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  • Carbohydrates  (15)
  • Wiley-Blackwell  (15)
  • Wiley
  • 2000-2004  (15)
  • 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).
    Additional Material: 1 Tab.
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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.
    Additional Material: 1 Ill.
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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.
    Additional Material: 1 Tab.
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    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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