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  • Carbohydrates  (15)
  • Amino acids  (11)
  • Wiley-Blackwell  (26)
  • Blackwell Publishing Ltd
  • Institute of Physics
  • University of Chicago Press
  • 2015-2019
  • 2000-2004  (26)
  • 1950-1954
  • 1
    Electronic Resource
    Electronic Resource
    Sialyltransferase Inhibitors Based on CMP-Quinic Acid (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1745-1758 
    Details
    ISSN: 1434-193X
    Keywords: CMP-Neu5Ac analogues ; Enzyme inhibitors ; Substrate analogues ; Transition state analogues ; Transferases ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quinic acid was transformed into phosphitamides 16, 25, and 36, which could be readily linked to 5′-O-unprotected cytidine derivative 17. Ensuing oxidation of the obtained phosphite triesters with tBuO2H and hydrogenolytic de-O-benzylation furnished the corresponding phosphate diesters 18, 26, and 38. Base catalyzed removal of acetyl protecting groups, and methyl ester hydrolysis furnished CMP-Neu5Ac analogues 1d, 1e, and 2. Quinic acid was also transformed into 1,2-unsaturated diallyl α-hydroxymethyl-phosphate derivatives (R)- and (S)-46, which on reaction with cytidine phosphitamide 47 afforded the phosphite triesters. Subsequent oxidation with tBuO2H and then treatment with NEt3 gave phosphate diester derivatives (R)- and (S)-48. Deallylation, acetyl group removal, and methyl ester hydrolysis furnished (R)- and (S)-3, respectively. Treatment of (R)- and (S)-48 with DBU as a base led to acetic acid elimination, thus yielding, after de-O-allylation, acetyl group cleavage, and ester hydrolysis, diene derivative (E)-4. Donor substrate analogues 1d and 1e exhibited good α(2-6)-sialyltransferase inhibition (Ki: 2.0·10-4 and 2.0·10-5 M). However, transition state analogues (R)-, and particularly (S)-3 showed excellent inhibition properties (Ki: 1.6·10-6 and 2.7·10-7 M).
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  • 2
    Electronic Resource
    Electronic Resource
    Reaction of 1,3-Disubstituted Acetone Derivatives with Pseudohalides: A Simple Approach to Spiro[4.4]nonane-Type Bis-Oxazolidines and -Imidazolidines (Bicyclic Carbamates, Thiocarbamates, Ureas, and Thioureas) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 205-209 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbohydrates ; Imidazolidines ; Oxazolidines ; Spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Prochiral 1,3-dihydroxyacetone forms racemic oxazolidine- and oxazoline-type spiro[4.4]nonanes upon reactions with potassium (thio)cyanate and cyanamide. In contrast, 1,3-diaminoacetone yields only the corresponding spiro-bisimidazolidinethione under similar conditions together with monocyclic by-products, but the spiro-bisimidazolidinone is accessible by reaction of 1,3-dichloroacetone with urea. The resolution of the racemic spiro-bisoxazolidinethione 2a was achieved by using brucine as the resolving agent.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of New Seven-Membered Ring Cyclic Dipeptides From Functionalized β-Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 251-255 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; coupling ; N-Substituted amide ; Cyclizations ; Cyclic dipeptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short synthesis of new, functionalized seven-membered ring cyclic dipeptides is described. After the coupling of N-protected β-amino acids to N-substituted α-amino tert-butyl esters, the protective groups of the terminal functions were removed and the cyclization took place diastereoselectively in the presence of the coupling agent BOP. Amide substitution was found to be effective in promoting the cyclization of linear dipeptides.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Lacto-N-neohexaose and Lacto-N-neooctaose Using the Dimethylmaleoyl Moiety as an Amino Protective Group (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 319-326 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Protecting groups ; Glycosylations ; Trichloroacetimidates ; Oligosaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The N-DMM-Protected lactosamine derivative 2 was readily transformed into the corresponding glycosyl donor 4 and into acceptor 5. A TMSOTf-catalyzed glycosidation afforded the derived tetrasaccharide 6 which led to glycosyl donor 9. Reaction of 9 with lactose derivative 10 as acceptor gave the desired hexasaccharide 11. Cleavage of all protective groups and N-acetylation afforded the target molecule 1b (lacto-N-neohexaose). Glycosylation of acceptor 10 with donor 4 furnished tetrasaccharide 16 which, employing standard procedures, gave acceptor 18. Glycosylation of 18 with donor 9 furnished, under standard conditions, octasaccharide 19. Cleavage of all protective groups and N-acetylation afforded the target molecule 1c (lacto-N-neooctaose). Both 1b and 1c were obtained in good overall yields.
