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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1211-1212 
    ISSN: 0170-2041
    Keywords: Fagomine ; Enzymes ; Transketolase ; Carbohydrates ; Yeast transketolase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 13.  -  A New, Efficient Synthesis of Fagomine2-Deoxy-L-threo-5-hexulosonitrile (4) is obtained in excellent chemical yield by yeast transketolase (EC 2.2.1.1)-catalyzed reaction of racemic 3-hydroxy-4-oxobutyronitrile [(R/S)-2] with lithium hydroxypyruvate (3). Catalytic hydrogenation of 4 exclusively gives fagomine (7).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 1295-1301 
    ISSN: 0170-2041
    Keywords: 2-Azidocarboxylates ; Rhenium catalysts ; Amino acids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amino Acids, 16. - Synthesis of N-Acyl-2,3-didehydro-2-amino Acid Esters[2]N-Acyl-2,3-didehydro-2-amino acid esters 3, 5, 7-12, with a great variety of N-substituents, are obtained in good yields by the perrhenate-catalyzed decomposition of methyl 2-azido carboxylates 1 in organic solvents in the presence of the corresponding acyl chlorides 2. By using methyl 2-azidoisovalerate (1a), the conditions (catalyst, solvent, temperature) for the reaction to give 3a were optimized. The reactivity of acyl chlorides can be strongly enhanced with equimolar amounts of dimethyl formamide, which allows a lowering of the decomposition temperature for this reaction. Under these mild reaction conditions also the unstable N-acyldehydroalanine derivative 5f can be obtained in good yield.
    Additional Material: 10 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1979 (1979), S. 842-857 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation of Aryl- and Heteroaryl-trimethylsilanes - Scope of “in situ” Grignard SynthesisAryl and heteroaryl halides react upon heating with magnesium and chlorotrimethylsilane in hexamethyl phosphoric triamide to give aryl and heteroaryl trimethylsilanes in good yields. The advantage of the “in situ” Grignard synthesis over other methods is demonstrated. The scope and limit of this synthesis is investigated for variously substituted aryl compounds and various hetero-cyclic systems.
    Notes: Aryl- und Heteroarylhalogenide reagieren beim Erwärmen mit Magnesium und Chlortrimethylsilan in Hexamethylphoshorsäuretriamid in guten Ausbeuten zu Aryl- und Heteroaryltrimethylsilanen. Die Vorteile dieser „in-situ“-Grignard-Synthese gegenüber anderen Verfahren werden be-schrieben, Anwendungsbreite und Grenzen dieser Methode bei verschieden substituierten Aroma-ten sowie unterschiedlichen Heterocyclen untersucht.
    Additional Material: 4 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1986 (1986), S. 1030-1043 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Amino Acids, 6. - Investigations on the Synthesis of L-SaccharopineN-Alkyl-5-oxoproline esters 4 or 6 are obtained by alkyl desilylation of N-trimethylsilyl-5-oxoproline esters 2 with 6- or 2-halohexanoates 3, 5 in the presence of KF and [18]crown-6. The higher reactivity of the 2-halo compounds 5 is established from competitive reactions of 2a with 3, 5 or the 2,6-dihalohexanoates 7, 8. Alkylation of 2a with methyl 6-bromo-2-phthalimidohexanoate (11), followed by removal of the phthaloyl group and hydrolysis, yields a mixture of the diastereomers pyrosaccharopine (13) and allosaccharopine (14a). - The optically pure hydroxyglutarates (2R)-15b and (2S)-15b are transformed into the respective triflates 18. These are treated with the Nα-protected lysine ester (S)-16b to give the esters 14b and 17b, which upon acid hydrolysis afford enantiomerically pure D-allosaccharopine (2R,5′S)-14a and L-saccharopine (2S,5′S)-14a.
