Acid uronic

Uronic Acids 64a, b, c) a. Preparation and Occurrence See also Chapter XII) 

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. 

The isolation of uronic acids from polysaccharides is not easy. Some of the linkages are very resistant to acid hydrolysis. Sulfuric acid (4%) at 120 for 10 to 24 hours 56) is often required. This harsh treatment may decompose the products considerably, and the yields are generally low. Cold 80 % sulfuric acid, 3 % oxalic acid at 100°, boiling 98 % formic acid 8 hours at 100° (for methylated alginic acid), and boiling 90% formic acid have been used for the hydrolysis of alginic acid (57). In the pectin field, enzymic hydrolysis has been used for the isolation of galacturonic acid the procedure is very mild and excellent yields are obtained. 

Two general methods for the synthesis of uronic acids have been developed (1) the reduction of the monolactones of aldaric acids, and (2) the oxidation of primary alcoholic groups of sugars or derivatives. The monolactones of dibasic acids can be reduced by sodium amalgam in acid solution 

Artz and E. M. Osman, Biochemistry of Glucuronic Acid. Academic Press, New York, 1950 G. O. Aspinall, Advances in Carbohydrate Chem. 9, 131 (1954). 

Uronic acids occur in seawater in the particulate polysaccharide fraction as the building blocks of the cell walls of bacteria and certain algae (Percival, 1968). Algal excretions have also been shown to contain uronic acids (Helle-bust, 1965) and phytoplankton and particulate organic matter have previously been analysed for total hexuronic acid (Williams and Craigie, 1970). Handa et al. (1972) isolated a glucuromannan from POM by extraction with 4% NaOH followed by acid hydrolysis. 

Although uronic acids are produced by marine biota and the residues may be found in particulate matter and sediments, with the exception of a limited number of analyses (Mopper, 1977 Mopper and Larsson, 1978), data on the occurrence of uronic acids, in either the monomeric or polymeric dissolved fractions of seawater, are non-existent. The values reported for five identified uronic acids by the above authors are in the range between 10— 100 nmole 1 for individual acids in a single sample of hydrolysed North Sea surface water. 

There is no standardised procedure for the hydrolysis of dissolved polymeric uronic acids. Mopper (1977) su ests much milder procedures than are used for sugars since uronic acids are much more labile towards decarboxylation or transformation reactions. The hydrolysis procedure suggested by Burney and Sieburth (1977) may therefore prove to be adequate. The use of cation-exchange resin in the form may also be effective. 

Determination of uronic acids in the free dissolved fraction of seawater poses several difficulties, not least the low expected levels ( 0.02 pmole 1 Mopper, 1977) and difficulties in removing inorganic salts from per se ionic organic compounds. 

The chromatographic analyses described by Mopper and Larsson (1978), with an improved version described by Mopper (1978b), rely on the separation of complex uronic acid mixtures on anion-exchange columns in the acetate form with acetate buffers as eluant and are capable of detecting uronic acids in the nanomole range with Cu-bicinchoninate as locating agent. 

The methods of synthesis of uronic acids by catalytic and nonspecific oxidation of sugars has been reviewed,and a study of the oxidation of octyl a-D-glucopyranoside to octyl a-o-glucopyranosiduronic acid by sodium hypobromite catalysed by some ruthenium complexes has been reported. The stability constants of metal ion-uronic acid complexes have been reviewed.  

The new sugar 3-0-[(R)-l-carboxyethyl]-D-glucuronic acid has been identified as a constituent of the exopolysaccharide produced by the bacterium Altermonas sp.l644 originally from deep sea hydrothermal vents.  

Methyl (methyl a- and jS-D-glucopyranosid)uronate and benzyl 2,3,4-tri-O-(chloroacetyl)-j8-D-glucopyranosiduronic acid and its methyl ester have been 

Zhdanov, G. V. Bogdanova, and O. V. Doron kina, Doklady Akad. Nauk S.S.S.R., 

Peciar, R. PalovSik, J. Alfoldi, T. Sticzay, and P. Kova5, Chem. Zvesti, 1975, 29, 397. 

Other uronic acid derivatives are referred to in Chapters 3,4, and 21. 

An authoritative review of the synthesis and chemistry of uronic acids and their derivatives has been published.  

