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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1745-1758 
    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.
    Type of Medium: Electronic Resource
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  • 12
    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.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramide-1-phosphates ; Inositols ; Glycophosphosphingolipids, synthesis ; Glycophosphoinositol anchors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 2,3:4,5-di-O-cyclohexylidene-D-myo-inositol derivative 3 was converted into the 1-O-unprotected D-myo-inositol derivative 6. Reaction with the phosphite derivative 7 of 3-O-tert-butyldimethylsilyl-protected ceramide furnished the target molecule D-erythro-ceramide-1-phosphoinositol (1). Reaction of O-(3,4,6-tri-O-acetyl-2-azido-β-D-glucopyranosyl)trichloroacetimidate (20) with 3 gave exclusively α(1→6)-connected glycoside 21 which was converted into the 1α-O-unprotected derivative 24. Reaction with the D-erythro-azidophytosphingosine-derived ceramide-1-phosphite derivative 17 led, after oxidation and removal of the cyanoethyl group, to protected 2-azido-D-glucopyranosyl-α(1→6)-D-myo-inositol-1-phospho-ceramide (25) which could be fully deprotected in two steps to afford the target molecule, the ceramide derivative of 2-amino-2-deoxy-D-glucopyranosyl-α(1→6)-D-myo-inositol-1-phosphate (2).
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2317-2322 
    ISSN: 1434-193X
    Keywords: C-Glycosyl compounds ; Flavones ; Flavanones ; O-Glycosyl trichloroacetimidates ; Fries rearrangement ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycosylation of the visnagin cleavage product 2 with O-acetyl-protected glycosyl donor 5a afforded O-glycoside 6a, which could be transformed into the O-benzyl-protected compound 6b. The latter underwent Fries-type rearrangement to afford C-glycoside 4b. The same product could be obtained directly from 2 and O-benzyl-protected glycosyl donor 5b. Reaction of 4b with benzaldehyde and anisaldehyde furnished chalcones 7A,B, which, upon treatment with base, furnished flavanone C-glycosides 10A,B. Selenium dioxide oxidation of 10A,B or of 7A,B led to the corresponding flavone C-glycosides 11A,B. The same result was obtained by Baker-Venkataraman rearrangement; on treatment with base, the O-aroyl compounds 12A-C gave C-aroyl compounds 13A-C, which, on addition of TMSOTf, furnished flavone C-glycosides 11A-C. Hydrogenolytic O-debenzylation of 11A afforded target molecule 3A, which was transformed into O-acetyl derivative 14A for characterization. Structural assignments of all compounds were based on 1H-NMR data.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1153-1165 
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramides-1-phosphates ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -For the design of a synthesis of target molecule 1 the retrosynthetic analysis yielded building blocks 2-5, of which ceramide 2-phosphite derivative 2 and aminoethyl phosphite derivative 5 are known. The generation of α-glucosaminyl (1→6)inositol building block 3 was based on pseudodisaccharide 6 which was selectively benzoylated at 6b-O and then selectively benzylated at 3b-O to give 3. The synthesis of tetramannosyl building block 4 started from known ortho ester derivative 8 which was transformed into versatile mannosyl donors 13 and 18 and into acceptor 22. Reaction of 13 with 22 gave α-disaccharide 23, deacetylation and then mannosylation with 18 gave trisaccharide 25; ensuing deacetylation and mannosylation with 13 gave tetrasaccharide 27; deallylation, acetylation, regioselective removal of the anomeric O-acetyl group and treatment with CCl3CN/DBU afforded 4. Glycosylation of 3 with donor 4 led to pseudohexasaccharide 31 in high yield. Replacement of the O-acyl groups by O-benzyl groups and then exchange of the menthyloxycarbonyl group by an O-acetyl group gave 36 which enabled regioselective attachment of 2 and 5. To this end, the 6e-O-silyl group was removed and then the aminoethyl phosphate residue was attached with reagent 5 to give 38 in high yield. 1a-O-Deacetylation and then reaction with 2 afforded 40 as fully protected 1 which was liberated in two steps; treatment with acid removed all acid labile protective groups and finally catalytic hydrogenation afforded the desired GPI anchor 1 which could be fully structurally assigned.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1573-4986
