Sugars acetylation

The C-NMR spectmm of HMW DOM also includes contributions from carboxyl (CO-(OH or NH), 5% of total carbon), and alkyl (CH 14% total carbon) functional groups, which may derive from proteins, lipids, or carbohydrates (deoxy-and methyl sugars). Hydrolysis of HMW DOM followed by extraction with organic solvent yields 4-8% of the total carbon in HMW DOM as acetic acid. Acetyl is easily recognized in the H-NMR spectra of HMW DOM, where it appears as a broad singlet centered at 2 ppm (Figure 6(b)). Free acetic acid and its derivatives are not retained by ultrafiltration, and the acetyl in HMW DOM must be covalently bound to macromolecular material, most likely as an A-acetyl amino sugar. Acetyl contributes up to half the carboxyl carbon in the C-NMR spectrum. 

Few solid derivatives suitable for identification of sugars are available. Osazones are not suitable since the same osazone can form from more than one sugar. Acetylation, in the case of a reducing sugar, is complicated by the possibility of formation of the a- or the j8-anomeric form, or a mixture of both. (See Chapter 52.)... 

J Hemicelluloses calculated from five-sugar, acetyl, and uronic acid content. 

Chitin. A homopolymer of the amino sugar, acetyl glucosamine acts as a structural component of the exoskeleton of insects and crustaceans. 

Type I polysaccharide contains an amino sugar, acetyl residues, and is one of the few bacterial polysaccharides to contain D-galacturonic acid, (another being one described by Hassid ). All the pneumococcus polysaccharides listed by Boyd contain acetyl residues, the presence of which in the case of Type I, has a distinct influence on the serological specificity. The structural studies made on the polysaccharide reveal that it may possess a fundamental trisaccharide unit containing two molecules of a uronic acid and one of an acetylamino sugar, together with an additional acetyl residue. 

Acetates. Complete acetylation of all the hydroxyl groups is desirable in order to avoid mixtures. In some cases, the completely acetylated sugars may be obtained in the a- and p-forms depending upon the catalyst, e.g., zinc chloride or sodium acetate, that is employed in the acetylation. The experimental details for acetylation may be easily adapted from those already given for a- and p-glucose penta-acetates (Section 111,137). 

The principal reactions of this class of compounds are summarized in Scheme 172. In most of these reactions the reactive nucleophilic center is the terminal NHj group, although the other exocyclic nitrogen may also be involved, as shown by acetylation, which yields 284 and 285. However, the structure of compound 281 is not the one proposed in a recent report (1582) that attributes the attack to the other exocyclic nitrogen. The formation of osazones (287) from sugars, 2-hydrazinothiazoles, and hydrazine has been reported (525, 531). 

Another structural variation is the replacement of a hydroxyl group m a carbohydrate by an ammo group to give an ammo sugar The most abundant ammo sugar is one of the oldest and most abundant organic compounds on earth N Acetyl d glucosamine is the... 

Anthralin [1143-38-0] is acetylated using acetyl chloride in toluene and a pyridine catalyst to furnish 1,8-dihydroxy-lO-acetylanthrone [3022-61-5], an intermediate in the preparation of medications used in treating skin disorders, such as warts, psoriasis, and acne (38). Sugar esters can be similarly prepared from acetyl chloride under anhydrous conditions (39). 

Fig. 9. Partial structural formulas and shorthand notations for principal hemiceUuloses found in wood, where the sugar units ate noted as P-D-xylopyranose (Xylp), 4-Omethyl-a-D-glucopyranosyluronic acid (GlupU), a-L-arabinofuranose (Araf), P-D-glucopyranose (Glup), P-D-mannopyranose (Manp), and P-D-galactopyranose (Galp) for (a) arabino-4-O-methylglucuronoxylan from softwood, (b) 0-acetyl-galactoglucomannan from softwood, and...

An in vitro ensymatic synthesis of sucrose was carried out ia 1944 (5). A successful chemical synthesis was performed by Lemieux and Huber (6) ia 1953 from acetylated sugar precursors. However, the economics and chemical complexities of both processes make them unlikely sources of supply. 

Unsaturated sugars are useful synthetic intermediates (11). The most commonly used are the so-called glycals (1,5- or 1,4-anhydroalditol-l-enes). In the presence of a Lewis-acid catalyst, 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabinohex-l-enitol [2873-29-2] commonly called D-glucal triacetate, adds nucleophiles in both kineticaHy controlled and thermodynamically controlled (soft bases predominately at C-3 and hard bases primarily at C-1) reactions (11,13). 

We are familiar with several examples of chemical activation as a strategy for group transfer reactions. Acetyl-CoA is an activated form of acetate, biotin and tetrahydrofolate activate one-carbon groups for transfer, and ATP is an activated form of phosphate. Luis Leloir, a biochemist in Argentina, showed in the 1950s that glycogen synthesis depended upon sugar nucleotides, which may be... 

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