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  • 11
    Electronic Resource
    Electronic Resource
    Investigation of the Uncatalyzed Hydration of CO2 and First Approximations to the Active Site of Carbonic Anhydrase - A Combined Ab initio and DFT Study - (1996)
    Springer
    Journal of molecular modeling 2 (1996), S. 358-361 
    Details
    ISSN: 0948-5023
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089460020358
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  • 12
    Electronic Resource
    Electronic Resource
    Theoretical Study of the Water Exchange Reaction on Divalent Zinc Ion using Density Functional Theory (1996)
    Springer
    Journal of molecular modeling 2 (1996), S. 354-357 
    Details
    ISSN: 0948-5023
    Keywords: Ab inito ; DFT ; Zinc complexes ; Hydration energies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Recent ab initio studies reported in the literature have challenged the mechanistic assignments made on the basis of volume of activation data [1,2]. In addition to that ab initio molecular orbital calculations on hydrated zinc(II)-ions were used to elucidate the general role of this ion in metalloproteins [3]. Due to our interest in both inorganic reaction mechanisms and enzymatic catalysis we started a systematic investigation of solvent exchange processes on divalent zinc-ion using density functional calculations. Our investigations cover aqua complexes of the general form [Zn(H2O)n]2+·mH20 with n=3-6 and m=0-2, where n and m represent the number of water molecules in the coordination and solvation sphere, respectively. The complexes [Zn(H2O)5]2+·2H2O and [Zn(H2O)4]2+·2H2O turnend out to be the most stable zinc complexes with seven and six water molecules, respectively. This implies that a heptacoordinated zinc(II) complex, where all water molecules are located in the co-ordination sphere, should be energetically highly unfavorable and that [Zn(H2O)6]2+ can quite readily push two coordinated water molecules into the solvation sphere. For the pentaqua complex [Zn(H2O)5]2+ only one water molecule is easily lost to the solvation sphere, which makes the [Zn(H2O)4]2+·H2O complex the most favorable in order to consider the limiting dissociative and associative water exchange process of hexacoordinated zinc(II). The dehydration and hydration energies using the most stable zinc(II) complexes [Zn(H2O)4]2+·2H2O, [Zn(H2O)5]2+·2H2O and [Zn(H2O)4]2+·H2O were calculated to be 24.1 and -21.0 kcal/mol, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s0089460020354.894
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  • 13
    Electronic Resource
    Electronic Resource
    The Important Role of Active Site Water in the Catalytic Mechanism of Human Carbonic Anhydrase II – A Semiempirical MO Approach to the Hydration of CO2 † (1998)
    Springer
    Journal of molecular modeling 4 (1998), S. 355-365 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Human Carbonic Anhydrase II ; Semiempirical MO Theory ; AM1 ; Enzyme Catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The approach of CO2 to a series of active site model complexes of human carbonic anhydrase   II (HCAII) and its catalytic hydration to bicarbonate anion have been investigated using semiempirical MO theory (AM1). The results show that direct nucleophilic attack of zinc-bound hydroxide to the substrate carbon occurs in each model system. Further rearrangement of the bicarbonate complex thus formed via a rotation-like movement of the bicarbonate ligand can only be found in active site model systems that include at least one additional water molecule. Further refinement of the model complex by adding a methanol molecule to mimic Thr-199 makes this process almost activationless. The formation of the final bicarbonate complex by an internal (intramolecular) proton transfer is only possible in the simplest of all model systems, namely {[Im3Zn(OH)]+·CO2}. The energy of activation for this process, however, is 36.8 kcal·mol−1 and thus too high for enzymatic catalysis. Therefore, we conclude that within the limitations of the model systems presented and the level of theory employed, the overall mechanism for the formation of the bicarbonate complex comprises an initial direct nucleophilic attack of zinc-bound hydroxide to carbon dioxide followed by a rotation-like rearrangement of the bicarbonate ligand via a penta-coordinate Zn2+ transition state structure, including the participation of an extra active site water molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050094
