Showing papers on "Pyranose published in 1992"
TL;DR: The conformation of the pyranose ring is confirmed by the excellent agreement between the experimental and calculated intracyclic scalar coupling constants, and the iso-energy contours displayed on the 'relaxed' map indicate an important flexibility about the glycosidic linkage.
52 citations
TL;DR: In this article, the 3JHH coupling constants of the free-radical precursors were estimated using the Karplus-Altona algorithm to obtain the conformational parameters of their constituent sugar moieties.
43 citations
TL;DR: The crystal structures of TM-β-CDx with m-iodophenol (MIP) and 4-biphenylacetic acid (BPA) have been determined by X-ray analysis as mentioned in this paper.
Abstract: Crystal structures of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CDx) complexes with m-iodophenol (MIP) and 4-biphenylacetic acid (BPA) have been determined by X-ray analysis. The macrocylic ring of TM-β-CDx is elliptically distorted in both complexes. The 2,3,6-tri-O-methylglucose residues incline against the plane through seven glycosidic oxygen atoms to relieve the steric hindrance involving methyl groups at the O(2), O(3) side. In the MIP complex, one glucose residue exhibits the skew (twist boat) conformation. The MIP molecule is fully included within the TM-β-CDx cavity, both ends of which are blocked by adjacent molecules, and the hydroxy group is hydrogen-bonded to O(2) of the host TM-β-CDx. In the BPA complex, the phenyl group is located at the centre of the cavity while half a molecule protrudes from the O(2), O(3) side. The carboxy group of BPA is located in intermolecular space to form a hydrogen bond with an adjacent TM-β-CDx molecule. The complex formation induces the chiral conformation in BPA. The biphenyl group is in the R-configuration with an angle of 42.4° between the two benzene rings.
32 citations
TL;DR: Two enzymes, pyranose 2-oxidase and a previously uncharacterized D-arabino-hexos-2-ulose-utilizing enzyme, may be sufficient for the biosynthesis of cortalcerone from glucose in vivo and another enzyme, which appears to be a dimer of 95-kDa subunits, has been purified 450-fold and has been named aldos- 2-ULose dehydratase.
32 citations
TL;DR: In this paper, the Intramolecular Diels-Alder routes for the preparation of bis-annulated pyranosides, as chiral precursors of functionalized trans-decalin rings of terpenoid natural products, have been investigated.
Abstract: Intramolecular Diels-Alder routes for the preparation of bis-annulated pyranosides, as chiral precursors of functionalized trans-decalin rings of terpenoid natural products, have been investigated
30 citations
TL;DR: The structure of this complex supports the hypothesis that an imidazole group catalyzes ring opening of the pyranose, and a stereochemically sensible model is produced which is consistent with other data.
Abstract: Crystal structures of complexes of D-xylose isomerase with deoxysugars have been determined. Deoxynojirimycin is a structural analogue of alpha-pyranose and mimics the binding of these aldose substrates. The structure of this complex supports the hypothesis that an imidazole group catalyzes ring opening of the pyranose. The steric restrictions in the active site of the enzyme prevent a beta-pyranose from binding in the same way. For the reverse reaction with ketoses, the anomeric specificity is less certain. Dideoxyimino-D-glucitol is a structural analogue of the ketose alpha-D-furanose. The binding of the inhibitor dideoxyimino-D-glucitol to the crystals of the enzyme does not mimic the binding of the reactive alpha-D-fructofuranose. Superposition of the nonphysiological substrate alpha-D-fructofuranose onto the atomic positions of dideoxyimino-D-glucitol is not possible due to the steric restrictions of the active site. However, by utilizing the approximate 2-fold symmetry of the sugar, a stereochemically sensible model is produced which is consistent with other data. In addition to reaction with alpha-D-furanose, the enzyme probably reacts with open ring keto sugars which are present at significant concentrations. Other sugars which resemble furanoses either do not inhibit significantly or are not observed in the crystals bound in a single conformation.
29 citations
TL;DR: In this paper, the Wittig-Horner reaction was used to obtain carbon-carbon bonding at the anomeric position of carbohydrates, which was first reported by Zhdanov ef.
23 citations
TL;DR: The n.m.r. spectrum of the amorphous, dehydrated trihydrate suggests the occurrence of a solid-state reaction forming the same isomeric mixture as was observed in crystalline anhydrous lactulose, although the mutarotation of the triHydrate when dissolved in Me2SO is very slow.
20 citations
TL;DR: The conformation of D-glucopyranose and 6-deoxy-6-fluoro-Dglucose (6DFG) in solution, as determined by 1H and 19F NMR, is reviewed in this paper.
