detailed manner.
    Additional Material: 1 Tab.
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  • 18
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 7-Methyloctahydroacridines 7a-d were obtained by a one-pot imine condensation/Lewis acid-catalyzed cyclization from aniline derivatives 5a-d and aldehyde 6. Only those compounds 7 could be oxidized with DDQ to the corresponding octahydroacridine-7-carbaldehydes 9, which bear a meta-chloro or bromo substituent (with respect to the methyl group) in addition to the para-amino group (i.e. 7c,d → 9c,d). Aldehyde 9c was further converted to the novel tripodand 11 which was characterized by X-ray crystal structure analysis.
    Additional Material: 1 Ill.
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  • 19
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ortho-, meta- and para-xylenes 1, 13a, 13b and 13c, with donor and acceptor substituents at the α- and α′ positions, lead to a remarkable variety of intermediates and reaction products after deprotonation of the benzylic proton. Thus, the reaction of para-(cyanomethyl)dialkyl[(methylthio)phenylmethylene]ammonium tetrafluoroborates 13a and 13b with sodium hydride affords the para-quinodimethanes 14a and 14b. Poly(meta-phenylenevinylene) 14c can be obtained when starting from 13c. We report the synthesis of para-quinodimethanes 14a and 14b and poly(meta-phenylenevinylene) 14c and describe a successive approach towards meta-phenylenevinylenes of definite length 16b and 17b starting from 12d. Moreover, we compare the stability and reactivity of para-quinodimethane 14a and 14b with those of the ortho-quinodimethane 2 and we focus on the characterization of the resulting donor and acceptor substituted compounds.
    Additional Material: 2 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998) 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 430-436 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cathodic reduction of dibenzofuran (2), 2-chlorodibenzofuran (4), and 3-chlorodibenzofuran (1) in deuterated methanol is investigated. The Birch-type reduction product 1,4-dibenzofuran (3) is formed from 1 via 2, whereas 2-chloro-1,4-dihydrodibenzofuran (5) is obtained as by-product besides 3 from 4 as starting compound. Deuterium is only incorporated into the reduction products if CH3OD or CD3OD but not if CD3OH are used. This observation is strongly indicative of a polar mechanism involving protonation rather than a radical mechanism with hydrogen atom abstraction to be operative.
    Additional Material: 4 Ill.
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  • 22
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two-phase Hydroformylation of Buta-1,3-diene and Hydrocarbon Mixtures Containing Buta-1,3-dieneThe two-phase hydroformylation of buta-1,3-diene with (HRh(CO)[P(m-C6H4SO3Na)3]3 the Kuntz catalyst system with excess P(m-C6H4SO3Na)3) gives high yields of C5-monoaldehydes. Main product in this mixture is the reactive trans- and cis-pent-3-enal. In consecutive reactions the pent-3-enal is partially hydrogenated to n-pentanal, but also-favoured by the protolytic milieu of the two-phase reaction- aldol condensated to 2-propenylheptadienal. The hydrogenation product of the propenylheptadienal, 2-propylheptanol-1, is a good plasticizer alcohol with a wanted low vapour pressure. Especially promising is the two-phase hydroformylation of the unrefined C4-fraction of the naphtha pyrolysis: after a more than 95 per cent conversion of the buta-1,3-diene also more than 80 per cent of the n-but-1-ene in the C4-fraction is hydroformylated mainly to wanted n-pentanal. Less than 5-10% of the n-but-2-enes and the isobutene in the C4-fraction react under these conditions to oxo-products (2- and 3-methylbutanal). Acetylenic compounds in the C4-fraction are converted quantitatively into products.
    Additional Material: 2 Ill.
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  • 23
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 479-482 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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  • 24
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 25
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998) 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 26
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 530-535 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of tricarbonyl(η5-cyclohexadienylium) iron tetrafluoroborate 3 with the methyl arylacetate 6, the dimethyl arylmalonate 12, and the di-tert-butyl arylmalonate 14 provides regio- and stereoselectively the tricarbonyliron-complexed 5-arylmethylcyclohexa-1,3-dienes 7, 13 and 15.
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  • 27
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The partially diethylamino substituted phenyl-chloromono- and -disilanes Cl2Ph(NEt2)Si(2) Cl2Ph(NEt2)2Si(3), [ClPh(NEt2)Si-]2 (7) and Cl(NEt2)PhSi—SiPh(NEt2)2 (8) were synthesized. 3 and 8 are able to react with lithium powder to form the corresponding silyllithium compounds. The resulting species were characterized in solution by 13C and 29Si NMR spectroscopy. To prove the expected substitution patterns of the silyllithium compounds some coupling reactions with chlorosilanes were carried out and the resulting new oligosilanes were characterized by means of NMR spectroscopy and MS.
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  • 28
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 576-577 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The exclusive O-alkylation reaction of hydroxy-phenothiazine 3 and hydroxy-diphenylamine derivates 1 and 2 by PTC without solvent is described.
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  • 29
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    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 585-585 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 30
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4,5-Disubstituted N-phenyl-isothiazolium salts 1 with active 5-methyl group react under the influence of anilines to form 3,4-disubstituted isothiazolium salts 3. The influence of donor and acceptor substituents in the 2-phenyl group of 1a-h and in the anilines 2 on the ring transformation were studied. The structure of the new salts was confirmed by X-ray analysis. The 3-hydroperoxy-2,3-dihydro-isothiazole 1,1-dioxides (12a,d) and the isothiazole-3(2H)-one 1,1-dioxides (14a,d) are obtained by oxidation of salts 3 with H2O2.
    Additional Material: 2 Ill.
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  • 31
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 642-648 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,6-Dimethoxy-(4a), 2,6-bis(dimethylamino)-(4b), 2,6-dichloro- (4c) and 2,6-dimethoxycarbonyl-9,10-dihydroanthracene (4d) were prepared by conventional methods and used as hydrogen transfer donors to α-methylstyrene (5) between 290-350 °C. The mechanism followed second order kinetics and the rate constants were only slightly influenced by the solvent polarity and the type of substituents introduced. The activation parameters are also closely similar in the series with ΔS≠ values between -21 and -28 cal/mol K. These results, together with the observation of a large isotope effect (kH/kD = 1.4-2.0 at 310-350 °C), suggest that the mechanism involves a primary kinetic H-atom-transfer from the donors to α-methylstyrene (5) in the rate determining step. The compounds 4a-4d constitute a new probe for investigating polar effects on H-transfer reactions.
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  • 32
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 669-675 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies on Stereoselective Electrophiic CyanationThe enantioselective, electrophilic cyanation of the enolates of 2-substituted 1-tetralones 3 is described. Enantiomerically pure 2-cyanato-1,1′-binaphthyl derivatives 2, 6a and b are used as cyanating agents. The influence of solvent, temperature, additives and the method of enolate formation are investigated. Best results are obtained with 48% ee in the case of compound 2 and 60% ee in the case of compound 6b if the enolate is prepared from the corresponding silyl enol ether 7 and Toluene is used as solvent.
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  • 33
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    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998) 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 34
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 733-737 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-Malic acid (2) reacts with trifluoroacetic anhydride under anhydrous conditions to give (S)-trifluoroacetoxy-succinic acid anhydride (3). The anhydride 3 undergoes regioselective ring opening with an excess of anilines or primary aliphatic amines leading to N-substituted-(S)-3-hydroxy-succinamic acids (4a-g). Structural elucidation of the reaction products 4a-g was based on analytical and spectroscopic data and on an X-ray structure analysis of 4b. Secondary aliphatic amines react with 3 by condensation and subsequent elimination to furnish N,N′-disubstituted fumaric acid amides 5a, b. Some N-substituted-2-hydroxysuccinamic acids (7a,b) were also prepared for spectral comparison with the 3-hydroxy compounds.
