Uronic acids preparation

Determination of xylan is frequently made by estimation of furfural production. Data so obtained, even when appropriately corrected for furfural that arises from uronic acid, may be high if araban is present in the polysaccharide preparation. In the absence of interfering carbohydrates, furfural estimation may lead to accurate xylan values. 

An alternative method for their preparation is by oxidation of uronic acids (XV) which are available from alginic acids (from kelp). 

All of the possibilities mentioned are credible perhaps each participates to some extent in the reaction. No studies similar to those with aldoses have been made of substituted uronic acids, and no intermediates have been isolated. Aso,96 who first suggested 72 as a precursor for 2-furaldehyde and reductic acid,92 has prepared 72, but its significance in the decarboxylation reactions has not been fully examined.123... 

Aso98 first proposed 5-hydroxy-2-oxo-3-pentenal (94) as an intermediate in the conversion of uronic acids to reductic acid,190 191 but this proposal does not appear to have been experimentally tested, although the intermediate was prepared.190 Isbell121 suggested a mechanism in which the formation of reductic acid and 2-furaldehyde from pentoses and uronic acids results from the reaction of different tautomers of 94. Although other mechanisms have been suggested,100 102 115 Isbell s original scheme seems adequate to explain the experimental facts. 

The sole component of the uridine diphosphate uronic acid fraction from animal tissues,10,124,139 Chlorella,4 red algae,83 and some bacteria118,119 is uridine 5 -(a-D-glucopyranosyluronic acid pyrophosphate) (32), whereas a similar preparation from Pneumococcus140 contains only the a-D-galactopyranosyluronic acid derivative. Both esters have been shown to occur in extracts of mung bean.141,142... 

It may be necessary to prepare an alternative dilution series depending on the uronic acid content of your samples. 

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