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of Silaproline, a New Proline Surrogate (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 807-811 
    Details
    ISSN: 1434-193X
    Keywords: Proline analogues ; Asymmetric synthesis ; Schöllkopf's method ; Silicon ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The asymmetric synthesis of a new proline surrogate, incorporating the dimethylsilyl group at position 4 of proline using Schöllkopf's bis-lactim ether method, is described.
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular Dynamics-Based Models Explain the Unexpected Diastereoselectivity of the Sharpless Asymmetric Dihydroxylation of Allyl D-Xylosides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 995-1005 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric hydroxylations ; Allyl ethers ; Carbohydrates ; Molecular modeling ; Molecular dynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The catalytic asymmetric dihydroxylation of several allyl 2-O-benzyl-α-D-xylosides with AD-mix β and PYR(DHQD)2 shows almost no diastereofacial selectivity if the 3- and 4-OH groups are unprotected or acetylated. Acetal, benzyl ethers and benzoyl esters enhance the diastereoselectivity, in the opposite sense to that predicted by the “AD mnemonic”, which is completely lost using AD-mix α. In an attempt to understand this behaviour, computational studies of the asymmetric dihydroxylation (AD) of olefins using Sharpless' and Corey's catalysts have been carried out using molecular dynamics. A three-step algorithm was developed taking advantage of the enzyme-like behaviour of catalyst-olefin systems and applied using an ESFF force field. To validate our approach, the first sampling step procedure was then refined and performed using a modified CVFF force field. This led to a U-shaped model in good agreement with that proposed by Corey for the AD of allyl 4-methoxybenzoates, which brings to the fore a role for the methoxy group. This model also accounts for the observed enantioselectivity of styrene dihydroxylation. When applied to the AD of allyl xylosides using AD-mix β, our model accounts well for the observed diastereoselectivity. Both synthetic and modelling results confirmed that aromatic groups on the olefin could be involved in π-π stacking interactions with the aromatic rings of the catalyst and should be important, if not a prerequisite, to achieve high enantio- and diastereoselectivity.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99372_s.pdf or from the author.
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  • 7
    Electronic Resource
    Electronic Resource
    New Strategies for an Efficient Removal of the 9-Fluorenylmethoxycarbonyl (Fmoc) Protecting Group in the Peptide Synthesis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 573-575 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Peptides ; Protecting groups ; Protecting groups ; Aluminium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The aluminium trichloride/toluene system is investigated as a novel, unusual and straightforward reagent for the removal of the 9-fluorenylmethoxycarbonyl (Fmoc) protecting group in the solution peptide synthesis. This procedure avoids any undesired side reactions, such as the frequently observed inversion of the amino acid configuration.
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  • 8
    Electronic Resource
    Electronic Resource
    Photoinduced Electron Transfer (PET) Promoted Oxidative Activation of 1-(N-Benzyl-N-methylglycyl)-(S)-prolinol: Development of Novel Strategies Towards Enantioselective Syntheses of α-Amino Acids, Their N-Methyl Derivatives and α-Hydroxy Acids Employing (S)-Prolinol as aRecyclable Chiral Auxiliary (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 657-664 
    Details
    ISSN: 1434-193X
    Keywords: Photoinduced electron transfer ; Enantioselective syntheses ; Amino acids ; α-Hydroxy acids ; (S)-Prolinol ; Recyclable chiral auxiliary ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---PET activation of 1-(N-benzyl-N-methylglycyl)-(S)-prolinol (1) in dry acetonitrile, utilizing 1,4-dicyanonaphthalene (DCN) as a light-harvesting electron-acceptor and methyl viologen (MV++) as an electron-transfer mediator, leads to the formation of 3-[benzyl(methyl)amino]perhydropyrrolo[2,1-c][1,4]oxazin-4-one (3). When this photolysis is carried out in aqueous acetonitrile, exclusively 3-hydroxyperhydropyrrolo[2,1-c][1,4]oxazin-4-one (4) is produced. The formation of 3 can be rationalized in terms of intramolecular cyclization of the in situ generated iminium cation intermediate (2) by the OH moiety of (S)-prolinol, while 4 is generated by hydrolysis of 2 followed by acetalization. Nucleophilic alkylation of 3 and 4, using Grignard reagents and allyltrimethylsilane/TiCl4, provides 12a-d & 15 and 17a-c & 21, respectively, in a highly stereoselective manner. Hydrolysis of the resultant amides (12, 15, 17, and 21) provides α-amino acid derivatives (14) and α-hydroxy acids, respectively, in optically active form, along with the recovered (S)-prolinol chiral auxiliary in its recyclable form.
