Carbon uronic acids

Uronic acids occupy an oxidation state between aldonic and aldanc acids They have an aldehyde function at one end of their carbon chain and a carboxyhc acid group at the other... 

The names of the individual compounds of this type are formed by replacing (a) the -ose of the systematic or trivial name of the aldose by -uronic acid , (b) the -oside of the name of the glycoside by -osiduronic acid or (c) the -osyl of the name of the glycosyl group by -osy luronic acid . The carbon atom of the (potential) aldehydic carbonyl group (not that of the carboxy group as in normal systematic nomenclature [13,14]) is numbered 1 (see 2-Carb-2.1, note 1). 

Neutral sugars increased in the water soluble fraction and didn t change on imidazole and carbonate ones. Uronic acids, on the other hand increased in the imidazole fraction and decreased in both water and carbonate ones. 

Over thirty publications resulted from Tipson s work in Levene s laboratory. Along with the work on nucleic acid components, he also studied the structures of gum arabic and other plant gums, and conducted a range of synthetic investigations on sugars, with particular emphasis on uronic acids and 5-carbon ketoses. His 1939 observation that acetylated glycosyl halides... 

There are three possible classes of sugar acids which may be produced by the oxidation of monosaccharides (Figure 9.11). The aldonic acids are produced from aldoses when the aldehyde group at carbon 1 is oxidised to a carboxylic acid. If, however, the aldehyde group remains intact and only a primary alcohol group (usually at carbon 6 in the case of hexoses) is oxidised then a uronic acid is formed. Both aldonic and uronic acids occur in nature as intermediates in... 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

Similarly, the C-1 resonance of an axial anomer is shielded relative to that of its eq.uatorial isomer. Also very distinctive are signals due to the carbon of a primary alcohol group (C-6, in the region of 6O-65 p.p.m.) and to the carboxyl group of an uronic acid moiety. Typically, as seen in Fig. 1, the carboxyl C=0 resonance is in the region of 1T5 p.p.m. although, as noted below (see Fig. 3), it is strongly pH dependent. 

Figure 4. Stick diagrams representing C-13 spectra at 22.63 MHz (22) of chon-droitins A, B, and C (4a, 4b and 4c, respectively). The vertical, light lines relate resonances for analogous C-13 nuclei in the three different polymers. Not included are sigrwls caused by the acetamido CH, and C==0 carbons, and the carboxyl carbons (U-6). Minor signals that demonstrate the presence of chon-droitin A in C, and of C in A, are found in Figure 1 of Ref. 22. A = acetamide-oxyhexose, U = uronic acid.

The formation of such chromones as 3,8-dihydroxy-2-methyl-chromone by treating uronic acids or pentoses with dilute acid was reported by Aso,119 and studied by Popoff and Theander,120 who obtained a number of these compounds in 3.5% yield, as well as some catechols. Although nothing is yet known about the mechanism of formation of these compounds, the fact that the chromones contain 10 carbon atoms and are produced both from pentoses and uronic acids suggests that they may be derived from 2-furaldehyde or re-ductic acid, or produced from a decarboxylated intermediate. 

Investigations of the mechanism of decarboxylation of hexuronic acids have largely involved kinetic and tracer studies. When either D-xylo-5-hexulosonic acid or D-glucuronic acid is converted into 27 in acidified, tritiated water, the resulting 27 contains 18% and 15%, respectively, of the activity of the solvent as carbon-bound tritium.21 Further degradation studies showed that the isotope is situated on the furan ring at either position 3 or 4, or both these atoms correspond to C-3 or C-4 of the starting uronic acid. 

URONIC ACID. Any of a class of compounds similar to sugars but differing from diem in that the terminal carbon has bee oxidized from an alcohol to carboxyl group. The most common are galacturomc acid and... 

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