Uronic acid derivatives, natural

Some examples of natural uronic acid derivatives... 

Glucuronic acid is widely distributed in nature, it is the uronic acid derived from glucose. 

The determination of the structure of a plant gum involves the establishment of its homogeneity, its equivalent weight, and rotation and its uronic acid and pentosan content by the well-known methods. The nature of the constituent sugars and the uronic acid are then determined, after hydrolysis of the gums, by ciystallization or by conversion into characteristic crystalline derivatives. As an example the hexose mannose may be identified as the free sugar or in the form of its anilide, methyl glycoside or phenylhydrazone. Autohydrolysis of the acid... 

Many important natural products are (formerly) derived by chain elongation at position 5 of pentoses, or at position 6 of hexoses. Uronic acids, which are easily prepared, can be converted into the 4 radical 90 by chemistry based on the thiohydroxamate 6.77 We postulated that, if the hindrance on the a-side of the molecule was great enough, the carbon-carbon bond formed by reaction of 90 with a suitable radicophilic olefin would be the natural / -bond. In fact, even a dimethyl-ketal as in 90 (B = natural base or protected derivative thereof) was sufficient to direct the bond formation very largely to the desired face.77 The diacetone ketal of glucuronic acid 91 upon conversion to its iV-hydroxy-2-thiopyridone derivative 92 and then photolysis in the usual way in the presence of methyl acrylate gave the expected derivative 93 as a mixture of... 

In contrast, two neutral amino acids can make only two different dipeptides an acidic and a basic amino acid can make only four different dipeptides. There are about 20 different common monosaccharides (including the amino sugars, uronic acids, and other derivatives). Thus, the potential for variability among polysaccharides is even greater than that of proteins. However, almost all polysaccharides found in nature are composed of repeating units of fewer than 5 different monosaccharides. 

The Tables list oligosaccharide polymers of simple monosaccharides and of the following naturally occurring derivatives amino sugars, 2-acetamido sugars, uronic acids, and mono-O-methyluronic acids. Although it was considered desirable to include only compounds whose structures had been established beyond doubt, such a rule would have excluded many important compounds. Exceptions to this rule were, therefore, made for compounds of incompletely established structure, provided that there was sufficient evidence to show that they were unlikely to be compounds already known. 

The uronic acids may be defined as carbohydrate derivatives possessing both aldehyde (or hemiacetal) and carboxyl groups. The formulas for the three naturally occurring acids are given below. 

In 1934, Karl Meyer and his colleague John Palmer isolated a previously luiknown chemical substance from the vitreous body of cows eyes. They found that the substance contained two sugar molecules, one of which was uronic acid. For convenience, therefore, they proposed the name hyaluronic acid . The popular name is derived from hyalos , which is the Greek word for glass + uronic acid [8], At the time, they did not know that the substance which they had discovered would prove to be one of the most interesting and usefirl natural macromolecules. HA was first used commercially in 1942 when Endre Balazs applied for a patent to use it as a substitute for egg white in bakery products[9]. 

Some natural sugar derivatives need special separation conditions. Uronic acids for instance, can be separated with solvent systems containing acetic, phosphoric or hydrochloric acid (50,51) and some amino sugars, and their derivatives can be satisfactorily separated with solvent systems containing ammonia. 

A number of uronic acids occur fairly abundantly in nature. Some are constituents of polysaccharides of importance in food processing, such as gel-forming and thickening agents, e. g. pectin (D-galacturonic acid) and sea weed-derived alginic acid (D-mannuronic acid, L-guluronic acid). 

The condensation of hexuronic acid derivatives with hexosaminides to give amide-linked disaccharides is referred to in Chapter D-Galacturonic acid has been identified as a component of Pneumococcus type 25 capsular polysaccharide," and 2-O-methyl-D-glucuronic acid has been isolated for the first time in Nature from an extracellular polysaccharide of a species (Porphyridium cruentum) of red alga. The acidic sugar component in Klebsiella type 37 capsular polysaccharide has been identified as 4-0-[(5)-l-carboxyethyl]-D-glucuronic acid. Antibiotic substances and nucleosides that contain uronic acid components are referred to in Chapters 20 and 21, respectively. 

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