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  • 35
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 36
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 490-490 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 37
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting with monochiral 1,2,3,4-tetrahydro-3,6-dimethyl quinoline 14a,b, (Schemes 1 and 2), we have synthsized the new chiral, symmetrical and unsymmetrical, tri- and pentamethinium streptocyanine dyes 2a, (Scheme 8), 4a, (Scheme 5), and 5a,b, (Scheme 4), resp. 9a, (Scheme 6), 10a,b, (Scheme 4), and 11a, (Scheme 7) with one or two stereogenic centers in the two heterocyclic end groups. The absolute configuration of 14a,b, and thus the absolute configuration of all monochiral polymethinium dyes derived from 14a,b, has been determined by a single-crystal X-ray analysis of its 4-bromobenzenesulfonyl derivative 17a, (Scheme 1 and Fig. 1). The UV/Vis spectroscopic and chiroptical properties of the new polymethinium dyes have been studied for the first time and compared with that of similar streptocyanine dyes synthesized earlier (Tables 1 and 2) in order to find possible correlations between chiroptical properties and molecular structure.
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  • 38
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 551-556 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclization of the enantiomerically pure α,β-unsaturated ketone 1, an aliphatic aldehyde 3 and ammonia or benzylamine gives diastereoselectively cis-piperidones 4/4′. Although only modest yields were obtained, the presented cyclization has the advantage of being a single step reaction. The products 4 can serve as precursors for all-cis-4-hydroxy-piperidones 5 and novel pipecolic acid derivates 9.
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  • 39
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 572-575 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ten N-alkylated lupininium derivatives 5-8 were prepared as potential enantioselective phase transfer catalysts. Compounds 5a-d, 6a-d contain four asymmetric centers (including one in the side chain) with known configuration resting on an X-ray structure. Preliminary PT catalytic experiments in several reactions gave high chemical yields but relatively disappointing enantioselectivities.
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  • 40
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 41
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 587-587 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 42
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 608-612 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses and the properties of new sulfurligated liquid crystalline sulfones, containing biphenyl units, as well as the influence of lateral nitro groups on their phase behaviour are described. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for most of the synthesized bis(4-alkoxy-biphenyl-3-yl)sulfones (4). The mesomorphic behaviour of these compounds is compared with that of the corresponding nitro compounds 6. The bis(4-alkoxy-6-nitrobiphenyl-3-yl)sulfones (6) are not mesogenic. The results demonstrate that lateral nitro groups introduced into the biphenyl unit, changing the length-breadth relation, depress the thermal stability and lead to the loss of the mesomorphic properties.
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  • 43
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 632-641 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular threads I-III incorporating 1,3,5-cycloheptatriene units have been synthesized by three methods. Bridges were designed as ether (9, 14, 18 and 22), ester (4 and 14) and amino functions (25), respectively, The attachment of a second aryl residue at the seven-membered ring by nucleophilic attack of activated aromatic compounds such as anilines on tropylium salts resulted in the formation of two regioisomers (26 and 27). The macrocycles 28 were formed under high dilution conditions in good yields.
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  • 44
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 662-668 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of racemic and enantiomerical enriched axial chiral liquid crystalline compounds incorporating a trisubstituted allene unit is described. All compounds 16-28 display the smectic C-phase and mostly also a nematic mesophase. All investigated enantiomerically enriched compounds have a ferroelectrically switchable chiral smectic SC*-phase.
    Additional Material: 5 Tab.
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  • 45
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 683-685 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Tab.
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  • 46
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    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions in Crystals. 136. Protonated Dipyridylamine Salts with Different Anions: Monomeric Tetraphenylborate as well as Bis(trifluormethylsulfonate), Dimeric Squarate and Polymeric Chloride DihydrateDi(pyrid-2-yl)amine is monoprotonated by acetic, squaric as well as hydrochloric acid and diprotonated by trifluoromethylsulfonic acid. To explore the anion and hydrogen-bridge dependency of its salts, crystals of the monomeric tetraphenylborate, the dimeric squarate as well as the bis(trifluoromethylsulfonate) and the polymeric chloride hydrate have been grown and their structures determined: Separated by bulky tetraphenylborate anions, pyrid-2-yl(2′-pyridinium) amine cation contains an intramolecular hydrogen bridge N⊕H…N and is slightly folded. The squarate salt dimer exhibits additional bridges, N—H…O⊖ and O—H…O. The severely twisted di(2-pyridinium)amine dication is connected to its trifluormethylsulfonate counter anions by altogether three H-bridges, two N⊕H…O and one N—H…O. The chloride dihydrate crystallizes in layers of 16-membered rings, formed from three Cl anions and five water molecules. The diversity of the hydrogen-bridge dominated salt structures is discussed based on comparison with selected literature examples and on PM3 calculations.
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  • 47
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 755-756 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal reaction of Fischer carbene complexes 1 - 3 with cyclooctyne 4 followed by oxidation with Ce(IV)ammonium nitrate furnished tricyclic quinone derivatives 5 - 7 incorporating an eight-membered ring.
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  • 48
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 112-121 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monofunctionalized Dendrons of Different Generations - as Reagents for the Introduction of Dendritic SubstituentsIn recent years dendrimers become more and more important not only in organic chemistry. They represent a new class of molecules with unique characteristic features. But dendrimers represent not only designed molecular architecture. They stand for a new concept in chemistry. They can be used to alter the properties of already existing molecular skeletons or they can be used to transfer new properties to a classical functional unit. This means that functionalized dendrimers and dendrons (dendritic building blocks) can be regarded as reagents for the preparation of new compounds with dendritic properties. In this article the synthesis and the practical use of appropriate dendritic reagents is explained. Furthermore we introduce the new technical terms „{n} dendryl-“ for dendritic substituents of n generations and „dendriagent“ which stands for dendritic reagents. Moreover we give a short outlook on future developments.
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  • 49
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthesis of the title crown via isoxazolo crown ether 7 and macrocyclic bis-β-eneaminoketone 10 is described. 7 can be synthesized in 14% yield by a non-template double-[3+2] cycloaddition of dinitrileoxide 5 prepared in situ from dinitropolyether 19 by dehydration with Ph-NCO and alkyne 6. The compounds 16, 17 and 18 are synthesized by the same synthetic strategy. Comparable IR and 1H NMR spectroscopic data of macrocyclic and non-cyclic compounds show, that macrocyclic conformation stabilizing effects can be ruled out. The structures of the macrocycles 1, 7, 10 and that of the Hg(II)-complex 25, synthesized by reaction of 1 with Hg(OAc)2 were established by single-crystal X-ray structure analyses. Both inter- and intramolecular hydrogen bonds are observed for the macrocyclic bis-β-eneaminoketone 10, whereas only intramolecular hydrogen bonds are formed by 1.In the Hg(II)-complex of 1 the mercury is bonded to two methylene groups. C—Hg—C is almost linear [177(1)°], the mean Hg—C distance amounts to 215(1) pm. In addition to the Hg—C bonds, each Hg makes a short contact to a carbonyl oxygen in a neighbouring molecule in the plane perpendicular to the C—Hg—C axis [Hg(1)—O(1) = 279(1) pm, Hg(2)—O(5) = 284(1) pm].
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  • 50
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 171-174 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base-catalyzed cyclization of the naphthoquinone 5 afforded the 1,2-dihydroanthraquinone 6a. The bisalkylation products 9 and 10 were obtained by Stille-type chain elongation of the corresponding triflate 6b with the stannanes 7 or 8. The dihydroanthraquinone 9 is a potential precursor for the SS-228 Y-type angucyclinones, where as the diketone 10 can be converted to 8-deoxytetrangomycin (11).
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  • 51
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 184-186 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 52
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 656-661 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the benzylidene lactone 3 of D-(-)-quinic acid the cyclohexyl fragment 15 (C-28-C-34 part) of the immunosuppressant FK506 was synthesized. Key steps include homolytic deoxygenation reactions on compounds 4 and 6 as well as a regioselective opening of the benzylidene acetal 5. Opening of the lactone 7 to provide the methyl ester 8 was followed by methylation of the hydroxy group to give 9. Further steps provided the aldehyde 12 which was elongated to the alkyne 15. This sequence provides 15 in gram quantities.
