Showing papers on "Aldose published in 2020"

Mechanistic aspects of saccharide dehydration to furan derivatives for reaction media design

Abstract: The conversion of abundant hexoses (eg glucose, mannose and galactose) and pentoses (eg xylose and arabinose) to 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) is subject to intensive research in the hope of achieving competitive production of diverse materials from renewable resources However, the abundance of literature on this topic as well as the limited number of studies systematically comparing numerous monosaccharides hinder progress tracking Herein, we compare and rationalize reactivities of different ketoses and aldoses Dehydration mechanisms of both monosaccharide types are reviewed regarding the existing experimental evidence Ketose transformation to furan derivatives likely proceeds through cyclic intermediates and is hindered by side-reactions such as isomerization, retro-aldol reactions and polymerization Different strategies can improve furan derivative synthesis from ketoses: limiting the presence of water, improving the dehydration rate, protecting 5-HMF and 2-F reactive moieties with derivatization or solvent interactions and extracting 5-HMF and 2-F from the reaction medium In contrast to ketoses, aldose conversion to furan derivatives is not favored compared to polymerization reactions because it involves their isomerization or a ring contraction Enhancing aldose isomerization is possible with metal catalysts (eg CrCl3) promoting a hydride shift mechanism or with boric/boronic acids promoting an enediol mechanism This catalysis is however far more challenging than ketose dehydration because catalyst activity depends on numerous factors: Bronsted acidity of the medium, catalyst ligands, catalyst affinity for monosaccharides and their accessibility to several chemical species simultaneously Those aspects are methodically addressed to support the design of new monosaccharide dehydration systems

Conversion of Unprotected Aldose Sugars to Polyhydroxyalkyl and C-Glycosyl Furans via Zirconium Catalysis.

Abstract: An efficient, zirconium-catalyzed conversion of unprotected aldose sugars with acetylacetone to polyhydroxyalkyl furans or C-glycosylfurans is reported. The furan products are formed in up to 93% yield using 5-10 mol % ZrCl4. Pentoses are readily converted at room temperature, while hexoses and their oligosaccharides require mild heating (i.e., 50 °C). Efficient conversions of glycolaldehyde, glyceraldehyde, erythrose, a heptose, and glucosamine are also demonstrated. This approach outpaces each of the previous Lewis acid-catalyzed methods in at least one the following ways: (i) lower catalyst loadings; (ii) reduced reaction temperatures; (iii) shorter reaction times; (iv) equimolar substrate stoichiometry; (v) expanded sugar scope; (vi) higher selectivities; and (vii) the use of an Earth-abundant Zr catalyst.

H3PMo12O40 Immobilized on Amine Functionalized SBA-15 as a Catalyst for Aldose Epimerization.

Abstract: In this work various amount of phosphomolybdic acid (PMo) were immobilized on amine functionalized SBA-15 and used as heterogeneous catalysts in the epimerization of glucose in aqueous solution. 13.3PMo/NH2-SBA-15 exhibited the best catalytic performance with a glucose conversion of 34.8% and mannose selectivity of 85.6% within two hours at 120 °C. The activation energy of 80.1 ± 0.1 kJ·mol-1 was lower than that of 96 kJ·mol-1 over the homogeneous H3PMo12O40 catalyst. The catalytic activities of 13.3PMo/NH2-SBA-15 for the transformation of some other aldoses including mannose, arabinose and xylose were also investigated.

The mechanism of a one-substrate transketolase reaction.

Abstract: Transketolase catalyzes the transfer of a glycolaldehyde residue from ketose (the donor substrate) to aldose (the acceptor substrate). In the absence of aldose, transketolase catalyzes a one-substrate reaction that involves only ketose. The mechanism of this reaction is unknown. Here, we show that hydroxypyruvate serves as a substrate for the one-substrate reaction and, as well as with the xylulose-5-phosphate, the reaction product is erythrulose rather than glycolaldehyde. The amount of erythrulose released into the medium is equimolar to a double amount of the transformed substrate. This could only be the case if the glycol aldehyde formed by conversion of the first ketose molecule (the product of the first half reaction) remains bound to the enzyme, waiting for condensation with the second molecule of glycol aldehyde. Using mass spectrometry of catalytic intermediates and their subsequent fragmentation, we show here that interaction of the holotransketolase with hydroxypyruvate results in the equiprobable binding of the active glycolaldehyde to the thiazole ring of thiamine diphosphate and to the amino group of its aminopyrimidine ring. We also show that these two loci can accommodate simultaneously two glycolaldehyde molecules. It explains well their condensation without release into the medium, which we have shown earlier.

Synthesis of 6-Mercaptohexanoylhydrazones of Mono- and Disaccharides as a Potential Glycoligands of Noble Metal Glyconanoparticles

Abstract: The 1H and 13C NMR spectroscopy was used to study the structure of previously unknown aldose series condensation products (L-fucose, L-rhamnose, D-mannose, D-galactose, D-glucose, N-acetyl-D-glucosamine, N-acetyl-D-mannosamine, D-lactose and D-maltose) with 6-mercapto­hexanoic acid hydrazide—promising glycoligands of noble metal nanoparticles. It was shown that L-fucose, L-rhamnose, D-mannose, D-galactose and N-acetyl-D-mannosamine derivatives exist in solution in DMSO-d6 as a tautomeric mixture of open hydrazone and cyclic pyranose forms. The linear hydrazone form is represented by a set of Z′,E′-conformational isomers, which differ in the arrangement of substituents relative to the C–N amide bond in comparable amounts. The condensation products obtained on the basis of D-glucose, N-acetyl-D-glucosamine, D-lactose and D-maltose in the crystalline state and in solutions in DMSO-d6 have an exclusively cyclic pyranose structure represented by α,β-configurational isomers. A similar transition to the pyranose form is observed in solutions of all the studied compounds in D2O.

Laundry formulation for removing fatty compounds having a melting temperature > 30°c deposited on textiles

Abstract: Laundry formulation comprising component (a): at least one compound of the general formula (I) wherein the variables in general formula (I) are as follows: R is unsubstituted branched C8-C18 alkyl, G1 is ketose residues and/or aldose residues, wherein ketose and/or aldose residues have 5 or 6 carbon atoms; x is in the range of from 1 to 10 and refers to average values; and component (b): at least one lipase.