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  • 9
    Electronic Resource
    Electronic Resource
    A General and Diastereoselective Synthesis of 1,2-cis-Hexofuranosides from 1,2-trans-Thiofuranosyl Donors (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1423-1431 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycofuranosides ; Thiofuranosides ; Glycosylations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The general formation of 1,2-trans-thioglycofuranosides derived from D-galactose, D-glucose and D-mannose was readily accomplished starting from the corresponding alkyl glycofuranosides via per-O-acetyl-hexofuranoses as key synthons. Glycosidation of ethyl or phenyl perbenzylated 1,2-trans-thiofuranosides afforded disaccharides containing a nonreducing 1,2-cis-hexofuranosyl unit, i.e. α-D-galactosyl, α-D-glucosyl or β-D-mannosyl, with interesting diastereoselectivities. Activation of the thiofuranosyl donors was performed by N-iodosuccinimide and a catalytic amount of tin(II) trifluoromethanesulfonate.
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  • 10
    Electronic Resource
    Electronic Resource
    N-Monoalkylation of α-Amino Acid Esters under Solid-Liquid PTC Conditions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1443-1449 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Alkylations ; Phase-transfer catalysis ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---N-(2-Nitrophenylsulfonyl)- (o-NBS-AA-OMe, 4) and N-(4-Nitrophenylsulfonyl)-α-amino acid methyl esters (p-NBS-AA-OMe, 5) were N-alkylated with a variety of alkyl halides 6 under solid-liquid phase-transfer catalysis (SL-PTC) conditions, affording the alkylated products o-NBS-N-R2-AA-OMe 7 and p-NBS-N-R2-AA-OMe 8 in excellent yields without any detectable racemization.
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  • 11
    Electronic Resource
    Electronic Resource
    Base- and Sugar-Modified Cytidine Monophosphate N-Acetylneuraminic Acid (CMP-Neu5Ac) Analogues - Synthesis and Studies with α(2-6)-Sialyltransferase from Rat Liver (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1467-1482 
    Details
    ISSN: 1434-193X
    Keywords: Glycosyl phosphates ; Nucleosidephosphate sugars ; Neuraminic acid ; Glycosyltransferase ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of sialyl phosphites 1, 22a-d, 28, 39, and 45 with acyl-protected riboside 5-phosphorous acids 2a,b and 23 directly furnished, without addition of a catalyst, under phosphite/phosphate exchange the corresponding β-configured sialyl riboside monophosphates 3a,b, 24a-d, 29, 46, and 47. The synthesis of the starting materials, formation of the products, and their treatment with sodium methanolate in methanol and subsequent hydrolysis of the sialic acid ester moiety to provide the unprotected target molecules 4a,b, 25a-d, 30, 48, and 49 is described. Investigations with α(2-6)-sialyltransferase from rat liver showed that base replacement in CMP-Neu5Ac (4a,b) is not tolerated by the enzyme but that modifications of the 5-, 8-, or 9-position of the neuraminic acid residue (25a-d, 30, 48, 49) are tolerated.
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  • 12
    Electronic Resource
    Electronic Resource
    Chemical Synthesis of a Tetrasaccharide Fragment Related to the Exopolysaccharide of Arthrobacter sp. CE-17 (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 181-186 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Oligosaccharides ; Glycosylations ; Organic synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetrasaccharide 5-aminopentyl glycoside β-D-Manp-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NH2(22) related to the exopolysaccharide of Arthrobacter sp. CE-17 was synthesized by coupling of the properly protected disaccharide blocks β-D-Manp-(1→4)-β-D-Glcp-1-S-Ph (11) and α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NHZ (20). Building block 11 was obtained by intramolecular β-mannosylation of a malonyl-tethered disaccharide glycoside which was prepared from phenyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1) and ethyl 2,3,4-tri-O-benzyl-1-thio-α-D-mannopyranoside (5) in 5 steps. Building block 20 was obtained by coupling N-Z-protected 5-aminopentyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (14) obtained from the non-benzylated counterpart 12 with ethyl 2,3-di-O-benzoyl-4-O-chloroacetyl-1-thio-α-L-rhamnopyranoside (18) obtained in 3 steps from ethyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside (15).