Periodate oxidation of l-0-benzoyl-2,3-0-isopropylidene-a-D-mannofuranose has afforded access to several derivatives of D-lyxuronic acid, and glyco-furanosyl halides of D-riburonic acid, which are of value in nucleoside synthesis, have been made by way of the corresponding thiofuranosides (see Chapter 7). 

Theoretical studies on the n.m.r. of uronic acids are referred to in Chapter 20. 

Aldol condensation of an acetyl iron anion with aldehyde-sugar derivatives (e.g. 36) and decomplexation of the iron led to chain-extended deoxy-uronic adds (e.g. 37 and its C-5 epimer), while addition of 2-trimethylsilylethynylmagnesium bromide to the 6-aldehyde derived from methyl 2,3,4-tri-O-benzyl-P-D-glucopyr-anoside followed by a multi-step procedure has afforded the amino-uronic add 38, the a-amino-acid on which miharamydn A is based. 

Four chiral liquid crystalline compounds, 39 and 40, were synthesized from d-glucose by standard means. It was determined that 39 (X = OC7H15) has the properties essential for ferroelectric liquid crystals.  

Baeyer-Villiger oxidation of the Ferrier carbocyclization products 41 and 42 derived from glucose, gave isomeric 5-deoxy-hexofuranosiduronic acids 43 and 

Two new chromones, (319) and (320), have been isolated and identified after heating D-glucuronic or D-galacturonic acids in slightly acidic aqueous solutions at 96 C. The chromone (320) was also formed when o-xylose was similarly 

of TMS ethers of hexuronic acid derivatives is referred to in Chapter 26. 

Brief treatment of methyl (methyl 2,3-0-isopropylidene-j8-D-ribofuranosid)-uronate (321) with an equimolar proportion, or a slight excess, of sodium methoxide did not yield the 3,4-unsaturated 3-deoxypentofuranosiduronate, but 

Reagents i, H+ ii, TsCl-py iii, AcOK-AcjO iv, MeONa v, p-NOgCeHiCOCl-py vi, BnOH-H+ vii, PhCHO-ZnCh viii, BnCl-KOH ix, Og-Pt x, CHsjNa 

The disaccharide (324), which contains D-galactopyranosylurono-6,3-lactone as its non-reducing residue, has been obtained in 40% yield by condensation of D-galactopyranosyluronic acid with 2-amino-2-deoxy-D-galactopyranose in 6M-hydrochloric acid at 40 °C under reduced pressure.  

Reagents i. (COCIla ii, CH2N2 iii. PhCOOAg, EtsN, MeOH 

D-Glucuronlc acid, isolated as the sodium salt, has been prepared 

Products from oxidative and non-oxidative alkaline treatment of D-galacturonic acid were analysed using glc-mass spectrometry and found to contain 13 hydroxymonocarboxyllc acids and 26 dicarboxylic acids. In the absence of oxygen the main products were 3-deoxy- 

Compounds (17), required for carcinogenicity studies, were prepared from either D-glucuronlc acid trlethylammonlum salt or D-glucurono-6,3-lactone by treatment with the corresponding aryl 

In the area of furanold uronic acids, a sterol conjugated as a 

Weidmann, Tetrahedron Lett., 1980, 21, 2135. 

The synthesis of 1-0-acyl-D-glucuronic acid derivatives has been achieved from the benzyl j3-pyranoside via its 2,3,4,6-tetra-0-(o -ethoxyethyl)derivative. The 1-0-methanesulphonyl ester of D-glucuronic acid was used to prepare acyl derivatives involving the attachment of biliverdin and bilirubin. In model experiments the sulphonate also afforded glucuronosides. D-Glucuronosides have also been prepared by standard Koenigs-Knorr glycosylation from various bile acids and A -tetrahydrocannabinol.  

L-lduronic acid glycosides are more readily hydrolysed by acid than the analogous neutral glycosides or the isomeric D-g /uco-acids, a difference that has been utilized in their isolation from glycosaminoglycans, e.g. heparin. Rate studies were carried out on several neutral and acidic glycosides and on 7V-acetyl-2-amino-2-deoxy-D-glucosides.  