Abstract: The conformation of D-glucopyranose and 6-deoxy-6-fluoro-D-glucose (6DFG) in solution, as determined by 1H and 19F NMR, is reviewed. The 1H NMR spectra of α- and β-methyl D-glucopyranosides and 6DFG in methanol, acetone, DMSO, and aqueous solution were acquired and fully analysed. A 19F NMR spectrum of the methanol 6DFG solution, together with a 1H COSY spectrum of α-6DFG in methanol, were recorded. Accurate analyses of the ABC and ABCX spectra produced by the CHCH2OH and CHCH2F moieities, respectively, were performed, and from the vicinal J(H-5,H-6) coupling constants the populations of the three possible staggered rotamers about the C-5C-6 bond were calculated. The rotamer in which F is antiperiplanar to the ring O is particularly disfavoured, whereas the rotamer with F antiperiplanar to H-5 is most favoured. This general trend was seen for both pyranose anomers in all four solvents.
20 citations
17 citations
TL;DR: In this article, the generation and fragmentation of the C1-alkoxy radicals of pyranose derivatives are nicely promoted by (diacetoxyiodo)benzene or lead tetraacetate in the presence of iodine catalyst under mild conditions to give the corresponding mixed-acetal formates which are further converted to the furanose derivative by acid-catalysed transacetalization.
TL;DR: A comparison of the free-energy profiles for the hydrolyses of lactose catalysed by the double mutant with those for the wild-type and the single mutants reveals that free- energy changes from the two mutations are not in general independently additive, but that the changes generally are in the direction predicted by the theory of Burbaum, Raines, Albery & Knowles.
Abstract: 1. The ratio of ebgA-gene product of ebgC-gene product in the functional aggregate of ebg beta-galactosidases was determined to be 1:1 by isolation of the enzyme from bacteria grown on uniformly radiolabelled amino acids and separation of the subunits by gel-permeation chromatography under denaturing conditions. 2. This datum, taken together with a recalculation of the previous ultracentrifuge data [Hall (1976) J. Mol. Biol. 107, 71-84], analytical gel-permeation chromatography and electron microscopy, strongly suggests an alpha 4 beta 4 quaternary structure for the enzyme. 3. The second chemical step in the enzyme turnover sequence, hydrolysis of the galactosyl-enzyme intermediate, is markedly slower for ebgab, having both Asp-97----Asn and Trp-977----Cys changes in the large subunit, than for ebga (having only the first change) and ebgb (having only the second), and is so slow as to be rate-determining even for an S-glycoside, beta-D-galactopyranosyl thiopicrate, as is shown by nucleophilic competition with methanol. 4. The selectivity of galactosyl-ebgab between water and methanol on a molar basis is 57, similar to the value for galactosyl-ebgb. 5. The equilibrium constant for the hydrolysis of lactose at 37 degrees C is 152 +/- 19 M, that for hydrolysis of allolactose is approx. 44 M and that for hydrolysis of lactulose is approx. 40 M. 6. A comparison of the free-energy profiles for the hydrolyses of lactose catalysed by the double mutant with those for the wild-type and the single mutants reveals that free-energy changes from the two mutations are not in general independently additive, but that the changes generally are in the direction predicted by the theory of Burbaum, Raines, Albery & Knowles [(1989) Biochemistry 28, 9283-9305] for an enzyme catalysing a thermodynamically irreversible reaction. 7. Michaelis-Menten parameters for the hydrolysis of six beta-D-galactopyranosylpyridinium ions and ten aryl beta-galactosides by ebgab were measured. 8. The derived beta 1g values are the same as those for ebgb (which has only the Trp-977----Cys change) and significantly different from those for ebgo (the wild-type enzyme) and ebga. 9. The alpha- and beta-deuterium secondary isotope effects on the hydrolysis of the galactosyl-enzyme of 1.08 and 1.00 are difficult to reconcile with the pyranose ring in this intermediate being in the 4C1 conformation.
TL;DR: The results confirm that GC/MS of the alkoxime-TMS derivatives is a viable method for measuring ( 13)C incorporations at individual carbon atoms in each of the sugar phosphates during photosynthetic experiments with (13)CO(2).
Abstract: The electron impact mass spectrometric fragmentation patterns of the per-O-trimethylsilyl (TMS) and alkoxime-TMS derivatives of D-glycerol-D-altro and D-glycerol-D-ido-octuloses were fully analysed using seven specifically labelled 13C analogues. Many of the more intense- ions in the spectra of the per-O-TMS furanose and pyranose derivatives have more than one origin. On the other hand, the mass spectra of the straight-chain methoxime and ethoxime hepta-O-TMS derivatives contain ions each of which in general originares from a single cleavage process. This makes gas chromatography/mass spectrometry of the aikoxime-TMS derivatives a suitable method for monitoring 13C incorporations at individual carbon atoms in the corresponding octulose phosphates during photosynthesis experiments with 13CO2.