    Keywords: Glycoside synthesis ; nitrile effect ; sialyl donors ; sialyl phosphites and phosphates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The importance and requirements for catalytic activation of sialyl donors are discussed, leading to the acid sensitive phosphite and phosphate moiety, respectively, as leaving group and nitriles as solvent. Therefore, from readily availableN-acetylneuraminic acid, derivative1 with phosphochloridites2a-f and Huenigs' base sialyl phosphites3a-f were prepared and isolated in high yields. Oxidation of3a, c withtert-butyl-hydroperoxide afforded the corresponding phosphates4a, c. As expected, phosphites3 could be activated in acetonitrile by catalytic amounts of TMSOTf; thus, from3a-e as donors and lactose derivatives8A, B as acceptors the ganglioside building blocks9A and9B, respectively, were obtained in good yields. The best results were obtained with diethyl phosphite derivative3a as sialyl donor, which exceeded by far the reults obtained with the corresponding phosphate derivative4a. Trisaccharide9B was transformed into known9A and into the fullyO-acetylated GM3-trisaccharide10.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Glycoconjugate journal 7 (1990), S. 229-234 
    ISSN: 1573-4986
    Keywords: glycosphingolipid ; synthesis ; polymer support ; lactosyl ceramide ; d-galactosyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a first example of a polymer-supported enzymic synthesis of glycosphingolipids, synthetic (2S,3R,4E)-2-amino-1-(β-d-glucopyranosyloxy)-3-hydroxy-4-octadecene (glucosylsphingosine) was converted to theN-4-carboxymethyl-2-nitrobenzyloxycarbonyl derivative and was subsequently attached to a water-soluble polymer. The material served as an acceptor in thed-galactosyltransferase reaction (36% transfer yield) and further photolysis, acylation and chromatography afforded (2S,3R,4E)-1-[4-O-(β-d-galactopyranosyl)-β-d-glycopyranosyloxy]-3-hydroxy-2-octadecanoylamino-4-octadecene (lactosylceramide, 54% yield).
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 1573-4986
    Keywords: Trypanosoma brucei ; α-galactosyltransferases ; sugar donor analogs ; competitive inhibitors ; UDP, uridine-5′-diphosphate ; UDP-Gal, uridine-5′-diphosphate galactose ; VSG, variant surface glycoprotein ; αGalT, α-galactosyltransferase ; Galα1,3GalT, UDP-Gal:β-d-Gal(1 → 4)-D-GlcNAc-α(1,3)-galactosyltransferase (EC 2.4.1.51) ; Galα1,3ManT, UDP-Gal:GPI-anchor-α(1,3)-galactosyltransferase ; Man, D-mannose ; Gal, D-galactose ; Man2-S-C8, Manα(1-6)Manα1S-(CH2)7-CH3 ; GlcNAc, D-N-acetylglucosamine ; LacNAc, D-N-acetyllactosamine ; Galα1,3Gal, α-d-Gal(1→3)-D-Gal epitope ; GPI, glycosyl-phosphatidylinositol ; DTT, dithiothreitol ; PIPES, piperazine-N,N′-bis(2-ethanesulfonic acid)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Since the α-D-galactose-(1→3)-D-galactose epitope has been identified to be the major target in the process of hyperacute rejection of xenografts transplanted from nonprimate donors to humans, specific inhibitors of α-galactosyltransferases are of broad interest. Using Trypanosoma brucei, a protozoan parasite causing sleeping sickness and Nagana, we have a very useful model system for the investigation of α-galactosyltransferase inhibitors, since the variant surface glycoprotein (VSG) accounts for about 10% of the total cell protein an this parasite expresses many different galactosyltransferases including the one catalysing the formation of the