    Notes: Alkyldesilylierung von N-Trimethylsilyl-5-oxoprolinestern 2 mit 6- bzw. 2-Halogenhexansäureestern 3 bzw. 5 führt in Gegenwart von KF und [18]Krone-6 zu den entsprechenden N-Alkyl-5-oxoprolinestern 4 bzw. 6. Kompetitive Umsetzungen von 2a mit 3 bzw. 5 sowie mit den 2,6-Dihalogenhexansäureestern 7, 8 zeigen eindeutig die höhere Reaktivität der 2-gegenüber den 6-Halogenverbindungen. Alkylierung von 2a mit 6-Brom-2-phthalimidohexansäure-methylester (11) ergibt nach Abspaltung der Phthaloylschutzgruppe und saurer Hydrolyse ein Diastereomerengemisch aus Pyrosaccharopin (13) und Allosaccharopin (14a). - Ausgehend von den enantiomerenreinen 2-Hydroxyglutarsäureestern (2R)-15b und (2S)-15b können über die Triflate 18 durch Umsetzung mit dem Nα-geschützten Lysinester (S)-16b die Ester 14b bzw. 17b hergestellt werden, die nach saurer Hydrolyse enantiomerenreines D-Allosaccharopin [(2R,5′S)-14a] bzw. L-Saccharopin [2S,5′S)-14a] ergeben.
    Additional Material: 2 Tab.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1297-1301 
    ISSN: 0170-2041
    Keywords: 5-Thiopentulofuranose ; 6-Thiohexulopyranose ; Rabbit muscle aldolase (RAMA) ; Yeast transketolase ; Carbohydrates ; Enzymes ; Transketolase ; Aldolase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 14.  -  Stereoselective Synthesis of Thiosugars from Achiral Starting Compounds by EnzymesA novel synthesis for thiosugars starting from achiral compounds by using enzymes as catalysts is described. 5-Thio-D-threo-2-pentulofuranose (4), for example, is prepared either by the RAMA (rabbit muscle aldolase)-catalyzed reaction of mercaptoacetaldehyde (1b) with dihydroxyacetonephosphate (2) or by the yeast transketolase-catalyzed reaction of 2-hydroxy-3-mercaptopanal (R/S)-6 with lithium 3-hydroxypyruvate (9). 6-Thio-D-arabino-2-hexulopyranose (8a) and 6-thio-L-xylo-2-hexulopyranose (8b) are obtained by the RAMA-catalyzed reaction of racemic (R/S)-6 with 2.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1986 (1986), S. 314-333 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Amino Acids, 4.  -  Enantioselective Synthesis of N-Substituted α-Amino Carboxylic Acids from α-Hydroxy Carboxylic AcidsWith primary and secondary amines, the (S)-α-(trifluoromethylsulfonyloxy) carboxylates (S)-3 afford in an SN2 reaction the N-substituted (R)-α-amino carboxylates (R)-5, (R)-9, and (R)-12, resp. The rates of α-substituted ethyl propionates decrease in the order of the substituents triflate (3a) ≫ bromide (8a) 〉 mesylate (7a) ≧ tosylate (7b) 〉 chloride (8b); in the reactions with amines, decreasing reactivity affords increasing racemisation and elimination as a consequence of the more drastic conditions which are required.
    Notes: (S)-α-(Trifluormethylsulfonyloxy)carbonsäureester (S)-3 reagieren mit primären und sekundären Aminen im Sinne einer SN2-Reaktion zu den N-substituierten (R)-α-Aminocarbonsäureestern (R)-5, (R)-9 bzw. (R)-12. Die Reaktionsgeschwindigkeit verschiedener in α-Stellung substituierter Propionsäure-ethylester mit Benzylamin nimmt in der Reihenfolge der Substituenten Triflat (3a) ≫ Bromid (8a) 〉 Mesylat (7a) ≧ Tosylat (7b) 〉 Chlorid (8b) deutlich ab. Abnehmende Reaktivität führt bei der Umsetzung mit Aminen aufgrund der erforderlichen härteren Bedingungen in zunehmendem Maße zu Racemisierung und Eliminierung.
