Polysaccharides anhydrides, preparation

A very successful approach to the preparation of starch-based emulsion stabilizers has been the development of polysaccharide derivatives of substituted dicarboxylic acids by Caldwell and Wurzburg (4). The invention involves the treatment of starch with substituted cyclic dicarboxylic acid anhydrides having the following structural formula ... 

Hydrogels prepared via homogeneous esterification of dextran with unsaturated carboxylic acids are advanced polysaccharide-based products useful for drug delivery systems and protective encapsulants, e.g. of viruses used in gene therapy [173]. Very promising in this regard is the dextran maleic acid monoester [174], which can be obtained by conversion of dextran in DMF/LiCl with the maleic anhydride in the presence of TEA. The DS of the products can be easily controlled with the amount of anhydride applied but... 

Copolymerization offers considerable potential of engineering the properties and degradation rate of PHB over a broad range. HB has been copolymerized with a number of related species, e.g., e-CL, LA, 4-hydroxybutyrate and hydrox-ypropionate. Furthermore, a number of PHB blends have been prepared. Miscibility of PHB with PCL, PLA, POE, poly(mandelic acid), and poly(sebacic anhydride) has been demonstrated. PHB-poly(sebacic anhydride) blends offered controlled release of bupivacaine at a rate dependent on the PHB content [141]. Blending of P(HB-co-HV) with natural polysaccharides was proposed as a way... 

Dextran monosuccinate ester. A monosuccinate ester of dextran was prepared as described before by reacting the polysaccharide with succinic anhydride (30 meq./anhydroglucopyranoside unit) in presence of catalytic amounts of 4-dimethylamino pyridine. 

In the field of aldobiouronic acid derivatives an ingenious method has been devised for the preparation of radioactive disaccharides for use as substrates for o-L-iduronidase, jS-D-glucuronidase, and 2-sulpho-L-iduronate 2-sulphatase. Heparin was cleaved by the deamination procedure and the products were reduced using sodium borotritide to afford access to a-L-idopyranosyluronic and j3-D-glucopyranosyluronic acid derivatives of 2,5-anhydro-D-[l- H]mannitol. Acidic treatment in methanol of the water-soluble polysaccharides of wobaku wood, followed by acetylation, have led to the isolation of the anhydride derivative (53) which was concluded to arise by way of the corresponding aldo-... 

DMSO/TBAF is highly efficient as a reaction medium for the homogeneous esterification of cellulose by transesterification and after the in situ activation (see below) of complex carboxylic acids. The acylation using acid chlorides and anhydrides is limited because the solution contains a certain amount of water caused by the use of the commercially available TBAF trihydrate and the residual moisture in the air-dried polysaccharides. Nevertheless, this system has shown a remarkable capacity for the esterification of lignocellulosic mataials, for example, sisal fibres, which contain about 14 per cent hemicellulose [28]. The DS values of cellulose acetate prepared from these fibres with acetic anhydride in mixtures of DMSO/TBAF were found to decrease with increasing TBAF concentration from 6 to 11 per cent (Table 16.4), due to the increased rate of hydrolysis both of the anhydride and the ester moieties. 

Trifluoroacetates of carbohydrates have been prepared 80), These substances, which are quite sensitive to hydrolysis, show some promise as intermediates in synthetic work. Trifluoroacetic anhydride is a powerful impelling reagent for the acetylation of polysaccharides 80),... 

Polysaccharide nitrates are prepared in the laboratory for the viscometric estimation of molecular weight and for fractionation according to chain length (138). For these purposes it is necessary that depolymerization be kept to a minimum. This is achieved by nitration of the polysaccharide with a mixture of nitric acid, acetic acid, and acetic anhydride at low temperatures (139). 

It is possible to react almost any acid with a polysaccharide to produce an ester, and a great variety of polysaccharide esters have been produced. Polysaccharide esters of aliphatic acids are readily prepared by reacting the free acid with the polysaccharide in the presence of an impelling agent consisting of a mixture of chloroacetic anhydride, chloroacetic acid, and magnesium perchlorate Mixed esters, especially the acetate-propio-... 

This type of polysaccharide may be prepared from anhydro disaccharides. Polymerization reactivity of anhydro disaccharide derivatives, however, is lower than that of the corresponding anhydro monosaccharide derivatives. In order to obtain comb-shaped polysaccharides of moderate molecular weight, highly reactive disaccharide anhydrides are required. Hence we gave attention to a dideoxygenated anhydro-ring structure. 

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