Galα1→3Gal epitope. In order to study inhibition of galactosylation on the VSG from Trypanosoma brucei, we designed, synthesized and tested substrate analogues of trypanosomal α-galactosyltransferases. Effective inhibitors were a pair of diastereoisomeric UDP-galactose analogs, in which the galactose residue is linked to UDP via a methylene bridge rather than an ester linkage. Hence, galactose cannot be transferred to the respective acceptor substrate VSG or the synthetic acceptor substrate Manα1→6Manα1S-(CH2)7-CH3, which was previously proven to replace VSG effectively [Smith et al. (1996) J Biol Chem 271:6476–82]. Inhibitors have been prepared starting from 1-formyl galactal. The final condensation was performed using UMP morpholidate leading to a pair of diastereomeric compounds in 39% or 30% yield, respectively. These compounds were tested using α-galactosyltransferases prepared from T. brucei membranes and lactose synthetase from bovine milk. While the KM-value for UDP-galactose was determined as 59 µM on bovine lactose synthetase, the KI-values for both inhibitors were 0.3 mM and 1.1 mM respectively, showing that these inhibitors are unable to inhibit enzyme activity significantly. However, using the N-glycan specific α-galactosyltransferase from trypanosomes, the KM-value was determined as 20 µM, while the KI-values were 34 µM and 21 µM respectively. Interestingly, other trypanosomal α-galactosyltransferases, which modify the GPI membrane anchor, are 2 orders of magnitude less effected by the inhibitor.
    Type of Medium: Electronic Resource
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  • 19
    ISSN: 1573-4986
    Keywords: CMP-Neu5Ac analogues ; synthesis ; sialyltransferase inhibitors ; sialyltransferase assay ; α(2-6)-sialyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Quinic acid (4) was transformed into phosphitamides 6, 14, and 15, which could be readily linked to 5′-O-unprotected cytidine derivative 7; ensuing oxidation of the obtained phosphite triesters with tert-butylhydroperoxide furnished the corresponding phosphate triesters 8, 16, and 17, respectively. Hydrogenolytic debenzylation of the phosphate moiety, base catalysed removal of acetyl protective groups, and basic hydrolysis of the methylester of the quinic acid moiety furnished CMP-Neu5Ac analogues 1-3. In order to measure their inhibition of sialyltransferases, a nonradioactive sialyltransferase assay [employed for α(2-6)-sialyltransferase from rat liver (EC 2.4.99.1)] based on reversed-phase HPLC separation of UV-abelled acceptor 20 (p-nitrophenyl glycoside of N-acetyllactosamine) from the UV-labelled product 21 (p-nitrophenyl glycoside of sialyl α(2-6′)-N-acetyllactosamine) and p-nitrophenylalanine as internal standard was developed. The assay reproduced the reported KM values for CMP-Neu5Ac and N-acetyllactosamine and the Ki values for CDP. 1 and 2 turned out to be potent sialyltransferase inhibitors. © 1998 Rapid Science Ltd
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Glycoconjugate journal 13 (1996), S. 547-553 
    ISSN: 1573-4986
    Keywords: glycophospholipids ; ceramide-1-phosphate sugars ; azidosphingosine-1-phosphate sugars ; glycosyl phosphite ; glycosyl phosphate ; O-glycosyl trichloroacetimidate ; N-acetylneuraminic acid (Neu5Ac)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ceramide-1-phosphate sugars were synthesized by direct glycosyl phosphite/phosphate andO-glycosyl trichloroacetimidate/phosphate exchange reactions, respectively. Thus, ceramide-1-O-phosphoric acid 5 gave with sialyl phosphite1 as sialyl donor directly β-linked sialyl phosphate6; deprotection afforded the corresponding glycophospholipid ceramide-1-phosphateN-acetylneuraminate7. Similarly, fromO-glucosyl- andO-galactosyltrichloroacetimidate10 and13 with phosphoric acid derivative5 glycosyl ceramide-1-phosphate sugars12 and15, respectively, were obtained.
    Type of Medium: Electronic Resource
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