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  • 14
    Electronic Resource
    Electronic Resource
    Interdisziplinärer Konsensus zur Diagnostik und Therapie von Hodentumoren Ergebnisse einer Update-Konferenz auf Grundlage evidenzbasierter Medizin (EBM) (2000)
    Springer
    Strahlentherapie und Onkologie 176 (2000), S. 388-405 
    Details
    ISSN: 1439-099X
    Keywords: Schlüsselwörter: Testikuläre Keimzelltumoren ; Evidenzbasierte Medizin (EBM) ; Interdisziplinäre Diagnostik- und Therapieempfehlungen ; Key Words: Testicular germ cell tumors ; Evidence-based medicine (EBM) ; Interdisciplinary diagnostic and treatment strategies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Background: An “Interdisciplinary Consensus Statement on the Diagnosis and Therapy of Testicular Tumors” was prepared in 1996 by the “Interdisciplinary Testicular Tumor Working Group” (IAH) with input from representatives from diagnostic and therapeutic disciplines of various working groups of the German Cancer Society (Strahlenther Onkol 1997;173:397–406). In 1998 the IAH met again together with the “Testicular Tumor Working Party” of the Urooncology Working Group (AUO) and formed the “German Testicular Cancer Study Group (GTCSG). Defined and accepted interdisciplinary standards from the initial meeting were revised based on current scientific developments and clinical results. This cooperating effort increases the quality of the initial recommendations and helped to put the recommendations for diagnosing and treating testicular on a broader scientific basis. Methods: According to the principles of “evidence-based medicine” (EBM), the Consensus from 1996 was modified, based on the current level of evidence from the published literature. The methodological process and evaluation criteria used were that of the “Cochrane Collaboration”. Results: An “Interdisciplinary Update Consensus Statement” summarizes and defines the diagnostic and therapeutic standards according to the current scientific practices in testicular cancer. For 21 separate areas scientifically based decision criteria are suggested. For treatment areas where more than one option exist without a consensus being reached for a preferred strategy, such as in seminoma in clinical Stage I or in non-seminoma Stages CS I or CS IIA/B, all acceptable alternative strategies with their respective advantages and disadvantages are presented. This “Interdisciplinary Update Consensus” was presented at the 24th National Congress of the German Cancer Society on March 21st and subsequently evaluated and approved by the various German scientific medical societies.
    Notes: Hintergrund: 1996 war von der “Interdisziplinären Arbeitsgruppe Hodentumoren” (IAH), in der Vertreter aller an der Diagnostik und Therapie des germinalen Hodentumors beteiligten Disziplinen aus den jeweiligen Fachgesellschaften und Arbeitsgruppen der Deutschen Krebsgesellschaft zusammenarbeiten, ein “Interdisziplinärer Konsensus zur Diagnostik und Therapie von Hodentumoren” erarbeitet worden (Strahlenther Onkol 1997;173–406). Die seinerzeit in interdisziplinärer Abstimmung definierten Empfehlungen wurden aufgrund fortschreitender Entwicklungen und klinischer Erkenntnisse dem aktuellen Wissensstand angepasst und überarbeitet. Hierfür sind durch den 1998 erfolgten Zusammenschluss der IAH mit der “Organgruppe Hodentumoren” der Arbeitsgemeinschaft Urologische Onkologie (AUO) zur “German Testicular Cancer Study Group (GTCSG) die wissenschaftliche