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  • 53
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 679-682 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 54
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 710-721 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reference Electrodes for Electrochemical MeasurementsRecent advances in the development of reference electrodes for amperometric and voltammetric measurements are reviewed. The suitability of all-solid-state electrodes as reference electrodes for pH measurement for use with an glass electrode and for other potentiometric measurements is evaluated. The role of new technologies, as thick film and as thin film technology, are discussed. References for microelectrodes are represented.
    Additional Material: 11 Ill.
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  • 55
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    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 744-754 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extended Conjugation in StilbenylsquarainesUnsymmetrical 1-aryl-3-stilbenylsquaraines 2a-e and 1,3-bis(stilbenyl)squaraines 3a-c were prepared by CC coupling reactions of the corresponding substituted arenes with derivatives of squaric acid (Schemes 2 and 3). Dialkylamino and alkoxy groups enhance the solubility of these dyes and enlarge the intramolecular charge transfer of these donor-acceptor-donor systems. The extended conjugation of the stilbene units - in comparison with arene building blocks - leads to significant bathochromic shifts in the Vis/NIR absorption spectra.
    Additional Material: 2 Tab.
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  • 56
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Goethe and the Earlier Chemical JournalsTwo hundred years ago the german “Allgemeines Journal der Chemie” was founded by the Bergrat Scherer from Weimar. His redaction was situated in the castle Belvedere. Goethe was a promoter of this chemist und editor. The concept of this journal, the citations of Goethe and his works in the following “Journal für Chemie und Physik”, edited by Schweigger, and the interests of Goethe as reader also on Crells oldest chemical journal from 1778 are described in detail.
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  • 57
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    Chirality 10 (1998), S. 321-324 
    ISSN: 0899-0042
    Keywords: NSAID ; esterification ; resolution ; Candida antarctica lipase ; rac-Indoprofen ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lipase from Candida antarctica, commercially available immobilised on acrylic resin as Novozym® 435, allows for enantioselective esterification of rac-indoprofen (±)-1, with methanol in a dioxane-toluene solvent system. A double esterification process affords methyl ester (-)-(R)-2 in 85% e.e. and enantiopure (+)-(S)-1, both in good chemical yield. Chirality 10:321-324, 1998. © 1998 Wiley-Liss, Inc.
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  • 58
    ISSN: 0899-0042
    Keywords: atropisomeric polychlorinated biphenyls (PCBs) ; Chirasil-Dex ; rotational barrier ; stopped-flow multidimensional gas chromatographic technique ; on-line enantiomerization kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers ΔG
    Additional Material: 3 Ill.
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  • 59
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    Chirality 10 (1998), S. 325-337 
    ISSN: 0899-0042
    Keywords: diastereomeric salts ; molecular recognition ; hydrogen bonding ; thermal analysis ; crystallography ; solubility ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (+)-(1S;2S)-Pseudoephedrine and racemic mandelic acid form three distinct diastereomeric salts from solutions in 95% ethanol. The least-soluble phase, a hemihydrate, contains the (2R)-mandelate. A salt phase of intermediate solubility is the unsolvated double salt, containing both the (2R)- and the (2S)-mandelate. The most-soluble salt phase contains the (2S)-mandelate. Mandelate configuration and order of solubility (based on the heats of fusion) is inverted from that found in the same system synthesized from chiral base and acid, and then crystallized from benzene solution. The (2R)-mandelate hemihydrate (-H2O at 349.5K, mp 391K), monoclinic, P21, a = 6.788(5), b = 29.415(35), c = 9.488(10)Å, β = 108.91(8)°, Z = 4 (2 ion-pairs/asymmetric unit). Intermediate double salt (2S)- and (2R)-mandelate, mp 377.6K, anorthic, P1, a = 7.758(4), b = 9.966(5), c = 13.366(6)Å, α = 72.99(4), β = 79.98(4), γ = 70.51(4)°, Z = 1 (2 ion-pairs/asymmetric unit). The (2S)-mandelate (mp 386.2K), orthorhombic, P212121, a = 7.079(6), b = 13.443(10), c = 18.820(14)Å, Z = 4 is identical to a salt made from a combination of enantiomeric moieties from benzene solution. While differing from ephedrine mandelates in configuration at one center, solubilities of pseudoephedrine mandelates in 95% ethanol are much larger. A comparison of molecular structure (non-polar and H-bonding) regions of pseudoephedrine and ephedrine mandelates shows similarities and differences that are tentatively linked to crystal properties. This study reemphasizes the necessity for consistency in solvent use in resolution and in phase identification and comparison because the phases produced are frequently dependent upon the solvent. Chirality 10:325-337, 1998. © 1998 Wiley-Liss, Inc.
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  • 60
    ISSN: 0899-0042
    Keywords: additive ; selectivity ; efficiency ; modifier ; subcritical fluid chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Subcritical fluid chromatography (SubFC) using a carbon dioxide-methanol mobile phase is used for the chiral resolution of IIb/IIIa receptor antagonist enantiomers. The chiral resolution of three analogs, each containing two chiral centers, is optimized using various mobile phase additives. The effects that acidic, basic, and neutral additives have on retention, efficiency, and resolution are examined. The additive that gives the best resolution was found to be dependent upon the functionality and charge of the chiral analyte. For charged analytes, additives that act as competing ions of the same charge as the chiral analyte dramatically improve efficiency and resolution. Resolution of neutral chiral analyte enantiomers is also greatly affected by the choice of mobile phase additive. Chirality 10:338-342, 1998. © 1998 Wiley-Liss, Inc.
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    Chirality 10 (1998), S. 343-348 
    ISSN: 0899-0042
    Keywords: chiral asymmetry generation ; chiral autocatalysis ; primary nucleation ; secondary nucleation ; chiral cobalt complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral asymmetry generation, the predominant production of one enantiomer in a non-chiral environment, could occur in the production of the chiral complex cis-[CoBr(NH3)(en)2]Br2 by the reaction of [Co(H2O)2{(OH)2Co(en)2}2](SO4)2 with ammonium bromide in an aqueous medium. The main kinetic steps in the reaction system have been determined. During the reaction, the product crystallizes at an early stage. When a very small amount of crystalline enantiomer was added to the reaction system at an early stage, the same enantiomer was produced preferentially; in addition, the enantiomeric excess of the product increased with increasing the stirring rate. Thus, it seems that each enantiomer generates chiral crystals that could self-replicate through secondary nucleation when the solution is stirred; these crystals in turn enhance the production of the same enantiomer. With a computer code that simulates such a kinetic mechanism, it is shown that enantiomeric excess observed in the experiments could be reproduced. Chirality 10:343-348, 1998. © 1998 Wiley-Liss, Inc.
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  • 62
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    Chirality 10 (1998), S. 362-363 
    ISSN: 0899-0042
    Keywords: Jacobsen's catalyst ; enantiomeric purity determination ; chiral HPLC ; cyclodextrin chiral stationary phases ; enantioseparation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A HPLC method is described for the chiral analysis of the commercially available Jacobsen's catalyst. A hydroxypropyl β-cyclodextrin stationary phase was used in conjunction with a nonaqueous, polar-organic mobile phase. The method can be applied to control the enantiomeric purity of the catalyst, which is of great importance for quality control of that product. High accuracy in the determination of trace levels of the unwanted enantiomer in the presence of large amounts of the desired enantiomer is demonstrated. Chirality 10:362-363, 1998. © 1998 Wiley-Liss, Inc.
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  • 63
    ISSN: 0899-0042
    Keywords: carbenicillin ; stereoselective ; secretion ; transport ; rabbit ; membrane vesicles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselectivity in the renal secretion of carbenicillin (CBPC) was studied in rabbits. Significant renal secretion of CBPC was observed in vivo, with the secretion of the S-epimer being greater than that of the R-epimer. Stereoselective transport of CBPC was further studied in vitro using basolateral and brush border membrane vesicles prepared from rabbit kidneys. The transport of CBPC by the organic anion transporter into the basolateral membrane vesicles (BLMV) was not stereoselective. In contrast, a distinct stereoselectivity was observed in the transport of CBPC by the organic anion transporter into the brush border membrane vesicles (BBMV), with the transport of the S-epimer being more favorable. Significant epimer-epimer interactions were also observed in the transport into BBMV. The stereoselectivity of the transport of CBPC was calculated from the kinetic parameters with consideration of epimer-epimer interactions and was similar to that observed in vivo. It was concluded that the observed stereoselectivity in the renal secretion of CBPC in vivo reflected that of transport via the organic anion transporter located at the brush border membrane. Chirality 10:349-357, 1998. © 1998 Wiley-Liss, Inc.
