Glucosamine acetylation

Chitosan is produced commercially by deacetylation of chitin. It is a linear polysaccharide composed of randomly distributed /i-( l-4)-linkcd D-glucosamine (deacetylated unit) and N -acetyl-D-glucosamine (acetylated unit). The degree of deacetylation in commercial chitosans is in the range 60-100% (Figure 5.19). 

Heparitin sulfate is composed of D-glucuronic acid, n-glucosamine, acetyl, and sulfate residues in approximately equimolar ratio (J12). The structure of heparitin sulfate still awaits final elucidation, but it may be distinguished from other sulfated mucopolysaccharides by means of its high positive rotation, electrophoretic behavior, and resistance to testicular, bacterial, and leech hyaluronidases. Final identification, however, usually requires its isolation and analysis. 

Chitin and chitosan, which are the deacetylated and consequently amine group bearing derivatives, are natural polymers composed of randomly distributed p-l,4-linked N-acetyl-D-glucosamine (acetylated) and o-glucosamine (deacetylated) units. In contrast to chitin, which is insoluble in aqueous media, chitosan can be dissolved under acidic conditions owing to the free protonable amine groups of the D-glucosamine units. As other natural polymers chitin as well as chitosan cannot be seen as one unique chemical substance but rather as a set of polymer chains that exhibit different... 

Generally, chitosan is formed of distributed p-(l )-linked D-glucosamine (deacetylated unit) and iV-acetyl-o glucosamine (acetylated unit), manufactured by deacetylation of chitin extracted from shells of crabs, shrimps and kriU. Chitosan that is accessible commercially is deacetylated 66-95% and has an average... 

Hydrolysis with boiling acids gives glucosamine and acetic add in equivalent amounts. A more careful hydrolysis with chitinase gives as the sole product N-acetylglucosamine, that is, glucosamine acetylated at its amino group. 

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... 

Fig. 3. The stmcture of the nodulation (Nod) factors of i bium meliloti 2011 (44), where is 2 or 3, R is —H or—COCH, and R is C 2 as shown, C gT, or ie, a fatty acid chain having from 1 to 3 double bonds. The A/-acetyl glucosamine residues and an acyl moiety, R, are present ia all...

Amino sugars, such as o-glucosamine, have an OH group leplaced by an -NH2. The N-acetyl amide derived from o-glucosamine is the monosaccharide unit from which chitm, the hard crust that protects insects and shellfish, is made. Still otheramino sugars are found in antibiotics such as streptomycin and gentamicin. 

Henry reaction of the (V-acetyl-D-glucosamine derived nitrosugar 1 with 2,3-O-cyclohexylidene-D-glyceraldehyde (2) furnishes a single product 3 in 85-90% yield7. 

Enhanced availability of exogenous glucosamine is beneficial for the synthesis of hyaluronan because endogenous glucosamine is insufficient to achieve the high concentration of UDP-N-acetyl glucosamine necessary to... 

Partially deacetylated chitin, a cellulose-like biopolymer consisting predominantly of N-acetyl-D-glucosamine chains, in the form of films or crosslinked hydrogels has been used for the delivery of drugs (28,29). The suitability of chitin as a vehicle for the sustained release of drugs was examined using indomethacin and papaverine hydrochloride as model drugs (30). In vitro studies showed that over 80% of the indomethacin was released within 7 hr, whereas papaverine hydrochloride dissolved almost immediately. 

Figure 13-10. Glucosamine (2-amino-D-glucopyra-nose) a form). Galactosamine is 2-amino-D-galactopy-ranose. Both glucosamine and galactosamine occur as N-acetyl derivatives in more complex carbohydrates, eg, glycoproteins.

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