- Dihydroxyacetone variants in the organocatalytic construction of carbohydrates: Mimicking tagatose and fuculose aldolases
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Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3- dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase.
- Suri, Jeff T.,Mitsumori, Susumu,Albertshofer, Klaus,Tanaka, Fujie,Barbas III, Carlos F.
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- L-Ribose: An easily prepared rare sugar
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A method to synthesize L-ribose was described by molybdate-catalyzed epimerization of the readily available L-arabinose. The synthesis is one-step and except for a catalytic amount of molybdic acid do not require any expensive reagents, while the solvents used are water and a small amount of methanol. The process can be carried out in 2-3 days. Although the yield of L-ribose is only 20%, being in equilibrium with arabinose, most of the unreacted arabinose is recoverable and can be used again.
- Angyal, Stephen J.
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- Selective electrocatalytic oxidation of sorbitol to fructose and sorbose
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A new electrocatalytic method for the selective electrochemical oxidation of sorbitol to fructose and sorbose is demonstrated by using a platinum electrode promoted by p-block metal atoms. By the studying a range of C4, C5 and C6 polyols, it is found that the promoter interferes with the stereochemistry of the polyol and thereby modifies its reactivity.
- Kwon, Youngkook,De Jong, Ed,Van Der Waal, Jan Kees,Koper, Marc T. M.
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p. 970 - 973
(2015/03/30)
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- A heterogeneous Pd-Bi/C catalyst in the synthesis of l-lyxose and l-ribose from naturally occurring d-sugars
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A critical step in the synthesis of the rare sugars, l-lyxose and l-ribose, from the corresponding d-sugars is the oxidation to the lactone. Instead of conventional oxidizing agents like bromine or pyridinium dichromate, it was found that a heterogeneous catalyst, Pd-Bi/C, could be used for the direct oxidation with molecular oxygen. The composition of the catalyst was optimized and the best results were obtained with 5:1 atomic ratio of Pd:Bi. The overall yields of the five-step procedure to l-ribose and l-lyxose were 47% and 50%, respectively. The synthetic procedure is advantageous from the viewpoint of overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the heterogeneous oxidation catalyst can be easily separated from the reaction mixture and reused with no loss of activity.
- Fan, Ao,Jaenicke, Stephan,Chuah, Gaik-Khuan
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supporting information; experimental part
p. 7720 - 7726
(2011/12/04)
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- Synthesis of racemic ribose from D-glucose
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Racemic ribose is a valuable starting material for investigations of the origins of biomolecular homochirality. It can be synthesized in seven steps starting from D-glucose.
- Miculka, Christian
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p. 948 - 950
(2007/10/03)
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- SYNTHESIS OF MONOSACCHARIDES WITH THE AID OF A NEW SYNTHETIC EQUIVALENT FOR THE GLYCOLALDEHYDE ANION
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The synthesis and characterization of previously unknown B-aryl- and B-alkyl-1,3,2-dioxaboroles is reported.These compounds can act as synthetic equivalents for the glycolaldehyde anion, because they undergo an aldol-type reaction with aldehydes yielding mono, and large amounts of multiple, addition products.By immobilizing the 1,3,2-dioxaboroles on a polymeric support, which accomplishes the site separation of the enediolate intermediates, further addition beyond the primary stage could be inhibited.As a first example of a synthetic application, the synthesis of the otherwise arduously accesible l-ribose was undertaken. 2,3-O-Cyclohexyliden-L-glyceraldehyde reacted with polymer-bound 1,3,2-dioxaborole to give a mixture of pentoses in good yield, from which 54percent of enantiomerically pure L-ribose could be isolated.This work provides a general methodology for the lengthening of sugar chains by two C-atoms, thus furnishing a novel route for the synthesis of rare sugars.
- Wulff, Gunther,Hansen, Achim
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p. 123 - 140
(2007/10/02)
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- Kinetics, Catalysis, and Mechanism of the Secondary Reaction in the Final Phase of the Formose Reaction
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In the final phase of the formose reaction sugars are formed by the reaction of glycolaldehyde, glyceraldehyde and dihydroxyacetone.The application of high-pressure liquid chromatography allows for the first time to investigate intermediate and final products quantitatively.The results of kinetical investigations allow to suggest a reaction mechanism for the secondary reaction in the final phase of the formose reaction.This mechanism is compared with that of the starting phase and other known mechanisms.From the results metal ion-catalyzed aldol reactions have to be assumed.
- Harsch, Guenther,Bauer, Hermann,Voelter, Wolfgang
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p. 623 - 635
(2007/10/02)
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- THE FORMOIN REACTION
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The formoin reaction, i.e., the autocondensation of formaldehyde in an aprotic solvent catalysed by the conjugate base of a thiazolium ion, has been studied in detail.Glucose, galactose, dihyroxyacetone dimer, xylose, and arabinose have been identified as products.The influence of catalysts, temperature, basicity, and reaction time is documented.N,N-Dimethylformamide is a more convenient solvent than ether, benzene, or diglyme.Ethyldi-isopropylamine affords better yields of carbohydrate material than triethylamine.At =60 deg, aldol condensations are reduced to a minimum.After 1-2 h of reaction (depending on the conditions), the yields begin to decrease and become zero after ca. 24 h.
- Castells, Josep,Lopez-Calahorra, Francisco,Geijo, Fernando
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p. 197 - 208
(2007/10/02)
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