Uronic acids esters

Uronic acid azides constitute important precursors for A -glycosyl amino acids and their various peptide derivatives, and may be formed by a comparable pathway. Thus, the treatment of acetyl-protected uronic acid esters with tri-methylsilyl azide and SnCU gives the desired acetylated 1,2-trans methyl (o-glycopyranosyl azide)uronates in crystalline form. " Whereas the yields for the gluco 61 and galacto derivatives 62 are satisfactory, the manno analog 63 was obtained in only 11 % yield. Even with an excess of trimethylsilyl azide, the results could not be improved. ... 

From the presented examples above it is clear that uronic acid building blocks have found widespread applicatiOTi both as donor and acceptor glycosides in the assembly of GAG-oligomers, notwithstanding their relatively low reactivity. In fact, the efficient synthesis of large oligomers has been made possible through the use of uronic acid esters. 

Uronic acids esters ean be activated as imidates, bromides or t 10 phenyl glycosides among others. Imidate donors are the cornmon activating groups for the synthesis of di- and example the synthesis of the putative pnon-associate containing two D-glucuronic acid units with 1 tag The... 

Dissociation constants of o-glucuronic acid, o-galacturonic acid, their methyl ethers, and the corresponding 4,5-unsaturated derivatives have been measured and rationalized in terms of various operating electronic factors. Observations on details of the reduction of uronic acid esters to hexopyrano-sides, on nitrogen-containing derivatives, and on branched-chain uronic acids are made in Chapters 3, 9, and 13, respectively. 

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

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. 

The repeating disaccharide contains glucosamine (GlcN) and either of the two uronic acids (Figure 48-9). Most of the amino groups of the GlcN residues are N-sulfated, but a few are acetylated. The GlcN also carries a Cg sulfate ester. 

Proportions of uronic acid and methyl and non-methyl esters in tobacco suspension cell walls (mol%)... 

Marsh grapefhiit (MGF) pulp was homogenized in 5 volumes of extraction buffer at 4 C and maintained at pH 8.0 (28). The homogenate was stirred for one hour, centrifuged and the supernatant used as the PE extract. Activity was measured by titration with a Brinkman (Westbury, NY) pH stat titrator at pH 7.5 and 30°C in 25 mL of 1 % high methoxyl pectin (Citrus Colloids Limited, Hereford, UK) with O.IM NaCl. PE units are expressed as the microequivalents of ester hydrolysed per minute. Uronic acid analyses were conducted based on the m-phenyl phenol (4) as modified for microplate reading (30). 

In non-saline sediments aliphatic and polyaromatic hydrocarbons, phthalate esters carboxylic acids, uronic acid aldoses chloroaliphatics haloaromatics chlorophenols chloroanisoles polychlorobiphenyls polychlorodibenzo-p-dioxins poychlorodibenzofurans various organosulphur compounds, chlorinated insecticides, organophosphorus insecticides mixtures of organic compounds triazine herbicides arsenic and organic compounds of mercury and tin. 

The mechanism of pyrolysis reactions of biomass was extensively discussed in an earlier study (Demirbas, 2000). Water is formed by dehydration. In the pyrolysis reactions, methanol arises from the breakdown of methyl esters and/or ethers from decomposition of pectin-like plant materials. Methanol also arises from methoxyl groups of uronic acid (Demirbas and Giillii, 1998). Acetic acid is formed in the thermal decomposition of all three main components of wood. When the yield of acetic... 

Polymers of uronic acids are encountered in nature in structures known as pectins, which are essentially chains of D-galacturonic acid residues linked al -> 4, though some of the carboxyl groups are present as methyl esters. These materials are present in the cell walls of fruit, and the property that aqueous solutions under acid conditions form gels is the basis of jam making. 

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