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  • 13
    Electronic Resource
    Electronic Resource
    Studies on the Mercury-Desilylation of Chiral Cyclopropylmethylsilanes - A Stereocontrolled Access to Carba-Sugars (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 401-418 
    Details
    ISSN: 1434-193X
    Keywords: Cyclopropanation ; Allylsilanes ; Mercury-desilylation ; Carbohydrates ; Dihydroxylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Mercury-desilylation of cyclopropylmethylsilanes affords a stereospecific access to homoallylic mercury intermediates, which can be elaborated further. This strategy is illustrated with a short access to carba-furanoses and carba-C-disaccharides.
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis of Highly Functionalised Carbohydrate-Derived Spiroacetals by Ring-Closing Metathesis and Pauson-Khand Reaction of Ketoglycosidic Enynes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 873-877 
    Details
    ISSN: 1434-193X
    Keywords: Spiro compounds ; Ring-closing metathesis ; Pauson-Khand reaction ; Carbohydrates ; Enynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of the ketoglycosidic enynes 5, 7 and 8 starting from 2,3,4,6-tetra-O-benzyl-D-glucopyranolactone (2) is described. These enynes are subjected to ruthenium-mediated ring-closing metathesis and Pauson-Khand cyclisation to afford the highly functionalised carbohydrate spiroacetals 9 and 11-14.
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  • 15
    Electronic Resource
    Electronic Resource
    A Two-Step Palladium-Catalyzed Coupling Scheme for the Synthesis of Ferrocene-Labeled Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    Details
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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  • 16
    Electronic Resource
    Electronic Resource
    Diastereoselective Synthesis of β2-Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 83-90 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Diastereoselective alkylation ; Oppolzer's sultam ; Sultam-imine enolate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---As part of an ongoing project concerning the synthesis of nonnatural amino acids, we have now developed a general strategy for the preparation of β2-amino acids (or 2-aminocarboxylic acid derivatives). Our procedure involves the synthesis of the sultam β-alaninate precursor 5 whose alkylation led with high yields and excellent diastereoselectivity to the precursor of β2-homophenylalanine, β2-homoalanine, and β2-homoleucine. Subsequent deprotection and Boc-protection yielded the expected β2-amino acids. X-ray analysis of the alkylation product established that (-)-sultam yielded (R)-β2-amino acids, conversely (+)-sultam yielded the enantiomer. The topicity of this alkylation is in agreement with the alkylation of Oppolzer's precursor for the synthesis of α-amino acids and opposite to that observed for gem-dialkylation.
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  • 17
    Electronic Resource
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    Preparation of Achiral and of Enantiopure Geminally Disubstituted β-Amino Acids for β-Peptide Synthesis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1-15 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Peptides ; Stereoselectivity ; Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---While geminally disubstituted α-amino acids are helix-inducing residues in α-peptides, gem-disubstituted β-amino acids are predicted not to fit into any of the three major secondary structures of β-peptides recognized to date [the 314 helix, the 12/10/12 helix, and the pleated sheet (Figure 1)]. In order to be able to synthesize and structurally identify β-peptides containing such building blocks, or consisting entirely of them, and in order to establish the chirality of secondary structures they may form, achiral and chiral gem-disubstituted β-amino acids must be readily available. The methods of preparation of 3-amino carboxylic acids with two carbon substituents at the 2- or 3-position (β2,2-/β3,3-amino acids, Figure 2) are reviewed. While there are numerous essentially classical routes to achiral and rac-β-amino acids of this type (Schemes 1-4), their EPC synthesis is currently the subject of investigations. These include the nucleophilic addition to (R)- or (S)-N-sulfinimines (Schemes 6-10) and other Mannich-type transformations (Schemes 19-22), stereoselective alkylations of various chiral hydropyrimidines (Schemes 11, 12, 18), of esters or amides of 2-cyano-alkanoic acids (Schemes 13, 14, 16), and of Li2 derivatives of non-racemic N-protected 3-amino-alkanoates (Scheme 17), as well as sequences of reactions involving enantiopure gem-disubstituted succinic acid derivatives and a Curtius degradation (Schemes 23-26). Oligomers of the achiral gem-disubstituted compounds 1-(aminomethyl)-cyclopropane and -cyclohexane carboxylic acid have already been shown to form 8- and 10-membered hydrogen-bonded rings, respectively (Figure 5), which provide novel motifs for the possible construction of turns, links, or steps in β-peptidic chains.
