Alduronic acids

Reduced galacturonic acid and oligogalacturonides (GalU-oI, diGalU-ol, triGalU-ol and pentaGalU-ol) were prepared by NaBH, reduction of the corresponding alduronic acids. For NMR experiments the compounds were lyophilized three times from D2O. 

Being an alternating copolymer of ahexosamine and an alduronic acid, heparin belongs to the class of glycosaminoglycans (GAG), formerly... 

Aldoses generally undergo benzilic acid-type rearrangements to produce saccharinic acids, as well as reverse aldol (retro-aldol) reactions with j3-elimination, to afford a-dicarbonyl compounds. The products of these reactions are in considerable evidence at elevated temperatures. The conversions of ketoses and alduronic acids, however, are also of definite interest and will be emphasized as well. Furthermore, aldoses undergo anomerization and aldose-ketose isomerization (the Lobry de Bruyn-Alberda van Ekenstein transformation ) in aqueous base. However, both of these isomerizations are more appropriately studied at room temperature, and will be considered only in the context of other mechanisms. 

Minimum amounts of 2-3 /ig of sialic acids can be determined in, for example, the orcinol-Fe3+ assay, if the volumes of the Bial reagents23 are one-fifth of those originally described.107 By using this method, sialic acids can be accurately determined only if they have been prepurified, as free or glycosidically bound pentoses, hexoses, or alduronic acids interfere with the reaction by giving green chromo-phores.107 In our experience, an approximate determination of the sialic acid in a complex carbohydrate is only possible if its sialic acid content is >5%. 

C. G. Francisco, C. C. Gonzalez, and E. Suarez, Fragmentation of carbohydrate anomeric alkoxy radicals. A new synthesis of alduronic acid lactones, Tetrahedron Lett., 37 (1996) 1687-1690. 

The oxidation of D-glucose 1-phosphate and analogues to the alduronic acid 1-phosphates by molecular oxygen over Pt on carbon occurred with... 

Treatment of the alduronic acid 180 with DAIB-I2 furnishes the formyloxylactone 182 (Scheme 52) (98JOC2099). This and related reactions proceed by a radical fragmentation-oxidation sequence, culminating in the formation and intramolecular capture of oxycarbenium ion intermediates (e.g., 181). 

The synthesis of glycosiduronic acids includes two main approaches one involves selective oxidation of the primary hydroxyl group of a neutral glycoside, and the other, condensation of the agly-con with an appropriately protected alduronic acid derivative. The present Section is concerned mainly with the synthetic methods leading to glycosiduronic acids. An attempt has been made to collate information on the reactions of glycosiduronic acids, and to illustrate some of the physical methods that have contributed to the characterization of these compounds. 

Physical Constants of Dithioacetals and Per-O-acetylated Dithioacetals of Disaccharides and of Alduronic Acid,... 

Alduronic Acid Derivatives D-Galacturonic acid methyl 166.0 + 11.2 MeOH 246... 

This article, therefore, deals with complexes (briefly designated as metal-sugar complexes ) that are formed, in detectable proportions, in aqueous solution from cations and un-ionized carbohydrates. As an excep- tion, we shall briefly discuss (in Section III,5) complexes of cations with aldonic and alduronic acids, because of their structural similarities to metal-sugar complexes. 

A similar methodology has been applied in the synthesis of various useful chiral synthetic intermediates. Representative examples include the syntheses of alduronic acid lactone 603 [637,638], chiral dispiroacetals 605 and 606 [639] and a-iodoalkyl ester 608 from respective carbohydrate derivatives 602, 604 and 607 (Scheme 3.237) [640]. 

Alkaline potassium permanganate for all vicinal polyhydroxy compounds (sugar, sugar alcohols, aldonic acids, alduronic acids, etc.). 

Mono- and disaccharides, alduronic acids, methylated sugars, polysaccharides (thickening agents) Silanized glass fiber paper 0.05 mol Sodium tetraborate, pH 9.0, 0.1 moll barium acetate, 0.1 moir zinc acetate, 0.1 moll calcium acetate 1,3-Dihydroxynaphthalene (naphthoresorcinol)-H2S04... 

The complexes formed between Cu(II) ions and a number of D-aldonic and D-alduronic acids in aqueous solution has been studied, and the complex obtained from methyl a-D-mannopyranoside and copper(II) hydroxide in the presence of lithium hydroxide has been identified as the square planar structure 17. The determination of stability constants of Ca complexes with /wyo-inositol 1,4,5-trisphosphate is discussed in Chapter 18. The interaction of L-ascorbic acid with some metal ions has b n studied in aqueous solution at pH 6-7, and the solid hydrated salts lithium, sodium, potassium, ammcHiium, rubidium and cesium ascorbate have been isolated and characterised by C n.m.r. and f.t.ix. spectroscopy... 

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