Acetolysis Acetylation

Barsha and Hibbert16 also demonstrated by meins of methylation, acetylation, acetolysis and hydrolysis experiments that the membranes synthesized by the action of A. xylinum on D-fructose and on glycerol were chemically identical with cotton cellulose. 

The partially methylated monosaccharides obtained on depolymerization of the permethylated sample are preferably analyzed as acetates by g.l.c.-m.s., as shown by Bjomdal and coworkers.41,42 The neutral sugars and the amino sugars obtained in acetolysis-acid hydrolysis are reduced, and acetylated for the analysis, and the amino-hexitol and the neuraminic acid residues are acetylated after methanolysis. Identification with the aid of g.l.c.-m.s. has been described for all of the common components of protein- and lipid-linked glycans and oligosaccharides from animal cells, namely, the neutral sugars,41-43 hexitols,44 hexosamines,29,43,45,46 aminohexitols,31,32 and neuraminic acids.33,34,47... 

The highly polymerised compound cellulose is broken down into its octa-acetyl disaccharide cellobiose by acetolysis (Franchimont, Skraup, Ost). The bioses belong to the important group of glucosides. 

Systematic studies of the acetolysis of disaccharides have been performed.57-803 Lindberg81,82 showed that anomerization and acetolysis of acetylated glycosides is retarded by the presence of electronegative groups in the aglycon. A mechanism involving an acyclic intermediate (20) was proposed for these reactions (see Scheme 2). 

The differences in the rates of hydrolysis of various linkage types by a particular glycosidase can be used to provide information about this aspect of structure. Jack-bean a-D-mannosidase cleaves a-(l- 2) and a-(l- 6) linkages much faster than a-(l -> 3). Oligosaccharides, obtained by endo-N-acetyl-/J-D-glucosaminidase hydrolysis of ovalbumin, were subjected to acetolysis, which selectively cleaved the a-(l - 6) bonds. A tetrasaccharide isolated after this treatment was then incubated with jack-bean o-d-... 

One of the few efficient reactions to have been reported of 5-bromohexose derivatives is the acetolysis [mercury(II) acetate in acetic acid] of methyl tetra-0-acetyl-5-bromo-/ -D-glucopyranuronate (10), which affords the crystalline methyl 5-acetoxy-tetra-O-acetyl-a-L-idopyranuronate (126) this was assigned the inverted configuration at C-5 on the grounds of a major optical rotational change during its formation. Likewise, methyl tetra-0-acetyL/f-L-xy/o-hexulopyranosonate (127) is obtained in excellent yield from the bromide 8, and it, too, is dextrorotatory and is produced from a levorotatory bromide, conceivably by way of a cyclic 4,5-acetoxonium ion. Compound 127 also differs in expected ways from its known C-5 epimer, and, on deprotection, affords L-ascorbic acid.21 28... 

Most of the amines could be acetylated at nitrogen and, under refluxing conditions, at the 1-position. Other routes to acetamidoindoli-zines are from the corresponding acetyl compounds via the Schmidt reaction,79-180 from pyridines via Tschitschibabin reactions, and from acetolysis of an azomethine79 such as 124, which may be derived from the reaction of an indolizine and diphenylformamidine.186... 

Another approach to achieve a fast and total breakdown of cellulose could be the preparation of a soluble derivative and its homogeneous hydrolysis. An example of an acetylation-acetolysis-hydrolysis sequence is given by Hestrin (4). Decomposition and darkening is considerable. 

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