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  • 18
    Electronic Resource
    Electronic Resource
    Short Enzymatic Synthesis of L-Fucose Analogs (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 125-132 
    Details
    ISSN: 1434-193X
    Keywords: Aldol condensations ; Carbohydrates ; C-C coupling ; Isomerases ; Controlled ozonolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short enzymatic route for the synthesis of L-fucose analogs modified at the nonpolar terminus is reported. In particular, fucose derivatives bearing extended linear (1b) and branched (1e) saturated, or various unsaturated (1c, 1d) aliphatic chains have been prepared, in order to increase hydrophobic contacts. The rather general approach involves a sequential application of the recombinant enzymes L-fuculose 1-phosphate aldolase (FucA) and L-fucose ketol isomerase (FucI) from E.coli. Enantiomerically pure L-fucose analogs have been prepared in up to 30% overall yield starting from the appropriate hydroxyaldehyde precursors and dihydroxyacetone phosphate as readily available components. Unsaturated 2-hydroxyaldehydes have been efficiently prepared by alk(en/yn)yl Grignard addition to cinnamaldehyde followed by controlled ozonolysis of the styrene fragment.
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  • 19
    Electronic Resource
    Electronic Resource
    Gabosines L, N and O: New Carba-Sugars from Streptomyces with DNA-Binding Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 149-153 
    Details
    ISSN: 1434-193X
    Keywords: Gabosine ; Secondary metabolite ; Carbohydrates ; Chemical screening ; Biomolecular-chemical screening ; DNA binding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In addition to the known gabosines A (4), B (5) and C (6), three new gabosines L (1), N (2) and O (3) were detected by chemical screening as secondary metabolites of Streptomyces (strains GT 041230, GT 051024 and S 1096). The constitutions of 1, 2 and 3 were established by spectroscopic techniques and derivatization reactions. The absolute stereochemistry of 1 and 2 was determined by Helmchen's method and has been verified in the case of gabosine N (2) by X-ray analysis. The DNA-binding properties of the gabosines were investigated and analyzed by binding studies using a recently developed thin-layer chromatography technique (bimolecular-chemical screening).
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  • 20
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    Modifications of Peptides by Chelate Claisen Rearrangements of Manganese Enolates (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1241-1251 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Enolates ; Rearrangements ; Metal complexes ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Deprotonation of allylic esters of peptides at -70 °C in the presence of metal salts results in the formation of metal peptide enolate complexes, which undergo Claisen rearrangement on warming to room temperature to produce stereoselectively modified peptides. By far the best results are obtained with manganese enolates. With these enolates, the amino acids incorporated in the peptide chain have no significant influence on the rearrangement, neither on the yield nor on the stereochemical outcome. Therefore, this protocol is extremely suitable for the stereoselective modification of peptides by using esters of chiral allylic alcohols. α-Alkylated amino acids can be incorporated into peptides as well.
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  • 21
    Electronic Resource
    Electronic Resource
    Synthesis of Highly Enantio-Enriched α-Amino Acids by Carboxylation of N-(α-Lithioalkyl)oxazolidinones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1297-1305 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Asymmetric synthesis ; Carboxylation ; N-(α-Lithioalkyl)oxazolidin-2-ones ; Isotopic labeling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -N-(α-Stannylalkyl)oxazolidinones can be obtained as a mixture of diastereomers in three steps from aldehydes with yields dependent on the R group of R-CHO. They can be transformed by a tin-lithium exchange to N-(α-lithioalkyl)oxazolidinones which equilibrate rapidly to one diastereomer. These compounds give rise, after carboxylation, to the diastereopure N-(α-carboxyalkyl)oxazolidinones. Transformation of the oxazolidinone moiety to a free amino group is accomplished by a Birch-type reduction. Using this method, L-methionine, L-alanine, L-leucine and L-homocysteine were obtained in good yields and ee = 92% to ≥ 95%. The short time required for the whole sequence makes this method ideal for synthesising 1-[11C]amino acids.