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  • 64
    ISSN: 0899-0042
    Keywords: cyclic imides ; barbiturates ; piperidine-2,6-diones ; mephenytoin ; chiral recognition ; enantioselectivity ; vancomycin chiral stationary phase ; normal-phase mode ; reversed-phase mode ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several cyclic imidic compounds (barbiturates, piperidine-2,6-diones, and mephenytoin) are enantiomerically resolved via high-performance liquid chromatography (HPLC) on a macrocyclic antibiotic covalently bonded to a silica gel support. The Chirobiotic V chiral stationary phase (CSP) column contains the antibiotic vancomycin as the chiral selector. The results of the analysis show that the substituents at the chiral carbon position of the racemic drugs affect chiral resolution. In addition, ring size may also play a role when considering the formation of analyte-CSP inclusion complexes. Contrary to the piperidine-2,6-diones, the chromatographic parameters for the barbiturates are much the same under normal- or reversed-phase conditions. The details of these results are discussed. Chirality 10:358-361, 1998. © 1998 Wiley-Liss, Inc.
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  • 65
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    Chirality 10 (1998), S. 371-372 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 66
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    Chirality 10 (1998), S. 375-381 
    ISSN: 0899-0042
    Keywords: retention mechanisms ; separation of enantiomers ; chiral stationary phases ; equilibrium isotherms ; bonding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The retention mechanisms and the separation of enantiomers on the classes of chiral stationary phases which are made by bonding isolated groups on the surface of an adsorbent are discussed. It is shown that retention on these phases originates from mixed mechanisms and how the individual contributions of these two mechanisms can be separated, by determining and modeling the equilibrium isotherms. A contribution originating from interactions of the isomers with the nonselective sites (type-I) and another one due to interactions with the enantioselective sites (type-II) can be determined and their importance studied as a function of several parameters, e.g., temperature or pH. This approach is illustrated with results obtained with different pairs of enantiomers on bovine serum albumin, 4-methylcellulose tribenzoate, or cellobiohydrolase immobilized on silica. Chirality 10:375-381, 1998. © 1998 Wiley-Liss, Inc.
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  • 67
    ISSN: 0899-0042
    Keywords: solubilization ; enhanced enantioselectivity ; chiral induction ; critical micellar concentration ; reaction place ; function of proline ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proline and prolylproline dipeptide derived surfactants promote the asymmetric hydrogenation of (Z)-methyl α-acetamidocinnamate in water in the presence of the catalytic system [Rh(cod)2]BF4 + BPPM. Activity and enantioselectivity are enhanced significantly and the results in water are similar to those obtained with organic solvents. The possibility of a chiral induction was investigated in the presence of the optically active amino acid and peptide amphiphiles and an achiral rhodium catalyst [Rh(bdpb)(cod)]BF4. The analysis of the low optical induction gave some indications of the site where the reaction takes place within the micelle. Selected critical micelle concentrations (cmc) of the new prepared surfactants were determined by surface tension measurements. Chirality 10:754-759, 1998. © 1998 Wiley-Liss, Inc.
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  • 68
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    Chirality 10 (1998), S. 779-785 
    ISSN: 0899-0042
    Keywords: optically active oxiranes ; liquid crystals ; epichlorohydrin ; glycidol ; chiral HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of racemic and optically active oxiranes, bearing mesogenic groups, precursors of liquid crystalline polyethers, has been synthesized from epichlorohydrin or glycidol. The enantiomeric excess of the optically active oxiranes has been determined by chiral stationary phase HPLC. Compounds bearing 4-cyanobiphenyl mesogenic group exhibit monotropic liquid crystalline behavior. A transfer of chirality to the mesophase has been observed for the optically active oxiranes, which present a cholesteric phase. Chirality 10:779-785, 1998. © 1998 Wiley-Liss, Inc.
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  • 69
    ISSN: 0899-0042
    Keywords: chiral HPLC ; principal component analysis (PCA) ; hierarchical clustering ; hydrogen bonding ability ; solvation of carbamate phases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromatographic resolution of 12 derivatives in the 4a-methyl-2,3,4,4a-tetrahydro-1H-fluorene and 4a-methyl-1,2,3,4,4a,9a-hexahydrofluoren-9-one series differing by the framework around position 9 and substitution in position 6, are reported on Chiralcel OD, Chiralpak AD, and Chiralpak AS under two elution conditions and according to the two classes of enantiomers. Results from principal component analysis (PCA) as well as hierarchical clustering show a clustering of the actual compounds depending on properties around position 9, the effect of the substituent in position 6 (methyl, chloro or fluoro) not being strong enough to intermesh the data. Carbamate phases show very different properties when they are used in the separation of a series of ketones C and α-chloroketones D, which differ in basicity and the steric requirement around the carbonyl. Analysis of the effect of 2-PrOH content in hexane on the retention is consistent with a large difference in solvation of the carbamate moiety by 2-PrOH, in the order Chiralcel OD 〉 Chiralpak AD 〉 Chiralpak AS. 4a-Methyl-2,3,4,4a-tetrahydro-1H-fluorene derivatives, which lack hydrogen bonding sites, are not discriminated on these CSPs and show identical k′ responses to 2-PrOH content changes on the three CSPs. Chirality 10:770-777, 1998. © 1998 Wiley-Liss, Inc.
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  • 70
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    Chirality 10 (1998), S. 786-790 
    ISSN: 0899-0042
    Keywords: enantioseparation ; peach-like aroma ; fatty acid bioconversion ; gas chromatography-mass spectrometry in selected ion monitoring mode ; Penicillium roqueforti ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Identification and enantiodifferentiation of γ-lactones produced during the bioconversion of soy bean fatty acids by Penicillium roqueforti spores in the presence of an exogenous lipase was performed using gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. It was shown that 4-dodecanolide and 4-hexanolide were first produced with an enantiomeric excess (99%) in favor of the (R) form, whereas an enantiomeric excess in favor of the (S) form (94%) is found for (6Z)-dodecen-4-olide, the major lactone produced by the fungus. If incubation was continued, mixtures of both enantiomers were found, more particularly for 4-decanolide (R/S:40/60), which was produced only after 120 hr of incubation. The results obtained can be explained by the stereoselective hydroxylation by a 10-hydratase and/or a 10-lipoxygenase of the unsaturated fatty acid precursors, oleic and linoleic acids, and by competition between different pathways. The results point out the limitations of chiral GC analysis as a criterion for the natural origin of relevant lactones, and the complexity of mechanisms involved in γ-lactone formation by microorganisms. Chirality 10:786-790, 1998. © 1998 Wiley-Liss, Inc.
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  • 71
    ISSN: 0899-0042
    Keywords: amylose ; 3,5-dimethylphenyl-carbamate ; polysaccharide phase ; tert-butyl 2-tert-butyl-4-methoxy-2,5-dihydro-1,3-imidazole-1-carboxylate; amino acid ester synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparative separation of the enantiomers of the title compound, a versatile chiral building block for the synthesis of unnatural amino acid esters, by high performance liquid chromatography on a chiral stationary phase (CSP), is reported for the first time. The CSP consists of amylose-(3,5-dimethylphenyl-carbamate), which has been coated onto the surface of macroporous aminopropyl-functionalized silica gel. The effect of mobile phase composition and the amount of amylose derivative on the silica gel has been thoroughly investigated. Using 2-propanol as organic modifier in hexane as mobile phase, on a semi-preparative column (200 mm × 40 mm ID, containing 192 g of stationary phase) about 200 mg of the racemate was separated per injection. Running the equipment under automatic conditions with repetitive injection mode allowed for the separation of 30 g per day. Both enantiomers were obtained with enantiopurities 〉99.75:0.25. Chirality 10:217-222, 1998. © 1998 Wiley-Liss, Inc.