    Additional Material: 7 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1986 (1986), S. 334-358 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Amino Acids, 5.  -  Stereoselective Synthesis of α,α′-Imino Dicarboxylic AcidsThe trifluoromethanesulfonates 1, 11, and 26, resp., of enantiomerically pure lactates, β-phenyllactates, and dimethyl α-hydroxyglutarate (25) react with (S)- and (R)-α-amino acid esters 2, 5, 8, 14, 17, 20, and 23, resp., to yield diastereoselectively the α,α′-imino dicarboxylates 3, 6, 9, 12, 15, 16, 18, 21, and 24, resp., which can be hydrolyzed without difficulties to the corresponding α,α′-imino dicarboxylic acids 4, 7, 10, 13, 19, and 22, resp. The very high diastereoselectivity in these reactions is caused by the excellent leaving ability of the trifluoromethanesulfonate ion, which allows reactions even with the relatively weak nucleophilic α-amino carboxylates at low temperatures in an exclusive SN2 reaction.
    Notes: Die Trifluormethansulfonate 1, 11 bzw. 26 von enantiomerenreinen Milchsäureestern, β-Phenylmilchsäureestern bzw. α-Hydroxyglutarsäure-dimethylester (25) reagieren mit (S)-bzw. (R)-α-Aminosäureestern 2, 5, 8, 14, 17, 20 bzw. 23 diastereoselektiv zu den α,α′-Iminodicarbonsäureestern 3, 6, 9, 12, 15, 16, 18, 21 bzw. 24, die sich ohne Schwierigkeiten zu den entsprechenden α,α′-Iminodicarbonsäuren 4, 7, 10, 13, 19 bzw. 22 verseifen lassen. Verantwortlich für die hohe Diastereomerenausbeute bei diesen Reaktionen ist die große Austrittstendenz des Trifluormethansulfonat-Ions, das auch bei tiefen Temperaturen den Austausch mit den relativ schwach nucleophilen α-Aminosäureestern nach einem reinen SN2-Mechanismus ermöglicht.
    Additional Material: 18 Tab.
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  • 8
    ISSN: 0170-2041
    Keywords: Cyanohydrins and cyanohydrin esters, optically active ; Resolutions, kinetic enzyme-catalyzed ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 71). - Enantioselective Esterification of Racemic Cyanohydrins and Enantioselective Hydrolysis or Transesterification of Cyanohydrin Esters by LipasesPure cyanohydrin enantiomers (S)-1/(R)-1 and their O-acyl derivatives (R)-3/(S)-3 are obtained from three different lipasecatalyzed reactions: i) enantioselective hydrolysis of aliphatic and aromatic racemic cyanohydrin esters 3, ii) enantioselective acylation of racemic cyanohydrins 1, iii) enantioselective transesterification of 3 with primary alcohols. Both the cyanohydrin esters and the free cyanohydrins (which are prone to racemization) are isolated as enantiomers with high optical purity on a preparative scale. Hydrolysis of the racemic butyrates 3b, e with Candida cylindracea lipase and pseudomonas sp. lipase, respectively, for example, affords the free (S)-cyanohydrins (S)-2-hydroxypentanenitril [(S)-1a] and (S)-mandelonitrile [(S)-1b)] in high yield with 97 and 96% ee, respectively. (S)-1a is obtained with the same optical purity by candida sp. lipase-catalyzed transesterification of 3b with 1-octanol.
    Additional Material: 4 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 269-273 
    ISSN: 0170-2041
    Keywords: 2-Amino alcohols ; Cyanohydrins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-Catalyzed Reactions, 8. - Stereoselective Synthesis of 2-Amino Alcohols from (R)- and (S)-Cyanohydrinserythro-2-Amino alcohols (1R,2S)- and (1S,2R)-4 may be synthesized stereoselectively by addition of Grignard compounds to cyanohydrins (R)-, (S)-1 and their O-trimethylsilyl derivatives 3, respectively, followed by hydrogenation. The threo-2-amino alcohols (1S,2S)- and (1R,2R)-4 are easily accessible by inversion at C-1 of the (1R,2S) and (1S,2R) compounds.
    Additional Material: 3 Tab.
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  • 10
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aus acyliertem Aminoacetonitril erhält man mit Trisformaminomethan und Ammoniak in Eisessig oder mit Formamidinacetat in einer Reaktionsstufe Purin. Ebenso lassen sich die Salze des Aminoacetonitrils sowie Methylenaminoacetonitril mit Trisformaminomethan oder Formamid zu Purin umsetzen. Die Ausbeuten betragen 20-60%.
    Additional Material: 2 Tab.
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