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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: PY54 is a temperate phage isolated from Yersinia enterocolitica. Lysogenic Yersinia strains harbour the PY54 prophage as a plasmid (pY54). The plasmid has the same size (46 kb) as the PY54 genome isolated from phage particles. By electron microscopy, restriction analysis and DNA sequencing, it was demonstrated that the phage and the plasmid DNAs are linear, circularly permuted molecules. Unusually for phages of Gram-negative bacteria, the phage genome has 3′-protruding ends. The linear plasmid pY54 has covalently closed ends forming telomere-like hairpins. The equivalent DNA sequence of the phage genome is a 42 bp perfect palindrome. Downstream from the palindrome, an open reading frame (ORF) was identified that revealed strong DNA homology to the telN gene of Escherichia coli phage N15 encoding a protelomerase. Similar to PY54, the N15 prophage is a linear plasmid with telomeres. The N15 protelomerase has cleaving/joining activity generating the telomeres by processing a 56 bp palindrome (telomere resolution site tel RL). To study the activity of the PY54 protein, the telN-like gene was cloned and expressed in E. coli. A 77 kDa protein was obtained and partially purified. The protein was found to process recombinant plasmids containing the 42 bp palindrome. Telomere resolution of plasmids under in vivo conditions was also investigated in Yersinia infected with PY54. Processing required a plasmid containing the palindrome as well as adjacent DNA sequences from the phage including an additional inverted repeat. Regions on the phage genome important for plasmid maintenance were defined by the construction of linear and circular miniplasmid derivatives of pY54, of which the smallest miniplasmid comprises a 4.5 kb DNA fragment of the plasmid prophage.
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  • 2
    ISSN: 1434-193X
    Keywords: Asymmetric dihydroxylation (Sharpless-AD) ; Wittig olefination ; α-Bromo α,β-unsaturated esters ; Diastereoselective aprotic Michael domino reaction ; Tricyclo[3.2.1.02,7]octanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral α-bromo α,β-unsaturated esters 3 and 9 are prepared by asymmetric Sharpless dihydroxylation (AD) of 5 and from ester 7 and the chiral diols 8 by transacetalization, respectively. Both types of α-bromo α,β-unsaturated ester react with the kinetic lithium dienolates of enone 10 to give functionalized tricyclo[3.2.1.02,7]octanes 11. Esters 3 give one single diastereomer (de ≥ 95%), whereas mixtures of diastereomers (de 28 to 46%) are obtained with the esters 9.
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  • 3
    ISSN: 0947-3440
    Keywords: Peterson olefination ; Horner Emmons olefination ; Diastereoselective aprotic Michael cascade reaction ; Tricyclo[3.2.1.02,7]octanes ; Bicyclo[3.2.1]octanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the easily accesible chiral aldehyde 2, we obtained enantiomerically pure (Z)- and (E)-α,-chloro-α,β-unsaturated esters 4c in good yields by olefination reactions. (Z)-and (E)-4c were allowed to react with the kinetically controlled generated lithium dienolate Li-7 to give the enantiomerically pure tricyclo[3.2.1.02,7]octanes 8 and 9, respectively. The „push-pull“ substituted cyclopropane moiety of 8 was opened to give solely bicyclo[3.2.1]octane 10.
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  • 4
    ISSN: 1434-193X
    Keywords: Cascade reaction ; Aprotic Michael reaction ; Tricyclo[3.2.1.02,7]octanes ; Bicyclo[3.2.1]octanes ; Deprotonated cyclopropanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2′-Alkoxytricyclo[3.2.1.02,7]octanes 4-R are obtained in good to excellent yields from methyl 2-chloro-2-cyclopropylideneacetate (3) and the dienolates derived from the 3-alkoxycyclohex-2-enones 1-R and 2-R, by a cascade of two consecutive Michael additions and a γ-elimination. Compounds 4-R are transformed to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 by treatment with acid. 2′-Methoxytricyclooctanes 4a-d-Me are readily deprotonated to give chelation-stabilized cyclopropyllithium derivatives 6-Me, which react with electrophiles to yield the 7′-substituted tricyclo[3.2.1.02,7]octanes 4f-i-Me (61-66%). By acidic workup of such reaction mixtures, or subsequent treatment of the isolated products 4f-i-Me with acid, efficient transformation to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 is observed.
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  • 5
    ISSN: 0091-7419
    Keywords: simian virus 40 ; flow cytometry ; DNA synthesis induction ; transformation ; human diploid cells ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Simian virus 40 (SV40) is capable of inducing cellular DNA synthesis in permissive and nonpermissive cells. Utilizing flow cytometry, we analyzed the DNA content changes in two diploid human cell strains and two monkey cell lines. The osteogenesis imperfects (OI) human skin fibroblasts were induced into DNA synthesis, and within one to two cell generations, a polyploid cell population was produced. With WI-38 phase II cells, a similar pattern of increased cycling of cells into DNA synthesis was observed; however, the majority (∼60%) of the cells were blocked in the G2 + M phase of the cell cycle. At later time intervals, an increase in the G1 population was demonstrated. The two monkey cell lines responded to SV40 virus with an accumulation of cells in the G2 + M phase of the cell cycle. Thus, two diploid human cell strains exhibited different cell cycle kinetics early after infection with SV40 virus. The one strain (WI-38) behaved similarly to the two monkey cell lines studied. The other strain (OI) responded similarly to nonpermissive (transformin) cells infected with SV40 virus.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 63-68 
    ISSN: 0170-2041
    Keywords: Michael addition, aprotic ; [2 + 2] Addition ; Bicyclo[2.2.2]octanes ; Tricyclo[5.3.1.03,8]undecanes ; Sesquiterpene synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (±)-2-Oxo-seychellene and (±)-2-Oxo-4-epi-seychelleneAprotic Michael additions, which generate the functionalized bicyclo[2.2.2]octane 8 from ethyl 2-methyl-2,3-butadienoate (10) and the lithium cyclohexadienolate 9a, are the key steps in the synthesis of 6 (and its 4-epimer). 6 was made from 8 in 10 steps. The alternative Diels-Alder reaction of 10 with the trimethylsiloxycyclohexadiene 9b gave exclusively the [2+2] adduct 14 as a 1:1 mixture of diastereomers.
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