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  • 72
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    Chirality 10 (1998), S. 229-237 
    ISSN: 0899-0042
    Keywords: deuterium labelling ; menthocitronellol ; citronellol ; enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS) ; dynamic headspace analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanistic aspects of the biogenesis of the chiral monoterpenoid rose oxide in Pelargonium graveolens L'Héritier are investigated using deuterium-labelled precursors. After administration of the precursors using the cut-stem method, the dynamic headspace extracts of the plants are analysed using multidimensional gas chromatography-mass spectrometry (enantio-MDGC-MS). It is unequivocally shown that this plant is able to convert citronellol and menthocitronellol into cis-/trans-rose oxide. Menthocitronellol is converted into rose oxide with a clearly detectable enantiodiscrimination. These facts may be explained with the presence of an oxidase, which is able to oxidize citronellol and menthocitronellol in allylic position. A photooxygenation mechanism including singlet oxygen as the oxidizing agent is rather unlikely. Chirality 10:229-237, 1998. © 1998 Wiley-Liss, Inc.
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  • 73
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    Chirality 10 (1998), S. 238-245 
    ISSN: 0899-0042
    Keywords: chiral selectivity ; amino acid crystallization ; molecular recognition ; stochastic kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of chirally selective interaction in the stirred crystallization of glutamic acid and lysine is presented. The crystallization of S-glutamic acid is influenced by the presence of S-lysine but not R-lysine. Crystal nuclei in stirred systems are produced due to secondary nucleation. Secondary nucleation is an autocatalytic process in which a crystal produces secondary nuclei due to fluid motion, and due to crystal stirrer and crystal-crystal collisions. As a result of this autocatalysis, small fluctuations in the nucleation rates are amplified and the kinetics show a marked stochastic behavior. We investigate the stochastic behavior in detail and propose a kinetic mechanism that explains both the increase and the statistical distribution of the crystallization times of S-glutamic acid due to the presence of S-Lysine. Chirality 10:238-245, 1998. © 1998 Wiley-Liss, Inc.
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  • 74
    ISSN: 0899-0042
    Keywords: thalidomide enantiomers ; in vitro kinetics ; blood distribution ; human serum albumin ; chiral inversion ; plasma protein binding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this investigation was to elucidate the distribution and reactions of the enantiomers of thalidomide at their main site of biotransformation in vivo, i.e., in human blood. Plasma protein binding, erythrocyte: plasma distribution, and the kinetics of chiral inversion and degradation in buffer, plasma, and solutions of human serum albumin (HSA) were studied by means of a stereospecific HPLC assay. The enantiomers of thalidomide were not extensively bound to blood or plasma components. The geometric mean plasma protein binding was 55% and 66%, respectively, for (+)-(R)- and (-)-(S)-thalidomide. The corresponding geometric mean blood:plasma concentration ratios were 0.86 and 0.95 (at a haematocrit of 0.37) and erythrocyte:plasma distributions were 0.58 and 0.87. The rates of inversion and hydrolysis of the enantiomers increased with pH over the range 7.0-7.5. HSA, and to a lesser extent human plasma, catalysed the chiral inversion, but not the degradation, of (+)-(R)- and (-)-(S)-thalidomide. The addition of capric acid or preincubation of HSA with acetylsalicylic acid or physostigmine impaired the catalysis to varying extents. Correction for distribution in blood enhances previously observed differences between the pharmacokinetics of the enantiomers in vivo. The findings also support the notion that chiral inversion in vivo takes place mainly in the circulation and in albumin-rich extravascular spaces while hydrolysis occurs more uniformly in the body. In addition, the chiral inversion and hydrolysis of thalidomide apparently occur by several different mechanisms. Chirality 10:223-228, 1998. © 1998 Wiley-Liss, Inc.
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  • 75
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    Chirality 10 (1998), S. 382-395 
    ISSN: 0899-0042
    Keywords: selector/selectand associates ; hydrogen bonding ; chiral separation ; chiral phases ; enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The progress made in the development of chiral stationary phases based on hydrogen-bonding selector/selectand associates is reviewed here. The structure of the different selectand/selector systems was established through X-ray diffraction and other spectroscopic techniques. The structure of the energetically more stable diastereomeric-associate was then correlated to the chromatographic results, namely to the elution order and the enantioselectivity of each of the systems. Chirality 10:382-395, 1998. © 1998 Wiley-Liss, Inc.
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  • 76
    ISSN: 0899-0042
    Keywords: chirality ; helicity ; GC-stationary phase ; conformations ; 1H-NMR-studies ; molecular mechanics calculations ; enantiomer separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The manner of hydrogen-bonding to peptide selectors in enantiomer separation is examined with the help of a structural model. This model relies on a C3-symmetric trispeptide selector, which is stabilized by a network of distinct intramolecular hydrogen bonds. A combination of experimental and theoretical tools enables us to identify the lowest-energy conformation of the trispeptide selector and the sites of selector-substrate interactions. Experimental tools include temperature dependent 1H-NMR studies, 1D-NOE-measurements, and titration experiments, with the theoretical tools being EFF and CFF91 molecular mechanics calculations. The structural information deduced from these investigations is shown to bear on the enantioseparation of the corresponding chiral stationary phase towards derivatized amino acids. These observations, taken together, help to rationalize the mode of enantiomer-separation by amide phases as involving predominantly C7-hydrogen bonding sites. Chirality 10:396-404, 1998. © 1998 Wiley-Liss, Inc.
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  • 77
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    Chirality 10 (1998), S. 195-209 
    ISSN: 0899-0042
    Keywords: molecular imprinting ; molecular recognition ; chirality ; chromatography ; catalysis ; biosensor ; immunoassay ; antibody mimic ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular imprinting is a technique for the fabrication of biomimetic polymeric recognition sites or “plastic antibodies/receptors” which is attracting rapidly increasing interest. By this technology, recognition matrices can be prepared which possess high substrate selectivity and specificity. In the development of this technology, several applications have been foreseen in which imprinted materials may be exchanged for natural recognition elements. Thus, molecularly imprinted polymers have been used as antibody/receptor binding mimics in immunoassay-type analyses, as enzyme mimics in catalytic applications and as recognition matrices in biosensors. The best developed application area for imprinted materials, though, has been as stationary phases for chromatography, in general, and chiral chromatography, in particular. This review seeks to highlight some of the more intriguing advantages of the technique as well as pointing out some of the difficulties encountered. The prospects for future development will also be considered. Chirality 10:195-209, 1998. © 1998 Wiley-Liss, Inc.
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  • 78
    ISSN: 0899-0042
    Keywords: hexahelicene ; sulphoxides ; carbohydrate carbamate ; chiral preparative ; silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparative enantiomeric resolutions of hexahelicen-7-yl acetic acid methyl ester and two sulphoxides were performed on cellulose tris(3,5-dimethylphenylcarbamate) coated onto aminopropylated 5-μm silica with 120-Å diameter pore. High enantiomeric purity was obtained for both enantiomers. The enantioselectivity of the amylose tris(3,5-dimethylphenylcarbamate), cellulose and amylose tris(phenylcarbamate) phases for the hexahelicen-7-yl acetic acid derivative were also investigated. Chirality 10:573-577, 1998. © 1998 Wiley-Liss, Inc.
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  • 79
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    Chirality 10 (1998), S. 587-591 
    ISSN: 0899-0042
    Keywords: snuff ; chewing tobacco ; Turkish tobacco ; Burley tobacco ; Virginia tobacco ; transdermal patches ; gum ; nasal spray ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric composition of nicotine in 18 smokeless tobaccos, 3 strains of tobacco leaf, 8 pharmaceutical products, and 4 commercial reagents was determined. The relative amount of the minor enantiomeric component, (R)-(+)-nicotine, ranged from ∼0.1% to ∼1.2% of the total nicotine in all samples. In some cases it appears that (R)-(+)-nicotine may be considered one of the five most common alkaloids in tobacco products. The highest level of (R)-(+)-nicotine was found in a commercial transdermal patch. The extraction and purification processes used in obtaining commercial (S)-(-)-nicotine supplies from tobacco do not appear to decrease the amount of (R)-(+)-nicotine present. Chirality 10:587-591, 1998. © 1998 Wiley-Liss, Inc.
