Acetic anhydride polysaccharides

The polysaccharide was acetylated with acetic anhydride in the presence of pyridine. Purification of the acetate consisted in precipitation of a 10% boiling benzene solution with petroleum ether. One hundred and fifty such precipitations were necessary before a constant-rotating product resulted [a]D20 = — 20.1° (c = 1.0, chloroform). Cryoscopic molecular weight determinations in benzene solution gave an average value of 3918. 

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form ester derivatives. Esterification of carbohydrates by acetic anhydride, especially cellulose, is a major industrial application for this compound. In aqueous solutions, however, esterification may be a minor product, since the oxygen of water is about as strong a nucleophile as the hydroxyls of sugar residues. 

Esterification is not difficult if xylan is first carefully precipitated from solution and dried to a fluffy, non-horny powder, or if the xylan can be highly swollen so as to make the polysaccharide molecules easily accessible to the esterifying reagents. Solechnik101 finds that swollen undried xylan, when treated with acetic anhydride containing sulfuric... 

The resistance of Bacillus cereus cell-wall peptidoglycan to lysozyme action200 is due to the majority of the 2-amino-2-deoxy-D-glucosyl residues having free (nonsubstituted) amino groups. Polysaccharide and peptide components of the cell walls were converted into material susceptible to lysozyme by N-acetylation with acetic anhydride. 

We met cellulose, the bulk polysaccharide of woody plants, in Chapter 49. It is a strong and flexible polymer but no use for making fabrics or films as it cannot be processed. One solution to this problem is to carry out chemical reactions that transform its properties. Acid-catalysed acetylation with acetic anhydride gives a triacetate with most of the free OH groups converted into esters. 

Although the reaction of acetic anhydride in the presence of an acid catalyst with carbohydrates of all classes, and their derivatives, has been studied for some ninety years, no survey on the topic has been written in this Series. The present brief article does not attempt to give a full historical development of the subject (particularly for polysaccharides), but it attempts to bring together in one place an account of the reactions possible with the reagents. Thus, the uses of reactions are stressed, rather than the mechanistic interpretations of them. Some aspects of this topic have been discussed in other articles in this Series, and mention of them will be made where appropriate. 

Muzzarelli et al. (2000) described a method for coating prosthetic articles with chitosan-oxychitin. Plates of titanium (Ti) and its alloys were plasma sprayed with hydroxyapatite and glass layers, and subsequently a chitosan coat was deposited on the plasma-sprayed layers using chitosan acetate. These layers were treated with 6-oxychitin to form a polyelectrolytic complex. This complex was optionally contacted with l-ethyl-3-(3-dimethylami-nopropyl) carbodiimide at 4°C for 2 hours to form amide links between the two polysaccharides, or acetylation with acetic anhydride in methanol to obtain a chitin film. In all cases, the modified coats were insoluble, uniformly flat, and smooth. Prosthetic materials coated with chitosan-oxychitin were capable of provoking colonization by cells, osteogenesis, and osteointegration. 

Most of the carbonyl groups involve C-3, and reduction of the oxidized dextrans gives modified polysaccharides containing n-allose, n-mannose, and D-galactose residues. Oxidation of 6-O-tritylamylose with methyl sulfoxide-acetic anhydride gives keto groups mainly at C-2. Similar oxidation of cellulose has been described. ... 

A new dialdose dianhydride, the 1,2 1 2-dianhydride of 3,4-di-0-acetyl- 3-L-rhamnopyranose and methyl 3,4-di-(9-acetyl-a-D-galactopyranosyluronic acid, has been obtained from an acid hydrolysate of the water-soluble polysaccharide of wobaku wood by successive treatment with methanolic hydrogen chloride and acetic anhydride-pyridine. ... 

---