Hirsch, R. Palovcik, I. TvaroSka, and S. Bystricky, CoU. Czedt. Chem. Comm., 1976, 41, 3119. 

The acidity constants of o-galacturonic and o-glucuronic acids in water have been determined by conductance and e.m.f. measurements/ The structures of the isomeric products obtained on trimethylsilylation of naturally occurring hexuronic acids and their sodium salts and lactones have been established using n.m.r. spectroscopy (for the anomeric configuration) and mass spectrometry (for the ring-size)/ ° The equilibria of some of the hexuronic acids in DMSO involved a larger proportion of furanoid forms than those in water or pyridine. 

Details have appeared on the synthesis of 3,7-anhydro-6-deoxyoctofuranuronic acid derivatives [e.g. (428)] related to the carbohydrate components of the octosyl acids isolated from the fermentation broth of Streptomyces cacaoi var. asoensis  

Details of the selective cleavage of o-glucuronidic linkages in saponins have been published (see Vol. 10, p. 117). A modified procedure for determining the sites of attachment of hexuronic acid residues in methylated acidic polysaccharides by base-catalysed degradation has been modelled on experiments with the methylated aldobiouronic acid derivative (430), which eliminated methyl 2,3,4-tri-O-methyl-p-D-glucopyranoside (89%) on treatment with sodium methylsulphinyl-methanide in DMSO at room temperature. When this procedure is applied to 

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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... 

Uronic acids are biosynthetic intermediates m various metabolic processes ascorbic acid (vitamin C) for example is biosynthesized by way of glucuronic acid Many metabolic waste products are excreted m the urine as their glucuronate salts... 

Octosyl Acids. Three octosyl uronic acid nucleosides, produced by S. cacaoi sub sp. asoensis are shown in Figure 3. The biosynthesis of (172) and (173) has been reported (1). The replacement of the pyrimidine chromophore of (171) with adenine results in a nucleoside analogue that is a competitive inhibitor of cAMP. 

Uronic acids are monosaccharides in which the terminal primary alcohol group is oxidized to a carboxyhc acid functional group, eg, D-glucuronic acid [6556-12-3] (11). 

The L-arabino-(4-0-methyl-D-glucurono)xylans are found in softwoods and annual plants. The L-arabinose is present primarily as a-L-arabinofuranosyl units, although P-L-arabinopyranosyl units may also be present. In either case, the arabinosyl units are often, but not always, present as single-unit side chains, as are the uronic acid units. 

From the presence of uronic acid, sulfate half-ester, pymvyl cycUc acetal, or succinate half-ester groups. 

Ion Exchange. Acidic polysaccharides containing uronic acids, sulfate, or phosphate groups are cation exchangers, binding metal ions. The... 

Uronic acid Class of aeidie eompounds of the general formula HOOC(CHOH) CHO that eontain both earboxylie and aldehydie groups, are oxidation produets of sugars, and oeeur in many polysaeeharides espeeially in the hemieelluloses. 

Monosaccharides can be oxidized enzymatically at C-6, yielding uronic acids, such as D-glucuronic and L-iduronic acids (Figure 7.10). L-Iduronic acid is similar to D-glucuronic acid, except for having an opposite configuration at C-5. Oxidation at both C-1 and C-6 produces aldaric acids, such as D-glucaric... 

Finally, if only the -CH2OH end of the aldose is oxidized without affecting the -CHO group, the product is a monocarboxylic acid called a uronic acid. The reaction must be done enzymatically no satisfactory chemical reagent is known that can accomplish this selective oxidation in the laboratory. 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

Uronic acid (Section 25.6) The monocarboxylic acid resulting from enzymatic oxidation of the -CH2OH group of an aldose. 

Uridine, biosynthesis of, 1124 Uronic acid, 994 from aldoses, 994 Urushiols, structure of, 600 UV, see Ultraviolet... 

The presence of uronic acids in microbial exopolysaccharides results in their polyanionic nature. 

Pyruvate ketals add to the anionic nature of the exopolysaccharide and are usually present in stoichiometric ratios with the carbohydrate component Pyruvate is normally attached to the neutral hexoses but may also be attached to uronic adds. In the absence of uronic acids, pyruvate alone contributes to the anionic nature of the exopolysaccharide. 

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