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  • 80
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    Chirality 10 (1998), S. 600-618 
    ISSN: 0899-0042
    Keywords: steroidal bile acids ; inclusion compounds ; crystal structures ; facial molecules ; amphiphilic molecules ; amphiphilic sheets ; hydrogen-bonding networks ; head-to-tail ; head-to-head ; tail-to-tail ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral compounds, N-methyl-, N-ethyl-, and N-n-propylcholamides, form crystalline inclusion compounds with water or small organic substances. The compounds were analyzed by X-ray diffraction methods. It was found that the crystals have bilayered structures accumulated by chiral molecular sheets. The chiral molecules associate in a unique head-to-head/tail-to-tail and right-to-left motif to give chiral and amphiphilic sheets. Such sheets stack by adhesions between the hydrophilic sides and between the lipophilic sides. The alkyl groups of the amides prompt the formation of a hydrogen-bonding network between the tails instead of a cyclic one between the head and tail. The guest molecules are accommodated into small cavities between the steroidal side chains. Chirality 10:600-618, 1998. © 1998 Wiley-Liss, Inc.
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  • 81
    ISSN: 0899-0042
    Keywords: chiral separation ; chiral selector ; separation of enantiomers ; liquid chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chiral stationary phase (CSP 1) prepared starting from (R)-4-hydroxyphenylglycine and then grafting (R)-N-butanoyl-4-allyloxyphenylglycine N-propyl amide to silica gel was found to be very effective in separating the enantiomers of N-(3,5-dinitrobenzoyl)-α-amino amides. From the chromatographic behaviors of the resolution of N-propyl amides, N,N-diethyl amides and ethyl esters of N-(3,5-dinitrobenzoyl)-α-amino acids and the resolution of various N-(substituted benzoyl)leucine N-propyl amides, the hydrogen bonding and the π-π donor-acceptor sites of the analyte for the interaction with the CSP have been proposed. Similarly, the hydrogen bonding donor and acceptor sites of the CSP for the interaction with the analyte have been proposed from the comparison of the chromatographic behaviors of the resolution of various N-(3,5-dinitrobenzoyl)-α-amino N-propyl amides on modified CSPs (CSP 7 containing trifluoroacetyl group instead of the butanoyl group of CSP 1 and CSP 8 containing N,N-diethyl group instead of the N-propyl group of CSP 1) with those on CSP 1. By correlating the interaction sites of the CSP and their complementary interaction sites of the analyte, a chiral recognition mechanism which utilizes the two hydrogen bonding interactions and the π-π donor-acceptor interaction between (R)-CSP 1 and more retained analytes, (S)-N-(3,5-dinitrobenzoyl)-α-amino amides, has been proposed. Chirality 10:592-599, 1998. © 1998 Wiley-Liss, Inc.
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  • 82
    ISSN: 0899-0042
    Keywords: nucleophilic aromatic substitution ; optical resolution ; asymmetric synthesis ; diastereoselective reaction ; Grignard reaction ; atrolactic acid derivatives ; biaryl coupling reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel 1-aryl-9H-fluoren-9-ols 1 were conveniently synthesized by using the ester-mediated nucleophilic aromatic substitution on 2,6-dimethoxybenzoate 2 by aryl Grignard reagents as the key step. Racemic 1-phenylfluorenol 1a was converted to the diastereomeric esters 8 of (S)-2′-methoxy-1,1′-binaphthyl-2-carboxylic acid, which were readily separable by silica-gel column chromatography. Reduction of the optically pure diastereomer (+)-8 with LiAlH4 accompanied an appreciable racemization to give (+)-1a of 89% ee, which provides the first isolation of an optically active fluorenol of defined enantiomeric purity. Intrinsic chiral induction abilities of the 9-fluorenols 1 were examined in the atrolactic acid synthesis from phenylglyoxylates 9 and methylmagnesium iodide with diastereoselectivity of up to 85% de and the binaphthyl coupling of 1-methoxy-2-naphthoates 11 with 2-methoxy-1-naphthylmagnesium bromide with up to 73% de. Chirality 10:619-626, 1998. © 1998 Wiley-Liss, Inc.
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  • 83
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    Chirality 10 (1998), S. 661-666 
    ISSN: 0899-0042
    Keywords: chiral dendrimers ; dendrimers ; axial chirality ; (R)-(+)-1,1′-bi-2,2′-naphthol ; optical rotation ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and optical activity of novel chiral dendrimers with axial chirality are reported. The dendrimers were constructed by coupling of the polyether dendritic bromides with (R)-(+)-1,1′-bi-2-naphthol (1). The uniform (2, 3, 4) and non-uniform double-O-alkylated (8, 9, 10) as well as mono-O-alkylated (5, 6, 7) products were thus obtained. These chiral molecules were characterized by 1H- and 13C-NMR, elemental analysis, optical rotation, adsorption spectra, and circular dichroism. It was found that the specific rotation decreases with the increase of the number of generation for each group of dendrimers (2-4, 5-7, and 8-10, respectively). In terms of the molar rotation, it was quite different; the molar rotation increased sharply for dendrimers, 2-4, but only slightly for dendrimers 5-7. The dihedral angle change of bi-naphthyl in the synthesized dendrimers was discussed based on the CD spectra. Chirality 10:661-666, 1998. © 1998 Wiley-Liss, Inc.
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  • 84
    ISSN: 0899-0042
    Keywords: avoparcin ; macrocyclic antibiotics ; enantiomeric separations ; chiral stationary phases ; verapamil ; thyroxine ; mephenytoin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Avoparcin is a macrocyclic glycopeptide antibiotic structurally related to vancomycin, teicoplanin, and ristocetin A. When attached to 5-μm spherical silica gel, the avoparcin proved to be an effective chiral stationary phase (CSP) that could be used in the reversed-phase, normal-phase, and polar-organic modes. The avoparcin CSP was complimentary to the other macrocyclic glycopeptide CSPs in that it could resolve some racemates that the others could not, and vice versa. Some important compounds resolved on the avoparcin CSP include verapamil, thyroxine, mephenytoin, and 2-imidazolidone-4-carboxylic acid. The use of this CSP and the optimization of separations on it are discussed. Avoparcin appears to be a useful addition to this family of CSPs. Chirality 10:627-660, 1998. © 1998 Wiley-Liss, Inc.
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  • 85
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    Chirality 10 (1998), S. 693-698 
    ISSN: 0899-0042
    Keywords: Pseudomonas cepacia ; lipase PS ; transesterification ; kinetic resolution ; 2-substituted 3-hydroxy ester ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic resolution of 2-substituted 3-hydroxy esters was examined by lipase PS catalyzed transesterification using vinyl acetate as an acyl donor. Resolution of (±)-syn- and -anti-1a, -1e possessing a small methyl group at the C-3 position was accomplished enantioselectively. The outcome of the resolution seems to be related to the differences in size of the substituents at the stereocenter bearing a secondary hydroxy group. Chirality 10:693-698, 1998. © 1998 Wiley-Liss, Inc.