TL;DR: In this paper, N-Acetylneuramimic acid (sialic acid) was synthesized through relatively short steps from d -glucose via a key intermediate 1,5-lactone derivative obtained from the pyranose isomer of the aldol condensation products of d -lucose with oxalacetic acid.
TL;DR: Reduction of carbohydrates by tritiated borohydride resulted in the production of alditols or glycosides with characteristically divergent specific radioactivities, which produced a characteristic and reproducible specific activity in which the values varied from 51 to 182% of that found for talose.
Abstract: Reduction of carbohydrates by tritiated borohydride resulted in the production of alditols or glycosides with characteristically divergent specific radioactivities. Simultaneous reduction of individual sugars in the presence of a reference standard, talose, permitted the assignment of a unique specific radioactivity with respect to talitol as 100%. A variety of structures was examined, including neutral hexoses, free and acetylated aminosugars, ketohexoses and glycosides containing a fixed pyranose ring adjacent to a carbonyl group. In the latter case, the resulting steric hindrance severely restricted the incorporation of tritium. In both of the ketohexoses tested, the minor product of the two epimeric alditols exhibited the higher specific radioactivity. In all cases, reduction produced a characteristic and reproducible specific activity in which the values varied from 51 to 182% of that found for talose. These results are interpreted on the basis of generalizations concerning mechanism and predictive value.
TL;DR: The major tautomers of D-fructose in water are the β-pyranose and β-furanose forms, the former predominating as discussed by the authors.
Abstract: The major tautomers of D-fructose in water are the β-pyranose and β-furanose forms, the former predominating. NMR studies have shown that when aqueous DNA is added, there is a shift in the β-pyranose ⇌β-furanose equilibrium, the latter form being favoured. It is suggested that this is caused by weak, preferential binding of the β-furanose form to DNA. This is supported by computer modelling, which shows that for the former, only two hydrogen bonds can be formed between sugar O–H groups and phosphate units, whereas three good bonds can be formed with the latter.Studies of the O–1H resonances of the anomeric groups of the two forms confirm this change in equilibrium. In addition this feature for the β-furanose form shifts to low-field without significant broadening. This indicates that strong hydrogen bonding to DNA occurs, but that the equilibrium is very rapid giving fast averaging of the NMR signals.
TL;DR: The fluoren-9-yl ether groups could be removed easily by catalytic hydrogenation or by hydrogenolysis with the Lewis acid-type mixed hydride AlCl 2 H as discussed by the authors.
TL;DR: The complexation of four 1,6,anhydro-β-D-hexopyranoses with europium(III) was studied in aqueous solution by natural abundance 17 O NMR as mentioned in this paper.
Abstract: The complexation of four 1,6,anhydro-β-D-hexopyranoses with europium(III) was studied in aqueous solution by natural abundance 17 O NMR. The paramagnetic ion induced contact shifts of individual hydroxy and ether resonances to low frequency. A clear indication of tridentate complexes was obtained, proving the involvement of the oxygen atom of the anhydro ring in talosan and mannosan and that of the pyranose ring in glucosan
TL;DR: In this paper, a highly selective ring opening reduction of methyl 3O-allyl-2,4-di-O-benzyl-6-deoxy-β-d -glucopyranose was proposed.
TL;DR: The title 1, 2-anhydro sugar (10) was synthesized from methyl 4, 6-O-benzylidene-α-D-glucopyranoside as mentioned in this paper.
TL;DR: In this article, it was shown that 4,6-O-benzylidene-1,2-dideoxy-3-C-(2-propenyl- or 2-methyl)-D-lyxo-hex-1-enopyranose gave the corresponding ribo isomer in a ratio ranging from 1 : 1 to 10 : 1
Abstract: 4,6-O-Benzylidene-1,2-dideoxy-D-threo-hex-1-enopyranose-3-urose reacted with allylic organometallic reagents, CH2=CR–CH2–Metal [R = H or CH3; Metal = MgCl, AlEt2, or Ti(OPri)3], to selectively give 4,6-O-benzylidene-1,2-dideoxy-3-C-(2-propenyl- or 2-methyl-2-propenyl)-D-lyxo-hex-1-enopyranose. On the other hand, the erythro isomer gave 3-C-(2-propenyl- or 2-methyl-2-propenyl)-D-arabino-hex-1-enopyranose and the corresponding ribo isomer in a ratio ranging from 1 : 1 to 10 : 1