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  • Organic Chemistry  (15)
  • Wiley-Blackwell  (15)
  • American Institute of Physics (AIP)
  • Blackwell Science Pty
  • Macmillian Magazines Ltd.
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1059-1074 
    ISSN: 0947-3440
    Keywords: Molecular glycobiology ; Oligosaccharides ; Carbohydrates ; Molecular recognition ; Polyvalent receptor-ligand interaction ; Enzyme inhibitors ; Carbohydrate mimetics ; Multienzyme synthesis ; Carbohydrate synthesis ; Recombinant enzymes ; Glycosyltransferases ; Glycosidases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbohydrates are increasingly appreciated for their critical roles in biological functions. Driving these studies addressing the molecular basis of carbohydrate-mediated events is the availability of natural and unnatural carbohydrates. Recently, new methods of enzymatic synthesis have been developed that now afford rapid access to complex, structurally diverse oligosaccharides on large scales. This methodology has been essential to gaining insight into the molecular details of important carbohydrate recognition phenomena that are associated with many signaling processes. This review summarizes recent chemical studies examining selectin/sialyl Lewisx binding, a key event in inflammation and metastasis, and describes the development of carbohydrate mimetics that may offer leads to new therapeutic agents. In addition, combinatorial synthesis has been used to prepare carbohydrate mimetics to neomycin B, an aminoglycoside that binds RNA involved in HIV infection, and chemoenzymatic methodology has been applied to the design and synthesis of mechanism-based inhibitors of glycoprocessing enzymes.
    Additional Material: 10 Ill.
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  • 2
    ISSN: 0170-2041
    Keywords: Iodination, ipso- ; Cross-coupling reaction ; Boroxines ; Furans ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Iodo-3-trimethylsilylfuran (2), obtained through the regio-Specific iodination of 3,4-bis(trimethylsilyl)furan (1), underwent either palladium- or nickel-catalyzed cross-coupling reactions with terminal alkenes, terminal alkynes, areneboronic acids, bis(p-methoxycarbonylbenzyl)zinc and Grignard reagents to give 4-substituted 3-(trimethylsilyl)furans 3-7, which were converted into boroxines 8. Regiospecific iodination of 8 gave iodofurans 9, which afforded in the usual way unsymmetrical 3,4-disubstituted furans 10. Boroxines 8 gave also 3,4-disubstituted furans 11 via palladium-catalyzed cross-coupling reactions with piperonyl chloride and vinyl bromide.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 1 (1987), S. 235-239 
    ISSN: 0268-2605
    Keywords: Environment ; Transmethylation ; Alkyllead ; Alkyltin ; Methylarsenic compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transmethylation reactions between organometals and metal ions in aqueous solutions in biotic and abiotic systems, with and without the presence of sediment, were investigated. It was found that alkyllead compounds can transfer their alkyl groups to Sn(II) and Sn(IV) ions to form various methyltin compounds in biotic and abiotic systems. The presence of sediment enhanced the transmethylation reactions. Methyltin compounds do not transfer their methyl groups of Pb(II). Methylarsenic acids transfer their methyl groups to Sn(II) and Sn(IV) in an abiotic system, but not in a biotic system containing sediment. The strong adsorption of tin onto sediment was the reason for the non-availability of tin ions for methylation. Methylarsenic acids do not transmethylate Pb(II). Other alkyllead compounds, such as ethyllead and butyllead species were also able to transfer their alkyl groups to tin. When both trimethyllead and triethyllead species are present in the same system, only the individual monoalkyl tin species were formed in both the Sn(II) and Sn(IV) solutions. No mixed alkyltin was produced. The findings of this study suggest that alkyllead compounds, if present in the environment, could be potential methylating agents for the formation of other methylmetals, such as methyltins. Methyltin compounds have already been documented to methylate mercuric ions in aqueous solution. Thus the study of transmethylation reactions opens up a new area of research that is essential in predicting the fate of organometals in the environment.
    Additional Material: 4 Tab.
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  • 4
    ISSN: 0268-2605
    Keywords: Bioaccumulation ; alkyllead ; sediment ; mussels ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bioconcentration of alkyllead compounds from water and from contaminated sediments by freshwater mussels (Elliptio complanata) has been investigated. Higher levels of trimethyllead than triethyllead species are accumulated for the same exposure period. In-vivo transformation of the trialkyllead species by a series of dealkylation reactions giving dialkyllead and inorganic lead(II) species appears to take place. Rates of accumulation are higher for the more contaminated sediments.
    Additional Material: 5 Ill.