    Additional Material: 3 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    Stereoselective Synthesis of carba- and C-Glycosyl Analogs of Fucopyranosides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1285-1296 
    Details
    ISSN: 1434-193X
    Keywords: Carbocycles ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Fucopyranoside analogs with methylene groups instead of endo- or exo-anomeric oxygens, carba- and C-fucopyranosides, respectively, were synthesized. For the synthesis of 5a-carba-L-fucose (1) two approaches were studied, which shared a common cyclitol building block (8), obtained from a SmI2-promoted carbocyclization of a D-mannitol derivative. The first route made use of a Stork radical cyclization onto a conduritol derivative 13 as the key step, which failed to give the silyl ether ring. The second route furnished the target 1, and involved regioselective elimination of a cyclic sulfate 9, and stereoselective hydrogenation of a double bond, controlled by substitution on the substrate. For the synthesis of 1-C-fucopyranosides (37, 38, and 42) a new method based on the use of fucosyl phenyl sulfoxides (35 and 41) was employed. An anomeric carbanion is generated through phenylsulfinyl-lithium exchange, which reacted with electrophiles with retention of configuration at the anomeric center. The required fucosyl sulfoxides were prepared from L-fucose by highly stereoselective thioglycosylation reactions.
    Additional Material: 2 Tab.
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  • 23
    Electronic Resource
    Electronic Resource
    Synthesis and Ring Opening of Methyl 2-Alkyl-3-(alkyl/aryl)-1-benzoylaziridine-2-carboxylates: Synthesis of Polysubstituted Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1569-1576 
    Details
    ISSN: 1434-193X
    Keywords: Aziridines ; Oxazolines ; Ring expansion reactions ; Amino acids ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new method for the preparation of 2,2,3-trisubstituted methyl 1-benzoylaziridine-2-carboxylates is reported. These compounds have been obtained starting from α-alkyl β-amino acids by formation of the lithium dianion and reaction with iodine. The aziridines undergo ring expansion or ring opening, depending on the substituents of the aziridine ring and on the reaction conditions. Following these methods, both α-substituted α-hydroxy β-amino acids and α-substituted β-hydroxy α-amino acids have been synthesised.
    Additional Material: 1 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Structural Diversity of 1-O-Acyl α-L-Rhamnopyranosides by Precursor-Directed Biosynthesis with Streptomyces griseoviridis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1875-1881 
    Details
    ISSN: 1434-193X
    Keywords: Metabolism ; Biosynthesis ; Glycosides ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The ability of Streptomyces griseoviridis (strain Tü 3634) to glycosylate various carboxylic acids with L-rhamnose was investigated by feeding mainly heteroaromatic and aromatic carboxylic acids to growing cultures. The special application of the precursor-directed biosynthesis (PDB) gave rise to a wide variety of acyl α-L-rhamnopyranosides as novel metabolites. The experiments resulted in furanyl, pyrrolyl, thienyl, indolyl, and pyridyl derivatives (1-8), the analogues 9-24 were generated by feeding fluoro-, hydroxy- or aminobenzoic acids or cinnamic acids. All results are discussed with respect to the substrate specificity of the corresponding enzyme system.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99567_s.pdf or from the author.
    Additional Material: 3 Tab.
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  • 25
    Electronic Resource
    Electronic Resource
    Biosynthesis of Gabosines A, B, and C, Carba Sugars from Streptomyces cellulosae (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1883-1887 
    Details
    ISSN: 1434-193X
    Keywords: Biosynthesis ; Gabosine ; Bioorganic chemistry ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The biosynthesis of the gabosines A-C (3-5) was studied by feeding cultures of Streptomyces cellulosae subsp. griseorubiginosus (strain S 1096) with 13C-labeled precursors. Although the carba sugars are structurally related to shikimic acid, the biosynthetic origin was found to be different to the shikimate pathway. The results revealed that the gabosines are formed via a pentose phosphate pathway by cyclization of a heptulose phosphate intermediate. This intermediate arises from a triose phosphate by successive transfer of two C2 fragments by transketolases. This pathway is identical as that described for valienamine (7), the aminocarba sugar moiety of validamycin, and acarbose (2). The results from biosynthetic studies are discussed on the background of the variety of gabosines found in nature.
    Additional Material: 2 Tab.
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  • 26
    Electronic Resource
    Electronic Resource
    The Conformational Behaviour of Non-Hydrolizable Lactose Analogues: The Thioglycoside, Carbaglycoside, and Carba-Iminoglycoside Cases (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1945-1952 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycosides ; Conformation analysis ; Molecular modeling ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The conformational behaviours of several nonhydrolizable lactose analogues, namely methyl α-thiolactoside (1), methyl β-carbalactoside (2) and methyl β-carbaiminolactoside (3) have been studied using a combination of NMR spectroscopy (J and NOE data) and molecular mechanics calculations. Analogies and differences with the natural compounds have been found.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99592_s.pdf or from the author.
    Additional Material: 3 Ill.
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