Showing papers on "Aldose published in 2015"

Computational Insight into the Effect of Sn-Beta Na Exchange and Solvent on Glucose Isomerization and Epimerization

Abstract: Sn-substituted zeolite Beta (Sn-Beta) is a promising catalyst for efficient aldose to ketose isomerization, a key step in the conversion of biomass to platform chemicals such as 5-(hydroxymethyl)furan and furfural. Recent experimental studies probing the mechanism and active site for glucose isomerization (to fructose) and competing epimerization (to mannose) have found that isomerization proceeds via a 1,2 intramolecular hydride transfer (HT) and epimerization by either two subsequent HT steps (on pure Sn-Beta; water and methanol) or one 1,2 intramolecular carbon shift (CS) step (on Na-exchanged Sn-Beta; water and methanol). In order to address remaining atomic-level mechanistic questions raised by this data, we investigate the various pathways with computational methods using several sizes of cluster models of Sn-Beta and density functional theory. First, we find an energetically plausible pathway for mannose formation via two subsequent HT steps that is consistent with experimental observations. Additi...

Kinetic study of the competitive hydrogenation of glycolaldehyde and glucose on Ru/C with or without AMT

Abstract: The competitive hydrogenation of glycolaldehyde and glucose over 1% Ru/C catalyst was studied in a batch reactor at 373–403 K and 6 MPa hydrogen pressure, with or without the presence of ammonium metatungstate (AMT). It was found that the presence of AMT retarded significantly the hydrogenation of both aldoses, and this suppressing effect was more pronounced on the glucose hydrogenation. The hydrogenation of glycolaldehyde occurred always preferentially to the glucose hydrogenation, with or without the presence of AMT. The kinetic data in the absence of AMT were well modeled based on Langmuir–Hinshelwood–Hougen–Watson kinetics assuming the surface reaction being rate-determining and noncompetitive adsorption of dissociatively chemisorbed hydrogen and aldose. However, in the presence of AMT, the complexing between AMT and aldose and the strong adsorption of AMT on Ru surface must be considered in the development of new kinetic model. The as-modified model described the data satisfactorily. © 2014 American Institute of Chemical Engineers AIChE J, 61: 224–238, 2015

Diastereoselective Synthesis of Glycosyl Phosphates by Using a Phosphorylase–Phosphatase Combination Catalyst

Abstract: Sugar phosphates play an important role in metabolism and signaling, but also as constituents of macromolecular structures. Selective phosphorylation of sugars is chemically difficult, particularly at the anomeric center. We report phosphatase-catalyzed diastereoselective "anomeric" phosphorylation of various aldose substrates with α-D-glucose 1-phosphate, derived from phosphorylase-catalyzed conversion of sucrose and inorganic phosphate, as the phosphoryl donor. Simultaneous and sequential two-step transformations by the phosphorylase-phosphatase combination catalyst yielded glycosyl phosphates of defined anomeric configuration in yields of up to 70 % based on the phosphate applied to the reaction. An efficient enzyme-assisted purification of the glycosyl phosphate products from reaction mixtures was established.

Process for the continuous production of ethylene glycol from carbohydrates

Abstract: A continuous process for converting carbohydrates to ethylene and propylene glycol. The carbohydrates are mixed with water and passed through a reactor at a temperature that hydrolyzes the carbohydrate mixture at least partially to monosaccharides. The reactor has a first zone comprising a retro-aldol catalyst and a second zone comprising a reducing catalyst. The aldose is converted in the first zone into glycolaldehyde by the retro-aldol catalyst and the glycolaldehyde, in the presence of hydrogen, is converted to ethylene glycol in the second zone of the reactor. The reaction products are removed from the reactor and the ethylene glycol is recovered. The selectivity to propylene glycol can be enhanced via feeding ketose as the carbohydrate.

Structure and function of Caulobacter crescentus aldose-aldose oxidoreductase.

Abstract: Aldose–aldose oxidoreductase ( Cc AAOR) is a recently characterized enzyme from the bacterial strain Caulobacter crescentus CB15 belonging to the glucose-fructose oxidoreductase/inositol dehydrogenase/rhizopine catabolism protein (Gfo/Idh/MocA) family. Cc AAOR catalyses the oxidation and reduction of a panel of aldose monosaccharides using a tightly bound NADP(H) cofactor that is regenerated in the catalytic cycle. Furthermore, Cc AAOR can also oxidize 1,4-linked oligosaccharides. In the present study, we present novel crystal structures of the dimeric Cc AAOR in complex with the cofactor and glycerol, D-xylose, D-glucose, maltotriose and D-sorbitol determined to resolutions of 2.0, 1.8, 1.7, 1.9 and 1.8 A (1 A=0.1 nm), respectively. These complex structures allowed for a detailed analysis of the ligand-binding interactions. The structures showed that the C1 carbon of a substrate, which is either reduced or oxidized, is close to the reactive C4 carbon of the nicotinamide ring of NADP(H). In addition, the O1 hydroxy group of the substrate, which is either protonated or deprotonated, is unexpectedly close to both Lys104 and Tyr189, which may both act as a proton donor or acceptor. This led us to hypothesize that this intriguing feature could be beneficial for Cc AAOR to catalyse the reduction of a linear form of a monosaccharide substrate and the oxidation of a pyranose form of the same substrate in a reaction cycle, during which the bound cofactor is regenerated. * Cc AAOR, : Caulobacter crescentus aldose–aldose oxidoreductase; PDB, : Protein Data bank; Zm GFOR, : Zymomonas mobilis glucose–fructose oxidoreductase

Kinetic effect of alcohols on hexose isomerization under subcritical aqueous conditions

Abstract: The kinetic effect of subcritical aqueous alcohols (methanol, ethanol, 1-propanol, 2-propanol, and t-butyl alcohol) on the isomerization of hexoses (mannose, glucose, and fructose) was examined at 180 °C at the alcohol concentrations ranging from 0 to 80% (v/v). The results showed that increase in the concentration of primary and secondary alcohols markedly promoted the aldose-to-ketose isomerization; however, the ketose was scarcely isomerized to aldose and predominantly decomposed. Further, the kinetic analysis revealed that the rate constants of isomerization and decomposition strongly depended on the dielectric constant of the aqueous alcohols. The rate constants for isomerization were more sensitive to the change in the dielectric constant than the decomposition rate constants. On the other hand, the isomerization reactions of mannose and fructose were suppressed in subcritical aqueous t-butyl alcohol despite the low dielectric constant of the solution.

Synthetic method of saponin

Abstract: The invention belongs to the field of organic synthesis, and involves a synthesis method of saponin, and in particular a method to construct glycosidic bond in saponin. The method includes the following steps: directly reacting an excessive amount of aldose or ketose with aglycone in an appropriate organic solvent under the action of an acid catalyst and reflux temperature of 30 DEG C to obtain the target product of saponin.

Method for synthesizing saponin

Abstract: The present invention belongs to the field of organic synthesis, relates to a method for synthesizing a saponin, and in particular, to a method for constructing a glycosidic bond in a saponin, and comprises the following steps: directly reacting an excessive amount of aldose or ketose with aglycone in a suitable organic solvent at 30 DEG C to a reflux temperature and with the presence of an acid catalyst, to obtain a target product saponin.

Fructose as an inducer of free radical peroxidation of natural lipid-protein supramolecular complexes.

Abstract: D-fructose strongly stimulates peroxidation of natural lipid-protein supramolecular complexes in vitro regardless of the oxidation initiation method. Fructose (ketose) intensifies free radical peroxidation to a much greater extent than glucose (aldose), which is important for the etiology and pathogenesis of diabetes mellitus.