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  • 86
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    Chirality 10 (1998), S. 676-681 
    ISSN: 0899-0042
    Keywords: β-glucosidase from almond ; reverse hydrolysis ; transglucosylation ; enantioselectivity ; enantiomeric excess ; absolute configuration ; alkyl β-D-glucopyranoside ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Almond β-glucosidase was used to catalyze the synthesis of alkyl β-d-glucopyranosides 1b-3b starting from either d-glucose (4) or phenyl-β-d-glucopyranoside (5) and the racemic alcohols 1a-3a. The enzymic reactions were provided in different acetonitrile/water mixtures [9:1 (v/v) for the reverse hydrolysis, and 1:9 (v/v) for the transglycosylation]. Both enzymic reactions, that is, the reverse hydrolysis and the transglucosylation, are enantioselective processes. The enantiomeric purity of products 1b-2b of the enzymic reactions varied between 75 and 86% ee, the values of which were based on the analysis of the aglyconic parts (1c-2c) of the alkyl β-d-glucopyranoside molecules (1b-2b). Chirality 10:676-681, 1998. © 1998 Wiley-Liss, Inc.
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  • 87
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 682-692 
    ISSN: 0899-0042
    Keywords: optically active ; epichlorohydrin ; 3-chloro-1,2-propanediol ; microbial resolution ; dehalogenation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Production of highly optically active C3 and C4 chlorohydrins was developed by using the bacteria stereoselectively dehalogenating and assimilating the racemic substrate: Pseudomonas sp. and Alcaligenes sp. These bacteria stereoselectively assimilate (RS)-2,3-dichloro-1-propanol (DCP) and (RS)-3-chloro-1,2-propanediol (CPD) followed by microbial preparation of (R)- and (S)-DCP, and (R)- and (S)-CPD with 〉99% ee. A novel dehalogenating enzyme, halohydrin dehydro-dehalogenase from one of the above strains, Alcaligenes sp. DS-S-7G, was applicable for preparation of optically active 1,2-diols with 60-99% ee. Moreover, microbial resolution of C4 chlorohydrins with whole cells of Pseudomonas sp. was carried out. This resolution reaction using the resting cells gave (R)- and (S)-4-chloro-3-hydroxybutyrate (CHB) and (S)-4-chloro-3-hydroxybutyronitrile (BN) with 〉98% ee. In the case of the resting cells of Enterobacter sp., both (R)-CHB (〉99% ee) and (S)-3-hydroxy-γ-butyrolactone (95% ee) with excellent yield were obtained. Also, some typical synthetic applications using the above chiral C3 and C4 synthons were introduced: ferroelectric liquid crystals, optically active β-blockers, and other chiral pharmaceuticals. Chirality 10:682-692, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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  • 88
    ISSN: 0899-0042
    Keywords: polysilane ; circular dichroism ; exciton couplet ; helix ; fluorescence ; poor solvent ; good solvent ; conformational property ; helix reversal ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An optically active, rigid rodlike helical polysilane with 6,9,12-trioxatetradecyl and (S)-2-methylbutyl substituents (1) was newly obtained as a very high molecular weight polymer of several million. Due to the presence of trietheral substituent, 1 was readily soluble in a polar solvent such as ethanol and a mixture of ethanol and water, but was insoluble in pure water. Polysilane 1 in pure ethanol at room temperature exhibited an intense and narrow ultraviolet (UV) and circular dichroism (CD) absorptions at 323 nm, associated with an almost mirror imaged fluorescence (FL) at 328 nm, that are characteristic of rigid rodlike, single-screw-sense helical polysilanes reported previously. When solution temperature was changed from 60°C to -104°C, a global shape of 1 expanded associated with an increase of segment length, whereas a screw pitch tended to be wound tightly. On the other hand, as a solvent polarity became poor, a global shape of 1 shrunk associated with an decrease of segment length and formed a chiral motif with an M-helicity between two helical segments with a kink. At a ratio of 50% of ethanol/water of 50:50 (v/v), 1 became insoluble and formed aggregates. Chirality 10:667-675, 1998. © 1998 Wiley-Liss, Inc.
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  • 89
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 711-716 
    ISSN: 0899-0042
    Keywords: stereospecific polymerization ; chiral α-substituted acrylate ; stereoregularity ; chiroptical property ; isotactic polymer ; regular arrangement ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel chiral monomer, benzyl α-[(1-phenylethoxy)methyl]acrylate was synthesized, and the stereoregularity and chiroptical property of the polymers obtained by radical and anionic polymerizations were investigated. Anionic polymerization in toluene provided a polymer with high isotacticity regardless of optical purity of the monomer and difference of counter cations, Li+ and Mg2+, while radical polymerization appears to yield an atactic polymer. The isotactic copolymers anionically obtained from a mixture of (R)- and (S)-monomers showed peak splitting probably due to the triad arrangement of (R) and (S) groups of side chains in the resonance of 13C-NMR spectra. The isotactic polymer prepared from enantiomerically pure (R)-monomer ([α] 25 365 = +157°) with n-BuLi in toluene exhibited higher specific rotation ([α] 25 365 = +262°) than that of the radical polymer ([α] 25 365 = +162°). This may be explained by regular arrangement of optically active groups along the polymer chain of the isotactic polymer. Chirality 10:711-716, 1998. © 1998 Wiley-Liss, Inc.
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  • 90
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 699-704 
    ISSN: 0899-0042
    Keywords: ormeloxifene ; chiral separation ; sulfated cyclodextrin ; enantiomers ; capillary electrophoresis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-Ormeloxifene, a drug candidate under development, was separated from (+)-ormeloxifene using capillary electrophoresis (CE) with sulfated β-cyclodextrin as chiral buffer additive. With conventional long-end injection the method showed high efficiency, since the theoretical plate number for (-)-ormeloxifene was over 1 million per m and the enantiomeric resolution was more than 100. However, the relatively long separation time of ∼22 min was a limiting factor. In order to reduce separation time, short-end injection experiments were carried out. By using the instrumental limits for capillary dimensions and field strength, the separation time was reduced to 〈40 sec. A further and significant reduction was achieved by applying extended short-end injection, which is a novel injection technique presented in this paper. With the extended short-end injection procedure, a plug of run buffer is injected after the sample has been injected, thus moving the sample closer to the detector and resulting in very short effective capillary lengths. Using the extended short-end injection technique, the separation was performed on 1.8 cm capillary (effective length) and the enantiomers were separated within 10 sec, which is a reduction of the original separation time by a factor of ∼155. Chirality 10:699-704, 1998. © 1998 Wiley-Liss, Inc.
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  • 91
    ISSN: 0899-0042
    Keywords: preferential enrichment ; enantiomeric enrichment ; mixed crystal ; solid solution ; racemic compound crystals ; X-ray crystallography ; chiral ammonium sulfonate ; reversal of chirality ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal structure of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylammonium p-nitrobenzenesulfonate [(±)-NNMe2], which shows the novel enantiomeric resolution phenomenon Preferential Enrichment, has been compared with that of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy) phenylcarbamoyl]ethyl]dimethylammonium p-toluenesulfonate [(±)-NTMe2], which does not show the phenomenon. The stable crystalline form of (±)-NNMe2 is a racemic compound, while that of (±)-NTMe2 is a mixed (disordered) crystal composed of the two enantiomers. The intermolecular hydrogen bonding mode in the crystal of (±)-NNMe2 was very different from that of (±)-NTMe2. Chirality 10:705-710, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 92
    ISSN: 0899-0042
    Keywords: zirconium ; binaphthol (BINOL) ; allylation ; asymmetric activation ; enantioselective carbon-carbon bond formation ; chiral high-performance liquid chromatography ; induction period ; product-like activator ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymmetric activation of binaphthol (BINOL)-zirconium catalysts is described on the enantioselective allylation of benzaldehyde with allyltin reagents. This model reaction has been used with the intention of establishing a protocol for a zirconium-based catalyst system, to be followed by structural studies. Initial results are reported that characterise a number of interesting features, namely the influence of an induction period and a high level of asymmetric activation obtained after addition of a product-like activator. Chirality 10:717-721, 1998. © 1998 Wiley-Liss, Inc.
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  • 93
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 95-99 
    ISSN: 0899-0042
    Keywords: β-amino alcohols ; enantiopure ; chiral ligands ; regioselective ; stereoselective ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both enantiomers of the important chiral β-amino alcohols erythro-2-amino-1,2-diphenylethanol were obtained via the separation of diastereoisomeric N-chlorinated derivatives of racemic trans-stilbene oxide and (S)-α-methylbenzylamine. The incorporation of chlorine in these precursors facilitated both the separation of diastereoisomers and the removal of the α-methylbenzyl chiral adjuvant. Each enantiopure β-amino alcohol was converted (Mitsunobu conditions) into the corresponding trans-2,3-diphenylaziridine in good overall yield. Chirality 10:95-99, 1998. © 1998 Wiley-Liss, Inc.
