Carbohydrates Conversion

Novel Hydride Transfer Catalysis for Carbohydrate Conversions... 

Fig. 2.3 Key reactions in carbohydrate conversion (the arrows represent the retro-Aldol and Michael reactions).

Vertebrates cannot convert fatty acids, or the acetate derived from them, to carbohydrates. Conversion of phosphoenolpyruvate to pyruvate (p. 532) and of pyruvate to acetyl-CoA (Fig. 16-2) are so exergonic as to be essentially irreversible. If a cell cannot convert acetate into phosphoenolpyruvate, acetate cannot serve as the starting material for the gluconeogenic pathway, which leads from phosphoenolpyruvate to glucose (see Fig. 15-15). Without this capacity, then, a cell or organism is unable to convert fuels or metabolites that are degraded to acetate (fatty acids and certain amino acids) into carbohydrates. 

As a consequence of bottle aging, carbohydrate conversions can occur, although slowly at cellar temperature, to form the caramel-like 2-furfural aroma for example, in aged Madeira wines. Rapp and Giintert (86MI141) have shown that such carbohydrate decomposition in Riesling wines leads to 2-furfural 9,2-acetylfuran 10, ethyl furan-2-carboxylate 11, 2-formyl pyrrole 12, and 5-hydroxymethylfurfural 13. 

J. Defaye and C. Pedersen, Hydrogen fluoride, solvent and reagent for carbohydrate conversion technology, in F. W. Lichtenthaler (Ed.), Carbohydrates as Organic Raw Materials, Vol. 1, VCH, Weinheim, 1991, pp. 247-265. 

The com industry makes widespread use of enzymes for carbohydrate conversion. The advent of enzyme technology in the corn industry in the 1960s dramatically changed the starch industry and allowed the development of new products. Today, enzyme hydrolysis of starch has largely replaced acid hydrolysis, which is used as an adjunct in starch conversion. Enzymes used to make corn syrups and HFCS include the following. 

Carbohydrate conversion. Write a balanced equation for the formation of glycogen from galactose. 

The fermentation of the corn fiber hydrolysate generated by the initial hydrolysis method proved to be successful in producing a high concentration of ethanol from glucose and xylose. The total carbohydrate conversion is lower than the best possible, but the fermentation method has not been optimized. 

Standard carbohydrate conversions were used to convert methyl 3,4-anhydro-2-deoxy-6-O-trityl-0 -D-n o-hyxopyranoside into the dithioacetal (32), which was then condensed with the dienal (33) in a synthesis of the natural enantiomer of jV-methylmaysenine (34) (the sugar carbon atoms are indicated). ... 

The majority of current industrial-scale applications of immobilized microbial cells in continuous biolechnical processes are based on single-enzyme-catalyzed transformations. Potential applications involve carbohydrate conversions, of which... 

Carbohydrate conversion into new industrial intermediates and end-products like propanediol, methane or syngas needs either net energy input ( reduction equivalents ) or decarboxylation, which results in a significant and costly yield loss and lowers the CO2 fixation net gain. This balance loss is also a conceptual draw-back of present fuel ethanol fermentation from sucrose and starch hydrolysates. So far, the only bulk intermediates with no or minimal... 

Derivatization of the reducing terminus, usually by reductive amination " (Figure 19.2), is necessary for detection of carbohydrates by optical methods and is frequently used for mass spectral analysis for purposes such as enhancement of signals or modification of fragmentation patterns. The reductive amination reaction with 2-aminopyridine (2-AP) can be reversed to recover the carbohydrate." Conversion to aminobenzoic acid alkyl esters increase hydrophobicity and can improve sensitivity, " " particularly for... 

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