Basis erweitert und die Qualität der erabeiteten diagnostischen und therapeutischen Standards für Hodentumoren erhöht worden mit der Zielsetzung, eine breite Umsetzung der interdisziplinär erstelltn Empfehlungen zu ermöglichen. Methodik: In Erweiterung der Erarbeitung des Konsensus von 1996 erfolgte die Überarbeitung auf Grundlage aktueller Literaturdaten in Anlehnung an die Prinzipien der “Evidence-bases Medicine” (EBM). Aussagen und Empfehlungen zu den von interdisziplinär besetzten Arbeitsgruppen recherchierten Themenkomplexen wurden nach dem Grad ihrer Qualität und Sicherheit bewertet. Das methodische Vorgehen entsprach dabei dem der Cochrane Collaboration, deren Bewertungskriterien übernommen wurden. Ergebnisse: Der zu 21 Themenkomplexen anhand wissenschaftliche begründeter Entscheidungskriterien erarbeitete “Interdisziplinärer Update-Konsensus” präzisiert und definiert diagnostische und therapeutischen Standards entsprechend dem aktuellen Wissensstand über diese Tumorentität. Für Therapiesituationen, bei denen mehrere Optionen bestehen und kein Konsens über die favorisierte Strategie erzielt wurde wie beim Seminom in klinischen Stadium I oder beim Nichtseminom in den Stadien CS I bzw. CS IIA/B, wurden jeweilige Alternativen mit deren Vor- und Nachteilen dargestellt. Der “Interdisziplinäre Update-Konsensus” wurde beim 24. Deutschen Krebskongress am 21.3.2000 vorgestellt, nachfolgend von den daran beteiligten wissenschaftlichen Fachgesellschaften geprüft und gebilligt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00002347
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  • 15
    Electronic Resource
    Electronic Resource
    Fungicide und Photochemie (1992)
    Springer
    European food research and technology 195 (1992), S. 15-16 
    Details
    ISSN: 1438-2385
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Description / Table of Contents: Zusammenfassung Bei Bestrahlung mit UV-Licht (λ〉280 nm) reagiert das Triazolfungizid Penconazol (1) unter Cyclokondensation zu 5H, 6H-(1,2,4-Triazolo)-[5,1-a]-9-chlor-6-propyl-isochinolin (2). Die Entstehung dieser Verbindung ist unabhängig von den verwendeten Modellösungen. Weiterhin entstand dieses interessante cyclische Photoprodukt auch bei der Bestrahlung des Handelspräparates Topas.
    Notes: Summary On UV irradiation atλ〉280 nm the triazole fungicide Penconazole (1) reacts by cyclocondensation, yielding 5H, 6H-(1,2,4-triazolo)-[5,1-a]-9-chloro-6-propyl-isoquinoline (2). The formation of this compound is not only independent of the investigated model solutions, but was also observed after irradiation of the formulation Topas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01197832
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  • 16
    Electronic Resource
    Electronic Resource
    Structural variations of N-acetylneuraminic acid, 14. Synthesis of the β-methyl ketosides of 4-oxo-, 7-oxo-, and 8-oxo-N-acetylneuraminic acid and the corresponding 7,7- and 8,8-dimethoxy derivatives their behaviour towards CMP-sialate synthase (1990)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 83-91 
    Details
    ISSN: 0170-2041
    Keywords: CMP-sialate synthase ; Sialic acids ; N-Acetylneuraminic acid derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 4-, 7-, and 8-oxo-sialic acid β-methyl ketosides 7, 10a, and 11a were obtained by transformation of easily available derivatives of N-acetylneuraminic acid (1a). The carbonyl migration from C-7 to C-8 can be carried out under well-defined conditions with formation of the ketone 11b. Starting from 7- and 8-ketones 17 and 20 the corresponding dimethyl acetals are prepared. The 4-ketone 7 behaves as a moderate competitive inhibitor of CMP-sialate synthase [EC 2.7.7.43], whereas the 8-ketone 11a, the 8,8-dimethyl acetal 19, and the 7,7-dimethyl acetal 23 prove not to be inhibitors of this enzyme. The 7-ketone 10a was not tested because of instability under test conditions at pH 8.5.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199019900112