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  • 94
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 120-124 
    ISSN: 0899-0042
    Keywords: libraries ; asymmetric reduction ; oxazaborolidine ; chiral hplc ; chiral benz- hydrols ; borane ; combinatorial chemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The advantages and disadvantages of the one-pot multi-substrate screening in asymmetric catalysis are discussed. The specific case of asymmetric reduction of ketones has been studied and is examplified by borane reduction catalyzed by an oxazaborolidine derived from (S)-diphenylproline. Chirality 10:120-124, 1998. © 1998 Wiley-Liss,Inc.
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  • 95
    ISSN: 0899-0042
    Keywords: chiral CE ; maltooligosaccharides ; cellooligosaccharides ; cis-diltiazem ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Twelve different disaccharides and a series of noncyclic malto- and cello-oligosaccharides were used as chiral selectors in capillary electrophoresis (CE). Most saccharides resolved the enantiomers of atropisomeric 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (BDHP) depending on the type (α or β) and position of the linkage between monosaccharides. The effect of chain length of malto- and cello-oligosaccharides on enantioseparation of BDHP was also investigated. The nature of cations in background electrolytes affected significantly the separation of BDHP enantiomers. Chirality 10:134-139, 1998. © 1998 Wiley-Liss,Inc.
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  • 96
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    Chirality 10 (1998), S. 125-133 
    ISSN: 0899-0042
    Keywords: molecular topology ; catenane ; trefoil knot ; template effect ; circular dichroism ; enantiomers ; resolution methods ; 1,10-phenanthroline ; (S)-(+)-1,1′-binaphthyl-2,2′-diyl phosphate ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of topologically chiral molecular objects cannot be interconverted by a continuous deformation. It must be noted that this behavior is opposite to that of molecules showing classical or Euclidian chirality. Interlocked oriented rings and the trefoil knot are prototypical topologically chiral objects. We have been designing a transition-metal templated route to the corresponding real molecules (i.e., [2]-catenanes and molecular knots) using copper(I) as the template and 2,9-diphenyl-1,10-phenanthroline (dpp) based ligands. The precursor to the catenane species was a tetrahedral Cu(dpp)2+ complex in which the two ligands fit in around Cu(I), thereby allowing the interlocking process. In the case of the knot, the precursor was a double-stranded helical complex in which two bis-phenanthroline ligands wrap around two Cu(I) ions. The compounds were obtained as racemates and were resolved as their Cu(I) complexes either by HPLC on chiral stationary phases or by diastereoselective crystallization. For the trefoil knot (K · 2Cu+), the latter method proved to be the most efficient. It took advantage of the dicationic nature of the species to be resolved. The original triflate anion was exchanged by an optically pure anion (S)-(+)-1,1′-binaphthyl-2,2′-diyl phosphate ((+)-BNP-) and the diastereomer (+)-K · 2Cu+ · 2(+)BNP- was selectively crystallized in a mixture of nitromethane and benzene. Removal of the Cu(I) ions by treatment with cyanide afforded an enantiomerically pure molecular knot (K), showing an optical rotatory power close to +2,000° · mol-1 · L · dm-1. Chirality 10:125-133, 1998. © 1998 Wiley-Liss,Inc.
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  • 97
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    Chirality 10 (1998), S. 106-119 
    ISSN: 0899-0042
    Keywords: porphyrin ; chiral ; oxidation ; mechanism ; enantioselective ; asymmetric catalysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective catalytic epoxidation of olefins is an important problem from both practical and mechanistic points of view. The origins of chiral induction by asymmetric porphyrin and salen complexes were investigated by FT-NMR T1 relaxation techniques. A new chiral vaulted porphyrin (1) that carries (S)-binaphthyl-L-alanine straps across both faces of the porphyrin macrocycle was synthesized and characterized. (R)-styrene oxide was obtained in 〉90% ee in the initial stages of styrene epoxidation with F5PhIO catalyzed by 1-Fe(III)Cl. The transition state for olefin epoxidation with high-valent metal-oxo species was modeled by coordinating epoxides to paramagnetic copper complexes of the corresponding ligands. The epoxide enantiomer that better fit the chiral cavity of the catalyst, as revealed by T1 relaxation measurements, was also the major product of catalytic olefin epoxidation. These results are consistent with the “lock-and-key” mechanism of asymmetric catalysis by metalloporphyrins. The copper complex of a chiral salen ligand showed no differentiation in terms of T1 relaxation rates between the enantiomers of cis-β-methylstyrene oxide in contrast to the high enantioselectivity observed for catalytic epoxidation. Chirality 10:106-119, 1998. © 1998 Wiley-Liss,Inc.
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  • 98
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    Chirality 10 (1998), S. 140-146 
    ISSN: 0899-0042
    Keywords: enantioselective chromatography ; chiral selectands ; chiral selectors ; peak coalescence ; enantiomer separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Six scenarios of peak coalescence are distinguished in enantioselective chromatography. Where appropriate, they are verified by an experiment. Chirality 10:140-146, 1998. © 1998 Wiley-Liss, Inc.
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  • 99
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 154-158 
    ISSN: 0899-0042
    Keywords: polycyclic aromatic hydrocarbons ; arynes ; cyclopentadienones ; conformation ; steric hindrance ; rotational barriers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two exceptionally crowded derivatives of octaphenylnaphthalene bearing ortho-methyls on the phenyl substituents - 2,3,5,6,7,8-hexaphenyl-1,4-di(o-tolyl)naphthalene (2) and 2,3,6,7-tetraphenyl-1,4,5,8-tetra(o-tolyl)naphthalene (3) - were prepared by the addition of tetraarylbenzynes to tetraarylcyclopentadienones. Both compounds exist as a mixture of conformational isomers which do not interconvert at ordinary temperatures. The yield of 2 and its distribution of conformers is strongly influenced by the choice of precursors in the final cycloaddition; one method gives a high yield of a 55:45 trans-2:cis-2 mixture, while another gives a very low yield of a 15:85 trans-2:cis-2 mixture. Kinetic epimerization of the latter indicated that the barrier to rotation about the tolyl-naphthalene bonds is 33.1 kcal/mol. Chirality 10:154-158, 1998. © 1998 Wiley-Liss, Inc.
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  • 100
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 147-153 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the chiral 9,12-dimethyl-4-oxa[7]paracyclophane 3 was achieved by the dithia route with subsequent sulfone pyrolysis. The conformational flexibility of the oxamethylene bridge with local Cs symmetry is evident from low temperature NMR experiments. Experimentally, an activation enthalpy of 11.4 kcal/mol is found for this process, which is in good agreement with the rotational barrier derived from semiempirical AM1 calculations (10.2 kcal/mol). Ab initio Hartree-Fock geometry optimizations have been performed for 3 and the corresponding hydrocarbon 9,12-dimethyl[7]paracyclophane 4. The distance of the O-atom to the center of the benzene ring in the structure of 3 is only 2.784 Å, i.e., significantly closer than the analogous C4-benzene ring distance in the slightly more strained 4 (3.112 Å). The enantiomeric separation of (±3) has been achieved by HPLC and the circular dichroism (CD) spectrum is reported. Ab initio all-electron DFT/SCI calculations of the CD spectrum are in good agreement with the experimental data and reveal the importance of p(O-atom)→ π* charge-transfer type excited states at relative low energies (6.6 eV, 188 nm) responsible for an intense negative CD band. The benzene type π → π* states are energetically lowered by 0.4-0.8 eV due to the boat-type deformation of the benzene moiety. By comparison of theoretical and experimental CD data the absolute configuration of 3 is assigned as (-)-(S). Chirality 10:147-153, 1998. © 1998 Wiley-Liss, Inc.
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