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  • 5
    ISSN: 0268-2605
    Keywords: Environmental analysis ; alkyllead ; tetraethyllead ; triethyllead ; lead ; fish ; clam ; macrophyte ; sediment ; water ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analyses of fish and other environmental samples (clams, macrophytes, sediments and waters) from areas upstream and downstream from two alkyllead manufactures beside the St Lawrence and St Clair Rivers, Ontario, show a clear indication of elevated alkyllead levels in samples near the industries. Most species of fish contained alkyllead compounds with tetraethyllead and triethyllead as the predominant forms. Most fish from the contaminated areas contained 50-75% of total lead as alkylleads. Carp, yellow perch and white sucker were generally the most contaminated species while pike, alewife and rock bass were the least contaminated. Average alkyllead levels varied from year to year but declined steadily after 1981. For example, the geometric mean of alkyllead compounds in carp from the St Lawrence River decreased from 4207 μg kg-1 in 1981 to 2000 μg kg-1 in 1982 and to 49 μg kg-1 in 1987, reflecting the reduction of alkylleads in the effluents and the closure of one of the manufactures in 1985. Alkyllead levels were consistently lower in muscle and carcass samples in comparison with whole fish containing fatty intestines. However, muscle levels were generally equal to carcass levels.The concentrations of alkyllead compounds were generally low in clams, macrophytes, sediments and waters except from the immediate vicinity of the manufactures' final effluent discharges.
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 8 (1994), S. 385-391 
    ISSN: 0268-2605
    Keywords: Butyltin ; marinas ; Severn Sound ; Lake Huron ; Canada ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Severn Sound is a heavily used recreational and beating area in the southeast corner of Georgian Bay, Lake Huron, Canada. Because of the concern over the possible release of tributyltin species (TBT) from antifouling paints on boat hulls and marinas, surveys were carried out in 1989 and 1992 to determine the presence of this species and its degradation products dibutyltin (DBT) and monobutyltin (MBT) in this area. Many fish (pike and young-of-the-year spottail shiners) and sediment samples collected in 1989 contained detectable levels of TBT. A maximum concentration of TBT was recorded in northern pike in the spring to be 240 ng Sn g-1. Maximum levels occurred in marinas during the beginning of the boating season and significantly reduced during the summer and early autumn, although the maximum value of TBT in sediment (392 ng Sn g-1) was observed in the summer of 1989. The seasonal variation of TBT levels was further substantiated in the subsequent 1992 study, in which sediments from three areas in a marina were sampled at monthly intervals from May to October. TBT levels were much higher in May and then generally decreased with time. Mussels (Elliptio complanta) caged in the marina for three months also contained TBT. DBT was frequently detected in the sediments but less frequently in fish and mussels. MBT was generally below detection limits. Plants (macrophytes and cladophora) contained very small amounts of butyltin compounds.
    Additional Material: 1 Ill.
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  • 7
    ISSN: 0947-3440
    Keywords: Furans ; Thiophens ; Palladium catalysis ; Coupling reactions ; Heterocycles ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiospecific synthesis of 3,4-disubstituted furans and thiophenes is reviewed. Our initial approach used 3,4-bis(tri-n-butylstannyl)furan as a building block, which led to many structurally diverse 3,4-disubstituted furans. Another avenue was explored by using 3,4-bis(trimethylsilyl)furan and 3,4-bis(trimethylsilyl)thiophene as precursors. A variety of unsymmetrically 3,4-disubstituted furans and thiophenes were prepared in this way. The advantages of our strategy lie in its stepwise manner as well as its prospect of yielding 3,4-disubstituted furans and thiophenes with rather different substitution pattern.
    Additional Material: 5 Tab.
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of tribenzo[a,c,e]cyclooctene (2) and its 2,3- and 1,4-dimethyl derivatives (4 and 5), as well as of 1,1-dimethyl-10,11-propane-2,2-diylidene-1H-benzo[5,6]cycloocta[1,2,3,4-def]fluorene (6) and its 5,6-didehydro derivative (7) was followed by cyclic voltammetry. The radical anions of these compounds and those of their derivatives (D)2, (D)5, and (D)6, deuteratsd at C(9) in 1 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. The cyclic-voltammetric and proton-hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order These deviations, due to steric or interferences in the peri-positions 1↔14 and 4↔5, are removed in and by the introduction of bridging groups. The non-plalarity affects the thermodynamic and kinetic stabilities of the radical anions and causes a shift in the π-spin distribution away from that benzene ring which is linked to the two others by the essential single bonds C(4a)—C(4b) and C(14a)—C(14b). This finding suggests that the steric hindrance in , and is alleviated by twisting this ring out of coplanarity with the remaining (Z)-stilbene-like π-system.
    Additional Material: 6 Ill.
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  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ESR.-spectra are reported for the radical anion and the radical cation of benzo[b]-biphenylene (III). Comparison of the proton coupling constants (aHμ) for III · ⊖ and III · ⊕ with π-spin populations (ϱμ), calculated by the McLachlan procedure, permits a lower limit of 0.77 to be set for the parameter κ = β′/β where β′ represents a reduced value of the HMO integral for the two essentially single bonds linking the benzene with the naphthalene π-system. The differences in the aHμ values for III · ⊖ and III · ⊕ are substantially larger than those generally found for the two corresponding radical ions of alternant, purely benzenoid hydrocarbons, but they closely parallel the analogous differences observed for the radical anion and the radical cation of biphenylene.
    Additional Material: 4 Ill.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anions of 5,6-didehydrobenzocyclooctene (3), 5,6,9,10-tetradehydrobenzocyclooctene (4) and 1,4,7,10-tetramethyl-5,6-didehydrodibenzo[a, e]-cyclooctene (6) were prepared in situ from dibromo-precursors and have been characterized by ESR and ENDOR spectroscopy.
    Additional Material: 3 Ill.
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