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  • 17
    Electronic Resource
    Electronic Resource
    Structural variations of N-acetylneuraminic acid, 9. A new useful approach to the epimers at C-7 and C-7,8 of N-acetylneuraminic acid (1988)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1988 (1988), S. 187-189 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new approach to 5-acetamido-3,5-dideoxy-L-glycero-L-altro-2-nonulopyranosonic acid (6; 7,8-bis-epi-Neu5Ac) and 5-acetamido-3,5-dideoxy-D-glycero-L-altro-2-nonulopyranosonic acid (9; 7-epi-Neu5Ac) is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198819880215
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  • 18
    Electronic Resource
    Electronic Resource
    Structural variations of N-acetylneuraminic acid, 23. Synthesis of 2-deoxy-2Heq-sialic Acid analogues structurally varied at C-4 (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 795-801 
    Details
    ISSN: 0170-2041
    Keywords: Sialic acids, 2-deoxy ; N-Acetylneuraminic acids, 2-deoxy ; Hemagglutinin inhibitors ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Deoxy-2-Heq-N-acetylneuraminic acid (1a) has been shown to be a versatile mimic for sialosyl 2-α-glycosides to study the hemagglutinin-sialic acid interaction. Starting with a 4-oxo derivative of 2-deoxy-2-Heq-sialic acid, we obtained the 4-C-methylax and 4-C-methyleq derivatives 4 and 5 as a separable mixture. The derivative 4 was formed as a single product by using tributoxymethylzirconium. The 4-C-methylene derivative 10 was formed by treatment of the ketone with Cp2ZrCl2/Zn/CH2I2. Catalytic hydrogenation of the exo-methylene compound 10 yielded the two 4-deoxy-4-C-methyl diastereomers 13 and 14. All above-mentioned derivatives could be transformed into the unprotected 4-branched 2-deoxy-2-Heq-sialic acids 7, 9, 12, 16, and 18. 2-Deoxy-2Heq-4-oxosialic acid (21) was synthesized by a different pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101136
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  • 19
    Electronic Resource
    Electronic Resource
    Structural variations of N-acetylneuraminic acid, 18. Synthesis of the side chain stereo and deoxy analogs of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-erythro-L-manno-nononic acid (1990)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 1185-1195 
    Details
    ISSN: 0170-2041
    Keywords: Sialic acids ; Hemagglutinin inhibitors ; N-Acetylneuraminic acid, deoxygenation and epimerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 5-acetamido-2,6-anhydro-3,5-dideoxy-D- erythro-L-manno-nonic acid (3b, 7,8-epi2-2-d-2-HeqNeu5Ac) and sodium 5-acetamido-2,6-anhydro-3,5-dideoxy-L-threo-L-manno-nonate (6b, 8-epi-2-d-2-Heq-Neu5Ac) could be realized by transformation of 5-acetamido-3,5-dideoxy-L-glycero-L-altro-2-nonulopyranosonic acid (2a, 7,8-bis-epi-Neu5Ac) and 5-acetamido-3,5-dideoxy-3-L-glycero-D-galacto-2-nonulosonic acid (5a, 8-epi-Neu5Ac) into the corresponding peracetylated 2-chloro derivatives and subsequent catalytic hydrogenation. As this procedure could not be applied to the synthesis of the 7-epi, 7-deoxy and 8-deoxy derivatives a new strategy, which started with the methyl 5-acetamido-2,6-anhydro-3,5-dideoxy-D-erythro-L-manno-nonoate (1e), was designed. For this purpose, a gram-scale preparation of 1e was developed. Transformation of protecting groups and radical reduction of selectively introduced tolylthiocarbonate groups led to the corresponding 5-acetamido-2,6-anhydro-3,5,7-trideoxy-D-glycero-L-manno-nonoic acid (12b, 2,7-d2-2Heq-Neu5Ac) and sodium 5-acetamido-2,6-anhydro-3,5,8-trideoxy-D-glycero-L-manno-nonate (11b, 2,8-d2-2Heq-Neu5Ac). An oxidation  -  reduction sequence yielded 5-acetamido-2,6-anhydro-3,5-dideoxy-D-threo-L-manno-nonoic acid (9c, 2d-2Heq-7-epi-Neu5Ac). Also the sialic acid analog 6b could be prepared according to this newly designed strategy.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1990199001216
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